Abstract:
A gel cushion that can be attached to an existing cursor pointing device (control stick) on a computer or keyboard, or be integrally formed with the cap during manufacture. The gel cushion is flexible enough to prevent tissue damage to the user&#39;s fingers due to repetitive motions over an extended period of use, yet firm enough to transmit the desired pressure to the control stick. The gel cushion designed to be used on an existing control stick can be applied with an adhesive to a cap, or with a frictional fit directly to the control stick. The gel cushion is designed to be easily installed and replaced when worn.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a Continuation of U.S. patent application Ser. No. 10/194,715, filed Jul. 12, 2002, which was a Continuation-In-Part of U.S. patent application Ser. No. 09/703,041, filed on Oct. 31, 2000, now U.S. Pat. No. 6,621,485, which was a Continuation-In-Part of U.S. patent application Ser. No. 09/281,126, filed on Mar. 29, 1999, now U.S. Pat. No. 6,140,998, which was a Divisional of application Ser. No. 08/717,220 filed Sep. 26, 1996, now U.S. Pat. No. 5,889,508. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates in general to a computer-input device and in particular to a cursor-pointing device (cursor control stick), of a notebook-type portable computer or similar device.  
           [0003]    A finger mouse or cursor control stick, as used in this application, is a man-machine interface device, which controls the motion of a computer display cursor. In particular, a control stick is a type of miniature joystick, which is intended to be operated by the tip of one finger of the user.  
           [0004]    Typically, a control stick is mounted in a central location on a computer keyboard, such as between the “G”, “H” and “B” keys on a standard “QWERTY”-type keyboard. The control stick has a position sensing mechanism, which detects horizontal pressure in any horizontal direction. The cursor moves in a direction that corresponds to the direction of pressure exerted on the control stick and, in some embodiments, at a speed that corresponds to the amount of pressure exerted on the control stick. The control stick includes an elongated shaft. The shaft of the control stick has a small diameter, thus allowing the control stick to be mounted between the keys of the computer keyboard without causing the placement of the keys to vary greatly from that expected by an experienced user. A cap is typically removably mounted on the upper end of the control stick shaft, in order to provide an enlarged contact surface for a user to press against on the small diameter shaft of the control stick.  
           [0005]    Heins, U.S. Pat. No. 6,019,534, discloses a gripping device for a writing instrument with a plurality of annular ribs formed of soft rubber with an internal gel filled chamber. It is known to use a gel material confined in a chamber as is shown in Heins.  
         SUMMARY OF THE INVENTION  
         [0006]    Some models of control sticks have a cap with a hard smooth surface, which became slippery during use from perspiration or a build-up of natural body oils. Thus a user has to press their finger with relatively great force against the cap to prevent their finger from slipping on the surface of the cap. The need to press hard on the cap makes control difficult, since the user cannot use the finesse and delicate movements typically needed for rapid, accurate cursor movement. Also, pressing hard on the control stick is physically tiring to the finger, hand and forearm muscles of a user, and causes irritation, inflammation, and bruising of the finger tissue after a period of extended use.  
           [0007]    A period of extended use, as used in this application, means a period of use of more than about one hour, and generally more than four hours and less than twelve hours. During such period of use, the user frequently manipulates the control stick. The frequency of manipulation of the control stick during a representative task, such as word processing, will typically be at least every ten minutes, on average, and may be much more frequently, depending on the particular task and the particular user.  
           [0008]    Another type of a cap for a control stick has a hard textured outer surface. For example, one known control stick is equipped with a cap which is stippled with bumps which are about the same size and spacing as the abrasive on 150 grit sandpaper. While this approach may help prevent the slipping common with the earliest model cap, the textured cap is still irritating to the finger of a user when used extensively, even with the lighter touch allowed by the textured surface. The uneven and relatively hard surface of such caps still can cause inflamed tissue, bruising, soreness and finger fatigue in users which limits their ability to comfortably use such a control stick for periods of extended use.  
           [0009]    The present invention provides a “cushioned” cap for a control stick, which cap may suitably be formed from two materials having different durometers (measures of hardness), with a finger contact surface which provides the needed finger-to-cap friction to easily use the control stick to move the cursor with a light touch, and which is formed of a relatively soft material, so that the cap does not irritate the body tissues of the user or result in finger fatigue, even after periods of extended use. A soft texturing may be added to the finger contact surface.  
           [0010]    Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a perspective view of a typical portable computer employing a control stick having a cushioned cap in accordance with this invention.  
         [0012]    [0012]FIG. 2 is a side view, partly in section, of the control stick illustrated in FIG. 1.  
         [0013]    [0013]FIG. 3 is an enlarged sectional side view of the cap and the control stick illustrated in FIGS. 1 and 2.  
         [0014]    [0014]FIG. 4 is a side view of the cushioned cap illustrated in FIGS. 1 through 3.  
         [0015]    [0015]FIG. 5 is a sectional side view of a second embodiment of a cushioned cap in accordance with this disclosure.  
         [0016]    [0016]FIG. 6 is a bottom plan view of the cap illustrated in FIG. 5.  
         [0017]    [0017]FIG. 7 is a flowchart illustrating a method of manufacturing a control stick in accordance with this disclosure.  
         [0018]    [0018]FIG. 8 is perspective view of a gel cushion for a keyboard cursor control stick.  
         [0019]    [0019]FIG. 9 is a side sectional view of the gel cushion of FIG. 8.  
         [0020]    [0020]FIG. 10 is a view similar to FIG. 9, except showing an alternate embodiment of the gel cushion.  
         [0021]    [0021]FIG. 11 is a view similar to FIG. 9, except showing an alternate embodiment of the gel cushion.  
