Detection of objects in a monitored area

Abstract

The present application relates to the detection of objects in a monitored area. An optoelectronic sensor (10) for detecting objects in a monitored area (18) is presented, having a light emitter (12) for emitting at least one light beam (14), a movable deflection unit (16) for periodically scanning the monitored area (18) with the at least one light beam (14), a light receiver (24) for generating a reception signal from light (20) diffusely reflected by an object, and a control and evaluation unit (32) designed to derive information about objects in the monitored area (18) from the reception signal and to identify a glare of the light receiver (24) and to switch into a glare state in the event that the glare impedes a safe detection. Here, a first phase in which there is a glare and a second phase in which there is no glare are identified, and it is decided on the basis of the distribution of the first and second phases whether the glare impedes a safe detection.

Description

[0001] The present invention relates to photoelectric sensors and methods for detecting objects in a monitored area according to claims 1 and 14.

[0002] Laser scanners are commonly used for optical surveillance. A beam of light generated by a laser periodically scans the monitored area using a deflection unit. The beam is diffusely reflected off objects within the monitored area and evaluated in the scanner. The angular position of the object is inferred from the angular position of the deflection unit, and the distance between the object and the laser scanner is further inferred from the time of light flight using the speed of light. Two fundamental principles for determining the time of light flight are known. In a phase-based method, the emitted light is modulated and the phase shift of the received light relative to the emitted light is evaluated. In a pulse-based method, such as the method preferred in security technology, the laser scanner measures the time of flight until the emitted light pulse is received again. In the pulse averaging method, known for example from EP 1 972 961 A2 or EP 2 469 296 B1, multiple single pulses are emitted for measurement, and the received pulses are evaluated statistically.

[0003] One important application is in security technology for protecting against hazards. Here, laser scanners monitor protected areas that operators are prohibited from entering during machine operation. Because the laser scanner acquires angular and distance information, it can determine the two-dimensional position of objects within the monitored area, and consequently, the two-dimensional position of objects within the protected area. If the laser scanner detects an unauthorized intrusion into the protected area (such as an operator's leg), it triggers an emergency shutdown of the machine.

[0004] Sensors used in safety technologies must operate with exceptional reliability and therefore meet high safety requirements, such as the standard EN 13849 concerning machine safety and the equipment standard EN 61496 concerning body control systems (BMS). To meet these safety standards, a range of measures are taken, such as safety electronic assessments using redundant and diverse electronics, functional monitoring, and / or providing individual test targets with defined reflectivities that must be identifiable at appropriate scanning angles. For example, safety laser scanners according to such standards are known from DE 43 40 756 A1.

[0005] According to the equipment standard EN 61496-3, even the interaction of external light or sensors must not lead to dangerous malfunctions. Detection loss is particularly prevalent if an external light source (such as an additional infrared sensor or building lighting) is located behind the dark object being detected. As a result, the actual measurement signal of the dark object is superimposed by the strong external light and becomes undetectable after a certain point. Such glare can be identified by determining the level of external light in the received signal, then the sensor is switched to a locked state, and the monitored machine is switched to a safe state. In this way, safety is established, and the standard is met. However, in the case of glare, even if the object in the monitored area itself is not dangerous, the system becomes unusable as long as the external light continues to shine on it.

[0006] In a yet-to-be-published European patent application (case number 21187348.4), glare detection has been further improved. If glare is detected, a glare warning is initially triggered. Only if this condition persists for at least 5 seconds will the sensor enter a locked state. If no glare occurs within a certain time, the glare warning is then canceled.

[0007] This improved glare detection avoids unnecessary cutoffs in cases of only brief glare. However, it doesn't improve usability in cases of pulsed external light sources, especially those in the presence of other sensor types (e.g., other laser scanners or 3D-ToF cameras). The latter's area illumination causes glare for many scanning devices, rendering measurements of the relevant proportions during the scan unavailable. In principle, there are sufficient time windows between external light pulses for measurements to be taken without glare. However, the glare warning is never cleared because the glare repeats too rapidly. Depending on the scanning frequency of the laser scanner with glare detection and the glare frequency of the external light source, such as the frame rate of an infrared camera, the time series of glare caused by pulsed external light can become even more complex due to beat frequency effects. In any case, even if the external light source is not too complex, the problem of excessively short glare repetition intervals persists, thus the glare warning is permanently activated, and the laser scanner switches to a continuous glare failure after 5 seconds.

[0008] Additional level measurements in laser scanners are also known in other literature, and an improved glare recognition method in the unpublished European patent application No. 21187348.4 is based on this. For example, in EP1 972 961 A2, which has already been briefly mentioned above, a histogram is constructed from multiple single pulses using a pulse averaging method, and in addition to the receiving time point of the distance measurement, the maximum value or integral is determined as a measure of intensity. EP 3 059 608 A1 determines the received level of the laser scanner in the power supply of the light receiver. However, the corresponding intensity or level information is not used for glare detection, but rather for, for example, black-and-white correction of the distance measurement or special adjustments for further evaluation to accommodate the high level of the reflector.

