US 3882295 A
A feedback switch mechanism for a manually operated, nonmechanical switch for keyboards, and the like, is provided through use of a spring-loaded cam follower carrier that has a cam follower which follows a cam surface that is integrally formed on the plunger of the switch. Upon depression of the plunger, a force build-up and release occurs due to the action of a bias spring on the cam follower carrier which simulates the actuation of a mechanical switch so that the operator is assured that a data entry has been completed. The cam follower carrier is preferably a one-piece plastic member.
Claims available in
Description (OCR text may contain errors)
. United States Patent 1191 Madland  May 6, 1975 TACTILE FEEDBACK SWITCH 3.757.068 9/1973 Muschim'. 200/159 R MECHANISM 3,767,022, .l0/l973 Olson ZOO/I59 R X  Inventor: gfg g f fi Madland Mount Primary Examiner-Robert K. Schaefer p Assistant Examiner-William J. Smith [731 Assignee; Illinois Tool Works Inc., Chicago,
Ill. 57] ABSTRACT  Filed: 1973 A feedback switch. mechanism for :a manually oper-  o ated, nonmechanical switch for keyboards, and the like, is provided through use of a spring-loaded cam follower carrier that has a cam follower which follows  Clww 200/159 340/365 R; 197/98 a cam surface that is integrally formed on the plunger  Int. Cl. H0lh 13/52 f the switch U d ression of the plunger; 21 force  F'eld Search 200/159 R 160; 197/98; build-up and release occurs due to the action of a bias 340/3 65 spring on the cam follower carrier which simulates the 7 actuation of a mechanical switch so that the'operator  References and is assured that a data entry has been completed, The UNITED STATES PATENTS cam follower carrier is preferably a one-piece plastic 3,375,340 3/1968 Wright 200/160 member. 7 3,387,184 6/1968 Angold 3,542,988 11/1970 Baldasare....., 200/153 J x 6 clams 10 Drawing f 24 F 4,52 A/ZO 38 7/ 7 PATENIEUMAY 61975 3.882295 sum U10F2 52 Fig 6 30 Fig 7 52-U 32 PATENIEDHAY 81975 3,882,295
+ Fig.9 9
MS/A I z I i I g i FORCE DISPLACEMENT Fig. /0
TACTILE FEEDBACK SWITCH MECHANISM BACKGROUND OF THE INVENTION Nonmechanical switches for use in keyboards. and the like, are being utilized to an increasingly extent in modern electronics systems. One of the major reasons for this is that mechanical switches tend to become unreliable after a large number of operations, due to corrosion and pitting of the contacts and to other mechanical failures. In addition, with mechanical switches there is always the problem of contact bounce which creates noise signals that can interfere with the proper operation of the associated device. A number of types of switches including electronic, magnetic, and Halleffect devices have been designed to provide a nonmechanical electrical switching action. One such device, with which the present invention may be employed, is shown in US. Pat. No. 3,638,221 issued in the name of Victor M. Bernin on Jan. 25, 1972, and assigned to the assignee of the present invention. In the switch of this patent, a saturable magnetic core and a pair of permanent magnets are employed. The permanent magnets are attached to a keystem that is depressed by the operator. which changes the state of magnetic saturation of the magnetic core, thereby determining whether or not an output signal will be produced.
While several of the nonmechanical switches, which have been developed, perform in a satisfactorily manner in many applications, they tend to be viewed unfavorably for many other applications because of the fact that the operator has no positive indication when a switch has been operated. This is due to the lack of noise or feel" in these switches resulting from the fact that no substantial mechanical action has taken place. Consequently, even though a nonmechanical, manually operated switch may be extremely reliable in itself, the increase of operator error that results during the use of the switches tends to restrict their wide scale application.
