JP2009251621A - Reference position correction device for machine tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the reference position correction device of a machine tool for improving working precision by reducing any measurement error which generates due to attachment of any foreign matter to a reference hole or a touch sensor. <P>SOLUTION: This reference position correction device includes: a repair tool 3 fixed to a table 16, and equipped with a first reference hole 31 and a second reference hole 32 whose distances are already known; a touch sensor 2 mounted on a main shaft 15, and configured to measure the positions of the reference holes 31 and 32; and an NC device 17 for automatically correcting the deviation of the relative positions of the main shaft 15 and a workpiece 5 based on the position of the first reference hole 31 measured by the touch sensor 2. The NC device 17 calculates an inter-reference hole distance between the first reference hole 31 and the second reference hole 32 based on the measurement result of the touch sensor 2, and determines the presence/absence of the correction of the reference position based on the comparison result of the calculated inter-reference hole distance and a preliminarily set allowable range. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a reference position correcting apparatus for a machine tool.

  In machining by a machine tool such as a machining center, the components that make up the machine tool due to the rotation of the spindle, the heat generated by the motor accompanying the axis feed of the table, saddle and spindle head, and changes in the environmental temperature at the machine tool installation location Thermal displacement occurs. Therefore, even if the relative position between the spindle and the table is once set as the reference position, the relative position between the spindle and the table may be shifted due to the thermal displacement described above. Such a shift in the relative position between the spindle and the table causes a machining error, which may lead to a reduction in machining accuracy.

  For such problems, conventionally, a touch sensor is mounted on the spindle of a machine tool, while a reference part (for example, a protruding part) is provided on the table side, and the position of the reference part is measured using the touch sensor. A technique for correcting a shift in the relative position between the spindle and the table based on the measurement result is known (see, for example, Patent Documents 1 to 4).

Japanese Examined Patent Publication No. 4-26975 Japanese Patent Publication No. 6-41088 JP-A-60-239602 JP-A 61-103756

  FIG. 6 shows, as an example, a front view of a jig used when correcting a shift in the relative position between the spindle and the table. The jig 103 shown in FIG. 6 is a block body made of metal, and is provided with a single reference portion (see FIG. 6) whose position can be measured by a touch sensor attached to a main shaft on one side surface 103a. 6 includes a hole portion 131 whose cross section is circular and whose axial direction is orthogonal to the side surface 103a (hereinafter referred to as a reference hole).

  Such a jig 103 is fixed on a table (not shown) such that the axial direction of the reference hole 131 is parallel to the axial direction of the main shaft (not shown), in other words, the side surface 103a faces the main shaft. When exchanging the workpiece, a touch sensor is attached to the spindle to measure the position of the reference hole 131, and the position obtained as a result of the measurement by the touch sensor in the reference position correction means (for example, NC device) is used as the reference position of the table. As a result, the deviation of the relative position between the spindle and the table is corrected.

  However, when correcting the displacement of the relative position between the spindle and the table using the jig 131 as described above, for example, the touch sensor is relatively moved with respect to the reference hole 131 in the x-axis direction and the y-axis direction shown in the figure. The position of the reference hole 131 is measured by reading the position (for example, points A, B, C, and D in the figure) where the contact point of the touch sensor contacts the inner wall of the reference hole 131 by the reference position correcting means. The center position O obtained based on the read value is recognized as the position of the reference hole 131.

  However, in machining a workpiece, foreign matter such as chips generated by cutting the workpiece may adhere to the reference hole 131 or the touch sensor probe (hereinafter referred to as the reference hole 131). For example, when the chips 4 adhere to the bottom of the reference hole 131 as shown in FIG. 6, the positions measured by the touch sensor are points A, B, C, and D ′ in the figure, and the measurement result is obtained. The center position O ′ of the reference hole 131 is shifted from the actual center position O. Such a measurement error may cause a reduction in machining accuracy.

  Therefore, in the conventional reference position correction apparatus, relative displacement with respect to the main axis of the center O ′ of the reference hole 131 measured using the touch sensor is performed in order to prevent a measurement error due to adhesion of foreign matter to the reference hole 131 or the like. A threshold is set for the quantity.

  That is, if the relative displacement of the center O ′ of the reference hole 131 obtained by measurement with respect to the main axis is smaller than the threshold value, the measurement result is regarded as normal, and the position of the center O ′ of the reference hole 131 obtained as a result of the measurement is a table When the relative displacement amount of the center O ′ of the reference hole 131 with respect to the main axis is larger than a threshold value, foreign matter adheres to the reference hole 131 or the like. It is considered to be.

