Light curtain

Abstract

The invention relates to a light curtain (1) for detecting objects in a monitoring region, comprising an arrangement of emitters (4) emitting a light beam (3), an arrangement of receivers (6, 6 ') receiving the light beam (3), and an evaluation unit (8), in which an object determination signal is generated as a function of a received signal of the receivers (6, 6'). The receivers (6, 6 ') form at least one cascade, and the amplifiers (12, 12') are individually switched on one after the other by means of multiplexers (11, 11 '), the amplifiers (12, 12') being deactivated when the switching of the receivers (6) is activated.

Description

Field of the Invention

[0001] The present invention relates to a light curtain. Background Art

[0002] This type of light curtain is known, for example, from DE 10 2008 050 943 A1. The light curtain is used to monitor objects in a monitoring area. In particular, the light curtain is configured as a safety light curtain, which is used in the field of safety technology to monitor a hazardous area. The light curtain includes an arrangement of transmitters mounted in a housing of a transmitter unit. In addition, an arrangement of receivers mounted in a housing of a receiver unit is provided. The transmitter and receiver units are arranged on opposite edges of the monitoring area. In the empty monitoring area, the light beams emitted from the transmitters are directed to the assigned receivers. The transmitters and the assigned receivers form light beam axes. When detecting an object, the received signals of the receivers are analyzed and processed in an analysis and processing unit, and a binary switch signal is generated therefrom as an object determination signal. The switch state of the binary switch signal indicates whether an object is located in the monitoring area. When at least one light beam axis is interrupted by an object, there is an object intervention.

[0003] The light curtain operates such that the light beam axes (i.e., the transmitters and receivers of the individual light beam axes) are activated successively one by one periodically. In the light curtain described in DE 10 2008 050943A1, the individual transmitters are activated one by one by a shift register. Similarly, the receivers are activated one by one by a shift register. The synchronization of the transmitter and receiver activation is carried out visually. For this purpose, the light beams of the selected light beam axes are used.

[0004] In order to improve the indication sensitivity of the light curtain, the received signal is amplified before being supplied to the analysis and processing unit.

[0005] Here, it is known to operate one or more amplifiers in a multiplexed operation mode such that a plurality of receivers are successively connected to the corresponding amplifier, so that their received signals are amplified in the amplifier.

[0006] Here, the advantage is that it is not necessary to provide a separate amplifier for each receiver, so that only a few components have to be provided on the receiving side.

[0007] The disadvantage in such an arrangement is that the switching process performed by the multiplexer (through which the other receivers are connected to the amplifier respectively) results in transient processes in the amplified received signal, that is, the amplified received signal is distorted. Therefore, after each switching process, a waiting time is required until the transient process subsides. However, this results in an undesired increase in the response time of the light curtain during object detection. Summary of the Invention

[0008] The present invention is based on the task of providing a light curtain of the type mentioned at the beginning, which has a structurally simple structure and with which safe object detection can be carried out with a short response time.

[0009] To solve this task, a light curtain according to the present invention is provided. Advantageous embodiments and expedient developments of the present invention are described below.

[0010] The present invention relates to a light curtain for detecting an object in a monitoring area, which has an arrangement of transmitters for emitting light beams, an arrangement of receivers for receiving light beams and an analysis and processing unit, in which an object determination signal is generated based on the received signals of the receivers. The receivers form at least one cascade. The receivers are successively connected to an amplifier individually by means of a multiplexer, wherein the amplifier is deactivated when the connection of the receiver is activated.

[0011] According to a first variant, the light curtain has an arrangement of transmitters, which are advantageously integrated in the housing of a transmitter unit. Furthermore, the light curtain advantageously has a receiver unit integrated in another housing, in which the arrangement of receivers is arranged. The transmitter unit and the receiver unit are arranged on opposite edges of the monitoring area. Advantageously, each transmitter is assigned a receiver for forming the light beam axis, such that in the case of an empty monitoring area the light beam of the transmitter is guided unhindered to the assigned receiver of the respective light beam axis. An object in the monitoring area is thus recognized: at least the light beam of the light beam axis is interrupted.

[0012] According to a second variant, transmitters and receivers are present as sensor components both in a first housing and in a second housing.

[0013] In particular, an alternating series arrangement of transmitters and receivers is present in each housing.

