Rotating distance measuring system

Abstract

A rotating distance measuring system comprising a motor (20), a transmitter and receiver unit (10), and a control and evaluation unit (30), wherein the transmitter and receiver unit (10) is rotatably mounted, connected to the motor (20), and configured to detect a scene (40) in a detection area around the distance measuring system by emitting light pulses (L1) and detecting remitted light pulses (L2), driven by the motor (20), wherein the distance measuring system is configured to output data of the detected scene (40) at an adjustable frame rate, and wherein the control and evaluation unit (30) is configured to control the motor (20) such that the motor (20) rotates the transmitter and receiver unit (10) at a frequency that is a multiple of the adjustable frame rate.

Description

The invention relates to a rotating light-based distance measuring system according to the preamble of the independent claim. A rotating light-based distance measurement system, such as a laser scanner or LiDAR (Light Detection and Ranging) sensor, is used, among other things, for distance measurements within a field of view or detection area around the measurement system, defined by a horizontal angular range. One possible technical embodiment of such a measurement system comprises a rotating part with a transmitter and receiver unit and a stationary part, which, among other things, processes the data acquired by the transmitter and receiver unit and controls a motor that drives the rotating part. The transmitter and receiver unit is typically implemented as a chip or an ASIC (Application Specific Integrated Circuit). However, some currently known transceiver chips are not capable of continuous measurement and data delivery. The data is delivered in the form of individual frames, each representing a 360° field of view around the scanner or sensor. Since the receiver chips, as already explained, cannot measure continuously, a pause is currently required between two frames. Seamless scanning of a 360° field of view with multiple consecutive frames is therefore not possible. With known solutions, a pause is inserted after approximately 360°, during which the scanner continues to rotate, for example, by about 50°. Only after this pause is it technically possible to capture the next frame. Consequently, either the field of view must be restricted, for example, to the difference between 360° and the pause angle, or each frame must begin at a different point within the field of view.A frame that only captures the difference covers only a portion of the total field of view, 310° in the example given. Both solutions are particularly disadvantageous for subsequent calculations and further processing of the scanned frames. One task, therefore, is to specify a rotating distance measurement system that overcomes the disadvantages of the prior art. In particular, it should enable the repeated provision of frames that essentially cover the entire field of view around the measurement system. The problem is solved by the rotating distance measuring system of claim 1. Further developments and embodiments of the invention are each the subject of the dependent claims. One embodiment of the invention relates to a rotating distance measuring system. The distance measuring system comprises a motor, a transmitter and receiver unit, and a control and evaluation unit. The transmitter and receiver unit is connected to the motor, rotatably mounted, and configured to detect a scene within a detection range around the distance measuring system by emitting light pulses and detecting reflected light pulses, driven by the motor. The distance measuring system is configured to output data of the detected scene at an adjustable frame rate. The control and evaluation unit is configured to drive the motor such that the motor rotates the transmitter and receiver unit at a frequency that is a multiple of the adjustable frame rate. The solution according to the invention therefore provides for rotating the transmitting and receiving unit by appropriately controlling the motor at a higher frequency and providing frames at a rate corresponding to a fraction of this rotational frequency. For example, if a frame rate of 20 Hz is desired, i.e., set, the motor rotates the transmitting and receiving unit at a frequency of, for example, 40 Hz. This enables seamless, repeated acquisition of the field of view around the sensor or the distance measuring system and the repeated provision of corresponding frames. The transmitter and receiver unit implements the functionalities of both a transmitter and a receiver. To this end, the transmitter and receiver unit comprises light-emitting elements for emitting light pulses and corresponding light-sensitive elements or detector elements for receiving light pulses that, after being emitted, are remitted or reflected within the scene in the detection range of the distance measurement system. For example, light-emitting diodes (LEDs) or laser diodes, such as VCSELs (Vertical Cavity Surface Emitting Lasers), are used to generate or emit light pulses, which is why the transmitter unit can also be called an emitter unit. If the transmitter unit includes several such emitters, they are arranged, for example, in the form of an array, and the transmitter unit is also referred to as an