Machining system and machining method

Abstract

This system provides a cutting system capable of accurately detecting abnormalities during vibration cutting. [Solution] The cutting system 10 is a cutting system for cutting a workpiece 22, and comprises a cutting tool 23, a first drive unit 24, a second drive unit 25, a load measurement sensor 26, and a control unit 31. The cutting tool 23 cuts the workpiece 22. The first drive unit 24 rotates the workpiece 22 relative to the cutting tool. The second drive unit 25 feeds the cutting tool 23 relative to the workpiece 22 along the machining direction A. The load measurement sensor 26 measures the load during cutting of the workpiece 22. In vibratory cutting, where the cutting tool 23 is vibrated relative to the workpiece 22 along the machining direction A, the control unit 31 detects a peak in the period of load fluctuation from the value detected by the load measurement sensor 26, and determines an abnormality based on the fluctuation of the peak value.

Description

Technical Field

[0001] The present disclosure relates to a cutting system and a cutting method.

Background Art

[0002] In machining such as cutting, when an abnormality such as chipping of a tool occurs, continuing the machining as it is will lead to damage to the workpiece and the tool. Therefore, for example, in Patent Document 1, determination of tool abnormality is performed based on a change in load during machining.

[0003] On the other hand, in the machine tool shown in Patent Document 2, in order to prevent chips from getting caught on the workpiece, a method of cutting the chips by vibrating the cutting tool in the machining direction with respect to the workpiece is used.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when performing vibration cutting as shown in Patent Document 2, since the machining load fluctuates, even if abnormality determination is performed as described in Patent Document 1, the change in load due to tool abnormality is masked by the load fluctuation due to vibration cutting, so the abnormality cannot be accurately determined.

[0006] An object of the present disclosure is to provide a cutting system and a cutting method capable of accurately detecting an abnormality in vibration cutting.

Means for Solving the Problems

[0007] A cutting system according to one aspect of the present disclosure is a cutting system for cutting a workpiece, comprising a cutting tool, a first drive unit, a second drive unit, a load measurement sensor, and a control unit. The cutting tool cuts the workpiece. The first drive unit rotates the workpiece relative to the cutting tool. The second drive unit feeds the cutting tool relative to the workpiece along the machining direction. The load measurement sensor measures the load during cutting of the workpiece. In a vibratory cutting process in which the cutting tool is vibrated relative to the workpiece along the machining direction, the control unit detects a peak in the period of load fluctuation from the value detected by the load measurement sensor and determines an abnormality based on the fluctuation of the peak value.

[0008] Another aspect of the present disclosure is a cutting method for detecting abnormalities when cutting a workpiece, comprising: a vibration cutting step; a load measurement step; a peak detection step; and a determination step. In the vibration cutting step, a cutting tool that rotates relative to the workpiece to cut the workpiece is vibrated relative to the workpiece along the cutting direction. In the load measurement step, the load during cutting of the workpiece is measured. In the peak detection step, a peak in the period of load fluctuation is detected from the detected value in the load measurement step during the vibration cutting step. In the determination step, an abnormality is determined based on the fluctuation of the peak value. [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide a cutting system and a cutting method that can accurately detect abnormalities in vibration cutting. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing the configuration of a cutting machine according to an embodiment. [Figure 2] This is a block diagram showing the configuration of the control unit of a cutting machine according to an embodiment. [Figure 3] (a) to (c) are illustrative diagrams of vibration cutting waveform creation. [Figure 4A] It is a diagram for explaining the frequency multiplication and amplitude multiplication of the embodiment. [Figure 4B] It is a diagram for explaining the frequency multiplication and amplitude multiplication of the embodiment. [Figure 4C] It is a diagram for explaining the frequency multiplication and amplitude multiplication of the embodiment. [Figure 4D] It is a diagram for explaining the frequency multiplication and amplitude multiplication of the embodiment. [Figure 5A] It is a schematic diagram for explaining the cutting of a workpiece by a cutting tool when no vibration is applied. [Figure 5B] It is a schematic diagram for explaining the cutting of a workpiece by a cutting tool when vibration is applied as shown in FIG. 4B. [Figure 6A] It is a diagram showing a graph of the time variation of the machining load when the peak of the machining load is divided into three groups. [Figure 6B] It is a diagram showing a graph of the time variation of the machining load when the peak of the machining load is divided into two groups. [Figure 6C] It is a diagram showing a graph of the time variation of the machining load when the peak of the machining load becomes one group. [Figure 7] It is a schematic diagram for explaining the difference in load by group. [Figure 8] It is a diagram showing a graph when an abnormality occurs in the graph shown in FIG. 6B. [Figure 9] (a) It is a diagram showing a graph of the time change of the machining load at the start of cutting. (b) It is a diagram showing a graph of the time change of the machining load at the end of cutting. [Figure 10] It is a flowchart showing the operation of abnormality detection of the cutting system of the present embodiment.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, a cutting system according to an embodiment of the present disclosure will be described with reference to the drawings.

[0012] The machining system 10 performs machining on a workpiece. FIG. 1 is a schematic diagram showing the configuration of the machining system 10. The machining system 10 includes a machining unit 20 and a machining control device 30. The machining unit 20 has a spindle 21, a workpiece 22 which is the object to be machined, a cutting tool 23, a first drive unit 24, a second drive unit 25, and a load measurement sensor 26.

[0013] In FIG. 1, a case where a metal round bar is used as the workpiece 22 and the outer shape of the round bar is machined into a desired outer shape by the cutting tool 23 will be described as an example. The spindle 21 rotates about the rotation axis L. The workpiece 22 is attached to the spindle 21. The workpiece 22 rotates about the rotation axis L together with the spindle 21.

