Push switch with improved actuator assembly

Abstract: A push switch of the invention comprises a switching-element assembly (100) and an actuator assembly (1a) arranged on the switching-element assembly, wherein the switching-element assembly comprises first and second contacts(110a, 110b), the second contact being arranged over and elastically movable towards the first contact and making contact with the first contact when depressed by the actuator assembly. The basic type of actuator assembly includes an airtight enclosure formed by a domed-shaped elastic film and containing a gas, whereby a bottom surface (12) of the airtight enclosure depresses said second contact when the top surface (11) is pressed down. Several modified types of actuator assembly are also disclosed.

Description: The present invention relates to a push switch comprising a switching-element assembly, and an actuactor assembly according to the preambles of claims 1 and 11 for opening and closing an electronic circuit. Such a switch can be used in a keyboard having a light weight and a compact structure. In information processing apparatus, push switches (also known as push-button switches) play an important role as a means of communication between apparatus and operator. Recently, demand has arisen for push switches which are more compact, lighter in weight and reduced in profile, whilst also having a comfortable feel when depressed. This demand is particularly strong in the field of portable OA (office automation) apparatus. Generally, a push switch is composed of a switching-element assembly which opens and closes an electronic circuit, and an actuator assembly for transmitting finger pressure to the switching-element assembly. Many types of switching-element assembly are known and utilised including a lead switch, mechanical switch, membrane switch, conductive rubber switch, etc., and an appropriate type is selected depending on the specific application. Figs. 1 and 2(a), 2(b) show an exemplary structure of a switching-element assembly 100 known as a membrane sheet-type switch, which is used in a low profile keyboard. Fig. 1 is an exploded perspective view and Figs. 2(a) and 2(b) show a cross-section. In Fig. 1, the switching-element assembly 100 comprises an upper sheet 111a and a lower sheet 111b of a flexible film of polyester or the like, having respective wiring patterns 113a and 113b and a plurality of contacts 110a and 110b, printed using an ink (printing material) of Ag (silver) or C (carbon), and a spacer 112 having holes at positions corresponding to the contacts 110a and 110b when these sheets are stacked together. Figs. 2(a) and 2(b) show off- and on-states of the switching-element assembly respectively, the latter occurring when contacts 110a and 110b are closed by pressing the push switch. Fig. 3(a) shows an overall cross-section of a push switch having a known membrane sheet-type switching-element assembly 100. The push switch is provided with a metal support panel 200 to which the switching-element assembly 100 is mounted. A housing 4 is disposed on the switching-element assembly 100, a slider 3 is slidably mounted in a hole 40 of the housing 4, and a key-top 2 is fixed on the slider 3. Two springs 70 and 80 are arranged for giving a comfortable feel when the key-top 2 is depressed. A key-bottom 5 which is fixed at the end of the spring 80 depresses the switching-element assembly 100 and makes a contact between two contacts 110a and 110b as previously explained. In this type of switch, all the constituent parts disposed on the switching-element assembly form an actuator assembly for the push switch. Fig. 3(b) shows a cross-section of another example of a known push switch. The difference between the structures of Fig. 3(a) and Fig. 3(b) is that the latter comprises only one spring 80 and an additional elastic member 50 made of sheet rubber having a curved protrusion adjacent the bottom of slider 3. This protrusion 50a is located at the centre of the inside wall surface, and functions like the key-bottom 5 in Fig. 3(a). The push switch of Fig. 3(b) has a comfortable click action when the contacts are closed. The actuator assembly of Fig. 3(b) is in a broad sense composed of an actuator assembly 50 in a narrow sense and a slider assembly including slider 3, housing 4, key-top 2, spring 80, etc. Generally speaking, a key-top stroke length of about 3 to 4 mm is preferable for obtaining a comfortable key-touch feel, and a slider length (length L shown in Fig. 3(a)) of about 12 mm is required in order to obtain a smooth movement of the slider without wobble. Even if smaller dimensions are used, the overall height of the push-button switch, which includes support panel 200, switching-element assembly 100, and the actuator assembly such as shown in Figs. 3(a) and 3(b), requires at least about 10 mm. By contrast, a switch element having a short stroke length such as about 1 mm to 2 mm has been put into practical use, by sacrificing the key-touch feel. However, for push switches used in an input apparatus which is in frequent use, it is not appropriate to sacrifice the feel. Furthermore, in the existing push-button switches such as shown in Figs. 3(a) and 3(b), most of the constituent parts are made of plastic material such as ABS resin, and the weight of the actuator including the slider assembly comprising housing, slider, key-top, spring, etc., is about 60% of the overall weight of the push switch. This weight is partly due to the long stroke length needed to give a satisfactory feel. On the other hand, in the field of portable apparatus, which require low key