Abstract:
A housing contains electronics used in determining locations of a writing instrument based on wireless signals, defines a chamber in which the writing instrument may be held when not in use, and includes a retention element to retain the writing instrument from falling out of the chamber. 
     In general, in one aspect, a writing instrument includes an elongate pen body, an electrical contact on a surface of the pen body, and a light source disposed near an end of the pen body. The light source includes a light guide having an optically conductive portion and an optically reflective portion.

Description:
[0001]    This patent is related to U.S. Pat. No. 6,577,299, Electronic Portable Pen Apparatus and Method, issued Jun. 10, 2003, and U.S. patent application Ser. Nos. 10/623,284, Tracking Motion of a Writing Instrument, filed Jul. 17, 2003, Ser. No. 11/327,292, Light Sources for Digital Pen, 11/327,302, Capturing Handwriting, and 11/327,303, Electronic Pen Holding, all filed Jan. 6, 2006 as continuations of application Ser. No. 10/623,284, 09/832,340, Using Handwritten Information, filed Apr. 10, 2001, Ser. No. 09/991,539, Capturing Hand Motion, filed Nov. 21, 2001, and Ser. No. 11/418,987, Efficiently Focusing Light, filed May 4, 2006, all incorporated here by reference. 
     
    
     BACKGROUND 
       [0002]    This description relates to holding and using an electronic pen and paper. 
         [0003]    Wireless electronic pens sometimes work with external sensors. Such sensors are sometimes mounted on a writing surface, for example, at the head of a clipboard or at the corners of a marker board. 
       SUMMARY 
       [0004]    In general, in one aspect, a housing contains electronics used in determining locations of a writing instrument based on wireless signals, defines a chamber in which the writing instrument may be held when not in use, and includes a retention element to retain the writing instrument from falling out of the chamber. 
         [0005]    Implementations may include one or more of the following features. The retention element is configured to retain the writing instrument in a direction normal to its length. The retention element is configured to retain the writing instrument in a direction parallel to its length. The chamber is defined by lower and upper plates extending beyond a body of the housing. The upper plate includes two portions separated by a void. The extent of the upper plate beyond the body defines a void. A center spring extends from the lower plate toward the void. The extent of the lower plate beyond the body defines a void. A center spring extends from the upper plate toward the void. A rib extends from the lower plate toward the upper plate. A circuit provides power to a writing instrument. The circuit to provide power to the writing instrument includes a center spring and at least one other contact. A rib extends from the upper plate toward the lower plate. A center spring extends from the lower plate toward the void. The center spring and the rib are configured to releasably hold the writing instrument between them. The chamber is defined by a first end unit and a second end unit extending from first and second ends of a body of the housing. The first and second end units each contain a resilient structure, in which the resilient structures define a space between them within which the writing instrument may be held such that one of the resilient structures presses on one end of the writing instrument and the other resilient structure presses on the other end of the writing instrument. A switch is triggered when the writing instrument is present in the chamber. A switch is triggered when the writing instrument is removed from the chamber. Sensors are located near openings in the housing. Lenses are located in the openings, and the housing includes a first section and a second section, the first section defines the openings, and the second section can be removed from the first section without compromising the operation of the sensors. A button receives user input. The housing includes a status indicator. The housing has an attached writing surface. 
         [0006]    A wireless communications interface is included. An electronic communications interface is included. The electronic communications interface is located on a face of the housing opposite the chamber. The communications interface is located on an end face of the housing. A foot is attached to a bottom surface of the housing and has a higher traction than a material of which the bottom surface is composed. A board is adapted to connect to the housing. The board includes protrusions to be inserted into holes in the housing. The board includes holes to accommodate protrusions on the housing, in which the board includes springs adapted to apply pressure to the housing to maintain pressure between a surface of the housing and the board. The springs are adapted to apply pressure to the housing through tabs extending from first and second ends of the housing. The housing, the board, and the springs are adapted to hold paper between the housing and the board. The board also includes an edge boundary to position the sheet of paper relative to the housing when the housing is connected to the board. The board is sized to accommodate a letter sized sheet of paper in either a landscape orientation or a portrait orientation relative to the housing. The board is sized to be inserted into a pad of paper. The board is configured to position the housing at the top of a pad of paper that is bound along one side. The board is configured to position the housing at the side of a pad of paper that is bound along its top edge. The board is adapted to connect to the housing in a position such that sheets of paper in a pad on the board can be flipped without blocking sensors included in the housing. 
         [0007]    The housing encloses a circuit board having a first section, a second section, and a third section. The first section includes communication circuitry and the second and third sections include sensor circuitry. The first section also includes a processor. The first, second, and third sections are separated sections of a single printed circuit board. The second and third sections are not coplanar with the first section. 
         [0008]    In general, in one aspect, a housing defines a chamber in which a writing instrument is held when not in use, is configured to be part of a clipboard structure for holding paper that is to be written on using the writing instrument, and is configured to communicate wirelessly with the writing instrument to determine locations of the writing instrument when the writing instrument is used to write on the paper. 
         [0009]    In general, in one aspect, a writing instrument includes an elongate pen body, a first electrical contact on a surface of the pen body, a writing tip disposed at an end of the pen body, and a light source disposed near the writing tip. 
         [0010]    Implementations may include one or more of the following features. The pen body includes electronics for generating light. The pen body includes a power supply. A second electrical contact is disposed near the writing tip. The first and second electrical contacts are adapted to receive power to charge the power supply. A second electrical contact and a third electrical contact are included, and electronics in the pen are adapted to provide power of a first polarity from the first contact to the power supply, and to provide power of a second polarity from the second and third contacts to the power supply. The first electrical contact extends over a circumference of the pen. 
