Patent Publication Number: US-2023144692-A1

Title: Wireless connector attaching and detaching method, robot device, wireless connector, and wireless connector unit

Description:
TECHNICAL FIELD 
     The invention relates to a wireless connector attaching and detaching method, a robot device, a wireless connector, and a wireless connector unit. 
     BACKGROUND TECHNOLOGY 
     Technology for supplying electric power wirelessly to a load is known. Hereinafter, such a technique is referred to as a “wireless power supply technique”. The wireless power supply technique is applied to industrial robots or the like. For example, Patent Document 1 discloses an example of a robot arm device as shown in  FIG.  36 A . The illustrated robot arm device comprises first to sixth joint portions J 1  to J 6 . The second and fourth joint portions J 2  and J 4  are provided with first and second wireless power supply units IHU 2  and IHU 4 , respectively. The first and the second wireless power supply units IHU 2  and IHU 4  wirelessly transmit electric power at the second and the fourth joint portions J 2  and J 4  via a pair of coils, respectively. 
     The above-mentioned Patent Document 1 also discloses a configuration of a part of a wireless power transmission system as shown in  FIG.  36 B . The illustrated wireless power transmission system is provided with a wireless power supply unit  1 , a power source device  2 , and a load  3 . The wireless power supply unit  1  is disposed between the power source device  2  and the load  3 . The wireless power supply unit  1  corresponds to the above-mentioned first wireless power supply unit IHU 2 . The wireless power supply unit  1  is provided with a power transmission device  10  and a reception device  20 , as shown in  FIG.  36 B . The power transmission device  10  is provided with a power transmission antenna  11  including a coil or the like, an inverter circuit  13 , and a power transmission control circuit  15 . The reception device  20  is provided with a power receiving antenna  21  including a coil or the like, and a rectifying circuit  23 . 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: JP 2018-117511 A 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     In general, a coil for wirelessly transmitting and receiving electric power often generates heat during operation. Therefore, the wireless power supply unit  1  may fail due to disconnection or the like resulting from heat generation of the coil. Such a failure in the wireless power supply unit  1  may interfere with the operation of the robot arm device. Accordingly, it is desirable that the wireless power supply unit  1  can quickly be repaired by replacement or the like. 
     Patent Document 1 does not disclose how the second and the fourth joint portions J 2  and J 4  are provided with the wireless power supply unit  1 , such as an arrangement of the pair of coils. Further, in the robot arm device described in Patent Document 1, it is conceivable to apply the wireless power supply unit  1  not only to the second and the fourth joint portions J 2  and J 4  but also to the first and the fifth joint portions J 1  and J 5 . However, Patent Document 1 does not disclose application of the wireless power supply unit  1  to the first and the fifth joint portions J 1  and J 5  at all. Therefore, it is difficult to obtain a wireless power supply unit that can quickly be repaired even if Patent Document 1 is referred to. 
     The present invention has been made in view of the above-mentioned situation, and an object thereof is to provide a wireless connector capable of being quickly repaired. 
     Means for Solving the Problem 
     In order to achieve the above-mentioned object, according to a first aspect of the present invention, there is provided a wireless connector attaching and detaching method for attaching and detaching a wireless connector to and from a first object and a second object which are rotatably connected around a rotation axis, the wireless connector being configured to wirelessly transmit electric power between the first object and the second object, wherein: 
     the wireless connector includes: 
     a first unit including a first transmission/reception unit provided with a first coil configured to wirelessly transmit the electric power and composed of a plurality of first coil parts which are separable from each other or which are separable at one position and bendable with respect to each other; and a first main connector portion configured to transmit the electric power to/from the first object; and 
     a second unit including a second transmission/reception unit provided with a second coil configured to wirelessly transmit the electric power to/from the first coil and composed of a plurality of second coil parts which are separable from each other or which are separable at one position and bendable with respect to each other; and a second main connector portion configured to transmit the electric power to/from the second object; 
     the first transmission/reception unit being configured to be openable and closable, and configured to be annular when the first transmission/reception unit is closed so that the first coil is formed by connecting the plurality of first coil parts via one or a plurality of first coil connectors; 
     the second transmission/reception unit being configured to be openable and closable, and configured to be annular when the second transmission/reception unit is closed so that the second coil is formed by connecting the plurality of second coil parts via one or a plurality of second coil connectors, 
     the wireless connector attaching and detaching method including: 
     a step of attaching the wireless connector to the first object and the second object in a state where the first transmission/reception unit and the second transmission/reception unit are faced to each other in a non-contact manner so as to wirelessly transmit the electric power; and 
     a step of detaching the wireless connector from the first object and the second object; 
     the step of attaching including: 
     a step of fitting the one or the plurality of first coil connectors from the outside of the first object so that the first transmission/reception unit is disposed in a closed annular shape so as to surround the rotation axis and that the first main connector portion is attached to the first object; and 
     a step of fitting the one or the plurality of second coil connectors from the outside of the second object so that the second transmission/reception unit is disposed in a closed annular shape so as to surround the rotation axis and that the second main connector portion is attached to the second object; 
     the step of detaching including: 
     a step of releasing fitting of the one or the plurality of first coil connectors by work outside the first object so that the first transmission/reception unit is put into an open state and that the first main connector portion is detached from the first object; and 
     a step of releasing fitting of the one or the plurality of second coil connectors by work outside the second object so that the second transmission/reception unit is put into an open state and that the second main connector portion is detached from the second object. 
     The first coil may comprise the plurality of first coil parts separable from each other. 
     The second coil may comprise the plurality of second coil parts separable from each other. 
     The first transmission/reception unit may be configured to be separable at a plurality of positions to be openable and closable and configured to be annular when the first transmission/reception unit is closed so that the first coil is formed by connecting the plurality of first coil parts via the plurality of first coil connectors. 
     The first unit may be assembled to be divisible into first to i-th primary pieces (i being an integer not smaller than 2), which are not annular, so that the first coil is separated into the plurality of first coil parts by releasing fitting of the plurality of first coil connectors. 
     The second transmission/reception unit may be configured to be separable at a plurality of positions to be openable and closable and configured to be annular when the second transmission/reception unit is closed so that the second coil is formed by connecting the plurality of second coil parts via the plurality of second coil connectors. 
     The second unit may be assembled to be divisible into first to j-th secondary pieces (j being an integer not smaller than 2), which are not annular, so that the second coil is separated into the plurality of second coil parts by releasing fitting of the plurality of second coil connectors. 
     The step of attaching may include: 
     a step of fitting the plurality of first coil connectors from the outside of the first object so that the first transmission/reception unit is disposed in a closed annular shape so as to surround the rotation axis and that the first main connector portion is attached to the first object; and 
     a step of fitting the plurality of second coil connectors from the outside of the second object so that the second transmission/reception unit is disposed in a closed annular shape so as to surround the rotation axis and that the second main connector portion is attached to the second object. 
     The first coil may comprise the plurality of first coil parts which are separable at one position and bendable with respect to each other. 
     The second coil may comprise the plurality of second coil parts which are separable at one position and bendable with respect to each other. 
     The first unit may include: 
     first to i-th primary pieces (i being an integer not smaller than 2) which are not annular and which include, respectively, the plurality of first coil parts bendable with respect to each other; and 
     a first connecting mechanism for connecting adjacent ones of the first to the i-th primary pieces so that the first coil is opened in a state of being bent into the plurality of first coil parts by releasing fitting of the one first coil connector. 
     The second unit may include: 
     first to j-th secondary pieces (j being an integer not smaller than 2) which are not annular and which include, respectively, the plurality of second coil parts bendable with respect to each other; and 
     a second connecting mechanism for connecting adjacent ones of the first to the j-th secondary pieces so that the second coil is opened in a state of being bent into the plurality of second coil parts by releasing fitting of the one second coil connector. 
     In order to achieve the above-mentioned object, according to a second aspect of the present invention, there is provided a robot device including: 
     a first object and a second object which are connected to each other to be rotatable around a rotation axis; and 
     a wireless connector for wirelessly transmitting electric power between the first object and the second object; 
     wherein the first object includes a first mating connector portion exposed to the outside; 
     wherein the second object includes a second mating connector portion exposed to the outside; 
     wherein the wireless connector comprises: 
     a first unit including:
         a first transmission/reception unit provided with a first coil configured to wirelessly transmit the electric power and composed of a plurality of first coil parts which are separable from each other or which are separable at one position and bendable with respect to each other; and   a first main connector portion connected to the first mating connector portion in order to transmit the electric power to/from the first object;       

     a second unit including:
         a second transmission/reception unit provided with a second coil configured to transmit the electric power to/from the first coil and composed of a plurality of second coil parts which are separable from each other or which are separable at one position and bendable with respect to each other; and   a second main connector portion connected to the second mating connector portion in order to transmit the electric power to/from the second object;       

     wherein the first transmission/reception unit is configured to be openable and closable and configured to be annular when the first transmission/reception unit is closed so that the first coil is formed by connecting the plurality of first coil parts via one or a plurality of first coil connectors; 
     wherein the second transmission/reception unit is configured to be openable and closable and configured to be annular when the second transmission/reception unit is closed so that the second coil is formed by connecting the plurality of second coil parts via one or a plurality of second coil connectors; 
     wherein the first transmission/reception unit and the second transmission/reception unit are arranged, when the first unit and the second unit are attached to the first object and the second object, respectively, each in a closed annular state and in a state of being faced to each other in a non-contact manner so as to transmit the electric power outside the first object and the second object. 
     The first coil may comprise the plurality of first coil parts separable from each other. 
     The second coil may comprise the plurality of second coil parts separable from each other. 
     The first transmission/reception unit may be configured to be separable at a plurality of positions to be openable and closable and configured to be annular when the first transmission/reception unit is closed so that the first coil is formed by connecting the plurality of first coil parts via the plurality of first coil connectors. 
     The first unit may be assembled to be divisible into first to i-th primary pieces (i being an integer not smaller than 2), which are not annular, so that the first coil is separated into the plurality of first coil parts by releasing fitting of the plurality of first coil connectors. 
     The second transmission/reception unit may be configured to be separable at a plurality of positions to be openable and closable and configured to be annular when the second transmission/reception unit is closed so that the second coil is formed by connecting the plurality of second coil parts via the plurality of second coil connectors. 
     The second unit may be assembled to be divisible into first to j-th secondary pieces (j being an integer not smaller than 2), which are not annular, so that the second coil is separated into the plurality of second coil parts by releasing fitting of the plurality of second coil connectors. 
     The first coil may comprise the plurality of first coil parts which are separable at one position and bendable with respect to each other. 
     The second coil may comprise the plurality of second coil parts which are separable at one position and bendable with respect to each other. 
     The first unit may include: 
     first to i-th primary pieces (i being an integer not smaller than 2) which are not annular and which include, respectively, the plurality of first coil parts bendable with respect to each other; and 
     a first connecting mechanism for connecting adjacent ones of the first to the i-th primary pieces so that the first coil is opened in a state of being bent into the plurality of first coil parts by releasing fitting of the one first coil connector. 
     The second unit may include: 
     first to j-th secondary pieces (j being an integer not smaller than 2) which are not annular and which include, respectively, the plurality of second coil parts bendable with respect to each other; and 
     a second connecting mechanism for connecting adjacent ones of the first to the j-th secondary pieces so that the second coil is opened in a state of being bent into the plurality of second coil parts by releasing fitting of the one second coil connector. 
     The wireless connector may be attached to a recess formed at a connecting part of the first object and the second object so as not to protrude outward beyond the first object and the second object when viewed along the rotation axis. 
     In order to achieve the above-mentioned object, according to a third aspect of the present invention, there is provided a wireless connector for wirelessly transmitting electric power between a first object and a second object, the wireless connector including: 
     a first unit detachably attached to the first object from the outside of the first object; and 
     a second unit detachably attached to the second object from the outside of the second object; 
     wherein the first unit includes: 
     a first transmission/reception unit provided with a first coil configured to wirelessly transmit the electric power and composed of a plurality of first coil parts which are separable from each other or which are separable at one position and bendable with respect to each other; and 
     a first main connector portion for transmitting the electric power to/from the first object by being detachably attached to the first object from the outside of the first object; 
     wherein the second unit includes: 
     a second transmission/reception unit provided with a second coil configured to wirelessly transmit the electric power to/from the first coil of the first transmission/reception unit and composed of a plurality of second coil parts which are separable from each other or which are separable at one position and bendable with respect to each other; and 
     a second main connector portion for transmitting the electric power to/from the second object by being detachably attached to the second object from the outside of the second object; 
     wherein the first transmission/reception unit is configured to be openable and closable and configured to be annular when the first transmission/reception unit is closed so that the first coil is formed by connecting the plurality of first coil parts via one or a plurality of first coil connectors; 
     wherein the second transmission/reception unit is configured to be openable and closable and configured to be annular when the second transmission/reception unit is closed so that the second coil is formed by connecting the plurality of second coil parts via one or a plurality of second coil connectors; 
     wherein the first transmission/reception unit and the second transmission/reception unit are arranged, when the first unit and the second unit are attached to the first object and the second object, respectively, each in a closed annular state and in a state of being faced to each other in a non-contact manner so as to wirelessly transmit the electric power. 
     The first coil may comprise the plurality of first coil parts separable from each other. 
     The second coil may comprise the plurality of second coil parts separable from each other. 
     The first transmission/reception unit may be configured to be separable at a plurality of positions to be openable and closable and configured to be annular when the first transmission/reception unit is closed so that the first coil is formed by connecting the plurality of first coil parts via the plurality of first coil connectors. 
     The first unit may be assembled to be divisible into first to i-th primary pieces (i being an integer not smaller than 2), which are not annular, so that the first coil is separated into the plurality of first coil parts by releasing fitting of the plurality of first coil connectors. 
     The second transmission/reception unit may be configured to be separable at a plurality of positions to be openable and closable and configured to be annular when the second transmission/reception unit is closed so that the second coil is formed by connecting the plurality of second coil parts via the plurality of second coil connectors. 
     The second unit may be assembled to be divisible into first to j-th secondary pieces (j being an integer not smaller than 2), which are not annular, so that the second coil is separated into the plurality of second coil parts by releasing fitting of the plurality of second coil connectors. 
     The first coil may comprise the plurality of first coil parts which are separable at one position and bendable with respect to each other. 
     The second coil may comprise the plurality of second coil parts which are separable at one position and bendable with respect to each other. 
     The first unit may include: 
     first to i-th primary pieces (i being an integer not smaller than 2) which are not annular and which include, respectively, the plurality of first coil parts bendable with respect to each other; and 
     a first connecting mechanism for connecting adjacent ones of the first to the i-th primary pieces so that the first coil is opened in a state of being bent into the plurality of first coil parts by releasing fitting of the one first coil connector. 
     The second unit may include: 
     first to j-th secondary pieces (j being an integer not smaller than 2) which are not annular and which include, respectively, the plurality of second coil parts bendable with respect to each other; and 
     a second connecting mechanism for connecting adjacent ones of the first to the j-th secondary pieces so that the second coil is opened in a state of being bent into the plurality of second coil parts by releasing fitting of the one second coil connector. 
     In order to achieve the above-mentioned object, according to a fourth aspect of the present invention, there is provided a wireless connector for wirelessly transmitting electric power between a first object and a second object; the wireless connector including: 
     a first unit detachably attached to the first object from the outside of the first object; and 
     a second unit detachably attached to the second object from the outside of the second object; 
     wherein the first unit includes: 
     a first transmission/reception unit provided with a first coil configured to wirelessly transmit the electric power and composed of a plurality of first coil parts which are separable from each other or which are separable at one position and bendable with respect to each other; and 
     a first main connector portion for transmitting the electric power to/from the first object by being detachably attached to the first object from the outside of the first object; 
     wherein the second unit includes: 
     a second transmission/reception unit provided with a second coil configured to wirelessly transmit the electric power to/from the first coil of the first transmission/reception unit and composed of a plurality of second coil parts which are separable from each other or which are separable at one position and bendable with respect to each other; and 
     a second main connector portion for transmitting the electric power to/from the second object by being detachably attached to the second object from the outside of the second object; 
     wherein the first transmission/reception unit is configured to be openable and closable and configured to be annular when the first transmission/reception unit is closed so that the first coil is formed by connecting the plurality of first coil parts via one or a plurality of first coil connectors; 
     wherein the second transmission/reception unit is configured to be openable and closable and configured to be annular when the second transmission/reception unit is closed so that the second coil is formed by connecting the plurality of second coil parts via one or a plurality of second coil connectors; 
     wherein the first coil and the second coil are arranged, when the first unit and the second unit are attached to the first object and the second object, respectively, each in a closed annular state and in parallel to each other in a state of being faced to each other in a non-contact manner so as to wirelessly transmit the electric power. 
     The first coil may comprise the plurality of first coil parts separable from each other. 
     The second coil may comprise the plurality of second coil parts separable from each other. 
     The first transmission/reception unit may be configured to be separable at a plurality of positions to be openable and closable and configured to be annular when the first transmission/reception unit is closed so that the first coil is formed by connecting the plurality of first coil parts via the plurality of first coil connectors. 
     The first unit may be assembled to be divisible into first to i-th primary pieces (i being an integer not smaller than 2), which are not annular, so that the first coil is separated into the plurality of first coil parts by releasing fitting of the plurality of first coil connectors. 
     The second transmission/reception unit may be configured to be separable at a plurality of positions to be openable and closable and configured to be annular when the second transmission/reception unit is closed so that the second coil is formed by connecting the plurality of second coil parts via the plurality of second coil connectors. 
     The second unit may be assembled to be divisible into first to j-th secondary pieces (j being an integer not smaller than 2), which are not annular, so that the second coil is separated into the plurality of second coil parts by releasing fitting of the plurality of second coil connectors. 
     The first coil may comprise the plurality of first coil parts which are separable at one position and bendable with respect to each other. 
     The second coil may comprise the plurality of second coil parts which are separable at one position and bendable with respect to each other. 
     The first unit may include: 
     first to i-th primary pieces (i being an integer not smaller than 2) which are not annular and which include, respectively, the plurality of first coil parts bendable with respect to each other; and 
     a first connecting mechanism for connecting adjacent ones of the first to the i-th primary pieces so that the first coil is opened in a state of being bent into the plurality of first coil parts by releasing fitting of the one first coil connector. 
     The second unit may include: 
     first to j-th secondary pieces (j being an integer not smaller than 2) which are not annular and which include, respectively, the plurality of second coil parts bendable with respect to each other; and 
     a second connecting mechanism for connecting adjacent ones of the first to the j-th secondary pieces so that the second coil is opened in a state of being bent into the plurality of second coil parts by releasing fitting of the one second coil connector. 
     In order to achieve the above-mentioned object, according to a fifth aspect of the present invention, there is provided a wireless connector for wirelessly transmitting electric power between a first object and a second object, the wireless connector including: 
     a first unit detachably attached to the first object from the outside of the first object; and 
     a second unit detachably attached to the second object from the outside of the second object; 
     wherein the first unit includes: 
     a first transmission/reception unit provided with a first coil configured to wirelessly transmit the electric power and composed of a plurality of first coil parts which are separable from each other or which are separable at one position and bendable with respect to each other; and 
     a first main connector portion for transmitting the electric power to/from the first object by being detachably attached to the first object from the outside of the first object; 
     wherein the second unit includes: 
     a second transmission/reception unit provided with a second coil configured to wirelessly transmit the electric power to/from the first coil of the first transmission/reception unit and composed of a plurality of second coil parts which are separable from each other or which are separable at one position and bendable with respect to each other; and 
     a second main connector portion for transmitting the electric power to/from the second object by being detachably attached to the second object from the outside of the second object; 
     wherein the first transmission/reception unit is configured to be openable and closable and configured to be annular when the first transmission/reception unit is closed so that the first coil is formed by connecting the plurality of first coil parts via one or a plurality of first coil connectors; 
     wherein the second transmission/reception unit is configured to be openable and closable and configured to be annular when the second transmission/reception unit is closed so that the second coil is formed by connecting the plurality of second coil parts via one or a plurality of second coil connectors; 
     wherein the first coil and the second coil are arranged, when the first unit and the second unit are attached to the first object and the second object, respectively, each in a closed annular state and in parallel to each other in a state of being faced to each other in a non-contact manner so as to be magnetically coupled to each other. 
     The first coil may comprise the plurality of first coil parts separable from each other. 
     The second coil may comprise the plurality of second coil parts separable from each other. 
