Note: Descriptions are shown in the official language in which they were submitted.
2170842
This invention relates to a display element which may
be used alone as an indicator but will be more commonly used
as a pixel in an array of such elements to form a changeable
display sign. The invention will be found particularly useful
for signs and displays which must be viewed over wide angles
such as bus destination signs. (As distinct from signs for
narrow angle viewing such as road signs).
The display element is of the type using a rotor disk
defining a median plane, having opposed sides which respectively
contrast and conform with their background and which is rotat-
able about a rotation axis approximately parallel to said
median plane to display the bright or dark sides of the disk
in a viewing direction which is considered the axis of a viewing
cone (not necessarily a surface of revolution) which surrounds
the viewing direction. The stator which forms the background
to each disk is coloured darkly to contrast with the disk
bright side; and conform to the disk dark side. The bright ,
and dark sides are displayed in the ON and OFF respective
positions.
A light emitting diode (LED) corresponding to each disk
is positioned to form part of the disk's pixel when the bright
side is displayed (called the ON position) the LED being
positioned to project or preferably to shine through a cut-out in the disk
when oriented to ON position. The LED is permanently on so must
be masked in the OFF position.
'Forward' and 'rearward' are respectively, the directions
from the display element toward the viewer,~and the opposite
direction. 'Higher' and 'lower' correspond~respectively to
'forward' and 'rearward'.
2110842
An ' array' is the entire bus sign or other sign, c~posed
of 'sub arrays' which are each made up of a column of individual
display elements.
Reference to an 'LED' herein is intended to include a
cluster of such LED's.
The 'viewing direction' is the general centre of the
locations (projected on a plane perpendicular to the viewing
direction) from which the display element, or any array
thereof, is intended to be viewed.
The 'viewing cone' surrounds the viewing direction and
includes the projections on such plane of the positions from
which the display element, or an array thereof is intended to
be viewed.
It is known to use such a disk augmented by the end
of an optic fibre. See for example patents .
U.S. 4,974,353 dated 04 DEC 90, Norfolk
U.S. 5,022,171 dated 11 JUN 91, Norfolk, et al
U.S. 5,055,832 dated 08 JUN 91, Browne
However, optic fibres while suitable for relatively narrow
angle viewing are not so suitable for viewing over wide angles,
as are LED's. Moreover, LED's are cheaper to a sufficiently
marked degree, that a display application with LED's may be
practical where a similar application with fibres would be
impractical.
Other patents have used LED's with a rotating disk.
See for example, U.S. Patent 5,050,325 dated 24 SEPT 91.
However, this patent does not provide for masking of the LED
by the disk per se nor for wide angle viewing. Hence the LED
-2-
217Q842
had to be switched off in OFF state. The design of the present
display element assumes that the LED will be continuously on
while the disk switches between ON and OFF positions, thus
avoiding the cost of individual switching circuitry for each
LED. Such switching requires design complexity and expense.
Accordingly, it is an object of this invention to
provide a display element, for use alone or in display of such
elements, wherein the appearance of a rotatable flip disk is
augmented in ON orientation by an LED, which LED must be masked
by the disk, to the viewer, in OFF orientation.
It is an object of this invention to provide a display
element allowing, in ON position, viewing over a wide angular range
and in OFF position masking the rays over a wide angular range.
It is an object of this invention to provide a display
element wherein the light source used is markedly maintenance
free and inexpensive in contrast to alternate designs.
It is an object of this invention to provide a display
element for forming a pixel which is suitable for relatively
large multiple pixel arrays (for example, of 20 by 40 pixels)
to provide good definition in the sense of providing a small
pixel relative to the size of the array and a pixel having a
relatively large effective area.
