Note: Descriptions are shown in the official language in which they were submitted.
p-305/6 lO 5'~ 9 6
FIELD OF THE INVENTION
This invention relates to information displays and
particularly to such displays as are capable of presenting any
of a number of alphanumeric displays.
BACKGROUND OF THE INVENTION
The problem of presenting a readily changeable alpha-
numeric readout in a small space has been solved in many
different fashions, as exemplified by neon-glow-discharge tubes,
liquid crystal readouts, solid-state electroluminescent devices,
and the like. Most such arrangements require operating signals
which themselves contain most or all of the information to be
displayed, and in any case are in general poorly adapted to
large scale readouts, such as may be seen readily from a consid-
erable distance. Further, a general problem with light-emitting
displays is illegibility when the ambient light level is high.
Opaque displays, in contrast, increase in visibility as the
ambient light increases.
A need exists for a mechanically sound, readily and
quickly changeable and accurate display for such diversified
uses as destination indicators for buses, advertising signs,
indicators of ambient temperature, time of day, and the like.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a
readily changeable display device adapted to displaying letters,
numerals, words and phrases and the like within the framework
of a mechanically sound apparatus.
Another object of the invention is to provide such a
device including positioning means whereby the display may
be selectively changed to any desired configuration, and is
especially well adapted to positioning by automatic devices,
particularly those under computer or machine control.
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A particular application of the subject invention is
in the field of destination signs for transit vehicles such as
buses and trains. Such destination signs must be changeable
according to the particular route of the vehicle and, in modern
day transit systems, each sign must be capable of displaying a
large number of different destination names in alphanumeric
form. A typical destination name may require forty or more
characters and the sign must be changeable quickly from one
name to another. In the past, destination signs have taken the
form of a roller curtain wide enough to accommodate the requisite
number of characters and long enough to hold a full set of
destination names required for a given vehicle. One great dif-
ficulty with this type of destination sign is that the roller
curtains must be printed with special destination names according
to the route of a particular vehicle or fleet of vehicles. This
requires the printing of a large number of different destination
signs for a given metropolitan area with attendant high cost.
Furthermore, with long sign curtains, it is difficult and
expensive to provide automatic sign changing systems.
The roller curtain destination sign, despite the
- above-mentioned difficulties, has an exceedingly important
attribute, namely, it affords excellent readability despite
wide variations in ambient light. Further, it lends itself to
large scale displays so the sign can be read from a distance.
As alluded to above, the roller curtain destination sign in the
form of an opaque display, is presently preferred for destina-
tion signs over all other known displays.
This invention seeks to take advantage of the read-
ability of an opaque display and to overcome the difficulties of
the roller curtain destination sign. In general, this is
accomplished by a sign having a plurality of window areas
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each of which is adapted to display one alphanumeric chara~ at a
time on a set of display tapes; each window area is capable of
selectively displaying any one set of characters by selectively
positioning the respective tapes of the set. Thus, a selected
destination name may be displayed by selective positioning of
the sets of tapes.
This scheme allows any destination name to be formed
and displayed using identical sets of character display tapes
for each character window area. Thus, the same set of character
display tapes may be produced in multiple copies to make up a
destination sign and the same destination sign may be used on
any route since any destination name may be formed by the sign.
To make practical this concept of a universal destina-
tion sign, this invention provides a broken-character, broken-
word arrangement. The broken-character utilizes plural display
tapes to form each character rather than a single tape showing
all characters in succession; by this technique; each tape is
shortened to a fraction of the length of the single tape.
Therefor the wrap-up of the tapes is minimized and the maximum
displacement of any tape to form any character is a fraction of
that required in the case of a single tape. The broken-word
arrangement utilizes the tapes in each set which are only one
character wide and which are used for only one window area.
The tapes of each set are positionable independently of the
tapes of any other set; this enables the number of character
portions disposed along the length of each tape to be kept at an
abso}ute minimum (since the tape is only one character wide and
no pairs or combinations of character portions are involved
laterally). This arrangement allows the sets of tapes to be
displaced simultaneously to form their respective characters.
