DE19801632C2 - Reflex light barrier, in particular for the detection of transparent, polarizing materials, and a method for improving the interference immunity of reflex light barriers - Google Patents

Description

The invention relates to a reflex light barrier, in particular for detection transparent, polarizing materials, according to the generic term of Claim 1 and a method for operating such a reflected light barrier according to the preamble of claim 17.

For the detection of objects, reflective light barriers are known, some Transmitter and a receiver of electromagnetic waves and one of them have spaced reflector. Ideally, the reflex light creates then and only then a signal if there is an object in the detection area between the transmitter and reflector. That from the broadcaster emitted light is transmitted through the reflector with almost vertical incidence Reflection on the slightly spaced beam path Receiver shown. The receiver is located at reflex light barriers usually in close proximity to the transmitter of the electromagnetic Waves, for example, in one and the same component, for. B. an optical Integrated sensor. Since the detection range, ie. H. about the area between the transmitter or receiver and reflector, in the Is usually large, for example a few meters, must be a transmitter Light source as little divergent light can be used. Especially Lasers are particularly suitable for this, for space and cost reasons in particular Diode lasers or light-emitting diodes, usually in combination with lenses or Lens systems to the light emitted by a divergent light source collimate. The wavelengths used are in the visible or infrared region of the spectrum.

During the operation of the reflex light barrier, the receiver measures the Intensity of the incident light, which is usually that of the reflector is reflected light. The reflex light barrier generates a Switch signal when the current intensity value by more than one predetermined amount of the intensity value at rest, d. H. without object in the detection area. By placing an object in the  The detection area is usually the one received in the idle state Intensity reduced, which is why light barriers are designed so that the Rest intensity must be undercut by a predetermined amount, to lead to an output signal. The recognition of objects whose Incorporation into the beam path does not lead to a significant reduction the intensity measured by the receiver is problematic.

The detection of objects that do not reflect or only reflect diffusely and little Transmitting intensity can be relative with such light barriers unproblematic and interference-free. Is a such an object in the beam path will in any case be that of the receiver measured light intensity reduced compared to the resting value, the Switching threshold was chosen so that it is undercut in this case. The detection of objects with a reflective surface can, however can be falsified by surface reflections. There is one Object in the detection area, in the worst case this can be from the sender transmitted light by reflection on the object surface directly and without the Reach reflector to be reflected on the receiver. In this case an intensity is measured which is not sufficiently lower than that Quiet intensity is or even exceeds it, so that the light barrier despite Object no output signal generated. So that the introduction of a Object in the detection area can not be reliably recognized as it not necessarily with a sufficient reduction in the measured Intensity goes hand in hand.

To reduce such interference from surface reflections, it is known, light of a defined transmission polarization in the detection area to couple, as well as to ensure that only light of a defined Receiving polarization is detected. Transmit and receive polarization are either linear and perpendicular to each other, so that the one reflecting surface polarization maintaining reflected light from Receiver is not detected or circular, the polarization receiving reflected light a second time in one direction through the birefringent layer of the polarizer is delayed by λ / 4 and therefore through the linear polarizing layer belonging to the circular polarizer  does not allow this light to be transmitted. Still an intensity of rest To be able to measure, reflectors are preferably non-ideal, i. H. non-polarization-maintaining, retroreflectors used. these are for example conventional plastic retroreflectors. In a defined Transmitted polarization state light is therefore through this Reflectors reflecting mixed polarization such that at least one Part of the light has the receiving polarization. So can contrast Changes due to the introduction of objects into the detection area can be detected without surface reflections falsifying the measurement.

Such a reflex light barrier is for example from DE 28 24 583 C3 known. This has a retroreflector that has a depolarizing ability has or a rotation of the transmission light between 10 ° and 170 ° caused. With this light barrier the detection of strong is successful reflective objects.

EP 328 709 B1 discloses a light barrier for improved detection of interruptions in the light path and to improve the Sabotage security of the light barrier known. Here comes polarized Light for use. The light beam in two parallel partial beams opposite polarity split, the radiation receiver a change in the ratio of intensities to the opposite polarized partial beams. For this purpose Polarization filters introduced into the beam path, which zones have different types of polarization.

