Dual-beam FMCW distance measuring method having compensation of a velocity-dependent distance measurement error

• US 10,634,788 B2
• Filed: 06/10/2019
• Issued: 04/28/2020
• Est. Priority Date: 06/11/2018
• Status: Active Grant

• Current Assignee: Hexagon Technology Center GmbH (Hexagon AB)
• Original Assignee: Hexagon Technology Center GmbH (Hexagon AB)
• Inventors: Rohner, Marcel
• Primary Examiner(s): Hansen, Jonathan M
• Application Number:
  US16/436,800
• Publication Number:
  US 20190377089A1
• Time in Patent Office: 323 Days
• CPC Class Codes: G01S 17/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 17/34 using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
• CPC Class Codes: G01S 7/4911 Transmitters
• CPC Class Codes: G01S 7/4915 Time delay measurement, e.g. operational details for pixel components signal extraction and conditioning G01S7/493; Phase measurement
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

A distance measuring method and a distance meter for a distance measurement according to the principle of a frequency-modulated continuous wave radar, wherein at least a part of a first laser radiation, which comprises a first frequency modulation defining a first modulation band, and at least a part of a second laser radiation, which comprises a second frequency modulation defining a second modulation band, are emitted as the first or as the second emission radiation, respectively, to a target. A parameter is determined, which is indicative of a frequency offset between the first and the second modulation band, and the parameter is taken into consideration during the determination of the at least one distance to the target to derive a frequency difference between the first frequency modulation and the second frequency modulation.

Claims

1. A distance measuring method comprising:

generating a first and a second laser radiation, wherein

the first laser radiation comprises a first frequency modulation defining a first modulation band, and

the second laser radiation comprises a second frequency modulation defining a second modulation band, wherein a gradient of the first frequency modulation is different from a gradient of the second frequency modulation in at least some time intervals;

simultaneously emitting at least a part of the first laser radiation and at least a part of the second laser radiation as the first or as the second emission radiation, respectively, toward the target;

receiving at least a part of the first emission radiation returning from the target and at least a part of the second emission radiation returning from the target as the first or as the second reception radiation, respectively;

generating a first and a second mixed signal based on a mixture of the first reception radiation with a first local oscillator radiation or based on a mixture of the second reception radiation with a second local oscillator radiation, respectively, for a distance measurement according to the principle of a frequency-modulated continuous wave radar; and

determining at least one distance to the target based on the first and the second mixed signal,

wherein;

a parameter is determined, which is indicative of a frequency offset between the first and the second modulation band, and

the parameter is taken into consideration during the determination of the at least one distance to the target to derive a frequency difference between the first frequency modulation and the second frequency modulation.

2. The distance measuring method according to claim 1, wherein the second frequency modulation comprises at least one time interval having a modulation direction opposing the modulation direction of the first frequency modulation.

3. The distance measuring method according to claim 1, wherein the parameter is an intersection point in time, at which the first and the second frequency modulation have the same frequency.

4. The distance measuring method according to claim 3, wherein the intersection point in time is determined from an interference curve of an overlay of at least a part of the first laser radiation and at least a part of the second laser radiation.

5. The distance measuring method according to claim 1, wherein:

a referencing of the frequency curve of the first and/or the second frequency modulation is carried out with respect to a reference parameter of a reference interferometer, and

nonlinearities during the generation of the first and/or the second frequency modulation are compensated for based on the referencing during the determination of the at least one distance.

6. The distance measuring method according to claim 1, wherein the frequency difference between the first and the second frequency modulation is determined based on the parameter, which is indicative of a frequency offset between the first and the second modulation band, and a first curve parameter with respect to the first frequency modulation and a second curve parameter with respect to the second frequency modulation.

7. The distance measuring method according to claim 1, wherein the determination of the at least one distance takes place during a measurement interval, wherein the measurement interval and the first and the second frequency modulation are adapted to one another in such a way that the first and the second emission radiation each comprise an essentially linear frequency modulation during the measurement interval.

8. A distance meter comprising:

a laser radiation source configured for generating a first and a second laser radiation, wherein;

the first laser radiation comprises a first frequency modulation defining a first modulation band, and

the second laser radiation comprises a second frequency modulation defining a second modulation band, wherein a gradient of the first frequency modulation is different from a gradient of the second frequency modulation in at least some time intervals,

i. an emission path configured for simultaneously emitting at least a part of the first laser radiation and at least a part of the second laser radiation as the first or as the second emission radiation, respectively, toward the target,

ii. a receiver configured for receiving at least a part of the first emission radiation returning from the target and at least a part of the second emission radiation returning from the target as the first or as the second reception radiation, respectively,

iii. a mixer configured for generating a first and a second mixed signal based on a mixture of the first reception radiation with a first local oscillator radiation or based on a mixture of the second reception radiation with a second local oscillator radiation, respectively, for a distance measurement according to the principle of a frequency-modulated continuous wave radar, and

iv. a processing unit configured for determining at least one distance to the target based on the first and the second mixed signal,

wherein the processing unit is configured to determine a parameter, which is indicative of a frequency offset between the first and the second modulation band, and to take the parameter into consideration during the determination of the at least one distance to the target to derive a frequency difference between the first frequency modulation and the second frequency modulation.

9. The distance meter according to claim 8, wherein the second frequency modulation comprises at least one time interval having a modulation direction opposing the modulation direction of the first frequency modulation.

10. The distance meter according to claim 8, wherein the parameter is an intersection point in time, at which the first (1A) and the second (1B) frequency modulation have the same frequency.

11. The distance meter according to claim 10, wherein:

the distance meter comprises an interferometer arrangement, configured to generate an interference curve of an overlay of at least a part of the first laser radiation and at least a part of the second laser radiation, and

the processing unit is configured to determine the intersection point in time from the interference curve.

12. The distance meter according to claim 11, wherein:

a threshold value for the interference signal strength of the interference curve is stored on the processing unit, and the intersection point in time is determined based on the threshold value and the interference curve.

13. The distance meter according to claim 8, wherein:

the distance meter comprises a reference interferometer, which is configured to carry out a referencing of the frequency curve of the first or second frequency modulation with respect to a reference parameter of the reference interferometer, and

the processing unit is configured to compensate for nonlinearities during the generation of the first or the second frequency modulation based on the referencing during the determination of the at least one distance.

14. The distance meter according to claim 8,

a first curve parameter with respect to the first frequency modulation and a second curve parameter with respect to the second frequency modulation are stored on the processing unit, and

the processing unit is configured to determine the frequency difference between the first and second frequency modulation based on the parameter, which is indicative of a frequency offset between the first and second modulation band, and also the first and second curve parameter.

15. The distance meter according to claim 8, wherein the distance meter is configured:

to determine a third curve parameter with respect to the first frequency modulation and a fourth curve parameter with respect to the second frequency modulation, and

to determine the frequency difference between the first and second frequency modulation based on the parameter, which is indicative of a frequency offset between the first and second modulation band, and also the third and the fourth curve parameter.