<p>This is a thesis for a Bachelor Degree Project, performed in the subject Mechanical</p><p>Engineering. The students Roger Malmberg and Simon Hagberg have carried out a</p><p>design project on behalf of the recently established company J&D Assisting systems,</p><p>located in Halmstad.</p><p>The project consisted in developing J&D's first prototype of a power assisting solution</p><p>for wheelchairs. A power assisted wheelchair combines human power, which is delivered</p><p>by the arms through the pushrims, with electrical motors, which are powered by a battery.</p><p>The power assisted wheelchair is aimed at customers, who have used a regular</p><p>wheelchair for a long time, but who have become weaker or just need additional power</p><p>when driving uphill. This kind of wheelchair will provide additional power for users,</p><p>which will spare their wrists, elbow and shoulders. The product is torque sensor free and</p><p>instead it relies on the velocity. Engines and gearboxes from the company All motion was</p><p>a requirement. The construction could not impair the wheelchair's trafficability and the</p><p>performance would at least match up with the performance of the first prototype. To build</p><p>a working prototype was a part of the task. The work was early focused on the specific</p><p>wheelchair Etac Next. At the same time, the result should be, as much as possible,</p><p>suitable for the most common wheelchairs.</p><p>The result is a design where the engine packet is assembled in a 90° angle towards the</p><p>wheelaxle. In the angle, the power is transferred by bevel gears, assembled on shafts</p><p>supported by ball bearings. Then, the force is transmitted via a modified wheel axle to a</p><p>structure mounted outside the hub. Eight stokes transfers the force to the hand rims.</p><p>An operational prototype has been built and then been assembled on the wheelchair Etac</p><p>Next. The part mounted outside of the wheel has got a plastic hood to cover up and to</p><p>protect the inner parts. The plastic hood has been produced with SLS technology.</p>

This is a thesis for a Bachelor Degree Project, performed in the subject Mechanical Engineering. The students Roger Malmberg and Simon Hagberg have carried out a design project on behalf of the recently established company J&D Assisting systems, located in Halmstad. The project consisted in developing J&D's first prototype of a power assisting solution for wheelchairs. A power assisted wheelchair combines human power, which is delivered by the arms through the pushrims, with electrical motors, which are powered by a battery. The power assisted wheelchair is aimed at customers, who have used a regular wheelchair for a long time, but who have become weaker or just need additional power when driving uphill. This kind of wheelchair will provide additional power for users, which will spare their wrists, elbow and shoulders. The product is torque sensor free and instead it relies on the velocity. Engines and gearboxes from the company All motion was a requirement. The construction could not impair the wheelchair's trafficability and the performance would at least match up with the performance of the first prototype. To build a working prototype was a part of the task. The work was early focused on the specific wheelchair Etac Next. At the same time, the result should be, as much as possible, suitable for the most common wheelchairs. The result is a design where the engine packet is assembled in a 90° angle towards the wheelaxle. In the angle, the power is transferred by bevel gears, assembled on shafts supported by ball bearings. Then, the force is transmitted via a modified wheel axle to a structure mounted outside the hub. Eight stokes transfers the force to the hand rims. An operational prototype has been built and then been assembled on the wheelchair Etac Next. The part mounted outside of the wheel has got a plastic hood to cover up and to protect the inner parts. The plastic hood has been produced with SLS technology.

<p>A power assisted wheelchair combines human power, which is delivered by the arms through the pushrims, with electrical motors, which are powered by a battery. Today’s electric power assisted wheelchairs use force sensors to measure the torque exerted on the pushrims by the user. The force sensors in the pushrims are rather expensive and this approach also makes the wheels a little bit clumsy. The objective with this project is to find a new, better and cheaper solution that does not use expensive force sensors in the pushrims. The new power assisted wheelchair will instead only rely on its velocity, which is measured with rotational encoders, as feedback signal and thereby the project name “Torque Sensor Free Power Assisted Wheelchair”. </p><p> </p><p>The project consisted of two main parts; an extensive construction part, where an ordinary joystick controlled motorized wheelchair has been rebuild to the new power assisted wheelchair without torque sensors and a development part, where different torque sensor free controllers has been designed, simulated, programmed and tested.</p><p>The project resulted in a torque sensor free power assisted wheelchair, where the final implemented design is a proportional derivative controller, which gives a very good assisting system that is robust and insensitive to measurement noise. The proportional derivative control design gives two adjustable parameters, which can be tuned to fit a certain user; one parameter is used to adjust the amplification of the user’s force and the other one is used to change the lasting time of the propulsion influence.</p><p>Since the new assisting control system only relies on the velocity, the torque sensor free power assisted wheelchair will besides giving the user assisting power also give an assistant, which pushes the wheelchair, additional power. This is a big advantage compared to the pushrim activated one, where this benefit for the assistant is not possible.</p>

A power assisted wheelchair combines human power, which is delivered by the arms through the pushrims, with electrical motors, which are powered by a battery. Today’s electric power assisted wheelchairs use force sensors to measure the torque exerted on the pushrims by the user. The force sensors in the pushrims are rather expensive and this approach also makes the wheels a little bit clumsy. The objective with this project is to find a new, better and cheaper solution that does not use expensive force sensors in the pushrims. The new power assisted wheelchair will instead only rely on its velocity, which is measured with rotational encoders, as feedback signal and thereby the project name “Torque Sensor Free Power Assisted Wheelchair”. The project consisted of two main parts; an extensive construction part, where an ordinary joystick controlled motorized wheelchair has been rebuild to the new power assisted wheelchair without torque sensors and a development part, where different torque sensor free controllers has been designed, simulated, programmed and tested. The project resulted in a torque sensor free power assisted wheelchair, where the final implemented design is a proportional derivative controller, which gives a very good assisting system that is robust and insensitive to measurement noise. The proportional derivative control design gives two adjustable parameters, which can be tuned to fit a certain user; one parameter is used to adjust the amplification of the user’s force and the other one is used to change the lasting time of the propulsion influence. Since the new assisting control system only relies on the velocity, the torque sensor free power assisted wheelchair will besides giving the user assisting power also give an assistant, which pushes the wheelchair, additional power. This is a big advantage compared to the pushrim activated one, where this benefit for the assistant is not possible.