Abstract:
A tactual computer monitor includes rows and columns of rectangular cells. Each cell includes four rows and two columns of movable pins which are felt and read by a blind person. The pins are driven by electromechanical impact drivers and are held in position by resilient elastomeric cords. The impact drivers are carried on a bi-directional printhead which travels beneath the movable pins. An erasing mechanism is provided to positively drive the pins downwardly to erase the characters produced by the printhead.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No.: 60/141,329, filed on Jun. 28, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to apparatus for displaying Braille characters and relates in particular to an economical Braille computer monitor which displays Braille characters using rectangular cells composed of eight tactile members arranged in two columns of four members each. Such cells are particularly compatible for use with ASCII 8 bit 256 symbol code. 
     2. Description of Prior Developments 
     Braille is a language of raised dots read by the fingers. In 1824, Louis Braille, a young blind teacher in Paris, perfected spelling in a sequence of dots, using a sharp stylus to punch indentations into paper fitted over a metal slate. Today, slate and stylus are available as lightweight portable tools, with Braille typewriters and electronic adaptions as well. 
     Braille, the tactual alphanumerics for the blind, is composed of “cells” with six tactile “dots” that are raised in various patterns. The cell is composed of two columns that have three dots each. By convention, the three dots in the first column are numbered top to bottom as dot  1 , dot  2 , and dot  3 . Similarly, the dots in the second column of dots are numbered as dot  4 , dot  5  and dot  6 . 
     Braille is read by passing a finger lightly over the dot patterns, which are “seen” or perceived as letters and words in the same way the sighted perceive ink print. 
     Sixty-four different symbols, including a blank space, can be made from a cell&#39;s 6-dot binary dot-no-dot permutations. Many different alphabets have been coded from the cells and Braille is published in many different languages, 35 in the U.S. alone. Braille prose is written using one of two codes, Grade I or II. There are other codes for mathematics, music, and computers. Grade I is a written Braille letter code for respective ink print letters. Grade II Braille uses symbols, not used for letters and marks, to express common letter combinations such as: ss, tt, ough, th, and the like. Some symbols are used to express whole words, part words and symbols. Symbols include two cell combinations and double duty single cells, for a total of 157 symbols. Grade II Braille increases the reading rate of skilled users by reducing the number of characters needed. 
     Braille has no dedicated capital or numeric symbols. Capitals are shown by a “6” dot “conditional sign” before a given letter or word. Two position “6” dots are used to indicate the whole word is capitalized. Numbers use the first ten letters of the alphabet (a-j), preceded by the number sign dots  3 ,  4 ,  5 , and  6 . A period is represented by dots  2 ,  5 , and  6  and a comma by a dot  5 . 
     Current state of the art paperless Braille machines use discrete piezoelectric benders (bimorphs) to raise each and every dot. Because bimorph parts are expensive, number in the hundreds and their assembly is complex, the average retail price for such parts was estimated in 1993 to be $25.00 per dot. 
     Bimorphs have not yielded economies of scale and thus the $6,500 cost per 20 cell (120 dot) unit of 18 years ago, is still about the same today. The latest 80 cell display can cost $20,000 and the host computer software is not included. 
     Single lines of bimorphs must be read in jerky segments, which can slow reading rates by as much as 50%. This makes them virtually useless as “powerbooks”. High costs have perpetuated awkward 6-dot “computer codes” instead of using easier 8-dot codes that are directly transliterable with ASCII&#39;s 8 bit 256 symbol codes. 
     SUMMARY OF THE INVENTION 
     The instant invention is directed to an 8-dot, multi-line, paperless Braille monitor that overcomes the above described disadvantages of single line bimorphs. Cell dots  1 - 6  are assigned the same row and column positions as before. Dots  7  and  8  are positioned in the first and second columns, respectively, just below dots  3  and  6 . The 8-dot numbering scheme within a single cell is shown in FIG.  1 A. This numbering scheme allows an 8-dot tactual computer monitor to not only display legacy 6-dot Braille, but also facilitates the large ASCII 8 bit, 256 symbol code. 
