Articulated shaft structure of robot and robot

The articulated shaft structure includes: a first joint member; a second joint member supported rotatable about a first axis; a ring-like output hypoid gear fixed to the second joint member coaxially with the first axis; a gear assembly attached to the first joint member; and a motor, wherein the gear assembly includes a housing member, an input hypoid gear, and gears, the housing member including a second joining surface fixed to a first joining surface, the input hypoid gear being supported by the housing member rotatable about a second axis, the gears decelerating rotation of the motor and transmitting the rotation to the input hypoid gear, the first joining surface is parallel to the first axis, the second joining surface is perpendicular to the second axis, and the bolt is fastened radially outside of the gears of all kinds assumed to be used, the kinds being defined by reduction ratios.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No. 2018-039607, the content of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an articulated shaft structure of a robot and the robot.

BACKGROUND ART

An articulated shaft structure has been known that allows a wrist unit at a distal end of a forearm of a robot to rotate about a longitudinal axis of the forearm (e.g., see Patent Literature 1).

In this articulated shaft structure, a ring-like output hypoid gear coupled with the wrist unit is supported by a proximal end of the forearm through bearings so as to be rotatable coaxially with the longitudinal axis of the forearm. Further, a unit including a housing member that rotatably supports the input hypoid gear and also supports a motor and gears for decelerating and transmitting rotation of the motor to the input hypoid gear is mounted on a proximal side surface of a part of the forearm. This causes the input hypoid gear to engage with the output hypoid gear.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

According to an aspect of the present invention, there is provided an articulated shaft structure of a robot, the structure including: a first joint member; a second joint member supported by the first joint member so as to be rotatable about a first axis; a ring-like output hypoid gear fixed to the second joint member coaxially with the first axis; a gear assembly attached to the first joint member; and a motor attached to the gear assembly, wherein the gear assembly includes a housing member, an input hypoid gear, and gears, the housing member including a second joining surface tightly fixed to a first joining surface of the first joint member with a bolt, the input hypoid gear being supported by the housing member so as to be rotatable about a second axis, the gears decelerating rotation of the motor and transmitting the rotation to the input hypoid gear, the first joining surface is parallel to the first axis, the second joining surface is perpendicular to the second axis, with the housing member being fixed to the first joint member, the input hypoid gear is situated at a position where the input hypoid gear engages with the output hypoid gear, and the bolt is fastened radially outside of the gears of all kinds that are assumed to be used, the kinds being defined by reduction ratios.

DESCRIPTION OF EMBODIMENTS

An articulated shaft structure10of a robot1and the robot1according to an embodiment of the present invention will be described below with reference to the drawings.

As shown inFIG. 1, the robot1according to the present embodiment is an upright articulated type robot. The robot1includes: a base2installed on an installation surface such as a floor; a rotary body3capable of rotating about a vertical number-one axis A and relative to the base2; a first arm4capable of swinging about a horizontal number-two axis B and relative to the rotary body3; a forearm (the first joint member)5provided at a distal end of the first arm4and capable of swinging about a horizontal number-three axis C and relative to the first arm4; a cylindrical second arm (the second joint member)6provided at a distal end of the forearm5and capable of rotating about a number-four axis (the first axis) D that extends along a plane perpendicular to the number-three axis C; a second wrist element7provided at a distal end of the second arm6and capable of swinging about a number-five axis E perpendicular to the number-four axis D; and a third wrist element8capable of rotating about a number-six axis perpendicular to the number-five axis E.

The articulated shaft structure10according to the present embodiment has a structure that, for example, drives the second arm6to rotate relative to the forearm5. More specifically, as shown inFIGS. 2 and 3, the articulated shaft structure10according to the present embodiment includes the forearm5, the second arm6, a ring-like output hypoid gear11fixed to a proximal end of the second arm6coaxially with the number-four axis D, a gear assembly12attached to the forearm5, and a motor13attached to the gear assembly12.

The forearm5includes a first joining surface14on its side surface. The first joining surface14lies in parallel with the number-four axis D and is mounted with the gear assembly12. The first joining surface14is provided with a through hole15that allows for insertion of an input hypoid gear19(described later), and a recess (the first recess, the second recess)16capable of accommodating a gear group21(described later).

