Title: Projection type cathode ray tube device
Abstract: A pair of magnets of which magnetizing direction differs from each other in the horizontal direction (X axis) are arranged at upper and lower portions of a funnel-side opening portion of a deflection yoke. The pair of magnets are held and fixed to a coil support body which supports horizontal deflection coils in a state where the magnets are embedded in the coil support body. In a projection type cathode ray tube of a single electron beam method, a locus of an electric beam which receives the deflection distortion is corrected so as to correct an electron beam shape on a screen to an approximately circular shape whereby a focusing performance of a display image on a screen is enhanced.
Patent Number: 7,015,634 Issued on 03/21/2006 to Watanabe, et al.
| Inventors:
|
Watanabe; Sakae (Mutsuzawa, JP);
Hirota; Katsumi (Urayasu, JP)
|
| Assignee:
|
Hitachi Displays, Ltd. (Chiba-ken, JP)
|
| Appl. No.:
|
612460 |
| Filed:
|
July 2, 2003 |
Foreign Application Priority Data
| Jul 08, 2002[JP] | 2002-198203 |
| Current U.S. Class: |
313/442; 313/431 |
| Current Intern'l Class: |
H01J 29/70 (20060101); H01F 1/00 (20060101) |
| Field of Search: |
313/440,412-414,477.R,421,426,431,442
315/370
335/212
|
References Cited [Referenced By]
U.S. Patent Documents
| 4939415 | Jul., 1990 | Iwasaki et al.
| |
| 5378961 | Jan., 1995 | Shiro et al.
| |
| 6373202 | Apr., 2002 | Ito et al.
| |
| 6750602 | Jun., 2004 | Hirota et al.
| |
| 2003/0173889 | Sep., 2003 | Tagami et al.
| |
| Foreign Patent Documents |
| 7-37526 | Feb., 1995 | JP.
| |
| 8-287845 | Nov., 1996 | JP.
| |
| 2001/-185053 | Jul., 2001 | JP.
| |
Other References
Patent Abstracts of Japan; Publication No. 08-287845, Jan. 11, 1996, Projection
Cathode-Ray Tube Device.
|
Primary Examiner: Guharay; Karabi
Attorney, Agent or Firm: Milbank, Tweed, Hadley & McCloy LLP
Claims
What is claimed is:
1. A projection type cathode ray tube device comprising a vacuum envelope which
includes a rectangular panel portion having a phosphor screen formed on an inner
surface thereof, a neck portion housing an electron gun which irradiates an electron
beam inside thereof, a funnel portion for connecting the panel portion and one
end of the neck portion, and a stem portion for sealing the other end of the neck
portion, a deflection yoke which makes the electron beam scan on the phosphor screen,
and a convergence yoke, wherein
the neck portion includes a first neck portion which is arranged at the funnel
portion side and has a first outer diameter, a second neck portion which is arranged
closer to the stem portion side than the first neck portion and has a second outer
diameter, and a third neck portion which connects the first neck portion with the
second neck portion, wherein the first outer diameter is smaller than the second
outer diameter,
the deflection yoke is arranged in a transitional region between the funnel portion
and the first neck portion and the convergence yoke is arranged to stride over
the second neck portion and the third neck portion, and
first magnets which have different polarities from each other in the horizontal
direction are arranged at upper and lower positions of a funnel-side opening portion
of the deflection yoke as the electron beam which is deflected to the upper and
lower portions of the screen receives a force to a center direction of the screen,
and the first magnet arranged at the upper side of said opening portion and the
first magnet arranged at the lower side of said opening portion differ in polarity
at left and right sides.
2. A projection type cathode ray tube device according to claim 1, wherein the
deflection yoke includes a coil support body which holds and fixes a pair of horizontal
deflection coils thereto, and the first magnets are mounted and fixed to the coil
support body.
3. A projection type cathode ray tube device according to claim 1, wherein the
deflection coil is arranged in a state where a distance between vertical deflection
coils is set to 0.8 mm or less.
4. A projection type cathode ray tube device comprising a vacuum envelope which
includes a rectangular panel portion having a phosphor screen formed on an inner
surface thereof, a neck portion housing an electron gun which irradiates an electron
beam inside thereof, a funnel portion for connecting the panel portion with one
end portion of the neck portion, and a stem portion for sealing the other end of
the neck portion, a deflection yoke which makes the electron beam scan on the phosphor
screen, and a convergence yoke, wherein
the neck portion includes a first neck portion which is arranged at the funnel
portion side and has a first outer diameter, a second neck portion which is arranged
closer to the stem portion side than the first neck portion and has a second outer
diameter, and a third neck portion which connects the first neck portion with the
second neck portion, wherein the first outer diameter is smaller than the second
outer diameter,
the deflection yoke is arranged in a transitional region between the funnel portion
and the first neck portion and the convergence yoke is arranged to stride over
the second neck portion and the third neck portion,
first magnets which have different polarities from each other in the horizontal
direction are arranged at upper and lower positions of a funnel-side opening portion
of the deflection yoke as the electron beam which is deflected to the upper and
lower portions of the screen receives a force to a center direction of the screen,
and the first magnet arranged at the upper side of said opening portion and the
first magnet arranged at the lower side of said opening portion differ in polarity
at left and right sides, and
second magnets which have polarities different from each other in the tube axis
direction of the cathode ray tube are arranged in a circumference of said opening
portion of the deflection yoke.
