Machine tool and estimation method

Abstract

To provide a machine tool and estimation method capable of estimating errors in thermal displacement correction processing. [Solution] The machine tool of this disclosure comprises a machining device that processes a workpiece with a cutting tool, a temperature sensor that outputs a detected value corresponding to the temperature of a thermal displacement part in the machine tool, and a control device that acquires the temperature of the thermal displacement part based on the detected value of the temperature sensor. The control device performs a wear correction process to correct machining errors caused by wear of the cutting tool, and a thermal displacement correction process to correct machining errors caused by thermal displacement of the thermal displacement part based on the temperature of the thermal displacement part and parameters, estimates the correction error in the thermal displacement correction process from the history of the wear correction process, and sets the parameters to be used in the thermal displacement correction process based on the estimated result.

Description

[Technical Field]

[0001] This disclosure relates to a machine tool that performs wear correction processing and thermal displacement correction processing, and to an estimation method for estimating the error of the correction in the machine tool. [Background technology]

[0002] Patent Document 1 below describes a machine tool that performs wear compensation processing and thermal displacement compensation processing. The machine tool in Patent Document 1 records the machining dimensions of the input workpiece. The machine tool also stores information on the thermal displacement compensation amount (temperature compensation amount in the document) calculated based on the detection values ​​of temperature sensors attached to various parts of the machine tool, and information on the wear compensation amount due to tool wear. Then, at the start of the next operation, the machine tool calculates the change in the machining dimensions of the workpiece if there were no thermal displacement compensation and wear compensation by inverse calculation from the machining dimensions of the workpiece, thermal displacement compensation amount, and wear compensation amount from the previous operation, and determines the parameters of the thermal displacement compensation formula from the calculated change using multiple regression analysis. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-005874 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In the parameter determination method described above, the parameters for thermal displacement compensation are determined based on the machining dimensions when neither of the two types of compensation are performed. As a result, the error value due to tool wear is reflected in the thermal displacement compensation parameters, and the amount of thermal displacement compensation calculated by the thermal displacement compensation formula after the parameters have been determined may differ from the amount of thermal displacement that actually occurs in the thermal displacement part of the machine tool. Consequently, there is a problem of errors occurring in the thermal displacement compensation.

[0005] This disclosure has been made in view of the above-mentioned problems, and aims to provide a machine tool and estimation method that can estimate errors in thermal displacement correction processing. [Means for solving the problem]

[0006] To solve the above problems, this specification discloses a machine tool comprising: a machining apparatus for machining a workpiece with a cutting tool; a temperature sensor that outputs a detected value corresponding to the temperature of a thermal displacement part in the machine tool; and a control device that acquires the temperature of the thermal displacement part based on the detected value of the temperature sensor, wherein the control device performs a wear correction process to correct machining errors caused by wear of the cutting tool, and a thermal displacement correction process to correct machining errors caused by thermal displacement of the thermal displacement part based on the temperature of the thermal displacement part and parameters, estimates the correction error in the thermal displacement correction process from the history of the wear correction process, and sets the parameters used in the thermal displacement correction process based on the estimated result. Furthermore, the contents of this disclosure are not limited to implementation as a machine tool, but are also extremely effective as an estimation method for estimating correction errors in machine tools. [Effects of the Invention]

[0007] According to the machine tool and estimation method of this disclosure, the error in the thermal displacement correction process included in the wear correction amount can be estimated from the history of the wear correction process. [Brief explanation of the drawing]

[0008] [Figure 1] Block diagram of the machine tool according to this embodiment. [Figure 2] A graph showing the waveform of the ideal wear compensation amount. [Figure 3] A graph showing the waveform of the actual wear correction amount. [Figure 4] A graph showing the waveform of the actual wear correction amount and the waveform of the ideal wear correction amount. [Figure 5] A diagram illustrating the processing flow of the comparative example and the processing flow of this embodiment. [Modes for carrying out the invention]

[0009] Hereinafter, an embodiment of the machine tool described herein will be explained with reference to the drawings. Figure 1 shows a block diagram of the machine tool 10 of this embodiment. As shown in Figure 1, the machine tool 10 includes a workpiece holding device 11, a processing device 12, a loader 13, a touch sensor 14, a plurality of temperature sensors 15, an operation panel 16, a control device 17, and the like.

[0010] The machine tool 10 is, for example, a lathe and is equipped with a workpiece holding device 11 on a bed (not shown). The workpiece holding device 11 is, for example, a workpiece spindle device and is equipped with a chuck mechanism for holding the workpiece. As the chuck mechanism, for example, a mechanism for opening and closing multiple chuck jaws or a collet chuck can be used.

[0011] The machining device 12 is, for example, a turret-type machining device, and is equipped with a tool post to which cutting tools (such as cutting tools or rotary tools) can be attached, a sliding mechanism for sliding the tool post, and a turret motor for rotating the tool post. The machining device 12 performs machining on a workpiece held by the workpiece holding device 11 using a cutting tool. The machining device 12 switches the cutting tool used to machine the workpiece by rotating the tool post.

