GB749250A - An improved optical method of detecting change of orientation and means for providing a signal to indicate such change - Google Patents

Abstract

749,250. Automatic control systems. BRITISH RAYON RESEARCH ASSOCIATION. March 10, 1954 (Dec. 18, 1952], No. 32166/52. Class 38 (4). [Also in Group XL (b)] In a method of detecting change of orientation of an object which has a directional reflective characteristic and, if desired, straightening it, two beams of light are directed on to the same area or identical areas of the object so that the intensity of light reflected in a given direction is constant when the object has a datum orientation but fluctuates when the object rotates. The invention is described with reference to straightening the weft of a fabric surface W. As shown, light from a source 5 is split into two beams by an adjustable strip B movable by a screw 17 to adjust the relative quantities of light in the two beams. The beams are then focused by planar-convex lenses L1 which are capable of axial adjustment, to diaphragm D1 also in the focal planes of lenses L2, L3, each of which has attached to it one of polarizing discs Z2, Z3, the polarizing planes of which are at right angles. Between diaphragm D1 and polarizing discs Z2, Z3 is a rotating polarizing disc Z1 driven through gearing by a synchronous motor 23. A prism P directs the two beams of light leaving lenses L2, L3 on to the same area of the web. Light reflected by the web is focused by a lens L4 on to an aperture in a diaphragm D2 and thence on to a photomultiplier tube E. A ground glass screen G may be pivoted into position above the web for adjustment purposes. With this screen in position the shutter B is adjusted until the beams emerging from the prism are of opposite phase and of equal intensity. The ground glass screen is replaced by the weft and the photo multiplier output will vary in phase and of equal intensity. The ground glass screen is replaced by the weft and the photo multiplier output will vary in phase sense according as the weft is rotated to one side or the other of the correct orientation. Circuit.-The multiplier output is amplified in a conventional amplifier tuned to twice the fre. quency of the rotary disc of polarizing material. The amplified output is then applied simultaneously to the grids of a pair of thyratrons the anodes of which are supplied in anti-phase from the same A.C. supply as operates the synchronous motnr. Each thyratron includes an anode relay. Thus one relay or the other is operated depending on the direction of twist of the web and may operate the motor of a known electro-mechanical weft straightening device.