Optoelectronic sensor and method for detecting an object

Abstract

The application relates to an optoelectronic sensor and a method for detecting objects. The optoelectronic sensor (10) has at least one light emitter (22) for emitting a plurality of mutually separate light beams (26), at least one light receiver (32) for generating a corresponding reception signal from a diffusely reflected light beam (28) in a monitored region (20), a movable scanning unit (12) by means of which the emitted light beams are periodically directed through the monitored region in order to scan a scanning layer (44) respectively with a separate light beam during the movement of the scanning unit (12), and a control and evaluation unit (40) which is designed to obtain information about objects (48) in the monitored region from the corresponding reception signals. Here, the presence of safety-relevant objects (48, 50) is determined for each scanning layer, and it is decided whether to trigger a safety-oriented response by a joint evaluation of the presence of safety-relevant objects determined for each scanning layer.

Description

Technical Field

[0001] This invention relates to photoelectric sensors, particularly laser scanners and methods for detecting objects in a monitored area. Background Technology

[0002] Laser scanners are commonly used for optical surveillance. A beam of light generated by a laser periodically sweeps across a monitored area using a deflection unit. The light is diffusely reflected at objects within the monitored area and evaluated within 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 also inferred from the time of flight of the light using the speed of light. Two fundamental principles for determining the time of flight of light 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, as preferred in security technologies, the laser scanner measures the time of flight until the emitted light pulse is received again. In a pulse averaging method, for example, known from EP 2 469 296 B1, multiple single pulses are emitted for measurement, and the received pulses are statistically evaluated.

[0003] One important application is in safety 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 location of an object within the monitored area and therefore within the protected area. If the laser scanner detects unauthorized interference within 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 machine safety standard EN13849 and the equipment standard EN61496 for non-contact protection systems (BMS). To meet these safety standards, a range of measures must be taken, such as safety electronics assessments using redundant and diverse electronics, functional monitoring, and / or providing individual test targets with limited reflectivity that can only be identified at corresponding scan angles.

[0005] Laser scanners are limited to their two-dimensional scanning plane. Furthermore, a high level of calibration is required so that the scanning plane extends parallel to the ground. This becomes even more challenging over long distances and at large scan angles. In environments with interfering objects, particularly in outdoor areas, usability issues can arise, leading to unnecessary shutdowns due to objects that are not actually relevant to safety. While the detection algorithm may filter out objects that are too small or transient, it will still respond to persistent interfering objects, such as a single blade of grass.

[0006] Laser scanners are well-known beyond safety technologies, monitoring a sector composed of multiple scanning layers (with regular or irregular angular spacing between them) to ultimately monitor a three-dimensional spatial region. Such laser scanners are called multilayer scanners or sometimes multiplane scanners. However, to date, there are no truly secure multilayer scanners—that is, multilayer scanners equipped and certified for safety technologies according to the aforementioned functional safety requirements. Existing secure laser scanners are always single-layer or single-plane scanners.

[0007] 3D cameras are known to be used for detecting three-dimensional spatial regions, and they also address security applications. Multilayer scanners and 3D cameras exhibit drastically different characteristics in terms of reichweie (range), field of view, resolution (especially in the elevation direction), and the quality of the detected 3D measurement points. Neither technique is generally considered superior; applicability depends on the specific application.

[0008] Therefore, the need for a safe laser scanner with 3D inspection capabilities remains unmet. However, the procedures for both single-layer scanners and 3D cameras cannot be easily transferred. If the identification of each object in one of multiple scanning layers in a multi-layer scanner (analogous to a single scanning plane in a single-layer scanner) is simply evaluated as safety-critical, unnecessary shutdowns will multiply. Furthermore, at least in downward-facing scanning layers, the ground must be taken into account to configure protected areas to at least avoid persistent erroneous shutdowns caused by the ground. On the other hand, the evaluation of 3D point clouds from 3D cameras is extremely complex and cannot be accomplished using the conventional computational and storage capabilities of laser scanners. Moreover, such evaluation is simply unsuitable for point clouds from laser scanners, for example, due to the completely different vertical resolution.

[0009] As a representative of numerous documents, EP 3 517 999 A1 is considered an open source for multilayer scanners. It incidentally mentions the possibility of monitoring protected areas in the field of security technology. However, this merely reiterates the protected area assessment and security design known from single-layer scanners, which cannot be transferred to multilayer scanners, or would lead to the numerous erroneous shutdowns mentioned above. The real essence of EP 3 517 999 A1 is a specific optical configuration that can also be used in secure multilayer scanners, but without contributing to their security and usability.

[0010] EP 1 927 867 B1 discloses a secure multilayer sensor that, in an embodiment, generates a fan-shaped distribution of monitoring layers. However, this multilayer sensor is not a laser scanner; the layers are detected by immobile and therefore spatially resolved light receivers. Furthermore, no specific characteristics for evaluating objects securely detected across multiple layers are discussed.

[0011] EP 3 220 164 B1 describes a laser scanner that can filter out objects that are too small and are detected as unrelated to safety during monitoring of a protected area. However, this assessment only involves the location of a single scanning plane of a single-layer scanner.

