Abstract:
The invention relates to a position monitoring device for establishing the position of a first part with respect to a second part, having a transceiver at the first part for emitting an interrogation signal and for receiving a response signal that can be emitted in reaction to the interrogation signal by a transponder, wherein a screen that attenuates signals between the transponder and the transceiver is provided, two members of the group consisting of the transceiver, the screen and the transponder being movable relative to one another.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to a position monitoring device as may be used for detecting a closed position of a door, a flap or the like or the standstill or rotation of rotational piece of machine tool or the telescoping position of an arm.  
       DESCRIPTION OF THE RELATED ART  
       [0002]     Known position switches, cf. for example DE 199 53 898 A1, DE 199 28 641 C1, DE 197 11 588 A1, DE 102 30 564 A1 or EP 0 987 726 A2, serve in particular for monitoring the closed position of access protection devices for machines or mechanical installations with hazard potential, for example a flap in the lining of a meat dicing machine or an access gate in fencing of a section of a production line having processing robots. Typically, the machine or mechanical installation is switched off when the access protection device is opened, and a renewed switch-on is prevented until the access protection device is closed again. For this purpose, a transponder is fitted to a closing part of the access protection device, e.g the flap or gate, which transponder can be identified by a transceiver at a part that can be closed off, e.g. the lining or fencing, if the distance between transponder and transceiver falls below a closed position limiting distance. In this case, it must be ensured by exact mounting of the transponder and transceiver that the closed position limiting distance is undershot only when the access protection device is completely closed. An adjustment that may be required after mounting requires an offset of the transponder and/or of the transceiver. Moreover, under confined space conditions it is not always possible to mount the transceiver and transponder at the required distance relative to one another. This may have the effect that when the access protection device is in a slightly open position, a completely closed position is signalled and the machine is not switched off.  
       SUMMARY OF THE INVENTION  
       [0003]     Therefore, the invention is based on the object of providing a position monitoring device that is more secure.  
         [0004]     This object is achieved in accordance with the features of Claim  1 .  
         [0005]     In the case of a position monitoring device for establishing the position of a first part with respect to a second part, said device having a transceiver at the first part for emitting an interrogation signal and for receiving a response signal that can be emitted in reaction to the interrogation signal by a transponder, a screen that attenuates signals between the transponder and the transceiver is therefore provided, two members of the group consisting of the transceiver, the screen and the transponder being movable relative to one another. This makes it possible to achieve a secure positional assignment of the part that is respectively movable relative to the other part since a specific, precisely adjusted positioning is not required.  
         [0006]     By virtue of the fact that the screen that can be adjusted between positions having a different screening strength in each case for the transponder or the transceiver can attenuate signals between the transponder and the transceiver, the position limiting distance, that is to say the limiting distance between a first and a second position of two parts that are movable relative to one another, can be set, in a simple manner, between zero and a maximum value prescribed by the transmission/reception power. In addition to the increased security on account of the capability of precisely setting the position limiting distance, the mounting of the transponder and of the transceiver is also simplified since a specific distance does not have to be taken into consideration.  
         [0007]     The position monitoring device may expediently be designed in the form of a position switch and is suitable for monitoring the closed position of an access protection device or generally for monitoring whether or not a first part is adjacent to a second part, for example a first part is retracted or extended relative to a second part, and in particular for establishing the closed position of a closing part with respect to a part that can be closed off of an access protection device for a machine or mechanical installation with hazard potential.  
         [0008]     Further objects, advantages and embodiments of the invention can be gathered from the description below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The invention is explained in more detail below on the basis of exemplary embodiments illustrated in the accompanying figures.  
         [0010]      FIG. 1  schematically shows a first exemplary embodiment of a position monitoring device in the form of a position switch.  
         [0011]      FIG. 2  schematically shows a second exemplary embodiment of a position monitoring device.  
         [0012]      FIG. 3  schematically shows a third exemplary embodiment of a position monitoring device.  
