Parallel link robot

A parallel link robot includes: a base part; a movable part including an accessory shaft; arms coupling the base and movable parts in parallel; and actuators that drive the respective arms, where each of the arms includes a driving link driven by each of the actuators, and two parallel passive links coupled to the driving link, between the passive links of at least one of the arms, an additional actuator having a rotating shaft disposed in parallel to the passive links is supported by a first link swingably coupled to each of the passive links, the accessory shaft, and the rotating shaft are coupled by a transmission shaft, and the transmission shaft is supported, at an intermediate position in a direction along a longitudinal axis thereof, on a second link rotatably around the longitudinal axis, the second link being swingably coupled to each of the passive links.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No. 2019-216659, the content of which is incorpo-rated herein by reference.

FIELD

The present disclosure relates to a parallel link robot.

BACKGROUND

There is known a parallel link robot including a plurality of arms coupling a base part and a movable part in parallel (see Japanese Unexamined Patent Application, Publication No. 2019-38051 for example). Each arm includes a driving link driven by an actuator, and two parallel passive links coupled to the driving link. An actuator for driving a wrist shaft provided in the movable part is disposed between the two passive links in parallel, and is supported by an auxiliary link laid between the passive links. The actuator and the wrist shaft are connected by a power transmission shaft.

SUMMARY

An aspect of the present disclosure is a parallel link robot including: a base part; a movable part including an accessory shaft; a plurality of arms that couple the base part and the movable part in parallel; and a plurality of actuators that are disposed in the base part, and drive the respective arms, wherein each of the arms includes a driving link driven by each the actuators, and two parallel passive links coupled to the driving link by joints, between the two passive links of at least one of the arms, an additional actuator having a rotating shaft disposed in parallel to the passive links is supported by a first auxiliary link laid between the passive links and swingably coupled to each of the passive links, the accessory shaft, and the rotating shaft of the additional actuator are coupled by a power transmission shaft, and the power transmission shaft is supported, at an intermediate position in a direction along a longitudinal axis of the power transmission shaft, on a second auxiliary link rotatably around the longitudinal axis by a bearing, the second auxiliary link being laid between the passive links and swingably coupled to each of the passive links.

DETAILED DESCRIPTION OF EMBODIMENTS

A parallel link robot1according to an embodiment of the present disclosure will be described hereinafter with reference to the drawings.

As illustrated inFIG. 1, the parallel link robot1according to this embodiment includes a base part3housed in a housing2, a disk-like movable plate (movable part)4, and three arms5that couple the base part3and the movable plate4in parallel.

In the base part3, three actuators6that drive the respective arms5are provided. The actuators6are each composed of a servo motor and a reducer, for example.

Each arm5includes a driving link7swung by the actuator6, and two parallel passive links8swingably coupled to the driving link7.

Both ends of each of the two passive links8are each swingably connected to the driving link7and the movable plate4by a ball joint (joint)9. That is, the driving link7, the two passive links8, and the movable plate4constitute a parallel four-bar linkage. Consequently, even when the angle of each passive link8to the driving link7is changed, a quadrangle obtained by sequentially connecting the four ball joints9by a straight line is always a parallelogram.

A wrist shaft (accessory shaft)10rotationally driven around a center axis X of the movable plate4is provided in the movable plate4.

As illustrated inFIG. 2, an additional actuator11for driving the wrist shaft10is disposed between the two passive links8of the one arm5such that a rotating shaft12is in parallel with the passive links8. The additional actuator11is, for example, a servo motor.

As illustrated inFIG. 2, the additional actuator11is supported by an auxiliary link (first auxiliary link)14that is laid between the two passive links8, and that is swingably coupled to the respective passive links8by bearings13. That is, the additional actuator11has one end swingably connected to a central portion of the auxiliary link14by a bearing13.

One end of a power transmission shaft15extending in the direction in which the rotating shaft12extends is connected to the rotating shaft12of the additional actuator11. As illustrated inFIG. 3, for example, a spline16and a spline hole17are fitted to each other, so that the rotating shaft12and the power transmission shaft15are connected so as to be movable in the direction along the rotating shaft12. Consequently, the rotating shaft12is rotated by the additional actuator11, so that the power transmission shaft15is rotated around a longitudinal axis C.

The power transmission shaft15has the other end connected to the wrist shaft10by a universal joint18.

FIG. 4illustrates an example of the wrist shaft10. Rotation of the power transmission shaft15is transmitted to the wrist shaft10through the universal joint18, a mounting flange20at a leading end is rotated round the center axis X of the movable plate4through a gear pair19.

In this embodiment, as illustrated inFIG. 2, the power transmission shaft15is also supported at an intermediate position in the longitudinal axis C direction by an auxiliary link (second auxiliary link)21laid between the two passive links8, and swingably coupled to the passive links8by bearings13. The auxiliary link21includes link bodies22supported on the passive links8swingably around mutually parallel swing axes A, and a support member23supported swingably with respect to the link bodies22around an axis B parallel to the swing axes A.

As illustrated inFIG. 5, the support member23is swingably supported on the link bodies22by bearings24, and includes a through hole (hole)25for allowing the power transmission shaft15to penetrate at a center. The power transmission shaft15is supported on the support member23rotatably around the longitudinal axis C by a bearing26disposed between the through hole25and the transmission shaft15.

According to this embodiment, a cylindrical elastic body27that supports the bearing26so as to enable the bearing26to slightly move in the longitudinal axis C direction of the power transmission shaft15by elastic deformation is disposed between the through hole25of the support member23and an outer ring26aof the bearing26.

