EP3602126A1

EP3602126A1 - Method and apparatus for scanning a solid angle

Info

Publication number: EP3602126A1
Application number: EP18712568.7A
Authority: EP
Inventors: Reiner Schnitzer; Tobias Hipp
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2017-03-20
Filing date: 2018-03-19
Publication date: 2020-02-05
Also published as: CN110462440A; US20200018859A1; US11703574B2; WO2018172260A1; DE102017204587A1; CN110462440B

Abstract

A method for scanning a scanning angle is disclosed, in which at least one electromagnetic beam is produced, the at least one electromagnetic beam is deflected along the scanning angle and the at least one electromagnetic beam reflected at an object is received and detected, wherein at least one second electromagnetic beam is produced after at least one first electromagnetic beam and wherein the second electromagnetic beam is produced with a lower energy than the first electromagnetic beam. Moreover, a LIDAR apparatus is disclosed.

Description

Description title

Method and device for scanning a solid angle

The invention relates to a method for scanning a scanning angle and a LI DAR device for scanning a scanning angle.

State of the art

Conventional LI DAR (Light Detection And Ranging) devices are pulsed direct time-of-flight systems, which determine the time between an emission and a reception of a short, high-energy radiation pulse or

Measure laser pulses. Over the time or time of flight of the beam can then be determined by knowing the speed of light, a distance between an object and the LI DAR device. As detectors for receiving reflected beams usually avalanche photodiodes or single photon avalanche diodes are used. In order to be able to scan or measure the longest possible ranges of 100 - 200m with a simultaneously poor reflectivity of an object of less than 10%, the necessary laser pulses within the eye safety guideline can be used depending on the system configuration

Achieve peak output in the kilowatt range. Due to the limited dynamic range of the usual detectors, reflections of the beams on closer objects rapidly saturate the detectors.

As a result, the shape of the received pulse can be falsified. Consequently, the determination of further measured variables on the basis of the pulse shape such as intensity, reflectivity, weather conditions, angle of the target object to the LIDAR device can be made difficult or prevented.

Disclosure of the invention The object underlying the invention can be seen to propose a LIDAR device and a method that can register objects in a near area without supersaturation of a detector despite high Reichweise.

This object is achieved by means of the subject matter of the independent claims. Advantageous embodiments of the invention are the subject of each dependent subclaims.

According to one aspect of the invention, there is provided a method of scanning a scan angle wherein at least one electromagnetic beam is generated and the at least one electromagnetic beam is deflected along the scan angle. The at least one electromagnetic beam reflected at an object is received and detected, wherein after at least a first electromagnetic beam at least a second electromagnetic beam is generated and wherein the second

electromagnetic beam with a lower energy than the first

electromagnetic beam is generated.

As a result, at least one first electromagnetic beam is generated and a short time later at least a second weaker electromagnetic beam. Weaker in this context means that an intensity and an energy content of the at least one second electromagnetic beam are less than the intensity and the energy content of the at least one first electromagnetic beam. Preferably, the otherwise usual or possible 100% of energy of an electromagnetic beam is now divided between the at least one first beam and the at least one second beam. The at least one first beam may, for example, have 80-90% of the energy to reach a maximum range of one LI DAR.

Do not restrict the device too seriously and make sure you do not miss an object. By contrast, the at least one second beam can have 10-20% of the energy. This also allows objects using the

at least one second beam with higher linearity can be detected. Such objects may be, for example, objects that are in a short time Distance to LIDAR device are positioned and / or have high reflectivity. These objects would cause saturation of the detector upon detection of the at least one first and high energy beam. According to one embodiment of the method, the energy of the at least one second electromagnetic beam is selected below a saturation of at least one detector. In this way, it can be prevented that the at least one second beam saturates the detector

can cause. Since in the at least one first high-energy beam, the danger of saturation of the detector is high, in particular in the case of near objects, the at least one second beam can still cause a

meaningful measurement of the scanning range can be ensured.

