Abstract: A key switch assembly for direct mounting on a PCB or similar substrate. The key switch has a body with depending mounting pin having retainers thereon to secure the key switch at apertures in the substrate. The key switch body has a hinged key and includes a snappable dome moveable from a non-actuated position to an actuated position in direct contact with conductive elements in the substrate by manual depression of a key.

Abstract: A low profile switch or keypad has one or more touch buttons of circular or polygonal shape in plan formed integrally with and raised from a surrounding membrane of elastomeric material by a wall of resiliently deformable material of thickness and angle relative to the membrane so that the wall can flex under finger pressure on the or each button without deflecting the surrounding membrane. The membrane and at least the periphery of the button are relatively thick and the wall is relatively thin so that deformation during the keystroke is localized in the wall. The length of the wall is about equal to the keystroke and is relatively small compared to the width of the touch button. The junction between the wall and the membrane is located a distance greater than the keystroke above the lower surfaces of the membrane so that the wall passes overcenter during the keystroke resulting in a change in tactile sensation.

Abstract: A hand-held calculator for use in conducting classroom demonstrations of the operation thereof, including use of the operation instruction key means. The calculator comprises a frame, a keyboard section, data processing means and a display section and where both the keyboard and display sections are transparent to permit images thereof to be projected on a screen for teaching purposes.

Abstract: An electrical switch assembly comprises a first, domed, flexible contact member plus at least one second, flexible, finger-type contact member positioned under the first contact member in normally spaced relation thereto. Actuator means are provided for pressing the first, domed contact member into contact with the second contact member to actuate the switch assembly. In accordance with this invention the second, flexible, finger-type contact member defines an end portion which is bent to permit increased-area contact with the first contact member when the first contact member is pressed into contact with the second contact member. This also provides improved wiping action between the first and second contacts as the increased-area contact is made and broken for removal of carbon build-up and the like.

Abstract: A keyboard of a membrane contact type comprises a membrane contact unit having movable contacts, fixed contacts disposed respectively opposite to the movable contacts, and a printed wiring board having electronic circuit elements and provided with printed wiring lines. The membrane contact unit comprises a flexible, insulating, membranous substrate having movable contacts formed in a movable contact section and fixed contacts formed in a fixed contact section demarcated by a folding line, in the same surface as the movable contacts and arranged symmetrically about the folding line. First and second wiring lines connect the movable contacts and the fixed contacts respectively in a predetermined connecting pattern. A first terminal section having first terminals is connected respectively to the first wiring lines, and a second terminal section having second terminals is connected respectively to the second wiring lines. The first and second terminal sections are formed near the folding line.

Abstract: A keyboard apparatus including a plurality of nested, identically configured, keys for use in computer keyboards, typewriters, electronic switches and the like. The keyboard apparatus preferably includes a chassis having a plurality of alignment pins to receive a plurality of nested keys and a plurality of electronic switches to be activated by the keys.

Abstract: A keyboard including a plurality of key switches and a plurality of keys mounted slidably on the keyboard over the key switches, each key overlying one of the key switches and the top of each key provided with a marking, upon each key being depressed into engagement with the underlying key switch, the key switch being operated to provide an indication of the marking provided on the top of the depressed key, and the number of plurality of keys being less in number by one than that of the key switches to provide a vacant key space on the keyboard to allow the keys to slide freely two-dimensionally over the key switches and through the vacent key space to permit each key to be slid over and overlie each of the key switches in a pattern as desired.

Abstract: A switch element including a ribbon-type spring member having a plurality of interconnected inner and outer loops and stressed to cause the member to take a substantially dome-shaped configuration and the loops to store a predetermined amount of energy. The spring member is made of electrically conductive material, and adapted to coact with contacts to open and close a circuit and to define a snap-acting function for the element that may be used for monostable or bistable switch operation.

Abstract: A combined calculator and puzzle game device including a calculator cover-board which is provided with guide pieces confined to intersecting guide grooves. Game pieces which have projecting necks are mounted on the guide pieces by inserting the projecting necks into the guide grooves allowing them to be slid along the guide grooves, but not be removed. The game pieces can be rearranged on the cover board to bear a particular pattern or a combination of characters. When the game pieces are depressed, they push rubber keys placed therebelow so as to operate the calculator.

