EP4182724A1

EP4182724A1 - Apparatus for testing lidar modules and test method

Info

Publication number: EP4182724A1
Application number: EP21745988.2A
Authority: EP
Inventors: Thomas WIERICH
Original assignee: Magna Electronics Europe GmbH and Co OHG
Current assignee: Magna Electronics Europe GmbH and Co OHG
Priority date: 2020-07-20
Filing date: 2021-07-15
Publication date: 2023-05-24
Also published as: US20230305159A1; WO2022017941A1; CN116113851A

Abstract

The invention relates to an apparatus for testing lidar sensor modules (1), comprising a camera (10), at least one laser (14, 15) for generating at least one return pulse on account of test signals from the at least one laser (14, 15), an optical beam splitter (11) in the beam path between the lidar sensor module (1) and an absorber (12a), wherein the camera (10) is arranged perpendicular to the beam path between lidar sensor module (1) and absorber (12a) and the camera (10) has an optical distance (L1) from an object (20) to be captured that is greater than the optical distance (L2) between lidar sensor module and the object (20) to be captured.

Description

Device for testing lidar modules and method for testing

The invention relates to a device for testing lidar modules and a method for testing lidar modules.

State of the art

Sensors play an increasingly important role in the automotive industry. The trend is reinforced by the goal of moving a vehicle autonomously, which requires sensors with high reliability and good resolution.

Lidar sensors play an important role in autonomous driving. Lidar, i.e. Light Detection and Ranging, is an optical measuring system for detecting objects. The position of the object to be detected can be determined via the propagation time of the light signals by the reflection of the emitted light on the object to be detected until the scattered light arrives at the receiver.

Lidar sensors are currently being used to develop systems for autonomous vehicles that can also drive on public roads. Lidar sensors complement the sensors of conventional assistance systems, such as ultrasonic or radar sensors in the vehicle.

With a LIDAR, the surroundings are illuminated line by line with a point of light from a pulsed laser light source. A contour of the environment is determined from the amplitude or intensity of the re flected and backscattered light. Furthermore, the distance to objects is determined from the propagation time of the light pulses, so that overall a three-dimensional image of the environment can be created, which can be evaluated in image processing software. The line-by-line scanning must take place so quickly that a response time suitable for ferry operations can be achieved. Either LEDs or laser diodes are used as the transmitter unit. They have the advantage of being quickly modulated. This allows fast pulses to be generated, which are important for the transit time measurement. To do this, a light pulse lasting a few nanoseconds in the near-infrared wavelength range is sent. Depending on the lidar sensor type, this wavelength is between 840 and 950 nm. The receiver consists of several segments and each segment receives a separate transmission pulse. Due to the complex structure of the receiver, each pixel from the incident light measures the propagation time of the transmission pulse intended for it. The transmitted pulse is reflected by the objects to be measured and recognized by the receiver.

DE 102008055 159 A1 discloses a lidar sensor in which the detection field can be specified in the vertical and in the horizontal direction by adjusting the oscillation amplitude of the micromechanical mirror. With the LIDAR, the surroundings are illuminated line by line with a point of light from a pulsed laser light source. The laser beam is deflected by a micromirror, which oscillates horizontally at 24 kHz and vertically at 60 Hz, so that 60 images of the surroundings are generated per second. According to the prior art, the mirror oscillates in both directions, each with a constant amplitude, so that fixed angular ranges are covered.

The final quality test is of great importance in the manufacture of the lidar sensors. Each individual lidar sensor has to be tested, which of course has to be done quickly and with as little effort as possible in series production

It is the object of the invention to present a device and a method for testing lidar modules, which at the same time measures important key figures of the lidar sensors in an uncomplicated manner. Description of the invention

The object is achieved with a device for testing lidar sensor modules comprising a camera, laser for generating at least one return pulse based on test signals from the laser, an optical beam splitter in the beam path between the lidar sensor module and an absorber, the camera perpendicular to the beam path between the lidar sensor module and the absorber is arranged and the camera has an optical distance to an object to be detected which is greater than the optical distance between the lidar sensor module and the object to be detected.

