Error estimation method for machine tool, and machine tool control device

Abstract

To provide an error estimation method in a machine tool and a control device of the machine tool capable of reducing influence of uneven thermal displacement and strain due to a temperature distribution and providing the machine tool of high precision with respect to a target size and shape.SOLUTION: An error estimation method in a machine tool includes a process S0 of correcting machine precisions, a succeeding process S1a of confirming that the machine tool and a workpiece have stable precisions to work a hole datum which becomes a measurement standard on S2 onto the workpiece, a process S1b of again confirming that the machine tool and the workpiece have stable precision, a process S3 of measuring the hole datum by using a touch probe to provide first measurement data, a succeeding process S4 of again measuring the hole datum by using the touch probe just before or during working the workpiece into a target shape to provide second measurement data and a further process S5 of estimating errors of the workpiece or the machine tool including the workpiece on the basis of the first and second measurement data.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a method for estimating an error in a machine tool, such as a workpiece or a machine tool including a workpiece, and a machine tool control device for implementing the error estimation method. [Background technology]

[0002] The components of machine tools and workpieces are thermally deformed due to environmental temperature, self-heating, and machining heat, resulting in positioning errors relative to the commanded position, i.e., thermal displacement. Machining a workpiece in the presence of thermal displacement can cause machining errors relative to the target shape, which can be problematic. For this reason, many techniques for compensating for thermal displacement have been devised. For example, Patent Documents 1 to 3 disclose methods for estimating and correcting thermal displacement of a workpiece from the linear expansion coefficients and temperatures of the components of the machine tool and the workpiece. Patent Document 4 shows a method in which a plurality of workpieces are machined while measuring the temperature of the machine tool in advance, the dimensions of the machined plurality of workpieces are measured with a measuring instrument, and when the workpieces are actually machined, corrections are made using the relationship between the measured temperature and the corresponding dimensional error. Patent Documents 5 and 6 disclose a method in which a reference gauge with known dimensions is attached to a table or a jig, and measurements are made with a touch probe, and thermal displacement is corrected based on the measured dimensional error. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-116654 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-281335 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-187683 [Patent Document 4] Japanese Patent Application Laid-Open No. 2005-52917 [Patent Document 5] Japanese Patent Application Laid-Open No. 2006-212765 [Patent Document 6] Japanese Patent Application Laid-Open No. 2018-30195 Summary of the Invention [Problem to be solved by the invention]

[0004] It is difficult to know the exact value of the linear expansion coefficient of machine tool components and workpieces. The linear expansion coefficient values provided by manufacturers have a certain tolerance, and if this value is used to estimate thermal displacement, an estimation error within the tolerance will occur. For example, if the linear expansion coefficient is (10±1)×10 -6 For a workpiece 2 m long at K / m, an estimation error of ±20 μm may occur. On the other hand, the temperature of an object is often not uniform but has a distribution, and when heat from machining is applied to the workpiece, the temperature distribution of the workpiece becomes wider. Therefore, if the temperature of the workpiece is measured locally using a temperature sensor and the thermal displacement is estimated from that temperature and the linear expansion coefficient that includes the above-mentioned error, the estimation error will be large. Therefore, the methods of Patent Documents 1 to 3, which estimate thermal displacement using the linear expansion coefficient or temperature of the workpiece, have the problem of estimation errors. The method of Patent Document 4 requires machining multiple reference workpieces and measuring their dimensions separately, and also requires machining at various machine temperatures to obtain the correspondence between machine temperature and dimensional error, which requires a great deal of time and effort. Furthermore, it is only applicable to mass-produced parts that can be mass-produced in a short time, and is not suitable for machining parts with small production numbers. In the method of Patent Document 5, correction is made based on the results of a reference measurement made on a low-expansion material, so unless the temperature of the machine is 20°C (the reference temperature for the linear expansion coefficient), there is a problem that an error occurs due to the expansion and contraction of the machine at the ambient temperature. Also, the method does not take into account the thermal displacement of the workpiece. The method of Patent Document 6 measures and corrects a reference gauge made of the same material as the workpiece, so errors due to ambient temperature do not occur. However, there is a problem in that errors occur when the reference gauge and the workpiece are not at the same temperature.

