Abstract:
The present invention is directed to an improved system and method in which a pen-sized and shaped device detects, recognizes and stores handwriting as it is written by the device. The invention employs both an active feedback network and a character recognition methodology of partitioning detected input into character components. The active feedback network continually monitors device output to determine the sufficiency of the data input. If the data input is insufficient, the device modifies its detection methodology to obtain data the device readily recognizes. Data recognition is performed in multiple asynchronous processes. Elements of individual characters are sampled by the detector. Character elements are processed and recognized on this elemental level. Recognized character elements are stored for subsequent assembly and recognition on a character level. Thus, preferably two recognition sub-processes take place, one on a character element level and another on a character level.

Description:
Priority of provisional application Ser. No. 60/175,127 filed on Jan. 6, 2000 in the USPTO is claimed under 35 .S.C. §119. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The field of the present invention relates to portable data entry and storage devices. In particular, the invention relates to pen-based devices that produce, recognize and store handwriting. 
   2. Background 
   In recent years, many products have been developed that attempt to feature the simplicity and ease of a pen and paper at recording information while enabling the ready transfer of such information to computers and other information systems. Very often people initially commit their thoughts to paper only to find themselves having to reenter the information into a computer or other electronic device. One development effort that in part seeks to eliminate the task of retyping is the development and commercialization of character recognition (both optical and nonoptical) software. Such software was developed to bridge the gap between the handwritten word on paper and the computer-readable and transferable representation of the word. While many such packages have been successfully commercialized, they also have inherent limitations. First, to use character recognition software, a page scanning system must initially capture information on a page. Thus, a scanning element is necessary to enable the character recognition software to perform its function. Second, the combination of the character recognition software and the page-scanning system become new elements that are added to the information transfer process. That is, they do not replace the pen and paper, but instead, introduce new task elements that replace rather than eliminate the task of reentering information. 
   On another front, portable digital assistants (PDAs) such as the Palm V™ by 3Com, Inc. have been commercialized in attempt to replace the need for pen and paper and eliminate the need to reenter information. However, when compared to pen and paper in terms of the ease with which to record information, they too are often impractical. While such devices have continually improved in terms of flexibility and performance, they remain relatively inflexible and limited in terms of the manner and type of information that can be entered and recorded. A structured writing style is often required that can reduce writing speed. Further, PDAs are bulkier than pens in that an electronic writing template is a necessary part of the device. Also, PDAs require a measure of training of the user to be useful. Thus, in these systems, to capably record information in a computer-readable format, much of the flexibility and ease of writing on paper by hand is sacrificed. 
   However, recently, numerous devices and systems have been described that claim to provide the recordation flexibility of pen and paper with the capability of storage in a computer-readable format. These devices are or use pen-like devices that, in real-time, store as computer-readable data, information as it is written on a paper medium. 
   Examples of such a device are disclosed in U.S. Pat. No. 5,774,602 issued to Taguchi et al. (“the &#39;602 patent”) which is incorporated herein by reference. The &#39;602 patent describes a writing device that uses a CCD detector to sense the handwriting written using the device. The device includes a microprocessor for converting the sensor&#39;s output into image data, a storage device for storing the image data, an output for downloading the image data, a stress sensor and a power supply. Similarly, U.S. Pat. No. 5,294,792 issued to Lewis et al. (“the 792 patent”) and incorporated herein by reference, describes a self-contained pen-computer that acquires data representative of written strokes of a stylus of a pen and then recognizes the symbols associated with the pen strokes. The recognized symbols are stored in a memory contained in the pen and are transmitted to a host computer using a transmitter integrated into the pen. 
   The devices disclosed in the &#39;602 and &#39;792 patents and others previously developed in the field of pen-based handwriting storage suffer from certain serious drawbacks. First, while many of the disclosed devices allow for initial training of a device before use to enhance the recognition performance for a specific user, the devices disclosed are limited to a particular writing regimen or style once use commences. After they are configured to a certain user, even the trainable devices such as the device disclosed in the &#39;792 patent, require that the specific user maintain a specific writing style that a device is designed to recognize. If the user deviates from the device&#39;s operational requirements, the device&#39;s performance markedly drops. Thus, a need exists for a device that is not constrained to a particular writing style or writing structure. 
   As another drawback, the highest performance character recognition devices, including many PDAs, tend to require user-specific training to achieve their recognition performance levels. By tailoring each device to a particular user, the portability or transferability of any given device becomes greatly limited because the performance degrades rapidly as the use migrates from the use the device was trained to recognize. Thus, a need further exists for a device the performance of which is not limited to a narrow recognition scheme that restricts its portability between users. 
   Further, the devices disclosed in the prior art such as those in the &#39;602 and &#39;792 patents, invite a host of undesirable consequences because of the design philosophy that they adopt in performing character recognition. By recognizing text on a character-by-character basis, the devices described demand additional, larger, and/or higher power-consuming components. In the context of a pen-based real-time handwriting recognition system, such demands are completely inapposite to the inherent limitations of a pen-like device. The enormous variability in the handwritten representation of any given character requires that a device that adequately performs recognition on a character level have a significant processing and character reference storage capability. Such demands readily lead to implementations that compromise the need for such devices to be low power and of a size and shape that is not far removed from the conventional ball-point pen. Thus, a need exists for a device that employs a character recognition methodology that meets the practical constraints inherent in a viable pen-based handwritten character recognition and storage device. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to an improved system and method in which a pen-sized and shaped device detects, recognizes and stores handwriting as the handwriting is written by the device in real-time. To meet the needs described above, the present invention first employs an active feedback mechanism in the device. By employing an active feedback mechanism, if a user of the device modifies his or her writing style while the device is in use, the device adapts, in real-time, to the new writing style. Similarly, if a new user uses the device, the device adapts to the writing style of the new user. The active feedback mechanism continually monitors the output of the device to determine the sufficiency of the data that is input. The sufficiency of the input is preferably guided by the sampling rate of the input. If the device detects that the quantity of data output is insufficient, the device modifies its detection to effect a sampling rate that is representative of the data that the device readily recognizes. 