The device has the advantage of being very compact and still having a significant test area in order to be able to measure the desired parameters for the lidar sensor module.

It is particularly advantageous if the optical distance from an object to be detected is twice the optical distance between the lidar sensor module and the object to be detected.

The test signals from the lasers produce uniformly diffuse illumination and/or illumination structured with a pattern.

It is advantageous that the beam splitter splits the output signals of the lidar sensor module, the test signals of the laser and the return signals from the object to be detected.

In an advantageous embodiment, one side of the beam splitter is 1% and the other 0.25% is reflective for the incident light.

It is advantageous that the device has a climate-controlled chamber for accommodating the Lidas sensor module to be tested, which chamber is separate from a test chamber. Description of the figures

Figure 1 shows the optical signal path of a lidar module,

FIG. 2 shows a structure of a test device.

FIG. 1 shows the optical signal path of an exemplary lidar module 1, which is constructed from a number of lidar sensor segments 2A, 2B, 2C, 2D.

Each of the lidar sensor segments 2A, 2B, 2C, 2D comprises a laser, a short-range detector 3, implemented for example with an avalanche photodiode, and a long-range detector 4, for example a photomultiplier 5. Each photomultiplier 5 is included in this example made up of eight individual detector segments in order to pick up scattered signals that are spatially separated from one another and pass them on for processing. The electrical and electronic control of the lasers and the connection of the receiver components, consisting of avalanche photodiodes and photomultipliers, to the evaluating controller are not shown in detail.

On a transmission path 6A, light goes from the laser of the lidar sensor segment 2A through optics (not shown in detail), onto a mirror 8A and with the light away 6B onto a deflection unit 7A consisting of MEMS. MEMS, Micro-Electro-Mechanical Systems, are tiny components that combine logic elements and micromechanical structures in one chip. They can process mechanical and electrical information and have small mirrors to deflect the laser light. A zone A is then illuminated pulse by pulse with the laser light from one of the mirrors of the deflection unit 7A.

Similarly, the other lidar sensor segments 2B, 2C, 2D send laser light onto the associated mirrors 8B, 8C, 8D and the associated deflection units 7A, 7B. The receive path of the lidar sensor module corresponds to the inverse transmit path. The light of a specific laser pulse scattered on the detected object hits the associated deflection unit 7A, 7B, the MEMS, and enters through the optics (not shown) of the lidar sensor segment 2A, 2B, 2C, 2D and hits the respective short plugs -Detector 3 and the respective long-range detectors 4.

In the embodiment of the lidar sensor module 1 selected as an example, the nominal optical resolution is 0.1° by 0.1°. The lidar sensor module 1 is defined for normal operation with a measuring range M to be covered of approximately 120° horizontally x 16° vertically. With the resolution, this results in a measurement in 1200 x 160 channels.

In order to test the quality of individual lidar sensor modules 1, the lidar sensor modules 1 must be subjected to a final functional test.

The structural configuration of the lidar sensor module 1 leads to five different groups of parameters for the lidar sensor module 1, which must be recorded by a test. These parameters fully characterize an individual lidar sensor module 1 relative to other individuals of the same basic lidar sensor module design.

All parameters are measured in a black box test since only the input and output of the lidar sensor module 1 needs to be present. The test module only deals with the fact that the light emitted by the lidar module is recorded and then a return is generated on a path that simulates a reflected signal on the receive path of the lidar module.

Parameter 1: A first parameter P(t) ₀ ut relates to the transmitted laser signal with its externally observable properties. For the transmitted laser signal of each of the existing lasers, the angular distribution of the emitted laser pulses is measured over a specified measuring range M in a frame and spatially the defined scanning area (deflection of the mirror) plus a peripheral area of the scanning with a scan pattern. In order not to have to calibrate, the scanning area is dimensioned somewhat more generously. Lidar sensors deflect the laser beam in different directions across the scene to capture their surroundings. This creates unique patterns in the point cloud, which are referred to as scan patterns. The pattern is controlled by the MEMS, which steer the laser beam through the mirror movements. _{The total energy P(t) 0} ut of the laser signal is determined by measuring the integral of the intensity for all individual laser pulses within a time frame, with the measurement taking place over the measuring range M. The light power is integrated over the time of a frame for all laser pulses.

