Monitoring apparatus

Claim 1

Compact monitoring apparatus, in particular for monitoring for holes or surface defects in webs or the like, the apparatus comprising a light transmitting device including a laser light source for projecting a light curtain towards a surface under investigation; light receiving means for receiving light reflected from said surface and for directing the received light to photoelectric detection means; a housing having a central plane of symmetry, said housing containing said light transmitting device and said light receiving means; and an electronic processing circuit for evaluating signals from said photoelectric detection means to signify the presence and/or nature of a defect in said surface; said light transmitting device comprising a plurality of inclined strip-like dividing mirrors arranged one behind the other in first and second rows in an alternating sequence, wherein the end regions of adjacent dividing mirrors of the sequence overlap in the direction of the rows and said first and second rows are disposed on respective sides of said central plane of symmetry, and means for scanning light from said laser light source to form first and second scanning light beams which are incident on respective ones of said rows in the directions of these rows and which are deflected through substantially 90° by said dividing mirrors to form said light curtain; said light receiving means comprising a plurality of light gathering devices associated one with each of said dividing mirrors and arranged in first and second rows parallel to said first and second rows of dividing mirrors on either side of said central plane of symmetry of the apparatus wherein the light gathering devices are positioned closely adjacent the associated dividing mirrors, said light gathering devices and said dividing mirrors are located within said housing, said photoelectric detection means comprises at least one photoelectric detector in respect of each light gathering device; wherein cylindrical lens means are positioned in said light curtain with first portions on either side of said central plane of symmetry to direct said light curtain onto said surface and with second portions extending to either side of said central plane of symmetry beyond said dividing mirrors to direct light reflected from said surface to said light gathering devices, the apparatus further comprising a guide drum for guiding a web or the like under investigation past said housing, said guide drum having an axis lying parallel to said rows and lying in said central plane of symmetry and having a predetermined radius such that light passing through said first portions of said cylindrical lens means, impinging upon the surface of said web or the like under investigation at said guide drum, and being specularly reflected thereby will impinge upon said second portions of said cylindrical lens means to be directed to said light gathering devices.