JPS6321733A - Focusing magnet - Google Patents

Abstract

PURPOSE:To make a spot diameter extremely small and an axial length short by providing, on the end of a case, radial slits which extend from the axis of a magnet serving as the center to the edge and inner and outer periphery. CONSTITUTION:Hollow cylindrical permanent magnets 1, 1 which are magnetized in the axial direction and provided with magnetic poles formed on their end faces are fixed coaxially via a yoke 2a with their opposite poles facing each other and yokes 2 fixed on other end faces of the permanent magnets. A central magnetic field control coil 3 is provided on the inner peripheries of the permanent magnets. Inner and outer periphery and the end faces of the magnet assembly consisting of the permanent magnets and the yokes are covered by a case 7 made of a nonmagnetic material. At least one end 7a of the case is provided with multiple radial slits 9 extending from the axis of the magnet assembly serving as the center to the edge and the inner and outer periphery, with the case diameter made variable and a band 11a wound around the outer periphery of the slits. by this constitution, only the half-width on the magnetic field curve can be increased and the conversion spot diameter of electron beams can be reduced and the axial length is made shorter.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a focus magnet for a projection type cathode ray tube used in, for example, a video projector, a projection wall, and a high-definition television. The present invention relates to improvements to the Focus Magneso 1.

[Prior Art] Conventionally, an electrostatic type 1aiZ has been used to focus the electron beam of a cathode ray tube, and is used for special tubes such as X-ray tubes, magtrons, and traveling wave tubes.

A magnetic field method was used. However, recently, high resolution TVs and other devices are required.

There is a transition to magnetic field methods. The electromagnetic type, which is one type of magnetic field type, has the drawbacks of being large and requiring a power source, so permanent magnets are mainly used. Figure 4 shows an example of this, in which a permanent magnet 1 is magnetized in the axial direction and provided with an N, 36ft pole on the end face, and is made of a ferromagnetic material on both end faces of a permanent magnet 1 formed into a hollow cylindrical shape. A magnetic circuit is formed by fixing a ring-shaped yoke 2, and a coil 3 is interposed on the inner circumference of the permanent magnet 1 via a bobbin 4. If the coil 3 is formed as described above and energized via a lead wire (not shown), the central magnetic field of the permanent magnet 1 can be adjusted, and the effect of converging the electron beam on the central axis can be expected. It can be done.

[The problem to be solved by the invention is that the spot diameter of the converged electron beam on the central axis by the conventional focus magnet is 0.3 to 0.35 mm, but for recent high-definition projectors, the above-mentioned The spot diameter is required to be 0.25 to 0.28 mm. In order to reduce the spot diameter, it is said to be effective to increase the integral value of the central magnetic field curve of the permanent magnet. However, due to the characteristics of the projector, it is impossible to increase the peak value of magnetic field strength or magnetic flux density and the distance between zero points on the horizontal axis. There is no way to increase it. Moreover, it is extremely difficult to realize the above-mentioned expansion to the half value without impairing other characteristics, and there is a problem that it is impossible to manufacture a focus magnet with an extremely small spot diameter. The focus magnet is housed in a cylindrical case 5 made of a non-magnetic material such as synthetic resin, and is inserted into a cathode ray tube. Since the members are interposed together, the interposition position is narrow. Furthermore, since the axial length of recent cathode ray tubes is gradually becoming shorter, the above-mentioned insertion position is becoming narrower and narrower. For this reason, the case 5 that houses the focus magnet is also required to have a short length in the axial direction. However, in the conventional one.

As shown in FIG. 4, there is a problem in that it requires a fixing part 6 to the cathode ray tube, and the axial length of the case 5 cannot be shortened, making it impossible to fully demonstrate the original function of the focus magnet. The present invention solves the problems existing in the above-mentioned prior art, has an extremely small slot and throat diameter, and
Another object of the present invention is to provide a focus magnet 27 with a short axial length.

[Means for solving problems]

In order to solve the above problems, in the present invention, two hollow cylindrical permanent magnets are magnetized in the axial direction and have magnetic poles on the end faces, and a hollow disc-shaped yoke is used, with different poles facing each other. The permanent magnet and the yoke are fixed coaxially through the permanent magnet, another hollow disc-shaped yoke is fixed to the other end surface of the permanent magnet, and a coil for adjusting a central magnetic field is provided on the inner periphery of the permanent magnet. A hollow cylindrical case made of a non-magnetic material is provided to surround the inner and outer peripheral surfaces and end surfaces of the magnet body,
At least one end of the case is provided with a plurality of radial cuts centered on the axis of the magnet body and continuous at the end and the inner and outer circumferential parts to make the diameter of the case variable;
A band is wrapped around the outer periphery of the cut. This technical method was adopted.

[Effect]

With the above configuration, it is possible to increase only the half-width without changing the peak value and other values on the central magnetic field curve, and it is possible to increase the integral value of the curve, resulting in the convergence spot of the electron beam. The diameter can be reduced. Furthermore, since the axial length can be shortened, winding around the cathode ray tube is extremely easy and just focus can be expected.

