In the past, wheelchairs have been either manual: propelled by hand using the wheel rims, or fully electric.  Many users find the full electric wheelchair with its joystick control cumbersome and unresponsive, yet the manual chair can be very tiring.

Thanks to a recent development from SR Drives Ltd, a power-assisted manual wheelchair provides users with an effective alternative. As the user pushes on the wheels, torque transducers measure the torque applied to the rims and provide electric assist.  Intelligent control is added, so that the assist is progressive and natural.  Hence, from the users perspective, the wheelchair glides across carpets as easily as a hard floor.

Switched Reluctance Drives Ltd provided the dual drive systems for the wheelchair.  The motors are sinusoidally driven permanent magnet machines, giving high efficiency and smooth torque.  The system uses a multiple DSP computer architecture to provide the cross-checking required in this safety-critical application.