Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1988-05-26
1990-03-27
Evans, F. L.
Optics: measuring and testing
By polarized light examination
With light attenuation
356 1, 356375, G01B 1124, G01C 310
Patent
active
049115510
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The invention relates to an apparatus for determining the real or virtual distance of a light source from a measurement plane, with an optical image reproduction system, which images the light emanating from the light source as a light spot on the measurement plane, defined by a series of electrodes, of a charge-coupled semiconductor sensor, and with an evaluation circuit, by means of which, from the pulses of the pulse train which is retrievable from the charge-coupled semiconductor sensor, the position of the point of concentration of the light spot on the measurement plane and thus the distance to the light source is calculated by averaging.
BACKGROUND OF THE INVENTION
Apparatuses of the above kind are known. An apparatus with a linear analog sensor is described in European Patent Application No. 81 106 262 of the present applicant. This known apparatus is also represented in FIG. 1. The apparatus is denoted by 2 and contains an illumination unit 3, from which a light ray 14 emanates. This falls on an object of measurement 1. Reflected light ray 15 is projected onto the linear analog sensor 4 by an optical image reproduction system 5. If the distance of the object 1 increases from X.sub.0 to X.sub.1, then reflected ray 16 arrives on the linear analog sensor 4 through the optical image reproduction system 5. Each of the two reflected rays 15, 16 strikes the sensor 4 at a different point. Currents i.sub.1 and i.sub.2 produced by the sensor 4 are evaluated in an evaluation circuit 6 working in an analog manner for determining light spot position on the sensor 4. From this position the distance of the object 1 in relation to the apparatus 2 or the illumination unit 3 or the measurement plane of the sensor 4 can, in turn, be determined.
FIG. 2 shows the construction of the linear analog sensor 4 slightly more precisely. This consists of an elongated semiconductor chip 5 which is equipped with electrodes 6, 7 at both its ends. The measurement plane 8 extends between the electrodes 6,7. The electrodes are biassed relative to the semiconductor chip by a battery 13. The incident light rays 15 or 16 produce light spots 9 or 10 on the measurement plane 8. The light spot 9 is at distance (position) y.sub.i from the electrode 7. The light spot 10 is at distance (position) y.sub.k from the electrode 7. The currents i.sub.1 and i.sub.2 measured by current measuring apparatus 11, 12 depend on the position of the light spot on the measurement plane 8.
The linear analog sensor 4 shown in FIG. 2 has the advantage that it reacts to the slightest changes to the light spot on the measurement plane and because of this has a high resolution. On the other hand, it has the disadvantage that with incidence of spurious light it produces a false reading. If one imagines, for example, that the light spot 10 is created by an undesired reflected light ray, which also originates from the illumination unit 3, then the influence of the light spot 10 on the measuring result cannot be eliminated even if the light ray 14 emanating from the illumination unit 3 is modulated and demodulation is effected in the evaluation circuit 6 in FIG. 1. The linear analog sensor 4 reacts therefore to both light spots 9, 10 simultaneously, as it simply adds the minority carriers released by both light spots. The measuring result established in this way would lead to a falsely calculated position, which lies between y.sub.i and y.sub.k.
In order to avoid the disadvantage outlined last, a linear charge-coupled semiconductor sensor is used, as shown in FIGS. 4a and 4b, in place of the linear analog sensor. Such a linear semiconductor sensor is described, for example, in DE-PS 22 59 008. It is also known as a CCD-sensor (charge-coupled-device). FIG. 4a shows the linear charge-coupled semiconductor sensor 104 in section, while FIG. 4b shows it from above. It consists of an elongated semiconductor chip 112, which is covered by an insulating layer 113. On the insulating layer 113 there are arranged electrode triplets 114a to c
REFERENCES:
patent: 4522492 (1985-06-01), Masunaga
patent: 4701047 (1987-10-01), Eibert et al.
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