Membrane for key switch and the key switch

The present invention provides a key switch diaphragm capable of obtaining a good click feeling and capable of avoiding contact failure and having a high durability. A key switch diaphragm 30 comprises a thin plate having flexibility and conductivity, and the key switch diaphragm 30 includes a truncated pedestal 16, and a spherical domical portion 18 being raised toward an upper portion of the pedestal 16 on the side of the upper portion of the pedestal 16. The domical portion 18 is provided at its substantially central portion with an outwardly raised portion 32 being raised toward an outer surface of the domical portion 18. An edge of the outwardly raised portion 32 on the side of its inner surface forms a contact 34.

TECHNICAL FIELD

The present invention relates to a key switch (flat switch) having a conical pedestal and a spherical domical portion on an upper end of the pedestal, and the invention also relates to a key switch.

BACKGROUND ART

FIGS. 1A and 1Bshow an outline structure of a first conventional key switch100.FIG. 1Ais a plan view of the key switch100, andFIG. 1Bis a sectional view taken along the line IB—IB inFIG. 1A.FIG. 2is a diagram showing a state where the key switch100is pressed. For example, the conventional key switch100used for a push button of a portable phone includes a base plate6provided with an annular wiring pattern2, and with a wiring pattern4which is disposed on substantially a central portion of the wiring pattern2and which is separated from the wiring pattern2. The key switch100also includes a key switch diaphragm102which is curved in a direction in which the central portion is separated away from the base plate6and which is disposed on the base plate6, and a cover film10covering the key switch diaphragm102and the base plate6. When the key switch100is used for the cellular phone and the like, the key switch100is generally required to have a durability to withstand million times presses.

One of surface (surface on the side of the base plate6) of the cover film10that is in contact with the base plate6and the key switch diaphragm102has adherence. Thus, the key switch diaphragm102is not displaced in a direction along the surface of the base plate6.

The edge of the key switch diaphragm102forms a contact12. In a state where the key switch diaphragm102is placed on the base plate6, the contact12and the wiring pattern2formed on the base plate6are electrically contacted with each other.

As shown inFIG. 2, a central portion of the key switch diaphragm102is pressed toward the base plate6, the central portion of the key switch diaphragm102is dented toward the base plate6, a contact104of the key switch diaphragm102formed in a recessed side of the central portion and the wiring pattern4formed on the base plate6are electrically connected to each other, and the wiring pattern2and the wiring pattern4are electrically connected to each other.

The key switch diaphragm102is formed by working or machining a metal thin plate having flexibility and conductivity. The key switch diaphragm102has a truncated pedestal16having appropriate height, and a spherical domical portion18being raised toward an upper portion of the pedestal16on the side of the upper portion of the pedestal16(constricted side of the pedestal).

When the key switch100is pressed, the pedestal16of the key switch diaphragm102is not deformed almost at all, and the domical portion18is mainly elastically deformed until the contact104and the wiring pattern4of the base plate6come into electric contact with each other. Thus, as compared with a case where there is no pedestal16, greater pressing stroke and greater pressing force can be secured and with this structure, a good click feeling can be obtained.

When the key switch100is pressed toward the base plate6or this pressing is released as shown inFIG. 2, the volume of space surrounded by the base plate6and the key switch diaphragm102is changed. In order to change the air pressure in the space, a through hole20is formed in the cover film10in the vicinity of the edge of the key switch diaphragm102. Since air passes through the through hole20, the air pressure in the space when the key switch100is pressed or the pressing is released is maintained substantially constantly.

DISCLOSURE OF THE INVENTION

When dust such as glass floss enters the space surrounded by the key switch diaphragm102and the base plate6, however, even if the key switch100is pressed, the wiring pattern4of the base plate6and the contact104of the key switch diaphragm102cannot contact with each other due to the glass floss. There is also a problem that a switching malfunction occurs due to contact failure of the key switch100in some cases.

To avoid this problem, as shown inFIGS. 3(A) and 3(B), it is conceived to form a key switch200or a key switch300using a key switch diaphragm102A or a key switch diaphragm102C in which the central portion is provided with a raised portion102B.

FIG. 3(A)is a sectional view of a second conventional key switch200. The key switch diaphragm102A of the key switch200is provided at its substantially central portion with the raised portion102B being raised toward the recessed side. When the key switch200is pressed, the contact104A and the wiring pattern4of the base plate6electrically contact with each other.

FIG. 3(B)is a sectional view of a third conventional key switch300. The key switch diaphragm102C of the key switch300is provided at its substantially central portion with a plurality of (three in this example) raised portions102B being raised toward the recessed side. When the key switch300is pressed, at least one of the contacts104A and the wiring pattern4of the base plate6electrically contact with each other.

