JP2948000B2 - Electromagnetic balance type weighing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic balance type weighing apparatus having an electromagnetic force generating mechanism for balancing the load of a weighing object.

[0002]

2. Description of the Related Art An electromagnetic balance type weighing device generates an electromagnetic force corresponding to a load of a measurement object to a force coil arranged in a magnetic field, and measures an amount of electricity used at this time to measure the measurement object. Measure weight or mass.

FIG. 4 shows the principle of measuring the load of an electromagnetic balance type weighing device. First, in the electromagnetic unit 50, the displacement of the force coil 51 due to the load W of the weighed object is detected by the position sensor 52. The force coil 51 disposed in the magnetic field formed by the permanent magnet 60 is feedback-controlled via the servo amplifier 53 so as to generate an electromagnetic force F corresponding to the load W. At this time, the current value (analog value) supplied to the force coil 51 is
4. The digital value is input to the central processing unit 56 through the A / D conversion circuit 55, where the A / D converted digital value is converted into the load of the weighing object, and the converted load is displayed on the display 57.
Is displayed.

FIG. 5 shows the details of the configuration of the electromagnetic section of the electromagnetic balance type weighing device.

A permanent magnet (hereinafter, referred to as "magnet") 60 for forming a magnetic field is disposed at the center bottom of a yoke 61, and a pole piece 62 made of a magnetically permeable material is disposed on the magnet 60. Peace 62
A magnetic field b is formed as shown by an arrow through the yoke 61 and the force coil 51 is arranged in the magnetic field b.

[0006]

In the above configuration, the magnet 60 has both poles formed in the axial direction and the magnetic field b is formed via the pole piece 62 and the yoke 61. The two poles are configured to be far apart in consideration of the moving distance of the magnetic field lines, and the magnetic flux density is reduced accordingly. In addition, even if both poles are brought close to each other with one magnet, the demagnetizing field increases, and the magnetic flux density eventually decreases.

Here, the load W and the electromagnetic force F of the force coil corresponding to the load W have a relationship represented by the following equation. In the equation, r is the radius of the force coil, n is the number of turns of the force coil, B is the magnetic flux density of the magnetic field b, and I is the current value supplied to the force coil.

W = F = 2πrnBI

As is apparent from the above equation, the magnet 60
If the magnetic flux density B of the magnetic field b formed by the above is higher, the current value I supplied to the force coil 51 can be reduced accordingly. If a current is supplied to the force coil, Joule heat is generated, and this heat is not preferable for the weighing device. That is, the air in the weighing device flows due to heat generation, and the flowing air causes problems such as instability of the load transmission mechanism and occurrence of measurement errors due to uneven temperature in the weighing device. Therefore, it is necessary to minimize heat generation in the electromagnetic section. However, the calorific value is proportional to the square of the current I, and the current I supplied to the force coil 51 is inversely proportional to the magnetic flux density B as apparent from the above equation. I increases and the heat value, which is proportional to the square of the current I, increases rapidly. In this regard, in order to increase the magnetic flux density based on the configuration shown in FIG.
Although it is necessary to increase the size of 0, an increase in the size of the magnet 60 results in an increase in the size and weight of the weighing device, which is contrary to the reduction in the size and weight of the device for which efforts are currently being made.

In the configuration shown in FIG. 5, a part of the magnetic field lines forming the magnetic field b jumps out into the space without being along the yoke 61 as indicated by reference numeral b ', so that a so-called leakage of magnetic force occurs. The magnetic flux density B in the magnetic field b will further decrease.

Further, there is a possibility that a measurement error may occur due to the leaked magnetic force. One of the reasons for the measurement error is that the leakage of the magnetic force is not constant, and consequently the force coil 5
1 means that the magnetic field b in which the position 1 is located becomes unstable. Magnetic field b
Is unstable, that is, the magnetic flux density B makes the current I for outputting the electromagnetic force F of the force coil 51 unstable as shown in the above equation, resulting in a measurement error. The leakage of the magnetic force varies depending on the place where the weighing device is arranged, for example, whether the desk is made of a non-permeable material such as wood or a permeable material such as iron, or depending on the permeability of the weighing object.

