Comprehensive Control Strategy Design for a Wheelchair Power-Assist Device

Rear add-ons are assistive devices developed to assist users who have difficulty propelling wheelchairs. Improving the mobility of wheelchair users and allowing them access to more activities is in line with the objective of the sustainable development goals SDG3, and SDG11. Currently, commercial rear add-on devices implement speed-based controls. The speed-based control consists in setting the reference speed that the device must keep constant which makes rear add-on devices suitable for long journeys but, makes them unsuitable for use in narrow spaces. In this paper an hybrid control is presented. The proposed control law takes into account the thrust exerted by the user (torque-based), the forward speed of the wheelchair (speed-based), as well as the surrounding environmental conditions. The total torque delivered by the device is evaluated as the sum of a contribution proportional to the user’s thrust, a delayed contribution as a function of forward speed, and the gravity compensation contribution. The proportional contribution synchronous with respect to the user’s push at low speeds improves manoeuvrability and controllability of the wheelchair, whereas, at higher speeds, the introduction of the delayed thrust distributes the assistance torque over a longer period, reducing the peak of torque provided by the device. A dynamic multibody model of a wheelchair was also developed and implemented in the Simulink environment to test the proposed control algorithm. As a future step the algorithm will be implemented on a rear add-on device and it will be tested experimentally by wheelchair users.