Machine tools and control devices

Abstract

The present invention provides a machine tool and control device that can obtain modal parameters without performing a hammering test. [Solution] A machine tool 10 comprising a spindle 110, a rotating mechanism 120, a tool 210, a moving mechanism for relatively moving the spindle 110 and the tool 210, a displacement detection unit 210X for detecting the displacement of the tool 210, and a cutting force detection unit 210Y, further comprising a control unit C having an acquisition unit C1 for acquiring detected machining data, a storage unit C2 for storing the machining data, and a calculation unit C3 for calculating the machining data, wherein the control unit C uses the machining data stored in the storage unit C2 under multiple machining conditions when chatter vibration occurs to cause the calculation unit C3 to identify the equivalent mass m, damping coefficient c, and spring constant k when the structure involved in holding the tool 210 is treated as a 1-degree-of-freedom vibration model.

Description

Technical Field

[0001] The present invention relates to a machine tool and a control device.

Background Art

[0002] In machine tools, it is known that a phenomenon called "chatter vibration" occurs, in which unstable vibrations occur during cutting of a cutting object. Therefore, in order to prevent chatter vibration from occurring during cutting, a stability limit diagram is widely used. In order to obtain this stability limit diagram, it is necessary to acquire modal parameters. Modal parameters are the equivalent mass m, damping coefficient c, and spring constant k when the structure involved in tool holding is modeled as a one-degree-of-freedom vibration model. Generally, modal parameters can be obtained by a hammering test. However, in a hammering test, measurement by measuring equipment and skilled operators is required, and the mounting position of the sensor for measurement may be restricted. Therefore, it is not easy to conduct the test at an actual work site.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a machine tool and a control device capable of obtaining modal parameters without performing a hammering test.

Means for Solving the Problems

[0005] The machine tool according to claim 1 is a spindle to which a cutting object is attached, a rotation mechanism for rotating the spindle, A tool for cutting the aforementioned object to be cut, A moving mechanism for moving the spindle and the tool relative to each other, A displacement detection unit for detecting the amount of displacement of the tool, A cutting force detection unit for detecting the cutting force the tool receives during machining, A machine tool equipped with, The control unit comprises an acquisition unit that acquires machining data detected by the displacement amount detection unit and the cutting force detection unit, a storage unit that stores the machining data, and a calculation unit that performs calculations on the machining data stored in the storage unit. The control unit is characterized in that it uses the processing data stored in the memory unit under multiple processing conditions when chatter vibration occurs to cause the calculation unit to identify the equivalent mass m, damping coefficient c, and spring constant k when the structure involved in holding the tool is treated as a one-degree-of-freedom vibration model.

[0006] The invention according to claim 2 is characterized in that, in addition to the configuration of the machine tool described in claim 1, the plurality of machining conditions are generated by changing at least one of the rotational speed of the spindle and the depth of cut of the tool into the workpiece.

[0007] The invention according to claim 3 is characterized in that, in addition to the configuration of the machine tool described in claim 1, the machining data used by the calculation unit for calculation is the detection result of the change in the displacement amount and the cutting force with respect to the elapsed time.

[0008] The invention according to claim 4 is characterized in that, in addition to the configuration of the machine tool described in claim 1, the machining data used by the calculation unit for calculation is data obtained from a sine wave approximated by the calculation unit based on the detection results of the change in the displacement amount and the cutting force with respect to elapsed time.

[0009] The invention according to claim 5 is characterized in that, in addition to the configuration of the machine tool described in claim 1, the machining data used by the calculation unit for calculation is data obtained by the calculation unit from which values ​​corresponding to the slope and area of ​​the Lissajous figure are calculated.

[0010] The invention according to claim 6 is characterized in that, in addition to the configuration of the machine tool described in claim 5, the Lissajous figure is an approximated virtual ellipse shape calculated by the calculation unit based on the detection results of the change in the amount of displacement and the cutting force with respect to the elapsed time.

[0011] The invention according to claim 7 is characterized in that, in addition to the configuration of the machine tool described in claim 1, it comprises a display unit that displays a stability limit diagram obtained based on the equivalent mass m, the damping coefficient c, and the spring constant k identified by the calculation unit.