[0012] The loader 13 is, for example, a gantry-type workpiece transfer device, and is equipped with a head having a chuck for holding the workpiece and a sliding mechanism for sliding the head. The loader 13 transfers workpieces between the workpiece holding device 11, the equipment of the preceding process, etc. The touch sensor 14 is, for example, a contact-type sensor (touch probe), and is used to measure the dimensions of the workpiece. The machine tool 10, for example, brings the touch sensor 14 into contact with the workpiece after machining and measures the machined dimensions of the workpiece based on the contact position. The machine tool 10 performs a wear correction process based on the measured machined dimensions.

[0013] Furthermore, the machine tool 10 is equipped with multiple temperature sensors 15. Each of the multiple temperature sensors 15 is mounted in a position that can detect the temperature of a thermally displaced part of the machine tool 10, and outputs a detected value corresponding to the temperature of the thermally displaced part. A thermally displaced part is, for example, a part that deforms, distorts, expands or contracts due to changes in machine temperature, and is a part that affects machining accuracy due to deformation, etc. Specifically, thermally displaced parts are the bed, headstock, tool post, etc. The control device 17 acquires the temperature of each thermally displaced part based on the detected value of each of the multiple temperature sensors 15. The control device 17 performs thermal displacement correction processing based on the acquired temperatures.

[0014] Furthermore, the control panel 16 is the user interface for the machine tool 10 and is equipped with a touch panel 18, operation switches 19, etc. Based on the control of the control device 17, the control panel 16 displays information related to the machine tool 10 on the touch panel 18. The control panel 16 also accepts user input on the screen displayed on the touch panel 18 and outputs a signal to the control device 17 corresponding to the received input. Note that the above-described configuration of the user interface is just one example. For example, the user interface may consist only of a touch panel 18, or it may not have a touch panel 18 but consist of operation switches 19 and a monitor (such as an LCD monitor).

[0015] As shown in FIG. 1, the control device 17 includes a numerical control device 21, a PLC 22, and an external IF (abbreviation of interface) 23. The numerical control device 21 includes a CPU 24 and a storage device 25. The storage device 25 includes, for example, a RAM, a ROM, a flash memory, a HDD, etc. The storage device 25 can store an NC program 26, a control program 27, a wear correction history 28, a thermal displacement correction history 29, and thermal displacement correction formula data 30. Note that the configuration of the storage device 25 that stores the NC program 26 etc. is not limited to the above-described configuration, and may be a configuration including an SSD instead of a HDD, or a configuration using an external storage medium such as a USB memory. Also, the storage device 25 may be a storage medium such as a DVD-RAM, or a combination of these. Also, the storage device 25 that stores the NC program 26 etc. may be a server or a network storage.

[0016] Further, the machine tool 10 includes a control device 17 and a plurality of drive circuits 20 that connect each of the above-described devices (work holding device 11, machining device 12, loader 13, touch sensor 14, temperature sensor 15, operation panel 16). The numerical control device 21 can control each device via the drive circuit 20 by executing the NC program 26 and the control program 27 stored in the storage device 25 with the CPU 24. The drive circuit 20 is, for example, a driver circuit (servo amplifier) or an amplifier circuit that amplifies signals. The PLC 22 is a Programmable Logic Controller. The PLC 22 executes, for example, a ladder program 31 stored in the PLC 22 and performs sequence processing of various signals by a ladder circuit. The PLC 22 is connected to the numerical control device 21 via a communication bus 32 and performs input / output of signals with the numerical control device 21.

[0017] Also, the control program 27 is, for example, a program that executes correction parameter setting processing described later. Further, the wear correction history 28 stores the history of wear correction processing. The thermal displacement correction history 29 stores the history of thermal displacement correction processing. The thermal displacement correction formula data 30 stores the correction formula (hereinafter referred to as the thermal displacement correction formula) used in the thermal displacement correction processing and the values of the parameters of the thermal displacement correction formula. Details of the wear correction history 28, the thermal displacement correction history 29, and the thermal displacement correction formula data 30 will be described later.

[0018] The external IF 23 is, for example, a network interface and is connected to the management PC 36 via the network 35. The network 35 is, for example, a LAN or the Internet. The management PC 36 is installed, for example, in the factory where the machine tool 10 is installed or at the vendor of the machine tool 10. The management PC 36 can acquire the wear correction history 28, the thermal displacement correction history 29, and the thermal displacement correction formula data 30 from the machine tool 10 via the network 35. The management PC 36 can also execute the correction parameter setting processing described later, the processing of displaying the graph in FIG. 4, and the processing of setting parameters. Note that the method of acquiring the wear correction history 28, etc. of the machine tool 10 is not limited to the method of acquiring via the network 35, and a method of writing to a DVD-RAM or a USB memory may also be used. Therefore, the correction parameter setting processing described later may be executed on a PC that has read a DVD-RAM or the like.

