JP2023084538A - ERROR ESTIMATION METHOD IN MACHINE TOOL, CONTROL DEVICE FOR MACHINE TOOL - Google Patents

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 The present disclosure relates to a method of estimating an error of a workpiece or a machine tool including the workpiece in a machine tool, and a machine tool control device for realizing the error estimation method.

Due to environmental temperature, self-heating, and processing heat, components of machine tools and workpieces are thermally deformed, causing positioning errors, ie, thermal displacement, with respect to command positions. If the workpiece is machined in the presence of thermal displacement, a machining error occurs with respect to the target shape, which poses a problem. For this reason, many correction techniques for thermal displacement have been devised so far.
For example, Patent Documents 1 to 3 disclose methods of estimating and correcting the thermal displacement of a workpiece from the linear expansion coefficient and temperature of the components of the machine tool and the workpiece.
In Patent Document 4, a plurality of workpieces are machined while measuring the temperature of the machine tool in advance, and the dimensions of the machined plurality of workpieces are measured with a measuring instrument. A method of correction using the relationship between temperature and the corresponding dimensional error is shown.
Patent Literatures 5 and 6 disclose a method of mounting a reference gauge with known dimensions on a table or a jig, measuring with a touch probe, and correcting thermal displacement based on the measured dimensional error.

JP 2006-116654 A JP 2006-281335 A JP 2012-187683 A JP-A-2005-52917 JP 2006-212765 A JP 2018-30195 A

It is difficult to know the exact values of linear expansion coefficients of machine tool components and workpieces. The value of the coefficient of linear expansion presented by the manufacturer has a certain tolerance, and if this value is used to estimate the thermal displacement, an estimation error within the tolerance occurs. For example, in the case of a workpiece with a coefficient of linear expansion of (10±1)×10 ⁻⁶ K/m and a length of 2 m, an estimation error of as much as ±20 μm can occur.
On the other hand, in most cases, the temperature of an object is not uniform and has a distribution, and when heat is applied to a workpiece due to processing, the width of the temperature distribution of the workpiece widens. Therefore, when the temperature of the workpiece is locally measured using a temperature sensor and the thermal displacement is estimated from the linear expansion coefficient including the temperature and the above error, the estimation error becomes large.
Therefore, the methods of Patent Documents 1 to 3, in which thermal displacement is estimated using the linear expansion coefficient and temperature of the workpiece, have a problem of estimation error.
In the method of Patent Document 4, it is necessary to machine a plurality of reference workpieces and separately measure their dimensions. There is a problem that it is necessary to perform many processes, and that it takes a lot of labor and time. Furthermore, it can only be applied to mass-produced parts that can be mass-produced in a short time, and is not suitable for parts processing with a small production volume.
In the method of Patent Document 5, since the correction is performed based on the reference measurement results applied to the low-expansion material, if the temperature of the machine is not 20 ° C. (the reference temperature of the coefficient of linear expansion), There is a problem that the error is due to the expansion and contraction of the machine. Moreover, it does not correspond to the thermal displacement of the workpiece.
In the method of Patent Document 6, since the reference gauge made of the same material as the workpiece is measured and corrected, no error occurs due to the environmental temperature, but an error occurs when the reference gauge and the workpiece are not at the same temperature. There is

Therefore, the present disclosure is an error estimation method in a machine tool that can reduce the effects of uneven thermal displacement and strain due to the temperature distribution of the workpiece and obtain a highly accurate workpiece with respect to the target size and shape. , and a control device for a machine tool.

