WO2018215251A1

WO2018215251A1 - Apparatus and method for distance measurement

Info

Publication number: WO2018215251A1
Application number: PCT/EP2018/062641
Authority: WO
Inventors: Reiner Schnitzer; Tobias Hipp
Original assignee: Robert Bosch Gmbh
Priority date: 2017-05-23
Filing date: 2018-05-16
Publication date: 2018-11-29
Also published as: DE102017208704A1

Abstract

Apparatus (100) for distance measurement, comprising: an optical transmitting device (10, 20, 30, 40, 50); an optical receiving device (10, 60, 70); and a random generator device (80), which is functionally connected to the optical transmitting device (10, 20, 30, 40, 50) and to the optical receiving device (10, 60, 70); wherein the optical transmitting device (10, 20, 30, 40, 50) is driven in a pulsed manner by means of the random generator device (80) in such a way that an optical transmission signal (S) is emittable by means of the optical transmitting device (10, 20, 30, 40, 50) per partial measurement cycle (tp), wherein in each partial measurement cycle (tp) a start time (t1...tn) of the transmission signal (S) is changeable by means of the random generator device (80).

Description

Description title

Device and method for distance measurement

The invention relates to a device for distance measurement. The invention further relates to a method for distance measurement. The invention further relates to a computer program product.

State of the art

Methods which send (pseudo-randomly) coded sequences of light pulses instead of single pulses are known. For the detection in the receiver, the received pulse sequence with the transmitted pulse sequence, e.g. correlated using a matched filter. This has the positive effect that the interference immunity compared to other parallel operated lidar systems increases, since the sensor is ideally only sensitive to the own sent pulse sequence, but not for pulses from other systems.

DE 10 2004 037 137 A1 discloses a method for distance measurement, in which an object is illuminated with intensity-modulated electromagnetic radiation and the intensity of the radiation reflected and / or scattered by the object is detected with at least one detector in a time-sensitive or phase-sensitive manner.

US 2010/0045965 A1 discloses a lidar system using a pseudorandom pulse sequence in which a pseudo-random sequence of light pulses is emitted within individual partial measurements.

It is an object of the invention to provide an improved distance measuring device. According to a first aspect, the invention provides a device for

Distance measurement, comprising:

an optical transmitter;

an optical receiving device; and

a random generator means operatively connected to the optical transmitter means and to the optical receiver means; in which

by means of the random generator means the optical transmitting device is pulsed so controlled that by means of the optical transmitting device per Teilmesszyklus an optical transmission signal is emitted, wherein in each Teilmesszyklus a start time of the transmission signal by means of the random number generator is changeable.

In this way, a device for distance measurement with increased immunity to interference is advantageously provided. This is achieved by using all the possible energy of a partial measurement for one pulse. An interference immunity is advantageously increased compared to known sensors because emitting sensors located in the environment do not affect the sensor itself.

According to a second aspect, the object is achieved with a method for operating a device for distance measurement, comprising the steps:

Pulsed driving of an optical transmitting device by means of a random generator device, wherein the optical transmitting device is controlled such that by means of the optical transmitting device per Teilmesszyklus a pulse-shaped optical transmission signal is emitted, wherein in each Teilmesszyklus a start time of the optical transmission signal is changed;

Receiving an optical reception signal by means of an optical reception device; and

Processing of the optical received signal by means of a signal processing device, wherein a runtime of the signals

Distance to the object is determined.

Preferred embodiments of the device are the subject

dependent claims. An advantageous development of the device is characterized in that a pulse repetition frequency corresponding to the start times is constant on average. In this way, objects can be detected in defined ranges by means of an average constant pulse repetition frequency.

Further advantageous development of the device are characterized in that a signal processing device for an optical received signal is at least one of: optimum filter, maxium search device, center of gravity calculation device. In this way, several alternative

Signal processing methods are carried out, by means of a

Optimal filters the best signal / noise ratio can be provided.

A further advantageous development of the device is characterized in that the optical transmitting device has a laser as the radiation element. In this way, the device for a variety of technical

Used purposes, especially in the automotive sector and / or in the tool area.

A further advantageous development of the device is characterized in that the device is a lidar sensor. In this way, a useful application for the device in the automotive field is provided.

The invention will be described below with further features and advantages with reference to several figures in detail. Same or functionally identical components have the same reference numerals. The figures are intended in particular to clarify the principles essential to the invention. For better clarity, it can be provided that not all the figures in all figures are marked.

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 device for distance measurement result analogously from corresponding embodiments, features and advantages of the method for operating a device for measuring distance, and vice versa. In the figures shows:

Fig. 1 is a schematic representation of an operation of a

conventional method for distance measurement;

Fig. 2 is an adverse effect of the conventional method of Fig. 1;

Fig. 3 is a schematic representation of an operation of an embodiment of a proposed method for

Distance measurement;

4 shows a basic representation of a conventionally coded sequence of pulses for distance measurement; a schematic representation of an embodiment of the proposed method with variable pulse start times within a Teilmesszyklus; a schematic block diagram of an apparatus for

Distance measurement; and

Fig. 7 is a schematic representation of an embodiment of a

Method for operating a device for distance measurement.

