Optical device provides a correct alignment for printing screen with

Abstract

Apparatus assures correct alignment of a plurality of cylindrical, patterned textile printing screens arrayed horizontally, parallel with one another in a sequence of screens on heads which are rotated by a drive. Optical encoders associated with the drive mechanism for each screen indicate the orientations of the heads as they rotate, and reflective markers are located on the screens with an edge in a plane perpendicular to the axis of the screens and in a predetermined relationship to the pattern to be printed by the screen. An overhead laser source scans the screens aimed at a rotating mirror aligned to reflect light from the laser source to scan the reflective markers on the screens to a light sensor. A computer receives signals from the orientation sensors and the light sensor, and a counter counts at a rate on the order of 10 megahertz and recognizes a reflective marker when light is detected by the light detector for a threshold number of pulses. A memory stores values indicative of a desired relationship of the timing of pulses reflected from the reflective markers and the timing of the orientation scanners, and a comparison means which compensates for non-simultaneous scanning of the reflective markers generates an error signal indicative of misalignments of the screens from one another when the received signals indicate a relationship that varies by more than a threshold amount from the stored values. A readout displays error data to permit an adjustment of the heads to reduce the error.