Vibration analysis method and vibration analysis device

Abstract

To provide a technique capable of analyzing vibration of a cutting tool or a workpiece by a simple method.SOLUTION: A vibration analysis method targeting a cutting tool or a workpiece for analysis comprises: a measurement step of acquiring cutting data and vibration data by measuring a cutting force and vibration of the target while cutting the workpiece by the cutting tool rotating at a fixed speed; an extraction step of extracting part data which is data of a length section corresponding to a time interval from contact of a blade of the cutting tool with the workpiece to next contact of the blade of the cutting tool with the workpiece from each acquired data; an addition step of adding addition data to the end of each part data; and an analysis step of deriving vibration characteristics of the target through frequency analysis using each part data which includes the addition data. The addition data is for expanding the time window length of the frequency analysis and composed of a plurality of zero values continuously arranged along a time sequence.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a vibration analysis method and a vibration analysis device. [Background technology]

[0002] In order to suppress chatter vibrations that occur when a workpiece is cut by a cutting tool, it is preferable to grasp the natural frequency and mechanical compliance of the cutting tool and the workpiece during cutting. For example, Patent Document 1 discloses a method for acquiring the natural frequency and mechanical compliance of the cutting tool and the workpiece during cutting, in which the workpiece is cut by the cutting tool while changing the rotation speed of the cutting tool in stages, and the displacement and cutting force of the cutting tool during cutting are measured to acquire the natural frequency and mechanical compliance of the cutting tool during cutting using data on the displacement and cutting force for each rotation speed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-094463 A Summary of the Invention [Problem to be solved by the invention]

[0004] Depending on the shape of the workpiece, it may be difficult to perform cutting on the workpiece while gradually changing the rotational speed of the cutting tool as in the above-mentioned method. Therefore, there is a demand for a technology that can analyze the vibration of the cutting tool and the workpiece in a simpler manner. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms.

[0006] (1) According to a first embodiment of the present disclosure, a vibration analysis method is provided for a cutting tool or a workpiece as an analysis object. The vibration analysis method includes a measurement step of acquiring cutting force data in which the cutting force is expressed in a time series and vibration data in which the vibration is expressed in a time series by measuring the cutting force applied to the workpiece from the cutting tool rotating at a constant speed while cutting the workpiece with the cutting tool and the vibration of the analysis object, an extraction step of extracting cutting force partial data, which is data of a section having a length corresponding to the time interval from when the blade of the cutting tool contacts the workpiece to when the blade of the cutting tool contacts the workpiece again, from the cutting force data and extracting vibration partial data, which is data of the section, from the vibration data, an addition step of adding additional data to an end of the cutting force partial data and an end of the vibration partial data, and an analysis step of deriving vibration characteristics of the analysis object by frequency analysis using the cutting force partial data and the vibration partial data including the additional data. The additional data is data for extending the time window length of the frequency analysis and is composed of a plurality of zero values ​​arranged consecutively along a time series. According to this vibration analysis method, since cutting force data and vibration data are acquired while cutting the workpiece with a cutting tool rotating at a constant speed, it is possible to suppress limitations on acquisition of cutting force data and vibration data due to the shape of the workpiece. Furthermore, since data for a section of length corresponding to the time interval from when the blade of the cutting tool comes into contact with the workpiece to when the blade of the cutting tool comes into contact with the workpiece again is extracted from the cutting force data and vibration data, and the time window length is extended by additional data before frequency analysis is performed, it is possible to improve the accuracy of vibration characteristics derived by frequency analysis. (2) In the vibration analysis method of the above aspect, the measuring step may further include measuring a rotation period of the cutting tool using a rotation detector which outputs a pulse signal each time the cutting tool rotates once, and the extraction step may calculate the time interval by dividing the rotation period by the number of teeth of the cutting tool, and then extracting the cutting force partial data and the vibration partial data by setting the timing at which a predetermined length of time shorter than the rotation period has elapsed from the timing at which the pulse signal is output as the start point of the section and setting the timing at which a length of time equal to the time interval has elapsed from the start point as the end point of the section. According to the vibration analysis method of this aspect, data on the length that accurately corresponds to the time interval can be extracted without being affected by fluctuations in the rotational speed of the cutting tool. (3) In the vibration analysis method of the above aspect, the measuring step may further include measuring a rotation period of the cutting tool using a rotation detector which outputs a pulse signal each time the cutting tool rotates once, and the extraction step may calculate the time interval by dividing the rotation period by the number of teeth of the cutting tool, and then extract the cutting force partial data and the vibration partial data by setting the timing at which the pulse signal is output as the start point of the section and setting the timing at which a time equal to the time interval has elapsed from the start point as the end point of the section. According to the vibration analysis method of this aspect, data on the length that accurately corresponds to the time interval can be extracted without being affected by fluctuations in the rotational speed of the cutting tool. (4) In the vibration analysis method of the above form, in the adding step, the additional data is added so that the number of data pieces of the cutting force partial data including the additional data is a power of two and the number of data pieces of the vibration partial data including the additional data is a power of two, and in the analysis step, a fast Fourier transform is performed on the cutting force partial data and the vibration partial data including the additional data to derive the vibration characteristics. According to the vibration analysis method of this aspect, the time required to convert the cutting force partial data including the additional data and the vibration partial data including the additional data from time domain data to frequency domain data can be shortened. (5) In the vibration analysis method of the above form, in the measurement process, the cutting force is measured by a sensor arranged at a position different from the machining point where the cutting force is applied from the cutting tool to the workpiece, and in the analysis process, the vibration characteristics may be derived after correcting the cutting force measured by the sensor to the cutting force at the machining point using a force transmission characteristic between the machining point and the sensor that has been derived in advance. According to the vibration analysis method of this aspect, the cutting force measured by the sensor is corrected to the cutting force at the machining point before deriving the vibration characteristics, so that the accuracy of the vibration characteristics can be further improved. (6) According to a second aspect of the present disclosure, there is provided a vibration analysis device including a vibration analysis unit configured to analyze vibrations of an analysis object, the analysis object being a cutting tool or a workpiece. The vibration analysis unit executes the following processes: an acquisition process for acquiring cutting force data in which the cutting force is represented in a time series and vibration data in which the vibration is represented in a time series, which are obtained by measuring the cutting force applied to the workpiece from the cutting tool rotating at a constant speed and the vibration of the analysis object while cutting the workpiece with the cutting tool; an extraction process for extracting cutting force partial data, which is data for a section having a length corresponding to a time interval from when the blade of the cutting tool comes into contact with the workpiece to when the blade of the cutting tool comes into contact with the workpiece again, from the cutting force data, and extracting vibration partial data, which is data for the section, from the vibration data; an addition process for adding additional data to an end of the cutting force partial data and an end of the vibration partial data; and an analysis process for deriving vibration characteristics of the analysis object by frequency analysis using the cutting force partial data and the vibration partial data including the additional data, wherein the additional data is data for extending a time window length of the frequency analysis, and is composed of a plurality of zero values ​​arranged consecutively along a time series. According to this embodiment of the vibration analysis device, since cutting force data and vibration data obtained by cutting a workpiece with a cutting tool rotating at a constant speed are acquired, it is possible to suppress the acquisition of cutting force data and vibration data being restricted by the shape of the workpiece. Furthermore, since data of a section having a length corresponding to the time interval from when the blade of the cutting tool comes into contact with the workpiece to when the blade of the cutting tool comes into contact with the workpiece again is extracted from the cutting force data and vibration data, and the time window length is extended by the additional data before frequency analysis is performed, it is possible to improve the accuracy of the vibration characteristics derived by the frequency analysis. The present disclosure may be realized in various forms other than a vibration analysis method and a vibration analysis device, for example, a stability limit diagram creation method, a stability limit diagram creation device, etc. [Brief description of the drawings]