         [0013]      FIG. 4  schematically shows a fourth exemplary embodiment of a position monitoring device in the form of a cable line switch. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0014]     The position switch—illustrated in  FIG. 1 —for establishing the closed position of a closing part  1  in the form of a sliding or swivelling gate or flap or the like with respect to a part  2  that can be closed off in the form of a gate opening or access opening in a machine lining, machine fencing or the like comprises a transponder  3 —fitted to the closing part  1 —with a screen  4  and also a transceiver  5 —which is fitted in a stationary manner to the part  2  that can be closed off and which is preferably accommodated in a housing—with a control logic  6  coupled via a direct wire-based or wire-free connection or via a bus  7 , for example a two-wire bus for the voltage supply and signal transmission, to a machine controller  8  for the control of the capability of switching on and the switching off of a machine with hazard potential in a manner dependent on the closed position of the closing part  1 .  
         [0015]     The control logic  6 , which is supplied with power via the bus  7 , a separate terminal, a battery or the like, excites a coil  9  of the transceiver  5 , in particular an air-core coil, preferably periodically to emit interrogation signals. The interrogation signals are electromagnetic waves radiated over a period of time. The electromagnetic waves may have a constant or varying frequency and/or be marked, for example contain information bits in amplitude- or frequency-modulated fashion.  
         [0016]     The interrogation signals are received by a coil  10   a  coupled to a transponder IC  10   b,  for instance a bar-type coil, in the transponder  3 . The received energy expediently supplies the operating energy for the transponder  3 , which, however, may also be supplied with power via the bus  7 , a separate terminal, a battery or the like. In reaction to the interrogation signals, the transponder  3  emits response signals expediently via the same coil  10   a  or, if appropriate, a further coil. In the simplest case, said response signals may have a specific frequency or be marked in some other way, in particular contain information bits, e.g a unique transponder identifier. The response signals may additionally depend on the received information bits; by way of example, a key may be stored in the transponder  3 , by means of which key received information bits are encrypted and subsequently sent back.  
         [0017]     The response signals are expediently received by means of the coil  9  or, if appropriate, a further coil in the transceiver  5  and can be evaluated by the control logic  6 . By way of example, the control logic  6  can evaluate the frequency of the response signals or the marking thereof and thus establish whether, in particular, a specific transponder  3  is present. In this case, the completely closed state is identified and provided to the machine controller  8 , in particular transmitted to the latter or kept ready for being called up. If no or not the correct transponder  3  is established, the open closed state is identified and provided to the machine controller  8 . In a further embodiment, the received signals can be evaluated in the machine controller  8 , in which case the control logic  6  can be omitted.  
         [0018]     The closed position limiting distance is set by means of the screen  4 , which can be adjusted, in particular in a continuously variable manner, between positions having different degrees of attenuation of the signals that propagate between the transceiver  5  and the transponder  3  and which can be fixed, in particular fixedly screwed or fixedly clamped, at least in two positions, but preferably in all or in a plurality of positions, relative to the transponder  3 . The screen  4  may in this case be, as illustrated, a metal sleeve into which the transponder  3  can be inserted and which forms a mount for the transponder  3 . In the inserted position, the screen  4  completely covers the coil  10   a,  thereby achieving a maximum possible attenuation. The closed position limiting distance is the smallest in this position, that is to say that the transponder  3  has to be very near to the transceiver  5  in order that the position switch signals a completely closed state. If the transponder  3  is not inserted into the screen  4 , the attenuation is the least and the closed position limiting distance is the largest, that is to say that the completely closed position is signalled even when there is a large distance between transponder  3  and transceiver  5 . If the transponder  3  is only partially inserted into the sceen  4 , the attenuation and thus the closed position limiting distance lies between the two extreme values.  