[0005] Therefore, the present disclosure aims to provide an error estimation method for a machine tool and a machine tool control device that can reduce the effects of uneven thermal displacement and distortion due to temperature distribution in the workpiece, thereby obtaining a workpiece with high accuracy relative to the target dimensions and shape. [Means for solving the problem]

[0006] In order to achieve the above object, a first configuration of the present disclosure is a method for estimating errors in a workpiece or the machine tool including the workpiece, in a machine tool having a rotatable spindle to which a tool can be attached, a table to which a workpiece can be fixed, and three or more linear axes, and capable of machining a workpiece fixed to the table using a tool attached to the spindle by controlling the relative position of the spindle with respect to the table, and capable of measuring the position and shape of the workpiece using a position measurement sensor attached to the spindle. The first configuration is the machine tool and the workpiece. The change in accuracy is smaller than the predetermined comparison value. an accuracy stability confirmation step for confirming that the accuracy is stable; The machine tool and the workpiece The change in accuracy is small a datum machining step of machining a datum serving as a measurement reference at a predetermined position of the workpiece in this state; The machine tool and the workpiece The change in accuracy is small a first datum measurement step of measuring the datum by the position measurement sensor in a state; a second datum measurement step of measuring the datum with the position measurement sensor immediately before or during machining of the workpiece into a target shape; and an error estimation step of estimating an error of the workpiece or the machine tool including the workpiece based on the first measurement data obtained in the first datum measurement step and the second measurement data obtained in the second datum measurement step. In this disclosure, "a state in which the accuracy of the machine tool and workpiece is stable" refers to a state in which it can be estimated that the change in accuracy of the machine tool and workpiece is small based on various information that can be obtained from the workpiece or machine tool and that affects thermal displacement, such as temperature information from temperature sensors installed in various parts of the machine tool and temperature sensors installed in the workpiece, machine operation information, whether cutting water is being discharged and the discharge time, etc. The estimation that the change in accuracy is small is made by diagnosing, for example, by comparing each piece of information with a predetermined threshold value or with average data over a predetermined period of time. Another aspect of the first configuration is characterized in that, in the above configuration, before the datum processing step, a machine accuracy calibration step is further performed in which the position measurement sensor is used to measure an accuracy master placed on the table, and the measurement result is used to calibrate the machine accuracy. Another aspect of the first configuration is characterized in that, in the above configuration, a first position measurement sensor calibration step of calibrating the position measurement sensor using a reference device is further performed before the first datum measurement step. Another aspect of the first configuration is characterized in that, in the above configuration, a second position measurement sensor calibration step of calibrating the position measurement sensor using a reference device is further performed before the second datum measurement step. In another aspect of the first configuration, in the above configuration, after the first datum measurement step, a datum quality determination step is executed to determine whether the shape accuracy of the datum is good or bad based on the first measurement data, Datum pass / fail judgment If the determination result in the step is negative, the datum machining step is repeated. Another aspect of the first configuration is, in the above configuration, after the second datum measurement step, a measurement data abnormality determination step is executed in which presence or absence of an abnormality in the second measurement data is determined based on the first measurement data and the second measurement data, Measurement data abnormality detection If the determination result in the step is abnormal, the second datum measurement step is repeated.

