Machine tool control device and machine tool control method

Abstract

The present invention relates to a control device for a machine tool including a control unit, wherein the control unit repeats the following processes in sequence: a tapping process, in which the front end of a tool for tapping is moved from a retreat point to a predetermined depth position while rotating forward, thereby performing tapping at the tapping position; a drawing process, in which the front end of the tool is moved from a predetermined depth position to a retreat point while reversing, thereby pulling the tool out of a workpiece; and a positioning process, in which the next tapping position is positioned relative to the tool, wherein the control unit further performs the following control: in the drawing process, the positioning process is started at the same time when the front end of the tool passes through a reference point, and in the tapping process, the positioning process is ended at the same time when the front end of the tool passes through the reference point, and based on the distance between the tapping positions, the control unit controls the end timing of acceleration of the relative movement of the workpiece and the tool in the tapping process and the start timing of deceleration of the relative movement of the workpiece and the tool in the drawing process.

Description

Technical Field

[0001] The invention relates to a control device of a machine tool and a control method of a machine tool. Background Art

[0002] Conventionally, there are known machine tools for performing tapping on a workpiece (see, for example, Patent Documents 1 to 3). Patent Document 3 describes a method for controlling a machine tool that moves a tool along a smooth continuous path relative to a workpiece to shorten a tapping cycle.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2015-187799

[0006] Patent Document 2: Japanese Patent Application Publication No. 2011-073069

[0007] Patent Document 3: Japanese Patent Application Laid-Open No. 09-120310 Summary of the invention

[0008] Problems to be solved by the invention

[0009] When tapping is performed sequentially at a plurality of tapping positions of a workpiece, the movement control of the tool suitable for increasing the cycle time differs depending on machining conditions such as the distance between the tapping positions.

[0010] Means used to solve problems

[0011] One aspect of the present application is a control device for a machine tool, comprising: a worktable, the worktable holding a workpiece; a spindle, the spindle holding a tool for tapping processing; a first conveying motor, the first conveying motor causing the worktable and the spindle to move relative to each other in a first direction parallel to the long side axis of the spindle; a second conveying motor, the second conveying motor causing the worktable and the spindle to move relative to each other in a second direction intersecting the long side axis; and a spindle motor causing the spindle to rotate around the long side axis, wherein the control device for the machine tool comprises a control unit, the control unit controlling the first conveying motor to move the front end of the tool between a retreat point retreated from the workpiece and a predetermined depth position of the workpiece, controlling the second conveying motor to position a plurality of tapping positions of the workpiece relative to the tool, and controlling the spindle motor to control the rotation of the tool, the control unit repeating the following steps in sequence: a tapping step, moving the front end of the tool from the retreat point to the predetermined depth position while rotating the tool in the forward direction; a step of moving the front end of the tool from the predetermined depth position to the retreat point without stopping the movement while rotating the tool in the reverse direction, thereby pulling the tool out of the workpiece; and a positioning step of positioning the next tapping position relative to the tool and switching the rotation direction of the tool from the reverse direction to the forward direction, wherein the control unit further performs the following control: in the drawing step, relative movement of the workpiece and the tool in the positioning step is started at the same time when the front end of the tool passes through a reference point between the workpiece and the retreat point, and relative movement of the workpiece and the tool in the positioning step is ended at the same time when the front end of the tool passes through the reference point in the tapping step, and the end timing of acceleration of the relative movement of the workpiece and the tool in the tapping step and the start timing of deceleration of the relative movement of the workpiece and the tool in the drawing step are controlled based on the distance in the second direction from one tapping position to the next tapping position. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a schematic diagram of a machine tool according to one embodiment.

[0013] Figure 2 A diagram for explaining relative movement between a workpiece and a tool by a method for controlling a machine tool according to an embodiment.

[0014] Figure 3 A diagram for explaining the movement path of the tool relative to the workpiece and the movement speed of the tool in the first control mode.

[0015] Figure 4 A diagram for explaining the movement path of the tool relative to the workpiece and the movement speed of the tool in the second control mode.

[0016] Figure 5 It is a graph showing the time changes of the speed and position of the main axis (Z axis) and the worktable (X axis) in the first control mode.

