Control device for machine tool and control method for machine tool

Abstract

The control device (1) of the machine tool (2) includes an index value calculation unit (14) that calculates a contact index value representing the temporal ratio of the cutting edge of the tool (T) contacting the workpiece (W) during one rotation of the tool for each of a plurality of sets of machining conditions including the relative position of the rotation center of the tool (T) with respect to the geometric center of the tool (T) and the eccentric control frequency, a machining condition setting unit (17) that selects a set of machining conditions based on the calculated contact index value, an eccentric control unit (19) that calculates an eccentric control signal for rotating the geometric center of the tool (T) around the target rotation center based on the target rotation center that is the rotation center included in the selected set of machining conditions and the target eccentric control frequency that is the eccentric control frequency included in the selected set of machining conditions, and a feed axis control unit (11) that drives and controls the feed axis of the tool (T) or the workpiece (W) based on the eccentric control signal.

Description

Technical Field

[0001] The present disclosure relates to a control device for a machine tool and a control method for a machine tool.

Background Art

[0002] A machine tool is a processing device that performs a removal process, which is a process of removing unnecessary portions from a workpiece by applying force or energy to the workpiece using a tool. In particular, in cutting, which is one of the removal processes, shear failure is caused on the workpiece surface by bringing the cutting edge of the tool into contact with the workpiece at high speed, and as a result, unnecessary portions of the workpiece are cut off, enabling the generation of a desired shape. The process in which the cutting edge of the tool penetrates the workpiece and forms a machined surface while generating chips is called a machining process.

[0003] Patent Document 1 discloses a method of superimposing minute vibrations on the feed axis during machining in order to suppress tool vibration. In this method, the operation of the feed drive system is changed so as to cancel out an amount corresponding to the tool vibration amount, thereby equalizing the cutting forces applied to each cutting edge of the tool. According to the machining vibration suppression method of Patent Document 1, an external input device for setting the vibration amount and phase for each cutting edge, an arithmetic device that acquires the tool one-rotation phase and calculates the angular velocity and phase for vibrating the two-axis feed axes of X and Y based on the input vibration amount and angular velocity for each cutting edge, and generates a feed axis control signal, and a numerical control device that controls the X-axis and Y-axis feeds, and the numerical control device relatively vibrates the workpiece in synchronization with the angular velocity of the tool based on the calculation result of the arithmetic device.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the machining vibration suppression method of Patent Document 1, the change in the contact state between the tool and the workpiece due to the change in the operation of the feed drive system was not quantified. In other words, in the method described in Patent Document 1, since the operation pattern of the feed drive system was limited to the operation for canceling the tool runout amount, there was a problem that processing conditions capable of forming a desired processed surface property could not be selected after quantitatively comparing the contact states between the tool and the workpiece in various operations including the operation pattern.

[0006] The present disclosure has been made in view of the above, and an object thereof is to obtain a control device for a machine tool that can quantify the contact state between a tool and a workpiece and select processing conditions capable of forming a desired processed surface property.

Means for Solving the Problems

[0007] In order to solve the above-described problems and achieve the object, for each of a plurality of sets of processing conditions including the relative position of the rotation center of the tool with respect to the geometric center of the tool and the eccentric control frequency, the control device for a machine tool according to the present disclosure of During one rotation period in Of the tool one The time ratio during which the cutting edge contacts the workpiece is the value averaged for all cutting edges An index value calculation unit that calculates a first index value, a processing condition setting unit that selects a set of processing conditions based on the calculated first index value, and a target rotation center that is the rotation center included in a set of processing conditions selected by the processing condition setting unit and a target eccentric control frequency that is the eccentric control frequency included in a set of processing conditions, an eccentric control unit that calculates an eccentric control signal for rotating the geometric center of the tool around the target rotation center, and a feed axis control unit that drives and controls the feed axis of the tool or the workpiece based on the eccentric control signal.

Advantages of the Invention

[0008] According to the control device for a machine tool of the present disclosure, there is an effect that the contact state between the tool and the workpiece can be quantified and processing conditions capable of forming a desired processed surface property can be selected.

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] Hereinafter, a control device for a machine tool and a control method for a machine tool according to an embodiment will be described in detail with reference to the drawings.

[0011] Embodiment FIG. 1 is a block diagram showing a configuration example of a machine tool system including a control device for a machine tool according to an embodiment. The machine tool system includes a machine tool 2 and a control device 1 that controls the machine tool 2.

[0012] The machine tool 2 includes an X-axis drive system 3 as a feed drive system, a Y-axis drive system 4 as a feed drive system, and a spindle drive system 5. Hereinafter, the direction of the central axis of the spindle, in other words, the rotation axis direction of the tool T is defined as the Z-axis direction, and two axial directions perpendicular to the Z-axis direction and perpendicular to each other are defined as the X-axis direction and the Y-axis direction. The X-axis drive system 3 drives the X-axis. The Y-axis drive system 4 drives the Y-axis. The spindle drive system 5 drives the spindle. Each of the X-axis drive system 3 and the Y-axis drive system 4 is composed of a motor and one or more structures connected to the motor. Each of the X-axis drive system 3 and the Y-axis drive system 4 is a servo axis and is composed of, for example, a servo motor, a coupling, a ball screw, and a table. The spindle drive system 5 is composed of, for example, a spindle motor, a gear, a shaft, and a tooling system. The spindle drive system 5 is connected to the X-axis drive system 3 and the Y-axis drive system 4, and the position of the spindle drive system 5 is controlled by the operations of the X-axis drive system 3 and the Y-axis drive system 4. A tool T is attached to the spindle, and the spindle drive system 5 rotates the tool T. The machine tool 2 further includes a table (not shown), and a workpiece W is fixed on the table. The machine tool 2 performs cutting on the workpiece W by controlling the tool T with the X-axis drive system 3, the Y-axis drive system 4, and the spindle drive system 5.

[0013] The motors provided in the X-axis drive system 3, the Y-axis drive system 4, and the spindle drive system 5 each include an encoder that detects a position or an angle. The X-axis drive system 3, the Y-axis drive system 4, and the spindle drive system 5 output their respective encoder signals and motor current signals to the control device 1.

[0014] The control device 1 controls the X-axis drive system 3, the Y-axis drive system 4, and the spindle drive system 5 according to an NC (Numerical Control) program given from the outside or held internally. The control device 1 controls the position, speed, current, etc. of each motor based on each encoder signal. The numerical control device 1 has a processor (not shown) and a memory (not shown), and the operation of the numerical control device 1 is realized by the processor reading and executing a program for executing the operation of the numerical control device 1 stored in the memory.

[0015] The NC program includes a relative position command of a tool or a position command of the X-axis drive system 3 and the Y-axis drive system 4, a spindle rotation speed command, and a feed speed command in a predetermined coordinate system. The above-described coordinate system used in the NC program is called the NC program coordinate system. The NC program coordinate system is, for example, a coordinate system fixed to the workpiece W.

[0016] The control device 1 includes a command generation unit 10, a feed axis control unit 11, a spindle control unit 12, a machining condition storage unit 13, a target value calculation unit 14, a display unit 15, an input unit 16, a machining condition setting unit 17, an initial eccentricity calculation unit 18, and an eccentricity control unit 19.