     In accordance with the invention, an 8-dot tactual paperless Braille computer monitor (TCM) is constructed as a paperless computer-controlled, realtime, refreshable, electromechanical, multi-line, Braille display or “monitor” device that enables the bind to read, write, or edit Braille documents directly from a mechanical display monitor, rather than from paper, and to communicate simultaneously with sighted computer users. The TCM serves the blind in the same way visual display monitor units serve sighted computer users. 
     To operate the TCM, the user switches on a host computer. The host computer&#39;s automatic self check is displayed and the system&#39;s prompts then appear on the top line of the TCM. The user may then call up text on file, edit, or write new text via the host computer&#39;s keyboard. The text can be manipulated in the standard manner by the keyboard&#39;s directional pad. 
     To edit the text on screen, the text is highlighted by entering CONTROL/″ on the computer keyboard. This is followed by a tap touch on the row and column cell coordinates on the TCM of the first letter of the word/passage to be edited. Next, a double tap touch is applied to the row and column cell coordinates on the TCM of the last letter of the word/passage to be edited. CONTROL/″ is entered. At this point the word or passage from the computer keyboard is edited. Then SAVE, RETURN is entered and the program does the rest. Other commands, such as DELETE, INSERT, or MOVE, work in the usual way. 
     Reading documents with a TCM is done smoothly, in multi-line increments of text which are displayed in an enhanced 8-dot Braille format, read by feel and then erased electro-mechanically, just prior to displaying the next increment of text. Of course, text can also be displayed on the TCM in the conventional 6-dot format. Thus, to read a given increment of a document, the user first prints the increment to the TCM display. Then, feeling the TCM display with one finger, or perhaps with a finger from each hand, the user is able to mentally translate into meaningful words and phrases the collective positions of the many individual dot pins comprising each line of text. Although the TCM can be made to display only a single line of Braille text, it is preferably made to be page size and therefor incorporate several lines, say six, twelve or more. The exact number of lines depends on customer or market preferences balanced by practical considerations for overall size. The instant TCM invention is described herein in terms of six lines each line having 40 tactual Braille cells per line. 
     When ready to read the next increment of text, the user operates a switch to erase the display of text just read. After the display is erased, the user then queues the print mechanism of the TCM to display the next successive increment of text, or alternatively, the user can scroll forward or backward to display any other increment. Thus, the user can advance or go back through a document in any manner chosen. 
     The aforementioned objects, features and advantages of the invention will, in part, be pointed out with particularity, and will, in part, become obvious from the following more detailed description of the invention, taken in conjunction with the accompanying drawings, which form an integral part thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1A is a schematic, top plan view of an 8-pin cell arranged in accordance with the invention and showing the position of a pair of elastomeric cords or strips between adjacent rows of pins; 
     FIG. 1B is an enlarged front elevation view of a tactile dot pin member constructed in accordance with the invention; 
     FIG. 2 is a top plan view of a retention plate constructed in accordance with the invention; 
     FIG. 3 is a side elevation view, partly in section, showing the arrangement of dot pins in six lines of the TCM and supported by three retention plates, silicone cords and a bottom eraser plate; 
     FIG. 4A is a side elevation view, partly in section, of a traveling printhead constructed in accordance with the invention; 
     FIG. 4B is a left end view of FIG. 4A; 
     FIG. 4C is a top plan view of FIG. 4A; 
     FIG. 4D is a schematic view showing the alignment of the printhead and Braille display, for clarity, solenoids and plungers are shown for Line  1  only; 
     FIG. 5A is a top plan view of an erasing mechanism constructed in accordance with the invention; 
     FIG. 5B is a side elevation view of FIG. 5A; 
     FIG. 5C is an end view of FIG. 5B; 
     FIG. 6A is a top plan view of the printhead  300 , of FIGS. 4A,  4 B and  4 C, that travels bi-directionally along the linear motions undercarriage  602  and  604  in firing alignment with the braille display through the optical reference plate  310 . 
     FIG. 6B is an end view of  6 A; 
     FIG. 6C is an end view of FIG. 6A; 
     FIG. 7A is a top plan view of an electric drive motor connected to a belt drive which drives the linear motion undercarriage; 
     FIG. 7B is a side view of FIG. 7A; 
     FIG. 7C is an end view of FIG. 7B; 
     FIG. 8 is a side elevation view, partly in section, of an alternate erasing mechanism using twin cam rods; 
     FIG. 9A is a top plan view of another alternate erasing mechanism using a pair of wedge actuators; 
     FIG. 9B is a side view of FIG. 9A; and 
     FIG. 9C is an end view of FIG.  9 B. 