[0017] Figure 6 It is a graph showing the time changes of the speed and position of the main axis (Z axis) and the worktable (X axis) in the second control mode.

[0018] Figure 7 It is a diagram for explaining a modification example of the movement path of the tool relative to the workpiece and the movement speed of the tool in the first control mode.

[0019] Figure 8 It is a graph showing the time changes of the speed and position of the main axis (Z axis) and the table (X axis) in the comparative example.

[0020] Fig. 9 It is a graph showing the time changes of the speed and position of the main axis (Z axis) and the worktable (X axis) in other comparative examples. DETAILED DESCRIPTION

[0021] Hereinafter, a machine tool 1 according to one embodiment will be described with reference to the drawings.

[0022] The machine tool 1 includes, for example, a tool magazine for storing a plurality of tools and a spindle for holding one tool, and is a machining center having a function of automatically exchanging tools between the tool magazine and the spindle.

[0023] like Figure 1 As shown, the machine tool 1 includes: a spindle 2, which holds a tool T; a worktable 3, which holds a workpiece W; a spindle motor 4, which rotates the spindle 2 around the long side axis of the spindle 2; a Z-axis conveying motor (first conveying motor) 5, which moves the spindle 2 in the Z direction (first direction) relative to the worktable 3; an X-axis conveying motor (second conveying motor) 6, which moves the worktable 3 in the X direction (second direction) relative to the spindle 2; and a control device 7, which controls the motors 4, 5, and 6.

[0024] The Z direction is a direction parallel to the long axis of the main axis 2 , and the X direction is a direction orthogonal to the long axis of the main axis 2 .

[0025] The main shaft 2 is arranged in the vertical direction and supported by a supporting mechanism (not shown) so as to be movable in the vertical direction. Figure 1 In the machine tool 1, the Z direction is the vertical direction and the X direction is the horizontal direction. The spindle 2 holds the tool T at the lower end. Figure 2As shown, the tool T is a tool for tapping for cutting a thread in a lower hole H formed in a workpiece W. The tool T is coaxial with the spindle 2 and rotates and moves integrally with the spindle 2 .

[0026] The table 3 is horizontally disposed below the spindle 2. The workpiece W placed on the upper surface of the table 3 is fixed to the table 3 by a fixture (not shown).

[0027] The spindle motor 4 is connected to the upper end of the spindle 2 .

[0028] The Z-axis conveying motor 5 and the X-axis conveying motor 6 are servo motors, respectively. A Y-axis conveying motor may also be provided for moving the worktable 3 in the Y direction. The Y direction is a horizontal direction perpendicular to the Z direction and the X direction.

[0029] The control device 7 is, for example, a numerical control device. The control device 7 includes a storage unit 7a and a control unit 7b.

[0030] The storage unit 7a includes, for example, a RAM, a ROM, and other storage devices. Figure 2 As shown, the storage unit 7a stores a machining program for sequentially performing tapping machining on the lower hole H at a plurality of tapping positions Pi (i=1, 2, ..., n, n+1, ...) of the workpiece W. The tapping positions Pi are arranged in the X direction at intervals ΔP from each other.

[0031] The control unit 7b has a processor such as a central processing unit, and sends control instructions to the motors 4, 5, and 6 according to the processing program, thereby controlling the movement of the spindle 2 and the table 3, and then performing tapping processing in the lower holes H at the plurality of tapping positions Pi in sequence through the tool T.

[0032] Specifically, the control unit 7 b controls the spindle motor 4 , thereby controlling the rotation direction and rotation speed of the spindle 2 and the tool T.

[0033] The control unit 7b controls the Z-axis conveying motor 5 to repeatedly lower and raise the spindle 2 in the Z direction, so that the front end of the tool T reciprocates between a predetermined R' point (retreat point) and a predetermined depth position of the workpiece W corresponding to the bottom of the lower hole H. The R' point is a position above the upper surface of the workpiece W and is a position where the front end of the tool T is retreated after the tapping process is performed at each tapping position Pi.

[0034] The control unit 7 b controls the X-axis conveying motor 6 to repeatedly move the table 3 in the X direction and temporarily stop the table 3 , thereby positioning the plurality of tapping positions Pi vertically below the tool T, respectively.