[0009] EP 3 267 218 A1 relates to the configuration of clutter filters for security laser scanners. Clutter refers to dust, rain, snow, etc. Optimized clutter filters can solve certain difficult detection situations, but this is a different problem than glare from external light sources.

[0010] In security laser scanners, so-called multiple assessments are also common, as described in EP 3 267 218 A1 or EP 3 916 286 A1. Protective field intrusions identified in only a single scan are still tolerated, with a safety-oriented response triggered only after two, three, or four, or up to 16 (depending on the design of the multiple assessment). However, this traditional multiple assessment refers to protective field intrusions, not glare from external light sources. Furthermore, multiple assessments are completed within fractions of a second, while glare only becomes safety-related several seconds later.

[0011] Therefore, the objective of this invention is to find an improved method for handling glare in general-purpose safety sensors.

[0012] This task is accomplished by the photoelectric sensor (particularly a laser scanner) and method for detecting objects in a monitored area according to claims 1 and 14. The sensor is preferably a safe sensor, i.e., a safety sensor or a safety laser scanner. Here, the terms "safe" or "secure" should be understood in the sense of the standards mentioned at the outset or similar standards concerning machine safety or non-contact protective devices, i.e., taking measures to control faults within a specified safety level.

[0013] A light emitter projects at least one light beam into a monitored area; the beam is preferably a collimated beam with a small cross-section. The emitted beam is periodically guided through the monitored area by means of a movable deflection unit. A light receiver generates a received signal from the reflected beam. Here, there is no conceptual distinction between directional reflection and non-directional scattering or diffuse reflection. Therefore, the planes in the monitored area are repeatedly scanned as the deflection unit moves. In some embodiments, the light emitter generates multiple beams spaced apart from each other, and the light receiver is accordingly designed to receive multiple beams. This achieves multi-plane scanning, making the sensor a multi-plane scanner.

[0014] The received signal is evaluated in the control and evaluation unit to obtain information about the detected object. Specifically, the time-of-flight method is used to measure the corresponding distance. Preferably, the measurement is based on pulses, so that the emitted light beam has at least one optical pulse, the time of flight of which is determined. In addition to the single-pulse method, the pulse averaging method, as described in EP 1 972 961 A2 or EP 2469 296B1 mentioned at the outset, can also be used.

[0015] In addition, the control and evaluation unit also identifies glare from the light receiver. If glare interferes with safety detection, particularly if a safe protective field assessment is no longer permitted, the sensor enters a glare state. Here, interfering with safety detection means that the safety required by the standard is no longer provided, and an actual object may no longer be detected. In individual cases, it may still be possible to detect an object, but the sensor can no longer guarantee this across the entire specified functional range in glare state. For example, glare state may be reported as a malfunction, the sensor's performance (e.g., range) may be limited to ensure safety only within a smaller functional range, or a safety-oriented response may be initiated, i.e., an output signal that transitions the monitored machine to a safe state.

[0016] The basic idea of ​​this invention is that not all glare from a sensor is safety-critical. To determine whether glare hinders safety detection and whether a glare state is necessary, a first phase with glare and a second phase without glare are identified, and the distribution of the first and second phases is evaluated. The sensor does not need to immediately switch to a glare state upon the first glare, but rather a certain time window, such as a 5-second window, is allowed to check and determine the distribution. It is not necessary to explicitly define the first and second phases, as one phase is the complement of the other; therefore, directly defining either the first or second phase is sufficient. For example, a phase could be the measurement period for determining a measurement value, particularly the distance value for determining the current angular position of the scanning unit, or the period of a movable scanning unit, also known as a scan.

[0017] By evaluating the distribution of the first and second stages, continuous glare and recurring or periodic short glare can be distinguished. While continuous glare often hinders security detection, periodic glare is tolerable as long as there is sufficient second stage to maintain glare-free conditions. A preferred criterion for evaluating the distribution could be whether the first stage exceeds a critical ratio. This can be understood as a duty cycle: a glare state is only adopted when the first stage with glare becomes dominant. The critical ratio is specified in more detail in the implementation; it can be the cumulative time ratio or the number of first stages relative to the number of second stages, but it also depends on the order.

[0018] In the glare recognition of this invention, two aspects need to be distinguished. First, it is identified whether glare has occurred at the light receiver in order to assign the stage to a first stage or a second stage. Then, the distribution of the first stage and the second stage is evaluated to determine whether the sensor can continue to safely detect the object despite at least occasional glare, or whether the glare hinders safe detection.

