Patent Description:
For example, Patent Documents <NUM> to <NUM> disclose link actuation apparatuses that have a compact configuration and are capable of operating in a precise and wide operating range. The link actuation apparatus of Patent Document <NUM> includes: a parallel link mechanism in which a distal-side link hub is coupled to a proximal-side link hub through three or more link mechanisms such that a posture of the distal-side link hub can be changed relative to the proximal-side link hub; and posture control drive sources provided to two or more of the three or more link mechanisms and configured to arbitrarily change the posture of the distal-side link hub relative to the proximal-side link hub.

In a link actuation apparatus having the above constitution, the positioning accuracy and/or rigidity of the apparatus can be improved by inserting shims between bearings disposed in respective revolute pair parts to apply a preload during assembly so as to reduce backlash in the revolute pair parts. The positioning accuracy and/or rigidity of the apparatus can also be improved by improving the rigidity of the revolute pair parts by the arrangement of the bearings (such as back-to-back (DB), face-to-face (DF)). However, desired positioning accuracy and/or rigidity may not be achieved in cases where the shims are left uninserted or are inserted in an overlapping manner during assembly of such revolute pair parts or in cases where the bearings are arranged improperly. In some cases, it is difficult to detect deterioration of the positioning accuracy and/or rigidity due to wear resulting from prolonged operation at an early stage. <CIT> Al discloses the measure of torque in relation with the motors of a parallel kinematic manipulator, in order to diagnose an abnormality in the link mechanisms and thus warn the user about the need of parts replacement.

In a parallel link mechanism having the constitution of Patent Document <NUM>, it is difficult to detect deterioration of the rigidity and positioning accuracy due to improper assembly and/or wear resulting from prolonged continuous operation and identify the cause of the deterioration because a link part has varying rigidity depending on a posture of the distal member. Therefore, a parallel link mechanism having the above constitution is required to be capable of easily detecting abnormality in pre-shipment inspection and/or during continuous operation.

In order to solve the above problem, an object of the present invention is to provide a link actuation apparatus capable of easily detecting deterioration of the rigidity and positioning accuracy of the apparatus due to improper assembly of a link actuation apparatus body and/or prolonged operation, without disassembling the apparatus and even with its operation continuing.

A link actuation apparatus of the present invention will be described using reference signs used in the description of embodiments. The link actuation apparatus of the present invention includes:.

According to the link actuation apparatus having this constitution, the control device <NUM> includes an abnormality detector <NUM> including: a measurement section <NUM> configured to measure a certain state value of the link actuation apparatus body <NUM>, which is affected by abnormality in the revolute pair parts <NUM> to <NUM>; and a determination section <NUM> configured to determine if the link actuation apparatus body <NUM> has abnormality in any of the revolute pair parts <NUM> to <NUM> on the basis of a measurement result obtained by the measurement section <NUM>. This makes it possible to easily detect deterioration of the rigidity and positioning accuracy of the apparatus due to improper assembly of the revolute pair parts <NUM> to <NUM> of the link actuation apparatus body <NUM>, which are constituted by bearings <NUM> and peripheral components, and/or due to prolonged operation, without disassembling the apparatus and even with its operation continuing.

In the present invention, the measurement section <NUM> is configured to measure rigidity of the link actuation apparatus body <NUM>, and the determination section <NUM> is configured to determine the abnormality according to a predetermined rule on the basis of a measurement value obtained by the measurement section <NUM>. The "rigidity" of the link actuation apparatus body <NUM> represents difficulty in changing the posture of the link actuation apparatus body <NUM>, and the rigidity of the link actuation apparatus body <NUM> results from overall difficulty in rotating the respective revolute pair parts <NUM> to <NUM> (i.e., rigidity of the respective revolute pair parts <NUM> to <NUM>).

The rigidity of the link actuation apparatus body <NUM> is greatly affected by improper assembly of the bearings <NUM> of the revolute pair parts <NUM> to <NUM> or wear due to prolonged operation. For this reason, abnormality in the revolute pair parts <NUM> to <NUM> of the link actuation apparatus body <NUM> can be accurately detected by measuring the rigidity of the link actuation apparatus body <NUM> and determining the presence of abnormality according to the predetermined rule. The predetermined rule may be arbitrarily defined. For example, it is possible to compare a present measurement value to a reference value specified by design and/or a reference value based on a measurement value collected during normal time and then to determine that there is abnormality when the measurement value does not fall within a tolerable range with respect to the reference value. It is also possible to determine that the measurement value does not fall within a tolerable range when it exceeds a threshold that serves as a reference value. Alternatively, it is possible to perform the measurement and comparison multiple times so as to determine whether there is abnormality or not.

