JPH01250024A - Magnetic circuit for electromagnetic balance - Google Patents

Abstract

PURPOSE:To conduct the Joule heat which is generated by a focus coil to a yoke through a heat conduction part by connecting a pole piece and the yoke by the heat conduction part and interposing a heat insulation part between a permanent magnet and the pole piece. CONSTITUTION:The pole piece 2 and yoke 3 are connected by the heat conduction part 6 and the heat insulation part 7 is interposed between the permanent magnet 1 and pole piece 2. The heat from the focus coil placed in a magnetic field space 4 is conducted to the pole piece 2, whose heat is conducted to the yoke 3 through the heat conduction part 6. The heat from the pole piece 2 is hardly conducted to the permanent magnet 1 directly because of the presence of the heat insulation part 7.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention places a force coil in a magnetic field space, and balances the electromagnetic force generated by passing a current through the force coil with the load on the dish. The present invention relates to a magnetic circuit for forming the above-mentioned magnetic field space of a so-called electromagnetic balance in which the load on the pan is determined from the current required for the balance.

<Prior Art> The structure of a conventional magnetic circuit of this type is shown in a vertical cross-sectional view in FIG. 11, and FIG. 12 shows the state in which it is used in an electromagnetic balance.

A conventional magnetic circuit has a structure in which a pole piece 2 is bonded to one magnetic pole side end surface of a permanent magnet 1 with adhesive, and the bottom inner surface of a cup-shaped yoke 3 is bonded to the other magnetic pole side end surface with adhesive as well. A static magnetic field space 4 is formed between the outer peripheral surface of the pole piece 2 and the inner peripheral surface of the yoke 3.

As shown in FIG. 12, in such a magnetic circuit, the yoke 3 is fixed to the balance base, and the magnetic field space 4 created by the yoke 3 is fixed to the balance base.
A force coil 12 wound around a movable winding frame 11 is arranged inside. The movable winding frame 11 is fixed to a lever 13, which is connected to an elastic support 14.15 and a lever.
It is engaged with the dish via a pallet mechanism (not shown) or the like.

The inclination of the lever 13 is detected by a displacement sensor 16,
Amplifier 17, P, 1. D, lever 13 via control section 18
A current is passed through the force coil 12 such that the slope of . That is, an electromagnetic force balanced with the load to be measured is generated, and the current at this time is converted into a voltage signal by the measurement resistor R, and digitized by the AD converter 19.

By the way, when a current i flows through the force coil 12, Joule heat of P=i''r is generated, where the resistance of this coil is r.For this reason, the larger the load is applied, the higher the heat is generated, and the force coil The temperature of the magnet 12 increases. This heat heats the pole piece 2 and is also conducted to the permanent magnet 1. Here, the temperature of the permanent magnet 1 is 12
There is a magnetic temperature change of 00 ppm (alnico magnet) to -400 ppm (rare earth magnet) to -1900 ppm (ferrite magnet). Precision balances are manufactured with a minimum display amount of as much as 0.25 p p m for the weighing capacity, and the change in magnetic field strength due to temperature changes is taken as an example when using a rare stone. Conventionally, a temperature sensor 5 is disposed approximately in the center of the permanent magnet 1, and based on the detection signal,
Measures are taken, such as changing the reference voltage from the reference voltage source 20 to be supplied to the A-D converter 19.

<Problems to be Solved by the Invention> Although the measures using the temperature sensor 5 described above can compensate for slow temperature changes, the heat generated by the force coil 12 immediately after applying a large load to the plate If there is a rapid temperature change like this, the average temperatures of the temperature sensor 5 and the permanent magnet 1 will not match, making it difficult to compensate with a predetermined accuracy. That is, the average temperature of the permanent magnet 1 affects the strength of the magnetic field, and -i, the permanent magnet material has a low thermal conductivity, so if it is rapidly heated, the permanent magnet 1 will have a large temperature. As a result, the temperature sensor 5 cannot correctly detect the average temperature, resulting in a creep phenomenon in the measured value.

