Machine tool, method for estimating a force applied to a tool, and computer-readable medium

Abstract

Provided is a technique for estimating a cutting force by a new method other than using a dynamometer. A machine tool capable of cutting a workpiece with a tool includes a first surface in the machine tool that is subjected to a force due to cutting of the workpiece, and a second surface in the machine tool that is subjected to a force due to cutting of the workpiece. The second surface is not parallel to the first surface, and the machine tool further includes a first strain sensor coupled to the first surface and the second surface, and an estimation unit configured to estimate a force applied to the tool based on an output value of the first strain sensor during cutting of the workpiece.

Description

Technical Field

[0001] This disclosure relates to a technique for estimating the force applied to a cutting tool. Background Technology

[0002] A technique has been developed for estimating the force (hereinafter also referred to as "cutting force") applied to the tool during the machining of a workpiece. Regarding this technique, Japanese Patent Application Publication No. 06-315853 (Patent Document 1) discloses a turning machine tool that uses a force gauge to estimate the cutting force. The force gauge is installed on the turret of the turning machine tool and detects the cutting force applied to the tool mounted on the turret.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 06-315853 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] Force gauges are expensive, so a new technique is desired that can estimate cutting forces using methods other than force gauges.

[0008] Solution for solving the problem

[0009] In one example of this disclosure, a machine tool capable of cutting a workpiece using a cutting tool includes: a first surface within the machine tool, which is subjected to force due to the cutting of the workpiece; and a second surface within the machine tool, which is subjected to force due to the cutting of the workpiece. The second surface is not parallel to the first surface. The machine tool further includes a first strain sensor and an estimation unit. The first strain sensor is connected to both the first and second surfaces. The estimation unit is used to estimate the force applied to the cutting tool based on the output value of the first strain sensor during the cutting process of the workpiece.

[0010] In one example of this disclosure, the machine tool further comprises: a spindle for rotating the cutting tool; and a housing for housing the spindle. The first surface is a surface forming a predetermined angle with the axial direction of the spindle and is a surface on the housing. The second surface is a surface parallel to the axial direction of the spindle and is a surface on the housing.

[0011] In one example of this disclosure, the machine tool further includes: a spindle for rotating the workpiece; and a tool holder configured to hold a cutting tool for cutting the workpiece. The first surface is a surface forming the predetermined angle with the axial direction of the spindle and is a surface on the tool holder. The second surface is a surface parallel to the axial direction of the spindle and is a surface on the tool holder or on its mounting surface.

[0012] In one example of this disclosure, the aforementioned specified angle is 90 degrees.

[0013] In one embodiment of this disclosure, the machine tool further comprises a second strain sensor, a third strain sensor, and a fourth strain sensor. The second strain sensor is connected to the first surface and a third surface subjected to force due to the cutting of the workpiece. The third surface is not parallel to the first surface. The third strain sensor is connected to the first surface and a fourth surface subjected to force due to the cutting of the workpiece. The fourth surface is not parallel to the first surface and faces the second surface. The fourth strain sensor is connected to the first surface and a fifth surface subjected to force due to the cutting of the workpiece. The fifth surface is not parallel to the first surface and faces the third surface.

[0014] In one embodiment of this disclosure, the machine tool further comprises a second strain sensor and a third strain sensor. The second strain sensor is connected to the first surface and a third surface subjected to force due to the cutting of the workpiece. The third surface is neither parallel to the first surface nor facing the second surface. The third strain sensor is connected to the first surface and a fourth surface subjected to force due to the cutting of the workpiece. The fourth surface is neither parallel to the first surface nor facing the second or third surface.

[0015] In another embodiment of this disclosure, a method for estimating the force applied to a cutting tool during the cutting of a workpiece in a machine tool is provided. The machine tool includes a first surface and a second surface within the machine tool. The first surface and the second surface are both subjected to force due to the cutting of the workpiece. The second surface is not parallel to the first surface. The machine tool also includes a strain sensor connected to both the first and second surfaces. The estimation method includes the steps of: acquiring the output value of the strain sensor during the cutting process of the workpiece; and estimating the force applied to the cutting tool based on the output value.

[0016] In another embodiment of this disclosure, a procedure for estimating the force applied to a cutting tool during the cutting of a workpiece in a machine tool is provided. The machine tool includes a first surface and a second surface within the machine tool. The first surface and the second surface are both subjected to force due to the cutting of the workpiece. The second surface is not parallel to the first surface. The machine tool also includes a strain sensor connected to both the first and second surfaces. The estimation procedure causes the machine tool to perform the following steps: acquiring the output value of the strain sensor during the cutting of the workpiece; and estimating the force applied to the cutting tool based on the output value.

[0017] The above-described objects, features, methods, and advantages of the invention, as well as other objects, features, methods, and advantages, will become apparent from the following detailed description relating to the invention in conjunction with the accompanying drawings. Attached Figure Description

[0018] Figure 1 This is a diagram illustrating an example of the structure of a machine tool device.

[0019] Figure 2 This is a diagram showing the spindle head with the strain sensor installed.

[0020] Figure 3 It is a graph that visually shows the degree of strain on the spindle head when an external force is applied.

[0021] Figure 4 This is a diagram illustrating an example of the functional structure of a machine tool.

[0022] Figure 5 This is a schematic diagram illustrating an example of the hardware structure of a CNC (Computer Numerical Control) unit.

[0023] Figure 6 This is a flowchart illustrating the process of estimating cutting forces.

