Patent Grant
11796649
This application claims the benefit of European Patent Application No. 19205601.8, filed on Oct. 28, 2019. The contents of the European Patent Application No. 19205601.8 are hereby incorporated by reference for all purposes.
This disclosure relates to a method as well as to a device for optically measuring distances.
Optical distance measurements, in particular for use in the driverless navigation of vehicles, are known from the prior art. They are based on the time-of-flight (ToF) principle, whereby a scanning sensor, in particular a LIDAR (abbreviation for “light detection and ranging”) is used, which periodically emits measuring pulses, which are reflected on objects, wherein the reflected measuring pulses are detected. From the determination of the time-of-flight of the measuring pulses from the sensor to the objects and back, a conclusion can be drawn to the distance to these objects with the help of the speed of light.
The principle of the ToF-measurements is limited in that measuring pulses have to be emitted with a certain distance from one another, in order to avoid so-called aliasing effects.
Generally, in the case of ToF measurements, twice the time-of-flight has to be awaited until the end of a measuring region, until a previously emitted measuring pulse has theoretically been received again after reflection. If this time is not awaited, a clear assignment of the received measuring pulses is not possible, because the emitting time is uncertain. This limits the possibility of ToF measurements because the time-of flight of the pulse, i.e. the time the measuring pulse needs until it reaches a sensor again, cannot be accelerated. So, in order to scan a large distance region, after the initiation of a measuring pulse, twice the time-of-flight to the possible object, which is farthest away, has to be awaited until a measuring pulse can be output again.
For the maximum detection range, the output energy is further an essential parameter in order to ensure that reflections of distant objects can still be detected.
As a whole, the increase of a likelihood of detection is generally only possible in the prior art by means of an increased time budget or increased energy, respectively. As part of the eye safety, however, a smallest possible peak power of the sent pulses is desirable thereby. A small time budget is also worthwhile, because only then are measuring results are present in a timely manner and can be used for time-critical applications, such as, for example, driving assistance.
DE 10 2016 011 299 A1 describes, for example, the use of encoded pulse sequences in order to avoid above-described ambiguities. However, the detection range also suffers in the case of pulse sequences, because measuring pulses are not detected and a recognition of the sequence is not possible in particular in the case of long distances.
The present solution is based on the object of improving a method as well as a device for measuring distances in such a way that the maximum detection range can be increased without changing the time budget, the peak power of measuring pulses can be decreased without changing the likelihood of detection, and an interference by means of internal or external pulses can be avoided.
The above-mentioned object is solved by means of a method for optically measuring distances, in the case of which a first plurality of measuring pulses is emitted during a first measuring interval by means of a transmitting element of a transmitting unit at first emitting times, and a second plurality of measuring pulses is emitted during a second measuring interval by means of a transmitting element of a transmitting unit at second emitting times. Reflected measuring pulses are received at receiving times by means of a receiving element of a receiving unit, which is assigned to the transmitting element.
The method comprises the determining of a first amount of times-of-flight for each received measuring pulse. The times-of-flight are thereby determined by using the first emitting times. The times determined in this way form the times-of-flight of the first amount. For this purpose, each first emitting time is preferably deducted from the receiving time of each received measuring pulse.
A second amount of times-of-flight is determined in the same way. In detail, the method comprises the determining of a second amount of times-of-flight for each received measuring pulse by using the second emitting times, namely preferably in that each second emitting time is deducted from the receiving time of the respective received measuring pulse.
The emitting times are preferably in each case determined in relation to the start time of the respective measuring interval. The receiving times are preferably determined in relation to the start time of the first measuring interval.
All combinations of receiving times are thus preferably considered at emitting times. Emitting times are thus also deducted from receiving times, which are later in time than said receiving times. This is the case, for example, when the receiving time (in relation to the start time of the first measuring interval) is larger than the emitting time (in relation to the start time of the second measuring interval), even though the emitting time is later than the receiving time. The correct time-of-flight can nonetheless be determined easily and effectively. Difficult and complex comparisons of emitted and received sequences of pulses can thus be forgone.
The method further comprises the creating of at least one histogram for the receiving element, and the entering of the first amount and/or of the second amount of times-of-flight in the histogram. In other words, at least one, in particular exactly one, histogram, can be created for each measuring interval. Measuring intervals can further be entered in a common histogram. Individually created histograms can further be added to form a common histogram.
