Optical sensor

Abstract

Optical sensor (1) with at least one transmitter (4) emitting light beams (3), with at least one receiver (6) which is designed to receive the light beams (3) of the transmitter (4), with at least one amplifier stage in which a received signal from the receiver (6) is amplified, and with an evaluation unit (9) in which an output signal (15b) is generated as a function of the amplified received signal, characterized in that at least one attenuation unit (14) is present, by means of which an attenuated received signal is generated from the received signal, only the attenuated received signal being fed to the amplifier stage.

Description

[0001] The invention relates to an optical sensor.

[0002] The optical sensor is used in particular for detecting objects in a surveillance area. For this purpose, the optical sensor comprises at least one transmitter that emits light beams and one receiver that receives light beams. Furthermore, the optical sensor comprises an evaluation unit in which an object detection signal is generated depending on the received signals from the receiver.

[0003] Typically, the optical sensor works according to the light barrier principle, so that object detection occurs by registering an interruption in the beam path of the light rays passing through the monitored area.

[0004] If the optical sensor has only one transmitter or receiver, it is designed as a light barrier or retro-reflective sensor. If the optical sensor has multiple pairs of transmitters and receivers, it is designed as a light curtain or reflex light curtain.

[0005] Received signals from the receiver are generally amplified in an amplifier stage before being fed to the evaluation unit.

[0006] The amplifier stage, which in the simplest case can be formed by a single amplifier, is advantageously set to an operating point before commissioning the optical sensor, with which the amplifier stage is operated in a working mode.

[0007] Since objects to be detected can be located at different distances from the optical sensor and due to strongly varying surface properties of the objects, strongly varying amplitudes of the received signals can be obtained during object detection, i.e. the amplifier stage requires a high dynamic range.

[0008] However, this dynamic range cannot be realized or can only be realized incompletely with known amplifier stages, so that the amplification of the received signals in the amplifier stage leads to signal distortions of the received signals and overloads of the amplifier stage, which can lead to considerable impairments in object detection.

[0009] The invention is based on the object of providing an optical sensor of the type mentioned above, in which safe and reliable object detection is guaranteed.

[0010] To achieve this object, the features of claim 1 are provided. Advantageous embodiments of the invention are described in the dependent claims.

[0011] The invention relates to an optical sensor with at least one transmitter emitting light beams and at least one receiver configured to receive the light beams from the transmitter. The optical sensor further comprises an amplifier stage in which a received signal from the receiver is amplified, and an evaluation unit in which an output signal is generated depending on the amplified received signal. At least one attenuation unit is provided, by means of which an attenuated received signal is generated from the received signal. Only the attenuated received signal is fed to the amplifier stage.

[0012] The basic idea of the invention is to use the attenuation unit to attenuate the received signal generated by at least one receiver of the optical sensor in such a way that no signal distortions or overloads of the amplifier stage occur during the amplification of the received signal in the subsequent amplifier stage, which could affect object detection. The attenuation of the received signal in the attenuation unit is adapted to the characteristics of the amplifier stage, so that the amplitude of the received signal lies in a range in which the amplifier stage amplifies the received signal without distortion. This reliably prevents false detections by the optical sensor.

[0013] The attenuation of the received signal is advantageously carried out in such a way that a partial current is derived from the received signal in the attenuation unit, whereby only the partial current is fed to the amplifier stage.

[0014] The partial current can be precisely specified, which enables optimal adaptation of the attenuated reception signal to the amplifier stage and its settings.

[0015] Advantageously, the attenuation unit is formed by an analog switch, a MOSFET transistor, a multiplier or a controllable voltage divider.

[0016] According to a further advantageous embodiment, the attenuation unit is formed by an arrangement of diodes.

[0017] Low-capacitance diodes such as PIN diodes are particularly suitable for forming attenuation units.

[0018] The at least one receiver whose received signals are attenuated is advantageously formed by a photodiode.

[0019] Of course, other designs of the receiver are also possible, such as phototransistors, avalanche diodes and the like.

[0020] Accordingly, the transmitter of the optical sensor can be formed by a light-emitting diode or a laser diode.

[0021] A significant advantage of the invention is that the at least one attenuation unit attenuates the received signals of the at least one receiver in a manner adapted to the properties of the at least one amplifier stage.