Abstract: A membrane keyboard blockout apparatus for a keyboard having an array of a plurality of flexible key members in respective ones of a plurality of apertures arranged in a grid forming the keyboard includes a cover plate dimensioned to span a flexible key member and to provide a tight fit within an aperture defining a key member. The cover plate has a thickness providing a substantially inflexible configuration in response to normal operator manipulation and a plurality of corner support pedestals contacting respective corners of the flexible key member when the cover plate is inserted in a key member aperture. Thus, the pedestals provide a support between the cover plate and the flexible key member at the edges of the key member to preclude, in combination with the inflexible structural characteristic of the cover, an actuation of the flexible key member under the cover.

Abstract: A full sized electronic keyboard with full travel keybuttons provides switches for controlling an electronic typewriter or for controlling other devices. The keyboard has a structure designed for reducing part count and switch component part size and for simplifying assembly to minimize manufacturing cost. The structure has integral one piece parts for accommodating several keybutton actions. The integral one piece parts include a main frame, a sheet steel spring, a rubber dome switch member, and a printed circuit switch panel.

Abstract: Novel composite products formed by bonding a flowable elastomer, such as silicone rubber, to a transparent or translucent silicone rubber preform are described. These products have utility in the field of electromechanical devices such as an illuminated switch or key or as a transparent rubber window permitting view of an underlying display device. The bond between the preformed elastomer and the flowable elastomeric material is improved by post-curing the preform for about 4 hours at about 200.degree. C. prior to contact of the flowable material with the preform. Methods of fabrication of the novel composites are also disclosed.

Abstract: The invention is directed to a membrane switch comprising a first layer 30 of flexible insulating material and a second layer 50 having relatively inflexible characteristics, each layer 30, 50 having an array of conductors 40, 54 disposed thereon and defining a plurality of switch point areas over a substantial portion of the respective layers. The first sheet is transparent and carries visible symbols on the inner surface thereof formed by a first layer 36 of inks printed thereon and further includes a barrier coating over such symbols to provide contrast therefore. The first array 40 of conductors is printed on the barrier coating. The second array 54 of conductors is printed on the inflexible layer.

Abstract: An elastic key top construction for supporting a key top comprising a key top push or support section on which the key top is mounted, a projection disposed below the key top support section, a first movable wall integral with the key top support section and the projection for connecting the key top support section to the projection while allowing relative movement to each, a second movable wall integral with the key top support section, the second movable wall being connected to a installment support member of the key top construction so as to allow up/down movement of the key top support section in respect to the base member.

Abstract: An electronic instrument comprises a printed circuit substrate on which electrical parts are actually mounted, a frame placed on the front side of the printed circuit substrate and having openings at least at positions corresponding to the electrical parts, a front sheet disposed at a position opposed to the printed circuit substrate with the frame interposed therebetween and provided with an adhesion margin on the peripheral portion thereof, a back sheet disposed on the back side of the printed circuit substrate and provided with an adhesion margin on the peripheral portion thereof, and an adhesive agent applied to the adhesion margins of the front sheet and the back sheet to cause the printed circuit substrate and the frame to be sandwiched between the front sheet and the back sheet.

Abstract: A keypad which prevents electrostatic discharge from occurring in electronic equipment such as printers, computers and the like. The keypad includes a switch mechanism positioned on the circuit board associated with the electronic equipment. Attached to the switch mechanism is an actuating lengthening member of sufficient length to isolate the switch mechanism from electrostatic discharge through the keypad. A light source is also positioned under the keypad and the light source has attached thereto a light conducting lengthening member of sufficient length to isolate the light source from electrostatic discharge through the keypad. A method of preventing electrostatic discharge through a keypad to a circuit board is also disclosed.

Abstract: A printed circuit board comprising a dielectric film substrate and a plurality of circuit patterns for a capacitor switch formed on said dielectric film substrate at a certain space from each other. Each of the circuit patterns comprises a switch electrode pair formed on one surface of the dielectric film substrate, a first fixed electrode connected to one of the switch electrode pair, a first lead pattern connected to the other of the switch electrode pair, a second fixed electrode formed on the other surface of the dielectric film substrate in such a manner as to be opposed to the first fixed electrode through the dielectric film substrate, said first and second fixed electrodes forming a fixed electrode pair, and a second lead pattern connected to the second fixed electrode.

