KEYBOARD HAVING LOWER CASING WITH INTEGRAL UPRAISED PORTION FOR SUPPORTING PC BOARD

Abstract: A keyboard including an upper casing (2) which has a key-holder member (4) for movably supporting keys (8) with a movable electrode (13), and a lower casing (4) which has an integrally formed upraised portion (12) which defines a recess (12b) open in the bottom wall (3a) of the lower casing. A printed-circuit board (14) is held in direct contact with the top wall (12a) of the upraised portion of the lower casing such that stationary electrodes (18) on the printed-circuit board are opposite to the corresponding movable electrodes. The printed-circuit board may be a flexible film-like member, on which an elastic sheet (16) having elastically collapsible cap portions (15) is disposed such that the cap portions cooperate with the film-like printed-circuit board to form enclosures (21), and such that the cap portions collapse upon operation of the keys, for moving of the movable electrodes toward the stationary electrodes. The film-like board has an air vent (19) communicating with each enclosure, while the top wall of the upraised portion of the lower casing has a groove (20) communicating with the air vent, so that the air in the enclosure may flow into the groove through the air vent upon collapse of the cap portion.

Description: The present invention relates to improvements in a keyboard used as a data input device for a typewriter and other instruments, and to improvements in key switches incorporated in such a keyboard. In a known keyboard, a printed-circuit board having circuit patterns including stationary electrodes is retained in place by a downwardly curved, rigid retainer plate which rests on a suitable support structure provided on a lower casing of the keyboard. An example of this type of keyboard is shown in U.S. Pat. Nos. 4,560,844 and 4,560,845 owned by the assignee of the present application, and another entity. In the keyboard disclosed in these Patents, the support structure consists of a plurality of spaced-apart support walls which are either integral with the lower casing of the keyboard, or separate from but fixed to the lower casing. In the former case, the retainer plate resting on the support walls is fastened to the upper casing. In the latter case, the retainer plate is fastened to the support walls. In the keyboard of the type indicated above, the use of the retainer plate results in an increase in the overall thickness of the keyboard. In particular, where the jumper wires connecting adjacent circuit patterns pass through slots formed in the retainer plate, a space must be provided between the retainer plate and the bottom of the lower casing. Therefore, the retainer plate cannot be supported directly on the bottom wall of the lower casing. This leads to a relatively large height of the operating face of the key switches from the bottom of the keyboard. In assembling the keyboard, the retainer plate must be fastened to the upper casing or to the support walls. If the support walls are members separate from the lower casing, the support walls must be fixed to the lower casing. This procedure is time-consuming. Usually, a movable electrode is secured to the underside of a top wall of each of multiple elastically collapsible cap portions formed on an elastic sheet which rests on the printed-circuit board, such that each cap portion cooperates with the corresponding area of the printed circuit board to define an enclosure in which the movable electrode and the stationary electrodes are accommodated. Normally, the movable electrode secured to the top wall of the cap portion is spaced apart from the stationary electrodes on the printed-circuit board. Multiple keys are supported movably in their axial direction between non-operated and operated positions. When each key is depressed to its operated position, the corresponding cap portion is pressed by the key, and elastically collapses, whereby the movable electrode is moved toward the stationary electrodes. Thus, a key switch consisting of the key and the movable and stationary electrodes is closed, producing an output corresponding to the operated key. For easy collapse of the cap portions of the elastic sheet upon depression of the keys, it is a conventional practice to provide the enclosures formed by the cap portions and the printed-circuit board with air vents for allowing the air in the enclosures to escape when the cap portions collapse. Such air vents are formed in the base of the elastic sheet; more precisely, air vent grooves are formed in the lower surface of the elastic sheet contacting the printed-circuit board, such that the grooves communicate with the enclosures. However, it has been found difficult for such air vent grooves to serve in a satisfactory manner. Namely, the grooves cannot be given a sufficient cross sectional area. To give the grooves a sufficient depth, the base of the elastic sheet must