Patent Publication Number: US-2017356506-A1

Title: Driving force transmission mechanism

Description:
TECHNICAL FIELD 
     The present invention relates to a driving force transmission mechanism including two input lines, one output line, and a brake. 
     BACKGROUND ART 
     In a device that actuates a driven member under the driving force from a motor, when the driving motor is stopped to stop the driven member, or if the driving motor untimely stops due e.g., to power outage, the driven member could change its position (attitude) under an external force such as gravity, thus causing various kinds of trouble. This problem is avoidable by mounting a brake configured to hold the position of the driven member when the driving motor stops (such a brake is hereinafter simply referred to as the “brake”), in the driving unit (including the driving motor and the reduction gear) of the device. Such a brake is mounted in a driving unit of many conventional industrial robots. 
     Such brakes are typically non-excitation electromagnetic brakes. Ordinary non-excitation electromagnetic brakes include a brake plate provided in the drive line between the driving motor and the driven member, a friction plate pressed against the brake plate by a spring, and an electromagnet configured to move the friction plate away from the brake plate when the driving motor is energized, and are configured such that while the motor is in operation (energized), the friction plate is separated from the brake plate by compressing the spring with the electromagnet, and when the motor is stopped (de-energized), the friction plate is pressed against the brake plate under the elastic force of the spring to restrict the rotation of the brake plate, thereby retaining the position of the driven member. 
     While a brake of this type is capable of keeping the position of the driven member while the motor is at a stop (i.e., not energized), this brake also makes it impossible to move the driven member manually while the motor is at a stop, thus making it difficult to perform e.g., maintenance with the device de-energized. 
     To avoid this problem, the below-identified Patent document 1 proposes to provide a nut portion at the end of the input shaft of a reduction gear joined to the rotary shaft of the driving motor such that by rotating the input shaft of the reduction gear by manually operating a rotary jig fitted to the nut portion, the position of the driven member, which is joined to the output shaft of the reduction gear, can be changed. Since this device has, as described above, two input lines (electric input line and manual input line), and one output line, even when the electric input line (first input line) is at a stop and the brake is applied, it is possible to move the driven member from the manual input line (second input line) for e.g., maintenance. 
     PRIOR ART DOCUMENT(S) 
     Patent Document(s) 
     
         
         Patent document 1: JP Patent Publication 6-285785A 
       
    
     SUMMARY OF THE INVENTION 
     Object of the Invention 
     In a driving force transmission mechanism including two input lines and one output line, when an attempt is made to move the driven member from the second input line with the first input line at a stop and the brake being applied, it is necessary to simultaneously rotate the shafts of the reduction gear, the driven member, and the rotary shafts of the driving motor, against the braking force of the brake. Thus, if the braking force of the brake is set to a high value, or a large driving motor is used, according to e.g., the weight of the driven member, a large force is required to drive the driven member from the second input line. This increases the workload of e.g., maintenance. 
     An object of the present invention is to provide a driving force transmission mechanism including two input lines, one output line, and a brake, and configured such that the driving force applied to either of the two input lines can be transmitted to the output line without interfering with the brake. 
     Means for Achieving the Object 
     In order to achieve this object, the present invention provides a driving force transmission mechanism comprising a first input member, a second input member, an output member, and an input switching clutch coupled to the first input member, the second input member, and the output member, and configured to selectively transmit either one of first and second driving forces for rotationally driving the first input member and the second input member, respectively, to the output member, wherein the driving force transmission mechanism further includes a reverse input blocking unit mounted in an input side of the first input member, and configured to allow transmission of the first driving force, which is applied from a driving source, to the first input member, and to lock up when reverse input is applied to the first input member through the input switching clutch, thereby keeping the first input member stationary, wherein the input switching clutch includes: an outer ring configured to rotate together with the first input member; an inner ring provided radially inwardly of the outer ring, and configured to rotate about a rotation axis of the second input member together with the output shaft; and a plurality of rollers disposed between the outer ring and the inner ring, wherein the input switching clutch is configured such that when the first driving force is applied to the first input member through the reverse input blocking unit, the outer ring becomes locked to the inner ring through the rollers so that the first driving force is transmitted to the inner ring and the output member, and such that when the second driving force is applied to the second input member, and the second input member is rotated under the second driving force, the outer ring and the inner ring are unlocked from each other first, and thereafter, the second driving force is transmitted to the inner ring and the output member. 
     With this arrangement, while no driving force is being applied to either of the input line including the first input member and the input line including the second input member, although an external force, such as gravity, applied to the driven member, which is connected to the output member in the output line, is applied as reverse input to the first input member through the output member, the inner ring, the rollers, and the outer ring, since the reverse input blocking unit locks up, thereby stopping the movements of the first input member and the outer ring, the inner ring and the output member also stop, so that the position of the driven member remain unchanged. The driving force transmission mechanism is further configured such that when the first input member is rotationally driven, the reverse input blocking unit allows transmission of a driving force from the driving source to the first input member, and when the second input member is rotationally driven, the reverse input blocking unit stops the outer ring so that a driving force is smoothly transmitted from the second input member to the inner ring and the output member. Thus, this driving force transmission mechanism allows the driving force applied to either of the two input lines to be smoothly transmitted to the output line without interfering with the reverse input blocking unit, which serves as a brake when reverse input is applied. 
     In a more specific arrangement, the inner ring of the input switching clutch has an outer periphery including a plurality of circumferentially arranged cam surfaces, and the outer ring of the input switching clutch has a cylindrical inner peripheral surface, to define, between each of the cam surfaces and the cylindrical inner peripheral surface, a wedge-shape space which narrows gradually toward respective circumferential ends thereof, and in which two of the rollers and a spring are mounted such that the rollers are pushed by the spring into respective narrow circumferential end portions of the wedge-shaped space, wherein the input switching clutch further includes an unlocking piece having crossbars inserted on both circumferential sides of the respective wedge-shaped spaces, and coupled to the second input member such that rotation can be transmitted to the second input member, wherein a torque transmission means is provided between the second input member and the inner ring such that rotation of the second input member is transmitted to the inner ring through the torque transmission means with a slight angular delay, wherein the driving force transmission device is configured such that when the first driving force is applied to the first input member, the outer ring, which is configured to rotate together with the first input member, becomes locked to the inner ring through the rollers so that the first driving force is transmitted to the inner ring and the output member, and such that when the second driving force is applied to the second input member, one of the two rollers in each of the wedge-shaped spaces, which are opposed to each other in a rotational direction, is pushed toward a wide portion of the wedge-shaped space by corresponding ones of the crossbars of the unlocking piece, which is configured to rotate together with the second input member, against an elastic force of the spring in the wedge-shaped space so that the outer ring and the inner ring are unlocked from each other, and thereafter, the second driving force is transmitted to the inner ring and the output member through the torque transmission means. 
