Apparatus and method for correcting for drift in production of objects by stereolithography

• US 5,059,021 A
• Filed: 11/08/1988
• Issued: 10/22/1991
• Est. Priority Date: 04/18/1988
• Status: Expired due to Term

• Current Assignee: 3D Systems, Inc. (3D Systems Corporation)
• Original Assignee: 3D Systems, Inc. (3D Systems Corporation)
• Inventors: Tarnoff, Harry L., Spence, Stuart T.
• Primary Examiner(s): Rosenberger, Richard A.
• Assistant Examiner(s): Pham, Hoa Q.
• Application Number:
  US07/268,907
• Time in Patent Office: 1,078 Days
• Field of Search: 356/121-123, 356/237, 356/356, 356/355, 356/153, 250/347, 250/239, 425/174, 425/174.1, 164/35
• US Class Current: 356/121
• CPC Class Codes: B29C 64/135 the energy source being concentrated, e.g. scanning lasers or focused light sources
• CPC Class Codes: B29C 64/40 Structures for supporting 3D objects during manufacture and intended to be sacrificed after completion thereof
• CPC Class Codes: B33Y 10/00 Processes of additive manufacturing
• CPC Class Codes: B33Y 30/00 Apparatus for additive manufacturing; Details thereof or accessories therefor
• CPC Class Codes: B33Y 40/00 Auxiliary operations or equipment, e.g. for material handling
• CPC Class Codes: B33Y 50/00 Data acquisition or data processing for additive manufacturing
• CPC Class Codes: G01J 1/4257 applied to monitoring the characteristics of a beam, e.g. laser beam, headlamp beam monitoring arrangements for lasers in general H01S3/0014
• CPC Class Codes: G03F 7/0037 Production of three-dimensional images
• CPC Class Codes: G03F 7/70416 2.5D lithography
• CPC Class Codes: G05B 2219/49013 Deposit layers, cured by scanning laser, stereo lithography SLA, prototyping
• CPC Class Codes: G06T 17/00 Three dimensional [3D] modelling, e.g. data description of 3D objects
• CPC Class Codes: G06T 17/10 Constructive solid geometry [CSG] using solid primitives, e.g. cylinders, cubes
• CPC Class Codes: G06T 17/20 Finite element generation, e.g. wire-frame surface description, tesselation

Abstract

An apparatus and a method for correcting for drift in production of objects by stereolithography is disclosed. A beam sensor comprising a pinhole in a plate and a photodector behind the pinhole is used to obtain the apparent position of the beam at calibration time and subsequently. A comparison between the prior and present apparent position of the sensor is made in order to determine a drift error correction term to be used to compensate for drift and thereby improve the accuracy and pointing repeatability of the scanning mechanism.

Claims

1. An apparatus for compensating for drift in position in a production of a three-dimensional object by stereolithography from a medium capable of solidification when exposed to a reaction means operating in a prescribed manner upon a working surface of the medium to provide successive adjacent solid laminae for forming the object including selective exposure of the medium to the reaction means between a first time and a second time, comprising:

(a) a sensor capable of detecting the reaction means and mounted at a predetermined location fixed with respect to a point on the working surface of the medium;

(b) positioning means for directing the reaction means based on use of positioning means information so that the sensor detects the reaction means, and selected positioning means information corresponding to the location of the sensor is determined;

(c) means for comparing the selected positioning means information at the second time to reference positioning means information obtained from directing the reaction means at the sensor at the first time occurring before the second time in order to determine drift of the positioning means between the first and second times; and

(d) means for compensating the positioning means for drift in position after the second time so that selective exposure of the medium after the second time occurs in registration with the selective exposure of the medium between the first and second times.