As illustrated inFIG. 6, a rigidity reduction structure for greatly reducing rigidity of the elastic body27along the axial direction compared to rigidity of the elastic body27along the radial direction is provided in the elastic body27. The rigidity reduction structure is composed of, for example, two circumferential grooves (grooves)28that are provided in an inner circumferential surface of the cylindrical elastic body27at an interval in the axial direction, and that are recessed radially outward over the whole circumference.

In an example ofFIG. 6, annular regions each having a thickness of ¼ of the axial length of the bearing26in the elastic body27are in close contact with two portions of an outer circumferential surface of the outer ring26aof the bearing26at an interval in the axial direction. In this case, the rigidity of the elastic body27is reduced in the axial direction compared to a case where the circumferential grooves28are not provided, and the annular region is in close contact over the whole thickness in the axial direction of the bearing26. On the other hand, the rigidity of the elastic body27is reduced in the radial direction. InFIG. 6, reference numeral27adenotes a shoulder part that is disposed on one side in the axial direction of the elastic body27, and abuts on the outer ring26aof the bearing26in the axial direction.

The elastic body27is formed of, for example, resin, and is maintained in a state of being in close contact with the outer circumferential surface of the outer ring26aof the bearing26and an inner circumferential surface of the through hole25of the support member23as illustrated inFIG. 5. When force in the direction along the longitudinal axis C acts on the power transmission shaft15, the bearing26can be slightly moved in the direction along the longitudinal axis C by elastic deformation of the elastic body27, as illustrated inFIG. 7.

An operation of the parallel link robot1thus configured, according to this embodiment will be hereinafter described.

FIG. 8andFIG. 9are each a schematic drawing for illustrating motion of the passive links8of the one arm5when the movable plate4moves. As is apparent from these drawings, the two passive links8are parallel to each other before and after the movable plate4moves. Then, the additional actuator11and the power transmission shaft15are also maintained in parallel to the two passive links8.

That is, the two passive links8and the power transmission shaft15are always parallel to each other, and the lengths thereof are not changed. Therefore, ideally, the auxiliary link21, the passive links8, the movable plate4, and the power transmission shaft15also constitute a parallel four-bar linkage.

However, in reality, when the length of the power transmission shaft15is increased, the power transmission shaft15receives external force in the direction orthogonal to the longitudinal axis C by the inertia amount of the power transmission shaft15itself during operation of the arm5. In a case where the power transmission shaft15is deflected by external force, and a dimension error, an assembly error, abrasion, or the like occurs, the aforementioned ideal parallel four-bar linkage is broken. In this case, a distance between the auxiliary link21and the universal joint18is changed, and therefore the power transmission shaft15moves in the longitudinal axis C direction with respect to the additional actuator11.

According to this embodiment, the power transmission shaft15is supported, at the intermediate position, on the auxiliary link21laid between the two passive links8, rotatably around the longitudinal axis C by the bearing26. Therefore, there is an advantage that external force that acts in the direction intersecting with the longitudinal axis C is supported by the two passive links8through the bearing26and the auxiliary link21, and it is possible to sufficiently suppress occurrence of deflection of the power transmission shaft15during the operation of the arm5.

In a case where the ideal parallel four-bar linkage is broken by the aforementioned cause, the power transmission shaft15sometimes moves in the longitudinal axis C direction, and the movement is absorbed by spline coupling at a connecting part of the additional actuator11and the power transmission shaft15. On the other hand, the bearing26that rotatably supports the power transmission shaft15on the auxiliary link21supports the power transmission shaft15so as to enable the power transmission shaft15to slightly move in the longitudinal axis C direction by the elastic body27.

As a result, even when the arm5moves in a state in which the parallel four-bar linkage is broken, and the power transmission shaft15moves in the longitudinal axis C direction, the elastic body27is elastically deformed, and the bearing26moves in the longitudinal axis C direction of the power transmission shaft15. Consequently, there is an advantage that while the power transmission shaft15is supported rotatably around the longitudinal axis C by the bearing26, excessive thrust force can be prevented from acting on the bearing26.

Particularly, in this embodiment, the circumferential grooves28that compose the rigidity reduction structure for greatly reducing axial rigidity compared to radial rigidity is provided in the cylindrical elastic body27, and therefore while the deflection of the power transmission shaft15is reliably prevent, thrust force applied to the bearing26can be reduced.

There is an advantage that as the rigidity reduction structure, a simple structure in which the circumferential grooves28is merely provided in the inner circumferential surface of the elastic body27is employed, so that it is possible to obtain a compact configuration without increase of the outer diameter of the elastic body27.

In this embodiment, as the rigidity reduction structure provided in the elastic body27, the two circumferential grooves28provided in the inner circumferential surface of the cylindrical elastic body27are exemplified. In place of this, the one or three or more circumferential grooves28may be employed. The shape of each circumferential groves28may be an arbitrary shape such as a U-shaped groove in which a cross-section of a bottom surface is an arc, a rectangular groove having a rectangle, and a V-shaped groove.

In place of a plurality of the independent circumferential grooves28, a spirally continued groove may be employed.

The circumferential grooves28that compose the rigidity reduction structure are provided in the inner circumferential surface of the cylindrical elastic body27. However, in place of the above, the circumferential groove may be provided in the outer circumferential surface, or the circumferential grooves may be provided in both the inner circumferential surface and the outer circumferential surface.

As the rigidity reduction structure, in place of the circumferential grooves28, as illustrated inFIG. 10, one or more slits29radially extending along the circumferential direction may be provided in at least one of the inner circumferential surface and the outer circumferential surface of the elastic body27. In this case, the rigidity of the elastic body27is reduced in the axial direction, and is not reduced in the radial direction, compared to a case where any slit29is not provided, and the annular region is in close contact over the whole thickness in the axial direction of the bearing26in the elastic body27. The elastic body27may be composed by stacking of a plurality of annular ring plates in the plate thickness direction.