profiles and light weight, push switches having a stroke length of about 1 mm to 2 mm, without any spring such as spring 70 shown in Fig. 3(a), have been utilised. In this type, there is a problem of contact error, in which the push switch does not make contact when the key-top is only lightly depressed, because the contacts are closed only when the key-top is depressed right down to the bottom of its travel (collide operation). Therefore, when typing on a keyboard using such push switches, frequent input errors are experienced and re-inputting is often necessary. In order to obtain a low profile push switch using a switching-element assembly of the membrane sheet type, several types of switch have been proposed. Among them, Japanese Unexamined Patent Publications SHO 57-55020 published 1st April 1982 (corresponding to U.S. Patent Series No. 4,520,248 filed 15th August 1980) discloses the use of a sheet of elastic foam material as an actuator assembly disposed on a membrane-type switching-element assembly. In addition, SHO 60-127619 published 8th July 1985 discloses the use of an actuator assembly composed of a convex-shaped transformable sheet and a planar sheet joined together at the periphery of the convex shape, both being of plastic material, as an actuator for obtaining a key click action. In the above two disclosures, no slider assembly is used for obtaining a low profile of the push switch. "Journal of Electronic Engineering", vol 24, no 251, pages 44-48 discloses a push switch having the features of the preamble of each of the accompanying independent claims. In this push switch, a so-called "rubber chip" is mounted over the switching-element assembly, and when a key top is depressed, the rubber chip pushes the second contact towards the first contact. According to a first aspect of the present invention, there is provided a push switch comprising a switching-element assembly, and an actuator assembly arranged on the switching-element assembly, wherein said switching-element assembly comprises first and second contacts, the second contact being arranged over, and elastically movable towards, the first contact and making contact with the first contact when depressed by said actuator assembly, characterised in that said actuator assembly comprises:- an airtight enclosure formed by an elastic film containing gas, whereby depression of a top surface of the actuator assembly causes a bottom surface of the actuator assembly to be bent downwardly by the pressure of the gas contained in the airtight enclosure and to depress said second contact. According to a second aspect of the present invention, there is provided a push switch comprising a switching-element assembly and an actuator assembly arranged on the switching-element assembly, wherein said switching-element assembly comprises first and second contacts, the second contact being arranged over, and elastically movable towards, the first contact and making contact with the first contact when depressed by said actuator assembly, characterised in that said actuator assembly comprises:- an actuator body made of an elastic foam material formed in a solid domed shape, and a sidewall of an elastic material covering the side surface of said actuator body, whereby depression of a top surface of the actuator assembly causes a bottom surface of the actuator assembly to depress said second contact. Preferred embodiments of the invention are defined in the dependent claims. An embodiment of the present invention can provide a push switch having a low profile and a light weight by a simple structure. An embodiment of the present invention can also provide a push switch having a comfortable key-touch feel. An embodiment of the present invention can provide a push switch which closes the switching element halfway through its travel. An embodiment of the present invention can provide a push switch in which an actuator assembly can be easily exchanged. Reference is made, by way of example, to the accompanying drawings in which:- Fig. 1 shows an exploded perspective view of a known membrane sheet-type switch, used in a push switch embodying the present invention; Figs. 2(a) and (b) show cross-sections of the switch of Fig. 1 in off- and on-states, respectively; Figs. 3(a) and 3(b) show examples of known types of push switch; Figs. 4(a) and 4(b) show a cross-section of a first embodiment of the present invention in off- and on-states respectively, having a domed actuator with an airtight enclosure; Fig. 5 shows a cross-section of a second embodiment of the present invention as a modified version of the first embodiment, having two airtight enclosures; Fig. 6 shows a cross-section of a third embodiment, in which the actuator assembly comprises a main body of elastic foam material and an airtight enclosure embedded in the main body; Figs. 7(a) and 7(b) show a cross-section of a fourth embodiment, in which a slider assembly is added to the structure of Figs. 4(a) and 4(b) respectively; Figs. 8(a) and 8(b) respectively show a schematic cross-section and a perspective view of a fifth embodiment, in which a key-top is added to the actuator assembly; and Figs 9(a) and 9(b) show a cross-section of a sixth embodiment, in which an actuator assembly comprises an actuator body of elastic foam material and a sidewall of another elastic material. Throughout the drawings, the same reference numerals designate the same or similar parts. First Embodiment Figs. 4(a) and 4(b) show a first embodiment of a push switch in accordance with the present invention, in which Fig. 4(a) shows a non-operating state and Fig. 4(b) shows the operating