2. The apparatus of claim 1 wherein said reaction means is a beam.

3. The apparatus of claim 2 wherein said beam is a beam of electromagnetic radiation.

4. The apparatus of claim 3 wherein said beam of electromagnetic radiation is a beam of light.

5. The apparatus of claim 3 wherein said beam of light is a laser beam.

6. The apparatus of claim 2 wherein said beam is an electron beam.

7. The apparatus of claim 1 wherein said medium is a photopolymerizable resin.

8. The apparatus of claim 1 wherein said medium is a powder.

9. The apparatus of claim 1 wherein said medium is a liquid.

10. A method for compensating for drift in position in a production of a three-dimensional object by setereolithography from a medium capable of solidification when exposed to a reaction means operating in a prescribed manner upon a working surface of the medium to provide successive adjacent solid laminae for forming the object, including selective exposure of the medium to the reaction means between a first and second time, comprising the steps of:

directing the reaction means by a positioning means based on positioning means information so that a sensor mounted at a predetermined location fixed with respect to a point on the working surface of the medium can detect each portion of the reaction means associated with particular positioning means information;

determining reference positioning means information at a first time, from a relative intensity of each portion of the reaction means and from the particular positioning means information associated with each portion of the reaction means by determining best positioning means information associated with a centroid-like mathematical function of intensity of the reaction means;

determining selected positioning means information at a second time, from the relative intensity of each portion of the reaction means and from the particular positioning means information associated with each portion of the reaction means by determining best positioning means information associated with a centroid-like mathematical function of intensity of the reaction means;

comparing the reference positioning means information to the selected positioning means information in order to determine drift in position of the positioning means between the first and second times; and

compensating for the determined drift in position after the second time so that the selective exposure of the medium after the second time occurs in registration with the selective exposure of the medium between the first and second times.

11. An apparatus for compensating for drift in position in a production of a three-dimensional object by stereolithography from a medium capable of solidification when exposed to a reaction means operating in a prescribed manner upon a working surface of the medium to provide successive adjacent solid laminae for forming the object including selected exposure of the medium to the reaction means between a first time and a second time, comprising:

a plurality of predetermined sensor locations with associated X and Y coordinates and at least one sensor locatable at any one of the said predetermined sensor locations wherein each of the predetermined sensor locations is fixed with respect to a point on the working surface of the medium and wherein the plurality of predetermined sensor locations have different X coordinates and different Y coordinates;

positioning means for directing the reaction means so that the at least one sensor detects the reaction means and supplies selected positioning means information corresponding to a desired set of at least two predetermined sensor locations;

means for comparing the selected positioning means information at the second time to reference positioning means information obtained from directing the reaction means at the at least one sensor when located at the desired set of at least two predetermined sensor locations at the first time, occurring before the second time, in order to determine drift of the positioning means between the first and second times;

means for compensating for drift in position with a polynomial correction function of order one less than the number of predetermined sensor locations in the desired set of at least two predetermined sensor locations after the second time so that the exposure of the medium after the second time occurs in registration with the selected exposure of the medium between the first and second times.

12. The apparatus of claim 11 wherein the selective exposure of the medium comprises the exposure of a first cross-section.

13. The apparatus of claim 12 wherein the desired set of at least two predetermined sensor locations comprises two predetermined sensor locations.

14. The apparatus of claim 13 wherein the polynominal correction function is first order and consists of a zeroth order term that compensates for an offset in position and a first order term that compensates for a gain in position.

15. A method for compensating for drift in position in a production of a three-dimensional object by stereolithography from a medium capable of solidification when exposed to a reaction means operating in a prescribed manner upon a working surface of the medium to provide successive adjacent solid laminae for forming the object, including selective exposure of the medium to the reaction means between a first and second time, comprising the steps of:

specifying a plurality of predetermined sensor locations with associated X and Y coordinates and at least one sensor locatable at any one of the said predetermined sensor locations wherein each of the predetermined sensor locations is fixed with respect to a point on the working surface of the medium and wherein the plurality of predetermined sensor locations have different X coordinates and different Y coordinates;

directing the reaction means by a positioning means based on positioning means information so that the at least one sensor can detect each portion of the reaction means and supplying particular positioning means information associated with each portion of the reaction means for each predetermined sensor location in a desired set of at least two predetermined sensor locations;

