Light curtain

Abstract

Light curtain (1) for detecting objects in a monitoring area, with an arrangement of light beams (3) emitting transmitters (4), with an arrangement of light beams (3) receiving receivers (6, 6'), and with an evaluation unit (8) in which an object detection signal is generated depending on received signals from the receivers (6, 6'), characterized in that the receivers (6, 6') form at least one cascade, and that the receivers (6, 6') are individually connected to an amplifier (12, 12') one after the other by means of a multiplexer (11, 11'), wherein when a receiver (6) is activated the amplifier (12, 12') is deactivated.

Description

[0001] The invention relates to a light curtain.

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

[0003] The light curtain operates by cyclically activating the beam axes, i.e., the transmitters and receivers of each beam axis, 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. The receivers are also activated individually via shift registers. Synchronization of the transmitter and receiver activation is achieved optically. For this purpose, the light beams of a selected beam axis are used.

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

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

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

[0007] One disadvantage of such arrangements is that switching operations performed with a multiplexer, in which a different receiver is added to the amplifier each time, lead to transient responses in the amplified received signals, i.e., the amplified received signals are distorted. 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 reaction time of the light curtain during object detection.

[0008] The invention is based on the objective 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] The features of the independent claims are provided to solve this problem. Advantageous embodiments and expedient further developments of the invention are described in the dependent claims.

[0010] The invention relates to a light curtain for detecting objects in a monitoring area, comprising an arrangement of light-beam emitting transmitters, an arrangement of light-beam receiving receivers, and an evaluation unit in which an object detection signal is generated depending on the received signals from the receivers. The receivers form at least one cascade. The receivers are individually and sequentially connected to an amplifier by means of a multiplexer, whereby the amplifier is deactivated when a receiver is activated.

[0011] According to a first embodiment, the light curtain comprises an array of transmitters, advantageously integrated within a transmitter unit housing. Furthermore, the light curtain advantageously comprises a receiver unit integrated within a separate housing, in which an array of receivers is arranged. The transmitter unit and the receiver unit are positioned at opposite edges of the monitored area. Each transmitter is advantageously assigned a receiver to form a beam axis such that, with the monitored area clear, the light beams from a transmitter are guided unimpeded to the assigned receiver of the respective beam axis. An object within the monitored area is detected by the interruption of at least the light beams of one beam axis.

[0012] According to a second variant, both the first and the second housing contain transmitters and receivers as sensor components.

[0013] In particular, each housing contains an alternating row arrangement of transmitters and receivers.

[0014] In this case as well, the transmitters and receivers are arranged so that, with a clear monitoring area, the light beams from each transmitter pass through the monitoring area unimpeded and reach their assigned receiver. In this case too, an object within the monitoring area is detected by the interruption of at least the light beams along one axis.

[0015] The light curtain generally generates an object detection signal when an object is detected.

[0016] According to one variant, the object detection signal is a binary switching signal whose switching states indicate whether an object is present in the monitored area or not.

[0017] According to a second variant, the object detection signal contains a geometric characteristic of a detected object.

[0018] The geometric parameter can be the object size or object contour of an object.

[0019] In an advantageous embodiment, the light curtain functions as a safety sensor. The light curtain then has a fail-safe design and can thus be used in safety-related applications. This fail-safe design can be implemented, in particular, by means of a multi-channel evaluation unit.

[0020] The light curtain according to the invention has at least one multiplexed amplifier on the receiving side, with which received signals from different receivers are amplified sequentially. For this purpose, each amplifier is assigned a multiplexer on the receiving side.

[0021] Because not every receiver needs to have its own amplifier, but rather each amplifier takes over the amplification of received signals from multiple receivers, a significant saving in components results, which reduces the design effort of the light curtain.

[0022] In the simplest case, the light curtain according to the invention has only a cascade of receivers, to which only a multiplexer and an amplifier are assigned.

[0023] Furthermore, the light curtain according to the invention can have several cascades of receivers, wherein the receivers of each cascade are connected to an amplifier by means of a multiplexer.

[0024] In any case, a multiplexer is used to connect the receivers of the respective cascade individually and sequentially to the respective amplifier.

[0025] According to the invention, when a receiver is connected to the amplifier, this amplifier is deactivated.

[0026] It is also particularly advantageous to deactivate the amplifier when a receiver is switched on.

