Electric lamp and discharge devices – Cathode ray tube – Beam deflecting means
Reexamination Certificate
1999-07-20
2002-07-23
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Beam deflecting means
C313S442000, C348S806000
Reexamination Certificate
active
06424085
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a cathode ray tube comprising an electron gun for generating at least one electron beam, a display screen, and a deflection unit for deflecting the electron beam(s) across the display screen, the deflection unit including line and frame coils for deflecting the electron beam(s) in two mutually perpendicular directions, a coil holder and a yoke ring which surrounds at least one of the coils. The invention also relates to a deflection unit.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a cathode ray tube of the type mentioned in the opening paragraph in which one or more of the above-mentioned problems are reduced. To this end, the invention provides a cathode ray tube and a deflection unit as defined by the independent claims. Advantageous embodiments are defined by the dependent claims.
In operation, the fan blows air past the deflection unit, thereby cooling said deflection unit. The inventors have recognized that, in operation, the fan generates an electromagnetic field which may have a disturbing effect on the deflection field, as a result of which the image quality is adversely affected.
In order to preclude, or reduce, these adverse effects, a measure is taken in the cathode ray tube in accordance with the invention, or the deflection unit is provided with means to counteract the disturbing effect of the electromagnetic field generated by the fan on the deflection.
In an embodiment, the measure includes the magnetic field of the fan, close to the fan, being directed so as to be approximately parallel to the electron beams. This results in a small disturbing effect.
In an embodiment, the measure includes the yoke ring being arranged between the fan and the coils. The yoke ring shields the coils from the disturbing field of the fan.
In an embodiment, the measure comprises an air-permeable magnetically conducting filter arranged between the fan and the coils. By virtue thereof, the stray field of the fan is substantially reduced.
In an embodiment, the measure comprises means for generating an electromagnetic field which is in opposition to the field of the fan.
Said means may be an auxiliary coil arranged close to, or preferably around, the fan, which auxiliary coil is energized in operation in order to generate an electromagnetic field which is in phase opposition relative to the field generated by the fan. In a further embodiment, the deflection unit may be provided with two fans which are arranged close to each other and which generate electromagnetic fields which are in opposition.
The measures may be roughly divided into passive measures or means and active measures or means. Active measures or means are used to generate an opposite electromagnetic field to compensate for the field generated by the fan. Passive means reduce the field, for example by the position of the fan behind the yoke ring or the type of field generated (a lateral field) or by shielding.
The coil constitutes a means for generating a compensating field which is in opposition to the interference field generated by the fan. The deflection unit may also be provided with two fans generating opposite interference fields, so that the sum of both fields is substantially zero. This can be achieved, for example, by arranging two fans in diametrically opposite positions (for example on the left and on the right), and driving these fans in such a way that the currents are in phase opposition. As a result, the sum of the two fields between the two fans is zero. The fans may alternatively be positioned one above the other, or both on one side of the deflection unit.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
REFERENCES:
patent: 4709220 (1987-11-01), Sakane et al.
patent: 5204649 (1993-04-01), Togane et al.
patent: 5734234 (1998-03-01), Smith et al.
patent: 6031327 (2000-02-01), Lee
patent: 6087768 (2000-07-01), Beirens
patent: 62-181585 (1987-08-01), None
Beirens Leopold C. M.
Jansen Martinus H. E.
Vinkenvleugel Lucius T.
Guharay Karabi
Kraus Robert J.
Patel Nimeshkumar D.
U.S. Philips Corporation
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