         [0011]    The light source includes a light guide to direct light from an illumination source within the pen body to a location outside the apparatus. The illumination source includes two or more LEDs and the light guide is configured to mix light form the LEDs into a uniform illumination field. The illumination field extends 360 degrees around the apparatus. The light guide includes a tapered section having a first end of a first diameter and a second end of a second diameter. The light guide includes a section having a uniform cross section of the first diameter and coupled to the tapered section at the first end of the tapered section. The light guide includes a reflective surface to cause light conducted through the light guide to exit through an outer surface of the light guide. The reflective surface includes a second electrical contact. The reflective surface defines a conical frustum having an angle of 45° from an axis of the light guide. A narrow end of the conical section is located about 1 mm from the end of the pen body. The light guide includes a channel to accommodate a pen cartridge through an axis of the light guide. The channel is configured to control the position of the pen cartridge. The writing tip includes a tip of a pen cartridge located within the pen body. The pen body also includes a guide member for receiving a pen cartridge. A coil spring, an end cap, and a flat spring are included, in which a portion of the writing tip, the guide member, the coil spring, the end cap, and the flat spring are each electrically conductive and together form a complete circuit path from the portion of the writing tip to a circuit contact. An end cap is disposed within the pen body and arranged to be connected to a pen cartridge. A grip is disposed between the first electrical contact and the light source. A switch is triggered when pressure is applied to the writing tip. The switch includes a first switch contact, a second switch contact, a switch spring, and a mechanical linkage from the writing tip to the switch spring, such that when pressure is applied to the writing tip, the mechanical linkage causes the switch spring to complete a circuit between the first and second switch contacts, and when pressure is not applied to the writing tip, the switch spring breaks the circuit. When pressure is not applied to the writing tip, there is a gap of around 0.2 mm between the switch spring and one or the first and second switch contacts. 
         [0012]    In general, in one aspect, a sensing device is attached to a clipboard, paper is attached to the clipboard, the paper is written on using a writing instrument wirelessly coupled to the sensing device, and at the sensing device a record is generated of the writing of the writing instrument. 
         [0013]    Implementations may include one or more of the following features. The record is generated by storing raw data representing movement of the writing instrument. The record is generated by applying calibration parameters to adjust raw data and storing adjusted data representing movement of the writing instrument. 
         [0014]    In general, in one aspect, a sensing device is positioned in a known location relative to a pre-printed form, the form is written on using a writing instrument wirelessly coupled to the sensing device, a record of the writing of the writing instrument is generated, and the record is associated with fields on the form. 
         [0015]    In general, in one aspect, a housing contains electronics used in determining locations of a writing instrument based on wireless signals and defines a chamber in which the writing instrument may be held when not in use. 
         [0016]    In general, in one aspect, a housing contains electronics used in determining locations of a writing instrument based on wireless signals, and defines a chamber in which the writing instrument may be held when not in use. The electronics include electrical contacts, such that when the writing instrument is present in the chamber, the contacts will couple to contacts on the writing instrument and provide power to the writing instrument. 
         [0017]    In general, in one aspect, a housing contains electronics used in determining locations of a writing instrument based on wireless signals, and defining a chamber in which the writing instrument may be held when not in use. The electronics includes three electrical contacts, such that when the writing instrument is present in the chamber, at least two of the contacts will couple to contacts on the writing instrument. The electronics detect which electrical contacts are coupled to the contacts on the writing instrument and provide a voltage to the identified contacts to charge a power supply in the writing instrument. In some implementations, the three electrical contacts include a contact located in the center of the chamber and contacts located at first and second ends of the chamber. 
         [0018]    In general, in one aspect, a writing instrument includes an elongate pen body, a first electrical contact on a surface of the pen body, and a light source disposed near an end of the pen body. The light source includes a light guide having an optically conductive portion and an optically reflective portion. The optically reflective portion is also electrically conductive and constitutes a second electrical contact. 
         [0019]    In general, in one aspect, a housing contains electronics used in determining locations of a writing instrument based on wireless signals, and defines a chamber in which the writing instrument may be held when not in use. A clipboard is sized to accommodate a sheet of paper, the housing and the clipboard having mating features to removably couple the housing to the clipboard. In some implementations, the mating features may include protrusions on the clipboard and holes in the housing. The mating features may include springs attached to the clipboard and tabs extending from the housing. 
         [0020]    In general, in one aspect, a clipboard for use with a housing contains electronics used in determining locations of a writing instrument based on wireless signals, and includes coupling features for aligning the housing in a controlled position and alignment features for aligning paper in a known position relative to the controlled position of the housing. 
         [0021]    In general, in one aspect, a clipboard is configured for use with a housing containing electronics used in determining locations of a writing instrument based on wireless signals, includes coupling features for aligning the housing in a controlled position, and is shaped to accommodate paper with a long edge of the paper aligned to the housing. 
         [0022]    In general, in one aspect, a clipboard is configured for use with a housing containing electronics used in determining locations of a writing instrument based on wireless signals, includes coupling features for aligning the housing in a controlled position, and paper retaining features to retain paper in a fixed location relative to the controlled position of the housing between times when the housing is removed and the housing is attached. 
         [0023]    In general, in one aspect, a light guide is adapted for use in a writing instrument, the light guide including a tapered section defining an axis and having a first end of a first diameter and a second end of a second diameter, the first end being adapted to receive light, and the second end being adapted to reflect the light received at the first end from a path from the first end to the second end and generally parallel to the axis to a path exiting the light guide in a direction generally perpendicular to the axis. 