[0007] In order to achieve the above object, a second configuration of the present disclosure is a control device that is provided on a machine tool having a rotatable spindle to which a tool can be attached, a table to which a workpiece can be fixed, and three or more linear axes, and that is capable of machining a workpiece fixed to the table using a tool attached to the spindle by controlling the relative position of the spindle with respect to the table, and that is capable of measuring the position and shape of the workpiece using a position measurement sensor attached to the spindle, and that estimates errors in the workpiece or the machine tool including the workpiece. The second configuration is a datum setting means for setting a datum that serves as a measurement standard for machining on the workpiece; The machine tool and the workpiece The change in accuracy is smaller than the predetermined comparison value. an accuracy stability determination means for determining whether the accuracy is stable; The accuracy stability determination means determines whether the machine tool and the workpiece are stable. The change in accuracy is small a datum machining means for machining the datum set by the datum setting means at a predetermined position on the workpiece when it is determined that the datum has been set. The accuracy stability determination means determines whether the machine tool and the workpiece are stable. The change in accuracy is small a first datum measurement means for measuring the datum using the position measurement sensor in a state where it is determined that the datum is a second datum measurement means for measuring the datum using the position measurement sensor immediately before or during machining of the workpiece into a target shape; and an error estimation means for estimating an error of the workpiece or the machine tool including the workpiece based on first measurement data obtained from the first datum measurement means and second measurement data obtained from the second datum measurement means. Another aspect of the second configuration is characterized in that, in the above configuration, the device further comprises a datum quality determination means for determining whether the shape accuracy of the datum is good or bad based on the first measurement data. Another aspect of the second configuration is characterized in that, in the above configuration, the device further comprises a measurement data abnormality determination means for determining an abnormality in the second measurement data based on the first measurement data and the second measurement data. Another aspect of the second configuration is, in the above configuration, a correction value generating means for calculating a correction value for correctively controlling each of the linear axes based on an error estimation value of the workpiece or the machine tool including the workpiece estimated by the error estimating means; The apparatus further comprises a correction control means for correctively controlling each of the linear axes using the correction value. [Effects of the Invention]

[0008] According to the present disclosure, by measuring the datum machined into the workpiece and correcting the machine accuracy, the effects of uneven thermal displacement and distortion due to the temperature distribution of the workpiece can be reduced, and a workpiece with high accuracy relative to the target dimensions and shape can be obtained. [Brief explanation of the drawings]

[0009] [Figure 1] This is a schematic diagram of a 3-axis controlled machining center. [Figure 2] FIG. 1 is a schematic diagram of ball array measurement using a touch probe. [Figure 3] FIG. 1 is a schematic diagram of a datum machined on a workpiece. [Figure 4] 1 is a flowchart of an error estimation method. [Figure 5] 5 is a flowchart showing the details of step S0 in FIG. 4. [Figure 6] 5 is a flowchart showing details of step S3 in FIG. 4. [Figure 7] 5 is a flowchart showing details of step S4 in FIG. 4. [Figure 8] FIG. 1 is a schematic diagram of a numerical control device. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. FIG. 1 is a schematic diagram of a three-axis controlled machining center, an example of a machine tool. A spindle head 2, which is equipped with a rotatable spindle and to which a tool 4 can be attached, has two degrees of translational freedom relative to a bed 1 along two orthogonal Y- and Z-axes. A table 3, to which a workpiece 5 can be fixed, has one degree of translational freedom relative to the bed 1 along a Y-axis, which is also a translational axis orthogonal to the X- and Z-axes. Therefore, the spindle head 2 has three degrees of translational freedom relative to the table 3. The X, Y, and Z feed axes are driven by servo motors and feed mechanisms (not shown) controlled by a numerical control device 7 (described later). The spindle is rotated by a motor (not shown) controlled by the numerical control device 7. The workpiece 5 is fixed to the table 3, a tool 4 is attached to the spindle head 2 and rotated. By controlling the feed axes, the relative positions of the workpiece 5 and the tool 4 can be controlled, allowing the workpiece 5 to be machined.

[0011] Figure 2 is a schematic diagram of a touch probe, an example of a position measurement sensor. Touch probe 6 is a sensor that emits a trigger signal when the ball at the tip of the stylus comes into contact with the workpiece. A numerical control device 7 acquires the current position of each feed axis at the moment the trigger signal is received upon contact, and measures the position of the contact point using each acquired current position and the touch probe calibration value. Touch probe 6 is attached to spindle head 2, and each feed axis is controlled so that the stylus ball of touch probe 6 comes into contact with the workpiece placed on table 3. By making contact at several points, the position of the workpiece can be measured.