In addition, the spatial form of each individual laser pulse in the measurement area M is determined for the distribution of the energy. In other words, the shape of the pulse is measured.

The response of the lidar sensor module to incident light P(t)in from an external source is determined as the second parameter P2, and the absolute sensitivity over the measuring range M is determined for both the close range and the far range.

Furthermore, as the third parameter P3, the angular coupling of the transmission and reception path must be measured over the measuring range M. Each point on the camera is mapped to a point. The laser 15 is pulsed and sends light through a shadow mask, this creates an image in the camera and from there the angular relationship can be evaluated. You can use it to measure the optical path and determine a misalignment of the lidar module if a software test has taken place.

The fourth parameter P4 is the angular resolution in the camera 10 over the measuring range M.

The fifth parameter P5 determines the influence of the backlight, the main source of which is the sun in the application. An interference variable is generated that largely determines the signal-to-noise ratio on the lidar module. This Signal to noise ratio defines a false alarm rate. The higher the threshold of the signal-to-noise ratio, the later the alarm, but the range sensitivity is reduced.

A test device 50 is used for testing, which accommodates the test object, the lidar module 1, in a climatically controlled chamber 51. The chamber 51 has a window 53 via which the lidar sensor module 1 is optically connected to the actual test chamber 52 . The test chamber 52 is filled with a dry gas in order to maintain defined test conditions.

To carry out the measurements, the transmission power P(t) ₀ ut of the lidar sensor module 1 is recorded by a camera 10 in the test chamber 52 . For this purpose, the laser signal is split into three directions at a beam splitter 11 . The beam passing through in a straight line is caught in an absorber 12a. A part of the laser power P(t)out_1 is imaged on the camera 10, another part P(t) ₀ ut_2 falls on the object 20 to be detected.

The horizontal resolution of the camera 10 is 4k, for example.

In order to enable a meaningful measuring range for the camera 10, the distance L1 to the object 20 to be detected must be greater than the distance L2 of the lidar sensor module 1 to the object 20 to be detected, which runs with a change of direction at the beam splitter 11 . The distance L2 is a combination of the distance from the lidar sensor module to the beam splitter 11 and the distance from the beam splitter 11 to the object 20. If twice the distance L1 to L2 is selected, the measuring range of the camera 10 is limited to around 60°.

The received signal P(t)in is simulated by using a laser pulse triggered by the transmit pulse P(t) ₀ ut.

The testing device must measure all the required parameters at different temperatures and supply voltages. To do this, it is essential to minimize the volume and mass that must be thermally controlled, which is achieved by keeping the lidar module 1 separate and the test chamber 52 not having to be opened.

The camera 10 has a 4k resolution, for example. The region of particular interest, ROI, is limited to a partial image of 4096×546 pixels.

The camera 10 must have a global shutter so that sharp images of fast-moving objects are possible because all pixels can be exposed at the same time. The global shutter is synchronized with the start of a data frame, ie with the activation of the lidar sensor module 1 . Only one image from the camera 10 is recorded per data frame.

The camera image must be deconvoluted, that is to say processed by computation, in order to remove the double image produced by the optical beam splitter 11 in the beam path. The camera 10 captures the scanning pattern, the pulse energy and the pulse shape.

A laser 14, simulating one of the return signals, diffusely uniformly illuminates the object to be detected 20 with light to produce a constant response pulse of the object to be detected. The illumination of the measuring area, which should be as homogeneous as possible, is then measured.

The laser 14 works with a variable delay between the transmitted pulse P(t) _ou t_i of the lidar module 1 _{detected by the camera and the return signal R x} from the object 20 to be detected.

In addition, for the return signal, the laser 14 must have the ability to regulate _{the energy of the return signal R x .} This arrangement tests the sensitivity to return signals R _x . A diffuser plate is used, which, when arranged in front of the laser 14, generates diffused light.