In order to alleviate this phenomenon, conventionally, permanent magnet 1
By increasing the size of both the pole piece 2 and the yoke 3 to increase the overall heat capacity, the temperature gradient is reduced (and at the same time, the magnetic field is strengthened), thereby reducing the coil current required to generate the same electromagnetic force. It was necessary to take measures such as widening the magnetic field space 4 and increasing the wire diameter of the force coil 12 to reduce resistance and heat generation.

According to this conventional measure, when setting up a magnetic circuit to generate electromagnetic force according to the weighing capacity of the balance, compared to a magnetic circuit with a capacity that only needs to be balanced with the weighing load, There was a problem in that a precision balance could not be obtained unless a magnetic circuit with a significantly large capacity was used. This tendency is particularly strong when rare earth magnets, which have recently started to be widely used, are used. This causes an increase in the cost of the balance and also becomes an obstacle to downsizing the balance.

The inventor has already proposed a balance in which the temperature gradient of the permanent magnet is reduced by covering the outer peripheral surface of the permanent magnet with a material having high thermal conductivity, thereby achieving highly accurate temperature compensation. However, the above-mentioned problems have not been completely solved.

The present invention was made in view of this point, and it has excellent creep characteristics, and it is possible to obtain the same performance as the conventional one even if it is made smaller.
Or, by using one with the same size as the conventional one, the occurrence of creep will be significantly reduced compared to the conventional one.
The purpose is to provide a magnetic circuit for electromagnetic balances.

Means for Solving the Problems> A configuration for achieving the above object will be described with reference to FIG. 1 corresponding to an embodiment.
, a pole piece 2 disposed on one magnetic pole side of the permanent magnet 1, and a bottom portion disposed on the other magnetic pole side of the permanent magnet 1, and the side portion reaches the vicinity of the pole piece 2, and the inner peripheral surface of the side portion and a yoke 3 that forms a magnetic field space 4 between the outer circumferential surfaces of the pole piece 2, a heat transfer section 6, and a heat insulating section 7, and the pole piece 2 and the yoke 3 are connected by the heat transfer section 6.
It is characterized by the fact that a heat insulating part 7 is interposed between the permanent magnet 1 and the pole piece 2.

Effect> The heat from the force coil placed in the magnetic field space 4 is transmitted to the pole piece 2, and the heat of this pole piece 2 is transferred to the heat transfer part 6.
It is conducted to yoke 3 via . Due to the presence of the heat insulating section 7, almost no heat from the pole piece 2 is directly transmitted to the permanent magnet 1. That is, as shown in FIG. 13 (al), which shows the temperature distribution in the longitudinal direction of this magnetic circuit (the magnetization direction of the permanent magnet 1), a temperature gradient (j2-*j,) occurs in the heat transfer section 6; The temperature of the magnet 1 is substantially the same as the temperature t of the yoke 3 and is uniform.

<Example> Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a central vertical sectional view showing the structure of an embodiment of the present invention.

The basic components of the magnetic circuit are the same as the conventional circuit shown in FIG. A magnetic field space 4 formed between
Furthermore, the usage conditions within the electromagnetic balance are the same as in the conventional one, and the temperature sensor 5 for temperature compensation is disposed at the same position.

Now, the difference from the conventional example is that a heat transfer part 6 is provided in contact with the pole piece 2 and the yoke 3, and a heat insulating part 7 is provided between the permanent magnet 1 and the pole piece 2. be.

That is, a ring-shaped heat transfer part 6 made of a non-magnetic material with high thermal conductivity such as copper or aluminum is arranged on the outer circumference of the permanent magnet 1, and its upper end surface is connected to the pole piece. The bottom surface of the yoke 2 and the lower end surface of the yoke 3 are respectively bonded to the bottom top surface of the yoke 3.