[0022] This makes it possible for the or each amplifier stage to be operated unchanged in a given operating state.

[0023] This greatly simplifies the received signal amplification.

[0024] According to an advantageous embodiment, the operating state of the or each amplifier stage is determined at the factory.

[0025] The amplifier stage can be set to an optimized operating point. This operating state is then maintained during the optical sensor's operation.

[0026] Advantageously, the or each amplifier stage is set to an operating point with defined transmission characteristics.

[0027] In particular, the operating state is determined by a predetermined distortion behavior and / or a predetermined overdrive behavior.

[0028] Advantageously, the or each amplifier stage has non-linear and / or frequency-dependent amplification characteristics.

[0029] According to an advantageous embodiment, the or each attenuation unit is controlled by a controller.

[0030] With the control, the attenuation of the received signals in the or each attenuation unit can be flexibly adapted to varying received signals, so that the subsequent amplification of the received signal in the or each amplifier stage can be carried out without distortion.

[0031] If multiple attenuation units are present, the controller can control each attenuation unit individually. Alternatively, groups of attenuation units or all attenuation units can be controlled jointly, i.e., in the same way and simultaneously, by the controller.

[0032] The or each attenuation unit can be controlled continuously or in stages by means of the control system.

[0033] The type of control can be specified depending on the design of the optical sensor or depending on the respective application.

[0034] According to a first variant, control values for the control of the or each attenuation unit are determined in a learning process and maintained unchanged in a subsequent working operation.

[0035] According to a second variant, control values for the control of the or each attenuation unit in a working operation are permanently updated.

[0036] This variant is advantageous when the received signal strengths change during operation. In this case, the control of the attenuation unit allows for fast and reliable adaptation to the received signals through time-dependent adaptation of the attenuation of the received signals.

[0037] In both variants, the control values are advantageously determined from the values of the received signals after amplification.

[0038] The sizes of the received signals can be, for example, pulse widths, pulse amplitudes and the like as characteristics of received signal pulses registered at the receiving end when the transmitter emits light beams in the form of light pulses.

[0039] This means that the control values are continuously adapted to the current amplified received signals, whereby these current received signals indicate whether there is a danger or a trend towards overloading or distortion in the received signals.

[0040] According to an advantageous further development, control processes are carried out with the control system.

[0041] The optical sensor according to the invention can be designed in different embodiments.

[0042] According to a first embodiment, this is a data transmission unit.

[0043] In particular, the optical sensor can be designed as a data light barrier. Codes containing information are imprinted on the light beams of the transmitter, which are received by the receiver and decoded in the evaluation unit.

[0044] Furthermore, the optical sensor can be a code reader, in particular a barcode reader. The light beams emitted by the transmitter are periodically deflected by a deflection unit and guided over codes to be read. Based on the received signals from the receiver, the codes are decoded in the evaluation unit.

[0045] Furthermore, the optical sensor can be a measuring device for determining optical measured quantities.

[0046] The measured quantities can, for example, be geometric dimensions of objects.

[0047] According to an advantageous embodiment, the optical sensor is designed to detect objects in a monitoring area.

[0048] In this case, it generates an object detection signal as an output signal.

[0049] The object detection signal can in particular be a binary switching signal whose switching states indicate whether an object is in the monitoring area or not.

[0050] According to an advantageous embodiment, the transmitter and receiver of the optical sensor form a light barrier arrangement. Object detection is based on the light barrier principle.

[0051] If the optical sensor has several transmitter-receiver pairs, the optical sensor forms a light curtain.

[0052] In this configuration, the transmitter and receiver of the or each transmitter-receiver pair are located at opposite edges of a monitored area. When the monitored area is clear, the light beams of the transmitter forming the measuring paths of each transmitter-receiver pair strike the assigned receiver, which is recorded by the analysis in the evaluation unit. If an object intrudes into the monitored area, the beam path of the light beams of the or at least one transmitter-receiver pair is interrupted.

[0053] According to a further advantageous embodiment, the transmitter and receiver of the optical sensor form a reflective light barrier arrangement. If this optical sensor has multiple transmitter-receiver pairs, it forms a reflective light curtain.

