U.S. patent number 3,752,288 [Application Number 05/116,361] was granted by the patent office on 1973-08-14 for electrographic printer with plural oscillating print head.
Invention is credited to Bertrand Boyson, Robert H. Detig.
United States Patent |
3,752,288 |
Detig , et al. |
August 14, 1973 |
ELECTROGRAPHIC PRINTER WITH PLURAL OSCILLATING PRINT HEAD
Abstract
A high speed, electrographic, non-impact printer for printing
matrix-type characters on the dielectric coated face of a paper
web. A print head having a plurality of linearly arranged styli
therein is transported in an oscillatory fashion across the
dielectric coated face of the web with the styli in virtual contact
therewith. Means are provided for selectively energizing the styli
for depositing dots of electric charge in image configuration on
the dielectric as the print head traverses the web in both
directions. The position of the print head as it traverses the web
in both directions is sensed for controlling the selective
energizing means for depositing dots of electric charge on the
dielectric only when the print head is in predetermined positions
in its path across the web. The dots of electrical charge are
developed by means of a toner system.
Inventors: |
Detig; Robert H. (Old Tappan,
NJ), Boyson; Bertrand (Manhasset, NY) |
Family
ID: |
22366699 |
Appl.
No.: |
05/116,361 |
Filed: |
February 18, 1971 |
Current U.S.
Class: |
400/322;
101/DIG.37; 400/613; 347/141; 400/82 |
Current CPC
Class: |
B41J
2/39 (20130101); Y10S 101/37 (20130101) |
Current International
Class: |
B41J
2/39 (20060101); G01d 015/06 (); G01d 015/08 ();
G01d 015/012 () |
Field of
Search: |
;101/DIG.13 ;197/1
;340/74ES |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Burr; Edgar S.
Claims
We claim:
1. An electrographic printer for printing dot matrix-type
characters on a web of dielectric coated paper comprising:
means for moving said web along a path;
a printing assembly including a slidable member and a plurality of
print heads mounted in said slidable member, the spaces between
adjacent print heads being equal, each of said print heads having a
plurality of styli, said slidable member being mounted for movement
transverse to the path of the said web with said styli in contact
with the dielectric coated face thereof;
means for transporting said slidable member in an oscillatory
fashion across said web; the amplitude of the oscillations being at
least equal to the distance between adjacent print heads;
means for selectively energizing said styli for depositing dots of
electric charge in image configuration on said dielectric coated
face of said web as said slidable member traverses said web in
either direction, each of said print heads being operational to
print a portion of a line simultaneously with the printing of other
portions of the line by the other print heads of said plurality of
print heads;
means coupled to said slidable member for sensing the position of
said slidable member as it traverses said web in either direction
and for enabling said selective energizing means for depositing
dots of electrical charge on said dielectric coated face of said
web only when said slidable member is in predetermined positions in
its path across said web, said means for moving said web operating
to advance said web by a predetermined amount after each traverse
of said slidable member across said web; and
processor means for developing said dots of electrical charge
deposited by said styli of said print heads.
2. The printer of claim 1 wherein said position sensing means
includes:
a light transmitting mask mounted for movement with said slidable
member;
a plurality of parallel opaque lines on said mask, said lines being
spaced by the intercolumn distance between the columns of dots of
said matrix-type characters being printed and being oriented
orthogonally with respect to the path of movement of said slidable
member;
means fixedly mounted for projecting light through said mask at a
point in its path from one side thereof;
means fixedly mounted opposite said light projecting means on the
other side of said mask for sensing the amount of light transmitted
through said mask at a point in its path; and
means responsive to the sensing of the passage of said opaque lines
by said sensing means for controlling the actuation of said
selective energizing means.
3. The printer of claim 2 wherein said light projecting means
include a lamp and a fiber optic bundle for transmitting light from
said lamp to a line portion of said path, said line portion being
parallel to said opaque lines on said mask.
4. The printer of claim 3 wherein the width of said line portion in
the path of said mask is less than the width of said opaque lines
on said mask.
5. The printer of claim 3 wherein said transmitted light sensing
means includes a photosensitive device and a fiber optic bundle for
delivering light from a line portion of the path of said mask
directly opposite the line portion illuminated by the fiber optic
bundle of said light projecting means to said photo-sensitive
device.
6. The printer of claim 1 wherein said means for transporting said
slidable member includes:
a motor;
a disc rotated at a constant angular velocity by said motor;
cable means connecting a point proximate the periphery of said disc
to both ends of said slidable member; and
resilient means connected in series with said cable means for
compensating for changes in length of said cable means during the
rotation of said disc.
