Patent Description:
Recently, demand for hybrid vehicles and electric vehicles has been increased, and permanent-magnet synchronous motors are intensively developed and manufactured. Strong magnets are indispensable to high-performance permanent-magnet synchronous motors. Thus, the machining accuracy of magnets to be incorporated in the permanent-magnet synchronous motors matters.

Generally, small measuring devices, such as micrometers or calipers, are convenient and suitable for measuring the machining accuracy of a small part, but main parts of a small measuring device, such as a frame and the like, are iron (cast iron) products. Thus, when an object to be measured that is a strong magnet is brought close to a small measuring device, those two are strongly stuck to each other. Then, measurement cannot be performed, and it is difficult to separate them. For this reason, if a small part is a strong magnet, it has been required to use a large measuring machine, such as a coordinate measuring machine or the like, to measure the small part. This considerably affects manufacturing efficiency and cost.

There have been proposed various small measuring devices suitable for being used in a magnetic field. However, there has been no digital type device that can be durable in practical use.

<CIT> discloses a caliper type micrometer, in which a pair of measuring jaws are attached to a body and to the end of an advancing rod which advances and retracts against the body, opposite each other and at right angles to the axis of the advancing rod, to measure the inner or outer dimensions of an object to be measured by bringing these measuring jaws into contact with a measuring part of the object to be measured.

<CIT> discloses a micrometer caliper which is so constructed that its final reading will be given automatically, eliminating manual adjustment and the necessity of relying upon the sense of touch, by forming the spindle of a micrometer caliper of two preferably concentric parts, the outer part constituting the micrometer screw, wherein the inner part may be moved in relation to the outer part by the pressure of a work piece to actuate the pin of an indicator of the usual spring type. A spring situated between the two parts returns the movable part to its original position when pressure is released, and a second spring situated between said parts prevents movements of the spindle.

<CIT> discloses an inside micrometer, including an inside micrometer body including a cylinder having a through-hole, the inner circumference of the through-hole being provided with an internal thread, a first spindle screwed to the internal thread in an advanceable and retractable manner from a first end of the through-hole, and a thimble provided on the outside of the cylinder, the thimble being capable of rotating integrally with the first spindle; a plurality of anvils having different lengths in increments of a predetermined dimension, the anvil being capable of attachment and detachment on a second end opposite to the first end of the through-hole of the cylinder; a first extension member provided with a through-hole to which the anvil is inserted, the first extension member being selectively interposed between the second end side of the cylinder and the anvil to adjust a measurement range; and a second extension member having a second spindle which advances and retracts together with the first spindle, the second extension member being selectively attached to the first end side of the first spindle in an attachable and detachable manner.

<CIT> discloses a tool having a transparent graduated body and a hollow arm which house a spindle. Jaws with rims are mounted on the ends of the hollow arm and spindle and grip a disk on operating a button attached to the spindle. The button is spring loaded in the direction of jaw opening and has a cursor attached which is read against the graduations.

<CIT> discloses a micrometer type measuring device, wherein: a coupling part is provided to a spindle, an inner sleeve formed with a slit for inserting the coupling is fixed to a U-shape main frame, a spiral groove is formed on an outer sleeve so as to make the spiral sleeve have relatively large pitch and the movement of the spindle is detected with the first detector of the U-shape main frame and the second detector of the spindle. The spindle is supported free of slide on the spindle main body provided with the second detector and the inner surface of the inner sleeve. Further, an end part having the dimension in perpendicular direction to the spindle axis larger than the spindle main body provided with the second detector is provided.

<CIT> discloses a portable displacement measuring instrument, notably a micrometer, that comprises a body, an anvil, a spindle moveable with respect to the body, an encoder detecting an axial displacement of the spindle, a rotationally-mounted thimble being actionable by a user for bringing the spindle into contact with a workpiece and a transmission mechanism being provided between the thimble and the spindle for converting a rotation of the thimble in a translation of the spindle towards the anvil. The transmission mechanism comprises a constant force mechanism configured for disengaging the transmission mechanism when a movement of the spindle towards the anvil is opposed by a load being equal or surpassing a threshold load. The constant force mechanism comprises an adjusting mechanism arranged for setting the threshold load within a predefined range.

In <CIT>, precision measuring instruments having highly parallel and wearresistant contact members and a method for fabricating these contact areas are disclosed. The measuring instruments preferably include two contact members each having diamond coated ceramic substrates. The metalized surface of the substrate is preferably affixed to the contact members of the measuring instrument by brazing, gluing or welding.