         [0024]    Implementations may include one or more of the following features. A face of the second end may define a conical frustum coaxial with recessed into the tapered section. The conical frustum may have an angle of around 45 degrees. The conical frustum begins at a distance of about 1 mm from a point where the light guide is to exit a body of the writing instrument. 
         [0025]    In general, in one aspect, a light guide is adapted for use in a writing instrument, the light guide including a first section having a first diameter and defining an axis, a tapered section coaxial with the first section and having a first end of the first diameter coupled to the first section and a second end of a second diameter, the first section being adapted to receive light and direct it to the tapered, and the second end being adapted to reflect light received from the first section from a path generally parallel to the axis to a path generally perpendicular to the axis. 
         [0026]    In general, in one aspect, a writing instrument includes an elongate pen body, a writing tip disposed at an end of the pen body, a light source disposed near the writing tip, a switch to detect when pressure is applied to the writing tip, and a contact for receiving power to charge electronics within the apparatus. In some implementations, the switch may be configured to be activated without allowing significant movement of the writing tip relative to the pen body. The switch may be configured to be activated while allowing axial movement of the writing tip of only 0.2 mm relative to the pen body. 
         [0027]    In general, in one aspect, a writing instrument includes a pen body, a light guide partially disposed within the pen body, and outside diameter of the light guide being about equal to an inside diameter of the pen body, a light source disposed within the pen body, a fiber optic fiber configured to couple light from the light source to the light guide, and a reflector disposed at an end of the light guide outside the pen body. In some implementations, the light guide may define a channel along an axis of the pen body sized to accommodate a pen cartridge. The reflector may be configured to reflect light from a direction substantially parallel to an axis of the pen body to a direction substantially perpendicular to the axis of the pen body. The light guide may have a cylindrical shape of about constant diameter along its length. 
         [0028]    Other features and advantages will be apparent from the description and the claims. 
     
    
     
       DESCRIPTION 
         [0029]      FIGS. 1A ,  13 , and  21  are front isometric views of a penholder and pen. 
           [0030]      FIG. 1B  is a top view of a penholder. 
           [0031]      FIG. 1C  is a side view of part of a penholder and pen. 
           [0032]      FIG. 2  is a rear isometric view of a penholder and pen. 
           [0033]      FIG. 3  is a bottom view of a penholder. 
           [0034]      FIG. 4A  is a front isometric view of internal components of a penholder. 
           [0035]      FIGS. 4B-4E  and  5 B are isometric views of details of internal components of a penholder. 
           [0036]      FIG. 5A  is a schematic view of a circuit board. 
           [0037]      FIGS. 6A-6D  are plan views of clipboards including penholders and pens. 
           [0038]      FIG. 7A  is a side view of a detail of a clipboard and penholder 
           [0039]      FIG. 7B  is a side view of a detail of a clipboard. 
           [0040]      FIGS. 8 and 22  are isometric views of pens. 
           [0041]      FIG. 9  shows components of a pen. 
           [0042]      FIG. 10A  is a plan view of a light guide. 
           [0043]      FIGS. 10B-10D  are cross-section views of light guides. 
           [0044]      FIGS. 11A and 11B  are schematic views of components of a pen. 
           [0045]      FIGS. 12 ,  14 ,  20 ,  23 A, and  23 B are front isometric views of penholders. 
           [0046]      FIGS. 15 and 18C  are schematic views of a penholder. 
           [0047]      FIGS. 16 ,  18 A- 18 B, and  19 A- 19 B are schematic views of a penholder and pen. 
           [0048]      FIG. 17  is a schematic view of a circuit board. 
       
    
    
       [0049]    A portable electronic device can include a pen and a holder for the pen that houses sensors to receive light emitted or reflected by the pen, for example, to determine the pen&#39;s location on a writing surface. In some examples, the device includes a clip that can be used to attach the device to a stack of paper. In some examples, the penholder is attached to a clipboard, and the entire penholder may serve as the clipboard&#39;s clip. Among other advantages, when the paper is held in the clip, the sensors have known locations relative to the paper. 
         [0050]    In some examples, as shown in  FIGS. 1A ,  1 B,  1 C,  2 , and  3 , a penholder  100  includes a body  102  that houses two light sensors  104  near opposite ends  103 ,  105  and (in some cases) a central sensor  106  and other electronics (not shown). The body may include or be attached to a lower plate  108  and an upper plate  110 . Switches  114 ,  116  and lights  118   a - 118   d  may also be included. A pen  10  (which may be a wireless electronic pen with or without ink, or any similar writing instrument, for example, a stylus, pencil, or marker) is housed between the lower plate  108  and upper plate  110 . Flanges  110   a ,  110   b  on the upper plate  110  extend partially around the pen to shelter it and help keep it in place. Other features may be used to allow the pen to be inserted and removed along its length, and retain it against falling out in that direction. A scallop  110   c  between the flanges  110   a ,  110   b  allows the user&#39;s finger to be inserted beneath the upper plate  110  to grip and remove the pen  10  in direction  107 . The pen  10  is also held in place by ribs  120   a  and  120   b  that project down from the underside (not shown) of the upper plate, a center spring  122  that projects up from the upper surface of the lower plate  108 , and end springs  124   a  and  124   b  (see cut-away view in  FIGS. 4A ,  4 C,  5 B) in wings  126   a  and  126   b . Details of this structure are shown in  FIG. 1B , with the ribs  120   a  and  120   b  shown through the flanges  110   a  and  110   b  using dashed lines and in which the pen  10  has been removed, and in  FIG. 1C , in which part of the end wing  126   b  has been removed to show the spring  122  from the side. In some examples, springs  124   a  and  124   b  are configured so that the pen  10  can be inserted with its tip at either end. As shown in  FIG. 1C , each of the ribs  120   b  includes a profiled segment  121  that matches an outer surface of the pen and holds the pen firmly in place when the pen is held in the penholder  100 . The lower plate  108  extends beyond the wings  126   a  and  126   b  to provide shelves  128   a  and  128   b  for attaching the penholder  100  to a clipboard, as described below. 
