Machine element or mechanism – Gearing – Plural power paths to and/or from gearing
Patent
1989-05-17
1990-11-27
Diehl, Dwight G.
Machine element or mechanism
Gearing
Plural power paths to and/or from gearing
901 29, F16H 3706
Patent
active
049727354
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a wrist assembly for an industrial robot, and more particularly to an improved wrist assembly comprising a first wrist portion provided on the free end of the robot arm and having a pair of projections in parallel with each other on the fore-end thereof, a second wrist portion disposed between the projections of the first wrist portion and supported on both of the projections so as to be rotatable about a first axis intersecting the longitudinal axis of the robot arm at right angles, a third wrist portion supported on the second wrist portion so as to be rotatable about a second axis intersecting the first axis at a right angle and constructed to allow work attachments to be secured thereto, and a motor for driving the second wrist portion and the third wrist portion through a power transmission mechanism.
BACKGROUND ART
In the past, generally a wrist assembly of an industrial robot has been provided with a first wrist portion secured to the free end of the robot arm so as to be rotatable about the longitudinal axis of the robot arm, or immovably fixed thereto. A second wrist portion is provided between a pair of projections formed at the fore-end of the first wrist portion, and supported on both of the projections of the first wrist portion so as to be rotatable about a first axis perpendicular to the longitudinal axis of the robot arm. A third wrist portion, constructed to allow work attachments such as robot hands and so forth to be secured thereto, is supported on the second wrist portion so as to be rotatable about a second axis perpendicular to the first axis. The second wrist portion and the third wrist portion are driven by electric motors connected thereto through power transmission mechanisms. Generally, it is necessary to carry out the reduction needed through power transmission mechanisms in such a manner that the ratio of the number of rotation of each wrist portion to the number of output shafts of motors may be the predetermined reduction gear ratio.
In the conventional aforementioned wrist assembly, the power transmission mechanism for the second wrist portion is provided with a pair of bevel gears disposed in one projection of the first wrist portion, and the power transmission mechanism for the third wrist portion is provided with a pair of bevel gears disposed in the other projection of the first wrist portion and a pair of bevel gears disposed in the second wrist portion.
However, generally the reduction gear ratio obtained through a bevel gear is limited to about 1/2, and therefore, it is necessary to reduce a rotative power of the motor by a further increase in the number of steps or to incorporate a reduction gear, used exclusively for reduction, with gears incorporated therein, in order to obtain a desired reduction gear ratio by the above-mentioned power transmission mechanism. However, this leads to an increase in the weight of the wrist assembly and an increase in the number of parts.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide an improved wrist assembly capable of obtaining a desired reduction gear ratio while decreasing the number of gears needed for transmitting power from the motor to the second wrist portion and the third wrist portion.
The present invention provides a wrist assembly for an industrial robot, comprising: a first wrist portion provided on the free end of a robot arm and having a pair of projections in parallel with each other on the fore-end thereof;
a second wrist portion provided between the projections and supported on both projections so as to be rotatable about a first axis intersecting the longitudinal axis of the robot arm at right angles;
a third wrist portion supported on the second wrist portion so as to be rotatable about a second axis intersecting the first axis at right angles and constructed to allow work attachments to be secured to the front end thereof;
a first motor for driving the second wrist portion;
a second motor for driving the third wrist portio
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Iwasaki Kyoji
Mizuno Hitoshi
Torii Nobutoshi
Diehl Dwight G.
Fanuc Ltd.
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