Method for laser-based two-dimensional navigation system in a structured environment

• US 4,796,198 A
• Filed: 10/17/1986
• Issued: 01/03/1989
• Est. Priority Date: 10/17/1986
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Department Of Energy
• Original Assignee: United States Department of Energy (Government of the United States of America)
• Inventors: Schoeneman, J. Lee, Boultinghouse, Karlan D., Tise, Bertice L.
• Primary Examiner(s): NOT, DEFINED
• Application Number:
  US06/919,994
• Time in Patent Office: 809 Days
• Field of Search: 364/513, 364/424, 180/167, 180/168, 180/169, 318/587, 901/1, 901/46, 901/47, 356/1, 356/4, 250/561
• US Class Current: 701/23
• CPC Class Codes: G01S 17/06 Systems determining position data of a target
• CPC Class Codes: G05D 1/0238 using obstacle or wall sensors G05D1/0246 and G05D1/0289 take precedence; lidar systems designed for anti-collision purposes G01S17/93
• CPC Class Codes: G05D 1/0244 using reflecting strips
• CPC Class Codes: G05D 1/027 comprising intertial navigation means, e.g. azimuth detector inertial navigation G01C21/16; inertial navigation combined with non-inertial navigation instruments G01C21/165
• CPC Class Codes: G05D 1/0272 comprising means for registering the travel distance, e.g. revolutions of wheels measuring distance traversed on the ground by vehicles, e.g. using odometers G01C22/00

Abstract

A low power, narrow laser beam, generated by a laser carried by a mobile vehicle, is rotated about a vertical reference axis as the vehicle navigates within a structured environment. At least three stationary retroreflector elements are located at known positions, preferably at the periphery of the structured environment, with one of the elements having a distinctive retroreflection. The projected rotating beam traverses each retroreflector in succession, and the corresponding retroreflections are received at the vehicle and focussed on a photoelectric cell to generate corresponding electrical signals. The signal caused by the distinctive retroreflection serves as an angle-measurement datum. An angle encoder coupled to the apparatus rotating the projected laser beam provides the angular separation from this datum of the lines connecting the mobile reference axis to successive retroreflectors. This real-time angular data is utilized with the known locations of the retroreflectors to trigonometrically compute using three point resection, the exact real-time location of the mobile reference axis (hence the navigating vehicle) vis-a-vis the structured environment, e.g., in terms of two-dimensional Cartesian coordinates associated with the environment.

Claims

1. A laser-based mobile navigation system, capable of locating a mobile vehicle in a two-dimensional coordinate frame of reference in a structured environment, said system comprising:

at least three stationary retroreflective elements spaced apart from each other at known coordinates in said two-dimensional coordinate frame of reference, one of said retroreflective elements having a distinctive retroreflection;

mobile laser source means supported by said mobile vehicle for projecting a mobile narrow laser beam rotating about a mobile reference axis normal to the two-dimensional coordinate frame of reference, whereby said mobile rotating laser beam sequentially interacts with said retroreflective elements to generate corresponding retroreflections therefrom;

retroreflection responsive signal generating and receiving means connected to said mobile laser source means, responsive to the retroreflections from said stationary retroreflective elements, for generating output signals corresponding to each retroreflection, including said distinctive retroreflection, for receiving input signals corresponding to each retroreflection, including said distinctive retroreflection, and for measuring angles corresponding to said sequentially encountered retroreflector element, with respect to a current datum corresponding to said distinctive retroreflection; and

computation means cooperating with said signal generating and receiving means for computing from said known coordinates of said retroreflective elements and said output signals, by three-point resection, the real-time coordinates of said mobile reference axis in said two-dimensional coordinate frame of reference.

2. A laser-based mobile navigation system, capable of locating a mobile vehicle in a two-dimensional coordinate frame of reference in a structured environment, said system comprising:

at least three stationary retroreflective elements spaced apart from each other at known coordinates in said two-dimensional coordinate frame of reference, one of said retroreflective elements having a distinctive retroreflection;

mobile laser source means supported by said mobile vehicle for projecting a mobile narrow laser beam rotating about a mobile reference axis normal to the two-dimensional coordinate frame of reference, whereby said mobile rotating laser beam sequentially interacts with said retroreflective elements to generate corresponding retroreflections therefrom;

a photoelectric element connected to said mobile laser source means, responsive to the retroreflections from said stationary retroreflective elements, generating first output signals corresponding to each retroreflection, including said distinctive retroreflection;

azimuth means connected to said mobile laser source means for determining current angular positions of said mobile projected laser beam corresponding to each of said first output signals, said current angular positions being measured with respect to a current datum corresponding to said distinctive retroreflection, and for generating updated second output signals indicating said current angular positions;

data storage means cooperating with said mobile laser source means for storing said known coordinates of said retroreflective elements and said updated second output signals; and

computation means cooperating with said data storage means for computing from said stored known coordinates of said retroreflective elements and said updated second output signals, by three-point resection, the real-time coordinates of said mobile reference axis in said two-dimensional coordinate frame of reference.