It is, therefore, an object of the present invention to provide a spring-loaded cam follower which is integrally formed on a cam follower carrier and is actuated by a cam that is integrally formed on theactuator of a manually operated, nonmechanical switch, wherein actuation of the actuator causes a force build-up and re lease which simulates mechanicalswitch actuation to the operator.-
It is an additional object of the present invention to provide a tactile feedback mechanism for keyboard switches, and the like, which require such provisions in order to reduce operator error, wherein the feedback mechanism comprises a three-dimensional cam integrally formed on the plunger of the switch, and a cam follower carrier which is removably secured to the housing of the switch and is biased by a spring that is inserted in a cavity in the housing so that the cam follower carrier is movable along a first axis and wherein the cam follower carrier has a resilient arm that carries the cam follower so that the cam follower is movable along a second axis as the plunger is released from its fully depressed position.
It is a further object of the present invention to provide a tactile feedback mechanism which may be secured to the housing of a manually operated, nonmechanical switch comprising a cam integrally formed on the plunger of the switch, a cam follower carrier, and a coiled spring inserted in a cavity in the housing for resiliently biasing the cam follower carrier along an axis of displacement normal to the axis of displacement of the plunger wherein the force vs. displacement characteristics of the switch during depression of the plunger may be predetermined by selection of the coiled spring and/or cam configuration that is used.
DESCRIPTION OF THE DRAWINGS The present invention is shown in the following drawings in which:
FIG. I is a side view of the tactile feedback switch of the present invention with a partial cross-sectional showing the carrier bias spring and the plunger return spring with the plunger in its undepressed position;
FIG. 2 is an end view of the switch with the plunger in its undepressed position;
FIG. 3 is a partial side view, which is similar to the showing of FIG. 1, but with the plunger depressed almost to the breakaway point;
FIG. 4 is a top view showing the tactile feedback mechanism in place on the switch housing;
FIG. 5 is a top view of the cam follower carrier removed from the switch housing;
FIG. 6 is an end view of the cam follower carrier;
FIG. 7 is a side view of the cam follower carrier;
FIG. 8 is a plan view of the cam portion of the switch 7 plunger;
FIG. 9 is a side elevation of the cam portion of the plunger; and
FIG. 10 is a force vs. displacement diagram for the plunger of the switch.
TECHNICAL DESCRIPTION OF THE INVENTION The tactile feedback switch mechanism of the present invention is applicable to manually operated, nonmechanical keyboard switches, and other types of switches, which require that stimuli be presented to the operator so that he is assured thatactuation of the switch has actually occurred. The stimuli that is presented to the operator includes both mechanical "feel and noise. "Feel" is accomplished by means of a cam on the plunger of the switch and a cam follower on a spring-loaded cam follower carrier. The loaded spring is selected to control the force buildup and force release which occurs upon depression of the switch plunger. Noise is provided by the striking of the cam follower on a portion of the housing after the breakaway point is passed.
The present invention is a relatively inexpensive addition to a nonmechanical switch, since it adds only two new components to the switch and requires modification of only the plunger and the housing of the switch. The two new components that are added area plastic one-piece camfollower carrier and a coiled bias spring for the carrier. The plunger of the switch, which is preferably made of plastic, must be designed to include an integral cam, and the housing, which is also perferably made of plastic, includes a cavity that receives the coiled bias spring, a stop means for the cam follower carrier and retaining tabs for the carrier.
In addition to the relatively low cost of the mechanism of the present invention and its simplicity of design, the mechanism has versatility since the force vs. displacement characteristic of the plunger can be predetermined by preselection of the appropriate coiled bias spring and/or cam configurationfln addition, the mechanism is advantageous because of its linear return characteristic, which results from the fact that the return of the plunger to its initial position after full depression is governed almost entirely by the spring characteristics of the plunger return spring.
A nonmechanical switch is shown generally by the reference numeral 20 in FIG. 1. This switch may be of the type shown in the previously mentioned U.S. Pat. No. 3,638,221, but the particular type of switch mechanism that is employed is not of importance with respect to the present invention. The switch mechanism itself is housed in the housing 22 and it is actuated by depressing the plunger 24. The housing 22 and the plunger 24 are preferably formed of plastic. The tactile feedback mechanism of the present invention requires the addition of only two new parts to the nonmechanical switch mechanism of the switch 20. One of these parts is a one-piece cam follower carrier, preferably molded of plastic, that is formed as shown in FIG. 5. The other part is the coiled bias spring 28 for the cam follower carrier 26. The cam follower carrier 26 has a front wing 30 and a rear wing 32 which slides under the front and rear retaining tabs 34 and 36, respectively, so that the rear end 38 of the cam follower 26 abuts against the stop member 40 that is integrally formed on the switch housing 22. The cam follower 26 is removable from the switch housing 22 by the application of pressure on the cam follower carrier 26 so as to displace it to the right, as shown in FIG. 4 and by lifting it up when the notch 43 reaches the tabs 34. The plunger 24 carries the integrally molded cam 42. When the plunger is in an undepressed position, as shown in FIG. 1, the end 38 of the cam follower carrier 26 is in abutment with the stop member 40. The cam follower carrier 26 has a resilient arm 44 which is integrally formed on the front 30 so that it is supported in cantilever fashion and extends towards the rear wing 32. A cam follower 46 is integrally formed on the end of the arm' 44, which is preferably of a generally circular cross-sectional shape. With the plunger 24 undepressed, the cam follower 46 rests in the cam slot 48, as shown in FIG. 8, at its lower most position 50.
Extending from the bottom of the cam follower carrier 26 is a tongue 52. The tongue 52 is utilized to receive one end of the coiled spring 28, the other end of which engages the righthand wall 56 of the generally rectangular shaped cavity 58 that is formed in the upper portion of the housing 22. The longitudinal axis of the coiled bias spring 28 lies along a line substantially parallel to the longitudinal axis of the elongated cam follower carrier. The left side of the cavity 58 is provided with a notch 60 of narrower dimensions than the remainder of the cavity 58 for receiving the cam follower carrier 26 when the plunger 24 is not depressed. The return spring 62 for the plunger 24 is inserted to abut the plunger wall 64 at its upper end and a portion of the housing or the switch mechanism at its lower end.
Operation of the switch mechanism of the present invention can best be understood by reference to FIGS. 8, 9 and 10. FIG. 8 shows an enlarged view of the cam section 42, which is integrally formed on the plunger 24. Interaction between the cam 42 and the cam follower 46 and between the cam follower carrier 26 and the bias spring 28 determines the force build-up and release characteristics of the switch during depression of the plunger 24 to the breakaway point 66 of the cam 42. The return spring 62 for the plunger 24 substantially determines by itself the return characteristics of the switch once the breakaway point 66 has been reached.
With the plunger 24 in its undepressed position. as shown in FIG. 1, the cam follower 42 is initially at its lower most point 50 on the cam 42. This point corresponds to the origin of the force vs. displacement curve of FIG. 10. A small amount of force is initially required to produce any displacement at all due to frictional resistance and the initial loading effect of the return spring 62. The force required to overcome the initial loading is represented by line 68 in FIG. 10. As the force is increased and the plunger 24 is depressed, the cam follower 46 moves relative to the cam 42 so that it rides in the groove 48 of the cam 42 to the point 70. Up to the point 70 the coiled bias spring 28 has not been compressed. As depression of the plunger continues, the cam follower 46 moves relative to the cam 42 so that it travels along the inclined wall 72. At this time, the cam follower carrier 26 is forced to the left, as shown in FIG. 7, by the bias spring 28 until the cam follower 46 reaches the breakaway point 66. The position of the plunger 24 and the cam follower carrier 26 at the breakaway point 66 is shown in FIG. 3. The amount of force needed to depress the plunger 24 during this segment of travel continually increases as a function of the spring characteristic of the bias spring 28, as represented by the line 74 in FIG. 10.
When the cam follower 46 is delivered past the breakaway point 66 by further depression of the plunger 24, the cam follower 46 is abruptly delivered to the left to the point 76. This is due to the force release effect of the spring 28 acting upon the cam follower carrier 26. When the cam follower carrier 26 is delivered to the point 76, the left end 38 of the carrier strikes the stop member 40 on the housing thereby providing actuation noise that may be heard by the operator.