  However, as described above, as indicated by a broken line in FIG. 7, the thermal displacement of the bed or the like is determined so that the relative displacement between the spindle and the table caused by the thermal displacement of the bed or the like is not recognized as an abnormal value. It is necessary to set the value after taking into consideration.

Therefore, for example, as shown at d ₁ in FIG. 7, when the relative displacement between the spindle and the table caused by the foreign matter adhering to the reference hole 131 etc. is larger than the threshold value, the foreign matter adhering to the reference hole 131 etc. is detected. However, as shown by d ₂ in the figure, if the relative displacement between the spindle and the table caused by foreign matter adhering to the reference hole 131 or the like is smaller than a threshold value, this may not be detected. .

  In other words, depending on the state of thermal displacement of the bed or the like, there is a possibility that the measurement may vary, for example, the adhesion of foreign matter to the reference hole 131 or the like may or may not be detected. Further, when the adhesion of foreign matter cannot be detected, there is a possibility that the processing accuracy may be lowered, and there is a need for improvement.

  Accordingly, an object of the present invention is to provide a machine tool reference position correction apparatus capable of reducing measurement errors caused by foreign matters adhering to a reference hole or a touch sensor and improving machining accuracy. And

  A machine tool reference position correction apparatus according to a first aspect of the invention for solving the above-described problem is a reference means fixed to a table of a machine tool and having a first reference part and a second reference part having a known distance; Reference portion position measuring means mounted on the spindle of the machine tool and measuring the position of the reference portion, and the spindle and the table based on the position of the first reference portion measured by the reference portion position measuring means. A reference position correction device for a machine tool, comprising a reference position correction means for correcting a relative position shift, wherein the reference position correction means is based on a result measured by the reference portion position measurement means. Calculating a distance between the reference parts between the reference part and the second reference part, and determining whether or not the reference position is corrected based on a result of comparing the calculated distance between the reference parts and a preset allowable range. West It is characterized in.

  In a machine tool reference position correction apparatus according to a second invention for solving the above-mentioned problems, in the first invention, the reference position correction means compares the distance between the reference portions and the allowable range. Based on the above, when the displacement amount of the distance between the reference portions is equal to or smaller than a preset threshold value, the reference position is corrected, and when the displacement amount of the distance between the reference portions is larger than the threshold value, the operation of the machine tool is stopped. It is characterized by doing.

  According to a third aspect of the present invention, there is provided a machine tool reference position correction apparatus according to the first aspect, wherein the reference position correction means compares the distance between the reference portions and the allowable range. If the displacement amount of the distance between the reference portions is equal to or less than a preset threshold value, the reference position is corrected. On the other hand, if the displacement amount of the distance between the reference portions is larger than the threshold value, the reference portion position measuring means The position measurement of the reference part is performed again according to the above.

  According to a fourth aspect of the present invention, there is provided a machine tool reference position correction apparatus according to a fourth aspect of the invention, wherein the first reference portion and the second reference portion are arranged in the vertical and horizontal directions. It arrange | positions in a mutually different position, It is characterized by the above-mentioned.

  According to a fifth aspect of the present invention, there is provided a machine tool reference position correcting apparatus according to the first invention, wherein the first reference portion and the second reference portion are respectively on the same surface of the reference means. Reference holes formed in a circular shape in cross-section and having different diameters.

  According to the reference position correcting apparatus for a machine tool according to the first aspect described above, the reference means fixed to the table of the machine tool and having a first reference portion and a second reference portion whose distances are known, and the machine tool Reference position measuring means mounted on the spindle for measuring the position of the reference section, and a relative position shift between the spindle and the table based on the position of the first reference section measured by the reference position measuring means. A reference position correction device for a machine tool comprising: a reference position correction means for correcting the reference position correction means, wherein the reference position correction means is based on a result measured by the reference portion position measurement means. Since the distance between the reference parts with the two reference parts is calculated, and whether or not the reference position is corrected is determined based on the result of comparing the calculated distance between the reference parts and a preset allowable range. Standard And foreign matter adhering to the reference section position measuring means it is possible to detect with high accuracy, it is to reduce the occurrence of measurement errors to improve the machining accuracy.

