Machine tool, machine tool control method and machine tool control program

Abstract

To provide a technique that can detect wear of a tool at least.SOLUTION: A machine tool comprises: a main spindle for rotating a tool; a housing for accommodating the main spindle; a plurality of strain sensors provided on the housing; and a detection part which detects wear or breakage of the tool on the basis of a cutting force waveform that is measured from each output signal of the plurality of strain sensors. The detection part mesures a waveform 700A of first cutting force, and after measurement of the waveform 700A of first cutting force, measures a waveform 700B of second cutting force, compares the waveform 700A of first cutting force and the waveform 700B of second cutting force, and on the basis of comparison result, detects wear of the tool.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present disclosure relates to machine tools, and more particularly to a technique for detecting abnormalities in a tool. [Background technology]

[0002] A technology has been developed for measuring the force applied to a tool during machining of a workpiece (hereinafter referred to as "cutting force"). Regarding this technology, JP 2022-106438 A (Patent Document 1) discloses a machine tool that uses a strain sensor to measure the cutting force applied to the tool. The strain sensor is provided on a flange of the machine tool and detects the cutting force applied to a tool attached to a spindle housed in the flange. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-106438 A Summary of the Invention [Problem to be solved by the invention]

[0004] A tool wears or breaks as a result of continuing to machine a workpiece. That is, as a result of the tool being continuously used, tool abnormalities such as wear or breakage may occur. Therefore, it is desirable for a machine tool to at least detect tool wear in some way. Furthermore, it is desirable for a machine tool to detect tool breakage in some way. According to the technology disclosed in Patent Document 1, it is possible to detect the force acting on the tool, but it is not possible to identify tool abnormalities such as wear or breakage. Therefore, a technology is needed that at least detects tool wear. Furthermore, a technology is desired that detects tool breakage.

[0005] The present disclosure has been made in view of the above-mentioned background, and an object of one aspect of the present disclosure is to provide a technique for detecting at least wear of a tool.An object of another aspect of the present disclosure is to provide a technique for detecting chipping of a tool. [Means for solving the problem]

[0006] According to one embodiment, there is provided a machine tool capable of cutting a workpiece using a tool. The machine tool includes a spindle for rotating the tool, a housing for accommodating the spindle, a plurality of strain sensors provided in the housing, and a detection unit for detecting wear or chipping of the tool based on a cutting force waveform measured from each output signal of the plurality of strain sensors. The detection unit measures a first cutting force waveform, measures a second cutting force waveform after measuring the first cutting force waveform, compares the first cutting force waveform with the second cutting force waveform, and detects tool wear based on a result of the comparison.

[0007] In one aspect, comparing the first cutting force waveform and the second cutting force waveform includes aligning the phases of the first cutting force waveform and the second cutting force waveform, and calculating a difference between the first cutting force waveform and the second cutting force waveform after the phase alignment. The detection unit detects tool damage based on the difference between the first cutting force waveform and the second cutting force waveform after the phase alignment.

[0008] In one aspect, the detection unit normalizes the first cutting force waveform and the second cutting force waveform.

[0009] In one aspect, the detection unit detects wear of the tool based on the amplitude of the second cutting force waveform being greater than the amplitude of the first cutting force waveform by a predetermined threshold or more.

[0010] In one aspect, the detection unit detects tool loss based on the amplitude of at least a portion of the second cutting force waveform being smaller than the amplitude of a corresponding at least a portion of the first cutting force waveform by a predetermined threshold or more.

[0011] In one aspect, the tool includes a plurality of blades, and each of the first cutting force waveform and the second cutting force waveform includes a plurality of amplitudes corresponding to each of the plurality of blades, and detecting wear or loss of the tool includes comparing amplitudes corresponding to the same blade included in each of the first cutting force waveform and the second cutting force waveform.

[0012] In one aspect, the first cutting force waveform and the second cutting force waveform are cutting force waveforms at positions on a machining path of the workpiece under the same machining conditions.

[0013] According to another embodiment, there is provided a control method for a machine tool capable of cutting a workpiece using a tool. In the control method, the machine tool includes a spindle for rotating the tool, a housing for accommodating the spindle, and a plurality of strain sensors provided in the housing. The control method includes detecting wear or chipping of the tool based on a cutting force waveform measured from each output signal of the plurality of strain sensors, measuring a first cutting force waveform, measuring a second cutting force waveform after measuring the first cutting force waveform, comparing the first cutting force waveform and the second cutting force waveform, and detecting tool wear based on a result of the comparison.

[0014] In one aspect, comparing the first cutting force waveform and the second cutting force waveform includes aligning the phases of the first cutting force waveform and the second cutting force waveform, and calculating a difference between the first cutting force waveform and the second cutting force waveform after the phase alignment. The control method further includes detecting a chipped tool based on the difference between the first cutting force waveform and the second cutting force waveform after the phase alignment.

[0015] According to another embodiment, there is provided a control program for a machine tool capable of cutting a workpiece using a tool. In the control program, the machine tool includes a spindle for rotating the tool, a housing for accommodating the spindle, and a plurality of strain sensors provided in the housing. The control program causes the machine tool to execute the following operations: detect wear or chipping of the tool based on a cutting force waveform measured from each output signal of the plurality of strain sensors; measure a first cutting force waveform; measure a second cutting force waveform after measuring the first cutting force waveform; compare the first cutting force waveform and the second cutting force waveform; and detect wear of the tool based on a result of the comparison.

[0016] In one aspect, comparing the first cutting force waveform and the second cutting force waveform includes matching the phases of the first cutting force waveform and the second cutting force waveform, and calculating a difference between the first cutting force waveform and the second cutting force waveform after the phase matching. The control program further causes the machine tool to detect tool breakage based on the difference between the first cutting force waveform and the second cutting force waveform after the phase matching. Effect of the Invention

[0017] According to one embodiment, at least tool wear can be detected, according to another embodiment tool loss can be detected.

[0018] The above and other objects, features, aspects and advantages of the present disclosure will become apparent from the following detailed description of the disclosure taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0019] [Figure 1] 1 is a diagram showing an example of a device configuration of a machine tool 10 according to the present embodiment. [Diagram 2] 13 is a diagram showing an example of a configuration of a housing 133 according to the present embodiment. FIG. [Diagram 3]It is a diagram showing an example of a cross-section of the housing 133. [Figure 4] It is a diagram showing an example of a procedure for calculating cutting force from a strain sensor. [Diagram 5] It is a diagram showing an example of the configuration of the control unit 50. [Figure 6] It is a diagram showing the relationship between the machining path of the workpiece and the cutting force, and an example of the cutting force to be compared. [Figure 7] It is a diagram showing an example of a process for aligning the phases of the waveforms of the cutting force to be compared. [Figure 8] It is a diagram showing an example of a normalization process for the waveforms of the cutting force to be compared. [Figure 9] It is a diagram showing an example of a method for detecting tool wear. [Figure 10] It is a diagram showing an example of a method for detecting tool breakage. [Figure 11] It is a diagram showing an example of an integration process for the waveforms of the cutting force to be compared. [Figure 12] It is a diagram showing an example of the correlation between the waveform of the first cutting force and the waveform of the second cutting force. [Figure 13] It is a diagram showing an example of the internal processing of the machine tool 10. [Figure 14] It is a diagram showing an example of the configuration of the machine tool 1400 according to a modified example.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the technical idea according to the present disclosure will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated. Also, each embodiment, each modified example, each software configuration, each hardware configuration, each function, and each process, etc. may be selectively combined as appropriate.

[0021] <A. Device Configuration> FIG. 1 is a diagram showing an example of the device configuration of a machine tool 10 according to the present embodiment. First, the device configuration of the machine tool 10 will be described with reference to FIG. 1. The machine tool 10 is any device that processes a workpiece. As an example, the machine tool 10 may be a machining center. The machine tool 10 may also be a horizontal machining center or a vertical machining center. Hereinafter, the machine tool 10 will be described as a machining center, but the machine tool 10 is not limited to a machining center. In a certain aspect, the machine tool 10 may be a lathe, a milling machine, an additional processing machine, or other cutting or grinding machines.

[0022] Machine tool 10 includes a control unit 50, a servo driver 111R, servo drivers 111X to 111Z, a servo motor 112R, servo motors 112X to 112Z, a movable body 113, a spindle head 131, a tool 134, and a table 136.

[0023] In this specification, the "control unit 50" is a device that controls the machine tool 10. The device configuration of the control unit 50 is arbitrary. The control unit 50 may be configured with a single control unit, or may be configured with multiple control units. As an example, the control unit 50 may include an NC (Numerical Control) unit, or may include a PLC (Programmable Logic Controller).

