Machine tool and tool movement path determination method

Abstract

To provide a technique that can improve the degree of freedom in processing a work-piece in an eccentric shape.SOLUTION: A control part (70) of a machine tool (1) obtains coordinates of a first process starting point SpA and a first process ending point EpA in eccentric shapes in a reference phase (θ=0°) of a work-piece W1 with a spindle central line AX0 as a center and coordinates of a second process starting point SpB and a second process ending point EpB in eccentric shapes in an antiphase (θ=180°); determines a movement path for a tool TO1 according to rotation of the work-piece W1, at least on the basis of the coordinates of the first process starting point SpA, the coordinates of the second process starting point SpB, the coordinates of the first process ending point EpA and the coordinates of the second process ending point EpB, so that the work-piece is formed in an eccentric shape (W1p) with an eccentric shaft AX3, which passes through a central starting point SpO between the first process starting point SpA and the second process starting point SpB and a central ending point EpO between the first process ending point SpA and the second process ending point EpB, as a center; and performs control by which a tool TO1 is moved in accordance with rotation of the work-piece W1.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a machine tool capable of forming an eccentric shape on a workpiece, and a method for determining a tool movement path. [Background technology]

[0002] A well-known machine tool is a numerically controlled (NC) lathe equipped with a spindle and a tool post. NC lathes machine a rotating workpiece held by the spindle using a tool attached to the tool post. When machining a rotating workpiece from the outside using a tooling tool, only a cylindrical shape centered on the spindle center line is formed on the workpiece unless the relative positional relationship between the spindle center line and the cutting edge of the tooling remains unchanged in the XY plane perpendicular to the spindle center line. Therefore, an eccentric shape is formed on the workpiece by rotating the cutting edge of the tooling tool in the XY plane in accordance with the rotation of the workpiece.

[0003] The NC lathe disclosed in Patent Document 1 accepts input of the eccentric distance (D) and the radius (R) of the eccentric shape, sets a virtual circle with a radius equal to the eccentric distance D, sets an offset virtual circle whose center is offset from the axis of the workpiece by the radius R in the radial direction of the workpiece, and moves the cutting edge of the tool bit along the circumference of the offset virtual circle in association with the rotation of the workpiece by the spindle. In this way, an eccentric shape is formed on the workpiece. If the eccentric shape is convex, a cylindrical shape is formed on the workpiece with its center at the eccentric axis parallel to the center line of the spindle. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 086238 Summary of the Invention [Problem to be solved by the invention]

[0005] The NC lathe described above can only form eccentric shapes on the workpiece that have a constant diameter centered on a center line parallel to the spindle center line. If the degree of freedom in machining eccentric shapes could be improved, the convenience of the NC lathe would be improved. The above-mentioned problems are not limited to lathes, but also exist in various machine tools such as machining centers.

[0006] The present invention discloses a technique that can improve the degree of freedom in machining an eccentric shape. [Means for solving the problem]

[0007] The machine tool of the present invention comprises: a spindle that rotates together with the workpiece around the spindle center line; a tool rest on which a tool for machining the workpiece is attached; a drive unit that changes the relative positional relationship between the spindle and the tool rest; a control unit that controls the relative positional relationship by the drive unit so as to form an eccentric shape on the workpiece about an eccentric axis that is shifted from the center line of the spindle, the eccentric shape formed on the workpiece has a machining start portion, which is a portion where machining of the workpiece rotating about the spindle center line starts, and a machining end portion, which is a portion where machining of the workpiece rotating about the spindle center line ends, a first machining start point is the position of the cutting edge of the tool that forms the machining start portion when the workpiece rotating about the spindle center line is in a reference phase, a second machining start point is a position at the machining start portion that is on the opposite side of the first machining start point with the eccentric shaft as the center, a first machining end point is the position of the cutting edge of the tool that forms the machining end portion when the workpiece is in the reference phase, and a second machining end point is a position at the machining end portion that is on the opposite side of the first machining end point with the eccentric shaft as the center, The control unit Acquire the coordinates of the first machining start point, the coordinates of the second machining start point, the coordinates of the first machining end point, and the coordinates of the second machining end point when the workpiece is in the reference phase, including the Z coordinate which is the coordinate of the Z axis along the spindle center line; determining a movement path of the tool in accordance with the rotation of the workpiece based at least on the coordinates of the first machining start point, the coordinates of the second machining start point, the coordinates of the first machining end point, and the coordinates of the second machining end point so that the eccentric shape is formed around the eccentric axis passing through a center start point which is the midpoint of a line segment connecting the first machining start point and the second machining start point, and a center end point which is the midpoint of a line segment connecting the first machining end point and the second machining end point; performing control to move the tool along the movement path in accordance with the rotation of the workpiece; The first processing start point and the second processing start point may have different Z coordinates, The first processing end point and the second processing end point may have different Z coordinates, At least, the Z coordinate of the first processing start point is different from the Z coordinate of the second processing start point, or the Z coordinate of the first processing end point is different from the Z coordinate of the second processing end point, before Dividing a first outer line connecting the first processing start point and the first processing end point and a second outer line connecting the second processing start point and the second processing end point minutes Divisor N The number of times the workpiece rotates around the spindle center line from the start of machining the eccentric shape to the end of machining. As, The control unit has an aspect in which it controls the relative positional relationship by the drive unit so that, each time the workpiece rotates once around the spindle center line, the Z coordinate of the relative positional relationship on the first outline changes by a value obtained by dividing the difference in Z coordinate between the first processing start point and the first processing end point by the number of divisions N, and the Z coordinate of the relative positional relationship on the second outline changes by a value obtained by dividing the difference in Z coordinate between the second processing start point and the second processing end point by the number of divisions N.

[0008] Further, a tool movement path determination method of the present invention is a tool movement path determination method for a machine tool including a spindle that rotates together with a workpiece about a spindle center line, and a tool post to which a tool for machining the workpiece is attached, and which changes a relative positional relationship between the spindle and the tool post so as to form an eccentric shape on the workpiece about an eccentric axis that is offset from the spindle center line, the eccentric shape formed on the workpiece has a machining start portion, which is a portion where machining of the workpiece rotating about the spindle center line starts, and a machining end portion, which is a portion where machining of the workpiece rotating about the spindle center line ends, a first machining start point is the position of the cutting edge of the tool that forms the machining start portion when the workpiece rotating about the spindle center line is in a reference phase, a second machining start point is a position at the machining start portion that is on the opposite side of the first machining start point with the eccentric shaft as the center, a first machining end point is the position of the cutting edge of the tool that forms the machining end portion when the workpiece is in the reference phase, and a second machining end point is a position at the machining end portion that is on the opposite side of the first machining end point with the eccentric shaft as the center, a first step of acquiring a coordinate of the first machining start point, a coordinate of the second machining start point, a coordinate of the first machining end point, and a coordinate of the second machining end point when the workpiece is in the reference phase, including a Z coordinate which is a coordinate of the Z axis along the spindle center line; a second step of determining a movement path of the tool in accordance with the rotation of the workpiece based at least on the coordinates of the first machining start point, the coordinates of the second machining start point, the coordinates of the first machining end point, and the coordinates of the second machining end point so that the eccentric shape is formed around the eccentric axis passing through a center start point which is the midpoint of a line segment connecting the first machining start point and the second machining start point, and a center end point which is the midpoint of a line segment connecting the first machining end point and the second machining end point, The first processing start point and the second processing start point may have different Z coordinates, The first processing end point and the second processing end point may have different Z coordinates, At least, the Z coordinate of the first processing start point is different from the Z coordinate of the second processing start point, or the Z coordinate of the first processing end point is different from the Z coordinate of the second processing end point, beforeDividing a first outer line connecting the first processing start point and the first processing end point and a second outer line connecting the second processing start point and the second processing end point minutes Divisor N The number of times the workpiece rotates around the spindle center line from the start of machining the eccentric shape to the end of machining. As, In the second step, a movement path of the tool is determined in accordance with the rotation of the workpiece so that, each time the workpiece rotates once around the spindle center line, the Z coordinate of the relative positional relationship on the first outer contour line changes by a value obtained by dividing the difference in Z coordinate between the first machining start point and the first machining end point by the number of divisions N, and the Z coordinate of the relative positional relationship on the second outer contour line changes by a value obtained by dividing the difference in Z coordinate between the second machining start point and the second machining end point by the number of divisions N. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a technique that improves the degree of freedom in machining an eccentric shape. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a front view schematically showing an example of the configuration of a machine tool. [Figure 2] FIG. 2 is a block diagram schematically illustrating an example of the configuration of an electric circuit of a machine tool. [Figure 3] 10A and 10B are diagrams illustrating an example of forming a tapered eccentric shape on a workpiece. [Figure 4] FIG. 10 is a diagram schematically showing an example in which a tool moves in accordance with the rotation of a workpiece on an XY plane. [Figure 5] 10A and 10B are diagrams illustrating an example in which a tapered eccentric shape is formed on a workpiece, the eccentric shape being centered on an eccentric axis that is not parallel to the center line of the spindle. [Figure 6] 10A and 10B are diagrams illustrating an example in which a workpiece is formed with a tapered eccentric shape in which the machining start portion and the machining end portion are tilted from the XY plane. [Figure 7] 10A and 10B are diagrams illustrating an example of determining the relative positions of a tool when forming a tapered, eccentric shape in a workpiece, in which the machining start portion and machining end portion are inclined from the XY plane. [Figure 8]10 is a flowchart schematically illustrating an example of an eccentricity processing process. [Figure 9] FIG. 10 is a block diagram schematically illustrating a modified example of an electrical circuit of a machine tool. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following describes embodiments of the present invention. Of course, the following embodiments are merely examples of the present invention, and not all of the features shown in the embodiments are necessarily essential to the solution of the invention.

[0012] (1) Overview of the technology included in this invention: First, an overview of the technology included in the present invention will be described with reference to the examples shown in Figures 1 to 8. Note that the figures in this application are diagrams showing schematic examples, and the magnifications in the directions shown in these figures may differ, and the figures may not be consistent. Of course, each element of the present technology is not limited to the specific example indicated by the symbol.