         [0022]    [0022]FIG. 12 is a bottom plan view of the gel cushion illustrated in FIG. 11.  
         [0023]    [0023]FIG. 13 is a view similar to FIG. 11, except showing an alternate embodiment of the gel cushion.  
         [0024]    [0024]FIG. 14 is a bottom plan view of the gel cushion illustrated in FIG. 13.  
         [0025]    [0025]FIG. 15 is a view similar to FIG. 11, except showing an alternate embodiment of the gel cushion and with stick guide.  
         [0026]    [0026]FIG. 16 is a bottom plan view of the gel cushion illustrated in FIG. 15.  
         [0027]    [0027]FIG. 17 is a view similar to FIG. 13, except showing an alternate embodiment of the gel cushion and with stick guide.  
         [0028]    [0028]FIG. 18 is a bottom plan view of the gel cushion illustrated in FIG. 17.  
         [0029]    [0029]FIG. 19 is a view similar to FIG. 16, with the gel cushion deformed under the pressure of a user&#39;s finger.  
         [0030]    [0030]FIG. 20 is a cross sectional view of the cushioned cap illustrated in FIG. 18.  
         [0031]    [0031]FIG. 20 a  is an enlarged top view of a third embodiment of the cushioned cap with textured surface illustrated in FIG. 20, taken along the line  20   a - 20   a.    
         [0032]    [0032]FIG. 21 is a plan view of an upper portion of another embodiment of the cushioned cap.  
         [0033]    [0033]FIG. 21 a  is a sectional view of the embodiment of the cushioned cap with textured surface illustrated in FIG. 21, taken along the line  21   a - 21   a.    
         [0034]    [0034]FIG. 22 is similar to FIG. 18, except showing an alternate embodiment of the textured surface.  
         [0035]    [0035]FIG. 23 is a cross sectional view of the cushioned cap illustrated in FIG. 22.  
         [0036]    [0036]FIG. 24 is a flowchart illustrating a method of manufacturing a gel cushion in accordance with this disclosure. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0037]    Referring now to the drawings, FIGS. 1 through 6 illustrate a first embodiment of a control stick, indicated generally at  10 , according to this invention. The illustrated control stick  10  is a miniature joy stick, such as the TrackPoint, TrackPoint II, or TrackPoint III control sticks on notebook computers sold by the International Business Machines Corporation. However, it will be appreciated, in light of the following disclosure, that the invention may be practiced on control devices other than such miniature joysticks. The cursor control stick of the present invention can be used in various devices such as computers, cellular phones, MP3 players, and personal digital assistants.  
         [0038]    The control stick  10  is mounted in a keyboard  12  of a typical notebook-style microcomputer  14  having a pivotally mounted display screen  15 . The control stick  10  is mounted at a first end (not shown) to the microcomputer  14 , between the keys of the keyboard  12 . A cap  18  is removably mounted on the other end  21  of the control stick  10 . The control stick  10  is usually made of a plastic material, and translates the pressure on the cap  18  into a command to move a cursor on a video display of the computer  14 .  
         [0039]    The cap  18  of the control stick  10  is made of a relatively hard elastomeric material. At least a central portion of the outer surface  17  of the cap  18  is provided with an attached cushion  20 . The cushion  20  can be made of any resilient material that can be attached to the outer surface  19  of the cap  18 . Examples, which may be suitable materials, include soft rubber, soft foam, and polyurethane foam. The preferred material for the cushion  20  is polyurethane foam such as the type used in expandable earplugs. This type of foam product provides a finger contact surface that is relatively soft so as not to damage the tissues in the finger of a user during periods of extended use.  
         [0040]    Hardness can be characterized by measuring the force applied to a given area which is required to compress or deflect a material a given distance. For example, a typical prior art cap, such as a cap supplied with the TrackPoint II control stick, is made of a relatively hard elastomeric material. During testing, a probe having a contact surface of approximately 1 square millimeter was pressed against such a cap to cause the probe to deflect the surface of the cap approximately 0.25 millimeters. A force of approximately 15 grams was required to compress the surface of the cap inwardly this small amount. In contrast, one embodiment of the cushion  20  of the present invention required a force of only 5 grams to be exerted by the probe to compress the surface of the cushion  20  the same distance. According to the invention, a cushion  20  having a measurement of hardness (or “durometer”) which would permit a probe having a contact surface of approximately 1 square millimeter to deflect the surface of the cushion  20  by at least 0.25 millimeters when urged by a force of 10 grams, would generally be acceptable. The preferred embodiment of the invention has a hardness such that only 5 grams of force is required to cause a probe having a contact surface of 1 square millimeter to deflect the surface of the cushion  20  by at least 0.25 millimeters.  
         [0041]    Preferably, the cushion  20  also provides a high coefficient of friction with the user&#39;s finger to permit easy positioning of the control stick  10 . The polyurethane foam of the cushion  20  is yielding to a degree dependent upon the thickness of the cushion  20 . The thickness of the cushion  20  can easily be modified during manufacture to any desired thickness.  
         [0042]    Referring to FIG. 2, when the display screen  15  is folded down over the keyboard  12  for storage, as is typical for most notebook computers, the display screen  15  may contact the cushion  20 . The cushion  20  is flattened as indicated by the phantom line  19 , but will resiliently return to the position indicated by the solid outline of the cushion  20 . The resiliency of the cushion  20  allows the cap  18  to have an enlarged contact surface area and greater height above the keyboard  12  for increased comfort of the user, without having to increase the spacing between the display screen  15  and the keyboard  12 . It will be appreciated by those skilled in the art that the cushion  20  will preferably not be made from a material which would damage or stick to the display screen  15  if the display screen  15  contacts the cushion  20 .  