The force vs. displacement curve of FIG. 10 shows that once the breakaway point 66 has been passed the force release of the spring 28 reduces the amount of force necessary to maintain the plunger 24 at its same level along its vertical axis of displacement. The minimum amount of force that is necessary to accomplish this is represented by the line in FIG. 10. This amount of force is not sufficient to completely bottom the plunger, which occurs when the cam follower 46 is delivered along the base level to the point 82, since the return spring 62 for the plunger 24 is also compressed slightly as the plunger is delivered beyond the breakaway point 66. The minimum amount of force required to deliver the plunger to its bottom displacement is represented by the line 84. The bottom displacement position is represented by the line 86. Actuation of the switch normally occurs in the vicinity of the breakaway point 66 before the plunger 24 is bottomed.
After the cam follower carrier 26 has been returned to its left most position along its horizontal axis of displacement, the cam follower 46 must be returned to its initial point 50. To accomplish this, the cam 42 has a sloped ramp section 86 which has a rear edge 88 that is further removed from the base level 90 than is the front edge 92. The cam follower 46 not delivered from the point 76 to the point 50 traverses the ramp section 86 and then passes over the flat portion 94 and finally goes over the dropoff into the cavity 96 where upon it returns to its initial point 50 upon return of the plunger to its undepressed position. The arm 44, during this time, flexes in and out along an axis of displacement that is substantially normal to the vertical axis of displacement of the plunger 24, and also to the horizontal axis of displacement of the cam follower 26, as represented in FIG. 4 by the arrows that are placed adjacent to the cam follower 46. The arrows adjacent to the plunger 24 in-FlG. 1 represent the notch of the plunger 24 along the vertical axis, while the arrows adjacent to the cam follower carrier 26 in FlG. 3 represent the horizontal movement of the cam follower. Upon return of the plunger 24 to its undepressed position, the return force on it is controlled substantially entirely by the return spring 62, as represented by the line 98 in FIG. 10.
While the present invention has been described by references to a specific embodiment, other embodiments and versions within the scope of the present invention will be apparent to those skilled in the art.
What is claimed is:
l. A manually operated electrical switch comprising a switching mechanism, a housing comprising a cavity and first and second pairs of retaining tabs, a plunger depressable along a first axis and comprising a cam, a return spring for said plunger, a unitary cam follower carrier comprising first and second spaced apart wing members, said first pair of retaining tabs being constructed to overlap said first wing member and said second pair of retaining tabs being constructed to overlap said second wing member, said cam follower carrier being displaceable with respect to said housing along a second axis that is substantially normal to said first axis and comprising a tongue which projects into said housing cavity and a resilient arm having a cam follower thereon, a coiled bias spring positioned in said cavity between said tongue and a wall of said cavity for biasing said cam carrier follower to an initial position and said cam carrier to a first point, said resilient arm being displaceable along a third axis that is substantially normal to both said first axis and second axis with said cam follower being in engagement with a first portion of said cam as said plunger is depressed to a breakaway point, said cam follower carrier being directed along said second axis against the force of said bias spring as said plunger is depressed beyond said breakaway point so that said cam follower is abruptly driven to a second point, said cam follower carrier being returned substantially to its initial position along said second axis as said plunger completes its return to its undepressed position aided by the force of said return spring with said cam follower completing its return to said first point over a second portion of said cam as a result of a deflection of said resilient arm along said third axis.
2. A switch as set forth in claim 1 wherein said resilient arm is supported in cantilever fashion.
3. A switch as set forth in claim 1 wherein said housing comprises a stop means and said cam follower carrier is driven against said stop means when said cam follower is driven to said second point so as to provide a noise indication of the operation of the switch.
4. A switch as set forth in claim 3 wherein said resilient arm is supported in cantilever fashion.
5. A switch as set forth in claim 4 wherein said resilient arm is supported from said first wing member and the portion of said cam follower carrier which strikes said stop means is adjacent said second wing member.
6. A switch as set forth in claim 5 wherein said second portion of said cam comprises a ramp which slopes upwardly from said second point to a flat portion which then drops off rapidly to a cavity defining said first point.