[0012] In DE 101 41 294 B4, a mirror arrangement is used to make the rear scanning area of ​​a laser scanner suitable for vehicles, in order to obtain additional scanning layers in the front scanning area. However, the goal is not multi-scanning, but redundancy, whether to increase the effective scanning frequency or to compensate for the pitch motion of the vehicle. Therefore, no evaluation suitable for a safe multi-scan scanner is found in the document. DE 101 41 294 B4 also describes ground identification. The latter is also described in EP 3 521860 A1 as a laser scanner with a more complex ground model. Summary of the Invention

[0013] Therefore, the objective of this invention is to improve security monitoring using universal sensors.

[0014] This task is accomplished by photoelectric sensors, particularly laser scanners, and methods for detecting objects in a monitored area, as described below. A light emitter emits multiple beams of light, separated from each other, into the monitored area, where multiple light sources and / or discrete optical elements can be arranged for this purpose. The emitted beams should not be understood as beams in the strahlenoptik sense within a larger beam, but rather as separate scanning beams, particularly collimated scanning beams with small cross-sections, thus producing correspondingly separate, spaced-apart light spots upon impact with an object in the monitored area.

[0015] When the emitted light beam is reflected at an object within the monitored area, at least one optical receiver is capable of generating a corresponding received signal from the diffusely reflected beam from different directions. For this purpose, multiple optical receiving elements and / or regions or pixels (groups) are provided with optical receivers. There is no conceptual distinction between directional reflection and non-directional scattering or diffuse reflection.

[0016] A movable, preferably rotatable, deflection unit periodically guides the emitted light beam through the monitoring area. Here, each emitted beam scans its own detection or scanning layer, resulting in a multi-layer scan, particularly a multi-layer scanner or multi-layer (laser) scanner. Preferably, the light emitter and / or light receiver are arranged to move together with the deflection unit. This creates a movable, particularly rotatable, measuring head or optical head. Alternatively, the light emitter and / or light receiver are fixed and thus stationary relative to the sensor or its housing, while the deflection unit is implemented, for example, as a rotating mirror. In this case, it should be noted that during the movement of the rotating mirror, these layers change their height position.

[0017] The control and evaluation unit detects objects by evaluating the received signals for each beam or scan layer, and specifically determines the light flight time to determine the distance to the object on the corresponding scan.

[0018] This invention is based on the fundamental idea of ​​security assessment for personnel identification across multiple scanning layers. To this end, security-related objects are first detected within the respective scanning layers. For each scanning layer, this assessment specifically corresponds to the assessment of a conventional single-layer security scanner, while for multiple scanning layers, the assessment multiplies. Subsequently, information on which scanning layers identified or determined the presence of security-related objects is evaluated on the scanning layers, and based on this, a decision is made as to whether to trigger a security-oriented response. This is specifically achieved by outputting appropriate protective signals to a machine monitored by sensors, which then transitions to a secure state, for example, by shutting down, braking, or avoiding the obstacle.

[0019] Therefore, according to the present invention, measurements from each scanning layer are not merged into a common 3D point cloud and evaluated together. Instead, the actual object detection remains within the respective scanning layer. Then, within each scanning layer, the processed presence information of safety-related objects is evaluated at a higher level and in a summary manner: whether the identified situation requires a safety-oriented response.

[0020] The advantage of this invention lies in its ability to achieve secure and robust object or person detection in multi-layer scanning. Unlike 3D cameras, a large scan angle and wide-range scanning detection are used. The sensor according to the invention is particularly suitable for mobile applications, such as those in vehicles. Better tolerance and robustness than single-layer scanners can be achieved. This addresses interfering objects such as dust or rain, sensor tilt due to installation location or movement in mobile applications, and uneven, tilted, or other contoured surfaces. Evaluation remains easily managed with low computational and storage requirements, and provides a clear theoretical demonstration of the secure detection capabilities required by the security technology. Furthermore, since the evaluation is initially limited to a single scan layer, existing software modules can be used.

[0021] Preferably, the control and evaluation unit is designed to trigger a safety-oriented response when the presence of an object is determined in multiple scan layers or in the lowest scan layer above the ground. Therefore, in principle, the presence of an object needs to be determined in multiple scan layers to trigger a safety-oriented response. This "AND" association of safety-related objects detected in multiple scan layers ensures improved robustness. A special case is a reclining person, who may only be detected in a single scan layer due to the small cross-section provided to the sensor for scanning. This scan layer must then be the lowest scan layer above the ground. For reclining persons, preferably exceptionally, determining the presence of a safety-related object only in the lowest scan layer above the ground is sufficient to trigger a safety-oriented response. Since the ground is the reference, the sensor is preferably limited to a horizontal protective device. The sensor is then aligned at least approximately and generally parallel to the ground; this, of course, cannot be applied to all individual scan layers, which in multi-layer scanners have formed non-parallel sectors.

[0022] Preferably, the control and evaluation unit is designed to determine the presence of an object in multiple scan layers when its presence is determined at the same or adjacent angular locations. Presence at the same or adjacent angular locations is a coherence condition. It should be the same object detected multiple times across scan layers. This only occurs when detection is performed at the same or similar scan angles or azimuth angles. Thus, multiple detections of objects at large azimuth intervals across multiple scan layers are not considered security-related, but rather random simultaneous interference. The same or adjacent angular locations are preferably checked through discretized angular sectors. It is then required that the object be detected in the same or adjacent angular sectors across multiple scan layers. Here, adjacent preferably means directly adjacent, i.e., there are no other angular sectors between adjacent angular sectors.