Abstract: There is provided a force sensitive device comprising a first conductive layer, a second conductive layer resiliently deformable to come into contact with the first conductive layer, a certain level of voltage being applied across the first and second conductive layers, a plurality of spacing members intervening between the first conductive layer and the second conductive layer and formed of an insulating material, and a resilient top layer of an insulating material overlaid on the second conductive layer and operative to cause the second conductive layer to come into contact with the first conductive layer under a force acting on a surface portion thereof, wherein the contact portion varies in area depending upon a position of the surface portion where the force acts so that the force sensitive device produces the signal having a voltage level which varies depending upon the position where the force acts.

Abstract: A key switch structure comprises a first insulating cover having on one surface thereof a first conductive layer and an anisotropically electrical conductive layer printed on the first conductive layer, a second insulating cover having one surface arranged at a side opposite to the anisotropically electrical conductive layer on the first cover member, and a second conductive layer sandwiched between the anisotropically electrical conductive layer and the second insulating cover. At least, one of the first and second insulating covers being flexible. A depression force is selectively introduced from the other surface side of the flexible cover through the anisotropically electrical conductive layer so as to form a conductive path between the first and second conductive layers.

Abstract: Apparatus including a calculator that can also function as a horn button is provided for a motor vehicle. The apparatus is mounted on the center of the steering wheel and its downward depression actuates the horn circuit of the vehicle in the same manner as does a conventional horn button. At other times, the keys associated with the calculator portion of the provided apparatus may be operated to perform whatever calculations the operator may desire during periods of time in which the operator's attention is not required for the operation of the motor vehicle.

Abstract: A keyboard assembly is disclosed comprising a waterproof portion which includes a sheet of printed key tips mounted on a cover support member overlying an indicia sheet identifying the key tips, first and second switch-matrix electrical conductors separated by an insulator sheet mounted on printed circuit board, a plurality of light-emitting diodes mounted in the printed circuit board for selectively lighting one of the key tips when operated, a plurality of I.C. circuit elements secured to the lower surface of the printed circuit board and connected to the electrical conductors forming an electrical circuit associated with the operation of the keyboard and a key operated switching mechanism extending through the keyboard to sense light emitted from elements mounted in the lower surface of the printed circuit board for controlling the operating mode of the keyboard.

Abstract: An open-contact membrane switch element (1,2) comprising a plastic film substrate (10) carrying a first conductive circuit (13), a dielectric coating (30) applied to cover the circuit (13) on the substrate (10) in a pattern defining uncoated zones (31,32,34) around each contact (14-17) of the circuit (13), and a second conductive circuit (35) applied on the dielectric coating (30) and having conductive tracks (36,37) electrically interconnected at the uncoated zones (31,32,34) to portions of the contacts (14-17) of the first conductive circuit (13).

Abstract: A push switch having a mount base 11 made of a heat resisting and insulating material and having a recess 11a in the top surface thereof, the recess 11a receiving a plurality of contact terminals 12a, 13a disposed such that contact portions constituting at least a pair of conductor circuits are arranged in the recess, a curved push spring 14 having an inverting function and disposed in the recess 11a, and an operating portion through which the push spring 14 is operated so as to turn the switch on and off. A flexible heat resistant film 15 constituting the operating portion is attached to the mount base in a manner such as to cover the entire area of opening of the recess. With this dust proof and semi-hermetic arrangement, it is possible to prevent invasion by dusts and other foreign matters which are strictly to be kept away from the switch. The invasion by flux and molten solder also is avoided so that the switch can be manufactured by new methods such as solder dipping.

Abstract: An electronic apparatus including a cabinet, and a lens provided in the cabinet, a transparent keyboard provided on the lens, so that images of things such as letters below the electronic apparatus are magnified and can be seen from the obverse side of said electronic apparatus.

Abstract: A sealed enclosure is provided for electrical circuitry to be located in a moist environment, as near a spa. The enclosure includes a housing of electrical insulating material, a display overlay adhesively bonded to the housing and covering certain openings in the housing for switches and displays, and a retaining bezel over the graphic overlay. Relief porting is provided in the bezel, and preferably also through a flange in a contiguous portion of the housing for assuring that water deposited on the display overlay will be drained away and thus not degrade the seal between the overlay and the housing.

Abstract: A switch control device for controlling a plurality of switches for actuating apparatuses of a motor vehicle, respectively, including at least one stop mode switch allowed to be operated only in a stop state of the motor vehicle and at least one running mode switch allowed to be operated in a running state of the motor vehicle and provided separately from the stop mode switch such that input operation of the stop mode switch and the running mode switch is regulated on the basis of whether the motor vehicle is in the stop state or in the running state.

