Abstract:
A laser printer for Braille that obviates the need for embossing mechanisms and specialized paper. A laser printer for Braille according to the present teachings increases an amount of a toner that adheres to an area of a paper that corresponds to the Braille element. The increased amount of toner yields a printed Braille element that may be read by touch.

Description:
BACKGROUND 
       [0001]    Braille is a writing system for visually impaired or sightless people, consisting of raised elements, e.g. bumps, that are read by touch. A Braille document may include a pattern of Braille elements that are embossed in a relatively thick paper. 
         [0002]    A Braille printer may be used to generate Braille documents using a computer system. A Braille printer may include a mechanism for embossing Braille elements into a relatively thick paper. For example, a Braille printer may include a mechanism for punching a pattern of bumps into a thick paper. The relative thickness of the paper is intended to hold the shape of the bumps in the paper. 
         [0003]    Unfortunately, prior Braille printers may be relatively expensive and cumbersome to use. For example, an embossing mechanism for punching Braille elements into paper may be relatively expensive to manufacture particularly in light of the relatively low volume of Braille printers that may be produced. In addition, the relatively thick paper used in prior Braille printers may be expensive and difficult to obtain in comparison to paper that is used in sight read text/graphics printers. 
       SUMMARY OF THE INVENTION 
       [0004]    A laser printer for Braille is disclosed that obviates the need for embossing mechanisms and specialized paper. A laser printer that prints a Braille element according to the present teachings increases an amount of a toner that adheres to an area of the paper that corresponds to the Braille element. The increased amount of toner yields a printed Braille element that may be read by touch. 
         [0005]    Other features and advantages of the present invention will be apparent from the detailed description that follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The present invention is described with respect to particular exemplary embodiments thereof and reference is accordingly made to the drawings in which: 
           [0007]      FIG. 1  shows a laser printer for printing Braille onto a paper according to the present techniques; 
           [0008]      FIG. 2  shows progressive close-up views of an example set of Braille characters written onto a drum of a laser printer according to the present techniques; 
           [0009]      FIG. 3  shows a set of control circuits in a laser printer that are employed in printing Braille. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]      FIG. 1  shows a laser printer  10  for printing Braille onto a paper  12  according to the present techniques. The paper  12  may be the same type of paper that may be used for printing text or graphics suitable for sight reading. 
         [0011]    The laser printer  10  includes a drum  26  that rotates, e.g. in a counter-clockwise direction as shown. The drum  26  includes a photoconductive material that may be discharged by light. As the drum  26  rotates, a drum charger  30  imparts a positive electrical charge onto the drum  26 . The drum charger  30  may be an electrical wire with electrical current passing through or may be a charged roller. 
         [0012]    The laser printer  10  writes a Braille element onto the drum  26  by performing an enhanced discharge of an area of the drum  26  that corresponds to the Braille element. The amount of the enhanced discharge may be selected to increase an amount of a toner  34  from a toner holder  35  that adheres to the area of the drum  26  that corresponds to the Braille element. For example, the enhanced discharge may be selected to yield a tactile feel, e.g. a bump feel, to the Braille element after the toner that adheres to the Braille element is transferred to and fused onto the paper  12 . 
         [0013]    In one embodiment, the enhanced discharge of the area of the drum  26  corresponding to the Braille element is provided by applying an enhanced amount of light from a laser  22  onto the area of the drum  26 . For example, a set of additional pulses of light may be applied from the laser  22  to the area of the drum  26  corresponding to the Braille element. 
         [0014]    The laser printer  10  includes a scanning mirror  24  that applies light pulses from the laser  22  onto the drum  26 . The combination of motions of the scanning mirror  24 , the rotation of the drum  26 , and the light pulses from the laser  22  are used to draw Braille elements onto the drum  26 . 
         [0015]    The laser printer  10  includes a roller  32  that rolls the toner  34  onto the surface of the drum  26  as it rotates. The toner  34  is positively charged and adheres to the negatively charged areas of the drum  26 . The enhanced discharge of the area of the drum  26  corresponding to the Braille element increases an amount of the toner  34  that adheres to the Braille element on the drum  26  in comparison to an amount of the toner  34  that adheres to areas not having an enhanced discharge, e.g. areas for printing text and graphics for sight reading. 
         [0016]    The laser printer  10  includes a paper charger  36  that applies a negative charge to the paper  12  as it approaches the drum  26 . The paper charger  36  may be an electrical wire with electrical current passing through. 
         [0017]    The negative charge on the paper  12  attracts the toner that has adhered to the drum  26 , thereby transferring the Braille element from the drum  26  onto the paper  12 . The paper  12  then passes through a fuser  28  that melts the deposited toner onto the paper  12 . The enhanced amount of toner transferred from the Braille element on the drum  26  to the paper  12  yields a tactile feel on the paper  12  after fusing. 
         [0018]    The laser printer  10  includes a drum discharger  29 , e.g. a bright lamp, that discharges the drum  26  to erase the Braille element from the drum  26 . 
         [0019]    In other embodiments, the above-described charge polarities may be reversed. For example, the drum  26  may initially be charged to a negative charge and then written by positively charging the Braille element areas of the drum  26 . 
         [0020]      FIG. 2  shows progressive close-up views of an example set of Braille characters  40 - 46  written onto the drum  26 . The Braille characters  40 - 46  are written using combination of motions of the scanning mirror  24 , the rotation of the drum  26 , and a series light pulses from the laser  22 . 
         [0021]    A close-up view of the Braille character  40  shows that it includes an arrangement of Braille elements  60 - 64 . The Braille elements  60 - 64  each define an area that will be perceivable to touch, i.e. a bump, when printed on the paper  12 . The laser  22  writes the Braille elements  60 - 64  by applying a series of light pulses  50  that discharge the areas of the drum  26  that correspond to the Braille elements  60 - 64  on the drum  26 . 