In the case of the key switch200, an area of the contact104A which contacts with the wiring pattern4of the base plate6is smaller than that of the contact104of the key switch100. Thus, even if dust such as glass floss enters the surrounded space, the contact failure of the key switch200is less likely to occur as compared with the key switch100.

The key switch300includes the plurality of contacts104. When the key switch300is pressed, if at least one of the contacts comes into contact with the wiring pattern4of the base plate6, the contact failure of the key switch can be avoided. Thus, the contact failure is further less likely to occur as compared with the key switch200.

When the dust which enters the surrounded space is glass floss or other fiber, however, since the raised portion102B pushes the dust away, the contact failure which is caused when the key switch200or key switch300is pressed is avoided, but when the dust is material which is prone to adhere such as adhesive droplets or resin droplets and such dust adheres to the contact104A of the key switch diaphragms102A,102C, there is a problem that the contact failure is likely to occur.

Furthermore, in the case of the key switch diaphragm102A of the key switch200or the key switch diaphragm102C of the key switch300, the raised portion102B is formed on the recessed side (on the side of the base plate6or pedestal16) of the central portion (pressed portion). Therefore, a distance between the contact104A formed on the tip end side of the raised portion102B and the wiring pattern4of the base plate6becomes shorter than the key switch100when the switch is not operated (in a state in which the key switch200or key switch300is not pressed as shown inFIGS. 3(A) and 3(B). Therefore, in the case of the key switch200or300, the pressing stroke becomes smaller than that of the key switch100, and a good click feeling cannot be obtained.

To secure the pressing stroke, it is conceived that the height of the pedestal16is increased. However, if the key switch diaphragm102A of the key switch200or the key switch diaphragm102C of the key switch300is molded using press such that the height of the pedestal16is increased, the key switch diaphragm102A or the key switch diaphragm102C must largely be plastically deformed especially at the pedestal16, and a large residual stress is generated in the key switch diaphragm102A or102C. Whenever the operation that the key switch200or key switch300is pressed and the pressing is released is repeated, the key switch diaphragm102A or key switch diaphragm102C are elastically deformed, the repeated load generated by this elastic deformation is added to the residual stress and the large stress is generated, and there is a problem that the key switch diaphragm102A or key switch diaphragm102C is prone to become fatigued and broken, and the durability is deteriorated.

In the case of the key switch300, since the key switch diaphragm102C includes the plurality of raised portions102B, the contact failure is less likely to occur as compared with the key switch200, but when the key switch300is pressed, if one of the contacts104A of the key switch diaphragm102C comes into contact with the wiring pattern4of the base plate6, since the one contact is decentered from the key switch diaphragm102C, a stress maldistributed in the key switch diaphragm102C is generated, and the durability is more deteriorated than the key switch200in some cases.

FIG. 3(C)is a sectional view of a fourth conventional key switch400. A key switch diaphragm102D of the key switch400is provided at its substantially central portion with a through hole102E instead of the raised portion102B.

When the key switch400is pressed, the edge portion of the base plate6on the side of the outer peripheral edge forms a contact104B, and this contact104B and the wiring pattern4of the base plate6are brought into contact with each other and are electrically connected. In the key switch400, the edge of the through hole102E formed in substantially central portion of the key switch diaphragm102D forms the contact104B. Thus, when the key switch400is pressed, even if dust exists in the surrounded space, the contact104B easily contacts with the wiring pattern4of the base plate6, and the contact failure can be avoided. Since there exists no raised portion on the recessed side of the key switch diaphragm102D, the pressing stroke can be ensured, and a good click feeling can be obtained, without increasing the height of the truncated pedestal16.

However, when the key switch400is pressed, the key switch diaphragm102D is elastically deformed, stresses are concentrated on the outer peripheral edge of the through hole102E, and there is a problem that cracks are generated from the outer peripheral edge of the through hole102E toward the outer periphery of the key switch diaphragm102D in some cases, and the durability of the of the key switch400is deteriorated in some cases.

When the key switch400is pressed, since there exists the through hole102E, an adhesive portion of a cover film10is transferred to the wiring pattern4of the base plate6, and there is a problem that the contact failure occurs in the key switch400.

It is conceived that a cover film having no adherence is used in a portion corresponding to the through hole102E. However, it is troublesome to produced such a cover film, and it is difficult to assemble a key switch such that a non-adhesive portion and the through hole102E are aligned with each other in position.

As shown inFIG. 1B, the key switch100comprising the key switch diaphragm102includes a press member (actuator) AC1for pressing the key switch diaphragm102. The actuator AC1is integrally formed together with a sheet-like elastic support member (such as silicon rubber sheet) (not shown) which is disposed on a front surface of the key switch100. The actuator AC1is laminated on the base plate6of the key switch and the key switch diaphragm102together with the silicon rubber sheet, and is disposed on the key switch100. When the actuator AC1is disposed, it is disposed such that the center CL12of the actuator AC1is deviated from the center CL10of the key switch diaphragm102by ΔL3in some cases.