[0024] Figure 7 This is a front view of the housing of the spindle head, shown from the Z direction.

[0025] Figure 8 This is a side view of the housing of the spindle head, shown from the X direction.

[0026] Figure 9 This is a front view of the housing of the spindle head, shown from the Z direction.

[0027] Figure 10 This is a side view of the housing of the spindle head, shown from the X direction.

[0028] Figure 11 This is a diagram illustrating various configuration modes of the strain sensor.

[0029] Figure 12 This is a diagram showing a machine tool according to a modified example. Detailed Implementation

[0030] Hereinafter, various embodiments according to the present invention will be described with reference to the accompanying drawings. In the following description, the same reference numerals are used to refer to the same parts and components. Their names and functions are also the same. Therefore, detailed descriptions of them will not be repeated. Furthermore, the various embodiments and modifications described below can be selectively combined as appropriate.

[0031] <A. Structure of Machine Tool 10>

[0032] First, refer to Figure 1 to describe the device structure of machine tool 10. Figure 1 is a diagram showing an example of the device structure of machine tool 10.

[0033] In Figure 1 machine tool 10 as a machining center is shown. Machine tool 10 can be either a horizontal machining center or a vertical machining center.

[0034] Hereinafter, machine tool 10 as a machining center will be described, but machine tool 10 is not limited to a machining center. For example, machine tool 10 can also be a lathe, an additive manufacturing machine, or other cutting machines or grinding machines.

[0035] As Figure 1 shown, machine tool 10 includes a control unit 50, servo drivers 111R, 111X to 111Z, servo motors 112R, 112X to 112Z, a moving body 113, a spindle head 131, a tool 134, and a worktable 136.

[0036] The "control unit 50" mentioned in this specification refers to the device that controls machine tool 10. The device structure of control unit 50 is arbitrary. Control unit 50 can be composed of a single control unit or multiple control units. As an example, control unit 50 can include an NC (Numerical Control) unit or a PLC (Programmable Logic Controller).

[0037] The spindle head 131 is composed of a spindle 132 and a housing 133. The housing 133 is used to house the spindle 132. A tool for machining a workpiece W as the object to be machined is installed on the spindle 132. In Figure 1 the example of

[0038] a tool 134 as an end mill is installed on the spindle 132.

[0039] Based on the received machining start instruction, control unit 50 starts to execute a pre-prepared machining program, and controls servo drivers 111R, 111X to 111Z according to this machining program, thereby machining the workpiece W fixed on the worktable 136. This machining program is described, for example, in the form of an NC program.

[0040] The servo driver 111R receives the target rotational speed input sequentially from the control unit 50 and controls the servo motor 112R (rotation drive unit). The servo motor 112R rotates the spindle 132 around the Z-axis. More specifically, the servo driver 111R calculates the actual rotational speed of the servo motor 112R based on the feedback signal from an encoder (not shown) used to detect the rotational angle of the servo motor 112R. If the actual rotational speed is lower than the target rotational speed, the rotational speed of the servo motor 112R is increased; if the actual rotational speed is higher than the target rotational speed, the rotational speed of the servo motor 112R is decreased. In this way, the servo driver 111R sequentially receives feedback on the rotational speed of the servo motor 112R and brings the rotational speed of the servo motor 112R closer to the target rotational speed.

[0041] The servo driver 111X receives target position inputs sequentially from the control unit 50 and controls the servo motor 112X. The servo motor 112X feeds the moving body 113, on which the spindle head 131 is mounted, via a ball screw (not shown), driving the spindle 132 to any position in the X direction. More specifically, the servo driver 111X calculates the actual position of the moving body 113 based on feedback signals from an encoder (not shown) used to detect the rotation angle of the servo motor 112X. If the actual position is smaller than the target position, the actual position of the servo motor 112X is increased; if the actual position is larger than the target position, the actual position of the servo motor 112X is decreased. In this way, the servo driver 111X sequentially receives feedback on the actual position of the servo motor 112X and brings the actual position of the servo motor 112X closer to the target position. Thus, the servo driver 111X drives the spindle 132 to any position in the X direction.

[0042] The servo driver 111Y receives the target position input sequentially from the control unit 50 and controls the servo motor 112Y. The servo motor 112Y feeds the moving body 113, on which the spindle head 131 is mounted, via a ball screw (not shown), driving the spindle 132 to any position in the Y direction. The control method of the servo driver 111Y over the servo motor 112Y is the same as that of the servo driver 111X, and therefore will not be described again.

[0043] The servo driver 111Z receives the target position input sequentially from the control unit 50 and controls the servo motor 112Z. The servo motor 112Z feeds the moving body 113, on which the spindle head 131 is mounted, via a ball screw (not shown), driving the spindle 132 to any position in the Z direction. The control method of the servo driver 111Z over the servo motor 112Z is ​​the same as that of the servo driver 111X, and therefore will not be described again.

[0044] <B. Summary>

[0045] Next, a summary of the method for estimating the cutting force of the machine tool 10 will be described.

[0046] The machine tool 10 uses a strain sensor to estimate the cutting force applied to the tool during workpiece machining. The strain sensor is a sensor for detecting the strain of its mounting part. Strain indicates the degree of deformation of the mounting part according to the external force applied to the mounting part. The strain sensor detects the degree of deformation of its mounting part as an electrical signal. This electrical signal is output to the control unit 50 of the machine tool 10 after being converted into a digital value by an AD (Analog-to-Digital) conversion circuit.