5. A projection type cathode ray tube device according to claim 4, wherein the
deflection yoke includes a coil support body which holds and fixes horizontal deflection
coils thereto, and the first magnets are mounted and fixed to the coil support body.
6. A projection type cathode ray tube device according to claim 4, wherein the
deflection coil is arranged in a state where a distance between vertical deflection
coils is set to 0.8 mm or less.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cathode ray tube device, and more particularly
to a projection type cathode ray tube device which is applicable to a projection
type image display device such as a projection type TV receiver, a video projector
or the like.
2. Description of the Related Art
In general, three projection type cathode ray tube devices which emit respective
colors of red, green and blue are mounted on a projection type image display device,
wherein images of respective projection type cathode ray tubes are magnified by
respective projection lenses arranged at frontal sides of respective panel portions
and are projected onto a screen and synthesized. In each projection type cathode
ray tube device, from a phosphor screen toward an electron gun, a deflection yoke,
a convergence yoke, an alignment magnet and the like are sequentially mounted and
arranged, wherein electron beams irradiated from the electron guns receive a deflection
action due to a deflection magnetic field which is generated by a deflection yoke
and reach the phosphor screen.
In the projection type image display device, the distortion of luster or the
misalignment
of three-color luster (also referred to as "color slurring" or "misconvergence")
due to the magnetic field generated in a convergence yoke served for aligning the
images projected from the above-mentioned three projection type cathode ray tubes
on a screen is corrected so as to obtain image with no color slurring. Here, as
this type of projection type cathode ray tube device, a cathode ray tube device
disclosed in Japanese Unexamined Patent Publication 287845/1996 or the like can
be named.
SUMMARY OF THE INVENTION
Recently, to enhance the color slurring correction efficiency while reducing
a deflection power supplied to a deflection circuit and enhancing focusing characteristics
of a displayed image, there has been developed a projection type cathode ray tube
adopting a different-diameter neck system having the constitution in which the
outer diameter of a neck portion at a position where a deflection yoke is mounted
is made smaller than the outer diameter of the neck portion at a position where
an electron gun is housed. BY mounting the above-mentioned convergence yoke for
performing the color slurring correction to the neck portion of this projection
type cathode ray tube adopting a different-diameter neck system where the outer
diameter dimension is relatively small (small neck-diameter portion), it is possible
to narrow the inner diameter of the convergence yoke per se and hence, it is possible
to enhance the color slurring correction sensitivity on the screen of the projection
type image display device.
Further, in improving the above-mentioned focusing characteristics, the
effect of the improvement can be enhanced by increasing the diameter of a main
lens of the electron gun. Accordingly, by mounting the main lens to the neck portion
having a relatively large outer diameter dimension (large neck-diameter portion),
the lens diameter can be increased and hence, an image quality on a screen of the
projection type image display device can be enhanced. Further, by mounting the
deflection yoke as close as possible to the electron gun, the deflection efficiency
is enhanced. That is, corresponding to the decrease of the outer diameter dimension
of the neck portion, the deflection power can be reduced. To be more specific,
the deflection power differs by approximately 25% between a case in which the deflection
yoke is mounted on the small-diameter neck portion and a case in which the deflection
yoke is mounted on the large-diameter neck portion. The projection type cathode
ray tube device adopting the different-diameter neck type projection type cathode
ray tube device which mounts the deflection yoke on the small neck-diameter portion
and inserts the electron gun in the large neck-diameter portion can exhibit the
approximately same image quality compared to the projection type cathode ray tube
device which is constituted of only the large neck diameter portion and, at the
same time, can suppress a deflection current.
In the projection type cathode ray tube device adopting the different-diameter
neck system, mounting of the convergence yoke to the large neck-diameter portion
and mounting of the deflection yoke to the small neck-diameter portion are indispensable
and hence, the enhancement of the correction sensitivity of color slurring has
been considered as a task to be achieved.
However, in the projection type cathode ray tube adopting the different-diameter
neck system, electron beams irradiated from the electron guns arranged in the large
neck-diameter portion strongly receive an influence of a deflection magnetic field
of the deflection yoke, thus generating the distortion of the shape of the electron
beams, that is, the so-called deflection distortion relatively in the peripheral
portion of a screen.
Accordingly, it is an object of the present invention to provide a projection
type cathode ray tube device adopting a different-diameter neck system which can
enhance a focusing function of display images and, at the same time, can enhance
the color slurring correction efficiency, and further can correct the deflection
distortion whereby the image quality in a peripheral portion of a screen can be enhanced.
A projection type cathode ray tube device according to the present invention
is
constituted such that first magnets having different polarities in the horizontal
direction are arranged at upper and lower sides of an opening portion of a deflection
yoke, and the first magnet which is arranged at the upper side of the opening of
the deflection yoke and the first magnet which is arranged at the lower side of
the opening of the deflection yoke have different polarities in the lateral direction.