[0035] Next, a control method by which the control unit 7b controls the motors 4, 5, and 6 according to the machining program will be described in detail.

[0036] like Figure 2 As shown, the control unit 7b repeats the tapping step S1, the drawing step S2, and the positioning step S3 in sequence. Figure 2 Graph 2 shows a path of relative movement of the tool T with respect to the workpiece W in a first control mode described later.

[0037] In the tapping process S1, the control unit 7b makes the spindle 2 rotate forwardly and descends while positioning a tapping position Pn relative to the tool T in the X direction, so that the front end of the forward rotating tool T descends from the R' point to a predetermined depth position. Thus, tapping is performed in the lower hole H at the tapping position Pn.

[0038] Here, the control unit 7b starts accelerating the spindle 2 in the Z direction at the same time as the tip of the tool T starts to move from the R' point, and accelerates the spindle 2 to the cutting feed speed. Next, the control unit 7b causes the spindle 2 to decrease at the cutting feed speed, and then decelerates the spindle 2 in the Z direction from the cutting feed speed so that the speed of the tip of the tool T in the Z direction becomes zero at a predetermined depth position. The cutting feed speed is determined by the rotation speed of the spindle 2 and the pitch of the tool T. For example, the cutting feed speed is a speed corresponding to the maximum rotation speed of the spindle 2.

[0039] The control unit 7 b accelerates the rotation of the spindle 2 in synchronization with the acceleration of the spindle 2 in the Z direction, and decelerates the rotation of the spindle 2 in synchronization with the deceleration of the spindle 2 in the Z direction.

[0040] Next, in the drawing process S2, the control unit 7b stops the rotation of the spindle 2 when the tip of the tool T reaches the predetermined depth position, and then reversely rotates the spindle 2. Next, the control unit 7b reversely rotates the spindle 2 while raising it, so that the tip of the tool T is raised to the predetermined depth position R without stopping the movement of the tool T in the Z direction. As a result, the tool T is pulled out from the lower hole H, and the tip of the tool T is retracted to a height that does not interfere with the workpiece W.

[0041] Here, the control unit 7b starts accelerating the spindle 2 in the Z direction at the same time as the tip of the tool T starts to move from the predetermined depth position, and accelerates the spindle 2 to the cutting feed speed. Next, the control unit 7b causes the spindle 2 to rise at the cutting feed speed, and then decelerates the spindle 2 in the Z direction from the cutting feed speed so that the speed of the tip of the tool T in the Z direction becomes zero at the R' point.

[0042] The control unit 7 b accelerates the rotation of the spindle 2 in synchronization with the acceleration of the spindle 2 in the Z direction, and decelerates the rotation of the spindle 2 in synchronization with the deceleration of the spindle 2 in the Z direction.

[0043] Next, in the positioning step S3, the control unit 7b fast-forwards the table 3 and moves it in the X direction to position the next tapping position Pn+1 vertically below the tool T. The control unit 7b switches the rotation direction of the spindle 2 from the reverse direction to the forward direction.

[0044] During the fast forward process, the X-axis conveying motor 6 moves the worktable 3 in the X direction at the fast forward speed. The fast forward speed is the maximum speed of the worktable 3 that can be achieved by the X-axis conveying motor 6. During the fast forward process, the X-axis conveying motor 6 accelerates the worktable 3 to the fast forward speed at the maximum acceleration of the X-axis conveying motor 6, and decelerates the worktable 3 from the fast forward speed at the maximum deceleration of the X-axis conveying motor 6.

[0045] The control unit 7b starts the positioning step S3 before the drawing step S2 is completed.

[0046] Specifically, the control unit 7b starts the movement of the worktable 3 in the positioning step S3 when the front end of the tool T that rises in the drawing step S2 passes through the predetermined R point (reference point). The R point is a position between the upper surface of the workpiece W and the R' point, and is a position above the upper surface of the workpiece W. For example, the interval between the upper surface of the workpiece W and the R point in the Z direction is 1 mm to 5 mm. Thus, before the front end of the tool T reaches the R' point from the R point, the movement of the spindle 2 in the Z direction and the movement of the worktable 3 in the X direction overlap in time, and the movement path of the front end of the tool T relative to the workpiece W during the period from the R point to the R' point becomes an arc or a nearly arc.