[0023] Preferably, the control and evaluation unit is designed to trigger a safety-oriented response when the presence of an object is determined in a certain number of scan layers, with the number of scan layers being greater when the object is near than when it is far away. In other words, for nearby persons or objects, a safety-oriented response is triggered only when their presence is determined in a larger number of scan layers. For distant persons or objects, fewer scan layers are sufficient. Furthermore, the coherence required for object detection across scan layers is higher at near locations than at distant locations. Preferably, angular conditions remain constant, meaning that an object must be detected across scan layers at the same or adjacent scan angles or azimuth angles to trigger a safety-oriented response.

[0024] Preferably, the control and evaluation unit is designed to trigger a safety-oriented response when the presence of an object is determined in all relevant scanning layers, for an object at a distance within a first safety range, where the first safety range specifically corresponds to the safety range of a safety laser scanner with only one scanning layer. Therefore, when the object is within the first safety range from the sensor, the object needs to be detected in all relevant scanning layers. This is understood under two conditions: object detection is preferably only related to a minimum height, since small individuals at a greater distance from the upper scanning plane are no longer detected. And object detection on the lowest scanning plane above the ground is preferably only sufficient to account for the exception of lying down individuals. Thus, on the one hand, scanning layers for those individuals who are expected to be upright under all conditions are "relevant." For curved positions, this can be a range of approximately 50 mm to 1000 mm above the ground. Furthermore, it must also be considered that lying down or sitting individuals must also be detected. Therefore, for object detection near the ground at heights of, for example, 50 mm to 250 mm, coherence conditions across multiple scanning layers are not required. However, loose spatial filtering can be performed here. For example, lying down or sitting individuals can be detected at an azimuth angle much larger than the legs. For example, it can be assumed that the minimum object resolution in the horizontal direction is 200 mm. Preferably, the first safety range corresponds to the safety range of a comparable single-layer scanner that detects even very dark targets and thus virtually identifies all objects. Therefore, it is impossible for the scanning layer to fail to detect a real object, and thus there is reason to require such detection for objects that are safety-related.

[0025] Preferably, the control and evaluation unit is designed to trigger a safety-oriented response when the presence of an object is determined in at least two or more scan layers that are particularly adjacent to each other, for an object located at a distance between a first and a second safety range. Therefore, the lower limit for the number of scan layers is preferably two, but it can also be higher. This is a lower limit where the condition for triggering a safety-related response is over-satisfied if a safety-related object is detected in more than this number of scan layers. The second safety range is greater than the first safety range, and the sensor only guarantees the detection of slightly brighter objects at these larger distances. In the range between these, it is conceivable that dark objects would be ignored in the scan layers. However, it is inconceivable that countless scan layers would encounter such dark object areas, as a person would not be completely enveloped in black velvet. Therefore, within the distance range between the first and second safety ranges, it is no longer expected that a person will be detected in all scan layers. On the other hand, the condition of detection in only a single scan layer is too weak, which would trigger many false alarms. Therefore, a safety-oriented response is triggered when the presence of an object is determined in at least two scan layers, where, as previously stated, the lower limit can be higher than two scan layers. The number of scanning layers that must simultaneously detect an object to trigger a safety-oriented response can decrease from "all" to "two" (or more) as the distance increases from a first safety range to a second safety range. Beyond the second safety range, sensor protection is no longer guaranteed.

[0026] Preferably, the control and evaluation unit is designed for protected area assessment, where an object is only safety-related if its location is within a configured protected area. Therefore, classic protected area assessments are performed across individual scan layers. Here, proven existing procedures, algorithms, and software modules of conventional single-layer scanners can be used. A protected field is used to configure portions of a scan layer into a safety-related geometry. Not every object detection within a protected area must automatically become a safety-related protected area intervention. Minimum object size and duration may be required, for example, repeated detection in m scans out of n scans, and permitted objects or deactivated portions (silent, hidden) may also exist within the protected area. EP 3 220 164 B1, mentioned at the outset, also proposes suitable filters for protected area assessment. Protected areas are preferably configured with the same shape in overlapping scan layers, where protected areas forming 3D shapes due to different geometries across scan layers are also conceivable, including defining protected areas only in some, but not all, scan layers. Following the protected area assessment, the presence of safety-related objects is identified in which scan layers, and preferably at which angular locations, and then a comprehensive assessment is performed across the scan layers to trigger a safety-oriented response if necessary.

[0027] Preferably, the measurement is pulse-based, for which the transmitted pulse is emitted together with the light beam and a corresponding received pulse is generated from the diffusely reflected light beam. Preferably, the control and evaluation unit is designed to sequentially emit multiple transmitted light pulses, sample the corresponding received pulses at at least one threshold, accumulate them in a histogram, and determine the light flight time from the histogram. Thus, this embodiment operates using the multi-pulse method as mentioned in EP 2 469 296 B1.

[0028] The control and evaluation unit is designed to detect the position and / or orientation of the ground using the lowest scanning layer or multiple lower scanning layers. Preferably, the sensor is mounted such that at least the lowest scanning layer is still impacting the ground within range. Ideally, the scanning beam of the lowest scanning layer forms a circle on the ground, or conversely, measures a constant distance anywhere. Deviations from this ideal can indicate that the sensor is mounted at an angle or that the ground is tilted or uneven. The sensor is familiarized with these conditions, preferably during the teaching phase, particularly during post-installation commissioning, especially in mobile applications, and also during operation. The sensor alignment and / or mounting height can be readjusted if necessary. With the ground understood, it becomes particularly clear for further operation which scanning layer at each distance is the lowest scanning layer not impacting the ground, and which scanning layer can be used to identify a reclining person.