     If two driving forces are an electric driving force and a manual driving force, the first driving force is preferably the electric driving force, and the second driving force is the manual driving force. This is because, if the first driving force is a manual driving force, the manual driving force is used to rotate the reverse input blocking unit and the driving motor, which is now used as the driving source of the second input member. Thus, if the toque of the motor is large, the output member may not be driven by the manual force. Conversely, if the second driving force is the manual driving force, the input line including the first input member does not influence the manual driving force, so that it is possible to reduce the manual driving force to drive the second input member. Also, if the driving force transmission mechanism is formed with a hollow space extending through the entire driving force transmission mechanism so that e.g., a cable can be passed therethrough, and if the second driving force is an electric driving force, since the driving motor has to be arranged around the center axis of the entire driving force transmission mechanism, a special hollow motor has to be used as the driving motor. If, conversely, the second driving force is a manual driving force, an ordinary motor can be used as the driving motor, which is now used as the driving source of the first input member, so that it is possible to reduce the cost. 
     The reverse input blocking unit may be a worm gear unit including a worm gear configured such that the first driving force is applied to the worm gear, and a worm wheel meshing with the worm gear and coupled to the first input member such that rotation can be transmitted to the first input member, the reverse input blocking unit having a self-locking function. Alternatively, the reverse input blocking unit may include a pinion shaft configured such that the first driving force is applied to the pinion shaft, and a helical bevel gear meshing with the pinion shaft and coupled to the first input member such that rotation can be transmitted to the first input member, the reverse input blocking unit having a self-locking function. 
     Further alternatively, the reverse input blocking unit may be a reverse input blocking clutch including an input portion configured such that the first driving force is applied to the input portion, an output portion coupled to the first input member such that rotation can be transmitted to the first input member, a locking means configured to lock the output portion to a fixed member, an unlocking means configured to unlock the output portion from the fixed member when the input portion rotates, and means configured to transmit rotation of the input portion to the output portion with a slight angular delay when the output portion is unlocked from the fixed member. Still further alternatively, the reverse input blocking unit may include a wave generator configured such that the first driving force is applied to the wave generator, a circular spline fixed at a position radially outwardly of the wave generator, and a flex spline disposed between the wave generator and the circular spline, and coupled to the first input member such that rotation can be transmitted to the first input member, the reverse input blocking unit having a self-locking function. 
     The second input member may extend through the entire driving force transmission mechanism, and have two rotatably supported ends. With this arrangement, the driving force transmission mechanism can be easily mounted in various types of devices, and once mounted in a device, it shows high rigidity and is capable of stably transmitting driving forces. 
     By using a second input member which is detachable from the unlocking piece and the inner ring, it is possible to reduce the size and weight of the entire driving force transmission mechanism. 
     If the second driving force is a manual driving force, by providing, between the second input member and a manual input member configured to be operated under the manual driving force, a reduction unit configured to transmit, after reducing, the rotation of the manual input member to the second input member, it is possible to reduce the manual driving force. 
     Preferably, the reduction unit is a planetary gear unit comprising a sun gear configured such that the manual driving force is applied to the sun gear from the manual input member, an internal gear disposed radially outwardly of the sun gear, a plurality of planetary gears meshing with the sun gear and the internal gear, and a carrier supporting the planetary gears such that each of the planetary gears is rotatable about an axis of the planetary gear, and coupled to the second input member such that rotation can be transmitted to the second input member, and the internal gear is integral with the first input member. With this arrangement, while the first input member is stationary, the internal gear also remains stationary, so that by operating the manual input member, its rotation can be transmitted to the second input member after being reduced in speed by the planetary gear unit. When the first input member is rotationally driven and its driving force is transmitted to the output member, the rotation of the first input member is transmitted through the rollers, which are provided in the driving force transmission path, the unlocking piece and the second input member to the carrier such that the carrier rotates at the same number of revolutions as the internal gear, which is integral with the first input member. As a result, the planetary gears orbit the sun gear without rotating about their own axes, and thus, as though the planetary gears, the internal gear, and the sun gear were an integral body, so that the planetary gear unit does not increase the rotation of the first input member when it is transmitted to the sun gear and the manual input member. That is, the manual input member is rotated at a relatively low speed. 
     If the first driving force is an electric driving force, by providing the driving motor as the source of the electric driving force separately from a rotation detector for controlling the driving motor, it is possible to reduce the size of the entire driving force transmission mechanism. In this case, for higher rotation detection accuracy too, the rotation detector is preferably arranged so as to be coaxial with the driving motor. 
     When a rotation detector is used for detecting the number of revolutions of the output member, such a rotation detector is preferably provided inside of a fixed cover member covering the output member from radially outside of the output member. With this arrangement, the rotation detector is protected against foreign matter. By forming the cover member from metal, the rotation detector can be protected against electromagnetic noise too, so that the number of revolutions of the output member can be detected with high accuracy, and the driven member connected to the output member can be positioned with high accuracy. 
     The present invention is particularly effectively applicable to a driving force transmission mechanism mounted in a joint driving unit of a robot. 
     Advantages of the Invention 
     Since, as described above, the driving force transmission mechanism according to the present invention includes two input lines, one output line, and a brake in the form of a reverse input blocking mechanism, and configured such that a driving force applied to the input line including the first input member is transmitted to the output member through the reverse input blocking unit, and a driving force applied to the input line including the second input member is transmitted to the output line without interfering with the reverse input blocking unit, while no driving force is being applied to either of the input lines, it is possible to keep the position of the driven member coupled to the output member unchanged. Also, no large force is required to move the driven member from the second input member with the first input member stationary for e.g. maintenance, so that the efficiency of maintenance improves. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a vertical sectional front view of a driving force transmission mechanism of a first embodiment. 
         FIG. 2  is a sectional view taken along line II-II of  FIG. 1 . 
         FIG. 3A  shows an operational state of the driving force transmission mechanism of  FIG. 1  when manual input is applied. 
         FIG. 3B  shows an operational state of the driving force transmission mechanism of  FIG. 1  when manual input is applied. 
         FIG. 4  is a vertical sectional front view of a driving force transmission mechanism of a second embodiment. 
         FIG. 5  is a sectional view taken along line V-V of  FIG. 4 . 
         FIG. 6  is a vertical sectional front view of a driving force transmission mechanism of a third embodiment. 
         FIG. 7  is a left-hand side view of an upper portion of the driving force transmission mechanism of  FIG. 6 . 
         FIG. 8  is a vertical sectional front view of a driving force transmission mechanism of a fourth embodiment. 
         FIG. 9  is a sectional view taken along line IX-IX of  FIG. 8 . 
