GB2083689A

GB2083689A - Self-convergent deflection yokes

Info

Publication number: GB2083689A
Application number: GB8124913A
Authority: GB
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1980-08-20
Filing date: 1981-08-14
Publication date: 1982-03-24
Also published as: GB2083689B; KR830006807A; DE3132834A1; KR850001389B1; JPS5738545A

Abstract

In a deflection yoke for a colour tube which avoids raster distortion and convergence error, both the saddle horizontal deflection coils (30) and the toroidal vertical deflection coils are wound to generate fields having a pincushion distribution. Front end magnetic members (62, 63 and 72, 73) extend the pincushion vertical deflection field toward the screen of the tube, while rear end magnetic members (80, 90) deform a portion of it into a barrel field. Additionally, front end permanent magnets (100, 101) are provided to correct raster distortion. <IMAGE>

Description

SPECIFICATION A deflection yoke for a cathode ray tube This invention relates to a deflection yoke for a cathode ray tube.

It has been proven by experiment that a deflection yoke for a colour cathode ray tube with in-line or delta electron gun assemblies can be formed which generates a pincushion distribution vertical deflection magnetic field to correct the right and left side distortion of the raster. This deflection yoke also can be formed to generate a pincushion distribution horizontal deflection magnetic field to correct the upper and lower side distortion of the raster. Raster distortion is largely dependent on the magnetic field generated at the portion of the deflection yoke which corresponds to the cone portion of the cathode ray tube.It is also well understood that, in order to prevent three electron beams from causing convergence error, the sum of the vertical deflection magnetic field generated in the vicinity of the deflection yoke, which corresponds to the area between the neck and cone portions of the cathode ray tube, must be a barrel distribution. On the contrary, the sum of the horizontal deflection magnetic field must be a pincushion distribution.

A prior art deflection yoke of the so-called selfconvergence type is formed to generate a barrel distribution in the vertical deflection field and a pincushion distribution in the horizontal deflection magnetic field. In such a yoke, satisfactory convergence characteristics of electron beams and correction of upper and lower side pincushion distortion of the raster can be obtained. However, distortion of the right and left side pincushion of the raster is increased.

At the present time, in order to correct the right and left side pincushion distortion of the raster, a correcting circuit is used to produce an output signal in synchronism with a vertical signal. The output signal has an amplitude which varies in a parabolic form and the signal is superimposed on the horizontal deflection signal. However, such a correcting circuit adds components, increases cost and increases the complexity of the construction.

According to the present invention from one aspect, there is provided a deflection yoke for a cathode ray tube having a viewing screen, which yoke comprises: a core surrounding said tube; a pair of horizontal deflection coils between said tube and said core for generating a horizontal deflection magnetic field having a pincushion distri butibn; a pair of vertical deflection coils wound around said core and facing each other for generating a vertical magnetic field having a pincushion distribution; front end magnetic means mounted at or adjacent a large diameter end of said core for picking up leakage flux caused by said vertical deflection coils and extending the pincushion type vertical deflection magnetic field toward said screen of said tube; and rear end magnetic means mounted at or adjacent a small diameter end of said core for deforming a portion of the vertical deflection magnetic field into a barrel distribution.

According to the present invention from another aspect, there is provided a deflection yoke for a colour cathode ray tube having a substantially rectangular screen, which yoke comprises: a core surrounding said tube; a pair of horizontal deflection coils between said tube and said core for generating a horizontal deflection magnetic field having a pincushion distribution; a pair of vertical deflection coils wound around said core and facing each other for generating a vertical deflection magnetic field having a pincushion distribution; front end magnetic members mounted at or adjacent a large diameter end of.said core, said members having arms at positions which substantially correspond to the corners of said screen of said tube; and a pair of rear end magnetic members mounted between said tube and said vertical deflection coils and at or adjacent a small diameter end of said core, said rear end magnetic members facing each other.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a front view of a deflection yoke according to an example of the present invention; Figure 2 is a rear view of the deflection yoke; Figure 3 is a partially cutaway side view of the deflection yoke; Figure 4 is a graph of the vertical deflection magnetic field distribution which is generated by the deflection yoke; Figure 5 is a perspective view of a front magnetic member used in the deflection yoke; Figure 6 is a perspective view of a rear magnetic member used in the deflection yoke; Figures 7(a) and (b) are perspective views of two forms of magnets which may be used in the deflection yoke; and Figure 8 is an illustration of raster distortion.

