JP2001165641A - Air micrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air micrometer easy to work and capable of precise measurement. SOLUTION: In this air micrometer, compressed air is blown from a measuring air nozzle to measure the inside diameter of a work while blowing compressed air from centripetal air nozzles 36A and 36B to retain a measuring head 32 in the central position of the work. An intermediate diaphragm 42 smaller in diameter than the centripetal air nozzles 36A and 26B is set in a passage 40C for supplying the compressed air of the centripetal air nozzles 36A and 36B. According to this, the compressed air blown from the centripetal air nozzles 36A and 36B corresponds to the compressed air blown from an air nozzle having a diameter smaller than that of the intermediate diaphragm 42. Accordingly, since the same effect as in smaller nozzle diameters can be obtained by the combination of large nozzle diameters, the workability of the nozzles can be improved. Further, the centripetal force can be increased to improve the precision of measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air micrometer, and more particularly, to an air micrometer capable of performing high-precision measurement with a repeatability (variation of measured values by repeated measurement) of 0.5 μm or less.

[0002]

2. Description of the Related Art In the case of measuring an outer diameter, for example, an air micrometer inserts a work into a ring-shaped measuring head and compresses the work from two to six air nozzles formed on the inner periphery of the measuring head. The measurement is performed by injecting air.

In order to perform high-precision measurement with this air micrometer, it is necessary to carry out measurement while holding the work inserted into the measurement head at the center position of the measurement head.

Therefore, conventionally, a centering air nozzle is separately arranged radially on the inner peripheral portion of the measuring head, and compressed air is jetted from the centering air nozzle to hold the work at the center position of the measuring head. (Japanese Patent No. 29043
No. 32).

[0005]

By the way, the centering action of the work by the centering air nozzle increases as the diameter of the centering air nozzle decreases.

However, the diameter of the centrifugal air nozzle is limited by the diameter of the drill used during machining.
It has the disadvantage that it can only be reduced to some extent.
In addition, if the diameter is too small, the drill may bend, etc., resulting in poor workability.

The present invention has been made in view of such circumstances, and has as its object to provide an air micrometer that can be easily processed and can perform high-precision measurement.

[0008]

According to the first aspect of the present invention,
In order to achieve the above object, a work is inserted into a measuring head, and air is blown out from a plurality of centering air nozzles arranged at equal intervals on an inner peripheral portion of the measuring head to move the work to a central position of the measuring head. In the air micrometer that measures the outer dimension of the work by blowing air from a plurality of measurement air nozzles arranged at equal intervals on the inner peripheral portion of the measurement head, while holding the measurement head, the air is applied to the centripetal air nozzle. An intermediate throttle having a diameter equal to the diameter of the centrifugal air nozzle is provided in the supply channel.

According to the present invention, the compressed air is once throttled by the intermediate throttle and then jetted from the centripetal air nozzle. As described above, once the compressed air is throttled by the intermediate throttle, the compressed air jetted from the centripetal air nozzle corresponds to the compressed air jetted from the air nozzle having a diameter equal to the diameter of the intermediate throttle. Therefore, the same effect as a smaller nozzle diameter can be obtained by a combination of a larger nozzle diameter, and the workability of the nozzle can be improved. In addition, the centripetal force can be increased thereby to improve the measurement accuracy.

According to a second aspect of the present invention, in order to achieve the above object, a work is fitted into a measuring head, and a plurality of centrifugal air nozzles arranged at equal intervals on an inner peripheral portion of the measuring head. While maintaining the workpiece at the center position of the measuring head by blowing air, the outer dimensions of the workpiece are measured by blowing air from a plurality of measuring air nozzles arranged at equal intervals on an inner peripheral portion of the measuring head. The centrifugal air nozzle is disposed on the front side and the rear side in the axial direction of the measurement head with the measurement air nozzle interposed therebetween.

According to the present invention, the centripetal air nozzle is disposed before and after the measuring air nozzle. Thus, the work can be inserted straight into the measuring head. As a result, measurement accuracy is improved.

According to a fourth aspect of the present invention, in order to achieve the above object, a measuring head is fitted into a work, and air is supplied from a plurality of centering air nozzles formed at equal intervals on an outer peripheral portion of the measuring head. An air micrometer that blows out air from a plurality of measurement air nozzles arranged at equal intervals on the outer peripheral portion of the measurement head to measure the inner dimensions of the work while blowing and holding the measurement head at the center position of the work. The meter is characterized in that an intermediate throttle having a diameter equal to the diameter of the centripetal air nozzle is provided in a flow path for supplying air to the centripetal air nozzle.

