Work processing method, program, and machine tool

Abstract

To shorten approaching time while maintaining the durability of a rotary tool.SOLUTION: A workpiece machining method comprises: rotating a rotary tool via a motor; moving the rotary tool at an approaching speed higher than a feeding speed set by a machining program in a first direction toward a workpiece; detecting contact of the rotary tool with the workpiece during the movement at the approaching speed in the first direction on the basis of a load of the motor; and changing the speed of moving the rotary tool in the first direction to the feeding speed upon detection of the contact with the workpiece. The approaching speed is determined so that a first amount of cutting per unit time at which the workpiece is cut by the rotary tool at the time of starting changing of the speed does not exceed an assumed amount of cutting, which is regarded by the machining program as the amount of cutting per unit time when the rotary tool cuts the workpiece at the feeding speed in the first direction.SELECTED DRAWING: Figure 16

Description

[Technical field]

[0001] The present invention relates to a workpiece machining method, a program, and a machine tool. Regarding. [Background technology]

[0002] Patent Document 1 describes a machine tool that shortens the time of the air-cut section from the end point of rapid traverse until a cutting tool such as a drill bites into a workpiece as much as possible. The method of Patent Document 1 determines the maximum speed, which is the approach speed that is the tool feed speed in the air-cut section, to be the maximum speed that does not exceed the limit value of the feed speed at which the tool is not damaged, so that the maximum value of the tool load that increases from when the cutting tool contacts the workpiece and when a detector detects the contact and starts to decelerate to the feed speed does not exceed the limit value of the feed speed at which the tool is not damaged. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 57-205013 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the approach speed is set to this extent, the tool load just before the cutting tool begins to decelerate becomes greater than the tool load assumed as the feed speed in the machining program, resulting in a shorter tool life than the user expected.

[0005] The objective of the technology disclosed in the present application is to realize a workpiece machining method, program, and machine tool that shorten the approach time while maintaining the tool life expected by the user. to provide. [Means for solving the problem]

[0006] A method for machining a workpiece according to a first aspect of the present disclosure includes rotating a rotating tool by a motor, moving the rotating tool in a first direction toward the workpiece at an approach speed higher than a feed rate set in a machining program, detecting contact of the rotating tool with the workpiece while moving in the first direction at the approach speed by a load of the motor, and changing the speed at which the rotating tool is moved in the first direction to the feed rate when contact with the workpiece is detected. The approach speed is determined so that a first cutting amount per unit time at which the rotating tool cuts the workpiece at the time when the speed change starts does not exceed a deemed cutting amount that is deemed to be a cutting amount per unit time when the rotating tool cuts the workpiece in the first direction at the feed rate in the machining program.

[0007] A method for machining a workpiece according to a second aspect of the present disclosure includes rotating a rotating tool by a motor, moving the rotating tool in a first direction toward the workpiece at an approach speed higher than a feed rate set in a machining program, detecting contact of the rotating tool with the workpiece while moving in the first direction at the approach speed by a load of the motor, and changing the speed at which the rotating tool is moved in the first direction to the feed rate when contact with the workpiece is detected. The approach speed is determined so that a first cutting amount per unit time at which the rotating tool cuts the workpiece at the time when the speed change starts is approximated to a deemed cutting amount that is deemed to be a cutting amount per unit time when the rotating tool cuts the workpiece in the first direction at the feed rate in the machining program.

[0008] A program according to a third aspect of the present disclosure is a program for causing a processor of a machine tool to execute the workpiece machining method according to the first or second aspect.

[0009] A machine tool according to a fourth aspect of the present disclosure includes a tool spindle, a motor, a driver, an actuator, and a processor. The tool spindle is configured to rotatably support a rotating tool around a rotation axis. The motor is configured to rotate the rotating tool around the rotation axis. The driver is configured to detect a load on the motor. The actuator is configured to move the tool spindle in a first direction toward a workpiece. The processor is configured to obtain a signal related to the load from the driver and control the motor and the actuator. The processor controls the actuator to move the rotating tool in the first direction at an approach speed that is higher than a feed rate set in a machining program. The processor detects, by the load, that the rotating tool has come into contact with the workpiece while moving in the first direction at the approach speed. When the processor detects that the rotating tool has come into contact with the workpiece, the processor controls the actuator to change the speed at which the rotating tool is moved in the first direction to the feed rate. The processor determines the approach speed so that a first cutting amount per unit time at which the rotating tool cuts the workpiece when the speed change is initiated does not exceed a deemed cutting amount which is deemed to be the cutting amount per unit time when the rotating tool cuts the workpiece in a first direction at a feed speed in the machining program.

[0010] A machine tool according to a fifth aspect of the present disclosure includes a tool spindle, a motor, a driver, an actuator, and a processor. The tool spindle is configured to rotatably support a rotating tool around a rotation axis. The motor is configured to rotate the rotating tool around the rotation axis. The driver is configured to detect a load on the motor. The actuator is configured to move the tool spindle in a first direction toward a workpiece. The processor is configured to obtain a signal related to the load from the driver and control the motor and the actuator. The processor controls the actuator to move the rotating tool in the first direction at an approach speed that is higher than a feed rate set in a machining program. The processor detects, by the load, that the rotating tool has come into contact with the workpiece while moving in the first direction at the approach speed. When the processor detects that the rotating tool has come into contact with the workpiece, the processor controls the actuator to change the speed at which the rotating tool is moved in the first direction to the feed rate. The processor determines the approach speed so that a first cutting amount per unit time at which the rotating tool cuts the workpiece when the speed change is initiated approximates a deemed cutting amount which is deemed to be the cutting amount per unit time when the rotating tool cuts the workpiece in a first direction at a feed speed in the machining program. Effect of the Invention