[0047] The control unit 7b starts the next tapping step S1 before the positioning step S3 is completed.

[0048] Specifically, the control unit 7b starts the descent of the tool T at the same time when the tip of the tool T that is descending in the next tapping step S1 passes through the point R, thereby completing the positioning of the tapping position Pn+1 in the positioning step S3. As a result, before the tip of the tool T reaches the point R from the point R', the movement of the table 3 in the X direction and the movement of the spindle 2 in the Z direction overlap in time, and the movement path of the tip of the tool T relative to the workpiece W during the period from the point R' to the point R becomes an arc or a nearly arc.

[0049] The control unit 7 b controls the rotation direction of the spindle 2 in the positioning step S3 so that the tip of the tool T passes through the R point while rotating the tool T in the forward direction in the tapping step S1 .

[0050] like Figure 3 and Figure 4As shown, the control unit 7b controls the end timing of the acceleration of the spindle 2 in the Z direction in the tapping process S1 and the start timing of the deceleration of the spindle 2 in the Z direction in the drawing process S2 in either the first control mode or the second control mode based on the distance ΔP in the X direction between the tapping positions Pn and Pn+1. By using the control mode corresponding to the distance ΔP in this way, the above-mentioned arc-shaped or nearly arc-shaped movement trajectory can be realized regardless of the distance ΔP.

[0051] Which of the first control mode and the second control mode is to be selected is automatically determined by the control unit 7 b based on the machining program, for example, or is determined by the user and set in the control device 7 .

[0052] exist Figure 3 and Figure 4 In FIG. 1 , a solid arrow indicates a movement trajectory of the tool T at a constant cutting feed speed, a dotted arrow indicates a movement trajectory of the tool T during deceleration, and a dashed arrow indicates a movement trajectory of the tool T during acceleration.

[0053] Figure 5 FIG. 2 shows the time variation of the speed and position of the spindle 2 (Z axis) and the table 3 (X axis) in the first control mode. Figure 6 The time variation of the speed and position of the spindle 2 (Z axis) and the table 3 (X axis) under the second control mode is shown in FIG. Figure 5 and Figure 6 , the horizontal axis is time.

[0054] like Figure 3 As shown, when the distance ΔP between the tapping positions Pn and Pn+1 is large, the first control mode is selected. Specifically, when the sum of the length of the acceleration time of the spindle 2 in the Z direction in the tapping process S1 and the length of the deceleration time of the spindle 2 in the Z direction in the drawing process S2 is less than the length of the positioning time in the positioning process S3, the first control mode is selected.

[0055] The deceleration time of the spindle 2 in the Z direction is the time required to decelerate the speed of the spindle 2 from the cutting feed speed to zero at a predetermined deceleration. The predetermined deceleration is, for example, the maximum deceleration of the Z-axis feed motor 5. The acceleration time of the spindle 2 in the Z direction is the time required to accelerate the speed of the spindle 2 from zero to the cutting feed speed at a predetermined acceleration. The predetermined acceleration is, for example, the maximum acceleration of the Z-axis feed motor 5.

[0056] The length of the positioning time is the length of time from when the table 3 starts to move to when the next tapping position Pn+1 is positioned relative to the tool T and the table 3 stops in the positioning step S3.

[0057] In the first control mode, the control unit 7b starts deceleration of the spindle 2 in the Z direction when the tip of the tool T passes through the point R in the drawing process S2. The control unit 7b stops acceleration of the spindle 2 in the Z direction when the tip of the tool T passes through the point R in the tapping process S1.

[0058] like Figure 4 As shown, when the distance ΔP between the tapping positions Pn and Pn+1 is close, the second control mode is selected. Specifically, when the sum of the length of the acceleration time of the spindle 2 in the Z direction in the tapping process S1 and the length of the deceleration time of the spindle 2 in the Z direction in the drawing process S2 is longer than the length of the positioning time in the positioning process S3, the second control mode is selected.