[0024] The spindle head 131 is composed of a spindle 132 and a housing 133. The housing 133 accommodates the spindle 132. A tool for machining a workpiece W, which is a workpiece, is attached to the spindle 132. In the example of Fig. 1, a tool 134 serving as an end mill is attached to the spindle 132. The tool 134 may include any tool other than an end mill, such as a drill, a tap, or a ball end mill.

[0025] In the following description, the axial direction of the main shaft 132 is referred to as the "Z direction", the direction of gravity (i.e., the up-down direction on the paper) is referred to as the "Y direction", and the direction perpendicular to both the Z direction and the Y direction is referred to as the "X direction".

[0026] The control unit 50 starts executing a machining program prepared in advance based on receiving a machining start command. The control unit 50 controls the servo driver 111R and the servo drivers 111X to 111Z in accordance with the machining program. In this way, the control unit 50 machines the workpiece W fixed to the table 136. The machining program is written, for example, in an NC program.

[0027] The servo driver 111R sequentially receives the input of the target rotation speed from the control unit 50 and controls the servo motor 112R (rotation drive unit). The servo motor 112R rotates and drives the main shaft 132 around the axis in the Z direction. More specifically, the servo driver 111R acquires a feedback signal from an encoder (not shown) for detecting the rotation angle of the servo motor 112R. The servo driver 111R calculates the actual rotation speed of the servo motor 112R from the feedback signal. When the actual rotation speed of the servo motor 112R is smaller than the target rotation speed, the servo driver 111R increases the rotation speed of the servo motor 112R. When the actual rotation speed of the servo motor 112R is larger than the target rotation speed, the servo driver 111R decreases the rotation speed of the servo motor 112R. In this way, the servo driver 111R sequentially receives the feedback of the rotation speed of the servo motor 112R and makes the rotation speed of the servo motor 112R approach the target rotation speed.

[0028] The servo driver 111X sequentially receives the input of the target position from the control unit 50 and controls the servo motor 112X. The servo motor 112X feeds and drives the moving body 113 to which the spindle head 131 is attached via a ball screw (not shown) or the like, and feeds and drives the spindle 132 to an arbitrary position in the X direction. More specifically, the servo driver 111X obtains a feedback signal from an encoder (not shown) for detecting the rotation angle of the servo motor 112X. The servo driver 111X calculates the actual position of the moving body 113 from the feedback signal. When the actual position of the moving body 113 is lower than the target position, the servo driver 111X raises the actual position of the servo motor 112X. When the actual position of the moving body 113 is higher than the target position, the servo driver 111X lowers the actual position of the servo motor 112X. In this way, the servo driver 111X sequentially receives feedback of the actual position of the servo motor 112X and causes the actual position of the servo motor 112X to approach the target position, whereby the servo driver 111X drives and feeds the spindle 132 to an arbitrary position in the X direction.

[0029] The servo driver 111Y sequentially receives inputs of target positions from the control unit 50 and controls the servo motor 112Y. The servo motor 112Y feeds and drives the movable body 113 to which the spindle head 131 is attached via a ball screw (not shown) or the like, and feeds and drives the spindle 132 to an arbitrary position in the Y direction. The method of controlling the servo motor 112Y by the servo driver 111Y is similar to that of the servo driver 111X, and therefore the description thereof will not be repeated.

[0030] The servo driver 111Z sequentially receives inputs of target positions from the control unit 50 and controls the servo motor 112Z. The servo motor 112Z feeds and drives the movable body 113 to which the spindle head 131 is attached via a ball screw (not shown) or the like, and feeds and drives the spindle 132 to an arbitrary position in the Z direction. The method of controlling the servo motor 112Z by the servo driver 111Z is similar to that of the servo driver 111X, and therefore the description thereof will not be repeated.

[0031] In the machine tool 10 as described above, the tool 134 repeatedly processes a large number of workpieces. Therefore, the tool 134 wears out every time the workpiece is repeatedly processed, and eventually breaks. In addition, the tool 134 may suddenly break at an unexpected timing due to an inappropriate setting being input to the machine tool 10. Here, "breakage" includes a part of the blade being broken and the tool 134 itself being broken. When the tool 134 is worn out or broken, the operator of the machine tool 10 needs to replace the tool 134. Therefore, it is desirable for the machine tool 10 to detect the wear or breakage of the tool 134 by some method and notify the operator of the detection result. In order to realize the function of detecting the wear or breakage of the tool 134, the machine tool 10 is provided with a plurality of strain sensors as shown in FIG. 2 and FIG. 3. The machine tool 10 measures the cutting force applied to the tool 134 using the plurality of strain sensors, and detects the wear or breakage of the tool 134 based on the cutting force.

[0032] Fig. 2 is a diagram showing an example of the configuration of housing 133 according to the present embodiment. With reference to Fig. 3, a strain sensor attached to housing 133 and a cutting force applied to tool 134 will be described.

[0033] As described above, the housing 133 accommodates the main shaft 132. The main shaft 132 rotates at high speed inside the housing 133 by power transmitted from the servo motor 112R. The housing 133 has a first surface 252 and a second surface 254. As shown in FIG. 2, the first surface 252 and the second surface 254 intersect at a right angle. The housing 133 shown in FIG. 2 is an example, and the first surface 252 and the second surface 254 do not have to intersect at a perfect right angle.

[0034] Housing 133 is configured to allow a plurality of strain sensors to be attached thereto. The strain sensors are attached to housing 133, for example, so as to be in contact with both first surface 252 and second surface 254. One end of the strain sensor is connected to first surface 252. The other end of the strain sensor is connected to second surface 254. That is, the strain sensor is attached to first surface 252 and second surface 254 like a rib. In one aspect, the strain sensor may be configured to be detachable from first surface 252 and second surface 254.

[0035] In the example of FIG. 2, strain sensors S1 to S4 are attached to the housing 133. More specifically, strain sensors S1 and S2 are arranged along the X direction. Strain sensors S3 and S4 are arranged along the Y direction. That is, each strain sensor is shifted by 90 degrees from the other adjacent strain sensors. In one aspect, there may be a gap between the strain sensor and the corner formed by the first surface 252 and the second surface 254. In another aspect, there may be no gap between the strain sensor and the corner formed by the first surface 252 and the second surface 254.

[0036] Next, the cutting force applied to the tool 134 will be described. Assume that the machine tool 10 uses an end mill to cut the workpiece W. In this case, the machine tool 10 presses the tip of the tool 134 against the workpiece W while rotating the tool 134. The tool 134 receives a repulsive force from the workpiece W. This becomes the cutting force. A cutting force Fx in the X direction, a cutting force Fy in the Y direction, and a cutting force Fz in the Z direction are applied to the tool 134.

[0037] The control unit 50 can measure the cutting force Fx in the X direction based on the output signals acquired from the strain sensors S1 and S2. The control unit 50 can also measure the cutting force Fy in the Y direction based on the output signals acquired from the strain sensors S3 and S4. The control unit 50 can also measure the cutting force Fz in the Z direction based on the output signals acquired from each of the strain sensors S1 to S4. These measured cutting forces are used to detect wear or damage to the tool 134.

[0038] In the example of FIG. 2, the number of strain sensors is described as four, but the number of strain sensors attached to the housing 133 is not limited to this. In one aspect, the housing 133 may be configured to allow three or fewer strain sensors to be attached. In another aspect, the housing 133 may be configured to allow five or more strain sensors to be attached. In this case, the control unit 50 may appropriately change the formula for calculating the cutting forces Fx, Fy, and Fz depending on the arrangement of each strain sensor and the number of strain sensors. The formula for calculating the cutting forces Fx, Fy, and Fz may be realized as a program.

[0039] Fig. 3 is a diagram showing an example of a cross section of the housing 133. The positional relationship between the strain sensor and the tool 134 will be described with reference to Fig. 3. Furthermore, the advantages of attaching the strain sensor to the housing 133 will be described.

[0040] Housing 133 accommodates main shaft 132 via bearing 320. Bearing 320 may be configured as an integral part of housing 133 or main shaft 132. Bearing 320 may also be configured as a component independent of housing 133 and main shaft 132. Furthermore, housing 133 is configured so that cover 330 for protecting the strain sensor can be attached. The number of covers 330 that can be attached to housing 133 is equal to the number of strain sensors that can be attached.

[0041] As described above, the strain sensor is attached to the second surface 254 near the base of the housing 133. Therefore, the distance 340 from the tip of the tool 134 to the strain sensor is relatively long. When a cutting force is generated at the tip of the tool 134, a portion of the housing 133 far from the tip of the tool 134 is distorted more than a portion close to the tip of the tool 134. That is, the strain sensor can measure the strain with high sensitivity because it is away from the tip of the tool 134. As a result, the control unit 50 can measure the cutting force with high accuracy from the output signal of the strain sensor. Furthermore, since the housing 133 is configured to allow the strain sensor to be attached, the operator can easily attach and detach the strain sensor.

