Steering Transparency Control of a Wheelchair Assistive Device Based on State Estimator Approach

The use of power-assisted devices (PADs) can help manual wheelchair users reduce physical strain and prove mobility. There are various types of PADs available, including pushrim-activated power-assisted wheelchairs (PAPAW), front-end attachments, and rear-end attachments. Among these devices, the most versatile in terms of weight, size, and ease of movement are the rear add-ons. However, the control logic and propulsion systems currently adopted make these devices unsuitable in narrow spaces. They are particularly inefficient and a hindrance during complex manoeuvres and fast changes of direction. In this work, we present a new add-on device with a steering wheel capable of providing directional assistance. During manoeuvres and turns, it is crucial that the steering angle is consistent with the wheelchair's kinematics; otherwise, the friction force arising from sliding would make the device ineffective. To improve the transparency and usability of the device, we propose a steering angle control based on state estimation techniques. This approach is validated through experimental tests. The findings suggest that a steerable rear add-on device with a coherent steering angle can provide suitable assistance for manual wheelchair users in both outdoor and indoor environments, improving mobility and reducing physical strain.