Method and Apparatus for Mounting a Cathode Ray Tube to Minimize Tube Shift and Respect to a Bezel

1. Field of the Invention

The present invention relates generally to the mounting of a cathode ray tube in a housing, and more particularly to the mounting of a cathode ray tube of the kind having mounting ears at corners of the enlarged end of the tube. Specifically, the present invention relates to a mounting arrangement that applies lateral force to the tube ears to restrict shifting of the tube with respect to the bezel of the housing and to rigidify the housing.

2. Description of the Related Art

A conventional cathode ray tube has mounting ears at corners of the enlarged end of the tube. The mounting ears are secured to the glass envelope of the tube by a tensioned metallic implosion-resisting band encircling the enlarged end of the tube. For mounting the cathode ray tube in a plastic housing, each of the mounting ears is secured by a screw to a front bezel portion of the housing. Because mounting ears are set back from the display screen of the cathode ray tube, the mounting ears must be mounted at a position set back from the front of the bezel portion, and typically the bezel portion is injection molded with standoffs or "bosses" to which the mounting ears are screwed. Due to insufficient friction between the mounting ears and the fastening hardware as well as the flexibility of the mounting bosses, this mounting arrangement permits the cathode ray tube to shift laterally with respect to the housing.

In some instances, the shifting of the cathode ray tube with respect to the bezel has been objectionable and has been limited to some degree by gluing wedge-shaped inserts into the housing between the bezel and the enlarged end of the cathode ray tube. Typically, two inserts were inserted at spaced locations along each of the four sides of the enlarged end of the tube, resulting in eight inserts per video display, although in some cases fewer inserts were used. But the installation of the inserts involved considerable labor and skill to ensure that the tube shift would be minimized by this method.

In a video display terminal having a housing and a cathode ray tube mounted in the housing, there is provided shift restricting means for applying a selected level of force between mounting ears of the tube and the housing in a direction generally perpendicular to the central axis of the tube. In a preferred embodiment, angle brackets are mounted inside the housing between the enlarged end portion of the cathode ray tube and inside corners of the housing, and lateral force is applied between the angle brackets and the enlarged end portion of the tube for rigidifying the housing. The lateral force is applied by wedges mounted in the brackets for sliding against the mounting ears, and screws are coupled to the brackets for forcing the wedges against the mounting ears, thereby minimizing tube shift with respect to the bezel of the housing.

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:

FIG. 1 is a perspective view of a video display terminal incorporating the present invention;

FIG. 2 is an exploded view showing the mounting of a cathode ray tube to a front bezel portion of the housing of the video display terminal of FIG. 1;

FIG. 3 is a perspective view illustrating shift restricting means for applying a selected level of force between mounting ears of the cathode ray tube and the video display housing in a direction generally perpendicular to the axis of the cathode ray tube;

FIG. 4 is a rear view of the bezel portion of the video display housing;

FIG. 5 is a cross-sectional view of the bezel along line 5--5 in FIG. 4;

FIG. 6 is a front view of an upper angle bracket used for mounting the cathode ray tube in the video display housing;

FIG. 7 is a side view of the angle bracket of FIG. 6;

FIG. 8 is a rear view of the angle bracket of FIG. 6;

FIG. 9 is a top view of the angle bracket of FIG. 6;

FIG. 10 is an enlarged sectional view of a portion of the angle bracket of FIG. 6 along line 10--10 in FIG. 9;

FIG. 11 is a top view of a wedge;

FIG. 12 is a front view of the wedge of FIG. 11; and

FIG. 13 is a side view of the wedge of FIG. 11.

While the invention is susceptible to various modification and alternative forms, a specific embodiment thereof has been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Turning now to the drawings, there is shown in FIG. 1 a video display terminal generally designated 20 which incorporates the present invention. The video display terminal 20 has a cathode ray tube generally designated 21 mounted in a two-piece housing having a front bezel portion 22 and a rear portion 23 engaging the bezel. Preferably the bezel 22 and rear portion 23 are made of injection molded thermoplastic resin, such as polyphenylene oxide which is sold, for example, by the General Electric Company as NOREL PX4400 resin. The thermoplastic resin is easily molded to the desired shape and is especially light weight, durable and impact resistant.

Turning now to FIG. 2, there is shown an exploded view illustrating the internal construction of the video display terminal 20. In FIG. 2, the rear portion of the housing 23 has been removed, and the cathode ray tube 21 is shown separated from the bezel 22. The cathode ray tube 21 has a glass portion with a display screen 24 at an enlarged end, and mounting ears 25-28 fastened by tensioned metal banding 29 to the glass portion.

To fasten the cathode ray tube 21 to the bezel 22, each mounting ear 25-28 is secured by a respective threaded stud 31-34 to a respective corner of the bezel 22. The studs, for example, are a quarter inch in diameter and have a 24 pitch thread. First, the studs 31-34 are screwed into the bezel 22, then the ears 25-28 are aligned over and engaged with the studs, and finally nuts 35-38 are threaded onto the studs to secure the mounting ears to the studs. This method of securing the mounting ears 25-28 to the bezel 22 prevents movement of the cathode ray tube 21 in the direction of the tube's central axis 39 which is generally perpendicular to the display screen 24, but some lateral movement of the mounting ears is permitted. Some lateral misalignment of the ears 25-28 with the threaded studs 31-34 is, in fact, desirable to account for rather imprecise lateral positioning of the mounting ears on the enlarged end of the cathode ray tube 21. Moreover, some lateral shifting of the mounting ears with respect to the threaded studs is to be expected during the handling of the video display terminal, and this lateral shifting is accommodated by a pair of washers 41-48 disposed on opposite sides of each mounting ear upon the respective threaded stud.

