Thermal displacement compensation device for machine tools

Abstract

To improve accuracy of thermal displacement correction in a thermal displacement correction device for a machine tool.SOLUTION: A thermal displacement correction device 100 comprises: a temperature sensor Si which is installed at a plurality of parts of an automatic lathe 200; a storage part 30 which stores a plurality of data tables 31 set corresponding to each of a plurality of environmental conditions different from each other as a correspondence between temperature distribution of the automatic lathe 200 and a thermal displacement amount of a position of a tool of the automatic lathe 200 that are detected by the temperature sensor Si corresponding to processing depending processing conditions; a comparison selection part 20 which selects the data table 31 of the plurality of data tables 31 stored in the storage part 30 that has temperature distribution close to the temperature distribution detected when the automatic lathe 200 performs processing on site; a thermal displacement estimation part 40 which estimates a thermal displace amount on the basis of the selected data table 31 and the detected temperature distribution; and a correction command part 50 which outputs a thermal displacement correction amount that cancels the estimated thermal displacement amount and corrects a position of the tool.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a thermal displacement correction device for a machine tool.

Background Art

[0002] In a machine tool, heat is generated in a drive source, a sliding part, etc. by operating a drive source to displace a workpiece or a tool such as rotation or movement. Further, heat is also generated at the contact portion between the workpiece and the tool. And these heats displace various parts of the machine tool due to thermal expansion or the like, so that the position of the tool with respect to the workpiece changes, which affects the dimensional accuracy of the product obtained by machining the workpiece.

[0003] Therefore, the machine tool is provided with a thermal displacement correction device for suppressing the influence of displacement due to this heat. The thermal displacement correction device includes a temperature sensor provided in various parts of the machine tool, a thermal displacement estimation unit that estimates the displacement amount of the position of the tool with respect to the workpiece that is displaced according to the temperatures respectively detected by these temperature sensors, and a correction command unit that outputs a correction command for correcting the position of the tool so as to cancel the displacement amount estimated by the thermal displacement estimation unit to the control unit of the machine tool.

[0004] Here, the thermal displacement estimation unit stores the correspondence relationship between the detected temperature Ti (i = 1, 2, 3,...) detected by each temperature sensor under each processing condition when the workpiece is processed under various processing conditions (for example, conditions related to the machining process such as the cutting depth of cutting, the rotational speed of the workpiece, the feed speed of the tool, etc.) in advance, and the measured displacement amount (thermal displacement amount) ΔA of the position between the workpiece and the tool as the following multiple regression formula (1). ΔA = α1*T1 + α2*T2 + α3*T3 +... (1)

[0005] αi (i = 1, 2, 3,...) in the formula (1) is a coefficient (thermal displacement coefficient) corresponding to the detected temperature Ti by each temperature sensor, and is set in advance so as to satisfy the formula (1) corresponding to various processing conditions.

[0006] The thermal displacement estimation unit then estimates the amount of thermal displacement ΔA based on the detected temperature Ti detected by each temperature sensor when the machine tool is actually used to manufacture a product and the stored formula (1). The output unit of the thermal displacement compensation device outputs a correction command to the machine tool's control unit to correct the amount of thermal displacement estimated by the thermal displacement estimation unit so as to cancel it out. Based on the correction command output from the correction command unit of the thermal displacement compensation device, the machine tool's control unit controls the tool's position relative to the workpiece so as to correct the amount of thermal displacement, thereby reducing the influence of thermal displacement on the dimensional accuracy of the product processed by the machine tool (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2004-154907 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Incidentally, the thermal displacement coefficient αi in equation (1) stored in the thermal displacement estimation unit of the thermal displacement compensation device is set under the assumption that the machine tool is placed in a predetermined standard environment. On the other hand, since machine tools are installed and used in the actual manufacturing sites, the environments in which these machine tools are installed vary greatly and may differ from the predetermined standard environment.

[0009] Therefore, in order to manufacture products with higher dimensional accuracy in an environment where machine tools are installed, it is necessary to improve the accuracy of the machine tools' compensation for thermal displacement.

