Tactile indicating device

Electromechanical apparatus for setting up and erasing alpha-numeric characters or other symbols in braille by means of a tactile display. Dot pins simulating braille are supported for movement within holes in a display plate to a position protruding therefrom to form tactile characters and for retraction to a withdrawn position flush with the surface of the display plate. Solenoid-operated plungers are arranged to selectively project the dot pins. Latch elements are movable by energization of the solenoid to a position to support the plungers in their operative position, a common support for the latch elements movable in a plane perpendicular to the axis of the support plungers to remove the latch elements and spring means for restoring the support plate to its initial position.

The present invention relates to tactile display devices and is concerned 
with electro-mechanical devices whereby braille characters can be 
displayed and erased. 
Braille was devised to enable the blind to read alpha-numeric characters 
and is in the form of a code, usually a six-unit code, for each cell 
representing a character or symbol. Thus with a six-unit code in each cell 
there is a matrix of two columns with three in a column. By employing a 
six-unit code 64 characters can be catered for which include the 26 
letters of the alphabet, the numbers 0 and 1 to 9 and various symbols such 
as full stops, commas, etc. For special purposes a braille code of four 
units and sometimes of seven units is employed. 
Hitherto braille has been provided in what is known as hard copy, i.e. on 
stiff paper, by embossing the paper to raise different patterns of dots in 
different cells representing different characters or symbols. 
Of recent times it has been proposed to extend the application of braille 
for enlarging job-opportunities for the blind by providing 
electromechanical apparatus whereby alpha-numeric characters and 
associated symbols can be set up for reading and erased as required. 
BACKGROUND OF INVENTION 
Such an apparatus is shown, for example, in U.S. Pat. No. 3,987,438. In the 
aforesaid patent, there is an array of plungers which are raised by 
energizing surrounding solenoids to project their upper ends from a 
display surface in imitation of braille and each plunger when raised is 
locked in its operative position by a ball which is moved under the 
plunger to prevent it from returning to its inoperative position. Each 
solenoid for lifting its associated plunger has an unlatching solenoid 
individual thereto, together with a plunger and spring. To unlatch a 
plunger, its associated unlatching solenoid has to be energized. This 
draws its plunger downwardly against the spring and the latching ball is 
drawn by the magnetic field into the unlocking position. Thus, for a row 
of 48 braille cells, 288 unlatching solenoids together with 280 plungers 
and 288 plunger springs are required for the unlatching process. In 
contrast with this, the present invention requires only a single 
unlatching plate for unlatching all of the 48 cells simultaneously. Thus, 
the structure and mode of operation for unlatching according to the 
present invention are very different and lead to an immense simplification 
over the prior art such as disclosed in the aforesaid patent. 
SUMMARY OF INVENTION 
As herein illustrated, the apparatus comprises dot pins simulating braille 
supported for movement within holes in a display plate to a position 
protruding therefrom to form characters simulative of braille and to be 
withdrawn to a position flush with the surface of the display plate, 
solenoid-operated plungers arranged to project the dot pins, latch means 
arranged to be moved into position by energization of the solenoids to 
support the plungers in operative position, a common support for removing 
the latch means from operative position to allow the plungers to return to 
their inoperative position and means for restoring the plungers to their 
inoperative position to erase the characters. More specifically, there is 
an array of spaced, parallel, ferromagnetic plungers, a supporting plate, 
means supporting the plungers with their lower ends adjacent the support 
plate for axial movement perpendicular to the supporting plate, a solenoid 
winding disposed about each plunger within which the plunger is axially 
movable by energization of the solenoid winding, means for selectively 
energizing the solenoid windings for moving the plungers into operative 
position such that their upper ends define any desired character and their 
lower ends are spaced from the supporting plate, rolling members on the 
support plate movable thereon into positions beneath the lower ends of the 
plungers when the latter are moved into operative position said rolling 
members being comprised of ferromagnetic material so as to be drawn into 
said position beneath the lower ends of the plungers when the solenoids 
are energized to move the plungers into their operative positions and 
means supporting the supporting plate for movement in a plane at right 
angles to the axes of the plungers for removing the rolling members from 
beneath the lower ends of the plungers to erase the characters. There are 
spring means which urge the plungers against the rolling members when the 
rolling members are moved beneath the lower end of the plungers operative 
to restore the plungers to their inoperative position when the rolling 
members are removed from the lower ends of the plungers. The display plate 
contains holes corresponding in number to the plungers and the dot pins 
are supported within the holes at the upper ends of the plungers from 
movement by the plungers to project the ends through the holes when the 
plungers are in their operative position and to be retracted by the spring 
means when the latch means are removed from the lower ends of the plungers 
so that their upper ends are flush with the surface. The upper ends of the 
dot pins are of a configuration to simulate brialle dots. A high 
permeability foil is wrapped around each solenoid to reduce substantially 
the amount of magnetic flux from one winding to another. Optionally high 
permeability metal bars may be arranged between them substantially 
parallel to the solenoid winding to effect such reduction of magnetic flux 
from one winding to the other.

