GB2122029A

GB2122029A - Pushbutton electrical switch

Info

Publication number: GB2122029A
Application number: GB08216832A
Authority: GB
Inventors: Masao Takakuwa
Original assignee: TOHO POLYMER; Toho Polymer KK
Current assignee: TOHO POLYMER; Toho Polymer KK
Priority date: 1981-04-06
Filing date: 1982-06-10
Publication date: 1984-01-04
Also published as: GB2122029B; DE3222747A1; JPS57166454A; FR2528620B1; FR2528620A1

Abstract

A pushbutton switch such as used on the keyboard of a small-size electronic computer, includes a main member (10) having a deformable pushbutton portion (11) carrying a movable contact (14) and one or more projections or studs (15) preferably of slightly lesser height than the movable contact (14). Opon application of finger pressure to the main member (10), the movable contact (14) is brought into uniform contact with a fixed contact (17) located below it without chattering and without tilting or skewing of the movable contact (14), should the finger pressure be applied eccentricaily of or in a diagonal direction to the pushbutton portion (11), by virtue of the supporting action of the studs (15). <IMAGE>

Description

SPECIFICATION Pushbutton switch This invention relates to a pushbutton switch for use on an electronic apparatus or the like.

In a keyboard of a small-size electronic computer, for example, a pushbutton switch having a movable contact is mounted on a printed circuit board or substrate having a fixed contact.

When the pushbutton switch is depressed by the pressure of the operator's finger, the movable contact is brought into contact with the fixed contact to close the electrical circuit connected to the fixed contact.

A known form of such a pushbutton switch is shown in Figures 1 and 2 of the drawings, in which: Figure 1 is a schematic side-sectional view of the known pushbutton switch in the unoperated position; and Figure 2 is a similar view to that of Figure 1, showing the switch in the position it assumes when subjected to off-centre finger pressure.

Referring to Figure 1, a main member 1 of the pushbutton switch has a pushbutton portion 2 and a skirt portion 3. The pushbutton portion 2 and the skirt portion 3 consist of an insulating resilient material, such as rubber, and are formed integrally with each other, as may be seen from the drawing.

A movable contact 4 made of resilient conducting material is secured onto the bottom face of the push-button portion 2 above a printed circuit board or substrate 5. A fixed contact 6 is provided on the substrate and forms a portion of a circuit pattern (not shown) of the substrate 5. In such a construction of the pushbutton switch, when finger pressure is applied to the pushbutton portion 2 of the main member 1 , the pushbutton portion 2 is deformed at an upstanding wall thereof so that the movable contact 4 is brought into contact with the fixed contact 6 to close the electrical circuit wired to the contact 6. However, this known push-button switch has the following defect. Assume that the movable contact 4 has been contacted with the fixed contact by a finger placed on the pushbutton portion 2.If the finger pressure is applied slightly off-centre, as indicated by the arrow in Figure 2, the contact 4 tends to tilt because of the resilient properties of the main member 1 of the pushbutton switch. Thus there is a tendency for the current flowing through the contacts to be interrupted because of a poor electrical connection. If the finger pressure acts on the pushbutton portion 2 in a diagonal direction, the latter is deformed transversely and causes both transverse and oblique displacement of the movable contact 4, so that the movable contact will be brought into only partial contact with the fixed contact 6, again resulting in an inadequate electrical connection.The foregoing phenomena causing displacement or tilting of the movable contact 4 with respect to the fixed contact 6, also occur when the finger is placed, not at the centre, but at the periphery of the pushbutton portion 2.

In addition, the known pushbutton switch may be deformed or levelled in a skewed manner depending on the direction in which finger pressure is exerted upon the pushbutton portion.

Hence, the switch may catch on a guide member which receives the pushbutton switch and may not close the contacts despite sustained finger pressure. The likely result would be an input error.

In view of the foregoing disadvantages ofthe previously known device, it is an object of the present invention to provide a pushbutton switch in which tilting of the movable contact is substantially prevented, even in cases where the pushbutton portion is not pressed vertically and substantially at the centre thereof, and in which an excellent contact between the movable and fixed contacts over a sufficient contact area is assured and the switch will not catch on the housing or on a guide member for the switch or on other mechanical components, so that input errors can be avoided by assuring good electrical contact.

It is another object of the present invention to provide a pushbutton switch in which contact chattering can be prevented so as to assure stable contact signals even in cases where the pushbutton portion is pressed obliquely and at an off-centre position.

It is yet another object of the present invention to provide a pushbutton switch in which contacts of predetermined surface areas can be disposed in vertical alignment with each other for enlarging the contact area and reducing the electrical resistance between the contacts to eliminate poor electrical connection.

According to the present invention, there is provided a pushbutton switch comprising a movable contact carried on a deformable support member and movable into and out of contact with an opposed fixed contact to close or open said contacts by deformation and release respectively of said support member, wherein at least one contact support member is or are provided between the planes of said contacts such that the contact member or members support does or do not inhibit the production of a good electrical connection between said contacts on closure of said contacts by deformation of said support member, but acts or act to prevent or reduce tilting of said movable contact with respect to said fixed contact on closure of said contacts by deformation of said support member.The contact support members are preferably provided on the support member and directed towards the fixed contact, and may be of a height which is lower than that of the movable contact. In a preferred embodiment, a respective contact support member is provided on either side of the movable contact and spaced at a predetermined distance therefrom. In another embodiment, three or more contact support members are provided around and at predetermined distances from the movable contact. The contact support members are preferably made of a resilient material having a high coefficient of friction, and formed as studs or like projections.