[0007] [Figure 1] 1 is a perspective view showing a schematic configuration of a machine tool according to a first embodiment. [Diagram 2] FIG. 4 is an explanatory diagram showing an example of a stability limit diagram. [Diagram 3] 4 is a flowchart showing a method for creating a stability limit diagram according to the first embodiment. [Figure 4] FIG. 4 is an explanatory diagram showing data measured during cutting processing in the first embodiment. [Diagram 5] FIG. 4 is an explanatory diagram showing additional data according to the first embodiment. [Figure 6] FIG. 4 is an explanatory diagram showing compliance data according to the first embodiment. [Figure 7] FIG. 11 is an explanatory diagram showing compliance data of a comparative example. [Figure 8] FIG. 11 is a perspective view showing a schematic configuration of a machine tool according to a second embodiment. [Figure 9] 10 is a flowchart showing a method for creating a stability limit diagram according to a second embodiment. [Figure 10] FIG. 11 is an explanatory diagram illustrating a schematic view of how cutting force is corrected. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] A. First embodiment: 1 is a perspective view showing a schematic configuration of a machine tool 11 used in a vibration analysis method in a first embodiment. In this embodiment, the machine tool 11 is configured as a horizontal machining center. The machine tool 11 has three coordinate axes, X, Y, and Z axes, which are perpendicular to each other. In this embodiment, the X axis is a coordinate axis along the left-right direction of the machine tool 11, the Y axis is a coordinate axis along the up-down direction of the machine tool 11, and the Z axis is a coordinate axis along the front-rear direction of the machine tool 11.

[0009] The machine tool 11 includes a bed 20, a table 30, a column 40, a spindle unit 50, a cutting force sensor 60, a vibration sensor 70, a rotation detector 80, and a control device 90. The table 30 and the column 40 are supported by the bed 20. A workpiece WK is fixed to the upper surface of the table 30. The table 30 moves along the X-axis while being guided by the bed 20. The column 40 moves along the Z-axis while being guided by the bed 20. The spindle unit 50 is supported by the column 40 and moves along the Y-axis while being guided by the column 40. The spindle unit 50 has a spindle 55. A cutting tool TL for machining the workpiece WK is attached to the spindle 55. The spindle unit 50 rotates the spindle 55 and the cutting tool TL around a rotation axis parallel to the Z-axis.

