Temperature estimation methods and thermal displacement correction methods for machine tools

Abstract

Temperature estimation method for a machine tool to estimate, in a machine tool which has a plurality of sections to which temperature sensors (S) are attached, and one section to which the temperature sensor (S) is not attached, a temperature of the section where the temperature sensor (S) is not attached, wherein the temperature estimation method includes: a temperature information acquisition step of obtaining temperature information from the temperature sensors (S) at two or more different sections where the temperature sensors (S) are attached; an operational information acquisition step of obtaining a predetermined operational information, which is represented by two types of states that are ON and OFF; a coefficient determination step of determining a coefficient for each part of the temperature information, such that if a time at which the operating information is switched from ON to OFF or from OFF to ON is a reference time, the coefficient for each part of the temperature information is changed according to a time that elapses from the reference time; and a temperature estimation step of estimating a temperature of the section where the temperature sensor (S) is not attached, based on the temperature information and the coefficient for the temperature information.

Description

[0001] The present invention relates to a method for estimating the temperature of a section in a machine tool, the temperature of which cannot be directly detected by a temperature sensing means, such as a temperature sensor, and a method for correcting a thermal displacement according to the estimated temperature.

[0002] In machining operations performed using a machine tool, thermal deformation of machine tool components can occur due to factors such as mechanical heat generation from spindle and feed shaft operations, temperature changes in the environment where the machine tool is installed, or temperature changes in the coolant. Such thermal displacement can cause a change in the relative position between a tool and a workpiece. Therefore, the machining accuracy of the workpiece can be reduced if thermal displacement occurs during machining.

[0003] In many cases, a coolant is used during machining. When a coolant is used, a significant displacement can occur when ejection is initiated due to a rapid temperature change caused by a temperature difference between the coolant and the workpiece or setup. Conversely, when coolant ejection is stopped, a rapid temperature change occurs due to the heat of vaporization generated by water evaporating from the surface of the workpiece or setup. These factors can also lead to significant displacement when machining is restarted.

[0004] A common method for preventing thermal displacement in a machine tool is thermal displacement correction, in which temperature sensors are attached to the machine tool's components, displacement is calculated based on the measured temperature, and the axis travel is adjusted accordingly. However, a machine tool has many rotating and moving parts, and temperature measurement in many of these parts is difficult due to wiring constraints and other factors. Furthermore, directly measuring the temperatures of a workpiece and a tool attached to or detached from the machine tool is challenging.Therefore, a method can be used in which a correction is applied according to the temperature of a section whose temperature is easy to measure, rather than according to the temperature of a section where it is difficult to measure. However, temperatures in different sections vary. Consequently, the accuracy in estimating thermal displacement is lower, and the correction error can increase. Furthermore, the section whose temperature is difficult to measure is often likely to be affected by a coolant, which tends to further increase the correction error.

[0005] To address the aforementioned problems, Japanese patent JP 3 897 884 B (hereinafter referred to as patent literature 1) discloses a technique in which a temperature simulation block is provided in a turret head, which is a rotating section and where attaching a temperature sensor is difficult, and the temperature of the turret head is measured indirectly using the temperature simulation block. The temperature simulation block is designed to have a heat capacity close to that of the turret head, and a coolant that has not yet been injected is brought into thermal contact with the temperature simulation block. Patent literature 1 states that by using the temperature of the temperature simulation block, thermal displacement can be accurately estimated.

[0006] The publication of the disclosed Japanese patent application JP 2002 - 301 637 A (hereinafter referred to as patent literature 2) discloses a technique in which coefficients are used to estimate a thermal displacement of a spindle in order to distinguish between a case in which a coolant is used and a case in which no coolant is used, and, if a coolant is used, the coefficient is adjusted according to a temperature difference between the spindle and the coolant in order to correct an error due to the influence of the coolant.

[0007] The publication of the disclosed Japanese patent application JP 2002 - 326 141 A (hereinafter referred to as patent literature 3) discloses a technique in which the tendency of a temperature change of a coolant is determined and a filter coefficient is changed in a case where the temperature increases and in a case where the temperature decreases, accurately estimating the temperature of a setup affected by a coolant.

[0008] However, the method disclosed in patent literature 1 is carried out under the assumption that machining is performed using a coolant. In a case where machining is performed without the use of a coolant, the temperature difference between the turret head and the temperature simulation block increases due to the difference in the environment, and a correction error may be amplified. Furthermore, if machines are modified and the size of the turret head is changed, the temperature simulation block must also be changed accordingly, and the labor and time required for designing and manufacturing the machine tool may increase.

[0009] In the method disclosed in patent literature 2, a coefficient is changed in a case where coolant is used and in a case where no coolant is used in order to estimate a thermal displacement of a spindle. Therefore, the method can be used in both cases where a coolant is used and cases where no coolant is used. However, in some respects, it is difficult to use this method in practice.

[0010] Patent literature 2 states that the coefficient is adjusted according to a temperature difference between the spindle and a coolant, and the adjustment procedure is determined experimentally. However, in practice, it can be difficult to simply adjust a coefficient based on the temperature difference between the spindle and the coolant. For example, even if a temperature difference is the same in a case where the spindle temperature is high and the coolant temperature is near room temperature, and in a case where the spindle temperature is not high and the coolant temperature is below room temperature, the effect may differ. In this case, a thermal displacement must be measured for various spindle and coolant temperatures to determine the coefficients, and a large amount of experimental data is required.Furthermore, patent literature 2 discloses a method for improving a change in a transitional state after the use of the coolant has ceased, but does not provide a description of a change after the start of the ejection.

[0011] In the method disclosed in patent literature 3, a difference between a case in which a coolant is used and a case in which no coolant is used is not considered, and a correction error can increase in a case in which no coolant is used.

