Optics: measuring and testing – Of light reflection
Reexamination Certificate
2002-01-25
2003-07-08
Mathews, Alan A. (Department: 2877)
Optics: measuring and testing
Of light reflection
C356S238100, C250S227290, C362S551000
Reexamination Certificate
active
06590663
ABSTRACT:
The present invention relates to a reflectometer, comprising an illuminator in a 45°/0° configuration with a light source formed by a lamp and an illuminator optic, light emitted by the lamp being passed after reflection via a measuring opening into a housing and supplied to a measuring system contained therein, and the illuminator optic being formed by a number of light guides which start at the light source and end in the form of a rim with a conoidal emission side. More in particular, the invention relates to a reflectometer used in a construction as spectrophotometer, in which the measuring system can be conventionally formed by a spectrophotometer system with dispersion means, optical components cooperating therewith, and detection means.
Such a reflectometer is known from the international patent application WO 96/13709. For the illuminator in such a reflectometer designed as spectrophotometer, ISO standards have been set up; with respect to the measuring geometry for a reflection measurement the most recent ISO standards for color measurement, namely ISO-5-4:1995(E), give the 45°/0° configuration, in which in the annular influx mode the illumination has to be effected on all sides at an angle of 45 (±5)° and the reflection measurement at 0 (±5)°.
It is known to realize an illumination on all sides at an angle of 45° by means of one or more lamps or LED's which, provided or not provided with a lens, are directed from different directions to a specimen to be exposed. To comply with the most recent ISO standards, however, this requires a large number of lamps, which makes the construction of the spectrophotometer relatively expensive. It is also known to use one or more light sources in a diffusion chamber, the light radiating to the specimen at 45° via an annular opening. The drawback of this solution is that such a diffusion chamber occupies relatively much space, which adversely affects the cost price and the dimensions of the spectrophotometer. Furthermore, U.S. Pat. No. 4,320,442 discloses an annular illuminator in which a system of reflectors is used, which are rather complicated owing to their shape. In the spectrophotometer as described in the opening paragraph, use is made of an illuminator in which the illuminator optic is formed by a number of optical guides which start at a light source and end in the form of a rim with a conoidal emission side. Such a spectrophotometer is known from U.S. Pat. No. 4,464,054. In the manufacture thereof, a rather labor-intensive finishing and mounting of a plurality of light guides in the form of glass fibers is necessary, both on the side of the light source and on the conoidal emission side.
The object of the invention is to provide the spectrophotometer with an illuminator optic which can be made in a simple and relatively inexpensive manner, and which illuminator optic also complies with the above-mentioned ISO standards.
According to the invention the reflectometer as described in the opening paragraph is characterized in that the illuminator optic consists of one group or of several groups of light guides, a group of light guides being made in one piece of plastic, said one piece having an entrance area, a transition area for gradually merging the entrance area into a number of mechanically separated light guides and an annular emission area in which the light guides are mechanically connected with each other. This solution enables inexpensive mass production of the illuminator optic, in particular by using injection molding techniques. It may be noticed that from U.S. Pat. No. 4,518,259 an illuminator optic, made from plastic, is known per se.
The illuminator optic is based on the principle of total internal reflection in the light guides; as a result of the difference ill refractive index with the surrounding air. This ensures that light radiated in can be transported practically without losses, as long as the geometric conditions for total reflection remain satisfied. In connection therewith, it is important that the illuminator optic contacts the further housing of the spectrophotometer in as few places as possible.
In connection with the geometric conditions imposed on the light guides, the composition of the material of the light guides, their thickness and curvature are adjusted to the angles at which light can enter the glass guides in such a manner that the requirements for total internal reflection are nearly completely satisfied.
For each group of light guides a lamp could be present. From considerations of cost, however, it is preferred to make use of only one lamp. Similarly, it is preferred if the illuminator optic is formed by only one group of light guides. The illuminator optic may then be formed by, for instance, one single injection molded part.
Preferably, the lamp is rigidly connected with the illuminator optic. Not only does this result in a saving of mounting cost, but an accurately positioned fastening method for the lamp with respect to the illuminator optic is obtained. The lamp can be directly attached to the illuminator with optically bright cement, thereby excluding both light losses through reflections and through possible soiling and alignment errors, while, furthermore, the stability of the light intensity radiated in becomes insensitive to unintentional displacement of the lamp. When using a separate lamp foot or supporting construction, displacements can be caused by, for instance, vibrations and warming up.
In a preferred embodiment the lamp is formed by a Xenon flash tube. Such tubes have advantages over the light bulbs frequently used in known spectrophotometers. The emitted light properly corresponds with daylight, while light bulbs contrarily have very little blue light and even less UV-radiation. In particular if the detection means are provided with silicon photodiodes, which actually have a low sensitivity to short wavelengths, in particular blue light and UV-radiation, Xenon flash tubes form an ideal light source. The cost price is low and the light output is high. If the flash power is properly selected, the life can be tens of millions of pulses. The diffuse light from a Xenon tube, however, cannot be simply directed to a specimen, while through their dimensions and shape and the required high-voltage feed they cannot be simply arranged close to a specimen either. To comply with the above-mentioned “annular 45°/0° ISO standard”, diffusion chambers, various reflectors and so-called integrating spheres were used in the past. All these solutions, however, are relatively expensive and occupy much space, with the result that a Xenon illumination is particularly used in larger and more expensive apparatus. The illuminator optic according to the invention, however, offers a solution for the use of Xenon flashlight which occupies little space and, moreover, can be made and arranged at low cost. The possibilities of the illuminator optic, however, are not limited to the combination with a Xenon tube. Also when using it with other sources, tubular or not tubular, a high illumination output can be obtained for an “annular 45°/0°” illumination with a form of the entrance area adapted to the light source, while only one light source is required or one LED of each color to be used.
The lamp is preferably tubular and completely surrounded by a reflector with the exception of a slit on the side of the entrance area of the illuminator optic. The Xenon tube may, as already mentioned, be glued to the entrance side of the illuminator optic. By further surrounding the lamp by a reflector, it is achieved that as little light as possible is emitted in directions other than to the illuminator optic.
In a specific design the light entrance of the entrance area of the illuminator optic has a rectangular cross-section with a thickness greater than that of the channels. The transition area following the light entrance provides a conical course, the channels, with decreasing thickness of the entrance area, being formed from the rectangular cross-section while diverging widthwise. This des
Mathews Alan A.
Spectrostar B.V.
Swanson & Bratschun L.L.C.
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