Method and apparatus for electro-optically determining the dimension, location and attitude of objects including light spot centroid determination

• US 5,164,579 A
• Filed: 06/06/1991
• Issued: 11/17/1992
• Est. Priority Date: 04/30/1979
• Status: Expired due to Term

• Current Assignee: Sensor Adaptive Machines, Inc.
• Original Assignee: Diffracto, Ltd. (Lmi Technologies Incorporated)
• Inventors: Pryor, Timothy R., Hockley, Bernard, Liptay-Wagner, Nick, Hageniers, Omer L., Pastorius, W. J.
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): Lee, John R.
• Application Number:
  US07/711,397
• Time in Patent Office: 530 Days
• Field of Search: 250/201.6, 250/202, 250/203.3, 250/203.4, 250/203.5, 250/203.6, 250/206.1, 250/206.2, 250/208.2, 250/208.3, 250/561, 356/1, 356/4, 356/5, 356/141, 356/152, 356/376
• US Class Current: 250/206.1
• CPC Class Codes: G01B 11/002 for measuring two or more coordinates
• CPC Class Codes: G01B 11/24 for measuring contours or curvatures
• CPC Class Codes: G01B 11/2416 of gears optical projection profile comparators G01B9/08
• CPC Class Codes: G01B 11/245 using a plurality of fixed, simultaneously operating transducers G01B11/2408 - G01B11/2425, G01B11/255 take precedence
• CPC Class Codes: G01S 17/46 Indirect determination of position data
• CPC Class Codes: G01S 17/48 Active triangulation systems, i.e. using the transmission and reflection of electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/87 Combinations of systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/88 Lidar systems specially adapted for specific applications
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/481 Constructional features, e.g. arrangements of optical elements
• CPC Class Codes: G01S 7/4811 common to transmitter and receiver
• CPC Class Codes: G01S 7/4813 Housing arrangements
• CPC Class Codes: G01S 7/491 Details of non-pulse systems

Abstract

A method and apparatus for optically determining the dimension of part surfaces. Particular embodiments describe optical triangulation based coordinate measurement machines capable of accurate measurement of complex surfaces, such as gear teeth and turbine blades. Other embodiments provide highly useful sensors for robot guidance and related purposes. Up to 5 axis sensing capability is provided on surfaces of widely varying form.

Claims

1. Apparatus for determining the centroid of an image of a zone of light on a light detector, said light detector comprising a linear array of discrete light sensitive elements, each of said elements being capable of generating an output signal responsive to light incident thereon, said apparatus comprising

means for forming an image of a zone of light on the detector array, said image having an intensity above a pre-determined value such that the output signal of light sensitive elements on which image is incident exceeds a threshold value;

means for scanning the array;

means for determining, from the array scan, a first array location at which the output signal rises above the threshold value and a second array location at which the output falls below the threshold value; and

means for determining from said first and second array locations, the location of the centroid of said light image on said detector.

2. Apparatus according to claim 1 wherein means for determining the centroid location comprises means for determining the mid-point on the array between said first and second location.

3. Apparatus according to claim 1 wherein the output signal of the light sensitive elements on which said image is incident exceeds a plurality of different threshold values, wherein said first and second array location determining means comprises means for effecting said determinations for each of said different threshold values, and wherein said centroid determining means comprises means for determining said centroid location from said first and second array location for each of said threshold values.

4. Apparatus according to claim 1 wherein said means for determining said first and second array locations comprises

means for determining the number of elements from one end of the array to the element nearest said end having an output signal in excess of said threshold value to give a first value, and

means for determining the number of elements of the array having an output signal in excess of said threshold signal to give a second value;

and wherein said means for determining the centroid location comprises;

means for doubling said first value of elements to give a third value,

means for adding said second and third values to give a sum, and

means for halving said sum to give said image a value representative of the location of the centroid of said image on said array.

5. A method for determining the centroid of an image of a zone of light on a light detector, said light detector comprising a linear array of discrete light sensitive elements, each of said elements being capable of generating an output signal responsive to light incident thereon, said method comprising the steps of:

forming an image of a zone of light on the detector array, said image having an intensity above a pre-determined value such that the output signal of light sensitive elements on which said image is incident exceeds a threshold value;

scanning the array;

determining, from the array scan, a first array location at which the output signal rises above the threshold value and a second array location at which the output falls below the threshold value; and

determining from said first and second array locations, the location of the centroid of said light image on said detector.

6. A method according to claim 5 wherein said step of determining the centroid location comprises determining the mid-point on the array between said first and second location.

7. A method according to claim 5 wherein the output signal the light sensitive elements in which said image is incident exceeds a plurality of different threshold values, wherein said first and second array locations are determined for each of said different threshold values, and wherein said centroid determining step comprises means for determining said centroid location from said first and second array location for each of said threshold values.

8. A method according to claim 5 wherein said step of determining said first and second array locations comprises

determining the number of elements from one end of the array to the element nearest said end having an output signal in excess of said threshold value to give a first value, and

determining the number of elements of the array having an output signal in excess of said threshold signal to give a second value;

and wherein said means for determining the centroid location comprises;

doubling said first value of elements to give a third value,

summing said second and third values to give a sum, and

dividing said sum by two to give said image a value representative of the location of the centroid of said image on said array.