US3826943A

US3826943A - Camera tube of vidicon style comprising single high melting-point metal seal provided with support for target

Info

Publication number: US3826943A
Application number: US00336335A
Authority: US
Inventors: T Kawamura; T Kawahara
Original assignee: Nippon Electric Co Ltd
Current assignee: NEC Corp
Priority date: 1972-02-29
Filing date: 1973-02-27
Publication date: 1974-07-30
Anticipated expiration: 1991-07-30
Also published as: NL7302777A; DE2309626A1

Abstract

A camera tube of the type of a vidicon, a scan converter, or the like comprises a single seal member of high melting-point metal having a first portion sealed to the periphery of the face plate, a second portion sealed to the adjacent end of the tubular casing, and a third portion disposed between the face plate and the tubular casing. The third portion is provided with a radially inwardly projecting portion of high melting-point metal. The target electrode is encircled by a ring member provided with a plurality of springs of resilient metal for engaging with the projecting portion to support the target electrode.

Description

United States Patent [191 Kawamura et al.

[451 July30,1974

[75] Inventors: Takuro Kawamura; Takashi Kawahara, both of Tokyo, Japan [73] Assignee: Nippon Electric Company, Limited,

Tokyo, Japan [22] Filed: Feb. 27, 1973 [21] Appl. No.: 336,335

[30] Foreign Application Priority Data Feb. 29, 1972 Japan 47-20127 Feb. 29, 1972 Japan 47-20128 [52] US. Cl. 313/65 R, 313/288 [51] Int. Cl HOlj 31/26, HOlj 29/02 [58] Field of Search 313/65 A, 94, 65 R [56] References Cited UNITED STATES PATENTS 2,984,759 5/1961 Vine 313/65 A 10/1966 Stoudenheimer ct a1 313/94 X 4/1967 Musselman 313/65 T Primary Examiner-Robert Segal Attorney, Agent, or Firm0strolenk Faber Gerb &

Soffen 5 7] ABSTRACT A camera tube of the type of a vidicon, a scan converter, or the like comprises a single seal member of high melting-point metal having a first portion sealed to the periphery of the face plate, a second portion sealed to the adjacent end of the tubular casing, and a third portion disposed between the face plate and the tubular casing. The third portion is provided with a radially inwardly projecting portion of high meltingpoint metal. The target electrode is encircled by a ring member provided with a plurality of springs of resilient metal for engaging with the projecting portion to support the target electrode.

2 Claims, 6 Drawing Figures CAMERA TUBE OF VIDICON STYLE COMPRISING SINGLE HIGH MELTING-POINT METAL SEAL PROVIDED WITH SUPPORT FOR TARGET BACKGROUND OF THE INVENTION This invention relates to a camera tube including an electron gun, beam focusing and deflecting means, and a target electrode. A camera tube of the type described may either be a vidicon or a scan converter.

In a vacuum envelope of a camera tube of the type described, use is made of a seal member of nonmagnetic metal, such as indium, from a point view of the image distortion and the mass production. This makes it impossible on exhausting air from the space enclosed with the vacuum envelope to raise the temperature of the envelope up to the baking temperature used for usual electron tubes because of the low melting point of indium. As a result, it has not been possible to attain excellent vacuum, thereby unduly reducing the life and the reliability of the camera tubes.