[0010] The cutting tool TL has a generally cylindrical shape centered on the central axis, and has at least one blade on the outer circumferential side surface. In this embodiment, the cutting tool TL is an end mill, and has two blades arranged at equal intervals on the outer circumferential side surface. Note that, in other embodiments, the number of blades of the cutting tool TL may be one, or three or more. The cutting tool TL may not be an end mill, but may be, for example, a milling tool.

[0011] The cutting force sensor 60 is provided on the spindle 55. The cutting force sensor 60 detects the cutting force applied to the workpiece WK from the cutting tool TL. Information related to the cutting force detected by the cutting force sensor 60 is transmitted to the control device 90.

[0012] The vibration sensor 70 is fixed to the workpiece WK. The vibration sensor 70 detects a physical quantity representing the magnitude of vibration of the workpiece WK. The physical quantity representing the magnitude of vibration includes acceleration, speed, and displacement. In this embodiment, the vibration sensor 70 detects the acceleration of the workpiece WK as the physical quantity representing the magnitude of vibration of the workpiece WK. Information on the acceleration detected by the vibration sensor 70 is transmitted to the control device 90. Note that in other embodiments, the vibration sensor 70 may detect the speed of the workpiece WK or the displacement of the workpiece WK instead of the acceleration of the workpiece WK as the physical quantity representing the magnitude of vibration of the workpiece WK.

[0013] The rotation detector 80 is provided in the spindle device 50. The rotation detector 80 detects the rotation angle of the spindle 55. In this embodiment, the rotation detector 80 outputs a pulse signal every time the spindle 55 rotates once. The pulse signal output from the rotation detector 80 is transmitted to the control device 90.

[0014] The control device 90 is configured as a computer equipped with a CPU, a memory, and an input / output interface. In this embodiment, the control device 90 has an NC control unit 91 and a vibration analysis unit 92. The NC control unit 91 controls each unit of the machine tool 11 to rotate the cutting tool TL and perform cutting processing on the workpiece WK. The vibration analysis unit 92 performs vibration analysis of the workpiece WK as an analysis object. In this embodiment, the vibration analysis unit 92 creates a stability limit diagram using the results of the vibration analysis. The control device 90 may be referred to as a vibration analysis device.

[0015] 2 is an explanatory diagram showing an example of a stability limit diagram. The horizontal axis of the stability limit diagram represents the rotation speed of the spindle 55, in other words, the rotation speed of the cutting tool TL, and the vertical axis of the stability limit diagram represents the cutting depth of the cutting tool TL in the Z-axis direction relative to the workpiece WK. The stability limit diagram shows a stability limit line, which is a boundary between a stable region and an unstable region. In the stable region on the low cutting depth side of the stability limit line, the occurrence of chatter vibration during cutting is suppressed, and in the unstable region on the high cutting depth side of the stability limit line, chatter vibration occurs during cutting.

[0016] The stability limit diagram can be created by analyzing the vibration of the analysis object, which is the cutting tool TL attached to the spindle 55 or the workpiece WK fixed to the table 30, and deriving the vibration characteristics of the analysis object. For example, the vibration characteristics of the analysis object can be derived by a hammering test performed during non-cutting. However, since the vibration characteristics of the analysis object differ between cutting and non-cutting, the stability limit diagram created based on the test results of the hammering test may not be able to suppress chatter vibration. Therefore, in this embodiment, as described later, the stability limit diagram is created by deriving the vibration characteristics of the analysis object during cutting.

[0017] Fig. 3 is a flow chart showing the contents of the stability limit diagram creating method including the vibration analysis method in this embodiment. Fig. 4 is an explanatory diagram showing data FD, VD measured during cutting. Fig. 5 is an explanatory diagram showing additional data AFD, AVD. Fig. 6 is an explanatory diagram showing compliance data CD. In this embodiment, the stability limit diagram creating method is executed by the control device 90. This method is started by the control device 90, for example, when a predetermined start operation is performed on the control device 90.

[0018] First, in step S110 of FIG. 3, the NC control unit 91 of the control device 90 rotates the cutting tool TL at a constant speed, and performs cutting processing on the workpiece WK by the cutting tool TL rotating at the constant speed. The vibration analysis unit 92 of the control device 90 measures the cutting force applied to the workpiece WK from the cutting tool TL using the cutting force sensor 60 during cutting processing, thereby obtaining cutting force data FD in which the cutting force is represented in a time series, and obtains vibration data VD in which the physical quantity representing the magnitude of vibration of the workpiece WK is represented in a time series by measuring the physical quantity representing the magnitude of vibration of the workpiece WK using the vibration sensor 70 during cutting processing. In this embodiment, the vibration analysis unit 92 obtains a pulse signal PS output from the rotation detector 80 during cutting processing in addition to the cutting force data FD and the vibration data VD. FIG. 4 shows an example of the cutting force data FD, the vibration data VD, and the pulse signal PS. In this embodiment, the vibration data VD indicates the acceleration of the workpiece WK as a physical quantity representing the vibration of the workpiece WK. The vibration analysis unit 92 acquires the cutting force data FD and the vibration data VD at a predetermined sampling frequency. Note that in another embodiment, the vibration data VD may represent, for example, the displacement of the workpiece WK instead of the acceleration of the workpiece WK as a physical quantity representing the magnitude of the vibration of the workpiece WK.