According to the present invention, the compressed air is once throttled by the intermediate throttle and then ejected from the centripetal air nozzle. As described above, once the compressed air is throttled by the intermediate throttle, the compressed air jetted from the centripetal air nozzle corresponds to the compressed air jetted from the air nozzle having a diameter equal to the diameter of the intermediate throttle. Therefore, the same effect as a smaller nozzle diameter can be obtained by a combination of a larger nozzle diameter, and the workability of the nozzle can be improved. In addition, the centripetal force can be increased thereby to improve the measurement accuracy.

According to a fifth aspect of the present invention, in order to achieve the above object, a measuring head is fitted into a work, and air is supplied from a plurality of centering air nozzles formed at equal intervals on an outer peripheral portion of the measuring head. An air micrometer that blows out air from a plurality of measurement air nozzles arranged at equal intervals on the outer peripheral portion of the measurement head to measure the inner dimensions of the work while blowing and holding the measurement head at the center position of the work. In the meter, the centripetal air nozzle is disposed on the front side and the rear side in the axial direction of the measurement head with the measurement air nozzle interposed therebetween.

According to the invention, the centripetal air nozzle is arranged before and after the measuring air nozzle. Thus, the measuring head can be inserted straight into the work. As a result, measurement accuracy is improved.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the air micrometer according to the present invention will be described below in detail with reference to the accompanying drawings.

First, an overall configuration of a back pressure air micrometer to which the present invention is applied will be outlined.

FIG. 1 is a block diagram showing the overall configuration of a back pressure air micrometer 10. As shown in FIG. As shown in the figure,
The compressed air supplied from the air source 12 is supplied to the regulator 1
At 4, the pressure is adjusted to a constant pressure, and the air is jetted from the air nozzles 34 </ b> A and 34 </ b> B of the jet (measuring unit) 30 through a throttle provided in the A / E converter 16. The A / E converter 16
The change in pressure (back pressure) between the air nozzles 34A, 34B and the throttle is converted into an electric signal by a built-in bellows and a differential transformer, and output to the amplifier 18. Amplifier 18
Calculates the inner diameter of the work 22 based on the electric signal, and displays it on a built-in monitor.

FIG. 2 is a front sectional view showing the configuration of a main part of an embodiment of an inner diameter measuring jet 30 of an air micrometer to which the present invention is applied. FIGS. 3 and 4 are a sectional view taken along line 3-3 and a sectional view taken along line 4-4 of FIG. 2, respectively.

As shown in FIGS. 2 to 4, measuring air nozzles 34A and 34B and centrifugal air nozzles 36A and 36B are alternately arranged at 90 ° intervals on the outer periphery of the tip of the measuring head 32 formed in a cylindrical shape. Is formed.

The measurement air nozzles 34A and 34B are respectively formed so as to be retracted from the outer peripheral surface of the measurement head 32 by a predetermined amount, and are each formed of a pair of measurement air branch flow paths 38A formed in parallel with the axis of the measurement head 32. , 38B. The pair of measurement air branch channels 38A, 38B
Are both connected to the measurement air flow path 38C, and the compressed air supplied from the measurement air flow path 38C is supplied to the measurement air nozzles 34A, 34B via the measurement air branch flow paths 38A, 38B. Is done. Then, the air is ejected from the measurement air nozzles 34A and 34B in opposite directions.

The compressed air supplied to the measurement air flow path 38C is supplied from the air source 12 as described above.
After being adjusted to a constant pressure by regulator 14, A / E
The air is supplied to the measurement air flow path 38C through a throttle provided in the converter 16.

Similarly, the centrifugal air nozzles 36A and 36B are also formed so as to be retracted from the outer peripheral surface of the measuring head 32 by a predetermined amount, and a pair of centrifugal air branch channels formed parallel to the axis of the measuring head 32. It is connected to 40A and 40B. The pair of centripetal air branch channels 40A, 40B
Are both connected to the centripetal air flow path 40C, and the compressed air supplied from the centripetal air flow path 40C is supplied to the centripetal air nozzles 36A, 36B via the centripetal air branch flow paths 40A, 40B. Is done. Then, the air is ejected from the centripetal air nozzles 36A and 36B in opposite directions.