By 'effective area' I mean the percentage of the sign
area which is occupied by the bright areas of the disks when
all are ON. This is a measure of the sign'sv.efficiency even
though it may not be strictly accurate in view of the effects
of the visible presence of LED's and the preferred angle of the
disk bright, panels to the viewing direction. The need to have
-3-
~ ~ ~os42
as large an effective surface as possible renders preferable
the use of rectilinear elements since these tend to have the
best 'packing factor' and hence provide the largest ON area
in a display. The need to supply pixels, small in area
relative to the size of the arrays suggests, therefore, the use
of square pixels.
Viewing direction is measured perpendicular to the
plane of the array, or in the intended direction for a single
element.
The invention therefore provides in one aspect, a
display element for viewing in locations defining a viewing
direction and having a rotor and a stator, where the stator
is preferably an open front housing usually of approximately
square shape, and an LED located on and projecting in front
of the base and located to be viewed in the viewing direction
and by viewers located in the viewing cone therearound. There
is a rotor mounted on the housing rotatable about an axis
forming an approximate diameter of such a square. The rotor
comprises a disk defining a median plane and having a bright
side and a dark side. A drive, preferably electromagnetic,
selectively causes rotation of said disk about through an
angle of between 160° and 180° about said axis between ON and
OFF orientations, where said bright and dark sides are,
respectively, visible in said viewing direction. Such disk
may be considered a near planar lamina when viewed in the
viewing direction, which may be considered as two planar semi-
lamina sectors on opposite sides of the rotary axis.
One semi-lamina of the disk is provided, contoured
-4-
2 ~ ~os42
in ON orientations to provide a cut-out to allow the passage
of light, in the~viewing direction, and to define the pro-
jection of the Viewing cone. The cut-out sector is also shaped
to allow the disk, in rotation between ON and OFF position,
to clear components, such as electromagnetic drive cores, and
the LED: which would be otherwise encountered in the travel
of the disk between ON and OFF position.
In a preferred form of the invention, a shroud is
provided preferably located a short distance forward of the
LED to shape the cone of light therefrom. (The LED is typic~~lly
mounted in a lens and the shroud located as above, surrounds a
rearward portion of the lens.
The LED and the disk are arranged to allow the LED in
ON position to be visible over a viewing cone comprising as
wide an angle as possible, particularly having regard to the
intended array use as a bus destination sign. Limitations on
the width of the included cone angle are set by the un-
desirability of having random reflections of LED light from the
sign mounting and by the necessity of masking the LED (which is
always on) in the OFF position of the disk. For these reasons,
the viewing cone is usually limited to an angle of about 45°
to the viewing direction, that is, the cone has about a 90°
included angle. The cone is not necessarily a surface of
revolution since the surrounding components whichlimit its
spread are not symmetrically disposed about the intended
viewing direction.The cone boundaries are usually~defined by
the point at which the light intensity is one half that in the
the viewing direction.
The shroud sets a suitable limit for undesired lateral
and backward radiation from the LED.
-5-
2170842
In a preferred form of the invention, the base forming
the LED mount is~provided with side walls and where the side
walls are forward of the pivot axis, the better to mask the
sideways escape of rays from the housing when in the OFF position,
the LED is masked by the disk in the viewing direction. The rays
potentially escaping include, not only those attempting to
follow a direct path, but those reflected back from the (then
rearwardly turned) bright face of the disk.
In the preferred use of the array, there is not as
much concern about upward escape of wide rays from about the
OFF disk since a bus is seldom viewed from that angle. Downward
escape of wide rays is, to a large degree prevented by oa~onents
of the next disk below in the array. 'Ihe escape of wide IUD radiation in
the OFF position of the disk is fuz-ther lessened by providing a f i rs t
side wall extending respectively to an edge forward and an edge
rearward. With such arrangement, in OFF position, the disk is
forward of a second or shorter side wall opposed to the first
side wall which has outward thereof a taller first side wall,
so that escaping light must follow a labyrinthine reflective
path.
With reference to the first side wall where
columns of such display elements are side by side, a
single high side wall is used in that role for each of two side
by side column elements so that each element xequires only one
first side wall.