[0047] The strain sensor is arranged to be connected to the first surface and the second surface inside the machine tool 10. The first surface and the second surface are surfaces that are subjected to force during the cutting of the workpiece and are surfaces that form the surfaces of the components inside the machine tool 10. The first surface and the second surface are not parallel to each other. In other words, the second surface forms a specified angle with the first surface.

[0048] Each of the first surface and the second surface can be a surface on the same component or a surface on different components. In addition, the first surface and the second surface can be either a plane or a curved surface.

[0049] When at least one of the first surface and the second surface is subjected to an external force during workpiece machining, the relative position of the surface of one of the first surface and the second surface with respect to the surface of the other changes slightly. Correspondingly, the strain sensor undergoes strain. The strain sensor outputs an output value corresponding to the degree of this strain. At this time, the greater the external force applied to the first surface and the second surface, the greater the degree of strain of the strain sensor and thus the greater the output value of the strain sensor.

[0050] Focusing on this point, the machine tool 10 estimates the cutting force applied to the tool based on the output value of the strain sensor during the cutting process of the workpiece. The strain sensor is cheaper compared to other sensors such as dynamometers. Therefore, by using the strain sensor, the price of the machine tool 10 itself becomes cheaper. In addition, the strain sensor can be installed on any component inside the machine tool 10 and can easily detect the cutting force applied to the tool during machining.

[0051] <C. Mounting Position of the Strain Sensor>

[0052] Next, specific examples of the mounting position of the strain sensor will be described with reference to Figure 2 and Figure 3 is a diagram showing the spindle head 131 on which the strain sensor 140 is mounted. Figure 2

[0053] ​The strain sensor 140 is mounted, for example, in the housing 133 of the spindle head 131. The housing 133 consists of a flange portion 133A and a cylindrical portion 133B. The flange portion 133A is connected to the end of the cylindrical portion 133B.

[0054] One end of the strain sensor 140 is connected to surface SF1 (first surface) on flange 133A. Surface SF1 is a surface that forms a predetermined angle with the axial direction (i.e., the Z direction) of the main shaft 132, and is not parallel to the Z direction. Typically, this predetermined angle is approximately 90 degrees. As an example, surface SF1 is a surface parallel to the XY plane.

[0055] On the other hand, the other end of the strain sensor 140 is connected to surface SF2 (the second surface) on the cylindrical portion 133B. Surface SF2 is not parallel to surface SF1. In other words, surface SF2 and surface SF1 form a predetermined angle. This predetermined angle is, for example, approximately 90 degrees. In this case, surface SF2 is orthogonal to surface SF1. As an example, surface SF2 is parallel to the axial direction (i.e., the Z direction) of the main shaft 132 and is a surface on the housing 133.

[0056] The strain sensor 140 includes a fixing member 141, a cover 142, and a sensing part 143. The sensing part 143 is made of a metal foil or the like, and detects the change in resistance value caused by the expansion and contraction of the metal foil as strain. The change in resistance value is output to the control unit of the machine tool 10 or the like via a wire (not shown) connected to the sensing part 143. The sensing part 143 is adhered to a hole formed in the fixing member 141 and sealed by the cover 142.

[0057] Figure 3 This is a graph visually illustrating the degree of strain on the spindle head 131 when an external force is applied. More specifically, in Figure 3 (A) shows a spindle head 131 subjected to a force from the positive to the negative side in the Y direction during machining. Figure 3 In (B), the degree of strain in each part of the spindle head 131 is shown by varying shades. Furthermore, for ease of explanation, in Figure 3 (B) shows the spindle head 131 in a bent state, but in reality, the degree of bending of the spindle head 131 during machining is different from that in other parts of the machine. Figure 3 The degree of curvature shown in (B) is relatively small.

[0058] like Figure 3 As shown in (B), when the spindle head 131 is subjected to force during machining, the degree of strain of the spindle head 131 is greatest at the connection between the flange portion 133A and the cylindrical portion 133B. Therefore, the strain sensor 140 is connected to both the flange portion 133A and the cylindrical portion 133B, and is thus easily affected by the strain of the spindle head 131, enabling it to detect the force applied to the spindle head 131 with high sensitivity.

[0059] In addition, in the above, an example in which the strain sensor 140 is installed on the spindle head 131 has been described. However, the installation position of the strain sensor 140 is not limited to the spindle head 131, and it can be installed on any member that is stressed due to cutting.

[0060] In addition, in the above, an example in which one strain sensor 140 is provided in the machine tool 10 has been described. However, two or more strain sensors 140 can also be provided in the machine tool 10.

[0061] <D. Functional Structure>

[0062] Next, refer to Figure 4 to describe the functional structure for implementing the estimation process of the cutting force. Figure 4 is a diagram showing an example of the functional structure of the machine tool 10.

[0063] As Figure 4 shown, the machine tool 10 includes an acquisition unit 52, an estimation unit 54, and an output unit 56 as functional structures.

[0064] The acquisition unit 52 is a functional module for acquiring the output value of the strain sensor 140. The acquisition unit 52 sequentially acquires the output value of the strain sensor 140 during the execution of the machining program. The acquisition unit 52 sequentially outputs the output value of the strain sensor 140 to the estimation unit 54.

[0065] The estimation unit 54 estimates the cutting force based on the correlation 126 between the output value of the strain sensor 140 and the cutting force determined in advance. The relationship between the output value of the strain sensor and the cutting force in the correlation 126 can be defined in tabular form or by a defined calculation formula. For example, in this calculation formula, the output value of the strain sensor 140 is set as the explanatory variable and the cutting force applied to the tool is set as the target variable.