     The first transmission/reception unit may be configured to be separable at a plurality of positions to be openable and closable and configured to be annular when the first transmission/reception unit is closed so that the first coil is formed by connecting the plurality of first coil parts via the plurality of first coil connectors. 
     The first unit may be assembled to be divisible into first to i-th primary pieces (i being an integer not smaller than 2), which are not annular, so that the first coil is separated into the plurality of first coil parts by releasing fitting of the plurality of first coil connectors. 
     The second transmission/reception unit may be configured to be separable at a plurality of positions to be openable and closable and configured to be annular when the second transmission/reception unit is closed so that the second coil is formed by connecting the plurality of second coil parts via the plurality of second coil connectors. 
     The second unit may be assembled to be divisible into first to j-th secondary pieces (j being an integer not smaller than 2), which are not annular, so that the second coil is separated into the plurality of second coil parts by releasing fitting of the plurality of second coil connectors. 
     The first coil may comprise the plurality of first coil parts which are separable at one position and bendable with respect to each other. 
     The second coil may comprise the plurality of second coil parts which are separable at one position and bendable with respect to each other. 
     The first unit may include: 
     first to i-th primary pieces (i being an integer not smaller than 2) which are not annular and which include, respectively, the plurality of first coil parts bendable with respect to each other; and 
     a first connecting mechanism for connecting adjacent ones of the first to the i-th primary pieces so that the first coil is opened in a state of being bent into the plurality of first coil parts by releasing fitting of the one first coil connector. 
     The second unit may include: 
     first to j-th secondary pieces (j being an integer not smaller than 2) which are not annular and which include, respectively, the plurality of second coil parts bendable with respect to each other; and 
     a second connecting mechanism for connecting adjacent ones of the first to the j-th secondary pieces so that the second coil is opened in a state of being bent into the plurality of second coil parts by releasing fitting of the one second coil connector. 
     The first object and the second object may be connected to each other to be rotatable around a rotation axis. 
     Each of the first transmission/reception unit and the second transmission/reception unit may form, in a closed state, a circular annular shape having a through-hole centered on the rotation axis or a polygonal annular shape having the through-hole. 
     The first object and the second object may be connected to each other to be rotatable around a rotation axis. 
     Each of the first coil and the second coil may be arranged, in a state where each of the first transmission/reception unit and the second transmission/reception unit is closed, in a circular annular region having a through-hole centered on the rotation axis or a polygonal annular region having the through-hole. 
     The first object and the second object may be connected to each other to be rotatable around a rotation axis. 
     Each of the first transmission/reception unit and the second transmission/reception unit may form, in a closed state, a circular disk shape having a through-hole centered on the rotation axis. 
     Each of the first coil and the second coil may form a spiral shape in a state where each of the first transmission/reception unit and the second transmission/reception unit is closed. 
     The first transmission/reception unit may include: 
     the first coil which is openable at least at one position so that the first coil is formed by connecting the plurality of first coil parts via the one or the plurality of first coil connectors; and 
     a first holding portion which has one main surface provided with the first coil and which is separable at a position common to the first coil. 
     The second transmission/reception unit may include: 
     the second coil which is openable at least at one position so that the second coil is formed by connecting the plurality of second coil parts via the one or the plurality of second coil connectors; and 
     a second holding portion which has one main surface provided with the second coil and which is separable at a position common to the first coil. 
     The one main surface of the first holding portion and the one main surface of the second holding portion may be those surfaces of the first holding portion and the second holding portion which are close to each other. 
     The first transmission/reception unit may include: 
     the first coil which is openable at least at one position so that the first coil is formed by connecting the plurality of first coil parts via the one or the plurality of first coil connectors; and 
     a first holding portion which accommodates the first coil and which is separable at a position common to the first coil. 
     The second transmission/reception unit may include: 
     the second coil which is openable at least at one position so that the second coil is formed by connecting the plurality of second coil parts via the one or the plurality of second coil connectors; and 
     a second holding portion which accommodates the second coil and which is separable at a position common to the second coil. 
     The first object and the second object may be connected to each other to be rotatable around a rotation axis. 
     Each of the first transmission/reception unit and the second transmission/reception unit may have, in a closed state, a cylindrical shape having a through-hole centered on the rotation axis. 
     Each of the first transmission/reception unit and the second transmission/reception unit may have, in the closed state, a circular cylindrical shape. 
     Each of the first coil and the second coil may have a spiral shape along the rotation axis in a state where each of the first transmission/reception unit and the second transmission/reception unit is closed. 
     The first transmission/reception unit and the second transmission/reception unit may be configured so that, when attached to the first object and the second object, respectively, the first transmission/reception unit and the second transmission/reception unit are spaced from each other along the rotation axis in the closed state. 
     The first transmission/reception unit may include: 
     the first coil which is openable at least at one position so that the first coil is formed by connecting the plurality of first coil parts via the one or the plurality of first coil connectors; and 
     a first holding portion of a cylindrical shape which is provided with the first coil on an inner surface or an outer surface thereof and which is separable at a position common to the first coil. 
     The second transmission/reception unit may include: 
     the second coil which is openable at least at one position so that the second coil is formed by connecting the plurality of second coil parts via the one or the plurality of second coil connectors; and 
     a second holding portion of a cylindrical shape which is provided with the second coil on an inner surface or an outer surface thereof and which is separable at a position common to the second coil. 
     The first transmission/reception unit may include: 
     the first coil which is openable at least at one position so that the first coil is formed by connecting the plurality of first coil parts via the one or the plurality of first coil connectors; and 
     a first holding portion of a cylindrical shape which accommodates the first coil and which is separable at a position common to the first coil. 
     The second transmission/reception unit may include: 
     the second coil which is openable at least at one position so that the second coil is formed by connecting the plurality of second coil parts via the one or the plurality of second coil connectors; and 
     a second holding portion of a cylindrical shape which accommodates the second coil and which is separable at a position common to the second coil. 
     The first transmission/reception unit and the second transmission/reception unit, each in the closed state, may be disposed so as to overlap each other when viewed from a direction perpendicular to the rotation axis by fitting the second transmission/reception unit to an inside of the first transmission/reception unit with a gap left therefrom. 
     The first transmission/reception unit may include: 
     the first coil which is openable at least at one position so that the first coil is formed by connecting the plurality of first coil parts via the one or the plurality of first coil connectors; and 
     a first holding portion of a cylindrical shape which is provided with the first coil on an inner surface thereof and which is separable at a position common to the first coil. 
     The second transmission/reception unit may include: 
     the second coil which is openable at least at one position so that the second coil is formed by connecting the plurality of second coil parts via the one or the plurality of second coil connectors; and 
     a second holding portion of a cylindrical shape which is provided with the second coil on an outer surface thereof and which is separable at a position common to the second coil. 
     The first transmission/reception unit may include: 
     the first coil which is openable at least at one position so that the first coil is formed by connecting the plurality of first coil parts via the one or the plurality of first coil connectors; and 
     a first holding portion of a cylindrical shape which accommodates the first coil and which is separable at a position common to the first coil. 
     The second transmission/reception unit may include: 
     the second coil which is openable at least at one position so that the second coil is formed by connecting the plurality of second coil parts via the one or the plurality of second coil connectors; and 
     a second holding portion of a cylindrical shape which accommodates the second coil and which is separable at a position common to the second coil. 
     In order to achieve the above-mentioned object, according to a sixth aspect of the present invention, there is provided a wireless connector for wirelessly transmitting electric power between a first object and a second object which are connected to each other to be rotatable around a rotation axis, the wireless connector including: 
     a first unit detachably attached to the first object from the outside of the first object; and 
     a second unit detachably attached to the second object from the outside of the second object; 
     wherein the first unit includes: 
     a first transmission/reception unit provided with a first coil configured to wirelessly transmit the electric power and composed of a plurality of first coil parts which are separable from each other or which are separable at one position and bendable with respect to each other; and 
     a first main connector portion for transmitting the electric power to/from the first object by being detachably attached to the first object from the outside of the first object; 
     wherein the second unit includes: 
     a second transmission/reception unit provided with a second coil configured to wirelessly transmit the electric power to/from the first coil of the first transmission/reception unit and composed of a plurality of second coil parts which are separable from each other or which are separable at one position and bendable with respect to each other; and 
     a second main connector portion for transmitting the electric power to/from the second object by being detachably attached to the second object from the outside of the second object; 
     wherein the first transmission/reception unit is configured to be openable and closable and configured to be annular when the first transmission/reception unit is closed so that the first coil is formed by connecting the plurality of first coil parts via one or a plurality of first coil connectors; 
     wherein the second transmission/reception unit is configured to be openable and closable and configured to be annular when the second transmission/reception unit is closed so that the second coil is formed by connecting the plurality of second coil parts via one or a plurality of second coil connectors; 
     wherein the first transmission/reception unit and the second transmission/reception unit are spaced from each other along the rotation axis in a closed state so as to be disposed in a state of being faced to each other in a non-contact manner 
     The first coil may comprise the plurality of first coil parts separable from each other. 
     The second coil may comprise the plurality of second coil parts separable from each other. 
     The first transmission/reception unit may be configured to be separable at a plurality of positions to be openable and closable and configured to be annular when the first transmission/reception unit is closed so that the first coil is formed by connecting the plurality of first coil parts via the plurality of first coil connectors. 
     The first unit may be assembled to be divisible into first to i-th primary pieces (i being an integer not smaller than 2), which are not annular, so that the first coil is separated into the plurality of first coil parts by releasing fitting of the plurality of first coil connectors. 
     The second transmission/reception unit may be configured to be separable at a plurality of positions to be openable and closable and configured to be annular when the second transmission/reception unit is closed so that the second coil is formed by connecting the plurality of second coil parts via the plurality of second coil connectors. 
     The second unit may be assembled to be divisible into first to j-th secondary pieces (j being an integer not smaller than 2), which are not annular, so that the second coil is separated into the plurality of second coil parts by releasing fitting of the plurality of second coil connectors. 
     The first coil may comprise the plurality of first coil parts which are separable at one position and bendable with respect to each other. 
     The second coil may comprise the plurality of second coil parts which are separable at one position and bendable with respect to each other. 
     The first unit may include: 
     first to i-th primary pieces (i being an integer not smaller than 2) which are not annular and which include, respectively, the plurality of first coil parts bendable with respect to each other; and 
     a first connecting mechanism for connecting adjacent ones of the first to the i-th primary pieces so that the first coil is opened in a state of being bent into the plurality of first coil parts by releasing fitting of the one first coil connector. 
     The second unit may include: 
     first to j-th secondary pieces (j being an integer not smaller than 2) which are not annular and which include, respectively, the plurality of second coil parts bendable with respect to each other; and 
     a second connecting mechanism for connecting adjacent ones of the first to the j-th secondary pieces so that the second coil is opened in a state of being bent into the plurality of second coil parts by releasing fitting of the one second coil connector. 
     In order to achieve the above-mentioned object, according to a seventh aspect of the present invention, there is provided a wireless connector for wirelessly transmitting electric power between a first object and a second object which are connected to each other to be rotatable around a rotation axis, the wireless connector including: 
     a first unit detachably attached to the first object from the outside of the first object; and 
     a second unit detachably attached to the second object from the outside of the second object; 
     wherein the first unit includes: 
     a first transmission/reception unit provided with a first coil configured to wirelessly transmit the electric power and composed of a plurality of first coil parts which are separable from each other or which are separable at one position and bendable with respect to each other; and 
     a first main connector portion for transmitting the electric power to/from the first object by being detachably attached to the first object from the outside of the first object; 
     wherein the second unit includes: 
     a second transmission/reception unit provided with a second coil configured to wirelessly transmit the electric power to/from the first coil of the first transmission/reception unit and composed of a plurality of second coil parts which are separable from each other or which are separable at one position and bendable with respect to each other; and 
     a second main connector portion for transmitting the electric power to/from the second object by being detachably attached to the second object from the outside of the second object; 
     wherein the first transmission/reception unit is configured to be openable and closable and configured to be annular when the first transmission/reception unit is closed so that the first coil is formed by connecting the plurality of first coil parts via one or a plurality of first coil connectors; 
     wherein the second transmission/reception unit is configured to be openable and closable and configured to be annular when the second transmission/reception unit is closed so that the second coil is formed by connecting the plurality of second coil parts via one or a plurality of second coil connectors; 
     wherein the first transmission/reception unit and the second transmission/reception unit are spaced from each other along a direction perpendicular to the rotation axis in a closed state so as to be disposed in a state of being faced to each other in a non-contact manner. 
     The first coil may comprise the plurality of first coil parts separable from each other. 
     The second coil may comprise the plurality of second coil parts separable from each other. 
     The first transmission/reception unit may be configured to be separable at a plurality of positions to be openable and closable and configured to be annular when the first transmission/reception unit is closed so that the first coil is formed by connecting the plurality of first coil parts via the plurality of first coil connectors. 
     The first unit may be assembled to be divisible into first to i-th primary pieces (i being an integer not smaller than 2), which are not annular, so that the first coil is separated into the plurality of first coil parts by releasing fitting of the plurality of first coil connectors. 
     The second transmission/reception unit may be configured to be separable at a plurality of positions to be openable and closable and configured to be annular when the second transmission/reception unit is closed so that the second coil is formed by connecting the plurality of second coil parts via the plurality of second coil connectors. 
     The second unit may be assembled to be divisible into first to j-th secondary pieces (j being an integer not smaller than 2), which are not annular, so that the second coil is separated into the plurality of second coil parts by releasing fitting of the plurality of second coil connectors. 
     The first coil may comprise the plurality of first coil parts which are separable at one position and bendable with respect to each other. 
     The second coil may comprise the plurality of second coil parts which are separable at one position and bendable with respect to each other. 
     The first unit may include: 
     first to i-th primary pieces (i being an integer not smaller than 2) which are not annular and which include, respectively, the plurality of first coil parts bendable with respect to each other; and 
     a first connecting mechanism for connecting adjacent ones of the first to the i-th primary pieces so that the first coil is opened in a state of being bent into the plurality of first coil parts by releasing fitting of the one first coil connector. 
     The second unit may include: 
     first to j-th secondary pieces (j being an integer not smaller than 2) which are not annular and which include, respectively, the plurality of second coil parts bendable with respect to each other; and 
     a second connecting mechanism for connecting adjacent ones of the first to the j-th secondary pieces so that the second coil is opened in a state of being bent into the plurality of second coil parts by releasing fitting of the one second coil connector. 
     The first object and the second object may be connected to each other to be rotatable around a rotation axis. 
     Each of the first transmission/reception unit and the second transmission/reception unit may have a center which substantially coincides with a center of the rotation axis. 
     The first object and the second object may be connected to each other to be rotatable around a rotation axis. 
     Each of the first coil and the second coil may have a center which substantially coincides with a center of the rotation axis. 
     The wireless connector may further comprise: 
     a protecting portion which includes an elastic member closing at least a part of a gap continuous to a facing space as a space between the first transmission/reception unit and the second transmission/reception unit in the state of being faced to each other, and which prevents intrusion of foreign matter into the facing space. 
     The protecting portion may further include a first protective cover portion and a second protective cover portion which seal and cover the first coil and the second coil in a closed state, respectively. 
     The elastic member may have a base end provided in one of the first protective cover portion and the second protective cover portion, and a top end brought into contact with the other of the first protective cover portion and the second protective cover portion, thereby closing at least a part of the gap continuous to the facing space. 
     Each of the first coil and the second coil may include a printed wiring. 
     Each of the first coil and the second coil may include a conductor wire. 
     In order to achieve the above-mentioned object, according to an eighth aspect of the present invention, there is provided a wireless connector unit which constitutes a wireless connector for wirelessly transmitting electric power between two objects and which is attached to each of the objects; the wireless connector unit including: 
     a transmission/reception unit provided with a coil configured to wirelessly transmit the electric power and composed of a plurality of coil parts which are separable from each other or which are separable at one position and bendable with respect to each other; and 
     a main connector portion for transmitting the electric power to/from the objects by being detachably attached to the objects from the outside of the objects; 
     wherein the transmission/reception unit is configured to be openable and closable and configured to be annular when the transmission/reception unit is closed so that the coil is formed by connecting the plurality of coil parts via at least one coil connector; 
     wherein the transmission/reception unit is disposed, when attached to one of the two objects in a closed state, in a state of being faced to a different transmission/reception unit in a non-contact manner so as to wirelessly transmit the electric power, the different transmission/reception unit being attached to the other of the two objects in the closed state. 
     Effect of the Invention 
     According to the present invention, the wireless connector can quickly be repaired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of a robot device according to a first embodiment of the present invention; 
         FIG.  2    is another perspective view of the robot device illustrated in  FIG.  1   ; 
         FIG.  3    is a perspective view of a first object and a second object used in the robot device illustrated in  FIGS.  1  and  2   ; 
         FIG.  4    is a perspective view of a wireless connector used in the robot device illustrated in  FIGS.  1  and  2   ; 
         FIG.  5    is a side view of a first unit used in the wireless connector illustrated in  FIG.  4   ; 
         FIG.  6    is a side view of a second unit used in the wireless connector illustrated in  FIG.  4   ; 
         FIG.  7    is a circuit configuration diagram of the wireless connector illustrated in  FIG.  4   ; 
         FIG.  8    is a diagram showing a flow of an attaching method of attaching the wireless connector illustrated in  FIG.  4    to the first object and the second object illustrated in  FIG.  3   ; 
         FIG.  9    is a side view showing a state where a second primary piece of the first unit illustrated in  FIG.  5    is attached to the first object illustrated in  FIG.  3   ; 
         FIG.  10    is a side view showing a state where a first primary piece of the first unit illustrated in  FIG.  5    is attached to the first object illustrated in  FIG.  9    and fixed to the second primary piece; 
         FIG.  11    is a side view showing a state where a second secondary piece of the second unit illustrated in  FIG.  6    is attached to the second object illustrated in  FIG.  10   ; 
         FIG.  12    is a side view showing a state where a first secondary piece of the second unit illustrated in  FIG.  6    is attached to the second object illustrated in  FIG.  11    and fixed to the second secondary piece; 
         FIG.  13    is a diagram showing a flow of a detaching method of detaching the wireless connector illustrated in  FIG.  4    from the first object and the second object illustrated in  FIG.  12   ; 
         FIG.  14    is a perspective view of a wireless connector according to a first modification of the present invention; 
         FIG.  15    is a perspective view of a wireless connector according to a second modification of the present invention; 
         FIG.  16    is a perspective view of a wireless connector according to a second embodiment of the present invention; 
         FIG.  17    is a side sectional view of the wireless connector illustrated in  FIG.  16   ; 
         FIG.  18    is a perspective view of a robot device according to a third embodiment of the present invention; 
         FIG.  19    is a perspective view showing a first unit and a second unit of a wireless connector used in the robot device illustrated in  FIG.  18   ; 
         FIG.  20    is a side sectional view of the wireless connector illustrated in  FIG.  19    in a state of being attached to the first object and the second object; 
         FIG.  21    is a diagram showing a flow of an attaching method of attaching the wireless connector illustrated in  FIG.  19    to the first object and the second object illustrated in  FIG.  20   ; 
         FIG.  22    is a perspective view of a robot device according to a fourth embodiment of the present invention; 
         FIG.  23    is a perspective view of a first unit of a wireless connector used in the robot device illustrated in  FIG.  22   ; 
         FIG.  24    is a perspective view of a second unit of the wireless connector used in the robot device illustrated in  FIG.  22   ; 
         FIG.  25    is a perspective view of a robot device according to a fifth embodiment of the present invention; 
         FIG.  26    is a side sectional view of a wireless connector attached to the robot device illustrated in  FIG.  25   ; 
         FIG.  27    is an enlarged side sectional view of the vicinity of an area surrounded by a dash-dot-dash line in  FIG.  26   ; 
         FIG.  28    is a perspective view of a first unit (second unit) constituting the wireless connector used in the robot device illustrated in  FIG.  25   ; 
         FIG.  29    is a perspective view of a first primary piece (first secondary piece) used in the first unit (second unit) illustrated in  FIG.  28   ; 
         FIG.  30    is a perspective view of a second primary piece (second secondary piece) used in the first unit (second unit) illustrated in  FIG.  28   ; 
         FIG.  31    is a perspective view of a robot device according to a sixth embodiment of the present invention; 
         FIG.  32    is a perspective view showing a closed state of a first unit constituting a wireless connector used in the robot device illustrated in  FIG.  31   ; 
         FIG.  33    is a cross-sectional view of the first unit (second unit) constituting the wireless connector used in the robot device illustrated in  FIG.  31   , taken along a first dividing plane (second dividing plane), enlargedly showing the vicinity of a first connecting mechanism (second connecting mechanism); 
         FIG.  34    is a perspective view showing an open state of the first unit illustrated in  FIG.  32   ; 
         FIG.  35    is a perspective view showing a closed state of the second unit constituting the wireless connector used in the robot device illustrated in  FIG.  31   ; 
         FIG.  36 A  is a diagram showing a configuration of a robot arm device according to the related art disclosed in Patent Document 1; and 
         FIG.  36 B  is a diagram showing a circuit configuration of a wireless power transmission system according to the related art disclosed in Patent Document 1. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, wireless connectors according to embodiments of the present invention will be described with reference to the drawings. Throughout all drawing figures, the same elements are assigned with the same reference numerals. 