Abstract: An improved transparent touch panel membrane switch for use and shielding in front of a visual display terminal is disclosed. The switch is made up of a plurality of plastic sheets arrayed substantially parallel to one another in a sandwich configuration. The outermost of the sheets has an antireflective hardcoat. Two adjacent but spaced apart inner sheets provide the electrical contact through transparent low reflectance conductive metal coatings. The switch additionally contains a further inner antireflective transparent electrically conductive coating which provides shielding against the passage of electromagnetic and radio frequency interference through the membrane switch. The layers in this switch all contribute to a relatively low transmittance of back lighting from the visual display terminal but also significantly reduce reflectance such that the overall signal-to-noise ratio is substantially enhanced.

Abstract: The first example of a keyboard apparatus of the invention intends to prevent the inclination and shake of a key button by forming retaining claws so as to project downwardly at locations near the corners of the quadrangular key button. The second example intends to prevent to shake of a small-sized key button by arranging the retaining claws formed for the small key button on a diagonal line of the key button, thereby elongating the distance between the retaining claws. The third example intends to automatically adjust the center of the position of the key button by forming the portion to restrict the top dead point of a key button so as to have almost a complementary zigzag shape.

Abstract: A key switch assembly for direct mounting on a PCB or similar substrate. The key switch has a body with depending mounting pin having retainers thereon to secure the key switch at apertures in the substrate. The key switch body includes a snappable dome moveable from a non-actuated position to an actuated position in direct contact with conductive elements in the substrate by manual depression of a key.

Abstract: Disclosed in a thin type electronic instrument having a structure comprising a circuit base plate for mounting an integrated circuit chip thereon and a power source battery for supplying power to the circuit base plate sandwiched between a pair of synthetic resin sheets opposed to each other, with the pair of synthetic resin sheets being plastered at the peripheral portions thereof, characterized in that a substrate made of a metal is interposed between the pair of synthetic resin sheet.The thin type electronic instrument of the present invention is improved in mechanical durability against mechanical shock such as warping or torsion by a stress during carrying or usage, whereby erroneous actuation or breaking can be inhibited.

Abstract: An apparatus for controlling the connection of an electrical module to an electrical receptacle. The module is provided with a power switch having a movable switch activator for inhibiting a flow of current to the electrical module when the switch activator is in a first position and for flowing a current to the electrical module when the switch activator is in a second position. The switch activator has a side portion which extends from a surface of the module when the switch activator is in the second position, but which does not extend from the surface of the module when the switch activator is in the first position. A lock member is disposed on a surface of the module and is slidable to a retracted position when the switch activator is in the first position. The lock member extends from the module and abuts against the side portion of the switch activator when the switch activator is in the second position.

Abstract: An operator panel for a data input unit has a printed circuit board on which key switches corresponding to a number of commodities are arrayed. A flexible sheet is bonded over the keytops of the key switches. Photographs depicting the external appearance and shape of the commodities, or sketches showing the characteristics of the commodities, are printed on the flexible sheet at positions overlying respective ones of the keytops. The sheet has enough flexibility to enable operation of the key switches without hindrance. To input data relating to a desired commodity, an operator finds the photograph or sketch of the commodity on the flexible sheet and presses this portion of the sheet, thereby pressing the underlying commodity key switch to effect the entry of the data.

Abstract: A sub-assembly (20) of a housing for electronic equipment and which is capable of carrying electronic components. The sub-assembly (20) comprises an injection moulded plastics body having an area (21) in which a regular array of apertures (22) are formed, pushbuttons (23) being mounted in each aperture of the regular array of apertures. The pushbuttons (23) are shaped and dimensioned so that they cover the whole of the first area (21), the gaps between the pushbuttons (23) being limited to those required to allow clearance for operation of individual pushbuttons (23). Some of the pushbuttons are replaced by cover plates (24,25) which are mounted in appropriate apertures of the array of apertures.The pushbuttons (23) operate on dome shape elastomeric switching elements (45) arranged between the pushbutton plungers (43) and the printed circuit board (40). The domes have an electrically conductive portion which bridges conductive tracks on the printed circuit board when the corresponding pushbutton is depressed.

