Closed loop low-velocity regulation of hybrid stepping motors amidst torque disturbances

• Published in: IEEE transactions on industrial electronics (1982) Vol. 42; no. 3; pp. 316 - 324
• Main Authors: Schweid, S.A., McInroy, J.E., Lofthus, R.M.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.06.1995; Institute of Electrical and Electronics Engineers
• Subjects: Applied sciences; Control systems; Damping; Eigenvalues and eigenfunctions; Electrical engineering. Electrical power engineering; Electrical machines; Exact sciences and technology; Motion control; Nonlinear control systems; Open loop systems; Position measurement; Special rotating machines; Steady-state; Torque; Velocity control
• ISSN: 0278-0046; 1557-9948
• DOI: 10.1109/41.382143

To regulate the velocity of hybrid stepper motor motion control systems, a control law which exploits the nonlinear dynamics to create an analog positional control in conjunction with a traditional linear control is introduced. This nonlinear approach allows a much coarser position sensor to be used, including position estimates based on back EMF measurements. The form of the control law admits the use of a wide variety of compensators, whereas earlier laws use only velocity damping compensation. Two specific compensators, i.e., velocity damping and integral control are analyzed in detail, then compared to each other and to open loop microstepping control. It is shown that velocity damping allows the design of the eigenvalues of the closed loop system and provides a linear system approach about a specified operating point. Unfortunately, this operating point includes the value of external DC torque (drag) present, so the closed loop dynamics cannot be guaranteed amidst steady state torque fluctuations. Integral feedback (within a PID controller) improves upon velocity damping by not only allowing the design of the closed loop eigenvalues, but also by completely linearizing the system regardless of external DC torque values. Furthermore, the integral feedback produces zero steady state position error (as expected from linear control theory) and significantly decreases the tendency of the motor to lose step. Experimental results validate the analyses.< >