[0017] The command generation unit 10 analyzes the NC program and calculates the position or angle of each moment that the X-axis drive system 3, the Y-axis drive system 4, and the spindle drive system 5 should realize.

[0018] The feed axis control unit 11 detects the encoder signal and the motor current signal output from the X-axis drive system 3 and the Y-axis drive system 4 according to the position of each moment calculated by the command generation unit 10, and calculates control signals for controlling the position, speed, and current of the X-axis drive system 3 and the Y-axis drive system 4 of the machine tool 2. Further, the feed axis control unit 11 gives an eccentric operation to the X-axis drive system 3 and the Y-axis drive system 4 based on the eccentric control signal calculated by the eccentricity control unit 19. The feed axis control unit 11 outputs the control signal of each moment to the X-axis drive system 3 and the Y-axis drive system 4.

[0019] The spindle control unit 12 calculates control signals for controlling the angle, rotational speed, and current of the spindle drive system 5 of the machine tool 2 while detecting the encoder signal and the motor current signal output from the spindle drive system 5 according to the angle at each moment calculated by the command generation unit 10. The spindle control unit 12 outputs the control signals at each moment to the spindle drive system 5.

[0020] The machining condition storage unit 13 stores one or more sets of machining conditions. The set of machining conditions may be information held internally in advance or information set from the outside.

[0021] The machining conditions will be described with reference to FIGS. 2 to 4. FIG. 2 is a side view showing a state at the moment when the tool T is cutting the workpiece W in the control device 1 of the machine tool 2 according to the embodiment. FIG. 3 is a cross-sectional view showing a state at the moment when the tool T is cutting the workpiece W in the control device 1 of the machine tool 2 according to the embodiment. FIG. 3 shows a cross-section at a certain height with respect to the bottom surface Ta of the tool. The bottom surface Ta of the tool T is shown in FIG. 2. The rotational direction K1 of the tool T and the rotational direction K2 of the geometric center Oa are shown in FIG. 3. In this specification, the height direction corresponds to the Z direction. The X, Y, and Z coordinate axes of the workpiece coordinate system are shown in FIG. 3.

[0022] The machining conditions include the first information to the fourth information shown below, and one set of machining conditions includes at least the first information to the fourth information below.

[0023] The first information is the shape information of the tool T including the number of cutting edges, diameter, and twist angle of the tool T. The number of cutting edges N of the tool T f is the number of cutting edges provided on the tool T. In the case of FIGS. 2 to 4, the number of cutting edges N of the tool T f is 4, and the tool T includes the first cutting edge G1, the second cutting edge G2, the third cutting edge G3, and the fourth cutting edge G4. The twist angle μ is the angle between one cutting edge and the geometric center Oa when viewed from the side of the tool as shown in FIG. 2.

[0024] The second information is the drive information of the machine tool including the spindle rotation speed S and the feed speed F. The spindle rotation speed S is the speed of the rotational movement imparted by the spindle drive system 5 to the tool T. The feed speed F is the moving speed imparted by the X-axis drive system 3 and the Y-axis drive system 4 as the feed drive system to the tool T.

[0025] The third information is the cutting information including the axial cutting depth δz and the radial cutting depth δr. In Fig. 2, the axial cutting depth δz represents the axial length of the tool T within the region where the workpiece W is cut by the tool T. The radial cutting depth δr represents the radial length of the tool T within the region where the workpiece W is cut by the tool T.

[0026] The fourth information is the tool eccentricity control information including the relative position of the rotation center Ob with respect to the geometric center Oa of the tool T and the eccentricity control frequency f ecc as described below. The geometric center Oa is the central axis passing through the centroid of the tool cross-section as shown in Fig. 3, and is the axis unique to the tool T. The rotation center Ob is the center when the geometric center Oa rotates in the tool eccentricity control described below, or the rotation center when the eccentric tool rotates in the normal control. The eccentricity control frequency f ecc as described below is the frequency when the geometric center Oa rotates around the rotation center Ob in the tool eccentricity control described below.

[0027] FIG. 4 is a cross-sectional view showing the positional relationship between the rotation center Ob and the geometric center Oa in the control device 1 of the machine tool 2 according to the embodiment. FIG. 4 shows the position of the rotation center Ob in the tool coordinate system fixed to the tool T with the geometric center Oa as the origin. Here, it is assumed that the rotation angle of the tool T is located at the reference angle of the spindle drive system 5. As shown in FIG. 4, the relative position of the rotation center Ob with respect to the geometric center Oa of the tool T in the tool coordinate system with the geometric center Oa of the tool T as the origin can be determined by the eccentricity distance α, which is the distance between the rotation center Ob and the geometric center Oa, and the eccentricity angle θ, which is the angle of the rotation center Ob with respect to the X-axis of the tool coordinate system. However, the rotation center Ob moves constantly on a circle having a radius corresponding to the eccentricity distance α in the tool coordinate system. Therefore, hereinafter, in order to uniquely represent the position of the rotation center Ob as tool eccentricity control information as a processing condition, the eccentricity distance α and the eccentricity angle θ are used as quantities representing the position of the rotation center Ob at the initial time when the spindle drive system 5 takes the reference angle.

[0028] Here, tool eccentricity, which is a term for explaining the embodiment, will be described. Tool eccentricity refers to a state in which the geometric center Oa of the rotating tool is displaced with respect to the rotation center Ob of the spindle. Tool eccentricity can be distinguished into eccentricity caused by tool eccentricity control described later and eccentricity caused by geometric errors (mounting errors of the tool T or assembly errors of the machine tool).

[0029] Furthermore, tool eccentricity control, which is a term for explaining the embodiments, will be described with reference to FIGS. 5 and 6. FIG. 5 is a diagram showing a state in which a workpiece W is cut while a four-edge tool T makes one rotation in the control device 1 of the machine tool 2 according to the embodiment. FIG. 6 is a diagram showing a state in which a workpiece W is cut while a four-edge tool T makes one rotation in the control device 1 of the machine tool 2 according to the embodiment. In FIG. 5, the geometric center Oa of the tool T coincides with the rotation center Ob, and the locus qa of the geometric center Oa coincides with the locus qb of the rotation center Ob. In FIG. 6, the geometric center Oa of the tool T does not coincide with the rotation center Ob, and the locus qa of the geometric center Oa does not coincide with the locus qb of the rotation center Ob. The tool T cuts the side surface of the workpiece W. FIGS. 5 and 6 show the feed direction β of the tool. In this case, the feed direction β coincides with the X direction.

[0030] In FIG. 5, the geometric center Oa of the tool T is fed along the side surface of the workpiece W. Therefore, the distances between the geometric center Oa of the tool T and the workpiece W at the moments when each cutting edge from the first cutting edge G1 to the fourth cutting edge G4 cuts the workpiece W are equal to each other. In other words, the cutting thicknesses, which are the amounts of cutting of the workpiece W by the first cutting edge G1 to the fourth cutting edge G4, are equal to each other.