         [0051]    Thus the front of the body  102 , the inner sides of the two wings  126   a  and  126   b , the upper side of the lower plate and the lower side of the upper plate define a chamber in which the pen can be stored safely when not in use. The pen can be held in place by the three springs and two ribs to permit the pen to be easily removed and replaced as needed. 
         [0052]    A connector  130  ( FIG. 2 ) may be located on the back  101  of the penholder  100 , as shown in  FIG. 2 , or it may be located at either end on one of the wings  126   a  or  126   b . The connector  130  may be a USB port or some other physical connection for transferring data and or power between the penholder  100  and an external device (not shown) such as a computer, a telephone or a PDA. Four feet  132  located on the bottom of the penholder  100  provide traction on whatever surface the penholder  100  is placed, or they may hold paper in place if the penholder  100  is used as part of the clip of a clipboard. In some examples the feet  132  are composed of a material having a greater traction than the materials from which the other parts are composed. Screws  134  may hold the lower plate, the upper plate, and the body of the penholder  100  together. In some examples, holes  136  where the screws  134  were inserted may be used to connect the penholder  100  to mounting features on a clipboard, as described below. One or more holes  136  may also be used specifically for this purpose, for example, if the plate  108  is integral to the body  102  or attached without fasteners. 
         [0053]    In some examples, the feet  132  can be inserted into holes in a plate to create an assembly that can be retained inside a notebook without movement relative to the pages. The pages can be turned back and forth without disturbing the penholder&#39;s ability to detect the use of the pen on each page. The feet  132  can be used together with the holes  136  for screws or other features in the bottom of the penholder  100 . 
         [0054]    The positioning and function of the sensors  104  and  106  depends on the hardware and software implementation of the device. In some examples, two sensors  104  positioned respectively near the opposite ends  103 ,  105  of the penholder  100  detect light emitted from the pen  10 , when the pen is removed from the penholder and is in use. Electronics in the penholder use the detected light to triangulate the pen&#39;s location. Other sensing technologies, such as ultrasonic emitters and detectors, may also be used. The central sensor  106  may be used, for example, to detect emissions from the pen to synchronize the timing of the operation of the end sensors  104  with a carrier signal in the light from the pen. Other information can be transmitted between pen and penholder by modulating a carrier signal, including light intensity of the emitter on the pen (which may be reduced, for example, to save battery life), the amount of battery charge left on the pen, the color of the ink cartridge being used, pressure applied to the pen, tilt of the pen, and use of an erase function. The penholder  100  may also communicate messages to the pen, for example, through an infrared emitter coupled to one of the sensors  104  or  106 . This may be used for various purposes, including synchronizing timing between the penholder and the pen or signaling to the pen that there is a problem with the signals being received at the sensors  104 . In some examples, the user may block one or both of the sensors due to the way he is holding the pen or turning pages, while switches in the pen (described below) indicate that the pen is in use. The penholder may signal to the pen that it is not receiving light, and the pen may illuminate a visible light to indicate that there is a problem. 
         [0055]    In some examples, the sensor  106  is replaced by a light source and the sensors  104  detect reflections from the pen  10 . Additional information about the use of the sensors in some implementations may be found in U.S. Pat. No. 6,577,299, Electronic Portable Pen Apparatus and Method, issued Jun. 10, 2003, and application Ser. No. 10/623,284, Tracking Motion of a Writing Instrument, filed Jul. 17, 2003, both incorporated here by reference. 
         [0056]    In some examples, the springs  122 ,  124   a ,  124   b  may be used both to hold the pen  10  in place and to provide power to recharge a battery within the pen  10  as described below. With the spring  122  located in the center of the chamber, the pen can be inserted with its tip contacting either spring  124   a  or  124   b , and a charging circuit can be completed in either orientation. In some examples, the electronics may detect which of springs  124   a  or  124   b  is in contact with a charging terminal on the pen  10  and provide an appropriate polarity voltage to that spring. In some examples, springs  124   a  and  124   b  may be energized with opposite polarity voltage to charge a pen  10  having contacts at both ends. Similarly, two contacts  122  may be provided to contact two electrodes along the length of the pen  10 . In some examples, one or more of the springs  122 ,  124   a ,  124   b  may be connected to switches to detect when the pen  10  is held in the penholder  100 . An additional switch may also be used, for example, a switch  150  located on a circuit board  144   b  and linked to a plunger  152  that protrudes into the space to be occupied by the pen, as shown in  FIG. 4B . This detection may be used, for example, to turn the penholder  100  on when the pen  10  is removed and to turn it off when the pen  10  is replaced into the penholder  100 . The springs  124   a ,  124   b , may also be shaped or include additional material to cover the tip of the pen and prevent it from leaking ink or smudging its surroundings when not in use. 
         [0057]    In some examples, the shape of the springs  124   a  and  124   b , as shown in  FIG. 4C , includes two pieces  125   a  and  125   b  joined by a bent segment  125   c . The piece  125   a  presented to the pen  10  has a hole  125   d  to receive the tip of the pen and to make contact with a contact near the tip as described below. The connection should be secure but soft to assure a good electrical contact of surfaces. 