[0019] The advantages of this invention are: significantly improved availability of sensors, particularly those spatially close to pulsed external light sources (primarily other sensors, such as other laser scanners or 3D-TOF cameras). Therefore, sensors are locked out less frequently due to glare, even when there are no objectively safety-critical objects in the monitored area. In many cases, the sensor reliably performs its function despite external light interference. Furthermore, glare sensitivity is even adjustable, as it can be determined which distributions of the first stage of glare, and in particular which critical ratios, hinder safety detection, are present based on the application, equipment variant, and, for example, the sensor configuration, particularly the protected area currently monitored by the sensor. Improved diagnostic capabilities are also provided, as the user can be shown which form of glare is involved, particularly periodic or continuous glare. This may allow for changes in the installation location and orientation of the sensor and external light interference to reduce or avoid glare.

[0020] Preferably, the control and evaluation unit is designed to count the first stage within a time interval and / or determine the cumulative duration of the first stage within that time interval. This is a summary observation of the distribution. The time interval is, for example, a few seconds, particularly 5 seconds, within which a decrease in detection capability is acceptable according to safety standards (e.g., EN 61496-3, etc.) without necessarily requiring a safety-oriented response. The time interval can always restart, or it can be counted repeatedly, or the cumulative duration can be determined. Furthermore, the stage is preferably a corresponding measurement cycle or scan. Then, counting and determining the cumulative duration are ultimately the same, since the cumulative duration is the product of the number of stages multiplied by the stage duration. Since the first stage is the complement of the second stage, both the first and second stages are determined simultaneously within the time interval or within the known total number of measurement cycles or scans within the time interval. Therefore, the second stage can also be counted or its cumulative duration determined, preferably without distinction, and this is also a form of counting or determining the cumulative duration of the first stage. Furthermore, it should be noted that the number of first stages and the cumulative duration are interrelated, being the product of the number and duration of individual first stages, provided that the first stage is understood as a regular process, such as a measurement cycle or scan.

[0021] Preferably, the control and evaluation unit is designed to determine the temporal patterns of the first and second stages and, based on these temporal patterns, to determine whether glare affects detection. This replaces or complements cumulative observation. Temporal patterns can be categorized into those that still allow safe detection and those that impede safe detection. This goes beyond a simple summative evaluation; for example, a long-lasting first stage or a direct sequence of many first stages may be more critical than multiple short, intermittent first stages, the sum of which may even extend to a longer duration. In particular, periodic patterns of pulsed external light sources may be identified, where this does not necessarily directly reveal the period of the external light source but can form a temporal pattern of beat frequency (Schwebung) between the sensor's periodic scanning frequency and the pulse repetition frequency of the external light source.

[0022] Preferably, the control and evaluation unit is designed to schedule object detection within the time frame predicted in the second stage based on the identified time pattern. Once the time pattern is understood, an expectation of how that pattern will proceed is also formed. Therefore, in some cases, a one-time or repeated time offset can be introduced into the measurement, and then, when glare occurs at the sensor, this time offset can be used for targeted measurement, i.e., measurement in the second stage. Particularly in security applications, glare monitoring continues to verify whether the expectation that glare no longer hinders security detection has also been achieved.

[0023] Preferably, the sensor has an additional light receiver for identifying glare. While the methods for assessing whether the distribution of the first and second phases hinders security detection due to glare have been described so far according to embodiments of the second aspect described above, it now relates to designing embodiments of the first aspect: how to identify glare, i.e., identify the first and second phases. For this purpose, a dedicated additional light receiver can be provided. This eliminates the need for actual measurement of diffusely reflected light beams using a light receiver. Security laser scanners typically have additional light receivers through which the transmittance of the windshield is monitored; these light receivers can also be used for the dual function of glare identification.

[0024] Preferably, the control and evaluation unit is designed to identify glare based on the received signal. In this embodiment, glare detection is performed based on the received signal, i.e., according to the diffusely reflected beam or the measurement beam, or the scanning beam. Then, no additional components are needed to further evaluate the received signal to identify glare, in addition to detecting information about the object or measuring distance. To better distinguish between useful light and external light from the diffusely reflected beam, glare identification can use the time segment of the received signal itself, such as at the beginning or end of the corresponding measurement cycle. Glare identification by means of an additional light receiver can be combined with glare identification based on the received signal.

[0025] Preferably, the control and evaluation unit is designed to identify glare based on the determination of the received signal level or the signal-to-noise ratio (SNR) of the received signal. For this purpose, the current flowing in the optical receiver is measured, for example, particularly the current flowing in the power supply of the optical receiver as described in EP 3 059 608 A1 mentioned at the outset. The level can be the total level, i.e., the superposition of the incoming light and the useful light, or, for example, only the incoming light as a continuous (Gleichlicht) component can be measured through low-pass filtering. However, low-pass filtering, in particular, will not detect pulsed incoming light sources. Therefore, integrating the current flowing in the optical receiver may be meaningful. When incoming light is incident, the level and noise increase, the SNR deteriorates accordingly, and when it exceeds a corresponding limit, the incoming light can be considered glare.