According to a further embodiment, the at least one electromagnetic beam is generated pulsed. As a result, depending on the pulse duration, a high intensity can be achieved with a constant energy content. Thus, multiple pulsed beams can be generated within a short period of time. According to a further embodiment of the device is between the

Generating the at least one first electromagnetic beam and generating the at least one second electromagnetic beam initiates a delay time. As a result, the at least one second beam can be generated delayed. Alternatively or additionally, a plurality of second beams may be generated with a second delay time between the plurality of second beams. The second delay time can

For example, be made smaller than the first delay time between the at least one first beam and the at least one second beam. According to a further embodiment, an intensity ratio of the at least one first electromagnetic beam and the at least one second electromagnetic beam is varied. This allows the generated beams to be flexibly adapted to a situation and in situ. For example, in an automotive application in a high-traffic environment, a low intensity ratio may be used, so that a close range can be scanned more effectively. On the other hand, the highest possible intensity ratio of the two beams could be set on a motorway, so that a corresponding LIDAR device has the highest possible range and can therefore also be used at higher speeds.

According to a further embodiment of the method, the

Delay time between the at least one first electromagnetic beam and the at least one second electromagnetic beam varies. In this case, the delay time can be adapted in particular to a distance of the object to the LIDAR device or at least one radiation source for generating at least one beam. With rising

Distance a generated beam needs more time to travel the distance to the object and back to the detector. Thus, the

Delay time can be adjusted so that at least one reflected beam from the at least one detector within a defined period of time or within a defined measurement cycle can be detected.

Advantageously, the delay time can be chosen such that at least one received reflected beam can not overlap in time with a generated beam.

According to a further embodiment, the delay time is chosen to be greater than a recovery time of a detector. Especially with a

Scanning of objects at a short distance and / or high

Reflectivity, a reflected beam of the at least one first high-energy beam can cause saturation of the detector, the at least one detector requires a period of time to be ready to receive again for the at least one second beam. Alternatively, a detector may be chosen that does not require a recovery time.

According to another aspect of the invention, there is provided a LIDAR device for carrying out a method according to one aspect of the invention. The LIDAR device has at least one radiation source for generating at least one electromagnetic beam, a deflection unit for deflecting the at least one generated electromagnetic beam along a Scanning angle and at least one detector for receiving and detecting at least one reflected on an object electromagnetic beam, wherein the at least one radiation source at least a first

generates electromagnetic beam and at least a second electromagnetic beam and wherein the second electromagnetic beam has a lower

Has energy as the first electromagnetic beam.

By generating at least one second weaker beam shortly after the at least one high-energy first beam, a working range of the LIDAR device can be expanded. An energetic beam reflected from an object may cause saturation of the at least one detector for an object that is a short distance away from the LIDAR device. High-energy rays that reach objects with a high

Reflectivity can also exceed the dynamic range of the detector. If the detector experiences saturation, further evaluation of the at least one received beam can be hindered or prevented. In particular, an evaluation of further measured variables based on a pulse shape of the beam, such as intensity,

Reflectivity, weather conditions, angle of the target object to LIDAR device and the like by the saturation of the detector no longer be possible. This ensures that even when using a high-energy beam, which is designed for the largest possible range, problematic objects can also be detected with a high linearity. According to one embodiment, a variable delay time is implemented between the at least one first generated beam and the at least one second generated beam. Depending on the detector must have a

Recovery time after saturation are taken into account. Thus, it can be ensured by the delay time that the at least one second beam can be regularly detected by the detector. This can be negative

Effects of a saturated detector are bypassed. Since the at least two beams have the same time base and can be sorted into the same histogram, no additional memory is needed in the LIDAR device. According to a further embodiment, an intensity ratio between the at least one first electromagnetic beam and the at least one second electromagnetic beam is variable. Depending on an application environment of the LIDAR device, the

Intensity ratio between the at least one first beam and the at least one second beam are set. The intensity ratio may be, for example, 90% to 10%, 80% to 20%, 50% to 50% and the like. Especially in applications that require a long range, the largest possible percentage of energy can be expended on the at least one first beam. Furthermore, in addition to the selection of the delay time, the intensity ratio may vary depending on one

Detecting close range such as below 50m can be selected. After each measuring cycle, at least two by the

Delay time separated generated and received again beams can be changed, the delay time and / or the intensity ratio.

The following are based on highly simplified schematic

Representations preferred embodiments of the invention explained in more detail. Show here

1 is a schematic representation of a LIDAR device according to a first embodiment,

2a shows a schematic sequence of generated beams according to a method according to a first exemplary embodiment,

2b shows a schematic intensity spectrum of detected rays after a

Method according to the first embodiment,

3a, 3b show a schematic sequence of generated and received beams according to a method according to the first embodiment, Fig. 4a shows a schematic sequence of generated beams according to a method according to a second embodiment and

4b, 4c show a schematic sequence of generated and received beams according to a method according to the second embodiment. In the figures, the same constructive elements each have the same reference numerals.