have a large thickness. This not only increases the cost of the elastic sheet, but also leads to a decrease in the operating stroke of the key unless the height of the cap portions is increased. If the height of the cap portions is increased, the overall thickness of the keyboard is increased. While the cross sectional area of the air vent grooves may be increased by increasing the width of the grooves, this is not practical, either. That is, such relatively wide grooves may be partially closed due to elastic deformation of the base of the elastic sheet by a force with which the elastic sheet is held against the printed-circuit board, or by a force exerted on the base of the elastic sheet when the cap portions are depressed by the keys. Thus, the air vent grooves have a relatively small effective cross sectional area, making it difficult to accomplish a high rate of escape flow of the air through the air vents from the enclosures. Further, the conventional air vents cannot function at the end of an operating stroke of the key, or at the end of a collapse of the cap portion. As indicated at P in Fig. 3, the peripheral part of the cap portion contacts the upper surface of the printed-circuit board, a short time before the cap portion has completely collapsed. In this condition, the peripheral part contacting the printed-circuit board blocks an air flow from the central portion of the enclosure into the air vent grooves. It is therefore an object of the present invention to provide a keyboard which is simple in construction and easy to assemble, and which has a comparatively small overall thickness. It is another object of the present invention to provide a keyboard which has simple and effective air breather means for allowing air to escape from enclosures defined by collapsible cap portions of an elastic sheet and the corresponding areas of a printed-circuit board, during collapse of the cap portions upon depression of keys of key switches. A further object of the present invention is the provision of a keyboard which has such air breather means but has a relatively small thickness. According to the present invention, there is provided a keyboard having an upper casing and a lower casing cooperating to form a keyboard frame, multiple keys projecting through the upper casing and guides to guide the keys for up and down movement to close switching circuits provided on a printed-circuit board located beneath the keys, the printed circuit board being supported by support means, characterised in that: said lower casing has an integral bottom wall including an integrally formed upraised portion which defines a downwardly open recess in a central part of the bottom wall, said upraised portion having a top wall which bounds the upper side of said recess, said top wall of said upraised portion being disposed below said printed-circuit board and providing said support means for supporting, at an upper surface thereof, said printed-circuit board. In the keyboard of the present invention constructed as described above, a conventionally used rigid retainer plate is not used for supporting the printed-circuit board. The elimination of the retainer plate provides a reduction in the overall thickness of the keyboard, simplifies the construction, and permits easier assembling. According to one preferred feature of the invention, the top wall of the upraised portion of the lower casing has a slight downward curvature in a plane parallel to a transverse direction of the keyboard and perpendicular to the upraised portion. According to another preferred feature of the invention, the top wall of the upraised portion of the lower casing is inclined in a plane parallel to a transverse direction of the keyboard such that a height of an upper surface of the top wall from the bottom wall increases in a direction from a front toward a rear of the keyboard. The lower casing having the upraised portion may be formed of a synthetic resin. Similarly, the upper casing and the key-holder member may consist of a one-piece structure formed of a synthetic resin. According to a further feature of the invention, said multiple keys have the same size and shape, and said upper frame includes a key-holder portion for movably supporting said multiple keys, said top wall of the upraised portion of said lower casing is downwardly curved in a plane perpendicular to a longitudinal direction of the keyboard, said key-holder portion including a downwardly curved base portion which has substantially the same curvature as said top wall, said key-holder portion supporting said keys such that a surface generally defined by top faces of said keys is downwardly curved in said plane. According to a further preferred feature of the invention, the printed-circuit board comprises a film substrate, and circuit patterns which include the stationary electrodes and which are disposed on an upper surface of the film substrate. The printed-circuit