DE102016006776A1 - Device and method for unambiguous distance measurement with modulated LIDAR - Google Patents

Device and method for unambiguous distance measurement with modulated LIDAR

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Publication number
DE102016006776A1
DE102016006776A1 DE102016006776.4A DE102016006776A DE102016006776A1 DE 102016006776 A1 DE102016006776 A1 DE 102016006776A1 DE 102016006776 A DE102016006776 A DE 102016006776A DE 102016006776 A1 DE102016006776 A1 DE 102016006776A1
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DE
Germany
Prior art keywords
light
transit time
characterized
position
preceding
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
DE102016006776.4A
Other languages
German (de)
Inventor
Anmelder Gleich
Original Assignee
Kai Wolf
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kai Wolf filed Critical Kai Wolf
Priority to DE102016006776.4A priority Critical patent/DE102016006776A1/en
Publication of DE102016006776A1 publication Critical patent/DE102016006776A1/en
Application status is Withdrawn legal-status Critical

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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/497Means for monitoring or calibrating
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06Systems determining position data of a target
    • G01S17/08Systems determining position data of a target for measuring distance only
    • G01S17/32Systems determining position data of a target for measuring distance only using transmission of continuous unmodulated waves, amplitude-, frequency-, or phase-modulated waves
    • G01S17/36Systems determining position data of a target for measuring distance only using transmission of continuous unmodulated waves, amplitude-, frequency-, or phase-modulated waves with phase comparison between the received signal and the contemporaneously transmitted signal
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06Systems determining position data of a target
    • G01S17/42Simultaneous measurement of distance and other co-ordinates
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06Systems determining position data of a target
    • G01S17/46Indirect determination of position data

Abstract

A light transit time scanner for detecting the geometry of a scene by determining the light transit time, comprising a transmitting element (7) emitting a modulated light beam which moves in a continuous scanning motion to measure at least one object (4) in the scene and one Receiving element (1) which receives light reflected from the object (4) and emits electrical signals, characterized in that the receiving element (1) has a lateral extent and emits one or more dependent on the position or the angle of the incident light electrical signals and is arranged so that the position or the angle of the received light by the scanning movement of the duration of the light and thus the distance of the or just measured objects (s) (4) is dependent.

