HORIZONTAL ARTICULATED ROBOT

A horizontal articulated robot includes: a base; a first arm that is supported by the base so as to be pivotable in a horizontal direction; a second arm that is supported by the first arm so as to be pivotable in the horizontal direction; a shaft that is supported by the second arm so as to be linearly movable in a vertical direction along a longitudinal axis; a stopper that is attached to the shaft and that restricts the movement of the shaft in the vertical direction within a movable range; and a buffering member provided in the second arm, wherein the buffering member is disposed between the stopper and a counterpart member that is provided in the second arm and that faces the stopper in the vertical direction, and buffers an impact exerted on the counterpart member from the stopper.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on Japanese Patent Application No. 2019-082854, the content of which is incorporated herein by reference.

FIELD

The present invention relates to a horizontal articulated robot.

BACKGROUND

In the related art, there is a known horizontal articulated robot including: a base; a first arm supported by the base so as to be pivotable in the horizontal direction; a second arm supported by the first arm so as to be pivotable in the horizontal direction; and a shaft supported by the second arm so as to be movable in the vertical direction (for example, see Japanese Unexamined Patent Application, Publication No. 2015-077649, and Japanese Unexamined Patent Application, Publication No. 2009-095937). A stopper for restricting the movement of the shaft within a prescribed range is attached to an end portion of the shaft. In addition, there is a known robot including a buffering mechanism that buffers an impact when coming into contact with an object (for example, see Japanese Unexamined Patent Application, Publication No. 2016-172296, and Japanese Unexamined Patent Application, Publication No. 2018-086703).

SUMMARY

An aspect of the present disclosure is directed to a horizontal articulated robot including: a base; a first arm that is supported by the base so as to be pivotable in a horizontal direction; a second arm that is supported by the first arm so as to be pivotable in the horizontal direction; a shaft that is supported by the second arm so as to be linearly movable in a vertical direction along a longitudinal axis; a stopper that is attached to the shaft and that restricts a movement of the shaft in the vertical direction within a movable range; and a buffering member provided in the second arm, wherein the buffering member is disposed between the stopper and a counterpart member that is provided in the second arm and that faces the stopper in the vertical direction, and buffers an impact exerted on the counterpart member from the stopper.

A horizontal articulated robot1according to an embodiment of the present invention will be described below with reference to the drawings. As shown inFIG. 1, the horizontal articulated robot1includes: a base2that is installed on an installation surface; a first arm3supported by the base2; a second arm4supported by the first arm3; and a shaft5supported by the second arm4.

The base2is connected to a controller (not shown) by means of a cable6and is connected to the second arm4by means of a cable7. The controller supplies a control signal and power to a first servomotor8in the base2via the cable6. In addition, the controller supplies control signals and power to a second servomotor9, a third servomotor10, and a fourth servomotor (not shown) in the second arm4via the cables6and7. Reference signs11and12indicate reducers.

An end portion of the first arm3is supported by the base2so as to be pivotable the horizontal direction. The first arm3is pivoted, by means of the first servomotor8, about a vertical-direction first axis A with respect to the base2. An end portion of the second arm4is supported by the other end portion of the first arm3so as to be pivotable in the horizontal direction. The second arm4is pivoted, by means of the second servomotor9, about a second axis B with respect to the first arm3. The second axis B is parallel to the first axis A. The shaft5passes through the other end portion of the second arm4in the vertical direction, and is supported by the second arm4so as to be linearly movable along a third axis C and rotatable about the third axis C. The third axis C is parallel to the first axis A and the second axis B, and is aligned with the longitudinal axis of the shaft5.

As shown inFIGS. 1 to 3, a ball screw nut13and a ball spline nut14that individually support the shaft5are provided in the interior of the second arm4. The ball screw nut13and the ball spline nut14are supported by means of bearings (not shown) so as to be rotatable about the third axis C with respect to the second arm4. The shaft5is moved in the vertical direction along the third axis C as a result of the ball screw nut13being rotated about the third axis C due to the rotation of the third servomotor10transmitted to the ball screw nut13by a belt15and a pulley16. The shaft5is rotated about the third axis C as a result of the ball spline nut14being rotated about the third axis C due to the rotation of the fourth servomotor transmitted to the ball spline nut14by a belt17and a pulley18.

In addition, the horizontal articulated robot1includes two stoppers21and22attached to the shaft5, a buffering member23secured to a counterpart member of the stopper21, and a buffering member24secured to a counterpart member of the stopper22. The counterpart member of the stopper21is a member that is provided in the second arm4and that faces the stopper21in the vertical direction. The counterpart member of the stopper22is a member that is provided in the second arm4and that faces the stopper22in the vertical direction. In the example inFIGS. 1 to 3, holes4band4cthrough which the shaft5passes are respectively provided in a top surface and a bottom surface of a cover4aof the second arm4. A top-end surface13aof the ball screw nut13is exposed outside the cover4avia the hole4b, and a bottom-end surface14aof the ball spline nut14is exposed outside the cover4avia the hole4c. In an example, the counterpart member of the upper-side stopper21is the ball screw nut13, and the counterpart member of the lower-side stopper22is the ball spline nut14.