         [0058]    The switches  114 ,  116  and lights  118  may have various uses. In some examples, the switch  116  is used to select one of several operating modes of the penholder  100 , such as instructing the penholder to save the detected handwriting to internal memory, to transmit it over USB or some other physical connection, or to transmit it over a Bluetooth® wireless link or some other wireless system, such as WiMax® or Zigbee® wireless technology. In some examples, the switch  114  is used to turn the penholder  100  on or to indicate to the penholder  100  that a user has turned to a new page. The switch  114  may be a rocking switch that allows the user to flip up or down between pages. Pages of writing may be stored in an on-board memory or transmitted to and loaded from a related device (not shown), such as a cell phone or PDA. A screen on the related device or an indicator on the pen itself, such as one of the lights  118  or a small screen (not shown) may show the current page. Using an external display on another device that a user would have anyway can allow the user to view a previously-created page she is now editing without requiring that the penholder itself have a display, saving both power and package space. The page to be edited may be selected by the other device, based on either user input to that device or the user&#39;s current handwriting, as interpreted by that device after being communicated to it by the penholder  100 . In some examples, an additional sensor (not shown) may detect that a page has been flipped, and the penholder  100  may automatically change which page it is storing input to, or it may use one or more of the lights  118  to indicate to the user that it thinks the page should be changed using the switch  114 . To preserve battery life in the penholder and related devices, the wireless connection may be put in a sleep mode after the data or commands have been sent and while new pen input is being recorded. 
         [0059]    One or more of the lights  118  may illuminate or flash to acknowledge that such a command has been received, that the penholder is ready to receive pen input, that the memory is full, that a page has been turned, or that the penholder is transmitting, among other functions. In some examples, the light  118   a  is amber and blinks once to indicate that the penholder is ready for the next page and blinks continuously to indicate that the internal memory is full. The light  118   b  is red and indicates that power is on or that the penholder is being charged. The light  118   c  is green and indicates that the pen is in use and writing is being received. The light  118   d  is blue and indicates that a data connection is in progress. Other colors and other uses for the lights are possible. The lights  118   a - 118   d  and the switches  114 ,  116  may be integrated, and more or fewer lights or switches may be used. Any of the functions of the switches  114 ,  116  and lights  118  may be performed on a related device connected to the penholder  100  through a physical or wireless connection. For example, hard or soft buttons on a cell phone may be used to select a page and input mode, and the cell phone&#39;s screen may indicate the writing being performed by the pen. Calibration data may be stored in the penholder  100  or in a device that is to receive information from the penholder about the movement of the pen. Such data may be used, for example, to correct for manufacturing variations in the sensors or other components. 
         [0060]    The penholder  100  may contain electronics and other structures, as shown in  FIGS. 4A-4E . These may include assemblies  138  to hold the sensors  104  or their components in place or to block or control light entering the sensors. The sensors  104 ,  106  and other circuit components  142  may be connected to circuit boards  144 . The circuit boards  144  may be printed circuit boards, flex boards, or other technology. In some examples, the supports may control light in such a way that the sensors  104 ,  106  remain operational with the body  102  of the penholder  100  opened to allow testing or calibrating. 
         [0061]      FIGS. 4D and 4E  show the support assemblies  138 . In some examples, the assemblies  138  form a chamber  137  ( FIG. 4E ) to control the orientation of a lens  154  relative to the sensor  104 , to enable easy assembly, to block ambient and other interfering light, including light from the pen itself other then the light being focused by the lens  154 , and to allow testing and calibration in a production environment. 
         [0062]    The lens  154  is inserted into an opening  158 , supported by a front lens support  160 . A top cover  162  protects the sensor  104  within the assembly  138 . As shown in  FIG. 4E , the sensor  104  is positioned in a cradle  164  within the assembly  138  in such a way that the sensor  104  is captured between two plastic features  164   a  and  164   b . This positions the sensor  104  relative to the lens  154  horizontally; vertically it is fixed by the bottom  164   c  of the cradle  164 . The lens  154  is supported vertically within its opening  158 . In some examples, flanges  154   a  and  154   b  on the side of the lens  154  block ambient and pen light, so that light is only admitted into the chamber  137  through the operational section  154   c  of the lens  154 . In examples where infrared sensors are used, the lens  154  may be composed of IR-filtering material that blocks most of the ambient light. The cover  162  keeps the lens  154  and sensor  104  in place. Glue may be used to keep the lens  154 , the cover  162 , and other components in place. With the cover and lens blocking stray light from reaching the sensor  104 , testing and calibration can be performed without risk that lens and sensor would move or that outside light will compromise readings. This can allow, for example, electronic and other troubleshooting to be performed without recalibrating the penholder electronics. 
         [0063]    In some examples, the sensors  104  are connected to daughter boards  144   a  that are each positioned at an angle relative to the main circuit board  144   b . In some examples, these circuit boards  144   a ,  144   b  may be cut from a single circuit board  144  after fabrication, as shown in  FIG. 5A . Jumpers or cables  146  may provide electrical communication between the sensors  104  on the daughter boards  144   a  and the rest of the electronics  106 ,  142  on the main circuit board  144   b , shown in detail in  FIG. 5B . Other shapes and configurations are possible, depending on the packaging requirements of the penholder and the operation of the sensors. 
