JPH09131642A - Numerical control machine tool precision inspection device and thermal displacement inspection method of numerical control machine tool and precision inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a numerical control machine tool precision inspection device which enables automatic measurement of precision of a machine tool by any worker other than highly skilled worker. SOLUTION: A controlling personal computer 5 receives an external output signal of a numerical control device 7, the controlling personal computer 5 outputs a change-over signal to a gage head selector 3 so that the result of measurement from a gage head 2a or 2c which corresponds to the external output signal is sent to an electrical micrometer 4, and the measured value from the electrical micrometer 4 is read, recorded, and output by the controlling personal computer 5 to output an external input signal for the numerical control device 7. Consequently, the precision of a numerical control machine tool is measured automatically.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a numerically controlled machine tool precision inspection device and a thermal displacement inspection method and precision inspection method for the numerically controlled machine tool precision inspection device. More specifically, the present invention relates to a machine tool for a machining center or a numerically controlled lathe. etc,
Measuring and calibrating the accuracy of machines that are frequently used and that require high accuracy maintenance, collecting axis correction data on the machine side that is supplied to the numerical control device, setting machine accuracy maintaining devices such as spindle cooling devices and column cooling devices The present invention relates to a numerically controlled machine tool precision inspection device that can be used for various purposes such as data collection, and a thermal displacement inspection method and an accuracy inspection method for the numerically controlled machine tool precision inspection device.

[0002]

2. Description of the Related Art Conventionally, in machine tools such as machining centers, precision measurement and calibration are performed by using measuring instruments and gauges at the time of machine installation, periodic maintenance during installation and during use. ing.

For measuring and calibrating the precision of such machine tools, the Japanese Industrial Standard (JISB6338) is applied, and the measurement data is obtained by using a direct ruler or a micrometer.

FIG. 12 shows an example of measuring and calibrating the minimum set unit feed of a machine tool. In FIG. 12, the straight edge ruler 51 is fixed on the table 52. The stand 58 is fixed to the main shaft 59, and the micrometer 60 is fixed to the stand 58.

[0007] In advance, after moving in the positive (or negative) direction by fast-forwarding and stopping, and then further fast-forwarding in the same direction, a few units of commands for each minimum setting unit are given and stopped, and the same direction is set again. A command for each minimum setting unit is continuously given to move a distance corresponding to 20 units or more as an actual moving distance, and a stop position for each command is measured.

Next, a command for each minimum setting unit is given in the negative (or positive) direction from the final measurement position until it returns to the reference position, and the stop position for each command is measured.
The results of these measurements are shown in FIG.

From these stop position values, the maximum value of the difference between the distance between adjacent stop positions and the minimum setting unit is obtained. In this case, as shown in FIG. 13, as a general rule, measurement points within the actual movement distance corresponding to several units after turning back are excluded. The measurement result of such measurement is expressed as follows. That is, measured value = | l1 -m | max. Where l1
Is the distance between adjacent stop positions, and m is the minimum setting unit. The machine is calibrated based on this measurement result.

For lost motion measurement, for example, the Japanese Industrial Standard (JIS B6330) is applied. That is, as shown in FIG. 14, a stand 78 is fixed on a table 72 of a numerically controlled machine tool, a micrometer 70 is fixed to the stand 78, and a gauge head of the micrometer 70 is attached to an axis of the numerically controlled machine tool. Abut 71.

In this state, as shown in FIG.
Move to a positive (or negative) direction by fast-forwarding and give an arbitrary command in the same direction with respect to the stopped position, and move it,
The difference between the stop position and the reference position when the same command is given and moved in the negative (or positive) direction from that position is measured.

Such measurement is repeated seven times at three points at the center and almost both ends of the movement, the average value at each point is obtained, and the maximum value of the obtained average values is measured as the lost motion. The value.

Further, in recent years, attention has been paid to the fact that the machining accuracy is greatly affected by the temporal heat change of the spindle of the machining center. In particular, when a work with high processing accuracy is handled, thermal displacement of the spindle is a problem that cannot be ignored.
In addition, when the vertical machining center is used, the two axes (X, X,
There is a problem that the amount of thermal displacement in the front-rear direction becomes large when viewed from the standing position of the worker in the Y direction. As a countermeasure against this, a device for keeping the temperature of the spindle or the column constant has been developed. For example, a spindle cooling device and a column cooling device.

