Methods for predicting thermal displacement of machine tools and machine tools

Abstract

[Topic] Even during transitional periods when the operating conditions of the cooling device change, it is possible to accurately predict thermal displacement without deteriorating machining accuracy. [Technical Content] Implementation: Temperature detection step (S2) to detect the temperature of the bearing part and the machine body of the spindle, and thermal displacement prediction step (S3~S12) to predict the thermal displacement of the spindle based on the detected temperature using a prediction model. In the thermal displacement prediction step, the coefficients for predicting thermal displacement from the detected temperature corresponding to the change in cooling capacity are determined (S6, S7). Based on the relationship between the cooling heat of the spindle cooling device (12) and the temperature equivalent to the cooling heat, the temperature change equivalent to the change in cooling heat before and after the change in cooling capacity is obtained. Based on the relationship between the conversion coefficient between the cooling heat and the temperature and displacement used to predict thermal displacement from the detected temperature, the temperature change equivalent to the change in conversion coefficient before and after the change in cooling capacity is obtained (S8). The thermal displacement of the spindle is predicted based on the temperature and coefficient after adding the equivalent temperature change to the detected temperature (S12).

Description

Methods for predicting thermal displacement of machine tools and machine tools This invention relates to a method for predicting temperature based on the thermal displacement of a machine tool, and a machine tool in which the method can be implemented. In machining processes using machine tools such as numerically automated machining centers, thermal displacement along the axial direction occurs due to frictional heat from bearings and motors during spindle rotation, leading to deterioration of machining accuracy. To prevent this, the machine structure includes a method for removing heat by flowing cooling oil through cooling pipes in the spindle housing (hereinafter referred to as "spindle cooling"). Furthermore, the electrical control system includes a method for predicting and correcting spindle thermal displacement based on machine body temperature information. In the former spindle cooling, the power consumed by the spindle cooling device used for machine body temperature control, which is supplied with cooling oil, accounts for a relatively high proportion of the power consumption in peripheral machines. Therefore, measures are needed to reduce the power consumption generated by the operation control of the spindle cooling device. For example, Patent Document 1 discloses an invention that stops the spindle cooling device when the machine stops and the spindle temperature near the spindle, calculated using the spindle temperature rise value based on the machine body temperature, meets any threshold value. According to this invention, power consumption can be reduced without deteriorating machining accuracy. Furthermore, Patent Document 2 discloses an invention that reduces power consumption by stopping the spindle cooling device when the rotational speed and heat source temperature are below a pre-set threshold, where the impact on machining accuracy is minimal. Regarding the latter thermal displacement prediction method, Patent Document 3 of this application proposes a calculation method for predicting spindle thermal displacement by changing the calculation coefficients of the thermal displacement prediction formula in accordance with rotational speed, time, or the number of corrections. [Prior Art Documents] [Patent Documents] [Patent Document 1] Japanese Patent No. 6445395 [Patent Document 2] Japanese Patent No. 6349276 [Patent Document 3] Japanese Unexamined Patent Publication No. 9-225781 [The problem the invention aims to solve] The reduction in power consumption means that, not only in Patent Document 1, it is preferable to stop the spindle cooling device when the machine is stopped, but also in Patent Document 2, it is preferable to stop the spindle cooling device when the machine is running. However, even if the cooling device is stopped when the spindle of a numerically automated machining tool is rotating, it would still be insufficient for 1000 minutes. -1 The spindle's thermal displacement increases over time due to varying rotational speeds, and the period during which the impact on accuracy is minimal is very short. Therefore, to maintain accuracy for a longer period, it is necessary to modify the spindle thermal displacement prediction as described in Patent Document 3. However, the thermal displacement characteristics of the spindle cooling system differ during operation and shutdown, making it impossible to accurately predict thermal displacement using the method in Patent Document 3. The purpose of this invention is to provide a method for predicting the thermal displacement of a machine tool and a machine tool in general, which can accurately predict thermal displacement even during transitions in the operating state of the cooling device, thereby reducing power consumption without deteriorating machining accuracy. [Technical means to solve the problem] To achieve the above objectives, the first embodiment of the present invention is a method for predicting the thermal displacement of a machine tool. In a machine tool equipped with a cooling device and a temperature measuring device, the method includes a temperature detection step, in which the temperature measuring device separately detects the temperatures of a predetermined heat-generating part and a predetermined body structure part; and a thermal