[0019] Note that the configuration of the machine tool 10 shown in Figure 1 is just one example. The machine tool disclosed is not limited to a lathe, but can be a machine with various configurations, such as a machining center, milling machine, drilling machine, or grinding machine. For this reason, the workpiece holding device 11 is not limited to a workpiece spindle device, but may be a device that fixes the position of the workpiece relative to the rotating tool of the processing device 12. Also, the processing device 12 equipped in the machine tool 10 is not limited to one unit, but may be multiple units. Furthermore, the machine tool 10 may be a multi-tasking machine equipped with a lathe and a machining center. Also, the device for transporting the workpiece is not limited to a loader 13, but may be other devices such as an articulated robot. Furthermore, the machine tool 10 may be configured without a device for transporting the workpiece. Furthermore, the machine tool 10 may be configured without an external IF 23.

[0020] Furthermore, in the following explanation, the numerical control device 21 of the control device 17 may simply refer to the device name when it executes programs such as the NC program 26 and the control program 27 to control each device. For example, the statement "The control device 17 controls the loader 13 to transfer the workpiece" means "The control device 17 executes the NC program 26 on the CPU 24, and controls the loader 13 based on the NC program 26 to transfer the workpiece."

[0021] The control device 17 controls each device in the configuration described above to perform machining on the workpiece. For example, when the control device 17 receives an instruction to start machining based on an operation input to the control panel 16, it executes the specified NC program 26 and controls each device. For example, the control device 17 controls the loader 13 to transfer the workpiece received from the preceding device to the workpiece holding device 11. The control device 17 controls the workpiece holding device 11 to rotate the workpiece around the workpiece spindle and controls the machining device 12 to machine the workpiece with a cutting tool. When machining is complete, the control device 17 transfers the workpiece from the workpiece holding device 11 to the loader 13 and transports the machined workpiece to the subsequent device, etc.

[0022] (Regarding wear correction treatment) The control device 17 of this embodiment performs wear compensation processing (hereinafter sometimes referred to as wear compensation) to compensate for machining errors caused by the amount of wear of the cutting tool worn during workpiece machining. The control device 17 performs wear compensation at predetermined intervals from the start of use of the cutting tool until it is replaced. For example, the control device 17 performs wear compensation for each workpiece. After machining the workpiece, the control device 17 contacts the machined workpiece with the touch sensor 14 to measure the dimensions after machining. The control device 17 detects the error between the measured machining dimensions and the target machining dimensions (hereinafter sometimes referred to as target dimensions) and sets the detected error as the wear compensation amount. The target machining dimensions here are, for example, the command value of the NC program 26, which is the target design value for machining. When machining the next workpiece, the control device 17 corrects the command value of the position command of the NC program 26 using the wear compensation amount set after the previous machining. For example, the control device 17 moves the cutting edge of the cutting tool closer to the workpiece by the wear compensation amount during machining, or moves it further away from the workpiece during machining. The control device 17 performs measurement of the machining dimensions, setting of the wear compensation amount, and correction based on the set wear compensation amount each time the workpiece changes.

[0023] The control device 17 stores the amount of wear correction used for wear correction in the wear correction history 28. The control device 17 stores in the wear correction history 28, for example, the date and time when wear correction was performed, the workpiece number, the identification information of the cutting tool (holder number, etc.), the amount of wear correction applied, and the temperature detected by each temperature sensor 15 at the time of wear correction, associating these with the wear correction history.

[0024] The wear correction process described above is merely an example. For instance, the wear correction amount may be a value obtained by multiplying the error between the measured machining dimension and the target dimension by a predetermined correction coefficient. Furthermore, the predetermined timing for performing wear correction is not limited to the timing for each machining operation of the workpiece. For example, the control device 17 may measure and correct the machining dimension each time a cutting tool is used (each machining process). Therefore, the control device 17 may perform machining dimension measurement and set the wear correction amount for each cutting tool, and use different wear correction amounts for each cutting tool. Alternatively, the control device 17 may use the same wear correction amount for different cutting tools. Furthermore, the timing for performing wear correction may be after a predetermined amount of machining time has elapsed.

[0025] Furthermore, the machine tool 10 may be equipped with a tool sensor for measuring the amount of wear on the cutting tool. The control device 17 may then contact the cutting tool with the tool sensor to measure the amount of wear on the cutting tool and set a wear compensation amount based on the measured amount of wear. Alternatively, the machine tool 10 may be equipped with both a touch sensor 14 and a tool sensor, and determine the wear compensation amount based on the machining dimensions and the amount of wear on the cutting tool. The user may also manually measure the machining dimensions and the amount of wear. The user inputs the measured machining dimensions, the amount of wear, or the error between the machining dimensions and the target dimensions via the control panel 16. The control device 17 may then set a wear compensation amount based on the input machining dimensions, etc.