However, even when such a device is attached, a large amount of thermal displacement may occur due to the correlation between the set temperature of each device and room temperature. It is necessary to measure the exact amount of thermal displacement.

A conventional method for measuring a thermal displacement amount is shown in FIGS.
It is shown in FIG. A stand 98 in which micrometers 90a to 90c for measuring thermal displacements of the main shaft 89 in the X-axis direction, the Y-axis direction, and the Z-axis direction are fixed to a table.
a to 98c to hold and fix the main shaft 8
The values of the micrometers 90a to 90c in the respective axial directions are read at regular time intervals, for example, every 5 minutes, during which the main shaft 89 is rotated while being brought into contact with each other from the respective axial directions of 9 as shown in FIG. Enter the value. The thermal displacement amount stabilizing device and the like (the thermal displacement amount stabilizing device such as the spindle cooling device and the column cooling device) are set so that the thermal displacement amount is minimized, that is, is stabilized at a constant value, and the machine is idling. Set the time.

[0014]

The accuracy measurement and calibration of the machine tool performed by using the above-mentioned measuring method is performed by reading the micrometer, moving the axis of the machine, and measuring results in the minimum setting unit feed test and the lost motion test. There is a problem that not only processing such as illustration is required and time is required, but also a high degree of skill of an operator is required. In addition, the operator's operation error may occur.

Further, in the case of measuring the amount of heat change with time of the machine tool, there is a problem that the measurer must measure the machine for several hours. Further, the measurement procedure may be manually performed by the measurer, and the measurement result may be influenced by the measurer. That is, the measurement takes time, and the measurement accuracy tends to be arbitrary.

In view of the above problems, the present invention makes it possible for anyone other than a highly skilled person to measure the accuracy of a machine tool, and the measurement result is reproducible and the measurement result does not depend on the person who performs the measurement. Provided are a numerically controlled machine tool precision inspection device, a thermal displacement inspection method and an accuracy inspection method for the numerically controlled machine tool.

[0017]

According to the first aspect of the present invention,
In a numerically controlled machine tool precision inspection device that measures the accuracy of a numerically controlled machine tool, a plurality of gauge heads that abut each axis of the numerically controlled machine tool, and a gauge that switches and outputs each measured value of each gauge head With a dead selector,
Based on the measured value from this gauge head selector, an electric micrometer for measuring the displacement of the spindle of the numerically controlled machine tool, and switching control of each gauge head, and receiving the measurement result from the electric micrometer. Storage means for storing the measurement result, operation means for performing an operation on the measurement result, means for calculating the time from the start of the inspection, communication means for exchanging signals with the numerical control device constituting the numerically controlled machine tool. With a control device,
An output device for outputting a calculation processing result by the control device is provided.

According to a second aspect of the present invention, in a thermal displacement inspection method for a numerically controlled machine tool, a plurality of gauge heads to be brought into contact with respective axes of the numerically controlled machine tool and respective measurement values of the respective gauge heads are switched. An output gauge head selector, an electric micrometer that measures the displacement of the spindle of the numerically controlled machine tool based on the measurement value from the gauge head selector, and switching control of each gauge head, and the electric micrometer. A storage unit that receives the measurement result from the storage unit and stores the measurement result, an operation unit that performs an operation on the measurement result, a unit that calculates the time from the start of the inspection, and a numerical control device and signals that constitute the numerically controlled machine tool. A control device having a communication means for delivering and receiving data, and an output device for outputting a calculation processing result by the control device, By setting the time to perform measurement in the control device, and when the set time has elapsed from the start of measurement, the control device reads and records the measurement side result from the electric micrometer, and then sends a switching signal to the gauge to the selector. By switching the gauge head selector and performing measurements on all axes of the numerically controlled machine tool, it is possible to automatically measure and output the displacement of all axes of the numerically controlled machine tool due to heat change over time for a long time. It is a thing.

