Display with improved frame surrounding display element

Abstract: Disclosed herein is a display to be applied to a digital switch. This display includes a casing (1) formed of a box-type casing (2) and a cover (3), a display element (8) facing a display window (2b) accommodated in the casing (1), a printed wiring board (9) for supporting the display element (8), and a printed wiring board (14) which is connected to the printed wiring board (9) and on which a control circuit (16) for displaying an external input signal on the display element (8), and the like are mounted. At the front portion of the casing (1) are formed frames (11a and 11b) extending over a display face (81) of the display element (8), and thus a portion of the printed wiring board (9) which is located at the outer periphery of the display element (8) cannot be seen from the outside. A conductive pattern (18) for discharging a static electricity is provided on the printed wiring board (9), corresponding to a region in which the frames (11a, 11b) engaged with each other. The frames (11a, 11b) have adhesive tapered faces, and thus a static electricity is hard to enter the display from the outside. Thus, it flows out of the display through the conductive pattern (18) even if it enters the display.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a display having an improved frame surrounding a display element. Description of the Background Art A display to be applied to a digital switch and the like comprises a display element for displaying numerals, a printed wiring board on which a circuit element for the display element is mounted, and a casing for accommodating the display element and the printed wiring board. A display window is provided in this casing, and the display element is provided in the casing with its display face facing the display window. When a portion of a human body electrostatically charged with frictional electrification is in proximate to or in contact with such a display and a charge enters through the display window to the inside of the casing, the circuit element mounted on the printed wiring board is liable to be destroyed by the electrical charge. In order to protect the circuit element, in the display of the background art of the present invention, provision of a metal frame attached onto the periphery of the display window of the casing and further provision of a ground lead within the casing to contact this metal frame causes the charge, which entered in the display, to flow out of the display through the metal frame and the ground lead. However, there were disadvantages of increases in the number of components and assemblies and in production cost since the metal frame is employed as described above. Further, it sometimes occurs that the metal frame is deformed by some external force in assembly of the display. Moreover, even if no abnormality occurs in the assembly of the display, a poor contact between the metal frame and the ground lead in use causes a charge to be stored in the display, leading to a fear of destruction of the circuit element. In addition, the display of the background art of the present invention involves another disadvantage that due to a gap between the display window and the display element, even if a filter is attached to the display window, the printed wiring board located at the peripheral portion of the display element can be viewed through the filter, resulting in the unattractive display in appearance. DE-U-87 17 181, representing the closest prior art, discloses a casing for receiving electronical parts. The casing comprises a base member having a first side panel portion integrally formed with the base member at the front face thereof, and a cover member in pair with said base member. The cover member has a second panel portion integrally formed with the cover member at the front surface thereof. When the base and cover members are mounted together, the side panel portions define an opening portion in the front part of the casing. Besides, EP-A-0 001 588 discloses a display comprising a casing having a base member and a cover member. A frame for supporting a display element on the cover member comprises two tongues cooperating with two slots provided in the cover member. The display element includes electrical contacts which, through corresponding openings in the cover member, are in contact with a circuit board disposed in the casing. Such a display, however, requires a plurality of components and manufacturing steps. Furthermore, RESEARCH DISCLOSURE, No. 268, August 1986, page 455, Emsworth, Hampshire, GB, provides a display with a grounded conductive bezel in order to protect the display from electrostatical discharge. SUMMARY OF THE INVENTION It is an object of the present invention to provide a display capable of achieving decreases in the number of components and assemblies and a high reliability. It is another object of the present invention to provide a display with a good appearance. The invention resides in a display of the kind described in claim 1. Particular embodiments of the invention are set out in the dependent claims 2 to 6. Since the conductive pattern for discharging the static electricity is formed on the board, particularly in a region in which the base and cover members forming the casing engage with each other, this display has a smaller number of components and assemblies than a display employing a metal frame and can be manufactured at lower cost. Further, few poor contacts of the conductive pattern allow provision of a display with enhanced reliability. Furthermore, since the side panel of the casing having the display window extends over the display face of the display element, no circuit or board for allowing the display element to display can be seen externally, resulting in a superior appearance of the display. Moreover, the integral formation of the side panel with the casing results in a simplified structure of the display. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded perspective view of a display of one embodiment of the present invention; Fig. 2 is a sectional view of the display of one embodiment of the present invention; Fig. 3 is a perspective view of a printed wiring board constituting the display of one embodiment of the present invention; Fig. 4 is a perspective view illustrating a path for a static electricity to enter in the display to which the present invention is applied; and Fig. 5 is a perspective view illustrating another path for a static electricity to enter and to be discharged, different from the one shown in Fig. 4. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figs. 1 and 2, a casing 1 made of synthetic resin comprises a box-type casing 2 which has an opening portion 2a at its front portion and has its upper portion released, and a cover 3 attached onto an upper portion of the box-type casing 2. Bosses 4a and 4b are provided in a central portion within the box-type casing 2, and bosses 5a and 5b are provided at its rear portion. Holes 6a and 6b are provided in the cover 3 corresponding to the bosses 4a and 4b, and holes 7a and 7b are provided corresponding to the bosses 5a and 5b. After a printed wiring board on which a display element (which will be described later) is mounted is attached to the box-type casing 2, the bosses 4a, 4b, 5a and 5b are fit respectively into the holes 6a, 6b, 7a and 7b of the cover 3, and then portions of the bosses are deformed or melted by heat. Accordingly, the cover 3 is fixed to the box-type casing or base member 2. The display element 8 has seven segments formed of light emitting diodes and is attached to the printed wiring board 9. The printed wiring board 9 is inserted into a guide 10 formed in the box-type casing 2. When the printed wiring board 9 is inserted into the guide 10, a display face 81 of the display element 8 faces a display window 2b stretching to the opening portion 2a. A frame (or side panel)11a formed with the box-type casing 2 is provided at the front face of the box-type casing 2, and a frame 11b integrally formed with the cover 3 is provided at the front face of the cover 3. The frames 11a and 11b define the display window 2b. A tapered end face 12 is formed at an upper end of the frame 11a, and an inclined end face 13 corresponding to the end face 12 is formed at a lower end of the frame 11b. When the cover 3 is attached to the box-type casing 2, the end face 12 of the frame 11a is adhered to the end face 13 of the frame 11b, as shown in Fig. 2, thus forming engagement portions of members 2,3. A printed wiring board 14 is provided at a right angle to the printed wiring board 9. Circular holes 15a and 15b are formed at a rear portion of the printed wiring board 14. The bosses 5a and 5b are fit respectively in these circular holes 15a and 15b of the printed wiring board 14. Thus, the printed wiring board 14 is carried within the box-type casing 2. On the printed wiring board 14 is mounted a control circuit element 16 for displaying an external input signal on the display element 8, and the like, and is electrically connected to the printed wiring board 9. At the rear end portion of the printed wiring board 14 is formed a terminal pattern 17 for connecting the display to an external cable. The printed wiring boards 9 and 14 are mechanically connected by employing solder and the like. Referring to Figs. 1 and 3, a conductive pattern 18 for discharging a static electricity is formed at one side out of four sides of the printed wiring board 9, the side corresponding to the end faces 12 and 13 being fitting portions of the box-type casing 2 and the cover 3. The conductive pattern 18 and an earth terminal 17a included in the terminal pattern 17 are electrically connected to each other by a lead pattern 19 formed on the printed wiring board 14. A colored filter member 20 is detachably fixed to the casing 1. Thus, as shown in Fig. 2, protrusions 21 are respectively formed on the box-type casing 2 and the cover 3, and holes 22 engageable with the protrusions 21 are formed in the colored filter member 20. Projection pieces 23 and protruding portions 26 are formed at the lower part of the box-type casing 2, and holes 25 and 27 are formed at their respective upper portions. Holes 24 are formed in the cover 3 corresponding to the holes 25. In case of using a plurality of displays connected as shown in Fig. 4, the protruding portions 26 formed on the box-type casing 2 of a display A are inserted into the holes 27 formed in the box-type casing 2 of an adjacent display B. Thus, these displays are positioned. The projection pieces 23 of the display A engage from the inside with the holes 25 of the box-type casing 2 of the display B through the holes 24 formed in the cover 3. As a result, the displays A and B are connected. In the display structured as above, when an external input signal is accepted in the printed wiring board 14 through the terminal pattern 17, a circuit provided