[0029] Preferably, the control and evaluation unit is designed to include only objects within a minimum height above the ground to determine the presence of safety-related objects. The minimum height corresponds to the lower limit of the height of personnel still requiring safety detection. For example, requiring detection at a height of 2 meters is meaningless, as most people are not that tall. However, some scanning layers can reach such heights, especially at greater distances, so their detection should be ignored when deciding whether to trigger a safety-oriented response.

[0030] Preferably, the control and evaluation unit is designed to determine the height above the ground based on the (detected) distance and the scan layer. This can be calculated from the ground shown and the position of the scan layer relative to the sensor, determined by sensor properties. The elevation angle of the thus known scan layer is preferably used to determine, for the corresponding distance from the sensor, which scan layer is the lowest scan layer above the ground and / or which scan layers extend above the minimum height limit for personnel, and then preferably ignores these scan layers when evaluating whether a safety-oriented response is triggered.

[0031] Preferably, the scanning layers have angular resolution relative to each other, at least near the ground, such that adjacent scanning layers have a spacing corresponding to the smallest size of the object to be detected within a maximum range, specifically defined as arctan(minimum size / range). Specifically, the maximum range is the second safe range defined above. The scanning layers form a vertical fan shape, so the vertical spacing between two scanning layers increases with increasing distance from the sensor. However, the smallest size object (e.g., a human body) should be safely detected even within the maximum range. For this purpose, the angular spread between scanning layers should not be too large. Typically, this can be calculated using the formula arctan(minimum size / range). The requirement is primarily above the ground, as it is impossible for a person to float between two higher scanning layers, even if the angular spread is greater there. Here, minimum size refers to the height dimension or elevation angle, and object detection within each scanning layer depends on variables other than the angular spread between scanning layers. The same or different angles can exist between any two scanning layers, thus the resolution of elevation scanning can be uniform or non-uniform.

[0032] Preferably, in the sense of safety standards for protective devices used for machine safety or non-contact actions, the sensor is designed as a safety sensor, particularly a safety laser scanner, and specifically has a safety output for outputting a safety-oriented protective signal. The safety sensor or safety (laser) scanner is a safety sensor or safety laser scanner in the sense of safety standards and can therefore be used for personnel protection at hazardous locations. In the introduction, some relevant safety standards currently in effect are exemplified. These standards may vary in their specific formulation by region and in the future, but they do not differ in their basic approach to avoiding errors or timely detection of errors to prevent accidents caused by defects or other unintended actions. If it is decided to trigger a safety-oriented response, or if the sensor cannot ensure its own functionality, it can be sent at the safety output, particularly an OSSD (Output Signal Switching Device), to the monitored machine or an intermediate safety controller. This safety output is securely implemented as part of standard compliance measures, for example, implemented as a dual-channel system, and is used, when necessary, to initiate safety-oriented measures, such as emergency stop, or more generally, to establish a safe state.

[0033] The method according to the invention can be further developed in a similar manner and exhibits similar advantages. These advantageous features are described, however, exemplarily and in detail, in the dependent claims which are subordinate to the independent claims. Attached Figure Description

[0034] Other features and advantages of the invention will now be described in more detail based on embodiments and with reference to the accompanying drawings. In the drawings:

[0035] Figure 1 A schematic diagram of a multilayer scanner is shown;

[0036] Figure 2 A schematic diagram of a scanned layer monitored by a multilayer scanner is shown;

[0037] Figure 3 A schematic diagram is shown showing the detection of a reclining person by a multi-layer scanner;

[0038] Figure 4 A schematic diagram showing the detection of personnel within the first safety zone is shown;

[0039] Figure 5 A schematic diagram is shown for detecting personnel who are outside the first safety zone but within the second safety zone;

[0040] Figure 6 A table is shown to illustrate the coherence conditions for detecting the same object in multiple scan layers;

[0041] Figure 7 A schematic diagram showing the detection of the ground using the bottommost scanning layer is shown;

[0042] Figure 8 It shows something similar to Figure 7 The diagram shows the ground being inspected; the ground is currently tilted.

[0043] Figure 9 It shows something similar to Figure 7 A schematic diagram of the ground detection, now using the two lowest scanning layers for detection; and

[0044] Figure 10 It shows something similar to Figure 7 The diagram shows the ground being inspected. The two bottommost scanning layers are now used for inspection, and the ground is tilted. Detailed Implementation

[0045] Figure 1 A schematic cross-sectional view of a photoelectric sensor 10 in an embodiment as a laser scanner, particularly a multilayer scanner, is shown. Roughly divided, the sensor 10 includes a movable scanning unit 12 and a base unit 14. The scanning unit 12 is an optical measuring head, while other components such as a power supply, evaluation electronics, and interfaces are also housed in the base unit 14. In operation, the scanning unit 12 is rotated about a rotation axis 18 by means of a driver 16 of the base unit 14 to periodically scan the monitoring area 20.