emitter array. The emitted light pulses may therefore be laser pulses.Photodiodes, particularly avalanche photodiodes (APDs) or single-photon avalanche diodes (SPADs), are used to detect the emitted light pulses, especially laser pulses. A large number of such light-sensitive elements, arranged in an array, can be used in the receiver unit. The receiver chip or ASIC described above, for example, comprises an array of SPADs. Typically, the described transmitter unit is integrated with the described receiver unit and rotatably connected to the motor. In addition to the light-emitting and light-sensitive elements, the transmitter and receiver unit includes a corresponding memory and a processing unit to process the detected signals. The control and evaluation unit comprises at least one processor, in particular a microprocessor, and a memory. The control and evaluation unit is coupled to the transmitter and receiver unit, for example, via a rotating coupler. The control and evaluation unit itself does not rotate. For example, when using an electric motor, it is arranged on the stator of the motor, while the transmitter and receiver unit is arranged on the rotor of this motor. The control and evaluation unit controls the motor, in particular its rotational speed. This rotational speed corresponds to the rotational rate of the transmitter and receiver unit. The distance measurement system is designed to provide or output data from the scene captured by the transmitting and receiving units, each in the form of a frame. This is done at a frame rate that can be preset for a specific application. In other words, the frame rate refers to the frequency with which the distance measurement system provides data from its detection range. The detection range can also be described as the line of sight. Output frames are then processed further, for example, by downstream electronics. According to further training, the transmitting and receiving unit is designed to capture the scene around the distance measuring system essentially completely, particularly within an angular range of at least essentially 270°, 300°, 330°, or 360°, as a single frame. The aforementioned angular ranges can therefore correspond to the field of view. A frame refers to the field of view, the detection area, or a scene within this field of view around the distance measurement system, which is approximately, and more precisely, 360°. To generate a frame, the transmitter and receiver unit performs a finite number of individual measurements while rotating as the motor does so. Light is emitted in pulsed form, and reflected light from the scene is detected. For example, with a suitable arrangement of detector elements, one column at a time is measured. In one example implementation, 1000 such columns are measured for a single frame. According to a training course, each frame begins and ends at a specific position within the detection range of the distance measuring system. This position is assigned a predefined angle. Successive frames can preferably begin and / or end at the same position. The rotating distance measuring system according to the invention thus enables the output of frames that each begin and end at precisely the same position in the field of view or detection area of ​​the measuring system and each depict the full field of view or a 360° scene. This enables meaningful further processing of the frames. According to further training, the control and evaluation unit is configured to alternately control the transmitting and receiving units between a first and a second operating mode. In the first operating mode, the scene is captured, while in the second operating mode, processing takes place. In the first operating mode, a scene is captured and a frame is generated internally. In the second operating mode, processing takes place. At the end of the second operating mode, the frame is made available by the distance measurement system, i.e., output externally. This processing can involve internal calculations or preprocessing of the just-captured frame, which is explained in more detail below. In another embodiment, the transmitting and receiving unit is configured in the second operating mode to pause the acquisition at least temporarily. In the second operating mode, the transmitter and receiver unit is inactive either temporarily, i.e., during a portion of a motor revolution, or for the entire duration of the second operating mode. Accordingly, the second operating mode is used, among other things, for an internal scan pause. The first and second operating modes are repeated cyclically, and at the end of each cycle, which includes a first and a second operating mode, a frame is provided. In one example implementation, during a 360° rotation of the transmitting and receiving unit in the first operating mode, a frame is captured. The transmitting and receiving unit then pauses capture in the second operating mode, which lasts for a second rotation. Capture of the next frame begins as soon as the transmitting and receiving unit returns to 0° after the second rotation. The cycle then starts again. According to further training, processing in the second operating mode involves the processing of a frame captured in the immediately preceding first operating mode by the transmitting and receiving unit and / or by the control and evaluation