Research ArticleAdaptive control of 5 DOF upper-limb exoskeleton robot with improved safety

- The proposed reliable controller design considers the modeling errors and the uncertainties to improve tracking performance.
- The proposed controller can guarantee the safety of the patients against large parameter variance, hardware malfunctions, even actuator faults.
- The estimation of velocity and acceleration provided by an adaptive observer without adding more sensors.
- The effect of the hardware malfunctions, even actuator faults is described in a unified model and automatically accommodated.
- The switching logic in the controller and the gain updated law will provide a natural and effective fault accommodation mechanism.

This paper studies an adaptive control strategy for a class of 5 DOF upper-limb exoskeleton robot with a special safety consideration. The safety requirement plays a critical role in the clinical treatment when assisting patients with shoulder, elbow and wrist joint movements. With the objective of assuring the tracking performance of the pre-specified operations, the proposed adaptive controller is firstly designed to be robust to the model uncertainties. To further improve the safety and fault-tolerance in the presence of unknown large parameter variances or even actuator faults, the adaptive controller is on-line updated according to the information provided by an adaptive observer without additional sensors. An output tracking performance is well achieved with a tunable error bound. The experimental example also verifies the effectiveness of the proposed control scheme.