[0046] In the scanning unit 12, a light emitter 22 having multiple light sources 22a, such as an edge emitter or an LED or laser in the form of a VCSEL, generates multiple emitted beams 26 that are angularly offset from each other by means of an emitting optics 24. These emitted beams are emitted into the monitoring area 20. Instead of multiple light sources 22a, a beam splitter can also be considered, which divides the light from a single or multiple light sources into multiple emitted beams 26. If an emitted beam 26 strikes an object in the monitoring area 20, the corresponding diffusely reflected beam 28 returns to the sensor 10. The diffusely reflected beam 28 is guided by a receiving optics 30 to a light receiver 32 having multiple light receiving elements 32a, each of which generates an electrical receiving signal. The light receiving elements 32a can be individual components or pixels of an integrated matrix device, such as photodiodes, APDs (Avalanche Diodes), or SPADs (Single-Photo Avalanche Diodes). Instead of the common lens as the emitting optics 24 or the receiving optics 30, other optical elements, such as the arrangement of microlenses, can be used.

[0047] Four light sources 22a and light receiving elements 32a are shown as an example, overlapping vertically. Instead, these light sources and light receiving elements can be arranged in a pattern entering or leaving the paper plane, for example, on a circumferential line. In this embodiment, the light emitters 22 and light receivers 32 are jointly arranged on a circuit board 34 located on the rotation axis 18 and connected to the shaft 36 of the driver 16. This should be understood as merely exemplary; in practice, any number and arrangement of circuit boards can be contemplated. The basic optical structure of dual-axis parallel light emitters 22 and light receivers 32 is not mandatory and can be replaced by the structure of any known single-beam photoelectric sensor or laser scanner. Examples of this are coaxial arrangements with or without beam splitters.

[0048] A non-contact power and data interface 38 connects the movable scanning unit 12 to the fixed base unit 14. A control and evaluation unit 40 is located within the base unit; this unit may also be at least partially mounted on the circuit board 34 or elsewhere on the scanning unit 12. The control and evaluation unit 40 controls the light emitter 22 and receives signals from the light receiver 32 for further evaluation. Furthermore, the control and evaluation unit controls the driver 16 and receives signals from an angle measurement unit (not shown), commonly found in laser scanners, which determines the corresponding angular position of the scanning unit 12.

[0049] For the first part of the evaluation, the distance to the object being scanned is preferably measured using the known time-of-flight method of light. Together with the information about the angular position from the angle measurement unit, the two-dimensional polar coordinates of all object points in the probe layer or scan layer can be obtained using the angle and distance after each scan cycle. The corresponding scan layer is also known through the identification of the diffusely reflected beam 28 and its detection in one of the light receiving elements 32a, thus allowing the entire three-dimensional spatial region to be scanned using multiple scan layers.

[0050] Sensor 10 is designed as a safety sensor for monitoring hazardous sources (e.g., dangerous machinery) in safety technology. Therefore, sensor 10 is designed to safely meet the aforementioned requirements of safety standards corresponding to its safety level (e.g., SIL (Safety Integrity Level) or PL (Performance Level)). For example, it monitors a pre-configured protected area that operators are prohibited from entering during machine operation. The protected areas are configured in one scan layer, multiple scan layers, or across all scan layers, and each scan layer has the same or different geometry. Reference will be made below. Figures 2 to 10 The text elaborates on how the control and assessment unit 40 collaboratively assesses protected area interventions across scan layers to identify potential hazards. If the assessment concludes that a safety-oriented response is necessary, a corresponding safety-oriented signal is output at output 42 (OSSD, Output Signal Switching Device).

[0051] The sensor 10 shown is a laser scanner with a rotating measuring head (i.e., scanning unit 12). Alternatively, it is conceivable to periodically deflect the light using a rotating mirror or a facettenspiegelrad. With multiple emitted beams 26, there is a disadvantage that how the multiple emitted beams 26 fall into the monitoring area 20 depends on the corresponding rotational position, because, as known geometric considerations indicate, the arrangement of these emitted beams is rotated by the rotating mirror. Another alternative implementation is to pivot the scanning unit 12 back and forth. Furthermore, the scanning motion used to generate the scanning layer can also be generated alternatively using other known methods, such as MEMS mirrors, optical phased arrays, or acousto-optic modulators, particularly in implementations where the light source generates multiple emission points.

[0052] During the rotation of sensor 10, each emitted beam 26 scans a surface respectively. Here, at an elevation angle of 0° (i.e., at...) Figure 1The non-existent horizontal emission beams 26 scan the plane of the monitored area 20 in a geometric sense. Strictly speaking, the remaining emission beams 26 scan the outer surface of the cone, which forms different sharp angles depending on the elevation angle. The multiple emission beams 26 emitted upward and downward at different angles collectively produce a nested structure of multiple hourglasses as a scanning structure. These geometric details will not be discussed further; for simplicity, the corresponding scanning areas of the emission beams 26 are considered as scanning layers, which, as already stated, roughly, but not geometrically, correspond to a precise scanning plane.

[0053] Figure 2 The scanning layer 44 of a horizontally mounted sensor 10 is schematically shown in a cross-sectional view. "Horizontal" means that the scanning layer 44 extends generally parallel to the ground 46, although precise parallelism cannot be achieved due to the fan-shaped arrangement of the scanning layer 44. The sensor 10 has a maximum range R... max Within this range, objects can still be reliably detected and protected areas can be configured. Personnel in the monitored area 20 should be detected in multiple scan layers 44. Therefore, the scan layers 44 should not extend too far, even at their maximum range. This results in a required vertical resolution Δh, which represents the spacing of the scan layers 44 in the height or elevation direction, where the extension (Spreizung) between every two scan layers 44 can be the same size or different sizes. Due to the different inclinations of the dispersed scan layers 44, the vertical resolution Δh depends on the spacing, which here refers to the spacing corresponding to the maximum range R. max The spacing.