[0066] Typically, the correlation 12 (should be 126 here) is defined as: the greater the output value of the strain sensor 140, the greater the cutting force as the estimated value. In other words, the correlation 126 is defined as: the smaller the output value of the strain sensor 140, the smaller the cutting force as the estimated value.

[0067] The output unit 56 outputs the cutting force estimated by the estimation unit 54 in various ways. In one way, when the estimated cutting force exceeds a specified value, the output unit 56 performs a predetermined abnormal response process. This abnormal response process is, for example, a process of outputting a warning indicating that an excessive force is applied to the tool to the operator. The output method of the warning is arbitrary. As an example, this warning can be displayed on the display of the machine tool 10, output by sound, or output as data in the form of a report.

[0068] In another mode, the output unit 56 controls a drive mechanism (such as the above-described servo drivers 111R, 111X, 111Y, 111Z) in the machine tool 10 based on the estimated cutting force. As an example, the output unit 56 stops the drive mechanism in the machine tool 10 based on the estimated cutting force exceeding a specified value. As another example, the output unit 56 controls the moving speed, rotational speed, etc. of the spindle 132 based on the estimated cutting force.

[0069] In another mode, the output unit 56 outputs the estimated cutting force as a log. The output format of the log is arbitrary. As an example, the output unit 56 outputs the estimated cutting force as a log after associating it with time. Thereby, an operator can identify the cause of an abnormality by checking the log.

[0070] <Hardware Structure of E.CNC Unit 30>

[0071] Next, refer to Figure 5 to describe the hardware structure of the CNC unit 30 as an example of the control unit 50. Figure 5 is a schematic diagram showing an example of the hardware structure of the CNC unit 30.

[0072] The CNC unit 30 includes a processor 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, a communication interface 104, a field bus controller 105, a storage device 120, and the above-described strain sensor 140. These components are connected to an internal bus 109.

[0073] The processor 101 is constituted by, for example, at least one integrated circuit. The integrated circuit can be constituted by, for example, at least one CPU (Central Processing Unit), at least one GPU (Graphics Processing Unit), at least one ASIC (Application Specific Integrated Circuit), at least one FPGA (Field Programmable Gate Array), or a combination thereof, etc.

[0074] The processor 101 controls the operation of the CNC unit 30 by executing various programs such as the machining program 122 and the estimation program 124. Based on receiving execution commands for various programs, the processor 101 reads the programs from the storage device 120 or the ROM 102 into the RAM 103. The RAM 103 functions as a working memory and temporarily stores various data required for executing the programs.

[0075] The communication interface 104 is connected to a LAN, an antenna, etc. The CNC unit 30 exchanges data with external devices (such as a server) via the communication interface 104. The CNC unit 30 can also be configured to download the machining program 122 and the estimation program 124 from the external device.

[0076] The fieldbus controller 105 is an interface for enabling communication between various units connected to the fieldbus. As an example of the units connected to the fieldbus, a PLC, an I / O unit, etc. can be cited.

[0077] The storage device 120 is a storage medium such as a hard disk, a flash memory, etc. The storage device 120 stores the machining program 122, the estimation program 124, and the above-mentioned correlation 126, etc.

[0078] The machining program 122 defines various commands for realizing the machining of a workpiece. The estimation program 124 is a program for estimating the cutting force based on the correlation 126 between the output value of the strain sensor 140 and the cutting force, and the output value of the strain sensor 140. This cutting force is referred to by the machining program 122, for example.

[0079] The storage locations of the machining program 122, the estimation program 124, and the correlation 126 are not limited to the storage device 120, and can also be stored in the storage area of the processor 101 (such as a flash memory, etc.), the ROM 102, the RAM 103, an external device (such as a server), etc.

[0080] The estimation program 124 may not be provided as a single program, but may be provided as being embedded in a part of an arbitrary program. In this case, in cooperation with the arbitrary program, the estimation process of the cutting force performed by the estimation program 124 is realized. Even for such a program that does not include a part of the module, it does not deviate from the gist of the estimation program 124 according to this embodiment. And, part or all of the functions provided by the estimation program 124 can also be realized by dedicated hardware. And, the machine tool 10 can also be configured in such a way that a part of the process of the estimation program 124 is executed by at least one server, i.e., a so-called cloud service.

[0081] <F. Control Flow>

[0082] Next, refer to Figure 6The control process related to the estimation of cutting forces will be explained. Figure 6 This is a flowchart illustrating the process of estimating cutting forces.

[0083] This is achieved by executing control procedures through the control unit 50. Figure 6 The process is illustrated. In another approach, part or all of the process may be performed by circuit elements or other hardware.

[0084] In step S110, the control unit 50 determines whether machining program 122 has been executed. If the control unit 50 determines that machining program 122 has been executed (step S110: "Yes"), the control unit 50 switches control to step S112. Otherwise (step S110: "No"), the control unit 50 executes the processing of step S110 again.

[0085] In step S112, the control unit 50 functions as the aforementioned acquisition unit 52 (see reference). Figure 4 It performs its function and obtains the output value of strain sensor 140.

[0086] In step S114, the control unit 50 functions as the aforementioned estimation unit 54 (see reference). Figure 4 The tool functions by estimating the cutting force applied to it based on the output value of the strain sensor 140. The method for estimating this cutting force has been described above and will not be repeated here.

