Abstract:
A tactile measuring instrument to be used primarily to measure and produce geometric quantities without use of sight, wherein a sliding jaw is configured to move over a guide to adjust the instrument to desired measurement, a mechanically controlled display mechanism is configured to place within tactile perception selected tactile forms or Braille dots, and condensed representation of tactile forms is configured to control display mechanism such that the numerical value of measurement is displayed; and because tactile forms are condensed and more may be packed in the same area, the instrument has high precision. As the display mechanism is small, lightweight and hidden, the instrument is small, portable and simple; and as all information is presented in Braille, it is quick-to-use and convenient. With different configurations of display mechanism and condensed tactile forms, the device may be used for applications other than measurement as well.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/920,838, filed Dec. 26, 2013, the disclosure of which is incorporated herein by reference. 
     
    
     FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable 
       FIELD OF THE INVENTION 
       [0003]    The present invention relates to measuring instruments to enable reading of measurements by identification of tactile forms and features, and more particularly, but not exclusively, by identification of Braille characters. Although the first embodiment of the measuring instrument uses a rigid linear guide to measure distances along straight lines, other embodiments may use a rigid angular guide, for example, to measure angles or non-rigid guides, for example, to measure distances along non-uniform lines. Although the discussed embodiments of the measuring instruments display measurements in Braille, other embodiments may display measurements in other appropriate tactile forms consisting of, but not limited to, dots, lines, shapes and textures. 
         [0004]    The present invention also relates to mechanical tactile displays to enable condensed representation of tactile forms on a surface, and to enable rendering, of the said condensed representation, to discernable tactile forms for a user to read or perceive. Although the discussed embodiments of the mechanical tactile display are as measuring instruments, other embodiments may be as devices with said mechanical tactile displays for applications other than measurement. 
       BACKGROUND OF THE INVENTION 
       [0005]    There are a number of traditional tactile measuring instruments available that are used by persons with blindness to measure lengths and angles in order to interpret or produce geometric features and constructions. Available as rulers and protractors, such instruments have tactile markings permanently etched, embossed or engraved on their surface. Adjacent tactile markings are spaced adequately so that users are able to distinguish between them by touch. Traditional instruments are therefore limited in precision. Precision of an instrument is related to its least count, which is the smallest change in measured dimension that can be resolved with the use of the instrument. Precision is higher for instruments with relatively smaller least counts. Least count of traditional tactile rulers is usually equal to or greater than half of a centimeter or to one-fourth of an inch, depending on the unit of measurement. That of traditional tactile protractors is usually equal to or great than five degrees. A few that have smaller least counts are difficult to use by touch. Some such traditional instruments also have embossed Braille characters accompanying the tactile markings to indicate the value of measurement at corresponding markings Due to the size of Braille characters and the limited space available, they accompany only some select markings. For other markings, value of the measurement is identified by counting the number of preceding markings To a Braille user, counting may be slower than reading Braille and may require more mental effort and concentration. Thereby, the use of traditional instruments is slow and inconvenient. 
         [0006]    A few tactile measuring instruments give precision higher than that of the traditional ones. Some such rulers have a threaded shaft with pitch length equal to the desired least count. Auditory or tactile cues are generated mechanically with each rotation of the shaft. These cues are counted to identify the measurement. Other such rulers, as described in U.S. Pat. No. 4,328,618 and U.S. Pat. No. 4,614,042, use gauge elements or tabs with one physical dimension equal to the least count. Unlike traditional tactile measuring instruments, such instruments may have a smaller least count and therefore higher precision. However, they are usually larger and heavier. Further, Braille characters, if any, indicate only coarse values of measurement. Fine values of measurement are still identified by counting tactile markings or auditory cues. Thereby, similar to traditional instruments, their use is also slow and inconvenient. 
         [0007]    Some measuring instruments have electronic systems that read out measurements either as discrete beeps or as synthetic speech. Compared to tactile measuring instruments, these auditory instruments have a higher accuracy. However, they run on a battery or an external power source, and are not suitable for all environments and situations of use. For instance, they are difficult to use in noisy environments and also when the user has other active sources of auditory information. Further, they are usually more expensive and delicate. 
