Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1997-02-28
1998-08-25
Tong, Nina
Communications: electrical
Condition responsive indicating system
Specific condition
340522, 340562, 340573, 340665, 340667, 307119, 307139, G08B 2100
Patent
active
057987033
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a mat sensor for dangerous locations where a person and a machine work together to carry out work, for ensuring the safety of an operator by stopping the operation of the machine when the presence of the operator is detected.
BACKGROUND ART
For example, with operating systems using robots, a safety control which prevents operation of a movable portion of a robot when an operator is present in a danger region around the robot (robot operating region), is incorporated into the operating system as a safety measure for the operator.
As a person sensor for this type of safety control, a mat sensor laid at the periphery of the movable portion of the machine is used. Such a mat sensor is shown for example in European Standard prEN1760 (Machine safety--Pressure sensing protection device--Part 1: Pressure sensing mat and floor).
With this type of mat sensor, a flexible intermediate insulation material is disposed between two mutually opposed electrode plates, while the outside is covered by an insulated covering. The construction is such that when an operator stands on the mat sensor, the upper electrode plate is pressed and bent by foot pressure so that the mutually opposed electrode plates come into contact, thus closing a circuit, so that an output indicating the presence of the operator is produced. This present detection output is used to stop the movable portion of a robot, thus ensuring the safety of the operator.
With a mat sensor of this construction however, there are a problems in that at the locations which are frequently stood on by the operator, eventually the intermediate insulation material becomes caught between the electrode plates, and also the electrode plates become contaminated with dust and dirt, or a hole forms in the outside insulated covering so that the electrode plates become corroded. Moreover, when used for a long time, there is always the possibility of deterioration in the electrical contact condition between the electrode plates due to the above problems. If a good electrical contact condition can no longer be obtained, then an operator absent detection output is produced in spite of the fact that an operator is in the danger region, which is highly undesirable from the point of ensuring operator safety.
Moreover, rather than occurring uniformly over the flat surface of the mat, it is common for such problems to occur at one part on the surface of the mat, while at other parts the mat sensor operates normally. Furthermore when such deterioration phenomena of the mat is in a partially advanced state, then it is common for erroneous detection attributable to this mat deterioration to occur sporadically, and in ways which cannot be easily reproduced.
The present invention addresses the above problems, with the object of a first aspect of the present invention being to provide a highly reliable mat sensor which prevents the occurrence of erroneous detection outputs attributable to mat deterioration or the like, by having the sensor portion as a dual system, and detecting agreement or disagreement between output conditions from the two systems. Moreover the object of a second aspect of the present invention is to provide a highly reliable mat sensor at a low cost by having the sensor portion as a single system, and detecting a change in electrostatic capacity between the electrode plates.
DISCLOSURE OF THE INVENTION
To meet the above objectives, a mat sensor according to a first aspect of the present invention comprises: a mat shaped body detection device including a plurality of sensor portions with pairs of mutually facing electrode plates which are contacted when the pressure from a body acts from above, thus producing a body present detection signal, and which are separated when the pressure is released, thus producing a body absent detection signal, an agreement or disagreement detection device for detecting agreement or disagreement between detection signals from the sensor portions of the body detection device, a judgment dev
REFERENCES:
patent: 4661880 (1987-04-01), Futsuhara
patent: 4757417 (1988-07-01), Futsuhara
patent: 5027114 (1991-06-01), Kawashima et al.
Japanese Search Report from PCT/JP96/01743, filed Jun. 24, 1996.
Futsuhara Koichi
Sakai Masayoshi
Shirai Toshihito
The Nippon Signal Co. Ltd.
Tong Nina
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