Keyboard switch with pivotal actuator lever

The present invention relates to a keyboard switch for use in combination with a membrane switch array. A keyboard switch of this type is known from EP-A-0 118 131, which falls within the terms of Art. 54(3)EPC.

The known keyboard switch comprises a reciprocative plunger mounted in a housing. An actuator is operatively connected to the electrical contacts for closing them in response to movement of the plunger. A first spring is located between the plunger and the actuator biasing these components apart. A reciprocative coupler is mounted in the housing and is engageable with the plunger during the first portion of the plunger stroke. The coupler includes a blocking tongue which engages the actuator during the first portion of the plunger stroke to prevent movement of the actuator. A second spring is located between the coupler and the housing to bias the coupler upwardly, this force being also transferred to the plunger when the coupler and the plunger are engaged. After a pre-determined amount of plunger travel, a trip mechanism separates the coupler . from the plunger with the resulting decrease in resistance to the plunger stroke, providing a tactile feedback to the operator. Simultaneously, the blocking tongue disengages the actuator, so the first spring is able to cause the actuator to close the switch.

This switch makes use of a plurality of moving parts which render the structure complicated and make assembly of the switch difficult.

It is the object of the present invention to provide a keyboard switch of the aforementioned kind which provides tactile feedback upon switch closing, comprises less parts and is thus easy to assemble.

This object is obtained by the features disclosed in claim 1. Preferred embodiments of the invention are the subject matter of the dependent claims.

The switch of the present invention comprises apart of the electrical component four separate elements only, namely, a housing, an actuator, a spring and a plunger, which are easy to assemble. In a preferred embodiment, in which the housing and the actuator are integrally connected to each other by a flexible hinge, said switch even comprises three separate parts only.

The invention is illustrated diagrammatically in the following drawings wherein:

• Figure 1 is a top plan view of the switch assembly with the cap removed, but illustrated in broken lines,
• Figure 2 is a section along plane 2-2 of Figure 1 illustrating the plunger in an unoperated position,
• Figure 3 is a section, similar to Figure 2, but illustrating the plunger in a switch closure position,
• Figure 4 is a view of the lever and plunger taken along the line 4-4 of Figure 1,
• Figure 5 is a view similar to Figure 4, but showing the plunger in a depressed position,
• Figure 6 is a partial view in section taken along place 6-6 of Figure 1,
• Figure 7 is a top plan view of the housing and the lever,
• Figure 8 is a top plan view of the plunger,
• Figure 9 is a side view of the plunger,
• Figure 10 is a side view of the plunger as viewed from the right side of Figure 9,
• Figure 11 is a bottom view of the plunger,
• Figure 12 is a section along plane 12-12 of Figure 9, and
• Figure 13 is a section along plane 13-13 of Figure 9.

The present invention relates to a keyboard switch in which the point of closure or "make point" is dependent on the geometry of the switch parts and not on the force applied to the switch. In other words, the switch will close only after the plunger has moved inwardly a given distance. Only upon such movement will the switch parts assume positions wherein the geometry of the parts allows application of a closing force to the membrane switch. The application of the closing force is sudden. Thereby, an effectively instantaneous jump in the force-deflection curve is deliberately created so the user can feel it and know when the switch has closed. This is called a tactile switch. Additionally thereto, the actuator lever is restrained from applying a switch closing force until the plunger has moved inwardly a given distance.

The tactile switch of the present invention finds utility in keyboards, such as computer terminals, typewriters, calculators and other applications in which it is desirable that the key have a very low profile. For example, the total height of the entire key structure disclosed herein normally will not be greater than 13 mm. With a key construction of this dimension, the travel of the key actuator from the unoperated to the operated position will normally be quite small. In the present instance such travel may be on the order of slightly more than 3 mm. Heretofore, it has been a problem in keyboards of this size for the operator of the key to feel confident that in fact the key has been pressed in a manner as to insure a switch closure in the underlying membrane switch array: Thus, it is necessary for there to be a tactile feel in operation of the key or some indication to the user that in fact the key has been pressed to the degree necessary to cause operation of the switch. The present invention is specifically directed to such a tactile key and to a means for providing a tactile feel in key operation. The tactile feel must not be a gradual sensation, but, rather, there must be an abrupt or sudden movement in operation of the key so that the operator is assured and in fact completely confident that switch operation has taken place.

Considering first Figures 1, 2 and 3, the tactile switch includes a housing indicated generally at 10 having a central opening 12 mounting a reciprocal plunger 14. The plunger may mount a keycap 16 of a conventional size and shape for keyboard operation. Pivotally mounted on the housing and in position to be in cooperative contact with plunger 14 is a lever 18 which will be described in more detail hereinafter.