[0011] According to the technology disclosed in the present application, the approach speed is determined so that the first cutting amount does not exceed the deemed cutting amount or is close to the deemed cutting amount, thereby shortening the approach time while maintaining the durability of the tool. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing the external configuration of a machine tool according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing the configuration of an electronic circuit of the machine tool according to the embodiment. [Diagram 3] FIG. 3 is a cross-sectional view showing an outline of a machining head of the machine tool shown in FIG. [Figure 4]FIG. 4 is an enlarged perspective view showing the tool magazine and the tool changer. [Diagram 5] FIG. 5 is a flowchart showing a machining method of the machine tool, that is, the operation of a control program. [Figure 6] FIG. 6 shows an example of cutting with a rotary tool. [Figure 7] FIG. 7 shows another example of cutting with a rotary tool. [Figure 8] FIG. 8 shows another example of cutting with a rotary tool. [Figure 9] FIG. 9 shows another example of cutting with a rotary tool. [Figure 10] FIG. 10 is a diagram showing the maximum planned cutting amount defined in the machining program 7 in the example of FIG. [Figure 11] FIG. 11 is a diagram showing the maximum estimated cutting amount estimated from the feed direction of the rotating tool T1 in the example of FIG. [Figure 12] FIG. 12 is a diagram showing the maximum planned cutting amount defined in the machining program 7 in the example of FIG. [Figure 13] FIG. 13 is a diagram showing the maximum estimated cutting amount estimated from the feed direction of the rotating tool T1 in the example of FIG. [Figure 14] FIG. 14 is a flowchart showing details of the calculation of the approach speed in step S2 in the case of cutting in FIG. [Figure 15] FIG. 15 is a flowchart showing details of the calculation of the approach speed in step S24 of FIG. [Figure 16] FIG. 16 is a diagram for explaining the effect of the machine tool according to the embodiment. [Figure 17] FIG. 17 shows a flowchart illustrating a modified example of the calculation of the approach speed in step S24 of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the drawings showing embodiments thereof. In the drawings, the same reference numerals indicate corresponding or substantially identical components. <Embodiment> <Configuration of machine tool 1> Fig. 1 is a perspective view showing an external configuration of a machine tool 1 for performing cutting processing according to an embodiment. Fig. 2 is a diagram showing a configuration of an electronic circuit of the machine tool 1 according to an embodiment. As shown in Fig. 1, the machine tool 1 includes a control panel 10, a machining table 11 for holding a workpiece W (see Figs. 3 and 4), a machining head 12 movable in the X, Y and Z directions relative to the workpiece W, a tool magazine 15, and a tool changer 16. Although not shown in Fig. 1, the machine tool 1 may further include a cover for covering the above-mentioned components other than the control panel 10.

[0014] 2, the control panel 10 includes a numerical control device 2 for controlling the operation of the machine tool 1, an input interface 10a such as keys, buttons, dials, and a touch panel for a user to input machining conditions and the like in the machining control executed by the numerical control device 2, and a display device 10b for displaying the machining conditions and detection results of various sensors to the user. The numerical control device 2 has a hardware processor 3, a memory 4, a bus 5, and an input / output interface 6. The memory 4 stores machining programs 7 such as a joining program and a cutting program, and a control program 8 for controlling the rotating tool T1 and the like. The memory 4 may be referred to as a storage means. The hardware processor 3 executes various programs. In the following embodiments, the hardware processor 3 may be simply referred to as a processor 3.

[0015] FIG. 3 is a cross-sectional view showing an outline of the machining head 12 of the machine tool 1 shown in FIG. 1. As shown in FIG. 3, the machining head 12 includes a hollow spindle frame 12a forming a housing, and a tool spindle 12b contained in the spindle frame 12a. The spindle frame 12a of the machining head 12 is attached to at least one actuator 13 shown in FIG. 2 and is movable in three axial directions of X, Y, and Z. The at least one actuator 13 is configured to move the tool spindle 12b in a first direction toward the workpiece W. The first direction may be parallel to any one of the axes X, Y, and Z, or may be a direction intersecting these axes. For example, each of the at least one actuator 13 includes a servo motor, a motion conversion mechanism such as a ball screw, and a rotation sensor such as an encoder for feedback control of the servo motor. In addition, one end of the tool spindle 12b is connected to a rotation drive device 14 including a motor 14M and a driver 14D shown in FIG. 2. The tool spindle 12b is configured to support the rotating tool T1 rotatably around the rotation axis AX1. The motor 14M is configured to rotate the rotating tool T1 around the rotation axis AX1. The motor 14M is preferably a servo motor and includes a stator 14s fixed to the spindle frame 12a and a rotor 14r fixed to the tool spindle 12b. At least one actuator 13 and the rotation drive device 14 are connected to the numerical control device 2 via the input / output interface 6.

[0016] A tool holder 17 is detachably attached to the lower end of the processing head 12. Fig. 3 shows a rotating tool T1 for cutting according to an embodiment. As shown in Fig. 3, the rotating tool T1 is held by the tool holder 17.

[0017] The tool holder 17 has a pull stud 18 at its upper end, and a holder flange 17F of a generally truncated cone shape connected to the pull stud 18. The holder flange 17F has a groove 17G cut out in a radial direction relative to the rotation axis AX1 of the tool spindle 12b. Meanwhile, the tool spindle 12b has a collet chuck 19 that can be fitted with the pull stud 18, and a key portion 12K that can be fitted with the groove 17G. The collet chuck 19 is movable in a rotation axis direction DX along the rotation axis AX1 of the tool spindle 12b. When the collet chuck 19 is shifted in the rotation axis direction DX to an open direction DRR from the pull stud 18 toward the rotating tool T1, the collet chuck 19 is configured to open in a radial direction relative to the rotation axis AX1, and the pull stud 18 can be attached and detached. When the collet chuck 19 is shifted in the rotation axis direction DX to a close direction DRC from the rotating tool T1 toward the pull stud 18, the collet chuck 19 is configured to close in a radial direction relative to the rotation axis AX1, and is fitted with the pull stud 18. The pull stud 18 fits into the collet chuck 19, thereby fixing the tool holder 17 to the spindle 14b. At this time, the key portion 12K of the tool spindle 12b fits into the groove portion 17G of the tool holder 17, thereby restricting the rotation of the tool holder 17 relative to the tool spindle 12b. Therefore, a rotating tool T1 for cutting can be attached to the tool spindle 12b. In the following embodiments, the tool attached to the tool spindle 12b will be referred to as the execution tool TE.

[0018] The tool magazine 15 can store both the tool holder 17 for holding the rotating tool T1 and the tool holder 17 for holding the replacement rotating tool T2. FIG. 4 is an enlarged perspective view showing the tool magazine 15 and the tool exchange device 16. The tool magazine 15 has a plurality of holding parts 15a for holding a plurality of tool holders 17, and a holding part moving device 15b for moving the plurality of holding parts 15a along a peripheral orbit. The tool magazine 15 may have a holder removal device 15c for moving the tool holder 17 stored in the tool magazine 15 to a standby position PH accessible to the tool exchange device 16.