7. The printer of claim 1 wherein said slidable member transporting
means include a motor, and a clutch brake mechanism between said
motor and said slidable member for selectively stopping said
slidable member at either end of its traverse of said web and
wherein said printer further includes means for causing said web
moving means to advance said web by a selected amount while said
slidable member is held at an extreme of its path by said clutch
brake mechanism.
8. The printer of claim 1 wherein said styli on said print heads
are oriented in a line perpendicular to the direction of motion of
said print heads and are spaced from one another by the row
distance of the dots of the matrix-type characters to be printed,
and further including an underlining stylus spaced from said
plurality of styli and selectively energizable for underlining
information printed by said plurality of writing styli.
9. The printer of claim 1 further including a grounding plate
directly opposite said print heads on the opposite side of said
web, said grounding plate being urged toward said print heads.
10. The printer of claim 9 wherein said print heads are slidably
mounted in said slidable member for movement perpendicular to said
web and said printing assembly further includes:
means for resiliently biasing said print heads against said
web.
11. The apparatus of claim 1 wherein said styli of said print heads
are arranged in a spaced linear relationship and wherein said print
heads further include:
insulating layers on either side of said line of spaced styli;
and
bearing members having a substantially higher resistance to wear
than said insulating layers attached to either side of said
insulating layers, said bearing members, insulating layers and
styli being arranged with a smooth flush face oriented towards said
web.
12. An electrographic printer for printing characters on the web of
dielectric coated paper comprising:
means for moving said web along a path;
a printing assembly including a slider having a printing face and a
plurality of groups of linearly arranged spaced styli therein, the
ends of said styli being substantially flush with said printing
face, said slider being mounted for oscillatory movement transverse
to the path of said web with said printing face in contact with the
dielectric coated face thereof;
means for transporting said slider in an oscillatory fashion across
said web;
means for selectively energizing said styli for depositing dots of
an electric charge in image configuration on the said dielectric
coated face of said web as said slider traverses said web in both
directions, said groups of said styli being arranged in equal
spaced relationship with one another for depositing charge on equal
adjacent segments of said web, each of said groups of styli being
operational to print a portion of a line simultaneously with the
printing of the other portions of the line by the other groups of
styli; and
processor means for developing said dots of electric charge
deposited by said styli.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to high-speed electrographic
non-impact printers and more particularly to high-speed
electrographic non-impact printers having oscillating printing
heads.
Impacting mechanical high-speed printers have long been used for
producing computer printout. These printers are capable of printing
an entire line of type essentially in parallel and the more
expensive ones are adequately fast for most present day
applications.
They do, however, have several serious drawbacks. They are
extremely noisy machines and must therefore be isolated, usually in
a separate room, from people who are expected to work. They are
also very complex and extremely expensive and are subject to a
fairly high rate of mechanical breakdown.
Recently electrographic line printers have been introduced which
solve some of the problems. These printers deposit electrostatic
charge latent images of the information to be printed on a web of
dielectric coated paper. The electrostatic image is developed by
means of liquid or dry toner developing systems. These machines
usually include a stationary printing head assembly having as many
as 1,000 or more individual styli arranged in contact with the
coated side of the web in a line normal to the direction of its
movement. A common electrode is also provided, usually on the
opposite side of the web and, as the web is stepped past the styli,
dots of electrostatic charge are deposited on the dielectric
coating by selectively pulsing the styli. Printers of this type are
usually arranged to print a character by depositing charge on
selected dots of a 5 .times. 7 dot matrix.
Line printers of this type offer a significant step forward over
the earlier impacting kind. They are very quiet in operation, print
at a high rate of speed, and produce quite acceptable print
quality.
There are, however, many problems with these machines that still
exist. Since they require an individual high voltage switch for
each of the 1,000 or more styli, and also the electronics for
controlling the activation of all the styli in parallel, these
machines are extremely expensive and quite complex electronically.
This electronic complexity also severely limits the reliability of
the machine.
A further problem with these known printers is that there is a
tendency to print "doughnuts," (i.e., dots having only the
periphery black) unless a rather expensive grade of paper is used
which has a very smooth and uniform coating. This is thought to be
because the styli tend to deposit charge on the paper only around
this periphery unless the paper surface is quite smooth. Dots of
this type appear light and faint to the eye since the eye tends to
integrate the black circle with the white interior.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the invention to improve
electrographic line printers.