[0054] The transmitter and receiver of the or each transmitter-receiver pair are then positioned at one edge of the surveillance area. A reflector is located at the other edge of the surveillance area. If the surveillance area is clear, the light beams from the transmitter of a transmitter-receiver pair reach the reflector unhindered and are then guided back to the assigned receiver. If an object is detected, the beam path of the light beams from at least one transmitter is interrupted.

[0055] When the optical sensor is designed as a light curtain, according to a first embodiment, each receiver is assigned an attenuation unit and an amplifier stage.

[0056] According to a preferred embodiment, one or more multiplexers are provided. By means of these, the received signals from all receivers or a group of receivers are connected sequentially and individually to an amplifier stage in a multiplexed mode.

[0057] In this case, too, an attenuation unit can be arranged downstream of each receiver, with attenuated received signals being fed to the multiplexer(s).

[0058] According to a further embodiment, received signals multiplexed in the or in a multiplexer are fed to an attenuation unit.

[0059] Finally, it is also possible that the or each multiplexer forms attenuation units.

[0060] In this case, the multiplexer(s) are advantageously constructed from switching diodes.

[0061] According to an advantageous embodiment, the optical sensor is designed as a safety sensor. Such a safety sensor can be used in safety-related applications, particularly in the area of personal protection. For this purpose, the safety sensor has a fail-safe design.

[0062] This can be achieved by the optical sensor having a two-channel evaluation unit, in particular in the form of two computer units that cyclically monitor each other.

[0063] The fault tolerance of the optical sensor is further increased by the fact that it has test means for testing the or each attenuation unit.

[0064] It is advantageous if the test equipment is part of the evaluation unit.

[0065] According to an advantageous embodiment, an attenuation for the attenuation unit is specified via one channel of the evaluation unit. The set attenuation is checked via the other or both channels of the evaluation unit.

[0066] Furthermore, it is possible to test the attenuation unit(s) by deactivating their attenuation at specified time intervals. The attenuation unit is tested by determining the signal differences between the received signals with and without activation.

[0067] The invention is explained below with reference to the drawings. They show: Fig. 1: Embodiment of the optical sensor according to the invention in the form of a light barrier. Fig. 2: Embodiment of the optical sensor according to the invention in the form of a light curtain. Fig. 3: Receiving-side circuit arrangement for an optical sensor according to the prior art. Fig. 4a-d: Signal waveforms of the optical sensor without distortion during overload. Fig. 5a-d: Waveforms of optical sensor signals with distortions during overload. Fig. 6a-d: Signal waveforms of the optical sensor with overshoots. Fig. 7: First block diagram of a receiving-side circuit arrangement according to the invention. Fig. 8: Second block diagram of a receiving-side circuit arrangement according to the invention. Fig. 9: Third block diagram of a receiving-side circuit arrangement according to the invention. Fig. 10: Another example of a receiving-side circuit arrangement according to the invention.

[0068] Fig. 1 shows an embodiment of the optical sensor 1 according to the invention in the form of a light barrier.

[0069] The light barrier has a first housing 2a, in which a transmitter 4 emitting light beams 3 is arranged, to which a transmitting optics 5 is assigned. Furthermore, the light barrier has a second housing 2b, in which a receiver 6 receiving light beams 3 is arranged, with an upstream receiving optics 7. The transmitter 4 can be formed by a light-emitting diode, and the receiver 6 by a photodiode.

[0070] The housings 2a, 2b are arranged at opposite edges of a monitoring area such that, when the monitoring area is clear, the light beams 3 impinge unhindered on the receiver 6, following a measuring path. If an object intrudes into the monitoring area, the light beams 3 are interrupted.

[0071] The transmitter 4 is controlled by a transmitter controller 8. An evaluation unit 9 is assigned to the receiver 6. The evaluation unit 9 controls the receiver 6 and evaluates the received signals from the receiver 6, generating a binary switching signal as an object detection signal, the switching states of which indicate whether or not an object is present in the monitoring area.

[0072] The evaluation unit 9 can have a multi-channel structure if the light barrier is a safety sensor.

[0073] Fig. 2 shows schematically the structure of an embodiment of the optical sensor 1 according to the invention in the form of a light curtain for detecting objects within a monitoring area.