         [0008]    The technique and designs of this invention, on the other hand, readily and simply overcome these limitations both in the area of tactile measuring instruments and in the more general area of condensed representation of tactile forms. They preferably involve the use of a guide, a sliding jaw and a display mechanism for presenting values of measurements in Braille or other appropriate tactile forms. They are such that the accuracy of measurement is not limited either by the user&#39;s ability to distinguish between adjacent tactile markings or by the size of Braille characters. The effect of this is that the instruments may have a smaller least count and therefore higher precision. Braille characters, or other appropriate tactile forms, indicate the complete value of measurement rather than only the coarse value. This overcomes the need to count individual markings, which otherwise makes instruments slow and inconvenient to use. Auditory cues, generated with every change of measurement, supplement the tactile output. This informs users of desired or undesired changes in measurement and thereby prevents errors. With only a few small parts, the instrument is not large and heavy. Unlike measuring instruments with electronic systems, it does not require a battery or an external power source. Also, it is not as expensive and is less delicate. Further, it can be used even in noisy environments and also when users have other active sources of auditory information. 
       SUMMARY 
       [0009]    An object of the present invention is to provide a novel method or technique for tactile measurement for attaining above described novel features while obviating the limitations of prior instruments of this type. 
         [0010]    Another object of the present invention is to provide such novel tactile measuring instruments that can be operated without the use of sight, to measure geometric quantities for interpreting existing geometric features or to produce new ones. 
         [0011]    Yet another object of the present invention is to provide, through examples of tactile measuring instruments, a novel method or technique for condensed representation of tactile forms on a surface, and for rendering of the said condensed representation to discernable tactile forms. 
         [0012]    Accordingly, in the present invention there is provided a tactile measuring instrument wherein a display mechanism functions in accordance with the value of measurement and places appropriate tactile forms that indicate the value, within tactile perception. In one embodiment, the instrument has a sliding jaw that may move over a guide to correspond to a measured length. A display mechanism attached to the sliding jaw controls the position of multiple Braille dots and selectively places them within or without tactile perception. The Braille dots that are positioned within perception are selected according to a condensed representation of Braille numbers on the guide. The numbers correspond to the value of measurement or a part of the value. A user tactually reads the numbers displayed in Braille to accurately interpret the measurement. 
         [0013]    As tactile forms are represented on the guide in a condensed manner, more tactile forms can be packed in the same area. This allows a higher precision in tactile measuring instruments compared to traditional instruments. As the mechanism to render the condensed tactile forms into tactually readable forms is small, lightweight and hidden, the instruments are small, portable and simple. As all information is presented preferably in Braille, the instruments are quick and convenient to use. Further, as the mechanism is not reliant on electronic systems, it is low-cost and independent from power sources. 
         [0014]    Additional objects and advantages of the present invention will be brought forward in and in part will be obvious from the drawings, the brief description and the detailed description herein. 
     
    
     
       DRAWINGS 
         [0015]    The present invention can be best understood in conjunction with the accompanying drawings, in which: 
           [0016]      FIG. 1  is a perspective view of a tactile measuring instrument formed as a linkage of a rigid linear guide and a sliding jaw in accordance with one embodiment; 
           [0017]      FIG. 2  is an orthographic projection in top view of the tactile measuring instrument of  FIG. 1 ; 
           [0018]      FIG. 3  is an orthographic projection in top view of the tactile measuring instrument of  FIG. 1 , illustrating range of movement of sliding jaw relative to guide; 
           [0019]      FIG. 4  is an illustration of the representation of numerical digits in Braille; 
           [0020]      FIG. 5  is an orthographic projection in top view of an alternative design of tactile measuring instrument; 
           [0021]      FIG. 6  is an exploded view of the tactile measuring instrument in  FIG. 1 ; 
           [0022]      FIG. 7A  is a partial sectional view of the tactile measuring instrument in  FIG. 1 , showing display mechanism with a Braille pin in downward state; 