state, i.e. state when the push switch is depressed. A switching-element assembly 100 of the push switch is disposed on a support panel 200 of steel, iron, aluminium, or the like. The switching-element assembly 100 comprises an upper sheet 111a and a lower sheet 111b of a flexible film of polyester or the like, each having respectively a wiring pattern and a contact 110a, 110b. These are printed using a conductive ink such as one containing silver or carbon. A spacer 112 has holes at positions corresponding to the contacts when two sheets are stacked together. On contact portion 110 of the switching-element assembly 100, a domed actuator 1a is disposed, the domed actuator being composed of a top member 11 and a bottom flat member 12 which are airtightly sealed together and made of an elastic film made of, for example, polyethylene film or silicone rubber. A gas is sealed in the enclosed space, the term "gas" here including air or any other mixture of gases. The top member 11 has a thickness of about 1 mm and the bottom member 12 has a thickness of about 0.3 to 0.5 mm. Conveniently, two members 11 and 12 may be joined together by an adhesive so as to enclose air at atmospheric pressure. The top member 11 of the actuator assembly may have a spherical (curved) surface, or a flat top finger-touch portion 20 with a conical side-wall portion for easy location by a finger. The dimensions of the domed actuator 1a are appropriately chosen for easy operation. As shown in Fig. 4(b), when the finger touch portion 20 of the domed actuator 1a is depressed by a finger tip 300, the pressure of the gas (air) contained therein rises and is exerted uniformly on the upper sheet 111a. Since the spacer 112 has a hole at the position of the contact portion of the switching-element assembly, upper sheet 111a is bent downwardly and the contact 110a touches contact 110b, thus closing a circuit connected to the contacts. In this operation, the finger touch portion 20 can be pushed down further after the contacts are closed. Therefore, the switching action can be achieved halfway through the downward finger stroke. When the finger tip 300 is removed, the domed actuator 1a returns to its original shape shown in Fig. 4(a) under the elastic force produced by the enclosed gas and the elastic top member 11 itself, and the contacts 110a and 110b are opened. Thus, in this embodiment, the actuator assembly has a simple structure and a push switch having a very light weight can be realised without a slider, housing, springs, etc. The compressed gas enclosed in the domed actuator 1a imparts a restoring or repulsion force to the finger, and this contributes to a comfortable key action. It is generally known that a restoring force which increases proportionally with stroke length during depression is found to be comfortable. The restoring force in this embodiment changes corresponding to the volume of the sealed gas. In this case, although the restoring force does not increase linearly and proportionally with an increase of the stroke length, nevertheless it is found to increase steadily, giving a satisfactory feel. The amount of restoring force sensed by the finger tip 300 can be arbitrarily set by changing the pressure of the sealed gas, or by changing the material of the airtight elastic film 11 to another material having a different elasticity from that of polyethylene or silicone rubber. Second Embodiment Fig. 5 shows a second embodiment of the present invention. A domed actuator 1b is formed by elastic films 11a, 11b and 12, such that two enclosures or compartments 13a and 13b are formed partitioned by the elastic film 11b. A first enclosure 13a is airtightly formed-by elastic films 11a and 11b and contains a first volume of gas, and a second enclosure 13b is also airtightly formed by elastic films 11b and 12 and holds a second volume of gas. Other parts are the same as those in the previous embodiment. The enclosures 13a and 13b may be separately formed and stacked together. Since the domed actuator 1b is divided into two separate airtight enclosures, gas pressures in the two enclosures can be set differently from each other, resulting in an enhanced key touch response. For example, when the pressure of the first gas is set to be lower than that of the second gas, the necessary stroke length for closing the switching-element assembly 100 can be increased. Third Embodiment Fig. 6 shows a third embodiment of the present invention. An actuator 1c comprises a main actuator body 14 of elastic foam material such as polyurethane sponge (called Moltoplen), and is formed in a domed shape. The term "domed shape" here includes shapes such as a truncated cone or pyramid in which the top surface thereof forms a finger touch portion 20. An airtight enclosure 13c is formed by elastic films 11b and 12, enclosing a gas, and is embedded in the main actuator body 14. The airtight enclosure 13c can be formed in a similar way to the domed actuator 1a of Fig. 4(a), so as also to have a domed shape; however, this is not essential. Other parts are the same as those previously explained. In this embodiment, the main actuator body 14 of elastic foam material replaces the enclosure 13a of Fig. 5. This embodiment makes it possible to obtain a longer stroke length than that shown in Fig. 5. The shapes and sizes of the main actuator body 14 and the domed enclosure 13c are chosen to suit the requirements of the push switch. Fourth Embodiment Figs. 7(a) and 7(b) show a fourth embodiment of the present invention, in which Fig. 7(a) shows the non-operating state and Fig. 7(b) shows the operating state. In Figs. 