According to a third aspect of the present invention, in a precision control method for a numerically controlled machine tool, a plurality of gauge heads to be brought into contact with respective axes of the numerically controlled machine tool, and respective measured values of the respective gauge heads are switched and output. A gauge head selector to be used, an electric micrometer that measures the displacement of the spindle of the numerically controlled machine tool based on the measurement value from this gauge head selector, and switching control of each gauge head, and from the electric micrometer. A storage unit that receives the measurement result and stores the measurement result, a calculation unit that performs an operation on the measurement result, a unit that calculates the time from the start of the inspection, a numerical control device that constitutes the numerically controlled machine tool, and a signal A control device having a communication means for delivering and receiving, and an output device for outputting a calculation processing result by the control device, The control device receives an external output signal of the value control device, the control device outputs a switching signal to the gauge head selector to send the measurement result from the gauge head corresponding to the external output signal to the electric micrometer, This control device reads the measured value from the electric micrometer, records and outputs it, and outputs the external input signal to the numerical control device to automatically perform the minimum setting unit feed test of the numerically controlled machine tool and repeat positioning. It is characterized by performing an accuracy inspection, a position direction positioning accuracy inspection, and a reverse positioning accuracy inspection.

According to the first aspect of the present invention, the control device switches the gauge head selector to the gauge head corresponding to the axis to be measured by the elapsed time from the start of measurement or the axis movement completion signal from the numerical controller. Is output. The gauge head selector switches the gauge head according to a signal from the control device and connects the gauge head to the electric micrometer. The control device reads and records the measurement result of the electric micrometer and performs necessary calculations. The control device further displays the measurement result and the calculation result on an output device such as a CRT.

In the invention of claim 2, the time for measuring is set in advance in the control device, and when the set time elapses from the start of measurement, the control device reads and records the measurement side result from the electric micrometer. Then, by sending a switching signal to the gauge head selector, the gauge head selector is switched, and measurement is performed on all axes of the numerically controlled machine tool. The displacement of the shaft is measured, and the measurement result is displayed and the calculation result is displayed on an output device such as a CRT.

According to another aspect of the present invention, the control device receives an external output signal of the numerical control device, and the control device sends the measurement result from the gauge head corresponding to the external output signal to the electric micrometer. Output a switching signal to the gauge head selector to send,
This control device reads the measured value from the electric micrometer, records and outputs it, and outputs the external input signal to the numerical control device to automatically perform the minimum setting unit feed test of the numerically controlled machine tool and repeat positioning. Perform accuracy inspection, position direction positioning accuracy inspection, and reverse positioning accuracy inspection.

[0023]

Embodiments of the present invention will be described below in detail.

(Embodiment 1) In Embodiment 1, a thermal displacement amount inspection device and a thermal displacement amount inspection method for a numerically controlled machine tool will be described. The configuration of the apparatus according to the first embodiment is shown in FIGS.

The thermal displacement inspection apparatus shown in FIGS. 1 and 2 has an X-axis gauge head 2a and a Y-axis gauge head 2 on the main shaft 9 of a machine tool from the X-axis direction, the Y-axis direction and the Z-axis direction.
The b and Z axis gauge heads 2c are abutted against each other, and these gauge heads 2a, 2b and 2c are fixed to a table (not shown) by a stand 8. That is, the stand 8 is configured to fix the gauge heads 2a, 2b, and 2c, and to fix the gauge heads 2a, 2b, and 2c to the table by a magnet built in the stand 8 on a table of a machine tool (not shown).

The gauge heads 2a, 2b, 2c are
Each is connected to the gauge head selector 3. The gauge head selector 3 is connected to an electric digital micrometer 4 and a control personal computer 5 which is a control device. In addition, the gauge head selector 3 receives the signal from the control personal computer 5, and the electric digital micro controller 4
The X-axis gauge head 2a, the Y-axis gauge head 2b, and the Z-axis gauge head 2c that are connected to each other are switched.

The electric digital micrometer 4
Can output the measured value of any of the gauge heads 2a, 2b, 2c connected by the gauge head selector 3. Also, control personal computer 5
Reads the measurement result of the electric digital micro-computer 4 and performs arithmetic processing and storage processing of the read measurement result.

Further, the control personal computer 5 is connected to a CRT 13 and a printer 14 which are output means, and a numerical control device (NC device) 7 which constitutes a numerically controlled machine tool,
The above-mentioned calculation processing result is displayed on the CRT 13 and the measurement result is drawn as a graph. Further, the control personal computer 5 sends the measurement result and the data of the drawn graph to the printer 14 and outputs them on the paper.

Further, the numerical control device 7 can output an M code which is not completed until a signal from the control personal computer 5 arrives, to the control personal computer 5, and, although not shown, in parallel with an externally connected device. Signals can be passed through the interface.

