Method for determining the position of an automated guided vehicle

• US 6,308,118 B1
• Filed: 04/11/2000
• Issued: 10/23/2001
• Est. Priority Date: 10/17/1997
• Status: Expired due to Fees

• Current Assignee: NDC Netzler & Dahlgren Company AB
• Original Assignee: NDC Netzler & Dahlgren Company AB
• Inventors: Holmquist, Fredrik
• Primary Examiner(s): Chin, Gary
• Application Number:
  US09/546,807
• Time in Patent Office: 560 Days
• Field of Search: 701/23, 701/24, 701/25, 701/26, 701/207, 701/300, 701/301, 318/587, 180/167, 180/168, 180/169
• US Class Current: 701/23
• CPC Class Codes: B66F 9/063 Automatically guided
• CPC Class Codes: G01S 17/74 Systems using reradiation of electromagnetic waves other than radio waves, e.g. IFF, i.e. identification of friend or foe
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 5/16 using electromagnetic waves other than radio waves
• CPC Class Codes: G05D 1/0236 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 method for position finding of an automated guided vehicle using detection of angle positions for anonymous reflectors (R₁-R₁₁). The anonymous reflectors are arranged in positions in a limited transport area, and the positions are stored. A concentrated beam (B) is emitted from a vehicle (10) and is made to pass over a search sector. The angle position in relation to a reference direction (D) of the vehicle (10) in reflective objects is continually detected during the sweep of the beam over the search sector, and corresponding angle values are determined. Initially the following measures are taken for association of the angle positions to physical reflectors, and for determination of the position of the vehicle (10); i) at least three angle values with a suitable distribution over the search sector is selected, ii) the angle values are associated to reflectors and a position is determined for the vehicle on the basis of the known position of the assumed reflectors, iii) if the vehicle position determined in this way is within a certain part of the transport area the other angle values are associated to reflectors, iv) for each angle value, existing deviation is determined between detected angle values and angle values expected between the vehicle position and known reflectors, v) the measures taken are repeated for each possible combination of selected angle values. A combination of associations with the best possible agreement on the vehicle position is selected, whereby the position and direction of the vehicle is determined.

Claims

1. A method for determining the position of an automated guided vehicle using detection of angle positions for anonymous reflectors (R₁-R₁₁), whereby

a) the anonymous reflectors are arranged in positions in a limited transport area,

b) the positions of the reflectors (R1-R11) are stored in memory,

c) a beam (B) is emitted from the vehicle (10) over a search sector,

d) the angle positions being detected in relation to a reference direction (D) of the vehicle (10) and the reflectors being detected over the search sector and corresponding angle values are determined, characterized by

e) storing multiple angle values determined over the search sector, and associating angle positions for the reflectors and determining the position of the vehicle (10) by:

i selecting an array of at least three angle values with a suitable distribution over the search sector,

ii associating the angle values to the reflectors and determining an assumed position for the vehicle on the basis of known positions of the reflectors,

iii associating other angle values to the reflectors if the assumed vehicle position is within a certain part of the transport area,

iv determining, for each angle value, a deviation between the detected angle value and an expected angle value,

v repeating steps i-iv for a number of combinations of selected reflectors, and

f) electing the combination of selected reflectors having the least deviation between the detected and expected angle values.

2. A method according to claim 1, characterized in that

distances between the reflectors (R₁-R₁₁) and a reference point on the vehicle (10) are determined, and

that relations between the determined distances and corresponding distances calculated between stored reflector positions and the assumed position for the vehicle are determined, and the elected combination of selected reflectors is allowed if the relations are within expected intervals.

3. A method according to claim 1, characterized in that

durations of reflected signals are detected as the beam is swept over the search sector, and values of the durations are determined,

that a relation between the values of the durations and expected values of the durations are determined, and

that the combination of selected reflectors is allowed, if the relation is within an expected interval.

4. A method according to claim 1, characterized in that

intensity of reflected signals are detected and intensity values of reflections from reflective objects is determined,

that a relation is established between the determined intensity values and expected intensity values of reflected signals at respective measured distances, and

that the combination of selected reflectors is allowed, if the relation is within an expected interval.

5. A method according to claim 2, characterized in that the reflectors (R₁-R₁₁) are planar reflectors,

that an expected intensity of a signal reflected from one of the reflectors (R₁-R₁₁) at different distances is established as intensity reference values,

that an expected duration of a signal reflected from one of the reflectors (R₁-R₁₁) at different distances is established as duration reference values,

that the expected intensity of a signal reflected from one of the reflectors (R₁-R₁₁) with respect to the angle position of the one of the reflectors (R₁-R₁₁), relative to a normal direction, is established as an angle factor,

that duration of one of the reflected signals is detected as the beam is swept over the search sector, and the value of the duration is determined,

that an angle position of one of the reflectors (R₁-R₁₁) in relation to the normal direction to the vehicle (10) is determined on the basis of a relation between the detected duration and the duration reference values,

that intensity of the reflected beam is detected and intensity values of reflections from reflective objects are determined,

that the expected intensity value from one of the reflectors (R₁-R₁₁) at a measured distance measured from the reference point is adjusted with regard to an intensity reference value and the angle factor, and

that the combination of selected reflectors is allowed, if the determined intensity value is within an expected interval around the adjusted intensity value.

6. A method according to claim 1, characterized in that the emitted beam (B) is modulated,

that the reflections received from objects in the transport area are compared with the emitted beam with regard to time delay, and

that the distances between the vehicle (10) and the objects are determined on the basis of respective time delays between a certain phase position of the emitted beam and a corresponding phase position of the received beam.

7. A method according to claim 6, characterized in that the emitted beam is modulated with a square wave with a frequency of approximately 2 MHz.

8. A method according to claim 1, characterized in that the emitted beam (B) is a laser beam.

9. A method according to claim 1, characterized in that the emitted beam (B) is a microwave beam.