Wrist unit of industrial robot

A wrist unit of an industrial robot including an eccentric rocking-type reduction gear. The eccentric rocking-type reduction gear includes a hollow forming part forming a hollow part along the rotation center axial line; a through shaft supported rotatably at the hollow forming part and passing through the hollow part to transmit a rotation from the third wrist drive motor from a first wrist element side to a second wrist element side; a plurality of crankshafts arranged around the through shaft and having input gears at ends of the side of the first wrist element; and a gear member provided rotatably centered about the rotation center axial line, the gear member having a first gear to which a rotational force from the second wrist drive motor is input and a second gear with which the input gears of the plurality of crankshafts engage.

RELATED APPLICATIONS

The present application is based on, and claims priority from, Japanese Application Number 2012-123066, filed May 30, 2012, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wrist unit of an industrial robot which has three wrist elements.

2. Description of the Related Art

In a conventional known apparatus, an eccentric rocking-type reduction gear is provided at a joint of a wrist element of a front end side of a robot arm, and a torque of a motor is transmitted through the eccentric rocking-type reduction gear to the wrist element of the front end side. This type of apparatus is, for example, described in International Publication No. 2009/098945 (WO2009-098945A1). In the apparatus described in WO2009-098945A1, at the inside of the eccentric rocking-type reduction gear, a shaft for driving a joint at a front end side from the eccentric rocking-type reduction gear (hereinafter referred to as a “through shaft” for convenience) is passed through. Drive power from the motor is input to the through shaft via a gear. The eccentric rocking-type reduction gear has crankshafts at positions offset from the center axial line in the radial direction. One of the crankshafts has an input gear at its end. The input gear of the crankshaft engages with a motor gear which is arranged at a position offset from the crankshaft in the radial direction. Drive power from the motor is input through the motor gear and the input gear to the crankshaft.

In the apparatus described in WO2009-098945 A1, the center axial line of the opposite side gear (motor gear) which engages with the input gear of the reduction gear at the end of the crankshaft cannot be arranged on the same axial line as the center axial line of the reduction gear. It is for this reason that only one of the plurality of crankshafts is provided at its end with an input gear for use as an input shaft. In this configuration, the load concentrates at the crankshaft which has the input gear, so the crankshaft and the bearings which support it have to be configured so as to be able to withstand that load. For this reason, the crankshaft and the bearings which support it become larger in size and the reduction gear as a whole becomes larger in size. Furthermore, since the opposite side gear which engages with the input gear of the reduction gear cannot be arranged with its center axial line coaxial with the center axial line of the reduction gear, when positioning the base end side of the reduction gear, it is necessary to position the center axial line of the reduction gear and then match the phase of the reduction gear so that the input gear of the reduction gear and opposite side gear engage. For this reason, separate parts used for matching the phase become necessary, and assembly and disassembly of the reduction gear become complicated.

SUMMARY OF INVENTION

One aspect of the present invention is a wrist unit of an industrial robot including: a first wrist element supported rotatably about a first axial line at a first joint of a front end side of a robot arm; a second wrist element supported rotatably about a second axial line at a second joint of a front end side of the first wrist element, the second axial line not being on an extension of the first axial line and not being parallel to the first axial line; a third wrist element supported rotatably about a third axial line at a third joint of a front end side of the second wrist element, the third axial line not being on an extension of the second axial line and not being parallel to the second axial line; a second wrist drive motor provided at the first wrist element or the robot arm to drive the second wrist element; a third wrist drive motor provided at the first wrist element or the robot arm to drive the third wrist element; and an eccentric rocking-type reduction gear provided at the second joint so that a rotation center axial line matches with the second axial line to decelerate and transmit a rotation from the second wrist drive motor to the second wrist element. The eccentric rocking-type reduction gear includes: a hollow forming part forming a hollow part along the rotation center axial line; a through shaft supported rotatably at the hollow forming part and passing through the hollow part to transmit a rotation from the third wrist drive motor from a side of the first wrist element to a side of the second wrist element; a plurality of crankshafts arranged around the through shaft, the plurality of crankshafts having input gears at ends of the side of the first wrist element, and a gear member provided rotatably centered about the rotation center axial line, the gear member having a first gear to which a rotational force from the second wrist drive motor is input and a second gear with which the input gears of the plurality of crankshafts engage.