         FIG. 10  is a vertical sectional front view of a driving force transmission mechanism of a fifth embodiment. 
         FIG. 11  is a sectional view taken along line XI-XI of  FIG. 10 . 
         FIG. 12  shows a manual input jig of  FIG. 10 , as seen from the right-hand side of  FIG. 10 . 
         FIG. 13  shows how the manual input jig of  FIG. 10  is fitted to the driving force transmission mechanism of  FIG. 10 . 
         FIG. 14  is a vertical sectional front view of a driving force transmission mechanism of a sixth embodiment. 
         FIG. 15  is a sectional view taken along line XV-XV of  FIG. 14 . 
         FIG. 16  is a sectional view taken along line XVI-XVI of  FIG. 14 . 
         FIG. 17  is a vertical sectional front view of a driving force transmission mechanism of a seventh embodiment. 
         FIG. 18  is a right-hand side view of  FIG. 17 . 
         FIG. 19  is a vertical sectional front view of a driving force transmission mechanism of an eighth embodiment. 
     
    
    
     BEST MODE FOR EMBODYING THE INVENTION 
     Now referring to the drawings, the embodiments of the present invention are described.  FIGS. 1-3B  show a driving force transmission mechanism of the first embodiment, which is mounted in a joint driving unit of an industrial robot such that the driven member of the joint driving unit can be driven both electrically and manually by the driving force transmission mechanism. As shown in  FIG. 1 , the driving force transmission mechanism is basically composed of: an electrically driven input gear (first input member)  1  rotationally driven by electric input; a manually driven input shaft (second input member)  2  rotationally driven by manual input; an output gear (output member)  3  meshing with a gear on the driven member side (now shown); an input switching clutch  4  coupled to the electrically driven input gear  1 , the manually driven input shaft  2 , and the output gear  3 , and configured to selectively transmit either one of the electric input and the manual input to the output gear  3 ; a driving motor  5  as a driving source of the electrically driven input gear  1 ; and a worm gear unit  6  disposed between the driving motor  5  and the electrically driven input gear  1 , as a reverse input blocking unit. 
     The electrically driven input gear  1  is a helical gear (worm wheel) of the worm gear unit  6  as will be de described below. The electrically driven input gear  1  includes a cylindrical portion  1   a  at one axial end thereof. The input switching clutch  4  is fitted into the electrically driven input gear  1  through an opening of cylindrical portion la. With the input switching clutch  4  fitted in the electrically driven input gear  1 , the opening of the cylindrical portions  1   a  is closed by a lid  7 . 
     The manually driven input shaft  2  has a large-diameter portion at the one end thereof; extends through the entire driving force transmission mechanism (i.e., through the input switching clutch  4  and the output gear  3 ); and are supported at both end portions thereof by fixed wall members  9  through sintered oil-containing bearings  8 . The large-diameter portion of the manually driven input shaft  2  has a portion protruding beyond the corresponding wall member  9  and having an outer periphery on which is fixedly fitted a manual input member  10  which can be directly manually operated. The large-diameter portion of the manually driven input shaft  2  has two flat surfaced sections  2   a  and  2   b  axially displaced from each other, and each having two opposite flat surfaces. 
     As shown in  FIGS. 1 and 2 , the input switching clutch  4  includes an outer ring  11  having a large-diameter cylindrical portion and a small-diameter cylindrical portion; an inner ring  12  disposed radially inside of the large-diameter cylindrical portion of the outer ring  11 ; rollers  13  and coil springs  14  mounted between the inner peripheral surface of the large-diameter cylindrical portion of the outer ring  11  and the outer peripheral surface of the inner ring  12 ; an unlocking piece  15  having crossbars  15   a  each opposed to each coil spring  14  with one of the rollers  13  disposed between the coil spring  14  and the crossbar  15   a,  and a side plate  16  disposed between the unlocking piece  15  and the lid  7 , and mounted to the outer ring  11 . 
     The outer ring  11  of the input switching clutch  4  has at the one end thereof a flange portion  11   a  including a plurality of cutouts  11   b  in the outer periphery of the flange portion  11   a.  The side plate  16  has, on the outer peripheral portion thereof, claws  16   a  which are fitted in some of the cutouts lib and bent to fix the side plate  16  to the flange portion  11   a.  The cylindrical portion  1   a  of the electrically driven input gear  1  has, on the inner periphery thereof, anti-rotation protrusions  1   b  fitted in the remainder of the cutouts  11   b  of the flange portion  11   a,  and in cutouts  16   b  of the side plate  16  which correspond in position to the remainder of the cutouts  11   b  of the flange portion  11   a,  respectively, so that the outer ring  11  and the side plate  16  rotate together with the electrically driven input gear  1 . 
     The inner ring  12  has, in the one end thereof, an engaging hole  12   a  in which is inserted the flat surfaced section  2   a,  which is at the other end portion of the manually driven input shaft  2 , and has, at the other end thereof, an integral hollow output shaft  17  through which the small-diameter portion of the manually driven input shaft  2  extends so that the inner ring  12  rotates about the rotation axis of the manually driven input shaft  2 . The output gear  3  is fixed by keys to the outer periphery of the output shaft  17  so that the inner ring  12  and the output shaft  17  rotate together with the output gear  3 . The output shaft  17  is rotatably supported by a sintered oil-containing bearing  18  fitted in the inner periphery of the small-diameter cylindrical portion of the outer ring  11 . 
     The engaging hole  12   a  of the inner ring  12  has substantially the same cross-sectional shape as the flat surfaced section  2   a  at the other end portion of the manually driven input shaft  2 , and is shaped so as to be opposed to the flat surfaced section  2   a  with a small gap in the rotational direction left therebetween so that the rotation of the manually driven input shaft  2  is transmitted to the inner ring  12  with a slight angular delay. 
     The inner ring  12  has, on its outer periphery, a plurality of cam surfaces  12   b  extending perpendicular to the radial direction of the inner ring  12  so that a wedge-shaped space  19  which gradually narrows toward the respective circumferential ends thereof is defined between each cam surface  12   b  and the inner cylindrical surface of the outer ring  11 . A pair of the rollers  13  and one of the coil springs  14  are received in each wedge-shaped space  19  with the coil spring  14  disposed between the pair of rollers  13  so that the pair of rollers  13  are pushed toward the respective narrow ends of the wedge-shaped space  19  by the coil spring  14 . Two of the crossbars  15   a  of the unlocking piece  15  are located at the respective circumferential ends of each wedge-shaped space  19 . The unlocking piece  15  is fixedly fitted around the flat surfaced section  2   b  at the one end portion of the manually driven input shaft  2  with no gap left therebetween. 