[0014] In this case, the transmitters and receivers are also arranged such that in the case of an empty monitoring area the light beam of each transmitter passes unhindered through the monitoring area and reaches the assigned receiver. In this case, an object in the monitoring area is also recognized thereby: at least the light beam of the light beam axis is interrupted.

[0015] Generally speaking, when detecting an object, an object determination signal is generated with the light curtain.

[0016] According to the first variant, the object determination signal is a binary switching signal, the switching state of which indicates whether an object is present in the monitoring area.

[0017] According to a second variant, the object determination signal comprises characteristic variables of the geometry of the detected object.

[0018] The characteristic variables of the geometry can be the object size of the object or the object contour.

[0019] According to an advantageous configuration, the light curtain is a safety sensor. The light curtain then has a fail-safe structure and can thus be used in applications of safety technology. The fail-safe structure can in particular be implemented by a multi-channel analysis and processing unit.

[0020] The light curtain according to the invention has at least one amplifier operating in a multiplexed mode of operation on the receiving side, with which the received signals of different receivers are amplified successively in time. For this purpose, a multiplexer is provided for each amplifier on the receiving side.

[0021] Since not every receiver has to be provided with an amplifier, but rather the amplifier or each amplifier takes over the amplification of the received signals of multiple receivers, a significant saving in components is achieved, which reduces the structural cost of the light curtain.

[0022] In the simplest case, the light curtain according to the invention only has a cascade with receivers, where these receivers are only provided with multiplexers and amplifiers.

[0023] Furthermore, in the light curtain according to the invention, there can be multiple receiver cascades, where the receivers of each cascade are connected to the amplifier by means of a multiplexer.

[0024] In any case, the respective receiver cascades are successively connected to the corresponding amplifier individually by means of the multiplexer.

[0025] According to the invention, when activating the connection of the receiver to the amplifier, the amplifier is deactivated.

[0026] Particularly advantageously, when deactivating the connection of the receiver, the amplifier is also deactivated.

[0027] In this way, it is simply prevented that the switching process of the multiplexer (which is used to connect individual receivers to the assigned amplifier) does not affect or does not significantly affect or interfere with the received signals amplified in the amplifier.

[0028] Since the amplifier is deactivated in the case of activation by means of the multiplexer and advantageously when connecting receiver to receiver, these amplifiers remain unaffected by these switching processes. The amplifier is only activated when these switching processes have passed.

[0029] Thereby, it is ensured in a simple manner that the received signal amplified in the amplifier is not hindered by switching interference, thereby ensuring safe and error-free object detection.

[0030] Another advantage lies in the very short response time when generating the object determination signal. Since the amplifier or each amplification is deactivated during the switching process of the assigned multiplexer, the switching interference caused by the multiplexer is not transmitted to the amplifier. Thereby, the waiting time in the case of receiving signal amplification is eliminated, which would otherwise be necessary to allow the switching interference present in the received signal to subside.

[0031] According to an advantageous embodiment, there is a cascade control device in the light curtain, by means of which the multiplexer or all multiplexers are controlled.

[0032] For example, the cascade control device can be constituted by a controller.

[0033] Since the cascade control device centrally controls all multiplexers and thus the activation time behavior of all receivers, the planned time for receiver activation can be optimized and controlled in a simple manner.

[0034] Particularly advantageously, the cascade control device is part of a computer component comprising an analysis and processing unit.

[0035] Therefore, the calculator component has a compact and efficient structure because the analysis and processing unit is directly assigned to the cascade control device.

[0036] In the simplest case, the analysis and processing unit is constructed single-channel and advantageously consists of only one CPU.

[0037] Advantageously, the analysis and processing unit consists of two CPUs that monitor each other. Therefore, the analysis and processing unit has a redundant, multi-channel structure, so that the light curtain can form a safety sensor.

[0038] According to an advantageous configuration, each multiplexer has a sliding chain or an addressing mechanism.

[0039] Generally, the addressing mechanism has addresses for addressing receivers and amplifiers. The sliding chain has a series arrangement of sliding register elements, where, advantageously, each sliding register element is provided with a receiver or an amplifier for its addressing within the sliding chain.

