JP2020193831A - Digital micrometer - Google Patents

Abstract

To provide a digital micrometer suitable for measuring a measuring object which is a strong magnet.SOLUTION: A digital micrometer includes a main body frame, a spindle, a thimble section, and a displacement detector for detecting displacement of the spindle. The main body frame has an U-shaped frame section, and a spindle holding section provided so as to have a length in a direction away from an anvil at the other end of the U-shaped frame section. The spindle is held by the spindle holding section, is provided to be movable so as to move forward or backward the anvil in an axis direction, and has a contactor on one end surface. The main body frame and the spindle are formed of a nonmagnetic material, the thimble section and the displacement detector are arranged at the other end of the spindle holding section, the length of the spindle holding section is equal to or larger than a predetermined value.SELECTED DRAWING: Figure 5

Description

The present invention relates to a digital micrometer.

In recent years, the development and production of permanent magnet synchronous motors have been spurred by the growing demand for hybrid vehicles and electric vehicles. A strong magnet is indispensable for a high-performance permanent magnet synchronous motor. Therefore, the processing accuracy of the magnet incorporated in the permanent magnet synchronous motor becomes a problem.

Generally, small measuring instruments such as micrometer and caliper are convenient and suitable for measuring the processing accuracy of small parts, but the main parts such as the frame of the small measuring instrument are iron (cast iron) products. Then, just by bringing the object to be measured, which is a strong magnet, close to a small measuring instrument, the two will strongly stick to each other, and it will not be possible to measure, but it will be difficult to peel it off. Therefore, conventionally, even if it is a small part, if it is a strong magnet, it has been necessary to use a large measuring machine such as a three-dimensional measuring machine. This has a considerable effect on production efficiency and manufacturing cost.

Various small measuring instruments suitable for use in a magnetic field have been proposed so far. However, there was no digital type that could withstand practical practical use.

Akira Mitsukai 51-82480 JP-A-60-236001 Akira Mikai 50-50053 JP-A-2009-243883 Patent 4072282 Utility model registration No. 3184265 JP-A-58-115301

In order to make a small measuring instrument suitable for use in a magnetic field, it is conceivable to use a non-magnetic material as a main component of the small measuring instrument. However, a strong non-magnetic material is a difficult-to-cut material. For example, in a micrometer, it is necessary to cut a high-precision male screw on the spindle or tap a high-precision female screw on the main body frame, but it was difficult to do this with a non-magnetic material. .. There is a great need for a digital micrometer that can measure a measurement object that is a strong magnet and has practical accuracy.

An object of the present invention is to provide a digital micrometer suitable for measuring an object to be measured, which is a strong magnet.

The digital micrometer of the present invention
A main body having a U-shaped frame portion having an anvil inside one end of the U-shaped frame and a spindle holding portion provided on the other end side of the U-shaped frame portion so as to have a length in a direction away from the anvil. With the frame
A spindle that is held by the spindle holding portion, is provided so as to advance and retreat with respect to the anvil, and has a contact on one end surface.
A thimble part that converts the rotation operation into the linear motion of the spindle,
A digital micrometer including a displacement detector for detecting the displacement of the spindle.
The main body frame and the spindle are made of a non-magnetic material.
The thimble portion and the displacement detector are arranged on the other end side of the spindle holding portion.
The spindle holding portion has a length of a predetermined value or more.

In one embodiment of the invention
When the distance between the anvil and the contact when the spindle is most separated from the anvil is defined as the measurement range d of the digital micrometer.
It is preferable that the length of the spindle holding portion is equal to or greater than the measurement range d.

In one embodiment of the invention
The length of the spindle holding portion is preferably 200 mm or more.

In one embodiment of the invention
The thimble part
An inner sleeve that has a slit along the axis and is fixedly provided on the other end side of the main body frame.
It has an outer sleeve that is externally fitted to the inner sleeve so as to be rotatable in the circumferential direction and has a spiral groove on the inner peripheral surface.
An engaging pin fixedly provided on the spindle engages the spiral groove through the slit.
The thimble portion is preferably provided at the other end of the spindle holding portion.