With the second side wall, the edge of the disk which is
near to a shorter side wall in OFF orientation, may be shaped
to partially overlie it to further mask wide escaping light. It
-6-
2170842
will be noted that the combination of the second and adjacent
first side wall provides a stepped arrangement which, in
combination with the disk edge provides a labyrinthine escape
path for light.
In a preferred form of the invention, the stop is
arranged so that said disk, in OFF orientation, has its cut
out sector rearward of the axis of rotation, thus improving
the restriction on the escape of reflected rays.
In a preferred form of the invention, the disk contains
a magnet with its polar axis arranged transversely to the
rotation axis and a major portion of such magnet is on the
full semi-lamina. In such arrangement, the cut-out semi-lamina
is usually down in ON position. In such arrangement, the disk
must oppose gravity in turning from ON to OFF. Arranging the
stop to lessen the ON position disk angle to the viewing
direction provides extra magnetic torque for movement in this
direction.
In drawings which illustrate a preferred embodiment of
the invention .
Figure 1 is a perspective view of a display element in
accord with the invention;
Figure 2 is a front view (that is, looking in the
viewing direction) of the element of Figure 1 in ON position;
Figure 3 is a front view of the element'of Figure 1 in
the OFF position;
Figure 4 is a section taken along the lines 4-4 of
Figure 2;
Figure 5 shows a column of the elements of Figure 1;
2170842
Figure 6 shows a section taken along the lines 6-6 of
Figure 3;
Figure 7 is a section taken along the lines 7-7 of
Figure 3;
Figure 8 shows a bus with a display element array;
Figure 9 demonstrates a section on 9-9 of Figure 8;
Figures 10A and lOB show schematically arrays mounted in
buses. Figure 10A shows the arrangement of a prior art array,
without LED's and Figure lOB shows an inventive array with LED's.
20 In the Figure 8 is shown a portion of a bus B containing
an array A, of pixels of the type shown herein and showing a
destination starting with the letter 'BR'. Figure 9 indicates
that the letters are made up of arrays of display elements. The
drawing is schematic only and does not show a typical bus
destination sign which might be, for example, 20 pixels high and
40 pixels wide.
Figures l-4 and 6 show a display element comprising, a
substantially square base 20 and short walls 22 projecting for-
wardly therefrom including one short side wall 22S ('second
30 side wall') and opposed end walls 22 E. Towers 24 project from
diametrically opposed corners of the array. In the preferred
orientation of the display element, the towers 24 are located
in the upper right and lower left corners of the array and
provide mutually facing wells 26 to receive the 'spindles 28 of
the disk 30. The wells 26 thus define the axis of rotation of
the disk 30. It will be noted that such axis~is locatedforwardly
of short walls 22S and rearwardly of the forward extremitites
of towers 24.
_g_
2170842
Opposing short side wall 22S (second side wall) a longer
side wall 32 (first side wall) is provided~on the side opposite
side 22S~of about the height (forward direction projection from
the base) of towers 24. The height of longer side wall 32
preferably coincides with the tower height. Although a longer
side wall 32 may be provided on each side of the element, it is
preferred to provide a side wall 32 on only one side while on
the opposite side of the element the side wall 32A of the next
adjacent element saves the light blocking function at the adjacent
sides of the first and second elements.
Although the presence of a first or forward side wall 32
is desireable on each side of the display element, an individual
display element will have only one, shown here on the right
side. The opposed or left hand side wall 32, to the one shown
is provided by the right hand side wall 32A of the element to
the left of that under discussion. The presence, in an array,
of this side wall 32A is indicated in dotted form on Figures
2-6. Thus each side wall 32 or 32A acts as a side wall for
the elements on each side.
In relation to the walls of the element, the terms
'side', 'end', 'top', 'bottom', 'left' and 'right' refer to
the preferred orientation of the element, as shown in the
drawings, but are not intended to limit the broad coverage of
the invention.