board rests on the support plate such that a lower surface of the film substrate is in direct contact with an upper surface of the support plate, that is, the top wall of the upraised portion of the bottom wall of the lower casing. Thus, no space is provided between the printed-circuit board and the bottom of the lower casing. In this case, the wires connecting the circuit patterns may be disposed along the edges of the printed-circuit board. Further, since the film substrate is comparatively thin, the thickness of the printed-circuit board is accordingly reduced. The above and other objects, features and advantages of the present invention will be better understood by reading the following detailed description of a preferred embodiment of the invention, when considered in connection with the accompanying drawings, in which: Fig. 1 is an elevational view in cross section of one embodiment of a keyboard of the invention; Fig. 2 is an elevational view of a key switch incorporated in the keyboard of Fig. 1; and Fig. 3 is an elevational view of the key switch of Fig. 2, showing a state in which the key is depressed. The present invention will be described in detail, by reference to the accompanying drawings showing one embodiment of the keyboard of the invention, which incorporates many key switches. Referring to the cross sectional view of Fig. 1, the keyboard has an upper casing 2 and a lower casing 3, which are both formed of a synthetic resin, and which engage each other to form a keyboard frame 1. The top wall of the upper casing 2 has a central rectangular aperture whose bottom is formed as a key-holder member 4 for movably supporting a multiplicity of keys 8, as described below. The key-holder member 4 has a base portion 4a which is downwardly curved in a plane parallel to the transverse direction of the keyboard (in the plane of Fig. 1), such that the base portion 4a descends in a direction from the rear (righ-hand side end of Fig. 1) toward the front (left-hand side end of Fig. 1) of the keyboard. Referring further to Fig. 2, each key 8 consists of a keystem 6 and a keytop 5 fixedly engaging the upper end of the keystem 6. The key-holder member 4 has a multiplicity of annular stem guides 10 integrally formed on the upper surface of the downwardly curved base portion 4a. These stem guides 10 are arranged in spaced-apart relation with each other, in five parallel straight rows which extend in the longitudinal direction of the keyboard. The keys 8 are supported by the key-holder member 4, such that the keystems 6 slidably extend through the respective stem guides 10. Thus, the keys 8 are also disposed in five parallel straight rows in the longitudinal direction of the keyboard. For preventing rotation of each key 8, the corresponding stem guide 10 has a recess (not shown), while the keystem 6 has a projection (not shown) which fits in the recess in the stem guide 10. The key-holder member 4 further has a multiplicity of integral annular downward protrusions 11 corresponding to the multiple keys 8. The protrusions 11 extend from the lower surface of the downwardly curved base portion 4a such that the protrusions 11 are concentric with the corresponding stem guides 10. The lower casing 3 has an integral bottom wall 3a which includes an integrally formed upraised portion 12. This upraised portion faces the key-holder member 4 of the upper casing 2. The upraised portion 12 is formed so as to define a recess 12b which is open in a central part of the bottom wall 3a. The upraised portion 12 has a top wall 12a which serves as a support plate which will be described. The top wall or support plate 12a has substantially the same downward curvature as the downwardly curved base portion 4a of the key-holder member 4. The support plate 12a supports a flexible film-like printed-circuit board 14 such that the lower surface of the board 14 is in direct contact with the upper surface of the support plate 12a. On the upper surface of the film substrate of the printed-circuit board 14, there are formed circuit patterns which include multiple pairs of stationary electrodes 13. On the upper surface of the printed-circuit board 14, there is disposed an elastic sheet 16 made of a silicone rubber. The elastic sheet 16 has a multiplicity of domed, elastically collapsible cap portions 15 which correspond to the multiple keys 8. The cap portions are located opposite to the pairs of stationary electrode 13. Each cap portion 15 cooperates with the corresponding area of the printed-circuit board 14 to define an enclosure 21 in which the corresponding pair of stationary electrodes 13 are accommodated. Each cap portion 15 formed on the elastic sheet 16 has a top wall 15a to which the keystem 6 of the corresponding key 8 is fixed in abutting relation with each other. As previously described, the thus supported keystem 6 slidably extends through the stem guide 10 of the key-holder member 4. Normally, the keytop 