Further reflection light barriers can be found in the publications DE 42 38 116 C2, DE 42 21 726 C1 and DE-OS 19 34 321 are known.

Particular problems arise if the objects to be recognized always or, depending on the transmission polarization, only a slight optical one Represent contrast for the reflex light barrier, i.e. fully transmit. This is for example in the case of transparent objects, in particular glass plates or clear plastic films, the case. Some materials are still coming added the problem of polarization; for example, have transparencies  through its composition of long-chain organic molecules, which during the manufacturing process by pulling the film polarizing properties that were aligned from place to place on the Foil can vary significantly and cannot be predetermined. At the The light passes through these foils within the reflex light barrier with defined transmission polarization, therefore, into an indefinable one Polarization state or brought into an overlay therefrom, from Receiver only the component with the receiving polarization is detected. It is obvious that this is from that of the recipient measured intensity hardly reliable on the presence of a Object in the detection area can be closed and light barriers are susceptible to interference for the detection of such foils.

An improvement in the interference immunity in the detection of transparent, Polarizing foils can currently be used with autocollimated systems can be achieved. The transmission and reception beam are in the detection area on an axis, which is achieved by coupling the emitted by the transmitter Light or coupling the back-reflected light to the receiver by means of a beam splitter or partially permeable mirror is reached. With that occurs the light finally falling on the detector both on the way to the Reflector and on the way back to the receiver at the same Pass through the film and experience a double polarization with each the same unknown polarization. This brings against the not auto collimated systems in which the transmit and receive beam apply the film different places with different optical properties passes through, improved results, since in the latter case two unknowns Polarizations can occur and affect the detected intensity. However, the autocollimated systems do not work properly either.

The invention is therefore based on the object of a light barrier To provide with which transparent, polarizing plastics and materials with similar optical properties more reliable and can be recognized more reliably.  

This object is achieved according to the invention by a reflex light barrier, in particular for recognizing transparent, polarizing materials, consisting of a transmitter ( 1 , 1 ', 1 ", 1 ''') and receiver ( 2 , 2 ', 2 ", 2 ''' ) electromagnetic waves, which are in spatial proximity to one another, and a reflector ( 3 , 3 ', 3 ", 3 ''') spaced apart from them, the emitted by the transmitter ( 1 , 1 ', 1 ", 1 ''') emitted electromagnetic waves are reflected by the reflector ( 3 , 3 ', 3 ", 3 ''') on the receiver ( 2 , 2 ', 2 ", 2 '''), which is an output signal dependent on the intensity of the received light emits that for the detection of in the area between transmitter ( 1 , 1 ', 1 ", 1 ''') or receiver ( 2 , 2 ', 2 ", 2 ''') and reflector ( 3 , 3 ', 3 ", 3 '''), the detection area ( 10 , 10 ', 10 ", 10 '''), introduced objects ( 14 , 14 '), and in front of the output of the transmitter ( 1 , 1 ', 1 ", 1 ''') a transmit polarizer ( 5 , 5 ', 5 "), which produces a defined polarization state P _S , or the transmitter ( 1 , 1 ', 1 ", 1 ''') emits polarized light of the polarization P _S , and is in front of the receiver ( 2 , 2 ', 2 ", 2 ''') is a receiving polarizer ( 6 , 6 ', 6 ") which transmits light of a defined polarization P _E to the receiver, characterized in that
that there is a reflector polarizer ( 4 , 4 ', 4 ", 4 ''') in front of the reflector ( 3 , 3 ', 3 ", 3 '''), which allows the polarization state P _{R to} pass through the reflected light,

• a) wherein the transmit polarization P _S and the receive polarization P _{E are} linear polarizations which are directed perpendicular to one another, and the reflection polarization P _{R is} a linear polarization which is approximately 30 ° to 60 °, preferably approximately 45 °, relative to the transmitted polarization P _{S is} rotated
• b) or the transmission polarization P _S and the reception polarization P _{E are} linear polarizations which are directed perpendicular to one another, and the reflection polarization P _{R is} any elliptical, preferably circular, polarization,
• c) or the transmit polarization P _S and the receive polarization P _{E are} circular polarizations which have the same direction of rotation, and the reflection polarization P _{R is} an arbitrarily oriented linear polarization,
• d) or the transmit polarization P _S and the receive polarization P _{E are} circular polarizations, which have the same direction of rotation, and the reflection polarization P _{R is} also a circular polarization.