     When input torque (driving force) is applied, through the electrically driven input gear  1 , to the outer ring  11  of the input switching clutch  4 , the rotationally forward rollers  13  are wedged into the rotationally forward narrow circumferential ends of the respective wedge-shaped spaces  19  under the biasing force of the coil springs  14 , so that the outer ring  11  and the inner ring  12  become locked together through the rotationally forward rollers  13 . As a result, the rotation of the outer ring  11  is transmitted to the inner ring  12 , the output shaft  17 , and the output gear  3 . Since the crossbars  15   a  of the unlocking piece  15  are pushed by the rotationally forward rollers  13  at that time, the manually driven input shaft  2 , to which the unlocking piece  15  is fixed, and the manual input member  10  are also rotated together with the outer ring  11 . 
     If, as is ordinarily the case, the rotation torque of the output members (the inner ring  12 , the output shaft  17 , the output gear  3 , and the driven member) is larger than the idle torque of the manual input members (the unlocking piece  15 , the manually driven input shaft  2 , and the manual input member  10 ), rotation is transmitted from the outer ring  11  to the inner ring  12  in the above-described manner. If, conversely, the idle torque of the manual input members is larger than the rotation torque of the output members, as soon as the outer ring  11  begins to rotates, the rotationally forward rollers  13  abut against the crossbars  15   a  of the unlocking piece  15 , and become unable to move any further. This causes the outer ring  11  and the inner ring  12  to become unlocked from each other, and the outer ring  11  to rotate alone. Thus, if the outer ring  11  rotates independently of the inner ring  12  when input torque is applied to the outer ring  11 , it is necessary to adjust the rotation torque of the output members to a value larger than the idle torque of the manual input members. 
     When input torque (driving force) is applied to the manually driven input shaft through the manual input member  10 , the rotationally rearward rollers  13  are, as shown in  FIG. 3A , pushed by the corresponding crossbars  15   a  of the unlocking piece  15 , which is rotating together with the manually driven input shaft  2 , against the elastic forces of the coil springs  14  into the wider portions of the wedge-shaped spaces  19 . This causes the rotationally rearward rollers  13  to become disengaged from the outer ring  11  and the inner ring  12 , thus unlocking the outer ring  11  and the inner ring  12  from each other. When the manually driven input shaft  2  rotates further in this state, the flat surfaced section  2   a  at the other end portion of the large-diameter portion of the manually driven input shaft  2  pushes the inner surface of the engaging hole  12   a  of the inner ring  12 , so that, as shown in  FIG. 3B , the rotation of the manually driven input shaft  2  is transmitted to the inner ring  12 . This causes the rotationally forward rollers  13  to become disengaged from the outer ring  11  and the inner ring  12 . As a result, the inner ring  12  and the output shaft  17  rotate together with the output gear  3 . 
     If input torques are applied simultaneously to both the outer ring  11  and the manually driven input shaft  2 , the unlocking piece  15 , which is fixed to the manually driven input shaft  2 , unlocks the outer ring  11  and the inner ring  12  from each other, thus preventing transmission of rotation from the outer ring  11  to the inner ring  12 , and allowing transmission of rotation from the manually driven input shaft  2  to the inner ring. (Thus, in such a situation, the manual input is preferentially transmitted to the inner ring  12 .) 
     The worm gear unit  6  is connected to the rotary shaft  5   a  of the driving motor  5 , and is comprised of a worm gear  20  to which driving force is directly applied from the driving motor  5 , and the electrically driven input gear  1 , which meshes with the worm gear  20  as the worm wheel. The worm gear unit  6  has a self-locking function. That is, the worm gear unit  6  allows the electrically driven input gear  1  to be rotated by the driving force from the driving motor  5 , but is configured to lock up, thereby keeping the electrically driven input gear  1  and the outer ring  11  stationary, when reverse input torque is applied to the electrically driven input gear  1  through the outer ring  11 . 
     As described above, this driving force transmission mechanism includes two input lines (electric input line and manual input line), and one output line. While no driving force is being applied to either of the two input lines (i.e., while the driving motor  5  is not activated, and no manual input is being applied), when an external force such as gravity is applied to the driven member connected to the output gear  3 , and is transmitted as reverse input torque to the electrically driven input gear  1  through the inner ring  12 , which is configured to rotate together with the output gear  3 , the rollers  13  and the outer ring  11 , the worm gear mechanism  6  acts as a brake to prevent movement of the electrically driven input gear  1  and the outer ring  11 , as well as the other output members, thus keeping the position (attitude) of the driven member unchanged. 
     When a driving force is applied from the driving motor  5  to the electrically driven input gear  1  through the worm gear unit  6 , the driving force is transmitted to the output members through the input switching clutch  4 , so that the driven member is driven. 
     When a driving force is applied to the manual input member  10  and the manually driven input shaft  2 , the driving force is transmitted to the output members through the input switching clutch  4 . At that time, since the electrically driven input gear  1  and the outer ring  11  are kept stationary by the worm gear unit  6 , the driven member can be moved with a small manual force. 
     Thus, a driving force applied to either of the above-mentioned two input lines of this driving force transmission mechanism can be transmitted to the output members without interfering with the brake. Thus, especially when, during e.g., maintenance, moving the driven member with the manual input only, and without the electric input, the manual input member  10  can be moved easily, so that the maintenance can be carried out with high efficiency. 
     Since the manually driven input shaft  2  extends through the entire driving force transmission mechanism, and has its both ends rotatably supported, the driving force transmission mechanism can be easily mounted in various machines and apparatus, and once mounted in a machine, it shows high rigidity and is capable of stably transmitting driving forces. 
       FIGS. 4 and 5  show the second embodiment of the present invention, which is basically the same as the first embodiment, and differs therefrom in that the large-diameter portion at the one end portion of the manually driven input shaft  2  is shorter than that of the first embodiment, and that a planetary gear unit (reduction gear)  51  is provided between the manually driven input shaft  2  and the manual input member  10  such that the rotation of the manual input member  10  is transmitted to the manually driven input shaft  2  after reducing its speed in the planetary gear unit  51 . Here (and in the below-described further embodiments), members identical in function to those of the first embodiment are denoted by the same numerals as used in the first embodiment, and their description is omitted. 
     The planetary gear unit  51  comprises a sun gear  52  coaxial with the manually driven input shaft  2  and the manual input member  10 ; an internal gear  53  located radially outwardly of the sun gear  52 , a plurality of planetary gears  54  meshing with both the sun gear  52  and the internal gear  53 ; and a carrier  55  supporting the planetary gears  54  for rotation about the axes of the respective planetary gears  54 . 
     The sun gear  52  has a shaft portion  52   a  extending from the one end of the sun gear  52  and supported by the fixed wall member  9  through a sintered oil-containing bearing  8 . The manual input member  10  is fixedly fitted on the outer periphery of the portion of the shaft portion  52   a  protruding beyond the wall member  9 . 
