Patent Publication Number: US-6981768-B2

Title: Hand held inkjet pen

Description:
BACKGROUND 
   An inkjet print recording system is a type of non-impact printing device which forms characters, symbols, graphics or other images by controllably spraying drops of ink. The inkjet system typically includes a cartridge which houses a printhead. The printhead has very small nozzles through which ink drops are ejected. To print an image the pen typically is propelled back and forth across a media sheet, while the ink drops are ejected from the printhead in a controlled pattern. 
   Inkjet print recording systems can be used in a variety of devices, such as printers, plotters, scanners, facsimile machines, copiers, and the like. There are various forms of inkjet printheads, including, for example, thermal inkjet printheads and piezoelectric printheads. In a thermal inkjet printing system, ink flows along ink channels from a reservoir into an array of vaporization chambers. Associated with each chamber is a heating element and a nozzle. A respective heating element is energized to heat ink contained within the corresponding chamber. The corresponding nozzle forms an ejection outlet for the heated ink. As the pen moves across the media sheet, the heating elements are selectively energized by a controller, which causes ink drops to be expelled in a controlled pattern. The ink drops dry on the media sheet shortly after deposition to form a desired image (e.g., text, chart, graphic or other image). 
   Some of the technologies for delivering ink to paper with a hand held pen, include ball point pen technology, felt tip pen technology, fountain pen technology, and quill pen technology. Each of these pen types are different with regard to ease of use, cost, print quality, and impacts on the writer. Different visual effects are sometimes observed for the different pen types. Also, different pressing forces are required of the pen holder when applying ink to the paper. 
   SUMMARY OF THE INVENTION 
   A hand held inkjet pen includes a housing, an ink reservoir, an inkjet printhead and a spacer. The ink reservoir is located within the housing. The inkjet printhead is located toward a distal end of the housing, and includes a plurality of nozzles for ejecting ink received from the reservoir. The spacer is located at the distal end of the housing for contacting a media sheet. Force applied to the spacer selects an on state for controlling ejection of ink from the plurality of nozzles. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a hand-held inkjet pen according to an embodiment of the invention; 
       FIG. 2  is a perspective view of a hand-held inkjet pen according to another embodiment of the invention; 
       FIG. 3  is a block diagram of the inkjet pen of  FIG. 2 ; 
       FIG. 4  is a diagram of a functional option palette for use with a hand-held inkjet pen; 
       FIG. 5  is a diagram of a pen at an angle relative to a writing surface; 
       FIG. 6  is a diagram of a hand-held inkjet pen and writing surface; 
       FIG. 7  is a block diagram of a hand-held inkjet pen according to another embodiment of the invention; 
       FIG. 8  is a perspective view of another hand-held inkjet pen; 
       FIG. 9  is a partial view of a pen distal portion for a pen having light beam output for illuminating an ink target location; and 
       FIG. 10  is a schematic diagram of an electrical circuit for one embodiment of a controller for a hand-held inkjet pen. 
   

   DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , a hand-held inkjet pen  10  includes one or more ink reservoirs  12  and an inkjet printhead  14  packaged within a housing  16 . The inkjet pen  10  is a stand-alone device providing ink output under the control of an operator holding the pen  10 . An on-off control  18  is linked to the printhead  14  to define an on state and an off state for ink output. Typically, an operator positions the pen over a writing surface to direct ink output onto a media  20 . In one embodiment the pen  10  includes a single reservoir storing ink of a given color. The operator controls the on-off control  18  to determine whether the pen  10  is in the on state or the off state. In the on state, ink is ejected from nozzles in the inkjet printhead. In the off state, ink is not output. 
   The printhead  14  includes a plurality of inkjet nozzles. Each nozzle includes an inkjet chamber with a firing resistor and an outlet orifice. Ink is received into each chamber from the reservoir  12 . The firing resistor is activated to eject a droplet of ink through the outlet orifice. 
   Referring to  FIGS. 2 and 3 , a hand-held inkjet pen  22  embodiment is illustrated in which like parts are given like numbers to the inkjet pen  10 . The inkjet pen  22  is packaged in a pen or marker sized container. In particular, the pen  22  has a housing  16  which is elongated and generally slender for hand holding comfort. The operator grasps the pen as would one implementing a conventional ball point pen, fountain pen, felt-tip pen or the like. Packaged within the housing  16  are one or more ink reservoirs  12  and electronics circuitry. At a distal end of the housing  16  is the inkjet printhead  14 . It is desirable to space the printhead from a writing surface to avoid damaging the printhead or clogging the orifices as might occur if the printhead contacted the writing surface. A spacer  24  is located at a distal end of the pen  22  to space the printhead from the writing surface. The spacer  24  fixes the distance between the printhead and the media for a given pen orientation. While writing, the spacer is the portion of the pen making contact with the media  20 . The spacer provides tactile feedback to the operator as the operator moves the pen along the media. 
   In addition, the spacer is coupled to the on-off control  18 . In one embodiment the on-off control  18  is formed by a strain gauge  26 . The strain gauge  26  defines an on state when a prescribed amount of pressure is applied at the spacer  24 . Such pressure is applied as the operator holding the pen presses the spacer to the media  20 . When the prescribed pressure is applied, the pen  22  ejects ink onto the media  20 . When the pressure is removed or becomes less than the prescribed pressure, the strain gauge  26  returns to the off state causing ink output to cease. 
   The pen  22  also includes a controller  28  and a power source  30 . The power source may, for example, be a battery packaged in the housing  16  and accessible for replacement as the battery life diminishes. The controller  28  is coupled to the on-off control  18 /strain gauge  26  and the inkjet printhead  14 . While the on-off control  18  defines the on state the controller  28  keeps the printhead  14  active so as to eject ink. While the on-off control  18  defines the off state, controller keeps the printhead inactive so as not to eject ink. 
   In some embodiments the pen also includes an optical sensor  32 . The sensor  32  is positioned to sense in the vicinity of the pen&#39;s output field (e.g., in the vicinity of the pen tip, the pen spacer and the pen printhead. In one embodiment the sensor  32  serves as an input device for allowing an operator to select specific functional features of the pen. For example, in a pen having the capability to print varying colors, the sensor  22  
 scans a colored surface and sets the pen color to such surface&#39;s color. The colored surface can be scanned from a palette accompanying the pen or can be scanned from a random surface selected by the operator. In this manner, the sensor provides the pen with a learning capability. 
   The random surface can be sampled from any object in the user environment. In one application, the pen is used as a touch-up device. The pen senses the desired surface to be programmed to the surface&#39;s color. The pen then is used to apply ink at blemishes elsewhere on the surface to touch-up the surface with matching color. Alternatively, the sampled color is saved and later output for color sampling or reproduction by another device. For example, the pen can reproduce the color by outputting ink or can link to another device to output a signal which specifies or otherwise identifies the previously sensed color. In one embodiment, the sampled color is downloaded in a digital or analog encoded signal through an interface  33  to a device which produces color-matched paint, cloth, or other color media. The interface  33  in various embodiments is an electrical interface, an infrared interface, or an optical interface. In other embodiments the interface  33  is omitted, and the color is reproduced in ink output from the printhead  14 . 
     FIG. 4  shows a palette  34  which defines several functional options for the pen  22 . The operator scans the desired option to select the pen output. For example, the operator may scan one of a group of colors  36   a – 36   f . The number of color options may vary according to the embodiment. As another example, the operator can select character boldness among a range of boldness values  38   a–c . The number of boldness values may vary according to the embodiment. As still another example, the operator can select among various line widths  40   a – 40   e , where the number of line width selections may vary according to the embodiment. In another example, the operator can select among a number of ink output textures  44   a – 44   c , where the number of selections may vary according to the embodiment. The operator can select to output a rainbow of colors  42 . The operator can select among a set of tip styles  46 , such as a ball point pen tip style, a felt tip pen tip style, a marker tip style. Various tip styles can be defined, even a quill pen tip if desired. Still another option that an operator may select in some embodiments is a superimposed pattern to the ink output. Various patterns can be implemented according to the embodiment. For illustration purposes two patterns are depicted. One pattern is a superimposed pattern of smiley faces  48 . Another pattern is a superimposed pattern of stars  49 . 