[0026] Preferably, the control and evaluation unit is designed to set a reflector bit when the level is above a reflector threshold and / or set a noise flag when the signal-to-noise ratio is below a noise threshold. A level above the reflector threshold means that the light beam falls on the reflector because other objects do not diffuse as much light. This is a function typically expected from reflector identification. However, the reason for setting a noise flag may also be glare from an external light source rather than the reflector itself. A noise flag indicates a low signal-to-noise ratio. Transmitting information in the form of a flag or bit is particularly advantageous, but the aforementioned threshold criteria can also be optionally applied and processed in other ways.

[0027] Preferably, the control and evaluation unit is designed to identify a glare-prone first stage when the received signal level is above a reflector threshold and / or the signal-to-noise ratio is below a noise threshold and no object is detected simultaneously. In this case, "and simultaneously" is to express an exception (Klammerung), namely, that in addition to the previously mentioned alternatives, there should also be a condition that no object is detected. This can be expressed particularly clearly by the symbol just introduced: (reflector and / or noise) AND (no object detected). That is, if no object is detected and no distance value is measured in the case of the time-of-flight method, the reflector threshold will not be exceeded due to a detected reflector, the distance to which would otherwise be measurable. Therefore, the fact that a high level or signal-to-noise ratio does not allow for measurement is attributed to glare. In a preferred embodiment, distance measurement signals the fact that no object was detected by an infinitely large distance value or an excessively high distance value. As mentioned earlier, the identification of the glare-prone first stage can also be complementary to the identification of the second stage with a corresponding inverse criterion.

[0028] Preferably, the control and evaluation unit is designed to determine whether an object is located within a protected area configured within the monitored area, and in this case, initiate a safety-oriented response. Therefore, the sensor includes the protected area assessment already described in the introduction. In the event of protected area intrusion, a cut-off signal is preferably output via the secure, particularly dual-channel output of the sensor (OSSD, Output Signal Switching Device), which is used to transition the monitored machine to a safe state, for example, by stopping or slowing the machine or performing an evasive maneuver. Glare detection may be limited to the actual protected area configuration.

[0029] The control and evaluation unit is preferably designed to determine the first and second stages based on the angular position of the deflection unit. Glare is then observed based on the angle. For each angle or each group of adjacent angles, it is determined whether glare occurs, the frequency of glare occurrence, the time of glare occurrence, or the time pattern of glare occurrence—that is, how the first and second stages are distributed relative to the angle. Glare flags or glare bits for each angle can be set in the first stage but not in the second stage, wherein, as mentioned above, the glare flags can be derived from reflector flags and / or noise flags. The evaluation of the distribution is by no means limited to a single angle; neighboring areas can be fully considered. A single glare angle is less critical than an entire sector with multiple glare angles adjacent to each other. For example, if only a finger-width angular range is affected by glare within this range, the angle or angular range where glare occurs can be small enough to reliably detect objects, such as legs or bodies, using the required detection capabilities. It is also conceivable to limit the scope of functionality, such as reducing it from finger detection to leg detection. This is certainly safety-critical if the application requires finger detection, but may not require it at all. It is also conceivable that this limitation in output detection capability would lead to finger monitoring being taken over by other measures or sensors. This is particularly helpful if such other sensors have limitations and therefore should not be used for this purpose in the long term, such as ultrasonic sensors or radar that cannot completely replace laser scanners. Another example already mentioned is that if the angle affected by glare is outside the protection field, there is no need to respond to it, as such glare is irrelevant to safety.

[0030] Preferably, the control and evaluation unit is designed to trigger a safety-oriented response in or upon transitioning to a glare state. In this embodiment, a glare state is unacceptable because it impedes safety detection. The sensor cannot guarantee its safety function. Prior to this, it is best to check whether only the functional range is reduced and this is still safe; for example, only a lower detection capability is temporarily available or the safety range must be limited, which is not necessary in the current application or the protected area monitoring currently in operation, or the glare only affects the angular range outside the protected area. A safety-oriented response corresponds to a response to an unacceptable protected area intrusion; specifically, a safety-oriented response transitions the monitored machine to a safe state.

[0031] Preferably, the control and evaluation unit is designed to output a limiting signal indicating the limited detection capability (particularly a reduced range) of the sensor. As previously mentioned, a glare state does not necessarily mean that safety is no longer guaranteed in all cases. There can be intermediate states where only the entire functional range is unavailable. For example, glare may limit the range at which an object can be detected. Therefore, as long as the glare state persists, a larger protective field cannot be provided. The reduced functional range can be transmitted to the monitored machine via a limiting signal. Processing steps requiring full detection capability, especially those requiring a larger full detection range to achieve a correspondingly greater protective field, are no longer controllable. For example, the movement speed of a monitored robot may be limited, remote processing steps may be temporarily unavailable, or the speed of a vehicle with sensors deployed in a mobile application may be limited.