[0054] The special case of a person lying on the floor must also be considered, as this may be detected by only a single scan layer 44. This means that the vertical resolution Δh must be finer than the minimum height HL of the lying person, at least near the ground. In a preferred embodiment, the spread of the scan layer 44 is uniform and maximum is arctan(minimum height HL / maximum range R). max ). In the maximum range R max In the numerical example where the minimum height HL = 200 mm and the minimum height is 10 m, the maximum vertical extension of the scanning layer 44 is obtained as arctan (200 mm / 10 m) = 1.15°.

[0055] Figure 3 A special case is illustrated where a person 48 is lying on the ground, modeled as a sphere with a diameter of 200 mm. The minimum height HL described herein is taken into account, as well as the worst-case scenario of horizontal extension, such as when person 48 is lying with their head or feet facing sensor 10, or wearing clothing that has only partially sufficient reflectivity.

[0056] To assess whether there are hazardous situations that should trigger a safety-oriented response from sensor 10, the scanning layer 44 itself is first evaluated individually, for example, using a standard protected area assessment with a single-layer sensor. Here, all validated procedures and filters can be used to ignore small or transient disturbances as safety-irrelevant or to allow for certain known objects.

[0057] Figure 3 The reclining person 48 is detected as a safety-related object only in the lowest scanning layer 44 above the ground 46, triggering a corresponding object recognition 50. This object recognition 50 preferably implies that all conditions regarding a significant event have been met within the affected scanning layer 44, specifically a breach of the protected area in a safety-related manner. In similar cases, a single-layer scanner would respond in a safety-oriented manner. In the case of a multi-layer scanner, a higher level of evaluation is first performed on the object recognition 50 of each scanning layer 44. The reclining person 48 is a special case here, as this situation may only be detected once. To cover this special case, when object recognition 50 is performed in the lowest scanning layer 44 above the ground 46, the sensor 10 should trigger a safety-oriented response.

[0058] Figure 4 and Figure 5 The illustration depicts a standing person 48 in a normal situation. Here, HS represents the maximum height expected to be reached by the object recognition 50. Since the person 48 may be standing in an unfavorable body posture (e.g., bent over), an exemplary reasonable predetermined value for the maximum height is HS = 1m.

[0059] Besides what has already been done Figure 3 Apart from the special case of the 48 people lying down discussed, in Figure 4 and Figure 5Two other cases are also distinguished in which the distance D between the person 48 and the sensor 10 is different. For a single-layer scanner, the minimum reflectivity R1 for reliable detection of an object is defined as 1.8% in the product standard IEC 61496-3. However, it can be assumed that no person 48 will be completely wrapped in a dark black velvet dress. Therefore, at least for some of the multiple scan layers 44, even if the reflectivity is higher (R2 > R1), for example at least 6%, detection can be expected. Therefore, there are limit ranges or a first safety range RW1 and a second safety range RW2 corresponding to the reflectivities R1, R2, where RW1 < RW2, within which objects with the corresponding reflectivities are reliably detected. The relationship is non-linear because the sensitivity of the detection decreases quadratically with an increase in the distance D. In a numerical example, it is assumed that for a reflectivity R1 = 1.8%, the first safety range RW1 = 5.5 m. For the second safety range RW2, at R2 = 6%, a value of RW2 = Sqrt(6% / 1.8%) * 5.5 m = 10 m can be estimated.

[0060] Based on these preliminary considerations, currently Figure 4 First, the case of the person 48 at a distance D up to and equal to the first safety range RW1 is shown. According to the definition of the first safety range RW1, the sensor 10 is sensitive within these distances D, such that as long as other conditions for safety relevance are met (for example, the position of the person 48 is within the protected area), relevant object recognition 50 occurs in all scan layers. At these distances D, the person 48 cannot be ignored, for example, due to dark clothing. Therefore, for distances D within the first safety range RW1, when relevant object recognition 50 occurs in all scan layers 44, a safety-oriented response is precisely triggered.

[0061] In principle, it can also be envisaged that the scan layer 44 sweeps across the person 48 at the distance D and thus misses the person 48. Preferably, such scan layers 44 above the maximum height HS at the distance D are ignored. Instead, the lowest scan layer 44 may hit the ground before the distance D. When setting the condition that relevant object recognition 50 should exist in all scan layers 44, this clearly does not refer to these too-high and too-low scan layers 44. Another hitherto unconsidered advantageous additional condition requires: detecting the person 48 across multiple scan layers 44 at the same or at least a similar angular position. This coherence condition will be considered in more detail later with reference to Figure 6 Consider this coherence condition in more detail.

[0062] Figure 5 The case of the person at a distance D between the first safety range RW1 and the second safety range RW2 is shown. Here, it is no longer guaranteed that all scan layers 44 provide relevant object recognition 50. At Figure 5In the illustration, the person is, for example, wearing dark trousers with a reflectivity less than R2. This is sufficient for detection within a reflectivity R1 and therefore a first safety range RW1, but insufficient for detection beyond the first safety range RW1. However, at least part of the person 48 has sufficient reflectivity R2, thus enabling associated object recognition 50 in multiple scan layers 44. For these reasons, the condition for triggering a safety-oriented response in the distance range RW1≤D≤RW2 is weakened, and only associated object recognition 50 in at least two scan layers 44 is required. Furthermore, preferably, the scan layers 44 must be adjacent. Figure 4 The argument about ignoring scan layers 44 that are too high or too low also applies here, and it is even more likely to happen here, since scan layers 44 further fan out as the distance D increases.

