JPH10142032A - Electromagnetic force generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure with which an electromagnetic force generating device used for electronic balance can be assembled accurately and easily. SOLUTION: At the center of a lower yoke 1, a bolt 2 is arranged in an erected state as a shaft body so that the bolt 2 can share the axis of the yoke 1. A lower magnet 3, a ball piece 4, and an upper magnet 5 are coaxially positioned on the belt 2 in this order by sliding them on the bolt 2 by using their holes 3a, 4a, and 5a and fixed on the bolt 2 when a nut 6 is engaged with the bolt 2. Finally, an upper yoke 7 is put on the upper end of the lower yoke 1. Therefore, each member can be automatically centered and an electromagnetic force generating device can be assembled with accurate positional relations between each member when the members are put on the bolt 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for generating an electromagnetic force, and more particularly to an electromagnetic force generating device which can be suitably used as an electromagnetic portion of an electromagnetic balance type weighing device commonly called an electronic balance.

2. Description of the Related Art In an electromagnetic balance type weighing device (hereinafter referred to as an "electronic balance"), an electromagnetic force is generated by an electromagnetic force generator which balances the load of a weighed object transmitted via a beam, so that the weight of the weighed object is reduced. Is digitally displayed.

[0003] The electromagnetic force generator has a configuration in which a movable coil that is displaced in accordance with the load of a weighing object is disposed in a magnetic field formed by a permanent magnet (hereinafter, referred to as a "magnet"). An electronic balance has a feedback circuit that balances displacement of a movable coil to zero by Lorentz force caused by a current flowing in the movable coil so as to be orthogonal to a magnetic flux of a static magnetic field of a magnet in an electromagnetic force generator. This is a device that is configured to calculate the amount of electricity to be balanced at this time as the load of the weighed object.

[0004] The magnet has a constant temperature coefficient, and the amount of magnetic flux generated from the magnet changes due to the influence of Joule heat generated by the current flowing through the movable coil, causing an error in the measured value of the weighed object. Therefore, a method of detecting a temperature change in the vicinity of the magnet and performing arithmetic processing on the temperature change as a correction value to correct the measured value has been adopted. However, in this method, it is difficult to accurately correct a short-time temperature change.

[0005] Here, if the amount of magnetic flux of the magnet is set to be large in advance, the current flowing through the movable coil can be reduced accordingly, so that Joule heat can be suppressed low. In response to such technical requirements, as shown in FIG. 5, an electromagnetic force generator using two magnets (for example, Japanese Utility Model Publication No. 6-18248) has been proposed. In this apparatus, a lower yoke 50, an intermediate yoke 51, and an upper yoke 52 are stacked and arranged, and a lower magnet 53 and a pole piece 54 are arranged in order from the bottom in the interior formed by these yokes. Has a configuration in which the upper magnets 55 are stacked so that the same poles as the poles of the lower magnet 53 face each other.

Reference numeral 56 denotes a pole piece 54 and an intermediate yoke 51
A movable coil disposed in an annular space between
The beam is connected to a beam 59 via a connecting member 57 inserted through the opening 51 a formed in the intermediate yoke 51 and another connecting member 58 connected to the connecting member 57. It is configured to be transmitted to the movable coil 56.

[0007]

The configuration shown in FIG. 5 is basically a very reasonable configuration for increasing the amount of magnetic flux, but this configuration is actually assembled and formed as an electromagnetic force generator. There are various problems at the stage of performing the following.

First, in order to realize the structure shown in FIG. 5, the upper and lower magnets 55, 53 and the yokes 50, 51, 52 are fixed, that is, actually fixed using an adhesive. For this reason, when the magnetization of the member to be a magnet is to be performed after assembly, the upper magnet 55
Therefore, it is necessary to apply a magnetic field in the opposite direction to the lower magnet 53 and the setting of the manufacturing equipment becomes difficult. Specifically, it is difficult to set the space for inserting the magnetic coil due to the spatial limitation of the magnetic circuit. When a magnet magnetized in advance is used, if the thickness of the pole piece 54 is sufficiently large so as not to be magnetically saturated, the upper and lower magnets 55 and 53 may have the same polarity even though they are opposite to each other. Tries to adsorb violently on the pole piece 54.