[0010] The present invention has been made in view of the above circumstances, and aims to provide a thermal displacement compensation device for a machine tool that can improve the accuracy of compensation for thermal displacement. [Means for solving the problem]

[0011] The present invention is a thermal displacement correction device for a machine tool, comprising: temperature sensors installed on multiple parts of the machine tool; a storage unit that stores a plurality of correspondences set to correspond to a plurality of different environmental conditions, as a correspondence between the temperature distribution of the machine tool detected by the temperature sensors in response to machining under predetermined pre-set machining conditions and the amount of thermal displacement of the position of the tool relative to the workpiece being machined by the tool of the machine tool; a comparison and selection unit that compares the temperature distribution of the machine tool detected by the temperature sensors when machining is performed under the environmental conditions in which the machine tool is installed with the temperature distribution of the machine tool in the plurality of correspondences stored in the storage unit, and selects one correspondence from the plurality of correspondences stored in the storage unit that is closest to the temperature distribution of the machine tool detected under the environmental conditions in which the machine tool is installed; a thermal displacement estimation unit that estimates the amount of thermal displacement under the environmental conditions in which the machine tool is installed based on the one correspondence selected by the comparison and selection unit and the temperature distribution of the machine tool detected under the environmental conditions in which the machine tool is installed; and a correction command unit that outputs a thermal displacement correction amount for correcting the position of the tool so as to cancel out the amount of thermal displacement estimated by the thermal displacement estimation unit. [Effects of the Invention]

[0012] The thermal displacement compensation device for machine tools according to the present invention can improve the accuracy of compensation for thermal displacement. [Brief explanation of the drawing]

[0013] [Figure 1] This is a block diagram showing the configuration of a thermal displacement compensation device. [Figure 2] This is a perspective view showing an automatic lathe where thermal displacement is corrected by a thermal displacement compensation device. [Figure 3] Table 1 shows an example of the relationship between the elapsed time t and the temperature Ti of each part under the first processing condition K1. [Figure 4] This is a flowchart illustrating the operation of the thermal displacement compensation device. [Modes for carrying out the invention]

[0014] An embodiment of the thermal displacement compensation device for machine tools according to the present invention will be described below with reference to the drawings.

[0015] <Structure> Figure 1 is a block diagram showing the configuration of the thermal displacement compensation device 100, and Figure 2 is a perspective view showing an automatic lathe 200 in which thermal displacement is compensated by the thermal displacement compensation device 100. The illustrated thermal displacement compensation device 100 is one embodiment of the thermal displacement compensation device for machine tools according to the present invention, and the automatic lathe 200 is one embodiment of a machine tool to which the thermal displacement compensation device for machine tools according to the present invention is applied.

[0016] (Automatic lathe) The automatic lathe 200 is an NC lathe whose operation is controlled by a computer that reads a predetermined program and operates accordingly. As shown in Figure 2, the automatic lathe 200 is equipped with a front spindle 210, a rear spindle 220, a turret tool post 230, and a control unit 240 on a bed 250. The rear spindle 220 is positioned opposite the front spindle 210. The front spindle 210 and the rear spindle 220 can each independently grip a workpiece to be machined and rotate it around its axis, and can also transfer workpieces to each other.

[0017] The front spindle 210 is mounted on a spindle base 260 provided on the bed 250. The rear spindle 220 is mounted on a sliding base 270 provided on the bed 250.

[0018] The turret tool post 230 has multiple tools for machining the workpiece mounted on the outer surface of the rotating turret. The tool is selected by the rotation of the turret tool post 230. The automatic lathe 200 then performs machining operations such as cutting and drilling on the workpiece by bringing the selected tool from the turret tool post 230 into contact with the workpiece while the front spindle 210 and rear spindle 220 rotate the workpiece around its axis. The turret tool post 230 is mounted on a slide support base 280.

[0019] The control unit 240 controls the positions, movements, speeds, etc. of the front spindle 210, the rear spindle 220, the turret tool post 230, the slide table 270, and the slide support table 280 by a computer that operates by reading a predetermined program. Further, the control unit 240 corrects the positions of the front spindle 210, the rear spindle 220, the turret tool post 230, the slide table 270, and the slide support table 280 in accordance with a correction command output from the correction command unit 50 of the thermal displacement correction device 100 described later. Note that the automatic lathe 200 includes a coolant system that emits coolant (not shown in the figure), and the control unit 240 also controls the operation of this coolant system.

[0020] (Thermal Displacement Correction Device) The thermal displacement correction device 100 is provided in the automatic lathe 200. The thermal displacement correction device 100 suppresses the influence of displacement (thermal displacement) caused by heat generated in the automatic lathe 200, and outputs a correction command to correct the position of the machining point so as to cancel the thermal displacement at the machining point (the point where the tool contacts the workpiece) in the automatic lathe 200 to the control unit 240 of the automatic lathe 200.