[0013] [Aspect 1] As illustrated in FIGS. 1 and 2, a machine tool (e.g., lathe 1) according to one aspect of the present technology includes a spindle 11, a tool rest 30, a drive unit DR, and a control unit (e.g., an NC device 70). The spindle 11 rotates together with a workpiece W1 about a spindle center line AX0. A tool TO1 for machining the workpiece W1 is attached to the tool rest 30. The drive unit DR changes the relative positional relationship between the spindle 11 and the tool rest 30. The control unit 70 controls the relative positional relationship by the drive unit DR so as to form an eccentric shape (e.g., a protrusion W1p) on the workpiece W1, the center of which is an eccentric axis AX3 that is offset from the spindle center line AX0, as illustrated in FIGS. 3 to 7. The control unit (70) acquires the coordinate of a first machining start point SpA of the eccentric shape (W1p) in a reference phase (e.g., θ=0°) of the workpiece W1 centered on the spindle center line AX0, the coordinate of a second machining start point SpB of the eccentric shape (W1p) in an opposite phase (e.g., θ=180°) that is 180° different from the reference phase (θ=0°), the coordinate of a first machining end point EpA of the eccentric shape (W1p) in the reference phase (θ=0°), and the coordinate of a second machining end point EpB of the eccentric shape (W1p) in the opposite phase (θ=180°). The control unit (70) determines a movement path (e.g., a virtual circle C1 shown in the figure) of the tool TO1 in accordance with the rotation of the workpiece W1 based on at least the coordinates of the first processing start point SpA, the coordinates of the second processing start point SpB, the coordinates of the first processing end point EpA, and the coordinates of the second processing end point EpB so that the eccentric shape (W1p) is formed around the eccentric axis AX3, which passes through a central start point SpO between the first processing start point SpA and the second processing start point SpB, and a central end point EpO between the first processing end point EpA and the second processing end point EpB. Furthermore, the control unit (70) controls the movement of the tool TO1 in accordance with the rotation of the workpiece W1 along the movement path (C1).

[0014] For example, in an XY plane perpendicular to the spindle center line AX0, if the distance between the first machining start point SpA and the second machining start point SpB is different from the distance between the first machining end point EpA and the second machining end point EpB, a tapered eccentric shape (W1p) is formed on the workpiece W1. When the coordinates of four points (the first machining start point SpA, the second machining start point SpB, the first machining end point EpA, and the second machining end point EpB) are acquired in the XY plane such that the X and Y coordinates of the center start point SpO are different from the X and Y coordinates of the center end point EpO, an eccentric shape (W1p) centered on an eccentric axis AX3 that is not parallel to the spindle center line AX0 is formed on the workpiece W1. As such, the eccentric shape (W1p) formed on the workpiece W1 is not limited to a shape whose diameter, centered on a center line parallel to the spindle center line AX0, remains constant. Therefore, the above-described first aspect can provide a machine tool that can improve the degree of freedom in machining eccentric shapes.

[0015] Here, the drive unit may change the relative positional relationship between the spindle and the tool post by moving the tool post, or may change the relative positional relationship between the spindle and the tool post by moving the spindle, or may change the relative positional relationship between the spindle and the tool post by moving both the tool post and the spindle. The eccentric shape may be a convex shape or a hole. The control unit may acquire one or more parameters in addition to the coordinates of the four points. The acquired parameters may include the feed pitch of the workpiece in the Z-axis direction along the spindle center line, the spindle rotation angle as a unit for determining the tool movement path, and the peripheral speed, which is the speed at the periphery of the workpiece in a rotating state. The control unit may add one or more parameters to the coordinates of the four points to determine the tool movement path. In this application, the terms "first", "second", etc. are terms for distinguishing between elements among a plurality of elements having similarities, and do not imply any order. The above remarks also apply to the following aspects.

[0016] [Aspect 2] 3 to 8, the control unit (70) may determine a diameter (SpD) of the eccentric shape (W1p) in a direction perpendicular to the spindle center line AX0 based on the coordinates of the first processing start point SpA and the coordinates of the second processing start point SpB. The control unit (70) may determine a diameter (EpD) of the eccentric shape (W1p) in a direction perpendicular to the spindle center line AX0 based on the coordinates of the first processing end point EpA and the coordinates of the second processing end point EpB. The control unit (70) may interpolate a diameter (WpD) at a processing mid-point center point WpO located on the eccentric axis AX3 between the center start point SpO and the center end point EpO from the diameter (SpD) and the diameter (EpD). Furthermore, the control unit (70) may determine the movement path of the tool TO1 to be a path along the circumference of a virtual arc (C1) centered on an arc center WpC that is shifted from the spindle center line AX0, based on the diameter (WpD).

[0017] When the diameter (SpD) of the eccentric shape (W1p) at the machining start point and the diameter (EpD) of the eccentric shape (W1p) at the machining end point are different, a tapered eccentric shape (W1p) is formed on the workpiece W1. Therefore, the above-mentioned mode 2 can provide a suitable example that improves the degree of freedom in machining the eccentric shape. Here, the concept of a virtual arc includes a virtual circle that is assumed when the spindle rotation angle is 360°. Therefore, the concept of the circumference of a virtual arc includes a virtual circumference. The above remarks also apply to the following aspects.

[0018] [Aspect 3] 3 to 8, the control unit (70) may determine the amount of eccentricity (SpE) of the center start point SpO from the spindle center line AXO based on the coordinates of the first processing start point SpA and the coordinates of the second processing start point SpB. The control unit (70) may determine the amount of eccentricity (EpE) of the center end point EpO from the spindle center line AXO based on the coordinates of the first processing end point EpA and the coordinates of the second processing end point EpB. The control unit (70) may determine the amount of eccentricity (WpE) of the mid-processing center point WpO from the spindle center line AXO by interpolating the amount of eccentricity (SpE) and the amount of eccentricity (EpE) using a point on the eccentric axis AX3 between the center start point SpO and the center end point EpO as a mid-processing center point WpO. Furthermore, the control unit (70) may determine the movement path of the tool TO1 to be a path along the circumference of a virtual arc (C1) having a size according to the amount of eccentricity (WpE).

[0019] When the eccentricity (SpE) of the central start point SpO and the eccentricity (EpE) of the central end point EpO are different, an eccentric shape (W1p) centered on an eccentric axis AX3 that is not parallel to the spindle center line AX0 is formed on the workpiece W1. Therefore, the above-mentioned aspect 3 can provide a suitable example that improves the degree of freedom in machining the eccentric shape.

[0020] [Aspect 4] The control unit (70) may acquire the coordinates of the first processing start point SpA, the coordinates of the second processing start point SpB, the coordinates of the first processing end point EpA, and the coordinates of the second processing end point EpB, including the Z coordinate, which is the coordinate of the Z axis along the spindle center line AX0. As illustrated in FIG. 7, the control unit (70) may control the relative positional relationship by the drive unit DR so that, each time the workpiece W1 rotates around the spindle center line AX0, the Z coordinate of the relative positional relationship on a first outline line (e.g., on a first line segment SpA-EpA) connecting the first processing starting point SpA and the first processing end point EpA changes by a value obtained by dividing the difference in Z coordinate between the first processing starting point SpA and the first processing end point EpA (e.g., movement amount ZdA) by the number of divisions N, and the Z coordinate of the relative positional relationship on a second outline line (e.g., on a second line segment SpB-EpB) connecting the second processing starting point SpB and the second processing end point EpB changes by a value obtained by dividing the difference in Z coordinate between the second processing starting point SpB and the second processing end point EpB (e.g., movement amount ZdB) by the number of divisions N. For example, as illustrated in FIG. 7, the control unit (70) may control the relative positional relationship by the drive unit DR so that, each time the workpiece W1 rotates around the spindle center line AX0, the relative positional relationship on a first line segment SpA-EpA connecting the first processing start point SpA and the first processing end point EpA changes by a length obtained by dividing the length of the first line segment SpA-EpA by the number of divisions N, and the relative positional relationship on a second line segment SpB-EpB connecting the second processing start point SpB and the second processing end point EpB changes by a length obtained by dividing the length of the second line segment SpB-EpB by the number of divisions N.

[0021] From the above, even if the difference in Z coordinate between the first processing start point SpA and the first processing end point EpA is different from the difference in Z coordinate between the second processing start point SpB and the second processing end point EpB, an eccentric shape (W1p) is formed on the workpiece W1. Therefore, the above-mentioned embodiment 4 can provide a suitable example that improves the degree of freedom in processing the eccentric shape. Here, the first and second outer contour lines are not limited to straight lines, but may be curved lines. This statement also applies to the following aspects.

[0022] [Aspect 5] Assuming that the mutually orthogonal X-axis and Y-axis are orthogonal to the Z-axis along the spindle center line AX0, the drive unit DR may include a tool post drive unit 31 that moves the tool post 30 along the X-axis and Y-axis, and a headstock drive unit 13 that moves the spindle 11 along the Z-axis, as exemplified in Figures 1 and 2. The control unit (70) may move the tool TO1 along the X-axis and Y-axis in accordance with the rotation of the workpiece W1, and may vibrate the workpiece W1 along the Z-axis in accordance with the rotation of the workpiece W1 when vibrating the relative positional relationship along the Z-axis in accordance with the rotation of the workpiece W1. As described above, when the tool rest 30 does not move along the Z axis, even if there is a difference in Z coordinate between the first processing start point SpA and the second processing start point SpB, or a difference in Z coordinate between the first processing end point EpA and the second processing end point EpB, the workpiece W1 vibrates along the Z axis in accordance with the rotation of the workpiece W1, thereby forming an eccentric shape (W1p) on the workpiece W1. Therefore, the above-mentioned aspect 5 can provide a suitable example that improves the degree of freedom in processing eccentric shapes.

[0023] [Aspect 6] 9, the drive unit DR may move the tool post 30 along the X-axis, Y-axis, and Z-axis. The control unit (70) may move the tool TO1 along the X-axis and Y-axis in accordance with the rotation of the workpiece W1, and may vibrate the tool TO1 along the Z-axis in accordance with the rotation of the workpiece W1 when vibrating the relative positional relationship along the Z-axis in accordance with the rotation of the workpiece W1. As described above, when the spindle 11 does not move along the Z axis, even if there is a difference in Z coordinate between the first machining start point SpA and the second machining start point SpB, or a difference in Z coordinate between the first machining end point EpA and the second machining end point EpB, the tool TO1 vibrates along the Z axis in accordance with the rotation of the workpiece W1, thereby forming an eccentric shape (W1p) on the workpiece W1. Therefore, the above-mentioned aspect 6 can also provide a suitable example that improves the degree of freedom in machining an eccentric shape.

[0024] [Aspect 7] Furthermore, a tool movement path determination method according to one aspect of the present technology is a tool movement path determination method for a machine tool (1) that includes a spindle 11 that rotates together with a workpiece W1 around a spindle center line AX0 and a tool post 30 to which a tool TO1 that processes the workpiece W1 is attached, and that changes the relative positional relationship between the spindle 11 and the tool post 30 so as to form an eccentric shape (W1p) on the workpiece W1 that is centered on an eccentric axis AX3 that is offset from the spindle center line AX0, and includes the following steps (A1) and (A2). (A1) A first step ST1 (e.g., step S102 in FIG. 8) of acquiring the coordinates of the first machining start point SpA of the eccentric shape (W1p) in the reference phase (θ=0°) of the workpiece W1 centered on the spindle center line AX0, the coordinates of the second machining start point SpB of the eccentric shape (W1p) in the opposite phase (θ=180°) that is 180° different from the reference phase (θ=0°), the coordinates of the first machining end point EpA of the eccentric shape (W1p) in the reference phase (θ=0°), and the coordinates of the second machining end point EpB of the eccentric shape (W1p) in the opposite phase (θ=180°). (A2) A second process ST2 (e.g., steps S104 to S112 in FIG. 8) determines a movement path (C1) of the tool TO1 in accordance with the rotation of the workpiece W1 based at least on the coordinates of the first machining starting point SpA, the coordinates of the second machining starting point SpB, the coordinates of the first machining end point EpA, and the coordinates of the second machining end point EpB so that the eccentric shape (W1p) is formed around the eccentric axis AX3 which passes through the central start point SpO between the first machining starting point SpA and the second machining starting point SpB, and the central end point EpO between the first machining end point EpA and the second machining end point EpB.