    
    
     In the various figures of the drawing, like reference characters designate like or similar parts. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with the invention, a tactual paperless Braille computer monitor, “TCM”, includes a two dimensional array of dot pins  100 , one of which is shown in detail in FIG.  1 B. The dot pins  100 , which are mechanically forced up and down to respectively display or erase Braille text, are held in place laterally from one another by a set of three perforated retention plates  200  (FIG.  2 ). A top plan view of one of the retention plates  200  is shown in FIG. 2 and a side elevation view of three of the retention plates aligned in a vertically spaced series is shown in FIG.  3 . 
     Although  48  cell pattern perforations are provided in each line, as seen in FIG. 2, only the middle forty sets or “cells” of dot pins  100  are moved up, four dot pins 100 per line at a time, to display a forty character line of Braille text. As shown in FIGS. 4A,  4 B, and  4 C and further in FIGS. 6A and 6B, printhead  300 , traveling beneath the retention plates  200 , electro-mechanically forces up the dot pins  100  to their raised positions so as to display text. To erase text, all raised dot pins  100  in the display are moved down together, in unison, by the erasing plate  402  of then erasing mechanism  400  shown in FIGS. 3,  5 A,  5 B and  5 C. Mechanical stops limit the vertical travel of the dot pins  100 . 
     As seen in section in FIG. 3, four lengths of small diameter  40  durometer silicone rubber cord  500  are used as detent material to hold the dot pins  100  in the raised position, within each line of Braille display, until they are erased. Once the pins are erased, the cords  500  hold the dot pins in a lowered or retracted position. The four lengths of rubber cord  500  are positioned such that two lengths are situated between the top and middle retention plates  200  and two similar cords  500  are positioned between the bottom and middle plates  200 . As further seen in FIGS. 1A and 3, the rubber cord  500  is located between the outer rows of the eight dot pins  100  making up each line of Braille cells, i.e., between row  1  (dots  1  and  4 ) and row  2  (dots  2  and  5 ) and between row  3  (dots  3  and  6 ) and row  4  (dots  7  and  8 ). In FIG. 1A, the two cords  500  illustrate the relative plan view position of the silicone rubber cords  500  relative to the dot pins  100 . 
     FIG. 3 helps to illustrate the position of the silicone detent material of cords  500  relative to the set of three retention plates  200  and to the dot pins  100  for a six line TCM. The rubber detent material of each cord  500  makes resilient physical contact with the dot pins  100  and the retention plates  200 . Four spacers  202  are positioned between the plates  200  for vertical separation of the retention plates. The upper rubber cords  500  act as resilient pin alignment members to help to keep the dot pins  100  in vertical alignment. The lower rubber cords  500  act as resilient pin retention members to hold the pins  100  in their raised position. 
     As seen in FIGS. 6A,  6 B,  7 A,  7 B and  7 C, integrated with the above described assembly are a linear motion undercarriage  600 , an electric drive motor  700 , a belt power transmission system  800 , and a support structure  900 . Not shown are a computer interface, an outer casing, a computer and an electronic control package of generally known arrangement. 
     In a preferred embodiment as shown in FIG. 1B, a 0.375″ long dot pin  100  is machined on a Swiss screw machine from {fraction (1/16)}″ diameter 2011 T3 aluminum wire stock. Pin  100  has a 0.010″ long, 45 degree chamfered surface  102  at the top end (the end felt by a blind person when the pins  100  are raised or displayed). Pin  100  further includes a top section  104  of uniform 0.050″ diameter, a double hour glass section with curves of revolution  106 ,  108 , and  110 , a lower uniform diameter section  112 , which is slightly longer than the top section  104  but of the same diameter, and a bottom uniform {fraction (1/16)}″ diameter section  114 , forming a square abutment shoulder  116  at the abutment or intersection with the lower cylindrical section  112 . 
     Curved sections  108  and  110  provide annular retention grooves for receiving and holding compliant cords  500 , with curved section  110  defining an annular ridge that separates the curved sections  108  and forces the lowermost cords  500  to comply with the overall curved shape of sections  106 ,  108  and  110 . Uniform diameter cylindrical sections  104  and  112  move up and down with a 0.040″ stroke in the pre-stamped 0.054″ diameter holes  201  (FIG. 2) provided in each one of the set of retention plates  200 . The double hour glass section, with curves of revolution  106 ,  108  and  110 , produces a compliant deformation in the detent material of the small diameter  40  durometer silicone rubber cord detent material interposed between adjacent outer cell rows of dot pins  100  and between the bottom and middle retention plates  200 . 
     The compliant deformation of the rubber cord  500  causes lateral elastomeric contact forces to be developed between adjacent outer row dot pins  100  and the lower silicone rubber cords  500 . These contact forces hold the dot pins  100  in their displayed or raised positions. The upper silicone rubber cords  500  also exert some lateral elastomeric pressure forces and thus help to keep the dot pins  100  aligned vertically, especially when some dot pins  100  are raised and others are not. 
     In a six line preferred embodiment, the TCM according to the present invention utilizes three parallel retention plates  200  (FIG. 3) vertically spaced from one another by rectangular block spacer members  202 . The retention plates  200  have stamped holes  201  to retain the dot pins  100  in each of the six lines of forty 8-dot cell holes  201 , for a total of 320 dot pins  100  per line. The retention plates  200  are stamped from a continuous roll of aluminum stock and cut to a 12″ length. As seen in FIG. 2, the retention plates  200  have 48 sets or cells  204  of 8-dot cell holes  201 . Only the center  40  8-dot cells or hole sets  204  are fitted with dot pins  100 . 
     The four sets  204  of 8-dot cell holes  201  available on each end of each line are used to facilitate assembly and alignment of the retention plates  200  and holes  201 . Also, one set  204  of 8-dot cell holes  201  at the beginning and end of each line can be utilized to designate the line number in a text editing process. An extra line of 8-dot cell holes  201  could also be stamped in the retention plates  200  to indicate cell column coordinates. Thus in this embodiment, six lines could be for Braille text, while a seventh line could be reserved for the text editing process. 
     As noted above, spacing between the parallel retention plates  200  is maintained by four spacer members  202 . Each spacer is 0.060 inch thick by 0.750″ wide by 12″ long. Two spacers  202  are used at the “north” or upper side of the TCM display and two at the “south” or lower side. As an option, the four spacers  202  can be cut from the sides of twelve 0.020 inch thick retention plates  200 . The tooling holes  206  (FIG. 2) in the spacers  202  (FIG. 3) can be lined up with the tooling holes  206  in the retention plates  200 . The tooling holes  206  can also serve as the cell column coordinate location holes  208 . 
     The most user friendly cell spacing between cells or cell hole patterns  204  in the same line was found to be about 0.250 while the preferred cell spacing between lines was found to be about 0.6000 inch. In the production of the retention plates  200 , the actual cell spacing will vary due to possible variations in production run settings and tool wear. A special tool is used to stamp the 8-dot pin cell hole pattern  204 . The horizontal and vertical hole spacing for the 8-dot cell hole pattern  204  is 0.0925 inch. The holes themselves are 0.054 inch in diameter. 
     Each retention plate  200  is preferably made of 0.0200 inch aluminum roll stock. A stamping tool is used to stamp 6 cells  204  at a time and is moved along the length of the retention plate in 0.2450 inch increments (possible production run variation). As further seen in FIG. 2, the stamping tool also stamps a tooling hole  206 , 0.1 inch diameter, on each top and bottom side or border of the 6 cell column. As the tool advances along the length of the retention plate, the tooling holes are used to hold the plate from moving during the stamping progression. 
     The retention plates  200  also have cell location coordinate holes  208  stamped along the top border and sides. The cell row and column coordinate location holes  208  are each fitted with an editing dot pin  100  corresponding to the coordinate locations of each cell. In this embodiment, there are 40 column editing dot pins  100  and 6 row editing dot pins  100  for a total of at least 46 editing dot pins  100 . 