Where the rigidity is measured to determine if there is abnormality, the measurement section <NUM> may be configured to measure a natural frequency of the link actuation apparatus body <NUM> and estimate the rigidity on the basis of the natural frequency. The rigidity of the link actuation apparatus body <NUM> is related to its natural frequency, and the rigidity decreases as the natural frequency decreases. Accordingly, the measurement value of the natural frequency of the link actuation apparatus body <NUM> can be used to determine if there is abnormality in the link actuation apparatus body <NUM>. Where the measurement value of the rigidity is used, the presence or absence of abnormality can be determined in an inspection by an operation test immediately after assembly and/or a measurement during operation, and therefore, it is possible to avoid supplying defective products which may cause malfunction or the like.

Where the rigidity is measured to determine if there is abnormality, the measurement section <NUM> may be configured to measure torque of the posture control drive sources <NUM> and estimate the rigidity of the link actuation apparatus body <NUM> on the basis of the measured torque. The rigidity of the revolute pair parts <NUM> to <NUM> (i.e., the difficulty in rotating them) is observed as torque of the posture control drive sources <NUM>. Accordingly, the torque of the posture control drive sources <NUM> can be measured to estimate the rigidity of the link actuation apparatus body <NUM> on the basis of the measured torque. This makes it possible to detect improper assembly and simplify the inspection work. In addition, the presence or absence of abnormality can be determined in an inspection by an operation test immediately after assembly and/or a measurement during operation, and therefore, it is possible to avoid supplying defective products which may cause malfunction or the like.

In the present invention, the determination section <NUM> may include a storage section <NUM> configured to store state values of the link actuation apparatus body <NUM> in a plurality of postures, which are obtained when the respective revolute pair parts <NUM> to <NUM> of the link actuation apparatus body <NUM> are in a normal state, and the determination section <NUM> may be configured to compare a state value measured by the measurement section <NUM> to a value defined on the basis of the stored state values in the plurality of postures to determine the abnormality.

The presence or absence of abnormality can be appropriately determined by storing the state values obtained during normal time and comparing a present measurement value to the stored state values or to a value defined on the basis of the stored state values. Further, since the load acting on the revolute pair parts <NUM> to <NUM> greatly varies depending on the posture of the link actuation apparatus body <NUM>, abnormality may not appear in a state value of the rigidity or the like of the bearings <NUM> of the revolute pair parts <NUM> to <NUM> depending on the posture. Accordingly, the determination of abnormality may be performed in a plurality of postures so as to accurately detect not only initial defects such as improper assembly, but also variation during prolonged use due to wear or the like. Moreover, it may also be possible to identify which of the revolute pair parts <NUM> to <NUM> has abnormality.

In the present invention, the control device <NUM> may include an abnormality determination motion command section 3c configured to drive the posture control drive sources <NUM> such that the link actuation apparatus body <NUM> assumes a predetermined posture for abnormality determination. In response to a command from the abnormality determination motion command section 3c, a motion for abnormality determination may be performed after assembly of the link actuation apparatus and/or before starting operation on each occasion, so as to surely and precisely detect not only initial defects such as improper assembly, but also variation during prolonged use due to wear or the like.

The present invention will be more clearly understood from the following description of preferred embodiments thereof, when taken in conjunction with the accompanying drawings. However, the embodiments and the drawings are given only for the purpose of illustration and explanation, and are not to be taken as limiting the scope of the present invention in any way whatsoever, which scope is to be determined by the appended claims. In the accompanying drawings, like reference numerals are used to denote like parts throughout the several views.

An embodiment of the present invention will be described with reference to the drawings.

The link actuation apparatus includes: a link actuation apparatus body <NUM> constituted by a parallel link mechanism <NUM> and posture control drive sources <NUM> (<NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>) for the parallel link mechanism; and a control device <NUM> configured to control the link actuation apparatus body <NUM>.

As shown in <FIG> and <FIG>, the parallel link mechanism <NUM> couples a distal-side link hub <NUM> to a proximal-side link hub <NUM> through three link mechanisms <NUM> such that a posture of the distal-side link hub <NUM> can be changed relative to the proximal-side link hub <NUM>. There may be four or more link mechanisms <NUM>.

<FIG> shows one of the link mechanisms <NUM>. As shown in <FIG>, the link mechanism <NUM> includes: a proximal-side end link member <NUM>; a distal-side end link member <NUM>; and an intermediate link member <NUM> and forms a quadric-chain link mechanism having four revolute pair parts <NUM> to <NUM>. Each of the proximal-side and distal-side end link members <NUM>, <NUM> has an L shape. The proximal-side end link member <NUM> has one end rotatably coupled to the proximal-side link hub <NUM>, and the distal-side end link member <NUM> has one end rotatably coupled to the distal-side link hub <NUM>. The intermediate link member <NUM> has opposite ends rotatably coupled to the other ends of the proximal-side and distal-side end link members <NUM>, <NUM>.