<CIT> discloses a micrometer providing a quick adjustment mode and a fine adjustment mode. A spline-like rotary coupling configuration constrains the micrometer thimble and a threaded element to move together with respect to rotation, but does not constrain the position of the threaded element relative to the thimble along the measurement axis. A gear in the micrometer frame includes gear teeth that mesh with the threaded element and roll thereon along the measurement direction. A locking arrangement, when unlocked, allows the meshed gear to be rotated by a user to drive the threaded element along the measuring axis in the quick adjustment mode. When locked, the locking arrangement prevents motion of the gear to provide the fine adjustment mode, wherein the user rotates the thimble to screw the threaded element through the meshed teeth of the gear, to adjust the spindle position.

In order for a small measuring device to be suitable for being used in a magnetic field, the constituent parts of the small measuring device can be formed of a non-magnetic material. However, a non-magnetic material having strength is a difficult-to-cut material. For example, in a micrometer, it is required to form an external thread on the spindle and to tap an internal thread on the main-body frame with high accuracy, but it is difficult to perform such machining on a non-magnetic material. For this reason, it is desired that a practically accurate digital micrometer capable of measuring an object to be measured that is a strong magnet.

A purpose of the present invention is to provide a digital micrometer suitable for measuring an object to be measured that is a strong magnet.

The solution to the above problem is defined in accordance with the subject-matter of independent claims <NUM> and <NUM>, wherein preferred embodiments based thereon are provided in accordance with the respective dependent claims.

In an embodiment, it is preferable that the length of the spindle holding part is <NUM> or more.

In the digital micrometer according to the invention as specified in claims <NUM> and <NUM>,.

In the embodiment specified in claim <NUM>, the displacement detector is provided on the other end of the thimble part.

In an embodiment, it is preferable that
the displacement detector includes:.

In an embodiment, the digital micrometer preferably includes a first protection member formed of a non-magnetic material and disposed, around the thimble part, at a position separated from the thimble part by a predetermined distance.

In an embodiment, the digital micrometer preferably includes a second protection member formed of a non-magnetic material and disposed, around the displacement detector, at a position separated from the displacement detector by a predetermined distance.

A digital micrometer according to claim <NUM> includes:.

In an embodiment, it is preferable that the anvil and the contactor is formed of ceramic.

In an embodiment, the digital micrometer preferably includes a guide bush provided, on the other end side of the main-body frame, closer to the anvil to bear the spindle, in which
the guide bush is formed of brass.

In an embodiment, it is preferable that the encoder is a capacitive encoder, a photoelectric encoder, an electromagnetic induction encoder, or a magnetic encoder.

Embodiments of the present invention are illustrated and described with reference to reference signs attached to elements in the drawings.

A digital micrometer <NUM> according to a first exemplary embodiment of the present invention is described below.

<FIG> is a front view of the external appearance of the digital micrometer <NUM>.

<FIG> is a cross-sectional view of the internal structure of the digital micrometer <NUM>.

The digital micrometer <NUM> includes a main-body frame <NUM>, a spindle <NUM>, a thimble part <NUM>, and a detecting unit <NUM>.

The main-body frame <NUM> has a U shape as a whole, and an anvil <NUM> is provided on the inner side of one end of the U shape.

The spindle <NUM> is provided on the other end side of the main-body frame <NUM> to be movable forward and backward.

At this time, on the other end side of the main-body frame <NUM>, a guide bush <NUM> is mounted closer to the anvil <NUM>, and the thimble part <NUM> is mounted farther from the anvil <NUM>.

In addition, on the front side of the main-body frame <NUM>, a display panel <NUM> is disposed. The display panel <NUM> is provided with a digital display unit <NUM> and a plurality of operation switches <NUM>. The display panel <NUM> is formed of a non-magnetic material, such as plastic, resin, or the like.

Here, the main-body frame <NUM> is preferably formed of austenitic stainless steel. Austenitic stainless steel has strength and a non-magnetic material.

Alternatively, the main-body frame <NUM> may be formed of pure aluminium or a non-magnetic aluminium alloy.

In addition, the anvil <NUM> is preferably formed of ceramic. As the composition of ceramic, zirconia is exemplified.