[0021] As shown in FIG. 1, the thermal displacement correction device 100 includes temperature sensors Si (i = 1, 2,..., 8), a storage unit 30, a comparison selection unit 20, a thermal displacement estimation unit 40, and a correction command unit 50.

[0022] As shown in FIG. 2, the temperature sensors Si are installed at a plurality of locations (in this embodiment, for example, eight locations (i = 1, 2,..., 8)) of the automatic lathe 200. Specifically, the temperature sensor S1 is installed on the front spindle 210, the temperature sensor S2 is installed on the rear spindle 220, the temperature sensor S3 is installed on the turret tool post 230, the temperature sensor S4 is installed on the spindle headstock 260, the temperature sensor S5 is installed on the slide table 270, the temperature sensor S6 is installed on the slide support table 280, the temperature sensor S7 is installed on the bed 250 at a location close to the spindle headstock 260, and the temperature sensor S8 is installed on the bed 250 at a location close to the slide table 270, and each detects the temperature of the location where it is installed.

[0023] In the following, when describing individual temperature sensors S1, S2, ..., S8 without distinguishing between them, they may be collectively referred to as temperature sensor Si.

[0024] The comparison and selection unit 20 compares the temperature distribution (thermal balance) of the automatic lathe 200 detected by the eight temperature sensors Si when the automatic lathe 200 is actually operated to manufacture a product with multiple temperature distributions stored in the storage unit 30 (described later) that were measured when the automatic lathe 200 performed predetermined machining operations under multiple preset environmental conditions. The unit then selects the temperature distribution from among the stored temperature distributions that is closest to the temperature distribution when the automatic lathe 200 is actually operated.

[0025] The memory unit 30 stores the above-mentioned temperature distribution as a data table 31. Specifically, first, the automatic lathe 200 is operated to process a predetermined workpiece according to a set of predetermined machining conditions Kp (p=1,2,…: for example, conditions related to the machining process by the automatic lathe 200 such as the depth of cut, the rotational speed of the workpiece, and the feed rate of the tool), thereby producing a product of a predetermined shape.

[0026] At this time, the elapsed time t [seconds] since the start of machining on the automatic lathe 200 when machining the workpiece under each machining condition Kp, and the temperatures Ti (T1, T2, ..., T8) of each part of the automatic lathe 200 detected by each temperature sensor Si (S1, S2, ..., S8) are detected and recorded, and the amount of thermal displacement ΔA of the position of the machining point where the tool of the turret tool post 230 contacts the workpiece at that time is also recorded.

[0027] For example, when a product is manufactured by processing a workpiece under the first processing condition K1, the elapsed time t [seconds], the detected temperature Ti (T1, T2, ..., T8) of each part, and the measured thermal displacement ΔA of the processing point are correlated as shown in Table 1.

[0028] [Table 1]

[0029] Figure 3 is an example showing the correspondence between elapsed time t and the temperature Ti of each part under the first processing condition K1 shown in Table 1. The elapsed time t and the temperature Ti of each part under the first processing condition K1 described above are as shown in Figure 3. Note that Figure 3 is a schematic diagram to simply explain the relationship between elapsed time t and the temperature Ti of each part, and does not represent the relationship between the elapsed time t and the temperature Ti of each part as actually measured.

[0030] In this way, the thermal displacement coefficient αi (i=1,2,3,…) corresponding to the temperature sensor Si is calculated such that the temperature Ti (T1,T2,…,T8) of each part and the thermal displacement amount ΔA of the position of the machining point at each elapsed time t under the first machining condition K1 satisfy the following multiple regression equation (1). ΔA=α1*T1+α2*T2+…+α8*T8 (1)

[0031] As a result of the calculation, as shown in Table 2, the elapsed time t under the first processing condition K1 is associated with a set of thermal displacement coefficients αi (i=1,2,…,8) of the temperature sensor Si (α1,α2,…,α8).

[0032] [Table 2]

[0033] Then, using the same workpiece, the elapsed time t [seconds], the detected temperature Ti (T1, T2, ..., T8) of each part, and the measured thermal displacement ΔA of the machining point are associated with each other under other machining conditions Kp (seconds K2, third machining conditions K3, ...), and the thermal displacement coefficient αi (i=1, 2, 3, ...) corresponding to the temperature sensor Si is calculated to satisfy the multiple regression equation (1). In the same way as in Table 2, a set of thermal displacement coefficients αi (i=1, 2, ..., 8) of the temperature sensor Si is associated with the machining condition Kp and the elapsed time t (α1, α2, ..., α8).

