Abstract: An optical detection system for a weighing scale includes an apparatus for generating a moire fringe. Unlike prior moire-type systems, however, the present scale is constructed with a substantially rigid tare, so that movement of the moire is limited to only a portion of one fringe line. Movement of the tare, and the pan carrying the load, are visually not apparent. Response time is greatly enhanced by the inventive system and accuracy is improved due to minimized hysteresis loss. The invention detects an optical shifting of the fringe line, rather than a counting of a number of fringe lines as with prior highly deflective scale systems.

Abstract: A weighing scale includes an optoelectronic system having apparatus for generating a moire fringe pattern and for detecting the moving of the pattern in accordance with scale tare deflection. One of a pair of ruled parallel grating sets is fixed with respect to the scale frame while the other is mounted for movement with the tare and close to and in a plane parallel with the fixed set. When a beam of light is projected through both grating sets in a transmissive mode towards a photodetector array the grating interference modulates the light beam into parallel moire fringes. Upon placement of a load on the scale, deflection of the tare results in movement of successive fringes across the photodetectors resulting in the sequential generation of weight indicative signals. The photodetectors are arrayed on and secured to a movable carrier which is adjustably positionable so that the effective spacings between the photodetectors corresponds to the spacings and proper phase angle required between said fringes.