Abstract:
A light barrier having at least one transmitter ( 6 ) and at least one receiver ( 8 ) for a light beam and having a light path ( 1 ), which runs between a first side ( 2 ) and a second side ( 4 ) of a region to be monitored, can be produced flexibly and with little complexity by virtue of the transmitter ( 6 ) and of the receiver ( 8 ) being situated on the first side ( 2 ) and by virtue of the second side ( 4 ) containing an optical system ( 10 ) which picks up the primary light beam ( 7 ) emitted by the transmitter and which deflects the primary light beam ( 7 ) and returns it to the receiver ( 8 ) via the light path ( 1 ) to the first side ( 2 ) as a secondary light beam ( 9 ), which is separate from the primary light beam ( 7 ), at a distance from the primary light beam ( 7 ).

Description:
FIELD OF THE INVENTION 
     The invention relates to a light barrier having a transmitter for a light beam and at least one associated receiver, and having a light path that runs between a first side and a second side of a region to be monitored. 
     BACKGROUND 
     Such light barriers are known in numerous embodiments. In these, they can be designed in very different sizes and meet very different aims. Thus, for example, the contour of a motor vehicle is scanned inside a car wash system with the aid of appropriately movably arranged light barriers, in order to ensure the vehicle dries as effectively as possible with the least possible outlay on air and energy. It is also known to design very small light barriers in the form of so-called fork light barriers, in the case of which the light path extends between two limbs of a housing. Such light barriers are used, for example, as edge detectors in production machines in which webbed materials are transported in an accurately positioned fashion. If a relatively large limb separation is required for such a fork light barrier, the fork light barrier is replaced by another fork light barrier whose housing has the required limb spacing and in which the supply line to the transmitter in the one limb and to the receiver in the other limb is laid in a suitable way. The use of light barriers of different size at a point of use therefore proves to be troublesome and complicated with reference to handling and stock keeping. 
     SUMMARY 
     It is the object of the invention to design a light barrier of the type mentioned at the beginning so that it can be flexibly constructed and used for different purposes. 
     In order to achieve this object, according to the invention a light barrier of the type mentioned at the beginning is characterized in that the transmitter and the at least one receiver are situated on the first side, and in that an optical system that picks up the primary light beam emitted by the transmitter is arranged on the second side, which deflects the primary light beam and returns it to the receiver via the light path to the first side as a secondary light beam, which is separate from the primary light beam, at a distance from the primary light beam. 
     The inventive light barrier therefore has a design by means of which the light beam emitted by the transmitter reaches via the light path an optical system on the other side of the region to be monitored and is deflected there such that there is returned from the second side to the first side a secondary beam that runs at a distance from the primary light beam. It is possible in this case to utilize only the secondary light beam for the light barrier function. In this case, the primary light beam at one point can run via the light path that is insensitive to interference to the light beam. For example, the primary light beam can also run inside a hose-like or tubular protective arrangement. 
     As an alternative hereto, it is also possible to utilize the primary light beam for the light barrier function by having the receiver detect an interruption of the primary light beam or of the secondary light beam. 
     In a preferred embodiment of the invention, the optical system arranged on the second side has a focusing device for the secondary light beam. A high signal intensity is provided in this way for the receiver, and so a high signal-to-noise ratio is attained for the light barrier function. 
     In one variant of the invention, the optical system on the second side can include an expanding device for forming an expanded secondary light beam. Light barrier monitoring can thereby be performed for a monitoring region of two-dimensional cross section, the receiver on the first side preferably having a converging lens arrangement. An interruption of only a part of the surface of the light beam then leads in the receiver to a reduction in amplitude that can be evaluated as measurement signal in the receiver. 
     Furthermore, the receiver in such an arrangement can be designed as a receiver sensitive in two dimensions, so that the position of the partial interruption of the widened light beam can be established in the receiver. In this case, the receiver can have a phototransistor array, for example. 
     The inventive arrangement generally has the advantage that the electronic components which need a power supply and, possibly, a signal line are located on the same side of the region to be monitored. In the case of a fork light barrier, these components are located in the same limb of the housing. Consequently, it is possible to avoid troublesome cable laying, particularly in the case of relatively long light paths. A particular advantage occurs owing to the fact that the arrangement of transmitter and receiver on the same side of the region to be monitored enables a compact control of the intensity of the light beam emitted by the transmitter as a function of the intensity of the light beam received by the receiver. Consequently, according to the invention this control does not require a control signal to be transmitted from the receiver to the transmitter via the light path. According to the invention, therefore, in a preferred embodiment there is arranged on the first side a control stage with the aid of which the intensity of the primary beam emitted by the transmitter can be controlled as a function of the intensity of the secondary beam received by the receiver. 