  According to the machine tool reference position correction apparatus according to the second aspect of the invention, the reference position correction means is configured to determine the distance between the reference parts based on a result of comparing the distance between the reference parts and the allowable range. The reference position is corrected when the amount of displacement is less than or equal to a preset threshold value, while the operation of the machine tool is stopped when the amount of displacement of the distance between the reference portions is greater than the threshold value. Even if a foreign object adheres to the probe of the instrument and an abnormal state is detected, if the foreign object is naturally removed afterwards, a normal value can be obtained by measuring again. Therefore, it is not necessary to stop the operation and the convenience is improved.

  According to the machine tool reference position correction apparatus of the third aspect of the invention, the reference position correction means is configured to determine the distance between the reference parts based on a result of comparing the distance between the reference parts and the allowable range. When the amount of displacement is less than or equal to a preset threshold, the reference position is corrected. On the other hand, when the amount of displacement of the distance between the reference portions is larger than the threshold, the position of the reference portion is measured again by the reference portion position measuring means. As a result, even if a foreign object adheres to the probe of the reference or contact-type measuring means and an abnormal state is detected, if the foreign object is naturally excluded after that, measure again. Since a normal value is obtained, there is no need to stop the operation unnecessarily, and convenience is improved.

  Further, according to the machine tool reference position correction apparatus according to the fourth invention, the first reference part and the second reference part are arranged at mutually different positions with respect to the vertical direction and the horizontal direction, Adherence of foreign matter to the reference portion or the reference portion position measuring means can be detected with high accuracy, and the processing accuracy can be improved.

  According to the machine tool reference position correction apparatus of the fifth invention, the first reference part and the second reference part are each formed in a circular cross-sectional view on the same surface of the reference means. In addition, since the diameters are different from each other, it is possible to detect the adhesion of foreign matter to the reference hole or the reference portion position measuring means with high accuracy, and to improve the processing accuracy.

  Embodiments of the present invention will be described below in detail with reference to the drawings.

  Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings. 1 is an overall configuration diagram of a machine tool to which a reference position correction apparatus according to the present embodiment is applied, FIG. 2 is a front view of a jig applied to the reference position correction apparatus for a machine tool according to the present embodiment, and FIG. FIG. 4 is a flowchart showing the flow of a reference position correction process performed by the machine tool reference position correction apparatus according to the present embodiment. FIG. 4 is an explanatory diagram showing an example of threshold values set in the machine tool reference position correction apparatus according to the present embodiment. It is. In this embodiment, the machine tool reference position correction apparatus according to the present invention is applied to a horizontal machining center.

  As shown in FIG. 1, in this embodiment, the machine tool 1 includes a guide 12 provided on a bed 11, with a spindle 15 supported on a column 12 placed on the bed 11 via a saddle 13 and a spindle head 14. A table 16 is supported on the surface 11a. Further, a touch sensor 2 as a reference portion position measuring means is detachably attached to the tip of the spindle 15, and a jig 3 as a reference means to which the workpiece 5 is attached is fixed on the table 16.

  The spindle 15 is rotatably supported by the spindle head 14, and the spindle head 14 is supported by the saddle 13 so as to be movable along the vertical direction (y-axis direction shown in FIGS. 1 and 2). It is supported so as to be movable along the left-right direction (x-axis direction shown in FIG. 2). As a result, the main shaft 15 is configured to be able to rotate a tool (not shown) attached to the tip of the main shaft 15 and move it in the x-axis direction and the y-axis direction.

  On the other hand, the table 16 is supported by the guide surface 11a so as to be movable in the front-rear direction (in the z-axis direction in FIG. 1) by axial feed, and thereby the workpiece fixed to the table 16 via the jig 3 is supported in the z-axis direction. It is comprised so that it can be moved to.

  In such a machine tool 1, the relative positions of the spindle 15 and the table 16 are changed by controlling the movement of the table 16, the saddle 13 and the spindle head 14 according to a command from the NC device 17, and are fixed to the table 16. The workpiece is processed.

  Further, the touch sensor 2 has a measuring element 2a at the tip thereof, the measuring element 2a is brought into contact with the object to be measured, and the NC device 17 reads the position where the measuring element 2a is in contact with the object to be measured. It is configured to detect the position.

Further, the jig 3 is a metal (for example, Invar) member formed in a block shape, and a first reference hole 31 as a first reference portion and a second reference portion as a second reference portion on one side surface 3a. A second reference hole 32 is recessed. As shown in FIG. 2, each of the first reference hole 31 and the second reference hole 32 has a circular cross section, and is configured such that its axial direction is substantially orthogonal to the side surface 3a. Further, the diameter of the second reference hole 32 is smaller than the diameter of the first reference hole 31, and the positions of the centers O ₁ and O ₂ have distances in the x-axis direction and the y-axis direction. The jig 3 is fixed to the table 16 so that the side surface 3 a faces the main shaft 15, in other words, the side surface 3 a is orthogonal to the axial direction of the main shaft 15.