[0025] As described above, the eccentric shape (W1p) formed on the workpiece W1 is not limited to a shape whose diameter does not change about a center line parallel to the spindle center line AX0. Therefore, the above-mentioned aspect 6 can provide a tool movement path determination method that can improve the degree of freedom in machining an eccentric shape.

[0026] (2) Specific examples of machine tool configurations: Fig. 1 is a front view that schematically illustrates the configuration of a lathe 1 as an example of a machine tool. Fig. 2 schematically illustrates the configuration of the electrical circuit of the lathe 1. Fig. 3 schematically illustrates the process of forming a protrusion W1p having an eccentric tapered shape on a workpiece W1. Fig. 3 also illustrates a view of the workpiece W1 viewed from the surface having the protrusion W1p. In FIG. 1, symbol D81 indicates the upward direction, symbol D82 indicates the downward direction, symbol D83 indicates the leftward direction, and symbol D84 indicates the rightward direction. These directions are based on the direction in which the lathe 1 shown in FIG. 1 is viewed. As shown in FIGS. 1 and 3, the control axes of the lathe 1 include an X-axis indicated by "X," a Y-axis indicated by "Y," a Z-axis indicated by "Z," and a C-axis indicated by "C." The Z-axis direction is a horizontal direction along the spindle center line AX0, which is the rotation center of the workpiece W1. The X-axis direction is a direction perpendicular to the Z-axis and may be a direction facing up and down (upward direction D81 and downward direction D82) or a direction facing left and right (leftward direction D83 and rightward direction D84). The Y-axis direction is a direction perpendicular to both the Z-axis and the X-axis. The C-axis is a rotation axis centered on the spindle center line AX0. The drawings referred to in this specification merely illustrate examples for describing the present technology and do not limit the present technology. The explanation of the positional relationship of each part is merely an example. Therefore, reversing the left and right, reversing the direction of rotation, etc. are also included in this technology. The identity of direction, position, etc. is not limited to exact agreement, but also includes deviation from exact agreement due to error.

[0027] The lathe 1 is an NC lathe equipped with a headstock 10 having a spindle 11 with a gripper 12, a headstock drive unit 13, a support table 25 having mounting holes 26 for guide bushes 14, a tool rest 30, a tool rest drive unit 31, an NC device 70, and the like. Here, the headstock 10 collectively refers to a front headstock 15 and a back headstock 20, also called an opposing headstock. The front headstock 15 incorporates a front spindle 16 having a gripper 17, such as a collet. The back headstock 20 incorporates a back spindle 21 having a gripper 22, such as a collet. The spindle 11 collectively refers to the front spindle 16 and the back spindle 21, also called an opposing spindle. The gripper 12 collectively refers to the gripper 17 and the gripper 22. The headstock drive unit 13 collectively refers to the front headstock drive unit 18, which moves the front headstock 15 along the Z axis, and the back headstock drive unit 23, which moves the back headstock 20 at least along the Z axis. The lathe 1 shown in Figures 1 and 2 is a moving spindle type lathe in which the front spindle 16 moves in the Z axis direction. The headstock drive unit 13 and the tool rest drive unit 31 are examples of drives DR that change the relative positional relationship between the spindle 11 and the tool rest 30. The NC device 70 is an example of a control unit that controls the above-mentioned relative positional relationship.

[0028] The front spindle 16 releasably grips a rod-shaped workpiece W1 inserted from the rear by the material feeder 8 (see FIG. 2) with a gripper 17, and is rotatable together with the workpiece W1 around the spindle center line AX1. The front end 16a of the front spindle 16 faces the back spindle 21, and the rear end 16b of the front spindle 16 faces the material feeder 8. The front spindle 16 has a through-hole 16h that runs along the spindle center line AX1. The workpiece W1 is inserted into the through-hole 16h from the rear. If the workpiece W1 before machining is a short material, the workpiece W1 may be fed from the front end 16a of the front spindle 16 to the gripper 17. The NC device 70 rotates the front spindle 16 around the spindle center line AX1 by driving the front spindle rotation drive unit 16c (see FIG. 2) and controls the gripping state of the gripper 17 by driving the gripping actuator 17a (see FIG. 2). The gripping unit 17 can be configured, for example, by a collet. The headstock driving unit 18 moves the headstock 15 in the Z-axis direction in accordance with commands from the NC device 70. Therefore, the workpiece W1 gripped by the head spindle 16 moves in the Z-axis direction. The rod-shaped workpiece W1 is not limited to a solid material such as a long columnar material, but may be a hollow material such as a long cylindrical material.

[0029] The front end 21a of the back spindle 21 faces the front end 16a of the front spindle 16. The back spindle 21 releasably grips the workpiece W1 in the middle of machining, which protrudes forward from the front end 16a of the front spindle 16, with a gripper 22, and is rotatable together with the workpiece W1 around the spindle center line AX2. The NC device 70 drives the back spindle rotation drive unit 21c shown in FIG. 2 to rotate the back spindle 21 around the spindle center line AX2, and drives the gripping actuator 22a shown in FIG. 2 to control the gripping state of the gripper 22. The gripper 22 can be configured, for example, with a collet. The back headstock drive unit 23 moves the back headstock 20 in the Z-axis direction and further in the X-axis or Y-axis direction in accordance with commands from the NC device 70. When both the front spindle 16 and the back spindle 21 grip the workpiece W1, the spindle center line AX2 is aligned with the spindle center line AX1. Here, the spindle center line AX0 collectively refers to the spindle center line AX1 and the spindle center line AX2. The forward direction of the front spindle 16 refers to the direction in which the workpiece W1 is pushed out from the front spindle 16, which is the rightward direction D84 in the example shown in FIG. 1. The rearward direction of the front spindle 16 refers to the direction from the front spindle 16 toward the material feeder 8, which is the leftward direction D83 in the example shown in FIG. 1. The forward direction of the back spindle 21 refers to the direction in which the back spindle 21 moves toward the front spindle 16, which is the leftward direction D83 in the example shown in FIG. 1.

[0030] The support base 25 is located between the front headstock 15 and the back headstock 20 in the Z-axis direction and has a mounting hole 26 that penetrates in the Z-axis direction. When a guide bush is used as shown in FIG. 1, the guide bush 14 is inserted into the mounting hole 26 and is removably attached to the support base 25. The guide bush 14 supports the workpiece W1 that protrudes forward from the through hole 16h of the front spindle 16 so that it can slide in the Z-axis direction. The portion of the workpiece W1 that protrudes from the guide bush 14 toward the back spindle 21 (rightward D84) is machined by the tool TO1. When a guide bush is not used, the front part of the front spindle 16 is inserted into the mounting hole 26. The portion of the workpiece W1 that protrudes forward (rightward D84) from the front spindle 16 is machined by the tool TO1.

[0031] The tool rest 30 is equipped with a plurality of tools TO1 for machining the workpiece W1 held by at least one of the front spindle 16 and the back spindle 21. The tools TO1 include tools including cut-off tools, rotary tools such as rotary drills and end mills, and the like. As will be described in detail later, the NC unit 70 of this example controls the forming of an eccentric shape on the workpiece W1 when using a tool TO1. The tool rest 30 may be a comb tool rest or a turret tool rest. As shown in FIG. 2, the tool rest driver 31 includes an X-axis driver 32 that moves the tool rest 30 along the X-axis in response to commands from the NC unit 70, and a Y-axis driver 33 that moves the tool rest 30 along the Y-axis in response to commands from the NC unit 70. If the plane along the X-axis and Y-axis is defined as the XY plane, the tool TO1 attached to the tool rest 30 moves on the XY plane. The tool rest 30 uses the tool TO1 to perform front machining of the workpiece W1 held by the front spindle 16, uses a cut-off bit to perform front-machining on the workpiece W1 held by both the front spindle 16 and the back spindle 21, and uses the tool TO1 to perform back machining on the workpiece W1 held by the back spindle 21 after cut-off. In this way, a product is formed from the workpiece W1. Although not shown, the lathe 1 may be provided with a tool rest other than the tool rest 30 shown in FIG. 1, such as a tool rest dedicated to back surface machining.

[0032] 2, the NC device 70 is connected to the material feeder 8, the operation unit 80, the headstock drive unit 18, the headstock rotation drive unit 16c, the gripping actuator 17a, the back headstock drive unit 23, the back spindle rotation drive unit 21c, the gripping actuator 22a, the X-axis drive unit 32, the Y-axis drive unit 33, etc. The headstock drive unit 18, the back headstock drive unit 23, the X-axis drive unit 32, and the Y-axis drive unit 33 each include a servo motor and a servo amplifier (not shown) and change the relative positional relationship between the spindle 11 and the tool rest 30 in accordance with commands from the NC device 70. The headstock rotation drive unit 16c and the back spindle rotation drive unit 21c each include a servo motor (e.g., a built-in motor) and a servo amplifier (not shown) and rotate the spindle 11 about the spindle center line AX0 in accordance with commands from the NC device 70. The NC unit 70 can control the C-axis angle θ, which is the rotation angle of the workpiece W1, by issuing commands to the front spindle rotation drive unit 16c and the back spindle rotation drive unit 21c. The gripping actuator 17a drives the gripping unit 17 of the front spindle 16. The gripping actuator 22a drives the gripping unit 22 of the back spindle 21. The NC unit 70 is equipped with a CPU 71, which is a processor, a ROM 72, which is a semiconductor memory, a RAM 73, which is also a semiconductor memory, a clock circuit 74, an I / F (interface) 75, etc. In FIG. 2, the interfaces for the material feeder 8, operation unit 80, front headstock drive unit 18, front spindle rotation drive unit 16c, gripping actuator 17a, back headstock drive unit 23, back spindle rotation drive unit 21c, gripping actuator 22a, X-axis drive unit 32, Y-axis drive unit 33, etc. are collectively referred to as I / F 75. A control program PR1 for interpreting and executing the machining program PR2 is written in the ROM 72. The ROM 72 may be a rewritable semiconductor memory. The machining program PR2 created by an operator is rewritably stored in the RAM 73. The machining program is also called an NC program. The CPU 71 uses the RAM 73 as a work area and executes the control program PR1 recorded in the ROM 72 to realize the functions of the NC device 70.

[0033] The operation unit 80 includes an input unit 81 and a display unit 82, and functions as a user interface for the NC device 70. The input unit 81 is configured, for example, by buttons or a touch panel for receiving operation inputs from an operator. The display unit 82 is configured, for example, by a display for displaying the contents of various settings received as operation inputs from the operator and various information related to the lathe 1. The operator can store the machining program PR2 in the RAM 73 using the operation unit 80 or an external computer (not shown).