     The internal gear  53  has a cylindrical fitting portion  53   a  extending from the outer peripheral portion of the other end of the internal gear  53 , and fixedly fitted on the outer periphery of the cylindrical portion  1   a  of the electrically driven input gear  1  so that the internal gear  53  is fixed to the electrically driven input gear  1 . The cylindrical fitting portion  53   a  is formed, on the inner periphery thereof, with a lid portion  53   b  as a substitute for the lid  7  of the electrically driven input gear  1  of the first embodiment. 
     The carrier  55  includes support shafts  55   a  slidably extending through the centers of the respective planetary gears  54 . While the carrier  55  is integral with the manually driven input shaft  2  in the embodiment, the carrier  55  may be formed separately from the manually driven input shaft  2 , and coupled thereto such that rotation can be transmitted therebetween. This embodiment is further different from the first embodiment in that the manually driven input shaft  2  has no flat surfaced section  2   b  at the one end portion thereof, and instead, the flat surfaced section  2   a  at the other end portion is longer than the flat surfaced section  2   a  of the first embodiment. The unlocking piece  15  is fixedly fitted on the outer periphery of the (longer) flat surfaced portion  2   a.    
     In the second embodiment, since a planetary gear unit  51  is provided between the manually driven input shaft  2  and the manual input member  10 , and its internal gear  53  is fixed to the electrically driven input gear  1  so that while the electrically driven input gear  1  is not rotating, the internal gear  53  also does not rotate, when the manual input member  10  is manually rotated, it is possible to transmit its rotation of the manual input member  10  to the manually driven input shaft  2  after reducing its speed in the planetary gear unit  51 . Thus, the manual input member  10  can be rotated manually with a light force compared with the first embodiment. 
     When the electrically driven input gear  1  is rotationally driven by electric input, and its rotation is transmitted to the output gear  3 , the carrier  55  and the internal gear  53  are rotated at the same number of revolutions because (1) the rotation of the electrically driven input gear  1  is transmitted to the carrier  55  through the rollers  13  of the input switching clutch  4 , which is located in the drive path, the unlocking piece  15 , and the manually driven input shaft  2 , and (2) the internal gear  53  is fixed to the electrically driven input gear  1 . Thus, the planetary gears  54  orbit the sun gear  52  without rotating about their own axes, and thus, as though the planetary gears  54 , the internal gear  53 , and the sun gear  52  were an integral body, so that the planetary gear unit  51  does not increase the rotation of the electrically driven input gear  1  when it is transmitted to the sun gear  52  and the manual input member  10 . This means that when the electrically driven input gear  1  is rotated, the manual input member  10  of this embodiment is rotated, not at a higher speed than, but at the same speed as, the electrically driven input gear  1 , and thus the manual input member  10  of the first embodiment. 
       FIGS. 6 and 7  show the third embodiment of the present invention, which is basically the same as the first embodiment, and is different therefrom in that an electrically driven input shaft  21  is connected to the rotary shaft  5   a  of the driving motor  5 ; that the electrically driven input gear  1  is in the form of a spur gear; and that instead of the worm gear unit  6 , a reverse input blocking clutch  22  is provided as a brake such that the driving force of the driving motor  5  is transmitted to the electrically driven input gear  1  through the electrically driven input shaft  21 , and the reverse input blocking clutch  22 . 
     The electrically driven input shaft  21  is substantially of the same structure as the manually driven input shaft  2 , and differs therefrom only in that it is connected to the rotary shaft  5   a  of the driving motor  5 , so that no manual input member  10  is fixedly fitted thereon, and that neither of its ends is supported by a bearing. 
     The reverse input blocking clutch  22  is substantially identical in structure to the input switching clutch  4  of the first embodiment, and differs therefrom in that (1) the side plate  16  mounted to the outer ring  11  has a tongue portion protruding from the outer periphery of the side plate  16  and mounted to a fixed member, not shown, using a mounting hole  16   c  formed in the tongue portion so that the outer ring  11  and the side plate  16  are fixed in position; and (2) a coupling gear  23  meshing with the electrically driven input gear  1  is fixed by keys to the outer periphery of the output shaft  17  integral with the inner ring  12 . 
     When reverse input torque is applied to the from the coupling gear  23  to the output shaft  17  and the inner ring  12  of the reverse input blocking clutch  22 , since the rotationally rearward rollers  13  are pushed into the narrow portions of the wedge-shaped spaces  19  under the elastic forces of the coil springs  14 , and are in engagement with the outer ring  11  and the inner ring  12 , so that the inner ring  12  becomes locked to the outer ring  11 , which is in turn fixed to the fixed member, and remains stationary along with the output shaft  17  and the coupling gear  23 . 
     When a driving force is applied from the driving motor  5  to the electrically driven input shaft  21 , the reverse input blocking clutch  22  operates in the same manner as the input switching clutch  4 . In particular, when input torque is applied to the electrically driven input shaft  21 , the unlocking piece  15  rotates together with the electrically driven input shaft  21 , so that crossbars  15   a  of the unlocking piece  15  push the rotationally rearward rollers  13  into the wide portions of the wedge-shaped spaces  19  against the elastic forces of the coil springs  14 , thereby unlocking the outer ring  11  and the inner ring  12  from each other. When the electrically driven input shaft  21  further rotates thereafter, and pushes the inner ring  12 , the rotation of the electrically driven input shaft  21  is transmitted to the inner ring  12 , so that the inner ring  12  and the output shaft  17  rotate together with the coupling gear  23 . 
     Thus, the reverse input blocking clutch  22  includes a locking means for locking the output portion (i.e., the portion coupled to the electrically driven input gear  1  such that rotation can be transmitted to the electrically driven input gear  1 , and comprising the inner ring  12 , the output shaft  17 , and the coupling gear  23 ) to the fixed member; an unlocking means for unlocking the output portion from the fixed member when rotation is applied to the input portion (i.e., the electrically driven input shaft  21 , to which a driving force is applied); and means for transmitting the rotation of the input portion to the output portion with a slight angular delay when the output portion is unlocked from the fixed member. 
     In the driving force transmission mechanism of the third embodiment, while no driving force is being applied to either of the two input lines, when an external force applied to the driven member is transmitted as reverse input torque to the reverse input blocking clutch  22  through the input switching clutch  4 , the electrically driven input gear  1 , and the coupling gear  23 , the reverse input blocking clutch  22  acts as a brake to keep the position of the driven member unchanged. When an electric driving force is applied from the driving motor  5  to the electrically driven input gear  1  through the reverse input blocking clutch  22 , or when a manual driving force is applied to the manual input member  10  and the manually driven input shaft  2 , either of these driving forces is transmitted to the output line through the input switching clutch  4 , and moves the driven member. While only a manual force is being applied, since the reverse input blocking clutch  22  keeps the electrically driven input gear  1  and the outer ring  11  stationary, the driven member can be moved manually with a light force. Thus, as with the first embodiment, this embodiment makes it possible to move the driven member manually with a light force, thus improving the efficiency of maintenance. 