     First Embodiment 
     (Configuration of Robot Device  100  According to First Embodiment) 
     A robot device  100  according to a first embodiment of the present invention is an industrial robot in which electric power is wirelessly transmitted between a first object  101  and a second object  102  via a wireless connector  103 . As shown in perspective views of  FIGS.  1  and  2   , the robot device  100  includes the first object  101 , the second object  102 , and the wireless connector  103  for wirelessly transmitting the electric power between the first object  101  and the second object  102 . 
     As shown in  FIG.  3    being a perspective view, the first object  101  and the second object  102  are members constituting the robot device  100 , and are connected to be relatively rotatable around a common rotation axis AR. 
     In the following description, as shown in  FIGS.  1  to  3   , a direction along the rotation axis AR is defined as an up-and-down direction, a direction in which the first object  101  is positioned with respect to the second object  102  is defined as a lower side, and its reverse direction is defined as an upper side. One direction perpendicular to the up-and-down direction is defined as a frond side, and its reverse direction is defined as a rear side. A left-and-right direction is defined according to a direction as seen from the front side. A back-and-forth direction may be referred to as a first direction or a thickness direction while the left-and-right direction may be referred to as a second direction or a transverse direction, and the up-and-down direction may be referred to as a third direction or a height direction. The first to the third directions are perpendicular to one another and define an orthogonal coordinate system. However, it is to be noted that those terms indicating these directions are used for the purpose of explanation and are not intended to limit the present invention. 
     In detail, the first object  101  is covered with a first outer shell (not shown). The first object  101  includes a base portion  104  fixed to a base (not shown), and a first shaft portion  105  provided above the base portion  104 . The second object  102  is covered with a second outer shell (not shown). The second object  102  includes a second shaft portion  106  disposed above the first shaft portion  105 , and a different member connecting portion  107  provided at an upper end of the second shaft portion  106 . 
     Inside the base portion  104  and first shaft portion  105 , electric components and the like are accommodated. In  FIGS.  1  to  3   , an example in which the base portion  104  has a columnar shape extending in the up-and-down direction around the rotation axis AR is shown. However, the shape of the base portion  104  may appropriately be changed. 
     Examples of the electric components accommodated in the base portion  104  and the first shaft portion  105  may be a driving mechanism including a motor, a gear, and the like for rotating the second object  102  around the rotation axis AR, a power source device, and components constituting various circuits. Since the first object  101  is covered with the first outer shell as described above, constituent components inside the first object  101 , such as the electric components accommodated in the base portion  104  and the first shaft portion  105 , are not exposed to the outside. 
     Inside the second shaft portion  106  and the different member connecting portion  107 , electric components and the like are accommodated. The different member connecting portion  107  is connected to a different member (an arm portion performing a turning operation, a hand portion for holding a component, and the like). 
     Examples of the electric components accommodated in the second shaft portion  106  and the different member connecting portion  107  may be a driving mechanism including a gear or the like for rotating with respect to the first object  101  around the rotation axis AR. In addition, the second shaft portion  106  and the different member connecting portion  107  may accommodate a driving mechanism including a motor, a gear, and the like for rotating the different member connected to the different member connecting portion  107 , components constituting various circuits, and so on. Since the second object  102  is covered with the second outer shell as described above, constituent components inside the second object  102 , such as the electric components inside the different member connecting portion  107 , are not exposed to the outside. 
     The first shaft portion  105  and the second shaft portion  106  are columnar parts having the same diameter and each extending in the up-and-down direction around the rotation axis AR, are arranged on the lower side and the upper side, respectively, and are configured to be relatively rotatable around the rotation axis AR. By rotatably connecting the first shaft portion  105  and the second shaft portion  106 , the first object  101  and the second object  102  can be relatively rotated around the common rotation axis AR. 
     An angle at which the first object  101  and the second object  102  are relatively rotatable may be limited within a predetermined range. However, the first object  101  and the second object  102  according to the first embodiment are configured to be rotatable at any desired angle in all directions around the rotation axis AR. 
     Since the first shaft portion  105  and the second shaft portion  106  have the same diameter as described above, their outer peripheral surfaces are configured to be flush with each other in the up-and-down direction. A lower surface of the first shaft portion  105  is smaller than an upper surface of the base portion  104 , and an upper surface of the second shaft portion  106  is smaller than a lower surface of the different member connecting portion  107 . Thus, in the vicinity of a connecting part between the first object  101  and the second object  102 , a recess which is recessed toward the rotation axis AR is formed. 
     When viewed along the rotation axis AR, the wireless connector  103  is attached to the recess so as not to protrude outward beyond the first object  101  and the second object  102 . Consequently, it is possible to reduce the possibility that the wireless connector  103  collides with the different member or the like during an operation of the robot device  100 , as compared with a case where the wireless connector  103  protrudes outward. Therefore, durability of the wireless connector  103  can be improved. 
     The first shaft portion  105  and the second shaft portion  106  include a first mating connector portion  108  and a second mating connector portion  109 , respectively, which are connected to the wireless connector  103 . The first mating connector portion  108  and the second mating connector portion  109  are connectors for transmitting the electric power to/from the wireless connector  103 , and are provided on the first object  101  and the second object  102 , respectively, so as to be exposed outside. 
     The second mating connector portion  109  is provided on the second shaft portion  106 .  FIG.  3    shows an example of a receptacle located on the rear side of the second shaft portion  106  and having a fitting surface facing the rear side. The first mating connector portion  108  is provided on the first shaft portion  105 .  FIG.  3    shows an example of a receptacle located on a left side of the first shaft portion  105  and having a fitting surface facing the left side. 
     The robot device  100  may be a humanoid robot or the like. In this case, the first object  101  and the second object  102  may be provided on a waist, a neck, a wrist, or the like of the humanoid robot. 
     The wireless connector  103  is a connector detachably attached from the outside of the first object  101  and the second object  102 . For example, as shown in  FIGS.  1  and  2   , the wireless connector  103  is attached to the above-mentioned recess formed on an object ( 101 ,  102 ). Here, the term the “object ( 101 ,  102 )” is a generic term for the first object  101  and the second object  102 . This applies in the following also. 
     When attached to the object ( 101 ,  102 ), the wireless connector  103  wirelessly transmits the electric power, for example, from the first object  101  to the second object  102  by magnetic field coupling (in detail, electromagnetic induction) without interfering with a relative rotating operation of the object ( 101 ,  102 ) around the rotation axis AR. The wireless connector  103  may wirelessly transmit the electric power from the second object  102  to the first object  101 . A method of wirelessly transmitting the electric power is not limited to an electromagnetic induction method, but may be a magnetic resonance method as another mode of the magnetic field coupling, or may be transmission/reception of electromagnetic waves such as microwaves. 
     As shown in the perspective views of  FIG.  1   ,  FIG.  2   , and  FIG.  4   , the wireless connector  103  includes a first unit  110  and a second unit  111 . The first unit  110  is detachably attached to the first object  101  from the outside of the first object  101 . The second unit  111  is detachably attached to the second object  102  from the outside of the second object  102 . 
     The first unit  110  and the second unit  111  are, when attached to the first object  101  and the second object  102 , respectively, arranged without contacting each other. Therefore, the first unit  110  and the second unit  111  are, when attached to the first object  101  and the second object  102 , respectively, allowed to be relatively rotated at any desired angle around the rotation axis AR. 
     Here,  FIG.  4    is a perspective view of the wireless connector  103 . As will later be described, the first unit  110  is configured to be divisible into first and second primary pieces  110 A and  110 B by being openable/closable at a plurality of positions. Similarly, the second unit  111  is configured to be divisible into first and second secondary pieces  111 A and  111 B by being openable/closable at a plurality of positions.  FIG.  4    shows a state where the first unit  110  is attached to the first object  101  (i.e., a state where the first unit  110  is closed). The same figure also shows a state where the second unit  111  is divided into the first and the second secondary pieces  111 A and  111 B which are pieces constituting the second unit  111  (i.e., a state where the second unit  111  according to the first embodiment is opened). 
     As shown in a side view of  FIG.  5    in the closed state, the first unit  110  includes a first transmission/reception unit  113  of an annular shape provided with a first coil  112 , two first guide portions  114  to which the first transmission/reception unit  113  is fixed, and a first main connector portion  115  for transmitting the electric power to/from the first object  101 . 
     In the closed state, the first transmission/reception unit  113  is, as a whole, a generally annular circular member having a through-hole centered on the rotation axis AR and, in the first embodiment, has a generally circular disc shape having the through-hole. The first transmission/reception unit  113  includes the first coil  112  for wirelessly transmitting the electric power, and a first holding plate  116 , serving as a first holding portion, for holding the first coil  112 . 
     The first holding plate  116  according to the first embodiment is composed of two rigid substrates. In the closed state, the first holding plate  116  has, as a whole, a generally circular annular shape having a circular through-hole centered on the rotation axis AR. In order to be fixed to the two first guide portions  114  as will later be described, the first holding plate  116  has a plurality of first protrusions  117  protruding outward as a direction away from the rotation axis AR. 
     The first coil  112  is composed of two first coil parts separable from each other. The first coil  112  is configured by connecting two printed wirings, which are conductors comprising the above-mentioned two first coil parts printed on one main surface (an upper surface in the first embodiment) of the first holding plate  116 , through two first coil connectors  118  in a state where the first holding plate  116  is closed. When viewed from above in a state where the first transmission/reception unit  113  is closed, the first coil  112  is arranged in a generally circular annular region having a through-hole centered on the rotation axis AR and, in the first embodiment, is configured to form a generally flat spiral shape. In detail, a part of each printed wiring that is formed at an end portion of each rigid substrate of the first holding plate  116  is electrically connected to the corresponding first coil connector  118  via a through-hole (not shown). Therefore, by electrically connecting the two printed wirings through the two first coil connectors  118 , the first coil  112  has a substantially spiral shape. In the first embodiment, a through-hole connector is used as the first coil connector  118 . However, the present invention is not limited thereto. Instead of the through-hole connector, for example, a SMT (Surface Mount Technology) connector, an adhesive film connector, or a combination of an FPC (Flexible Printed Circuit) connector and an FPC may be used as the first coil connector  118 . 
     Here, the “spiral shape” means a linear or belt-like shape that is turning from an end portion closest to the rotation axis AR around the rotation axis AR and gradually receding from the rotation axis AR. Alternatively, the “spiral shape” means a linear or belt-like shape that is turning from an end portion farthest from the rotation axis AR around the rotation axis AR and gradually approaching the rotation axis AR. “Spiral” may be formed exclusively by a smooth curve, or may include a bent part. 
     The first transmission/reception unit  113  may be configured by fixing a flexible substrate with the first coil  112  printed thereon to the first holding plate  116  made of resin or the like by an adhesive, a double-sided tape, or the like. 
     The two first guide portions  114  are provided separately on the left side and a right side. The two first guide portions  114  are parts to which the first transmission/reception unit  113  is fixed in order to reinforce the first transmission/reception unit  113 , and function as a guide when the first unit  110  is attached to the first object  101 . 
     In the state where the first unit  110  is closed, the two first guide portions  114  are generally annular as a whole and have first peripheral surface portions  119  forming an inner surface positioned on a circumference centered on the rotation axis AR when viewed from above. Each of the two first guide portions  114  is made of metal, resin or the like as a material, and the first protrusions  117  are fixed thereto by screwing via first spacers  120 . 
     When viewed from above in the state where the first unit  110  is closed, the first peripheral surface portions  119  are positioned on a circumference that is the same as or smaller than the through-hole of the first transmission/reception unit  113 , and are provided on a circumference having the substantially same diameter as the outer peripheral surface of the first shaft portion  105 . Therefore, when the first unit  110  is attached to the first object  101 , the first peripheral surface portions  119  are disposed in contact with the outer peripheral surface of the first shaft portion  105 . 
     A method of fixing the two first guide portions  114  and the first transmission/reception unit  113  may be any appropriate method such as an adhesive. For example, if the first transmission/reception unit  113  need not be reinforced, the two first guide portions  114  may not be provided. In this case, similarly to the first peripheral surface portions  119 , a part surrounding the through-hole of the first transmission/reception unit  113  may be disposed in contact with the outer peripheral surface of the first shaft portion  105  when the first unit  110  is attached to the first object  101 . 
     The first main connector portion  115  transmits the electric power to/from the first object  101  by being detachably attached to the first object  101  from the outside of the first object  101 . In detail, the first main connector portion  115  is a plug fitted to the first mating connector portion  108 , and is electrically connected to each of both end portions of the first coil  112 . The first main connector portion  115  may be a receptacle whereas the first mating connector portion  108  may be a plug. 
     The first unit  110  is assembled to be divisible into the first primary piece  110 A and the second primary piece  110 B, which are not annular, so that the first coil  112  can be formed by connecting the two first coil parts constituting the first coil  112  via the two first coil connectors  118 . The first unit  110  is only required to be divisible into i primary pieces (i being an integer equal to or greater than two) which are not annular, and the number thereof is not limited to two. 
     In detail, the first transmission/reception unit  113  is configured to be separable at two positions on the front side and the rear side where the two first coil connectors  118  are provided, so that, by releasing fitting of the two first coil connectors  118 , the first coil  112  is separated into the two first coil parts. Therefore, the first unit  110  is divisible into the first primary piece  110 A on the right side and the second primary piece  110 B on the left side via a first dividing plane including the rotation axis AR, and is formed by combining these primary pieces  110 A an and  110 B. 
     The two first coil connectors  118  are composed of a plug and a receptacle and their fitting planes generally coincide with the above-mentioned first dividing plane. The two first coil parts are connected via the two first coil connectors  118  to thereby form the first coil  112  which is separable and has a spiral shape. 
     Further, the first holding plate  116  is configured to be divisible via the first dividing plane common to the first coil  112 . Thus, it is possible to obtain the first transmission/reception unit  113  which is divisible via the first dividing plane generally coinciding with the fitting planes of the two first coil connectors  118  (i.e., which forms an annular shape openable and closable at two positions). 
     It should be noted that the first dividing plane may be set so as to open the first transmission/reception unit  113  of the annular shape. Therefore, the first coil connectors  118  may be provided depending on the number of the primary pieces constituting the first unit  110  so that their fitting planes coincide with the first dividing plane. 
     The first guide portion  114  on the right side is included in the first primary piece  110 A, and the first guide portion  114  on the left side is included in the second primary piece  110 B. 
     The first main connector portion  115  may be included in either of the first primary piece  110 A and the second primary piece  110 B. In the first embodiment, the first main connector portion  115  is included in the second primary piece  110 B, and is fixed to the first guide portion  114  on the left side via a first circuit portion  121 . 
     The first circuit portion  121  is a circuit board including a power transmission circuit  122  (see  FIG.  7   ) connecting the both end portions of the first coil  112  to the first main connector portion  115 , and so on. 
     The first primary piece  110 A and the second primary piece  110 B are fastened by two first bolts  123  serving as fastening members to be fixed to each other in order to prevent easy release when the first unit  110  is attached to the first object  101 . 
     In detail, in a state where the first unit  110  is assembled, the two first guide portions  114  have, on the front side and the rear side, two first bolt holes  124  continuous in the left-and-right direction for insertion of the two first bolts  123 . 
     The first bolt hole  124  provided in the first guide portion  114  on the left side is opened on the left side. By inserting the first bolt  123  from the left side, a head of the first bolt  123  is locked in the second primary piece  110 B whereas a thread of the first bolt  123  is fitted by a screw action in the first primary piece  110 A. 
     As shown in a side view of  FIG.  6    in a closed state, the second unit  111  generally has a configuration obtained by vertically inverting the first unit  110 . 
     Specifically, the second unit  111  includes a second transmission/reception unit  126  of an annular shape provided with a second coil  125 , two second guide portions  127  to which the second transmission/reception unit  126  is fixed, and a second main connector portion  128  for transmitting electric power to/from the second object  102 . 
     In the closed state, the second transmission/reception unit  126  has, as a whole, a generally circular annular shape having a through-hole centered on the rotation axis AR and, in the first embodiment, has a generally circular disc shape having the through-hole. The second transmission/reception unit  126  and the first transmission/reception unit  113  according to the first embodiment are spaced from each other along the rotation axis AR so as to be disposed in a state of being faced to each other in a non-contact manner. The second transmission/reception unit  126  includes the second coil  125  for wirelessly transmitting the electric power and a second holding plate  129 , serving as a second holding portion, for holding the second coil  125 . 
     The second holding plate  129  according to the first embodiment is composed of two rigid substrates. In the closed state, the second holding plate  129  has, as a whole, a generally circular annular shape having a through-hole centered on the rotation axis AR. In order to be fixed to the two second guide portions  127  as will later be described, the second holding plate  129  has a plurality of second protrusions  130  protruding outward as the direction away from the rotation axis AR. 
     The second coil  125  is composed of two second coil parts separable from each other. The second coil  125  is configured by connecting two printed wirings, which are conductors comprising the two second coil parts printed on one main surface (a lower surface in the first embodiment) of the second holding plate  129 , through two second coil connectors  131  in a state where the second holding plate  129  is closed. When viewed from above in a state where the second transmission/reception unit  126  is closed, the second coil  125  is arranged in a generally circular annular region having a through-hole centered on the rotation axis AR and, in the first embodiment, is configured to form a generally flat spiral shape. In detail, a part of each printed wiring that is formed at an end portion of each rigid substrate of the second holding plate  129  is electrically connected to the corresponding second coil connector  131  via a through-hole (not shown). Therefore, by electrically connecting the two printed wirings through the two second coil connectors  131 , the second coil  125  has a substantially spiral shape. In the first embodiment, a through-hole connector is used as the second coil connector  131 . However, the present invention is not limited thereto. Instead of the through-hole connector, for example, a SMT connector, an adhesive film connector, or a combination of an FPC connector and an FPC may be used as the second coil connector  131  as described above. 
     The second transmission/reception unit  126  may be configured by fixing a flexible substrate with the second coil  125  printed thereon to the second holding plate  129  made of resin or the like by an adhesive, a double-sided tape, or the like. 
     The two second guide portions  127  are provided separately on the front side and the rear side. Each of the two second guide portions  127  is a part to which the second transmission/reception unit  126  is fixed in order to reinforce the second transmission/reception unit  126 , and functions as a guide when the second unit  111  is attached to the second object  102 . 
     In a state where the second unit  111  is closed, the two second guide portions  127  are generally annular as a whole and have second peripheral surface portions  132  forming an inner surface positioned on a circumference centered on the rotation axis AR when viewed from above. Each of the two second guide portions  127  is made of metal, resin or the like as a material, and the second protrusions  130  are fixed by screwing via second spacers  133 . 
     When viewed from above in the state where the second unit  111  is closed, the second peripheral surface portions  132  are positioned on a circumference that is the same as or smaller than the through-hole of the second transmission/reception unit  126 , and is provided on a circumference having the substantially same diameter as the outer peripheral surface of the second shaft portion  106 . Therefore, when the second unit  111  is attached to the second object  102 , the second peripheral surface portions  132  are disposed in contact with the outer peripheral surface of the second shaft portion  106 . 
     A method of fixing the two second guide portions  127  and the second transmission/reception unit  126  may be any appropriate method such as an adhesive. For example, if the second transmission/reception unit  126  need not be reinforced, the second guide portions  127  may not be provided. In this case, similarly to the second peripheral surface portions  132 , a part surrounding the through-hole of the second transmission/reception unit  126  may be disposed in contact with the outer peripheral surface of the second shaft portion  106  when the second unit  111  is attached to the second object  102 . 
