Active optical sensor system with improved eye safety

Abstract

An active optical sensor system (2) comprises first and second light emitters (10a, 10b), first and second energy storage elements (11a, 11b) and a control circuit (3, 17a, 17b, 18). The control circuit (3, 17a, 17b, 18) is configured to selectively charge the first and second energy storage elements (11a, 11b) and discharge via the first light emitter (10a) and the second light emitter (10b), respectively, to emit light during respective emission periods. A monitoring unit (4) of the sensor system (2) is coupled to the energy storage elements (11a, 11b) and is configured to compare a monitoring signal representative of a total amount of electrical energy stored by the two energy storage elements (11a, 11b) with a predetermined threshold value and to generate a fault signal in dependence on a result of the comparison.

Description

Technical Field

[0001] The present invention relates to an active optical sensor system including a first light emitter and a second light emitter, and a corresponding method for operating the active optical sensor system. Background Technology

[0002] To ensure eye safety and avoid serious damage caused by strong light emission, active optical sensor systems are typically required to limit the emitted light power within a certain range.

[0003] Document EP2568547B1 describes a driver for a laser diode, wherein the driver includes a sensing element in the power supply path for the laser diode. This ensures that the DC forward voltage supplied to the laser diode is always below the laser threshold. Therefore, the laser diode cannot emit laser light when powered by a DC voltage. The arrangement of the sensing element ensures that laser light can be emitted during pulsed operation.

[0004] Document US2020 / 0052466A1 describes a VCSEL module in which optical elements are arranged in the path of the output beam. An optical detector is arranged to receive radiation reflected from the optical elements, and in the event of a fault, the control circuitry can cut off the power supply current to the VCSEL based on the signal from the optical detector.

[0005] However, active optical sensor systems may include more than one light emitter. In this case, even if the eye safety requirements of each light emitter are met individually, a malfunction may occur, resulting in parallel emission from more than one light emitter. Even if the light power emitted by each light emitter is below the permissible maximum, the total emitted light power may exceed the maximum, still causing harm. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide an improved concept for active optical sensor systems having more than one light emitter, which allows for increased eye safety.

[0007] This objective is achieved through the relevant subject matter of the independent claims. Further embodiments and preferred embodiments are the subject matter of the dependent claims.

[0008] The improved concept is based on the idea of ​​monitoring the total amount of electrical energy stored by two different energy storage elements, where each energy storage element can discharge through a corresponding light emitter in order to emit light.

[0009] According to an improved concept, an active optical sensor system including a first light emitter and a second light emitter is provided. The sensor system includes a first energy storage element connected to the first light emitter and a second energy storage element connected to the second light emitter. The sensor system includes control circuitry configured to selectively charge the first and second energy storage elements. The control circuitry is configured to discharge the first energy storage element via the first light emitter to emit light through the first light emitter during a first emission cycle. The control circuitry is also configured to discharge the second energy storage element via the second light emitter to emit light through the second light emitter during a second emission cycle. The sensor system includes a monitoring unit coupled to the first and second energy storage elements. The monitoring unit is configured to compare a value of a monitoring signal representing the total amount of electrical energy stored by the first and second energy storage elements with a predetermined threshold, and to generate a fault signal based on the comparison result.

[0010] By definition, an active optical sensor system includes light sources for emitting light or light pulses. For example, the light source can be implemented as a laser, particularly an infrared laser. In a modified concept, the light source includes first and second light emitters. Furthermore, by definition, an active optical sensor system includes a detection unit with at least one optical detector to detect the reflected portion of the emitted light. Specifically, an active optical sensor system is configured to generate one or more sensor signals based on the detected portion of the light, and to process and / or output the sensor signals. For example, a lidar system represents an active optical sensor system.

[0011] The control circuit may include, for example, a control unit and a switching circuit having multiple switching elements. Specifically, the switching circuit includes a first switching element that switchesably connects a first energy storage element to a power supply terminal of the sensor system, and a second switching element that switchesably connects a second energy storage element to the power supply terminal. A power supply unit, which may be part of an active optical sensor system or may be located external to the active optical sensor system, may be connected to the power supply terminal to provide electrical energy to charge the first and second energy storage elements.

