Patent Application
20060125778
Electric paper is a re-writable medium that affords the convenience of paper in an electronic medium. In particular, electric paper is usually lightweight, thin and flexible and displays images indefinitely while consuming little or no power. Ideally, electric paper is also reusable and displays images using reflected light and allows a very wide viewing angle.
One form of electric paper is a gyricon system disclosed in various patents and articles such as U.S. Pat. No. 4,126,854 by Sheridon titled “Twisting Ball Display”. The gyricon system includes a host layer a few millimeters thick that is heavily loaded with bichromal elements, possibly spheres, tens of microns in diameter. Each bichromal element has halves of contrasting colors, such as a white half and black half. Each bichromal element also posses an electric dipole, orthogonal to the plane that divides the two colored halves. Each bichromal element is contained in its own cavity filled with a dielectric liquid. Upon application of an electric field, the bichromal elements rotate depending on the polarity of the field presenting one or the other colored half to an observer. Other forms of electric paper include electrophoretic particles (such as U.S. Pat. Nos. 6,829,078 and 5,961,804) and electrochromic medium (such as U.S. Pat. No. 6,587,250).
One way to make electric reusable paper cheaper and enable the use of cheap flexible plastic films in packaging the electric paper is to completely remove the driving electronics from the electric paper. Instead, an “electric paper printer” includes external addressing electronics to write and erase images. This approach reduces the per unit cost of electronic paper sheets. Multiple electronic paper sheets can then be addressed by a single set of external driving electronics, much as multiple sheets of pulp paper are printed on by a single printer. Such a system is described in U.S. Pat. No. 6,456,272 entitled “Field Addressed Displays Using Charge Discharging in Conjunction with Charge Retaining Island Structures” which is hereby incorporated by reference in its entirety.
One problem facing the use of such external electric paper printers is that external addressing devices are limited by the slow response speed of electric paper optical display elements. In example bichromal element electric paper substrates, complete rotation of bichromal elements is achieved when the addressing electric field is maintained for the entire bichromal element rotation time, typically on the order of 400 milliseconds. For a sheet that includes many rows of an image, it could take many seconds or possibly minutes to print the entire image.
Thus a technique for enabling an electric paper printer to more rapidly output electric paper sheets is needed.
An electric paper printer is described. The electrical paper printer includes a two dimensional array of electric paper printing elements. Each electrical paper printing element outputs an electrical characteristic. The electric characteristic sets the color of a pixel in the electric paper. The electric paper printer also includes a paper handler mechanism that moves a sheet of electric paper and creates a relative motion between the sheet of electric paper and the two dimensional array of electric paper printing elements.
A circuit adjusts the electrical characteristics of the two dimensional array of electric paper printer elements such that a particular electrical write characteristic approximately tracks a corresponding pixel of the electric paper for a duration of time that the corresponding pixel remains approximately adjacent the two dimensional array of electric paper printer elements.
A system for printing electric paper is described. The system moves an electrical characteristic used to write to the electric paper at a speed that approximately matches the electric paper speed. In one embodiment, the electrical characteristic is an electric field output by the printer.
A high enough density of microcapsules are included such that the electric paper appears a uniform color when all the spheres are rotated to a common position. A fixed polymer coating layer may be used to protect the electric surface. A printer applies a write characteristic, in this case an electric field, which passes through the polymer coating layer and rotates the microencapsulated spheres.
Other forms of electric paper may also be used. For example, U.S. Pat. No. 6,017,583 by E-Ink Corporation describes an electrophoretic material that may be used as an electric paper medium. The electrophoretic material includes particles that adjust to an applied electric field. The position of the particles determines the reflective characteristics. By appropriately positioning particles, an image can be made on the electric paper. The particle response time to an applied electric field limits the speed at which a printer can print to the electrophoretic electric paper.
An alternative electric paper has been developed by Ntera Corporation of Dublin, Ireland. The electric paper works on electrochromic principles. When a current passes through a pixel of the electrochromic paper, the current changes either the light transmissivity or color of the pixel. Thus an electric paper printer “prints” an image on electrochromic paper by selectively applying current to selected pixels on the paper.
Various techniques may be used to “print” on the different types of electric paper. In one embodiment, a laser printer structure is used to write onto an electric paper that is sensitive to electric fields. In a traditional laser printer, the charges on a laser printer drum are used to attract and control toner layout. In an electric paper laser printer, the charges are used to control electric paper elements, such as gyricon spheres, electrophoretic material and the like. U.S. Pat. No. 5,866,284 entitled “Print Method and Apparatus for Rewritable Medium” and assigned to Hewlett Packard corporation describes such a laser printer and is hereby incorporated by reference. However, the slow electric paper response time due to the slow sphere rotation or the electrophoretic response time renders such printing slow.