           [0023]      FIG. 7B  is a partial sectional view showing display mechanism of  FIG. 7A  with a Braille pin in upward state; 
           [0024]      FIG. 8  is a partial sectional view of the tactile measuring instrument in  FIG. 1  illustrating the movement of a tooth between two resting positions; 
           [0025]      FIG. 9A  is a partial sectional view showing an alternative design of display mechanism with a Braille pin in downward state; 
           [0026]      FIG. 9B  is a partial sectional view showing display mechanism of  FIG. 8A  with a Braille pin in upward state; 
           [0027]      FIG. 10A  is a partial sectional view showing another alternative design of display mechanism with a Braille pin in downward state; 
           [0028]      FIG. 10B  is a partial sectional view showing display mechanism of  FIG. 9A  with a Braille pin in upward state; 
           [0029]      FIG. 11A  is a partial sectional view showing yet another alternative design of display mechanism with a Braille pin in downward state; 
           [0030]      FIG. 11B  is a partial sectional view showing display mechanism of  FIG. 10A  with a Braille pin in upward state; 
           [0031]      FIG. 12  is an orthographic projection in top view of display mechanism of the tactile measuring instrument in  FIG. 1 ; 
           [0032]      FIG. 13  is an illustration of virtual division of a track into rows and columns for the tactile measuring instrument in  FIG. 1 ; 
           [0033]      FIG. 14  is an illustration of virtual division of the track into rows and columns, and the layout of lands and benches for the tactile measuring instrument in  FIG. 1 ; 
           [0034]      FIG. 15  is an orthographic projection in top view of still another alternative design of display mechanism; 
           [0035]      FIG. 16  is an illustration of virtual division of a track into rows and columns on a guide that is according to the display mechanism in  FIG. 15 ; 
           [0036]      FIG. 17  is an orthographic projection in top view of a tactile measuring instrument formed as a linkage of a rigid angular guide and a sliding jaw in accordance with another embodiment; 
           [0037]      FIG. 18  is a perspective view of a tactile measuring instrument formed as a linkage of a sliding measuring tape and a housing in accordance with yet another embodiment; 
           [0038]      FIG. 19A  is an orthographic projection in top view of a display mechanism for display of one character or symbol in Braille with maximum four dots; 
           [0039]      FIG. 19B  is orthographic projection in top view of a display mechanism for display of one character or symbol in Braille with maximum six dots; 
           [0040]      FIG. 19C  is an orthographic projection in top view of a display mechanism for display of one character or symbol in Braille with maximum eight dots; 
           [0041]      FIG. 20A  is an orthographic projection in top view of another display mechanism for display of a character or symbol in Braille with maximum six dots; 
           [0042]      FIG. 20B  is an orthographic projection in top view of yet another display mechanism for display of a character or symbol in Braille with maximum six dots; 
           [0043]      FIG. 20C  is an orthographic projection in top view of still another display mechanism for display of a character or symbol in Braille with maximum six dots; 
           [0044]      FIG. 21A  is an orthographic projection in top view of a display mechanism for display of two adjacent characters or symbols in Braille with maximum four dots each; 
           [0045]      FIG. 21B  is an orthographic projection in top view of a display mechanism for display of two adjacent characters or symbols in Braille with maximum six dots each; 
       
    
    
       [0046]    In the drawings, embodiments of the invention are illustrated by way of example, it being expressly understood that the description and drawings are only for the purpose of illustration and preferred designs, and are not intended as a definition of the limits of the invention. 
       DETAILED DESCRIPTION 
       [0047]    First embodiment of the present invention is a tactile measuring instrument to measure length along a straight line and to draw straight lines of known lengths.  FIG. 1  is a perspective view of this embodiment formed as a linkage between rigid linear guide  100  and sliding jaw  200 , shown with measuring contact  201  at a distance from measuring contact  101  of guide  100 .  FIG. 2  is an orthographic projection in top view of the first embodiment. Display mechanism  300  is linked to sliding jaw  200  and is in physical contact with track  102  on top surface  103  of guide  100 . Braille pins  301  of display mechanism  300  are concentric with through holes  202  on display surface  203  of sliding jaw  200 . Braille characters  204  are permanently embossed on display surface  203 . Track  102  is composed of appropriate elevations and depressions etched, embossed or engraved on top surface  103  of guide  100 . Tactile markings or divisions  104  are marked on top surface  103  along back edge  106 . Braille characters  105  are permanently embossed along each division  104 . 
