Abstract:
The invention is embodied in a wireless stylus that incorporates, for example, an infrared emitter for communicating with a receiver associated with a computer. The stylus is provided with push-buttons near its tip that can be actuated by the user during the course of pointing the stylus at a touch screen location. Accordingly, by the combined actuation of the touch screen and a concurrent actuation of one or more of the push buttons, a mouse input to the computer is accomplished.

Description:
FIELD OF THE INVENTION 
     This invention relates to input devices for computers and, more particularly, to a stylus type input device that incorporates means for inputting right and left mouse button control signals to a computer. 
     BACKGROUND OF THE INVENTION 
     Touch screens are widely used as input devices for computers and are broadly classified according to how they sense touches. Resistive matrix-touch screens typically comprise a transparent plastic membrane that overlays a glass substrate. Too and bottom layers are patterned with parallel metal wires that are perpendicularly aligned to form a grid. Pressing on the top membrane forces the wires together to register a touch. 
     Resistive analog touch screens are constructed like resistive matrix screens, but are not etched to define a wire grid. Instead, the entire surface acts as one large active area sensor. Touches are registered by measuring voltage dividers in the X and Y directions. Support circuits alternately apply voltage across bus bars on opposite sides of one layer (usually the bottom), first in the X direction and then in the Y direction. When the tap layer contacts the bottom, acts as a probe and measures the X and Y voltage components. These values define the location of the touch point. 
     In the past, resistive membrane touch screens have been most often used for dedicated applications, such as public access kiosks or manufacturing process control, where the basic interaction is selection from a small set of icons or other targets. In this case, it is sufficient to select an icon as soon as it is touched, or perhaps touched and released. A typical software strategy is for the touch screen device driver to interact with the normal mouse device driver to generate emulated mouse button changes, in accordance with the state of the screen contact. Usually, several emulation options are provided. This is generally satisfactory for a dedicated program, especially if the underlying operating system is hidden from the user. 
     Now, however, resistive screens, often equipped with a stylus, are increasingly being installed in general purpose computers. For this case, both the operating system and most standard application programs are designed to be controlled by a two-button mouse input device. In such configurations, it is difficult to provide a consistent and intuitive mouse button emulation that allows the touch screen to be used in place of a mouse or other pointing device. As an example, most operations require an ability to drag a cursor to some particular place, and then to start an operation, either by clicking a button (e.g., for a selection of a menu item), or by depressing it and holding a button (e.g., a window drag). 
     Most of these operations fail if the button is pressed before the cursor is properly positioned. It is then difficult to emulate the left button, using only the touch screen contact signal, without resorting to awkward procedures. For example, one such procedure is to emulate a left-button actuation if no motion occurs after one second. Such a gesture technique is hard to use reliably. The Windows operating system (Windows is a registered trademark of the Microsoft Corporation) also uses the right button, for example, to open special menus. This action can be emulated by more complex procedures involving multiple taps and/or gestures. In addition to being awkward, such procedures may be misinterpreted and cause unintended effects. 
     Lastly, special difficulties arise when a stylus is used for handwritten inputs. Here it is essential to use the contact signal to segment the handwriting rather than for mouse button emulation. 
     The prior art, for example, U.S. Pat. No. 4,814,552 to Stefik et al. employees a stylus system using both ultrasonic and infrared transducers. The transducers are used in combination to determine stylus tip location by timing the arrival of ultrasonic signals from the stylus. In addition, the infrared transducers are used to transmit to an associated computer the state of a stylus contact switch and two push buttons. 
     The use of a wireless link to transmit the button state is essential, as a stylus with connecting wires is clumsy to use. It is preferable, however, to sense position with a resistive touch screen, as such screens are the dominant technology for flat panel displays. As such, they are available at low cost, can be used with fingers as well as with styli, and provide an inherent contact signal with negligible displacement so that the computer can segment handwriting into strokes. In contrast, stylus contact switches often require significant longitudinal displacement for actuation. This can produce segmentation artifacts when used for handwriting, for example noticeable “hooks” at the end of some strokes. 
     A further problem with the prior art is that it does not deal with a situation which can arise if the stylus is withdrawn from sensing range at a time when a pushbutton is depressed. The button will then appear to be pressed even if it is later released. This will effectively disable the operating system and/or application programs unless some provision is made to reset the button state. 