The guide bush <NUM> is preferably formed of brass. Brass is a non-magnetic and free-cutting material.

Note that, the guide bush <NUM> may be formed of austenitic stainless steel.

However, it is preferable to have the difference in hardness in consideration of the relationship between a sliding shaft and a hole.

In the case of a micrometer, it is preferable to design the hardness of the spindle to be high and the hardness of the guide bush to be low in such a manner that the guide bush wears when enduring.

Austenitic stainless steel cannot be quenched.

This is because that quenching causes slight magnetism or softening. Thus, difference in the hardness of austenitic stainless steel cannot be controlled by quenching. For this reason, different materials have to be selected for the spindle and the guide bush, and the guide bush <NUM> is preferably formed of brass if the spindle <NUM> is formed of austenitic stainless steel.

The spindle <NUM> is substantially a long rodlike columnar body and is manufactured to be straight. The spindle <NUM> has one end face provided with an contactor <NUM>. In measurement of an object to be measured, the spindle <NUM> is moved forward and backward to sandwich the object to be measured between the contactor <NUM> and the anvil <NUM>. The middle portion of the spindle <NUM> is borne by the guide bush <NUM>, and the other end side of the spindle <NUM> is inserted into the thimble part <NUM>.

The other end of the spindle <NUM> is coupled to an engaging piece member <NUM>. The piece member is an annular member and is fixedly fitted on the other end of the spindle <NUM>. Specifically, the other end of the spindle <NUM> is provided with a taper <NUM> whose diameter is gradually reduced, and the engaging piece member <NUM> is provided with a taper hole <NUM> for receiving the other end of the spindle <NUM>. An engaging pin <NUM> is provided by being press-fitted into the engaging piece member <NUM> in such a manner that the engaging pin <NUM> projects in the direction perpendicular to the axial direction of the spindle <NUM>.

In the present embodiment, no external thread is formed on the spindle <NUM>, and the spindle <NUM> itself does not rotate. The spindle <NUM> moves forward and backward in the axial direction in a non-rotating state.

The spindle <NUM> is formed of austenitic stainless steel.

In addition, the contactor <NUM> is preferably a thin chip formed of ceramic similarly to the anvil <NUM>.

The engaging piece member is preferably formed of brass.

<FIG> is an exploded perspective view of the thimble part <NUM>.

The thimble part <NUM> is provided on the other end side of the main-body frame <NUM> and is a cylindrical unit as a whole. The thimble part <NUM> receives the other end side of the spindle <NUM> inside it. A user moves the spindle <NUM> forward and backward by rotationally operating the thimble part <NUM>. The thimble part <NUM> includes an inner sleeve <NUM>, an outer sleeve <NUM>, and a cover member <NUM>.

The inner sleeve <NUM> is a cylindrical member having openings on both ends and includes one slit <NUM> along the axial line. One end side of the inner sleeve <NUM> is fixedly mounted on the other end side of the main-body frame <NUM>. The other end of the spindle <NUM> is inserted from the opening on the one end side of the inner sleeve <NUM>. At this time, the other end of the spindle <NUM> is inserted into the inner sleeve <NUM>, and the engaging pin <NUM> is press-fitted into the engaging piece member <NUM> through the slit <NUM> in such a manner that the engaging pin <NUM> protrudes from the slit <NUM>. The inner diameter of the inner sleeve <NUM> is designed to be the same as the outer diameter of the engaging piece member <NUM>. While the engaging piece member <NUM> is borne by the inner peripheral surface of the inner sleeve <NUM>, the engaging piece member <NUM> together with the spindle <NUM> slides inside the inner sleeve <NUM>. At this time, since the engaging pin <NUM> protrudes from the slit <NUM>, the spindle <NUM> moves forward and backward while the rotation thereof is stopped by the engaging pin <NUM>.

Into the opening on the other end side of the inner sleeve <NUM>, a cap <NUM> is screwed.

The outer sleeve <NUM> is a cylindrical member having openings on both ends and is provided by being fitted on the outer surface of the inner sleeve <NUM>.

At this time, the outer sleeve <NUM> is rotatable in the peripheral direction with respect to the inner sleeve <NUM>. Here, on the inner peripheral surface of the outer sleeve <NUM>, one spiral groove <NUM> is formed. The engaging pin <NUM> is engaged with the spiral groove <NUM>.

