Two dimensional surface motion sensing system using registration marks and linear array sensor

In a xerographic printing apparatus having a photoreceptor belt for developing images thereon, said photoreceptor belt having optical sensing marks, and said photoreceptor belt having a primary movement direction, said xerographic printing apparatus also having a photoreceptor registration system for the registration of said photoreceptor belt relative to said images on said photoreceptor belt, said photoreceptor registration system including at least one sensing marks sensor for optically detecting the movement of said optical sensing marks of said photoreceptor belt, the improvement wherein;

• said optical sensing marks of said photoreceptor belt have at least one edge extending transversely of said primary movement direction and at least one other edge extending at an angle to said primary movement direction, and
• said sensing marks sensor comprises a linear array of a multiplicity of individual optical sensors which optically detect said optical sensing marks to provide positional signals in said primary movement direction from said at least one edge extending transversely of said primary movement direction and also provide positional signals orthogonal to said primary movement direction from said at least one other one edge extending at an angle to said primary movement direction by respective said individual optical sensors actuated by the movement of said surface in said primary movement direction in between said at least one edge extending transversely of said primary movement direction and said at least one other one edge extending at an angle to said primary movement direction.