[0012] FIG. 4 shows a flowchart of an error estimation method as an example of the first configuration of the present disclosure. First, in step (hereinafter simply referred to as "S") 0, the mechanical accuracy is calibrated using the accuracy master as a reference (mechanical accuracy calibration step). Details of S0 will be described later. In S1a, it is diagnosed whether the accuracy of the machine or workpiece is stable (accuracy stability confirmation step). From the temperature information from the temperature sensors installed at various parts of the machine tool in Figure 1 and the temperature sensors installed on the workpiece, as well as various information that can be obtained from the workpiece or machine tool and that affects thermal displacement, such as machine tool operation information, whether cutting water is being discharged and the discharge time, it is estimated whether the change in accuracy of the machine or workpiece is small (for example, by comparing with a specified threshold value or average data over a specified time period), and a diagnosis is made as to whether the accuracy is stable. In S2, while the accuracy of the machine and workpiece is stable, multiple datums that serve as measurement standards are machined onto the workpiece (datum machining step).

[0013] FIG. 3 is a schematic diagram of an example in which a plurality of hole-shaped hole datums 11 are machined into a workpiece 5. Multiple hole datums 11 are machined in locations that do not affect the final target shape of the workpiece 5, and in this embodiment, they are machined parallel to the X-axis or Y-axis. However, if the target shape has a portion that can serve as a datum, part of that portion may be used as the datum. Also, in this embodiment, the datum shape is a hole, but it may also be a pocket shape, a cylindrical shape, a rectangular prism shape, a surface, or the like, as long as it is sized so that its center position, vertex position, etc. can be measured by the touch probe 6. In S1b, it is again diagnosed whether the accuracy of the machine or workpiece is stable (accuracy stability confirmation step). The diagnosis method is the same as S1a, so a description thereof will be omitted. However, if it can be separately determined that the accuracy of the machine or workpiece is stable, S1b may be omitted.

[0014] In S3, when the accuracy of the machine and workpiece is stable, a plurality of hole datums 11 machined in the workpiece 5 are measured with the touch probe 6 and stored as initial datum information. Figure 6 shows the details of S3. In S3-1, the touch probe 6 is calibrated to reduce the uncertainty in the measurement accuracy of the touch probe 6 (first position measurement sensor calibration step). As a calibration method, existing technology can be used, such as obtaining correction values using a reference device such as a reference sphere. However, if it is determined that there is no problem with the measurement accuracy of the touch probe 6, this step may be omitted. In S3-2, while the accuracy of the machine and workpiece is stable, the center position and bottom height of each cylindrical surface of the multiple hole datums 11 machined in S2 are measured using the touch probe 6 (first datum measurement step). At the same time, the diameter, roundness, and surface roughness are measured to obtain information for determining whether the center position measurement results are good or bad in S3-3, which will be described later.

[0015] Here, if the datum shape is a pocket, the measurement targets include the pocket center position, bottom height, pocket width, and surface roughness. If it is a cylindrical shape, the measurement targets include the cylinder center position, top height, roundness, and surface roughness. If it is a prismatic shape, the measurement targets include the prismatic center position, top height, width between two side surfaces, and surface roughness. If it is a surface shape, the measurement targets include the surface position and surface roughness. In S3-3, the measurement results (shape accuracy) of the hole datum 11 measured in S3-2 are judged to be good or bad (datum good or bad judgment step). In the case of the hole datum 11, if the values of diameter, roundness, and surface roughness are greater than preset thresholds, it is judged to be a machining defect. If it is judged to be a machining defect, the process returns to S1a to diagnose the accuracy state, and then machining and measurement of the hole datum 11 are performed again from S2 onwards. For each hole datum 11, the measurement of S3-2 and the pass / fail judgment of S3-3 may be performed as a set. In S3-4, the measurement values of the center positions, diameters, and roundness of the plurality of hole datums 11 measured in S3-2 are stored as initial datum information (first measurement data).

