Rotating swivel unit for sensors of a coordinate measuring apparatus and method for determining corrective parameters of the rotating swivel unit

1. A method for determining corrective parameters of a rotating swivel unit to which a sensor of a coordinating measuring apparatus is attached with said sensor measuring in at least one dimension, the rotating swivel unit having a swivel joint and the method comprising the steps of:

carrying out a calibration of said sensor for at least three rotational positions of said swivel joint;

computing at least parameters of a first parameter field (M S ) for each of said rotational positions with said first parameter field (M S ) describing the transformation of a sensor coordinate system (u,v,w) into a machine coordinate system (X M , Y M , Z M ) of the coordinate measuring apparatus;

computing parameters of a second parameter field (p s ) describing an offset of said sensor coordinate system (u,v,w) with respect to a point (AB) in said machine coordinate system (X M , Y M , Z M ); and,

determining corrective parameters of said swivel joint from said parameters of said first and second parameter fields.

2. The method of claim 1 , wherein said corrective parameters include at least one of the following: position of the rotational axes to each other, angular position deviations and course deviations.

3. The method of claim 1 , wherein a rotational axis (a a ) of said swivel joint is vertically aligned during the calibration of said sensor.

4. The method of claim 1 , wherein measurement values are measured during the calibration which are substantially uniformly distributed over the measuring range of said sensor.

5. The method of claim 1 , wherein said sensor is connected directly to said swivel joint and the corrective parameters are determined only for said swivel joint.

6. The method of claim 1 , comprising the further steps of:

providing a calibration sphere having a known radius (r K ) in the measuring space of said coordinate measuring apparatus and determining the center point (p K ) of said calibration sphere in said machine coordinate system (X M , Y M , Z M );

measuring points (p o,i ) on the surface of said calibration sphere utilizing said sensor to be calibrated;

recording measured values (s′ i ) over wide regions of said measuring ranges; and,

determining said parameters of said first parameter field (M S ) and said second parameter field (p S ) for said sensor from said measured values (s′ i ) while considering that said center point (p k ) and said radius (r K ) of said calibration sphere are known.

7. The method of claim 6 , comprising the further step of determining the parameters of said parameter fields (M S , p S ) while using the following relationship:

|p o,i −p K |=r K

wherein:

p o,i is a measuring point on the surface of the calibration sphere;

p K is the center point of the calibration sphere;

r K is the radius of the calibration sphere; and,

wherein, in the relationship, the center point (p K ) of the calibration sphere and the radius of the calibration sphere are known.

8. The method of claim 7 , wherein the parameters of said parameter fields (M S , p S ) are determined via the following relationship:

|p M +p S +M S s′−p K |=r K

wherein:

p K is a vector to the center point of the calibration sphere in said machine coordinate system;

r K is the radius of said calibration sphere;

p M is a vector from the origin of the machine coordinate system (X M , Y M , Z M ) to said point (AB) in the measuring arm of said coordinate measuring apparatus with said sensor being attached to said measuring arm;

p S is a vector from point (AB) in said measuring arm to said origin of said sensor coordinate system (u,v,w);

s′ is a vector of a measuring point on the surface of said calibration sphere with said measuring point being measured in said sensor coordinate system (u,v,w); and,

M S is said first parameter field (sensor matrix).

9. A rotating swivel unit for a sensor of coordinate measuring apparatus, the sensor measuring in at least one dimension and the rotating swivel unit comprising:

at least two swivel joints for aligning the sensor with respect to angle;

a corrective unit for correcting the measured values of the sensor, when measuring, in correspondence to the rotational position of said swivel joints;

means for picking up corrective values which include functioning to:

carry out a calibration of said sensor for at least three rotational positions of one of said swivel joints with said sensor measuring in at least one dimension;

compute at least parameters of a first parameter field (M S ) for each of said rotational positions with said first parameter field (M S ) describing the transformation of a sensor coordinate system (u,v,w) into a machine coordinate system (X M , Y M , Z M ) of the coordinate measuring apparatus;

compute parameters of a second parameter field (p s ) describing an offset of said sensor coordinate system (u,v,w) with respect to a point (AB) in said machine coordinate system (X M , Y M , Z M ); and,

determine corrective parameters of said swivel joint from said parameters of said first and second parameter fields.

10. The rotating swivel unit of claim 9 , wherein said corrective parameters include at least one of the following: position of the rotational axes to each other, angular position deviations and course deviations.

11. The rotating swivel unit of claim 9 , wherein a rotational axis (a a ) of said swivel joint is vertically aligned during the calibration of said sensor.

12. The rotating swivel unit of claim 9 , wherein measurement values are measured during the calibration which are substantially uniformly distributed over the measuring range of said sensor.

13. The rotating swivel unit of claim 9 , wherein said sensor is a two-dimensional measuring optical probe.

14. The rotating swivel unit of claim 9 , wherein the pick up of corrective parameters for different angular positions of the swivel joints is carried out.

15. The rotating swivel unit of claim 9 , wherein said three rotational positions of said swivel joint are distributed substantially uniformly over the rotational range of said swivel joint.

16. The rotating swivel unit of claim 9 , wherein said corrective unit functions to carry out the calibration of said sensor by performing the method steps of:

providing a calibration sphere having a known radius (r K );

determining the center point (p K ) of a calibration sphere in said machine coordinate system (X M , Y M , Z M );

measuring points (p o,i ) on the surface of said calibration sphere utilizing said sensor to be calibrated;

recording measured values (s′ i ) over wide regions of said measuring ranges; and,

determining said parameters of said first parameter field (M S ) and said second parameter field (p S ) for said sensor from said measured values (s′ i ) while considering that said center point (p K ) and said radius (r K ) of said calibration sphere are known.

17. The rotating swivel unit of claim 16 , wherein the corrective unit determines the parameters of said parameter field (M S ) while using the following relationship:

|p o,i −p K |=r K

wherein:

p o,i is a measuring point on the surface of the calibration sphere;

p K is the center point of the calibration sphere;

r K is the radius of the calibration sphere; and,

wherein, in the relationship, the center point (p K ) of the calibration sphere and the radius of the calibration sphere are known.

18. The rotating swivel unit of claim 17 , wherein the corrective unit determines the parameters of said parameter field (M S ) via the following relationship:

| p M +p S +M S s′−p K |=r K

wherein:

p K is a vector to the center point of the calibration sphere in said machine coordinate system;

r K is the radius of said calibration sphere;

p M is a vector from the origin of the machine coordinate system (X M , Y M , Z M ) to said point (AB) in the measuring arm of said coordinate measuring apparatus with said sensor being attached to said measuring arm;

p S is a vector from point (AB) in said measuring arm to said origin of said sensor coordinate system (u,v,w);

s′ is a vector of a measuring point on the surface of said calibration sphere with said measuring point being measured in said sensor coordinate system (u,v,w); and,

M S is said first parameter field (sensor matrix).

19. The rotating swivel unit of claim 9 , wherein said sensor is attached to said rotating swivel unit so as to be exchangeable.