Modelling, identification and control of thermal deformation of machine tool structures, part 4: A multi-variable closed-loop control system

A multi-variable closed-loop control system is proposed to compensate for t he thermal deformation of machine tool structures. The control system recog nizes the fact the relative thermal displacement between the tool and workp iece is not accessible for direct measurement. Using the generalized thermo elastic transfer functions of the structure, which provide satisfactory inp ut-output dynamic dependencies, the heat input to the structure and thermal displacements are estimated in real time. Artificial heating elements are used as the actuation mechanism of the control system, since they provide a n economical solution for retrofitting existing conventional machine tools, and can also be combined with NC controllers to effect the desired compens ation of the expansion and bending modes of deformation. Computer simulatio n test results indicated that even when the random temperature measurement and power actuation errors are taken in consideration, an accuracy of bette r than 2.5 mu m and a control cycle of the order of 1 second are achievable .