     The second main connector portion  128  transmits the electric power to/from the second object  102  by being detachably attached to the second object  102  from the outside of the second object  102 . In detail, the second main connector portion  128  is a plug fitted to the second mating connector portion  109 , and is electrically connected to each of both end portions of the second coil  125 . The second main connector portion  128  may be a receptacle whereas the second mating connector portion  109  may be a plug. 
     The second unit  111  is assembled to be divisible into the first secondary piece  111 A and the second secondary piece  111 B, which are not annular, so that the second coil  125  can be formed by connecting the two second coil parts constituting the second coil  125  via the two second coil connectors  131 . The first unit  110  is only required to be divisible into j secondary pieces (j being an integer equal to or greater than two) which are not annular, and the number thereof is not limited to two. 
     In detail, the second transmission/reception unit  126  is configured to be separable at two positions on the left side and the right side where the two second coil connectors  131  are provided, so that, by releasing fitting of the two second coil connectors  131 , the second coil  125  is separated into the two second coil parts. Therefore, the second unit  111  is divisible into the first secondary piece  111 A on the front side and the second secondary piece  111 B on the rear side via a second dividing plane including the rotation axis AR, and is formed by combining these secondary pieces  111 A an and  111 B. 
     The two second coil connectors  131  are composed of a plug and a receptacle and their fitting planes (planes positioned between the plug and the receptacle fitted to each other) generally coincide with the second dividing plane. The two second coil parts are connected via the two second coil connectors  131  to thereby form the second coil  125  which is separable and has a spiral shape. 
     Further, the second holding plate  129  is configured to be divisible via the second dividing plane common to the second coil  125 . Thus, it is possible to obtain the second transmission/reception unit  126  which is divisible via the second dividing plane generally coinciding with the fitting planes of the two second coil connectors  131  (i.e., which forms an annular shape openable and closable at two positions). 
     It should be noted that the second dividing plane may be set so as to open the second transmission/reception unit  126  of the annular shape. Therefore, the second coil connectors  131  may be provided depending on the number of secondary pieces constituting the second unit  111  so that their fitting planes coincide with the second dividing plane. 
     The second guide portion  127  on the front side is included in the first secondary piece  111 A, and the second guide portion  127  on the rear side is included in the second secondary piece  111 B. 
     The second main connector portion  128  may be included in either of the first secondary piece  111 A and the second secondary piece  111 B. In the first embodiment, the second main connector portion  128  is included in the second secondary piece  111 B, and is fixed to the second guide portion  127  on the rear side via a second circuit portion  134  of a box-like shape. 
     The second circuit portion  134  is a circuit board including a power reception circuit  135  (see  FIG.  7   ) connecting the both end portions of the second coil  125  to the second main connector portion  128 , and so on. 
     The first secondary piece  111 A and the second secondary piece  111 B are fastened by two second bolts  136  serving as fastening members to be fixed to each other in order to prevent easy release when the second unit  111  is attached to the second object  102 . 
     In detail, in a state where the second unit  111  is assembled, the two second guide portions  127  have, on the left side and the right side, two second bolt holes  137  continuous in the front-and-rear direction for insertion of the two second bolts  136 . 
     The second bolt hole  137  provided in the second guide portion  127  on the rear side is opened on the rear side. By inserting the second bolt  136  from the rear side, a head of the second bolt  136  is locked in the second secondary piece  111 B whereas a thread of the second bolt  136  is fitted by a screw action in the first secondary piece  111 A. 
     (Operation of Wireless Connector  103  According to First Embodiment) 
     Now, the operation of the wireless connector  103  according to the first embodiment will be described with reference to a circuit configuration diagram of  FIG.  7   . 
     As shown in  FIG.  7   , electric power (DC power) supplied from the first object  101  (power supply side) is converted into AC power (high frequency power) through the first main connector portion  115  and the power transmission circuit  122  and supplied to the first coil  112 . The power transmission circuit  122  includes, for example, a capacitor connected in series or in parallel to the first coil  112 . The power transmission circuit  122  includes a DC/AC converter, such as an inverter, for converting the DC power into the AC power (high-frequency power). Thus, AC current flows through the first coil  112  and an AC magnetic field is generated around the first coil  112 . 
     The first coil  112  and the second coil  125  are spaced from each other along the rotation axis AR to be disposed in a state of being faced to each other in a non-contact manner Therefore, the first coil  112  and the second coil  125  are magnetically coupled, so that an induced electromotive force corresponding to the AC magnetic field generated around the first coil  112  is generated in the second coil  125 . Thus, in the first embodiment, the first coil  112  functions as a power transmission coil whereas the second coil  125  functions as a power reception coil. 
     Electric power (AC power) generated in the second coil  125  is converted into DC power through the power reception circuit  135  and the second main connector portion  128 , and supplied to the second object  102  (load side). The power reception circuit  135  includes, for example, a capacitor connected in series or in parallel to the second coil  125 . The power reception circuit  135  includes an AC/DC converter, such as a rectifier, for converting the AC power into the DC power. Thus, the wireless connector  103  can wirelessly transmit the electric power between the first object  101  and the second object  102 . 
     In the first embodiment, as described above, the object ( 101 ,  102 ) rotates around the rotation axis AR and, in association therewith, the first unit  110  and the second unit  111  rotate around the rotation axis AR. 
     The first coil  112  and the second coil  125  are fixed in the first unit  110  and the second unit  111 , respectively. Therefore, even when the first unit  110  and the second unit  111  are rotated, the first coil  112  and the second coil  125  are disposed in the state of being faced to each other in a non-contact manner along the rotation axis AR, and are magnetically coupled by electromagnetic induction. 
     The magnetic field coupling between the first coil  112  and the second coil  125  is maintained regardless of a relative rotation angle of the first object  101  and the second object  102  around the rotation axis AR and even during the rotating operation of the first object  101  and the second object  102 . As a result, regardless of the angle of rotation of the first object  101  and the second object  102  and the rotating operation, the wireless connector  103  can operate in the manner similar to the above-described operation to wirelessly transmit the electric power between the first object  101  and the second object  102 . 
     In the first embodiment, the first coil  112  and the second coil  125  are provided on mutually adjacent surfaces among the main surfaces of the first holding plate  116  and the second holding plate  129 . Therefore, the first coil  112  and the second coil  125  can be disposed in close proximity. As a result, coupling force of the magnetic field coupling between the first coil  112  and the second coil  125  is increased to enable efficient wireless power transmission. 
     (Wireless Connector Attaching and Detaching Method According to First Embodiment) 
     Heretofore, the operation of the wireless connector  103  according to the first embodiment of the present invention has been described. Now, a wireless connector attaching and detaching method according to the first embodiment will be described with reference to  FIGS.  8  to  13   . 
     The wireless connector attaching and detaching method according to the first embodiment is a method of attaching and detaching the wireless connector  103  to/from the object ( 101 ,  102 ) included in the robot device  100 , and includes an attaching method and a detaching method for the wireless connector  103 . 
     (Method of Attaching Wireless Connector  103 ) 
       FIG.  8    is a flowchart illustrating a flow of an attaching method of attaching the wireless connector  103  to the object ( 101 ,  102 ). The method of attaching the wireless connector  103  to the object ( 101 ,  102 ) is started by preparing the robot device (see  FIG.  3   ) including the object ( 101 ,  102 ), and the wireless connector  103 . The wireless connector  103  may be prepared in a state where the first unit  110  and the second unit  111  are opened, that is, in a state of being divided into the first primary piece  110 A, the second primary piece  110 B, the first secondary piece  111 A, and the second secondary piece  111 B. 
     As shown in  FIG.  8   , the first unit  110  is attached to the first object  101  from the outside of the first object  101  (step  1 ; step of attaching the first unit). 
     In detail, in step  1 , the second primary piece  110 B is attached to the first object  101  (step  1 A: step of attaching the second primary piece). 
     In the first embodiment, the second primary piece  110 B is disposed so that, in a state where one of the two first coil parts constituting the first coil  112  is directed to the upper side, the first peripheral surface portion  119  is brought into contact with the outer peripheral surface of the first shaft portion  105  while the first main connector portion  115  is fitted to the first mating connector portion  108 . Consequently, the first main connector portion  115  and the first mating connector portion  108  are electrically connected to each other, and the second primary piece  110 B is attached to the first object  101  as shown in a side view of  FIG.  9   . 
     As shown in  FIG.  8   , the first primary piece  110 A is attached to the first object  101  so as to surround the rotation axis AR together with the second primary piece  110 B (step  1  B; step of attaching the first primary piece). 
     In the first embodiment, the first primary piece  110 A is disposed so that, in a state where the other of the two first coil parts constituting the first coil  112  is directed to the upper side, the first peripheral surface portion  119  is brought into contact with the outer peripheral surface of the first shaft portion  105 . At this time, each of the one first coil connectors  118  provided in the first primary piece  110 A is fitted to a corresponding one of the other first coil connectors  118  provided in the second primary piece  110 B. Consequently, the first primary piece  110 A is attached to the first object  101  to form the first coil  112  comprising the two first coil parts connected via the two first coil connectors  118 . In addition, the first transmission/reception unit  113  is put into the closed state and forms an annular shape. 
     As shown in  FIG.  8   , the first primary piece  110 A and the second primary piece  110 B are fastened and fixed by the two first bolts  123  (step  1 C; step of fixing the first unit). 
     In detail, the two first bolts  123  are inserted from the left side of the two first bolt holes  124  and fastened. Consequently, as shown in a side view of  FIG.  10   , the first unit  110  is assembled and fixed to the first object  101 . 
     As shown in  FIG.  8   , the second unit  111  is attached to the second object  102  from the outside of the second object  102  (step  2 ; step of attaching the second unit). 
     In detail, in step  2 , the second secondary piece  111 B is attached to the second object  102  (step  2 A: step of attaching the second secondary piece). 
     In the first embodiment, the second secondary piece  111 B is disposed so that, in a state where one of the two second coil parts constituting the second coil  125  is directed to the lower side, the second peripheral surface portion  132  is brought into contact with the outer peripheral surface of the second shaft portion  106  while the second main connector portion  128  is fitted to the second mating connector portion  109 . Consequently, the second main connector portion  128  and the second mating connector portion  109  are electrically connected to each other, and the second secondary piece  111 B is attached to the second object  102  as shown in a side view of  FIG.  11   . 
     As shown in  FIG.  8   , the first secondary piece  111 A is attached to the second object  102  so as to surround the rotation axis AR together with the second secondary piece  111 B (step  2 B; step of attaching the first secondary piece). 
     In the first embodiment, the first secondary piece  111 A is disposed so that, in a state where the other of the two second coil parts constituting the second coil  125  is directed to the lower side, the second peripheral surface portion  132  is brought into contact with the outer peripheral surface of the second shaft portion  106 . At this time, each of the one second coil connectors  131  provided in the first secondary piece  111 A is fitted to a corresponding one of the other second coil connectors  131  provided in the second secondary piece  111 B. Consequently, the first secondary piece  111 A is attached to the second object  102  to form the second coil  125  comprising the two second coil parts connected via the two second coil connectors  118 . In addition, the second transmission/reception unit  126  is put into the closed state and forms an annular shape. 
     As shown in  FIG.  8   , the first secondary piece  111 A and the second secondary piece  111 B are fastened and fixed by the second bolts  136  (step  2 C; step of fixing the second unit). 
     In detail, the two second bolts  136  are inserted from the rear side of the two second bolt holes  137  and fastened, respectively. Consequently, as shown in a side view of  FIG.  12   , the second unit  111  is assembled and fixed to the second object  102 . 
     Thus, the method of attaching the wireless connector  103  to the object ( 101 ,  102 ) is finished, and the wireless connector  103  is attached to the first object  101  and the second object  102  in a fixed state. In addition, the first transmission/reception unit  113  and the second transmission/reception unit  126  are disposed generally in parallel to each other in a direction generally perpendicular to the rotation axis AR in a state of being faced to each other in a non-contact manner along the rotation axis AR outside the first shaft portion  105  and the second shaft portion  106  so as to wirelessly transmit the electric power. 
     For the wireless connector  103  according to the first embodiment, the order of performing the first unit attaching step (step  1 ) and the second unit attaching step (step  2 ) may be replaced. In step  1 , the order of performing the second primary piece attaching step (step  1 A) and the first primary piece attaching step (step  1 B) may be replaced. Similarly, in step  2 , the order of performing the second secondary piece attaching step (step  2 A) and the first secondary piece attaching step (step  2 B) may be replaced. 
     (Method of Detaching Wireless Connector  103 ) 
       FIG.  13    is a flowchart illustrating a flow of a detaching method of detaching the wireless connector  103  from the object ( 101 ,  102 ). The method of detaching the wireless connector  103  from the object ( 101 ,  102 ) is typically performed as necessary after the wireless connector  103  is attached to the robot device  100  by the above-mentioned method of attaching the wireless connector  103  to the object ( 101 ,  102 ). An example where detachment of the wireless connector  103  from the object ( 101 ,  102 ) is necessary may be a case where the failed wireless connector  103  is replaced with the normal wireless connector  103 . 
     As shown in  FIG.  13   , the first unit  110  is detached from the first object  101  by work outside the first object  101  (step  3 ; step of detaching the first unit). 
     In detail, in step  3 , fixation between the first primary piece  110 A and the second primary piece  110 B is released (step  3 A; step of releasing fixation of the first unit). 
     In the first embodiment, after the two first bolts  123  are loosened to release fitting by the screw action, the two first bolts  123  are pulled out from the left side of the two first bolt holes  124 . Thus, the fixation of the first unit  110  is released. 
     The first primary piece  110 A is detached from the first object  101  (step  3 B; step of detaching the first primary piece). 
     In the first embodiment, the first primary piece  110 A is pulled out to the right side. Consequently, fitting of the two first coil connectors  118  is released and the first primary piece  110 A is detached from the first object  101 . In addition, the first transmission/reception unit  113  is put into an open state and has a shape which is not annular. 
     The second primary piece  110 B is detached from the first object  101  (step  3 C; step of detaching the second primary piece). 
     In the first embodiment, the second primary piece  110 B is pulled out to the left side. Consequently, fitting of the first main connector portion  115  and the first mating connector portion  108  is released and the second primary piece  110 B is detached from the first object  101 . 
     The second unit  111  is detached from the second object  102  by work outside the second object  102  (step  4 ; step of detaching the second unit). 
     In detail, in step  4 , fixation between the first secondary piece  111 A and the second secondary piece  111 B is released (step  4 A; step of releasing fixation of the second unit). 
     In the first embodiment, after the two second bolts  136  are loosened to release fitting by the screw action, the two second bolts  136  are pulled out from the rear side of the two second bolt holes  137 . Thus, fixation of the second unit  111  is released. 
     The first secondary piece  111 A is detached from the first object  101  (step  4 B; step of detaching the first secondary piece). 
     In the first embodiment, the first secondary piece  111 A is pulled out to the front side. Consequently, fitting of the two second coil connectors  131  is released and the first secondary piece  111 A is detached from the second object  102 . In addition, the second transmission/reception unit  126  is put in an open state and has a shape which is not annular. 
     The second secondary piece  111 B is detached from the second object  102  (step  4 C; step of detaching the second secondary piece). 
     In the first embodiment, the second secondary piece  111 B is pulled out to the rear side. Consequently, fitting of the second main connector portion  128  and the second mating connector portion  109  is released and the second secondary piece  111 B is detached from the second object  102 . 
     Thus, the method of detaching the wireless connector  103  from the object ( 101 ,  102 ) is finished, and the wireless connector  103  is detached from the object ( 101 ,  102 ). 
     For the wireless connector  103  according to the first embodiment, the order of performing the first unit detaching step (step  3 ) and the second unit detaching step (step  4 ) may be replaced. In step  3 , the order of performing the first primary piece detaching step (step  3 B) and the second primary piece detaching step (step  3 C) may be replaced. Similarly, in step  4 , the order of performing the first secondary piece detaching step (step  4 B) and the second secondary piece detaching step (step  4 C) may be replaced. 
     According to the first embodiment, when the first main connector portion  115  and the second main connector portion  128  are attached to the first mating connector portion  108  and the second mating connector portion  109 , respectively, the first transmission/reception unit  113  and the second transmission/reception unit  126  are disposed in a state of being faced to each other in a non-contact manner along the rotation axis AR outside the first object  101  and the second object  102  so as to wirelessly transmit the electric power. 
     In other words, when the first unit  110  and the second unit  111  are attached to the first object  101  and the second object  102 , respectively, the first transmission/reception unit  113  and the second transmission/reception unit  126  are disposed, each being in a closed annular state, in a state of being faced to each other in a non-contact manner so as to wirelessly transmit the electric power. In this case, the first coil  112  and the second coil  125  are arranged in parallel with each other in a state of being faced to each other in a non-contact manner so as to wirelessly transmit the electric power. 
     Thus, it is possible to wirelessly transmit the electric power between the first object  101  and the second object  102  even without providing parts interfering with each other between the first unit  110  and the second unit  111  or a part restricting a rotation range of the first object  101  and the second object  102  when the first object  101  and the second object  102  are relatively rotated. 
     Therefore, it is possible to transmit the electric power between the first object  101  and the second object  102  without restricting a relative rotation range between the first object  101  and the second object  102 . 
     Further, according to the first embodiment, the wireless connector  103  can easily be attached to and detached from the first object  101  and the second object  102  from the outside. Therefore, it is possible to quickly repair the wireless connector  103  when failure occurs. 
     Heretofore, the first embodiment of the present invention has been described. The present invention is not limited to the first embodiment but includes modes obtained by modifying the first embodiment as follows. 
     For example, in the first embodiment, an example in which the first coil  112  and the second coil  125  have a flat spiral shape is described. However, the first coil  112  and the second coil  125  may be provided, for example, on curved surfaces having complementary shapes forming a mountain shape and a valley shape, respectively, around the rotation axis AR and may be configured into a spiral shape having a height. 
     For example, in the first embodiment, description has been made of the case in which the first transmission/reception unit  113  and the first coil  112  in the closed state have the generally circular disc shape having the through-hole, and the second transmission/reception unit  126  and the second coil  125  in the closed state also have the generally circular disc shape having the through-hole. However, the shape of each of the first transmission/reception unit, the first coil, the second transmission/reception unit, and the second coil is only required to be annular in the closed state and is not limited to the generally circular disc shape having the through-hole. The first transmission/reception unit, the first coil, the second transmission/reception unit, and the second coil may have a polygonal annular shape in the closed state. In first and second modifications which will later be described, an example in which the first transmission/reception unit and the first coil have a regular polygonal annular shape in the closed state and the second transmission/reception unit and the second coil also have a regular polygonal annular shape will be described with reference to the drawings. 
     &lt;First Modification&gt; 
     As shown in a perspective view of  FIG.  14   , a wireless connector  203  according to a first modification includes a first unit  210  including a first transmission/reception unit  213  instead of the first transmission/reception unit  113 , and a second unit  211  including a second transmission/reception unit  226  instead of the second transmission/reception unit  126 . 
     Each of the first transmission/reception unit  213  and the second transmission/reception unit  226  is a generally equilateral-triangular annular member having an equilateral-triangular through-hole around the rotation axis AR as a center (center of gravity) in a closed state, and has a plate shape. 
     The first transmission/reception unit  213  includes a first coil wound in a generally triangular spiral shape by connecting two first coil parts via the two first coil connectors similar to those of the first embodiment, and a first holding plate  216  provided with the first coil on its upper surface. The second transmission/reception unit  226  includes a second coil wound in a generally triangular spiral shape by connecting two second coil parts via the two second coil connectors  131  similar to those of the first embodiment, and a second holding plate  229  provided with the second coil on its lower surface. 
     As described above, in the wireless connector  203  according to the first modification, the shapes of the first transmission/reception unit  213 , the first coil, the first holding plate  216 , the second transmission/reception unit  226 , the second coil, and the second holding plate  229  are different from the respective shapes according to the above-mentioned first embodiment. 
     Except the above-mentioned points, the wireless connector  203  is configured similarly to the wireless connector  103  according to the first embodiment. 
     Specifically, for example, the first unit  210  is configured by combining a first primary pierce  210 A on the front side and a second primary piece  210 B on the rear side, which are divisible via the first dividing plane including the rotation axis AR. The second unit  211  is configured by combining a first secondary piece  211 A on the front side and a second secondary piece  211 B on the rear side, which are divisible via the second dividing plane including the rotation axis AR. Each of the first primary piece  210 A, the second primary piece  210 B, the first secondary piece  211 A, and the second secondary piece  211 B, when divided, is not annular. 