If the actuator AC1is deviated in this manner, in the case of the conventional key switch100using the key switch diaphragm102, a later-described click rate (one of indices for objectively showing the quality of the click feeling by means of numerical value) is lowered in substantially proportion to the deviation amount. That is, there is a problem that the click feeling is deteriorated by the deviation amount. This problem occurring with the deviation amount also happens in the other key switches200,300, and400.

The present invention has been achieved in view of the above problems, and the present invention provides a key switch diaphragm and a key switch having a high durability and capable of obtaining a good click feeling when the switch is pressed, and capable of avoiding generation of contact failure.

A first technical aspect of the present invention provides a key switch diaphragm comprising, a first leaf spring having conductivity and having a base fixed in position with respect to a reference surface and a plate portion being raised in a direction away from the reference surface, and a second leaf spring having conductivity and formed on a central portion of the plate portion raised in a direction away from the reference surface, wherein when an external force acting toward the reference surface is applied to the second leaf spring, an edge of the central portion comes into contact with the reference surface.

According to a second technical aspect of the invention, the diaphragm further comprises at least one raised portion being raised toward the reference surface, wherein when an external force acting toward the reference surface is applied to the second leaf spring, at least the raised portion comes into contact with the reference surface.

A third aspect of the invention provides the key switch diaphragm according to the first aspect, wherein the diaphragm further comprises a third leaf spring formed on the second leaf spring raised in a direction away from the reference surface, and wherein when an external force acting toward the reference surface is applied to the third leaf spring, an edge of at least the third leaf spring comes into contact with the reference surface.

A fourth aspect of the invention provides the key switch diaphragm according to the first aspect, wherein the diaphragm further comprises an opening formed in the second leaf spring, and wherein when an external force acting toward the reference surface is applied to the second leaf spring, an edge of at least the opening comes into contact with the reference surface.

A fifth aspect of the invention provides the key switch diaphragm according to the second aspect, wherein the diaphragm further comprises the raised portion comprises three raised portion, the raised portions are disposed at equal distances from one another on the circumference of a circle formed around a center of the second leaf spring.

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

FIGS. 4A and 4Bshow an outline structure of a key switch diaphragm30constituting a key switch1according to a first embodiment of the present invention.FIG. 4Ais a plan view of the key switch diaphragm30,FIG. 4Bis a sectional view taken along the line IV B—IV B inFIG. 4A.FIG. 5shows a state where the key switch1constituted by the key switch diaphragm30is pressed. InFIG. 4A, a base plate6, a cover film10and a wiring pattern2,4of the base plate6are omitted to facilitate understanding.

The key switch diaphragm30is integrally formed by pressing a thin plate (e.g., metal thin plate) having flexibility and conductivity. The key switch diaphragm30is formed such that the key switch diaphragm30is squeezed toward a substantially central portion of a spherical domical portion18, and an outwardly raised portion32being raised toward an upper side (raised side) of the domical portion18is formed. That is, the key switch diaphragm30includes the spherical domical portion18raised in a direction (negative direction in an axial Z) where the domical portion18is separating away from a reference surface PL defined by the conductor pattern2, on an upper side of a truncated pedestal16. The key switch diaphragm30also includes the outwardly raised portion32being raised toward an outer surface side (raised side) in a direction separating away from the reference surface PL. The outwardly raised portion32is provided at substantially central portion of the domical portion18. An edge of the domical portion18on the side of inner surface (recessed side) functions as a contact34.

In other words, the key switch diaphragm30is made of thin plate having flexibility and conductivity. The key switch diaphragm30includes the truncated pedestal16, and the spherical domical portion18being raised toward an upper portion of the pedestal16on the side of the upper portion (constricted side) of the pedestal16. The key switch diaphragm30also includes the circular outwardly raised portion32being raised toward the outer surface (raised side; opposite side from the pedestal) of the domical portion18. The outwardly raised portion32is located at substantially central portion of the domical portion18. The edge (boundary portion between the outwardly raised portion32and the domical portion18) of the inner surface side (pedestal side, recessed side of the domical portion18) forms the contact34.

The outwardly raised portion32includes a spherical domical portion32B being raised toward an upper portion of a cylindrical truncated pedestal32A. The domical portion32B is located closer to the upper portion of the pedestal32A (constricted side of the pedestal32A). The outwardly raised portion32also includes a raised portion (inwardly raised portion)36being raised toward the inner surface (recessed side) of the domical portion32B. A tip end of the raised portion36constitutes a contact38. The raised portion36is located at substantially central portion of the domical portion32B.

In other words, the outwardly raised portion32is provided at its substantially central portion with the raised portion36being raised toward the inner surface of the outwardly raised portion32(pedestal side, and recessed side of the domical portion18) to constitute the contact38.