The parallel link mechanism <NUM> has a structure in which two spherical link mechanisms are combined. In this structure, the center axis O1 of each revolute pair part <NUM> between the proximal-side link hub <NUM> and the proximal-side end link member <NUM> intersects with the center axis O2 of each revolute pair part <NUM> between the proximal-side end link member <NUM> and the intermediate link member <NUM> at a spherical link center PA, (<FIG>). Similarly, the center axis O1 of each revolute pair part <NUM> between the distal-side link hub <NUM> and the distal-side end link member <NUM> intersects with the center axis O2 of each revolute pair part <NUM> between the distal-side end link member <NUM> and the intermediate link member <NUM> at a distal-side spherical link center PB (<FIG>).

There is a same distance from each revolute pair part <NUM> between the proximal-side link hub <NUM> and the proximal-side end link member <NUM> to the spherical link center PA and from each revolute pair part <NUM> between the distal-side link hub <NUM> and the distal-side end link member <NUM> to the spherical link center PB. Similarly, there is also a same distance from each revolute pair <NUM> of the proximal-side end link member <NUM> and the intermediate link member <NUM> to the spherical link center PA and from each revolute pair <NUM> between the distal-side end link member <NUM> and the intermediate link member <NUM> to the spherical link center PB. The center axes of the respective revolute pair parts <NUM>, <NUM> between the end link members <NUM>, <NUM> and the intermediate link members <NUM> may have an intersection angle γ or may be parallel to each other.

<FIG> is a cutaway plan view of the link actuation apparatus. <FIG> shows a relationship among the center axis O1 of each revolute pair part <NUM> between the proximal-side link hub <NUM> and the proximal-side end link member <NUM>, the center axis O2 of each revolute pair part <NUM> between the intermediate link member <NUM> and the proximal-side end link member <NUM>, and the spherical link center PA on the proximal side. That is, the point of intersection of the center axis O1 and the center axis O2 corresponds to the spherical link center PA. Although, in <FIG>, an angle α of <NUM>° is defined by the center axis O1 of each revolute pair part <NUM> (<NUM>) between the link hub <NUM> (<NUM>) and the end link member <NUM> (<NUM>) and the center axis O2 of each revolute pair part <NUM> (<NUM>) between the end link member <NUM> (<NUM>) and the intermediate link member <NUM>, the angle α may not necessarily be <NUM>°.

The three link mechanisms <NUM> have geometrically the same shape in any posture. The expression "geometrically the same shape" means that, as shown in <FIG>, a geometric model that represents the respective link members <NUM>, <NUM>, <NUM> with straight lines, that is, a model that is expressed by the respective revolute pair parts <NUM> to <NUM> and the straight lines connecting these revolute pair parts <NUM> to <NUM>, has such a shape that a proximal-side part and a distal-side part are symmetrical to each other with respect to a central part of the intermediate link member <NUM>.

<FIG> illustrates one link mechanism <NUM> with straight lines. The parallel link mechanism <NUM> of this embodiment is of a rotationally symmetrical type. That is, the positional relationship of a proximal side region composed of the proximal-side link hub <NUM> and the proximal-side end link member <NUM> relative to a distal side region composed of the distal-side link hub <NUM> and the distal-side end link member <NUM> is rotationally symmetrical with respect to the center line C of the intermediate link member <NUM>. The central parts of the respective intermediate link members <NUM> are located on a common orbital circle.

The proximal-side link hub <NUM>, the distal-side link hub <NUM>, and the three link mechanisms <NUM> cooperate together to form a mechanism having two degrees of freedom that allows the distal-side link hub <NUM> to rotatably move relative to the proximal-side link hub <NUM> about two orthogonal axes. In other words, the posture of the distal-side link hub <NUM> can be changed relative to the proximal-side link hub <NUM> with two degrees of freedom of rotation. This mechanism having two degrees of freedom makes it possible to achieve a compact configuration and to provide a wide operating range in which the distal-side link hub <NUM> can be moved relative to the proximal-side link hub <NUM>.

For example, a center axis QA of the link hub <NUM> may refer to a line that passes through the spherical link center PA and orthogonally intersects with the center axis O1 (<FIG>) of each revolute pair part <NUM> between the link hub <NUM> and the end link member <NUM>. Similarly, a center axis QB of the link hub <NUM> may refer to a line that passes through the spherical link center PB and orthogonally intersects with the center axis O1 (<FIG>) of each revolute pair part <NUM> between the link hub <NUM> and the end link member <NUM>. In this case, a bend angle θ between the center axis QA of the proximal-side link hub <NUM> and the center axis QB of the distal-side link hub <NUM> may have a maximum value of about ± <NUM>°. A turn angle ϕ of the distal-side link hub <NUM> with respect to the proximal-side link hub <NUM> may be set in a range from <NUM>° to <NUM>°. The bend angle θ is a vertical angle at which the center axis QB of the distal-side link hub <NUM> is tilted with respect to the center axis QA of the proximal-side link hub <NUM>. The turn angle ϕ is a horizontal angle at which the center axis QB of the distal-side link hub <NUM> is tilted with respect to the center axis QA of the proximal-side link hub <NUM>.