   Also, the present invention partitions detected input into components of characters, i.e. strokes that in combination form a character. By partitioning data into character components, the data processing, recognition and storage complexities and requirements are simplified such that the size, shape and power limitations for the device need not be compromised. The partitioning of data is the basis of a pyramidal recognition process. Data is sampled from the detector such that the initially processed input represents character elements. Character elements are initially processed and recognized on this elemental level. Once recognized, recognized character elements are stored for subsequent assembly and recognition on a character level. Thus, preferably two recognition sub-processes take place, one on a character element level and another on a character level. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is a diagram depicting a top view of a preferred pen-based writing storage system. 
       FIG. 1B  is a diagram depicting a side view of a preferred printed circuit board layout for a preferred pen-based writing storage system. 
       FIG. 1C  is a diagram depicting a side view of the preferred pen-based writing storage device. 
       FIG. 1D  is a diagram depicting a head on view of the preferred pen-based writing storage device. 
       FIG. 1E  is a diagram depicting a head on view of an alternative embodiment for the detection system in the preferred pen-based writing storage device. 
       FIG. 1F  is a diagram depicting a head on view of an alternative embodiment for the detection system in the preferred pen-based writing storage device. 
       FIG. 1G  is a diagram depicting a head on view of an alternative embodiment for the detection system in the preferred pen-based writing storage device. 
       FIG. 1H  is a diagram depicting a pen-based writing storage device positioned in a cradle for communication of stored handwritten data to a computer. 
       FIG. 2  is a schematic of a circuit for the preferred pen-based writing storage device depicted in  FIGS. 1A-D . 
       FIG. 3A  is a flow chart depicting the basic steps formed by the preferred pen-based writing storage device. 
       FIG. 3B  is a table depicting an example of an index of possible quadrature components. 
       FIG. 3C  depicts the functional elements in the quadrature analysis performed by the preferred pen-based writing storage device. 
       FIG. 3D  is a table depicting an example of a character set that is represented in a reference character matrix. 
       FIG. 3E  is a table depicting a character set in a reference character matrix represented as a composition of quadrature components. 
       FIG. 3F  depicts a set of sub-tables, one for each type of quadrature component or stroke, where each sub-table lists frequency and weighting characteristics for a set of English capital letters that generally require the stroke. 
       FIGS. 4A-C  are flow diagrams depicting preferred specific steps performed by the preferred pen-based writing storage device in processing handwriting. 
       FIGS. 5A and 5B  are diagrams depicting an alternative embodiment of microfeeler based detection for the detection system in the preferred pen-based writing storage device. 
       FIG. 5C  is a graph depicting examples of the current output from the apparatus of  FIGS. 5A and 5B . 
       FIGS. 6A-C  depict an alternative embodiments of the detection subsystem in the preferred pen-based writing storage device using induction coils to detect ball rotation. 
       FIGS. 6D-F  are graphs depicting examples of the current output from the alternative detection subsystems of  FIGS. 6A-C , respectively. 
       FIG. 7  is a schematic depicting a preferred embodiment of a circuit for processing microfeeler-based input as depicted in  FIGS. 5A and 5B  and induction coil input as depicted in  FIGS. 5C-F . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1A-D  depict several views of a preferred hardware configuration for a pen-based handwriting detection, recognition and storage device  98 .  FIG. 1A  is a top view of the device  98  which is preferably comprised of a pen body  100 , a pen point  102 , a pen cartridge body  104 , a snap body  106 , a recess for an optical path  108 , an optical input/output data path  110 , an optical analog-to digital (A/D) input buffer  112 , a programmable clock  114 , a primary application-specific integrated circuit (ASIC)  116 , a secondary ASIC  118 , a read-only memory (ROM)  120 , other memory  122 , and battery cells  124 . The pen body  100  is preferably of a size and shape that is no larger than a large pen, i.e. about ½″ in diameter and about six inches in length. Near the last ¾″ of the length of the pen body  100 , the pen body  100  preferably has a cone-like shape that narrows in diameter to the pen point  102 . The ink cartridge contains standard amount of ink. The pen body  100  is preferably made from or coated with an electrically insulating material such as plastic, and may be for example, polyamide, polypropylene, or polyvinylchloride. The pen cartridge  104  is preferably positioned near the pen point  102  and provides ink for the pen point  102 . The snap body  106  is a means for separating the pen body  100  near its center to enable removal or replacement of the pen cartridge  104 . The top end of the pen body  100  preferably opens for access to or removal of the battery cells  124 . 