     The inventive light barrier further permits the optical system receiving the primary light beam, on the second side to use beam splitter arrangements to generate a plurality of secondary light beams that are preferably fed back to the first side in a fashion parallel to one another. Here, for each secondary light beam it is possible to provide a dedicated receiver on the first side. However, it is also possible to guide the different secondary light beams generated on the second side to a common receiver which either has a sufficiently large sensitive surface, or is essentially designed as a point receiver for which the secondary light beams traverse the light path obliquely relative to one another so that all secondary light beams strike the same receiver and add together optically. However, in this case information relating to the secondary light beam interrupted by an object is lost, and so the parallel arrangement of the secondary light beams and a receiver arrangement, which can detect each secondary light beam differentially, is generally preferred. The receiver therefore preferably has a plurality of receiver elements for in each case one secondary light beam. 
     Conversely, the present invention also enables a design having a plurality of primary light beams which are condensed on the second side to form a common secondary light beam. 
     The invention enables the simple design of a fork light barrier whose limb spacing is variable. Since cabling need be done only in one limb, there is no problem in adjusting the distance of the other limb telescopically, because no cables or lines need also be guided. Such a fork light barrier can be used with a plurality of secondary light barriers for differentiated monitoring, for example of the instantaneous position of the edge of a material web, and is therefore suitable, for example, for edge monitoring even of material webs of different width. It is also conceivable to indicate that a position of the edge of the material web has been reached and, for example, to trigger an alarm when another position within the light barrier is reached by the edge of the material web. 
     The customary expressions “light barrier” and “light beam” are being used to explain the invention without hereby intending a restriction to the visible light. Of course, the “light beam” in the meaning of the invention can also have a wavelength outside visible light, that is to say be an infrared beam or ultraviolet beam, for example. The suitability of appropriate transmitters and receivers for the formation of a “light barrier” depends on the respective intended use and is known without more ado to the person skilled in the art. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention is to be explained in more detail below with the aid of exemplary embodiments illustrated in the drawing, in which: 
         FIG. 1  is a schematic of an inventive light barrier; 
         FIG. 2  is a schematic of possible arrangements on the first side and on the second side; 
         FIG. 3  is a schematic of a first embodiment of a fork light barrier; 
         FIG. 4  is a schematic of a fork light barrier having one primary light beam and a plurality of secondary light beams, or a plurality of primary light beams and one secondary light beam; 
         FIG. 5  is a schematic of a fork light barrier in accordance with  FIG. 3  for the purpose of emitting an expanded primary light beam; 
         FIG. 6  shows an exemplary embodiment of a light barrier in a housing, in use with expanded light beams; 
         FIG. 7  shows another exemplary embodiment of a light barrier having an expanded light beam; 
         FIG. 8  is a schematic of the design of a car wash system having numerous light barriers; 
         FIG. 9  is a schematic of the design of a light barrier for the purpose of scanning the contour of a motor vehicle in a car wash system; and 
         FIG. 10  is a schematic of the design of a light barrier arrangement for the purpose of detecting a vehicle position in a wash system. 
     
    
    
     DESCRIPTION 
       FIG. 1  is a schematic of a light path  1  that runs through a region to be monitored and is limited on a first side  2  by a first part  3 , and on a second side  4  by a second part  5  of a light barrier. 
     The first part  3  of the light barrier includes a transmitter  6  for emitting a primary light beam  7  and a receiver  8 , arranged offset from the transmitter  6 , for receiving a secondary light beam  9 . 
     The second part  5  of the light barrier does not include any electronic components, but merely an optical system that serves to deflect the primary beam  7  and returns the light beam to the first part  3  of the light barrier as secondary light beam  9  at a distance from the first light beam  7 . In the exemplary embodiment illustrated, the primary light beam  7  and secondary light beam  9  run parallel to one another. 