[0031] On the other hand, in FIG. 6, the geometric center Oa of the tool T swings with reference to the rotation center Ob. Therefore, the distances between the geometric center Oa of the tool T and the workpiece W at the moments when each cutting edge from the first cutting edge G1 to the fourth cutting edge G4 cuts the workpiece W are different from each other. In the example of FIG. 6, only the first cutting edge G1 and the second cutting edge G2 cut the workpiece W, and their cutting thicknesses are different from each other. Furthermore, since the third cutting edge G3 and the fourth cutting edge G4 do not contact the workpiece W, they do not contribute to cutting.

[0032] When cutting is performed while maintaining a state where the geometric center Oa of the tool T does not coincide with the rotation center Ob, the contact state between the cutting edge and the workpiece W and the cutting thickness by each cutting edge change. The contact state between the cutting edge and the workpiece W and the cutting thickness are determined by the amplitude and frequency of the rocking motion of the geometric center Oa. The rotation angle of the tool T is controlled by the spindle drive system 5, and the position of the geometric center Oa is controlled by the X-axis drive system 3 and the Y-axis drive system 4 which are feed drive systems. Therefore, by controlling the positions of the X-axis drive system 3 and the Y-axis drive system 4 which are feed drive systems while synchronizing with the angle of the spindle drive system 5, a rocking motion with a specific amplitude and frequency can be imparted to the geometric center Oa. Accordingly, the contact state between the cutting edge and the workpiece W and the cutting thickness can be controlled for each cutting edge by the synchronous operation of the spindle drive system 5 and the X-axis drive system 3 and the Y-axis drive system 4 which are feed drive systems.

[0033] Tool eccentricity control is a control method that imparts a motion of rotating at a specific frequency around a specific rotation center Ob to the geometric center Oa of the tool while synchronizing the X-axis drive system 3 and the Y-axis drive system 4 which are feed drive systems with respect to the spindle drive system 5 that rotates the tool T. In other words, tool eccentricity control is a control method that imparts tool runout to the tool T by controlling the X-axis and the Y-axis which are feed axes. Hereinafter, the conventional feed control without tool eccentricity control is referred to as normal control. In tool eccentricity control, when the rotation center Ob and the geometric center Oa coincide, the motion of the tool T is equivalent to normal control.

[0034] Hereinafter, in order to distinguish the eccentricity given by the tool eccentricity control executed by the X-axis drive system 3 and the Y-axis drive system 4 which are feed drive systems from the eccentricity caused by the mounting error of the tool T or the assembly error of the machine tool, the former is called control eccentricity and the latter is called geometric eccentricity. In addition, the rotation center of the former is called the target rotation center, and the rotation center of the latter is called the initial rotation center. Furthermore, a tool T whose initial rotation center does not coincide with the geometric center Oa is called an eccentric tool.

[0035] The relationship between the eccentricity control frequency and the spindle rotation speed in tool eccentricity control will be described using the mathematical formula (1). f eccis the eccentricity control frequency [Hz], n is an integer of 1 or more, f s is the spindle rotation frequency [Hz], N f is the number of tool edges.

[0036]

Equation

[0037] In tool eccentricity control, the eccentricity control frequency f ecc is given by Equation (1). Equation (1) shows that the eccentricity control frequency f ecc is N s times the spindle rotation frequency f f divided by n.

[0038] When n is a divisor of the number of tool edges N f , during one rotation of the tool T, N f / n eccentric motions occur. When n = N f , that is, when the eccentricity control frequency f ecc is equal to the spindle rotation frequency f s , as shown in Fig. 6, one oscillation occurs during one rotation of the tool T. When n = 2, as shown in Fig. 22 to be described later, two oscillations occur. When n is a divisor of the number of tool edges N f , since N f / n is an integer, N f / n oscillations occur during one rotation of the tool T. Therefore, the cutting edge that takes the maximum cutting thickness is always the same regardless of the rotation of the tool. For this reason, when n is a divisor of the number of tool edges N f , it is possible to simulate cutting with a tool T having N f / n tool edges while using a tool T with N f edges.

[0039] On the other hand, when n is a natural number that is not a divisor of the number of tool edges N f , since N f / n is a non-integer, N fThere are n oscillations. Therefore, the cutting edge that takes the maximum cutting amount changes every time the tool T rotates. When the cutting thickness by the j-th cutting edge is maximum when the tool T makes one rotation, the next time the cutting thickness by the j-th cutting edge becomes maximum is after the tool rotates by the number of times equal to the least common multiple of n and N f Since this is the case, when n is a natural number that is not a divisor of the number of tool edges N f Since the cutting load on the cutting edge changes sequentially, tool wear can be made uniform.

[0040] FIG. 7 is a diagram showing an example of a set of machining conditions stored in the machining condition storage unit 13 in the control device 1 of the machine tool 2 according to the embodiment. In FIG. 7, the values of the machining conditions excluding the tool eccentricity control information are fixed values, the eccentricity distance α and the eccentricity angle θ are a plurality of continuous values included within a specific value range, and the eccentricity control frequency f ecc is shown as a plurality of fixed values. Note that the value of each eccentricity control frequency f ecc in FIG. 7 takes the value determined by the mathematical formula (1).

[0041] The index value calculation unit 14 calculates a contact index value SI for each set of machining conditions stored in the machining condition storage unit 13. The contact index value SI, which is the first index value, represents the ratio of the time during which the cutting edge of the tool T contacts the workpiece W during one rotation of the tool T. Specifically, it is a value obtained by averaging, for all cutting edges, the ratio of the time during which one cutting edge contacts the workpiece W within one rotation period of the tool T.

[0042] The contact index value SI can be expressed by the mathematical formula (2). SI is the contact index value, N T is the number of time divisions within one rotation period of the tool T, N ap is the number of divisions when the axial cutting amount δz of the tool T is divided into minute regions, φ t,j,k is the axial cutting amount δz of the tool T divided into N ap pieces, the rotational angle [°] at time t of the j-th blade (j = 1 to N ap ) of the tool cross-section at the height of the k-th (k = 1 to N f ) from the bottom surface Ta of the tool, and H is a binary function for determining whether the cutting edge is in contact with the workpiece W.

[0043]

Number

[0044] Hereinafter, the calculation process of the contact index value SI by the mathematical formula (2) will be described. Using FIGS. 8 to 11, the contact determination between the cutting edge and the workpiece W in the contact determination function H will be described. FIG. 8 is a cross-sectional view showing the positional relationship between the j-th cutting edge Gj, which is the j-th cutting edge in the case where the geometric center Oa and the rotation center Ob coincide with each other in the control device 1 of the machine tool 2 according to the embodiment, and the workpiece W. FIG. 9 is a cross-sectional view showing the positional relationship between the j-th cutting edge Gj, which is the j-th cutting edge in the case where the geometric center Oa and the rotation center Ob coincide with each other in the control device 1 of the machine tool 2 according to the embodiment, and the workpiece W. In FIG. 8, the rotation angle of the cutting edge is between the engagement angle εe and the disengagement angle εde. In FIG. 9, the rotation angle of the cutting edge is not between the engagement angle εe and the disengagement angle εde. The engagement angle εe and the disengagement angle εde are values determined by the diameter of the tool T and the radial cutting amount. The engagement angle εe is the angle at which the cutting edge of the tool T penetrates the workpiece W, and the disengagement angle εde is the angle at which the cutting edge of the tool T detaches from the workpiece W. For the sake of explanation, in FIGS. 8 and 9, the engagement angle εe and the disengagement angle εde are shown based on the Y-axis of the coordinate system fixed to the machine tool 2.