displacement prediction step, in which a prediction model is used to predict the thermal displacement of the aforementioned heat-generating part based on the detected temperatures. In the thermal displacement prediction step, a coefficient relating to the time response for predicting the thermal displacement from the detected temperatures is determined based on the change in cooling capacity caused by the operation control of the aforementioned cooling device during machine operation. The relationship between the time response and the cooling capacity is then obtained from the following relationship. The relationship between the change in cooling capacity and the change in temperature is equivalent to the change in heat before and after the change in force. This relationship includes: a pre-set cooling capacity of the aforementioned cooling device, and the relationship between the conversion coefficient between temperature and displacement used to predict thermal displacement from the aforementioned detected temperature; a temperature change equivalent to the conversion coefficient before and after the change in cooling capacity, and / or the pre-set cooling capacity and the temperature equivalent to that cooling capacity; and the prediction of the thermal displacement of the aforementioned heating element based on the temperature after adding the temperature change equivalent to the conversion coefficient and / or the temperature change equivalent to the cooling capacity to the aforementioned detected temperature, and the aforementioned coefficient. In another embodiment of the first configuration, the change in cooling capacity of the aforementioned cooling device is either the operation and shutdown of the aforementioned cooling device, or an increase and decrease in the amount of cooling oil used for cooling, or both. In yet another embodiment of the first configuration, the aforementioned heating element is a rotating shaft, and the temperature change equivalent to the conversion coefficient is calculated based on the rotational speed of the aforementioned rotating shaft and the time elapsed after the change in the aforementioned cooling capacity of the aforementioned cooling device. Another embodiment of the first configuration is that, in the above configuration, the temperature change equivalent to the 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 embodiment of the first configuration is that, in the above configuration, the condition for the change in the cooling capacity of the cooling device is to use pre-set upper and lower limits as threshold values; when the temperature rise of the detected temperature is below the lower limit, the cooling capacity is reduced; when the temperature rise of the detected temperature is above the upper limit, the cooling capacity is increased. Another embodiment of the first configuration is that, in the above configuration, the heating element is a rotating shaft, and the temperature rise of the bearing portion of the rotating shaft or the vicinity of the bearing portion, based on the temperature of the main body structure, is used for thermal displacement prediction.To achieve the above objectives, the second embodiment of the present invention is a machine tool having a cooling device and a temperature measuring device, comprising: a temperature detection means for separately detecting the temperatures of a predetermined heating element and a predetermined body structure part by means of the temperature measuring device, and a heat displacement prediction means for predicting the heat displacement of the heating element based on the detected temperatures using a prediction model. The heat displacement prediction means determines a time response coefficient for predicting heat displacement from the detected temperature in response to changes in cooling capacity caused by the operation control of the aforementioned cooling device during machine operation, and obtains a temperature change equivalent to the change in cooling heat before and after the change in cooling capacity from the following relationships: the aforementioned relationships include: a pre-set cooling heat of the aforementioned cooling device, and a conversion coefficient between temperature and displacement for predicting heat displacement from the aforementioned detected temperature; a temperature change equivalent to the conversion coefficient equivalent to the change in the aforementioned conversion coefficient before and after the change in cooling capacity, and / or a pre-set relationship between the aforementioned cooling heat and a temperature equivalent to the cooling heat; and predicting the heat displacement of the heating element based on the temperature after adding the temperature equivalent to the conversion coefficient and / or the temperature equivalent to the aforementioned cooling heat to the aforementioned detected temperature, and the aforementioned coefficient. Furthermore, the "prediction model" in this invention refers to a series of pre-modeled processes for predicting thermal displacement. Examples include a formula containing, for instance, coefficients of 1 or complex numbers, and a discrimination process. [Effects of the Invention]. According to the present invention, by taking into account the temperature change corresponding to the difference between the conversion coefficients of temperature and displacement before and after a pre-set change in the operation control of the cooling device, and / or the temperature change corresponding to the difference in cooling heat, the accuracy of thermal displacement prediction during the cooling transition state in mechanical operation under the condition of cooling device operation control can be addressed. Therefore, thermal displacement can be accurately predicted even during the transition state