ARM DRIVING DEVICE OF INDUSTRIAL ROBOT

Abstract: An arm driving device of an industrial robot, wherein one end of a first arm (2) is fixed to a first rotary shaft (21) rotatably supported on a base (1), one end of a second arm (3) is fixed to a second rotary shaft (31) rotatably suported by the other end of the first arm (2), parallel link rotary shafts (44, 54) concentrically rotatably provided with the first rotary shaft (21) and the second rotary shaft (21) are connected to each other through parallel links (4, 5), and wherein follower bars (41, 51) of the two parallel links (4, 5) art respectively fixed to opposite ends of the second rotary shaft (31) with the first arm (2) interposed therebetween, two connecting bars (42, 52) for connecting driving bars (43, 53) fixed to the parallel link rotary shafts (44, 54) to the follower bars (41, 51) are offset to the outsides of the driving bars (43, 53) and of the follower bars (41, 51). With this arrangement, the parallel links (4, 5) are prevented from interferrring with each other and the operating spaces of the arms (2, 3) can be greatly expanded.

Description: The present invention relates to an arm-driving device for an industrial robot having a plurality of articulations. See for example EP-A-0078522 defining the closest prior art. [BACKGROUND OF THE INVENTION] There is a conventional method of pivoting an arm of an industrial robot by directly driving pivot axes of the arm with driving motors through speed reducers. However, this method is not suitable for those robot having a heavy arm or load because an unbalanced moment at the arm increases the load to the pivot axes. Therefore, in an industrial robot having relatively heavy arms and loads, parallel links are normally constituted by an arm A which corresponds to a driven bar, an arm B, driving bar C, and a connecting bar D as shown in Fig. 5. However, when the arms are configurated using parallel links, there is interference between the arm B and connecting bar D and the operating range is thus narrowed. As a solution to this problem, the description of US patent No. 4,329,111 and unexamined Japanese published patent application No. 59-110578 disclose a type wherein the swinging plane of driving bars and driven bars are shifted. In the above-described conventional configuration, however, when an articulated arm is driven, a driving motor of a second parallel link constituting an arm at the end portion must be secured to the end of a first link supporting a second parallel link to constitute an arm. This increases the weight of the first link and, consequently, the load applied to the driving motor of the first link. Thus, a problem arises in that the rigidity of the first link must be high and the capacity of the driving motor must be large. It is an object of the present invention to provide an arm-driving device wherein the arms are lightweight so that the operation of the arms can be quick, and wherein the interference of a parallel link driving a second arm is eliminated to enable expansion of the operating range. [DISCLOSURE OF THE INVENTION] The present invention as defined in Claim 1 is an arm-driving device for an industrial robot having a first pivot axis pivotally supported by a base, a first arm secured to said first pivot axis on one end thereof, a second pivot axis pivotally supported by the other end of said first arm, a second arm secured to said second pivot axis on one end thereof, and parallel links connecting a parallel link pivot axis pivotally provided in a concentric relationship with said first pivot axis, to said second pivot axis, wherein the driven bars of said two parallel links are secured to both ends of said second pivot axis with said first arm sandwiched therebetween; and two connecting bars connecting the driving bars secured to said parallel link pivot axis and said driven bars are offset outside said driving bars and driven bars, respectively. The driving bars and driven bars of said two parallel links are secured to the parallel link pivot axis and second pivot axis so that a phase difference at a predetermined angle is provided between them. Two parallel links, each having two connecting bars which are outwardly offset, are connected to both sides of the pivot axis driving the second arm so that said pivot axis can be driven by a driving motor. This eliminates the possibility of interference from the parallel links. Further, when the driving bar, connecting bar, driven bar and first arm that constitute a parallel link straightly extend, this single parallel link cannot cause a rotation. However, there is provided another parallel link having another driving bar secured to the pivot axis at a predetermined phase angle with respect to said driving bar. As a result, when one of the parallel links straightly extends, the other parallel link does not straightly extend, and, therefore, it can swing the second arm by the other parallel link. [BRIEF DESCRIPTION OF DRAWINGS] Fig. 1 is a sectional elevation showing an embodiment of the present invention. Fig. 2 is a side view