MULTI-JOINTED ROBOT

Abstract: A multi-jointed robot of high-speed and high-precision motion with reduced stress is disclosed. This robot has a first arm (4) which is pivotal on a base (2), and a second arm (13) which is pivotal on the first arm. The first arm is directly moved by a first motor (1) on the base, while the second arm is moved by a double parallel link mechanism (12,19,22,23,30,31) driven by a second motor (6) which has two shafts (7,8) at its both ends and which is supported on the base.

Description: This invention relates generally to robots, and more particularly to a robot with a multi-jointed arm. Higher speeds and greater precision in the motion of robots, such as multi-jointed robots utilised in assembly lines, are important, since they result in shorter "tact-time" and higher productivity. The term "tact-time" refers to the time during which a robot performs its assigned operation. Conventional speed reducers, such as harmonic drive gears, often are poor in rigidity, exhibit back-lash, and have narrow design limits with respect to input revolution rate and speed reduction ratio. Therefore, direct driving of arms using low-speed, high-torque motors without speed reducers has been developed. However, if a motor is arranged far from the pivotal center on an arm, an excess moment of inertia is added to the arm due to the mass of the motor. Therefore, it is preferable that the motor be arranged at the pivotal center of the arm. Japanese Patent Disclosure (Kokai) 60-76992 discloses a directly driven multi-jointed robot. In this disclosure, a first arm pivots in response to a first motor. A second arm, which is attached to a shaft passing through an aperture in the first arm, is driven by a second motor with a double parallel link mechanism. The second motor is set at the pivotal center of the first arm. A single crank shaft, which is directly driven by the second motor, drives the double parallel link mechanism. However, since the crank shaft is driven at one side of the second motor, the crank shaft is highly stressed. Thus, the shaft must have a high strength and rigidity. Furthermore, since the second motor is supported on the first arm, the mass and the inertia of the second motor are added to the first arm, and the reaction torque of the second motor is added to the first motor load. Therefore, the first motor requires large torque and large power. European patent publication no. EP-A-118012 discloses a robot joint comprising a first arm (16) and second arm (34) which are probably connected by a joint having an integral motor (12), the motor being mounted on the first arm and connected to the second arm, for causing pivotal movement thereof, at both ends of the motor shaft so as to reduce the strain on the motor. In this case also, however, because the motor is incorporated in the joint, its mass must be supported by the first arm. The present invention seeks to provide an arrangement which reduces the stress in the crank shaft of a motor of a multi-jointed robot. The invention also seeks to reduce the torque and power requirements of a motor for a multi-jointed robot. According to one aspect of the invention, there is provided a multi-jointed robot comprising: a first arm pivotable about a first axis, and a second arm pivotably connected to the first arm; first drive means connected to the first arm to cause pivotal movement of said arm about said axis; second drive means connected to said second arm for causing pivotal movement of said second arm relative to said first arm, said second drive means comprising a motor which is connected to the second arm by means of a first pair of crank arms which extend from opposite ends of the motor shaft and are perpendicular to the shaft and to each other, and a second pair of crank arms which extend from opposite ends of the second arm pivot and each of which is parallel to its corresponding first crank arm and is connected to it by a connecting rod. Some embodiments of the invention will now be described by way of example with reference to the accompanying drawings, wherein: Figure 1 is a perspective view of an embodiment of a robot of this invention; Figure 2 is an elevational sectional view showing the major components of the embodiment shown in Figure 1; Figure 3 is a plan view of the embodiment shown in Figure 1 to display its motion; Figure 4 is a partial plan view of the embodiment shown in Figure 1 showing the motion of essential parts; and Figure 5 is a perspective view of another embodiment of a robot of this invention. Referring to Figures 1 and 2, a first motor 1 of low speed and high torque which is fixed on a base 2 has a vertically pivoted shaft 3. A first arm 4 is fixed to the shaft 3. A supporting frame 5 is fixed to a side of the base 2, and a second motor 6 of low speed and high torque is supported by the supporting frame 5. The second motor 6 has two pivotal second-motor shafts 7 and 8, respectively, at its top and bottom, and the first-motor shaft 3 and the second-motor shafts 7 and 8 are arranged coaxially. A pair of first-arm bearings 9 and 10 are arranged on the first arm 4, and the first arm 4 and the second motor 6 are pivotably supported with the first-arm bearings 9 and 10. Second-arm bearings 11 and 12 are arranged near the tip of