[0034] In this embodiment, the number of processing conditions p is, for example, 10 (p=1,2,...,10), but it may be between 1 and 9, or between 11 and 10.

[0035] Next, the environmental conditions MQ corresponding to the environment of the site where the automatic lathe 200 is installed are changed, and the temperature Ti and thermal displacement ΔA for each of the machining conditions Kp described above are measured for each of the multiple environmental conditions MQ, and a set of thermal displacement coefficients αi (i=1,2,…,8) of the temperature sensor Si for each machining condition Kp for each environmental condition MQ is associated with each set (α1,α2,…,α8).

[0036] Here, environmental condition MQ is a condition that assumes the environment of the site where the automatic lathe 200 is actually installed, other than the machining condition Kp mentioned above, and is particularly a condition that affects the thermal displacement of the machining point of the tool. Specifically, environmental condition MQ is a condition that can change the temperature of the automatic lathe 200, such as the ambient temperature (room temperature) of the site where the automatic lathe 200 is installed, partial sunlight exposure, and the positional relationship with surrounding heat sources.

[0037] The number of pre-set environmental conditions MQ, q, is, for example, 10, but it can be multiple (2 or more), and may be 9 or less, or 11 or more.

[0038] In this way, before the automatic lathe 200 is actually installed in an environment where products are manufactured, the automatic lathe 200 is experimentally installed under various assumed environmental conditions Mq, and the relationship between the temperature Ti distribution of each part and the thermal displacement ΔA for each elapsed time t, obtained by machining a workpiece under various machining conditions Kp for each of the multiple environmental conditions Mq, is stored in the storage unit 30 as a data table 31 (Table 1 as an example).

[0039] Furthermore, each data table 31 also includes the correspondence between the temperature Ti distribution of each part and the set of thermal displacement coefficients αi (α1, α2, ..., α8) obtained by machining the workpiece under various machining conditions Kp for each environmental condition MQ, and further for each elapsed time t (Table 2 as an example).

[0040] As described above, the memory unit 30 stores numerous data tables 31 for each assumed environmental condition Mq of the site where the automatic lathe 200 will be installed, before the automatic lathe 200 is actually installed at the site where the product is manufactured. The comparison and selection unit 20 compares the temperature Ti (temperature distribution) of each part of the automatic lathe 200 detected by the eight temperature sensors Si at a predetermined elapsed time t when the automatic lathe 200 is installed at a specific site to manufacture a product and processes a workpiece, with the temperature distribution in the temperature distribution data table 31.

[0041] The comparison and selection unit 20 then selects one data table 31 from among the many data tables 31 stored in the storage unit 30 that has a temperature distribution closest to the temperature Ti (temperature distribution) actually detected from the automatic lathe 200 installed at a specific site, and outputs it to the thermal displacement estimation unit 40 along with the actually detected temperature Ti (temperature distribution).

[0042] The thermal displacement estimation unit 40 uses the set of thermal displacement coefficients αi (α1, α2, ..., α8) from the data table 31 input from the comparison and selection unit 20, and the temperature Ti of each part actually detected when the machine is installed and operating at a specific site, to calculate and estimate the amount of thermal displacement ΔA at the position of the processing point in that temperature distribution using a multiple regression equation (1), and outputs the estimated amount of thermal displacement ΔA to the correction command unit 50.

[0043] The correction command unit 50 calculates a thermal displacement correction amount to correct the position of the tool machining point of the automatic lathe 200 to a position that cancels out the thermal displacement amount ΔA input from the thermal displacement estimation unit 40, and outputs this thermal displacement correction amount to the control unit 240 of the automatic lathe 200.

[0044] <Operation> Figure 4 is a flowchart illustrating the operation flow of the thermal displacement compensation device 100. The thermal displacement compensation device 100 of this embodiment operates as follows using the flowchart in Figure 4.

[0045] The automatic lathe 200 is installed in the factory where products are manufactured by actually machining workpieces with tools, and then the automatic lathe 200 is put into operation to start machining. The comparison and selection unit 20 acquires a predetermined elapsed time t since the automatic lathe 200 started machining, and the temperature Ti (temperature distribution) of each part of the automatic lathe 200 detected by the eight temperature sensors Si installed on the automatic lathe 200 (#1).

