US 3815066 A
A key mechanism has co-axial permanent magnets as a biasing means for key operator and co-axial permanent magnets operable to cause snap action operation of a cylindrical cup within a housing. The co-axial biasing magnets are magnetized in parallel to their common axis and have a polarity of opposite direction. The actuator permanent magnets are magnetized in parallel with their common axis and have a polarity in the same direction. The force-displacement characteristic of the biasing magnets is matched to the force-displacement characteristic of the actuator magnets to provide a predetermined tactile force-displacement characteristic for the operator.
Description (OCR text may contain errors)
United States Patent [191 Vinal MAGNETIC KEY MECHANISM OR THE LIKE lnventor: Albert W. Vinal, Owego, N.Y.
International Business Machines Corporation, Armonk NY.
Filed: June 19, 1972 Appl. No.: 263,831
US. Cl. 335/306, 335/207, 200/67 F Int. Cl. l'l0lf 7/02 Field of Search 335/207, 306, 188; 200/67 F I References Cited UNITED STATES PATENTS 9/l962 Lucas 335/207 X- 9/l966 Wales '2/1968 Hamrick.... 3357207 x 4/1968 Risk 333/207 [111' 3,815,066 June 4, 1974 7/1969 Davis .335/207 9/1970 Gardiner .335/207 Primary Examiner-George Harris Attorney, Agent, or Firm.lohn S. Gasper [57 ABSTRACT A key mechanism has co-axial permanent magnets as a biasing means for key operator and co-axial permanent'magnets operable to cause snap action operation of a cylindrical cup within a housing. The co-axial biasing magnets are magnetized in parallel to their common axis and have a polarity of opposite direction.
The actuator permanent magnets are magnetized in parallel with their common axis and have a polarity in the same direction. The force-displacement characteristic of the biasing magnets is matched to the forcedisplacem'ent characteristic of the actuator magnets to provide a predetermined tactile force-displacement characteristic for the operator.
8 Claims, 18 Drawing Figures PATENTEBJuu 4 I914 SHEET 2 OF 4 PATENTEBJuu 4am 3.815.066
saw u or 4 I l I I I I I I I I20 140 I60 I I I 120 I40 I60 I60 DISPLACEMENT IN MILS o DISPLACEMENT m MILS DISPLACEMENT IN MILS O O o 6 w 0 mm 0 O O m M 3 2 4 3 2 @5165 5x8 22% 5 M28 II I) FIG.8
1 MAGNETIC KEY MECHANISM OR THE LIKE BACKGROUND OF THE INVENTION 2. Description Of Prior Art Actuators using co-axial permanent magnets are well-known in the art. Specific examples of prior art are disclosed in U.S. Pats. Nos. 3,458,841; 3,376,527; 3,273,091; 3,529,269 and German Pat. No. 1,141,000.
The foregoing prior art discloses various types of magnetic actuators using co-axial permanent magnets as part of the operating mechanisms of switch devices. As described therein, axial displacement of one magnet causes the other to move relative to the first with a snap action to perform a switch function. From the prior art, little is taught concerning the nature of the tactile properties of these mechanisms. Essentially the prior art teaches that translational displacement of one magnet is opposed by a magnetic force from the other magnet which increases continuously until the spatial relation of the magnets reaches acritical position whereupon a sharp decrease and reversal in force occurs due to the snap action displacement of one of the magnets. lt is also stated that a human operator cannot feel and anticipate the point at which snap action occurs. Beyond this teaching nothing is disclosed which would enable one skilled in the art to control or selectively vary the tactile properties of key mechanisms or the like using such magnetic actuators to satisfy varying condition of applications of such mechanisms particularly where manual operation is involved.
It is also desirable in keyboard devices to have key mechanisms which are capable of high speed operation and in which the switching action always occurs at precisely the same location and with the same feel for each operation. lt is also desirable that the key mechanisms retain these qualities of feel and precision in spite of a large number of operations for an extended period of time. It is also desirable from the user point of view that each of the key mechanisms of multiple key devices be substantially identical in their tactile and operating characteristics. Prior art key devices have employed spring elements which affect the tactile properties of the operation of the mechanism. Precision spring elements are generally costly items and even the best quality spring elements tend to alter after normally extensive use. Thus, operator efficiency tends to be affected or repair and replacement becomes a relatively frequent and costly expedient.