[0034] When a cutting tool is used as the tool TO1, the NC device 70 of this example controls the relative positional relationship between the spindle 11 and the tool post 30 using the drive unit DR so as to form a protrusion W1p, which is an eccentric shape as shown in FIG. 3 and other figures, on the workpiece W1. The protrusion W1p has an eccentric shape centered on an eccentric axis AX3 that is offset from the spindle center line AX0. In FIG. 3 and other figures, the spindle 11 that grips the workpiece W1 may be the front spindle 16 or the back spindle 21. Therefore, the spindle center line AX0 shown in FIG. 3 and other figures may be the spindle center line AX1, which is the center of rotation of the front spindle 16, or the spindle center line AX2, which is the center of rotation of the back spindle 21. Here, when an eccentric protrusion is formed on a workpiece by receiving input of the eccentric distance and the radius of the protrusion, a cylindrical shape centered on an eccentric axis parallel to the spindle center line is formed on the workpiece. Therefore, simply inputting the eccentric distance and the radius of the protrusion makes it impossible to form an eccentric tapered protrusion, a protrusion centered on an eccentric axis that is not parallel to the spindle center line, or a protrusion whose machining start portion or machining end portion is tilted from the XY plane.

[0035] The NC device 70 of this example performs control to form the protrusion W1p on the workpiece W1 based on the coordinates of four points of the protrusion W1p shown in FIG. 3 etc., specifically, the coordinates of the first machining start point SpA, the coordinates of the second machining start point SpB, the coordinates of the first machining end point EpA, and the coordinates of the second machining end point EpB. Here, the first machining start point SpA is the machining start point of the protrusion W1p in a reference phase (θ=0°) of the workpiece W1 centered on the spindle center line AX0. The second machining start point SpB is the machining start point of the protrusion W1p in an opposite phase (θ=180°) that is 180° different from the reference phase. The first machining end point EpA is the machining end point of the protrusion W1p in the reference phase (θ=0°). The second machining end point EpB is the machining end point of the protrusion W1p in the opposite phase (θ=180°).

[0036] The NC device 70 sets a central start point SpO between the first processing start point SpA and the second processing start point SpB, and sets a central end point EpO between the first processing end point EpA and the second processing end point EpB. The central start point SpO is preferably the midpoint of the line segment SpA-SpB connecting the first processing start point SpA and the second processing start point SpB, and the central end point EpO is preferably the midpoint of the line segment EpA-EpB connecting the first processing end point EpA and the second processing end point EpB. In this specific example, the central start point SpO is assumed to be the midpoint of the line segment SpA-SpB, and the central end point EpO is assumed to be the midpoint of the line segment EpA-EpB. The NC device 70 determines a movement path of the cutting edge TOt of the tool TO1 in accordance with the rotation of the workpiece W1 based on at least the coordinates of four points (SpA, SpB, EpA, EpB) so that a protrusion W1p is formed around an eccentric axis AX3 that passes through the central start point SpO and the central end point EpO. The NC device 70 then controls the movement of the cutting edge TOt along the determined movement path while moving the workpiece W1 in the Z-axis direction. Therefore, the NC device 70 can move the cutting edge TOt along the movement path while changing the relative position of the cutting edge TOt with respect to the workpiece W1 on the Z-axis. The value of the Z coordinate (coordinate on the Z-axis) increases as the workpiece W1 moves in the right direction D84 shown in FIG. 3 . Therefore, the value of the Z coordinate at the relative position based on the cutting edge TOt, which does not move in the Z-axis direction, increases as the workpiece W1 moves in the left direction D83. For convenience, the Z coordinate of the workpiece W1 corresponding to the cutting edge TOt may be described as the Z coordinate of the position where the cutting edge TOt is located on the protrusion W1p. For the above reasons, the NC device 70 vibrates the workpiece W1 along the Z axis in accordance with the rotation of the workpiece W1, as necessary.

[0037] The NC device 70 sets a machining intermediate center point WpO between a center start point SpO and a center end point EpO on the eccentric shaft AX3 according to the Z coordinate of the position where the cutting edge TOt is located at the protrusion W1p. The NC device 70 obtains the eccentricity WpE of the machining intermediate center point WpO from the spindle center line AX0 and the diameter WpD (WpD>0) of the protrusion W1p at the machining intermediate center point WpO based on the coordinates of four points (SpA, SpB, EpA, EpB). Here, let the eccentricity of the center start point SpO from the spindle center line AX0 be SpE, and the eccentricity of the center end point EpO from the spindle center line AX0 be EpE. As shown in FIG. 3, when the eccentric shaft AX3 is parallel to the spindle center line AX0, WpE = SpE = EpE.

[0038] (3) Example of the movement path of the tool centered on the machining intermediate center point WpO: FIG. 4 schematically illustrates how the tool TO1 moves in accordance with the rotation of the workpiece W1 in the X-Y plane including the machining intermediate center point WpO when the eccentricity from the spindle center line AX0 is WpE and the diameter of the protrusion W1p at the machining intermediate center point WpO is WpD. Incidentally, the cutting edge TOt of the tool TO1 at the C-axis angle θ = 0° is assumed to be at the position with the largest X coordinate (coordinate on the X axis). Also, the direction in which the X coordinate increases on the X axis is defined as the +X direction, the direction in which the X coordinate decreases on the X axis is defined as the -X direction, the direction in which the Y coordinate (coordinate on the Y axis) increases on the Y axis is defined as the +Y direction, and the direction in which the Y coordinate decreases on the Y axis is defined as the -Y direction.

[0039] At the C-axis angle θ = 0°, the cutting edge TOt of the tool TO1 on the X-Y plane only needs to be at the X coordinate obtained by adding the eccentricity WpE to the radius WpD / 2 of the protrusion W1p on the X axis. Also, at the C-axis angle θ = 180°, the cutting edge TOt of the tool TO1 on the X-Y plane only needs to be at the X coordinate obtained by subtracting the eccentricity WpE from the radius WpD / 2 of the protrusion W1p on the X axis. In the example shown in FIG. 4, since (WpD / 2)>WpE, it is shown that the cutting edge TOt is in the +X direction from the spindle center line AX0 at θ = 180°. If (WpD / 2)<WpE, the cutting edge TOt will be in the -X direction from the spindle center line AX0 at θ = 180°.

[0040] While the workpiece W1 rotates once in the direction of rotation R1 around the spindle center line AX0, the cutting edge TOt rotates once in the direction of rotation R2 along the circumference of an imaginary circle C1, whose diameter is the line segment connecting the 0° position at θ = 0° and the 180° position at θ = 180°. Here, the concept of the imaginary circle C1 is included in the concept of an imaginary arc, and the concept of the circumference of the imaginary circle C1 is included in the concept of the circumference of the imaginary arc. The X-coordinate WpRc of the center of the imaginary circle C1 (arc center WpC) is the midpoint of the line segment connecting the 0° position and the 180° position, so the radius of the protrusion W1p is WpD / 2. Furthermore, the radius of the imaginary circle C1 (arc radius WpRr) is the eccentricity WpE of the mid-machining center point WpO from the spindle center line AX0. As shown in Figure 4, when the cutting edge TOt moves along the circumference of the imaginary circle C1 while the C-axis angle θ changes from 0° to 90°, 180°, and 270° and then returns to 0°, the outer periphery of the protrusion W1p is formed by the tool TO1 on the XY plane including the mid-machining center point WpO.

[0041] (4) Example of changing the relative positional relationship between the spindle and the tool post: By acquiring the coordinates of the four points (SpA, SpB, EpA, EpB), the NC device 70 can realize various eccentric shapes on the workpiece W1, as exemplified in FIGS. 3, 5, and 6. Here, the coordinates of the four points (SpA, SpB, EpA, EpB) are represented by (x, y, z). x represents the X coordinate of the point, y represents the Y coordinate of the point, and z represents the Z coordinate of the point. Furthermore, the coordinates of the first machining start point SpA are represented by (SpAx, SpAy, SpAz), the coordinates of the second machining start point SpB are represented by (SpBx, SpBy, SpBz), the coordinates of the first machining end point EpA are represented by (EpAx, EpAy, EpAz), and the coordinates of the second machining end point EpB are represented by (EpBx, EpBy, EpBz). Note that the Z coordinate value increases as the workpiece W1 moves in the right direction D84, so EpAz>SpAz and EpBz>SpBz. If the eccentric shaft AX3 is eccentric in the X-axis direction from the spindle center line AX0, then SpAy=SpBy=EpAy=EpBy=0. In this specific example, the coordinates of four points (SpA, SpB, EpA, EpB) are obtained on the assumption that the eccentric shaft AX3 is eccentric in the X-axis direction from the spindle center line AX0. Note that even if the Y coordinates SpAy, SpBy, EpAy, EpBy are not 0, as long as SpAy=SpBy=EpAy=EpBy, the eccentric shaft AX3 is simply displaced in the Y-axis direction, so the protrusion W1p can be formed on the workpiece W1.

[0042] In the example shown in FIG. 3, SpAz = SpBz and EpAz = EpBz, and SpAz = SpBz < EpAz = EpBz. Let the coordinates of the center starting point SpO be (SpOx, SpOy, SpOz). Then SpOx = (SpAx + SpBx) / 2, SpOy = 0, and SpOz = SpAz = SpBz. Therefore, the eccentricity SpE of the center starting point SpO is SpOx = (SpAx + SpBx) / 2, and the diameter SpD of the protrusion W1p at the machining start portion is |SpAx - SpBx|. The machining start portion means the portion surrounding the eccentric axis AX3 so as to pass through the first machining start point SpA and the second machining start point SpB at the protrusion W1p. Let the coordinates of the center end point EpO be (EpOx, EpOy, EpOz). Then EpOx = (EpAx + EpBx) / 2, EpOy = 0, and EpOz = EpAz = EpBz. Therefore, the eccentricity EpE of the center end point EpO is EpOx = (EpAx + EpBx) / 2, and the diameter EpD of the protrusion W1p at the machining end portion is |EpAx - EpBx|. In the example shown in FIG. 3, SpOx = EpOx. The machining end portion means the portion surrounding the eccentric axis AX3 so as to pass through the first machining end point EpA and the second machining end point EpB at the protrusion W1p. The movement amount ZdA in the Z-axis direction from the first machining start point SpA to the first machining end point EpA is EpAz - SpAz. The movement amount ZdB in the Z-axis direction from the second machining start point SpB to the second machining end point EpB is EpBz - SpBz. In the example shown in FIG. 3, ZdA = ZdB. Let the number of rotations of the work W1 from the machining start portion to the machining end portion be RevC (RevC > 1). Then the feed pitch (denoted as Zpt) by which the work W1 advances in the Z-axis direction every time it makes one rotation is ZdA / RevC = ZdB / RevC. The unit of the feed pitch Zpt is, for example, mm / rev.