[0016] In S4, immediately before or during machining of the workpiece 5, a plurality of hole datums 11 machined in the workpiece 5 are measured by the touch probe 6 and stored as datum information during machining. Fig. 7 shows the details of S4. In S4-1, the touch probe 6 is calibrated to reduce the uncertainty in the measurement accuracy of the touch probe 6 (second position measurement sensor calibration step). The calibration method is the same as in S3-1, so a description thereof will be omitted. However, if it is determined that there is no problem with the measurement accuracy of the touch probe 6, this step may be omitted. In S4-2, immediately before or during machining of the workpiece 5, the center position and bottom height of each cylindrical surface of a plurality of hole datums 11 on the workpiece 5 are measured using the touch probe 6 (second datum measurement step). In S4-3, the measurement results (second measurement data) of the hole datum 11 measured in S4-2 are judged to be abnormal (measurement data abnormality judgment step). In the case of a hole datum 11 of a hole shape, the diameter and roundness of the measurement results are compared with the first measurement data stored in S3-4, and if each difference value is greater than a preset threshold, the second measurement data is judged to be abnormal. If an abnormality is judged, the data is cleaned using air blowing or the like, and the measurement in S4-2 is performed again. Here, too, for each hole datum 11, the measurement of S4-2 and the determination of S4-3 may be performed as a set. In S4-4, the measurement values of the center positions, diameters, and roundness of the plurality of hole datums 11 measured in S4-2 are stored as datum information during machining.

[0017] In S5, the initial datum information and the as-machined datum information are used to identify the errors of the workpiece or the combined errors of the machine tool and the workpiece (error estimation step). In the case of the hole datum 11 of the workpiece 5 in Figure 3, the positioning error and straightness of the X-axis and the positioning error and straightness of the Y-axis, which include the error components of the workpiece, can be identified. By performing steps S4 and S5 as needed during machining of the workpiece 5 to estimate errors and then performing correction control based on the identified errors, high-precision machining is possible even if the workpiece is thermally deformed.

[0018] Next, the details of S0 will be explained using the flowchart of FIG. In S0-1, it is determined whether the machine accuracy is stable. The method of diagnosis is the same as in S1a, so the explanation is omitted here. In S0-2, the touch probe 6 is calibrated to reduce the uncertainty in the measurement accuracy of the touch probe 6. The calibration method is the same as in S3-1, so a description thereof will be omitted. In S0-3, a calibrated precision master with known dimensions is measured with a touch probe 6. Figure 2 shows a ball array 10 having multiple balls with calibrated center positions as an example of a precision master. Other precision masters include hole gauges with multiple holes with calibrated center positions, step gauges with multiple blocks with calibrated face-to-face distances, block gauges, straightness masters, and right-angle masters. The required precision master is measured depending on the error of the machine to be calibrated.

[0019] In S0-4, machine errors are identified based on the measurement results of the precision master in S0-3. For example, with the ball array 10, the positioning error and straightness of each axis can be identified using the results of measurement performed by installing it parallel to each feed axis. In addition, the squareness between each two axes can be identified using the results of measurement performed by installing a right-angle master parallel to the plane formed by the two feed axes. In S0-5, the machine errors identified in S0-4 are converted into compensation parameters, and the compensation parameters are set in the numerical control device 7. By performing compensation control using these compensation parameters, it is possible to perform machining and touch probe measurement while eliminating the effects of machine errors. Here, as a method for reflecting the identified errors in machining and measurement, the identified errors may be set as parameters in CAM software that generates machining and measurement programs, and machining and measurement may be performed using the programs generated by this CAM software. Alternatively, the identified errors may be reflected directly in the operation programs.

[0020] 8 is a schematic diagram of a numerical control device 7 of a machine tool that implements the error estimation method described above. This numerical control device 7 is an example of a machine tool control device having the second configuration of the present disclosure. The numerical control device 7 includes an accuracy stability determination means 20, a datum setting means 21, a datum command generation means 22, an axis control means 23, a measurement value acquisition means 24, an initial datum pass / fail determination means 25, an initial datum information storage means 26, a machining datum abnormality determination means 27, a machining datum information storage means 28, an error identification calculation means 29, and a correction value generation means 30. The accuracy stability determining means 20 determines whether the accuracy of the machine tool and the workpiece 5 in the above-mentioned S1a and S1b is stable. The datum setting means 21 can set information such as the type, size, number, and machining position of the datum to be machined on the workpiece, and this information is stored. The datum command generating means 22 generates commands for machining the datum and commands for measuring the datum with the touch probe 6 based on the datum information set and stored by the datum setting means 21 .