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The invention is realized in a sign having plural
window areas each adapted to display a single character with
portions of the character allocated to discrete window segments.
Plural sets of display tapes are disposed at respective window
areas for collectively forming any character at a time. Each
tape has character segments imprinted thereon in a predetermined
order at discrete segments of the tape along the length thereof
with the number of character segments being equal to the number
of characters to be displayed and each character segment cor-
responding to that segment which is to occupy the correspondingdiscrete window segment when the character is displayed. Movable
support means are provided for supporting each set of tapes so
that a selected segment of each tape can be seen at a time in
each discrete window segment. A separate clutch means connects
each movable support means with a common motor and the clutch
means are selectively actuated for concurrently butindependently
displacing all sets of display tapes to change the plural
character of the sign.
Also, according to this invention, a changeable display
of printed alphanumeric characters is provided which faithfully
reproduces each character, one at a time with a minimum of
translatory motion required in changing from one character to
another. In general, this is accomplished by using a set of
display tapes with each tape bearing discrete character segments
25 which are imprinted on both front and back surfaces of the tape.
A driving roller is connected with one end of each tape and a
driven roller is connected with the other end, and the tape is
supported for displaying one surface segment of the front and of
the back of each tape in respective segments of each window.
The set of surface segments being displayed together in the
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window all bear different character segments of the same
character so that an entire character is displayed. Means are
provided for displacing the tapes in unison along their length
to successively present the character segments in registry with
S the respective window segments whereby all characters of the
set may be successively displayed. The number of display tapes
in the set is equal to one-half the number of character segments.
The length required for each tape varies inversely with the
number of segments which is chosen to make up each full character.
Further, in accordance with the invention, faithful
reproduction of the characters is provided by means which
ensures proper positioning of the character segments within the
respective window segments. This is accomplished by placing the
character segments on respective surface segments of the tape
with the surface segments being progressively longer from one
end of the tape to the other to allow for wrap-up of the tape
on the rollers. Further, the character segments are nonuniformly
spaced along the length of the tape so that equal angular dis-
placements of the driving roller causes proper alignment of the
character segments in the window segments.
Further, according to the invention, the proper posi-
tioning of the character segments is enhanced by relating the
roller size to the length of character segments. In particular,
the diameter of the rollers should be approximately equal to the
length of two character segments.
Further, according to the invention, the display of
each character, even though it is a composite of several seg-
ments, is produced without distortion. For this purpose the
number of character segments is selected so that the horizontal
baxs of a character may be carried all on one segment and yet be
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properly located in the character format. Preferably, the
number of character segments is eight. Additionally, distortion
between adjacent segments is minimized by fairing of the
character line at the upper and lower extremities of the segments.
Further, according to the invention, the driving and
driven rollers are disposed in a minimum of space and may be
driven by a single input shaft so the rollers mdve only in unison.
This is accomplished by placing the driving roller of each set
behind the display window and the driven roller immediately
behind the driving roller with equal size gears on all rollers
and meshing with at least one adjacent gear.
DETAILED DESCRIPTION
A more complete understanding of this invention may
be obtained from the following description, taken with the
accompanying drawings in which:
FIGURE 1 is a front view of three display units in
accordance with the invention, each exhibiting a different
numeral or figure;
FIGURE 2 is a partially cut-away perspective view of
a typical embodiment of the inventive display unit:
FIGURES 3a and 3b are respectively the front and back
sides of a display tape such as may be used in the device;
FIGURE 4 is a diagrammatic side view of the device
showing the winding mode of the display tape on the rollers;
FIGURE 5 is a sectional view showing the detailed con-
struction of a slave roller;
FIGURE 6 is a diagrammatic side view showing the inter-
meshing coupling means whereby the driving rollers are rotated
and showing an optional positioning code disc;
FIGURE 7 is a top fragmentary view of the code disc
shown in FIGURE 6;
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FIGURE 8 shows a destination sign according to this
inventiOn î
FIGURE 9 shows a positioning control system for use in
this invention;
FIGURE 10 is a diagrammatic showing of the relative
positioning of the character segments on the tape;
FIGURE 11 shows a modification of the invention; and
FIGURE 12 is a sectional view taken on lines 11-11
of FIGURE 11.
