GB2306768A - Magnetron antenna feeders - Google Patents

Abstract

To facilitate assembly of an antenna feeder 5 in the exhaust tube 23 of a magnetron, e.g. for a microwave oven, the exhaust tube is provided with a frustroconical portion and the feeder may taper to a point. The feeder can therefore be easily and reliably assembled centrally of the tube without damage to either.

Description

Combination Construction of Maanetron for Microwave Oven The present invention relates to a magnetron for a microwave oven. Particularly, it relates to a combination construction of a magnetron for a microwave oven designed not to deform or change the position of the antenna feeder when assembling the antenna feeder and the exhaust pipe playing a transmitting role to radiate high-frequency energy to outside.

The present invention seeks to provide a combination construction in a magnetron which facilitates the swift assembly of an antenna feeder with an exhaust pipe without deformation. The invention also seeks to keep the exhaust pipe and the antenna feeder from being deformed, or the position of the antenna feeder from changing, during the tip off work. In this way, the characteristics of the output part, noise and stability of the magnetron can be maintained.

According to the present invention, a combination construction of a magnetron for a microwave oven is designed to fix one side of an antenna feeder on a vane, and to facilitate assembly of the body of the antenna feeder on the exhaust pipe by placing it on the centre of the anode seal to perform the tip off work on its top. To achieve this, the exhaust pipe is formed with adjacent sections of different internal diameters for successively receiving the antenna feeder, normally oriented to receive first the antenna feeder in the section of larger diameter. Between the exhaust pipe sections of larger and smaller diameter, the pipe can be gradually narrowed, typically in a frusto-conical connecting part. Usually, the body part of the antenna feeder to be inserted into the small diameter part through the large diameter part of the exhaust pipe is formed in a stick type.

The invention will be better understood from the following description, given by way of example only, of a known magnetron assembly, and a magnetron embodying the present invention. Reference will be made to the accompanying drawings wherein: FIG. 1 is a longitudinal sectional view illustrating a known magnetron construction; FIG. 2 is an enlarged longitudinal section view showing the outlet part of the magnetron of FIG. 1; FIG. 3 shows in enlarged perspective, the antenna feeder and the exhaust pipe of FIG. 2.

FIG. 4 is a longitudinal sectional view showing the outlet part of a magnetron embodying the present invention; and FIG. 5 shows in enlarged perspective the antenna feeder and the exhaust pipe of FIG. 4.

The construction of the conventional magnetron is shown in Figure 1. A serial filament 1 is installed axially along the internal centre, and a cylindrical anode 2 is also established around the filament, thus forming a diode vacuum tube. Permanent magnets 4a, 4b and magnetic pole 20, applying magnetic flux and thereby generating magnetic field to a space of action 10 located between the filament 1 and the anode 2 are formed orderly on the surface, reverse side and the centre of a lower plate 3 to form a magnetic circuit.

An antenna ceramic 6 and an antenna cap 7, all transmitting high-frequency energy sent by the anode 2 to outside (cavity) are established at an upper plate 19 (if provided) fixed with the lower plate 3. A plurality of vanes 8 are fixed radially inside the anode 2.

A plurality of laminated radiator pins 9 are established between the lower plate 3 and the vanes 8 to swiftly radiate to outside the heat created by the collision of thermoelectrons at the vanes 8. A filter box 11, a choke coil 12 and a condenser 13 are established at the bottom of the lower plate 3. These prevent the backward flow of nonessential high harmonic elements; integral multiples of the fundamental wave of 2,450KHz generated from the space of action 10.

The filament 1, radiating the thermoelectron, is sustained by a upper-end shield 14 and a lower-end shield 15. At the lower-end shield 15, both centre lead 16 and side lead (not shown) are fixed barely inside the filter box 11. The part of the exposure inside the filter box is fixed at the terminal 17. The centre lead 16 and the side lead are insulated by a cylindrical cathode ceramic 18.

When the magnetic field of the permanent magnets 4a and 4b forms a magnetic circuit at the upper and lower plates 19, 3 and the magnetic pole 20, an electric field is formed between the vane 8 and the filament 1. As a result, the thermoelectron radiated from the filament starts a cycloid motion by the electric and magnetic fields in the space of action. Accordingly, the thermoelectron, initiating an acceleration motion is converted into high-frequency energy, also known as electron energy. At this time, most of the high-frequency energy transmit not only the fundamental wave of 2,450KHz, but also the high harmonics which are multiplied integral number than the fundamental wave.

The high harmonics, however, are eliminated by the choke 22 established inside the anode seal 21.

As shown in FIG. 3, for the purpose of placing the centre of the antenna feeder 5 on the centre of the anode 21 to be assembled in the exhaust pipe 23, the conventional art formed the exhaust pipe 23 in a cylindrical shape, and formed a sustaining part 5a of a flat shape at the inserting end of the antenna feeder 5 slightly smaller than the inside diameter of the exhaust pipe, thus placing the antenna feeder 5 on the centre of the anode seal 21 when connecting the sustaining part 5a to the exhaust pipe 23.