The present method is carried out in particular by means of a transmitting unit, comprising a plurality of transmitting elements and a receiving unit, comprising a plurality of receiving elements. Each transmitting element of the transmitting unit is in particular assigned to a defined subregion of the measuring region, in other words to a room element of the measuring region. The same applies for the receiving unit. A subregion of the measuring region is likewise assigned to each receiving element. This results in an unambiguous assignment between transmitting elements of the transmitting unit and receiving elements of the receiving unit. From the fact which receiving element thus receives a measuring pulse, a conclusion can be drawn about the position of the reflecting object, on which the measuring pulse was reflected.
A reflected measuring pulse is a measuring pulse, which had been emitted previously, so that its direction of propagation has changed due to the reflection on an object. The reflected measuring pulse can thus be understood as echo of the emitted measuring pulse. The time-of-flight of the measuring pulses to the objects on which they were reflected is determined in particular by means of the method, and the distance to the object covered by the respective measuring pulse is determined from said time-of-flight with the help of the speed of light.
An optical measuring of distances is characterized in that distances are determined by using optical signals, here optical measuring pulses. The term “distance” is to be understood as a range. The distance covered by the measuring pulse is to be understood as the route between the transmitting element which has emitted the measuring pulse and the object which has reflected said measuring pulse, plus the route between the object and the receiving element, which has received the corresponding reflected measuring pulse. The method comprises in particular the consideration of the exact position of the transmitting element and of the receiving element, in particular in relation to one another. Due to the fact that the at least one object is typically a three-dimensional object, so that some regions of the object can be arranged closer, and other regions of the object can be arranged further away, the term “distance to the object” refers to the range to at least one point of the object, namely the point which the measuring pulse has struck and on which said measuring has been reflected. Time-of-flight is to be understood to be the time which the measuring pulse required for the above-described distance.
The method preferably serves for measuring the distance for use in the driverless navigation or driving assistance of vehicles.
A measuring pulse is in particular an electromagnetic, in particular an optical signal. This signal preferably has a wavelength, which does not originate from the region visible for the human eye. For safety reasons, invisible infrared is preferably used. Due to the fact that the measuring pulse is an electromagnetic signal, and the speed of the measuring pulse is thus known, a conclusion as to which route the measuring pulse has covered can be drawn from the time-of-flight of a measuring pulse with the help of the speed of light.
When determining first amounts of times-of-flight, the received measuring pulses are evaluated in a very specific way. In that the receiving times are correlated with all possible emitting times, a multiple compensation takes place, whereby a compensation is to be understood as a shift of the receiving time of a received measuring pulse in the histogram on the basis of an emitting time. In other words, each measuring pulse is compensated by each plausible or possible emitting time, respectively, whereby all results are entered in a histogram.
In this way, exactly one “correct entry” results for each measuring pulse, because the receiving time was compensated with the correct emitting time. However, a plurality of “incorrect entries” results as well, because the receiving time of a measuring pulse was compensated with “incorrect emitting times”, i.e. emitting times of other measuring pulses. Due to the fact, however, that a plurality of measuring pulses was emitted within a measuring region, it is not known, which of these emitting times is correct. This is solved by means of the present method. It increases the entries in the histogram, whereby the entries of the “correct compensations” overlap only at one position. All further times-of-flight, which result due to compensation with “incorrect emitting times”, additionally appear as interference in the histogram symmetrically around this correct position. The first and second amount of times-of-flight for one measuring pulse thus comprise all possible times-of-flight, whereby only one of them is “correct”, because the correct emitting time formed the basis for the determination.
The correct distance to an object on which the measuring pulses were reflected can thus be determined. The method comprises in particular the determination of a distance on the basis of the histogram, which can be assigned in particular to the receiving element. This takes place in particular by means of determination of the time-of-flight at which most entries are present. This corresponds in particular to the “correct” time-of-flight, from which the distance can be determined easily by considering the speed of light.
Due to the fact that a plurality of measuring pulses is emitted, but corresponding ambiguities can be solved unambiguously, the maximum detection range can be increased without changing the time budget and/or the peak power of the measuring pulses is reduced while likewise not changing the likelihood of detection. In particular, the increase of the measuring pulses per time unit increases the likelihood of detection and the signal-to-noise ratio. The present invention is thus able to solve the limitation of the time budget (based, for example, on the requirement on the image sequence for detecting a scene with movement) and the limitation of the energy (based on the eye safety).
The plurality of the measuring pulses emitted within a measuring interval can also be understood as pulse sequence. The term refers in particular to a time sequence of measuring pulses, which is determined by the number of the measuring pulses, the pulse lengths thereof, and in chronological pulse distances between the measuring pulses. In the present method, however, a single time-of-flight is not assigned to the entire pulse sequence, as it is known from the prior art, even if the measuring pulses can be understood as pulse sequence. Instead, each measuring pulse is evaluated individually, and one correct and a plurality of “incorrect times-of-flight” is assigned to the measuring pulse.