of the cooling device operation state change, and power consumption can be reduced without deteriorating machining accuracy. According to another aspect of the present invention, in addition to the above effects, the change in cooling capacity of the cooling device is due to either or both of the operation and shutdown of the cooling device and the increase and decrease in the amount of cooling oil used for cooling. Therefore, thermal displacement prediction can be performed not only when the cooling device is operated or stopped, but also when the amount of cooling oil increases or decreases. According to another aspect of the present invention, in addition to the above effects, the temperature change corresponding to the conversion coefficient is calculated based on the rotational speed of the rotating shaft and the time after the change in cooling capacity. Therefore, the change in cooling capacity corresponding to the rotational speed can be addressed, and thermal displacement can be predicted with high accuracy. According to another embodiment of the present invention, in addition to the effects described above, the amount of temperature change corresponding to the cooling heat is easily set because it is calculated based on a pre-set temperature-time constant before the change in cooling capacity of the cooling device, a pre-set temperature-time constant after the change in cooling capacity of the cooling device, and the time after the change in cooling capacity. According to another embodiment of the present invention, in addition to the effects described above, by pre-setting an upper and lower limit value for the temperature rise as conditions for the change in cooling capacity of the cooling device, when the temperature rise exceeds the upper limit value, increasing the cooling capacity can avoid the risk of abnormal heating such as bearing burnout caused by a decrease in cooling capacity. On the other hand, when the temperature rise falls below the lower limit value, decreasing the cooling capacity can reduce power consumption. According to another embodiment of the present invention, in addition to the effects described above, when a rotating shaft is the object to be cooled, thermal displacement can be predicted 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. Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 1 is a block diagram showing an example of the configuration of a machine tool with a second structure, namely a numerical automatic machining tool M. The numerical automatic machining tool M includes a table 1, a machine body 2, a spindle head 3, a spindle assembly 4, and a mounting stage 5. Furthermore, the numerical automatic machining tool M includes a temperature measuring device 10, an NC device 11, a spindle cooling device 12, and a correction calculation device 13. The NC device 11 includes a central processing unit (CPU) and memory connected to the CPU, which can reliably execute the operation. The temperature measuring device 10 detects the temperature rise of the bearing portion of the spindle by a temperature sensor 8 provided on the spindle assembly 4, and detects the machine body temperature, which serves as a reference temperature, by a temperature sensor 9 provided on the machine body 2. The spindle cooling device 12 has a cooling oil inlet 6 that supplies cooling oil to the outer cylinder of the spindle housing and returns it from the cooling oil outlet 7. The NC device 11, in addition to controlling the rotation of the spindle and the movement of the feed axis, also controls the operation of the spindle cooling device 12. This operation control is based on a pre-set upper and lower limit of the temperature difference (hereinafter referred to as the "temperature rise value") between the temperature sensors 8 and 9. Specifically, when the temperature rise value falls below the lower limit, the operation of the spindle cooling device 12 is stopped; 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 in the temperature measuring device 10 using a known method at a pre-set period, and then sent to the correction calculation device 13. The temperature sensors 8 and 9 and the temperature measuring device 10 are examples of the temperature detection means of the present invention. In the correction calculation device 13, the spindle thermal displacement is predicted based on the predicted spindle temperature calculated from the quantified temperature data and a prediction model that includes a pre-set thermal displacement prediction formula using a conversion coefficient from the spindle temperature to the spindle thermal displacement. The correction amount obtained based on the predicted thermal displacement is output to the NC device 11. The correction calculation device 13 is an example of the thermal displacement prediction method of the present invention. The NC device 11 corrects the movement of each feed axis based on the correction amount. The following explains the prediction of the spindle thermal displacement in the correction calculation device 13. First, based on Equation 1, the prediction is made according to the temperature θ1 measured by the temperature sensor 8. n and the temperature θ2 measured by temperature sensor 9 n Calculate the temperature rise θ n For the calculated temperature rise θ nAdd: The temperature θ, as shown in Equation 2, is equivalent to the change in heat before and after the change in the cooling capacity of the spindle cooling device 12. Equn The temperature θ, expressed by Equations 3-1 and 3-2, is equivalent to the temperature change (equivalent to the amount of cooling heat) and the difference between the conversion coefficients between temperature and displacement before and after the change in the cooling capacity of the spindle cooling device 12. Gn (Conversion coefficient equivalent to temperature