The posture of the distal-side link hub <NUM> relative to the proximal-side link hub <NUM> is changed in such a manner that a rotation center is located at an intersection O of the center axis QA of the proximal-side link hub <NUM> and the center axis QB of the distal-side link hub <NUM>. In a state at an origin position where the center axis QA of the proximal-side link hub <NUM> and the center axis QB of the distal-side link hub <NUM> are on the same line (<FIG>), the distal-side link hub <NUM> faces directly downward. <FIG> and <FIG> show a state where the center axis QB of the distal-side link hub <NUM> makes a certain operation angle with respect to the center axis QA of the proximal-side link hub <NUM>. Even where the posture is changed, the distance L (<FIG>) between the spherical link centers PA, PB on the proximal side and the distal side does not change.

Where each of the link mechanisms <NUM> satisfies the following conditions <NUM> to <NUM>, the proximal side region composed of the proximal-side link hub <NUM> and the proximal-side end link member <NUM> move in the same manner as the distal side region composed of the distal-side link hub <NUM> and the distal-side end link member <NUM> because of the geometric symmetry. Therefore, the parallel link mechanism <NUM> functions as a constant velocity universal joint that makes the same rotation angle on the proximal side and the distal side and rotates at a constant velocity, when rotation is transmitted from the proximal side to the distal side.

Condition <NUM>: The angles and the lengths of the central axes O1 of the revolute pair parts <NUM>, <NUM> between the link hubs <NUM>, <NUM> and the end link members <NUM>, <NUM> in each link mechanism <NUM> are equal to each other.

Condition <NUM>: The central axes O1 of the revolute pair parts <NUM>, <NUM> between the link hubs <NUM>, <NUM> and the end link members <NUM>, <NUM> and the central axes O2 of the revolute pair parts <NUM>, <NUM> between the end link members <NUM>, <NUM> and the intermediate link members <NUM> intersect each other at the spherical link centers PA, PB on the proximal side and the distal side, respectively.

Condition <NUM>: The geometrical shapes of the proximal-side end link member <NUM> and the distal-side end link member <NUM> are the same.

Condition <NUM>: The geometrical shapes of the proximal-side portion and the distal-side portion of the intermediate link member <NUM> are the same.

Condition <NUM>: The angular positional relationships between the intermediate link member <NUM> and the end link members <NUM>, <NUM> with respect to the symmetry plane of the intermediate link member <NUM> are identical on the proximal side and the distal side.

As shown in <FIG>, the proximal-side link hub <NUM> includes a proximal member <NUM> and three rotation support members <NUM> integrally provided with the proximal member <NUM>. The three rotation support members <NUM> are disposed at equal intervals in a circumferential direction of the link hub <NUM>. A rotation shaft <NUM> is rotatably coupled to each of the rotation support members <NUM>, and the axis of the rotation shaft <NUM> intersects with the center axis QA of the proximal-side link hub <NUM>. The rotation shaft <NUM> is coupled to one end of the proximal-side end link member <NUM>.

The distal-side link hub <NUM> includes a plate-like distal member <NUM> and three rotation support members <NUM> provided to an inner surface of the distal member <NUM> at equal intervals in a circumferential direction of the link hub <NUM>. A rotation shaft <NUM> is rotatably coupled to each of the rotation support members <NUM>, and the axis of the rotation shaft <NUM> intersects with the center axis QB of the distal-side link hub <NUM>. The rotation shaft <NUM> of the distal-side link hub <NUM> is coupled to one end of the distal-side end link member <NUM>. The other end of the distal-side end link member <NUM> is coupled to a rotation shaft <NUM> which is rotatably coupled to the other end of the intermediate link member <NUM>. The rotation shaft <NUM> of the distal-side link hub <NUM> and the rotation shaft <NUM> of the intermediate link member <NUM> also have the same shape as that of the rotation shaft <NUM> and are rotatably coupled to the other end of the rotation support member <NUM> and to the other end of the intermediate link member <NUM>, respectively, through two bearings (not illustrated).

<FIG> shows a relation among the proximal-side end link members <NUM> illustrated as a cross section, the respective posture control drive sources <NUM>, and the proximal-side link hub <NUM>. <FIG> shows an enlarged sectional view of a part of <FIG>, and <FIG> shows a further enlarged sectional view of a part of <FIG>.

The proximal-side link hub <NUM> includes the three rotation shaft support members <NUM> for supporting the proximal-side end link members <NUM>, the rotation shaft support members <NUM> protruding on an upper surface of the proximal member <NUM>. Each rotation shaft support member <NUM> rotatably supports the rotation shaft <NUM> through two bearings <NUM>, <NUM> arranged in two rows as shown in <FIG> and <FIG>, and one end of the corresponding proximal-side end link member <NUM> is fixed to the rotation shaft <NUM>. The connecting part between the proximal-side link hub <NUM> and the proximal-side end link member <NUM> via the bearings <NUM>, <NUM> constitutes one revolute pair part <NUM>.

