US3668356A

US3668356A - Mechanical key actuator including a cantilever beam restoring force means

Info

Publication number: US3668356A
Application number: US103557A
Authority: US
Inventors: Dennis H Kekas
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1971-01-04
Filing date: 1971-01-04
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06
Also published as: FR2121212A5; DE2165679A1; CH534418A; NL7117227A; DE2165679C3; JPS5221192B1; JPS4714668A; CA958452A; DE2165679B2; ES398485A1; GB1329370A; IT945731B

Abstract

An actuating device having a keytop, base, and an actuator assembly affixed to the base, the assembly including a rod and a cantilever beam arrangement for providing a snap action response to key force and for driving the rod to form an electrical makebreak contact, the base and assembly constituting a unitary flexible-tough thermoplastic body.

Description

United States Patent Kekas [451 June 6,1972

[54] MECHANICAL KEY ACTUATOR I INCLUDING A CANTILEVER BEAM RESTORING FORCE MEANS [72] Inventor: Dennis H. Kekas, Raleigh, N.C.

[73] Assignee: International Business Machines Corporation, Armonk, NY. e

22 Filed: Jan. 4, 1971 21 Appl.No.: 103,557

3,582,584 6/1971 Best ..200/l68C Primary Exaniiner--H. 0. Jones AttorneyHanifin & Jancin and Robert B. Brodie [57] ABSTRACT An actuating device having a keytop, base, and an actuator assembly affixed to the base, the assembly including a rod and a cantilever beam arrangement for providing a snap action response to key force and for driving the rod to form an electrical make-break contact, the base and assembly constituting aunitary flexible-tough thermoplastic body.

12 Claims, 6 Drawing Figures PATENTEBJIJN smz 3.666.356

FIG. 2a FlG.2b FlG.2c

INVENTOR DENNIS H. KEKAS ATTORNEY MECHANICAL KEY ACTUATOR INCLUDING A CANTILEVER BEAM RESTORING FORCE MEANS BACKGROUND OF THE INVENTION DESCRIPTION OF THE PRIOR ART In the prior art, many examples of mechanical actuating devices for use with electric switches may be found. Typically, the device comprises a keytop, a base or reference surface, and an actuating assembly affixed to the base. The assembly itself frequently comprises a rod engaging the keytop. The rod is movable along a constrained path, responsive to manual pressure on the key. At or towards the end of its travel, the rod drives an electrical make-break contact. Repositioning of the rod after release of manual pressure or stroking is achieved by having the assembly include a spring bias or other form of restoring force working opposite the force driving the rod.

. It has been found desirable to incorporate some form of tactile feedback to the operator of the'key to indicate that the key stroke has been completed. This is often accommodated by designing the restoring force means to exhibit a linear force versus rod travel characteristic which at some point suddenly decays. Illustrative examples may be the sud den buckling of a restoring spring in compression or the snap of a flexible and stressed diaphragm being turned inside out.

An elastic diaphragm switch consists of a pair of conductive surfaces, spaced apart by an apertured insulator, electrical BRIEF DESCRIPTION OF THE DRAWINGS FIG. la exhibits a partia lly exploded perspective view of one embodiment of the actuating device including the keytop and the unitary body forming the base and actuator assembly.

FIGS. lb and 1c are respective perspective and bottom views of another embodiment of the actuating device.

contact being madeby bringing the two surfaces together through the aperture. At least one of the surfaces is moved to engage the other surface by the action of an actuating device,

Keyboards are fabricated from distributing numbers of the actuators usually in matrix array opposite one of the dia hragm surfaces and over corresponding apertures of the insulator. In order to minimize non-uniform flexing of the relevant diaphragm surface, the force and travel of the actuators must be uniform. Furthermore, it is desired to foster a uniform tactile feedback and not one which varies with flexure as is the case with spring biased key stems. Lastly, the number of separate components adds to both cost anddecreaseof reliability.

