Finishing method and finishing device for finish machining of rolling element raceways

Abstract

The invention relates to a finishing method for finish machining of a workpiece having at least one raceway for rolling elements that extends around a workpiece axis, the method comprising the following steps: providing a finishing tool which has an abrasive working surface; applying the finishing tool to a workpiece holder, generating spinning of the workpiece about a raceway axis at a rotational frequency; generating an oscillating movement of the tool holder, which is superimposed on the spinning of the workpiece and oscillates at an oscillating frequency; and pressing the finishing tool onto the workpiece surface in a pressing direction with a pressing force so that the abrasive working surface acts on the workpiece in the region of the raceway. The finishing method is characterised by continuous detection of a force signal, which is caused by the pressing force, within a detection time period which partly or completely overlaps a machining time period of the finish machining, and by time-resolved evaluation of the force signal in order to determine at least one geometry parameter which represents (i) a workpiece geometry in the region of the machined raceway and/or (ii) a geometric relationship between the workpiece geometry in the region of the machined raceway and a position of an oscillating apparatus.

1 . A finishing method for the finish machining of a workpiece having at least one raceway for rolling elements which runs in encircling fashion about a raceway axis, comprising the following steps:
 providing a finishing tool which has an abrasive working surface;   attaching the finishing tool to a tool holder;   generating an intrinsic rotation of the workpiece about a raceway axis at a rotational frequency;   generating an oscillating movement of the tool holder, said oscillating movement being superposed on the intrinsic rotation of the workpiece and oscillating at an oscillation frequency;   pressing the finishing tool with a press-on force in a press-on direction onto a workpiece surface of the workpiece in such a way that the abrasive working surface engages in the region of the raceway on the workpiece;   wherein   the finishing method further comprises a continuous detection of a force signal, caused by the press-on force, within a detection time period which partially or completely overlaps a machining time period of the finish machining, and   the finishing method further comprises a temporally resolved evaluation of the force signal to determine at least one geometry parameter representing (i) a workpiece geometry in the region of the machined raceway and/or (ii) a geometric relationship between the workpiece geometry in the region of the machined raceway and a position of an oscillation device.   
     
     
         2 . The finishing method as claimed in  claim 1 , wherein the workpiece has a raceway in the form of at least one of a ball raceway for spherical rolling elements, and a ball raceway having a substantially semicircular cross-sectional profile, and in that the oscillating movement comprises an oscillating pivoting movement of the tool holder at a predefinable pivoting frequency about a pivot axis which runs substantially through a curvature center of a profile of the ball raceway. 
     
     
         3 . The finishing method as claimed in  claim 1 , wherein, in addition to the temporally resolved evaluation of the force signal, a spatially resolved evaluation of the force signal is effected, by virtue of force signals detected during the machining at locations of a workpiece surface that are successively passed over being assigned to corresponding spatial coordinates in a workpiece coordinate system. 
     
     
         4 . The finishing method as claimed in  claim 1 , wherein the finishing method further comprises a force-controlled closed-loop axial position control, in which an axial relative position between an oscillation device and the workpiece, in particular between the pivot axis and the workpiece, is automatically changed in dependence on the at least one geometry parameter, by virtue of the workpiece and/or an oscillation device, in particular pivoting device, bearing the tool holder being displaced in a direction running parallel to the raceway axis in dependence on the force signal. 
     
     
         5 . The finishing method as claimed in  claim 2 , wherein the finishing method further comprises an automatic centering of the axial position of the pivot axis in relation to the machined ball raceway on the basis of the geometry parameter. 
     
     
         6 . The finishing method as claimed in  claim 1 , wherein the temporally resolved evaluation comprises a frequency-specific evaluation of the force signal. 
     
     
         7 . The finishing method as claimed in  claim 6 , wherein the evaluation comprises ascertainment of a signal curve component of the force signal, said signal curve component varying substantially periodically at the oscillation frequency, in particular the pivoting frequency, and analysis of this signal curve component. 
     
     
         8 . The finishing method as claimed in  claim 6 , wherein the evaluation comprises ascertainment of a signal curve component of the force signal, said signal curve component varying substantially periodically at a rotational frequency of the intrinsic rotation of the workpiece, and analysis of this signal curve component. 
     
     
         9 . The finishing method as claimed in  claim 1 , wherein the finishing method further comprises a direction-selective detection of force components in two or more sensitivity directions which are oriented transversely, in particular perpendicularly, with respect to one another. 
     