The gear assembly12includes: a housing member18including a second joining surface17tightly mounted on the first joining surface14of the forearm5; the input hypoid gear19supported so as to be rotatable about an axis (the second axis) G perpendicular to the second joining surface17of the housing member18; a motor mounting part20mounted with the motor13; and the gear group (the gears)21decelerating rotation of the motor13and transmitting the rotation to the input hypoid gear19.

In the case of a standard weight capacity, the gear group21consists of, for example, a small gear (the gears)22that is a spur gear attached to a shaft of the motor13and a large gear (the gears)23that is a spur gear coaxially fixed to the input hypoid gear19. The input hypoid gear19is supported by the housing member18through bearings24so as to be rotatable about the axis G.

The motor mounting part20includes a mounting surface25parallel to the second joining surface17. The mounting surface25is provided with screw holes (not shown in the figure) to which respective bolts (not shown in the figure) for fixing the motor13are fastened. The motor mounting part20is further provided with a fitting hole26into which a mating part of the motor13is fitted, and a through hole27that allows for insertion of the shaft and the small gear22. The shaft and the small gear22are inserted through the through hole27, the mating part of the motor13is fitted into the fitting hole26, and a flange of the motor13is brought into tight contact with the mounting surface25. This causes the small gear22to engage with the large gear23. In this state, the bolts are fastened to the respective screw holes, whereby the motor13may be fixed to the housing member18.

As shown inFIG. 3, the second joining surface17of the housing member18is provided with an opening28that exposes the small gear22and the large gear23engaging with each other. The opening28has a shape that surrounds the small gear22and the large gear23with a certain gap formed in an outward radial direction.

With the input hypoid gear19having the large gear23and the motor13having the small gear22being attached to the housing member18, at least a part of the input hypoid gear19, the large gear23and the small gear22protrudes in a direction perpendicular to the second joining surface17.

By the way, in order to adapt the robot1and the articulated shaft structure10of the robot1according to the present embodiment to an application that requires an increased weight capacity (heavy weight capacity) without changing the motor13, a reduction ratio of the gear group21needs to be changed. Thus, for example, a two-stage gear29is disposed between the small gear22attached to the motor13and the large gear23attached to the input hypoid gear19, as shown inFIG. 4.

In this case, the two-stage gear29integrally includes a number-two large gear30engaging with the small gear22and a number-two small gear31engaging with the large gear23. The two-stage gear29is supported by a housing member33, which is shaped differently from the housing member18, through bearings (not shown in the figure) so as to be rotatable about an axis parallel to the axis G of the input hypoid gear19.

Further, in this case, the second joining surface17of the housing member33is provided with an opening32that exposes the small gear22, the large gear23and the two-stage gear29, as shown inFIG. 4.

The recess16of the first joining surface14on the side surface of the forearm5lies in the area that covers both of the opening28of the second joining surface17in the case of the standard weight capacity shown inFIG. 3and the opening32of the second joining surface17in the case of the heavy weight capacity shown inFIG. 4. Also, the depth of the recess16of the first joining surface14from the top of the first joining surface14is set greater than the protruding amount of the gear group21protruding from the second joining surface17of the housing member33.

Further, with the first joining surface14and the second joining surface17tightly contacting each other, the bolts for fixing the gear assembly12to the forearm5are fastened into the respective screw holes located outside of the recess16of the first joining surface14. The screw holes are outwardly spaced from the recess16, and a seal member (not shown in the figure) is inserted into the space. This liquid-tightly seals the first joining surface14and the second joining surface17.

An operation of the robot1and the articulated shaft structure10of the robot1according to the present embodiment configured as above will be explained below.

In the robot1according to the present embodiment, the motor13is actuated to rotate the second arm6about the number-four axis D and relative to the forearm5.

The rotation of the motor13is decelerated at the reduction ratio equal to the gear ratio of the small gear22to the large gear23when being transmitted to the large gear23through the small gear22fixed to the shaft of the motor13. This causes the input hypoid gear19fixed to the large gear23to rotate, which in turn causes the output hypoid gear11engaging with the input hypoid gear19to rotate about the number-four axis D. This makes it possible to rotate the second arm6, to which the output hypoid gear11is fixed, about the number-four axis D and relative to the forearm5.

In this case, when the need arises to increase the torque of the second arm6in order to adapt the robot1and the articulated shaft structure10of the robot1according to the present embodiment to an application that requires a heavier weight capacity, the gear assembly12is replaced.

