Method for estimating thermal displacement of a machine tool and machine tool

Abstract

To be able to accurately estimate thermal displacement without deteriorating processing accuracy, even in a transient state where an operation status of a cooling device is changed.SOLUTION: A thermal displacement estimating method for a machine tool executes: a temperature detecting step S2 of detecting temperatures of a bearing part of a main spindle and of a column; and thermal displacement estimating steps (S3-S12) of estimating thermal displacement of the main spindle using an estimation model on the basis of the detected temperatures. The thermal displacement estimating steps includes: determining a coefficient for estimating thermal displacement from the detected temperatures in accordance with change of a cooling capacity (S6 and S7); determining, from a relation between the amount of heat of cooling of a main spindle cooling device 12 and a temperature corresponding to the amount of heat of cooling, a temperature-change amount corresponding to an amount of heat of cooling that is corresponding to an amount of change of heat determined after and before the cooling capacity changes, and, from a relation between a temperature for estimating the thermal displacement from the amount of heat of cooling and the detected temperatures and the conversion coefficient during the displacement, a temperature-change amount corresponding to a conversion coefficient that is corresponding to an amount of change of the conversion coefficient determined after and before the cooling capacity changes (S8); and estimating thermal displacement of the main spindle, on the basis of a temperature determined by adding the corresponding temperature change amount to the detected temperatures and the coefficient (S12).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This disclosure relates to a method for estimating the thermal displacement of a machine tool based on temperature, and to a machine tool on which this method can be implemented. [Background technology]

[0002] In machining using machine tools such as machining centers, thermal displacement in the axial direction occurs due to frictional heat generated by the bearings during spindle rotation and heat generated by the motor, which degrades machining accuracy. To prevent this, one mechanical method is to remove heat by installing a cooling circuit in the spindle housing and circulating cooling oil (hereinafter referred to as "spindle cooling"). Another electrical control method is to estimate and correct the spindle thermal displacement from the machine temperature information. In the former case of spindle cooling, the power consumption of the spindle cooling device, which controls the temperature of the supplied cooling oil to the machine body temperature, accounts for a high proportion of peripheral equipment, and measures to reduce power consumption by controlling the operation of the spindle cooling device are widely implemented. For example, Patent Document 1 discloses an invention that stops the spindle cooling device when the spindle vicinity temperature, calculated using the spindle temperature rise value based on the machine body temperature when the machine is stopped, meets an arbitrary threshold. According to this invention, power consumption can be reduced in a situation where machining accuracy does not deteriorate. Furthermore, Patent Document 2 discloses an invention that reduces power consumption by stopping the spindle cooling device in a situation where the rotation speed and heat source temperature meet a preset threshold or lower, thus minimizing the impact on machining accuracy. In the latter method of estimating thermal displacement, Patent Document 3 by the present applicant proposes a calculation method for estimating the spindle thermal displacement by changing the calculation coefficients of the thermal displacement estimation formula according to the rotational speed and time or the number of corrections. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 6445395 [Patent Document 2] Patent No. 6349276 [Patent Document 3] Japanese Patent Application Laid-Open No. 9-225781 [Summary of the Invention] [Problems to be Solved by the Invention]

[0004] Reducing power consumption is not only achieved by stopping the spindle cooling device during machine downtime as in the invention of Patent Document 1, but it is also desirable to stop the spindle cooling device during machine operation as in the invention of Patent Document 2. However, in the spindle of a machining center, when the cooling device is stopped during spindle rotation, even at a rotational speed of about 1000 min -1 the amount of spindle thermal displacement increases with time. Therefore, the period during which the impact on accuracy is small is limited to a short time. For this reason, in order to maintain accuracy for a longer period, it is necessary to estimate and correct spindle thermal displacement as in the invention of Patent Document 3. However, since the thermal displacement characteristics are different between when the spindle cooling device is operating and when it is stopped, it is not possible to accurately estimate thermal displacement by the method of Patent Document 3.