         [0048]      FIG. 3  is an orthographic projection in top view of the first embodiment illustrating the range of movement of sliding jaw  200  with respect to guide  100 . Sliding jaw  200  rests and slides on sliding contacts, not shown, along back edge  106  and front edge  107  of guide  100 . Distance between measuring contacts  101  and  201  along back edge  106  corresponds to the measured length. Sliding jaw  200  may be moved relative to guide  100  to change this distance. The maximum length that ought to be measured determines the range of motion. Accordingly, length of the guide may be equal to or different from the length of guide  100  of the first embodiment. In operation, guide  100  may be held stationary against a plane on its back surface, not shown, or held in the user&#39;s hand and force may be applied on sliding jaw  200 . Component of the force parallel to edges  106  and  107  of guide  100  may move it in a direction towards and not beyond positions illustrated in  FIG. 3 . Similarly, sliding jaw  200  may be held in the user&#39;s hand and force may be applied on guide  100  to move it in either direction. 
         [0049]    For the purpose of precision, a measurement is split into coarse and fine measurements with different least counts. For measurement of length in imperial system of units, coarse measurements can be in whole inches and fine measurements can be in fractions of an inch. For metric units, coarse measurements can be in whole centimeters and fine measurements in millimeters or fractions of a centimeter. In the first embodiment, length is measured in imperial units and therefore, coarse measurements are in inches and fine measurements in sixteenths of an inch. The least count of coarse measurements is one inch and that of fine measurements is one-sixteenth of an inch. Alternative designs, not shown, of the first embodiment may have different unit systems and least counts of coarse and fine measurements. In the first embodiment, coarse measurements are read from top surface  103  of guide  100  and fine measurements are read from display surface  203  of sliding jaw  200 . Alternative designs, not shown, may have both the coarse and fine measurements read from the display surface of the sliding jaw. 
         [0050]    In the first embodiment, coarse measurements are indicated with tactile markings or divisions  104  and corresponding Braille characters  105 . First of divisions  104  has its center aligned with the edge of measuring contact  101 . The corresponding Braille character reads as number zero. Subsequent divisions  104  are spaced so that their centers are precisely at all whole inches from the center of the first division. Braille characters  105  next to each division read as numbers indicating corresponding divisions&#39; distance from the first division in inches. In an alternative design, not shown, for measurement of length in metric units, the divisions may be spaced at whole centimeters and Braille characters may indicate the distance accordingly. In other alternative designs, not shown, tactile markings or divisions may be marked on surfaces other than the top surface, along edges other than the back edge, along multiple edges, or not along any particular edge. Braille characters, or other tactile or visual features, may accompany the markings. 
         [0051]    In the first embodiment, fine measurements are indicated as fractions with numerator, slash sign and denominator in Braille. Braille pins  301 , of which only some select pins are within perception when display surface  203  is touched, present the numerator. In the first embodiment, the select pins form appropriate numbers, from zero to fifteen. They are determined and operated by the interaction of display mechanism  300  and track  102 . Embossed Braille characters  204  on display surface  203  form the slash sign and the denominator. The denominator is sixteen in the first embodiment. In an alternative design, not shown, for measurement of length in metric units, the select pins may form numbers from zero to nine and the denominator may be ten. In other alternative designs, not shown, the fine measurement may be displayed in forms other than fractions. Embossed Braille characters on display surface may be read as characters other than slash signs or numerals, or may be absent altogether. 
         [0052]    Braille characters are formed by spatial arrangements of one or more tactile dots. For any Braille script standard, characters have unique arrangements of dots. All characters can be shown with a maximum of six dots (or eight dots in some codes and standards) distributed in two columns and three rows (or two columns and four rows in some standards). Characters in a line and lines of multiple characters are spaced according to standards in order to be distinguishable by touch. Numerical digits and mathematical symbols are also represented in Braille.  FIG. 4  is an illustration of the representation of numerical digits zero to nine in Braille. The circles represent raised dots that form the digits. According to many Braille script standards, representation of numerical digits requires a maximum of four dots, in two columns and two rows, per digit. In alternative designs, not shown, Braille codes and standards other than those employed in the first embodiment may be used to represent characters in Braille. 
         [0053]    In the first embodiment, as illustrated in  FIG. 3 , Braille pins  305 - 309  and through holes  202  are in a certain layout so as to display any number from zero to fifteen on display surface  203 . Four Braille pins  305 - 308  may display any number from zero to nine. Braille pin  309  may display either display no number or only the number one. As value of fine measurement changes with movement of sliding jaw  200  relative to guide  100 , Braille pins  305 - 309  appropriately move between upward and downward positions, and thereby within or without perception, to change the displayed fine measurement. A user may find it convenient to have the display change dynamically as measured distance changes. In alternative designs, not shown, the user may have the choice to control when the Braille pins display or when they change. 