[0014] The cutting tool 23 is used for machining the workpiece 22. The cutting tool 23 moves in the machining direction A. Thereby, the cutting tool 23 machines the workpiece 22 while relatively moving along the machining direction A with respect to the workpiece 22. The machining direction A is the so-called feed direction.

[0015] As will be described later, the cutting tool 23 moves along the machining direction A while vibrating on the feed side and the reverse feed side. The feed side Af is the side where the machining of the workpiece 22 proceeds in the machining direction A, and the reverse feed side Ar is the side opposite to the feed side in the machining direction A.

[0016] The first drive unit 24 rotationally drives the spindle 21. The first drive unit 24 rotates the spindle 21 at a predetermined rotational speed based on a drive command from the machining control device 30. When the spindle 21 is rotationally driven, the workpiece 22 rotates relative to the cutting tool 23. As the first drive unit 24, for example, a servo motor can be used.

[0017] The second drive unit 25 vibrates the cutting tool 23 on the feed side Af and the reverse feed side Ar, moving the cutting tool 23 along the machining direction. The second drive unit 25 moves on the feed side Af or the reverse feed side Ar based on a movement command from the cutting control device 30. For example, a servo motor can be used as the second drive unit 25. The second drive unit 25 can also appropriately move the cutting tool 23 in the radial direction (X-axis direction) perpendicular to the rotation axis L (parallel to the Z-axis).

[0018] The load measurement sensor 26 measures the current value when the spindle 21 is rotated at a predetermined rotational speed. When the workpiece 22 becomes difficult to rotate due to cutting by the cutting tool 23, the current value required to maintain the predetermined rotational speed increases. By measuring such changes in current value, the load on the first drive unit 24 is measured. The load measurement sensor 26 is, for example, a load meter.

[0019] The cutting control device 30 controls the cutting unit 20. The cutting control device 30 includes a control unit 31, an input unit 32, and a display unit 33 (notification unit).

[0020] The control unit 31 includes, for example, a processor 31a and a storage unit 31b. The processor is, for example, a CPU (Central Processing Unit). Alternatively, the processor may be a different processor from the CPU. The processor 31a drives the spindle 21 and the cutting tool 23 by outputting commands to the second drive unit 25 and the first drive unit 24 according to the NC program (Numerical Control) stored in the storage unit 31b. The processor 31a detects abnormalities in the cutting system 10 according to an abnormality detection program stored in the storage unit 31b.

[0021] The memory unit 31b records the NC program and anomaly detection program used for cutting the workpiece 22 with the cutting tool 23. The memory unit 31b includes non-volatile memory such as ROM (Read Only Memory) and volatile memory such as RAM (Random Access Memory). The memory may also include auxiliary storage devices such as HDD (Hard Disk Drive) or SSD (Solid State Drive). The memory is an example of a non-transitory processor-readable recording medium. Details of the functions of the control unit 31 will be described later.

[0022] The input unit 32 includes, for example, a keyboard, mouse, or touch panel. The display unit 33 is, for example, a display. The operator inputs various settings by operating the input unit 32 while looking at the display unit 33. A speaker or the like may be provided together with the display unit 33, or separately from the display unit 33, enabling audio output.

[0023] Figure 2 is a block diagram showing the functional configuration of the control unit 31. As shown in Figure 2, the control unit 31 includes a cutting execution unit 41, a load acquisition unit 42, a peak detection unit 43, a group number calculation unit 44, a group distribution unit 45, and an abnormality determination unit 46. The processor 31a executes the programs (NC program and abnormality detection program) stored in the storage unit 31b, thereby enabling the cutting execution unit 41, load acquisition unit 42, peak detection unit 43, group number calculation unit 44, group distribution unit 45, and abnormality determination unit 46 to perform their functions.

[0024] The cutting execution unit 41 outputs commands to the second drive unit 25 and the first drive unit 24 to drive the spindle 21 and the cutting tool 23. When cutting a workpiece, the cutting execution unit 41 outputs a movement command to the second drive unit 25 so that the cutting tool 23 vibrates relative to the cutting tool 23 along the machining direction A based on a predetermined vibration waveform.

[0025] The cutting execution unit 41 calculates a cutting vibration waveform based on the frequency multiplier I and amplitude multiplier K input to the input unit 32, and outputs a movement command to the second drive unit 25 in accordance with the calculated cutting vibration waveform, thereby realizing vibration cutting by NC program.

[0026] Figures 3(a) to 3(c) show an image of the creation of cutting vibration waveforms. Figure 3(a) shows graph g1 of the feed operation set for the cutting tool 23 during cutting. No vibration is applied to the feed operation shown in graph g1. In Figure 3(a), the horizontal axis represents elapsed time (s), and the vertical axis represents coordinate C. Coordinate C represents the position of the cutting tool 23 along the machining direction A relative to the workpiece 22. When the machining direction A is a straight line, coordinate C represents the position along the straight line. When the machining direction A is an arc, coordinate C represents the position along the arc. Coordinate C can also be said to be the distance traveled along the machining direction A.

[0027] Figure 3(a) shows the case where the cutting tool 23 is advanced in the feed direction as shown in Figure 1. If C is the coordinate (mm), Cstart is the starting coordinate (mm) of cutting, Fave is the average feed rate, and T is the elapsed time (s), then the graph g1 shown in Figure 3(a) is represented by the following equation (1).

[0028] C=Cstart+Fave×T...Formula (1) This graph g1 (an example of a set feed operation) is pre-set for each type of workpiece 22 and cutting shape, and is stored as an NC program in the memory unit 31b.