the first arm 4, and the second arm 13 is pivotably supported by the second-arm bearing 11 and 12 with a second-arm shaft 14 which is fixed to the second arm 13. The first arm 4 has a cavity 15 around the second-arm shaft 14 such that the second arm 13 can pivot without interference with the first arm 4. The second-arm shaft 14 is arranged vertically, so that the second arm 13 pivots horizontally as does the first arm 4. The second arm 13 has a vertically sliding axis 16 at a tip 41, and the vertically sliding axis 16 has a revolving axis 17. The revolving axis 17 has an endeffector 40 at its bottom end which manipulates objects, such as parts to be assembled (not shown). A first lever 18 and a second lever 19 are respectively fixed to the second-motor shafts 7 and 8, and extend perpendicular to the shafts 7 and 8, at right angles to each other. First and second connecting rods 22 and 23 include tips 20 and 21 which are pivotably connected to the first and the second levers 18 and 19 via shafts 24 and 25 (shown in Fig. 4) and bearings 26 and 27 (not shown), respectively. The opposite tips 28 and 29 of the first and the second connecting rods 22 and 23 are likewise pivotably connected to a third lever 30 and a fourth lever 31, respectively, via shafts 32 and 33 (shown in Fig. 4) and bearings (not shown). The third lever 30 and the fourth lever 31 are fixed to the top and the bottom,respectively, of the second-arm shaft 14, and extend perpendicular to the second-arm shaft 14, at a right angle to each other. The connecting rods 22 and 23 have span adjusters 34 and 35 which are used to adjust the lengths of the connecting rods 22 and 23. This adjustment can make the first lever 18 and the third lever 30, and the second lever 19 and the fourth lever 31 parallel. The motion of the robot is described below. When the first-motor shaft 3 pivots counter-clockwise, the first arm 4 also pivots counter-clockwise, as shown at 4-4a-4b in Fig. 3. At that time, the second-motor shafts 7 and 8, the first lever 18 and the second lever 19 do not move. Therefore, the orientation of the second arm 13 does not change, as shown at 13-13a-13b in Fig. 3, so that the part of the load on the first motor 1 resulting from the revolution of the second arm 13 is eliminated. When the second-motor shafts 7 and 8 pivot, the second arm 13 pivots, as shown at 13c-13-13d in Figs. 3 and 4, in accordance with the movement of the levers 18, 19, 30 and 31, and the connecting rods 22 and 23. Since the first and the second levers 18 and 19, and the third and the fourth levers 30 and 31 are arranged at right angles, there are no "dead points" where the second arm 13 is unstable in position, and the second arm 13 can be freely driven unless the first arm 4 interferes the second arm 13 in the cavity 15. Since the second motor 1 is supported by the supporting frame 5, which is fixed to the base 2, the reaction of the second motor 6 does not add loads on the first motor 1. Since no gears for speed reduction are used, high-speed and high-precision motion of the second arm 13 can be obtained by using the levers 18, 19, 30 and 31, and connecting rods 22 and 23 of sufficient rigidity. Since the two second motor shafts 7 and 8 are arranged at both ends of the second motor 6, the stress in the second motor shafts 7 and 8 is mitigated compared with the stress in the conventional one sided crank shaft. As for another embodiment of the present invention, the second motor 6 can be supported on the first arm 4, instead of the base 2, as shown in Figure 5. In this embodiment, stress in the second motor shafts (not shown) is mitigated as in the above described embodiment, although the load on the first motor 1 is not mitigated. The foregoing description has been set forth merely to illustrate preferred embodiments of the invention and is not intended to be limiting, other than by reference to the appended claims.

Claims: A multi-jointed robot comprising: a first arm pivotable about a first axis, and a second arm pivotably connected to the first arm; first drive means connected to the first arm to cause pivotal movement of said arm about said axis; second drive means connected to said second arm for causing pivotal movement of said second arm relative to said first arm, said second drive means comprising a motor which is connected to the second arm by means of a first pair of crank arms which extend from opposite ends of the motor shaft and are perpendicular to the shaft and to each other, and a second pair of crank arms which extend from opposite ends of the second arm pivot and each of which is parallel to its corresponding first crank arm and is connected to it by a connecting rod. A robot according to claim 1 further comprising a base to which the first drive means is fixed, and means for supporting the motor relative to the base. A robot according to claim 2 also including means for supporting the motor with the base in such a way as to reduce the torque requirements of the first drive means. A robot according to any preceding claim in which the motor is mounted on the base coaxially with the first axis.

Inventors: MUNAKATA, TADASHI C/O PATENT DIVISION
Applicants: KABUSHIKI KAISHA TOSHIBA
Application year: 1987
Main classification: B25J9
IPC codes: F16H21, H02K7, B25J9, B25J17