Article positioner with zero position sensing means

Claim 1

In an article handling system comprising an X-Y table for supporting and moving the article, selectively actuated reversible X and Y stepping motors for moving said table in small increments to position the article in only one lineal direction along X and Y axes relative to zero positions on said axes, and motor control means responsive to digital control command signals including ones specifying the direction and extent of incrementing movement, to clock signals and to a GO signal, said table comprising a stationary first member, a second member mounted on said first member for movement along said X axis, and a third member mounted on said second member for movement along said Y axis, the improvement comprising the combination of: X and Y zero position sensing means for detecting and defining said zero positions on said X and Y axis, each of said sensing means comprising an opaque plate mounted on one of said members and having a first track including a first edge adjacent a cutout extending in one direction of movement and a second track including a second edge adjacent an opaque portion extending in said one direction of movement, said first and second edges extending perpendicularly to said one direction of movement, light source means mounted on another of said members on one side of said opaque plate, first and second light detectors mounted on said another of said members on the other side of said plate and providing output signals proportional to the amount of light received thereby, said detectors being respectively aligned with said first and second tracks, whereby relative movement between said one and another of said members produces a relative movement between said plate and said light source means and said detectors, said plate, light source means and detectors being located to establish a zero position whereby the output of one detector increases while the output of the other detector decreases due to movement of said first and second edges between said light source means and said detectors, and first circuit means connected to said detectors for comparing said output signals and providing a zero position signal when said output signals have a predetermined ratio; a command register for receiving digital command signals defining the direction and extent of movement, said command register being connected to said motor control means to supply said command signals thereto whereby said motors are actuated solely in response to said command signals and to said GO signal; and second circuit means connected to said first circuit means and being operative to inhibit actuation of said motors in response to said zero position signal, to thereby position said table in said zero positions.