Force sensor-less power assist control for low friction systems

Nowadays aging population is increasing in many country. As a consequence power assist devices are growing in importance. Knowing the force that the user applies is a key aspect in the control of these devices. Force sensors are often used, even though they are generally expensive, heavy and characterized by time delay. To overcome these aspects, force sensor-less power assist control (FSPAC) aims to estimate the force to assist by using only encoders. However, FSPAC is generally not robust against plant uncertainties. In this paper, FSPAC with variable gain is proposed and implemented on a system representing a door, actuated by a linear motor. The results show that the proposed control design increases FSPAC´s safety and robustness.