The upper and lower magnets 55 and 53 are small and have a small thickness in the direction of magnetization, and are made of a relatively brittle material such as a rare earth magnet having a large coercive force. It is very likely to break if it sticks violently to the piece. As a result, a special jig is required to configure the apparatus shown in the same figure, in order to prevent the pole piece 54 from being strongly attached to the pole piece 54, and to prevent it from being attached to the surrounding yoke.
In addition, the assembling work requires skill.

Further, in order to make the magnetic flux density uniform, the upper and lower magnets, yokes, and other components need to be accurately arranged at predetermined positions, but the components are attracted and repelled mainly by the magnetic force of the magnets. An attempt is made to behave in a selfish manner, which makes it very difficult to accurately arrange and fix (glue) these components. Furthermore, the moving coil 5
Since the movable coil 6 is disposed in a very narrow space, if the movable coil is in slight contact with the intermediate yoke 51 or the pole piece 54, the movable coil 56 is accurately displaced with respect to the load of the weighing object. No longer. For this reason, it is necessary to make fine adjustments regarding the arrangement of the movable coil 56 even after assembling the entire apparatus.
Is effectively glued and fixed to the intermediate yoke 51,
Adjustment of the movable coil 56 after the upper yoke 52 is attached becomes very difficult.

[0011]

SUMMARY OF THE INVENTION The present invention is directed to an electromagnetic force generating device constructed in view of the above-mentioned problems of the prior art, wherein a lower magnet, a pole piece, and an upper magnet are arranged in a yoke from a lower stage. The yoke is formed of a lower yoke and an upper yoke, and a shaft body is arranged upright so as to share an axis with the central axis of the lower yoke, and the shaft body is made of a non-magnetic material. The lower magnet, the pole piece, the upper magnet, and the upper yoke are sequentially inserted through the shaft body in the order of a lower magnet, a pole piece, an upper magnet, and an upper yoke so as to be common to the shaft center of the shaft body. It is a force generator.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A lower yoke constitutes a main body of an electromagnetic force generating device, and an upper yoke also has a function as a lid for closing the inside of the lower yoke. An opening is formed at the center of the lower yoke, and a bolt is erected in the opening as a shaft so as to share a central axis with the lower yoke. This bolt is made of a non-magnetic material such as brass, aluminum, stainless steel and the like.

Each of the upper and lower magnets and the pole piece disposed in the middle has a shaft body insertion hole formed at the center. When the shaft body passes through this insertion hole, each member becomes the pole piece outer diameter and the yoke inner diameter. By performing the above positioning, the arrangement can be made in an exact positional relationship, that is, the centering can be performed. First, a lower magnet is inserted through the shaft body. The lower magnet may be magnetized beforehand, or may be fixed to the lower yoke with an adhesive or the like and then magnetized.

A pole piece, an upper magnet, and an upper yoke are stacked on the lower magnet in this order. Of course, since the shaft is inserted at the center of each of these members, each member can be properly centered without using any special jig, and the assembly of the electromagnetic force generator is accurate. And it can be easily performed. The assembling order does not need to correspond to the final vertical positional relationship of each member. For example, an upper magnet (not yet magnetized) is bonded and fixed to the upper yoke in advance, and then the upper yoke is integrated. It is also possible to adopt a method in which the magnet is magnetized and the magnet is inserted through the shaft. As in the case of the lower magnet, by magnetizing during the assembly, the upper magnet can also be prevented from being adversely affected by the attraction and repulsion of the magnet during assembly.

If the outer diameter of the pole piece is made larger than the outer diameter of the magnet, not only does the positioning of each magnet become easy, but also the horizontal component of the magnetic flux concentrated on the pole piece increases. This prevents leakage of the magnetic flux in the vertical direction, and as a result, the effective magnetic flux can be increased, which leads to a decrease in the moving coil current.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings.

FIGS. 1 and 2 show the configuration of an electromagnetic force generating device according to a first embodiment of the present invention. Reference numeral 1 denotes a lower yoke constituting a main body of the electromagnetic force generating device, which is formed in a cylindrical shape having an open upper end. A recess 1a is formed at the center of the back surface of the floor 1c of the lower yoke 1, and an insertion hole 1b is formed so as to share an axis with the recess 1a. Numeral 2 denotes a bolt serving as a shaft body which is inserted upright through the insertion hole 1b and arranged in the lower yoke 1 and which is formed of a non-magnetic material such as brass, aluminum, stainless steel or the like.

