Laser obstacle detection method and sensor

• US 5,970,433 A
• Filed: 02/12/1997
• Issued: 10/19/1999
• Est. Priority Date: 06/24/1996
• Status: Expired due to Term

• Current Assignee: Mitsui Engineering & Shipbuilding Company Limited (Mitsui E&S Holdings Co., Ltd.)
• Original Assignee: Mitsui Engineering & Shipbuilding Company Limited (Mitsui E&S Holdings Co., Ltd.)
• Inventors: Takehara, Toru, Oka, Koji, Hisatani, Masujiro, Imajo, Hiroshi
• Primary Examiner(s): WACHSMAN, HAL D
• Application Number:
  US08/799,484
• Time in Patent Office: 979 Days
• Field of Search: 364/525, 364/526, 364/805, 364/556, 364/551.01, 364/561, 364/580, 364/604, 701/28, 701/96, 701/211, 701/301, 340/901, 340/903, 340/904, 340/937, 340/942, 340/435, 340/436, 340/437, 340/433, 342/69, 342/70, 342/54, 356/4.01, 356/4.07, 356/5.01, 356/152.3, 356/4.04, 356/375, 356/380, 356/386, 356/387, 356/5.03, 180/167, 180/169, 359/205, 359/208, 359/221, 359/154, 359/155, 359/561, 359/731, 359/857, 359/861, 359/864, 359/869, 250/559.38, 250/559.39, 250/559.13, 250/559.26, 250/234-236, 372/15, 372/24, 235/467, 702/40, 702/94, 702/97, 702/134, 702/135, 702/136, 702/143, 702/150, 702/159, 702/158, 702/172
• US Class Current: 702/159
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G01S 7/4811 common to transmitter and receiver
• CPC Class Codes: G01S 7/4816 of receivers alone
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G01S 7/4873 by deriving and controlling a threshold value
• CPC Class Codes: G02B 26/105 with one or more pivoting mirrors or galvano-mirrors G02B26/101 takes precedence
• CPC Class Codes: G05D 1/024 in combination with a laser lasers per se H01S
• 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 sensor detects the presence or the absence of an obstacle by radiating a laser beam to the outside of a casing through a light projecting mirror and by letting the reflected light from an obstacle enter a light receiving element through a light receiving mirror. A light projecting window with a light projecting mirror positioned and a light receiving window with a light receiving mirror are positioned in the casing with a space therebetween to prevent reflected light from directly entering the light projecting window. The mirrors are attached to a rotation shaft of a motor, or rotation shafts of motors, synchronously rotatable provided between both mirrors. The optical axis of light radiated to the outside of the casing is set to face in a higher direction than horizontal to radiate in a cone-shaped form. By comparing a received light signal from a light receiving circuit to an output signal from a circuit for a previously set threshold, which has a correlation between detected distance and light intensity, a light receiving trigger is output. The distance is calculated when a signal is greater than the threshold. The presence or the absence of an obstacle is determined by the detection of reflected light intensity. This laser obstacle detection method and sensor, which can be used on an automated guided vehicle (AGV), will not misdetect rainfall as an obstacle.

Claims

1. A laser obstacle detection method that uses a sensor disposed in a casing for detecting the presence or the absence of an obstacle outside of the casing by radiating a laser light beam from a light source to the outside of the casing and when a potential obstacle is present receiving light reflected from the potential obstacle to a light receiving element disposed in the casing, the method comprising the steps of:

determining a threshold light intensity signal based on a correlation of detected distance and light intensity;

radiating a laser light beam outward from the casing and generating a light projecting signal;

receiving a light beam reflected back to the light receiving element and generating a light receiving signal;

comparing the generated light receiving signal to the threshold light intensity signal;

calculating and outputting a distance detected to a potential obstacle based on the generated light receiving signal and the light projecting signal when the reflected light beam has an intensity greater than the threshold light intensity signal; and

determining whether the potential obstacle is an obstacle based on a relationship between the detected distance and a relative direction of the sensor to the potential obstacle.

2. The laser obstacle detection method of claim 1 wherein the step of radiating a laser light beam outward from the casing includes reflecting the laser beam with a light projecting mirror.

3. The laser obstacle detection method of claim 1 wherein the step of receiving a light beam reflected back to the light receiving element includes using a light receiving mirror disposed in the casing.

4. The laser obstacle detection method of claim 1 wherein the step of determining a threshold light intensity signal based on a correlation of detected distance and light intensity includes establishing a plurality of predetermined threshold values based on intensity of the light beam reflected to the light receiving element and distance, resulting in a generally hyperbolic relationship.

5. A laser obstacle detection sensor assembly for detecting presence of an obstacle using light radiated from a light source and reflected back from a potential obstacle, comprising:

a casing from which light is radiated therefrom, the casing having a central driving section;

a light projecting window formed in the casing;

a light projecting mirror disposed in the casing facing the light projecting window;

a light receiving window formed in the casing, the light receiving window being spaced from the light projecting window, wherein the central driving section is located between the light projecting window and the light receiving window and extends outwardly from the light projecting window and light receiving window thus forming an eave that prevents raindrops from directly contacting the light projecting window;

a light receiving mirror disposed in the casing facing the light receiving window to prevent light directly reflected from the light projecting window from entering the light receiving window; and

a drive source housed in the central driving section and coupled to the light projecting mirror and the light receiving mirror that drives the light projecting mirror and the light receiving mirror in synchronous rotation.