[0029] Figure 3(b) shows graph g2, which is the vibration waveform to be added to graph g1. In Figure 3(b), the horizontal axis represents elapsed time (s), and the vertical axis represents coordinate C. If f is the feed rate (mm / rev) when the spindle rotates once, θ is the rotation angle (°) of the vibration sine wave, K is the amplitude multiplier, and I is the frequency multiplier, then the vibration waveform graph g2 is expressed by the following equation (2). As will be explained in more detail later, the amplitude multiplier K specifies how many times the amplitude of the vibration is compared to the feed rate per rotation of the spindle 21. The frequency multiplier I (information on the relationship between the rotational speed of the workpiece and the vibration frequency) specifies how many times the spindle 21 vibrates during one rotation.

[0030] C=Kfsinθ···Formula (2) Figure 3(c) shows graph g3, which represents the vibration cutting waveform obtained by adding graph g2 to graph g1. In Figure 3(c), the horizontal axis represents elapsed time (s), and the vertical axis represents coordinate C. Graph g3 is represented by the following equation (3).

[0031] C=Cstart+Fave·T+Kfsinθ···Formula (3) Furthermore, when the cutting tool 23 moves in the reverse direction, graph g1 becomes C = Cstart - Fave·T, and graph g2 is expressed as C = -Kfsinθ, so graph g3 is expressed as C = Cstart - Fave·T - Kfsinθ...equation (4).

[0032] Next, the frequency multiplier I and amplitude multiplier K mentioned above will be explained.

[0033] Figure 4A is a graph showing the change in the coordinate C of the cutting tool 23 during one rotation of the spindle 21. In Figure 4A, the horizontal axis represents the rotation angle (deg), and the vertical axis represents the coordinate C.

[0034] In Figure 4A, graph m1 shows the case when no vibration is applied during the first rotation of the spindle 21, graph m2 shows the case when no vibration is applied during the second rotation of the spindle 21, graph m3 shows the case when no vibration is applied during the third rotation of the spindle 21, and graph m4 shows the case when no vibration is applied during the fourth rotation of the spindle 21. Graphs m1, m2, m3, and m4 are drawn by plotting graph g1 from Figure 3(a) such that the rotation angle becomes 0 degrees when the rotation angle of the spindle 21 reaches 360 degrees. m1 to m4 are shown as dotted lines.

[0035] As shown in graph m1, in the first rotation of the spindle 21, the cutting tool 23 is advanced relative to the workpiece 22 from coordinate Cstart to coordinate C1 along the machining direction A. Next, as shown in graph m2, in the second rotation of the spindle 21, the cutting tool 23 is advanced relative to the workpiece 22 from coordinate C1 to coordinate C2 along the machining direction A. Next, as shown in graph m3, in the third rotation of the spindle 21, the cutting tool 23 is advanced relative to the workpiece 22 from coordinate C2 to coordinate C3 along the machining direction A. Next, as shown in graph m4, in the fourth rotation of the spindle 21, the cutting tool 23 is advanced relative to the workpiece 22 from coordinate C3 to coordinate C4 along the machining direction A.

[0036] Graphs n1 to n4 are graphs m1 to m4 with the vibration waveforms added. Graphs n1, n2, n3, and n4 are plotted by drawing graph g3 in Figure 3(c) such that the rotation angle becomes 0 degrees when the rotation angle of the principal axis 21 reaches 360 degrees.

[0037] The graph for the first rotation of the main shaft 21 is shown by n1 (solid line), the graph for the second rotation of the main shaft 21 is shown by n2 (dotted line), the graph for the third rotation of the main shaft 21 is shown by n3 (solid line), and the graph for the fourth rotation of the main shaft 21 is shown by n4 (double-dotted line).

[0038] The frequency multiplier I specifies how many times the cutting tool 23 vibrates relative to the workpiece 22 in the machining direction A during one rotation of the spindle 21. The amplitude multiplier K specifies how many times the amplitude of the vibration is compared to the feed rate per rotation of the spindle 21.

[0039] In Figure 4A, the frequency multiplier I is set to 0.5 (=1 / 2) and the amplitude multiplier K is set to 1.0. Therefore, as shown in the solid line graph n1, during the first rotation of the spindle 21, the cutting tool 23 oscillates for half a period, moving towards the feed side and then returning. Then, as shown in the dashed line graph n2, during the second rotation of the spindle, the cutting tool 23 oscillates for half a period, moving towards the reverse feed side and then returning. Also, because the amplitude multiplier K is set to 1.0, if the feed amount for one rotation of the spindle is XΔs and the amplitude is XΔ, then as shown in Figure 4A, XΔs and XΔ are set to the same length.

[0040] Here, the graph n1 of the first rotation of the spindle 21 and the graph n2 of the second rotation of the spindle 21 overlap. This overlapping region R is the area that was cut during the first rotation, so the cutting tool 23 moves away from the workpiece 22 during the second rotation. No chips are generated in this region R during the second rotation, so the chips are broken up. Also, the graph n3 of the third rotation of the spindle 21 and the graph n4 of the fourth rotation of the spindle 21 overlap, and the chips are broken up in the overlapping region R.

[0041] Figure 4B is a graph showing the change in the coordinate C of the cutting tool 23 during one rotation of the spindle 21, when the frequency multiplier I of the vibration waveform is set to 1.5 (=3 / 2) and the amplitude multiplier K is set to 1.0. In Figure 4B, the horizontal axis represents the rotation angle (deg), and the vertical axis represents the coordinate C. In Figure 4B, graphs m1 to m4 and graphs n1 to n4 are shown, similar to Figure 4A.