[0019] The tool change device 16 is configured to change tools between the tool magazine 15 and the tool spindle 12b. The tool change device 16 has a tool change arm 16a, an arm rotation device 16b that rotates the tool change arm 16a, and an arm movement device 16c that moves the tool change arm 16a linearly. The arm rotation device 16b rotates the tool change arm 16a around the additional rotation axis AX2. The arm movement device 16c moves the tool change arm 16a in a direction parallel to the additional rotation axis AX2. The tool change device 16 has grippers 16d and 16e that are configured similarly to a magic hand and can hold the tool holder 17 before and after tool change.

[0020] <Control program operation> Next, the operation of the control program 8 in FIG. 2, that is, the details of the control of the machine tool 1 will be described. The hardware processor 3 is configured to obtain a signal related to a load from the driver 14D and control the motor 14M and at least one actuator 13. FIG. 5 is a flowchart of the machining method of the machine tool 1, that is, the operation of the control program 8. The control program 8, when executed by the hardware processor 3 of the machine tool 1, includes instructions for causing the hardware processor 3 to execute the processing of the machining method described in FIG. 5 and FIG. 15 to FIG. 16 accompanying FIG. 5. Referring to FIG. 5, in step S1, in the machining method, the hardware processor 3 executing the control program 8 rotates the rotating tool T1 by the motor 14M. Specifically, the hardware processor 3 reads the rotation speed of the rotating tool T1 from the machining program 7 and sends a signal to the driver 14D to rotate the motor 14M at that rotation speed.

[0021] In step S2, the machining method includes moving the rotating tool T1 in a first direction DR1 toward the workpiece W at an approach speed F' that is higher than the feed speed F set in the machining program 7. The hardware processor 3 executing the control program 8 controls at least one actuator 13 to move the rotating tool T1 in the first direction DR1 at an approach speed F' that is higher than the feed speed F set in the machining program 7. The first direction DR1 is the feed direction set in the machining program 7. FIGS. 6 to 9 show an example of cutting by the rotating tool T1. The dotted lines in the workpiece W in FIGS. 6 to 9 represent the final machining shape.

[0022] FIG. 6 illustrates a case where the rotating tool T1 is a milling tool, the rotation axis AX1 is along the Z axis, and the first direction DR1 is the X-axis positive direction perpendicular to the rotation axis AX1. FIG. 7 illustrates a case where the rotating tool T1 is moved so that the first direction DR1 is oblique to the corner of the workpiece W (X-axis positive direction and Y-axis positive direction) and the rotation axis AX1 passes through the position of the corner, which is different from the example of FIG. 6. FIG. 8 illustrates a case where the rotating tool T1 is a countersinking tool, the rotation axis AX1 is along the Z axis, and the first direction DR1 is the Z-axis negative direction parallel to the rotation axis AX1. FIG. 9 illustrates a case where the rotating tool T1 is a milling tool, the rotation axis AX1 is perpendicular to the X axis, and perpendicular to the Y and Z axes, and the first direction DR1 is parallel to the rotation axis AX1. Different values ​​are set for the approach speed F' in each of FIG. 6 to FIG. 9, but how to determine the approach speed F' will be described later.

[0023] Returning to FIG. 2, in step S3, the machining method detects, by the load of the motor 14M, that the rotating tool T1 has come into contact with the workpiece W while moving in the first direction DR1 at the approach speed F'. The hardware processor 3 executing the control program 8 detects, by the load, that the rotating tool T1 has come into contact with the workpiece W while moving in the first direction DR1 at the approach speed F'. Specifically, in step S1, the driver 14D sends a drive current to the motor 14M so as to perform feedback control so that the rotation speed of the motor 14M is constant. Therefore, when the load of the motor 14M increases due to contact with the workpiece W, the drive torque of the motor 14M is increased, and the drive current output from the driver 14D is also increased. The hardware processor 3 monitors the drive current, and when the magnitude of the drive current exceeds a predetermined threshold value, determines that the rotating tool T1 has come into contact with the workpiece W. If it is not determined that the rotating tool T1 has come into contact with the workpiece W (No in step S3), step S3 is repeated.

[0024] In step S4, when contact with the workpiece W is detected (Yes in step S3), the machining method controls at least one actuator 13 to change the speed at which the rotating tool T1 moves in the first direction DR1 to the feed speed F. When contact with the workpiece W is detected (Yes in step S3), the hardware processor 3 executing the control program 8 controls at least one actuator 13 to change the speed at which the rotating tool T1 moves in the first direction DR1 to the feed speed F.

[0025] In step S2 of FIG. 6, the approach speed F′ is a first cutting amount V per unit time at which the rotary tool T1 cuts the workpiece W at the time when the speed change to the feed speed F is started. F is the assumed cutting amount V which is assumed to be the cutting amount per unit time when the rotary tool T1 cuts the rotary tool T1 in the first direction DR1 at the feed rate F in the machining program 7. ESTThat is, the hardware processor 3 executing the control program 8 determines the first cutting amount V per unit time when the rotary tool T1 cuts the workpiece W at the time when the speed change to the feed rate F is started. F is the assumed cutting amount V per unit time when the rotary tool T1 cuts the workpiece W in the first direction DR1 at the feed rate F in the machining program 7. EST The approach speed F' is determined so as not to exceed

[0026] Deemed cutting amount V EST is the theoretical maximum cutting amount per unit time when the rotating tool T1 cuts the workpiece W at the feed rate F. Specifically, the assumed cutting amount V EST is the maximum planned cutting amount V specified in the machining program 7. limp and the maximum estimated cutting amount V estimated from the feed direction of the rotary tool T1. lime The maximum planned cutting amount V specified in the machining program 7 is either limp is the theoretical maximum cutting amount per unit time when the rotary tool T1 is advanced into the workpiece W at the feed rate F in the machining program 7. The maximum estimated cutting amount V estimated from the feed direction of the rotary tool T1 lime is the cutting amount when it is assumed that all the surfaces of the rotating tool T1 overlapping the workpiece W as viewed in the first direction DR1 are in contact with the workpiece W, and the cutting amount is the volume equivalent to the value obtained by multiplying the area of ​​the surface of the rotating tool T1 overlapping the workpiece W as viewed in the first direction DR1 by the feed rate F. In other words, the maximum estimated cutting amount V lime is the theoretical cutting amount per unit time when it is assumed that the rotating tool T1 enters the workpiece W to a depth in the first direction DR1 where the contact area between the rotating tool T1 and the workpiece W is maximum when viewed in the first direction DR1, and cutting is performed in the first direction DR1 at a feed speed F.