Referring to FIG. 1, this shows part of a braille display-plate 10 which 
contains a row of 48 braille cells of which three are shown at 11, 12 and 
13 each cell containing a matrix of six dot-positions 14 to 19 in two 
columns of three each as shown. Beneath the display plate 10 there is 
provided for each cell, electro-mechanical apparatus whereby different 
patterns of braille dots can be raised through the display plate to be 
read and whereby they can be retracted for erasure. 
The electro-mechanical apparatus for each cell comprises an array of six 
solenoid windings of which two are shown schematically at 20 and 21 in 
FIG. 2 for the cell 11 of FIG. 1 and associated with the dot positions 16 
and 19. The solenoids are arranged parallel to and closely adjacent one 
another. Each winding has a ferro-magnetic plunger therein such as the 
plungers 22 and 23, each plunger having an inoperative position in which 
the plunger 22 is shown and, upon energisation of its associated winding, 
an operative position in which the plunger 23 is shown. 
For each plunger there are provided independent latching means whereby the 
plunger can be latched in its operative position. In addition unlatching 
means are provided common to all plungers. 
In FIG. 2 each independent latching means comprises a rolling member in the 
form of a steel ball such as the balls 24 and 25. Normally each latching 
ball sits in a pocket such as the pockets 26 and 27 the ball 24 being 
shown in this position. When a winding such as the winding 21 is energised 
the plunger 23 moves upwardly into its operative position shown whereby a 
gap 28 is created between the lower end of the plunger 23 and an 
unlatching plate 29 on which the lower end of the plunger sits i.e. when 
the plunger is in its inoperative position as shown for the plunger 22. As 
the gap 28 is created, magnetic flux from the plunger 23 attracts the ball 
25 into the gap 28 whereby the plunger is latched in its operative 
position to be held there when the energising current in the winding 21 is 
removed. 
The unlatching plate 29 is common to all the plungers and to unlatch all 
plungers which are in their operative positions and permit them to return 
to their inoperative positions the unlatching plate 29 is made laterally 
slidable as indicated by the arrow 44. When the plate 29 is so moved all 
balls, such as the ball 25, which are in latching positions are rolled to 
one side back into their pockets such as 24 whereby their associated 
plungers are unlatched and can return to their inoperative positions as 
shown for the plunger 22. 
Referring now to the structure of FIG. 2 in more detail, the windings shown 
schematically at 20 and 21 are on formers 30 and 31 which extend between 
two frame members 32 and 33 of non-magnetic material. The member 33 
includes the pockets such as 26 and 27 in which the latching balls are 
normally located. Apertures such as 34 and 35 are provided in the member 
32 through which the plungers extend and contact the lower ends of 
dot-pins such as 36 and 37 which project into apertures such as those 
indicated at 16 and 19 in the braille display-plate 10. The dot-pins are 
spring loaded by springs such as those shown at 38 and 39 whereby they are 
normally retracted downwardly as shown for the dot-pin 36 and urge their 
associated plungers such as 22 into their inoperative positions. Each 
dot-pin has a domed upper end as shown whereby when a dot-pin is urged 
upwardly by energisation of its associated winding the domed upper end in 
projecting above the display-plate 10 as shown for the dot-pin 37 
simulates a braille dot. 