In replacing the gear assembly12, the second arm6is rotated to the angle at which the torque of the second arm6is minimized. In this state, the motor13is removed from the housing member18, and the bolts fixing the housing member18to the forearm5are removed. The gear assembly12is thus removed from the forearm5.

Then, another gear assembly12that includes a gear group21having a different reduction ratio is attached to the forearm5. Although at least a part of the input hypoid gear19and the gear group21protrudes from the second joining surface17of the housing member18of the gear assembly12, the first joining surface14of the forearm5is provided with the recess16that is dimensioned to be capable of even accommodating the new gear group21. Thus, aligning the input hypoid gear19with the through hole15of the forearm5and moving the second joining surface17close to the first joining surface14results in the gear group21being accommodated in the recess16of the first joining surface14. With the first joining surface14and the second joining surface17being positioned in tight contact with each other, the input hypoid gear19engages with the output hypoid gear11. Then, fastening of the bolts makes it possible to fix the gear assembly12to the forearm5.

Then, the motor13, which has been removed, is fixed to the mounting surface25of the motor mounting part20. This allows the small gear22fixed to the shaft of the motor13to engage with the number-two large gear30attached to the housing member33. As a result, the rotation of the motor13is more greatly decelerated before being transmitted to the input hypoid gear19, so that the robot1and the articulated shaft structure10of the robot1may be adapted to an application that requires a heavier weight capacity.

That is, just by replacing the gear assembly12, the robot1and the articulated shaft structure10of the robot1according to the present embodiment may be adapted to applications each requiring a different weight capacity. In this case, the input hypoid gear19engaging with the output hypoid gear11can be shared by two gear assemblies12, and the large gear23fixed to the input hypoid gear19and other parts including bearings rotatably fixing these gears19,23to the housing member18or33can also be shared.

Further, as shown inFIGS. 5 and 6, positions and sizes of the gears22,23,30and31protruding from the second joining surface17are different between the two gear assemblies12, depending on the presence of the two-stage gear29for changing the reduction ratio. Accordingly, the recess16of the first joining surface14is sized to be capable of even accommodating any of the gears22,23,30and31. Further, the bolts for fixing the gear assembly12to the forearm5are located and fastened outside of the opening28or32accommodating the gears22,23,30,31. This makes it possible to tightly contact the first joining surface14and the second joining surface17and bring them into a sealed state, regardless of which of the two gear assemblies12are used.

As a result, the robot1and the articulated shaft structure10of the robot1according to the present embodiment give an advantage in that they can be adapted to various applications requiring different weight capacities just by replacing the gear assembly12on the spot where the robot1is installed. That is, two kinds of robots1having different weight capacities can share the same parts of the forearm5. The same motor13can also be shared, giving an advantage in that a great change in an outer shape can be avoided.

Further, in the present embodiment, at least a part of the gears22,23protrudes from the second joining surface17, and the recess16for accommodating this protruding part of the gears22,23is provided on the first joining surface14. This eliminates the need for accommodating the gears22,23entirely in the housing member18and thus allows the housing member18, which is subject to replacement, to be thinner. This gives an advantage in that the gear assembly12can be lighter for easier replacement.

The present embodiment has exemplarily described the case of replacing two gear assemblies12that are respectively composed of gear groups21having mutually different reduction ratios. Instead of this, the present invention may be applied to the case of replacing three or more gear assemblies12. In that case too, the recess16capable of accommodating the gears22,23of each gear assembly12may be provided on the first joining surface14of the forearm5, and the bolts may be fastened outside of the opening28that is provided on the second joining surface17of each gear assembly12to accommodate the gears22,23.

Also, instead of protruding at least a part of the gears22,23from the second joining surface17as described above, only the input hypoid gear19may be protruded from the second joining surface17and other gears22,23may be accommodated in the opening28so as not to protrude from the second joining surface17, as shown inFIG. 7. This eliminates the need for providing the recess16on the first joining surface14to accommodate the gears22,23, simplifying the configuration of the forearm5.

In the present embodiment, the first joining surface14of the forearm5is provided with the recess16shaped to be capable of accommodating the gear group21of each of multiple gear assemblies12that are assumed to be used. Instead of this, the first joining surface14may be provided with a recess (the second recess)16shaped to be capable of accommodating the gear group21of any one gear assembly12, and the forearm5may have a shape that allows for formation of another recess (the first recess)16capable of accommodating the gear group21of each of other gear assemblies12that are assumed to be used. That is, this configuration at least allows materials of the forearm5to be shared by robots1having different weight capacities, which in turn allows for an easy parts management.