SUMMARY OF THE INVENTION The foregoing disadvantages of the prior art are overcome by forming the base and actuating assembly including'the rod and restoring force means as a unitary flexible-tough thermoplastic body. The assembly includes a cantilever beam arrangement secured to the base and connected to the rod by a rigid hinging engagement. As the rod translates, the movement is converted through the hinging engagement into flexure of the beams. An acute angle between the beam and the axis of the hinging engagement to the rod is maintained. Rod is stopped as the angle approaches 90. The composition of forces becomes substantially normal to the rod at this pointsuch that a sudden decay or decrease in the restoring force is sensed. This constitutes the tactile feedback.

The rod is repositioned when manual pressure is removed. This is due to the force component operating on the rod through the hinges becoming more longitudinal as the beams return to their unflexed position, and the angle becomes more acute.

- The cantilever beam arrangement may preferably be embodied as a pair of spaced longitudinal members or as a substantially cylindrically shaped flexing member surrounding a portion of therod. In the first embodiment, rigid members may be hinged to the rod and corresponding longitudinal members by very thin hinging segments. Each hinging segment is formed from thinned cross sections of the thermoplastic in which the long chain polymers have an orientation transverse to the axis of thehinge. Similarly, the same hinging segments can also be fashioned for the flexible diaphragm securing the cylindrical shaped flexing member.

FIGS. 2a, b, and c respectively show the actuating device in its unstroked restored position, its stroked distended position, and in an elevation cut-away view.

DESCRIPTION OF PREFERRED EMBODIMENT Referring now to FIG. In of the drawings, there is shown a partially exploded perspective view of one embodiment of the invention. Keytop l is illustrated as a separate moldable part used as a finger strokable surface. It is fashioned sufficiently large to satisfy the dimensional requirements normally imposed on manually operable keytops found for example on typewriters and adding machines.

Base 3 and actuating assembly 5 constitute a unitary body formed from any thermoplastic material or material exhibiting a thermoplastic-elastomeric response. The material should preferably be selected from at least one of the group consisting of polypropylene, nylon, delrin, polyphenylene oxide, and an injection moldable polyurethane. One materialfound especially significant was polypropylene 20 percent or less volume filled with antimony oxide. The materials aspect of this invention will be described subsequently in greater detail.

The base 3 forms a rigid reference surface to which the actuation assembly is secured and the-movement of the keytop and assembly parts referenced. In this regard, the base thickness dimension is selected to obtain the desired rigidity.

The actuator assembly 5 comprises an actuating rod 13 freely translatable through an aperture 9 in base 3.

Longitudinal members

15 and 17 form a cantilever arrangement with rod 13 through hinging

members

19 and 21. One end of the longitudinal members is moldably secured to the base. The other end is moldably fastened to the hinging members. In turn, the hinging members are moldably fastened to the rod. Lastly, rod end 23 mechanically engages protrusion 11 of keytop 1 to complete the actuating device.

Referring now to FIG. 2a, there is shown the actuating device ,in its rest or non-finger stroked position. The keytop l is fixedly mounted on the rod end so that its bottom edge 22 extends a distance d above the base surface 25.

Longitudinal members

15 and 17 fonn a cantilever beam arrangement secured to base 3 at one of their respective ends.

Members

19 and 21 of length l hinge the beams to rod 13. They thereby define an acute angle 0 between member 19 and beam 15 and a member 21 and beam 17. The requirement of acuteness of angle 6 may be restated as 0 should be in the range defined by actuating device is ordinarily used to distend, for example, an

elastic diaphragm switch

25, 27, 29. Such a switch has a pair of deformable

conductive surfaces

25 and 29 spaced apart by an apertured insulating layer 27.

Keytop l, in FIG. 2b is manually depressed such that rod 13 translates downward through distance d. This translation is converted into an equivalent bending moment about

beams

15 and 17 through corresponding hinge members .19 and 21. The deflective loading and beam shaping and displacement of the beams for any constitutive material may be determined by reference to any standard treatise in strength of materials such as, Strength of Materials by Timoshenko, Vol. 1 and 2, A Van Nostrand Reinhold Co., 450 33rd St., N. Y. 10001, copyright 1955. The bending moment restores the rod 13 to the position shown in FIG. 2a upon the release of keytop 1.

