DISTANCE MEASURING DEVICE

• US 3,779,645 A
• Filed: 05/13/1971
• Issued: 12/18/1973
• Est. Priority Date: 05/20/1970
• Status: Expired due to Term

• Current Assignee: Nikon Corporation
• Original Assignee: Narihiko Nakazawa, Taiji Nakamura, Teruyoshi Kitahara, Yoshio Habuka
• Inventors: Nakazawa, Narihiko, Nakamura, Taiji, Kitahara, Teruyoshi, Habuka, Yoshio
• Primary Examiner(s): Wilbur, Maynard R.
• Assistant Examiner(s): Buczinski, S. C.
• Application Number:
  US05/143,048
• Time in Patent Office: 950 Days
• Field of Search: 356/4,5 250/229,231,204
• US Class Current: 356/5.13
• CPC Class Codes: G01S 17/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 7/4811 common to transmitter and receiver
• CPC Class Codes: G01S 7/4918 Controlling received signal intensity, gain or exposure of sensor

Abstract

An improved distance measuring device of the type which utilizes an amplitude-modulated light wave to measure the phase difference between the transmitted and the received modulated wave and thereby determine the distance of an object, the device being characterized by a feedback path combined with the optical system of the device so that the difference in magnitude between a reception signal and a standard signal or a reference signal may be zero or within a predetermined range, whereby the phase difference between the two signals can be measured independently of the non-linearity of the circuits and thus highly accurate measurement of the phase difference and accordingly of the distance of the object can be attained.

Claims

1. A distance measuring device comprising:

a source of amplitude-modulated light, wherein a light beam produced from said source is modulated at predetermined modulation frequency;

a light receiver for converting said light beam incident thereon into an electrical signal having a magnitude corresponding to the intensity of said incident light beam;

a reception optical system for directing said light beam from said source to a reflective object spaced from said course at a distance to be measured, and for directing the light beam reflected from said object to said receiver, wherein said receiver converts said light beam passing through said reception optical system into a reception electrical signal;

a reference optical system having a predetermined optical path and operable to direct said light beam from said source through said predetermined optical path to said receiver, wherein said receiver converts said light beam passing through said reference optical system into a reference electrical signal;

change-over means for selectively passing said light beam through said reception and reference optical systems one at a time;

phase difference measuring means for measuring the phase difference between said reception electrical signal and said reference electrical signal to determine the distance to be measured;

comparison means connected to said receiver for comparing the magnitudes of said reception and reference electrical signals and including memory means connected to said receiver for storing the magnitude of the electrical signal corresponding to the light beam passing through the other of said two optical systems while said change-over means selectively prevents the light beam passing through said one of said optical systems from entering said receiver, and a comparator connected to said receiver and said memory means for comparing the magnitude of the electrical signal corresponding to the light beam passing through said one of said optical systems with the said magnitude stored in the memory means while said change-over means prevents the light beam passing through said optical system from Entering said receiver, wherein said comparator provides said output of said comparison means; and

a light quantity regulator responsive to an output of said comparison means and disposed in one of said reception and reference optical systems for regulating the quantity of light entering said receiver through one of said optical systems so that the magnitude difference between said signals is within a predetermined range.

2. A distance measuring device according to claim 1, wherein said one optical system is said reception optical system.

3. A distance measuring device according to claim 2, wherein said source includes a modulator for providing said amplitude-modulated light, and said phase difference measuring means includes a phase meter connected to said modulator and said receiver for measuring a first phase difference between a standard signal produced from said modulator and said reception electrical signal, and for measuring a second phase difference between said standard signal and said reference electrical signal;

and further comprising phase difference memory means connected to said phase meter for storing said second phase difference, and operating circuit means connected to said phase difference memory means and said phase meter for computing the phase difference between the reception and reference signals from both said first phase difference from said phase meter and said second phase difference from said phase difference memory means to determine the distance to be measured.

4. A distance measuring device according to claim 3, wherein said phase difference memory means stores the second phase difference while said change-over means selectively prevents the light beam passing through said reception optical system from entering said receiver, and wherein said operating circuit means is actuated while said change-over means prevents the light beams passing through said reference optical system from entering said receiver.

5. A distance measuring device according to claim 1, wherein said one of said two optical system is said reference optical system.

6. A distance measuring device according to claim 5, wherein said source includes a modulator for providing said amplitude-modulated light, and said phase difference measuring means includes a phase meter connected to said modulator and said receiver for measuring a first phase difference between a standard signal produced from said modulator and said reception electrical signal, and for measuring a second phase difference between said standard signal and said reference electrical signal;

and further comprising phase difference memory means connected to said phase meter for storing said first phase difference, and operating circuit means connected to said phase difference memory means and said phase meter for computing the phase difference between the reception and reference signals from both said first phase difference from said phase difference memory means and said second phase difference from said phase meter to determine the distance to be measured.

7. A distance measuring device according to claim 6, wherein said phase difference memory means stores the first phase difference while said change-over means selectively prevents the light beam passing through said reference optical system from reaching said receiver, and wherein said operating circuit means is actuated while said change-over means prevents the light beam passing through said reception optical system from reaching said receiver.

8. A distance measuring device comprising:

a source of light including a modulator for producing amplitude-modulated light, wherein a light beam produced from said source is modulated at a predetermined modulation frequency;

a light receiver for converting said light beam incident thereon into an electrical signal having a magnitude corresponding to the intensity of said incident light beam;

a reception optical system for directing said light beam from said source to a reflective objeCt spaced from said source at a distance to be measured, and for directing the light beam reflected from said object to said receiver, wherein said receiver converts said light beam passing through said reception optical system into a reception electrical signal;

a reference optical system having a predetermined optical path and being operable to direct the light beam from said source through said predetermined optical path to said receiver, wherein said receiver converts said light beam passing through said reference optical system into a reference electrical signal;

change-over means for selectively passing said light beam through said reception and reference optical systems one at a time;

phase difference measuring means including a phase meter connected to said modulator and said receiver for measuring a first phase difference between a standard signal produced from said modulator and said reception electrical signal and for measuring a second phase difference between said standard signal and said reference electrical signal;

a generator for generating a set signal having a predetermined magnitude;

comparison means connected to said receiver and said generator for comparing the magnitudes of said reception electrical signal and said set signal;

a light quantity regulator responsive to an output of said comparison means and disposed in said reception optical system for regulating the quantity of said light beam entering said receiver through said reception optical system so that the magnitude difference between said reception and reference signals may be zero or a predetermined range;

phase difference memory means connected to said phase meter for storing said second phase difference; and

operating circuit means connected to said phase difference memory means and said phase meter for computing the phase difference between the reception and reference signals from both said first phase difference from said receiver and said second phase difference from said phase difference memory means to determine the distance to be measured.