[0026] (Regarding thermal displacement correction processing) Furthermore, the control device 17 performs a thermal displacement correction process (hereinafter sometimes referred to as thermal displacement correction) that corrects machining errors caused by thermal displacement of the thermal displacement parts based on the temperature and parameters of the thermal displacement parts. The machine tool 10 generates heat due to various causes such as motor operation, sliding mechanism drive, contact between the cutting tool and workpiece, and chip generation, causing thermal displacement (thermal deformation) in thermal displacement parts such as the bed, spindle head, and tool post. This thermal displacement results in errors in machining accuracy. For example, the control device 17 obtains the temperature of each thermal displacement part from the detection values ​​of multiple temperature sensors 15, and calculates the amount of thermal displacement correction based on the obtained temperature and a thermal displacement correction formula with parameters. For example, the following thermal displacement correction formula (1) can be used as the thermal displacement correction formula.

number

[0027] The control device 17, for example, detects the temperature tk using the temperature sensor 15 at a predetermined timing, substitutes the detected temperature tk into the thermal displacement correction formula (1) to calculate the thermal displacement correction amount δ, and corrects the command value of the position command in the NC program 26 based on the calculated thermal displacement correction amount δ. The timing for executing the thermal displacement correction can be, for example, at predetermined time intervals during machining. Alternatively, the execution timing can be various timings, such as the timing when machining the workpiece starts, the timing when machining the workpiece ends, or the timing when switching cutting tools.

[0028] The control device 17 stores the thermal displacement correction amount δ used for thermal displacement correction in the thermal displacement correction history 29. For example, the control device 17 stores the date and time when thermal displacement correction was performed, the workpiece number, the cutting tool identification information (holder number, etc.), the applied thermal displacement correction amount δ, the temperature tk at the time of thermal displacement correction, and the coefficient α. k The values ​​of the constant β and other related information are stored in the thermal displacement correction history 29.

[0029] (Regarding the correction parameter setting process) The control device 17 updates the wear compensation amount for each workpiece machining operation, correcting the error between the machined dimensions and the target dimensions, and adjusting the machined dimensions to match the target dimensions. Whether the control device 17 automatically sets the wear compensation amount or the user manually sets the wear compensation amount by measuring the dimensions, the machined dimensions are set to match the target dimensions.

[0030] Figure 2 shows the wear compensation amount when there are no errors in thermal displacement and cutting tool mounting position. In the following explanation from Figure 2 onward, to avoid complexity, we will explain the case when a throwaway cutting tool is used. However, the method of setting the parameters of the thermal displacement compensation formula described below can also be applied to brazed cutting tools, solid cutting tools, or cutting tools other than cutting tools such as drills and end mills, in the same way as with throwaway cutting tools.

[0031] In Figure 2, the vertical axis represents the wear compensation amount, and the horizontal axis represents the usage time of the throwaway tool tip. The turning point in the graph in Figure 2 indicates the timing of tip replacement. For example, if there is no thermal displacement in the machine tool 10, no mounting position error occurs when replacing the tip, no errors due to other factors, and the tip wears ideally, the wear compensation amount increases as the amount of tip wear increases and increases linearly in direct proportion to the tip usage time. That is, Figure 2 shows the wear compensation amount in an ideal environment, and the wear compensation amount increases by a constant amount depending on the tip usage time. The change in the wear compensation amount Δδ from the start of use of a tip until replacement is the same for all tips. The wear compensation amount matches the amount of tip wear, and the waveform is the same each time the tip is replaced. Therefore, in an ideal environment without thermal displacement compensation or mounting position errors, if workpiece-specific corrections are performed to match the machining dimensions to the target dimensions, the wear compensation amount will be as shown in the graph in Figure 2.

[0032] On the other hand, thermal displacement occurs in the machine tool 10, and the amount of thermal displacement varies depending on the temperature of the heat generated at any given time and the amount of displacement of the part where the heat was generated. Furthermore, it is extremely difficult to directly measure the amount of thermal displacement, and the coefficient α of the thermal displacement correction formula (1) k It is difficult to determine whether the constant β is an appropriate value. Even in machines that undergo thermal displacement, if the thermal displacement compensation is accurate, the waveform of the wear compensation amount should be ideal, as if no thermal displacement were occurring in the machine. However, in reality, the result of comparing the machined dimensions after processing with the design target dimensions is input as the wear compensation amount, so the wear compensation amount, which includes errors in thermal displacement compensation and mounting position errors, is stored as data. Therefore, in the machine tool 10 of this embodiment, the waveform of the ideal wear compensation amount is estimated from the stored wear compensation history 28, and the parameter (coefficient α) is calculated from the error between the estimated ideal waveform and the actual wear compensation amount. k The correction parameter setting process is executed to determine the constant β).

[0033] Figure 3 shows an example of the wear compensation amount stored in the wear compensation history 28. The vertical axis in Figure 3 shows the wear compensation amount in μm units, for example, and the horizontal axis shows the number of workpieces processed. As shown in Figure 3, the wear compensation amount increases as the amount of chip wear increases and as the number of workpieces processed increases. Also, the turning point in the graph of Figure 3 indicates the timing of chip replacement, similar to Figure 2. For example, the wear compensation amount is reset when a new chip is replaced and counted again from the wear compensation amount of the first workpiece. In the example in Figure 3, the chip is replaced every 10 workpieces, and the example shows a case where the chip has been replaced 3 times. This wear compensation amount is stored in the wear compensation history 28.

