JPH0531091B2 - - Google Patents

Description

[Detailed description of the invention] (b) Industrial application fields The present invention relates to an electromagnetic force generating device.

(b) Prior Art A conventional electromagnetic force generating device consisting of a magnetic circuit and an electromagnetic coil used in an electromagnetic balance type balance has a structure as shown in FIG. 1, for example, and includes a permanent magnet 11, a magnetic pole piece 12, and a magnetic field generated between the magnetic pole piece 12 and the magnetic pole part 14 of a static magnetic circuit consisting of a bottomed cylindrical yoke 15 having a magnetic pole part 14 on the upper inner circumference, and an electromagnetic coil 13 flowing orthogonally to this magnetic field. The magnetic field is generated in a direction perpendicular to the plane of the permanent magnet, that is, in the axial direction of the permanent magnet. However, in devices with this type of structure, the permanent magnets are inserted into the vertical part of the magnetic path, which limits the ability to reduce the height of the device, especially when used as a balance force generating means for a balance. It is very difficult to lower the position of the weighing pan in conjunction with the mechanism. Furthermore, in such a device, the magnetic field created by the current flowing through the electromagnetic coil 13 also affects the magnetic field of the static magnetic circuit.
Strictly speaking, there is no linear relationship between the generated electromagnetic force and the current, so if high accuracy is required, it is necessary to correct the magnetic field using the compensation coil 16. In addition, as in the invention of Utility Model Application No. 55-164519, each of the two semicircular parts symmetrical with respect to one diameter of the cylindrical electromagnet is perpendicular to the coil surface and
In an electromagnetic force generator configured to apply static magnetic fields in opposite directions to generate electromagnetic force in a direction perpendicular to the diameter of the electromagnetic coil, the influence of the magnetic field generated by the electromagnetic coil on the static magnetic field is static. The magnetic field is canceled across the entire circuit, and there is no need for field correction by compensation coils. However, this device has the disadvantage that the effective length of the electromagnetic coil conductor part involved in the generation of electromagnetic force is reduced to 2/π of the geometric length. Figure 2 shows a device that overcomes these drawbacks, has a low overall height, does not require a means for compensating the static magnetic field, and allows the entire length of the electromagnetic coil conductor to work 100% effectively in generating electromagnetic force. Some devices have such a configuration. In the figure, a cylindrical outer yoke 3 and a cylindrical inner yoke 7 made of the same ferromagnetic material constitute a coaxial double cylindrical yoke. Annular permanent magnet 2 and permanent magnet 1 with opposite magnetization direction
is fixed. Coaxially formed coils 4 and 5 are located in the gaps between the permanent magnets 2 and 1 and the inner yoke 7, respectively, and are held by a common winding frame 6. The winding frame 6 is held movably in the axial direction of the yoke (a holding mechanism is omitted). Note that the outer yoke 3 and the inner yoke 7 are supported by a support plate 8 made of a non-magnetic material. FIG. 3 is a partially enlarged view of the vicinity of the coil in FIG. 2. In the figure, dotted lines and arrows indicate the direction of the static magnetic field, and the cross sections of coils 4 and 5 indicate the direction of current in the coils. . In the direction of the magnetic field and current shown in the figure, a downward electromagnetic force is generated throughout the coil, but as is clear from the figure, the direction of the current in both coils is opposite to each other, so the magnetic field created by them is influenced by the static magnetic field. The effects of are canceled out, so that compensating means for the static magnetic field become unnecessary.

However, in these conventional electromagnetic force generators, no consideration is given to the temperature dependence of the generated electromagnetic force due to reversible temperature changes in the strength of the magnet, and when there are temperature fluctuations, a highly accurate linear relationship is required. It was not possible to maintain this temperature, and errors caused by temperature changes were a problem. In other words, in general, the strength of the magnetic field of a permanent magnet tends to become weaker as the temperature rises, so for example in Fig. 2, as the temperature near magnets 2 and 1 rises, the magnetic field from these magnets becomes weaker and the magnetic field is perpendicular to this magnetic field. There was a problem in that the electromagnetic force generated by the interaction with the flowing current of the electromagnetic coil 13 also varied to become weaker.

(c) Purpose An object of the present invention is to overcome the above-mentioned problems associated with the prior art and to provide an electromagnetic force generating device configured to suppress reversible temperature changes in the strength of a magnet, that is, the influence of temperature fluctuations.

(D) Structure In order to achieve the above object, the electromagnetic force generating device according to the present invention has the following features: at least one of the inner circumferential surface of the outer yoke and the outer circumferential surface of the inner yoke formed in a coaxial double cylindrical shape of a ferromagnetic material. A first permanent magnet whose magnetization direction is directed outward in the radial direction of the coaxial double cylinder and has an annular shape as a whole is placed on the surface at a predetermined interval in the axial direction of the coaxial double cylinder; A magnetic circuit is formed by fixing a permanent magnet and a second permanent magnet having an annular shape as a whole opposite to the permanent magnet, and a frame body movably held in the annular gap between the inner and outer yokes in the yoke axis direction as a winding frame. and an electromagnetic coil unit in which first and second annular coils are wound opposite to the first and second permanent magnets, and a current flows between the first and second coils. In an electromagnetic force generation mechanism in which the circuit is connected so that the current direction is opposite to each other, at least one of the inner and outer yokes is divided by a slit in the direction of the cylinder axis, and this yoke has a coefficient of thermal expansion that is different from the yoke itself. The present invention is characterized in that the gap between the inner and outer yokes can be finely adjusted in accordance with temperature changes by holding the inner and outer yokes with different supports.