In one embodiment of the invention
The displacement detector is preferably provided at the other end of the thimble portion.

In one embodiment of the invention
The displacement detector is
A contact that is inserted into the thimble portion from the other end of the thimble portion and moves integrally with the other end of the spindle.
It is preferable to have a scale that moves integrally with the contact and an encoder having a detection head that detects a relative position or a relative displacement amount with respect to the scale.

In one embodiment of the invention
further,
It is preferable that a first protective member made of a non-magnetic material is arranged around the thimble portion at a position separated from the thimble portion by a predetermined distance.

In one embodiment of the invention
further,
It is preferable that a second protective member made of a non-magnetic material is arranged around the displacement detector at a position separated from the displacement detector by a predetermined distance.

It is a front view which shows the appearance of a digital micrometer. It is a partial cross-sectional view which shows the internal structure of a digital micrometer. It is an exploded perspective view of the thimble part. It is an exploded perspective view of the detection part. It is an external view of the digital micrometer which concerns on 2nd Embodiment. It is sectional drawing of the digital micrometer which concerns on 2nd Embodiment. It is sectional drawing of the thimble part 400 in 2nd Embodiment. It is a graph which plotted the force acting between a neodymium magnet having a mass of about 1 kg and a plate having a sufficiently large area made of ferromagnet iron by changing the distance between the magnet and the iron plate. It is a figure which illustrates the 3rd Embodiment.

An embodiment of the present invention will be illustrated and described with reference to the reference numerals attached to each element in the drawing.
(First Embodiment)
A first embodiment according to the digital micrometer 100 of the present invention will be described.
FIG. 1 is a front view showing the appearance of the digital micrometer 100.
FIG. 2 is a cross-sectional view showing the internal structure of the digital micrometer 100.
The digital micrometer 100 includes a main body frame 200, a spindle 300, a thimble unit 400, and a detection unit 500.

The main body frame 200 is U-shaped as a whole, and an anvil 210 is provided inside one end of the U-shape.
A spindle 300 is provided on the other end side of the main body frame 200 so as to be able to advance and retreat.
At this time, on the other end side of the main body frame 200, the guide bush 220 is attached to the side closer to the anvil 210, and the thimble portion 400 is attached to the side far from the anvil 210.
Further, a display panel 201 is arranged on the front side of the main body frame 200. The display panel 201 is provided with a digital display unit 230 and a plurality of operation switches 240. The display panel 201 is made of a non-magnetic material such as plastic or resin.

Here, the main body frame 200 is preferably made of austenitic stainless steel. Austenitic stainless steel is a strong and non-magnetic material.

Alternatively, the body frame 200 may be made of pure aluminum or a non-magnetic aluminum alloy.

Further, the anvil 210 is preferably made of ceramic. As an example, the composition of the ceramic is zirconia.

The guide bush 220 is preferably made of brass. Brass is a non-magnetic material and a free-cutting material.
The guide bush 220 may be made of austenitic stainless steel.
However, it is considered preferable to have a hardness difference in the relationship between the sliding shaft and the hole.
In the case of a micrometer, it is preferable to design the spindle hardness to be high and the guide bush hardness to be low so that the guide bush wears during durability.
Austenitic stainless steel cannot be hardened.
This is because when it is hardened, it becomes slightly magnetic or softens. Therefore, the hardness difference of austenitic stainless steel cannot be controlled due to the difference in quenching. Therefore, when different materials have to be selected for the spindle and the guide bush, and the spindle 300 is made of austenitic stainless steel, the guide bush 220 is preferably brass.

The spindle 300 is generally a long rod-shaped cylinder, which is manufactured straight. A contactor 310 is provided on one end surface of the spindle 300. When measuring the object to be measured, the spindle 300 is moved forward and backward to sandwich the object to be measured between the contactor 310 and the anvil 210. The intermediate portion of the spindle 300 is bearing by the guide bush 220, and the other end side of the spindle 300 is inserted into the thimble portion 400.