[0012] None of the methods disclosed in patent literature 2 and patent literature 3 can handle rapid changes that occur in a case where there is a large temperature difference between a workpiece or assembly and a coolant at the start of ejection.

[0013] Therefore, it is an object of the present invention to provide a temperature estimation method for a machine tool in which the temperature of a section, where it is difficult to measure the temperature directly, is accurately estimated in a simple manner, and a thermal displacement correction method that is carried out on the basis of the estimated temperature.

[0014] The problem is solved using the features of independent claims. Advantageous further developments are the subject of dependent claims.

[0015] To solve the aforementioned problem, a first aspect of the present invention is a temperature estimation method for a machine tool for estimating the temperature of a section without a temperature sensor in a machine tool that has a plurality of sections, each with a temperature sensor attached, and one section without a temperature sensor. The temperature estimation method may comprise a temperature information acquisition step, an operational information acquisition step, a coefficient determination step, and a temperature estimation step. The temperature information acquisition step is a step for obtaining temperature information from the temperature sensors at two or more different sections where the temperature sensors are attached.The operational information acquisition step is a step in acquiring predetermined operational information, represented by two types of states: ON and OFF. The coefficient determination step is a step in determining a coefficient for each part of the temperature information, such that if the time at which the operational information switches from ON to OFF or from OFF to ON is a reference time, the coefficient for each part of the temperature information is changed according to the time elapsed since the reference time. The temperature estimation step is a step in estimating the temperature of the section where the temperature sensor is not attached, based on the temperature information and the coefficient for that temperature information.

[0016] The “section where the temperature sensors are attached” and the “section where the temperature sensor is not attached” include a space, such as a machining area, within the machine tool.

[0017] In a second aspect of the present invention, which is based on the first aspect, the operating information in the coefficient determination step can be represented by a marker, one or more time constants can be preset, and a delayed process can be carried out using the time constants for the marker to determine the coefficient for each part of the temperature information at any given time.

[0018] In a third aspect of the present invention, which is based on the second aspect, the value of the time constant can be different at a time when the operating information is switched from ON to OFF and at a time when the operating information is switched from OFF to ON.

[0019] In a fourth aspect of the present invention, which is based on one of the first to third aspects, it is possible to use a coolant for the machine tool, and the temperature information includes a temperature of a setup or a machining area of ​​the machine tool, and a temperature of the coolant, and the operating information represents an ejection or a stopping of the coolant.

[0020] In the fourth aspect, in the coefficient determination step, if a time at which a coolant discharge changes to a stop, or a time at which the coolant stop changes to a coolant discharge, is a reference point, a coefficient for the temperature information can be determined for each temperature of the setup or machining area and the coolant temperature, so that the coefficient for the temperature information changes according to a time that has elapsed from the reference time, and In the temperature estimation step, the temperature of the section where the temperature sensor is not attached is estimated based on the temperature of the setup or machining area, the temperature of the coolant, and the coefficient for the temperature information.

[0021] In a fifth aspect of the present invention, which is based on the fourth aspect, in the coefficient determination step the number of time constants that are preset can be two and the coefficient for the temperature information can be determined using the time constants by performing a delayed process for the marker, and in the temperature estimation step, by multiplying by a predetermined coefficient a difference between the two time constants with which the delayed process is performed, a temperature change due to heat of vaporization after stopping the coolant can be estimated, and a temperature of the section where the temperature sensor is not attached can be estimated in view of the temperature change.

[0022] In a sixth aspect of the present invention, which is based on the fifth aspect, a hygrometer can be placed around the setup or in the processing space, and the time constants and / or the predetermined coefficient can be changed according to the humidity measured by the hygrometer.

[0023] In a seventh aspect of the present invention, based on one of the first to third aspects, the machine tool includes a heating device capable of heating a workpiece for machining or heat treatment, wherein the temperature information includes a temperature of a setup or machining area of ​​the machine tool and a heating temperature for the workpiece, and the operating information represents an operation or a stopping of the heating device.

[0024] In the seventh aspect, in the coefficient determination step, if a time at which the heating device switches from operation to a stop, or a time at which the heating device switches from stopping to operation, is a reference time, a coefficient for the temperature information can be determined for each of the temperature of the setup or the processing area, and the heating temperature, so that the coefficient for the temperature information is changed according to a time that has elapsed from the reference time, and In the temperature estimation step, the temperature of the section where the temperature sensor is not attached can be estimated based on the temperature of the setup or machining area, the heating temperature, and the coefficient for the temperature information.

[0025] In an eighth aspect of the present invention, which is based on one of the second, third, fifth or sixth aspects, the time constant can be set according to at least one of a workpiece, a tool, a clamping device or tooling.

[0026] To solve the aforementioned problem, a ninth aspect of the present invention is a thermal displacement correction method for a machine tool for correcting, in a machine tool comprising a plurality of sections, each with a temperature sensor attached, and a section without a temperature sensor, a thermal displacement of the section without the temperature sensor. The thermal displacement correction method may include a section-without-sensor temperature estimation step, a thermal displacement calculation step, and a correction step. The section-without-sensor temperature estimation step is a step of estimating the temperature of the section without the temperature sensor using the temperature estimation method according to one of the first through eighth aspects.The thermal displacement calculation step is a step in calculating the extent of thermal displacement using the estimated temperature. The correction step is a step in correcting the cutting edge position of a workpiece based on the calculated extent of thermal displacement.

[0027] According to the present invention, the temperature of a section whose temperature is difficult to measure directly and on which the temperature sensor is not attached can be accurately estimated in a simple method based on the result of a temperature measurement on a section on which the temperature sensor is attached.

