Calibration method for a spherical measurement probe

A computer program stored on a non-transitory medium and comprising machine code which, when loaded into a control device for a machine tool and executed by the control device, causes the control device to perform a calibration method for calibrating a spherical measurement probe, which is fastened in a tool spindle of a machine tool and configured for rotation about a spindle axis, with a calibration sphere attached to an element of the machine tool, with the calibration method comprising the steps of:

• positioning the tool spindle relative to the element of the machine tool with at least three axis drives of the machine tool in three mutually independent translational directions,
• performing four basic measurements while during all four basic measurements holding the tool spindle constant at an identical longitudinal position, as viewed in a direction of the spindle axis, and holding the calibration sphere constant at the same orientation for all four basic measurements
• moving in each basic measurement the measurement probe with the axis drives towards the calibration sphere in a corresponding transverse direction and measuring a corresponding basic position of the tool spindle relative to the element of the machine tool at which the measurement probe touches the calibration sphere, wherein the four transverse directions corresponding to the four basic measurements meet in a plane spanned by the four transverse directions in a common point and are evenly distributed around the common point,
• rotating the measurement probe with a spindle drive from one basic measurement to a next basic measurement by an identical angle about the spindle axis, wherein the identical angle corresponds to an angle between the respective transverse directions with one another,
• determining based on the basic positions a reference position of the tool spindle above the calibration sphere relative to the element at which the spindle axis extends through a center point of the calibration sphere, and
• taking the determined reference position into account in a further calibration of the measurement probe.

A control device for a machine tool, wherein the control device is programmed with a computer program stored on a non-transitory medium and comprising machine code which, when loaded into a control device for a machine tool and executed by the control device, causes the control device to perform a calibration method for calibrating a spherical measurement probe, which is fastened in a tool spindle of a machine tool and configured for rotation about a spindle axis, with a calibration sphere attached to an element of the machine tool, with the calibration method comprising the steps of:

• positioning the tool spindle relative to the element of the machine tool with at least three axis drives of the machine tool in three mutually independent translational directions,
• performing four basic measurements while during all four basic measurements holding the tool spindle constant at an identical longitudinal position, as viewed in a direction of the spindle axis, and holding the calibration sphere constant at the same orientation for all four basic measurements
• moving in each basic measurement the measurement probe with the axis drives towards the calibration sphere in a corresponding transverse direction and measuring a corresponding basic position of the tool spindle relative to the element of the machine tool at which the measurement probe touches the calibration sphere, wherein the four transverse directions corresponding to the four basic measurements meet in a plane spanned by the four transverse directions in a common point and are evenly distributed around the common point,
• rotating the measurement probe with a spindle drive from one basic measurement to a next basic measurement by an identical angle about the spindle axis, wherein the identical angle corresponds to an angle between the respective transverse directions with one another,
• determining based on the basic positions a reference position of the tool spindle above the calibration sphere relative to the element at which the spindle axis extends through a center point of the calibration sphere, and
• taking the determined reference position into account in a further calibration of the measurement probe.

A machine tool, comprising:

• a tool spindle,
• a spindle drive constructed to rotate the tool spindle around a spindle axis,
• an element carrying a calibration sphere,
• at least three axis drives for positioning the tool spindle relative to the element in three mutually independent translational directions,
• position sensors assigned to the axis drives and configured to detect a position of the tool spindle relative to the element, and
• a control device configured to perform a calibration method for calibrating the calibration sphere by:
• positioning the tool spindle relative to the element of the machine tool with at least three axis drives of the machine tool in three mutually independent translational directions,
• performing four basic measurements while during all four basic measurements holding the tool spindle constant at an identical longitudinal position, as viewed in a direction of the spindle axis, and holding the calibration sphere constant at the same orientation for all four basic measurements
• moving in each basic measurement the measurement probe with the axis drives towards the calibration sphere in a corresponding transverse direction and measuring a corresponding basic position of the tool spindle relative to the element of the machine tool at which the measurement probe touches the calibration sphere, wherein the four transverse directions corresponding to the four basic measurements meet in a plane spanned by the four transverse directions in a common point and are evenly distributed around the common point,
• rotating the measurement probe with a spindle drive from one basic measurement to a next basic measurement by an identical angle about the spindle axis, wherein the identical angle corresponds to an angle between the respective transverse directions with one another,
• determining based on the basic positions a reference position of the tool spindle above the calibration sphere relative to the element at which the spindle axis extends through a center point of the calibration sphere, and
• taking the determined reference position into account in a further calibration of the measurement probe.