SENSOR FOR MONITORING AN AREA

Description

[0001] The invention relates to a sensor which is designed to monitor an area in the vicinity of the sensor with regard to the presence of at least one object.

[0002] This could be, in particular, a lidar sensor (from English: Light Detection and Ranging).

[0003] Such sensors for monitoring a specific area or space are used, for example, for collision avoidance in autonomous or semi-autonomous vehicles, or for monitoring buildings or outdoor areas against unauthorized access. Furthermore, these sensors can be used to trigger specific events, such as activating a barcode or RFID (radio frequency identification) reader in a portal where, for example, certain properties of packages are determined. When packages are transported to the portal via a conveyor belt, a lidar sensor detects when each package enters a predefined area in front of the portal, and the readers in the portal are activated accordingly by the lidar sensor before the respective package reaches the portal.

[0004] To reliably detect the presence of specific objects in an area using such a sensor, it is necessary to filter out or disregard objects that fall below a certain size or whose dimensions are below a specific value. Such small objects are referred to as interfering objects. Conversely, only objects of a certain size, or at least one dimension of which exceeds a certain value, should be detected by the sensor in a specific area. If the sensor is designed to determine at least one dimension of an object, certain parameters can be set during the evaluation of the signals detected by the sensor, such that only the desired objects, whose size exceeds a predefined value, are detected in the monitored area.

[0005] Certain sensors, such as those based on lidar systems, discretely scan objects within the predetermined or monitored area using individual beams. The size, or at least one dimension, of an object is determined by the spatial separation of at least two beams at a specific distance of the object relative to the sensor. Due to the dispersion of the discrete beams, the number of beams that intersect an object depends on the object's distance and lateral position relative to the sensor.The number of rays striking the object can decrease and increase abruptly as the object's distance and lateral position change. This is because, for example, one or more rays that initially strike the object may miss it if the distance between the object and the sensor increases and / or if the object is laterally displaced. As a result, the measured size or dimension of the object fluctuates depending on its distance and lateral position relative to the sensor.

[0006] If the minimum dimension or size at which an object can be detected by the sensor in the predetermined area is almost exactly the same as the object's size or dimension, and the object is moving relative to the sensor, the object will be detected at certain distances relative to the sensor, while at other distances it will be ignored as an interfering object. If the sensor outputs either a free or occupied state for the monitored area, the output state for the monitored area can therefore switch between "free" and "occupied" at short intervals. This can be described as "flickering" of the monitored state for the monitored area.However, such a rapid change between the states "free" and "occupied" is problematic, especially, for example, when a sensor integrated into an autonomous vehicle and an obstacle on the road approach each other, and the monitoring state determined by the sensor influences the braking process of the autonomous vehicle.

[0007] From US patent 2012 / 0176592 A1, a sensor and a method with the features according to the respective preamble of claim 1 and 9 respectively are known.

[0008] EP 4 109 127 A1 describes a sensor designed as a multi-layer scanner.

[0009] One object of the invention is to create a sensor that enables time-robust and reliable monitoring of a predetermined area with regard to the presence of at least one object.

[0010] This problem is solved by a sensor having the features of claim 1. Advantageous embodiments of the invention are specified in the dependent claims, the description, and the drawings.

[0011] The sensor is designed to monitor an area for the presence of at least one object and comprises a transmitter, a receiver, and an evaluation unit. The transmitter emits signals into the monitored area. The receiver receives detection signals, which include signals reflected or remitted within the monitored area. The evaluation unit is configured to determine, based on the detection signals, at least one measurement related to at least one dimension of an object in the monitored area.The evaluation unit is further configured to determine and output an occupied state of the monitored area when at least one measured variable is greater than an entry threshold, and to determine and output a free state of the monitored area when at least one measured variable is less than an exit threshold. The exit threshold differs from the entry threshold.

[0012] The area to be monitored can be a surface area or a spatial area in the immediate or wider vicinity of the sensor. The initial state for the sensor's output can initially be assumed to be the "free" state, i.e., for example, when the sensor is first activated and has not yet detected any object in the monitored area. The evaluation unit can determine and output that the monitored area transitions from the "free" to the "occupied" state when the measured value, which is related to at least one dimension of an object, is greater than the entry threshold, and that the monitored area transitions from the "occupied" to the "free" state when the measured value is less than the exit threshold.

[0013] Such transitions between the output of the occupied and unoccupied states of the monitored area can occur, for example, when the area is continuously monitored by the sensor. This is achieved by repeatedly emitting signals at a specific frequency and capturing the corresponding detection signals to constantly re-determine the measured quantity. This can be done, for instance, with repeated scans of a lidar sensor. However, the switch to indicating the occupied state only occurs when the measured quantity exceeds the entry threshold, while the switch to indicating the unoccupied state only occurs when the measured quantity falls below the exit threshold.