[0042] 4 is a diagram showing an example of a procedure for calculating the cutting force from the strain sensor. A method for measuring each of the cutting force Fx in the X direction, the cutting force Fy in the Y direction, and the cutting force Fz in the Z direction will be described with reference to FIG.

[0043] The cutting force measurement module 400 shown in FIG. 4 is a program that measures cutting forces Fx, Fy, and Fz. In one aspect, the cutting force measurement module 400 may be realized as a part of the abnormality detection program 524 (see FIG. 5). In another aspect, the cutting force measurement module 400 may be realized as a program separate from the abnormality detection program 524 (see FIG. 5). In this case, the abnormality detection program 524 cooperates with the cutting force measurement module 400. The control unit 50 may execute the following processes using the cutting force measurement module 400.

[0044] As described above, the strain sensor S1 and the strain sensor S2 are arranged along the X direction. Therefore, in the XY plane, the strain sensor S1 and the strain sensor S2 detect only the strain in the X direction. In reality, the strain sensor S1 and the strain sensor S2 may be affected by the strain in the Y axis direction, but the influence of the strain in the Y axis direction is small. Therefore, the control unit 50 can calculate (measure) the cutting force Fx in the X direction based on the composite value Ux of the output signal SO1 of the strain sensor S1 and the output signal SO2 of the strain sensor S2. As an example, the composite value Ux can be calculated by the formula "SO1-SO2". More specifically, the control unit 50 inputs the composite value Ux to the cutting force measurement module 400. The cutting force measurement module 400 calculates the cutting force Fx by multiplying the composite value Ux by the gain TL. Alternatively, the cutting force measurement module 400 may calculate the cutting force Fx by substituting the composite value Ux and the gain TL into a function. In one aspect, the cutting force measurement module 400 may receive SO1 and SO2. In this case, the cutting force measurement module 400 calculates a composite value Ux from SO1 and SO2. The cutting force measurement module 400 may calculate (measure) the composite value Ux using data 526 (see FIG. 5) of the correlation between the strain and the cutting force. In this case, the correlation data 526 may include information on the gain TL and the function. The cutting force measurement module 400 may calculate (measure) Ux from a table or formula of the correlation between the strain and the cutting force.

[0045] The strain sensor S3 and the strain sensor S4 are arranged along the Y direction. Therefore, in the XY plane, the strain sensor S3 and the strain sensor S4 detect only the strain in the Y direction. In reality, the strain sensor S3 and the strain sensor S4 may also be affected by the strain in the Z axis direction, but are less affected by the strain in the X axis direction. Therefore, the control unit 50 can calculate (measure) the cutting force Fy in the Y direction based on the composite value Uy of the output signal SO3 of the strain sensor S1 and the output signal SO4 of the strain sensor S2. As an example, the composite value Uy can be calculated by the formula "SO3-SO4". More specifically, the control unit 50 inputs the composite value Uy to the cutting force measurement module 400. The cutting force measurement module 400 calculates the cutting force Fy by multiplying the composite value Uy by the gain TL. Alternatively, the cutting force measurement module 400 may calculate the cutting force Fy by substituting the composite value Uy and the gain TL into a function. In one aspect, the cutting force measurement module 400 may receive SO3 and SO4. In this case, the cutting force measurement module 400 calculates a composite value Uy from SO3 and SO4. The cutting force measurement module 400 may also calculate (measure) the composite value Uy using data 526 of the correlation between the strain and the cutting force. In this case, the correlation data 526 may include information on the gain TL and the function. The cutting force measurement module 400 may also calculate (measure) Uy from a table or formula of the correlation between the strain and the cutting force.

[0046] The strain sensors S1 to S4 are all distorted in the Z-axis direction. Therefore, the control unit 50 can calculate (measure) the cutting force Fz in the Z direction based on the composite value Uz of the output signals SO1 to SO4 of the strain sensors S1 to S4. As an example, the composite value Uz can be calculated by the formula "-(SO1+SO2+SO3+SO4)". More specifically, the control unit 50 inputs the composite value Uz to the cutting force measuring module 400. The cutting force measuring module 400 calculates the cutting force Fz by multiplying the composite value Uz by a gain TL. Alternatively, the cutting force measuring module 400 may calculate the cutting force Fz by substituting the composite value Uz and the gain TL into a function. In a certain aspect, the cutting force measuring module 400 may receive inputs SO1 to SO4. In this case, the cutting force measuring module 400 calculates the composite value Uz from SO1 to SO4. The cutting force measuring module 400 may also calculate (measure) the composite value Uz using the data 526 of the correlation between the strain and the cutting force. In this case, the correlation data 526 may include the gain TL and function information. The cutting force measuring module 400 may also calculate (measure) Uz from a table or formula of the correlation between the strain and the cutting force.

[0047] The control unit 50 may calculate a composite cutting force from the cutting forces Fx, Fy, and Fz in each direction. In this case, the control unit 50 may treat the composite cutting force as a cutting force applied to the tool 134 and execute the process shown in FIG. 6 and subsequent figures. In one aspect, the control unit 50 may calculate a composite cutting force of any two of the cutting forces Fx, Fy, and Fz. In this case, the control unit 50 may treat the composite cutting force consisting of the two cutting forces as a cutting force applied to the tool 134 and execute the process shown in FIG. 6 and subsequent figures. In another aspect, the control unit 50 may treat one of the cutting forces Fx, Fy, and Fz as a cutting force applied to the tool 134 and execute the process shown in FIG. 6 and subsequent figures. The process of calculating the composite cutting force may be executed by the cutting force measurement module 400.

[0048] Fig. 5 is a diagram showing an example of the configuration of the control unit 50. Next, a hardware configuration of the control unit 50 will be described with reference to Fig. 5. In one aspect, the control unit 50 may be a CNC (Computer Numerical Control) unit, a CNC controller, a PLC, or any information processing device.

[0049] The control unit 50 includes a processor 501, a read only memory (ROM) 502, a random access memory (RAM) 503, a communication interface 504, a field bus controller 505, a storage device 507, and one or more strain sensors 506. These components are connected to an internal bus 509. The one or more strain sensors 506 correspond to the strain sensors S1 to S4. In one aspect, the control unit 50 may be configured to be able to communicate with an external strain sensor instead of including the one or more strain sensors 506.

[0050] The processor 501 is, for example, configured by at least one integrated circuit. The integrated circuit may be, for example, configured by at least one central processing unit (CPU), at least one graphics processing unit (GPU), at least one application specific integrated circuit (ASIC), at least one field programmable gate array (FPGA), or a combination thereof.

[0051] The processor 501 controls the operation of the control unit 50 by executing various programs such as a machining program 522 and an abnormality detection program 524. Upon receiving an execution command for each program, the processor 501 reads the program from the storage device 507 or the ROM 502 to the RAM 503. The RAM 503 functions as a working memory and temporarily stores various data required for executing the program.

[0052] The communication interface 504 is configured to be able to communicate with an external device. A LAN, an antenna, or the like is connected to the communication interface 504. The control unit 50 exchanges data with an external device (e.g., a server, etc.) via the communication interface 504. The control unit 50 may be configured to be able to download the machining program 522, the abnormality detection program 524, and the correlation data 526 from the external device.

[0053] The field bus controller 505 is an interface for implementing communication with various units connected to the field bus, such as a PLC or an I / O unit.

[0054] The storage device 507 is any storage medium, such as a hard disk, a flash memory, an SSD (Solid State Drive), etc. The storage device 507 stores a machining program 522, an abnormality detection program 524, correlation data 526, and the like.

[0055] The machining program 522 defines various commands for realizing machining of the workpiece. The abnormality detection program 524 detects wear or loss of the tool 134. The abnormality detection program 524 also has a function of acquiring the output signals of the strain sensors S1 to S4 and measuring (calculating) the cutting force. The correlation data 526 indicates the correlation between the output values ​​of the strain sensors S1 to S4 and the cutting force. The correlation may be defined in a table format or may be defined by a predetermined mathematical formula. The mathematical formula, for example, has the output values ​​of the strain sensors S1 to S4 as explanatory variables and the cutting force applied to the tool as objective variables. The table or formula of the correlation data 526 may be appropriately changed based on the number and arrangement of the strain sensors. The processor 501 can execute the processes shown in FIG. 4 and FIG. 6 to FIG. 13 by referring to the correlation data 526 and executing the abnormality detection program 524.

[0056] The storage locations of the machining program 522, the abnormality detection program 524, and the correlation data 526 are not limited to the storage device 507. In certain aspects, the machining program 522, the abnormality detection program 524, and the correlation data 526 may be stored in the storage area of the processor 501, the ROM 502, the RAM 503, or an external device, etc.