     Located in the first part  3  of the light barrier between the transmitter  6  and the receiver  8  is an evaluation and control stage  11  that can be used to execute the actual light barrier function by having the evaluation and control stage  11  establish whether the secondary light beam  9  has been interrupted by an object. Moreover, the evaluation and control stage  11  can further establish the intensity of the secondary light beam  9  received by the receiver  8 , and set the intensity of the primary light beam  7  emitted by the transmitter  6  as a function of the established intensity of the secondary light beam  9 . This prevents the evaluation of the light barrier function by the evaluation and control stage  11  from being impaired by an excessively strong or excessively weak primary light beam  7 . The evaluation and control stage  11  is therefore capable of controlling the transmitter  6  so that an effectively evaluable signal of an intensity within a prescribed intensity interval arrives at the receiver  8 . Furthermore, it is possible to provide on the first side  2  a switching stage (not illustrated) with the aid of which the light beam  7  from the transmitter  6  can be emitted in sections or in pulsed form. In this case, the receiver  8  or the evaluation and control stage  11  can be driven by the switching stage with the aid of appropriate switching signals, in order to receive or evaluate secondary light beams  9  only during the emitted light beams  7 . 
       FIG. 2  shows a plurality of possible designs of the inventive light barrier. On the second side  3 , the primary light beam  7  emitted by the transmitter  6  on the first side  2  of the light path  1  reaches a converging lens  12  with the aid of which the light is coupled into a light guide  13 . The deflection of the primary light beam  7  on the second side  3  is undertaken with the aid of the light guide. Located at the output of the light guide  13  is a concave lens  14  with the aid of which the secondary light beam  9  is formed by expansion. The secondary light beam  9  strikes a converging lens  15  on the first side  2  and can, in turn, be coupled into a light guide  16  for guiding the secondary light beam  9  to the receiver  8  on the first side  2 . As has already been described with the aid of  FIG. 1 , the evaluation and control stage  11  is arranged between the receiver  8  and the transmitter  6 . 
     The design explained is illustrated in  FIG. 2  with unbroken lines, while a conceivable alternative embodiment is depicted with stages drawn with dashes. Accordingly, the primary light beam  7  reaches a deflecting mirror  17  via the converging lens  12  on the second side  3 , and can then be coupled into a light guide  13 ′. This light guide  13 ′ can, if appropriate, also be omitted. Via a further deflecting mirror  18 , the light beam is deflected anew by 90° and strikes the concave lens  14 . In a corresponding way, after traversing the converging lens  15  the secondary light beam  9  can be guided on the first side  2  onto a deflecting mirror  19 , in order to be directed onto the receiver  8 . If appropriate, the light beam can be guided to the receiver  8  via a light guide  16 ′. 
     In the case of the exemplary embodiment illustrated in  FIG. 3 , a light barrier is formed by a housing  19  that is of L-shaped design with two limbs  20 ,  21 . 
     The first limb  20  includes the electronic components, while the second limb  21  carries in a displaceable fashion a housing part  22  in which the optical system  10  (not illustrated here) for deflecting the light beam is located. 
     It is indicated schematically in  FIG. 3  that the transmitter  6  and receiver  8  are arranged in the first limb  20  so that the limb  20  forms the first side  2  of the light path  1  located between the first limb  20  and the housing part  22 . The transmitter  6  emits the primary light beam  7  that is deflected in the housing part  22  and guided back to the receiver  8  as secondary light beam  9 . For reasons of clarity, the evaluation and control stage  11  also present here is not depicted. 
       FIG. 3  indicates by elements, depicted with dashes, for the transmitter  6  and receiver  8 , and for an appropriately inverted beam path with the primary light beam  7  and the secondary light beam  9  that the locations for the transmitter  6  and the receiver  8  can also be interchanged inside the first limb  20 . 
     Provided in the first limb  20  in the case of the exemplary embodiment illustrated in  FIG. 4 , whose mechanical design corresponds to that of the exemplary embodiment from  FIG. 3 , are three transmitters  6  which therefore emit three primary light beams  7 . The three light beams are combined in the optical system in the housing part  22  and guided back to the receiver  8  as a secondary light beam  9 , as is illustrated in  FIG. 4  by continuous boxes. 
