WO2013179311A1

WO2013179311A1 - A system for generating refreshable tactile text and graphics

Info

Publication number: WO2013179311A1
Application number: PCT/IN2013/000347
Authority: WO
Inventors: P.V. Madhusudhan RAO; Pranay JAIN; Anshul SINGHAL; Meenakshi BALAKRISHNAN; Kshitij Gupta
Original assignee: Indian Institute Of Technology, Delhi
Priority date: 2012-05-31
Filing date: 2013-05-31
Publication date: 2013-12-05

Abstract

The present invention discloses a refreshable tactile display device for displaying tactile forms including Braille characters and planar graphics. The device comprises a plurality of electronic units, a cooling unit (18), and a filter (19). The electronic unit comprises a plurality of Braille dots (2b, 20a), a plurality of tactile elements (2), an upper structure element (1), a wire housing (6), and a lower structure element (7). Each of the tactile elements (2) includes a shape memory alloy wire (3), crimp terminals (4) at both ends of said wire (3) and a pair of concentric parallel compression springs (5). The invention uses shape memory alloy to selectively project and retain Braille dots, for use in modular tactile displays of multiple character rows that form the primary tactile output devices.

Description

A SYSTEM FOR GENERATING REFRESHABLE TACTILE TEXT AND GRAPHICS

FIELD OF THE INVENTION The present invention relates to a device for refreshable mechanical projection of tactile forms including Braille characters and planar graphics on a surface to allow tactual examination of textual and graphical information. In particular, the invention relates to a tactile display module, which uses shape memory alloy to selectively project and retain discrete Braille dots, for use in modular tactile displays of multiple Braille character rows that form the primary output devices in products and systems developed for the visually impaired.

BACKGROUND OF THE INVENTION

Braille is a tactile script used by the visually impaired to read via tactual examination. Its six- dot and eight-dot configurations have been adapted and standardised for use with various languages (refer World Braille Usage, published by UNESCO, France and Library of Congress, USA in 1990). Braille embossed on regular paper, generally bulky and expensive, usually loses readability due to damage from repeated reading. Electronically controlled Braille displays provide an alternative to the use of embossed paper and also enable personal computers and other products and systems to display Braille text; otherwise inaccessible to the visually impaired for reading through touch. Such displays hence provide the visually impaired competence in educational and occupational activities and help improve their quality of life. Such displays can also be developed to display tactile forms other than Braille characters for tactile presentation of planar graphical information.

Notable inventions and commercial devices related to such displays are based on the piezoelectric effect. U. S. Pat. No. 4,283,178 and Dutch Pat. No. 8600453 disclose devices with piezoelectric reeds, which when subjected to a high electric potential difference bend to project Braille dots on a surface. Such devices are usually expensive to manufacture. Also, mechanisms and structures therein extend beyond the character space on the display surface limiting the display to a maximum of two character rows. The latter disadvantage is alleviated by use of vertical instead of horizontal reeds, as disclosed in French Pat. No. 2 565 050 and Japanese Pat. No. 6-301335. However, the disadvantage of high manufacturing cost is experienced equally in these as well.

Shape memory alloys change mechanical properties, including stiffness, when subjected to phase transformation that usually occurs due to change of the alloy's temperature across a transition temperature range specific to the alloy. This characteristic has been utilised in various actuation applications and proposed for use in tactile displays as well. U. S. Pat. No. 5,685^,721 discloses a Braille display actuated using shape memory alloy. The display uses a pressurised medium, pneumatic or hydraulic, to provide a bias force to the actuator. Requirement of a compressor or pump renders the display immobile. Further, refresh rate of displayed Braille characters is low since enclosing electrically conducting tubes for individual actuators inhibit cooling, which is responsible for a reverse phase transformation to allow resetting of Braille dots. U. S. Pat. No. 6,022,220 discloses a computer peripheral device with Braille display actuated using shape memory alloy wires. The display suffers from a poor refresh rate due to absence of outlets for heat. Further, since electrically conductive materials are used in multiple attaching parts to act as a common electrical terminal for the shape memory wires and since electrically conductive materials are usually thermally conductive as well, heat gained by individual shape memory alloy wires, due to their resistance to electrical current channelled through them for desired actuation, is readily dissipated through conduction to neighbouring wires. This leads to errors in displayed Braille characters and complicates electronic control of the display.