[0019] In step S120 of FIG. 3, the vibration analysis unit 92 extracts data for one blade from the cutting force data FD and extracts data for one blade from the vibration data VD. The data for one blade means data for a section of a length corresponding to the time interval from when the blade of the cutting tool TL comes into contact with the workpiece WK to when the blade of the cutting tool TL comes into contact with the workpiece WK again. The time interval from when the blade of the cutting tool TL comes into contact with the workpiece WK to when the blade of the cutting tool TL comes into contact with the workpiece WK again means, for example, when the cutting tool TL has two blades, the time interval from when one of the two blades comes into contact with the workpiece WK to when the other of the two blades comes into contact with the workpiece WK. In the following description, the data extracted from the cutting force data FD is called cutting force partial data PFD, and the data extracted from the vibration data VD is called vibration partial data PVD. The time interval from when the blade of the cutting tool TL comes into contact with the workpiece WK to when the blade of the cutting tool TL comes into contact with the workpiece WK again is called the cutting blade passing period.

[0020] In this embodiment, as shown in Fig. 4, the vibration analysis unit 92 derives the rotation period T1 of the cutting tool TL from the time interval at which the pulse signal PS rises, and calculates the number of pieces of data per one rotation period of the cutting tool TL by multiplying the rotation period T1 by the above-mentioned sampling frequency. The vibration analysis unit 92 calculates the number of pieces of data per one rotation period by the number of blades of the cutting tool TL. In the example shown in Fig. 4, the cutting tool TL has two blades, and the rotation angle of the cutting tool TL when the rotation detector 80 outputs the pulse signal PS is different from the rotation angle of the cutting tool TL when the blades of the cutting tool TL cut into the workpiece WK. When the rotation angle of the cutting tool TL when the rotation detector 80 outputs the pulse signal PS is different from the rotation angle of the cutting tool TL when the blade of the cutting tool TL cuts into the workpiece WK, the vibration analysis unit 92 extracts cutting force partial data PFD from the cutting force data FD and extracts vibration partial data PVD from the vibration data VD using data for one blade in a section whose start point is a timing when a predetermined time shorter than the rotation period T1 of the cutting tool TL has elapsed from the timing when the pulse signal PS rises and whose end point is a timing when a time length equal to the cutting blade passing period T2 has elapsed from the start point. The time from the timing when the pulse signal PS rises to the start point can be determined according to the difference between the rotation angle of the cutting tool TL when the rotation detector 80 outputs the pulse signal PS and the rotation angle of the cutting tool TL when the blade of the cutting tool TL cuts into the workpiece WK, and the rotation speed of the cutting tool TL. The number of pieces of cutting force partial data PFD and the number of pieces of vibration partial data PVD are the same as the number of pieces of cutting force data FD and the number of pieces of vibration data VD per cutting blade passing period T2. When the rotation angle of the cutting tool TL when the rotation detector 80 outputs the pulse signal PS is the same as the rotation angle of the cutting tool TL when the blade of the cutting tool TL cuts into the workpiece WK, the vibration analysis unit 92 extracts the cutting force partial data PFD from the cutting force data FD and extracts the vibration partial data PVD from the vibration data VD, using the data of a section whose start point is the timing when the pulse signal PS rises and whose end point is the timing when the same length of time as the cutting blade passing period T2 has elapsed from the start point as the data for one blade.

[0021] In step S130 in FIG. 3, the vibration analysis unit 92 adds the cutting force addition data AFD to the cutting force partial data PFD, and adds the vibration addition data AVD to the vibration partial data PVD. The cutting force addition data AFD and the vibration addition data AVD are data for extending the time window length of the Fourier transform described later. The cutting force addition data AFD and the vibration addition data AVD are composed of a plurality of "0" values ​​arranged consecutively along a time series. As shown in FIG. 5, in this embodiment, the vibration analysis unit 92 adds the cutting force addition data AFD to the rear end of the cutting force partial data PFD, and adds the vibration addition data AVD to the rear end of the vibration partial data PVD. In another embodiment, the vibration analysis unit 92 may add the cutting force addition data AFD to the front end of the cutting force partial data PFD, and add the vibration addition data AVD to the front end of the vibration partial data PVD. The vibration analysis unit 92 may add the cutting force additional data AFD to both ends of the cutting force partial data PFD, and may add the vibration additional data AVD to both ends of the vibration partial data PVD.

[0022] The vibration analysis unit 92 adds the cutting force addition data AFD to the cutting force partial data PFD and adds the vibration addition data AVD to the vibration partial data PVD so that the sum of the number of data in the cutting force partial data PFD and the number of data in the cutting force addition data AFD is equal to the sum of the number of data in the vibration partial data PVD and the number of data in the vibration addition data AVD. In this embodiment, the vibration analysis unit 92 adds the cutting force addition data AFD to the cutting force partial data PFD so that the sum of the number of data in the cutting force partial data PFD and the number of data in the cutting force addition data AFD is a power of two, and adds the vibration addition data AVD to the vibration partial data PVD so that the sum of the number of data in the vibration partial data PVD and the number of data in the vibration addition data AVD is a power of two.