[0028] In particular, using information about an operation represented by two types of states, ON / OFF, a process is performed to obtain coefficients for temperatures at two or more different locations. These coefficients are then adjusted according to a time interval, starting from a reference time at which the state is switched. Therefore, the temperature used can be changed to differentiate between the ON and OFF operating states. Furthermore, the estimated temperature at the time of the state switch does not change abruptly but rather gradually.

[0029] In the machine tool, the estimated temperature of a section where the temperature sensor is not attached is used to calculate a thermal displacement extent, thereby improving the accuracy of a thermal displacement correction, i.e., machining accuracy.

[0030] According to the second aspect of the present invention, in addition to the effects achieved above, the operating information is represented by a marker, a time constant is set, and the marker is subjected to a delayed process to obtain a coefficient for the temperature. Therefore, the tendency of a temperature change in the case of a changed operating state can be expressed by a parameter that is a time constant, and the calculation expression can be represented in a simple form. Thus, parameter setting for an accurate estimation of an actual temperature change is simplified.

[0031] According to the third aspect of the present invention, in addition to the effects achieved above, the value of the time constant is chosen differently between a change from ON to OFF and a change from OFF to ON. Therefore, the temperature can be accurately estimated in each case.

[0032] According to the fourth aspect of the present invention, in addition to the effects achieved above, information about the coolant discharge / stop state is used to adapt to a temperature change due to the influence of the coolant, whereby the temperature can be estimated regardless of whether the coolant is used or not. Furthermore, both temperatures of the coolant and the assembly are used, thus also addressing a state in which there is a large difference between the two temperatures when the coolant discharge is initiated.

[0033] Furthermore, both the time at which the coolant flow changes from discharge to cessation and the time at which the coolant flow changes from cessation to discharge are chosen as reference times, and a process of changing the coefficients of the system temperature and the coolant temperature over time is performed. Therefore, the estimated temperature at the time of the state change does not change abruptly but rather smoothly. Due to the aforementioned effects, even a large temperature change in a transition state after the state in which the coolant flow changes from discharge to cessation or from cessation to discharge can be addressed.

[0034] According to the fifth aspect of the present invention, in addition to the effects achieved above, a temperature change due to the heat of vaporization can be accurately estimated in order to address an abrupt temperature decrease due to heat of vaporization that occurs when the coolant is stopped, provided that two time constants and coefficients are suitably set.

[0035] According to the sixth aspect of the present invention, in addition to the effects achieved above, even if the amount of heat of vaporization changes due to ambient humidity or the opening / closing of an operating door, the humidity in the processing room or the like is monitored using a hygrometer, and the parameter is adjusted accordingly. Therefore, the influence of the heat of vaporization can be accurately estimated, even if the environment changes.

[0036] According to the seventh aspect of the present invention, in addition to the effects achieved above, attention is paid to a temperature change due to the influence of a heating device, such as a laser. Therefore, both a heating temperature and a temperature of the setup or processing chamber are used, and the coefficients for the heating temperature and the temperature of the setup or processing chamber can be changed over time based on the reference time at which the process changes from a stop to a heating state or vice versa. Thus, the estimated temperature at the time of the state change does not change abruptly but rather smoothly. The aforementioned effects allow for the mitigation of a large temperature change in a transition state after a change from a stop to a heating state or after a change from heating to a stop state.Furthermore, if the tendency of a temperature change in the case of the heating device used is expressed by a parameter that is a time constant, the calculation expression can be represented in a simple form, and, even if, for example, a workpiece to be processed is changed, parameter adjustment for an accurate estimate of an actual temperature is simplified.

[0037] According to the eighth aspect of the present invention, the temperature change of a workpiece, tool, or the like can be estimated by setting the time constant according to the type of workpiece, tool, or the like. Even if the workpiece, tool, or the like is changed, the temperature change can be estimated accurately. Fig. Figure 1 is a schematic diagram representing an NC lathe. Fig. Figure 2 is a flowchart showing a temperature estimation and a thermal displacement correction. Fig. Figure 3 is a diagram showing a change in cutting tool holder temperature, actual measured turret head temperature, coolant-in-tank temperature, and estimated turret head temperature under a given operating condition. Fig. Figure 4 is a diagram showing an estimation error of the temperature of a turret head both in the case where an estimated temperature is achieved and in the case where a substitute temperature is used. Fig. Figure 5 is a diagram showing a coefficient for both a cutting tool holder temperature and a coolant temperature in the case where a first-order delay process is performed for coolant ejection / stopping, and a coefficient for each temperature is changed.

[0038] An embodiment of the present invention is described below with reference to the drawings.

[0039] Fig. Figure 1 represents an NC lathe, which is an example of a machine tool. It is unnecessary to say that the present invention is also applicable to other types of machine tools, such as a machining center and a combination machine tool.

[0040] The in Fig. Figure 1 shows an NC lathe comprising a cutting tool holder 1, a bed slide 2, a bed 3 (which forms a base), and a spindle housing 4. Temperature sensors S, S, ... are attached to each of the cutting tool holder 1, the bed slide 2, the bed 3, and the spindle housing 4 (sections where the temperature sensors are attached). Furthermore, the cutting tool holder 1 has a turret 5 mounted on it, and the turret 5 has a plurality of pre-mounted tools and can rotate to change the tool being used. The temperature sensor is not attached to the turret 5 (section where the temperature sensor is not attached). The reason for this is that the turret 5 is a rotating section, and wiring it with a standard temperature sensor would be difficult.

