Method and device for suppression of leakage of magnetic flux in display apparatus

Abstract: A device for suppression of leakage of the magnetic flux in a cathode ray tube display apparatus which comprises at least a cathode ray tube having a face plate and horizontal beam deflection circuit generating the leakage, the deflection circuit comprising a pair of upper and lower coils each of which has a bend-up section producing a first magnetic field which deflects an electron beam of the cathode ray tube, and a second magnetic field produced as the leakage the first and second magnetic field forming a boundary plane therebetween, so that two boundary planes are formed of said upper and lowser deflection coils, respectively, said device comprising; a pair of conductors each of which has a main portion and a lead portion connected to the main portion, said main portion of the pair of conductors being disposed approximately within said boundary plane and along approximately top and bottom rims of the face plate, respectively, said lead portion of the pair of conductors disposed along a side wall of a funnel of the cathode ray tube in such a form that one end of the lead portion is bent along a side rim of the face plate to couple with said main portion and another end of the lead portion extends toward a rear of the horizontal beam deflector, the pair of conductors being driven with a current proportional to a horizontal deflection current flowing through the horizontal beam deflectors.

Description: This invention relates to a method and a device for suppression of leakage of magnetic flux in a cathode ray tube display apparatus, which is adapted to suppress leakage magnetic flux generated from the deflection yoke. There are many display apparatuses of the type utilizing a magnetic field generated from the deflection coil, etc. as the method of deflecting an electron beam. For this reason, in display apparatus of this kind, magnetic flux from the deflection coil, etc. leaks out beyond the cathode ray tube itself. Such an unnecessary electromagnetic ray may exert a bad or adverse influence on the operation of electronic equipment in the vicinity thereof. Recently, studies on the influence exerted on the human being and animals of the magnetic field have been conducted. For example, a magnetic field from the cathode ray tube is considered to be also harmful. In view of this, the research institution of SSI (Statens Stralskydds Institut) in Sweden has announced, with regard to the super low frequency magnetic field, recommended values of the change rate, i.e., time-derivative (dB/dt) of a magnetic flux density at 80 positions on a spherical body having a radius of 65 cm centred on a point within 15 cm of the centre of the display surface of the cathode ray tube and the strength of a magnetic flux density at these positions, in the frequency band of 10 to 300 KHz. The change rate of the maximum magnetic field is recommended to be lower than 25 mT/sec (mili tesla per second), and the strength of the maximum magnetic flux density is recommended to be lower than 50 nT (nano tesla). In the above description, T represents Tesla which is the unit of the strength of a magnetic field, and 1 T = 10000 Gauss and 1 mT = 10 Gauss. To ensure that the change rate of a maximum magnetic field in all relevant positions with respect to the display apparatus satisfies the requirement to be lower than 25 mT/sec, it is proposed by display manufacturers and sellers (e.g., IBM, etc.) that the change rate of the maximum magnetic field should be lower than 15mT/sec as the standard requirement in the state of the cathode ray tube to which the deflection yoke is attached. i.e., the cathode ray tube display apparatus in what is called an ITC (Integrated Tube Component). Technologies for suppression of leakage magnetic flux from the deflection yoke on the display surface of the cathode ray tube have been proposed and there are two such prior arts described below. The first prior art is the technology shown in Figs. 1A to 1C. This has been already filed at the Japanese Patent Office by N.V. Philips Gloellampenfabrieken (Japanese Patent Application Laid Open no. 223952/1987). Namely, Figs. 1A to 1C show examples where an electric wire 1 is electrically coupled to the deflection unit and the electric wire 1 is disposed on a face-plate 2. In these figures, reference numerals 3a and 3b represent ordinary connection terminals of the deflection unit. In the case of the example of Fig. 1A (system I), the electric wire 1 is connected in series with deflection coils 4a and 4b, and two horizontal sections 1a and 1b of the electric wire are directly attached to the upper and lower side edge portions of the face-plate 2, or are attached in a manner that they are extremely close thereto. In the case of the example of Fig. 1B (system II), for compensating for stray magnetic flux of individual deflection coils, deflection coil 4a is coupled in series with the upper side electric wire horizontal section la and deflection coil 4b is coupled in series with the lower side electric wire horizontal section 1b. In the case of the example of Fig. 1C (system III), a control current source 5 is disposed between the deflection coils 4a and 4b and the electric wire sections 1a and 1b. In this case, the electric wire sections are wound a plurality of times, i.e., as a plurality of loops at the upper and lower side edge portions of the face-plate 2. The second prior art has been proposed by the same assignee as one of this invention. (Japanese Patent Application No. 156411/1987, EP-A-0348205, published after the priority date of the present patent). Namely, the example shown in Fig. 2 (system IV) is as follows. In this figure, reference numeral 6 represents a cathode ray tube, reference numeral 7 a deflection coil, and reference numerals 8a and 8b electric wires for producing cancellation magnetic flux, respectively. The electric wires 8a and 8b are positioned around the upper and lower halves of the display surface 10, respectively. A horizontal deflection current is delivered in a direction indicated by an arrow in the figure. The deflection coil 7 is provided in the vicinity of an electron gun 9 so that it deflects an electron beam. A horizontal deflection current is delivered from the deflection circuit to the deflection coil 7. At the same time as a signal from the deflection circuit is delivered to the deflection coil 7, this signal is also delivered to the electric wires 8a and 8b, and varies in synchronism with the signal flowing in the deflection coil 7. The leakage magnetic flux was measured under the following condition in connection with the systems I to IV according to the above-described first and second prior arts. For measuring the recommended value announced by the above SSI in Sweden, a meter (MAGNETIC FIELD METER MODEL MFM 1000) capable of measuring a low frequency leakage magnetic field developed by Combinova Company in Sweden is used. An actual measurement was conducted as follows. Antennas capable of measuring magnetic fields were installed at positions A, C and E shown in Fig. 3. The CRT display apparatus was then rotated clockwise and anticlockwise using the central point of the display apparatus as a center. The change rate of the magnetic field and the strength of the magnetic field under the condition in Figs. 3 and 4 (particularly at positions and angles of the antenna relative to the cathode ray tube), i.e., at the positions where antennas are installed, labelled A0, A1, A2, A14, A15, C0, C1, C2, C14, C15, E0, E1, E2, E14, E15, are measured by allowing a sawtooth current 7.8 A p-p having a horizontal deflection frequency of 20 KHz to flow in a horizontal deflection coil (not shown) of the deflection yoke 12 of the cathode ray tube 11, and by allowing a sawtooth current having a vertical deflection frequency of 60 Hz to flow in a vertical deflection coil (not shown). As a result, the maximum values and the minimum values of measured values at 15 positions in accordance with the above-described systems I to IV are as shown in Fig. 5. All the measured values shown in this figure vary to a great extent depending upon the wiring position of a lead wire for conducting current into the electric wire in order to cancel leakage magnetic flux in the vicinity of the face-plate of the cathode ray tube. By changing the wiring position of the lead wire, a value at a specific position on the above-mentioned electric wire may be minimized. However, if measurement is made with the lead wire in the above-described first and second prior arts hanging down in a direction of gravity, it was impossible to minimize, in a well-balanced manner, measured values on the measurement spherical body constituted by the above-described 15 positions. Further, cathode ray tube display apparatus could be hardly mass-produced in such an unbalanced state. Also, in the above-described arrangement shown in Figs. 1A and 1B, the two electric wire sections la and 1b for cancellation of leakage magnetic flux along the upper and lower side edge portions of the face-plate 2 are connected by electric wires indicated by broken lines, which are positioned on the diagonal of the display apparatus. Magnetic flux in the same direction as that of magnetic flux (leakage flux) produced by the deflection coils 4a, 4b is produced by the electric wire on the diagonal. This reduces the leakage magnetic flux cancellation effect by the electric wire sections la and 1b, and also this arrangement would not be expected to exhibit the leakage. Magnetic flux cancellation effect uniformly on the above-described spherical body designated by the SSI institution. Further, also in the arrangement shown in Fig. 1C, magnetic flux generated from the electric wire indicated by broken lines causes a decrease in the leakage magnetic flux cancellation effect. Thus, a sufficient effect could not be expected. Furthermore, in the above-described second prior art (EP-A-0348205), it is suggested that the source from which a leakage magnetic flux is produced in front of the display surface of the cathode ray tube is a bent-up portion of the horizontal deflection coil. In addition, as shown in Figs. 11, 12 and 17 which will be described later, a leakage magnetic flux B 2c in the same direction as that of the main magnetic flux B 2a component is produced also from the side surface portions of the cathode ray tube or the side surface portions of the deflection yoke. Since this leakage magnetic flux B 2c exerts an effect also in the forward direction of the display surface, unless such leakage magnetic flux B 2c is suppressed together with the other leakage magnetic flux, the leakage magnetic flux of the entirety of the cathode ray tube display apparatus cannot be reduced to a low level. In particular, suppression of the leakage magnetic flux B 2c toward the side surfaces was not envisaged by the prior art. Accordingly, none of the above-described prior arts are capable of reducing the strength of an unnecessary magnetic flux over the entire periphery of the cathode ray tube, or producing apparatus which can satisfy the standard requirement of recent display manufacturers and sellers. Thus, it is still necessary to reduce efficiently the leakage magnetic flux radiated from cathode ray tube display apparatus and to cause the value of the leakage magnetic flux to fall within the above-mentioned recommend limit. This invention has been made in view of the above, and its object is to provide a method and a device for suppression of leakage of magnetic flux in a cathode ray tube display apparatus, which can satisfy the standard requirements of display manufacturers and sellers. Namely, the object of this invention is to provide a method and a device for suppression of leakage of magnetic flux, in which magnetic flux produced from a coil for suppression of leakage of magnetic flux actually suppresses rather than reinforces leakage magnetic flux in a specific direction around CRT, and which is capable of reducing, efficiently and to such an extent as to have no serious harmful influence on the human body, a leakage magnetic flux produced from CRT, having a bad influence on other equipment and being harmful to the human body. The present invention provides a device for suppression of leakage of magnetic flux in a cathode ray tube display apparatus which comprises at least a cathode ray tube having a face plate and horizontal beam deflection means which generates said leakage, said deflection means comprising a first coil having a bent-up portion and a second coil having a bent-down portion, producing a main magnetic field, which deflects an electron beam of the cathode ray tube, and a leakage magnetic field having, at the boundary between the main magnetic field and the leakage magnetic field, a direction component opposite to a parallel direction component in the main magnetic field wherein two parts of said boundary are formed at said first and second deflection coils, respectively, said device comprising: a pair of conductor means each of which has a main portion disposed along one of the top and bottom rims of the face plate, each of said main portions thereby being substantially at said boundary, said pair of conductor means being driven with a current proportional to a deflection current flowing through said horizontal beam deflection means; wherein each conductor means further comprises two lead portions connected to the main portion, each of said lead portions being disposed along a side wall of a funnel of the cathode ray tube in such a form that one end of each lead portion is bent along a side rim of the face plate to couple with the respective main portion and another end of each lead portion extends toward a rear end of said beam deflection means so as to connect with said deflection means, and wherein each of said lead portions progressively approaches a horizontal plane which intersects the face plate at its centre as the lead portion extends toward the rear of the beam deflection means. The present invention also provides a device for suppression of leakage of magnetic flux in a cathode ray tube display apparatus which comprises at least a cathode ray tube having a face plate and horizontal beam deflection means which generates said leakage, said deflection means comprising a first coil having a bent-up portion and a second coil having a bent-down portion, producing a main magnetic field, which deflects an electron beam of the cathode ray tube, and a leakage magnetic field having, at the boundary between the main magnetic field and the leakage magnetic field, a direction component opposite to a parallel direction component in the main magnetic field wherein two parts of said boundary are formed at said first and second deflection coils, respectively, said device comprising: a pair of conductor means each of which has a main portion disposed along one of the top and bottom rims of the face plate, each of said main portions thereby being substantially at said boundary, said pair of conductor means being driven with a current proportional to a deflection current flowing through said horizontal beam deflection means; wherein each conductor means further comprises two lead portions connected to the main portion, each of said lead portions being disposed along a side wall of a funnel of the cathode ray tube in such a form that one end of each lead portion is bent along a side rim of the face plate to couple with the respective main portion and another end of each lead portion extends toward a rear end of said beam deflection means so as to connect with said deflection means, and wherein said one end of each of said lead portions extends substantially along said side rim of the face plate from a position substantially on a horizontal plane which intersects the face plate at its centre to couple with the respective main portion. There is also proposed a method for suppression of leakage of magnetic flux in a cathode ray tube display apparatus, the method comprising the steps of: arranging first and second electric wires at the upper and lower side edge portions of a face-plate portion of a CRT as close as possible to the display surface in the vicinity of the boundary between a main deflection magnetic flux produced from a horizontal deflection coil of a deflection yoke in a cathode ray tube display apparatus provided with a cathode ray, tube, the deflection yoke attached at the neck portion of the cathode ray tube, the face-plate portion for holding the display surface, and a funnelled portion, and a magnetic flux radiating from the forward direction of the display surface and produced from the bent-up portion of the horizontal deflection coil, arranging and bending the first and second electric wires in the vicinity of the boundary between the main deflection magnetic flux radiating toward the both left and right side wall portions of the face-plate portion and the magnetic flux produced from the bend-up portion of the horizontal deflection coil between respective corner portions of the face-plate portion and the portions in the vicinity of the left and right side wall portions of the face-plate portion intersecting with the horizontal plane of the cathode ray tube, arraying first and second lead portions contiguous to the first and second electric wires from the both left and right sides wall portions of the face-plate portion toward the portion in the vicinity of the neck portion side of the horizontal deflection coil, arranging the first and second lead portions so that a spacing between the first and second lead portions gradually becomes small, between the portion in the vicinity of a boundary and the horizontal plane, the boundary being formed between the main deflection magnetic flux radiating toward the side wall portions of the funnelled portion and the side wall portions of the deflection yoke, a leakage magnetic flux component of the main deflection magnetic flux, and a magnetic flux produced from the bend-up portion of the horizontal deflection coil, delivering, into the first and second lead wires, a current creating a magnetic flux in the same direction as that of the horizontal deflection current delivered to the horizontal deflection coil, and cancelling, by the first and second electric wires and the first and second lead portions, a leakage magnetic flux radiated from the cathode ray tube display apparatus with the deflection yoke attached thereto over the entire surround of the cathode ray tube. As described above, in accordance with this invention, electric wires and lead portions contiguous thereto for generating magnetic flux for suppression of leakage magnetic flux from the deflection coil are arranged on the upper and lower surface, and left and right side surface of the face-plate near the fluorescent display screen surface of the cathode ray tube, the side wall of the cathode ray tube, and the side surfaces of the deflection yoke, thus allowing a current in the same direction as that of a current flowing in the horizontal deflection coil to flow in the electric wires and the lead portions. Thus, the advantages are provided as follows. The strength and the change rate of a magnetic flux from the side surface of the cathode ray tube and/or the fluorescent display screen surface are reduced to a great extent all round the cathode ray tube display apparatus. Further, interference with other equipment and/or harmful influence on the human body is reduced. In addition, by arranging the electric wire for suppressing a leakage magnetic flux on the demagnetization coil, as in some preferred embodiments, labour used in attaching an electric wire separate from the demagnetization coil is saved, and positioning for such an attachment work or fixing of the electric wire is facilitated. In the accompanying drawings: Figs. 1A to 1C and fig. 2 are schematic diagrams and a perspective view showing the arrangement of the first and second prior arts, respectively; Figs. 3 and 4 are diagrams showing conventional measurement methods for measuring a low frequency leakage magnetic flux; Fig. 5 is a Table collectively showing measured values obtained by the measurement methods shown in figs. 3 and 4; Fig. 6 is a perspective view showing a device of a first embodiment according to this invention attached to a cathode ray tube display apparatus; Figs. 7A to 7D are circuit diagrams showing possible connections between horizontal deflection coils 50a, 50b and electric wires 51a, 51b for producing a magnetic flux for cancelling a leakage magnetic flux; Figs. 8 to 11 are diagrams showing distributions of magnetic flux produced in the case where the device according to this invention attached to a cathode ray tube display apparatus is used; Fig. 12 is a diagram showing the distribution of magnetic flux of a deflection yoke produced in the case where the cathode ray tube display apparatus is in use; Fig. 13 is a rear perspective view showing a cathode ray tube display apparatus; Figs. 14 and 15 are perspective views showing the state where devices of second and third embodiments according to this invention are attached to a cathode ray tube display apparatus, respectively; Figs. 16 and 17 are perspective views showing the state where devices of fourth and fifth embodiments according to this invention are attached to a cathode ray tube display apparatus, respectively; and Figs. 18 and 19 are perspective view showing devices of fourth and fifth embodiments according to this invention, respectively. Preferred embodiments of a method and a device for suppression of leakage of magnetic flux in a cathode ray tube display apparatus will be described in conjunction with Figs. 6 to 19, respectively. The outline of the method and the device for suppression of leakage of magnetic flux in a cathode ray tube display apparatus will be seen particularly by making reference to a first embodiment of a device according to this invention. Accordingly, attention is first directed to Fig. 6 showing the state where the device of the first embodiment is attached to a cathode ray tube display apparatus. As shown in this figure, the outline of the cathode ray tube display apparatus A is composed of a cathode ray tube 53 including a fluorescent display screen surface 53a, a funnelled portion 53c, a neck portion 53d, and a side wall 56, and a deflection yoke 54 having a horizontal deflection coil (not shown) attached to the neck portion 53d. Further, electric wires 51a, 51b and four lead portions 51 a1 , 51 a1 , 51 b1 , 51 b1 contiguous thereto for producing a magnetic flux for suppressing a leakage magnetic flux are attached to the side wall 56 of the cathode ray tube 53 and the upper and lower side edge portions 53 b3 , 53 b4 of the plate portion 53 b . The ends of both 51 a1 and 51 b1 are connected to connection portions 60, 60 of the deflection yoke 54 and extend in the vicinity of the side walls 56, 56. In Fig. 6, four metal fittings 53 f1 , 53 f4 , 53 f3 and 53 f2 are affixed on four corner portions 53 b5 , 53 b6 , 53 b7 and 53 b8 of the face-plate portion 53 b of the cathode ray tube 53, respectively. Further, electric wires 51a and 51b are arranged in the vicinity of the fluorescent display screen surface 53a along the upper and lower side edge portions 53 b3 and 53 b4 of the face-plate portion 53b from the vicinity of the metal fittings 53 f1 and 53 f4 on one side surface portion 53 b1 side of the face-plate portion 53b to the vicinity of the metal fittings 53 f2 and 53 f3 on the other side surface portion 53 b2 side, and are bent thereat. Then, a pair of electric wires 51a and 51b are disposed approximately along top and bottom rims of the face-plate portion 53b and are contiguous with lead portions 51 a1 and 51 b1 which extend to terminal portion 60 which is located at a rear of the deflection yoke 54 and on a horizontal plane which is approximately perpendicular to the face-plate portion 53b and crosses horizontally the face-plate portion 53b at its centre thereof, so that lead portions 51 a1 and 51 b1 progressively approach the horizontal plane toward the rear of the deflection yoke 54 along the side walls 56 and 56 of the funnel portions 53c. The lead portions 51 a1 and 51 b1 are bent along respective side rims of the face-plate portion 53b to couple with main portions of the electric wires 5la and 51b, which are located respectively at the top and bottom rims of the face-plate portion 53b as described above. Electric wires 51a and 51b may be made contiguous with the four lead wires 51 a1 , 51 b1 and 51 a1 , 51 b1 , or alternatively electric wires 51a and 51b may be made longer by the length of the lead wires in place of using these lead wires if desired. Fig. 7A to 7D are circuit diagrams showing possible connections between horizontal deflection coils 50a, 50b and electric wire portions 51a, 51b for producing a magnetic flux for suppressing a leakage magnetic flux. In Fig. 7A, the above-mentioned electric wire portions 51a, 51b connected in parallel are connected in series to the horizontal deflection coils 50a, 50b in parallel within the deflection yoke 54. Alternatively, the connections shown in Figs. 7B to 7D, which will be described later, may be employed. In Fig. 7B, a variable or fixed inductance L is connected in parallel with the electric wire portions 51a, 51b connected in parallel. In Fig. 7C, variable resistance R is connected thereto in place of the variable or fixed inductance L shown in Fig. 7B. In Fig. 7D, electric wire portions 51a, 51b are connected in series to the horizontal deflection coils 50a, 50b which are connected in parallel. In all of the circuit arrangements shown in Figs. 7A to 7D, a current approximately proportional to the deflection current flowing through the horizontal deflection coils 50a and 50b, flows through the electric wires 51a and 51b. In Figs. 7A to 7D, the horizontal deflection coils 50a and 50b may be connected to each other in series to obtain the same effect. Referring to Figs. 8 to 11, there are shown distributions of magnetic flux produced when the device of this invention is attached to a cathode ray tube display apparatus. As shown in Fig. 8, when a main magnetic flux (main deflection magnetic flux) B 2a is produced by the horizontal deflection coils 50a, 50b, a partial magnetic flux B 2b of the main magnetic flux B 2a leaks out toward the outside from the fluorescent display screen surface 53a. In Fig. 8, currents I 50a1 , I 50b1 , I 50a2 , I 50b2 flow, in the bent-up portions 50 a1 , 50 b1 on the coils 50a, 50b and the bent-up portions 50 a2 , 50 b2 . Thus, a leakage magnetic flux B 1 is produced. (The directions of the currents are conventionally shown by the symbols "⊙" and "⊗".) In Fig. 8, two boundaries between the main magnetic flux B 2a and the leakage magnetic flux B 1 exist substantially at the positions 55a, 55b indicated by broken lines (such boundaries may exist on the display screen surface depending on the kind of cathode ray tube). Electric wires 51a, 51b are arranged in the vicinity of the two boundaries 55a and 55b and at the upper and lower side edge portions 53 b3 , 53 b4 of the face-plate portion 53b as close as possible to the fluorescent display screen surface 53a, respectively. When currents I 51a , I 51b are caused to flow in these electric wires in directions shown in Figs. 8 and 9, respectively, magnetic flux B 3a , B 3b are thereby generated. These magnetic flux B 3a , B 3b act to reduce leakage magnetic flux B 1 , B 2b outside the boundaries 55a, 55b and forward of the fluorescent display screen surface 53a. Especially, leakage magnetic flux B 2b radiated from the fluorescent display screen surface 53a toward the outside, and leakage magnetic flux B 1 radiated from the upper and lower side edge portions 53 b3 , 53 b4 of the face-plate portion 53b and the upper and lower sides of the funnelled portion 53c toward the outside is suppressed. On the other hand, as shown in Fig. 12, when a current is caused to flow in the horizontal deflection coils 50a, 50b, a main magnetic flux B 2a is produced in the horizontal plane direction of the deflection yoke 54. A portion of the main magnetic flux B 2a leaks out from the cores 58a, 58b of the deflection yoke toward the outside. Thus, leakage magnetic flux B 2c is produced. Leakage magnetic flux B 2c , which is associated with the main magnetic flux B 2a , is produced on the side wall 56 (x-axis plane) of the cathode ray tube 53 as shown by slanting lines in the rear perspective view of a cathode ray tube display apparatus shown in Fig. 13, i.e., between the corner portion 53 b5 and the corner portion 53 b6 of the face-plate portion between which the horizontal plane is present and between the corner portion 53 b7 and the corner portion 53 b8 thereof as shown in Figs. 9 and 10. The boundary between the leakage magnetic flux B 1 and the leakage magnetic flux B 2c exists substantially along the positions indicated by broken lines 57a, 57b shown in Fig. 13, i.e., four corner portions of the cathode ray tube 53 (i.e., four corner portions 53 b5 , 53 b6 , 53 b7 , 53 b8 of the face-plate portion 53b). To suppress these leakage magnetic flux B 1 , B 2c , shown in Figs. 10 and 11, four lead portions 51 a1 , 51 b1 , 51 a1 , 51 b1 of the electric wires 51a, 51b are arranged such that the spacing β between respective lead wires gradually increases up and down from the horizontal plane as the distance between the left and right side surface portions 53 b1 , 53 b2 of the face-plate portion 53b close to the fluorescent display screen surface 53a of the cathode ray tube 53 and the deflection yoke 54 decreases. When a current is caused to flow in the direction shown in Figs. 10 and 11, a magnetic flux B 3 is produced which acts to reduce the magnetic flux B 2c . Thus, leakage flux B 2c radiated from the side surface portions of the deflection yoke 54 and/or the side wall 56 of the cathode ray tube 53 can be suppressed. It is to be noted that if the spacing β in Fig. 6 between lead portions 51 a1 and 51 b1 arranged at positions spaced from the side walls 56 of the cathode ray tube 53 at a predetermined interval is made too great the leakage magnetic flux B 2c becomes smaller than the cancellation magnetic flux B 3 . As a result, the cancellation magnetic flux B 3 has an effect on the upper and lower portions of the boundaries 57a, 57b between the leakage magnetic flux B 2c and the leakage magnetic flux B 1 , thus to strengthen the leakage magnetic flux at the upper and lower portions of the boundaries 57a, 57b. For this reason, as shown in Fig. 6, electric wires 51a, 51b and four lead portions 51 a1 , 51 b1 , 51 a1 , 51 b1 are positioned such that they pass from the side surface portion (near the horizontal plane) on the neck portion 54d side of the deflection yoke 54 through the corner portions 53 a1 to 53 a4 of the fluorescent display screen surface 53a of the cathode ray tube 53, i.e., the portions in the vicinity of the side surface portions 56, 56 of the four metal fittings 53 f1 , 53 f4 , 53 f3 , 53 f2 provided on the four corner portions 53 b5 , 53 b6 , 53 b7 , 53 b8 , of the face plate 53b. In this arrangement, lead portions 51 a1 , 51 b2 are located at positions closer to the horizontal plane than the boundary lines 57a, 57b. Thus, leakage magnetic flux b 2c can be effectively suppressed, resulting in an improved leakage magnetic flux suppression effect. Meanwhile, since the horizontal deflection coils 50a, 50b swing an electron beam (not shown) in a lateral direction of the cathode ray tube 53 as shown in fig. 9, a main magnetic flux B 2a is generated in a longitudinal direction perpendicular to the scanning direction (horizontal plane direction) of the electron beam. For this reason, horizontal deflection coils 50a, 50b are provided at the upper and lower positions on the horizontal plane of the cathode ray tube 53. Accordingly, the horizontal deflection coils 50a, 50b interchangeably produce, as magnetic flux B 1 , B 1a , B 2b produced therefrom, magnetic flux having directions opposite to the direction indicated by respective arrows shown in figs 10 and 11 in correspondence with the horizontal deflection frequency. As shown in figs. 8, 10 and 11, the boundary (the portions 55a and 55b) is the surface at which the magnetic flux or field changes direction or diverges. If the suppression means, comprising the conductor means having a main portion and lead portion, is positioned at the boundary, especially at a position near the screen surface, when the suppressing magnetic field is generated, there are many suppression components between the suppressing magnetic field and the leakage magnetic field components leaked from the CRT (deflection means) and there is only a very small component of the suppressing field when reinforces the leakage field which is generated in the CRT. This arrangement therefore maximizes the suppression effect between the suppressing magnetic field generated by the suppression means (conductor means) and the leakage magnetic field from the CRT. As is clear from the drawings, there are many magnetic components opposite to the magnetic field generated by the conductor means (the components leaked from the deflection means of the CRT), while the magnetic components having the same direction as the magnetic field generated by the conductor means (the magnetic field components generated inside the CRT) are the minimized. Some research results teach that since a relatively larger power is delivered to the horizontal deflection coils 50a, 50b, leakage magnetic flux toward the outside of the cathode ray tube itself as shown in fig. 13 is apt to interfere with other electronic equipment, and a low frequency magnetic flux is harmful to the human body. The standard requirement for such phenomona is severe. As stated above, the place where two electric wires 51a, 51b and four lead portions 51 a1 , 51 b1 , 51 a1 , 51 b1 are attached is not limited to the cathode ray tube in this invention, but a leakage magnetic flux suppression device according to this invention may be attached to a structure in the vicinity of the display screen surface 53a of the cathode ray tube 53, such as a cabinet for accommodating the cathode ray tube 53 so that a predetermined leakage magnetic flux suppression effect is provided. The object to which or place where the device according to this invention is attached is not limited. Since the power of magnetic flux is generally attenuated in verse proportion to the cube of the distance from the source thereof, the conductor generating the field for suppressing the leakage magnetic field is advantageously positioned at the front surface of the monitor set, this position being most distant from the source of the leakage flux (deflection means), or at the screen surface of the CRT. That is, if the suppression magnetic field is generated near the position where the leakage magnetic field is desired to be reduced (in particular where the leakage field can be reduced by a small suppression magnetic field), at the screen surface of CRT, the attenuation of the suppression magnetic field is minimized, and it is possible to use a relatively low