taken along the line II-II in Fig. 1. Fig. 3 is a side view showing another embodiment. Fig. 4 is a sectional elevation showing another embodiment. Fig. 5 is a side view showing the prior art. [DESCRIPTION OF THE PREFERRED EMBODIMENT] The present invention will now be described with reference to the illustrated embodiments. Fig. 1 is a sectional elevation showing an embodiment of the present invention. A forked portion 11 is formed on the top of a base 1 so that it sandwiches one end of a first arm 2 to pivotally support the first arm 2 through a bearing 12 provided between a first hollow pivot axis 21 secured to the first arm 2 and the base 1. A forked portion 22 is formed at the other end of the first arm 2 so that it sandwiches one end of a second arm 3 to pivotally support the second arm 3 through a second pivot axis 31 secured to the second arm 3. A pulley 23 is secured to the first pivot axis 21 to rotate the pivot axis 21 by a driving motor 26, secured to the base 1, through transmission devices such as a timing belt 24 and a pulley 25. One end of a driven bar 41 constituting one parallel link 4 is secured to one end of a second pivot axis 31 secured to the second arm 3 while one end of a connecting bar 42 is pin-connected to the other end of the driven bar 41 so that the connecting bar 42 is offset outside the driven bar 41. One end of a driving bar 43 is pin-connected to the other end of the connecting bar 42 so that the driving bar 43 is offset inside the connecting bar 42. The other end of the driving bar 43 is secured to one end of a parallel link pivot axis 44 which extends through the first hollow pivot axis 21 to be pivotally supported. A pulley 45 is secured to the parallel link 44 to swing the parallel link pivot axis 44 by use of a driving motor 48, secured to the base 1, through transmission devices such as a timing belt 46 and a pulley 47. One end of a driven bar 51 constituting another parallel link 5 is secured to the other end of the second pivot axis 31 such that the driven bar 51 and said driven bar 41 are angled towards each other at a phase difference of an phase angle α that is close to a right angle (about 70 deg in the example shown in Fig. 2). One end of a connecting bar 52 is pin-connected to the other axis of the driven bar 51 such that the connecting bar 52 is offset outside the driven bar 51. One end of a driving bar 53 is pin-connected to the other end of the connecting bar 52 such that the driving bar 53 is offset inside the connecting bar 52. The other end of the driving bar 53 is secured to the other end of the parallel link pivot axis 44. Therefore, the driving bar 53 is also angled to the driving bar 43 at a phase difference of a phase angle α. To swing the first arm 2, the first pivot axis 21 is rotated by the driving motor 26 through the pulley 25, timing belt 24, and pulley 23. To swing the second arm 3, the parallel link pivot axis 24 is rotated by the driving motor 48 through the timing belt 26 and pulley 45 to swing the second arm 3 together with the second pivot axis 31 through the driving bar 43, connecting bar 42, and driven bar 41. At the same time, the parallel link pivot axis 44 swings the second arm 3 together with the second pivot axis 31 through the driving bar 53, connecting bar 52, and driven bar 51. No interference occurs at the parallel links when the second arm 3 is swung because the second pivot axis 31 is driven by the driving motor 48 so that the parallel links 4 and 5 having the connecting bars 42 and 52, respectively, offset outside thereof, are connected to both sides of the second pivot axis 31. This allows the operating range of the second arm 3 to be expanded to the range of 360 deg minus the range limited by the interference with the first arm 2. Further, as shown in Fig. 2, a swing can not be caused by only the parallel link 5 when the driving bar 53, connecting bar 52, driven bar 51, and first arm 2 straightly extend. However, since there is provided the parallel link 4 having the driving bar 43 secured to the parallel link pivot axis at a predetermined phase angle to the driving bar 53, the parallel link 4 does not straightly extend at this time and, therefore, the second arm 3 can be swung by the parallel link 4. Further, in order to share the load applied to the parallel links and the transmission devices for driving their respective parallel links when the second arm 3 has the maximum load, the driving bars 43 and 53, and driven bars 41 and 51 may be secured to the parallel link pivot axes 44 and 54, and second pivot axis 31, respectively, so that they are inclined in opposite directions at the same angle β, e.g., 45 deg to the perpendicular from the second pivot axis to the ground, to set the phase angle at 90 deg. In addition, the parallel link pivot axis and the driving bars, and the driven bars and the second pivot axis may be secured so that phase angles of the driving bars of the two parallel links can be adjusted depending on the weights and operating ranges of the arms to minimize the load. Further, as shown in Fig. 4, it is possible