Viewing device and method for three-dimensional noncontacting measurements

• US 5,778,548 A
• Filed: 05/16/1996
• Issued: 07/14/1998
• Est. Priority Date: 05/16/1995
• Status: Expired due to Term

• Current Assignee: Brown and Sharpe DEA SpA (Hexagon AB)
• Original Assignee: Dea-Brown & Sharpe SPA (Hexagon AB)
• Inventors: Cerruti, Piero
• Primary Examiner(s): Fulton, Christopher W.
• Application Number:
  US08/645,647
• Time in Patent Office: 789 Days
• Field of Search: 33/503, 33/504, 33/1 M
• US Class Current: 33/503
• CPC Class Codes: G01B 11/002 for measuring two or more coordinates
• CPC Class Codes: G01B 21/042 Calibration or calibration artifacts G01B3/30, G01B9/02072 take precedence

Abstract

A viewing device wherein a measuring machine presents a movable element movable along three coordinate axes of the measuring machine; the movable element is fitted with an articulated measuring head supporting a viewing sensor presenting a television camera and a laser beam source; by analyzing the two-dimensional image picked up by the television camera and the position of the laser beam in the two-dimensional image, the coordinates of a point in relation to a reference system of the viewing sensor are determined; and the measurement is subsequently related to the reference system of the measuring machine.

Claims

1. A three-dimensional noncontacting measuring device, characterized by comprising:

a measuring machine (10) presenting a movable ele ment (12) movable in a three-dimensional measuring space (T);

said measuring machine (10) presenting means for determining a first vector (CTPOS) defining the position of a reference point (CT) of said movable element (12) in relation to a first reference system of the measuring machine (10) itself and defined by a first cartesian reference frame (X,Y,Z) comprising perpendicular coordinate X,Y,Z axes;

a viewing sensor (25) of a measuring head (15) fitted to said movable element (12);

said measuring head (15) presenting positioning means (18) for orienting said viewing sensor (25) in said measuring space (T);

said viewing sensor (25) comprising at least a television camera (31) and a source (33) of a laser beam

said television camera (31) covering a three-dimensional space (38), in particular a space in the form of a solid angle and presenting an optical axis (41);

said laser beam (35) presenting an axis of symmetry (44) intersecting said three-dimensional space (38);

the intersection of said optical axis (41) and said axis of symmetry (44) defining the origin of a second Cartesian reference frame (X'"'"',Y'"'"',Z'"'"') forming part of a second reference system of said viewing sensor;

said second Cartesian reference frame comprising perpendicular coordinate X'"'"',Y'"'"',Z'"'"' axes, one axis (Z'"'"') of which is oriented along said optical axis (41);

said television camera (31) picking up a two-dimensional image defining an image plane, at the center (CI) of which is definable a point corresponding to the origin of said second reference system located with first and second coordinate axes (Y'"'"', X'"'"') perpendicular to each other and in the image plane;

said viewing sensor (25) supplying, for a point (P) in the measuring space, a measurement expressed by a measuring vector (m'"'"') relative to and oriented in relation to said second reference system (X'"'"',Y'"'"',Z'"'"');

said device (1) comprising calculating means for calculating a number of extrinsic parameters, including;

at least an OFFSET vector extending from the origin (O'"'"') of said second reference system (X'"'"',Y'"'"',Z'"'"') to said reference point (CT) of said movable element (12);

said OFFSET vector being defined for at least a first arrangement of said positioning means;

at least a rotation matrix (ROT-MAT) defining the relationships between said first Cartesian reference frame (X,Y,Z) and said second Cartesian reference frame (X'"'"',Y'"'"',Z'"'"');

said device (1) comprising calculating means for calculating a second vector (V) expressing the distance between the origins of said first and said second reference system;

said second vector (V) being calculated on the basis of said first vector and said OFFSET vector;

said device (1) presenting vectorial calculating means for calculating a correct measurement (m) by relating said measurement vector (m'"'"') to said first reference system via said rotation matrix; and

said vectorial calculating means relating said correct measurement (M=m+V) to said first reference system by means of said second vector (V).