Coming now to FIGURES 2 and 4, it will be seen that the
device comprises an array of display rollers, 1, 2, 3, 4, 5, 6,
7, 8, 9, 10, etc., which are arranged in spaced pairs, 1,2; 3,4;
etc., and in which two adjacent pairs form groups of four rollers
each, such as 1-4 inclusive, 5-8 inclusive, and so forth. Further-
more, all of the axes of the cylindrical display rollers 1, 2, 3,
etc., are in the same plane so that all of the cylindrical dis -
play rollers are tangent to a display plane, the position of this
tangent display plane being indicated in the drawings by those
segments of the tapes which lie flat on the front of the display
device, as shown, for example, in FIGURE 2 by that portion of the
uppermost tape lying between the points indicated~as 11,12,13 and 14
It will be apparent from the drawings and in particular
from FIGURES 1 and 2 that those portions of the display tapes
visible from the outside form an array of essentially horizon-
tal segments which may be viewed as a whole, thus for examplein FIGURE 2 displaying the letter "A" made up of eight horizontal
segments.
Reverting now to FIGURE 4, this illustrates the fashion
in which the tapes are wound on and over their respective rollers
Each group of four display rollers, 1-4,5-8,9-12, etc., is backed
up by a driving roller 15, 16, 17 and 18, and by a slave roller
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19, 20, 21 and 22, A tape 23 is fastened at one end to the
driving roller 15, and after looping over the back of the driving
roller is threaded over display rollers 2 and 1 and thence back
over driving roller 15 and thence is threaded over display rol-
lers 3 and 4 and is finally taken up by slave roller 19, to whichits opposite end is fastened.
It will be observed that in passing over display rol-
lers 1 and 2, one face of the tape 23 is exposed to view, where-
as when the tape passes over display rollers 3 and 4 the back or
reverse side of the same tape is displayed.
It will be further noted that the next unit in the
stack comprising display roller 5, 6, 7 and 8, driving roller 16
and slave roller 20, has its own tape 24. The same is true
for the remaining units in this stack involving driving rollers
17 and 18, slave rollers 21 and 22, and tapes 25 and 26 respec-
tively. Further, proceeding from the top of the stack downward
each successive driving roller together with all the rollers
actuated thereby rotates in a sense opposite to that of its
neighbor next below, for reasons which will appear later.
In the embodiment shown in the drawings, four units are
shown in a vertical stack. It will be clear that more or fewer
could be used in accordance with the nature of the information
to be displayed. Likewise, FIGURE 1 shows three such four-
stack arrays in horizontal juxtaposition. This enables the
information on each of the three devices to be varied indepen-
dently of the others, which in some instances is advantageous,
as for example when various numbers or various words are to be
shown. Clearly, if for example 20 devices are assembled in a
hori~ontal array and if each device can display each of the
26 letters of the alphabet and the ten digits from 0 to 9, then
any word of up to 20 letters or any digit up to 1 X 102 - 1
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can be displayed at will.
~everting once more to the drawings, the slave rollers
19, 20, 21 and 22 are take-up rollers which serve to wind up,
or as the case may be, to unwind the tape when the display is
changed, A11 of the driving rollers 15, 16, 17 and 18 and
the slave rollers 19, 20, 21 and 22 are geared together as may
be seen from FIGURE 6, and because of the relative sense of
rotation of the various rollers this may be done in the extra-
ordinarily simple fashion shown in FIGURE 6. Thus, all of the
gears are meshed together at their points of contact, which
leads to a complete avoidance of any slippage problems which
might otherwise cause the tapes in a given stack to become
out of phase. As a given tape is wound from its driving roller
onto its slave roller, or contrariwise, it will be clear that a
given amount of angular rotation will correspond to a slightly
varying linear payout or uptake because of the finite thickness
of the wound tape. We compensate for this slight disparity in
the required angular rotation between a given driving roller and
its slave roller by providing a spring loading in torque for
each slave roller, as may be seen from FIGURE 5. It will be
clear from that drawing that the gear 27 does not drive the
roller 19 directly and positively but only through the inter-
mediary of a helical spring 28, which is set so as to impart a
moderate degree of tension in the tape. Spring 28 is engaged
at one end to endpiece 29 forming part of the slave roller 19;
whereas at the other end it engages anchor pin 30 which is
fixedly attached to the drive shaft 31 which in turn is fixedly
attached to gear wheel 27. A stop pin 32 is attached to end-
piece 49 of slave roller 19, and serves to limit the rotation
of shaft 31 with respect to slave roller 19. It serves to
hold the spring 28 from being overstressed during operation if
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the tape or roller should stick. The arrangement of course
is repeated for each unit in the stack.