In order to form a unitary body of the base and actuator assembly, the material selected and its preparation should receive careful consideration. It is evident referencing FIGS. 2a and b that the material must be rigid at base 3 and the base attached portions of

beams

15 and 17 and rod 13.

Hinge members

19 and 21 must be sufficiently rigid to transmit the bending force to displace beam ends 15 and 17. Notably, the beams must be susceptible of flexure. Concomitantly, material forming the

actual hinging engagements

33 and 35 must also be substantially elastomeric. In order to fabricate both a unitary body and a reliable hinge" it was found that a material forrnable by a molding process would be advantageous.

It was unexpectedly discovered that flexible-tough thermoplastics could be molded, i.e., injection molded into a unitary body and that flexible-tough therrnoplastics also had long oriented polymer chains which constituted a good hinge.

Some therrnoplastics such as plexiglas are rigid and brittle materials. Normally, such thermoplastics do not have the stretch or elastic recovery for hinge flexing purposes. However, polypropylene, nylon, delrin, polyphenylene oxide, and moldable polyurethanes exhibited the appropriate mechanical and fabrication characteristics. Accordingly, thermoplastics having the flexure-elastic properties of interest are denominated flexible-tough therrnoplastics. In contrast, thermosetting materials except for hard rubbers do not exhibit the desired rigidity and furthermore do not have orientable polymer chains for the desired hinge action.

Referring now to FIG. 20, there is shown a cut-away or sectional view of the actuator in its undistended position. Keytop l is set forth as a molded piece separated from rod 13 and base 3. Protrusion 11 of the keytop constitutes a stem having a keyway 37 into which key 23 of the rod may be snugly fitted. The keytop also has a hollowed out cavity 45 formed interior which generates a distinctive acoustic snap when the cavity is brought into sharp contact with base 3.

In FIG. 2c, the base, rod, and translating means such as

rigid members

19 and 21 and their hinging

attachments

33 and 35 are formed from the same material. In this regard, it was found that an injection molding process could be used. The process comprised the steps of gating material into the mold positioned as in FIGS. 2a, b, and along the outer base and flowing the material down the beam sections and 17, across the outer hinge 33 to inner hinge 35, and finally into rod 13. This manner of flowing the material under suitable pressure and temperature serves to align the polymer chains in a plane transverse to the hinge axes. This polymer chain orientation will produce a hinge capable of sustained flexing and reflexing. Note also, that lip 7 may be molded as part of base 3. Lip 7 is designed to engage apertured retaining plate 43. Any rigid plate can be used and against whose apertured sides lip 7 is flexed.

Referring now to FIG. lb, there is shown another embodiment of the invention. In this embodiment, a longitudinally slotted cylindrical shell 47 replaces

beams

15 and 17 shown in FIG. la. One end of the cylindrical shell is moldably secured to base 3. The shell surrounds at least a portion of the rod extent. The shell ls longitudinally slotted 49 to permit flexure of the other end.

In FIG. 10, a bottom view of the assembly illustrated in FIG. lb is set forth. A rigid diaphragm 51 is hingedly attached 33 to the cylindrical end along the diaphragm outer periphery. It is likewise hingedly attached 35 to rod 13 towards the nose end 31. Flexure is achieved in the same manner as shown in FIGS. 2a, b, and c.

It is contemplated that the embodiments will be considered for use only in a suitable temperature environment. That is, recognition must be accorded both the limits as well as the advantages of thermoplastic materials. Furthermore, some variation in material flexibility and toughness may occur as a function of the tacticity of the thermoplastic.

It should be noted that flexure and hinge performance varies inversely with hinge thickness. Relatedly, hinge thicknesses in the range between 0.010 to 0.001 are adequate.

This description of the present invention has been given as an example and it will be understood that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. In an actuating device more particularly adapted to electric switches and having a keytop, a base, and an actuator assembly affixed to the base, the assembly including an actuating rod mechanically engaging the keytop, and means for translating the rod along a defined path relative to the base responsive to keytop stroking, and for restoring the rod to its former position in the absence of stroking, the base and the assembly constituting a unitary flexible tough thermoplastic body; wherein the translating means comprise:

hinging means;

a first and second rigid member;

a first and second beam member secured to the base at one of their ends and forming at the other of their ends a hinging engagement with the rod through the hinging means and the corresponding rigid member, each beam member being deflected by a corresponding rigid member as the rod translates; and

means for limiting the excursion of the rod such that an acute angle is maintained between the longitudinal axis of each beam member and the axis of the hinging means and corresponding rigid member.