[0005] Therefore, an object of the present disclosure is to provide a method for estimating thermal displacement of a machine tool and a machine tool that can accurately estimate thermal displacement even in a transient state where the operating state of the cooling device changes, and reduce power consumption without deteriorating machining accuracy. [Means for Solving the Problems]

[0006] To achieve the above object, a first configuration of the present disclosure is a method for estimating thermal displacement of a machine tool having a cooling device and a temperature measuring device, the method including a temperature detection step of detecting the temperatures of a predetermined heat generating part and a predetermined body structure part by the temperature measuring device, and a thermal displacement estimation step of estimating the thermal displacement of the heat generating part by an estimation model based on the detected temperature, wherein in the thermal displacement estimation step, a coefficient related to the time response for estimating thermal displacement from the detected temperature is determined according to a change in cooling capacity due to the operation control of the cooling device during machine operation, Used in temperature calculations and From the relationship between the pre-set cooling heat quantity of the cooling device and the conversion coefficient between temperature and displacement for estimating thermal displacement from the detected temperature, the conversion coefficient equivalent temperature change amount, which corresponds to the change in the conversion coefficient before and after the change in cooling capacity, and / or, from the relationship between the pre-set cooling heat quantity and the temperature corresponding to that cooling heat quantity, the cooling heat quantity equivalent temperature change amount, which corresponds to the change in heat before and after the change in cooling capacity, is determined. The temperature obtained by adding the temperature change amount equivalent to the conversion coefficient and / or the temperature change amount equivalent to the cooling heat amount to the detected temperature, and Regarding time response The method is characterized by estimating the thermal displacement of the heat-generating part based on a coefficient. Another aspect of the first configuration is characterized in that, in the above configuration, the change in the cooling capacity of the cooling device is either the operation and stopping of the cooling device, or the increase and decrease in the amount of cooling oil used for cooling, or both. Another aspect of the first configuration is characterized in that, in the above configuration, the heat-generating part is a rotating shaft, and the amount of temperature change equivalent to the conversion coefficient is calculated based on the rotational speed of the rotating shaft and the time after the change in cooling capacity. Another aspect of the first configuration is characterized in that, in the above configuration, the amount of temperature change equivalent to the amount of cooling heat is calculated based on the temperature time constant before the change in cooling capacity, the temperature time constant after the change in cooling capacity, and the time after the change in cooling capacity. Another aspect of the first configuration is characterized in that, in the above configuration, the conditions for changing the cooling capacity of the cooling device are set with a preset upper limit and lower limit as thresholds, and when the temperature rise of the detected temperature falls below the lower limit, the cooling capacity is reduced, and when it rises above the upper limit, the cooling capacity is increased. Another aspect of the first configuration is characterized in that, in the above configuration, the heat-generating part is a rotating shaft, and the temperature rise of the bearing portion or the vicinity of the bearing portion of the rotating shaft, based on the temperature of the main body structure, is used for estimating thermal displacement. To achieve the above objective, a second configuration of this disclosure is a machine tool having a cooling device and a temperature measuring device, A temperature detection means that detects the temperature of a predetermined heat-generating part and a predetermined main body structure part using a temperature measuring device, The system includes a thermal displacement estimation means that estimates the thermal displacement of the heat-generating part using an estimation model based on the detected temperature, The thermal displacement estimation means is In accordance with the change in cooling capacity due to the operation control of the cooling device during machine operation, the thermal displacement is estimated from the detected temperature. Used in temperature calculations Determine the coefficients related to the time response. From the relationship between the pre-set cooling heat quantity of the cooling device and the conversion coefficient between temperature and displacement for estimating thermal displacement from the detected temperature, the conversion coefficient equivalent temperature change amount, which corresponds to the change in the conversion coefficient before and after the change in cooling capacity, and / or, from the relationship between the pre-set cooling heat quantity and the temperature corresponding to that cooling heat quantity, the cooling heat quantity equivalent temperature change amount, which corresponds to the change in heat before and after the change in cooling capacity, is determined. The temperature obtained by adding the temperature change amount equivalent to the conversion coefficient and / or the temperature change amount equivalent to the cooling heat amount to the detected temperature, and Regarding time response The method is characterized by estimating the thermal displacement of the heat-generating part based on a coefficient. In this disclosure, "estimation model" refers to a pre-patterned series of processes for estimating thermal displacement. Examples include one or more mathematical formulas including coefficients, or a decision process. [Effects of the Invention]