         [0054]      FIG. 5  is an orthographic projection in top view of an alternative design of the first embodiment. It is shown with a finite distance between measuring contact  121  of guide  120  and measuring contact  221  of sliding jaw  220 . The figure illustrates features that add to the first embodiment&#39;s function and usability. Locking screw  222  may be used to lock sliding jaw  220  at any position within range of movement relative to guide  120 . In other embodiments, not shown, clips, pins, pawls, compliant members or alternatives of the like may be used to similarly lock or partially restrain sliding jaw  220  at any position. Roller  223  is attached to sliding jaw  220 . When roller  223  is in frictional contact with top surface  122  of guide  120  and is rotated, it may move sliding jaw  220  with respect to guide  120 . The direction of motion depends on the direction of rotation of roller  223 . A user may use roller  223  to change measured distance slowly. In alternative designs, not shown, the roller may be in frictional contact with front or the back surfaces, not shown, or may be replaced with a pinion over a rack or alternatives of the like for the same or similar function. Through hole  123  in projection  124  on guide  120  and through hole  224  in projection  225  on sliding jaw  220  may be used to calibrate other measuring and drawing instruments with pointed or needle-like ends, drawing compass for example, to the measured length. The distance between centers of through holes  123  and  224  is equal to that between measuring contacts  121  and  221 . Projections  124  and  225  may be in different planes so that they align when measuring contacts  121  and  221  are in contact. 
         [0055]      FIG. 6  is an exploded view of the first embodiment. The figure illustrates the structure of display mechanism  300  and its position and orientation with respect to sliding jaw  200  and guide  100 . In display mechanism  300 , Braille pins  301  and teeth  303  are physically attached to, or are parts of, respective members  302 . All members  302  are attached to, or are parts of, base  304 . Display mechanism  300  is assembled with sliding jaw  200 . For the purpose of assembly, base  304  of display mechanism  300  is attached to sliding jaw  200  by the use of adhesives, mechanical fasteners, snap-fits, or other joining technique of the like. The assembly is such that Braille pins  301  and through holes  202  are concentric. The subassembly of display mechanism  300  and sliding jaw  200  is further assembled with guide  100 . The assembly is such that sliding jaw  200  may slide along guide  100  and teeth  303  may rest on track  102  in individual rows. The sliding jaw may be retained on the guide using physical constraints, not shown, such as snap fits, clips, pins, pawls, compliant members or alternatives of the like. In alternative designs, not shown, the assembly sequence may be different and sliding jaw and display mechanism may be fabricated as a single part. 
         [0056]      FIGS. 7A and 7B  are partial sectional views of the first embodiment. They illustrate the working of display mechanism  300  by showing a member  302 , a Braille pin  301  and a tooth  303  with respect to sliding jaw  200  and guide  100 . In  FIG. 7A  Braille pin  301  is in downward position and not perceivable to touch on display surface  203 . Tooth  303  rests on land  108  in track  102 . In  FIG. 7B  Braille pin  301  is in upward position and perceivable to touch on display surface  203 . Tooth  303  rests on bench  109  in track  102 . Track  102  is composed of lands  108  and benches  109 , which are surfaces on two separate parallel planes. Member  302  connects tooth  303  and Braille pin  301  in such a way that when tooth  303  rests on land  108 , Braille pin  301  is in the downward position, and when tooth  303  rests on bench  109 , Braille pin  301  is in the upward position. In the first embodiment, member  302  is compliant and is rigidly attached to, or is a part of, base  304 . It bends approximately as a beam in response to strain applied at tooth  303 . The resting position of tooth  303  changes between bench  109  and land  108  as display mechanism  300 , attached to sliding jaw  200 , moves with respect to track  102  of guide  100 . With the change in resting position, the strain applied on compliant member  302  changes and as a result, the member&#39;s bending profile changes. With it the position of Braille pin  301  changes with respect to display surface  203 . 