DETAILED DESCRIPTION

Hereinafter, an embodiment of the present invention will be explained with reference toFIG. 1toFIG. 4.FIG. 1is a view which shows the general configuration of a wrist unit of an industrial robot according to an embodiment of the present invention. The wrist unit100shown inFIG. 1is, for example, applied to a multiarticulated industrial robot which has a robot arm supported rotatably at a base. Below, the base side will be referred to as the “base end side”, while the direction moving away from the base (opposite side to base end side) will be referred to as the “front end side”. The wrist unit100of the present embodiment is, for example, provided at the front end of the robot arm and holds or works a workpiece.

As shown inFIG. 1, the wrist unit100has a first wrist element11supported rotatably about a first axial line L1at a first joint10of a front end of a robot arm101, a second wrist element21supported rotatably about a second axial line L2at a second joint20of a front end of the first wrist element11, and a third wrist element31supported rotatably about a third axial line L3at a third joint30of a front end of the second wrist element21.

The first axial line L1passes through the center of the robot arm101, the second axial line L2intersects the first axial line L1by a predetermined angle (90°), and the third axial line L3intersects the second axial line L2by a predetermined angle (90°). InFIG. 1, although the first axial line L1and the third axial line L3are positioned on the same line, they need not be on the same line. The second axial line L2need not intersect the first axial line L1so long as not on an extension of the first axial line L1and not parallel to the first axial line L1. The third axial line L3need not intersect the second axial line L2so long as not on an extension of the second axial line L2and not parallel to the second axial line L2.

At the base end of the robot arm101, a first motor12for driving the first wrist element11, a second motor22for driving the second wrist element21, and a third motor32for driving the third wrist element31are attached. At the first joint10, second joint20, and third joint30, a first reduction gear1, a second reduction gear2, and a third reduction gear3are respectively provided. Among these, in particular, the first reduction gear1and the second reduction gear2are configured as eccentric rocking-type reduction gears. The detailed structure of the second reduction gear2will be explained later. The rotations from the first motor12, second motor22, and third motor32are decelerated by the first reduction gear1, second reduction gear2, and third reduction gear3respectively.

Inside the robot arm101, a cylinder shaped shaft13extends along the first axial line L1. The shaft13is supported rotatably centered about the first axial line L1at support parts (not shown) inside of the robot arm101. Inside of the shaft13, a cylinder shaped shaft23extends along the first axial line L1. The shaft23is supported rotatably centered about the first axial line L1at the inner circumferential surface of the shaft13. Inside of the shaft23, a column shaped shaft33extends along the first axial line L1. The shaft33is supported rotatably centered about the first axial line L1at the inner circumferential surface of the shaft23.

Inside of the first wrist element11, a cylinder shaped shaft24extends along the first axial line L1. The shaft24is supported rotatably centered about the first axial line L1at support parts (not shown) inside of the first wrist element11. Inside of the shaft24, a column shaped shaft34extends along the first axial line L1. The shaft34is supported rotatably centered about the first axial line L1at the inner circumferential surface of the shaft24. Furthermore, inside of the first wrist element11, a cylinder shaped shaft25extends along the second axial line L2. Inside the shaft25, a column shaped shaft35extends. The shaft35is supported rotatably centered about the second axial line L2by the second reduction gear2. The shaft25is supported rotatably centered about the second axial line L2at the outer circumferential surface of the shaft35.

Inside of the second wrist element21, at the side of the second reduction gear2, a shaft36extends in parallel with the second axial line L2. The shaft36is supported rotatably at support parts (not shown) inside of the second wrist element21. Furthermore, inside of the second wrist element21, an input shaft37extends along the third axial line L3. The input shaft37is supported rotatably centered about the third axial line L3by the third reduction gear3.

At a front end of an output shaft14of the first motor12, a flat gear141is attached. The flat gear141is engaged with a flat gear131attached to a base end of the shaft13. At the front end of the shaft13, a flat gear132is attached. The flat gear132is engaged with a flat gear151attached to an end of an input shaft15of the first reduction gear1.