It will be clear from the foregoing and particularly
from FIGURE 2, that the array of gears attached to the driving
rollers are not only intermeshed with each other, but are
also intermeshed with the array of gears which are attached
to the slave rollers, and both arrays are intermeshed so that
all of the gears may only rotate in unison, taking into account
the opposite senses of rotation of adjacent gears. ThuS each
driving roller gear engages at least one other driving roller
gear as well as its corresponding slave roller gear; and the
same may be said for each of the slave roller gears, each one
of these engaging at least one other slave roller gear while at
the same time engaging its corresponding driving gear.
Turning for the moment to FIGURES 3a and 3b, these
show respectively the front and back sides of tape 23, which as
will be appreciated from the foregoing explanation has,
depending upon the particular setting of the device, a segment
of one side displayed between display rollers 1 and 2, and
another segment from the other side displayed between the
display rollers 3 and 4. FIGURE 1 shows the setting of the de-
vice so as to display the letter "A". In FIGURE 3a, that
segment forming the top half of the upper one-quarter of the let-
ter "A" is indicated by 33; whereas that portion of the reverse
of the tape shown on FIGURE 3 b which forms the lower half of
the uppermost one-quarter of the letter "A" is indicated by 34.
The tape shown in FIGURES 3a and 3b bears sufficient markings
to form the upper one-quarter portion, that is, between rollers
1 and 4, of all 26 letters of the alphabet, all ten digits from
0 through 9, a period (.), a dash (-), a slash (/), and a blank
space.
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It may be remarked that for convenience in explaining
our invention we have shown the various rollers as horizontal,
with the stacking vertical; but the terms "horizontal" and
"vertical" are used mainly for convenience. It is self-evident
that the entire apparatus shown may be rotated through 90, so
that the rollers will then be vertically disposed. Obvious
changes will then have to be made in the arrangement of the
subject matter to be displayed, except in the infrequent case
that the material consists of symbols having four-fold symmetry
such as circles, plus signs, crosses of equal arm length and
the 1, 4 and 5 spots on dice and the like.
As already noted, the display is shifted to a new posi-
tion by the rotation of any of the driving or slave rollers
by one-quarter turn, that is, by 90, for the relative propor-
tions of the particular apparatus depicted in the drawings. Of
course, it is a simple matter to change the ratio of the dia-
meter of the driving and slave rollers to the spacing distance
between a single display roller pair so as to vary the amount
of rotation required to produce a new setting in the display.
We find the ratios shown and described to be best, however,
for it leads to a comfortable amount of working space behind
the display rollers. On FIGURE 6, four index marks 45, 46, 47
and 48 are shown on the face of gear 27, and it will be clear
from the foregoing that the display can be changed by rotating
the driving/slave gear assembly by 90, This may readily be
done by hand with the aid of either knob 50 on the face of
gear 27 or knob 51 on the face of gear 35. Exact positioning
is facilitated by observing the four index markings on the
face of gear 27. Remote control of rotation may of course be
effected by any of the means well known to those skilled in
the art, such as by the use of cables, pulleys and the like.
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Such repositioning of the display by hand is adequate
in many cases where the destination is changed infrequently or
where only two or three display devices are used, as in FIGURE 1.
In many other cases, however, it is desirable to be able to
reposition the display device automatically. In a destination
sign for buses where a large number of characters are displayed,
an automatic system is desirable. A destination sign, as shown
in FIGURE 8, comprises an enclosure or case 60 which i~
provided with a plurality of windows 62~which display respective
alphanumeric characters making up a destination name. A sign
module 64 is positioned within the case 60 behind each window 62
so as to present its character display through the window.