[0014] Due to the limited measurement accuracy of the detection signals, which is determined, for example, by a specific signal-to-noise ratio, the evaluation unit may also indicate the occupied and unoccupied states of the monitored area even if the measured value is equal to the entry or exit threshold. According to one embodiment, it may also be intentionally specified that the occupied and unoccupied states of the monitored area are also detected or indicated even if the measured value is equal to the entry or exit threshold.

[0015] The measured quantity can be, for example, a dimension of the object estimated from the detection signals, or a number of discrete beams emitted by the transmitting device and remitted or reflected by at least one object within the area. The angular spacing of the emitted beams determines the resolution of the sensor, and the number of reflected or remitted beams is therefore related to the actual dimension of an object in the area being monitored.

[0016] In the first case, where the estimated dimension or size of the object is considered, the estimated dimension of all objects detectable in the monitored area must, for example, fall below a predetermined value representing the exit threshold for the evaluation unit to determine and indicate that the monitored area is in a clear state or is transitioning from an occupied state to a clear state. Conversely, to detect an occupied state or a transition to it using the evaluation unit, it is necessary, for example, for the estimated dimension of at least one object to exceed another, larger, predetermined value representing the entry threshold.

[0017] In the second case, where the number of detected rays is considered, the number of discrete rays reflected or remitted by at least one object must be less than a predetermined number for the evaluation unit to determine and output that the monitored area is in or transitioning to a free state. The predetermined number of discrete rays could be, for example, one or two, or another small integer, and thus represents the exit threshold. Conversely, to detect an occupied state or a transition to it using the evaluation unit, the number of detected discrete rays must exceed a predetermined value, which represents the entry threshold.

[0018] The term "entry threshold" symbolizes that at least one object must have entered the monitored area for the sensor to detect an occupied state. Conversely, the term "egress threshold" symbolizes that all objects exceeding a predetermined size that could be present in the monitored area must have left it for the sensor to detect an unoccupied state.

[0019] One advantage of the sensor is that it uses two different threshold values ​​to indicate whether the monitored area is occupied or unoccupied. For detecting occupancy, the predetermined threshold can be set high enough to filter out interfering objects that might cause the evaluation unit to falsely indicate occupancy. Conversely, for detecting unoccupied status, or for the transition from occupied to unoccupied, a different predetermined value is used. This value is used, for example, to compare the estimated dimensions of the object or another measurement derived from the detection signals that relates to the object's actual dimensions.

[0020] This ensures that the detection of the area's free state, or the transition to a free state, occurs under conditions that are independent of, for example, a minimum size of objects to be detected within the monitored area. For instance, the evaluation unit may only be permitted to indicate the free state of the monitored area, or a transition to it, if only objects with dimensions significantly smaller than the entry threshold are detected within the area, or if the number of discrete beams reflected or remitted by objects within the area is nearly zero. This prevents the evaluation unit from reporting a rapid change between the occupied and free states of the monitored area, particularly when the object is moving relative to the sensor.The occupied and unoccupied states of the monitored area can therefore be detected by the sensor in a robust manner over time without rapid fluctuations.

[0021] According to one embodiment, the measured quantity can include a value for a dimension (hereinafter also referred to as "estimated dimension") of the object, estimated from the detection signals. In this embodiment, the entry threshold can comprise a first predetermined length, while the exit threshold can comprise a second predetermined length. The first predetermined length can be greater than the second predetermined length. The exit threshold can, for example, be defined as a predetermined percentage of the entry threshold. The entry threshold can be set within the range of a minimum expected object size.

[0022] In this embodiment, the occupied state of the monitored area, or the transition to it, is indicated by the evaluation unit when the object's estimated dimension exceeds the entry threshold or the first length, while the free state, or a transition to it, is only indicated by the evaluation unit when the object's estimated dimension falls below the smaller exit threshold or the smaller second length. Therefore, a hysteresis is incorporated for detecting the free or occupied state, or for the transitions between them, using the sensor. This hysteresis prevents rapid changes between the indication of the free and occupied states of the monitored area, and thus a "flickering" effect when determining and outputting the monitoring status of the area using the sensor, even if the object is moving relative to the sensor.

[0023] In this embodiment, in addition to the estimated dimensions of the object, no further parameters need to be derived from the detection signals to indicate the free or occupied state, or a transition between these, using the sensor. This reduces the effort required to evaluate the detection signals.

[0024] According to the invention, the sensor comprises a lidar sensor that transmits signals as beams with at least one predetermined angular spacing between them into the area to be monitored. The entry and exit thresholds are defined by this angular spacing. The transmitted signals are thus designed as discrete beams from the lidar sensor that cover the area or space to be monitored. Since the predetermined angular spacing determines the resolution of the lidar sensor, the entry and exit thresholds can be adapted to the resolution of the lidar sensor by defining them based on the predetermined angular spacing. This improves the robustness of the sensor in determining whether the monitored area is free or occupied.

[0025] The lidar sensor can also be configured as a multi-layer sensor in which the angular spacing between several adjacent beams differs in the horizontal and vertical directions. The evaluation unit can further be configured to determine the horizontal and vertical dimensions of the object within the monitored area based on the detection signals. The entry and exit thresholds can have different values ​​depending on the angular spacing of adjacent beams, differing between the horizontal and vertical directions.

