Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1992-05-15
1994-04-12
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356 4, G01V 904
Patent
active
053028198
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of detecting an object, comprising the steps of: generating radiation by means of a source of radiation; emitting the radiation in the direction of the object; and detecting a first radiation component at a first angle of deflection of substantially 180.degree..
The invention further relates to apparatus for carrying out the method.
Such a method and apparatus are disclosed in U.S. Pat. No. 4,339,660, and are used to detect the presence of the object in the detection field of the apparatus. In the known method and apparatus, light is emitted to a retro-reflecting mirror, and the light retro-reflected by the mirror is detected.
The known apparatus is of the type sometimes called "light barrier". Its operation is based solely on the interruption by a given object of a beam of radiation reflected at a fixed reflector, in which arrangement the detector does measure radiation when no object is present in the detection field, and does not measure or detect radiation when an object is present in the detection field , that is to say, when an object interrupting the light beam is present in the light path between the transmitter and the mirror and/or between the mirror and the receiver. The detected signal generated by the presence of the object can be processed further for control purposes, for example, to increase the position of a counter (for instance for monitoring production).
A disadvantage of the known method and apparatus is, however, that no selective detection of objects is possible, that is to say, that the presence of an object in the detector's detection field is detected irrespective of its nature and identity.
A further disadvantage of the known method and apparatus is that they only enable a yes
o detection of an object, that is to say, there is only a discrimination between a presence situation, in which the light beam is interrupted by an object, on the one hand, and an absence situation, in which the light beam is not interrupted by an object, on the other More specifically, the known method and apparatus do not enable detection of the position of the detected object.
There are also prior methods and apparatuses for detecting an object, in which the detection is based upon the reception of light reflected by the object to the detector, and in which the detector does not detect radiation when the object is absent. A disadvantage experienced in that arrangement is that the detector does not discriminate between the radiation reflected by the intended object, on the one hand, and ambient radiation and/or radiation reflected by any other objects, on the other, so that selective detection is not possible or not reliably possible.
Generally speaking, the above data obtained from the detected radiation are sufficient for detecting whether an object is present in the detection field of the apparatus, for example, for counting purposes or protection purposes. It may be desirable, however, to increase the accuracy of the detection. In case the system is to be used for counting purposes, a problem may be that a detected object, due to its shape, reflects the beam of radiation more than once in the direction of the detector, so that the counter position is increased by more than one by the object.
It may also be desirable to increase the selectivity of the detection. Thus, when the system is used for counting purposes, it may be desirable to detect certain objects and not to detect others. Also, for example, for robot vision or other automation applications, it may be desirable to detect a given object from a collection of different objects. This is not possible with the data obtained by the prior methods, because these data do not contain information about the identity of the detected object. Moreover, it is possible that the measurement is disturbed by ambient radiation and/or by radiation reflected at spurious objects.
This can be solved by analyzing the spectral contents (colour) of the reflected signal, but colour recognition is not generally a water-tight method of
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Nelms David C.
Shami K.
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