Further, the permanent magnet 1 and the pole piece 2 are not in direct contact with each other, and a gap is interposed between them to form a heat insulating section 7.

According to this structure, Joule heat due to energization of the force coil placed in the magnetic field space 4 is transferred to the pole piece 2.
The heat of the pole piece 2 is transmitted to the yoke 3 through the heat transfer section 6 without the intervention of the permanent magnet 1. That is, due to the existence of the heat transfer section 6 and the heat insulation section 7, which have extremely different thermal resistances, most of the heat from the pole piece 2 is transmitted to the yoke 3 via the heat transfer section 6, which has a small thermal resistance, and is transferred to the balance. It does not escape to the base etc. and heat the permanent magnet 1.

FIG. 2 is a central vertical sectional view showing the structure of another embodiment of the present invention. This example is different from the example shown in FIG.
The point is that

In the example shown in FIG. 1, the heat transfer part 6 and the permanent magnet 1 are in contact with each other, and as mentioned above, the permanent magnet 1 normally has a low thermal conductivity, and although the heat conduction due to this contact is small, this By providing the heat insulating portion 71 as in the example shown in FIG. 2, the heat insulating effect becomes more complete.

FIG. 13 is a graph showing the difference in temperature distribution in each part of the magnetic circuit between the embodiment of the present invention as described above and the conventional example shown in FIG. ), the horizontal axis shows the temperature, (a) is the example of the present invention, (b)
l indicates a conventional example.

In each of these graphs, the temperature of the yoke 3 is equal to that of the balance base, etc., and is 1. Assume that the heat iQ transmitted from the force coil to the pole piece 2 is also equal. In the conventional example, the heat of the pole piece 2 is transferred to the yoke 3 via the permanent magnet 1, which has a large thermal resistance.
A large temperature gradient of tl occurs. On the other hand, according to the embodiment of the present invention, the heat of the pole piece 2 is efficiently transferred to the yoke 3 via the heat transfer section 6 with low thermal resistance, so the temperature gradient of the heat transfer section 6 becomes smaller. Therefore, the temperature t2-t3 of the pole piece 2 is also lower than the conventional temperature t21-t3', that is, 12<1. .

13<1. °, and due to the presence of the heat insulating section 7, the temperature of the permanent magnet 1 is almost entirely 1. Therefore, almost no temperature gradient occurs.

In addition, in the above embodiment, an example was shown in which the heat insulating portion 7 or 71 was formed by a void, but any suitable heat insulating material such as a porous material or ceramics may be used. Figure 3 is the second
This is an example in which the heat insulating parts 7 and 71 made of voids shown in the figure are replaced with heat insulating parts 7a and 71a made of a heat insulating material, respectively.

Further, FIG. 4 shows a heat insulating section 7a made of a heat insulating material.

In addition to 71a, this is an example in which a heat insulating material is also provided between the permanent magnet 1 and the yoke 3 and is bonded to the yoke 3, with a heat insulating part 72a interposed here as well.

In this example, the entire surface of the permanent magnet 1 is thermally insulated, which is more effective, but the magnetic resistance increases accordingly, and the magnetic field strength in the magnetic field space 4 decreases.

5 and 6 show an example in which the upper edge of the heat transfer portion 6 in FIGS. 2 and 4, respectively, is replaced with a heat transfer portion 61 that extends to the outer peripheral surface of the pole piece 2. FIG. According to these examples, the heat from the force coil is transferred to pole piece 2.
The heat is transmitted directly to the yoke 3 via the heat transfer section 61 without passing through the heat transfer section 61, and the temperature distribution becomes ideal.

However, there is also a drawback that the magnetic field space 4 becomes narrower or the magnetic field becomes weaker if the magnetic field space 4 is made the same. Ultimately, which of the examples in Figures 1 to 3, or the examples in Figures 4, 5, and 6 to be adopted should be decided by taking into account the performance of the balance, the capacity, etc. is desirable.