Taking into purview the devices that are currently available for electronically controlled tactile display, need for^~ a device that overcomes the above mentioned drawbacks and limitations is well understood. SUMMARY

An object of the present invention is to provide a device that can be electronically controlled to mechanically project tactile forms composed of points, lines and planes on a refreshable display surface. Another object of the present invention is to provide a tactile display that is suitable for display of Braille characters of standard sizes and dimensions.

Still another object of the present invention is to provide a tactile display that is suitable for multiple rows of Braille characters, is easily adaptable for application in various devices and systems, and is suitable for use in hand-held and portable devices. Yet another object of the present invention is to provide a tactile display that is inexpensive to manufacture, maintain, repair and replace, and has a refresh rate suitable for user convenience.

To achieve the above mentioned objectives, one embodiment of the present invention describes a refreshable tactile display device for displaying tactile forms and chiefly Braille characters. The device comprises a plurality of electronic units, a cooling unit (18), and a filter (19). Each of the electronic units comprises a plurality of Braille dots (2b, 20a), a plurality of tactile elements (2), each of said tactile element (2) includes a shape memory alloy wire (3), crimp terminals (4) at both ends of said wire (3) and a pair of concentric parallel compression springs (5), an upper structure element (1) for mounting said pair of concentric parallel compression springs (5), a wire housing (6) coupled to said wire (3) through said crimp terminals (4), and a lower structure element (7) for coupling said wire (3) with connecting wire (9) through said wire housing (6) and said crimp terminals (4, 10).

Another embodiment of the present invention describes an electronic unit. The electronic unit comprises a plurality of Braille dots (2b, 20a), a plurality of tactile elements (2), each of said tactile element (2) includes a shape memory alloy wire (3), crimp terminals (4) at both ends of said wire (3) and a pair of concentric parallel compression springs (5), an upper structure element (1) for mounting said pair of concentric parallel compression springs (5), a wire housing (6) coupled to said wire (3) through said crimp terminals (4), and a lower structure element (7) for coupling said wire (3) with connecting wire (9) through said wire housing (6) and said crimp terminals (4, 10). The present invention also describes a method for displaying tactile forms on a refreshable tactile display device. The method comprises providing a controlled power to at least one shape memory alloy wire, retracting the corresponding tactile element to withdraw the corresponding Braille dot from tactile perception, and providing a controlled cooling to bring the said tactile element and Braille dot to their original positions. Accordingly, in the present invention there is provided an independently controllable electronic unit, a number of which when positioned together in single or multiple rows form a modular Braille display, configurable according to desired application in product or system of concern. In a preferred embodiment, individual modules for refreshable display of unit Braille characters have a plurality of tactile elements selectively set or reset to display desired Braille character. Wires of shape memory alloy are engaged with these tactile elements, biased with concentric parallel compression springs, connected to a source of low electric potential difference via digitally controlled switches and heated selectively with controlled pulses of electric current to set and retain the setting of corresponding tactile elements. Structure elements combine the constituent components including the tactile elements, shape memory alloy wires, printed boards and electrical contacts, while providing constraints on motion and facilitating desired actuation during operation.

The modules have provisions to allow accelerated cooling of shape memory alloy wires, preferably using forced or induced air draught through a part or whole of the display, to attain a suitable display refresh rate. The modules can be mounted on an underlying printed circuit so as to be individually removable and replaceable. Connections, attachments and fastenings within the module are such that allow easy assembly and disassembly, and maintenance and repair. Tactile elements and the part with user contact surface may be detachable to facilitate cleaning of the module and replacement of the portion which comes in contact with users, the latter required in case of damage due to wear.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned aspects and other features of the present invention will be explained in the following description, taken in conjunction with the accompanying drawings, wherein:

Figure 1 illustrates an exploded view of an electronic unit according to an embodiment of the present invention.

Figure 2 illustrates an exploded view of a final built up structure of an electronic unit according to an embodiment of the present invention. Figure 3 illustrates a perspective view of a structure of multiple-row Braille display constituted of a plurality of electronic unit according to an embodiment of the present invention.

Figure 4A and 4B illustrate perspective and orthographic front views respectively showing a structure of a tactile element with shape rnemory alloy wire, springs and crimp terminals according to an embodiment of the present invention.

Figure 5 illustrates a perspective view showing a structure of a lower frame element with connection housing, connecting wires and crimp terminals according to an embodiment of the present invention.