The operation of the thermal displacement amount inspection apparatus of the first embodiment will be described with reference to FIGS. 3, 4 and 5. First, in advance, numerical control (N
C) Create a program. M120 in this numerical control program outputs a signal (hereinafter also referred to as "DO") to an externally connected device such as this inspection device, and is completed until a signal (hereinafter also referred to as "DI") from the external connection device arrives. Not an M code.

The contents of the numerical control program shown in FIG. 4 will be described below. Block number 1 indicates the program number, block number 2 indicates the external device input / output M code,
The block number 3 indicates that the spindle is rotated at 10000 rpm, the block number 4 indicates the external device input / output M code, the block number 5 indicates the spindle stop, and the block number 6 indicates the program end and rewind. .

First, the numerical control device 7 is started by executing the numerical control program shown in FIG. The activated numerical control device 7 stops with the signal from the control personal computer 5 at the second MI 20 in the numerical control program.

The control state of the control personal computer 5 thereafter is shown in FIG.
It will be described with reference to the flowchart shown in FIG. First, the control personal computer 5 determines whether DO is issued,
If the DO is not issued, it is determined that the numerical control device 7 is not prepared, and the numerical control device 7 is held until it is prepared (step S1). D
When O is output, the numerical controller 7 determines that the preparation is completed (Yes in step S1), and sends DI to the numerical controller 7. Upon receiving the DI, the numerical controller 7 proceeds to the next step of the program and rotates the spindle (step S2, block number 3 in FIG. 4). After that, the control personal computer 5 shown by M120 of block number 4 enters the DI waiting state.

Next, the control personal computer 5 outputs a signal to the gauge head selector 3 to connect the X-axis gauge head 2a and the electric digital micrometer 4. afterwards,
The control personal computer 5 is an electric digital micrometer 4
The measurement result in the X-axis direction is read from (step S3).
Similar operations are performed in the Y-axis direction and the Z-axis direction (steps S4 and S5).

Next, the control personal computer 5 records the data obtained as described above, and calculates the maximum change amount of each axis from the start of measurement (step S6). Then, the acquired measurement result and calculated value are displayed on the CRT 13 as shown in FIG. 3, and a graph is drawn (step S7). Then 5
Pause for a minute (step S8).

Next, the control personal computer 5 determines whether or not the time from the start of measurement has passed 4 o'clock (step S
9) If the time has not passed, the processes from step S3 to step S8 are repeated.

If four hours have elapsed, DI is output to the numerical control device 7 to give a machine stop instruction, and the process ends (step S10). Upon receiving the signal from the control personal computer 5, the numerical controller 7 stops the spindle 9 (block number 5) and the program ends. The measurement result is sent to the reprinter 14 according to an instruction from the control personal computer 5, and the measurement result and the graph are output on the paper.

As will be apparent from the first embodiment, on the side of the thermal displacement gauge on which the present apparatus is attached to a machine tool, the operator does not need to perform measurement on the machine, and long-time measurement is unattended. In addition, it can be performed automatically, and there is no variation in measurement results depending on the measurer. Furthermore, since a graph can be created from the conventional measurement result and the tendency can be seen automatically at the time of measurement, the tendency of the measurement result can be quickly seen.

(Second Embodiment) Next, a second embodiment of the present invention will be described. In the second embodiment, an apparatus and method for the minimum set unit feed test will be described. In the second embodiment, repetitive positioning accuracy inspection, one-way positioning accuracy inspection, and reverse positioning accuracy inspection are realized by the same device and method as those in the first embodiment.

The structure of the second embodiment adopts the structure shown in FIG. 1 and, as shown in FIG.
The stand 8 is fixed to the stand 8 by a magnet built in the stand 8, and the gauge head 2 is attached to the stand 8.
Is fixed. The straight edge 11 is fixed on the table 12 of the machine tool, and the gauge head 2 is abutted on the straight edge 11 from the X-axis direction and is used as a reference.

Next, the operation of the second embodiment of the present invention will be described with reference to FIG.
It will be described with reference to FIGS. First, a numerical control program for the minimum set unit feed test having the content shown in FIG. 8 is created in advance.

