Abstract:
A writing device for marking on a capacitive touch screen and a paper substrate is disclosed. The device features a writing tip deployable through a hole in a conductive rubber stylus tip. The stylus tip connects to a distal end of a shaft. The stylus tip may be held in place by a ring. Electric connection is formed from a human user, through the shaft, and to the stylus tip onto the touch screen when a sufficient contact patch if formed through pressing lightly on the stylus tip. The stylus tip may be coated with a protective material that adjusts the coefficient of friction and prevents carbon from depositing on the touch screen. The writing tip (e.g., pen or pencil) moves from a working position where it extends through a hole in the stylus tip to a position where it is disposed within a hollow cavity formed by the stylus tip.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This non-provisional patent application is a continuation of U.S. Non-Provisional patent application Ser. No. 13/300,100, filed on Nov. 18, 2011, which further claims priority to U.S. Provisional Patent Application No. 61/476,309, filed on Apr. 17, 2011. These applications are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to marking utensils and computer input devices. More specifically, the invention is directed at multi-function writing devices that can physically mark on traditional writing surfaces and can also digitally mark on, or be used as other input means in association with, computerized digital displays. 
     BACKGROUND OF THE INVENTION 
     Historically, a stylus is an elongated, sharp, pointed instrument used for writing, marking, and engraving. More recently styli are being modified for use with inputting data to computer devices. 
     In the context of touch screen computer interfaces, a stylus provides many benefits to users. For example, a user can more accurately use a stylus for computer touch screen input than they can their own finger. The accuracy is due to the fact that a computer stylus has a smaller tip than do most human fingers, and so can achieve an accordingly higher degree of accuracy on a touch screen. This increase in accuracy, in turn, allows for smaller user interface elements, and provides increased ease of use for many users. Additionally, some users prefer to use a stylus simply to avoid depositing the natural oils from their hands on the screen. 
     One disadvantage to stylus use is that it necessitates carrying an additional personal item. This is especially problematic given the already large number of personal items commonly carried by individuals such as: keys, pens, glasses, wallet, and a smart phone. One solution to this problem is the combination pen and stylus. 
     A touch screen is, generally speaking, a combination touchpad and computer display that can detect the presence and location of a touch within the display area. Although this patent application will refer generally to touch screens, much of the technology disclosed herein will work with other similar human machine interfaces, such as a touchpad. There are many touch screen technologies including resistive, capacitive, surface acoustic wave, infrared, strain gauge, optical imaging, dispersive signal technology, inductive sensor systems that may be placed under an LCD, and acoustic pulse recognition. Of these, the first two (resistive and capacitive) are the most common. 
     Resistive touch screens have been used on smart phones and tablet computers. An example of a resistive touch screen is the PALM PILOT®. Resistive touch screens comprise two very slightly separated optically transparent sheets, at least one flexible, and both coated with a transparent electrically conductive material. Normally, there is no contact between the two sheets, however, when the surface of the touch screen is touched at a point by a stylus or other object, the two sheets contact each other at that point, registering to the related computer system the precise location of the touch. This type of touch screen can sense contact from nearly any solid object pressed against it. Accordingly, nearly any pointed object can serve as a stylus. Combination pen/stylus devices already exist for resistive touch screens. For example, the Dr. Grip 1+1 Stylus Pen Combo manufactured by PILOT® is a combination ballpoint pen and stylus for use with resistive touch screens. The tips of such devices are typically plastic or a similar polymer, so as not to damage or scratch the screen. 
     Capacitive touch screens are quickly replacing resistive touch screens, and are used with many modern small digital devices. For example, the newer iPhones® and iPads® from APPLE® are all equipped with capacitive touch screens. Capacitive touch screens generally comprise a flat insulative transparent sheet such as glass having an inside portion coated with a transparent conductor such as indium tin oxide (ITO), films made from graphene (carbon nanotubes), or other suitable material. Conductive materials that touch or are in very close proximity to this type of touch screen alter the electrostatic field of the screen, thereby creating a registerable change in capacitance. At the physical level a changing electrical potential difference causes a flow of electrons as an alternating current (AC) through a capacitor and it is this current flowing to a sink or source of electrons that is detected by the touch screen device. For some conductive materials such as biological tissue, these charged carriers could be predominantly ions—cations and/or anions. This sink or source of electrons, sometimes called a “ground” is necessary to complete the flow of electrons in most types of capacitive touch screens that can be activated by human touch. The effectiveness of a body as a ground is directly proportional to the product of its volume and conductivity. For alternating current and complex materials such as biological tissue it is also dependent on the frequency of the alternating current. 