     &lt;Second Modification&gt; 
     As shown in a perspective view of  FIG.  15   , a wireless connector  303  according to a second modification includes a first unit  310  instead of the first unit  110 , and a second unit  311  instead of the second unit  111 . 
     The first unit  310  includes a first transmission/reception unit  313  instead of the first transmission/reception unit  113 , and two first guide portions  314  instead of the two first guide portions  114 . The second unit  311  includes a second transmission/reception unit  326  instead of the second transmission/reception unit  126 , and two second guide portions  327  instead of the two second guide portions  127 . 
     Each of the first transmission/reception unit  313  and the second transmission/reception unit  326  is a generally regular-octagonal annular member having a regular-octagonal through-hole around the rotation axis AR as a center (center of gravity) in a closed state, and has a plate shape. 
     The first transmission/reception unit  313  includes a first coil wound in a generally octagonal spiral shape by connecting two first coil parts via the two first coil connectors  118  similar to those of the above-mentioned first embodiment, and a first holding plate  316  provided with the first coil on its upper surface. The second transmission/reception unit  326  includes a second coil wound in a generally octagonal spiral shape by connecting two second coil parts via the two second coil connectors  131  similar to those of the above-mentioned first embodiment, and a second holding plate  329  provided with the second coil on its lower surface. 
     As described above, in the wireless connector  303  according to the second modification, the shapes of the first transmission/reception unit  213 , the first coil, the first holding plate  216 , the second transmission/reception unit  226 , the second coil, and the second holding plate  229  are different from the respective shapes according to the above-mentioned first embodiment. 
     Each of the two first guide portions  314  and the two second guide portions  327  has, as an outer shape viewed from above, a generally octagonal shape or a square shape having four corners cut in a gentle arc shape. 
     Except the above-mentioned points, the wireless connector  303  is configured similarly to the wireless connector  103  according to the above-mentioned first embodiment. 
     Specifically, for example, the first unit  310  is configured by combining a first primary piece  310 A on the front side and a second primary piece  310 B on the rear side, which are divisible via the first dividing plane including the rotation axis AR. The second unit  311  is configured by combining a first secondary piece  311 A on the front side and a second secondary piece  311 B on the rear side, which are divisible via the second dividing plane including the rotation axis AR. Each of the first primary piece  310 A, the second primary piece  310 B, the first secondary piece  311 A, and the second secondary piece  311 B, when divided, is not annular. 
     By the wireless connectors  203  and  303  according to the first and the second modifications, it is possible to wirelessly transmit the electric power between the first object  101  and the second object  102  without restricting the relative rotation range between the first object  101  and the second object  102 , similarly to the wireless connector  103  according to the above-mentioned first embodiment. In addition, it is possible to quickly repair the wireless connectors  203  and  303 . 
     Second Embodiment 
     In the above-mentioned first embodiment and the above-mentioned first and the second modifications described above, description has been made of the examples in which each of the first transmission/reception units  113 ,  213 ,  313  and the second transmission/reception units  126 ,  226 , and  326  has a flat-plate shape. However, the shape of each of the first transmission/reception unit and the second transmission/reception unit is only required to be an openable and closable annular shape, and may be an annular shape having a length in the up-and-down direction, that is, a tubular shape. In the second embodiment which will be described below, an example in which each of the first transmission/reception unit and the second transmission/reception unit has a generally circular cylindrical shape, among tubular shapes, will be described. 
     (Configuration of Robot Device According to Second Embodiment) 
     A robot device according to a second embodiment of the present invention includes the first object  101  and the second object  102  similar to those of the first embodiment described above, and a wireless connector  403  for wirelessly transmitting the electric power between the first object  101  and the second object  102 . 
     As shown in a perspective view of  FIG.  16    and a side sectional view of  FIG.  17   , the wireless connector  403  includes a first unit  410  instead of the first unit  110  and a second unit  411  instead of the second unit  111 . The first unit  410  includes a first transmission/reception unit  413  instead of the first transmission/reception unit  113 , and the second unit  411  includes a second transmission/reception unit  426  instead of the second transmission/reception unit  126 . 
     Except the configurations of the first transmission/reception unit  413  and the second transmission/reception unit  426 , the wireless connector  403  according to the second embodiment may be configured generally similarly to the wireless connector  103  according to the above-mentioned first embodiment. In order to simplify the description, in the second embodiment, different points between the first transmission/reception unit  413  and the first transmission/reception unit  113  according to the above-mentioned first embodiment, and different points between the second transmission/reception unit  426  and the second transmission/reception unit  126  according to the first embodiment will mainly be described. 
     In a closed state, the first transmission/reception unit  413  is, as a whole, a generally circular annular member having a through-hole centered on the rotation axis AR and, in the second embodiment, has a generally circular cylindrical shape having the through-hole. The first transmission/reception unit  413  includes a first coil  412  for wirelessly transmitting the electric power and a first holding portion  438  for holding the first coil  412 . 
     The first holding portion  438  according to the second embodiment is composed of two semi-circular-cylindrical members. In a closed state, the first holding portion  438  is, as a whole, a generally circular cylindrical member having a columnar through-hole centered on the rotation axis AR, and is made of, for example, resin. The first holding portion  438  has flange-shaped first protrusions  417  formed at a lower end and protruding outward to be fixed to the first guide portions  114  similar to those of the first embodiment. 
     The first coil  412  is composed of two first coil parts separable from each other. The first coil  412  is configured by connecting two wiring patterns, which include the two first coil parts provided on an outer peripheral surface of the first holding portion  438 , via two first coil connectors  418  in the state where the first holding portion  438  is closed. The first coil  412  has a spiral shape along the rotation axis AR in a state where the first transmission/reception unit  413  is closed, and is provided in a generally circular annular region (generally on a circumference in the second embodiment) having a through-hole centered on the rotation axis AR when viewed from above. The first coil  412  may be provided on an inner peripheral surface of the first holding portion  438 . 
     The first transmission/reception unit  413  according to the second embodiment may be configured by fixing a flexible substrate with the first coil  412  printed thereon to the first holding portion  438  by an adhesive, a double-sided tape, or the like/ 
     In a closed state, the second transmission/reception unit  426  is, as a whole, a generally circular annular member having a through-hole centered on the rotation axis AR and, in the second embodiment, has a generally circular cylindrical shape having a through-hole similarly to the first transmission/reception unit  413  described above. The dimension thereof is substantially the same as that of the first transmission/reception unit  413 . 
     The second transmission/reception unit  426  and the first transmission/reception unit  413  are, when attached to the second object  102  and the first object  101 , respectively, spaced from each other along the rotation axis AR to be disposed in a state of being faced to each other in a non-contact manner, similarly to the above-mentioned first embodiment. Therefore, the second transmission/reception unit  426  and the first transmission/reception unit  413  are arranged so as not to overlap each other when viewed from a direction perpendicular to the rotation axis AR. 
     The second transmission/reception unit  426  includes a second coil  425  for wirelessly transmitting the electric power and a second holding portion  439  for holding the second coil  425 . 
     Similarly to the above-mentioned first holding portion  438  mentioned above, the second holding portion  439  according to the second embodiment is composed of two semi-circular-cylindrical members. In a closed state, the second holding portion  439  is, as a whole, a generally circular cylindrical member having a columnar through-hole centered on the rotation axis AR, and is made of, for example, resin. The dimension of the second holding portion  439  is generally the same as that of the first holding portion  438 . The second holding portion  439  has flange-shaped second protrusions  430  protruding outward to be fixed to the second guide portions  127  similar to those of the above-mentioned first embodiment. 
     The second coil  425  is composed of two second coil parts separable from each other. The second coil  425  is configured by connecting two wiring patterns, which include two second coil parts provided on an outer peripheral surface of the second holding portion  439 , via two second coil connectors  431  in a state where the second holding portion  439  is closed. The second coil  425  has a spiral shape along the rotation axis AR in a state where the second transmission/reception unit  426  is closed, and is provided in a generally circular annular region (generally on a circumference in the second embodiment) having a through-hole centered on the rotation axis AR when viewed from above. The second coil  425  may be provided on an inner peripheral surface of the second holding portion  439 . 
     The second transmission/reception unit  426  according to the second embodiment may be configured by fixing a flexible substrate with the second coil  425  printed thereon to the second holding portion  439  by an adhesive, a double-sided tape, or the like. 
     Except these points, the wireless connector  403  may be configured similarly to the wireless connector  103  according to the above-mentioned first embodiment. 
     Specifically, for example, the first unit  410  is configured by combining a first primary piece  410 A on the front side and a second primary piece  410 B on the rear side, which are divisible via the first dividing plane including the rotation axis AR. The second unit  411  is configured by combining a first secondary piece  411 A on the front side and a second secondary piece  411 B on the rear side, which are divisible via the second dividing plane including the rotation axis AR. Each of the first primary piece  410 A, the second primary piece  410 B, the first secondary piece  411 A, and the second secondary piece  411 B, when divided, is not annular. 
       FIG.  16    and  FIG.  17    show an example in which the first and the second transmission/reception units  413  and  426  are directly fixed to the first and the second guide portions  114  and  127 , respectively. However, it is needless to say that, as in the above-mentioned first embodiment, the first and the second transmission/reception units  413  and  426  may be fixed to the first and the second guide portions  114  and  127  via the first and the second spacers  120  and  133 , respectively. 
     (Operation and Attaching and Detaching Method for Wireless Connector  403  According to Second Embodiment) 
     In the wireless connector  403  according to the second embodiment, the first coil  412  and the second coil  425  are magnetically coupled in the manner similar to the first coil  112  and the second coil  125  of the wireless connector  103  according to the above-mentioned first embodiment described with reference to  FIG.  7   , respectively. Therefore, the wireless connector  403  can operate similarly to the wireless connector  103  according to the above-mentioned first embodiment. 
     The wireless connector  403  according to the second embodiment can also be attached and detached by the method similar to that for the wireless connector  103  according to the above-mentioned first embodiment described with reference to  FIG.  8    and  FIG.  13   . 
     By the wireless connector  403  according to the second embodiment also, it is possible to wirelessly transmit the electric power between the first object  101  and the second object  102  without restricting the relative rotation range between the first object  101  and the second object  102 , as in the above-mentioned first embodiment. Further, the wireless connector  403  can easily be attached to and detached from the first object  101  and the second object  102  from the outside, similarly to the wireless connector  103  according to the above-mentioned first embodiment. Therefore, it is possible to quickly repair the wireless connector  403  when failure occurs. 
     Third Embodiment 
     In the second embodiment described above, description has been made of the example in which the first transmission/reception unit  413  and the second transmission/reception unit  426  have circular cylindrical shapes substantially same in size. However, the first transmission/reception unit  413  and the second transmission/reception unit  426  may have cylindrical shapes fitted to each other. In the third embodiment which will be described below, an example in which the first transmission/reception unit and the second transmission/reception unit are fitted to each other by having cylindrical shapes different in diameter will be described. 
     (Configuration of Robot Device  500  According to Third Embodiment) 
     As shown in a perspective view of  FIG.  18   , a robot device  500  according to the third embodiment of the present invention includes the first object  101  and the second object  102  similar to those of the above-mentioned first embodiment, and a wireless connector  503  for wirelessly transmitting the electric power between the first object  101  and the second object  102 . 
     As shown in a perspective view of  FIG.  19    and a side sectional view of  FIG.  20   , the wireless connector  503  includes a first unit  510  instead of the first unit  410  and a second unit  511  instead of the second unit  411 . The first unit  510  includes a first transmission/reception unit  513  instead of the first transmission/reception unit  413 , and the second unit  511  includes a second transmission/reception unit  526  instead of the second transmission/reception unit  426 . 
     Except the configurations of the first transmission/reception unit  513  and the second transmission/reception unit  526 , the wireless connector  503  according to the third embodiment may be configured substantially similarly to the wireless connector  403  according to the above-mentioned second embodiment. In order to simplify the description, in the third embodiment, different points between the first transmission/reception unit  513  and the first transmission/reception unit  413  according to the above-mentioned second embodiment, and different points between the second transmission/reception unit  526  and the second transmission/reception unit  426  according to the above-mentioned second embodiment will be described. 
     In a closed state, the first transmission/reception unit  513  is, as a whole, a generally circular annular member having a through-hole centered on the rotation axis AR, and has a generally circular cylindrical shape having the through-hole as in the above-mentioned second embodiment. The first transmission/reception unit  513  includes a first coil  512  for wirelessly transmitting the electric power, and a first holding portion  538  for holding the first coil  512 . 
     The first holding portion  538  according to the third embodiment may be configured similarly to the first holding portion  438  according to the above-mentioned second embodiment. Specifically, the first holding portion  538  is composed of two semi-circular-cylindrical members. In a closed state, the first holding portion  538  is, as a whole, a generally circular cylindrical member having a columnar through-hole centered on the rotation axis AR, and is made of, for example, resin. The first holding portion  538  has flange-shaped first protrusions  517  formed at a lower end and protruding outward to be fixed to the first guide portions  114  similar to those of the above-mentioned first embodiment. 
     The first coil  512  is composed of two first coil parts separable from each other. The first coil  512  is configured by connecting two wiring patterns, which include the two first coil parts provided on an inner peripheral surface of the first holding portion  538 , via two first coil connectors  518  in the state where the first holding portion  538  is closed. The first coil  512  has a spiral shape along the rotation axis AR in the state where the first transmission/reception unit  513  is closed, and is provided in a generally circular annular region (generally on a circumference in the third embodiment) having a through-hole centered on the rotation axis AR when viewed from above. 
     The first transmission/reception unit  513  according to the third embodiment may be configured by fixing a flexible substrate with the first coil  512  printed thereon to the inner peripheral surface of the first holding portion  538  by an adhesive, a double-sided tape, or the like. 
     In a closed state, the second transmission/reception unit  526  is, as a whole, a generally circular annular member having a through-hole centered on the rotation axis AR, and has a generally circular cylindrical shape having the through-hole similarly to the above-mentioned first transmission/reception unit  513 . 
     In the third embodiment, in the closed state, the diameter of an outer peripheral surface of the second transmission/reception unit  526  is smaller than the diameter of an inner peripheral surface of the first transmission/reception unit  513 . Thus, the second transmission/reception unit  526  attached to the second object  102  is fitted to the inside of the first transmission/reception unit  513  attached to the first object  101  with a gap left therefrom. Therefore, when the first unit  510  and the second unit  511  are attached to the first object  101  and the second object  102 , respectively, the second transmission/reception unit  526  and the first transmission/reception unit  513  are arranged so as to overlap each other when viewed from a direction perpendicular to the rotation axis AR. Thus, the second transmission/reception unit  526  and the first transmission/reception unit  513  according to the third embodiment are spaced from each other along the direction perpendicular to the rotation axis AR to be disposed in a state of being faced to each other in a non-contact manner. 
     The second transmission/reception unit  526  includes a second coil  525  for wirelessly transmitting the electric power and a second holding portion  539  for holding the second coil  525 . 
     The second holding portion  539  according to the third embodiment is composed of two semi-cylindrical members. In a closed state, the second holding portion  539  is, as a whole, a generally circular cylindrical member having a columnar through-hole centered on the rotation axis AR, and is made of, for example, resin. The dimension of the second holding portion  539  in the direction of the rotation axis AR is generally the same as that of the first holding portion  538 . In contrast, the dimension of the second holding portion  539  in a radial direction is smaller than that of the first holding portion  538 . The second holding portion  539  has flange-shaped second protrusions  530  formed at an upper end and protruding outward to be fixed to the second guide portions  127  similar to those of the above-mentioned first embodiment. 
     The second coil  525  is composed of two second coil parts separable from each other. The second coil  525  is configured by connecting two wiring patterns, which include the two second coil parts provided on an outer peripheral surface of the second holding portion  539 , via two second coil connectors  531  in the state where the second holding portion  539  is closed. The second coil  525  has a spiral shape along the rotation axis AR in a state where the second transmission/reception unit  526  is closed, and is provided in a generally circular annular region (generally on a circumference in the third embodiment) having a through-hole centered on the rotation axis AR when viewed from above. 
     The second transmission/reception unit  526  according to the third embodiment may be configured by fixing a flexible substrate with the second coil  525  printed thereon to the outer peripheral surface of the second holding portion  539  by an adhesive, a double-sided tape, or the like. 
     Except these points, the wireless connector  503  may be configured similarly to the wireless connector  403  according to the above-mentioned second embodiment. 
     Specifically, for example, the first unit  510  is configured by combining a first primary piece  510 A on the right side and a second primary piece  510 B on the left side, which are divisible via the first dividing plane including the rotation axis AR. The second unit  511  is configured by combining a first secondary piece  511 A on the front side and a second secondary piece  511 B on the rear side, which are divisible via the second dividing plane including the rotation axis AR. Each of the first primary piece  510 A, the second primary piece  510 B, the first secondary piece  511 A, and the second secondary piece  511 B, when divided, is not annular. 
       FIG.  18    to  FIG.  20    show an example in which the first and the second transmission/reception units  513  and  526  are directly fixed to the first and the second guide portions  114  and  127 , respectively. However, it is needless to say that, as in the above-mentioned first embodiment, the first and the second transmission/reception units  513  and  526  may be fixed to the first and the second guide portions  114  and  127  via the first and the second spacers  120  and  133 , respectively. 
     (Operation of Wireless Connector  503  According to Third Embodiment) 
     According to the wireless connector  503  of the third embodiment, the first coil  512  and the second coil  525  are spaced from each other along the direction perpendicular to the rotation axis AR to be disposed in a state of being faced to each other in a non-contact manner. Similarly to the first coil  112  and the second coil  125  of the wireless connector  103  according to the above-mentioned first embodiment described with reference to  FIG.  7   , the first coil  512  and the second coil  525  are magnetically coupled. Therefore, the wireless connector  503  can operate similarly to the wireless connector  103  according to the above-mentioned first embodiment. 
     In the third embodiment, the first coil  512  and the second coil  525  are provided on those peripheral surfaces, which are closely adjacent to each other, among the inner peripheral surfaces and the outer peripheral surfaces of the first holding portion  538  and the second holding portion  539 , respectively. Consequently, the first coil  512  and the second coil  525  can be disposed in close proximity. As a result, coupling force of magnetic field coupling between the first coil  512  and the second coil  525  is increased to enable efficient wireless power transmission. 
     (Wireless Connector Attaching and Detaching Method According to Third Embodiment) 
     In the wireless connector  503  according to the third embodiment, the second transmission/reception unit  526  is disposed inside the first transmission/reception unit  513 . Therefore, in the method of attaching the wireless connector to the object ( 101 ,  102 ) according to the third embodiment, as shown in a flowchart of  FIG.  21   , a second unit attaching step (step  2 ) is performed first, followed by a first unit attaching step (step  1 ). Details of the step  2  and the step  1  are generally similar to those of the above-mentioned first embodiment. 
     The detaching method of detaching the wireless connector  503  according to the third embodiment from the object ( 101 ,  102 ) may be the method similar to that for the wireless connector  103  according to the above-mentioned first embodiment described with reference to  FIG.  13   . 
     By the wireless connector  503  according to the third embodiment also, it is possible to wirelessly transmit the electric power between the first object  101  and the second object  102  without restricting the relative rotation range between the first object  101  and the second object  102 , as in the above-mentioned first embodiment. Further, similarly to the wireless connector  103  according to the above-mentioned first embodiment, the wireless connector  503  can easily be attached to and detached from the first object  101  and the second object  102  from the outside. Therefore, it is possible to quickly repair the wireless connector  503  when failure occurs. 
     Fourth Embodiment 
     In the above-mentioned first to the third embodiments, description has been made of the example in which the first coils  112 ,  412 ,  512  and the second coils  125 ,  425 , and  525  are formed by printed wirings. However, the first coil and the second coil may be a conductor wire, a coated conductor wire obtained by coating the conductor wire, or the like. In a fourth embodiment which will be described below, an example in which first coil and second coil formed by coated conductor wires are used in place of the first coil  112  and the second coil  125  of the wireless connector  103  according to the above-mentioned first embodiment will be described. 
     The first coil and the second coil formed by the coated conductor wires as described below may be used as the first coil and the second coil according to the other embodiments, such as the second and the third embodiments. 