[0045] As shown in FIG. 8, if the j-th cutting edge and the workpiece W are in contact with each other in a state where the rotation angle of the j-th cutting edge is within the range of the engagement angle εe and the disengagement angle εde, cutting by the j-th cutting edge Gj is possible. However, even if the rotation angle of the cutting edge is within the range of the engagement angle εe and the disengagement angle εde, the cutting edge and the workpiece W do not always contact. The reason will be explained with reference to FIGS. 10 and 11.

[0046] FIG. 10 is a cross-sectional view showing the positional relationship between the j-th cutting edge Gj, which is the j-th cutting edge of the tool T with four cutting edges shown in FIGS. 10 and 11, and the workpiece W when the geometric center Oa and the rotation center Ob do not coincide in the control device 1 of the machine tool 2 according to the embodiment. FIG. 11 is a cross-sectional view showing the positional relationship between the (j + 2)-th cutting edge Gj+2, which is the (j + 2)-th cutting edge of the tool T with four cutting edges shown in FIGS. 10 and 11, and the workpiece W when the geometric center Oa and the rotation center Ob do not coincide in the control device 1 of the machine tool 2 according to the embodiment. In FIGS. 10 and 11, the rotational angle of the cutting edge is between the engagement angle εe and the disengagement angle εde. In the four-edge tool T shown in FIGS. 10 and 11, the rotational radius of the j-th cutting edge Gj is longer than those of the other three cutting edges, and the rotational radius of the (j + 2)-th cutting edge Gj+2 is shorter than those of the other three cutting edges. The rotational radius is the distance between the rotation center Ob and the cutting edge.

[0047] In FIGS. 10 and 11, the rotational angles of the j-th cutting edge Gj and the (j + 2)-th cutting edge Gj+2 are each between the engagement angle εe and the disengagement angle εde. However, as shown in FIG. 10, the j-th cutting edge Gj contacts the workpiece W, while as shown in FIG. 11, the (j + 2)-th cutting edge Gj+2 does not contact the workpiece W. This is because, as shown in FIGS. 10 and 11, in the tool T with eccentricity, the cutting thickness, which is the thickness of the chips removed from the workpiece W by each cutting edge, is different from each other. In the tool T as shown in FIGS. 10 and 11, the cutting thickness of the j-th cutting edge can be calculated by Equation (3). h t,j,k is the cutting thickness [mm] of the j-th cutting edge at time t, p is the feed per edge [mm], and Δr j,k represents the variation due to eccentricity [mm] of the j-th cutting edge at time t, and Δr j-1,k represents the variation due to eccentricity [mm] of the (j - 1)-th cutting edge at time t.

[0048]

Equation

[0049] In Equation (3), the feed per edge p is a value determined by Equation (4). Δr in Equation (3)j,k is the amount obtained by projecting the position vector from the geometric center Oa to the rotation center Ob in the rotational angle direction of the j-th cutting edge. The definition of k included in Equation (3) is the same as k in Equation (2). S is the spindle rotational speed [min -1 , and S = 60f s . F is the feed rate [mm / min].

[0050]

Number

[0051] In addition to the examples shown in FIGS. 10 and 11, even when the geometric center Oa coincides with the rotation center Ob, when the tool T or the workpiece W vibrates, the relative position between the tool T and the workpiece W fluctuates, so the cutting edge may instantaneously separate from the workpiece W. By using the method described in International Publication No. 2019 / 043852, it is possible to calculate the cutting thickness considering the vibration of the tool T or the workpiece W when the tool T and the workpiece W are in contact.

[0052] Therefore, the determination by the contact determination function H, which is a binary function, is performed based on the sign (+, -, 0) of the cutting thickness by the cutting edge when the cutting edge is between the engagement angle εe and the disengagement angle εde. In other words, if the cutting thickness, which is the thickness of the chips removed from the workpiece W by one cutting edge, is a positive value +, the contact determination function H returns 1, and if the cutting thickness is 0 or a negative value -, the contact determination function H returns 0.

[0053] On the other hand, in the case shown in FIG. 9, the rotational angle of the j-th cutting edge Gj is not between the engagement angle εe and the disengagement angle εde. In this case, since there is no contact between the j-th cutting edge Gj and the workpiece W, the contact determination function H returns 0.

[0054] Note that for the tool T having the twist angle μ, the arrangement angle of the cutting edge varies according to the height from the tool bottom surface Ta. For all the minute cross-sections included between the height of the axial cutting amount δz from the tool bottom surface Ta (see Fig. 2), by using the same method as described above, the contact between the j-th cutting edge and the workpiece W can be determined. The sum of these determination results is divided by N, which is the number of divisions of the axial cutting amount δz ap to calculate the average contact state between the j-th cutting edge and the workpiece W at a certain time t. Further, by applying this method to all the cutting edges provided on the tool T, the average contact state between the tool T and the workpiece W at a certain time can be calculated. By calculating the average values obtained here at each time within one rotation time of the tool and calculating their temporal average values, the contact index value SI shown in the formula (2) can be calculated

[0055] The display unit 15 displays the contact index value SI calculated by the index value calculation unit 14 in association with the set of machining conditions. The display unit 15 may be configured to be directly installed on the machine tool 2, or may be configured to be installed remotely from the machine tool 2 through wired or wireless communication means

[0056] An example of the display of the contact index value SI by the display unit 15 will be described with reference to FIGS. 12 to 20. FIG. 12 is a diagram showing a first display example of the contact index value SI in the control device 1 of the machine tool 2 according to the embodiment. FIG. 13 is a cross-sectional view showing the initial position of the rotation center when the first display example of FIG. 12 is displayed in the control device 1 of the machine tool 2 according to the embodiment. FIG. 14 is a diagram showing a second display example of the contact index value SI in the control device 1 of the machine tool 2 according to the embodiment. FIG. 15 is a cross-sectional view showing the position of the rotation center when the second display example of FIG. 14 is displayed in the control device 1 of the machine tool 2 according to the embodiment. The XT and YT coordinates of the rotation center Ob1 in FIG. 12 and the XT and YT coordinates of the rotation center Ob1 in FIG. 13 are the same. In FIG. 12, in FIG. 7, the eccentricity control frequency f eccWhen it is = 41.7 Hz (when n = 4 in Equation (1)), the contact index values SI corresponding to all combinations of the eccentricity distance α (0.0 to 0.1 mm) and the eccentric angle θ (0° to 360°) in FIG. 7 are represented in a contour line form. FIG. 12 shows the XT and YT coordinates fixed to the tool T with the origin being the geometric center Oa of the tool T.

[0057] Note that the rotation centers Ob1 to Ob4 rotate within the tool coordinate system around Ob0 as time elapses. In the eccentricity control, the eccentricity control frequency f ecc Once the eccentricity control frequency f, the eccentricity distance α, and the eccentric angle θ at the initial time are determined, the movement of the rotation center Ob of the tool coordinate system can be uniquely determined. Therefore, once the eccentricity distance α1 and the eccentric angle θ1 at the initial time are determined, the contact index values SI corresponding to the rotation centers Ob1 to Ob4 can be calculated. FIG. 12 can be said to be a diagram represented in a contour line form when the eccentricity control frequency f ecc = f s is determined.