     The most common input device used with capacitive touch screens is the human finger. Although the conductivity of the human body is not particularly high, its relatively high volume nevertheless allows it to act as an effective ground. At low frequencies typical biological tissues have conductivities on the order of 1 to 10 S/m (Siemens per meter) compared to metals like copper and aluminum which are 58 and 35 MS/m (million Siemens per meter) respectively. Traditional plastic or polymer-based styli are not effective in marking on capacitive touch screens because they are not sufficiently conductive. The problem is exacerbated if the user of the stylus is wearing gloves or has extremely dry skin. This is common in colder environments, where people may often need to mark on handheld devices while outside. These situations are problematic because the user is further insulated from the stylus which prevents the flow of alternating current to the human body ground. Though other materials providing better conductivity could be used, such as aluminum or other metals, they would likely scratch or otherwise damage the touch screen. Furthermore, many capacitive touch screens are tuned to detect inputs from human fingers and thus may not register a hard pointed input, simply due to the goal of minimizing false inputs. 
     One solution that enables a stylus to be used with a capacitive touch screen is the use of conductive rubber or a similar conductive elastomeric material. Conductive rubber is a rarer and more expensive form of rubber that contains suspended graphite carbon, carbon nanotubes, nickel or silver particles. Its electrical impedance decreases when it is compressed, and the capacitance increase as a result of the larger surface area in contact with the touch screen, thereby making it useful for capacitive touch screen applications. In addition, the rubber durometer can be set so as to deform at its tip in a manner similar to the deformation exhibited by a human finger as it presses down on a flat surface. 
     What is missing in the present art is a writing device that can seamlessly transition between marking on paper and marking on a capacitive screen. Such combinations for resistive-screen styli like the PILOT® pen proved easy because a rigid, non-conductive end of a pen could be used. For capacitive screens, no such device exists in the prior art because of the challenges with mounting a writing pen within a sufficiently flexible, sufficiently conductive material. 
     SUMMARY OF THE INVENTION 
     The invention described herein may be operated to write on paper substrates, or as a stylus for interacting with a capacitive touchpad or touch screen. The device is easy to use, and conversion between the two modes is accomplished by any standard retractable interface, such as a push button or twisting movement. An embodiment of the device works even if the user is effectively insulated from the electrically conductive stylus pen, e.g., if the user is wearing gloves. The device comprises electrically conductive rubber with a proper screen-protective coating, and features a compliant tip which generates the proper contact area when the stylus is depressed against a touch screen. 
     According to certain embodiments, the invention provides a writing device with a conductive, flexible tip. The invention allows for the formation of a contact patch with the flexible tip to improve conductivity. It is this contact patch that determines the electrical impedance (i.e. capacitance in this case), because the substrate of the touch screen is usually a very good insulator (e.g., glass). It is an object of the present invention to provide a writing device having a writing tip (e.g., for writing on a paper substrate) and a stylus tip (e.g., for writing on a capacitive touch screen) which may be employed by a user with very dry skin or who is wearing gloves, e.g. a user who does not make conductive contact with the combination writing device. 
     It is an additional object of the invention to provide a stylus rubber tip in electrical contact with a good conductor such as, but not limited to, copper or aluminum of such mass that the product of its electrical conductivity and volume, at the frequency of operation, is functionally equivalent to that of the human body. 
     It is an additional object of the invention to provide a writing device, wherein a writing tip deploys and retracts from within a housing created by the stylus tip, and wherein the housing comprises a sufficient air cavity to promote a proper contact area with the touch screen when the writing tip is retracted. 
     It is an additional object of the invention to provide a plurality of removable styli caps for a writing device that can be placed over the writing device, the plurality of caps having an adjustable range of end tip pliability so as to adjust the conductivity and contact patch for different environmental conditions and touch screen device characteristics. 
     While certain features and embodiments are referenced above, these and other features and embodiments of the present invention will be, or will become, apparent to one having ordinary skill in the art upon examination of the following figures and detailed description. It is intended that all such additional embodiments and features included within this description, be within the scope of the present invention, and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The present invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. In the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is an environmental view of the writing device with the writing tip retracted and the stylus in operation on a touch screen in accordance with a certain embodiment. 
