Display tube

Abstract: Display tube including an envelope portion 2 coated with a first electrically conducting layer 7 and a display window 1 coated with a second electrically conducting layer 8. A connection means having two tongue-shaped members 11 and 12 is fastened to a high-­ voltage contact 13. The tongue-shaped members 11 and 12 extend on both sides of the high-voltage contact 13 and bear against the electrically conducting layers 7 and 8, respectively.

Description: The invention relates to a display tube comprising an envelope portion which at its interior side is coated with a first electrically conductive layer and a display window which at its interior side is coated with a second electrically conductive layer and which is secured to the envelope portion and further comprising a high-voltage contact provided through the wall of the envelope portion and connection means having a base portion which is connected to said high-voltage contact and having extensions which bear against the first and second conductive layer, as disclosed in independent claim 1 and dependent claims 2 to 5. U.S. Pat. 4,344,015 discloses a cathode ray tube having a funnel portion with an electrical terminal extending through a wall surface and a faceplate sealed to the funnel portion. The faceplate is internally coated with an aluminium coating and the funnel with an electrically conductive coating. The electrical terminal consists of an anode button being projected inwardly by a stud and a locking nut. The screen contact assembly includes a conductive strip attached at one end to the electrical terminal. At the other end of the strip and attached thereto is a relatively flexible first contact member which is in pressured electrical contact with the aluminum layer on the faceplate. A display tube of the type defined in the opening paragraph is generally used for the display of monochrome pictures, colour pictures or for displaying figures or letters (Data Graphic Displays). In practice it was, however, found that in some cases the display of a picture is not always effected in the desired manner and disadvantageous effects occur. It is inter alia an object of the invention to provide a display tube in which at least in a number of cases the occurrence of the said disadvantageous effects is prevented. According to the invention, a display tube of the type defined in the opening paragraph is therefore characterized, in that the high-voltage contact comprises a nipple which protrudes inside the tube and has a widened end portion, in that the base portion of the connection means comprises a hole which engages with said nipple such that said base portion bears against said widened portion of said nipple, in that the extensions comprise tongue shaped members which are connected under pre-tension to the high-voltage contact and each tongue-shaped member bears against the associated electrically conducting layer under the action of a spring, in that the extensions comprise a first tongue shaped member bearing against the first conductive layer at the envelope side of the high-voltage connection, a second tongue shaped member bearing against the second conductive layer and a third and fourth tongue shaped member bearing against the first conductive layer at the display window side of the high-voltage connection, and in that the second, the third and the fourth tongue shaped member extend in the direction to the display window, the second tongue shaped member being located between the third and fourth tongue shaped member. The invention is based on the recognition that at least part of the disadvantageous effects is caused in that the first electrically conducting layer is not electrically connected to a sufficient extent to the second electrically conducting layer and the supply of a voltage to the layers is not adequate in some cases. Electron beams generated by an electron generating system provided in the envelope portion can disadvantageously be influenced on their path to a display screen provided at the interior side of the display window by unwanted electromagnetic fields which are caused by an insufficient electrical connection between the two conducting layers. This causes an uncontrollable and unwanted shift of the electron beams which results in a distortion in a picture to be displayed. A display tube of the invention has been found to ensure an adequate electrical connection between the two conducting layers because of the mechanically very stable connection provided by the fact that the two tongue-shaped members extend on both sides of the supporting element. In addition, an appropriate voltage supply to the layers is obtained in a simple manner because the high-voltage contact is used as an electrical feed-through. A display tube of the invention comprises a connection member with third and fourth tongue-shaped members which extend substantially in the same direction from the base portion as the second tongue-shaped member, that the third and fourth tongue-shaped members bear against the first layer, the second tongue-shaped member being located between the third and fourth tongue-shaped members. As a result thereof the electrical connection between the two conducting layers is preserved even at the occurrence of heavy vibrations and shocks. A display tube of the invention also comprises a base portion that is connected to the high-voltage contact whilst a bias voltage is applied thereto and each tongue-shaped member bears against the associated electrically conducting layer under the action of a spring. This provides in a simple manner an appropriate contact of each tongue-shaped