For a measurement with a pattern in the return signal R _xP att, a second laser 15 for the pattern return signal has to have the object 20 to be detected spatially illuminate structured lighting pulses. The pattern consists, for example, of randomly oriented short bars, a line pattern or Fischmus ter, which is designed as a screen to be transilluminated.

As an alternative to the two lasers 14, 15, a single laser can also be used, with the diffuser disk and grid disk being mounted pivotably in the beam direction in front of the laser in an upstream filter changer and being alternatively illuminated.

It is provided that the entire object 20 to be detected is uniformly illuminated with the pattern. The second laser 15 creates a point cloud that is captured by the camera.

The laser 15 also requires a variable delay between the transmission signal P(t) ₀ ut detected on the camera 10 and the return _{signal R xP} att.

In addition, the laser 15 for the return _{signal R x-patt must have} the ability to generate the energy of the return signal by regulating the test signal.

The arrangement tests the transmit signal to return signal alignment and the resolution.

The optical splitter 11 consists of a glass plate coated on both sides. Coatings are readily available for the infrared at 905nm range. The two sides must have different reflectivities with a ratio greater than 2:1. An exemplary embodiment is selected in such a way that one side reflects 1% and the other 0.25% of the incident light.

The absorbers 12a and 12b are used to absorb unnecessary light. The absorber 12a absorbs the transmission pulse of the lidar module and the absorber 12b absorbs the return pulse from the object 20 to be detected.

Infrared LEDs are used for the background lighting 13 . You can work with different light intensities and threshold sizes measurable do. The light intensity is varied in order to be able to recognize thresholds. The background lighting 13 simulates solar radiation and assumes the function of a disturbance variable.

The camera 10 records a greatly reduced light signal from the lidar module 1, which is branched off by the optical splitter 11. The camera captures the scan pattern frame by frame. The lidar module and the test module work with an image frequency of 15 Hz.

The camera 10 provides a trigger signal to trigger the signals from the lasers 14 and 15 and to generate a simulated response signal.

The raster disk generates a corresponding input signal in the camera 10. The point cloud generated by the raster disk and the laser 15 is recorded on the lidar module 1, and the camera image is transferred to a test controller outside of the tester.

The tester is just an optoelectronic head that generates light and records light in a camera.

Claims

Expectations

1. A device for testing lidar sensor modules (1) comprising a Ka mera (10), at least one laser (14, 15) for generating at least one return pulse based on test signals of the at least one laser (14,15), an optical Beam splitter (11) in the beam path between the lidar sensor module (1) and an absorber (12a), the camera (10) being arranged perpendicularly to the beam path between the lidar sensor module (1) and absorber (12a). and the camera (10) has an optical distance (L1) to an object (20) to be recorded which is greater than the optical distance (L2) between the lidar sensor module and the object (20) to be recorded.

2. Method for testing according to claim 1, characterized in that the optical distance (L1) to an object (20) to be detected is twice the optical distance (L2) between the lidar sensor module and the object (20) to be detected.

3. Method for testing according to claim 1 or 2, characterized in that the test signals of the at least one laser (14,15) generate a uniformly diffuse illumination.

4. Method for testing according to claim 1 or 2, characterized in that the test signals of the at least one laser (14, 15) generate an illumination structured with a pattern.

5. Method for testing according to one of the preceding claims, characterized in that the beam splitter (1 1) both the output signals (Pout) of the lidar sensor module, the test signals of the lasers (14, 15) and the return signals (R _x ) from the object to be detected.

6. Method of testing according to any one of the preceding claims, characterized in that one side of the beam splitter reflects 1% and the other 0.25% of the incident light.

7. Method for testing according to claims 3 and 4, characterized in that a single laser with an upstream filter changer generates both diffuse light and illumination structured with a pattern.

8. Method for testing according to one of the preceding claims, characterized in that background lighting (13) with LEDs is used, which work with different light intensities and is used as a disturbance variable of the measurement.

9. Device for testing with the method according to any one of the preceding claims, characterized in that the test chamber (50) has a climatically controlled chamber (51) for receiving the lidar sensor module (1) to be tested is separated from a test chamber (52).

10. The device according to claim 7, characterized in that the test chamber (52) is filled with a dry gas.