A method for operating a reflex light barrier, in particular for recognizing transparent, polarizing materials and for improving interference immunity, the relex light barrier consisting of

• a transmitter ( 1 , 1 ', 1 ", 1 ''') and a receiver ( 2 , 2 ', 2 ", 2 ''') of electromagnetic waves which are located in close proximity to one another,
• - a reflector ( 3 , 3 ', 3 ", 3 ''') spaced therefrom,
  the electromagnetic waves emitted by the transmitter ( 1 , 1 ', 1 ", 1 ''') by means of the reflector ( 3 , 3 ', 3 ", 3 ''') onto the receiver ( 2 , 2 ', 2 ", 2 ''') are reflected, which emits an output signal which is dependent on the intensity of the received light and which is used to detect the area between the transmitter ( 1 , 1 ', 1 ", 1 ''') or receiver ( 2 , 2 ', 2 ", 2 ''') and reflector ( 3 , 3 ', 3 ", 3 '''), the detection area ( 10 , 10 ', 10 ", 10 '''), objects ( 14 , 14 ') serves
• - A transmitter polarizer ( 5 , 5 ', 5 ") located in front of the output of the transmitter ( 1 , 1 ', 1 ", 1 '''), which produces a defined polarization state P _S , or the transmitter ( 1 , 1 ', 1 ", 1 ''') polarized light of polarization P _{S is} emitted,
• and a receiving polarizer ( 6 , 6 ', 6 ") located in front of the receiver ( 2 , 2 ', 2 ", 2 ""), which transmits light of a defined polarization P _E to the receiver, is characterized in that

that in front of the reflector (

3

.

3

'

3

"

3

'' ') a reflector polarizer (

4

.

4

'

4

"

4

'''), the polarization state P _R from the reflected light

passes, the light on its way from the transmitter (

1

.

1

'

1

"

1

'' ') to the reflector (

3

.

3

'

3

"

3

'' ') and on its way from the reflector (

3

.

3

'

3

"

3

'' ') to the Receiver (

2

.

2

'

2

"

2

'' ') the reflector polarizer (

4

.

4

'

4

"

4

'' ') penetrates,

• a) wherein the transmit polarization P _S and the receive polarization P _{E are} linear polarizations which are directed perpendicular to one another, and the reflection polarization P _{R is} a linear polarization which is approximately 30 ° to 60 °, preferably approximately 45 °, relative to the transmitted polarization P _{S is} rotated
• b) or the transmission polarization P _S and the reception polarization P _{E are} linear polarizations which are directed perpendicular to one another, and the reflection polarization P _{R is} any elliptical, preferably circular, polarization,
• c) or the transmit polarization P _S and the receive polarization P _{E are} circular polarizations which have the same direction of rotation, and the reflection polarization P _{R is} an arbitrarily oriented linear polarization,
• d) or the transmit polarization P _S and the receive polarization P _{E are} circular polarizations, which have the same direction of rotation, and the reflection polarization P _{R is} also a circular polarization.

There is a polarizer (transmitter polarizer) in front of the output of the transmitter, which produces a defined polarization state P _S , or the transmitter already emits polarized light of polarization P _S. There is a polarizer (receiving polarizer) in front of the receiver which transmits light of a defined polarization P _E to the receiver. P _S and P _E are linear polarizations, which are directed perpendicular to each other, or circular polarizations, which have the same direction of rotation. Furthermore, there is a polarizer (reflector polarizer) in front of the reflector which allows the polarization state P _{R to} pass through the reflected light.

In this context, the polarization P _R is understood to mean the state of polarization which the light has after reflection at the reflector and after passing through the polarizer P _R before it is incident again on the object to be detected. The receive polarization P _E is the polarization before or when it hits the receive polarizer that is maximally transmitted by the receive polarizer. The polarization of the light after transmission by the receiving polarizer can be different, in particular in the case of a circular polarizer.