The cover member <NUM> is a cover covering the outer surface of the outer sleeve <NUM> and has a knurled surface. There is no slippage between the cover member <NUM> and the outer sleeve <NUM>, and the cover member <NUM> and the outer sleeve <NUM> integrally rotate.

When the cover member <NUM> is rotationally operated in the peripheral direction, the cover member <NUM> and the outer sleeve <NUM> rotate in the peripheral direction. Here, the engaging pin <NUM> is engaged with the spiral groove <NUM> on the inner peripheral surface of the outer sleeve <NUM>, and the rotation of the engaging pin <NUM> is regulated by the slit <NUM> of the inner sleeve <NUM>. Thus, by rotationally operating the cover member <NUM>, the engaging pin <NUM> is pushed by the spiral groove <NUM> and moves forward and backward.

Since the engaging pin <NUM>, the engaging piece member <NUM>, and the spindle <NUM> are integrated, the spindle <NUM> also moves forward and backward when the engaging pin <NUM> moves forward and backward.

Since the spindle <NUM> is formed of austenitic stainless steel, it is difficult to form a thread on the spindle itself as a mechanism for moving the spindle <NUM> forward and backward. In this regard, the engaging pin <NUM> whose rotation is regulated is moved by the spiral groove <NUM> of the outer sleeve <NUM> in the present embodiment.

Here, the inner sleeve <NUM> is formed of brass.

Brass is a non-magnetic and free-cutting material.

Since the inner sleeve <NUM> is a bearing member, the machining accuracy of its inner diameter is required. In addition, the inner sleeve <NUM> is formed with the slit <NUM>, and the slit <NUM> secures the straight movement of the spindle <NUM> and stops the rotation. As described later, in order for an encoder <NUM> to detect the movement of the spindle <NUM>, a main scale <NUM> is directly or indirectly mounted on the spindle in the present embodiment.

Thus, if the spindle <NUM> slightly rotates, the detection accuracy of the encoder is affected. In this respect, since it is difficult to machine austenitic stainless steel, brass is considered to be suitable as a material of the inner sleeve <NUM>.

Alternatively, the inner sleeve <NUM> is formed of pure aluminium or a non-magnetic aluminium alloy. In the case of pure aluminium or an aluminium alloy, it has some disadvantages in large thermal expansion (a large linear expansion coefficient) and stiffness (Young's modulus) but has advantages in easily machining and light weight. If the main-body frame <NUM> is formed of austenitic stainless steel, the inner sleeve <NUM> is formed of pure aluminium or an aluminium alloy, considering the total weight balance.

It is desirable that a small measuring device (small tool) has a weight that is not burden when held with one hand for a long time. Such a device hardly damages itself and is safe when dropped.

On the other hand, if the main-body frame <NUM> is formed of pure aluminium or a non-magnetic aluminium alloy, the inner sleeve <NUM> is formed of brass.

Austenitic stainless steel is preferable as a material of a measuring device among non-magnetic materials since it has small thermal expansion and high strength. However, it has problems of difficulty in machining and of increasing the weight.

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

Next, the configuration of the detecting unit <NUM> is described.

<FIG> is an exploded perspective view of the detecting unit <NUM>.

The detecting unit <NUM> includes an encoder <NUM> and a head fixing part <NUM>.

The encoder <NUM> is a linear encoder <NUM> and includes an elongate main scale <NUM> and a detection head <NUM>.

The main scale <NUM> and the detection head <NUM> are relatively movable along the longitudinal direction of the main scale <NUM>, and the detection head <NUM> detects the position or displacement with respect to the main scale <NUM>. In the present embodiment, the detection head <NUM> is fixedly provided to the main-body frame <NUM>, and the main scale <NUM> moves forward and backward together with the spindle <NUM>.

In this description, the linear encoder <NUM> is a capacitive type. That is, the main scale <NUM> is formed by arranging grid electrodes in the longitudinal direction at a predetermined pitch on a glass substrate. The detection head <NUM> is formed by providing a plurality of sets of transmitting electrodes and receiving electrodes on a glass substrate. Then, a predetermined AC signal is transmitted from the transmitting electrodes of the detection head <NUM> to the grid electrodes of the main scale <NUM>, and the receiving electrodes read the potential of the grid electrodes induced by the AC signal. Consequently, the detection head <NUM> detects the position or displacement with respect to the main scale <NUM>.