2. A device as claimed in claim 1, characterized in that said calculating means for calculating said rotation matrix comprise:

preliminary measuring means (98) for performing a cycle of initial calculating operations wherein a gauge (60) is placed on the measuring machine (10), and the positions of reference elements of the gauge (60) in relation to the first reference system (X,Y,Z) are measured;

said gauge (60) presenting a number of faces, each of which presents a central reference element (63);

positioning means (100) for positioning said viewing sensor facing a face of the gauge (60) and oriented according to a selected axis (Z) of the first cartesian reference frame;

said television camera (31) picking up a reference element (63) in the image plane;

first repositioning means (110) for enabling an automatic procedure by which said measuring head (15) is repositioned in a first position (p1) so that the center of the image of the reference element is located exactly at the image center (CI) and the Z'"'"' axis of the second Cartesian reference frame passes exactly through the center of the reference element;

first shift means (120) wherein a movement along the selected axis (Z) of the measuring machine (10) is imparted to said measuring head (15);

said movement causing the image of the reference element to move away from the center of the image plane;

second repositioning means (130) wherein an automatic procedure is enabled to reposition said measuring head (15) in a second position (p2) so that the center of the image of the reference element is located exactly at the image center (CI);

in which position, the Z'"'"' axis of the second reference system passes exactly through the center of the reference element;

first axis calculating means (140) for calculating a first line through the first and second positions (p1, p2) and relative to the first reference system;

said first line corresponding to the Z'"'"' axis;

third repositioning means (150) wherein the measuring head (15) is repositioned automatically in such a manner that, in the image picked up by the television camera (31), the reference element is located close to the first coordinate axis Y'"'"';

fourth repositioning means (160) wherein an automatic procedure is enabled to reposition said measuring head (15) in a third position (p3) so that the center of the image of the reference element is located exactly on the first coordinate axis Y'"'"';

in which position, the Y'"'"' axis passes exactly through the center of the reference element;

second shift means (170) wherein a movement in relation to the Y axis of the first reference system is imparted to said measuring head (15);

said movement causing the image of the reference element to move away from the Y'"'"' axis;

fifth repositioning means (180) wherein an automatic procedure is enabled to reposition the measuring head (15) in a fourth position (p4) so that the center of the image of the reference element is located exactly on the first coordinate axis Y'"'"';

in which position, the Y'"'"' axis passes exactly through the center of the reference element;

second axis calculating means (190) for calculating a second line relative to the first reference system (X,Y,Z) and through said third and fourth positions (p3, p4);

said second line corresponding to the Y'"'"' axis;

third axis calculating means (200) wherein, given the Z'"'"' and Y'"'"' axes of the second reference system, the X'"'"' axis perpendicular to the Z'"'"' and Y'"'"' axes is calculated to fully define the second reference system (X'"'"',Y'"'"',Z'"'"');

final calculating means (210) for calculating said rotation matrix (ROT-MAT) expressing the rotation relationship between the X,Y,Z axes of the first reference system and the X'"'"',Y'"'"',Z'"'"' axes of the second reference system.

3. A device as claimed in claim 2, characterized in that said gauge (60) presents cross sections defined by regular octagons, and is defined by twenty-six flat lateral walls;

the gauge comprising eighteen square walls and eight triangular walls;

each square and triangular wall presenting, in the center, a circular dead hole (63) defining said reference element.

4. A device as claimed in claim 2, characterized in that said calculating means for calculating said OFFSET vector comprise:

sixth repositioning means (250) for enabling an automatic procedure by which the measuring head (15) is moved along the Z'"'"' axis of the second reference system (X'"'"',Y'"'"',Z'"'"') to a fifth position (p5) wherein a laser line (50), formed by the intersection of said beam (35) and a face of said gauge, is located exactly in the center of the image plane, and the center of the reference element is located exactly at the image center (CI);

said fifth position having been determined previously.by said preliminary measuring means (98);

recalling means for reading the value of said fifth position (p5) in said first reference system;

vector calculating means (260) for calculating the OFFSET vector on the basis of the distance, relative to said first reference system, between the fifth position (p5) and the position of said reference point (CT) of said movable element (12) for which said fifth position is determined.