It is a further object of the invention to increase the reliability
of and to simplify electrographic line printers by reducing the
number of styli in the printer.
It is another object of the present invention to provide an
electrographic printer which prints solid, dark appearing dots.
In accordance with these and other objects of the invention there
is provided a high speed electrographic line printer for printing
lines of information on a web having a charge retaining surface
normal to the direction of its movement which includes a plurality
of print heads mounted for movement across the web in contact
therewith, and means for moving the print heads in an oscillatory
fashion across said paper. Also provided are means mechanically
coupled to the print heads for movement therewith for sensing the
position thereof and means for selectively activating the styli for
depositing a line of character-shaped electrostatic latent charge
images on said paper for each sweep of said styli across said paper
in either direction, and means for developing said latent images on
said paper with a visible toner.
Various other objects, advantages and features of the invention
will become more fully apparent in the following specification with
its appended claims and accompanying drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of an embodiment of an electrographic printer
according to the invention;
FIG. 2 is a back view of the printer of FIG. 1;
FIG. 3 is a schematic showing the mechanical drive for the various
parts of the printer of FIG. 1;
FIG. 4 is a cut-away view of the print head and slider
assembly;
FIG. 5 is a detail drawing of the print head of FIG. 4;
FIG. 6 shows the printing face of the print head of FIG. 5;
FIG. 7 shows a spring-mounted print head according to the
invention;
FIG. 8 is another view of the spring-mounted print head of FIG.
7;
FIG. 9 shows a second embodiment of a spring-mounted print head
according to the invention;
FIG. 10 is another view of the spring-mounted print head of FIG.
9;
FIG. 11 shows an embodiment of the invention in which the print
head is integral with the slider;
FIG. 12 shows the position sensing device according to the
invention;
FIG. 13 is a sectional view of the position sensing device of FIG.
12;
FIG. 14 is a schematic diagram of the electronic drive and conrol
circuitry for the printer according to the invention;
FIG. 15 is a more detailed schematic of a portion of the control
circuitry of FIG. 14;
FIG. 16 serves the control circuitry for the motors and power
supplies of the printer according to the invention;
FIG. 17 shows an embodiment of the device for sensing when the
slider is at the end of the line;
FIG. 18 is a schematic diagram of a high voltage amplifier for
driving a stylus of a print head according to the invention.
DETAILED DESCRIPTION
The invention can best be understood by referring to the following
detailed description of the illustrated embodiments.
Referring to FIG. 1 of the drawings, there is shown an embodiment
of an electrographic line printer according to the invention. The
printing is performed on dielectric coated paper 11 which is
threaded over the roller 13 from the back of the machine through
successive stations where it is imaged, developed, dried and
finally displayed. The latent electrostatic image is deposited on
the dielectric coating by means of four print heads 17 which are
mounted for movement normal to the plane of the drawing in a slider
19. The slider 19 slides in ways 20. The grounding bar 21 operates
both to hold the paper web 11 firmly in contact with the print
heads 17 and to act as the voltage reference for the activation of
the styli of print heads 17. In order to insure good contact
between the print heads 17 and the web 11, the grounding bar 21
should have a resilient or a solid surface facing the print heads
17 depending on whether the print heads 17 are fixedly or
resiliently mounted respectively.
After being imaged, the paper web 11, which, for this embodiment of
the invention has perforated feed holes along either side thereof,
is fed by means of tractors 23 mounted for engagement with the
perforated feed holes on the web 11 to the developing station
25.
The dielectric coated paper used in the printer according to the
invention may be of the standard type used for electrographic
printing and is available from several manufacturers. Preferably
the coating should be such that it does not flake or smear and
thereby interfere with the operation of the print heads 17.
In the illustrated embodiment of the invention, the latent image on
the paper web 11 is developed by means of a liquid developer system
which brings the developer into contact with only the imaged side
of the web 11 by means of the developing roller 27. The developer
roller 27 is rotated at a high speed (on the order of 850 to 1,500
rpm) in an inner tray 29 which is partially full with the liquid
developer. The roller 27 picks up a wave of this developer and
brings it into contact with the latent image on the dielectric
coated side of the web 11. The web 11 is held slightly out of
contact with the roller 27 by means of the roller 31. The spacing
between the web and the roller 27 may be on the order of between
0.075 and 0.125 inches.