Next, a case where an external force is applied to the key switch1in the positive direction of the Z-axis will be explained usingFIGS. 5(A) and 5(B). The positive direction means a direction approaching the base plate6or the reference surface PL. If the substantially central portion of the key switch1is pressed toward the base plate6, the key switch diaphragm30is elastically deformed (the domical portion32B and the domical portion18of the key switch diaphragm30are mainly elastically deformed). The contact34and contact38of the key switch diaphragm30come into contact with the wiring pattern4of the base plate6. As shown inFIG. 5(B), the contact portion is formed of an annular contact surface C21, and a circular contact surface C22formed on an inside substantially central portion of the contact surface C21.

The domical portion18and the pedestal16function as a first leaf spring having a toggle mechanism which has two states, i.e., a stable state shown inFIG. 4Aand a balanced state shown inFIG. 5(A)under an external force (in the Z-axis normal direction) is applied. An upwardly raised portion32functions as a second leaf spring. The edge34functions as a contact which connects these two leaf springs. Thus, the key switch diaphragm30of this embodiment also includes first leaf springs18having the base16and the plate portion18, and a second leaf spring32connected to the plate portion18through the contact34. An outer edge17of the plate portion18is fixed relative to the reference surface PL by the base16.

In the key switch diaphragm according to the invention, the first leaf spring and the second leaf spring are not limited to concentric elliptic disc springs shown inFIG. 4A, only if one cross section thereof is a leaf spring shown inFIGS. 4B and 5(A). That is, the present invention is applied to a diaphragm having such a cross section that both ends (outer edges)17and17of the plate portion18are fixed relative to the reference surface PL by the bases16and16, and the second leaf spring32is fixed to the first leaf springs18and18by the edges34and34. For example, if the diaphragm comprises a ribbon-like leaf spring, the contact pattern C21of the edge34is not annular in shape, and there exist two contact patterns C21substantially located at two separate symmetric positions with respect to the contact pattern C22.

When the key switch1is not pressed, the contact38of the key switch diaphragm30is located at the same level as or slightly higher than the contact34. That is, the distance from the reference surface PL is substantially the same as the contact34or the contact38is slightly separated from the contact34with respect to the reference surface PL. Thus, when the key switch1is pressed, the domical portion18which is the first leaf spring and the domical portion32B which is the second leaf spring are appropriately elastically deformed, and both the contact34and contact38come into contact with the wiring pattern4(substantially simultaneously for example). With this structure, it is possible to avoid a case where the click feeling is abruptly changed halfway when the key switch1is pressed.

If the contact and the wiring pattern contact with each other, the wiring pattern2and the wiring pattern4of the base plate6are electrically connected to each other. If the external force is not applied to the key switch diaphragm30in the direction of the wiring pattern4(positive direction of Z-axis), the state shown inFIG. 5(A)becomes unstable, the pressed position is released, and the key switch diaphragm30is returned to its initial position (stable state) before the key switch diaphragm30is elastically deformed. As a result, the contact34and contact38of the key switch diaphragm30are separated from the wiring pattern4of the base plate6, and the electric connection between the wiring pattern2and the wiring pattern4of the base plate6is cut off.

According to the key switch1, which comprises the key switch diaphragm30, the edge which connects the domical portion18and the upwardly raised portion32with each other function as the ring-like contact34which surrounds the contact38. Thus, when the key switch1is pressed, the edge contact34comes into contact with the wiring pattern4. As a result, even if dust enters into the space surrounded by the key switch diaphragm30and the base plate6or adhesive droplets or resin droplets adheres to a portion of the contact34, the contact34and the wiring pattern4can reliably contact with each other. Thus, the contact failure caused when the key switch1is pressed can be avoided.

It is preferable that the outer diameter of the outwardly raised portion32is 20% of the outer diameter of the 30% or more, and 2.5 mm or less. With this size, the edge34functions as electric contact, stresses around the edge of the outwardly raised portion32are effectively dispersed, and the durability is also enhanced.

Since the contact38also comes into contact with the wiring pattern4together with the contact34, the contact failure caused when the key switch1is pressed can further be avoided. When the key switch1is pressed, if the raised portion36provided on the substantially central portion of the outwardly raised portion32comes into contact with the wiring pattern4, the spherical domical portion32B of the outwardly raised portion32as the second leaf spring is not deformed further. As a result, the domical portion32B does not receive excessive stresses, and the durability of the key switch diaphragm30can be enhanced.