         [0064]    In some examples, as shown in  FIGS. 6A-C ,  7 A, and  7 B, a clipboard  200  may be provided in which the penholder  100  is attached to a board  202 . In some examples, the pen may be tethered to the board  202 , and the tether may be used to provide power or data to the pen (not shown). The penholder  100  may also form the clip of the clipboard. Such a clipboard may be configured to hold a stack of paper sheets  204  either in a portrait ( FIG. 6A ,  6 C) or a landscape ( FIG. 6B ) orientation. The penholder can be positioned at either the top  206  or bottom  208  of a portrait orientation and either the left side  210  or right side  212  of a landscape orientation, depending on the preference of the user. If the paper is bound in a pad  220  ( FIG. 6B ), the clipboard  200  may be oriented so that the penholder  100  is on an edge  222  other than the spine  224  of the pad  220 , permitting the pages to be flipped without interfering with the sensors  104 . In some examples, as discussed below, the sensors can be repositioned relative to each other to best accommodate the shape of the paper. 
         [0065]      FIG. 6C  shows an example of a clipboard being used for pre-printed forms. Guides  232  surround a form  234  and hold it in place, assuring that the markings on the form are in known locations relative to the penholder, so that the position of the pen  10  detected by the penholder  100  can be correlated to fields in the form. The layout of the form is also known in advance and may be stored in the memory of the penholder  100 . In some examples, the penholder  100  converts the pen&#39;s positions to input on the form and transmits only the input to another device, e.g., a PC. In some examples, the penholder  100  transmits the pen&#39;s motion in an unprocessed state and the PC itself relates the motion to the contents of the form. 
         [0066]    In some examples, as shown in  FIG. 6D , the board  202  may be inserted into the pad  220 , so that the penholder  100  can be easily removed (arrow  236 ) and the board  202  will remain inserted in to the pad  220 . This way, the orientation of the sensors  104  to the pad will be the same when the penholder  100  is returned to the clipboard  200 , so the user can continue writing on the same document and the penholder will know where markings have already been made on the paper from the last time it was used, thus the user may edit a single document in more than one session. This may also be accomplished by consistently placing the board  202  in the pad  220  in a specific location, for example, with the board against the binding and the penholder  100  against the edge of the pad  220 . The user could then put the board  202  between different pages as he moved through the pad. In some examples, the board  202  may be made smaller, to be used more like a bookmark than a clipboard, still holding the penholder  100  in a consistent position relative to the pad  220 . In some examples, the user may write directly on the board, with or without actually leaving marks, depending on the configuration of the pen. 
         [0067]    In some examples, the clipboard  202  may include electronic circuitry  203  to complement that in the penholder  100 , such as an antenna for wireless communication or sensors to detect when pages have been turned, as mentioned above, or the number of pages between the penholder  100  and the board  202 . A use may be prompted to change pages when the number of pages changes. The penholder  100  may communicate to another devise to display a new page when the page is changed. 
         [0068]      FIG. 7A  shows details of how the penholder  100  may be secured to the clipboard  200 . As noted above, the holes  136  on the bottom of the penholder  100  may receive a mounting feature  240  attached to the board  202 . Alternatively, the feet  132  may be inserted into holes in the board  202  (not shown). In some examples, a spring  242  may be attached to the board  202  via a mounting block  244 . In some examples, the spring  242  may be an extension of the board  202  or directly fastened to the board, e.g., by a rivet or screw. This spring  242  may press down on the penholder  100  via the shelves  128   a  and  128   b , also as mentioned above. Such an arrangement may allow the penholder  100  to pivot upward to accommodate the paper  204 . In some examples, the front foot  132   a  may help hold the paper in place. In some examples, the rear foot  132   b  may provide a point for the penholder  100  to rock on, or may limit its range of motion. In some examples, the spring  242  or its mounting block  244  may hold the paper in place independently of the penholder  100 , as shown in  FIG. 7B . 
         [0069]    In some examples, the pen is constructed as shown in  FIGS. 8 and 9 .  FIG. 8  shows the exterior of the pen and  FIG. 9  shows internal components with the pen body  20  absent. The writing end  11  of the pen  10  has a writing tip  12 , a front face  13 , light source  14 , a forward body  16 , and a grip  18 . The middle  15  of the pen has a main body  20  and a charging contact  22  and houses electronics  28 . In some examples, the charging contact is a band around the entire circumference of the body  20  so that it will make contact with the center spring  122  of the penholder  100  described above regardless of the pen&#39;s rotation about its long axis  21 . A second contact may be located at the front face  13  at the writing end  11  of the pen. As noted above, there could be two or more charging contacts  22  to contact two or more springs  122  or other electrical contacts. One or more of the charging contacts may be integrated with a retaining feature to hold the pen within the penholder. An advantage of charging through the front face  13  and a single center contact  22  is that is allows a conventional pen appearance, with only one metal ring contact on the body of the pen where most pens have a band to hide a joint between two parts of the body. Thus the center contact  22  serves the conventional function of joining two parts of the pen, and the front face  13  may be made indistinguishable from other pen&#39;s tips. Placing the ring contact into the center of the pen also has the advantage of allowing the pen to be inserted into the penholder  100  in either direction, convenient for serving both right- and left-handed users. 
         [0070]    The tail end  17  of the pen  10  has a rear body  24  that houses a battery  26 . The writing tip  12  may be part of a pen cartridge  30 , such as a refillable or disposable ink cartridge. The pen  10  may include a pen guide  50  to provide an electrical pathway from the electronics  28  to the front face  13 . The light source  14  may be a lamp  34 , such as one or more LEDs, or a reflector. In some examples, the light source  14  is an end of a light guide  32  as shown in  FIGS. 10A and 10B  that guides light  33  from lamps  34  deeper within the pen body. Additional information about examples of pens may be found in patent application Ser. No. 10/623,284 cited above. 
