JPH0131260B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a beam focusing device for a cathode ray tube.

There is a system in which the image formed on the phosphor of a cathode ray tube is enlarged and projected onto a large screen, but there are three cathode ray tubes (red, green, and blue) [hereinafter referred to as CRT].
In the three-tube system, the brightness characteristics of the image projected onto the screen are determined by the phosphor materials used in the three CRTs, the CRT's beam current value, high voltage, and other factors. The set value of the CRT's beam current is mostly determined by the lifespan of the phosphor material, and the high voltage is mostly determined by the safety of the CRT. When increasing the CRT beam current as a means of increasing the brightness on the screen, due to the characteristics of the red, green, and blue phosphor materials,
The beam current of red, green, and blue CRTs can be increased up to a predetermined current value. However, when the entire system is operated at a relatively high current density, such as in a projection color television system, the blue phosphor material becomes saturated when the beam current is increased beyond a certain amount, and the overall effect of the three CRTs is At present, it is difficult to increase brightness.

Therefore, the present invention controls the electron movement of the scanning beam using a beam focusing system so that the scanning beam has a vertically elongated beam spot shape, increases the scanning area on the phosphor target, and uses methods other than increasing the high voltage and beam current. Therefore, the present invention provides something that can increase brightness.

Examples of the present invention will be described below in comparison with conventional examples.

Conventionally, in a device that uses three CRTs to project a color image on a screen by projecting the three primary colors of red, green, and blue, the current amount of the scanning beam is determined by the phosphor material of each primary color projector, and the high voltage is determined by the CRT. The brightness was determined mostly based on safety, and the brightness was determined by conditions such as the amount of beam current flowing through the phosphor and high voltage. Furthermore, electromagnetic focusing circuits are often used as a scanning beam focusing method that meets one of the above conditions.

Figure 1 shows the basic type of an electromagnetic focusing circuit, where 1 is a cathode from which an electron current is emitted, and the electron current is generated by a uniform magnetic field _Bz in the Z-axis direction generated by a focusing coil 2 as a focusing lens system. Fluorescent surface target 3
focused on. 4 is a deflection coil that provides horizontal and vertical scanning on the target 3; Although Fig. 1 shows a system in which an image appears on the beam side, the same applies to a system in which an image appears from the outside of a glass surface coated. In FIG. 1, the electron flow passes through an axially symmetrical focusing coil 2, and if there is no aberration, an axially symmetrical circular spot is generated on the target 3. In such a system, by superimposing the three primary colors of each CRT on a screen and passing a certain amount of beam current through each phosphor, an image with a certain brightness can be obtained. To make this image brighter while keeping the optical system constant, you can increase the beam current and high voltage of each CRT, but the maximum value for high voltage is limited by the life of the CRT, glass withstand voltage, X-ray leakage, etc. has been done. Therefore, when using a beam current that can be properly controlled, red R, green G,
The relationships between the three CRT beam currents for blue B and the brightness are as shown in R, G, and B in FIG. 8, respectively. blue
When the CRT increases the beam current beyond a certain amount,
Because brightness saturation occurs earlier than with other two-color CRTs, it is not possible to increase the beam current by the same amount as red and green, and the brightness increase rate of blue is lower than that of red and green, resulting in an increase in overall brightness. A difficult problem arose.

The present invention controls only the focus system to lengthen the spot shape of the scanning beam in the direction perpendicular to the horizontal scanning direction, increasing the spot area on the target and, for example, increasing the beam current compared to the other two CRTs. This increases the brightness of blue CRTs, which have a strong tendency to saturate brightness, as shown in Figures 2 and 3.
The figure shows one embodiment. Here, the horizontal scanning direction is
Assuming that the vertical scanning direction is the Y axis and the beam traveling direction is the Z axis direction, in FIG. plane perpendicular to the axis
As shown in Figure 3, the control coil section generates a magnetic flux distribution between the
It consists of a core 10 having four core poles 6 to 9 arranged on the Y' axis so as to surround the Z axis, and windings 11 and 12 wound around the opposing core poles 6 and 7. As shown in Figure 4, the control magnetic field in the coil section has a magnetic flux density of zero at the center and increases in magnitude as it moves away from the Z-axis, and the direction of the magnetic flux density is parallel to the Z-axis in the X-axis direction. They are different on both sides and on both sides of the Z-axis in the Y-axis direction, and constitute a magnetic field generating device. Here, B _x is the X-axis component of the control magnetic field,
It shows the magnitude of the magnetic flux density when it changes along the Y axis, and B _y shows the magnitude when it changes along the X axis. Further, (+) and (-) indicate the direction of magnetic flux density. When the beam 13 passes through the control magnetic field of the control coil section 5 with a width d having a circular distribution, the beam 1
3, a force of magnitude f is applied to the beam 1 in the X-axis direction.
3 is compressed in the Z-axis direction and acts as a tensile force in the Y-axis direction, controlling the movement of electrons. Further, the direction of the current flowing through the windings 11 and 12 is such that magnetic flux is generated in the direction toward the center of the shaft. Conversely, if the core poles 6 and 7 are made to have different polarities, the central magnetic field becomes a constant magnetic field, a deflection magnetic field is generated, and the beam 13 is displaced, so that the windings 11 and 1
The directions of the two must be the same polarity. Figure 7 is the second
The beam spot 14 at the crossover point near the cathode 1 is connected to the focusing lens 1.
5 to the position _Z1 . Control coil section 5
Since the beam spot 16 passing through has a certain size, it receives a force f as it moves away from the Z-axis direction. For example, the trajectory is displaced by the force f, passes through the focusing lens 15, and the electrons near the Y-axis direction are focused at a position _Z2 that is farther than the position _Z1 . Therefore, the beam spot 17 at position _Z1
The shape of is a vertically elongated spot. That is, this is equivalent to a partial change in focal length due to the magnetic field distribution in the plane X-Y of the control coil section 5. Here, the control current required to make the beam spot 17 about 5 times as long as it is vertically elongated is, for example, 40 [mA] in a 36.5〓, 30KV electromagnetic focus system with a 400T winding, which requires only a small amount of power. only need.