Reference numeral 3 denotes a lower magnet which is inserted through the erected bolt 2, and is inserted through the bolt 2 by forming a bolt insertion hole 3a at the center of the lower magnet 3. The lower magnet 3 is set at the center of the lower yoke 1 by using a jig for increasing the assembly position accuracy, and the centering is completed. A pole piece 4 also having a bolt insertion hole 4a formed at the center is disposed above the lower magnet 3, and an upper magnet 5 also having a bolt insertion hole 5a also disposed at the center above the pole piece 4. When the bolt 2 is inserted through the insertion holes 4a and 5a of the pole piece 4 and the upper magnet 5, the respective members are automatically centered and arranged at predetermined positions.

When the upper magnet 5 is disposed, the nut 6 is screwed into the screw portion 2a of the bolt 2 projecting from the center of the upper magnet 5, and each member is fixed. An electromagnetic force generator is formed by inserting and fixing the open end of the lower yoke 1. Sign H
Is an opening through which a member (see reference numeral 57 in FIG. 5) for connecting a movable coil and a beam (both not shown) arranged therein is inserted. In the above configuration, when the upper yoke 7 is inserted into the upper end of the lower yoke 1, the centering is practically completed.

There are several possible processes for assembling the electromagnetic force generating device. An example of the process will be described below.

First, on the premise that the upper and lower magnets 5, 3 are magnetized after assembly, the lower magnet 3, which is not magnetized, is fixed to the lower yoke 1 in advance by fixing means such as an adhesive. Similarly, the pole piece 4 and the upper magnet 5 are fixed. In addition, since these magnets are not magnetized yet, they are not affected by magnetic force, and are fixed in the respective insertion holes 1b and 3b.
a, 4a and 5a can be easily centered only by making them coincide with each other, so that there is no difficulty in the operation. If the magnet contact surface of the pole piece or the lower yoke is formed as a recess as in the configuration shown in FIGS. 3 and 4 of the embodiment described later, the centering becomes easier. Next, after magnetizing each magnet, each part is assembled so as to have the configuration shown in FIG.
In this method, the nut 6 is housed in the opening 7a of the upper yoke 7 before the upper magnet is bonded. Also, as in the embodiment described later, the nut 6 itself is discarded and the opening 7 of the upper yoke is opened.
By setting a as a female screw portion, the upper yoke 7 may be directly screwed into the screw portion 2a of the bolt 2.

In the above method, since the upper and lower magnets are separately magnetized, a conventional magnetizing (magnetizing) device can be used as it is. By the way, if the magnet shown in FIG. 5 is to be magnetized after assembly, it is necessary to construct a special magnetizing device for exclusive use, which is extremely uneconomical.

FIG. 3 shows a second embodiment. First bolt 2
A screw portion 2b is formed at the base of the lower yoke 1, and the insertion hole 1b of the lower yoke 1 is a female screw portion to be screwed with the screw portion 2b. Thereby, the bolt 2 is configured to be able to be reliably erected on the lower yoke 1. The pole piece 4 has an outer diameter larger than the outer diameter of the upper and lower magnets, and the contact surfaces of the upper and lower magnets in the pole piece 4 are formed as recesses 4b and 4c, and the lower magnet 3 is The upper magnet 5 is configured so that a part of the upper magnet 5 is fitted and arranged in the recess 4c. This makes the arrangement (centering) of the upper and lower magnets more reliable and easier. In the illustrated configuration, similarly to the configuration of FIG. 1, the nut 6 is screwed into the screw portion 2a of the bolt 2. However, the nut 6 may be fixed to the upper yoke 7 side, or a third embodiment to be described later. The upper yoke 7 may be screwed to the bolt 2 by removing the nut 6 and using the opening itself of the upper yoke 7 as a female thread portion as described above.

FIG. 4 shows a third embodiment of the present invention. An opening 7a formed at the center of the upper yoke 7 is formed as a female screw portion, and the screw portion 2a of the bolt 2 is configured to directly screw into the opening 7a. The thickness W of the peripheral flange portion is formed to be slightly smaller than that of the above embodiment, and a gap S is provided between the flange portion of the upper yoke 7 and the upper edge of the lower yoke 1 after the assembly of the electromagnetic force generating device. Is formed, and the gap S is used to absorb assembly errors of the apparatus. In this configuration, since the upper magnet 5 and the upper yoke 7 are always in contact with each other, the upper magnet 5 and the upper yoke 7 which are the second assembling method among the assembling methods described in the first embodiment are fixed in advance. This is a very convenient configuration for implementing the method.