         [0043]    Referring to FIGS. 3 and 4, the cushion  20  is, preferably, a disk of material having a generally semi-circular cross section. However, the cushion  20  may have any suitable shape, such as that of a flat-ended or hollow-ended cylinder. In the illustrated embodiment, the cushion  20  has a convex end  22 , and a second end  24 . The convex end  22  is the contact surface of the cushion  20 , that is, the surface that the user of the control stick  10  will contact to move the control stick  10 . The convex end  22  will generally be a surface providing a good frictional interface. In the preferred embodiment, the convex end  22  is a sealed, smooth, easily cleaned surface, such as a closed cell skin formed on polyurethane foam. The resiliency of the cushion  20  permits the cushion  20  to be deformed and still provide excellent friction, even when the surface thereof is smooth. However, if desired, the surface of the convex end  22  may be textured or knurled. The second end  24  of the cushion  20  will be attached to the outer surface  19  of the cap  18  on the control stick  10 . In the preferred embodiment, a suitable adhesive is used to attach the cushion  20  to the outer surface  19  of the cap  18 .  
         [0044]    [0044]FIG. 5 is a sectional view of a second embodiment of the cushion of this invention, indicated generally at  30 . The cushion  30  is generally cylindrical and includes a convex end  32 , and a relatively flat end  33  opposite the end  32 . Although in the illustrated embodiment the end  32  is convex, the end  32  may be formed to any suitable shape, such as a flat or a concave surface, as may the end  22  of the cushion  20 .  
         [0045]    A recess  34  is defined in the cushion  30 , which generally conforms to the outer surface of the end  21  of the control stick  10 . For example, as shown in FIG. 6, the recess  34  may have a square perimeter, if the end  21  of the control stick  10  is square in cross-section. The control stick  10  extends into the recess  34 . Preferably, to install the cushion  30  onto the control stick  10 , a suitable adhesive is applied to the upper end  21  of the control stick, to the interior surface of the recess  34  in the cushion  30 , or to both the upper end  21  of the control stick and to the interior surface of the recess  34  in the cushion  30 . The cushion  30  is placed on the end  21  of the control stick  10  so that the cushion  30  adheres to the end  21  of the control stick  10 . Of course, the cushion  30  could also be affixed to the control stick  10  by a resilient fit between the recess  34  of the cushion  30  and the end  21  of the control stick  10 . The cushion  30  is comprised of a soft material to permit use for an extended period of time without causing irritation to the finger tissue.  
         [0046]    It may be desirable to manufacture the cushion  30  with portions having different levels of hardness. For example, the convex end  32  could be softer than the area of the cushion  30  surrounding the recess  34 . The harder area surrounding the recess  34  would assist in retaining the cushion  30  on the control stick  10  by maintaining its form, while the convex end  32  of the cushion could be relatively soft.  
         [0047]    One method of manufacturing the cushion  30  with portions having different levels of hardness would involve simultaneously injecting two separate types of material simultaneously into a cavity of single mold to form the cushion  30 . For example, a first material having relatively soft properties would be injected in the mold at the area where the convex end  32  is formed, and a second material which is harder than the first material would be injected in the mold at the area where the recess  34  is formed. Accelerating agents, compatabilizing agents, fillers, mold release agents, and coloring agents can be introduced as well, as will be appreciated by those skilled in the art. Somewhere between the two ends  32  and  33 , the first and second materials come into contact and become affixed to one another. The cushion  30  would, therefore, be a single structure formed from two different materials, having different hardness characteristics when set or cured. For the purposes of the present invention, curing can be accomplished by using any suitable methods of solidifying or hardening a material, such as for example, by adding or removing heat, inducing a catalytic reaction, or containment for a period of time to allow hardening to occur.  
         [0048]    Another method of manufacturing the cushion  30  having multiple areas with different levels of hardness would be to form the cushion  30  from a single material, but altering the setting or formation of the material so that the different areas have different hardness characteristics. This alteration of the formation process can be accomplished by varying the temperature gradient surrounding the mold, creating miniature air pockets within selected portions of the material, or by any other suitable manufacturing process.  
         [0049]    As an alternate embodiment, it is contemplated that a cushion of the invention could be formed to completely encompass the cap  18  shown in FIGS. 2 and 3, except where the shaft of the control stick  10  extends outwardly therefrom. Such a cushion would have a cavity therein, which includes a flange of material about an opening into the cavity. Such a flange of material would restrict the size of the opening into the cavity to a diameter which is less than the diameter of the cap  18 , and thus retain the cushion on the cap  18 , either alone or in combination with a suitable adhesive. The opening into such a cushion could be resiliently expanded to slip the cushion onto the cap  18  during assembly, or when the cushion is replaced.  
         [0050]    Although the preferred embodiment of the cushion  20  or  30  is for use on a portable notebook computer  14 , it is envisioned that the cushion  20  or  30  could be used on any keyboard or in any convenient location on any instrument requiring a control stick-like movement.  
         [0051]    It is contemplated that the cushions  20  or  30  of the present invention can be sold separately from a notebook-type portable computer as replacements or substitutes to the original control stick and cap configuration. The cushions  20  or  30  can be sold in a kit form, which preferably includes the necessary materials to affix the cushions  20  or  30  to a control stick of a computer. The kit may include a plurality of cushions  20  or  30  and a suitable adhesive material, such as a container of contact cement or a pressure sensitive self-adhesive strip which is pre-applied to the cushions  20  or  30 . For example, if contact cement is supplied with the kit, the user simply applies a coating of contact cement to either the originally supplied cap  18  or the end  21  of the control stick  10 , depending on the type of cushion  20  or  30  used. A coating of contact cement is also applied to the cushion  20  or  30 . The coatings of contact cement are then allowed to dry. The cushion  20  or  30  is then pressed against the coated portion of the original cap  18  or control stick  10 , thereby affixing the cushion  20  or  30  to the control stick  10 .  
