Process and apparatus for the measurement of object topographies by means of projected fringe patterns

• US 5,379,107 A
• Filed: 05/14/1993
• Issued: 01/03/1995
• Est. Priority Date: 05/29/1992
• Status: Expired due to Fees

• Current Assignee: Carl-Zeiss-Stiftung
• Original Assignee: Carl-Zeiss-Stiftung
• Inventors: Hof, Albrecht, Hanssen, Adalbert
• Primary Examiner(s): Rosenberger, Richard A.
• Assistant Examiner(s): Pham, Hoa Q.
• Application Number:
  US08/063,175
• Time in Patent Office: 599 Days
• Field of Search: 356/376, 356/375, 356/243, 356/43, 356/1, 250/237 G, 250/238, 250/561, 358/107
• US Class Current: 356/604
• CPC Class Codes: G01B 11/2531 using several gratings, projected with variable angle of incidence on the object, and one detection device
• CPC Class Codes: G01C 11/02 Picture taking arrangements specially adapted for photogrammetry or photographic surveying, e.g. controlling overlapping of pictures

Abstract

In a process and apparatus for measuring object topographies by means of projected fringe patterns, to enlarge the region of certainty, different periodicities are evaluated. Calibration of the measurement apparatus is carried out in at least two parallel planes, situated in the forward and in the rearward regions of the measurement volume. Corrected phase values are first calculated from the phase measurement values of the measurement object. By combination of the phase measurement values relating to the pattern of long periodicity and of the pattern of short periodicity, the fringe order of the phase values relating to short periodicity is calculated. By interpolation of the correction values between the two planes in which the reference measurements were carried out, the measurement process and a corresponding measurment apparatus provide highly accurate measurement values, with simultaneously reduced requirements on the accuracy of mechanical and/or optical adjustment.

Claims

1. Process for the measurement of object topographies by means of fringe patterns projected onto a measurement object within a measurement volume by the aid of a measurement apparatus, which measurement apparatus deviates in unknown manner from its desired set up, the method comprising:

evaluating phase measurement values from projections such that first phase measurement values arise relating to a first spatial periodicity with a large distance between contour surfaces and second phase measurement values arise relating to a second spatial periodicity with a small distance between contour surfaces,

carrying out at least a first calibration measurement with respect to a calibration surface in a forward region of said measurement volume and generating first reference phase values,

carrying out at least a second calibration measurement with respect to a calibration surface in a rearward region of said measurement volume remote from said measurement apparatus and generating second reference phase values, and

correcting said phase measurement values taking into account said first and second reference phase values of said at least first and second calibration measurements, the correcting step comprising the steps of

calculating a phase value, defining an apparent phase value, relating to said second spatial periodicity from said first phase measurement value under consideration of said first and second reference phase values and theoretical phase values calculated from the desired set up of the measurement apparatus for said at least first and second calibrations measurement,

dividing said apparent phase value into a fringe order and phase remainder, and

comparing said phase remainder with a value calculated from said second phase measurement value.

2. Process according to claim 1, further comprising calculating a corrected fringe order (NK) from said fringe order (NK'"'"') according to:

NK=NI'"'"'+1 for RI'"'"'-DK'"'"'>

0.5,

NK=NK'"'"'-1 for DK'"'"'-RK'"'"'>

0.5, and

NK=NK'"'"'in all other cases

3. Process according to claim 2, further comprising calculating the three space coordinates (X, Y, Z) of any measurement object point from said corrected fringe order (NK) and said offset-corrected phase value (DK'"'"') relating to short periodicity.

4. Process according to claim 1, further comprising calculating corrected phase values utilizing a function that is linear with respect to said first and second phase measurement values which function reproduces theoretical phases for points on said calibration surfaces.

5. Process according to claim 1, further comprising carrying out correction of said phase measurement values depending upon temperature.

6. Process for the measurement of object topographies by means of fringe patterns projected onto a measurement object within a measurement volume by the aid of a measurement apparatus, which measurement apparatus deviates in unknown manner from its desired set up, the method comprising:

evaluating phase measurement values from projections such that first phase measurement values arise relating to a first spatial periodicity with a large distance between contour surfaces and second phase measurement values arise relating to a second spatial periodicity with a small distance between contour surfaces,

carrying out at least a first calibration measurement with respect to a calibration surface in a forward region of said measurement volume and generating first reference phase values, and

carrying out at least a second calibration measurement with respect to a calibration surface in a rearward region of said measurement volume remote from said measurement apparatus and generating second reference phase values,

wherein said at least first and second calibration measurements are carried out on a single white matt surface in two parallel positions.

7. Process according to claim 6, wherein the distance between the position of the calibration surface in said forward region and the calibration surface in said rearward region of said measurement volume is chosen such that the reference values of calibration measurements relating to said second spatial periodicity differ by a non-integer number greater than unity.

8. Process for the measurement of object topographies by means of fringe patterns projected onto a measurement object within a measurement volume by the aid of a measurement apparatus, which measurement apparatus deviates in unknown manner from its desired set up, the method comprising:

evaluating phase measurement values from projections such that first phase measurement values arise relating to a first spatial periodicity with a large distance between contour surfaces and second phase measurement values arise relating to a second spatial periodicity with a small distance between contour surfaces,

carrying out at least a first calibration measurement with respect to a calibration surface in a forward region of said measurement volume and generating first reference phase values, and

carrying out at least a second calibration measurement with respect to a calibration surface in a rearward region of said measurement volume remote from said measurement apparatus and generating second reference phase values,

wherein the distance between the position of the calibration surface in said forward region and the calibration surface in said rearward region of said measurement volume is chosen such that the reference values of calibration measurements relating to said second spatial periodicity differ by a non-integer number greater than unity.

9. Apparatus for the measurement of object surfaces by means of projection, recording and phase evaluating of brightness patterns, the evaluation generating phase values being corrected by correction data recorded during two calibration measurements, comprising:

at least one projector for the projection of periodic fringe patterns onto an object surface,

at least one camera for recording fringe patterns deformed by said object surface, and

an evaluating computer connected to said camera in which the object surface topography is calculated from the phase values of the recorded fringe patterns, utilizing a first pattern with long periodicity and at least a second pattern with short periodicity and resulting in first and second phase values relating to the pattern with long periodicity and short periodicity, respectively, wherein said evaluation computer includes

two image memories for storing first correction data relating to said pattern with long periodicity obtained by said two calibration measurements,

two further image memories for storing second correction data relating to said pattern with short periodicity obtained by said two calibration measurements,

at least one stored table for estimating a phase value, defining an apparent phase value, for the pattern with short periodicity from said first phase value for the pattern with long periodicity under consideration of said first and second correction data, and

at least a second stored table for calculating a fringe order relating to the pattern with short periodicity by comparing said apparent phase value and a further phase value calculated from said second phase value.

10. Apparatus according to claim 9, further comprising means for temperature measurement and means for taking into account during correction of the phase measurement values, temperature-dependent phase offsets that take into account temperature drift of the measurement apparatus.