Reference numeral 1d denotes a magnet storage recess formed in the floor surface 1c of the lower yoke 1, which is formed to have the same outer diameter as the lower magnet 3, and a part of the lower magnet 3 is inserted and arranged. It has a configuration. Lower magnet 3
The centering of the lower magnet 3 is automatically performed only by arranging the lower magnet 3 in the recess 1d, and this configuration is also extremely effective in implementing the second assembling method.

[0026]

As described above, according to the present invention, the shaft is inserted through all of the yoke, the upper and lower magnets, and the pole pieces, and the shaft center of each member and the shaft is common. Therefore, these members are automatically arranged with an accurate positional relationship without using a special jig merely by inserting the shaft into each member, and the assembly is very easy.

Further, the upper and lower magnets can be assembled regardless of the magnetization before the assembly or the magnetization after the assembly, and the assembly procedure can be freely set in accordance with the process of the entire apparatus. It is possible to increase the reliability of the entire apparatus while maintaining economy.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an electromagnetic force generating device according to a first embodiment of the present invention.

2A and 2B show a horizontal cross section of the electromagnetic force generator shown in FIG. 1, wherein FIG. 2A is a cross sectional view taken along line AA, and FIG.
It is sectional drawing by a line.

FIG. 3 is a longitudinal sectional view of an electromagnetic force generating device showing a second embodiment of the present invention.

FIG. 4 is a longitudinal sectional view of an electromagnetic force generating device according to a third embodiment of the present invention.

FIG. 5 is a longitudinal sectional view of a conventional electromagnetic force generator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lower yoke 1b Bolt insertion hole 1c Floor surface of lower yoke 2 Bolt (shaft) 3 Lower magnet 3a Bolt insertion hole 4 Pole piece 4a Bolt insertion hole 4b, 4c Magnet insertion recess 5 Upper magnet 5a Bolt insertion hole 6 Nut 7 Upper yoke 7a Opening

Claims (7)

[Claims] 1. A lower magnet, a pole piece, and an upper magnet are arranged inside a yoke in order from a lower stage, and a movable coil is arranged in an annular space between the lower magnet, the pole piece, the upper magnet, and the yoke. In the device configured as described above, a shaft made of a non-magnetic material is erected at the center of the yoke so as to share the axis, and the lower magnet, the pole piece, and the upper magnet share the axis with the shaft. An electromagnetic force generator characterized in that it is arranged so as to be inserted. 2. A lower magnet, a pole piece, and an upper magnet are arranged inside the yoke in order from the lower stage, and a movable coil is arranged in an annular space between the lower magnet, the pole piece, the upper magnet, and the yoke. In the device configured as described above, the yoke includes a lower yoke,
An upper yoke functioning as a lid of the lower yoke is provided.A shaft body made of a non-magnetic material is erected at the center of the lower yoke so as to share an axis. An electromagnetic force generator, wherein the electromagnetic force generating device is inserted and arranged so as to share an axis with a shaft body, and an upper yoke is inserted and arranged at an upper end of a lower yoke. 3. A screw portion is formed at an end of the shaft body erected on the shaft center, and a nut is screwed to the screw portion to thereby form a lower yoke, a lower magnet, a pole piece,
3. The electromagnetic force generator according to claim 1, wherein the upper magnet is configured to be fixed via a shaft. 4. An opening at the center of the upper yoke is formed as a female screw portion, and the lower yoke, the lower magnet, the pole piece, the upper magnet, and the upper yoke form a shaft by screwing with a screw at the end of the shaft. The electromagnetic force generating device according to claim 3, wherein the electromagnetic force generating device is configured to be fixed via a pin. 5. The pole piece is formed to have a diameter larger than the diameter of the upper and lower magnets, and at least one of the upper and lower magnet contact surfaces of the pole piece is the same as the magnet so that a part of the magnet is inserted. The electromagnetic force generator according to any one of claims 1 to 4, wherein a recess having a diameter is formed. 6. A contact surface of the lower yoke on the floor surface of the lower yoke, wherein a recess having the same diameter as the lower magnet is formed so that a part of the lower magnet is fitted and inserted. Item 6. The electromagnetic force generator according to any one of Items 1 to 5. 7. The upper yoke lower surface is configured to be in contact with the upper magnet upper surface, and a gap for error adjustment is formed between the peripheral edge of the upper yoke lower surface and the lower yoke upper end surface. The electromagnetic force generator according to any one of claims 4 to 6.