An estimation method on the initial pole position of a z-axis PMLSM

This paper presents an estimation method on the initial pole position of a z-axis permanent magnet linear synchronous motor (PMLSM) without a magnetic pole sensor such as a Hall sensor. It takes account of the gravitational force of a z-axis motor and also the variation of load mass. First it approximately estimates the value of a given initial pole position by monitoring movements due to test current at predefined different test q-axes. Then it starts the successive estimation by the correction term from the initial estimate of the first step and continues until the estimate converges. The correction term is made of three values corresponding to force due to the test current at three test q-axes in order to avoid the effect of load mass. Experimental results on the test rig show that the proposed algorithm accurately estimates the initial pole position within a small moving range irrespective of load mass.