Abstract:
A computer pointing device on a single, small printed wiring board includes all electronics necessary for providing a standard mouse-type output signal. The pointing device uses a balanced bridge strain gauge isometric sensor having a manipulation lever for user input. The computer pointing device includes a receiving space for accepting one of a large-size strain gauge sensor and a small-size strain gauge sensor, depending upon the specific application. The computer pointing device includes internal power regulation and has input for up to two momentary switches and two of the pointing devices can be daisy chained with a single, composite output signal. The small-size strain gauge sensor permits use of the pointing device in ultra thin keyboard applications.

Description:
RELATED APPLICATION 
     This Application is related to a co-pending U.S. patent application entitled “A Mini-TrackPoint IV Pointing Device,” filed on the same date as the present Application, also to co-pending U.S. patent application entitled “Force Transducer With Screen Printed Strain Gauges,” Ser. No. 08/181,648, filed Jan. 14, 1994, which is the parent to Ser. No. 08/688,614, filed Aug. 6, 1996 now U.S. Pat. No. 5,867,808 and to U.S. patent application entitled “Floating Triangle Analog-to-Digital Conversion System and Method,” Ser. No. 08/773,420, filed Dec. 27, 1996, now U.S. Pat. No. 5,894,282 all assigned to the International Business Machines Corporation. The disclosure of each related Application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention generally relates to information processing systems, and more specifically, to computer pointing devices used with graphical user interfaces to information processing systems. The invention has a particular applicability to the IBM® TrackPoint® IV pointing device. (IBM and TrackPoint are registered trademarks of the International Business Machines Corporation.) 
     BACKGROUND OF THE INVENTION 
     The TrackPoint class of pointing devices employ a ceramic strain gauge balanced resistive bridge network as an isometric sensor for user input. A manipulation lever is attached to a central point on the strain gauge. Force applied to the lever causes the four resistive elements to change resistance in proportion to the amount each is distorted by the applied force. The resistances are measured and a mathematical transformation is performed to convert the changes in resistance to standard mouse-type output signals. In a specific embodiment, the output signals conform to the IBM P/S-2 computer pointing device standard. Basically, the standard mouse-type signals represent velocity in a two-dimensional space. The velocity in a given direction is proportional to the applied force in that direction. Such a pointing device is used, for example, to manipulate a graphical user interface on a computer display screen. 
     A prior art figure (“PRIOR ART”) illustrates the manner in which specific embodiments of the TrackPoint pointing devices are used. The manipulation lever  1  extends from a strain gauge  2 , through an opening between several keys  3  of a computer keyboard  4 . The circuits  5  which are connected to the strain gauge are located at some distance from the strain gauge and include analog-to-digital converters, digital formatting and power regulation. The low-level analog signals from the strain gauge are connected to the circuits via a cable  6 . Though the combination works well, the cable must be assembled and connected by hand, thus increasing the manufacturing cost of the whole assembly. 
     It would be desirable to eliminate the cost of the manufacturing and assembly steps involving the inter connecting cable. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a lower cost alternative to existing in-keyboard isometric pointing devices, such as earlier versions of the TrackPoint pointing device. 
     It is another object of the invention to provide a single pointing device which can use one of two alternative sizes of strain gauge for differing applications. 
     It is another object of the invention to provide a pointing device in which all the low-level analog signals are carried on very short printed wiring and are located in close proximity to the other circuits forming part of the pointing device. 
     These objects, and others that will become apparent to those skilled in the art, are provided by a computer pointing device including a printed wiring board having two sets of electrical pads defining a receiving space for connection and mechanical support of a large-size and, alternatively, a small-size strain gauge bridge network. The pointing device also includes a manipulation lever connected to the strain gauge for user input. The strain gauge is connected via the printed wiring board to a comparator and bias network. The comparator and bias network is connected via the printed wiring board to a micro-controller and power regulation circuit. 
     In a specific embodiment, the computer pointing device receives operating power input and a user manipulation input and provides a standard mouse-type output signal as defined by the IBM P/S-2 standard. 
