Abstract

A threaded ball screw is stationarily non-rotatably mounted in a machine tool to extend parallel to the line of action traversed by a carriage. A pair of threaded ball nuts are laterally restrained in and mounted for free rotation thereof in a drive mechanism of the carriage and threadably and concentrically engage the ball screw in laterally spaced apart co-axial relationship therealong. A pair of digitally controlled electric drive motors are mounted in the carriage for individually imparting rotational torque to the nuts. A conventional programmably CNC controller is programmed to synchronously control both motors for causing the ball nuts to conjointly produce computer controlled linear motion and positioning of the carriage along the stationary ball screw, and to develop anti-backlash pre-load forces between the ball nuts relative to the ball screw. The system can also produce an electromotive and/or frictional braking force for decelerating and/or holding the carriage in a selected stationarily fixed position along the line of action. The two motor rotors can exert rotational torque on the ball nuts simultaneously in the same or opposite rotary directions with the carriage moving and/or stationary. Pre-load forces exerted between the ball nut can be dynamically adjusted by monitoring the load and/or position of each of the motor rotors and adjusting the power input thereto individually while producing conjoint rotary motion of the motors to drive the carriage along the ball screw. The angular phase relationship between the motor rotors and hence between the ball nuts can be controlled to vary screw-to-nut backlash clearance as a function of carriage travel position and/or mode of machine tool operation.

Other References

• Machine Design--Feb. 7, 1994--p. 2