[0046] The comparison and selection unit 20 compares the temperature Ti (temperature distribution) of the automatic lathe 200 at the acquired elapsed time t with the temperature Ti distribution at each elapsed time t in the multiple data tables 31 stored in the storage unit 30, and selects the one with the closest temperature distribution (#2).

[0047] Here, "closest temperature distribution" can be defined as, for example, when the number of temperature sensor Sis whose temperature Ti corresponds to a temperature Ti in the corresponding temperature sensor Si in data table 31 that falls within an approximate range of, for example, ±5[%] for each acquired temperature Ti is greater than or equal to a preset number.

[0048] The approximate range for each acquired temperature Ti is not limited to the ±5% range mentioned above; it may also be ±10%, or any other preset range may be applied. Furthermore, when specifying "closest temperature distribution," the number of temperature sensors Si in the approximate range may be three or more, four or more, five or more, or any other number as appropriate.

[0049] Furthermore, "closest temperature distribution" means, for example, if there is an order of temperature sensors Si in terms of the magnitude of their influence on the thermal displacement ΔA due to temperature Ti, then the temperature sensors Si with the greatest influence may be weighted when calculating the number of sensors. The specific degree of weighting may be changed according to the environmental conditions of the site where the automatic lathe 200 is installed.

[0050] The thermal displacement estimation unit 40 uses a multiple regression equation (1) to estimate the thermal displacement of the automatic lathe 200 based on the set of thermal displacement coefficients αi (α1, α2, ..., α8) from the data table 31 selected by the comparison selection unit 20 and the temperature Ti (temperature distribution) of the automatic lathe 200 at the acquired elapsed time t. But actually We estimate the thermal displacement ΔA under the conditions in which it is being used (#3).

[0051] The correction command unit 50 calculates a thermal displacement correction amount to correct the position of the machining point of the tool of the automatic lathe 200 to a position that cancels out the thermal displacement amount ΔA, based on the thermal displacement amount ΔA estimated by the thermal displacement estimation unit 40, and outputs the calculated thermal displacement correction amount to the control unit 240 of the automatic lathe 200 (#4).

[0052] As described in detail above, the thermal displacement compensation device 100 of the automatic lathe 200 of this embodiment stores a data table 31 of thermal displacement coefficient αi and temperature Ti (temperature distribution) for each of several environmental conditions assumed to be the environment at the site where the automatic lathe 200 is actually installed, and corrects the amount of thermal displacement at the site using the data table 31 of temperature Ti (temperature distribution) that is closest to the temperature Ti (temperature distribution) acquired at the actual installation site.

[0053] Therefore, it is possible to perform thermal displacement correction that is appropriate for the environment at the site where the automatic lathe 200 is installed, and the accuracy of the correction for thermal displacement can be improved.

[0054] In this embodiment, the thermal displacement correction device 100 has a comparison selection unit 20 that selects the data table 31 with the closest temperature distribution. However, there may be cases where no data table 31 with a similar temperature distribution exists according to the specified criteria. Therefore, the storage unit 30 stores a set of reference thermal displacement coefficients αsi (i=1,2,…,8) (αs1,αs2,…,αs8) set in accordance with a pre-set reference environmental condition K0 as a reference data table. The comparison selection unit 20 then selects this reference data table (#2).

[0055] The thermal displacement estimation unit 40 uses a multiple regression equation (1) to estimate the thermal displacement of the automatic lathe 200 based on the set of reference thermal displacement coefficients αsi (αs1, αs2, ..., αs8) from the reference data table and the temperature Ti (temperature distribution) of the automatic lathe 200 at the acquired elapsed time t. But actually The thermal displacement ΔA is estimated in the state in which the machine is in use (#3). Based on the thermal displacement ΔA estimated by the thermal displacement estimation unit 40, the correction command unit 50 calculates a thermal displacement correction amount to correct the position of the machining point of the tool of the automatic lathe 200 to a position that cancels out the thermal displacement ΔA, and outputs the calculated thermal displacement correction amount to the control unit 240 of the automatic lathe 200 (#4).

[0056] When a data table 31 with a temperature distribution close to the specified temperature distribution does not exist, the thermal displacement correction device 100 can correct the amount of thermal displacement corresponding to the standard environmental conditions by applying a set of thermal displacement coefficients αsi (αs1, αs2, ..., αs8) from a reference data table. This allows for a standard correction, although not necessarily the optimal correction, for a wide range of environmental conditions.