[0027] This prevents, in a simple way, the switching operations of the multiplexer, which serve to connect individual receivers to the assigned amplifier, from affecting or significantly impairing the received signals amplified in the amplifier.

[0028] Since the amplifier is deactivated during activation via a multiplexer, and advantageously also during deactivation of the connection of a receiver to the receiver, it remains unaffected by these switching processes. The amplifier is only activated once these switching processes are complete.

[0029] This ensures in a simple way that the received signals amplified in the amplifier are not affected by switching interference, thus guaranteeing reliable and error-free object detection.

[0030] Another advantage is the very short response time when generating the object detection signal. Since each amplifier is deactivated during switching operations of the associated multiplexer, switching disturbances caused by the multiplexer are not transmitted to the amplifier.

[0031] This eliminates waiting times for amplifying the received signals, which would otherwise be necessary to allow any switching disturbances present in the received signal to subside.

[0032] According to an advantageous embodiment, a cascade control is provided in the light curtain, by means of which the multiplexer or all multiplexers are controlled.

[0033] The cascade control can, for example, be formed by a controller.

[0034] Because the cascade control centrally controls all multiplexers and thus the timing of the activation of all receivers, the timing of receiver activation can be easily optimized and controlled.

[0035] Cascade control is particularly advantageous as part of a computer assembly that contains the evaluation unit.

[0036] The computer assembly thus has a compact, efficient design, since the evaluation unit is directly assigned to the cascade control.

[0037] In the simplest case, the evaluation unit is designed as a single channel and advantageously consists of only one CPU.

[0038] Advantageously, the evaluation unit consists of two mutually monitoring CPUs. This gives the evaluation unit a redundant, multi-channel design, allowing the light curtain to function as a safety sensor.

[0039] According to advantageous embodiments, each multiplexer has a sliding chain or an addressing unit.

[0040] The addressing unit generally has addresses for addressing the receivers and amplifiers. The shift chain has a series arrangement of shift register elements, with each shift register element advantageously assigned to a receiver or amplifier for addressing within the shift chain.

[0041] The addressing unit can be implemented in a computer unit. The shift chain can consist of a series of flip-flops, with the flip-flops forming the shift register elements of the shift chain.

[0042] Advantageously, the activation and deactivation of receivers and / or amplifiers is derived from the shift chain or the addressing unit.

[0043] Alternatively, the activation and deactivation of receivers and / or amplifiers is carried out using cascade control.

[0044] The functionality of the multiplexers can be further extended by activating display devices via the shift chain or the addressing unit.

[0045] The addresses of the addressing unit or shift register elements of the shift chain are then extended in such a way that display devices can also be addressed and thereby activated with them.

[0046] The display devices can consist of light-emitting diodes or alphanumeric displays, on which status messages or the like are displayed, in particular also with spatial resolution for the individual cascades.

[0047] According to a further advantageous embodiment, the assigned amplifier is tested using the shift chain or the addressing unit.

[0048] In particular, test pulses are generated for testing in the shift chain or addressing unit, fed to the amplifier, and read back from it. In the shift chain or addressing unit, the returned test pulses are compared with an expected value.

[0049] Target values ​​corresponding to a fault-free state can be specified as expectations. If the returned test pulses deviate from the target values, an error message can be generated. Alternatively, a safety function can be triggered. In particular, the light curtain can be stopped.

[0050] In the event that the light curtain has several cascades of receivers, each amplifier is assigned an amplifier addressing unit, which is controlled by the assigned multiplexer.

[0051] The amplifier addressing units select the amplifiers of the individual cascades.

[0052] According to a beneficial further development, the amplifier addressing units can also be used to test the amplifiers of the individual cascades.

[0053] Particularly advantageous is the cascade control of each amplifier addressing unit for activating or deactivating the assigned amplifier.

[0054] Then, the timing of the activations of the individual components can be centrally specified and controlled via cascade control.

[0055] The invention will be explained below with reference to the drawings. The drawings show: Fig. 1: Schematic representation of a first embodiment of the light curtain according to the invention. Fig. 2: Schematic representation of a second embodiment of the light curtain according to the invention. Fig. 3: First example of a receiver-side circuit arrangement for the light curtain according to Fig. 1. Fig. 4: Assignment of an evaluation unit to the cascade control according to Fig. 3. Fig. 5: Timing diagrams for the circuit arrangement according to Fig. 3. Fig. 6: Second example of a receiver-side circuit arrangement for the light curtain according to Fig. 1. Fig. 7: Third example of a receiver-side circuit arrangement for the light curtain according to Fig. 1.

