Abstract: Apparatus for measuring stress at a point on an object comprising: means for applying a cyclically varying load of period T to the object; detector means for collecting and measuring thermal radiation from said point over a sample time interval t, wherein t<T; means for determining the phase of the first interval t with respect to the cyclic variation of thermal radiation produced by said point in response to said applied load and, from said collected and measured value of thermal radiation and said phase, for providing a measure of stress at said point.

Abstract: Apparatus for measuring the distance from the apparatus to a surface comprising means for passing a beam of light to the surface at an angle other than normal, means for receiving light reflected from the area of the surface illuminated by the beam and means for measuring the movement of the received beam whereby to measure the position of the surface area, means being provided to scan the surface.

Abstract: An optical inspection system for determining various features of, for example, painted surfaces, by analyzing light reflected from the surface in a plurality of ways. In one case the cross sectional diameter of a beam of radiation, which gives information regarding the surface, is measured by passing the beam through a filter means (104) having transmissive and absorptive portions (107,108), the arcuate width at each radial distance from the optical axis (100) being such that there is a predetermined relationship between the diameter of the beam and the amount of radiation passed by the filter.

Abstract: Apparatus for measuring surface defects or the distance from the apparatus to a surface comprising means (37,38,43,44) for passing a beam (48) of light to the surface (11) at an angle other than normal, means (51) for viewing the area (47) of the surface (12) illuminated by the beam (48) and means (53-50) for measuring the movement of the illuminated area (47) whereby the measure the position of the illuminated area (47), means (17) being provided to rotate the apparatus and means (53) being provided to derotate the image of the illuminated area so as to enable, for example, the interior of cylinders (10) to be inspected.

Abstract: Apparatus for detecting discontinuities in a radiation diffusing surface (10) such as paper. Radiation is passed to the surface and a radiation collector (19) receives the diffused radiation (18) from a limited area of the surface (10). The radiation collector receives the diffuse radiation from a limited area only and from within predetermined angular limits other than normal to the surface. The radiation collector (19) defines said predetermined angular limits through total internal reflection.

Abstract: Apparatus for comparing a test surface 23 with a reference surface 8 comprising detector means 16.17, a test channel TC for receiving radiation from the test surface 23 and a reference channel RC for receiving radiation from the reference surface 8. A selector means 12 is provided to pass radiation from the test channel means TC and the reference channel means RC to the detector means. Varying means 5 is provided to vary the radiation passed along the test channel TC and reference channel RC. Cycle means is provided to cycle the selector means 12 between a first state in which more radiation from the test channel TC than the reference channel RC is passed to the detector means and vice versa. Control means is provided to control the radiation varying means 5 to provide a zero or minimum variation of radiation received by the detector means as the selector means 12 is cycled.

Abstract: An inspection apparatus for inspecting, for example, sheet material, in which a beam of radiation 12 is scanned across a sheet 13 by means of a first facet 41 of a rotating mirror drum 22. Scattered radiation from the sheet is received by a second facet 46 and 2 is passed to a photodetector 49 for analysis.

Abstract: A beam of radiation is scanned across a sheet 13 and is either reflected therefrom or transmitted therethrough. Faults in the sheet 13 deflect, scatter or alternate the beam which is then passed to a retroreflector screen 24 where it forms an image 15. Analysis of the image 15 is carried out via the scanning means 22 to determine the faults in the sheet 13.

Abstract: A method and apparatus for producing an aspherical surface, for example, an aspherical optical surface, on a workpiece, on which the workpiece is rotated about a first axis, a cutting tool is rotated about a second axis, and at a radial distance from the second axis, and the second and first axes meet at a point and at an angle with respect to one another, the second axis being moved with respect to the first axis so that the point moves along the first axis and the angle changes.