[0074] The light curtain comprises a first housing 2a with a series arrangement of transmitters 4 emitting light beams 3 and associated transmitting optics 5. Furthermore, the light curtain comprises a second housing 2b with a series arrangement of receivers 6 receiving light beams 3, each of which is preceded by a receiving optics 7.

[0075] The housings 2a, 2b are arranged at opposite edges of the monitored area so that a receiver 6 is positioned opposite a transmitter 4. This transmitter-receiver pair forms a beam axis. In this case, six beam axes are provided. Of course, the light curtain can also have a different number of beam axes.

[0076] The transmitters 4 are controlled by a transmitter controller 8. An evaluation unit 9 is assigned to the receivers 6. The beam axes are activated cyclically, one after the other. The evaluation unit 9 controls the receivers 6 and evaluates the received signals from the receivers 6 to generate a binary switching signal, the switching states of which indicate whether or not an object is located in the monitored area. In general, this evaluation can be carried out not only in a temporal sequence for several light beams 3 one after the other, but also simultaneously for several light beams 3. If the monitored area is clear, the light beams 3 of the beam axes reach the receiver 6 of the respective beam axis unhindered. If an object is intruded upon, at least one beam axis is interrupted. The evaluation unit 9 can have a multi-channel structure if the light curtain forms a safety sensor.

[0077] Fig. 3 shows a receiving-side circuit arrangement for a light barrier, ie an optical sensor 1 according to Fig. 1, as known from the prior art.

[0078] Fig. Figure 3 shows a receiver 6 in the form of a photodiode that receives light rays 3 from the transmitter 4. A resistor 10 generates a bias voltage for the receiver 6.

[0079] Receive signals generated in the receiver 6 are fed to an amplifier stage, which in the present case is formed by only one amplifier 11, which, however, is not mandatory.

[0080] Advantageously, the or each amplifier stage has non-linear and / or frequency-dependent amplification characteristics.

[0081] The received signals amplified in amplifier 11 are fed to a threshold switch 12 and digitized there. The digitized received signals are fed to an evaluation logic 13, which is part of the evaluation unit 9. There, the object detection signal is generated depending on the received signals.

[0082] The Fig. 4a to 4d show time diagrams of signal waveforms for the optical sensor 1 according to Fig. 1 with the circuit arrangement according to Fig. 3.

[0083] In the present case, the transmitter 4 emits light beams 3 in the form of sequences of light pulses, where Fig. 4a shows two light pulses.

[0084] Fig. 4b shows the time course of the analogue reception signal of the receiver 6 when receiving the light pulses according to Fig. 4a. The dash-dotted line represents a non-overdriven received signal with a small amplitude. The solid line represents an overdriven received signal with a large amplitude.

[0085] Fig. 4c shows for the non-overdriven received signal according to Fig. 4b shows the digitized received signal obtained at the output of the threshold switch 12. Corresponding to the received light pulses, received signal pulses with pulse widths Tp are obtained, with the rising edges of the received signal pulses being offset by time T1 and the falling edges by time T2.

[0086] Fig. 4d shows for the overdriven received signal according to Fig. 4b shows the received signal obtained at the output of the threshold switch 12. Due to the overdriving of the received signal, digitized received signal pulses are obtained whose pulse widths Tp and their time intervals T1', T2' are distorted, which can lead to false detections.

[0087] The Fig. 5a to 5d show further time diagrams of signal curves for the optical sensor 1 according to Fig. 1 with the circuit arrangement according to Fig. 3.

[0088] Fig. 5a shows analogous to Fig. 4a shows the time course of light pulses emitted by the transmitter 4.

[0089] Fig. 5b shows for the light pulses according to Fig. 5a shows the time course of the analogue reception signals of the receiver 6 without distortion.

[0090] In this case, the error-free received signal pulses are output at the output of the threshold switch 12 as in Fig. 4c shown.

[0091] Fig. 5c shows for the light pulses according to Fig. 5a shows the time course of the analogue reception signals of the receiver 6 with distortion.

[0092] Due to the distortions, 12 digitized received signal pulses with corrupted pulse widths T11, T21 and corrupted time intervals T1' T2' are obtained at the output of the threshold switch, which can lead to false detections.

[0093] The Fig. 6a to 6d show further time diagrams of signal curves for the optical sensor 1 according to Fig. 1 with the circuit arrangement according to Fig. 3.

