METHOD, NUMERICAL CONTROL DEVICE AND MACHINE TOOL FOR MACHINING A WORKPIECE

Abstract

Relative movement between a tool and a workpiece for machining the workpiece with a machine tool is controlled by defining a machine coordinate system (MKS) relative to a machine base of the machine tool and a rotation coordinate system (RKS) relative to the MKS by defining the origin of the RKS in the MKS, defining the orientation of a selected coordinate axis of the RKS in the MKS, defining an axis of rotation around which the RKS rotates in the MKS, defining an angular velocity with which the RKS rotates around the axis of rotation, defining a tool path in the RKS, and controlling the relative movement according to the defined tool path. With this procedure, complex movements of a machine tool, in particular in connection with so-called interpolation turning, can be described or programmed in a relatively simple manner.

Claims

1. A method for controlling a relative movement between a tool and a workpiece to be machined with a machine tool, the method comprising: defining a machine coordinate system (MKS) in relation to a machine base of the machine tool, defining a rotation coordinate system (RKS) in relation to the machine coordinate system (MKS) by: defining an origin of the rotation coordinate system (RKS) in the machine coordinate system (MKS), defining in the machine coordinate system (MKS) an orientation of at least one selected coordinate axis of the rotation coordinate system (RKS), defining an axis of rotation about which the rotation coordinate system (RKS) rotates in the machine coordinate system (MKS), defining an angular velocity with which the rotation coordinate system (RKS) rotates about the axis of rotation, defining at least one tool path in the rotation coordinate system (RKS), and controlling the relative movement according to the tool path defined in the rotation coordinate system (RKS).

2. The method of claim 1, further comprising: defining a workpiece machining axis of a workpiece section of the workpiece to be machined with the tool, and aligning the axis of rotation relative to the workpiece such that the axis of rotation lies on the workpiece machining axis.

3. The method of claim 2, wherein the workpiece machining axis is an axis of symmetry of the workpiece section.

4. The method of claim 1, wherein the selected coordinate axis is oriented parallel to the axis of rotation.

5. The method of claim 1, wherein the position and orientation of the rotation coordinate system (RKS) is specified in the machine coordinate system (MKS) such that the selected coordinate axis lies on the axis of rotation.

6. The method of claim 1, wherein the machine coordinate system (MKS) and/or the rotation coordinate system (RKS) are realized as Cartesian coordinate systems.

7. The method of claim 1, wherein the tool is moved relative to the workpiece by way of at least three translational axes and at least one rotational axis.

8. The method of claim 1, further comprising affixing the tool in a tool spindle for rotation about a tool spindle axis.

9. The method of claim 8, wherein a position and an orientation of the tool spindle axis is defined in the rotation coordinate system (RKS).

10. The method of claim 9, wherein the tool spindle is aligned relative to the rotation coordinate system (RKS) such that the tool spindle axis lies in a plane defined by two coordinate axes of the rotation coordinate system (RKS).

11. The method of claim 10, wherein the tool spindle is aligned parallel to the selected coordinate axis of the rotation coordinate system (RKS).

12. The method of claim 1, further comprising specifying an orientation of a cutting edge of the tool in the rotation coordinate system (RKS), wherein the tool path includes the orientation of the cutting edge.

13. The method of claim 12, wherein the orientation of the cutting edge in the rotation coordinate system (RKS) is retained during machining of the workpiece.

14. The method of claim 2, wherein the tool path is determined based on a specified contour of the workpiece section

15. The method of claim 1, wherein the tool path is defined by a turning cycle programmed for a conventional turning tool operation.

16. A numerical controller controlling a relative movement between a tool and a workpiece to be machined with a machine tool, the numerical controller configured to: define a machine coordinate system (MKS) in relation to a machine base of the machine tool, define a rotation coordinate system (RKS) in relation to the machine coordinate system (MKS) by: define an origin of the rotation coordinate system (RKS) in the machine coordinate system (MKS), define in the machine coordinate system (MKS) an orientation of at least one selected coordinate axis of the rotation coordinate system (RKS), define an axis of rotation about which the rotation coordinate system (RKS) rotates in the machine coordinate system (MKS), define an angular velocity with which the rotation coordinate system (RKS) rotates about the axis of rotation, define at least one tool path in the rotation coordinate system (RKS), and control the relative movement according to the tool path defined in the rotation coordinate system (RKS).

17. The numerical controller of claim 16, wherein a selected coordinate axis of the rotation coordinate system (RKS) is defined as the axis of rotation.

18. The numerical controller of claim 16, wherein the machine coordinate system (MKS) and/or the rotation coordinate system (RKS) are Cartesian coordinate systems.

19. The numerical controller of claim 16, wherein an orientation of at least one cutting edge of the tool is defined in the rotation coordinate system (RKS), and wherein the tool path includes the orientation of the at least one cutting edge.