The outwardly raised portion32provided on the substantially central portion of the domical portion18of the key switch diaphragm30being raised outward of the domical portion18, i.e., in a direction separating from the wiring pattern4with respect to the domical portion18(negative direction of Z-axis). Thus, even if the height of the pedestal16is not so high, large stroke can be secured like the conventional key switch100when the key switch1is pressed, and a good click feeling can be obtained. Since it is not necessary that the height of the pedestal16is high, residual stresses generated in the key switch diaphragm30when the key switch diaphragm30is pressed can be suppressed low, and the durability of the key switch diaphragm30can be enhanced.

When the key switch1is pressed, the substantially central portion of the key switch diaphragm30comes into contact with the wiring pattern4of the base plate6. Therefore, eccentric stresses are not generated in the key switch diaphragm30, stresses generated in the key switch diaphragm30can equally dispersed. Thus, durability against repeatedly pressing and release of pressing of the key switch diaphragm30can be enhanced.

As compared with the conventional key switch400, the key switch1includes the raised portion32and the edge34of first leaf springs, in addition to the domical portion18of the first leaf spring provided at its central portion with the through hole. Thus, since stresses generated at peripheral edge of the hole are not concentrated, the durability of the key switch1is enhanced. In the key switch diaphragm30, the raised portion36provided on the substantially central portion of the domical portion32B may be omitted.

Since the raised portion32is raised in a direction separating away from the wiring pattern4(negative direction of Z-axis) with respect to the domical portion18, the cover film10is elastically deformed at this portion, tension is increased, the pressure against the raised portion32is also increased and thus, the force of the cover film10applied to the key switch1for adhering and holding that can be increased.

Second Embodiment

FIGS. 6(A) and 6(B)show an outline structure of a key switch diaphragm40constituting a key switch according to a second embodiment of the present invention. In the key switch diaphragm40, the domical portion32B of the outwardly raised portion32is provide at its substantially central portion with an outwardly raised portion42, instead of the raised portion36of the first embodiment provided at the substantially central portion of the domical portion32B of the outwardly raised portion32. Other elements of the key switch diaphragm40are structured substantially the same as that of the key switch diaphragm30.

That is, the key switch diaphragm40includes the outwardly raised portion42provided at the substantially central portion of the domical portion32B of the outwardly raised portion32. An inner surface side (recessed side) edge of the domical portion32B functions as a contact44. The outwardly raised portion42is raised such as to separate from the reference surface PL toward the outer surface side (projecting side) of the domical portion32B. The outwardly raised portion42is provided at its upper side (constricted side of a pedestal42A) of the truncated pedestal42A with a spherical domical portion42B being raised toward an upper portion of the pedestal42A. Thus, the outwardly raised portion42functions as a third leaf spring formed on the outwardly raised portion32which functions as the second leaf spring.

In other words, the substantially central portion of the outwardly raised portion32is provided with the outwardly raised portion42being raised toward an outer surface (opposite from the pedestal16) of the outwardly raised portion32. The edge (boundary with respect to the outwardly raised portion32) of the inner surface side (on the side of the pedestal16) of the outwardly raised portion32functions as an annular contact44.

If the substantially central portion of the key switch constituted by the key switch diaphragm40is pressed, the key switch diaphragm40is elastically deformed, and the contacts34and44of the key switch diaphragm40comes into contact with the wiring pattern4of the base plate6. As shown inFIG. 6(B), the contact portion is formed of an annular contact surface C31and an annular contact surface C32formed on the inner substantially central portion of the contact surface. With this contact, the wiring patterns2and4of the base plate6are electrically connected to each other through the key switch diaphragm40.

The key switch constituted by the key switch diaphragm40functions substantially in the same manner as the key switch1of the first embodiment and can obtain substantially the same effect. Unlike the key switch1, the contact44is formed in the form of an edge. Thus, even if dust enters the space surrounded by the base plate6and the key switch diaphragm40, the contact44can easily contact with the wiring pattern4in addition to the contact34, and contact failure when the key switch is pressed can further be avoided.

Third Embodiment

FIGS. 7(A) and 7(B)show an outline structure of a key switch diaphragm50constituting a key switch according to a third embodiment of the present invention. The key switch diaphragm50is different from the key switch diaphragm30of the first embodiment in that the substantially central portion of the domical portion32B of the outwardly raised portion32is provided with a through hole52instead of the raised portion36. Other elements of the key switch diaphragm40are structured substantially the same as that of the key switch diaphragm30. In other words, the outwardly raised portion32is provided at its substantially central portion with the through hole52. A contact58is formed on an edge of an inner surface side (on the side of the pedestal16) of the through hole52.

If the substantially central portion of the key switch constituted by the key switch diaphragm50is pressed, the key switch diaphragm50is elastically deformed, and the contact34of the key switch diaphragm50and the contact58formed from the edge of the inner surface side (recessed side of the domical portion32B) of the through hole52come into contact with the wiring pattern4of the base plate6. As shown inFIG. 7(B), the contact portion is formed from an annular contact surface C41and an annular contact surface C42formed at an inner substantially central portion of this contact surface C41.

