|Stable Assist-as-Needed Controller Design for a Planar Cable-Driven Robotic System
Hamed Jabbari Asl and Jungwon Yoon*
International Journal of Control, Automation, and Systems, vol. 15, no. 6, pp.2871-2882, 2017
Abstract : "Robot-assisted rehabilitation systems have shown promising advantages over traditional therapist-based
methods. The type of the controller has an important role in the efficiency of such systems. In this regard, this
paper presents a new assist-as-needed (AAN) controller for 4-cable planar robots. The main purpose is to design
a bounded-input AAN controller with an adjustable assistance level and a guaranteed closed-loop stability. The
proposed controller involves the advantages of both the model-based and non-model-based AAN controllers, and in
this way can increase the efficiency of rehabilitation. The controller aims to follow a desired trajectory by allowing
an adjustable tracking error, which enables the human subject to freely move the target limb inside this error area.
This feature of the controller gives an important advantage over the existing model-based controllers. The controller
also compensates for the dynamic modeling uncertainties of the system through an adaptive neural network. The
adaptive term includes a forgetting factor to adjust the assistance level of neural network term. The stability of the
closed-loop system is analysed, and the uniformly ultimately bounded stability is proven. The effectiveness of the
proposed control scheme is validated through simulations conducted for gait rehabilitation."
Adaptive control, assist-as-needed control, neural network, parallel robot, rehabilitation.