OPTICAL-ELECTRONIC DISTANCE MEASURING DEVICE

• US 20100296078A1
• Filed: 02/03/2009
• Published: 11/25/2010
• Est. Priority Date: 02/11/2008
• Status: Active Grant

• Current Assignee: Leica Geosystems AG (Hexagon AB)
• Original Assignee: Leica Geosystems AG (Hexagon AB)
• Inventors: Giger, Kurt, Forrer, Peter
• Granted Patent: US 8,279,421 B2
• Time in Patent Office: Days
• US Class Current: 356/5.1
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 17/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 7/484 Transmitters
• CPC Class Codes: G01S 7/491 Details of non-pulse systems
• CPC Class Codes: G01S 7/4912 Receivers

Abstract

The invention relates to an optical-electronic distance measuring method according to the phase measurement principle by emitting of optical measuring radiation, which is modulated according to the burst modulation principle, having a burst period duration made of an active burst time and a dead time, receiving at least a part of the measuring radiation (23), which is reflected on the measured object, wherein transforming into an input measuring signal (ES) is performed, and determining a distance to the measured object by analyzing a measuring signal (MS, gMS) generated from the input measuring signal (ES).

Claims

1-16. -16. (canceled)

17. An optoelectronic distance measuring method according to the phase measurement principle, comprising the steps:

emitting optical measuring radiation in the direction of a measured object, the optical measuring radiation modulated according to the burst modulation principle with a burst period comprising an active burst time and a dead time;

receiving at least a part of measuring radiation reflected by the measured object and converting the received measuring radiation into an input measuring signal; and

determining a distance to the measured object by evaluation of a measuring signal generated from the input measuring signal, wherein;

on reception and conversion, superposition, in particular continuous superposition, with a mixer signal is effected in such a way that the input measuring signal substantially has burst pulses of constant width which is determined by the active burst time and modulated amplitude, a curve enveloping the burst pulses, as an LF envelope curve, varies approximately sinusoidally with a low envelope curve frequency;

the measuring signal assumes values dependent on the input measuring signal in each case during a sampling time linked to the active burst time; and

the measuring signal is kept substantially at a value which the measuring signal has in each case at the end of the sampling time, in each case during a hold time linked to the dead time.

18. A distance measuring method according to claim 17, wherein on reception and conversion, continuous superposition, with a mixer signal is effected in such a way that the input measuring signal substantially has burst pulses of constant width which is determined by the active burst time and modulated amplitude, a curve enveloping the burst pulses, as an LF envelope curve, varies approximately sinusoidally with a low envelope curve frequency.

19. A distance measuring method according to claim 17, wherein the input measuring signal is filtered by a low-pass filter so that frequency components in the frequency range around a modulation frequency with which the measuring radiation is modulated during the active burst time are blocked.

20. A distance measuring method according to claim 17, wherein the measuring signal assumes values dependent on the amplitude of the burst pulse during the sampling time.

21. A distance measuring method according to claim 20, wherein:

during the sampling time, the measuring signal approaches the amplitude of the burst pulse exponentially.

22. A distance measuring method according to claim 20, wherein:

during the sampling time, the measuring signal approaches the amplitude of the burst pulse exponentially in such a way that the value of the measuring signal;

substantially corresponds to the value of the amplitude of the burst pulse only at the end of the sampling time;

or

is slightly below the amplitude of the burst pulse at the end of the sampling time.

23. A distance measuring method according to claim 17, wherein the measuring signal is filtered before the evaluation with a bandpass filter which allows through substantially only frequencies around the low envelope curve frequency.

24. A distance measuring method according to claim 17, wherein:

the measuring radiation is modulated during the active burst time with a modulation frequency greater than 100 MHz; and

the superposition with the mixer frequency is effected in such a way that the low envelope curve frequency is in the range between 0.5 and 500 kHz.

25. A distance measuring method according to claim 17, wherein the burst period and the low envelope curve frequency are chosen so that the LF envelope curve period is sixteen times the burst period.

26. A distance measuring method according to claim 17, wherein a duty cycle, which is defined by the ratio of the active burst time to the burst period, of about 5% to about 50% is achieved.

27. A distance measuring method according to claim 17, wherein a duty cycle, which is defined by the ratio of the active burst time to the burst period of about 10% to about 40% is achieved.

28. A distance measuring method according to claim 17, wherein the evaluation of the measuring signal with regard to a phase position is effected relative to a reference signal which is generated from the detection and conversion of a component of the measuring radiation which is passed through a known reference distance.

29. A receiving circuit for an optoelectronic distance measuring device, comprising:

a receiver for converting at least a part of optical measuring radiation reflected by a measured object into an electrical input measuring signal, the measuring radiation being modulated according to the burst modulation principle with a burst period comprising an active burst time and a dead time;

the receiving circuit being formed for generating a measuring signal, suitable for evaluation according to the phase measurement principle, from the input measuring signal;

means for applying a modulated mixer voltage to the receiver so that the input measuring signal substantially has burst pulses of constant width which is determined by the active burst time, and modulated amplitude, and a curve enveloping the burst pulses, as LF envelope curve, varies approximately sinusoidally with a low envelope curve frequency; and

a sample-and-hold member with a sampling time linked to the active burst time and a hold time linked to the dead time.

30. A receiving circuit according to claim 29, wherein the modulated mixer voltage is continuously applied to the receiver.

31. A receiving circuit according to claim 29, further comprising a bandpass filter connected down-circuit of the sample-and-hold member and having passing frequencies in a range around the low envelope curve frequency.

32. A receiving circuit according to claim 29, wherein the receiving circuit has a transimpedance amplifier which is connected between the receiver and the sample-and-hold member and is formed for low-pass filtering, so that frequency components of the input measuring signal in the frequency range around a modulation frequency with which the measuring radiation is modulated during the active burst time are blocked.

33. A receiving circuit according to claim 29, wherein a response time of the sample-and-hold member is chosen to be about equal to or somewhat longer than the sampling time.

34. A receiving circuit according to claim 29, wherein the sample-and-hold member includes:

a switch for fixing the sampling time and the hold time;

a capacitor for keeping a signal value constant during the hold time; and

a charging resistor for designing the sample-and-hold member, inter alia with regard to a response time.

35. A receiving circuit according claim 29, wherein the sample-and-hold member is configured for sampling the input measuring signal which is generated by superposition with the mixer frequency and is enveloped by the LF envelope curve which has a low frequency in relation to the modulation frequency of the measuring radiation.

36. An optoelectronic distance measuring device, in particular in the form of a hand-held device, comprising

a transmitter for emitting optical measuring radiation in the direction of a measured object, the optical measuring radiation being modulated according to the burst modulation principle with a burst period comprising an active burst time and a dead time;

a receiving circuit according to claim 29; and

a signal processing unit for determining a distance by evaluating the measuring signal according to the phase measurement principal.

37. An optoelectronic distance measuring device, in particular in the form of a hand-held device, comprising

a transmitter for emitting optical measuring radiation in the direction of a measured object, the optical measuring radiation being modulated according to the burst modulation principle with a burst period comprising an active burst time and a dead time;

a receiving circuit according to claim 29; and

a signal processing unit for determining a distance by evaluating the measuring signal according to the phase measurement principle, a reference path being provided for passage of a component of the measuring radiation along a known reference distance to a reference receiver formed for generating a reference signal, and the signal processing unit evaluating the measuring signal with regard to a phase position relative to the reference signal.