[0012] Specifically, the control circuit can control the switching circuit to close the first switching element to charge the first energy storage element, and to open the first switching element when the first energy storage element is not being charged. Similarly, the control unit can control the switching circuit to close the second switching element to charge the second energy storage element through the power supply unit, and to open the second switching element when the second energy storage element is not being charged. Therefore, selectively charging the first and second energy storage elements can be understood as configuring the control unit to control the switching circuit to charge the first and second energy storage elements independently of each other.

[0013] Specifically, the first and second emission cycles are different from each other. For example, the first and second emission cycles do not overlap. In other words, under fault-free operation of the active optical sensor system, the second light emitter does not emit light during the first emission cycle, and the first light emitter does not emit light during the second emission cycle.

[0014] The value of the monitoring signal compared to the threshold can, for example, correspond to the amplitude value of the monitoring signal, especially the absolute value of the amplitude of the monitoring signal.

[0015] An active optical sensor system according to the improved concept is configured to charge a first energy storage element and use the electrical energy stored in the charged first energy storage element to drive a first light emitter to emit light during a first emission cycle. Similarly, a second energy storage element is charged and the electrical energy stored in the charged second energy storage element is used to drive a second light emitter to emit light during a second emission cycle.

[0016] Therefore, the total electrical energy stored in the first and second energy storage elements determines the theoretical maximum optical power that can be emitted by the first and second optical transmitters. Even in the event of a fault, where the two optical transmitters emit light in parallel or simultaneously, the emitted optical power cannot exceed the value determined by the total electrical energy stored in the first and second energy storage elements. Thus, by monitoring the total electrical energy stored in the first and second energy storage elements by comparing a monitoring signal with a threshold, it is possible to determine whether, in principle, the optical transmitter can emit light with an optical power exceeding a certain maximum value corresponding to the total electrical energy threshold at a given time.

[0017] Therefore, a fault signal can contain information about whether the monitored signal exceeds a threshold. Exceeding the threshold could lead to a potentially dangerous situation where the light emitter might emit more power than allowed. In this case, the control unit can, for example, disable or shut down the active optical sensor system at least partially based on the fault signal. By adjusting the threshold to correspond to the maximum permissible light output power, eye safety of the active optical sensor system can be improved.

[0018] Specifically, during trouble-free or normal operation, the first and second energy storage elements are not charged simultaneously. However, this does not necessarily mean that one of the energy storage elements is always fully discharged while the other is always fully charged. For example, the energy storage element may include one or more corresponding capacitors. Therefore, there exists an associated time constant that determines the actual state of charge of the energy storage element during normal operation. However, during normal operation, the total energy or monitoring signal will not exceed a threshold, respectively.

[0019] According to several embodiments of the active optical sensor system based on the improved concept, the control circuit is configured to connect a first energy storage element to the power supply terminal of the sensor system, specifically by closing a first switching element, during a first charging cycle prior to a first transmission cycle, specifically for charging the first energy storage element; and during the first charging cycle, specifically by opening a second switching element, disconnect a second energy storage element from the power supply terminal. Furthermore, the control circuit is configured to connect the second energy storage element to the power supply terminal of the sensor system, specifically by closing a second switching element, during a second charging cycle prior to a second transmission cycle, specifically for charging the second energy storage element; and during the second charging cycle, specifically by opening a first switching element, disconnect the first energy storage element from the power supply terminal.

[0020] Connecting two components to each other, particularly by closing the corresponding switching element, can be understood as including keeping the two components connected, particularly by keeping the switching element closed. Similarly, disconnecting two components from each other, particularly by disconnecting the corresponding switching element, can be understood as including disconnecting these components, particularly by disconnecting the corresponding switching element.

[0021] A power supply terminal may be connected to a power supply unit. The power supply unit may be part of an optical sensor system. In other embodiments, the power supply unit is not part of an active optical sensor system.

[0022] The first and second energy storage elements may each be connected to a reference terminal, such as a ground terminal.

[0023] Specifically, if the first energy storage element includes a first capacitor, the first capacitor may be connected between the reference terminal and the first switching element. Similarly, if the second energy storage element includes a second capacitor, the second capacitor may be connected between the second switching element and the reference terminal.

[0024] According to several embodiments, the control circuit is configured to connect a first optical transmitter and a second optical transmitter to a reference terminal during a first transmission cycle to discharge a first energy storage element via the first optical transmitter. The control circuit is also configured to connect the first optical transmitter and the second optical transmitter to the reference terminal during a second transmission cycle to discharge a second energy storage element via the second optical transmitter.

