Distance measuring apparatus using pulse light

• US 6,226,076 B1
• Filed: 03/03/2000
• Issued: 05/01/2001
• Est. Priority Date: 09/04/1997
• Status: Expired due to Term

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Yoshida, Hisashi
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US09/518,245
• Time in Patent Office: 424 Days
• Field of Search: 356/5.01-5.08
• US Class Current: 356/5.06
• CPC Class Codes: G01C 15/002 Active optical surveying means optical plumbing G01C15/105
• 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 7/481 Constructional features, e.g. arrangements of optical elements
• CPC Class Codes: G01S 7/4813 Housing arrangements
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: G01S 7/51 Display arrangements

Abstract

The present invention relates to a distance measuring apparatus and method having a structure enabling highly accurate distance measurement. In particular, the distance measuring apparatus according to the present invention comprises at least a measurement system for detecting, of measurement pulse light emitted into a measurement optical path toward a target, information concerning a reflected beam from the target. In order to prevent undesirable reflected beams, which form erroneous information, among reflected beams of the measurement pulse light from being received, an operation for detecting reflected beams of the measurement pulse light is inhibited for a predetermined period of time from the emitting time at which the measurement pulse light is emitted.

Claims

1. A distance measuring apparatus comprising:

an emitter for emitting measurement pulse light into a measurement optical path between said apparatus and a target;

a receiver for receiving a reflected component of the measurement light emitted into said measurement optical path;

a detector for specifying a receiving time at which the reflected component of said measurement pulse light is received; and

a controller for controlling a main measurement operation and a pre-measurement operation performed prior to the main measurement operation each measuring the period of time between an emitting time at which said measurement pulse light is emitted and the receiving time of the reflected component of said measurement pulse light and calculating a length of said measurement optical path on the basis of thus obtained time information;

said controller inhibiting, when the calculated value obtained in the pre-measurement operation is not greater than a predetermined value, said detector from effecting the specifying operation for a predetermined period of time from the emitting time of said measurement pulse light in the main measurement operation.

2. The apparatus according to claim 1, further comprising:

a reference optical path which is different from said measurement optical path; and

a switching mechanism for causing said receiver to selectively receive one of the reflected component of said measurement pulse light propagated through said measurement optical path and a reference pulse light propagated through said reference optical path.

3. A distance measuring apparatus comprising:

an emitter for emitting measurement pulse light into a measurement optical path between said apparatus and a target;

a receiver for receiving a reflected component of the measurement light emitted into said measurement optical path;

a detector for specifying a receiving time at which the reflected component of said measurement pulse light is received;

a collimator having an optical system for focusing an image of said target onto a predetermined position; and

a controller for controlling a measurement operation measuring the period of time between an emitting time at which said measurement pulse light is emitted and the receiving time of the reflected component of said measurement pulse light and calculating a length of said measurement optical path on the basis of thus obtained time information;

said controller inhibiting, when a distance value from said apparatus to said target corresponding to an in-focus position of the optical system in said collimator is not less than a predetermined value, said detector from effecting the specifying operation for a predetermined period of time from the emitting time of said measurement pulse light in the measurement operation.

4. The apparatus according to claim 3, further comprising:

a reference optical path which is different from said measurement optical path; and

a switching mechanism for causing said receiver to selectively receive one of the reflected component of said measurement pulse light propagated through said measurement optical path and a reference pulse light propagated through said reference optical path.

5. The apparatus according to claim 3, further comprising:

a limit switch for specifying the in-focus position of the optical system in said collimator so as to judge whether the distance value from said apparatus to said target corresponding to the in-focus position of said optical system exceeds the predetermined value or not.

6. A method of measuring a distance from a target to a distance measuring apparatus utilizing pulse light, said method comprising:

a first step of effecting a pre-measurement operation measuring a length of a measurement optical path between said target and a pulse generating source and comprising;

a first substep of emitting measurement pulse light into said measurement optical path,

a second substep of receiving a reflected component of said measurement pulse light emitted into said measurement optical path,

a third substep of specifying a receiving time at which the reflected component of said measurement pulse light is received, and

a fourth substep of measuring the period of time between an emitting time at which said measurement pulse light is emitted and the receiving time of the reflected component of said measurement pulse light and calculating the length of said measurement optical path on the basis of thus obtained time information; and

a second step, effected subsequent to said first step, of executing a main measurement operation measuring a length of measurement optical path between said target and a pulse generating source and comprising;

a first substep of emitting measurement pulse light into said measurement optical path,

a second substep of receiving a reflected component of said measurement pulse light emitted into said measurement optical path,

a third substep of specifying a receiving time at which the reflected component of said measurement pulse light is received, and

a fourth substep of measuring the period of time between an emitting time at which said measurement pulse light is emitted and the receiving time of the reflected component of said measurement pulse light and calculating the length of said measurement optical path on the basis of thus obtained time information,

wherein the main measurement operation is executed in a state where, when a calculated value obtained in the pre-measurement operation is not greater than a predetermined value, said third substep in said second step is inhibited for a predetermined period of time from the emitting time of said measurement pulse light.

7. The method according to claim 6, wherein emission of the measurement pulse light into said measurement optical path and emission of a reference pulse light into a reference optical path different from said measurement optical path are selectively switched therebetween so as to measure the respective lengths of said measurement optical path and the reference optical path.

8. A method of measuring a distance from a target to a distance measuring apparatus equipped with a collimator having an optical system for focusing an image of said target onto a predetermined position, said method comprising:

a first step of adjusting said optical system so as to focus the image of said target onto the predetermined position, thereby obtaining a distance from said collimator to said target corresponding to an in-focus position of said optical system; and

a second step of effecting a measurement operation, the measurement operation comprising;

a first substep of emitting measurement pulse light into said measurement optical path,

a second substep of receiving a reflected component of said measurement pulse light emitted into said measurement optical path,

a third substep of specifying a receiving time at which the reflected component of said measurement pulse light is received, and

a fourth substep of measuring the period of time between an emitting time at which said measurement pulse light is emitted and the receiving time of the reflected component of said measurement pulse light and calculating the length of said measurement optical path on the basis of thus obtained time information,

wherein, when a distance value obtained in said first step is not less than a predetermined value, said third substep in said second step is inhibited for a predetermined period of time from the emitting time of said measurement pulse light.

9. The method according to claim 8, wherein emission of the measurement pulse light into said measurement optical path and emission of a reference pulse light into a reference optical path different from said measurement optical path are selectively switched therebetween so as to measure the respective lengths of said measurement optical path and the reference optical path.