SUMMARY OF THE INVENTION It is therefore an object of this invention to provide an improved magnetic actuator mechanism which meets the above requirements.
' It is a specific object of this invention to provide an .a key mechanism which accomplishes all of the above objectives and advantages and which is relatively inexpensive and easy to service.
The above, as well as other objects, are attained in accordance with this invention by providing a key mechanism or the like actuator mechanisms with a biasing means and co-axial actuator permanent magnets which have force-displacement characteristics that are matched to provide a predetermined forcedisplacementcharacteristic to the operator member of the key mechanism. Fundamental to the practice of this invention is the discovery that the interactive force between reciprocating co-axial magnets, contrary to previous belief, decreases with displacement of one of the magnets for a controllable finite distance prior to the snap action motion of its cooperating magnet. On the basis of this discovery this invention features the matching of the decreasing force-displacementcharacteristic of co-axial permanent magnets with an increasing force-displacement characteristic of a biasing means to provide a preselected force-displacement characteristic of the operator of the key mechanism as a means for providing a preselected tactile quality to the operator member. In general, the matching is such that a reciprocating key operator member has a constant tactile force-displacement characteristic. ln a preferred form of the invention the force-displacement characteristic of the bias means is linear while the force-displacement characteristic of the co-axial permanent magnets is inversely linear. Thus, a constant tactile force-displacement characteristic is obtained for the key operator member which effectuates displacement of the permanent magnet in opposition to the force of the biasing means. It is also within the purview of this invention to provide co-axial permanent actuator magnets having a decreasing force-displacement characteristic the rate of which is greater than the increase force-displacement characteristic of the biasing means. Thus, the force-displacement characteristic of the operator member is decreasing or negative over the range of its displacement in an operating member of the key mechanism.
It is also a feature of this invention that the biasing means comprise a pair of coaxial permanent magnets operating on a pair of relatively movable operating members. The permanent magnets are magnetized in parallel with a common axis but are, oppositely polarized. In the preferred form the co-axial biasing magnets are cylindrical and ring type and their relative lengths are adjusted to a factor of 2.0. This assures that the coaxial biasing magnets will have, if desired, a linear force-displacement characteristic. It thus becomes possible with combinations of co-axial permanent magnets to eliminate the need for mechanical springs as a biasing means for a key mechanism. It is further possible with co-axial permanent magnets that have a linear force-displacement characteristic to match them with snap action type co-axial permanent magnets to obtain predetermined tactile properties for the operator member of the key mechanism. Since both the biasing means and the actuating means are designed from longlife permanent magnet materials, the switching and tactile properties of the key mechanism will be substantially unchanged over indefinite periods of time regardless of the amount of use. Such structures are relatively simple to manufacture and may be readily reproduced in large quantities.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 6 is a graph showing force-displacement characteristic curves for various combinations of coaxial permanent magnets;
FIGS. 7a-7i are sequence drawings illustrating the operation of the key mechanism ofFIGf 2; and