The transmit and receive polarizations P _S and P _E are preferably linear polarizations which are directed perpendicular to one another. They are produced by means of linear polarizers, which are arranged in front of the output of the transmitter or input of the receiver. The transmitter polarizer can be omitted if the transmitter already emits polarized light. With this measure, surface reflections can be reliably suppressed by reflections on the object surface.

The sensitivity of the light barrier in this case can be significant be reduced if a linear polarizer with a Forward direction, which is about 30 to 60 °, preferably about 45 °, is rotated relative to the linear transmission polarization. The Reliability of any reflex light barriers with transmission and reception polarizers to suppress light reflections of the detected Object can be independent in this way through the additional polarizer improved by the design and construction of the reflex light barrier become.

However, the polarization state P _R can also be any elliptical, preferably circular polarization. Such a polarizer can be achieved by combining a birefringent element with a linear polarizer, the linear polarizer being arranged between the birefringent element and the reflector. In order to produce a circular polarization, the birefringent element is a λ / 4 plate which is matched to the wavelength of the light source. If the circular polarizer has the linearly polarizing layer on the side facing away from the reflector, it behaves in the present invention in a manner comparable to a simple linear polarizer and can therefore be replaced by one in this case. The orientation of the linear polarizer used to set up the circular polarizer is basically arbitrary in the case of linear transmission and reception polarization.

As an alternative, transmit and receive polarization can be circular Polarizations with the same direction of rotation. This is achieved mechanically by arranging circularly polarizing elements, that is Linear polarizer and λ / 4 plate, in front of transmitter and receiver with the same Installation position, same layer arrangement and same orientation of the Linear polarizer. Such a circular polarizer poses when illuminated the side with the linear polarizer made of unpolarized Circular light, e.g. B. clockwise, polarized light. When lighting  from the other side, light is polarized with the same direction of rotation maximum transmitted, but after transmission is in one linearly polarized state. The intensity of the right circular component measured, the left circular Component that corresponds to surface reflections is suppressed.

In the case of circular transmission and reception polarization, the reflector polarization P _{R can be} linear with any orientation of the polarization direction or circular.

In order to create mechanically easy-to-assemble units, the polarizer is preferably applied directly to the reflector, placed on, glued on or otherwise attached in close proximity to the reflector. The polarizer can be a linear polarizing film that is glued to the reflector. Components of this type can be produced particularly cost-effectively. During assembly, no more than the usual adjustment effort and the alignment or rotation of the polarizer with respect to the transmission or reception polarization direction, P _S or P _E , are necessary.

In principle, any reflective element serves as a reflector for example simple plastic retroreflectors. Furthermore, the reflector also by mirroring and / or the geometric change of the Surface structure of the back of the polarizer can be formed. As well can use circular polarizers in front of the transmitter and receiver arrive, the circular polarizers being identical in orientation and Layer arrangement must be and their linearly polarizing layer the sender and receiver facing side is secure to object reflections to suppress.

To create circular transmit and receive polarizations with opposite direction of rotation can advantageously be a common Circular polarizer can be used in front of transmitter and receiver. The linear polarizing layer faces transmitter and receiver while  the birefringent λ / 4 layer on the one facing the reflector Side.

According to the invention, the interference immunity of conventional reflected light barriers can be improved in an advantageous manner that before Reflector a polarizer is installed. This turns the light into operation barrier used in a known manner, in which an optical sensor Sender and receiver are integrated. For example, the transmitter is a Laser, a laser diode or a light emitting diode in the desired wavelength Area. A phototransistor or, for example, serves as the receiver / detector a photodiode. An evaluation electronics is also in the optical sensor integrated, which the output signal of the receiver with a compares predetermined switching threshold and accordingly a binary Output signal of the sensor generated.

Optical sensors are known in which transmitter and receiver or the corresponding exit window in the immediate vicinity are arranged to each other on a front surface of the sensor. Furthermore are With such sensors, transmission and reception polarization are already vertical to each other, e.g. B. by appropriate arrangement of polarizing films at the exit windows and / or by using a polarized light emitting light source. Such optical sensors can be advantageous to build a reflex light barrier according to the invention Maintaining interference immunity in the detection of partially strong self-reflecting objects can be used.

Furthermore, known autocolimated systems with a definier For example, transmission or reception polarization for suppression specular reflections of the objects to be detected are advantageous in their Interference immunity can be increased.

