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.< >

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 coarse position sensors to be used, including position estimates based on back EMF measurements. 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. However, this operating point includes the value of external DC torque (drag), 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

Hybrid stepping motors exhibit a back EMF voltage from which absolute position measurements may be extracted. This work analyses a novel technique for extracting these position measurements for constant velocity applications. The method produces accurate measurements (/spl plusmn/0.1 mechanical degrees). To increase the utility of these measurements, Kalman filtering techniques have been employed. To reject unmodeled disturbance step functions, the nonlinear dynamics have been exploited. The resulting control law is able to use Kalman filtering to improve the bandwidth while retaining disturbance step rejection.

A model of the torque ripple induced when linearizing hybrid stepping motors is developed. Using this model, the optimal waveforms for linearization are derived. These optimized waveforms require only a slightly different table look-up, yet they reduce the square root of the mean square torque ripple approximately five-fold, thus making square wave commutation possible for some applications. Frequency analysis of the resulting torque ripple provides a method of trading-off linearization computations for performance. Experimental results validate this analysis.