   In an alternative embodiment the output sensor  32  is implemented with the controller  28  to detect pen  22  angle  50  relative to the writing surface  52 , as shown in  FIG. 5 . The sensor samples the media surface  52  at a specific frequency (e.g., thousands of times per second) and processes the samples to determine the pen angle. Based on the detected pen angle, the controller  28  adjusts the firing sequence of the printhead nozzles to correct for pen angle. Such correction is beneficial for providing desired line widths, ink texture, superimposed patterns or other ink output function. 
   In another embodiment pen  22 ′ further includes a compensation adjustment input  58 . In such embodiment the sensor  32  is used for tracking the pen  22  relative to the writing surface  52 . Motion is tracked along various axes  54 ,  56 . The compensation adjustment input allows the operator to adjust pen output to compensate for a trembling hand (e.g., pen shaking). For example, an operator with a trembling hand will direct a conventional pen to produce jagged lines. Referring to  FIGS. 6 and 7 , a trembling hand may produce jagged letters  60 . An operator can turn on compensation control to compensate for the trembling or shaking hand. In some embodiments the input  58  is adjustable to determine the sensitivity for detecting trembling and shaking. In other embodiments, the input  58  is simply an on-off input for selecting compensation or not.  FIG. 7  shows the sensitivity adjustment device as a potentiometer, although other input control mechanisms may be implemented instead. 
   As the pen motion is tracked by the sensor  32 , the selected sensitivity is used by control processing to determine what motion variation is considered to be undesired pen shaking as opposed to desired pen direction change. In some embodiments, the sensor  32  may be an accelerometer which measures the instantaneous acceleration of the pen. This signal is processed to track pen displacement of the pen spacer  24  over time. The displacement information is filtered to distinguish between low frequency changes in displacement (e.g., taken to be the intended motion of the pen) and the higher frequency changes in displacement occurring within the slower frequency changes (e.g., the shaking occurring while moving the pen). The threshold for distinguishing between low frequency displacements and high frequency displacements may be varied using the sensitivity adjustment device. The sensitivity control device selects or adjusts one or more compensation control filters (not shown). In some embodiments changes in pen acceleration are detected. Acceleration changes exceeding a threshold change correspond to shaking. High frequency shaking is filtered out contributing to a natural writing experience. The inkjet printhead nozzle firing pattern is adjusted by the control processing based on the filter output and the sensitivity adjustment so that, in effect, all or a portion of the shaking motion is filtered out. The result is an improvement in the writing quality, specifically an improved smoothness to the lines and lettering  62 . 
   Referring to  FIG. 8  in another embodiment a hand-held pen  66  includes a user interface  68 . Like parts are given like functions relative to the pens  10 ,  22  and  22 ′. The hand-held pen  66  also may include an optical sensor (not shown in  FIG. 8 ) in some embodiments. Such sensor performs as described above for the other pen embodiments (e.g., sense pen angle, track pen motion). In some embodiments the shaking compensation and sensitivity input also may be included. 
   The user interface  68  may vary according to the embodiment. In an exemplary embodiment the user interface includes a one-line LCD  70  and one or more buttons  72   a ,  72   b . In some embodiments the input buttons may be integral to the LCD, as in a touch-sensitive LCD. The operator uses the buttons to display and select pen functional options. Such options include those described above. By way of example, various ink output styles may be selected, such as: ink color, line thickness, ink boldness, ink texture. In some embodiments, a superimposed output pattern may be selected. Examples were previously described with regard to  FIG. 4 , and may vary. In some embodiments a pen tip style may be simulated, such as ball point, felt tip, marker, calligraphy or other tip style. The ink output features are defined for the various tip styles. In some embodiments the tip style also determines the required pressure to be applied at the spacer  24  to place the pen in the on state. 