Figure 6 illustrates a cut-away sectional view depicting independent operation of individual tactile element according to an embodiment of the present invention.

Figure 7 illustrates a perspective view depicting accelerated cooling through induced air draught according to an embodiment of the present invention. Figure 8 illustrates an exploded view of an electronic unit according to another embodiment of the present invention.

Figure 9 illustrates a flow diagram of method for displaying tactile forms on a refreshable tactile display device according to an embodiment of the present invention.

DETAILED DESCRIPTION:

The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments. The present invention can be modified in various forms. Thus, the embodiments of the present invention are only provided to explain more clearly the present invention to the ordinarily skilled in the art of the present invention. In the accompanying drawings, like reference numerals are used to indicate like components.

The specification may refer to "an", "one" or "some" embodiment(s) in several locations. This does not necessarily imply that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.

As used herein, the singular forms- "a", "an" and "the" are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms "includes", "comprises", "including" and/or "comprising" when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. Furthermore, "connected" or "coupled" as used herein may include operatively connected or coupled. As used herein, the term "and/or" includes any and all combinations and arrangements of one or more of the associated listed items.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Figure 1 illustrates an exploded view of an electronic unit according to an embodiment of the present invention. The electronic unit comprises a plurality of Braille dots (2b, 20a), a plurality of tactile elements (2), an upper structure element (1), a wire housing (6), and a lower structure element (7). Each of the tactile element (2) includes a shape memory alloy wire (3), crimp terminals (4) at both ends of said wire (3) and a pair of concentric parallel compression springs (5) along each of said tactile element(2). The upper structure element (1) mounts the pair of concentric parallel compression springs (5). The wire housing (6) is connected to the wire (3) through the crimp terminals (4). The lower structure element (7) couples the wire (3) with connecting wire (9) through the wire housing (6) and the crimp terminals (4, 10). The terms "electronic unit" and "electronic module" are used interchangeable throughout the specification. The assembly method and structure of an electronic module according to the first embodiment of the present invention will be described with reference to Figures 1 and 2. As shown in Figure 1, reference numeral 1 denotes an upper structure element, a moulded part made of a synthetic resin or the like. Reference numeral 2 denotes tactile elements each having a shape memory alloy wire 3, with crimp terminals 4 at both ends, attached to it and a pair of concentric parallel compression springs 5 mounted over it in a manner to be described later. Individual tactile elements 2, with wire 3, crimp terminals 4 and springs 5, are mounted on stepped holes la of upper structure element 1 such that the crimped ends of wire 3 project downwards from upper structure element 1, springs 5 rest against steps lb of stepped holes la and lower portions 2a of tactile elements 2 partially project downwards from upper structure element 1. Wires 3 are in turn attached to wire housings 6, products made of an insulated material, by inserting crimp terminals 4 in recesses 6a therein. Crimp terminals 4 are locked with locking features (not shown) in recesses 6a of wire housings 6.

Reference numeral 7 denotes a lower structure element, a moulded part made of a synthetic resin or the like. Connection housings 8, products made of an insulating material, are mounted on it and insulated connecting wires 9 crimped with crimp terminals 10 are attached to it in a manner to be described later. Locking catches 6b of wire housings 6 are engaged with through holes 8a of connection housing 8. Each shape memory alloy wire 3 is thus connected to a pair of connecting wires 9 at its ends via contacting crimp terminals 4 and 10, without use of any solder-based contact.

Upper structure element 1 is thus connected to lower structure element 7 through a plurality of parallel series of springs 5, tactile elements 2, shape memory alloy wires 3 and crimp terminals 4, and wire housings 6 and connection housing 8, as in Figure 2. Upper Structure element 1 is gradually distanced from lower structure element 7 in the vertical direction such that distance along the vertical direction between the centres of cylindrical protrusions 7c on lower structure element 7 and cylindrical protrusion le on upper structure element 1 is equal to that between the centres of through holes 11a and through hole lib on printed board 11, and that between the centres of cylindrical protrusion Id on lower structure element 7 and cylindrical protrusions If on upper structure element 1 is equal to that between the centres of through hole 12a and through holes 126 on printed board 12. The distance is such that shape memory alloy wires 3 are under tension and compression springs 5 are under compression. The distance is temporarily maintained with help of removable manual or mechanical aids (not shown).