An engaging piece member 330 is connected to the other end of the spindle 300. The piece member is an annular member and is fixedly fitted to the other end of the spindle 300. Specifically, the other end of the spindle 300 is provided with a taper 320 having a reduced diameter, and the engaging piece member 330 is provided with a taper hole 331 for receiving the other end of the spindle 300. The engaging pin 332 is press-fitted into the engaging piece member 330, and the engaging pin 332 is provided so as to project in a direction perpendicular to the axial direction of the spindle 300.

In this embodiment, the spindle 300 is not threaded and the spindle 300 itself does not rotate. The spindle 300 moves forward and backward in the axial direction in a non-rotating state.

The spindle 300 is preferably made of austenitic stainless steel.

Further, the contact 310 is preferably a flaky chip made of ceramic, like the anvil 210.

The engaging piece member is preferably made of brass.

FIG. 3 is an exploded perspective view of the thimble portion 400.
The thimble portion 400 is a tubular unit as a whole provided on the other end side of the main body frame 200. The other end side of the spindle 300 is received inside the thimble portion 400. The user advances and retreats the spindle 300 by rotating the thimble unit 400. The thimble portion 400 has an inner sleeve 410, an outer sleeve 420, and a cover member 430.

The inner sleeve 410 is a cylindrical member with both ends open, and has one slit 411 along the axis. One end side of the inner sleeve 410 is fixedly attached to the other end side of the main body frame 200. The other end of the spindle 300 is inserted through the opening on one end side of the inner sleeve 410. At this time, the other end of the spindle 300 is inserted into the inner sleeve 410, and the engaging pin 332 is press-fitted into the engaging piece member 330 through the slit 411 so that the engaging pin 332 protrudes from the slit 411. The inner diameter of the inner sleeve 410 is designed to be the same as the outer diameter of the engaging piece member 330. The engaging piece member 330 slides inside the inner sleeve 410 together with the spindle 300 in a state where the engaging piece member 330 is bearing on the inner peripheral surface of the inner sleeve 410. At this time, since the engaging pin 332 protrudes from the slit 411, the spindle 300 moves forward and backward in a state of being stopped by the engaging pin 332.

A cap 412 is screwed into the opening on the other end side of the inner sleeve 410.

The outer sleeve 420 is a cylindrical member having both ends open, and the outer sleeve 420 is provided so as to fit outside the inner sleeve 410.
At this time, the outer sleeve 420 is rotatable in the circumferential direction with respect to the inner sleeve 410. Here, a single spiral groove 421 is formed on the inner peripheral surface of the outer sleeve 420. The engagement pin 332 engages with the spiral groove 421.

The cover member 430 is a cover that covers the outer side of the outer sleeve 420, and has a knurled surface. There is no slip between the cover member 430 and the outer sleeve 420, and the cover member 430 and the outer sleeve 420 rotate integrally.

When the cover member 430 is rotated in the circumferential direction, the outer sleeve 420 rotates in the circumferential direction together with the cover member 430. Here, the engaging pin 332 is engaged with the spiral groove 421 on the inner circumference of the outer sleeve 420, and the engaging pin 332 is restricted from rotating by the slit 411 of the inner sleeve 410. Therefore, the engagement pin 332 is pushed by the spiral groove 421 by the rotation operation of the cover member 430 to move forward and backward.
Since the engaging pin 332, the engaging piece member 330, and the spindle 300 are integrated, the spindle 300 also advances and retreats as the engaging pin 332 advances and retreats.

Since the spindle 300 is made of austenitic stainless steel, it is difficult to thread the spindle itself as a mechanism for advancing and retreating the spindle 300. In this respect, in the present embodiment, a configuration is adopted in which the rotation-regulated engaging pin 332 is moved by the spiral groove 421 of the outer sleeve 420.

Here, the inner sleeve 410 is preferably made of brass.
Brass is a non-magnetic material and a free-cutting material.
Since the inner sleeve 410 is a bearing material, processing accuracy of the inner diameter is required. Further, a slit 411 is formed in the inner sleeve 410, and the slit 411 secures the straightness of the movement of the spindle 300 and realizes the rotation prevention. In this embodiment, the main scale 511 is directly or indirectly attached to the spindle when the movement of the spindle 300 is detected by the encoder 510 as described later.
Therefore, even a slight rotation of the spindle 300 affects the detection accuracy of the encoder. From this point of view, since it is difficult to process austenitic stainless steel, brass is considered to be preferable as the material of the inner sleeve 410.