A deflection yoke 10 according to an example of the present invention is shown in Figures 1 to 3 and a graph of the vertical deflection magnetic field distribution of deflection yoke 10 is shown in Figure 4. A pair of saddle-shaped horizontal deflection coils 30 are disposed at the interior periphery of a funnelshaped coil separator 20. The coil separator 20 is disposed around the outer periphery of a colour cathode ray tube (not shown). Horizontal deflection coils 30 generate a horizontal deflection magnetic field having a pincushion distribution. A substantially cylindricai core 40 is located around the outer periphery of separator 20. A pair of vertical deflection coils 50 and 51 are wound in a toroid around the upper and lower parts of core 40.The width of vertical deflection coils 50 and 51 is narrow in order to generate a vertical deflection magnetic field having a pincushion distribution as shown by the dot-dash line B1 in Figure 4, in which A indicates the neck side of the tube and C indicates the cone side of the tube, magneticfield portions above the horizontal axis having a pincushion distribution and magnetic field portions below the horizontal axis having a barrel distribution.

A pair of front end magnetic members 60 and 70 are attached to the large diameter end of core 40.

Since these magnetic members 60 and 70 are identical, only one of these front end magnetic members is shown in Figure 5 with duplicate numerals indicating the corresponding part numbers for the two different magnetic members 60 and 70. As shown in Figure 5, the front end magnetic members 60 and 70 have curved bars 61 and 71 which have substantially the same curvature as the large diameter end of the outer periphery of core 40.

Thus, these curved bars 61 and 71 fit on core 40.

Curved bars 61 and 71 of the front end magnetic members 60 and 70 cross the side of core 40 in the vicinity of vertical deflection coils 50 and 51. Each of magnetic members 60 and 70 also includes a pair of arms 62 (72) and 63 (73) at opposite ends of the curved bar 61 (71). Each arm 62 (63) is at a substantially right angle to curved bar 61 (71) and the end of each arm 62 (63) is bent to fit on a flange 21 on the large diameter side of separator 20. When both front end magnetic members 60 and 70 are attached to the large diameter end of the outer periphery of core 40, their arms 62, 63,72 and 73 substantially correspond to the four corners of the cathode ray tube screen.

Leakage flux from vertical deflection coils 50 and 51 is picked up by front end magnetic members 60 and 70. For example, leakage flux may be picked up by curved bar 61 of front end magnetic member 60 and passed from arms 62 and 63 of members 60 to arms 72 and 73 of member 70. The magnetic field between the arms 62 and 63 of member 60 and arms 73 and 72 of member 70 is synchronized with the vertical deflection magnetic field generated byvertical deflection coils 50 and 51, which is distributed in pincushion form. As a result, the pincushion vertical deflection magnetic field is extended toward the screen side of the cathode ray tube as shown by broken line B22 in Figure 4 because the arms of each of front end magnetic members 60 and 70 extend toward the screen of the tube.

Each of a pair of rear end magnetic members 80 and 90 is attached to the outer periphery of separator 20 under the small diameter end of core 40. Rear end magnetic members 80 and 90 are also positioned under vertical deflection coils respectively 50 and 51 and face each other. As shown in Figure 6, each of rear end magnetic members 80 and 90 has substantially the same curvature as the outer periphery of the portion of separator 20 which corresponds to the small diameter end of core 40. The reluctance of rear end magnetic members 80 and 90 is smaller than that of air so the magnetic fluxes generated by the vertical deflection coils tend to pass in the vicinity of rear end magnetic members 80 and 90. Therefore, the magnetic fluxes generated by vertical deflection coils 50 and 51 deflect toward the inner periphery of core 40.In otherwords, the vertical deflection magnetic field is in the form of a barrel distribution at the small diameter end of core 40, as shown by broken line B21 in Figure 4.