2. In an actuating device according to claim 1, wherein:

the flexible-tough thermoplastic body is formed from a material selected from at least one of the group consisting of polypropylene, nylon, delrin, polyethylene, polyphenylene oxide, and injection moldable polyurethane.

3. In an actuating device according to claim 1, wherein:

the keytop forms a substantially hollowed out cavity facing one surface of the base and being spaced apart therefrom such that a distinct acoustic wave is generated upon the keytop being stroked and the cavity impacting the base surface.

4. In an actuating device more particularly adapted to electric switches and having a keytop, a base, and an actuator assembly affixed to the base; the assembly including an actuating rod mechanically engaging the keytop; and means for translating the rod along a defined path relative to the base responsive to keytop stroking, and for restoring the rod position in the absence of stroking, the base and assembly constituting a unitary flexible tough body; wherein:

the translating means comprise:

a cantilever beam arrangement secured to the base at one end thereof and further including means for forming a spaced and rigid hinging engagement between the other end of the beam arrangement and the rod, the beam arrangement flexing as the rod translates: and

means for limiting the excursion of the rod such that an acute angle is maintained between the flexing beam arrangement and the axis of its spaced and rigid hinging engagement to the rod.

5. In an actuating device according to claim 4, wherein:

the cantilever beam arrangement comprises:

a substantially cylindrically shaped flexing member surrounding at least a portion of the rod extent, the cylindrical flexing member being secured to the base at one of its ends; and

rigid diaphragm means hingedly attached to the other cylindrical flexing member end along the diaphragm outer periphery and hingedly attached to the rod along the diaphragm inner periphery.

6. In an actuating device according to claim 4, wherein:

the base and assembly constituting the unitary body are formed from a flexible-tough thermoplastic material.

7. In an actuating device according to claim 4, wherein:

the base and assembly constituting the unitary body are formed from a material selected from at least one of a group of materials consisting of polypropylene, nylon, delrin, polyethylene, polyphenylene oxide, and moldable polyurethanes.

8. In an actuating device according to claim 4, wherein:

the base and assembly constituting the unitary body are formed from polypropylene suffused with antimony oxide.

9. In an actuating device according to claim 8, wherein:

the antimony oxide constitutes no more than 20 percent of the propylene and antimony oxide volume.

10. In an actuating device according to claim 4, wherein:

each hinging engagement is fashioned from a segment of thermoplastic material having a cross section thickness T parallel to the hinging axis in the range 0.001 inches T s 0.01 inches and further wherein the long chain polymers are oriented transverse to the hinging axis.

11. in a mechanical key actuator having a keytop, a base, and an actuator assembly affixed to the base, the assembly including a rod engaging the keytop, and means for moving the rod along a path of distance d relative to the base responsive to keytop stroking, and for restoring the rod to its former position as the stroking force is removed, the base and assembly constituting a unitary flexible tough body, wherein the translating means comprise:

a cantilever beam secured to the base at one end thereof and including means for forming a spaced and rigid hinging engagement of length 1 between the other end of the and the rod, the beam flexing as the rod moves; and means for limiting the excursion of the rod with respect to the beam and the base such that an angle 0 between the beam longitudinal axis and the rigid hinging engagement axis lies within the range 0 5 cos whereby the resulting composition of forces urged by the beam upon the rod includes a force component lying in the restoring force direction.

12. In a mechanical key actuator according to claim 11, where the restoring force component F varies as a simple sinusoidal function of angle 0 for 0 s 0 qr/n, n 2 and as a complex sinusoidal function for 1r/n s 0 1r/2.