[0041] Furthermore, a coolant tank 6 is arranged laterally to the bed 3, and the temperature sensor S for measuring the temperature of a coolant is mounted inside the coolant tank 6. A flow sensor 7 is also mounted in a pipe from the coolant tank 6 to the cutting tool holder 1, and a signal for ejecting / stopping a coolant pump 8 located in the coolant tank 6 is transmitted to an NC device (not shown).

[0042] The temperature sensor for measuring the coolant can be located in a different section, in the piping, or the like, which is sensitive to the influence of a temperature change of the coolant, instead of the temperature sensor provided within the coolant tank 6. Furthermore, a method for obtaining a signal to discharge / stop the coolant can, for example, not only be a method for obtaining a signal from the flow sensor 7, which, as in Fig. 1 shown, in the piping provided, but also a method for reading an instruction value from an NC device to the coolant pump 8, or a method for causing a sensor to detect a rotation of the coolant pump 8, can be used.

[0043] Next, a method for estimating the temperature of the turret head 5, to which the temperature sensor is not attached, is described in the Fig. The NC lathe shown in 1 is described on the basis of the theory of heat transfer.

[0044] First, a temperature change is described in the case of a started discharge of a coolant.

[0045] If a relationship between the temperature change of the turret head 5 and a heat exchange that takes place between the turret head 5 and the coolant is represented as a differential equation in which θ t the temperature of the turret head 5 and θ cThe following expression (1) is obtained to represent the temperature of the coolant. [Numeric expression 1] pCVdθdt=hcA(θc−θt)

[0046] In expression (1), p, C and V represent the density, specific heat and volume of the turret head 5, respectively. Furthermore, h represents c A represents a heat transfer coefficient of a heat transfer between the coolant and the turret head 5, and A represents the surface area of ​​the turret head 5. Expression (1) can be rewritten into the following expressions (2) and (3), in which T c represents a temperature change time constant for the coolant. [Numeric expression 2] Tcdθdt=θc−θt Tc=pCV / hcA

[0047] The turret head temperature θ can be determined by solving the differential equation (2). tin the case where the turret head is exposed to the coolant. The form of the solution to the differential equation is assumed to be the following expression (4) (C1, C2, C3: constant). [Numerical expression 3] θt=C1eC2t+C3

[0048] When expression (4) is substituted into expression (2), C2 and C3 are obtained and the following expression (5) is obtained. [Numerical expression 4] θt=C1e−t / Tc+θc

[0049] The time at which coolant discharge begins is represented as t=0, and it can be assumed that the turret head temperature θ t (0) before the coolant is discharged, the temperature is equal to the machining chamber temperature θ air is represented by the following expression (6). [Numerical expression 5] θt(0)=C1+θc=θair

[0050] Therefore, C1 = θ air - θ cfulfilled, and, when this is substituted into expression (5), the following expression (7) is obtained. [Numerical expression 6] θt=(θair−θc)e−t / Tc+θc

[0051] Furthermore, when the expression is rewritten, the following expressions (8) to (10) are obtained. [Numerical expression 7] θt=pcθc+pairθair pc=1−e−t / Tc pair=1−(1−e−t / Tc)

[0052] If the coolant ejection is controlled by a step input (changing from 0, representing stopping, to 1, representing ejection), then a coefficient p is c of θ c equivalent to a response of a first-order delay of a time constant T c in the case where the coolant temperature is an input. During this time, a coefficient p can be used. air of θ air as 1 - p ccan be expressed. Thus, it is found that a coolant discharge state is represented by a marker, the marker is subjected to the first-order delay process, and the subjected marker is set as a coefficient, whereby the temperature change in the case of the turret head exposed to the coolant can be simulated.

[0053] In expressions (6) to (8) the machining chamber temperature θ air used. However, even if a machine body temperature θ is used instead. m The same calculation is performed when used.

[0054] Next, a case in which the discharge of the coolant is stopped is described. At this time, the differential equations represented by the following expressions (11) and (12) are satisfied, where θ t represents the temperature of the turret head 5 and θ air represents the temperature of the processing room. [Numerical expression 8] Tairdθtdt=θair−θt+Q(t)hairA Tair=pCV / hairA

[0055] The temperature change of the turret head in the case where the coolant is stopped is described by a heat transfer coefficient h. air a heat transfer between air in the machining chamber and the turret head is affected, and is therefore influenced using a time constant T. air , which differs from the time constant for ejection. Furthermore, Q(t) in expression (11) is a function representing a heat of vaporization. Based on experience, the heat of vaporization is assumed to be as follows. Q(t) / hairA=−K0e−t / Tv

[0056] The influence of the heat of vaporization at t=0 (immediately after the coolant is stopped) is -K0, and the amount of heat extracted per unit time is given by the rate of a time constant T. Vclose to 0, since the evaporation of water from the surface of the turret head is reduced. The constants K0 and T are assumed to be... V can be changed according to the amount of water on the turret head 5, the type of coolant, the humidity and the like.

[0057] By substituting a differential equation, the following expression (13) is obtained. [Numerical expression 9] Tairdθtdt=θair−θt+K0e−t / Tv

[0058] The form of the solution to the differential equation is assumed to be the following expression (14) (K1, K2, K3: constant) [Numerical expression 10] θt=K1e−t / Tair+K2e−t / Tv+K3

[0059] If expression (14) is replaced by expression (13), expressions (15) and (16), which are the expressions for the constants, are obtained. [Numeric expression 11] K2=T2T2−T1K0 K3=θair

[0060] A time at which the coolant is stopped is represented as t=0, and the turret head temperature θ is assumed to be t , before the coolant is stopped, as specified in the following expression (17), equal to the coolant temperature θ c K1 is determined, and expression (18) is obtained. [Numeric expression 12] θt(0)=K1+K2+K3=θc K1=θc−θair+TvTv−TairK0