[0056] Fig. Figure 1 schematically shows a first example of the light curtain 1 according to the invention. The light curtain 1 comprises a transmitter unit 2, in the housing of which a series of light-beam-emitting transmitters 4 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 the housing of which a series of receiving receivers 6 in the form of receiving diodes are provided. The receiving diodes are formed by photo-PIN diodes or photodiodes. Alternatively, phototransistors can also be used.

[0057] The transmitter unit 2 and the receiver unit 5 are arranged at opposite edges of a monitoring area. When the monitoring area is clear, the light beams 3 emitted by each transmitter 4 strike an associated, opposite receiver 6. Each transmitter 4 and its associated receiver 6 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 succession by optical synchronization of the light curtain 1. The parallel light beams 3 of the beam axes monitor a protective field extending in a plane.

[0058] In 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 message, the second switching state to a clear protective field. Alternatively, a geometric characteristic of an object, such as its size or contour, can be output as the object detection signal.

[0059] The light curtain 1 forms a safety sensor for use in security 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 computer units that cyclically monitor each other.

[0060] Fig. Figure 2 shows a second embodiment of the light curtain 1 according to the invention. In this case, the light curtain 1 has two transmitter-receiver units 9a, 9b, each integrated in a housing. Each transmitter-receiver unit 9a, 9b contains a series arrangement of transmitters 4 and receivers 6, with an alternating arrangement of transmitters 4 and receivers 6 in this case. Each transmitter-receiver unit 9a, 9b contains a control and evaluation unit 10a, 10b, by means of which the transmitters 4 located therein are controlled and received signals from the receivers 6 located therein are evaluated. Otherwise, the light curtain 1 corresponds to the invention shown in Figure 2. Fig. 2 according to the light curtain 1 Fig. 1.

[0061] Fig. Figure 3 shows a receiver-side circuit arrangement for the light curtain 1 according to Fig. 1. A largely corresponding circuit arrangement is also available for the light curtain 1 according to Fig. 2 are planned.

[0062] The circuit arrangement according to Fig. 3 comprises a multiplexer 11, to which an amplifier 12, which in particular forms a preamplifier, is connected.

[0063] The receivers 6 of the light curtain 1 form a cascade in this case. Accordingly, all receivers 6 are connected to the multiplexer 11.

[0064] Furthermore, a cascade control unit 13 is present, which is formed by a controller or the like. A first control line 14 runs from the cascade control unit 13 to the multiplexer 11. Control signals are sent from the cascade control unit 13 to the multiplexer 11 via control line 14. A second control line 15 also runs from the cascade control unit 13 to the amplifier 12. Control signals are sent from the cascade control unit 13 to the amplifier 12 via the second control line 15.

[0065] A line 16 leads from amplifier 12 to the cascade control unit 13. The amplifiers 12 and 12' send amplified received signals from the receivers 6 to the cascade control unit 13 via line 16.

[0066] According to advantageous embodiments, each multiplexer 11, 11' has a sliding chain or an addressing unit.

[0067] The addressing unit generally has addresses for addressing the receivers 6 and amplifiers 12. The shift chain has a series arrangement of shift register elements, wherein each shift register element is advantageously assigned a receiver 6 or amplifier for addressing within the shift chain.

[0068] The addressing unit can be implemented in a computer unit. The shift chain can consist of a series of flip-flops, with the flip-flops forming the shift register elements of the shift chain.

[0069] The control signal from the cascade control 13, which is fed to the multiplexer 11 via the control line 14, activates the receivers 6 cyclically, one after the other, and connects them to the amplifier 12, where the received signals of that receiver 6 are amplified. In principle, the activation of receivers 6 could also be carried out directly via the multiplexer 11.

[0070] The amplified received signals are fed to the evaluation unit 8 by the cascade control 13. Fig. Figure 4 shows an example that applies to all embodiments of the Fig. 3, Fig. 5, Fig. 6 is valid.

[0071] The amplified received signals from the cascade control unit 13 are fed via lines 17, 17' in a dual-channel configuration to two CPUs 18a, 18b, which form the evaluation unit 8. Depending on the amplified received signals, the object detection signal is generated in the CPUs 18a, 18b, which is output via a dual-channel output structure formed by outputs 19a, 19b of the CPUs 18a, 18b.