[0057] The abnormality detection program 524 may be provided incorporated into a part of any program, rather than as a single program. In this case, the abnormality detection process (the detection process of wear or breakage of the tool 134) by the abnormality detection program 524 is realized in cooperation with any program. Even a program that does not include such a part of the module does not deviate from the gist of the abnormality detection program 524 according to the present embodiment. Further, part or all of the functions provided by the abnormality detection program 524 may be realized by dedicated hardware. Further, at least one server may execute a part of the process of the abnormality detection program 524. In this case, the machine tool 10 is configured to be communicable with a server having a part of the functions of the abnormality detection program 524.

[0058] <B. Detection Method of Wear or Breakage> Next, with reference to FIGS. 6 to 12, a specific procedure for the machine tool 10 to detect wear or breakage of the tool 134 will be described. The control unit 50 can execute the abnormality detection process of the tool 134 by referring to the correlation data 526 and executing the abnormality detection program 524.

[0059] FIG. 6 is a diagram showing the relationship between the machining path of the workpiece and the cutting force, and an example of the cutting force to be compared. The machine tool 10 detects wear or breakage of the tool 134 based on the change in the waveform of a part of the cutting force on the machining path of the tool 134 as described below.

[0060] Machine tool 10 machines a workpiece based on machining program 522. Machining program 522 is an NC program or the like. Machining program 522 indicates a machining path of tool 134. For example, as shown in FIG. 6, assume that machine tool 10 cuts a workpiece into a quadrangle. In this case, tool 134 moves repeatedly on the same machining path (quadrature path). In reality, machine tool 10 moves spindle head 131 slightly in the Z-axis direction each time tool 134 makes one revolution of the machining path.

[0061] Machining path 600A is the first machining path. Cutting force waveform 610A is the cutting force waveform corresponding to machining path 600A. Machining path 600B is the second or subsequent cutting force. Cutting force waveform 610B is the cutting force waveform corresponding to machining path 600B. Although the cutting force waveforms 610A and 610B are simplified, in reality, they are waveforms similar to cutting force waveforms 800A and 800B in FIG. 8.

[0062] The machine tool 10 stores in the RAM 503 a first cutting force waveform 620A corresponding to an arbitrary position 630 on the machining path 600A as a reference waveform. Next, the machine tool 10 stores in the RAM 503 a second cutting force waveform 620B corresponding to a position 630 on the machining path 600B. The position 630 may not be a point, but may be a section having a certain length. Next, the machine tool 10 compares the first cutting force waveform 620A (reference waveform) with the second cutting force waveform 620B. Then, the machine tool 10 detects how the cutting force has changed based on the result of the comparison. Furthermore, the machine tool 10 detects wear or damage of the tool 134 based on the change in the cutting force waveform. That is, the machine tool 10 compares the cutting force waveforms at positions of the same machining conditions on the machining path of the workpiece. The machining conditions include any settings related to machining, such as the rotation speed, cutting amount, feed amount, and coordinates of the tool 134.

[0063] The machine tool 10 repeatedly executes the comparison between the first cutting force waveform 620A (reference waveform) and the second cutting force waveform 620B. For example, assume that the tool 134 moves 100 times along the machining path. In this case, the machine tool 10 may compare the first cutting force waveform 620A in the first machining with each of the second cutting force waveforms 620B in the second to 100th machining. In one aspect, the machine tool 10 may compare the first cutting force waveform 620A with the second cutting force waveform 620B every time a specific number of machinings (such as 10) are performed along the machining path. In another aspect, the machine tool 10 may compare the first cutting force waveform 620A (reference waveform) in the first machining with an average value of the second cutting force waveform 620B in multiple machinings from the second time onward.

[0064] FIG. 7 is a diagram showing an example of a process for matching the phases of the waveforms of cutting forces to be compared. As shown in FIG. 6, the machine tool 10 repeatedly executes a comparison between a first cutting force waveform (reference waveform) and a second cutting force waveform at the same machining position. However, the phase of the cutting force waveform acquired by the machine tool 10 may shift slightly each time. Therefore, the machine tool 10 matches the phases of the first cutting force waveform and the second cutting force waveform. Note that, as will be described with reference to FIG. 8, the machine tool 10 may normalize the first cutting force waveform and the second cutting force waveform before matching the phases.

[0065] The first cutting force waveform 700A is obtained by normalizing the first cutting force waveform 620A by the maximum value. The second cutting force waveform 700B is obtained by normalizing the second cutting force waveform 620B by the maximum value. When the first cutting force waveform 700A and the second cutting force waveform 700B are compared, it is found that there is a phase shift 705. In this state, the machine tool 10 cannot compare the first cutting force waveform 700A and the second cutting force waveform 700B. Therefore, the machine tool 10 matches the phases of the first cutting force waveform 700A and the second cutting force waveform 700B. The first cutting force waveform 710A is a waveform after a process of matching the phase to the first cutting force waveform 700A is executed. The second cutting force waveform 710B is a waveform after a process of matching the phase to the second cutting force waveform 700B is executed.

[0066] In one aspect, the machine tool 10 may align the positions of the rising parts of the amplitudes of the first cutting force waveform 700A and the second cutting force waveform 700B. In another aspect, the machine tool 10 may align the positions of the peaks of the amplitudes of the first cutting force waveform 700A and the second cutting force waveform 700B. Furthermore, in another aspect, the machine tool 10 may align the phases of the first cutting force waveform 700A and the second cutting force waveform 700B by using any means. Note that the amplitude of the cutting force waveform indicates the cutting force. Therefore, in the following description, the amplitude of the cutting force waveform may be read as the cutting force. For example, the amplitude of the first cutting force waveform may be read as the first cutting force. Also, the cutting force waveform represents the change in the magnitude of the cutting force (the cutting force in a certain section). Therefore, the cutting force waveform may be expressed as the cutting force. For example, comparing a first cutting force waveform with a second cutting force waveform can be said to be comparing the first cutting force with the second cutting force. Similarly, calculating the difference between the first cutting force waveform and the second cutting force waveform can be said to be calculating the difference between the first cutting force and the second cutting force.

[0067] The waveforms in sections 720 to 750, in which the amplitude is large, are waveforms that indicate the cutting force applied to each blade. For example, assume that the tool 134 has two blades. In this case, the waveforms in sections 720 and 740 indicate the cutting force applied to the first blade of the tool 134. The waveforms in sections 730 and 750 indicate the cutting force applied to the second blade of the tool 134. The machine tool 10 can compare the first cutting force waveform 710A and the second cutting force waveform 710B on a blade-by-blade basis by performing a process of matching the phases of the waveforms of the two cutting forces. For example, the machine tool 10 can compare the waveform in section 720 of the first cutting force waveform 700A with the waveform in section 720 of the second cutting force waveform 710B. That is, the machine tool 10 can precisely detect the change in the cutting force on a blade-by-blade basis by performing a process of matching the phases of the waveforms of the two cutting forces.

[0068] As described above, the machine tool 10 capable of cutting a workpiece using the tool 134 includes a spindle 132 for rotating the tool 134, a housing 133 for accommodating the spindle 132, a plurality of strain sensors S1 to S4 provided in the housing 133, and a detection unit (control unit 50) for detecting wear or damage to the tool 134 based on the waveform of the cutting force measured from the output signals of each of the plurality of strain sensors S1 to S4. The detection unit (control unit 50) measures a first cutting force waveform, measures a second cutting force waveform after measuring the first cutting force waveform, compares the first cutting force waveform with the second cutting force waveform, and detects wear of the tool based on the comparison result. The detection unit (control unit 50) can detect wear of the tool 134 by comparing the change in the magnitude of the overall amplitude of the first cutting force waveform with that of the second cutting force waveform. Therefore, when detecting only wear and not loss of the tool 134, the detection section (control section 50) does not need to match the phases of the waveform of the first cutting force and the waveform of the second cutting force.

[0069] In one aspect, in order to detect a loss of the tool 134, the detection unit (control unit 50) may match the phases of the waveform of the first cutting force and the waveform of the second cutting force. That is, comparing the waveform of the first cutting force and the waveform of the second cutting force includes matching the phases of the waveform of the first cutting force and the waveform of the second cutting force, and calculating the difference between the waveform of the first cutting force and the waveform of the second cutting force after the phases are matched. The detection unit (control unit 50) detects the loss of the tool 134 based on the difference between the waveform of the first cutting force and the waveform of the second cutting force after the phases are matched. In this way, the detection unit (control unit 50) can detect not only wear of the tool 134 but also loss of the tool 134 by matching the phases of the waveform of the first cutting force and the waveform of the second cutting force.