[0087] In step S120, the control unit 50 determines whether the cutting force estimated in step S114 exceeds a predetermined value. If the control unit 50 determines that the cutting force exceeds the predetermined value (step S120: "Yes"), the control unit 50 switches control to step S122. Otherwise (step S120: "No"), the control unit 50 switches control to step S130.

[0088] In step S122, the control unit 50 functions as the aforementioned output unit 56 (see reference). Figure 4 The system then functions to output stop commands to the drive mechanisms (such as the aforementioned servo drives 111R, 111X, 111Y, and 111Z) within the machine tool 10, thereby stopping the machining process.

[0089] In step S130, the control unit 50 determines whether the processing has ended. For example, the control unit 50 determines that processing has ended if it receives a user's stop operation, the processing program reaches its last line, or the processing program has been executed a predetermined number of times. When the control unit 50 determines that processing has ended (step S130: "Yes"), it terminates the process. Figure 6 The process is as shown. Otherwise (step S130: "No"), the control unit 50 returns the control to step S112.

[0090] <G. Variant Example 1>

[0091] Next, refer to Figure 7 and Figure 8 to describe the machine tool 10 according to Variant Example 1. Figure 7 is a front view of the housing 133 of the spindle head 131 shown from the Z direction. Figure 8 is a side view of the housing 133 of the spindle head 131 shown from the X direction.

[0092] In the above-mentioned machine tool 10, one strain sensor 140 is provided in the housing 133. In contrast, in the machine tool 10 according to this variant example, four strain sensors 140A to 140D are provided in the housing 133. The strain sensors 140A to 140D are the same sensors as the above-mentioned strain sensor 140.

[0093] As described above, the housing 133 of the spindle head 131 is composed of a flange portion 133A and a cylindrical portion 133B. The flange portion 133A is connected to the end of the cylindrical portion 133B.

[0094] The flange portion 133A includes a surface SF1 that receives force from the workpiece during machining. The surface SF1 is a connecting surface of the flange portion 133A and is a surface parallel to the XY plane.

[0095] The cylindrical portion 133B includes surfaces SF2 to SF5 that receive force from the workpiece during machining. The surfaces SF2 to SF5 respectively form a part of the outer surface of the cylindrical portion 133B and are surfaces parallel to the axial direction of the spindle 132 (i.e., the Z direction).

[0096] The surface SF2 is not parallel to the surface SF1. In other words, the surface SF2 forms a specified angle with the surface SF1. This specified angle is, for example, about 90 degrees. In this case, the surface SF2 is orthogonal to the surface SF1. [[ID=2S]]

[0097] The surface SF3 is not parallel to the surface SF1. In other words, the surface SF3 forms a specified angle with the surface SF1. This specified angle is, for example, about 90 degrees. In addition, when viewed from the axial direction of the spindle 132 (i.e., the Z direction), the angle between the direction from the rotation center of the spindle 132 to the center of the surface SF3 and the direction from the rotation center of the spindle 132 to the center of the surface SF2 is about 90 degrees.

[0098] Surface SF4 is not parallel to surface SF1. In other words, surface SF4 forms a predetermined angle with surface SF1. This predetermined angle is, for example, approximately 90 degrees. Furthermore, surface SF4 faces surface SF2. More specifically, when viewed from the axial direction (i.e., the Z direction) of the main shaft 132, the angle formed by the direction from the center of rotation of the main shaft 132 toward the center of surface SF4 and the direction from the center of rotation of the main shaft 132 toward the center of surface SF2 is approximately 180 degrees.

[0099] Surface SF5 is not parallel to surface SF1. In other words, surface SF5 forms a predetermined angle with surface SF1. This predetermined angle is, for example, approximately 90 degrees. Furthermore, surface SF5 faces surface SF3. More specifically, when viewed from the axial direction (i.e., the Z direction) of the main shaft 132, the angle formed by the direction from the center of rotation of the main shaft 132 toward the center of surface SF5 and the direction from the center of rotation of the main shaft 132 toward the center of surface SF3 is approximately 180 degrees.

[0100] One end of strain sensor 140A is connected to surface SF1, and the other end of strain sensor 140A is connected to surface SF2. Additionally, one end of strain sensor 140B is connected to surface SF1, and the other end of strain sensor 140B is connected to surface SF3. Furthermore, one end of strain sensor 140C is connected to surface SF1, and the other end of strain sensor 140C is connected to surface SF4. Finally, one end of strain sensor 140D is connected to surface SF1, and the other end of strain sensor 140D is connected to surface SF5. The result is as follows: Figure 7 and Figure 8 As shown, strain sensors 140A to 140D are arranged at equal intervals of 90 degrees when viewed from the axis center of the main shaft 132.

[0101] The machine tool 10 estimates the cutting force in each of the X, Y, and Z directions based on the output values ​​of the strain sensors 140A to 140D. For example, the cutting force in each direction is estimated based on the following equation (1).

[0102] F = M·S···(1)

[0103] The “F” shown in equation (1) is the cutting force (F) in each of the X, Y, and Z directions. x F y F z The vector is represented by a component of ) . “S” is the output value (S) of each strain sensor 140A~140D. A S B S C S D) is a vector of components. "M" is a matrix composed of fixed values. The values of "M" are determined in advance, such as when designing the machine tool 10, based on the positional relationship of the strain sensors 140A to 140D, etc.

[0104] <H. Modified Example 2>

[0105] Next, refer to Figure 9 and Figure 10 to describe the machine tool 10 according to Modified Example 2. Figure 9 is a front view of the housing 133 of the spindle head 131 shown from the Z direction. Figure 10 is a side view of the housing 133 of the spindle head 131 shown from the X direction.

