Electricity: circuit makers and breakers – Solid contact – Membrane type
Reexamination Certificate
2003-03-10
2004-09-28
Scott, James R. (Department: 2832)
Electricity: circuit makers and breakers
Solid contact
Membrane type
C200S0050EA, C200S306000, C200S344000, C361S679090
Reexamination Certificate
active
06797906
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
(1) The present invention relates to a membrane switch having a so-called three-layered structure consisting of an upper membrane sheet, a lower membrane sheet and a spacer layer formed between both sheets, and more particularly to a membrane switch which can prevent plastic deformation of the upper membrane sheet which is pushed at the time of performing switching and can maintain a resilient restoring force for a long period, a key switch using such a membrane switch, a key board having such key switches, and a personal computer having the keyboard.
(2) Further, the present invention relates to a membrane switch which ensures stable pushing of an upper membrane sheet at the time of performing switching thus providing a stable switching operation, a key switch using such a membrane switch, a key board having such key switches, and a personal computer having the keyboard.
(3) Further, the present invention relates to a membrane switch which is capable of surely fixing a membrane sheet by adhesion to an adhesive surface of a support plate always in a flat posture without leaving bubbles between a lower surface of the lower membrane sheet of membrane switch and the adhesive surface of the support plate at the time of fixing the lower membrane sheet to the support plate, a key switch using such a membrane switch, a key board having such key switches, and a personal computer having the keyboard.
(4) Still further, the present invention relates to a key switch which guides the vertical movement of a key top by way of a pair of link members, and more particularly to a key switch which is configured to bias a key top upwardly by way of a spring member formed of a metal thin resilient plate, a key board having such key switches, and a personal computer having the keyboard.
2. Description of Related Art
(1) Conventionally, there have been proposed various membrane switches each having a three-layered structure which is comprised of a lower membrane sheet forming a lower electrode on an upper surface thereof, an upper membrane sheet forming an upper electrode on a lower surface thereof corresponding to the lower electrode, and a spacer sheet interposed between both upper and lower membrane sheets and served for making the lower electrode and the upper electrode spaced apart from each other through a switching hole formed therein corresponding to the lower electrode and the upper electrode.
In this type of membrane switch, to perform a switching operation, the upper electrode portion of the upper membrane sheet is pushed down from above using a finger directly or indirectly by way of a rubber spring, a key top or the like. Due to this switching operation, the upper electrode formed on the lower surface of the upper membrane sheet is brought into contact with the lower electrode formed on the upper surface of the lower membrane sheet through the switching hole formed in the spacer sheet so that a given switching operation is performed.
Here, there may be a case that a situation in which goods are placed on the membrane switch or a situation in which a lid cover is mounted on the membrane switch while placing goods on the membrane switch is left as it is for a long time.
In such a case, the upper membrane sheet is constituted of a resin film made of polyethylene terephthalate or the like in general and hence, the upper membrane sheet is deformed by pushing with an extremely small load. Accordingly, when the goods are placed on the membrane switch, a switch portion which corresponds to the upper electrode of the upper membrane sheet is pushed by way of the goods. As a result, a state that the upper electrode of the upper membrane sheet and the lower electrode of the lower membrane sheet are brought into contact with each other, that is, a state that the switch is turned on is continued for a long period. Here, the switching portion corresponding to the upper electrode of the upper membrane sheet is in a state that the switch portion is pushed downwardly and deformed and hence, such deformed state by pushing is held for a long period.
When the deformed state of the switch portion by pushing in the upper membrane sheet is left as it is for a long period, the switch portion is subjected to the plastic deformation and maintains the deformed state by pushing and it is no more possible to restore the original state. In such a case, the upper electrode of the upper membrane sheet and the lower electrode of the lower membrane sheet assume a switch-on state in which they are always in contact with each other and hence, there arises a drawback that the membrane switch no more performs a switching function.
The present invention has been made to solve the above-mentioned drawback of the prior art and it is an object of the present invention to provide a membrane switch which can prevent the plastic deformation of an upper membrane sheet which is pushed at the time of performing switching thereby enabling the holding of the resilient restoring force for a long period, a key switch using such a membrane switch, a keyboard having the key switches, and a personal computer having the keyboard.
(2) Further, the membrane switch has a flat laminate sheet structure, wherein the upper membrane sheet is also formed flat in general. In such a membrane switch, when the upper membrane sheet is pushed directly using a finger, although a pushing portion is formed on an upper surface of the upper membrane sheet by printing or the like for facilitating finding of the pushing portion with eyes, it is not always possible to push an appropriate position of the pushing portion with the finger and hence, it is difficult to perform a stable switching operation.
Further, when the flat upper membrane sheet is indirectly pushed by way of a so-called rubber spring or a key top which is generally known, there exist the irregularities in the accuracy of size attributed to manufacturing thereof and such irregularities in the accuracy of size directly affects influences on the pushing characteristics of the membrane switch. Accordingly, although it is possible to push the appropriate position of the pushing portion of the upper sheet by way of the rubber spring or the key top so long as the accuracy in size of the rubber spring or the key top falls within proper range, when the accuracy in size does not fall within proper range, there may be a case that the upper sheet is pushed in a state that the rubber spring or the key top is inclined. In such a case, it is difficult to perform the stable switching operation in the manner as the above-mentioned case.
The present invention has been made to solve the above-mentioned drawback of the prior art and it is an object of the present invention to provide a membrane switch which can push the upper membrane sheet in a stable manner at the time of performing switching thereby ensuring the stable switching operation, a key switch using such a membrane switch, a keyboard having the key switches, and a personal computer having the keyboard.
(3) Further, the lower membrane sheet, the spacer sheet and the upper membrane sheet which constitute the membrane switch are formed of a polyethylene terephthalate film in general and their thickness is small. Accordingly, the membrane switch per se has large resiliency and hence, handling of the membrane switch is cumbersome and difficult in many case.
It is not often that such a membrane switch is used in a single form and the membrane switch is generally used in a state that the membrane switch is mounted on a support plate or the like. In many cases, the membrane switch is fixed by adhesion to the support plate or the like using an adhesive agent or a pressure sensitive adhesive double coated tape. To fix the membrane switch to the support plate or the like by adhesion, an adhesive agent is applied to the lower surface of the lower membrane sheet or a pressure sensitive adhesive double coated tape is laminated to the lower surface of the lower membrane sheet and then the lower membrane sheet is fixe
Brother Kogyo Kabushiki Kaisha
Scott James R.
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