Alternatively, the inner sleeve 410 may be made of pure aluminum or a non-magnetic aluminum alloy. In the case of pure aluminum or aluminum alloy, there are some inferior points in terms of large thermal expansion (large coefficient of linear expansion) and rigidity (Young's modulus), but there are advantages such as easy processing and light weight. .. If the main body frame 200 is made of austenitic stainless steel, the inner sleeve 410 may be made of pure aluminum or an aluminum alloy in consideration of the overall weight balance.
For a small measuring instrument (small tool), it is desirable that the weight is such that it will not be a burden even if it is held with one hand for a long time, and it is also safe because it is not easily damaged when dropped.
On the contrary, if the main body frame 200 is made of pure aluminum or a non-magnetic aluminum alloy, the inner sleeve 410 may be made of brass.
Further, the inner sleeve 410 may be made of austenitic stainless steel.
Among non-magnetic materials, austenitic stainless steel is preferable as a material for measuring instruments because of its small thermal expansion and high strength. However, there are problems that it is difficult to process and that the weight increases.

The outer sleeve is a resin molded product (for example, a liquid crystal polymer). The cover member is preferably formed of a resin molded product.

Next, the configuration of the detection unit 500 will be described.
FIG. 4 is an exploded perspective view of the detection unit 500.
The detection unit 500 includes an encoder 510 and a head fixing unit 530.
The encoder 510 is a linear encoder 510 and has a longitudinal main scale 511 and a detection head 512.
The main scale 511 and the detection head 512 are relatively movable along the longitudinal direction of the main scale 511, and the detection head 512 detects a position or displacement with respect to the main scale 511. In the present embodiment, the detection head 512 is fixedly provided with respect to the main body frame 200, and the main scale 511 moves forward and backward together with the spindle 300.

Here, the linear encoder 510 is a capacitance type. That is, the main scale 511 is provided with lattice electrodes arranged at a predetermined pitch in the longitudinal direction on a glass substrate. The detection head 512 is provided with a plurality of sets of transmission electrodes and reception electrodes on a glass substrate. Then, a predetermined AC signal is transmitted from the transmitting electrode of the detection head 512 to the lattice electrode of the main scale 511, and the potential of the lattice electrode induced by this AC signal is read by the receiving electrode. As a result, the detection head 512 detects the position or displacement with respect to the main scale 511.

A flat surface is formed on the side surface of the spindle 300, and this flat surface serves as a scale pedestal 520. The main scale 511 is attached and fixed to the scale pedestal 520. As a result, the main scale 511 moves back and forth together with the spindle 300.

The head fixing portion 530 has a head holding plate 531, a holding plate 533, and a fixing plate 534.

The detection head 512 is attached to one surface (back surface) of the head holding plate 531.
A plurality of (three) protrusions 532 are formed on one surface of the head holding plate 531 at positions that do not interfere with the detection head 512, and the tips of the protrusions 532 slidably contact the main scale 511. As a result, the detection head 512 faces the main scale 511 while locating a predetermined gap.

The pressing plate 533 is a leaf spring that pushes the other surface (front surface) of the head holding plate 531 to press the head holding plate 531 against the main scale 511. The pressing plate 533 pushes the head holding plate 531 from the front surface with a cantilever-shaped leaf spring.

The fixing plate 534 holds the holding plate 533 in a cantilever shape. Further, the fixing plate 534 is screwed to the mounting pedestal 250 formed on the main body frame 200.

For example, the head fixing portion 530, the head holding plate 531 and the holding plate 533, and the fixing plate 534 are made of austenitic stainless steel.

A flexible printed circuit board 540 is provided inside the main body frame 200, and includes encoder 510 (main scale 511, detection head 512), external output terminal 541, GND terminal 542, arithmetic processing circuit, digital display unit 230, and operation switch 240. Wiring is done.