7(a) and 7(b), an actuator assembly 10 may be any selected from those (1a to 1c) used in the preceding embodiments; as an example, the domed actuator 1a of Fig. 4(a) is illustrated here. On the actuator assembly 10, a slider assembly 30 is arranged so that a slider 3 slides up and down through a hole of a housing 4, a key-bottom 5 of the slider 3 contacting with the actuator assembly 10. At the top of the slider 3, a key-top 2b having a finger touch portion 20 is fixed, thereby giving the push switch of Figs. 7(a) and 7(b) the same tactile quality as keys of a conventional keyboard. The housing 4 is fixed to a support panel 200 by screw means or insertion means (not shown). Other parts except the slider assembly 30 are the same as explained previously. As shown in Fig. 7(b), when finger tip 300 depresses the finger touch portion 20, the key-bottom 5, i.e. the bottom end of the slider 3, deforms the domed actuator 10 so that the pressure of the gas inside it rises and uniformly pushes a contact portion 110 arranged below. As a result, the contact 110a is urged downwards, closing the contacts and performing a switching action. Previously, for a push switch having a low profile and light weight, a slider assembly which directly depresses the contact portion 110 of the switching-element assembly 100 has been proposed. However, in this embodiment, the contact portion is depressed indirectly by the slider 3, the actuator assembly 10 intervening therebetween. Therefore, if the gas pressure is properly selected, the contacts can be made to close before the slider 3 reaches the end of its stroke, and the slider 3 can be depressed further against the restoring force of elastic actuator assembly 10. Therefore, the switching action can be achieved halfway through the stroke movement. Fifth Embodiment Figs. 8(a) and 8(b) show a fifth embodiment of the present invention, in which Fig. 8(a) is a cross-section and Fig. 8(b) is a perspective view of an actuator assembly. In the Figures, a domed actuator 1 may be any of those (1a, 1b, 1c) shown in Figs. 4(a), 5 or 6. A key-top 2a is made of vinyl chloride, or any like material which is transparent and can be formed as a hard thin layer, and has a concave top surface. On the bottom surface thereof, a mark 21 such as a character or symbol is printed in a reversed manner such that, when the mark is seen from above through the transparent key-top 2a, the normal character or symbol can be seen. The domed actuator 1 and key-top 2a are fixed together by adhesive as shown in the Figures. The embodiment is particularly suitable for use in a keyboard. Generally, since each key-top of the keyboard is printed with a character or symbol designating its function, there is a problem that frequent finger contact will eventually erase the printing. The present embodiment can solve this problem using the same printing method and at low cost. Sixth Embodiment Figs. 9(a) and 9(b) show a sixth embodiment in cross-section, in which Fig. 9(a) shows the non-operated state and Fig. 9(b) the operated state. A domed actuator 1d comprises an elastic body 14 of foam material such as polyurethane sponge (e.g. Moltoplen), and a slide support elastic member 15 which is made of flexible material but has enough rigidity to stand by itself. Other parts are the same as in the previous embodiments. In Japanese Unexamined Patent Publication SHO 57-55020 mentioned above, the actuator used therein is unsupported at its sidewall. Therefore, if the foam material used is too elastic, the actuator wobbles when the switch is depressed, and a smooth stroke cannot be obtained. On the contrary, the domed actuator of this embodiment has a side support elastic member 15 surrounding the elastic body 14, made of a material which although elastic is still rigid enough to be self-supporting. Therefore, even when the elastic body 14 is not self-supporting, the domed actuator assembly does not wobble, and the key action is smooth and stable. As the material for the side support elastic member 15, a plastic material having a suitable stiffness such as vinyl chloride, polystyrene, etc., or silicone rubber, may be used. Further, when the side support member 15 is formed in a corrugated shape, it can be made of metal. Whatever material is used, it is important that the side support elastic member is formed in such a way that it is easily deformed in the vertical direction (stroke direction) but it is hard to deform in the lateral direction. Modifications Throughout the preceding explanation, structures of a single push switch have been considered. However, when a plurality of switches according to the present invention are utilised, a matrix switch array or a keyboard is easily formed, in which the support panel 200, the switching-element assembly 100 and the flat elastic member 140 are modified into an integrated structure provided in common for all the switches. In some cases, even a plurality of domed actuators can be formed all together in a continuous form by an integral molding technique, if necessary. This will improve machining and assembling efficiencies. The actuator assembly including all types of domed actuators 1a to 1d and 10 described above is normally permanently fixed to the switching-element assembly 100. However, the actuator assembly may be detachably mounted such that it can be removed or replaced with another type of actuator assembly, by use of an adhesive or insertion mechanism. By replacing the domed actuator with a different type having different characteristics, a keyboard having a different feel, which meets an individual's taste, can be obtained.