  Hereinafter, the flow of the reference position correction process performed using the reference position correction apparatus according to this embodiment will be described with reference to FIG.

  As shown in FIG. 3, when the reference position is corrected in the present embodiment, first, the first reference hole 31 and the second reference hole are mounted with the touch sensor 2 attached to the spindle 15 by an automatic tool change function or the like. 32 positions are measured (step S1).

Specifically, the table 16, the spindle 15 and the spindle 15 are positioned so that the probe 2 a of the touch sensor 2 is positioned in the first reference hole 31 by driving the table 16, the saddle 13 and the spindle head 14 with respect to the first reference hole 31. Then, the saddle 13 is driven to move the measuring element 2a in the x-axis direction in the first reference hole 31, and the inner wall of the first reference hole 31 and the measuring element 2a are in contact with each other (in this embodiment). Then, the positions of the points A ₁ and C ₁ are read by the NC device 17.

Furthermore, the spindle head 14 is driven to move the measuring element 2a in the y-axis direction in the first reference hole 31, and the position where the inner wall of the first reference hole 31 and the measuring element 2a are in contact with each other (point B in this embodiment). ₁ and D ₁ positions) are read by the NC unit 17. Similarly, the position of points A ₂ , B ₂ , C ₂ , D ₂ where the probe 2 a of the touch sensor 2 is in contact with the second reference hole 32 is read by the NC device 17.

When the measurement of the positions of the first reference hole 31 and the second reference hole 32 is completed, subsequently, in the reference position correction unit as the reference position correction means, for example, the NC device 17 having a calculation processing function, the first reference hole 31, The center position of the second reference hole 32 is calculated (step S2). Specifically, the calculation is performed by the calculation processing function of the NC device 17, and the position of the middle point o _ix (i = 1 or 2; the same applies hereinafter) between the point A _i and the point C _i , the point B _i and the point D _i. the position of the midpoint o _iy respectively calculated with a point is the result obtained _{O 1 (o 1x, o 1y} ), O 2 (o 2x, o 2y) a first reference hole 31, the second reference hole 32 is the center position.

After calculating the position of the center O ₁ of the first reference hole 31 and the position of the center O ₂ of the second reference hole 32, the distance d _x between the centers O ₁ and O _{2 in} the x-axis direction and the y-axis direction respectively. _{(= o 1x -o 2x),} d y (= o 1y -o 2y) the calculated respectively (step S3).

The distance d _x, After calculating the d _y, followed by these distances d _x, whether within tolerance d _y is set respectively in advance, specifically, the center O ₁ at normal temperature, O ₂ threshold S _x where x-axis direction of the distance x _0, y displacement relative axial distance y ₀ [Delta] d _x, the absolute value of [Delta] d _y are preset respectively between judges whether greater than S _y (step S4 ).

If the result of determination in step S4, the absolute value threshold S _x, respectively, is less than or equal S _y (No) is found position of the center O ₁ of the first reference hole 31 for example, in the NC apparatus 17 of the displacement amount [Delta] d _x, [Delta] d _y Is set as a reference position to correct the relative position (X value, Y value) between the spindle 15 and the table 16 (step S5), and the touch sensor 2 is replaced with a tool (not shown) using an automatic tool change function or the like. Machining of the workpiece 5 is started (step S6).

On the other hand, the result of determination in step S4, the displacement amount [Delta] d _x, the absolute value of either one but the threshold S _x of [Delta] d _y, is greater than S _y (Yes), the first reference hole 31, the second reference hole 32, Alternatively, the operation is stopped assuming that the chips 4 or the like are attached to the probe 2a of the touch sensor 2 (step S7).

For example, as shown in FIG. 2, when the chip 4 is attached to the first reference hole 31, the measurement of the first reference hole 31 by the touch sensor 2 is performed at points A ₁ , B ₁ , C _{1 in} FIG. , D ₁ ′, the position of the center point O ₁ ′ of the first reference hole 31 obtained is a position higher by Δy (for example, 40 μm) than the actual center point O ₁ . Accordingly, the distance d _y ′ between the centers of the first reference hole 31 and the second reference hole 32 calculated by the calculation processing function of the NC device 17 is Δy compared to the actual distance d _y between the centers. Only a large value.

