A STUDY OF PRE-COMPENSATION FOR THERMAL ERRORS OF NC MACHINE-TOOLS

Thermally-induced errors are major contributors to the overall accurac y of machine tools. In this paper, an error pre-compensation system is developed to correct the thermal errors of the spindle and lead screw s. A simple gauge 1-D ball array is used to accelerate and simplify th e error measurement. An auto-regressive model based on spindle rotatio n speed is then developed to describe the thermal errors. Using the mo del, the thermal errors can be predicted without measuring the tempera ture field of the machine tool as soon as the workpiece NC machining p rogram is made. By correcting the program, the errors can be pre-compe nsated before machining. Thus the process of compensation is greatly s implified and the cost is reduced. The test results on a vertical mach ining center show that a 70% reduction of thermal errors has been gain ed after compensation. (C) 1997 Elsevier Science Ltd.