[0072] The functionality of the multiplexer 11 can be further extended by activating display devices via the shift chain or the addressing unit.

[0073] The addresses of the addressing unit or shift register element of the shift chain are then extended in such a way that display devices can also be addressed and thereby activated with them.

[0074] The display devices can consist of light-emitting diodes or alphanumeric displays.

[0075] According to a further advantageous embodiment, the assigned amplifier 12 is tested by means of the shift chain or by means of the addressing unit.

[0076] In particular, test pulses are generated for testing in the shift chain or addressing unit, fed to amplifier 12, and read back from it. In the shift chain or addressing unit, the returned test pulses are compared with an expected value.

[0077] Target values ​​corresponding to a fault-free state can be specified as expectations. If the returned test pulses deviate from the target values, an error message can be generated. Alternatively, a safety function can be triggered. In particular, light curtain 1 can be stopped.

[0078] Fig. Figure 5 shows timing diagrams for the activation according to the invention of receivers 6 and the amplifier 12 of the circuit arrangement according to Fig. 3. For the sake of clarity, only 6 time diagrams are shown for four recipients.

[0079] The upper time graph of Fig. Figure 5 shows the activation intervals T1a, T1b, T1c, T2d, within which only one of the receivers 6 is activated.

[0080] To activate a receiver 6, the multiplexer 11 generates a switching pulse Ta, Tb, Tc, Td.

[0081] According to the invention, amplifier 12 is deactivated during the switching processes. For this purpose, amplifier 12 is only activated during the activation intervals T2a, T2b, T2c, T2d, which lie outside the switching pulses Ta, Tb, Tc, Td ( Fig. 5 middle diagram).

[0082] The activation intervals T2a, T2b, T2c, T2d are dimensioned such that the amplifier 12 is activated when the receivers 6 receive light beams 3 in the form of light pulses L1, L2, L3, L4 from the associated transmitters 4 ( Fig. 5 lower diagram).

[0083] Since the amplifier 12 is deactivated during the switching operations of the receivers 6, no interference caused by the switching operations is transmitted to the amplifier 12.

[0084] Fig. Figure 6 shows another receiver-side circuit arrangement for the light curtain 1 according to Fig. 1.

[0085] In this case, two cascades with receivers 6 and 6' are provided. In a first cascade, receivers 6 are connected to a first multiplexer 11 with a first amplifier 12. A first amplifier addressing unit 20 is assigned to the first amplifier 12, which is controlled by the cascade control unit 13 via the control line 15.

[0086] The first multiplexer 11 controls the first amplifier addressing unit 20 via a control line 21.

[0087] Accordingly, a second cascade of receivers 6' is connected to a second multiplexer 11' with a second amplifier 12'. A second amplifier addressing unit 20' is assigned to the second amplifier 12', which is controlled by the cascade control unit 13 via the control line 15.

[0088] The second multiplexer 11' controls the second amplifier addressing unit 20' via a control line 21'.

[0089] The cascade control 13 controls the operation of both cascades via the control lines 14, 14', which are led to the multiplexers 11, 11' and via the control line 15, which is led to the amplifier addressing units 20, 20'.

[0090] The receivers 6, 6' to be activated are selected via control lines 14, 14', while the activation of the amplifiers 12, 12' is controlled via control line 15. The selection of the amplifiers 12, 12' is made via control lines 21, 21'. These control lines 21, 21' can also be used to test the amplifiers 12, 12'.

[0091] The received signals amplified in the amplifiers 12, 12' are fed via line 16 to the cascade control 13 and then to the evaluation unit 8.

[0092] Otherwise, the functionality of the circuit arrangement corresponds to Fig. 6 of the embodiment according to Fig. 3, in particular also the time diagrams according to Fig. 4 are valid.

