Abstract
An electric control for a power-driven wheelchair designed at the Electro-Mechanical Laboratory of the National Spinal Injuries Centre is demonstrated, whereby a patient with a very high cervical lesion can be made more independent. The young lady was admitted with a complete tetraplegia below C4. She was critically ill, had to have a tracheostomy done quickly, but fortunately she recovered to a certain extent as she has now some function of deltoid and biceps but no finger movements whatsoever. One does not need to stress how difficult it is to make patients with these high cervical lesions relatively independent. We have devised a gadget by which the patient with her left arm can control the chair quite easily.
The disadvantage for this level of lesion with the conventional power-drive chair is first of all that the joy-stick is operating against four micro-switches and, therefore, one has only on/off control. The speed is usually switched by two quite stiff toggle switches, both of which have to be moved to get one through four speed ranges. So, first of all the jerkiness caused by the simple micro-switches meant that above speed 2 the acceleration imparted by the motors threw the arm backward so there was then a tendency for the motor to switch on and off rapidly and the arm would go into oscillation. Therefore, we devised a system whereby the same joystick now controls two potentiometers, and these go to a transistorised device which gives proportional speed control. This means that when the arm pushes the joy-stick forward it starts at a speed slightly below the bottom previously switch-control speed. This means that there is no tendency for the arm to be thrown into oscillation. Further movement of the arm forward progresses through to the full former speed obtained by the ordinary switches. The voltage drop by this system does not adversely affect top speed of the system.
Now we have proportional control over speed, and by pushing the joy-stick sideways the proportional characteristic also applies to the steering, so both speed and steering are now smooth.
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Guttmann, L., Maling, R. Demonstration of a special electric control for a power-driven wheelchair for high spinal cord lesions. Spinal Cord 3, 197–198 (1965). https://doi.org/10.1038/sc.1965.27
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DOI: https://doi.org/10.1038/sc.1965.27