Due to this configuration, the rotation of the first motor12is input through a first transmission path comprised of the output shaft14, flat gear141, flat gear131, shaft13, flat gear132, flat gear151, and input shaft15to the first reduction gear1and is decelerated by the first reduction gear. This decelerated rotational force is used to drive the first wrist element11. The rotation of the first motor12can be decelerated in the first transmission path as well.

At a front end of an output shaft26of the second motor22, a flat gear261is attached. The flat gear261is engaged with a flat gear231attached to a base end of the shaft23. The front end of the shaft23is provided with a spline232. The shaft23is connected through the spline232to the shaft24. At the front end of the shaft24, a bevel gear241is attached. The bevel gear241is engaged with a bevel gear251attached to a base end of the shaft25. At the front end of the shaft25, a flat gear252is attached. The flat gear252is engaged with flat gears271attached to ends of input shafts27of the second reduction gear2.

Due to this configuration, rotation of the second motor22is input through a second transmission path comprised of the output shaft26, flat gear261, flat gear231, shaft23, spline232, shaft24, bevel gear241, bevel gear251, shaft25, flat gear252, flat gears271, and input shafts27to the second reduction gear2and is decelerated at the second reduction gear2. This decelerated rotational force is used to drive the second wrist element21. The rotation of the second motor22can be decelerated in the second transmission path as well.

At the front end of an output shaft of the third motor32, a spline381is provided. The output shaft38is connected through the spline381to the base end of the shaft33. At the front end of the shaft33, a spline331is provided. The shaft33is connected through the spline331to the shaft34. At the front end of the shaft34, a bevel gear341is attached. The bevel gear341is engaged with a bevel gear351attached to a base end of the shaft35. At a front end of the shaft35, a flat gear352is attached. The flat gear352is engaged with a flat gear361attached to a base end of the shaft36. At a front end of the shaft36, a bevel gear362is attached. The bevel gear362is engaged with a bevel gear371attached to an end of the input shaft37.

Due to this configuration, the rotation of the third motor32is input through a third transmission path comprised of the output shaft38, spline381, shaft33, spline331, shaft34, bevel gear341, bevel gear351, shaft35, flat gear352, flat gear361, shaft36, bevel gear362, bevel gear371, and input shaft37to the third reduction gear3and is decelerated by the third reduction gear3. This decelerated rotational force is used to drive the third wrist element31. The rotation of the third motor32can be decelerated in the third transmission path as well.

The present embodiment has a particularly special feature in the second reduction gear2(eccentric rocking-type reduction gear).FIG. 2is a cross-sectional view which shows the configuration of the second reduction gear2,FIG. 3Ais a cross-sectional view along the line IIIA-IIIA ofFIG. 2, andFIG. 3Bis a cross-sectional view along the line IIIB-IIIB ofFIG. 2. Below, the direction parallel to the second axial line L2will be defined as the “axial direction”, the direction moving away from the second axial line L2(radial direction of circle centered about axial line L2) will be defined as the “diametrical direction”, and the peripheral direction of the circle centered about the second axial line L2will be defined as the “peripheral direction”.

As shown inFIGS. 2 and 3A, the second reduction gear2has a cylinder shaped or substantially cylinder shaped casing4and a carrier5which is supported rotatably inside of the casing4by a pair of main bearings40. The casing4has a fitting part41which fits in the casing of the first wrist element11side at its outer circumferential surface. The carrier5has a first plate member51and a second plate member52which is separated from the first plate member51in the axial direction and is arranged facing the first plate member51. At the surface of the first plate member51which faces the second plate member52, columnar parts53are provided at equal intervals projecting out toward the second plate member52at three locations in the peripheral direction. Bolts54which pass through the second plate member52are screwed into the columnar parts53whereby the first plate member51and the second member52are integrally fastened. The carrier5has a fitting part42which fits in the casing of the second wrist element21side at the end of the first plate member51.

At the center portions of the first plate member51and the second plate member52, through holes511,521are formed. At the inside of the second reduction gear2, a hollow part55is formed along the second axial line (center axial line of reduction gear2) L2. At the inner circumferential surfaces of the through holes511,521, bearings56are provided. The shaft35for driving the third wrist element passes through the hollow part55and is supported rotatably with respect to the carrier5by the pair of bearings56. That is, the shaft35constitutes a through shaft.