The compressed air supplied to the centripetal air flow path 40C is supplied from the air source 12 as shown in FIG. 5, is adjusted to a constant pressure by the regulator 15, and then is supplied to the centripetal air flow path 40C. Supplied.

Here, an intermediate throttle 42 is provided in the centripetal air flow path 40C, and its diameter φA is formed to be smaller than the diameter φB of the centripetal air nozzles 36A and 36B. After the compressed air is once throttled by the intermediate throttle 42 in this manner, the compressed air is injected from each of the centrifugal air nozzles 36A and 36B, so that the centrifugal air nozzles 36A and 36B are compressed.
6B has a diameter φA of the intermediate throttle 42.
This corresponds to compressed air ejected from an air nozzle having the same diameter as. Thereby, the centripetal action of the work can be enhanced.

The operation of the inner diameter measuring jet 30 configured as described above is as follows.

First, magnification adjustment and zero adjustment using the master are performed. Next, the measuring head 32 is inserted into the work,
The compressed air is supplied from the air source 12.

A part of the compressed air supplied from the air source 12 is supplied to the measurement air flow path 38C of the measurement head 32 via the regulator 14 and the A / E converter 16, and the measurement air branch flow path 38A , 38B and are injected into the work from the measurement air nozzles 34A, 34B. Another part of the compressed air supplied from the air source 12 is supplied to the centrifugal air flow path 40 of the measuring head 32 via the regulator 15.
C, and is injected into the workpiece from the centrifugal air nozzles 36A, 36B through the centripetal air branch channels 40A, 40B.

Here, the centrifugal air nozzles 36A, 3A
When passing through the centripetal air flow path 40C, the compressed air jetted from 6B is once throttled by the intermediate throttle 42, and then jetted into the workpiece from each centripetal air nozzle 36A, 36B.

After the aperture has been once squeezed by the intermediate aperture 42 as described above, compressed air is ejected from the centrifugal air nozzles 36A and 36B, so that the centrifugal air nozzles 36A and 36B are compressed.
The compressed air ejected from B corresponds to compressed air ejected from an air nozzle having a diameter equal to the diameter φA of the intermediate throttle 42. Thereby, the centripetal effect of the centrifugal air nozzles 36A and 36B can be enhanced, and the center of the work and the center of the measuring head 32 can be easily matched. As a result, measurement accuracy is improved.

Further, the same effect as a smaller nozzle diameter can be obtained by a combination of a larger diameter, so that the workability of the air nozzle is improved.

In the present embodiment, the intermediate diaphragm 42 is installed in the centripetal air flow path 40C formed in the measuring head 32. However, the intermediate aperture 42 is separately installed in the centripetal air branch paths 40A and 40B. It may be.

When performing high-precision measurement with a repetition accuracy of 0.5 μm or less, the clearance of the jet 30, that is, the difference between the inner diameter of the work 22 and the outer diameter of the measuring head 32 is set to 5 μm to 20 μm. It is preferable to set.

FIG. 6 is a side sectional view showing the structure of a main part of another embodiment of the jet 50 for measuring the inner diameter of an air micrometer to which the present invention is applied. The same constituent members as the inner diameter measuring jet 30 of the above-described embodiment include:
The same reference numerals are given.

As shown in the figure, in the jet 50 for measuring the inner diameter of the present embodiment, the air nozzles 34A, 34A for measurement are used.
B centering air nozzles 36A, 36B, 36
C and 36D are formed. That is, in the inner diameter measuring jet 50 of the present embodiment, a total of four centripetal air nozzles 36A to 36D are formed.

In FIG. 6, the centrifugal air nozzles 36A and 36C formed on the upper surface side of the measurement head 32 are both connected to a centripetal air branch channel 40A formed parallel to the axis of the measurement head 32. .

In FIG. 6, centering air nozzles 36B and 36D formed on the lower surface of the measuring head 32 are shown.
Are connected to a centripetal air branch channel 40B formed in parallel with the axis of the measuring head 32.

The centripetal air branch passages 40A and 40B are both connected to a centripetal air passage 40C, and the compressed air supplied from the centripetal air passage 40C is supplied to the centripetal air branch passage 40A, Centrifugal air nozzle 36 through 40B
A to 36D. An intermediate throttle 42 is provided in the centripetal air flow path 40C. The intermediate throttle 42 is formed with a diameter φA smaller than the diameter φB of the centrifugal air nozzles 36A to 36D, and the compressed air injected from each of the centrifugal air nozzles 36A to 36D is once throttled by the intermediate throttle 42. Later, each centripetal air nozzle 36A ~
Injected from 36D.