Approximately midway along the inside of the bottom
wall 22E and approximately midway along the inside of the left
side wall 22S are the cores 34B and 34L which respectively act
to drive the permanent magnet 36 on the rotor, to be described.
_g_
CA 02170842 2003-03-31
The ends of cores 34B, 34 L are preferably symmetrically
disposed (as viewed in the viewing direction) on each side of the rotation
axis,
and in the preferred embodiment act as stops for the disk 30. As shown in
F=igure 4 core 34B projects from the base father than core 34L for reasons to
k>e discussed. Mechanical stops separate from the cores can, if desired, be
provided by cooperating members on the stator and rotor providing the same
stopping positions. At preferably the upper left corner of the base, a LED 36
in a transparent lens is mounted to project forwardly from the base in the
viewing direction. As with other possible spindle orientations for example
parallel to one of the opposed skies the LED will be designed to radiate
widely. A shroud 38 is preferably provided extending from the stator base
preferably to a position a little forward of the LED 36 to set an upper limit
on its
radition angle from the viewing direction. The shroud thus preferably covers
the rearward portion of lens 43. A bias magnet 40 having a forward, rearward
axis is provided in the centre of the base. This is to provide a resultant
field in
combination with the field between the ends of cores 34L and 34B to improve
the starting torque of the disk. This drive will not be described in detail
here
and is described in U.S. Patenl: 3,518,664 dated 30 June 1970 to M.K. Taylor.
The cores 34B, 34L project rearwardly from the base to each receive
windings 42. The cores which are of relatively high remanence material and
are bridged at their rearward ends by soft iron members 44W, carry the leads
45 to pulse the windings to set the cores in the desired polarity and react
with
disk magnet 21 to flip the disk. As is well known, the high remanence cores
will hold their polarity to retain the disk in its latest pulsed orientation
and to
-10-
CA 02170842 2003-03-31
return it to this orientation if it is mechanically disturbed. Pin 46 also
extending
rearwardly from the base of the stator carries the leads 48 to energize the
cores. In the operation of the invention, the LED is kept continuously on
regardless of disk orientation, by power from a source, not shown, to leads
49,
and is masked against transmission of its rays in the viewing direction by the
rotor 30 to be described, when in the OFF orientation.
The rotor 30 is shown in 'set' or ON position in Figures 1 and 2 and in
'reset' or OFF position in Figures 3 and 6. The disk 30 is provided with a
bright reflecting side 47 facing the viewing direction in the ON position and
a
dark light-absorbent side 50 facing the viewing direction in the reset or OFF
position. The median plane of the disk, at least in ON position, will
preferably
deviate by an angle of about 20° from the parallel to base 20 magnetic
drive
lout this will not be significant tc~ the viewer. The deviation is in the
rotational
sense toward the other limiting position so that the rotation is about
165°
between liming positions instead of 180°.
The disk is preferably made in accord with the teachings of U.S. patents
3,953,274, Winrow et al., and 3,871,945, Winrow et al., such disk having a
central and two outer layers (each of which may be composed by sub layers)
with a recess cut in the central layer 31 to receive the magnet 21 which is
approximately the thickness of the central layer. The ON side of the disk is
-11-
2170842
usually a bright vinyl. The OFF side of the disk is usually
dull black, preferably having a graphite coating to avoid
static electricity build up which might otherwise interfere
with the dot operation. The stator surfaces which form the
background for the disk are coloured to conform to the disk
surface 50..
The spindles 29 are preferably extensions of a mylar
central layer.
The cores are always oppositely polarized, with the
polarity reversed at each pulse of the coils. The disk magnet
21 defines a magnetic axis N-S transverse to the disk axis and
lies in the median plane of the disk. The disk limiting
positions are chosen so that, with each reversal of the cores'
polarity, the disk will rotate about 165° between ON and OFF
positions.