[0043] Here, the coordinates of the center point WpO during machining are represented as (WpOx, WpOy, WpOz), and it is assumed that among the RevC rotations of the workpiece W1, the rotation adjusted to the center point WpO during machining is the (n + 1)-th rotation (0 ≦ n < RevC). Note that the first rotation with n = 0 is the rotation adjusted to the center starting point SpO, and as the rotation count n increases, the center point WpO during machining approaches the center end point EpO along the eccentric shaft AX3. The X coordinate WpOx of the center point WpO during machining is the eccentricity WpE of the center point WpO during machining, which coincides with the eccentricity SpE of the center starting point SpO and the eccentricity EpE of the center end point EpO. The Y coordinate WpOy of the center point WpO during machining is 0. The Z coordinate WpOz of the center point WpO during machining, when the C-axis angle θ is 0°, WpOz = SpAz + {(n / RevC) × ZdA} …(1) is obtained. The diameter WpD of the protrusion W1p at the center point WpO during machining, when the C-axis angle θ is 0°, WpD = SpD + {(n / RevC) × (EpD - SpD)} …(2) is obtained. In this way, the NC device 70 can interpolate the diameter WpD at the center point WpO during machining from the diameter SpD at the center starting point SpO and the diameter EpD at the center end point EpO.

[0044] As described with reference to FIG. 4, the movement path of the cutting edge TOt is a path along the circumference of a virtual circle C1 corresponding to the Z coordinate of the position where the cutting edge TOt is located at the protrusion W1p. The X coordinate WpRc of the center of the virtual circle C1 (arc center WpC) is the radius WpD / 2 corresponding to the Z coordinate WpOz of the center point WpO during machining at the protrusion W1p. Note that the X coordinate of the arc center WpC (referred to as SpRc) at the Z coordinate SpOz = SpAz = SpBz of the center starting point SpO is the radius SpD / 2 at the machining start part. The X coordinate of the arc center WpC (referred to as EpRc) at the Z coordinate EpOz = EpAz = EpBz of the center end point EpO is the radius EpD / 2 at the machining end part.

[0045] The radius of the imaginary circle C1 (arc radius WpRr) is the eccentricity WpE of the machining midpoint WpO from the spindle center line AXO. The arc radius (referred to as SpRr) at the Z coordinate SpOz of the center start point SpO is the eccentricity SpE of the center start point SpO from the spindle center line AXO. The arc radius (referred to as EpRr) at the Z coordinate EpOz of the center end point EpO is the eccentricity EpE of the center end point EpO from the spindle center line AXO. The NC device 70 moves the cutting edge TOt along the circumference of an imaginary circle C1 with an arc radius WpRr centered at an arc center WpC at an X-coordinate WpRc corresponding to the Z-coordinate WpOz of the mid-machining center point WpO in an XY plane including the mid-machining center point WpO in accordance with the rotation of the workpiece W1. In this way, the NC device 70 determines the movement path of the tool TO1 to be a path along the circumference of the imaginary circle C1 centered at the arc center WpC offset from the spindle center line AX0, based on the diameter WpD at the mid-machining center point WpO. By setting the arc center WpC and arc radius WpRr in accordance with the movement of the workpiece W1 in the Z-axis direction and moving the cutting edge TOt along the circumference of the imaginary circle C1 in accordance with the rotation of the workpiece W1, a tapered protrusion W1p centered on the eccentric axis AX3 is formed on the workpiece W1.

[0046] The X and Y coordinates of the cutting edge TOt may be determined in units of a rotation angle smaller than one rotation of the workpiece W1 (referred to as resolution Reso). Here, resolution Reso is a C-axis angle greater than 0° and less than 360°. The Z coordinate of the arc center WpC is the Z coordinate WpOz of the mid-machining center point WpO, and changes by (ZdA / RevC) every time the workpiece W1 rotates. Therefore, when the workpiece W1 rotates by the C-axis angle θ, the Z coordinate of the arc center WpC changes by (θ / 360) × (ZdA / RevC). Therefore, the Z coordinate WpOz of the mid-machining center point WpO, which is the Z coordinate of the arc center WpC, is WpOz=SpAz+{(n / RevC)×ZdA} +{(θ / 360)×(ZdA / RevC)} =SpAz+{n'×(ZdA / RevC)} …(3) However, the number of rotations n' is the value obtained by adding (θ / 360) to the number of rotations n. The diameter WpD of the protrusion W1p at the center point WpO during processing is WpD=SpD+{(n' / RevC)×(EpD-SpD)} …(4) As described above, the X coordinate WpRc of the arc center WpC is WpD / 2. The arc radius WpRr is the amount of eccentricity WpE.

[0047] The NC device 70 calculates the X-coordinate WpRc of the arc center WpC and the arc radius WpRr in units of the resolution Reso. In an XY plane including the mid-machining center point WpO, the NC device 70 moves the cutting edge TOt along the periphery of a virtual arc (virtual circle C1) of arc radius WpRr centered at the arc center WpC of the X-coordinate WpRc corresponding to the Z-coordinate WpOz of the mid-machining center point WpO in accordance with the rotation of the workpiece W1. In this way, the NC device 70 moves the cutting edge TOt along the periphery of the virtual arc (virtual circle C1) in accordance with the rotation of the workpiece W1, thereby forming a protrusion W1p on the workpiece W1 centered on the eccentric axis AX3.

[0048] 5 is a schematic diagram illustrating the formation of a protrusion W1p on a workpiece W1 as a tapered eccentric shape centered on an eccentric axis AX3 that is not parallel to the spindle center line AX0. FIG. 5 also shows a view of the workpiece W1 viewed from the surface having the protrusion W1p. The example shown in Fig. 5 also has SpAz = SpBz and EpAz = EpBz, and SpAz = SpBz < EpAz = EpBz. The coordinates (SpOx, SpOy, SpOz) of the center starting point SpO are represented by SpOx = (SpAx + SpBx) / 2, SpOy = 0, and SpOz = SpAz = SpBz. Therefore, the eccentricity SpE of the center starting point SpO is SpOx = (SpAx + SpBx) / 2, and the diameter SpD of the protrusion W1p at the machining start part is |SpAx - SpBx|. The coordinates (EpOx, EpOy, EpOz) of the center end point EpO are represented by EpOx = (EpAx + EpBx) / 2, EpOy = 0, and EpOz = EpAz = EpBz. Therefore, the eccentricity EpE of the center end point EpO is EpOx = (EpAx + EpBx) / 2, and the diameter EpD of the protrusion W1p at the machining end part is |EpAx - EpBx|. In the example shown in Fig. 5, SpOx > EpOx.

[0049] The Z coordinate WpOz of the center point WpO during machining is represented by the above formula (1) or the above formula (3). The eccentricity WpE of the center point WpO during machining is when the C-axis angle θ is 0°, WpE = SpE + {(n / RevC) × (EpE - SpE)} …(5) It becomes like this. When considering the C-axis angle θ, taking the value obtained by adding (θ / 360) to the number of rotations n as the number of rotations n', WpE = SpE + {(n' / RevC) × (EpE - SpE)} …(6) It becomes like this. According to the above formula (5) or the above formula (6), the NC device 70 can interpolate the eccentricity WpE of the center point WpO during machining from the spindle center line AX0 from the eccentricity SpE of the center starting point SpO and the eccentricity EpE of the center end point EpO.

[0050] The diameter WpD of the protrusion W1p at the center point WpO during machining is represented by the above formula (2) or the above formula (4).

[0051] As explained with reference to Figure 4, the movement path of the cutting edge TOt is a path along the circumference of an imaginary circle C1 that corresponds to the Z coordinate of the position of the cutting edge TOt on the protrusion W1p. The X coordinate WpRc of the arc center WpC is a radius WpD / 2 that corresponds to the Z coordinate WpOz of the mid-machining center point WpO on the protrusion W1p. The arc radius WpRr is the eccentricity WpE of the mid-machining center point WpO from the spindle center line AX0. The NC device 70 moves the cutting edge TOt in accordance with the rotation of the workpiece W1 in the XY plane including the mid-machining center point WpO along the periphery of a virtual arc (virtual circle C1) with an arc radius WpRr and centered at an arc center WpC at an X coordinate WpRc corresponding to the Z coordinate WpOz of the mid-machining center point WpO. In this way, the NC device 70 determines the movement path of the tool TO1 to be a path along the periphery of the virtual arc (virtual circle C1) whose size corresponds to the eccentricity amount WpE. By setting the arc center WpC and the arc radius WpRr in accordance with the movement of the workpiece W1 in the Z axis direction and moving the cutting edge TOt along the periphery of the virtual arc in accordance with the rotation of the workpiece W1, a protrusion W1p centered on an eccentric axis AX3 that is not parallel to the spindle center line AX0 is formed on the workpiece W1.

[0052] 6 is a schematic diagram illustrating how the protrusion W1p is formed on the workpiece W1 as a tapered eccentric shape inclined from the XY plane at the machining start and end portions of the workpiece W1. FIG. 6 also shows a view of the workpiece W1 as seen from the surface having the protrusion W1p. In the example shown in Figure 6, the Z-coordinate SpAz of the first processing start point SpA is different from the Z-coordinate SpBz of the second processing start point SpB, and the Z-coordinate EpAz of the first processing end point EpA is different from the Z-coordinate EpBz of the second processing end point EpB. Furthermore, the movement amount ZdA in the Z-axis direction from the first processing start point SpA to the first processing end point EpA is different from the movement amount ZdB in the Z-axis direction from the second processing start point SpB to the second processing end point EpB. Note that Figure 6 shows that SpAz > SpBz, EpAz > EpBz, and ZdB > ZdA. The coordinates (SpOx, SpOy, SpOz) of the central start point SpO are expressed as SpOx = (SpAx + SpBx) / 2, SpOy = 0, and SpOz = (SpAz + SpBz) / 2. Therefore, the eccentricity SpE of the center start point SpO is SpOx = (SpAx + SpBx) / 2. The diameter SpD of the protrusion W1p at the start of machining is |SpAx - SpBx|. The coordinates (EpOx, EpOy, EpOz) of the center end point EpO are expressed as EpOx = (EpAx + EpBx) / 2, EpOy = 0, and EpOz = (EpAz + EpBz) / 2. Therefore, the eccentricity EpE of the center end point EpO is EpOx = (EpAx + EpBx) / 2. The diameter EpD of the protrusion W1p at the end of machining is |EpAx - EpBx|. The eccentricity WpE of the mid-machining center point WpO is expressed by the above formula (5) or (6). The diameter WpD of the protrusion W1p at the midpoint WpO during processing is expressed by the above formula (2) or (4).

[0053] In order to form the protrusions W1p as shown in FIG. 6 on the workpiece W1, it is necessary to vibrate the workpiece W1 along the Z axis in accordance with the rotation of the workpiece W1 about the spindle center line AX0.