[0027] FIG. 10 shows the maximum planned cutting amount V limp FIG. 11 is a diagram showing the maximum estimated cutting amount V estimated from the feed direction of the rotary tool T1 in the example of FIG. lime10 and 11, the cutting stock CS is shorter than half the diameter Td of the rotary tool T1. Strictly speaking, the cutting stock CS is determined by the size of the workpiece W and the machining target (dotted line in the workpiece W in Figs. 6 to 10) defined in the machining program 7. Since the size of the workpiece W includes an error, the exact value is unknown, but the maximum cutting stock CS assuming the error may be given in the machining program 7 or separately from the machining program 7. In the following description, the cutting stock CS is assumed to be given in this way. In this case, the maximum cutting amount defined in the machining program 7 is the value obtained by multiplying the distance Td' between both ends of the polka dot pattern in Fig. 10 by the feed rate F and the cutting depth Ad in the rotary axis direction DX (the length of the rotary tool T1 in the rotary axis direction DX that contacts the workpiece W). The position shown in the polka dot pattern in Fig. 10 is the position where the rotary tool T1 cuts up to the cutting stock CS. Td' is shorter than Td. In Fig. 11, the position where the rotary tool T1 has entered the workpiece W to a depth in the first direction DR1 where the contact area between the rotary tool T1 and the workpiece W is maximum as viewed in the first direction DR1 is indicated by a two-dot chain line. In Fig. 11, the position where the speed at which the rotary tool T1 is moved in the first direction DR1 is changed to the feed speed F is indicated by a solid line. The maximum estimated cutting amount V estimated from the feed direction of the rotary tool T1 lime is the volume equivalent to the area of ​​the surface of the rotating tool T1 overlapping with the workpiece W when viewed in the first direction DR1 multiplied by the feed speed F, and is therefore the product of the diameter Td of the rotating tool T1 multiplied by the feed speed F and the cutting depth Ad.

[0028] FIG. 12 shows the maximum planned cutting amount V limp FIG. 13 is a diagram showing the maximum estimated cutting amount V estimated from the feed direction of the rotary tool T1 in the example of FIG. lime12 and 13, the machining allowance CS is shorter than half the diameter Td of the rotating tool T1. In this case, the maximum cutting amount specified by the machining program 7 is a value obtained by multiplying the distance Td" between both ends of the polka dot pattern in FIG. 12 by the feed rate F and the cutting amount Ad in the rotation axis direction DX (the length of the rotating tool T1 in the rotation axis direction DX that comes into contact with the workpiece W). The position shown in the polka dot pattern in FIG. 12 is the position where the rotating tool T1 has cut up to the machining allowance CS. Td" is shorter than Td. As shown in FIG. 13, the maximum estimated cutting amount V estimated from the feed direction of the rotating tool T1 is lime is the volume equivalent to the area of ​​all surfaces of the rotating tool T1 overlapping with the workpiece W when viewed in the first direction DR1 multiplied by the feed speed F, and is therefore the diameter Td of the rotating tool T1 multiplied by the feed speed F and the cutting depth Ad.

[0029] In the examples of Figures 6 and 7, the assumed cutting amount V EST is the maximum estimated cutting amount V estimated from the feed direction of the rotary tool T1. limeAssuming that the diameter of the rotating tool T1 is Td, the speed change delay time until the rotating tool T1 comes into contact with the workpiece W and the speed change from the approach speed F' to the feed speed F is Te, and the cutting depth in the rotation axis direction DX (the length of the rotating tool T1 in the rotation axis direction DX that comes into contact with the workpiece W) is Ad, in the case of FIG. 6, the approach speed F' is determined to satisfy (Equation 1). In the case of FIG. 7, the approach speed F' may be determined to satisfy (Equation 1). In reality, in the case of FIG. 7, the approach speed F' can be set higher than (Equation 1) by the amount that the contact area is smaller than that in FIG. 6, but there is no problem because it is determined so that the load on the tool is reduced. This speed change delay time Te is the sum of the detection delay time Te1 from when the rotating tool T1 comes into contact with the workpiece W until the contact with the workpiece W is detected and the lag time Te2 from when the contact with the workpiece W is detected until the speed change from the approach speed F' to the feed speed F is started. In other words, the approach speed F' is determined based on the detection delay time Te1. The hardware processor 3 executing the control program 8 determines the approach speed F' based on the detection delay time Te1. The approach speed F' is determined based on the speed change delay time Te, which is the sum of the detection delay time Te1 and the lag time Te2. The hardware processor 3 executing the control program 8 determines the approach speed F' based on the speed change delay time Te, which is the sum of the detection delay time Te1 and the lag time Te2. The time units of the feed speed F, approach speed F', and speed change delay time Te are the same. In other words, when the feed speed F and approach speed F' are expressed in the unit system of mm / min, the speed change delay time Te is expressed in minutes.

[0030]

number

[0031] The left side of (Equation 1) is the first cutting amount per unit time V F The right side of (Equation 1) is the maximum estimated cutting amount V estimated from the feed direction of the rotary tool T1. lime is equivalent to.

[0032] Deemed cutting amount V EST If is the maximum cutting amount defined in the machining program 7, the approach speed F' in the case of FIG. 6 is determined to satisfy (Equation 2). The approach speed F' in the case of FIG. 7 is determined to satisfy (Equation 3) as an example. The left side of (Equation 2) and (Equation 3) is the first cutting amount V per unit time. F The right-hand sides of (Equation 2) and (Equation 3) correspond to the maximum cutting amount specified in the machining program 7. Since Td” is smaller than Td', the right-hand side of (Equation 3) is smaller than the right-hand side of (Equation 2). When the rotation axis AX1 does not pass through the position of the corner of the workpiece W, the value obtained by multiplying the left-hand side of (Equation 3) by an appropriate coefficient from 1 to 2 according to the positional deviation from the corner is determined as the first cutting amount V. F Alternatively, even when passing through a corner, the calculation may be performed assuming (Equation 2).

[0033]

number

[0034]

number

[0035] In the example of FIG. 8, if the minor axis of the rotating tool T1 is Td1 and the major axis is Td2, the approach speed F' is determined so as to satisfy (Equation 4).

