Electro-optic distance measuring apparatus

• US 6,229,598 B1
• Filed: 01/20/2000
• Issued: 05/08/2001
• Est. Priority Date: 02/14/1997
• Status: Expired due to Term

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Yoshida, Hisashi
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US09/487,810
• Time in Patent Office: 474 Days
• Field of Search: 356/5.01-5.08, 356/5.12
• US Class Current: 356/5.01
• CPC Class Codes: G01C 1/02 Theodolites
• 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

Abstract

A distance measuring apparatus has a light sending unit for sending pulsed light into a ranging optical path, a photodetective element for receiving pulse light reflected, and a signal processing section for measuring a period between The time of sending and the time of reception, the signal processing section determines whether to apply a first state in which one reflected pulsed beam is detected in response to the sending of the pulsed light or a second state in which two reflected pulsed beams are detected in response to the sending of the pulsed light. The signal processing section measures a period from the time of sending to reception of the first reflected pulsed beam in the first state, while the signal processing section measures a period from the time of sending to reception of the second reflected pulsed beam in the second state.

Claims

1. A distance measuring apparatus for measuring a distance to a target, the apparatus comprising:

a housing;

a lens mounted to the housing so that light passing through the lens enters or exits the housing;

a light emitting element disposed in the housing for emitting pulsed light toward the target through the lens;

a photo-detective element disposed in the housing;

an optical system including;

a first optical path provided in the housing for emitting pulsed light from the light emitting element to the target through to the lens;

a second optical path provided in the housing for receiving pulsed light from the lens to the photo-detecting element, wherein the distance is measured based on a timing difference between a first time at which a pulsed light is emitted from the light emitting element toward the target and a second time at which pulsed light reflected off the target is incident on the photo-detecting element, after the pulsed light is emitted,

wherein the lens is positioned in the path of both the first and second optical paths;

a filter for adjusting light quantity arranged in the housing, in the second optical path;

a light flare detecting means for detecting the existence of light flare based on an output from the photo-detecting element, wherein the light flare to be detected is generated in response to the pulsed light in the first optical path reflecting off at least an inner surface side of the lens, and wherein the second optical path guides the generated light flare to the photo-detecting element;

a reference optical path extending in the housing from the light emitting element to the photo-detecting element, without passing through the lens; and

a shutter disposed in the reference optical path, wherein a pulsed light emitted from the light emitting element becomes incident on the photo-detecting element when the shutter is open.

2. A distance measuring apparatus according to claim 1, further comprising an attenuator disposed in the reference optical path.

3. A distance measuring apparatus according to claim 2, further comprising a display.

4. A distance measuring apparatus according to claim 3, further comprising control means for calculating a first length of the reference optical path by opening the shutter to direct a pulsed light through the reference optical path, emitting the pulsed light from the light emitting element, and receiving the pulsed light that has traveled through the reference optical path by the photo-detecting element, the control means calculating the first length based on a period between emission of the pulsed light from the light emitting element and detection of the pulsed light by the photo-detecting element.

5. A distance measuring apparatus according to claim 4, wherein the control means further calculates a second length, which is the length of a pulsed light traveled through the first path, from the lens to the target, from the target to the lens, and the second optical path, by closing the shutter to direct the pulsed light through the first and second optical paths, emitting the pulsed light from the light emitting element, detecting the pulsed light at the photo-detecting element after the pulsed light travels through the first optical path, from the lens to the target, from the target to the lens, and the second optical path, the control means calculating the second length based on a period between emission of the pulsed light from the light emitting element and detection of the pulsed light by the photo-detecting element.

6. A distance measuring apparatus according to claim 5, wherein the control means calculates a true distance to the target by subtracting the first length from the second length and dividing the result by two.

7. A distance measuring apparatus according to claim 6, further comprising a rotary encoder, the housing being rotatable in a vertical plane around a horizontal axis, the rotary encoder measuring an angle of rotation of the housing, the control means calculating a horizontal distance component based on an output of the rotary encoder and the calculated true distance.

8. A distance measuring apparatus according to claim 5, wherein the control means further determines whether a distance measurement is possible based on detecting levels of pulsed light detected by the photo-detecting element while the light quantity adjusting filter is open and the shutter is closed, wherein the control means displays an error message on the display when the measurement is not possible to measure.

9. A distance measuring apparatus according to claim 8, wherein the control means controls a drive of the light quantity adjusting filter so that equal levels of pulsed light travels through the reference optical path and through the path in which the second length travels when the measurement is possible.