[0025] In other words, during each of the first and second emission cycles, both light emitters are connected to the reference terminal. Therefore, the electrical energy stored in the first energy storage element during one emission cycle causes a current to flow through the first light emitter, which in turn causes the first light emitter to emit light. The same applies to the energy stored in the second energy storage element during one of the emission cycles, causing the second light emitter to emit light.

[0026] However, in the absence of any malfunctions, during the first transmission cycle, only the first energy storage element stores enough electrical energy to enable the first light emitter to emit light, while the second energy storage element does not store enough electrical energy to enable the second light emitter to emit light. Similarly, in the absence of any malfunctions, during the second transmission cycle, only the second energy storage element stores enough electrical energy to enable the second light emitter to emit light, while the first energy storage element does not store enough electrical energy to enable the first light emitter to emit light. Therefore, for normal operation, only one light emitter emits light during each transmission cycle.

[0027] On the other hand, in the event of a fault, the second energy storage element can be at least partially charged during the first charging cycle, and / or the second energy storage element can be at least partially charged during the first charging cycle. In this case, both light emitters can emit light during either the first or second emission cycle. This situation can be identified by the monitoring unit in the aforementioned manner, thus preventing parallel emission.

[0028] The advantage of connecting the first and second optical transmitters to the reference terminal during each transmission cycle is that only a single switching element is required for both optical transmitters. This saves on cost and assembly space.

[0029] Specifically, the third switching element of the switching circuit is arranged between the reference terminal and the first optical transmitter, and between the reference terminal and the second optical transmitter. Therefore, if the third switching element is closed, both the first and second optical transmitters are connected to the reference terminal, and if the third switching element is open, both the first and second optical transmitters are disconnected from the reference terminal.

[0030] According to several implementations, the monitoring unit is configured to further compare the value of the monitoring signal with a predetermined threshold, and generate another fault signal based on the result of the further comparison. Different fault types can be represented by different thresholds.

[0031] Specifically, the comparison of the monitored signal value with a threshold and another threshold can be performed at different times. For example, the monitored signal can be time-dependent.

[0032] For example, an active optical sensor system can be configured to repeatedly generate sensor signals representing the environment during multiple consecutive frames. The first and second light emitters operate similarly in each consecutive frame. Therefore, the monitoring signal behaves similarly in each consecutive frame.

[0033] In the case of a specific fault type, the monitoring signal may exceed a threshold, for example, at a specific time or within a specific time period of a given frame. The comparison of the monitoring system's value with the threshold can then be performed, for example, at the corresponding time or time period. For another fault type, the monitoring signal may exceed the threshold, for example, at different times or different time periods within a frame. The comparison of the monitoring system's value with another threshold can then be performed, for example, at corresponding different times or time periods.

[0034] According to various embodiments, the sensor system includes a summing unit having a first input terminal coupled to a first energy storage element, a second input terminal coupled to a second energy storage element, and an output terminal providing a summing signal. The monitoring signal corresponds to or depends on the summing signal. The summing signal is, in particular, an analog signal.

[0035] In a particularly simple implementation, the summing unit may, for example, include a first resistor arranged between the monitoring unit and the first energy storage element and a second resistor arranged between the monitoring unit and the second energy storage element, or the summing unit may be composed of the first and second resistors.

[0036] According to several embodiments, the summing unit is configured to receive a first input signal at a first input terminal representing a first amount of electrical energy stored in a first energy storage element, and a second input signal at a second input terminal representing a second amount of electrical energy stored in a second energy storage element.

[0037] Specifically, the input signals are provided by the corresponding output voltages of the respective energy storage elements. Specifically, the summing unit is configured to sum the first and second input signals to generate a summed signal.

[0038] According to various embodiments, the sensor system includes a signal adaptation unit having an input terminal connected to the output terminal of a summing unit and an output terminal connected to the input terminal of a monitoring unit. The signal adaptation unit is configured to generate an adaptation signal, specifically an adapted summing signal, based on a summing signal. A monitoring signal is then given by or depends on the adaptation signal.

[0039] Because the output voltage of the storage element can be significantly higher than the voltage that the monitoring unit can handle in order to drive a light emitter, such as a laser diode, the signal adaptation unit can adapt the corresponding different voltage domains to each other. For example, although the output voltage of the energy storage element can rise to tens of volts, the monitoring unit can be configured to operate at voltages on the order of a few volts.