     In another specific embodiment, the computer pointing device permits components of the bias network to be selected for balancing the strain gauge bridge network. 
     Another class of embodiments of the invention define an electrical interconnection component for a computer pointing device. 
     Finally, another class of embodiments of the invention define a computer pointing device sub-assembly, complete with all components except the strain gauge and the selectable bias components. 
     It is an advantage of the present invention to reduce the manufacturing cost of the TrackPoint computer pointing device by placing all the components on a single, small printed wiring board, thereby eliminating the cost of interconnecting a strain gauge sensor with remote electronics assemblies. 
     It is another advantage of the present invention to maintain control over potential electrical noise affecting low-lever analog signals by maintaining strict control over the low-level printed wiring line lengths. 
     Finally, it is an advantage of the invention to provide a single sub-assembly, including a strain gauge receiving space and all the necessary support electronics, which will accept one of a large-size strain gauge and a small size strain gauge. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a further understanding of the objects, features and advantages of the present invention, reference should be had to the following description of the preferred embodiment, taken in conjunction with the accompanying drawing, in which like parts are given like reference numerals and wherein: 
     FIG. 1 is a top view of a computer pointing device according to one aspect of the present invention. 
     FIG. 2 is a bottom view of the computer pointing device of FIG.  1 . 
     FIG. 3 is a side view of the computer pointing device of FIGS  1 ,  2 . 
     FIG. 4 is a simplified block diagram of a computer pointing device according to another aspect of the invention. 
     FIG. 5 is a top view of a printed wiring board illustrating placement of contact pads relative to a large size isometric strain gauge. 
     FIG. 6 is a top view of the printed wiring board of FIG. 5 illustrating placement of contact pads relative to an alternative small size isometric strain gauge. 
     FIG. 7 is a side view of the printed wiring board of FIG. 5 with a large strain gauge attached. 
     FIG. 8 is a side view of the printed wiring board of FIG. 6 with a small strain gauge attached. 
     FIG. 9 is a side view of the printed circuit board and large strain gauge of FIG. 7 relative to a portion of a standard (thick) keyboard. 
     FIG. 10 is a partial side view of the printed circuit board and small strain gauge of FIG. 8 relative to a portion of a thin keyboard. 
     FIG. 11 is a simplified schematic diagram of a computer pointing device according to another aspect of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 1 there is shown a top view of a computer pointing device according to one aspect of the present invention. The computer pointing device is designated generally by the numeral  10  and includes a printed wiring board  12 , a cross-shaped strain gauge  14  having a finger-tip manipulable lever  16 , mechanical attachment openings  18 , and electrical cable connection pads  20 . 
     FIG. 2 is a bottom view of the computer pointing device  10  of FIG. 1, and shows a reverse side of the printed wiring board  12 , a clock signal oscillator module  22 , a comparitor circuit  24 , a micro-controller  26 , several operating power filter capacitors  28 , and a solder-side of the electrical cable connection pads  20 . An outline of the strain gauge  14  is shown with a broken line. 
     FIG. 3 is a side view of the computer pointing device  10  of FIGS  1 ,  2  showing an edge view of the printed circuit card  12 , the micro-controller  26 , one filter capacitor  28 , and the strain gauge  14  attached to the finger-tip manipulable lever  16 . A user&#39;s finger tip  30  is shown manipulating the lever  16  for positioning in a planar X-Y coordinate system typical of mouse-type computer pointing devices. 
     FIG. 4 is a simplified block diagram illustrating an electrical circuit for a computer pointing device according to FIGS  1 - 3 . The computer pointing device electrical circuit is designated generally by the numeral  32 , and includes a two-dimensional strain gauge  34  (defining a bridge circuit), comparitor circuits  36 , a bias network  38 , and a micro-controller and power regulator  40 . The strain gauge  34  is manipulated by a user finger-tip input  30 . The simplified computer pointing device  32  shown in FIG. 4 receives operating power on an input line  42  and distributes regulated operating power  44  to other elements of the circuit. The simplified computer pointing device  32  also receives the user finger-tip manipulation input  30  and provides a P/S-2 type computer pointing device output signal  46 . 
