EAGER: Refinement and Evaluation of a Robotic Wheelchair System

Oregon State University, Corvallis OR

Investigators

Abstract

The interfaces used by full-time wheelchair users with ALS, quadriplegia, and similar conditions are typically single-tasking, direct control interfaces. For example, a person with ALS with whom the PI works drives his wheelchair through a combination of head- and shoulder-activated switches, and speaks with the assistance of a computer he controls with head movements. He cannot drive the chair and communicate at the same time, in the way that normally-abled people take for granted. For most of us, walking is an unconscious activity; we decide where to go in the room, and then forget about it. Adding autonomy to a powered wheelchair would allow many wheelchair users to recover some of this ability, by essentially turning the wheelchair into a robot that can take advantage of the vast body of existing software and techniques for navigating about the world. The user of such a wheelchair would select a location on a map displayed on his/her computer, and then forget about it as the wheelchair drives itself to that location, reducing the dependence on caregivers and increasing independence. The PI's goal in this exploratory project is to develop a low-cost, open-source electronics package that will provide this capability for a (somewhat arbitrary) total hardware cost of $500 since medical insurance will not pay for such a system so potential users must pay for it out-of-pocket and the PI is anxious to ensure that project outcomes will find their way into the lives of real wheelchair users. Instrumenting a wheelchair in this way will have additional benefits (e.g., knowing where the wheelchair is in the home could allow a simpler and faster interface to control home automation). And because the system will have an open software API, it will provide a common platform for researchers and developers working on assistive systems for full-time wheelchair users. To these ends, the PI has designed and implemented a prototype electronics package for Permobil powered wheelchairs, and has tested this on a Permobil M300 powered wheelchair on loan from the ALS Association of Oregon and Southwest Washington. The electronics package is mounted underneath the seat at the front of the chair on a custom-fabricated metal plate, and includes two Hokuyo laser range-finders (one on each side), a small computer mounted on the front of the chair body behind the footrest, and custom electronics to supply power from the wheelchair batteries. An Arduino microcontroller connected to the computer allows movement commands to be sent to the wheelchair through a Permobil I/O Module. Integration with ROS allows the system to build maps of the environment, to use these to localize the wheelchair, and to take advantage of extensive autonomous navigation abilities. Once the wheelchair is localized within a map, the user can provide it with a goal point either via an on-screen map-based interface or by means of a Google Glass; the chair can then autonomously navigate to that point avoiding obstacles as it goes, using the standard ROS navigation system. Preliminary trials in a cluttered office environment have been encouraging, although additional refinement of the URDF and kinematic models of the system are needed, and the localization needs to be improved by adding an IMU to the electronics package. The intellectual merit of the current work lies in three areas: understanding the design pressures behind the envisaged electronics package, if it is to be deployed on a range of powered wheelchairs in the real world; the redesign and implementation of mapping, localization, and path-planning algorithms for this setting; and designing a system that is fault-tolerant and capable of running for months and years at a time, without intervention by trained roboticists. Specific tasks will include: to improve and generalize the hardware and electronic design; to improve the localization algorithm; to improve the quality of wheelchair movement; to investigate replacements for the current laser range-finders; to document how to integrate everything onto a chair; and to build a number of additional kits.