FIELD OF THE INVENTION
This invention relates generally to a pressure-sensitive stylus of
the type used with a digitizer tablet. In particular, the invention relates to
stylus having a layer of pressure-sensitive ink, the stylus being intended especially
for use in a signature verification system or graphics digitizer tablet.
BACKGROUND OF THE INVENTION
In operation, electrical coupling is produced between the stylus
and the digitizer tablet and position of the stylus on the digitizer surface is
determined from the coupled signals. A combination of stylus and digitizer tablet
is commonly referred to as a "digitizer". The earliest digitizers were mechanical
devices with restrained arms. More advanced digitizers have free moving styluses
and use various forms of coupling phenomenon between a stylus and a digitizing
tablet to determine stylus position. Coupling has been based upon electromagnetic,
electrostatic, sonic, piezoelectric, magnetostrictive, optical, etc. principles.
The tablet surfaces have included crossed grids of wires, matrices of electrodes
and resistive surfaces. Generally, these devices depend upon monitoring of signals
introduced into a plurality of X and Y oriented conductors or into a resistive
Styluses are generally hand-held devices which press against the
digitizer tablet surface with a point similar to that on a conventional ball-point
pen. Within the stylus housing are mounted various circuit elements including electrodes
for coupling to the digitizer tablet surface where capacitive coupling is used,
electrical windings where an inductive coupling is used, etc., as is appropriate
for the concept, as indicated above, upon which operation of the digitizer is based.
Data from the stylus/tablet combination is input to electronic circuits which
convert the signals into data representative of the coordinate position of the
stylus on the tablet or into signals which in conjunction with a microprocessor
are used to drive a display. The display can indicate either or both the numeric
coordinates of the location of the stylus or a graphical representation indicating
the stylus position by a displayed dot.
It is desirable for orderly operation of the apparatus and for elimination
of spurious data inputs, that the entire system be operative only when the stylus
is intentionally pressed against the digitizer tablet surface. For this reason,
switching elements are generally included within the stylus housing to isolate
the stylus from the data processing circuits or connect the stylus as required
in operation. The switching elements are varied in construction and include simple
electro-mechanical switches which are actuated by a small movement of the stylus
point into the stylus housing when the point is presed against the digitizer tablet
In another construction, a core is moved within an induction coil
when the stylus point is pressed against the digitizwer tablet surface and the
point recedes slightly within the stylus housing. This core movement changes the
output from the induction coil and provides a signal to activate the stylus. Capacitive
switching is also used wherein a capacitive plate is connected to the stylus and
moves in relation to an opposing capacitor plate when the stylus is pressed against
a digitizer tablet surface. This movement induces a signal which activates the
Switches operated directly by the stylus user are available in the
form of switch buttons and switch handles located on the outside of the stylus
However, a disadvantage in the prior art styluses is the added bulk,
complexity, and cost of switches for initiating active use of the stylus as described
above. What is needed is a stylus construction including reliable on/off switching
or pressure function using small and economical components.
A further disadvantage of the prior art styluses is that substantial
tip travel in the axial direction is required to activate the switch.
SUMMARY OF THE INVENTION
In accordance with the invention, a stylus switch of the type which
is activated automatically when the stylus is pressed against a digitizer tablet
is provided. The subject stylus pressure switch comprises a transducer in the form
of an ink layer having electrical resistance which varies as a function of the
pressure applied to the layer. Electrodes contact the ink layer transducer, providing
a circuit including a variable resistance. Each electrode is formed as a layer
of conductive ink.
When the switch is used in a stylus, a small segment of this layered
construction is positioned such that in response to pressing of the stylus against
a hard surface, as is used in a digitizer tablet, mechanical force is transmitted
by a surface to compress the transducer. The resistance of the transducer layer
varies with the application of pressure. Accordingly, current which flows between
the two conductive ink electrodes varies as the pressure applied to the switch
is varied, providing an analog output indicating pressure. Processing circuitry
connected to the electrodes detects a threshold level of change in output as an
indication of changed on/off conditions of the stylus and activated associated
digitizer circuitry as is appropriate.
In other words, the data flow fromthe stylus is processed only when
the pressure with which the stylus tip contacts the digitizer tablet is above a
predetermined value. This predetermined value is selected to be less than the pressure
produced with the stylus is used to write a signature, for example. Thus, the
data flow will be processed during signature writing. Removal of the digitizer
point from the tablet surface allows the stylus to return to a standby condition
wherein no pressure is exerted on the ink layer.
