Abstract:
A cursor control device is taught that provides a compact and easily manufactured design. A shaft or actuator surface attaches around the periphery of a substrate. The substrate carries at least one strain sensitive resistor that provides an electrical signal indicative of the stress placed on the actuator. The substrate is attached to a supporting structure at a point in general proximity to the center of the substrate.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     Computers use various cursor control mechanisms to provide a physical control over cursor placement on the computer screen. The most common form of cursor control device is a mouse. Because a mouse is used in a position physically remote from the computer, it is not the preferred cursor control device for portable or laptop computers. In these computers, users want the freedom to operate the computer without any additional external devices. One frequently used cursor control mechanism incorporated into portable computers is that of a pointing stick. These devices have been described in many patents including U.S. Pat. No. 5,966,117 to Seffernick incorporated herein by reference. The Seffernick device provides a pointing stick mechanism including the ability for sensing a z-axis deflection. This z-axis deflection can be used to provide the mouse click function in place of providing separate buttons on the chassis of the computer. 
     One problem with existing pointing stick devices is the height of the device above the keyboard of the computer. When the screen is folded over the keyboard to close the computer, heavy objects can be placed on top of the computer. The screen may deflect when loaded in this manner causing the center of the screen to be impacted by the pointing stick. As the load is increased, it is possible for the deflection to cause damage to either the pointing stick or the screen. 
     One approach to resolve some of the problems associated with pointing stick devices has been to mount the strain sensitive resistors on a supporting member rather than the shaft of the pointing stick. However, these devices have placed the shaft connection to the underlying substrate towards the center of the device with a supporting electrical connection towards the periphery of the device. This can result in poor performance because of the distance between the connection points. The ceramic material used for the substrate typically expands and contracts in response to temperature differently than the underlying printed circuit board to which the substrate is mounted. As the temperature within the computer increases or decreases, the connections between the substrate and the printed circuit board are therefore stressed. Placing the connections as close together as possible can minimize this harmful effect. An additional problem with traditional approaches is that as keys are pressed on the keyboard or as the computer is flexed slightly, the support for the pointing stick is correspondingly flexed. This can cause unwanted cursor movement. Placing the physical connections towards the center of the substrate similarly minimizes this effect. 
     The present invention overcomes this problem by providing a pointing device that is compact in design. The present invention is also easily manufactured and the structure is simplified over other compact pointing devices. 
     The present invention is directed to a pointing stick especially for use as a cursor control device for a computer that incorporates strain sensitive resistors. The pointing stick includes a shaft mounted to a substrate around the periphery of the substrate. The substrate is fixedly attached to a printed circuit board or other structure. The substrate carries at least one strain sensitive resistor. As the shaft is deflected, the substrate is stressed relative to its attachment to the printed circuit board which in turn causes the strain sensitive resistor to vary resistance to correspond to the desired cursor movement by the user. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a computer device incorporating the present invention. 
     FIG. 2 shows a pointing stick according to the present invention. 
     FIG. 3 shows the substrate of the present invention. 
     FIG. 4 shows an alternative embodiment of the present invention. 
     FIG. 5 shows the substrate of the alternative embodiment of FIG.  4 . 
     FIG. 6 shows a second alternative embodiment of the present invention. 
     FIG. 7 shows the substrate of the second alternative embodiment of FIG.  6 . 
     FIG. 8 shows the electrical schematic representing the preferred embodiments. 
     It should be noted that the drawings are not to scale. 
    
    
     DETAILED DESCRIPTION 
     Computers typically are controlled by users through the use of various input control devices including a cursor control and keyboard. Computer  7  typically has a program running thereon that provides for movement of a cursor  8  on display device  11  in response to the user operating cursor control device such as a pointing stick  10 . One such program is Microsoft Windows ME. Display device  11  can be any of a number of different devices, such as an LCD attached to a laptop computer; other similar devices such as a computer monitor employing a cathode ray tube (CRT) may also be used. Computer  7  as shown in FIG. 1 is a laptop computer, although the invention is not limited to any particular configuration. For example, computer  7  may also be a desktop or tower system. As shown in FIG. 1, pointing stick  10  is mounted between the “g” “h” and “b” keys on a standard “QWERTY” laptop keyboard  9 . The term “QWERTY” is a common term used to describe the layout of the keyboard based upon the first six letters across the top row of keys. 