Description of embodiments

A key idea of the present invention is, in particular, to provide a more robust device for distance measurement.

It is proposed to use a variable Wederholfrequenz instead of a fixed pulse repetition frequency in order to resolve a time base between own and possible other interfering devices (eg Lidar sensors). This advantageously provides a maximum range of a non-coded system with simultaneously increased interference immunity.

The proposed device is constructed like a typical pulsed lidar sensor, wherein a measurement consists of several pulse repetitions (partial measurements) (multipulse lidar). The measured time of arrival of the reflected light pulse from the partial measurements are sorted into a histogram with which after several (typically 10 ... 500) repetitions using appropriate signal processing (eg maximum search, center of gravity calculation, matched filter, etc.) Position of the received pulse and thus the time of flight or the distance to the object is determined.

A special feature of the proposed method is that the partial measurements are repeated not with a fixed but with a variable (for example, pseudo-noise modulated) frequency. However, times of the pulse emissions are always known to the sensor, whereby a fixed time base is still ensured for the measurement, whereas the time base between the sensor and other interfering optical systems is resolved and thus a disturbing effect is eliminated.

This advantageously leads to the fact that light pulses which are sent by a disturbing sensor are sorted in a different position in the histogram in each partial measurement and thus no accumulation is formed. The actual light pulses of the system are still due to the time correlation for each

Cumulative partial measurement in the same place in the histogram, so that the measuring capability of the sensor is unaffected, while the immunity to interference is increased compared to a conventional pulsed lidar sensor. 1 shows by way of example the pulse sequence of a conventional multipulse lidar

Sensor with a fixed pulse repetition rate tR. The emitted measuring pulses are detected after a flight time tr and sorted accordingly into a histogram shown in the lower section of FIG. 1. After several repetitions, the histogram shows an accumulation of detections corresponding to the target distance to be measured. Furthermore, randomly distributed misdetections due to background light or other noise are to be expected. FIG. 2 shows an adverse effect of the configuration of FIG. 1, with another interfering lidar sensor present in the measurement scenario. Due to the fixed pulse repetition rate of both lidar sensors, the interfering light pulses Est of the second lidar sensor are always accumulated at the same point in the histogram, for which reason the subsequent signal processing recognizes a decoupling target at this point. Thus, in the histogram due to the disturbing light pulses Est, object detection occurs, although in the measurement scenario no real object exists at this point. This problem can become significantly larger with increasing number of external sensors in the environment of the own sensor.

If, instead of a single pulse, a coded sequence of light pulses with the same energy is emitted, the immunity to interference increases but the range of the system decreases. This is shown schematically in FIG. 3, which shows a transmission scheme of optical transmission signals with pseudo-randomly coded pulse chains known from US 2010/0045965 A1.

It can be seen that, although a random sequence of individual pulses is emitted within a partial measurement, these have a reduced intensity, because eye safety always has to be guaranteed and, as a result, an energy of the pulses must not be exceeded. The entire optical

Transmission energy is thus distributed in each case to all individual pulses within a partial measurement cycle tp, whereby a maximum range can be considerably limited. Recognizable is a measuring cycle tM, which is subdivided into individual partial measuring cycles tp.

It can be seen that in the individual partial measuring cycles tp a grid of the measuring pulses is identical, with starting times of the measuring pulses being the same in each case. This is indicated for the first pulse with the start time ti, t2 and t3, which are identical in each case. Thus, the total transmission energy is divided within a Teilmesszyklus tp on several pulses whose height is indicated by "1".

Fig. 3 shows a conventional sequence of pulse sequences, which are performed in several partial measurements. In this case, a total measurement duration TM comprises a defined number of individual measurement cycles tp. It can be seen in FIG. 3 that within the partial measurements in each case five pulses are sent, each of which is the same Timing scheme have. In the case of a new overall measurement, the sequence of pulses in the partial measuring cycles tp can in turn be varied.

4 shows a principal mode of operation of an embodiment of the proposed method.

It is provided that the lidar sensor operates with a variable pulse repetition frequency. Due to the fact that the measurement of the sensor is now started at different times in relation to a start of a partial measurement cycle tp, the disturbance measurement pulse Est received in the fixed grid is distributed in the histogram in different time slots, whereby advantageously no accumulation occurs. Since the sensor is always aware of the start times of the respective own measurements, the time correlation for the own measuring pulses still exists. For the target to be measured so there is still an accumulation in the histogram, which is why a correct object detection at the same time

Noise suppression is possible.

In Fig. 5 it can be seen that the proposed method provides that in the individual partial measuring cycles tp only a single pulse is sent, but this maximum possible energy. It can be seen that the individual pulses have approximately five times the amplitudes of those of the individual pulses in the conventional partial measuring cycles tp according to FIG. 3.