[0012] The invention according to claim 8, in addition to the configuration of the machine tool described in claim 1, is further comprising a vibration mechanism that causes the spindle and the tool to vibrate relative to each other in a direction parallel to the direction of movement by the moving mechanism, The cutting object is characterized by rotating the main spindle with the rotation mechanism, while moving the cutting object and the tool while vibrating them relative to each other using the moving mechanism and the vibration mechanism.

[0013] The control device of the invention according to claim 9 is A control device for controlling a machine tool comprising: a spindle to which a workpiece is attached; a rotation mechanism for rotating the spindle; a tool for cutting the workpiece; a movement mechanism for moving the spindle and the tool relative to each other; a displacement detection unit for detecting the amount of displacement of the tool; and a cutting force detection unit for detecting the cutting force that the tool receives during machining, wherein An acquisition unit that acquires machining data detected by the displacement detection unit and the cutting force detection unit, A storage unit for storing the aforementioned processing data, A calculation unit that performs calculations on the processing data stored in the storage unit, Equipped with, Using the machining data stored in the storage unit under a plurality of machining conditions when chatter vibration occurs, the equivalent mass m, damping coefficient c, and spring constant k are identified by the arithmetic unit when the structure involved in holding the tool is a one-degree-of-freedom vibration model.

[0014] In addition, each of the above configurations can be adopted in combination as much as possible.

Advantages of the Invention

[0015] As described above, according to the present invention, modal parameters can be obtained without performing a hammering test.

Brief Description of the Drawings

[0016] [Figure 1] FIG. 1 is a schematic configuration diagram of a machine tool according to an embodiment of the present invention. [Figure 2] FIG. 2 is an operation explanatory diagram in the first cutting mode in the machine tool according to an embodiment of the present invention. [Figure 3] FIG. 3 is an operation explanatory diagram in the second cutting mode in the machine tool according to an embodiment of the present invention. [Figure 4] FIG. 4 is a block diagram of the generation mechanism of regenerative self-excited vibration. [Figure 5] FIG. 5 is a diagram showing an example of a stability limit diagram. [Figure 6] FIG. 6 is a diagram showing a one-degree-of-freedom vibration model when chatter vibration occurs. [Figure 7] FIG. 7 is a diagram showing a theoretical Lissajous figure and a figure in which measured values are plotted. [Figure 8] FIG. 8(a) shows an example of the dynamic displacement waveform of chatter vibration, and FIG. 8(b) is a graph showing the result of FFT conversion. [Figure 9] FIG. 9(a) shows an example of the dynamic displacement waveform of chatter vibration, and FIG. 9(b) is an explanatory diagram of fitting to a sine wave.

Embodiments for Carrying Out the Invention

[0017] The embodiments for carrying out this invention will be described in detail below with reference to the drawings, based on examples. However, unless otherwise specifically stated, the dimensions, materials, shapes, and relative arrangements of the components described in these embodiments are not intended to limit the scope of this invention to those components alone.

[0018] (Examples) Referring to Figures 1 to 9, the processing apparatus and control device according to this embodiment will be described. First, before describing the processing apparatus and control device according to this embodiment, an overview of the method for obtaining modal parameters will be explained. In Figures 1 to 3, for the sake of explanation, the directions of three mutually orthogonal axes (X axis, Y axis, and Z axis) are shown. The axis direction of the main spindle 110 is the Z axis, and the X axis and Y axis are mutually orthogonal and are also orthogonal to the Z axis.

[0019] <Overview of methods for obtaining modal parameters> In a one-degree-of-freedom vibration model when chatter vibration occurs (a one-degree-of-freedom vibration model of a structure involved in holding a tool), the equation of motion for the dynamic displacement yd, excluding the average value component of the chatter vibration, is expressed by the following equation (1), using the equivalent mass m, damping coefficient c, spring constant k, and dynamic cutting force Fd(t) excluding the average value component at time t.

[0020]

number

[0021] For the Lissajous figure obtained from the actually measured dynamic displacement of the tool and the dynamic cutting force component during chatter vibration, in Equation (1), when m, c, and k are tentatively determined, m, c, and k can be identified by making the Lissajous figure obtained from the dynamic displacement and dynamic cutting force of the tool coincide. And when m, c, and k in Equation (1) are identified, the stability limit diagram for the material can be obtained using the specific cutting resistance K of the material to be cut. This point will be briefly explained in the <Method for Calculating the Stability Limit Diagram> in the following section.