[0054] FIG. 7 is a schematic diagram illustrating how the relative position of the tool TO1 is determined when forming a tapered protrusion W1p on the workpiece W1, the machining start portion and machining end portion of which are inclined from the XY plane. As shown in Figure 7, the Z coordinate of the first line segment SpA-EpA connecting the first machining start point SpA and the first machining end point EpA does not correspond to the Z coordinate of the second line segment SpB-EpB connecting the second machining start point SpB and the second machining end point EpB. For this reason, the section on the first line segment SpA-EpA where the cutting edge TOt is located corresponds to the section on the first line segment SpA-EpA where the cutting edge TOt is located for each rotation of the workpiece W1. Here, the section on the first line segment SpA-EpA where the cutting edge TOt is located is between adjacent points, and the section on the second line segment SpB-EpB where the cutting edge TOt is located is also between adjacent points.

[0055] If the workpiece W1 rotates RevC times from the machining start point to the machining end point, the division number N is the number of rotations RevC, and the first line segment SpA-EpA and the second line segment SpB-EpB are each equally divided by the division number N. If the number of rotations RevC is not an integer, the final sections of the first line segment SpA-EpA and the second line segment SpB-EpB (the sections leading to the first machining end point EpA and the second machining end point EpB) can be shortened. In FIG. 7, the point on the first line segment SpA-EpA at the number of rotations n (n is an integer) is indicated by An, and the point on the second line segment SpB-EpB at the number of rotations n is indicated by Bn. Point An+1 (Z coordinate Zan+1) is the point on the first line segment SpA-EpA at the number of rotations n+1, and point Bn+1 (Z coordinate Zbn+1) is the point on the second line segment SpB-EpB at the number of rotations n+1. The first processing start point SpA can be said to be point A0 when the number of rotations n=0, and the second processing start point SpB can be said to be point B0 when the number of rotations n=0.

[0056] Here, the coordinates of point An are (Xan, Yan, Zan), and the coordinates of point Bn are (Xbn, Ybn, Zbn). However, in this specific example, Yan = Ybn = 0. The coordinates of point An projected onto the XY plane are (Xan, 0), and the coordinates of point bn projected onto the XY plane are (Xbn, 0). During rotation at the number of rotations n, the NC device 70 controls the position of the cutting edge TOt by considering the protrusion W1p to be a circle on the XY plane whose diameter is the line segment connecting points (Xan, 0) and (Xbn, 0). The center of the circle on the XY plane is the mid-machining center point WpO. The eccentricity amount of the mid-machining center point WpO is WpE, and the diameter WpD of the circle on the XY plane is Xan - Xbn. The NC device 70 sets an imaginary circle C1 as shown in FIG. 4 based on the eccentricity WpE and the diameter WpD, and moves the cutting edge TOt along the circumference of the imaginary circle C1 on the XY plane.

[0057] Because the change in the Z coordinate where the cutting edge TOt is located differs between the first line segment SpA-EpA and the second line segment SpB-EpB, one of the first line segment SpA-EpA and the second line segment SpB-EpB is used as the basis for the division number N. In this specific example, the larger change in Z coordinate between the first line segment SpA-EpA and the second line segment SpB-EpB is used as the basis for the division number N. Here, the larger of the movement amount ZdA in the Z axis direction from the first machining start point SpA to the first machining end point EpA and the movement amount ZdB in the Z axis direction from the second machining start point SpB to the second machining end point EpB is represented by MAX(ZdA:ZdB). The number of rotations RevC, which is the division number N, can be calculated as MAX(ZdA:ZdB) / Zpt using the feed pitch Zpt, which is the amount of advance in the Z axis direction for each rotation of the workpiece W1.

[0058] The Z coordinate of the position of the cutting edge TOt on the protrusion W1p can be controlled to be the Z coordinate Zan of point An when the C-axis angle θ=0°, and the Z coordinate Zbn of point Bn when the C-axis angle θ=180°. First, if the amount of change in the Z coordinate of the position of the cutting edge TOt on the first line segment SpA-EpA per one rotation of the workpiece W1 is Zac, then Zac = ZdA / RevC. Also, if the amount of change in the Z coordinate of the position of the cutting edge TOt on the second line segment SpB-EpB per one rotation of the workpiece W1 is Zbc, then Zbc = ZdB / RevC.

[0059] The Z coordinate Zan of point An at rotation number n is Zan=SpAz+n×Zac =SpAz+n×(ZdA / RevC) …(7) Furthermore, the Z coordinate Zbn of point Bn at rotation number n is Zbn=SpBz+n×Zbc =SpBz+n×(ZdB / RevC) …(8) This becomes:

[0060] The midpoint of the line segment An-Bn connecting points An and Bn corresponds to the midpoint WpO of the machining process, and the Z coordinate of the midpoint of the line segment An-Bn is (Zan+Zbn) / 2. Furthermore, the vibration of the workpiece W1 in the Z-axis direction based on the midpoint of the line segment An-Bn is expressed as {(Zan-Zbn) / 2}×cos(θ). Therefore, the Z coordinate Znc at the C-axis angle θ at the rotation number n is: Znc={(Zan+Zbn) / 2} +{(Zan-Zbn) / 2}×cos(θ) …(9) It can be calculated as follows. The NC device 70 controls the Z coordinate of the workpiece W1 in accordance with the above equation (9), thereby vibrating the workpiece W1 along the Z axis in accordance with the rotation of the workpiece W1. As the cutting edge TOt moves along the circumference of the imaginary circle C1 in the XY plane, with each rotation of the workpiece W1, the relative positional relationship between the spindle 11 and the tool rest 30 on the first line segment SpA-EpA changes by a length obtained by dividing the length of the first line segment SpA-EpA by the number of divisions N, and the relative positional relationship between the spindle 11 and the tool rest 30 on the second line segment SpB-EpB changes by a length obtained by dividing the length of the second line segment SpB-EpB by the number of divisions N.

[0061] The X and Y coordinates of the cutting edge TOt may be calculated in units of rotation angle (resolution Reso) smaller than one rotation of the workpiece W1. Here, if the movement amount in the Z-axis direction from the central start point SpO to the central end point EpO is ZdO, then ZdO = (ZdA + ZdB) / 2. The Z coordinate of the arc center WpC is the Z coordinate WpOz of the mid-machining center point WpO, and changes by (ZdO / RevC) per rotation of the workpiece W1. Therefore, when the workpiece W1 rotates through the C-axis angle θ, the Z coordinate of the arc center WpC changes by (θ / 360) × (ZdO / RevC). Therefore, the change in the Z coordinate of the arc center WpC when the workpiece W1 rotates through the C-axis angle θ (θ / 360) × (ZdO / RevC) may be added to the right side of the above equation (9). Znc={(Zan+Zbn) / 2} +{(Zan-Zbn) / 2}×cos(θ) +(θ / 360)×(ZdO / RevC) …(10) In addition, the Z coordinate WpOz of the machining center point WpO, which is the Z coordinate of the arc center WpC, is WpOz=SpOz+{(n / RevC)×ZdO} +{(θ / 360)×(ZdO / RevC)} =SpOz+{n'×(ZdO / RevC)} …(11) However, the number of rotations n' is the value obtained by adding (θ / 360) to the number of rotations n. The diameter WpD of the protrusion W1p projected onto the XY plane containing the center point WpO during machining is WpD=SpD+{(n' / RevC)×(EpD-SpD)} …(12) As described above, the X coordinate WpRc of the arc center WpC is WpD / 2. The arc radius WpRr is the amount of eccentricity WpE.

[0062] The NC device 70 calculates the Z coordinate Znc, the X coordinate WpRc of the arc center WpC, and the arc radius WpRr at the C-axis angle θ for the number of rotations n in units of resolution Reso. The NC device 70 moves the cutting edge TOt in accordance with the rotation of the workpiece W1 along the periphery of a virtual arc (virtual circle C1) with an arc radius WpRr and centered at the arc center WpC with an X coordinate WpRc corresponding to the Z coordinate WpOz of the mid-machining center WpO in the XY plane including the mid-machining center WpO. The NC device 70 also moves the workpiece W1 along the Z axis in accordance with the rotation of the workpiece W1 so that the workpiece W1 has the Z coordinate Znc. As explained above, the NC device 70 moves the cutting edge TOt along the circumference of the virtual arc (virtual circle C1) in accordance with the rotation of the workpiece W1, and vibrates the workpiece W1 along the Z axis in accordance with the rotation of the workpiece W1, thereby forming a tapered protrusion W1p on the workpiece W1, with the machining start portion and machining end portion tilted from the XY plane. Note that even if one of the machining start portion and machining end portion is along the XY plane, the relative positional relationship between the spindle 11 and the tool post 30 can be controlled in a similar manner.

[0063] (5) Examples of eccentric machining: Fig. 8 shows a schematic example of an eccentric machining process for forming a protrusion W1p as an eccentric shape on the workpiece W1. The NC device 70 shown in Fig. 2 starts the eccentric machining process when an instruction to display an eccentric machining command creation screen for creating an eccentric machining command for forming an eccentric shape on the workpiece W1 is received at the input unit 81. When the eccentric machining process is performed, an eccentric machining method including a tool movement path determination method is executed. The eccentric machining method includes the following steps (A1), (A2), and (A3). (A1) First process ST1 (corresponding to step S102) acquires the coordinates of the first machining start point SpA and the first machining end point EpA of the protrusion W1p in the reference phase (θ=0°) of the workpiece W1 centered on the spindle center line AX0, and the coordinates of the second machining start point SpB and the second machining end point EpB of the protrusion W1p in the opposite phase (θ=180°). (A2) A second process ST2 (corresponding to steps S104 to S112) determines the movement path (virtual circle C1) of the tool TO1 in accordance with the rotation of the workpiece W1 based at least on the coordinates of four points (SpA, SpB, EpA, EpB) so that a protrusion W1p is formed centered on an eccentric axis AX3 that passes through the central starting point SpO between the first machining starting point SpA and the second machining starting point SpB, and the central ending point EpO between the first machining ending point EpA and the second machining ending point EpB. (A3) A third process ST3 (corresponding to step S114) in which the tool TO1 is moved along the movement path (imaginary circle C1) in accordance with the rotation of the workpiece W1. Hereinafter, the description of "step" will be omitted.

[0064] When the eccentric machining process starts, the NC device 70 acquires the coordinates (x, y, z) of the four points (SpA, SpB, EpA, EpB), the feed pitch Zpt in the Z-axis direction, and the resolution Reso of the C-axis angle θ (S102). The coordinates (x, y, z) of the four points (SpA, SpB, EpA, EpB) are accepted when the first machining start point SpA and the first machining end point EpA are at θ=0°, and the second machining start point SpB and the second machining end point EpB are at θ=180°. In this specific example, it is assumed that the eccentric axis AX3 is eccentric in the X-axis direction from the spindle center line AX0, SpAy=SpBy=EpAy=EpBy=0 SpAx>SpBx EpAx>EpBx SpAz <EpAz SpBz <EpBz If all of the above conditions are satisfied, the NC device 70 accepts the coordinates (x, y, z) of the four points (SpA, SpB, EpA, EpB). Even if the Y coordinates SpAy, SpBy, EpAy, and EpBy are not zero, if SpAy = SpBy = EpAy = EpBy, the eccentric shaft AX3 only shifts in the Y-axis direction, so the NC device 70 may accept the coordinates of the four points. When SpAx < SpBx, if EpAx < EpBx, the reference phase (θ = 0°) only becomes the -X direction, so the NC device 70 may accept the coordinates of the four points. When SpAz > EpAz, if SpBz > EpBz, the moving direction of the workpiece W1 only reverses, so the NC device 70 may accept the coordinates of the four points.