     The light barrier function can be carried out over a specific region with the aid of the three primary light beams, the illustrated design of a fork type light barrier having a housing part  22  whose distance from the first limb  20  is variable being advantageous. The evaluation of the secondary light beam  9  received by the receiver  8  can be performed by detecting the received intensity, indicating whether only one of the primary light beams  7 , two of the primary light beams  7 , or all three of the primary light beams  7  have been interrupted by an object within the fork light barrier. If it is also the aim in this case further to detect which of the three primary light beams has, as the case may be, been interrupted, it is possible to emit the three primary light beams  7  in multiplex form with the aid of the transmitters  6 , the evaluation and control stage  11  (not illustrated) included in the first limb having information available as to which of the three primary light beams  7  has been emitted within a specific time window. The alternating frequency between the emitted primary light beam sections can in this case be so high that continuous primary light beams  7  are emitted in practice for the light barrier function, although the evaluation and control stage  11  can distinguish the three primary light beams  7  on the basis of the respective time window even when only one secondary light beam  9  is generated. 
       FIG. 4  shows with dashed boxes that here, as well, the reverse beam path is possible by having the transmitter  6  emit a primary light beam  7  that is split into three secondary and mutually parallel running light beams  9  in the optical system  10  (not illustrated) in the housing part  22 . In this case, it is possible to provide in the first limb  20  of the housing  19  three receivers  8  that are respectively assigned one of the secondary light beams  9 . It is primarily the secondary light beams  9  that serve here as measuring beams. However, the utilization of the primary light beam  7  as measuring light beam is also not excluded. 
       FIG. 5  shows an exemplary embodiment that corresponds to the exemplary embodiment illustrated with the aid of  FIG. 3 , the only point being that the primary light beam  7  emitted by the transmitter  6  is shaped into an expanded parallel light beam by a diverging optical system (not illustrated). In the housing part  22  on the second side  4 , the expanded light beam  7  is recondensed by a focusing optical system into a narrow light beam and deflected in the housing part  22 , in order to be guided back again to the receiver  8  on the first side  2  as a narrow secondary light beam  9 . On being expanded, the primary light beam  7  covers a larger cross section of the light path  1 . Through the use of an analog evaluation of the amplitude of the secondary light beam  9  received via the transmitter  8 , it is possible in this case to establish the extent to which the expanded light beam  7  has, if appropriate, been interrupted by an object. It is possible hereby to reach conclusions on the size of the object interrupting the light beam  7 , and on the position of the object between the limb and the housing part  22 , as can follow from the respective application. 
       FIG. 6  illustrates an arrangement of a housing  19 ′ that is provided with a further second limb  21 ′ so that the housing part  22  is guided at both its ends into the second limbs  21 ,  21 ′, while the electronic system of the light barrier is arranged in the first limb  20 . 
     Provided in  FIG. 6  are two transmitters  6 , whose emitted light beam has been widened in two dimensions by a lens arrangement (not illustrated) so as to produce a two-dimensional light beam which extends in the plane of the drawing in  FIG. 5 . The deflecting optical system  10  that is present in the housing part  22  and illustrated separately in a schematic fashion in  FIG. 6  is arranged so that in the illustration of  FIG. 6  the incident primary light beam  7  is deflected downward, that is to say below the plane of the drawing, and is guided back as a secondary two-dimensional light beam  9  to the first limb  20 , where the two secondary light beams  9  respectively strike a receiver  8 , it being possible to cancel the expansion of the light beam  7 ,  9  by an appropriate focusing optical system. 
     The arrangement of  FIG. 6  permits objects passing through the rectangular inner surface of the housing  19 ′ to be detected, for example for counting purposes. 
     A similar arrangement results for an annular detector such as is illustrated in  FIG. 7 . The primary light beam  7  of a transmitter  6  is also expanded in two dimensions here, it being possible to detect in  FIG. 7  only the portion of the primary light beam  7  that fills up the inner free space of an annular diaphragm  23 . Provided at the end, opposite the transmitter  6 , of the annular diaphragm  23  is the deflecting optical system  10  (illustrated separately in  FIG. 7 ) which deflects the incident primary light beam  7  downward with the aid of a total reflection prism so that a corresponding two-dimensional secondary light beam  9  below the plane of the drawing in  FIG. 7  is guided back onto the receiver  8  arranged under the transmitter  6 . This light barrier also serves for counting all the objects that fall through the interior of the perforated diaphragm  23 . It is clear that what matters here is not the material of the objects, and so—as opposed to conventional ring sensors—all the objects can be detected irrespective of their material. 