Now, in each of the above embodiments, the permanent magnet 1 and the pole piece 2 or the yoke 3, and the heat transfer part 6 and the pole piece 2
Alternatively, we have shown an example of assembling a magnetic circuit by joining the yokes 3, etc. with adhesive, but as with the past, joining each member with adhesive requires time to harden, so it can be quickly There is a problem that the process cannot proceed to the next step, resulting in poor work efficiency.Furthermore, if foreign matter such as iron powder gets in, it is difficult to remove it, and there is also the problem that there is often no reserve available for disposal.

The examples shown in FIGS. 7 to 10 solve these problems, and each member is assembled without using adhesive. That is, they are assembled by fitting the upper and lower ends of the heat transfer member 6 to the pole piece 2 and the yoke 3, respectively, and are held together using the attractive force of the permanent magnet 1.

The examples shown in FIGS. 7 and 8 show structures suitable for the case where a rare earth magnet is used as the permanent magnet 1. Rare earth magnets have a large coercive force but do not have a large residual magnetic flux density, so in order to use the magnet's energy effectively, it is best to have a large diameter and a flat shape.

Therefore, when using the permanent magnet 1 having such a shape, as shown in FIG. It is effective to fit the inner circumferential surface of the heat transfer section 6 into this protrusion.

Then, due to the magnetic force of the permanent magnet 1 housed inside, the permanent magnet 1. Pole piece 2. The yoke 3 and the heat transfer section 6 are mutually attracted and held. Even in this case, the heat insulating part 7.71 made of the void can be replaced with a heat insulating part 7 a +71a made of a heat insulating material such as a porous material, as shown in FIG.

The examples shown in FIGS. 9 and 10 show a structure suitable for the case where an alnico magnet or the like is used as the permanent magnet 1. Alnico magnets have a small coercive force but a large residual magnetic flux density, so in order to use the magnet's energy effectively,
It is necessary to have a columnar shape with a relatively small diameter and thick wall. When using the permanent magnet 1 having such a shape, as shown in FIG. 9, the fitting between the pole piece 2 and the yoke 3 and the heat transfer part 6 is achieved by recessing the center sides of the pole piece 2 and the yoke 3, and It is effective to fit the outer peripheral surface of the heat transfer part 6 into this recess, and similarly, the magnetic force of the permanent magnet 1 causes the permanent magnet 1. Pole piece 2. The yoke 3 and the heat transfer section 6 can be mutually attracted and held. Further, the heat insulating part 7.71 formed by the void is a heat insulating part 7a made of a heat insulating material, as shown in FIG.

Similarly, it can be replaced with 71a.

In the examples shown in Figures 7 to 10 above, since no adhesive is used, it is possible to proceed to the next process immediately without the need for curing time as in conventional methods, improving work efficiency. Can be done. Furthermore, if foreign matter gets inside, it can be easily disassembled and removed, and it can be reused.

The magnetic circuits with the structures shown in Figures 1 to 10 above can be used not only for electromagnetic balances but also for speakers and other applications, and can also be used for magnets of other shapes. Application of the invention is possible.

The magnetic circuit of the present invention includes various embodiments as described above, but in summary: 1) Connecting the pole piece and the yoke with a heat transfer part;
Based on a structure in which a heat insulating part is interposed between the permanent magnet and the pole piece, ■A mode characterized in that the heat transfer part extends to the outer peripheral surface of the pole piece (Fig. 5, Fig. 6), ■A mode characterized in that a heat insulating section is also interposed between the permanent magnet and the heat transfer section (Figs. 2 and 3).

(Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8, Fig. 9, Fig. 10), ■ A mode in which the heat insulating part is a void (Fig. 1,
(Figs. 2, 5, 7, 9), ■ A mode in which the heat insulating portion is made of a porous or other heat insulating material (Figs. 3, 4, 6, 8) figure.