[0023] 3, the vibration analysis unit 92 performs a Fourier transform on the cutting force partial data PFD to which the cutting force additional data AFD has been added, and the vibration partial data PVD to which the vibration additional data AVD has been added, thereby converting the cutting force partial data PFD and the vibration partial data PVD from time domain data to frequency domain data. In this embodiment, the vibration analysis unit 92 converts the cutting force partial data PFD and the vibration partial data PVD from time domain data to frequency domain data by fast Fourier transform.

[0024] In step S150, the vibration analysis unit 92 generates compliance data CD representing the relationship between the frequency and the mechanical compliance of the workpiece WK, using the cutting force partial data PFD and the vibration partial data PVD converted into frequency domain data. Specifically, the vibration analysis unit 92 calculates the acceleration represented in the vibration partial data PVD as (2π×frequency) for each frequency represented in the vibration partial data PVD. 2 The relationship between frequency and displacement is calculated by dividing the displacement by the cutting force, and the frequency and mechanical compliance are calculated by dividing the displacement by the cutting force for each frequency, thereby generating compliance data CD.

[0025] In step S160 of FIG. 3, the vibration analysis unit 92 acquires the vibration characteristics of the workpiece WK using the compliance data CD. The vibration characteristics include the mass M of the object to be analyzed, the damping coefficient C, and the spring constant K. It is generally known that chatter vibration occurs at a natural frequency, that is, a frequency at which the mechanical compliance is high. Therefore, in this embodiment, the vibration analysis unit 92 identifies the frequency at which the mechanical compliance is maximum as the frequency at which chatter vibration occurs, and calculates a transfer function G(s)=1 / (M×s 2+C×s+K) by curve fitting processing to obtain the mass M, damping coefficient C, and spring constant K of the object to be analyzed. Note that when the mechanical compliance represented in the compliance data CD has multiple peak shapes and it is difficult to determine at which frequency chatter vibration occurs due to the small difference between the peak values, the vibration analysis unit 92 may derive the vibration characteristics for each peak shape.

[0026] In step S170, a stability limit diagram is created using machining conditions such as the tool diameter and cutting depth of the cutting tool TL in addition to the mass M, damping coefficient C, and spring constant K. The vibration analysis unit 92 can create the stability limit diagram in accordance with the method for determining a chatter stability limit diagram as shown in, for example, the Japan Society of Mechanical Engineers, Seminar No. 10-24 - Basic Manufacturing and Machining Course - Let's Learn Through Practice "Basic Knowledge of Cutting and Chatter Vibration", Seminar Text, pp. 1-12, held on March 4, 2010.

[0027] After the stability limit diagram is created, this method is terminated. The stability limit diagram created by this method is displayed, for example, on a display device (not shown) connected to the control device 90. Note that step S110 may be referred to as a measurement process, and the part of step S110 in which the vibration analysis unit 92 acquires the cutting force data FD and the vibration data VD may be referred to as an acquisition process. Step S120 may be referred to as an extraction process or an extraction process. Step S130 may be referred to as an addition process or an addition process. The processes from step S140 to step S160 may be referred to as an analysis process or an analysis process. Step S170 may be referred to as a stability limit diagram creation process or a stability limit diagram creation process.

[0028] FIG. 7 is an explanatory diagram showing compliance data CDb in a comparative example. In FIG. 7, as a comparative example, the compliance data CDb in the case where the Fourier transform is performed without adding the cutting force addition data AFD and the vibration addition data AVD is shown by a solid line, and the compliance data CD shown in FIG. 6 is shown by a dashed line. The frequency resolution of the compliance data CDb in the comparative example is lower than that of the compliance data CD in this embodiment. Therefore, in the compliance data CDb in the comparative example, the accuracy of the mechanical compliance is reduced compared to the compliance data CD in this embodiment, and the accuracy of the stability limit diagram is reduced. It is preferable to determine the number of data of the cutting force addition data AFD and the number of data of the vibration addition data AVD according to the required frequency resolution.

[0029] In the vibration analysis method of the present embodiment described above, the cutting force data FD and the vibration data VD are acquired while the workpiece WK is being cut by the cutting tool TL rotating at a constant speed, so that the acquisition of the cutting force data FD and the vibration data VD can be prevented from being limited by the shape of the workpiece WK. Furthermore, in this embodiment, the data PFD and PVD of the section of the length corresponding to the cutting edge passing period T2 are extracted from the cutting force data FD and the vibration data VD, and the time window length of the Fourier transform is extended by each additional data AFD and AVD before performing the frequency analysis, so that the accuracy of the vibration characteristics acquired by the frequency analysis can be improved. Note that, in a form in which the data PFD and PVD of the section of the length corresponding to the cutting edge passing period T2 are not extracted from the cutting force data FD and the vibration data VD, and the cutting force data FD and the vibration data VD are used directly for the frequency analysis, cutting forces other than the cutting edge passing frequency, which is the reciprocal of the cutting edge passing period T2, and the multiple components of the cutting edge passing frequency are not input, so in order to acquire the vibration characteristics with high accuracy, it is necessary to perform machining with a different cutting edge passing frequency. In contrast, in this embodiment, data PFD and PVD of a length corresponding to the cutting edge passing period T2 are extracted from the cutting force data FD and the vibration data VD. The extracted data PFD and PVD include one contact between the blade of the cutting tool TL and the workpiece WK, and represent a state in which the blade of the cutting tool TL is impulsively exciting the workpiece WK. When this data PFD and PVD are frequency-analyzed, it also includes exciting forces other than the cutting edge passing frequency, so that highly accurate vibration characteristics can be obtained in one machining operation.

