LIGHT CURTAIN

Description

[0001] The invention relates to a light curtain.

[0002] Such a light curtain is previously known, for example, from DE 102010 048 941 A1 or DE 10 2008 050 943 A1. The light curtain is used to monitor objects in a monitored area. In particular, the light curtain is designed as a safety light curtain, which is used in the field of security technology for monitoring hazardous areas. The light curtain comprises an arrangement of transmitters housed in the housing of a transmitter unit. Furthermore, an arrangement of receivers is provided, which are housed in a housing of a receiver unit. The transmitter and receiver units are arranged at opposite edges of the monitored area. When the monitored area is clear, the light beams emitted by a transmitter are guided to an associated receiver. The transmitter and the associated receiver form a beam axis.For object detection, the evaluation unit evaluates the received signals from the receivers and, based on this, generates a binary switching signal as an object detection signal. The switching states indicate whether an object is within the monitoring area or not. An object intrusion occurs when at least one beam axis is interrupted by an object.

[0003] The light curtain operates in such a way that the beam axes, i.e., the transmitters and receivers of the individual beam axes, are cyclically activated one after the other. In the light curtain described in DE 10 2008 050 943 A1, the individual transmitters are activated individually via shift registers. Likewise, the receivers are activated individually via shift registers. Synchronization of the transmitter and receiver activation occurs optically. The light beams of a selected beam axis are used for this purpose.

[0004] To increase the detection sensitivity of the light curtain, the received signals are amplified before they are fed to the evaluation unit.

[0005] It is known to operate one or more amplifiers in a multiplex mode in such a way that several receivers are connected to the respective amplifier one after the other, so that their received signals are amplified in the amplifier.

[0006] The advantage here is that a separate amplifier does not have to be provided for each receiver, so that only a few components have to be provided on the receiving side.

[0007] A disadvantage of such arrangements is that switching operations performed with a multiplexer, which connect a different receiver to the amplifier each time, lead to transient responses in the amplified received signals, meaning the amplified received signals are corrupted. Therefore, a waiting period is required after each switching operation until the transient responses have subsided. However, this leads to an undesirable increase in the light curtain's response time during object detection.

[0008] The invention is based on the object of providing a light curtain of the type mentioned above, which has a structurally simple design and with which reliable object detection can be carried out with short reaction times.

[0009] To achieve this object, the features of the independent claims are provided. Advantageous embodiments and expedient developments of the invention are described in the dependent claims.

[0010] The invention relates to a light curtain for detecting objects in a surveillance area, comprising an array of transmitters emitting light beams, an array of receivers receiving light beams, and an evaluation unit in which, depending on the received signals from the receivers, an object detection signal is generated in the form of a binary switching signal, the switching states of which indicate whether or not an object is present in the surveillance area. At least one amplifier is provided, which is operated in a multiplex mode such that it amplifies received signals from different receivers one after the other. During switching operations in the multiplex mode, any switching interference that occurs in the amplified received signals is compensated for by a compensation signal generated in a controller.

[0011] The invention further relates to a corresponding method.

[0012] The light curtain according to the invention comprises an array of transmitters, which are advantageously integrated into a transmitter unit. Furthermore, the light curtain advantageously comprises a receiver unit in which an array of receivers is arranged. The transmitter unit and the receiver unit are arranged at opposite edges of the monitored area. Each transmitter is advantageously assigned a receiver to form a beam axis such that, when the monitored area is clear, the light beams from one transmitter are guided unhindered to the assigned receiver of the respective beam axis. Objects in the monitored area are detected by interrupting at least the light beams of one beam axis.

[0013] In principle, the light curtain can also be designed as a reflective light curtain. In this case, the transmitters and receivers are housed in a common transmitter / receiver unit located at one edge of the monitored area. At the other edge of the monitored area, a reflector is located as a further component of the light curtain. When the monitored area is clear, the light beams from each transmitter are directed to the reflector and from there reflected back to the assigned receiver.

[0014] The light curtain according to the invention has at least one amplifier operated in multiplex mode on the receiving side, with which received signals from different receivers are amplified sequentially. For this purpose, a multiplexer is provided on the receiving side, which controls the amplifier(s).

[0015] The fact that an amplifier does not have to be assigned to each receiver, but rather that the amplifier or each amplifier takes over the amplification of received signals from several receivers, results in a considerable saving in components, which reduces the design effort of the light curtain.

[0016] According to the invention, switching noise in the amplified received signals that occurs during switching processes in multiplex operation is reduced by outputting compensation signals generated in a controller to the amplifier(s). The compensation signals compensate for, i.e., largely suppress, switching noise, particularly transient phenomena in the amplified received signals.