         FIG. 1A  is an environmental view of the writing device with a writing tip deployed in accordance with a certain embodiment. 
         FIG. 2  is a perspective view of the electrically conducive touch pen in a first configuration according to a certain embodiment of the invention. 
         FIG. 3  is a perspective view of the electrically conducive touch pen in a second configuration according to a certain embodiment of the invention. 
         FIG. 4  is a side view of the writing device in the configuration of  FIG. 3 . 
         FIG. 5  is the same view of  FIG. 4 , but after the stylus tip has engaged a touch screen surface. 
         FIG. 6  is a cross sectional view taken along cutline A-A of  FIG. 4 , with additional cross sections  7 - 7  and  8 - 8  shown. 
         FIG. 7  is a cross sectional view taken along cutline B-B of  FIG. 6 . 
         FIG. 8  is a cross sectional view taken along cutline C-C of  FIG. 6 . 
         FIG. 9  is a cross sectional view similar to  FIG. 7 , but representing an alternative embodiment of the invention. 
         FIG. 10  is a perspective view representing an alternative embodiment of the invention. 
         FIGS. 11-13  are side views of an alternative embodiment of the invention with certain parts removed or partially removed to focus on the different extension lengths. 
         FIGS. 14 and 15  are side views of the embodiment of  FIGS. 11-13 , but with the pen tip included in first and second positions. 
         FIG. 16  is an isometric view of the touch pen according to a particular embodiment. 
         FIG. 17  is an exploded view of the components of the touch pen shown in  FIG. 16 . 
         FIGS. 18 ,  19 ,  20 , and  21  are sectioned side views of the writing end of touch pens having modified tip geometries according to particular embodiments. 
         FIGS. 18A ,  19 A,  20 A and  21 A are sectioned perspective views of the inside of conductive rubber sleeves having modified tip geometries according to particular embodiments. 
         FIG. 22  is a section view of another embodiment of the touch pen, wherein a separate ring is used as a connection piece. 
         FIG. 22A  is an exploded view of the touch pen of  FIG. 22 , wherein the ring has been removed. 
     
    
    
     DETAILED DESCRIPTION 
     The description that follows describes, illustrates and exemplifies one or more particular embodiments of the present invention in accordance with its principles. This description is not provided to limit the invention to the embodiments described herein, but rather to explain and teach the principles of the invention in such a way to enable one of ordinary skill in the art to understand these principles and, with that understanding, be able to apply them to practice not only the embodiments described herein, but also other embodiments that may come to mind in accordance with these principles. The scope of the present invention is intended to cover all such embodiments that may fall within the scope of the appended claims, either literally or under the doctrine of equivalents. 
     It should be noted that in the description and drawings, like or substantially similar elements may be labeled with the same reference numerals. However, sometimes these elements may be labeled with differing numbers, such as, for example, in cases where such labeling facilitates a more clear description. Additionally, the drawings set forth herein are not necessarily drawn to scale, and in some instances proportions may have been exaggerated to more clearly depict certain features. Such labeling and drawing practices do not necessarily implicate an underlying substantive purpose. As stated above, the present specification is intended to be taken as a whole and interpreted in accordance with the principles of the present invention as taught herein and understood to one of ordinary skill in the art. 
       FIGS. 1 and 1A  are environmental views showing a touch pen  10  in use with a touch screen  3  and a sheet of paper  4 , respectively. For purposes of this application, where a touch screen is shown, it will be presumed that it is a capacitive type touch screen as defined in more detail in the background section. In  FIG. 1 , the touch pen, which may also be referred to herein as an input device or marking device, is in a first configuration where the writing tip  12  is in a stored or retracted position within the stylus tip  22 . In this first configuration, the touch pen  10  is prepared to mark on or otherwise interact with the touch screen  3 . In  FIG. 1A , the writing tip  12  has been deployed to an operating position where it extends from the stylus tip. In this second configuration, the touch pen  10  is prepared to mark on a traditional writing surface such as paper  4 . 