Due to such a constitution, it is possible to correct a locus of an electron beam
which enters the inside of a deflection magnetic field and can correct the electron
beam distorted in the longitudinal direction to an electron beam shape which is
a substantially circular shape.
Another projection type cathode ray tube device according to the present
invention is constituted such that first magnets having different polarities in
the horizontal direction are arranged at upper and lower sides of an opening portion
of a deflection yoke, the first magnet which is arranged at the upper side of the
opening of the deflection yoke and the first magnet which is arranged at the lower
side of the opening of the deflection yoke have different polarities in the lateral
direction, and second magnets having different polarities in the tube axis direction
of a cathode ray tube are formed in the periphery of the opening portion of the
deflection yoke. Due to such a constitution, it is possible to correct an electron
beam which is distorted in the longitudinal direction to an approximately circular
shape and to correct an electron beam which is distorted in the radial direction
to an approximately circular shape.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial cross-sectional view showing the constitution of a projection
type cathode ray tube device according to the present invention.
FIG. 2A and FIG. 2B are constitutional view of a deflection yoke for explaining
one embodiment of the projection type cathode ray tube device according to the
present invention. FIG. 2A is a plan view of the device as viewed from the phosphor
screen side, and FIG. 2B is a side view the device.
FIG. 3A and FIG. 3B are an explanatory view of the constitution of a vertical
deflection coil incorporated into the deflection yoke.
FIG. 4A, FIG. 4B, FIG. 4C and FIG. 4D are schematic view for explaining the
change of a barrel magnetic field between coils of a pair of vertical deflection coils.
FIG. 5A and FIG. 5B is a schematic view showing a shape of an electron beam
on a screen affected by a deflection distortion generated by a horizontal deflection coil.
FIG. 6 is a schematic view for explaining a state in which a locus of the electron
beam is corrected by the deflection yoke.
FIG. 7 is a schematic view showing a shape of an electron beam on a screen due
to horizontal deflection yokes.
FIG. 8A and FIG. 8B are constitutional view of a deflection yoke of another
embodiment of the projection type cathode ray tube device according to the present invention.
FIG. 9 is a schematic view for explaining a state in which a locus of the electron
beam is corrected by the deflection yoke.
FIG. 10. is a schematic view showing a concept of a system of a projection type TV.
FIG. 11 is a schematic cross-sectional view of a back-surface projection type TV.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention are explained hereinafter
in conjunction with drawings which show the embodiments.
FIG. 1 is a partial cross-sectional view for explaining an embodiment of a projection
type cathode ray tube device according to the present invention. In FIG. 1, the
projection type cathode ray tube is constituted of a vacuum envelope in which a
panel
1 and one end of a neck
3 are connected by way of a funnel
2 and the other end of the neck
3 is sealed by a stem
5. On
the stem
5, a plurality of pins
51 which are served for supplying
voltages to respective electrodes of an electron gun
6 are mounted in an
erected manner. A base
4 is served for protecting the stem
5 and
the pins
51.
Further, in the projection type cathode ray tube, a monochromatic and approximately
rectangular-shaped phosphor screen is formed on an inner surface of an approximately
rectangular panel
1 and one electron beam is irradiated from the electron
gun
6. The electron beam receives a deflection action in the horizontal
direction as well as in the vertical direction due to a deflection yoke
7
and scans on the phosphor screen, so that the screen is emitted.
The panel
1 has an approximately flat outer surface and an inner surface
which is convexed toward the electron gun
6 side, thus forming a convex
lens. In this embodiment, the inner surface of the panel
1 is formed in
a spherical shape having a radius R of curvature of 350 mm. Further, to reduce
the aberration, the inner surface of the panel
1 may be formed in a non-spherical
shape. Further, a thickness To of the panel
1 at the center thereof is 14.1
mm. The profile size of the panel
1 in the diagonal direction is set to
7 inches and the size of the effective screen on which a phosphor screen is formed
in the diagonal direction is set to 5.5 inches. Further, a total length L
1
of the projection type cathode ray tube is set to 276 mm.
The neck
3 includes a small-diameter neck portion
31 which is connected
to a funnel
2, a large-diameter neck portion
32 which is sealed to
a stem
5 and a neck connecting portion
33 which connects the small-diameter
neck portion
31 with the large-diameter neck portion
32. On an outer
circumference of a transitional area between the small-diameter neck portion
31
and the funnel portion
2, a deflection yoke
7 is mounted. The outer
diameter of the small-diameter neck portion
31 is set to 29.1 mm. Further,
the electron gun
6 is housed inside the large-diameter neck portion
32.
The outer diameter of the large-diameter neck portion
32 is set to 36.5
mm and is formed to have a size larger than the small-diameter neck portion
31
by 7 mm. The projection type cathode ray tube of a type having the neck which differs
in outer diameter is referred to as "cathode ray tube of a different-diameter neck
system". Further, in addition to the above-mentioned specific sizes, dimensional
errors on manufacturing should be taken into consideration.
In this manner, a horizontal deflection coil
71 and a vertical deflection
coil
72 of the deflection yoke
7 which deflects the electron beam
are mounted on the small-diameter neck portion
31 having the small outer
diameter dimension. Accordingly, it is possible to suppress the deflection power.
In this case, the deflection power can be saved by approximately 25% compared to
a case in which the neck outer diameter dimension is 36.5 mm. Further, a main lens
forming electrode of the electron gun
6 which focuses the electron beam
is housed in the large-diameter neck portion
32 having the large outer diameter
and hence, it is possible to increase the diameter dimension of the electron lens.
Further, a first grid electrode (control electrode)
61 of the electron
gun
6 is formed in a cup shape and a cathode which emits electron beam is
housed inside the first grid electrode
61. Further, a second grid electrode
(acceleration electrode)
62 forms a prefocusing lens together with the first
grid electrode
61. Further, to a third grid electrode (first anode)
63,
an anode voltage of approximately 30 kV which is approximately equal to a voltage
applied to a fifth grid electrode (second anode)
65 which constitutes a
final electrode is applied. In general, the anode voltage of the projection type
cathode ray tube is approximately 25 kV or more.
When the beam deflection area and the beam focusing area have different neck
outer diameter respectively, the electron gun is arranged away from the phosphor
screen due to a mechanical restriction. When the electron gun is arranged away
from the phosphor screen, the focusing characteristics of the electron beam is
degraded. However, by elevating an anode voltage in the projection type cathode
ray tube, it is possible to easily cope with problems on deterioration of focusing.
It is possible to operate the projection type cathode ray tube with the maximum
anode voltage of approximately 30 kV or more in the projection type cathode ray.
Further, a fourth grid electrode (focusing electrode)
64 is divided
into a fourth-grid-electrode first member (focusing-electrode first member)
641
and a fourth-grid-electrode second member (focusing-electrode second member)
642.
A focusing voltage of approximately 8 kV is applied to both electrode members.
The focusing-electrode second member
642 has a diameter dimension thereof
increased at a phosphor screen and the phosphor screen side is inserted into the
inside of a second anode
65 to form a final-stage main lens having a large
diameter. Corresponding to the increase of the neck outer diameter, the main lens
exhibits the more effective improvement of focusing characteristics and can increase
a lens diameter. The center position of the final-stage main lens is defined by
a phosphor-screen-side distal end portion ML of the focusing-electrode second member
642 and a distance L
2 in the tube axis direction from the final-stage
lens position ML to the center of an inner surface of the panel
1 is set
to 139.7 mm.
Further, since the projection type cathode ray tube requires high brightness,
a beam current (cathode current) becomes approximately 4 mA or more. To maintain
the high focusing performance even under such a large current, it is extremely
important to maintain the diameter of the main lens as large as possible. Since
a voltage of the phosphor screen is high in the projection type cathode ray tube,
spreading of the beam due to a repulsion of space charge at the time of supplying
a large current becomes relatively small and the size of electron beam spots on
the phosphor screen at the time of supplying a large current is substantially determined
based on spreading of the beam due to the spherical aberration of the electron
gun. That is, in the projection type cathode ray tube, the influence caused by
increasing the lens diameter of the electron gun is larger than the influence caused
by shifting the electron gun away from the phosphor screen with the neck diameter different.
Further, a shield cup
66 is integrally formed with the second anode
65 so as to form the main lens. The phosphor-screen-side diameter of the
shield cup
66 is made gradually smaller. According to the decrease of the
outer diameter of the neck connecting portion
33 in the vicinity of the
distal end of the electron gun
6 is also made smaller, the diameter of the
vicinity of the distal end of the electron gun
6 is also made small so as
to prevent the electron gun
6 from being arranged far away from the phosphor screen.
In the projection type cathode ray tube adopting a single electron beam method,
in contrast to a shadow mask type color cathode ray tube adopting three electron
beam method in an in-line arrangement, it is unnecessary to take an impingement
of both-side electron beams on an inner wall of the neck into account. In the projection
type cathode ray tube adopting the different-diameter neck system according to
the present invention, to satisfy both of the reduction of the deflection power
and the enlargement of diameter of main lens which are in a trade-off relationship,
the neck diameter difference between the large-diameter neck portion
32
and the small-diameter neck portion
31 is made as large as possible. It
is effective to set the neck diameter difference to 5 mm or more.
On the other hand, the neck connecting portion
33 which connects the large-diameter
neck portion
32 and the small-diameter neck portion
31 defines a
region where the neck diameter is gradually changed along the tube axis direction.
Accordingly, when the neck diameter difference between the large-diameter neck
portion
32 and the small-diameter neck portion
31 becomes large,
a length of the neck connecting portion
33 in the tube axis direction is
also elongated. When the outer diameter dimension of the large-diameter neck portion
32 is 36.5 mm and the outer diameter dimension of the small-diameter neck
portion
31 is 29.1 mm as mentioned previously, the length of the neck connecting
portion
33 in the tube axis direction is 8 mm. This neck connecting portion
33 constitutes an extra space.
Further, on the projection type cathode ray tube, a convergence yoke
8,
a speed modulation coil
9 and centering magnets
10,
11 are
mounted on a region ranging from the deflection yoke
7 to the base
4.
The deflection yoke
7 includes horizontal deflection coils
71 which
make the electron beam scan in the horizontal direction, vertical deflection coils
72 which make the electron beam scan in the vertical direction, and a coil
separator
73 which holds the horizontal deflection coils
71 and the
vertical deflection coils
72 at separate positions. The base
4 side
of the deflection yoke
7 is mounted on the small-diameter neck portion
31
having the small outer diameter dimension.
Here, although the deflection yoke
7 is not illustrated in detail in
this embodiment, to be more specific, the deflection yoke
7 is configured
such that the horizontal deflection coils
71 are incorporated into the inside
of a coil support body, the vertical deflection coils
72 are incorporated
into the inside of a coil support body by way of the coil separator
73,
outer surface sides of the vertical deflection coils
72 are covered with
by a core made of a magnetic material to be held and fixed, and the deflection
yoke
7 is mounted on the small-diameter neck portion
31.
Further, the convergence yoke
8 includes a toroidal coil which generates
a convergence magnetic field. The convergence yoke
8 is also arranged to
stride over the large-diameter neck portion
32 having the large outer diameter
and the neck connecting portion
33 and is mounted on a convergence yoke
holder
81 mounted on the base-
4-side end portion of the coil separator
73 of the deflection yoke
7. The convergence yoke
8 is mounted
on the large-diameter neck portion
32 for preventing a case where when the
small-diameter neck portion
31 is extended toward the base
4, the
distance L
2 from the position ML of the final-stage main lens of the electron
gun to the center of the phosphor screen and the total length L
1 of the
projection type cathode ray tube are excessively elongated.
Further, a convergence yoke
8 has an inner surface thereof formed
in an approximately cylindrical surface and has a large inner diameter corresponding
to the large-diameter neck portion
32 along the whole tube axis direction.
This provision is made to allow mounting of the convergence yoke
8 from
the base
4 side. In spite of the fact that the inner diameter of the neck
connecting portion
33 of the convergence yoke
8 is equal to the diameter
of the large-diameter neck portion
32, a total length of the convergence
coil
8 is elongated using the neck connecting portion
33 which constitutes
the above-mentioned extra space and hence, it is possible to enhance the color
slurring correction sensitivity even when the convergence yoke
8 is not
mounted on the small-diameter neck portion
31.
It is also considered to elongate or extend the total length of the convergence
yoke
8 toward the base
4 to enhance the color slurring correction
sensitivity. However, since neck parts such as speed modulation coil
9,
centering magnets
10,
11 and the like are fixed closer to the base
4 than the convergence yoke
8 using a clamp
12 by way of neck
part holder
13, it is necessary to consider a provision which prevents the
convergence yoke
8 from interfering with these neck parts. Further, there
exists a possibility that the tube-axis-direction center position CY of the coil
of the convergence yoke
8 is shifted to the base
4 side from the
final-stage main lens position ML of the electron gun and effects the focusing
action applied to electron beams. Accordingly, it is preferable that the tube-axis-direction
center position CY of the convergence yoke
8 is arranged closer to the phosphor
screen than the final-stage main lens position ML.
The speed modulation coil
9 is used for enhancing the contrast of images.
Since the speed modulation coil
9 is mounted on the large-diameter neck
portion
32 having an outer diameter of 36.5 mm, the color slurring correction
sensitivity must be taken into consideration. To enhance the sensitivity of the
speed modulation coil
9, the focusing electrode
64 is divided into
the focusing-electrode first member
641 and the focusing-electrode second
member
642, and a gap is formed between the first member
641 and
the second member
642 so as to facilitate applying of a magnetic field of
the speed modulation coil
9 to the electron beam.
FIG. 2 is a constitutional view of a deflection yoke according to one embodiment
of the projection type cathode ray tube device of the present invention. FIG. 2A
is a plan view of the device as viewed from the phosphor screen side, and FIG.
2B is a side view the device. Parts identical with the parts shown in FIG. 1 are
given same numerals and their explanation is omitted. The deflection yoke is configured
such that horizontal deflection coils
71 are assembled into and is held
by and fixed to a coil support body
20 which is molded in an approximately
funnel shape using synthetic resin material having an insulation performance and
a supporting function, and vertical deflection coils
72 are assembled into
the inside of the coil support body
20 by way of a coil separator (not shown
in the drawing) which is integrally formed with the vertical deflection coil
72.
Outside surfaces of the vertical deflection coil
72 are covered with a core
21 made of a magnetic material. The deflection yoke is mounted on the small-diameter
neck portion
31 shown in FIG. 1 and is fixed by fastening using a band
22.
Further, on upper and lower portions of a funnel-side opening portion of
the horizontal deflection coils
71 of the coil support body
20, a
pair of first magnets
23,
24 which have magnetizing directions different
from each other in the horizontal direction (parallel to the X axis) are mounted.
These pair of first magnets
23,
24 are embedded into and are held
by and fixed to the upper and lower portions of the funnel-side opening inside
the coil support body
20 which supports the horizontal deflection coils
71. Further, each magnet arranges an N and S poles in the same direction
as the direction of the long sides of the panel (parallel to the X axis).
The projection type cathode ray tube adopting a different-diameter neck system
has the large neck diameter. Accordingly, when the deflection yoke
7 is
assembled prior to mounting thereof to the cathode ray tube, the deflection yoke
7 cannot be mounted from the base
4 side. Accordingly, the deflection
yoke
7 should not be mounted after assembling and adjustment and it is necessary
to directly mount the deflection yoke
7 to the projection type cathode ray
tube and to adjust the deflection yoke
7 thereafter.
Here, in the assembling operation, the horizontal deflection coils
71
are incorporated inside of the coil support body
20 and is held by a coil
separator not shown in the drawing and hence, irregularities of mounting attributed
to the displacement of mounting position which is liable to easily occur at the
time of incorporating the horizontal deflection coils
71 can be reduced.
However, the vertical deflection coils
72 are mounted on an outer
surface side of the coil separator to hold the insulation performance with respect
to the horizontal deflection coils
71. Accordingly, when the profile dimension
of the vertical deflection coils
72 is excessively large, it is impossible
to incorporate the core
21.
To facilitate such incorporating of the core
21, it is necessary to provide
a type of resilient structure in which the vertical deflection coils
72
which are formed in a pair are combined with each other using a proper force. To
absorb the dimensional error of the resilient structure, it is necessary to expand
the mating distance dimension between a pair of vertical deflection coils
72.
FIG. 3A and FIG. 3B are constitutional views of the vertical deflection coils
72 explained in conjunction with FIG. 2, wherein FIG. 3A is a plan view
as viewed from above and FIG. 3B is a plan view as viewed from a phosphor screen
side. A distance D between a pair of vertical deflection coils
72 is set
to 0.8 mm or less.
FIG. 4A, FIG. 4B, FIG. 4C and FIG. 4D are schematic views of a magnetic field
showing a state in which the magnetic field distribution is changed depending on
the distance D between a pair of vertical deflection coils
72. A pair of
vertical deflection coils
72 form a barrel magnetic field BA which is referred
to as a bulged barrel (barrel shape). When the profile dimension of the vertical
deflection coils
72 is smaller than the outer diameter dimension of the
coil separator, due to the necessity of widening the mating distance D between
a pair of vertical deflection coils
72, the mating distance D is increased
as shown in FIG. 4C thus giving rise to a gap.
Further, when a pair of vertical deflection coils
72 are arranged
close to each other (distance D being small), the magnetic field is bulged in a
barrel shape. When the distance D is large, the magnetic field bulged in a barrel
shape is distorted.
The vertical deflection magnetic field has a function of elongating or extending
the electron beam in the vertical direction.
FIG. 4A is a cross-sectional view of the vertical deflection coil having the
small distance D. FIG. 4B is a view showing the relationship between a magnetic
field BA
1 generated by the vertical deflection coils shown in FIG. 4A and
a passing position of the electron beam. A magnetic field of a region where the
electron beam which is deflected to a corner portion of the screen passes has a
strong degree of bulging. Accordingly, the electron beam B
1 which is deflected
to the corner portion of the screen receives a less force in the vertical direction
than the electron beam which is deflected on the Y axis in the screen.
FIG. 4C is a cross-sectional view of the vertical deflection coil having the
large distance D. FIG. 4D is a view showing the relationship between a magnetic
field BA
2 generated by the vertical deflection coil shown in FIG. 4C and
a passing position of the electron beam. When the distance D is large, a deflection
magnetic field enters the gap and hence, the deflection magnetic field is distorted.
In the vicinity of the Y axis where the distance D is large, the magnetic field
BA
2 exhibits the large degree of bulging and exhibits the small degree of
bulging at a position remote from the Y axis.
The degree of bulging of the magnetic field BA
2 in the vicinity of the
gap is strong and hence, the magnetic field is inclined. Accordingly, the electron
beam which passes the inclined magnetic field receives the weak force acting on
in the vertical direction. On the other hand, at the position remote from the Y
axis, the degree of bulging of the magnetic field BA
2 which is bulged in
a barrel shape is weak. Accordingly, with respect to the electron beam B
2
which is deflected to the corner portion of the screen, the force which the electron
beam B
2 receives in the vertical direction from the deflection magnetic
field is stronger than the force which the electron beam B
1 shown in FIG.
4B receives in the vertical direction from the deflection magnetic field. As a
result, the electron beam B
2 exhibits a distorted electron beam spot shape
on the screen.
FIG. 5A is a view showing the electron beam spot shapes on the screen. The magnetic
field distribution is adjusted such that, in a state where the left and right vertical
deflection coils
72 are brought into contact with each other, the spot shape
of the electron beam assumes a circular shape at respective portions of the screen
(a phosphor screen) G. Here, although some deformation of shape due to the geometric
dimensional difference between the electron gun and the screen G cannot be obviated,
it is preferable that the spot shape of the electron beam assumes a circular shape
substantially over the whole region of the screen G.
However, there may be a case where the distance D is increased at the time
of assembling the deflection yoke. FIG. 5B shows the spot shape of the electron
beam when the vertical deflection coils shown in FIG. 4B are used. Since the electron
beam B
2 receives a strong force in the vertical direction, the spot shape
of the electron beam on the screen G is distorted. In an actual operation, the
electron beam also receives a horizontal deflection component and hence, the spot
shape of the electron beam on the screen G assumes a shape which is extended in
the radial direction.