on the printed wiring board 14 causes the display element 8 mounted on the printed wiring board 9 to be driven, and then the input signal is displayed by the 7-segment light emitting element. A display of the display element 8 is externally viewed through the display window 2b. The display element 8 is enclosed by the frames 11a and 11b, as shown in Fig. 2, and thus the printed wiring board 9 in the casing 1 cannot be seen from the outside through the filter member 20. Therefore, the display can retain a good appearance in design. In addition, the frames 11a and 11b are integrally formed with the box-type casing 2 and the cover 3, respectively, resulting in a decrease in the number of components and a simplification in structure, compared to the case that the frames 11a and 11b are formed separately from the box-type casing 2 and the cover 3. Further, it is also possible to attach a rating plate for displaying the standard of the display, and the like onto the frames 11a and 11b. Next, a description will be given on a path for a charge to enter and a path for discharge in case that a portion of a human body electrostatically charged is in proximate to or in contact with the display in use. In using the plurality of connected displays mounted on a panel 40 such as of a control board, as shown in Fig. 4, a charge of the human body enters through gaps between the displays into the casing 1 through the end faces 12 and 13 being the fitting portions of the box-type casing 2 and the cover 3 as shown by the chain dotted arrow. This charge is discharged to the outside through the conductive pattern 18, the lead pattern 19 and the earth terminal 17a. Therefore, the circuits on the printed wiring boards 9 and 14 are protected from a static electricity, thus retaining a suitable operation. The static electricity, as described above, passes through the end faces 12 and 13 of the frames 11a and 11b and enters in the casing 1. Locating the discharge pattern 18 on this entry path ensures that the charge flows into the discharge pattern 18 and then flows out of the display. Since the end faces 12 and 13 are adhered to each other, the charge is hard to enter the casing 1. When the display is employed alone, the charge enters between the display and the panel. Since the path after the entry of the charge is the same as in the above case, the description will not be repeated. Fig. 5 shows another path different from the one in the above described case. Referring to Fig. 5, a charge enters through the holes 27 and their peripheries provided in the box-type casing 2 and reaches the printed wiring board 9, passing through the side face of the guide 10. Also in this case, the charge flows out of the display through the conductive pattern 18 provided in most proximate to the holes 27, and hence does not affect the circuit. While the configuration of the above described conductive pattern 18 is one example, any configuration which can flow the charge entering the casing 1 may be substituted for the conductive pattern 18. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being limited only by the terms of the appended claims.

Claims: A display comprising: a casing (1) including a base member (2) and a cover member (3) in pair with said base member (2); at the front face of said base member (2) and at the front face of said cover member (3) a first side panel portion (11a) and a second side panel portion (11b) being integrally formed, respectively; a display window (2b) which is defined by said side panel portions (11a, 11b) and in which a display face (81) of a display element (8) is arranged, with said side panel portions extending over the display face (81) and enclosing said display element (8); engagement portions (12, 13) provided at fitting portions of said first and second side panel portions (11a, 11b); and a board (9, 14) provided in said casing (1); said board (9, 14) comprising a conductive pattern (18, 19) for discharging a static electricity entering the casing (1) and including thereon an electrical circuit (16) for operating said display element (8). A display in accordance with claim 1, wherein said conductive pattern (18) is formed at a side of the board (9, 14) corresponding to a region in which said engaging portions (12, 13) are provided. A display in accordance with claim 1 or 2, wherein said engagement portion (12) of said first panel portion (11a) has an inclined face inclining at a predetermined angle; and said engagement portion (13) of said second panel portion (11b) has an inclined face which can adhere to the inclined face of said first panel portion (11a). A display in accordance with any of claims 1 to 3, wherein said casing (1) comprises connecting means (23, 24, 25, 26 and 27) for connecting said display to another display (A, B). A display in accordance with claim 4, wherein said connecting means comprise protruding pieces (23, 26) at the lower part of the base member (2) and corresponding holes (24, 27) at the upper part of the base member (2). A display in accordance with any preceding claim, wherein said display element (8) is covered by a filter member (20) being detachably fixed to said casing (1), protrusions (21) engaging into holes (22).

Inventors: EHARA-KITAMURA SAWAKO, KAZUSAKA SHOJI, OHMORI KOUJI, EHARA - KITAMURA, SAWAKO, KAZUSAKA, SHOJI, OHMORI, KOUJI
Applicants: OMRON TATEISI ELECTRONICS CO, OMRON CORPORATION
Application year: 1989
Main classification: G09F9
IPC codes: H05K1, G09F9, H05K3