FIG. 1 shows a first exemplary embodiment of a LIDAR device 1. The LIDAR device 1 has a radiation source 2 for generating at least one electromagnetic beam 4. The radiation source 2 according to the exemplary embodiment is a laser 2 which generates beams 4 in a pulse shape.

According to the embodiment, the laser 2 is for generating a beam 4 having a wavelength in the non-visible infrared range. The wavelength can be greater than 800 nm, for example. The beam 4 generated by the laser 2 is deflected by a deflection unit 6 or a rotatable mirror 6. The mirror 6 is in this case pivotable along a rotation axis R. Thus, the mirror 6 can deflect the generated beam 4 along a defined scanning angle H. In addition, the mirror 6 is orthogonal to the horizontal scanning angle H pivotally and thus covers a vertical scanning angle V from. As a result, the LIDAR device 1 can scan a solid angle W = VxH and locate any objects 8, 9 positioned in this solid angle W. The at least one generated beam 4 is at least partially reflected by the object 8, 9 and becomes the reflected or incoming beam 10, 30. The reflected beam 10, 30 is received by a receiving optical system 12 and directed to a detector 14. The detector 14 consists of a plurality of detector cells 16, which are single photon avalanche diodes according to the embodiment.

FIG. 2 a shows a schematic sequence of generated beams 4, 5 according to a method according to a first exemplary embodiment. In particular, an intensity I of a first generated beam 4 and a second generated beam 5 is illustrated against a time t. The generated beams 4, 5 are pulse-shaped and form a measuring cycle 18. In the measuring cycle 18, the generated beams 4, 5 by a delay time 20 from each other in time. Between the second generated beam 5 and a next measuring cycle 18 there is likewise a second interruption time 22 which belongs to the first measuring cycle 18. By the second interruption time 22, a decay phase of the radiation source 2 can be realized. Furthermore, can be controlled by the interruption time 22 of the total output via the measuring cycle 18 energy content per unit time t.

FIG. 2b shows a schematic intensity spectrum of detected beams 10, 11 according to the method according to the first exemplary embodiment. In particular, the time recorded by a detector cell 16 is

Intensity distribution illustrates. The time segment shown corresponds to a first time range from the measurement cycle 18. The first detected beam 10 has such a high intensity I that the detector cell 16 reaches a saturation state 24 and is, as it were, overexposed. After a short period of time, the second beam 11 is detected. The second beam 1 1 was generated with a lower energy content and has after

Reflect on the object 8 an intensity I, which is below the

Saturation state 24 of the detector cell 16 is located.

FIGS. 3a and 3b show schematic time sequences of reflected or detected beams 10, 11, 30, 31 recorded by at least one detector cell 16 of the detector 14 within a time frame t. In this case, the measurement cycle 18 already described in FIG. 2a was used to detect two objects 8, 9. The beams 10, 11 reflected by a first object 8 and the beams 30, 31 reflected by a second object 9 have been recorded here within the same temporal intensity profile I. Thus, no separate time string is necessary for the evaluation of the detected beams 10, 11, 30, 31. So an evaluation process can be accelerated. FIG. 3b shows, for example, that the detected beams 10, 11, 30, 31 of two different objects 8, 9 can overlap. In particular, this is the case when a distance between the two objects 8, 9 is present, the flight duration of the generated beams 4, 5 correspond to the

Delay time 20 is present. Thus, according to the method, in a next or a next but one measurement cycle 18, the delay time 20 can be varied in order to clearly differentiate the intensities I of the detected beams 10, 11 of the first object 8 and the detected beams 30, 31 of the second object 9 enable. FIG. 4 a shows a schematic sequence of generated beams 4, 5 according to the method according to a second exemplary embodiment. The radiation source 2 generates according to the embodiment a first high-energy beam 4 in the form of a pulse and two further second energy-weaker beams 5. Between the first generated beam 4 and the two second generated

Rays 5 is also a delay time 20 available. The

Delay time can also be carried out variably depending on the measurement cycle 18 and adapted to a type or distance of the object 8, 9 or to a number of expected objects 8, 9. After generating the two second energy-weaker beams 5 are for a second

Delay time 22 or interruption time 22 no further beams 4, 5 generated. Rather, the interruption time 22 as the decay of the

Radiation source 2 can be used. Depending on the duration of the respective beams 4, 5, the delay time 20 and the interruption time 22 can be adapted to a defined measurement cycle 18. As a result, the energy content emitted by the generated beams 4, 5 per unit time t can also be adjusted. According to the embodiment, the first generated beam 70% of the energy content in the measurement cycle 18 and the two second generated beams 5 each 15% of the energy content.

