Optical sensing system for determining the angular orientation of weft

Abstract

An optical sensing system that detects the angular orientation of weft threads in a moving web of a textile has a sensor array that receives light transmitted through the web from a light source. A first lens system forms a converging light beam of generally uniform intensity directed at a normal to the web. A second lens system focuses the portion of the beam transmitted through the web onto the sensor array. Both lens systems can each consist of a single, circular, plano-aspheric lens. The second lens is preferably movable with respect to the sensor array to adjust the magnification of this system and has a low f number. The sensor array is preferably a single monolithic chip that includes a radial pattern of photosensitive areas that each generate an electrical signal proportional to the total intensity of the light incident on the area. The areas are elongated and narrow so the moving shadow of a weft thread passing over the area will modulate the output signal. The modulation is strongest when the thread is generally aligned with the area. Electronic circuitry generates a DC signal associated with each area that is proportional both to the magnitude and frequency of the modulation of the signal. The circuitry also compares these signals, selects the largest one, and generates an analog output voltage characteristic of the area associated with the largest signal. The circuitry optionally further includes a feedback circuit responsive to the selected maximum signal which controls a variable power supply for the light source and a switched gain amplifier responsive to extremes of light source voltage level.