A 9-DoF Wheelchair-Mounted Robotic Arm System: Design, Control, Brain-Computer Interfacing, and Testing

A wheelchair-mounted robotic arm (WMRA) system was designed and built to meet the needs of mobility-impaired persons with limitations of upper extremities, and to exceed the capabilities of current devices of this type. The control of this 9-DoF system expands on the conventional control methods and combines the 7-DoF robotic arm control with the 2-DoF power wheelchair control. The 3-degrees of redundancy are optimized to effectively perform activities of daily living (ADLs) and combine wheelchair mobility and arm manipulation to overcome singularities, joint limits and some workspace limitations. The control system is designed for teleoperated or autonomous coordinated Cartesian control, and it offers expandability for future research. Several interchangeable user interfaces were implemented in the design, including a Brain Computer Interface (BCI). That BCI system was modified and integrated to the control of the WMRA system for users who are totally paralyzed or “locked-in” and cannot use conventional augmentative technologies, all of which require some measure of muscle control. Testing and data collection were performed on human subjects, and the design, various optimized control methods and test results are presented in this paper. According to the 2006 US Census Bureau report (US Census Bureau, 2002), about 51.2 million Americans (18.1 percent of the US population) had some level of disability and 32.5 million of them (11.5 percent) had a severe disability. About 10.7 million Americans older than 6 years of age needed personal assistance with one or more activities of daily living (ADL). This work focuses on people who have limited or no upper extremity mobility due to spinal cord injury or dysfunction, or genetic predispositions, or people who are “lockedin” (e.g., by end-stage amyotrophic lateral sclerosis, brainstem stroke, or severe polyneuropathy). Robotic aides used in these applications may vary from advanced limb orthosis to robotic arms (Reswick, 1990). A wheelchair mounted robotic arm can enhance the manipulation capabilities of individuals with disabilities that are using power wheelchairs, and reduce dependence on human aides. 3