to employ a configuration wherein the low speed axis of a speed reducer 13 whose securing portion is secured to the base 1, is connected to the first pivot axis 21 while the high speed axis thereof is driven by the driving motor 26 through the pulley 23, timing belt 24, and pulley 25, and the transmission devices of the two parallel links are provided. That is, the parallel link pivot axis 44 driving the parallel links 4 and 5 is divided into parallel link pivot axes 44 and 45, and low speed axes 61 and 61' of speed reducers 6 and 6', whose securing portions are secured to the base 1, are connected to the parallel link pivot axes 44 and 45, respectively. A high speed axis 62 is driven by the driving motor 48 through the pulley 45, timing belt 46, and pulley 47. A high speed axis 62' is driven by the driving motor 48through a pulley 55, a timing belt 56, and pulleys 71 and 72 secured to a counter shaft 7, a timing belt 73, and a pulley 57 secured to the driving motor 48. Therefore, the parallel link pivot axes 44 and 45 are rotated synchronically through the speed reducers 6 and 6', and the force for driving the second arm 3 is divided by the two speed reducers. This results in a reduction in the size of the speed reducing mechanism as a whole in spite of the increase in the number of speed reducers. The parallel link pivot axes driving the parallel links 20 may be driven by separate driving motors, to simplify the configuration of the transmission devices, by controlling the two driving motors for synchronous operation. As described above, according to the present invention, the connecting bars of two parallel links connected to both sides of a pivot axis pivoting an arm are offset outside the driving bars and driven bars to avoid creating interference between the parallel links. As a result, the operating range of the arm can be expanded. In addition, a phase difference is provided between the driving bars and driven bars of the two parallel links to allow the arm to be swung by one of the parallel links even when the other parallel link straightly extends. As a result, there is an advantage that an arm-driving device performing stable swing operations can provide. [INDUSTRIAL FEASIBILITY] The present invention can be used in those fields wherein processing and work are carried out using industrial robots.

Claims: An arm-driving device for an industrial robot comprising: a base (1) having a forked portion (11) at a top end thereof; a first arm (2) whose one end is sandwiched between said forked portion (11), and having a forked portion (22) at another end thereof; a first pivot axis (21) pivotally supported by a bearing (12) at the forked portion (11); a second arm (3) sandwiched between said forked portion (22) at one end; a second pivot axis (31) pivotally supported at another end of said second arm (3); a pair of parallel links (4) and (5) connecting between the first pivot axis (21) and the second pivot axis (31), so as to provide a phase difference at a predetermined angle; characterized in that said parallel links (4) and (5) are secured separately both outside of said first arm (2); said first pivot axis (21) is driven by a pulley (23) secured to said first pivot axis (21), a timing belt (24) and a pulley (25) secured to an axis of a driving motor (26), for swinging said first arm (2);and said second pivot axis (31) is driven by said parallel links (4) and (5), through a parallel link pivot axis (44), a pulley (45) secured to said parallel link pivot axis (44), a timing belt (46) and a pulley (47) secured to an axis of a driving motor (48), for swinging said second arm (3). An arm-driving device for an industrial robot according to claim 1, wherein said first pivot axis (21) is hollow, and said parallel link pivot axis (44) extends through said first hollow pivot axis (21). An arm-driving device for an industrial robot according to claim 1, wherein said first pivot axis (21) is connected to the low speed axis of a speed reducer (13) whose high speed axis is secured to the pulley (23) and low speed axis is secured to said first arm (2), and said second pivot axis (31) is rotated by the speed reducers (6) and (6') whose high speed axes (62) and (62') are secured to the pulleys (45) and (55) and low speed axes (61) and (61') are secured to parallel link pivot axes (44) and (54), and said arm-driving device further comprising a counter shaft (7), a pulley (71) secured to said counter shaft (7) connecting to the pulley (55) by a timing belt (56), and a pulley (72) secured to said counter shaft (7) connecting to a pulley (57) secured to the axis of the driving motor (48) by a timing belt (73), and a pulley (47) secured to the driving motor (48) connecting to the pulley (45) by timing belt (46).

Inventors: IWANAGA TOSHIAKI, TOHNAI SHUICHI, IWANAGA, TOSHIAKI, TOHNAI, SHUICHI, IWANAGA, TOSHIAKI, KABUSHIKI KAISHA YASKAWA DENKI, TOHNAI, SHUICHI, KABUSHIKI KAISHA YASKAWA DENKI
Applicants: YASKAWA DENKI SEISAKUSHO KK, KABUSHIKI KAISHA YASKAWA DENKI
Application year: 1991
Main classification: B25J9
IPC codes: B25J9