         [0019]     In the course of mounting the position switch, therefore, firstly the transponder  3  together with the screen  4  is mounted on the closing part  1  and the transceiver  5  is mounted on the part  2  that can be closed off, or vice versa, at an arbitrary distance, e.g. the transponder  3  adjacent to the edge on a gate and the transceiver on a gate frame, so that transponder  3  and transceiver  5  are adjacent to one another in the closed state of the gate. The transponder  3 , together with the screen  4 , may also project from the surface of the gate, for example in the form of a pin or as part of a mechanical blocking device with an opening for a bolt, in which case a corresponding cutout may then be provided in the transceiver  5  and extend in particular through the interior of the coil  9 , into which at least part of the transponder  3  together with screen  4  engages in the closed state of the access protection device.  
         [0020]     Afterwards, the closed position limiting distance is set by displacing the screen  4  with regard to the transponder  3  or the transponder  3  with regard to the screen  4  such that it is possible to reliably distinguish the completely closed state from the open closed state of the access protection device.  
         [0021]     Instead of being a metal sleeve, the screen  4  may also be formed as a metal sheet or a grid or some other structure which, in an attenuating position, covers at least part of the coil  10   a  of the transponder  3 . The screen  4  may additionally or alternatively also be provided on the transceiver  5 .  
         [0022]     In the embodiment with a transponder  3  engaging into the interior of the coil  9 , the screen  4  may be an inner sleeve which can be inserted into the coil  9  and which, if appropriate, has an axially varying attenuation power and, for this purpose, is thicker for example at one end than at the other end.  
         [0023]     If it is assumed in connection with  FIG. 1  that part  1  is movable vertically to the paper plane, by positioning the screen  4  it is possible to adjust the lateral displacement at which the transponder  3  is still within the reading area of the transceiver  5 . Accordingly it is also possible to adjust the duration interval of the transponder  3  within the reading area and thus the detection time of the transponder  3 . In the case part  1  with the transponder  3  is rotating relative to part  2 , it is possible to adjust the minimum and maximum rotational speed at which the transponder  3  is still detected by the position of the screen  4 .  
         [0024]     In the case of the embodiment illustrated in  FIG. 2 , provision is made of two transponders  3   a,    3   b  arranged on a stationary or movable, for instance longitudinally displaceable, part  11  at a distance from one another in the direction of movement. For each of the two transponders  3   a,    3   b,  there is a coil  9   a,    9   b  arranged in a stationary manner in this regard, which coils are in each case connected to a separate transceiver  6   a,    6   b,  which, for their part, are connected to an evaluation logic  12 . If appropriate, the coils  9   a,    9   b  may enclose the part  11 , as illustrated. The part  11  and a screen  4 , for instance a screening sleeve, are movable relative to one another for instance between two end positions, so that the screen  4 , in the respective end position, can screen one of the two transponders  3   a,    3   b  with respect to its coil  9   a  or  9   b.    
         [0025]     The part  11 , for instance, a bolt, may be movable in its longitudinal direction in accordance with the arrow  14  for example on a closing part such as a gate, while the screen  4  is arranged on a with regard to the closing part stationary closable part in the form of a wall, fencing or the like with gate or access opening in a machine lining, machine fencing or the like, or is Notionally coupled thereto. In accordance with the relative position of the screen  4  with regard to the respective transponder  3   a,    3   b,  it is thus possible to establish the closed or open state of the closing part. If an echo with a sufficient level does not come from any of the transponders  3   a,    3   b,  the closing part is open. If an echo returns from both transponders  3   a,    3   b  or only from a specific one of the two transponders  3   a,    3   b,  the closed position has not yet been reached. If, by contrast, only the other specific one of the two transponders  3   a,    3   b  responds, the closing part is in the closed state with respect to the part that can be closed off.  
         [0026]     What may also be involved in this case, however, is a part e.g. sliding gate, that can be extended or moved with respect to another part, so that it is possible to establish whether the retracted or extended state of the screen-carrying part, for instance, with respect to the part  11  that carries the transponders  3   a,    3   b  is present.  