unit. This processing specifically includes the application of an edge and / or neighborhood filter. A frame recorded or captured in the first operating mode is therefore preprocessed in the immediately following second operating mode of the same cycle. This preprocessing can also be referred to as preprocessing. For example, in the second operating mode, a frame is preprocessed by filtering it. The entire frame is already available for this filtering in the second operating mode. Thus, the entire 360° scene can be processed in the second operating mode. This is particularly advantageous when edge or neighborhood filters are used. A filter aimed at blooming effects also benefits from the preprocessing of the entire scene. In further training, the processing in the second operating mode includes an internal calibration of the transmitting and receiving unit, in particular the internal calibration of a distance accuracy of the transmitting and receiving unit, in each case especially using an internal reference target. Alternatively or additionally, the second operating mode can be used to calibrate the transmitter and receiver internally. This internal calibration can be performed directly within the transmitter and receiver's control unit. This control unit is implemented, for example, using a field-programmable gate array (FPGA) and is referred to as the rotor control / evaluation unit. During calibration, an internal reference target is used and measured, as is standard practice. Advantageously, the data does not need to leave the transmitter and receiver unit, i.e., the rotating part of the measuring system, but can be processed directly within it. Only in the event of a fault detection, for example, if it is determined that the transmitter unit has completely failed, can a corresponding signal be forwarded to the control and evaluation unit.In addition, the distance accuracy of the transmitting and receiving unit can be calibrated or readjusted. According to further training, the processing in the second operating mode includes a configuration of the transmitting and receiving unit for internal calibration, a subsequent measurement of the reference target, and a subsequent configuration of the transmitting and receiving unit for capturing the scene around the distance measurement system. According to this embodiment, for example, during a first quarter turn of the transmitting and receiving unit in the second operating mode, this unit, and in particular a rotor control / evaluation unit included therein, is configured for internal calibration. Subsequently, the internal reference target is measured, for example, during another quarter turn of the transmitting and receiving unit in the second operating mode. During this calibration, a different type of signal processing is used in the transmitting and receiving unit due to the configuration. This can have a higher temporal resolution than the type of signal processing used during periods when no internal calibration takes place.After the measurement of the internal reference target is complete, the transmitting and receiving unit is reset to the original configuration used before the internal calibration, for example, during another quarter turn in the second operating mode. Finally, a pause may be scheduled for a last quarter turn in the second operating mode, as described in the example. According to further training, the processing in the second operating mode includes an evaluation of a frame captured in the immediately preceding first operating mode by the transmitting and receiving unit and an adjustment of a configuration of the transmitting and receiving unit based on this evaluation. The second operating mode, in which data acquisition is paused at least temporarily, can be used to reconfigure the transmitting and receiving unit, such as the rotor control / evaluation unit, from frame to frame. Following the internal calibration described above, or based on this calibration, adaptive adjustments can be made to the scene captured in the frame. Preprocessing can only take place in the rotor control / evaluation unit. This allows for a short and fast control loop. The process can be summarized as follows: - Recording a frame in the first operating mode, e.g., during one rotation; - During half a rotation in the second operating mode, evaluating the frame and determining relevant parameters, such as the presence of reflectors; - During the second half rotation in the second operating mode, configuring the transmitting and receiving unit based on the determined parameters. This advantageously allows for stepless adaptive configuration adjustment without restricting the field of view. According to another embodiment, the multiple of the frame rate is an integer multiple, in particular two. Consequently, the transmitter and receiver unit rotates at twice the frequency of the set frame rate. In the previously described example of a 20 Hz frame rate, the transmitter and receiver unit is driven by, for example, a brushless DC motor rotating at 40 Hz. This achieves a high frame rate, ensuring that frames with the full field of view are provided, even if the transmitter and receiver unit contains a receiver that requires a scan pause. Any other multiple of the frame rate can also be used as the rotational frequency for the motor and the associated