FIG. 5 shows another embodiment, in which windings 18 to 21 are wound around the four-pole cores 6 to 9 of the control coil section 5, respectively, and the direction of the current to each winding is the same as that of the opposing core 6. 7 and cores 8 and 9 have the same polarity, and adjacent cores have different polarities in a direction in which magnetic flux is generated. In this case, the distribution characteristics of B _x and B _y will be similar to that shown in FIG. 4, and a vertically elongated beam spot will be formed similarly to that shown in FIG. 3. The major difference between the cases of FIG. 3 and FIG. 5 is that leakage of the magnetic flux _Bz in the Z-axis direction is improved. Figure 6 A and B are the third
5 shows the magnitude of the magnetic flux B _z due to the control coil section 5 in FIG. 5. If there is a magnetic flux B _z , it acts on the focus, so the configuration in FIG. 5 is effective against leakage magnetic flux. However, when the magnetic flux B _z is small, the control coil section 5 shown in FIG. 3 has a simple structure and there is no problem in practical use. Further, when the main focus lens is an electromagnetic focus lens, image rotation may occur by θ° due to the lens 15, but in that case, the four-pole cores 6 to 9 of the core 10 of the control coil section 5 If the angle is corrected in advance by θ°, a vertically elongated image in the vertical scanning direction can be obtained on the target.

Next, the effect when the image on the target is made vertically elongated in the vertical scanning direction will be explained. For example, the above 3
If a tube-type blue CRT equipped with the control coil section 5 is used and the vertically elongated spot is used, as shown in Figure 9, the blue CRT has a stronger tendency for brightness saturation with respect to the beam current than the other two CRTs. The brightness characteristic B is improved as shown by the broken line B', and the brightness increases. Experimentally, the brightness increase rate is about 50% at around 4 [μA/cm ³ ], where the beam current density is low, and when the beam current density is high at around 40 μA/cm 3 .
In the vicinity of [μA/cm ³ ], the increase is about 30 [%]. By making the spot vertically elongated and increasing the area of the scanning beam, an increase in brightness can be achieved, and since the spot is vertically elongated in the vertical scanning direction, no deterioration in horizontal resolution occurs. Further, the decrease in vertical resolution caused by the increase in width in the scanning width direction is hardly noticeable. Furthermore, in a composite image of red, green, and blue, the resolution of green has a large effect, and the influence of blue is small, so there is no problem with images of the three primary colors. If the saturation characteristics were improved simply by blurring the focus while keeping the spot circular, the horizontal resolution would deteriorate and it would not be practical. This is very useful, and the longitudinal ratio of the beam spot can be easily controlled by applying current to the winding of the control coil section 5. In focus adjustment, the main lens is adjusted without any control, and after setting the optimum focus, the vertically elongated spot can be formed simply by switching the current. Furthermore, as is clear from FIG. 7, the focusing lens can be used for both electromagnetic and electrostatic focusing.

Although the control magnetic field is generated by the windings 11, 12 and 18 to 21 in FIGS. 3 and 5 above, it can also be realized by a combination with permanent magnets, and the control magnetic field can be generated by using the four core poles. The shape of is also not limited to the example. Furthermore, although the magnitudes of the control magnetic fields B _x and B _y were equal, the magnitudes of the two do not have to be the same.

As explained above, the present invention has the following effects.

(1) Since brightness can be increased without increasing high voltage or beam current, the life characteristics of cathode ray tubes are also advantageous.

(2) The control power required to increase brightness is minimal.

(3) The focusing lens system only needs to act axially symmetrically to focus without any action, and can be easily added to a conventional device.

(4) Since it is added to the blue cathode ray tube of a three-tube color video device, it is possible to increase the overall brightness near the brightness saturation region.

(5) The elongation ratio of the beam spot can be easily controlled by the current flowing to the winding of the magnetic field generator composed of the core winding, and the brightness characteristics can be improved according to the level of the beam current.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a conventional focusing system, FIG. 2 is a configuration diagram of a focusing system according to the present invention, FIG. 3 is a configuration diagram of a main part of one embodiment, and FIG. 5 is a diagram of a main part of another embodiment. 4 to 9 are operation explanatory diagrams. DESCRIPTION OF SYMBOLS 1... Cathode, 2... Focusing coil, 3... Target, 4... Deflection coil, 5... Control coil section, 6-9... Core pole, 11, 12... Winding wire, 1
7... Beam spot, 18-21... Winding wire, X
...Horizontal scanning direction, Y...Vertical scanning direction, Z...
beam axis.

Claims (1)

[Claims] 1. An electromagnetic or electrostatic focusing lens system for focusing the electron beam, a deflection device that provides horizontal and vertical scanning to the electron beam focused by the focusing lens system, and a beam image that reproduces the deflected beam image. In a three-tube color imaging device equipped with red, green, and blue cathode ray tubes each having a reproduction surface, only the blue cathode ray tube has an electron beam that Consists of a core winding that generates a control magnetic field in which the direction of magnetic flux density in a perpendicular plane is different on both sides of the beam axis in the horizontal scanning direction and on both sides of the beam axis in the vertical scanning direction, and the magnetic flux density is zero at the center of the beam axis. 1. A beam focusing device characterized in that a magnetic field generator is provided to obtain a vertically elongated spot image on the beam image reproduction surface of a blue cathode ray tube.