In order to obviate the demerits of the low meltingpoint metal seal, a camera tube of the type described has been proposed which comprises at least one seal member of high melting-point metal although the temperature to which the seal is raised during operation of the tube is well below 100C. Inasmuch as the metal seal member has to provide an airtight seal with glass, it is made of ferromagnetic metal, such as is known by a trade name of Kovar (an alloy of iron, nickel, and cobalt). According to one of the proposals that will be described later in greater detail with reference to FIG. 1, the target electrode is held independently of the metal seal member which serves also as a lead wire device for the target. Poor electric contact is therefore provided between the target and the seal member. Furthermore, the magnetic property of the seal member gives rise to distortion of the image. The process of sealing is difficult. It is impossible to place the target in close proximity to the face plate. In accordance with another proposal which also will be described later with reference to FIG. 2, use is made of three Kovar seal members. The camera tube is therefore expensive. The sealing process is complicated and difficult. In particular, the seal is weak and susceptible to thermal shocks. Moreover, it is necessary to prepare a specific beam focusing and deflecting coil assembly. In any one of the proposals, the seal has insufficient strength to protect the tube against mechanical shocks. It has therefore been necessary to handle the camera tubes with the greatest possible care. In addition, the seal member is readily covered with an oxide of the metal which harms the electric contact between the seal member and the circuit for the camera tube.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a camera tube of the type of a vidicon, a scan converter, or the like, which has high reliability and long life and is produced with a high rate of yield.

It is another object of this invention to provide a camera tube of the type described, which comprises a single seal member of magnetic metal and yet does not give rise to image distortion.

It is still another object of this invention to provide a camera tube of the type described, which comprises additional means for protecting the seal against damage due to mechanical shocks. The additional means serves also to prevent mechanical vibrations from reaching the target electrode.

As described, a camera tube to which this invention is applicable is of the type of a vidicon, a scan converter, or the like. A camera tube of this type includes a transparent face plate and a tubular casing airtightly sealed together to form a vacuum envelope by sealing means having a first portion sealed to the periphery of the face plate, a second portion sealed to the adjacent end of the tubular casing, and a third portion disposed between the face plate and the tubular casing. The camera tube further comprises a ring member disposed around the target electrode and placed within the envelope adjacent to the face plate. The camera tube still further comprises means for causing an electron beam to scan the target electrode to deliver video signals to the sealing means.

In accordance with this invention, a camera tube of the type described comprises a single seal member of high melting-point metal as the sealing means. The camera tube further comprises first means of high melting-point metal projecting radially inwardly projecting from the inside surface of the third portion of the single seal member. The camera tube still further comprises second means of resilient metal attached to the outside surface of the ring member for the target electrode for engaging with the first means to support the target in juxtaposed relation to the face plate.

A camera tube according to this invention may further comprise a ring member of stainless metal attached to the outside surface of the first portion of the seal member with a layer of low melting-point metal interposed therebetween.

Inasmuch as only one seal member is used, the sealing may easily be carried out in two steps, one for the peripheral surface of the face plate by way of face seal as called herein and the other separately for the adjacent end of the tubular casing, as by way of the socalled Housekeeper seal. This ensures high yield and renders the cost of manufacture inexpensive.

The presence of the third portion of the seal member prevents the molten mass of the tubular casing from flowing to the peripheral portion of the face plate during sealing. It becomes therefore possible to place the target electrode in close proximity to the face plate.

The seal does not require use of the argon arc welding. This enables the seal member to be of a small diameter and to support the target electrode. Besides, the small diameter of the seal member renders it possible to use a conventional beam focusing and deflecting coil assembly.

The use of the radially inwardly directed projection of the seal member and the resilient metal member attached to the ring member for the target electrode makes it possible to place the target electrode and the associated mesh electrode in position just before the final sealing process for the other end of the tubular casing and a stem having the electron gun assembly. It is therefore possible to obviate undesired oxidation of the target and the mesh electrodes and attachment of foreign substances thereto. This reduces occurrence of the image defect and further raises the yield.

The ring member for the target electrode, if made of ferromagnetic metal, makes it possible to cancel the image distortion produced by the magnetic property of the seal member. This enables a camera tube according to this invention to be used in transmitting pictures of high quality.

The engagement of the resilient metal member attached to the ring member for the target electrode with the radially inwardly directed projection of the seal member provides excellent electrical contact leading from the target electrode to the seal member. This dispenses with the conventional transparent electroconductive film provided on the inside surface of the face plate and consequently raises the optical transparency of the face plate.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and FIG. 2 are partial axial sectional view of conventional camera tubes;

FIG. 3 is a similar view of a first embodiment of the present invention;

FIG. 4 is a partial axial sectional view of a target assembly to be used in a first embodiment shown in FIG.

