Magnetic shield for video monitor yokes

• US 5,319,332 A
• Filed: 11/12/1991
• Issued: 06/07/1994
• Est. Priority Date: 11/12/1991
• Status: Expired due to Fees

• Current Assignee: LPI Acquisition Co.
• Original Assignee: Computron Display Systems
• Inventors: Espinosa, Israel
• Primary Examiner(s): Broome, Harold
• Application Number:
  US07/791,578
• Time in Patent Office: 938 Days
• Field of Search: 335/214, 335/212, 315/8, 315/85
• US Class Current: 335/214
• CPC Class Codes: H01J 2229/0023 Passive means
• CPC Class Codes: H01J 29/003 Arrangements for eliminating unwanted electromagnetic effects, e.g. demagnetisation arrangements, shielding coils H01J29/06, H01J29/867 take precedence; demagnetisation in general H01F13/00; circuit arrangements therefor H04N9/29; screening of apparatus against electric or magnetic fields H05K9/00
• CPC Class Codes: H01J 29/06 Screens for shielding; Masks interposed in the electron stream
• CPC Class Codes: H01J 29/701 Systems for correcting deviation or convergence of a plurality of beams by means of magnetic fields at least

Abstract

A yoke for a cathode ray tube has deflection coils and a plurality of trim magnets mounted thereon. A tubular shield of Mu-metal slides over the coil to suppress an electromagnetic field radiated therefrom. In one embodiment, the trim magnets are inside the shield so that it has to be removed in order to adjust the magnets. In another embodiment, the trim magnets are outside the shield, so that they may be adjusted without necessarily having to remove the shield. The shield greatly reduces outwardly directed electromagnetic radiation in the vicinity of the cathode ray tube which allegedly might produce a health hazard to an operator at a video monitor terminal.

Claims

1. An electromagnetic field control device for cathode ray tubes, said device comprising yoke means having at least a deflection coil, means for positioning said yoke means on a cathode ray tube envelope at a position determined by an effect of said deflection coil upon an electron beam within said cathode ray tube, a plurality of permanent magnets adjustably mounted on said yoke to cooperate with said effect produced upon said electron beam by said deflection coil, said permanent magnets having a keying means for enabling a manual movement of said magnets in order to adjust a display on said cathode ray tube, and removable magnetic shield means surrounding said deflection coil for reducing stray electromagnetic fields extending from said coil outwardly and beyond said shield without adversely affecting said electromagnetic field acting inwardly through said envelope forming said cathode ray tube and upon said electron beam, said keying means being accessible to enable said movement of said magnet while said shield remains in place surrounding said deflection coil.

2. The device of claim 1 wherein each of said plurality of permanent magnets is a shape which may rotate about an axis of rotation, and means for rotatably mounting said magnets on said yokes.

3. The device of claim 2, where the shape of said permanent magnet is cylindrical.

4. The device of claim 2 wherein each of said shaped permanent magnets has said keying means associated therewith for enabling a suitable tool to rotate the permanent magnet.

5. The device of claim 2 wherein said yoke has a plurality of clips adjacent a periphery thereof, each of said shaped magnets being rotatably supported in an individually associated one of said clips.

6. The device of any one of the claims 2-5, wherein said shield means is a tubular member made of Mu-metal which fits over at least said deflection coil and which is long enough to suppress said outwardly radiated electromagnetic field.

7. An electromagnetic field control device for cathode ray tubes, said device comprising yoke means having at least a deflection coil, means for positioning said yoke means on a cathode ray tube envelope at a position determined by an effect of said deflection coil upon an electron beam within said cathode ray tube, a plurality of permanent magnets adjustably mounted on said yoke to cooperate with said effect produced upon said electron beam by said deflection coil, said yoke means including a plurality of spoke-like posts radiating from said yoke, each of said permanent magnets being mounted to rotate about an individually associated one of said posts in order to make a geometric adjustment of said electron beam, and removable magnetic shield means surrounding said deflection coil for reducing stray electromagnetic fields extending from said coil outwardly and beyond said shield without adversely affecting said electromagnetic field acting inwardly through said envelope forming said cathode ray tube and upon said electron beam.

8. The device of claim 7 wherein each of said permanent magnets is a square plate having a mounting means in the middle of the square for movably engaging an individually associated one of said posts.

9. The device of any one of the claims 7 or 8, wherein said shield means is a tubular member made of Mu-metal which fits over at least said deflection coil and which is long enough to suppress said outwardly radiated electromagnetic field.

10. The device of claim 8, wherein said tubular shield member surrounds both said permanent magnets and said deflection coil.

11. The device of claim 8 wherein said tubular shield member surrounds said coil with said permanent magnets outside of said tubular member.

12. The device of claim 8, wherein said tubular shield member has a notch in one end for enabling wires to pass between said shield and a bell on the envelope of said cathode ray tube.

13. The device of claim 8, wherein said tubular shield member surrounds both said deflection coil and said permanent magnets.

14. An electromagnetic shielding device for a video display monitor, said monitor including a cathode ray tube mounted within a restricted area which makes it difficult to work on or near said tube and within said area, a yoke having a deflection coil and at least one trim magnet mounted on a neck of said tube, a shield made of magnetic material slidably positioned over and surrounding at least said deflection coil for suppressing at least some electromagnetic effects generated by said deflection coil in order to reduce an electromagnetic field in the vicinity of said monitor, keying means for adjusting said trim magnet without necessarily having to remove said shield, said keyed means being a hole formed in an end of the magnet, said trim magnet being a magnet which is mounted for axial rotation, and means associated with said magnet for rotating it in response to a manipulation of a tool which may reach said hole formed in said magnet from outside said area and into said restricted area.

15. The device of claim 14, wherein said shield is a cylinder having a radius which enables it to fit over and contain said deflection coils while said magnets remain outside said shield and exposed to be positionally adjusted without necessarily having to remove said shield.

16. The device of claim 15 where said shield is made of Mu-metal.