In the present embodiment, as the moving mechanism of the spindle 300, a configuration is adopted in which the engaging pin 332 is moved by the rotation of the spiral groove 421. However, in this configuration, since the accuracy of the spiral groove 421 is limited, it is difficult to accurately determine the displacement amount of the spindle 300 from the rotation amount of the thimble portion 400. In this respect, in the present embodiment, a configuration is adopted in which the displacement of the spindle 300 is detected by the encoder 510.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIGS. 5 to 8.
The basic configuration of the second embodiment is the same as that of the first embodiment, but in the second embodiment, the spindle holding portion 720 between the U-shaped frame portion 710 and the thimble portion 400 has a length of a predetermined value or more. It is characterized by having.
Elements common to the second embodiment and the first embodiment are designated by corresponding reference numerals, and the description thereof will be omitted.

FIG. 5 is an external view of the digital micrometer 600 according to the second embodiment.
In FIG. 5, the main body frame 700 has a U-shaped frame portion 710 and a spindle holding portion 720.
An anvil 210 is provided inside one end of the U-shaped frame portion 710. A tubular spindle holding portion 720 is provided on the other end side of the U-shaped frame portion 710. The U-shaped frame portion 710 and the spindle holding portion 720 constituting the main body frame 700 are made of a non-magnetic material. Examples of the non-magnetic material forming the main frame 700 include austenitic stainless steel, pure aluminum, and non-magnetic aluminum alloy.

FIG. 6 is a cross-sectional view of the digital micrometer 600 according to the second embodiment.
The spindle 300 is inserted into the tubular spindle holding portion 720. The spindle 300 protrudes from one end of the spindle holding portion 720 so that it can move forward and backward in the axial direction with respect to the anvil 210. A contactor 310 is provided on one end surface of the spindle 300.

Here, it is desirable that the spindle holding portion 720 has a simple tubular shape. The main body frame 700 of the second embodiment does not require a space for incorporating an electrical system like the main body frame 700 of the first embodiment.

Further, in the second embodiment, the length of the spindle holding portion 720 is one of the features, which will be described later.

A thimble portion 400 is attached to the other end of the spindle holding portion 720. Further, a displacement detector 800 is attached to the other end of the thimble portion 400.

FIG. 7 is a cross-sectional view of the thimble portion 400 according to the second embodiment.
Basically, the configuration of the thimble portion 400 itself may be the same as the configuration of the thimble portion 400 described in the first embodiment. However, in the thimble portion 400 of the second embodiment, the constituent material does not necessarily have to be a non-magnetic material. For example, the inner sleeve may be made of an iron-based (steel-based) material.

In FIG. 7, the engaging pin 332 is directly attached to the spindle 300, but the engaging piece member 330 is attached to the rear end of the spindle 300 and engaged with the engaging piece member 330 as in the first embodiment. Pin 332 may be attached.

The displacement detector 800 may digitally detect the amount of advance / retreat of the rod-shaped stylus 830. It is a so-called digital dial gauge or indicator, which is a length measuring instrument (measuring instrument). The displacement detector 800 includes a housing 810, a stem 820 attached to the side surface of the housing 810, a stylus 830 provided so as to be able to move forward and backward in the axial direction through the stem 820, and an encoder that detects the displacement of the stylus 830. , Have. Further, the displacement detector 800 has an arithmetic processing unit, a display function unit, a connector terminal for external communication, or a wireless communication device.

A tubular joint 840 is attached (screwed) to the other end of the thimble portion 400, and a stem 820 of the displacement detector 800 is fixed to the other end of the tubular joint 840. Then, the stylus 830 is in contact with the rear end of the spindle 210, and follows the advance / retreat of the spindle 210. Therefore, the displacement (position) of the spindle 210 is detected as the displacement (position) of the stylus 830. The constituent material of the displacement detector 800 may be a non-magnetic material or a magnetic material. For example, the stylus 830 may be made of iron (a steel-based material).

By the way, at the time of measurement work for measuring an object to be measured, the object to be measured is sandwiched between one end and the other end of the U-shaped frame portion 710. If the object to be measured is a strong magnet, the region between one end and the other end of the U-shaped frame portion 710 is the region where the magnetic field is strongest. If there is a magnetic material near the U-shaped frame portion 710 during the measurement work, it will strongly attract the object to be measured (strong magnet) during the measurement work.
The area between one end and the other end of the U-shaped frame portion 710 will be referred to as a measurement object placement area.