Housing 10 is seated upon a membrane switch array which may consist of the conventional lower substrate 20, intermediate spacer 22 and membrane 24. Conventionally, the membrane and substrate will have electrical contacts thereon which normally will be positioned beneath plunger 14. There will be the usual opening 26 in the spacer beneath the switch so that movement of keycap 16 and thus plunger 14 can effect a switch closure between the membrane and substrate.

Housing 10 has a cylindrical wall 28 which defines opening 12 and that portion of housing 10 beneath opening 12 may have arcuate slots 30 just inside of wall 28, with slots 30 cooperating with arcuate projections 32 on the bottom of the plunger to maintain alignment and relative position between these two elements during switch operation. The bottom of the housing may have an opening 31 which will permit lever 18 to effect a switch closure. Further, in order to maintain the plunger within opening 12, housing 10 has oppositely-disposed hook elements 34, illustrated in Figure 6, which will ride in cooperating grooves 36 on the sides of the plunger. Note that grooves 36 have a lower surface 38 forming a stop which prevents removal of the plunger from the housing opening. When the plunger is initially inserted during assembly, the plunger will be pushed past hooks 34 which will flex to permit assembly. Once assembled, the plunger cannot be removed from the housing.

Lever 18 has a pivot portion 40 which is positioned within a slot 42 of housing portion 44 formed at one corner of the housing. Lever 18 is accordingly mounted for pivotal movement between the Figure 2 and 3 positions. Lever 18 has a spring support portion 46 which extends through an opening in wall 28 of the housing and provides a spring seat 48 which will seat a coil spring 50 which is captured between the spring seat and an inner surface 52 of plunger 14. In addition, spring seat portion 46 of lever 18 includes a downward projecting boss 54 which is positioned, as specifically illustrated in Figure 3, to provide a closure of the underlying membrane switch by forcing a portion of membrane 24 through opening 26 in the spacer so that there is contact between the electrical conductive areas of the membrane and substrate.

The side of plunger 14 which faces level 18 has a reset ramp 56 and a threshold ramp 58 with the reset ramp and threshold being separated by an open area or slot 60. To cooperate with the cam areas on plunger 14, lever 18 has a nose 62 which is positioned in alignment with reset ramp 56 and an arm 64 which cooperates with threshold 58 to hold the lever in the non-actuated position of Figures 2 and 4 until such times as arm 64 is in alignment with threshold 58. Lever 18 further has a stop 66 positioned directly behind arm 64 which restricts movement of the arm to a single plane.

The unoperated position of the switch is illustrated in Figure 2. Coil spring 50 is seated upon that portion 48 of lever 18 which extends into opening 12 and the spring maintains plunger 14 and keycap 16 in the up or unoperated position. As the keycap, and hence the plunger, are depressed during switch operation, spring 50 will be compressed as the keycap moves toward the underlying membrane switch array. However, as illustrated in Figure 4, lever 18 will be maintained in the Figure 2 position because its arm 64 will bear against the face of threshold 58. Only when plunger 14 has been depressed a sufficient distance for arm 64 to clear threshold 58 can there be inward movement of the lever. Once the arm has cleared the threshold, the lever will suddenly move to the position of Figure 3 to effect a switch closure. The force which will drive the lever through such movement is that provided by spring 50. The spring is compressed as the keycap is moved inward. Once the lever is permitted to move to the switch closure position of Figure 3, the compressed spring will provide the necessary force to effect such sudden movement.

During reset or outward movement of the keycap nose 62 of lever 18 will bear against reset ramp 56. The cooperation between these two surfaces will cause the lever to pivot in a clockwise direction as the force of spring 50 moves the keycap back to the position of Figure 2. Arm 64, as it is bearing against threshold 58, will to some degree retard the outward movement of the keycap, but the arm will flex in the single plane of its movement, as indicated in broken lines in Figure 5, as the plunger and keycap retract. Stop 66 will prevent the arm from moving in any direction other than in the vertical plane parallel with threshold 58. Thus, the arm is protected by stop 66 and is permitted the flexing movement required so that the keycap and plunger can retract. Movement of the lever during the retraction of the plunger is controlled by nose 62 riding upon reset ramp 56.

Of particular importance in this aspect of the invention is the provision of a tactile feel driving switch closure. The sudden movement can be felt by the operator of the key, thereby giving the required tactile sensation to tell the operator that in fact the key has been moved to a switch closure position. The switch closure force is effected by the compression of the return spring during the downward movement of the key. The spring is compressed until such time as the plunger has moved inwardly a distance to permit the sudden movement required for a switch closure and this sudden movement is effected by the stored force in spring 50.

We show the compound movement of the rocker member by pivotal movement in one plane and by flexing in another plane. The same type of compound movement can be derived by having the rocker mounted on a universal pivot or ball so that it can pivot in two planes. The lever may be integrally connected to the housing by a flexible hinge, commonly referred to as a living hinge.