The contents of the numerical control program shown in FIG. 8 will be described below. Block number 1 shown in FIG. 8 shows a program number, and M120 of block number 2 shows an externally connected device input / output M code. M120 is an M code that outputs a signal to an external connection device and is not completed until a signal comes from the external connection device.

Block number 3 means substituting 1 for variable 1 (counter), and block number 4
Means that the block number 9 is repeated until the variable 1 becomes 25 in the WHILE control statement.
Is the minimum set unit amount in the positive direction along the X-axis and the feed speed is 100m.
Block number 6 means moving at m / min
Means 0.5 second dwell.

Further, block number 7 indicates an externally connected device input / output M code, and block number 8 indicates WHILE.
It means the end of the control statement, block number 10 means clearing the counter 0, and block number 11 means WHILE.
In the control statement, it means that the block number 16 is repeated until the variable 1 becomes 30, and the block number 12 is the minimum set unit amount in the negative direction of the X axis and the feed rate is 100 mm / min.
Means to move in.

Further, the block number 13 is 0.5 seconds.
Dwell, block number 14 represents externally connected device input / output M code, block number 15 means counter addition, block number 16 means end of WHILE control statement, block number 17 means Means the end of the program.

First, the numerical controller 7 is started by executing the numerical control program shown in FIG. The activated numerical control device 7 stops with the signal from the control personal computer 5 at the second MI 20 in the numerical control program.

The control state of the control personal computer 5 thereafter is shown in FIG.
It will be described with reference to the flowchart shown in FIG. First, the control personal computer 5 determines whether DO is issued,
If the DO is not issued, it is determined that the numerical control device 7 is not prepared, and the numerical control device 7 is held until it is prepared (step S21).

When DO is output, the numerical controller 7 determines that the preparation is completed (Yes at step S21), and sends DI to the numerical controller 7. Upon receiving the DI, the numerical control device proceeds to the next step of the program, reads the measured value (step S22), and sends a measurement start signal to the numerical control device 7 (step S23).

Upon receiving the signal, the numerical controller 7 proceeds to the next block of the program, moves the X-axis toward the minimum set unit amount in the positive direction, stops for 0.5 seconds, and then measures the measured value to the control personal computer 5. Issue a read command (block numbers 5, 6,
7).

The control personal computer 5 judges whether or not a measurement value reading request is issued from the numerical control device 7 side (step S24), and if not, waits until it is issued, and if it is issued. First, the measured value is read, recorded, and calculated (step S25). Here, the operation is |
Measurement value-previous measurement value |, and the measurement result is the maximum value of the calculated values.

The control personal computer 5 sends the measured value data to the CRT 13 and displays the measured value and draws a graph as shown in FIG.
(Step S26).

After that, the control personal computer 5 outputs a signal to continue the measurement to the numerical controller 7 (step S27).
The numerical controller 7 shifts to the processing of the next step by the completion signal represented by M120 from the control personal computer 5.

The numerical controller 7 determines the above-mentioned step S2.
The processing from 4 to step S27 is measured 55 times (the processing of block numbers 5, 6, 7, and 8 is 25 times, the block number 1
The processes of 2, 13, 14, and 15 are repeated 30 times).

Next, the control personal computer 5 measures 55 times.
It is determined whether or not it is the number of times (step S28), and if it is 55 times or less, the processing from step S24 to step S27 is performed,
If it is 55 times, the process ends.

The result of the measurement is sent to the reprinter 14 according to an instruction from the control personal computer 5, and the result and the graph are output on the paper.

According to the second embodiment, as an effect different from that of the first embodiment, it is possible to perform the inspection by the numerical control device 7 with less operation as compared with the accuracy inspection by the conventional manual operation, and the numerical control device may be operated erroneously. Inspection errors can be prevented.

[0057]

As is apparent from the above, according to the present invention, anyone who is not a highly skilled person can perform the precision measurement of the machine tool, and the measurement result is reproducible by the measurer. A numerically controlled machine tool precision inspection device that can perform automatic measurement without being affected and that can accurately perform accuracy inspection even when applied to existing equipment, and a heat of the numerically controlled machine tool. A displacement inspection method and an accuracy inspection method can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a mounted state of the gauge head according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an output state of measurement results according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram showing contents of a numerical control program according to the first embodiment of the present invention.

FIG. 5 is a flowchart showing an inspection operation according to the first embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a mounted state of a gauge head according to a second embodiment of the present invention.