The pressure transducer includes a layer formed of a force-sensitive
resistnat (FSR) transducer ink, for example, as manufactured by Interlink Electronics,
Santa Barbara, California. Such material changes its resistance when compressed
by the application of a force on the surface thereof. Electrically conductive
electrodes contact separated portions of the surface of the FSR transducer ink
layer such that a complete circuit is formed between the conductors by way of the
FSR transducer ink layer.
The conductors are formed by a layer of conductive ink, for example,
as manufactured by E. I. Dupont Corporation. The conductive ink electrodes and
theink layer transducer are printed on a thin Mylar layer which is folded together.
The electrodes are pressed against the transducer to complete the electrical circuit.
It can be appreciated that when the digitizer apparatus is turned
on but the stylus is not yet in use, a voltae can be provided across the FSR transducer
by way of the stylus terminals and conductive electrodes. Then, when the tip of
the stylus is pressed against a digitizer tablet surface, the FSR transducer ink
layer is compressed between the surfaces fo two opposing parts, one part being
displaceable when pressure is exerted on the stylus tip and the other part being
stationary. As the FSR transducer ink layer is compressed, the electrical resistance
thereof changes such that a current and/or voltage change is produced at the output
terminal. This change is used as a trigger to enabke processing by the digitizer
electronis of the acquiree data. In the preferred embodiment, the coordinate determination
dat is acquired from the stylus, which is capacitively coupled to driven electrodes
in the charge ratio tablet. However, it will be obvious to one of ordinary skill
in the art that the coordinate determination data could be acquired from the electrodes
of the charge ratio tablet in response to driving of the stylus.
In one preferred embodiment of the invention, the part which is displaceable
against the FSR transducer when the pressure is applied to the stylus tip is resilient
and substantially planar. The change in resistance of the transducer ink layer
in this case is a function of pressure. In this way an analog signal is derived
which is related to the force applied to the stylus tip. This analog signal can
be used advantageously in mechanical or electrical drawing, where varying force
indicateds the use of or need for lines of varying thickness, for example, when
digitizing a blueprint or circuit, in addition to the use already noted in connection
with signature verification.
In another embodiment of the invention, the part which is displaceable
against the transucer when the pressure is applied to the stylus tip is resilient
and rounded, whereby the area of the part pressed against the transducer increases
as the pressure increases. The change in resistance in this case is a function
of both the pressure and the change in the surface area of contact between the
displaceable part and the transducer.
Accordingly, an object of this invention is to provide an improved
digitizer stylus which provides on/off switching in response to displacement of
the stylus tip relative to the stylus housing during writing.
Another object of this invention is to provide an improved stylus
switch which is reliable, small, and inexpensive to produce.
A further object of this invention is to provide an improved digitizer
stylus which provides an analog output indicative of pressure exerted by the stylus
tip against a digitizer tablet surface.
Another object of the invention is to provide tactile feedback to
the user indicating when a pressure sufficient to activate the flow of data from
the stylus has been applied.
Still other objects and advantages of the invention will in part
be obvious and will in part be apparent from the specification.
BRIEF DESCRIPTION OF THE DRAWINGS
The preferred embodiments in accordance with the invention will be
hereinafter described in detail with reference to the drawings, wherein:
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
- FIG. 1 is a partial longitudinal sectional view of the assembled stylus in
accordance with a preferred embodiment.
- Fig. 2 is a side view of the pen refil incorporated in the stylus of FIG. 1.
- FIG. 3 is a partial longitudinal sectional view of the inner barel assembly
incorporated in the stylus of FIG. 1.
- FIG. 4 is a cross-sectional view taken along section Z-Z of FIG.1.
- FIG. 5B is a longitudinal sectional view of the refil interface plug shown
in FIG. 3, and FIGS. 5A and 5C are respective end views of the refil interface
plug of FIG. 5B.
- FIG. 6B is a longitudinal sectional view of the inner barrel plug shown in
FIG. 3, and FIGS. 6A and 6C are respective end views of the inner barrel plug of
- FIG. 7B is a longitudinal sectional view of the inner barrel shown in FIG.
3, and FIGS. 7A and 7C are respective end views of the inner barrel shown in FIG.
- FIG. 8 is a side view of the wrapped flex board incorporated in the stylus
of FIG. 1.
- FIG. 9 is a view of the flex board of FIG. 8 in its unwrapped condition.