         [0052]    [0052]FIG. 7 is a flow diagram of a method of forming a cushioned control stick according to the invention. The method of forming a cushioned control stick may be summarized as follows: In a first step  100 , a cursor pointing device (control stick) with a cap having a first hardness is provided. In a second step  200 , a soft cushion is provided which has an outer surface of a second hardness which is less than the first hardness of the cap (i.e., the cushion is softer than the cap). In a third step  300 , the soft cushion is affixed to the relatively harder cap.  
         [0053]    It will be appreciated that the soft cushions described above may be formed in a variety of ways, of a variety of materials. For instance, in an embodiment shown in FIG. 8, a cushion, indicated generally at  400 , is formed of a gel material. As used herein, the term gel means a semi-rigid solid, and includes a colloidal suspension of a solid dispersed in a liquid, and materials with similar characteristics as load bearing surfaces (e.g., stiffness, hardness, malleability, etc.).  
         [0054]    The cushion  400  preferably has a generally cylindrical lower portion  402 , and a generally conic upper portion  404 , which increases in diameter toward an upper surface  406  of the cushion  400 . Thus, at least a portion of the upper portion  404  is generally frustoconical. The upper surface  406  is preferably formed with a depression  408  therein that is suitable to receive a fingertip of a user.  
         [0055]    Like the cushions described in the other embodiments above, the cushion  400  will deform if pressed against the computer display screen. It is contemplated that the cushion  400  may be manufactured to have a suitable relatively rigid pocket (seen in FIGS. 9 and 10) to accept the upper end of a control stick of a computer, such as the control stick  10 . It is also contemplated that the cushion  400  could otherwise be fixed to a control stick cap like the cap  18  in FIG. 2, such as by adhesively fixing the cushion  400  to the cap. It is also contemplated that the cushion  400  may be manufactured to form an integral part of a removable control stick or portion of a control stick (not shown).  
         [0056]    [0056]FIG. 9 is a cross sectional view of the cushion  400 . The upper portion  404  of the cushion  400  is made from a different material than the lower portion  402 . The upper portion  404  may be made from any suitable material. It is believed that thermoplastic elastomeric compounds such as KRATON® thermoplastic elastomers (available from the Royal Dutch/Shell Group) or thermoplastic rubber compounds such as SANTOPRENE® (available from Advanced Elastomer Systems, L.P., 388 South Main Street, Akron, Ohio, U.S.A. 44311) may be particularly suitable for this application. The material from which the upper portion  404  is formed is selected to have a relatively low hardness, so that the upper portion  404  is relatively soft and compliant. The upper portion  404 , in a preferred embodiment, is cured to a Shore A durometer of about 3 to about 10, though of course some variance from this softness may be desirable in certain applications, particularly if other features, such as air pockets in the material of the cushion  400 , are provided that affect the overall feel of the cushion  400 . The material of the upper portion  404  may be a gel or a gel contained in a non-gel pocket. The lower portion  402  defines a pocket  410  in a lower surface  412  thereof. The pocket  410  is adapted to receive the upper end of a cursor control stick, such as the cursor control stick  10 . The lower portion  402  is preferably formed of a material with a higher durometer than the upper portion  404 . The lower portion  402  may, nevertheless, be formed of any suitable material. It is believed that thermoplastic rubber compounds may be particularly suitable for this application. The lower portion  402  is preferably cured to be relatively harder than the upper portion  404 , such as to a Shore A durometer of about 55 to about 65.  
         [0057]    These thermoplastic elastomeric and rubber materials are believed to be particularly suitable because of the tack their surfaces have, which gives the cushion  400  a smooth, non-irritating, yet non-slip surface for improved performance.  
         [0058]    The cushion  400  may be formed with any suitable machinery of any suitable material by any suitable process. Thermoplastic rubber compounds, for example, can be injection molded, extruded, blow molded and thermoformed with the efficiency and economy associated with thermoplastic materials. As a further example, the cushion  400  may be formed of thermoplastic rubber compounds using a two-step injection process on standard thermoplastic injection molding equipment. In a preferred process, illustrated in FIG. 23, the cushion  400  is formed in a two step injection molding process.  
         [0059]    In a first step  451 , a first mold is provided, shaped to form one of the lower portion  402  and the upper portion  404 . In one preferred embodiment, the first mold is shaped to form the lower portion  402 .  
         [0060]    In a second step  452 , a first material curing to a first durometer is injected into the first mold. In the preferred embodiment in which the first mold is the lower portion  402 , the first material is a thermoplastic rubber material that will have a Shore A durometer of about 55 to about 65 when fully cured.  
         [0061]    In a third step  453 , a second mold is provided, shaped to form the other of the lower portion  402  and the upper portion  404 . In the preferred embodiment in which the first mold is the lower portion  402 , the second mold is shaped to form the upper portion  404 .  
         [0062]    In a fourth step  454 , the molded first material is removed while only partially cured, and placed into the second mold. In the preferred embodiment, the first material is removed from the first mold as soon as sufficiently cured to be parted from the first mold.  
         [0063]    In a fifth step  455 , a second material curing to a second durometer, different from the first durometer, is injected into the second mold in contact with the partially cured first material so that the second material bonds to portions of the partially cured first material with which the second material comes into contact. In the preferred embodiment in which the first mold provided in step  451  is the lower portion  402 , the second material is a thermoplastic rubber material that will have a Shore A durometer of about 3 to about 10 when fully cured and will form the upper portion  404 . The upper portion  404  is thus overmolded onto the partially cured lower portion  402 , with the material of the upper portion  404  chemically bonding with the material of the lower portion  402 .  