20. The numerical controller of claim 19, wherein the orientation of the at least one cutting edge in the rotation coordinate system (RKS) is constant during machining of the workpiece.

21. The numerical controller of claim 16, wherein the axis of rotation is aligned relative to the workpiece such that the axis of rotation lies on a workpiece machining axis of a workpiece section of the workpiece to be machined by the tool.

22. The numerical controller of claim 21, wherein the workpiece machining axis is defined as an axis of symmetry of the workpiece section of the workpiece to be machined by the tool.

23. The numerical controller of claim 16, wherein the tool is affixed in a tool spindle for rotation about a tool spindle axis, and wherein the tool spindle is aligned relative to the rotation coordinate system (RKS) such that the tool spindle axis lies in a plane defined by two coordinate axes of the rotation coordinate system (RKS).

24. A machine tool for machining a workpiece affixed to a workpiece holder of the machine tool, comprising: a tool spindle rotatable about a tool spindle axis and holding a tool constructed to machine the workpiece, at least three translational axes and at least one rotational axis, and a numerical controller controlling a relative movement between the tool and the workpiece, wherein the numerical controller is configured to: define a machine coordinate system (MKS) in relation to a machine base of the machine tool, define a rotation coordinate system (RKS) in relation to the machine coordinate system (MKS) by: define an origin of the rotation coordinate system (RKS) in the machine coordinate system (MKS), define in the machine coordinate system (MKS) an orientation of at least one selected coordinate axis of the rotation coordinate system (RKS), define an axis of rotation about which the rotation coordinate system (RKS) rotates in the machine coordinate system (MKS), define an angular velocity with which the rotation coordinate system (RKS) rotates about the axis of rotation, define at least one tool path in the rotation coordinate system (RKS), and control the relative movement according to the tool path defined in the rotation coordinate system (RKS).

Description

BRIEF DESCRIPTION OF THE DRAWING

[0083] Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:

[0084] FIG. 1 shows a schematic diagram of a machine tool suitable for executing the present invention,

[0085] FIGS. 2 to 7 show measures for executing the method according to the invention, and

[0086] FIG. 8 shows major method steps for executing the method according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0087] Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

[0088] Turning now to the drawing, and hi particular to FIG. 1, there is shown a schematic, highly simplified diagram of an embodiment of the invention with a machine tool 1 having three translational axes L1, L2 and L3 (linear axes) configured to move a tool 2 relative to a workpiece 3 in three linear spatial axes. The machine tool 1 includes a (fixed) machine base 4 to which a workpiece holder 5 is affixed. One point on the fixed machine base 4 is selected as a reference point (origin) for an MKS (also fixed) with the coordinate axes x, y and z. The coordinate axes x, y and z of the MKS are advantageously selected such that the x axis is aligned parallel to L1, the y axis is aligned parallel to L2 and the z axis is aligned parallel to L3, Furthermore, a tool head that can be pivoted around a rotational axis B (rotary axis), with which the tool 2 can be pivoted around a B axis that is parallel to the y axis, is provided on the machine tool 1. The tool 2 is affixed to a tool spindle 6 enclosed within the tool head 10 and can be rotated around a tool spindle axis SA. Like the other axes, the tool spindle 6 is provided with a position-controlled drive such that any angle can be set for the tool spindle 6 and as a result a cutting edge 7 of the workpiece 2 can be oriented with respect to the tool spindle axis SA. A numerical controller 8 is provided for the coordinated position control of the individual axes of the machine tool 1.

[0089] FIGS. 2 to 7 show in more detail a process according to the present invention for turning the workpiece 3 shown in the exemplary embodiment of FIG. 1 when clamped, To this end, FIG. 2 once more shows the MKS with the coordinate axes x, y and z and the rotationally asymmetrical workpiece 3 clamped in a fixed position in the machine tool with a workpiece section 9 to be machined, which is rotationally symmetrical with respect to a workpiece machining axis WA.

[0090] In accordance with the invention, a Cartesian RKS with the coordinate axes x, y and z is first defined for the machining of the workpiece 3 to be performed. As can be seen in FIG. 3, for this purpose a displacement vector {right arrow over (v)} for the coordinate point of origin is first determined such that the origin 0 of the RKS coordinate system lies on the workpiece machining axis WA of the workpiece 3. In the exemplary embodiment, the workpiece machining axis WA is an axis of symmetry of a workpiece section 9 which is to be machined in accordance with the invention.

[0091] Furthermoreas can be seen in FIG. 4the z axis is oriented such that lies on the workpiece machining axis WA of the workpiece 3. In this exemplary embodiment, the workpiece machining axis WA lies in the x-z plane of the MKS after corresponding positioning and orientation of the workpiece 3. The orientation of the z axis is then produced from the MKS by means of a single pivoting movement of the z axis around the y axis. It is therefore sufficient to specify a single angle through which the x axis and the z axis must be pivoted around the y axis in order to define the orientation of the RKS in the MKS. If the workpiece machining axis WA did not lie in the x-z plane of the MKS, at least one further pivoting movement would be necessary in order to cause the z axis to He on the workpiece machining axis WA.