[0007] According to this disclosure, by incorporating a temperature change amount equivalent to the conversion coefficient, which corresponds to the difference between the temperature and displacement before and after a preset change in the operating control of the cooling device, and / or a temperature change amount equivalent to the amount of cooling heat, into the detected temperature of the heat-generating part or its vicinity, it becomes possible to address the deterioration of thermal displacement estimation accuracy that occurs in the cooling transient state when the operating control of the cooling device is performed during machine operation. Therefore, thermal displacement can be accurately estimated even in transient states when the operating state of the cooling device changes, and power consumption can be reduced without degrading processing accuracy. According to another aspect of this disclosure, in addition to the above effects, the change in the cooling capacity of the cooling device is defined as either the operation and stopping of the cooling device, or the increase and decrease in the amount of cooling oil used for cooling, or both. Therefore, thermal displacement estimation can be performed that corresponds not only to the operation and stopping of the cooling device, but also to increases and decreases in the amount of cooling oil. According to another aspect of this disclosure, in addition to the above effects, the conversion coefficient equivalent temperature change is calculated based on the rotational speed of the rotating shaft and the time after the change in cooling capacity, so that the thermal displacement can be estimated with high accuracy in response to the change in cooling capacity according to the rotational speed. According to another aspect of this disclosure, in addition to the above effects, the amount of temperature change equivalent to the amount of cooling heat is calculated based on a preset temperature time constant before the change in the cooling capacity of the cooling device, a preset temperature time constant after the change in the cooling capacity of the cooling device, and the time after the change in cooling capacity, making it easier to set the amount of temperature change equivalent to the amount of cooling heat. According to another aspect of this disclosure, in addition to the above effects, by pre-setting upper and lower limits for the temperature rise as conditions for the change in the cooling capacity of the cooling device, and increasing the cooling capacity when it exceeds the upper limit, it is possible to avoid the risk of abnormal heat generation such as bearing seizure due to a reduction in cooling capacity. On the other hand, by decreasing the cooling capacity when the temperature rise falls below the lower limit, power consumption can be reduced. According to another aspect of this disclosure, in addition to the above effects, when the rotating shaft is the object to be cooled, the thermal displacement can be estimated with high accuracy by using the temperature rise value of the rotating shaft bearing portion or the vicinity of the bearing portion, based on the temperature of the main body structure. [Brief explanation of the drawing]

[0008] [Figure 1] This is a block diagram showing the configuration of a machining center. [Figure 2] This is a flowchart of the thermal displacement estimation method. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure will be described below with reference to the drawings. Figure 1 shows a block diagram illustrating the configuration of a machining center M, which is an example of a machine tool with the second configuration. Machining center M is equipped with a bed 1, a column 2, a spindle head 3, a spindle unit 4, and a table 5. Machining center M is also equipped with a temperature measuring device 10, an NC device 11, a spindle cooling device 12, and a compensation amount calculation device 13. The temperature measuring device 10 detects the temperature rise of the bearing portion of the spindle using a temperature sensor 8 provided on the spindle unit 4, and detects the machine body temperature, which is the reference temperature, using a temperature sensor 9 provided on the column 2. The spindle cooling device 12 has a cooling circuit that supplies cooling oil to the cooling oil inlet 6 of the outer cylinder of the spindle housing and returns it from the cooling oil outlet 7.

