Advanced 3D Control Techniques for Powered Wheelchairs

Principal Investigator: Rory A. Cooper, PhD

Co-Investigator: Dan Ding, PhD                     

2005-2007 

Over 200,000 people in the United States use electric-powered wheelchairs (EPWs) as their primary means of mobility. Electric-powered wheelchairs provide functional mobility for people with both lower and upper extremity impairments. While electric powered wheelchairs have made great advances over the past 20 years, the control algorithms remain virtually unchanged since the early 1980’s. The simple proportional-integral (PI) controller used on electric-powered wheelchairs for velocity control is antiquated, and does not perform well with disturbances, sensors uncertainties and load variations. In addition, wheelchair users may encounter different environments and road conditions when driving outdoors. We have successfully implemented the shared control system for a pushrim activated power assisted wheelchair. In addition, kinematic and dynamic models of an EPW were developed to simulate the wheelchair motion and were validated by experimental results. With these preliminary studies, we have designed a model based controller for electric powered wheelchairs that includes velocity control and traction control. The velocity control algorithm based on an improved wheelchair model aims to improve the safety and efficacy of EPWs in the face of external disturbances, parameters variations and uncertainties. The traction control algorithm coping with wheel slips and cases where the wheelchair becomes stuck will increase mobility and ensure safe navigation under less favorable surface conditions (i.e., wet grass, iced sidewalk, snow). In order to validate the controller, we evaluated the effects of model based control methods on driving speed variation and wheel-slip of an electric-powered wheelchair (EPW) compared with PID and open loop control. A focus group was also conducted to identify control strategies employed by EPW users’. A kinematic model as well as 3-D dynamic model was developed to control the velocity and traction of the wheelchair. A smart wheelchair platform was designed and built with a computerized controller and encoders to record wheels speeds and to detect the slip. The speed errors, variation, rise time, settling time and slip coefficient were calculated and compared for a speed step-response input. Experimental results showed that model based control performed best on all surfaces across the speeds.
 

In the future, our work could transform EPW driving by greatly improving control over difficult services. Furthermore, the success and power of the smart controller hardware may be used for next generation EPWs as well as being used for advanced research and graduate education.