Method for calibrating a dressing spindle of a machine tool

Abstract

A method for calibrating a dressing spindle of a machine tool having a main spindle arranged in a machine head and the dressing spindle arranged in the machining area, wherein a grinding tool can be mounted on the main spindle and a dressing tool can be mounted on the dressing spindle and the grinding tool and the dressing tool can be moved relatively to each other for dressing the grinding tool by the dressing tool.

What is claimed is: 
     
         1 . A method for calibrating a dressing spindle of a machine tool having a main spindle arranged in a machine head and the dressing spindle arranged in the machining area, wherein a grinding tool can be mounted on the main spindle and a dressing tool can be mounted on the dressing spindle and the grinding tool and the dressing tool can be moved relatively to each other for dressing the grinding tool by the dressing tool, the method comprising:
 a. providing a test mandrel with an elongated body and a seat;   b. mounting the test mandrel on the dressing spindle by connecting the seat with the dressing spindle such that the axial axis of the body is in parallel with the rotation axis of the dressing spindle;   c. measuring a plurality of positions on the body by contacting a measuring device with the body of the test mandrel at the plurality of positions;   d. determining the tilt angle of the rotation axis of the dressing spindle based on the measured plurality of positions on the test mandrel by a processing unit, wherein the tilt angle is the angulation of the rotation axis of the dressing spindle with respect to the vertical direction;   e. mounting a calibration sphere having a connecting portion and a jig on the top of the connecting portion on the dressing spindle, wherein the calibration sphere is concentrically arranged on the dressing spindle;   f. mounting a touch probe on the main spindle;   g. measuring a plurality of positions on the jig by contacting the touch probe with the jig at the plurality of positions;   h. determining the center position (P) of the calibration sphere in accordance with the measured plurality of calibration sphere positions by the processing unit; and   i. determining by the processing unit the position of a referencing point (R) of the dressing spindle based on the determined center position of the calibration sphere, the tilt angle of the rotation axis of the dressing spindle and the dimension of the calibration sphere, wherein the referencing point is located at the center position on a referencing surface (FR) of the dressing spindle.   
     
     
         2 . The method according to  claim 1 , wherein the measuring device is a touch probe or a dial indicator. 
     
     
         3 . The method according to  claim 1 , wherein three-dimensional coordinates are measured at all measuring positions. 
     
     
         4 . The method according to  claim 1 , wherein the determined position of the referencing point is added into a kinematic compensation model, in particular the determined referencing position is automatically fed into the kinematic compensation model. 
     
     
         5 . The method according to  claim 1 , wherein the touch probe is controlled by a control unit of the machine tool to conduct the measurement. 
     
     
         6 . The method according to  claim 1 , wherein the touch probe is calibrated before conducting the measurement. 
     
     
         7 . The method according to  claim 1 , wherein the calibration sphere is first applied for determining a primary center position before mounting the test mandrel on the dressing spindle to determine the tilt angulation of the dressing spindle. 
     
     
         8 . The method according to  claim 1 , wherein the height of the calibration sphere is considered for determining the referencing point of the dressing spindle. 
     
     
         9 . A method for grinding a workpiece by a machine tool having a main spindle arranged in a machine head and a dressing spindle arranged in the machining area, wherein a grinding tool can be mounted on the main spindle for grinding the workpiece mounted on the machine table, wherein a dressing tool can be mounted on the dressing spindle and the grinding tool and the dressing tool can be moved relatively to each other for dressing the grinding tool by the dressing tool, wherein the rotation axis of the dressing spindle has an inclination Tα to the vertical direction comprising:
 a. calibrating the dressing spindle according to  claim 1 ; 
 b. dressing the grinding tool by the dressing tool; and 
 c. grinding the workpiece by the dressed grinding tool. 
 
     
     
         10 . A machine tool for grinding a workpiece comprising a main spindle arranged in a machine head and a dressing spindle arranged in the machining area, wherein a grinding tool can be mounted on the main spindle for grinding the workpiece mounted on the machine table, wherein a dressing tool can be mounted on the dressing spindle and the grinding tool and the dressing tool can be moved relatively to each other for dressing the grinding tool by the dressing tool, wherein the rotation axis of the dressing spindle has an inclination Tα to the vertical direction. 
     
     
         11 . The machine tool according to  claim 10 , wherein a control unit is provided in the machine tool. 
     
     
         12 . The machine tool according to  claim 10 , wherein the machine tool includes a calibration sphere and a test mandrel which can be mounted on the dressing spindle for calibrating a dressing spindle, wherein the calibration sphere comprises a connecting portion and a jig on the top of the connecting portion, wherein the test mandrel comprises a seat and an elongated body formed on the top of the seat.