Method and apparatus for noncontact surface contour measurement

• US 5,446,549 A
• Filed: 01/14/1993
• Issued: 08/29/1995
• Est. Priority Date: 01/14/1993
• Status: Expired due to Fees

• Current Assignee: United States Navy (U.S. Department Of Defense)
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Mazumder, Jyotirmoy, Voelkel, David D.
• Primary Examiner(s): EVANS, FANNIE L
• Application Number:
  US08/004,763
• Time in Patent Office: 957 Days
• Field of Search: 356/376, 348/87, 348/90, 348/126, 348/129, 348/130, 382/8
• US Class Current: 356/613
• CPC Class Codes: G01B 11/24 for measuring contours or curvatures

Abstract

Light at known angles is impinged onto an object whose contour is to be mured and a camera is used to receive the reflected light which is then recorded. A computer processes the images, mathematically manipulating them so that surface slopes are known. The slopes are than integrated to obtain local elevations which represent the object contour.

Claims

1. A noncontact measurement system for determining the contour of an object comprising:

an object to be measured,

a first light source focused close to the surface of said object,

a flat metal strip,

a wedged shaped platform on one end of said strip,

optical fiber means with an input and an output the output of which is mounted on said wedged shaped platform for directing light at said object,

a second light source for sending a beam to the input of said optical fiber means,

a translation stage in physical contact with said metal strip and capable of moving said metal strip so as to change the angle of the output of said optical fiber means,

a camera for receiving reflected light from said object,

a narrow beam filter between said object and said camera,

a recording means for recording light angle reflections given off by said object and received by said camera, and

controller means connected to the translation stage for varying the position of said translation stage.

2. The system of claim 1 further including a first computer means to process the data recorded by said recording means and capable of calculating values needed for further analysis of the recorded data.

3. The system of claim 2 including a second computer means for integrating the data obtained by said first computer means.

4. A system in accordance with claim 3 in which said first and second light sources are lasers.

5. The system of claim 4 further including a reference rod between the object and the translation stage so that a shadow is cast on said object when the object, the rod, and the output of said fiber optic means are in line with each other.

6. A system in accordance with claim 5 in which said controller means operates so that the angle of incident light from said optical fiber means is varied to allow the reflected light received by the camera to travel over the entire surface of said object.

7. The system of claim 1 in which said object rests on a second translation stage.

8. The system of claim 7 in which said second translation stage moves horizontally.

9. An on-line, noncontact method of measuring the surface contour of an object comprising the steps of:

aligning a measuring system which comprises at least a laser, a camera, an optical fiber having an input for receiving light from said laser and having an output, a reference piece between said optical fiber output and said camera, and a flat polished workpiece disposed so that laser light is reflected from the workpiece to establish a surface reference angle which is in the camera'"'"'s field of view and is recorded,

measuring the geometry of said system,

replacing said flat workpiece with the object whose contour is to be measured,

moving said optical fiber so that multiple paths are traced over the object by the laser light,

recording the angle of the laser reflected light at multiple locations of the object on videotape frames,

calculating a scaled fiber angle relative to the flat surface reference angle for each frame of videotape,

selecting and digitizing certain of the videotape frames so as to obtain two composite images at each of said selected multiple locations, and

determining the elevation of the surface at each said location.

10. The method of claim 9 in which the optical fiber angle is varied by changing the angle of a hinged arm to which the optical fiber is attached.

11. The method of claim 10 in which said hinged arm is attached to a translator stage which is moved by a motion controller.

12. The method of claim 11 in which said calculating is done by means of a first computer program.

13. The method of claim 12 in which said determining is done by means of a second computer program.