       FIGS. 8 and 9  show the fourth embodiment of the present invention, which differs from the first embodiment in that the input switching clutch  4  of the first embodiment is partially modified; that a hollow space is formed that extends through the entire driving force transmission mechanism so that a cable can be passed therethrough; and that instead of the worm gear unit  6 , a wave gear unit  24  is used as a brake. This embodiment also differs from the first embodiment in the support structure of the entire driving force transmission mechanism, and the structure of the output line. These differences are now described. 
     The driving force transmission mechanism of the fourth embodiment includes a housing  25  in which is received the input switching clutch  4  and the output members, and is, in its entirety, fixedly supported in a joint driving unit of a robot by using mounting holes  25   a  formed in a flange portion of the housing  25  at its one end. 
     The hollow space extending through the entire driving force transmission mechanism is formed by hollow spaces defined in the manually driven input shaft  2 , the driving motor  5 , and the inner ring  12  of the input switching clutch  4 . The manually driven input shaft  2  includes no portion extending toward the output members, and is rotatably supported by the inner periphery of the driving motor  5  through three ball bearings  26 . As will be described hereinafter, the outer members also have hollow spaces. Another ball bearing  27  is provided at the one end of the inner periphery of the manually driven input shaft  2  so that the manually driven input shaft  2  can rotate smoothly without interfering with e.g., the cable passed through the driving force transmission mechanism. 
     The driving motor  5  includes a hollow rotary shaft  5   a,  a rotor  5   b  mounted on the outer periphery of the rotary shaft  5   a,  a motor housing  5   c,  a stator  5   d  mounted on the inner periphery of the motor housing  5   c,  and a lid  5   e  closing the one end of the motor housing  5   c.  The driving motor  5  has a built-in rotation detector comprising a magnetic wheel  28  mounted on an outer side surface of a flange portion of the rotary shaft  5   a  at its one end, and a sensor  29  mounted on the inner side surface of the lid Se to face the magnetic wheel  28 . 
     The wave gear unit  24  includes a wave generator  30  joined by bolts to an inwardly extending flange portion of the rotary shaft  5   a  of the driving motor  5  at its other end, a circular spline  31  arranged radially outwardly of the wave generator  30 , and a flex spline  32  having a large-diameter portion sandwiched between the wave generator  30  and the circular spline  31 . 
     The wave generator  30  includes a cam  30   a  having an oval diametric section, and a ball bearing  30   b  having an inner race fixedly fitted on the outer periphery of the cam  30   a.  The circular spline  31  is an annular member having teeth on the inner periphery thereof, and is sandwiched between, and fixedly joined by bolts to, the housing  25  and the motor housing  5   c  of the driving motor  5 . The flex spline  32  is a thin-walled, cup-shaped member made from a metal elastic body. The flex spline  32  has teeth formed on the outer periphery of the large-diameter portion of the flex spline  32  to mesh with the teeth on the inner periphery of the circular spline  31 , and includes a small-diameter portion joined by bolts to the outer ring  11  of the input switching clutch  4 . The flex spline  32  thus takes the place of the electrically driven input gear  1  of the first embodiment as the first input member. 
     The wave gear unit  24  is configured such that when the wave generator  30  is rotated under the driving force of the driving motor  5 , the outer race of the ball bearing  30   b  of the wave generator  30  presses the inner periphery of the large-diameter portion of the flex spline  32 , thus causing the flex spline  32  to be elastically deformed such that the flex spline  32  rotates together with the outer ring  11  of the input switching clutch  4  at a speed corresponding to the difference in number between the teeth of the flex spline  32  and the circular spline  31  due to the movement of the meshing position between the flex spline  32  and the circular spline  31 . 
     Since, as will be apparent from the above description, the reduction ratio of this wave gear unit  24  is as large as that of the worm gear unit  6  of the first embodiment, the wave gear unit  24  has a self-locking function. That is, while the flex spline  32  rotates under the driving force of the driving motor  5 , the flex spline  32  locks up when reverse input torque is applied to the flex spline  32  through the outer ring  11  of the input switching clutch  4 , thus keeping the outer ring  11 . stationary. The wave gear unit  24  thus acts as a brake of the driving force transmission mechanism. 
     The input switching clutch  4  is partially different in structure from that of the first embodiment. First, the outer ring  11  is, as described above, joined to the flex spline  32  of the wave gear unit  24  for rotation together with the flex spline  32 , and is rotatably supported by the housing  25  through a ball bearing  33 . The inner ring  12  is, as described above, a hollow member, and has, instead of the engaging hole  12   a  of the first embodiment, a plurality of circumferentially spaced apart, elongated engaging holes  12   c  in the one end surface of the inner ring  12 . The manually driven input shaft  2  has input pins  34  protruding from the other end thereof, and each having its distal end portion inserted in one of the engaging holes  12   c  with a circumferential gap left therebetween. The input pins  34  extend through the unlocking piece  15 , coupling the unlocking piece  15  to the manually driven input shaft  2  so as to rotate together with the manually driven input shaft  2 . 
     The input switching clutch  4  of this embodiment operates substantially in the same manner as the counterpart of the first embodiment. In particular, when input torque is applied to the outer ring  11  through the flex spline  32 , the rotation of the outer ring  11  is transmitted to the inner ring  12 , and simultaneously, the rotationally forward rollers  13  push the crossbars  15   a  of the unlocking piece  15 . As a result, the manually driven input shaft  2  and the manual input member  10  rotate together with the unlocking piece  17 . When input torque is applied to the manually driven input shaft  2  through the manual input member  10 , the crossbars  15   a  of the unlocking piece  15  unlock the outer ring  11  and the inner ring  12  from each other, and then, the input pins  34  push the inner surfaces of the engaging holes  12   c  of the inner ring  12 , thereby transmitting the rotation of the manually driven input shaft  2  to the inner ring  12 . When input torques are simultaneously applied to the outer ring  11  and the manually driven input shaft  2 , rotation is transmitted from the manually driven input shaft  2  to the inner ring  12 . 
     In the fourth embodiment, as in the first embodiment, either of the driving forces applied to electric input line and the manual input line can be transmitted to the output line without interfering with the brake. 