FIG. 4b shows the measuring cycle 18 described in FIG. 4a with the signals received from at least one detector cell 16 of the detector 14 or

detected beams 10, 1 1 of the first object 8 and the detected beams 30, 31 of the second object 9 shown. The delay time 20 is set at the distances of the objects 8, 9 such that the pulses of the beams 10, 11, 30, 31 recorded within a time axis t do not overlap or overlap. Thus, each individual pulse of the beams 10, 1 1, 30, 31 can be uniquely identified and evaluated. FIG. 4c shows, for example, beams 10, 11, 30, 31 of two objects 8, 9 which are at a distance from one another and which are separated by beams 10, 11, 30, 31 within a time of flight of the order of magnitude of FIG Delay 20 can be covered. As a result, the detected beams 10, 11, 30, 31 of both objects 8, 9 have overlays or overlaps in certain areas. Thus, an evaluation of the detected Strahll O, 1 1, 30, 31 are only incomplete. To avoid this, over several measuring cycles 18 across the Delay time 20 defined and continuously changed, so that a superposition of several detected beams 10, 1 1, 30, 31 can be seen or the detected beams 10, 1 1, 30, 31 no longer overlap. Alternatively, for example, every second measurement cycle 18 can be recorded in a separate time axis, so that an overlay of detected

Strahlenl O, 1 1, 30, 31 can be prevented.

Claims

claims

A method of scanning a scan angle (W) comprising the steps of:

Generating at least one electromagnetic beam (4, 5)

Deflecting the at least one electromagnetic beam (4, 5) along the scanning angle (W)

Receiving and detecting the at least one electromagnetic beam (10, 11, 30, 31) reflecting on at least one object (8, 9),

characterized in that after at least a first

electromagnetic beam (4) at least a second electromagnetic beam (5) is generated and wherein the second electromagnetic beam (5) is generated with a lower energy than the first electromagnetic beam (4).

2. The method of claim 1, wherein the energy of the at least one second electromagnetic beam (5) below a saturation (24) of at least one detector (14, 16) is selected.

3. The method of claim 1 or 2, wherein the at least one

electromagnetic beam (4, 5) is pulsed generated.

4. The method according to any one of claims 1 to 3, wherein between generating the at least one first electromagnetic beam (4) and generating the at least one second electromagnetic beam (5) a

Delay time (20) is initiated.

5. The method according to any one of claims 1 to 4, wherein an intensity ratio of the at least one first electromagnetic beam (4) and the at least one second electromagnetic beam (5) is varied.

6. The method of claim 1, wherein the delay time between the at least one first electromagnetic beam and the at least one second electromagnetic beam is varied.

7. The method according to any one of claims 1 to 6, wherein the delay time (20) is greater than a recovery time of a detector (14, 16) is selected.

8. LI DAR device (1) for carrying out the method according to one of the preceding claims, with at least one radiation source (2) for generating at least one electromagnetic beam (4, 5), with a deflection unit (6) for deflecting the at least one generated electromagnetic beam (4, 5) along a scanning angle (W), with at least one detector (14, 16) for receiving and detecting at least one electromagnetic beam (10, 11, 30, 31) reflected at at least one object (8, 9) ), thereby

in that the at least one radiation source (2) has at least one first electromagnetic beam (4) and at least one second

generates electromagnetic beam (5) and wherein the second electromagnetic beam (5) has a lower energy than the first electromagnetic beam (4).

The LI DAR apparatus of claim 8, wherein a variable delay time (20) is implemented between the at least one first generated beam (4) and the at least one second generated beam (5).

10. LI DAR device according to claim 8 or 9, wherein an intensity ratio between the at least one first electromagnetic beam (4) and the at least one second electromagnetic beam (5) is variable.