[0021] The axis control means 23 controls the operation of the feed axes for machining the S2 datum and measuring S3-2 and S4-2 based on the commands generated by the datum command generation means 22. It can also perform correction control of each feed axis based on the correction values generated by the correction value generation means 30. The axis control means 23 and the datum command generation means 22 are an example of the datum machining means of the present disclosure. The measurement value acquiring means 24 acquires measurement values based on the detection values of detectors for each feed axis (not shown) when the touch probe 6 is brought into contact with the measurement object. The measurement value acquiring means 24 and the axis control means 23 are examples of the first and second datum measurement means of the present disclosure.

[0022] The initial datum quality determination means 25 performs quality determination in S3-3 on the initial datum information acquired in S3-2 by the measurement value acquisition means 24. This initial datum quality determination means 25 is an example of the datum quality determination means disclosed herein. The initial datum information storage means 26 stores the initial datum information. The machining datum abnormality determination means 27 performs an abnormality determination in S4-3 on the machining datum information acquired by the measurement value acquisition means 24 in S4-2, based on the initial datum information stored in the initial datum information storage means 26. This machining datum abnormality determination means 27 is an example of the measurement data abnormality determination means of the present disclosure. The machining datum information storage means 28 stores the machining datum information.

[0023] The error identification calculation means 29 identifies and calculates the error of the workpiece or the error between the machine tool and the workpiece as in S5, based on the initial datum information recorded in the initial datum information storage means 26 and the as-machined datum information recorded in the as-machined datum information storage means 28. This error identification calculation means 29 is the error estimation means of the present disclosure. The correction value generating means 30 converts the errors of the workpiece identified by the error identifying and calculating means 29 or the errors between the machine tool and the workpiece into correction values for each feed axis. By performing correction control using the axis control means 23 based on this correction value, it is possible to cancel errors between the workpiece or the machine tool and the workpiece, and perform machining or measurement of the workpiece. This axis control means 23 is an example of the correction control means of the present disclosure.

[0024] The error estimation method and numerical control device 7 of the above-described form machines a hole datum 11 into the workpiece 5 while the machine tool and workpiece 5 are in a stable state in terms of accuracy, measures the hole datum 11 with a touch probe 6 to obtain first measurement data, and then measures the hole datum 11 again with the touch probe 6 immediately before or during machining of the workpiece 5 into a target shape to obtain second measurement data, and estimates an error of the workpiece 5 or the machine tool including the workpiece 5 based on the obtained first and second measurement data. In this way, by measuring the hole datum 11 machined in the workpiece 5 and correcting the machine accuracy, it is possible to reduce the effects of non-uniform thermal displacement and distortion due to the temperature distribution in the workpiece 5. As a result, it is possible to obtain a workpiece 5 with high accuracy relative to the target dimensions and shape.

[0025] In particular, before machining the hole datum 11, the ball array 10 placed on the table 3 is measured using the touch probe 6, and the measurement results are used to calibrate the machine accuracy, so that the machining of the hole datum 11 and measurement using the touch probe 6 can be performed while eliminating the influence of machine errors. Furthermore, since the touch probe 6 is calibrated using a reference device before each datum measurement step, the measurement accuracy by the touch probe 6 can be improved. Furthermore, after the first datum measurement step, the shape accuracy of the first measurement data is judged to be good or bad, and if the judgment result is bad, the machining of the hole datum 11 is redone, thereby avoiding inaccurate estimation of errors based on the first measurement data of the hole datum 11 that would result in poor machining. Similarly, after the second datum measurement step, the presence or absence of an abnormality in the second measurement data is determined based on the first measurement data and the second measurement data, thereby avoiding estimation of errors based on inaccurate second measurement data due to the inclusion of foreign matter, etc. [Explanation of symbols]

[0026] 1 Bed, 2 Spindle, 3 Table, 4 Tool, 5 Workpiece, 6 Touch probe, 7 Numerical control device, 10 Ball array, 11 Hole datum, 20 Accuracy stability determination means, 21 Datum setting means, 22 Datum command generation means, 23 Axis control means, 24 Measurement value acquisition means, 25 Initial datum pass / fail determination means, 26 Initial datum information storage means, 27 Machining datum abnormality determination means, 28 Machining datum information storage means, 29 Error identification calculation means, 30 Correction value generation means.

