The present invention relates to a lidar device. The present invention further relates to a method for operating a lidar device. The present invention further relates to a computer program product.
Highly automated vehicles (SAE levels 3-5) will be increasingly used on public roads in the coming years. All conventional designs of automated vehicles require a combination of different conventional environment detection sensors, such as camera, radar, lidar, etc. The latter environment detection sensors are basically laser scanners that emit laser light pulses and measure and evaluate times of the arrival of laser light reflected from an object. The lidar sensors can determine a distance to the object from the measured time of flight.
Some conventional radar sensors are able to measure speeds of objects via the Doppler shift of frequencies.
Some lidar sensors use a similar principle (frequency-modulated continuous wave technology, FMCW) to measure the Doppler shift of light, although these sensors are currently still in the research stage.
European Patent No. EP 2 819 901 B1 describes a method for ascertaining the speed of a vehicle equipped with at least one environment sensor that ascertains environmental data of the vehicle relative to at least one non-moving object.
It is an object of the present invention to provide an improved lidar device.
According to a first aspect, the present invention provides a lidar device. According to an example embodiment of the present invention, the lidar device includes:
Advantageously, in this way a lidar device is provided with which the radial speed of objects can also be measured.
Advantageously, in this way the use of a radar system for an automated vehicle can be saved, in some circumstances.
According to a second aspect of the present invention, the problem is solved with a method for operating a lidar device.
According to an example embodiment of the present invention, the method includes the following steps:
Preferred specific embodiments of the lidar device are disclosed herein.
According to advantageous developments of the lidar device of the present invention, a number of the laser elements and a number of the detector pixels is the same or different.
Advantageously, different measurement and evaluation designs for ascertaining the radial speed of the objects are supported in this way.
In a further advantageous development of the lidar device according to the present invention, the evaluation is carried out directly on a detector pixel or on a central computing unit. Advantageously, this provides various possibilities for evaluating the acquired data; here, for reasons of efficiency, an evaluation of the data as close to hardware as possible, using a detector ASIC or detector FPGA, can be expedient.
Another advantageous development of the lidar device of the present invention provides that the measurements are carried out individually for each detector pixel.
Another advantageous further development of the lidar device of the present invention provides that the measurements for a plurality of detector pixels are carried out simultaneously.
Advantageously, in these ways different measurement and evaluation designs for determining the radial speed are made possible.
Another advantageous development of the lidar device of the present invention provides that a minimum error square is used for the adjustment between measurement values. Used by a simple mathematical method for the efficient evaluation of the measurement data for the purpose of extracting the radial speed.
According to a further advantageous development of the lidar device of the present invention, a further object can be detected from a goodness of fit of a mathematical function between the measurement values. This provides an option by which an erroneous measurement can be recognized, enabling, e.g., a central control unit to interpret the acquired data correctly.
In further advantageous specific embodiments of the lidar device of the present invention, the detector pixel is one of the following: SPAD diode, avalanche photodiode, CCD sensor.
Advantageously, the detector pixel in the form of the SPAD diode can thus be used to carry out repetitive measurements anyway, whereby the proposed evaluation of the data and extraction of the speed provides an additional benefit without additional measurement time. Alternatively, other types of detector pixels can be used, allowing a variety of different detector pixels to be used.
The present invention is described in detail below with further features and advantages, on the basis of several figures.
Identical or functionally identical components have the same reference signs. The figures are intended in particular to illustrate the main features of the present invention, and are not necessarily to scale.
Disclosed device features result analogously from corresponding disclosed method features, and vice versa. This means in particular that features, technical advantages, and embodiments relating to the lidar device result in an analogous manner from corresponding embodiments, features, and advantages of the method for operating a lidar device and vice versa.
A main feature of the present invention is in particular to provide a lidar sensor capable of carrying out both distance and radial speed measurements of detected objects.
In this context, for the lidar device according to an example embodiment of the present invention, a detector device having a plurality of detector pixels is provided, a defined high number of repeating measurements being carried out for each detector pixel, and radial speeds of the detected objects being extracted from these data.
A second lens (not shown) situated in front of the detector matrix maps the reflected radiation pulses onto detector pixels 20a . . . 20n, which are also configured in the form of a matrix, similar to laser elements 10a . . . 10n of the laser matrix. The lens is formed in such a way that each detector pixel 20a . . . 20n the reflected radiation pulses that were emitted by an associated laser element 10a . . . 10n are measured and evaluated according to the present invention.
In an alternative specific embodiment of the proposed lidar device 100, the number of laser elements 10a . . . 10n is different from the number of detector pixels 20a . . . 20n, so that, for example, n laser elements 10a . . . 10n are mapped onto m detector pixels 20a . . . 20n. For example, a single laser element 10a . . . 10n may be used in each column, its radiation pulses being mapped onto the corresponding column of the detector pixel 20a . . . 20n. In another embodiment, a single laser element 10a . . . 10n can be used to completely and instantaneously illuminate the entire field of view of lidar device 100 (flash lidar).
