Material or article handling – Vertically swinging load support – Grab
Patent
1985-08-13
1987-08-25
Spar, Robert J.
Material or article handling
Vertically swinging load support
Grab
74665C, 901 26, 901 29, B25J 1702
Patent
active
046889841
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a wrist driving mechanism for an industrial robot, and more specifically, to a wrist driving mechanism for driving the fore wrist unit of an industrial robot for rotary motion about three axes.
2. Background Art
There has been proposed a three-axis wrist driving mechanism including three power transmitting chains extended in parallel to each other along the robot arm to drive the fore wrist of the wrist device of an industrial robot for rotary motion about three axes. Such a conventional three-axis wrist driving mechanism is shown in FIG. 1. As shown in FIG. 1, a first base wrist unit 2 is joined to the free end of a robot arm 1 so as to be rotatable about an axis .gamma.. A second base wrist unit 3 is joined to the first base wrist unit 2 so as to be rotatable about an axis .alpha.. A fore wrist unit 4 is joined to the second base wrist unit 3 so as to be rotatable about an axis .alpha.. Three sprockets 8, 9, and 10 are disposed rotatably within the free end of the robot arm 1. The sprockets 8, 9, and 10 are interlocked with the first base wrist unit 2, the second base wrist unit 3, and the fore wrist unit 4 respectively. Three chains 5, 6, and 7 are extended in parallel to each other within and along the longitudinal direction of the arm 1. The chains 5, 6, and 7 interconnect the sprockets 8, 9, and 10 and three corresponding driving sprockets, not shown, disposed side by side at the base end of the arm 1. The driving sprockets are connected through reduction gear mechanisms to driving motors, respectively. Ordinarily, functional equipment, such as a robot hand, a welding gun or a spray gun, is mounted on the fore wrist unit 4.
The rigidities of the output system about the axes .alpha., .beta. and .gamma. of a three axis wrist driving mechanism of the above-mentioned constitution are dependent on the spring constants k (k are fixed values) of the chains 5, 6, and 7. Particularly, when a torque about the axis .beta. is applied to the second base wrist unit 3, the first base wrist unit 2 tends to be turned about the axis .gamma.. Therefore, the rigidity of the output system about the axis .beta. is dependent on the spring constants of the two chains 5 and 6. That is, the total spring constant k.beta. of the output system about the axis .beta. is expressed by an expression: k.beta.=k/2.
When a torque about the axis .alpha. is applied to the fore wrist unit 4, the second base wrist unit 3 tends to be turned about the axis .beta., and hence the first base wrist unit 2 also tends to be turned about the axis .gamma.. Accordingly, the rigidity of the output system about the axis .alpha. is dependent on the spring constants of the three chains 5, 6, and 7. Consequently, the total spring constant k.alpha. of the output system about the axis .alpha. is expressed by an expression k.alpha.=k/3.
Accordingly, for the output system about the axis .alpha., the total spring constant is k/3 and the actual rigidity of the output system is one-third of the inherent rigidity thereof, even if chains of spring constant k are employed. Furthermore, since the spring constant k of a chain is in inverse proportion to the length of the chain, the rigidity of the output system about the axis .alpha. is reduced with the length of the chains.
In the above-mentioned wrist driving mechanism, a rotative motion of a reduced speed controlled by the reduction gear mechanism is transmitted through a gear train to the fore wrist unit. Therefore, backlash between the teeth of the gears reduces the rigidity of the output system.
DISCLOSURE OF THE INVENTION
Accordingly, in view of the disadvantages of the above-mentioned three-axis wrist driving mechanism of the chain-drive type, it is an object of the present invention to provide a wrist driving mechanism for an industrial robot, capable of enhancing the rigidity of the fore wrist unit of the three-axis wrist device about the axes of rotation thereof.
The present invention provides a wrist driving mechanism for an industrial rob
REFERENCES:
patent: 4496278 (1985-01-01), Kaise
patent: 4507046 (1985-03-01), Sugimoto et al.
patent: 4545263 (1985-10-01), Fickelscher
patent: 4586868 (1986-05-01), Nakashima et al.
Mizuno Hitoshi
Nakashima Seiichiro
Nihei Ryo
Toyoda Kenichi
Fanuc Ltd.
Spar Robert J.
Underwood Donald W.
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