In the second embodiment, the thimble portion 400 and the displacement detector 800, which may contain a ferromagnet (steel-based material) as a constituent material, are separated from the measurement object placement area by a predetermined distance or more.
Those arranged within a predetermined distance from the measurement object arrangement area, for example, the main body frame 700, the spindle 300, and the anvil 210 including the U-shaped frame portion 710 and the spindle holding portion 720 need to be made of a non-magnetic material. ..
On the other hand, a ferromagnet (steel-based material) can be used as a constituent material of the thimble portion 400 and the displacement detector 800 that are arranged at a distance of a predetermined distance or more from the measurement object arrangement area.

After changing the structure of the micrometer as in the second embodiment, the present inventors diligently examined how much the length L of the spindle holding portion 720 is required.
(Here, the length L of the spindle holding portion 720 corresponds to the distance between the measurement object placement area and the thimble portion 400, or the distance between the measurement object placement area and the displacement detector 800.)

Now, FIG. 8 shows the force acting between a neodymium magnet having a mass of about 1 kg and a plate (hereinafter referred to as an iron plate) having a sufficiently large area made of ferromagnet iron, between the magnet and the iron plate. It is a graph plotted at different distances.
Since the mass of a magnet used in a typical HEV (electric hybrid electric vehicle) or motor of an electric vehicle is about 1 kg, the force is calculated here with the mass of the magnet as about 1 kg.
From FIG. 8, it can be seen that when the distance from the magnet is 200 mm, the force with which the magnet attracts the iron plate is 0.04 N, which is almost unaffected by the magnet. Therefore, in the second embodiment, it is desirable to set the length L of the spindle holding portion 720 to 200 mm or more.
(In other words, the distance between the measurement object placement area and the thimble portion is 200 mm or more, or the distance between the measurement object placement area and the displacement detector is 200 mm or more.)
As a result, even when measuring the strong magnet constituting the HEV motor, the micrometer of the present embodiment and the object to be measured (strong magnet) hardly attract each other, and high-precision measurement becomes possible.

Note that the object to be measured is not always a strong magnet of 1 kg, and the smaller the size of the object to be measured, the smaller the magnetic force of the object to be measured. Therefore, the length L of the spindle holding portion 720 is planned. It may be determined according to the size of the object to be measured.
Now, the distance between the anvil 210 and the contact 310 when the spindle 300 is most separated from the anvil 210 is defined as the measurement range d of the digital micrometer.
At this time, the length L of the spindle holding portion 720 is preferably d or more.
Furthermore, it is preferable that the length L of the spindle holding portion 720 is 1.5 times or more the measurement range d.
Further, the length L of the spindle holding portion 720 may be twice or more the measurement range d.
Further, the length L of the spindle holding portion 720 may be set to 3 times or more the measurement range d.

If the length L of the spindle holding portion 720 is shorter than the measurement range d, the measurement target and the thimble portion 400 or the measurement target and the displacement detector 800 attract each other during the measurement operation, which affects the measurement accuracy. there is a possibility.
If the length L of the spindle holding portion 720 is 1.5 times or twice or more the measurement range d, the measurement target and the thimble portion 400 or the measurement target and the displacement detector 800 attract each other during the measurement operation. The force is considered to be small enough.
Further, if the length L of the spindle holding portion 720 becomes three times or more the measurement range d, the measurement object is brought closer to the thimble portion 400 and the displacement detector 800 even when the measurement object is replaced. It is thought that the number of accidents will be considerably reduced.

If the length of the spindle holding portion 720 becomes long, the amount of expansion and contraction due to the temperature change of the spindle holding portion 720 may increase.
If the spindle holding portion 720 expands and contracts during the measurement work, it will be superimposed as an error of the measured value. Therefore, by covering the spindle holding portion 720 with rubber or synthetic resin, it is possible to reduce the occurrence of an error in the measured value even when the micrometer of the present embodiment is used while being held by a person. Is preferable.