[0070] In one aspect, the machine tool 10 may notify an operator of wear or loss of the tool 134. As an example, the machine tool 10 may display a notification on a display (not shown) provided on the machine tool 10. As another example, the machine tool 10 may transmit a notification to an operator's terminal or the like via a network. In another aspect, the machine tool 10 may replace the broken tool 134 with a new tool based on the detection of wear or loss of the tool 134. As described above, it can be said that the waveform of the cutting force indicates the cutting force itself. Therefore, it can also be said that comparing the waveforms of the cutting forces is comparing the cutting forces. Therefore, it can also be said that the machine tool 10 detects wear or loss of the tool 134 based on the difference between the first cutting force and the second cutting force after the phases are aligned.

[0071] Also, the tool 134 may include multiple blades. In this case, each of the first cutting force waveform and the second cutting force waveform includes multiple amplitudes corresponding to each of the multiple blades. Detecting wear or damage to the tool 134 includes comparing the amplitudes corresponding to the same blade included in each of the first cutting force waveform and the second cutting force waveform. As an example, the tool 134 may include multiple blades, such as a first blade and a second blade. In this case, each of the first cutting force waveform and the second cutting force waveform includes a first amplitude (first cutting force) corresponding to the first blade and a second amplitude (second cutting force) corresponding to the second blade. Detecting wear or loss of the tool 134 includes comparing a first amplitude (first cutting force) included in the waveform of the first cutting force with a first amplitude (first cutting force) included in the waveform of the second cutting force, and comparing a second amplitude (second cutting force) included in the waveform of the first cutting force with a second amplitude (second cutting force) included in the waveform of the second cutting force. As another example, the tool 134 may include three or more blades. For example, the tool 134 may include N (any integer) blades. In this case, detecting wear or loss of the tool 134 includes comparing each of the first to N amplitudes included in the waveform of the first cutting force with each of the first to N amplitudes included in the waveform of the second cutting force.

[0072] Furthermore, as described with reference to Fig. 6, the first cutting force waveform and the second cutting force waveform are cutting force waveforms at positions on the machining path of the workpiece under the same machining conditions. In one aspect, the first cutting force waveform and the second cutting force waveform may be a composite value (integral value or average value, etc.) of cutting force waveforms at positions under the same machining conditions. In another aspect, the first cutting force waveform and the second cutting force waveform may be cutting forces (Fx, Fy, Fz) of each vector (axis) at positions under the same machining conditions, or a composite force of these.

[0073] FIG. 8 is a diagram showing an example of normalization processing of the waveform of the cutting force to be compared. The machine tool 10 normalizes the acquired waveform of the cutting force. Normalization refers to processing of adjusting the unit of data to one that is easy to handle. The machine tool 10 may normalize the magnitude (amplitude) of the cutting force. As an example, the machine tool 10 may scale the range of the magnitude (amplitude) of the cutting force to 0 to 1. Note that the minimum and maximum values ​​may be any values. Furthermore, the machine tool 10 may normalize both the magnitude (amplitude) of the cutting force and the cutting time. By normalizing the acquired waveform of the cutting force, the machine tool 10 may detect various tool defects using the same standard (threshold value, etc.).

[0074] The cutting force waveform 800A shows the waveform of the first cutting force in a certain machining path. The cutting force waveform 800B shows the waveform of the second or subsequent cutting force in a certain machining path. Assume that the machine tool 10 compares the first cutting force waveform 820A and the second cutting force waveform 820B at the same position on the machining path. In this case, as shown in the waveform graph 840, the machine tool 10 normalizes the first cutting force waveform 820A to generate a normalized first cutting force waveform 830A. Similarly, the machine tool 10 normalizes the second cutting force waveform 820B to generate a normalized second cutting force waveform 830B. Next, as shown in the waveform graph 850, the machine tool 10 aligns the phases of the normalized first cutting force waveform 830A and the normalized second cutting force waveform 830B. In one aspect, the machine tool 10 may perform a normalization process after aligning the phases of the first cutting force waveform 820A and the second cutting force waveform 820B.

[0075] The above process is executed by the control unit 50. That is, the detection unit (control unit 50) normalizes the first cutting force waveform and the second cutting force waveform. Then, the detection unit (control unit 50) aligns the phases of the normalized first cutting force waveform and the normalized second cutting force waveform.

[0076] Fig. 9 is a diagram showing an example of a method for detecting wear of a tool. Next, with reference to Fig. 9, how the cutting force applied to the tool 134 changes due to wear of the tool 134 will be described.

[0077] Photo 900 shows a new tool blade of tool 134. Photo 910 shows a worn blade of tool 134. The worn blade, as shown in photo 910, has a chipped cutting edge. Therefore, the worn blade experiences greater resistance when cutting a workpiece, compared to the blade of a new tool. In other words, when the blade of tool 134 is not worn, the cutting force applied to tool 134 is small. And, the more worn the blade of tool 134 is, the greater the cutting force applied to tool 134 becomes.

[0078] Waveform graph 920 shows an example of the relationship between wear of tool 134 and cutting force. Cutting force waveform 922 is a waveform when the flank wear width is "0.02 mm". Cutting force waveform 924 is a waveform when the flank wear width is "0.13 mm". Cutting force waveform 926 is a waveform when the flank wear width is "0.30 mm". Cutting force waveform 928 is a waveform when the flank wear width is "0.63 mm". Comparing cutting force waveforms 922 to 928 with each other, it can be seen that the greater the wear of tool 134, the greater the amplitude of the cutting force overall.

[0079] Machine tool 10 judges whether the amplitude of the second cutting force waveform is greater than or equal to a predetermined threshold value, in comparison with the amplitude of the first cutting force waveform (reference waveform). Then, machine tool 10 detects wear of tool 134 based on the difference between the amplitude of the first cutting force waveform and the amplitude of the second cutting force waveform (the difference between the first cutting force and the second cutting force) being greater than or equal to the threshold value. That is, the detection unit (control unit 50) detects wear of tool 134 based on the difference between the amplitude of the second cutting force waveform and the amplitude of the first cutting force waveform being greater than or equal to a predetermined threshold value.

[0080] In one aspect, the machine tool 10 may determine whether the amplitude of the waveform of the second cutting force has increased to a predetermined threshold or more, on a blade-by-blade basis, compared with the amplitude of the waveform of the first cutting force (reference waveform). In this case, as an example, the machine tool 10 determines whether the amplitude of the waveform of the cutting force at the first blade of the tool 134 has increased to a predetermined threshold or more, compared with the amplitude of the reference waveform. The reference waveform in this case is the reference waveform of the cutting force at the first blade (waveform of the initial cutting force). Similarly, the machine tool 10 determines whether the amplitude of the waveform of the cutting force at the second blade of the tool 134 has increased to a predetermined threshold or more, compared with the amplitude of the reference waveform. The reference waveform in this case is the reference waveform of the cutting force at the second blade (waveform of the initial cutting force).

[0081] In another aspect, the machine tool 10 may determine, for each tool, whether the amplitude of the second cutting force waveform has increased to or above a predetermined threshold value, as compared with the amplitude of the first cutting force waveform (reference waveform). In this case, as an example, the machine tool 10 determines whether the average value of the amplitude of the cutting force waveform for each blade of the tool 134 has increased to or above a predetermined threshold value, as compared with the average value of the amplitude of the reference waveform. The reference waveform in this case is the reference waveform of the cutting force for each blade (initial cutting force waveform).

[0082] In one aspect, the machine tool 10 may compare the maximum amplitude (wave crest) of the waveform of the first cutting force with the maximum amplitude of the waveform of the second cutting force. In another aspect, the machine tool 10 may compare the integrated value of the amplitude of the waveform of the first cutting force with the integrated value of the amplitude of the waveform of the second cutting force.

[0083] Fig. 10 is a diagram showing an example of a method for detecting a chipped tool. Next, with reference to Fig. 10, a description will be given of how the cutting force applied to the tool 134 changes due to the chipped tool 134.

[0084] Photo 1000 shows a new tool blade of tool 134. Photo 1010 shows a chipped blade of tool 134. A chipped blade as in photo 1010 has a smaller area that bites into the workpiece compared to a new tool blade as in photo 1000. Therefore, the chipped blade receives a smaller cutting force when cutting the workpiece compared to a new tool blade. In other words, when the blade of tool 134 is not chipped, the cutting force applied to tool 134 is relatively large. And when the blade of tool 134 is chipped, the cutting force applied to tool 134 becomes smaller.

[0085] Waveform graph 1020 shows an example of the relationship between the breakage of tool 134 and the cutting force. The waveform in section 1030 shows the waveform of the cutting force of the first blade. The waveform in section 1040 shows the waveform of the cutting force of the second blade. In the example of FIG. 10, the second blade is broken. Referring to section 1030, there is no significant change in the cutting force waveform before and after the breakage occurs. This is because the first blade is not broken. In contrast, referring to section 1040, it can be seen that the amplitude of the cutting force waveform changes significantly before and after the breakage occurs. Waveform 1060A shows the cutting force of the second blade before the breakage. Waveform 1060B shows the cutting force of the second blade after the breakage. Comparing waveforms 1060A and 1060B, it can be seen that the cutting force applied to tool 134 is greatly reduced due to the breakage of the blade.