[0040] According to several embodiments, the sensor system includes a temperature sensor arranged and configured to generate a temperature signal based on the operating temperature of the sensor system. A signal adaptation unit is configured to generate an adaptation signal based on the temperature signal.

[0041] Specifically, the signal adaptation unit can be configured to compensate for temperature changes when converting the summation signal into an adaptation signal. This prevents the monitoring unit from misinterpreting changes in the summation signal under temperature variations.

[0042] According to various implementations, the monitoring unit is configured to generate a monitoring signal based on a summation signal, particularly based on an adaptation signal.

[0043] In particular, sensor systems, such as monitoring units, include analog-to-digital converters configured to generate monitoring signals based on summation signals, especially based on adaptation signals.

[0044] For example, the monitoring signal can correspond to a digital version of the adaptation signal.

[0045] According to several embodiments, the threshold is greater than the value of the monitoring signal corresponding to the maximum amount of electrical energy that the first energy storage element can store, and is also greater than the value of the monitoring signal corresponding to the maximum amount of electrical energy that the second energy storage element can store.

[0046] In other words, if one of the first and second energy storage elements is in a fully discharged state, the threshold cannot be exceeded.

[0047] According to several embodiments, the first light emitter includes a first laser diode, particularly a first infrared laser diode, and the second light emitter includes a second laser diode, particularly a second infrared laser diode.

[0048] For example, a sensor system can be designed such that a positive voltage is provided at the power supply terminal, and the reference terminal corresponds to the ground terminal. The cathode of the laser diode is then connected to the ground terminal, and the anode of the laser diode is connected to a corresponding energy storage element and switchably connected to the power supply terminal. In cases where the sensor system is designed to provide a negative voltage at the power supply terminal, the polarity of the laser diode is reversed.

[0049] A failure in one laser diode can cause an increase in the conductivity of the corresponding laser diode in the opposite direction. In other words, this failure can be simulated by a parasitic resistor connected between the anode and cathode of the corresponding laser diode. For example, suppose the laser diode of the second light emitter has such a failure. The first energy storage element is charged during the first charging cycle. However, due to the parasitic resistor across the laser diode of the second light emitter, current can flow from the first energy storage element through the first and second light emitters to the second energy storage element, at least partially charging it. During the subsequent first emission cycle, the cathodes of both laser diodes are connected to the ground terminal, and therefore, both energy storage elements discharge through the corresponding laser diodes. Thus, the two laser diodes emit in parallel.

[0050] This situation can be identified early by monitoring the monitoring signals in the manner described, and in particular, it can be avoided by disabling the sensor system based on the fault signals.

[0051] However, other types of faults can also be detected by monitoring signals. For example, a similar effect may occur if one of the switching elements fails. For instance, if the first switching element connecting the first energy storage element to the power supply terminal fails and therefore remains significantly conductive even in the off state, the first energy storage element can still be charged during the second charging cycle even when the first switching element is off. In the same situation, both light emitters could emit during the subsequent second emission cycle. This situation can also be avoided or detected through improved concepts.

[0052] According to various embodiments, an active optical sensor system includes a detection unit configured to detect a reflected portion of light emitted by a first light emitter and / or a second light emitter, and to generate one or more sensor signals based on the detected reflected portion.

[0053] According to various implementations, the sensor system is implemented as a lidar system, such as a flash lidar system or a laser scanner.

[0054] According to several embodiments, a first optical transmitter is configured or arranged to emit light according to a first emission direction during a first emission cycle, and a second optical transmitter is configured or arranged to emit light according to a second emission direction different from the first emission direction during a second emission cycle.

[0055] Based on the improved concept, a motor vehicle including an active optical sensor system according to the improved concept is also provided.

[0056] According to the improved concept, a method for operating an active optical sensor system is also provided, particularly an active optical sensor system according to the improved concept. According to the method, during a first charging cycle, a first energy storage element of the active optical sensor system is charged. During a first emission cycle, particularly after the first charging cycle, the first energy storage element is discharged, particularly via a first light emitter, and light is emitted using the first light emitter of the sensor system. During a second charging cycle, a second energy storage element of the sensor system is charged. During a second emission cycle, particularly after the second charging cycle, the second energy storage element is discharged, particularly via a second light emitter, and light is emitted using the second light emitter of the sensor system. The value of a monitoring signal representing the total electrical energy stored by the first and second energy storage elements is compared with a predetermined threshold, particularly by a monitoring unit of the sensor system. Based on the comparison result, a fault signal is generated, particularly by the monitoring unit.