- FIG. 10 is a graphical depiction of the measured variation of the resistance
of the FSR transducer as a function of pressure for three different sample styluses.
- FIG. 11 is a side view of the refill interface plug and the rounded resilient
plunger incorporated in a second preferred embodiment of the invention.
- FIG. 12 is a longitudinal sectional view of the refill interface plug, membrane
switch and plunger incorporated in a third preferred embodiment of the invention.
- FIG. 13 is a longitudinal sectional view of the inner barrel plug, membrane
switch and plunger incorporated in a fourth embodiment of the invention
The stylus 1 is shown in the partial sectional view of FIG. 1. A
pen refill 2 is arranged in the bore of inner barrel extrusion 4. The pen refill
2 can be a standard pen refill, as shown in FIG. 2. The plastic cap 3, shown in
phantom in FIG. 2, which comes with the refill, is removed prior to assembly of
the stylus. In the preferred embodiment, the pen refill is made of stainless steel
and is supplied by A. T. Cross Co., Lincoln, Rhode Island. The inner barrel extrusion
4 is a cylindrical sleeve having a bore with a radius sufficiently large to enable
easy insertion of the pen refill 2.
The tip of pen refill 2 extends through a hole in nose cap 6 with
sufficient play to enable the refill to be axially displaced relative to the nose
cap. The nose cap 6 is made of molded plastic. A rubber washer 8 is arranged between
the nose cap 6 and one end of inner barrel extrusion 4 to prevent electrostatic
discharge from the metal refil 2 to the flex board 22. The other end of inner barrel
extrusion 4 is frictionally fit into inner barrel 10, as best seen in FIG. 3. Various
views of inner barel 10 are presented in FIGS. 7A-7C, and will be discussed in
The end of the refill 2 extends beyond the end of the inner barrel
extrusion 4 and inside the inner barrel 10. This end of refill 2 is received by
the refill interface plug 12 (see FIG. 3), which is arranged inside inner barrel
10. Refill interface plug 12 is frictionally fit onto this end of refill 2 by means
of four circumferentially distributed ribs 14 extending axially in the bore 15
(see FIGS. 5B and 5C). The base 16 of refill interface plug 12 has a planar radial
surface 18. A circular cylindrical plunger 20 (see FIG. 3) is arranged inside inner
barrel 10, with a planar radial end face 21 abutting the planar radial surface
18 of refill interface plug 12.
The inner barrel 10 and the inner barrel extrusion 4 have a flex
board 22 wrapped therearound. Flex board 22 is a flexible substrate having an electrical
circuit 24a-24g and a circular layer of force-sensing resistant (FSR) ink forming
the FSR transducer 26 applied thereon. The flex board 22 is shown in its unwrapped
condition in FIG. 9. The electrical circuit includes anode 24a, and conductive
connections 24b, 24c and 24h. The connection 24h electrically connects the termial
24e and the electrode 24f. The connection 24c electrially connects the terminal
24d and the electrode 24g. The connection 24b electrically connects anode 24a to
connection 24c. In the preferred embodiment, the electrical circuit and the FSR
transucer are formed by the application of layers of conductive ink.
The flexible substrate takes the form of Mylar film. As can be seen
in FIG. 9, the substrate has asymmetrical configuration, including a rectangular
portion 28a, a polygonal portion 28c, a bridge or neck portion 28b connecting the
portions 28sa and 28c, and curvilinear portion 28d having a configuration formed
by a pair of circular portions connected in series to portion 28b via respective
neck or bridging portions.
The portion 28a is wrapped around the inner barrel extrusion 4 and
the portion 28c is wrappd around the inner barrel 10, as best seen in FIG. 8. The
finger tab 88, by which flex board 22 is handled during wrapping, is ultimately
removed by cutting along perforation 90 after the wrapping step has been completed.
The portion 28d is folded twice during assembly to the stylus, as best seen in
Fig. 3. The FSR transducer 26 is folded 180° so as to underlie and contact the
electrodes 24f and 24g, which electrodes are in furn folded inwardly 90° relative
to portion 28b. As best seen in Fig. 7B, the inner barrel 10 has a bore comprising
the sections 34a-34d and has a recess 30 communicating with bore section 34d, through
which foled FSR transucer 26 and electroduces 24f and 24g pass during the 90 folding.
