§
Luxuse
Patent Intelligence
Sign In
← Back to Patent Explorer
US3740141A Expired / Lapsed US ⏱️ 0.0 years remaining

Timing and measuring methods and means for laser distance measurements

Assignee: Laser Systems and Electronics Inc
•
Filing: 1971-09-20
•
Granted: 1973-06-19
•
Expires: 1991-09-20
📄 Original PDF 🌐 Google Patents 🔄 Sync Now

Abstract

Abstract An improved laser distance measuring apparatus of the type that automatically calculates distance to a remote reflection target based upon a measured phase difference between a modulated transmitted laser beam and a reflected return beam from the remote target. The improved apparatus incorporates means for insuring that phase measurements for the return beam are made only when the amplitude of the demodulated return signal is within predetermined limits thereby insuring a desired degree of accuracy for the resulting phase measurement. Furthermore, rather than performing an absolute phase difference measurement, better overall accuracy is obtained by calculating a relative phase difference corresponding to the difference between external and internal reflected beam path distances. Since reflected laser beam components usually exhibit rather severe scintillations due to rapidly changing atmospheric conditions over the beam path length, means are disclosed for insuring that successive phase difference measurements are taken from different packets or bunches of reflections thus insuring that an average of several such measurements is not taken from only a single packet and hence insuring that the resultant average measurement more accurately represents the true distance to the remote target site. In addition, added electrical phase shift means are switched into operation for substantially one-half of the predetermined number of distance measurements on the most critical phase measurements to substantially cancel nonlinearities inherent in such measurements due to corresponding nonlinearities in the demodulated return signals having a significant harmonic content therein. Furthermore, when the detectable phase difference measurement is less than a predetermined limit, there is a possibility of phase ''''jitter'''' causing a counter ''''stop'''' signal to occur before the counter ''''start'''' signal thereby resulting in erratic counter operation and correspondingly erroneous phase measurement. Accordingly, means are provided for detecting such an ''''overlap'''' condition and for automatically accepting the second instead of the first available ''''stop'''' counter signal whenever such overlap conditions occur thereby introducing an additional 180* phase difference which is then compensated by complementing the counter in compensation for this fixed added phase difference. The net result is stable counter operation and the elimination of completely erroneous phase difference measurements due to phase jitter.

Inventors

  • 👤 Witt J De

Bibliographic Details

Application Number —
Jurisdiction US
Data Source google_patents
Last Synchronized 2026-10-23 19:36
CPC Classifications
G; G01; G01S; G01S17/00; G01S17/02; G01S17/06; G01S17/08; G01S17/32