power suppressing magnetic field to reduce the leakage magnetic flux. Referring to figs 14 and 15, there are shown arrangements in which the second and third embodiments of the device according to this invention are attached to the cathode ray tube display device. The same components as those described above are designated by the same reference numerals, respectively, and their explanation will be omitted. As shown in fig. 14, the second embodiment of the device according to this invention has substantially the same structure as the first embodiment shown in fig. 6, but differs from the first embodiment in the following points. In the device according to the second embodiment, lead portions 51 a1 , 51 b1 , contiguous with electric portions 5la, 51b respectively, are arranged on the side walls 56, 56 of the cathode ray tube 53, and extend toward the side surface portion 54a and the deflection yoke 54, from intermediate positions on the side surface portions 53 b1 53 b2 of the face-plate 53b. In fig. 14 these intermediate position are approximately one quarter of the length of the side of the face plate from the respective corners. Further, these lead portions 51 a1 , 51 b1 are arranged such that the spacing β between lead portions 51 a1 and 51 b1 gradually becomes narrow as illustrated. Lead portions 51 a1 , 51 b1 extending to terminal portions 60, 60 of the deflection yoke 54 are arranged adjacent and parallel to each other from a position approximately mid-way along their length to the terminal portions 60, 60 of the deflection yoke 54. As shown in fig. 15, the third embodiment of the device according to this invention has substantially the same structure as that of the above-described first embodiment shown in fig 6, but differs from the first embodiment in the following point. The device according to the third embodiment is characterized in that lead portions 51 a1 , 51 b1 contiguous to electric portions 5la, 51b are positioned on the side surface portion 56 of the cathode ray tube 53 adjacent to each other for the full length from deflection yoke 54 to a position close to the fluorescent display screen surface 53a. Usually in a colour cathode ray tube display apparatus, a demagnetizing coil is positioned around the CRT to prevent the shadow mask of the CRT from being magnetised by the earth's magnetism. In such apparatus, the above-mentioned leakage flux suppression wiring may utilize the demagnetizing coil as a support. Several embodiments of this type are shown in fig. 16 to fig. 19. Fig. 16 is a perspective view showing the state where the device according to this invention shown in fig. 18 which will be described later is attached to a cathode ray tube display apparatus, and fig. 17 is a perspective view showing the state where the device according to this invention shown in fig. 19 which will be described later is attached to a cathode ray tube display apparatus. The same components as those described above are designated by the same reference numerals, respectively and their explanation will be omitted. As shown in fig. 16, the cathode ray tube display apparatus B has a demagnetization coil 62, which will be described later, additionally provided which is not present in the arrangement of the above-described cathode ray tube display apparatus A . As shown in figs. 16 and 18, the ends of electric portions 51a, 51b for producing a magnetic flux for suppressing the above-described leakage magnetic flux are attached, with a predetermined spacing therebetween, to the demagnetization coil 61 for demagnetizing magnetization, etc of the shadow mask portion 53a attached on the funnelled portion 53c. In order to reduce leakage magnetic flux B 2c which is a portion of the main magnetic flux B 2a , as shown in fig. 10 mentioned above, electric portions 51a, 51b extend along the left and right side surface portions 53 b1 , 53 b2 of the face-plate portion 53b close to the fluorescent display screen surface 53a of the cathode ray tube 53, respectively. Then lead portions 51 a1 , 51 b1 , 51 a1 , 51 b1 contiguous thereto are conducted to the side surfaces 54a, 54a of the deflection yoke 54 substantially along a horizontal plane in the vicinity of the side walls 56, 56 of the cathode ray tube 53, and are fixed at ( predetermined positions (e.g., terminal portions 60, 60). A current is caused to flow in these lead wires in a direction shown in fig. 10, thus generating a magnetic flux B 3 in a direction to reduce the magnetic flux B 2c . Thus, leakage magnetic flux B 2c which leaks out from the side walls 56, 56 of the cathode ray tube 53 and the side surfaces 54a, 54a of the deflection yoke 54 can be suppressed. Further, electric portions 51a, 51b are arranged on the upper and lower side edge portion 53 b3 , 53 b4 of the face-plate 53b of the above-described cathode ray tube 53 as shown fig. 8. A current is caused to flow in these electric wires in a direction shown in fig. 8, to produce a magnetic flux B 3 for reducing the leakage magnetic flux B 2b , B 1 . Thus, leakage magnetic flux B 2b , B 1 radiated from the fluorescent display screen surface 53a can be suppressed. The fourth embodiment of the device according to this invention is constructed as shown in fig. 18. Reference numeral 61a denotes a connection appliance provided on the lead wire end of the demagnetization coil 61. Reference numerals 51, 51' denote connectors attached to the initial ends 51 c1 , 51 c2 and the terminating ends 51 d1 , 51 d2 of the electric portions 51a, 51b, respectively. In place of using these connectors 51, 51', such electric wires may be soldered to the respective predetermined portions. The fifth embodiment of the device according to this invention is constructed as shown in fig. 19. This embodiment has substantially the same structure as that of the above-described fourth embodiment shown in fig. 18, but differs from