The spindle <NUM> has a side face having a plane surface, and the plane surface serves as a scale base <NUM>. The main scale <NUM> is fixedly mounted on the scale base <NUM>. Consequently, the main scale <NUM> moves forward and backward together with the spindle <NUM>.

The head fixing part <NUM> includes a head holding plate <NUM>, a pressing plate <NUM>, and a fixing plate <NUM>.

The head holding plate <NUM> has a face (rear face) provided with the detection head <NUM>.

On the face of the head holding plate <NUM>, a plurality of (three) protrusions <NUM> is formed at a position where the protrusions <NUM> do not interfere with the detection head <NUM>, and the tips of the protrusions <NUM> slidably abut the main scale <NUM>. Consequently, the detection head <NUM> faces the main scale <NUM> while keeping a position with a predetermined gap.

The pressing plate <NUM> is a flat spring that presses the other face (front face) of the head holding plate <NUM> to press the head holding plate <NUM> against the main scale <NUM>. The pressing plate <NUM> is a cantilever flat spring that presses the head holding plate <NUM> from the front face.

The fixing plate <NUM> holds the pressing plate <NUM> in a cantilever manner. In addition, the fixing plate <NUM> is screwed to a mounting base <NUM> formed on the main-body frame <NUM>.

For example, the head fixing part <NUM>, the head holding plate <NUM>, the pressing plate <NUM>, and the fixing plate <NUM> are formed of austenitic stainless steel.

Inside the main-body frame <NUM>, a flexible printed circuit board <NUM> is provided. The flexible printed circuit board <NUM> includes the wiring of the encoder <NUM> (the main scale <NUM> and the detection head <NUM>), an external output terminal <NUM>, a GND terminal <NUM>, an arithmetic processing circuit, the digital display unit <NUM>, and the operation switches <NUM>, that is, incorporates what is called an electrical system.

In the present embodiment, as the movement mechanism of the spindle <NUM>, the configuration for moving the engaging pin <NUM> by the rotation of the spiral groove <NUM> is employed. However, with this configuration, the accuracy of the spiral groove <NUM> is limited, and it is difficult to accurately acquire the displacement amount of the spindle <NUM> from the rotation amount of the thimble part <NUM>. In this regard, the configuration for detecting the displacement of the spindle <NUM> with the encoder <NUM> is employed in the present embodiment.

A second exemplary embodiment of the present invention is described below with reference to <FIG>.

The basic configuration in the second exemplary embodiment is common to that in the first exemplary embodiment, but the second exemplary embodiment has a characteristic that a spindle holding part <NUM> provided between a U-shaped frame part <NUM> and a thimble part <NUM> has a length of a predetermined value or more.

The elements common to the second exemplary embodiment and the first exemplary embodiment are denoted by the same reference signs, and the description thereof is omitted.

<FIG> is an external view of a digital micrometer <NUM> according to the second exemplary embodiment.

In <FIG>, a main-body frame <NUM> includes a U-shaped frame part <NUM> and a spindle holding part <NUM>.

On an inner side of one end of the U-shaped frame part <NUM>, an anvil <NUM> is provided. On the other end side of the U-shaped frame part <NUM>, a cylindrical spindle holding part <NUM> is provided. Then, the U-shaped frame part <NUM> and the spindle holding part <NUM> constituting the main-body frame <NUM> are formed of a non-magnetic material. The non-magnetic material of the main-body frame <NUM> is, for example, austenitic stainless steel, pure aluminium, or a non-magnetic aluminium alloy.

<FIG> is a cross-sectional view of the digital micrometer <NUM> according to the second exemplary embodiment.

Inside the cylindrical spindle holding part <NUM>, a spindle <NUM> is inserted. The spindle <NUM> protrudes from one end of the spindle holding part <NUM> and is movable forward and backward in the axial direction with respect to the anvil <NUM>. The spindle <NUM> has one end face provided with a contactor <NUM>.

Here, the spindle holding part <NUM> desirably has a simple cylindrical shape. The main-body frame <NUM> in the second exemplary embodiment does not need a space for incorporating an electrical system unlike the main-body frame <NUM> in the first exemplary embodiment.

In addition, the length of the spindle holding part <NUM> is a characteristic of the second exemplary embodiment, but this is described later.

The thimble part <NUM> is mounted on the other end of the spindle holding part <NUM>. Furthermore, a displacement detector <NUM> is mounted on the other end of the thimble part <NUM>.