[0010] In addition to controlling the rotation of the spindle and the movement of the feed axis, the NC device 11 also controls the operation of the spindle cooling device 12. This operation control is performed based on preset upper and lower limits of the temperature difference (hereinafter referred to as "temperature rise value") between temperature sensor 8 and temperature sensor 9. Specifically, when the temperature rise value falls below the lower limit, the operation of the spindle cooling device 12 is stopped, and when the temperature rise value rises above the upper limit, the operation of the spindle cooling device 12 is restarted. The temperatures detected by each temperature sensor 8 and 9 are converted from analog signals to digital signals by a known method according to a preset period in the temperature measuring device 10, quantified, and sent to the correction amount calculation device 13. Each temperature sensor 8 and 9 and the temperature measuring device 10 are examples of temperature detection means in this disclosure. The correction amount calculation device 13 estimates the spindle thermal displacement based on the estimated spindle temperature calculated from the digitized temperature data and an estimation model that includes a pre-set thermal displacement estimation formula using a conversion coefficient from spindle temperature to spindle thermal displacement. The correction amount based on the estimated thermal displacement is output to the NC device 11. The correction amount calculation device 13 is an example of the thermal displacement estimation means of this disclosure. The NC device 11 corrects the amount of movement of each feed axis based on the correction amount.

[0011] The following describes the estimation of the main shaft thermal displacement in the correction amount calculation device 13. First, in Equation 1, the temperature θ1 measured by the temperature sensor 8 n and the temperature θ2 measured by the temperature sensor 9 n are used to calculate the temperature rise value θ n . The calculated temperature rise value θ n is added with the temperature θ Equn shown in Equation 2 corresponding to the heat quantity change before and after the change in the cooling capacity of the main shaft cooling device 12 (temperature change amount corresponding to the cooling heat quantity), and the temperature θ Gn shown in Equations 3-1 and 3-2 corresponding to the difference in the conversion coefficient between the temperature and displacement before and after the change in the cooling capacity of the main shaft cooling device 12 (temperature change amount corresponding to the conversion coefficient) (Equation 4). Based on the obtained temperature θ CORn , the estimated main shaft temperature θ ESTn is calculated using Equation 5.

[0012] θ n = θ1 n - θ2 n ·· Equation 1 θ1 n : The temperature of the bearing part of the main shaft detected by the temperature sensor 8 at the nth time θ2 n : The body temperature detected by the temperature sensor 9 at the nth time θ n : The temperature rise value at the nth time θ Equn = β1 × exp(Δt × n / T1)-β2 × exp(Δt × n / T2) ·· Equation 2 Δt: The time interval of the estimation calculation process β1: The calculation coefficient 1 of θ<​​​​​​​​​​​​​​​​​​​​​​​​​​​​Equn )×G n ·Formula 3-2 G n : nth θ G Calculation coefficient G0 :θ G Convergence value of the calculation coefficient Δt: Time interval for estimation calculation processing T3: Time constant relating to the conversion coefficient between temperature and displacement after the change in cooling capacity. θ Gn : nth conversion coefficient equivalent temperature change θ CORn =θ n +θ Equn +θ Gn ·Formula 4 θ CORn : The temperature obtained by adding the temperature corresponding to the change in heat before and after the change in cooling capacity and the temperature corresponding to the difference in the conversion coefficient between the temperature and displacement before and after the change in cooling capacity to the temperature rise value of the nth time. θ ESTn =θ ESTn-1 +(θ CORn -θ ESTn-1 )×[Δt / (Δt+α)] Formula 5 Δt: Time interval for estimation calculation processing α: Time response coefficient θ ESTn :nth estimated principal axis temperature

[0013] Next, in equation 6, the estimated principal axis temperature θ ESTn The thermal displacement of the main shaft Z is determined by the temperature displacement conversion coefficient γ. n The coefficient γ is a temperature displacement conversion coefficient that is set in advance for the operating state of the spindle cooling device 12. Z n =θ ESTn ×γ ···Equation 6 γ: Temperature displacement conversion coefficient Z n : nth principal shaft thermal displacement