transmitter and receiver unit. The only limitation here is the restriction of the motor's rotational frequency. The effect according to the invention is also achieved if an original rotation frequency of the transmitting and receiving unit is maintained, and the frame rate is simultaneously halved, for example. In another embodiment, the distance measurement system, as described above, is implemented as a LiDAR sensor or as a laser scanner. The disclosure also relates to a method for operating a rotating distance measuring system, which comprises a motor, a transmitter and receiver unit, and a control and evaluation unit. The transmitter and receiver unit, which is rotatably mounted and connected to the motor, emits light pulses driven by the motor, detects reflected light pulses, and thereby captures a scene within a detection range around the distance measuring system. The distance measuring system outputs data of the captured scene at an adjustable frame rate. The control and evaluation unit controls the motor such that the motor rotates the transmitter and receiver unit at a frequency that is a multiple of the adjustable frame rate. The process is implemented, for example, within the rotating distance measuring system as described above. The advantages and further training opportunities apply accordingly. This method makes it possible to fully capture a scene surrounding the distance measurement system multiple times in succession. The aforementioned embodiments and further developments can be combined with each other, unless explicitly stated otherwise or described. The invention is described below by way of example only, with reference to the drawing. Figure 1 shows a schematic representation of an embodiment of a rotating distance measuring system as proposed. Fig. 1 shows a schematic representation of an embodiment of a rotating distance measuring system as proposed. The light-based measuring system comprises a transmitter and receiver unit 10, a motor 20, and a control and evaluation unit 30. The transmitter and receiver unit 10 is rotatably mounted and connected to the motor 20, for example, via a rotating coupler 21. The rotating coupler 21, which is shown here as a shaft, enables the transmitter and receiver unit 10 to rotate a full 360° driven by the motor 20. The transmitter and receiver unit 10 has a transmitter unit 11, a receiver unit 12, and a driver unit 13. The transmitter unit 11 has at least one light-emitting element 111, which emits light pulses L1. For example, the light-emitting element 111 is implemented as a laser diode. Alternatively, the transmitter unit 11 can also have an array of light-emitting elements 111. The receiver unit 12 comprises an array 121 with light-sensitive elements 121a, 121b, ..., 121h. The light-sensitive elements are, for example, each implemented as a SPAD. Each SPAD is configured to detect at least one remitted light pulse L2. A light pulse emitted by the transmitter and receiver unit 10, orLaser pulse L1 is remitted by a scene 40 - only partially shown here - in the example shown by an object 41 which is located within the scene 40, and reaches the transmitting and receiving unit 10 as reflected or remitted laser pulse L2. The driver unit 13 controls the light-emitting element(s) 111 and the light-sensitive elements 121a to 121h. The driver unit 13 is typically implemented as an FPGA and can also be referred to as a rotor control / evaluation unit. The rotor control / evaluation unit 13 can also incorporate computing power to preprocess the signals detected by the receiver 12. For example, a newly acquired frame can be preprocessed in the rotor control / evaluation unit 13. The control and evaluation unit 30 controls the motor 20 such that the motor 20 rotates the transmitter and receiver unit 10 at a frequency that is a multiple of the frame rate. As already described, the frame rate indicates how often per unit of time the distance measurement system outputs an image of scene 40. A frame is thus provided, for example, by the control and evaluation unit 30. Furthermore, the control and evaluation unit 30 alternately controls the transmitter and receiver unit 10 between a first and a second operating mode. In the first operating mode, the transmitter and receiver unit 10 acquires scene 40. In the second operating mode, processing takes place. In an exemplary implementation, the motor's rotational frequency is twice the frame rate. Consequently, during the first rotation, the transmitter / receiver unit 10 records the scene 40 around the distance measurement system within an angular range of approximately or exactly 360°. During the subsequent rotation of the motor 20, the second operating mode is adopted, in which at least the receiver unit 12, particularly immediately after the completion of the first rotation of the motor 20, is at least temporarily inactive. In the inactive state, no further data from the scene 40 is acquired, even though the transmitter / receiver unit 10 continues to rotate due to the drive of the motor 20. The resulting internal scan pause is advantageously used for internal calculations either within the rotor control / evaluation unit 13 or in the control and evaluation unit 30.At the end of the second operating mode, which in this example is the end of the second revolution of motor 20, the distance measurement