Pushbutton Switch

1. Field of the Invention

The present invention relates to a pushbutton switch and more particularly to, a pushbutton switch construction for use in a keyboard.

2. Description of the Prior Art

A keyboard as a data entry device for use with a microcomputer, generally has a plurality of pushbutton switches arranged on the front panel thereof. The pushbutton switches are arranged on a membrane sheet which comprises an array of contact circuits allocated by a known printed circuit technique and disposed together with a spacer between two synthetic resin layers sheets so that when the two layers are depressed against each other, a corresponding number of the contact circuits are closed. For each pushbutton switch, an elastic material such as a rubber spring having an inverted bowl shape is placed on the contact circuit of the membrane sheet. When the rubber spring is pressed down by the click action of a key, the circuit closes.

However, the elastic material of such a conventional pushbutton switch has a relatively long stroke for switching action. This results in an increase of the height of the pushbutton switch. For eliminating the above drawback, a modified pushbutton switch has been disclosed in Japanese Patent Laid-open Publication 4-2484432 (1992) or U.S. Pat. No. 5,203,448 where an intermediate element is disposed between the contact region of a key and the substrate on a membrane sheet so that it can slide along the key contact region and the substrate. In action, when the key is depressed, its contact region comes into direct contact with and lowers the intermediate element. The switching stroke of the key is equal to a sum of the clearance between the key and the intermediate element and the clearance between the intermediate element and the substrate. Accordingly, even if the switching stroke of the elastic material is set identical to that of the conventional pushbutton switch, the overall height of the modified pushbutton switch, i.e. from the membrane sheet to the top of the key, can be decreased.

The modified pushbutton switch has the intermediate element mounted between the substrate of the membrane sheet and the contact region of the key so that it can slide along both the substrate and the key contact region and will thus be decreased in overall height. The disadvantage of the modified pushbutton switch is that dimensional error on the sliding element is as large as two times that of the conventional switch because two sliding actions are involved between the key and the intermediate element and between the intermediate element and the substrate. This will cause the vertical movement of the key to wobble more or less and to attenuate the stability. Also, the key is supported by the intermediate element which is not anchored to the substrate or stationary base, thus failing to contribute to the structural strength of the pushbutton switch.

The present invention is directed towards eliminating the above disadvantages and its object is to provide an improved pushbutton switch for opening and closing a contact circuit by way of the resiliency of an elastic material actuated through an intermediate element by a key, in which the switching action of the key is made stable and ensured by the physical strength of an inventive arrangement including the intermediate element and the elastic material on a membrane sheet.

For elimination of the foregoing disadvantage of the prior art pushbutton switch, the present invention provides an improved pushbutton switch.

The pushbutton switch of the present invention for opening and closing a contact circuit by means of the resiliency of an elastic material actuated through an intermediate element by a key cap, comprises: a membrane sheet carrying the circuit contacts; a keyboard frame guide disposed on a substrate; a stem having an opening therein where an external actuating force is applied to move the stem along the keyboard frame guide; a rubber spring disposed between the stem and the membrane sheet for making the circuit when being pressed down by the stem and lifting up the stem to its original position when the stem is released from a pressure; and a stabilizer assembly mounted at one end to the substrate for pivotal movement and formed of an X shape in cross section by intersecting at least two arms at center to each other, each arm having an actuator rod mounted to a central region thereof and accommodated in the opening of the stem for sliding movement. The upper ends of the arms of the stabilizer assembly are supported by the back side of the key cap for pivotal movement.

The operation of the above pushbutton switch will now be explained.

When the key cap is pressed down, the stabilizer assembly starts being compressed. As the upper end of the stabilizer assembly is pivoted on the key cap, the key cap moves straight down without wobbling while being guided by the keyboard frame guide. Simultaneously, the two actuator rods of the stabilizer assembly travel in opposite directions along the opening of the stem and the pivot axles of the same slide outwardly along the support slits. Accordingly, the downward movement of the stem presses down the rubber spring to bottom. When the stem reaches its lowest position, the rubber spring is flattened with its pressing projection acting on a corresponding switch region of the membrane sheet for switching on. When the key cap is released, the rubber spring returns back by its resiliency to lift up the stem. As in a reverse movement, the stabilizer assembly expands and the key cap is returned back to its original height.