<FIG> is a cross-sectional view of the thimble part <NUM> in the second exemplary embodiment.

Basically, the configuration of the thimble part <NUM> may be the same as that of the thimble part <NUM> described in the first exemplary embodiment. However, the constituent material of the thimble part <NUM> in the second exemplary embodiment is not necessarily a non-magnetic material. For example, the inner sleeve may be formed of an iron (iron and steel) material.

In <FIG>, an engaging pin <NUM> is directly mounted to the spindle <NUM>. However, an engaging piece member <NUM> may be mounted on the rear end of the spindle <NUM>, and the engaging pin <NUM> may be mounted to the engaging piece member <NUM> similarly to the first exemplary embodiment.

The displacement detector <NUM> is only required to digitally detect the amount of forward/backward movement of a rodlike contact point <NUM>. The displacement detector <NUM> is a length-measuring device (measuring device) that is called a digital dial gauge or an indicator. The displacement detector <NUM> includes a casing <NUM>, a stem <NUM> mounted on a side face of the casing <NUM>, the contact point <NUM> provided through the stem <NUM> to be movable in the axial direction, and an encoder that detects the displacement of the contact point <NUM>. The displacement detector <NUM> further includes an arithmetic processing unit, a display function unit, and a connector terminal or wireless communication device for external communication.

To the other end of the thimble part <NUM>, a cylindrical joint <NUM> is mounted (screwed), and the stem <NUM> of the displacement detector <NUM> is fixed on the other end of the cylindrical joint <NUM>. The contact point <NUM> abuts the rear end of a spindle <NUM> and follows the forward/backward movement of the spindle <NUM>. Thus, the displacement (position) of the spindle <NUM> is detected as the displacement (position) of the contact point <NUM>. The constituent material of the displacement detector <NUM> may be a non-magnetic material or a magnetic material. For example, the contact point <NUM> may be formed of iron (an iron and steel material).

At a measurement operation time 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 part <NUM>. If the object to be measured is a strong magnet, the magnetic field is strongest in the area between the one end and the other end of the U-shaped frame part <NUM>. If there is a magnetic material near the U-shaped frame part <NUM> at a measurement operation time, the magnetic material strongly attracts the object to be measured (strong magnet) at the measurement operation time.

The area between the one end and the other end of the U-shaped frame part <NUM> is referred to as an object-to-be-measured placement area.

In the second exemplary embodiment, the thimble part <NUM> and the displacement detector <NUM>, which can include a ferromagnetic material (iron and steel material) as the constituent material, are to be separated from the object-to-be-measured placement area by a predetermined distance or more.

The parts that are disposed within the predetermined distance from the object-to-be-measured placement area, such as the main-body frame <NUM> constituted by the U-shaped frame part <NUM> and the spindle holding part <NUM>, the spindle <NUM>, and the anvil <NUM>, need to be formed of a non-magnetic material.

On the other hand, as the constituent material of the thimble part <NUM> and the displacement detector <NUM> that are disposed to be separated from the object-to-be-measured placement area by the predetermined distance or more, a ferromagnetic material (iron and steel material) is usable.

The inventors has changed the structure of the micrometer as in the second exemplary embodiment and diligently studied about the necessary length L of the spindle holding part <NUM>.

(Here, the length L of the spindle holding part <NUM> is equivalent to the distance between the object-to-be-measured placement area and the thimble part <NUM> or the distance between the object-to-be-measured placement area and the displacement detector <NUM>.

<FIG> is a graph in which the force acting between a neodymium magnet having a mass of about <NUM> and a plate having a sufficiently large area and made of iron, which is a ferromagnetic material, (hereinafter, referred to as an iron plate) is plotted, changing the distance between the magnet and the iron plate.

Since the mass of a magnet used for the motor of a typical hybrid electric vehicle (HEV) or electric vehicle is about <NUM>, the force is calculated on the assumption that the mass of the magnet is about <NUM> in this description.

<FIG> shows that the force with which the magnet attracts the iron plate is <NUM> N when the iron plate is separated from the magnet by <NUM>, and that the iron plate is hardly affected by the magnet. For this reason, the length L of the spindle holding part <NUM> is desirable to be set to <NUM> or more in the second exemplary embodiment.

(In other words, the distance between the object-to-be-measured placement area and the thimble part is set to be <NUM> or more, or the distance between the object-to-be-measured placement area and the displacement detector is set to be <NUM> or more.