Brief description of the drawing, showing:

Fig. 1 is a reflex light barrier, each with a linear polarizer as a transmit or receive polarizer

Fig. 2 shows another reflex light barrier as an autocollimated system

Fig. 3 is a reflex light barrier, each with a circular polarizer as a transmit or receive polarizer

Fig. 4 is a reflex light barrier with a common circular polarizer as a transmit and receive polarizer

In Fig. 1, a reflex light barrier according to the invention is shown schematically, which consists of the components transmitter 1 and receiver 2 for electromagnetic waves, reflector 3 and a polarizer 4 arranged in front of it. Transmitter 1 and receiver 2 are integrated in a commercially available optical sensor 9 , which is designed for use in the visible and / or infrared range of the electromagnetic spectrum. Fig. 1 shows a reflex light barrier, wherein an object 14 in the detection area 10 between the optical sensor 9 and the polarizer 4 is with reflector 3. Object 14 is shown in broken lines to distinguish it from the components of the light barrier.

Transmitter 1 and receiver 2 are installed in the optical sensor 9 such that the light emitted by the transmitter 1 can leave the sensor housing via a window in the front surface 12 . It is emitted essentially perpendicular to the front surface 12 and strikes the reflector 3, which is spaced parallel to the front surface 12 . By using a slightly divergent light source as the transmitter 1 , in particular a laser, or suitable optics integrated in the sensor 9 for collimation of the light emitted by a divergent light source, as indicated in FIG. 1, an almost parallel, non-divergent one can be produced Transmitting beam 7 , which is converted into the receiving beam 8 by reflection at the reflector 3 . The reflex light barrier is adjusted so that the beam direction of the transmitted beam 7 and the distance from the sensor 9 and reflector 3 are matched to one another in such a way that the received beam 8 strikes the receiver 2 .

The receiver 2 generates an output signal which depends on the intensity of the incident light, that is to say as a rule the light reflected back by the reflector 3 . If the output signal falls below a predetermined switching threshold, the sensor 9 emits a switching signal which ideally indicates the presence of an object 14 in the detection area 10 of the light barrier. For this purpose, the measured output signal is compared by an evaluation electronics with this switching threshold and a binary switching signal is generated.

In order to avoid disturbances of the light barrier operation by surface reflections on reflecting objects 14 , which can lead to the object not being recognized, there is a transmitting polarizer 5 in front of the transmitter 1 , which only allows light in a polarization state P _S. The transmission beam is thus polarized with the polarization P _S. In front of the receiver 2 there is another polarizer 6 , which only allows the polarization P _{E to} pass, so that from the received beam 8 only this polarization component P _E contributes to the detected intensity. One possibility for suppressing surface reflections is to construct the transmit polarizer 5 and the receive polarizer 6 from a single shared circular polarizer. Another possibility is to use two separate linear polarizers for the transmitter and receiver. In this case, the linear polarization directions are perpendicular to each other. In both cases, light of the polarization P _S which is polarization-maintaining is reflected completely suppressed by the receiving polarizer 6 on a specular object.

The core of the reflex light barrier according to the invention, with which the susceptibility to interference in the detection of polarizing materials is reduced, lies in the additional polarizer 4 , which is arranged in the region of the reflector 3 . This polarizer 4 filters out the received beam 8 reflected by the reflector 3 , the component with the polarization P _R , which then falls again on the object to be recognized with unknown polarization 14 and because of its transparency falls on the receiver 2 . The polarizer 4 is arranged parallel to the reflector 3 and to the front surface 12 of the sensor 9 , ie the transmit and receive beams 7 and 8 strike the polarizer 4 approximately perpendicularly.

The polarizers 4 , 5 and 6 can be linear polarizers, e.g. B. polarizing films that are glued directly to the exit window of transmitter 1 or receiver 2 or on the reflector 3 , or circular polarizers. The polarizations P _S , P _E and P _R are linear, with P _S and P _{E being} perpendicular to one another and P _{R being} rotated by approximately 45 °. With this arrangement, reliable detection of transparent polarizing materials, such as polarizing foils, is achieved.