         [0064]    In a sixth step  456 , both the first and second materials are removed from the second mold. One or both of the first and second materials may be fully cured before the bonded first and second materials are removed from second mold. Similarly, one or both of the first and second materials may only be partially cured before the bonded first and second materials are removed from second mold.  
         [0065]    In a preferred embodiment, the mold for the upper portion  404  has an abraded inner surface such that the upper surface  406  of the upper portion  404  is textured corresponding to the abraded surface of the mold. The inner surface of the mold may be abraded in any conventional manner, such as by sand blasting or by electrical discharge machine. In a preferred embodiment, the mold for the upper portion  404  has an inner surface with a textured pattern such that the upper surface  406  of the upper portion  404  is textured corresponding to the textured surface of the mold.  
         [0066]    An alternate embodiment of the cushion  400  is illustrated by the cross sectional view of FIG. 10. A cushion  400 ′ is similar in outer shape to the cushion  400  illustrated in FIG. 8, and has similar qualities of deformation for comfort and protection of computer display screens, and smoothness and tack for ergonomic reasons. However the cushion  400 ′ is constructed somewhat differently, as will be described.  
         [0067]    Like the cushion  400 , the cushion  400 ′ preferably has a generally cylindrical lower portion  402 ′, and a generally conic upper portion  404 ′, which increases in diameter toward an upper surface  406 ′ of the cushion  400 ′. The upper surface  406 ′ is preferably formed with a depression  408 ′ therein that is suitable to receive a fingertip of a user.  
         [0068]    The lower portion  402 ′ of the cushion  400 ′ is formed of any suitable material, and, like the cushion  400 , is preferably formed of a thermoplastic rubber compound such as SANTOPRENE® thermoplastic rubber. The lower portion  402  defines a pocket  410 ′ in a lower surface  412 ′ thereof. The pocket  410 ′, like the pocket  410  in the cushion  400 , is adapted to receive the upper end of a cursor control stick, such as the cursor control stick  10 .  
         [0069]    The upper portion  404 ′ of the cushion  400 ′ is of somewhat different structure that the cushion  400 . The outer surface of the upper portion  404 ′ is an envelope  428 , which may be formed of any suitable material. It is believed that a thermoplastic rubber compound such as SANTOPRENE® thermoplastic rubber would be suitable in this application, and the envelope  428  is preferably formed integrally with the lower portion  402 ′. The envelope  428  is filled with a suitable material  430 . The material  430  may be any suitable gel, such as a silicone gel, or a thermoplastic elastomeric compound such as KRATON® thermoplastic elastomer formulated to form a low durometer (hardness) (i.e., to form a very soft) material.  
         [0070]    [0070]FIG. 11 is a cross sectional view of an alternate embodiment of the cushion of this invention, indicated generally at  500 . The cushion  500  preferably has a generally cylindrical lower portion  502 , and a generally cup-shaped upper portion  504 . The upper portion  504  overlays and is bonded to a portion of the lower portion  502  that is disposed within the cup-shaped upper portion  504   
         [0071]    The upper portion  504  includes a central portion  505  that may be generally described as convex-concave lens shaped, in that the central portion  505  is dished and increases in thickness toward the center of the central portion  505 . The upper portion  504  includes an upper surface  505   a . The upper surface  505   a  may be textured as is described in the embodiments illustrated in FIGS. 20 through 23. The upper portion  504  also includes a depending skirt portion  506  formed at the circumferential periphery of the central portion  505 . The upper portion  504  may be made from any suitable material, such as a foam or a gel or a thermoplastic rubber. The material from which the upper portion  504  is formed is selected to have a relatively low hardness, so that the upper portion  504  is relatively soft and compliant. The upper portion  504  is preferably formed from a material like the suitable material described for the upper portion  404  of FIGS. 8 and 9, and will have a Shore A durometer of about 3 to about 10 when fully cured.  
         [0072]    As shown in FIGS. 11 and 12, the lower portion  502  is generally cylindrical and partially disposed within the depending skirt  506  of the upper portion  504 . The lower portion  502  preferably includes a flange  508  that extends radially outwardly from a lower-most part of the lower portion  502 . The depending skirt  506  abuts the flange  508 , and is preferably bonded thereto. The lower portion  502  has a lower surface  509 . The lower surface  509  defines a pocket  510  in a central portion thereof. The pocket  510  is adapted to receive the upper end of a cursor control stick, such as the cursor control stick  10  (seen in FIGS. 1 and 2). Preferably, the pocket  510  (and indeed, any of the pockets described in this application as receiving a cursor control stick) is preferably sized to receive the cursor control stick with a stretch fit; the pocket  510  as formed is slightly smaller in cross-section than the cursor control stick. When installing the cushion  500  on a cursor control stick, the cursor control stick is forced into the pocket  510 , which stretches the material of the lower portion  502  to accommodate the larger cross section of the cursor control stick. The resulting elastic forces hold the cushion  500  on the cursor control stick through friction, creating an elastic or stretch fit between the pocket  510  and the cursor control stick  10 .  
         [0073]    The lower portion  502  is preferably formed of a material with a higher durometer than the upper portion  504 , but the lower portion  502  may, nevertheless, be formed of any suitable material, such as the material described as suitable for the lower portion  402  of the cushion  400  illustrated in FIGS. 8 and 9.  
