A control system for a printer

Claim 1

A control system for controlling the movement of a print head (22) mounted on a carriage (54) in a printer (12) including drive means (46,48) for moving said carriage (54) in a reciprocal manner along a rectilinear guide path, an elongate member (68) having a plurality of spaced openings (72) therealong and secured to the frame of said printer (12) so as to be fixed relative to said guide path and detector means secured to said carriage (54) and positioned to sense said openings (72) and to provide output signals when said openings (72) are scanned by said detector means, characterized in that said detector means (74) is arranged to generate output signals of first and second values dependent on whether or not said detector means (74) is sensing one of said openings (72), a change in said output signals between said values defining a signal transition and the time interval between consecutive signal transitions defining a signal transition period, and control means (76,78,80) for determining whether said carriage (54) has stopped in a correct predetermined position along said guide path, said control means (76,78,80) being responsive to said output signals for moving said carriage (54) in a predetermined direction for verifying said predetermined position of said carriage (54) dependent upon a pattern of signal transition periods monitored during said movement in said predetermined direction and for determining a jam condition indicating non-motion of said carriage (54) when a predetermined period greater than one expected signal transition period expires without the occurrence of at least one signal transition.