Fig. 2 shows a further reflex light barrier according to the invention, which is designed as an autocollimated system. The illustration of FIG. 1 in accordance with, the transmitter 1 'and the receiver 2' 'are integrated, wherein the transmission beam 7' into an optical sensor 9 'of the sensor 9' off as well as through a window in the Frontffläche 12 of the reception beam 8 'through the same Window re-enters. The transmission beam 7 'emerges perpendicular to the front surface, strikes the reflector 3 ' perpendicularly, as a result of which the reception beam 8 'is imaged in the transmission beam 7 ' and has the same beam axis outside the sensor. Within the sensor, the transmission and reception beams 7 'and 8 ' are separated by means of a partially transparent mirror 13 which is introduced into the beam path at 45 ° relative to the beam direction of the transmission beam 7 '. In the detection area 10 'of the light barrier, the transmit and receive beams are therefore one above the other and have a common beam axis. The light therefore traverses the transparent object 14 'to be recognized at approximately the same location and undergoes polarization of approximately the same degree and the same direction on the way there and back, as a result of which polarizing objects 14 ' can also be recognized more reliably.

In this example, too, for reflection suppression, the transmission and reception beams 7 'and 8 ' are polarized perpendicularly to one another by a polarizer 5 'and 6 ' arranged in front of the transmitter 1 'and the receiver 2 ', respectively. Alternatively, instead of an ordinary beam splitter 13, a polarizing beam splitter can be used, each of which transmits a polarization component and reflects the perpendicular to it. As an alternative to this, the polarizers 5 'and 6 ' can consist of a single circular polarizer which is equally inserted into the transmission and reception beam.

The improvement in the detection reliability of such autocollimated systems is likewise achieved by a polarizer 4 'arranged in front of the reflector 3 '. The orientation of the polarizer 4 'relative to the polarizers 5 ' and 6 'is selected so that it produces a polarization state P _R which is rotated by approximately 45 ° with respect to P _S and P _E. Here too, as an alternative, the polarizers can consist of a single circular polarizer that is equally introduced into the transmission and reception beam.

With such an arrangement, on the one hand, suppression of Surface reflections, on the other hand reliable detection more transparent Materials with undefined optical properties, especially with unknown, locally varying polarization behavior.

Fig. 3 shows a further reflection light barrier, in which the polarizers 5 "and 6" in front of the transmitter 1 'and the receiver 2' are circular polarizers of the same type and orientation. Transmitting and receiving polarizers 5 "and 6 " each consist of a linear polarizer 15 or 15 'facing transmitter 1 "or receiver 2 ", and a λ / 4 plate 16 or 16 ' facing reflector 3 ". The polarization direction of the linear polarizer 15 or 15 'is rotated by approximately 45 ° relative to the slow and fast axis of the birefringent λ / 4 layer 16 or 16 ' in order to produce a circular polarization when light falls on the side of the linear polarizer both linear polarizers 15 and 15 'in front of transmitter 1 "and receiver 2 " agree with each other.

The light emitted by the transmitter 1 "therefore arrives as a transmission beam 7 " with a circular transmission polarization P _S in the detection area 10 "between the transmitter 1 " or receiver 2 "and reflector 3 ". From the receiving polarizer 6 ", light is maximally transmitted from the receiving beam 8 ", which has a receiving polarization P _E that corresponds to this transmitting polarization P _S , but is in a linearly polarized state after passing through the receiving polarizer 6 ". Reflection on surfaces results in right-hand circular incident light, left-circular exit light and vice versa; reflections of this type are thus suppressed by the receiving polarizer.

According to the invention, a further polarizer 4 "is located directly in front of the reflector 3 ", which is a retroreflector. This is a linear polarizer with any orientation or also a circular polarizer, consisting of a linear polarizer facing the reflector and a λ / 4 plate. In the case of a circular polarizer as a reflector polarizer 4 ", the direction of rotation thereof is preferably opposite to the direction of rotation of the transmitting or receiving polarizer 5 " or 6 ".

FIG. 4 shows an embodiment corresponding to FIG. 3, in which a common circular polarizer 17 , consisting of a linear layer 15 "and a λ / 4 layer 16 ", is located in front of the transmitter 1 '''and the receiver 2 ''' , which serves as a transmit or receive polarizer. Otherwise, the light barrier from FIG. 4 corresponds to that from FIG. 3.