[0058] The contour lines a to f in FIG. 12 are lines connecting points with the same contact index value SI within the XY coordinate system. The contact index values SI of the contour lines a to f are 0.14, 0.12, 0.10, 0.08, 0.06, and 0.04 respectively. In FIG. 12, the closer to the origin of the coordinate system, the higher the contact index value SI. This indicates that the closer the rotation center Ob of the tool T is to the geometric center Oa, the longer the average time the cutting edge contacts the workpiece W within one rotation period of the tool T. On the other hand, the farther away from the origin of the coordinate system, the lower the contact index value SI, and furthermore, the shape of the contour line deviates from a circular shape. For non-circular contour lines, even if the eccentricity distance α is the same, the contact index value SI is different when the eccentric angle θ is different. This is because in the four-edge tool T as shown in FIG. 13, the cutting edges are arranged every 90°, so there are cases where the value of the eccentric angle θ is close to and far from the cutting edge angle. Such magnitudes of the contact index value SI correspond to different calculation results of the contact determination function H in Equation (2) depending on the selection of the position of the rotation center Ob. The reason for the magnitudes of the contact index value SI will be explained using FIG. 16.

[0059] FIG. 16 is a diagram in which, in the control device 1 of the machine tool 2 according to the embodiment, the number of cutting edges of the tool bottom surface Ta that contacts the workpiece W during one rotation of the tool T is classified for each position of the rotation center. In FIG. 16, a classification diagram is shown in the coordinate system fixed to the tool T. FIG. 17 is a diagram in the control device 1 of the machine tool 2 according to the embodiment, showing each divided region, the number of cutting edges of the tool bottom surface Ta that contacts the workpiece W during one rotation of the tool T, and the ratio of the cutting edges of the tool bottom surface Ta that contacts the workpiece W during one rotation of the tool T. In FIG. 16, region A indicates that the rotation center is close to the geometric center Oa. At this time, as shown in FIG. 17, in region A, all 4 cutting edges of the tool bottom surface Ta contact the workpiece W. The number of cutting edges that contact the workpiece W is 3 in region B, 2 in region C, and 1 in region D. That is, the larger the eccentricity distance α, the smaller the number of cutting edges that contact the workpiece W during one rotation of the tool T. Therefore, the contact index value SI corresponds to the number of cutting edges that contact the workpiece W. Note that for the tool T having the twist angle μ, the arrangement angle of the cutting edges is different according to the height from the tool bottom surface Ta. As shown by the formula (2), the contact index value SI is a value obtained by averaging the contact time of the cutting edges along the tool axis direction. Therefore, FIG. 12 represents the contact index value SI for each position of the rotation center Ob1, and it can also be said that it is a value obtained by averaging the ratio of the cutting edges that contact the workpiece W along the tool axis direction.

[0060] Return to the description of FIG. 12. In FIG. 12, the position of the specific rotation center Ob1 at the initial time is illustrated by the marker M1. The position of the rotation center Ob1 is on the contour line c. The initial position of the rotation center Ob1 corresponds to the eccentricity distance α1 and the eccentricity angle θ1 at the initial time in the tool coordinate system in FIG. 13. Therefore, FIG. 12 displays the contact index value SI when the position of the rotation center Ob1 at the initial time is the position shown in FIG. 13.

[0061] As shown in FIG. 14, by illustrating a plurality of markers M0 to M4, the contact index values SI corresponding to the plurality of rotation centers Ob0 to Ob4 can be compared. In FIG. 14, the contact index values SI of the contour lines a to f are 0.14, 0.12, 0.10, 0.08, 0.06, and 0.04, respectively, similar to FIG. 12.

[0062] FIGS. 12 and 14 show the eccentricity control frequency f ecc = 41.7 Hz, which is equal to the spindle rotation speed of 2500 min -1 (= 41.7 Hz), and is an example of the display of the contact index value SI. FIG. 18 is a diagram showing a third display example of the contact index value SI in the control device 1 of the machine tool 2 according to the embodiment. FIG. 18 is a contour map of the contact index value SI when the eccentricity control frequency f ecc is 33.3 Hz (when n = 5 in Equation (1)). FIG. 19 is a diagram showing a fourth display example of the contact index value SI in the control device 1 of the machine tool 2 according to the embodiment. FIG. 19 is a contour map of the contact index value SI when the eccentricity control frequency f ecc is 27.8 Hz (when n = 6 in Equation (1)). In FIGS. 18 and 19, the contact index values SI of the contour lines a to f are 0.14, 0.12, 0.10, 0.08, 0.06, and 0.04, respectively, similar to FIG. 12. As can be seen from the above, when the value of the eccentricity control frequency f ecc is different, the pattern of the contour line changes. Therefore, even if the rotation center Ob is the same, by changing the eccentricity control frequency f ecc , the contact index value SI changes. This tendency is particularly prominent when the rotation center Ob is far from the geometric center Oa.

[0063] The display unit 15 executes the same display control as described above for other eccentricity control frequencies included in the tool eccentricity control information of FIG. 7, that is, the eccentricity control frequencies f ecc = 166.7 Hz, 83.3 Hz, 55.6 Hz, 23.8 Hz, 20.8 Hz. FIG. 20 is a diagram showing a fifth display example of the contact index value SI in the control device 1 of the machine tool 2 according to the embodiment. FIG. 20 shows the eccentricity control frequency f eccIt is a contour map of the contact index value SI when it is 83.3 Hz (when n = 2 in Equation (1)). FIG. 20 shows the contact index value SI for each position of the rotation center Ob5.

[0064] Furthermore, the display unit 15 can display a marker corresponding to the machining conditions selected by the machining condition setting unit 17 described later within the contour map. Thereby, the operator or the external system can modify the machining conditions with reference to the machining conditions selected by the machining condition setting unit 17.

[0065] When illustrating the contact index value SI, the eccentricity α may be normalized using the feed per tooth p calculated by Equation (4). By normalizing the eccentricity α, the contact index value SI can be illustrated on the same scale even when the values of machining conditions such as the axial depth of cut δz, the radial depth of cut δr, and the feed per tooth p are different. Therefore, the operator can easily compare a plurality of display diagrams.

[0066] Also, when illustrating the contact index value SI in each figure, the contact index value SI may be normalized using the maximum value of the contact index value SI in each figure. The maximum value is the contact index value SI at the center of each figure and corresponds to the contact index value SI during normal control. By normalizing the contact index value SI, the magnitude of the contact index value SI at the position of each rotation center Ob can be evaluated based on the contact index value SI during normal control. Therefore, the operator can easily discriminate the change in the contact index value SI due to eccentricity control.

[0067] In the above, an example of displaying the contact index value SI in the form of a two-dimensional contour map has been described, but the display method of the display unit 15 is not limited to the above. Instead of the two-dimensional contour map, a three-dimensional contour map, a two-dimensional color map, or the like may be adopted, or a table format may be adopted.