In order to achieve the above object, a first configuration of the present disclosure has a spindle on which a tool is mounted and rotatable, a table on which a workpiece can be fixed, and three or more rectilinear axes, the table By controlling the relative position of the spindle with respect to the workpiece, it is possible to machine the workpiece fixed to the table using the tool attached to the spindle, and using the position measurement sensor attached to the spindle, A method for estimating an error of a workpiece or a machine tool including the workpiece in a machine tool capable of measuring the position and shape of the workpiece.
A first configuration includes an accuracy stability confirmation step for confirming that the machine tool and the workpiece are in an accurate and stable state;
a datum machining step of machining a datum, which serves as a reference for measurement, at a predetermined position of the workpiece while the machine tool and the workpiece are stable in accuracy;
a first datum measurement step of measuring the datum with the position measurement sensor in a state in which the machine tool and the workpiece are accurately stabilized;
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;
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, an error of the workpiece or the machine tool including the workpiece is calculated. and an estimating error estimation step.
In the present disclosure, "the state in which the machine tool and the workpiece are stabilized with accuracy" refers to temperature information from temperature sensors installed in each part of the machine tool, temperature sensors installed in the workpiece, and Based on various information that can be obtained from the workpiece or machine tool and affects thermal displacement, such as operation information, presence or absence of cutting water discharge, discharge time, etc., it can be estimated that the accuracy change of the machine tool and workpiece is small. . The estimation that the accuracy change is small is diagnosed by comparing each piece of information with a predetermined threshold value or comparing it with average data over a predetermined period of time, for example.
Another aspect of the first configuration is that in the above configuration, before the datum processing step, the position measurement sensor is used to measure the accuracy master placed on the table, and the measurement result is used to measure the machine accuracy is further performed by a machine precision calibration step for calibrating the
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 executed before the first datum measurement step. and
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 executed before the second datum measurement step. and
Another aspect of the first configuration is that in the above configuration, after the first datum measurement step, a datum quality determination step of determining quality of shape accuracy of the datum based on the first measurement data is performed, and If the determination result in the step is negative, the datum processing step is redone.
According to another aspect of the first configuration, in the above configuration, after the second datum measuring 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. and, if the determination result in this step is abnormal, the second datum measurement step is redone.

In order to achieve the above object, a second configuration of the present disclosure has a spindle on which a tool is mounted and rotatable, a table on which a workpiece can be fixed, and three or more rectilinear axes, the table By controlling the relative position of the spindle with respect to the workpiece, it is possible to machine the workpiece fixed to the table using the tool attached to the spindle, and using the position measurement sensor attached to the spindle, The control device is provided in a machine tool capable of measuring the position and shape of the workpiece, and estimates an error of the workpiece or the machine tool including the workpiece.
A second configuration includes datum setting means for setting a datum as a measurement reference for machining on the workpiece;
Accuracy stability determination means for determining whether the machine tool and the workpiece are in an accurate stable state;
A datum for processing the datum set by the datum setting means at a predetermined position on the workpiece in a state in which the accuracy stability determining means determines that the machine tool and the workpiece are stable in accuracy. a processing means;
a first datum measuring means for measuring the datum with the position measuring sensor in a state in which the accuracy stability determining means determines that the machine tool and the workpiece are stable in accuracy;
a second datum measuring means for measuring the datum with the position measuring sensor immediately before or during machining of the workpiece into a target shape;
Based on the first measurement data obtained from the first datum measuring means and the second measurement data obtained from the second datum measuring means, an error of the workpiece or the machine tool including the workpiece is calculated. and error estimating means for estimating.
Another aspect of the second configuration is the above configuration, further comprising datum quality determination means for determining quality of shape accuracy of the datum based on the first measurement data.
Another aspect of the second configuration is the above configuration, further comprising measurement data abnormality determination means for determining abnormality of the second measurement data based on the first measurement data and the second measurement data. Characterized by
According to another aspect of the second configuration, in the above configuration, correction control is performed on each of the linear axes based on the estimated error value of the workpiece or the machine tool including the workpiece estimated by the error estimating means. a correction value generating means for calculating a correction value for
correction control means for correcting and controlling each of the rectilinear axes using the correction value.

According to the present disclosure, by measuring the datum machined on the workpiece and correcting the machine accuracy, it is possible to reduce the influence of uneven thermal displacement and strain due to the temperature distribution of the workpiece, and the target dimension・It is possible to obtain workpieces with high precision for their shapes.

1 is a schematic diagram of a three-axis control machining center; FIG. FIG. 4 is a schematic diagram of measurement of a ball array with a touch probe; FIG. 4 is a schematic diagram of a datum machined into a workpiece; 4 is a flow chart of an error estimation method; FIG. 5 is a flowchart showing details of step S0 in FIG. 4; FIG. FIG. 5 is a flowchart showing details of step S3 in FIG. 4; FIG. FIG. 5 is a flowchart showing details of step S4 in FIG. 4; FIG. 1 is a schematic diagram of a numerical controller; FIG.