     Accordingly, it is an object of this invention to provide a stylus input device with the capability to input right and left mouse button signals. 
     It is another object of this invention to provide a stylus, having no direct wire connection to the computer, with an ability to input right and left mouse button control input signals. 
     It is yet another object of this invention to provide a stylus, having no direct wire connection to a computer, with an ability to input at least one button control signal to the computer, and to clear the signal in the event that the wireless link fails while a button is actuated. 
     SUMMARY OF THE INVENTION 
     The invention is embodied in a wireless stylus that incorporates, for example, an infrared emitter for communicating with a receiver associated with a computer. The stylus is provided with push-buttons near its tip that can be actuated by the user when the stylus is in the range of a wireless detection sensor. Accordingly, by the combined actuation of the touch screen and a concurrent actuation of one or more of the push buttons, a mouse input to the computer is accomplished. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of an overall arrangement of the invention. 
     FIG. 2 is a schematic sectional view of the stylus of FIG. 1 that incorporates the invention. 
     FIG. 3 is a high-level schematic of a circuit that generates an infrared pulse signal sequence. 
     FIG. 4 illustrates the waveforms generated by the circuit of FIG.  3 . 
     FIG. 5 is a high level block diagram of an infrared detection module and processor chip used to detect signals from the stylus of FIG.  1 . 
     FIG. 6 is a waveform diagram illustrating sampling actions that occur to detect the presence of pulse signals that indicate button actuations. 
     FIG. 7 is a chart illustrating logic states that, are assumed upon finding a pulse in a window time during the sampling sequence shown in FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, stylus  10  is provided with buttons  12  and  14  close to tip  16 . While two buttons are shown, more may be incorporated in stylus  10 . Within stylus  10  is found an infrared light emitting diode  18  (shown in FIG. 2) that is caused to emit encoded modulated infrared light from a transparent section  20  located near tip  16 . Stylus  10  is positioned over a touch screen  22  and, when pressed thereagainst, causes touch screen  22  to indicate to an attached computer (not shown) the location of tip  16 . Also coupled to the computer is an infrared detection module  24 , preferably located near an upper corner of the processor&#39;s display, that receives the transmitted infrared signals, causes them to be decoded by a small incorporated processor, and passes the decoded signals to the computer as mouse button inputs. 
     Stylus  10  is shown in more detail in FIG. 2 where buttons  12  and  14  are indicated as being positioned close to tip  16 . Push buttons  12  and  14  are connected to a microcontroller  26  that is, in turn, powered by a battery  28 . Microcontroller  26  is normally in a “sleep” mode and in this state draws only a few microamps from battery  28 . Microcontroller  26  is caused to automatically exit its sleep mode when one of buttons  12  or  14  is depressed or released. It then pulses light emitting diode (LED)  18 , via an output pin, to indicate the new button state. 
     When LED  18  is pulsed, it emits light towards a reflector cone  30  that is positioned within stylus  10 . As a result, the light pulses emanating from LED  18  are reflected outwardly through transparent portions  20  towards detection module  24  (FIG.  1 ). 
     FIG. 3 is a high level schematic illustrating the LED drive circuit. Each transmission from microcontroller  26  comprises one or more pulses, each pulse comprising a burst of sub-pulses having a repetition rate frequency of, for example, 36 kiloHertz. The complete pulse sequence comprises a start pulse  40  (see FIG. 4) followed, after a delay T 1 , by pulse  42  if button  12  is actuated and/or a pulse  44 , after delay T 2 , if button  14  is actuated. Thereafter, a stop pulse  46  signals the end of the sequence. The sequence is repeated once, after a delay, to increase the probability of detection by detection module  24 . 
     After emitting the second pulse sequence, microcontroller  26  is returned to the sleep mode, with a wake-up timer now set to a predetermined time value. Upon time out of the wake up timer, microcontroller  26  awakens and checks the button states, emitting a regular pulse sequence if either of buttons  12  or  14  is still depressed. It then returns to the sleep mode. Thus, with one of buttons  12  or  14  down, stylus  10  is caused to re-emit the pulse sequence at the expiration of each sleep time. 
