Key Switch

The present invention relates to a key switch for a keyboard which produces little friction force and effectively eliminates the formation of a vacuum during the operation of the key switch.

Various key switches have been disclosed for computer keyboards. FIGS. 4 and 5 show a structure of key switch according to the prior art. This structure of key switch comprises an open key base 1' made on the frame of a keyboard, a key body 2' movably received within the key base 1', a key cap 3' spaced above the key base 1' and coupled to the key body 2', and a rubber cone 4' mounted on the circuit of the keyboard and disposed below the key body 2'. The key cap 3' has triangular bottom rods 3A respectively extended from the bottom thereof in four corners. The key base 1' has four longitudinal grooves 1A of arched cross section in the four corners thereof on the inside. The key body 2' comprises four triangular mounting slots 2A at the top, which receive the four triangular bottom rods 3A of the key cap 3' respectively, a flat bottom wall 2C supported on the rubber cone 4' at the top, four longitudinal flanges 2D of arched cross section respectively raised from the outside wall thereof in the four corners and side-matched with the four longitudinal grooves 1A of the key base 1'. The longitudinal flanges 2D of the key body 2' have each a bottom end terminating in a respective hooked portion 2B, which stops below an inward top flange on the key base 1' to keep the key body 2' coupled to the key base 1' when the key cap 3' is not depressed. A key switch has drawbacks. Because the longitudinal flanges 2D are side-matched with the longitudinal grooves 1A through surface contact but not point contact, a great friction force will be produced when the key body 2' is moved relative to the key base 1', and therefore the movement of the key body 2' will be affected. Because the top of the rubber cone 4' is closely attached to the flat bottom 2C of the key body 2', a vacuum will be produced upon each stroke of the key cap 3', causing the upward stroke of the key body 2' to be hindered. Furthermore, the design of the triangular slots 2A and longitudinal flanges 2D with hooked portions 2B complicates the injection molding process of the key body 2', causing the manufacturing cost of the key switch to be relatively increased.

The present invention has been accomplished to provide a key switch which eliminates the aforesaid drawbacks. It is therefore an object of the present invention to provide a key switch which produces little friction force during its operation so that the movement of the key body thereof is smoothed. It is another object of the present invention to provide a key switch which eliminates the formation of a vacuum during its operation. It is still another object of the present invention to provide a key switch which is inexpensive to manufacture and easy to assemble.

To achieve the aforesaid objects, there is provided a key switch comprised of a square key base having an inward facing top flange around the four sides thereof, four 45.degree. angle bevel edges on the inward facing in the four corners thereof, and four notches on the inward facing flange in the middle of either side thereof; a key base having four air passage holes longitudinally disposed in the four corners of the square center through-hole thereof, four cylindrical flanges longitudinally raised from the four corners thereof and side-matched with either 45.degree. angle bevel edge on the inward top flange of the key base, four stub rods respectively extended down from the cylindrical flanges and stopped below the inward top flange, and a projection raised from one side thereof in the middle at the top and vertically disposed in line with one notch on the inward top flange of the key base for guiding vertical movement of the key body within the key base; and a key cap having a plunger fitted into the square center through-hole on the key body and moved to compress a rubber cone below in triggering a circuit, and a inside hole on the plunger communicating with the air passage holes for exhaust of compressed air. Because the cylindrical flanges of the key body are respectively disposed in contact with the key base at three contact points, less friction force is produced when the key body is moved relative to the key base. When the key cap is depressed, compressed air is guided out of the key switch through the inside hole on the plunger and the air passage holes on the key body, and therefore no vacuum is produced.

FIG. 1 is an exploded view of a key switch according to the present invention;

FIG. 2 is a sectional elevation of the key switch shown FIG. 1;

FIG. 3 is a top plain view of the key switch shown in FIG. 2;

FIG. 4 is an elevational view of a key switch according to the prior art; and

FIG. 5 is a sectional elevation of the key switch shown in FIG. 4.

Referring to FIG. 1, a key switch in accordance with the present invention is generally comprised of a key base 1, a key body 2, a key cap 3, and a rubber cone 4. The key cap 3 and the key body 2 are respectively molded integrally from plastics. The key base 1 is a square open frame having an inward extending flange 11 horizontally disposed at the top around the four sides thereof, four 45.degree. angle bevel edges 13 on the inward flange 11 in the four corners 17 thereof, four notches 12 on the inward flange 11 in the middle of either side thereof. The key body 2 comprises a square center through hole 20, four air passage holes 21 longitudinally disposed through (i.e., along) the four corners of the square center through hole 20, four cylindrical flanges 22 raised from the four corners thereof in the longitudinal direction, four stub rods 23 respectively extended downwards from the cylindrical flanges 22, and a projection 24 raised from one side thereof in the middle at the top. The key cap 3 comprises a unitary plunger 31 at the bottom fitted into the square center through hole 20 of the key body 2. The plunger 31 is made in a hollow structure having an inner hole 310. The rubber cone 4 is disposed beneath the key body 2 and compressed to trigger the circuit below (not shown).

Referring to FIGS. 2 and 3 and FIG. 1 again, the key base 1 is integrally made on the frame of a computer keyboard; the key body 2 is inserted into the key base 1 from the bottom with the cylindrical flanges 22 respectively side-matched with the bevel edges 13 and the stub rods 23 stopped below the inward flange 11 and the projection 24 disposed in line with one notch 12 on the key base 1; the plunger 31 is squeezed into the square center through hole 20 of the key body 2 from the top causing the key body 2 and the key cap 3 to be joined together. When assembled, the cylindrical flanges 22 of the key body 2 are disposed in contact with the key base 1 through a respective three-point contact, i.e. each cylindrical flange 22 has three contact points respectively disposed in contact with either bevel edge 13 and the inward flange 11. Because the key base 1 has four notches 12 respectively disposed on the inward flange 11 thereof at the four sides, the key body 2 and the key base 1 can be quickly assembled without considering the direction of the projection 24. When the key cap 3 is depressed, compressed air can be smoothly guided out through the inner hole 310 on the plunger 31 of the key cap 3 and the air passage holes 21 on the key body 2 eliminate vacuum between the key body 2 and the rubber cone 4, and therefore the reciprocating movement of the key body 2 is smoothed.

Because the key cap 3 and the key body 2 are respectively molded integrally from plastics and the key base 1 is directly made integrally on the frame of the keyboard, the manufacturing cost of the key switch is greatly reduced.