Optics: measuring and testing – By shade or color
Patent
1990-05-09
1992-07-14
Evans, F. L.
Optics: measuring and testing
By shade or color
356400, 356407, 356425, G01J 350, G01N 2127
Patent
active
051297264
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an apparatus for colour control of an object, the apparatus containing a light source for illuminating the object and a detector for filtering and measuring the light reflected from the object.
In industrial colour control or colour sorting it is often necessary to control objects which move with a great velocity, have different sizes, are hot or wet or are difficult being into contact with colour control equipment for other reasons. It is therefore desirable that the colours of the objects can be controlled at a distance.
It is known, e.g. from German Patent DE 3 244 286 to perform colour control by illuminating an object with light from a pulsed source of light, whereupon the reflected light is detected. The reflected light is imaged through a lens system on a sensors of the detector unit. Since the light source is pulsed, light having another timewise variation may be filtered by suitable signal processing. The detected light is then compared with a reference signal from the pulsed object source, the colour of the light is determined.
CH 612.760 relates to an optical system, where an object is illuminated by obliquely incident light, and where the reflected light is collected by a lens system and passed to sensors through an optical fibre system.
It is a problem in colour measurement that the colour detectors have a finite light-sensitive area. The sensitivity in this area is constant for an ideal sensor, but in practice the sensitivity of the sensors can vary very strongly even within small distances of the light-sensitive area. This gives problems when an object point is imaged in an image point. Thus, the detected light intensity will depend upon the position of the object, where even small changes in the position of the object will entail that different light intensities are measured. Since known colour measuring devices, where the measurement takes place without contact between the object and the detector, mainly image the object on a plurality of sensors, it will be impossible to obtain a constant colour measurement when an object, e.g. a shrimp, passes through the measurement area on a conveyor belt, or if the measurement area is very large, e.g. 1 m.sup.2. When imaging is performed on the sensors, a non-controllable, weighted averaging of the colour of the measurement area is effected. In addition, a lens system is to be trimmed to minimize the chromatic aberrations. To minimize these aberrations it is known to use an aperture diaphragm so that the used part of the lenses is limited, thus reducing the light intensity. For the measurement area to be imaged on, e.g. three detectors, the system must be strictly symmetrical.
Another problem associated with prior art apparatuses is that it is not possible to perform colour measurement where the object and the detector/light source are separated by a great distance. Thus, the close proximity of the detection/light source to the object in prior art apparatuses poses a cleaning problem when the colour of wet or dusty objects, e.g., fish, shell fish, chips, egg white, etc., on a conveyor belt is to be measured. Additionally, objects having different thicknesses pose problems if their mutual thickness variation is not small with respect to the measurement distance. Such a variation causes problems. In particular, in a system where the measurement is imaged on the sensors.
For objects to be conveyed with an even speed it is necessary to perform simultaneous colour measurements.
In the prior art it is often a problem that the useful wavelength range is small. This band limitation is caused by the fact that the known colour measuring apparatuses contain different sophisticated components whose losses are wavelength dependent, e.g. imaging components. Frequently, it may be advantageous to have a measurement range from 300 nm (ultra violet) to 2000 nm (infra red) at disposal.
Therefore, the object of the invention is to provide an apparatus which is capable of giving reproducible measurements of a colour of an object, irrespective of t
REFERENCES:
patent: 4131540 (1978-12-01), Husome et al.
patent: 4171909 (1979-10-01), Kramer et al.
patent: 4546700 (1985-10-01), Kishner et al.
patent: 4647211 (1987-03-01), Browne
patent: 4721389 (1988-01-01), Dejaiffe
Evans F. L.
Keire Fred A.
McConoughey David M.
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