This brings the folded portions from a position substantially tangential to the
outer periphery of inner parrel 10 to a position inside the inner barre 10 and
substantially tranverse to the inner barrel axis 32. In this latter position,
the FSR transucer 26 lies between the electrodes 24f, 24g and the opposing radial
planar surface 23 of plunger 20.
As shown in FIG. 7B the inner bareel 10 has a series of communicating
bore sections 34a-34d arranged alon the longitudinal axis. Bore section 34a is
a conical bore having axial ribs 36 circumferentially distributed thereon. The
end of bore section 34a has a chamfer 38. Ribbed bore section 34a receives the
end of the inner barrel extrusion 4, which is held in place in bore section 34a
by friction fit. The endface of inner barrel extrusion 4 abuts against the annular
sholder 42 on one side of bore section 34b. On the other side of bore section
34b, another annular shoulder 40 is provided, against which refill interface plug
12 abuts (see FIG. 3). The sleeve portion 17 of refill interface plug 12 is seated
in bore section 34c. The base 16 of refill interface plug 12 is seated in bore
section 34d, along with plunger 20 and the sleeve portion 54 of inner barrel plug
46. The refill interface plug 12 and plunger 20 are axially slidably displaceable
relative to inner barrel 10. The inner barrel plug 46 is glued inside the inner
barrel 10 so as to be axially fixed. Teh shoulder of flange 52 of inner bareel
plug 46 (see FIG. 6B) abuts against the end face 44 of inner barrel 10, which
end face is annular except for the discontinuity corresponding to recess 30.
The plunger 20 in the preferred embodiment is in the form of a Neoprene
slug. Plunger 20 is elastically compressed during the application of pressure on
the stylus tip. When the pressure is removed from the stylus tip, the refill interface
plug 12 and refill 2 are restored to their original position by the expansion
of the elastic material of plunger 20.
The inner barrel plug 46 includes a flange 52, a sleeve portion 54,
an axial bore 50 thruogh flange 52, and a base 48 closing one end of bore 50 (see
FIG. 6B). The outer circumferential surface of sleeve portion 54 is slightly conical
and has axial grooves 56 circumferentially distributed thereon (see FIG. 6C).
The base 48 has a planar end face 58 which is substantially transverse to axis
32 when inner barrel plug 46 is force-fit inside bore section 34d of inner barrel
The FSR transducer 26 and electrodes 24f, 24g are pressed between
opposing planar radial surfaces, i.e. end face 23 of plunger 20 and end face 58
of inner barrel plug 46, when the tip of the stylus is pressed against a surface.
As is obvious, the pressure exerted on FSR transducer 26 by these opposing surfaces
is substantially equal to the pressure exerted on the tip of the refill 2 by the
user. When the refill tip is pressed against the working surface of a data tablet,
the other end of the refill 2 presses against the inner surface of base 16 of refill
interface plug 12. Radial end face 18 of base 16 in turn transmits the compressive
force to the radial end face 21 of plunger 20, and the other radial end face 23
of plunger 20 in turn transmits the compressive force to the FSR transducer 26.
Radial end face 58 of inner barrel plug 46, which is firmly held in place, provides
a stable base against which the FSR transducer 26 and electrodes 24f, 24g can
be pressed by movalbe plunger 20.
As best seen in FIG. 1 the cable assembly 60 is coupled to the body
halves 66, 68 by means of two radially outwardly directed projections 92, 92′
formed on the circumference of sleeve portion 94 of cable assembly 60. The projections
92, 92′ respectively interlock with a pair of holes formed along the juncture
of the assembled body halves 66, 68, each body half forming half of each hole.
The holes, of course, have the same shape as the projections. The interlocking
of projections 92, 92′ and the aforementioned holes axially fixes the cable
assembly 60 relative to the assembled body halves 66, 68. Each body half has a
circumferential rib 96 formed on its inner bore surface. When the body halves 66
and 68 are assembled, the opposing ribs 96 (only one of which can be seen in FIG.
1) block leftward axially displacement of inner barrel assembly 64. Because the
inner barrel assembly 64 cannot undergo leftward (as seen in FIG. 1) axial displacement,
when movable plunger 20 (see FIG. 3) is leftward axially displaced in response
to the stylus tip being pressed against a surface, the FSR transducer 26 and electrodes
24f, 24g are pressed between planar radial surfaces 23 and 58.
In what follows, the assembly of inner barrel 10, refill interface
plug 12, plunger 20, and inner barrel plug 46 will be generally referred to as
the inner barrel assembly 64.