[0094] Fig. 6a shows analogous to Fig. 4a shows the time course of light pulses emitted by the transmitter 4.

[0095] Fig. 6b shows for the light pulses according to Fig. 6a shows the time course of the analogue reception signals of the receiver 6 without distortion.

[0096] In this case, the error-free received signal pulses are output at the output of the threshold switch 12 as in Fig. 4c shown.

[0097] Fig. 6c shows for the light pulses according to Fig. 5a shows the time course of the analogue received signals of the receiver 6 with overshoots.

[0098] Due to the distortions, 12 digitized received signal pulses with corrupted pulse widths T11, T21 and corrupted time intervals T1' T2' are obtained at the output of the threshold switch, which can lead to false detections.

[0099] Corresponding signal curves are also used for the receivers 6 of the light curtain according to Fig. 2 received.

[0100] Fig. 7 shows an embodiment of the receiving-side circuit arrangement according to the invention for the light barrier according to Fig. 1.

[0101] The analogue reception signal of the photodiode forming the receiver 6 is attenuated in a defined manner in an attenuation unit 14 before it is fed to the amplifier 11, the threshold switch 12 and the evaluation logic 13.

[0102] The evaluation logic 13 forms a control for the attenuation unit 14. For this purpose, a control line 15a leads from the evaluation logic 13 to the attenuation unit 14.

[0103] With the attenuation unit 14, controlled by the controller, the received signal is attenuated so that the amplifier 11 can be constantly operated at an ideal operating point, so that when amplifying the received signals no errors due to distortion, overmodulation or overshoot, as in the Fig. 4 to 6 shown.

[0104] For this purpose, the controller controls the attenuation unit 14 depending on the amplified received signals of the receiver 6.

[0105] Advantageously, a partial current is derived from the received signal in the attenuation unit 14, whereby only the partial current is fed to the amplifier stage.

[0106] In particular, the attenuation unit 14 is formed by an analog switch, a MOSFET transistor, a multiplier or a controllable voltage divider.

[0107] By adapting the attenuation unit 14, it is possible for the or each amplifier stage to be operated unchanged in a given operating state.

[0108] Advantageously, the operating state of the or each amplifier stage is factory-set.

[0109] In particular, the operating state is determined by a predetermined distortion behavior and / or a predetermined overdrive behavior.

[0110] In general, it is advantageous if the or each amplifier stage has non-linear and / or frequency-dependent amplification characteristics.

[0111] Fig. 8 shows an embodiment of the receiving-side switching arrangement according to the invention for an optical sensor 1 according to Fig. 2, i.e. for a light curtain.

[0112] For the sake of clarity, Fig. 2 only two of the receivers 6 of the light curtain are shown, whereby the receivers 6 are again formed by photodiodes.

[0113] Each receiver 6 is followed by an attenuation unit 14 for attenuating the received signals of the respective receiver 6. Advantageously, the attenuation units 14 are identical and each correspond to the embodiment of the Fig. 7.

[0114] Analogous to the embodiment according to Fig. 7, each attenuation unit 14 is controlled by the evaluation logic 13 forming the control system, whereby for this purpose each movable attenuation unit 14 is connected to the evaluation logic 13 by a control line 15a.

[0115] A signal switch 16 is arranged downstream of each attenuation unit 14. All signal switches 16 together form a multiplexer, through which the received signals attenuated in the attenuation unit 14 are fed individually, one after the other, to the amplifier 11. Thus, all attenuated received signals are amplified one after the other in the amplifier 11, digitized in the threshold switch 12, and finally fed to the evaluation logic 13 for generating the object detection signal.

[0116] The signal switches 16 are controlled by the evaluation logic 13 via the control lines 15a.

[0117] Fig. 9 shows a variant of the embodiment according to Fig. 8.

[0118] In this case, the signal switches 16 forming the multiplexer are arranged directly downstream of the receivers 6. The received signals are thus fed individually, one after the other, to a common attenuation unit 14 in a multiplexed mode.

[0119] In the attenuation unit 14, the received signals from the receivers 6 are attenuated one after the other and then amplified in the amplifier 11. The received signals amplified in the amplifier 11 are then digitized in the threshold switch 12 and evaluated in the evaluation logic 13.