A closed-loop positioning system may be employed for
automatic selection of the desired character display~ In the
device of FIGURES 2 and 4, the uppermost tape 23 bears a coded
endstrip 36 in the portion shielded from view. This strip bears
positioning markers in an array of parallel channels, the mark-
ings consisting of opaque portions in an otherwise transparent
or translucent tape. The momentary position of tape 23 is
registered by an optical code sensor 38 which may conveniently
comprise a light source 37 and a multiple photodiode or like
receptor means, none of which requires to be set forth in any
detail since this general type of coded positioning sensing and
registration is well known in the art. The signal given by
sensor 38 is used to actuate a drive motor 39 (see FIGURE 6),
which again is a matter of well-known technology. It is of
course unnecessary to provide more than one of the display tapes
with the coded edge portion since all of the tapes are in effect
geared together and move simultaneously as already described.
As is conventional in closed-loop positioning systems, a command
signal is applied to the input according to the positioning
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desired, i.e. according to the character to be displayed~ The
command signal causes the drive motor 39 to be energized. The
tapes are displaced in unison and the sensor 38 continuously
produces a follow-up signal corresponding to the actual posi-
tioning of the tapes The follow-up signal is compared with
the command signal and when correspondence or equality is
achieved, the motor is stopped and the selected character is
displayed by the tapes. In a closed-loop system, precise posi-
tioning of the tapes may be achieved since the positioning code
is applied to the tape itself and may be positionally correlated
with the respective character segments distributed along thelength of the tape. While positioning of the tapes by use of
a closed-loop positioning system does circumvent certain posi-
tioning pxoblems, it is disadvantageous in certain respects.
In paxticular, where two or more modules are to be used
together and adapted to display different characters, it isnecessary to use a separate positioning system for each display
device. Further, in a closed-loop system a failure in locating
the correct positional code signal will result in the display
of a wrong or garbled character, or perhaps, damage to the
device. As will be discussed below, an open-loop type of posi-
tioning system is preferred and the display device of this
invention is adapted for such positioning.
For changing the display from one character to
another, an open-loop control system is preferred. For this
purpose, it is desirable that succeeding characters may be
selected by advancing or reversing the tapes through equal
increments of angular displacement of the driving rollers.
Th~s will enable two or more display modules to be operated
from a single drive motor with individual clutches for each
module. However, because the tape is wrapped in varying -~
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amounts on the rollers according to the tape positioning, the
effective roller diameter varies and a given angular displace-
ment of a roller does not correspond to the same lineal displace-
ment of the tape. In the illustrative example, the relative
dimensions have been chosen so that the effective diameter of the
drivinq roller is such that one-fourth of a revolution forward
from its home or reference position will take up a length of
the tape equal to the axial length of each window segment.
(In this home position, the effective diameter includes the
roller diameter plus any tape leader wound thereon.) Accordingly,
the first revolution of the roller will take up the first four
character segments. However, during the next revolution the
roller will have an effective diameter which is larger by
twice the thickness of the tape and will take up a length of
tape greater than the next four character segments. The effec-
tive diameter of the roller continues to increase with approxi-
mately each succeeding group of four character segments. Thus,
it can be seen that as the tape is advanced or taken up further
on the driving roller, each ninety degree increment of roller
rotation will take up slightly more tape than the previous
increment. So that equal angular increments of roller dis-
placement will provide accurate positioning of successive
character segments, the character segments are nonuniformly
spaced along the length of tape, as will be described subse-
quently.
An open-loop positioning system which is especially
adapted for a destination sign is illustrated in FIGURE 9.
Each of the sign modules 64 in this system is the same as that
shown in FIGU~E 2 except that the coding strip 36 and sensor
38 are omitted. For the open-loop positioning system, a shaft
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position encoder 40, as shown in FIGURE 6, is geared to the
drive shaft for the display devices. As noted in FIGURE 6, the
drive motor 39 drives each display device through a drive gear
41 and also drives an encoder 40 through a pinion gear on the
same shaft. The shaft position encoder 40 bears an annular
coding strip 42. The coding strip coacts with a light source
43 and an optical sensor 44, as depicted in FIGURE 7, to produce
an electrical signal corresponding to the angular position of
the driving shaft.