FIGS. 8, 9 and 10 show three different tactile forcedisplacement plots for different kinds of key mechanisms utilizing this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS As seen in FIG. 1, a first embodiment of this invention is illustrated in a single key mechanism 10 mounted on a printed circuit board 11. Key mechanisms I and board 11 are representative parts of a keyboard assembly, further details of which are omitted to simplify the description. The key mechanism basically comprises an external housing 12 fixedly attached to the board 11 and an internal operating mechanism actuatable by manual pressure applied to button 13. Button 13, FIG. 2, is attached by suitable means such as pin 14 to the upper end of a reciprocating plunger assembly which comprises shaft 15 having an upper bearing 16 and a lower bearing 17 connected by connector pin 18. The plunger assembly is normally subjected to an upward biasing force. Various types of biasing means may be provided; however, it is a feature of this invention that the biasing means comprise coaxial permanent magnets. 19 and 20. In the embodiment of FIG. 2 the biasing means takes the form of a cylindrical permanent magnet 19 which has an aperture for receiving pin 18 in order that it may be sandwiched between the bearings 16 and 17 so as to be movable as part of the plunger assembly. Permanent magnet 19 co-acts with and is surrounded by permanent ring magnet 20 which is mounted externally to housing 12. Biasing magnet 19 is magnetized in parallel v 4 with biasing magnet 20 but with opposite polarity. The bearings 16 and 17 of plunger assembly reciprocably slides within chamber 21 of the upper section of housing 12. The limits of the displacement of the plunger assembly are established by a stop rim 22 formed in housing 12 and by flange 23, which is part of the attachment'pin 14 for button 13. The upward displacement of the plunger assembly is limited by the engagement of stop 22 by the upper surface of the upper bearing portion 16 while the downward displacement of the plunger is limited by the abutment offlange 23 on the upper edge surface 24 of housing 12. It is to be noted that the bearing portion 16 and housing 12 are designed so that at the upper displacement position of the plunger assembly, the magnetic center line 25 of bias ing magnet 19 is displaced a finite distance below the magnetic center line 26 of biasing magnet 20. With the biasing magnets magnetized as shown, permanent magnet 19 is constantly subjected to an upwardly directed magnetic force in which permanent magnet 19 attempts to move upwardly until the center lines 25 and 26 coincide. By fixing the stop position so that center line 25 is displaced to one side of center line 26 a constant magnetic biasing force exists which holds the plunger assembly in its upper displacement position to maintain shaft 15 fully extended for depression by application of pressure to key 13. Y
The operating mechanism in accordance with this invention further includes a pair of snap action co-axial permanent magnets 27 and 28. Permanent magnet 27 is, preferably a cylindrical disc magnet attached by some suitable means, such as pin 29, which extends through an aperture in permanent magnet 27, and supports it on the bottom surface of bearing 17 of the plunger assembly. Permanent magnet 28 is attached to the upper open end of a cylindrical cup 30 which is reciprocally slidable within chamber 31 in the lower section of housing 12. Permanent magnets 27 and 28 are magnetized in the same direction parallel to their common axis. The reciprocal displacement of permanent magnet 27 relative to ring magnet 28 by down/up application of manual force to key 13 causes permanent magnet 28 and cup 30 to move with snap action in a reciprocating manner within chamber 31 in the lower section of housing 12. The limits of displacement of cup 30 are controlled by stop rim 32 on the upper end of chamber 31 in housing 12 and an annular base rim 33 on the bottom surface of cup 30 which abuts printed circuit board 1]. A switching means is also attached to cup 30 such that when it reciprocates within chamber 31 of housing 12, a circuit or the like (not shown) is activated or deactivated on printed circuit board 11. In the preferred embodiment the switching means comprises a permanent magnet structure 34 mounted within a recess in the center of the bottom of cup 30. The magnetic switch structure 34 basically comprises a cylindrical or disc type permanent magnet 35 with a soft iron magnetic keeper 36. This permanent magnet structure is designed to provide an intense concentrated localized field which is capable of operating a magnetic sensor element such as a Hall effect cell (not shown) mounted as part of an integrated circuit semiconductor chip on the upper surface of printed circuit board ll. Further details of the magnetic switching structure and its operation may be obtained by reference to copending application of Michael Sulich and Albert W. Vinal, Ser. No. 263,832 filed June 19, I972,
and assigned to the same assignee as this invention. Other switching mechanisms, either of the capacitive or mechanical type, may be attached to the bottom of the cup for performing other switching operations for circuit devices mounted on printed circuit board 1 1.
