Assembly fixtures for mass producible weight measuring system

Abstract

A mass produced weight measuring system includes an optical transducer for determining the displacement of a scale load support structure with respect to a scale frame. The detector includes a transducer subassembly which carries a plurality of photodetectors positioned at the end of a light path which is modulated by a pair of optical gratings. One of the gratings is fixed relative to the scale frame, and the other is mounted to the load support structure in alignment with the fixed grating. To facilitate mass fabrication, the optical transducer is produced and both gratings adjusted for alignment as a subassembly unit independent of the scale frame and load support structure; the clearance between the grating planes is set and the movable grating temporarily fixed. Grating adjustment is facilitated by a clamping jig which mounts on the transducer. The jig includes two adjustment screws which contact an edge of the movable grating. Nonlinearities in scale load support deflection inherent with the scale linkage and providing components other than true vertical deflection are compensated by predetermined placement of the grating angle from a horizontal plane. During scale assembly, the scale frame and load support structure are placed in a main fixture, a transducer subassembly unit is selected, mounted to a subfixture and the grating planes referenced to scale assembly reference planes; then the transducer body is epoxy potted relative to the frame and the movable grating potted relative to the tare structure. The movable grating is then freed for movement relative to the transducer body.