     FIG. 1B  is a side view showing a preferred printed circuit board (PCB)  126  on which are the chips for the electronic components including the programmable clock  114 , the optical A/D buffer  112 , the primary and secondary ASICs  116 ,  118 , and the memories  120 ,  122 .  FIG. 1C  is a side view of the device  98  in which the PCB  126  is viewed from its side. The PCB  126  provides for communication between the components. The PCB  126  is preferably positioned along a radial line through the central axis of the pen body  100 . By so positioning the PCB  126 , space is provided to position the components on opposing sides of the PCB  126  without contacting the pen body  100  or requiring a pen body  100  with a larger diameter. Additionally, such positioning is preferably designed to allow the weight and feel of the device  98  to more closely resemble that of a traditional pen. The primary and secondary ASICs  116 ,  118  perform separate and asynchronous signal recognition processing tasks. In performing their respective processing tasks, the ASICs communicate bidirectionally. 
     FIG. 1D  is a head-on view depicting the elements of a detector subsystem  128  for a preferred embodiment of the device  98 . The detector subsystem  128  preferably includes a photo emitter  130  and a photo detector  132  that are preferably positioned on opposing sides of the pen point  102 . The photo emitter  130  preferably emits a pulsed infrared signal that is, at least in part, reflected from the writing surface to the photo detector  132  which tracks the position of the pen point  102 . The photo emitter preferably pulses between about 40 kHz and about 100 kHz. Alternatively, the photo emitter emits a non-pulsed constant infrared signal. The optical data path  110  preferably runs along the inner surface of the pen body  100  and provides the data I/O connection between the PCB  126  and the detector subsystem  128 . The signal received by the photo detector  132  is transmitted along the optical data path  110 . 
     FIGS. 1E-G  depict head on views of alternative embodiments of the detector subsystem  134 ,  136 ,  138  for the pen-based writing and storage device that also use photo emitters and photo detectors.  FIG. 1E  depicts a single photo emitter  140  and two photo detectors  142 ,  144 .  FIG. 1F  depicts a multi-segment photo emitter  146  and two photo detectors  148 ,  150 .  FIG. 1G  depicts an array  152  comprised of at least one photo emitter and at least one photo detector. Preferably, the array  152  comprises up to eight (8) photo emitters and up to eight (8) photo detectors. The number of each element in the array  152  is preferably complimentary to the number of the other element. For example, a device configured with six detectors preferably has one or two emitters. In another example, a device with two detectors may have from one to 6 emitters—it may be impractical to load a detector device array with more emitters than detectors. This emitter adaptation uses a taller package to host the emitter/detector arrays. In each of these alternative embodiments, the photo emitters and the photo detectors preferably operate as previously described, and where more than one photo detector is employed, the device preferably includes a comparator (not depicted) for each photo detector employed. 
   As will be discussed in more detail, the device  98  preferably detects and recognizes handwriting based on the relative X-Y movements of the pen point  102  as would be produced during writing. In order to appropriately detect and recognize the written characters, the device  98  may employ one or more methods to ensure correct orientation in relation to the detected handwriting. One such preferred method is to have the device  98  self-orient upon initialization. Self-orientation comprises having the user write a pre-specified sample letter and the device, using the sample letter as a reference for orientation. As an alternative or additional option, the pen is ergonomically contoured to be held by a user in a particular orientation. 
   In a preferred embodiment, when the device  98  is to be secured for nonuse, requires recharging of the battery cells, or contains data that is desired to be transferred to a computer or other electronic data storage device, the device  98  may be placed in a holder that performs these functions.  FIG. 1H  depicts a preferred embodiment of a system  160  for interfacing the device  98  with a computer  162  via a device cradle  164 . The device cradle  164  preferably includes an infrared transmitter  166  to enable preferably linear mass data dumps of handwritten character data, preferably already converted into a standardized form, from the device  98  to the computer  162 . The computer  162  preferably includes an infrared receiver  168  to receive data transmitted from the transmitter  166  and electronic memory storage to store received data. Alternatively, any wired or other wireless mechanism for transmitting the data from the device  98  to the computer  162  is used. Further, the computer  162  may be any device that may receive and store data. Once stored by the computer  162 , data that has been received may be error-checked, manipulated or reformatted in any manner desired by the user of the system  160 . Optionally, the data is manipulated using any known text-editing application. The device cradle  164  preferably includes a button  170  or, alternatively, another form of actuator to enable the initiation of data transmission. In an alternative embodiment, the data transmission function of the device cradle  164  is incorporated into the device  98 , allowing the device  98  to transmit data directly to the computer  162 . The preferably simplified design that allows device  98  to have a relatively small size readily enables alternative embodiments that feature functional extensions to the device  98 , including a data transmission function. In such an embodiment, the data transmission function is performed by incorporating into the device  98  an infrared, or alternatively, an radio frequency (RF) transmitter. In another alternative embodiment, if the transmitted data is not in a recognized character format, the computer  162  includes software to convert received data into data in a standard character format such as ASCII. 
     FIG. 2  depicts a detailed circuit schematic  200  preferably implemented in the detector subsystem  128  and on the PCB  126  for a preferred embodiment of the pen-based writing storage device  98 . In  FIG. 2 , the photo-detector is a photodiode  202  powered using a preferably 3.5-volt DC power source  204  and resistor  206  combination. Since in the preferred embodiment the photo emitter  130  emits a pulsed light signal, the photodiode  202  will detect spectrally reflected light. However, in the alternative embodiment in which the photo emitter  130  emits a non-pulsed light signal, the photodiode  202  will detect a diffusely reflected light. 