     In operation, the computer pointing device  32  is connected to a source of operating power (e.g., +5V DC) and the output signal  46  is connected to a P/S-2 mouse input on a computer. The user puts a finger tip  30  against a distal end of the manipulation lever  16  and applies force in the direction he desires a displayed cursor to move on a computer display screen (not shown). 
     The manipulation lever  16  is attached to the strain gauge  14  at a central point such that force applied in any direction changes the resistance of one or more legs of the bridge circuit  34 . The bridge circuit  34  is coupled to the comparator circuit  36  via lines  35  (FIG.  4 ). The micro-controller generates a ramp analog voltage which it supplies on lines  37  to the comparator circuit  36 . The comparator circuit compares the ramp voltage with a low-amplitude analog voltage developed across each leg of the bridge, and generates a digital pulse for each low-amplitude analog voltage whose duration is proportional to the level of the low-amplitude analog voltage. These pulses are coupled to the microcontroller via lines  39 . The micro-controller  40  measures the pulse duration provided for each leg of the bridge, and from those measurements determines the direction and amount of force applied by the user to the manipulation lever  16 . The micro-controller  40  then converts the measurements into a standard P/S-2 output signal, which is presented on line  46 . 
     Please note that a convention followed in the electronics industry refers to a signal and also to a line carrying the signal by the same name. That convention is followed here. A distinction between the two will be made only when believed necessary to avoid confusion. 
     In a specific embodiment, the bias network  38  includes components which are selected to balance the bridge after a particular strain gauge has been installed. There are two sizes of strain gauge: a large size, and a small size. Each size has its own electrical characteristics. The use of selectable components in the bias network permits the bridge  34  to be balanced once the strain gauge is installed in the pointing device and when no force is applied to the lever  16 . The bias network  38  is connected to the comparator circuit  36  via lines  41 . 
     In another specific embodiment, the micro-controller  40  includes a power regulation circuit used to regulate the DC power received on line  42 . The regulated power is distributed to the other elements of the computer pointing device  32 , for example via line  44 . 
     Another embodiment of the invention is shown in FIG. 5, a simplified top view of an electrical interconnection component for a computer pointing device of a type using a finger-tip manipulable two-dimensional strain gauge for user input. The interconnection component is designated generally by the numeral  50 , and includes a printed wiring board  52  and electrical contact pads  54 - 68  disposed on a surface  70  of the printed wiring board  52 . The electrical contact pads  54 - 68  are disposed for a compatible electrical mating with corresponding electrical contact pads of a first (large) size two-dimensional strain gauge (pads  54 - 60 ) and alternatively, of a second (small) size two-dimensional strain gauge (pads  62 - 68 ). 
     An outline  71  of a top view of the large size strain gauge is shown having four legs  72 - 78  connected at a common center at right angles to one another. A distal end of each leg includes an electrical contact pad for compatible mating with contact pads  54 ,  56 ,  58  and  60 , respectively. The strain gauge does not form part of the interconnect component  50 . 
     FIG. 6 is a top view of the electrical interconnection component  50  showing an outline  80  of a top view of the small size strain gauge. The distal ends of the legs of the small size strain gauge include electrical contact pads for compatible mating with contact pads  62 - 68 , respectively. 
     In FIG. 5, the outline  71  of the large strain gauge and the contact pads  54 - 60  define a receiving space for a large size two-dimensional strain gauge. In FIG. 6, the outline  80  of the small strain gauge and the contact pads  62 - 68  define a receiving space for a small size two-dimensional strain gauge. 
     The interconnect component  50  also includes printed wiring (not shown), including the electrical contact pads  54 - 68 , defining an electrical interconnection network for a computer pointing device of the type described. The defined electrical interconnection network includes printed wiring electrical component pads for receiving electrical bias components for adjusting bias for a two-dimensional strain gauge. The interconnected bias components define a bias network ( 38  of FIG.  4 ). 