Abstract: The diaphragm keyboard comprises a baseboard from the bottom of which pins (11) project in vertical direction. These pins (11) pass through apertures (22) in an encoding plate (20) and extend beyond the surface thereof, thus presenting spacers for a diaphragm (30). In addition, they serve for retaining and aligning the encoding plate (20).

Abstract: A keyboard key top mounting structure including a plurality of lever support means provided on the back of a key top, the lever support means being each provided with wing portions for abutment therewith of a lever to prevent the lever from pivoting during mounting of the lever, and a plurality of lever sliding members provided on the side of a stationary member and each having a lever sliding slot, in which the lever is supported by the lever support means and inserted into the sliding slots.

Abstract: An improved keyboard is provided with a flexible metal cover, normally closed switches, and multiple throw switches. The metal cover is made flexible in the area of each key or switch by the provision of grooves in the metal surrounding each flexible portion. The normally closed and multiple throw switches include pellets which transmit the actuating force on a key or switch through a substrate on which a switch is mounted. The device may be configured in such a way that the pellet will push the normally closed contacts of a switch out of contact, or the pellet or pellets may mechanically link a stacked set of switches in order to provided ganged, multiple throw operation.

Abstract: A keyboard includes a plurality of keys thereon, each of which is capable of three different switching actions for entry of data or commands into a word processor, typewriter, computer or the like. Each key includes a first inclined surface for generating a first switching action responsive to finger contraction, a second inclined surface for generating a second switching action responsive to finger extension, and a horizontal surface for actuating a third switching action responsive to finger depression. Each key is connected to a respective switch. Each switch includes a carriage operating horizontally against spring-loaded horizontal plugs. The carriage houses a spring-loaded vertical stem attached to the respective key. In one embodiment each key-switch combination is substantially identical to the other. The base is formed into different levels upon which key-switch combinations are mounted.

Abstract: The invention provides an elastomer-made push button switch covering member having a dome-like configuration integrally composed of a base portion, a top portion and a riser portion connecting the base portion and the top portion. By virtue of the specific elastic properties of the elastomer with a Shore D hardness of at least 35 or, preferably, in the range from 35 to 60 and a rebound of at least 40%, the covering member can give the operator's finger tip a very definite and reliable feeling of clicking touch in pushing different from or superior to conventional rubber-made push button switch covering members.

Abstract: A keyboard assembly has a PC board providing a series of switch contacts and a molded rubber keyboard providing a rubber base sheet overlying the PC board and having a series of rubber keys integral with the base sheet. Each key has contacts on its bottom surface for closing each of the switch contacts when its key is depressed. Stabilizing membranes prevent the keys from wobbling or binding. The membrane snugly engages each key, and the membrane is flexible along its Z axis but sufficiently stiff along its X and Y axes to limit the movement of the keys to strictly linear movement toward and away from their respective PC board switches.

Abstract: An electronic apparatus comprising a plurality of assembly elements and a heat-sensitive adhesive synthetic resin film tape inserted between the plurality of assembly elements and the heat adhesive synthetic resin tape to integrally bond the elements together into a composite structure which is thin in size and sufficiently elastic to resist bending and twisting.

Abstract: A multiple contact switch having at least one elastically deformable contact spring that is deformed by means of projections from a plunger to initiate contact with normally-open electrical contacts within the switch. A normally-closed contact piece within the switch also confronts the normally-open contact. Upon deformation of the elastically deformable spring contact, contacts are made and interrupted by means of contacts affixed to the movable contact springs.

Abstract: A keyboard including an upper casing which has a key-holder member for movably supporting keys with a movable electrode, and a lower casing which has an integrally formed upraised portion which defines a recess open in the bottom wall of the lower casing. A printed-circuit board is held in direct contact with the top wall of the upraised portion of the lower casing such that stationary electrodes 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 having elastically collapsible cap portions is disposed such that the cap portions cooperate with the film-like printed-circuit board to form enclosures in which the corresponding movable and stationary electrodes are accommodated, and such that the cap portions collapse upon operation of the keys for moving of the movable electrodes toward the stationary electrodes.

Abstract: A thimble-shaped button actuator largely formed of insulating material has a cup-like base with an inside step and is symmetrical about an axis. A thimble is reciprocable in the base along the axis. A spring is seated against the closed end of the base and the closed end of the thimble and urges the thimble in a direction away from the base and against a snap ring in the base in the path of a flange on the thimble. An electrically conducting ring on the thimble is moved by axial pressure on the thimble to abut a pair of electrical conductors seated in the base and overlying the step. Electrically conducting binding screws are recessed in and pass into the base to engage threads in the conductors.