However, since the conventional sustaining part 5a was bigger than the body of the antenna feeder 5, there was a problem deforming the sustaining part 5a because of its hitting at the lower part of the exhaust pipe 23 when inserting the antenna feeder 5 into the anode seal 21. As a consequence, considerable care was required during assembly.

In addition to the above, upon completion of the assembly of the antenna feeder 5, a wide space S was also seen between the outside diameter (1) of the body of the antenna feeder and the inside diameter (2) of the exhaust pipe. For this reason, when cutting off the exhaust pipe by the tip off work of the vacuum sealing work, the antenna feeder was deformed by pressing down or pulling up, with a significant affect on the coupling degree of the magnetron output section. As a result, the characteristics of the output, noise and stability of the magnetron could be damaged.

The overall assembly of the magnetron illustrated with reference to FIGS 4 and 5 is the same as that of the magnetron described above. However, the outlet part is significantly different. As indicated in the drawing, the body part of the antenna feeder 5 with one side of its lower part fixed on the vane 8 is formed in a stick shape, and its end is sharp-pointed. In other words, the inside diameter of the small diameter part 23a of the exhaust pipe 23 being inserted in the body part of the antenna feeder 5 and be tipped off is formed slightly bigger than the outside diameter of the antenna feeder 5. The large diameter part 23b of the exhaust pipe is formed to be bigger than the small diameter part 23a. The connection part 23c, linking the large diameter part 23b and the small diameter part 23a, forms a slope 23d with its outside diameter also reduces gradually.

When assembling the antenna feeder 5 into the exhaust pipe 23, the antenna feeder 5 is inserted into the small diameter part 23a through the large diameter part 23b of the exhaust pipe 23.

The shape of the exhaust pipe 23 is designed to lead the upper end of the antenna feeder 5 to the slope 23d of the connection part 23c when assembling the antenna feeder 5 into the exhaust pipe 23 without deforming the end of the antenna feeder, and to lead the end of the antenna feeder more smoothly into the small diameter part 23c.

The ratio of the outside diameter (ffi1) of the antenna feeder 5 and the inside diameter (2) of the small diameter part is set at 0.8 - 0.9. The setting of the above causes no trouble during the assembling of the antenna feeder 5 with the small diameter part 23a of the exhaust pipe 23. When completing the assembly work, the gap between them is minimized so that pressing or pulling up of the antenna feeder during the tip off work can be prevented.

The operational motion and effect of the present invention are as follows: In order to place the antenna feeder 5 on the centre of the anode seal 21, one side of the antenna feeder 5 is fixed on a vane 8 through a hole formed at the magnetic pole 20. When the upper end of the antenna feeder 5 is pushed in through the large diameter part 23b of the exhaust pipe 23, the upper end of the antenna feeder forms a sharp-pointed slope within the range of 500-700. Therefore, the contact area of the upper end with the large diameter part 23b of the exhaust pipe is minimized, and the antenna feeder can more easily be inserted into the exhaust pipe 23 through the large diameter part 23b.

When the upper end of the antenna feeder 5 is inserted into the large diameter part 23b of the exhaust pipe 23, the sharp-pointed upper end of the antenna feeder 5 is led to the slope 23d formed inside the connection part 23c of the exhaust pipe 23 and is further inserted into the inside of the small diameter part 23a without difficulty as shown in FIG. 4.

When the antenna feeder 5 is inserted into the exhaust pipe 23 as described above, the ratio of the outside diameter (1) of the antenna feeder 5 and the inside diameter (+2) of the small diameter part should be in the range 0.8 - 0.9. Thus, the antenna feeder 5 is not deformed by pressing or pulling during the tip off work for the vacuum sealing of the magnetron.

In addition, when the cutting point of the antenna feeder 5 is matched to the point where the connection part 23c of the exhaust pipe 23 and the small diameter part 23a are met, the deviation of the tip off point can also be reduced.

Claims (8)

1. A combination construction of an antenna feeder and an exhaust pipe in a magnetron for a microwave oven, in which magnetron one side antenna feeder is at the centre of an anode seal on the exhaust pipe, and the top of the antenna feeder is tipped off, wherein the exhaust pipe is formed with adjacent sections of different internal diameters for successively receiving the antenna feeder.

2. A combination construction according to Claim 1 wherein the exhaust pipe is oriented to receive first the antenna feeder in the section of larger diameter.

3. A combination construction according to Claim 1 or Claim 2 wherein the diameter of the exhaust pipe is gradually narrowed between a section of larger diameter and a section of smaller diameter.

4. A combination construction according to any preceding Claim wherein the portion of antenna feeder to be received in the smaller diameter section of the exhaust pipe has the shape of a stick.

5. A combination construction according to any preceding Claim wherein the ratio of the outside diameter of the antenna feeder to the inside diameter of the smaller diameter section of the exhaust pipe is in the range 0.8 to 0.9.

6. A combination construction according to any preceding Claim wherein the end of the antenna feeder has a sharp point.

7. A combination construction of an antenna feeder and an exhaust pipe in a magnetron for a microwave oven substantially as described herein with reference to Figures 4 and 5 of the accompanying drawings.

8. A magnetron for a microwave oven including an antenna feeder and exhaust pipe combination according to any preceding claim.