The measuring air nozzles 34A, 34B
Are formed in a direction orthogonal to the centering air nozzles 36A to 36D.

The operation of the inner diameter measuring jet 50 constructed as described above is as follows.

First, the measuring head 32 is inserted into a work, and compressed air is supplied from the air source 12. A part of the compressed air supplied from the air source 12 is supplied to the regulator 14, A
The air is supplied to the measurement air flow path 38C of the jet 30 via the / E converter 16, and the measurement air branch flow paths 38A, 38B
Through the air nozzles 34A and 34B for measurement. Another part of the compressed air supplied from the air source 12 is supplied to the jet 3 via the regulator 15.
0 is supplied to the centripetal air flow path 40C and passes through the centripetal air branch flow paths 40A and 40B.
It is injected into the work from 36D.

Here, the centrifugal air nozzles 36A to 36D
Are formed before and after the measurement air nozzles 34A and 34B, so that the centering air nozzle 36A
When the compressed air is injected from .about.36D, the inclination of the measuring head 32 inserted into the work is corrected. As a result, highly accurate measurement can be performed without causing a posture error.

The compressed air jetted from the centrifugal air nozzles 36A to 36D is once throttled by the intermediate throttle 42 and then jetted from each of the centripetal air nozzles 36A to 36D. Of compressed air ejected from the air nozzle. As a result, the centripetal effect of the centrifugal air nozzles 36A to 36D can be enhanced, and the center of the work and the center of the measuring head 32 can be easily matched. As a result, measurement accuracy is improved.

Further, the same effect as a smaller nozzle diameter can be obtained by a combination of a larger diameter, so that the workability of the air nozzle is improved.

FIG. 7 is a front sectional view showing the configuration of an outer diameter measuring jet 60 of an air micrometer to which the present invention is applied. Since the configuration other than the jet is the same as the above-described air micrometer for measuring the inner diameter, only the configuration of the jet will be described here.

The ring-shaped measuring head 62 has six mounting holes 64, 64,... Formed radially at intervals of 60 °. The measurement nipples 66A, 66B, 66C and the centripple nipples 68A, 68B, 68C are alternately fitted into the mounting holes 64, 64,.

The measurement nipples 66A to 66C are respectively formed with measurement air nozzles 70A to 70C at the ends thereof. The measurement air nozzles 70A to 70C are
The distal end surface is formed so as to be retracted from the inner peripheral surface of the measuring head 62 by a predetermined amount.

Similarly, centering air nozzles 72A to 72C are formed at the tips of the centering nipples 68A to 68C, respectively. The centrifugal air nozzles 72A to 72C
Is formed such that the front end surface is retracted from the inner peripheral surface of the measurement head 62 by a predetermined amount. In addition, the nipple 68A for centripetal movement
Intermediate throttles 74A to 74C are provided in the air flow paths 68a to 68c of the 68C, respectively. Intermediate aperture 74A ~
74C is a centrifugal air nozzle 72A-72 whose diameter φC is
It is formed with a diameter smaller than the diameter φD of C.

The operation of the outer diameter measuring jet 60 constructed as described above is as follows.

First, a work is inserted into the measuring head 62,
The compressed air is supplied from the air source 12. A part of the compressed air supplied from the air source 12 is supplied to the regulator 14, the A / E
Each measuring nipple 6 of the jet 60 via the converter 16
It is supplied to 6A-66C and is jetted from each of the measurement air nozzles 70A-70D through the air flow paths 66a-66c. Another part of the compressed air supplied from the air source 12 is supplied to each centripple nipple 68A to 68C of the jet 60 via the regulator 15, and the air flow path 68a
６８68c from the respective centripetal air nozzles 72A to 72C.

Here, each of the centering nipples 68A to 68C
In the air passages 68a-68c, intermediate throttles 74A-
74C, each centripetal air nozzle 72
The compressed air injected from A to 72C is once throttled by the intermediate throttles 74A to 74C,
It will be injected from 4A to 74C. Then, after the compressed air is squeezed by the intermediate throttles 74A to 74C in this manner, the compressed air ejected from the centrifugal air nozzles 72A to 72C ejects the compressed air from the centrifugal air nozzles 72A to 72C. Diameter φ of ~ 74C
This corresponds to compressed air ejected from an air nozzle having the same diameter as D.