[0022] More specifically, m, c, and k are identified by acquiring machining data (yd and Fd(t), or data related thereto) under a plurality of machining conditions during chatter vibration. To identify m, c, and k, it is necessary to input different chatter vibration frequencies under a plurality of machining conditions, and a plurality of machining conditions are generated by changing at least one of the rotational speed of the spindle and the depth of cut of the tool with respect to the material to be cut. More specifically, for example, for yd and Fd(t), m, c, and k are identified by acquiring two sets of measured values under two conditions with different chatter vibrations. This point will be explained in detail in the <Method for Identifying m, c, and k Based on the Acquisition of yd and Fd(t)> in the following section.

[0023] From the above, m, c, and k can be identified by regarding the figure obtained by plotting the measured values of the displacement and cutting force of the tool under a plurality of machining conditions with different chatter vibration frequencies during chatter vibration as corresponding to the Lissajous figure.

[0024] When m, c, and k are identified, the stability limit diagram can be generated using the specific cutting resistance K of the material to be cut. The specific cutting resistance K is determined by the material of the object to be cut, and the values of the specific cutting resistance K of various materials can be used from those published in various documents and the like. Also, for materials with an unknown specific cutting resistance K, it can be derived from the slope of the experimental data obtained by measuring the cutting resistance by changing the feed rate of the cutting tool.

[0025] In this embodiment, the processing apparatus described measures the tool displacement and cutting force when chatter vibration occurs under two conditions with different chatter vibration frequencies, and generates a stability limit diagram.

[0026] <Machine tool configuration> Referring to Figure 1, the configuration of the machine tool 10 according to an embodiment of the present invention will be described. Figure 1 is a schematic diagram of the machine tool 10 according to an embodiment of the present invention, and is a diagram that simply shows the configuration of each part. In this embodiment, the machine tool that performs low-frequency vibration cutting, which finely breaks up chips by performing cutting while vibrating the tool (cutting tool), will be described as an example. However, the present invention is also applicable to machine tools that perform conventional cutting, which cuts without vibrating the tool.

[0027] The machine tool 10 comprises a spindle 110 to which the workpiece W is attached, a rotating mechanism 120 for rotating the spindle 110, and a cutting tool 210 for cutting the workpiece W. A chuck for holding the workpiece W is provided at the tip of the spindle 110. The rotating mechanism 120 can employ known technologies such as various motors.

[0028] Furthermore, the machine tool 10 is equipped with a moving mechanism for relatively moving the spindle 110 and the tool 210. The moving mechanism according to this embodiment has a first moving mechanism 130 and a second moving mechanism 220. The first moving mechanism 130 is a mechanism for relatively moving the spindle 110 and the tool 210 with respect to the axial direction of the spindle 110 (Z-axis direction). The second moving mechanism 220 is a mechanism for relatively moving the spindle 110 and the tool 210 with respect to a direction perpendicular to the Z-axis direction (Y-axis direction). Various known technologies such as linear servo motors, ball screw mechanisms, and rack and pinion mechanisms can be used as these moving mechanisms.

[0029] Furthermore, the machine tool 10 is equipped with a vibration mechanism that vibrates the spindle 110 and the tool 210 relative to each other in a direction parallel to the direction of movement by the moving mechanism. The vibration mechanism according to this embodiment has a first vibration mechanism 140 and a second vibration mechanism 230. The first vibration mechanism 140 is a mechanism that vibrates the spindle 110 and the tool 210 relative to each other in the axial direction of the spindle 110 (Z-axis direction). The second vibration mechanism 230 is a mechanism that vibrates the spindle 110 and the tool 210 relative to each other in a direction perpendicular to the Z-axis direction (Y-axis direction). These vibration mechanisms can employ various known technologies that can reciprocate the vibration of the object to be vibrated.