[0093] Fig. Figure 7 shows a variant of the embodiment according to Fig. 6. The embodiment according to Fig. 7 differs from the embodiment according to Fig.6 only because no control line 15 is led from the cascade control 13 to the amplifier addressing units 20, 20'. Consequently, the multiplexers 11, 11' take over the complete control of the amplifier addressing units 20, 20' via the control lines 21, 21'. List of reference symbols 1 light curtain 2 transmitter units 3 light beam 4 transmitters 5 receiver unit 6, 6' receiver 7 Control unit 8 evaluation units 9a, b Transmitter-receiver unit 10a, b Control and evaluation unit 11, 11' Multiplexer 12, 12' Amplifier 13 Cascade control 14, 14' Control line 15 Control line 16 Line 17, 17' Line 18a, b CPU 19a, b Exit 20, 20' Amplifier addressing unit 21, 21' Control line QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2008 050 943 A1 [0002, 0003]

Claims

[1] Light curtain (1) for detecting objects in a surveillance area, with an arrangement of transmitters (4) emitting light beams (3), with an arrangement of receivers (6, 6') receiving light beams (3), and with an evaluation unit (8) in which an object detection signal is generated depending on the received signals of the receivers (6, 6'), characterized by that the receivers (6, 6') form at least one cascade, and that the receivers (6, 6') are connected individually one after the other to an amplifier (12, 12') by means of a multiplexer (11, 11'), wherein when a connection of a receiver (6) is activated, the amplifier (12, 12') is deactivated. [2] Light curtain (1) according to claim 1, characterized by that when a receiver (6) is deactivated, the amplifier (12, 12') is deactivated. [3] Light curtain (1) according to one of claims 1 or 2, characterized bythat several cascades of receivers (6, 6') are present, wherein the receivers (6, 6') of each cascade are connected to an amplifier (12, 12') by means of a multiplexer (11, 11'). [4] Light curtain (1) according to one of claims 1 to 3, characterized by that a cascade control (13) is provided by means of which the or all multiplexers (11, 11') are controlled. [5] Light curtain (1) according to claim 4, characterized by that the cascade control (13) is part of a computer module which contains the evaluation unit (8). [6] Light curtain (1) according to claim 5, characterized by that the computer module has a CPU or two mutually monitoring CPUs (18a, 18b) as the evaluation unit (8). [7] Light curtain (1) according to one of claims 1 to 6, characterized by that each multiplexer (11, 11') has a shift chain or an addressing unit. [8] Light curtain (1) according to claim 7, characterized bythat the activation and deactivation of receivers (6, 6') and / or amplifiers (12, 12') is derived from their shift chain or the addressing unit. [9] Light curtain (1) according to one of claims 4 to 6, characterized by that the activation and deactivation of receivers (6, 6') and / or amplifiers (12, 12') is carried out by means of the cascade control (13). [10] Light curtain (1) according to one of claims 7 to 9, characterized by that display means are activated by means of the sliding chain or by means of the addressing unit. [11] Light curtain (1) according to one of claims 7 to 10, characterized by that the associated amplifier (12, 12') is tested by means of the shift chain or by means of the addressing unit. [12] Light curtain (1) according to claim 11, characterized bythat test pulses are generated for testing in the shift chain or in the addressing unit, fed to the amplifier (12, 12') and read back by the latter, wherein test pulses read back in the shift chain or in the addressing unit are compared with an expected setting. [13] Light curtain (1) according to claim 3, characterized by that each amplifier (12, 12') is assigned an amplifier addressing unit (20, 20') which is controlled by the assigned multiplexer (11, 11'). [14] Light curtain (1) according to claim 13, characterized by that the multiplexer (11, 11') controls the amplifier addressing unit (20, 20') for selecting an amplifier (12, 12') and / or for testing an amplifier (12, 12'). [15] Light curtain (1) according to one of claims 4 and 13, characterized by that each amplifier addressing unit (20, 20') is controlled by the cascade control (13) to activate or deactivate the associated amplifier (12, 12'). [16] Light curtain (1) according to one of claims 1 to 15, characterized by that the object detection signal is a binary switching signal whose switching states indicate whether an object is present in the monitoring area or not. [17] Light curtain (1) according to one of claims 1 to 16, characterized by that the object detection signal contains a geometric characteristic of a detected object. [18] Light curtain (1) according to one of claims 1 to 17, characterized by that it has two housings arranged at opposite edges of the monitoring area, each of which contains sensor components. [19] Light curtain (1) according to claim 18, characterized by that a series arrangement of transmitters (4) is present as sensor components in a first housing, and that a series arrangement of receivers (6, 6') is present in the second housing. [20] Light curtain (1) according to claim 18, characterized bythat both the first and the second housing contain transmitter (4) and receiver (6, 6') as sensor components. [21] Light curtain (1) according to claim 20, characterized by that in each housing there is an alternating series arrangement of transmitters (4) and receivers (6, 6'). [22] Light curtain (1) according to one of claims 1 to 21, characterized by that this is a safety sensor.

Images