(e) Examples Examples of the present invention will be described below based on the drawings. FIG. 6 is a diagram showing the structure of an embodiment of the present invention, and FIG. 5 is a perspective view showing the structure of the inner yoke of this embodiment. In the figure, a cylindrical outer yoke 3 and a cylindrical inner yoke 7 made of the same ferromagnetic material constitute a coaxial double cylindrical yoke. A permanent magnet 2 and a permanent magnet 1 whose magnetization direction is opposite to this permanent magnet 2 are fixed. In the gaps between the permanent magnets 2 and 1 and the inner yoke 7, coils 4 and 5 formed coaxially with the coaxial double cylindrical yoke are located, respectively, and are held by a common winding frame 6. The winding frame 6 is held movably in the axial direction of the yoke (a holding mechanism is omitted). In addition,
The outer yoke 3 and the inner yoke 7 are supported by a support plate 8 made of a non-magnetic material. inner yoke 7
is fixed to a cylinder 9 made of a material having a coefficient of thermal expansion larger than that of the yoke 7 itself, and the yoke itself is divided by slits provided in the axial direction of the coaxial double cylinder. According to the configuration of this embodiment, by appropriately selecting the thermal expansion coefficient of the cylinder 9 within a range that is larger than the thermal expansion coefficient of the yoke 7 itself, the gap between the inner and outer yokes due to temperature changes can be reduced. Therefore, the temperature dependence of the generated electromagnetic force due to a reversible change in the strength of the magnetic field can be suppressed.

In addition, in the present invention, the annular permanent magnets 2 and 1 are
As shown in the partially cutaway perspective view of FIG. 4, it can also be implemented by having a divided structure on an arc.

Further, in this embodiment, the inner yoke 7 is fixed to the outer peripheral surface of the cylinder 9 made of a material having a coefficient of thermal expansion larger than that of the inner and outer yokes themselves. The inner and outer yokes may be fixed to the inner circumferential surface of an annular support made of a material having a coefficient of thermal expansion smaller than that of the inner and outer yokes themselves.

(F) Effect As is clear from the above explanation, according to the present invention, even when a temperature change occurs in the electromagnetic force generating device and the strength of the magnetic field of the permanent magnet fluctuates, the difference in thermal expansion coefficients can be utilized. This allows the gap between the inner and outer yokes to be finely adjusted according to temperature changes, thereby canceling out fluctuations in the strength of the magnet's magnetic field, thereby suppressing fluctuations in the electromagnetic force generated. Therefore, it is possible to provide an electromagnetic force generating device that has a highly accurate linear relationship even when there are temperature fluctuations.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an electromagnetic force generating device according to the prior art. FIG. 2 is a configuration diagram of another example of an electromagnetic force generating device according to the prior art. FIG. 3 is a partially enlarged view for explaining the operation of the conventional example shown in FIG. FIG. 4 is a partially cutaway perspective view showing the structure of an outer yoke and a permanent magnet in another embodiment of the present invention. FIG. 5 is a perspective view showing the configuration of the inner yoke in the embodiment of the present invention shown in FIG. 6, and FIG. 6 is a configuration diagram of the embodiment of the electromagnetic force generating device according to the present invention. 1, 2, 11... Permanent magnet, 3... Outer yoke, 4, 5, 13... Electromagnetic coil, 6... Winding frame,
7... Inner yoke, 8... Support plate, 9... Inner yoke support cylinder, 16... Compensation coil.

Claims (1)

[Claims] 1. At least one of the inner circumferential surface of the outer yoke and the outer circumferential surface of the inner yoke formed in the shape of a coaxial double cylinder made of ferromagnetic material is provided with a predetermined interval in the axial direction of the coaxial double cylinder. Separated from each other, a first permanent magnet whose magnetization direction is directed outward in the radial direction of a coaxial double cylinder and has an annular shape as a whole, and a second permanent magnet whose magnetization direction is opposite to that of the first permanent magnet and which has an annular shape as a whole. The first and second annular coils include a magnetic circuit having a permanent magnet fixed thereto, and a frame movably held in the annular gap between the inner and outer yokes in the yoke axis direction.
an electromagnetic coil unit wound opposite to a second permanent magnet;
In an electromagnetic force generating mechanism in which a circuit is connected between two coils so that the directions of current flowing through the two coils are opposite to each other, at least one of the inner and outer yokes is divided by a slit in the direction of the cylinder axis, An electromagnetic force generating device characterized in that the gap between the inner and outer yokes can be finely adjusted according to temperature changes by holding the yoke by a support member having a coefficient of thermal expansion different from that of the yoke itself.