[0017] Since there are no longer any significant amounts of transient phenomena in the amplified received signals, the amplified received signals can be evaluated more quickly and without long waiting times in the evaluation unit to generate the object detection signal, resulting in short reaction times.

[0018] In the simplest case, there is only one amplifier with which all receivers are operated in multiplex mode.

[0019] Alternatively, several amplifiers are available, each of which operates a group of receivers in multiplex mode.

[0020] The groups of receivers can form cascades, which essentially form independent, separately controllable sensor units.

[0021] According to an advantageous embodiment, the controller is part of the evaluation unit.

[0022] This results in a particularly compact design of the electronic components on the receiving side.

[0023] Compensation signals can advantageously be fed to at least one amplifier via a coupling circuit.

[0024] The compensation signals are fed to the amplifier(s) without any feedback.

[0025] Non-reactive means that the compensation signals do not affect the respective receiver, i.e., its received signals are unaffected by the compensation signals. This can be achieved, in particular, by deactivating the compensation circuit in the receiver during reception of light beams.

[0026] The compensation signals can be implemented in the form of voltage dividers or passive networks.

[0027] The compensation signals can be diodes or transistors with a preferred direction. The passive networks can consist of semiconductors and passive components. Amplifier elements can also be used to implement compensation signals.

[0028] According to an alternative embodiment, the compensation signals are bus signals.

[0029] The compensation signals are then generated in a controller of a bus system.

[0030] In this case, bus signals can contain test signals by means of which one or more amplifiers are tested.

[0031] It is advantageous to generate test signals at times when the receiver is not expecting any signals, i.e., when the receiver is not receiving any light beams from the transmitter. The test signals are read back into the controller via the bus system and compared there with expected values, i.e., target signals, to determine whether the respective receiver is operating correctly.

[0032] It is advantageous to attenuate received signals amplified by means of the compensation signals.

[0033] This effectively suppresses transient phenomena in the amplified received signals.

[0034] Advantageously, the amplitudes and / or curve shapes of compensation signals are specified by means of the control.

[0035] Furthermore, pulse-shaped compensation signals can be present, the pulse widths of which can be specified by the controller.

[0036] Another advantage is that the compensation signals are regulated during the switching processes.

[0037] The compensation signals are generally in the form of current or voltage signals. The compensation signals are controlled to specified setpoints. In particular, differential controllers can be used, which enable an immediate response to disturbance pulses.

[0038] It is particularly advantageous if the compensation signals are routed to an output and / or input of the or each amplifier.

[0039] In any case, the amplifiers are directly supplied with the compensation signals.

[0040] According to a first variant, the compensation signals are specified the same for all receivers.

[0041] According to an alternative embodiment, the compensation signals are specified individually for all receivers.

[0042] According to a further alternative embodiment, the compensation signals are specified individually for different groups of receivers.

[0043] According to an advantageous embodiment, the compensation signals are determined in a learning process.

[0044] The compensation signals thus learned can then be adopted for a working operation of the light curtain following the learning process.

[0045] Furthermore, it is possible for the learned compensation signals to be used as basic compensation signals in a subsequent operating mode following a teach-in process. In addition, partial compensation signals can be generated to supplement the basic compensation signals.

[0046] The basic compensation signals then form a baseline compensation for the start of operation. The partial compensation signals can then be used to additionally compensate for interference caused by component drift and the like.

[0047] According to an advantageous embodiment, the light curtain is a safety sensor. The light curtain then has a fail-safe design and can thus be used in safety-related applications. The fail-safe design can be implemented, in particular, by means of a multi-channel evaluation unit.

[0048] The invention is explained below with reference to the drawings. They show: Figure 1: Schematic representation of an embodiment of the light curtains according to the invention. Figure 2: Receiving-side circuit arrangement for the light curtain according to Figure 1 . Figure 3:Exemplary embodiments of coupling circuits for the circuit arrangement according to Figure 2Figure 4: Timing diagram for amplified received signals from light curtain receivers with switching noise caused by switching operations of a multiplexer. Figures 5a-d: Examples of compensation signals for compensating switching noise in amplified received signals from light curtain receivers. Figure 6: Timing diagram for amplified received signals from light curtain receivers with switching noise compensated with compensation signals. Figures 7a-b: Timing diagrams for feeding test signals into the circuit arrangement according to Figure 2 .

[0049] Figure 1shows the basic structure of the light curtain 1 according to the invention. The light curtain 1 comprises a transmitter unit 2, in whose housing a series arrangement of transmitters 4 emitting light beams 3 in the form of transmitting diodes is arranged. The transmitting diodes are formed by light-emitting diodes or the like. The light curtain 1 further comprises a receiver unit 5, in whose housing a series arrangement of receivers 6 receiving light beams 3 in the form of receiving diodes is provided. The receiving diodes are formed by photo-PIN diodes or photodiodes. Alternatively, phototransistors can also be used.