Thus, the centering air nozzles 72A to 72A
The centripetal effect by C can be enhanced, and the center of the work and the center of the measuring head 62 can be easily matched. As a result, measurement accuracy is improved.

Further, the same effect as a smaller nozzle diameter can be obtained by a combination of a larger diameter, so that the workability of the air nozzle is improved.

FIG. 8 is a side sectional view showing the structure of a main part of another embodiment of the jet 80 for measuring the outer diameter of an air micrometer to which the present invention is applied.

As shown in the figure, the outer diameter measuring jet 80 of the present embodiment has centering nipples 84A and 84B disposed at front and rear positions of a measuring nipple 82.

Four measuring nipples 82 are provided on the measuring head 86, and are fitted into four measuring nipple mounting holes 88 formed in each measuring head 86. Each measurement nipple mounting hole 88, 88, ...
Are formed radially at 90 ° intervals on the same cross section of the measuring head 86. In addition, each measurement nipple 82 has a measurement air nozzle 90 formed at the distal end thereof, and the distal end surface of each measurement air nozzle 90 is connected to the measurement head 8.
6 is retracted from the inner peripheral surface by a predetermined amount.

Four nipples 84A and 84B for centrips are installed on the front side and the rear side of the nipple 82 for measurement, respectively.

4 is disposed on the front side of the measurement nipple 82.
Each of the centering nipples 84A is provided with a measuring head 86
Centering nipple mounting holes 92A, 92 formed in
A,. Nipple mounting hole 92 for each centering
A, 92A,...
It is formed radially at intervals of °. Further, each of the centering nipples 84A has a centering air nozzle 94A formed at the front end thereof, and the front end surface of each centering air nozzle 94A is formed so as to be retracted by a predetermined distance from the inner peripheral surface of the measuring head 86. ing. Furthermore, each centripple nipple 84A
Is provided with an intermediate throttle 96A in its air flow path 84a, and its diameter φC is formed smaller than the diameter φD of the centrifugal air nozzle 94A.

On the other hand, the four centering nipples 84B disposed on the rear side of the measuring nipple 82 are provided with four centering nipple mounting holes 92 formed in the measuring head 86, respectively.
B, 92B,... The centering nipple mounting holes 92B, 92B,... Are formed radially at 90 ° intervals on the same cross section of the measuring head 86. Further, each of the centering nipples 84B has a centering air nozzle 94B formed at the front end thereof, and the front end surface of each centering air nozzle 94B is formed to be retracted by a predetermined distance from the inner peripheral surface of the measuring head 86. ing. Further, each centering nipple 84B is provided with an intermediate throttle 96B in the air flow path 84b, and has a diameter φC smaller than the diameter φD of the centering air nozzle 94B.

The operation of the outer diameter measuring jet 80 constructed as described above is as follows.

First, a work is inserted into the measuring head 86 and compressed air is supplied from the air source 12. A part of the compressed air supplied from the air source 12 is supplied to the regulator 14, A
It is supplied to each nipple 82 for measurement of the jet 80 via the / E converter 16, and is jetted from each air nozzle 90 for measurement through the air flow path 82a. Another part of the compressed air supplied from the air source 12 is supplied to the centripple nipples 84A and 84B of the jet 80 via the regulator 15, and passes through the air flow paths 84a and 84b. Injected from 94A, 94B.

Here, the centering air nozzles 94A, 94B
Are formed at the front and rear positions of the measurement air nozzle 90. Thus, when the compressed air is injected from the centripetal air nozzles 94A and 94B as described above, the inclination of the work inserted into the measurement head 86 is corrected. As a result, highly accurate measurement can be performed without causing a posture error.

The compressed air injected from the centrifugal air nozzles 94A and 94B is once throttled by the intermediate throttles 96A and 96B and then injected from the respective centrifugal air nozzles 94A and 94B. This corresponds to compressed air ejected from an air nozzle having the same diameter as. Thus, the centripetal effect of the centrifugal air nozzles 94A and 94B can be enhanced, and the center of the workpiece and the measuring head 86
Can easily be matched with the center.
As a result, measurement accuracy is improved.

Further, the same effect as a smaller nozzle diameter can be obtained by a combination of a larger diameter, so that the workability of the air nozzle is improved.