The surfaces of the stator forming a background to the
disk, in either its ON or OFF orientation, are of a dark, not
highly reflectant, colouring~matching as nearly as possible
the OFF side of the disk.
The disk may be slightly curved but is nearly planar
and hence is considered as defining a median plane.
The disk is shaped to conform generally to the square
outline of the housing. The disk is considered as a sector
on each side of the axis. In the ON position of the disk, the
LED remote sector 56 is generally of the shape of one half a
diagonally divided square, with truncated end corners to clear
the towers 24. Section 56 will rotate forwardly of the stator
between OFF and ON position. The LED adjacent sector 58 will
-12-
2170842
rotate rearwardly between ON and OFF position and hence is cut
away to allow it to clear stator components including the cores
and the LED.
In OFF position the stop (core 34L) is arranged so that
the disk is approximately perpendicular to the viewing axis
and the edge 60 is preferably shaped to overlap short wall 22S
which provides a labyrinthine path including high wall 32A for
the escape of radiation to the left side of the stator. The
same overlap cannot be provided on the right side 58 of the
disk since the right hand edge segment must rotate downwardly
past wall 22SR. The rightward escape of light in the OFF
position is reduced or prevented, by the disk which (Figure 6)
covers the large area to the right of the LED and by the high
wall 32.
In ON position, the disk is preferably maintained at a
greater angle to the base, and at less than 90° to the viewing
direction. The reason is that the full sector 56 of the disk
is heavier than the cut out sector 58. The magnet 21 is also
eccentrically mounted (as hereinafter discussed) so that most
of its weight is in the sector 58. The summed imbalance adds
to the torque required to move the full semi plane up from ON
to OFF orientation. The core 34B end (or other alternate stop)
is located forwardly of its counterpart core 34L end to give
the disk magnet 21 a better starting torque. ,On the other hand
when moving from OFF to ON, the disk rotation is aided by gravity
and may be limited by its stop 34L to a vertical position. The
presence of the bias magnet 40 does, in this orientation (as in
the other), improve the starting torque in leaving OFF position.
-13-
217842
'Ihe magnet is located so that most of its length is in
sector 56. The primary reason for this is to increase the
distance between the pole of magnet 21 in sector 58 and the
bias magnet 40 as the former passes the latter; to avoid having
the bias magnet 40 unduly affect the disk's rotational velocity.
It is further noted that if the disk magnet 21 is too
close to a core end in either limiting position, the disk
magnet because of its higher coercivity will demagnetize the
core magnet, causing latching. Accordingly, the extent and
location of the disk magnet is chosen to avoid this.
Figure 5 shows a preferred arrangement where 7 display
elements are combined in a single plastic moulding. Such 7
elements are preferably oriented as a column. The reason is
that the bus mount for the array may curve in plan view. Thus
the 7 element columns may be conveniently arranged to comply
with this curvature. Alternatively, with such a curved arrange-
ment the display elements may be arranged in planar sub-array
and the sub-arrays arranged as chords of the curved bus surface.
Of course, any other number of elements than 7 may be combined
in any single moulding. The area for a bus destination sign
may thus be filled by a combination of multiple and single
element units.
Figures 10A and lOB which are schematic longitudinal
vertical sections along a bus for comparison of an array in
accord with the invention (Figure 10B) with.a common prior
arrangement.
-14-
2170842
In Figure 10A a flip disk array A without LED's must,
in a bus B be set back from the windshield C to allow (for
use at night and during poor lighting) illumination of the
disks in the array by a halogen tube D. In figure 10B the
array AI is provided with disks augmented by LED's in accord
with the invention and Figures 1-9 so it may be moved much
closer to the windshield C for better viewing. The closer
location of the array to the windshield renders preferable
the use of display elements in single vertical columns to
conform if necessary to a curved or otherwise irregular
windshield contour in plan view.
-15-