[0050] The transmitter unit 2 and the receiver unit 5 are arranged at opposite edges of a monitored area. When the monitored area is clear, the light beams 3 emitted by each transmitter 4 strike an associated, opposite receiver 6. A transmitter 4 and the associated receiver 6 each form a beam axis. Transmitter operation is controlled and evaluated by a control unit 7 in the transmitter unit 2. Receiver operation is controlled by an evaluation unit 8 in the receiver unit 5. The transmitters 4 and receivers 6 of the individual beam axes are cyclically activated individually or in groups one after the other by optical synchronization of the light curtain 1. The parallel light beams 3 of the beam axes monitor a protective field running in one plane.

[0051] In the evaluation unit 8, the received signals from the receiving diodes are evaluated to generate a binary switching signal as an object detection signal. The first switching state corresponds to an object detection, the second switching state to a free protective field.

[0052] The light curtain 1 forms a safety sensor for use in safety technology. For this purpose, the light curtain 1 has a fail-safe design. In particular, the evaluation unit 8 has a multi-channel, redundant design, for example, in the form of two cyclically monitoring computer units.

[0053] Figure 2 shows a receiving-side circuit arrangement for the light curtain 1 according to Figure 1 .

[0054] For the sake of clarity, only four of the receivers 6 of the light curtain 1 are shown in Figure 2 shown.

[0055] The circuit arrangement includes a controller 9, which in this case is part of the evaluation unit 8. The controller 9 controls a multiplexer 10 by outputting control signals 11. As a result, in multiplex operation, the receivers 6 are connected to an amplifier 12 one after the other. Thus, only one amplifier 12 is required to amplify the received signals of all receivers 6.

[0056] The order according to Figure 2 can also be extended to several amplifiers 12, with each amplifier 12 being assigned a group of receivers 6.

[0057] The controller 9 outputs compensation signals via a first line 13 to a first coupling circuit 14a, which feeds the compensation signals to the input of the amplifier 12. The controller 9 further outputs compensation signals via a second line 15 to a second coupling circuit 14b, which feeds compensation signals to the output of the amplifier 12. Furthermore, the controller 9 feeds compensation signals via the first line 13 to coupling circuits 14c, each of which is assigned to a receiver 6.

[0058] The coupling circuits 14a to 14c do not all have to be provided simultaneously. It is particularly advantageous to have only the coupling circuit 14a or the coupling circuit 14b present.

[0059] Figure 3 shows possible components for the coupling circuits 14a to 14c, which can be assigned to an amplifier 12.

[0060] These components include a passive network, which in this case is a voltage divider 16, semiconductor elements, such as a diode 17, amplifier elements 18 and / or a damping circuit 19.

[0061] Figure 4 shows timing diagrams for amplified received signals without the injection of compensation signals for the arrangement according to Figure 2 . T 1 , T 2 , T 3 denote time intervals in which a receiver 6 is activated one after the other and whose received signals are amplified in the amplifier 12.

[0062] How Figure 4As shown, switching disturbances II caused by the switching processes of the multiplexer 10 are superimposed on the useful signals (denoted by I). In order to carry out error-free evaluation of the useful signals I in the evaluation unit 8, a settling time T must be waited for until the switching disturbances II have subsided. Only then is an evaluation of the amplified received signals in the evaluation unit 8 possible, which undesirably increases the reaction time b when generating the object detection signal.

[0063] These disadvantages are avoided by the compensation signals according to the invention.

[0064] The Figures 5a to 5d show pulse sequences of different pulse-shaped compensation signals. In the embodiment according to Figure 5a the pulse heights of the compensation signals vary. In the embodiment according to Figure 5b The pulse widths of the compensation signals vary. In the embodiment according to Figure 5cPulse widths and pulse widths of the compensation signals vary. In the embodiment according to Figure 5d The waveforms of the compensation signals vary. The compensation signals are specified by controller 9.

[0065] It is advantageous to attenuate received signals amplified by means of the compensation signals.

[0066] Furthermore, the compensation signals can be controlled during the switching processes.

[0067] In the simplest case, the compensation signals are specified the same for all receivers 6.

[0068] Alternatively, the compensation signals are specified individually for all receivers 6.

[0069] The result of the compensation of switching disturbances using compensation signals shows Figure 6. The switching disturbances due to transient processes are almost completely eliminated in the amplified received signals, so that the useful signals I of the amplified received signals can be transferred to the evaluation unit 8 for evaluation with a short waiting time T'.

[0070] According to a variant of the embodiment according to Figure 2 the controller 9 can be part of a bus system, in which case compensation signals are fed to the amplifier 12 via bus lines.