6. The laser obstacle detection sensor assembly of claim 5 wherein the drive source comprises a single motor with a rotation shaft that supports the light receiving mirror and the light projecting mirror.

7. The laser obstacle detection sensor assembly of claim 5 wherein the drive source comprises motors having drive shafts that are synchronously rotatable and that support the light receiving mirror and the light projecting mirror.

8. The laser obstacle detection sensor assembly of claim 5 wherein the light projecting window and the light receiving window are annular and provide 360 degree radiation and receipt of light.

9. The laser obstacle detection sensor assembly of claim 5 wherein the light projecting mirror has a reflecting surface with an optical axis that is disposed in a direction higher than horizontal and light is reflected from the reflecting surface in a cone-shaped form.

10. A laser obstacle detection sensor assembly for detecting presence of an obstacle using light radiated from a light source and reflected back from a potential obstacle, comprising:

a casing from which light is radiated therefrom;

a light projecting window formed in the casing;

a light projecting mirror disposed in the casing facing the light protecting window;

a light receiving window formed in the casing, the light receiving window being spaced from the light projecting window;

a light receiving mirror disposed in the casing facing the light receiving window to prevent light directly reflected from the light projecting window from entering the light receiving window; and

a drive source coupled to the light protecting mirror and the light receiving mirror that drives the light projecting mirror and the light receiving mirror in synchronous rotation,

wherein the light receiving mirror has a reflecting surface including a flat reflecting portion and a curved reflecting portion having varied curvature.

11. A laser obstacle detection sensor for detecting presence of an obstacle based on a light radiated from the sensor and reflected back to the sensor, comprising:

a light receiving element that receives a light signal reflected back from a potential obstacle;

a light receiving circuit connected to the light receiving element that converts the received light signal into a photoelectric signal representative of reflected light intensity;

a threshold setting circuit that generates a preset threshold output signal based on a correlation between a distance from an obstacle and light intensity; and

a determiner coupled to the threshold setting circuit and the light receiving circuit that compares the photoelectric signal of reflected light intensity to the preset threshold output signal and, when the photoelectric signal of reflected light intensity is greater than the threshold output signal, determines the presence of the obstacle.

12. The laser obstacle detection sensor of claim 11, wherein the determiner also determines a distance to the obstacle.

13. The laser obstacle detection sensor of claim 11 wherein the threshold setting circuit sets a plurality of predetermined threshold values based on intensity of light beam reflected to the light receiving element and distance, resulting in a generally hyperbolic relationship.

14. A laser obstacle detection sensor assembly for detecting presence of an obstacle using light radiated from a light source and reflected back from a potential obstacle, comprising:

a casing from which light is radiated therefrom;

a light projecting window formed in the casing;

a light projecting mirror disposed in the casing facing the light projecting window;

a light receiving window formed in the casing, the light receiving window being spaced from the light projecting window;

a light receiving mirror disposed in the casing facing the light receiving window to prevent light directly reflected from the light projecting window from entering the light receiving window;

a drive source coupled to the light projecting mirror and the light receiving mirror that drives the light projecting mirror and the light receiving mirror in synchronous rotation;

a light receiving element coupled to the light receiving mirror that receives a light signal from light reflected back from the potential obstacle;

a light receiving circuit connected to the light receiving element that converts the received light signal into a photoelectric signal representative of reflected light intensity;

a threshold setting circuit that generates a preset threshold output signal based on a correlation between a distance from an obstacle and light intensity; and

a determiner coupled to the threshold setting circuit and the light receiving circuit that compares the photoelectric signal of reflected light intensity to the preset threshold output signal and, when the photoelectric signal of reflected light intensity is greater than the threshold output signal, determines the presence of the obstacle.

15. The laser obstacle detection sensor assembly of claim 14 wherein the light projecting mirror has a reflecting surface with an optical axis that is disposed in a direction higher than horizontal and light is reflected from the reflection surface in a cone-shaped form.

16. The laser obstacle detection sensor assembly of claim 15 wherein the light receiving mirror has a reflecting surface including a flat reflecting portion and a curved reflecting portion having varied curvature.

17. A laser obstacle detection sensor assembly that detects the presence of an obstacle, comprising:

a laser light source that radiates a laser light beam;

a light projecting mirror that reflects the laser light beam toward a potential obstacle;

a light receiving element that receives light reflected back from the potential obstacle; and

a light receiving mirror that reflects light from the potential obstacle to the light receiving element, wherein the light receiving mirror has a reflecting surface including a flat reflecting surface and raised elongate reflecting surface generally centrally disposed on the flat reflecting surface, the raised reflecting surface having a curved projecting portion.

18. The laser obstacle detection sensor assembly of claim 17, wherein the raised reflecting surface has a generally T-shape.

19. The laser obstacle detection sensor assembly of claim 17, wherein the curved projecting portion has more than one radius of curvature.

20. The laser obstacle detection sensor assembly of claim 17, wherein the curved projecting portion flares upwardly to a projecting point.