[0057] According to various embodiments of the method, the second transmission cycle follows a second charging cycle, particularly immediately following the second charging cycle. The second charging cycle follows a first transmission cycle, particularly immediately following the first transmission cycle. The first transmission cycle follows a first charging cycle, particularly immediately following the first charging cycle.

[0058] Specifically, the first launch cycle and the first charging cycle do not overlap, the second charging cycle and the first launch cycle do not overlap, and the second launch cycle and the second charging cycle do not overlap.

[0059] According to various implementations, during the first and / or second transmission cycles, the value of the monitored signal is compared with a threshold.

[0060] It has been found that a failure in the optical emitter, particularly the laser diode, can lead to an increase in the monitoring signal during the emission cycle, which can be detected by comparing it with a threshold.

[0061] According to several implementation methods, the value of the monitoring signal is compared with another predetermined threshold, and another fault signal is generated based on the comparison result between the value of the monitoring signal and the other threshold.

[0062] Specifically, outside the first and second emission cycles, particularly during times when neither the first nor the second light emitter emits light, the value of the monitored signal is compared with another threshold.

[0063] A faulty switching element may cause an increase in the monitoring signal outside the transmission cycle, which can be detected by comparing the monitoring value with another threshold.

[0064] According to various implementation methods, the fault type is determined based on a monitoring signal, such as a comparison of the monitoring signal with a threshold or another threshold.

[0065] The type of fault can be determined by the monitoring unit, particularly by the control unit of the monitoring unit or by another computing unit coupled to the monitoring unit.

[0066] Further implementations of the method according to the improved concept arise directly from various implementations of the sensor system according to the improved concept, and vice versa. In particular, the active optical sensor system according to the improved concept can be configured to perform the method according to the improved concept or to perform such a method.

[0067] Further features of the invention will be apparent from the claims, drawings, and description of the drawings. Features and combinations of features mentioned in the foregoing description, as well as features and combinations of features mentioned and / or shown individually in the drawings below, can be included not only in the improved concept within the separately specified combinations, but also in other combinations. Therefore, embodiments of the improved concept are included and disclosed, which may not be explicitly shown or explained in the drawings, but arise and generate from separate combinations of features from the explained embodiments. Embodiments and combinations of features that do not have all the features of the initially stated claims can be included in the improved concept. Furthermore, embodiments and combinations of features that extend beyond or deviate from the features set forth in the claims can be included in the improved concept. Attached Figure Description

[0068] In the attached diagram:

[0069] Figure 1 A schematic diagram of a motor vehicle having an exemplary embodiment of an active optical sensor system according to an improved concept is shown;

[0070] Figure 2 A schematic block diagram of another exemplary embodiment of an active optical sensor system according to an improved concept is shown;

[0071] Figure 3 This illustrates the case of the first type of fault. Figure 2 Active optical sensor system;

[0072] Figure 4 This illustrates the case of the second type of fault. Figure 2 Active optical sensor system;

[0073] Figure 5 The diagram schematically illustrates the fitted signal as a function of time; and

[0074] Figure 6 Another adapted signal as a function of time is schematically shown. Detailed Implementation

[0075] Figure 1 An exemplary embodiment of a motor vehicle 1 is shown, which includes an active optical sensor system 2 according to an improved concept, such as a lidar system.

[0076] Sensor system 2 includes a transmitting unit 5 configured to emit light, particularly infrared light, into the environment of vehicle 1. Sensor system 2 also includes a detector unit 6 capable of detecting portions of the emitted light reflected by external objects 7 in the environment of vehicle 1. Based on the detected portions, detection unit 6 can generate one or more detector signals. Sensor system 2 also includes a control unit 3 capable of receiving one or more detector signals and determining, for example, the distance of object 7 from sensor system 2 or vehicle 1 based on time-of-flight measurements dependent on the one or more detector signals. Furthermore, control unit 3 can determine a three-dimensional point cloud representing points in the environment of vehicle 1 from which light emitted is reflected back to sensor system 2 and detected by detection unit 6.