(Fig. 10), ■The heat transfer part, pole piece, and yoke are assembled by fitting each other, and due to the magnetic force of the internal permanent magnet,
An embodiment characterized in that the permanent magnet, the pole piece, the yoke, and the heat transfer part attract and hold each other (Fig. 7,
8, 9, 10), etc., and appropriate combinations of these aspects are also possible.

<Effects of the Invention> As explained above, according to the present invention, the pole piece and the yoke are connected by the heat transfer part, and the heat insulating part is interposed between the permanent magnet and the pole piece. The Joule heat generated by passing the current escapes to the yoke via the heat transfer portion, and does not heat the permanent magnet and create a temperature gradient therein. As a result, when it is incorporated into an electromagnetic balance and a load is placed on the pan,
As shown in Figure 14, which shows the relationship between the elapsed time and the output (the magnitude of the current flowing through the force coil), in the conventional example (dashed line), the temperature of the permanent magnet increases and the magnetic field it creates weakens, resulting in an imbalance. Whereas the so-called creep phenomenon occurs in which the current increases over time, the example to which the present invention is applied (solid line) shows only a very slight leap phenomenon.

From the above, according to the present invention, it is possible to obtain an electromagnetic balance that is less affected by the heat generated by the force coil and therefore has excellent creep characteristics. Alternatively, in order to obtain an electromagnetic balance with the same performance as a conventional one, a magnetic circuit smaller than that of the conventional one can be used, which contributes to cost reduction and downsizing of the balance. In particular, when rare earth magnets are used as permanent magnets, the effects based on the present invention are extremely large. In other words, rare earth magnets have a thermal conductivity of 0.025 cal/cm, s, compared to other permanent magnets.
F is as small as "c" and is a material for pole pieces, yokes, etc.
O of e, 18 cal/cm, s, 'C, 0.94 or 0.53 of Cu or AI used in the heat transfer part
cal/cm, s, “c”, Cu
If used in the heat transfer part, the difference will be about 40 times,
The effects of the present invention are extremely large compared to other magnet materials.

[Brief explanation of the drawing]

FIG. 1 is a central longitudinal cross-sectional view showing the structure of an embodiment of the present invention, and FIGS. 2 to 10 are central longitudinal cross-sectional views showing the structures of other embodiments of the present invention. FIG. 11 is a central vertical cross-sectional view showing the structure of a conventional magnetic circuit, and FIG. 12 is an explanatory diagram of its use in an electromagnetic balance. FIG. 13 is a graph showing a comparison of temperature distributions in various parts of the magnetic circuit, where Ta) shows the embodiment of the present invention and fb) shows the conventional example. FIG. 14 is a graph showing the difference in output changes over time when the embodiment of the present invention and the conventional example are incorporated into an electromagnetic balance. 1...Permanent magnet 2...Pole piece 3...Yoke 4...Magnetic field space 5...Temperature sensor 6.61...Heat transfer part 7.71 .7a, 71a, 72a...insulation section 12...
・Force coil patent applicant Shimadzu Corporation Agent Patent attorney Nishi 1) New construction 1 Figure 2 Figure 8 Figure 4 Figure 7 Figure 8 Figure 9 Figure 1O Figure 11 (Q) (b )

Claims (1)

[Claims] In a balance, the electromagnetic force generated by passing a current through a force coil placed in a magnetic field space is balanced with the load on the pan, and the load on the pan is determined from the current required for equilibrium.
A magnetic circuit for forming the magnetic field space, comprising a permanent magnet, a pole piece disposed on one magnetic pole side of the permanent magnet, and a bottom portion disposed on the other magnetic pole side of the permanent magnet. A yoke whose portion reaches near the pole piece to form the magnetic field space between the inner circumferential surface of the side portion and the outer circumferential surface of the pole piece, a heat transfer portion and a heat insulating portion, and the pole piece and the yoke are connected by the heat transfer portion. A magnetic circuit for an electromagnetic balance, characterized in that a heat insulating section is interposed between the permanent magnet and the pole piece.