[0092] Assuming that the x axis should also lie in the x-z plane, the orientations of the x axis and y axis and therefore the whole RKS are then also determined unambiguously in relation to the MKS.

[0093] In the inventive procedure, the tool paths for machining the workpiece 3 are specified not in the MKS, but rather in the RKS. FIG. 5 illustrates the starting situation for this purpose, in which the position and orientation of the tool head 10 and in particular of the tool cutting edge 7 are specified in the RKS. In the advantageous starting position in accordance with FIG. 5, the spindle axis SA lies in the x-z plane and is oriented parallel to the z axis. The tool 2 is oriented opposite to the x direction.

[0094] According to a particular feature of the coordinate transformation in accordance with the invention, the RKS defined as described above now rotates continuously with a constant angular velocity around the z axis. This causes a constant position and orientation of the tool 2 specified in the RKS to perform, from the perspective of the MKS, a circular movement of the tool 2 with the angular velocity around the z axis, with the orientation of the cutting edge 7 thus also changing with the angular velocity . The angular velocity , with which the tool spindle rotates 6 around the tool spindle axis SA, is hence identical to the angular velocity with which the RKS rotates around the z axis. The rotation of the tool spindle 6 is therefore synchronous with the rotation of the RKS. In the exemplary embodiment, the cutting edge 7 therefore remains oriented parallel to the x axis at all times, such that the cutting edge 7 points at all times toward the z axis as the tool 2 rotates. This is illustrated in FIGS. 6 and 7, which show the workpiece machining at two different points in time. An observer moving in conjunction with the RKS therefore sees a fixed tool with a constant orientation and a workpiece section 9 rotating around the z axis. However this represents the typical starting situation for the machining mode turning when using a conventional turning tool.

[0095] Starting from this starting situation, the (rotationally symmetrical) contour of the workpiece section 9 to be machined is specified in the x-z plane. The tool paths are then calculated in the controller 8 from the specified contour as with a conventional turning tool, Taking into consideration the coordinate transformation described above, the controller 8 then converts the tool paths calculated for the RKS into tool paths with respect to the MKS and the corresponding coordinated movements of the relevant machine tool axes L1 to L3 and B of the machine tool 1.

[0096] FIG. 8 illustrates major method steps in the execution of a method according to the invention. In a first method step S1, an MKS that is fixed with respect to the employed machine tool is defined. In a method step S2, a workpiece machining axis is defined for a workpiece section of the workpiece to be machined, with the workpiece to be machined being clamped in the machine tool. The workpiece machining axis is an axis of symmetry of the workpiece section of the workpiece to be machined. In a method step S3, the origin of an RKS is defined on the workpiece machining axis in the MKS, for example by defining a displacement vector. In a method step S4, the orientation of the RKS in relation to the MKS is defined, for which typically three pivoting movements are required. For the special case in which the workpiece machining axis lies in the x-z plane of the MKS, a rotation around the y axis is sufficient so that the z axis of the RKS coincides with the workpiece machining axis. In a method step S5, the tool path is defined in the RKS, preferably with respect to the axes x and z where y=0. The definition of the tool path then largely corresponds to that used in the case of normal turning. In a method step S6, the rotation of the tool spindle is started with the angular velocity , In a method step S7, the rotation of the RKS about the z axis with the angular velocity is started simultaneously. Preferably =. These rotations cause the tool with the oriented cutting edge to rotate around the workpiece section to be machined. Finally, in a method step S8, the tool path specified in step 5 is traversed.

[0097] A significant advantage achieved by the invention compared to conventional interpolation turning is that existing turning cycles or existing tool paths for turning can be used, and these need only be specified in the RKS. The transformation then allows the machine to execute intrinsically complex axis movements that result in the desired machining, but specifying these axis movements in the RKS is relatively simple and largely corresponds to the guidelines used with conventional turning.

[0098] The basic principle illustrated by the exemplary embodiment can also be applied analogously to more complex machining processes. In particular, it is not essential for the workpiece machining axis to lie in the x-z plane of the MKS. In principle, the workpiece machining axis can lie anywhere in the machine tool working area. However, at least one additional rotary axis of the machine tool may then be required, for example an A axis for executing a pivoting movement of the tool about the x axis or an axis parallel to the x axis.

[0099] With respect to the coordinate transformation, a displacement and orientation of the RKS with respect to the MKS in three-dimensional space would generally be required, which causes greater computing complexity in the controller and more complex machine movements compared with the exemplary embodiment. However this in no way affects the advantages for the user of a machine tool configured in this way.

[0100] While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.

[0101] What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: