U.S. patent number 3,887,833 [Application Number 05/040,827] was granted by the patent office on 1975-06-03 for color purity adjusting device for a color picture tube.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Eiichi Yamazaki.
United States Patent |
3,887,833 |
Yamazaki |
June 3, 1975 |
Color purity adjusting device for a color picture tube
Abstract
A color purity adjusting device for a color picture tube,
provided with one or more types of correcting coils which are wound
on the outer periphery of the color picture tube in order to
correct any mislanding of an electron beam due to deformation which
might take place during the manufacturing process of the color
picture tube, such as, a distortion of a shadow mask or of a glass
bulb and to correct any mislanding of the same due to the influence
of same external magnetic field such as the earth's magnetism,
thereby to obtain a picture of improved color purity.
Inventors: |
Yamazaki; Eiichi (Ichihara,
JA) |
Assignee: |
Hitachi, Ltd.
(JA)
|
Family
ID: |
12759365 |
Appl.
No.: |
05/040,827 |
Filed: |
May 27, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Jun 16, 1969 [JA] |
|
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44-46870 |
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Current U.S.
Class: |
315/368.27;
335/213; 315/8 |
Current CPC
Class: |
H01J
29/702 (20130101); H01J 29/003 (20130101); H01J
2229/5637 (20130101); H01J 2229/003 (20130101); H01J
2229/0053 (20130101) |
Current International
Class: |
H01J
29/00 (20060101); H01J 29/70 (20060101); H01j
029/70 () |
Field of
Search: |
;315/31TV,27XY,13C
;335/210-213 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wilbur; Maynard R.
Assistant Examiner: Potenza; J. M.
Attorney, Agent or Firm: Craig & Antonelli
Claims
I claim:
1. A color purity adjusting device for a color picture tube having
a phosphor screen, comprising a first coil formed of component
magnetic coils connected to form magnetic poles in the vicinity of
the four corners of the phosphor screen of said color picture tube
to provide a quadripole magnetic pole arrangement, each of said
component magnetic coils being disposed to produce a magnetic field
in a plane perpendicular to the axis of said color picture
tube.
2. A color purity adjusting device for a color picture tube
according to claim 1, further comprising a second coil which is
disposed on the neck portion of said color picture tube and which
produces a magnetic field for correction of magnetic field effects
in a horizontal direction perpendicular to the axis of said color
picture tube.
3. A color purity adjusting device for a color picture tube,
comprising a first coil formed of component magnetic elements
connected to form magnetic poles in the vicinity of the four
corners of the phosphor screen of said color picture tube to
provide a quadripole magnetic pole arrangement, each of said
component magnetic elements being disposed to produce a magnetic
field in a plane perpendicular to the axis of said color picture
tube, and a second coil which is constituted by winding a
conductive wire on the outer periphery of said color picture tube
adjacent said first coil.
4. A color purity adjusting device for a color picture tube
according to claim 3, further comprising a third coil which is
disposed on the neck portion of said color picture tube and which
produces a magnetic field for correction of magnetic field effects
in a horizontal direction perpendicular to the axis of said color
picture tube.
5. A color purity adjusting device for a color picture tube
according to claim 4, further comprising a potentiometer connected
to said second and said third coils, and a single knob joined to
sliding terminals of said potentiometer for adjustment of currents
caused to flow through said second and said third coils.
6. A color purity adjusting device for a color picture tube,
comprising a first coil which is disposed on the neck portion of
said color picture tube and which produces a magnetic field for
compensation of magnetic field effects in a direction perpendicular
to the axis of said color picture tube, and a second coil which is
constituted by winding a conductive wire on the outer periphery of
said color picture tube substantially in the plane of the phosphor
screen and which produces a magnetic field for compensation of
magnetic field effects along the direction of the axis of said
color picture tube.
7. A color purity adjusting device for a color picture tube
according to claim 6, further comprising a potentiometer connected
to said first and said second coils, and a single knob joined to
sliding terminals of said potentiometer and for adjustment of
currents caused to flow through said first and second coils.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a color purity adjusting device for use
in a color picture tube.
Deterioration in color purity occurs due to the so-called
"mislanding" which in turn appears because an electron beam
produced by an electron gun is not correctly projected onto each
color phosphor dot, and the invention is concerned with a color
purity adjusting device for a color picture tube, for removal of
the particular mislanding of an electron beam because the shadow
mask has been subjected to distortion during the manufacturing
process of the color picture tube. The device of the invention
further removes a mislanding due to an external magnetic field such
as the earth's magnetism, thereby making a satisfactory adjustment
of the color purity in the color picture tube.
2. Description of the Prior Art
As is well known, a color picture tube is subjected to a
temperature of about 400.degree.C or so during the manufacturing
process thereof, e.g., in the baking or evacuation step.
Consequently, the glass bulb or shadow mask may become thermally
distorted, and an electron beam passing through the shadow mask is
prevented from being correctly bombarding the phosphor dot or the
so-called mislanding takes place with the result that the color
purity is deteriorated.
In order to prevent such mislanding due to thermal deformation of
the bulb or mask, it is sufficient to lower the temperature in the
baking, exhausting or the like step to avoid the thermal distortion
of the glass bulb or the shadow mask. On the other hand, however,
this is disadvantageous in that degassing from the interior of the
tube will become insufficient and thereby undesirably shorten the
life of the picture tube. Therefore, prevention of thermal
distortion is extremely difficult under the present
circumstances.
Accordingly, corrections have been made, for example, in such a
manner that an additional means as will be described later, the
so-called guard ring for example, with which an aperture in the
shadow mask is made smaller than the size of a phosphor dot, to
prevent the beam from missing the phosphor dot or from bombarding a
phosphor dot of a different color, even if occurance of some
mislanding due to thermal distortion be seen, and/or that a purity
adjusting device consisting of a coil which is wound around a
phosphor screen, is used to produce a magnetic flux in the
direction of the tube axis, thereby to correct a rotational
deviation (as will be described later). However, the former measure
or that one in which the mask aperture is made smaller in diameter
than the beam has had a drawback in that the reduction in size of
the aperture of the shadow mask will naturally result in lowering
the brightness of the phosphor screen by that amount, while the
latter measure or with a purity adjusting device consisting of a
coil winding has permitted correction to be carried out to some
extent for the rotational deviation, but it has exhibited a
drawback in that it has no effect on other deviations such as a
radial one (as will be described later) thus allowing for no
satisfactory corrections to be expected.
Furthermore, in a color TV receiver using such a color picture tube
taking advantage of parallax as the shadow mask type color picture
tube, there is noted a phenomenon in which the color purity of a
picture deteriorates under the influence of the earth's magnetism.
More specifically, when the installed direction of the receiver is
changed, the angle at which the horizontal component of the earth's
magnetism crosses the receiver will vary so that the passage of an
electron beam will change, thus resulting in an incorrect landing
of the beam onto the phosphor dot, consequently bringing about a
deterioration in the color purity.
In order to obviate such a defect, although a magnetic shield has
heretofore been installed in a color picture tube and means in
which a degaussing coil is added thereto has been widely employed,
these are not complete either and merely reduce the influence of
the external magnetic field to one-second that when no such
magnetic shield is used. Accordingly, the so-called guard ring is
provided by means of which the diameter of a beam (the diameter of
a mask aperture) is made smaller relative to the diameter of a
phosphor dot of a color picture tube so that even when some landing
errors exist, the beam may be prevented from coming out of line
with the phosphor dot or from striking a dot of a different color.
With such a measure, however, it is inevitable that the brightness
of a picture will be lowered by that amount corresponding to the
reduction of the diameter of the mask aperture.
In addition, any prior art adjusting devices as suggested have been
impractical in that they are complicated in handling and that they
have a number of portions requiring adjustment.
SUMMARY OF THE INVENTION:
It is accordingly an object of the invention to provide a color
purity adjusting device for a color picture tube, which is free
from the above-mentioned defects.
Another object of the invention is to provide a color purity
adjusting device to compensate for any deterioration in the color
purity due to mislanding caused by a distortion of a shadow mask of
a color picture tube.
Still another object of the invention is to provide a color purity
adjusting device for compensation of deterioration in the color
purity due to mislanding caused by the adverse influence of an
external magnetic field such as the earth's magnetism.
According to the present invention, a variety of color purity
adjusting devices for a color picture tube may be obtained by
combining, dependent upon the result of manufacture of the
individual color picture tubes or upon the type thereof the
presence or absence of the aforementioned magnetic shield, a first
coil which is connected so as to form magnetic poles in the
vicinity of the four corners of a phosphor screen of a color
picture tube thus forming quadripole magnetic poles in all, a
second coil which is constituted by winding a conductive wire on
the outer periphery of the color picture tube and which produces a
magnetic field in the direction of the tube axis, and a third coil
which is wound on the outer periphery of the color picture tube and
which produces a magnetic field for correcting the magnetic field
on a horizontal plane at right angles to the axis of the tube.
Then, mislandings as mentioned may be prevented through the
adjustment of the currents flowing through the respective coils,
whereby a picture of improved color purity may be obtained.
Furthermore, according to the present invention, a particular color
purity adjusting device may be obtained which, in a color purity
adjusting device including the above-mentioned second and third
coils, is provided with a potentiometer connected to these second
and third coils and with a single knob joined to sliding terminals
of the potentiometer and adjusting currents flowing through the
second and third coils, whereby there may be made easier the
adjustment for correcting mislanding which occurs dependent upon
the installed direction of a color TV receiver and thereby
preventing the color purity from being lowered.
BRIEF DESCRIPTION OF THE DRAWINGS:
FIGS. 1 and 2 are diagrammatic views showing the thermal distortion
of a shadow mask;
FIG. 3 is a diagrammatic view showing a deviation of landing due to
torsion of the shadow mask;
FIG. 4 is a schematic front view showing a color purity adjusting
device for a color picture tube, embodying the present
invention;
FIG. 5 is a view showing an example of an adjusting coil for
correction of a rotational deviation of landing, which coil is used
in the purity adjusting device of the invention;
FIG. 6 is a view showing an example of an adjusting coil for
correction of a deviation due to torsion of the mask, which coil is
likewise used in the purity adjusting device of the invention;
FIG. 7 is a schematic front view showing an embodiment of the
purity adjusting device in a color TV receiver, of the
invention;
FIG. 8 is a diagram of electrical connection in the purity
adjusting device shown in FIG. 7; and
FIG. 9 is a similar view to FIG. 7, showing another embodiment of
the purity adjusting device of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
A color picture tube is subjected to a temperature of about
400.degree.C or so during the manufacturing process, i.e., either
in the baking or evacuation step. Therefore a glass bulb or a
shadow mask undergoes thermal deformation, with the result that the
phenomenon of so-called "mislanding" is observed in which an
electron beam having passed through the shadow mask does not strike
the desired phosphor dot. This phenomenon will now be described
with reference to the drawings. The above-mentioned thermal
deformations of the glass bulb and the shadow mask are extremely
irregular, but they may, when broadly classified, be practically
represented by a rotation of a shadow mask 1 into the directions
shown by arrows 2, 21, 22 and 23 as illustrated in FIG. 1, and by a
torsion of the shadow mask 1 into the directions shown by the
arrows 3, 31, 32 and 33 as illustrated in FIG. 2. The rotation
actually appears in the form of movements of pins for holding the
mask which are embedded in the side wall of a glass bulb (not
shown). The landing deviations accompanied by the deformations or
distortions may be a rotational deviation in the same directions as
those of the arrows 2, 21, 22 and 23 (hereinbelow termed the
"rotational deviation") as shown in FIG. 1 and/or a deviation in
the directions represented by arrows 5, 51, 52 and 53 on a phosphor
screen 4 (hereinafter termed the "radial deviation") as shown in
FIG. 3 (due to the torsion as shown in FIG. 2).
FIG. 4 is a view showing an embodiment of a purity adjusting device
of the invention, with those other than the essential parts
omitted. In FIG. 4, numeral 6 designates a color picture tube, and
numeral 7 an adjusting coil which is wound around and disposed on a
phosphor screen 61. The adjusting coil 7 has an example of the
structure thereof illustrated in FIG. 5, and through such an
adjusting coil 7 is caused to flow D.C. current thus providing a
magnetic flux in the direction of the axis of the tube to adjust
the rotational deviation. The adjusting coil 7 may, of course,
effectively also correct any rotational deviation which occurs when
the tube axis (not shown) of the color picture tube 6 is directed
to the north or south. Numeral 8 represents an adjusting coil which
is disposed so as to provide quadripole magnetic poles on the
periphery of the phosphor screen. The adjusting coil 8 has an
example of the structure thereof depicted in FIG. 6, and by
adjusting the polarity and strength of current of the coil 8 in a
similar manner to the adjusting coil 7 for adjustment of the
rotational deviation, it is imparted with a polarity, e.g., as
shown by the dotted lines in FIG. 6 whereby it makes adjustments to
such radial deviation as shown in FIG. 3. In this case, the
provision of four component coils 81 - 84 in the four corners of
the adjusting coil 8 and connected in series as shown in FIG. 6 to
adjust currents flowing through such coils by means of only one
adjusting knob is usually sufficient to achieve the object of the
invention. In addition, adjustment is easier by using this coil
than with the two former measures. Furthermore, the adjusting coil
8 may be formed integrally with, but electrically independent of
the aforementioned adjusting coil 7.
In operation, when first the color picture tube starts, there will
appear on the phosphor screen simultaneously both or either one of
the rotational deviation and the radial one as shown in FIG. 3,
with the result that the color purity will be lowered. These
deviations will sometimes occur simultaneously and sometimes
separately, and in any cases, the corresponding adjusting coil or
coils are respectively selected dependent upon the conditions and
types of the deviations produced. More specifically, in case both
the deviations appear simultaneously, the adjusting coils 7 and 8
are selected, and in case either one appears, the adjusting coil 7
is chosen for the rotational deviation while the adjusting coil 8
for the radial deviation as shown in FIG. 3. Then, the selected
coil or coils have currents caused to flow therethrough and the
polarity as well as the strength of the currents are adjusted,
whereby the deviations are corrected to prevent the color purity
from being deteriorated.
In the embodiment thus far described, where it is apparent in the
manufacturing process of the color picture tube, especially at the
stage when all the heat-treatment steps have been completed, such
as at the inspection step, that only one of the above described
rotational and radial deviations appears or would possibly occur or
that even when both deviations are produced, either one will be
very small and negligible, then omission of either one of the
adjusting coils 7 and 8 will cause no inconvenience.
As described above, the purity adjusting device of this embodiment
is provided with two coils, one of which forms quadripole magnetic
poles on the periphery of the color picture tube in order to
correct the radial deviation, and the other of which comprises a
conductive wire wound around and disposed on the outer periphery of
the color picture tube and produces a magnetic field along the axis
of the tube in order to correct for rotational deviation.
Accordingly, the adjustment of currents will enable the greater
part of mislanding due to thermal deformation of the color picture
tube to be corrected, and hence a bright color picture of good
purity is obtainable without the need for disposing an
unnecessarily large guard ring as in the prior art.
FIG. 7 shows another embodiment of the invention or a purity
adjusting device for correcting the lowering of the color purity,
especially due to an external magnetic field such as the earth's
magnetism. The figure illustrates the device when assembled into a
color TV receiver, and those other than the essential parts are
omitted therefrom.
Referring to FIG. 7, numeral 9 designates a color picture tube,
numeral 10 a chassis, numeral 11 a cabinet, and numeral 12 a
correcting coil for correction of an external magnetic field along
the tube axis (not shown) of the color picture tube 9. The
correcting coil 12 is wound and disposed in the vicinity of the
periphery 92 of an image screen 91 of the color picture tube 9 so
that a magnetic flux may be produced along the axis of the tube 9.
Numeral 13 designates a correcting coil for correction of an
external magnetic field being in the horizontal direction and at
right angles to the tube axis, and the correcting coil 13 is
disposed at a necked portion 93 of the color picture tube 9 so that
a magnetic flux may be produced in the horizontal direction and at
right angles to the tube's axis. At 14 is shown a potentiometer, an
example of which is illustrated in FIG. 8. More particularly, the
potentiometer 14 in FIG. 8 is a ring-shaped one, and includes
terminals 15 - 18 at intervals of 90.degree. and two sliding
terminals 19 and 20 which are interlocked and rotated, while
maintaining an interval of 180.degree. to each other. To the
sliding terminals 19 and 20 is joined a knob 24, and they are
adapted to be simultaneously slid by moving the knob 24. Numerals
25 and 26 represent semi-fixed resistors, which adjust currents
flowing through the correcting coils 12 and 13 respectively,
thereby making appropriate corrections.
Now description will be made of the operation of this embodiment.
Firstly, the polarity of the correcting coil 12 is previously
connected so that it will make corrections for a TV receiver facing
north when the sliding terminal 19 is set into the direction of the
terminal 15 (i.e., the other sliding terminal 20 is set at the
terminal 17), while the polarity of the correcting coil 13 is
connected so that it will provide corrections for a TV receiver
facing east when the sliding terminal 19 is set in the direction of
the terminal 16 (i.e., the other sliding terminal 20 is set at the
terminal 18). In case the color TV receiver having been adjusted to
be normal under such conditions is changed in direction, it will be
lowered in color purity under the influence of an external magnetic
field. In order to counteract this lowering, first the knob 24 is
turned to move the sliding terminals 19 and 20. The slide of the
sliding terminals 19 and 20 will cause current to flow through the
correcting coil 12 and/or the correcting coil 13 thereby to produce
a magnetic flux to cancel the external magnetic field, with the
result that the influence of the external magnetic field is removed
whereby the TV receiver is reset to the normal state with no
lowering in color purity. In this case, it is also possible that
whenever the knob is faced to the north (This is a mere instance,
and any one direction of the east, south, west, north and any
intermediate ones therebetween, etc. may be previously determined.)
irrespective of the installed direction of the receiving set, a
suitable correction may be made. With such a setting, the
adjustment may be very easily performed. In addition, it is more
convenient to previously assemble a magnet into the receiver set in
order to know directions. Yet in addition, although not shown, the
correcting coils may of course be provided with means with which
D.C. bias currents are caused to flow as may be needed, whereby
stationary corrections are made, and therefor any inherent faults
in a cathode ray tube used due to distortion having been brought
about during the manufacturing process, are corrected. Of course,
it presents no problem to jointly use these correcting coils with a
coil employed for the usual degaussing coil.
As described above, the purity adjusting device according to this
embodiment comprises a skillful combination of correcting coils and
a potentiometer. Accordingly, the correction in case of installing
the TV receiver into an optional direction and for the influence of
an external magnetic field may be easily performed by causing the
single knob which is joined to the sliding terminals of the
potentiometer, to face any one of the north, south, east and west
as set on a dial, in accordance with the installed direction of the
TV receiver. Therefore no lowering in the color purity occurs, and
it is not required as in the embodiment described with reference to
FIGS. 4 to 6, to make the guard ring for the phosphor dots
unnecessarily large. As result, a bright color picture is
obtainable.
This embodiment may, of course, be jointly used with a magnetic
shield which has hitherto been employed. In this case, when the
shielding effect is particularly effective either in the direction
of the tube's axis or in the direction at right angles therewith,
then either one of the correcting coils may be omitted.
Although in the above description only one potentiometer was
included, the combined use of two or more will also be able to
provide the same effect.
In addition, although in this embodiment no reference was made to
the correction of an external magnetic field in the vertical
direction, the magnetic field in the vertical direction is always
constant irrespective of the installed direction of the TV
receiver, and hence this correction may be sufficiently attained
with the usual purity magnet.
Although, in the foregoing, description was separately made of the
first embodiment with reference to FIGS. 4 to 6 and the second
embodiment with reference to FIGS. 7 and 8, these are not
necessarily used individually but may also be combined to provide a
purity adjusting device which is expanded in function. More
specifically, the adjusting coil 7 in FIG. 4 and the correcting
coil 12 in FIG. 7 may be joined to constitute a correcting coil 28
as shown in FIG. 9. In this case, as previously described, a D.C.
current is caused to flow through the correcting coil 28 for
correction of mislanding due to inherent faults of a cathode-ray
tube as caused by a deformation having appeared during the
manufacturing process thereof, in addition to a current producing a
magnetic field for correction of an external magnetic field along
the axis of the tube. This latter current, however, is also a D.C.
current, and hence supplying the D.C. bias current is actually for
varying the magnitude of the D.C. current value of the correcting
coil 28 in accordance with the addition of difference between the
current values required for the corrections of mislanding due to
the external magnetic field and that due to the deformation. These
variations may, therefore be easily carried out, such as by
previously changing the positions of the terminals 15 - 18 in FIG.
8 according to the correction of mislanding caused by a
deformation.
* * * * *