   Light input into the photodiode  202  results in an analog signal input that indicates the X-Y movement of the pen point  102  of the device  98 . The analog signal preferably is then amplified by an op-amp  208  that then feeds a preferably eight-bit A/D converter  210  on the PCB  36 . The A/D converter  210  preferably converts the amplified analog signal to an 8-bit digital sample. The 8-bit A/D converter  210  preferably includes pins for ground, a pin to receive power from a 3-volt source, Vcc, a pin to receive an input clock signal, a pin to transmit an output clock signal, and a pin to transmit each of the bits that represent the signal. In  FIG. 2 , the eight bits produced by the A/D converter  210  and the output clock signal are input to an input buffer  212  for a processor that is preferably comprised of primary and secondary ASICs  214 ,  216 . Alternatively, the processor is implemented as a single ASIC or more than two ASICs. As another alternative, some or all of the processing is implemented with other hard-wired circuitry such as a field-programmable gate array (FPGA) or other logic device. In another alternative embodiment, if the size and power limitations are met, the processor is a general purpose central processing unit (CPU) wherein the processing logic is implemented in software. Furthermore, the processor alternatively represents multiple processors that perform different processing tasks or have the same tasks distributed between processors. Thus, as used herein, the term “processor” refers to any computational devices or means that meet the processing requirements and the size and power preferences of the device  98 . 
   However, in the preferred embodiment depicted in  FIG. 2 , the input buffer  212  buffers the input to the primary ASIC  214 , which has the task of performing quadrature component logic operations on the digital input data signal. The quadrature logic operations are steps to characterize or identify the input signal as an element of a character. By doing so, the data that is thereafter processed is greatly simplified as the input data is characterized as preferably one of a reference set of strokes. Preferably, the input buffer  212  is loaded when two A/D clock cycles are completed. The input buffer  212  is sized to allow for dynamic changes in the frequency and resolution of input data because preferably possible dynamic increases in sampling frequency result in more data that is input to the buffer  212  for each base clock cycle of the device  98 . When the input buffer  212  has acquired a sufficient amount of data, the input buffer  212  preferably sets a flag for the primary ASIC  214  to commence quadrature logic operations on the buffered data. 
   The reference set of strokes is preferably stored in and accessed from an 8-bit dynamic random access memory (DRAM)  218 , preferably with a memory capacity of between 64 k and 128 k bytes, which is estimated to be capable of holding up to approximately 60 handwritten pages of writing. As smaller, higher capacity memory is developed in the art, such memory may be used in the device  98 . The DRAM  218  holds reference data after a boot-up process in which the ROM  120  (not shown in FIG.  2 ), which permanently holds all of the reference data and initialization data, initializes the device  98  and loads the reference data into DRAM  218 . Using a memory buffer  220  electrically interposed between the primary ASIC  214  and the DRAM  218 , the primary ASIC  214  reads the reference data in the DRAM  218  to enable the identification of the input data as specific character components. Moreover, the DRAM  218  may store the identified data. Preferably, the DRAM  218  also stores temporary runtime data and logarithm tables. The DRAM  218  as shown in  FIG. 2 , includes pins to ground, a pin to the 3-volt power source, Vcc, a pin for a clock input signal, a memory clock output signal to the memory buffer  220 , and eight pins for eight bits of data I/O with the memory buffer  220 . 
   The primary ASIC  214  also communicates with the secondary ASIC  216  and a clock control integrated circuit (IC)  222 . The primary ASIC  214  transmits signals to the clock control IC  222  when the quadrature logic operations require a change in the output from the programmable clock  224  to one of the components of the device  98 , preferably normally the A/D converter  210  which samples the analog input. This capability of modifying the clock reflects an overall active feedback network design for the device  98  that enables the device  98  to adapt to the different writing styles and writing speeds of different users. The clock control IC  222  processes the signals from the primary ASIC  214  and transmits preferably 4-bit clock control signals to the programmable clock  224 . Thus, the clock control IC  222  provides the logic and interface for communicating with and modifying the operation of the programmable clock  224 . The clock control IC  222  handles communication contention with the programmable clock  224  from the other logic components, including the secondary ASIC, and provides a standard method of clock function interaction. The clock control IC  222  also provides for synchronization between the components. 
   In communicating with the secondary ASIC  216 , the primary ASIC  214  transmits quadrature result data to enable the secondary ASIC  216  to perform cell-blocking operations, i.e. operations to assemble the character components into an identifiable character. The secondary ASIC  216  also communicates with the primary ASIC  214  preferably along the same electrical connection, to under certain circumstances, instruct the primary ASIC  214  on the acquisition of additional data from the A/D converter  210 . 
   Like the primary ASIC  214 , the secondary ASIC  216  similarly has a connection to the clock control IC  222  for interfacing the secondary ASIC  216  with the programmable clock  224 . The clock control IC  222  preferably provides synchronization between the input buffer  212  and the secondary ASIC  216 . Like the primary ASIC  214 , the secondary ASIC  216  also accesses the DRAM  218  via memory buffer  220  to retrieve reference data to perform comparisons with the assembled quadrature components, yet preferably operates asynchronously with respect to the primary ASIC  214 . For the secondary ASIC  216 , the reference data is character data stored in a character matrix in the DRAM  218 . The character matrix preferably contains a list of sets of preferably four integers that correspond to a combination of preferably four quadrature components that correspond to a particular character. Each set of preferably four integers therefore preferably describes one character in the character matrix. The secondary ASIC  216  also outputs a digital representation of a recognized character to the memory buffer  220  and/or an external latch  226  which preferably buffers the output to an 8-bit D/A converter  228 . The D/A converter  228  preferably includes connections from a 3-volt power source, from a ground, and from the external latch  226  that provides eight bits of digital input. The output of the D/A converter  228  is then fed to a transmitter (not shown) for output preferably to the external system  162  as shown in FIG.  1 H. 