[0061] Thus, the solution to the differential equation is the following expression (19) and, if the expression is rewritten to be simplified, the expression can be expressed as the following expressions (20) to (23). [Numeric expression 13] θt=e−t / Tairθc+(1−e−t / Tair)θair−TvTv−TairK0(e−t / Tv−e−t / Tair) θt=pc'θc+pair'θair−α(e−t / Tv−e−t / Tair) pc'=e−t / Tair pair'=1−e−t / Tair α=TvTv−TairK0

[0062] e-t / Tair In expression (21), a first-order delay is present in the case where the input is changed stepwise from 1 to 0. That is, it can be found that if a coolant discharge state is represented using a marker such that the marker 0 represents a stop of the coolant and the marker 1 represents a discharge of the coolant, the coolant coefficient can be represented as a first-order delay of the marker in the same way in the case of a discharge of the coolant. Furthermore, the coefficient p' can be air of θ air in the second term as 1-p' c in the case of ejection, they will be represented in the same way.

[0063] The relevant time constants, in the case where the coolant temperature is entered, are the time constant T. c for ejection, and in the case where the processing chamber temperature is entered, the time constant Tair for a halt. In general, in a case where the inlet is liquid, heat is transferred more easily and the temperature change is accelerated, and the time constant is reduced compared to a case where the inlet is gaseous. Therefore, it can be found that the time constant is preferably different in a process during ejection and in a process during halting.

[0064] In expression (20), the first and second terms are approximately the same as they are during discharge. When the coolant is stopped, a third term is added due to the influence of a heat of vaporization. The third term is obtained by multiplying the difference between the two time constants (time constant T). air of the turret head with respect to the machining chamber temperature, and time constant T V, which represents a reduction in the heat of vaporization) in a step response with a specific coefficient α.

[0065] Thus, the coolant discharge state is represented using a marker such that marker 0 represents a stop of the coolant flow and marker 1 represents a discharge of the coolant flow. A first-order delay response is provided in the case where the marker is input, for the three time constants (the time constant T). C of the turret head with respect to a coolant temperature, the time constant T air of the turret head with respect to a machining chamber temperature, the time constant T V , which represents a reduction in the heat of vaporization) is obtained, and a multiplication by the coolant temperature θ c and the processing room temperature θ air or the machine body temperature θ mis carried out, whereby both a temperature change during ejection and the temperature change during stopping can be represented in consideration of a heat of vaporization.

[0066] Fig. Figure 2 shows the above contents as a flowchart. In the present embodiment, the NC device estimates according to the diagram in Fig. In the process flow shown in Figure 2, the temperature of the turret head 5 is estimated based on signals from the temperature sensors S and the coolant pump 8 (S1-S4: section-without-temperature-sensor estimation step), and a thermal displacement correction is performed for a cutting edge position based on the estimated temperature of the turret head 5.

[0067] First, information about a coolant discharge / stop state is obtained (S1: operational information acquisition step). A marker is used to represent the coolant discharge / stop state, such that marker 1 represents the discharge state and marker 0 represents the stop state.

[0068] Next, measured temperature data are obtained from the temperature sensors S, which are provided in the components of the machine tool, the machining area and the coolant tank 6 (S2: temperature information acquisition step).

[0069] Next, a delay process is performed for the coolant discharge / stop state marker and coefficients for measured temperatures of the coolant and the machine structure (the cutting tool holder 1 in the present embodiment) are calculated (S3: coefficient determination step).

[0070] Next, the measured temperatures are multiplied by the coefficients and an estimated temperature of a section (estimated temperature of the turret head 5 in the present embodiment) where the temperature sensor is not attached is calculated (S4: temperature estimation step).

[0071] Next, using the estimated temperature obtained in S4, an estimated thermal displacement is calculated (S5: thermal displacement calculation step). For example, the estimated thermal displacement is X. C at the cutting edge in the Fig. 1 NC lathe shown according to the following expression (24) where Θ0 represents the estimated turret head temperature, θ1 represents the measured cutting tool holder temperature, θ2 represents the measured bed slide temperature, θ3 represents the measured bed temperature, θ4 represents the measured headstock temperature and C0 to C4 represent coefficients for the respective temperatures. [Numeric expression 14] Xc=C0Θ0+C1θ1+C2θ2+C3θ3+C4θ4

[0072] In S6, the thermal displacement correction is performed such that the cutting edge position is adjusted by the estimated thermal displacement X calculated in S5. C is changed (correction step).

[0073] This effectively inhibits the thermal displacement that occurs due to temperature changes in the machine structure.

[0074] Next, a method for calculating the estimated temperature Θ0 of the turret head 5 and its effect will be described using an example.

[0075] It is assumed that an actually measured turret head temperature θ0, a cutting tool holder temperature θ1 and the coolant temperature θ c under a specific condition of use, as in Fig. Figure 3 shows that the operation can be modified. During machining, after one hour has elapsed, machining is performed using the coolant until eleven hours have elapsed. At times other than those mentioned above, machining is stopped and the coolant discharge is also stopped. Before machining begins, the coolant temperature is approximately 5°C lower than the temperatures of the turret head 5 and the cutting tool holder 1. The temperature difference between the machine and the coolant occurs, for example, when a section near the ground is cool, such as in the early morning in winter, or when coolant is being supplied.When ejection is started in this state, the temperatures of the turret head 5 and the cutting tool holder 1 are reduced by exposing the turret head 5 and the cutting tool holder 1 to a cooled coolant, whereas the temperature of the coolant rises rapidly due to the heat from the machine.