[0106] In the machine tool 10 according to Modified Example 1, four strain sensors 140A to 140D are provided on the housing 133. In contrast, in the machine tool 10 according to this modified example, three strain sensors 140A to 140C are provided on the housing 133.

[0107] As described above, the housing 133 of the spindle head 131 is composed of a flange portion 133A and a cylindrical portion 133B. The flange portion 133A is connected to the end of the cylindrical portion 133B.

[0108] The flange portion 133A includes a surface SF1 that receives force from the workpiece during machining. The surface SF1 is a connecting surface of the flange portion 133A and is a surface parallel to the XY plane.

[0109] The cylindrical portion 133B includes surfaces SF2 to SF4 that receive force from the workpiece during machining. The surfaces SF2 to SF4 respectively form a part of the outer surface of the cylindrical portion 133B and are surfaces parallel to the axial direction of the spindle 132 (i.e., the Z direction).

[0110] The surface SF2 is not parallel to the surface SF1. In other words, the surface SF2 forms a specified angle with the surface SF1. This specified angle is, for example, about 90 degrees. In this case, the surface SF2 is orthogonal to the surface SF1.

[0111] The surface SF3 is not parallel to the surface SF1. In other words, the surface SF3 forms a specified angle with the surface SF1. This specified angle is, for example, about 90 degrees. In addition, the surface SF3 is not facing the surface SF2. As an example, when viewed from the axial direction of the spindle 132 (i.e., the Z direction), the angle between the direction from the rotation center of the spindle 132 to the center of the surface SF3 and the direction from the rotation center of the spindle 132 to the center of the surface SF2 is about 120 degrees.

[0112] The surface SF4 is a surface that is not parallel to the surface SF1. In other words, the surface SF4 forms a specified angle with the surface SF1. This specified angle is, for example, approximately 90 degrees. Additionally, the surface SF4 does not face both the surface SF2 and the surface SF3. More specifically, when viewed from the axial direction of the main shaft 132 (i.e., the Z direction), the angle formed by the direction from the rotation center of the main shaft 132 towards the center of the surface SF4 and the direction from the rotation center of the main shaft 132 towards the center of the surface SF2 is approximately 120 degrees.

[0113] One end of the strain sensor 140A is connected to the surface SF1, and the other end of the strain sensor 140A is connected to the surface SF2. Additionally, one end of the strain sensor 140B is connected to the surface SF1, and the other end of the strain sensor 140B is connected to the surface SF3. Additionally, one end of the strain sensor 140C is connected to the surface SF1, and the other end of the strain sensor 140C is connected to the surface SF4. As a result, as Figure 9 and Figure 10 shown, the strain sensors 140A to 140C are arranged at equal intervals with a 120-degree interval when viewed from the axis center of the main shaft 132.

[0114] The machine tool 10 estimates the cutting forces in each of the X, Y, and Z directions based on the output values of the strain sensors 140A to 140C respectively. For example, the cutting forces in each direction are estimated based on the following formula (2).

[0115] F = M·S ···(2)

[0116] "F" shown in the formula (2) is a vector with components of the cutting forces in the X, Y, and Z directions (F x , F y , F z ). "S" is a vector with components of the output values of the strain sensors 140A to 140C respectively (S A , S B , S C ). "M" is a matrix composed of fixed values. The value of "M" is determined in advance based on the positional relationship of the strain sensors 140A to 140C, etc. when designing the machine tool 10.

[0117] <I. Modified Example 3>

[0118] Next, refer to Figure 11 to describe other examples of the configuration patterns of the strain sensors 140. Figure 11 is a diagram showing various configuration patterns of the strain sensors 140. In Figure 11 , the patterns (A) to (F) are shown as the configuration patterns of the strain sensors 140.

[0119] In the above Figure 7 and Figure 8 In the example, the strain sensors 140A to 140D are arranged at 90-degree intervals when viewed from the axial direction of the main shaft 132, but the strain sensors 140A to 140D can also be arranged as shown in the modes (A) to (C).

[0120] In addition, in the above Figure 9 and Figure 10 example, the strain sensors 140A to 140C are arranged at 120-degree intervals when viewed from the axial direction of the main shaft 132, but the strain sensors 140A to 140C can also be arranged as shown in the modes (D) and (E). In addition, the strain sensors 140A to 140C can also be arranged as shown in Figure 11 mode (F).

[0121] <J. Modified Example 4>

[0122] Next, the machine tool 10 according to Modified Example 4 will be described with reference to Figure 12 FIG. Figure 12 is a view showing the machine tool 10 according to Modified Example 4.

[0123] The machine tool 10 in this modified example is a compound machine tool having the following functions: a turning function for machining a workpiece by bringing a tool into contact with a rotating workpiece; and a milling function for machining a workpiece by bringing a rotating tool into contact with the workpiece.

[0124] As Figure 12 shown, the machine tool 10 has a machine base 236, a workpiece spindle 211, an opposing workpiece spindle 216, a tool spindle 221, and a tool rest 231.

[0125] The machine base 236 is a base member for supporting the workpiece spindle 211, the opposing workpiece spindle 216, the tool spindle 221, the tool rest 231, etc., and is provided on the ground of a factory or the like. The machine base 236 is formed of a metal such as cast iron.