     The editing pins  100  normally stay in the raised position and are used to mark or highlight the beginning and ends of text to be edited. The editing dot pins  100  are tapped twice to form communication links to the computer to identify beginning and end line coordinate positions. The editing pins  100  have a spring that returns them to the raised position. The twice tapping requirement insures intentional versus accidental communicative desires and is similar to double clicking with a mouse. 
     As seen in FIGS. 4A,  4 B and  4 C, a traveling printhead  300  travels back and forth in the direction of the directional arrows in FIG.  4 C and drives the dot pins  100  from their lowered or depressed (erased) position to their raised or tactile position. The pins  100  in each line of the TCM display are raised by four miniature solenoids  302 , such as Electromechanisms, Inc. Model P25. The solenoids  302  have a preset maximum stroke of 0.0625 inch and have the capacity to deliver a 20 ounce impact force to the bottom of a dot pin  100 . 
     Since the dot pin stroke is 0.0400 inch, it is necessary to set a clearance of 0.0225 inch between the tips of the solenoid plungers  304  and the bottom of the dot pins  100 . The solenoids  302  are mounted on a bracket  306  (FIG.  4 B), which is attached to a linear motion device  600  as best seen in FIG.  4 B and FIG.  6 C. 
     As seen in FIG. 4D, four solenoids  302  (“_” symbol) are used to print each line, e.g., line  1 , and are aligned or spaced from one another diagonally so that there is a solenoid  302  for each of four adjacent 8-dot cells  204  (0.245 ″ x-(east) direction spacing) but in different dot rows (0.0925″ y-(north) direction spacing). 
     The left (south) to right (north) solenoids  302  line up diagonally with column  1  in cells  5  to  8  respectively. However, in order for every dot pin  100  to be able to be printed, it is necessary, when printing from left to right, for the uppermost leading or “north” solenoid  302  to line up with column  1  of cell  5 . Therefore, when prig from left to right first commences, the four leftmost solenoids are not fired, as there are no dot pins  100  in the 8-dot cell hole patterns  1 - 4  corresponding to their location. Similarly, when printing from right to left, the leading or “south” solenoid  302  must line up with column  2  of cell  45 . In the latter situation, the four rightmost solenoids corresponding to cells  45 - 48  do not fire. 
     The firing of solenoids  302  and thus the raising of dot pins  100  is controlled by a computer and an optical switch  308  (FIGS. 4A,  4 B and  4 C). The optical switch  308  is mounted on the traveling printhead assembly  300 . The optical switch  308  is used in conjunction with an optical reference plate  310 . The optical reference plate  310  is cut from one of the retention plates  200  so as to utilize a single row of at least forty-three 8-dot cell holes. The optical reference plate  310  is stationary and is mounted parallel to the retention plates  200  with its single row of holes aligned with the dot pin holes  201  in the retention plates  200 . 
     In the embodiment shown, each cell  204  contains eight dot pins  100 . Each dot pin  100  has an up and a down position. In the up or raised display position, the exposed tips of the top portions  104  of dot pins  100  extend 0.032 inches above a TCM display surface typically provided in the form of a cover surface. In the down or erased position, the dot pins  100  are recessed 0.008 inches below the TCM display surface, so as to prevent the reader from interpreting a slightly exposed, but erased dot pin  100  as a printed dot pin  100 . Therefore, each dot pin  100  has a travel or stroke of 0.040 inches. 
     The bottom surface of each dot pin  100  serves as an anvil when struck by a solenoid  302  to drive the dot pin  100  into its raised position. The square shoulder portion  116  of each dot pin  100  limits the upward vertical travel of the dot pin  100  when the shoulder comes into contact with the bottom of the erasing mechanism  400 . 
     The dot pins  100  of the TCM are designed to move in an up and down fashion through the aligned guide holes  201  in each of the three equally spaced (0.080 inch spacing) parallel retention plates  200 , of 0.020 inch thickness each. Spacing between the parallel retention plates  200  is maintained by spacers  202  which are 0.060 inch thick. The dot pins  100  also pass through aligned holes in the erasing mechanism  400  noted above. 
     In operation of the TCM, vertical up and down motion of the erasing plate  402  is limited by the erasing mechanism  400  described below. The lower end of each dot pin  100  is configured with a square shoulder  116  so that when a dot pin  100  is in the raised position, its shoulder  116  acts as a mechanical stop against the bottom end of the erasing plate  402 . This prevents the top of the dot pin  100  from extending above the display surface of the TCM more than 0.032 inches. 