〔Example〕

1 and 2 are a longitudinal sectional view and a front view of essential parts showing an embodiment of the present invention, respectively, and the same parts are designated by the same reference numerals as in FIG. 4. In the figure, hollow cylindrical permanent magnets 1, 1 magnetized in the axial direction and provided with magnetic poles on the end faces are made to have different poles facing each other, and are fixed coaxially through a hollow disc-shaped yoke 2a. . 7.8 is a case 1 made of a non-magnetic material such as synthetic resin, and the permanent magnet l
and is formed to surround the inner and outer circumferential surfaces and end surfaces of the yokes 2, 2a. In addition, at the end 7a of the case 7, which is located on the phosphor screen side when attached to a cathode ray tube, there is a magnet located at the end 7a of the case 7, centered on the axis of the permanent magnet 1 or the yokes 2, 2a, and
A plurality of continuous radial cuts 9 are provided on the end portion 7a and the inner and outer peripheral portions.

The diameter of the case 7 is made variable. On the other hand, the end 8a of the case 8, which becomes the electron gun side when attached to a cathode ray tube, is made to protrude as a fixed part as in the conventional case, and has a radial cut 10 centered on the axis of the permanent magnet l or the yokes 2, 2a. , the diameter of the end portion 8a is made variable. Next, lLa,
Each band llb is wound around the ends 7a and 8a of the case 7 and the case 8, respectively. 12 is a tightening screw.

With the above configuration, after being mounted on a cathode ray tube (not shown) and positioned, the bands lla and ll are tightened using the tightening screws 12.
By reducing the diameter of each end portion 7a, 8a of the case 7.8 via b, the function as a focus magnet can be achieved.

FIG. 3 is a magnetic field curve showing the value of the axial position of the central magnetic field of the focus magnet shown in FIGS. 1 and 2. FIG. Note that the curve shown by a broken line is a magnetic field curve corresponding to the conventional one shown in FIG. As is clear from FIG. 3, in the first embodiment of the present invention, although the width WO at the point where the magnetic field strength is O and the peak value Bp of the magnetic field are the same, the half width wh is lower than that of the conventional one. It is increased from wh in that of . Therefore, it is clear that the integral value of the magnetic field curve, that is, the area surrounded by the horizontal axis and the magnetic field curve, is much larger in the embodiment of the present invention shown by the solid line than in the conventional case shown by the broken line. It is.

In other words, it is clear that this method is extremely effective in reducing the convergence spot diameter of the electron beam.

The hollow cylindrical permanent magnet used in the present invention is preferably an alnico magnet, for example, and is preferably manufactured by cooling in a magnetic field to avoid biased magnetism. We also use rare earth cobalt magnets as permanent magnets.

It is also preferred to use rare earth magnets, such as rare earth iron boron magnets. Note that the hollow disk-shaped yoke interposed between the two permanent magnets may be divided along a plane perpendicular to the axis. If formed in this manner, a manufacturing method can be employed in which a magnet unit is formed in advance, in which a coil is disposed on the inner periphery of a permanent magnet and a yoke is fixed to both end faces, and then both units are fixed coaxially. In addition, in this example, 9
Although we have shown an example in which continuous radial cuts are provided at the ends of both cases and on the inner and outer peripheries, it is of course possible to provide these cuts at the end of only one case. be.

〔Effect of the invention〕

Since the focus magnet of the present invention has the configuration and function as described above, it is possible to increase only the half maximum on the magnetic field curve, and as a result, the integral value of the curve can be greatly increased, so that the electron beam The convergence spot diameter can be reduced. In addition, since the axial length is short, it is extremely easy to attach to a cathode ray tube, and it is possible to ensure just focus.

[Brief explanation of the drawing]

1 and 2 are longitudinal cross-sectional views and front views of main parts showing embodiments of the present invention, respectively, and FIG. 3 shows the values of the axial position of the central magnetic field of the focus mag independent 'h;'i field. The curved line diagram, FIG. 4, is a longitudinal sectional view of the main part showing the conventional one. ■, Permanent magnet 2.2a, Yoke 1.3: Coil 55.
1.8: Case, 9: Cut.

Claims (5)

[Claims] (1) Two hollow cylindrical permanent magnets magnetized in the axial direction and provided with magnetic poles on the end faces are fixed coaxially with different poles facing each other through a hollow disc-shaped yoke, and the permanent magnets Another hollow disc-shaped yoke is fixed to the other end face of the permanent magnet, and a coil for adjusting the central magnetic field is provided on the inner periphery of the permanent magnet, surrounding the inner and outer circumferential surfaces and end faces of the magnet body consisting of the permanent magnet and the yoke. A hollow cylindrical case made of a non-magnetic material is provided, and a radial cut is formed on at least one end of the case, centered on the axis of the magnet and continuous with the end and the inner and outer peripheries. A focus magnet characterized in that a plurality of focus magnets are provided to make the diameter of the case variable, and a band is wrapped around the outer periphery of the cut. (2) The focus magnet according to claim 1, wherein the non-magnetic material forming the case is a synthetic resin. (3) The focus magnet according to claim 1 or 2, wherein the case has a dividing plane perpendicular to the axis. (4) The focus magnet according to any one of claims 1 to 3, wherein the permanent magnet is an alnico magnet or a rare earth magnet. (5) The focus magnet according to any one of claims 1 to 4, wherein the hollow disk-shaped yoke provided between the hollow cylindrical permanent magnets has a dividing plane perpendicular to the axis.