Embodiments of the present disclosure will be described below with reference to the drawings.
FIG. 1 is a schematic diagram of a three-axis control machining center, which is an example of a machine tool. A spindle head 2 on which a tool 4 can be mounted and a rotatable spindle is mounted is capable of translational movement with two degrees of freedom with respect to the bed 1 by the Y-axis and the Z-axis which are translational axes and are orthogonal to each other. A table 3 capable of fixing a workpiece 5 is capable of translational movement with one degree of freedom with respect to the bed 1 by means of the Y-axis, which is a translational axis and is perpendicular to the X-axis and the Z-axis. Therefore, the spindle head 2 is capable of translational motion with three degrees of freedom with respect to the table 3 . The X, Y, and Z feed axes are driven by servomotors and feed mechanisms (not shown) controlled by a numerical controller 7, which will be described later. A motor (not shown) controlled by the numerical controller 7 rotates the main shaft. The workpiece 5 is fixed to the table 3, the tool 4 is mounted on the spindle head 2 and rotated, and each feed axis is controlled to control the relative positions of the workpiece 5 and the tool 4. Can be processed.

FIG. 2 is a schematic diagram of a touch probe that is an example of a position measurement sensor. The touch probe 6 is a sensor that emits a trigger signal when the ball at the tip of the stylus is brought into contact with the object to be measured. Using each acquired current position and the touch probe calibration value, the position of the touch point is determined. A touch probe 6 is mounted on the spindle head 2, and each feed axis is controlled so that the stylus ball of the touch probe 6 contacts the object to be measured placed on the table 3. position can be measured.

FIG. 4 shows a flowchart of an error estimation method that is an example of the first configuration of the present disclosure.
First, in step (hereinafter simply referred to as "S") 0, the machine accuracy is calibrated based on the accuracy master (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).
Workpiece or machine tool such as temperature sensors installed in each part of the machine tool in FIG. From the various information that can be obtained from and that affects thermal displacement, it is estimated whether the accuracy change of the machine or workpiece is small (for example, compared with a predetermined threshold value, or compared with the average data over a predetermined period of time), Diagnose whether the accuracy is stable.
In S2, while the accuracy of the machine and workpiece is stable, a plurality of datums that serve as measurement references are machined on the workpiece (datum machining step).

FIG. 3 is a schematic diagram of an example in which a plurality of hole-shaped hole datums 11 are machined on the workpiece 5. As shown in FIG.
A plurality of hole datums 11 are machined at locations that do not affect the final target shape of the workpiece 5, and in this embodiment are machined parallel to the X-axis or the Y-axis. However, if the target shape has a part that can be used as a datum, part of it may be used as the datum. In this embodiment, the shape of the datum is a hole shape, but it may be a pocket shape, a cylinder shape, a prism shape, a surface, or the like, and the size may be set so that the 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). Since the diagnosis method is the same as that of S1a, the explanation is omitted. However, S1b may be omitted if it can be separately determined that the accuracy of the machine or workpiece is stable.

In S3, a plurality of hole datums 11 machined on the workpiece 5 are measured by the touch probe 6 while the accuracy of the machine and workpiece is stable, and stored as initial datum information. FIG. 6 shows details of S3.
In S3-1, the touch probe 6 is calibrated in order to reduce the uncertainty of the measurement accuracy of the touch probe 6 (first position measurement sensor calibration step). As a calibration method, an existing technique such as acquiring a correction value using a reference device such as a reference sphere can be used. However, if it can be 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 or workpiece is stable, the center positions and bottom heights of the cylindrical surfaces of the plurality of hole datums 11 machined in S2 are measured using the touch probe 6. (first datum measurement step). At S3-3, which will be described later, the diameter, roundness, and surface roughness are also measured at the same time as information for judging whether the measurement result of the center position is good or bad.