determining reference positioning means information for each predetermined sensor location in the desired set of at least two predetermined sensor locations at a first time, from a relative intensity of each portion of the reaction means and from the particular positioning means information associated with each portion of the reaction means by determining best positioning means information associated with a centroid-like mathematical function of intensity of the reaction means for each predetermined sensor location in the desired set of at least two predetermined sensor locations;

determining selected positioning means information for each predetermined sensor location in the desired set of at least two predetermined sensor locations at a second time, from the relative intensity of each portion of the reaction means and from the particular positioning means information associated with each portion of the reaction means by determining best positioning means information associated with a centroid-like mathematical function of intensity of the reaction means for each predetermined sensor location in the desired set of at least two predetermined sensor locations;

comparing the reference positioning means information to the selected positioning means information for each predetermined sensor location in the desired set of at least two predetermined sensor locations in order to determine drift in position of the positioning means between the first and second times; and

compensating for drift in position with a polynomial correction function of order one less than the number of predetermined sensor locations in the desired set of at least two predetermined sensor locations after the second time so that the selective exposure after the second time of the medium occurs in registration with the selective exposure of the medium between the first and second times.

16. The method of claim 15 wherein the selective exposure of the medium comprises the exposure of a first cross-section.

17. The method of claim 16 wherein the desired set of at least two predetermined sensor locations comprises two predetermined sensor locations.

18. The method of claim 17 wherein the polynominal correction function is first order and consists of a zeroth order term that compensates for an offset in position and a first order term that compensates for a gain in position.

19. An apparatus for compensating for drift in position in a production of a three-dimensional object by stereolithography from a medium capable of solidification when exposed to a reaction means having various portions, operating in a prescribed manner upon a working surface of the medium to provide successive adjacent solid laminae for forming the object, including selective exposure of the medium to the reaction means between a first and second time, comprising:

positioning means for positioning the reaction means based on positioning means information;

a sensor mounted at a predetermined location fixed with respect to a point on the working surface of the medium for detecting each portion of the reaction means associated with particular positioning means information;

means for determining reference positioning means information at a first time and selected positioning means at a second time, from a relative intensity of each portion of the reaction means and from the particular positioning means information associated with each portion of the reaction means by determining best positioning means information associated with a centroid-like mathematical function of intensity of the reaction means;

means for comparing the reference positioning means information to the selected positioning means information in order to determine drift in position of the positioning means between the first and second times; and

means for compensating for the determined drift in position after the second time so that the selective exposure of the medium after the second time occurs in registration with the selective exposure of the medium between the first and second times.

20. An apparatus for compensating for drift in position in a production of a three-dimensional object by stereolithography from a medium capable of solidification when exposed to a reaction means operating in a prescribed manner upon a working surface of the medium to provide successive adjacent solid laminae for forming the object, including selective exposure of the medium to the reaction means between a first time and a second time, comprising:

means for specifying a plurality of predetermined sensor locations with associated X and Y coordinates;

at least one sensor locatable at any one of the said predetermined sensor locations wherein each of the predetermined sensor locations is fixed with respect to a point on the working surface of the medium and wherein the plurality of predetermined sensor locations have different X coordinates and different Y coordinates;

positioning means for directing the reaction means based on positioning means information so that the at least one sensor can detect each portion of the reaction means and supply particular positioning means information associated with each portion of the reaction means for each predetermined sensor location in a desired set of at least two predetermined sensor locations;

means for determining reference positioning means information at a first time and selected positioning means information at a second time for each predetermined sensor location in the desired set of at least two predetermined sensor locations, from a relative intensity of each portion of the reaction means and from best positioning means information associated with each portion of the reaction means by determining the particular positioning means information associated with a centroid-like mathematical function of intensity of the reaction means for each predetermined sensor location in the desired set of at least two predetermined sensor locations;

means for comparing the reference positioning means information to the selected positioning means information for each predetermined sensor location in the desired set of at least two predetermined sensor locations in order to determine drift in position of the positioning means between the first and second times; and

means for compensating for drift in position with a polynomial correction function of order one less than the number of predetermined sensor locations in the desired set of at least two predetermined sensor locations after the second time so that the selective exposure after the second time of the medium occurs in registration with the selective exposure of the medium between the first and second times.