     The driving force transmission mechanism of the fourth embodiment does not include the output gear  3  and the output shaft  17  of the first embodiment, and includes a cross roller bearing  36  between the inner ring  12  of the input switching clutch  4  and a hollow connecting member  35  provided instead of the output shaft  17  and connected, as an output member, to the driven member. The cross roller bearing  36  includes a plurality of rollers  39  disposed between a hollow inner race  37  and an outer race  38  such that the circumferentially adjacent rollers  39  cross each other at a right angle. The inner race  37  is joined by bolts to, so as to rotate together with, the inner ring  12  of the input switching clutch  4  and the connecting member  35 , while the outer race  38  is joined to the housing  25  by bolts, so that the entire driving force transmission mechanism of this embodiment shows increased rigidity against thrust forces, and thus rotation can be transmitted stably. 
     An additional rotation detector similar to the rotation detector mounted in the driving motor  5  is provided between the outer race  38  of the cross roller bearing  36  and the connecting member  35 . The additional rotation detector includes a magnetic wheel  28  mounted to the connecting member  35 , and a sensor  29  mounted on the outer side surface of the outer race  38  of the cross roller bearing  36  to face the magnetic wheel  28 . It is possible to rotate the connecting member  35  with high accuracy by correcting the number of revolutions of the driving motor  5  such that the number of revolutions of the connecting member  35  coincides with the target number of revolutions, based on the number of revolutions of the connecting member  35  as detected by the additional rotation detector, and the number of revolutions of the driving motor  5  as detected by the rotation detector mounted in the driving motor  5 . 
       FIGS. 10-13  show the fifth embodiment of the present invention, which is basically the same as the fourth embodiment, and differs therefrom in that the electric input line of the first embodiment is partially modified in structure, and the manual input line of the first embodiment is changed in structure. A driving force is transmitted basically in the same manner as in the fourth embodiment. The above-mentioned differences are now described. 
     The electric input line of the fifth embodiment comprises an electrically driven input gear  1  integral with the outer ring  11  of the input switching clutch  4 , two worm gear assemblies  6  of which the electrically driven input gear  1  serves as a common worm wheel, and two driving motors  5  each connected to the one end of the worm gear  20  of each worm gear unit  6 . While not shown, each driving motor  5  has a built-in rotation detector similar to the one used in the fourth embodiment. 
     A lid  7  is fixed by screws to the electrically driven input gear  1  to close its opening at the one end thereof. A ball bearing  40  is disposed between the electrically driven input gear  1  and the inner ring  12  of the input switching clutch  4  to rotatably support the inner ring  12 . 
     The rotary shafts  5   a  of the driving motors  5  extend through, and fixed to, respective motor fixing portions  25   b  provided at the one end surface of the housing  25 . Each worm gear  20  has, at its end remote from the driving motor  5 , a small-diameter non-threaded portion  20   a  rotatably supported by a bearing  41  fixed to a bearing fixing portion  25   c  on the one end surface of the housing  25 . The housing  25  has a short axial length such that the input switching clutch  4  is not received in the housing  25 . The outer race  38  of the cross roller bearing  36  is fixed to a bearing fixing plate  25   d  which is a separate member from the housing  25 , and which is fixedly fitted in the inner periphery of the housing  25  at the other end of the housing  25 . 
     For the manual input line, instead of the manually driven input shaft  2 , the unlocking piece  15  of the input switching clutch  4  and a manual input jig  42  detachably mounted to the inner ring  12  are used as second input members. The manual input jig  42  comprises a substantially U-shaped control plate  43 , and a plurality of input pins  34  extending through the control plate  43  in the thickness direction of the control plate  43 . As with the input pins of the fourth embodiment, the input pins  34  of this embodiment are configured to be inserted through the unlocking piece  15  without gaps therebetween, and inserted into the elongated engaging holes  12   c  in the inner ring  12  with circumferential gaps left therebetween. Thus, when the manual input jig  42  is fitted in position (by inserting the input pins  34  through the unlocking piece  15  and into the inner ring  12 ), and rotated with a tool (spanner) T having the shape as shown by one-dot chain line of  FIG. 12 , in the same manner as in the fourth embodiment, the outer ring  11  and the inner ring  12  are unlocked from each other by the crossbars  15   a  of the unlocking piece  15 , and thereafter, the input pins  34  push the inner surfaces of the engaging holes  12   c  of the inner ring  12 , thereby transmitting the rotation of the manual input jig  42  to the inner ring  12 . 
     As shown in  FIG. 13 , the driving force transmission mechanism A of the fifth embodiment is mounted in a robot arm, with the housing  25  fixed to a driving arm B, with the members on the input side of the housing  25  received in the driving arm B, and with the connecting member  35  connected to a driven arm C as the driven member. A cable D extending from inside the driving arm B extends through the driving force transmission mechanism A, and is introduced into the driven arm C. Thus, the driven arm C can be manually moved for e.g., maintenance by removing a cover E provided on the surface of the driving arm B opposite from its surface facing the driven arm C, setting the manual input jig  42  to axially face the unlocking piece  15  with the cable D received in a cutout in the control plate  43 , inserting the input pins  34  through the unlocking piece  15  and into the inner ring  12 , fitting the tool T on the outer periphery of the control plate  43 , and turning the tool T. 
     In the fifth embodiment, although the driving force transmission mechanism has a hollow space extending through the entire driving force transmission mechanism as in the fourth embodiment, since the electric input line is configured such that the electrically driven input gear  1  is rotationally driven by driving motors  5  arranged at positions offset from the center axis of the driving force transmission mechanism through the worm gear assemblies  6 , it is possible to use ordinary motors for the driving motors  5 , thus making it possible to reduce the manufacturing cost and the maintenance cost, compared with the fourth embodiment, in which a special hollow motor  5  is used. 
     Also, for the manual input line, since a detachable manual input jig  42  is used instead of the manually driven input shaft  2  of the fourth embodiment, the entire driving force transmission mechanism is compact in size and thus lightweight compared with the fourth embodiment. 
       FIGS. 14-16  show the sixth embodiment, which differs from the fifth embodiment in that the electric input line is partially modified, but the driving force is transmitted basically in the same manner as the fifth embodiment. Below, only what differs from the fifth embodiment is described. 
     For the electric input line of the sixth embodiment, as with the fifth embodiment, the bearings  41  supporting the non-threaded portions  20   a  of the respective worm gears  20  are fixed to the bearing fixing portions  25   c  of the housing  25 . However, this embodiment differs from the fifth embodiment in that each bearing fixing portion  25   c  is provided with a rotation detector  44  used to control the corresponding driving motor  5 , and that the driving motor  5  has no built-in rotation detector. By providing a rotation detector  44  for controlling each driving motor  5  separately from the driving motor  5 , and by using driving motors  5  having no built-in rotation detectors, it is possible to reduce the size of the entire driving force transmission mechanism compared with the fifth embodiment, while maintaining as high accuracy of rotation detection as with the fifth embodiment. 
