Precision motion control of a sustainable magnet-free tubular linear switched reluctance actuator using a modified PID controller with anti-windup compensation

Abstract

The demand for sustainable industrial automation systems is growing, and so is the demand for actuation technologies that are not only highly accurate in positioning, but also have a low environmental impact. Tubular linear switched reluctance actuators (T-LSRAs) are a potential alternative to conventional linear actuators, because they do not use rare-earth materials, and thus have an inherently lower environmental impact throughout their life cycle. But, T-LSRAs have very nonlinear electromagnetic characteristics and have a large force ripple that negatively impact positioning accuracy and transient response. This study proposes a modified proportional–integral–derivative (PID) controller with anti-windup compensation and a nonlinear current–displacement linearizer to improve the precision motion control of a laboratory-scale T-LSRA. The control parameters were first adjusted by the Ziegler–Nichols method and then adjusted by experimental trial and error. The proposed control scheme also includes a phase switching mechanism to control the excitation currents according to the mover displacement. Experimental validation was carried out in fully aligned, half-aligned and specific reference positions in point-to-point positioning. The proposed controller was able to achieve steady state positioning error less than 0.2 μm, the resolution limit of the encoder, at most positions and greatly improve transient performance than the conventional PID controller. For instance, settling time was reduced from 2.03 × 10⁻¹ s to 1.85 × 10⁻¹ s at 10 mm, and from 2.91 × 10⁻¹ s to 1.99 × 10⁻¹ s at 15 mm. Overshoot was reduced by up to 97.0% at the 5 mm fully aligned position, with a residual positioning error of 6.00 × 10⁻¹ μm. The results show that the combination of a nonlinear linearizer and anti-windup compensation in a PID framework is an effective and computationally efficient solution for precision control of magnet-free linear actuators, which can be used in industrial automation and smart manufacturing applications to achieve high accuracy positioning.