At the outer circumferential surface of the through shaft35, a pair of bearings57are attached at the outside from the pair of bearings56in the axial direction (base end side from second plate member52). Due to the bearings57, the shaft25for driving the second reduction gear is supported rotatably with respect to the shaft35. At the second plate member52side of the shaft25(front end side), a flat gear252is attached, while at the opposite side of the second plate member52of the shaft25(base end side), a bevel gear251with a diameter larger than the flat gear252(inFIG. 2, for convenience, illustrated as a flat gear) is attached. That is, the shaft25is a cylindrical shaft which transmits the drive power input through the bevel gear251to the input shafts27through the flat gear252. Between the pair of bearings57, a cylinder shaped spacer253is interposed. The cylinder shaft25is arranged around the spacer253.

Between the first plate member51and the second plate member52, a pair of plate-shaped gear plates6,7are arranged in parallel in the axial direction to be parallel to the first plate member51and the second plate member52. At the outer circumferential surfaces of the gear plates6,7, external gears61,71are formed. Facing the external gears61,71, at the inner circumferential surface of the casing4, a plurality of internal tooth pins43, of a number just one pin larger than the number of teeth of the external gears61,71, are provided at equal intervals in the peripheral direction (seeFIG. 3B). The internal tooth pins43extend between the pair of spindle bearings40in the axial directions. While illustration is omitted, the gear plates6,7engage with the internal tooth pins43in the state offset from each other by 180° in phase. That is, as shown inFIG. 3B, when the gear plate6engages with the internal tooth pins43of the part A, the gear plate7engages with the internal tooth pins43of the part B which is offset from the part A by 180° in phase, that is, at the opposite side from the part A.

As shown inFIG. 2, at the center portions of the gear plates6,7, through holes60,70are formed. The through holes60,70are passed through by the shaft35. At one end of the through shaft35(base end), the bevel gear351(inFIG. 2, for convenience, illustrated as a flat gear) is attached at the outside from the bevel gear251in the axial direction (opposite side from second plate member52), while at the other end (front end), the flat gear352is attached. The bevel gear251and the bevel gear351are arranged in parallel with each other.

The gear plates6,7are formed with through holes63,73at three locations in the peripheral direction corresponding to the columnar parts53of the first plate member51. Inside the through holes63,73, the columnar parts53are inserted with clearance, that is, are loosely fit. Furthermore, the gear plates6,7are formed with through holes62,72at equal intervals at three locations in the peripheral direction between through holes63,73adjoining in the peripheral direction. In the through holes62,72, input shafts27are respectively inserted. The input shafts27are crankshafts. Corresponding to the crankshafts27, the first plate member51and the second plate member52are formed with through holes512,522at three locations in the peripheral direction.

Ends of the crankshafts27at the first wrist element sides are passed through the through holes522of the second plate member52. At the ends of the three crankshafts27which stick out from the second plate member52, flat gears271are respectively attached. These three flat gears271engage with the center flat gear252. The other ends of the crankshafts27at the second wrist element sides are inserted into through holes512of the first plate member51. The through holes512,522are provided with bearings59. The crankshafts27are supported rotatably through the bearings59at the carrier5(first plate member51, second plate member52). At the through holes512, covers513are attached from the outsides. The through holes512are closed by the covers513.

Each of the crankshafts27has two eccentric parts272,273at the center in the axial direction.FIG. 3Cis an enlarged cross-sectional view which generally shows the configuration of a crankshaft27. As shown inFIG. 3C, the eccentric parts272,273are offset from the center axial line L27of the crankshaft27by equal amounts to each other and are offset in phase from each other by 180° in the peripheral direction. That is, the center axial lines L272, L273of the eccentric parts272,273are offset from the center axial line L27of the crankshaft27in the diametrical direction by predetermined amounts, while the phases are offset from each other about the center axial line L27by 180°. As shown inFIG. 2, the eccentric parts272,273are supported rotatably through roller bearings274inside of the through holes62,72of the gear plates6,7.

