US3808568A

US3808568A - Stator yoke

Info

Publication number: US3808568A
Application number: US00383137A
Authority: US
Inventors: C Sawyer
Original assignee: DISPLAY CO Inc
Current assignee: DISPLAY CO Inc
Priority date: 1973-07-27
Filing date: 1973-07-27
Publication date: 1974-04-30
Anticipated expiration: 1991-04-30
Also published as: CH581388A5; FR2239002A1; DE2433989A1; CA992129A; JPS5725941B2; JPS5045515A; GB1466443A; NL7410110A; FR2239002B3

Abstract

An improved electromagnetic deflection yoke core comprising an annular member of ferromagnetic material in which a plurality of slots are disposed along the interior perimeter thereof and are distributed in a given quadrant with respect to horizontal and vertical orthogonal axes which divide the core into four equal quadrants, the disposition or location of the slots being in accordance with an approximate cosine distribution about a 45* diagonal to said orthogonal axes.

Description

United States Patent [191 Sawyer 1 Apr. 30, 1974 STATOR YOKE [75] Inventor: Carleton E. Sawyer, Littleton, Mass.

[73] Assignee: Display Components, Inc., Littleton Common, Mass.

[22] Filed: July 27, 1973 [2l] Appl. No.: 383,137

52 US. CL ..33s/21o,335/213 s11 Int.Cl. ..H0lt7/00 5s FieldoiSearch 335/210,213;3l3/76 [56] References Cited UNITED STATES PATENTS 2,846,606 8/1958 Jones et al. 335/213 x FOREIGN PATENTS OR APPLICATIONS 218,216 10/1958 Australia 313/76 Primary Examiner-George Harris Attorney, Agent, or Firm-Schiller & Pandiscio ABSTRACT An improved electromagnetic deflection yoke core comprising an annular member of ferromagnetic material in which a plurality of slots are disposed along the interior perimeter thereof and are distributed in a given quadrant with respect to horizontal and vertical orthogonal axes which divide the core into four equal quadrants, the disposition or location of the slots being in accordance with an approximate cosine distribution about a 45 diagonal to said orthogonal axes.

6 Claims, 2 Drawing Figures STATOR YOKE This invention relates to electromagnets and more particularly to improved electromagnetic deflection yokes capable of being used with cathode ray tubes.

It is well known that electromagnets' can be used to create a magnetic field to control the path of an electron beam passing through the field. Consequently, electromagnets have been used to form deflection yokes which generally comprise a system of magnetic poles arranged around the neck of a cathode ray tube, between the electron gun and the face of the tube. The poles provide a magnetic .field to bend in a controlled manner an electron beam 'from its straight line path as it is transmitted from the electron gun toward the face of the tube. By suitably varying the magnetic field and simultaneously modulating'the intensity of the beam, the electron beam can'be made to sweep up and down and back and forth across the face of the tube forming a visual presentation or picture on the face of the tube.

One type of deflection yoke has saddle shaped coils, and is capable of two-directional beam deflection. Examples can be found in US. Pat. Nos. 2,766,407 and 3,430,169 respectively issued to Sanford and Gabor, and will be seen to comprise two pairs of coils. Each of the coils are formed of windings of conductive wire which are bunched together to form a figure similar to a saddle. The coils of each pair are located on opposite sides of the tube neck, and the coil pairs are displaced 90 around the tube. When energized, the two pairs of coils produce orthogonal magnetic fields through the neck of the tube perpendicular to the path of the undeflected electron beam generated in the tube. By appropriately varying the currents in the coil pairs, the direction and magnitude of the magnetic fields can be varied to deflect the electron beam to give the proper pattern on the face of the tube. Generally, yokes having saddle shaped coils also include a jacket or a sleeve of low reluctance material fitted snugly around the windings to help constrain the magnetic field and to increase the flux density through the neck of the tube.

Saddle shaped coil yokes, however, have generally been unsatisfactory since bunching the windings of each coil tend to produce a distorted deflection field. In deflection yokes used to provide relatively narrow deflection angles, this characteristic of bunched windings is not critical. Where a wide angle deflection field is desired, however, such as in cathode ray tubes of most television receivers, the beam must then scan into the region physically closer to the conducting wire itself, which region contains these distorted field patterns due to bunched windings. The usual result of this distorted field (which is called a pin-cushion field) is a defocusing of the electron beam within the field. The effects of a pin-cushion field are shown in US. Pat. No. 2,l08,523 issued to Bowman-Manifold. The results of a pin-cushion field generally produce astigmatic distortion in the viewed image on the screen of the tube. Astigmatic distortion usually is at a maximum at a 45 diagonal to the horizontal and vertical deflection axes.