It is possible to change the spot shape of the electron beam on the screen G
by
changing the distance D between the vertical deflection coils. However, the screen
corner portions and the spot shape of the electron beam at the upper and lower
portions of the screen have the trade-off relationship. That is, when the distance
D between the vertical deflection coils is widened, the electron beam which is
deflected toward the corner portion of the screen receives a strong force by which
the electron beam is elongated in the vertical direction, while the electron beam
which is deflected to the upper and lower portions of the screen receives a weak
force by which the electron beam is elongated in the vertical direction.
On the other hand, when the distance D between the vertical deflection coils
is
narrowed, the electron beam which is deflected toward the corner portion of the
screen receives a weak force by which the electron beam is elongated in the vertical
direction, while the electron beam which is deflected to the upper and lower portions
of the screen receives a strong force by which the electron beam is elongated in
the vertical direction.
In this manner, the relationship between the upper and lower portions and the
corner portions on the screen G and the mating distance D of the vertical deflection
coils
72 has the trade-off relationship. To improve this relationship, the
upper and lower portions of the screen G correct the locus of the electron beam
which enters the inside of the deflection yoke
7 using a pair of magnets
23,
24, thus correcting the shape of the electron beam on the screen.
FIG. 6 is a schematic view for explaining the correction state of the locus
of the electron beam on the screen G due to the constitution in which a pair of
magnets
23,
24 which differ in magnetizing direction from each other
are arranged at the upper and lower portions of the opening portion of the deflection
yoke
7 explained in conjunction with FIG. 2. In FIG. 6, assuming the direction
of a current as I and the direction of magnetic field generated by a pair of magnets
23,
24 as H, the direction F to which the correction is applied acts
toward the center of the screen as indicated by a white-matted arrow based on the
Fleming's rule.
Due to this correction direction F, elliptical electron beams B which are generated
at upper and lower points of the screen G are corrected into the electron beam
B shape having an approximately circular shape as shown in FIG. 7. As a result,
it is possible to obtain the electron beam shape which is substantially equal to
an ideal electron beam shape when the electron beam receives no influence of deflection distortion.
Further, in addition to such a constitution, by setting the mating distance
D between a pair of above-mentioned vertical deflection coils
72 to 0.8
mm or less, it is possible to absorb the dimensional error at the time of assembling
the deflection yoke
7 and, at the same time, the assembling is facilitated.
Further, the locus of the electron beam can be corrected and the electron beam
shape can be corrected into an approximately circular shape so that the approximately
circular shape electron beam can be obtained In this manner, it is possible to
obtain both advantageous effects at the same time.
FIG. 8A and FIG. 8B are constitutional views of a deflection yoke for explaining
another embodiment of the projection type cathode ray tube device according to
the prevent invention. FIG. 8A is a plan view of the deflection yoke as viewed
from a phosphor screen side and FIG. 8B is a side view of the deflection yoke.
Parts identical with the parts shown in FIG. 2 are given the same symbols and their
explanation is omitted. A pair of first magnets
23,
24 are arranged
at upper and lower portions of a coil support body
20 which is formed in
a funnel shape. Two pairs of second magnets
25,
26,
27,
28
which differ from each other in magnetizing direction in the tube axis direction
(Z axis direction) are arranged between the pair of first magnets
23,
24
in the circumferential direction with a given interval. Mounting of these two pairs
of magnets
25,
26,
27,
28 is performed such that these
magnets are mounted, held and fixed at the opening portion side of the horizontal
deflection coils
71 inside the coil support body
20 and in the same
direction as the tube axis direction.
In this case, among these two pairs of magnets
25,
26,
27,
28, the first pair of magnets
25 and
26 are respectively arranged
with a distance of 25 degree±10 degree from Y axis direction to the circumferential
direction with respect to the magnet
23 arranged on the upper portion of
the opening of the deflection yoke
7. Further, the second pair of magnets
27 and
28 are also respectively arranged with a distance of 25 degree±10
degree from Y axis direction to the circumferential direction with respect to the
magnet
24.
FIG. 9 is a schematic view for explaining a correction state of an electron
beam locus on a screen G obtained by the following constitution. A pair of magnets
23,
24 are arranged at upper and lower portions of a coil support
body
20 at the opening portion of the deflection yoke
7. Two pairs
of magnets
25,
26,
27,
28 which differ from each other
in the magnetizing direction in the tube axis direction (Z axis direction) are
arranged with a given distance between the pair of magnets in the circumferential direction.
In FIG. 9, assuming the direction of a current which flows toward the deflection
center of the electron beam as I and the direction of magnetic fields generated
by a pair of magnets
26,
28 as M
1, M
2, the direction
F to which the correction is applied acts toward the X axis as indicated by a white-matted
arrow based on the Fleming's rule. Here, in FIG. 9, the action of the right-side
portion as viewed toward the screen G, that is, the action of a pair of magnets
26,
28 is only explained. However, with respect to the action of
a pair of magnets
25,
27 which are arranged in the direction symmetrical
with respect to the Y axis, although not shown in the drawing, such an action takes
the geometric symmetry with respect to the Y axis at the left-side portion of the
screen G and acts toward the X axis direction in the same manner.