Claims

1. A method for estimating an error of a workpiece or the machine tool including the workpiece in a machine tool having a rotatable spindle on which a tool is attached, a table to which a workpiece can be fixed, and three or more linear axes, the method being capable of machining a workpiece fixed to the table using a tool attached to the spindle by controlling the relative position of the spindle with respect to the table, and capable of measuring the position and shape of the workpiece using a position measurement sensor attached to the spindle, comprising: an accuracy stability confirmation step of confirming that a change in accuracy of the machine tool and the workpiece is smaller than a predetermined comparison value; a datum machining step of machining a datum serving as a measurement standard at a predetermined position of the workpiece while the change in accuracy of the machine tool and the workpiece is small; a first datum measurement step of measuring the datum by the position measurement sensor in a state in which the change in accuracy of the machine tool and the workpiece is small; a second datum measurement step of measuring the datum with the position measurement sensor immediately before or during machining of the workpiece into a target shape; an error estimating step of estimating an error of the workpiece or the machine tool including the workpiece based on first measurement data obtained in the first datum measuring step and second measurement data obtained in the second datum measuring step; 1. A method for estimating an error in a machine tool, comprising:

2. 2. The method for estimating errors in a machine tool according to claim 1, further comprising the step of measuring a precision master placed on the table using the position measurement sensor before the datum machining step, and calibrating the precision of the machine using the measurement results.

3. 3. The method for estimating errors in a machine tool according to claim 1, further comprising the step of calibrating the position measurement sensor using a reference device before the first datum measurement step.

4. 4. An error estimation method for a machine tool according to claim 1, further comprising the step of calibrating the position measurement sensor using a reference device before the second datum measurement step.

5. 5. The method for estimating errors in a machine tool according to claim 1, further comprising the steps of: after the first datum measurement step, executing a datum quality determination step for determining whether the shape accuracy of the datum is good or bad based on the first measurement data; and if the determination result in the datum quality determination step is bad, redoing the datum machining step.

6. 6. An error estimation method for a machine tool according to claim 1, wherein after the second datum measurement step, a measurement data abnormality determination step is executed in which presence or absence of an abnormality in the second measurement data is determined based on the first measurement data and the second measurement data, and if the determination result in the measurement data abnormality determination step is an abnormality, the second datum measurement step is repeated.

7. A control device is provided in a machine tool that has a rotatable spindle on which a tool is attached, a table to which a workpiece can be fixed, and three or more linear axes, and that can machine a workpiece fixed to the table using a tool attached to the spindle by controlling the relative position of the spindle with respect to the table, and that can measure the position and shape of the workpiece using a position measurement sensor attached to the spindle, and that estimates an error of the workpiece or the machine tool including the workpiece, a datum setting means for setting a datum on the workpiece as a measurement standard for machining; an accuracy stability determination means for determining whether a change in accuracy of the machine tool and the workpiece is smaller than a predetermined comparison value; a datum machining means for machining the datum set by the datum setting means to a predetermined position on the workpiece when the accuracy stability determination means has determined that the change in accuracy of the machine tool and the workpiece is small; and a first datum measurement means for measuring the datum with the position measurement sensor in a state in which the accuracy stability determination means has determined that the change in accuracy of the machine tool and the workpiece is small; a second datum measuring means for measuring the datum using the position measuring sensor immediately before or during machining of the workpiece into a target shape; an error estimation means for estimating an error of the workpiece or the machine tool including the workpiece based on first measurement data obtained from the first datum measurement means and second measurement data obtained from the second datum measurement means; A control device for a machine tool comprising:

8. 8. A machine tool control device according to claim 7, further comprising a datum quality determining means for determining whether the shape accuracy of the datum is good or bad based on the first measurement data.

9. 9. The control device for a machine tool according to claim 7, further comprising measurement data abnormality determination means for determining an abnormality in the second measurement data based on the first measurement data and the second measurement data.

10. a correction value generating means for calculating a correction value for correctively controlling each of the linear axes based on the error estimated value of the workpiece or the machine tool including the workpiece estimated by the error estimating means; a correction control means for correctively controlling each of the linear axes using the correction value; 10. The control device for a machine tool according to claim 7, further comprising:

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