[0086] As described above, the machine tool 10 judges whether the amplitude of the second cutting force waveform is smaller than or equal to a predetermined threshold value, in comparison with the amplitude of the first cutting force waveform (reference waveform). Then, the machine tool 10 detects the loss of the tool 134 based on the difference between the amplitude of the first cutting force waveform and the amplitude of the second cutting force waveform being equal to or greater than a threshold value. That is, the detection unit (control unit 50) detects the loss of the tool 134 based on the amplitude of at least a part of the second cutting force waveform being smaller than or equal to a predetermined threshold value, in comparison with the amplitude of at least a part corresponding to the first cutting force waveform. The amplitude of at least a part of the second cutting force waveform is, for example, the amplitude of the cutting force of a certain blade included in the second cutting force waveform. Also, the amplitude of at least a part corresponding to the first cutting force waveform is, for example, the amplitude of the cutting force of the certain blade included in the first cutting force waveform.

[0087] In one aspect, the machine tool 10 may perform a process of detecting a chipped portion of the tool 134 on a per-tool basis. In another aspect, the machine tool 10 may perform a process of detecting a chipped portion of the tool 134 on a per-tool basis. In this case, the machine tool 10 may use an average value or an integrated value of the resistance of all the blades of the tool 134. Furthermore, in another aspect, the machine tool 10 may simultaneously perform a process of detecting wear of the tool 134 and a process of detecting a chipped portion of the tool 134. For example, suppose that the waveform of the cutting force of the first blade becomes larger than the reference waveform, and the waveform of the cutting force of the second blade becomes smaller than the reference waveform. In this case, the machine tool 10 may determine that the first blade is worn and the second blade is chipped.

[0088] In the process of FIG. 9 and FIG. 10, the machine tool 10 may compare the integrated values ​​of the waveforms of the cutting forces. In this case, as an example, the machine tool 10 calculates an integrated value of the amplitude of the first blade included in the waveform of the first cutting force. Next, the machine tool 10 calculates an integrated value of the amplitude of the first blade included in the waveform of the second cutting force. The calculation of the integrated value may be performed on a blade-by-blade basis or on a tool-by-tool basis. Next, the machine tool 10 calculates the difference between these integrated values. Next, the machine tool 10 determines whether the difference between the integrated values ​​has increased to a predetermined first threshold value or more. If the difference between the integrated values ​​has increased to a predetermined first threshold value or more, the machine tool 10 may determine that wear has occurred in the first blade. In addition, the machine tool 10 determines whether the difference between the integrated values ​​has decreased to a predetermined second threshold value or more. If the difference between the integrated values ​​has decreased to a predetermined second threshold value or more, the machine tool 10 may determine that chipping has occurred in the first blade.

[0089] Also, in the processing of FIG. 9 and FIG. 10, the machine tool 10 may compare the peak values ​​of the waveforms of the respective cutting forces. In this case, as an example, the machine tool 10 acquires the peak value of the amplitude of the first blade included in the waveform of the first cutting force. Next, the machine tool 10 acquires the peak value of the amplitude of the first blade included in the waveform of the second cutting force. Next, the machine tool 10 calculates the difference between these peak values. Next, the machine tool 10 determines whether or not the difference between the peak values ​​has increased to a predetermined first threshold value or more. If the difference between the peak values ​​has increased to a predetermined first threshold value or more, the machine tool 10 may determine that wear has occurred in the first blade. Also, the machine tool 10 determines whether or not the difference between the peak values ​​has decreased to a predetermined second threshold value or more. If the difference between the peak values ​​has decreased to a predetermined second threshold value or more, the machine tool 10 may determine that chipping has occurred in the first blade.

[0090] Fig. 11 is a diagram showing an example of an integration process of cutting force waveforms to be compared. As described with reference to Figs. 6 to 10, the machine tool 10 may compare a first cutting force waveform (reference waveform) with a second cutting force waveform. Each of these waveforms to be compared (first and second cutting force waveforms) may be a composite value of multiple waveforms. A procedure for calculating an integrated value of the waveforms will be described with reference to Fig. 11.

[0091] Assume that tool 134 has a first blade and a second blade. The first blade is new, as shown in photo 1100. The second blade is chipped, as shown in photo 1110. Cutting force waveform 1120A is the waveform (first cutting force waveform) before the second blade is chipped. Cutting force waveform 1120B is the waveform (second cutting force waveform) after the second blade is chipped.

[0092] The machine tool 10 may calculate an integrated value of the waveform for each blade. For example, the machine tool acquires cutting force waveform 1120A for a certain period of time. Then, the machine tool 10 integrates the waveform of the second blade included in cutting force waveform 1120A (such as the waveform of sections 1150, 1160). Similarly, the machine tool acquires cutting force waveform 1120B for a certain period of time. Then, the machine tool 10 integrates the waveform of the second blade included in cutting force waveform 1120B (such as the waveform of sections 1150, 1160).

[0093] 1130A shows the waveform of the cutting force of the second blade included in the superimposed cutting force waveform 1120A. The machine tool 10 can obtain a composite value of the cutting force waveform of the second blade before chipping by integrating these waveforms. 1130B shows the waveform of the cutting force of the second blade included in the superimposed cutting force waveform 1120B. The machine tool 10 can obtain a composite value of the cutting force waveform of the second blade after chipping by integrating these waveforms.

[0094] The machine tool 10 may compare the waveform of the first cutting force after synthesis with the waveform of the second cutting force after synthesis. The waveform of the first cutting force after synthesis and the waveform of the second cutting force after synthesis may be waveforms obtained for each blade. The synthesis value may be an integrated value, an average value, or a median value. By using the synthesis value, the machine tool 10 may reduce the influence of sudden changes in resistance value caused by factors other than wear or chipping (so-called noise).

[0095] Fig. 12 is a diagram showing an example of the correlation between the first cutting force waveform and the second cutting force waveform. In the examples of Fig. 6 to Fig. 11, the machine tool 10 detects wear or damage to the tool 134 based on the variation in amplitude between the first cutting force waveform and the second cutting force waveform. Separately, the machine tool 10 may detect damage to the tool 134 based on the change in the value of the correlation coefficient between the first cutting force waveform and the second cutting force waveform.

[0096] Graph 1240 plots the correlation coefficient values ​​of the first cutting force waveform 1210A and the second cutting force waveform 1210B. The closer the correlation coefficient is to 1, the stronger the correlation between the first cutting force waveform 1210A and the second cutting force waveform 1210B. In other words, the closer the correlation coefficient is to 1, the more similar the first cutting force waveform 1210A and the second cutting force waveform 1210B are. Conversely, the farther the correlation coefficient is from 1, the weaker the correlation between the first cutting force waveform 1210A and the second cutting force waveform 1210B are. In other words, the closer the correlation coefficient is to 0, the more different the first cutting force waveform 1210A and the second cutting force waveform 1210B are.

[0097] The machine tool 10 can detect a missing tool 134 based on the value of the correlation coefficient becoming equal to or less than a predetermined value. That is, the machine tool 10 can detect a missing tool 134 based on the value of the correlation coefficient decreasing from 1 by a certain amount or more. In one aspect, the correlation data 526 may include a threshold value of the correlation coefficient for detecting a missing tool 134. In this case, the machine tool 10 can detect a missing tool 134 based on the value of the correlation coefficient decreasing from 1 by the threshold or more.

[0098] <C. Internal Processing of Machine Tool 10> FIG. 13 is a diagram showing an example of the internal processing of machine tool 10. In a certain aspect, the processor 501 can read the abnormality detection program 524 for performing the processing of FIG. 13 from the storage device 507 into the RAM 503. Further, the processor 501 can execute the abnormality detection program 524 read into the RAM 503. In another aspect, the abnormality detection program 524 may be read from the ROM 502 into the RAM 503. Furthermore, in another aspect, part or all of the said processing can also be realized as a combination of circuit elements configured to execute the said processing. That is, machine tool 10 can realize the method shown below by executing a program. Further, the processor 501 can read the machining program 522 and the correlation data 526 into the RAM 503 and execute or refer to them as necessary.

[0099] In step S1310, machine tool 10 acquires (measures) the waveform of the first cutting force (reference waveform). The processing of this step corresponds to the processing of acquiring, as the reference waveform, the waveform 620A of the first cutting force corresponding to the position 630 on the first machining path 600A shown in FIG. 6.

[0100] In step S1315, machine tool 10 repeatedly executes the processing from steps S1320 to S1370 until the job is completed. For example, assume that the job includes an instruction to move the tool 134 ten times on the same machining path. In this case, machine tool 10 acquires the waveform of the first cutting force in the first machining. Machine tool 10 repeatedly executes the processing from steps S1320 to S1370 nine times in the machining after the first time.