[0032] The method according to the invention can be further developed in a similar manner and exhibits similar advantages. These advantageous features are described, exemplarily but not exhaustively, in the dependent claims which are subordinate to the independent claims. Attached Figure Description

[0033] Other features and advantages of the invention will now be described in more detail, based on exemplary embodiments and with reference to the accompanying drawings. In the drawings:

[0034] Figure 1 A schematic cross-sectional view of a laser scanner is shown;

[0035] Figure 2 An exemplary diagram is shown of status indicators, including reflector indicators and noise indicators, during multiple scans within an angular range of a laser scanner under glare from a continuous external light source.

[0036] Figure 3 It shows the corresponding Figure 2 An exemplary illustration of distance measurement over multiple scans and within an angular range;

[0037] Figure 4 It shows the corresponding Figure 2 An exemplary illustration of glare markings in multiple scans and within a corner area;

[0038] Figure 5 This shows the current glare situation under periodic external light source conditions, corresponding to... Figure 2 An exemplary diagram of the status flags;

[0039] Figure 6 The current situation is shown as follows: Figure 5 In the case of glare from a periodic external light source, corresponding to Figure 3 An exemplary diagram of distance measurement; and

[0040] Figure 7 The current situation is shown as follows: Figure 5 In the case of glare from a periodic external light source, corresponding to Figure 4 An exemplary illustration of a glare sign.

[0041] Figure 1 A schematic cross-sectional view of the laser scanner 10 is shown. A light beam 14 generated by a light emitter 12 (e.g., a laser) is directed into a monitoring area 18 via a deflector 15 and a rotatable deflection unit 16, and diffusely reflected by any objects present in the monitoring area. The diffusely reflected light 20 returns to the laser scanner 10 and is guided via the deflection unit 16 through a receiving optics 22 to a light receiver 24, such as a photodiode, that generates a received signal.

[0042] The deflection unit 16 is typically designed as a rotating mirror unit that rotates continuously driven by the motor 26. Alternatively, the measuring head (light emitter 12 and preferably also includes a light receiver 24) rotates. The corresponding angular position is detected via the encoder 28. Thus, the light beam 14 sweeps across the monitoring area 18 created by the rotational motion. If the light receiver 24 receives diffusely reflected light 20 from the monitoring area 18, the angular position of the object in the monitoring area 18 can be inferred from the angular position of the deflection unit 16 by means of the encoder 28.

[0043] Furthermore, the distance between the object and the laser scanner 10 can be inferred using the received signal from the optical receiver 24, for example, in a manner known per se, such as pulse averaging, phase averaging, or FMCW, by inferring the distance between the object and the laser scanner 10 from the time of flight from the emission of a single light pulse until it is reflected at the object in the monitoring area 18 and then received.

[0044] The distance between the object and the laser scanner 10 is measured in the control and evaluation unit 32, which is connected to the light receiver 24, the light emitter 12, the motor 26, and the encoder 28. Therefore, the two-dimensional polar coordinates of all objects in the monitoring area 18 can be obtained by measuring the angle and distance. In another embodiment, multiple beams 14 are emitted at different elevation angles to form a multi-scanner and detect multiple layers in the three-dimensional monitoring area 18. All measurements can be output via the output terminal 34. All the aforementioned functional components are arranged in a housing 36, which has a front window 38 in the areas of the light outlet and light inlet.

[0045] In safety technology applications, the control and evaluation unit 32 uses one or more protective fields to compare the location of detected objects. The geometry of these protective fields is pre-given or configured to the control and evaluation unit 32 via corresponding parameters. Thereby, the control and evaluation unit 32 identifies whether a protective field has been violated, i.e., whether an unauthorized object is present, and switches the output terminal 34, which is designed as a safety output terminal (OSSD, Output Signal Switching Device) in this embodiment, based on the result. This triggers a safety-oriented response, such as an emergency stop, braking, deceleration, or evasive maneuver of a connected machine monitored by the laser scanner 10. For example, the monitored machine may be an industrial machine, a robot, or, in mobile applications, particularly an autonomous vehicle. By meeting the criteria mentioned at the outset and the necessary measures, this laser scanner is designed as a safety laser scanner.