[0036]

number

[0037] The left side of (Equation 4) is the first cutting amount per unit time V F The right side of (Equation 4) is the maximum planned cutting amount V limp In this case, the maximum planned cutting amount V limp Since it is easy to calculate, the maximum estimated cutting amount V estimated from the feed direction of the rotating tool T1 is limeThe maximum planned cutting amount V specified in the machining program 7 can be obtained without calculating limp The assumed cutting amount V EST It is also possible to use the following.

[0038] In the example of FIG. 9, the time delay until the speed change from the approach speed F' to the feed speed F is Te, and the angle between the normal vector (positive direction of the Z axis) of the cutting surface of the workpiece W and the vector in the opposite direction of the first direction DR1 is θ. The volume obtained by multiplying the area of ​​the polka dots in the enlarged view of FIG. 9 (the contact area between the rotating tool T1 and the workpiece W when viewed in the first direction DR1) by the approach speed F' is the first cutting amount V. F The first cutting amount V F is expressed by (Equation 5). Substituting the value of φ shown in FIG. 9 into (Equation 5), we obtain (Equation 6). Note that θ may be regarded as 0, and the approach speed F' may be set to satisfy (Equation 7). In this case, the approach speed F' coincides with the feed speed F defined in the machining program 7.

[0039]

number

[0040]

number

[0041]

number

[0042] The angles in (Equation 5) and (Equation 6) are expressed in radians.

[0043] At this time, the first cutting amount V F is the volume V shown in (Equation 8) lim It is determined as follows: V lim is the maximum planned cutting amount V specified in the machining program 7. limp In this case, the maximum planned cutting amount Vlimp Since it is easy to calculate, the maximum estimated cutting amount V estimated from the feed direction of the rotating tool T1 is lime The maximum planned cutting amount V specified in the machining program 7 can be obtained without calculating limp The assumed cutting amount V EST It is also possible to use the following.

[0044]

number

[0045] 1st cutting amount V F depends on the speed change delay time Te described above. Therefore, the approach speed F' is determined based on the detection delay time Te1. The hardware processor 3 executing the control program 8 determines the approach speed F' based on the detection delay time Te1. The approach speed F' is determined based on the speed change delay time Te, which is the sum of the detection delay time Te1 and the lag time Te2. The hardware processor 3 executing the control program 8 determines the approach speed F' based on the speed change delay time Te, which is the sum of the detection delay time Te1 and the lag time Te2.

[0046] Preferably, the approach speed F′ is a first cutting amount V per unit time at which the rotary tool T1 cuts the workpiece W at the time when the speed change to the feed speed F is started. F is the assumed cutting amount V per unit time when the rotary tool T1 cuts the workpiece W in the first direction DR1 at the feed rate F in the machining program 7. EST In the machining method, the hardware processor 3 executing the control program 8 determines a first cutting amount V per unit time at which the rotary tool T1 cuts the workpiece W at the time when the speed change to the feed speed F is started. F is the assumed cutting amount V per unit time when the rotary tool T1 cuts the workpiece W in the first direction DR1 at the feed rate F in the machining program 7. EST The approach speed F' is determined so as to approximate to the above. Note that the above "approximate" includes the case where the speed is "equal to" the above.

[0047] This is done so that the left and right sides of (Equation 1) to (Equation 4) are roughly equal, and V in (Equation 6) F and V in (Equation 8) lim This means that the approach speed F' is determined so that the left and right sides of (Equation 1) to (Equation 4) are approximately equal. F and V in (Equation 8) lim Since the equations when and are equal cannot usually be solved algebraically, it is preferable to find an approximate solution for F'. Note that the equations when the left and right sides of (Equation 4) and (Equation 7) are made equal can be solved algebraically, but in that case, it is preferable to use the solutions of these equations as the approach speed F'.

[0048] Furthermore, the assumed cutting amount V EST and the first cutting amount V F An approximate solution in which the difference between the two is a positive value closest to 0 can be found by using a search algorithm such as the hill climbing method. At this time, the approach speed F' is determined by selecting the assumed cutting amount V from among multiple candidate speeds. EST From the first cutting amount V F In this machining method, the hardware processor 3 executing the control program 8 selects the assumed cutting amount V from among a plurality of candidate speeds. EST From the first cutting amount V F The approach speed F' is determined as the speed at which the difference between the

[0049] Next, an algorithm for calculating the approach speed F' using the relationship of (Equation 1) in the case of Fig. 6 will be specifically explained with reference to Figs. 14 and 15. Note that approximate solutions for other cases may also be calculated as in Figs. 14 and 15, or by using a known approximate solution calculation algorithm such as the Newton-Raphson method.

[0050] 14, in step S2, in step S21, in the machining method, the hardware processor 3 executing the control program 8 first reads the diameter Td of the rotating tool T1, the feed rate F, the length Ad of the rotating tool T1 in the rotation axis direction DX that contacts the workpiece W, and the speed change delay time Te. The speed change delay time Te is previously obtained as an empirical value and stored in the memory 4. The hardware processor 3 may read the speed change delay time Te from the memory 4. The hardware processor 3 may read the diameter Td of the rotating tool T1 from the tool information stored in the memory 4. The hardware processor 3 may read the feed rate F and the cutting depth Ad from the machining program 7.

[0051] In step S22, the hardware processor 3 executing the control program 8 in the machining method determines whether F·Te is equal to or greater than Td / 2. If F·Te is equal to or greater than Td / 2 (Yes in step S22), in step S23, the hardware processor 3 executing the control program 8 in the machining method sets the approach speed F' to the feed speed F. If F·Te is less than Td / 2 (No in step S22), in step S24, the hardware processor 3 executing the control program 8 in the machining method calculates tempF. This tempF satisfies, for example, the above inequality or magnitude relationship and is equal to or greater than the deemed cutting amount V EST From the first cutting amount V F The approach speed F' is determined so that the value obtained by subtracting

[0052] Fig. 16 is a flowchart detailing step S24. The solution in Fig. 16 is a solution for one approximate solution, and other algorithms for calculating the approximate solution may be used. In step S241 in Fig. 16, the hardware processor 3 executing the control program 8 assigns 1 to the variable ACD. This variable ACD is a variable that is provisionally determined as being switched from the approach speed F' to the feed speed F at a location where the rotating tool T1 has entered the workpiece W by a distance obtained by dividing the radius Td / 2 of the rotating tool T1 by 100 and multiplying it by ACD.