Consequently, in the case of measuring a strong magnet constituting the motor or an HEV, the micrometer in the present embodiment hardly attracts an object to be measured (strong magnet), and it is possible to perform the measurement with high accuracy.

Note that, this does not mean that an object to be measured is always a strong magnet of <NUM>. However, as the size of an object to be measured decreases, the magnetic force of the object to be measured also decreases, and the length L of the spindle holding part <NUM> may be determined depending on the size of a scheduled object to be measured.

Here, the distance between the anvil <NUM> and the contactor <NUM> when the spindle <NUM> is most separated from the anvil <NUM> is referred to as a measuring range d of the digital micrometer.

At this time, the length L of the spindle holding part <NUM> is preferably d or more.

In addition, the length L of the spindle holding part <NUM> is preferably <NUM> times or more the measuring range d.

Furthermore, the length L of the spindle holding part <NUM> may be twice or more the measuring range d.

Moreover, the length L of the spindle holding part <NUM> may be three times or more the measuring range d.

If the length L of the spindle holding part <NUM> is shorter than the measuring range d, an object to be measured and the thimble part <NUM> or an object to be measured and the displacement detector <NUM> can attract each other during the measurement operation, which can affect the measurement accuracy.

If the length L of the spindle holding part <NUM> is <NUM> times or twice or more the measuring range d, the force with which an object to be measured and the thimble part <NUM> or an object to be measured and the displacement detector <NUM> attract each other during the measurement operation will be sufficiently small.

Furthermore, if the length L of the spindle holding part <NUM> is three times or more the measuring range d, the number of accidents that an object to be measured is brought close to the thimble part <NUM> or the displacement detector <NUM> will be considerably reduced in the case of changing the object to be measured.

Note that, if the length of the spindle holding part <NUM> is longer, the expansion/contraction amount of the spindle holding part <NUM> due to a temperature change can be increased.

When the spindle holding part <NUM> expands or contracts during a measurement operation, the expansion/contraction amounts are accumulated as measurement value errors. Thus, it is preferable to reduce measurement value errors by covering the spindle holding part <NUM> with rubber or synthetic resin although the micrometer in the present embodiment is used by a user holding it with a hand.

<FIG> shows an example of a third exemplary embodiment of the present invention.

In the third exemplary embodiment, a protection member is further added to the digital micrometer described in the second exemplary embodiment.

As the protection member, a front protection member (first protection member) <NUM> and a rear protection member (second protection member) <NUM> are provided.

The front protection member (first protection member) <NUM> is disposed around a thimble part <NUM> and prevents an object to be measured (strong magnet) from being close to or contact with the thimble part <NUM>.

The front protection member <NUM> is constituted by a plurality of (in this description, three) front arm parts <NUM> arranged at predetermined angular intervals (in this description, at <NUM>° intervals, for example).

The front arm parts <NUM> include a mounting part <NUM>, an extending part <NUM>, and a front arch part <NUM>.

The mounting part <NUM> is mounted closer to the other end of a spindle holding part <NUM> (closer to the thimble part) to be fitted on the spindle holding part <NUM>.

All of the (three) front arm parts <NUM> are connected by one mounting part <NUM>.

The extending part <NUM> is continuous from the mounting part <NUM> and extends substantially parallel with the spindle holding part <NUM> to the middle of the spindle holding part <NUM>.

The front arch part <NUM> is continuous from the tip of the extending part <NUM>, is directed toward the thimble part <NUM> while being separated from the spindle holding part <NUM> in an arc, and has its tip around the thimble part <NUM>.

The rear protection member (second protection member) <NUM> is disposed around the displacement detector <NUM> and prevents an object to be measured (strong magnet) from being close to or contact with the displacement detector.

The rear protection member <NUM> is constituted by a plurality of (in this description, three) rear arm parts <NUM> arranged at predetermined angular intervals (in this description, at <NUM>° intervals, for example).

The rear arm parts <NUM> include an extension rod <NUM> mounted on a cap <NUM> of the displacement detector <NUM> and a rear arch part <NUM>.

The rear arch part <NUM> is continuous from the other end (rear end) of the extension rod <NUM>, is directed toward the displacement detector <NUM> while being separated from the extension rod <NUM> in an arc, and has its tip around the displacement detector <NUM>.