   The programmable clock  224 , as noted above, is controlled by four clock control connections from the clock control IC  222 . The programmable clock  224  also preferably includes connections from a preferably 3.5-volt power source and from ground. For its output, the programmable clock  224  provides synchronization for the ASICs  214 ,  216  and memory components on the PCB  126 , and provides independent programmable clock signals that drive the detection of handwriting input data and the output of recognition data to the external system or the DRAM  218 . The clock signals from the programmable clock  224  are continuously provided to the various components, insuring the continuous flow of data into the device  98  and safeguarding against the possibility of not capturing handwritten characters. When power is first applied to the device  98 , the programmable clock  224  is initialized to a predetermined sampling and output frequency. The time base for the programmable clock  224  is preferably a 4-MHz quartz crystal oscillator  230 . Preferably, at regular intervals, the clock control IC  222  resynchronizes the independent clock signals of the programmable clock  224  with the time base of the crystal oscillator  230 . 
     FIG. 3A  depicts basic steps in a preferred process  300  of recognizing and storing handwritten characters that are preferably produced on paper by the handwriting storage device  98 . A first step  302  is the acquisition of analog data regarding the X-Y movement of the pen point  102  as would be produced during a writing session. The next step  304  is to convert the analog data to digital data. The sampling of the digital data is preferably at a rate that provides for the representation of a discrete “quadrature” component or stroke of a character. Quadrature components are components of characters that, in an ideal case, if combined in a group of preferably from one to four components form single characters, such as upper and lower case English letters, punctuation characters and numbers. A quadrature component of a character is preferably defined according to a discrete period of time in generating a character, whether a “null” in the generation of a character has occurred, or the length of the path in the generation of the character. Thresholds for each of these parameters may specify the bounds (in time or space) of a stroke. The “null” point normally is observed in manuscript writing where the pen point performs distinct movement in the generation of a single character. 
   In the next step  306 , the digital data is then normalized into a form for comparison with a reference matrix of quadrature components. The reference matrix is preferably a previously generated library of quadrature component representations that are used for comparison against input data. An example of a representation of a reference matrix of quadrature components is shown in FIG.  3 B. Preferably, the reference matrix contains a representation of a set of strokes that in various combinations may form every character that is commonly handwritten by the user.  FIG. 3B  is an example of a set of possible strokes. Beside each stroke is a stroke index that is preferably used to represent the individual strokes in the reference and character matrices. Before comparing the input data with the reference matrix of quadrature components, the data normalization step  306  preferably converts the digital data of each character component into a polynomial form or alternatively an eigenvector form. Alternatively, the normalization step  306  characterizes the component data in a standardized form by converting the data into vector representations, by performing spline fitting methods as are known in the art, or applying fast Fourier transform/wavelet operations, preferably configured to use a log table to minimize processing requirements, the output of which distinguishes between ellipses, curvatures, lines and intersections. In each case, the reference matrix represents the quadrature information in a standardized form that is in accord with the normalization processing of the input data. For example, in polynomial-based normalization step, the reference matrix stores polynomial representations of quadrature components having an ideal form or another known level of quality. Alternatively, the reference matrix stores Fast Fourier Transform (FFT) transformations of similar reference data. Regardless of the means used to implement the normalization step  306 , the step  306  of converting the input data into quadrature components simplifies the subsequent processing steps and reduces the overall reference storage requirements. With the preferred polynomial representation implementation, the reference matrix stores idealized polynomial representations of character components. An advantage of this tiered recognition process is that with respect to this first tier, the process is character independent. The character components are discrete and generic such that generally they may be used in the formation of a character set representing any written language or symbology. 
   In the next step  308 , a quadrature component search is performed. This step  308  is the first of a two-tiered recognition process that characterizes the input data in phases and simplifies the data following each stage of recognition. In the polynomial-based implementation, once the data has been represented in polynomial form, the polynomial coefficients for the data are compared to the polynomial coefficients that are used in the reference matrix to represent the complete set of quadrature components. By representing the data and the references as polynomial coefficients the process of comparison between them is greatly simplified. Preferably a closest match type of comparison is used to identify the polynomial-represented stroke. 
   In the eigenvector-based implementation, the set of eigenvectors is compared to a reference matrix of eigenvectors to identify the character components. Preferably, an XOR operation is performed as a comparison scheme. When the eigenvectors are identified as a particular quadrature component from the reference matrix, the identified quadrature component is propagated for further processing. 