Claims: A push switch comprising a switching-element assembly (100), and an actuator assembly (1a, 1b, 1c, 10) arranged on the switching-element assembly, wherein said switching-element assembly comprises first and second contacts (110b, 110a), the second contact (110a) being arranged over, and elastically movable towards, the first contact (110b) and making contact with the first contact (110b) when depressed by said actuator assembly (1a, 1b, 1c, 10), characterised in that said actuator assembly comprises:- an airtight enclosure (13; 13a, 13b; 13c) formed by an elastic film (11, 12; 11a, 11b, 12; 11b, 12) containing gas, whereby depression of a top surface (20) of the actuator assembly (1a, 1b, 1c, 10) causes a bottom surface (12) of the actuator assembly (1a, 1b, 1c, 10) to be bent downwardly by the pressure of the gas contained in the airtight enclosure (13; 13a, 13b; 13c) and to depress said second contact (110a). A push switch as claimed in claim 1, wherein said elastic film comprises a top member (11) having a curved surface and a bottom flat member (12). A push switch as claimed in claim 1 or 2, wherein said elastic film includes a partition member (11b) which divides said airtight enclosure (13) into first and second airtight compartments (13a, 13b) each containing gas. A push switch as claimed in claim 3, wherein the second compartment (13b) is contained within the first (13a) and has a bottom surface contacting an upper surface of the switching-element assembly (100). A push switch as claimed in claim 3 or 4, wherein the gas pressures in the two compartments (13a, 13b) are different. A push switch as claimed in any preceding claim, wherein the material of said elastic film (11, 12; 11a, 11b, 12; 11b, 12) is either thermoplastic resin or silicone rubber. A push switch as claimed in claim 1, wherein said airtight enclosure (13c) is embedded in a main body (14) of an elastic foam material having a domed shape, a bottom surface (12) of the airtight enclosure (13c) being arranged over said second contact (110a) of the switching-element assembly (100), the airtight enclosure (13c) and the main body (14) together forming said actuator assembly (1c). A push switch as claimed in claim 7, wherein said elastic foam material of the main body (14) is polyurethane sponge. A push switch as claimed in any preceding claim, further comprising a slider assembly (30) disposed on the actuator assembly (10), the slider assembly (30) comprising a fixed housing (4) having a vertical hole, a slider (3) movable up and down in said hole, and a key-top (2b) fixed on the slider (3), the bottom end of the slider (3) contacting the top surface of the actuator assembly (10), whereby depression of the key-top (2b) is transformed into said depression of the top surface of the actuator assembly (10). A push switch as claimed in any of claims 1 to 8, further comprising a key top (2a) made of transparent material and fixed to the top surface of the actuator assembly (1a, 1b, 1c), said key top (2a) having a printed mark (21) such as a character or symbol on a bottom surface thereof. A push switch comprising a switching-element assembly (100) and an actuator assembly (1d) arranged on the switching-element assembly (100), wherein said switching-element assembly comprises first and second contacts (110b, 110a), the second contact (110a) being arranged over, and elastically movable towards, the first contact (110b) and making contact with the first contact (110b) when depressed by said actuator assembly (1d), characterised in that said actuator assembly (1d) comprises:- an actuator body (14) made of an elastic foam material formed in a solid domed shape, and a sidewall (15) of an elastic material covering the side surface of said actuator body (14), whereby depression of a top surface (20) of the actuator assembly (1d) causes a bottom surface of the actuator assembly to depress said second contact (110a). A push switch as claimed in claim 11, wherein the material of said actuator body (14) is polyurethane sponge. A push switch as claimed in claim 11 or 12, wherein said sidewall (15) is formed in a corrugated shape. A push switch as claimed in claim 11, 12 or 13, wherein said sidewall (15) is made of thermoplastic resin, silicone rubber or metal. A push switch as claimed in any preceding claim, wherein said actuator assembly (1a, 1b, 1c, 10, 1d) is detachably mounted to said switching-element assembly (100). A keyboard, comprising at least one push switch as claimed in any preceding claim, arranged on a support panel (200).

Inventors: IWASA SEIICHI C O FUJITSU LIMI, IWASA, SEIICHI, C/O FUJITSU LIMITED
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1991
Main classification: H01H13
IPC codes: H01H13