Design of a high speed linear motor driven gantry table

This paper will describe the design optimization of a high speed, high accuracy, linear motor driven gantry table, for use in a semiconductor packaging machine. An air cored, moving coil, 3-phase linear motor will drive the upper axis upon which the load is placed, while two similar, independently controlled linear motors will drive the bottom axis. Each linear motor will have an associated high-resolution linear optical encoder, so that moment loading of the linear guides, caused by movement of the centre of gravity can be eliminated, leading to high dynamic performance. The system design of the gantry table will be presented, emphasising the magnetic circuit modeling, as well as the design optimization and choice of the linear motor topology. Mechanical design aspects, such as the selection of the bearings, gantry system construction and placement of the encoders will also be explored. Three dimensional, lumped parameter, magnetic circuit analysis will be used to estimate the pertinent motor parameters and analytical beam equations for evaluation of the bending and resonant frequencies of the gantry system. To validate the analytical predictions, both electromagnetic and mechanical finite element analyses (FEA) will be used to verify the motor performance and natural frequencies respectively.