Description

  • The invention relates to a light transit time scanner which detects the geometry of a scene by determining the light transit time.
  • description
  • Under the term LIDAR optical scanners are known which gain distance information by means of light propagation time. In particular, pulse methods (eg. DE 10 2009 057 104B4 or DE 3429062C2 ) and modulating methods (e.g. EP 1 160 585 A2 ) known. Both methods have their specific advantages and disadvantages.
  • The pulse method has the following advantages: clear measurement over the entire measuring range. With appropriate evaluation multi-target detection is possible. The disadvantages are the very high time requirement for the components used. Times must be mastered in the ns range, both on the transmitting side and on the receiving side. Although there are some technical optimizations, all electronics are always the limiting factor in achieving greater accuracy. Furthermore, the individual pulses must always have a sufficiently large time interval from one another to obtain no ambiguity even at maximum object distance. This can be particularly problematic when used outdoors, since a well-reflective object often returns a signal at a very great distance.
  • The modulating methods have the following advantages: good accuracy and that the required bandwidth both in the transmitting branch and in the receiving branch is essentially determined by the wavelength used (eg 30 MHz for a wavelength of 10 m with a sine modulation). In addition, the selectivity to external light influences by the demodulation is extremely good. Basically, a continuous operation is possible, but not necessary. The transmission power can be adapted to the reception range with simple methods. The disadvantages are the ambiguity in the fields of measurement, which are greater than the wavelength, as well as the lack of multi-target capability.
  • The indicated in claim 1 invention is based on the problem of eliminating the restriction of ambiguity and the non-possible multi-target capability of the modulating process.
  • The solution according to the invention is listed in claim 1.
  • A device and the associated method for the determination of multiple distance values with the aid of the light transit time is described. The modulated light beam is guided over the scene in a continuous scan movement. The distance determination is carried out simultaneously with two different methods. On the one hand by a known modulation of intensity. From this, the distance can be determined with a phase algorithm, but not absolutely unambiguously, but only clearly within a wavelength of the modulation frequency used. The second determination method utilizes the fact that the reception angle of the reflected light is increased by the scanning movement (eg with the aid of an oscillating mirror) as a function of the transit time. By means of a suitable receiving element, it is therefore also possible to carry out a distance measurement, albeit less accurate, from the lateral deviation. As long as the accuracy is sufficient to resolve the ambiguity of the first distance measurement, the method can easily overcome the respective disadvantages (ambiguity or inaccuracy) and thus represent an accurate and at the same time absolute measurement method. Furthermore, some technical implementation options are described.
  • The drawing shows in
  • 1A to 1C emitting a light beam and receiving the reflected light,
  • 2 a receiving element, and
  • 3 an array of single-capture elements.
  • The arrangement according to the invention initially corresponds to that of a known scanning LIDAR with modulated light. This consists essentially of a transmitting element 7 and a receiving element 1 , The transmitting element can be a coherent (laser) or an incoherent (eg LED) light source. The inventive idea is that the receiving element 1 has a lateral extent and one or more depending on the position or the angle of the incident light emitting electrical signals and is arranged so that the position or the angle of the received light by the scanning movement of the duration of the light and thus the removal of the or the object being measured (s) 4 is dependent. The functionality is in 1 shown schematically. At time t 1 , the deflection, represented here by a designed as a vibrating mirror 3 , at the angular position φ 1 . The observed point of light is currently at the mirror 3 and becomes in the direction of the measuring object 4 distracted. At the time t 2 at the Point of light on the object ( 4 ) arrives the mirror is already further deflected in the angular position φ 2 . At time t 3 , the reflected light spot hits the mirror again 3 back. This is now in the angular position φ 3 . In the further course the point on the receiving element becomes 1 detected by the position dx compared to the stationary mirror moved. The deviation dx can be measured directly and provides a second possibility for determining the depth of the object 4 ,
  • The advantage described in claim 2 is now that two different methods for depth measurement can be performed simultaneously with only one transmitting element and only one receiving device. The disadvantage of the ambiguity of the modulated method can thus be eliminated without reducing the advantages. Although the achieved accuracy of the depth measurement by the deflection dx will generally be significantly lower than the phase measurement accuracy, it must only be sufficiently good to eliminate the ambiguity of the pure phase measurement. Specifically, this can be done as follows: the relatively inaccurate depth measurement by measuring dx is expressed in multiples of the wavelengths of the modulation. Now round to the nearest integer n. The measurement result is now the sum of depth measurement of the phase difference plus n times the wavelength. The measurement itself thus has the accuracy of the pure phase measurement with simultaneous absolute distance determination.
  • Some possible embodiments of the scanning process are specified in claim 3. In order to carry out the scanning movement, either the entire scan head can basically be moved or the light beam is deflected by means of a moving mirror. The movement can be continuously rotating or oscillating. Oscillating mirrors, rotating oblique mirrors, polygon wheels or micromechanical mirrors or mirror arrays come into question as possible embodiments of the moving game gel.