Here, when the shape of the datum is a pocket, the center position, bottom height, pocket width, surface roughness, etc. of the pocket are to be measured. In the case of a cylinder shape, the measurement targets include the center position of the cylinder, the height of the upper surface, the roundness, the surface roughness, and the like. In the case of a prismatic shape, the measurement targets include the center position of the prism, the height of the upper surface, the width between two sides, the surface roughness, and the like. In the case of the surface shape, the position of the surface, the surface roughness, etc. are to be measured.
In S3-3, the quality of the measurement result (shape accuracy) of the hole datum 11 measured in S3-2 is determined (datum quality determination step). In the case of the hole datum 11, if the values of the diameter, roundness, and surface roughness are larger than preset threshold values, it is determined that the hole datum 11 is defective. If it is determined that the machining is defective, the process returns to S1a to diagnose the accuracy state, and then the hole datum 11 is machined and measured again from S2 onward.
For each hole datum 11, the measurement in S3-2 and the pass/fail judgment in S3-3 may be performed as a set.
In S3-4, the measured values of the center position, diameter, and roundness of the plurality of hole datums 11 measured in S3-2 are stored as initial datum information (first measurement data).

In S4, a plurality of hole datums 11 machined on the workpiece 5 are measured by the touch probe 6 immediately before or during machining of the workpiece 5, and stored as machining datum information. FIG. 7 shows details of S4.
In S4-1, the touch probe 6 is calibrated in order to reduce the uncertainty of the measurement accuracy of the touch probe 6 (second position measurement sensor calibration step). Since the calibration method is the same as in S3-1, the description is omitted. However, if it can be determined that there is no problem with the measurement accuracy of the touch probe 6, this step may be omitted.
In S4-2, the center positions and bottom heights of the cylindrical surfaces of the plurality of hole datums 11 on the workpiece 5 are measured using the touch probe 6 immediately before or during machining of the workpiece 5 (second 2 datum measurement step).
In S4-3, the measurement result (second measurement data) of the hole datum 11 measured in S4-2 is judged to be abnormal (measurement data abnormality judgment step). In the case of the hole-shaped hole datum 11, the diameter and roundness of the measurement results are compared with each of the first measurement data stored in S3-4, and if each difference value is greater than a preset threshold value Then, it is determined that the second measurement data is abnormal. If it is judged to be abnormal, it is cleaned by air blow or the like, and the measurement of S4-2 is performed again.
Here, 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 measured values of the center position, diameter, and roundness of the plurality of hole datums 11 measured in S4-2 are stored as machining datum information.

In S5, the initial datum information and the machining datum information are used to identify the error of the workpiece or the combined error of the machine tool and the workpiece (error estimation step). In the case of the hole datum 11 of the workpiece 5 in FIG. 3, it is possible to identify the X-axis positioning error and straightness and the Y-axis positioning error and straightness that include the error components of the workpiece.
By performing S4 and S5 as necessary during machining of the workpiece 5, estimating the error, performing correction control based on the identified error, and machining, if there is thermal deformation of the workpiece. However, it can be processed with high precision.

Next, details of S0 will be described with reference to the flowchart of FIG.
In S0-1, it is diagnosed whether the machine accuracy is stable. Since the diagnosis method is the same as that of S1a, the explanation is omitted.
In S0-2, the touch probe 6 is calibrated in order to reduce the uncertainty of the measurement accuracy of the touch probe 6. FIG. Since the calibration method is the same as in S3-1, the description is omitted.
In S0-3, the touch probe 6 measures a calibrated precision master whose dimensions and the like are known. FIG. 2 shows a ball array 10 having a plurality of spheres with calibrated center positions as an example of an accuracy master. Other accuracy masters include hall gauges with calibrated center positions and multiple holes, step gauges and block gauges with calibrated face-to-face distances, block gauges, straightness masters, square masters, and the like. Measure the required accuracy master according to the error of the machine you want to calibrate.

In S0-4, machine errors are identified based on the measurement result of the accuracy master in S0-3. For example, in the ball array 10, the positioning error and straightness of each axis can be identified by using the results of the measurement performed in parallel with each feed axis. Moreover, the perpendicularity between each two axes can be identified using the result of measuring by setting a right angle master parallel to the plane formed by the two feed axes.
In S0-5, the machine error identified in S0-4 is converted into a correction parameter, and the correction parameter is set in the numerical control device . By performing correction control using these correction parameters, machining and touch probe measurement can be performed while eliminating the effects of machine errors. Here, as a method of reflecting the identified error in machining and measurement, the identified error is set in the parameters of the CAM software that generates the program for machining and measurement, and the program generated by this CAM software is used for machining. or measurements may be taken. Also, the identified error may be directly reflected in the operating program.