Abstract: In compact card-like equipment having an IC chip and a power source cell, an equipment case has a multilayered structure of a pair of upper and lower sheets and a pair of upper and lower panels laminated on a frame, respectively. A flexible substrate and a paper-like cell as a primary cell are provided in the equipment case. The paper-like cell has a pair of positive and negative electrode sheets and a power generating unit interposed therebetween. A sealing member seals the peripheries of the electrode sheets of the paper-like cell. The paper-like cell is received in a receptacle space formed in the frame. The flexible substrate is received in another receptacle space formed in the frame. The electrode sheets of the paper-like cell are electrically connected to terminals of the flexible substrate by means of a film-like connecting member. This compact card-like electronic equipment such as a calculator is thin and compact in size.

Abstract: A control system for entering data into a copier controller relating to the parameters of an original to be copied, having a platen upon which the original is placed for exposure, comprising electrically sensitive membrane strips applied adjacent to the platen, said strips being formed with touch sensitive portions whereupon touching by an operator effects a signal indicative of the location of the touch, and means connecting the strips to the controller for transmitting the signals thereto, the signals being representative of document size. Also included is a special switch to convert the touch sensitive portions of the membrane strips into document editing functions.

Abstract: A switch designed to be activated by touch contact has a switching chamber ith contact surfaces on opposite sides thereof. A flexible switching film carries one of the contact surfaces and is arched over one side of the chamber. In order to prevent an increase in length of the switching film due to climatic effects from leading to incorrect switching, the switching film has at least one punctiform or linear deformation placed so as to cause the film to arch away from the opposite side of the chamber.

Abstract: A resilient pad for keyboards, such as computer keyboards, is disclosed. The pad is composed of EPDM blended with a copolymer of propylene oxide and allyl glycidyl ether. Each of the polymers is present in the amount of 10-90 parts. An accelerator system for the polymer blend is also disclosed. The pad has substantially improved resilience as measured by the hysteresis of the pad.

Abstract: The present invention is a simplified membrane keyboard employing a single flexible sheet. This membrane keyboard is employed in an electronic apparatus having an external case with a nonconducting keyboard surface. This nonconducting keyboard surface has a plurality of depressions corresponding to key switch positions. The keyboard surface is covered by a keyboard sheet. This keyboard sheet has a flexible membrane with opposed first and second surfaces, the first surface disposed adjacent to and substantially covering the keyboard surface of the external case. An interconnection pattern is placed upon the first surface of the flexible membrane. This interconnection pattern has a plurality of conductors and most particularly has a pair of conductors in proximity at each key switch position. Pressure applied to the second surface of the flexible membrane causes the flexible membrane to flex until the two conductors contact a conductive layer disposed in the bottom of the corresponding depression.

Abstract: A keyboard switch apparatus for an electronic musical instrument has first, second and third layers, and first and second switches. The second layer has elasticity and is separated from the first layer. The third layer has elasticity and is inserted between the first and second layers at a distance therefrom. The first switch consists of conductors respectively formed on opposite surfaces of the second and third layers. The second switch consists of conductors respectively formed on opposite surfaces of the first and third layers. The second and third layers are sequentially urged and deformed by an actuator interlocked with key depression. The first and second switches are sequentially closed. A time requred for closing the first switch is different from that for closing the second switch. The closure time difference corresponds to a key depression speed, which is used to generate a signal corresponding to the depression speed, and a musical tone signal corresponding to the depression speed.

Abstract: A keyboard assembly having key-switches, comprising a key holder plate supporting multiple keys in plural rows and movably across the thickness of the plate, and further comprising an upper casing which has a rectangular aperture closed by the key holder plate. The key holder plate has holes through which the keys extend, and integral guide portions concentric with the holes and .[.extend.]. .Iadd.extending .Iaddend.toward the rectangular aperture. Opposite right and left sides of the aperture perpendicular to the rows of the keys are defined by side walls of the upper casing each of which has a downward extension toward the key holder plate. The extension has a convex lower end profile with which the key holder plate is held in pressed contact by fasteners, with elastic deformation thereof following the convex lower end profile of the downward extension, such that a surface generally defined by top faces of the keys is curved in cross section across the rows of the keys.