[0076] Within 20-30 minutes of the start of the ejection, the temperature of the coolant and the temperature of the machine become approximately equal, and heat generated by machining and heat generated by the coolant pump 8 is subsequently transferred to the coolant, with the coolant temperature θ c The temperature in the coolant tank rises slightly. Simultaneously, the measured turret head temperature Θ0 and the cutting tool holder temperature θ1 also increase. However, when machining is stopped, each temperature decreases.

[0077] Furthermore, the actually measured turret head temperature Θ0 is changed more sensitively than the cutting tool holder temperature θ1 due to the difference in heat capacity between the turret head 5 and the cutting tool holder 1, and due to a difference in the way the coolant is applied, and a difference occurs as shown by a dashed line in the Fig. As shown in graph 4, the temperature difference between Θ0 and θ1 is significant. Therefore, if the cutting tool holder temperature is used instead of the turret head temperature 5 to perform the thermal displacement correction, the correction error due to the temperature difference may occur. This error can be reduced by modifying the method for calculating an estimated temperature based on the coolant discharge / stop state to calculate the estimated temperature Θ0 of the turret head 5.

[0078] A specific procedure for calculating the estimated temperature Θ0 is as follows. This means that, according to the process sequence in Fig. 2, first the cutting tool holder temperature θ1 in a section near the turret head 5 and the coolant temperature θ c Temperature information is obtained. Furthermore, information about the coolant discharge / stop state is obtained as a marker u, which represents 1 for the discharge state and 0 for the stop state.

[0079] Furthermore, a delay process is carried out for the marker and coefficients q1, q2, a coefficient p1 for the cutting tool holder temperature and the coefficient p c The coolant temperature is calculated. Δ t(n) represents time intervals at which data are obtained, (n) represents the current value, (n-1) represents a value at the immediately preceding sample, and k represents a degree in the case where sufficient time has elapsed since a marker value was changed. The procedure for calculating the estimated temperature Θ0 is represented by the following expressions (25) to (27). These expressions are presented in the form of differential equations based on expressions (8) to (10) and expressions (20) to (23). [Numerical expression 15] q1(1)=0, q2(1)=0 q1(n)=q1(n−1)+ΔtΔt+T1{u(n)−q1(n−1)} q2(n)=q2(n−1)+ΔtΔt+T2{u(n)−q2(n−1)} u(n)={1:Expulsion of coolant0:Stopping of coolant T1 <T2 Pc(n)=kq1(n)p1(n)=1−kq1(n)0≤k≤1 Θ0(n)=pc(n)θc(n)+p1(n)θ1(n)−α{q1(n)−q2(n)}

[0080] Expression (25) performs a first-order delay filtering operation for the marker u(n), which represents the coolant discharge state, in the case of T1 and T2, which represent time constants. In the present embodiment, a digital first-order delay filter is used. However, the delay process can also be carried out using a different method.

[0081] In expression (26), the coefficient obtained through expression (25) is multiplied by the degree k to obtain the coefficient p. cto calculate the coolant temperature. Furthermore, expression (26) represents a condition that the sum of the coefficients for the respective temperatures is 1. The coefficients for the respective temperatures are determined such that they generally satisfy the conditions that the scale for the measured temperature and the scale for the estimated temperature correspond. Expression (26) provides an example where two temperatures are used to make an estimate. However, three or more temperatures can be used to obtain an estimated temperature if the coefficients for the respective temperatures are determined such that they satisfy the condition that their sum is 1.

[0082] Fig. Figure 5 shows a diagram using the marker u, which represents the coolant discharge / stop state, and the coefficient p. cThe coolant temperature and the coefficient p1 for the cutting tool holder temperature, which are calculated by expressions (25) to (26), are expressed. As can be seen from the diagram, when the coolant is not expelled, that is, when u=0, p approaches c 0 on, in order to p c to satisfy =0 and p1 approaches 1 in order to satisfy p1=1, and the estimated temperature Θ0 of the turret head 5 is equal to the cutting tool holder temperature θ1.

[0083] Meanwhile, if a sufficient time has elapsed after the coolant has been discharged, the value of p will be cequal to k, and the value of p1 becomes equal to 1-k. k represents a constant in the range of 0 to 1 and is preset, for example, according to the results of experiments. In general, k is a value close to 1. Therefore, the estimated temperature Θ0 of the turret head 5, in the case where the coolant is used, is a value close to the coolant temperature θ. c is.

[0084] Furthermore, when a switch occurs between the coolant discharge state and the coolant stop state, i.e., when the value of marker u is changed, the coefficient p cThe time constant T1 is modified so that the larger the value of the time constant, the greater the delay with respect to the change of the marker u. This prevents a rapid change from occurring at the switching time. The time constant T1 can remain constant. However, if the time constant T1 differs between ejection and stopping, an estimation with improved accuracy can be performed. Examples of methods for determining the time constant T1 include a method in which an analysis is performed in advance during development and the obtained result is input, and a method in which a matching is performed based on the result of a trial.

[0085] In expression (26), a linear sum of the temperatures is obtained using the coefficients obtained in expression (25), and a correction term is further subtracted to account for the heat of vaporization, thereby calculating the estimated temperature. The correction term is calculated by filtering with the two time constants to obtain the difference between them.

[0086] When the estimated temperature Θ0 of the turret head 5 is reached in the procedure described above, a Fig. 3, a solid black line is obtained. This indicates that the estimated temperature Θ0 of the turret head 5 closely follows the actually measured turret head temperature Θ0. Furthermore, if a difference is obtained between the estimated temperature Θ0 of the turret head 5 and the cutting tool holder temperature θ1, a Fig.The result shown in Figure 4 is represented by a solid black line. A comparison between this result and the θ1-θ0 represented by the dashed line indicates that, in a case where the coolant temperature is used when the coolant is discharged, the temperature estimation error is greatly reduced.