         [0074]    Like the cushions described in the other embodiments in this application, the cushion  500  will deform if pressed against the display screen. It is contemplated that the cushion  500  may be manufactured to have a suitable relatively rigid pocket  510  (shown in FIGS. 11 and 12) to accept the upper end of a control stick of a computer, such as the control stick  10 . It is also contemplated that the cushion  500  could otherwise be fixed to a control stick cap like the cap  18  in FIG. 2, such as by adhesively fixing the cushion  500  (with an appropriately shaped pocket  510 ) to such a control stick cap. It is also contemplated that the cushion  500  could be fixed to such a control stick cap by having a pocket  510 , which is sufficiently deep to completely contain such a cap therein. In this embodiment, an inwardly extending flexible flange (not shown) of the lower portion  502  of the cushion  500  will resiliently extend under a portion of the cap after the cap is inserted into the pocket  510  to retain the control stick cap in the pocket  510 . It is also contemplated that the cushion  500  may be manufactured to form an integral part of a removable control stick or portion of a control stick (not shown).  
         [0075]    The cushion  500  may be formed by any suitable process on standard thermoplastic equipment. Thermoplastic rubber compounds or thermoplastic elastomeric compounds, for example, can be injection molded, extruded, blow molded and thermoformed with the efficiency and economy associated with such materials. In a preferred process, the cushion  500  is formed in a two step injection molding process, such as was described above with respect to the cushion  400  and illustrated in FIG. 23.  
         [0076]    An alternate embodiment of the cushion  500  is illustrated at  500 ′ in FIGS. 13 and 14. The cushion  500 ′ is similar in outer shape to the cushion  500  illustrated in FIG. 11, and has similar qualities of deformation for comfort and protection of computer video screens, and smoothness and tack for ergonomic reasons and may be constructed of similar material as the cushion  500 . However the cushion  500 ′ is constructed somewhat differently, as will be described.  
         [0077]    Like the cushion  500 , the cushion  500 ′ preferably has a generally cylindrical lower portion  502 ′ and a generally cup-shaped upper portion  504 ′. The upper portion  504 ′ may have a structure and composition identical to the upper portion  504  described above. The upper portion  504 ′ includes an upper surface  505   a ′. The upper surface  505   a ′ may be textured as is described in the embodiments illustrated in FIGS. 20 through 23.  
         [0078]    The lower portion  502 ′ of the cushion  500 ′ may be formed of any suitable material. Like the cushion  500 , the lower portion  502 ′ is preferably formed of a thermoplastic rubber compound such as SANTOPRENE® thermoplastic rubber with a formulation that cures to a Shore A durometer above 55. The lower portion  502 ′ has a lower surface  509 ′. The lower surface  509 ′ defines a pocket  510 ′ in a central portion thereof. The pocket  510 ′, like the pocket  510  in the cushion  500 , is shaped to receive the upper end of a cursor control stick, such as the cursor control stick  10 . In the illustrated embodiment the pocket  510  is rectilinear, having a rectangular cross section adapted to receive a control stick with a rectangular cross-section.  
         [0079]    The pocket  510 ′ of the cushion  500 ′ is of somewhat different structure than that of pocket  510  of the cushion  500 , being a stepped recess. A first recess  512 ′ is defined in the interior end surface of the pocket  510 ′ with slightly larger cross-section than that of a second recess  513 ′. A step  514 ′ is thereby formed between the first recess  512 ′ and the second recess  513 ′. As illustrated, a cursor control stick (not shown) does not engage the second recess  513 ′ of the pocket  510 ′, although such is not required. The second recess  513 ′ creates a void of stiff material below the central portion  505 ′. The void gives the central portion  505 ′ a softer feel to the user. An alternate embodiment of the cushion of this invention, indicated generally at  600 , is shown in FIGS. 15 and 16. The cushion  600  preferably has a generally cylindrical lower portion  602 , and a generally cup-shaped upper portion  604 . The upper portion  604  overlays and is bonded to a portion of the lower portion  602  that is disposed within the cup-shaped upper portion  604 .  
         [0080]    The upper portion  604  includes a central portion  605  that is preferably flat in shape. The upper portion  604  also includes a depending skirt portion  606  formed at the circumferential periphery of the central portion  605 . The upper portion  604  may be made from any suitable material, such as a foam or a gel or a thermoplastic rubber or thermoplastic elastomeric compound. The material from which the upper portion  604  is formed is selected to have a relatively low hardness, so that the upper portion  604  is relatively soft and compliant. The upper portion  604  is preferably formed from a material like the suitable material described for the upper portion  404  of the cushion  400  illustrated in FIGS. 8 and 9.  
         [0081]    As shown in FIGS. 15 and 16, the lower portion  602  is generally cylindrical and partially disposed within the depending skirt  606  of the upper portion  604 . The lower portion  602  preferably includes a relatively thick flange  608  that extends radially outwardly from a lower-most part of the lower portion  602 . The depending skirt  606  abuts the flange  608 , and is preferably bonded thereto. The lower portion  602  has a lower surface  609 . The lower surface  609  defines a pocket  610  in a central portion thereof. The pocket  610  is a stepped recess, having a first recess  612  defined in the interior end surface of the pocket  610  with slightly larger cross-section than that of the second recess  613 . A step  614  is thereby formed between the first recess  612  and the second recess  613 . The pocket  610  is adapted to receive the upper end of a cursor control stick  10 ′. Preferably, the second recess  613  of the pocket  610  (and indeed, any of the pockets described in this application as receiving a cursor control stick) is sized with a cross-section greater than the cross-section of the cursor control stick  10 ′, and the cross-section of the first recess  612  being slightly smaller than the cross-section of the cursor control stick  10 ′. During the installation of the cushion  600  on the cursor control stick  10 ′, the cursor control stick  10 ′ is fitted into the pocket  610 , with the upper end of the cursor control stick  10 ′ engaging the step  614 , the cushion  600  is thereby roughly aligned with the cursor control stick  10 ′. The cushion  600  is then pushed downwardly onto the cursor control stick  10 ′, driving the cursor control stick  10 ′ relatively upwardly into the second recess  613 , to engage the walls of the second recess  613  with a stretch fit; in the same manner described above for the pocket  510  of the cushion as illustrated in FIG. 11. As is indicated in the phantom view, when the cursor control stick  10  is received in the pocket  610 , the lower portion  602  of the cushion  600  may be slightly deformed as a result of the stretching as shown.  