[0059] In the second control mode, the control unit 7b starts deceleration of the spindle 2 in the Z direction before the tip of the tool T passes through the R point in the drawing process S2. The control unit 7b ends acceleration of the spindle 2 in the Z direction after the tip of the tool T passes through the R point in the tapping process S1. The shorter the distance ΔP, the earlier the timing of starting deceleration. Preferably, the control unit 7b controls the timing of starting deceleration of the spindle 2 in the drawing process S2 so that the length of time from the tip of the tool T passing through the R point in the drawing process S2 to the tip of the tool T passing through the R point in the next tapping process S1 is the same as the length of the positioning time.

[0060] Next, the operation of machine tool 1 will be described.

[0061] The control unit 7b repeatedly moves and temporarily stops the table 3 in the X direction via the X-axis feed motor 6, thereby sequentially positioning a plurality of tapping positions Pi of the workpiece W vertically below the tool T. The control unit 7b repeatedly lowers and raises the spindle 2 in the Z direction via the Z-axis feed motor 5 in synchronization with the movement of the table 3 while rotating the spindle 2 and the tool T via the spindle motor 4. Thus, the tool T sequentially performs tapping processing in the lower holes H at the plurality of tapping positions Pi.

[0062] Here, while the tip of the tool T moves in the Z direction between the R' point and the R point, the Z direction movement of the spindle 2 and the X direction movement of the table 3 overlap in time. Thus, compared with the case where the next positioning step S3 is started after the drawing step S2 is completely completed and the tapping step S1 is started after the positioning step S3 is completely completed, the cycle can be shortened.

[0063] The timing of starting the deceleration of the ascending spindle 2 and the timing of ending the acceleration of the descending spindle 2 are controlled by a control mode corresponding to the distance ΔP between the tapping positions Pn and Pn+1. According to such control, the movement trajectory of the tool T relative to the workpiece W from the tapping position Pn to the tapping position Pn+1 can be smoothly continuous regardless of the distance ΔP, that is, the tool T can move from the tapping position Pn to the tapping position Pn+1 relative to the workpiece W without stopping temporarily. As a result, the table 3 can always be moved in a fast-forward manner regardless of the distance ΔP, thereby further shortening the cycle.

[0064] Figure 8 It is shown in Figure 3 Comparative example of the control method of the first control mode, Fig. 9 It is shown in Figure 4 A comparative example of the control method of the second control mode.

[0065] exist Figure 8 In the process, the positioning step S3 is started at the same time when the drawing step S2 is completed, and the tapping step S1 is started at the same time when the positioning step S3 is completed.

[0066] exist Fig. 9 In the drawing step S2 , the spindle 2 starts to decelerate when the tip of the tool T passes through the R point, and in the tapping step S1 , the spindle 2 ends to accelerate when the tip of the tool T passes through the R point.

[0067] according to Figure 3 and Figure 8 comparison, and Figure 4 and Fig. 9 As can be seen from the comparison, the cycle is shortened by the first control mode and the second control mode of this embodiment.

[0068] A point R is set above the upper surface of the workpiece W, and above the point R, the moving path of the tip of the tool T becomes an arc or a nearly arc. Thus, regardless of the thickness deviation of the workpiece W, the tip of the tool T moving along the arc or nearly arc path can be prevented from interfering with the corner of the opening of the lower hole H.

[0069] In the above-mentioned embodiment, the acceleration of the spindle 2 in the Z direction between the R point and the R' point in the first control mode can also be reduced to a speed lower than the maximum acceleration within a range where the period does not increase, and the deceleration of the spindle 2 in the Z direction between the R point and the R' point in the first control mode can also be reduced to a speed lower than the maximum deceleration within a range where the period does not increase.

[0070] When the deceleration is lower than the maximum deceleration, the deceleration distance of the spindle 2 becomes longer, so the distance between the R point and the R′ point in the Z direction becomes larger, and the tip of the tool T retreats to a higher position.

[0071] The greater the acceleration and deceleration, the greater the power consumption and heat generation of the Z-axis conveying motor 5 during acceleration and deceleration. By reducing the acceleration and deceleration of the spindle 2, the power consumption and heat generation of the Z-axis conveying motor 5 can be suppressed.

[0072] For example, in Figure 2 In the example, there is a period of time when the spindle 2 moves linearly along the X direction relative to the worktable 3 between the tapping positions Pn and Pn+1. Figure 7 As shown in Figure 2, even if spindle 2 decelerates at the reduced deceleration and then immediately starts accelerating at the reduced acceleration, its cycle is the same as Figure 2 The same situation.

