Acceleration control of AC servo motor considering cogging torque at low velocities for haptics

Abstract

AC servo motors are used for care/welfare robots and small home robots. The surface permanent magnet synchronous motor (SPMSM) is usually used for AC servo motors. However, for a low-velocity and high-torque drive SPMSM are sometimes not suitable for smooth robot motion control. A hybrid-type stepping motor (HBSTM) is more suitable for such robot motion control because it has many pole pairs and drives at a lower velocity in comparison with SPMSM. Therefore, the acceleration control using disturbance observer for haptics should be applied to the HBSTM. However, the HBSTM has a high frequency periodic disturbance torque caused by cogging torque. When the HBSTM has the high frequency periodic disturbance torque, the cogging torque is not appropriately compensated by the phase lag, which occurs in the low pass filter (LPF) in the disturbance observer. Therefore, this paper proposes a new acceleration control method of AC servo motor considering cogging torque at low velocities for haptics. The proposed acceleration control is applied to the HBSTM. Moreover, this paper discusses a velocity calculation method for the low range of velocities.