5 fixed to the keystem 6 is maintained in its non-operated position of Fig. 2, due to an elastic force of the cap portion 15. Since all of the keys 8 have the same size and shape, an operating surface 9 of the keys 8 which is generally defined by the top faces of the keytops 5 is downwardly curved following the curvature of the support plate 12a, i.e., the top wall of the upraised portion 12 of the lower casing 3. The top wall 15a of each cap portion 15 has a sponge member 17 fixed to its inner surface, and a movable electrode 18 fixed to the sponge member 17 such that the movable electrode 18 is opposite to the corresponding pair of stationary electrodes 13, 13 formed on the upper surface of the printed-circuit board 14. In the non-operated position of Fig. 2, the movable electrode 18 is spaced away from the stationary electrodes 13. The key 8, stationary electrodes 13, movable electrode 18, etc. constitute each key switch. The flexible film-like printed-circuit board 14 has two air vents 19, 19 formed through the thickness in each of the areas covered by the cap portions 15. More specifically, the two air vents 19 are formed adjacent to the respective two stationary electrodes 13 in each enclosure 21, and are positioned radially outside the stationary electrodes 13 with respect to the circular opening of the domed cap portion 15. The air vents 19 for each key 8 communicate with the corresponding enclosure 21, and the air vents 19 for each row of the keys 8 lie on a straight line in the longitudinal direction of the keyboard. As described later, the air vents 19 are positioned so that a substantially entire volume of air in the enclosure 21 may escape through these vents. The support plate 12a has five parallel grooves 20 formed in its upper surface, extending parallel to the rows of the keys 8, such that each groove 20 communicates with the air vents 19, 19 corresponding to the keys 8 in each row. In this arrangement, the air in the enclosures 21 may flow into the appropriate grooves 20 through the air vents 19, when the cap portions 15 elastically collapse upon depression of the keys 8 to the operated position of Fig. 3. As a result of this collapse, a peripheral wall 15b of the cap portion 15 adjacent to the open end of the cap 15 contacts the upper surface of the printed-circuit board 14, along a closed loop which is located inside the periphery of the open end of the cap portion 15, as indicated at P in Fig. 3. For better air breathing, the location of the air vents 19, 19 is determined so that at least a part of each air vent 19 is located inside the above-indicated closed loop that defines the line of contact between the peripheral wall 15a of the cap portion 15 and the upper surface of the printed-circuit board 14. The operation of the key switch will be described. When the key 8 is depressed at its keytop 5 against an elastic force of the cap portion 15 of the elastic sheet 16, the key 8 is moved downward with the keystem 6 being slidably guided by the stem guide 10 of the key-holder member 4. As the keystem 6 is moved down and the cap portion 15 elastically collapses, the movable electrode 18 fixed to the top wall 15a of the cap portion 15 via the sponge member 17 is moved down toward the pair of stationary electrodes 13 on the printed-circuit board 14. Eventually, the movable electrode 18 contacts the two spaced-apart stationary electrodes 13. Thus, the stationary electrodes 13 are capacitively coupled to each other, whereby a signal is transmitted from one of the stationary electrodes 13 to the other as a key signal. As the cap portion 15 collapses, the air within the enclosure 21 escapes into the appropriate groove 20 via the air vents 19. Consequently, the key 8 may be easily moved to its operated position of Fig. 3. Further, since the movable electrode 18 is fixed to the cap portion 15 via the sponge member 17 in this embodiment, the sponge member 17 elastically yields if a depression force continuously acts on the keytop 5 after the movable electrode 18 has contacted the stationary electrodes 13 with the cap portion 15 considerably deformed. This elastic yielding of the sponge member 17 assures complete contact of the movable electrode 18 with the stationary electrodes 13, and reliable switching operation of the key switch. When a depression force is released from the keytop 5, the key 8 is moved toward its non-operated position, by the resilient forces of the sponge member 17 and the cap portion 15, as the air is sucked into the enclosure 21 through the groove 20 and the air vents 19. As a result, the movable electrode 18 is separated from the stationary electrodes 13, whereby the key switch is opened. It is to be understood that the invention is not limited to the details of the illustrated embodiment, but may be embodied with various changes and modifications, for example, in connection with the configuration and location of the air vents 19 and grooves 20.

