GB2283860A

GB2283860A - Key switch

Info

Publication number: GB2283860A
Application number: GB9323163A
Authority: GB
Inventors: Ching-Cheng Tsai
Original assignee: Chicony Electronics Co Ltd
Current assignee: Chicony Electronics Co Ltd
Priority date: 1993-11-05
Filing date: 1993-11-10
Publication date: 1995-05-17
Anticipated expiration: 2013-11-10
Also published as: GB9323163D0; GB2283860B; NL9301918A; DE9317990U1

Abstract

A key switch includes a key cap 1 having a rectangular plunger 11 movable through a rectangular through hole in key base 2 for compressing a hollow rubber cone 4 having a solid stub portion 42 for pressing a contact 511 on an upper membrane 51 through a hole 54 in an intermediate insulating layer 53 and into engagement with a contact 512 on a lower layer 52. The plunger 11 has four pairs of longitudinal ribs (114, Fig.5) respectively spaced around its four sides and longitudinal gaps 111 on two opposite sides defining two spring hooks 112 engageable with stepped surfaces 213 at the bottom of the key base 2. Each spring hook 112 has two sloping edges 113 for guiding the spring hooks 112 into the engaged position after each down stroke of the plunger 11 without causing noises. <IMAGE>

Description

KEY SWITCH The present invention relates to key switches.

The keyboard in a computer system is a device for data input, which consists of a set of keys. Once either key is pressed, a specific circuit is connected to produce a specific input signal. Various key switches have been disclosed for this purpose.

Figure 1 is an exploded view of a key switch according to the prior art which is generally comprised of a key cap, a key base, and a rubber cone. The key cap is retained to the key base by two opposite bottom hooks theèo "As the key cap is pressed or pushed back by the-rubber cone, it oscillates, causing noises to occur.

Figures 2 and 4 show another structure of key switch according to the prior art which is also comprised of a rubber cone, a key base, and a key cap.

The key cap comprises a square bottom plunger inserted into a square center hole on the key base. The square bottom plunger of the key cap comprises four longitudinal ribs disposed along the four corners thereof, and two opposite spring strips disposed on two opposite sides and respectively curved outwards. By means of engaging the- spring strips with two opposite notches on the bottom wall of the key base, the key cap is retained to the key base. This structure of key switch is still not satisfactory in function. During the assembly process, the square bottom plunger of the key cap may be inserted into the square center hole on the key base in a wrong direction. The spring force of the spring strips must be properly controlled so that the key cap can be moved vertically without escaping from the key base. However, it is not easy to properly control the spring force of the spring strips. As the top edge of the square center hole of the the spring strips is made in an acute angle and the bottom edge of the plunger of the key cap is made in right angle, it is difficult to guide the plunger of the key cap into the square center hole of the key base during the assembly process. Furthermore, simply using the four longitudinal ribs to guide the movement of the plunger in the square center hole of the key base still cannot keep the key cap moved in course. Therefore, the key cap oscillates when pressed or pushed back by the rubber cone (see Figure 3), causing noises to occur.

This invention provides a key switch comprising a membrane which comprises a bottom circuit layer having a first contact, an upper circuit layer having a second contact spaced above said first contact, an intermediate insulative layer having a hole aligned between said first and second contacts; a rubber cone which comprises a hollow hornlike body supported on said member, a top ring on said horn-like body at the top, a solid stub rod suspended within said horn-like body below said top ring and spaced above said second contact; a frame spaced above said rubber cone and having a hole in line with said top ring of said rubber cone; a key base which comprises a hollow, rectangular trough having an inside wall defining a through hole in line with the hole on said frame and the top ring of said rubber cone, two stepped bottom edges disposed on a bottom surface thereof at two opposite sides by said rectangular trough; a key cap having a rectangular w tom plunger inserted through the through hole on said key base and stopped above said top ring of said rubber cone, said bottom plunger comprising two symmetrical pairs of longitudinal gaps on two opposite sides thereof, two spring hooks disposed on two opposite sides thereof between either pair of said longitudinal gaps and respectively hooked on said stepped bottom edges of said key base at the bottom; and wherein when said top ring of said rubber cone is squeezed by said rectangular bottom plunger of said key cap, said rubber cone is deformed, and the stub rod of said rubber cone is moved downward to connect said second contact to said first contact in producing a signal.