Claims Analysis

Total Claims: 6
Claim 1
Independent Claim 331 words
Laser distance measuring apparatus comprising: a laser means for providing a transmitted beam of substantially coherent light, modulating means for modulating said transmitted beam at a predetermined frequency and for providing a reference electrical signal having a known frequency relationship with said predetermined frequency, detecting means for detecting the modulated information in a reflection of said transmitted beam from a remote target and for providing a return electrical signal in response thereto, said detecting means including: a zero-cross detector means for detecting when the modulated information in said reflection passes through a zero reference level, window detecting means for detecting when the modulated information in said reflection is within predetermined amplitude limits whereby the accuracy of a detected zero-cross time is determined as being within acceptable limits, and signal generating means effectively connected to both said zero-cross detecting means and to said window detecting means for generating said return electrical signal corresponding to a detected zero-cross time within said acceptable limits, clock means for providing clock pulses at a predetermined clock frequency, gate means operatively connected to said clock means, to said modulating means and to said detecting means for gating said clock in response to said reference and return electrical signals whereby the number of passed clock pulses is a measure of the electrical phase difference between the modulated information on said transmitted beam and its reflection, digital computation means connected to said gate means for counting the number of passed clock pulses and for computing a distance proportional to said phase difference, means for automatically performing a predetermined number of distance measurements, phase shift means connected to said detecting means for providing a predetermineD added electrical phase shift to demodulated signals coming from reflection, and means for effectively switching said phase shift means into operation for substantially one-half of the predetermined number of distance measurements whereby nonlinearities in said demodulated signals are effectively cancelled from a resultant measurement representing an average of all of said predetermined number of measurements.
Claim 2
Dependent Claim 331 words
Laser distance measuring apparatus comprising: a laser means for providing a transmitted beam of substantially coherent light, modulating means for modulating said transmitted beam at a predetermined frequency and for providing a reference electrical signal having a known frequency relationship with said predetermined frequency, detecting means for detecting the modulated information in a reflection of said transmitted beam from a remote target and for providing a return electrical signal in response thereto, said detecting means including: a zero-cross detector means for detecting when the modulated information in said reflection passes through a zero reference level, window detecting means for detecting when the modulated information in said reflection is within predetermined amplitude limits whereby the accuracy of a detected zero-cross time is determined as being within acceptable limits, and signal generating means effectively connected to both said zero-cross detecting means and to said window detecting means for generating said return electrical signal corresponding to a detected zero-cross time within said acceptable limits, clock means for providing clock pulses at a predetermined clock frequency, gate means operatively connected to said clock means, to said modulating means and to said detecting means for gating said clock in response to said reference and return electrical signals whereby the number of passed clock pulses is a measure of the electrical phase difference between the modulated information on said transmitted beam and its reflection, digital computation means connected to said gate means for counting the number of passed clock pulses and for computing a distance proportional to said phase difference, means for automatically performing a predetermined number of distance measurements, phase shift means connected to said detecting means for providing a predetermineD added electrical phase shift to demodulated signals coming from reflection, and means for effectively switching said phase shift means into operation for substantially one-half of the predetermined number of distance measurements whereby nonlinearities in said demodulated signals are effectively cancelled from a resultant measurement representing an average of all of said predetermined number of measurements.
Claim 3
Dependent Claim 23 words
Laser distance measuring apparatus as in claim 1 wherein said predetermined added electrical phase shift substantially corresponds to a one-fourth wavelength phase shift.
Claim 4
Dependent Claim 166 words
An improvement for use in a laser distance measuring apparatus comprising a modulated laser source, detecting and demodulating means for obtaining a demodulated return signal from a reflected laser beam and computing means for computing distance to a reflecting target based on a measured phase difference between first signals modulated onto the transmitted laser beam and second signals demodulated from the reflected laser beam, said improvement helping to compensate for nonlinearities in the demodulated return signal caused by harmonics introduced in the demodulation process and said improvement comprising: means for automatically performing a predetermined number of distance measurements, phase shift means connected to said detecting means for providing a predetermined added electrical phase shift to demodulated signals coming from said reflection, and means for effectively switching said phase shift means into operation for substantially one-half of the predetermined number of distance measurements whereby nonlinearities in said demodulated signals are effectively cancelled from a resultant measurement representing an average of all of said predetermined number of measurements.
Claim 5
Dependent Claim 166 words
An improvement for use in a laser distance measuring apparatus comprising a modulated laser source, detecting and demodulating means for obtaining a demodulated return signal from a reflected laser beam and computing means for computing distance to a reflecting target based on a measured phase difference between first signals modulated onto the transmitted laser beam and second signals demodulated from the reflected laser beam, said improvement helping to compensate for nonlinearities in the demodulated return signal caused by harmonics introduced in the demodulation process and said improvement comprising: means for automatically performing a predetermined number of distance measurements, phase shift means connected to said detecting means for providing a predetermined added electrical phase shift to demodulated signals coming from said reflection, and means for effectively switching said phase shift means into operation for substantially one-half of the predetermined number of distance measurements whereby nonlinearities in said demodulated signals are effectively cancelled from a resultant measurement representing an average of all of said predetermined number of measurements.
Claim 6
Dependent Claim 21 words
An improvement as in claim 3 wherein said predetermined added electrical phase shift substantially corresponds to a one-fourth wavelength phase shift.

References Cited (Backward Citations)

US3522992A Cited

USPTO Annuity & Maintenance Windows

Annuity Stage Window Opens Payment Deadline Surcharge Period Until Estimated Fee Status
3.5 Years (Year 4) 1976-06-18 1976-12-18 1977-06-19 $2000.00 Window Closed / Lapsed
7.5 Years (Year 8) 1980-06-18 1980-12-18 1981-06-19 $3760.00 Window Closed / Lapsed
11.5 Years (Year 12) 1984-06-18 1984-12-18 1985-06-19 $7700.00 Window Closed / Lapsed

Assigned Categories & Tags

No categories assigned to this patent yet.

Assign Category Tag