[0126] The workpiece spindle 211 and the opposing workpiece spindle 216 are configured to be able to hold a workpiece. The workpiece spindle 211 and the opposing workpiece spindle 216 are arranged to face each other in the Z-axis direction. The workpiece spindle 211 and the opposing workpiece spindle 216 are mainly provided to rotate the workpiece during turning machining using a fixed tool. The workpiece spindle 211 is arranged to be able to rotate about a central axis 201 parallel to the Z-axis. The opposing workpiece spindle 216 is arranged to be able to rotate about a central axis 202 parallel to the Z-axis. A first chuck mechanism 213 for holding the workpiece in a detachable manner is provided on the workpiece spindle 211, and a second chuck mechanism 218 for holding the workpiece in a detachable manner is provided on the opposing workpiece spindle 216.

[0127] The workpiece spindle 211 is fixed on the machine base 236. The opposing workpiece spindles 216 are configured to move along the Z-axis direction via various feed mechanisms, guide mechanisms, and servo motors.

[0128] The tool spindle 221 and the tool holder 231 are configured to hold the tool used for cutting the workpiece. The tool spindle 221 is positioned above the tool holder 231.

[0129] The tool spindle 221 is configured to rotate about a central axis 203 that is parallel to the Y-axis extending in the vertical direction. A clamping mechanism (not shown) is provided on the tool spindle 221 for removably holding the tool.

[0130] The tool spindle 221 is configured to also rotate around a central axis 204 that extends horizontally and is parallel to the X-axis orthogonal to the Z-axis (B-axis rotation). The rotation range of the tool spindle 221 is, for example, with the spindle end face 223 of the tool spindle 221 facing downwards. Figure 12 The range is ±120° based on the posture shown in the figure.

[0131] The tool spindle 221 is supported on the base 236 by a column (not shown). The tool spindle 221 is configured to move along the Y-axis, X-axis, and Z-axis directions via various feed mechanisms, guide mechanisms, and servo motors provided on the column.

[0132] The tool holder 231 is a so-called turret shape, with multiple tools mounted radially for rotary indexing.

[0133] More specifically, the tool holder 231 has a rotating section 232. The rotating section 232 is configured to rotate about a central axis 206 parallel to the Z-axis. Tool holders for holding the tool are installed at circumferentially spaced positions centered on the central axis 206. As the rotating section 232 rotates about the central axis 206, the tool held in the tool holder moves circumferentially, and the tool for machining the workpiece is indexed.

[0134] The tool post 231 is supported on the machine base 236 by a saddle (not shown). The tool post 231 is configured to move along the Y-axis and Z-axis directions via various feed mechanisms, guide mechanisms, and servo motors provided in the saddle, etc. Furthermore, the tool post 231 may also be configured to move along the Z-axis direction and in a diagonal upward / downward direction orthogonal to the Z-axis direction and including a vertical component. In this case, the tool post 231 may also be configured to move in a diagonal upward / downward direction orthogonal to the Z-axis direction and including a vertical component by simultaneously feeding along the Y-axis and X-axis directions.

[0135] The tool spindle 221 and the tool holder 231 can each hold a rotary tool or a stationary tool. A rotary tool is a tool that processes a workpiece while rotating, such as a drill bit, an end mill, or a reamer. When the tool holder 231 holds a rotary tool, the tool holder 231 incorporates a motor that outputs rotation and a power transmission mechanism that transmits the rotation output from the motor to the rotary tool.

[0136] The machine tool 10 also has a shield 210. The shield 210 forms the appearance of the machine tool 10 and demarcates a machining area 200 for the workpiece.

[0137] The machine tool 10 uses a strain sensor 140 provided on the tool holder 231 to estimate the cutting force applied to the tool. One end of the strain sensor 140 is connected to a surface SF1 (first surface). The surface SF1 is a surface that forms a prescribed angle with the axial direction (i.e., the Z direction) of the tool spindle 221 and is a surface on the tool holder 231. Typically, this prescribed angle is approximately 90 degrees. As an example, the surface SF1 is a surface parallel to the XY plane.

[0138] On the other hand, the other end of the strain sensor 140 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 prescribed angle with the surface SF1. This prescribed angle is, for example, approximately 90 degrees. As an example, the surface SF2 is a surface parallel to the axial direction (i.e., the Z direction) of the tool spindle 221 and is a surface on the tool holder 231. Or, the surface SF2 is a surface parallel to the axial direction of the tool spindle 221 and is a surface on the installation surface of the tool holder 231 (i.e., on the machine base 236). Typically, the surface SF2 is orthogonal to the surface SF1.

[0139] The strain sensor 140 detects the degree of strain of the tool holder 231 during machining. The machine tool 10 estimates the cutting force based on the correlation between the output value of the strain sensor 140 and the cutting force determined in advance according to the output value of the strain sensor 140. The relationship between the output value of the strain sensor and the cutting force in this correlation can be specified in tabular form or by a prescribed calculation formula. In this calculation formula, for example, the output value of the strain sensor 140 is set as the explanatory variable, and the cutting force applied to the tool is set as the target variable.

[0140] <K. Summary>

[0141] As described above, strain sensor 140 is connected to surfaces SF1 and SF2, which are subjected to external forces during machining. Surfaces SF1 and SF2 form a predetermined angle. When surfaces SF1 and SF2 are subjected to external forces, their relative positions change slightly, and correspondingly, strain sensor 140 experiences strain. The greater the external force on the tool, the greater the strain in strain sensor 140, and thus the larger the output value of strain sensor 140. In this way, the output value of strain sensor 140 is related to the cutting force applied to the tool. Therefore, machine tool 10 can estimate the cutting force applied to the tool based on the output value of strain sensor 140. Strain sensors are inexpensive compared to other sensors such as force gauges. Therefore, by using strain sensors, the price of machine tool 10 itself becomes cheaper.