The open-loop positioning system is shown in block
diagram in FIGURE 9. The motor 39 is a reversible electric
motor and is provided with an elongated drive shaft 66
mechanically coupled with the encoder 40. Each of the display
modules 64 is separately coupled with the drive shaft 66 through --
a respective clutch 68. A selector means 72 is adapted to
produce an electrical signal corresponding to the desired posi-
tioning for each of the modules 64. The selector means 72
receives an input signal from the encoder 40 which is indicative
of the actual positioning of the motor shaft 66. The encoder
40 also provides a position signal to a motor control means 74
which controls the energization of the motor 39. The output of
the selector means 72 is connected with the input of a clutch
control means 76 which supplies individual control signals to
the respective clutches 68. In operation, the selector means 72
is set acaording to the desired position for each of the display
modules~ This setting initiates the energization of the motor
39 through the motor control means 74 which causes the motor to
drive all of the display devices in the reverse direction to a
home position. The motor is automatically reversed by the
motor control means upon reaching the home position and the
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clutches are selectively engaged and disengaged through the
clutch control means 76 so that each display module is positioned
according to the setting of the selector means. Thus the display
modules 64 are controlled independently and are driven concur-
rently from the home position to the respective display positions.
So that equal angular increments of roller displace-
ment will provide accurate positioning of successive character
segments, the character segments are nonuniformly spaced along
the length of the tape. This is depicted in FIGURE 10 which is
a diagrammatic representation of tape 23 showing the front sur-
face and back surface thereof side-by-side with the respective
display window segments therebetween for showing the positional
correlation. The front surface of the tape 23 is shown in
fragmentary sections on the left side of FIGURE 10 and these
sections are enlarged relative to the showing of the front
surface in FIGURE 3a. Similarly, the back surface of the tape
23 is shown in enlarged, fragmentary sections on the right side
of FIGURE 10. The back surface view in FIGURE 10 shows the tape
as it would appear if it were turned side-for-side from the
front surface view, i.e. the tape is turned over by rotation
about its longitudinal axis. (In FIGURES 3a and 3b, the tape
in FIGURE 3b is turned end-for-end from the position shown in
FIGURE 3a, i.e. it is turned over by rotation about a transverse
axis.) The tape 23 comprises a leader 162 at one end thereof
which is secured to the driving roller 15. It also comprises a
leader 164 at the other end thereof which is secured to the
slave roller 19. The tape 23, between the leaders, comprises a
plurality of tape surface segments 166, each of which is of
xectangular shape and extends the full width of the tape. The
surface segments 166 in a group, A, are of the same length; the
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surface segments 166 in successive groups B,C, etc. are
progressively longer. The shoxtest surface segments are adjacent
the leader 162 and the longest are adjacent the leader 164. The
surface segments 166 accommodate the various character segments,
such as character segment 3~ which is shown in actual configura-
tion in FIGURE 10 and in FIGURE 3a. The other character segments
are represented in FIGURE 10 in dummy form by the hatched
sections, one of which is superposed upon each of the tape sur-
face segments 166. It is noted that each of the character
segments is allotted an axial length, C. This length, C, is
suitably equal to the axial dimension of the shortest of the
tape segments 166. The tape segments in each succeeding group
are longer than those in the preceding group by an incremental
length, so that an extension 168 is provided for the character
segments, as indicated. This extension will vary from zero length
for the character segments in the first group (group A) to a
maximum length for the character segments in the last group. In
practice, the extensions 168 are not left blank; instead, the
character configuration is extended through that portion so as
to avoid showing a blank line in a character display in case of a
positioning error.