change) (Equation 4), based on the obtained temperature θ CORn The predicted spindle temperature θ is calculated using Equation 5. ESTn . θ1 n The temperature θ2 of the spindle bearing section detected by temperature sensor 8 in the nth time. n The body temperature θ detected by temperature sensor 9 in the nth time. n The temperature rise value at the nth time Δt: Time interval for prediction operation; β1: θ Equ The coefficients 1 β2 :θ are calculated. Equ The calculated coefficients are: T1: temperature-time constant relating to the cooling heat before the change in cooling capacity; T2: temperature-time constant relating to the cooling heat after the change in cooling capacity. Equn The amount of heat generated during the nth cooling event corresponds to the temperature change. G n : θ of the nth time G The coefficients G0 and θ are calculated. G The calculated convergence value Δt: the time interval T3 for the prediction calculation; θ: the time constant θ for the conversion coefficient between temperature and displacement after the change in cooling capacity. Gn The conversion coefficient for the nth time corresponds to the temperature change. θ CORn The temperature calculated by adding the temperature corresponding to the change in heat before and after the change in cooling capacity in the nth temperature rise value, and the temperature corresponding to the difference between the conversion coefficient between the temperature and displacement before and after the change in cooling capacity. Δt: Time interval for prediction processing; α: Time response coefficient; θ ESTn Predicted spindle temperature for the nth time Next, using Equation 6, the spindle temperature θ is predicted. ESTn The thermal displacement Z of the spindle is predicted using the temperature-displacement conversion coefficient γ. n The coefficient γ is a temperature displacement conversion coefficient that is preset under the operating conditions of the spindle cooling device 12. γ: Temperature displacement conversion coefficient Z n The nth spindle thermal displacement The following describes, based on the flowchart in Figure 2, a thermal displacement prediction method for the first scenario where the operation of the spindle cooling device 12 is controlled by an arbitrary spindle rotation speed. The prediction calculation is performed over a time interval Δt. In S1, a counter begins counting the number of processing operations. In S2, the temperature of the bearing section is measured by temperature sensor 8, and the mechanical temperature is measured and quantified by temperature sensor 9. The current temperature data is obtained, and the temperature rise θ is calculated using Equation 1. n In S3, it is determined whether the thermal displacement correction process is the first time. If it is the first time, the process proceeds to S7; if it is the second time or subsequent times, the process proceeds to S4. In S4, it is determined whether the time condition for the change in the operation control of the spindle cooling device 12 is met. This time condition is determined by whether either a pre-set upper limit or lower limit of the temperature rise value is reached. When the temperature rise value is below the lower limit, the operation of the spindle cooling device 12 is stopped; when it is above the upper limit, the operation of the spindle cooling device 12 is restarted. For example, the temperature rise value when the spindle cooling device 12 is operating at its maximum rotational speed is set as the upper limit, and the temperature rise value when the spindle cooling device 12 is operating at half the maximum rotational speed is set as the lower limit. If the operation of the spindle cooling device 12, which meets the time condition in S4, changes, the calculation count is reset in S5, and the counter starts counting 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 pre-set optimal coefficients according to the operating or stopped state of the spindle cooling device 12. These coefficients can be fixed values, can be different in the operating or stopped state, or can be functions of the temperature in the operating or stopped state. And θ GThe convergence value G0 of the calculated coefficients can also be a function of the spindle rotation speed. In this case, the change in cooling capacity corresponding to the rotation speed can be correlated, and thermal displacement can be predicted with high accuracy. In S8, by Equation 2, the cooling heat is equivalent to the temperature change θ. Equn Calculate the temperature change θ equivalent to the conversion coefficient using equations 3-1 and 3-2. Gn Each is calculated separately. In S9, it is determined whether cooling heat equivalent to temperature change θ is implemented. Equn and the conversion coefficient equivalent to the temperature change θ Gn The addition is performed. The judgment condition is, for example, the relationship between the added equivalent temperature change and a pre-set threshold, or the relationship between the number of calculations and the threshold. In the former case, if the added equivalent temperature change is above the threshold, the process proceeds to S10; if it is below the threshold, the process proceeds to S11. In the latter case, if the number of calculations is below the threshold, the process proceeds to S10; if it is above the threshold, the process proceeds to S11. In S10, according to Equation 4, for the temperature rise θ calculated from S2... n Add the cooling heat equivalent to the temperature change θ calculated from S8. Equn and the conversion coefficient equivalent to the temperature change θ Gn In S11, the predicted spindle temperature θ is calculated using Equation 5. ESTn In S12, based on the predicted spindle temperature θ calculated from S11... ESTn The predicted thermal displacement Z of the