         [0027]     If appropriate, provision may be made of more than two transponders  3   a,    3   b  arranged at a distance relative to one another with associated coils and transceivers in order to detect different states of extension that are determined by the screening of one of the transponders by the screen.  
         [0028]     The part  11  may also be formed as a plunger of a contactless position switch in a manner displaceable in the housing  13  thereof in a manner coupled to a part that is movable relative to the housing  13 .  
         [0029]     If appropriate, a further transponder  14   a,    14   b  may also be provided in a manner arranged in stationary fashion with respect to each of the at least two coils  9   a,    9   b,  which further transponder can be addressed by the respective coil  9   a,    9   b  in order thus to be able to test the functionality of the position monitoring device.  
         [0030]     If a plurality of position switches are provided, the respective housing  13  may be provided with at least one window  15 , while at least one additional transponder  14   a,    14   b  is arranged on the part to which the housing  13  is fixed, which transponder can be permanently detected by a corresponding coil  9   a,    9   b  in order to supply a corresponding address for the respective position switch in order to be able to distinguish between signals of position switches situated at different locations on the bus  7 . The abovementioned possibility of testing for functionality is afforded if a respective transponder  14   a,    14   b  is present for a respective coil  9   a,    9   b.    
         [0031]     In the case of the embodiment of  FIG. 3  the sceen  4  consists of a sheet strip provided with equidistant holes  16  and is fastened at the moving part  1 , whereby the transponder  3  and the transceiver  5  are stationary with respect to part  1  and thus to sceen  4 . Thus, a kind of an electromagnetic “light barrier” by which for instance the rotational or longitudinal speed of part  1  with respect to part  2  can be determined according to the time distance of detecting the transponder  3  between the interruptions provided by the sceen  4 .  
         [0032]     In the case of the embodiment of  FIG. 4  in the form of a cable line switch, part  1  in the form of a plunger provided with two transponders  3   a,    3   b  spaced to each other in longitudinal direction of part  1  is guided within a housing  17 , extends to the outside of the housing  17  and is provided with a cable line  18  which normally is in tension. Two sceens  4   a,    4   b  which may be sleeve-like and are able to screen the transponders  3   a,    3   b  against the coil  9  of the transceiver  5  are provided. Part  1  is biased by a spring  19  with respect to the housing  17  in the direction against the tension of the cable line  18 . The cable line  18  holds part  1  in a starting position which is a medium position between the transponders  3   a,    3   b  and thus between the sceens  4   a,    4   b  so that both transponders  3   a,    3   b  are in the reading area of the coil  9 . In the case the cable line  18  is actuated, i.e. is pulled, the transponder  3   b  reaches the area of the sceen  4   b  and is thus no more detectable by the coil  9 . This provides the release of a corresponding signal via the coil  9 . In the case the cable line  18  ruptures so that the cable line switch is out of order, the spring  19  pushes part  1  in a position wherein the transponder  3   a  reaches the area of the sceen  4   a  so that the transponder  3   a  is no more detectable by the coil  9 . Because of the transponder codes thus a failure of the switch is detectable and a corresponding disorder signal can be produced.  
         [0033]     It is also possible to use transponders  3  connectable to electronic (digital or analog) transmitters. The transponder  3  can then submit switching conditions and measuring values via his response signal. This may be used in the case information and measuring values of rotating parts  1  have to be transmitted to stationary parts  2 .  
         [0034]     Instead of a metallic sceen  4  it is possible to use one out of a ferromagnetic plastic material or the like.  
         [0035]     The sceen  4  does not need to be sleeve-like, but can also have any geometric form, for instance it can be plate- or spheresurface-like.  
         [0036]     While the invention has been shown and described with reference to preferred embodiments, it should be apparent to one of ordinary skill in the art that many changes and modifications may be made without departing from the spirit and scope of the invention as defined in the claims.