This makes it possible that a maximum range per pulse is achievable and there can be no interference with other sensors. Within the individual partial measurements, the beginning of the pulse varies according to mathematical principles, which is indicated by three different offset times ti, t ₂ , t3 from the beginning of the respective partial measuring cycle tp. The aforementioned offset times ti, t ₂ , t3 are also known to the detector, so that now no disturbing influence of harmful opposing lidar sensors can occur because fictitious targets can not add up in a histogram. As a result, a random modulation of the pulse start times within the partial measurement cycles tp is thereby realized. On average, a pulse repetition frequency is preferably constant, with a pulse repetition frequency of approximately 700 kHz to approximately 800 kHz being set for distance measurements in the automotive sector with a range of approximately 200 m. Fig. 6 shows a highly simplified block diagram of an embodiment of the

Device 100 for distance measurement of objects. The device 100 comprises a control element 10 (time-of-flight controller) which comprises a driver element 20 for a radiation element 30 (eg light source in the visible range, laser, in particular in the form of a solid-state laser, a laser diode, eg a near IR Laser diode). The radiating element 30 emits an optical transmission signal S in the form of optical pulses through a transmission lens 40 onto an object 200. A random number generator 80 is provided which determines the transmission times ti ... t _{n of} the transmission pulses within the partial measurement cycles tp pseudorandom or according to another suitable random principle determines and provides.

Via a reference detector 50, which is usually realized via a parasitic reflection path within the device, a part of the transmission signal S is fed to the control element 10, so that the control device 10 is always informed about the offset times ti ... t _n . The optical

Receiving signal E is fed via a receiving lens 60 to a detector element 70, wherein the detector element 70 is functionally connected to the control element 10. Final signal processing is carried out by means of a signal processing device 90 which is functionally connected to the control element 10 and which is preferably as an optimum filter, a maximum search device or a center of gravity calculation device or another suitable element.

FIG. 7 shows a basic sequence of an embodiment of the proposed method for operating a device 100 for distance measurement.

In a step 200, a pulsed driving of an optical transmitting device is carried out by means of a random-generator device, wherein the optical transmitting device is controlled such that by means of the optical transmitting device per Teilmesszyklus a pulse-shaped optical transmission signal is emitted, wherein in each part measuring cycle, a start time of the optical transmission signal is changed.

In a step 210, reception of an optical reception signal is performed by means of an optical reception device.

In a step 220, a processing of the optical received signal is carried out by means of a signal processing device, wherein a distance to the object is determined from a transit time of the signals.

Advantageously, the proposed method can be as a software

implemented on the control element 10 of the device for

Distance measurement takes place, whereby a simple adaptability of the method is supported.

Although the invention has been described above mainly with reference to a distance measuring device designed as a lidar sensor, it goes without saying that the method according to the invention is not bound to a specific type of optical radiation element and that the proposed method comprises a multiplicity of distance measuring devices Form of pulsed direct-time-of-flight sensors.

The person skilled in the art therefore recognizes that a large number of modifications of the invention is possible without departing from the essence of the invention.

Claims

claims

1. Device (100) for distance measurement, comprising:

an optical transmitter (10, 20, 30, 40, 50);

an optical receiving device (10, 60, 70); and

a random number generator means (80) operatively connected to the optical transmitter means (10, 20, 30, 40, 50) and to the optical one

Receiving means (10, 60, 70) is connected; in which

the optical transmitting device (10, 20, 30, 40, 50) can be driven in a pulsed manner by means of the random-number generator device (80) such that an optical transmission signal (10, 20, 30, 40, 50) is provided per partial measuring cycle (tp). S) is emissable, wherein in each partial measuring cycle (tp) a starting time (ti ... t _n ) of the transmission signal (S) by means of the random generator means (80) is changeable.

2. Device (100) according to claim 1, characterized in that a start times (ti ... t _n ) corresponding pulse repetition frequency is constant on average.

3. Device (100) according to claim 1 or 2, characterized in that a signal processing device (90) for an optical received signal is at least one of: optimum filter, Maxiumsucheinrichtung, center of gravity calculation device.

4. Device (100) according to one of the preceding claims, characterized

in that the optical transmission device (10, 20, 30, 40, 50) has a laser as the radiation element.

5. Device (100) according to claim 4, characterized in that the

Device (100) is a lidar sensor.

6. A method for measuring a distance of an object (200), comprising the steps of:

Pulsed driving of an optical transmitting device (10, 20, 30, 40, 50) by means of a random generator device (80), wherein the optical transmitting device (10, 20, 30, 40, 50) is controlled such that by means of the optical transmitting device (10, 20, 30, 40, 50) per

Teilmesszyklus (tp) a pulse-shaped optical transmission signal (S) is emitted, wherein in each partial measuring cycle (tp) a start time (ti ... t _n ) of the optical transmission signal (S) is changed;

Receiving an optical reception signal (E) by means of an optical reception device (10, 60, 70); and

Processing of the optical received signal (E) by means of a signal processing device (90), wherein a distance to the object (200) is determined from a transit time of the signals (S, E).

Computer program product with program code means for carrying out the method according to claim 6, when it runs on a control device (10) or is stored on a computer-readable data medium.