[0030] A first vibration mechanism 140 is fixed to a movable table 131, which is configured to be movable in the Z-axis direction by the first moving mechanism 130. The first vibration mechanism 140 then configures the rotation mechanism 120, which rotates the spindle 110, to vibrate in the Z-axis direction. With the above configuration, the workpiece W is configured to be movable in the Z-axis direction by the first moving mechanism 130 (see arrow S1), and to be vibrated in the Z-axis direction by the first vibration mechanism 140 (arrow (See mark T1), and is configured to be rotatable by a rotating mechanism 120 (see arrow R).

[0031] The second vibration mechanism 230 is fixed to a movable table 221, which is configured to be movable in the Y-axis direction by the second moving mechanism 220. Therefore, the tool 210 is configured to be movable in the Y-axis direction by the second moving mechanism 220 (see arrow S2) and to be vibrated in the Y-axis direction by the second vibration mechanism 230 (see arrow T2).

[0032] The machine tool 10 is equipped with a control unit C that controls the operation of the various mechanisms described above. The machine tool 10 is also equipped with an input means 311 for the operator to input data such as machining conditions to the control unit C, and a display unit 312 for displaying various information. Specific examples of the input means 311 include a keyboard, keypad, and mouse. Specific examples of the display unit 312 include a display that shows images. In this embodiment, the machine tool 10 is shown equipped with a control unit C and a display unit 312. However, it is also possible to provide a separate control device and display device, with the control device controlling the machine tool 10 and the display device displaying images. In this case, the control unit C in the figure corresponds to a control device, which is a separate device from the machine tool 10, and the display unit 312 corresponds to a display device, which is a separate device from the machine tool 10. The same applies to the input means 311.

[0033] In this embodiment, in order to move and vibrate the workpiece W and the tool 210 relative to each other in two axial directions, the workpiece W is configured to be movable and vibrable in the Z-axis direction, and the tool 210 is configured to be movable and vibrable in the Y-axis direction. However, the tool 210 may be fixed, and the workpiece W may be configured to be movable and vibrable in two axial directions, thereby enabling the workpiece W and the tool 210 to move and vibrate relative to each other in two axial directions. Similarly, the workpiece W may be fixed, and the tool 210 may be configured to be movable and vibrable in two axial directions, thereby enabling the workpiece W and the tool 210 to move and vibrate relative to each other in two axial directions.

[0034] Furthermore, in this embodiment, a configuration is shown in which the moving mechanism and the vibration mechanism are provided independently and controlled independently. However, a configuration that combines the functions of both the moving mechanism and the vibration mechanism is also acceptable. For example, by using a linear servo motor and controlling the linear servo motor to move and vibrate the workpiece W or the tool 210, the same operation as when the moving mechanism and vibration mechanism are provided and operated independently can be achieved.

[0035] Furthermore, this embodiment shows a configuration in which the workpiece W and the tool 210 are moved and vibrated relative to each other in two axial directions. However, a configuration in which the workpiece W and the tool 210 are moved and vibrated relative to each other in three axial directions can also be adopted. That is, in addition to the above configuration, a configuration can be further provided in which the workpiece W and the tool 210 are also moved and vibrated relative to each other in the X-axis direction.

[0036] With the machine tool 10 configured as described above, the spindle 110 is rotated by the rotation mechanism 120, and the workpiece W and the tool 210 are moved while being vibrated relative to each other by the moving mechanism and the vibration mechanism, thereby enabling cutting of the workpiece W. In the machine tool 10 according to this embodiment, cutting is possible in at least one cutting mode and cutting in a second cutting mode. This point will be explained below.

[0037] <Cutting Mode> The cutting modes will be explained with reference to Figures 2 and 3. Figures 2 and 3 are explanatory diagrams of the operation of the cutting modes in a machine tool according to an embodiment of the present invention. Figure 2 shows the operation in the case of the first cutting mode, with Figure (a) showing the workpiece W and tool 210 as viewed in the X-axis direction, and Figure (b) showing them as viewed in the Z-axis direction. Figure 3 shows the second cutting mode. The diagram shows the operation in cutting mode. Figure (a) shows the workpiece W and tool 210 as viewed in the X-axis direction, and Figure (b) shows them as viewed in the Z-axis direction.