For example, when the weighing object is a magnetically permeable material, the weighing object may be affected by the leaked magnetic force to cause a measurement error, or the place where the weighing device is disposed may be, for example, an iron desk or the like. A measurement error will still occur in a place where it has.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and the shape of the magnet is, as represented by a cylindrical shape, an inner peripheral wall and a fixed thickness. An annular shape having an outer peripheral wall formed through a thickness,
And this annular magnet is magnetized so that the inner peripheral wall and the outer peripheral wall form both poles, and two large and small annular magnets have a common axis, and the opposed wall surfaces of both magnets are arranged to be different magnetic poles. An electromagnetic balance type weighing device having an electromagnetic portion configured to arrange a force coil in a gap formed between both magnets.

[0014]

The wall surfaces of the two coaxial magnets facing each other have different magnetic poles, and since different magnetic poles of the two magnets are arranged close to each other, there is almost no leakage magnetic flux. Lines of magnetic force flow with high magnetic flux density between the wall surfaces to form a magnetic field. A current for supplying an electromagnetic force corresponding to the applied load is supplied to the force coil disposed in the formed magnetic field.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show a first embodiment of the present invention. Arrow 1 indicates the electromagnetic portion of the electromagnetic balance type weighing device. Reference numeral 2 denotes an inner annular magnet of the pair of annular magnets, which is formed in a cylindrical shape. The inner annular magnet 2 is configured such that the inner wall surface 2a and the outer wall surface 2b form both poles. For example, in the illustrated configuration, the inner wall surface 2a is an N pole and the outer wall surface 2b is an S pole. The inner annular magnet 2 is fixed to the center of the yoke 3 by being fitted to the central projection 3a of the yoke 3. In this case, the locking position of the inner annular magnet 2 can be accurately set by forming the step portion 3a 'with respect to the central convex portion 3a.

Reference numeral 4 denotes a larger outer annular magnet formed in a shape similar to the inner annular magnet 2, so that the inner wall surface 4a and the outer wall surface 4b have the same pole as the inner annular magnet 2, that is, the configuration shown in the drawing. In the figure, the inner wall surface 4a is magnetized so as to have the N pole, and the outer wall surface 4b is magnetized so as to have the S pole. The outer annular magnet 4 is disposed concentrically with the inner peripheral wall of the cylindrical outer wall 3b of the yoke 3 so as to have the same axis as the inner annular magnet 2. When the outer annular magnet 4 is attached, the locking position of the outer annular magnet 4 can be accurately set by forming the step 3b 'on the inner peripheral wall of the outer wall 3b.

The inner annular magnet 2 and the outer annular magnet 4 are arranged in the yoke 3 so as to have a common axis, so that the outer wall surface 2b of the inner annular magnet 2 and the inner peripheral surface 4a of the outer annular magnet 4 are formed. Are facing each other, and one of the two wall surfaces is an S pole (the outer wall surface 2 of the inner annular magnet 2).
b) the other is the N pole (the inner circumferential surface 4 of the outer annular magnet 4);
a) and the opposite pole are opposed to each other.

Reference numeral 5 denotes a force coil formed on the bobbin 9, and an inner and outer annular magnets 2, 4 and an axial center are inserted into an annular gap 6 formed between the inner annular magnet 2 and the outer annular magnet 4. Are arranged to be equal.

In the above configuration, a magnetic field as indicated by a symbol b is formed between the inner annular magnet 2 and the outer annular magnet 4 located on the outer periphery of the inner annular magnet 2. In this case, the magnetic pole b has a very high magnetic flux density because the opposite pole of the magnet is opposed to a position close to the force coil 5. That is, if the magnetic flux density is the same as in the prior art, the size of the magnet can be reduced, and if the magnet has the same size as in the prior art, the magnetic flux density can be increased.

Since the inner annular magnet 2 and the outer annular magnet 4 have different poles facing each other, the magnetic flux source and the magnetic flux inlet are close to each other, and the magnetic field b is almost completely applied to the inner and outer magnets 2 and 4. And the lines of magnetic force hardly leak to the outside.

FIG. 3 shows a second embodiment.