In the thus configured eccentric rocking-type reduction gear2, if the bevel gear251of the cylindrical shaft25receives as input the drive power from the second motor22(FIG. 1), that drive power is transmitted through the flat gears252,271to the three crankshafts27whereby these crankshafts27rotate (turn) centered about their center axial lines L27. Due to this, the eccentric parts272,273eccentrically rotate inside the through holes62,72, and the gear plates6,7eccentrically rotate (orbit) centered about the axial line L2in the state offset in phase by 180°. Here, the number of the internal tooth pins43is one greater than the number of teeth of the external gears61,71, so the eccentric rotations of the gear plates6,7cause the carrier5to rotate and the second wrist element21to be driven.

On the other hand, if the bevel gear351of the through shaft35receives as input the drive power from the third motor32(FIG. 1), that drive power is transmitted through the through shaft35to the flat gear352whereby the flat gear352rotates. Due to this, the drive power from the third motor32can be transmitted to the second wrist element21side through the hollow part55of the eccentric rocking-type reduction gear2efficiently in space. This drive power can be used to drive the third wrist element31.

The above second reduction gear2is assembled in the state ofFIG. 2in advance, then attached to the casing of the first wrist element11. At this time, the second reduction gear2is positioned by the fitting part41of the casing4with respect to the first wrist element11. For this reason, the bevel gears251,351which stick out from the base end side of the second reduction gear2can be precisely engaged with the bevel gears241,341at the front end of the first wrist element11. After that, the second wrist element21is attached to the second reduction gear2. In this case, the second reduction gear2is positioned by the fitting part42of the carrier5with respect to the second wrist element21. For this reason, the flat gear352which sticks out from the front end side of the second reduction gear2can be precisely engaged with the flat gear361of the base end of the second wrist element21. Due to this, assembly and disassembly of the wrist unit100becomes easy and the wrist unit100can be easily maintained and inspected etc.

According to the present embodiment, the following function effects can be exhibited:(1) The through holes511,521,60, and70are used to form the hollow part55along the center axial line L2of the eccentric rocking-type reduction gear2, the through shaft35is supported rotatably passing through this hollow part55at the inside of the reduction gear2, and the rotational force from the third motor32is transmitted from the first wrist element11side to the second wrist element21side. Furthermore, the eccentric rocking-type reduction gear2is provided with the plurality of crankshafts27which have flat gears271at first ends around the through shaft35offset from the axial line L2in the diametrical direction, and the cylindrical shaft25which can rotate centered about the axial line L2. The cylinder shaft25is provided with the bevel gear251to which drive power from the second motor22is input, at one end thereof, and the flat gear252which engages with the flat gears271of the plurality of crankshafts27, at the other end.

Due to this, it is possible to input drive power to the plurality of crankshafts27from the second motor22and possible to transmit drive power from the third motor32through the eccentric rocking-type reduction gear2to the flat gear352of the second wrist element21. Furthermore, it is possible to arrange the second reduction gear2, bevel gear251, and bevel gear351, which have to be positioned with respect to the first wrist element11, with their rotation center axes all on the same line (L2), so when positioning the base end side of the second reduction gear2at the first wrist element11, it is not necessary to match the reduction gear2in phase. That is, according to the present embodiment, it is possible to prevent the eccentric rocking-type reduction gear2which has the through shaft35for driving the third wrist element from becoming larger and to make the structure easy to assemble and disassemble.(2) At the outer circumferential surface of the through shaft35at the outside from the hollow part55of the eccentric rocking-type reduction gear2in the axial direction, bearings57which support rotatably the cylinder shaft25are attached. Due to this, the only parts which are arranged inside of the hollow part55become the shaft35and the bearings56, so the eccentric rocking-type reduction gear2can be reduced in size. As opposed to this, in the comparative example of the present embodiment, as shown inFIG. 4, at the outside of the through shaft35in the diametrical direction, a cylinder shaped shaft254is provided integrally with the cylinder shaft25. If providing a pair of bearings57between this shaft254and the through shaft35to support rotatably the cylinder shaft25, since the hollow part55has the shaft35, bearings57, shaft254, and bearings56arranged in it, the hollow part55becomes enlarged and the eccentric rocking-type reduction gear2becomes larger in size.(3) At one end of the through shaft35, the bevel gear351which extends in the diametrical direction is attached. Between this bevel gear351and the flat gears271of the ends of the crankshafts27, the bevel gear251which is provided on the cylinder shaft25is arranged so as to extend in the diametrical direction in parallel to the gears351,271. Due to this, the axial direction length of the eccentric rocking-type reduction gear2can be kept to the necessary minimum extent and the eccentric rocking-type reduction gear2can be compactly configured.