As shown inFIG. 4, the individual stoppers21and22are annular or cylindrical members secured to outer circumferential surface of the shaft5and are formed from a high-rigidity material such as a metal. The stopper21is secured to a top end portion of the shaft5and the stopper22is secured to a bottom end portion of the shaft5.

For example, the stopper21has a slit21athat splits the stopper21in a circumferential direction and a bolt hole21bthat is orthogonal to the slit21a. As a result of fastening a bolt into the bolt hole21bin a state in which the stopper21is disposed in the periphery of the shaft5, the stopper21can be secured to the shaft5by means of friction between an inner circumferential surface of the stopper21and the outer circumferential surface of the shaft5by decreasing the inner diameter of the stopper21. As with the stopper21, the stopper22also has a slit and a bolt hole and is secured to the shaft5by means of friction. The stoppers21and22may be secured to the shaft5by another means such as welding.

The movement of the shaft5in the vertical direction with respect to the second arm4is mechanically restricted within a prescribed movable range by means of the two stoppers21and22provided at the upper side and the lower side of the second arm4. Specifically, as a result of the upper-side stopper21abutting the counterpart member13of the second arm4, further lowering of the shaft5is restricted. As a result of the lower-side stopper22abutting the counterpart member14of the second arm4, further raising of the shaft5is restricted.

The individual buffering members23and24are formed from an elastic material such as a rubber, a sponge, or a foam body. The upper-side buffering member23is secured to the top-end surface13aof the ball screw nut13, which is the counterpart member of the upper-side stopper21, and is disposed between the stopper21and the ball screw nut13. The lower-side buffering member24is secured to the bottom-end surface14aof the ball spline nut14, which is the counterpart member of the lower-side stopper22, and is disposed between the stopper22and the ball spline nut14.

FIGS. 5 to 7show examples of the shape and arrangement of the buffering member23,24. The buffering member23,24is substantially evenly arranged on the circumference surrounding the shaft5. For example, as shown inFIG. 5, the buffering member23,24may be a single annular member that is disposed over the entire circumference in the periphery of the shaft5. Alternatively, as shown inFIGS. 6 and 7, the buffering member23,24may be configured with a plurality of members that are substantially evenly arrayed in the periphery of the shaft5.

The controller supplies the first, second, and third servomotors8,9, and10, as well as the fourth servomotor with the control signals and power in accordance with an operating program, and thus, controls motions of the first arm3, the second arm4, and the shaft5. As shown inFIG. 1, a stroke range S of the shaft5in the vertical direction is set in the operating program. The controller controls the movement of the shaft5in the vertical direction within the stroke range S. Each of the stoppers21and22is secured to the shaft5at a position at which the stopper21or22comes into contact with the counterpart member13or14when the shaft5is moved beyond a limit S1or S2of the stroke range S.

Next, the operation of the horizontal articulated robot1will be described. With the horizontal articulated robot1, the position of a wrist portion5aat a tip of the shaft5is two-dimensionally changed in a horizontal direction as a result of the first arm3being pivoted about the first axis A and the second arm4being pivoted about the second axis B. In addition, the position of the wrist portion5ais changed in a vertical direction as a result of the shaft5being linearly moved along the third axis C, and the orientation of the wrist portion5ais changed about the third axis C as a result of the shaft5being rotated about the third axis C.

The vertical movement of the shaft5is restricted, by means of the controller, within the stroke range S set in the operating program. So long as the shaft5is moved within the stroke range S, the stoppers21and22do not interfere with the counterpart members13and14and the buffering members23and24. However, the shaft5is sometimes moved beyond the normal stroke range S in the case in which the moving range of the shaft5is not normally restricted by the controller, caused by erroneous setting of the stroke range S in the operating program or the like. At this time, the stoppers21and22mechanically restrict the movement of the shaft5.

Specifically, when the shaft5is about to be lowered beyond the lower limit S2of the stroke range S, further lowering of the shaft5is prevented as a result of the upper-side stopper21abutting the top-end surface13aof the ball screw nut13via the buffering member23. When the shaft5is about to be raised beyond the upper limit S1of the stroke range S, further raising of the shaft5is prevented as a result of the lower-side stopper22abutting the bottom-end surface14aof the ball spline nut14via the buffering member24.

If the stoppers21and22directly collide with the counterpart members13and14when the heavy shaft5is linearly moving at a high speed, the stoppers21and22and the counterpart members13and14are subjected to high impacts, and thus, the stoppers21and22and the counterpart members13and14may be damaged. For example, in the case in which the stoppers21and22are secured to the shaft5by means of friction, the positions of the stoppers21and22may be shifted or the stoppers21and22may fall off from the shaft5due to the high impacts. In addition, the nuts13and14could fail to move normally, as a result of the impacts forming indentations in ball rolling surfaces of the nuts13and14or the shaft5.