Claims: A keyboard having an upper casing (2) and a lower casing (3) cooperating to form a keyboard frame (1), multiple keys projecting through the upper casing (8) and guides (10) to guide the keys for up and down movement to close switching circuits (13) provided on a printed-circuit board (14) located beneath the keys, the printed circuit board being supported by support means, characterised in that: said lower casing (3) has an integral bottom wall (3a) including an integrally formed upraised portion (12) which defines a downwardly open recess (12b) in a central part of the bottom wall, said upraised portion having a top wall (12a) which bounds the upper side of said recess, said top wall of said upraised portion being disposed below said printed-circuit board (14) and providing said support means for supporting, at an upper surface thereof, said printed-circuit board (14). A keyboard according to claim 1, wherein said printed-circuit board (14) is a flexible film-like member. A keyboard according to claim 1 or 2, wherein said top wall (12a) of said upraised portion (12) of the lower casing (3) has a slight downward curvature in a plane parallel to a transverse direction of the keyboard and perpendicular to said upraised portion. A keyboard according to claim 3, wherein said top wall (12a) supports said printed-circuit board (14) such that a lower surface of the printed-circuit board is in direct contact with the upper surface of said top wall (12a) and follows said slight downward curvature. A keyboard according to any one of claims 1 to 4, wherein said top wall (12a) of said upraised portion (12) of the lower casing is inclined in a plane parallel to a transverse direction of the keyboard such that the height of the upper surface of said top wall from said bottom wall (3a) increases in a direction from the front toward the rear of the keyboard. A keyboard according to any one of claims 1 to 5, wherein said lower casing (3) having said upraised portion (12) is formed of a synthetic resin. A keyboard according to any one of claims 1 to 6, wherein said multiple keys (8) have the same size and shape, and said upper frame (2) includes a key-holder portion (4) for movably supporting said multiple keys, said top wall (12a) of the upraised portion (12) of said lower casing (3) is downwardly curved in a plane perpendicular to a longitudinal direction of the keyboard, said key-holder portion (4) including a downwardly curved base portion (4a) which has substantially the same curvature as said top wall (12a), said key-holder portion supporting said keys such that a surface (9) generally defined by top faces of said keys is downwardly curved in said plane. A keyboard according to any one of claims 1 to 7, wherein each of said multiple keys (8) is moved with a movable electrode (18) which is movably supported by a cap portion (15) of an elastic sheet (16) disposed on said printed-circuit board (14), said movable electrode closing a corresponding one of said switching circuits (13) when the corresponding key is depressed. A keyboard according to claim 8, wherein said printed-circuit board (14) has an air vent (19) formed through its thickness in communication with an enclosure (21) which is partially defined by said cap portion (15) of said elastic sheet (16). A keyboard according to claim 9, wherein said top wall (12a) of said upraised portion (12) of said lower casing (3) has a groove (20) formed in the upper surface, in communication with enclosure (21) through said air vent (19). A keyboard according to claim 10, wherein said groove (20) communicates with the enclosures (21) which correspond to at least two of said multiple keys (8). A keyboard according to claim 11, wherein said multiple keys (8) are arranged in at least three parallel straight rows which extend in the longitudinal direction of the keyboard, said groove (20) extending in said longitudinal direction, corresponding to each of said at least three straight rows of said keys. A keyboard according to claim 12, wherein said groove (20) communicates with the enclosures (21) formed by the cap portions (15) corresponding to said each straight row of the keys. A keyboard according to any one of claims 9 to 13, wherein said cap portion (15) of said elastic sheet (16) has a peripheral wall (15b) adjacent to an opening thereof at which said cap portion is closed by said printed-circuit board (14) to form said enclosure (21), said peripheral wall contacting, upon collapse of said cap portion, the upper surface of the printed-circuit board, along a closed loop (P) which is located inside an inner periphery of said cap portion which defines said opening thereof, said air vent (19) being positioned such that at least a part of the air vent is located inside said closed loop (P) of said peripheral wall (15b).

Inventors: FUKAO, SATOSHI, KAKO, MITSUMASA, SUZUKI, MAKOTO
Applicants: BROTHER KOGYO KABUSHIKI KAISHA
Application year: 1987
Main classification: H01H13
IPC codes: H01H13