     (Configuration of Robot Device  600  According to Fourth Embodiment) 
     As shown in a perspective view of  FIG.  22   , a robot device  600  according to the fourth embodiment of the present invention includes the first object  101  and the second object  102  similar to those of the above-mentioned first embodiment, and a wireless connector  603  for wirelessly transmitting the electric power between the first object  101  and the second object  102 . 
     As shown in a perspective view of  FIG.  22   , the wireless connector  603  includes a first unit  610  instead of the first unit  110  and a second unit  611  instead of the second unit  111 . As shown in a perspective view of  FIG.  23   , the first unit  610  includes a first transmission/reception unit  613  instead of the first transmission/reception unit  113 . As shown in a perspective view of  FIG.  24   , the second unit  611  includes a second transmission/reception unit  626  instead of the second transmission/reception unit  126 . 
     Except the configurations of the first transmission/reception unit  613  and the second transmission/reception unit  626 , the wireless connector  603  according to the fourth embodiment may be configured generally similarly to the wireless connector  103  according to the above-mentioned first embodiment. In order to simplify the description, in the fourth embodiment, different points between the first transmission/reception unit  613  and the first transmission/reception unit  113  according to the above-mentioned first embodiment, and different points between the second transmission/reception unit  626  and the second transmission/reception unit  126  according to the above-mentioned first embodiment will be described. 
     As shown in  FIG.  23   , in a closed state, the first transmission/reception unit  613  is, as a whole, is a generally circular annular member having a through-hole centered on the rotation axis AR, and has a generally circular disc shape having the through-hole as in the above-mentioned first embodiment. The first transmission/reception unit  613  includes a first coil  612  for wirelessly transmitting the electric power and a first holding portion  638  for holding the first coil  612 . 
     In a closed state, the first holding portion  638  according to the fourth embodiment is, as a whole, a generally circular annular member having a circular through-hole centered on the rotation axis AR, and is made of, for example, resin. The first holding portion  638  has a plurality of first annular groove portions  640  on one main surface (an upper surface in the fourth embodiment). The first annular groove portions  640  according to the fourth embodiment are provided in three rows, each forming a circular annular groove. It is required to provide one or more first annular groove portions  640 . 
     The first holding portion  638  has a plurality of through-holes penetrating in the up-and-down direction, and is fixed to the first guide portions  114 , similar to those of the above-mentioned first embodiment, by screws provided through the respective through-holes. A method of fixing the first holding portion  638  to the first guide portions  114  is not limited to screwing, and any appropriate method such as an adhesive or a double-sided tape may be adopted. 
     The first coil  612  is composed of two first coil parts separable from each other. The first coil  612  is configured by connecting two coated conductor patterns, which constitute the two first coil parts fitted to the first annular groove portions  640 , via two first coil connectors  618  in the state where the first holding portion  638  is closed. The coated conductor wires constituting the first coil  612  are accommodated in the first holding portion  638  by being fitted into the first annular groove portions  640 . The first coil  612  is provided in a generally circular annular region having a through-hole centered on the rotation axis AR when viewed from above in the state where the first transmission/reception unit  613  is closed, and has a generally flat spiral shape in the fourth embodiment. An upper side of the first coil  612  may be covered by fixing a lid (not shown) to the first holding portion  638 . 
     As shown in  FIG.  24   , in a closed state, the second transmission/reception unit  626  is, as a whole, a generally circular annular member having a circular through-hole centered on the rotation axis AR, and has a generally circular disc shape having the through-hole as in the above-mentioned first embodiment. The second transmission/reception unit  626  includes a second coil  625  for wirelessly transmitting the electric power and a second holding portion  639  for holding the second coil  625 . 
     In a closed state, the second holding portion  639  according to the fourth embodiment is, as a whole, a generally circular annular member having a circular through-hole centered on the rotation axis AR, and is made of, for example, resin. The second holding portion  639  has a plurality of second annular groove portions  641  on one main surface (a lower surface in the fourth embodiment). The second annular groove portions  641  according to the fourth embodiment are provided in three rows, each forming a circular annular groove. It is only required to provide one or more second annular groove portions  641 . 
     The second holding portion  639  has a plurality of through-holes penetrating in the up-and-down direction, and is fixed to the second guide portions  127 , similar to the above-mentioned first embodiment, by screws provided through the respective through-holes. A method of fixing the second holding portion  639  to the second guide portions  127  is not limited to screwing, and any appropriate method such as an adhesive or a double-sided tape may be adopted. 
     The second coil  625  is composed of two second coil parts separable from each other. The second coil  625  is configured by connecting two coated conductor patterns, which constitute the two second coil parts fitted to the second annular groove portions  641 , via two second coil connectors  631  in the state where the second holding portion  639  is closed. The coated conductor wires constituting the second coil  625  are accommodated in the second holding portion  639  by being fitted into the second annular groove portions  641 . The second coil  625  is provided in a generally circular annular region having a through-hole centered on the rotation axis AR when viewed from above in the state where the second transmission/reception unit  626  is closed, and has a generally flat spiral shape in the fourth embodiment. A lower side of the second coil  625  may be covered by fixing a lid (not shown) to the second holding portion  639 . 
     Except these points, the wireless connector  603  may be configured similarly to the wireless connector  103  according to the above-mentioned first embodiment. 
     Specifically, for example, the first unit  610  is configured by combining a first primary piece  610 A on the right side and a second primary piece  610 B on the left side, which are divisible via the first dividing plane including the rotation axis AR. The second unit  611  is configured by combining a first secondary piece  611 A on the front side and a second secondary piece  611 B on the rear side, which are divisible via the second dividing plane including the rotation axis AR. Each of the first primary piece  610 A, the second primary piece  610 B, the first secondary piece  611 A, and the second secondary piece  611 B, when divided, is not annular. 
       FIG.  22    to  FIG.  24    show an example in which the first and the second transmission/reception units  613  and  626  are directly fixed to the first and the second guide portions  114  and  127 , respectively. However, it is needless to say that, as in the above-mentioned first embodiment, the first and the second transmission/reception units  613  and  626  may be fixed to the first and the second guide portions  114  and  127  via the first and the second spacers  120  and  133 , respectively. 
     (Operation and Attaching and Detaching Method for Wireless Connector  603  According to Fourth Embodiment) 
     According to the wireless connector  603  of the fourth embodiment, the first coil  612  and the second coil  625  are magnetically coupled similarly to the first coil  112  and the second coil  125  of the wireless connector  103  according to the above-mentioned first embodiment described with reference to  FIG.  7   . Therefore, the wireless connector  603  can operate similarly to the wireless connector  103  according to the above-mentioned first embodiment. 
     The wireless connector  603  according to the fourth embodiment can also be attached and detached by the method similar to that for the wireless connector  103  according to the above-mentioned first embodiment described with reference to  FIG.  8    and  FIG.  13   . 
     By the wireless connector  603  according to the fourth embodiment also, it is possible to wirelessly transmit the electric power between the first object  101  and the second object  102  without restricting the relative rotation range between the first object  101  and the second object  102 , as in the above-mentioned first embodiment. Further, similarly to the wireless connector  103  according to the above-mentioned first embodiment, the wireless connector  603  can easily be attached to and detached from the first object  101  and the second object  102  from the outside. Therefore, it is possible to quickly repair the wireless connector  603  when failure occurs. 
     Fifth Embodiment 
     The first transmission/reception units  113 ,  213 ,  313 ,  414 ,  513  and  613  and the second transmission/reception units  126 ,  226 ,  326 ,  426 ,  526 , and  626 , which have been described above, are arranged so as to face each other in a non-contact manner with a gap left from each other. Therefore, foreign matters such as liquid droplets and dust may enter a space therebetween. Examples of the dust include metal powder, gravel, and the like which are scattered around. 
     In a case where such foreign matter is relatively large, rotating operation between the first transmission/reception units  113 ,  213 ,  313 ,  414 ,  513 , and  613  and the second transmission/reception units  126 ,  226 ,  326 ,  426 ,  526 , and  626  may possibly be interfered and these units may be damaged by the foreign matter. Even if the foreign matter is very small, coupling force between the coils due to magnetic field coupling may be weakened when the foreign matter is accumulated together with oil droplets or the like. 
     In order to prevent such intrusion of the foreign matter into the space between the first transmission/reception units  113 ,  213 ,  313 ,  414 ,  513 , and  613  and the second transmission/reception units  126 ,  226 ,  326 ,  426 ,  526 , and  626 , a protecting portion may be provided. In the fifth embodiment, description will be made of an example in which the protecting portion is provided in a wireless connector as a modification of the wireless connector  103  according to the above-mentioned first embodiment. Note that the protecting portion according to the fifth embodiment may be appropriately modified and applied to the wireless connectors according to the other embodiments such as the second to the fourth embodiments. 
     (Configuration of Robot Device  700  According to Fifth Embodiment) 
     As shown in a perspective view of  FIG.  25   , a robot device  700  according to the fifth embodiment of the present invention includes the first object  101  and the second object  102  similar to those of the above-mentioned first embodiment, and a wireless connector  703  for wirelessly transmitting electric power between the first object  101  and the second object  102 . 
     As shown in  FIGS.  25  to  30   , the wireless connector  703  includes a first unit  710  instead of the first unit  110  and a second unit  711  instead of the second unit  111 . Further, the wireless connector  703  includes an elastic member  742  interposed between the first unit  710  and the second unit  711 . 
     Herein,  FIG.  25    is a perspective view of the robot device  700  according to the fifth embodiment.  FIG.  26    is a view of a cross section of the wireless connector  703  attached to the object ( 101 ,  102 ) of the robot device  700  at the first dividing plane including the rotation axis AR as viewed from a right side.  FIG.  27    is an enlarged sectional view of the vicinity of a part surrounded by a dash-dot-dash line C in  FIG.  26   . 
       FIG.  28    is a perspective view of the first unit  710  constituting the wireless connector  703  according to the fifth embodiment. In  FIG.  28   , reference numerals of constituent components of the second unit  711  are indicated in parentheses following reference numerals of corresponding constituent components of the first unit  710 . Arrows in parentheses indicating frontward, rearward, upward, downward, leftward, and rightward directions correspond to the second unit  711 . 
     Also in the fifth embodiment, the first unit  710  is configured by combining a first primary piece  710 A on the right side and a second primary piece  710 B on the left side, which are divisible via the first dividing plane including the rotation axis AR.  FIG.  29    is a perspective view showing the first primary piece  710 A, and  FIG.  30    is a perspective view showing the second primary piece  710 B. 
     The second unit  711  is configured by combining a first secondary piece  711 A on the front side and a second secondary piece  711 B on the rear side, which are divisible via the second dividing plane including the rotation axis AR. The first secondary piece  711 A and the second secondary piece  711 B have generally the same configurations as the first primary piece  710 A and the second primary piece  710 B, respectively, except that the elastic member  742  is not provided. 
     Therefore, in  FIG.  29   , reference numerals of constituent components of the first secondary piece  711 A are indicated in parentheses following reference numerals of the corresponding components of the first primary piece  710 A. In addition, in  FIG.  29   , arrows in parentheses indicating frontward, rearward, upward, downward, leftward, and rightward directions correspond to the first secondary piece  711 A. 
     Similarly, in  FIG.  30   , reference numerals of constituent components of the second secondary piece  711 B are indicated in parentheses following reference numerals of corresponding constituent components of the second primary piece  710 B. In addition, in  FIG.  30   , arrows in parentheses indicating frontward, rearward, upward, downward, leftward, and rightward directions correspond to the second secondary piece  711 B. 
     As shown in  FIGS.  26  to  30   , the first unit  710  includes the first main connector portion  115  similar to that of the above-mentioned first embodiment, and a first transmission/reception unit  713  and two first guide portions  714  instead of the first transmission/reception unit  113  and the two first guide portions  114  according to the above-mentioned first embodiment. Further, the first unit  710  includes a first protective cover portion  743 . 
     The first transmission/reception unit  713  includes the first coil  112  similar to that of the above-mentioned first embodiment, and a first holding plate  716  instead of the first holding plate  116  according to the above-mentioned first embodiment. 
     In a closed state, the first holding plate  716  is, as a whole, a generally circular annular rigid substrate having a circular through-hole centered on the rotation axis AR, and holds the first coil  112  as a first holding portion. The first holding plate  716  is different from the first holding plate  116  according to the above-mentioned first embodiment in that the first protrusions  117  are not provided. 
     The first coil  112  is not provided in a belt-like annular part along an outer edge of the first holding plate  716 . Through through-holes formed in that part, the first holding plate  716  is screwed to the first guide portions  714 . Without being limited to screwing, the first holding plate  716  may be fixed to the first guide portions  714  by any appropriate method. 
     Similarly to the two first guide portions  114  according to the above-mentioned first embodiment, the two first guide portions  714  are provided separately on the left side and the right side, are parts to which the first transmission/reception unit  713  is fixed in order to reinforce the first transmission/reception unit  713 , and function as a guide when the first unit  710  is attached to the first object  101 . 
     The two first guide portions  714  are generally annular as a whole in a state where the first unit  710  is closed, and each include a first flat plate portion  745 , a first protruding portion  746 , a first inner groove portion  747 , and a first outer groove portion  748 . 
     The first flat plate portion  745  is a flat circular annular part and has the first peripheral surface portions  119  similar to those of the above-mentioned first embodiment. The first protruding portion  746  is a part protruding to the upper side from the first flat plate portion  745 . The first inner groove portion  747  forms a groove, which is recessed outward, on an inner peripheral surface of the first protruding portion  746 . The first outer groove portion  748  forms a groove, which is recessed inward, on an outer peripheral surface of the first protruding portion  746 . 
     The first protective cover portion  743  is fixed to the two first guide portions  714 , and seals and covers the first coil  112 , thereby forming the substantially liquid-tight first unit  710  together with the two first guide portions  714 . However, terminal parts of the first main connector portion  115  are exposed so as to be fitted with the first mating connector portion  108 . Here, “liquid-tight” means sealing to the extent that liquid is not allowed to pass through. 
     In detail, the first protective cover portion  743  includes first inner sealing members  749 , first outer sealing members  750 , first coil cover portions  751 , first connection cover portions  752 , and a first connector cover portion  753 . 
     Each of the first inner sealing members  749  and the first outer sealing members  750  is a sealing member made of an elastic material such as rubber, and is generally annular as a whole. Each first inner sealing member  749  is fitted to the first inner groove portion  747 , and each first outer sealing member  750  is fitted to the first outer groove portion  748 . 
     Each first coil cover portion  751  is an arc-shaped part provided in correspondence to the printed wiring of the first coil  112 , and is made of, for example, resin. Each first coil cover portion  751  includes a first annular flat plate portion  751 A of an arc shape disposed above the printed wiring of the first coil  112 , a first outer wall portion  751 B extending downward from an outer peripheral part of the first annular flat plate portion  751 A, and a first inner wall portion  751 C extending downward from an inner peripheral part of the first annular flat plate portion  751 A. 
     The first outer wall portion  751 B and the first inner wall portion  751 C are arranged to sandwich the first outer sealing member  750  and the first inner sealing member  749  in close contact therewith. Consequently, the first coil cover portions  751  liquid-tightly cover an upper side and lateral sides of the printed wiring of the first coil  112 . 
     Each first connection cover portion  752  is a hollow arc-shaped part provided in correspondence to the first coil connectors  118 . The first connection cover portions  752  include first interposed portions  752 A, for example, made of resin or the like, and first elastic portions  752 B covering almost the whole of both end faces of the first interposed portions  752 A. By disposing the first coil connectors  118  inside, the first connection cover portions  752  liquid-tightly cover the periphery of the first coil connectors  118 . 
     In a state where the first unit  710  is assembled, end faces of the first coil cover portions  751  and the first elastic portions  752 B are brought into close contact with each other by fastening the two first bolts  123 . End faces of the first inner sealing members  749  and the first outer sealing members  750  are also in close contact with the first elastic portions  752 B. Therefore, in the state where the first unit  710  is assembled, the first transmission/reception unit  713  is liquid-tightly covered by the first protective cover portion  743  and the first guide portions  714 . 
     The first connector cover portion  753  liquid-tightly covers the first main connector portion  115  and the first circuit portion  121  except the terminal parts of the first main connector portion  115 . 
     When the first unit  710  is divided into the first primary piece  710 A and the second primary piece  710 B, the first connection cover portion  752  may be provided, one at each connecting part between the first primary piece  710 A and the second primary piece  710 B. In the fifth embodiment, as shown in  FIG.  29   , the first connection cover portions  752  are fixed to respective end portions of the second primary piece  710 B provided with the first main connector portion  115 . 
     The second unit  711  generally has a configuration obtained by vertically inverting the first unit  710 . As shown in  FIGS.  26  to  30   , the second unit  711  includes the second main connector portion  128  similar to that of the above-mentioned first embodiment, and a second transmission/reception unit  726  and two second guide portions  727  instead of the second transmission/reception unit  126  and the two second guide portions  127  according to the above-mentioned first embodiment, respectively. Further, the second unit  711  includes a second protective cover portion  744 . 
     In a closed state, the second transmission/reception unit  726  is, as a whole, a generally circular annular member having a through-hole centered on the rotation axis AR and, in the fifth embodiment, has a generally circular disc shape having the through-hole. Similarly to the above-mentioned first embodiment, the second transmission/reception unit  726  and the above-mentioned first transmission/reception unit  713  according to the fifth embodiment are spaced from each other along the rotation axis AR to be disposed in a state of being faced to each other in a non-contact manner. The second transmission/reception unit  726  includes the second coil  125  similar to that of the above-mentioned first embodiment, and two second holding plates  729  instead of the two second holding plates  129  according to the above-mentioned first embodiment. 
     In a closed state, the two second holding plates  729  are, as a whole, generally circular annular rigid substrates having circular through-holes centered on the rotation axis AR, and hold the second coil  125  as a second holding portion. The two second holding plates  729  are different from the two second holding plates  129  according to the above-mentioned first embodiment in that the second protrusions  130  are not provided. 
     Further, the second coil  125  is not provided in belt-like annular parts along outer edges of the two second holding plates  729 . Through through-holes formed in those parts, the two second holding plates  729  are screwed to the two second guide portions  727 . Without being limited to screwing, the two second holding plates  729  may be fixed to the two second guide portions  727  by any appropriate method. 
     Similarly to the two second guide portions  127  according to the above-mentioned first embodiment, the two second guide portions  727  are provided separately on the front side and the rear side. The two second guide portions  727  are parts to which the second transmission/reception unit  726  is fixed in order to reinforce the second transmission/reception unit  726 , and function as a guide when the second unit  711  is attached to the second object  102 . 
     The two second guide portions  727  are generally annular as a whole in a state where the second unit  711  is closed, and includes a second flat plate portion  754 , a second protruding portion  755 , a second inner groove portion  756 , and a second outer groove portion  757 . 
     The second flat plate portion  754  is a flat circular annular portion and has the second peripheral surface portion  132  similar to that of the above-mentioned first embodiment. The second protruding portion  755  is a part protruding downward from the second flat plate portion  754 . The second inner groove portion  756  forms a groove, which is recessed outward, on an inner peripheral surface of the second protruding portion  755 . The second outer groove portion  757  forms a groove, which is recessed inward, on an outer peripheral surface of the second protruding portion  755 . 
     The second protective cover portion  744  is fixed to each of the two second guide portions  727 , and seals and covers the second coil  125 , thereby forming the substantially liquid-tight second unit  711  together with the two second guide portions  727 . However, in the second protective cover portion  744 , terminal parts of the second main connector portion  128  are exposed so as to be fitted with the second mating connector portion  109 . 
     In detail, the second protective cover portion  744  includes second inner sealing members  758 , second outer sealing members  759 , second coil cover portions  760 , second connection cover portions  761 , and a second connector cover portion  762 . 
     Each of the second inner sealing members  758  and the second outer sealing members  759  is a sealing member made of an elastic material such as rubber, and is generally annular as a whole. The second inner sealing members  758  are fitted to the second inner groove portion  756 , and the second outer sealing members  759  are fitted to the second outer groove portion  757 . 
     Each second coil cover portion  760  is an arc-shaped part provided in correspondence to the printed wiring of the second coil  125 , and is made of, for example, resin. Each second coil cover portion  760  includes an arc-shaped second annular flat plate portion  760 A disposed above the printed wiring of the second coil  125 , a second outer wall portion  760 B extending downward from an outer peripheral portion of the second annular flat plate portion  760 A, and a second inner wall portion  760 C extending downward from an inner peripheral portion of the second annular flat plate portion  760 A. 