[0040] The addressing mechanism can be implemented in a computer unit. The sliding chain can consist of a series arrangement of trigger circuits, where the trigger circuits form the sliding register elements of the sliding chain.

[0041] Advantageously, the activation and deactivation of the receiver and / or amplifier are derived from a sliding chain or an addressing mechanism.

[0042] Alternatively, the activation and deactivation of the receiver and / or amplifier are performed by means of a cascade control device.

[0043] The function of the multiplexer can be extended thereby: The display device is activated by means of a sliding chain or by means of an addressing mechanism.

[0044] Then, the addressing mechanism of the sliding chain or the addresses of the sliding register elements are extended as follows: The display device can also be addressed by these addresses and thus activated.

[0045] The display device can consist of light-emitting diodes or an alphanumeric display, on which status messages or the like are displayed, in particular also a location-resolved display for individual cascades.

[0046] According to a further advantageous configuration, the assigned amplifier is tested by means of a sliding chain or by means of an addressing mechanism.

[0047] In particular, for testing, test pulses are generated in the sliding chain or in the addressing mechanism, supplied to the amplifier and read back by it. In the sliding chain or in the addressing mechanism, the read-back test pulses are compared with the expected values.

[0048] As desired, set values corresponding to an error-free state can be preset. If the read-back test pulses deviate from the set values, an error message can be generated. Alternatively, a safety function can be triggered. In particular, the light curtain can be stopped.

[0049] In the case of a light curtain having a plurality of receiver cascades, each amplifier is provided with an amplifier addressing mechanism, which is controlled by the assigned multiplexer.

[0050] The selection of individual amplifier cascades is carried out by means of the amplifier addressing mechanism.

[0051] According to an advantageous expansion scheme, the amplifier addressing mechanism can also be used to test individual amplifier cascades.

[0052] Particularly advantageously, each amplifier addressing mechanism for activating or deactivating the assigned amplifier is controlled by a cascade control device.

[0053] Then, the planned times of individual activations can be preset and controlled centrally by means of the cascade control device. Description of the Drawings

[0054] The present invention will be explained below with reference to the drawings. The drawings show:

[0055] Figure 1 Schematic view showing a first embodiment of a light curtain according to the present invention.

[0056] Figure 2 Schematic view showing a second embodiment of a light curtain according to the present invention.

[0057] Figure 3 Shows for Figure 1 A first example of a circuit arrangement for the receiving side of a light curtain.

[0058] Figure 4 Shows according to Figure 3 The assignment relationship between the analysis processing unit and the cascade control device.

[0059] Figure 5 Shows for Figure 3 A timeline diagram of the circuit arrangement.

[0060] Figure 6 Shows for Figure 1 A second example of a circuit arrangement for the receiving side of a light curtain.

[0061] Figure 7 Shows for Figure 1 A third example of a circuit arrangement for the receiving side of a light curtain. Detailed Description

[0062] Figure 1 Schematically shows a first example of a light curtain 1 according to the present invention. The light curtain 1 includes a transmitter unit 2, in the housing of which a series arrangement of transmitters 4 in the form of light-emitting diodes that emit light beams 3 is arranged. The light-emitting diodes are composed of light-emitting diodes or the like. In addition, the light curtain 1 has a receiver unit 5, in the housing of which a series arrangement of receivers 6 in the form of receiving diodes that receive the light beams 3 is provided. The receiving diodes are composed of photoelectric PIN diodes or photodiodes. Alternatively, phototransistors can also be used.

[0063] The transmitter unit 2 and the receiver unit 5 are arranged on opposite edges of the monitoring area. In the free monitoring area, the light beams 3 respectively emitted by the transmitters 4 reach the assigned, opposite receivers 6. The transmitters 4 and the associated receivers 6 respectively form light beam axes. The operation of the transmitters is controlled and evaluated by a control unit 7 in the transmitter unit 2. The operation of the receivers is controlled by an analysis processing unit 8 in the receiver unit 5. Through the optical synchronization of the light curtain 1, the transmitters 4 and receivers 6 of the individual light beam axes are periodically activated individually or multiple ones successively. The protection area extending in a plane is monitored with the light beams 3 extending parallel to the light beam axes.