[0026] Furthermore, the evaluation device can be configured to determine and output an occupied state of the monitored area if the horizontal or vertical dimension of the object is greater than the respective entry threshold for the horizontal or vertical direction, and to determine and output a free state of the monitored area if the horizontal and vertical dimensions of the object are less than or equal to the respective exit threshold for the horizontal and vertical direction.

[0027] The angular separation between adjacent rays can be smaller in the horizontal direction than in the vertical direction. Accordingly, the difference between the entry threshold and the exit threshold can be smaller for the horizontal direction than for the vertical direction.

[0028] If the lidar sensor is designed as a multi-layer sensor, it can, for example, have different resolutions in two directions arranged at right angles to each other, with the resolution in the horizontal direction being significantly higher than in the vertical direction. The entry and exit thresholds for detecting or indicating whether the monitored area is occupied or unoccupied can each have different values, adapted to the direction-dependent resolution or the direction-dependent angular spacing between adjacent beams of the multi-layer sensor. Consequently, the entry and exit thresholds are not constant values, but can change over time and / or have different values ​​for different dimensions, such as the horizontal and vertical directions.

[0029] If the exit threshold is set relative to the entry threshold, for example, the exit threshold for the horizontal direction with high resolution or small angular spacing between adjacent beams might be 90% of the entry threshold, while the exit threshold for the vertical direction with lower resolution or larger angular spacing between adjacent beams might only be 50% of the corresponding entry threshold. In other words, the entry and exit thresholds for the horizontal direction are nearly identical, whereas for the vertical direction they can differ significantly, for example by a factor of 2.

[0030] The evaluation unit can be configured to determine the exit threshold based on an estimated minimum value for at least one dimension of the object. Specifically, the exit threshold can be set to be smaller than the estimated minimum value for at least one dimension of the object, for example, approximately 90% of that value. This ensures that the evaluation unit always detects an occupied state for the monitored area as soon as an object at any position within the monitored area exceeds the estimated minimum value for any of its dimensions.

[0031] Additionally, a position-dependent error for estimating the object's dimensions based on the detection signals can be determined within the monitored area. Specifically, for example, with a sensor emitting discrete beams, an error in estimating the dimensions can be specified as a function of the distance between the object and the sensor. The estimated minimum value for at least one dimension of the object can be based on this position-dependent error and thus also depend on the object's position within the monitored area.

[0032] The entry and exit thresholds can also be configured by the user. In such a configuration, the entry threshold should preferably be set based on the expected minimum size of an object for which the sensor should indicate an occupied state in the monitored area. The exit threshold, however, should preferably be set such that, on the one hand, there is no rapid switching between the detection or indication of the "free" and "occupied" states for the monitored area, as the exit threshold is set too high, and on the other hand, there is no unnecessary susceptibility to interference from interfering objects, as the exit threshold is set too low.

[0033] According to a further embodiment, in which the sensor is again designed as a lidar sensor that transmits the signals as beams with at least a predetermined angular spacing between them into the area to be monitored, the at least one measured quantity can comprise a number of those beams that are reflected or remitted by at least one object in the area to be monitored. The entry threshold can comprise a first predetermined number of detected beams, while the exit threshold can comprise a second predetermined number of detected beams. The first predetermined number is greater than the second predetermined number.

[0034] In this embodiment, the evaluation unit can be configured to determine the occupied and unoccupied states of the monitored area whenever the number of rays reflected or remitted by the at least one object is greater or less than a predetermined number, respectively. In the simplest case, the first predetermined number can be set to one, so that the detection or indication of the unoccupied state or a change from "occupied" to "unoccupied" only occurs when no ray of the transmitted signal strikes an object within the monitored area. Alternatively, the predetermined number can be set to a small integer, for example, two or three, so that a maximum of only one or two rays may strike one or more objects for the evaluation unit to determine and output the unoccupied state or the change from "occupied" to "unoccupied" for the monitored area.This increases the robustness in determining the correct state of the area to be monitored in the face of interference.

[0035] According to yet another embodiment, in which the sensor is again designed as a lidar sensor which sends the transmission signals as rays with at least a predetermined angular distance between them into the area to be monitored, the at least one measured quantity can comprise a dimension of the object estimated by means of the detection signals and a number of those rays which are reflected or remitted by at least one object in the area to be monitored.

[0036] In this embodiment, two measured quantities are determined based on the detection signals: an estimated dimension or size of at least one object and the number of rays reflected or remitted by at least one object. Furthermore, one of the threshold values, i.e., the entry or exit threshold, can refer to one of the two measured quantities to determine and output whether the monitored area is occupied or unoccupied.