[0057] The thermal displacement compensation device 100 of this embodiment is equipped with eight temperature sensors Si (i=1,2,...,8), but the number of temperature sensors Si is not limited to eight; it may be two to seven, or nine or more. Furthermore, the location where the temperature sensors Si are installed is not limited to the automatic lathe 200 described in this embodiment, but may be installed in other locations.

[0058] In this embodiment, the thermal displacement compensation device 100 is applied to an automatic lathe 200 equipped with a front spindle 210, a rear spindle 220, and a turret tool post 230 as an example of a machine tool. However, the automatic lathe 200 may have one spindle (only the front spindle), or three or more spindles, and a comb-shaped tool post may be provided instead of the turret tool post 230.

[0059] In this embodiment, the thermal displacement compensation device 100 is applied to an automatic lathe 200 as an example of a machine tool. However, the thermal displacement compensation device for machine tools according to the present invention is not limited to automatic lathes, but can be applied to machine tools other than automatic lathes that perform various plastic deformation processes on a workpiece. [Explanation of symbols]

[0060] 20 Comparison and Selection Section 30 Storage section 31 Data Tables 40 Thermal displacement estimation unit 50 Correction command section 100 Thermal displacement compensation device 200 Automatic Lathes Ki machining conditions Kp processing conditions Mq environmental conditions Si temperature sensor Ti temperature t elapsed time ΔA Thermal displacement αi Thermal displacement coefficient

Claims

1. Temperature sensors installed in multiple parts of the machine tool, A storage unit stores multiple correspondences set to correspond to multiple different environmental conditions, which are the correspondence between the temperature distribution of the machine tool detected by the temperature sensor in response to machining under predetermined pre-set machining conditions, and the amount of thermal displacement of the position of the tool relative to the workpiece being machined by the tool of the machine tool. A comparison and selection unit compares the temperature distribution of the machine tool detected by the temperature sensor when machining is performed under the environmental conditions in which the machine tool is installed with the temperature distribution of the machine tool in a plurality of corresponding relationships stored in the storage unit, and selects the one corresponding relationship from the plurality of corresponding relationships stored in the storage unit that is closest to the temperature distribution of the machine tool detected under the environmental conditions in which the machine tool is installed. The system includes a thermal displacement estimation unit that estimates the amount of thermal displacement in the environmental conditions in which the machine tool is installed, based on one of the correspondence relationships selected by the comparison and selection unit and the temperature distribution of the machine tool detected in the environmental conditions in which the machine tool is installed, and a correction command unit that outputs a thermal displacement correction amount for correcting the position of the tool so as to cancel out the amount of thermal displacement estimated by the thermal displacement estimation unit. The memory unit stores, as one of the multiple correspondence relationships set in response to each of the multiple different environmental conditions, a reference correspondence relationship set in response to a reference environmental condition. The comparison and selection unit selects one correspondence that is closest to the temperature distribution of the machine tool from among the multiple corresponding temperature distributions of the machine tool stored in the memory unit, from among the corresponding temperature distributions in which the number of temperature sensors whose temperatures fall within ±10% of the temperature detected by the temperature sensor is equal to or greater than a preset number. The comparison and selection unit is a thermal displacement compensation device for a machine tool, which, when there is no single correspondence among the multiple correspondences stored in the memory unit that is closest to the temperature distribution of the machine tool detected under the environmental conditions in which the machine tool is installed, selects the standard correspondence.

2. The thermal displacement compensation device for a machine tool according to claim 1, wherein, when the comparison and selection unit selects the one correspondence that is closest to the temperature distribution of the machine tool, if there is an order among the multiple temperature sensors, the temperature sensors with the greatest influence are weighted in the calculation of a preset number.

3. The temperature sensors are installed in eight locations on the machine tool, The comparison and selection unit selects, as the one closest to the temperature distribution of the machine tool, a temperature distribution correspondence among a plurality of correspondences of the machine tool stored in the storage unit, wherein the number of temperature sensors with temperatures within ±10% of the temperature detected by the temperature sensor is three or more. This is the thermal displacement compensation device for a machine tool according to claim 1.

4. The thermal displacement compensation device for a machine tool according to any one of claims 1 to 3, wherein the aforementioned environmental conditions are conditions that affect the temperature of the machine tool in the environment in which the machine tool is installed.

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