         [0082]    The lower portion  602  is preferably formed of a material with a higher durometer than the upper portion  604 , but the lower portion  602  may, nevertheless, be formed of any suitable material, such as the material described as suitable for the lower portion  402  illustrated in FIGS. 8 and 9.  
         [0083]    Like the cushions described in the other embodiments in this application, the cushion  600  will deform if pressed against the display screen. As discussed above, it is contemplated that the cushion  600  may be manufactured to have a suitable relatively rigid pocket  610  (shown in FIGS. 15 and 16) to accept the upper end of the control stick  10 . It is also contemplated that the cushion  600  could otherwise be fixed to a control stick cap like the control stick cap  18  illustrated in FIG. 2, such as by adhesively fixing the cushion  600  (with an appropriately shaped pocket  610  to such a control stick cap. It is also contemplated that the cushion  600  could be fixed to such a control stick cap by having a pocket  610 , which is sufficiently deep to completely contain such a cap therein. The lower portion  602  of such a cushion  600  could have an inwardly extending flexible flange (not shown) which would resiliently extend under a portion of the cap after the cap is inserted into the pocket  610  to retain the control stick cap in the pocket  610 . It is also contemplated that the cushion  600  may be manufactured to form an integral part of a removable control stick or portion of a control stick (not shown).  
         [0084]    The cushion  600  may be formed by any suitable process on standard equipment. Thermoplastic rubber compounds and thermoplastic elastomeric compounds, for example, can be injection molded, extruded, blow molded and thermoformed with the efficiency and economy associated with thermoplastic materials. In a preferred process, the cushion  600  is formed in a two step injection molding process, as was described above with respect to the cushion  400  and FIG. 23.  
         [0085]    An alternate embodiment of the cushion  600  is illustrated at  600 ′ in FIGS. 17 and 18. The cushion  600 ′ is similar in outer shape to the cushion  600  illustrated in FIG. 15, and has similar qualities of deformation for comfort and protection of computer video screens, and smoothness and tack for ergonomic reasons and may be constructed of similar material as the cushion  600 . However the cushion  600 ′ is constructed somewhat differently, as will be described.  
         [0086]    Like the cushion  600 , the cushion  600 ′ preferably has a generally cylindrical lower portion  602 ′ and a generally cup-shaped upper portion  604 ′. The upper portion  604 ′ may have a structure and composition identical to the upper portion  604  described above. However, the upper portion  604 ′ may include a flange portion  611 ′. The flange portion  611 ′ extends radially outwardly from the upper portion  604 ′.  
         [0087]    The lower portion  602 ′ of the cushion  600 ′ may be formed of any suitable material. Like the cushion  600 , the lower portion  602 ′ is preferably formed of a thermoplastic rubber compound such as SANTOPRENE® thermoplastic rubber with a formulation that cures to a Shore A durometer above 55. The lower portion  602 ′ has a lower surface  609 ′. The lower surface  609 ′ defines a pocket  610 ′ in a central portion thereof. The pocket  610 ′, like the pocket  610  in the cushion  600 , is shaped to receive the upper end of a cursor control stick, such as the cursor control stick  10 ′. In the illustrated embodiment the pocket  610 ′ has a rectangular cross section adapted to receive the cursor control stick  10 ′ which has a rectangular cross-section.  
         [0088]    The pocket  610 ′ of the cushion  600 ′ is of somewhat different structure than that of pocket  610  of the cushion  600 , being a two-stepped recess. A first recess  612 ′ defined in the interior surface of the pocket  610 ′ with slightly larger cross-section than that of second first recess  613 ′. A step  614 ′ is thereby formed between the first recess  612 ′ and the second recess  613 ′. A third recess  616 ′ with a slightly smaller cross-section than that of the second recess  613 ′ is defined in the interior end surface of the pocket  610 ′. A step  618 ′ is thereby formed between the second recess  612 ′ and the third recess  616 ′. During the installation of the cushion  600 ′ on the cursor control stick  10 ′, the cursor control stick  10 ′ is fitted into the pocket  610 ′, with the upper end of the cursor control stick  10 ′ engaging the step  614 ′, the cushion  600 ′ is thereby roughly aligned with the cursor control stick  10 ′. The cushion  600 ′ is then pushed downwardly onto the cursor control stick  10 ′, driving the cursor control stick  10 ′ relatively upwardly into the second recess  613 ′, to engage the walls of the second recess  613 ′ with a stretch fit; in the same manner described above for the pocket  510  of the cushion as illustrated in FIG. 11. As is indicated in the phantom view, when the cursor control stick  10  is received in the pocket  610 ′, the lower portion  602 ′ of the cushion  600 ′ may be slightly deformed as a result of the stretching as shown. As illustrated, the cursor control stick  10 ′ does not engage the third recess  616 ′ of the pocket  610 ′, although such is not required. The third recess  616 ′ creates a void of stiff material below the central portion  605 ′. This void gives the central portion  605 ′ a soft feel to the user similar to the soft feel of the central portion  505 ′, without having the thickness of soft material of the central portion  505 ′.  
         [0089]    As is illustrated in FIG. 19, the cursor control stick  10 ′ is received in the pocket  610  of the cushion  600 . The lower portion  602  of the cushion  600  may deform as shown when the cursor control stick  10 ′ is received in the pocket  610 . As is also indicated in the phantom view, the cushion  600  may deform under the pressure of a user&#39;s finger  650 .  