The first measuring interval and the second measuring interval are in particular not identical. They preferably each have a start time and an end time, whereby the start times and/or the end times preferably do not coincide.
The first and/or the second measuring interval preferably have a length, wherein the length is adapted to the single length or to the double length of the measuring region. The measuring intervals thus in particular have the same length, wherein the length of the measuring interval is selected in such a way that it corresponds to the time, which a measuring pulse needs to completely pass through the measuring region once (i.e. to the end of the measuring region) or twice (i.e. to the end of the measuring region and back again).
The length of the measuring interval thus corresponds to an emission window, in which measuring pulses are emitted. The detection interval, in which measuring pulses can be received, can start simultaneously with the corresponding, preferably the first, measuring interval.
The length of the detection interval can further correspond to twice or four times the length of the measuring interval. The method comprises in particular the memorization of the emitting times of the measuring intervals, so that receiving times can be correlated with them.
A detection interval can be assigned to each measuring interval. The detection region then overlaps in particular with the following, in particular second, measuring interval or encompasses it completely.
A common detection interval can further be assigned to several measuring intervals, in particular to the first and the second measuring interval. The detection interval then begins with the start time of the first measuring interval and preferably ends after the period of a further measuring interval has also gone by after the end time of the second or last measuring interval.
The first and the second measuring interval can overlap thereby. The start point of the second measuring interval is thus earlier than the end time of the first measuring interval. The first measuring interval and the second measuring interval in particular follow one another directly.
The first measuring interval and the second measuring interval can further be spaced apart from one another in time, can thus not follow one another directly. The start point of the second measuring interval is thus later than the end time of the first measuring interval, whereby the detection interval and the second measuring interval nonetheless at least overlap. In particular, the detection region always comprises the second measuring interval. This means that even though measuring pulses of a measuring interval are still traveling and can still be detected due to the detection interval, which is preferably twice as long, a new measuring interval can already follow with the emission of new measuring pulses. The pulse sequences of adjacent measuring pulses are thus simultaneously “on air”.
The method preferably comprises conducting further measurements in further measuring intervals, wherein adjacent measuring intervals follow one another directly in time.
The histogram in particular comprises the length of the measuring intervals. In particular, only times-of-flight which are larger than 0 and smaller than the length of the measuring interval are entered in the histogram.
An identical number of measuring pulses can in particular be emitted in the measuring intervals, for example a number N. Due to the fact that the measuring pulses emitted during this measuring interval as well as the measuring pulses emitted during the previous measuring interval can be received during a measuring interval, 0 to 2 N measuring pulses can thus be received, wherein N is the number of the emitted measuring pulses per time interval.
Adjacent measuring pulses of the plurality of measuring pulses emitted during a measuring interval can further preferably have a random distance from one another. In particular, the emitting times of the measuring pulses of the first measuring interval and of the second measuring interval or of adjacent measuring intervals can differ. Due to the randomness of the positions of individual measuring pulses during a sequence, the evaluation and thus the determination of the distance is thus robust during the sequences with regard to interferences of own adjacent sequences as well as with regard to interferences from the outside, because they are distributed over the histogram.
Due to the random emitting times, the incorrect entries in the histogram are also distributed randomly, so that the correct entries, which overlap, stand out clearly.
Further preferably, the plurality of measuring pulses emitted during the first or second measuring interval can be encoded. At least two measuring pulses emitted in the first measuring interval or in the second measuring interval thereby differ, in particular by their pulse shape. Each measuring pulse can in particular differ from any other measuring pulse, but only two different encoding states can be possible as well. Measuring pulses can further differ by their pulse length. An encoding state can thus be understood as a pulse shape and/or a pulse length.
Based on the states, one histogram per encoding state can be created, as described above. For this purpose, the method can comprise the memorization of the encoding states of the emitted measuring pulses and the determination of the encoding states of the received measuring pulses. The determination of a first amount of times-of-flight for each received measuring pulse only considers the emitting times of the measuring pulses with the same encoding state. The same applies to the second amount of times-of flight. An independent histogram, in which the times-of-flight of the correspondingly encoded received measuring pulses are entered, is then created for each encoding state. The entries in the respective histograms thus decrease because measuring pulses can already be differentiated on the basis of their encoding states.