[0046] An external light source 40 may cause glare to the laser scanner 10. Here, the external light source 40 does not necessarily need to be located within the monitoring area 18. It is sufficient if the external light 42 emitted by the external light source 40 reaches the light receiver 24 of the laser scanner 10 and causes glare there. The control and evaluation unit 32 identifies this glare and is able to distinguish between continuous glare, such as that caused by building lighting, that affects safety functions, and periodic glare, such as that from another laser scanner or 3D-TOF camera. This further enhances secure object detection within the limited functional scope sufficient for current security applications. (See later...) Figures 2 to 7 Glare recognition is described in more detail. If intolerable glare is detected, a safety-oriented response is preferably triggered in safety technology applications; otherwise, a glare warning may be issued or the functionality may be reduced.

[0047] Figures 2 to 4 First, an example of the evaluation results of multiple scans within an angular range under continuous glare is shown, then... Figures 5 to 7 The corresponding evaluation results under glare from periodic external light are shown. Here, a purely exemplary angular portion of seven measurements taken at consecutive angular positions is plotted on the X-axis, and the scan sequence number, corresponding to the time axis, is plotted on the Y-axis, as each scan continues for one rotation cycle of the deflection unit 16. This forms a grid of cells in which the relevant angle and scan measurement or evaluation results are entered, respectively. In the case of the pulse averaging method, the individual measurements have been summarized in the cells for histogram detection and distance determination.

[0048] Figure 2The status flags obtained during the measurement process are shown. In this example, there are four such flags or bits, thus values ​​ranging from 0 to 15, but only the reflector flag (bit 0) and the noise flag (bit 1) are of interest here. This particular representation of reflector and noise identification should be understood purely as exemplary and can be modified. Figure 2 In the diagram, only measurements with the reflector indicator set are displayed in light-colored cells, while measurements with both the reflector and noise indicators set are displayed in dark-colored cells. It should be noted that the diagram illustrates a case of continuous glare, in which a 70mm sample positioned directly in front of a horizontally oriented 1500W halogen illuminator is being tested. In other measurement cases, it is customary not to set the reflector or noise indicators.

[0049] This is because the reflector flag is actually for reflector identification, that is, identifying whether the object being measured is a reflector, so as to output it as additional measurement information or to correct the distance measurement. The noise flag indicates strong noise or a poor signal-to-noise ratio. Both were originally just indicators of glare. Reflectors and strong noise or a poor signal-to-noise ratio can be identified through level evaluation and other evaluations of the received signal. For example, the reflector bit is set when the current in the optical receiver 24 exceeds a threshold. In particular, noise can be measured when the optical transmitter 12 is inactive or at times that do not correspond to the received light pulse. The continuous light portion of the incoming light can also be isolated by low-pass filtering.

[0050] Figure 3 The measured distance value is shown. Figures 2 to 4 Entries in cells at the same location correspond to each other. Figure 3 In the light-colored cells, the distance to the object is entered in meters or other units of length. In the dark-colored cells, the value "65" represents "infinity," meaning no object was detected or the distance could not be measured. In the light-colored cells, the distance was measured despite the reflector and noise indicators. In the dark-colored cells, the laser scanner 10 is unaware whether an object might have been missed. In fact, this is the case in the example, as the sample also extends into the dark-colored cells.

[0051] Figure 4 It shows how to combine Figure 2 and Figure 3 The glare markers obtained from the assessment. Figure 4 In this context, glare indicators are highlighted with a "1" and a dark color. Glare is present if a high level of glare is present and distance cannot be measured simultaneously. The former... Figure 2 The indicator is provided by the reflector symbol and / or noise symbol, the latter being... Figure 3The value is represented by "65" or infinity. Therefore, the assessment can be summarized by the following formula: Glare Mark = (Reflector Mark and / or Noise Mark) AND (No Object or Infinity).

[0052] As illustrated, in this example, glare did not occur in all individual measurements or cells, but rather in all scans or rows. This limited detection capability. The subsequent evaluation then determined whether this form of glare was tolerable. Spatially, at least in terms of coarser detection capability (such as arm protection, leg protection, or body protection), safe detection might still be permissible only in isolated or a few adjacent corner segments, or in any case, safe detection would still be possible within a small area. Furthermore, glare outside the protected area is unrelated to safety and can be ignored.

[0053] Of particular interest is observing the temporal distribution of glare measurements or scans. Detection capability can degrade over a certain period, preferably within 5 seconds according to standard EN61496-3. Therefore, this time period can be used to determine whether the glare is safety-related and whether the laser scanner 10 must output a safety-oriented cut-off signal. According to the unpublished European patent application No. 21187348.4 mentioned in the introduction, if a certain number of scans show no glare, the glare warning is reset. If the glare warning persists for a full five seconds, a safety-oriented cut-off signal is output.

[0054] According to Figures 2 to 4 In cases of persistent glare, the glare warning will never be reset. This is the nature of the problem and cannot be eliminated through smarter assessments. However, there is considerable potential for improvement in cases of periodic glare from external light sources (such as another laser scanner or a 3D-TOF camera). Similar to... Figures 2 to 4 , Figures 5 to 7 The case of periodic interference is illustrated. In this example, with a scanning period of 40ms for laser scanner 10, interference occurs every 30ms.