     The second outer wall portion  760 B and the second inner wall portion  760 C are arranged to sandwich the second outer sealing member  759  and the second inner sealing member  758  in close contact therewith. Consequently, the second coil cover portions  760  liquid-tightly cover an upper side and lateral sides of the printed wiring of the second coil  125 . 
     Each second connection cover portion  761  is a hollow arc-shaped part provided in correspondence to each of the second coil connectors  131 . The second connection cover portions  761  include second interposed portions  761 A, for example, made of resin or the like, and second elastic portions  761 B covering almost the whole of both end faces of the second interposed portions  761 A. By disposing the second coil connectors  131  inside, the second connection cover portions  761  liquid-tightly cover the periphery of the second coil connectors  131 . 
     In a state where the second unit  711  is assembled, end faces of the second coil cover portions  760  and the second elastic portions  761 B are brought into close contact with each other by fastening the two second bolts  136 . End faces of the second inner sealing members  758  and the second outer sealing members  759  are also in close contact with the second elastic portions  761 B. Therefore, in the state where the second unit  711  is assembled, the second transmission/reception unit  726  is liquid-tightly covered by the second protection cover portion  744  and the second guide portions  127 . 
     The second connector cover portion  762  liquid-tightly covers the second main connector portion  128  and the second circuit portion  134  except the terminal parts of the second main connector portion  128 . 
     When the second unit  711  is divided into the first secondary piece  711 A and the second secondary piece  711 B, the second connection cover portion  761  may be provided, one at each connecting part between the first secondary piece  711 A and the second secondary piece  711 B. In the fifth embodiment, as shown in  FIG.  29   , the second connection cover portions  761  are fixed to respective end portions of the second secondary piece  711 B provided with the second main connector portion  128 . 
     The elastic member  742  is a member which closes a gap continuous to a facing space. Herein, the “facing space” is a space between the first transmission/reception unit  713  and the second transmission/reception unit  726  in a state of being faced to each other by attaching the first unit  710  and the second unit  711  to the first object  101  and the second object  102 , respectively. 
     The elastic member  742  is a member having elasticity and made of rubber or the like as a material. When the first unit  710  and the second unit  711  are attached to the first object  101  and the second object  102 , respectively, the elastic member  742  generally forms a circular annular shape. 
     In detail, the elastic member  742  has a base end fixed to an upper surface of the first protective cover portion  743  and a top end brought into contact with a lower surface of the second protective cover portion  744 , so as to close the gap continuous to the facing space. 
     The elastic member  742  may be provided in either one of the first protective cover portion  743  and the second protective cover portion  744 , with the top end kept in contact with the other of the first protective cover portion  743  and the second protective cover portion  744 . In addition, the elastic member  742  may close at least a part of the gap continuous to the facing space. For example, the top end of the elastic member  742 , if extending so as to be close to the other of the first protective cover portion  743  and the second protective cover portion  744 , may not be in contact therewith. With this, it is also possible to reduce the possibility that the foreign matter intrudes the facing space. 
     Except these points, the wireless connector  703  may be configured similarly to the wireless connector  103  according to the above-mentioned first embodiment. 
     Specifically, as described above, for example, the first unit  710  is configured by combining the first primary piece  710 A on the right side and the second primary piece  710 B on the left side which are divisible via the first dividing plane including the rotation axis AR. The second unit  711  is configured by combining the first secondary piece  711 A on the front side and the second secondary piece  711 B on the rear side which are divisible via the second dividing plane including the rotation axis AR. Each of the first primary piece  710 A, the second primary piece  710 B, the first secondary piece  711 A, and the second secondary piece  711 B, when divided, is not annular. 
       FIG.  25    to  FIG.  30    show an example in which the first and the second transmission/reception units  713  and  726  are directly fixed to the first guide portions  714  and the second guide portions  727 , respectively. However, as a matter of course, the first and the second transmission/reception units  713  and  726  may be fixed to the first guide portion  714  and the second guide portion  727  via the first spacers  120  and the second spacers  133 , respectively, as in the first embodiment. 
     (Operation and Attaching and Detaching Method for Wireless Connector  703  According to Fifth Embodiment) 
     According to the wireless connector  703  of the fifth embodiment, the first coil  112  and the second coil  125  are magnetically coupled similarly to the first coil  112  and the second coil  125  of the wireless connector  103  according to the above-mentioned first embodiment described with reference to  FIG.  7   . Therefore, the wireless connector  703  can also operate similarly to the wireless connector  103  according to the above-mentioned first embodiment. 
     The wireless connector  703  according to the fifth embodiment can also be attached and detached by the method similar to that for the wireless connector  103  according to the above-mentioned first embodiment described with reference to  FIG.  8    and  FIG.  13   . 
     By the wireless connector  703  according to the fifth embodiment also, it is possible to wirelessly transmit the electric power between the first object  101  and the second object  102  without restricting the relative rotation range between the first object  101  and the second object  102 , as in the above-mentioned first embodiment. Further, similarly to the wireless connector  103  according to the above-mentioned first embodiment, the wireless connector  703  can easily be attached to and detached from the first object  101  and the second object  102  from the outside. Therefore, it is possible to quickly repair the wireless connector  703  when failure occurs. 
     Further, in the fifth embodiment, the elastic member  742  as the protecting portion is provided. Therefore, it is possible to prevent foreign matter from intruding into the facing space and to reduce the possibility that the foreign matter intrudes into the facing space. This reduces the possibility of a failure, such as a damage of the wireless connector  703  and weakened coupling force in the magnetic field coupling between the first coil  112  and the second coil  125 , due to intrusion of foreign matter into the facing space. Therefore, the durability of the wireless connector  703  can be improved. 
     Further, in the fifth embodiment, the first coil  112  is sealed by the first protective cover portion  743 , and the second coil  125  is sealed by the second protective cover portion  744 . Consequently, it is possible to prevent the coupling force in the magnetic field coupling between the first coil  112  and the second coil  125  from being weakened due to adhesion or accumulation of dirt and foreign matter. Therefore, the durability of the wireless connector  703  can further be improved. 
     Sixth Embodiment 
     In the above-mentioned first to the fifth embodiments, description has been made the examples in which the first transmission/reception unit is connected by the plurality of first coil connectors whereas the second transmission/reception unit is connected by the plurality of second coil connectors, so that each of the first transmission/reception unit and the second transmission/reception unit is configured in an annular shape which is openable and closable at a plurality of positions. Description has also been made of the examples in which the first unit is divided into a plurality of independent primary pieces together with the first transmission/reception unit and the second unit is divided into a plurality of independent secondary pieces together with the second transmission/reception unit. 
     However, if the first transmission/reception unit has the openable/closable annular shape, the plurality of primary pieces may be connected by a connection mechanism such as a hinge. Similarly, if the second transmission/reception unit has the openable/closable annular shape, the plurality of secondary pieces may also be connected by a connection mechanism such as a hinge. In the sixth embodiment, an example in which the connection mechanisms are applied to the wireless connector  103  according to the above-mentioned first embodiment will be described. The connection mechanisms according to the sixth embodiment may appropriately be modified and applied to the wireless connectors according to the other embodiments such as the second to the fifth embodiments. 
     (Configuration of Robot Device  800  According to Sixth Embodiment) 
     As shown in a perspective view of  FIG.  31   , a robot device  800  according to the sixth embodiment of the present invention includes the first object  101  and the second object  102  similar to those of the above-mentioned first embodiment, and a wireless connector  803  for wirelessly transmitting the electric power between the first object  101  and the second object  102 . 
     As shown in  FIG.  31   , the wireless connector  803  includes a first unit  810  instead of the first unit  110  and a second unit  811  instead of the second unit  111 . 
     As shown in  FIG.  32    being a perspective view showing a closed state, the first unit  810  is configured by combining a first primary piece  810 A on the right side and a second primary piece  810 B on the left side, which are separable from each other at one position on the rear side via the first dividing plane including the rotation axis AR. 
     The first unit  810  according to the sixth embodiment further includes a first connecting mechanism  863  connecting the first primary piece  810 A and the second primary piece  810 B, which are adjacent primary pieces, on the front side. By providing the first connecting mechanism  863 , the first primary piece  810 A and the second primary piece  810 B are connected so as to open and close on the rear side. 
     In detail, the first unit  810  includes the first main connector portion  115  similar to that of the above-mentioned first embodiment, and a first transmission/reception unit  813  and first guide portions ( 814 A,  814 B) instead of the first transmission/reception unit  113  and the first guide portions  114  according to the above-mentioned first embodiment. Further, the first unit  810  according to the sixth embodiment includes a first connecting element  864 . 
     Similarly to the first transmission/reception unit  113  according to the above-mentioned first embodiment, in a closed state, the first transmission/reception unit  813  has, as a whole, a generally circular disc shape having a through-hole centered on the rotation axis AR. The first transmission/reception unit  813  includes a first coil  812  instead of the first coil  112  according to the above-mentioned first embodiment, and the first holding plate  116  similar to that of the above-mentioned first embodiment. The first coil  812  is composed of two first coil parts separable at one position and bendable with respect to each other. 
     The first coil  812  is configured by connecting two printed wirings, which are conductors comprising the two first coil parts printed on one main surface (an upper surface in the sixth embodiment) of the first holding plate  116 , via the one first coil connector  118  and a first connection wiring  865 . The first connection wiring  865  is, for example, a conductor wire coated with an insulator. 
     In detail, among four end portions of the two printed wirings formed on two rigid substrates of the first holding plate  116 , the two end portions close to the first connecting mechanism  863  are connected by the first connection wiring  865 , whereas the two end portions far from the first connecting mechanism  863  are connected by the first coil connector  118 . 
     Consequently, the first coil  812  is provided in a generally circular annular region having a through-hole centered on the rotation axis AR when viewed from above in the state where the first transmission/reception unit  813  is closed and, in the sixth embodiment, is configured to form a generally flat spiral shape. In detail, parts of the printed wiring formed at the two end portions of each rigid substrate of the first holding plate  116 , which are far from the first connecting mechanism  863 , are electrically connected to the first coil connector  118  via a through-hole (not shown). Therefore, by electrically connecting the two printed wirings via the one first coil connector  118  and the first connection wiring  865 , the first coil  812  has a substantially spiral shape. In the fifth embodiment, the through-hole connector is used as the first coil connector  118 . However, the present invention is not limited thereto. Specifically, similarly to the above-mentioned first embodiment, for example, an SMT connector, an adhesive film connector, or a combination of an FPC connector and an FPC may be used as the first coil connector  118 , as described above, instead of the through-hole connector. 
     Similarly to the above-mentioned first embodiment, the four end portions of the two printed wirings formed on the first holding plate  116  may be connected by the two first coil connectors  118 . 
     The first guide portions ( 814 A,  814 B) are composed of a first primary guide piece  814 A on the right side and the second primary guide piece  814 B on the left side. This point is similar to the first guide portions  114  according to the above-mentioned first embodiment. Unlike the above-mentioned first embodiment, the first guide portions ( 814 A,  814 B) according to the sixth embodiment are connected by the first connecting mechanism  863  so as not to be completely separated. 
     In detail, the first primary guide piece  814 A includes a first primary guide body  866 A and a first primary connecting segment  867 A. Similarly, the second primary guide piece  814 B includes a second primary guide body  866 B and second primary connecting segments  867 B. 
     The first primary guide body  866 A and the second primary guide body  866 B are configured similarly to the first guide portions  114  according to the above-mentioned first embodiment. Specifically, in a state where the first unit  810  is closed, the first primary guide body  866 A and the second primary guide body  866 B have a generally annular shape as a whole, and have the first peripheral surface portions  119  disposed in contact with the first shaft portion  105  as in the above-mentioned first embodiment. 
     The first primary connecting segment  867 A is a flat-plate-shaped part extending leftward from one end face of the first primary guide body  866 A. In the sixth embodiment, the first primary connecting segment  867 A is one flat-plate-shaped part extending leftward from a front end face among those end faces of the first primary guide body  866 A which face the second primary guide body  866 B, and is provided with a through hole in the up-and-down direction. 
     The second primary connecting segments  867 B are flat-plate-shaped parts extending rightward from one end face of the second primary guide body  866 B. In the sixth embodiment, the second primary connecting segments  867 B are two flat-plate-shaped parts extending rightward from upper and lower ends of a front end face among those end faces of the second primary guide body  866 B which face the first primary guide body  866 A, and is provided with a through-hole in the up-and-down direction. 
     The first primary connecting segment  867 A is disposed between the pair of second primary connecting segments  867 B, so that the first primary connecting segment  867 A is sandwiched in the up-and-down direction by the pair of second primary connecting segments  867 B. The through-holes formed in the first primary connecting segment  867 A and the pair of second primary connecting segments  867 B are arranged to penetrate in the up-and-down direction. 
     As shown in  FIG.  33   , the first connecting element  864  is composed of a first connecting pin  864 A and a first fastener  864 B. 
     Here,  FIG.  33    is a sectional view of the first unit  810  on the first dividing plane (a plane including the rotation axis AR and facing the front-and-rear direction), and is an enlarged view of the vicinity of the first connecting mechanism  863 . 
     The first connecting pin  864 A is a member formed to penetrate the through-holes of the first primary connecting segment  867 A and the pair of second primary connecting segments  867 B, and is, for example, a metal pin having a head portion locked around the through-holes. The first fastener  864 B is a C-shaped (an annular shape with a cutout) member locked to a tip of the first connecting pin  864 A so that the first connecting pin  864 A does not escape from the through-holes, and is, for example, a C-shaped (an annular shape with a cutout) member made of metal. 
     The first connecting mechanism  863  is a hinge composed of the first primary connecting segment  867 A, the pair of second primary connecting segments  867 B, and the first connecting element  864 , and connects the first primary guide body  866 A and the second primary guide body  866 B so as to be rotatable around the first connecting pin  864 A. 
     The first transmission/reception unit  813  is configured so that, by releasing fitting of the first coil connector  118  included in the first coil  812 , the first coil  812  can be separated into the two first coil parts at one position on the rear side where the first coil connector  118  is provided. 
     Further, the first primary piece  810 A on the right side and the second primary piece  810 B on the left side are connected on the front side by the first connecting mechanism  863  to be rotatable around the first connecting pin  864 A which is directed in the up-and-down direction. 
     Therefore, the first unit  810  can be separated on the rear side into the first primary piece  810 A and the second primary piece  810 B via the first dividing plane including the rotation axis AR, and opened on the front side in the left-and-right direction to the extent that the first shaft portion  105  is allowed to pass through, as shown in a perspective view of  FIG.  34   . 
     In the state where the first unit  810  according to the sixth embodiment is closed, the first primary guide piece  814 A and the second primary guide piece  814 B are fastened on the rear side to be fixed to each other by the first bolt  123  inserted into and fitted to the first bolt hole  124 , like in the above-mentioned first embodiment. Consequently, the first unit  810  can maintain the closed state so as not to be easily opened during rotating operation of the robot device  800  or the like. 
     In the sixth embodiment, description has been made of the example in which the first primary piece  810 A and the second primary piece  810 B are connected by the first connecting mechanism  863  provided in the first primary guide piece  814 A and the second primary guide piece  814 B. However, the first primary guide piece  814 A and the second primary guide piece  814 B may not be provided. In this case, a mechanism corresponding to the first connecting mechanism  863  may be provided in the first transmission/reception unit  813 . Further, a plurality of the first connecting mechanisms  863  may be provided. Further, the first unit may include three or more primary pieces, where some of the primary pieces are connected by the first connecting mechanism  863  and the remaining primary pieces are configured to be completely separable. 
     As shown in  FIG.  35    being a perspective view showing a closed state, the second unit  811  is configured by combining a first secondary piece  811 A on the right side and a second secondary piece  811 B on the left side, which are separable at one position on the rear side via the second dividing plane including the rotation axis AR. 
     The second unit  811  according to the sixth embodiment further includes a second connecting mechanism  868  for connecting the first secondary piece  811 A and the second secondary piece  811 B on the front side, which are adjacent secondary pieces. By providing the second connecting mechanism  868 , the first secondary piece  811 A and the second secondary piece  811 B are connected so as to open and close on the rear side. 
     In detail, the second unit  811  includes the second main connector portion  128  similar to that of the above-mentioned first embodiment, and a second transmission/reception unit  826  and second guide portions ( 827 A,  827 B) in place of the second transmission/reception unit  126  and the second guide portions  127  according to the above-mentioned first embodiment, respectively. Further, the second unit  811  according to the sixth embodiment includes a second connecting element  869 . 
     Similarly to the second transmission/reception unit  126  according to the above-mentioned first embodiment, in a closed state, the second transmission/reception unit  826  has, as a whole, a generally circular disc shape having a through-hole centered on the rotation axis AR. The second transmission/reception unit  826  includes a second coil  825  instead of the second coil  125  according to the above-mentioned first embodiment, and the second holding plate  129  similar to that of the above-mentioned first embodiment. Similarly to the first coil  812 , the second coil  825  is composed of two second coil parts separable at one position and bendable with respect to each other. 
     The second coil  825  is configured by connecting two printed wirings, which are conductors comprising the two second coil parts printed on one main surface (a lower surface in the sixth embodiment) of the second holding plate  129 , via the one second coil connector  131  and a second connection wiring  870 . The second connection wiring  870  is, for example, a conductor wire coated with an insulator. 
     In detail, among four end portions of the two printed wirings formed on two rigid substrates of the second holding plate  129 , the two end portions close to the second connecting mechanism  868  are connected by the second connection wiring  870 , whereas the two end portions far from the second connecting mechanism  868  are connected by the second coil connector  131 . 
     Consequently, the second coil  825  is provided in a generally circular annular region having a through-hole centered on the rotation axis AR when viewed from above in the state where the second transmission/reception unit  826  is closed and, in the sixth embodiment, is configured to form a generally flat spiral shape. In detail, parts of the printed wiring formed at the two end portions of each rigid substrate of the second holding plate  129 , which are far from the second connecting mechanism  868 , are electrically connected to the second coil connector  131  via a through-hole (not shown). Therefore, by electrically connecting the two printed wirings via the one second coil connector  131  and the second connection wiring  870 , the second coil  825  has a substantially spiral shape. In the fifth embodiment, the through-hole connector is used as the second coil connector  131 . However, the present invention is not limited thereto. Specifically, similarly to the case of the above-mentioned first embodiment, for example, an SMT connector, an adhesive film connector, or a combination of an FPC connector and an FPC may be used as the second coil connector  131 , as described above, instead of the through-hole connector. 
     Similarly to the above-mentioned first embodiment, the four end portions of the two printed wirings formed on the second holding plate  129  may be connected by the two second coil connectors  131 . 
     The second guide portions ( 827 A,  827 B) is composed of the first secondary guide piece  827 A on the right side and the second secondary guide piece  827 B on the left side. This point is similar to the second guide portions  127  according to the above-mentioned first embodiment. Unlike the above-mentioned first embodiment, the second guide portions ( 827 A,  827 B) according to the sixth embodiment are connected by the second connecting mechanism  868  so as not to be completely separated. 
     In detail, the first secondary guide piece  827 A includes a first secondary guide body  871 A and a first secondary connecting segment  872 A. Similarly, the second secondary guide piece  827 B includes a second secondary guide body  871 B and second secondary connecting segments  872 B. 
     The first secondary guide body  871 A and the second secondary guide body  871 B are configured similarly to the second guide portions  127  according to the above-mentioned first embodiment. Specifically, in the state where the first unit  810  is closed, the first secondary guide body  871 A and the second secondary guide body  871 B have a generally annular shape as a whole, and have the second peripheral surface portions  132  disposed in contact with the second shaft portion  106  as in the above-mentioned first embodiment. 
     The first secondary connecting segment  872 A is a flat-plate-shaped part extending leftward from one end face of the first secondary guide body  871 A. In the sixth embodiment, the first secondary connecting segment  872 A is one flat-plate-shaped part extending leftward from a front end face among those end surfaces of the first secondary guide body  871 A which face the second secondary guide body  871 B, and is provided with a through-hole in the up-and-down direction. 
     The second secondary connecting segments  872 B are flat-plate-shaped part extending rightward from one end face of the second secondary guide body  871 B. In the sixth embodiment, the second secondary connecting segments  872 B are two flat-plate-shaped parts extending rightward from upper and lower ends of a front end face among those end faces of the second secondary guide body  871 B which face the first secondary guide body  871 A, and is provided with a through-hole in the up-and-down direction. 
