Method of Machine Tool Calibration

• US 20090183610A1
• Filed: 12/11/2006
• Published: 07/23/2009
• Est. Priority Date: 12/13/2005
• Status: Active Grant

• Current Assignee: Renishaw PLC
• Original Assignee: Renishaw PLC
• Inventors: Watson, Christopher Ray, Saunders, Marc Thomas Berkeley, McMurtry, David Roberts, Maxted, Paul
• Granted Patent: US 8,250,952 B2
• Time in Patent Office: Days
• US Class Current: 82/1.110
• CPC Class Codes: B23B 25/06 Measuring, gauging, or adjusting equipment on turning-machines for setting-on, feeding, controlling, or monitoring the cutting tools or work measuring devices or gauges G01B
• CPC Class Codes: B23B 3/06 Turning-machines or devices characterised only by the special arrangement of constructional units B23Q37/00 takes precedence; such features of general applicability B23Q
• CPC Class Codes: G05B 19/401 characterised by control arrangements for measuring, e.g. calibration and initialisation, measuring workpiece for machining purposes G05B19/19 takes precedence
• CPC Class Codes: G05B 2219/45136 Turning, lathe
• CPC Class Codes: G05B 2219/50022 Null point on tool relative to null point of toolholder, rotationcenter
• CPC Class Codes: G05B 2219/50029 Go to pivotable, rotatable reference plane
• CPC Class Codes: G05B 2219/50032 On one axis only, derive from inclined surface offsets for other axis
• CPC Class Codes: G05B 2219/50139 Calibration, setting tool after measurement on tool
• CPC Class Codes: G05B 2219/50152 Align axis cylinder, tube with rotation axis machine
• CPC Class Codes: Y10T 82/10 Process of turning
• CPC Class Codes: Y10T 82/2502 with program control

Abstract

Methods are described for calibrating a turning machine having a first rotatable portion or chuck for holding a workpiece. The first rotatable portion has a first feature associated therewith. The method comprises the steps of using a measurement probe to determine the position of the first feature, rotating the first rotatable portion through an angle, and using said measurement probe to determine the new position of the first feature. The extension of the technique to swivel head mill-turn machines is also described.

Claims

1. A method of calibrating a turning machine having a first rotatable portion for holding a workpiece, the first rotatable portion having a first feature associated therewith, wherein the method comprises the steps of;

(i) using a measurement probe to determine the position of the first feature,

(ii) rotating the first rotatable portion through an angle, and

(iii) using said measurement probe to determine the new position of the first feature.

2. A method according to claim 1 and further comprising the step of (iv) calculating the position of the axis of rotation of the first rotatable portion using the position measurements determined in steps (i) and (iii).

3. A method according to claim 1 wherein step (ii) comprises rotating the first rotatable portion through an angle of 180°

.

4. A method according to claim 1 wherein step (ii) comprises rotating the first rotatable portion through an angle of less than 180°

.

5. A method according to claim 4 wherein step (ii) comprises rotating the first rotatable portion through an angle of no more than 90°

.

6. A method according to claim 4 comprising an initial step of determining the position of the axis of rotation of the first rotatable portion in a first machine axis.

7. A method according to claim 6 wherein step (i) comprises orientating the first rotatable portion so that the first feature is located substantially on said first machine axis.

8. A method according to claim 1 wherein steps (ii) and (iii) are repeated one or more times.

9. A method according to any claim 1 in which the turning machine comprises a tool holder, wherein the measurement probe is held by said tool holder.

10. A method according to claim 9 wherein the tool holder comprises a second rotatable portion, the measurement probe being held by said second rotatable portion.

11. A method according to claim 10 comprising the step of rotating the second rotatable portion through an angle.

12. A method according to claim 11 wherein step (ii) comprises rotating the first and second rotatable portions through 90°

, and steps (ii) and (iii) are performed four times.