FIG. 1 is an exploded perspective view showing one embodiment of the present invention;

FIG. 2 is a cross sectional view of the same;

FIG. 3 is a cross sectional view of the same without a stabilizer assembly;

FIG. 4 is a cross sectional view of the same explaining a switching action;

FIG. 5 is a cross sectional view of a part of the same illustrating the action of a rubber spring.

Preferred embodiments of the present invention will be described referring to the accompanying drawings. FIG. 1 is an exploded perspective view of a pushbutton switch according to the present invention. As shown, a key cap 1 having in common a character or numeral printed on the upper surface thereof is provided for switching action by the operator. The key cap 1 has four pivot supports 1a provided on the back surface thereof for pivotably supporting a stabilizer assembly as will be explained later. The stabilizer assembly 2 comprises two actuator frames 2a and 2b of ladder shape which are joined to each other to form an X shape in cross section. More particularly, the actuator frame 2a comprises two arms 2d and 2e joined approximately at a center thereof by an actuator rod 2c to each other. Actuator frame 2a also comprises three pivot axles 2f, 2h, and 2i mounted to both ends of the arms 2d and 2e. similarly, the actuator frame 2b comprises two arms 2k and 2m joined approximately at a center thereof by an actuator rod 2j to each other. Actuator frame 2b also comprises three pivot axles 2n, 2g, and 2r mounted to both ends of the arms 2k and 2m. The actuator frame 2a is wider in distance between the two arms 2d and 2e than the two arms 2k and 2m of actuator frame 2b.

A stem 3 is provided for transmitting the pressing force applied to the key cap 1 through the two actuator rods 2c and 2j of the stabilizer assembly 2 to a membrane switch, which will be explained later in more detail. The stem 3 has a center opening 3a, provided in the center thereof, for movably accommodating the two actuator rods 2c and 2j of the stabilizer assembly 2. The stem 3 also has two guide arms 3b and 3c extending downwardly from both sides thereof. The stem 3 has a slot 3d provided on the top thereof for passing the two actuator rods 2c and 2j to the center opening 3a during assembly.

There is also provided a rubber spring 4 made of a highly elastic synthetic resin or rubber material of substantially an inverted bowl shape. More specifically, the rubber spring 4 comprises a pressing head 4a having such a thickness such that no deformation occurs, a ring foot 4b for installation on the membrane switch, and a thin spring body 4c between the head 4a and the foot 4b for producing a spring effect. Also, a downward projection 4d is provided beneath the pressing head 4a of the rubber spring 4 for directly actuating the membrane switch.

A keyboard frame guide 5 is arranged integrally with a keyboard frame (base) 6, thus designating an upper part of the membrane switch. More particularly, the keyboard frame guide 5 comprises a four-sided vertical wall 5a extending upwardly from the keyboard frame 6 and defining a center opening 5b at the inside which allows a switch region 7a of a membrane sheet 7 to be exposed. Also, two pairs of support slits 5c and 5d are provided outside the wall 5a for accommodating the pivot axles 2g and 2r of the actuator frame 2b and the pivot axles 2h and 2i of the actuator frame 2a respectively. Two long recesses 5e are provided in the keyboard frame 6 for accepting the arms 2d and 2e of the stabilizer assembly 2 on both sides of the four-sided wall 5a.

A procedure of assembling the foregoing components of the pushbutton switch will now be described. First, the rubber spring 4 is placed in the opening 5b of the keyboard frame guide 5 with its ring foot 4b directly seated over the switch region 7a of the membrane sheet 7. The keyboard frame guide 5 is then covered from above with the stem 3 so that its opening 5b accepts the guide arms 3b and 3c of the stem 3 which are thus sustained by two opposite sides of the four-sided wall 5a respectively. The actuator rods 2c and 2j of the stabilizer assembly 2 are fitted through the slit 3d into the opening 3a of the stem 3 while the pivot axles 2g and 2r of the actuator frame 2b are accepted in the support slits 5c and the pivot axles 2h and 2i of the actuator frame 2a are accepted in the support slits 5d. Finally, the key cap 1 is coupled to the stabilizer assembly 2 by fitting the pivot axles 2f and 2n of their respective actuator frames 2a and 2b into the pivot supports 1a.