[0142] The embodiments disclosed herein should be considered illustrative in all respects and not limiting. The scope of the invention is not defined by the foregoing description but by the claims, which are intended to include all modifications within the meaning and scope equivalent to the claims.

[0143] Explanation of reference numerals in the attached figures

[0144] 10: Machine tool; 30: CNC unit; 50: Control unit; 52: Acquisition unit; 54: Estimation unit; 56: Output unit; 101: Processor; 102: ROM; 103: RAM; 104: Communication interface; 105: Fieldbus controller; 109: Internal bus; 111R, 111X, 111Y, 111Z: Servo drivers; 112R, 112X, 112Y, 112Z: Servo motors; 113: Moving body; 120: Storage device; 122: Machining program; 124: Estimation program; 126: Correlation; 131: Spindle head; 132: Spindle; 133: Housing; 133A: Flange; 133B: Cylindrical section; 134: Tool; 136: Worktable; 140, 140A, 140B, 140C, 140D: Strain sensors; 141: Fixing component; 142: Cover; 143: Sensing unit; 200: Machining area; 201, 202, 203, 204, 206: Central shaft; 210: Sheath; 211: Workpiece spindle; 213: First chuck mechanism; 216: Opposing workpiece spindle; 218: Second chuck mechanism; 221: Tool spindle; 223: Spindle end face; 231: Tool holder; 232: Rotating part; 236: Machine base.

Claims

1. A machine tool capable of cutting a workpiece using a cutting tool, said machine tool comprising: The first surface inside the machine tool is subjected to force due to the cutting of the workpiece; The second surface within the machine tool is subjected to force due to the cutting of the workpiece, wherein, The second surface is not parallel to the first surface. The machine tool also features: A first strain sensor, which is connected to the first surface and the second surface; and An estimation unit is used to estimate the force applied to the cutting tool based on the output value of the first strain sensor during the cutting process of the workpiece. The first strain sensor is not in contact with the connecting portion used to connect the first surface and the second surface.

2. The machine tool according to claim 1, wherein, The first strain sensor includes: A fixing member, which is connected to the first surface and the second surface; and The sensing element is installed in a hole provided in the fixing member.

3. The machine tool according to claim 1 or 2, wherein, The machine tool also features: Spindle, which is used to rotate the tool; and Housing, which is used to house the spindle, The first surface is a surface that forms a predetermined angle with the axial direction of the main shaft, and it is a surface on the housing. The second surface is a surface parallel to the axial direction of the main shaft and is a surface on the housing.

4. The machine tool according to claim 1 or 2, wherein, The machine tool also features: A spindle, used to rotate the workpiece; and A tool holder, configured to hold a tool used for cutting the workpiece. The first surface is a surface that forms a predetermined angle with the axial direction of the spindle, and it is a surface on the tool holder. The second surface is a surface parallel to the axial direction of the spindle, and is a surface on the tool holder or on the mounting surface of the tool holder.

5. The machine tool according to claim 3, wherein, The specified angle is 90 degrees.

6. The machine tool according to claim 5, wherein, The machine tool also features: Second strain sensor; The third strain sensor; and The fourth strain sensor, The second strain sensor is connected to the first surface and the third surface subjected to force due to the cutting of the workpiece, wherein the third surface is not parallel to the first surface. The third strain sensor is connected to the first surface and the fourth surface subjected to force due to the cutting of the workpiece. The fourth surface is not parallel to the first surface and faces the second surface. The fourth strain sensor is connected to the first surface and the fifth surface subjected to force due to the cutting of the workpiece. The fifth surface is not parallel to the first surface and faces the third surface.

7. The machine tool according to claim 5, wherein, The machine tool also features: The second strain sensor; and Third strain sensor, The second strain sensor is connected to the first surface and the third surface subjected to force due to the cutting of the workpiece. The third surface is neither parallel to the first surface nor facing the second surface. The third strain sensor is connected to the first surface and the fourth surface subjected to force due to the cutting of the workpiece. The fourth surface is not parallel to the first surface and is not facing the second surface or the third surface.

8. An estimation method for estimating the force applied to the cutting tool when cutting a workpiece in a machine tool. The machine tool includes: The first surface within the machine tool is subjected to force due to the cutting of the workpiece; and The second surface within the machine tool is subjected to force due to the cutting of the workpiece, wherein, The second surface is not parallel to the first surface. The machine tool also includes a strain sensor, which is connected to the first surface and the second surface. The strain sensor is not in contact with the connecting portion used to connect the first surface and the second surface. The estimation method includes the following steps: The output value of the strain sensor is acquired during the cutting process of the workpiece; and The force applied to the tool is estimated based on the output value.

9. A non-transient computer-readable medium storing a program for estimating the forces applied to a cutting tool when cutting a workpiece in a machine tool. The machine tool includes: The first surface within the machine tool is subjected to force due to the cutting of the workpiece; and The second surface within the machine tool is subjected to force due to the cutting of the workpiece, wherein, The second surface is not parallel to the first surface. The machine tool also includes a strain sensor, which is connected to the first surface and the second surface. The strain sensor is not in contact with the connecting portion used to connect the first surface and the second surface. The estimation procedure causes the machine tool to perform the following steps: The output value of the strain sensor is acquired during the cutting process of the workpiece; as well as The force applied to the tool is estimated based on the output value.

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