     As shown, the combination touch pen  10  comprises an elongated shaft  14  having a writing or marking end (the distal end) and an opposite end (the proximate end). Though not shown, the proximate end may be equipped with various features such as a mechanism for deploying the writing tip  12 , a light, an eraser (if the tip  12  is lead-based), etc. The pen also comprises a sheath or sleeve  20  that covers and extends beyond the distal end of the shaft  14 . This sleeve  20  is formed of an elastic material with conductive properties that are sufficiently resilient, yet rebound to an original molded shape after moderate deformation. Non-limiting examples of such material are silicone rubber, natural latex rubber, thermoplastic elastomers (TPE), thermoplastic vulcanizates (TPE-v), thermoplastic urethanes (TPU), and ethylene-vinyl acetates (EVA), each having additives such as carbon, copper, nickel or silver fragments. Different variations of these materials and additives may be used to affect the appearance, color and translucence of the sleeve. Where the term “rubber” is used herein, it will be understood that any of the above materials could be substituted. 
     As an alternative to the metal fragments, a metal mesh or other configuration (not shown) could be used as an insert to the mold such that the elastomeric compound would be formed around and cover over it. In this case, the mesh would be thin enough to be sufficiently flexible and may not extend all the way to the end of the style tip  22 . In the embodiment shown, the sleeve  20  extends some distance up the shaft  14  such that it is gripped by the hand of a user. In this fashion, shaft  14  may be formed of any rigid material, whether conductive or not. For example, shaft  14  could be an inexpensive, non-conductive plastic or other polymer. This is because touch pen  10  is designed in this embodiment such that the conductive sleeve  20  directly contacts the user for a sufficient ground. 
       FIGS. 2 and 3  show closer views of the distal end of the touch pen  10 . In  FIG. 2 , the writing tip  12  is extended through a central hole  24  along the stylus tip  22 . In  FIG. 3 , the writing tip is retracted and the stylus tip  22  is ready to engage a touch screen. The conductive sleeve  20  expands in diameter along its out surface from the stylus tip  22  until it reaches a necking point  26 . The increased diameter from the necking point  26  rearward is sized to accommodate the shaft  14  and/or other internal components of the touch pen  10 , as shown in later figures. Further up the sleeve is a shoulder that expands to an even larger diameter used across a gripping section  19  of the touch pen. The gripping section may have contours, as shown, to increase comfort for a user and invite that particular portion of the touch pen  10 , which is covered by the conductive sleeve, to be gripped in hand to form a ground. 
       FIGS. 4 and 5  show the distal end of touch pen  10  in the stylus configuration first preparing to, and then engaging, a touch screen surface  3 . The stylus tip  22  noticeably deforms when it is pressed against the surface of the touch screen  3 . Again, this is by design in order to increase the contact area, and thus the capacitive properties of the elastomeric material that forms the stylus tip  22 . It also increases the surface area in a manner so as to model the size and footprint of a human finger as a method to overcome touch screen logic that may be designed to ignore false (non-finger) inputs. 
     The stylus material should be soft and highly elastic to achieve this desired level of deformation, yet it should have exceedingly good positional memory to return to its proper shape in order to correctly position the central hole  24  from which the writing tip  12  protrudes. This challenge is exacerbated by the fact that adding the required carbon-based material to the rubber (or other elastic material as described above) to obtain the desired level of conductivity tends to stiffen the compound. To offset this factor, one method is to use softer rubber (i.e., having a lower durometer). For a solid rubber tip, or one with a narrow internal diameter hole, one needs a very soft rubber. The use of such a soft rubber is difficult due to problems with manufacture, structural effect, aesthetics, and durability. Another alternative, as shown in later figures, is to alter the wall thickness of the sleeve  20  beyond the necking point  26 , thus creating an internal air cavity. As will become more clear, the ideal scenario involves a combination of proper durometer rubber and specific wall thickness variance. 
       FIG. 6  shows a section view taken along section line A-A shown in  FIG. 4 . The stylus tip of  FIG. 6  has a solid rubber tip with no air cavity. As explained above, it would require a very soft elastomeric material in order to have the flexibility needed to produce the desired surface contact. The sleeve  20  of  FIG. 6  is comprised of the conductive cover  28  and an inner molding  29 . In this case, only the conductive cover  28  portion of sleeve  20  is formed of the conductive elastic materials as described above. The inner molding  29  need not be conductive, and should be rigid or semi-rigid so as to properly house and provide support for the ink cartridge  13  that is disposed within it. The conductive cover  28  comprises the entire tip portion from the necking point  26  down to the far end of the stylus tip  22 . Though it thins out considerably, the conductive cover  28  also covers the inner molding  29  as the cover extends back up toward the shaft  14  (not shown). Again, this is to ensure contact with a ground source. 