  • An advantageous embodiment of the invention is specified in claim 4. Since the deflection dx is usually very small (order of magnitude μm), the measurement accuracy achieved thereby can be achieved by an adapted magnifying optics 2 be increased. This can be embodied for example as a lens, lens system or mirror element such as cylindrical mirror or as a diffractive optical element. With coherent optical illumination, an interference element can also be used.
  • An advantageous embodiment of the invention is specified in claim 5. Since the measuring arrangement simultaneously allows two separate distance measurements, the distance measurement can be carried out temporarily or permanently with only one of the two possibilities, with the respective disadvantages. The decision can be made individually for each measuring point. For example, if the detector is overdriven and therefore no good demodulation of the phase position is possible, the distance measurement can be accessed by means of dx to determine an albeit more inaccurate distance value. For further evaluation, the estimated measuring accuracy can be added to the measured values.
  • An advantageous embodiment of the invention is specified in claim 6. In order to produce the highest possible contrast for a given average light output, for example due to technical limitations or regulatory (eye safety) conditions, the output of the modulated light signals with the transmitting element 7 only temporarily with correspondingly higher performance. This increases the external light distance and at the same time produces a less lateral extended measured value expansion. This can lead to an improvement of the individual measurement, in particular for small objects or for objects which are observed to be highly tangential, since the changes in distance integrated within the measuring point are smaller. This can be done so far that a strong pulse-shaped transmission signal is used.
  • An advantageous embodiment of the receiving element 1 is specified in claim 7. As in 2 sketched the receiving element ( 1 ) as an analog "position sensitive device" (PSD), such as a lateral diode. Here, an optical element is described which, in the one-dimensional case, provides two output signals. The amplitude of the signals indicates the position of the received light in relation to the respective side of the element. The sum of the two signals is independent of the position and can be advantageous for the determination of the phase position by means of a phase detector 5 be used. The phase detector described here determines the phase difference and the intensity I of the received signal with the aid of a reference phase predetermined by the modulation, for example by demodulation. Accordingly, from the difference of the two signals with a demodulator 6 the location dx of the received light can be determined.
  • An advantageous embodiment of the receiving element 1 is specified in claim 8. As in 3 outlines the receiving element 1 be constructed as an array of individual receiving elements. In this case, the demodulation of the phases and amplitude modulation, for example, with a photonic mixer detector (PMD, DE19704496C2 ) Element done or by separate phase detectors 5 , A conventional one- or two-dimensional PMD array can also be used. An essential advantage of this arrangement is the possible multi-target capability in the case of separate evaluation of individual photosensitive elements. Since the light transit time due to the scanning movement leads to a spatial separation of the signals reflected at different distances, a measured value including the modulation amplitude (correlated with the accuracy or probability of a target object) can be calculated in each photosensitive element. This makes the system multi-target capable.
  • An advantageous embodiment in order to compensate for mechanical or electronic inaccuracies, for example assembly inaccuracies or temperature drifts, is specified in claim 9. In order to be able to automatically compensate inaccuracies of whatever kind, known reference surfaces (calibration targets) can be applied in the scanner. During the regular scanning process, these calibration targets are also measured and can be used for a computational compensation of the actual measured values. Depending on the selected distribution of the calibration targets, this can be done for a mathematical compensation model or individually for each measured value position. The calibration target (s) may be laterally distributed, for example before the first and after the last measured value. However, they can also be distributed over a larger or the entire angular range as individual calibration targets, for example, in each case between two provided measured values. The exit area of the scanner would then be covered by the calibration targets, such as through a sieve. If, for example, the light output has been throttled in a targeted manner due to the eye safety, then in this case it can be raised again so far that the mean beam power in the outer area again meets the safety requirements. Furthermore, alternatively or additionally, a spatially extended, advantageously the entire angular range comprehensive, partially reflecting interface in the scanner can be used as a reference. The reflectance should be chosen so that the objects to be measured provide a much stronger signal and thus the reference measurement only comes into effect in areas without an object to be measured. In the case of a multi-target scanner, the first distance range can also be completely occupied by the reference measurement. Even in the case of an extended reference target, the light output can possibly be increased as far as the application allows.
  • An advantageous embodiment of the invention is specified in claim 10. Since the measurement is based on the determination of the light transit time, this is for one or more measured object (s) 4 known. In a continuous or at least short-term continuous operation of the measurement time t may be 1, having at which the measured light beam leaving the scanner, are calculated back by the measured time of flight. With this knowledge, the original angle φ 1 at which the light beam has left the scanner can also be determined. This angle can be used to improve the accuracy in place of the angle of the received light. As a result, the angle error is compensated by the light transit time.
  • LIST OF REFERENCE NUMBERS
  • 1
    receiving element
    2
    optics
    3
    mirror
    4
    object
    5
    phase detector
    6
    demodulator
    7
    transmitting element
  • QUOTES INCLUDE IN THE DESCRIPTION
  • This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.
  • Cited patent literature
    • DE 102009057104 B4 [0002]
    • DE 3429062 C2 [0002]
    • EP 1160585 A2 [0002]
    • DE 19704496 C2 [0019]