     Pointing stick  10  allows a computer user to move the cursor  8  on display device  11 . Pointing stick  10  therefore translates movement by the user into an electronic signal provided to the computer via a communications link which is internal to the computer  7  of FIG.  1 . Not shown is that computer  7  typically includes a central-processing unit (CPU), a random-access memory (RAM), and a read-only memory (ROM). The CPU, RAM, and ROM may be of any type; the invention is not particularly limited. In one embodiment, the CPU is an Intel Pentium IV processor, there are sixty-four megabytes of RAM, and the ROM contains such functionality as a basic input/output system (BIOS). Also not shown is that computer  7  usually comprises a fixed storage device such as a hard disk drive with software resident thereon, and a removable storage device such as a floppy disk drive. 
     Referring to FIG. 2, pointing stick  10  according to the present invention is shown. In particular, the pointing stick  10  is made up of an actuator  12 , a substrate  14  for supporting the actuator  12  and a structural support  30  such as a printed circuit board. Actuator  12  is preferably generally circular in cross-section, but can be any shape desired based upon space available and other physical constraints. A rubber actuator  13  is placed over the top of the actuator  12 . The rubber cap  13  provides a better surface texture for the user to contact. The actuator  12  includes a base portion  16  which is dimensionally larger than the actuator  12 . The base  16  includes a peripheral flange  18  which extends downward from the base  16 . The actuator  12  also includes overlimit protectors  15 . 
     As described in FIG. 3, a ceramic substrate  14  is provided which is formed to mate with the flange  18  on the base  16 . The substrate  14  is dimensionally smaller than the base  16 . The substrate includes four strain sensitive resistors  22   a,b,c,d  on the side opposing the base  16 . The strain sensitive resistors  22   a,b,c,d  are preferably thick film devices screen printed onto the ceramic substrate  14 . The screening process is done using strain sensitive paints in a manner known to one skilled in the art. The resistors  22   a,b,c,d  are selected so that when the substrate  14  is placed under stress, the electrical resistance of the resistors  22   a,b,c,d  will vary in direct relation to the amount and relative direction of stress. Electrically conductive traces  24  are screened on the substrate  14  to provide an electrical interconnection of the resistors  22   a,b,c,d  to contact pads  26 . 
     The strain sensitive resistors  22   a,b,c,d  and electrically conductive traces  24  are shown located on the same side as the contact pads  26 . These components could, however, be located on the opposite side, facing the actuator with an electrical via provided to make electrical contact between the strain sensitive resistors  22   a,b,c,d  and the contact pads  26 . As used herein, the spatial relationships between the strain sensitive resistors  22   a,b,c,d , the outer edge  28  and the contact pads  26  are independent of the side on which they are located. Thus, describing the strain sensitive resistors  22   a,b,c,d  as being located between the outer edge  28  and the contact pads  26  allows the strain sensitive resistors to be on either side of the substrate  14 . 
     The contact pads  26  are designed to allow an electrical connection with a printed circuit board using standard solder techniques. The contact pads  26  are located proximal or close to the center of substrate  14 . This is done to focus the stress between the center of the substrate  14  and the contact point with the actuator or actuator  12  around the periphery of the substrate  14 . The resistors  22   a,b,c,d  are located in this stress region. The outer edge  28  of the substrate  14  and the flange  18  of the base  16  are formed to mate in a snap-fit arrangement. Alternatively, the flange  18  could be attached to the outer edge  28  using some epoxy or other adhesive material. 
     The overlimit protectors  15  are provided on the actuator  12  to prevent the user from damaging the sensor by over-stressing the pointing stick. As the actuator  12  is stressed by the user, the base  16  will deflect relative to the substrate  14 . If the user continues to stress the actuator  12 , the overlimit protectors  15  will contact the substrate  14 , limiting any further travel of the actuator  12 . In this way, additional stress placed on the actuator  12  will not be transferred to the substrate  14  at its periphery, but will instead be transferred through the overlimit protectors  15  to the substrate  14  closer to the center. This helps to prevent damage to the actuator  12  and substrate  14 . 
