Investigation and resonance compensation in hybrid stepper motor

Abstract

Hybrid Stepper Motors (HSM) are mainly used for precise newlineposition control applications, due to their durability, small step angle and newlineability to operate in open loop. The stepping rate normally follows the newlineexcitation rate. However, at certain speeds vibration and resonance are noted newlinewhich may lead to missing of steps. The machine vibrates excessively when newlinethe excitation frequency matches the natural frequency leading to oscillations newlineknown as resonance. It is also influenced by electrical parameters like newlineinductance and resistance of the motor. This behavior of the HSM nullifies the newlinepossible open loop control and hence this needs to be addressed. Excitation schemes like full step and half step modes can be newlinegenerated with simple digital devices which is another major attraction in the newlineuse of stepper motors. More sophisticated micro step kind of excitation is also newlineemployed to obtain smooth operation. For a given stepper motor, prediction of newlinespeed at which resonance occurs is challenging. newlinePrecise position control may be possible with direct mechanical newlinemeasurement, where the resonance can be identified easily. Mechanical newlinemeasurements include rotor position, speed and torque using sensors, which newlineadd to additional cost for required resolution and precision. Modern approach is to use electrical measurements to estimate newlinemechanical variables. Electrical measurements include the measurement of newlinephase current and excitation voltage. The motivation of this research work has newlinebeen to identify resonance through electrical measurements. Phase current is newlineobserved for various speeds and load conditions and it is found that the current newlinecarries information to distinguish Resonance (R) and Non-Resonance (NR) newlineconditions. Suitable schemes are proposed to investigate the phase current for newlineresonance identification and resonance compensation. The wave shape of the newlineobserved phase current is found altered during resonance condition. As a first approach, harmonic contents of phase currents are newlineobserved. newline newline