     
         10 . A finishing apparatus for the finish machining of a workpiece having at least one raceway for rolling elements which runs in encircling fashion about a raceway axis, comprising:
 a workpiece receiving device for receiving the workpiece;   a rotary drive for generating an intrinsic rotation of the workpiece received in the workpiece receiving device about the raceway axis at a predefinable rotational frequency;   a tool holder for receiving a finishing tool which has an abrasive working surface,   an oscillation device having an oscillatory drive for generating an oscillating movement of the tool holder at a predefinable oscillation frequency;   a press-on device for pressing the finishing stone onto the workpiece with a predefinable press-on force in a press-on direction;   a control unit for controlling the rotary drive, the oscillatory drive, the press-on device and further controllable devices of the apparatus;   a force transducer for the continuous detection of reaction forces generated by pressing of the finishing tool onto the workpiece and for the generation of a force signal representing the reaction forces; and   an evaluation device for the temporally resolved evaluation of the force signal to determine at least one geometry parameter representing (i) a workpiece geometry in the region of the machined raceway and/or (ii) a geometric relationship between the workpiece geometry in the region of the machined raceway and a position of the oscillation device.   
     
     
         11 . The finishing apparatus as claimed in  claim 10 , wherein the oscillation device has a pivoting device having an oscillatory drive in the form of a pivoting drive for generating an oscillating pivoting movement of the tool holder at a predefinable pivoting frequency about a pivot axis and the press-on device is designed to generate a press-on force which is oriented perpendicularly with respect to the pivot axis. 
     
     
         12 . The finishing apparatus as claimed in  claim 10 , wherein the control unit is configured to control at least one controllable device of the finishing apparatus in dependence on the geometry parameter. 
     
     
         13 . The finishing apparatus as claimed in  claim 11 , wherein the finishing apparatus has devices for automatic groove middle identification and/or devices for identifying and compensating for pitch errors on ball screw drives. 
     
     
         14 . The finishing apparatus as claimed in  claim 10 , wherein the evaluation unit has an FT module for ascertaining a signal curve component of the force signal, said signal curve component varying substantially periodically at the oscillation frequency, and/or at the rotational frequency, and analysis of this signal curve component. 
     
     
         15 . The finishing apparatus as claimed in  claim 10 , wherein a force transducer is arranged in the region of a finishing tool receptacle of the tool holder between the finishing tool, and the tool holder. 
     
     
         16 . The finishing apparatus as claimed in  claim 10 , wherein, for direction-selective detection of force components in two or more sensitivity directions which are oriented transversely, in particular perpendicularly, with respect to one another, a multi-component force transducer or a group of force transducers with two, three or more different sensitivity directions is provided. 
     
     
         17 . The finishing apparatus as claimed in  claim 10 , wherein the control unit is configured, in at least one operating mode, to control the finishing apparatus for finish machining of the workpiece;
 wherein the oscillatory drive is further for superposing said oscillating movement on the intrinsic rotation of the workpiece and oscillating at the predefinable oscillation frequency; and   wherein the force transducer is further for the continuous detection of the reaction forces generated by pressing of the finishing tool onto the workpiece at the predefinable press-on force, within a detection time period which partially or completely overlaps a machining time period of the finish machining.   
     
     
         18 . The finishing method as claimed in  claim 2 , wherein the press-on force is oriented perpendicularly with respect to the pivot axis. 
     
     
         19 . The finishing method as claimed in  claim 3 , wherein a rotational position of the workpiece is ascertained during the intrinsic rotation and spatially dependent analysis of the force signal is carried out on the basis of the rotational position. 
     
     
         20 . The finishing method as claimed in  claim 5 , wherein the position of the pivot axis is automatically set to an axial groove middle to minimize a groove offset and/or any pitch errors are automatically identified during the machining of ball screw spindles and are automatically compensated for during the machining. 
     
     
         21 . The finishing method as claimed in  claim 6 , wherein spectral distribution function methods are used during the evaluation. 
     
     
         22 . The finishing method as claimed in  claim 7 , wherein at least one asymmetry parameter is ascertained during the analysis and represents a systematic asymmetry of the signal curve component with respect to a zero point position of the oscillating movement, in particular of a pivoting movement, of the finishing tool. 
     
     
         23 . The finishing method as claimed in  claim 8 , wherein at least one waviness parameter is ascertained during the analysis. 
     
     
         24 . The finishing apparatus as claimed in  claim 12 , wherein the finishing apparatus has a linear machine axis for changing an axial relative position between the oscillation device, in particular the pivot axis, and the workpiece in a displacement direction running parallel to the workpiece axis and the control unit is configured to control this machine axis in dependence on the geometry parameter.