It will be appreciated that when a ball is in its latching position, as 
shown for the ball 25, and the energising current is removed from its 
associated winding, the effect of the spring, such as 39, is to urge the 
plunger into firm contact with the latching ball which makes the latch 
secure and ensures the rolling action of the ball when the unlatching 
plate is slid to its unlatching position. Furthermore, to ensure that a 
ball, such as 25, when in its latching position is centralised with the 
end of its associated plunger the stroke of the plunger 23 is made long 
enough to ensure that the ball, held on the end of the plunger by magnetic 
attraction, enters the mouth of the former 30. When the energising current 
is removed the magnetic retentivity of the steel ball ensures that the 
ball remains in its central position as shown for the ball 25 when the 
plunger is urged back by the return spring 39 to its final operative and 
latched position. 
The unlatching plate is preferably so spring-loaded as to be normally urged 
to the right in FIG. 2 into a normal or rest position ready for its 
unlatching function. It can be arranged to slide the unlatching plate 
manually when erasure is required or alternatively or in addition it can 
be actuated by a solenoid (not shown). 
In one example of the embodiment shown in FIGS. 1 and 2, the pitch of the 
dot-locations 14 to 19 is 0.1" and the cell pitch is 0.25". The plungers 
are 0.041" in diameter and 0.66" long and of cold-drawn, soft iron. The 
latching balls are of 0.8 mm diameter and of non-corrodable steel. The 
formers for the windings are of extruded brass tube of 0.056" diameter and 
0.807" long. The wall thickness of the brass tube is 0.010" which ensures 
a rigid assembly and good magnetic coupling between the windings and their 
associated plungers. With such an arrangement a pulse of energising 
current of about 10 m.s. has been found sufficient for reliable operation. 
Thus to set up a braille character in any one cell, the windings for that 
cell are selected and windings appropriate to the character to be set up 
in braille are then selected and energised. 
When using an arrangement as shown in FIGS. 1 and 2 it has been found that 
a compact array of windings and plungers can lead to erratic operation by 
the effect of stray magnetic field from one winding linking with the 
plungers of adjacent windings. Two different ways of preventing such 
erratic operation have been successfully applied. In one of these a 
single-turn wrapping of high-permeability foil such as mu-metal is 
provided around each winding. The foil can be of about 0.005" in thickness 
whereby the cross-sectional area of the mu-metal is about the same as the 
cross-sectional area of the plunger. In the other method each cell has 
four bars of high-permeability, soft iron located between the windings as 
shown in dotted lines in FIG. 1 at 40 and extending between the members 32 
and 33. 
It will be appreciated that the invention enables an electromechanical 
tactile braille display to be provided in a form sufficiently compact as 
to conform with the standard size of a braille cell. 
The manner in which the solenoids of each cell are energised to provide 
braille display will depend upon the application concerned. 
Referring now to FIG. 3 this is a diagram of an elementary circuit for 
controlling the solenoids in a row of the devices shown in FIG. 2. 
Normally there will be 48 in a row but for convenience in the drawing only 
three are shown at 11, 12 and 13 corresponding to 11, 12 and 13 in FIG. 1. 
In FIG. 3 the positive pole of a battery 41 is connected through six spring 
loaded push-button switches into a selector switch 43. Initially the 
selector switch 43 is so set as to connect the switches 42 to the six 
solenoid windings shown of the device 11. Thus a pattern of the windings 
in the device 11 can be energised from the battery 41 by transient 
depression of a corresponding pattern of the push-buttons 42 whereby a 
corresponding tactile display is set up and latched. The selector switch 
43 is then operated to disconnect the push-button switches from the 
windings of the device 11 and to connect them to the windings of the 
device 12. The push-buttons 42 are again transiently depressed in a 
required pattern to set up a corresponding tactile display with the device 
12. This process is repeated for all 48 devices. 
When all 48 devices have been set-up and read operation of a common 
unlatching member (not shown) erases the displays on all 48 devices 
simultaneously. 
Although mechanical, manually-operated push-button and selector switches 
can be used as described, electronic switches will normally be employed.