     Thus, in the printing mode, upward motion of a dot pin  100  is arrested when its square shoulder  116  comes into contact with the eraser plate  402 . The square shoulder  116  is also captured by the eraser plate  402  when the display is erased. Several variations of the erasing mechanism are considered possible. All variations accomplish the same task: the 0.0400 downward movement of the eraser plate  402 . 
     In the first variation shown in FIGS. 5A,  5 B and  5 C, the easing mechanism  400  is a simply supported, channel shaped, beam structure whose assembly includes the eraser plate  402  and two parallel beams  404  laterally connected at their tops by the eraser plate  402 . The four ends of the beams  404 , in controlled motion, are moved down in unison by linear actuators  406  by the amount of desired dot pin travel (0.040 inch). After the solenoids  406  fire, thereby erasing the display, spring washers  408  on the plungers  410  of the solenoids  406  return the eraser plate  402  back to its normally up position. 
     The eraser plate  402  and the beams  404  can be configured as a one piece uniformly thick flat plate bent into the shape of a channel. In any configuration, the erasing plate  402  has to resist shear and bending forces imposed by drag forces that resist the motion of the dot pins  100 . The beams  404  should be dimensioned such that all bending deflections are about two or three orders of magnitude smaller than the amount of beam travel, e.g., 0.0004 inch. The ends of the beams  404  are mounted on linear actuators  406  capable of delivering the forces necessary to effect desired beam motion. 
     For example, the linear actuators  406  can be electromechanical solenoids, air cylinders, or cam operated devices attached to the beam to cause the desired motion. Past experience with a three piece integrated beam structure for a single line TCM was fraught with difficulty, owing to the inadequate metal thicknesses of the eraser plate  402  and the beams  404 , and their resulting inability to resist bending moment deflections imposed by dot pin drag forces. Part of the difficulty was from working with legacy dot pin dimensions. Therefore, in configuring an erasing mechanisms  400  especially for multi-line TCMs, the following are recommended: 
     A. Accurately determine dot pin  100  drag forces 
     B. Configure a robust one-piece channel-shaped beam structure for the erasing mechanism  400 . This configuration may require drilling or laser cutting the 8-dot cell hole patterns  204 . 
     C. Lengthen the lower diameter section  112  of the dot pins  100  to accommodate the increased metal thickness of the erasing mechanism  400 . 
     In the second variation shown in FIG. 8, the erasing mechanism  400  includes the erasing plate  402  as described above and two cam rods  412 . The cam rods  412  are located between the bottom retention plate  200  and the erasing plate  402  along the length of their sides. To erase the display, the twin rods  412 , with cam-shaped cross-sections, are given a 90 degree angular rotation, thereby exerting a uniformly distributed separating force along the entire length of the sides of the erasing plate  402  and the bottom retention plate  200 . The erasing plate  402  is still subject to the same bending as that of the first variation noted above. The cam rods  412  must be of sufficient cross-section to resist torsional twist. 
     The twin cam rods  412  have geared ends  414  that mesh with a drive pinion  416  located midway between them. The drive pinion  416  has a spring  418  to return the drive pinion from its rotated position back to its normal position. A 90 degree rotation of the drive pinion  416  causes the cam rods  412  to rotate 90 degrees, forcing the erasing plate  402  and the dot pins  100  to move downward relative to the retention plate  200 , thereby erasing the TCM display. The erasing plate is floated and supported on springs  420  to lift the erasing plate back up against the bottom retention plate  200  after erasing occurs. 
     In a third variation of erasing mechanism shown in FIGS. 9A,  9 B and  9 C, twin tapered wedges  422  are moved laterally inwards towards one another to increase the vertical space between the erasing plate  402  and the bottom retention plate  200 , thereby erasing the display. The wedges  422  are moved by linear actuators  424 . The actuators  424  can be operated by mechanical, electrical, pneumatic, or other means and can have mechanical springs  426  to return the wedges to their normal outward position. 
