Arrangement for rapid depth measurement using lens focusing

• US 4,640,620 A
• Filed: 12/29/1983
• Issued: 02/03/1987
• Est. Priority Date: 12/29/1983
• Status: Expired due to Term

• Current Assignee: Robotic Vision Systems, Inc. (Acuity Brands, Inc.)
• Original Assignee: Robotic Vision Systems, Inc. (Acuity Brands, Inc.)
• Inventors: Schmidt, Richard
• Primary Examiner(s): Rosenberger, R. A.
• Application Number:
  US06/566,688
• Time in Patent Office: 1,132 Days
• Field of Search: 356/375, 356/376, 356/127, 350/162.12, 350/163.13, 250/201 AF
• US Class Current: 356/609
• CPC Class Codes: G01B 11/25 by projecting a pattern, e.g. one or more lines, moiré fringes on the object G01B11/255 takes precedence ; image analysis for depth or shape recovery G06T7/50

Abstract

A pattern of light is projected upon a surface to be measured which may be devoid of surface detail. A sharply focused image of the surface provides distance discrimination. Although the projected pattern may be separate from the imaging optics, a common optics path removes distortion, provides maximum sensitivity and eliminates processing for misalignment between projector and imager. Parallel detection of regions within the image receiving light intensities above a threshold enables rapid availability of measurements. Optical cross-correlation and Fourier transform processing methods may be employed to enhance image processing with no processing delay. Three-dimensional co-ordinate measurements relative to the sensor are reported for all in-focus regions of the image. Refocusing the lens provides depth coverage.

Claims

1. A method for simultaneously acquiring the three-dimensional co-ordinates relative to a sensor of at least two spatially separated points on a surface that may be devoid of detail, comprising the steps of:

projecting a pattern of light with a projector from a light source;

imaging reflected light from said pattern with a lens onto a light-sensitive detector array;

focusing said image sharply by said lens within a narrow object plane;

calibrating the image on said detector array for each unique location of the said sharply focused narrow object plane;

storing calibration data from said calibration in a memory;

adjusting said object plane focal distance with said lens to intersect the surface of an object to be measured at an intersection;

said intersection containing at least two spatially separated points;

comparing each measured response to a threshold value; and

conveying each response above threshold value into a three-dimensional measurement report from said calibration data.

2. A method as defined in claim 1, and cross-correlating optically said image of reflected light with a stored reference pattern;

and enhancing said image in regions of sharp focus for detection by said light-sensitive detector array.

3. A method as defined in claim 1, and processing said image of reflected light by Fourier transforming said image, passing the Fourier transformed image through a transform filter for producing a transformed and filtered image, and then inverse transforming the transformed and filtered image;

said processing step enhancing said image of reflected light in regions of sharp focus for detection by said light-sensitive detector array.

4. An arrangmeent for simultaneously obtaining three-dimensional measurements of at least two spatially separated points on objects which may be devoid of surface detail, comprising:

projector means for projecting a pattern of light from a light source;

lens means for imaging reflected light from said pattern in a narrow object plane;

light-sensitive detector means for parallel detection of light in regions of the image;

means for storing calibration data;

means for adjusting said object plane focal distance with said lens means to intersect the surface of an object to be measured at an intersection;

said intersection containing at last two spatially separated points; and

means for reporting three-dimensional meaurements from said calibration data for each detected element indicating a light level above a threshold.

5. An arrangement as defined in claim 4, including a liquid crystal light valve with input and output, said image of reflected light being imaged onto said liquid crystal light valve input;

a reference light pattern of collimated monochromatic light being projected onto said output of said liquid crystal light value;

analyzer means selectively transmitting signals corresponding to coincidence of said image and said reference pattern for producing an enhanced image;

said enhanced image passing on to said parallel detection means.

6. An arrangement as defined in claim 4, including a liquid crystal light valve for converting said image of reflected light to an image of collimated monochromatic light;

means for Fourier transforming said monochromatic image;

a transform filter for passing the Fourier transformed image therethrough to produce a transformed and filtered image, and means for inverse transforming the transformed and filtered image thereafter for enhancing said image of reflected light in regions of sharp focus detection by said parallel detection means.