In order to increase printing speed,
In
In some embodiments, the photoconductive drum erases the old image on electric paper 408 as it writes the new image. However, more typically, charge neutralized regions of drum 412 do not write to the electric paper at all. In such cases, separate erase stations 424 may be used to uniformly erase any content on the electric paper prior to writing by photoconductive drum 412.
As electric paper 408 moves in the direction indicated by arrow 428, electric paper 408 first contacts the photoconductive drum 412 at contact point 432. As the drum rotates along direction 436, the electric paper moves at a corresponding speed such that each point on the photoconductive drum 412 remains in contact with a corresponding electric paper 408 point. After electric paper passes through release point 436, the electric paper and the drum surface separates. The contact time is approximately contact length 440 (the paper path distance from contact point 432 to release point 436) divided by the speed of electric paper 408. This contact time should be sufficient for an electrical characteristic (in this case, the charge generated electric field) to fully write to each pixel of the electric paper. In one example. The contact time is the time to fully rotate microsphere 444. Typical contact times are 400 milliseconds.
Once the image has been written, eraser 448 erases or otherwise resets the charge distribution on photoconductive drum 412. Drum resetting allows writing additional images or completion of an image.
In
Each actuator or writing element may be a pixel driver such as a charge coupled device (CCD). Each writing element outputs an electrical characteristic that writes to the electric paper. The electrical writing characteristic depends on the type of electric paper used. In particular, the writing characteristic as used herein is defined as the electrical characteristic used to set an image in the electric paper. For example, in an electrochromic paper, the writing characteristic is a current. In a gyricon paper, the writing characteristic is an electric field.
In one example, a sheet of electric paper moves along direction 524. In an alternate embodiment, the array of writing elements is incorporated into a “wand” or other print head type of structure that moves over the electric paper. Whether the electric paper moves, the printing elements in a wand moves, or both move simultaneously, a relative motion is created between the electric paper and the writing elements. A motion sensor or other sensing mechanism may be used to determine the direction and speed of the relative motion. Alternately, the speed and direction of the relative motion may be know from the paper handling mechanism that feeds and controls motion of the electric paper or the structure that moves the writing elements. In either case, information on the speed and direction of the relative motion is communicated to electronics that control TDI imager output. The TDI imager adjusts each writing element such that the writing characteristic output by a column of writing elements shifts in the same direction 528 as the relative electric paper motion. The shift rate is adjusted to result in an effective “speed” of the writing characteristic. This “effective speed” approximately matches the relative speed of the electric paper with respect to the writing elements. By matching speeds, the imager effectively integrates the writing characteristic by the number of writing elements in a column.
Using the described system enables much higher print speeds. For example, gyricon electric paper utilizes spheres that have typical rotation times on the order of 100 milliseconds or longer. A simple linear array of actuators printing a 11.5 length paper at 300 dpi with a 100 ms reaction time would take over five minutes a page. (300 dots per inch×11.5 inches×100 ms/pixel) However, a column of 600 write elements could reduce the print time enabling a theoretical print speed of 110 pages per minute.
A secondary benefit of the time domain integration system results from writing element averaging. A long pixel column means that each printed pixel is a result of many writing elements. In a system where each printed pixel results from several hundred writing elements, failure of a single writing element usually has a negligible effect on image contrast. (For example, the failure of a sphere to rotate by 1/100th is usually negligible) In the event that the effect is nonnegligible, electronics can disable actuators in other columns to correct the problem. In particular, disabling a corresponding number of writing elements in other columns removes any contrast differentials which may result.
Large area electronics technologies may be used to form the two dimensional array of writing elements. Possible technologies include solution processed electronics, polymer organics, short-chain organics, amorphous silicon, and laser crystallized polysilicon among others. Transfer of signals from writing element to adjacent writing element in a column may be achieved by bucket brigade electronics that actually transfer a signal in the direction of electric paper motion. Alternately, pixel-drive electronics may simply turn writing elements on and off as the electric paper moves such that each electric paper pixel is consistently under an “on” write element or an “off” write element.
In an analog implementation of the printing system, analog shift registers may be used. Analog shift registers shift charge from write element to adjacent write element such that the electric field generated by the analog charge moves with the electric paper motion. Thus an approximately constant charge remains positioned over the electric paper as it moves through the printer.
In a very large array of write elements, a form of “electronic lithography” may be performed.
The preceding description describes various methods of improving and accelerating printing to electric paper. The description includes electric papers moving through printers, although it should be understood that it is just as easy to move a wand or other printing device over the electric paper instead. The description also includes a number of details such as speeds, example circuits, example types of electric paper, and example response times. The details are provided as examples and facilitate understanding of ways in which the invention may be implemented. These details should not be used to limit the invention. Instead, the invention should only be limited by the claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