In the above embodiment, although the first motor12(first wrist drive motor), second motor22(second wrist drive motor), and third motor32(third wrist drive motor) are respectively provided at the robot arm101, at least one of the second motor22and the third motor23may also be provided at the first wrist element11.FIG. 5shows an example of provision of the third motor32at the first wrist element11. InFIG. 5, the output shaft38of the third motor32extends on the second axial line L2, and the output shaft38is connected through a spline etc. to the shaft35which passes through the second reduction gear2(eccentric rocking-type reduction gear). By attaching the third motor32to the first wrist element11in this way, there is no need to form a third transmission path inside of the robot arm101and therefore the configuration of the robot arm101can be simplified.

FIG. 6shows an example of provision of the second motor22and the third motor32inside of the first wrist element11. InFIG. 6, the output shaft26of the second motor22extends in parallel with the second axial line L2. At the base end of the cylinder shaft25of the second reduction gear2, not a bevel gear251, but a flat gear255is attached. Between the flat gear261of the end of the output shaft26and the flat gear255of the end of the cylinder shaft25, a flat gear256is arranged. Through the flat gear256, drive power from the second motor22is transmitted to the second reduction gear2.

Inside the first wrist element11, the output shaft38of the third motor32extends in parallel to the second axial line L2. At the base end of the through shaft35, not a bevel gear351, but a flat gear353is attached. Between the flat gear382of the end of the output shaft38and the flat gear353of the end of the through shaft35, a flat gear383is arranged. Through the flat gear383, drive power from the third motor32is transmitted to the through shaft35. In the second wrist element21, at the end of the through shaft35, not a flat gear352, but a bevel gear354is attached. Inside the second wrist element21, a shaft39extends in parallel with the third axial line L3. At the base end of the shaft39, a bevel gear391is attached, while at the front end, a flat gear392is attached. At the input shaft37, not a bevel gear371, but a flat gear372is attached. Rotation of the through shaft35is input through the bevel gears354,391, shaft39, and flat gears392,372to the input shaft37.

In the above embodiment (FIG. 1), although the first reduction gear1and the second reduction gear2are configured as eccentric rocking-type reduction gears, as shown inFIG. 6, it is also possible that only the second reduction gear2be configured as an eccentric rocking-type reduction gear. Although the through holes511,512of the first plate member51and the second plate member52are used to form the hollow part55inside of the second reduction gear2along the rotation center axial line L2, the configuration of a hollow forming part is not limited to this. So long as supported rotatably at the hollow part55and so long as transmitting rotational force from the third motor32from the first wrist element11side to the second wrist element21side, the through shaft35can be configured in any way.

Although three crankshafts27are arranged around the through shaft35, the number of the plurality of crankshafts27is not limited to this. So long as having gears271for inputting rotational force at the end of the first wrist element11sides (input gears), the crankshafts27can be configured in any way. Although a cylinder shaft25is provided rotatably through bearings57at the outer circumferential surface of the through shaft35, so long as having a gear251to which rotational force from the second motor22is input (first gear) and a gear252with which the gears271of the plurality of crankshafts27engage (second gear) and being provided rotatably centered about the second axial line L2, the shaft25as a gear member can be configured in any way. The arrangement of the shaft25is also not limited to that explained above.

One or more of the above embodiment and the modifications may be freely combined.

According to the present invention, it is possible to input drive power from the motor to the through shaft which passes through the eccentric rocking-type reduction gear while inputting drive power from another motor to the plurality of crankshafts through a gear member. Further, it is possible to just position the reduction gear in its center axial line so as to assemble the reduction gear base end side.