The so-called magnetic toroid deflection yoke was developed to provide wide angle deflection with minimized pin-cushion distortion.'This type of deflection yoke, which by way of example, is shown and described in U.S. Pat. No. 2,881,341 issued to Schlesinger, comprises an annular core or ring having longitudinally directed slots formed equiangularly around the interiorperimeter of the core. lnwardly directed teeth are thereby provided which are defined by those portions of the core between the slots. The slots are identical with one another in terms of cross-sectional width and depth; and the teeth, although tapered in an axial direction are also identical with one another. The number of slots and corresponding number of teeth are symmetrically arranged about'the horizontal or X axis and the vertical or Y axis in order to provide symmetry of both the X and Y field components. Accordingly, the number of slots or teeth are a multiple of four. A coil section is provided for each of the slots, wherein wire is wound around the core through the respective slot. It is known that with this arrangement the structure when energized will approximate linear fields. The intensity of these fields is a function of the number of ampere turns or current density of each of the coils. Ampere turns or current densities of a coil section can be defined as the product Nl, where N is the number of turns of the coil section and I is the current transmitted therethrough.

Generally, in order to provide a uniform field in a toroid deflection yoke having equiangularly disposed slots, the ampere turns distribution of the coil section of each quadrant theoretically requires a cosine distribution with respect to the horizontal or X axis for horizontal deflection, and a sine distribution with respect to the horizontal axis for vertical deflection. By connecting those coil sections which are distributed for horizontal deflection and disposed on one side of the vertical axis in order to provide one of two horizontal deflection coils, and connecting the corresponding coil section which are diametrically opposed on the core from the first mentioned connected coil sections to provide the'other'horizontal deflection coil, the magnetic field in the horizontal or X direction can be controlled by controlling the current to the connected coil sections. Similarly by connecting those coil sections distributed for vertical deflection and disposed on one side of the horizontal axis in order to provide one of the two vertical deflection coils, and connecting the corresponding coil sections which are diametrically opposed on the core from the first mentioned vertical axis symmetrically arranged connected coil sections to provide the other vertical deflection coil, the magnetic field in the vertical or Y direction can be controlled by controlling the current to the connected coil sections.

The magnetic toroid deflection yoke having equiangularly arranged slots, however, has been found to be not wholly satisfactory. The speed of deflection of the electron beam is proportional to the time rate of change of the number of ampere-turns. For rapid changes in beam position therefore, it is necessary that the coil sections provide a low inductance. Thus, for high speed changes in beam position the number of turns, N, for each coil section must be small because the inductance has to be small. Since it is additionally known that the ampere turns distribution or the number of ampere turns for X deflection are based upon a cosine distribution and for Y deflection a sine distribution, it has been found necessary to approximate the number of turns of each of the slots because obviously one cannot provide fractional turns. Since N is small, the approximation will have a significant effect on the magnetic field so that the field intensity throughout the field will not be constant as desired. This results in defocusing of the beam passing therethrough. Although the field intensity along the X axisor along the Y axis may be at the level desired, the field intensity along a diagonal will be different.

Prior to the present invention it has been necessary therefore, to use small currents and a large number of turns for each. coil section to minimize the conse quences of approximation. However, this in turn introduces several problems. With small currents, any transient currents present would have a greater distortion effect on the field, than if a large current were used. Additionally, using a large number of turns for each coil section, as opposed to a small number, creates a greater chance of a defect in the coil which may cause a larger amount of heat to be generated and increases the chance of failure. Use of a large number of turns creates increased manufacturing costs of each yoke attributable to such defects, failures and additional materials. Additionally, the large number of turns and small current may involve excessive weight and greater electrical resistance.

Accordingly, an object of the present invention is to provide a deflection yoke which overcomes the above noted problems of the prior art.

Another object of the present invention is to provide a magnetic deflection yoke in which errors resulting from coil turn approximation are substantially reduced.

Yet another object of the present invention is to provide a deflection yoke capable of providing a uniform magnetic field intensity.

Still another object of the present invention is to provide a deflection yoke which is particularly useful with large currents And yet another object of the present invention is to provide a deflection yoke in which a small number of turns for each coil section may be utilized.

Theforegoing and other objects are achieved by a deflection yoke comprising an annular core member having slots formed on the interior perimeter thereof and spaced from one another so that the slot density distribution approximates a cosine distribution about the 45 diagonal. Y

Other features and many of the attendant advantages of the invention are described or rendered obvious by the following detailed description which is to be considered together with the accompanying drawings wherein:

FIG. 1 is a side elevational view of a deflection yoke in accordance with the invention positioned on a cathode ray tube;

FIG. 2 illustrates cross-sectional view taken across the axis of symmetry of a deflection yoke designed in accordance with the invention.

Referring to the drawing wherein like numerals designate like parts, FIG. 1 shows deflection yoke 8 located in operative position on cathode ray tube 10 which conventionally comprises a generally cylindrical neck portion 12 housing the usual electron gun 16. Neck 12 is joined to flared or bulbous portion 14 of the tube, the end of which includes target screen 18 comprising a suitable electron-responsive material for emitting light in response to electron impingement. Such a tube is well known and need not be described in further detail.

Deflection yoke 8, which is shown in greater detail in FIG. 2, comprises annular core member 20 having a plurality of radially directed alternating slots 22 and teeth 24 formed around the interior perimeter of the core in a manner which will be described in greater detail hereinafter. Member 20 is made of any material which exhibits small magnetic losses, and has a relative permeability greater than'unity, such as any of the ferromagnetic materials.

Typically the core is made of a ferrite, since ferrites assure low eddy-current losses. It is preferable to use a ferrite having a high maximum permeability and saturation with low coercive force and electrical conductivity. Manganese zinc ferrites which meet these requirements'are particularly useful since they can be made from inexpensive raw materials. The core is typically made as a solid piece of ferrite. Alternatively, a laminated metal construction may be used, such as is provided by stacking a plurality of thin laminations of silicon iron.

Slots 22 are-preferably formed identically with one another so that they are of equal and constant cross sectional width and of equal cross sectional depth. The number of slots are symmetrically arranged about the intersections of X and Y axes (the directions respectively of the horizontal and vertical components of the composite magnetic field. that is created) in order to provide horizontal and vertical field components. Accordingly, the total number of slotsare a multiple of four. Although the total number of slots is a matter of choice, a typical slotted yoke for sonar or radar use typically has sixteen slots.

Theangular position, of the center. of each of the slots which are located in the first quadrant (where i is the number of the given slot) is determined in a counter clockwise direction from the horizontal X axis and is defined as follows:

Where n is even, n being the total number of slots in the first quadrant on the core;

1. 0i= cos V512 V22; 1 /2n' 17/4 and where n is odd;

2. 01' cos Vi/ V2i/n) 1 1r/4 The slot positions of the other quadrants are arranged in a similar manner so that the slots are symmetrically arranged about both the X and Y axes.

As a result of the slot configuration in accordance with equation (1) or (2), teeth 24 will vary in width, thereby providing linear magnetic fields of varying intensities.

A coil section 26 is provided for each of the slots 22, wherein wire is wound around the core member and as it is wound, it is disposed in the slot. The turns of each coil section is typically equal in number so that each of the sections are equal in inductance. The invention works particularly well as mentioned above, when the number of turns is small.

As is well known in the art, the coil sections 26 are electrically connected together as well as to horizontal and vertical deflection control circuits (not shown) of the tube. The horizontal deflection of the electron beam is controlled by the horizontal control circuit and the vertical deflection is controlled by the vertical control circuit.

Typically the coil sections designated for horizontal deflection on each side of the Y axis are connected together in series to provide the horizontal deflection coils. These horizontal deflection coils are connected to the horizontal control circuit of the tube. Similarly the coil sections designated for vertical deflection on each side of the X axis are connected together in series to provide the vertical coils. These vertical coils are connected to the vertical control circuit.

The slot configuration described in equations l and (2), above, generally is derived from the fact that when the electron beam is being deflected at a 45 diagonal to the X and Y axes, where the maximum distortion would occur, and the X and Y coil sections 26, are equal in inductance and in number of turns, in order to minimize the distortion, it can be shown that the ideal ampere turn distribution should be a cosine distribution about the 45 diagonal, or,

3. N1 ACos (0 11/4) where A is a constant.

Looking at the distribution, therefore, in the first quadrant where there are k slots, each slot has L wire turns from the X coil and Mi wire turns from the Y coil, where i is the number of the slot, as defined above. Since the inductance of each of the coil sections is equal about the 45 diagonal, the following criterion can be established:

4. 1. 1. 1.4 L etc.

Thus, under these conditions each slot will have an equal number of turns or,

and the amount of current in each coil section will b equal.

Further referring to equation (3);

7. N B cos (0 11/4),

where B=A/I, a constant. Accordingly, when the density distribution of the slots approximates a cos (0 1r/4) function, otT-axis distortion is minimized.

Accordingly, the slots are arranged in accordance with equation (1) or (2).

in operation, the yoke is positioned on the neck 12 of tube 10. As well known in the art, the coil sections which are connected together to provide horizontal deflection are energized by the horizontal control circuit to deflect the beam in a horizontal direction as well known in the art. Similarly, the coil sections which are connected together to provide vertical deflection are energized by the vertical control circuit to deflect the beam in a vertical direction. When current is provided by the control circuits to the coils, the magnetic fields produced, which extend out from the teeth 24 will clearly provide the compensation necessary to minimize spot aberrations and landing distortions such as pin-cushioning. As a consequence by varying the currents through the coils, as well known in the art, wide angle deflection can be accomplished with little or no distortion in the beam that is focused on the screen 18 of tube 10.

Since certain obvious changes may be made in the illustrated embodiment of the device without departing from the scope of the invention, it is intended that all matter contained herein be interpreted as illustrative and not in the limiting sense.

What is claimed is:

1. A core for an electromagnetic deflection yoke, said core comprising,

an annular member of ferromagnetic material having a plurality of radially-directed slots disposed about the interior perimeter thereof, all of said slots being substantially equal to one another in crosssectional width and depth, said slots being distributed along said perimeter in a given quadrant with respect to horizontal and vertical orthogonal axes which divide said core into four equal quadrants, in accordance with an approxi mate cosine distribution about a 45 diagonal to said orthogonal axes. 2. A core for an electromagnetic deflection yoke, said core comprising;

an annular member of ferromagnetic material having a plurality of radially-directed slots disposed about the interior perimeter thereof, each of said slots being distributed along said perimeter of said core in a given quadrant with respect to horizontal and vertical orthogonal axes which divide said core into four equal quadrants, in accordance with the following relationships: 0i cos- V272 when n is even, and

0i cos Vi/Z Vii/m1 when n is odd,

wherein i is an integer indicating the particular slot in said given quadrant counting the slots from said horizontal axis, 61' is the angular position of the ith slot with respect to said horizontal axis, and n is the total number of slots in said given quadrant.

3. An electromagnetic deflection yoke core in accordance with claim 1, wherein each of said slots is equal in cross-sectional width and depth.

4. An electromagnetic deflection yoke comprising,

an annular core member of ferromagnetic material having a plurality of radially-directed slots disposed about the interior perimeter thereof, and

a plurality of coil sections, each of said coil sections having a plurality of turns and being disposed in a corresponding slot, wherein said slots are distributed in a given quadrant with respect to horizontal and vertical orthogonal axes which divide said core into four equal quadrants, in accordance with the following relationships: 0i cos \[2/2 when n is even, and

wherein i is an integer indicating the particular slot in said given quadrant counting the slots from said horizontal axis,

6i is the angular position of the ith slot with respect to said horizontal axis, and

n is the total number of slots in said given quadrant.

5. An electromagnetic deflection yoke core in accordance with claim 4 wherein the number of turns of each of said coil sections is equal.

6. An electromagnetic deflection yoke core in accordance with claim 5, wherein said core is disposed on the neck of a cathode ray tube.

Claims

1. A core for an electromagnetic deflection yoke, said core comprising, an annular member of ferromagnetic material having a plurality of radially-directed slots disposed about the interior perimeter thereof, all of said slots being substantially equal to one another in cross-sectional width and depth, said slots being distributed along said perimeter in a given quadrant with respect to horizontal and vertical orthogonal axes which divide said core into four equal quadrants, in accordance with an approximate cosine distribution about a 45* diagonal to said orthogonal axes.

2. A core for an electromagnetic deflection yoke, said core comprising; an annular member of ferromagnetic material having a plurality of radially-directed slots disposed about the interior perimeter thereof, each of said slots being distributed along said perimeter of said core in a given quadrant with respect to horizontal and vertical orthogonal axes which divide said core into four equal quadrants, in accordance with the following relationships: theta i COS 1 ( Square Root 2/2 - Square Root 2 (2i -1)/2n) - pi /4 when n is even, and theta i COS 1 ( Square Root 2/2 - ( Square Root 2 i/n)) -pi /4 when n is odd, wherein i is an integer indicating the particular slot in said given quadrant counting the slots from said horizontal axis, theta i is the angular position of the ith slot with respect to said horizontal axis, and n is the total number of slots in said given quadrant.

4. An electromagnetic deflection yoke comprising, an annular core member of ferromagnEtic material having a plurality of radially-directed slots disposed about the interior perimeter thereof, and a plurality of coil sections, each of said coil sections having a plurality of turns and being disposed in a corresponding slot, wherein said slots are distributed in a given quadrant with respect to horizontal and vertical orthogonal axes which divide said core into four equal quadrants, in accordance with the following relationships: theta i cos 1 ( Square Root 2/2 - Square Root 2 (2i -1)/2n) - pi /4 when n is even, and theta i cos 1 ( Square Root 2/2 - ( Square Root 2 i/n)) - pi /4 when n is odd, wherein i is an integer indicating the particular slot in said given quadrant counting the slots from said horizontal axis, theta i is the angular position of the ith slot with respect to said horizontal axis, and n is the total number of slots in said given quadrant.