The invention will now be further described with reference to Figures 3 and 4 of the drawing, in which: Figure 3 is a schematic side-sectional view of a pushbutton switch according to a preferred embodiment of the present invention; and Figure 4 is a schematic view from below of a pushbutton switch member according to a modification of the embodiment of Figure 3.

Referring to Figure 3, the pushbutton switch according to the invention illustrated therein, has a main member 10 which is formed integrally of a pushbutton portion 11 and a skirt portion 12, from a resilient electrically insulating material such as rubber. The portions 11 and 12 are connacted together by a connecting portion 13 of reduced thickness to permit the deformation of the main member 10 thereat. A movable contact 14 made of a resilient conducting material is mounted at substantially the centre of the underside of the pushbutton portion 11, and a plurality of projections or studs 1 5 are arranged adjacent to the movable contact 14. These studs 1 5 are of slighly lesser height than the movable contact 14 and are preferably made of a material having a high coefficient of friction, such as rubber.The studs 1 5 may be formed integrally with the pushbutton portion of the main member 10 of the switch so as to ensure adequate mechanical strength. In the embodiment shown in Figure 3, two studs 1 5 are provided one on either side of and spaced at the same distance from the movable contact 14. In the embodiment shown in Figure 4, three studs 1 5 are arranged in the corners of a triangle around and spaced at the same distance from the movable contact 14. The present invention is not, however, limited to these embodiments but may comprise cases wherein only one stud is provided near the movable contact or four or more studs are provided around the movable contact 14.What is important is to provide a support member or members in the neighbourhood of the movable contact 14 so as to prevent skewing of the main body 10 of the switch. A printed circuit board or substrate having a fixed contact 1 7 mounted thereon is indicated at16.

The main member 10 of the switch has its skirt portion 12 secured to the substrate 1 6 so that the movable contact 14 is disposed above the fixed contact 1 7.

The pushbutton switch operates as follows.

When the pushbutton portion 11 of the main member 10 is pressed from above, the pushbutton portion 11 is moved down by deformation of the connecting portion 1 3 until the movable contact 14 is pressed against the fixed contact 1 7. The studs 1 5 adjacent to the movable contact 14 may then be pressed against the substrate 1 6 owing to the resiliency of the movable contact. The pushbutton portion 11 is now supported at at least two points so that tilting of the movable contact 14 can be reliably prevented.When finger pressure is applied to the pushbutton portion 11 diagonally, the entire pushbutton portion 11 is subject to both horizontal and vertical force components and moved downwardly while shifting to the left in Figure 3 by the resilient deformation of the skirt portion 1 3. The studs 1 5 then contact the substrate 1 6 at substantially the same time that the movable contact 14 is brought into abutting contact with the fixed contact 1 7. Since the studs 1 5 are in frictional contact with the substrate 16, the contact 14 will not shift horizontally along the substrate 1 6. Moreover, the movable contact 14 in contact with the fixed contact 17 will not tilt, because of the supporting action of the studs 1 5.

Assuming that finger pressure has been applied to the peripheral zone of the pushbutton portion 11, tilting of the movable contact 14 will likewise be prevented by the supporting action of the studs 1 5. It will be obvious from the foregoing description that at least three or more studs 1 5 may be provided equiangularly around the movable contact 14 to positively eliminate omnidirectional displacement as well as tilting of the movable contact 14 in one plane.

The pushbutton switch of the present invention has the following advantages.

Since the studs abut against the substrate at substantially the same time as the movable contact is pressed against the fixed contact, the movable contact is not tilted with respect to the substrate, thereby resulting in a stable electrical connection. In cases where the pushbutton portion has been pressed obliquely or near an end zone thereof, both the horizontal shifting as well as the tilting of the movable contact is inhibited by the studs 14 so that the risk of contact chattering or insufficient electrical connection can be minimized. In addition, the studs act to correct for switch tilt and displace the contact in the normal direction so that the risk of the switch engaging with the switch housing, and the consequent occurrence of an input error, are eliminated or at least greatly reduced.

With the pushbutton switch of the invention, contacts of predetermined size can be disposed in vertical alignment with each other so as to enlarge the contact and reducing the electrical resistance between the contacts to eliminate poor electrical connection.

As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended Claims.

Claims

1. A pushbutton switch comprising a movable contact carried on a deformable support member and movable into and out of contact with an opposed fixed contact to close or open said contacts by deformation and release respectively of said support member, wherein at least one contact support member is or are provided between the planes of said contacts such that the contact member or members support does or do not inhibit the production of a good electrical connection between said contacts on closure of said contacts by deformation of said support member, but acts or act to prevent or reduce tilting of said movable contact with respect to said fixed contact on closure of said contacts by deformation of said support member.

2. A switch as claimed in Claim 1, wherein the or each said contact support member is provided on said deformable support member adjacent said fixed contact and extends towards said fixed contact.

3. A switch as claimed in Claim 2, wherein the or each said contact support member is in the form of a stud or like projection on said deformable support member.

4. A switch as claimed in any one of Claims 1 to 3, wherein the or each said contact support member has a height which is lower than that of said movable contact.

5. A switch as claimed in any one of the preceding Claims, wherein said contact support member or members is or are spaced at a predetermined distance away from said movable contact.

6. A switch as claimed in any one of the preceding Claims, wherein a respective contact support member is provided on either side of the movable contact at a predetermined distance therefrom.

7. A switch as claimed in any one of Claims 1 to 5, wherein three or more contact support members are provided around and at predetermined distances from the movable contact.

8. A switch as claimed in any one of the preceding Claims, wherein the or each said contact support member is made of a resilient material having a high coefficient of friction.

9. A pushbutton switch substantially as hereinbefore described with reference to and as shown in Figure 3 or Figure 4 of the drawing.