FIGURE 10 also depicts the positional relationship
of the front and back surfaces of the tape 23 in relation to a
viewing window 170. The viewing window is an aperture or area
bounded by the sides of the character segments and the top and
bottom, respectively, of the uppermost and lowermost character
segments. In the device as depicted in FIGURE 2, the window
170 is defined by the opening in the front of the frame of the
device. It is noted that in FIGURE 10 the tape 23 is depicted
as being laid flat alongside the window 170, whereas, in fact,
the tape 23 is disposed within the window and is looped over the
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display rollers and partially wound on the driving and slave
rollers. The window 170 is divided into plural window segments
172a,172b and so forth, according to the total number of character
segments to be displayed at a time. Each window segment has an
axial length, L, equal to the axial length, C, of the character
segments. It will be understood that the window segments are not
separated by physical boundaries, instead, each window segment
is an allotment of space from the total window area to a
character segment which has the same relative position in the
character format as the window segment has in the window area.
In FIGURE 10, the tape 23 is shown in the same position
relative to the display window 170 as it is in FIGURE 2, i.e.
the letter A is displayed and the character segment 33 is dis-
played in the window segment 172a. The back side of the tape
15 23, as shown in FIGURE 8, is comprised of tape surface segments -
166' which are progressively longer, by groups, as described
above with reference to the front surface. The character seg-
ments are all of the same length and the extensions 168' vary -
in the same manner as described above. With the tape 23 in the
position for displaying the character A, as described, the
character segment 34 is displayed in the window segment 172b.
The remaining segments of the character A will appear in the
respective window segments as depicted in FIGURE 2.
In the illustrative embodiment, it is to be noted
that ninety degree increments of rotation of the driving rollers
will successively present the successive character segments
in accurate alignment with the respective window segments.
It will be understood that the relative dimensions of the roller
diameter and the character segments may be changed to suit a
particular design.
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The tape material is preferably a thin sheet stock
which has high tensile strength and which is dimensionally stable
under varying ambient temperature and humidity conditions. One
preferred material is polyester film such as that sold under the
trademark "Mylar" by E.I. du Pont de Nemours of Wilmington,
Delaware, Even with a thin tape, the wrap-up of the tape on the
roller has a significant effect upon the accurate positioning
of the character segments. It has been found that this problem
of tape wrap-up is exaggerated by the use of small rollers.
The small roller requires a large increment of roller rotation,
as compared to a large roller, for producing a given character
segment length. It can be shown that the length of successive
tape segments for equal increments of roller rotation varies
as the square of the angular increment. Accordingly, a large
angular increment which is required for small rollers will
result in a large variation in tape segment length and hence
there will be inefficient use of the tape due to the unused space ;
between character segments, i.e. the extensions 168 shown in
FIGURE 10 and described above. To minimize this effect, it is
desirable to use large rollers. Further, the tape thickness
will differ somewhat from the design value and this will con- `~
tribute to positioning error. The positioning error due to tape
thickness variation will vary with the square of the incremental
angle of roller rotation for each character segment and with -
the square of the number of character segments. Therefore this
error is minimized by the use of a larger roller. It is prefer-
red that the roller diameter be made approximately equal to the
sum of the distance spanned by two window segments, i.e.
approximately equal to twice the distance between the points
of tangency ll and 12 in FIGURE 2. This provides a tape segment
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angle of about ninety degrees or about four tape segments per
circumference.
Although an open-loop positioning system is advanta-
geous in many respects, it does not provide absolute accuracy
in positioning the tapes for the character displays. Accordingly,
the foregoing features of character segment spacing and roller
diameter are of great importance in producing characters with
faithful reproduction, especially where a large number of
characters, for example forty or so, are represented in a
single module. Additionally, the fidelity of character reproduc-
tion is enhanced by proper selection of the number of segmentsper character. The number of segments per character should be
selected so that each horizontal bar in a character is provided
by one, and only one, character segment; further, such character
segment should carry no portion of the character other than the
horizontal bar. With this arrangement, the upper and lower
edges of the horizontal bar necessarily occur at the cracks
between segments. It has been found that this requirement is
fulfilled best with eight segments per character because it
permits proper relative positioning of the horizontal bars in all
characters in all classes or fonts of character styles. It is
found that six segments per character does not permit proper
placement of the horizontal bars without fragmenting a bar,
With parts on two segments; ten segments per character is too
many and horizontal bars would have to be fragmented to obtain
pxoper placement.
