A workpiece shift apparatus includes a bottom plate, a middle plate slidably attached on the bottom plate, and a top plate slidably attached on the middle plate and defining cutouts. In one embodiment a column assembly is disclosed, comprising a first column portion and a second column portion. A transistor is turned on and off by the pulse signal having the buzzer-driving frequency. Electrical signals are transmitted from the camera to the projector, the electrical signals being indicative of the position of the illuminated area in relation to the projection surface.