[0068] The input unit 16 receives the input of machining conditions from the operator or an external management system. The input unit 16 may be configured to be directly installed on the machine tool 2, or may be configured to be installed remotely from the machine tool 2 through wired or wireless communication means. When the input unit 16 receives an input from the outside, it transmits an input signal to the machining condition setting unit 17.

[0069] Based on the contact index value SI, the machining condition setting unit 17 selects a set of machining conditions from one or more sets of machining conditions stored in the machining condition storage unit 13 and transmits it to the eccentricity control unit 19. However, when the input unit 16 receives an external input, the machining condition setting unit 17 transmits the value of the machining conditions input to the input unit 16 to the eccentricity control unit 19.

[0070] Below, among the machining conditions described in FIG. 7, the position of the rotation center Ob composed of the eccentricity distance λ and the eccentricity angle θ, and the eccentricity control frequency f ecc The selection method will be described.

[0071] FIGS. 21, 22, and 23 show the operations of the tool T when the combinations of the position of the rotation center Ob and the eccentricity control frequency f ecc are different. In FIGS. 21, 22, and 23, the machining conditions other than the combination of the position of the rotation center Ob and the eccentricity control frequency f ecc are common.

[0072] FIG. 21 is a diagram showing a first example in which the four-edge tool T cuts the workpiece W during one rotation in the control device 1 of the machine tool 2 according to the embodiment. In FIG. 21, the geometric center Oa rotates around the rotation center Ob0 (contact index value SI = 0.14) in FIG. 14. Since the rotation center Ob0 coincides with the geometric center Oa, the cutting thicknesses by the first blade G1 to the fourth blade G4 are all equal. That is, in FIG. 21, no control eccentricity occurs, and the tool T operates in the same manner as the normal control.

[0073] FIG. 22 is a diagram showing a second example of cutting the workpiece W while the four-edge tool T makes one revolution in the control device 1 of the machine tool 2 according to the embodiment. In FIG. 22, around the rotation center Ob4 (contact index value SI = 0.06) in FIG. 14, the geometric center Oa rotates at an eccentric control frequency f ecc = 41.7 Hz (when n = 4 in Equation (1)). The eccentric control frequency f ecc in FIG. 22 is equal to the spindle rotation speed. Further, the rotation center Ob4 is located on the contour line with a low contact index value SI as shown in FIG. 14. Therefore, in FIG. 22, the cutting edges of the tool T are the third edge G3 and the fourth edge G4, which are two consecutive edges, and are in contact with the workpiece W.

[0074] FIG. 23 is a diagram showing a third example of cutting the workpiece W while the four-edge tool T makes one revolution in the control device 1 of the machine tool 2 according to the embodiment. In FIG. 23, around the rotation center Ob5 (contact index value SI = 0.06) in FIG. 20, the geometric center Oa rotates at an eccentric control frequency f ecc = 83.3 Hz (when n = 2 in Equation (1)). The eccentric control frequency f ecc in FIG. 23 is twice the spindle rotation speed. Therefore, in FIG. 23, the oscillation frequency of the geometric center Oa is twice that of FIG. 22. In FIG. 23, among the four cutting edges, the first edge G1 and the third edge G3, which are two opposing cutting edges, cut the workpiece W. Therefore, in FIG. 23, the cutting when using a two-edge tool in a four-edge tool is realized.

[0075] Comparing FIGS. 21 to 23, in the case of the rotation center Ob0 where the contact index value SI is 0.14, all four cutting edges cut the workpiece W, and in the case of the rotation centers Ob4 and Ob5 where the contact index value SI is 0.06, two cutting edges cut the workpiece W. That is, by changing the combination of the position of the rotation center Ob and the eccentric control frequency f ecc , the number of cutting edges contributing to cutting can be changed. And the magnitude of the contact index value SI changes according to the combination of the position of the rotation center Ob and the eccentric control frequency f ecc . In other words, the position of the rotation center Ob and the eccentric control frequency fecc The combination corresponds to the magnitude of the contact index value SI.

[0076] The machining condition setting unit 17 selects, based on the contact index value SI, the combination of the position of the rotation center Ob and the eccentricity control frequency f that satisfies the requirements for the machining surface properties defined for the workpiece W. The requirements for the machining surface properties are, for example, the machining surface roughness, the uniformity of the cutter marks, or the pitch of the cutter marks. ecc When the requirement for the machining surface properties is the machining surface roughness, the machining condition setting unit 17 selects the combination of the position of the rotation center Ob and the eccentricity control frequency f at which the vibration amplitude between the tool T and the workpiece W does not diverge. As described above, the contact index value SI represents the time ratio of the contact of the cutting edge during one rotation of the tool T. That is, the larger the contact index value SI, the larger the time ratio during which the cutting force between the tool T and the workpiece W vibrates the tool T and the workpiece W during one rotation of the tool T. Therefore, the larger the contact index value SI, the larger the amplitude between the tool T and the workpiece W. Thus, the machining condition setting unit 17 selects, from the sets of machining conditions stored in the machining condition storage unit 13, the sets of machining conditions that are less than the threshold value Th. The threshold value Th represents the limit contact index value SI at which the vibration between the tool T and the workpiece W does not diverge. The threshold value Th can be determined in advance by performing cutting simulations a plurality of times using a known method described in a reference (Kazuki Takahei, Norikazu Suzuki, Eiji Shamoto “Identification of the model parameter for milling process simulation with sensor-integrated disturbance observer” Precision Engineering, vol. 78, pp. 146 - 162, November 2022) or the like.

[0077] When the requirement for the machining surface properties is the machining surface roughness, the machining condition setting unit 17 selects the combination of the position of the rotation center Ob and the eccentricity control frequency f at which the vibration amplitude between the tool T and the workpiece W does not diverge. ecc As described above, the contact index value SI represents the time ratio of the contact of the cutting edge during one rotation of the tool T. That is, the larger the contact index value SI, the larger the time ratio during which the cutting force between the tool T and the workpiece W vibrates the tool T and the workpiece W during one rotation of the tool T. Therefore, the larger the contact index value SI, the larger the amplitude between the tool T and the workpiece W. Thus, the machining condition setting unit 17 selects, from the sets of machining conditions stored in the machining condition storage unit 13, the sets of machining conditions that are less than the threshold value Th. The threshold value Th represents the limit contact index value SI at which the vibration between the tool T and the workpiece W does not diverge. The threshold value Th can be determined in advance by performing cutting simulations a plurality of times using a known method described in a reference (Kazuki Takahei, Norikazu Suzuki, Eiji Shamoto “Identification of the model parameter for milling process simulation with sensor-integrated disturbance observer” Precision Engineering, vol. 78, pp. 146 - 162, November 2022) or the like.

[0078] For example, when the specific cutting resistance between the tool T and the workpiece W is 1700 MPa, the tool T is a rigid body, and the dynamics of the workpiece W can be expressed by a set of modal parameters consisting of a natural frequency of 534 Hz, a damping ratio of 0.015, and a maximum compliance of 2.09 μm / N, chatter vibration occurs under the set of machining conditions in Fig. 21 (when machining at the rotation center Ob0 where the contact index value SI is 0.14). That is, in the case of normal control, chatter vibration occurs.