     Between the electrically driven input gear  1  (i.e., the outer ring  11  of the input switching clutch  4 ) and the inner ring  12  of the input switching clutch  4 , sintered oil-containing bearings  45  and  46  are provided which are in sliding contact with the electrically driven input gear  1 , instead of the lid  7  and the ball bearing  40  of the fifth embodiment. One of these two bearings  45  and  46  is joined by bolts to the one end of the inner ring  12 , while the other of the bearings is  45  and  46  is joined by bolts to the outer periphery of the inner ring  12  at the other end of the inner ring  12 . 
     The unlocking piece  15  of the input switching clutch  4  of this embodiment has no radially extending portion, and is arranged and shaped such that the tips of the input pins  34  of the manual input jig  42  can be inserted into portions of the unlocking piece  15  between adjacent crossbars  14  without circumferential gaps therebetween. As a result, the inner ring  12  has no engaging holes  12   c  in which the input pins  34  are to be inserted, and instead, the sintered oil-containing bearing  45 , which is joined by bolts to the inner ring  12 , is formed with circular engaging holes  45   a  into which the input pins  34  can be inserted with circumferential gaps left therebetween so that, as in the fifth embodiment, a manual driving force can be applied from the manual input jig  42 . 
       FIGS. 17 and 18  show the seventh embodiment, in which instead of the two worm gear assemblies  6  of the sixth embodiment, a reverse input blocking unit is used which comprises a pinion shaft  47  to which the driving force from a driving motor  5  is directly applied, and an electrically driven input gear  1  in the form of a helical bevel gear meshing with the pinion shaft  47 . Since this reverse input blocking unit has a structural feature that a reduction ratio larger than that of the worm gear assemblies  6  is easily obtainable, it serves as a brake due to its self-locking function in the same manner as the worm gear assemblies  6 . In  FIGS. 17 and 18 , the manual input jig  42  is not shown. 
     The electrically driven input gear  1  of this reverse input blocking unit is, as with the counterpart of the sixth embodiment, integral with the outer ring  11  of the input switching clutch  4 . The pinion shaft  47  is rotatably supported at its proximal end by a bearing (not shown) mounted in a motor fixing portion  25   b  of the housing  25 . The pinion shaft  47  has a shaft portion  47   a  axially extending from the distal end of the pinion shaft  47 , and rotatably supported by a bearing  41  fixed to a bearing fixing portion  25   c  of the housing  25 . The driving motor  5  is controlled based on the rotation of the driving motor  5  as detected by a rotation detector  44  provided at the bearing fixing portion  25   c.    
       FIG. 19  shows the eighth embodiment, in which the positions of the connecting member  35  and the cross roller bearing  36  of the seventh embodiment are reversed such that the inner race  37  of the cross roller bearing  36  serves as the output member to be connected to the driven member. The connecting member  35  and the inner race  37  of the cross roller bearing  36  are joined to, so as to rotate together with, the inner ring  12  of the input switching clutch  4  by means of common bolts. A rotation detector is provided which comprises a magnetic wheel  28  mounted to the connecting member  35 , and a sensor  29  mounted to the inner surface of the housing  25  to face the magnetic wheel  28 , and which is configured to detect the number of revolutions of the inner race  37  of the cross roller bearing  36  which rotates together with the connecting member  35 . 
     In the eighth embodiment, since the rotation detector for detecting the number of revolutions of the inner race  37  of the cross roller bearing  36  as the output member is located inside of the outer race  38  of the cross roller bearing  36 , which serves as a fixed cover member covering the output member from radially outside of the output member, and inside of the housing  25 , the rotation detector is protected against foreign matter. By forming the outer race  38  of the cross roller bearing  36  and the housing  25  from metal, the rotation detector can be protected against electromagnetic noise too. Thus, compared with the seventh embodiment, the number of revolutions of the inner race  37  of the cross roller bearing  36  can be detected with high accuracy, so that the driven member connected to the inner race  37  can be positioned with high accuracy. 
     The input switching clutch according to the present invention is not limited to those of the above-described embodiments, provided it includes an outer ring configured to rotate together with the first input member, an inner ring provided radially inwardly of the outer ring, and configured to rotate about the rotation axis of the second input member together with the output shaft, and a plurality of rollers disposed between the outer ring and the inner ring, and is configured such that when a driving force is applied to the first input member, the outer ring becomes locked to the inner ring through the rollers so that the driving force is transmitted to the inner ring and the output member, and such that when a driving force is applied to the second input member, and the second input member is rotated, the outer ring and the inner ring are unlocked from each other first, and thereafter, the driving force is transmitted to the inner ring and the output member. 
     While the helical gears of the first, second, fifth and sixth embodiments, the flex spline of the fourth embodiment, and the helical bevel gear of the seventh embodiment are shown to be integral with the first input member, they may be formed separately from the first input member, and coupled to the first input member so that rotation can be transmitted to the first input member. While the outer ring of the input switching clutch of each of the fifth to seventh embodiments are integral with the first input member, the former may be formed separately from the latter, and coupled to the later so that rotation can be transmitted to the latter. 
     The concept of the present invention is applicable not only to a driving force transmission mechanism to be mounted in a joint driving unit of an industrial robot, such as shown in the above-described embodiments, but to other driving force transmission mechanisms including two input lines, one output line, and a brake. 
     DESCRIPTION OF THE NUMERALS 
     
         
           1 . Electrically driven input gear (first input member) 
           2 . Manual driven input shaft (second input member) 
           3 . Output gear (output member) 
           4 . Input switching clutch 
           5 . Driving motor 
           6 . Worm gear unit (reverse input blocking unit) 
           10 . Manual input member 
           11 . Outer ring 
           12 . Inner ring 
           13 . Roller 
           14 . Coil spring 
           15 . Unlocking piece 
           15   a.  Crossbar 
           17 . Output shaft 
           19 . Wedge-shaped space 
           20 . Worm gear 
           21 . Electrically driven input shaft 
           22 . Reverse input blocking clutch (reverse input blocking unit) 
           23 . Coupling gear 
           24 . Wave gear unit (Reverse input blocking unit) 
           25 . Housing 
           30 . Wave generator 
           31 . Circular spline 
           32 . Flex spline (first input member) 
           34 . Input pin 
           35 . Connecting member (output member) 
           36 . Cross roller bearing 
           42 . Manual input jig (second input member) 
           43 . Control plate 
           44 . Rotation detector 
           47 . Pinion shaft 
           47   a.  Shaft portion 
           51 . Planetary gear unit (reduction gear) 
           52 . Sun gear 
           53 . Internal gear 
           54 . Planetary gear 
           55 . Carrier 
         A. Driving force transmission mechanism 
         B. Driving arm 
         C. Driven arm 
         D. Cable 
         E. Cover 
         T. Tool