     In the illustrated embodiment, the molding  29  has a hollow inner core  27 , so as to save unnecessary material costs. The molding  29  connects to the shaft  14  further up the touch pen  10 . The conductive cover  28  may be bonded to the molding  29 , or it may simply be stretched or rolled over the molding  29 , adhering thereto by way of an interference fit. Either way, the conductive cover  28  and inner molding  29  may typically be removed from the shaft as one assembly. In other embodiments, the molding  29  may be replaced completely by the shaft  14 , which would extend further down and be covered directly by the conductive cover  28 . 
       FIGS. 7 and 8  show radial cut-away views along section lines B-B and C-C, respectively. As may be seen, the electrically conductive flexible material is continuous around the outer surface of the touch pen at the section B point, but does not completely surround the touch pen at the section C point. The conductive material content at the Section C point is sufficient to form a steady contact with a user&#39;s fingers, and is less costly than completely covering the circumference of the inner molding  29 . This arrangement offers the additional advantage of providing a textured surface for the user to contact, which improves a user&#39;s ability to grip the electrically conductive stylus pen. 
       FIG. 9  depicts a cut-away view along line B-B of an alternative embodiment of the touch pen  10 . In this alternative embodiment the single pen tip of the preferred embodiment has been replaced by a plurality of pen tips  12   a ,  12   b , and  12   c , each of which is attached to separate ink cartridges. This serves to show that the stylus/pen combination of the present design can accommodate numerous variations and combinations of known writing utensil features and functions. In this case,  FIG. 9  depicts a touch pen  10  that can write in various colors on paper, yet still make marks or selections on a touch screen. 
       FIGS. 10-15  depict an alternative embodiment of the touch pen  10 , where the inner molding  29  is replaced by a former  39  that is ideally metallic. This alternative embodiment is designed to address the aforementioned problems attendant to a user wearing gloves, having very dry skin, or situations in which the user does not make good conductive contact with the touch pen  10 . In such cases the conductive cover  28  needs to be in good electrical contact with a volume of metal V (m3) of conductivity σ (Siemens per meter S/m) which is a direct measure of the effective number of free electrons or other charged carriers per unit volume, Ne. Ne is directly proportional to σ so Nv=V*σ or Ne=k*V*σ where k is a constant of proportionality. This is obtained empirically by adding metal material so that the stylus tip operates even when held by an extremely good insulator. 
     As an exemplary embodiment, a pen comprising a copper former  39   a  may have a minimum size smaller than the minimum size of a pen comprising an aluminum former  39   b . Because the ratio of the density of copper to that of aluminum is much greater than the ratio of their conductivity (σ), such a copper former would likely be heavier for the same electron sink or source effect. In use, the stylus tip  22  is in good electrical contact with a good conductor such as copper or aluminum of such mass that the product of its electrical conductivity and volume, at the frequency of operation, is about the same as that of the human body. This provides an adequate ground for the alternating current i.e. an adequate sink or source of electrons for the stylus to be operated with an insulated or gloved hand. Alternatively, the former  39  could be of a non-conductive material such as plastic. However, this would hamper a user&#39;s ability to operate the touch pen  10  with gloves. 
     As may be seen in  FIG. 10 , the flexible conductive cover  28  extends up the former so that a user will contact the flexible conductive cover  28 . The former  39  provides sufficient free electrons such that the electrically conductive stylus pen will function with a conductive touch screen even if the user is wearing non-conductive gloves. The user could also make direct contact with the former but it is generally desirable for the user to have contact with a soft grip surface. 
       FIGS. 11-13  provide a cut-away view of the alternative embodiment of  FIG. 10 . Though not shown, the ink cartridge  13  is housed within a central hole in the former  39 . Unlike the solid rubber tip of  FIG. 6 , here is shown that the wall thickness of the stylus tip  22  is trimmed away so as to create an air cavity  32  to increase the flexibility of the stylus tip  22 . As explained above, this allows for the conductive cover  28  to be of a more ideal durometer, providing more durability and ease of manufacture. The larger the air cavity  32 , the more flexible the stylus tip  22  will become. However, too much flexibility can also lead to false positives. As shown, the former  39  comprises an extension  41  of various sizes. The size of this extension directly controls the size of the air cavity  32 . In some embodiments, this extension may be a controllable feature of the touch pen  10 , such as by twisting the proximate end counterclockwise relative of the former to increase the length of the extension or clockwise to decrease its length. Because the inherent settings on touch screens may vary as to what surface area or conductivity they require, such a flexible feature would allow a user to “dial-in” the touch pen  10  to work optimally in association with a particular touch screen. 