Claims (10)

  1. Light transit time scanner for detecting the geometry of a scene by determining the light transit time, with a transmitting element ( 7 ) which emits a modulated light beam which moves in a continuous scanning motion to at least one object ( 4 ) in the scene and a receiving element ( 1 ), that of the object ( 4 ) receives reflected light and emits electrical signals, characterized in that the receiving element ( 1 ) has a lateral extent and emits one or more electrical signals dependent on the position or the angle of the incident light and is arranged so that the position or the angle of the received light by the scanning movement of the duration of the light and thus the removal of the light or the object (s) being measured ( 4 ) is dependent.
  2. The light transit time scanner according to claim 1, characterized in that the evaluation of the object distance is effected by the determination of the phase difference between emitted and received light, the ambiguity of the phase measurement being determined by the simultaneous determination of the position or the angle of the received radiation on the receiving element ( 1 ) is resolved.
  3. Light transit time scanner according to one of the preceding claims, characterized in that the scanning movement by a movable mirror ( 3 ), which can be embodied, for example, as a vibrating mirror, as a rotating inclined mirror, as a polygonal wheel or as a micromechanical mirror or mirror array, with a fixed transmitting element (FIG. 7 ) and fixed receiver ( 1 ) or that the scanning movement is realized by a sensor head rotating or oscillating as a whole.
  4. Light transit time scanner according to one of the preceding claims, characterized in that the image of the received light on the receiving element ( 1 ) by an optic ( 2 ) is increased.
  5. Light transit time scanner according to one of the preceding claims, characterized in that the object distance temporarily, for. B. with overdriven receiver, or permanently with possibly reduced accuracy exclusively by the position or angle determination of the receiver ( 1 ) is carried out; Alternatively, the distance measurement temporarily or permanently, z. B. are performed at known small object distances exclusively by the phase measurement, for which purpose a suitable wavelength of the modulation is selected.
  6. Light transit time scanner according to one of the preceding claims, characterized in that the transmitting element ( 7 ), the modulated light signals not continuously but only temporarily surrenders, in which case advantageously at the same average transmission power, the power in the active time can be increased accordingly.
  7. Light transit time scanner according to one of the preceding claims, characterized in that the receiving element ( 1 ) provides a continuous position dependent signal (PSD - Position Sensitive Detector) such. B. a lateral diode.
  8. Light transit time scanner according to one of the preceding claims, characterized in that the receiving element ( 1 ) consists of several receiving sub-elements, with the aid of which the position determination can be performed and / or the individual receiving sub-elements are evaluated separately with respect to their phase position, so as to achieve a multi-targeting capability of the scanner.
  9. Light transit time scanner according to one of the preceding claims, characterized in that one or more individual known reference areas are applied within the scanner to compensate for the temperature drift or other mechanical or electrical deviations; Alternatively, the reference can also be spatially extended by a partially reflective material, which either reflects so weakly that an object to be measured provides a much stronger signal, or which lies in the multi-target capability of the scanner within the first distance range.
  10. The light transit time scanner according to one of the preceding claims, characterized in that, in order to improve the geometric accuracy, the angle φ is corrected by means of the measured distance.
DE102016006776.4A 2016-05-25 2016-05-25 Device and method for unambiguous distance measurement with modulated LIDAR Withdrawn DE102016006776A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
DE102016006776.4A DE102016006776A1 (en) 2016-05-25 2016-05-25 Device and method for unambiguous distance measurement with modulated LIDAR

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE102016006776.4A DE102016006776A1 (en) 2016-05-25 2016-05-25 Device and method for unambiguous distance measurement with modulated LIDAR

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3429062C2 (en) 1984-08-07 1988-10-06 Erwin Sick Gmbh Optik-Elektronik, 7808 Waldkirch, De
DE19704496C2 (en) 1996-09-05 2001-02-15 Rudolf Schwarte Method and apparatus for determining an electromagnetic wave of the phase and / or amplitude information
EP1160585A2 (en) 2000-05-31 2001-12-05 Sick Ag Method of rangefinding and rangefinder
DE102009057104B4 (en) 2009-12-04 2014-05-28 Sick Ag Distance measuring laser scanner

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3429062C2 (en) 1984-08-07 1988-10-06 Erwin Sick Gmbh Optik-Elektronik, 7808 Waldkirch, De
DE19704496C2 (en) 1996-09-05 2001-02-15 Rudolf Schwarte Method and apparatus for determining an electromagnetic wave of the phase and / or amplitude information
EP1160585A2 (en) 2000-05-31 2001-12-05 Sick Ag Method of rangefinding and rangefinder
DE102009057104B4 (en) 2009-12-04 2014-05-28 Sick Ag Distance measuring laser scanner

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R119 Application deemed withdrawn, or ip right lapsed, due to non-payment of renewal fee