[0042] In Figure 4B, compared to Figure 4A, the number of waves in the cutting vibration waveform per rotation of the spindle 21 is greater, with waves for one and half periods being shown. In this case, the region R where the graph n1 for the first rotation and the graph n2 for the second rotation overlap occurs twice per rotation of the spindle 21. Similarly, the region R where the graph n3 for the third rotation and the graph n4 for the fourth rotation overlap also occurs twice per rotation of the spindle 21.

[0043] Figure 4C is a graph showing the change in coordinate C during one rotation of the main shaft 21, when the frequency multiplier I of the vibration waveform is set to 0.5 (=1 / 2) and the amplitude multiplier K is set to 1.5. In Figure 4C, the horizontal axis represents the rotation angle (deg), and the vertical axis represents the coordinate C. In Figure 4C, graphs m1 to m4 and graphs n1 to n4 are shown, similar to Figure 4A.

[0044] In Figure 4C, the amplitude of the vibration waveform is larger compared to Figure 4A. The length of XΔ is set to 1.5 times XΔs. In this case, the width of region R in the machining direction A is larger compared to the case in Figure 3(a).

[0045] Figure 4D is a graph showing the change in the coordinate C of the cutting tool 23 during one rotation of the spindle 21, when the frequency multiplier I of the vibration waveform is set to 2 / 3 and the amplitude multiplier K is set to 0.75. In Figure 4C, the horizontal axis represents the rotation angle (deg), and the vertical axis represents the coordinate C. The length of XΔ is set to 0.75 times XΔs.

[0046] In Figure 4D, graphs m1 to m6 show the case where no vibration is applied during the 6 rotations of the spindle 21. Graphs n1 to n6 show the case where vibration is applied. Compared to Figures 4A and 4B, Figure 4D adds graphs m5 for the 5th rotation and m6 for the 6th rotation when no vibration is applied. Coordinates C5 of the cutting tool 23 after the 5th rotation of the spindle 21 and C6 of the cutting tool 23 after the 6th rotation of the spindle 21 are also added. Furthermore, compared to Figures 4A and 4B, Figure 4D adds graphs n5 for the 5th rotation and n6 for the 6th rotation when vibration is applied.

[0047] In Figure 4D, n1 and n4 are shown as solid lines, n2 and n5 as dashed lines, and n3 and n5 as double-dashed lines. In Figure 4C, as shown in graphs n1 to n3, the cutting tool 23 vibrates for two periods when the spindle 21 rotates three times. As shown in graphs n4 to n6, the cutting tool 23 vibrates for two more periods when the spindle 21 rotates three more times. In this way, the vibration of the cutting tool 23 for two periods for three rotations of the spindle 21 is repeated. The chip is divided in the overlapping region R of graph n1 for the first rotation and graph n2 for the second rotation, and in the overlapping region R of graph n2 for the second rotation and graph n3 for the third rotation.

[0048] Figure 5A is a schematic diagram illustrating the cutting of a workpiece by the cutting tool 23 when no vibration is applied. Figure 5A shows cutting lines m1', m2', m3', and m4', which correspond to graphs m1, m2, m3, and m4. As shown by these cutting lines m1', m2', m3', and m4', the workpiece 22 is cut toward the feed side Af over time.

[0049] Figure 5B is a schematic diagram illustrating the cutting of a workpiece by the cutting tool 23 when vibration is applied as shown in Figure 4B. Figure 5B shows cutting lines n1', n2', n3', and n4', which correspond to graphs n1, n2, n3, and n4 in Figure 4B. As shown by these cutting lines n1', n2', n3', and n4', the workpiece 22 is cut toward the feed side Af over time while vibrating in the machining direction A. The chip is cut in the overlapping region R described above.

[0050] The load acquisition unit 42 shown in Figure 2 acquires the load measured by the load measurement sensor 26. Figure 6A is a graph showing an example of the time variation of the machining load. Graph Q1 shown in Figure 6A shows the time variation of the machining load when the frequency multiplier is set to 3 / 2, for example, as in Figure 4B. In Figure 6A, the horizontal axis represents time, and the vertical axis represents the machining load (%). The machining load represents the ratio of the current value actually supplied to the first drive unit 24 to the maximum current value that can be supplied according to the specifications. As shown in Figure 6A, three types of peaks appear due to vibration cutting: a peak with a large machining load, a peak with a small machining load, and a peak in between. Thus, in the case of Figure 6A, the detected peaks are divided into three groups: a group of types with a large machining load, a group of types with a small machining load, and a group of types with machining loads in between. Note that the number of groups differs because the number of types of peaks differs depending on the set frequency multiplier. Figure 6B is a graph Q2 showing the time change of the machining load when there are two groups of peaks. Graph Q2, shown in Figure 6B, shows the time variation of the machining load when the frequency multiplier is set to 2 / 3, for example, similar to Figure 4D. Figure 6C shows graph Q3, which represents the time variation of the machining load when there is only one peak group. Graph Q3, shown in Figure 6C, shows the time variation of the machining load when the frequency multiplier is set to 1 / 2, for example, similar to Figure 4A. Similar to Figure 6A, the horizontal axis in Figures 6B and 6C represents time, and the vertical axis represents the machining load. Thus, the number of groups differs depending on how many times the spindle 21 vibrates during one rotation. The calculation of the number of groups will be described later.

[0051] The peak detection unit 43 detects peaks in load fluctuations acquired by the load measurement sensor 26. The method for detecting peaks is not particularly limited. For example, if it is determined that the load values ​​acquired in a time series increase and then decrease, the value immediately preceding the decreased value (the last value of the increase) may be considered the peak. However, even if the peak detection unit 43 detects a peak, it will not treat it as a peak if the load value is less than a predetermined value V1. This prevents the detection of small load fluctuations at the start of cutting operations, as shown in Figure 9(a) later, as peaks.