[0038] First, with reference to Figure 2, the cutting operation in the first cutting mode will be explained. In this case, cutting is performed by rotating the spindle 110 with the rotation mechanism 120, while moving the workpiece W and the tool 210 in the Z-axis direction while vibrating them relatively with the first moving mechanism 130 and the first vibrating mechanism 140. The operator only needs to input data related to the rotational speed of the spindle 110 per unit time, the feed rate by the first moving mechanism 130 (feed rate in the direction of arrow S1 in Figure 2), the radial cutting width, and the frequency and amplitude of the vibration by the first vibrating mechanism 140 into the input means 311. Regarding the data to be input, it is possible to set it to input various data directly, or to input various data indirectly. In other words, even if the necessary data is not directly input, it is also possible to set it to input data that can be derived through calculation.

[0039] Referring to Figure 3, the cutting operation in the second cutting mode will be explained. In this case, cutting is performed by rotating the spindle 110 with the rotation mechanism 120, while moving the workpiece W and the tool 210 in the Y-axis direction while vibrating them relative to each other using the second moving mechanism 220 and the second vibration mechanism 230. The operator only needs to input data related to the rotational speed of the spindle 110 per unit time, the feed rate by the second moving mechanism 220 (feed rate in the direction of arrow S2 in Figure 3), the cutting width in the axial direction, and the frequency and amplitude of the vibration by the second vibration mechanism 230 into the input means 311. As described above, the input data can be set to be entered directly or indirectly.

[0040] <Control Unit (Control Device)> The control unit C (control device) will be explained in more detail. The control unit C is responsible for operating the rotation mechanism 120, the movement mechanism, and the vibration mechanism based on the data input to the input means 311.

[0041] And in this embodiment, the control unit C further plays a role in identifying modal parameters (equivalent mass m, damping coefficient c, and spring constant k) and causing the stability limit diagram to be displayed on the display unit 312. Hereinafter, this point will be described.

[0042] As shown in FIG. 1, the machine tool 10 according to this embodiment includes a displacement detection unit 210X that detects the displacement amount of the tool 210 by the moving mechanism. The displacement detection unit 210X is configured to be able to detect the displacement amount of the tool 210 in the moving direction by the first moving mechanism 130 and the displacement amount of the tool 210 in the moving direction by the second moving mechanism 220, respectively. The machine tool 10 also includes a cutting force detection unit 210Y that detects the cutting force received by the tool 210 during machining.

[0043] The control unit C includes an acquisition unit C1 that acquires the machining data detected by the displacement detection unit 210X and the cutting force detection unit 210Y, a storage unit C2 that stores the machining data acquired by the acquisition unit C1, and a calculation unit C3 that calculates the machining data stored in the storage unit C2.

[0044] With the control unit C configured as described above, according to the method described in <Outline of the method for obtaining the stability limit diagram>, the modal parameters can be identified and the stability limit diagram can be displayed on the display unit 312. Hereinafter, as described in <Outline of the method for obtaining the stability limit diagram>, the <Method for deriving the stability limit diagram>, the <Relational expressions for deriving m, c, k>, and the <Method for identifying m, c, k based on the acquisition of yd and Fd(t)> will be described respectively.

[0045] <Calculation method of the stability limit diagram> As described above, if the modal parameters (m, c, k) are identified, the stability limit diagram for the material can be obtained using the specific cutting resistance K of the material of the cutting object W. Therefore, it will be briefly described here with reference to FIG. 4.

[0046] For example, during machining by the machine tool 10, if vibration y in the Y direction occurs in the tool 210, not only the current cutting thickness but also the cutting thickness after one rotation (time difference T) will vary, the cutting force F will also vary, and the tool will be further excited in the Y direction. When the amplitude of the vibration y(t) at that time is greater than the amplitude of the vibration y(t - T) before one rotation, the vibration amplitude will continue to increase. This is the generation mechanism of regenerative self-excited vibration. The block diagram of this mechanism is shown in Fig. 4. In the figure, Δh(t) corresponds to the variation of the cutting thickness, and ΔF(t) corresponds to the variation of the cutting force. Also, a is the cutting width, and K is the specific cutting resistance.

[0047] And the dynamic characteristics G(iω) of the workpiece W are expressed using the modal parameters as G(iω)=1 / (-mω 2 +icω + k) where i is the imaginary unit and ω is the angular frequency of vibration.