[0034] As described above, the wear compensation amount is set based on the error between the machined dimensions and the target dimensions, and the input value includes not only the amount of chip wear but also the error for thermal displacement compensation. Therefore, the changes in the wear compensation amount Δδ1, Δδ2, Δδ3, and Δδ4 from the start of use of each chip until replacement will be different values.

[0035] Furthermore, the wear compensation amounts (hereinafter referred to as initial values) δa1, δa2, δa3, and δa4 set after machining the first workpiece for each chip will vary. This is because, when considering the position where the chip is attached to the shank on a scale such as micrometers, it is difficult to perfectly match it each time the chip is replaced, and errors occur each time the chip is replaced. For this reason, the initial values ​​δa1 to δa4 set after machining the first workpiece will be different values.

[0036] Furthermore, even if the replaced chip is not a new chip but a chip that is already worn, the initial values ​​δa1 to δa4 will fluctuate. For this reason, when the control device 17 estimates the waveform of the ideal wear correction amount, as described later, it may calculate the initial values ​​and changes in the ideal waveform by only considering new chips. For example, when a chip is replaced, the control device 17 may receive information indicating whether it was replaced with a new chip or a used chip that has been used at least once, and store this information in the wear correction history 28. Then, when calculating the initial values ​​and changes in the ideal waveform, the control device 17 may perform processing limited to the wear correction amount of a new chip.

[0037] The control device 17 estimates an ideal wear correction waveform, which eliminates the thermal displacement correction error and mounting position error shown in Figure 2, from the wear correction amount data, which includes the thermal displacement correction error and mounting position error shown in Figure 3. The error between this estimated ideal waveform and the actually stored wear correction amount is taken as the thermal displacement correction error. Therefore, the difference between the ideal wear correction waveform shown in Figure 2 and the actual wear correction waveform shown in Figure 3 is taken as the error (correction mistake) in thermal displacement correction, and the parameters of the thermal displacement correction formula are corrected accordingly.

[0038] For example, when the production of workpieces for the day is completed, the control device 17 executes a correction parameter setting process and corrects the parameters of the thermal displacement correction formula from the wear correction history 28 data stored for that day. The control device 17 also executes the correction parameter setting process, for example, during a pre-set downtime (such as the late-night period when the machine tool 10 is shut down). The process of correcting parameters will be explained below using the case shown in Figure 3 as an example.

[0039] First, the control device 17 reads the wear correction amount for the day from the wear correction history 28 and calculates the change in wear correction amount Δδ1 to Δδ4 for each chip. The control device 17 sets (estimates) the average of the calculated change amounts Δδ1 to Δδ4 as the ideal change amount Δδ'. In the case of Figure 3, the change amount Δδ' of the ideal waveform is as follows. The ideal change Δδ' = (Δδ1 + Δδ2 + Δδ3 + Δδ4) / 4

[0040] Furthermore, the control device 17 sets the average of the initial values ​​Δδa1 to Δδa4 of the wear compensation amount for each chip as the initial value of the ideal waveform. In the case of Figure 3, the initial value Δδa' of the ideal waveform is as follows. The ideal initial value Δδa' = (Δδa1 + Δδa2 + Δδa3 + Δδa4) / 4

[0041] Figure 4 shows the waveform of the actual wear correction amount, i.e., the waveform in Figure 3, superimposed with the ideal waveform estimated from the actual waveform. When the control device 17 receives a predetermined operation input from the user to the control panel 16, for example, it displays the waveform screen shown in Figure 4 on the touch panel 18. As shown in Figure 4, for each chip, the control device 17 displays two waveforms, aligned with the position corresponding to the first workpiece processed and the position corresponding to the last workpiece processed (in the case of Figure 4, the 10th workpiece processed). As shown in Figure 4, the ideal waveform has an initial value of Δδa' and a change of Δδ'.

[0042] By using the average value of the change amount Δδ', the error in thermal displacement correction can be averaged, and the change amount of the ideal waveform shown in Figure 4 can be approximated to the change amount of the waveform shown in Figure 2. Furthermore, by using the average value of the initial value Δδa', the error in the mounting position can be averaged, and the initial value of the ideal waveform shown in Figure 4 can be approximated to the initial value of the waveform shown in Figure 2. Preferably, by calculating the initial value from the wear correction amount of only a new tip, the error in the mounting position can be further reduced. Note that the relationship between the actual wear correction amount waveform and the ideal waveform shown in Figure 4 is just one example. Therefore, it is possible that the actual wear correction amount waveform may be located below the ideal waveform, or that the two waveforms may intersect.

[0043] As shown in Figure 4, an error δt occurs between the waveform of the actual wear correction amount and the ideal waveform. The control device 17 sets the parameters of the thermal displacement correction formula (1) from this error δt. For example, the control device 17 performs multiple regression analysis on the error δt of the two waveforms and sets the parameters (coefficient α) of the thermal displacement correction formula (1) so that the error in the two waveforms is eliminated. k The constant β) is set. For example, the wear correction history 28 stores the temperature detected by each temperature sensor 15 at the time of wear correction. The control device 17 performs multiple regression analysis based on the error δt of the wear correction amount and the temperature detected by each temperature sensor 15 at that time, and sets the coefficient α of the thermal displacement part where each temperature was detected. k Alternatively, a constant β is set. This corrects the error in the thermal displacement correction amount, making it closer to the actual thermal displacement value, and preferably matching the actual thermal displacement value.