member with its associated conducting layer. In a preferred embodiment of a display tube in accordance with the invention, in which the base portion of the connection means includes a strip-shaped element from the ends of which the tongue-shaped members extend, the connection means can be produced as one integral whole in a simple manner. The base portion of the connection element can be fastened in many different ways to the supporting element. A display tube of the invention comprises a high-voltage contact that includes an element which extends from the inner wall of the envelope portion, which element is provided at its end with an at least partially flaring portion and that the base portion partially bears against the flaring portion, the connection (in this case the bearing against) is also used in a simple manner to obtain a proper bearing of the tongue-shaped members against the conducting layers under spring action. Fastening the connection means to the supporting element and the bearing of the tongue-shaped members is thus realised in an integrating manner, so that the connection means comprises the lowest possible number of components. Preferably, the end of each tongue-shaped member is spoon-shaped, which provides an appropriate bearing against the associated conducting layer and there is no risk of loose parts or scratches being produced during assembling of the tube components. The mechanical stability of the connection means renders it particularly suitable for supporting a getter device suitable for containing getter material. These and further more detailed features of the invention will now be described and explained with reference to the accompanying drawings and the examples. Some embodiments of a display tube according to the invention will be described in greater detail by way of example with reference to the accompanying drawing, in which: Fig. 1 is a schematic cross-sectional view of a display tube according to the invention, Fig. 2 shows a connection means, which is not according with those provided in the display tube of the invention, since it does not contain a third and a forth tongue shaped members. Figs. 3 to 4 show some embodiments of connection means provided in the display tube of the invention, and Figs. 5 and 6 are schematic views of a connection means connected to a high-voltage contact in a display tube in accordance with the invention. The display tube shown in Fig. 1 in a longitudinal cross-sectional view comprises a glass envelope comprising a display window 1, a cone-shaped envelope portion 2 and a neck portion 3. The neck portion 3 includes an electron generating system 4 for generating an electron beam 5 which is directed to a display screen (not shown) provided on the interior of the display window 1. On its path to the display screen the electron beam 5 is deflected over the display screen with the aid of a plurality of deflection coils 6 which are coaxially positioned around the tube axis. The interior wall of the envelope portion 2 is provided with a first electrically conducting layer 7 and the interior wall of the display window 1 is provided with a second electrically conducting layer 8. The first electrically conducting layer 7 can be made of a resistance material composed of, for example, a mixture of ferrioxide, graphite and potassium silicate, and the second electrically conducting layer 8 is, for example, a thin aluminium layer provided on the overall display screen. The two electrically conducting layers 7 and 8 are electrically interconnected by means of a connection means 9 which comprises a base portion 10, a first (11) and a second (12) tongue-shaped member. The base portion. 10 is connected to a high-voltage contact 13 which is provided, for example, by means of welding or in an alternative embodiment by means of a clamping structure, in the envelope portion 2. The two tongue-shaped members 11 and 12 extend on both sides of the high-voltage contact 13 from the base portion 10. The end of the first tongue-shaped member 8 bears against the first electrically conducting layer 7 and the end of the second tongue-shaped member 12 bears against the second electrically conducting layer 8. The desired voltage can be applied to the conducting layers 7 and 8 via the high-voltage contact 13. The connection means 9 provides a very stable electrical interconnection of the two electrically conducting layers 7 and 8. Some embodiments of connection means in a display tube according to the invention will be described in greater detail by way of example with reference to the Figs. 3 and 4. Fig. 2 shows schematically a connection means, which is not according with those provided in the display tube of the invention, since it does not contain a third and a forth tongue shaped members having a base portion 10 which is constituted by a disc-shaped or cylindrical element connected to the high-voltage contact. The first tongue-shaped member 11 is provided with a bulge 14 which, when the base portion 10 is connected to the high-voltage contact bears against the electrically conducting layer on the envelope portion. The second tongue-shaped member 12 is provided with two bulges 15 and 16, of which bulge 15 is intended to bear against the electrically conducting layer on the display window and bulge 16 is intended to bear against the electrically conducting layer on the envelope portion. Fig. 3 shows a connection means having a base portion 10 which at one side has a tongue-shaped portion 11 and at the opposite side a (long) tongue-shaped portion 12 arranged between (short) tongue-shaped portions 19 and 20. (Alternatively, two tongue-shaped