         [0057]    The display mechanism  300 , and particularly compliant member  302  are designed to facilitate proper display function. For proper function, Braille pins  301  should move a certain minimum distance between upward and downward positions. The distance is determined by the height of Braille pins specified in the chosen Braille standard, and additionally by the preferred clearance below display surface  203 . Further, Braille pins  301  should require a certain minimum downward force to be displaced from their upward position. This force is usually a result of pressure applied by fingers when observing the display surface by touch. A recommended minimum downward force is thirty grams per Braille dot. With appropriate materials, dimensions and cross-sectional shape of members  302 , and appropriate positions of teeth  303  and Braille pins  301  on members  302 , the requirements can be easily met. Deriving these parameters to be appropriate is obvious to those skilled in the art. In the first embodiment, members  302  preferably have a rectangular cross section and are composed of a polymer, a metal, or a combination of both. For appropriate stiffness, compliant members  302  may have a bent or twisted natural position, not shown, and may act as a spring to the applied strain. 
         [0058]      FIG. 8  is a partial sectional view of the first embodiment illustrating the movement of teeth  303  between their two resting positions, lands  108  and benches  109 , on track  102 . In the first embodiment, teeth  303  are triangular prisms, each with one rounded edge  310  and two flat faces  311  and  312 . A cross-section of track  102  may contain multiple lands  108  and benches  109 . Along a row in a track, adjacent lands  108  and benches  109  are connected by inclined planes  110 . When a tooth  303  is at rest, rounded edge  310  touches either a land  108  or a bench  109 . When tooth  303  changes position between land  108  and bench  109 , flat face  311  or  312 , depending on direction of motion, touches inclined plane  110  and moves along it. In the first embodiment, flat faces  310  and  311  have the same slopes as inclined planes  110 . Therefore, as tooth  303  moves between land  108  and bench  109 , it moves at an angle determined by the slope of inclined plane  110 . The slope of inclined plane  110  affects the speed with which Braille pins  301  change states between the upward and downward positions. It also affects the force required to move sliding jaw  200  along guide  100 . In alternative designs, not shown, the shape and geometry of teeth may be spherical, conical, cylindrical or another appropriate profile. Also, the inclined planes may have varying slopes or may be rounded. 
         [0059]      FIGS. 9A and 9B  illustrate the working of an alternative design of the display mechanism. Similar to display mechanism  300  of the first embodiment, display mechanism  330  is composed of Braille pins  331 , members  332 , teeth  333  and base  334 . In contrast to members  302 , members  332  may have a circular cross-section and are preferably made out of a wire. Teeth  333  are parts of respective members  332  and are formed by appropriate plastic deformation or shaping of the wires. Functionally similar to mechanism  300 , mechanism  330  operates by bending of compliant members  332  according to their stiffness and geometry. In alternative designs, not shown, display mechanism  330  may constitute of compliant members made of different materials or combination of materials and with constant or varying cross-section shapes and areas. 
         [0060]      FIGS. 10A and 10B  illustrate the working of another alternative design of the display mechanism. Similar to display mechanism  300  of the first embodiment, display mechanism  340  is composed of Braille pins  341 , members  342 , teeth  343  and base  344 . In contrast to members  302 , mechanism  340  has revolute joints  346  between members  342  and base  344 . Helical compression springs  345  are placed between members  342  and bottom surface  205  of sliding jaw  200 . Functionally similar to mechanism  300 , mechanism  340  operates by rotation of members  342  about respective revolute joints  346  according to their geometry and the stiffness of springs  345 . 
         [0061]      FIGS. 11A and 11B  illustrate the working of yet another alternative design of the display mechanism. Similar to display mechanism  300  of the first embodiment, display mechanism  350  is composed of Braille pins  351 , members  352 , teeth  353  and base  354 . However, members  352  and base  354  are coupled via torsion springs  355  rather than revolute or rigid joints. Functionally similar to mechanism  300 , mechanism  350  operates by movement of members  352  according to their geometry and the stiffness of springs  355 . Still other embodiments, not shown, of the display mechanism may have combinations of rigid and compliant members, helical and torsion springs and attached or separate Braille dots. 
         [0062]      FIG. 12  is an orthographic projection in top view of display mechanism  300  of the first embodiment. Members  302  are connected with teeth  303  and Braille pins  305 - 309 , respectively. All members  302  are connected with a common base  304 .  FIG. 13  illustrates virtual division of track  102  into rows  111  and columns  112 . Width of individual virtual columns  112  is equal to the least count of the instrument. In the first embodiment, their width is equal to one-sixteenth of an inch. Widths of virtual rows  111  are such that they accommodate the widths of teeth  303  of display mechanism  300 . When assembled, as in  FIG. 2 , display mechanism  300  is over guide  100  and teeth  303  rest on track  102 . Each tooth  303  occupies one virtual row  111  and moves along it as sliding jaw  200  moves with respect to guide  100 . Virtual rectangles  113 - 117  on track  102  in  FIG. 13  illustrate the positions at which teeth  303  contact track  102  for one position of sliding jaw  200 . Either a land  108  or a bench  109  is created in individual virtual rectangles  113 - 117  to thereby display a number appropriate for that position of sliding jaw  200 . 