List of reference numbers

1

.

1

'

1

"

1

''' Channel

2

.

2

'

2

"

2

''' Receiver

3

.

3

'

3

"

3

'''Reflector

4

.

4

'

4

"

4

'''Reflector polarizer

5

.

5

'

5

"Transmit polarizer

6

.

6

'

6

"Reception polarizer

7

.

7

'

7

"

7

'''Broadcasting beam

8th

.

8th

'

8th

"

8th

'''Receive beam

9

.

9

'' optical sensor

10

.

10

'

10

detection range

12

.

12

'' Front surface

13

beamsplitter

14

.

14

'Object

15

.

15

'

15

"linear polarizing layer / linear polarizer

16

.

16

'

16

"λ / 4 plate

17

circular polarizer

Claims (16)

1. reflex light barrier, in particular for recognizing transparent, polarizing materials, consisting of a transmitter ( 1 , 1 ', 1 ", 1 ''') and receiver ( 2 , 2 ', 2 ", 2 ''') of electromagnetic waves, which are in spatial proximity to one another, and a reflector ( 3 , 3 ', 3 ", 3 ''') spaced apart therefrom, the electromagnetic waves emitted by the transmitter ( 1 , 1 ', 1 ", 1 ''') using of the reflector ( 3 , 3 ', 3 ", 3 ''') are reflected onto the receiver ( 2 , 2 ', 2 ", 2 '''), which emits an output signal which is dependent on the intensity of the received light and which is used for Detection of the area between transmitter ( 1 , 1 ', 1 ", 1 ''') or receiver ( 2 , 2 ', 2 ", 2 ''') and reflector ( 3 , 3 ', 3 ", 3 '''), the detection area ( 10 , 10 ', 10 ", 10 '''), introduced objects ( 14 , 14 '), and in front of the exit of the transmitter ( 1 , 1 ', 1 ", 1 ''') is a transmitting polarizer ( 5 , 5 ', 5 "), which has a defined polarization s state produces P _S , or the transmitter ( 1 , 1 ', 1 ", 1 ''') emits polarized light of the polarization P _S , and in front of the receiver ( 2 , 2 ', 2 ", 2 ''') Receiving polarizer ( 6 , 6 ', 6 "), which transmits light of a defined polarization P _E to the receiver, characterized in that
that there is a reflector polarizer ( 4 , 4 ', 4 ", 4 ''') in front of the reflector ( 3 , 3 ', 3 ", 3 ''') which allows the polarization state P _{R to} pass through the reflected light,

• a) wherein the transmission polarization P _S and the reception polarization P _{E are} linear polarizations which are directed perpendicular to one another, and the reflection polarization P _{R is} a linear polarization which is rotated by 30 ° to 60 ° with respect to the transmission polarization P _S ,
• b) or the transmission polarization P _S and the reception polarization P _{E are} linear polarizations which are directed perpendicular to one another, and the reflection polarization P _{R is} any elliptical, polarization,
• c) or the transmit polarization P _S and the receive polarization P _{E are} circular polarizations which have the same direction of rotation, and the reflection polarization P _{R is} an arbitrarily oriented linear polarization,
• d) or the transmit polarization P _S and the receive polarization P _{E are} circular polarizations, which have the same direction of rotation, and the reflection polarization P _{R is} also a circular polarization.