[0071] In this case, in addition to compensation signals, test signals a can also be fed to the amplifier 12 ( Figure 7a ). The response of amplifier 12 (in Figure 7b (denoted by b) is read back into the controller 9 and compared there with an expected value, which can be specified in the form of setpoints. This allows the amplifier 12 to be tested. List of reference symbols

[0072] (1)Light curtain (2)Transmitter unit (3)Light beam (4)Transmitter (5)Receiver unit (6)Receiver (7)Control unit (8)Evaluation unit (9)Control (10)Multiplexer (11)Control signal (12)Amplifier (13)Cable (14a)Coupling circuit (14b)Coupling circuit (14c)Coupling circuit (15)Cable (16)Voltage divider (17)Diode (18)Amplifier element (19)Damping circuit (T)Settling time (T)Waiting time (T 1 )Time interval (T 2 )Time interval (T 3 )Time interval IUseful signal IISwitching fault (a)Test signal (b)Reaction time

Claims

1. A light curtain (1) for detecting objects in a monitoring area, having an arrangement of transmitters (4) emitting light beams (3), having an arrangement of receivers (6) receiving light beams (3), and having an evaluation unit (8) in which an object detection signal in the form of a binary switching signal, the switching states of which indicate whether an object is present in the monitoring area or not, is generated as a function of received signals from the receivers (6), is generated, characterised in that at least one amplifier (12) is provided which is operated in a multiplex mode in such a way that it is used to amplify received signals from different receivers (6) in succession over time, and in that switching interference II occurring in the amplified received signals during switching operations of the multiplex mode is compensated for by compensation signals generated in a controller (9).

2. A light curtain (1) according to claim 1, characterised in that only one amplifier (12) is present, with which all receivers (6) are operated in multiplex mode.

3. A light curtain (1) according to claim 1, characterised in that a plurality of amplifiers (12) are provided, by means of which a group of receivers (6) is operated in multiplex mode in each case.

4. A light curtain (1) according to one of claims 1 to 3, characterised in that the control unit (9) is part of the evaluation unit (8).

5. A light curtain (1) according to one of claims 1 to 4, characterised in that compensation signals can be fed to the at least one amplifier (12) via a coupling circuit (14a-c).

6. A light curtain (1) according to claim 5, characterised in that the compensation signals are fed to the amplifier or amplifiers (12) without feedback.

7. A light curtain (1) according to one of claims 1 to 3, characterised in that the compensation signals are bus signals.

8. A light curtain (1) according to claim 7, characterised in that bus signals comprise test signals (a) by means of which the amplifier or amplifiers (12) are tested.

9. A light curtain (1) according to one of claims 1 to 8, characterised in that amplified received signals are attenuated by means of the compensation signals.

10. A light curtain (1) according to one of claims 1 to 9, characterised in that the compensation signals are regulated during the switching operations.

11. A light curtain (1) according to one of claims 1 to 10, characterised in that the compensation signals are routed to an output and / or input of the or each amplifier (12).

12. A light curtain (1) according to one of claims 1 to 11, characterised in that the compensation signals are specified in the same way for all receivers (6).

13. A light curtain (1) according to one of claims 1 to 12, characterised in that the compensation signals are specified individually for all receivers (6).

14. A light curtain (1) according to claim 3, characterised in that the compensation signals are specified individually for different groups of receivers (6).

15. A light curtain (1) according to one of claims 1 to 14, characterised in that the amplitude and / or waveform of compensation signals is predetermined by means of the controller (9).

16. A light curtain (1) according to one of claims 1 to 15, characterised in that pulse-shaped compensation signals are present, the pulse widths of which can be preset by the controller (9).

17. A light curtain (1) according to one of claims 1 to 16, characterised in that the compensation signals are determined in a teach-in process.

18. A light curtain (1) according to claim 17, characterised in that the taught-in compensation signals are used as basic compensation signals in an operating mode following a teach-in process, and in that additional partial compensation signals are generated to supplement the basic compensation signals.

19. A light curtain (1) according to claim 18, characterised in that this is a safety sensor.

20. A method for detecting objects in a surveillance area by means of a A light curtain (1) with an arrangement of transmitters (4) emitting light beams (3), with an arrangement of receivers (6) receiving light beams (3), and with an evaluation unit (8) in which an object detection signal in the form of a binary switching signal, the switching states of which indicate whether an object is present in the surveillance area or not, is generated as a function of received signals from the receivers (6), is generated, characterised in that at least one amplifier (12) is present which is operated in a multiplex mode in such a way that it is used to amplify received signals from different receivers (6) in succession over time, and in that switching interference II occurring in the amplified received signals during switching operations of the multiplex mode is compensated for by a compensation signal generated in a controller (9).