[0037] Additionally, the evaluation unit can be configured to determine and output the free state of the monitored area, or to switch to a "free" monitoring state, only if two beams reflected or remitted within the area are not adjacent beams. In other words, at least one other beam must be located between any two such beams, and this beam must not be reflected or remitted by any object within the monitored area. With this embodiment, the number of beams reflected or remitted within the monitored area that are detected is therefore at least two. If the two beams reflected or remitted within the area are not adjacent beams, this reflection or remission occurs randomly, i.e., with a high probability, at two interfering objects that should not be detected in the monitored area.This embodiment further improves robustness against interfering objects.

[0038] According to a further embodiment, the evaluation device can also be configured to determine several values ​​of the measured quantity based on the detection signals for several successive time points. The evaluation device can determine that the area to be monitored is in the occupied state or is transitioning from the unoccupied state to the occupied state if a predetermined number of successive values ​​for at least one dimension of the object, i.e., for the several successive time points, is greater than the entry threshold, and it can determine that the area to be monitored is in the unoccupied state or is transitioning from the occupied state to the unoccupied state if a predetermined number of successive values ​​of the measured quantity, i.e., for several successive time points, is less than the exit threshold.

[0039] This embodiment thus uses the principle of multiple evaluation of the detection signals for several consecutive time points. Consequently, in this embodiment, the number of values ​​determined by the evaluation unit that exceed the entry threshold or fall below the exit threshold must be greater than a predetermined number so that a change from "free" to "occupied" or vice versa for the state of the monitored area can be determined and output by the evaluation unit. This improves the robustness of the sensor and the evaluation of the state of the monitored area against random fluctuations and interfering objects.

[0040] A further aspect of the invention is a method for monitoring an area for the presence of at least one object, comprising the features of claim 8. According to the method, transmission signals are emitted into the area to be monitored, and detection signals are received, including transmission signals that are reflected or remitted within the area to be monitored. Based on the detection signals, at least one measured quantity is determined that is related to at least one dimension of an object in the area to be monitored. An occupied state of the area to be monitored is then determined and output if the at least one measured quantity is greater than an entry threshold, while a clear state of the area to be monitored is then determined and output if the at least one measured quantity is less than an exit threshold. The exit threshold differs from the entry threshold.

[0041] The descriptions of the sensor apply accordingly to the method, particularly with regard to advantages and preferred embodiments. Furthermore, it is understood that all features mentioned herein are combinable unless explicitly stated otherwise.

[0042] The invention is described below by way of example with reference to advantageous embodiments and the accompanying figures. These show, schematically: Fig. 1 shows a sensor for monitoring a predetermined area, Fig. 2 shows a diagram illustrating the determination of an object size as a function of the object's distance, Fig. 3 shows another diagram illustrating the determination of the object size as a function of the object's distance, and Fig. 4 shows a state diagram illustrating a method for monitoring a predetermined area.

[0043] Fig. 1 Figure 100 schematically shows a sensor 100 designed as a lidar system and comprising a transmitter 110 that emits signals in the form of discrete measurement beams 120 into a monitored area 130. The transmitter 110 thus performs a discrete scanning of the area 130 using the measurement beams 120. The sensor 100 is designed to monitor the area 130 for the presence of at least one object 140, which, for simplicity, is represented as... Fig. 1 illustrated by a line. In Fig. 1 The object 140 is shown at various positions within the monitored area 130, at each of which the object 140 has different distances and different lateral positions relative to the sensor 100. The actual size or dimension of the object 140 is illustrated by the arrow 142.

[0044] The sensor 100 further comprises a receiving device (not shown) that receives detection signals, which include reflected or remitted transmitted signals. The transmitted signals 120 are reflected or remitted by the object 140 within the area 130 to be monitored in order to generate the detection signals that are received by the sensor's receiving device.

[0045] Furthermore, the sensor 100 has an evaluation unit (not shown) configured to determine a measured quantity in the form of at least one estimated dimension 150 of the object 140 in the monitored area 130 based on the detection signals. Specifically, the evaluation unit determines the estimated dimension 150 based on the distance or length between the two outermost measuring beams 120, each of which strikes the object 140. The length 150, which corresponds to the estimated dimension of the object 140 in a spatial direction, is in Fig. 1 Each is represented as a double arrow for different distances of object 140 relative to sensor 100.

[0046] How to in Fig. 1 As can be observed, the estimated size or dimension 150 of object 140 changes with its distance from sensor 100, even though object 140 has a constant actual size or dimension 142. The reason for this fluctuation in the estimated dimension 150 of object 140 is that the estimation of dimension 150 is based on the acquired lidar data with discrete angular distances between the measuring beams 120, whereby the distance between the intersection points of two measuring beams 120 and object 140 at the respective distance relative to sensor 100 is determined as the estimated dimension 150. Due to the limited angular resolution or the finite angular distances between the discrete measuring beams 120, it is generally not possible to detect exact intersection points between an imaginary beam emanating from sensor 100 and a specific edge of object 140.