[0073] The deceleration and acceleration between point R and point R' are as follows: Figure 7 As shown, it can be determined that the moving path of the tool T between the point R and the point R' relative to the workpiece W does not include a straight line, but becomes a smooth arc or a curve approximately in an arc shape. As a result, between deceleration and acceleration, the moving speed of the spindle 2 is changed as slowly as possible within a range that does not cause a cycle extension, which can more effectively suppress power consumption and heat generation.

[0074] In the above embodiment, the second direction is set to the X direction, but the second direction may be any direction perpendicular to the Z direction. That is, the second direction may be the Y direction, or may be both the X and Y directions.

[0075] As an example, when a plurality of tapping positions Pi are arranged in the Y direction, the control unit 7b may control the Y-axis transport motor (second transport motor) to move the table 3 in the Y direction in the positioning step S3.

[0076] As another example, when a plurality of tapping positions Pi are two-dimensionally arranged in the X direction and the Y direction, the control unit 7b may simultaneously control both the X-axis feed motor 6 and the Y-axis feed motor in the positioning step S3 to move the worktable 3 in both the X direction and the Y direction.

[0077] In the above embodiment, the table 3 moves in the X direction and the Y direction intersecting the long axis of the spindle 2, but the relative movement of the spindle 2 and the table 3 in the X direction and the Y direction can be achieved by moving either or both of the spindle 2 and the table 3. Similarly, in the above embodiment, the spindle 2 moves in the Z direction parallel to the long axis of the spindle 2, but the relative movement of the spindle 2 and the table 3 in the Z direction can be achieved by moving either or both of the spindle 2 and the table 3.

[0078] For example, instead of the transport motors 5 and 6 , a first transport motor for moving the table 3 in the Z direction and a second transport motor for moving the spindle 2 in the X direction and the Y direction may be provided.

[0079] In the above embodiment, the first direction is the vertical direction (Z direction) and the second direction is the horizontal direction (X direction and Y direction), but the specific directions of the first direction and the second direction can be appropriately changed according to the design of the machine tool. For example, in a machine tool in which the spindle 2 is horizontally arranged, the first direction can also be the horizontal direction, and the second direction can also be any direction intersecting the first direction.

[0080] Description of Reference Numerals

[0081] 1: Machine tools

[0082] 2: Spindle

[0083] 3: Workbench

[0084] 4: Spindle motor

[0085] 5: Z-axis conveying motor (first conveying motor)

[0086] 6: X-axis conveying motor (second conveying motor)

[0087] 7b: Control Department

[0088] H: Bottom hole

[0089] Pn, Pn+1: tapping position

[0090] R': retreat point

[0091] R: Reference point

[0092] T: Tools

[0093] W: Workpiece

Claims

1. A control device for a machine tool, comprising: A workbench, the workbench holds a workpiece; a spindle, the spindle holds a tool for tapping; a first conveying motor, which enables the worktable and the spindle to move relative to each other in a first direction parallel to the long side axis of the spindle; and a second conveying motor, which enables the worktable and the spindle to move relative to each other in a second direction intersecting the long side axis; and a spindle motor, the spindle motor causing the spindle to rotate around the long side axis, wherein, The control device of the machine tool includes a control unit, which controls the first conveying motor to move the front end of the tool between a retreat point from the workpiece and a predetermined depth position of the workpiece, controls the second conveying motor to position a plurality of tapping positions of the workpiece relative to the tool, and controls the spindle motor to control the rotation of the tool. The control unit repeats the following steps in sequence: a tapping step of moving the front end of the tool from the retreat point to the predetermined depth position while rotating the tool in the forward direction, thereby performing a tapping process at one of the tapping positions; a pulling step of moving the front end of the tool from the predetermined depth position to the retreat point without stopping the movement while rotating the tool in the reverse direction, thereby pulling the tool out of the workpiece; and a positioning step of positioning the next tapping position relative to the tool and switching the rotation direction of the tool from the reverse direction to the forward direction, The control unit also performs the following control: In the drawing step, when the front end of the tool passes through the reference point between the workpiece and the retreat point, the relative movement of the workpiece and the tool in the positioning step is started. In the tapping step, when the front end of the tool passes through the reference point, the relative movement of the workpiece and the tool in the positioning step is terminated. Based on the distance in the second direction from one tapping position to the next tapping position, the end timing of acceleration of the relative movement of the workpiece and the tool in the tapping process and the start timing of deceleration of the relative movement of the workpiece and the tool in the drawing process are controlled.

