Light-wave distance meter based on light pulses

• US 5,619,317 A
• Filed: 11/18/1994
• Issued: 04/08/1997
• Est. Priority Date: 11/18/1993
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Topcon
• Original Assignee: Kabushiki Kaisha Topcon
• Inventors: Ohtomo, Fumio, Oishi, Masahiro
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Laufer, Pinchus M.
• Application Number:
  US08/342,264
• Time in Patent Office: 872 Days
• Field of Search: 356/5.07, 356/5.08, 356/5.05, 342/136, 342/93, 342/94, 342/97
• US Class Current: 356/5.05
• 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 17/14 wherein a voltage or current pulse is initiated and terminated in accordance with the pulse transmission and echo reception respectively, e.g. using counters
• CPC Class Codes: G01S 7/4865 Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak peak detection in noise, signal conditioning G01S7/487

Abstract

In a light-wave distance meter based on light pulses, a light pulse radiation device radiates light pulses emitted by a light source device to a target of measurement, a light reception device receives reflected light pulses from the target, a sampling device samples reception signals, a timing device applies a dither of a certain range to the light pulse emission timing and sampling timing, a cumulative memory device stores sampled signals at a certain interval cumulatively, and a computation device calculates the distance to the target. The distance meter is capable of measuring the position of received light pulses at a resolution higher than the sampling timing.

Claims

1. A distance meter comprising:

a light source device for emitting light pulses at nominally equal emission time intervals;

a light radiator device optically coupled to the light source device for radiating the emitted light pulses to a reflective measurement target at a distance to be determined;

a light receiver device configured and disposed for receiving light pulses reflected from the measurement target and converting the reflected light pulses into reception signals;

a data former device operatively coupled to the light receiver device for forming, from the reception signals, data representing frequency of occurrence of the reflected light pulses at nominally equal sampling time intervals, the data former device comprising a sampler device for sampling into the reception signals to produce sampled values and a cumulative memory device for cumulating the sampled values and storing the cumulated values as the frequency of occurrence of the reflected light pulses;

a timer device operatively coupled to the light source device and/or the data former device for applying a dither within a prescribed dither range to the emission time intervals and/or the sampling time intervals; and

a distance calculator device operatively coupled to the data former device for using the data to determine the distance to the measurement target.

2. The distance meter according to claim 1, wherein the sampler device is for producing the sampled values in binary form.

3. The distance meter according to claim 1 or 2 wherein the timer device is for applying the dither to the emission time intervals and the sampling time intervals with uniform probability in the dither range.

6. The distance meter according to claim 2 or 5, wherein the cumulative memory device comprises:

an adder device for adding, at successive receptions of binary data from the sampler device, the received binary data to binary data that have been previously received and cumulated; and

a memory store for storing a resulting cumulated final value.

7. The distance meter according to claim 6, wherein the cumulative memory device comprises:

a first memory store for temporarily storing part of the sampled values from an individual light pulse emission of the light source;

a second memory store for storing cumulated values; and

an adder device for adding a value stored in the first memory device to a previously stored cumulated value in the second memory store.

8. The distance meter according to claim 6, wherein the cumulative memory device comprises:

a first memory store for temporarily storing all of the sampled values from an individual light pulse emission of the light source;

a second memory store for storing cumulated values; and

an adder device for adding a value stored in the first memory device to a previously stored cumulated value in the second memory store.

10. The distance meter according to claim 1 or 4, wherein the light receiver device comprises a band-pass amplifier operatively coupled to the sampler device.

11. The distance meter according to claim 10, wherein the band-pass amplifier comprises a tuned amplifier.

12. The distance meter according to claim 1 or 4, wherein the timer device is for applying the dither to the emission time intervals as a function of the sampling time intervals.

13. The distance meter according to claim 1 or 4, wherein the timer device is for applying the dither to the sampling time intervals as a function of the emission time intervals.

14. The distance meter according to claim 1 or 4, wherein the sampler device is for producing the sampled values in binary form.

15. The distance meter according to claim 1 or 4, wherein the dither range, Δ

T, is prescribed in relation to the sampling time interval, T₁, such that Δ

T≧

T₁.

16. The distance meter according to claim 1 or 4, wherein the dither range, Δ

T, is prescribed in relation to the sampling time interval, T₁, a number of transitions Ne of the reception signal resulting from one light pulse, a transition time interval T₃ of the reception signal, a difference T₂ between the sampling time interval T₁ and the transition time interval T₃, and time intervals Δ

T₀, . . . , Δ

T_Nc formed when the difference between a transition time and a sampling time lies in one transition time interval such that max{Δ

T₀, . . . , Δ

T_Nc }≦

Δ

T where Nc=[T₃ (Ne-1)/T₁ ]+1 and the sampling time is

space="preserve" listing-type="equation">Δ

T.sub.2 *k-[Δ

T.sub.2 *k/T.sub.3 ]*T.sub.3

where k takes any value from 0 to Nc, and brackets [ ] stand for the Gaussian symbol so that, for a real number x and an integer n, if n≦

x<

n+1, then [x]=n.

4. A distance meter comprising:

a light source device for emitting light pulses at nominally equal emission time intervals, with each light pulse comprising a measurement light pulse and a reference light pulse;

a light radiator device optically coupled to the light source device for radiating the measurement light pulses to a reflective measurement target at a distance to be determined;

a light receiver device configured and disposed for receiving light pulses reflected from the measurement target, receiving the reference light pulses, and converting the received light pulses into reception signals;

a data, former device operatively coupled to the light receiver device for forming, from the reception signals, data representing frequency of occurrence of the received light pulses at nominally equal sampling time intervals, the data former device comprising a sampler device for sampling the reception signals to produce sampled values and a cumulative memory devices for cumulating the sampled values and storing the cumulated values as the frequency of occurrence of the reflected light pulses;

a timer device operatively coupled to the light source device and/or the data former device for applying a dither within a prescribed dither range to the emission time intervals and/or the sampling time intervals; and

a distance calculator device operatively coupled to the data former device for using he data to determine the distance to the measurement target.

5. The distance meter according to claim 4, wherein the sampler device is for sampling the reception signals to produce the sampled values in binary form.

9. The distance meter according to claim 4, wherein the distance calculator device is instructed for determining a correlation between cumulated values derived from the reflected light pulses and cumulated values derived from the reference light pulses.