[0052] The group number calculation unit 44 calculates the number of groups to which the detected peaks belong. The number of peak types changes depending on the frequency multiplier I entered by the operator in the input unit 32. Therefore, the group number calculation unit 44 can calculate the number of groups from the frequency multiplier I entered by the operator in the input unit 32. The group number calculation unit 44 can calculate the number of groups based on the vibration frequency during one rotation of the spindle 21. As described above, the frequency multiplier I specifies how many times the spindle 21 vibrates during one rotation, and if I = N / M, and N and M are relatively prime integers, then the number of groups can be found to be N. Note that if M=1, it is theoretically impossible to break the chips by vibration cutting, so this case is not used in actual operation, and M≠1.

[0053] For example, if the spindle 21 vibrates with a period of 0.5 during one rotation, N / M = 1 / 2, and N is 1, so the peaks form one group. The peaks are the positions of the vibration crests. The vibration graph for the case of a 1 / 2 period is shown in Figure 4A above, where the peak is indicated by P. As shown in Figure 4A, when vibrating with a period of 0.5, the load peak P occurs when the rotation angle is 180 degrees. Also, for example, if the spindle 21 vibrates with a period of 0.25 during one rotation, N / M = 1 / 4, and N is 1, so the peaks form one group.

[0054] When the main shaft 21 vibrates with a period of 1.5 (3 / 2) during one rotation, N becomes 3, and the peaks are divided into three groups. The vibration graph for the 3 / 2 period is shown in Figure 4B above, where the peaks are indicated by P. As shown in Figure 4B, when vibrating with a 3 / 2 period, load peaks P occur when the rotation angle is 60 degrees, 180 degrees, and 270 degrees.

[0055] When the spindle 21 vibrates with a period of 2 / 3 during one rotation, N becomes 2, and the peaks are divided into two groups. The vibration graph for the 2 / 3 period case is shown in Figure 4D above, where the peaks are indicated by P. As shown in Figure 4D, when vibrating with a 2 / 3 period, load peaks P occur when the rotation angle is 150 degrees and 330 degrees. Also, for example, when the spindle 21 vibrates with a period of 0.4 (2 / 5) during one rotation, N becomes 2, and the peaks are divided into two groups.

[0056] The group assignment unit 45 assigns the detected peaks to groups in chronological order. In the example shown in Figure 6A, the group number calculation unit 44 calculates that there are 3 groups from the input of the frequency multiplier I to the input unit 32. The group assignment unit 45 assigns the peaks detected by the peak detection unit 43 to groups in chronological order. For example, the first peak P1 shown in Figure 6A is assigned to group G1, the second peak P2 detected next in chronological order is assigned to group G2, the third peak P3 detected next is assigned to group G3, and the fourth peak P4 detected next is assigned to group G1. The fifth peak P5 is assigned to group G2, the sixth peak P6 is assigned to group G3, the seventh peak P7 is assigned to group G1, the eighth peak P8 is assigned to group G2, and the ninth peak P9 is assigned to group G3. In this way, the detected peaks are assigned in chronological order according to the predetermined number of groups. In Figure 6A, the peaks of group G1 are shown as triangles, the peaks of group G2 are shown as circles, and the peaks of group G3 are shown as squares.

[0057] For example, peaks P1, P4, P7, etc., assigned to group G1 correspond to peak P at 60 degrees shown in Figure 4B. Peaks P2, P5, P8, etc., assigned to group G2 correspond to peak P at 180 degrees shown in Figure 4B. Peaks P3, P6, P9, etc., assigned to group G3 correspond to peak P at 270 degrees shown in Figure 4B.

[0058] Figure 7 is a schematic diagram illustrating the differences in load among the groups. In Figure 7, the workpiece remaining after cutting is shown as Wa (solid line), and the workpiece before cutting is shown as Wb (dotted line). The cut workpiece Wa is created from workpiece Wb. When the frequency multiplier I of the vibration waveform is set to 1.5 (=3 / 2), peaks occur at rotation angles of 60°, 180°, and 270°, similar to Figures 4B and 6A. For example, in Figure 7, the uppermost position is set to 0°, and the positions of 60°, 180°, and 270° are set toward the rotation direction B.

[0059] During cutting, a discrepancy occurs between the center Ob of the workpiece Wb and the center Oa where the workpiece Wb actually rotates. Therefore, the amount of material removed changes depending on the rotation angle. The amount of material removed at 60° is d. 60 The amount of material removed at 180° is d. 180 The amount of material removed at 270° is d. 270 Therefore, if the center Ob is offset from the center of rotation Oa as shown in Figure 7, then d 60 >d 180 >d 270 Therefore, the magnitude of the load decreases in the order of 60°, 180°, and 270°, and the load will vary depending on the group. Note that the degree of deviation of the center Ob relative to the rotation center Oa differs for each workpiece, so the angle at which the peak load is greatest will differ depending on the workpiece. For example, the load value for group G3 may be the greatest.

[0060] Even if the group number calculation unit 44 calculates that there are two groups, the peaks detected in chronological order are assigned to the two groups, just as in the case of three groups. For example, the first detected peak P1 shown in Figure 6B is assigned to group G1, and the second detected peak P2, which is the next to be detected in chronological order, is assigned to group G2. The third detected peak P3 is assigned to group G1, the fourth detected peak P4 is assigned to group G2, and the fifth detected peak P5 is assigned to group G1. In Figure 6B, the peaks in group G1 are shown as triangles, and the peaks in group G2 are shown as circles. For example, the peaks P1, P3, P5, etc., assigned to group G1 in Figure 6B correspond to the peak P at 150 degrees shown in Figure 4D. The peaks P2, P4, P6, etc., assigned to group G2 correspond to the peak P at 330 degrees shown in Figure 4D.