     The linear motion undercarriage  600  in the embodiment shown in FIGS. 4A,  6 A,  6 B and  6 C can be any one of several commercially available linear motion devices such as a Thomson Miniature Accu-Glide Model 10. The undercarriage  600  includes a carriage  602  that moves linearly along a fixed guide  604 . 
     An electric drive motor  700  shown in FIGS. 7A,  7 B and  7 C can be any one of several miniature commercially available reversing d.c. electric motors, commonly used in various printing devices. The motor  700  is mounted underneath one end of the TCM display, vertically between the retention plates  200  and the linear motion undercarriage  600 . The electric drive motor  700  is fitted with a toothed drive pulley  702  for driving a toothed power transmission belt  802 . During the printing mode, the electric drive motor  700  drives the traveling printhead  300  along the linear motion undercarriage  600 . Because, the motor  700  is reversible, it enables the traveling printhead  300  to print the Braille display in either direction of travel. 
     As further seen in FIGS. 7A,  7 B and  7 C, the belt power transmission system  800  includes a lightweight, toothed, plastic power transmission belt  802 , a fixed pulley  804 , an idler pulley  806 , pulley mounting brackets  808 , a spring loaded belt tensioning mechanism  810 , and a belt coupling clamp  812 . The belt  802  is held in tension by the tensioning mechanism  810  against the drive, fixed, and idler pulleys  702 ,  804 , and  806  and is coupled to the traveling printhead  300  via the belt coupling clamp  812 , such that electric motor  700  operation transforms motor  700  output shaft rotational motion into linear motion along the linear motion undercarriage  600 . The structural relationship of the undercarriage  600  and the printhead  300  is shown in FIGS. 6A,  6 B and  6 C. 
     As seen in the various figures, a support structure  900  such as the framework of the TCM serves as a foundation and mounting base for all other parts. Location of functional parts relative to one another is accomplished through precision machining and provision of vernier adjustment capabilities. 
     The user interface for the erasing mechanism  400  is a hand operated electronic switch that is surface mounted on the outer casing of the TCM, so as to be easily and readily accessible to the user for the purpose of erasing the Braille display. This normally open switch, when closed, connects an external TCM power supply to the devices that erase the display, e.g., the electro mechanical solenoids. 
     A standard computer interface is connector-mounted on the traveling printhead  300  and connects the TCM to a standard computer. The printhead solenoid  302  and optical switch  308  are hard wired to the connector. The outer casing of the TCM is a conformal shell or wrapper that provides a smooth interface for the user while preventing the user from exposure to the inner workings of the TCM. 
     The computer can be any computer which is compatible with the computer command and control electronics software adapted for the TCM. The computer command and control electronics hardware and software permits the user to read, write, and edit computer documents. 
     As can be understood from a review of FIGS. 4A,  4 B and  4 C, as the printhead  300  travels linearly underneath the TCM display, the optical switch  308  lines up sequentially with one of a series of holes in the timing reference plate  310 . The linear spacing of the holes in the timing reference plate  310  is identical to the linear spacing of holes  201  and pins  200  in the retention plates  200  and in the eraser plate  402 . Just an instant before precise optical alignment occurs, the solenoids  302  mounted on the print head  300  fire against the dot pins  100  and thereby display Braille text. The solenoids  302  receive the signal to fire from the computer and the electronic control and software package. 
     The TCM provides means for a blind person to incrementally read, write, or edit a computer document directly from a display, rather than from paper. Thus, a blind person is enabled to read books, magazines, newspapers, and other articles of interest without being encumbered by paper. Further, a blind person is enabled to compose or edit computer documents in much the same way sighted computer users do. 
     There has been disclosed heretofore the best embodiment of the invention presently contemplated. However, it is to be understood that the various changes and modifications may be made thereto without departing from the spirit of the invention. 
     For example, more rows and cells could be added, or the TCM could be reduced to a single line display device, or other departures could be made from the descriptions made of various preferred embodiments. 
     In another example, a display consisting of a single sheet of material such as polyethylene containing Braille cells formed in a pattern of binary flaps, hemispheres, or other shapes that are arranged in an ASCII 8 bit 256 symbol code are used in lieu of the combination of dot pins  100  and retention plates  200 . The hemisphere bubbles are pushed up or down to display or erase Braille text after a manner developed above or utilizing peg punch technology.