System and method for precisely positioning a robotic tool

• US 5,321,353 A
• Filed: 05/13/1992
• Issued: 06/14/1994
• Est. Priority Date: 05/13/1992
• Status: Expired due to Term

• Current Assignee: Storage Technologies Corporation (Oracle Corporation)
• Original Assignee: Storage Technologies Corporation (Oracle Corporation)
• Inventors: Furness, Duncan
• Primary Examiner(s): IP, SHIK LUEN PAUL
• Application Number:
  US07/882,343
• Time in Patent Office: 762 Days
• Field of Search: 318/560-646, 395/80-89, 395/93-96, 901/1, 901/3, 901/5, 901/9, 901/13, 901/12, 901/15-23, 901/40, 901/47, 358/88, 358/101, 358/107, 364/188, 364/559, 356/376, 350/130
• US Class Current: 318/568.11
• CPC Class Codes: B25J 9/1697 Vision controlled systems

Abstract

A system and method for precisely positioning a robotic tool relative to a worksite, wherein the worksite includes a positioning target located at a fixed position relative thereto is disclosed. A camera coupled to the robotic tool detects the target and generates a position signal representing a current position of the robotic tool relative to the worksite. A system controller receives the position signal and computes a parallax-corrected position based on the distance to the worksite. In addition, the system controller produces a correction signal representing the difference between the parallax-corrected position and the current position. A mechanical arm precisely positions the robotic tool and the worksite relative to each other.

Claims

1. An apparatus for precisely positioning a robotic tool relative to a worksite, wherein the worksite has a target located at a fixed position relative thereto, the apparatus comprising:

(a) a camera, mounted to the robotic tool at an angle, operable to;

(1) focus an image of the target onto a focal plane so that when the robotic tool is at a nominal distance from the worksite, said image appears at a specified position on the focal plane, and to

(2) generate a position signal indicating a current position of the robotic tool relative to the worksite, as indicated by an actual position on said focal plane where said image of the target appears;

(b) a system controller, in communication with said camera, operable to

(1) determine a parallax corrected position of said image of the target on said focal plane, wherein said parallax corrected position is separated from said specified position for tool distances other than said nominal distance, said parallax corrected position corresponds to parallax free positioning of the robotic tool relative to the worksite, and said parallax corrected position is based on

(i) said nominal distance between the robotic tool and the worksite and any variation in distance from said nominal distance,

(ii) said angle, and

(iii) a focal length of said camera, and

(2) generate a position correction signal representing a difference between said current position of the robotic tool relative to the worksite and said desired position of the robotic tool relative to the worksite; and

(c) a positioning mechanism, in communication with said system controller, to reposition the robotic tool relative to the worksite in response to said position correction signal.

2. The apparatus of claim 1, wherein said positioning mechanism is coupled to the robotic tool and is configured to reposition the robotic tool relative to the worksite by moving the robotic tool.

3. The apparatus of claim 1, wherein said positioning mechanism is coupled to the worksite and is configured to reposition the robotic tool relative to the worksite by moving the worksite.

4. The apparatus of claim 1, wherein said positioning mechanism comprises a plurality of position arms, position encoders and electric motors.

5. The apparatus of claim 1, further comprising means for measuring said distance between the worksite and the robotic tool.

6. The apparatus of claim 1, further comprising memory means for storing said distances measured by said means for measuring.

7. The apparatus of claim 1, wherein said positioning mechanism further comprises means for coarsely positioning the robotic tool and the worksite relative to each other.

8. A method for precisely positioning a robotic tool relative to a worksite, wherein the robotic tool has a camera mounted at an angle thereto, and wherein the worksite has a target located at a fixed position relative thereto, the method comprising the steps of:

(1) focusing an image of the target onto a focal plane of the camera so that when the robotic tool is at a nominal distance from the worksite, said image appears at a specified position on the focal plane;

(2) generating an image position signal representing an actual position on said focal plane where said image of the target appears, said image position signal representing a perceived position of the robotic tool relative to the worksite;

(3) computing a parallax-corrected position of said image of the target on said focal plane, said parallax-corrected position representing the focal plane position on which said image must appear for the tool to be in a precise position relative to the worksite, wherein said parallax-corrected position is determined based on the angle of the camera, a focal length of the camera, said nominal distance between the tool and the worksite, and any variation from said nominal distance;

(4) computing a difference between said actual position of said image and said parallax-corrected position of said image, said difference representing a difference between said perceived position and said actual position of the robotic tool relative to the worksite;

(5) generating a position correction signal based on a difference between said actual position of said image and said parallax-corrected position of said image; and

(6) repositioning the robotic tool to said precise position relative to the worksite in response to said position correction signal.

9. The method of claim 8, further comprising a step:

measuring the distance from the robotic tool to the worksite.

10. The method of claim 8, wherein said parallax corrected position is stored in a memory for later use.

11. The method of claim 8, wherein said step (3) of determining said parallax corrected position is performed in advance for each worksite and each of said parallax corrected positions determined in said step (3) is stored for later use.

12. The method of claim 8, further comprising the step of measuring an actual distance from said robotic tool to said worksite in advance for each of a plurality of worksites and storing said actual distance, wherein said actual distance includes said nominal distance and said variation therefrom.

13. The method of claim 12, further comprising the step of determining said variation from said nominal distance and storing said variation.

14. The method of claim 8, further comprising the steps of:

measuring an actual distance from said robotic tool to said worksite in advance for each of a plurality of worksites; and

determining a difference between said actual distance measured and said nominal distance, and storing said difference as said variation from said nominal distance.

15. The method of claim 8 further comprising a step before step (1) of coarsely positioning said robotic tool relative to the worksite.

16. The method of claim 8, wherein said parallax corrected position is determined as an offset from a center of the focal plane, wherein said offset can be determined in each dimension by the equation:

##EQU5## wherein, ψ

_cc is said offset, f is said focal length, d_nom is said nominal distance, Δ

d is said variation from said nominal distance, and γ

is said angle of said camera to said tool.