         [0022]    A close-up view of the Braille element  60  shows that the series of light pulses  50  discharge an arrangement of dots  70 . Each dot  70  corresponds to the resolution of the laser  22  and the scanning mirror  24 , i.e. the maximum resolution of the laser printer  10 . 
         [0023]    The pattern used to make up the Braille element  60  may have a significant impact on the amount of toner transferred. Depending on the embodiment, the pattern may be a solid fill of toner, or a specific pattern of dots designed to maximize the toner pile height. For example, on jump gap systems in which the roller  32  is not in contact with the drum  26 , a solid filled area has higher amounts of toner at the edges than in the center. A series of rings or separate larger dots that are larger than the native resolution of the laser printer  10  may yield a significant increases in toner over a solid filled area. 
         [0024]    The laser printer  10  when printing a Braille element uses the laser  22  to provide a greater discharge of the drum  26  so that the discharge pattern on the drum  26  attracts more of the toner  34  from the roller  32 . In one embodiment, the laser printer  10  when printing a text or graphics image for sight reading applies one pulse of the laser  22  per dot of resolution. For a Braille element, the laser printer  10  applies two or more pulses of the laser  22  to each of the dots  70 . Each pulse of the laser  22  on each dot  70  produces a greater negative charge on the drum  26 . 
         [0025]      FIG. 3  shows a set of control circuits in the laser printer  10  that are employed in printing Braille. The laser printer  10  includes a printer controller  80  that receives print files from a computer system via a communication path  86 . Examples of the communication path  86  includes a USB port, parallel port, serial port, Ethernet, etc. 
         [0026]    The laser printer  10  includes a printer memory  82  that holds a bit map of the dots to be printed onto the paper  12  when printing Braille. In some embodiments, the bit map is generated on a computer system and transferred to the laser printer  10  via the communication path  86 . In other embodiments, the printer controller  80  generates the bit map in response to information contained in a print file obtained via the communication path  86 . 
         [0027]    The laser printer  10  includes a laser controller  84 . The printer controller  80  issues commands to the laser controller  84 . The commands cause the laser controller  84  to issue control signals  88  to the laser  22  and the scanning mirror  24  to hit the drum  26  with pulses of light. When printing Braille, the printer controller  80  causes the laser controller  84  to generate additional pulses of light for each dot of a Braille element. 
         [0028]    The laser printer  10  includes a bias control circuit  94  that generates a set of control signals  90  for controlling biases applied to the toner holder  35  that contains the toner  34  and for controlling an amount of charge applied to the drum  26  by the drum charger  30 . The bias control circuit  94  enables the printer controller  80  to print Braille elements by controlling the charge on the drum  26  together with a bias applied to the toner holder  35  so that more of the toner  34  is attracted to the drum  26  when printing Braille elements. In one embodiment of the laser printer  10 , the bias that is used to adjust the amount of the toner  34  placed on an area of the paper  12  is a DC bias for primary charging of the drum  26  and developing using the toner holder  35  of approximately 700 VDC. For wider ranges of density, i.e. more toner deposition, both the DC and AC biases may be adjusted. The biases used on the toner  34  and the drum charger  30  may be independently controlled or may be controlled in concert. An interaction of the biases used on the toner  34  and the drum charger  30  may significantly influence how much toner is applied to the paper  12 . 
         [0029]    The printer controller  80  uses the bias control circuit  94  to control the charge on the drum  26  together with a bias applied to the toner holder  35  on a page by page basis. The control of charge on the drum  26  with the bias to the toner holder  35  provides a density setting. The density is a measure of how much of the toner  34  is applied to the paper  12 . The density may be used to provide a “Braille page” setting for the laser printer  10  such that the amount of the toner  34  applied to the drum  26  (and ultimately the paper  12 ) is maximized. The Braille page setting may be used in combination with extra light pulses from the laser  22  when printing Braille elements. 
         [0030]    The particles of the toner  34  may be enlarged to facilitate the formation of tactile bumps for Braille elements. If toner particle size is changed, the DC and AC biases may be adjusted to compensate for the changed particle size. 
         [0031]    The laser printer  10  includes a fuser control circuit  96  that generates a set of control signals  92  to the fuser  28 . The fuser control circuit  96  enables the printer controller  80  to control an amount of pressure applied by a set of rollers in the fuser  28  to the paper  12 . For example, the printer controller  80  may reduce the amount of pressure applied by the rollers when printing a Braille page. The reduced pressure increases the height of Braille bumps. In addition, the fuser control circuit  96  enables the printer controller  80  to control the temperature applied by the fuser  28 . For example, the temperature of the fuser  28  may be reduced when printing a Braille page so that the height of Braille bumps is increased. 
         [0032]    The printer controller  80  may reduce the speed of movement of the paper  12  when printing a Braille page. For example, the laser printer  10  in one embodiment includes a motor control circuit  110  that generates a set of control signal  112  that provide paper speeds of one-half, one-third, and one quarter normal speed. The different speeds may be employed for different types of media that require significantly more heating. A slower print speed enables the paper  12  to spend more time in the fuser  28  to increase heat to the toner without generating more heat in the fuser  28 . The increased time in the fuser  28  increases the heat applied to the paper  12  and facilitates the heating of larger amounts of toner on Braille elements. 
         [0033]    The foregoing detailed description of the present invention is provided for the purposes of illustration and is not intended to be exhaustive or to limit the invention to the precise embodiment disclosed. Accordingly, the scope of the present invention is defined by the appended claims.