The distance between the front arch part <NUM> and the thimble part <NUM> is a predetermined distance or more, for example, is preferably about <NUM> or more. Similarly, the distance between the rear arch part <NUM> and the displacement detector <NUM> is preferably about <NUM>.

This is because that the magnetic force between them is expected to be about <NUM> N or less when the distance between an object to be measured (strong magnet) and iron (the constituent material of the thimble part <NUM> and the displacement detector <NUM>) is <NUM> or more as shown in <FIG>.

The front protection member (first protection member) <NUM> and the rear protection member (second protection member) <NUM> are formed of a non-magnetic material.

The front protection member <NUM> and the rear protection member <NUM> have gaps for an operator to insert a hand, which does not interfere when the operator rotates the thimble part <NUM>, sets the displacement detector <NUM>, and reads a measurement value. Meanwhile, providing the front protection member <NUM> and the rear protection member <NUM> physically prevents an object to be measured from being close to the thimble part <NUM> or the displacement detector <NUM> and also catches an operator's attention not to insert an object to be measured (strong magnet) inside the protection members <NUM> and <NUM>.

Note that, the present invention is not limited to the above exemplary embodiments and can be appropriately modified without deviating from the scope.

In the above exemplary embodiments, the materials of the main-body frame, the anvil, the guide bush, the spindle, the engaging piece member, and the thimble part (the inner sleeve and the outer sleeve) have been exemplified. In addition to those examples, a non-magnetic material may be selected from austenitic stainless steel, such as high manganese austenitic stainless steel or the like, pure aluminium, a non-magnetic aluminium alloy, a titanium alloy, ceramic, plastic (synthetic resin), such as carbon fiber reinforced plastic or the like, beryllium copper, a magnesium alloy, and brass, provided it is not in contradiction with the scope of protection defined in claim <NUM>, which requires austenitic stainless steel for the spindle.

As the encoder, a capacitive linear encoder has been exemplified.

In addition to this, a photoelectric encoder, an electromagnetic induction encoder, or a magnetic encoder is applicable.

In the encoder, glass substrates are preferably used for the main scale and the detection head.

However, only the chip of the arithmetic processing circuit may be covered in a magnetic shield material (for example, a ferromagnetic metal). If the chip is sufficiently small, the force (magnetic force) generated between the chip and an object to be measured (workpiece) that is a strong magnet is not very large.

In the second exemplary embodiment, the thimble part is mounted on the other end of the spindle holding part, and the displacement detector is provided on the other end of the thimble part.

Claim 1:
A digital micrometer (<NUM>) comprising:
a main-body frame (<NUM>) including an U-shaped frame part including an anvil provided on an inner side of one end of the U-shaped frame, and a spindle holding part (<NUM>) being provided on the other end side of the U-shaped frame part and having a length in an axial direction;
a spindle (<NUM>) held by the spindle holding part (<NUM>), provided to be movable forward and backward in the axial direction, protruding from one end of the spindle holding part (<NUM>), and including a contactor (<NUM>) on one end face;
a thimble part (<NUM>) configured to convert rotational operation into linear motion of the spindle (<NUM>), one end of the thimble part (<NUM>) being coupled on the other end of the spindle holding part (<NUM>); and
a displacement detector (<NUM>) configured to detect displacement of the spindle (<NUM>),
wherein
the main-body frame (<NUM>) and the spindle (<NUM>) are formed of a non-magnetic material,
the thimble part (<NUM>) and the displacement detector (<NUM>) are disposed on the other end side of the spindle holding part (<NUM>), and
the length of the spindle holding part (<NUM>) is a predetermined value or more, such that a ferromagnetic material is usable for the thimble part and the detector,
wherein
the thimble part (<NUM>) includes:
an inner sleeve (<NUM>) having a slit (<NUM>) along an axial line and fixedly provided on the other end side of the main-body frame (<NUM>); and
an outer sleeve (<NUM>) fitted on the inner sleeve (<NUM>) to be rotatable in a peripheral direction and having a spiral groove (<NUM>) on an inner peripheral surface,
the spindle (<NUM>) includes an engaging pin (<NUM>),
the engaging pin (<NUM>) is fixedly provided to the spindle (<NUM>) and engaged with the spiral groove (<NUM>) through the slit (<NUM>), and
the thimble part (<NUM>) is provided on the other end of the spindle holding part (<NUM>),
wherein the displacement detector (<NUM>) is disposed on the other end side of the thimble part (<NUM>).