Push-Button Switch

The present invention relates to a push-button switch feasible for various kinds of electronic apparatuses and, more particularly, to a push-button switch capable of surely operating a switch element thereof and restoring an original position even when pressed at a corner thereof, while having a waterproof and dust-proof arrangement.

Electronic apparatus are generally provided with push-button switches each implementing a particular purpose and each having a push button. When the push button of such a switch is pressed by the operator's finger, it brings contacts of the switch into connection. The problem with this kind of switch is that the operator is apt to press a corner portion of the push button around the expected central portion. Then, it is likely that the push button fails to operate the switch element correctly or even fails to restore the original position thereof. In addition, the conventional switch of the kind described cannot fully prevent water and dust from penetrating thereinto.

It is, therefore, an object of the present invention to provide a push-button switch capable of operating correctly and restoring the original position thereof even when pressed at a corner portion.

It is another object of the present invention to provide a push-button switch capable of fully intercepting water and dust otherwise penetrating thereinto.

A push-button switch of the present invention comprises a switch body, a push button having a stub for pressing the switch body at the tip thereof, a casing having an opening through which the stub is passed, and a guide member fitted on the stub such that when the push button is pressed at a corner thereof, the guide member contacts the rear of the casing to form a fulcrum, whereby the push button is inclined about the fulcrum.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which:

FIG. 1 is an exploded perspective view of a push-button switch embodying the present invention;

FIGS. 2A and 2B are sections showing the embodiment in a non-pressed condition and a pressed condition, respectively;

FIG. 3 is a section showing a conventional push-button switch;

FIG. 4 is a perspective view showing another conventional push-button switch; and

FIG. 5 is a section showing still another conventional push-button switch.

To better understand the present invention, a brief reference will be made to a conventional push-button switch, shown in FIG. 3. As shown, the switch has frame 101 and a push button 100 disposed in the frame 101. The push button 100 is tiltable about a contact point Z defined on the inner periphery of the frame 101. The problem with t h i s configuration is that when the button 100 is tilted about the fulcrum Z excessively, it also contacts the frame 101 at two other points X and Y and fails to operate correctly or even fails to return to the original position thereof.

Another conventional push-button switch is shown in FIG. 4 and disclosed in Japanese Patent Laid-Open Publication No. 1-197920. This switch is elaborated in consideration of the fact that when the push button 100 of FIG. 3 is brought into contact with the frame 101 at three points X, Y and Z, a return spring 102 cannot exert a sufficient returning force since it biases only the central part of the push button 100. As shown, the switch has a button base 111, return springs 112 fitted in four corners of the button base 111, and a plurality of parallel sets of movable contacts 113 positioned in the button base 111. Assume that a push button, not shown, is pressed at one corner thereof with the result that the button base 111 brought into contact with a fame, not shown, in an unusual way. Then, the return springs 112 effectively act on respective contact points to allow the push button to surely restore the original position thereof. However, even this kind of approach cannot obviate the excessive inclination of the push button which is the major cause preventing the push button from returning to the original position. Specifically, when the degree of the three-point contact of the push button with the frame overcomes the forces of the return springs 112, the push button cannot return. Should the preload of the return springs 112 be increased to eliminate this problem, the operator would be required to exert a greater force for operating the switch.

FIG. 5 shows still another conventional push-button switch which includes measures against the penetration of water and dust as well as a measure against the above-stated occurrence. As shown, the switch has a push button 120, an O-ring 121 fitted on the side of the push button 120 to intercept water and dust, and a resilient rib 122 extending out from the bottom of the push button 120. In assembly, the push button 120 is inserted into an opening formed in a casing 130 from the inside of the casing 130, and then the end 122a of the rib 122 is affixed to the casing 130 by heat caulking or similar technology. In this configuration, the push button 120 inclines about the fixed end 122a thereof at all times without regard to the portion being pressed. This is successful in eliminating the excessive inclination of the push button 100, as discussed with reference to FIG. 3.

However, the switch shown in FIG. 5 has some problems left unsolved, as follows. The push button 120 is affixed to the casing 130 via the rib 122 extending from one end of the push button 120, as stated above. Hence, when the button 120 is pressed at a certain corner thereof, a great load acts on one end portion of the O-ring 121 while no noticeable load acts on the other end portion of the same. Such unbalanced compression locally increases the friction acting between the O-ring 121 and the casing 130. As a result, it is likely that the button 120 fails to restore the original position even when it is not inclined excessively. In addition, the unbalanced compression of the O-ring 121 prevents the ring 121 from sufficiently sealing the gap between the button 120 and the casing 130, degrading the waterproof and dust-proof effects.