[0120] In both versions of the Fig. 7 to 9, the mode of operation is such that the or each attenuation unit 14 is controlled continuously or in stages by means of the control.

[0121] According to a first alternative, control values for controlling the or each attenuation unit 14 are determined in a learning process and maintained unchanged in a subsequent working operation.

[0122] According to a second alternative, control values for controlling this or each attenuation unit 14 are permanently updated in a working mode.

[0123] In both alternatives, the control values are determined from the values of the received signals after amplification.

[0124] According to an advantageous further development, control processes are carried out with the control system.

[0125] According to an advantageous embodiment, the optical sensor 1 has test means for testing the or each attenuation unit 14.

[0126] Advantageously, the test equipment is part of the evaluation unit 9.

[0127] In particular, to test the attenuation unit 14, its attenuation is deactivated at specified time intervals. The attenuation unit 14 is tested by determining the signal differences of the attenuation unit 14 with and without activation.

[0128] If the optical sensor 1 is a safety sensor and the evaluation unit 9 is multi-channel, an attenuation for the attenuation unit 14 is specified via one channel of the evaluation unit 9. The set attenuation is checked via the other or both channels of the evaluation unit 9.

[0129] Fig. 10 shows a further embodiment of the inventive, receiving-side circuit arrangement for a light curtain, ie an optical sensor 1 according to Fig. 2.

[0130] The receivers 6 of the light curtain, of which only two are shown, are again formed by photodiodes.

[0131] Each receiver 6 is assigned a switching diode X1. The operating points of receiver 6 and amplifier 11 are adjusted via a voltage U1 and a resistor R1.

[0132] The voltages U0, U0' also serve to adjust the operating point of the photodiodes forming the receivers 6.

[0133] The switching diodes X1 form a multiplexer, with which the received signals of the receivers 6 are fed one after the other to the amplifier 11. The received signals amplified in the amplifier 11 are then fed back to the threshold switch 12 and the evaluation logic 13 (in Fig. 10 not shown).

[0134] A capacitor C1, a diode P1, and a resistor R2 form the attenuation unit 14 of the circuit arrangement. The capacitor C1 diverts a portion of the dynamic signal currents Ix of the received signals from the receivers 6 to the resistor R2, so that the resistor R2 is missing from the amplifier 11.

[0135] The attenuation by current discharge can be adjusted via the voltages U2, U3.

[0136] The circuit arrangement according to Fig.10 can also be operated without multiplexing. List of reference symbols 1 optical sensor 2a Housing 2b Housing 3 light beam 4 channels 5 Transmitting optics 6 recipients 6a Received signal 7 Receiving optics 8 Transmitter control 9 Evaluation unit 10 Resistance 11 amplifiers 12 threshold switches 13 Evaluation logic 14 Attenuation unit 15a control line 15b Output signal 16 signal switches C1 capacitor Ix signal current P1 Diode R1 resistor R2 resistor Tp pulse width T11 incorrect pulse width T12 incorrect pulse width T21 falsified pulse width T1 time T2 time T1' time interval T2' time interval U0 voltage U0' voltage U1 voltage U2 voltage U3 voltage X1 switching diode