5. A device as claimed in claim 4, characterized in that said calculating means for calculating intrinsic parameters comprise:

calculating means for calculating a number of intrinsic parameters described in the internal performance of the viewing sensor and for correlating the dimensions of an object picked up in said two-dimensional image to the real dimensions of the object;

seventh repositioning means (265) for moving said measuring head along the Z'"'"' axis of said second reference system to reach a first initial position Kl(Xl,Yl,Z1) wherein the image of the reference element is located exactly at the center of the image plane;

third shift means (270) wherein the measuring head (15) is moved along the Z'"'"' axis to reach a first final position K2 (X2,Y2,Z2);

first image analyzing means (275) for determining, in said two-dimensional image, a first pixel shift (y-pix), along the Y'"'"' axis through the image plane, of the laser line formed by the intersection of said beam and said face of said gauge (60);

first parameter calculating means (280) for calculating a parameter on the basis of the first pixel shift (y-pix) and said first initial and final position;

eighth repositioning means (285) wherein said measuring head (15) is moved along the Z'"'"' axis to reach a second final position K3(X3,Y3,Z3);

second image analyzing means (290) for determining, in said two-dimensional image, a second pixel shift (yl-pix), along the Y'"'"' axis through the image plane, of the laser line from the X'"'"' axis;

second parameter calculating means (295) for calculating at least one intrinsic parameter on the basis of at least said first and second pixel shifts (y-pix, yl-pix).

6. A device as claimed in claim 5, characterized in that said calculating means for calculating intrinsic parameters comprise:

ninth repositioning means (300) for moving the measuring head (15) along the Z'"'"' axis of the second reference system to reach a first preliminary position P3(X3,Y3,Z3) in which the image of the reference element is located exactly in the center of the image plane;

tenth repositioning means (310) for moving the measuring head (15) along three axes to reach a first end position Pl(Xl,Yl,Z1);

third image analyzing means (320) for determining, in said two-dimensional image, first pairs of pixel shifts (x-pix, y-pix) of the image of said reference element along two coordinate axes (X'"'"'and Y'"'"') through the image plane and relative to displacement between the first preliminary position and the first end position;

third parameter calculating means (340) for calculating a first number of parameters on the basis of said first pair of pixel shifts (x-pix, y-pix) and said first preliminary and end position;

eleventh repositioning means (350) wherein the image of a reference element is repositioned in the center of the image plane by moving the measuring head (15) along the Z'"'"' axis to reach a second preliminary position;

twelfth repositioning means (360) for moving the measuring head (15) along three axes to reach a second end position P2(X2,Y2,Z2);

fourth image analyzing means (362) for determining, in said two-dimensional image, second pairs of pixel shifts (x'"'"'-pix, y'"'"'-pix) of the image of said reference element along two coordinate axes (X'"'"'and Y'"'"') through the image plane and relative to displacement between the second preliminary position and the second end position;

fourth parameter calculating means (365) for calculating a second number of parameters on the basis of said second pairs of pixel shifts (x'"'"'-pix, y'"'"'-pix) and said second preliminary and end position;

means (366) for defining said intrinsic parameters as a function of said first and second number of parameters.

7. A device as claimed in claim 1, characterized by comprising calculating means for calculating a number of intrinsic parameters describing the internal performance of the viewing sensor (25) and for correlating the dimensions of an object picked up in said two-dimensional image to the real dimensions of the object.

8. A three-dimensional noncontacting measuring method, characterized by comprising the steps of:

determining a first vector (CTPOS) defining the position, in relation to a first reference system, of a reference point (CT) of a movable element (12) of a measuring machine (10);

said first reference system being of the machine (10) itself, and being defined by a first Cartesian reference frame (X,Y,Z) comprising perpendicular coordinate X,Y,Z axes;

determining, by means of a viewing sensor (25) fitted to a measuring head (15) of said movable element (12), a measuring vector (m'"'"') relative to a second reference system (X'"'"',Y'"'"',Z'"'"') of the viewing sensor (25) itself and defined by a second Cartesian reference frame (X'"'"',Y'"'"',Z'"'"');

calculating a number of extrinsic parameters, including;