[0044] Figure 5 schematically shows the process of setting the parameters of the thermal displacement correction formula in a comparative example and the process of this embodiment (correction parameter setting process). The process flow of the comparative example corresponds to the process flow of the prior art document (Japanese Patent Application Publication No. 2019-005874). In the process of the comparative example, the transition of the workpiece's machining dimensions when there is no thermal displacement correction or wear correction is calculated by inverse calculation from the actually recorded workpiece machining dimensions, thermal displacement correction amount, and wear correction amount (Figure 5 (1a)) (1b). That is, the transition of the machining dimensions that fluctuates due to errors when no correction is made at all is calculated. Then, in the comparative example, the parameters of the thermal displacement correction formula are determined from the calculated transition (1c). With this processing method, since the parameters of the thermal displacement correction formula are determined from a state without correction, there is a risk that all machining errors will be reflected in the thermal displacement correction formula as if no wear correction had been made (ignored).

[0045] On the other hand, as shown in (2a) and (2b) of Figure 5, the correction parameter setting process of this embodiment estimates an ideal waveform from the actual wear correction amount. This ideal waveform is the error that should be corrected for the original purpose of wear correction, as shown in Figure 2 (2b). Then, as shown in (2c), the difference between the actual wear correction amount and the estimated ideal waveform is estimated as the thermal displacement correction error δt. In the process of this embodiment, the parameters of the thermal displacement correction formula are modified so that the estimated thermal displacement correction error δt is included (2d). As a result, the thermal displacement correction error can be clearly reflected in the thermal displacement correction formula compared to the process of the comparative example. This suppresses the reflection of the error value due to wear of the cutting tool in the thermal displacement correction formula, and prevents the thermal displacement correction amount calculated by the thermal displacement correction formula after parameter modification from deviating from the actual thermal displacement amount that occurs in the thermal displacement part of the machine tool. Furthermore, since the ideal waveform is estimated from the recorded wear correction amount, there is no need to appropriately input the dimensions of the workpiece after processing into the machine tool, as in the prior art documents.

[0046] Furthermore, before executing the correction parameter setting process, the control device 17 accepts the selection of a cutting tool from among the cutting tools used in the machine tool 10. For example, based on a predetermined operation input to the control panel 16, the control device 17 accepts the holder number to which the cutting tool of the turret of the processing device 12 is attached. The control device 17 then performs the correction parameter setting process and sets the parameters based on the wear correction history 28 (wear correction amount) of the cutting tool used with the accepted holder number. That is, the control device 17 estimates the error in thermal displacement correction from the wear correction history 28 of the cutting tool specified by the user and sets the parameters.

[0047] Cutting tools have various structures, and differences in structure result in different amounts of deflection and vibration (chatter). Therefore, differences in cutting tool structure may reduce the accuracy of estimating the ideal waveform and the error δt. To address this, the control device 17 accepts the selection of a cutting tool to be used for the correction parameter setting process. This allows, for example, the user to specify a cutting tool with high rigidity and less deflection and chatter from among the cutting tools they will be using—that is, a cutting tool less prone to errors other than thermal displacement and wear. By focusing on cutting tools less prone to errors other than thermal displacement and wear, parameters can be determined from the wear correction amount, allowing for accurate parameter setting. Note that the method of specifying a cutting tool is not limited to specifying the holder number. For example, the control device 17 may accept the selection of wear correction amount data to be used for parameter setting from the wear correction history 28. Alternatively, the control device 17 may accept the specification of the cutting tool to be used for the correction parameter setting process within the NC program 26. Furthermore, the control device 17 may execute the correction parameter setting process for each cutting tool, or it may set common parameters for all cutting tools.

[0048] Furthermore, the control device 17 estimates the error δt of thermal displacement correction based on the change amounts Δδ1 to Δδ4 of the wear correction amount stored in the wear correction history 28. By estimating the error δt of thermal displacement correction from the change amounts Δδ1 to Δδ4 in multiple wear corrections, the error δt can be estimated more accurately.

[0049] Furthermore, the wear compensation history 28 stores the amount of wear compensation for each of the multiple chips from the start of use to replacement for each workpiece. Based on the wear compensation history 28, the control device 17 calculates the average value (change amount Δδ') of the changes in wear compensation amounts Δδ1 to Δδ4 for the multiple chips as the ideal change amount. The control device 17 compares the ideal change amount Δδ' with the wear compensation amount for each chip in the wear compensation history 28 (see Figure 4), and sets the parameters used in the thermal displacement compensation formula (1) based on the comparison result.