The present invention has been accomplished under the aforesaid circumstances. In at least preferred embodiments thereof, the present invention provides a key switch which does not oscillate when operated, which can allleviate the problem of causing the hands to ache after a length of time in operation, which greatly reduces noise during operation, and which is inexpensive to manufacture.

According to at least preferred embodiments of the present invention, a key switch comprises a key cap having a plunger inverted through a through hole on a key base and pressed to compress a rubber cone in triggering a circuit inside a membrane wherein the plunger has four pairs of longitudinal ribs spaced around the four sides thereof and disposed in the four corners of the smooth inside wall of the key base, and two spring hooks engaged with stepped edges on the key base at the bottom. Each spring hook has a hook body bilaterally spaced from the plunger by gaps, a hooked portion at the bottom of the hook body, and two sloping edges bilaterally connected between the hooked portion and the hook body for guiding the hooked portion into the engaged position after each down stroke of the plunger without causing noises. Because the plunger is made of rectangular shape, it is prohibited from being inserted into the rectangular trough in a wrong direction during the assembly process of the key switch.

The inner top edge of the rectangular trough of the key base is smoothly curved, therefore the rectangular bottom plunger of the key cap can be conveniently guided into rectangular trough of the key base. As the plunger of the key cap is disposed in contact with the smooth inside wall of the rectangular trough of the key base by means of the four pairs of longitudinal ribs thereof, the contact area between the plunger and the trough is reduced, and therefore less friction force will be produced. The gaps on the plunger at two opposite sides of either spring hook permit the spring hooks to be oscillated without causing the plunger to oscillate upon a strike, and therefore the key cap stably moves in course when it is pressed. As sloping edges are respectively made on the spring hooks to guide the hooked portions into the respective hooked position in engagement with the stepped edges on the key base respectively, the plunger does not oscillate during its up stroke, and therefore little noise will be produced.

Furthermore, the rubber cone is also superior than that of the prior art. After depressed, the rubber cone can smoothly return to its former shape.

Figure 7 shows the differences on spring force between the rubber cone defined above and the rubber cone of the prior art. The curve &commat; g mad made by the rubber cone defined above is more smooth than the curve 0' made by the rubber cone of the prior art.

The invention will now be described by way of example with reference to the accompanying drawings, throughout which like parts are referred to by like references, and in which: Fig. 1 is an exploded view of a key switch according to the prior art; Fig. 2 is an exploded view of another structure of key switch according to the prior art; Fig. 3 shows the plunger of the key cap of the key switch of Figure 2 oscillated upon a strike; Fig. 4 is a sectional plain of the key switch of Figure 2; Fig. 5 is an exploded view of a key switch according to the preferred embodiment of the present invention; Fig. 6 is a sectional plain of the key switch of Figure 5; and Fig. 7 is a comparison chart between the present embodiment and the prior art showing the relation between the stroke of key cap and the spring force of rubber cone.

Referring to Figures 5, 6, and 7, a key switch

is generally comprised of a key cap 1, a key base 2, a frame 3, a rubber cone 4, and a membrane 5. The membrane 5 is disposed at the bottom.

The frame 3 is spaced above the membrane 5 to hold the key base 2. The key cap is mounted on the key base 2.

The rubber cone 4 is supported on the membrane 5 beneath the frame 3 in line with the key cap 1.

The key cap 1 is made of square shape. The top of the key cap 1 curves inwards for comfortable touch of the fingers. A rectangular plunger 11 extends downward from the key cap 1. The plunger 11 comprises four pairs of longitudinal guide ribs 114 respectively disposed around the four corners thereof, two symmetrical pairs of longitudinal gaps 111 on two opposite sides thereof, two spring hooks 112 on two opposite sides thereof and disposed between either pair of longitudinal gaps 111, and a bottom flange 115 raised from the bottom surface thereof. Each spring hookjl12 has two sloping edges 113 bilaterally disposed between the hook body and hooked end thereof. The key base 2 comprises a hollow, rectangular trough 21 having a smooth inside surface 212 around four sides and a smoothly curved guide edge 211 around the smooth inside surface 212 at the top for guiding the rectangular plunger 11 of the key cap 1 into the rectangular trough 21, two stepped bottom edges 213 respectively engaged with the spring hooks 112 of the key cap 1. The frame 3 is spaced above the membrane 4 to support the key base 2, having an opening (not shown) in line with the rectangular trough 21 for passing the rectangular plunger 11 of the key cap 1. The rubber cone 4 comprises a small top ring 41, which is blocked at the bottom, a big bottom ring 44, a horn-like taper wall 43 connected between the top ring 41 and the bottom ring 44 and made gradually smaller toward the top ring 41, and a solid stub rod 42 suspended from the bottom wall of the blocked top ring 41 in the center within the sloping wall 43. The membrane 5 comprises an upper circuit layer 51 having a contact 511 of silver, a bottom circuit layer 52 having a contact 512 of silver, and an intermediate insulative layer 53 having a hole 54 aligned between the contacts 511;512.