[0055] Similar to Figure 2 , Figure 5 The reflector and noise indicators are now shown in the presence of periodic glare. It can be clearly seen that the cell with the reflector indicator set on a gray background appears in the periodically repeating scans, while neither the reflector nor the noise indicator is set between these scans.

[0056] Similar to Figure 3 , Figure 6This shows the distance measured under periodic glare. In cells with a dark background, objects cannot be detected or distances cannot be measured, so "65" is entered here as an infinity value.

[0057] Similar to Figure 4 ,exist Figure 7 Lieutenant General Figure 5 The reflector markings and noise markings are related to Figure 6 The distance measurement results are combined to form a glare indicator. Glare occurs in approximately 30% of scans in one or two repeated scan sets. The temporal pattern of glare scanning is a beat frequency generated by the scan frequency and the repetition frequency of periodic external light radiation.

[0058] According to the glare recognition in the unpublished European patent application No. 21187348.4 mentioned at the beginning, the glare warning will only be reset if no glare is detected for a sufficiently long period of time. Figure 7 Four glare-free scans in each section are insufficient for this purpose. It is also impossible to simply shorten the duration before the glare warning reset, as this would mean the glare would be ignored; furthermore, the stated beat frequency cannot guarantee a sufficiently short duration before reset. Therefore, despite only periodic glare, the glare warning remains permanently active until a safety-oriented cutoff due to glare is triggered after five seconds.

[0059] Therefore, according to the present invention, the control and evaluation unit 32 analyzes the time pattern of the cell or scan in which glare occurs, such as Figure 7 The example is illustrated below. In one embodiment, the number of scans or cells where glare occurs is counted within a predetermined time period that allows for a reduction in detection capability. Specifically, this can be done continuously or in a rolling fashion. For example, if the scan cycle is 50 ms, 100 scans can be evaluated within 5 seconds. If the number of scans where glare occurs exceeds a previously defined critical ratio or limit, it is considered a critical glare state, and a safety-oriented cutoff signal is output.

[0060] Therefore, the laser scanner 10 can identify scans without continuous glare, but can detect glare in 30% of the scans, and can determine whether this is still tolerable. It can also output information indicating the identification of periodic glare, which makes diagnosis easier and allows for the reduction or elimination of the effects of glare.

[0061] From a security perspective, glare caused by another laser scanner or 3D-TOF camera is generally not critical, because even the smallest dark object that still needs to be detected according to the required detection capability will not be brightened by the typical illumination optics of such an interfering sensor. Therefore, periodic external light interference is unlikely to cause security-related detection failures. On the other hand, large halogen headlights, especially horizontally oriented large halogen headlights, can illuminate the aforementioned dark objects well. If, from a geometric point of view, smaller objects are also brightened by the illumination device of another laser scanner or 3D-TOF camera, then glare recognition according to the invention can be deactivated to obtain correspondingly fine detection capabilities, or the possibility of application can be limited to certain protective field configurations and ranges.

[0062] according to Figure 7 For example, observing temporal patterns in cells or scans where glare occurs can be more complex than simple counting. In fact, any pattern recognition approach can be conceived that classifies some temporal patterns as critical and others as non-critical, or distinguishes between continuous and periodic glare. A vast library of well-known filters and pattern recognition methods is provided here (Arsenal). For instance, glare-occurring and non-glare-occurring scans can be understood as a time series, and periodicity can be found in the time series using Fourier analysis, autocorrelation, or simplified methods based on them.

[0063] Knowing the glare time pattern allows for the exclusion of affected scans or measurements, or the ability to consistently perform targeted measurements in the absence of glare. Pulses from the 3D-TOF camera can be avoided on very short timescales through appropriate time offsets. This measure can be taught the time pattern during periods when the device is not performing its own measurements and when the monitored machine is not releasing data via output 34.

[0064] In the preceding embodiments, the scan or measurement in which glare occurs is located by evaluating the received signal of the light receiver 24. Alternatively or additionally, a separate light receiver for identifying glare can be used for this purpose. This could be a dedicated light receiver, but an existing light receiver from a windshield monitoring device could also be used, for example.

[0065] A beneficial supplement is an alert function or object tracking. This allows immediate awareness of where an object has been detected after a glare event. This is particularly useful in multi-assessment scenarios, where intrusion into the protected area must be confirmed in several consecutive scans before protection can be implemented. If an object has already been detected at the corresponding location, or if object tracking indicates an object is expected, the number of required multi-assessments can be reduced, even to a single one.