(Third Embodiment)
FIG. 9 illustrates a third embodiment of the present invention.
As the third embodiment, a protective member is further added to the digital micrometer described in the second embodiment.
As the protective member, a front side protective member (first protective member) 910 and a rear side protective member (second protective member) 930 are provided.
The front protective member (first protective member) 910 is arranged around the thimble portion 400 to prevent the object to be measured (strong magnet) from approaching or coming into contact with the thimble portion 400.
The front protective member 910 includes a plurality of (here, three) front arm portions 920 arranged at predetermined angular intervals (here, for example, 120 ° intervals).

The front arm portion 920 has a mounting portion 921, an extending portion 922, and a front arch portion 923.
The mounting portion 921 is mounted so as to fit outside the spindle holding portion 720 at the other end side (closer to the thimble portion) of the spindle holding portion 720.
All (three) front arm portions 920 are connected by one mounting portion 921.
The extending portion 922 is continuous from the mounting portion 921 and extends to the middle of the spindle holding portion 720 substantially in parallel with the spindle holding portion 720.
The front arch portion 923 is continuous from the tip of the extending portion 922 and faces the thimble portion 400 while being separated from the spindle holding portion 720 in an arc, and the tip is around the thimble portion 400.

The rear protective member (second protective member) 930 is arranged around the displacement detector 800 to prevent the object to be measured (strong magnet) from approaching or coming into contact with the displacement detector.
The rear side protective member 930 includes a plurality of (here, three) rear arm portions 940 arranged at predetermined angular intervals (here, for example, 120 ° intervals).
The rear arm portion 940 has an extension rod 941 attached to the cap 821 of the displacement detector 800 and a rear arch portion 942.
The rear arch portion 942 is continuous from the other end (rear end) of the extension rod 941 and faces the displacement detector 800 while moving away from the extension rod 941 in an arc, and the tip of the displacement detector 800 It is around.

The distance between the front arch portion 923 and the thimble portion 400 is preferably a predetermined distance or more, for example, about 100 mm or more. Similarly, it is preferable to secure a distance of about 100 mm between the rear arch portion 942 and the displacement detector 800.
From FIG. 8, if the distance between the object to be measured (strong magnet) and iron (the constituent material of the thimble portion 400 and the displacement detector 800) is 100 mm or more, the magnetic force between the two is about 1 N or less. It depends on what you can expect to be.

The front protective member (first protective member) 910 and the rear protective member (second protective member) 930 are made of a non-magnetic material.

Since the front protection member 910 and the rear protection member 930 have a gap for the operator to insert a hand, the operator can turn the thimble portion 400, set the displacement detector 800, and read the measured value. It doesn't get in the way. On the other hand, the presence of the front protective member 910 and the rear protective member 930 not only physically prevents the object to be measured from approaching the thimble portion 400 or the displacement detector 800, but also allows the operator to use the protective member 910, It also calls attention not to put a measurement object (strong magnet) inside the 930.

The present invention is not limited to the above embodiment, and can be appropriately modified without departing from the spirit.
In the description of the above embodiment, the materials of the main body frame, anvil, guide bush, spindle, engaging piece member, and thimble portion (inner sleeve, outer sleeve) have been exemplified, but in addition to the examples given above, non-magnetic materials are used. Materials include austenitic stainless steel such as high manganese austenitic stainless steel, pure aluminum, non-magnetic aluminum alloy, titanium alloy, ceramics, plastic (synthetic resin) such as carbon fiber reinforced plastic, beryllium copper, magnesium alloy, and You may choose from brass.

As the encoder, a capacitance type linear encoder was exemplified.
In addition, a photoelectric encoder, an electromagnetic induction encoder, and a magnetic encoder can be adopted.
As an encoder, it is considered preferable to use a glass substrate for both the main scale and the detection head.
However, only the chip of the arithmetic processing circuit may be surrounded by a magnetic shield material (for example, a ferromagnetic metal). If the tip is sufficiently small, the force (magnetic force) generated between the strong magnet and the object to be measured (work) will not be so large.