On the other hand, the thermal displacement of the jig 3 caused by a change in temperature due to the coolant or a change in the environmental temperature at the place where the machine tool is installed is about 2 to 3 μm at most, although it depends on the material constituting the jig. Very few. Therefore, if the threshold _values S _x and S _y are set to about 5 μm, for example, it is possible to reliably detect the adhesion of foreign matter while taking into account the thermal displacement of the jig 3 being processed.

That is, according to the reference position correcting apparatus according to the present embodiment, the jig 3 is provided with the two reference holes 31 and 32 whose distances are known, and the absolute value of the displacement amount of the distance between the two reference holes 31 and 32. 4 is larger than the threshold _values S _x and S _y , the position of the reference hole measured by the touch sensor 2 is regarded as an abnormal value due to adhesion of foreign matter, etc., and as shown in FIG. The threshold _values S _x and S _y can be set so as to vary in accordance with the thermal displacement of the members constituting the machine tool 1 such as the bed 11. In other words, the threshold _values S _x and S _y can be set regardless of the measurement error due to the thermal displacement of the component of the machine tool.

Accordingly, as d ₂ shown in FIG. 4, generated by the attachment of foreign matter into the reference holes 31 and the like, the range of thermal displacement of the bed 11 and the like (e.g., in FIG. 4, the start of exercise - displacement between end of the exercise) Even if the displacement is small compared to the above, the displacement of the relative position between the spindle 15 and the table 16 can be corrected with high accuracy, and the machining error can be reduced.

Further, since the diameter of the first reference hole 31 and the diameter of the second reference hole 32 are different from each other, for example, the same size of swarf is formed at the bottom of the first reference hole 31 and the bottom of the second reference hole 32. Even if each of them adheres to each other, the distance d _y 'between the centers obtained as a result of measurement by the touch sensor 2 can be calculated as a value different from the actual distance d _y between the centers. Adhesion can be reliably detected.

  A second embodiment of the present invention will be described in detail with reference to the drawings. FIG. 5 is a flowchart showing the flow of the reference position correction process by the reference position correction apparatus for the machine tool according to the present embodiment. The present embodiment is partially different from the first embodiment described above in the processing performed by the reference position correction apparatus. The configuration of the apparatus is substantially the same as that shown in FIGS. 1 and 2 and described above. Hereinafter, the same members are denoted by the same reference numerals, and redundant description is omitted.

As shown in FIG. 5, the process of step S11 to step S16 is the same as the process of step S1 to step S6 shown in FIG. That is, first, the position of the first reference hole 31 and the second reference hole 32 is measured with the touch sensor 2 attached to the spindle 15 by an automatic tool change function or the like (step S11), the first reference hole 31, and the second reference hole 31. calculating the center position of the reference hole 32 (step S12), the perform center point O _1, O ₂ between the x-axis direction, y-axis direction of the distance d _x, the calculation of d _y (step S13), and followed by displacement [Delta] d _x, the absolute value of the threshold S _x a preset respectively, determines whether the larger S _y of [Delta] d _y (step S14).

Then, the result of determination in step S14, the displacement amount [Delta] d _x, [Delta] d the absolute value of the threshold each _y S _x, is equal to or less than S _y (No) is similar to Example 1, for example, the first reference in the NC device 17 The reset of the relative position between the spindle 15 and the table 16 is corrected by resetting the center point O ₁ of the hole 31 as a reference (step S15), and the touch sensor 2 is replaced with a tool (not shown) using an automatic tool change function or the like. Then, machining for the workpiece is started (step S16).

On the other hand, the result of determination in step S14, the displacement amount [Delta] d _x, the absolute value of either one but the threshold S _x of [Delta] d _y, is greater than S _y (Yes), the displacement amount [Delta] d _x, the absolute value of [Delta] d _y is It is determined whether or not the number m determined to be greater than the thresholds S _x and S _{y is} greater than a preset number n (for example, n = 3) (step S17). Here, the displacement amount [Delta] d _x, [Delta] d absolute value the threshold S _x of _y, as a means for counting the number of times m that is determined to be greater than S _y, may be such as provided for example NC apparatus 17 to the counter function.

As a result of the judgment in the step S17, if the displacement amount [Delta] d _x, the absolute value of either one but the threshold S _x of [Delta] d _y, the number of times m that is determined to be greater than S _y greater than the set number n (Yes), the reference hole It is assumed that foreign matter is attached to 31, 32, etc., and the machine is stopped (step S18).

