Load angle estimation for two‐phase hybrid stepping motors

Abstract

Stepping motors are often used for low-power open-loop positioning. In conventional stepping motor drives, a step rate or speed is imposed. To avoid step loss in open-loop, most stepping motors are driven at maximum current resulting in a poor energy efficiency. However, when position feedback is available, the drive current can be optimised. A position sensor adds costs and complexity to the system. Therefore, rotor position estimators are developed, often referred to as sensorless controllers. A drawback in some of these methods is the requirement of information on the mechanical load which is usually not available or varies over time. In this study, an alternative estimator is proposed, based on the load angle between the current excitation vector and the instantaneous rotor flux position. This load angle reflects the capability of the system to follow the speed setpoint and gives an indication of the robustness to torque disturbances. Therefore the load angle estimation is interesting to provide feedback to a controller which adapts the drive current. Here, an estimator is proposed solely based on electrical motor parameters and electrical measurements. The algorithm, based on a sliding discrete Fourier transformation, is applicable with the typical full-, half-and micro-stepping drive algorithms. Finally, measurement results validate the estimation algorithm.

Robust sensorless load angle control for stepping motors

“…Simulations and measurements discussed in [8], [11] show that the load angle can be estimated based on the fundamental waveform of the electrical signals. Fig.…”

“…1 is known. In [8], [11] it is suggested to use the sliding discrete Fourier transform (SDFT) [12]- [14] to calculate the fundamental voltage U s1 and current I s1 components based on consecutive measurement samples (shown in Fig. 6) in a computationally efficient manner.…”

“…This means positioning by sending step command pulses is no longer possible. On the other hand, the control structure [8], used in this paper will only manipulate the current level. This means the relation between the step command pulses and current excitation vector stays the same as in standaard stepping motor drive algorithms.…”

Implementation of Closed-Loop Stepper Motor Driver Based on Lead Angle Estimation

“…In order to prevent stepper motors from encountering the step-out problem, closed-loop position control algorithms were applied [1], [7]- [12]. In a closed-loop stepper motor driver, control algorithms, such as PID (Proportional Integral Derivative) position control [1], [7], optimal control [8], global learning control [9], and lead angle control [1], [7], [10]- [12] could be implemented. Even though the PID position control method is easy to apply for a stepper motor driver, however, the produced motor torque is not optimal because the torque angle of Manuscript received June 16, 2018; revised September 7, 2018.…”

“…The optimal and global learning control approaches [8], [9] could achieve high speed motion but they require a complex computation. In the lead angle control methods [10]- [12], the value of the lead angle is calculated based on the produced motor torque, the motor speed, and the compensation for back Electromagnetic Force (EMF). Therefore, by using these techniques, the stepper motor can operate at high speed with the high torque.…”