The terminals 24d and 24e are soldered to the respective terminals
62, 62′ of cable assembly 60. Teh sectional view of FIG. 4 shows the connection
of terminal 62 to terminal 24e and the connection of terminal 62′ to terminal
In addition, one end of a lead spacer tube 70, consisting of a cylindrical
sleeve, is inserted into bore 50 of inner barrel plug 46. Bore 50 is slightly conical,
enabling lead spacer tube 70 to be force-fit therin. Lead spacer tube 70 prevents
coupled terminals 62-24d from coming into contact with coupled terminals 62′-24e.
The soldereed subassembly comprising cable assembly 60 and inner
barrel assembly 64 is arranged inside right and left body halves 66, 68. The flex
board terminals 24d, 24e are aligned with the keying ribs 96 of body halves 66,
68 (see FIG. 4). As can be best seen in FIG. 4, left body half 68 has a pair of
axial projections 72 and 72′ which engage right body half 66. The body halves
are ultrasonically bonded along this projection/body halft interface, which ultrasonic
bond contributes to the electrostatic discharge immunity of the stylus.
During assembly, O-rings 76 and 78 are installed in circumferential
grooves formed on the outer periphery of body halves 66 and 68. The O-rings 76
and 78 hold the body halves together during ultrasonic bonding. The circumferential
overlap of body halves 66, 68 in the area of the ultrasonicaly bonded junctures
furthe rcontribute to the excellent immunity from external electromagnetic interference.
After body halves 66 and 68 have been bonded together, the self-sticking
rubber washer 8 is installed into the recess provided in nose cone 6. The nose
cone 6 is then bonded to the ultrasonically bonded body halves 66 and 68 using
Outer barrel 80 is then slid onto ultrasonically bonded body halves
66 and 68 up to O-ring 76 near nose cone 6. Outer barrel 80 is bonded to bonded
body halves 66 and 68 by adhesive applied along a circumference denoted by reference
Thereafter end cap 84 is respectively bonded to the other end of
outer barrel 80 and to the strain relief portion of cable assembly 60.
The cable assembly 60 includes a coaxial cable. The shield of the
coaxial cable is connected to terminal 24e of the flex board 22, i.e. terminal
24e is connected to ground. The terminal 24d is connected to provide an analog
signal by way of the coaxial cable to the digitizer electronics (not shown) for
determining the level of dc bias. The level of dc bias between terminals 24d and
24e is changed by connecting the variable resistance of the FSR transducer therebetween.
The pressure-sensitive stylus according to the invention is used
in connection with a charge ratio digitizer tablet. As disclosed in co-pending
U.S. patent application Ser. No.       , which
is assigned to the assignee of the present application, the stylus output signal
can be sampled during a separate sampling cycle to determine the amplitude of a
signal which is a function of the pressure being exerted on the stylus tip. In
this sampling cycle the stylus is disabled in the sense that no current is capacitively
induced in anode 24a of the stylus. Instead a voltage is applied across terminals
24d and 24e which produces a current in the circuit formed by terminal 24d, conductor
24c, electrode 24g, FSR transducer 26, electrode 24f, conductor 24h, and terminal
The FSR transducer 26, which is folded to contact electrodes 24f
and 24g, acts as a variable resistor. FSR transducer 26 is made of a force-sensing
resistant (FSR) material, the resistance of which varies in dependence on the
amount of compressive force being exerted in a direction substantially perpendicular
to the plane of the transducer layer. The graph of the resistance of the FSR tranducer
as a function of the compressive force exerted thereon is shown in FIG. 10 for
three sample styluses. As can be seen in FIG. 10, the resistance of FSR transducer
26 decreases as the magnitude of the compressive force increases. This variation
in resistance of the FSR material produces a corresponding change in the dc level
of the analog signal output at terminal 24d in response to the reference signal
input at terminal 24e during the pressure sampling cycle by the electronic circuitry
incorporated in the digitizer tablet.
The dc level of the analog signal can be detected using a comparator
(not shown) incorporated in the digitizer electronics. The dc level of the analog
signal is compared with a reference voltage supplied tothe comparator. As the pressure
on the stylus tip is increased, the resistance of the FSR transucer 26 decreases,
whereby the dc level of the analog signal increases. When the dc level of the analog
signal exceeds the reference voltage, the comparator output goes high. In response
to the comparator output high, a switch is closed which enables the flow of digitizing
data from the stylus to the processing circuitry of the digitizer electronics during
the electrode driving cycles. The digitizing data, corresponding to the signals
induced in anode 24a by the driven electrode or electrodes of the charge ratio
tablet during the driving cycles as disclosed in U.S. patent application Ser. No.