the fourth embodiment in that lead portions 51 a1 , 51 b1 , 52 a1 , 51 b1 contiguous to the electric wires 51a, 51b are arranged such that the spacing between two sets of lead portions is gradually widened as the lead wires approach the fluorescent display screen surface 53a. As stated above, this invention is not limited to the described first to fifth embodiments, but includes various implementations which can be considered to be identical in principle in the method of suppressing magnetic flux. It is to be noted that while leakage magnetic flux from the deflection coil 54 varies depending upon the shape or deflection current of the cathode ray tube display apparatus, electric wires 51, 51b may be connected in series with both ends of the horizontal deflection coils 50a, 50b as shown in fig. 7D, or they may be connected, as shown in figs. 7B and 7C, in parallel with electric wires 51a, 51b to which inductance L or resistance R is connected in parallel to adjust a current flowing therein, thus to balance such a leakage magnetic flux. For reference, values of leakage magnetic flux from the fluorescent display screen surface 53a in the case of the embodiments according to this invention shown in fig. 6 and figs. 7a to 7d and in the case where this invention is not implemented (no measure is taken), which are measured at positions installed of the above-described antennas A0 to A15, B0 to B15, C0 to C15, D0 to D15, and E0 to E15 shown in figs. 3 and 4 are shown in the following Table. As a result, it has been found that the method according to this invention advantageously permits the change rate and the strength of leakage magnetic flux to be reduced to about 1/3 to 1/7 of those of the method in which no measure is taken.

Claims: A device for suppression of leakage of magnetic flux in a cathode ray tube display apparatus which comprises at least a cathode ray tube (53) having a face plate (53a) and horizontal beam deflection means (54) which generates said leakage, said deflection means comprising a first coil (50a) having a bent-up portion and a second coil (50b) having a bent-down portion, producing a main magnetic field, which deflects an electron beam of the cathode ray tube, and a leakage magnetic field having., at the boundary between the main magnetic field and the leakage magnetic field, a direction component opposite to a parallel direction component in the main magnetic field wherein two parts of said boundary are formed at said first and second deflection coils, respectively, said device comprising: a pair of conductor means (51a, 51b) each of which has a main portion disposed along one of the top and bottom rims of the face plate, each of said main portions thereby being substantially at said boundary, said pair of conductor means being driven with a current proportional to a deflection current flowing through said horizontal beam deflection means; wherein each conductor means further comprises two lead portions (51a 1 , 51b 1 ) connected to the main portion, each of said lead portions being disposed along a side wall (56) of a funnel of the cathode ray tube in such a form that one end of each lead portion is bent along a side rim of the face plate to couple with the respective main portion and another end of each lead portion extends toward a rear end of said beam deflection means so as to connect with said deflection means, and wherein each of said lead portions progressively approaches a horizontal plane which intersects the face plate at its centre as the lead portion extends toward the rear of the beam deflection means. A device for suppression of leakage of magnetic flux in a cathode ray tube display apparatus which comprises at least a cathode ray tube (53) having a face plate (53a) and horizontal beam deflection means (54) which generates said leakage, said deflection means comprising a first coil (50a) having a bent-up portion and a second coil (50b) having a bent-down portion, producing a main magnetic field, which deflects an electron beam of the cathode ray tube, and a leakage magnetic field having, at the boundary between the main magnetic field and the leakage magnetic field, a direction component opposite to a parallel direction component in the main magnetic field wherein two parts of said boundary are formed at said first and second deflection coils, respectively, said device comprising: a pair of conductor means (51a, 51b) each of which has a main portion disposed along one of the top and bottom rims of the face plate, each of said main portions thereby being substantially at said boundary, said pair of conductor means being driven with a current proportional to a deflection current flowing through said horizontal beam deflection means; wherein each conductor means further comprises two lead portions (51a 1 , 51b 1 ) connected to the main portion, each of said lead portions being disposed along a side wall (56) of a funnel of the cathode ray tube in such a form that one end of each lead portion is bent along a side rim of the face plate to couple with the respective main portion and another end of each lead portion extends toward a rear end of said beam deflection means so as to connect with said deflection means and wherein said one end of each of said lead portions extends substantially along said side rim of the face plate from a position substantially on a horizontal plane which intersects the face plate at its centre to couple with the respective main portion. A device for suppression of leakage of magnetic flux as set forth in claim 1 or 2; wherein said pair of conductor means is at least partially supported by demagnetizing means with which said cathode ray tube is equipped.

Inventors: HISHIKI HIDEO, HISHIKI, HIDEO
Applicants: VICTOR COMPANY OF JAPAN, VICTOR COMPANY OF JAPAN, LIMITED
Application year: 1989
Main classification: H01J29
IPC codes: H01J29, H04N9