FIG. 5 is a like view of another target assembly; and

FIG. 6 is a partial axial sectional view of a second embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a conventional camera tube of the vidicon type comprises a glass face plate 101 permeable to a light signal, a glass tube 102, and a ring 103 of magnetic metal for sealing the face plate 101 and the tube 102 together to form a vacuum envelope. The camera tube further comprises a transparent electroconductive film 104, such as of stannic oxide, coating the inside surface of the face plate 101, a mesh electrode 105 serving as a fourth grid and supported by the vacuum envelope in a conventional manner, an annular insulating member 106 attached to the support for the mesh electrode 105, and a photoelectric target 107 disposed in the space enclosed with the vacuum envelope. An annular spring 108 is placed between the target 107 and the transparent electroconductive film 104 to urge the target 107 relative to the insulating member 106 and to provide electric contact between the target 107 and the seal member 103 through the film 104.

In this structure, the magnetic metal ring 103 forms a part of the electric circuit leading from the target 107 to the outside of the vacuum envelope. It is, however, difficult to make the metal ring 103 support the target 107 because of the configuration of the seal. This structure leads to several defects, such as imperfect electric contact between the target 107 and the seal member 103 and the resulting abnormal noises which arise during operation. Defective operation is further caused by the ferromagnetic nature of the metal ring 103, which disturbs the uniform focussing and deflecting magnetic field which results in barrel-shaped image distortion. It is difficult to correct such an image distortion with the construction of the support for the target 107. A further disadvantage is introduced by the process for carrying out the seal. As the metal ring 103 is simultaneously sealed both to the face plate 101 and the tube 102, it is important to adjust the thickness and heat capacity of the face plate 101, the thickness and heat capacity of the tube 102, and the heat capacity of the metal ring 103. However, the allowable range for this adjustment is narrow, which fact renders the sealing process difficult and reduces the yield. In addition, these factors make it impossible to optionally select a desired form of each of the components during designing of the camera tube. Furthermore, the quantity of glass of the tube 102 which flows radially inwardly along the surface of the metal ring 103 differs from seal to seal due to the fluctuation of glass working temperature. This makes it impossible to place the target 107 of a given size, such as a silicon diode array target, as close to the face plate 101 as possible.

Referring to FIG. 2, another prior art camera tube of the vidicon type comprises a face plate 101, a glass tube 102, a mesh electrode 105 serving as a fourth grid, and a silicon photodiode array target 107. Instead of a single metal ring 103 illustrated with reference to FIG. 1, the camera tube depicted in FIG. 2 further comprises a first Kovar seal member 111 sealed to the periphery of the face plate 101 and extending radially and axially inwardly, a ring-shaped glass seal member 112 having a first end sealed to the first Kovar seal member 111, a second Kovar seal member 113 sealed to a second end of the glass seal member 112, and a third Kovar seal member 114 sealed to the glass tube 102. The target 107 is supported and provided with the electric contact by the first Kovar seal member 111. The second Kovar seal member 113 provides a support for the mesh electrode 105. The second Kovar seal member 113 of a first assembly including the face plate 101 is sealed to the third Kovar seal member 114 of a second assembly including the glass tube 102 by an argon arc.

This structure also has several defects. Firstly, the cost of production is high because of the three

Kovar seal members

111, 113, and 114 and the requirement that four parts must be sealed. Secondly, the sealing work for the seals between the first Kovar seal member 111 and the face plate 101 and between the first Kovar seal member 1 11 and the glass seal member 112 is difficult and provides only low yield as described in conjunction with FIG. I. In the third place, the seal between the glass seal member 112 and the second Kovar seal member 113 is weak in construction and is sensitive to thermal shocks'although the seal between the second and the third Kovar seal members 113 and 114 is strong. In order to prevent the temperature of the Kovar-to-glass seals from unduly rising during the argon arc welding, the second and the third Kovar seal members 113 and 114 are provided with large diameters. It is, however, still insufficient to avoid sudden rise and fall of the temperature during the argon arc welding because of the small total heat capacity of the first and the second assemblies. Particularly during cooling, cracks occur in the seal between the glass seal member 112 and the second Kovar seal member 113. Therefore, manufacture is very difficult. In the fourth place, it should be understood at first that the argon arc welding is brought into effect after the space in which the target 107 and the mesh electrode 105 are disposed is substituted with argon. It is, however, impossible to prevent the oxidizing gas absorbed in the respective components from reacting with the copper of the mesh electrode 105 at a high temperature to produce the oxide. In addition, minute dust particles adhere to the mesh electrode 105 and the target 107 during welding to introduce a defective image and to further reduce the yield. In the fifth place, the large diameter of the second and the third Kovar seal members 113 and 114 makes it necessary to use a specific complex beam focusing and deflecting coil assembly instead of a standard one.

Referring now to FIG. 3, a first embodiment of the instant invention as applied to a silicon vidicon tube comprises a glass face plate 101, a glass tubular casing 102, a mesh electrode 105, and a silicon photodiode array target electrode 107, which are the counterparts of the elements shown in'FIGS. l and 2 and are designated with like reference numerals. It should be understood that a camera tube to which the invention is applicable comprises an electron gun (not shown) for producing an electron beam and a beam focusing and deflecting coil assembly (not shown) for causing the electron beam to scan the target electrode 107. The face plate 101 is ordinarily a plane-parallel glass plate. The tubular casing 102 may be a glass tube available on the market for use in manufacturing a l-inch vidicon. According to this invention, a single seal member 121 of high melting-point metal is provided with a first portion sealed to the periphery of the face plate 101, a second portion sealed to the adjacent end of the tubular casing 102, and a third portion disposed between the face plate 101 and the tubular casing 102. The face plate 101, the tubular casing 102, and the seal member 121 thus form a vacuum envelope. In this connection, it is to be noted that the tubular casing 102 as called herein comprises a glass tube shown and a stem member (not shown) sealed to the remote end (not shown) of the glass tube. The seal member 121 may be made of Kovar, a trade name of a nickel-chromium-iron alloy, a nickel-iron alloy, molybdenum, or copper. As mentioned above, the face plate 101 and the tubular casing 102 may be made of glass whose thermal expansion is suitable to that of the substance of which the seal member 121 is made. For example, Kovar glass is selected in the case of a Kovar seal member 121. The thickness of the seal member 121 depends on the substance thereof and may be from 0.1 mm to 0.8 mm in the case of Kovar. The seal member 121 is further provided with a radially inwardly directed projection 122 made of the same material as the seal member 121 and welded to the inside surface of the third portion of the seal member 121. Alternatively, the seal member 121 having an integral projection 122 of the type described may be manufactured by machining a rod of Kovar. The first embodiment further comprises a ring member 123 disposed around the target electrode 107. In further accordance with the invention, a plurality of leaf springs 124 are spot-welded to the outside surface of the ring member 123. The ring member 123 is made of nonmagnetic metal, such as nonmagnetic stainless steel or nichrome. The leaf springs 124 are made of resilient metal, such as an alloy of nickel, chromium, and iron known by a trademark Inconel or unannealed nonmagnetic stainless steel. The projection 122 and the leaf springs 124 thus support the target electrode 107 in juxtaposed relation to the face plate 101. As is known in the art, the camera tube comprises a third grid 126.

The face seal between the face plate 101 and the metal seal member 121 may be formed by making use of high-frequency induction heating. The seal between due to mechanical and the thermal shocks. In order to make the ring member 123 snugly engage the radially inwardly directed projection 122, it is convenient to use a tool having pawls for supporting the leaf springs 124 in the state pressed against the outside surface of the ring member 123.