         [0063]    In the first embodiment, for change in measurement by one inch, starting from an absolute inch, the numerator of the fine measurement displayed on display surface  203  changes from zero to fifteen and starts again at zero.  FIG. 14  illustrates the part of track  102  that, as per the first embodiment, is responsible for determining the display of fine measurements in Braille for measurements between zero and one inch. The figure illustrates virtual division of track  102  into rows  111  and columns  112 . Since all teeth  303  are not in one column, as illustrated in  FIG. 13 , rows  111  are offset from each other. The placement of lands  108  and benches  109  in each virtual rectangle in accordance with the first embodiment is also shown. The virtual rectangles that are darkened correspond to lands  108 , and those that are not correspond to benches  109 . The distribution of lands  108  and benches  109  in  FIG. 14  represents the layout of track  102  for fine measurement between zero and one inch. The pattern is serially repeated for fine measurements between other inches. 
         [0064]      FIG. 15  is an orthographic projection in top view of an alternative design of display mechanism. Although display mechanism  810  principally provides the same function as that provided by display mechanism  300  in the first embodiment, its additional features provide a higher accuracy to the instrument. Display mechanism  810  has members  811 , teeth  812 , additional member  813  and additional tooth  814 . Additional member  813  has no associated Braille pin and may differ from members  811  in shape, size, form, structure and material. Additional tooth  814  may differ from teeth  812  in shape and size.  FIG. 16  is an illustration of virtual divisions of track  131  into rows and columns on guide  130 , which is according to display mechanism  810 . Track  131 , illustrated with virtual divisions into rows and columns, has an additional row  132 . Tooth  814  occupies row  132  and moves along it as the sliding jaw moves with respect to guide  130 . Virtual columns divide row  132  into virtual rectangles. Each virtual rectangle in row  132  is a land, and walls, not shown, separate adjacent lands. Therefore, tooth  814  always rests on a land and moves over a separating wall to go to an adjacent land. When tooth  814  moves over a wall, strain of member  813  changes and so does its bending profile. The effect of this is that mechanism  810  resists continuous movement and tends to be more stable at discrete positions where tooth  814  rests over a land. Resistance offered by mechanism  810  and its stability at discrete positions principally depends on stiffness of member  813  to bending. Other factors including shape and size of tooth  814  and separating walls also affect resistance and stability. In addition to improving the precision of the instrument, the additional features make the instrument easier to control and use. The sound created by tooth  814  as it moves over separating walls may give an auditory cue to the user, thereby helping the user in operating it. Auditory cues, generated with every change of measurement, supplement the tactile output. This informs users of desired or undesired changes in measurement and thereby prevents errors. 
         [0065]    Second embodiment of the present invention is an instrument to measure angles between straight lines or to draw straight lines at known angles between them.  FIG. 17  is an orthographic projection in top view of this embodiment illustrating a linkage between rigid angular guide  400  and sliding jaw  500  shown with a non-zero angle between measuring contact  401  of guide  400  and measuring contact  501  of sliding jaw  500 . Display mechanism, not shown, is attached to sliding jaw  500  and is in physical contact with track  402  on top surface  403  of guide  400 . Tactile markings or divisions  404  are marked on top surface  403  along outer edge  405 . Braille characters, not shown, may accompany individual tactile markings In an alternative design of second embodiment, not shown, the divisions may be along inner edge  406 . In the second embodiment, angles are measured in degrees. Coarse measurements are in multiples of ten degrees and fine measurements in whole degrees. Alternative designs, not shown, may have different units and least counts of coarse and fine measurements. In the second embodiment, coarse measurements are read from top surface  403  of guide  400  and fine measurements are read from display surface  502  of sliding jaw  500 . Alternative designs, not shown, may have both coarse and fine measurements read from the display surface of the sliding jaw. 
