Light wave distance measuring instrument of the pulse type

• US 5,054,911 A
• Filed: 12/20/1989
• Issued: 10/08/1991
• Est. Priority Date: 12/30/1988
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Topcon
• Original Assignee: Kabushiki Kaisha Topcon
• Inventors: Ohishi, Masahiro, Ohtomo, Fumio
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US07/453,904
• Time in Patent Office: 657 Days
• Field of Search: 356/4, 356/5
• US Class Current: 356/5.07
• CPC Class Codes: G01B 11/026 by measuring distance between sensor and object G01B11/0608 takes precedence
• 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 7/4818 using optical fibres

Abstract

A light wave distance measuring instrument uses a light receiving diode for receiving both light from a light source diode coupled via an internal light passage and light from the light source diode coupled via an external light passage. A beam splitter separates light pulses from a single source diode to supply light pulses for both internal and external passages. A reference signal is sampled using detected signals representing the timing of received internal reference light pulses and external measurement light pulses to provide first and second signals with phase difference representing measured distance. These signals are processed in a CPU for calculating distance with reduced errors due to frequency drift. By introducing an optical fiber delay medium, reflected light pulses are separated in time from the internal reference pulses so that these pulses can be used directly for differential time determination purposes and the measurement of distances to objects close to the measuring instrument is made possible.

Claims

1. A light wave distance measuring instrument of the pulse type comprising:

signal generating means for providing a reference signal of a reference frequency and an output driver signal of a frequency different from said reference frequency;

light source means, coupled to said signal generating means, for periodically emitting pulses of light in response to said output driver signal;

beam splitter means, optically coupled to said light source means, for optically separating said pulses of light into internal reference light pulses and external measurement light pulses;

external passage light coupling means, optically coupled to said beam splitter means, for coupling said external measurement light pulses toward an external object at distance to be measured and for receiving reflected light pulses from said external object;

internal passage light coupling means, optically coupled to said beam splitter means, for coupling said internal reference light pulses without reflection from said external object;

light pulse receiving means, responsive to said internal reference light pulses and said reflected light pulses, for converting said light pulses into internal pulse timing signals and reflected pulse timing signals, respectively;

sampling means, coupled to said light pulse receiving means and said signal generating means, for providing a first signal representing sampling of said reference signal at the timing of said internal pulse timing signals and a second signal representing sampling of said reference signal at the timing of said reflected pulse timing signal; and

calculating means, coupled to said sampling means, for determining the distance to said external object based on phase difference between said first and second signals representing sampling of said reference signal.

2. A light wave distance measuring instrument according to claim 1, wherein said external passage light coupling means includes optical delay means for introducing an additional delay in the coupling of said external measurement light pulses.

3. A light wave distance measuring instrument according to claim 1, wherein said external passage light coupling means includes optical fiber delay means for providing a delay in the coupling of said external measurement light pulses of a duration greater than the duration represented by the width of said light pulses.

4. A light wave distance measuring instrument according to claim 1, wherein said output driver signal is provided by said signal generating means at a frequency equal to said reference frequency multiplied by a constant factor.

5. A light wave measuring instrument according to claim 1, additionally comprising pulse counter means wherein said calculating means is arranged to determine said distance to said external object by first making a rough determination of distance based on a count of elapsed pulses and then making a final determination of distance based on said phase difference determination.

6. A light distance measuring instrument of the pulse type, comprising:

signal generating means, including a reference oscillator for providing a reference signal of a reference frequency and means for deriving from said reference signal an output driver signal of a frequency equal to said reference frequency multiplied by a constant factor;

a light source means, coupled to said signal generating means, for periodically emitting light pulses of predetermined duration in response to said output driver signal;

beam splitter means, optically coupled to said light source means, for optically separating said pulses of light into internal reference light pulses and external measurement light pulses;

external passage light coupling means, optically coupled to said beam splitter means and including optical fiber delay means for providing a delay greater than said light pulse duration, for directing said external measurement light pulses toward an external object at a distance to be measured and for receiving reflected light pulses from said external object;

internal passage light coupling means, optically coupled to said beam splitter means, for coupling said internal reference light pulses without reflection from said external object;

light pulse receiving means, responsive to said internal reference light pulses and said reflected light pulses, for converting said light pulses into internal pulse timing signal and reflected pulse timing signals, respectively;

sampling means, coupled to said light pulse receiving means and said reference oscillator, for providing a first signal representing sampling of said reference signal at the timing of said internal reference pulse timing signals and a second signal representing sampling of said reference signal at the timing of said reflected pulse timing signals; and

calculating means, coupled to said sampling means, for determining the distance to said external object based on phase difference between said first and second signals representing sampling of said reference signal.