[0079] On the other hand, chatter vibration does not occur under the set of machining conditions in Fig. 22 (when machining with a combination of the rotation center Ob4 where the contact index value SI is 0.06 and an eccentricity control frequency of 41.7 Hz) and the set of machining conditions in Fig. 23 (when machining with a combination of the rotation center Ob5 where the contact index value SI is 0.06 and an eccentricity control frequency of 83.3 Hz). That is, in the case of tool eccentricity control, chatter vibration does not occur. Thus, in the display examples of the contact index value SI shown in Figs. 12, 14, 18 to 20, the threshold Th can be set to 0.06 or less. Therefore, the machining conditions that satisfy the requirements for the machined surface properties are the combination of the position of the rotation center Ob where the contact index value SI is 0.06 or less and the eccentricity control frequency f ecc and.

[0080] Note that when there are multiple combinations of the position of the rotation center Ob and the eccentricity control frequency f that satisfy the requirements for the machined surface properties, the machining condition setting unit 17 selects the combination that includes the position of the rotation center Ob with the minimum eccentricity distance α among the multiple combinations of the position of the rotation center Ob and the eccentricity control frequency f ecc and. By selecting the minimum eccentricity distance α, the power consumption required for tool eccentricity control by the feed drive system can be minimized. ecc Furthermore, in addition to the above requirements, the machining condition setting unit 17 can select combinations of the position of the rotation center Ob and the eccentricity control frequency f corresponding to contact index values SI that satisfy different requirements. For example, when the uniformity of the cutter marks is added to the requirements for the machined surface roughness in addition to the machined surface roughness, the machining condition setting unit 17 sets n to the number of tool edges N in Equation (1)

[0081] and. ecc and. fThe eccentric control frequency f when it is an integer that is not a divisor of ecc is selected. Here, the uniformity of the cutter marks means that the same cutter marks are continuously formed while preventing vibrations and tool wear between the tool T and the workpiece W.

[0082] Hereinafter, the case where the specific cutting resistance ratio between the tool T and the workpiece W is the above-mentioned value of 1700 MPa and the dynamics of the workpiece W can be expressed by the above-mentioned set of modal parameters will be described. As described above, when cutting the workpiece W with normal control of the rotation center Ob0, chatter vibration occurs. Therefore, the cutter marks cannot be made uniform under normal control. On the other hand, when cutting the workpiece W with eccentric control of the rotation center Ob4 or the rotation center Ob5, the load is concentrated only on the cutting edge to be cut. Therefore, if machining is continued for a long time, the wear of the cutting edge to be cut may progress. When n is an integer that is not a divisor of the number of tool edges N f since the cutting load on the cutting edges is sequentially switched, the cutting load on each cutting edge can be made uniform. For this reason, the machining condition setting unit 17, when n is an integer that is not a divisor of the number of tool edges N f selects the rotation center Ob that gives a contact index value SI of 0.06 or less that satisfies the requirements of the machined surface roughness among the eccentric control frequencies f ecc In this way, vibrations and tool wear between the tool T and the workpiece W can be prevented.

[0083] As another example, when the requirement for the machined surface property is the pitch of the cutter marks, the machining condition setting unit 17 determines the position of the rotation center Ob and the eccentric control frequency f ecc such that the pitch of the cutter marks becomes the specified value. Here, the pitch of the cutter marks is the interval between the cutting edges that have performed cutting. Under the machining conditions shown in FIG. 7, the feed per tooth is 0.05 mm based on Equation (3). When 0.10 mm is specified as the pitch of the cutter marks according to the requirements of the machined surface property, the machining condition setting unit 17 sets the eccentric control frequency f such that n = 2 in Equation (1) eccSelect. For example, when performing eccentric control around the rotation center Ob5 in FIG. 20, two swings occur during one rotation of the tool as shown in FIG. 23. That is, the number of times the cutting edge contacts the workpiece W is once every two times. Therefore, by tool eccentric control, the pitch of the cutter marks can be made 0.10 mm. In the region where the contact index value SI in FIG. 20 is 0.06 or less, the cutting edge contacts the workpiece W at intervals of once every two times as in the example of FIG. 20. Therefore, the machining condition setting unit 17 selects the rotation center Ob with the minimum eccentricity distance α from among the contact index values SI of 0.06 or less in FIG. 20.

[0084] As described above, the machining condition setting unit 17 determines the position of the rotation center Ob and the eccentric control frequency f based on the contact index value SI according to the requirements of the machined surface properties. ecc and selects a combination. Note that the requirements for the machined surface properties are not limited to the above three examples and can be appropriately changed according to the workpiece W. Hereinafter, the machining conditions selected by the machining condition setting unit 17 are referred to as target machining conditions. Further, the rotation center selected by the machining condition setting unit 17 is called the target rotation center Ob', and the eccentric control frequency f ecc selected by the machining condition setting unit 17 is called the target eccentric control frequency f ecc '.

[0085] The initial eccentricity calculation unit 18 calculates the relative position of the initial rotation center Ob with respect to the geometric center Oa of the tool T. The relative position of the initial rotation center Ob can be calculated by using the measurement results of tool runout or machining surface displacement. As shown in FIG. 6, the tool runout or machining surface displacement at each moment represents the oscillation of the geometric center Oa. By using a numerical solution method such as the least squares method to calculate the eccentricity distance Δr0, which is the eccentricity α of the initial rotation center Ob, and the eccentricity angle θ0, which is the eccentricity angle θ of the initial rotation center Ob, that satisfy the following formula (5) from the positions of a plurality of sets of geometric centers Oa, the position of the initial rotation center Ob with respect to the geometric center Oa can be obtained. In formula (5), x(t) and y(t) represent the position [mm] of the geometric center Oa in the workpiece coordinate system, X0(t) and Y0(t) represent the position [mm] of the initial rotation center Ob in the workpiece coordinate system, t represents time [s], Ω represents the spindle angular velocity [rad / s], Δr0 represents the eccentricity distance α of the initial rotation center Ob, and θ0 represents the eccentricity angle θ of the initial rotation center Ob.

[0086]

Number

[0087] As another method, by using the parameter identification method shown in the above-mentioned reference, the position of the initial rotation center Ob can be estimated based on in-process data without the need for prior measurement work.

[0088] The eccentricity control unit 19 calculates an eccentricity control signal synchronized with the feed axis control unit 11 and the spindle control unit 12 based on the position of the target rotation center Ob' selected by the machining condition setting unit 17 and the target eccentricity control frequency f ecc '. When there is no geometric eccentricity (when the initial rotation center Ob coincides with the geometric center Oa), the positional relationship between the geometric center Oa and the target rotation center Ob' can be expressed by formula (6). In this case, the eccentricity control signal corresponds to the second term of formula (6). In formula (6), x(t) and y(t) represent the position [mm] of the geometric center Oa in the workpiece coordinate system, X ecc (t), Y ecc (t) represent the position [mm] of the target rotation center Ob' in the workpiece coordinate system, Δr eccis the eccentricity distance α, f from the target rotation center Ob’ ecc is the target eccentricity control frequency, θ ecc represents the eccentricity angle θ of the target rotation center Ob’.