system outputs a frame that covers 360° of scene 40. The internal scan pause in the second operating mode, as described above, is used, for example, to perform an internal calibration of the transmitter and receiver unit 10. For this purpose, an internal reference target is measured, and the resulting data is evaluated using a different type of signal processing within the rotor control / evaluation unit 13. The data thus remains within the rotor control / evaluation unit 13. For example, the distance accuracy of the transmitter and receiver unit 10 is then adjusted. The faster sampling of scene 40, due to the rotational frequency of the motor 20 being at least twice that of the frame rate, also reduces the so-called rolling shutter effect. Advantageously, even transmitter and receiver units that do not necessarily require a scan pause can benefit from the advantages of operating the distance measurement system in the first and second operating modes. In the rotor control / evaluation unit 13, for example, data from the reference target is processed to determine parameters that are subsequently used in the processing of a normal scan, i.e., a frame recorded in the first operating mode. The reference target is located in the transmit and receive unit 10. The control and evaluation unit 30 processes the frames recorded in the first operating mode and, as is known, calculates a point cloud from them. Reference symbol list 10 Transmit and receive unit 11 Transmit unit 12 Receive unit 13 Rotor control / evaluation unit 20 Motor 21 Rotating coupler 30 Control and evaluation unit 40 Scene 41 Object L1, L2 Light pulse 111 Light-emitting element 121 Receiver array 121a, ..., 121h Light-sensitive element

Claims

A rotating distance measuring system comprising a motor (20), a transmitter and receiver unit (10), and a control and evaluation unit (30), wherein the transmitter and receiver unit (10) is rotatably mounted, connected to the motor (20), and configured to detect a scene (40) in a detection area around the distance measuring system by emitting light pulses (L1) and detecting remitted light pulses (L2), driven by the motor (20), wherein the distance measuring system is configured to output data of the detected scene (40) at an adjustable frame rate, and wherein the control and evaluation unit (30) is configured to control the motor (20) such that the motor (20) rotates the transmitter and receiver unit (10) at a frequency that is a multiple of the adjustable frame rate. Distance measuring system according to claim 1, wherein the transmitting and receiving unit (10) is configured to capture the scene (40) around the distance measuring system substantially completely, in particular in an angular range of substantially 360 degrees, as one frame. Distance measuring system according to claim 1 or 2, wherein a frame begins and ends at one, in particular exactly one, position in the detection range of the distance measuring system and wherein a predefined angle is assigned to this position. Distance measurement system according to one of the preceding claims, wherein the control and evaluation unit (30) is configured to alternately control the transmitting and receiving unit (10) into a first and a second operating mode, wherein in the first operating mode the scene (40) is detected and in the second operating mode processing takes place. Distance measuring system according to the preceding claim, wherein the transmitting and receiving unit (10) in the second operating mode is configured to pause the acquisition at least temporarily. Distance measurement system according to claim 4 or 5, wherein the processing in the second operating mode comprises processing of a frame captured in the immediately preceding first operating mode by the transmitting and receiving unit (10) and / or by the control and evaluation unit (30), wherein the processing in particular comprises the application of an edge and / or neighborhood filter. Distance measuring system according to one of claims 4 to 6, wherein the processing in the second operating mode comprises an internal calibration of the transmitting and receiving unit (10), in particular the internal calibration of a distance accuracy of the transmitting and receiving unit (10), in each case in particular using an internal reference target. Distance measurement system according to the preceding claim, wherein the processing in the second operating mode comprises a configuration of the transmitting and receiving unit (10) for internal calibration, a measurement of the reference target and a subsequent configuration of the transmitting and receiving unit (10) for capturing the scene (40) around the distance measurement system. Distance measuring system according to claim 7, wherein the processing in the second operating mode comprises an evaluation of a frame captured in the immediately preceding first operating mode by the transmitting and receiving unit (10) and an adjustment of a configuration of the transmitting and receiving unit (10) based on the evaluation. Distance measuring system according to one of the preceding claims wherein the multiple is an integer multiple, in particular two. Distance measuring system according to one of the preceding claims which is implemented as a lidar sensor or as a laser scanner.

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