[0014] The following describes a method for estimating thermal displacement related to the first configuration when the operation of the spindle cooling device 12 is controlled at an arbitrary spindle rotation speed, based on the flowchart in Figure 2. The estimation calculation process is performed at time intervals Δt, and in S1, the counter for the number of processing attempts starts. In S2, the bearing temperature is measured by temperature sensor 8 and the machine temperature by temperature sensor 9, and the current temperature data is obtained, and the temperature rise value θ is calculated using Equation 1. n Calculate. In S3, it is determined whether the thermal displacement correction process is being performed for the first time. If it is the first time, proceed to S7; otherwise, proceed to S4. In S4, it is determined whether the timing conditions for the change in the operation control of the spindle cooling system 12 are met. The timing conditions here are whether the temperature rise value has reached either the upper limit or lower limit of a preset value. If the temperature rise value falls below the lower limit, the operation of the spindle cooling system 12 is stopped, and if it rises above the upper limit, the operation of the spindle cooling system 12 is restarted. For example, the upper limit is set to the temperature rise value when the spindle cooling system 12 is operating at its maximum rotational speed, and the lower limit is set to the temperature rise value when the spindle cooling system 12 is operating at half the maximum rotational speed.

[0015] When the operation of the spindle cooling system 12 changes due to the timing conditions being met in S4, the count is reset in S5 and the counter starts again. In S6 and S7, the coefficients β1, β2, T1, T2, G0, T3, and α used in equations 2, 3, and 5 are changed or set to preset optimal coefficients according to the operating or stopped state of the spindle cooling system 12. These coefficients may be fixed values, may differ depending on the operating or stopped state, or may be functions of temperature according to the operating or stopped state. Also, θ G The convergence value G0 of the calculation coefficient can also be expressed as a function of the spindle rotation speed. In this case, thermal displacement can be estimated with high accuracy in response to changes in cooling capacity according to the rotation speed. In S8, from Equation 2, the temperature change amount equivalent to the amount of heat cooled is θ. Equn From equations 3-1 and 3-2, the conversion coefficient equivalent to the temperature change θ is obtained. Gn Calculate each of them. In S9, the temperature change amount θ is equivalent to the amount of heat cooled.Equn and the conversion coefficient equivalent temperature change θ Gn A decision is made as to whether to perform the addition. The decision condition is, for example, the relationship between the amount of equivalent temperature change to be added and a preset threshold, or the relationship between the count and the threshold. In the former case, if the amount of equivalent temperature change to be added is greater than or equal to the threshold, the process proceeds to S10; if it is less than the threshold, the process proceeds to S11. In the latter case, if the count is less than or equal to the threshold, the process proceeds to S10; if it is greater than the threshold, the process proceeds to S11.

[0016] In S10, the temperature rise value θ calculated in S2 is obtained from Equation 4. n The temperature change amount θ equivalent to the amount of cooling heat calculated in S8. Equn and the conversion coefficient equivalent temperature change θ Gn Add it. In S11, the estimated principal axis temperature θ is obtained from Equation 5. ESTn Calculate. In S12, the estimated principal axis temperature θ calculated in S11 is used. ESTn Based on this, the principal shaft thermal displacement Z is derived from Equation 6. n We estimate and calculate the correction amount. In S13, a decision is made as to whether to continue with thermal displacement correction. If so, the process returns to S2 and starts again from temperature measurement.