Various materials may be used for making the key mechanism of FIGS. 1 and 2, however, in the preferred embodiment housing 12, shaft 15, along with bearing portions 16 and 17 and cup 30, are made of a plastic non-magnetic material. Likewise, pins 18 and 29 are also preferably non-magnetic. With the structural arrangement shown in FIG. 2 the permanent magnets 19, 20, 27 and 28 are capable of being very precisely located relative to each other so that the switching operation occurs at precisely the same physical location every. time. Also, by using these structures the stop positions'for the plunger assembly and cup 30 and hence,
the. permanent magnets, are very precisely controllable. It is also to be noted that the use of cup 30 as the support for permanent magnet 28 in combination with housing structure 12 permits the actuating permanent magnets 27 and 28 to be very precisely positioned radially as well as longitudinally. Thus, permanent magnets 27 and 28 are supported such that there are no intervening structures which would affect the efficiency or control of the magnetic forces which produce the snap action operation of these two magnets. With this arrangement the concentric actuating permanent magnets 27 and 28 can have a relatively small air gap 39, FIG. 4, which also can be precisely maintained so that the interactive magnetic forces experienced by the op erator on plunger assembly and key 13 does not deviate even after long periods of use. It is also to be noted that with the structures provided in the embodiment of FIG. 2, the permanent magnets 19, 20, 27 and 28 are movable withoutbeing subjected to mechanical wearing which would degrade its magnetic properties. By using plastic materials as supporting mechanisms for the permanent magnets the key mechanism is capable of being manufactured economically and due to the long wear and self-lubricating properties of available plastic materials the operating characteristics of the key mechanism will not be appreciably altered after long periods of intensive use. While various permanent magnetic materials can be utilized to practice this invention, a preferred magnetic material comprises barium ferrite particles embedded in a synthetic rubber matrix. Such a permanent magnetic material is available commercially under the trade name of 1-H type Plastiform, manufactured by the Dialectric Materials Division of 3M Company. Permanent magnet material of this type is available in sheet form. Consequently, the variouspermanent magnets 19, 20, 27 and 28 are readily produced from such by a stamping operation. Not only is this economical, but the dimensions of the magnet can be very precisely maintained for use in a key mechanism. While the subject invention of embodiments shown in FIGS. 1 and 2 is illustrated as a single key mechanism, it will be appreciated that for a keyboard mechanism using multiple key mechanisms the housing 12 might constitute a single block of non-magnetic material having a plurality of chambers of the type illustrated for housing 12 with plural individual plunger assemblies movable within the individual chambers. The location and position of the chambers and plunger assemblies would coincide with the arrangement of plural sensors and related circuit on the printed circuit board 1 l.
FIG. 3 shows a second embodiment of a key mechanism in which the biasing means has a coil spring 40 mounted under button I 42 which is integral with plunger shaft 41. The other end of the coil spring 40 is held within annular recess 43 in the upper portion of housing 44. Shaft 41 has a recess 45 in the bottom thereof which carries a cylindrical permanent actuator magnet 46. A cup 47 slidable within recess 48 in the bottom section of housing 44 carries a ring type permanent magnet 49 such that it surrounds the permanent magnet 46. Stop rim 50 on chamber 48, engages stop flange 51 on plunger 41 tolimit its upward displacement under the operation of biasing spring 40. Downward displacement of the permanent magnet 46 relative to permanent magnet 49 and cup 47 is limited by engagement of the under surface of cap 42 on the upper rim 52 of housing 44. A switch mechanism may be attached to the bottom surface of cup 47 for contacting a circuit element or the like on printed circuit board 11. Like the embodiment of FIG. 2, housing 44, shaft 41 and cup 47 are a non-magnet plastic and the permanent magnets 46 and 49 are barium ferrite impregnate rubber.
In the embodiment of FIG. 5 the actuator ring magnet 55 is part of the manually operable plunger 56 which slides reciprocally on housing 57. A biasing spring 58is held between the upper end of housing 57 and plunger 56. Aco-axial cylinder permanent magnet 59 reciprocates in snap action manner within vented chamber 60 of housing 57. A switch element 61 is attached by pin 62 through an opening in the bottom of housing 57 to cylinder magnet 59. A base structure 63, which may be part of a keyboard support housing 57 and has a chamber 64 for guiding switch element 61. It is understood that switch element 61 could be operative for either a capacitive or resistive circuit (not shown) which might be mounted on a printed circuit board such as 11 in FIGS. 1 and 2.
The operation of the key mechanisms of the described embodiments is understood by reference to the sequence drawings, FIGS. 7a-7i. FIG. 7a shows the key mechanism at start position, as shown in complete detail in FIG. 2. At start position the magnetic center line 37 of the actuator magnet 27 is located a finite distance above the magnetic center line 38 of actuator 28. In this position a repulsion force between the actuator magnets-27 and 28 causes cup 30 to be depressed downwardly to its fullest extent such that rim 33 on the bottom of cup 30 presses on the upper surface of printed circuit board 11. In this start position the plunger assembly is held at its upper limit by an upward force due to the interacting repulsion of the actuator magnets 27 and 28, as well as the previously described biasing force of the magnets 19 and 20. Thus, the upper bearing 16 of the plunger assembly is pressed against the upper stop rim 22 of housing 12 (see FIG. 2).