[0061] If the group number calculation unit 44 calculates that there is one group, then, as shown in Figure 6C, all peaks will belong to the same group G1. Therefore, the group allocation unit 45 does not need to allocate the peaks to groups. The peak in Figure 6C occurs at 180° in Figure 4A.

[0062] The anomaly detection unit 46 determines an anomaly based on the difference between the value of the most recently detected peak and the values ​​of other peaks in the group to which that peak is assigned. The values ​​of other peaks are, for example, the values ​​of the peak immediately preceding the new peak in the same group as the most recently detected peak (also called the new peak). The anomaly detection unit 46 calculates the difference between the value of the new peak and the value of the peak detected immediately preceding the new peak in the same group as the new peak, and determines that an anomaly has occurred if the difference is greater than or equal to a reference value. Figure 8 shows graph Q2' when an anomaly has occurred in graph Q2 shown in Figure 6B. If the third peak detected, P3, is the most recently detected peak, the anomaly detection unit 46 detects the difference between the value of peak P3 and the value of peak P1 detected immediately preceding peak P3 in the same group G1 as peak P3, and determines whether the difference is greater than or equal to a predetermined threshold. Since the load values ​​of peak P3 and peak P1 are almost the same, the difference is smaller than the reference value, and the anomaly detection unit 46 does not determine that an anomaly has occurred. If the eighth detected peak P8 is the most recently detected peak, the anomaly detection unit 46 detects the difference Δd between the value of peak P8 and the value of the previous peak P6 in the same group G2 as peak P8. Since the difference Δd is large and greater than or equal to the reference value, the anomaly detection unit 46 determines that an anomaly has occurred. The reference value for the difference is set to be greater than the detection error.

[0063] When the abnormality detection unit 46 determines that an abnormality has occurred, it notifies the operator of the abnormality through the display unit 33 and stops the cutting process. If a speaker is provided, the abnormality may also be notified to the user by voice.

[0064] The abnormality determination unit 46 does not determine an abnormality even if the difference is greater than or equal to a predetermined threshold when it determines that it is the start or end of the cutting process. Figure 9(a) is a graph showing the time change of the machining load at the start of the cutting process. Figure 9(a) shows, for example, the start of the cutting process for graph Q2 in Figure 6B. Peaks where the load value is less than the predetermined value V1 are not used for abnormality determination and are not treated as peaks, so for example, peak P11 becomes the first peak detected by the peak detection unit 43. This peak P11 is assigned to group G1 by the group assignment unit 45. Next, peak P12 detected by peak detection unit 43 is assigned to group G2 by the group assignment unit 45. Next, peak P13 is assigned to group G1 by the group assignment unit 45. Here, the abnormality determination unit 46 detects the difference between peak P13 and the previous peak P11 in the same group G1, and determines that the difference is greater than or equal to a predetermined threshold. However, since the values ​​of peak P11, peak P12, and peak P13 are increasing monotonically in chronological order, it is determined that this is the start time and not that an anomaly has occurred.

[0065] Furthermore, since the value of peak P14, which is detected after peak P13 as shown in Figure 9(a), is lower than the value of peak P13, the anomaly detection unit 46 determines that it does not correspond to a monotonically increasing pattern and assigns peak P14 to group G2 as the first peak, and assigns the next detected peak P15 to group G1 as the first peak. Then, for peak P16, which is detected after peak P15, the difference between the value of peak P16 and the value of peak P14 is calculated to determine if it is an anomaly.

[0066] Furthermore, Figure 9(b) shows, for example, the end of the cutting process in graph Q2 of Figure 6B. The group distribution unit 45 assigns the peak P21 shown in Figure 9(b) to group G1, and the next detected peak P22 is assigned to group G2 by the group distribution unit 45. The group distribution unit 45 assigns the next detected peak P23 to group G1. The abnormality determination unit 46 detects the difference between peak P23 and the previous peak P21 in the same group G1, and determines that the difference Δd is greater than or equal to a predetermined threshold. However, since the values ​​of peak P21, peak P22, and peak P23 are monotonically decreasing in chronological order, it determines that it is the end of the process and does not determine that an abnormality has occurred.

[0067] Thus, even if the difference between the value of a new peak and the value of the peak immediately preceding the new peak in the same group as the new peak is greater than or equal to a predetermined threshold, the anomaly detection unit 46 does not determine it to be an anomaly if, when the two peaks from which the difference was detected and the peaks between them are arranged in chronological order, the values ​​are monotonically increasing or monotonically decreasing.

[0068] (Abnormal detection operation in the cutting system) Next, the abnormality detection operation of the cutting system 10 of this embodiment will be described. Figure 10 is a flowchart showing the abnormality detection operation of the cutting system 10 of this embodiment.

[0069] Before starting the cutting process, the operator uses the input unit 32 to input various parameters necessary for the cutting process. These parameters include the frequency multiplier I and the amplitude multiplier K. The group number calculation unit 44 calculates the number of groups to which the peaks will be distributed based on the frequency multiplier I, and the calculated number of groups is stored in the storage unit 31b.

[0070] First, in step S10, the cutting execution unit 41 controls the first drive unit 24 and the second drive unit 25 according to a predetermined NC program to start the cutting process. Step S10 corresponds to an example of a vibration cutting process step.

[0071] Next, in step S11, the load measurement sensor 26 measures the value of the load generated on the main shaft 21, and the load acquisition unit 42 acquires the measured value. Step S11 corresponds to an example of a load measurement step.