[0017] As described above, the thermal displacement estimation method of the above form is performed in a machining center M having a spindle cooling device 12 (an example of a cooling device) and a temperature measuring device 10, and includes a temperature detection step S2 in which the temperature measuring device 10 detects the temperature of the spindle bearing part (an example of a predetermined heat-generating part) and the column 2 (an example of a predetermined main body structure part), and a thermal displacement estimation step (S3 to S12) in which the thermal displacement of the spindle is estimated based on the detected temperature using an estimation model consisting of equations 1 to 6. Then, in the thermal displacement estimation step, a coefficient for estimating thermal displacement from the detected temperature is determined according to the change in cooling capacity due to the operation control of the spindle cooling device 12 during machine operation (S6, S7). From the relationship between the predetermined cooling heat quantity of the spindle cooling device 12 and the temperature corresponding to that cooling heat quantity, the amount of temperature change equivalent to the amount of heat change before and after the change in cooling capacity is determined, and from the relationship between the cooling heat quantity of the cooling device 12 and the conversion coefficient between temperature and displacement for estimating thermal displacement from the detected temperature, the amount of temperature change equivalent to the amount of change in the conversion coefficient before and after the change in cooling capacity is determined (S8). Based on the temperature obtained by adding the equivalent temperature change to the detected temperature and the coefficient, the thermal displacement of the spindle is estimated (S12). This configuration makes it possible to address the deterioration in thermal displacement estimation accuracy that occurs during cooling transients when the operation of the spindle cooling device 12 is controlled during machine operation. Therefore, thermal displacement can be accurately estimated even during transients when the operating state of the spindle cooling device 12 changes, and power consumption can be reduced without degrading machining accuracy.

[0018] In particular, the change in the cooling capacity of the spindle cooling device 12 is defined as either the operation and stopping of the spindle cooling device 12, or the increase and decrease in the amount of cooling oil used for cooling, or both. Therefore, thermal displacement estimation can be performed not only in response to the operation and stopping of the spindle cooling system 12, but also to increases and decreases in the amount of cooling oil. The temperature change equivalent to the amount of heat cooled is calculated based on the temperature time constant before the change in cooling capacity, the temperature time constant after the change in cooling capacity, and the time elapsed since the change in cooling capacity. Therefore, it becomes easier to set the temperature change amount equivalent to the amount of heat cooled.

[0019] The conditions for changing the cooling capacity of the spindle cooling device 12 are as follows: when the temperature rise of the detected temperature falls below the lower limit, the cooling capacity is reduced; and when it exceeds the upper limit, the cooling capacity is increased. Therefore, the risk of abnormal heat generation, such as bearing seizure due to reduced cooling capacity, can be avoided. On the other hand, if the temperature rise falls below the lower limit, power consumption can be reduced by decreasing the cooling capacity. The heat-generating part is the main shaft (an example of a rotating shaft), and the temperature rise value near the bearing section of the main shaft, based on the temperature of column 2, is used to estimate the thermal displacement. Therefore, thermal displacement can be estimated with high accuracy.

[0020] In the above configuration, the explanation described the case where both the temperature change equivalent to the amount of cooling heat and the temperature change equivalent to the conversion coefficient are used. However, for main shafts and other parts with small thermal displacements, improving the accuracy of thermal displacement estimation can be expected by using either the temperature change equivalent to the amount of cooling heat or the temperature change equivalent to the conversion coefficient, so it is also acceptable to use only one of them. In the above configuration, step S9 determines whether to add the equivalent temperature change to the measured temperature data based on the judgment conditions, but this judgment can be omitted and the equivalent temperature change may always be added. In the above configuration, the change in coefficient in S6 is performed according to the operating and stopped states of the spindle cooling system. However, the change in coefficient may be performed not only when the spindle cooling system is ON or OFF, but also when the amount of cooling oil is changed or when the cooling capacity is changed (for example, when only the chiller is stopped but the pump is running), even when the system is ON. The rotating shaft from which thermal displacement is estimated is not limited to the main shaft. Temperatures other than those in the bearing area may also be detected. Multiple temperature sensors may be provided in both the heat-generating part and the main body structure, and the average of the measured values ​​may be used. The cooling devices described herein are not limited to those for the spindle. The machine tools described herein are not limited to machining centers. [Explanation of Symbols]

[0021] 1. Bed, 2. Column, 3. Spindle head, 4. Spindle unit, 5. Table, 6. Cooling oil inlet, 7. Cooling oil outlet, 8,9. Temperature sensor, 10. Temperature measuring device, 11. NC device, 12. Spindle cooling device, 13. Correction value calculation device, M. Machining center.