spindle is calculated using Equation 6. n The correction amount. In S13, it is determined whether to continue thermal displacement correction. If it continues, return to S2 to perform processing based on temperature measurement. Thus, the above-described thermal displacement prediction method is implemented in a numerical automatic machining tool M equipped with 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 of the spindle bearing part (an example of a defined heat-generating part) and the machine body 2 (an example of a defined main body structure part) are detected separately by the temperature measuring device 10; and a thermal displacement prediction step (S3 to S12), in which the thermal displacement of the spindle is predicted based on the detected temperature using a prediction model composed of Equations 1 to 6. Furthermore, in the thermal displacement prediction step, in response to the change in cooling capacity caused by the operation control of the spindle cooling device 12 during machine operation, a coefficient for predicting thermal displacement from the detected temperature is determined (S6, S7). Based on the pre-set relationship between the cooling heat of the spindle cooling device 12 and the temperature equivalent to that cooling heat, and based on the temperature change equivalent to the cooling heat before and after the change in cooling capacity, and the relationship between the temperature and displacement used for thermal displacement prediction from the cooling heat of the spindle cooling device 12 and the detected temperature, a temperature change equivalent to the change in the conversion coefficient before and after the change in cooling capacity is obtained (S8). Based on the temperature and coefficient, which are calculated to include the temperature equivalent to the detected temperature, the thermal displacement of the spindle is predicted (S12). With this configuration, the thermal displacement prediction accuracy can be addressed during the cooling transition state when the spindle cooling device 12 is under operation during machine operation. Therefore, even in the transition state where the operating state of the spindle cooling device 12 changes, thermal displacement can be accurately predicted, and power consumption can be reduced without deteriorating machining accuracy. In particular, the change in cooling capacity of the spindle cooling device 12 is due to either or both of the operation and shutdown of the spindle cooling device 12 and the increase and decrease in the amount of cooling oil used for cooling. Therefore, it is not only possible to predict the thermal displacement corresponding to the increase and decrease in the amount of cooling oil, but also to predict the operation and shutdown of the spindle cooling device 12. The temperature change corresponding to the 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. Therefore, setting the temperature change corresponding to the cooling heat is easy. The cooling capacity of the spindle cooling device 12 is adjusted by using pre-set upper and lower threshold values. When the detected temperature rise falls below the lower threshold, the cooling capacity is reduced; when it rises above the upper threshold, the cooling capacity is increased. This avoids the risk of abnormal heating, such as bearing burnout, caused by reduced cooling capacity. Furthermore, by reducing the cooling capacity when the temperature rise falls below the lower threshold, power consumption is reduced. The heat-generating component is the spindle (an example of a rotating shaft). The temperature rise near the bearing portion of the spindle, based on the temperature of the machine body 2, is used for thermal displacement prediction. Therefore, thermal displacement can be predicted with high accuracy. Furthermore, the above description explains the use of both the equivalent temperature change of cooling heat and the equivalent temperature change of conversion coefficient. However, in spindles with small thermal displacement, either the equivalent temperature change of cooling heat or the equivalent temperature change of conversion coefficient can be used to improve the accuracy of thermal displacement prediction, so either one is acceptable. In the above description, whether to add the equivalent temperature change to the measured temperature data in S9 is determined based on a discrimination condition, but it is also possible to add the equivalent temperature change without performing this discrimination. In the above description, the change of coefficient in S6 corresponds to the operating and stopping states of the spindle cooling device, but it is not limited to the ON / OFF state of the spindle cooling device. For example, even when the spindle cooling device is ON, the coefficient can be changed at the time when the cooling oil volume is changed or the cooling capacity is changed (e.g., the chiller is stopped and the pump is running). The rotating shaft for predicting thermal displacement is not limited to the spindle. Temperatures other than those in the bearing section can also be detected. Alternatively, multiple temperature sensors can be separately installed in the heating element and the main body structure, and the average of the measured values ​​can be used. The cooling device of the present invention is not limited to those targeting a spindle. The machine tool to which the present invention is applicable is not limited to numerical automatic machining tools. 1: Bed; 2: Machine body; 3: Spindle head; 4: Spindle assembly; 5: Stage; 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 calculation device; M: Numerical automatic machining tool [Figure 1] Block diagram showing the structure of a numerical automatic machining tool. [Figure 2] Flowchart of the thermal displacement prediction method.

