Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-07-07
2001-11-13
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S221000, C250S222100
Reexamination Certificate
active
06316762
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an optoelectronic device for detecting objects in a monitoring range, with one end of the range being provided with a transmitter that emits transmitting light rays and two receivers for receiving light rays that have respectively a first and a second linear polarizing element installed in front, for which the polarization directions are turned relative to each other by an angle &agr; in the range of 450<&agr;<135°, while the other end of the range has a reflector unit, comprising a reflector and a third linear polarizing element that is installed in front, for which the polarization direction essentially coincides with the polarization direction of the first or second polarizing element.
Such a device is known from the German Patent 42 38 116. This device concerns a reflection light barrier with two receivers, having a beam-dividing, partially transmitting reflector installed in front as polarizing means. The polarizing device for the receiving light rays that penetrate the partially transmitting reflector and arrive at the first receiver and the polarizing device for the receiving light rays that are reflected at the partially transmitting reflector and arrive at the second receiver are turned such that they are displaced by 90° to each other. The difference between the receiving signals present at the receiver outputs is formed to identify objects in the monitoring range. A value is assigned to this signal difference by means of a threshold value.
It is the object of the invention to design a device of the aforementioned type in such a way that it can be used in the area of protection for persons.
SUMMARY OF THE INVENTION
The above object generally is achieved according to the invention by an optoelectronic device for detecting objects in a monitoring range, one end of which is provided with a transmitter that emits transmitting light rays and two receivers for receiving light rays that have respectively a first and a second linear polarizing element installed in front, for which the polarization directions are turned relative to each other by an angle &agr; in the range of 45°<&agr;<135°, while the other end has a reflector unit, comprising a reflector and a third linear polarizing element that is installed in front, for which the polarization direction essentially coincides with the polarization direction of the first or second polarizing element, and wherein receiving signals present at the outputs of the receivers are assigned respectively two different threshold values S
1
and S
2
(S
2
>S
1
), the distance between the receiver is selected such that only with a clear beam path is the receiving signal of one receiver above S
2
and the receiving signal of the second receiver below S
1
, means are provided for testing the device and by actuating these means during an error-free operation, the receiving signals of the receivers will assume predetermined switching states with respect to the threshold values S
1
and S
2
. Advantageous embodiments and useful modifications of the invention are described and disclosed.
In accordance with a first alternative of the invention, the receiving signals present at the receiver outputs are respectively assigned two different threshold values S
1
and S
2
, wherein the threshold value S
2
is higher than S
1
. The interval between threshold values is selected such that the signal received by one receiver is above S
2
and the signal received by the other receiver is below S
1
, but only with a clear optical path. As an alternative, the output signals at the receivers can also be assigned separate threshold values. In that case, the receiving signals for the threshold values are amplified differently by means of amplifiers, wherein the difference in the amplification factors corresponds to the difference in the threshold values S
1
and S
2
. In principle, it would also be conceivable that the signals received by the receivers are respectively assigned the same threshold value for the same amplification. However, it would then be impossible to differentiate safely and unambiguously between the signals for a clear optical path and the signals for an optical path with object located therein.
In that case, the signal received by the receiver having a polarizing element with the same or nearly the same polarization direction as the polarizing element for the reflector unit is located above S
2
. The polarizing element of the other receiver is turned by an angle &agr; in the range of 45°<&agr;<135°, preferably 90°, relative to the polarization direction of the polarizing element of the reflector unit. Consequently, only a small amount of light impinges on this receiver if the optical path is clear.
This device makes it possible to detect with certainty all types of objects that depolarize the impinging light. Comparable amounts of light arrive at the receiver owing to the depolarizing effect of the object.
A diffuse and extremely weak reflection of the light by the object means that the signals received by both receivers are below the threshold value S
1
.
If a strongly reflecting object is located in the optical path, a large amount of light arrives at the receivers so that their receiving signals are respectively above S
2
.
In any case, the switching states at the receiver outputs deviate from the switching states for a clear optical path, so that a secure detection of the objects is ensured.
In accordance with another alternative of the invention, the quotient of the signals present at the receiver outputs is formed. Forming the quotient will eliminate systematic measuring errors, which result from differences in the dimensions of the monitoring range. Thus, it is preferable to form a quotient of the receiving signals rather than to form a difference, which is also conceivable in principle. The quotient of the receiving signals is assigned a threshold value S. This threshold value S is selected such that for a clear optical path of the device, a different switching state results than if an object is located in the optical path, that is to say independent of its reflective characteristics. In addition, the signals received by the receiver are valued individually with the threshold value S
1
.
The device according to the invention additionally comprises means for testing, which can be used to test the operability of the transmitter and the receiver, either cyclically or at predetermined intervals. The test is carried out in such a way that when actuating the testing means during an error-free operation, the signals received by the receivers must occupy predetermined switching states with respect to the threshold values S
1
and S
2
or the threshold value S.
Internal equipment malfunctions can be detected and displayed immediately as a result of this testing. When used in the field of protection of persons, the device is normally used to monitor a machine or the like. If an internal equipment malfunction occurs in the device, the machine is turned off for safety reasons.
REFERENCES:
patent: 4224608 (1980-09-01), Lederer
patent: 4339660 (1982-07-01), Buchholz et al.
patent: 4710760 (1987-12-01), Kasday
patent: 4734575 (1988-03-01), Wagli et al.
patent: 4847448 (1989-07-01), Müller et al.
patent: 4847488 (1989-07-01), Müller
patent: 3514643A1 (1986-10-01), None
patent: 3733656C1 (1989-02-01), None
patent: 4238116A1 (1994-06-01), None
patent: 4343457C1 (1994-10-01), None
patent: 19621120C1 (1997-05-01), None
patent: 0310932A2 (1989-04-01), None
Argast Martin
Fauth Siegfried
Loffler Harald
Kunitz Norman N.
Lee John R.
Leuze Electronic GmbH & Co.
Spencer George H.
Venable
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