         [0071]    The light guide  32  may include a straight section  38  that receives light  33  (short-dashed line) from the lamps  34 , and a tapered section  40 , that exits the pen body and emits light. The lamps  34  may be molded into the light guide  32  or may be separate from it. The tapered section  40  may include a reflector, such as reflective surface  44 , configured so that light is emitted at an angle selected to increase the amount of light that will reach the sensors  104 . The reflector have various forms, including a distinct component, a polished face of the light guide  32 , or a coating on a face of the light guide. In some examples, the surface  44  defines a conical frustum having a smaller diameter matching a channel  48  through the center of the light guide along the axis  21 . In some examples, the conical frustum has an angle of 45 degrees from the axis  21  so that light  33  is reflected approximately perpendicular to the axis  21 . The reflective surface  44  may begin a distance  47  from the position  49  at which the light guide  32  exits the pen body (see  FIG. 8 ) to assure that light  33  has room to diverge after leaving the light guide  32 . In some examples, this distance  47  is about 1.0 mm. A ridge  46  may be included to attach the light guide  32  to the forward body  16 . The channel  48  guides the pen cartridge  30  and may include space for a pen guide  50  described below. The outside diameter of the straight section  38  may be close to the inside diameter of the pen body  20  to assure that the pen cartridge  30  can be inserted through the center of the pen body  20  and light guide  32  without hitting the lamps  34  or other electronic components. 
         [0072]    The tapered section shown in  FIGS. 10A and 10B  can reduce the efficiency with which light is conducted from the lamps  34  to the reflector  44 . This effect can be reduced by making the straight section  38  close in diameter to the outside diameter of the reflector  44 , i.e., making the entire light guide cylindrical or nearly so, as shown in  FIG. 10C . In the example of  FIG. 10C , the light guide  32  has a single cylindrical section  39 . In the example of  FIG. 10D , the light guide  32  has a single tapered section  41 . To accommodate a smaller diameter at the lamp end of the section  39 , smaller LEDs may be used for lamps  34 , or the lamps  34  may be connected to the light guide  32  by fiber optic guides  35 . The LEDs may be mounted directly on the surface of a circuit board. In some examples, the diameter of the light guide is around 4 mm. In some examples, the light guide has a diameter of around 7 mm at the end coupled to the lights  34  and around 4-5 mm at the end where the light  33  exits. 
         [0073]    As the light  33  moves from the fiber  35  to the reflector  44 , the light guide mixes it to encourage a uniform distribution of light at the tip. To help maintain high efficiency, the surfaces of the light guide  32  should be protected from scratches and direct contact with foreign materials, especially those with a high coefficient of refraction, which may absorb light and prevent the light guide  32  from channeling it to the reflector  44 . The pen body  20  can provide this protection for the outer surface, and the pen guide  50  may be used to protect the inner surface of the channel  48 . In some example, surfaces of the light guide may be coated with an aluminum paint or other reflective material, which may also serve to enhance reflection and provide electrical conductivity in addition to protecting the surfaces. 
         [0074]    In some examples, the lamps  34  may include LEDs or other light sources that emit light in more than one frequency. Infrared may be used for communicating with the sensors  104  and  106  in the penholder  100 , while visible frequencies are used to communicate with the user, for example, using different colors to indicate the pen&#39;s status or battery charge. 
         [0075]      FIG. 11A  shows a switch mechanism  52  that detects when the pen  10  is in use. The cartridge  30  extends through a guide  50  and ends in an end cap  54 . At the end of the guide  50  it expands to form both the reflector  44  for the light guide and the front face  13  of the pen (the length and width are not to scale in  FIG. 11A  and other figures). In some examples, the guide  50  is integral to the light guide  32  or some other body structure of the pen  10 . A coil spring  56  provides pressure between the end cap  54  and the guide  50 . This keeps the end cap  54  in contact with a flat spring  58 . The flat spring  58 , in an equilibrium position, maintains a small gap  64  between itself and a contact pad  60  on a circuit board  66 . The flat spring  58  is also in contact with a second contact  62 . When the pen is in use, the pressure of writing presses back on the pen cartridge  30 , deflecting the flat spring  58  and causing it to contact the pad  60 . This completes a circuit between the contact pad  60  and the second contact  62 , indicating to the pen&#39;s circuitry (not shown) that the pen is in use. To avoid interfering with the writing of the pen, the gap  64  between the flat spring  58  and contact pad  60  may be on the order of 0.2 mm. The springs  56  and  58  together may be configured to allow this small movement with a force sufficiently small that a user will not notice the movement or the force required to achieve it. Other methods of sensing that pressure is being applied to the pen cartridge  30  may also be used. In some examples, the end cap  54 , coil spring  56 , and guide  50  may all be conductive to provide a current path, including the flat spring  58 , from the pad  62  to the front face  13  of the pen to route power from one of the springs  124   a  or  124   b  to charge the battery  26  in combination with the charging contact  22  at the center of the pen. 
         [0076]    In some examples, the pen  10  is structured as shown in  FIG. 11B . The end cap  54  is sized to occupy the entire diameter of the pen body  20 . A lip  68  retains the end cap within the pen body  20 . The pen cartridge  30  directly plugs into the end cap  54 , avoiding the need to attach an end cap to the cartridge before installing it in the pen. The spring  58  maintains tension against the end cap, so that the spring  58  can work in the same manner as in  FIG. 11A . In this example, no circuit is made through the front face  13 , which may be made of plastic. The pen may be charged using two contacts  22  or a second contact may be located at the tail end of the pen (not shown). The pen body  20  may be connected directly to the light guide  32  using threads  72 , with surfaces of the light guide coated with a suitable material, such as aluminum paint or other protective materials. Aluminum paint may serve to enhance internal reflection by the faces of the light guide and to lessen the effects of scratches on the reflection. This construction may more readily work with off-the-shelf pen cartridges. 