Two printed boards 11 and 12 with mounted electronic circuits 11c and 12c respectively are attached to lower structure element 7 on front surface 7a and back surface lb respectively and upper structure element 1 on front surface lc and back surface Id respectively. Cylindrical protrusions 7c and le are engaged with through holes 11a and lib respectively on printed board 11 and cylindrical protrusions Id and If are engaged with through holes 12a and 126 respectively on printed board 12. Screws 13 are driven into blind holes le and If formed in lower structure element 7, and lg and lh formed in upper structure element 1 such that screw heads 13a rest on corresponding flat surfaces lid or 12o^*, thus attaching printed boards 11 and 12 to lower structure element 7 and upper structure element 1. The printed boards maintain the desired distance between upper and lower structure elements 1 and 7 facilitating removal of manual or mechanical aids. Insulated connecting wires 9 are connected to printed boards 11 and 12 correspondingly through connector housings 14, products made of an insulating material, plugged into connector receptacles lie and lie on lower portions 11/ and 12/ of printed boards 11 and 12 respectively. The electronic module is completed by attaching a cap 15 to upper structure element 1. Locking catches 1/ of upper structure element 1 are engaged with through holes 15a of cap 15. Tactile elements 2, shape memory alloy wires 3 and springs 4 thus partially enter stepped holes 15b of cap 15, such that Braille dots 2b project out of stepped holes 156 upward on user contact surface 15c of cap 15 during assembly. Constraint features 2c of tactile elements 2 move in constraining recesses (not shown) of cap 15 which prevent twisting about the vertical direction of tactile elements 2 and thus that of wires 3. Figure 3 illustrates a perspective view of a refreshable tactile display device for displaying tactile forms including Braille text and planar graphics according to an embodiment of the present invention. The plurality of electronic units/ modules are attached to a base printed board 16 with electronic control circuits (not shown) and attachment housings 16a to form a multiple-row Braille display with size and dimensions according to requirements and constraints enforced by device or system of application. Attachment housings llg and 12g are plugged into attachment receptacles 16a and fastened with screws 17, which are driven through holes (not shown) in base printed board 16. Individual modules can be independently unfastened from base printed board 16 with ease for purposes of maintenance, repair and replacement.

Figure 4A and 4B illustrate perspective and orthographic front views respectively showing a structure of a tactile element with shape memory alloy wire, springs and crimp terminals according to an embodiment of the present invention. A strand of shape memory alloy wire 3, of a length obvious to a person skilled in the art, is crimped at one end with a crimp terminal 4, a product made of an electrically conductive material. Two identical compression springs 5 are driven into each other to become a pair of concentric parallel compression springs with effective stiffness higher than that of an individual spring. Open end 3a of wire 3 is drawn through spring pair 5 and through hole 2d of lower portion 2a of tactile element 2, as shown in Figure 4A. Open end 3a is crimped with another crimp terminal 4 after drawing it in reverse through spring pair 5. The wires are positioned along grooves 2e and the spring pair 5 is pulled up to be mounted on lower portion 2a of tactile element 2, as shown in Figure. 4B such that the spring pair may rest against collar 2/ of tactile element 2. Figure 5 illustrates a perspective view showing a structure of a lower frame element with connection housing, connecting wires and crimp terminals according to an embodiment of the present invention. The sub-assembly of lower structure element 7, connection housings 8, insulated connecting wires 9 and crimp terminals 10 is described. Locking catches 8b of connection housings 8 are engaged with through holes Ig of lower structure element 7. Stripped ends 9a of insulated connecting wires are crimped with crimp terminals 10, which are in turn inserted into recesses 8c via through holes Ih. Crimp terminals 10 are locked with locking features (not shown) in recesses 8c of wire housings 8.

Figure 6 illustrates a cut-away sectional view illustrating independent operation of individual tactile elements according to an embodiment of the present invention. Adjacent tactile elements 2 have collar 2/ placed within corresponding stepped holes ISd of cap 15. Collar 2/ may be abutted against the step of stepped hole 15rf in the default state of the module when no electric current is supplied to shape memory alloy wires 3, as is the case with the leftmost tactile element 2. Braille dot 2b thus projects upward from hole 15b on user contact surface 15c of cap 15 and hence is perceivable tactually by users. Tactile elements 2 are at equilibrium position where forces due to compression of springs 5 and tension of wire 3 are balanced. Motion of tactile elements 2 is limited to linear motion in the vertical direction due to arresting of other degrees of freedom by features in upper structure element 1 and cap 15. Linear motion in upwards direction is limited by stepped hole 15rf in cap 15.