portions 11 can be provided for the purpose of increasing the stability.) The connection means as shown in Fig. 3 provides that the electrical connection between the two layers is preserved, even at the occurrence of heavy vibrations and shocks, because the second tongue-shaped member 12 is located between a third and a fourth tongue-shaped member 19 and 20, respectively. An appropriate contact of the tongue-shaped members against the conducting layer is obtained by connecting the base portion to the high-voltage contact by pre-tension so that each tongue-shaped member bears against the associated electrically conducting layer under spring action. The pre-tension is, for example, obtained by imparting a curved shape to the connection means, as is shown in Fig. 4. Connected to the high-voltage contact 13 is an element 21 which more specifically may be in the form of a nipple and extends from the base portion 2 and has an at least partly widening free end 22, in this case a spherical form (see the schematic views in Figs. 5 and 6). If the base portion 10 bears against the widened end 22 then the curvature of the connection means is reduced and the spoon-shaped ends 14, 15 and 16 bear against the electrically conducting layers under spring action. Connecting the connection means to the high-voltage contact 13 can be effected with the aid of a clamping structure 23 (see Fig. 6) but is preferably effected by providing the base portion 10 of the connection means with such an aperture 18 (see Figs. 3 and 5) that a part of the base portion 10 bears around the aperture on the widening end 22. More specifically, the aperture 18 in the base portion 10 is in the form of a slotted hole with an ample insert portion and a narrow fixing portion (Fig. 3). If the orientation of the aperture (slotted hole) 18 is as shown in Fig. 3, then the connection means can be positioned such that the ample portion of the aperture 18 is over an anode contact ("22" in Figs. 5 and 6) and the connection means can be secured on the anode contact by pushing the narrow portion of aperture 18 towards the display screen. This is a very suitable method especially for small display tubes, such as projection TV tubes. When the connection means is used in larger tubes, the aperture (slotted hole) 18 may be rotated through 180° as compared with the situation shown in Fig. 3 as this provides more room. In that case the connection means is fixed, after having been placed in position, by means of the narrow portion of the aperture 18 on the anode contact by pulling (in a direction away from the screen). In view of the adequate stability of the connection of the connection means of the invention to the high-voltage contact the connection means is perfectly suitable for supporting a getter device suitable for containing getter material. In that case the getter arrangement may be secured on, for example, the barrel-shaped portion of the structure shown in Fig. 3.

Claims: A display tube comprising an envelope portion which at its interior side is coated with a first electrically conductive layer and a display window which at its interior side is coated with a second electrically conductive layer and which is secured to the envelope portion and further comprising a high-voltage contact provided through the wall of the envelope portion and connection means having a base portion which is connected to said high-voltage contact and having extensions which bear against the first and second conductive layer characterized in that the high-voltage contact comprises a nipple which protrudes inside the tube and has a widened end portion, in that the base portion of the connection means comprises a hole which engages with said nipple such that said base portion bears against said widened portion of said nipple, in that the extensions comprise tongue shaped members which are connected under pre-tension to the high-voltage contact and each tongue-shaped member bears against the associated electrically conducting layer under the action of a spring, in that the extensions comprise a first tongue shaped member bearing against the first conductive layer at the envelope side of the high-voltage connection, a second tongue shaped member bearing against the second conductive layer and a third and fourth tongue shaped member bearing against the first conductive layer at the display window side of the high-voltage connection, and in that the second, the third and the fourth tongue shaped member extend in the direction to the display window, the second tongue shaped member being located between the third and fourth tongue shaped member. A display tube as claimed in claim 1 characterized in that the tongue shaped members have spoon shaped extremes. A display tube as claimed in claim 1 or 2 characterized in that the connection means carries a getter device suitable for containing a getter material. A display tube as claimed in claim 1, 2 or 3 characterized in that the base portion of the connection means comprises a slotted hole with an ample insertion portion at the display window side and a narrow fixing portion at the opposite side and in that said fixing portion engages said nipple. A display tube as claimed in any one of the preceding Claims, characterized in that the base portion of the connection means includes a strip-shaped element from whose ends the tongue-shaped members extend.

Inventors: OVERBEEK JOHANNES JOSEPH MARIA, VERKUIJLEN HENDRIK AUGUSTINUS, OVERBEEK, JOHANNES JOSEPH MARIA, VERKUIJLEN, HENDRIK AUGUSTINUS
Applicants: PHILIPS ELECTRONICS NV, PHILIPS ELECTRONICS N.V.
Application year: 1990
Main classification: H01J29
IPC codes: H01J29