, are also output from the flexboard
via terminal 24d, but at different times in the sampling cycle.
Thus, the FSR transducer 26 functions as a variable resistor, a switch
in the digitizer electronics being closed in response to the variable resistance
attaining a predetermined value. This predetermined resistance value should be
attained at a pressure slightly less than the amount of pressure generally exerted
on the tip of the pen refill when the stylus is used to write by a user. This feature
makes it possible to digitize the handwriting of an individual, especialy for signature
verification purposes. The coordinates of the stylus tip relative to the digitizer
tablet are determined only for those positions of the stylus tip at which the pressure
of the tip against the tablet exceeds a predetermined pressure value, i.e. for
those positions when the stylus is being used to write. This predetermined pressure
value is the pressure at which the analog signal output from the stylus exceeds
a stored predetermined analog value. In response to the stylus output signal surpassing
the predetermined stored value, determination of the coordinates of the stylus
tip will begin. Likewise when the pressure exerted by the stylus tip falls below
the predetermined stored value, coordinated determination is halted.
In the preferred embodiment described in connection with FIGS. 1-10,
the FSR transducer is compressed between two substantially rigid planar radial
sufaces. In another preferred embodiment (depicted in FIG. 11) the movable plunger
20 is made of resilient material and has a rounded surface 21 (denoted by the
dashed line in FIG. 11) for compressing the FSR transducer. In the case of such
a resilient rounded pressing surface, the area of contact of surface 21 with the
portion of the flex board 22 against which it is pressed increases as the pressure
on the stylus tip increases. FIG. 11 shows the condition where rounded surface
21 elastically deforms to become a substantially planar surface 21′ when
applied against an opposing planar surface with sufficient pressure. In this case
the resistance of the FSR transducer 26 is a function of the pressure on the stylus
tip and the area of contact (i.e. the resilience of the plunger material).
Figure 12 indicates another embodiment of a pressure transducer in
whih a layer 100 of flexible material, for example, a thin sheet of silver or other
metal, formed with a dome 102 is positioned between, for example, the refill interface
plug 12 and the plunger 20. The dome 102 is surrounded by a planar annular portion
106 which is seated onthe radial end face of refill inerface plug 12. When a predetermined
pressing force is applied to the dome by refill interface plug 12 and plunger
20, the dome undergoes reversibel collapse. The metal dome is designed so that
the collapse of the bubble takes place at a pressure which is substantially equal
to the pressue at which the processing of data from the stylus is enabled, as previously
described. The snap action during collapse of the dome can be sensed by the stylus
user, providng a definite tactile feedback indicating to the user that the digitizing
apparatus has switched from the disabled state to the enanabled state. When pressure
is removed from the stylus tip, the dome snaps back to its original undeformed
state, ready for the next operation.
In Figure 13, another embodiment of a pressure-sensitive transducer
in accordance with the invention is shown. The transducer includes a pair of electrodes
104 which are, for example, respectively arranged on the planar radial surface
58 of inner barrel plug 46. These electrodes 104 may be formed as ink layers on
a folded portion of a wrap-around flex board of the type already discussed. These
electrodes 104 are electrically connected to respective terminals (not shown),
which terminals are in turn respectively coupled tothe terminals of a cable assembly.
As in the embodiment of FIG. 12, a layer 100 of silver or other metal, comprising
a dome 102 and an annular portion 106, is arranged such that the concave surface
of the dome opposes the electrodes 104. When the movable plunger 20 moves toward
the inner barrel plug 46, the dome 102 collapses and brings the dome of conductive
silver or other conductive material into contact with electrodes 104, thereby bridging
the gap between the electrodes 104 and completing an electrical path between the
electrodes. When the pressure on the stylus tip is relieved, movable plunger 20
moves away from the inner barrel plug 46 and the collapsed dome 102 is resiliently
restored to its original shape.
The foregoing description of the preferred embodiments is presented
for illustrative purposes only and is not intended to limit the scope of the invention
as defined in the appended claims. Modifications may be readily effected by one
having ordinary skill in the art without departing from the spirit and scope of
the invention concept herein disclosed.