Claims

[1] Optical sensor (1) with at least one transmitter (4) emitting light beams (3), with at least one receiver (6) which is designed to receive the light beams (3) of the transmitter (4), with at least one amplifier stage in which a received signal of the receiver (6) is amplified, and with an evaluation unit (9) in which an output signal (15b) is generated depending on the amplified received signal, characterized by that at least one attenuation unit (14) is present, by means of which an attenuated received signal is generated from the received signal, wherein only the attenuated received signal is fed to the amplifier stage. [2] Optical sensor (1) according to claim 1, characterized by that this is a data transmission unit. [3] Optical sensor (1) according to claim 1, characterized by that this is a code reader. [4] Optical sensor (1) according to claim 1, characterized bythat this is a measuring device for determining optical measured quantities. [5] Optical sensor (1) according to claim 1, characterized by that it is designed to detect objects in a surveillance area. [6] Optical sensor (1) according to claim 5, characterized by that it generates an object detection signal as output signal (15b). [7] Optical sensor (1) according to one of claims 5 or 6, characterized by that this is a light barrier. [8] Optical sensor (1) according to one of claims 5 or 6, characterized by that this is a light curtain. [9] Optical sensor (1) according to claim 8, characterized by that it has a multiple arrangement of transmitter-receiver pairs. [10] Optical sensor (1) according to one of claims 8 or 9, characterized by that each receiver (6) is assigned an attenuation unit (14) and an amplifier stage. [11] Optical sensor (1) according to one of claims 8 or 9, characterized by that one or more multiplexers are present, by means of which the received signals of all receivers (6) or a group of receivers (6) are connected to an amplifier stage in a multiplex operation. [12] Optical sensor (1) according to claim 11, characterized by that an attenuation unit (14) is arranged downstream of each receiver (6), with attenuated received signals being fed to the multiplexer(s). [13] Optical sensor (1) according to claim 11, characterized by that received signals multiplexed in the or in a multiplexer are fed to an attenuation unit (14). [14] Optical sensor according to claim 11, characterized by that the or each multiplexer forms attenuation units (14). [15] Optical sensor (1) according to one of claims 1 to 14, characterized bythat in the attenuation unit (14) a partial current is derived from the received signal, whereby only the partial current is fed to the amplifier stage. [16] Optical sensor (1) according to one of claims 1 to 15, characterized by that the attenuation unit (14) is formed by an analog switch, a MOSFET transistor, a multiplier or a controllable voltage divider. [17] Optical sensor (1) according to one of claims 1 to 13, characterized by that the attenuation unit (14) is formed by an arrangement of diodes. [18] Optical sensor (1) according to one of claims 1 to 17, characterized by that the or each receiver (6) is a photodiode. [19] Optical sensor (1) according to one of claims 1 to 18, characterized by that the or each amplifier stage is operated unchanged in a given operating state. [20] Optical sensor (1) according to claim 19, characterized bythat the operating state of the or each amplifier stage is factory-set. [21] Optical sensor (1) according to one of claims 19 or 20, characterized by that the operating state of the amplifier stage is determined by a predetermined distortion behavior and / or a predetermined overload behavior. [22] Optical sensor (1) according to one of claims 19 to 21, characterized by that the or each amplifier stage is set to an operating point with defined transmission characteristics. [23] Optical sensor (1) according to one of claims 19 to 22, characterized by that the or each amplifier stage has non-linear and / or frequency-dependent amplification characteristics. [24] Optical sensor (1) according to one of claims 1 to 23, characterized by that the or each attenuation unit (14) is controlled by a controller. [25] Optical sensor (1) according to claim 24, characterized bythat there are several attenuation units (14) which are controlled individually, in groups or jointly by the controller. [26] Optical sensor (1) according to one of claims 24 or 25, characterized by that the or each attenuation unit (14) is controlled continuously or in stages by means of the control. [27] Optical sensor (1) according to one of claims 24 to 26, characterized by that control values for the control of the or each attenuation unit (14) are determined in a learning process and are maintained unchanged in a subsequent working operation. [28] Optical sensor (1) according to one of claims 24 to 26, characterized by that control values for the control of the or each attenuation unit (14) are permanently updated in a working operation. [29] Optical sensor (1) according to one of claims 27 or 28, characterized bythat the control values are determined from the values of the received signals after amplification. [30] Optical sensor (1) according to one of claims 24 to 29, characterized by that control processes are carried out using the control system. [31] Optical sensor (1) according to one of claims 1 to 30, characterized by that this is a safety sensor. [32] Optical sensor (1) according to claim 30, characterized by that it has a two-channel evaluation unit (9). [33] Optical sensor (1) according to one of claims 1 to 32, characterized by that it has test means for testing the or each attenuation unit (14). [34] Optical sensor (1) according to claim 33, characterized by that the test equipment is part of the evaluation unit (9). [35] Optical sensor (1) according to one of claims 32 and 34, characterized bythat an attenuation for the attenuation unit (14) is specified via one channel of the evaluation unit (9) and the set attenuation is checked via the other or both channels of the evaluation unit (9). [36] Optical sensor (1) according to one of claims 33 or 34, characterized by that for testing the or an attenuation unit (14) its attenuation is deactivated at predetermined time intervals and the attenuation unit (14) is tested by determining the signal differences of the received signals with and without activation.

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