[0063] Figure 4 and Figure 5 The diagram illustrates a clear distinction where relevant object identification needs to be performed in all scan layers 44 within the first safety range RW1, or in at least two scan layers 44 between the first safety range RW1 and the second safety range RW2. More refined gradations can be considered, where the required number decreases as the distance D beyond the first safety range RW1 increases.

[0064] It should also be noted that, according to Figure 3 The reclining person 48 is detected in the vertical direction by only a single scanning layer 44. However, in this case, it is reasonable to assume that at least one point with a reflectivity of at least R2 is located above the reclining body in the horizontal scan. Therefore, for the reclining person 48, there is no need to distinguish between the first safety range RW1 and the second safety range RW2.

[0065] Figure 6 This is a table used to illustrate the advantageous additional coherence conditions already mentioned. The associated object identification 50 should be associated with the same object. This can be checked by the similar angular positions, scan angles, or azimuth angles of the associated object identification 50. For simplicity, the table shown contains only seven angular sectors in its columns. In practice, with typical angular resolutions less than 1 degree and viewing angles such as 270°, significantly more angular sectors can be distinguished, where the associated object identification 50 does not necessarily exhaust the underlying physical resolution. Three scan layers 44 are exemplarily listed in these rows; actual values ​​will be higher, such as four, eight, ten, sixteen, or other or higher numbers of scan layers 44. The scan layers 44 are uniformly rasternized within the angular sectors. Associated object identification is represented by X, with 0 indicating no security-related object detection or no security-related object detection after appropriate filtering.

[0066] Preferably, the coherence condition should only be considered satisfied if the corner sectors of the relevant object identification 50 overlap, are directly adjacent, or are contiguous with each other. Figure 6 In the example, scan layers #1 and #2 are given in columns 2-4. The remaining scan layer pairs do not meet the coherence condition.

[0067] Checking coherence conditions based solely on corner sectors is particularly resource-efficient. More complex methods could be considered, such as including corresponding object recognition at a distance D of 50.

[0068] Now according to Figures 7 to 10 The ground identification of sensor 10 is described. For example, knowing the location of ground 46 is important for... Figure 3 It is useful to consider the special circumstances of a lying person 48 to determine which of the lowest scanning layers 44 are above the ground 46 or which scanning layers 44 have hit the ground 46 at a distance D or have crossed the minimum height HL. Typically, the height H of the object recognition 50 at a distance D can be determined.

[0069] Figure 7 First, the case of a flat ground 46 or a correctly horizontally aligned sensor 10 is shown. The sensor 10 is mounted at a height H0 above the ground 46. The lowermost scanning layer 44a points towards the ground 46 at an angle α1 and preferably impacts the ground 46 at all azimuth angles. Here, the angle of incidence should not be too flat, so that sufficient signal return is still possible, especially if the ground 46 is glossy. For example, during the teaching or calibration phase, when the sensor 10 begins operation, the alignment of the ground 46 is analyzed based on the measurements from the lowermost scanning layer 44a. Figure 7 Under ideal conditions, the same distance D1 from the ground 46 should be measured at all azimuth angles. A deviation ΔD exceeding the tolerance range means that the line of sight from the lowest scanning layer 44a to the ground 46 is obstructed by an object, or that there is a ground structure, such as a hole in the ground 46. To reliably detect nearby objects, the latter case should be excluded by pre-determining the maximum value of the unevenness of the ground 46.

[0070] Figure 8 The diagram shows a comparison of ground tilt 46 and / or sensor 10 being installed at an angle. Given the installation height H0, this tilt can be determined based on measurements of distance D1' in each scanning angular direction.

[0071] Figure 9 and Figure 10The detection of ground 46 using at least two lower scanning layers 44a-44b is illustrated similarly in both flat and sloping conditions. Two distances, D1' and D2', are then detected separately, enabling more differentiated analysis of ground 46. For detecting more complex ground structures, such as curbs, ramps, broken edges, and curved surfaces, more sophisticated ground recognition algorithms can be used, potentially including even more scanning layers 44. In mobile applications, the alignment of sensor 10 relative to ground 46 changes during operation, necessitating periodic monitoring of ground 46 and its alignment.

[0072] Using the knowledge of the installation height H0, the elevation angle of the corresponding scanning layer 44 known from the construction of sensor 10, and the height and inclination of the ground 46 in the corresponding scanning direction, the height of the object being detected can be determined for the corresponding object distance D. Finally, a numerical example will be used to illustrate this. The optical center of sensor 10 should form the origin of the coordinate system. The scanning layers 44 have an extension angle of 1° relative to each other, with the eighth scanning layer being horizontal. Sensor 10 is mounted at a known installation height H0 = 200 mm. When detecting the ground 46, the distance D1 = 1754 mm is measured using the lowest scanning layer 44a with an azimuth angle of 90° (purely exemplarily). The lowest (first) scanning layer 44a is tilted downwards by 7° relative to the horizontal eighth scanning layer, i.e., tilted by seven 1°. Thus, by basic trigonometry, it is concluded that the ground 46 is tilted by -0.5° at an azimuth angle of 90° relative to the coordinate system of sensor 10. Now, the tenth scanning layer with an azimuth angle of 90° detects an object at a distance of 5 meters. The tenth scanning layer is tilted upwards by 2° relative to the horizontal eighth scanning layer, which is equivalent to two 1° tilts. We also need to consider the -0.5° inclination of the ground at 46° and the installation height H0 = 200 mm. Therefore, a good approximation of the height is obtained: sin(2° + 0.5°) * 5,000 mm + 200 mm = 418 mm.