         [0077]    In some examples, as shown in  FIGS. 12-16 , the penholder  100  is configured to be used as a cap for the pen  10 , thus the pen is inserted into a channel  1002  in the body of the penholder  100 . In some examples, the sensors  104  and the circuit boards that support them are mounted so that they can pivot between positions, as described below. 
         [0078]    As shown in  FIG. 12 , when the pen  10  is removed, the sensors  104  pivot into the body  102  so that they are positioned at an angle that improves the accuracy of their measurements. As shown in  FIG. 13 , when the pen is inserted into the channel  1002 , the sensors  104  are pushed out into a flat position. In some examples, the sensors move in the opposite direction, such that when the pen  10  is removed, the sensors  104  extend out from the body  102 , and when the pen is inserted into the channel  1002 , the sensors  104  are pulled back into their unextended position. 
         [0079]    As shown in  FIG. 14 , one of the sensors  104   a  and surrounding packaging may also extend along the length of the penholder  100  in order to give the two sensors  104   a  and  104   b  greater separation which in turn allow for higher accuracy in the overall reading of the pen&#39;s position. In some examples, the entire penholder body may extend. This may allow the sensors to be placed in different locations or relative angular orientations according to the shape or orientation of the paper being written on. 
         [0080]    In some examples, the moving sensors  104  of  FIGS. 12 and 13  may be implemented as shown in  FIGS. 15 and 16 . When the pen is absent ( FIG. 15 ), springs  1010  and  1012  push the outer ends  1013 ,  1015  of the sensors  104  out from or pull the inner ends  1014 ,  1016  in to the body  102 . When the pen is present ( FIG. 16 ), it pushes a linkage  1018  that pulls or pushes the ends  1014 ,  1016  back to a flat position. The movable sensors may also be used to position charging contacts  1020  and  1022  in contact with charging contacts  22   a  and  22   b  on the pen  10 . In some examples, only one charging contact  22  is present along the length of the pen, with the second charging contact of the pen  10  located at the front face  13  of the pen  10  as above and a second charging contact  1024  of the penholder  100  located deep inside the channel  1002 . This contact  1024  could be constructed in the same manner as the springs  124   a  and  124   b , shown in  FIG. 4C . 
         [0081]    In some examples, circuit elements may be mounted to a flexible board  1102  that is folded into shape as shown in  FIG. 17 . In some examples, the board  1102  has four portions corresponding to the top  1104 , rear face  1106 , bottom  1108 , and front face  1110  of the penholder  100 . They are folded as shown by arrows  1112   a - 1112   e  to form a box  1114 . In some examples, the front face portion  1110  may be longer than the others so that the part  1110   b  holding the sensor  104   a  may be extended as shown in  FIG. 14 . When not extended, the longer part  1110   b  of the face portion  1110  may be folded as shown, partially overlapping the shorter part  1110   a . One of the faces may include an extension  1116  that can be folded to form the internal end contact  1024 . More or fewer sections could be used, for example, the bottom section  1108  could be eliminated if no circuitry is needed on the bottom of the penholder, or additional sections may allow more complex shapes. 
         [0082]    As shown in  FIGS. 18A-18C , the penholder  100  may be in the form of a pen cap as in  FIGS. 12-14 , but may be configured to unfold in two sections  2020  and  2022 , joined by a center section  2024 , when the pen  10  is removed. The two sections  2020  and  2022  would fold back into a pen cap configuration when the pen  10  is reinserted into the center section  2024 . The sensors  104  could be located in the sections  2020  and  2022 , and the sections configured to place the sensors  104  at the proper positions when unfolded. The pen  10  may be charged through a first charging contact  2026  located in the center section  2024  and a second charging contact  2028  located in one of the side sections, e.g., section  2020 . 
         [0083]    As shown in  FIGS. 19A and 19B , a more compact penholder design may be used, in which the circuit board  144  is moved closer to the pen  10 , allowing the outer shell  2030  to be reduced in size relative to the penholder body  102  described above. This may, for example, allow the penholder to itself resemble a large pen that can be unobtrusively carried in a user&#39;s pocket. Internal components such as the charging contact  1024  may still function as above, modified as needed to accommodate the repositioned circuit board  144 . The penholder  100  in this example may include any of the features described above, for example, structures  2032  for attaching to a pad of paper or to the board of a clipboard or bookmark while a clip  2034  is used in the manner of a pocket clip in a standard pen. 
         [0084]    Other embodiments are within the scope of the following claims. For example, as shown in  FIGS. 20 and 21 , the penholder  100  may have a wide variety of other shapes. A clip  2000  can be provided that opens to release the pen and can be used to attach the penholder  100  to a stack of paper  2002 . In some examples, the clip  2000  may be of a material transparent to IR light so that it does not obstruct signals from the pen  10  to the sensors  104 ,  106 . The pen  10  may also have a wide variety of shapes including the one shown in  FIG. 22 . As shown in  FIGS. 23A and 23B , the penholder  100  may include a retractable writing surface  2004  that is pulled out from the penholder  100  by a tab  2006  (arrow  2008 ), which may be a reusable writing surface or may accommodate small pieces of paper  2010 . Although the examples discussed earlier include sensors in a penholder that can also serve as a clip of a clipboard, the sensing device could serve as a clip without also holding the pen. Although we have referred to a pen in much of the earlier discussion, many of the features apply to other kinds of writing instruments and styli.