[0050] If no errors such as thermal displacement occur, ideally, the amount of chip wear increases linearly in proportion to the usage time. Furthermore, wear compensation is repeatedly applied to eliminate the error between the machined dimension and the target dimension. Similarly, thermal displacement compensation is applied to eliminate thermal displacement errors. However, the heat generated by the machine tool 10 varies from time to time. Therefore, the average of multiple change amounts Δδ1 to Δδ4 is estimated as the ideal change amount Δδ' for wear compensation. By comparing the estimated ideal change amount Δδ' with the actual wear compensation amount, it is possible to evaluate how the actual wear compensation amount deviates from the ideal change amount Δδ'. In other words, the change in the thermal displacement compensation error can be evaluated. Based on this comparison result, parameters can be appropriately set.

[0051] Furthermore, the control device 17 analyzes the difference between the estimated ideal change amount Δδ' and the wear correction amount for each chip in the wear correction history 28, estimates the analyzed difference as the thermal displacement correction error δt, and determines the parameters. According to this, the parameters can be determined by analyzing the error δt using multiple regression analysis or the like. The difference between the actual change amounts Δδ1 to Δδ4 of the wear correction amount and the ideal change amount Δδ' is estimated as the error δt to be corrected by thermal displacement correction, and can be corrected by thermal displacement correction.

[0052] Furthermore, the control device 17 calculates the average value (initial value Δδa') of the wear correction amounts (initial values ​​δa1 to δa4) that were first applied to each of the multiple chips after the start of use of that chip, and estimates the calculated average value as the ideal initial value Δδa'. The control device 17 determines the parameters from the difference between the waveform that changes from the ideal initial value Δδa' with an ideal change amount Δδ' and the waveform of the wear correction amount for each chip in the wear correction history 28.

[0053] If the initial values ​​δa1 to δa4 fluctuate due to errors in the chip's mounting position, the effect of mounting position errors can be reduced by calculating the average value of the initial values ​​δa1 to δa4. The average value can be estimated as the ideal initial value Δδa', and the waveform of the ideal wear correction amount can be estimated using the ideal change amount Δδ'. This reduces the effect of mounting position errors and allows for more accurate parameter setting.

[0054] Incidentally, the correspondence between the terms in the present embodiment and the terms described in the claims will be described below. The wear correction history 28 in the present embodiment is an example of the history in the present disclosure. The coefficient α k , and the constant β are examples of parameters. The change amount Δδ’ is an example of an ideal change amount. The initial values δa1 to δa4 are examples of the wear correction amounts applied first. The initial value Δδa’ is an example of an ideal initial value.

[0055] As described above, according to the present embodiment, the following effects can be obtained. In one aspect of the present embodiment, the control device 17 performs a wear correction process for correcting a machining error caused by wear of a cutting tool, and a thermal displacement correction process for correcting a machining error caused by thermal displacement of a thermal displacement portion based on the temperature of the thermal displacement portion and the thermal displacement correction formula (1). The control device 17 estimates the thermal displacement correction error δt from the wear correction history 28, and sets the parameters (coefficient α k、 constant β) of the thermal displacement correction formula based on the estimated result.

[0056] The wear correction history 28 stores a wear correction amount corresponding to the error between the machining dimension and the target dimension. While performing both wear correction and thermal displacement correction, the correction is repeated so that the machining dimension approaches the target dimension. Thus, the wear correction amount includes the thermal displacement correction error δt. Therefore, the control device 17 detects the thermal displacement correction error δt included in the wear correction amount from the wear correction history 28, and corrects appropriate parameters. As a result, the thermal displacement correction amount calculated by the thermal displacement correction formula after correcting the parameters can be made closer to or coincide with the thermal displacement amount actually generated in the thermal displacement portion of the machine tool 10.

[0057] Needless to say, the present disclosure is not limited to the above-described embodiment, and various improvements and changes can be made without departing from the spirit of the present disclosure. For example, the processing details of the correction parameter setting process described above are just an example and can be changed as appropriate. For example, the timing of starting the correction parameter setting process can be changed as appropriate. The control device 17 may calculate the ideal change amount Δδ' and initial value Δδa' while performing machining and modify the parameters of the thermal displacement correction formula as appropriate. Alternatively, the control device 17 may start the correction parameter setting process at a timing instructed by the user.

[0058] Furthermore, the above-described methods for setting the ideal waveform and deriving parameters from the ideal waveform are merely examples. For example, the control device 17 may set the median of the change amounts Δδ1 to Δδ4 as the ideal change amount Δδ'. Alternatively, the control device 17 may set the median of the initial values ​​δa1 to δa4 as the ideal initial value Δδa'. Also, the method of setting parameters from the error δt between the actual wear correction amount and the ideal waveform is not limited to multiple regression analysis; for example, parameters may be set from the error δt using machine learning with AI (artificial intelligence). Or, a person may manually set the parameters while comparing the two waveforms. Moreover, the control device 17 does not have to set the ideal initial value Δδa'. For example, the control device 17 may calculate the change amount Δδ' and set the waveform that changes by the change amount Δδ' from each of the initial values ​​δa1 to δa4 as the ideal waveform.