When shape memory alloy wire 3 is heated by passing controlled electric current, resulting stiffness and contraction of wire 3 change the equilibrium position, as is the case with the central and rightmost tactile element 2 in Figure 6. The new equilibrium position is such that Braille dots 2b do not project upwards on user contact surface 15c and are no more perceivable to users through touch. These Braille dots 2b are contained in holes 15A. The earlier equilibrium position restores as wire 3 cools after discontinuation of electric current. The restoration rate is faster when accelerated cooling aids are utilized.

Figure 7 illustrates a perspective view depicting an accelerated cooling through induced air draught according to an embodiment of the present invention. The device comprises a plurality of electronic units, a cooling unit (18), and a filter (19). According to a preferred embodiment, forced or induced air draughts may be utilised for accelerated cooling of shape memory alloy wires 3 during refresh period of the display. The draughts may be localised to a single row of modules or be globalised to the whole display as per utility. Figure 7 illustrates selective induced air drafts through a row of modules. Miniature fans 18 attached to an end of a row are electrically driven to induce an air draught through the row via individual modules. Shape memory alloy wires 3 exposed to the draught cool faster, so that tactile elements 2 return to their default state fast. Also, electronic circuits 11c and 12c on printed boards 11 and 12 are exposed to the draught, facilitating removal of excess and unwanted heat. A filter 19 for removal of suspended particulate matter to prevent damage to modules may be attached to the display at the other end of rows. The filter may be detachable to allow periodic cleaning and maintenance. Figure 8 illustrates an exploded view of an electronic unit according to another embodiment of the present invention wherein the structure of tactile elements 2 is partially modified. Tactile elements 2 are limited to lower portion 2a and collar 2f. Through hole 2d, grooves 2e and constraint feature 2c are still on each tactile element 2. Auxiliary tactile elements 20 are provided with Braille dot 20a, collar 206 and constraint feature 20c. Auxiliary tactile elements 20 are inserted in cap 15 while the latter is being attached to upper structure element 1, as shown in FIG. 8. Auxiliary tactile elements 20 thus rest on tactile elements 2 and are positioned according to the latter' s equilibrium position. Braille dot 20a on auxiliary tactile elements bear damage due to wear and are individually replaceable. The module in FIG. 8 is for an eight-dot Braille character. The eight-dot and six-dot configuration is not specific to the embodiment.

Figure 9 illustrates a flow diagram of method for displaying tactile forms on a refreshable tactile display device according to an embodiment of the present invention. A controlled power is provided to at least one shape memory alloy element in step 901. The shape memory alloy element is contracted to retract the corresponding tactile element in order to withdraw the corresponding Braille dot from tactile perception in step 902. A controlled cooling is provided to bring the said tactile element and Braille dot to their original positions in step 903.

When an individual shape memory alloy wire is powered, it contracts and places the corresponding tactile element and Braille dot without perception. Controlled supply of electric power heats the wire to beyond a specific temperature. Due to the wire's inherent property, it contracts when beyond the said temperature. The contraction pulls the corresponding tactile element and Braille dot to a position below the contact surface.

The display's electronic system sends digital signals to each electronic unit's control system indicating which Braille dots and tactile elements are to be put without perception. The electronic control circuit thus switches power, drawn from the power supply, for individual actuators according to received signal. There are three notable families of alloys which exhibit the said shape memory effect:

• CuAl: Alloys of Copper and Aluminium

• CuZn: Alloys of Copper and Zinc

• NiTi: Alloys of Nickel and Titanium

NiTi Alloys exhibit the most appreciable shape memory effect. Binary alloys (with only Nickel and Titanium), Ternary (Nickel and Titanium with a third alloying element) and Quaternary (Nickel and Titanium with two other alloying elements) are known for the same. The third and fourth alloying element can be selected from the elements such as Fe, Cu, Co, V, Cr, Mn, Al, Au, Ta, Hf, Zr, Pt, Pd, Nb. The composition of each alloying element is usually varied to get the most desirable mechanical properties from the alloy.

Although the invention of the device and method has been described in connection with the embodiments of the present invention illustrated in the accompanying drawings, it is not limited thereto. It will be apparent to those skilled in the art that various substitutions, modifications and changes may be made thereto without departing from the scope and spirit of the invention.

