Model-Based Compensation of Thermal Disturbance in a Precision Linear Electromagnetic Actuator

Thermal disturbance is a major source of positioning error in precision-positioning systems. The conventional approach of using special materials for construction and sophisticated geometric design based on advanced computer simulation can be costly as well as time consuming to implement. Moreover, dynamic thermal disturbances cannot be effectively compensated for by such methods. The approach presented in this paper uses model estimated position error coupled with sensor measurement as a feedback compensator of the output shaft position. A state-space model is used in a modified Kalman Filter to reduce the total number of temperature sensors needed for estimation of the thermally induced position error. A maximum temperature estimation error of 1.8% of the measurement range is recorded. An online parameter estimation method is implemented to “fine tune” a transfer function model during a calibration stage before compensation. The model-based compensation method resulted in a mean unidirectional positioning deviation of -0.2 μm and repeatability of ± 0.7 μm during a 5-h continuous operation.