[0089]

Equation

[0090] On the other hand, when geometric eccentricity exists, the eccentricity control unit 19 performs compensation to cancel out the geometric eccentricity caused by the initial rotation center Ob. Specifically, the second and third terms of Equation (7) obtained by combining Equation (5) and Equation (6) are calculated as the eccentricity control signal. Therefore, when the tool originally has eccentricity, eccentricity control can be performed around the target rotation center Ob’ after compensating for the eccentricity.

[0091]

Equation

[0092] Note that when the target rotation center Ob’ coincides with the geometric center Oa, the eccentricity distance α of the target rotation center Ob’ is 0. Therefore, in any of the above cases, the tool eccentricity control is equivalent to the normal control.

[0093] Next, the operation of the control device 1 according to the embodiment will be described with reference to FIG. 24. FIG. 24 is a flowchart showing the operation of the control device 1 of the machine tool 2 according to the embodiment. In step S101, the index value calculation unit 14 calculates the contact index value SI for each set of machining conditions described in the machining condition storage unit 13. In step S102, the display unit 15 displays the contact index value SI. In step S103, when the input unit 16 receives an input of machining conditions from the operator or an external system, it proceeds to step S104. If no input is received, it proceeds to step S105.

[0094] In step S104, the machining condition setting unit 17 sets the machining conditions input from the outside as the target machining conditions. In step S105, the machining condition setting unit 17 selects the machining conditions based on the magnitude of the contact index value SI in accordance with the requirements of the machined surface properties. In step S106, the machining condition setting unit 17 sets the selected machining conditions as the target machining conditions.

[0095] In step S107, the initial eccentricity calculation unit 18 calculates the position of the initial rotation center Ob. In step S108, the eccentricity control unit 19 generates an eccentricity control signal for the X-axis drive system 3 and the Y-axis drive system 4, which are the feed drive systems, in accordance with the target machining conditions. In step S109, the feed axis control unit 11 executes eccentricity control in accordance with the eccentricity control signal and controls the positions of the X-axis drive system 3 and the Y-axis drive system 4, which are the feed drive systems, at each moment.

[0096] According to the embodiment in this way, the control device 1 calculates the contact index value SI representing the temporal ratio of the contact between the tool T and the workpiece W for a set of machining conditions, and displays it in association with the set of machining conditions. With this configuration, the operator or the external system can quantitatively evaluate the temporal ratio of the contact between the tool T and the workpiece W for each set of machining conditions. Further, the control device 1 can select a set of machining conditions that satisfy the requirements of the machined surface properties based on the contact index value SI.

[0097] Furthermore, the control device 1 is configured to apply controlled eccentricity to the tool T in accordance with the target machining conditions. With this configuration, the control device 1 can form a machined surface property according to the requirements. In particular, the control device 1 of the embodiment is N f While using a multi-edge tool T, virtually realizes cutting corresponding to a tool T with N f / n edges.

[0098] In the above embodiment, the case of generating an eccentricity control signal in a sine wave shape has been described, but if it is a periodic signal, it is not limited to a sine wave. For example, a rectangular wave or a triangular wave also has the same effect. In the above embodiment, an end mill is used as an example of the rotary tool, but a milling cutter also has the same effect.

[0099] Also, the number of axes of the machine tool 2 is arbitrary, and the technology of the embodiment can be applied as long as it is provided with two or more feed axes that drive in a plane perpendicular to the tool axis. Further, the machine tool 2 shown in the above embodiment has a structure provided with a feed drive system on the spindle side, but it may be provided with a feed drive system on the workpiece W side. In a machine tool provided with a feed drive system on the workpiece side, by inverting the sign of the eccentricity control signal to give an eccentric motion to the workpiece W, the tool relatively moves eccentrically in the coordinate system fixed to the workpiece W.

[0100] The configurations shown in the above embodiments are examples of the content of the present disclosure, and it is possible to combine them with other known technologies, and it is also possible to omit or change a part of the configuration without departing from the gist of the present disclosure.

Description of Reference Numerals

[0101] 1 Control device, 2 Machine tool, 3 X-axis drive system, 4 Y-axis drive system, 5 Spindle drive system, 10 Command generation unit, 11 Feed axis control unit, 12 Spindle control unit, 13 Machining condition storage unit, 14 Index value calculation unit, 15 Display unit, 16 Input unit, 17 Machining condition setting unit, 18 Initial eccentricity calculation unit, 19 Eccentricity control unit, f ecc Eccentricity control frequency, f ecc ’ Target eccentricity control frequency, Oa Geometric center, Ob, Ob0 to Ob5 Rotation center, Ob’ Target rotation center, SI Contact index value, T Tool, Ta Tool bottom surface, W Workpiece.

Claims

1. For each of a plurality of sets of machining conditions including the relative position of the rotation center of the tool with respect to the geometric center of the tool and the eccentricity control frequency, an index value calculation unit that calculates a first index value which is an average value of the temporal ratio of the contact time of one cutting edge of the tool with the workpiece during one rotation of the tool for all cutting edges; A machining condition setting unit that selects a set of machining conditions based on the calculated first index value; An eccentricity control unit that calculates an eccentricity control signal for rotating the geometric center of the tool around the target rotation center based on the target rotation center which is the rotation center included in the set of machining conditions selected by the machining condition setting unit and the target eccentricity control frequency which is the eccentricity control frequency included in the set of machining conditions; A feed axis control unit that drives and controls the feed axis of the tool or the workpiece based on the eccentricity control signal; A control device for a machine tool, characterized by comprising:

2. A display unit that associates and displays the first index value with the set of machining conditions, comprising: The control device for a machine tool according to claim 1, characterized by:

3. An input unit that receives the input of the machining conditions, comprising: The machining condition setting unit sets the machining conditions input to the input unit to the target rotation center and the target eccentricity control frequency. The control device for a machine tool according to claim 1 or 2, characterized by:

4. An initial eccentricity calculation unit that calculates the position of the initial rotation center which is the position of the rotation center of the tool during normal control when eccentricity control is not performed, comprising: When calculating the eccentricity control signal for rotating the geometric center of the tool around the target rotation center, the eccentricity control unit compensates for the eccentricity caused by the initial rotation center. The control device for a machine tool according to claim 1 or 2, characterized by:

5. The target eccentricity control frequency is a value obtained by dividing the multiplication value of the spindle rotation speed multiplied by the number of tool edges by an integer. The control device for a machine tool according to claim 1 or 2, characterized by:

6. An index value calculation step of calculating a first index value which is an average value of the temporal ratio of the contact time of one cutting edge of the tool with the workpiece during one rotation of the tool for all cutting edges for each of a plurality of sets of machining conditions including the relative position of the rotation center of the tool with respect to the geometric center of the tool and the eccentricity control frequency; A machining condition setting step of selecting a set of machining conditions based on the calculated first index value; An eccentricity control step of calculating an eccentricity control signal for rotating the geometric center of a tool around the target rotation center based on the target rotation center that is the rotation center included in the selected set of machining conditions and the target eccentricity control frequency that is the eccentricity control frequency included in the set of machining conditions; A feed axis control step of driving and controlling the feed axis of the tool or the workpiece based on the eccentricity control signal; A control method for a machine tool, characterized by comprising the above.

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