In the second embodiment, a thimble portion is attached to the other end of the spindle holding portion, and a displacement detector is provided at the other end of the thimble portion.
The positions of the thimble portion and the displacement detector may be reversed so that the displacement detector is attached to the other end of the spindle holding portion and the thimble portion is attached to the other end of the displacement detector.
However, as in the second embodiment, it is preferable to arrange the displacement detector having a built-in arithmetic processing unit, communication function, etc. as far as possible from the measurement object arrangement area.

100 ... Digital micrometer,
200 ... Body frame,
210 ... Anvil, 220 ... Guide bush, 230 ... Digital display, 240 ... Operation switch, 250 ... Mounting pedestal,
300 ... Spindle, 310 ... Contact, 320 ... Taper,
330 ... Engagement piece member, 331 ... Tapered hole, 332 ... Engagement pin,
400 ... Thimble part,
410 ... Inner sleeve, 411 ... Slit, 412 ... Cap,
420 ... outer sleeve, 421 ... spiral groove,
430 ... Cover member,
500 ... Detector,
510 ... encoder, 511 ... main scale, 512 ... detection head,
520 ... Scale pedestal,
530 ... Head fixing part,
531 ... Head holding plate, 532 ... Protrusion, 533 ... Holding plate, 534 ... Fixed plate.
540 ... Flexible printed circuit board,
600 ... Digital micrometer,
700 ... Main body frame, 710 ... Character frame part, 720 ... Spindle holding part,
800 ... displacement detector, 810 ... housing, 820 ... stem, 830 ... stylus, 840 ... fitting,
910 ... Front protection member,
920 ... front arm part, 921 ... mounting part, 922 ... extending part, 923 ... front arch part,
930 ... Rear protection member,
940 ... rear arm part, 941 ... extension rod, 942 ... rear arch part.

Claims (8)

A main body having a U-shaped frame portion having an anvil inside one end of the U-shaped frame and a spindle holding portion provided on the other end side of the U-shaped frame portion so as to have a length in a direction away from the anvil. With the frame
A spindle that is held by the spindle holding portion, is provided so as to advance and retreat with respect to the anvil, and has a contact on one end surface.
A thimble part that converts the rotation operation into the linear motion of the spindle,
A digital micrometer including a displacement detector for detecting the displacement of the spindle.
The main body frame and the spindle are made of a non-magnetic material.
The thimble portion and the displacement detector are arranged on the other end side of the spindle holding portion.
A digital micrometer characterized in that the length of the spindle holding portion is equal to or greater than a predetermined value. In the digital micrometer according to claim 1,
When the distance between the anvil and the contact when the spindle is most separated from the anvil is defined as the measurement range d of the digital micrometer.
A digital micrometer characterized in that the length of the spindle holding portion is equal to or greater than the measurement range d. In the digital micrometer according to claim 1 or 2.
A digital micrometer characterized in that the length of the spindle holding portion is 200 mm or more. In the digital micrometer according to any one of claims 1 to 3.
The thimble part
An inner sleeve that has a slit along the axis and is fixedly provided on the other end side of the main body frame.
It has an outer sleeve that is externally fitted to the inner sleeve so as to be rotatable in the circumferential direction and has a spiral groove on the inner peripheral surface.
An engaging pin fixedly provided on the spindle engages the spiral groove through the slit.
The thimble portion is a digital micrometer characterized in that the thimble portion is provided at the other end of the spindle holding portion. In the digital micrometer according to claim 4.
The displacement detector is a digital micrometer characterized in that it is provided at the other end of the thimble portion. In the digital micrometer according to claim 5.
The displacement detector is
A contact that is inserted into the thimble portion from the other end of the thimble portion and moves integrally with the other end of the spindle.
A digital micrometer comprising: a scale that moves integrally with the contact and an encoder having a detection head that detects a relative position or displacement with respect to the scale. In the digital micrometer according to any one of claims 1 to 6.
further,
A digital micrometer characterized in that a first protective member formed of a non-magnetic material is arranged around the thimble portion at a position separated from the thimble portion by a predetermined distance. In the digital micrometer according to any one of claims 1 to 7.
further,
A digital micrometer characterized in that a second protective member made of a non-magnetic material is arranged around the displacement detector at a position separated from the displacement detector by a predetermined distance.