Specifically, the proximal-side end link member <NUM> has one end having a pair of branched pieces 15a, 15b of a bifurcated shape, and the rotation shaft support member <NUM> and the bearings <NUM>, <NUM> are interposed between these branched pieces 15a, 15b. An outer peripheral fitting member <NUM> is fittedly fixed to an outer periphery of a large diameter part of the rotation shaft <NUM>, such that an end face of the outer peripheral fitting member <NUM> is in contact with an outer surface of one branched piece 15b. Then, a fixing member <NUM> such as a bolt is inserted from the inside to fix the branched piece 15b to the outer peripheral fitting member <NUM>.

The bearings <NUM>, <NUM> are rolling bearings such as angular ball bearings. A shim <NUM> (see <FIG>) is interposed between outer rings (not illustrated) of the bearings <NUM>, <NUM>. A thin shaft part of the rotation shaft <NUM> is inserted through inner rings (not illustrated) of the bearings <NUM>, <NUM>, and ring-shaped spacers <NUM>, <NUM> are inserted between the inner rings and the branched pieces 15a, 15b. Then, a nut <NUM> (see <FIG>) is screwed onto a male thread part 22a at a tip of the thin shaft part to fasten the branched pieces 15a, 15b, the inner rings of the bearings <NUM>, <NUM>, and the spacers <NUM>, <NUM> so as to apply a preload to the bearings <NUM>, <NUM>.

In <FIG>, the revolute pair part <NUM> that is a connecting part between the distal-side end link hub <NUM> and the distal-side end link member <NUM> has a similar constitution to that of the revolute pair part <NUM> between the proximal-side link hub <NUM> and the proximal-side end link member <NUM> as described above.

As shown in <FIG>, the proximal-side end link member <NUM> has the other end having a pair of branched pieces 15c, 15d of a bifurcated shape, and an end portion of the intermediate link member <NUM> is interposed between these branched pieces 15c, 15d. Bearings <NUM>, <NUM>, which are rolling bearings such as angular ball bearings, are arranged in two rows at the end portion of the intermediate link member <NUM> in a similar manner as that in the revolute pair part <NUM> between the proximal-side link hub <NUM> and the proximal-side end link member <NUM>.

Outer rings of these bearings <NUM> are fittedly fixed to the intermediate link member <NUM>, and the rotation shaft <NUM> is fitted into the inner rings. Similarly to the connection to the proximal-side link hub <NUM>, a shim is interposed between the outer rings of the bearings <NUM>, <NUM>. Spacers are disposed in contact with the inner rings on the opposite sides of the rows of the bearings <NUM>, <NUM>. The rotation shaft <NUM> is a bolt having a male thread part and a head. A nut <NUM> is screwed onto the male thread part to fasten the pair of branched pieces 15c, 15d along with the two bearings <NUM>, <NUM>, the shim and the spacers, so as to apply a preload to the bearings <NUM>, <NUM>. Note that although the rotation shaft <NUM> of this part is a shaft for supporting rotation and is not configured to rotate, the shaft may be configured to rotate.

The revolute pair part <NUM> between the distal-side end link member <NUM> (see <FIG>) and the intermediate link member <NUM> has a similar constitution to that of the revolute pair part <NUM> between the proximal-side end link member <NUM> and the intermediate link member <NUM>, which has been described with reference to <FIG>.

As shown in <FIG>, each of the posture control drive sources <NUM> is a rotary actuator having a speed reduction mechanism <NUM> and is disposed on a lower surface of the proximal member <NUM> of the proximal-side link hub <NUM> so as to be coaxial with the rotation shaft <NUM>. The posture control drive source <NUM> and the speed reduction mechanism <NUM> are integrally provided, and the speed reduction mechanism <NUM> is fixed to the proximal member <NUM> by a drive source fixing member <NUM>. In this example, each of the three link mechanisms <NUM> is provided with the posture control drive source <NUM>. However, as long as at least two of the three link mechanisms <NUM> are provided with the posture control drive sources <NUM>, the posture of the distal-side link hub <NUM> relative to the proximal-side link hub <NUM> can be defined.

The parallel link mechanism <NUM> rotationally drives the respective posture control drive sources <NUM> to change the posture. Specifically, when the posture control drive sources <NUM> are rotationally driven, the rotation is transmitted to the rotation shafts <NUM>, with the speed of the rotation reduced by the speed reduction mechanisms <NUM>. This changes the angle of the proximal-side end link member <NUM> relative to the proximal-side link hub <NUM> and thereby changes the posture of the distal-side link hub <NUM> relative to the proximal-side link hub <NUM>.

In <FIG>, the distal-side link hub <NUM> is provided with an end effector (not illustrated) for performing a work on a work target (not illustrated), and the link actuation apparatus and the end effector constitute a work apparatus. Examples of the end effector may include an application nozzle, an air nozzle, a welding torch, a camera, and a clamping mechanism.