[0101] In step S1320, machine tool 10 acquires (measures) the waveform of the second cutting force. The processing of this step corresponds to the processing of acquiring the waveform 620B of the second cutting force corresponding to the position 630 on the machining paths 600B after the second time in FIG. 6.

[0102] In step S1325, the machine tool 10 normalizes each waveform (the waveforms of the first and second cutting forces) and further aligns the phases of each waveform. In one aspect, the machine tool 10 may align the phases of each waveform and then execute normalization processing for each waveform. The processing in this step corresponds to the processing in Figs. 7 and 8.

[0103] In step S1330, the machine tool 10 compares the cutting force for each tooth in each waveform. In step S1335, the machine tool 10 repeatedly executes the processes from step S1340 to step S1365 the number of times corresponding to the number of tool teeth.

[0104] In step S1340, the machine tool 10 judges whether the cutting force of the blade has increased by a predetermined first threshold or more. More specifically, the machine tool 10 compares the cutting force (amplitude) of a certain blade in the waveform of the second cutting force with the cutting force (amplitude) of a certain blade in the waveform of the first cutting force to obtain a difference. The machine tool 10 judges whether the difference (increase in cutting force) is a predetermined first threshold or more. If the machine tool 10 judges that the cutting force of the blade has increased by a predetermined first threshold or more (YES in step S1340), the machine tool 10 transfers control to step S1345. If not (NO in step S1340), the machine tool 10 transfers control to step S1350. In step S1345, the machine tool 10 judges that the blade is worn. The processes of steps S1340 and S1345 correspond to the process of FIG. 9.

[0105] In step S1350, the machine tool 10 judges whether the cutting force of the blade has decreased to a predetermined second threshold or more. More specifically, the machine tool 10 compares the cutting force (amplitude) of a certain blade in the waveform of the second cutting force with the cutting force (amplitude) of a certain blade in the waveform of the first cutting force to obtain a difference. The machine tool 10 judges whether the difference (amount of reduction in cutting force) is equal to or greater than the predetermined second threshold. If the machine tool 10 judges that the cutting force of the blade has decreased to the predetermined second threshold or more (YES in step S1350), the machine tool 10 transfers control to step S1355. If not (NO in step S1350), the machine tool 10 transfers control to step S1360. In step S1355, the machine tool 10 judges that the blade is missing. The processes in steps S1350 and S1355 correspond to the process in FIG. 10. In step S1360, the machine tool 10 determines that there is no abnormality in the blade.

[0106] In step S1365, the machine tool 10 determines whether or not the processing of all the blades has been completed. If the machine tool 10 determines that the processing of all the blades has been completed (YES in step S1365), the machine tool 10 transfers control to step S1370. If not (NO in step S1365), the machine tool 10 transfers control to step S1315.

[0107] In step S1370, the machine tool 10 determines whether the job is completed. If the machine tool 10 determines that the job is completed (YES in step S1370), the machine tool 10 ends the processing. If not (NO in step S1370), the machine tool 10 transfers control to step S1335.

[0108] In one aspect, the waveform of the first cutting force and the cutting force of the second blade may be a composite value of the waveforms, as described with reference to Fig. 11. In another aspect, the machine tool 10 may determine (detect) wear or chipping of the tool 134 based on a correlation coefficient between the waveform of the first cutting force and the cutting force of the second blade, as described with reference to Fig. 12.

[0109] As described above, when the abnormality detection program 524 is executed by the processor 501, based on the waveforms of the cutting forces measured from the output signals of the plurality of strain sensors S1 to S4, the machine tool 10 can be made to detect wear or chipping of the tool 134, measure the waveform of the first cutting force, measure the waveform of the second cutting force after measuring the waveform of the first cutting force, compare the waveforms of the first and second cutting forces, and detect tool wear based on the result of the comparison.

[0110] In one aspect, comparing the waveforms of the first and second cutting forces includes aligning the phases of the waveforms of the first and second cutting forces and calculating the difference between the waveforms of the first and second cutting forces after the phases are aligned. The abnormality detection program 524 further causes the machine tool to detect tool chipping based on the difference between the waveforms of the first and second cutting forces after the phases are aligned.

[0111] Furthermore, the abnormality detection program 524 can cause the machine tool 10 to perform a process of normalizing the waveforms of the first and second cutting forces. Also, the process of acquiring (measuring) the waveforms of the first and second cutting forces may include a process of acquiring (measuring) the composite value of each of the waveforms of the first and second cutting forces.

[0112] <D. Modified Example> FIG. 14 is a diagram showing an example of the configuration of a machine tool 1400 according to a modified example. The technology of the present disclosure can be used in any machine tool that processes a workpiece using a tool. With reference to FIG. 14, the machine tool 1400, which is a modified example, will be described.

[0113] Machine tool 1400 is a multi-tasking machine equipped with a turning function for machining a workpiece by bringing a tool into contact with the rotating workpiece, and a milling function for machining a workpiece by bringing a rotating tool into contact with the workpiece. Machine tool 1400 has bed 236, workpiece spindle 211, counter workpiece spindle 216, tool spindle 221, and tool rest 231. Machine tool 1400 also has a control unit (not shown) equivalent to control unit 50.

[0114] The bed 236 is a base member for supporting the workpiece spindle 211, the counter workpiece spindle 216, the tool spindle 221, the tool rest 231, etc., and is installed on the floor of a factory, etc. The bed 236 is made of a metal such as cast iron.

[0115] The work spindle 211 and the counter work spindle 216 are configured to be able to hold a workpiece. The work spindle 211 and the counter work spindle 216 are provided opposite each other in the Z-axis direction. The work spindle 211 and the counter work spindle 216 are provided mainly to rotate a workpiece during turning using a fixed tool. The work spindle 211 is provided so as to be rotatable about a central axis 201 parallel to the Z-axis. The counter work spindle 216 is provided so as to be rotatable about a central axis 202 parallel to the Z-axis. The work spindle 211 and the counter work spindle 216 are provided with a first chuck mechanism 213 and a second chuck mechanism 218, respectively, for detachably holding a workpiece.

[0116] The workpiece spindle 211 is fixed on a bed 236. The opposing workpiece spindle 216 is provided so as to be movable in the Z-axis direction by various feed mechanisms, guide mechanisms, servo motors, and the like.

[0117] The tool spindle 221 and the tool rest 231 are configured to be able to hold a tool for cutting a workpiece. The tool spindle 221 is provided above the tool rest 231.

[0118] The tool spindle 221 is provided rotatably about a central axis 203 that is parallel to the Y-axis that extends in the vertical direction. The tool spindle 221 is provided with a clamp mechanism (not shown) for detachably holding a tool.

[0119] The tool spindle 221 is further provided so as to be rotatable about a central axis 204 that extends horizontally and is parallel to the X-axis perpendicular to the Z-axis direction (B-axis rotation). The rotation range of the tool spindle 221 is, for example, within a range of ±120° based on the attitude in which the spindle end surface 223 of the tool spindle 221 faces downward (the attitude shown in FIG. 14).

[0120] The tool spindle 221 is supported on a bed 236 by a column or the like (not shown). The tool spindle 221 is provided so as to be movable in the Y-axis direction, the X-axis direction, and the Z-axis direction by various feed mechanisms, guide mechanisms, servo motors, and the like provided on the column or the like.

[0121] The tool rest 231 is a so-called turret type, and a plurality of tools are attached radially to perform swivel indexing. More specifically, the tool rest 231 has a swivel unit 232. The swivel unit 232 is provided so as to be rotatable about a central axis 206 parallel to the Z-axis. Tool holders for holding tools are attached at positions spaced apart in the circumferential direction from the central axis 206. As the swivel unit 232 swivels about the central axis 206, the tools held by the tool holders move in the circumferential direction, and the tool to be used for machining the workpiece is indexed.

[0122] The tool rest 231 is supported on the bed 236 by a saddle or the like (not shown). The tool rest 231 is provided so as to be movable in the Y-axis direction and the Z-axis direction by various feed mechanisms, guide mechanisms, servo motors, and the like provided on the saddle or the like. The tool rest 231 may be provided so as to be movable in the Z-axis direction and in a diagonal upward and downward direction perpendicular to the Z-axis direction and including a vertical component. In this case, the tool rest 231 may be configured to move in a diagonal upward and downward direction perpendicular to the Z-axis direction and including a vertical component by being fed simultaneously in the Y-axis direction and the X-axis direction.

[0123] Either a rotating tool or a fixed tool may be held on each of the tool spindle 221 and the tool rest 231. The rotating tool is a tool that processes a workpiece while rotating, such as a drill, an end mill, or a reamer. When the tool rest 231 holds a rotating tool, the tool rest 231 has a built-in motor that outputs rotation and a power transmission mechanism that transmits the rotation output from the motor to the rotating tool.

