Machine element or mechanism – Rotary member or shaft indexing – e.g. – tool or work turret – Preselected indexed position
Patent
1986-11-17
1989-07-11
Wright, Dirk
Machine element or mechanism
Rotary member or shaft indexing, e.g., tool or work turret
Preselected indexed position
901 23, 901 28, F16H 128
Patent
active
048460184
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. TECHNICAL FIELD
The present invention relates to an articulation drive apparatus of an industrial robot and in particular to an improved articulation drive apparatus which prevents occurrence of resonance vibration of the robot drive system.
2. BACKGROUND ART
In industrial robots, in general, an electric servo motor or electric pulse motor having a characteristic of high speeds and low torques, and a reduction gear apparatus for converting the output of the electric motor into low speeds and high torques have been employed in the drive system of articulated portions of robot arms and the like in order to obtain output torque suitable for operation.
Also, such a reduction gear apparatus is required to have a large reduction gear ratio of the order of 1/120 and a small backlash and be light in weight to minimize influence of force of inertia.
A conventional reduction gear apparatus which meets such requirements is described, for example, as a harmonic gear apparatus (trade name: harmonic drive) in Japanese Laid-open Publication No. 59-175986 and as a planetary differential gear of the eccentric-rotation type in Japanese Laid-open Publication No. 59-106744. In general, the former reduction gear ratio is in the range of between about 1/80 and about 1/320, and the latter reduction gear ratio is in the range of between about 1/6 and about 1/200. Also, the former harmonic gear apparatus is smaller in diameter per reduction gear ratio and lighter in weight per reduction gear ratio than the latter, and at the same time has a reduction gear ratio and mechanical strength which are required of a reduction gear apparatus for driving articulated portions of most robot arms. Harmonic gear apparatuses are therefore employed widely as a reduction gear apparatus for driving articulated portions of robot arms. In rare case, when a large reduction gear ratio which cannot be obtained by the harmonic gear apparatus is required of the reduction gear apparatus, for example, when a large reduction gear ratio of the order of 1/625 is required in the case that a motor of the small capacity and high rotation type (for example, the output is less than 1000 watt and the number of rotations is 5000 rpm) is used to drive robot arms, the harmonic gear apparatus has been used in cooperation with a primary reduction gear apparatus as shown in Japanese Laid-open Publication No. 56-152594.
However, in the case the above-noted reduction gear apparatuses are each employed in the articulation drive apparatus of the robot, difficulties were involved in that torsional resonance of the reduction gear and the robot arms, etc. occurred at the region in which the number of rotations of the electric motor, which is inputted to the reduction gear apparatus, is low. Torsional phenomenon is produced frequently in the vicinity of articulated portions of robot arms as a resonance phenomenon, so that the end portions of the robot arms cannot be positioned as desired. It had been considered that the reason why the resonance occurs was that, since the rigidity of each of the above-noted reduction gear apparatuses, which are torque transmission mechanism of the electric motor, is relatively small, the natural or characteristic torsional frequency f.sub.o of the drive system including such a reduction gear apparatus (the system comprising an electric motor, a reduction gear apparatus and robot arms) becomes small, and therefore, the vibration frequency of the reduction gear apparatus which is caused to vibrate by error of gear cutting, etc. becomes equal to the above noted natural torsional frequency f.sub.o at the region in which the number of rotations of the electric motor is low.
In regard to these problems, in Japanese Laid-open Publication No. 58-211881 there has been proposed an electrical control method which varies a command signal indicative of speed of the electric motor so that the vibration produced is eliminated. However, in this method, the system becomes unstable if the feed back gain is increased. In particular, in a robot drive
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Hashimoto Masataka
Iwata Michiyoshi
Matsumoto Kazuyuki
Teijin Seiki Co. Ltd.
Wright Dirk
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