In order to compensate for positioning errors of the
charactex segments in displaying a given character, the appear-
ance of misalignment is minimized by fairing of the character
segments at the upper and lower extremities thereof. This is
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illustrated in FIGURE 10 which shows the character segments 33
and 34. In these segments, for example, the character lines
at the upper extremities 176 and at the lower extremities 178
are faired toward the vertical direction, i.e. the lines are
diverted from the trend line of the character style to approach
asymptotically a vertical line. Consequently, when two adjacent
character segments are not accurately positioned the appearance
of misalignment of the character trend line is minimized.
As described above, the driving rollers 15, 16, 17
and 18 are directly driven by the roller shafts and the slave
xollers 19, 20, 21 and 22 are spring driven by the roller
shafts to compensate for the disparity in the required angular
rotation for linear payout and uptake in transferring tape from
one roller to the other. The driving rollers are positioned
immediately behind the window segments and the driven rollers
are immediately behind the driving rollers. Each pair of
driving and slave rollers, being of a diameter approximately
equal to two window segments, is accommodated in the space of
the projected area of the respective window segments. This
enables the module to be of compact design within a rectangular
box having a height and width substantially equal to that of
the window.
Reverting again to the winding arrangement of the
tapes, it is observed that the tape is always held in tension
by reason of the spring loading in the slave roller. It is
desirable to maintain the tape tension at a value such that it
will be stretched tightly across the display rollers but,
of course, the spring loading varies with the amount of tape -
windup on the driving roller. The spring loading is the smallest
when most of the tape is on the slave roller and in this
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condition the spring torque, working aginst the friction in
the tape and roller system, may tend to allow the tape to become
somewhat slack across the display rollers. This is overcome
in the winding arrangement, as shown in FIGURE 4, by laying the
loop of tape from the display rollers directly upon the driving
roller. Note that for each set of rollers, the tape passes
immediately from the driving roller over a first set of display
rollers and thence is looped back over the driving roller in
engagement therewith over more than 180 before it is passed
over the second set of display rollers to the slave roller.
This causes the driving roller to serve as a feed roller and
obviates the need for idler rollers for looping the tape. As
a feed roller it tends to keep the tape tight over the display
rollers for both directions of rotation of the driving roller.
A modification of the invention is shown in FIGURES 11
and 12. In this embodiment of the invention, the tapes are
wound upon and displayed from the surfaces of the driving and
slave rollers; the display rollers used in the embodiment of
FIGURE 2 are dispensed with. Referring to FIGURES 11 and 12,
the display module 80 comprises a frame 82 and plural sets of
driving and slave rollers. Each driving roller 84, 85, 86 and
87 is directly connected with its respective shaft and carries
a gear 88, 89, 90 and 91 which is fixedly connected therewith.
Each of the slave rollers 92, 93, 94 and 95 is spring loaded
in the same manner as slave roller 19 described with reference
to FIGURE 5. Each of the slave rollers is connected through a
spring loaded shaft with respective gears 96, 97, 98 and 99.
An input gear 101 is manuallly operable by a crank 102 and is
meshed directly with gear 97 of the slave roller 93. All of the
30 driving and slave rollers are of the same diameter and all of ~'
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the gears, except the input gear 101, are of the same size. It
is noted that the rollers are of a diameter approximately equal
to a single window segment of the display where a window segment
is that portion of the total display area which is allotted to a
single character segment. A tape 103 has one end secured to the
driving roller 84 and the other end secured to the slave roller
92, the tape being wound between the rollers in an "S" configura-
tion. Similarly, a tape 104 is connected between the driving
roller 85 and the slave roller 93, the tape 105 is connected
between the driving roller 86 and the slave roller 94 and the
tape 106 is connected between the driving roller 87 and the slave
roller 95. The various characters represented by the module are
displayed successively by rotation of the input gear through
successive angular increments of equal value.
Although the description of this invention has been
given with reference to a particular embodiment, it is not to be
construed in a limiting sense, many variations and modifications
will now occur to those skilled in the art. For a definition
of the invention reference is made to the appended claims.
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