In FIG. 7b an external manual force has been applied to button 13 causing the plunger assembly to move downward as shown by the arrow. Center line 37 of actuator magnet 27 is still above the center line 38 of permanent actuator magnet 28 causing cup 30 to be maintained in the downward position. Plunger assembly, and hence the human operator, continues to experience opposition force from the repelling forces of actuator magnets 27 and 28 in combination with a biasing force from permanent magnets 19 and 20.
FIG. 76 shows the plunger assembly further depressed to the point where the center lines 37 and 38 of the actuator magnets 27 and 28 are substantially in alignment. At this point a first critical position is reached just prior to the reversal of the interacting magnetic forces between the actuator permanent magnets 27 and 28.
FIG. 7d shows the displacement of permanent magnet 28 and cup 30 at the time when the center line'37 of actuator magnet 27 crosses the center line 38 of actuator magnet 28. When this relative displacement occurs the center lines 37 and 38 are reversed from the positions shown in FIG. 7a, cup 30 and magnet 28 has moved upwardly with rapid snap action motion (as shown by the arrow). Magnets 27-28 now interact with an upwardly directed repulsion force thereby holding magnet 28 against rim 32 on chamber 31 of housing 12. In this figure, the plunger assembly is still moving downward in opposition to the force of biasing magnets I9 and 20, but with repulsion force of magnets 27 and 28 downwardly directed.
FIG. 7e shows the plunger assembly depressed to its maximum downward limit. At this point, flange 23 (see FIG. 2) rests on the upper rim 24 of housing '12. In this position the center line 37 of permanent magnet 27 is below the center line 38 of permanent magnet 28. Cup 30, therefore, will continue to be maintained up with permanent magnet 28 abutting rim 32 of housing 12 due to the upwardly directed repulsion force interacting between magnets 27 and 28. Simultaneously, permanent magnets 19 and 20 will continue to exert upward biasing force on the plunger assembly to key 13 and the operator's finger. This bias force is greater than the downward repulsion force of magnet 28 on magnet 27.
Having reached its downward most limit of displacement, as shown in FIG. 7e, the plunger assembly will begin upward motion upon removal or lessening of external manual force on button 13.
FIG. 7/ shows theplunger assembly in motion upwards. As seen in FIG. 7f, the plunger has moved partially upward under the force of the biasing magnets 19 and 20. Since the center line 37 of permanent magnet 27 is below the center line 38 of permanent magnet 28, repulsion force of the actuator magnets 27 and 28 is downward on the plunger assembly but upward on cup 30. In this position the interactive repulsion magnetic force between the permanent magnets 27 and 28 continue to cause cup 30 to be held at its upper limit against a rim 32 ofhousing 12.
FIG. 7g shows the position of the actuator permanent magnets 27 and 28 at the position where their center lines 37 and 38 virtually coincide. This is again at the critical position of instability just prior to the time when the repulsion force between the actuator magnets reverses direction.
FIG. 7h shows the position of the actuator magnets 27 and 28 when their center lines 37 and 38 have crossed over with plunger still moving upward. In this position cup 30 will have moved rapidly downward to its bottom limit with rim 33 resting on printed circuit board II. Thus, the second switching action of the switch structure 34 takes place. In this position the upward force on the operator is considerably increased since now the repulsion force of the permanent magnets 27 and 28 operates upwardly in conjunction with the biasing force of the permanent magnets 19 and 20. In this position, the plunger assembly is slightly depressed. Bias and repulsion forces act in combination in an upward direction.
FIG. 71' shows the key mechanism back in its original position of FIG. 7a with plunger fully released in upper limit position set by rim 22 of housing 12 (see FIG. 2).
As previously mentioned, one of the significant features of this invention is the combination of a biasing means having a preselected force-displacement characteristic with a pair of co-axial permanent magnets havthat each pair of coaxial magnets has a forcedisplacement characteristic which intersects the abscissa at least three times. The abscissa intersection points represent the stable and unstable force positions for co-axial magnets. In the case of co-axial magnets whose magnetization is parallel and in the same direction, the abscissa intersection at the 0 point is an unstable force position, whereas the abscissa intersections of the curves are the stable force positions. Thus, in connection with the key mechanism embodiment of FIG. 2, the 0 intersection of the abscissa for each of the curves in the graph of FIG. 6 represents the unstable positions for thepermanent magnesium 28 when there has been a relative displacement such that their respective center lines 37 and 38 coincide, as previously described in connection'with drawings FIG. and FIG. 7g. It is atthis position of instability where the permanent magnets experience a magnetic force which is at the threshold of changing direction from the positive to the negative force direction or vice versa which brings about the snap action motion of the permanent magnets and cup 30. The abscissa intersections at the positive or negative positions on either side of the O abscissa position represent the stable positions for permanent magnets 29 and 28 provided the displacement of the magnets is permitted to extend sufficiently far to permit the magnets to assume these stable positions. In accordance with this invention, however, the stops 22 and 32 for the plunger assembly and cup 30 are set so that the stable positions of magnets 27 and 28 will not be reached.