[0048] By formulating the vibration system shown in Fig. 4 into equations and graphing them, a stability limit diagram can be obtained. That is, the cutting width a lim which is the boundary condition between stability and instability is a lim =-1 / (2KGr(iω c )) where Gr(iω) is the real part of the dynamic characteristics G(iω), and ω c is the angular frequency of self-excited vibration (chatter angular frequency).

[0049] Fig. 5 shows an example of the stability limit diagram. The horizontal axis is the spindle speed, and the vertical axis is the cutting width. Below the graph, it is stable and the occurrence of chatter vibration is suppressed. Above the graph, it becomes unstable and the possibility of chatter vibration occurring is high. In Fig. 5, the region shown in a grid pattern is the stable pocket. By setting the spindle speed within the range of this region, even if the cutting width is widened, chatter vibration is less likely to occur, and the productivity of machining can be increased.

[0050] <Relational expressions for deriving m, c, and k> Figure 6 shows a one-degree-of-freedom vibration model when chatter vibration occurs. This model shows the case where chatter vibration occurs in the y-axis direction. The tool-workpiece system is assumed to be a spring-mass-damper system vibration model, and the chatter vibration frequency is assumed to be constant. In this model, the equation of motion for the dynamic displacement yd, excluding the average value component of the chatter vibration, is expressed by equation (1) above.

[0051] Assuming that the dynamic displacement of chatter vibration is a sine wave, the dynamic displacement yd can be expressed as shown in equation (2) using the chatter vibration amplitude Ayd and the chatter vibration angular frequency ωc. Furthermore, by using equation (2), the equation of motion when the dynamic displacement is a sine wave can be rewritten as shown in equation (3).

[0052]

number

[0053]

number

[0054]

number

[0055] [Number] ··· Equation (5) Therefore, when the chatter angular vibration frequency ωc and the inclination of the Lissajous ellipse are known as a result of measurement or the like, the relationship between the equivalent mass m and the stiffness (spring constant k) can be obtained from Equation (5). However, with respect to Equation (5), for the known chatter angular vibration frequency ωc and βlisajue, since m and k are unknowns, in order to identify the values of the equivalent mass m and the spring constant k as unique values, two different sets of values of the chatter angular vibration frequency ωc and the magnitude of the inclination βlisajue are required. When two sets of known numbers are obtained, if those values are ωc1, ωc2, βlisajue1, βlisajue2, then the equivalent mass m is identified as shown below, and by substituting its value into Equation (5), the spring constant k is also identified.

[0056] [Number] ··· Equation (6) Also, with respect to the damping coefficient c, it is independent of the equivalent mass m and the spring constant k. Therefore, by equating the energy dissipation due to the damping term shown in Equation (7) and the internal area of the Lissajous considered as the input energy to the vibration system by the dynamic cutting force Fd, the value of the damping coefficient c is identified as shown in the following Equation (8).

[0057] [Number] ··· Equation (7)

[0058] [Number] ··· Equation (8) <Method for Identifying m, c, and k Based on Acquisition of yd and Fd(t)> In the control unit C, using the processing data acquired by the acquisition unit C1, the calculation unit C3 performs calculations to determine m, c, and k as follows.

[0059] From the dynamic displacement yd and dynamic cutting force Fd(t) obtained under two machining conditions with different chatter vibration frequencies, the chatter vibration amplitude and chatter angular vibration frequency corresponding to each condition are determined as follows. What is needed here is the dynamic displacement and dynamic cutting force, and for both displacement and cutting force, the waveform of the dynamic component obtained by subtracting the average value component is used. Note that if the measured waveform contains noise components such as harmonics of chatter vibration or other frequency components, a waveform in which components other than the chatter vibration frequency component have been removed using a bandpass filter may be used.

[0060] Assuming that a graph like the one shown in Figure 8(a) is obtained as the dynamic displacement waveform of the chatter vibration, the chatter vibration amplitude Ayd can be determined from it. It is also possible to use the maximum and minimum values ​​within a certain interval, or multiple values. Alternatively, you can find the maximum and minimum values ​​by averaging them.

[0061] Next, we determine the chatter angular vibration frequency ωc. By performing an FFT (Fast Fourier Transform) on the measured chatter vibration displacement waveform or cutting force waveform, a graph like the one shown in Figure 8(b) can be obtained. The frequency at which the largest peak appears in this graph is the chatter vibration frequency fc. The chatter angular vibration frequency ωc can be derived from the relationship ω = 2πf. This process can be performed using either the dynamic component or the raw waveform.