[0047] The fluctuation of the estimated object size or dimension 150 of object 140 with its distance from sensor 100 is in the in Fig. 2 The diagram illustrates this. The diagram shows the object size or dimension 150 of object 140, estimated by sensor 100, as a function of the respective distance of object 140 relative to sensor 100. The upper curve 210 in Fig. 2 The curve 210 was determined for an object 140 with a real size or dimension 142 of 1500 mm. As can be seen, the curve 210 assumes maximum values ​​approximately corresponding to the real object size or dimension of about 1500 mm, specifically when the discrete measuring beams 120 intersect the object 140 in a boundary region very close to a respective object edge. This is the case, for example, in Fig. 1 - viewed from the left - the third distance of object 140 is the case, which is labelled 144.

[0048] Between the respective distances relative to sensor 100, at which the actual object size or dimension of object 140 is estimated, curve 210 for the estimated object size or dimension 150 of object 140 shows considerable fluctuations, which increase with the distance of object 140 relative to the sensor. Fig. 2 The maximum fluctuation of curve 210 is approximately 600 mm. The estimated object size or dimension 150 of object 140 therefore exhibits a position-dependent error, which depends on the distance between object 140 and sensor 100, and thus on the position of object 140 within the monitoring area 130, and has a maximum value of approximately 600 mm.

[0049] However, sensor 100 is intended to monitor area 130 only with regard to the presence of objects 140, so that a precise determination of the object size or dimensions is not required. Instead, sensor 100 is only intended to detect whether an object 140 of a specific size or dimension is present in area 130 or not.

[0050] However, when detecting such objects (140), objects that fall below a certain size or dimension and are designated as interfering objects should be ignored. In the example of Fig. 2 In addition to curve 210, which is assigned to a detectable object 140, curve 220 is shown, which is assigned to a disturbance object with a size or dimension of 700 mm and indicates an estimated size or dimension of the disturbance object. As can be seen in Fig. 2 As can be seen, curve 220 reaches the actual dimension of 700 mm as respective maxima at certain distances of the interfering object relative to sensor 100. Between these maxima, a considerable fluctuation in the estimated object size or dimension of the interfering object occurs depending on the distance.

[0051] In order to detect only those objects 140 in area 130 that are actually expected to be present in that area 130 using sensor 100, and to eliminate the influence of interfering objects, a threshold value for the minimum dimension of the objects 140 to be detected in area 130 is typically defined. In other words, when monitoring area 130 using sensor 100, only those objects 140 whose size or dimension exceeds this threshold value for the minimum dimension of the object 140 are taken into account.

[0052] In Fig. 2 Such a threshold value of 230 is represented by the horizontal line for an object size of 800 mm. In the example of Fig. 2 Consequently, only those objects 140 whose estimated size or dimension 150 is greater than 800 mm are considered when monitoring area 130. The interfering object with an actual size of 700 mm is not considered when monitoring area 130, since its estimated size, represented by curve 220, is always below the threshold 230.

[0053] For object 140, which corresponds to curve 210 of Fig. 2 Since an object 140 is assigned and has a size or dimension of 1500 mm, the evaluation unit of sensor 100 can unambiguously determine and output an occupied state of the monitored area 130, because the dimension of object 140 is always estimated to be greater than the threshold value 230 of 800 mm, regardless of its distance from sensor 100. In other words, the entry of an object 140, whose estimated dimension is given by curve 210 of Fig. 2 The area 130 is always represented in order to indicate that the evaluation unit reports a confirmed state of the monitored area 130.

[0054] Conversely, the evaluation unit of sensor 100 determines the disturbance object that corresponds to curve 220. Fig. 2 Since the object 140, whose presence or entry into the monitored area 130 is to be detected, is assigned a real object size or dimension of 700 mm, the monitored area 130 is always free of obstructions, as the estimated dimension or object size according to curve 220 is below the threshold value 230 of 800 mm for all distances relative to sensor 100. In other words, the object sizes of object 140, whose presence or entry into the monitored area 130 is to be detected, and the interfering object are so different that the interfering object and the object 140 to be detected are distinguishable from each other.

[0055] However, if the sizes of a detectable object 140 and a disturbance object are similar, and especially if the size of object 140 is only slightly above the threshold 230, disturbance objects and detectable objects 140 may no longer be distinguishable. For a given object, the evaluation unit may no longer be able to clearly indicate whether the monitored area 130 is occupied or unoccupied due to that object.

[0056] Such things are in Fig. 3 illustrated. Just like with Fig. 2 A threshold of 230 mm out of 800 mm is used for a minimum object size. Furthermore, the following is used to estimate the object size or dimensions: Fig. 3 An object with a real object size 142 of 900 mm is assumed. Objects 140 with a size or dimension larger than the threshold value 230 are therefore to be considered as objects to be detected, for which the evaluation unit of the sensor 100 is to determine an occupied state of the monitored area 130. The estimated object size or dimension 150 for object 140 with a real dimension of 900 mm is in Fig. 3 The distance of object 140 relative to sensor 100 is represented by curve 310.

