Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-04-12
2001-05-22
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S555000
Reexamination Certificate
active
06236038
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an optical barrier formed of a set of optical emitter and receiver elements, comprising elements emitting or receiving optical beams.
DISCUSSION OF THE BACKGROUND
Optical barriers, also called immaterial barriers, are used particularly to protect operators working near dangerous machines. These barriers are usually composed of a set of contiguous individual beams defining a detection plane. The beams are laid out systematically, since this is necessary to define a detection sensitivity. This sensitivity represents the ability of the barrier to detect intrusion of an obstacle into the barrier. For example, in tests it can be defined by simultaneously blanking off two beams. But it must be certain that the blanked off beams are not replaced by light falling on receivers originating from other beams.
Most barriers used at the present time use one or several light pulses for each beam, in order to setup an emitter receiver dialogue. These pulses are repeated identically for each beam in one or several barriers. The result is the following disadvantages that can result in serious weaknesses:
lack of certainty about the synchronization of beams between sending and receiving,
risk of loss of sensitivity,
possible interference when several barriers are installed close to each other,
when a failure occurs, it is impossible to know which side is causing it (emitter or receiver).
The operation of a barrier may also be disturbed by parasite reflections of a beam, such that the beam, or a beam forming part of another barrier, is reflected onto its receiver.
These situations may become very dangerous if a barrier is thus completely or partially neutralized by parasite signals.
In general, the problem of reliability and consequently safety of a light barrier depends on the ability to know with certainty that the beam received by a receiver is actually the beam emitted by the emitter associated with it.
It would undoubtedly be possible to identify each beam by a unique code, but this type of solution would require calculation means incompatible with industrial and economic constraints.
OBJECTS OF THE INVENTION
The purpose of this invention is to develop a safety light barrier that can be made with simple means and which can be used particularly to automatically and cyclically verify correct operation.
SUMMARY OF THE INVENTION
Consequently, the invention relates to an optical barrier of the type defined above, characterized in that:
A—each barrier is identified by a number with hexadecimal digits,
B—emitter and receiver elements associated with each other through their beam are grouped into modules with not more than 16 emitter and/or receiver elements,
elements are in order in each module and are distributed into a group of one or several first elements (beams), and a group of several second elements (beams),
elements emit/receive beams in accordance with words formed of pulses.
C—words are formed of binary pulses coded for their identification, and their work cycle is close to or equal to one.
D—elements of modules of a barrier are coded to assign a word to each element (beam):
by assigning an elementary binary code to each first element (beam) taken in the order of the modules, and to each second element (beam), the elementary binary code being obtained by:
transcription of the digits of the hexadecimal number of the barrier into binary code, giving a sequence of binary digits,
assignment of the binary digit of the binary sequence of the transcribed number, to each position in a module,
by defining a set of groups of two words for the first module elements and associating two words with the first element of each module, and selecting from these two words the word which has the same elementary binary code as was assigned to the first element of this module, and
by defining a group of two words associated with each of two binary states, for all second elements in all modules, and by associating the word with the same elementary binary code that was assigned to the second element, with this second element.
Thus in this barrier, each beam is identified by a number, which is consequently a pair of numbers for the second beams and is a single number for the first beams. The first beam in each module of a barrier has a unique code in the barrier, and a quasi-unique code between two barriers since the number of the barriers is different and therefore its binary state is different.
The second beams each have a code, in other words a word that actually corresponds to a double code; the module code which is actually the code of the first beam and the code of the beam inside the module. In order to simplify the description, the first beam or beams are the first beams of a module and the second beams are the other beams of the same module. But the first beams could occupy a different location, for example they could be nested in the second beams. On reception, the situation will be same since the reception module will have receivers associated with the emitters under the same conditions.
In general, given the bijective association between an emitter and a receiver or group of receivers, the concepts of the position of an emitter or of a receiver in a module, and the beam between the emitter and the receiver, will be considered as being equivalent in the description of the invention.
The modulation of the beam by the code assigned to it can be used to determine if the beam received by a receiver is actually the beam that was intended for it. This beam which is intended for it may be either the beam emitted by the emitter associated with this receiver which corresponds to normal operation of the barrier, or it may be the beam emitted by another emitter but intentionally redirected or received by this receiver if the barrier is being scanned obliquely.
Usually, but not necessarily, emitters and receivers exchange a beam in which the modulation for the word defined above is specific to the beam. This operating mode corresponds to a barrier with a very fine resolution or sensitivity.
Beams can also be grouped in pairs, or possibly in groups of three.
In this case, the beams in each pair or triplet will be modulated by the same code word defined as described above for a single beam. This is applicable to the first and second beams.
In general, beams are emitted in sequence by the different emitters in the same module or different emitters in all modules, following cyclic repetition in a given order for the first and second beams in the same module and the sequence of modules such that the beams can be recognized perfectly by the control circuit that manages the associated receivers.
For controls or modifications to the structure of the barrier or its sensitivity, the association between emitters and receivers can be modified simply by changing the scanning program (association of beams between an emitter and one or several receivers) in the optical barrier control and management circuits.
According to other advantageous characteristics:
the number of each module comprises any N=4 hexadecimal digits and the elementary number of positions in each module is equal to not more than 4 N=16;
each word is 8 digits long and it is preceded and terminated by a word start bit and a word end bit.
This choice of the number of digits making up the barrier number provides a large number of coding possibilities such that barriers composed of 16 modules each with 16 beams are possible, which covers almost all cases that may be envisaged.
For checking, it is particularly advantageous to perform oblique optical scanning making use of the optical defect that consists of natural divergence of the beam.
REFERENCES:
patent: 4650990 (1987-03-01), Jonsson
patent: 5015840 (1991-05-01), Blau
patent: 5218196 (1993-06-01), Dogul et al.
patent: 0 797 109 (1997-09-01), None
patent: 2 278 916 (1994-12-01), None
Le Que T.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Schneider Electric SA
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