     The first secondary connecting segment  872 A is disposed between the pair of second secondary connecting segments  872 B, so that the first secondary connecting segment  872 A is sandwiched in the up-and-down direction by the pair of second secondary connecting segments  872 B. The through-holes formed in the first secondary connecting segment  872 A and the pair of second secondary connecting segments  867 B are arranged to penetrate in the up-and-down direction. 
     As shown in the sectional view of  FIG.  33   , the second connecting element  869  is composed of a second connecting pin  869 A and a second fastener  869 B. 
       FIG.  33    is an enlarged view of the vicinity of the first connecting mechanism  863  as described above. An enlarged view of the vicinity of the second connecting mechanism  868  is also shown in the same manner to the enlarged view of the vicinity of the first connecting mechanism  863 . Specifically,  FIG.  33    is a sectional view of the second unit  811  on the second dividing plane (a plane including the rotation axis AR and facing the front-and-rear direction), and is also an enlarged view of the vicinity of the second connecting mechanism  868 . 
     In  FIG.  33   , reference numerals of the constituent components of the second unit  811  are indicated in parentheses following reference numerals of the corresponding components of the first unit  810 . Arrows in parentheses indicating frontward, rearward, upward, and downward directions corresponds to the second unit  811 . 
     The second connecting pin  869 A is a member formed to penetrate the through-holes of the first secondary connecting segment  872 A and the pair of second secondary connecting segments  872 B, and is, for example, a metal pin having a head portion locked around the through-holes. The second fastener  869 B is a member locked to a tip of the second connecting pin  869 A so that the second connecting pin  869 A does not escape from the through-holes, and is, for example, a C-shaped (an annular shape with a cutout) member made of metal. 
     The second connecting mechanism  868  is a hinge composed of the first secondary connecting segment  872 A, the pair of second secondary connecting segments  872 B, and the second connecting element  869 , and connects the first secondary guide body  871 A and the second secondary guide body  871 B so as to be rotatable around the second connecting pin  869 A. 
     The second transmission/reception unit  826  is configured so that, by releasing fitting of the second coil connector  131  included in the second coil  825 , the second coil  825  can be separated into the two second coil parts at one position on the rear side where the second coil connector  131  is provided. 
     Further, the first secondary piece  811 A on the right side and the second secondary piece  811 B on the left side are connected on the front side by the second connecting mechanism  868  to be rotatable around the second connecting pin  869 A which is directed in the up-and-down direction. Therefore, the second unit  811  can be separated on the rear side into the first secondary piece  811 A and the second secondary piece  811 B via the second dividing plane including the rotation axis AR, and opened on the front side in the left-and-right direction to the extent that the second shaft portion  106  is allowed to pass through. 
     In the state where the second unit  810  according to the sixth embodiment is closed, the first secondary guide piece  827 A and the second secondary guide piece  827 B are fastened on the rear side to be fixed to each other by the second bolt  136  inserted into and fitted to the second bolt hole opened on the right side, like in the above-mentioned first embodiment. Consequently, the second unit  811  can maintain the closed state so as not to be easily opened during the rotating operation of the robot device  800  or the like. 
     In the sixth embodiment, description has been made of the example in which the first secondary piece  811 A and the second secondary piece  811 B are connected by the second connecting mechanism  868  provided in the first secondary guide piece  827 A and the second secondary guide piece  827 B. However, the first secondary guide piece  827 A and the second secondary guide piece  827 B may not be provided. In this case, a mechanism corresponding to the second connecting mechanism  868  may be provided in the second transmission/reception unit  826 . Further, a plurality of the second connecting mechanisms  868  may be provided. Further, the second unit may include three or more secondary pieces, where some of the secondary pieces are connected by the second connecting mechanism  868  and the remaining secondary pieces are configured to be completely separable. 
     (Operation of Wireless Connector  803  According to Sixth Embodiment) 
     According to the wireless connector  803  of the sixth embodiment, the first coil  812  and the second coil  825  are magnetically coupled similarly to the first coil  112  and the second coil  125  of the wireless connector  103  according to the above-mentioned first embodiment described with reference to  FIG.  7   . Therefore, the wireless connector  803  can also operate similarly to the wireless connector  103  according to the above-mentioned first embodiment. 
     (Wireless Connector Attaching and Detaching Method According to Sixth Embodiment) 
     Heretofore, the operation of the wireless connector  803  according to the sixth embodiment of the present invention has been described. Now, a wireless connector attaching and detaching method according to the sixth embodiment will be described with reference to the drawings. 
     Also in the sixth embodiment, the wireless connector  803  can be attached to the object ( 101 ,  102 ) and can be detached from the object ( 101 ,  102 ) in the process substantially same as that of the above-mentioned first embodiment. Therefore, in the sixth embodiment also, the wireless connector attaching and detaching method will be described with reference to  FIGS.  8  and  13   . 
     (Method of Attaching Wireless Connector  803 ) 
     A method of attaching the wireless connector  803  is started by preparing the robot device (see  FIG.  3   ) including the object ( 101 ,  102 ), and the wireless connector  803 . 
     As shown in  FIG.  8   , the first unit  810  is attached to the first object  101  from the outside of the first object  101  (step  1 ; step of attaching the first unit) 
     In detail, in step  1 , the second primary piece  810 B is attached to the first object  101  (step  1 A: step of attaching the second primary piece) 
     In the sixth embodiment, in a state where the first coil  812  is faced upward and the first unit  810  is opened together with the first transmission/reception unit  813 , the first shaft portion  105  passes through an open space on the rear side of the first primary piece  810 A and the second primary piece  810 B. The second primary piece  810 B is disposed so that the first peripheral surface portion  119  is brought into contact with the outer peripheral surface of the first shaft portion  105 . 
     Then, the first main connector portion  115  is fitted to the first mating connector portion  108 . Consequently, the first main connector portion  115  and the first mating connector portion  108  are electrically connected to each other, and the second primary piece  810 B is attached to the first object  101 . 
     As shown in  FIG.  8   , the first primary piece  810 A is attached to the first object  101  so as to surround the rotation axis AR together with the second primary piece  810 B (step  1 B; step of attaching the first primary piece). 
     In the sixth embodiment, since the first primary piece  810 A is connected to the second primary piece  810 B by the first connecting mechanism  863 , the first coil  812  is faced upward. 
     Therefore, the first primary piece  810 A is rotated around the first connecting pin  864 A so that the first peripheral surface portion  119  is brought into contact with the outer peripheral surface of the first shaft portion  105 . Then, the first coil connector  118  provided in the first primary piece  810 A is fitted to the first coil connector  118  provided in the second primary piece  810 B, and the first unit  810  is closed together with the first transmission/reception unit  813 . 
     Consequently, the first primary piece  810 A is attached to the first object  101 , and the first coil  812  connected via the first coil connector  118  is formed. 
     As shown in  FIG.  8   , the first primary piece  810 A and the second primary piece  810 B are fastened and fixed by the first bolt  123  (step  1 C; step of fixing the first unit). 
     In detail, the first bolt  123  is inserted from the right side of the first bolt hole  124  and tightened. Consequently, the first unit  810  is assembled and fixed to the first object  101  in the state where the first unit  810  is closed together with the first transmission/reception unit  813 . 
     As shown in  FIG.  8   , the second unit  811  is attached to the second object  102  from the outside of the second object  102  (step  2 ; step of attaching the second unit). 
     In detail, in step  2 , the second secondary piece  811 B is attached to the second object  102  (step  2 A: step of attaching the second secondary piece). 
     In the sixth embodiment, in a state where the second coil  825  is faced downward and the second unit  811  is opened together with the second transmission/reception unit  826 , the second shaft portion  106  passes through an open space on the rear side of the first secondary piece  811 A and the second secondary piece  811 B. The second secondary piece  811 B is disposed so that the first peripheral surface portion  119  is brought into contact with the outer peripheral surface of the second shaft portion  106 . 
     Then, the second main connector portion  128  is fitted to the second mating connector portion  109 . Thus, the second main connector portion  128  and the second mating connector portion  109  are electrically connected to each other, and the second secondary piece  811 B is attached to the second object  102 . 
     As shown in  FIG.  8   , the first secondary piece  811 A is attached to the second object  102  so as to surround the rotation axis AR together with the second secondary piece  811 B (step  2 B: step of attaching the first primary piece). 
     In the sixth embodiment, since the first secondary piece  811 A is connected to the second secondary piece  811 B by the second connecting mechanism  868 , the second coil  825  is faced downward. 
     Therefore, the first secondary piece  811 A is rotated around the second connecting pin  869 A so that the first peripheral surface portion  119  is brought into contact with the outer peripheral surface of the second shaft portion  106 . Then, the second coil connector  131  provided in the first secondary piece  811 A is fitted to the second coil connector  131  provided in the second secondary piece  811 B, and the second unit  811  is closed together with the second transmission/reception unit  826 . 
     Consequently, the first secondary piece  811 A is attached to the second object  102 , and the second coil  825  connected via the second coil connector  118  is formed. 
     As shown in  FIG.  8   , the first secondary piece  811 A and the second secondary piece  811 B are fastened and fixed by the second bolt  136  (step  2 C; step of fixing the second unit). 
     In detail, the second bolt  136  is inserted from the right side of the second bolt hole  137  provided in the first secondary guide piece  827 A and tightened. Consequently, the second unit  811  is assembled and fixed to the second object  102  in the closed state. 
     Thus, the method of attaching the wireless connector  803  to the object ( 101 ,  102 ) is finished, and the wireless connector  803  is attached to the first object  101  and the second object  102  in a fixed state. In addition, the first transmission/reception unit  813  and the second transmission/reception unit  826  are disposed generally in parallel to each other in a direction generally perpendicular to the rotation axis AR in a state of being faced to each other in a non-contact manner along the rotation axis AR outside the first shaft portion  105  and the second shaft portion  106 , so as to wirelessly transmit the electric power. 
     Also in the method of attaching the wireless connector  803  to the object ( 101 ,  102 ) according to the sixth embodiment, the order of performing the first unit attaching step (step  1 ) and the second unit attaching step (step  2 ) may be replaced, like in the above-mentioned first embodiment. In step  1 , the order of performing the second primary piece attaching step (step  1 A) and the first primary piece attaching step (step  1 B) may be replaced. Similarly, in step  2 , the order of performing the second secondary piece attaching step (step  2 A) and the first secondary piece attaching step (step  2 B) may be replaced. 
     (Method of Detaching Wireless Connector  803 ) 
     A method of detaching the wireless connector  803  from the object ( 101 ,  102 ) is typically performed as necessary after the wireless connector  803  is attached to the robot device  100  by the above-mentioned method of attaching the wireless connector  803 . This is similar to the method of detaching the wireless connector  103  according to the above-mentioned first embodiment. 
     As shown in  FIG.  13   , the first unit  810  is detached from the first object  101  by work outside the first object  101  (step  3 ; step of detaching the first unit). 
     Specifically, in step  3 , fixation between the first primary piece  810 A and the second primary piece  810 B is released (step  3 A; step of releasing fixation of the first unit). 
     In the sixth embodiment, after the first bolt  123  is loosened to release fitting by the screw action, the first bolt  123  is pulled out from the right side of the first bolt hole  124 . Thus, fixation of the first unit  810  is released. 
     The first primary piece  810 A is detached from the first object  101  (step  3 B; step of detaching the first primary piece). 
     In the sixth embodiment, fitting of the first coil connector  118  is released and the first primary piece  810 A is rotated around the first connecting pin  864 A. Consequently, fitting of the first coil connector  118  is released and the first primary piece  810 A is detached from the first object  101 . At the same time, the first unit  810  is put into an open state together with the first transmission/reception unit  813 . 
     The second primary piece  810 B is detached from the first object  101  (step  3 C; step of detaching the second primary piece). 
     In the sixth embodiment, the second primary piece  810 B is pulled out to the left side. Consequently, fitting of the first main connector portion  115  and the first mating connector portion  108  is released and the second primary piece  810 B is detached from the first object  101 . 
     By making the first shaft portion  105  pass through the open space on the rear side of the first primary piece  810 A and the second primary piece  810 B, the first unit  810  is detached from the first object  101 . 
     The second unit  811  is detached from the second object  102  by work outside the second object  102  (step  4 ; step of detaching the second unit). 
     In detail, in step  4 , fixation between the first secondary piece  811 A and the second secondary piece  811 B is released (step  4 A; step of releasing fixation of the second unit) 
     In the sixth embodiment, after the second bolt  136  is loosened to release fitting by the screw action, the second bolt  136  is pulled out from the right side of the second bolt hole  137 . Thus, fixation of the second unit  811  is released. 
     The first secondary piece  811 A is detached from the first object  101  (step  4 B; step of detaching the first secondary piece). 
     In the sixth embodiment, fitting of the second coil connector  131  is released, and the first secondary piece  811 A is rotated around the second connecting pin  869 A. Consequently, fitting of the second coil connector  131  is released, and the first secondary piece  811 A is detached from the first object  101 . At the same time, the second unit  811  is put in an open state together with the second transmission/reception unit  826 . 
     The second secondary piece  811 B is removed from the second object  102  (step  4 C; step of detaching the second secondary piece). 
     In the sixth embodiment, the second secondary piece  811 B is pulled out to left side. Consequently, fitting of the second main connector portion  128  and the second mating connector portion  109  is released and the second secondary piece  811 B is detached from the second object  102 . 
     By making the second shaft portion  106  pass through the open space on the rear side of the first secondary piece  811 A and the second secondary piece  811 B, the second unit  811  is detached from the second object  102 . 
     Thus, the method of detaching the wireless connector  803  is finished, and the wireless connector  803  is detached from the object ( 101 ,  102 ). 
     In the wireless connector  803  according to the sixth embodiment, the order of performing the first unit detaching step (step  3 ) and the second unit detaching step (step  4 ) may be replaced. In step  3 , the order of performing the first primary piece detaching step (step  3 B) and the second primary piece detaching step (step  3 C) may be replaced. Similarly, in step  4 , the order of performing the first secondary piece detaching step (step  4 B) and the second secondary piece detaching step (step  4 C) may be replaced. 
     According to the sixth embodiment, similarly to the above-mentioned first embodiment, when the first main connector portion  115  and the second main connector portion  128  are attached to the first mating connector portion  108  and the second mating connector portion  109 , respectively, the first transmission/reception unit  813  and the second transmission/reception unit  826  are disposed in a state of being faced to each other in a non-contact manner along the rotation axis AR outside the first object  101  and the second object  102  so as to wirelessly transmit the electric power. 
     In other words, when the first unit  810  and the second unit  811  are attached to the first object  101  and the second object  102 , respectively, the first transmission/reception unit  813  and the second transmission/reception unit  826  are disposed in a state of being faced to each other in a non-contact manner so as to wirelessly transmit the electric power. In this case, the first coil  812  and the second coil  825  are arranged in parallel with each other in a state of being faced to each other in a non-contact manner so as to wirelessly transmit the electric power. 
     Thus, it is possible to wirelessly transmit the electric power between the first object  101  and the second object  102  without providing parts interfering with each other between the first unit  810  and the second unit  811  or a part restricting the rotation range of the first object  101  and the second object  102  when the first object  101  and the second object  102  are relatively rotated. 
     Similarly to the above-mentioned first embodiment, the wireless connector  803  according to the sixth embodiment can wirelessly transmit the electric power between the first object  101  and the second object  102  without restricting the relative rotation range between the first object  101  and the second object  102 . In addition, similarly to the wireless connector  103  according to the above-mentioned first embodiment, the wireless connector  803  can easily be attached to and detached from the first object  101  and the second object  102  from the outside. Therefore, it is possible to quickly repair the wireless connector  803  when failure occurs. 
     Further, in the sixth embodiment, the first primary piece  810 A and the second primary piece  810 B are connected by the first connecting mechanism  863 . Therefore, the first unit  810  can more easily be attached and detached than the above-mentioned first embodiment. Since the first secondary piece  811 A and the second secondary piece  811 B are connected by the second connecting mechanism  868 , the second unit  811  can more easily be attached and detached than the above-mentioned first embodiment. Therefore, attachment to and detachment from the first object  101  and the second object  102  from the outside can more easily be performed. Thus, it is possible to further quickly repair the wireless connector  803  when failure occurs. 
     Heretofore, the embodiments and the modifications of the present invention have been described. However, the present invention is not limited thereto. For example, the present invention also encompasses modes obtained by appropriately combining a part or a whole of the embodiments and the modifications described above, as well as modes obtained by adding any modification to the above-mentioned modes. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
         
           
               100 ,  500 ,  600 ,  700 ,  800  robot device 
               101  first object 
               102  second object 
               103 ,  203 ,  303 ,  403 ,  503 ,  603 ,  703 ,  803  wireless connector 
             AR rotation axis 
               104  base portion 
               105  first shaft portion 
               106  second shaft portion 
               107  different member connecting portion 
               108  first mating connector portion 
               109  second mating connector portion 
               110 ,  210 ,  310 ,  410 ,  510 ,  610 ,  710 ,  810  first unit 
               110 A,  210 A,  310 A,  410 A,  510 A,  610 A,  710 A,  810 A first primary piece 
               110 B,  210 B,  310 B,  410 B,  510 B,  610 B,  710 B,  810 B second primary piece 
               111 ,  211 ,  311 ,  411 ,  511 ,  611 ,  711 ,  811  second unit 
               111 A,  211 A,  311 A,  411 A,  511 A,  611 A,  711 A,  811 A first secondary piece 
               111 B,  211 B,  311 B,  411 B,  511 B,  611 B,  711 B,  811 B second secondary piece 
               112 ,  412 ,  512 ,  612 ,  812  first coil 
               113 ,  213 ,  313 ,  413 ,  513 ,  613 ,  713 ,  813  first transmission/reception unit 
               114 ,  314 ,  714 ,  814 A,  814 B first guide portion 
               115  first main connector portion 
               116 ,  216 ,  316 ,  716  first holding plate 
               117 ,  417 ,  517  first protrusion 
               118 ,  418 ,  518 ,  618  first coil connector 
               119  first peripheral surface portion 
               120  first spacer 
               121  first circuit portion 
               122  power transmission circuit 
               123  first bolt 
               124  first bolt hole 
               125 ,  425 ,  525 ,  625 ,  825  second coil 
               126 ,  226 ,  326 ,  426 ,  526 ,  626 ,  726 ,  826  second transmission/reception unit 
               127 ,  327 ,  727 ,  827 A,  827 B second guide portion 
               128  second main connector portion 
               129 ,  229 ,  329 ,  729  second holding plate 
               130 ,  430 ,  530  second protrusion 
               131 ,  431 ,  531 ,  631  second coil connector 
               132  second peripheral surface portion 
               133  second spacer 
               134  second circuit portion 
               135  power reception circuit 
               136  second bolt 
               137  second bolt hole 
               438 ,  538 ,  638  first holding portion 
               439 ,  539 ,  639  second holding portion 
               640  first annular groove portion 
               641  second annular groove portion 
               742  elastic member 
               743  first protective cover portion 
               744  second protective cover portion 
               745  first flat plate portion 
               746  first protruding portion 
               747  first inner groove portion 
               748  first outer groove portion 
               749  first inner sealing member 
               750  first outer sealing member 
               751  first coil cover portion 
               751 A first annular flat plate portion 
               751 B first outer wall portion 
               751 C first inner wall portion 
               752  first connection cover portion 
               752 A first interposed portion 
               752 B first elastic portion 
               753  first connector cover portion 
               754  second flat plate portion 
               755  second protruding portion 
               756  second inner groove portion 
               757  second outer groove portion 
               758  second inner sealing member 
               759  second outer sealing member 
               760  second coil cover portion 
               760 A second annular flat plate portion 
               760 B second outer wall portion 
               760 C second inner wall portion 
               761  second connection cover portion 
               761 A second interposed portion 
               761 B second elastic portion 
               762  second connector cover portion 
               814 A first primary guide piece 
               814 B second primary guide piece 
               827 A first secondary guide piece 
               827 B second secondary guide piece 
               863  first connecting mechanism 
               864  first connecting element 
               864 A first connecting pin 
               864 B first fastener 
               865  first connection wiring 
               866 A first primary guide body 
               866 B second primary guide body 
               867 A first primary connecting segment 
               867 B second primary connecting segment 
               868  second connecting mechanism 
               869  second connecting element 
               869 A second connecting pin 
               869 B second fastener 
               870  second connection wiring 
               871 A first secondary guide body 
               871 B second secondary guide body 
               872 A first secondary connecting segment 
               872 B second secondary connecting segment