In a summary, the vertical deflection magnetic field due to yoke 10 is in the form of a pincushion distribution a the cone side of the tube; however, its total sum B2 (see Figure 4) also provides a portion B21 which forms a barrel distribution. The horizontal deflection magnetic field generated by horizontal deflection coils 30 is in the form of a pincushion distribution, as mentioned above. Accordingly, yoke 10 does not cause raster distortion and convergence error.

Furthermore, a pair of plate type permanent magnets 100 and 101, which are shown in Figure 7(a), are attached to the upper and lower portions of the rear of flange 21 on a vertical centre line Lv of yoke 10. When the deflection angle of the cathode ray tube increases, the raster normally develops a wave-shaped distortion (the so-called sea gull distortion) in the horizontal direction and an inside distortion in the vertical direction, as shown in Figure 8. The magnetic fields generated by magnets 100 and 101 correct the above distortions and improve the linearization of the raster. As a substitute for magnets 100 and 101, a pair of pole-shaped permanent magnets 100' and 101' may be mounted on flange 21 of separator 20 by a humped attachment 110 as shown by Figure 7(b).

The above deflection yoke 10 can be easily fabricated without the necessity for fine adjustments. The vertical deflection coils 50 and 51 also are simple to wind and construct. Finally, the deflection yoke 10 need not be modified or adjusted in accordance with the deflection angle of the cathode ray tube on which it is used.

Claims

1. A deflection yoke for a cathode ray tube having a viewing screen, which yoke comprises: a core surrounding said tube; a pair of horizontal deflection coils between said tube and said core for generating a horizontal deflection magnetic field having a pincushion distribution; a pair of vertical deflection coils wound around said core and facing each other for generating a vertical magnetic field having a pincushion distribution; front end magnetic means mounted at or adjacent a large diameter end of said core for picking up leakage flux caused by said vertical deflection coils and extending the pincushion type vertical deflection magnetic field toward said screen of said tube; and rear end magnetic means mounted at or adjacent a small diameter end of said core for deforming a portion of the vertical deflection magnetic field into a barrel distribution.

2. A deflection yoke according to claim 1, where- in it further comprises a pair of permanent magnets mounted at or adjacent the large diameter end of said core and facing each other.

3. A deflection yoke for a colour cathode ray tube having a substantially rectangular screen, which yoke comprises: a core surrounding said tube; a pair of horizontal deflection coils between said tube and said core for generating a horizontal defle-ction magnetic field having a pincushion distribution; a pair of vertical deflection coils wound around said'core and facing each other for generating a vertical deflection magnetic field having a pincushion distribution; front end magnetic members mounted at or adjacent a lage diameter end of said core, said members having arms at positions which substantially correspond to the corners of said screen of said tube; and a pair of rear end magnetic members mounted between said tube and said vertical deflection coils and at or adjacent a small diameter end of said core, said rear end magnetic members facing each other.

4. A deflection yoke according to claim 3, wherein each of said front end magnetic members includes a curved magnetic bar arranged across facing ends of said vertical deflection coils, each of said front end magnetic members further having two of said arms mounted at opposite ends of the curved bar.

5. A deflection yoke according to claim 4, wherein said arms extend toward the four corners of said screen.

6. A deflection yoke according to any of claims 3 to 5, wherein it further comprises a pair of permanent magnets mounted at the large diameter end of said core and substantially on a vertical centre line of said tube, said permanent magnets facing each other.

7. A deflection yoke for a cathode ray tube, substantially as herein described with reference to the accompanying drawings.