Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1994-03-30
1996-07-30
Allen, Stephone B.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
340556, G01V 904
Patent
active
055414036
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method in an optically operated proximity switch having at least one transmitter means for generating and sending a beam into the environment of the proximity switch in a first direction. The proximity switch is fitted with two groups of receiver means, both groups comprising at least one receiver means. According to the method, the receiver means of the first group are directed at least in one second direction deviating from the first direction in a way that the receiving direction of each receiver means intersects the beam of the transmitter means in the detection zone in the environment of the proximity switch. Thus the receiver means of the first group receive emission which is reflected from an object possibly in the detection zone, or scanning region, and derived from emission from the transmitter means. Further, according to the method, the receiver means of the second group are arranged to receive emission coming and/or reflected back from the background outside the detection zone of the proximity switch. In addition, processing means are used in the method by which the output signals of the receiver means of the first and second groups are processed and compared to monitor the situation in the area of the proximity switch.
A method similar to that presented above is in its essential parts known from the solution disclosed in U.S. Pat. No. 4,899,041. According to the publication, the proximity switch is fitted with lense systems arranged on both sides of the transmitter means, through which the emission reflected from the detection zone and from the background is reflected by a mirror arrangement on three parallel receivers. The two outer receivers receive the emission which is collected by the said lense system and correlates to the situation in the detection zone; correspondingly, the central receiver receives the emission which correlates to the situation in the background. Furthermore, the proximity switch is fitted with an electronic circuit for processing output signals from the said receivers for determination of the situation in the detection zone.
As described above, the method according to U.S. Pat. No. 4,899,041 with its technical application is based on utilizing lense optics and mirrors. A solution of this kind has the disadvantages of the high price of optics, the dependency of the optical properties on environmental conditions, and the regular service required of the optics. Moreover, the precise directing obtained by the lenses often results in a narrow cone of detection. Converging lenses can be used to obtain a longer distance of detection, but the detection zone becomes narrower, whereas diverging lenses (mirrors) can be used to obtain a wider detection zone, but the distance of detection becomes shorter. It is, of course, possible to extend and limit the distance of detection obtained by optical lenses either by increasing the radiation intensity of the transmitter means or by widening the light collection surface of the receiver means, whereby the emission entering the sensor of the receiver means increases in proportion to the surface areas of the lense and the sensor. The relative signal level of the sensor of the receiver means is high only when the optical emission is received by the sensor directly or at an angle of not more than a few degrees. It is clear that using either of the ways mentioned above, also the radiation transmitting and receiving angles become more narrow. It is also obvious that the use of lenses involves other problems in practice, in addition to the narrow detection zone. In particular, the properties of the lenses are vulnerable to changes in the environment. Consequently, dust collected and water possibly condensed on the surface of the lenses reduce the intensity and may change the focus of the lense, thus weakening the reliability of the detection of the object. In addition, high temperature changes and the weakening of the optics of the lense due to e.g. scratching as well as possible displacing of the lenses due to iner
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patent: 4532867 (1985-08-01), Mitchell
patent: 4709142 (1987-11-01), Dahl
patent: 4899041 (1990-02-01), Fetzer et al.
patent: 4973837 (1990-11-01), Bradbeer
patent: 5099113 (1992-03-01), Oi et al.
Heinonen Ilkka
Hellsten Markku
Malm Timo
Allen Stephone B.
Mitron Oy
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