     The processor in detection module  24  is programmed to reset its “button-actuated state” if it fails to detect a predetermined number (e.g., one or two) of these periodic pulse sequences. Without this mode of operation, if the user removes stylus  10  from the detection range of module  24 , with one of buttons  12  or  14  depressed, detection module  24  would assume that one of the buttons was still in the actuated state, even if released, thereby resulting in a disabling of the system. Thus, the system maintains its state of operation, even though the user may have removed stylus  10  from the detection range with one of buttons  12  or  14  depressed. 
     In addition to the use of sleep mode, power consumption from battery  28  is reduced by the use of reflector cone  30 , which reflects the infrared light emitted by LED  18 . Cone  30  is used, in conjunction with the angular spread of the LED emission, to direct the infrared light into a useful direction, i.e. towards the infrared receiver. That is, the included angle of reflector cone  30  is chosen to deflect the infrared light generally into a plane parallel to the surface of touch screen  22  when stylus  10  is held at a normal writing angle of about 45 degrees to the surface of touch screen  22 . The angular spread of the LED emission provides the necessary tolerance in stylus writing angle. By this means, an LED  18  with a relatively narrow angular spread can be used. As an example, if the LED emission falls to half power at an angle of 40 degrees from the axis, then an included cone angle of about 65 degrees is suitable and will result in a theoretical tilt tolerance of about +/−20 degrees. In practice, the tolerance will be greater because internal reflection of the infrared light will broaden the emission pattern. 
     Referring to FIG. 5, detector module  24  includes a lensed IR detector  24  that comprises a gain controlled amplifier tuned to the center frequency of the emitted subpulses, an AC to DC converter, a filter and a voltage comparator. Exemplary modules are the SFH 5110 or SFH 5111 series manufactured by Infineon Technologies AG. The lens, which also serves as a narrow band infrared filter, has a wide acceptance angle (e.g., +/−55°). 
     The output from IR detector  24  is a logic level signal which tracks the envelope of the infrared transmissions, apart from a short, fixed delay. These pulses are fed to a processor chip  50  for decoding. Processor chip  50  checks the timing and number of logic level transitions to ensure that the signal is valid, in order to reject IR interference from other transmitters. It then determines which, if any, of the extra pulses shown in FIG. 4 are present in order to detect button state. Two processor output pins  52 ,  54  are connected across mouse button input pins of a standard mouse processor chip  56  which is, in turn, connected to a regular mouseport of a computer. A low voltage across a button switch appears to mouse  56  as a contact closure. Mouse  56  automatically transmits all such changes to the computer where they are interpreted as button changes. While the aforementioned is one way to interface processor chip  50  to a computer, there are other ways to accomplish the interface action. For example, interface processor chip  50  may be directly connected to the touch screen processor or to the computer&#39;s serial port. 
     Turning now to FIGS. 6 and 7, the algorithm used to enable detection of signals from stylus  10  will be described using a stylus with two buttons, as an example. The expected signal is a set of two to four pulses, depending on the button state. Additional buttons may be accommodated by adding and detecting additional pulses. The detection algorithm is designed to test the waveform for validity by checking for the correct number and spacing of edge transitions of the pulses, while tolerating normal timing variations. Initially, processor chip  50  runs in a loop, checking the output pin voltage from detector  24  for a positive going edge. Such a positive going edge is assumed to mark the start of transmission, consisting of a start pulse  40 , two button state pulses ( 42 ,  44 ) followed by a stop pulse  46 . Processor  50  then executes an algorithm which checks for a valid start pulse  40 , two possible button pulses and a stop pulse. In addition, the intervals after the pulse locations are checked for 0 values (see the table of FIG.  7 ). Each check is done by sampling. the input signal as rapidly as possible. The sampling is done within a window inside of each expected region, chosen to allow for normal. timing variations. 
     All samples within each window are required to have the same value, i.e., there should be no unexpected transitions. This state is checked, and an error flag is set if any transitions occur within a sampling window. Similarly, if the value within each sampling window differs from an expected value, such as shown in the. table of FIG. 7, the error flag is set. If the error flag is clear at the end of the entire sequence, then the button states are taken from the bit values of the third and fifth sampling intervals. 
     Processor chip  50  then sets two output bits to reflect the button state. As discussed above, processor  50  also checks for repeated sequences at the time-out of a sleep state counter (e.g., 150 milliseconds). If the last detected signal state indicated a button-actuated condition, the processor clears the button state if a new pulse sequence is missing. 
     It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.