[0077] exist Figure 2 The exemplary block diagram illustrates the sensor system 2 in more detail. For clarity, Figure 2 Detector unit 6 is not shown.

[0078] The emitting unit 5 includes a first laser diode 10a and a second laser diode 10b, whose anodes are switchably connected to the power supply terminal 19 via a first switch 17a and a second switch 17b, respectively. The cathodes of the two laser diodes 10a and 10b are connected to the ground terminal 12 via a common third switch 18. The power supply unit 8 of the motor vehicle 1 or the sensor system 2 is connected to the power supply terminal 19 and provides a positive voltage.

[0079] Sensor system 2 includes a first capacitor 11a and a second capacitor 11b, serving as corresponding energy storage elements for laser diodes 10a and 10b. A first terminal of the first capacitor 11a is connected between the first switch 17a and the anode of the first laser diode 10a, and a second terminal of the first capacitor 11a is connected to a ground terminal 12. Similarly, a first terminal of the second capacitor 11b is connected between the second switch 17b and the anode of the second laser diode 10b, and a second terminal of the second capacitor 11b is connected to a ground terminal 12. Control unit 3 is coupled to switches 17a, 17b, and 18 to control them and accordingly open or close them.

[0080] The sensor system 2 also includes a summing unit 13, which is connected to the first terminals of the first and second capacitors 11a and 11b at their respective inputs and is configured to generate a summing signal as the output of the summing unit 13.

[0081] Specifically, the summation signal is proportional to the sum of the voltages across capacitors 11a and 11b, particularly when switches 17a and 17b are open. In a particularly simple embodiment, the summation unit 13 consists of a first resistor 13a connected between the first terminal of the first capacitor 11a and the output of the summation unit 13, and a second resistor 13b connected between the first terminal of the second capacitor 11b and the output of the summation unit 13. However, in more complex embodiments, different designs of the summation unit 13 are possible.

[0082] The active optical sensor system 2 includes a monitoring unit 4, which can be implemented, for example, on a field-programmable gate array (FPGA) or another, particularly a digital processing unit. Furthermore, the sensor system 2 may include a signal adaptation unit 9 configured to adapt a summed signal and provide the adapted signal to the monitoring unit 4. Because the laser diodes 10a and 10b can operate as monitoring unit 4 at significantly higher voltages, this signal adaptation may include reducing the signal level in a defined manner. In particular, the adapted signal may be proportional to the summed signal. Additionally, in some embodiments, the sensor system 2 may include a temperature sensor (not shown) arranged to determine the temperature of the sensor system 2 (e.g., laser diodes 10a and 10b) and coupled to the signal adaptation unit 9. The signal adaptation unit 9 can then generate an adaptation signal based on the temperature to compensate for temperature variations and allow for consistent evaluation of the adapted signal.

[0083] The summation signal is, in particular, an analog voltage signal, so the adaptation signal can also be an analog signal. Therefore, the monitoring unit 4 may include an analog-to-digital converter (ADC) to generate a digital version of the adaptation signal, which can be represented as the monitoring signal.

[0084] The monitoring unit 4 compares the monitoring signal with one or more thresholds to determine whether a fault exists in the sensor system 2, and in some embodiments, it can also determine the type of fault.

[0085] During the first charging cycle, control unit 3 closes the first switch 17a to charge the first capacitor 11a. During the first charging cycle, the second switch 17b is open, and the third switch 18 is also open. At the end of the first charging cycle, control unit 3 opens the first switch 17a and closes the third switch 18 during the subsequent first emission cycle. Then, the energy stored in the first capacitor 11a is discharged via the first laser diode 10a, causing the first laser diode 10a to emit light. After the first emission cycle, the third switch 18 is opened again, and during the subsequent second charging cycle, the second switch 17b is closed by control unit 3 to charge the second capacitor 11b. After the second charging cycle, during the subsequent second emission cycle, control unit 3 opens the second switch 17b and closes the third switch 18 again. Now, the energy stored in the second capacitor 11b is discharged via the second laser diode 10b, causing the second laser diode 10b to emit light.

[0086] In normal operation, i.e., when there are no faults in the sensor system 2, the first and second laser diodes 10a and 10b therefore emit light alternately. However, note that other laser diodes (not shown) can be arranged similarly.