Claims

1. A photoelectric sensor (10) for detecting an object (48) in a monitoring area (20), the sensor (10) comprising: at least one light emitter (22) for emitting a plurality of beams (26) separated from each other; at least one light receiver (32) for generating a corresponding received signal from the beams (28) diffusely reflected in the monitoring area (20); a movable scanning unit (12) by means of which the emitted beams are periodically guided through the monitoring area (20) to scan a scanning layer (44) respectively using the separated beams during the movement of the scanning unit (12); and a control and evaluation unit (40) designed to obtain information about the object (48) in the monitoring area (20) from the corresponding received signals. Its features are, The control and evaluation unit (40) is also designed to determine the presence of a safety-related object (48) for each scan layer (44) and to determine whether to trigger a safety-oriented response by a joint evaluation of the presence of the safety-related object (48) determined for each scan layer (44), wherein, in order to improve the robustness of triggering the safety-oriented response, it is necessary to determine the presence of the safety-related object (48) on multiple scan layers (44), wherein, in order to identify a person lying down, it is sufficient to determine the presence of the safety-related object only in the lowest scan layer above the ground (46).

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

3. The sensor (10) according to claim 1, wherein, The control and evaluation unit (40) is designed to measure distance using the time-of-flight method.

4. The sensor (10) according to any one of claims 1-3, wherein, The control and evaluation unit (40) is designed to determine the presence of an object (48) in multiple scan layers (44) when the object is determined to be present at the same or adjacent angular positions in the same scan layer (44).

5. The sensor (10) according to any one of claims 1-3, wherein, The control and evaluation unit (40) is designed to trigger a safety-oriented response when the presence of an object (48) is determined in a certain number of scan layers (44), where the number of scan layers when the object (48) is near is greater than the number of scan layers when the object (48) is far away.

6. The sensor (10) according to any one of claims 1-3, wherein, The control and evaluation unit (40) is designed to trigger a safety-oriented response when the presence of an object (48) is determined in all relevant scan layers (44) for an object (48) at a distance within a first safety range.

7. The sensor (10) according to claim 6, wherein, The first security range corresponds to the security range of a security laser scanner with only one scanning layer.

8. The sensor (10) according to any one of claims 1-3 and 7, wherein, The control and evaluation unit (40) is designed to trigger a safety-oriented response when the presence of an object (48) is determined in at least two or more scan layers (44) for an object (48) located at a distance beyond the first safety range up to the second safety range.

9. The sensor (10) according to claim 8, wherein, A safety-oriented response is triggered when the presence of an object (48) is determined in at least two or more adjacent scan layers (44).

10. The sensor (10) according to any one of claims 1-3, 7 and 9, wherein, The control and assessment unit (40) is designed for protected area assessment, wherein an object (48) is only safety-related if its location is within a configured protected area.

11. The sensor (10) according to any one of claims 1-3, 7 and 9, wherein, The control and evaluation unit (40) is designed to detect the position and / or orientation of the ground (46) using the lowest scanning layer or multiple lower scanning layers.

12. The sensor (10) according to any one of claims 1-3, 7 and 9, wherein, The control and evaluation unit (40) is designed to include only objects (48) within a minimum height above the ground (46) to determine the presence of safety-related objects (48).

13. The sensor (10) according to any one of claims 1-3, 7 and 9, wherein, The control and evaluation unit (40) is designed to determine the height above the ground (46) based on the distance and the scanning layer (44).

14. The sensor (10) according to any one of claims 1-3, 7 and 9, wherein, The scanning layers (44) have angular resolution relative to each other at least near the ground, such that adjacent scanning layers (44) have at most a spacing corresponding to the smallest size of the object to be detected (48) over the maximum range.

15. The sensor (10) according to claim 14, wherein the spacing is defined as arctan (minimum size / range).

16. The sensor (10) according to any one of claims 1-3, 7, 9 and 15 is designed as a safety sensor in the sense of a safety standard for protective devices used for machine safety or non-contact operation.

17. The sensor (10) according to claim 16, wherein, The sensor is designed as a secure laser scanner.

18. The sensor (10) according to claim 16, wherein, The sensor has a safety output terminal (42) for outputting a safety-oriented protection signal.

19. A method for detecting an object (48) in a monitored area (20), wherein, Multiple beams (26) are emitted separately from each other and periodically guided through the monitoring area (20) by a movable scanning unit (12) so that a scanning layer (44) is scanned by the separate beams (26) during the movement of the scanning unit (12), a corresponding received signal is generated from the beams (28) diffusely reflected in the monitoring area (20), and information about the object (48) in the monitoring area (20) is obtained from the corresponding received signal. Its features are, The presence of a safety-related object (48) is determined for each scan layer (44), and a safety-oriented response is triggered by a joint evaluation of the presence of the safety-related object (48) determined for each scan layer (44). In order to improve the robustness of triggering the safety-oriented response, the presence of the safety-related object (48) needs to be determined on multiple scan layers (44). In order to identify a person lying down, it is sufficient to determine the presence of the safety-related object only in the lowest scan layer above the ground (46).

20. The method according to claim 19, wherein, Distance is measured using the time-of-flight method of light.

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