The key switch having the key switch diaphragm50functions substantially in the same manner as the key switch1of the first embodiment and can obtain substantially the same effect. Unlike the key switch1, the contact58is formed in the form of an edge. Thus, even if dust enters the space surrounded by the base plate6and the key switch diaphragm50, the contact58can easily contact with the wiring pattern4in addition to the contact34, and contact failure when the key switch is pressed can further be avoided.

According to the key switch using the key switch diaphragm30or the key switch diaphragm50, since there exists no raised portion on the outer side (side separating away from the base plate6) of the domical portion32B of the outwardly raised portion32, the height of the key switch diaphragm30or the key switch diaphragm50becomes smaller than that of the key switch diaphragm40, and since the height of the key switch is suppressed, the key switch can be reduced in size.

As compared with the conventional key switch400, the key switch50includes the through hole in the central portion, like the conventional key switch400, but the through hole (opening)52of the key switch diaphragm50is formed above the second leaf spring32which is an elastic element independent from the first leaf spring18. Thus, the contact pattern of the key switch diaphragm50is constituted by the two annular patterns C41and C42as shown inFIG. 7(B)and the stresses are appropriately dispersed. Therefore, since stresses generated in the peripheral edge of the opening52are not concentrated, the durability of the key switch1is enhanced.

Fourth Embodiment

FIGS. 8A and 8Bshow an outline structure of a key switch diaphragm60constituting a key switch according to a fourth embodiment of the present invention.FIG. 8Ais a plan view of the key switch diaphragm60, andFIG. 8Bis a sectional view taken along the line VIII B—VIII B inFIG. 8A.

The key switch diaphragm60is different from the key switch diaphragm30of the first embodiment in that the domical portion32B of the outwardly raised portion32is provided with a plurality of (three, for example) raised portions36at locations except the key switch diaphragm60and the center CL2of the outwardly raised portion32. Other structure is substantially the same as that of the key switch diaphragm30.

That is, the key switch diaphragm60includes the raised portions36being raised from the inner surface side (on the side of the pedestal16) of the outwardly raised portion32as the second leaf spring to constitute the contact38. Each raised portion36is disposed on the circumference of a circle CL3formed around the center CL2of the key switch diaphragm60. In this embodiment, the number of raised portions36is three, and they are disposed at locations equally divided on the circumference.

According to the key switch diaphragm of this embodiment, in addition to the characteristics described in the first to the third embodiments, the following effects can be obtained. As shown inFIGS. 8A and 8B, since the outwardly raised portion32is provided with the plurality of raised portions36, the deformation stresses of the domical portion32B of the outwardly raised portion32are increased. When an external force from an upper surface is applied to the key switch diaphragm60, the surface of the domical portion32B is not deformed almost at all, and operation by the deformation of the domical portion18is carried out. That is, if an external force is applied to the key switch diaphragm60at a location displaced by ΔL1as shown inFIG. 8B, since the deformation of the domical portion18is generated before the outwardly raised portion32is deformed, the original click feeling of the key switch diaphragm60is not deteriorated almost at all if the displacement caused by the external force is in a range of the domical portion32B of the outwardly raised portion32, and a stable click feeling can be obtained.

Key Switch

A key switch constituted using the key switch diaphragm according to the present invention will be explained. The key switch includes a base plate (not shown) which comes into contact with an edge (contact12) of the key switch diaphragm60. The key switch diaphragm60is placed on one of surfaces of the base plate. The key switch also includes a press member (actuator) AC1, which is movably fixed in position in a direction intersecting the reference surface PL (for example, the direction of orthogonal Z direction) toward the key switch diaphragm60, and which applies an external force to the key switch diaphragm60toward the reference surface PL. The press member AC1presses the key switch diaphragm60through a sheet-like support member (not shown) such as an elastic material provided on a front surface of the key switch. More specifically, the key switch includes a flat contact AC3on one end side (end facing the diaphragm60) of the press member AC1. The contact AC3moves and comes into contact with the diaphragm60, and applies the external force toward the reference surface PL (positive direction of Z-axis).

In a normal position (in a state where an external force is not applied to the diaphragm60), the contact34of the outwardly raised portion32of the key switch diaphragm60is separated from the base plate and the key switch diaphragm60is maintained in its stable state. If the press member AC1presses, the external force is applied to the key switch diaphragm60and is elastically deformed, and the contact34of the outwardly raised portion32of the key switch diaphragm60comes into contact with the base plate (or reference surface). Each contact38of the outwardly raised portion32also comes into contact with the base plate (or reference surface).