With this embodiment, the impacts are absorbed by elastic compression of the buffering member23between the stopper21and the counterpart member13, thus buffering the impacts exerted on the stopper21and the counterpart member13. In addition, the impacts are absorbed by elastic compression of the buffering member24between the stopper22and the counterpart member14, thus buffering the impacts exerted on the stopper22and the counterpart member14. By doing so, it is possible to prevent the stoppers21and22and the counterpart members13and14from being damaged, and thus, it is possible to enhance the reliability of the horizontal articulated robot1.

In addition, because the buffering members23and24are substantially evenly disposed over the entire circumference in the periphery of the shaft5, the impacts exerted on the stoppers21and22and the counterpart members13and14are spatially evenly dispersed. By doing so, it is possible to more reliably prevent the stoppers21and22and the counterpart members13and14from being damaged. In particular, it is possible to prevent the formation of indentations in the ball rolling surfaces. In addition, because increases in the size and the weight of the stoppers21and22could affect the operation of the horizontal articulated robot1, it is preferable that the stoppers21and22be small and light. With this embodiment, the buffering members23and24are separate components from the stoppers21and22, and are secured to the counterpart members13and14provided in the second arm4. Therefore, it is possible to add the buffering members23and24to the horizontal articulated robot1without affecting the operation of the shaft5.

In this embodiment, although the buffering members23and24are disposed on the end surfaces13aand14aof the counterpart members13and14, alternatively, the buffering members may be disposed away from the end surfaces13aand14ain the vertical direction. In this case, the buffering members are secured to the counterpart members13and14at surfaces other than the end surfaces13aand14aof the counterpart members13and14facing the stoppers21and22, or to securing members that are provided in the second arm4and that are different from the counterpart members13and14.

The securing members are members that are secured to the cover4aor members that are disposed in the second arm4and secured with respect to the cover4a. In an example, the securing members are supporting members19and20that are secured to the cover4aand that respectively support the nuts13and14in a rotatable manner, as shown inFIGS. 8 and 9.

FIG. 10shows an example of a buffering member25that is secured to the supporting member19,20. The buffering member25is a cylindrical member that is disposed substantially coaxially with the shaft5. At one end of the buffering member25, a flange25athat expands radially outward is provided. The flange25ais a portion to be secured to the supporting member19,20, and a plurality of holes25binto which bolts28are inserted are provided therein. At the other end of the buffering member25, an annular end wall25cthat faces the stopper21or22is provided. The end wall25cis disposed away from the counterpart member13,14in the vertical direction. The buffering member25is formed of, for example, a cast product or a sheet metal, and absorbs an impact by being plastically deformed as a result of a collision with the stopper21or22. In order to increase the impact absorption, the end wall25cmay additionally be provided with a buffering member23or24formed of an elastic material.

As a result of disposing the buffering members25away from the end surfaces13aand14aof the counterpart members13and14in the vertical direction, spaces are formed between the buffering members25and the end surfaces13aand14a. With these spaces, it is possible to reduce impacts exerted on the counterpart members13and14from the stoppers21and22. Furthermore, as a result of the buffering members25being secured to the securing members19and20, which are different from the counterpart members13and14, it is possible to more effectively reduce the impacts exerted on the counterpart members13and14from the stoppers21and22. The same effect is afforded in the case in which the buffering members25are secured to the counterpart members13and14at surfaces other than the end surfaces13aand14a.

In addition, because the buffering members25are mechanically secured to the securing members19and20by means of the bolts28, the buffering members25are attachable to the securing members19and20and detachable therefrom. Therefore, after the buffering members25are damaged due to collisions with the stoppers21and22, it is possible to easily replace the damaged buffering members25with new buffering members25.

The buffering member25may have a structure that facilitates plastic deformation due to a collision with the stopper21or22. For example, as shown inFIG. 10, the buffering member25may have a plurality of slits25dextending in the vertical direction in a side wall, thus facilitating deformation in the vertical direction. Alternatively, the buffering member25may have, in an intermediate portion of the side wall, a low-rigidity portion having a lower rigidity than other portions do, thus being configured so as to buckle at the low-rigidity portion.

As shown inFIG. 11, a buffering member26may be formed from two members26aand26bthat allow the relative positions thereof to be changed in the vertical direction. The member26ais a fixed portion secured to each of the securing members19and20, and is, for example, a cylindrical member having a flange26csimilar to the flange25a. The member26bis a movable portion that allows the position thereof to be changed in the vertical direction with respect to the fixed portion26a, and is, for example, a cylindrical member having an end wall26dsimilar to the end wall25c. The fixed portion26aand the movable portion26bare disposed in a nested manner with each other, and, by doing so, it is possible to extend and contract the buffering member26in the vertical direction in a telescopic manner. The movable portion26bis secured to the fixed portion26aby means of, for example, screws26e.

With such a buffering member26, it is possible to adjust the position of the movable portion26bin the vertical direction by changing the position of the movable portion26bwith respect to the fixed portion26a. By doing so, it is possible to easily adjust the position at which the stopper21,22collides with the buffering member26by changing the distances between the stopper21,22and the buffering member26.

In the above-described embodiment, although two sets of stoppers21and22and buffering members23and24are provided, one set each on the upper side and the lower side of the second arm4, alternatively, one set consisting of a stopper and a buffering member may be provided only on one of the upper side and the lower side of the second arm4.