   In the event that the quadrature comparison with the reference matrix cannot identify the data because the data is malformed or has been misinterpreted, then the process  300  proceeds on an alternative path that is characteristic of the active feedback design of the device  98 . In the alternative path, the next step  310  preferably is to alter the detection sampling rate to attempt to acquire more easily characterized or identifiable data. Preferably, the sampling rate is adjusted by instructing the clock control IC  222  to modify the programmable clock  224 , shown as step  312  in FIG.  3 A. Preferably, as a temporary measure, additional bits of data are received to aid in the recognition of the quadrature component until the detection sampling rate is modified. Specifically, the primary ASIC  214  preferably additionally instructs the input buffer  212  to receive additional data into the input buffer  212  at the original sampling rate as a temporary adjustment measure until the sampling rate is modified by the programmable clock  224 . For example, in the polynomial-based configuration, if only the lower order polynomial coefficients of the normalized input data do not match the reference matrix polynomial coefficients, then the detection sampling rate is preferably reduced. On the other hand, if higher order coefficients of the normalized input data do not match the reference matrix polynomial coefficients or if they are too high, the clock speed and/or the number of bits that are received for the quadrature are preferably increased. 
   Preferably, once the sampling rate is modified, the number of bits sampled for each quadrature component returns to a preferred operational amount, i.e. preferably 16 or 32 bits for each quadrature component. After the step  312  of modifying the programmable clock  224 , the step  302  of acquiring analog data is repeated where new analog data is sampled at the potentially modified sampling rate. As discussed below, the initially unidentified quadrature data is stored and retained for use with up to preferably three subsequent quadrature components to decipher the character that includes the unidentified quadrature component. 
   In relation to the above active feedback design, when the device  98  is first activated, the sampling rate for the device  98  is initially set by requiring the user to hand-write a single character such as an “S.” Based on the detection, quadrature and recognition processing of the “S,” the programmable clock  224  may be modified to require an increase or decrease in the data-sampling rate. By requiring an initial test pattern, the device  98  limits the amount of data that may be initially lost. 
   Along the first process path, where the quadrature component comparison with the reference matrix identifies the eigenvector or polynomial represented data, the process  300  performs a step  314  of reconstructing the written character based on the resolved quadrature components. This is the cell-blocking sub-process and represents a second tier of the preferred tiered recognition process  300 . If the input quadrature component to the cell-blocking sub-process is the first component of a new quadrature component set representing a character, then the sub-process may not successfully reconstruct the character. In this case, the process  300  proceeds to a step  316  of storing the quadrature component. Then, the process returns to the data acquisition step  302  to enable the capture of additional data. The process steps are repeated to resolve a second and potentially third and fourth quadrature components. Each time though the process  300 , an attempt is made to reconstruct the cell based on the freshly resolved quadrature component and the quadrature components that have been previously resolved and stored. Preferably, at least two quadrature components are resolved before the reconstruction step  314  is successfully performed. If the character cannot be reconstructed, then the detection sampling rate dictated by the programmable clock  224  may again be modified as part of the active feedback mechanism to improve the detection and processing efficiency. In a preferred embodiment, an LED at the base of the device  98  is lit when processed data cannot be resolved as a character. Preferably, in such an event, the user initializes the device to recommence handwriting detection by writing a predetermined initialization character, such as the “S” discussed above. 
   Preferably, if the cell is identified based on a set of quadrature components, the process  300  proceeds to a step  318  of converting the assembled cell to a character format and storing a digital, preferably compressed, representation of the character in memory. In that event, the quadrature memory buffer is preferably purged to allow new data for a new character to be acquired and stored. 
     FIG. 3C  depicts the basic elements of the quadrature processing logic of step  314  in FIG.  3 A. Digital representations of a character  320  are partitioned and processed on a quadrature component basis. The partitioning  322  provides the elements of the first tier recognition process or quadrature analysis  324 . In the quadrature analysis  324 , a first quadrature component is received. The quadrature analysis  324  preferably commences only after a second quadrature component is received. The quadrature analysis  324  then preferably attempts to identify the character based on the receipt of two quadrature components. The quadrature analysis  324  is performed by scanning a character matrix  326  that represents characters as composites of quadrature components.  FIG. 3D  depicts an example of a character set that is represented in the character matrix  326 . The character set includes upper and lower case English characters.  FIG. 3E  depicts a representation of the character set in the character matrix  326  as a composition of quadrature components. If the pair of quadrature data sets cannot be identified from the character matrix  326 , a third and potentially a fourth quadrature component is input to the character matrix  326  and the quadrature analysis  324  is reattempted. 
   Preferably, the quadrature analysis  324  is optimized according to the frequency of certain letters being written. For example,  FIG. 3F  is a table comprised of a set of sub-tables, one for each type of stroke. Each sub-table lists a set of English capital letters that generally require the stroke. In each sub-table, in the row below each letter, is a stroke frequency value representing the number of times that a given stroke is written for each English capital letter, with the minimum being one (1). Such data is preferably used in the cell blocking sub-process in initially making “intelligent guesses” as to the identity of a character based on the identification of one or more quadrature components. Also in  FIG. 3F , to the right of each sub-table for a stroke, is a stroke weight value representing the relative frequency in written English of the respective stroke in relation to other potential strokes. This value is preferably applied to enable the quadrature analysis to test the most likely strokes first, and thus optimize its overall efficiency. In the second row of each sub-table is a character weight. This weight reflects the frequency that a particular character is written. Like the stroke frequency value, these weights are preferably used in the cell blocking sub-process to improve the efficiency of character identification. Preferably, weighted Huffman encoding is applied in generating the stroke frequency and character weights. Further, the quadrature analysis  324  is preferably also optimized based on the likelihood of certain characters based on their likely relationship to characters that have previously been identified. Once the quadrature analysis  324  reconstructs the quadrature components into a character, that character is preferably stored in a character buffer  328  and/or converted into a 6-bit ASCII, Unicode or other character format  330  for storage in a character storage buffer  332 . 