[0087] Since both laser diodes 10a and 10b are connected to the ground terminal 12 via a single switch 18 during each emission cycle, it must be ensured that only the first capacitor 11a is charged during the first charging cycle and only the second capacitor 11b is charged during the second charging cycle to avoid parallel emission of light from the two laser diodes 10a and 10b, which could result in the total emitted optical power exceeding the maximum permissible optical power.

[0088] During normal operation, this is ensured by switching switches 17a, 17b, and 18 in the manner described. However, in the event of a malfunction, capacitors 11a and 11b may be unintentionally charged, which could result in parallel emission of the two laser diodes 10a and 10b.

[0089] exist Figure 3 In, it is shown Figure 2The active optical sensor system 2 is in a situation where the first laser diode 10a fails as a parallel parasitic resistor 14. In other words, there may be leakage current flowing in the reverse direction along the first laser diode 10a. When the second capacitor 11b is charged and the voltage at the first terminal of the second capacitor 11b is greater than the voltage at the first terminal of the first capacitor 11a, and additional switches 17a, 17b, 18 are open, current can flow from the second capacitor 11b through the second laser diode 10b and the parasitic resistor 14 to the first capacitor 11a, and at least partially charge it. If the third switch 18 is subsequently closed to discharge the second capacitor 11b used for emitting light through the second laser diode 10b, the first capacitor 11a also discharges through the first laser diode 10a, which can cause the two laser diodes 10a and 10b to emit light in parallel.

[0090] To detect this situation, monitoring unit 4 compares the monitoring signal with a first threshold and generates a fault signal based on the comparison result. Depending on the fault signal, particularly if the monitoring signal exceeds the first threshold, the active optical sensor system 2 can, for example, be shut down or enter a fault mode. For example, control unit 3 can shut down the active optical sensor system 2 or control it to enter a fault mode.

[0091] Figure 5 A schematic example of an adaptation signal 16 as a function of time is shown. It is assumed that the monitoring signal is a digital version of the adaptation signal 16. During the first time period T1, neither laser diodes 10a nor 10b emits light. The adaptation signal 16 has a nearly constant value, for example, it may be zero or close to zero. During the subsequent second time period T2, laser diodes 10a and 10b emit light alternately as described above. Therefore, the adaptation signal 16 increases to a level essentially given by the time constants of capacitors 11a and 11b and the repetition frequency of the emission period. If the repetition period changes during the second time period T2, the value of the adaptation signal 16 may also change during the second time period T2 (not shown). After the second time period T2, there is a third time period T3, during which laser diodes 10a and 10b again do not emit light.

[0092] exist Figure 5 In the example, a reference appeared. Figure 3 The fault is described. Therefore, the adapter signal 16 and similar monitoring signals increase beyond the first threshold V1 during the second time period T2. In this way, the monitoring unit 4 can detect the fault.

[0093] exist Figure 4 In, it is shown Figure 2The sensor system 2 is in the presence of various types of faults. For example, the second switch 17b has a fault that acts as a parasitic resistor 15 across its terminals. As a result, the second capacitor 11b is charged regardless of whether the second switch 17b is open. This can also lead to parallel emission of light during the first emission cycle.

[0094] Figure 6 The corresponding adaptation signal according to this fault type is shown. During the first time period T1 and the third time period T3, the adaptation signal 16, and therefore the monitoring signal, exceeds the second threshold V2. The monitoring unit 4 can then compare the monitoring signal with the second threshold V2 to determine the corresponding fault type.

[0095] from Figure 5 and Figure 6 As can be seen, different types of faults can be observed in the adaptation signal 16 and the monitoring signal during different time periods of operation of sensor system 2. Therefore, monitoring unit 4 can perform the corresponding comparison at the appropriate time.

[0096] As described, and particularly with respect to the accompanying drawings, the improved concept allows for monitoring the state of an active optical sensor system to avoid parallel emission of light from two optical emitters designed to emit light only in an alternating manner. Therefore, for each optical emitter, the maximum permissible optical output power can be utilized, as the risk of parallel emission and thus excessive output power is reduced. Furthermore, this monitoring can be used for system diagnostics. Unintentional parallel emission of light from two optical emitters can impair measurements in an active optical system. This can cause the active optical system to generate disturbed point clouds.