[0057] How to in Fig. 3 As can be seen, curve 310 again assumes maximum values ​​at certain distances, corresponding to the actual object size or dimension of 900 mm. However, between these maxima, the estimated object size fluctuates considerably depending on the distance of object 140 relative to sensor 100. An angular spacing of 5° between the beams of the lidar system was assumed when determining curve 310. This corresponds to the typical angular spacing of a multi-layer lidar sensor.

[0058] Furthermore, in Fig. 3 A range 320 above the threshold value 230 of 800 mm is shown, for which the evaluation unit of sensor 100 determines an occupied state of the monitored range 130. Similarly, in a range 330 below the threshold value 230, the evaluation unit of sensor 100 determines a free state of the monitored range 130.

[0059] Since curve 310 lies above the threshold value 230 or in the range 320 of the occupied state for some distance ranges and below the threshold value 230 or in the range 330 of the free state of the monitored area 130 for other distance ranges, it depends for the example of the Fig. 3 The specific distance of object 140 relative to sensor 100 determines whether the evaluation unit of sensor 100 indicates a free or occupied state of the monitored area 130. For example, Fig. 3 The evaluation unit is therefore unable to clearly indicate the occupied or unoccupied state of the monitored area 130, since the object size of 900 mm differs from the threshold value 230 of 800 mm by only 100 mm and the fluctuations of the estimated object size 150 are significantly greater than the difference of 100 mm between the actual object size 142 and the threshold value 230.

[0060] If object 140, with an actual size of 900 mm, moves within the monitored area 130, the estimated size or dimension 150 of object 140 lies above the threshold 230 in area 320 (occupied state) at certain times and below the threshold 230 in area 330 (free state) at other times, as soon as the distance or lateral position of object 140 changes during its movement. Therefore, the object size can be estimated according to the example of Fig. 3 When object 140 moves, the evaluation unit of sensor 100 detects a rapid change between the occupied and unoccupied states of the monitored area 130. This rapid change is also referred to as a "flickering" of the monitored state of area 130. For example, if sensor 100 is used in an autonomous vehicle, it can be problematic during braking if the monitored state of an area located outside the vehicle rapidly switches or flickers between "unoccupied" and "free."

[0061] To avoid such rapid changes between the determination of the occupied state and the free state for the monitored area 130, an inventive method or configuration of the evaluation device of the sensor 100 is provided, as described in Fig. 4 are shown.

[0062] At 410, an object 140 enters the monitored area 130. As stated in 420, the monitoring state of area 130 is undefined at this time. Alternatively, it can also be assumed that the monitoring state initially has a free initial state, since no object 140 was previously in monitoring area 130.

[0063] The transmitter 110 of the sensor 100 (see Fig. 1 and in Fig. 4 The additional representations in the dashed blocks 440, 470 and 480) emit transmit signals in the form of the measuring beams 120 into the monitoring area 130, and the receiving device of the sensor 100 receives detection signals which include such transmit signals which are reflected or remitted in the monitoring area 130.

[0064] Based on the detection signals, the evaluation unit of sensor 100 determines an estimated object size or at least an estimated dimension 150 of object 140. The evaluation unit of sensor 100 compares the estimated object size 150 at 430 with an entry threshold value 160 and at 432 with an exit threshold value 170 (see the dashed blocks 440 and 470).

[0065] If the estimated object size at 430 is greater than the entry threshold value of 160, the evaluation unit of sensor 100 determines an occupied state 450 of the monitoring area 130 and outputs the occupied state 450. However, if the estimated object size at 430 is smaller than the entry threshold value of 160, the undefined monitoring state 420 remains.

[0066] That the condition for transitioning to the output of the occupied state 450 or for transitioning to the monitoring state "occupied" is met at 430 is in Fig. 4 Designated 440 and additionally illustrated in the dashed block 440, block 440 shows the transmitter 110 of the sensor 100 with its field of view, represented by two boundary lines, which covers the monitoring area 130. Additionally, the estimated object size or dimension 150, determined by the evaluation unit of the sensor 100, is shown.

[0067] Block 440 further shows that the estimated object size or dimension 150 of object 140 is larger than the entry threshold 160, which is illustrated by a double arrow. Therefore, the occupied state 450 is indicated for the monitoring area 130. Since the comparison of the estimated object size or dimension 150 of object 140 with the entry threshold 160 is decisive for the transition to the output of the occupied state 450, the reference numeral 160 in block 440 is highlighted with a border. The occupied state is further illustrated in block 440 by a solid boundary line of the monitoring area 130.

[0068] If, however, the estimated object size at 432 is smaller than the exit threshold value 170, the evaluation unit of sensor 100 determines a free state 460 of the monitoring area 130 and outputs the free state 460. If, however, the estimated object size at 432 is larger than the exit threshold value 170, the undefined monitoring state 420 remains.

[0069] That the condition for the transition to the output of the free state 460 or for the transition to the monitoring state "free" is fulfilled at 432 is in Fig. 4 Designated 470 and additionally illustrated in the dashed block 470. Block 470, like block 440, shows the transmitter 110 of the sensor 100 with its field of view, the monitoring area 130, the estimated object size or dimension 150, and the entry and exit threshold values ​​160 and 170, respectively.