[0087] Furthermore, even when the coolant's state changes between the coolant discharge state and the coolant stop state, the change is not abrupt but gradual. This can be understood to mean that the temperature of the machine body is used when the coolant is stopped, and the coolant temperature is used in addition to the temperature of the machine body when the coolant is discharged, thus reducing any error even if a temperature difference occurs between the coolant and the machine body when discharge has begun.

[0088] Furthermore, an abrupt change occurs if the temperature to be used is changed instantaneously. However, this problem can be prevented by the delay process. It can also be understood that an error is greatly reduced after the coolant flow is stopped, and the temperature can be estimated accurately.

[0089] After the coolant is stopped, the actual measured turret head temperature θ0 changes abruptly due to the heat of vaporization, and the actual measured turret head temperature θ0 changes, compared to the cutting tool holder temperature θ1 and the coolant temperature θ c , faster. However, if different time constants are used to perform a calculation as given in expression (26), a reproduction for an abrupt temperature change due to heat of vaporization can be performed.

[0090] Thus, in the temperature estimation method and the thermal displacement correction method according to the embodiment described above, the temperature of a section (in the description, the turret head 5), whose temperature is difficult to measure directly and on which the temperature sensor is not attached, can be accurately estimated using a simple method based on the result of a temperature measurement on a section on which the temperature sensor S is attached.

[0091] Furthermore, using information about the operation of the coolant, represented by two states (ON / OFF, eject / stop), a process is performed to obtain coefficients for temperatures at two or more different positions. These coefficients are then adjusted according to the time elapsed since a reference time at which the state is switched. Therefore, the temperature used can be changed to differ between the ON and OFF operating states. Moreover, the estimated temperature at the time of the state switch does not change abruptly, but rather gradually.

[0092] In the machine tool, the estimated temperature of a section where the temperature sensor is not attached is used to calculate the extent of thermal displacement, thereby improving the accuracy of thermal displacement correction, i.e., the accuracy of machining.

[0093] In particular, the operating information in the description is represented by a marker, and a time constant is set. This marker is then subjected to a delay process to obtain a coefficient for the temperature. Therefore, the tendency of a temperature change in the case of a changed operating state can be expressed by a parameter that is a time constant, and the calculation can be represented in a simple form. Thus, parameter setting for accurately estimating an actual temperature change is simplified.

[0094] Furthermore, the value of the time constant is used differently when switching from coolant discharge to coolant cessation and vice versa. Therefore, the temperature can be accurately estimated in each case.

[0095] Furthermore, information about the coolant discharge / stop state is used to adapt to temperature changes caused by the coolant, allowing the temperature to be estimated regardless of whether the coolant is in use or not. Additionally, both the coolant temperature and the system temperature are considered, including a scenario where there is a large temperature difference when coolant discharge begins.

[0096] Furthermore, a time interval for when the coolant is discharged and when it is stopped is set as a reference time, and a time interval for when the coolant is stopped and discharged is performed to change the coefficients of the system temperature and the coolant temperature over time. Therefore, attention can also be paid to a large temperature change in a transition state after the coolant has changed from discharge to stop, or vice versa.

[0097] Additionally, a temperature change due to heat of vaporization can be accurately estimated in order to address an abrupt decrease in temperature due to heat of vaporization that occurs when the coolant is stopped.

[0098] In the present embodiment, the temperature of the cutting tool holder near the turret head and the coolant temperature are used to perform an estimation. However, instead of the cutting tool holder temperature, the temperature in the machining area can be measured and used for the estimation. Furthermore, a multiple temperature readings can be combined and used to perform the estimation. That is, for example, an average value of the temperature in the machining area and the temperature of the machine body can be used.

[0099] Furthermore, the amount of heat of vaporization is also influenced by the humidity in the machining area. Therefore, a method in which both the humidity and temperature in the machining area are measured, and one or both of the values ​​of T2 in expression (25) and α in expression (27) can be adjusted according to the humidity to estimate the heat of vaporization with improved accuracy, can be considered. For example, if the humidity is high, vaporization is less likely to occur, and the influence of the heat of vaporization is small, and the value of α can thus be reduced. If the humidity is low, the influence of the heat of vaporization is large, and the value of α can thus be increased.Thus, even if the amount of heat of vaporization changes due to ambient humidity or the opening / closing of a work door, the humidity in the processing area or similar is monitored using a hygrometer, and the parameter is adjusted accordingly. Therefore, the influence of the heat of vaporization can be accurately estimated, even if the environment changes.

[0100] Furthermore, the estimation of the turret head temperature is described as an example in the present embodiment. However, the section whose temperature is estimated can be any section affected by the coolant. For example, the estimation can be performed for a table, a pallet, a clamping device, a workpiece, a tool, a tool assembly, or the like. At this time, the time constants T1 and T2 in expression (25) can be modified according to the type of workpiece or tool or the like. In general, if the volume of the workpiece or tool is large, the heat capacity is increased, and the time constant is increased.Therefore, the NC system can be structured so that a temperature change time constant, corresponding to the workpiece or tool, can be set as a parameter. If the workpiece or tool mounted on the machine is changed, the parameter is read according to its type, and a temperature estimation and thermal displacement correction are performed. In the method for setting the temperature change time constant, the constant can be calculated and entered in advance based on the workpiece's size or similar characteristics. Alternatively, the temperature change time constant can be estimated and set automatically based on a weight sensor, imaging information, or similar data.Thus, by setting the time constant according to the type of workpiece, tool, or the like, the temperature change can be estimated, and even if the workpiece, tool, or the like is changed, a temperature change can be accurately estimated.