FIG. 8 is a schematic diagram of the numerical controller 7 of the machine tool that implements the error estimation method. This numerical control device 7 is an example of a control device for a machine tool having the second configuration of the present disclosure.
The numerical controller 7 includes accuracy stability determination means 20, datum setting means 21, datum command generation means 22, axis control means 23, measured value acquisition means 24, initial datum quality determination means 25, and initial datum information. It comprises storage means 26 , machining datum abnormality determination means 27 , machining datum information storage means 28 , error identification calculation means 29 , and correction value generation means 30 .
Accuracy stability determination means 20 determines whether or not the accuracy of the machine tool and workpiece 5 in S1a and S1b described above is stable.
The datum setting means 21 can set information such as the type, size, number, and machining position of datums to be machined on the workpiece, and these information are stored.
Based on the datum information set and stored by the datum setting means 21 , the datum command generation means 22 generates a command for processing the datum and a command for measuring the datum with the touch probe 6 .

Based on the commands generated by the datum command generating means 22, the axis control means 23 controls the processing of the datum of S2 and the operation of the feed axis for the measurement of S3-2 and S4-2. Also, each feed axis can be corrected and controlled based on the correction value generated by the correction value generating means 30 . The axis control means 23 and the datum command generation means 22 are examples of the datum processing means of the present disclosure.
The measured value acquiring means 24 acquires measured values based on the detected values of the detectors of each feed axis (not shown) when the touch probe 6 is brought into contact with the object to be measured. The measured value acquisition means 24 and the axis control means 23 are examples of the first and second datum measurement means of the present disclosure.

The initial datum quality determination means 25 performs quality determination in S3-3 on the initial datum information acquired by the measured value acquisition means 24 in S3-2. The initial datum quality determination means 25 is an example of the datum quality determination means of the present disclosure.
The initial datum information storage means 26 stores initial datum information.
Based on the initial datum information stored in the initial datum information storage means 26, the machining datum abnormality determination means 27 determines S4 -3 abnormality judgment is performed. The 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.

The error identification calculation means 29 identifies the workpiece as in S5 based on the initial datum information recorded in the initial datum information storage means 26 and the machining datum information recorded in the machining datum information storage means 28. or the error between the machine tool and the workpiece. This error identification calculation means 29 is the error estimation means of the present disclosure.
The correction value generation means 30 converts the workpiece error identified by the error identification calculation means 29 or the error between the machine tool and the workpiece into a correction value for each feed axis.
By performing correction control by the axis control means 23 based on this correction value, it is possible to process or measure the workpiece while canceling the error between the workpiece or the machine tool and the workpiece. This axis control means 23 is an example of the correction control means of the present disclosure.

The error estimating method and numerical control device 7 of the above embodiment machine the hole datum 11 on the workpiece 5 and measure the hole datum 11 with the touch probe 6 while the machine tool and the workpiece 5 are accurately stabilized. After obtaining the first measurement data, the hole datum 11 is again measured by the touch probe 6 immediately before or during machining of the workpiece 5 into the target shape to acquire the second measurement data, and the obtained first, An error of the workpiece 5 or the machine tool including the workpiece 5 is estimated based on the 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 uneven thermal displacement and strain due to the temperature distribution of the workpiece 5 . Therefore, it is possible to obtain a highly accurate workpiece 5 with respect to the target size and shape.

In particular, before machining the hole datum 11, the touch probe 6 is used to measure the ball array 10 placed on the table 3, and the measurement results are used to calibrate the machine accuracy, so the influence of machine error is minimized. Machining of the hole datum 11 and measurement by the touch probe 6 can be performed by excluding it.
In addition, since the touch probe 6 is calibrated using a reference device before each datum measurement step, the measurement accuracy of the touch probe 6 can be improved.
Furthermore, after the first datum measurement step, it is determined whether the shape accuracy of the first measurement data is good or bad. Inaccurate error estimation based on single measurement data can be avoided.
Similarly, after the second datum measurement step, it is determined whether there is an abnormality in the second measurement data based on the first measurement data and the second measurement data. error estimation based on

DESCRIPTION OF SYMBOLS 1--bed, 2--spindle, 3--table, 4--tool, 5--work piece, 6--touch probe, 7--numerical controller, 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 Measured value acquisition means 25 Initial datum quality determination means 26 Initial datum information storage means, 27 Datum abnormality determination means during machining, 28 Datum information storage means during machining, 29 Error identification calculation means, 30 Correction value generation means.