In accordance with an important aspect of the present invention, lateral shifting of the cathode ray tube 21 with respect to the housing is restricted by shift restricting means for applying a selected level of force between the mounting ears 25-28 and the housing 22 (and 23 in FIG. 1). As shown in FIG. 2, such shift restricting means is incorporated into an angle bracket 49, 50, 51 disposed at each corner of the housing. The lower angle brackets, only one of which 51 is shown in FIG. 2, are interconnected by a perforated rail 52 which provides support for some electrical components (not shown) of the video display terminal 20.

Each of the angle brackets 49-51 is secured by two screws 53-55 and 56-58 which are threaded into the bezel 22. The preferred shift restricting means includes a respective guide 59-61 formed in each angle bracket 49-51, a respective wedge 62-64 received in each guide, and a respective screw 65-67 threaded into each angle bracket for driving its associated wedge against an adjacent one of the mounting ears 25-28. Preferably the angle brackets 49-51 and the wedges 62-64 are formed from 16 gage (0.060 inch thick) cold rolled steel sheet metal and are finished with zinc and blue-bright chromate.

The operation of the shift restricting means is more clearly discerned from the illustration in FIG. 3. As shown, the mounting ear 26 has been secured to the bezel 22 by the threaded stud 32 and the nut 35. In addition, the angle bracket 50 has been screwed to the bezel 22.

To restrict lateral motion of the mounting ear 26 in the direction of arrows 68, the wedge 63 is engaged in the slide 60 and is forced by the screw 66 to abut against the mounting ear 26 at a contact point 69. The screw is turned, for example, by a torque wrench to apply a selected level of force between the wedge 63 and the mounting ear 26. Therefore, the shift restricting means applies a selected level of force between the enlarged end of the cathode ray tube 21 and the housing of the video display terminal. In addition, the angle bracket 50 protrudes from the bezel 22 so that it abuts against the inside corner of the rear portion of the housing (23 in FIG. 1) when the rear portion is assembled onto the bezel 22.

Turning now to FIG. 4, there is shown a rear view of the bezel 22. The bezel defines a rectangular aperture 71 for the display screen of the cathode ray tube, and is injection molded with a number of reinforcing ribs 72. For securing the mounting ears of the cathode ray tube to the bezel, the bezel is injection molded with a boss in each of its four corners such as the boss 73 which receives the threaded stud 34 in FIG. 2. Also at each corner, there are disposed two bosses such as the bosses 74 and 75 which receive the screws for securing a respective one of the angle brackets to the bezel. Moreover, there are provided a pair of bosses such as the bosses 76 and 77 in the middle of each of the four sides of the bezel 22 for receiving screws (not shown) which fasten the rear portion of the housing (23 in FIG. 1) to the bezel.

Turning now to FIG. 5, the bosses 73 and 74 are shown in cross section. The bosses are cylindrical and hollow and receive respective threaded brass inserts 75 and 76. Preferably, the insert 75 is knurled and the insert 76 is tapered to hold the inserts into their respective bosses 73, 74.

Turning now to FIGS. 6 to 9, there are shown various views of the upper corner bracket 49. The bracket is mounted to the bezel (22 in FIG. 4) via two end flanges 81 and 82. The opposite end of the bracket also has a flange 83 which abuts against an inner surface of the rear portion of the housing (23 in FIG. 1) after assembly. To mount the adjusting screw (66 in FIG. 3), the bracket 49 is formed with an intermediate right angle bend 84 to which is mounted a threaded steel insert 85 which receives the respective adjusting screw (65 in FIG. 2).

The guide 59 for the wedge (62 in FIG. 2) is shown in FIGS. 9 and 10. It should be evident that the guide can be formed by a punching and stamping operation. A central portion 86 of the guide 59 includes a detent 87 that firmly engages the wedge (62 in FIG. 2) into the guide.

Turning now to FIGS. 11 to 13, there are shown various views of the wedge 62. The wedge is formed by stamping and bending sheet metal. To ensure smooth contact between the wedge and its abutting mounting ear (25 in FIG. 2), the inclined edges of the wedge are formed by folds 91 and 92. For retaining the wedge in the guide (59 in FIG. 10), the top of the wedge has extending portions 93 and 94.

In view of the above, there has been described a means for restricting the lateral shifting of a cathode ray tube in a video display terminal. The shift restricting means is easily adjusted during the assembly process. In particular, the video terminal is assembled by laying the bezel 22 (see FIG. 2) face down, mounting the angle brackets 49-51 to the bezel, aligning the enlarged end 24 of the cathode ray tube 21 with the aperture of the bezel, and then securing the mounting ears 25-27 to the bezel by threading the nuts 35-37 to the studs 31-33. Then the wedges 62-64 are installed into the guides 59-61 in the brackets over the mounting ears 25-27, and the adjusting screws 65-67 are turned to drive the wedges to contact the mounting ears and obtain a selected amount of force between the mounting ears and the bezel. Despite the fact that the mounting ears are imprecisely located on the enlarged end of the tube, a simple adjustment of the screws 65-67 with a torque wrench precisely locates the wedges 62-63 into contact with the mounting ears 25-27 to minimize shifting of the cathode ray tube 21 with respect to the bezel 22.

The shift restricting means holds the cathode ray tube in its aligned position during shipping. It also helps support the load of the cathode ray tube which is typically cantilevered off four bosses in the bezel. In addition, the shift restricting means is incorporated into four angle brackets that abut the inside corners of the housing to rigidify the housing. External loads tending to deform the housing are applied to the mounting ears of the cathode ray tube to prevent these loads from being applied directly to the glass portion of the tube. The rigidification of the housing is especially useful in video display terminals which do not have an internal chassis.