Active damping applied to HSM-driven mechanical loads with elasticity ?

Hybrid Stepper Motors (HSM), together with the microstepping driving technique, are widely used in many motion control applications, given their low cost and high reliability. On the other hand, being controlled in an open loop fashion, they cannot achieve high levels of performance, this mainly due to the absence of a load-side position sensor. In this paper, we address the problem of controlling the motion of a mechanical load, driven by a HSM, in presence of a flexible mechanical transmission between motor and load. This is a typical industrial scenario, in which the problem of the oscillations arising from the excitation of the mechanical resonance by various disturbances (including torque ripple) is usually addressed by severely limiting the overall dynamic performance. In this paper, we propose the use of an active damping strategy, which allows for the improvement of the dynamic response and an excellent rejection of the oscillations caused by the torque ripple. The proposed technique does not require the re-design of the existing equipments, since it is based on an enhancement of the standard microstepping, in which the angle of the stator flux is properly modulated, to produce a compensating torque and, in turn, damp the oscillatory modes. Such modulation is based on the proper processing of the measurements obtained from a load-side MEMS accelerometer, which can be easily fitted into existing setups. Experimental results confirm the effectiveness of the proposed solution.