2. Reflex light barrier according to claim 1, characterized in that the transmit polarization P _S and the receive polarization P _{E are} circular polarizations which have the same direction of rotation, and the reflection polarization P _{R is} a circular polarization with an opposite direction of rotation. 3. Reflex light barrier according to claim 1, characterized in that the transmit polarization P _S and the receive polarization P _{E are} linear polarizations which are directed perpendicular to one another, and the reflection polarization P _{R is} a linear polarization, the reflector polarizer ( 4 , 4 ', 4 ", 4 ''') is a circular polarizer whose linear polarizing layer faces away from the reflector ( 3 , 3 ', 3 ", 3 '''). 4. reflex light barrier according to claim 1, characterized in that the transmit polarization P _S and the receive polarization P _{E are} circular polarizations which have the same direction of rotation, the transmit polarizer ( 5 , 5 ', 5 ") and the receive polarizer ( 6 , 6 ' , 6 ") are each circular polarizers with linearly polarizing layers oriented in the same direction and each facing away from the reflector ( 3 , 3 ', 3 ", 3 ""). 5. reflex light barrier according to claim 4, characterized in that the reflector polarizer ( 4 , 4 ', 4 ", 4 ''') is a circular polarizer, the linearly polarizing layer of the reflector ( 3 , 3 ', 3 ", 3 ''' ) is facing. 6. Reflex light barrier according to claim 1, characterized in that the transmit polarization P _S and the receive polarization P _{E are} linear polarizations which are directed perpendicular to one another, the transmit polarizer ( 5 , 5 ', 5 ") and the receive polarizer ( 6 , 6 ' , 6 ") are circular polarizers each with linearly polarizing layers oriented perpendicular to one another and each facing the reflector ( 3 , 3 ', 3 ", 3 ""). 7. reflex light barrier according to one of the preceding claims, characterized in that the reflector polarizer ( 4 , 4 ', 4 ", 4 ''') arranged directly on the reflector ( 3 , 3 ', 3 ", 3 '''), in particular attached, glued or attached in close proximity to the reflector ( 3 , 3 ', 3 ", 3 '''). 8. reflex light barrier according to one of the preceding claims, characterized in that the transmitter ( 1 , 1 ', 1 ", 1 ''') and receiver ( 2 , 2 ', 2 ", 2 ''') facing away from the reflector polarizer ( 4 , 4 ', 4 ", 4 '''), the back is mirrored and represents the reflector ( 3 , 3 ', 3 ", 3 '''). 9. reflex light barrier according to claim 1, characterized in that the reflector polarizer ( 4 , 4 ', 4 ", 4 ''') is a linear polarizer or circular polarizer, in particular a film, which on the reflector ( 3 , 3 ', 3 " , 3 ''') is glued on. 10. reflex light barrier according to one of the preceding claims, characterized in that further birefringent elements in spatial proximity to the polarizer ( 4 , 4 ', 4 ", 4 ''') are introduced into the beam path. 11. Reflex light barrier according to one of the preceding claims, characterized in that the transmitter ( 1 , 1 ', 1 ", 1 ''') and receiver ( 2 , 2 ', 2 ", 2 ''') in an optical sensor ( 9 , 9 ') are integrated. 12. Reflex light barrier according to one of the preceding claims, characterized in that the transmitted and back-reflected reception beam ( 7 , 7 ', 7 ", 7 ''' or 8 , 8 ', 8 ", 8 ''') in the detection area ( 10 , 10 ', 10 ", 10 ''') lie on a common beam axis and it is therefore an autocollimated system. 13. Reflex light barrier according to claim 12, characterized in that a beam splitter is used to build up the autocollimated system, which couples a part of the transmitted, possibly unpolarized light into the detection area ( 10 , 10 ') and part of that of the reflector ( 3 , 3 ', 3 ", 3 ''') coming light into the receiver ( 2 , 2 ', 2 ", 2 ''') transferred, the polarizers ( 5 ', 6 ') from a single equally in the Circular polarizer inserted in the transmit and receive beam. 14. Reflex light barrier according to claim 12, characterized in that a polarizing beam splitter ( 13 ) is used to build up the autocollimated system, which couples the polarization state P _S into the detection range ( 10 , 10 ') from the transmitted, possibly unpolarized light and from the Light coming from the reflector ( 3 , 3 ', 3 ", 3 ''') transfers the polarization state P _E into the receiver ( 2 , 2 ', 2 ", 2 '''), where P _S and P _{E are} linear, vertical are polarizations directed towards each other. 15. Reflex light barrier according to one of the preceding claims, characterized in that the reflector ( 3 , 3 ', 3 ", 3 ''') is a retroreflector. 16. Reflex light barrier according to one of the preceding claims, characterized in that to suppress surface reflections, the transmitting polarizer ( 5 , 5 ', 5 ") and the receiving polarizer ( 6 , 6 ', 6 ") two of the mounting position, the mounting direction and the optical properties are identical circular polarizers or are constructed from a single shared circular polarizer ( 17 ).