The control device <NUM> is configured to mainly control the posture control drive sources <NUM> (<NUM>-<NUM> to <NUM>-<NUM>) to control the posture of the parallel link mechanism <NUM>. Examples of the control device <NUM> may include a computer, a program executed thereon, and an electronic circuit. The control device <NUM> includes: a controller <NUM> configured to control the posture; and an abnormality detector <NUM> configured to detect abnormality.

The controller <NUM> includes: a control section 3a configured to decode and execute a control program; a normal motion command section 3b; and an abnormality determination motion command section 3c. The normal motion command section 3b includes a control program for causing the link actuation apparatus body <NUM> to perform posture control for a work or the like. The abnormality determination motion command section 3c includes a control program for causing the link actuation apparatus body <NUM> to perform posture control for abnormality detection.

The abnormality detector <NUM> is operable to detect abnormality in the revolute pair parts <NUM> to <NUM> of the link actuation apparatus body <NUM> and includes a measurement section <NUM> and a determination section <NUM>. Examples of abnormality may include improper arrangement or wear of the bearings <NUM>, the peripheral shims <NUM> and spacers <NUM>. In this example, the abnormality detector <NUM> further includes a data collection section <NUM>.

The measurement section <NUM> is operable to measure a certain state value that is affected by abnormality in the bearings <NUM> of the revolute pair parts <NUM> to <NUM> of the link actuation apparatus body <NUM>. For example, the state value may be rigidity of the link actuation apparatus body <NUM>. The determination section <NUM> determines if the link actuation apparatus body <NUM> has abnormality in any of the revolute pair parts <NUM> to <NUM> on the basis of a measurement result obtained by the measurement section <NUM>. The determination section <NUM> determines the abnormality according to a predetermined rule on the basis of a measurement value obtained by the measurement section <NUM>.

In this embodiment, the measurement section <NUM> measures a natural frequency of the link actuation apparatus body <NUM> and estimates the rigidity of the link actuation apparatus body <NUM> on the basis of the natural frequency. Specifically, the measurement section <NUM> includes: a sensor 5a disposed on the proximal-side link hub <NUM> of the link actuation apparatus body <NUM>; and a rigidity estimator 5b installed in a computer constituting the control device <NUM>. For example, the sensor 5a may be a vibrograph such as an acceleration pickup.

Instead, the measurement section <NUM> may measure torque of the posture control drive sources <NUM> and estimate the rigidity of the link actuation apparatus body <NUM> on the basis of the measured torque. In this case, for example, an ammeter (not illustrated) for detecting a current flowing to the posture control drive sources <NUM> may be used for measuring torque, and the rigidity estimator 5b estimates the rigidity of the link actuation apparatus body <NUM> on the basis of the detected current.

The determination section <NUM> stores a state value, that serves as a reference for determination (for example, reference rigidity), as a reference value in a storage section <NUM> and compares a state value measured by the measurement section <NUM> to the reference value to perform the determination of abnormality. In this case, the storage section <NUM> stores reference values of the link actuation apparatus body <NUM> in a plurality of postures.

The reference values stored in the storage section <NUM> may be values determined by design or simulation, or state values such as the rigidity or frequency or the like of the link actuation apparatus body <NUM>, which are obtained when the respective revolute pair parts <NUM> to <NUM> of the link actuation apparatus body <NUM> are in a normal state. The data collection section <NUM> causes the storage section <NUM> to store the state values of the link actuation apparatus body <NUM> in a plurality of postures, which are obtained when the respective revolute pair parts <NUM> to <NUM> of the link actuation apparatus body <NUM> are in a normal state.

The abnormality determination motion command section 3c gives a command for driving the posture control drive sources <NUM> such that the link actuation apparatus body <NUM> assumes a predetermined posture for abnormality determination. As described above, the abnormality determination motion command section 3c includes a control program to be executed by the control section 3a.

The link actuation apparatus body <NUM> of the present embodiment is constituted by the parallel link mechanism <NUM> having two degrees of freedom of rotation. The mechanism is characterized in that the rigidity of the respective link mechanisms <NUM> and of the link actuation apparatus body <NUM> varies depending on the posture of the parallel link mechanism <NUM>. Where abnormality occurs in the parallel link mechanism <NUM> of the link actuation apparatus body <NUM>, the rigidity (or "resistance") of the respective link mechanisms <NUM> and/or the rigidity of the respective revolute pair parts <NUM> to <NUM> vary. Change in the rigidity of the respective link mechanisms <NUM> and/or the rigidity of the respective revolute pair parts <NUM> to <NUM> causes a change in the natural vibration of the link actuation apparatus body <NUM> and/or in the torque of the respective posture control drive sources <NUM>.