[0065]

As described above, according to the present invention,
By once narrowing the compressed air ejected from the centripetal air nozzle with the intermediate throttle, the same effect as a smaller nozzle diameter can be obtained with a combination of large nozzle diameters. Thereby, the workability of the nozzle can be improved. In addition, the centripetal force can be increased thereby to improve the measurement accuracy.

Further, according to the present invention, since the centripetal air nozzle is arranged before and after the measuring air nozzle, the work can be inserted straight into the measuring head. As a result, measurement accuracy is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a back pressure air micrometer.

FIG. 2 is a front sectional view showing a configuration of a main part of an inner diameter measuring jet.

FIG. 3 is a sectional view taken along line 3-3 in FIG. 2;

FIG. 4 is a sectional view taken along line 4-4 of FIG. 2;

FIG. 5 is a block diagram showing a piping configuration of centripetal air.

FIG. 6 is a side sectional view showing a configuration of a main part of another embodiment of the inner diameter measuring jet.

FIG. 7 is a side sectional view showing a configuration of an outer diameter measuring jet.

FIG. 8 is a side cross-sectional view showing the configuration of another embodiment of the outer diameter measuring jet.

[Explanation of symbols]

10 air micrometer, 12 air source, 14 regulator, 15 regulator, 16 A / E converter,
18 amplifier, 20 monitor, 30 inner diameter measurement jet, 32 measurement head, 34A, 34B measurement air nozzle, 36A, 36B centripetal air nozzle, 42 intermediate throttle, 50 inner diameter measurement jet, 60 Jet for outer diameter measurement, 66A-66C ... Nipple for measurement, 68A-6
6C: centripple nipple, 70A to 70C: measurement air nozzle, 72A to 72C: centripetal air nozzle, 74A to 7
4C: Intermediate drawing, 80: Jet for outer diameter measurement, 82: Nipple for measurement, 84A, 84B: Nipple for centripetal, 86
... Measurement head, 90 ... Measurement air nozzle, 94A, 94
B: Centrifugal air nozzle, 96A, 96B: Middle throttle

Claims (6)

[Claims] 1. A work is inserted into a measuring head, and air is blown out from a plurality of centering air nozzles arranged at equal intervals on an inner peripheral portion of the measuring head to hold the work at a central position of the measuring head. Meanwhile, in an air micrometer for measuring the outer dimensions of the work by blowing air from a plurality of measurement air nozzles arranged at equal intervals on the inner peripheral portion of the measurement head, a flow of supplying air to the centripetal air nozzle An air micrometer characterized in that an intermediate throttle having a diameter equal to the diameter of the centripetal air nozzle is installed in a path. 2. A work is inserted into a measuring head, and air is blown out from a plurality of centering air nozzles arranged at equal intervals on an inner peripheral portion of the measuring head to hold the work at a central position of the measuring head. An air micrometer that measures the outer dimension of the work by blowing air from a plurality of measurement air nozzles arranged at equal intervals on an inner peripheral portion of the measurement head, wherein the centripetal air nozzle is configured to include the measurement air nozzle. An air micrometer, which is disposed on the front side and the rear side in the axial direction of the measurement head with the air micrometer interposed therebetween. 3. The air micrometer according to claim 2, wherein an intermediate throttle having a diameter equal to the diameter of the centripetal air nozzle is provided in a flow path for supplying air to the centripetal air nozzle. 4. A measuring head is fitted into a work, and air is blown out from a plurality of centripetal air nozzles formed at equal intervals on an outer peripheral portion of the measuring head to hold the measuring head at a central position of the work. In an air micrometer that measures the inner dimension of the work by blowing air from a plurality of measurement air nozzles arranged at equal intervals on an outer peripheral portion of the measurement head, the flow path for supplying air to the centripetal air nozzle An air micrometer characterized in that an intermediate throttle having a diameter equal to the diameter of a centripetal air nozzle is provided. 5. A measurement head is fitted into a work, and air is blown out from a plurality of centering air nozzles formed at equal intervals on an outer peripheral portion of the measurement head to hold the measurement head at a central position of the work. In an air micrometer that measures the inner dimension of the work by blowing air from a plurality of measurement air nozzles arranged at equal intervals on an outer peripheral portion of the measurement head, the centripetal air nozzle sandwiches the measurement air nozzle. An air micrometer, which is provided on the front side and the rear side in the axial direction of the measuring head. 6. The air micrometer according to claim 5, wherein an intermediate throttle having a diameter equal to a diameter of the centripetal air nozzle is provided in a flow path for supplying air to the centripetal air nozzle.