[0062] From the displacement and cutting force waveforms obtained in the manner described above, two sets of measured chatter vibration amplitudes Ayd and chatter angular vibration frequencies ωc are obtained.

[0063] The chatter vibration amplitude Ayd and chatter angular vibration frequency ωc may also be determined using approximate waveforms based on the displacement and cutting force waveforms obtained above. Suppose a graph like the one shown in Figure 9(a) is obtained as the dynamic displacement waveform of the chatter vibration. By fitting the graph shown in Figure 9(a) to a sine wave, as shown by the solid line in Figure 9(b), the chatter vibration amplitude Ayd and chatter angular vibration frequency ωc can be determined. The dotted line in Figure 9(b) is the graph shown in Figure 9(a).

[0064] Here, the sine wave is set as follows:

[0065] yd = Ayd·sin(ωc(t-dt)) Note that dt is the phase difference time.

[0066] Using Ayd, ωc, and dt as variables, we search for the Ayd, ωc, and dt values ​​that best approximate the waveform. For fitting, methods such as the least squares method can be used. Additionally, software functions or programs can be used to find the optimal combination of values.

[0067] As described above, based on the acquired displacement and cutting force waveforms, two sets of chatter vibration amplitudes Ayd and chatter angular vibration frequencies ωc can be derived from the approximated sinusoidal waveforms.

[0068] Next, we derive the equivalent mass. As shown in equation (6) above, the equivalent mass m can be determined from the slope βlisajue of the Lissajous diagram of the tool displacement and cutting force, so we first determine βlisajue. βlisajue is expressed by the following equation, as shown in equation (5) and Figure 7.

[0069] βlisajue=(Fd(0.5π / ωc)) / Ayd Here, Fd is derived from the cutting force waveform, which is measured in the same way as the chatter vibration amplitude of tool displacement, Ayd, as the vibration amplitude of the cutting force.

[0070] By substituting the two sets of chatter vibration amplitudes Ayd and chatter angular vibration frequencies ωc derived above respectively, βlisajue1 and βlisajue2 are derived, and substituting them into Equation (6) to derive m. At this time, the chatter vibration frequencies under the two conditions need to be different values. Next, the spring constant k is obtained from Equation (5). That is, substituting m derived earlier and βlisajue derived using one of the values of the two chatter angular vibration frequencies ωc into Equation (5) That's fine. Note that the spring constant k can also be derived respectively and used as its average value.

[0071] The damping coefficient c is derived from Equation (8). The contour integral of the Lissajous figure of the displacement and cutting force waveforms obtained above

Number

[0072] As described above, a method for identifying m, c, and k using the equations derived from <the relational expressions for identifying m, c, and k> has been shown. However, a part of this derivation process can also be replaced by a method of fitting a virtual Lissajous ellipse shape to the obtained Lissajous figure of displacement and cutting force. As described above, in FIG. 7, the dotted line is a figure obtained by plotting measured values. This measured value can be regarded as a theoretical Lissajous figure shown by the solid line, which is an approximated virtual ellipse shape by, for example, the least squares method, and calculations can be performed.

[0073] If the measured waveform contains other frequencies, such as harmonics of the chatter vibration, a bandpass filter may be used to remove components other than those surrounding the chatter vibration frequency. Alternatively, processing such as smoothing may be used to adjust the measured value to be closer to an ellipse.

[0074] Specifically, equation (3) above can be transformed from equation (2) as follows.

[0075]

number

[0076]

number

[0077] k is one of the two pairs of βlisajue and ωc mentioned above, and is substituted into equation (5). This is derived from the above. k may be either one of the two types of k derived above, or its average value may be used.

[0078] As explained above, m, c, and k can also be identified by fitting a virtual Lissajous figure to the dynamic displacement and dynamic cutting force obtained from cutting experiments.

[0079] After identifying m, c, and k, the control unit C displays a stability limit diagram on the display unit 312 based on m, c, k, and the specific cutting resistance K of the workpiece.

