Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2002-03-05
2004-11-02
Porta, David (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C340S549000, C340S545300, C356S004060, C356S003110
Reexamination Certificate
active
06812450
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for monitoring a protected zone in which a light ray is transmitted by an apparatus in the direction of the protected zone, a light ray reflected/remitted by an object disposed in the protected zone is received and the distance between the apparatus and the object is determined. The invention further relates to an apparatus for monitoring a protected zone comprising a transmitter unit for transmitting a light ray in the direction of the protected zone, a receiver unit for receiving a light ray reflected/remitted by an object disposed in the protected zone and an evaluation unit for determining the distance between the apparatus and the object.
Such methods and apparatuses are known from the prior art and serve, for example, to detect objects which move into a protected zone, whereupon a specific action, for example a warning signal or a switching off of a machine, is triggered. It is important, in particular if the methods and apparatuses are used for securing hazardous machinery, that objects penetrating into the protected zone are reliably recognized, which means that, on the one hand, the operability of the apparatus must be checked constantly and, on the other hand, it must be ensured that the apparatus cannot be manipulated.
SUMMARY OF THE INVENTION
In one embodiment, a method in accordance with the invention includes at least two transmitted light rays which include an angle between them; wherein, with an object present within the protected zone, a first light ray reflected/remitted by the object is received; wherein, with the protected zone free of an object, a second light ray reflected/remitted from a position disposed outside the protected zone is received; and wherein the distance from the apparatus of both the object and the second position is determined.
In another embodiment, an apparatus includes a transmitter unit designed to transmit at least two light rays which include an angle between them; a receiver unit designed for the reception of a first light ray reflected/remitted by an object disposed within the protected zone and of a second light ray reflected/remitted from a position disposed outside the protected zone; and an evaluation unit designed to determine the distance from the apparatus of both the object and the position located outside the protected zone.
In accordance with an embodiment of the invention, work is therefore carried out not only with one, but at least with two light rays which have different orientations. The second light ray is oriented in this connection such that it is reflected/remitted from a position which lies outside the protected zone if the light path of this light ray is not interrupted by an object present inside the protected zone. The first light ray is oriented such that it is reflected/remitted by an object if this object is present in the protected zone. If the protected zone is object-free, the first light ray does not necessarily have to be oriented such that it is reflected/remitted from a position disposed outside the protected zone; it can rather also be directed into “infinity”. It is only decisive for the first light ray that it is oriented such that if an object to be detected is present in the protected zone, it will also actually impinge on this object.
In accordance with an embodiment of the invention, the first light ray therefore serves to detect an object present in the protected zone, whereas the second light ray serves to constantly detect the background lying outside the protected zone and/or to determine the distance of this background from the apparatus. It thereby becomes possible to constantly and actively check the operability of the apparatus, since when no background is recognized or if the background is displaced, then either an object is present in the protected zone or a malfunction or a manipulation/maladjustment of the apparatus is present.
Moreover, it becomes possible in certain cases to determine the distance from the apparatus of an object disposed inside the protected zone by both light rays in a redundant manner—and thus with increased reliability, with a valid measurement only being present when at least substantially the same distance result is obtained via both light rays.
Embodiments of the invention thus make possible the operation of an apparatus of the kind initially named with the highest possible reliability since the operability of the apparatus can be constantly checked, manipulations of the apparatus are immediately recognized and maladjustments of the apparatuses can be determined and in certain applications the reliability of the distance determination between the object to be detected and the apparatus can also be increased by redundant measurement.
The emitted light rays for the periodic scanning of the protected zone are preferably deflected inside a plane which extends at least substantially perpendicular to the plane containing the transmitted light rays. It is achieved by this measure that not only a protected zone can be monitored which extends frontally, substantially on a straight line in front of the apparatus, but rather that the monitoring of an angular range surrounding the apparatus is possible. Such an angular range can amount to, for example, 180° or 360°.
It is preferred if the respective deflection angles of the emitted light rays are detected, since then the positions from which the light rays are reflected/remitted can be determined from the distance values and the associated deflection angles. It can then therefore not only be determined whether an object is disposed inside the protected zone, but it furthermore becomes possible to determine the position of the object within the protected zone.
The distance values determined can be compared with previously stored distance values or positions determined from distance, and deflection angle values can be compared with previously stored positions. A warning signal or error signal can be produced in this case, for example, when at least a pre-set difference occurs between the determined distance values and the previously stored distance values or between the determined positions and the previously stored positions. It is moreover possible to define specific stored distance values or positions as permitted distance values or positions, with then no warning signal or error signal being emitted when the currently determined distance values or positions correspond to these stored distance values or positions.
It is of advantage if the positions of the protected zone boundaries are stored, since it can be determined in this case whether an object is located inside or outside the protected zone. With an object disposed outside the protected zone, for example, the emission of a warning signal or of an error signal can then be suppressed.
It is preferred if the second emitted light ray is directed at least in a first range of deflection angles onto the floor or the ceiling of a region surrounding the protected zone. Since the location of the floor or the ceiling does not change as a rule during the operation of the apparatus, it is achieved in this manner that the second transmitted light ray is in each case reflected/remitted from unchanged positions when the protected zone is object-free so that the information is unchanging which is supplied via the second light ray and relates to the background lying outside the protected zone. This variant of the invention is thus advantageous with respect to an alternative variant in which the second light ray is directed, for example, to walls and doors, since in this case, for example, the opening of a door brings about a change in the background information and can thus result in a triggering of a warning signal or of an error signal.
It is, however, also generally possible that the second transmitted light ray is directed in a second range of deflection angles to objects disposed outside the protected zone such as walls or stationary machinery. These articles are, however, preferably immovable relative to the
Porta David
Sick AG
Townsend and Townsend / and Crew LLP
Yam Stephen
LandOfFree
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