         [0066]    The display mechanism, not shown, and track  402  in the second embodiment is similar to display mechanism  300  and track  102  of the first embodiment, but with obvious differences according to difference in units and sliding motion. Layout of lands and benches on track  402  is not shown in  FIG. 17 . However, that should be obvious to a person skilled with the teaching provided of the same for the first embodiment. Operation of the measuring instrument in the second embodiment is similar to the operation of the measuring instrument of the first embodiment with obvious differences according to design. 
         [0067]    Third embodiment of the present invention is an instrument similar to a tape measure for measurement of length along non-uniform lines.  FIG. 18  is a perspective view of this embodiment illustrating a sliding measuring tape  600 , and a housing  700  with a part of tape  600  outside housing  700  and the rest, not shown, coiled inside it. Display mechanism, not shown, is linked to housing  700  and is in physical contact with track  601  on top surface  602  of tape  600 . Tactile markings or divisions  603  are marked on top surface  602 . Braille characters, not shown, may accompany individual tactile markings Coarse measurements are read from top surface  602  of tape  600  and fine measurements are read from display surface  701  of housing  700 . Alternative designs, not shown, may have both coarse and fine measurements read from the display surface of the housing. 
         [0068]    The scope of the present invention is not limited to the three embodiments of measuring instruments discussed so far. Other embodiments may relate to mechanical tactile displays to enable condensed representation of tactile forms on a surface, and to enable rendering of the said condensed representation to discernable tactile forms for a user to read or perceive. The tactile forms may be Braille characters or may be other forms, consisting of, but not limited to, dots, lines, shapes and textures. Embodiments may not be limited to measuring instruments alone. They may be of other devices with said mechanical tactile displays. 
         [0069]    In the first embodiment, track  102  is a form of condensed representation of appropriate numerical digits on top surface  103  of guide  100 . Display mechanism  300  enables rendering of the digits represented on track  102  to Braille characters on display surface  203  of sliding jaw  200 . Other embodiments within the scope of the invention may have parts and structures that perform functions similar to those performed by track  102 , display mechanism  300  and display surface  103  of the first embodiment, but may not be limited to them. 
         [0070]    The design of a display mechanism is according to the tactile forms that are to be displayed. In the first, second and third embodiments, the design of respective display mechanisms is according to display of numerical digits in Braille.  FIG. 19A  shows display mechanism  820  meant for display of any digit ranging from zero to nine in Braille. Four members  822  are attached to four Braille pins  821  and four teeth  823 .  FIG. 19B  shows a display mechanism  830  according to display of any character or symbol in Braille, according to standards that use a maximum of six dots per character. Six members  832  are attached to six Braille pins  831  and six teeth  833 .  FIG. 19C  shows a display mechanism  840  meant for display of any character or symbol in Braille, according to standards that use maximum eight dots per character. Eight members  842  are attached to eight Braille pins  841  and eight teeth  843 . 
         [0071]    The design of a display mechanism is also according to space available, direction of motion and layout of condensed tactile forms.  FIG. 20A  shows a display mechanism  850 . Six members  852  are attached to six Braille pins  851  and six teeth  853 .  FIG. 20B  shows a display mechanism  860 . Six members  862  are attached to six Braille pins  861  and six teeth  863 .  FIG. 20C  shows a display mechanism  870 . Six members  872  are attached to six Braille pins  871  and six teeth  873 . Like mechanism  830  in  FIG. 19B , mechanisms  850 ,  860  and  870  are also for display of characters or symbols in Braille with maximum six dots per character. Space available, direction of motion and layout of condensed tactile forms may govern which of these or other designs are best suited for a particular application. 
         [0072]      FIG. 21A  shows a display mechanism  880  meant for display of two adjacent numerical digits, each ranging from zero to nine, in Braille. Eight members  882  are attached to eight Braille pins  881  and eight teeth  883 . Other designs, not shown, may be according to display of more than two digits in Braille.  FIG. 21B  shows a display mechanism  890  meant for display of two adjacent characters or symbols in Braille with maximum six dots per character. Twelve members  892  are attached to twelve Braille pins  891  and twelve teeth  893 . Other designs, not shown, may be according to display of more than two adjacent characters in Braille. 
         [0073]    It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. Further modifications of the invention will also occur to persons skilled in the art and all such are deemed to fall within the spirit and scope of the invention. 
         [0074]    Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.