[0053] In step S242, the hardware processor 3 executing the control program 8 calculates the variables CalcuRD, TmF, and JudgeRD based on the following (Equation 9) to (Equation 12), respectively.

[0054]

number

[0055]

number

[0056]

number

[0057] CalcuRD is the width in the direction perpendicular to the rotation axis direction DX when the contact part between the rotating tool T1 and the workpiece W is seen in the first direction DR1 at the place where the rotating tool T1 has entered the workpiece W by a distance obtained by dividing the radius Td / 2 of the rotating tool T1 by 100 and multiplying it by ACD. TmF is the maximum estimated cutting amount V at that place. lime The feed rate is the feed rate when it is assumed that the cutting amount V is 1 / TmF. JudgeRD is the width in the direction perpendicular to the rotation axis direction DX when the contact portion between the rotating tool T1 and the workpiece W is seen in the first direction DR1 at the place where the approach speed F' is switched to the feed rate F when it is assumed that TmF is the approach speed F'. In other words, when JudgeRD is larger than CalcuRD, the first cutting amount VF is the maximum estimated cutting volume V lime means greater than.

[0058] Therefore, in step S243, the hardware processor 3 executing the control program 8 determines whether JudgeRD is equal to or less than CalcuRD. If JudgeRD is greater than CalcuRD (No in step S243), in step S244, the hardware processor 3 executing the control program 8 adds 10 to ACD and executes the process of step S242 again. If JudgeRD is equal to or less than CalcuRD (Yes in step S243), in step S245, the hardware processor 3 executing the control program 8 subtracts 10 from ACD, and in step S246, the hardware processor 3 executing the control program 8 adds 1 to ACD.

[0059] In step S247, the hardware processor 3 executing the control program 8 calculates the variables CalcuRD, TmF, and JudgeRD using (Equation 9) to (Equation 11) based on the changed ACD. In step S248, the hardware processor 3 executing the control program 8 determines whether JudgeRD is equal to or smaller than CalcuRD. When JudgeRD is greater than CalcuRD (No in step S248), in step S249, the hardware processor 3 executing the control program 8 adds 1 to ACD and executes the process of step S247 again. When JudgeRD is equal to or smaller than CalcuRD (Yes in step S248), in step S250, the hardware processor 3 executing the control program 8 determines the value of the variable TmF at this time as tempF. The tempF calculated in this way is the maximum value of tmF that satisfies the following (Equation 12), and therefore satisfies (Equation 1), and is an approximate solution in which the value obtained by subtracting the right side from the left side of (Equation 1) is closest to 0.

[0060]

number

[0061] Returning to FIG. 14, in step S25, the hardware processor 3 executing the control program 8 in the machining method determines whether or not tempF is greater than twice the feed rate F. If tempF is greater than twice the feed rate F (Yes in step S25), in step S26, the hardware processor 3 executing the control program 8 in the machining method determines whether or not the approach speed F' is greater than or equal to twice the feed rate F. In other words, the hardware processor 3 determines whether or not the first cutting amount V F The assumed cutting amount V EST When the approach speed F' is greater than twice the feed speed F when the approach speed F' is approximated (equal to) the first cutting amount V, the approach speed F' is determined to be twice the feed speed F. In other words, in this machining method, the approach speed F' is set to be equal to the first cutting amount V. F The assumed cutting amount V EST When the approach speed F' when approximating (equaling) the feed speed F is greater than twice the feed speed F, it is determined to be twice the feed speed F. In order to prevent a sudden increase in the load on the rotating tool T1, changes in the normal feed speed of the machine tool are also limited to within about twice the feed speed F, and changes in this approach speed F' are also limited to less than twice the feed speed F in accordance with this policy.

[0062] 14 and 15 show a specific approach speed calculation algorithm for the machining method of FIG. 6, but the machining methods of FIGS. 7 to 9 can also be calculated using similar approximate calculations or known approximate calculation algorithms. In addition, in the examples of FIGS. 14 and 15, the maximum estimated cutting amount V lime The cutting amount used is V limp When using this formula, the numerator of the variable TmF should be F·Ad·Td′ (see FIG. 10). Note that the processes in steps S25 to S27 are similarly applied to the processing methods in FIGS. <Features and Effects of the Machining Method of the Machine Tool in the Present Embodiment> The effects of the machine tool 1, its machining method, and its program according to this embodiment will be described. FIG. 16 is a diagram for explaining the effects of the machine tool according to the embodiment. In FIG. 16, the solid line represents the feed rate and the cutting amount per unit time of the machine tool 1 according to the present invention, and the dashed line represents the feed rate and the cutting amount per unit time of the rotary tool of JP-A-57-205013 as a comparative example. Time t0 in FIG. 16 is the time when the rotary tool T1 is placed at the approach point, which is the cutting feed start point set in the machining program 7. t1 is the time when the rotary tool T1 starts to contact the workpiece W. The rotary tool T1 is rotating idly during the time from t0 to t1. t2 is the time when the contact with the workpiece W is detected from the signal of the driver 14D. The time from t1 to t2 corresponds to the detection delay time Te1. t3 is the time when the speed change from the approach speed F' to the feed speed F starts. The time from t2 to t2 corresponds to the lag time Te2. t4 is the time when the feed rate changes to the feed rate F set in the machining program 7.

[0063] In the machine tool 1 and the machining method and program thereof according to this embodiment, the approach speed F′ is a first cutting amount V per unit time at which the rotating tool T1 cuts the workpiece W at the time t3 when the speed change from the approach speed F′ to the feed speed F is started. F is the assumed cutting amount V per unit time when the rotary tool T1 cuts the workpiece W in the first direction DR1 at the feed rate F in the machining program 7. EST More preferably, the first cutting amount V F The assumed cutting amount V EST Therefore, the feed rate and the cutting amount per unit time change as shown by the solid lines in Fig. 16. Therefore, the approach time can be shortened as much as possible while maintaining the tool life assumed by the user when constructing the machining program 7.