     A support member  30  is provided beneath the substrate  14 . The support member  30  is preferably a printed circuit board containing other electrical or electronic devices in addition to the pointing stick  10 . The pointing stick  10  is attached to the support member  30  via conductive solder paste  32 . The solder paste  32  also provides electrical interconnection between electrical traces on the support member and the contact pads  26  on the substrate  14 . 
     The thermal coefficient of expansion for the support member  30  is different from that of the substrate  14 . Thus, as the computer  7  heats up, the support member  30  and the substrate  14  will expand at different rates. The contact pads  26  on the substrate  14  are initially in alignment with the contact points (not shown) on the support member  30 . As the two members expand at different rates, the relative contact points will shift slightly, generating stress on the solder joint. As the contact pads  26  are separated by greater distances, the total shift will correspondingly increase. Thus, by placing the contact pads  26  proximal to the center of the substrate  14 , the total distance between these points is reduced and the shift caused by the varying coefficient of thermal expansion is minimized. 
     Another advantage to locating the contact pads  26  proximal to the center of the substrate  14  is a reduction in susceptibility to keyboard flexing. The pointing stick  10  is mounted adjacent to the keyboard  9 . As keys are depressed, the support member  30  may be flexed slightly. This deflection can be sensed by the strain sensitive resistors  22   a,b,c,d  and will then be converted to an unwanted movement of the cursor  8  on the display device  11 . By placing the contact pads  26  close together, these keyboard deflections are minimized reducing the risk of spurious cursor movement. 
     The electrical output from the strain sensitive resistors  22   a,b,c,d  is generally relatively low-level and is thus susceptible to electro-magnetic interference. In order to minimize the impact of such interference, it is common to provide signal conditioning circuitry that amplifies the output signal. The signal conditioning circuitry may also provide an analog to digital conversion in order to provide a digital signal indicative of the pointing stick  10  output. The signal conditioning circuitry may be included as an integrated circuit  34  located on a printed circuit board functioning as the support member  30 . In practice, the four strain sensitive resistors  22   a,b,c,d  are connected to form a bridge circuit as shown in FIG.  8 . 
     An alternative, even more compact design incorporating the present invention is shown in FIGS. 4-5. In this embodiment, a rubber actuator  100  is provided which includes a peripheral flange  102  and a center post  104 . The end  106  of the post  104  extending furthest from the cap  108  includes an extension  110  that has a radius wider than that of the post  104 . The substrate  120  includes strain sensitive resistors  122   a,b,c,d  configured similarly to those previously discussed. The substrate  120  is mounted to support member  30  as previously described herein. The substrate  120  additionally includes a receptacle  124  located in the center of the substrate  120 . The receptacle  124  is formed to receive the post  104  in a slight interference fit. By pressing the post  104  into the receptacle  124 , the extension  110  is compressed until it protrudes beyond the bottom of the receptacle  124 . The extension  110  thus provides a secure mechanism to hold the actuator  100  to the substrate  120 . 
     As the user applies stress to the actuator  100 , the flange  102  correspondingly presses on the edge of the substrate  120 . The strain sensitive resistors  122   a,b,c,d  are stressed by the resulting deflection in the substrate  120 . As with the prior embodiment, this stress causes the resistance of the resistors  122   a,b,c,d  to vary which provides an electrical indication of the user&#39;s desire to move the cursor. 
     A third alternative embodiment is shown in FIGS. 6-7. In this embodiment, strain sensitive resistors  222   a,b,c,d  are located between contact pads  226 . In other respects this embodiment resembles that of FIGS. 2-3. The strain sensitive resistors  222   a,b,c,d  are placed between contact pads  226  because the region closest to the contact pads receives the maximum amount of stress. Thus, the strain sensitive resistors  222   a,b,c,d  will have an increased output with increased sensitivity due to this placement. 
     It should be apparent that the detailed description above is illustrative only and should not be taken as limiting the scope of the invention. Similarly, not all of the functions performed by the embodiment disclosed need be performed in any one mechanism or circuit. Accordingly, the invention should be understood to include all such modifications as come within the scope and spirit of the following claims and equivalents thereto.