As described above, the control device <NUM> includes the abnormality detector <NUM> for detecting abnormality in the link actuation apparatus body <NUM>. The abnormality detector <NUM> includes: the measurement section <NUM> for measuring the rigidity of the link actuation apparatus body <NUM>; and the determination section <NUM> for determining whether a value of the rigidity is normal or abnormal.

In the determination, since the determination section <NUM> includes the storage section <NUM> storing the state values of natural vibration or torque during normal time as reference values, it is possible to compare measurement values in various postures to the data (reference values) of the storage section <NUM> so as to detect abnormality. The rigidity of the link actuation apparatus body <NUM> can be estimated on the basis of the natural frequency or the torque of the posture control drive source <NUM>. For example, as the rigidity increases, the amplitude and frequency of the natural vibration increase, and the driving torque also increases. For this reason, the rigidity of the link actuation apparatus body <NUM> can be estimated by measuring the natural vibration using the sensor 5a (such as an acceleration pickup) for detecting vibration, which is attached to the link actuation apparatus body <NUM>, or by measuring the natural vibration or torque on the basis of a motor driving current of the posture control drive sources <NUM>.

Although, in <FIG>, the sensor 5a is attached to the proximal-side link hub <NUM>, it may be attached to the distal-side link hub <NUM> where the vibration is greater. Where the distal-side link hub <NUM> of the link actuation apparatus has a posture as shown in <FIG>, the three link mechanisms <NUM> support a substantially equal amount of load. In contrast, where the posture of the distal-side link hub <NUM> is changed to a posture as shown in <FIG>, the three link mechanisms <NUM> unequally support the load and moment of inertia, resulting in a change in the rigidity of the entire link actuation apparatus body <NUM>. Therefore, it is necessary to store values of the rigidity in various postures beforehand.

The link actuation apparatus of the present embodiment stores normal data in various postures because the rigidity varies depending on the posture of the link actuation apparatus body <NUM>. The term "data" as used herein means the reference values or values for obtaining the reference values, that is, the rigidity estimated from the natural vibration and torque. The normal data is derived from previous inspections or simulation models, and a threshold that serves as a reference value in abnormality determination is defined on the basis of the normal data and is stored in the storage section <NUM>.

The abnormality detection by the abnormality detector <NUM> is carried out in an inspection process after assembly, during continuous operation which is normal operation, and in a check process before starting the continuous operation. <FIG> shows an exemplary flowchart of the inspection process after assembly; <FIG> shows another exemplary flowchart of the inspection process after assembly; <FIG> shows an exemplary flowchart of the check process before starting the continuous operation; and <FIG> shows another exemplary flowchart of an inspection during the continuous operation.

In the inspection process after assembly of the link actuation apparatus, the measurement section <NUM> measures data of a state value of the link actuation apparatus body <NUM> in a certain posture (step Q1). The determination section <NUM> compares the data to a threshold stored in the storage section <NUM> (step Q2). Where it is determined as normal as a result of the comparison (step Q3: Yes), the data collection section <NUM> of the abnormality detector <NUM> stores, in the storage section <NUM>, the data measured in the certain posture (step Q4). The stored data will be used as normal data in subsequent inspections performed in the inspection process after assembly and will also be used as data specific to the link actuation apparatus in abnormality determination during continuous operation.

Where the determination section <NUM> determines that there is abnormality (step Q3: No), a warning is displayed to show a determination result indicating that there is abnormality (step Q5). This is displayed on a liquid crystal display device (not illustrated) provided to the control device <NUM>. Where a warning is given, a product (not illustrated) handled by an operator or provided in a target body combined with the link actuation apparatus is subjected to reinspection or component replacement or is discarded as an unacceptable product (defective product).

Although the series of the inspection process after assembly of <FIG> repeats the data measurement and determination of normality/abnormality in a single posture, it is also possible, as in the example of <FIG>, to measure the data in various postures in advance (step R1) and then to collectively perform the determination of normality/abnormality (steps R2, R3). In such a case, the data obtained in various postures is stored collectively (step R4), and the warnings are also displayed collectively (step R5).

Before the link actuation apparatus performs continuous operation, which is normal operation, the abnormality determination motion command section 3c gives a command for causing the link actuation apparatus to perform a motion for carrying out the check process for the abnormality determination. The motion in the check process may be the same as the motion during the continuous operation or a dedicated motion for the check.

In the check process, the measurement section <NUM> measures the data in various postures during the motion at regular intervals of time or in each certain motion step (step S1) and compares the measured data to a threshold derived from the data stored in the storage section <NUM> during the inspection process (step S2). Where it is determined as normal as a result of the comparison (step S3: Yes), the link actuation apparatus is stopped, and a warning is displayed (step S4). The measurement in various postures (step S1) may be carried out every time a predetermined posture is assumed, instead of being carried out at regular intervals of time. Different thresholds may be used for the inspection after assembly, the check process, and the inspection during the continuous operation. The normal data may be used both as the accumulated normal data and the initial data specific to the link actuation apparatus.