Claims

1. In an actuating device more particularly adapted to electric switches and having a keytop, a base, and an actuator assembly affixed to the base, the assembly including an actuating rod mechanically engaging the keytop, and means for translating the rod along a defined path relative to the base responsive to keytop stroking, and for restoring the rod to its former position in the absence of stroking, the base and the assembly constituting a unitary flexible tough thermoplastic body; wherein the translating means comprise: hinging means; a first and second rigid member; a first and second beam member secured to the base at one of their ends and forming at the other of their ends a hinging engagement with the rod through the hinging means and the corresponding rigid member, each beam member being deflected by a corresponding rigid member as the rod translates; and means for limiting the excursion of the rod such that an acute angle is maintained between the longitudinal axis of each beam member and the axis of the hinging means and corresponding rigid member.

2. In an actuating device according to claim 1, wherein: the flexible-tough thermoplastic body is formed from a material selected from at least one of the group consisting of polypropylene, nylon, delrin, polyethylene, polyphenylene oxide, and injection moldable polyurethane.

3. In an actuating device according to claim 1, wherein: the keytop forms a substantially hollowed out cavity facing one surface of the base and being spaced apart therefrom such that a distinct acoustic wave is generated upon the keytop being stroked and the cavity impacting the base surface.

4. In an actuating device more particularly adapted to electric switches and having a keytop, a base, and an actuator assembly affixed to the base; the assembly including an actuating rod mechanically engaging the keytop; and means for translating the rod along a defined path relative to the base responsive to keytop stroking, and for restoring the rod position in the absence of stroking, the base and assembly constituting a unitary flexible tough body; wherein: the translating means comprise: a cantilever beam arrangement secured to the base at one end thereof and further including means for forming a spaced and rigid hinging engagement between the other end of the beam arrangement and the rod, the beam arrangement flexing as the rod translates: and means for limiting the excursion of the rod such that an acute angle is maintained between the flexing beam arrangement and the axis of its spaced and rigid hinging engagement to the rod.

5. In an actuating device according to claim 4, wherein: the cantilever beam arrangement comprises: a substantially cylindrically shaped flexing member surrounding at least a portion of the rod extent, the cylindrical flexing member being secured to the base at one of its ends; and rigid diaphragm means hingedly attached to the other cylindrical flexing member end along the diaphragm outer periphery and hingedly attached to the rod along the diaphragm inner periphery.

6. In an actuating device according to claim 4, wherein: the base and assembly constituting the unitary body are formed from a flexible-tough thermoplastic material.

7. In an actuating device according to claim 4, wherein: the base and assembly constituting the unitary body are formed from a material selected from at least one of a group of materials consisting of polypropylene, nylon, delrin, polyethylene, polyphenylene oxide, and moldable polyurethanes.

8. In an actuating device according to claim 4, wherein: the base and assembly constituting the unitary body are formed from polypropylene suffused with antimony oxide.

9. In an actuating device according to claim 8, wherein: the antimony oxide constitutes no more than 20 percent of the propylene and antimony oxide volume.

10. In an actuating device according to claim 4, wherein: each hinging engagement is fashioned from a segment of thermoplastic material having a cross section thickness T parallel to the hinging axis in the range 0.001 inches < or = T < or = 0.01 inches and further wherein the long chain polymers are oriented transverse to the hinging axis.

11. In a mechanical key actuator having a keytop, a base, and an actuator assembly affixed to the base, the assembly including a rod engaging the keytop, and means for moving the rod along a path of distance d relative to the base responsive to keytop stroking, and for restoring the rod to its former position as the stroking force is removed, the base and assembly constituting a unitary flexible tough body, wherein the translating means comprise: a cantilever beam secured to the base at one end thereof and including means for forming a spaced and rigid hinging engagement of length l between the other end of the beam and the rod, the beam flexing as the rod moves; and means for limiting the excursion of the rod with respect to the beam and the base such that an angle theta between the beam longitudinal axis and the rigid hinging engagement axis lies within the range whereby the resulting composition of forces urged by the beam upon the rod includes a force component lying in the restoring force direction.

12. In a mechanical key actuator according to claim 11, where the restoring force component F varies as a simple sinusoidal function of angle theta for theta < or = theta < pi /n, n > 2 and as a complex sinusoidal function for pi /n < or = theta < pi /2.