3. A laser-based navigation system according to claim 2, wherein:

said mobile laser source means comprises rotating means for redirecting laser beams, rotating about said mobile reference axis such that a non-rotating laser beam parallel to said mobile reference axis is received by said rotating means and is redirected to be a rotating beam projected substantially radially outward of said mobile reference axis while radially inwardly directed incident retroreflections of said rotating beam are redirected to be substantially parallel to said mobile reference axis.

4. A laser-based navigation system according to claim 3, wherein:

said laser source means further comprises an apertured mirror inclined at 45°

to said mobile reference axis, said apertured mirror being formed with an aperture large enough to pass therethrough said non-rotating laser beam parallel to said mobile reference axis and directed to be received by said rotating means, said aperture also being smaller than the cross-section of said retroreflection redirected by said rotating means to be substantially parallel to said mobile reference axis, whereby a portion of said redirected retroreflection is finally reflected by said apertured mirror toward said photoelectric element.

5. A laser-based navigation system according to claim 4, further comprising:

laser beam focusing means for focusing said finally reflected redirected retroreflection onto a portion of said photoelectric element.

6. A laser-based navigation system according to claim 3, wherein:

said azimuth means comprises an angle encoder.

7. A laser-based navigation system according to claim 6, wherein:

said angle encoder is rotatably connected to said rotating means to rotate at a predetermined speed ratio therewith.

8. A laser-based navigation system according to claim 2, wherein:

said mobile narrow rotating beam is powered at a level low enough as to be harmless to a human being exposed thereto.

9. A laser-based navigation system according to claim 8, wherein:

said laser source means comprises a He-Ne laser.

10. A method for laser-based locating of a mobile vehicle in a two-dimensional coordinate frame of reference associated with a structured environment, comprising the steps of:

locating at least three stationary retroreflective elements spaced apart from each other at known coordinates in said two-dimensional coordinate frame of reference, one of said retroreflective elements having a distinctive retroreflection;

projecting from laser source means mounted on said mobile vehicle a mobile narrow laser beam rotating about a mobile reference axis normal to the two-dimensional coordinate frame of reference, whereby said mobile rotating laser beam sequentially interacts with said retroreflective elements to generate corresponding retroreflections therefrom;

receiving the retroreflections from said stationary retroreflective elements at the mobile vehicle, measuring angles corresponding to said sequentially encountered retroreflector elements, with respect to a current datum corresponding to said distinctive retroreflection, and generating therefrom output signals corresponding to each retroreflection including said distinctive retroreflection; and

computing from said known coordinates of said retroreflective elements and said output signals, by three-point resection, the real-time coordinates of said mobile reference axis in said two-dimensional coordinate frame of reference.

11. A method for laser-based locating of a mobile vehicle in a two-dimensional coordinate frame of reference in a structured environment, comprising the steps of:

locating at least three stationary retroreflective elements spaced apart from each other at known coordinates in said two-dimensional coordinate frame of reference, one of said retroreflective elements having a distinctive retroreflection;

projecting from laser source means mounted on said mobile vehicle a mobile narrow laser beam rotating about a mobile reference axis normal to the two-dimensional coordinate frame of reference, whereby said mobile rotating laser beam sequentially interacts with said retroreflective elements to generate corresponding retroreflections therefrom;

receiving the retroreflections from said stationary retroreflective elements at a photoelectric element connected to said laser source means, and generating therefrom first output signals corresponding to each retroreflection, including said distinctive retroreflection;

determining current angular positions of said mobile projected laser beam corresponding to each of said first output signals by azimuth means connected to said laser source means, said current angular positions being measured with respect to a current datum corresponding to said distinctive retroreflection, and for generating updated second output signals indicating said current angular positions;

storing said known coordinates of said retroreflective elements and said updated second output signals; and

computing from said known coordinates of said retroreflective elements and said updated second output signals, by three-point resection, the real-time coordinates of said mobile reference axis in said two-dimensional coordinate frame of reference.

12. A method according to claim 11, wherein:

said projected rotating laser beam is powered at a low level so that interception thereof by human beings will not cause them harm.

13. A method according to claim 11, wherein:

said projected laser beam is a He-Ne laser beam.