[0064] For this purpose, the received signal of the receiving diode is analyzed and processed in the analysis and processing unit 8 in order to generate a binary switching signal as the object determination signal. The first switching state corresponds to the object notification, and the second switching state corresponds to the free protection area. Alternatively, geometric characteristic variables of the object (such as, for example, the object size or the object contour) can be output as the object determination signal.

[0065] The light curtain 1 is configured for use as a safety sensor in the field of safety technology. For this purpose, the light curtain 1 has a fail-safe structure. In particular, the analysis and processing unit 8 has a multi-channel redundant structure, for example, a structure in the form of two periodically monitored calculator units.

[0066] Figure 2 Fig. 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, which are each integrated in a housing. A series arrangement of the transmitter 4 and the receiver 6 is located in each of the transmitter-receiver units 9a, 9b, where, in the present case, there is an alternating arrangement of the transmitter 4 and the receiver 6. Control and analysis processing units 10a, 10b are located in each of the transmitter-receiver units 9a, 9b, by means of which the transmitter 4 present there is controlled and the received signal of the receiver 6 present there is analyzed and processed. In addition, according to Figure 2 the light curtain 1 corresponds to the light curtain according to Figure 1 ...

[0067] Figure 3 Fig. shows the receiving-side circuit arrangement for the light curtain 1 according to Figure 1 ... Figure 2 the light curtain 1. A largely corresponding circuit arrangement is also provided for the light curtain 1 according to

[0068] According to Figure 3 the circuit arrangement includes a multiplexer 11, and in particular an amplifier 12 configured as a preamplifier is connected to the multiplexer.

[0069] In the present case, the receivers 6 of the light curtain 1 are configured in a cascade. Correspondingly, all the receivers 6 are connected to the multiplexer 11.

[0070] In addition, there is a cascade control device 13 constituted by a controller or the like. A first control line 14 is led from the cascade control device 13 to the multiplexer 11. A control signal is sent from the cascade control device 13 to the multiplexer 11 through the control line 14. In addition, a second control line 15 is led from the cascade control device 13 to the amplifier 12. A control signal is sent from the cascade control device 13 to the amplifier 12 through the second control line 15.

[0071] Line 16 leads from amplifier 12 to the cascade control device 13. The received signals amplified by amplifiers 12, 12’ of the receiver 6 are sent to the cascade control device 13 via line 16.

[0072] According to an advantageous configuration, each multiplexer 11, 11’ has a sliding chain or an addressing mechanism.

[0073] Generally speaking, the addressing mechanism usually has addresses for addressing the receiver 6 and the amplifier 12. The sliding chain has a series arrangement of sliding register elements, where advantageously, the sliding register elements are equipped with the receiver 6 or amplification means for its addressing within the sliding chain.

[0074] The addressing mechanism can be implemented in a calculator unit. The sliding chain can consist of a series arrangement of trigger circuits, where the trigger circuits form the sliding register elements of the sliding chain.

[0075] Via the control signal of the cascade control device 13 (the control signal is provided to the multiplexer 11 via the control line 14), the receivers 6 are periodically activated individually and successively, and the amplifier 12 is switched on, where the received signal of the receiver 6 is amplified. In principle, the activation of the receiver 6 can also be carried out directly by the multiplexer 11.

[0076] The amplified received signal is provided from the cascade control device 13 to the analysis and processing unit 8. For this purpose, Figure 4 An example is shown, which is applicable to Figure 3 all embodiments of

[0077] The amplified received signal is provided from the cascade control device 13 to two CPUs 18a, 18b in a two-channel manner via lines 17, 17’, and the two CPUs form the analysis and processing unit 8. According to the amplified received signal, object determination signals are generated in the CPUs 18a, 18b, and the object determination signals are output via a two-channel output structure formed by the output terminals 19a, 19b of the CPUs 18a, 8b.

[0078] The function of the multiplexer 11 can also be extended in this way: activating the display device by means of the sliding chain or by means of the addressing mechanism.

[0079] Then, the addressing mechanism of the sliding chain or the addresses of the sliding register elements are extended as follows: the display device can also be addressed by these addresses and thus activated.

[0080] The display device can be composed of light-emitting diodes or alphanumeric display devices.

[0081] According to a further advantageous configuration, the assigned amplifier 12 is tested by means of a slip ring or by means of an addressing mechanism.