Claims

We claim:

1. A refreshable tactile display device for displaying tactile forms including Braille text and planar graphics, the device comprising: a plurality of electronic units; a cooling unit (18); and a filter (19); wherein each of said electronic unit comprises: a plurality of Braille dots (2b, 20a); a plurality of tactile elements (2), each of said element (2) includes a shape memory alloy wire (3), crimp terminals (4) at both ends of said wire (3) and a pair of concentric parallel compression springs (5) along each of said tactile ^* element(2); an upper structure element (1) for mounting said pair of concentric parallel compression springs (5); a wire housing (6) coupled to said wire (3) through said crimp terminals (4); and a lower structure element (7) for coupling said wire (3) with connecting wire (9) through said wire housing (6) and said crimp terminals (4, 10).

2. The device as claimed in claim 1 , wherein said Braille dot (2b) is attached to said tactile element through a constraint feature (2c).

3. The device as claimed in claim 1 , wherein said Braille dot (20a) is replaceable, said Braille dot (20a) is attached to said tactile element through a collar (20b) and a constraint feature (2c).

4. The device as claimed in claim 1, wherein said tactile element (2), said wire (3), said crimp terminals (4), and said springs (5) are mounted on stepped holes (la) of said upper structure element (1).

5. The device as claimed in claim 1, wherein said upper structure element (1 ) is made of a synthetic resin.

6. The device as claimed in claim 1, wherein said wires (3) are connected to said wire housing (6) by inserting crimp terminals in a recess 6a.

7. The device as claimed in claim 1, wherein said wire housing (6) is made up of

insulating material.

8. The device as claimed in claim 1, wherein a connection housing (8) is mounted on said lower structure element (7).

9. The device as claimed in claim 1 , wherein said wire housing (6) is connected to a connection housing (8) through a locking means.

10. The device as claimed in claim 9, wherein said locking means comprises at least one locking catch (6b) on said wire housing (6) and at least one hole (8a) on said housing (8)·

1 1. The device as claimed in claim 1 comprising at least two printed boards (1 1 & 12) connected to said lower structure element 7 for providing controlled power to said electronic Unit.

12. The device as claimed in claim 1 comprising a cap (15) attached to said upper

structure element (1) through at least two stepped holes (15a, 15b) and at least two locking catches (li).

13. The device as claimed in claim 1, wherein said cooling unit (18) comprises at least one miniature fan.

14. The device as claimed in claim 1, wherein said filter (19) is attached to the display device to filter dust particles.

15. An electronic unit comprising: a plurality of Braille dots (2b, 20a); a plurality of tactile elements (2), each of said element (2) includes a shape memory alloy wire (3), crimp terminals (4) at both ends of said wire (3) and a pair of concentric parallel compression springs (5) along each of said tactile element(2); an upper structure element (1) for mounting said pair of concentric parallel compression springs (5); a wire housing (6) coupled to said wire (3) through said crimp terminals (4); and a lower structure element (7) for coupling said wire (3) with connecting wire (9) through said wire housing (6) and said crimp terminals (4, 10).

16. The electronic unit as claimed in claim 15, wherein said Braille dot (2b) is attached to said tactile element through a constraint feature (2c).

17. The electronic unit as claimed in claim 15, wherein said Braille dot (20a) is

replaceable, said Braille dot (20a) is attached to said tactile element through a collar (20b) and a constraint feature (2c).

18. The device as claimed in claim 15, wherein said tactile element (2); said wire (3), said crimp terminals (4), and said springs (5) are mounted on stepped holes (la) of said upper structure element (1).

19. A method for displaying tactile forms including Braille text and planar graphics on a refreshable tactile display device, the method comprising: providing a controlled power to at least one shape memory alloy element; contracting said shape memory alloy element to retract the corresponding tactile element in order to withdraw the corresponding Braille dot from tactile perception; and providing a controlled cooling to bring said tactile element and Braille dot to their original positions.

20. A refreshable tactile display device for displaying tactile forms including Braille text and planar graphics substantially as herein described with reference to the

accompanying drawings.

21. An electronic unit in a refreshable tactile display device substantially as herein described with reference to the accompanying drawings.

22. A method for displaying tactile forms including Braille text and planar graphics on a refreshable tactile display device substantially as herein described with reference to the accompanying drawings.