A Digital Design Approach and Implementation for Thermal Error Compensation in Machine Tools by Precision Positioning and Feedback Signal Manipulation

The proposed paper aims at designing a real time precision positioning control circuitry for a numerical control device used to control a machine tool with encoder type feedback. More particularly it is intended to design a digital compensating circuit for modifying a position control signal to effect a correction for repeatable linear errors such as the dimensional changes in the machine structure due to changes induced into the structure by operating temperature ranges. The error correction is performed by modifying encoder type position feedback signals supplied to the machine tool controller. This provides real time compensation for thermal errors in positioning of computer numerically controlled machine tools, coordinate measuring machines (CMMs), robots, assembly systems, and the like.

The error correction being accomplished by the Error Correction Circuit(ECC), which adds or subtracts a predetermined number of pulses to the pulses coming from a feedback device such as encoder to compensate for over shoot or under shoot of the machine tool respectively.