Due to such a constitution, it is possible to correct not only the elliptical
electron beams B generated at the upper and lower points on the screen Gas shown
in FIG. 5B but also elliptical electron beams generated at respective right and
left points on the screen G into the approximately circular electron beam B shape
shown in FIG. 7. As a result, it is possible to obtain the electron beam shape
which is substantially equal to the shape of the ideal electron beam B when the
electron beam B is not affected by the deflection distortion as shown in FIG. 5A
over the entire region of the screen G.
Further, in such a constitution, the first pair of magnets
25 and
26 are arranged respectively at an interval within a range of 25 degree±10
degree from the Y axis foward the circumferential direction with respect to the
magnet
23 at the upper portion of the opening of the deflection yoke
7,
and the second pair of magnets
27 and
28 are also arranged respectively
at an interval within a range of 25 degree±10 degree from the Y axis toward
the circumferential direction with respect to the magnet
24. In this manner,
by mounting the respective magnets
25,
26,
27 and
28
suitably adjusting the arrangement position of respective magnets
25,
26,
27 and
28 within the above-mentioned range of ±10 degree, it
is possible to cope with not only a screen area of 4:3 which is usually used in
the projection type cathode ray tube device but also with a wide screen area of
16:9 and can obtain image qualities (focusing) substantially equal to those of
a large diameter lens without increasing the deflection power.
FIG. 10 is a schematic view showing a system concept of a projection TV receiver.
In the projection TV receiver, as shown in FIG. 10, images from three projection
type cathode ray tube devices consisting of a red projection type cathode ray tubes
device rPRT, a green projection type cathode ray tube device gPRT and a blue projection
type cathode ray tube device bPRT are converged on a screen SRN after passing through
respective lenses LNS so as to form a projected image. Although the rough adjustment
of the convergence is performed by inclining respective projection type cathode
ray tubes from each other, the fine adjustment is performed by the convergence
yokes
8 mounted on respective projection type cathode ray tubes.
FIG. 11 is a schematic cross-sectional view of a back-surface projection TV
receiver. The image projected from the projection type cathode ray tube PRT is
magnified by the lens LNS, is reflected on the mirror MR and is projected onto
the screen SRN. A convergence driving circuit CGC is connected to the convergence
yokes
8 mounted on the projection type cathode ray tubes PRT. By providing
a pair of magnets or by further providing at least another pair of magnets to the
deflection yoke
7 mounted on the projection type cathode ray tube of the
present invention, it is possible to project the image having favorable focusing
characteristics onto the screen SRN.
Further, since the projection TV receiver uses three projection type cathode
ray tubes, the projection TV receiver exhibits the deflection power saving effect
and the electron beam shape correction effect which is three times higher than
that of a usual TV receiver. Further, the projection TV receiver usually has a
large screen of which diagonal size is nominal 40 inches or more. In such a large
screen, scanning lines become apparent thus deteriorating the image quality when
usual NTSC signals are used. To prevent this phenomenon, in the projection TV receiver,
the ADVANCED TV method which has a large number of scanning lines is adopted in
many cases. In these cases, the number of scanning lines becomes two or three times
larger than that of the usual NTSC method so that the deflection power is increased.
Further, the color slurring correction of high accuracy is required. Accordingly,
with the use of the projection type cathode ray tube according to the present invention,
without increasing the deflection power in the projection TV receiver, it is possible
to obtain the great advantageous effect on the enhancement of the focusing characteristics
brought about by the electron beam shape correction effect.
Here, although the present invention has been explained with respect to a case
in which the present invention is applied to the projection type cathode ray tube
for different-diameter neck method projection as the projection type cathode ray
tube, the present invention is not limited to such a projection type cathode ray
tube and it is needless to say that the substantially same advantageous effects
can be obtained by applying the present invention to a general projection type
cathode ray tube which uses three projection type cathode ray tubes.
As has been described heretofore, according to the projection type cathode ray
tube of the present invention, by arranging a pair of magnets which differ in magnetizing
direction from each other in the longitudinal direction at the upper and lower
portions of the opening portion of the deflection yoke, the locus of the electron
beam which receives the deflection distortion can be corrected so as to correct
the electron beam shape on the upper and lower points on the screen into the substantially
circular shape whereby it is possible to obtain the extremely excellent advantageous
effect that the focusing performance on the screen can be largely enhanced and
hence, the display image which is close to normal video signals can be reproduced.
Further, according to another projection type cathode ray tube device of
the present invention, at least one pair of magnets which are magnetized in the
same direction as the tube axis direction are arranged in the circumferential direction
between a pair of magnets which are arranged at upper and lower portions of the
opening portion of the deflection yoke and differ in the magnetizing direction
from each other. Accordingly, the locus of the electron beam which receives the
deflection distortion can be corrected so as to correct the electron beam shape
over the whole region of the screen into the substantially circular shape whereby
it is possible to obtain the extremely excellent advantageous effect that the focusing
performance on the whole region of the screen can be largely enhanced and hence,
the display image which is close to normal video signals can be reproduced.
*