[0082] In particular, for testing, test pulses are generated in the slip ring or in the addressing mechanism, the test pulses are supplied to the amplifier 12 and the test pulses are read back by the amplifier. In the slip ring or in the addressing mechanism, the read-back test pulses are compared with the expected values.

[0083] As the expected values, set values corresponding to an error-free state can be predefined. If the read-back test pulses deviate from the set values, an error message can be generated. Alternatively, a safety function can be triggered. In particular, the light curtain 1 can be stopped.

[0084] Figure 5 Shows a timeline diagram of the inventive activation of the receiver 6 and the amplifier 12 for a circuit arrangement according to Figure 3 For reasons of clarity, only the timeline diagram is shown here for four receivers 6.

[0085] Figure 5 The upper timeline diagram above shows activation intervals T1a, T1b, T1c, T2d, within which only one of the receivers 6 is activated respectively.

[0086] To activate the receiver 6, the multiplexer 11 generates switching pulses Ta, Tb, Tc, Td.

[0087] According to the invention, the amplifier 12 is deactivated during the switching process. For this purpose, the amplifier 12 is only activated during activation intervals T2a, T2b, T2c, T2d which are outside the switching pulses Ta, Tb, Tc, Td ( Figure 5 middle timeline diagram).

[0088] The duration of the activation intervals T2a, T2b, T2c, T2d is determined such that the amplifier 12 is activated when the receiver 6 receives light beams 3 in the form of light pulses L1, L2, L3, L4 from the assigned transmitter 4 ( Figure 5 lower timeline diagram).

[0089] Since the amplifier 12 is deactivated during the switching process of the receiver 6, no interference caused by the switching process is transmitted to the amplifier 12.

[0090] Figure 6 Shows a further receiving-side circuit arrangement for the light curtain 1 according to Figure 1 .

[0091] In this case, two cascades with receivers 6, 6' are provided. In the first cascade, the receiver 6 is led to a first multiplexer 11 with a first amplifier 12. The first amplifier 12 is equipped with a first amplifier addressing mechanism 20, which is controlled by a cascade control device 13 via a control line 15.

[0092] The first multiplexer 11 controls the first amplifier addressing mechanism 20 via a control line 21.

[0093] Correspondingly, the second receiver 6' cascade is led to a second multiplexer 11' with a second amplifier 12'. The second amplifier 12' is equipped with a second amplifier addressing mechanism 20', which is controlled by the cascade control device 13 via a control line 15.

[0094] The second multiplexer 11' controls the second amplifier addressing mechanism 20' via a control line 21'.

[0095] The cascade control device 13 controls the operation of the two cascades via control lines 14, 14', which are led to the multiplexers 11, 11' and are guided via a control line 15, which is led to the amplifier addressing mechanisms 20, 20'.

[0096] The selection of the receivers 6, 6' to be activated is carried out via the control lines 14, 14', and the activation of the amplifiers 12, 12' is controlled via the control line 15. The selection of the amplifiers 12, 12' is carried out via the control lines 21, 21'. The amplifiers 12, 12' can also be tested via these control lines 21, 21'.

[0097] The received signals amplified in the amplifiers 12, 12' are provided to the cascade control device 13 via a line 16 and then to the analysis and processing unit 8.

[0098] Furthermore, according to Figure 6 the function of the circuit arrangement corresponds to the embodiment according to Figure 3 wherein, in particular, the timeline diagram according to Figure 4 is also valid.

[0099] Figure 7 Shows a variant of the embodiment according to Figure 6 The embodiment according to Figure 7 differs from the embodiment according to Figure 6 only in that no control line 15 is led from the cascade control device 13 to the amplifier addressing mechanisms 20, 20'. Thus, the multiplexers 11, 11' take over the complete control of the amplifier addressing mechanisms 20, 20'.