Referring to FIG. 4, the ring member 123 is cupshaped and has a circular hole 131 at the bottom of the cup which is to be brought into contact with the face plate 101. The diameter of the circular hole 131 should preferably be the same as the photosensitive area of the target electrode 107 in order to provide the widest possible sensitive area. Alternatively, the ring member 123 may be of the shape of a simple hollow cylinder, particularly when the axially very short ring member 123 is desirable. Within the space defined by the cup-shaped ring member 123 to which the leaf springs 124 are preliminarily welded, the target electrode 107'is placed with an annular waving spring (hereinafter called a wave washer) 132 interposed between the target electrode 107 and the bottom of the cup. The target electrode 107 is placed in position by means of a plurality of axially directed clicks 133 bent into the space with a cap ring 134 interposed between the clicks 133 and the target electrode 107. The clicks 133 maybe any one of other locking means.

The height or the axial length and the wall thickness of the ring member 123 are chosen in accordance with the coil assembly in use, the size of the cap ring 134, the distance between the target electrode 107 and the mesh electrode 105, the size of the metal seal member 121, the relation of the ring member 123 relative to the seal member 121, and some other factors. Coil assemblies of various standard sizes are available on the market. The height of the ring member 123 may be from 0.5 mm to 0.4mm. Within this range, it is generally possible to select an optimum height from the viewpoint of reducing the image distortion to a minimum.

Referring to FIG. 5, the ring member 123 is made of a nommagnetic stainless steel sheet of the thickness of 0.5 mm and disposed in juxtaposed relation around the target electrode 107. The target electrode 107 is held against the ring member 123 having leaf springs 124 with a wave washer 132 of Inconel interposed therebetween by a set cap 136 welded directly to the ring member 123. In this case, use is made of four spring members 124.

Referring to FIG. 6, a second embodiment of this invention comprises a face plate 101, a tubular glass casing 102, a high melting-point metal seal member 103, a target electrode 107, and a ring member 123 therefor, all similar to the corresponding parts shown in FIG. 3 and thereby designated with like reference numerals. In addition, the second embodiment comprises an additional ring member 141 attached to the outside surface of the first portion of the seal member 103 with a layer 142 of low melting-point metal interposed therebetween. The additional ring member 141 is made of stainless metal, such as nonmagnetic stainless steel or nichrome. The low melting-point metal may be indium. The stainless nature of the additional ring member 141 provides excellent electric contact between the seal member 103 and the electrical circuit (not shown) for the camera tube. The layer 142 enables the additional ring member 141 to be attached to the seal member 103 without adversely affecting the seal and serves as a shock absorber for the camera tube. The layer 142 may extend beyond the space between the first portion of the seal member 103 and the additional ring member 141 to cover the entire outer surface of the seal member 103 and protect against any chemical damages which would otherwise be caused to the seal member 103. Alternatively, the outer surface of the seal member 103 may be covered with masses (not shown) of hermetic binder, such as a silicone resin or an epoxy resin, to protect the otherwise exposed surface of the seal member 103 against the chemical damages. The hermetic binder augments the attachment of the additional ring member 141 to the seal member 103 and is particularly desirable when use is made of the seal members of thin wall thickness.

What is claimed is:

1. A camera tube including a transparent face plate and a tubular casing airtightly sealed together to form a vacuum envelope by sealing means having a first portion sealed to the periphery of said face plate, a second portion sealed to the adjacent end of said tubular casing, and a third portion disposed between said face plate and said tubular casing, said camera tube further including a ring member disposed around a target electrode and placed within said envelope adjacent to said face plate, an electron gun, and means for scanning electrons from said gun over said target electrode to deliver video signals to said sealing means, wherein the improvement comprises a single seal member of high melting-point metal as said sealing means, first means of high melting-point metal radially inwardly projecting from the inside surface of said third portion, and second means of resilient metal attached to the outer surface of said ring member for engaging with said first means to support said target electrode in juxtaposed relation to said face plate, said ring member being made of nonmagnetic metal.

2. A camera tube according to claim 1, further comprising a ring member of stainless metal attached to the outside surface of said first portion with a layer of low melting-point metal interposed therebetween.