Where the co-axial permanent magnets are magnetized in parallel, but with polarization opposite in direction, the curves of the graph of FIG. 6 are conversely significant. Namely, the 0 abscissa intersection point indicates the stability position whereas the i abscissa intersection points represent unstable force positions. in reference to the biasing magnets 19 and 20 of the key mechanism embodiment of FIG. 2, this means that the 0 abscissa intersection point would occur if the center lines 25 and 26 of said magnet were to coincide. However, as indicated in connection with the description of FIG. 2, the biasing magnets 19 and 20 are not It will be noted further in connection with the curves 65-68 of the graph in FIG. 6 that co-axial permanent magnets magnetized in the same direction, when moving from the stability positions, have a force characteristic which increases and reaches a maximum value at some point prior to the arrival at the displacement position in which their magnetic center lines coincide. From this peak position, the interacting magnetic force of the co-axial magnets decreases to the instability position prior to the reversal of direction which produces the snap action. It will also be noted that in connection with curves 66-68 that the portion of the curve from the peak positions to the abscissa intersection point is virtually linear. In accordance with this invention,
a thickness ratio of 2.0, Curve 68. By furthercomparison, a key mechanism in which the thickness ratio of the coaxial magnet is in the neighborhood of 0.5 would require substantially greater amount of displacement of the plunger assembly by the operator and would have a non-linear characteristic in the initial portion of the tactile force curve. A significant feature to be further understood in connection with th e curves of FIG. 6
that they apply to co-axial permanent magnets whose polarity direction in the same, as well as opposite, where the polarization is parallel to their common axis. For this reason, in accordance with this invention, it is possible to have an all-magnetic key mechanism in which the biasing means comprises co-axial permanent magnets, as well as the actuating means comprises coaxial permanent magnet.
this characteristic is used to'permit the matching of the I force of the biasing means and the force of the actuator magnets to produce a controlled tactile force displacement characteristic. In the embodiments of the key mechanisms illustrated in FIGS. 1 through 6 it means that the stops for the plunger assemblies and the cup for the actuator magnet are located such that their limits of displacement occur so that the magnets are operating over the linear portion of the curves 6668. While limiting is not necessarily required to get controlled tactile force-displacement characteristics, as previously indicated, this is a preferred way to design a key mechanism since as a practical matter it would be easier to match a linear force-displacement characteristic of a biasing means with the linear forcedisplacement characteristic of a pair of co-axial magnets.
F rorri the curves 65-68 of the graph of F IG. 6 it is to be noted further that the location of the peak force of a pair of co-axial permanent magnets occurs at different displacement positions relative to the 0 abscissa intersection point. It can be shown that the location of this peak, as well as the linearity characteristics and the slope of the curves for a pair of co-axial magnets is directly related to the ratio of the thicknesses of the coaxial magnet. Specifically, curve 65 represents a pair of co-axial magnets whose thickness ratio is 0.5. The thickness ratio of the magnets for curve 66 is 1.0 while the thickness ratios for curves 67 and 68 are 1.5 and 2.0, respectively. Other parameters for a pair of coaxial permanent magnets of l-H type Plastiform representingcurves 65 through 68 are as follows:
Outside Diameter, cylinder magnet 300 mils Cylinder magnet ratio-thickness/diameter 0.90
Inside and outside diameter ratios of ring magnets are 1.3 and 2.0 times the diameter of the cylinder magnet.