A first electric wire (first conductor pattern) being provided on one of the surfaces of the base plate and functioning as a contact, and a second electric wire (second conductor pattern) which is electrically connected to the pedestal16are disposed on the base plate such that they are electrically isolated. In the normal position, the first electric wire and the second electric wire are left isolated. If the press member AC1pressed the key switch diaphragm60, the contact34or the contact38of the central portion of the key switch diaphragm60comes into contact with the first electric wire of the base plate, and the first electric wire and the second electric wire are electrically conducted with each other through the key switch diaphragm60.

The key switch using the key switch diaphragm60of the fourth embodiment of the present invention is explained above. And it is apparent that the above explanation can also be applied to key switches using other key switch diaphragms30,40, and50. According to the key switch having the key switch diaphragm60, the same effect as that of the key switch1of the first embodiment can be obtained.

According to the key switch constituted using the key switch diaphragm60, even if the key switch1is pressed in a position where the center of the actuator AC1is deviated from the center of the key switch diaphragm60by ΔL1, since the domical portion18is deformed before the outwardly raised portion32is deformed, the original click feeling of the key switch diaphragm60is not deteriorated (deterioration of click rate) almost at all if the deviation value ΔL1is in a range of the domical portion32B of the outwardly raised portion32, and a stable click feeling can be obtained. That is, since the outwardly raised portion32is an elastic element (second leaf spring) independent from the domical portion18and the like, if an external force is applied to any position of the outwardly raised portion32, the outwardly raised portion32is moved and deformed as a whole, the external force can equally be distributed to the domical portion18. As a result, a stable click feeling can be obtained even if the displacement ΔL1is generated. Thus, a person skilled in the art will easily understand that even if other key switch diaphragm30,40, or50of the first, the second, or the third embodiment is used, the same effect can be obtained.

Next, a measurement result of the click feeling (click rate) when the actuator is deviated in position will be explained.FIG. 9is a graph for explaining the click rate.FIG. 10is a graph showing a relationship between a deviation of an actuator position and a click rate of the key switch diaphragm, and a relationship between the deviation of the actuator position and a displacement load value of the key switch diaphragm.

The click rate means one of indices for objectively showing the quality of the click feeling. As the click rate value is smaller, the click feeling is generally deteriorated more. A lateral axis inFIG. 9shows a displacement amount (stroke) in the moving direction (Z-axis direction inFIG. 8B) when the key switch diaphragm is pressed, and this amount is more increased as the key switch diaphragm approaches closer to the reference surface PL. A vertical axis shown inFIG. 9indicates a load when the key switch diaphragm is pressed.

That is, if a pressing operation of the key switch diaphragm is initiated from the normal position (external force is not applied to the diaphragm), the load is gradually increased from “0”, and reaches the maximum value P1. If the key switch diaphragm is further pressed, the load assumes the minimum value and then, the value is increased. Thus, the key switch diaphragm has a contact structure utilizing a toggle mechanism.

In a case where the key switch diaphragm constitutes the key switch placed on the base plate, the contact of the central portion of the key switch diaphragm comes into contact with the conductor (first electric wire) located at the reference surface PL when the stroke amount is a stroke amount S2before reaching a stroke amount S3. If the load at that time is defined as P2, the click rate η is expressed as η(%)=100×(P1−P2)/P1.

A lateral axis inFIG. 10shows the deviation of the displacement amount ΔL1, and a vertical axis inFIG. 10shows the maximum load P1and the click rate. In the graph shown inFIG. 10, G1shows the maximum value load P1of the key switch diaphragm60, and G3shows the maximum value load P1of the conventional key switch diaphragm102C (seeFIG. 3(B)). Furthermore, G5inFIG. 10shows the click rate of the key switch diaphragm60, and G7shows the click rate of the conventional key switch diaphragm102C. As shown inFIG. 10, the maximum value loads are almost the same between the key switch diaphragm60and the conventional key switch diaphragm106C, and the value is substantially constant (160gf=1.57 N) irrespective of the deviation of the actuator position as the displacement between the center of the key switch diaphragm and the center of the actuator.

On the other hand, in the key switch diaphragm60, the value is substantially constant (about 40%) irrespective of the center CL2of the key switch diaphragm60and the center CL4of the actuator AC1, but in the conventional key switch diaphragm102C, the value is gradually reduced as the displacement amount between the center of the key switch diaphragm and the center of the actuator is increased, and when the deviation reaches 0.8 mm, the click rate is reduced to about “0”.

The outer diameter d4of the key switch diaphragm60shown inFIG. 8Bis 5 mm, the outer diameter d2of the outwardly raised portion32is 2 mm, and the outer diameter of the conventional key switch diaphragm102C is also 5 mm. The outer diameter of the actuator AC1is 2 mm.

Key switches are constituted using the various key switch diaphragms, the key switches are pressed and released, and ON/OFF operation of the key switches are repeated. As a result, the volume and pressure in the space surrounded by the key switch diaphragm and the base plate on which the key switch diaphragm is place are varied, and air and fine dust may enter the surrounded space from a narrow gap between the base plate and the outer edge of the key switch diaphragm in some cases.