On the other hand, the result of determination in step S17, the displacement amount [Delta] d _x, the absolute value of either one but the threshold S _x of [Delta] d _y, if the number of times m that is determined to be greater than S _y is equal to or less than the set number n (No) is Returning to step S11, the process is repeated.

  For example, as shown in FIG. 2, even when the chips 4 adhere to the reference hole 22 and foreign matter adhesion is detected in the first measurement by the touch sensor 2, the above-described steps S <b> 12 to S <b> 14 are performed. While the above process is being performed, there may be a case where the accurate positions of the reference holes 22 and 23 can be detected, for example, when the chips 4 are blown off.

  In such a case, according to the reference position correcting apparatus according to the present embodiment, when it is determined that no foreign matter has adhered in the second or third measurement, the machining of the workpiece is started without stopping the machine. Therefore, working efficiency can be improved.

  In addition, this invention is not limited to the Example mentioned above, For example, the reference holes 31 and 32 do not need to be circular. Further, in FIG. 1, in order to correct the thermal displacement in the Z-axis direction, two different locations on the side surface 3a may be measured in the Z-axis direction, and a threshold may be provided for the displacement in the Z-axis direction. The position of the second reference hole 32 may be used as a reference for the relative position between the spindle 15 and the table 16, and it goes without saying that various changes can be made without departing from the spirit of the present invention.

  The present invention is suitable for application to a reference position correction apparatus having a function of correcting a relative position shift between a spindle of a machine tool and a workpiece.

1 is an overall configuration diagram of a machine tool to which a reference position correction apparatus according to Embodiment 1 of the present invention is applied. It is a front view of the jig | tool applied to the reference position correction apparatus of the machine tool which concerns on Example 1 of this invention. It is a flowchart which shows the flow of the reference position correction process by the reference position correction apparatus of the machine tool which concerns on Example 1 of this invention. It is explanatory drawing which shows an example of the threshold value set in the reference position correction apparatus of the machine tool which concerns on Example 1 of this invention. It is a flowchart which shows the flow of the reference position correction process by the reference position correction apparatus of the machine tool which concerns on Example 2 of this invention. It is a front view which shows an example of the conventional jig | tool. It is explanatory drawing which shows an example of the threshold value set in the reference position correction apparatus of the conventional machine tool.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Machine tool 2 Touch sensor 2a Measuring element 3 Jig 4 Chip 5 Work 11 Bed 12 Column 13 Saddle 14 Spindle head 15 Spindle 16 Table 17 NC device 31 First reference hole 32 Second reference hole

Claims (5)

A reference means having a first reference part and a second reference part fixed to the table of the machine tool and having a known distance;
A reference portion position measuring means mounted on the spindle of the machine tool and measuring the position of the reference portion;
A reference position correcting device for a machine tool, comprising reference position correcting means for correcting a deviation of a relative position between the spindle and the table based on the position of the first reference part measured by the reference part position measuring means. ,
The reference position correcting means calculates a distance between the reference parts between the first reference part and the second reference part based on the result measured by the reference part position measuring means, and the calculated distance between the reference parts And a reference position correction apparatus for a machine tool, wherein the presence / absence of correction of the reference position is determined based on a result of comparison between a predetermined allowable range and a preset allowable range. The reference position correction means corrects the reference position when the amount of displacement of the reference portion distance is equal to or less than a preset threshold, based on the result of comparing the reference portion distance and the allowable range. 2. The machine tool reference position correction apparatus according to claim 1, wherein the operation of the machine tool is stopped when a displacement amount of the distance between the reference parts is larger than the threshold value. The reference position correction means corrects the reference position when the amount of displacement of the reference portion distance is equal to or less than a preset threshold, based on the result of comparing the reference portion distance and the allowable range. 2. The machine tool reference position correction apparatus according to claim 1, wherein when the displacement amount of the reference part distance is larger than the threshold value, the reference part position measurement unit measures the position of the reference part again. 3. 2. The machine tool reference position correction apparatus according to claim 1, wherein the first reference part and the second reference part are arranged at mutually different positions in the vertical direction and the horizontal direction. 2. The machine tool according to claim 1, wherein each of the first reference portion and the second reference portion is a reference hole formed in a circular cross-sectional view on the same surface of the reference means, and has a diameter different from each other. Machine reference position correction device.

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