[0124] The machine tool 1400 further includes a splash guard 210. The splash guard 210 defines the outer appearance of the machine tool 1400 and defines a machining area 200 for the workpiece.

[0125] The machine tool 1400 measures the cutting force acting on the tool using a strain sensor S provided on the tool rest 231. One end of the strain sensor S is connected to a surface SF1 (first surface). The surface SF1 is a surface that forms a predetermined angle with the axial direction of the tool spindle 221 (i.e., the Z direction), and is one surface on the tool rest 231. Typically, the predetermined angle is about 90 degrees. As an example, the surface SF1 is a surface parallel to the XY plane.

[0126] On the other hand, the other end of the strain sensor S is connected to a surface SF2 (second surface). The surface SF2 is a surface that is not parallel to the surface SF1. In other words, the surface SF2 forms a predetermined angle with the surface SF1. The predetermined angle is, for example, about 90 degrees. As an example, the surface SF2 is a surface that is parallel to the axial direction (i.e., Z direction) of the tool spindle 221 and is a surface on the tool rest 231. Alternatively, the surface SF2 is a surface that is parallel to the axial direction of the tool spindle 221 and is a surface on the installation surface of the tool rest 231 (i.e., on the bed 236). Typically, the surface SF2 is perpendicular to the surface SF1.

[0127] The strain sensor S detects the degree of strain of the tool rest 231 during machining. The machine tool 1400 measures the cutting force applied to the tool of the tool rest 231 from the output value of the strain sensor S based on a predetermined correlation between the output value of the strain sensor S and the cutting force. The machine tool 1400 can acquire the predetermined correlation between the output value of the strain sensor S and the cutting force by referring to the correlation data 526. The machine tool 1400 executes the same processing as that described with reference to FIGS. 6 to 13 based on the acquired (measured) cutting force. Thereby, the machine tool 1400 can detect wear or chipping of the tool of the tool rest 231.

[0128] <E.まとめ> As described above, the machine tool according to this embodiment measures a first cutting force waveform that is a reference waveform. After measuring the first cutting force waveform, the machine tool measures a second cutting force waveform. The machine tool also aligns the phases of the first cutting force waveform and the second cutting force waveform. The machine tool also compares the first cutting force waveform and the second cutting force waveform. The machine tool further detects tool wear based on the comparison result. In this way, the machine tool can easily detect tool wear based on the output signal of the strain sensor.

[0129] In one aspect, the machine tool aligns the phases of the first cutting force waveform and the second cutting force waveform. The machine tool also calculates a difference between the first cutting force waveform and the second cutting force waveform after the phase alignment. The machine tool further detects tool damage based on the difference between the first cutting force waveform and the second cutting force waveform after the phase alignment. In this way, the machine tool can easily detect tool damage based on the output signal of the strain sensor.

[0130] In another aspect, the machine tool may compare the first cutting force waveform and the second cutting force waveform for each blade of the tool. This allows the machine tool to detect wear or chipping of each blade of the tool. Furthermore, the machine tool normalizes the first cutting force waveform and the second cutting force waveform.

[0131] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. In addition, the disclosure contents described in the embodiments and each modified example are intended to be implemented, as far as possible, either alone or in combination. [Explanation of symbols]

[0132] 10,1400 Machine tool, 50 Control unit, 111R, 111X, 111Y, 111Z Servo driver, 112R, 112X, 112Y, 112Z Servo motor, 113 Moving body, 131 Spindle head, 132 Spindle, 133 Housing, 134 Tool, 136 Table, 200 Machining area, 201, 202, 203, 204, 206 Central axis, 210 Splash guard, 211 Work spindle, 213 First chuck mechanism, 216 Opposing work spindle, 218 Second chuck mechanism, 221 Tool spindle, 223 Spindle end face, 231 Tool rest, 232 Swivel unit, 236 Bed, 252 First surface, 254 Second surface, 320 Bearing, 330 Cover, 340 Distance, 400 Measurement module, 501 Processor, 502 ROM, 503 RAM, 504 Communication interface, 505 Field bus controller, 506, S, S1, S2, S3, S4 Strain sensor, 507 Storage device, 509 Internal bus, 522 Machining program, 524 Anomaly detection program, 526 Correlation data, 600A, 600B Machining path, 610A, 610B, 800A, 800B, 922, 924, 926, 928, 1120A, 1120B Cutting force waveform, 620A, 700A, 710A, 820A, 830A, 1210A First cutting force waveform, 620B, 700B, 710B, 820B, 830B, 1210B Second cutting force waveform, 630 Position, 705 Displacement, 720,730,740,750,1030,1040,1150,1160 Section, 840,850,920,1020 Waveform graph, 900,910,1000,1010,1100,1110 Photograph, 1060A,1060B Waveform, 1240 Graph.

Claims

1. A machine tool capable of cutting a workpiece using a tool, A spindle for rotating the tool; a housing for accommodating the spindle; A plurality of strain sensors provided in the housing; a detection unit that detects wear or chipping of the tool based on a waveform of a cutting force measured from each output signal of the plurality of strain sensors; The detection unit is Measuring a first cutting force waveform; measuring a second cutting force waveform after measuring the first cutting force waveform; comparing the first cutting force waveform and the second cutting force waveform; The machine tool detects wear of the tool based on a result of the comparison.

2. Comparing the first cutting force waveform and the second cutting force waveform includes: aligning the first cutting force waveform and the second cutting force waveform in phase; calculating a difference between the waveform of the first cutting force and the waveform of the second cutting force after the phases are aligned; The machine tool according to claim 1 , wherein the detection unit detects a break in the tool based on a difference between the waveform of the first cutting force and the waveform of the second cutting force after phase alignment.

3. The machine tool according to claim 1 , wherein the detection unit normalizes the waveform of the first cutting force and the waveform of the second cutting force.

4. 3. The machine tool according to claim 1, wherein the detection unit detects wear of the tool based on an amplitude of the second cutting force waveform being greater than or equal to a predetermined threshold value compared to an amplitude of the first cutting force waveform.

5. 3. The machine tool according to claim 2, wherein the detection unit detects a break in the tool based on an amplitude of at least a portion of the second cutting force waveform being smaller than an amplitude of a corresponding at least a portion of the first cutting force waveform by a predetermined threshold or more.

6. The tool comprises a plurality of blades; each of the first cutting force waveform and the second cutting force waveform includes a plurality of amplitudes corresponding to each of the plurality of blades; 3. The machine tool of claim 2, wherein detecting wear or loss of the tool includes comparing amplitudes corresponding to the same blade contained in each of the first cutting force waveform and the second cutting force waveform.

7. 3. The machine tool according to claim 1, wherein the first cutting force waveform and the second cutting force waveform are cutting force waveforms at positions on a machining path of the workpiece under identical machining conditions.

8. A method for controlling a machine tool capable of cutting a workpiece using a tool, comprising the steps of: The machine tool comprises: A spindle for rotating the tool; a housing for accommodating the spindle; a plurality of strain sensors provided in the housing; The control method includes: Detecting wear or chipping of the tool based on a waveform of a cutting force measured from output signals of each of the plurality of strain sensors; Measuring a first cutting force waveform; measuring a second cutting force waveform after measuring the first cutting force waveform; comparing the first cutting force waveform and the second cutting force waveform; and detecting wear of the tool based on a result of the comparison.

9. Comparing the first cutting force waveform and the second cutting force waveform includes: aligning the first cutting force waveform and the second cutting force waveform in phase; calculating a difference between the waveform of the first cutting force and the waveform of the second cutting force after the phases are aligned; The control method according to claim 8 , further comprising detecting a break in the tool based on a difference between the first cutting force waveform and the second cutting force waveform after phase alignment.

10. A control program for a machine tool capable of cutting a workpiece using a tool, comprising: The machine tool comprises: A spindle for rotating the tool; a housing for accommodating the spindle; a plurality of strain sensors provided in the housing; The control program includes: Detecting wear or chipping of the tool based on a waveform of a cutting force measured from output signals of each of the plurality of strain sensors; Measuring a first cutting force waveform; measuring a second cutting force waveform after measuring the first cutting force waveform; comparing the first cutting force waveform and the second cutting force waveform; and detecting wear of the tool based on a result of the comparison.

11. Comparing the first cutting force waveform and the second cutting force waveform includes: aligning the first cutting force waveform and the second cutting force waveform in phase; calculating a difference between the waveform of the first cutting force and the waveform of the second cutting force after the phases are aligned; The control program according to claim 10, further causing the machine tool to detect a break in the tool based on a difference between the first cutting force waveform and the second cutting force waveform after phase alignment.

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