Inner annular magnet 2 for obtaining high magnetic force
The outer annular magnet 4 is generally formed of a sintered material mainly composed of a rare earth element. However, the sintered material is slightly structurally non-uniform when viewed as a whole. Is inevitable. The non-uniform composition causes non-uniform magnetic field lines, which may adversely affect the measurement accuracy of the weighing device. This embodiment is configured to make the lines of magnetic force of these magnets even more uniform.

In the figure, reference numeral 7 denotes a cylindrical cover which is fitted and fixed to the outer wall surface 2b of the inner annular magnet 2.
For example, it is formed of the same magnetically permeable metal material as the material forming the yoke 3. Since the coating 7 is a metal crystal having a much higher density and uniformity as compared with the sintered material forming the inner annular magnet 2, even if the lines of magnetic force coming out of the inner annular magnet 2 are not uniform, this coating is not necessary. By passing through the body 7, the magnetic flux density is made uniform.

A cylindrical covering 8 made of the same material as the covering is inserted into an inner wall surface 4a of the inner wall surface of the outer annular magnet 4 which faces the outer wall surface 2b of the inner annular magnet 2. It is fixed so that more uniform magnetic field lines can be achieved.

The case where the inner annular magnet 2 and the outer annular magnet 4 are cylindrical is described above as an example.
It is not necessarily intended to limit the inner and outer magnets to this shape. That is, the magnetic field formed in the direction along the wall surface of the magnet is most uniform in a cylindrical shape. However, when it is difficult to arrange the cylindrical magnet due to the arrangement space inside the weighing device, a flat surface is used. Almost the purpose can be achieved even with a square magnet.

[0027]

According to the present invention, since the annular magnets are arranged so that their axes are common and the opposite wall surfaces of the two magnets have different poles as described above in detail, the two magnets are used. The magnetic flux density of the magnetic field formed by the above can be made larger than the size of the magnet. For this reason, it is possible to reduce the current to the force coil disposed in the magnetic field, thereby reducing the Joule heat and improving the measurement accuracy of the weighing device.

Further, since the lines of magnetic force leaking from the electromagnetic section to the outside can be almost eliminated, the magnetic flux density of the magnetic field in which the force coil is located is stabilized, and the weighing object is not affected by the leaked magnetic force. High measurement accuracy can always be ensured regardless of the arrangement environment of the device.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an electromagnetic unit according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sectional view of an electromagnetic unit according to a second embodiment.

FIG. 4 is a block diagram showing a measurement principle of the electromagnetic balance type weighing device.

FIG. 5 is a schematic view of a conventional electromagnetic unit of an electromagnetic balance type weighing device.

[Explanation of symbols]

Reference Signs List 1 electromagnetic portion 2 inner annular magnet 2a inner wall surface of inner annular magnet 2b outer wall surface of inner annular magnet 3 yoke 4 outer annular magnet 4a inner wall surface of outer annular magnet 4b outer wall surface of outer annular magnet 5 force coil 6 (with inner annular magnet Gap between outer annular magnet) 7 coating 8 coating

Claims (3)

(57) [Claims] 1. An electromagnetic balance type weighing device for measuring a load by supplying a current to a force coil disposed in a magnetic field of an electromagnetic section and balancing the load with a load on a weighing object, wherein two large and small annular magnets are formed. And these large and small rings
The inner and outer walls of the magnet have the same magnetic pole
These large and small annular magnets share the axis.
By being placed in the yoke it has, and the inner wall surface of the outer annular magnet opposing position to the outer wall surface of the inner ring magnet is configured to be different poles, between the inner ring magnet and the outer annular magnet An electromagnetic balance type weighing device, wherein a force coil is disposed in a gap formed in the weighing device. 2. A yoke formed by an outer wall.
A central convex portion is formed inside the workpiece and shares an axis with the outer wall.
The small ring magnet is used as the inner ring magnet
The large annular magnet that is inserted and placed in the central convex
The inner annular magnet and shaft as the outer annular magnet
The yoke is inserted and arranged on the inner peripheral surface of the outer wall so as to share the heart.
The electromagnetic balance type balance according to claim 1, wherein
Quantity device. Wherein electromagnetic equilibrium according to claim 1 or 2, characterized in that the coating of magnetically permeable are in close contact formed to at least one of the outer wall surface and the inner wall surface of the outer ring magnet of the inner ring magnet Type weighing device.