Claims

1. An active optical sensor system comprising a first light emitter and a second light emitter, characterized in that, The sensor system (2) includes: - A first energy storage element connected to a first light emitter and a second energy storage element connected to a second light emitter; - A control circuit configured to selectively charge a first energy storage element and a second energy storage element, discharge the first energy storage element via a first light emitter to emit light during a first emission cycle, and discharge the second energy storage element via a second light emitter to emit light during a second emission cycle; and - A monitoring unit (4) coupled to a first energy storage element and a second energy storage element, and configured to compare the value of a monitoring signal representing the total amount of electrical energy stored by the first energy storage element and the second energy storage element with a predetermined threshold, and generate a fault signal based on the comparison result.

2. The active optical sensor system according to claim 1, Its features are, The control circuit is configured to: - During the first charging cycle prior to the first launch cycle, the first energy storage element is connected to the power terminal (19) of the sensor system (2) and the second energy storage element is disconnected from the power terminal (19); and - During the second charging cycle prior to the second launch cycle, the second energy storage element is connected to the power supply terminal (19) and the first energy storage element is disconnected from the power supply terminal (19).

3. The active optical sensor system according to claim 1 or 2, Its features are, The control circuit is configured to: - During the first emission cycle, the first optical transmitter and the second optical transmitter are connected to the reference terminal to discharge the first energy storage element via the first optical transmitter; and - During the second emission cycle, the first and second optical transmitters are connected to the reference terminal to discharge the second energy storage element via the second optical transmitter.

4. The active optical sensor system according to claim 1 or 2, Its features are, The monitoring unit (4) is configured to further compare the value of the monitoring signal with another predetermined threshold, and generate another fault signal based on the result of the further comparison.

5. The active optical sensor system according to claim 1 or 2, Its features are, The sensor system (2) includes a summing unit (13) having a first input terminal coupled to the first energy storage element, a second input terminal coupled to the second energy storage element, and an output terminal providing a summing signal, wherein the monitoring signal depends on the summing signal.

6. The active optical sensor system according to claim 5, Its features are, The summing unit (13) is configured to receive a first input signal at the first input terminal representing a first amount of electrical energy stored in the first energy storage element, and a second input signal at the second input terminal representing a second amount of electrical energy stored in the second energy storage element.

7. The active optical sensor system according to claim 5, Its features are, - The sensor system (2) includes a signal adapter unit (9) having an input terminal connected to the output terminal of the summing unit (13) and an output terminal connected to the input terminal of the monitoring unit (4); and - The signal adaptation unit (9) is configured to generate an adaptation signal (16) based on the summation signal, wherein the monitoring signal depends on the adaptation signal (16).

8. The active optical sensor system according to claim 7, Its features are, - The sensor system (2) includes a temperature sensor arranged and configured to generate a temperature signal based on the operating temperature of the sensor system (2); and - The signal adaptation unit (9) is configured to generate the adaptation signal (16) based on the temperature signal.

9. The active optical sensor system according to claim 5, Its features are, The monitoring unit (4) is configured to generate the monitoring signal based on the summation signal.

10. The active optical sensor system according to claim 5, Its features are, The sensor system (2) includes an analog-to-digital converter configured to generate the monitoring signal based on the summing signal.

11. The active optical sensor system according to claim 1 or 2, Its features are, The threshold is greater than the value of the monitoring signal corresponding to the maximum amount of electrical energy that the first energy storage element can store, and is also greater than the value of the monitoring signal corresponding to the maximum amount of electrical energy that the second energy storage element can store.

12. The active optical sensor system according to claim 1 or 2, Its features are, The first light emitter includes a first laser diode, and the second light emitter includes a second laser diode.

13. A method for operating an active optical sensor system (2), Its features are, - During the first charging cycle, the first energy storage element is charged; - During the first emission cycle, light is emitted by the first light emitter of the sensor system (2) by discharging the first energy storage element; - During the second charging cycle, the second energy storage element is charged; - During the second emission cycle, light is emitted by the second light emitter of the sensor system (2) by discharging the second energy storage element; - The value of the monitoring signal representing the total amount of electrical energy stored by the first and second energy storage elements is compared with a predetermined threshold; as well as - Generate a fault signal based on the comparison results.

14. The method according to claim 13, Its features are, The fault type is determined based on the monitoring signals.

15. The method according to any one of claims 13 or 14, Its features are, The value of the monitoring signal is compared with the threshold during the first transmission cycle and / or during the second transmission cycle.

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