Referring to Figure 6 again, the plunger 11 of the key cap 1 is guided by the smoothly curved guide edge 211 of the key base 2 to insert into the rectangular trough 21. When inserted, the bottom end of the plunger 11 is stopped at the top ring 41 of the rubber cone 4 with the bottom flange 115 stopped above the stub rod 42, and the spring hooks 112 are respectively engaged with the stepped bottom edges 213.

Therefore, pressing the key cap 1 causes the bottom plunger 11 to squeeze the top ring 41 of the rubber cone 4. When squeezed by the bottom plunger 11, rubber cone 4 is forced to deform permitting the contact 511 of the upper circuit layer 51 to be moved downward by the stub rod 42 to pass through the hole 54 on the intermediate insulative layer 53 and then to contact the contact 512 of the bottom circuit layer 52, and therefore the circuit inside the membrane 5 is triggered and a specific input signal is transmitted by the keyboard to the computer. When the key cap 1 is released from the pressure, the rubber cone 4 immediately returns to its former shape, and therefore the key cap 1 is moved back to its former position. During the up stroke of the plunger 11, the spring hooks 112 are guided by the respective sloping edges 113 to hook on the stepped bottom edges 213 respectively, and therefore no noises will be produced.

Figure 7 is a comparison chart between the present embodiment and the prior artthowing the relation between the stoke of key cap and the spring force of rubber cone.

Claims

1. A key switch comprising: a membrane which comprises a bottom circuit layer having a first contact, an upper circuit layer having a second contact spaced above said first contact, an intermediate insulative layer having a hole aligned between said first and second contacts; a rubber cone which comprises a hollow hornlike body supported on said member, a top ring on said horn-like body at the top, a solid stub rod suspended within said horn-like body below said top ring and spaced above said second contact; a frame spaced above said rubber cone and having a hole in line with said top ring of said rubber cone; a key base which comprises a hollow, rectangular trough having an inside wall defining a through hole in line with the hole on said frame and the top ring of said rubber cone, two stepped bottom edges disposed on a bottom surface thereof at two opposite sides by said rectangular trough; i- a key cap having a rectangular be tom plunger inserted through the through hole on said key base and stopped above said top ring of said rubber cone, said bottom plunger comprising two symmetrical pairs of longitudinal gaps on two opposite sides thereof, two spring hooks disposed on two opposite sides thereof between either pair of said longitudinal gaps and respectively hooked on said stepped bottom edges of said key base at the bottom; and wherein when said top ring of said rubber cone is squeezed by said rectangular bottom plunger of said key cap, said rubber cone is deformed, and the stub rod of said rubber cone is moved downward to connect said second contact to said first contact in producing a signal.

2. The key switch of claim 1 wherein said key cap has a top surface curved inwards for touch of the fingers.

3. The key switch of claim 1 wherein said rectangular bottom plunger of said key cap comprises four pairs of longitudinal ribs respectively disposed around four corners thereof in contact with the inside wall of said hollow, rectangular trough of said key base.

. .

4. The key switch of claim 1 wherein the inside wall of said hollow, rectangular trough of said key base is formed of four smooth planes linked around the through hole being defined within said hollow, rectangular trough, and a smoothly curved guide edge around the through hole being defined within said hollow, rectangular trough.

5. The key switch of claim 1 wherein each spring hook of said rectangular bottom plunger of said key cap comprises a hook body, a hooked portion extended from said hook body at the bottom, and two sloping edges bilaterally connected between said hook body and said hooked portion.

6. A key switch substantially as hereinbefore described with reference to the accompanying Figures 5, 6 and

7.