his to be noted further from FIG. 6 that curve 66,for
example, has a peak force greater than that for other thickness ratios and that a linear force displacement property exists at relatively small displacements to either side of the abscissa intersection. This means that fast acting low profile keys can be constructed which are also characterized by small plunger displacements. Key mechanisms requiring long plunger travel and extensive linear regions of the tactile force function, are best satisfied by use of a pair of co-axial magnets having F. Q-. il t at st sifis astilwrsss splassms t characteristic of one type of key mechanism utilizing the principles of co-axial permanent magnets described in connection with FIG. 6. As shownin FIG. 8, the ordiits: repre sen ts f ofie ap plied 16m; iiiiittg as'smry via button 13 of the key mechanism of FIG. 2, for example, while the abscissa represents displacement of the plunger assembly. Curve 70 represents the force displacement curve of the biasing means only while curves 71 and 72 represent the total tactile force displacement of the key mechanism. With reference to the sequencedrawing 7a, FIG. 8 shows that at the undepressed -passioniirexr waratsrssarise"Kansas nism exceeds grams of which approximately 19 grams is supplied by the biasing means. As the plunger assembly is depressed, (as shown in FIGS. 7b and 70,) the net force on the plunger assembly increases slightly upward until it reaches the critical set position point 73 on curve 71. Under these circumstances the rate of increase in force due to the bias means dominates the reciprocal force rate due to the actuator magnet interaction. Point 73 represents the physical displacement where the magnetic center lines 37'and 38 of actuator magnets 27 and 28, respectively, coincide, as shown in FIG. 70. At the set point 73 on curve 71 the tactile force, reflected to the operators finger, decreases rapidly as permanent magnet 28 and cup 30 switch positions to its upper limit, as shown in FIG. 7d. Further de pression of the plunger assembly as shown in FIG. 7e occurs at a force level illustrated by curve 72 to the right of point 74.
, Having displaced the plunger assembly to its maximum downward displacement, the operator releases the pressure and the plunger assembly under force supplied by the biasing magnets 19 and 20 moves upwardly. As shown in FIG. 7f, the operator experiences a slightly decreasing force as shown by curves 72 moving in the direction to the left of point 74. When the plunger assembly has moved to the position where the magnetic center lines 37 and 38 of the actuator magnets 27 and 28 again virtually coincide, as shown in FIG. 7g, the tactile force has a magnitude substantially as represented by reset point 75 on curve 72. Again, at this reset point which represents the instability position for magnets 27 and 28, magnet 28 will with cup 30 move rapidly downward, as shown in FIG. 7h. The tactile force experienced by the operator will rapidly increase, as shown by point 76 on curve 71. Further release of the plunger assembly to the point where it arrives at its upper limit position will cause the tactile force to decrease slightly to the rest position along curve 71. 7
FIG. 9 shows a tactile force displacement curve in whic h t h e force-displacement characteristic of the biasing means is linear and the force-displacement characteristic of the actuator magnet is inversely linear. Curve 80 is the force displacement curve for the biasing means. Curves 81 and 82 are the composite tactile force displacement curves for the plunger assembly of the key mechanism which includes the force from the biasing means. Set point 83 and reset point 85 are the critical positions for the actuator magnets at which snap'action occurs to either decrease the tactile force level or to increase it, depending on whether the plunger assembly is being depressed or released.'lt is to be noted that between points 86 and 83 on curve 81 and between points 84 and 85 on curve 82 that the tactile force is substantially flat over the displacement range of approximately 60 mils. This indicates that the repulsion forces between the actuator magnets 27 and 28 are decreasing on a force displacement curve of FIG. 6 at substan tially the same the force is increasing f ro nTthe displacement of the biasing means. Thus, the key mechanism operator experiences a substantially uniform tactile force from the key mechanism during its reciprocal operation, both in the depression and release operations while providing for a tactile force level during depression which is higher than the force level during the release motion.
51o mhows a mil a d sa ss me r a key mechanism in which the force displacement characteristics of the biasing means, as represented by curve 90, increases in a linear manner on depression at a lower rate than the decrease in the force displacement characteristics of the actuator magnets. The result is represented by curve 91, for depressions of the plunger assembly up to the critical set point 93. Conversely, release curve 92 shows that the force displacement of the biasing means decreases at a lesser rate than the force displacement of the actuator magnets up to the critical rest point 95 when reset snap action occurs. lt is to be noted that the tactile force characteristic of the mechanism during depression to the point 93,
is actually decreasing. This means that the operator,
when depressing the key from initial force level, applies a decreasing force to operate the key mechanism over a displacement range in the neighborhood of 60 mils. An abrupt decrease in force is experienced by the operator when the set snap action occurs, point 93. Conversely, on release the operator experiences a gradually increasing force during the release of the plunger assembly up to critical reset point 95, whereupon a very substantial increase occurs to the level shown by point 96 on curve 91.