[0030] In this embodiment, the rotation period T1 of the cutting tool TL is obtained using the pulse signal PS output from the rotation detector 80, and the cutting edge passing period T2 is calculated by dividing the rotation period T1 by the number of teeth of the cutting tool TL. Then, the cutting force partial data PFD and the vibration partial data PVD are extracted with a timing at which a predetermined time shorter than the rotation period T1 has elapsed from the timing at which the pulse signal PS was output as the start point of the section, and a timing at which a time equal to the cutting edge passing period T2 has elapsed from the start point as the end point of the section. Therefore, data of a length that accurately corresponds to the cutting edge passing period T2 can be extracted without being affected by unevenness in the rotation speed of the cutting tool TL.

[0031] In this embodiment, the additional data AFD and AVD are added so that the sum of the number of data in the cutting force partial data PFD and the number of data in the cutting force additional data AFD is a power of 2, and the sum of the number of data in the vibration partial data PVD and the number of data in the vibration additional data AVD is a power of 2, and then a fast Fourier transform is performed on the cutting force partial data PFD and the vibration partial data PVD. Therefore, the time required to convert the cutting force partial data PFD and the vibration partial data PVD from time domain data to frequency domain data can be shortened.

[0032] B. Second embodiment: 8 is a perspective view showing a schematic configuration of a machine tool 12 used in a vibration analysis method in the second embodiment. This embodiment is different from the first embodiment in that a transfer characteristic memory unit 93 is provided in a control device 190 of the machine tool 12, which stores transfer characteristic data representing the transfer characteristic of the force between a processing point where a cutting force is applied from a cutting tool TL to a workpiece WK and the cutting force sensor 60, and that a vibration analysis unit 92 of the control device 190 uses the transfer characteristic data stored in the transfer characteristic memory unit 93 to correct the cutting force measured by the cutting force sensor 60 to the cutting force at the processing point, and then calculates the mechanical compliance of the workpiece WK. The other configurations are the same as those of the first embodiment unless otherwise described.

[0033] In this embodiment, the control device 190 is provided with a transfer characteristic storage unit 93 that stores transfer characteristic data representing the transfer characteristic of the force between the processing point and the cutting force sensor 60, as described above. A method for acquiring the transfer characteristic data will be described later. Furthermore, the control device 190 is connected to an impact hammer 100. In this embodiment, the impact hammer 100 is used to vibrate the processing point at the tip of the cutting tool TL. The impact hammer 100 is provided with an excitation force sensor 105 that detects the excitation force applied by the impact hammer 100. Information regarding the excitation force detected by the excitation force sensor 105 is transmitted to the control device 190.

[0034] Fig. 9 is a flow chart showing the contents of the stability limit diagram creating method including the vibration analysis method in the second embodiment. Fig. 10 is an explanatory diagram showing a state in which the cutting force measured by the cutting force sensor 60 is corrected to the cutting force at the processing point. As shown in Fig. 9, in the stability limit diagram creating method of this embodiment, first, in step S200, the vibration analysis unit 92 derives the transfer characteristic of the force between the processing point and the cutting force sensor 60 to generate transfer characteristic data, and stores the transfer characteristic data in the transfer characteristic storage unit 93.

[0035] Specifically, first, an excitation force is applied to the processing point at the tip of the cutting tool TL by the impact hammer 100. In this embodiment, the application of the excitation force to the processing point by the impact hammer 100 is performed by an operator. The vibration analysis unit 92 measures the excitation force applied to the processing point from the impact hammer 100 using the excitation force sensor 105 and measures the excitation force using the cutting force sensor 60, thereby acquiring first excitation force data in which the excitation force measured using the excitation force sensor 105 is represented in a time series, and second excitation force data in which the excitation force measured using the cutting force sensor 60 is represented in a time series. Next, the vibration analysis unit 92 converts the first excitation force data and the second excitation force data from time domain data to frequency domain data by Fourier transform. The vibration analysis unit 92 uses the first excitation force data and the second excitation force data converted into frequency domain data to derive the force transfer characteristics between the machining point and the cutting force sensor 60 to generate transfer characteristic data TD, and stores the transfer characteristic data TD in the transfer characteristic storage unit 93. As shown in FIG. 10, the transfer characteristic data TD represents the ratio of the excitation force at the machining point measured using the excitation force sensor 105 to the excitation force at the measurement point measured using the cutting force sensor 60 as the force transfer characteristics between the machining point and the cutting force sensor 60 for each frequency. In order to improve the accuracy of the transfer characteristic data TD, the first excitation force data and the second excitation force data may be obtained, and the ratio of the excitation force at the machining point to the excitation force at the measurement point may be calculated multiple times, and the transfer characteristic data TD may represent the average value of the ratio of the excitation force at the machining point to the excitation force at the measurement point for each frequency.