FIG. 2 is a cross sectional view of the pushbutton switch after completion of the assembly procedure. As shown, a back plate 8 is mounted to the back surface of the membrane sheet 7. FIG. 2 illustrates no pressure on the rubber spring 4. More specifically, the rubber spring 4 supports the stem 3 from below, as best shown in FIG. 3. In this state, the stabilizer assembly 2 is held with its pivot axles 2g, 2r and 2h, 2i in the deepest locations of the support slits 5c and 5d, thus restricting upward movement of the stem 3.

When the key cap 1 is pressed downwardly, the stabilizer assembly 2 is compressed. More particularly, as the arms 2d and 2e of the stabilizer assembly 2 move about the pivot supports 1a of the key cap 1, the key cap 1 can be lifted down vertically as guided with the stem 3 moving along the keyboard frame guide 5. Also, the actuator rod 2c and 2j of the stabilizer assembly 2 in the opening 3a of the stem 3 presses down the stem 3 as they move horizontally in opposite directions. Simultaneously, the pivot axles 2g and 2r of the stabilizer assembly 2 slide outwardly in their respective support slits 5c while the pivot axles 2h and 2i slide outwardly in their respective support slits 5d.

The stem 3 moves downward and presses against the rubber spring 4 for distortion, as shown in FIG. 5. Aperture 3e, provided in the bottom deck of stem 3 accepts a part of rubber spring 4 for easing any unwanted stress. When the stem 3 reaches its lowest position, shown in FIG. 4, the rubber spring 4 under the stem 3 becomes under a maximum pressure so that its pressing projection 4d directly acts on the switch region 7a of the membrane sheet 7 for switching on. When the key cap 1 is released, the resiliency of the rubber spring 4 presses up the stem 3 and thus, the stabilizer assembly 2 expands to its original position. As a result, the key cap 1 returns to the off position, as shown in FIG. 2.

It would be understood that the present invention is not limited to the above described embodiments. For example, an array of the pushbutton switches of any embodiment may be disposed in a unit on a substrate thus forming a keyboard. The pushbutton switches of the embodiment may be installed in their respective casings for defining a pushbutton unit. Although the opening 3a of the stem 3 shown in FIGS. 1, 3, and 4 is flat at the bottom, an aperture 3e may be provided in the bottom deck of the stem 3 to lessen the pressing force exerted on the rubber spring 4. Aperture 3e is illustrated in FIG. 5. This arrangement will allow the pressing projection 4d of the rubber spring 4 to not give an excessive stress to the membrane switch 7a when being urged downwardly by the stem 3 and prevent it from being ruptured. Also, the resilient movement of the rubber spring 4 will be eased, thus increasing the operation life of itself as well as of the membrane sheet 7.

It is thus apparent to those skilled in the art that various changes and modifications will be possible without departing from the scope of the present invention.

As set forth above, the pushbutton switch of the present invention comprises: a membrane sheet carrying the circuit contacts; a keyboard frame guide disposed on a substrate; a stem having an opening therein where an external actuating force is applied to move the stem along the keyboard frame guide; a rubber spring disposed between the stem and the membrane sheet for making the circuit when being pressed down by the stem and lifting up the stem to its original position when the stem is released from a pressure; and a stabilizer assembly mounted at one end to the substrate for pivotal movement and formed of an X shape in cross section by intersecting at least two arms at center to each other, each arm having an actuator rod mounted to an central region thereof and accommodated in the opening of the stem for sliding movement; and a key cap supporting at back the upper ends of the arms of the stabilizer assembly for pivotal movement. When the key cap is pressed down, it moves straight down with its body kept in horizontal as being controlled by the stabilizer assembly. Accordingly, the stem is lifted down vertically and presses the rubber spring straight down to bottom. As the downward movement of the key cap is controlled by the stabilizer assembly, it will hardly be affected by a clearance between the stem and the keyboard guide. The pushbutton switch is also increased in physical strength. The stem has an aperture for easing a stress exerted on the rubber spring, whereby the return movement of the rubber spring will be encouraged and thus, the life of the membrane sheet will increase.