Each individual detector pixel 20a . . . 20n of the detector matrix can be formed, for example, as a single photon avalanche diode (SPAD), i.e., as a photodetector with a singular detection sensitivity. It is also possible to realize detector pixels 20a . . . 20n as avalanche photodiodes (APD) or as CCD elements.
An electronic evaluation circuit 30 reads out each individual detector pixel 20a . . . 20n (e.g., SPAD element), and the associated time of arrival of the photon is recorded. 0 ns corresponds here to the time at which the radiation pulse associated with the received photon was emitted. Due to the binary detection characteristic of the SPAD pixels, multiple repetitive measurements for each detector pixel 20a . . . 20n are necessary to make it possible to distinguish useful signals from noise signals such as background light. After that, a statistic or histogram of all registered events is created as a function of the arrival time. A number of repetitions for each detector pixel 20a . . . 20n is preferably on the order of about 100 repetitions, making it possible, using the histogram, to distinguish true detection events from background photons.
An extraction of data relating to a radial speed of an object in the following way is provided according to the present invention:
If the histogram indicates that the lidar device 100 detects an object, the histogram can be used to determine the individual arrival time, i.e., the temporal arrival of the photon after the emission of an associated laser pulse) as a function of the measurement time M (e.g. UTC time), for example by plotting the arrival time A as a function of the absolute measurement time M, as indicated for example in
From the ascertained straight line slope, the radial speed of the object can be ascertained as follows:
v=S×c/2 (1)
Here, the factor 2 results from the fact that the light has to travel a path between lidar device 100 and the object twice. For example, in
The proposed lidar sensor preferably operates at a frame rate of the order of approximately 10 Hz, the frame rate corresponding to a sum of all detector pixels 20a . . . 20n of detector device 20. This means a time duration of approximately 100 ms is required for all measurements of a complete frame with all detector pixels 20a . . . 20n. With a typical time resolution of the SPAD pixels of about lns, this allows speeds to be measured with a resolution of about 1 m/s, which is approximately the speed of a pedestrian. At a frame rate of 25 Hz, the speed resolution is about 2.5 m/s, which is approximately the speed of a slow cyclist.
As a result, when an object is detected, an analysis of the detected events is carried out in this way, the arrival times of the repetitions per detector pixel 20a . . . 20n being analyzed as a function of the measurement time M.
The named measurements and evaluations of the individual detector pixels 20a . . . 20n can be carried out in parallel, so that a number of radiation pulses and the corresponding measurements can be carried out simultaneously.
Alternatively, the detector pixels 20a . . . 20n can also be measured and evaluated one after the other. In order to measure speeds, it can be convenient to distribute the repetitions of the individual detector pixels 20a . . . 20n as broadly as possible in time. Instead of carrying out 100 repetitions for a single detector pixel 20a . . . 20n directly one after the other, it may be convenient to carry out measurements and evaluations of a single detector pixel 20a . . . 20n with all provided repetition measurements completely at first, before carrying out the measurement and evaluation of the next detector pixel 20a . . . 20n.
The provided method is advantageously able to distinguish between true velocity measurements and measurements of artifacts that are detected, for example, when another object moves into the signal path in the center of a measurement frame. In this case, the arrival time shows a discontinuity with respect to the measurement time, as is shown as an example in
If the minimum error square value is greater than a predefined threshold value, the system cannot assign a speed to a detected object and in this case can, for example, transmit a signal to a central computing unit, signaling that a detector pixel 20a . . . 20n is showing disturbance. In this way, the proposed lidar device 100 is also capable of providing an item of confidence information for a speed value.
The proposed lidar device 100 may be designed, for example, as an ASIC or FPGA of the detector pixels 20a . . . 20n, which enables an evaluation of the extensive measurement data that is close to the hardware and thus efficient. Alternatively, it is also possible to carry out the evaluation of the data on a central computing unit inside or outside the automated vehicle equipped with lidar device 100. As a result, the proposed method can be realized as a computer program product that is executed on associated computer hardware.
Advantageously, the proposed lidar device 100 can be used in partially or highly automated vehicles (SAE levels 1-5).
In a step 200, a repetitive emission takes place of transmit signals of a transmitting device 10 with at least one laser element 10a . . . 10n.
In a step 210, a reception takes place of receive signals reflected by an object.
In a step 220, an evaluation takes place of the arrival times of the receive signals acquired per detector pixel 20a . . . 20n in relation to transmission times of the transmit signals, a speed of a detected object being ascertained.
In sum, the present invention proposes a lidar sensor and a method for operating a lidar sensor that provides an acquisition of radial speed in a simple manner.
The person skilled in the art will recognize that a large number of modifications are possible without departing from the core of the present invention.
Number | Date | Country | Kind |
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10 2020 213 383.2 | Oct 2020 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2021/076610 | 9/28/2021 | WO |