FIG. 7 is an explanatory diagram showing an output state of measurement results according to the second embodiment of the present invention.

FIG. 8 is an explanatory diagram showing the contents of a numerical control program according to the second embodiment of the present invention.

FIG. 9 is a flowchart showing an inspection operation according to the second embodiment of the present invention.

FIG. 10 is an explanatory diagram showing a configuration in the case of conventional thermal displacement measurement.

FIG. 11 is an explanatory diagram showing an output of a measurement result of a conventional thermal displacement measurement with time.

FIG. 12 is an explanatory diagram showing a configuration of a conventional minimum setting unit feed test.

FIG. 13 is an explanatory diagram showing an output of a conventional minimum setting unit feed test.

FIG. 14 is an explanatory diagram showing a configuration of a conventional lost motion measurement.

FIG. 15 is an explanatory diagram showing an output of a conventional lost motion measurement.

[Explanation of symbols]

 2a X-axis gauge head 2b Y-axis gauge head 2c Z-axis gauge head 3 Gauge head selector 4 Electric digital micrometer 5 Control personal computer 7 Numerical control device 8 Stand 9 Spindle 13 CRT 14 Printer

Claims (3)

[Claims] 1. A numerical control machine tool precision inspection apparatus for measuring the accuracy of a numerical control machine tool, wherein a plurality of gauge heads to be brought into contact with respective axes of the numerical control machine tool and respective measurement values of the gauge heads are switched. And a gauge head selector for outputting the electric power, an electric micrometer for measuring the displacement of the spindle of the numerically controlled machine tool based on the measured value from the gauge head selector, and switching control of each of the gauge heads, and the electric micrometer. A storage unit that receives the measurement result from the meter and stores the measurement result, a calculation unit that performs calculation on the measurement result, a unit that calculates the time from the start of the inspection, and a numerical control device that constitutes the numerically controlled machine tool. A control device having a communication means for transmitting and receiving signals, and an output device for outputting a calculation processing result by the control device Numerically controlled machine accuracy testing apparatus comprising the. 2. A method for inspecting thermal displacement of a numerically controlled machine tool, comprising: a plurality of gauge heads that are brought into contact with respective axes of the numerically controlled machine tool; and a gauge head selector that switches and outputs each measured value of each gauge head. , The electric micrometer that measures the displacement of the spindle of the numerically controlled machine tool based on the measurement value from this gauge head selector, and the switching control of each gauge head, and receive the measurement result from the electric micrometer. A storage means for storing the lever measurement result, a calculation means for calculating the measurement result, a means for calculating the time from the start of the inspection, and a communication means for exchanging signals with the numerical control device constituting the numerically controlled machine tool. And a output device that outputs the calculation processing result by this control device, and performs measurement in advance on the control device. When the time is set and the set time has elapsed from the start of measurement, the control device reads the meter side result from the electric micrometer, records and displays it, and then sends a switching signal to the gauge selector to switch the gauge selector. By measuring all axes of a numerically controlled machine tool, the temperature of the numerically controlled machine tool is automatically measured for a long time and the displacement of all axes of the numerically controlled machine tool is measured and output. Displacement inspection method. 3. A precision control method for a numerically controlled machine tool, comprising: a plurality of gauge heads that are in contact with respective axes of the numerically controlled machine tool; and a gauge head selector that switches and outputs each measurement value of each gauge head. Based on the measured value from this gauge head selector, an electric micrometer for measuring the displacement of the spindle of the numerically controlled machine tool, and switching control of each gauge head, and receiving the measurement result from the electric micrometer. Storage means for storing the measurement result, operation means for performing an operation on the measurement result, means for calculating the time from the start of the inspection, communication means for exchanging signals with the numerical control device constituting the numerically controlled machine tool. And a output device for outputting the arithmetic processing result by this control device, The control device receives the signal, and the control device outputs a switching signal to the gauge head selector so as to send the measurement result from the gauge head corresponding to the external output signal to the electric micrometer. By reading the measured value from the meter, recording and outputting it, and outputting an external input signal to the numerical control device, the minimum setting unit feed test of the numerically controlled machine tool, repeatable positioning accuracy inspection, position direction positioning are automatically performed. An accuracy inspection method for a numerically controlled machine tool characterized by performing an accuracy inspection and a reverse positioning accuracy inspection.