[0070] Block 470 further shows that the estimated object size or dimension 150 of object 140 is smaller than the exit threshold 170, which is illustrated by a double arrow. Therefore, the free state 460 is indicated for the monitoring area 130. Since the transition to the output of the free state 460 depends on comparing the estimated object size or dimension 150 of object 140 with the exit threshold 170, the reference numeral 170 in block 470 is highlighted with a border. The free state is illustrated in block 470 by a dotted boundary line of the monitoring area 130.

[0071] After either the occupied state 450 or the free state 460 of the monitoring area 130 has been determined for the first time, the monitoring area 130 continues to be monitored by means of the sensor 100 (see Fig. 1 The system monitors, for example, by means of further scans from a lidar sensor. Each new scan provides further detection signals, enabling a renewed or iterative determination of the estimated object size or dimension 150 of object 140. Therefore, for blocks 434 and 436, starting from the current indication of the occupied state 450 or the free state 460, it is checked again whether the newly estimated object size or dimension 150 of object 140 is smaller than the exit threshold 170 or larger than the entry threshold 160. This determines whether a transition from "occupied" to "free" or vice versa should occur when indicating the monitored state.

[0072] When the occupied state 450 of the monitoring area 130 is determined, a check is performed at 434 to see if the estimated object size or dimension 150 of object 140 is smaller than the exit threshold value 170. If this is not the case, and the estimated object size or dimension 150 is therefore larger than the exit threshold value 170, the evaluation unit of sensor 100 continues to output the occupied state 450 of the monitoring area 130.

[0073] Maintaining the output of the occupied state 450 for the monitoring area 130 is designated by 480 and additionally illustrated in the dashed block 480. Block 480, like blocks 440 and 470, shows the transmitting device 110 of the sensor 100 with its field of view, the monitoring area 130, the estimated object size or dimension 150, and the entry and exit threshold values ​​160 and 170, respectively.

[0074] The estimated object size or dimension 150 of object 140 in block 480 is smaller than the entry threshold 160, but larger than the exit threshold 170, which is set to be smaller than the entry threshold 160. Therefore, the evaluation unit of sensor 100 continues to output the occupied state 450 for the monitoring area 130. The occupied state is again illustrated by the solid boundary line of the monitoring area 130.

[0075] If the estimated object size 150 at 434 is smaller than the exit threshold value 170, the evaluation unit of sensor 100 determines the free state 460 of the monitoring area 130 and outputs the free state 460. The fact that the condition for the transition to the output of the free state 460, or for the transition to the monitoring state "free" at 434, is met is again indicated by 470. This condition is also additionally illustrated in the dashed block 470. Therefore, due to the fulfillment of condition 470, a change from "occupied" to "free" occurs after 434 when the monitoring state is output.

[0076] If, however, the free state 460 of the monitoring area 130 was previously determined and output, at 436 it is checked whether the estimated object size or dimension 150 of object 140 is greater than the entry threshold 160. If this is the case, and the estimated object size or dimension 150 is therefore greater than the entry threshold 160, the evaluation unit of sensor 100 outputs the occupied state 450 of the monitoring area 130.

[0077] In other words, the monitoring status changes from "free" to "occupied" when the condition in block 436 is met. This is illustrated in block 440, which shows that the estimated object size or dimension 150 of object 140 is greater than the entry threshold 160.

[0078] However, if the estimated object size 150 at 436 is smaller than the entry threshold 160, the evaluation unit of sensor 100 still determines the free state 460 of the monitoring area 130 and outputs the free state 460. In this case, the estimated object size 150 can either be smaller than the exit threshold 170, as illustrated in 470, or larger than the exit threshold 170 and simultaneously smaller than the entry threshold 160, as shown in 480. The entry threshold 160 thus defines a minimum object size that must be detected in the monitoring area in order to determine the occupied state 450 for that area.

[0079] Since the exit threshold 170 is set lower than the entry threshold 160, the detection of the free and occupied states of the monitoring area 130, as well as the detection of a transition between the occupied and free states and vice versa, is carried out using hysteresis. This prevents rapid changes or flickering between the indication of the occupied and free states, or vice versa. Thus, the state of the monitoring area 130 can be indicated reliably and with robust timing by the evaluation unit of the sensor 100. Bezugszeichenliste

[0080] 100 Sensor 110 Transmitting device 120 Measuring beam 130 Area to be monitored 140 Object 142 Actual dimension or size of the object 144 Specific distance of the object relative to the sensor 150 Estimated object size orObject dimension 160 Entry threshold 170 Exit threshold 210 Curve for the estimated object size of a detectable object 220 Curve for the estimated object size of a disturbance object 230 Threshold for object size 310 Curve for the estimated object size of a special object 320 Area for the occupied state 330 Area for the free state 410 Entry of an object into the monitoring area 420 Undefined monitoring state 430 Comparison of object size with the entry threshold 432 Comparison of object size with the exit threshold 434 Comparison of object size with the exit threshold 436 Comparison of object size with the entry threshold 440 Condition for transition to the occupied monitoring state fulfilled 450 Occupied monitoring state 460 Free monitoring state 470 Condition for transition to the free Monitoring state fulfilled 480 Condition for maintaining the documented monitoring state fulfilled.

