Sewing needle is driven by PMSM (permanent magnet synchronous motor) in our system and it must be stopped at set position accurately and quickly. If the disturbance from environment or the system itself changes the load torque, the speed response and stop position of servo motor will
be affected. To avoid the problem, a load observer is presented to predict the load variation and the velocity PI parameters are adjusted in real time to compensate the load change. The simulation results show that this method can accurately predict the load change trend and improve the speed
response performance. In the sewing test, the output speed can follow the input control speed well and make the needle stop at required position range.
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