As described above, there is a strong tendency that the fine dust interferes with air which enters the surrounded space from narrow gaps formed substantially uniformly along the entire outer periphery of the key switch diaphragm, and the dust is converged to the central portion of the key switch diaphragm and accumulated thereon.

According to the key switch constituted by the key switch diaphragm60, since the raised portions36constituting the contacts38are disposed on the inner surface side of the outwardly raised portion32on the circumference of the circle formed around the key switch diaphragm60. In other words, the central portion of the key switch diaphragm60is not formed with the contact38. Therefore, a contact failure occurring with the fine dust converted to and accumulated on the central portion of the key switch diaphragm60and by repeated using of the key switch can be suppressed as low as possible.

Furthermore, according to the key switch having the key switch diaphragm60, the raised portions36constituting the contacts38are disposed on the inner surface side of the outwardly raised portion32at locations equally divided into three on the circumference of a circle CL3formed around the center CL2of the outwardly raised portion32. That is, the raised portions36are disposed in well balance such that when the key switch diaphragm60is suppressed, the contacts38on the tip ends of the raised portions36and the edge contact34of the outwardly raised portion32define one flat surface. Thus, even if the key switch diaphragm is pressed in a direction which is not perpendicular to the base plate surface (reference surface PL) but in a direction slightly deviated from the direction perpendicular (the Z-axis), any one of the contacts of the key switch diaphragm easily comes into contact with the conductor located on the reference surface.

Thus, according to the key switch using the key switch diaphragm60, even if the key switch is pressed slightly obliquely, the contact failure of the contact of the key switch can be suppressed.

Although it is possible that the number of raised portions constituting the contacts on the inner surface side of the outwardly raised portion32may be four or more, the structure of the key switch diaphragm becomes complicated. Furthermore, internal stresses of the key switch diaphragm may be increased. Thus, if the number of raised portions constituting the contacts is set to three, the structure of the key switch diaphragm is simplified, and contact failure of the key switch using the key switch diaphragm can be reduced as small as possible.

Next, comparison of lifetime of the key switch diaphragm according to the present invention and lifetime of the conventional key switch diaphragm102C (seeFIG. 3(B)) will be explained. A lifetime test was carried out with respect to ten samples of key switch diaphragm60(type I), ten samples having no raised portion36on the key switch diaphragm60(type II), and ten samples of the conventional key switch diaphragm102C (type III). The type having no raised portion36corresponds to the key switch diaphragm having the second leaf spring and is one of the typical embodiments of the present invention. To ensure the same click feeling, the distance between the raised portion and the reference surface was set equally.

In the test, a key switch was pressed two million times under the load of 320 gf (3.1 N) at frequency of three to five times per second. As a result of the pressings, a crack or abnormal restoration (left dented) was generated in all of the conventional key switch diaphragms102C. In the key switch diaphragm of the second conductor pattern of the type of this invention, no crack or no abnormal restoration was generated, and six samples had 30% variation amount of the maximum value load P1, and four samples had 30% to 40% variation amount. In the key switch diaphragm60of the type having the raised portions, no crack or no abnormal restoration was generated, and all samples had the variation amount of 30% of the maximum value load P1shown inFIG. 9and thus, no abnormality before and after the test in the restoration load was generated. Therefore, it becomes apparent that the lifetime of the key switch diaphragm according to the invention is enhanced. It becomes apparent that the lifetime is enhanced of the raised portion is provided.

It is conceived that the reason why the lifetime of the key switch diaphragm according to the present invention is enhanced is that since the first leaf spring is provided at its central portion with the second leaf spring, the contacts34are not located at a point but are annularly distributed toward the reference surface PL, and since the load is shared between the plurality of bent portions17,34, and35as shown inFIG. 4Band thus stresses are appropriately dispersed, and elasticity of each leaf spring is maintained. A reason why the lifetime of the key switch diaphragm60having the raised portions is long is that when the same pressing stroke as that of the conventional key switch diaphragm102C is to be obtained, since the outwardly raised portion32is provided with the raised portions36, the pedestal which generates large internal stresses at the time of production can be made lower. Thus, the magnitude of the internal stresses generated when it is produces is smaller in the key switch diaphragm60. Furthermore, it is conceived that since the raised portions36function as stoppers which limit the deformation amount (Z direction) of the diaphragm60irrespective of the magnitude of the external force applied to the diaphragm60, excessive stresses to the first leaf spring or the second leaf spring are limited and thus, the lifetime is enhanced.

According to the present invention as described above, there is an effect that the key switch diaphragm capable of obtaining a good click feeling when a switch is pressed, capable of avoiding contact failure, and having a high durability.