[0101] Furthermore, the present embodiment describes, as an example, a temperature estimation in the case where the coolant is used. However, the temperature can be estimated in the same way even if the workpiece is heated by a laser application or the like. That is, a set temperature of the heating device or the like is used instead of the temperature of the coolant, the ON / OFF switching of the heating device is represented using a marker, and a delay process is carried out, whereby a temperature change due to the influence of heating can be estimated.

[0102] Thus, the estimated temperature at the time of state transition does not change abruptly, but rather gradually, and a large temperature change can be addressed in a transitional state after switching from a stop to a heating state or vice versa. Furthermore, if the tendency of a temperature change in the case where the heating device is used is expressed by a parameter that is a time constant, the calculation can be represented in a simpler form, and even if, for example, the workpiece being processed is changed, parameter adjustment for an accurate estimation of the actual temperature is simplified.

[0103] It is explicitly stated that all features disclosed in the description and / or the claims are intended to be disclosed separately and independently of one another for the purpose of original disclosure and for the purpose of limiting the claimed invention, irrespective of the combination of features in the embodiments and / or the claims. It is explicitly stated that all ranges of values ​​or specifications of groups of units disclose any possible intermediate value or unit for the purpose of original disclosure and for the purpose of limiting the claimed invention, in particular as limits of ranges of values.

Claims

[1] Temperature estimation method for a machine tool to estimate, in a machine tool which has a plurality of sections to which temperature sensors (S) are attached, and one section to which the temperature sensor (S) is not attached, a temperature of the section where the temperature sensor (S) is not attached, wherein the temperature estimation method includes: a temperature information acquisition step of obtaining temperature information from the temperature sensors (S) at two or more different sections where the temperature sensors (S) are attached; an operational information acquisition step of obtaining a predetermined operational information, which is represented by two types of states that are ON and OFF; a coefficient determination step of determining a coefficient for each part of the temperature information, such that if a time at which the operating information is switched from ON to OFF or from OFF to ON is a reference time, the coefficient for each part of the temperature information is changed according to a time that elapses from the reference time; and a temperature estimation step of estimating a temperature of the section where the temperature sensor (S) is not attached, based on the temperature information and the coefficient for the temperature information. [2] Temperature estimation method for a machine tool according to claim 1, wherein in the coefficient determination step the operating information is represented by a marker, one or more time constants are preset, and a delay process for the marker is performed using the time constant to determine the coefficient for each part of the temperature information at any given time. [3] Temperature estimation method for a machine tool according to claim 2, wherein a value of the time constant is different at a time when the operating information is switched from ON to OFF and at a time when the operating information is switched from OFF to ON. [4] Temperature estimation method for a machine tool according to one of claims 1 to 3, wherein a coolant can be used for the machine tool, The temperature information includes the temperature of a setup or machining area of ​​the machine tool and the temperature of the coolant. the operating information indicates an ejection or stopping of the coolant, In the coefficient determination step, if a time at which a coolant discharge changes to a coolant stop, or a time at which a coolant stop changes to a coolant discharge, is a reference time, a coefficient for the temperature information is determined for each of the setup or machining area temperature and the coolant temperature such that the temperature information coefficient changes according to a time elapsed from the reference time, and In the temperature estimation step, the temperature of the section where the temperature sensor (S) is not attached is estimated based on the temperature of the setup or machining area, the temperature of the coolant, and the coefficient for the temperature information. [5] Temperature estimation method for a machine tool according to claim 4, wherein In the coefficient determination step, the number of preset time constants is two, and the coefficient for the temperature information is determined by performing a delay process for the marker using the time constants, and In the temperature estimation step, a temperature change due to heat of vaporization after stopping the coolant is estimated by multiplying a difference between the two time constants with which the delay process is carried out by a predetermined coefficient, and a temperature of the section where the temperature sensor (S) is not attached is estimated in consideration of the temperature change. [6] Temperature estimation method for a machine tool according to claim 5, wherein a hygrometer is placed around the structure or in the machining area, and at least one of the time constants and the predetermined coefficient is changed according to a humidity measured by the hygrometer. [7] Temperature estimation method for a machine tool according to one of claims 1 to 3, wherein The machine tool contains a heating device capable of heating a workpiece in order to perform machining or heat treatment. The temperature information includes the temperature of a setup or machining area of ​​the machine tool and a heating temperature for the workpiece. the operating information indicates whether the heating device is operating or stopping, In the coefficient determination step, if a time at which the heating device switches from operation to a stop, or a time at which the heating device switches from a stop to operation, is a reference time, a coefficient for the temperature information is determined for each of the temperature of the setup or processing area and the heating temperature such that the coefficient for the temperature information changes according to a time that elapses from the reference time, and In the temperature estimation step, the temperature of the section where the temperature sensor (S) is not attached is estimated based on the temperature of the setup or processing area, the heating temperature, and the coefficient for the temperature information. [8] Temperature estimation method for a machine tool according to one of claims 2, 3, 5 or 6, wherein the time constant is set according to at least one of a workpiece, a tool, a clamping device and a tool assembly. [9] Thermal displacement correction method for a machine tool for correcting, in a machine tool which has a plurality of sections to which temperature sensors (S) are attached, and one section to which the temperature sensor (S) is not attached, a thermal displacement of the section to which the temperature sensor (S) is not attached, wherein the thermal displacement correction method comprises: a section-without-sensor temperature estimation step of estimating a temperature of the section to which the temperature sensor (S) is not attached, using the temperature estimation method according to any one of claims 1 to 8; a thermal displacement calculation step of calculating a thermal displacement magnitude using the estimated temperature; and a correction step of correcting a cutting edge position of a tool based on the calculated thermal displacement extent.

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