Claims

1. A method for predicting the thermal displacement of a machine tool, comprising the following steps: a temperature detection step in which the temperature of a predetermined heating element and a predetermined body structure is detected separately by the temperature measuring device in a machine tool having a cooling device and a temperature measuring device; and a thermal displacement prediction step in which the thermal displacement of the heating element is predicted by a prediction model based on the detected temperature; in the thermal displacement prediction step, a time response coefficient for predicting thermal displacement from the detected temperature is determined in relation to the change in cooling capacity caused by the operation control of the cooling device during machine operation; a temperature change equivalent to the change in the conversion coefficient before and after the change in cooling capacity is obtained from a pre-set cooling heat of the cooling device and the relationship between the conversion coefficient between temperature and displacement for predicting thermal displacement from the detected temperature; and / or a temperature change equivalent to the change in cooling heat is obtained from a pre-set cooling heat and the relationship between the temperature equivalent to the cooling heat and the temperature equivalent to the cooling heat before and after the change in cooling capacity; and the thermal displacement of the heating element is predicted based on the temperature after adding the temperature equivalent to the conversion coefficient and / or the temperature equivalent to the cooling heat to the detected temperature, and the aforementioned coefficient.

2. The method for predicting the thermal displacement of a machine tool, as described in Request 1, wherein, The change in the cooling capacity of the aforementioned cooling device is due to any one or both of the operation and shutdown of the aforementioned cooling device and the increase and decrease in the amount of cooling oil used for cooling.

3. A method for predicting the thermal displacement of a machine tool, as requested in item 1 or 2, wherein, The aforementioned heating element is a rotating shaft, and the aforementioned conversion coefficient, which corresponds to the temperature change, is calculated based on the rotational speed of the aforementioned rotating shaft and the time elapsed after the change in the cooling capacity of the aforementioned cooling device.

4. A method for predicting the thermal displacement of a machine tool, as requested in item 1 or 2, wherein, The aforementioned temperature change equivalent to the cooling heat is calculated based on the temperature-time constant before the aforementioned change in cooling capacity, the temperature-time constant after the aforementioned change in cooling capacity, and the time after the aforementioned change in cooling capacity.

5. A method for predicting the thermal displacement of a machine tool, as requested in item 1 or 2, wherein, The cooling capacity of the aforementioned cooling device changes under the condition of using a pre-set upper and lower limit as thresholds. When the temperature rise of the aforementioned detected temperature is below the aforementioned lower limit, the cooling capacity is reduced; when the temperature rise of the aforementioned detected temperature is above the aforementioned upper limit, the cooling capacity is increased.

6. The method for predicting the thermal displacement of a machine tool as described in request item 5, wherein, The aforementioned heating element is a rotating shaft, and the temperature rise value of the bearing portion of the aforementioned rotating shaft or the vicinity of the aforementioned bearing portion, based on the temperature of the aforementioned main body structure portion, is used in thermal displacement prediction.

7. A machine tool having a cooling device and a temperature measuring device, comprising: a temperature detection means for separately detecting the temperatures of a predetermined heating element and a predetermined body structure using the temperature measuring device; and a heat displacement prediction means for predicting the thermal displacement of the heating element based on the detected temperatures using a prediction model; wherein the heat displacement prediction means determines a time response coefficient for predicting the heat displacement from the detected temperature in response to changes in cooling capacity caused by the operation control of the cooling device during machine operation; obtains a temperature change equivalent to the change in the conversion coefficient before and after the change in cooling capacity from a pre-set cooling heat of the cooling device and a conversion coefficient between temperature and displacement for predicting the heat displacement from the detected temperature; and / or obtains a temperature change equivalent to the change in cooling heat before and after the change in cooling capacity from a pre-set cooling heat and a temperature equivalent to the cooling heat; and predicts the thermal displacement of the heating element based on the temperature after adding the temperature equivalent to the conversion coefficient and / or the temperature equivalent to the cooling heat to the detected temperature, and the aforementioned coefficient.

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