13. A method according to claim 10 wherein the second rotatable portion is carried by a swivel head, the swivel head being rotatable about an axis.

14. A method according to claim 10 comprising the step of determining the relative displacement of the axes of rotation of the first rotatable portion and the second rotatable portion.

15. A method of determining the position of the axis of rotation of the first rotatable portion as a function of displacement along a translational axis of the turning machine, the method comprising the steps of:

(A) determining the position of the axis of rotation of the first rotatable portion using a method according to claim 1,

(B) translating at least one of the measurement probe and the first rotatable portion along said translational axis, and

(C) repeating step (A).

16. A method according claim 15 and further comprising the step of (D) determining the angular alignment of the axis of rotation of the first rotatable portion relative to an axis of the turning machine.

17. A method of aligning a swivel axis turning machine having a first rotatable portion for holding a workpiece and a second rotatable portion for holding a tool or tool accessory, wherein the axis of rotation of the first rotatable portion can be tilted relative to the axis of rotation of the second rotatable portion and the first rotatable portion has a second feature associated therewith, the method comprising the steps of:

(a) taking a swivel axis turning machine in which the relative displacement of the axes of rotation of the first rotatable portion and the second rotatable portion have been determined using the method according to claim 14,

(b) using a measurement probe held by the second rotatable portion to determine the position of the second feature, and

(c) altering the tilt between the axis of rotation of the first rotatable portion and the axis of rotation of the second rotatable portion and repeating step (b).

18. A method according to claim 17 in which the swivel axis turning machine comprises a swivel head turning machine and the second rotatable portion is carried by the swivel head, wherein step (c) comprises rotating the swivel head to a different orientation and repeating step (b).

19. A method according to claim 17 comprising the step of determining the position of the pivot point between the axis of rotation of the first rotatable portion and the axis of rotation of the second rotatable portion.

20. A method according to claim 17 comprising the step of determining tool offset error as a function of the relative tilt between the axes of rotation of the first rotatable portion and the second rotatable portion.

21. A method according to claim 17 wherein step (b) is repeated with a different displacement between the second feature and the second rotatable portion.

22. A method according to claim 21 wherein step (b) is repeated using two or more stylus tips, each stylus tip having a different displacement from the second rotatable portion.

23. A method according to claim 22 wherein step (b) is performed using a multi-tip stylus.

24. A method according to claim 22 wherein step (b) is performed using two different length styli.

25. A method according to claim 21 wherein step (b) is performed at least once using the shank of the stylus of the measurement probe to determine the position of the second feature.

26. A method according to claim 21 comprising the step of determining tool offset error as a function of tool length and the relative tilt between the axes of rotation of the first rotatable portion and the second rotatable portion.

27. A method according to claim 17 wherein a common feature provides both the first feature and the second feature.

28. A method according to claim 17 wherein the second feature comprises a datum sphere.

29. A method according to claim 17 wherein the second feature comprises a shaft comprising two or more datum spheres.

30. A method according to claim 1 wherein the first rotatable portion of the turning machine comprises said first feature.

31. A method according to claim 1 wherein the first rotatable portion holds a part comprising said first feature.

32. A method according to claim 31 wherein the part comprises a protrusion forming said first feature.

33. A method according to claim 1 comprising the step of using the measurement probe to determine the position of a tool setting device relative to the position of the axis of rotation of the first rotatable portion.

34. Automated turning machine apparatus suitably programmed to implement a method according to claim 1.

35. A computer program for controlling a turning machine, the computer program being such that, when loaded into the computer controller of a suitable turning machine, the machine can implement the method according to claim 1.

36. A machine readable medium containing a computer program according to claim 35.

37. A turning machine comprising a first rotatable portion for holding a workpiece, the first rotatable portion having a first feature associated therewith,

wherein the turning machine comprises a machine controller that is arranged to determine the position of the first feature, rotate the first rotatable portion through an angle and determine the new position of the first feature.

38. (canceled)