[0036] In step S210, the vibration analysis unit 92 acquires the cutting force data FD, the vibration data VD, and the pulse signal PS. In step S220, the vibration analysis unit 92 generates cutting force partial data PFD by extracting data for one blade from the cutting force data FD, and generates vibration partial data PVD by extracting data for one blade from the vibration data VD. In step S230, the vibration analysis unit 92 adds cutting force additional data AFD to an end of the cutting force partial data PFD, and adds vibration additional data AVD to an end of the vibration partial data PVD. In step S240, the vibration analysis unit 92 performs a fast Fourier transform on the cutting force partial data PFD to which the cutting force additional data AFD has been added, and the vibration partial data PVD to which the vibration additional data AVD has been added, thereby converting the cutting force partial data PFD and the vibration partial data PVD from time domain data to frequency domain data.

[0037] In step S245, the vibration analysis unit 92 corrects the cutting force at the measurement point represented by the cutting force partial data PFD converted into frequency domain data to the cutting force at the processing point using the transfer characteristic data TD stored in the transfer characteristic storage unit 93, as shown in Fig. 10. Thereafter, in step S250, the vibration analysis unit 92 generates compliance data CD representing the relationship between the frequency and the mechanical compliance of the workpiece WK using the cutting force partial data PFD in which the cutting force has been corrected and the vibration partial data PVD. In step S260, the vibration analysis unit 92 acquires the vibration characteristics of the workpiece WK using the compliance data CD, and in step S270, the vibration analysis unit 92 creates a stability limit diagram.

[0038] In the vibration analysis method of this embodiment described above, the cutting force measured using the cutting force sensor 60 is corrected to the cutting force at the machining point before deriving the vibration characteristics of the workpiece WK, so that the vibration characteristics of the workpiece WK can be derived with even greater accuracy than in the first embodiment, and ultimately, a stability limit diagram can be created with even greater accuracy than in the first embodiment.

[0039] C. Other embodiments: (C1) In the vibration analysis method of each of the above-described embodiments, vibration analysis is performed with the workpiece WK as the analysis object. In contrast, vibration analysis may be performed with the cutting tool TL as the analysis object. In this case, the vibration data VD represents a physical quantity representing the magnitude of vibration of the cutting tool TL. The physical quantity representing the magnitude of vibration of the cutting tool TL is, for example, the acceleration of the cutting tool TL. The acceleration of the cutting tool TL can be measured non-contact during cutting processing, for example, by using a laser Doppler vibrometer.

[0040] (C2) In the vibration analysis method of each of the above-mentioned embodiments, in step S120 and step S220, the pulse signal PS output from the rotation detector 80 is used as a marker for determining the interval for extracting each of the data PFD and PVD. In contrast, the pulse signal PS output from the rotation detector 80 does not have to be used as a marker for determining the interval for extracting each of the data PFD and PVD. For example, the timing at which the magnitude of the cutting force exceeds a predetermined value may be used as a marker for determining the start point or end point of the interval.

[0041] (C3) In the vibration analysis method of each of the above-described embodiments, in step S140 or step S240, the time domain data may be converted into frequency domain data by a method other than the fast Fourier transform. For example, the time domain data may be converted into frequency domain data by the discrete Fourier transform.

[0042] (C4) In each of the above-described embodiments, the machine tools 11, 12 are horizontal machining centers. However, the machine tools 11, 12 do not have to be horizontal machining centers. The machine tools 11, 12 may be, for example, vertical machining centers or NC milling machines.

[0043] (C5) In the first embodiment described above, the control device 90 of the machine tool 11 has an NC control unit 91 and a vibration analysis unit 92. In contrast, the vibration analysis unit 92 may be provided outside the control device 90. For example, the vibration analysis unit 92 may be provided on a computer separate from the control device 90. In this case, the vibration analysis unit 92 may acquire the cutting force measured using the cutting force sensor 60, and acquire a physical quantity indicating the magnitude of the vibration measured using the vibration sensor 70, by wired communication or wireless communication.

[0044] (C6) In the second embodiment described above, the control device 190 of the machine tool 12 has the NC control unit 91, the vibration analysis unit 92, and the transfer characteristic storage unit 93. In contrast, the vibration analysis unit 92 and the transfer characteristic storage unit 93 may be provided outside the control device 190. For example, the vibration analysis unit 92 and the transfer characteristic storage unit 93 may be provided on a computer other than the control device 190. In this case, the vibration analysis unit 92 may acquire physical quantities representing the excitation force measured using the excitation force sensor 105, the excitation force measured using the cutting force sensor 60, the cutting force measured using the cutting force sensor 60, and the magnitude of the vibration measured using the vibration sensor 70, by wired communication or wireless communication.