       FIGS. 14 and 15  provide similar views to those of  FIGS. 11-13 , however they also depict an ink cartridge  13 , which extends through the hollow core of the former  39 . The ink cartridge  13  (and its associated writing tip  12 ) is shown first in the extended (operating) position, and then in the retracted (storage) position. Notably, retraction of the ink cartridge  13  largely empties out the air cavity  32 , allowing for the stylus tip  22  to operate with the desired flexibility. 
     Like with the touch pen of  FIGS. 1-9 , the cover portion  28  in  FIGS. 10-15  may either be bonded to the former  39  such as with an adhesive, or simply be stretched over the former  39  with an interference fit. In some embodiments, an adhesive may be used to make the fit permanent. In other embodiments, it may be desirable to allow for removal of the cover portion  28 . As explained below, the exterior surface of the cover portion  28  (or at least the stylus tip portion  22  that contacts the touch screen) may require a different type of external coating. 
     A problem with rubber containing carbon sufficient for conductivity is that it may leave black marks on substrates to which it comes into contact. In the case of touch screens, these black marks may ultimately obscure the screen. Additionally, conducting metal suspensions such as nickel and silver suspended in rubber may scratch the touch screen glass substrate. These problems can be solved by coating the rubber, or selectively the rubber tip, with a very thin layer of Parylene. This conformal coating, with strong adherence even to rubber, can be made very thin down to 10 to 50 microns. Because the dielectric constant of Parylene is so high and its thickness so small, it has virtually zero effect on reducing the capacitance of the contact area from that caused by the thickness of the glass substrate alone. Additionally, the Parylene coating has a relatively low coefficient of friction, thereby allowing a coated rubber to gently glide over a glass surface. In contrast, due to its high coefficient of friction, a “juddering” effect is often experienced when an uncoated rubber tip is moved over a glass surface. Other coatings may also be supplemented, such as, for example, Flourobond® by Orion Industries. 
       FIGS. 16-21  depict components of a touch pen  10  that could have either an inner molding  29  or a former  39 . However, as discussed below, it is the geometry of the stylus tips  22  that vary.  FIG. 16  shows an isometric view of a touch pen  10  having a shaft  14  and a sleeve  20 . In this case, the shaft  14  could extend down toward the stylus tip  22  inside the sleeve  20 , or the sleeve could comprise an exterior conductive cover  28  bonded to an inner non-conductive molding  29 . At the end opposite the stylus tip  22  (referred to herein as the proximate end because it is closer to the user when the touch pen is in use), the pen provides a standard plunger  42  for deploying the writing tip of an ink cartridge (not shown) through the central hole  24  along the end of the sleeve  20 . It will be understood that a variety of conventional methods could be used to deploy the writing tip, such as a twisting action of the shaft  14  relative to the sleeve  20 , etc. 
       FIG. 17  shows an exploded view of the touch pen embodiment depicted in  FIG. 16 , and reveals that it has an inner molding  29 , which is in this case threaded so as to provide a connection to the shaft  14 . The shaft may be a conductive material such as metal, or a non-conductive material such as plastic, because the conductive cover  28  is directly connected to a user as a ground when the touch pen  10  is held in a traditional manner. Also shown is the full ink cartridge  13  with writing tip  12  that is housed within the sleeve  20  and shaft  14  during operation. At the proximate end of the ink cartridge is the cartridge controller  44 , which can take any conventional form to locate and facilitate the deployment and retraction of the ink cartridge  13 . 
       FIG. 18  shows the components of  FIG. 17  in an assembled position inside of the sectioned sleeve  20 , with the writing tip  12  in a stored position. In this configuration, touch pen  10  would be ready to mark on or provide input to a capacitive touch screen. As shown, spring  17  is captured within a spring housing  18  formed by the inner wall of the inner molding  29  of sleeve  20 . Note that the inner molding  29  extends slightly beyond the necking point  26  where the sleeve begins to taper toward the stylus tip  22   a . The length of this extension has an effect similar to the length of the extension  41  of the former  39  in  FIGS. 11-13 . That is, the further it extends, the smaller the air cavity  32 , which is a significant determinant in the flexibility (and the related conductivity and ability to simulate a human finger) of the stylus tip  22   a.    
