New approach to force sensor-less power assist control for high friction and high inertia systems

In recent years world aging population is increasing always more and more. Consequently power assist devices such as electro mechanical suits and electric wheelchair are growing in importance. A key aspect in the control of power assist robots is the knowledge of the force that the user applies on the device. Force sensors are often used even though they are generally expensive, heavy, and can measure the force only if applied in a limited area. To overcome these aspects, force sensor-less control, which is based on disturbance observer, can estimate the force to assist by only using encoders. The main problem of force sensor-less control is the limited robustness against plant uncertainties and inevitable modelling errors. In this paper, force sensor-less power assist control (FSPAC) with variable gain is proposed and implemented on a high friction and high inertia system. The results show that the proposed control design considerably increases robustness of FSPAC, guarantees safety and provides assistance to the user in a smoother way.