Referring to FIG. 1, a push-button switch embodying the present invention is shown in an exploded view. As shown, the switch has a push button 1 having an oblong shape. A stub 2 extends downward from the center of the underside of the push button 1 and is formed with an annular groove 2a and notches 2b. An O-ring 3 and a guide 5 are received in the groove 2a and the notches 2b, respectively, as will be described later. The tip of the stub 2 is tapered to facilitate the attachment of the O-ring 3 and guide 5. A casing 4, which will also be described later, is formed with an opening 4b. When the stub 2 is inserted into the opening 4b of the casing 4, the O-ring 3 received in the groove 2a seals the gap between the stub 2 and the casing 4.

A recess 4a is formed in the casing 4 and provided with a shape corresponding to that of the push button 1. The above-mentioned opening 4b is contiguous with the center of the recess 4a. The bottom of the recess 4a is inclined outward at opposite sides thereof, as illustrated. This allows the button 1 to be pressed deep enough to operate a switch element or push switch 6, which will be described, even when pressed at a certain corner thereof.

The guide 5 is implemented by a rectangular flat piece having substantially the same contour as the push button 1. The central part of the guide 5 is perforated generally in the form of a letter H to form a pair of resilient lugs 5a which face each other. A hole 5b is defined at the center of the H-shaped perforation, i.e., between the facing ends of the resilient lugs 5a in order to receive the stub 2. Opposite edges of the H-shaped perforation delimiting the hole 5b are rounded to facilitate the insertion of the stub 2. When the tip of the stub 2 is press-fitted in the hole 5b of the guide 5 via the opening 4b of the casing 4, the resilient lugs 5a of the guide 5 respectively snap into the notches 2b of the stub 2. As a result, the guide 5 is firmly affixed to the stub 2 in a position parallel to the push button 1.

The push switch 6 is provided with a spring thereinside and constantly biased thereby such that it urges the stub 2 of the push button 1 upward.

A reference will be made to FIGS. 2A and 2B for describing the operation of the embodiment. As shown in FIG. 2A, when the push button 1 is not pressed, the button 1 is raised by the push switch 6 via the stub 2 thereof. In this condition, the guide 5 is held in a horizontal position, contacting the underside of the casing 4 evenly. As shown in FIG. 2B, when the button 1 is pressed at one end thereof in a direction indicated by an arrow P in the figure, it inclines about a fulcrum Q, where the other end of the guide 5 and the rear of the casing 4 contact, and operates the push switch 6.

As stated above, when the push button 1 is pressed at a corner thereof, the guide 5 fitted on the stub 2 of the button 1 causes the button 1 to incline about the end of the guide 5. This prevents the end of the push button 1 from inclining excessively about the end thereof and, therefore, allows the button 1 to surely operate the push switch 6 and then restore the original position thereof.

Further, the guide 5 has a contour substantially matching that of the push button 1 and is fitted on the stub 2 in parallel to the button 1. In this condition, when any corner of the push button 1 is pressed, the guide 5 contacts the rear of the casing 4 to form a fulcrum. This, coupled with the fact that the guide 5 contacts the rear of the casing 4 easily only if any corner of the push button 1 is weakly pressed, prevents the button 1 from inclining excessively, whatever the manner in which the button 1 is pressed. Hence, the button 1 surely operates the push switch 6 and regains the original position thereof even when pressed at a corner thereof.

In the illustrative embodiment, the push button 1 is not directly affixed to the casing 4. In this condition, when the button 1 is pressed at a corner, the stub 2 moves in a certain direction with the result that a load acts on the 0-ring 3 evenly, by contrast to the conventional switch shown in FIG. 3. It follows that the O-ring 3 surely inhibits water and dust from penetrating into the assembly even when the button 1 is pressed at a corner. When the button 1 is not pressed, the guide 5 prevents the button 1 from slipping out of the switch assembly.

Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof. For example, while the guide 5 has been shown and described as substantially corresponding in contour to the push button 1, the contour may be modified in various ways in conformity to the contour of the button 1 and the amount in which the button 1 should move when pressed at a corner. By changing the contour, or size, of the guide 5, it is possible to change the position of the fulcrum and the amount of pressing. If desired, the guide 5 may be provided with a rod- or frame-like configuration in place of the flat rectangular configuration shown and described. In the embodiment, the button 1 has a generally T-shaped section, including the center stub 2. However, the present invention is applicable to other various kinds of push-button switches, e.g., the conventional switch in which a spring or springs are positioned beneath a push button.