[0072] Next, in step S12, the peak detection unit 43 calculates the peak in the load fluctuation. Step S12 corresponds to an example of a peak detection step.

[0073] If the peak detection unit 43 detects a new peak in step S13, the control proceeds to step S14. If no new peak is detected in step S13, the control returns to step S11.

[0074] In step S14, the group allocation unit 45 allocates the new peaks to groups and records the peaks in chronological order. If there is only one group, all detected peaks belong to the same group, so the group allocation unit 45 does not need to allocate them to new peak groups.

[0075] Next, in step S15, the abnormality determination unit 46 determines whether there are any peaks detected before the new peak within the same group as the new peak. If there are no peaks detected before the new peak, the control returns to step S11. On the other hand, if there are peaks detected before the new peak, the control proceeds to step S16.

[0076] Next, in step S16, the abnormality detection unit 46 calculates the difference between the new peak and the peak detected immediately before the new peak, which belongs to the same group as the new peak. For example, in Figure 8, the difference between the load value of peak P8 and the load value of peak P6 is calculated.

[0077] Next, in step S17, the abnormality determination unit 46 determines whether the difference is less than or equal to the reference value. If it is less than or equal to the reference value, in step S18, the cutting execution unit 41 determines whether the cutting process has been completed. If it is determined that the cutting process has not been completed, control returns to step S11.

[0078] On the other hand, if the abnormality determination unit 46 determines in step S18 that the difference is not below the reference value, the control proceeds to step S19.

[0079] In step S19, the abnormality determination unit 46 determines whether or not the change in peak is at the start or end of the cutting process.

[0080] If it is determined in step S19 that the change in peak is at the start or end of the cutting process, the control proceeds to step S18. For example, in the case shown in Figure 9(a), the abnormality determination unit 46 determines that the change in the load value of peak P13 relative to peak P11 within the same group G1 is a peak change at the start of the cutting process because the value of the new peak P13, the value of peak P11 which is in the same group G1 as the new peak P13 and is the peak immediately preceding the new peak P13, and the value of peak P12 which is between peak P11 and peak P13 are all increasing monotonically in time series. For example, in the case shown in Figure 9(b), the abnormality determination unit 46 determines that the change in the load value of peak P23 relative to peak P21 within the same group G1 is a peak change at the stop of the cutting process because the value of the new peak P23, the value of peak P21 which is in the same group G1 as the new peak P23 and is the peak immediately preceding the new peak P23, and the value of peak P22 which is between peak P21 and peak P23 are all decreasing monotonically in time series.

[0081] On the other hand, if step S19 determines that the change in peak is not at the start or end of the cutting process, then in step S20, the abnormality determination unit 46 determines that an abnormality has occurred. For example, in the case shown in Figure 8, the abnormality determination unit 46 determines that the change in peak is not at the start or end of the cutting process because, regardless of group distinction, the value of the new peak P8, the value of the peak P6 in the same group G2 as the new peak P8 and the peak P6 that preceded the new peak P8, and the value of the peak P7 between peak P6 and peak P8 are neither monotonically increasing nor monotonically decreasing in time series. Steps S16, S17, S19, and S20 correspond to examples of determination steps.

[0082] Next, in step S21, the cutting execution unit 41 interrupts the cutting process and terminates the control.

[0083] As described above, in the cutting system 10 of this embodiment, the control unit 31 detects a peak in the period of load fluctuation from the detected value of the load measurement sensor 26 while performing vibratory cutting, in which the cutting tool 23 is vibrated relative to the workpiece 22 along the machining direction A, and determines an abnormality based on the fluctuation of the peak value. In this way, by extracting the peak that appears in vibratory cutting, it is possible to detect abnormalities in vibratory cutting as well, based on the changes in the peak value.

[0084] In the cutting system 10 of this embodiment, as shown in Figure 8 for example, the control unit 31 acquires the number of groups G1 and G2 (two) for distributing pre-acquired peaks. If there are multiple groups, the control unit 31 distributes the detected peak P8 to group G2 and determines an anomaly based on the difference between the value of the detected peak P8 and the value of another peak P7 in the same group G2. This makes it possible to detect anomalies even when multiple types of peaks with different loads appear due to vibration cutting, as the fluctuation of the peaks can be detected according to their type.

[0085] In the cutting system 10 of this embodiment, the control unit 31 sequentially distributes the detected peaks P1, P2, P3, etc., into multiple groups G1, G2, etc., according to their time series. Since the number of groups can be determined in advance from the set frequency multiplier I, by distributing them into groups in chronological order, peaks of the same type can be assigned to the same group.

[0086] In the cutting system 10 of this embodiment, the control unit 31 obtains the number of groups to which previously acquired peaks are to be sorted. When there is one group, the control unit 31 determines an anomaly based on the difference between the value of the detected peak P8 and the value of another peak P7, as shown in Figure 6C. In this case, when there is only one group, there is no need to sort into groups, so an anomaly can be determined based on the variation of the value of the detected peak from the value of a previously detected peak.

[0087] In the cutting system 10 of this embodiment, for example, as shown in Figure 8, the control unit 31 calculates the difference between the detected peak P8 value and the value of another peak P7, and determines that an abnormality has occurred if the difference is greater than or equal to a reference value. This makes it possible to determine that an abnormality has occurred due to a large fluctuation in load.

[0088] In the cutting system 10 of this embodiment, the control unit 31 stops the cutting process if it detects an abnormality. This prevents the continuation of cutting in the event of an abnormality, such as a broken cutting tool.

[0089] In the cutting system 10 of this embodiment, the control unit 31 does not use peaks with values ​​less than a predetermined value V1 for determining abnormalities. This makes it possible to exclude small load peaks that occur at the start or end of the cutting process from the above determination.