         [0090]    In some applications it may be desirable to provide a textured surface on the cap. Any suitable texture pattern may be provided. Raised nubs and raised ridges are among the patterns which may be suitable.  
         [0091]    Referring now to FIGS. 20 and 20 a , an alternative embodiment of an upper portion  804  of the cushion of this invention, indicated generally at  800 , is shown. FIG. 20 a  is an enlarged plan view of a portion of the upper portion  804  illustrated in FIG. 20. The upper portion  804  of the cushion  800  has a top surface containing one or more nubs  830 . The nubs  830  may be of any suitable height. However, in one preferred embodiment the nub height is 0.5 millimeters to 1.0 millimeter. As illustrated, the nubs  830  are hexagonal in shape, but it is to be understood that the nubs may be any shape and may be spaced in any configuration. Without excluding circular nubs from the scope of the invention, it is believed that having side walls of the nubs  830  extend at right angles from the upper surface of the upper portion  804  (as shown in FIG. 20) will provide a more non-slip surface, while the relatively soft material of the upper portion  804  will help keep the cushion  800  from irritating the finger of a user. The nubs  830  are spaced from about 0.5 millimeters to about 1.0 millimeters on center and the nubs are about 0.5 millimeters to about 0.10 millimeters in width. Spacing the nubs  830  apart creates an open pattern texture. It is believed that the open pattern of the spaced-apart nubs  830  will make the cushion  800  relatively easy to keep clean and allows the user to maintain accuracy with the cursor control stick.  
         [0092]    Referring now to FIGS. 21 and 21 a , an alternative embodiment of an upper portion  804 ′ of the cushion of this invention, indicated generally at  800 ′, is shown. FIG. 21 is a plan view of an upper portion of the cushioned cap. FIG. 21 a  is a sectional view of the upper portion shown in FIG. 21, taken along the line  21   a - 21   a . The upper portion  804 ′ of the cushion  800 ′ has a top surface containing one or more nubs  830 ′. The nubs  830 ′ may be of any suitable height and may be of different heights from one another. However, in one preferred embodiment the nub height is about 0.25 millimeters to about 1.0 millimeter. As illustrated, the nubs  830 ′ are round in shape, but it is to be understood that the nubs may be any shape and may be spaced in any configuration. Without excluding rounded nubs from the scope of the invention, it is believed that having side walls of the nubs  830 ′ extend at right angles from the upper surface of the upper portion  804 ′ (as shown in FIG. 21) will provide a more non-slip surface, while the relatively soft material of the upper portion  804 ′ will help keep the cushion  800 ′ from irritating the finger of a user. The nubs  830 ′ are spaced from about 0.25 millimeters to about 1.0 millimeters on center and the nubs are about 0.5 to about 1.0 millimeters in width. Spacing the nubs  830 ′ apart creates an open pattern texture. It is believed that the open pattern of the spaced-apart nubs  830 ′ will make the cushion  800 ′ relatively easy to keep clean and allows the user to maintain accuracy with the cursor control stick.  
         [0093]    Another alternate embodiment of an upper portion  804 ″ of the cushion of this invention, indicated generally at  800 ″, is shown in FIGS. 22 and 23. In this embodiment, the texture is provided in the form of concentric rings  830 ″, each preferably having a rectangular cross-section.  
         [0094]    Additionally, the upper portion  804 ″ increases in thickness from the center of the upper portion  804 ″ of the cushion  800 ″ toward the circumferential periphery of the upper portion  804 ″ of the cushion  800 ″ as shown. The resulting upper portion of the cushion  800 ″ is concave in shape, as is shown in FIG. 23. This concave shape may be considered another form of texture, and as illustrated, may be used in conjunction with other forms of texture, such as the concentric rings  830 ″ (as shown in FIGS. 22, 23), or the nubs  830 ′ (as shown in FIGS. 21, 21 a ), or the nubs  830  (as shown in FIGS. 20, 20 a ). Of course, concentric rings could be added to a flat or convex upper portion.  
         [0095]    In summary, various aspects of this invention include:  
         [0096]    A control stick with a contact surface which is relatively soft and non-irritating to the body tissue of a user.  
         [0097]    A cushion for a control stick, the cushion being softer than the control stick.  
         [0098]    A cushion for a control stick, the cushion being formed of a gel material softer than the control stick.  
         [0099]    A control stick cushion, which can contact a display screen of a computer display, deform elastically, and not damage the display screen.  
         [0100]    A cushion for a control stick, joystick, or similar device, which is soft and non-irritating to the body tissue of a user during extended periods of normal use.  
         [0101]    A control stick cushion formed of two or more materials having different hardnesses.  
         [0102]    A control stick cushion formed from a two-step injection process.  
         [0103]    A control stick cushion formed from a two-step injection process, with an upper surface with a texture created by a mold with an abraded surface.  
         [0104]    A control stick cushion having an upper portion of a relatively soft material, preferably having a Shore A durometer of about 3 to about 10; the upper surface of the upper portion may be provided with a surface texture.  
         [0105]    A control stick cushion having an upper portion and a lower portion; the lower portion of a material relatively harder than the material of the upper portion, preferably having a Shore A durometer of about 55 to about 65.  
         [0106]    A control stick cushion having a concave upper surface.  
         [0107]    A control stick cushion surface texture, the pattern of which is an open pattern.  
         [0108]    A control stick cushion surface texture, the pattern of which is shaped as spaced hexagonal nubs.  
         [0109]    A control stick cushion surface texture, the pattern of which is shaped as concentric rings.  
         [0110]    A control stick cushion surface texture, the sidewalls of which texture rises at approximately right angles to the surrounding upper surface.  
         [0111]    The principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.