[0045] (C7) In the above-mentioned second embodiment, the cutting force sensor 60 is provided on the spindle 55 to which the cutting tool TL is attached, and the transmission characteristic data TD represents the ratio between the excitation force measured by the excitation force sensor 105 when the excitation force is applied to the processing point of the tip of the cutting tool TL by the impact hammer 100, and the excitation force measured by the cutting force sensor 60. In contrast to this, for example, a cutting force sensor may be provided on the table 30 to which the workpiece WK is fixed, and the transmission characteristic data TD may represent the ratio between the excitation force measured by the excitation force sensor 105 when the excitation force is applied to the processing point of the workpiece WK by the impact hammer 100, and the excitation force measured by the cutting force sensor.

[0046] The present disclosure is not limited to the above-mentioned embodiment, and can be realized in various configurations without departing from the spirit of the present disclosure. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention column can be appropriately replaced or combined to solve some or all of the above-mentioned problems or to achieve some or all of the above-mentioned effects. Furthermore, if the technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0047] 11...machine tool, 20...bed, 30...table, 40...column, 50...spindle device, 55...spindle, 60...cutting force sensor, 70...vibration sensor, 80...rotation detector, 90, 190...control device, 91...NC control unit, 92...vibration analysis unit, 93...transmission characteristic storage unit, 100...impact hammer, 105...vibration force sensor, TL...cutting tool, WK...workpiece

Claims

1. A vibration analysis method for analyzing a cutting tool or a workpiece, the method comprising the steps of: a measurement process for measuring a cutting force applied to the workpiece from the cutting tool rotating at a constant speed and a vibration of the analysis object while cutting the workpiece with the cutting tool, thereby obtaining cutting force data in which the cutting force is represented in a time series and vibration data in which the vibration is represented in a time series; an extraction step of extracting cutting force portion data, which is data for a section having a length corresponding to a time interval from when the blade of the cutting tool comes into contact with the workpiece until when the blade of the cutting tool next comes into contact with the workpiece, from the cutting force data, and extracting vibration portion data, which is data for the section, from the vibration data; an adding step of adding additional data to an end of the cutting force partial data and an end of the vibration partial data; an analysis step of deriving vibration characteristics of the analysis object by frequency analysis using the cutting force part data and the vibration part data including the additional data; having The additional data is data for extending a time window length of the frequency analysis, and is composed of a plurality of zero values ​​arranged consecutively along a time series. Vibration analysis method.

2. 2. The vibration analysis method according to claim 1, The measuring step further includes measuring a rotation period of the cutting tool by a rotation detector that outputs a pulse signal every time the cutting tool rotates once, In the extraction step, the time interval is calculated by dividing the rotation period by the number of teeth of the cutting tool, and then the cutting force partial data and the vibration partial data are extracted with a timing at which a predetermined length of time shorter than the rotation period has elapsed from the timing at which the pulse signal is output as the start point of the interval, and a timing at which a length of time equal to the time interval has elapsed from the start point as the end point of the interval.

3. 2. The vibration analysis method according to claim 1, The measuring step further includes measuring a rotation period of the cutting tool by a rotation detector that outputs a pulse signal every time the cutting tool rotates once, In the extraction step, the time interval is calculated by dividing the rotation period by the number of teeth of the cutting tool, and then the cutting force partial data and the vibration partial data are extracted with the timing when the pulse signal is output as the start point of the interval and the timing when a time equal to the time interval has elapsed from the start point as the end point of the interval.

4. The vibration analysis method according to any one of claims 1 to 3, In the adding step, the additional data is added so that the number of pieces of cutting force partial data including the additional data is a power of two, and the number of pieces of vibration partial data including the additional data is a power of two, A vibration analysis method, wherein in the analyzing step, a fast Fourier transform is performed on the cutting force partial data and the vibration partial data including the additional data to derive the vibration characteristics.

5. The vibration analysis method according to any one of claims 1 to 4, In the measuring step, the cutting force is measured by a sensor arranged at a position different from a processing point where the cutting force is applied from the cutting tool to the workpiece, A vibration analysis method in which, in the analysis process, the cutting force measured by the sensor is corrected to the cutting force at the processing point using a force transmission characteristic between the processing point and the sensor that has been derived in advance, and then the vibration characteristics are derived.

6. A vibration analysis device, comprising: a vibration analysis unit configured to analyze vibrations of an analysis object, the analysis object being a cutting tool or a workpiece; The vibration analysis unit is an acquisition process for acquiring cutting force data in which the cutting force is represented in a time series and vibration data in which the vibration is represented in a time series, the cutting force being applied to the workpiece from the cutting tool rotating at a constant speed and the vibration of the object to be analyzed being measured while the workpiece is being cut by the cutting tool; an extraction process for extracting cutting force portion data, which is data for a section having a length corresponding to a time interval from when the blade of the cutting tool comes into contact with the workpiece until when the blade of the cutting tool next comes into contact with the workpiece, from the cutting force data, and extracting vibration portion data, which is data for the section, from the vibration data; an addition process of adding additional data to an end of the cutting force partial data and an end of the vibration partial data; an analysis process of deriving vibration characteristics of the analysis object by frequency analysis using the cutting force part data and the vibration part data including the additional data; Run The additional data is data for extending a time window length of the frequency analysis, and is composed of a plurality of zero values ​​arranged consecutively along a time series. Vibration analysis equipment.

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