Claims

1. A photoelectric sensor for detecting objects in a monitored area (18), comprising: a light emitter (12) for emitting at least one light beam (14); a movable deflection unit (16) for periodically scanning the monitored area (18) with at least one light beam (14); a light receiver (24) for generating a received signal from light (20) diffusely reflected by the object; and a control and evaluation unit (32) designed to acquire information about the object in the monitored area (18) from the received signal, and to identify a first glare-prone stage and a second glare-free stage of the light receiver (24), and to switch to a glare state if the glare interferes with security detection, wherein, A phase is a measurement cycle or a cycle of a movable scanning unit that determines the measured value; this is also known as one scan. Its features are, The control and evaluation unit (32) is designed to determine whether glare hinders safety detection based on the distribution of the first and second phases; In order to evaluate the distribution, the first phase is counted or the cumulative duration of the first phase within a time interval of a few seconds is determined. As a criterion for evaluating the distribution, it is checked whether the first stage exceeds a critical ratio, and / or the time pattern of the first stage and the second stage is determined, wherein glare-free and glare-free scans are understood as a time series, and periodicity is found in the time series using Fourier analysis, autocorrelation, or simplified methods based on them, in order to tolerate periodic glare, as long as there is a sufficient second stage to remain glare-free.

2. The sensor according to claim 1, wherein, The control and evaluation unit (32) is designed to schedule the detection of the object within the time period in which the second stage is expected to occur based on the identified time pattern.

3. The sensor according to claim 1, wherein the sensor has an additional light receiver for glare detection.

4. The sensor according to claim 2, wherein the sensor has an additional light receiver for glare detection.

5. The sensor according to any one of claims 1-4, wherein, The control and evaluation unit (32) is designed to identify glare based on the received signal.

6. The sensor according to any one of claims 1-4, wherein, The control and evaluation unit (32) is designed to identify glare based on the determination of the level of the received signal or the determination of the signal-to-noise ratio of the received signal.

7. The sensor according to claim 6, wherein, The control and evaluation unit (32) is designed to set a reflector flag when the level is above the reflector threshold, and / or set a noise flag when the signal-to-noise ratio is below the noise threshold.

8. The sensor according to claim 6, wherein, The control and evaluation unit (32) is designed to identify a phase as a first phase with glare when the level of the received signal is higher than a reflector threshold and / or the signal-to-noise ratio is lower than a noise threshold, and no object is detected at the same time.

9. The sensor according to claim 7, wherein, The control and evaluation unit (32) is designed to identify a phase as a first phase with glare when the level of the received signal is higher than a reflector threshold and / or the signal-to-noise ratio is lower than a noise threshold, and no object is detected at the same time.

10. The sensor according to any one of claims 1-4 and 7-9, wherein, The control and evaluation unit (32) is designed to determine whether an object is located in a protected area configured within the monitoring area (18), and in this case initiate a safety-oriented response.

11. The sensor according to any one of claims 1-4 and 7-9, wherein, The control and evaluation unit (32) is designed to determine the first stage and the second stage based on the angular position of the deflection unit (16).

12. The sensor according to any one of claims 1-4 and 7-9, wherein, The control and evaluation unit (32) is designed to trigger a safety-oriented response in the glare state or when transitioning to the glare state.

13. The sensor according to any one of claims 1-4 and 7-9, wherein, The control and evaluation unit (32) is designed to output a limiting signal that indicates the limited detection capability of the sensor.

14. The sensor according to claim 1, wherein, The sensor is a laser scanner (10).

15. The sensor according to claim 1, wherein, Obtaining information about objects in the monitored area (18) from the received signal includes measuring distances using the time-of-flight method of light.

16. The sensor according to claim 13, wherein, The limited detection capability refers to a narrowed range.

17. A method for detecting objects in a monitored area (18), wherein, At least one light beam (14) is emitted, and the monitoring area (18) is periodically scanned with the at least one light beam (14). A light receiver (24) generates a received signal from the light (20) diffusely reflected by the object, and the received signal is evaluated to obtain information about the object in the monitoring area (18). A first glare phase and a second glare-free phase of the light receiver (24) are also identified, and a glare state is entered if glare interferes with security detection. A phase is a measurement cycle for determining a measurement value or a cycle of a movable scanning unit, which is also referred to as one scan. Its features are, The distribution of the first and second phases determines whether glare hinders safety detection. In order to evaluate the distribution, the first phase is counted or the cumulative duration of the first phase within a time interval of a few seconds is determined. As a criterion for evaluating the distribution, it is checked whether the first stage exceeds a critical ratio, and / or the time pattern of the first stage and the second stage is determined, wherein glare-free and glare-free scans are understood as a time series, and periodicity is found in the time series using Fourier analysis, autocorrelation, or simplified methods based on them, in order to tolerate periodic glare, as long as there is a sufficient second stage to remain glare-free.

18. The method according to claim 17, wherein, Obtaining information about objects in the monitored area (18) includes measuring distances using the time-of-flight method of light.

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