[0064] Fig. 16 shows a method of controlling the approach speed shown in Japanese Patent Laid-Open Publication No. 57-205013 as a comparative example with the present invention. The invention shown in Japanese Patent Laid-Open Publication No. 57-205013 aims to shorten the time of the air cutting section as much as reasonably possible, and for that purpose, the power that is the upper limit for tool damage is determined, and the approach speed F" is determined so that it does not exceed the power that is the upper limit for tool damage even when the speed change delay time Te is taken into consideration. More specifically, the approach speed F" is set so that the power at time t3 when the speed change from approach speed F" to feed speed F is started is high enough not to exceed the power that is the upper limit for tool damage. V in Fig. 16 CP This shows the amount of cutting per unit time when the force that causes the tool to break is applied. CP is the assumed cutting volume V EST Furthermore, the feed rate F", which is set so that the power at time t3 does not exceed the upper limit of the power at which the tool breaks, is greater than the approach rate F' required by the machine tool 1, the machining method thereof, and the program according to this embodiment. Therefore, in the invention shown in JP-A-57-205013, although damage to the tool is prevented, there is a risk that the tool life will fall short of what the user assumed when constructing the machining program 7. <Modification> In the above embodiment, the approach speed F′ is the first cutting amount V F The assumed cutting amount V EST The approach speed F' is determined so as not to exceed the first cutting amount V F The assumed cutting amount V EST It may be greater than or equal to a level close to that of the

[0065] For example, the approach speed F' is increased or decreased by a certain value from the initial value, and the assumed cutting amount V EST and the first cutting amount V F The difference between these two is calculated, and an approximate solution that makes this difference closest to 0 is found by using a search algorithm such as the hill climbing method. In this case, the approach speed F' is calculated by selecting the assumed cutting amount V from among multiple candidate speeds (initial value + integer multiple of a fixed value). EST and the first cutting amount VF In the machining method, the hardware processor 3 executing the control program 8 selects the first cutting amount V F Deemed cutting amount V EST The approach speed F' is determined as the speed at which the absolute value of the difference between

[0066] Fig. 17 shows a flowchart showing a modified example of the calculation of the approach speed in step S24 in Fig. 16 when calculating such an approximate solution. This algorithm uses a hill climbing method on the premise that there is only one minimum value of |CalcuRD-JudgeRD| when ACD transitions from 1 to 100. In step S251 in Fig. 17, the hardware processor 3 executing the control program 8 assigns 1 to the variable ACD and assigns Td to the variable tempRD. In step S242, the hardware processor 3 executing the control program 8 calculates the variables CalcuRD, TmF, and JudgeRD based on the above-mentioned (Equation 9) to (Equation 11), respectively.

[0067] In step S253, the hardware processor 3 executing the control program 8 determines whether or not |CalcuRD-JudgeRD| is less than tempRD. When |CalcuRD-JudgeRD| is less than tempRD (Yes in step S253), in step S254, the hardware processor 3 executing the control program 8 assigns |CalcuRD-JudgeRD| to tempRD and assigns TmF to the variable preTmF. In step S254, the hardware processor 3 executing the control program 8 adds 1 to ACD and executes the process of step S242 again. When |CalcuRD-JudgeRD| is equal to or greater than tempRD (No in step S253), in step S256, the hardware processor 3 executing the control program 8 determines the value of the variable preTmF at this time to be tempF. With tempF determined in this manner, the processes of steps S25 to S27 in FIG. 14 may be additionally applied. Even if the approach speed F' is determined in this manner, it is possible to shorten the approach time as much as possible while maintaining the tool life assumed by the user when constructing the machining program 7.

[0068] In the above-described embodiment, an example is shown in which the machine tool 1 is a vertical machining center, but the contents of this embodiment can also be applied to machine tools including horizontal machining centers, lathes, and additive manufacturing devices as long as the machine tool 1 is capable of cutting processing.

[0069] A part or all of the functions of the logic of the control program 8 of the above-mentioned numerical control device 2 may be realized by a dedicated processor or integrated circuit. The above-mentioned control program 8 may be recorded not only in the memory 4 built into the numerical control device 2 but also in a storage medium that is removable from the numerical control device 2 and readable by the numerical control device 2, such as a disk such as a floppy disk, an optical disk, a CD-ROM or a magnetic disk, an SD card, a USB memory, or an external hard disk.

[0070] In this application, the term "comprises" and its derivatives are open-ended terms that describe the presence of elements and do not exclude the presence of other elements not listed. This also applies to the terms "have", "include" and their derivatives.

[0071] The terms "member," "part," "element," "body," and "structure" may have multiple meanings, such as a single part or multiple parts.

[0072] Ordinal numbers such as "first" and "second" are merely terms used to identify components and do not have any other meaning (such as a particular order). For example, the presence of a "first element" does not imply the presence of a "second element," and the presence of a "second element" does not imply the presence of a "first element."

[0073] Words expressing degree, such as "substantially," "about," and "approximately," may mean a reasonable deviation that does not significantly change the final result, unless otherwise specified in the embodiment. All numerical values ​​described in this application may be interpreted to include words such as "substantially," "about," and "approximately."

[0074] In this application, the phrase "at least one of A and B" should be interpreted as including A only, B only, and both A and B.

[0075] It is apparent that various changes and modifications of the present invention are possible in light of the above disclosure, and therefore, the present invention may be practiced otherwise than as specifically disclosed herein without departing from the spirit and scope of the present invention.

Claims

1. The rotating tool is rotated by a motor, Moving the rotary tool in a first direction toward a workpiece at an approach speed that is greater than a feed rate set in a machining program; detecting, based on a load of the motor, that the rotary tool has come into contact with the workpiece while moving in the first direction at the approach speed; When the contact with the workpiece is detected, a speed at which the rotary tool is moved in the first direction is changed to the feed speed. Including, The approach speed is determined so that a first cutting amount per unit time when the rotating tool cuts the workpiece at the time when the speed change is started does not exceed a deemed cutting amount which is deemed to be a cutting amount per unit time when the rotating tool cuts the workpiece in the first direction at the feed speed in the machining program. Method of machining the workpiece.

2. 2. The method for machining a workpiece according to claim 1, wherein the deemed cutting amount is a cutting amount that can be regarded as a theoretical maximum cutting amount per unit time when the rotary tool cuts the workpiece at the feed rate.

3. The method for machining a workpiece according to claim 1 , wherein the assumed cutting amount is a volume equivalent to a value obtained by multiplying an area of ​​a surface of the rotating tool seen in the first direction by the feed rate.

4. A rotation axis of the rotary tool is perpendicular to the first direction, 2. The method for machining a workpiece according to claim 1, wherein the assumed cutting amount is a volume equivalent to a product of an axial cutting amount along the rotation axis of the rotating tool, a diameter of the rotating tool, and the feed rate.