     FIGS. 4A-C  illustrate one embodiment of a detailed functional flow for processing handwriting in real-time in the preferred pen-based handwriting storage device  98 . The functional flow is preferably divided into two sub-processes, a quadrature component or stroke detection sub-process (phases 1 and 2)  400 ,  402  and a cell-blocking sub-process (phase 3)  404 . In the first phase of the detection sub-process, input data is received and normalized for comparison with the quadrature component reference matrix that occurs in the second phase. When the cell blocking sub-process (phase 3)  404  commences processing of the data, the process also returns to the first phase of the detection process to obtain further data. Thus, the two sub-processes preferably operate asynchronously such that a quadrature analysis can be performed on a set of data while simultaneously the cell blocking process may work to resolve the same character. 
   In  FIG. 4A , where initially all global flags are set to “false” and all registers empty, analog data  405  is received from the detector at timed intervals according to the programmable clock  407 . The data  405  is digitized and stored in an 8-bit input buffer  406 . The input buffer  406  is then examined  408  to determine if any data is present. If the input buffer  406  is empty, the Null Termination (F_N) flag is set  410  to “true” to indicate that no data was received. The Quad Start (F_Q) flag is then examined  412  to determine if the empty input buffer  406  represents the start of the next quadrature. If the null data does represent the start of a new quadrature, then the empty input buffer  406  value is passed  414  into the second phase  402 . However, if the null data does not represent the start of the next quadrature, then the Cell Start (F_C) flag is examined  416  to determine if the empty input buffer  406  represents the start of the next character. If the null data does represent the start of the next character, then the empty input buffer  406  value is passed  414  into the second phase  402 . If, however, the null data does not represent the start of the next character, then the input buffer  406  is again examined  408  for more data. This cycle repeats itself until data is present in the input buffer  406 . 
   When data does exist in the input buffer  406 , F_N is set to “false”, the data is copied  418  into a copy buffer (RC) and the Data Max (F_D) flag is examined  420  to determine if RC is full. When RC is full, the data in RC is passed  414  into the second phase  402 . However, if RC is capable of storing more data, the Quad Time (F_T) flag is examined  422  to determine if the time elapsed detecting the current quadrature is such that the quadrature has been fully detected. When the quadrature has been fully detected, RC is passed  414  into the second phase. However, if the quadrature still potentially has more data to detect, the previous copy (RP) of the input buffer  406  is examined  424 . If RP is empty, RC is copied  426  into RP, and if RP is full, RC is copied  428  into a forward copy (RF) of the input buffer  406 . After RC is copied into either RP or RF, then the bit extent for the quadrature (VE) is incremented  430  to track the amount of data obtained for the quadrature and RC is passed  414  into the second phase  402 . 
   In  FIG. 4B , the data in RC enters  432  into the second phase  402  of the detection sub-process where F_N is first examined  434  to determine if the current quadrature has completed data. If the current quadrature has completed data, RC is stored  436  directly into the quad vector. When more data is needed to complete the current quadrature, F_C is examined  438  to determine if the data in RC represents either part of the current character or the start of the next character. If the data in RC represents the start of the next character, then F_C and F_Q are both set  440 . If the data in RC represents part of the current character, F_Q is examined  442  to determine if the data represents part of the current quadrature or the start of a new quadrature. For the start of a new quadrature, F_Q is set  444 . After determining what character and quadrature the data belongs to, the data in RC and the data in RP are used to calculate and store  446  the difference in X/Y coordinates in a difference register (RD). Following this calculation, RC is stored  436  in the quad vector. 
   Once RC is stored  436  in the quad vector, the quad vector is transformed  448  to a basis form which is compared  450  to the basis forms from the set of reference strokes and approximately fit to the closest match in the set of reference strokes. If transform can be matched  452  to a transform in the set of reference strokes, then F_Q is reset  454  to “false” to indicate that a new quadrature is being examined and the matched stroke is passed  456  into the cell-blocking sub-process (phase 3)  404 . If no reasonably close match can be found for the basis transform among the set of reference strokes, F_N is examined  458  to determine if the input buffer  406  has a null value. A null value at this point indicates the end of the quadrature has been reached, and the null value is passed  456  into phase 3  404 . If the data does not have a null value, the quad vector is examined  460  to determine if it is full. If the quad vector is full, F_D is set  461  to “true” and the adaptive event control (VS) is set to “clock” to indicate that the sampling rate may need to be adjusted to allow a full quadrature of data to be obtained without overflowing the quad vector. The quad vector is then passed  456  into the phase 3  404 . If the quad vector is not full, then the elapsed time is examined  464  to determine if sufficient time has elapsed to detect an entire quadrature. If sufficient time has not elapsed, then phase 1  400  is reentered  466  to obtain more data. However, if sufficient time has elapsed, then F_T is set  465  to “true” and VS is set  468  to “bitwidth” to indicate that the bit-width resolution may need adjusting to more accurately obtain a full quadrature of data. The quad vector is subsequently passed  456  into phase 3  404 . 
   In  FIG. 4C , the first step in the cell-blocking sub-process  404  is to convert  470  the cell data to a transform. The next step is to determine  472  whether the transform is complete. That is, if the last quadrature component for this character has been received, then the character may be resolved. If the transform is complete, the sub-process  404  converts  474  the character to a Unicode or ASCII format, and then stores the character  476 . All flags are then reset and the detector is initialized  478  for acquisition of new data. The sub-process  404  then exits and returns  480  to the first phase  400  for more input. Thus, the cell-blocking sub-process  404 , at the point of completion, returns the detector systems to their initial states and is prepared to acquire new character data. 
