Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1995-06-07
1997-06-17
Le, Que
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250214B, 340556, G01V 800
Patent
active
056400063
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a high safety fail-safe multi-axis light beam type sensor, wherein multiple light emitting elements and light receiving elements arranged so as to face each other across a danger region to be monitored, are sequentially synchronized to be scan driven. When light beams from the light emitting elements are received by the light receiving elements, an output of logic value "1" is generated indicating a safe situation with nothing present in the danger region, while when the light beams are not received, an output of logic value "0" is generated indicating a dangerous situation with something present in the danger region.
BACKGROUND ART
Multi-axis light beam type sensors such as disclosed in U.S. Pat. No. 4,309,693 have been adopted as one method of ensuring the safety of an operator in situations such as where the operation of an industrial machine such as a press is carried out manually by the operator.
With such multi-axis light beam type sensors, a danger region wherein it is dangerous for the operator to be present when the machine is operating, and a safe region wherein it is safe to be present are prescribed. At the boundary between these regions, a plurality of light emitting elements and light receiving elements are arranged facing each other so that light beams from the light emitting elements are emitted towards the light receiving elements. When a portion of an operator's body blocks at least one of the light beams so that a light received output is not generated from the light receiving element, it is judged that an operator has entered the danger region, and the machine is stopped to thus ensure the safety of the operator.
In order to construct a fail-safe light beam type sensor however, there are three important signal treatments essential to the construction, as discussed below: signal.
As shown by oscillations between B1 and B0 in FIG. 1, the output signal from a light transmitter T (light beam B) is transmitted to a light receiver R, as an alternating signal wherein a light present condition (B1) and a light absent condition (B0) are output alternately. With this method, as seen from the light receiver R side, a level of B1 (light present) implies that the light beam is not being cut off by an object (i.e. a safe condition), while a level of B0 (light absent) implies that the light beam is being cut off by an object (i.e. an unsafe condition). A light receiving element and an amplifier which constitute the light receiver R take this alternating signal and amplify it. Thus when an object is actually in a region X (the region to be confirmed safe), the alternating signal is not received, while when the object is absent, the alternating signal is received. In other words with this method, even when there is no object present (i.e. a safe condition), the received signal indicating this also includes the signal (B0) indicating danger. alternating current signal.
The output signal of the AC amplifier in FIG. 1 is rectified by a voltage doubler rectifier circuit to give a direct current output signal y=1. In FIG. 1, only when the input signal level B0 (indicating danger) is received by a capacitor CA, a charge of the polarity shown in FIG. 1 builds up through a diode DA. Then the input signal level B1(indicating safety) is superimposed on this charging voltage and is stored in the capacitor CB through a diode DB as a direct current output voltage V.sub.DC. This stored voltage V.sub.DC is not produced as long as the capacitor CA is not being charged by the input signal level B0. That is, the direct current output voltage V.sub.DC indicating safety is only produced when the input signal level B0 indicating danger is received.
The signal receiving method illustrated by FIG. 1, thus becomes one which can verify, at the time of generation of the signal indicating safety (V.sub.DC), that the light receiving element and the AC amplifier are able to indicate danger. If this operation is expressed logically, then an output signal y=1 is produced by the log
REFERENCES:
patent: 4015122 (1977-03-01), Rubinstein
patent: 4309693 (1982-01-01), Craven
patent: 4661880 (1987-04-01), Futsuhara
patent: 4757417 (1988-07-01), Futsuhara
patent: 5218196 (1993-06-01), Dogul et al.
Anzai Hiroji
Ishioroshi Tetsuya
Kato Masakazu
Sugiyama Takashi
Le Que
The Nippon Signal Co. Ltd.
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