     FIG. 7 is a side view of the electrical interconnection component  50  of FIG. 5 showing attachment of a large-size strain gauge. The strain gauge is designated generally by the numeral  82 , and includes a cross-shaped strain gauge member  84  and an attached manipulation lever  86 . The electrical contact pads located at the distal ends of the four legs of the strain gauge member  84  are shown attached, mechanically and electrically to corresponding electrical pads  56 ,  58  and  60  on the surface  70  of the printed wiring board  52  (the solder connection to electrical pad  54  is hidden behind pad  58  and is not shown). In a specific embodiment, the strain gauge is attached to the mating pads of the printed wiring board  52  by solder. 
     FIG. 8 is a side view of the electrical interconnection component  50  of FIG. 6 showing attachment of a small-size strain gauge, designated generally by the numeral  88 . As stated above, the strain gauge  88  is not an element of the electrical interconnection component  50 , but is shown to aid in understanding this specific embodiment of the invention. 
     FIG. 9 is a side view of the electrical interconnection component  50  and the large-size strain gauge  82  of FIG. 7 in relation to a portion of a standard size keyboard (showing individual keys  90 - 96 ). The printed wiring board  52  and attached strain gauge  82  are located below the keys, while the manipulation lever  86  extends through an opening  98  formed at the intersection of keys  92 ,  94 , so that a distal end of the lever  86  extends above the tops of the keys for user manipulation. 
     FIG. 10 is a side view of the electrical interconnection component  50  and the small-size strain gauge  88  of FIG. 8 in relation to a portion of a thin keyboard (keys  100 - 106  are shown). A manipulation lever  108  extends through opening  110  formed at the intersection of keys  102 ,  104 . 
     Another embodiment of the invention is illustrated in FIG. 11, a simplified schematic diagram. This embodiment defines a computer pointing device sub-assembly, designated by the numeral  120 . The sub-assembly  120  includes a printed wiring board (not shown, but see printed wiring board  12  of FIG.  1 ), electrical contacts  122 - 129 , an adjustable bias and comparitor network  130 , and a micro-controller and power regulation circuit  132 . 
     The electrical contacts  122 - 129  define a receiving space for a strain gauge  138 . The strain gauge  138  defines an electrical bridge network in which the resistance of each leg of the bridge varies proportionally to a force applied to a manipulation lever  140 . The adjustable bias network includes electrical contact pads which define a receiving space for bias components used to balance the bridge network when no force is applied to the lever  140 . It will be appreciated that the strain gauge  138  and the bias components are not a part of the sub-assembly  120 . However, the addition of a strain gauge  138  and bias components to the defined receiving spaces of the sub-assembly  120  forms a complete computer pointing device. 
     The electrical contacts  122 - 129  are arranged about a common center on one surface of the printed wiring board as illustrated in FIGS  5 ,  6 . And the strain gauge receiving space defined by the electrical contacts  122 - 129  are immediately adjacent the networks  130  and the micro-controller  132 , as illustrated in FIGS  1 - 3 . The receiving space and one set of the electrical contacts  122 ,  124 ,  126  and  128  are arranged to receive a large-size strain gauge, as illustrated in FIGS  5 ,  7  and  9 . The receiving space and the other set of the electrical contacts  123 ,  125 ,  127  and  129  are arranged to receive a small-size strain gauge, as illustrated in FIGS  6 ,  8  and  10 . The bias components are selected from precision resistors (±1% tol.) for balancing the bridge network of the received strain gauge. 
     The sub-assembly  120  includes printed wiring for connecting up to two manually operated momentary switches  134 ,  136  to micro-controller  132  input lines  142 ,  144 . The sub-assembly  120  also includes printed wiring for connecting a P/S-2 output line of a second daisy-chained pointing device (not shown) to an input line  146  of the micro-controller  132 . Again, it will be appreciated that neither the second pointing device nor the momentary switches  134 ,  136  form part of the sub-assembly  120 . 
     The sub-assembly  120  also includes printed wiring for connecting an output line  148  of the micro-controller  132  to another electrical assembly. 
     While the invention has been described in relation to the embodiments shown in the accompanying Drawing figures, other embodiments, alternatives and modifications will be apparent to those skilled in the art. It is intended that the Specification be exemplary only, and that the true scope and spirit of the invention be indicated by the following Claims.