In this case, it is difficult to adapt the robot1having a different weight capacity on the spot. However, the robot1can be adapted for a different weight capacity just by adding the recess16to the first joining surface14of the forearm5and changing the gear assembly12.

Although the spur gears have been given as an example of the gears22,23constituting the gear group21, any other gear may be used.

From the above-described embodiment, the following invention is derived.

According to an aspect of the present invention, there is provided an articulated shaft structure of a robot, the structure including: a first joint member; a second joint member supported by the first joint member so as to be rotatable about a first axis; a ring-like output hypoid gear fixed to the second joint member coaxially with the first axis; a gear assembly attached to the first joint member; and a motor attached to the gear assembly, wherein the gear assembly includes a housing member, an input hypoid gear, and gears, the housing member including a second joining surface tightly fixed to a first joining surface of the first joint member with a bolt, the input hypoid gear being supported by the housing member so as to be rotatable about a second axis, the gears decelerating rotation of the motor and transmitting the rotation to the input hypoid gear, the first joining surface is parallel to the first axis, the second joining surface is perpendicular to the second axis, with the housing member being fixed to the first joint member, the input hypoid gear is situated at a position where the input hypoid gear engages with the output hypoid gear, and the bolt is fastened radially outside of the gears of all kinds that are assumed to be used, the kinds being defined by reduction ratios.

According to the above aspect, when the second joining surface of the housing member constituting the gear assembly tightly contacts the first joining surface of the first joint member, the input hypoid gear rotatably supported by the housing member engages with the output hypoid gear fixed to the second joint member rotatably supported by the first joint member. In this state, the bolt is fastened to fix the gear assembly to the first joint member and also the motor is fixed to the housing member. This constitutes the articulated shaft structure.

The rotation of the motor is decelerated by the gears before being transmitted to the input hypoid gear. The rotation of the input hypoid gear is decelerated depending on a gear ratio of the input hypoid gear to the output hypoid gear before being transmitted to the output hypoid gear, which causes the second joint member to rotate about the first axis and relative to the first joint member.

In this case, when the sizes and numbers of the gears are changed to adapt to an application requiring a heavier weight capacity without changing the size of the motor, the opening provided in the second joining surface of the housing member has its shape changed. According to the above aspect, whichever of gear assemblies each having a differently shaped opening is attached to the first joint member, the bolt can be fastened outside of the opening. This makes it possible to seal the opening.

In the above aspect, at least a part of the gears may protrude from the second joining surface, the first joint member may have a shape that allows for formation of a first recess to accommodate the gears of the kinds each having a different reduction ratio, and the first joining surface may include a second recess capable of accommodating the gears of at least one of the kinds.

With this configuration, when a gear assembly of gears having a reduction ratio is attached to the first joint member, a part of the gears protruding from the second joining surface is accommodated in the second recess provided on the first joining surface, whereby the first joining surface and the second joining surface may tightly contact with each other. This helps avoid increase in the thickness of the housing member in the direction of the second axis.

In the case where the first joining surface includes the second recess capable of accommodating the gears of all kinds that are assumed to be used, one gear assembly may be removed and another gear assembly may be attached to the first joint member. This makes it possible to easily adapt to an application requiring a heavier weight capacity.

On the other hand, in the case where the first joining surface includes the second recess only capable of accommodating the gears of one kind, the recess may be processed to be capable of even accommodating gears of other reduction ratios, and thereby a gear assembly of gears of a different reduction ratio may be attached to the first joint member. In other words, use of the first joint member having a shape that allows for formation of the first recess to accommodate gears of multiple kinds each having a different reduction ratio at least allows materials to be shared by first joint members before being processed.

In the above aspect, the second recess may have a size equal to that of the first recess.

This configuration allows one gear assembly to be removed and another gear assembly to be attached to the first joint member. This makes it possible to easily adapt the robot to an application requiring a heavier weight capacity. In adapting the robot, additional processing on the first joint member is unnecessary; the gear assembly may be replaced on the spot to easily increase the weight capacity

According to another aspect of the present invention, there is provided a robot including at least one joint having an articulated shaft structure of any one of the above aspects.

REFERENCE SIGNS LIST