2. The control device for a machine tool according to claim 1, wherein: In the tapping process and the drawing process, the control unit accelerates the relative speed of the workpiece and the tool in the first direction to a cutting conveying speed, causes the workpiece and the tool to move relative to each other at the cutting conveying speed, and decelerates the relative speed of the workpiece and the tool in the first direction from the cutting conveying speed.

3. The control device for a machine tool according to claim 1 or 2, wherein: When the sum of the length of the acceleration time in the tapping step and the length of the deceleration time in the drawing step is less than the length of the positioning time in the positioning step, The control unit performs the following control: In the drawing step, when the front end of the tool passes through the reference point, the relative speed of the workpiece and the tool in the first direction starts to be decelerated. In the tapping step, the acceleration of the relative speed between the workpiece and the tool in the first direction is terminated at the same time when the front end of the tool passes through the reference point.

4. The control device for a machine tool according to claim 3, wherein: The control unit reduces the acceleration of the workpiece and the tool in the first direction in the tapping process to a speed lower than the maximum acceleration within a range in which a cycle does not increase, and reduces the deceleration of the workpiece and the tool in the first direction in the drawing process to a speed lower than the maximum deceleration within a range in which a cycle does not increase.

5. The control device for a machine tool according to claim 1 or 4, wherein: When the sum of the length of the acceleration time in the tapping step and the length of the deceleration time in the drawing step is longer than the length of the positioning time in the positioning step, The control unit performs the following control: In the drawing step, before the front end of the tool passes through the reference point, the relative movement of the workpiece and the tool in the first direction is decelerated. In the tapping step, after the tip of the tool passes through the reference point, acceleration of the relative speed between the workpiece and the tool in the first direction is terminated.

6. The control device for a machine tool according to claim 5, wherein: The control unit controls the start timing of the deceleration in the drawing process so that the length of time from when the tip of the tool passes through the reference point in the drawing process to when the tip of the tool passes through the reference point in the next tapping process is the same as the length of the positioning time.

7. A method for controlling a machine tool, the machine tool comprising: A workbench, the workbench holds a workpiece; a spindle, the spindle holds a tool for tapping; a first conveying motor, which enables the worktable and the spindle to move relative to each other in a first direction parallel to the long side axis of the spindle; and a second conveying motor, which enables the worktable and the spindle to move relative to each other in a second direction intersecting the long side axis; and a spindle motor, the spindle motor causing the spindle to rotate around the long side axis, wherein, The control method of the machine tool comprises: The first conveying motor is controlled so that the front end of the tool moves between a retreat point from the workpiece and a predetermined depth position of the workpiece, the second conveying motor is controlled so that a plurality of tapping positions of the workpiece are respectively positioned relative to the tool, and the spindle motor is controlled so as to control the rotation of the tool. The control method of the machine tool repeats the following steps in sequence: a tapping step of moving the front end of the tool from the retreat point to the predetermined depth position while rotating the tool in the forward direction, thereby performing a tapping process at one of the tapping positions; a pulling step of moving the front end of the tool from the predetermined depth position to the retreat point without stopping the movement while rotating the tool in the reverse direction, thereby pulling the tool out of the workpiece; and a positioning step of positioning the next tapping position relative to the tool and switching the rotation direction of the tool from the reverse direction to the forward direction, The control method of the machine tool is also used to perform the following control: In the drawing step, when the front end of the tool passes through the reference point between the workpiece and the retreat point, the relative movement of the workpiece and the tool in the positioning step is started. In the tapping step, when the front end of the tool passes through the reference point, the relative movement of the workpiece and the tool in the positioning step is terminated. Based on the distance in the second direction from one tapping position to the next tapping position, the end timing of acceleration of the relative movement of the workpiece and the tool in the tapping process and the start timing of deceleration of the relative movement of the workpiece and the tool in the drawing process are controlled.

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