[0065] The acquisition of the feed pitch Zpt in the Z-axis direction may be omitted if it is predetermined. The acquisition of the resolution Reso of the C-axis angle θ may also be omitted if it is predetermined. Further, in order to control the rotational speed of the workpiece W1 so as to lengthen the usage period of the tool TO1, the NC device 70 may acquire the peripheral speed of the workpiece W1 (the speed in the circumferential direction of the workpiece W1) at the position of the cutting edge TOt in S102. When the NC device 70 acquires at least the coordinates of the four points (SpA, SpB, EpA, EpB) that satisfy the above-described conditions, it incorporates an eccentric machining command having at least the coordinates of the four points as arguments into the machining program PR2 (see FIG. 2). In the eccentric machining command, at least one of the feed pitch Zpt and the resolution Reso may not be described as an argument. Thereafter, when the NC device 70 reads the eccentric machining command from the machining program PR2, it acquires the coordinates of at least the four points (SpA, SpB, EpA, EpB) from the eccentric machining command.

[0066] Next, the NC device 70 calculates the eccentricity WpE of the machining intermediate center point WpO from the eccentricity SpE of the center start point SpO and the eccentricity EpE of the center end point EpO (S104). For the calculation of the eccentricity WpE, as shown in FIGS. 6 and 7, it is only necessary to assume a protrusion W1p whose machining start portion and machining end portion are inclined from the X-Y plane. The coordinates (SpOx, SpOy, SpOz) of the central start point SpO are SpOx = (SpAx + SpBx) / 2, SpOy = 0, and SpOz = (SpAz + SpBz) / 2. Therefore, the eccentricity SpE of the central start point SpO is SpOx = (SpAx + SpBx) / 2. The coordinates (EpOx, EpOy, EpOz) of the central end point EpO are EpOx = (EpAx + EpBx) / 2, EpOy = 0, and EpOz = (EpAz + EpBz) / 2. Therefore, the eccentricity EpE of the central end point EpO is EpOx = (EpAx + EpBx) / 2. The Z coordinate WpOz of the mid-process center point WpO is calculated from the above formula (11), i.e., WpOz = SpOz + {n' × (ZdO / RevC)}. The eccentricity WpE of the mid-process center point WpO is the X coordinate WpOx of the mid-process center point WpO, and is calculated from the above formula (6), i.e., WpE = SpE + {(n' / RevC) × (EpE - SpE)}.

[0067] In this manner, the NC device 70 interpolates the eccentricity WpE of the machining midpoint WpO from the spindle center line AX0 from the eccentricity SpE of the center start point SpO and the eccentricity EpE of the center end point EpO.

[0068] The NC device 70 also calculates the diameter WpD of the mid-machining center point WpO from the diameter SpD of the machining start portion and the diameter EpD of the machining end portion (S106). The diameter WpD can also be calculated by assuming that the machining start portion and the machining end portion form protrusions W1p tilted from the XY plane, as shown in Figures 6 and 7. The diameter WpD of the mid-machining center point WpO is found from the above formula (4), i.e., WpD = SpD + {(n' / RecC) × (EpD - SpD)}. In this manner, the NC device 70 interpolates the diameter WpD at the mid-machining center point WpO from the diameter SpD at the machining start point and the diameter EpD at the machining end point.

[0069] After calculating the eccentricity WpE and the diameter WpD, the NC device 70 determines the movement path of the cutting edge TOt on the XY plane in accordance with the rotation of the workpiece W1 (S108). As described with reference to FIG. 4, the movement path of the cutting edge TOt is a path along the circumference of a virtual arc (virtual circle C1) that corresponds to the Z coordinate of the position of the cutting edge TOt on the protrusion W1p. The X coordinate WpRc of the arc center WpC is a radius WpD / 2 that corresponds to the Z coordinate WpOz of the mid-machining center point WpO on the protrusion W1p. The arc radius WpRr is the eccentricity WpE of the mid-machining center point WpO from the spindle center line AX0. The NC device 70 determines, in units of the resolution Reso of the C-axis angle θ, as the movement path of the cutting edge TOt, on the XY plane, the movement path along the circumference of a virtual arc (virtual circle C1) with the X coordinate WpRc as the arc center WpC and the arc radius WpRr.

[0070] The NC device 70 also calculates the Z position Zan on the first line segment SpA-EpA and the Z position Zbn on the second line segment SpB-EpB at rotation number n (S110). The Z position Zan on the first line segment SpA-EpA is calculated from the above formula (7), i.e., Zan = SpAz + n × (ZdA / RevC). The Z position Zbn on the second line segment SpB-EpB is calculated from the above formula (8), i.e., Zbn = SpBz + n × (ZdB / RevC).

[0071] After calculating the Z positions Zan and Zbn, the NC device 70 calculates the Z position Znc at the C-axis angle θ for the rotation number n (S112). The Z position Znc is found from the above formula (9), i.e., Znc = {(Zan + Zbn) / 2} + {(Zan - Zbn) / 2} × cos(θ). The NC device 70 may also calculate the Z position Znc from the above formula (10), i.e., Znc = {(Zan + Zbn) / 2} + {(Zan - Zbn) / 2} × cos(θ) + (θ / 360) × (ZdO / RevC).

[0072] Thereafter, the NC device 70 moves the tool TO1 along the X-axis and Y-axis in accordance with the determined virtual arc (virtual circle C1) in accordance with the rotation of the workpiece W1, and when vibrating the workpiece W1 about the Z-axis, vibrates the workpiece W1 along the Z-axis in accordance with the rotation of the workpiece W1 according to the Z position Znc (S114). As the cutting edge TOt moves along the circumference of the virtual arc (virtual circle C1) in the XY plane and the workpiece W1 vibrates about the Z-axis, the relative positional relationship between the spindle 11 and the tool rest 30 on the first line segment SpA-EpA changes by a length obtained by dividing the length of the first line segment SpA-EpA by the number of divisions N, and the relative positional relationship between the spindle 11 and the tool rest 30 on the second line segment SpB-EpB changes by a length obtained by dividing the length of the second line segment SpB-EpB by the number of divisions N, with each rotation of the workpiece W1. As a result of the above, a protrusion W1p is formed on the workpiece W1, the protrusion W1p being centered on the eccentric axis AX3 that is offset from the spindle center line AX0.

[0073] As explained above, the protrusion W1p formed on the workpiece W1 is not limited to a shape having a constant diameter centered on a center line parallel to the spindle center line AX0. The protrusion W1p formed on the workpiece W1 can have various shapes, such as a tapered eccentric shape as shown in Fig. 3, a tapered eccentric shape centered on an eccentric axis AX3 that is not parallel to the spindle center line AX0 as shown in Fig. 5, and a tapered eccentric shape in which at least one of the machining start portion and machining end portion is tilted from the XY plane as shown in Fig. 6. Therefore, this specific example improves the degree of freedom in machining eccentric shapes.

[0074] (6) Variation: The present invention can be modified in various ways. For example, the machine tool to which the present technology can be applied is not limited to a lathe, but may also be a machining center or the like. The lathe 1 may be a fixed spindle type lathe in which the front spindle 16 does not move in the Z-axis direction. In this case, the present technology is applied by moving the tool rest 30 in the Z-axis direction in addition to the X-axis and Y-axis directions. The spindle 11 that grips the workpiece W1 is not limited to the front spindle 16, but may be the back spindle 21. The tool TO1 for machining the workpiece W1 having an eccentric shape is preferably a cutting tool, but may also be a fixed tool such as a fixed drill or a rotary tool such as an end mill. The eccentric shape formed by the tool TO1 is not limited to a protrusion, but may also be a hole with an enlarged opening, such as a trumpet-shaped hole.

[0075] 8 can be changed as needed, such as by changing the order of the steps. For example, the step S104 for calculating the eccentricity amount WpE and the step S106 for calculating the diameter WpD can be switched. Furthermore, to determine the movement path of the tool TO1, the radius WpD / 2 may be calculated instead of the diameter WpD. In the eccentricity machining process shown in FIG. 8, at least a part of the processes from S102 to S112 may be performed by a device other than the lathe 1, such as an external computer.

[0076] In the process of S102 shown in Fig. 8, since it is sufficient to finally obtain the coordinates of the four points (SpA, SpB, EpA, EpB), it is possible to omit some of the coordinates of the four points (SpA, SpB, EpA, EpB) from the arguments of the eccentricity machining command. For example, if a cylindrical eccentricity machining command for forming a cylindrical eccentric shape on the workpiece W1 is prepared as the eccentricity machining command, the coordinates of the first machining end point EpA or the second machining end point EpB may be omitted from the arguments of this cylindrical eccentricity machining command. Furthermore, if the arguments of the cylindrical eccentricity machining command include the length of the eccentric shape in the Z-axis direction, the coordinates of both the first machining end point EpA and the second machining end point EpB may be omitted from the arguments of the cylindrical eccentricity machining command.

[0077] 3, 5, 6, and 7, a straight line connects the first machining start point SpA and the first machining end point EpA, and a straight line connects the second machining start point SpB and the second machining end point EpB. However, curved lines may be used instead. For example, the curved first outer contour connecting the first machining start point SpA and the first machining end point EpA can be determined by circular interpolation, and the curved second outer contour connecting the second machining start point SpB and the second machining end point EpB can also be determined by circular interpolation. In this case, the NC device 70 controls the relative positional relationship between the spindle 11 and the tool rest 30 so that the Z coordinate on the first outer contour changes by the value obtained by dividing the movement amount ZdA from the first machining start point SpA to the first machining end point EpA by the number of divisions N, and the Z coordinate on the second outer contour changes by the value obtained by dividing the movement amount ZdB from the second machining start point SpB to the second machining end point EpB by the number of divisions N. This allows the workpiece W1 to have an eccentric shape in which the first machining start point SpA and the first machining end point EpA are connected by a curve, and the second machining start point SpB and the second machining end point EpB are connected by a curve.

[0078] FIG. 9 illustrates a schematic diagram of the electrical circuit configuration of the fixed-spindle lathe 1. Compared to the movable-spindle lathe 1 illustrated in FIG. 2, the fixed-spindle lathe 1 illustrated in FIG. 9 does not include the front headstock drive unit 18, but instead includes a Z-axis drive unit 34 in addition to the tool post drive unit 31. The Z-axis drive unit 34 moves the tool post 30 along the Z axis in accordance with commands from the NC device 70. Therefore, the tool post drive unit 31 moves the tool post 30 along the X, Y, and Z axes. In this case, the NC device 70 controls the tool TO1 to move along the X and Y axes in accordance with the rotation of the workpiece W1, and to oscillate the tool TO1 along the Z axis in accordance with the rotation of the workpiece W1 relative to the spindle 11 and the tool post 30 along the Z axis. This allows the fixed-spindle lathe 1 to form an eccentric shape on the workpiece W1.