The measuring region can preferably be divided into at least one short section, a mid-section, and a far section. The short section is the spatially next section, preferably directly adjacent to a device for carrying out the method, while the far section represents the rearmost section, in other words a section at the end of the measuring region. The mid-section is located therebetween. The first third of the measuring region can, for example, represent the short section, the middle third can represent the mid-section, and the last third can represent the far section. Each receiving element in particular has an imaging region, in particular a photosensitive area, wherein the latter can be divided into different regions, in particular depending on the section of the measuring region, in which the measuring pulse was reflected. Reflected measuring pulses from the short section, the mid-section, and the far section are thus received at different regions of a receiving element.
In other words, a shift of the imaging region is present, at which a pulse occurs on a receiving element, namely as a function of the range of the object, on which the measuring pulse was reflected. The shift results from a parallax error.
A short interval of the measuring interval and a short region of the receiving element can be assigned to the short section, a mid-interval of the measuring interval and a mid-region of the receiving element can be assigned to the mid-section, and a far interval of the measuring interval and a far region of the receiving element can be assigned to the far section. This corresponds to the temporal sections of the measuring interval, into which the corresponding times-of-flight fall in the sections of the measuring interval, which vary in ranges. The first third of the measuring interval can, for example, represent the short interval, the middle third can represent the mid-interval, and the last third can represent the far interval.
The different regions of the imaging region of the receiving element can be controlled separately. The short region of the receiving element can preferably be formed to be less sensitive than the mid-region and the far region of the receiving element. This serves the purpose of preventing a “dazzling” of the short region, for example because a highly reflective object is located in very close range.
The short region, the mid-region, and the far region of the receiving element can be controlled on the basis of the short interval, of the mid-interval, and of the far interval of the first measuring interval. The different regions of the receiving element are in particular activated if and only if the measurement is in the corresponding short interval, mid-interval, or far interval. In detail, the short region is activated during the short interval, the mid-region during the mid-interval, and the far region during the far interval. Elsewhere, the corresponding regions are deactivated.
The control in particular takes place only on the basis of the first measuring interval, wherein the emission of the measuring pulses of the second measuring interval does not have an impact on the activation of the regions. It can be advantageous, however, to deactivate all regions of the receiving element in the corresponding short interval of the second measuring interval, in order to avoid a dazzling.
The second measuring interval can in particular be followed by a third measuring interval, on the basis of which the regions are controlled. Each second measuring interval thus preferably controls the activation or deactivation, respectively, of the regions of the receiving element, while the measuring intervals located therebetween do not influence the control, except for the deactivation of all regions during the corresponding short interval.
By means of the method, the above-mentioned steps are in particular performed for several transmitting elements of a transmitting unit and corresponding receiving elements of a receiving unit, in particular all transmitting elements and receiving elements. In other words, several transmitting elements emit corresponding measuring pulses during a measuring interval at emitting times, and are in each case received by corresponding receiving elements at receiving times, wherein a first amount and a second amount of times-of-flight are then in each case determined for the measuring pulses received by each receiving element. A corresponding histogram is thereby in each case created for all receiving elements.
In a further aspect, the invention relates to a device for carrying out the above-described method. The device is thus formed to carry out a method according to the invention.
The device in particular comprises a transmitting unit and a receiving unit. The transmitting unit in particular comprises transmitting elements, and the receiving unit comprises receiving elements, in particular sensor pixels. The transmitting elements and receiving elements are preferably combined at a transmission matrix or a receiving matrix, respectively. A matrix can in particular be understood as three-dimensional, in particular plate-shaped, body, on the one surface of which the corresponding elements are arranged.
The device is in particular a scanning device, preferably a LIDAR sensor. In each case, the transmitting elements are preferably a laser, in particular VCSEL. The transmitting elements can further be laser diodes, fiber lasers, or LEDs. The transmitting elements can further comprise addressable liquid crystals. The transmitting unit can further be an optical phased array. The transmitting elements can be controlled individually.
The receiving elements are in particular linear or non-linear detectors, in particular in the form of an array, preferably a focal plane array, in particular an ADP array, most preferably a SPAD array. The array can further comprise quantum film structures based on quantum dots.
The receiving elements can be individually controlled or activated, respectively. Each receiving element in particular comprises different regions, in particular a short region for receiving measuring pulses from a short section of the measuring region, a mid-region for receiving measuring pulses from a mid-section of the measuring region, and a far region for receiving measuring pulses from a far section of the measuring region. The different regions can be individually controlled or activated, respectively, and evaluated.
Further preferably, the device comprises at least one evaluating unit, which is preferably formed to determine the first amount and second amount of times-of-flight, and to create a histogram. The evaluating unit can further be configured to read a distance from the histogram.