During continuous operation, the measurement section <NUM> measures the data in various postures at regular intervals of time or in each certain motion step (step T1) and compares the measured data to a threshold derived from the data stored in the storage section <NUM> during the inspection process (step T2), as in the same manner as that of the check process. Where it is determined as abnormal as a result of the comparison (step T3: Yes), the link actuation apparatus is stopped, and a warning is displayed (step T4).

For example, the expression "at regular intervals of time" may mean every hour. The expression "in each certain motion step" may mean every step or every multiple motion steps. The "motion step(s)" as used herein means a motion that is a unit of posture change of the link actuation apparatus.

<FIG> shows the above embodiment with improper assembly in which drive source fixing members <NUM> and the rotation support members <NUM> are attached at displaced angles. Normally, the link actuation apparatus of the present embodiment is assembled such that all of the center axes O1 of the revolute pair parts <NUM> between the proximal-side end link members <NUM> and the rotation support members <NUM> intersect with all of the center axes O2 of the revolute pair parts <NUM> between the proximal-side end link members <NUM> and the intermediate link members <NUM> at the center of the proximal-side link hub <NUM>, as shown in <FIG>.

In the example of improper assembly as shown in <FIG>, the drive source fixing members <NUM> and the rotation support members <NUM> are attached at displaced angles, and as a result, the respective center axes O1 of the revolute pair parts <NUM> between the proximal-side end link members <NUM> and the rotation support members <NUM> do not intersect with the respective center axes O2 of the revolute pair parts <NUM> between the proximal-side end link members <NUM> and the intermediate link members <NUM> at the center of the proximal-side link hub <NUM>.

If, in the state of <FIG>, an attempt is made to control the posture control drive sources <NUM> in order to control the posture of the distal-side link hub <NUM>, they do not operate normally due to the displacement of the mechanisms. For this reason, the link actuation apparatus has different natural vibration, and the posture control drive sources <NUM> have different torque, as compared with those in a normal state. By measuring the natural vibration or torque, the improper assembly can be detected.

The link actuation apparatus shown in the present embodiment is provided with the bearings <NUM> in each of the revolute pair parts <NUM> to <NUM> as rotation torque reducers. The bearing <NUM> are arranged in two rows, and a shim <NUM> is interposed between the outer rings of the bearings in order to increase the distance between the outer rings as shown in <FIG>. A preload is applied to the inner rings of the bearings <NUM> by bolts and nuts through the proximal-side end link member <NUM> and the spacers <NUM> so as to increase the rigidity.

In such a constitution, improper assembly may be performed when the bearings <NUM> are disposed on the intermediate link member <NUM>, in such a way that a shim <NUM> is not placed between the bearings <NUM>, <NUM>, or more than two shims <NUM> are placed between the bearings <NUM>, <NUM>. Due to such improper arrangement of the shim(s) <NUM>, a dimensional difference may occur, which may lead to deformation of the proximal-side end link member <NUM> due to undesired force applied thereto. Moreover, change in the rigidity of the revolute pair parts <NUM> to <NUM> or the like may cause deterioration of accuracy, reduction of service life, and vibration. Lack of the shim may lower the rigidity and thus lead to deterioration of accuracy and vibration, whereas inclusion of extra shims may cause reduction of service life due to increased surface pressure.

Conventionally, it has been difficult to check improper arrangement of shims after assembly of the link actuation apparatus. For example, visual inspection requires disassembly of the apparatus, which takes time or labor. Moreover, it is not possible to non-destructively disassemble the apparatus. By use of the natural frequency or torque as in the above embodiment, however, it is possible to detect such improper assembly in a non-destructive and easy manner.

Claim 1:
A link actuation apparatus comprising:
a parallel link mechanism (<NUM>) including a proximal-side link hub (<NUM>), a distal-side link hub (<NUM>), link mechanisms (<NUM>) each coupling the distal-side link hub to the proximal-side link hub such that a posture of the distal-side link hub can be changed relative to the proximal-side link hub, and revolute pair parts (<NUM>-<NUM>) which serve as connections in the link mechanisms;
posture control drive sources (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, ...) configured to arbitrarily change the posture of the distal-side link hub relative to the link mechanisms; and
a control device (<NUM>) configured to control the posture control drive sources, wherein
the control device includes an abnormality detector (<NUM>) including:
a measurement section (<NUM>) configured to measure a predetermined state value which is affected by abnormality in the revolute pair parts of a link actuation apparatus body (<NUM>) constituted by the parallel link mechanism and the posture control drive sources; and
a determination section (<NUM>) configured to determine if the link actuation apparatus body has abnormality in any of the revolute pair parts on the basis of a measurement result obtained by the measurement section,
wherein the measurement section is configured to measure rigidity of the link actuation apparatus body, and the determination section is configured to determine the abnormality according to a predetermined rule on the basis of a measurement value obtained by the measurement section.