A finite element model for real-time compensation of the thermal deformation of the platen of a planar step motor

A planar step Sawyer-motor system consists of a Sawyer-motor riding on an air-bearing over a thin steel platen. The platen has a fine grid of teeth which the motor uses to move on the platen. Due to the heat generated from the motor, the platen along with the grid deforms such that the actual position of a point on the platen is equal to the nominal position of the point plus some thermal deformation. Thus, the maximum accuracy is limited to the maximum error from the thermal deformation, which was about 60 μm over a range of 0.5m, in our test system. This paper presents a finite element model for real-time prediction of the thermal deformation of the platen of a planar step motor, along with experimental verification of the model. The model can be used to compensate for the thermal deformation, thus improving the positional accuracy of the motor. The results show that an improvement in positional accuracy of about a factor of five can be achieved