     Another feature that significantly affects the size of the air cavity is the wall thickness of the conductive cover  28   a  between the necking point  26  (or the distal end of the inner molding  29  where an extension is used) and the distal end of the stylus tip.  FIGS. 18 and 18A  depict a conductive cover  18  that has a uniformly thin wall across this section. Such a cover provides a high level of flexibility and a large contact patch without having to compromise the integrity of the design with the use of an overly soft rubber or other elastomeric compound. However, such a thin wall may be less durable, and various factors such as environmental conditions, user preference for the amount of friction/resistance, user preference for input pressure, or particulars of a given touch screen, may drive a desire for a different tip geometry. 
       FIGS. 19 ,  20  and  21  all provide alternative tip geometries by altering the wall thickness of the conductive cover  28  along the air cavity section  33  of the touch pen  10 . The air cavity section  33  is defined as the longitudinal region from the distal end of the stylus tip  22  to the first rigid structure in contact with the flexible conductive cover  28 , which may be on either side of the necking point  26 . As shown in the diagrammed embodiments, this first rigid structure is the inner molding  29 , but it could be a component of shaft  14  or former  39  that extends downward such as extension  41  of  FIGS. 11-13  in other embodiments. By altering the wall thickness along the air cavity section, the touch pen  10  can achieve different conductive properties that will tailor its use to a particular user and a particular touch screen. In embodiments where the entire sleeve  20  is removable, the touch pen  10  may come with multiple sleeves  20 , each having different tip geometries such as those shown in  FIGS. 18 through 21 , so as to provide a user with options to fit different scenarios. 
     Whereas  FIGS. 18 and 18A  feature a uniformly thin wall thickness across the air cavity section  33 , stylus tip  22   b  of  FIGS. 19 and 19A  essentially fills in as much of the air cavity  32  as possible without obstructing the central hole  24 . In this case, the conductive cover  28   b  and stylus tip  22   b  will provide a less flexible tip that will likely require a softer rubber. However, this may be preferable to users in some scenarios. For example, a stiffer tip will provide more precise inputs with some touch screens. 
       FIGS. 20 and 20A  features stylus tip  22   c  at the end of conductive cover  28   c . Stylus tip  22   c  is a hybrid design between that of tip  22   a  of  FIG. 18  and tip  22   b  of  FIG. 19 , and will provide an intermediate option as to flexibility and material properties. Finally,  FIGS. 21 and 21A  feature multiple air cavity slots  32   a ,  32   b , and  32   c  falling in between a plurality of structural ribs  25 . Other variations of the conductive sleeve geometry along the air cavity section, such as positioning small air bubbles within the walls of the stylus tip  22  during the molding process, are also envisioned. 
     As shown in  FIGS. 22 and 22A , other embodiments feature a conductive cover  28  portion of the sleeve  20  that is merely the stylus tip  22  component, and a separate ring  50  is used to connect the stylus tip  22  to the inner molding  29 . The ring  50  and the stylus tip  22  feature an overlapping lip and groove such that the ring snaps over the lip of the stylus tip. The ring  50  and the inner molding  29  feature interlocking threads  31 A and  31 B used to adhere the ring  50  and the stylus tip  22  to the touch pen  10 . In this fashion, the stylus tips  22  are interchangeable by unscrewing the ring  50  from the inner molding  29 . Thus, multiple stylus tip variations, such as  22 A- 22 D of  FIGS. 18-21 , could be changed easily. This embodiment also features a longer shaft  14  that fills the void created by the missing portion of the sleeve  20 . This shaft may be metallic (then enabling the embodiment to work well with gloved hands) or non-conductive material such as plastic. If non-conductive, the ring may be made of metal and elongated so as to provide contact to the users hand for a ground. 
     Accordingly, it should now be clear how the touch pen  10  provides an efficient all-in-one marking solution for both traditional writing surfaces and capacitive touchscreens, and how optimal performance can be achieved through variations in the stylus tip geometries and placement of a rigid extension or inner molding. Although the stylus has been described with respect to a pen, other advantages are apparent in still other alternative embodiments wherein the stylus is used in combination with a smartpen, which in common forms may include a microphone to record audio, a speaker for playback, a display, and or an internal memory for capturing handwritten notes, audio, and drawings. 
     It should be emphasized that the above-described exemplary embodiments of the present invention, and particularly any “preferred” embodiments, are possible examples of implementations, merely set forth for a clear understanding of the principles of the invention. Many other variations and modifications may be made to the above-described embodiments of the invention without substantially departing from the spirit and principles of the invention. All such modifications are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.