   Referring to  FIGS. 8 and 9 , in some embodiments the hand-held inkjet pen also includes one or more projected beams of light to illuminate where ink is to be delivered. For example, one or more light emitting diodes or laser diodes  74   a ,  74   b  output a respective beam  76  directed toward a writing surface. In an embodiment including multiple beams  76   a ,  76   b , the beams intersect at a point  78  which identifies where ink is to be delivered by the printhead  14 . In an embodiment including only one beam, the beam is directed long a path of ink output to approximate where ink is to be delivered. Although the spacer  24  is shown in the embodiments including the output light beams, in alternative embodiments the spacer  24  is omitted. Further, although the light beams are illustrated for pen  66 , the light source(s)  74  also may be included in the pen embodiments  10 ,  22  and  22 ′. 
   In various embodiments the controller  28  may be formed using an integrated circuit microcontroller. Alternatively, a controller embodiment may be formed using an electrical circuit  90 , including an oscillator  92 , a sequencer  94  and a plurality of firing transistors  96 . Referring to  FIG. 10 , the circuit  90  receives a power signal from a power source  98 . The oscillator  92  is configured as a multivibrator circuit. When the on-off control  18  is in the on state the circuit  90  outputs a sequence of firing signals  100   a–n  to the printhead  14 . In particular the oscillator  92  drives a shift register  94  which sequences the firing of transistors  96   a – 96   n . Each firing resistor  96  is coupled to a printhead nozzle to control firing of the corresponding nozzle. Each of the firing signals  100   a–n  has a predetermined frequency for driving output of the corresponding nozzle. 
   To improve consistency among ink drops output from each nozzle, it is desirable that the drive signal triggering a nozzle have substantially the same amount of energy as the drive signal for the other nozzles. More specifically, it is desirable that the active pulse of a given firing signal  100   a–n  delivers substantially the same amount of energy to its corresponding nozzle firing resistor as the active pulse of any other firing signal  100   a–n . Further, an active pulse of a given firing signal  100   a–n  delivers substantially the same amount of energy to its corresponding nozzle firing resistor as any prior or later active pulse of the same firing signal  100 . The amount of energy may be set for a given pen architecture. 
   One manner of improving consistency among each active pulse of each firing signal  100  is to generate a substantially constant pulse width and a substantially constant pulse voltage level for each such active pulse. When implementing a battery-powered pen, there is a challenge in achieving such goal because the battery&#39;s output voltage typically drops as the battery life progresses. In one embodiment a voltage regulator is used to maintain the uniformity among active pulses of each firing signal over the life of the battery. To avoid the added cost and complexity of including a voltage regulator, a non-linear device may be implemented in an alternative embodiment. 
   Referring again to  FIG. 10 , a zener diode  102  is placed in parallel with a discharge resistor  104  of the multivibrator circuit. The resistor  104 , as configured with the zener ediode  102 , causes the multivibrator circuit to discharge more rapidly at higher voltages, while have less or no effect on pulse width at lower voltages. When the battery  98  is fully charged, the active pulse voltage of firing signal  100   a–n  is relatively high, while the pusle width is relatively shortened. As the battery life progresses, the active pulse voltage declines, while the pulse width increases. More specifically, the active pulse&#39;s voltage is relatively lower, while the pulse width is relatively longer compared to the voltage and width of a pulse generated by a more charged battery. The zener diode  102  functions to at least partially counteract the declining output voltage of the battery, so that the multivibrator circuit generates firing signals having an approximately constant energy pulse over a range of battery voltages. This allows nozzle firing to occur relatively reliably over the life of the battery in the presence of changes in the delivered output voltage. As a result, the pen functions for a longer time. For example, in an embodiment using a 12 volt battery, the pen operates down to a battery voltage of approximately 8 volts. A similar circuit without the adjustment introduced by the zener diode  102  would not work as well once the battery voltage dipped below approximately 11 volts. Replacing the battery at the 11 volt output level would result in wasting more than half of the battery energy, otherwise available to the pen. 
   While the above is discussed in terms of preferred and alternative embodiments, the invention is not intended to be so limited.