at least an OFFSET vector extending from the origin (O'"'"') of said second reference system (X'"'"',Y'"'"',Z'"'"') to said reference point (CT) of said movable element (12);

at least a rotation matrix (ROT-MAT) defining the relationship between said first Cartesian reference frame (X,Y,Z) and said second Cartesian reference frame (X'"'"',Y'"'"',Z'"'"');

calculating a second vector (V) expressing the distance between the origins of said first and said second reference system;

said second vector (V) being calculated on the basis of said first vector and said OFFSET vector;

calculating a correct measurement (m) by relating said measuring vector (m'"'"') to said first reference system via said rotation matrix; and

relating said correct measurement (M =m +V) to said first reference system by means of said second vector.

9. A method as claimed in claim 8, characterized by comprising the step of positioning said viewing sensor (25) in relation to said movable element (12) by orienting said viewing sensor (25) in a measuring space (T) of said measuring machine (10).

10. A method as claimed in claim 8, characterized in that said viewing sensor (25) comprises at least a television camera (31) and a source (33) of a laser beam (35);

said television camera (31) covering a three-dimensional space (38), in particular a space in the form of a solid angle and presenting an optical axis (41);

said laser beam (35) presenting an axis of symmetry (44) intersecting said three-dimensional space (38);

the intersection of said optical axis (41) and said axis of symmetry (44) defining the origin of said second Cartesian reference frame (X'"'"',Y'"'"',Z'"'"') of said viewing sensor;

said second cartesian reference frame comprising perpendicular coordinate X'"'"',Y'"'"',Z'"'"' axes, one axis (Z'"'"') of which is oriented along said optical axis;

said television camera (31) picking up a two-dimensional image defining an image plane, at the center (CI) of which is definable a point corresponding to the origin of said second reference system arranged with first and second coordinate axes (X'"'"', Y'"'"') perpendicular to each other and in the image plane.

11. A method as claimed in claim 10, characterized in that said step of calculating said rotation matrix comprises the substeps of:

performing (98) a cycle of initial calculating operations wherein the positions of reference elements of a gauge (60) in relation to the first reference system (X,Y,Z) are measured;

said gauge (60) presenting a number of faces, each of which presents a central reference element (63);

positioning (100) said viewing sensor facing a face of the gauge (60) by orienting said viewing sensor according to a selected axis (Z) of the first Cartesian reference frame;

said television camera (31) picking up a reference element (63) in the image plane;

automatically repositioning (110) said measuring head (15) in a first position (pi) so that the center of the image of the reference element is located exactly at the image center (CI) and the Z'"'"' axis of the second cartesian reference frame passes exactly through the center of the reference element;

shifting (120) said measuring head (15) along the selected axis (Z) of the measuring machine (10);

said shift causing the image of the reference element to move away from the center of the image plane;

automatically repositioning (130) said measuring head (15) in a second position (p2) so that the center of the image of the reference element is located exactly at the image center (CI);

in which position, the Z'"'"' axis of the second reference system passes exactly through the center of the reference element;

calculating (140) a first line through the first and second positions (pl, p2) and relative to the first reference system;

said first line corresponding to the Z'"'"' axis;

automatically repositioning (150) the measuring head (15) in such a manner that, in the image picked up by the television camera (31), the reference element is located close to the first coordinate axis Y'"'"';

automatically positioning (160) said measuring head (15) in a third position (p3) so that the center of the image of the reference element is located exactly on the first coordinate axis Y'"'"';

in which position, the first coordinate axis Y'"'"' passes exactly through the center of the reference element;

shifting (170) said measuring head (15) so that the image of the reference element moves away from the first coordinate axis Y'"'"';

automatically repositioning (180) the measuring head (15) in a fourth position (p4) so that the center of the image of the reference element is located exactly on the first coordinate axis Y'"'"';

in which position, the Y'"'"' axis passes exactly through the center of the reference element;

calculating (190) a second line relative to the first reference system (X,Y,Z) and through said third and fourth positions (p3, p4);

said second line corresponding to the first coordinate axis Y'"'"';

calculating (200), given the Z'"'"' and Y'"'"' axes of the second reference system, the X'"'"' axis perpendicular to the Z'"'"' and Y'"'"' axes to fully define the second reference system (X'"'"',Y'"'"',Z'"'"');

calculating (210) said rotation matrix (ROT-MAT) expressing the rotation relationship between the X,Y,Z axes of the first reference system and the X'"'"',Y'"'"',Z'"'"' axes of the second reference system.