[0100] List of Reference Numerals

[0101] (1) Light curtain

[0102] (2) Transmitter unit

[0103] (3) Light beam

[0104] (4) Transmitter

[0105] (5) Receiver unit

[0106] (6, 6’) Receiver

[0107] (7) Control unit

[0108] (8) Analysis and processing unit

[0109] (9a, b) Transmitter-receiver unit

[0110] (10a, b) Control and analysis processing unit

[0111] (11, 11’) Multiplexer

[0112] (12, 12’) Amplifier

[0113] (13) Cascade control device

[0114] (14, 14’) Control line

[0115] (15) Control line

[0116] (16) Line

[0117] (17, 17’) Line

[0118] (18a, b) CPU

[0119] (19a, b) Output terminal

[0120] (20, 20’) Amplifier addressing mechanism

[0121] (21, 21’) Control line

Claims

1. A light curtain (1) for detecting an object in a monitoring area, having an arrangement of transmitters (4) that emit light beams (3), an arrangement of receivers (6, 6') that receive the light beams (3), and an analysis and processing unit (8) in which an object determination signal is generated based on the received signals of the receivers (6, 6'), characterized in that, The receivers (6, 6') form at least one cascade, and the receivers (6, 6') successively activate the amplifiers (12, 12') individually by means of multiplexers (11, 11'), wherein when the activation of the receiver (6) is turned on, the amplifiers (12, 12') are deactivated.

2. The light curtain (1) according to claim 1, wherein When the activation of the receiver (6) is turned off, the amplifiers (12, 12') are deactivated.

3. The light curtain (1) according to claim 1 or 2, characterized in that, There are cascades of multiple receivers (6, 6'), wherein each cascaded receiver (6, 6') activates the amplifier (12, 12') by means of a multiplexer (11, 11').

4. The light curtain (1) according to any one of claims 1 to 3, characterized in that, There is a cascade control device (13) by means of which the multiplexer (11, 11') or all multiplexers (11, 11') are controlled.

5. The light curtain (1) according to claim 4, characterized in that, The cascade control device (13) is part of a calculator component that includes the analysis and processing unit (8), wherein the calculator component has a CPU or two CPUs (18a, 18b) that monitor each other as the analysis and processing unit (8).

6. The light curtain (1) according to any one of claims 1 to 5, characterized in that, Each multiplexer (11, 11') has a sliding chain or an addressing mechanism.

7. The light curtain (1) according to claim 6, characterized in that, The activation and deactivation of the receivers (6, 6') and / or the amplifiers (12, 12') result from their sliding chain or from the addressing mechanism.

8. The light curtain (1) according to claim 4 or 5, characterized in that, The activation and deactivation of the receivers (6, 6') and / or the amplifiers (12, 12') are performed by means of the cascade control device (13).

9. The light curtain (1) according to any one of claims 6 to 8, characterized in that, The display device is activated by means of the sliding chain or by means of the addressing mechanism, and / or the assigned amplifier (12, 12') is tested by means of the sliding chain or by means of the addressing mechanism.

10. The light curtain (1) according to claim 9, characterized in that, For the test, test pulses are generated in the sliding chain or in the addressing mechanism, the test pulses are supplied to the amplifier (12, 12') and the test pulses are read back by the amplifier, wherein the read-back test pulses are compared with the expectation in the sliding chain or in the addressing mechanism.

11. The light curtain (1) according to claim 3, characterized in that, Each amplifier (12, 12') is equipped with an amplifier addressing mechanism (20, 20') that is controlled by the assigned multiplexer (11, 11').

12. The light curtain (1) according to claim 11, characterized in that, The multiplexer (11, 11') controls the amplifier addressing mechanism (20, 20') to select the amplifier (12, 12') and / or test the amplifier (12, 12').

13. The light curtain (1) according to any one of claims 4 and 11, characterized in that Each amplifier addressing mechanism (20, 20') is controlled by the cascade control device (13) to activate or deactivate the assigned amplifier (12, 12').

14. The light curtain (1) according to any one of claims 1 to 13, characterized in that, The object determination signal is a binary switch signal, and the switch state of the binary switch signal indicates whether an object exists in the monitoring area, or the object determination signal includes geometric characteristic variables of the detected object.

15. The light curtain (1) according to any one of claims 1 to 14, characterized in that, The light curtain has two housings arranged on opposite edges of the monitoring area, in which there are respectively sensor components. Among them, in the first housing, there is a series arrangement of transmitters (4) as sensor components, and in the second housing, there is a series arrangement of receivers (6, 6'), or there are both transmitters (4) and receivers (6, 6') in the first housing and in the second housing as sensor components, where there is an alternating series arrangement of transmitters (4) and receivers (6, 6') in each housing.

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