[0079] (7) Conclusion: As explained above, the present invention can provide a technique for improving the degree of freedom in machining eccentric shapes through various aspects. Of course, even a technique consisting only of the constituent elements of the independent claims can achieve the basic functions and effects described above. Furthermore, it is possible to implement configurations in which the components disclosed in the above examples are substituted with each other or the combination is changed, or configurations in which the components disclosed in the publicly known techniques and the above examples are substituted with each other or the combination is changed, etc. The present invention also includes these configurations. [Explanation of symbols]

[0080] 1...Lathe (example of machine tool), 10...headstock, 11...main spindle, 12...gripping section, 13...headstock drive section, 15...Front headstock, 16...Front spindle, 16c...Front spindle rotation drive section, 17...Gripping section, 18...Front headstock drive unit, 20...Rear spindle, 21...Rear spindle, 21c...Rear spindle rotation drive unit, 22...Gripping unit, 23... Rear headstock drive unit, 30... Tool rest, 31... Tool rest drive unit, 32... X-axis drive unit, 33... Y-axis drive unit, 70...NC device (example of control unit), AX0,AX1,AX2…Spindle center line, AX3…Eccentric shaft, C1: Imaginary circle, DR...Drive unit, EpA: first processing end point, EpB: second processing end point, EpD: diameter, EpE: eccentricity, EpO: central end point, R1, R2...Rotation direction, Reso...resolution, RevC...number of rotations, SpA...first machining start point, SpB...second machining start point, SpD...diameter, SpE...eccentricity, SpO...center starting point, ST1...first process, ST2...second process, ST3...third process, TO1...Tool, TOt...Cutting edge, W1...workpiece, W1p...protrusion (example of eccentric shape), WpC: arc center, WpD...diameter, WpE...eccentricity, WpO...center point during machining, WpRc...X coordinate of the arc center, WpRr...Arc radius, ZdA, ZdB...movement amount in the Z-axis direction, Zpt...feed pitch.

Claims

1. a spindle that rotates together with the workpiece around the spindle center line; a tool rest on which a tool for machining the workpiece is attached; a drive unit that changes the relative positional relationship between the spindle and the tool rest; a control unit that controls the relative positional relationship by the drive unit so as to form an eccentric shape on the workpiece about an eccentric axis that is shifted from the center line of the spindle, the eccentric shape formed on the workpiece has a machining start portion, which is a portion where machining of the workpiece rotating about the spindle center line starts, and a machining end portion, which is a portion where machining of the workpiece rotating about the spindle center line ends, a first machining start point is the position of the cutting edge of the tool that forms the machining start portion when the workpiece rotating about the spindle center line is in a reference phase, a second machining start point is a position at the machining start portion that is on the opposite side of the first machining start point with the eccentric shaft as the center, a first machining end point is the position of the cutting edge of the tool that forms the machining end portion when the workpiece is in the reference phase, and a second machining end point is a position at the machining end portion that is on the opposite side of the first machining end point with the eccentric shaft as the center, The control unit Acquire the coordinates of the first machining start point, the coordinates of the second machining start point, the coordinates of the first machining end point, and the coordinates of the second machining end point when the workpiece is in the reference phase, including the Z coordinate which is the coordinate of the Z axis along the spindle center line; determining a movement path of the tool in accordance with the rotation of the workpiece based at least on the coordinates of the first machining start point, the coordinates of the second machining start point, the coordinates of the first machining end point, and the coordinates of the second machining end point so that the eccentric shape is formed around the eccentric axis passing through a center start point which is the midpoint of a line segment connecting the first machining start point and the second machining start point, and a center end point which is the midpoint of a line segment connecting the first machining end point and the second machining end point; performing control to move the tool along the movement path in accordance with the rotation of the workpiece; The first processing start point and the second processing start point may have different Z coordinates, The first processing end point and the second processing end point may have different Z coordinates, At least, the Z coordinate of the first processing start point is different from the Z coordinate of the second processing start point, or the Z coordinate of the first processing end point is different from the Z coordinate of the second processing end point, The number of divisions N for dividing the first outline connecting the first machining start point and the first machining end point and the second outline connecting the second machining start point and the second machining end point is set as the number of times the workpiece rotates around the spindle center line from the start of machining the eccentric shape to the end of machining, The control unit controls the relative positional relationship by the drive unit so that, each time the workpiece rotates once around the spindle center line, the Z coordinate of the relative positional relationship on the first outline changes by a value obtained by dividing the difference in Z coordinate between the first processing start point and the first processing end point by the number of divisions N, and the Z coordinate of the relative positional relationship on the second outline changes by a value obtained by dividing the difference in Z coordinate between the second processing start point and the second processing end point by the number of divisions N.

2. The control unit A first diameter (SpD) that is a diameter of the eccentric shape in a direction perpendicular to the spindle center line is calculated based on the coordinates of the first machining start point and the coordinates of the second machining start point; a second diameter (EpD) that is a diameter of the eccentric shape in a direction perpendicular to the spindle center line is calculated based on the coordinates of the first processing end point and the coordinates of the second processing end point; A third diameter (WpD) is a diameter at a processing center point between the center start point and the center end point on the eccentric shaft, and is interpolated from the first diameter (SpD) and the second diameter (EpD); The machine tool according to claim 1 , wherein the movement path of the tool is determined to be a path along the periphery of a virtual arc whose center is offset from the center line of the spindle, based on the third diameter (WpD).

3. The control unit A first eccentricity amount (SpE) which is an eccentricity amount of the center start point from the spindle center line is calculated based on the coordinates of the first processing start point and the coordinates of the second processing start point; A second eccentricity amount (EpE) that is an eccentricity amount of the center end point from the spindle center line is calculated based on the coordinates of the first processing end point and the coordinates of the second processing end point; a third eccentricity amount (WpE) which is the eccentricity amount of the mid-machining center point from the spindle center line is interpolated using a point on the eccentric shaft between the center start point and the center end point as the mid-machining center point, from the first eccentricity amount (SpE) and the second eccentricity amount (EpE); 3. The machine tool according to claim 1, wherein the movement path of the tool is determined to be a path along the circumference of a virtual arc having a size corresponding to the third eccentricity amount (WpE).

4. Assuming that the X-axis and Y-axis, which are orthogonal to each other, are orthogonal to the Z-axis along the main shaft center line, the drive unit includes a tool rest drive unit that moves the tool rest along an X-axis and a Y-axis, and a headstock drive unit that moves the spindle along a Z-axis, The machine tool according to any one of claims 1 to 3, wherein the control unit moves the tool along the X-axis and Y-axis in accordance with the rotation of the workpiece, and vibrates the workpiece along the Z-axis in accordance with the rotation of the workpiece when vibrating the relative positional relationship along the Z-axis in accordance with the rotation of the workpiece.

5. Assuming that the X-axis and Y-axis, which are orthogonal to each other, are orthogonal to the Z-axis along the main shaft center line, the drive unit moves the tool rest along the X-axis, the Y-axis, and the Z-axis; The machine tool according to any one of claims 1 to 3, wherein the control unit moves the tool along the X-axis and Y-axis in accordance with the rotation of the workpiece, and when vibrating the relative positional relationship along the Z-axis in accordance with the rotation of the workpiece, vibrates the tool along the Z-axis in accordance with the rotation of the workpiece.

6. the control unit interprets and executes a machining program incorporating an eccentric machining command for forming the eccentric shape on the workpiece, the eccentric shape being centered on the eccentric axis deviated from the center line of the spindle, thereby controlling the relative positional relationship by the drive unit so as to form the eccentric shape on the workpiece; the eccentric machining command has at least the coordinate of the first machining start point, the coordinate of the second machining start point, the coordinate of the first machining end point, and the coordinate of the second machining end point as arguments when the workpiece is in the reference phase, including a Z coordinate which is a coordinate of the Z axis along the spindle center line; The machine tool according to any one of claims 1 to 5, wherein when the control unit reads out the eccentric machining command from the machining program, it acquires at least the coordinates of the first machining start point, the coordinates of the second machining start point, the coordinates of the first machining end point, and the coordinates of the second machining end point from the eccentric machining command.

7. A tool movement path determination method for a machine tool comprising: a spindle that rotates together with a workpiece about a spindle center line; and a tool post to which a tool for machining the workpiece is attached, the method varying a relative positional relationship between the spindle and the tool post so as to form an eccentric shape on the workpiece about an eccentric axis that is offset from the spindle center line, the eccentric shape formed on the workpiece has a machining start portion, which is a portion where machining of the workpiece rotating about the spindle center line starts, and a machining end portion, which is a portion where machining of the workpiece rotating about the spindle center line ends, a first machining start point is the position of the cutting edge of the tool that forms the machining start portion when the workpiece rotating about the spindle center line is in a reference phase, a second machining start point is a position at the machining start portion that is on the opposite side of the first machining start point with the eccentric shaft as the center, a first machining end point is the position of the cutting edge of the tool that forms the machining end portion when the workpiece is in the reference phase, and a second machining end point is a position at the machining end portion that is on the opposite side of the first machining end point with the eccentric shaft as the center, a first step of acquiring a coordinate of the first machining start point, a coordinate of the second machining start point, a coordinate of the first machining end point, and a coordinate of the second machining end point when the workpiece is in the reference phase, including a Z coordinate which is a coordinate of the Z axis along the spindle center line; a second step of determining a movement path of the tool in accordance with the rotation of the workpiece based at least on the coordinates of the first machining start point, the coordinates of the second machining start point, the coordinates of the first machining end point, and the coordinates of the second machining end point so that the eccentric shape is formed around the eccentric axis passing through a center start point which is the midpoint of a line segment connecting the first machining start point and the second machining start point, and a center end point which is the midpoint of a line segment connecting the first machining end point and the second machining end point, The first processing start point and the second processing start point may have different Z coordinates, The first processing end point and the second processing end point may have different Z coordinates, At least, the Z coordinate of the first processing start point is different from the Z coordinate of the second processing start point, or the Z coordinate of the first processing end point is different from the Z coordinate of the second processing end point, The number of divisions N for dividing the first outline connecting the first machining start point and the first machining end point and the second outline connecting the second machining start point and the second machining end point is set as the number of times the workpiece rotates around the spindle center line from the start of machining the eccentric shape to the end of machining, In the second step, a tool movement path determination method is provided in which a movement path of the tool is determined in accordance with the rotation of the workpiece so that, each time the workpiece rotates once around the spindle center line, the Z coordinate of the relative positional relationship on the first outer contour line changes by a value obtained by dividing the difference in Z coordinate between the first machining start point and the first machining end point by the number of divisions N, and the Z coordinate of the relative positional relationship on the second outer contour line changes by a value obtained by dividing the difference in Z coordinate between the second machining start point and the second machining end point by the number of divisions N.

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