The device can further comprise a control unit, which is configured to control the transmitting unit, the receiving unit, and the evaluating unit.
The present invention further relates to a computer program product, which comprises a computer-readable storage device, on which a program is stored, which, after it was loaded into the memory of the computer, makes it possible for a computer to carry out an above-described method, optionally together with an above-described device. The invention furthermore relates to a computer-readable storage device, on which a program is stored, which, after it was loaded into the memory of the computer, makes it possible for a computer to carry out an above-described method, optionally together with an above-described device.
A process diagram of a method 100 according to the invention is illustrated in
The method 100 comprises the emitting 101 of a first plurality of measuring pulses 13 during a first measuring interval 10 at first emitting times, and the emitting 101 of a second plurality of measuring pulses 13 during a second measuring interval 11 at second emitting times. The method 100 comprises the reception 103 of reflected measuring pulses by means of a receiving element of a receiving unit assigned to the transmitting element at receiving times.
Beforehand, a short region of the receiving element and a short interval of the corresponding measuring interval can thereby be assigned to a short section of the measuring region. A mid-interval of the measuring interval and a mid-region of the receiving element can further be assigned to a mid-section of the measuring region, and a far region of the receiving element and a far interval of the measuring interval can be assigned 104 to a far section of the measuring region. The short region, the mid-region, and the far region can be controlled 105 on the basis of the short interval, of the mid-interval, and of the far interval of the first measuring interval 10.
The method 100 comprises the determining 106 of a first amount of times-of-flight and the determining 107 of a second amount of times-of-flight for each received measuring pulse. The method 100 further comprises the creating 108 of a histogram for the receiving element, and the entering of the first amount and/or second amount of times-of-flight in the histogram 15. The method can further comprise the determining 109 of a distance from the histogram 15.
The creating of a histogram 15 of a first measurement of a first measuring interval 10 after receipt of two measuring pulses 13, of a first measuring pulse 13a and of a second measuring pulse 13b, is illustrated in a simplified manner in
The emitting times of the two measuring pulses 13 can be seen clearly in
The histogram 15, which plots entries 16 over the time 12, from the start of the first measuring interval 10, is shown in
The short arrows on the bottom side of the histogram 15 show a shift of these “uncorrected positions by the first emitting time 14a of the first measuring pulse 13a. The above-illustrated longer arrows show the respective shift 19 by the second emitting time of the second measuring pulse 13b. The shifts ensure a compensation with regard to the different emitting times. In other words, all possible emitting times are considered in that they are deducted from the receiving times. The shaded entries are not entered, while the other times-of-flight determined by the compensations are entered. As a whole, four times-of-flight are thus determined, which form the first amount of times-of-flight, and which are entered at the respective positions. It can be seen clearly how two entries, namely in each case one based on the receipt of the first measuring pulse 13a, and one based on the receipt of the second measuring pulse 13b, overlap at one position. This marks the correct time-of-flight 20, while the incorrect times-of-flight 21 are distributed symmetrically around the correct time-of-flight 20 in the histogram 15.
A second measurement of a second measuring interval 11 is shown in
It is shown in
It can be seen clearly again, how an entry based on both measuring pulses in each case overlaps at the correct position of the time-of-flight, while all other entries are distributed symmetrically around them. Due to the compensation with regard to the emitting times of the measuring pulses of the same measuring interval, a first amount is formed, wherein a second amount of times-of-flight is formed compared to the emitting times of the previous measuring interval.
The histograms 15 of the different measurements of
An overlapped histogram 15 of the two measurements is shown in
| Number | Name | Date | Kind |
|---|---|---|---|
| 9268013 | Rieger | Feb 2016 | B2 |
| 10466342 | Zhu | Nov 2019 | B1 |
| 20130148101 | Yoo | Jun 2013 | A1 |
| 20170329010 | Warke | Nov 2017 | A1 |
| 20180203122 | Grauer | Jul 2018 | A1 |
| 20180259645 | Shu | Sep 2018 | A1 |
| Number | Date | Country |
|---|---|---|
| 10 2016 011 299 | Mar 2018 | DE |
| 10 2017 208 704 | Nov 2018 | DE |
| 102017208704 | Nov 2018 | DE |
| 2012135874 | Oct 2012 | WO |
| Entry |
|---|
| European Search Report issued for corresponding European Patent Application No. EP 19205601, dated Apr. 27, 2020, 2 pages, Munich, Germany. |
| Number | Date | Country | |
|---|---|---|---|
| 20210124027 A1 | Apr 2021 | US |