12. A method as claimed in claim 11, characterized in that said gauge (60) presents cross sections defined by regular octagons, and is defined by twenty-six flat lateral walls;

the gauge comprising eighteen square walls and eight triangular walls;

each square and triangular wall presenting, in the center, a circular dead hole (63) acting as a reference element.

13. A method as claimed in claim 11, characterized in that said step of calculating said OFFSET vector comprises the substeps of:

automatically positioning (250) the measuring head (15) along the Z'"'"' axis of the second reference system (X'"'"',Y'"'"',Z'"'"') to a fifth position (p5) wherein a laser line (50), formed by the intersection of said beam (35) and a face of said gauge, is located exactly in the center of the image plane, and the center of the reference element is located exactly at the image center (CI);

the value of said fifth position (p5) having been determined in said initial cycle (98);

calculating (260) the OFFSET vector on the basis of the distance, relative to said first reference system, between the fifth position (p5) and the position of said reference point (CT) of said movable element (12) for which said fifth position is determined.

14. A method as claimed in claim 10, characterized by comprising the step of calculating a number of intrinsic parameters describing the internal performance of the viewing sensor (25) and for correlating the dimensions of an object picked up in said two-dimensional image to the real dimensions of the object.

15. A method as claimed in claim 14, characterized in that said step of calculating a number of intrinsic parameters comprises the substeps of:

repositioning (265) said measuring head along the Z'"'"' axis of said second reference system to reach a first initial position Kl(X1,Y1,Z1) wherein the image of the reference element is located exactly at the center of the image plane;

shifting (270) said measuring head (15) along the Z'"'"' axis to reach a first final position K2(X2,Y2,Z2);

analyzing (275) said two-dimensional image to determine a first pixel shift (y-pix), along the Y'"'"' axis through the image plane, of the laser line formed by the intersection of said laser beam and a face of said gauge (60);

calculating (280) parameters on the basis of the first pixel shift (y-pix) and said first initial and final position;

repositioning (285) said measuring head (15) along the Z'"'"' axis to reach a second final position K3(X3,Y3,Z3);

analyzing (290) said image to determine a second pixel shift (yl-pix) of the laser line along the Y'"'"' axis through the image plane;

calculating (295) at least one intrinsic parameter on the basis of at least said first and second pixel shifts (y-pix, yl-pix).

16. A method as claimed in claim 14, characterized in that said step of calculating said intrinsic parameters comprises the substeps of:

positioning (300) the measuring head (15) along the Z'"'"' axis of the second reference system to reach a first preliminary position P3(X3,Y3,Z3) in which the image of the reference element is located exactly in the center of the image plane;

repositioning (310) said measuring head (15) by moving it along three axes to reach a first end position P1(X1,Y1,Z1);

analyzing (320) said two-dimensional image to determine first pairs of pixel shifts (x-pix, y-pix) of the image of said reference element along two coordinate axes (X'"'"'and Y'"'"') through the image plane and relative to displacement between the first preliminary position and the first end position;

calculating (340) first numbers of parameters on the basis of said first pair of pixel shifts (x-pix, y-pix) and said first preliminary and end position;

repositioning (350) said measuring head (15) along the Z'"'"' axis, so that the image of a reference element is located in the center of the image plane in a second preliminary position;

repositioning (360) the measuring head (15) along three axes to reach a second end position P2(X2,Y2,Z2);

analyzing (362) said image to determine second pairs of pixel shifts (x'"'"'-pix, y'"'"'-pix) of the image of said reference element along two coordinate axes (X'"'"' and Y'"'"') through the image plane and relative to displacement between the second preliminary position and the second end position;

calculating (365) second numbers of parameters on the basis of said second pairs of pixel shifts (x'"'"'-pix, y'"'"'-pix) and said second preliminary and end position;

defining (366) said intrinsic parameters as a function of said first and second numbers of parameters.