[0090] In the cutting system 10 of this embodiment, the abnormality detection unit 46 does not determine an abnormality even if the difference between the value of the new peak P13 and the value of the peak P11 that is in the same group G1 as the new peak P13 and is the peak immediately preceding the new peak P13 is greater than or equal to a predetermined threshold, if the two peaks P11 and P13 from which the difference was detected, and the peak P12 between them, are arranged in chronological order and their values ​​are monotonically increasing. This makes it possible to exclude load fluctuations at the start of cutting from the above determination and to accurately detect abnormalities.

[0091] In the cutting system 10 of this embodiment, the abnormality detection unit 46 does not determine an abnormality even if the difference between the value of the new peak P23 and the value of the peak P21 that preceded the new peak P23 and is in the same group G1 as the new peak P23 is greater than or equal to a predetermined threshold, if the two peaks P21 and P23 from which the difference was detected, and the peak P22 between them, are arranged in chronological order and the values ​​are monotonically decreasing. This makes it possible to exclude load fluctuations during cutting stoppages from the above determination and to accurately detect abnormalities.

[0092] This disclosure is not limited to the embodiments described above, and various modifications or alterations are possible without departing from the scope of this disclosure.

[0093] In the above embodiment, the number of groups is determined using the frequency multiplier I input to the input unit 32 by the operator, but this is not the only method. For example, the number of groups may be determined based on the type of peak measured by the load measurement sensor 26 after performing test machining. Alternatively, the operator may directly input the number of groups to the input unit 32.

[0094] In the above embodiment, the workpiece 22 rotates and the cutting tool 23 vibrates along the machining direction, but this is not the only option, and which of the workpiece 22 and the cutting tool 23 rotates and which vibrates may be changed as appropriate.

[0095] In the above embodiment, the difference between the value of the new peak and the value of the peak immediately preceding the new peak in the same group as the new peak is calculated. However, the embodiment is not limited to this, and the difference between the value of the new peak and any one of the other peaks in the same group as the new peak, or the average value of the other peaks, may also be calculated. [Industrial applicability]

[0096] According to this disclosure, it is possible to provide a cutting system and a cutting method that can accurately detect abnormalities in vibration cutting. [Explanation of symbols]

[0097] 10: Machining System 22: Work 23:Cutting tools 24: First drive unit 25: Second drive unit 26: Load measurement sensor 31: Control Unit

Claims

1. A cutting system for machining a workpiece, A cutting tool for cutting the aforementioned workpiece, A first drive unit that rotates the workpiece relative to the cutting tool, A second drive unit that relatively feeds the cutting tool along the machining direction relative to the workpiece, A load measurement sensor for measuring the load during cutting of the workpiece, In a vibratory cutting process in which the cutting tool is vibrated relative to the workpiece along the machining direction, the system includes a control unit that detects a peak in the period of load fluctuation from the detected value of the load measurement sensor and determines an abnormality based on the fluctuation of the peak value, Machining system.

2. The control unit obtains the number of groups to which the previously acquired peaks are to be distributed. If there are multiple groups, the control unit distributes the detected peaks to the groups and determines an anomaly based on the difference between the value of the detected peak and the values ​​of one or more other peaks in the same group as the detected peak. The cutting system according to claim 1.

3. The control unit distributes the detected peaks sequentially into multiple groups according to the time series. The cutting system according to claim 2.

4. The control unit calculates the difference between the value of the detected peak and the value of the peak detected immediately before the detected peak in the same group as the detected peak, and determines that an abnormality has occurred if the difference is greater than or equal to a reference value. The cutting system according to claim 2.

5. The control unit obtains the number of groups to which the previously acquired peaks are to be distributed. If the number of groups is one, the control unit determines an anomaly based on the difference between the detected peak value and the values ​​of one or more other peaks. The cutting system according to claim 1.

6. The control unit calculates the difference between the value of the detected peak and the value of the peak detected immediately before the detected peak, and determines that an abnormality has occurred if the difference is greater than or equal to a reference value. The cutting system according to claim 5.

7. The system further includes a notification unit that notifies the operator of any abnormalities. If the control unit detects an abnormality, it controls the notification unit to notify the operator of the abnormality. The cutting system according to claim 1.

8. If the control unit detects an abnormality, it will stop the cutting process. The cutting system according to claim 1.

9. The control unit uses the peak with a value greater than or equal to a predetermined value for determining an abnormality. The cutting system according to claim 1.

10. When the difference is greater than or equal to a reference value, the control unit determines that the peak change is at the start of the cutting process and does not determine it to be abnormal if the two peak values ​​for which the difference was calculated and the value of one or more peaks detected between the two peaks are monotonically increasing in the order of the detected time series. The cutting system according to claim 4.

11. When the difference is greater than or equal to a reference value, the control unit determines that the peak change is due to the stopping of the cutting process and does not determine it to be abnormal if the two peak values ​​for which the difference was calculated and the value of one or more peaks detected between the two peaks are monotonically decreasing in the order of the detected time series. The cutting system according to claim 4.

12. An input unit for inputting information regarding the relationship between the rotational speed and vibration frequency of the aforementioned workpiece, The control unit determines the number of groups based on the input information. The cutting system according to claim 2 or 5.

13. A cutting method for cutting a workpiece, A vibration cutting step in which a cutting tool that rotates relative to the workpiece to cut the workpiece is vibrated relative to the workpiece along the machining direction, A load measurement step for measuring the load during cutting of the workpiece, During the vibration cutting step, a peak detection step is performed to detect the peak in the period of the load fluctuation from the detected value in the load measurement step, The system includes a determination step of determining an abnormality based on the fluctuation of the peak value, Cutting method.

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