   If the transform is determined  472  to be incomplete, such that an incomplete quadrature component set has been received by the cell-blocking sub-process  404 , then the sub-process  404  attempts to resolve the character with the extent of data that has been received. In resolving data describing a partial character, the subprocess  404  determines  482  the depth of the data and attempts to identify the character based on the partial character data received and using the information stored in RD, RP and RF. The process attempts to determine whether a specific character is represented by the partial set of data that has been acquired. 
   The sub-process  404  then preferably determines  484  whether to proceed along one of preferably two paths based on whether an identification of the character was made. If the character can be identified with the partial set of data, then the sub-process  404  proceeds to the step  474  of converting the character to a Unicode or ASCII format and processes thereafter as though the transform had been complete. If the character cannot be resolved, the process waits  486  for more data from the second phase  402  of the detection sub-process. Once additional data is thereafter received in the cell-blocking sub-process  404 , the sub-process  404  again determines whether the transform is complete enough to resolve the character or whether another attempt at character identification based on the availability of partial data can be performed. 
     FIGS. 5A-B  and  6 A-D depict alternative detector subsystems for the pen-based writing storage device.  FIG. 5A  illustrates a mechanical microfeeler-based detector subsystem  500  as shown from a side view.  FIG. 5B  illustrates the same subsystem  500  as shown from a head on view. The microfeeler detector subsystem  500  is disposed at the pen tip  102 , the pen tip comprising a ball  501  similar to that found in a ball point pen, and comprises two microfeelers  502 , each resting against the ball  501  coupled to a surface contact  504 , preferably a friction roller. Each microfeeler preferably comprises a resistive potentiometer having multi-turn cyclical output with no stops on the shaft rotation. The surface contacts  504  are used for reading resistance and impedance changes on the microfeelers  502  and are coupled to the logic circuitry of the device  98 . The microfeelers  502  are preferably located 90 degrees apart relative to a z-axis, the z-axis running through the center of the device  98 . Additionally, the microfeelers  502  are preferably disposed near a great circumference of the ball  501  that is normal to the z-axis. With the microfeelers  502  positioned in this way, this subsystem  500  measures ball rotation along two orthogonal axes as changes in resistance or impedance of the microfeelers  502 . Therefore, the use of a microfeeler detection system  500  allows for ready determination of when the pen tip  102  is actually writing mode versus when the device  98  is simply moving in space.  FIG. 5C  is a graph depicting an example of the current output from a microfeeler-based detector subsystem  500 . 
     FIGS. 6A-C  depict three embodiments centered around an impedance coil based detection subsystem  610 ,  630 ,  650 . The first embodiment, illustrated in  FIG. 6A , comprises a ball  612  in the tip of a pen, again similar to the kind used in a ball point pen, the ball  612  having magnetic domains  614  of the same relative size evenly distributed across its surface. Induction coils  616  are coupled to the logic circuit of the device  98  and positioned just above the surface of the ball  612  without actually contacting it, the induction coils  616  having windings that are asymmetrically wound with linearly increasing space between the windings. Preferably, the induction coils  616  are positioned along a z-axis that runs through the center of the device  98  and near a great circumference of the ball  612  that is normal to the z-axis. Positioned thusly, the each induction coil  616  generates a current as the ball  612  rotates during writing and the magnetic domains  614  pass underneath. The current generated by each induction coil  616  enables measurement of ball rotation along two orthogonal axes.  FIG. 6D  is a graph depicting an example of the current output from an induction coil based detector subsystem  610 . 
   Alternative embodiments of impedance coil based detection subsystems  630 ,  650  are illustrated in  FIGS. 6B and C . These embodiments differ from that depicted in  FIG. 6A  in the composition and distribution of the magnetic domains on the ball and in the windings of the induction coils.  FIG. 6B  illustrates a ball  632  having magnetic domains  634  that are non-uniform in size and are distributed in a characterized non-uniform pattern across the surface of the ball  632 . Additionally, the induction coils  636  for this subsystem  630  are symmetrically wound with evenly spaced windings.  FIG. 6E  is a graph depicting an example of the current output from such an induction coil based detector subsystem  630 .  FIG. 6C  illustrates an induction coil detector subsystem  650  having similarly symmetrically wound and evenly spaced induction coils  654  as in the subsystem  630  shown in FIG.  6 B. However, the ball  652  in this subsystem  650  comprises a magnetized outer shell  658  over an inner ball  660 , the outer shell  658  giving the ball  652  a single magnetic domain  662 .  FIG. 6F  is a graph depicting an example of the current output from such an induction coil based detector subsystem  630 . 
     FIG. 7  depicts a preferred embodiment of logic for interfacing the microfeeler based detection subsystem of  FIGS. 5A-B  and the impedance coil based detection subsystems of  FIGS. 6A-C . In the preferred embodiment, four XOR and four NAND gates are used to process positive and negative X and Y movements of the pen tip. 
   Although the present invention has been described with reference to preferred embodiments, it will be readily appreciated to those of ordinary skill in the art that many modifications and adaptations of the invention are possible without departure from the spirit and scope of the invention as claimed hereinafter.