Assistive technology is an emerging area where some robotic devices can be used to strengthen the residual abilities of individuals with motor disabilities or to substitute their missing function. Substantial work has been done in the development of smart power wheelchair system for disabled. However, most of current developments have not proved to be really accepted by disabled people. The object of this research is to provide an actual aid to increase mobility for severely spinal cord injured people who is able to bend, stretch and rotate his neck (C4) and also able to raise his shoulder (C5). The overall wheelchair system includes two innovative human-machine interfaces, motor control module, ultrasonic sensors for detecting obstacle, and strategy of navigation control.
First of all, two input devices are developed by considering human-device coupled design, the easy-to-use, wearability, and low cost. One is ‘shoulder belt’ input device by using raising motion of each shoulder. The other is ‘cap’ input device which can measure the roll and pitch angle displacement of head. In this study two input devices are using FSR(Force Sensing Register) sensors which exhibit a decrease in resistance with increase in the force applied on the active surface. The notable feature of ‘Shoulder belt’ device is a natural design product that can be put on inside an overcoat. Moreover two devices are very cheap compared with other commercial input device.
As a real-world application of above new interfaces, clinical evaluation was performed with real end-users (people with spinal cord injury). Six male subjects participate in the evaluation by using each device. According to the results of clinical evaluation, severely injured person can move to their destination just by using input devices but the performance is not satisfied. For supplementing limit muscle function and slow response time of disabled, auto-navigation system was added.
Just adding a good input interface to a severely disabled is not a solution to satisfy the user’s need that they want to go their own way without assistance. So fluent steering task for avoiding obstacle and other specific task can be solved using autonomous wheelchair control. Twelve ultrasonic sensors were used to detect obstacles. Simple obstacle detecting algorithm (grid method) and obstacle avoidance (Virtual Force Field) method using ultrasonic sensors make an autonomous wheelchair control possible.
The ultimate goal of this research is mutual cooperation naturally between manual and autonomous control mode for performing various tasks. Namely supervisory control architecture between human interface for manual mode and sensor system for autonomous control is used for eliminating continuous disabled attention, achieving accuracy and reliability, and making control faster and easer. Supervisory control was embodied with using fuzzy algorithm that have three variables. (The first is angle with respect to wheelchair direction which demonstrates confliction between user and wheelchair. The second is length with respect to center point which demonstrates user’s confidence. The third is autonomy of wheelchair. )
Also Vibro-tactile actuator plays an important pole in the supervisory control, which is used for informing disabled of computer intention of next motion(for example, turn right ,left or stop) and warning obstacle existence in the backward area. So it is a medium between user and wheelchair.
