Kinematic calibration

1. A calibration method for a numerical controlled machine tool, wherein the numerical controlled machine tool comprises a working table and a machine head with a main spindle, the numerical controlled machine tool further comprises at least 3 linear axes (X, Y, Z) and at least 2 rotation axes (A, B, C) by which the main spindle and the working table can be moved relatively to each other, the numerical controlled machine tool having a jig with a calibration ball mounted on the working table and the main spindle having mounted a touch probe, wherein the calibration method includes the step to measure the position of the calibration ball by conducting with the touch probe at least 4 contact measurements with the mounted touch probe, wherein the position of the calibration ball is changed at least three times by rotating the working table or the machine head around the rotation axes (A, B, C) and the step of measuring the position of the calibration ball is repeated for every position change of the calibration ball, and wherein the calibration method uses a kinematic model for generating from the at least three measured positions of the calibration ball a compensation model to compensate the kinematic errors occurring with a relative movement between the working table and the main spindle, wherein the calibration method measures the positions of the calibration ball with a measurement sequence which includes the combined movement of the calibration ball around at least two rotation axes (A, C, B), wherein the measurements around a first rotation axis (C, B, A) include at least two rotational position movements around a second axis (B, A, C);

wherein the position of the calibration ball is measured in the coordinates of the linear axes X, Y and Z, wherein each measured calibration ball position (X k , Y k , Z k ) is memorized in a position table; and

wherein the kinematic model of the calibration method calculates the kinematic error occurring by the movement of the rotation axes (A, B, C) based on the linear axis positions (X k , Y k , Z k ) memorized in the position table.

2. The calibration method for a numerical controlled machine tool according to claim 1 , wherein the measurement sequence for the rotational positions (C i ; B i ) of the calibration ball is

(

C

1

;

B

1

)

,

(

C

2

;

B

1

)

,

(

C

3

;

B

1

)

⁢

⁢

…

⁢

⁢

(

C

n

;

B

1

)

(

C

1

;

B

2

)

,

(

C

2

;

B

2

)

,

(

C

3

;

B

2

)

⁢

⁢

…

⁢

⁢

(

C

n

;

B

2

)

(

C

1

;

B

3

)

,

(

C

2

;

B

3

)

,

(

C

3

;

B

3

)

⁢

⁢

…

⁢

⁢

(

C

n

;

B

3

)

…

⁢

(

C

1

;

B

m

)

,

(

C

2

;

B

m

)

,

(

C

3

;

B

m

)

⁢

⁢

…

⁢

⁢

(

C

n

;

B

m

)

or

⁢

(

C

1

,

1

;

B

1

)

,

(

C

2

,

1

;

B

1

)

,

(

C

3

,

1

;

B

1

)

⁢

⁢

…

⁢

⁢

(

C

n

,

1

;

B

1

)

(

C

1

,

2

;

B

2

)

,

(

C

2

,

2

;

B

2

)

,

(

C

3

,

2

;

B

2

)

⁢

⁢

…

⁢

⁢

(

C

n

,

2

;

B

2

)

(

C

1

,

3

;

B

3

)

,

(

C

2

,

3

;

B

3

)

,

(

C

3

,

3

;

B

3

)

⁢

⁢

…

⁢

⁢

(

C

n

,

3

;

B

3

)

…

⁢

(

C

1

,

m

;

B

m

)

,

(

C

2

,

m

;

B

m

)

,

(

C

3

,

m

;

B

m

)

⁢

⁢

…

⁢

⁢

(

C

n

,

m

;

B

m

)

.

3. The calibration method for a numerical controlled machine tool according to claim 1 , wherein to describe the relative movements between the working table and the main spindle the kinematic model uses homogeneous transformation matrices for considering the kinematic errors of the rotation axes (A, B, C).

4. The calibration method for a numerical controlled machine tool according to claim 1 , wherein the touch probe is mounted in the main spindle and is a trigger-based contact measurement device transmitting its trigger signal to the numerical controlled machine tool through wireless transmission, wherein the touch probe is also used to determine the position of a part to be machined.

5. The calibration method for a numerical controlled machine tool according to claim 1 , wherein the compensation model generated by the kinematic model includes an optimization algorithm for compensating the kinematic errors occurring with a relative movement between the working table and the main spindle.

6. The calibration method for a numerical controlled machine tool according to claim 1 , wherein when the measurement sequence includes the combined movement of the calibration ball around two rotation axes (C, B, A), the kinematic model considers 8 compensation parameters characterizing the kinematic errors of the rotation axes (A 0 C, B 0 C, X 0 C, Y 0 C, A 0 B, C 0 B, X 0 B, Z 0 B or A 0 C, B 0 C, X 0 C, Y 0 C, B 0 A, C 0 A, Y 0 A, Z 0 A, respectively).

7. The calibration method for a numerical controlled machine tool according to claim 1 , wherein the kinematic model uses the position errors of the calibration ball in respect of the calibration ball's theoretically correct position to generate a compensation model for the numerical controlled machine tool to compensate the positioning error of the working table movements in respect of the main spindle.

8. The calibration method for a numerical controlled machine tool according to claim 1 , wherein the kinematic model generating a compensation model is calculated by a processing unit located outside the numerical controlled machine tool and wherein the compensation model is transmitted to the numerical control system of the numerical controlled machine tool.

9. A numerical controlled machine tool using a calibration method according to claim 1 , wherein the calibration method is applied by the machine control unit of the numerical controlled machine tool.

10. The numerical controlled machine tool according to claim 1 , wherein the kinematic model generating a compensation model is calculated by a processing unit located outside the numerical controlled machine tool, the calculated compensation model being transmitted from the processing unit to the numerical controlled machine tool.