Thus, it will be seen that key mechanisms and magnetic actuator devices therefore have been provided in which tactile force properties can be selectively controlled by matching force-displacement characteristics of biasing means and actuator magnet means preferably using co-axial biasing magnets to produce unique key mechanism force tactile displacement properties not previously obtainable.
Thickness=240 mils Outside Diam.=6()0 mils Thickness=l 20 mils Biasing Means Weight Factors Material=Spring Key Stem=6 g. Non-depressed Force=25 g. Cup=2.2 g.
Spring Rate=0.394 glmil FIG. 10
Magnet 46 Magnet 49 Material=Plastiform l-H Material=Plastiform l-H Diam.=300 mils lnside Diam.=405 mils Thickness=240 mils Outside Diam,=600 mils Thickness=l 20 mils Biasing Means Weight Factors Spring Rate=0.228 g./mil
, While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.
We claim: I v 1. A key mechanism comprising in combination a stationary housing of non-magnetic material, an operator member guided by said housing for reciprocal motion along an axis, means for biasing said operator member along said axis, an actuator member of non-magnetic material guided for reciprocal motion by said housing co-axially relative to said operator member, means carried by said actuator for performing a switch operation or the like, means for imparting a bidirectional snap action motion to said actuator member upon reciprocal displacement of said operator member'and comprismg a first actuator permanent magnet carried by said operator member, a second actuator permanent magnet surrounding and eo-axial with said first actuator magnet and carried by said actuator member,
said actuator magnets being magnetized parallel with their common axis and in the same polar direction,
and means associated with said housing for limiting thefrelative translational positions of said operator and actuator members and said actuator magnets movable therewith, said biasing means comprising a pair of co-axial permanent magnets mounted on said housing and said operator member respectively, said biasing magnets being magnetized mutually parallel and in opposite polar directions. 2. A key mechanism in accordance with claim 1 in which said biasing magnets have a linear forcedisplacement characteristic.
i 13 v 3. A key mechanism in accordance with claim 1 in which said biasing magnets and said first and second actuator magnets have equal and opposite forcedisplacement characteristics whereby the tactile forcedisplacement characteristic on .said push actuator is substantially uniform throughout the range of displacement thereof. v
4. A key mechanism in accordance with claim 3 in which said thickness ratio of said biasing magnets and of said actuator magnetsiis substantially equal to 2.0. 5. In a key mechanism or the like, an operating mechanism comprising in combination a pair of operator members, i said members being relatively reciprocally movable parallel to a common axis, means for exerting a bias force on said members parallel to said axis comprising t a first permanent magnet attached to one of said members, a second permanent magnet attached to the'other of said members and surrounding said first magnet, said magnets being magnetized in a direction parallel with said axis and in opposite polar directions, and means for performing a switch operation or the like comprising third and fourth co-axial actuator magnets longitudinally displaced from said bias magnets, one of said actuator magnets being movable with one of said bias magnets and the other of said magnets being independently movable relative to both of said operator members and its associated actuator magnet, said actuator magnets being magnetized in parallel '14 with a common axis and in the same polar direction whereby a magnetic repulsion force exists between said actuator magnets operable for producing snap I action displacement of said independently movable actuator magnet upon displacement of its related actuator magnet conjointly with a corresponding operator member. 6. In a key mechanism or the like, an operating mechanism in accordance with claim 5 in which said bias magnets have a unidirectional linear forcedisplacement characteristic, and said. actuator magnets have a force-displacement characteristic preselected to match the forcedisplacement characteristic of said biasing magnets whereby a preselected tactile force-displacement characteristic is obtainable for said operating members. 7. in a key mechanism or the like, an operating mechanism in accordance with claim 6 in which said force-displacement characteristic of said actuator magnets is inversely linear over at least a portion of the range of displacement of said actuator magnets. 8. In a key mechanism or the like, an operating mechanism in accordance with claim 7 in which said inversely linear force-displacement characteristic of said actuator magnets is substantially equal in magnitude to said linear force-displacement characteristic of said bias magnets whereby a substantially uniform tactile force-displacement characteristic is provided to said operator members.