Claims

1. In a machine tool having a cooling device and a temperature measuring device, a temperature detection step is performed in which the temperature measuring device detects the temperature of a predetermined heat-generating part and a predetermined main body structure, A method for estimating the thermal displacement of a machine tool, comprising: a thermal displacement estimation step of estimating the thermal displacement of the heat-generating part using an estimation model based on the detected temperature; In the thermal displacement estimation step, In accordance with the change in cooling capacity due to the operation control of the cooling device during machine operation, a coefficient relating to the time response used in temperature calculations to estimate thermal displacement from the detected temperature is determined. From the relationship between the pre-set cooling heat quantity of the cooling device and the conversion coefficient between temperature and displacement for estimating thermal displacement from the detected temperature, the conversion coefficient equivalent temperature change amount, which corresponds to the change in the conversion coefficient before and after the change in cooling capacity, and / or, from the relationship between the pre-set cooling heat quantity and the temperature corresponding to that cooling heat quantity, the cooling heat quantity equivalent temperature change amount, which corresponds to the change in heat before and after the change in cooling capacity, is determined. A method for estimating the thermal displacement of a machine tool, characterized by estimating the thermal displacement of the heat-generating part based on a temperature obtained by adding the temperature change amount equivalent to the conversion coefficient and / or the temperature change amount equivalent to the cooling heat amount to the detected temperature, and a coefficient relating to the time response.

2. The method for estimating the thermal displacement of a machine tool according to claim 1, characterized in that the change in the cooling capacity of the cooling device is either the operation and stopping of the cooling device, or the increase and decrease in the amount of cooling oil used for cooling, or both.

3. The method for estimating the thermal displacement of a machine tool according to claim 1 or 2, characterized in that the heat-generating part is a rotating shaft, and the amount of temperature change equivalent to the conversion coefficient is calculated based on the rotational speed of the rotating shaft and the time elapsed after the cooling capacity of the cooling device has changed.

4. The method for estimating the thermal displacement of a machine tool according to claim 1 or 2, characterized in that the amount of temperature change equivalent to the amount of cooling heat is calculated based on the temperature time constant before the change in cooling capacity, the temperature time constant after the change in cooling capacity, and the time after the change in cooling capacity.

5. The method for estimating thermal displacement of a machine tool according to claim 1 or 2, characterized in that the conditions for changing the cooling capacity of the cooling device are defined by a preset upper limit and lower limit, wherein the cooling capacity is reduced when the temperature rise of the detected temperature falls below the lower limit, and the cooling capacity is increased when it falls above the upper limit.

6. The method for estimating thermal displacement of a machine tool according to claim 5, characterized in that the heat-generating part is a rotating shaft, and the temperature rise of the bearing part or the vicinity of the bearing part of the rotating shaft, based on the temperature of the main body structure, is used for estimating thermal displacement.

7. A machine tool having a cooling device and a temperature measuring device, A temperature detection means that detects the temperature of a predetermined heat-generating part and a predetermined main body structure part using a temperature measuring device, The system includes a thermal displacement estimation means that estimates the thermal displacement of the heat-generating part using an estimation model based on the detected temperature, The thermal displacement estimation means is In accordance with the change in cooling capacity due to the operation control of the cooling device during machine operation, a coefficient relating to the time response used in temperature calculations to estimate thermal displacement from the detected temperature is determined. From the relationship between the pre-set cooling heat quantity of the cooling device and the conversion coefficient between temperature and displacement for estimating thermal displacement from the detected temperature, the conversion coefficient equivalent temperature change amount, which corresponds to the change in the conversion coefficient before and after the change in cooling capacity, and / or, from the relationship between the pre-set cooling heat quantity and the temperature corresponding to that cooling heat quantity, the cooling heat quantity equivalent temperature change amount, which corresponds to the change in heat before and after the change in cooling capacity, is determined. A machine tool characterized by estimating the thermal displacement of the heat-generating part based on the temperature obtained by adding the temperature change amount equivalent to the conversion coefficient and / or the temperature change amount equivalent to the cooling heat amount to the detected temperature, and a coefficient relating to the time response.

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