[0080] The operator can suppress chatter vibrations during machining by selecting the rotational speed and cutting width based on the stability limit diagram displayed on the display unit 312. Alternatively, instead of the operator selecting the rotational speed and cutting width, the control unit C can automatically select multiple rotational speed and cutting width conditions that do not cause chatter vibrations, and the operator can select from these conditions. Furthermore, if the rotational speed and cutting width entered by the operator are conditions that may cause chatter vibrations, the control unit C can correct them to conditions that are close to the entered conditions but less likely to cause chatter vibrations. [Explanation of Symbols]

[0081] 10: Machine tools 110: Main shaft 120: Rotation mechanism 130: First moving mechanism 131: Mobile platform 140: First vibration mechanism 210: Tools 210X: Displacement detection unit 210Y: Cutting force detection unit 220: Second Mobile Mechanism 221: Mobile platform 230: Second vibration mechanism 311: Input method 312: Display section C: Control section C1: Acquisition part C2: Storage part C3: Arithmetic section W: Cutting object

Claims

1. The spindle to which the workpiece to be cut is attached, A rotating mechanism for rotating the main shaft, A tool for cutting the aforementioned object to be cut, A moving mechanism for moving the spindle and the tool relative to each other, A displacement detection unit for detecting the amount of displacement of the tool, A cutting force detection unit for detecting the cutting force the tool receives during machining, A machine tool equipped with, The control unit comprises an acquisition unit that acquires machining data detected by the displacement amount detection unit and the cutting force detection unit, a storage unit that stores the machining data, and a calculation unit that performs calculations on the machining data stored in the storage unit. The control unit is characterized in that it uses the processing data stored in the memory unit under multiple processing conditions when chatter vibration occurs to cause the calculation unit to identify the equivalent mass m, damping coefficient c, and spring constant k when the structure involved in holding the tool is treated as a one-degree-of-freedom vibration model.

2. The machine tool according to claim 1, characterized in that the plurality of machining conditions are generated by changing at least one of the rotational speed of the spindle and the depth of cut of the tool into the workpiece.

3. The machine tool according to claim 1, characterized in that the machining data used by the calculation unit for calculation is the detection result of the change in the amount of displacement and the cutting force with respect to the elapsed time.

4. The machine tool according to claim 1, characterized in that the machining data used by the calculation unit for calculation is data obtained from a virtual sine wave approximated by the calculation unit based on the detection results of the change in the amount of displacement and the cutting force with respect to elapsed time.

5. The machine tool according to claim 1, characterized in that the processing data used by the calculation unit for calculation is data obtained by the calculation unit from which values ​​corresponding to the slope and area of ​​a Lissajous figure are calculated.

6. The machine tool according to claim 5, characterized in that the Lissajous figure used is a virtual ellipse shape approximated by the calculation unit based on the detection results of the change in the amount of displacement and the cutting force with respect to the elapsed time.

7. The machine tool according to claim 1, further comprising a display unit that displays a stability limit diagram obtained based on the equivalent mass m, the damping coefficient c, and the spring constant k identified by the calculation unit.

8. The system includes a vibration mechanism that vibrates the main shaft and the tool relative to each other in a direction parallel to the direction of movement by the aforementioned moving mechanism, The machine tool according to claim 1, characterized in that the workpiece is cut by rotating the spindle with the rotation mechanism, while moving the workpiece and the tool while vibrating them relative to each other with the moving mechanism and the vibration mechanism.

9. A control device for controlling a machine tool comprising: a spindle to which a workpiece is attached; a rotation mechanism for rotating the spindle; a tool for cutting the workpiece; a movement mechanism for moving the spindle and the tool relative to each other; a displacement detection unit for detecting the amount of displacement of the tool; and a cutting force detection unit for detecting the cutting force that the tool receives during machining, wherein An acquisition unit that acquires machining data detected by the displacement detection unit and the cutting force detection unit, A storage unit for storing the aforementioned processing data, A calculation unit that performs calculations on the processing data stored in the storage unit, Equipped with, A control device characterized in that, using the machining data stored in the memory unit under multiple machining conditions when chatter vibration occurs, the calculation unit identifies the equivalent mass m, damping coefficient c, and spring constant k when the structure involved in holding the tool is treated as a one-degree-of-freedom vibration model.

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