X-Y Position input device for display system

Claim 1

An X-Y input device comprising a rotatable ball, a first driven roller held in contact with said rotatable ball and rotatable in response to rotation of said rotatable ball, a second driven roller held in contact with said rotatable ball and rotatable in response to rotation of said rotatable ball, said second driven roller having an axis of rotation extending substantially perpendicularly to that of said first driven roller, first angle detector means for detecting an angle of rotation of said first driven roller, second angle detector means for detecting an angle of rotation of said second driven roller, and a casing housing said rotatable ball, said first and second driven rollers, and said first and second angle detector means, said casing having a lower opening with said rotatable ball partly projecting downwardly therethrough for rolling movement on a base, said casing having at least one rejector projection having a free outer end on a lower surface thereof for rejecting foreign matter on said base to prevent said foreign matter from reaching said ball, said projection being integral with the casing at said lower surface and being an annular shape surrounding said opening in said casing, wherein the said free outer end of said projection and the contact point of said ball with said base are essentially in the same plane when the case is moved.