[0059] Furthermore, the control device 17 does not need to perform the modification of the parameters of the thermal displacement correction formula. For example, the control device 17 does not need to automatically modify the parameters by displaying the graph shown in Figure 4 on the touch panel 18. In this case, the user can estimate the error δt of the thermal displacement correction by looking at the two waveforms. Also, by comparing the actual wear correction amount value with the ideal waveform, the thermal displacement correction can be evaluated more accurately, and the parameters of the thermal displacement correction formula can be modified. Therefore, parameter modification can be done by the user (person) checking the two waveforms and operating the touch panel 18, etc., to change the parameters so that the two waveforms are similar. In addition, the control device 17 may use a tool sensor to correct the error in the mounting position. This makes it possible to reduce or eliminate the error in the mounting position.

[0060] Furthermore, the entity that performs the correction parameter setting process is not limited to the machine tool 10 (control device 17). For example, a management PC 36 connected to the machine tool 10 may acquire the wear correction history 28 from the machine tool 10 via the network 35 and perform the display of the graph shown in Figure 4 and the setting of parameters. Therefore, the vendor side of the machine tool 10 may also perform the verification of thermal displacement correction errors and the setting of parameters. Furthermore, the machine tool 10 may be configured without a thermal displacement correction history 29.

[0061] Furthermore, the contents of this disclosure are not limited to the dependent relationships described in the claims. For example, this specification also discloses a technical concept in which "the machine tool described in claim 1 or claim 2" in claim 6 is changed to "the machine tool described in any one of claims 1 to 5". [Explanation of symbols]

[0062] 10 Machine tool, 12 Processing equipment, 15 Temperature sensor, 17 Control device, 28 Wear correction history (history), tk Temperature, α kCoefficient (parameter), β constant (parameter), δt error, Δδ1~Δδ4 change, Δδ' change (ideal change), δa1~δa4 initial value (initial wear correction amount applied), Δδa' initial value (ideal initial value).

Claims

1. A machining device that processes a workpiece using a cutting tool, A temperature sensor that outputs a detected value corresponding to the temperature of the thermal displacement part in a machine tool, A control device that acquires the temperature of the thermal displacement part based on the detected value of the temperature sensor, Equipped with, The control device is A wear compensation process for correcting machining errors caused by wear of the cutting tool, A thermal displacement correction process that corrects the machining error caused by the thermal displacement of the thermal displacement part based on the temperature and parameters of the thermal displacement part, Execute, A machine tool that estimates the error in the thermal displacement correction process from the history of the wear correction process, and sets the parameters used in the thermal displacement correction process based on the estimated result.

2. The history of the wear correction process includes: A wear correction amount, which is a correction amount that compensates for the wear that occurs on the cutting tool, is stored. The control device is The machine tool according to claim 1, wherein the error in the thermal displacement correction process is estimated based on the amount of change in the wear correction amount stored in the history of the wear correction process.

3. The history of the wear correction process includes: For each of the multiple cutting tools, the amount of wear correction at predetermined intervals from the start of use of the cutting tool until its replacement is stored. The control device is Based on the history of the wear correction process, the average value of the change in the wear correction amount is calculated for multiple cutting tools. The average value of the calculated change is estimated as the ideal change in the wear correction amount. The machine tool according to claim 2, wherein the estimated ideal amount of change is compared with the amount of wear correction for each cutting tool in the history of the wear correction process, and the parameters used for the thermal displacement correction process are set based on the comparison result.

4. The control device is The machine tool according to claim 3, wherein the difference between the estimated ideal amount of change and the amount of wear correction for each cutting tool in the history of the wear correction process is analyzed, the analyzed difference is estimated to be the error of the correction in the thermal displacement correction process, and the parameters used in the thermal displacement correction process are determined.

5. The control device is For each of the multiple cutting tools, the average of the wear compensation amounts initially applied after the start of use of that cutting tool is calculated, and the average of the calculated wear compensation amounts initially applied is estimated as the ideal initial value. The machine tool according to claim 4, wherein the parameters used for the thermal displacement correction process are determined from the difference between a waveform that changes from the ideal initial value by the ideal amount of change and the waveform of the wear correction amount for each cutting tool in the history of the wear correction process.

6. The control device is The machine tool according to claim 1 or claim 2, which accepts the selection of a cutting tool from among the cutting tools used in the machine tool, and estimates the error in the correction in the thermal displacement correction process from the history of the wear correction process of the selected cutting tool.

7. An estimation method for estimating the error of corrections in a machine tool, The aforementioned machine tool is A machining device that processes a workpiece using a cutting tool, A temperature sensor that outputs a detected value corresponding to the temperature of the thermal displacement part in the machine tool, A control device that acquires the temperature of the thermal displacement part based on the detected value of the temperature sensor, Equipped with, The control device is A wear compensation process for correcting machining errors caused by wear of the cutting tool, A thermal displacement correction process that corrects the machining error caused by the thermal displacement of the thermal displacement part based on the temperature and parameters of the thermal displacement part, Execute, The estimation method described above is An estimation method for estimating the error in the thermal displacement correction process from the history of the wear correction process.

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