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Disclosed is a joystick apparatus for effecting a plurality of variable voltage changes using one or more partial spheres concentrically mounted on the joystick shaft having longitudinally or latitudinally variable, light-detectable surfaces. A first light emitter/detector combination senses a first Cartesian coordinate axis tilting movement of the joystick control shaft and a second light emitter/detector combination senses a second Cartesian coordinate axis tilting movement of the control shaft to produce corresponding first and second voltages indicative of joystick position in the respective Cartesian coordinate directions. A handle portion of the joystick is rotatable and connected for carrying, in the preferred embodiment, a second spherical surface concentric with the first, and having a latitudinally variable, light-detectable surface. A third light emitter/detector combination senses the rotational movement of the shaft to produce a corresponding third voltage output. A thumb control rod extending from the free end of the joystick handle may also be provided to achieve two Cartesian coordinate axes by tilting of the thumb rod with respect to a third axis and utilizes a miniature spherical surface of similar structure to the first spherical surface. Suitable orthogonal light emitter/detector combinations with respect thereto provide respective fourth and fifth voltage outputs. In a preferred arrangement, each of the emitter/detector combinations discussed above is preferably connected in a differential mode with another, in-line similar combination to minimize the effects of surface and component aging, eccentricities in initial mounting and the effects of wear in the mounting structures.
Fincher, Jeffrey L. (1985). Optical joystick. United States. Patent and Trademark Office; Texas A&M University. Libraries. Available electronically from