The present invention refers to an optical distance detecting or measuring device, comprising a light source with an emitting optic for projecting a light beam according to the axis of the emitting optic onto a target to be measured and a first detector defining the receiving axis contained in the same reference plane as the emitting axis.
Prior art devices including optical reflection sensors with background suppression or distance measuring devices generally make use of the triangulation principle described by FIG. 1. Beyond a maximum distance, the operation of the sensor is impaired due to the fact that the angular sensitivity decreases with the distance. When attempting to increase this distance, the result is an enlargement of the dead zone which excludes an operation in the proximity of the sensor.
In order to adapt this limited measuring range to varying situations, certain manufacturers use an adjustable mirror that allows the best adaptation of the measuring range. Such a solution is e.g. described in U.S. Pat. No. 3,759,614.
Other solutions are known as well: Different references such as GB-A-2 069 286 and DE-A-196 19 308 suggest a pulsed emission and an analysis of two receiver channels. DE-A-24 55 733 alternatingly uses two lighting optics located in the same plane. DE-C-40 04 530, DE-C-40 40 225, DE-C-41 40 614 as well as DE-C-198 08 215 suggest that a plurality of alternatingly emitting light sources are provided in the same optical channel. The receiver channel is formed by multiple detectors or by a position-sensitive detector, e.g. PSD, the electronic circuit being capable of processing the signals corresponding to each one of the light sources to obtain information concerning the distance to the target. A sophisticated treatment of this information allows a slight extension of the range of the measuring system.
However, the inherent limitations of the principle of triangulation between elements that are situated in the same plane as defined by the optical axes of the emitting and receiving systems do not allow a substantial improvement of the performance with respect to distance, linearity, and the dead zone. Thus, in the case of a measuring sensor or of a background suppression triangulation sensor, a calculation of the ratio between the maximum detection distance and the minimum distance of the measuring range yields a quality number that is rarely greater than 5. On the other hand, such detectors are very often sensitive to the amount of light reflected by the target, which depends on the texture and the color of the latter.
On the background of this prior art, a first object of the present invention consists in substantially improving the results of measurements by triangulation without the need for complex analyzing circuits. This is accomplished by an optical distance detecting or measuring device wherein said device comprises at least a second detector that is aligned with the first detector on an axis contained in a plane that is inclined at an angle with respect to the reference plane, said angle being comprised between 10° and 170°.
A second object is to allow the realization of efficient measuring or background suppression sensors having small dimensions. This is accomplished by an optical distance detecting or measuring device, comprising a light source and receivers, wherein the light source emits light pulses of different intensities that are intended alternatingly for each one of said receivers, the emitted intensities being regulated in such a manner as to produce signals having identical amplitudes or corresponding to a predetermined function on the receivers, and an optical distance detecting or measuring device, comprising a sensor with a single lens including distinct emitting and receiving sectors, each sector being provided with a prism for focusing the light beams on the emitting and the receiving elements, respectively.
The invention will be explained in more detail hereinafter with reference to the accompanying drawings.
In
The detecting system is thus formed of an assembly of two or more detectors, and the same detecting function can also be realized by a position-sensitive detector such as PSD. The electronic circuit processing the signals delivered by the detectors will determine the position of the luminous impact and deduce the information of the measured distance from that position.
The performance of such an arrangement depends on the number of detectors and on the space therebetween, as well as on their position with respect to the emitting optic. With regard to basis X, which is defined as the distance between the emitting optic and the receiving optic, it appears that the measuring range M is limited and the dead zone Z is large. Linearity is affected by the sensitivity of the detectors to angular variations of the incident beam, which decreases as the distance from the target increases.
The present invention provides a different arrangement of the detectors. The novel arrangement is shown in
It will be shown that when an additional detector 5, defining a new receiving axis Or1, is situated in a plane B that is inclined at an angle α with respect to reference plane A, the intensities measured by the detectors allow to obtain a highly linear information in function of the distance in a large measuring range. The optimum value of inclination α is 90°, but any other inclination α between 10° and 170° is advantageous. In the text, reference will be made to 90°, while it is understood that the angle α may be different.
If the ratio between the intensity of principal receiving beam i and that of secondary beam i1 is calculated and this ratio is represented in function of the distance d measured between the detector and the target, the diagram of
In order to obtain these results, it is important that the envelope curves of the beams are as cylindrical as possible. This must be the case over a distance corresponding to the measuring range. To this effect, the real rather than the punctual dimensions of the source and of the detectors must be taken into account. The distances between these components and the lenses must be adapted to the focal distances in such a manner that the beams are as close to the cylindrical shape as possible.
A device realized according to this principle, comprising an emitter LED and two receiving photodiodes, is suggested and schematically described by
The described principle, according to which the alternating emitting intensities E3 and E5 are regulated such that the respective amplitude of the signals R3 and R5 measured by each one of the receivers are identical or correspond to a predetermined function, applies both to an optical device where the photodiodes are situated in the same plane as the emitter diode or in an inclined plane.
However, the advantage of this principle combined with the advantage of the inclined plane results in a particularly advantageous device.
An example of a compact sensor that is adapted for realizing a device according to
The solutions according to
The preceding demonstration of the performance of a measuring system based on one emitter and two detectors may be extended to a greater number of detectors and also to a position-sensitive detector such as PSD, whose axis of sensitivity may be situated either in the plane A defined by the emitting axis and the reference receiver axis, or inclined at an angle α, preferably at 90°, with respect to the plane A.
The principle described above is also applicable in the case of the measuring system of
Number | Date | Country | Kind |
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02405556 | Jul 2002 | EP | regional |
Number | Name | Date | Kind |
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3759614 | Harvey | Sep 1973 | A |
4384199 | Ogino et al. | May 1983 | A |
4976543 | Scheck et al. | Dec 1990 | A |
5109161 | Horiuchi et al. | Apr 1992 | A |
5137350 | Misawa et al. | Aug 1992 | A |
5519204 | Rudd et al. | May 1996 | A |
6636300 | Doemens et al. | Oct 2003 | B2 |
Number | Date | Country |
---|---|---|
24 55 733 | May 1976 | DE |
40 40 225 | Jan 1994 | DE |
41 40 614 | Mar 1994 | DE |
196 19 308 | Nov 1997 | DE |
40 04 530 | Jul 1999 | DE |
198 08 215 | Mar 2001 | DE |
0 419 082 | Mar 1991 | EP |
0 843 155 | May 1998 | EP |
2 069 286 | Aug 1981 | GB |
WO 9821550 | May 1998 | WO |
Number | Date | Country | |
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20040066499 A1 | Apr 2004 | US |