5. the approach speed is determined to be twice the feed speed when the approach speed becomes greater than twice the feed speed when the first cutting amount is made equal to the deemed cutting amount; A method for machining a workpiece according to claim 1.

6. The rotating tool is rotated by a motor, Moving the rotary tool in a first direction toward a workpiece at an approach speed that is greater than a feed rate set in a machining program; detecting, based on a load of the motor, that the rotary tool has come into contact with the workpiece while moving in the first direction at the approach speed; When the contact with the workpiece is detected, a speed at which the rotary tool is moved in the first direction is changed to the feed speed. Including, the approach speed is determined so that a first cutting amount per unit time at which the rotary tool cuts the workpiece at the time when the change in speed is started is approximated to a deemed cutting amount which is deemed to be a cutting amount per unit time when the rotary tool cuts the workpiece in the first direction at the feed speed in the machining program. Method of machining the workpiece.

7. 7. The method for machining a workpiece according to claim 6, wherein the deemed cutting amount is a cutting amount that can be regarded as a theoretical maximum cutting amount per unit time when the rotary tool cuts the workpiece at the feed rate.

8. The approach speed is determined to be a speed among a plurality of candidate speeds, the speed at which an absolute value of a difference between the first cutting amount and the deemed cutting amount is smallest. The method for machining a workpiece according to claim 6 or 7.

9. The approach speed is determined as a speed among a plurality of candidate speeds, the speed at which a difference obtained by subtracting the first cutting amount from the assumed cutting amount is a smallest positive value. The method for machining a workpiece according to claim 6 or 7.

10. the approach speed is determined to be twice the feed speed when the approach speed when the first cutting amount is approximated to the deemed cutting amount is greater than twice the feed speed; The method for machining a workpiece according to claim 6 or 7.

11. The approach speed is determined based on a detection delay time from when the rotating tool comes into contact with the workpiece to when the contact with the workpiece is detected. A method for machining a workpiece according to any one of claims 1 to 7.

12. The approach speed is determined based on a speed change delay time which is the sum of a lag time from when contact with the workpiece is detected until when the speed change from the approach speed to the feed speed is started and the detection delay time. The method for machining a workpiece according to claim 11.

13. A program for causing a processor of a machine tool to execute the workpiece machining method according to any one of claims 1 to 7.

14. a tool spindle configured to rotatably support a rotary tool about a rotation axis; a motor configured to rotate the rotary tool about the axis of rotation; a driver configured to detect a load on the motor; at least one actuator configured to move the tool spindle in a first direction toward a workpiece; a processor configured to receive signals related to the load from the driver and to control the motor and the at least one actuator; Equipped with The processor, controlling the at least one actuator to move the rotary tool in the first direction at an approach speed that is greater than a feed rate set in a machining program; detecting, by the load, that the rotary tool has come into contact with the workpiece while moving in the first direction at the approach speed; When contact with the workpiece is detected, the at least one actuator is controlled to change a speed at which the rotary tool is moved in the first direction to the feed speed; determining the approach speed so that a first cutting amount per unit time when the rotating tool cuts the workpiece at a time point when the speed change is started does not exceed a deemed cutting amount which is deemed to be a cutting amount per unit time when the rotating tool cuts the workpiece in the first direction at the feed speed in the machining program; Machine tools.

15. The machine tool according to claim 14 , wherein the deemed cutting amount is a cutting amount that can be regarded as a theoretical maximum cutting amount per unit time when the rotary tool cuts the workpiece at the feed rate.

16. The machine tool according to claim 14 , wherein the assumed cutting amount is a volume equivalent to a value obtained by multiplying an area of ​​a surface of the rotary tool seen in the first direction by the feed rate.

17. A rotation axis of the rotary tool is perpendicular to the first direction, The machine tool according to claim 14 , wherein the assumed cutting amount is a volume equivalent to a product of an axial cutting amount along the rotation axis of the rotating tool, a diameter of the rotating tool, and the feed rate.

18. when the approach speed when the first cutting amount is equal to the deemed cutting amount is greater than twice the feed speed, the processor determines the approach speed to be twice the feed speed. A machine tool according to any one of claims 14 to 17.

19. a tool spindle configured to rotatably support a rotary tool about a rotation axis; a motor configured to rotate the rotary tool about the axis of rotation; a driver configured to detect a load on the motor; at least one actuator configured to move the tool spindle in a first direction toward a workpiece; a processor configured to receive signals related to the load from the driver and to control the motor and the at least one actuator; Equipped with The processor, controlling the at least one actuator to move the rotary tool in the first direction at an approach speed that is greater than a feed rate set in a machining program; detecting, by the load, that the rotary tool has come into contact with the workpiece while moving in the first direction at the approach speed; When contact with the workpiece is detected, the at least one actuator is controlled to change a speed at which the rotary tool is moved in the first direction to the feed speed; determining the approach speed so that a first cutting amount per unit time at which the rotary tool cuts the workpiece at a time point when the change in speed is started is approximate to a deemed cutting amount which is deemed to be a cutting amount per unit time when the rotary tool cuts the workpiece in the first direction at the feed speed in the machining program; Machine tools.

20. The machine tool according to claim 19 , wherein the deemed cutting amount is a theoretical cutting amount per unit time when a contact area between the rotary tool and the workpiece is maximized.

21. The processor determines the approach speed as a speed among a plurality of candidate speeds, which is a speed at which an absolute value of a difference between the first cutting amount and the assumed cutting amount is smallest.

21. A machine tool according to claim 19 or 20.

22. The processor determines the approach speed as a speed among a plurality of candidate speeds, the speed being a minimum positive value of a difference obtained by subtracting the first cutting amount from the assumed cutting amount.

21. A machine tool according to claim 19 or 20.

23. when the approach speed when the first cutting amount is approximate to the deemed cutting amount is greater than twice the feed speed, the processor determines the approach speed to be twice the feed speed.

21. A machine tool according to claim 19 or 20.

24. The processor determines the approach speed based on a detection delay time from when the rotary tool comes into contact with the workpiece to when the contact with the workpiece is detected.

21. A machine tool according to claim 19 or 20.

25. The processor determines the approach speed based on a speed change delay time that is the sum of a lag time from when contact with the workpiece is detected until when a change in the speed from the approach speed to the feed speed is started and the detection delay time.

25. The machine tool according to claim 24.

Images