       FIG. 8  is a schematic of a car wash system  24  with a car  25  located therein. In order for the car  35  to be driven into the car wash system  24 , a roller door  26  located at the entrance to the car wash system  24  is opened, specifically by means of a light barrier  27  with the aid of which the presence of a car  25  in front of the car wash system  24  is detected. The car  25  is positioned in the car wash system  24  with the aid of light barrier detectors  28 ,  29  that are located on a support frame  30  which can be moved on rails in the longitudinal direction of the car wash system  24 , as indicated by a double arrow A. The support frame comprises two movable side pillars  31  planted on either side of the car  25  on rails, rollers or the like. At their lower end, the pillars  31  have a light barrier detector  32  for detecting the position of wheels  33  of the car  25 . 
     The upper ends of the pillars  31  are interconnected by a cross beam (not illustrated) so that the support frame has the form of an inverted U. The cross beam is fitted so high that the support frame  30  can be moved alongside and over the top of cars  25  of a maximum permissible total height. 
     Whereas for the wash operation, for example with the aid of rotating brushes, the contour of the car  25  is scanned by measuring the pressure at the brush holders, contact with the car  25  is not desired for the subsequent drying. Consequently, the contour of the car  25  is scanned with the aid of light barrier detectors  34  or  35 . The two light barrier detectors are arranged on the support frame  30  such that the height can be moved, so that they can, in particular, determine the upper contour of the car  25  when the support frame  30  is moved axially at the car  25  along the upper contour of the car  25  required for drying. This makes it plain that there is no need for the light barrier detectors  34  and  35  to be present at the same time in a car wash system  24 , since one of the two light barrier detectors  34 ,  35  regularly suffices. 
     According to the invention, an advantageous utilization of the present invention is provided for the various light barrier detectors that are illustrated in  FIG. 8 . 
     In the view of  FIG. 8 , the first side may be located downstream of the car  25 . Located on this side are the transmitter  6 , receiver  8  and evaluation and control stage  11 , which are indicated here schematically in a circle. A primary light beam is transmitted by means of the transmitter  6  to the second side, which lies in front of the car  25  in  FIG. 8 , it also being possible for this transmission to take place in the cross beam of the support frame  30  so that losses in intensity owing to air humidity, water droplets and the like can be avoided. 
     On the second side, the primary light beam is split by means of the optical system (not illustrated) into three secondary light beams  9  with the aid of which the light barrier detectors  28 ,  29  and  32  are formed. The secondary light beams  9  form the light barrier functions and reach the receivers  8  arranged on the first side via the light path  1  (not illustrated) running between the pillars  31 . 
     The arrangement for the light barrier detector  34  and the light barrier detector  35  is provided in a corresponding way. 
       FIG. 9  is a schematic of the design of the light barrier detector  34 . On the first side  2  of the light path  1 , which extends in  FIG. 7  to the second side  3  from behind the car  25  to in front of the car, said light barrier detector has a transmitter  6  which emits a primary light beam  7  onto the second side  3 . The primary light beam  7  is split into three secondary light beams  9 , which are located at the three corners of a triangular housing, on the second side  3 . The three secondary light beams  9  pass back to the first side  2  via the light path  1  and strike the receiver  8  there. 
     The three secondary light beams  9  preferably serve as measuring beams for the light barrier function, which is used here to scan the upper contour of the car  25 . 
       FIG. 10  illustrates the arrangement of, for example, the light barrier detector  35 , which can also be used to scan the contour of the car  25 . 
     Located in the support  31  on the first side  2  are the transmitter  6  and receiver  8  with the associated optical systems. It is illustrated schematically that the primary light beam  7  emitted by the transmitter inside the cross beam  36  of the support frame  30  is deflected onto the second side  3  and split into four secondary light beams  9 . The four secondary light beams  9  are received by receivers  8  on the first side  2  if the secondary light beams  9  have not been interrupted by the car  25 . With the aid of the evaluation and control stage  11  (not illustrated) the determined contour is converted into a control signal for the drying nozzle guided at a distance over the upper contour of the car  25 . 
     It is to be seen that owing to the undertaking to split the light beam into a plurality of secondary light beams  9  it is possible to use a single light barrier, that is to say a single evaluation and control stage  11 , to fulfil a plurality of functions, since a plurality of measuring beams are available. There is the advantage in this case that the electronic system need be present only on the first side  2  so that no signal lines or electrical supply lines need be guided from the first side  2  to the second side  3 , or vice versa. 
     Owing to the evaluation and control stage  11 , it is possible in this case to control the intensity of the primary beam  7  emitted by the transmitter  6  on the first side  2  so that effectively evaluable secondary light beams  9  are always received by the receivers  8 .