Claims

1. A sensor (100) for monitoring a zone (130) with regard to the presence of at least one object (140), said sensor (100) comprising: a transmission device (110) which emits transmission signals into the zone (130) to be monitored, a reception device which receives detection signals that comprise transmission signals reflected or remitted in the zone (130) to be monitored, and an evaluation device which is configured: to determine at least one measurement variable based on the detection signals, said measurement variable being related to at least one dimension (142) of an object (140) in the zone (130) to be monitored, to determine and output an occupied state (450) of the zone (130) to be monitored if the at least one measurement variable is greater than an entry threshold value (160), and to determine and output a free state (460) of the zone (130) to be monitored if the at least one measurement variable is smaller than an exit threshold value (170), wherein the exit threshold value (170) is different from the entry threshold value (160), characterized in that the sensor (100) comprises a lidar sensor which transmits the transmission signals as beams with at least a predetermined angular distance between them into the zone (130) to be monitored, and the entry threshold value (160) and the exit threshold value (170) are defined based on the at least one predetermined angular distance.

2. A sensor (100) according to claim 1, characterized in that the at least one measurement variable comprises a dimension (150) of the object (140), said dimension (150) being estimated based on the detection signals, the entry threshold value (160) comprises a first predetermined length and the exit threshold value (170) comprises a second predetermined length, and the first predetermined length is greater than the second predetermined length.

3. A sensor (100) according to claim 1 or 2, characterized in that the lidar sensor is configured as a multi-layer sensor in which the angular distance between adjacent beams is different in a horizontal direction and in a vertical direction, the evaluation device is further configured to determine a horizontal dimension and a vertical dimension of the object (140) in the zone (130) to be monitored based on the detection signals, the entry threshold value (160) and the exit threshold value (170) have respective values in dependence on the respective angular distance of adjacent beams, said respective values being different from one another for the horizontal direction and the vertical direction, and the evaluation device is further configured: to determine and output an occupied state (450) of the zone (130) to be monitored if the horizontal dimension or the vertical dimension of the object (140) is greater than or equal to the respective entry threshold value (160) for the horizontal direction or the vertical direction, and to determine and output a free state (460) of the zone (130) to be monitored if the horizontal dimension and the vertical dimension of the object (140) are smaller than or equal to the respective exit threshold value (170) for the horizontal direction and the vertical direction.

4. A sensor (100) according to claim 3, characterized in that the angular distance between adjacent beams in the horizontal direction is smaller than in the vertical direction and a difference between the entry threshold value (160) and the exit threshold value (170) for the horizontal direction is smaller than for the vertical direction.

5. A sensor (100) according to claim 1, characterized in that the at least one measurement variable comprises a number of beams which are reflected or remitted at at least one object (140) in the zone (130) to be monitored, the entry threshold value (160) comprises a first predetermined number of beams and the exit threshold value (170) comprises a second predetermined number of beams, and the first predetermined number is greater than or equal to the second predetermined number.

6. A sensor (100) according to claim 5, characterized in that the evaluation device is further configured to determine the free state (460) of the zone (130) to be monitored only if two beams reflected or remitted within the zone (130) are not adjacent beams.

7. A sensor (100) according to any one of the claims 1 to 6, characterized in that the evaluation device is further configured: to determine a plurality of values of the measurement variable, in each case based on the detection signals, for a plurality of consecutive points in time, to determine and output that the zone (130) to be monitored has the occupied state (450) if a predetermined number of consecutive values of the measurement variable is greater than the entry threshold value (160), to determine and output that the zone (130) to be monitored has the free state (460) if a predetermined number of consecutive values of the measurement variable is smaller than the exit threshold value (160).

8. A method for monitoring a zone (130) with regard to the presence of at least one object (140), said method comprising: transmission signals being emitted into the zone (130) to be monitored, detection signals being received that comprise transmission signals reflected or remitted in the zone to be monitored, at least one measurement variable being determined based on the detection signals, said measurement variable being related to at least one dimension (142) of an object (140) in the zone (130) to be monitored, an occupied state (450) of the zone (130) to be monitored being determined and output if the at least one measurement variable is greater than an entry threshold value (160), and a free state (460) of the zone (130) to be monitored being determined and output if the at least one measurement variable is smaller than an exit threshold value (170), wherein the exit threshold value (170) is different from the entry threshold value (160), characterized in that a lidar sensor transmits the transmission signals as beams with at least a predetermined angular distance between them into the zone (130) to be monitored, and the entry threshold value (160) and the exit threshold value (170) are defined based on the at least one predetermined angular distance.