Image Number 4 for United States Patent #4995782.
An apparatus for rotating a wrist shaft of a robot comprising an indexing plate which is rotated by a motor through a friction coupling, a roller which is pressed against the indexing plate and which is disengaged from recesses in the indexing plate by an air cylinder. The motor and air cylinder are controlled by a timing mechanism which is responsive to indexing signals and to signals from a series of proximity switches, there being one proximity switch actuable at each of the several indexing positions. Indexing positions are selected by transmitting indexing signals to the timing mechanism. Upon receipt of an indexing signal requiring movement of the wrist shaft, the timing mechanism actuates the air cylinder, releasing the indexing plate. Immediately thereafter, it starts the motor. In the case of a single step indexing operation, the roller is released to engage the indexing plate after a predetermined time interval, and the power to the motor is thereafter cut off. In the case of a multiple step indexing operation, the timing mechanism releases the roller to engage the indexing plate following a predetermined interval after actuation of the proximity switch corresponding to the indexing position immediately preceding the selected indexing position. Again, the power to the motor is cut off after the roller engages the indexing plate. In each case, the roller engages the outer periphery of the indexing plate and the action of the roller against rounded transitions between the outer periphery and the recesses assists in rotating the wrist shaft to the selected indexing positions.