Claims (10)

It has a rotatable spindle with a tool mounted thereon, a table on which a workpiece can be fixed, and three or more rectilinear axes, and is fixed to the table by controlling the relative position of the spindle with respect to the table. A machine tool capable of machining a workpiece using a tool attached to the spindle and capable of measuring the position and shape of the workpiece using a position measurement sensor attached to the spindle, A method of estimating an error of a machine tool including an object or the workpiece, comprising:
an accuracy stability confirmation step of confirming that the machine tool and the workpiece are in an accurate stable state;
a datum machining step of machining a datum, which serves as a reference for measurement, at a predetermined position of the workpiece while the machine tool and the workpiece are stable in accuracy;
a first datum measurement step of measuring the datum with the position measurement sensor in a state in which the machine tool and the workpiece are accurately stabilized;
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;
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, an error of the workpiece or the machine tool including the workpiece is calculated. an estimated error estimation step;
A method for estimating an error in a machine tool, characterized by performing Before the datum machining step, the position measurement sensor is used to measure the accuracy master placed on the table, and a machine accuracy calibration step is further executed to calibrate the machine accuracy using the measurement result. The error estimation method in the machine tool according to claim 1. 3. The error in the machine tool according to claim 1, further comprising: before the first datum measuring step, a first position measuring sensor calibrating step of calibrating the position measuring sensor using a reference device. estimation method. 4. The machine tool according to any one of claims 1 to 3, wherein a second position measuring sensor calibrating step of calibrating said position measuring sensor using a reference device is further executed before said second datum measuring step. A method of error estimation in machines. After the first datum measurement step, a datum quality determination step of determining quality of the shape accuracy of the datum based on the first measurement data is performed. 5. An error estimation method for a machine tool according to claim 1, wherein the machining step is redone. After the second datum measurement step, a measurement data abnormality determination step is performed for determining whether or not there is an abnormality in the second measurement data based on the first measurement data and the second measurement data. 6. The error estimating method for a machine tool according to claim 1, wherein the second datum measuring step is redone when the determination result is abnormal. It has a rotatable spindle with a tool mounted thereon, a table on which a workpiece can be fixed, and three or more rectilinear axes, and is fixed to the table by controlling the relative position of the spindle with respect to the table. A machine tool capable of machining a workpiece using a tool attached to the spindle and capable of measuring the position and shape of the workpiece using a position measurement sensor attached to the spindle, A control device for estimating an error of the workpiece or the machine tool including the workpiece,
datum setting means for setting a datum that serves as a measurement reference for machining on the workpiece;
Accuracy stability determination means for determining whether the machine tool and the workpiece are in an accurate stable state;
A datum for processing the datum set by the datum setting means at a predetermined position on the workpiece in a state in which the accuracy stability determining means determines that the machine tool and the workpiece are stable in accuracy. a processing means;
a first datum measuring means for measuring the datum with the position measuring sensor in a state in which the accuracy stability determining means determines that the machine tool and the workpiece are stable in accuracy;
a second datum measuring means for measuring the datum with the position measuring sensor immediately before or during machining of the workpiece into a target shape;
Based on the first measurement data obtained from the first datum measuring means and the second measurement data obtained from the second datum measuring means, an error of the workpiece or the machine tool including the workpiece is calculated. error estimating means for estimating;
A control device for a machine tool, comprising: 8. The control device for a machine tool according to claim 7, further comprising datum quality determination means for determining quality of shape accuracy of said datum based on said first measurement data. 9. The machine tool according to claim 7, further comprising measurement data abnormality determination means for determining abnormality of said second measurement data based on said first measurement data and said second measurement data. Control device. correction value generating means for calculating a correction value for correcting and controlling each of the linear axes based on the estimated error value of the workpiece or the machine tool including the workpiece estimated by the error estimating means;
correction control means for correcting and controlling each of the rectilinear axes using the correction value;
10. The machine tool control device according to any one of claims 7 to 9, further comprising:

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