In order to keep the toner concentration in the developer uniform
and at the proper level, the developer may be constantly
recirculated. An overflow port (not shown) may be provided in the
inner tray 29 to allow the developer to overflow into an outer tray
33. A drain tube 35 is provided for the outer tray 33 to allow the
developer to flow at a preselected rate from the outer tray to a
developer reservoir 37. Developer is pumped from the reservoir 37
back to the inner tray 29 by means of pump 39.
The volume of and toner concentration in the developer in tank 37
drops during use at different rates and must be controlled. In
order to hold the volume of developer in tank 37 constant,
developer at the proper concentration is metered into the developer
tank 37 from the container 38 by means of a pump 40. The actuation
of the pump 40 is controlled by a switch (not shown) which senses
the level of the developer in the tank 37 and activates the pump 40
when the developer level falls below a predetermined level. The
concentration of the developer is sensed by well known means (not
shown) and concentrated developer is metered into tank 37 from a
concentrate container (not shown) as needed.
The use of the wave of developer on the roller 27 to develop the
image on the web 11 has the advantage that, when the system is not
in use, no developer is in contact with the paper. This avoids the
presence of unsightly black splotches across the paper.
It should be apparent that other developing systems may also be
used to develop the latent image on the paper web 11. Liquid
fountain developing systems or magnetic brush dry toner systems,
for example, would each be applicable.
In transporting the web 11 through the developing system 25, the
rollers 41 and 43 receive the web 11 after it leaves the tractors
23. Guides 42 and 44 act to guide the leading edge of the web 11
around the lower side of roller 31.
After being developed by the roller 27, the web 11 passes through
squeegee rollers 45 and 47 in order to remove the excess developer
therefrom. The squeegee rollers 45 and 47 may be of standard type.
In the preferred embodiment of the invention, roller 45 is metal,
while roller 47 is a rubber roller. It is possible to use a rubber
roller for roller 45 also. However, under some conditions, some of
the image may be transferred from the paper onto the rubber roller
which will then reprint on a following portion of the web 11 on the
next revolution of the roller 45. The use of a metal roller avoids
this problem. The excess developer which is removed from the web 11
by the squeegee rollers 45 and 47 drops into the outer tray 33.
After leaving the squeegee rollers, the web passes through guides
49 and 51 which guide the leading edge of the web 11 to the nip
between rollers 53 and 55. Roller 53 also serves as one of the
guide rollers for an "0" ring conveyor 57. The "0" ring conveyor
passes over guide rollers 53, 59 and 61 and serves to transport the
web past a drying blower 63 to a viewing station 65. After the web
11 is viewed it is carried rearwardly to the back of the
machine.
Rollers 67 and 69 act in conjunction with rollers 49 and 61
respectively, for guiding the web on the "0" ring conveyor 57.
In the illustrated embodiment of the invention, the drying of the
web is performed by the blower 63, which directs a stream of hot
air at the web 11. The heating of the air may be performed by an
electric heating element (not shown) disposed in the air stream of
the blower. It would be equally possible to perform this drying
function by the use of a heated roller, which the paper is wrapped
around. Roller 59, for instance, could easily perform this function
if a heating element were disposed therein.
Referring now to FIG. 2 of the drawings, there is illustrated a
rear view of the electrographic line printer according to the
invention, showing the driving mechanism for the slider 19. In the
illustrated embodiment of the invention, the slider 19 carries four
spaced printing heads 17, each of which images one-fourth of the
width of the paper web 11. It is, of course, possible to use a
different number of printing heads 17 in other embodiments of the
invention. In practice there is a trade off between the amplitude
of the oscillation of the slider 19 and the complexity of the
electronics necessary to control the printing. The fewer printing
heads 17, the simpler the electronics, but the larger the amplitude
of oscillation of the slider 19 and, therefore, the lower the
speed.
In the illustrated embodiment, the slider 19 is driven in an
approximately sinusoidal manner by means of the cable 71 and the
disc crank 73. The cable 71 extends from one end of the slider 19
around the pulley 75 to the pin 77 on the disc crank 73. From pin
77, the cable 71 extends around pulley 79 to the other end of the
slider 19. The spring 81 is provided to allow for the difference in
length of the cable 71 for each 90.degree. rotation of the disc
crank 73.
During operation of the printer, the disc crank 73 is driven at a
constant rotational speed through a clutch/brake mechanism 83 (FIG.
1) by means of a motor. If the printer is operating at a printing
speed of 600 lines per minute, the disc crank 73 must rotate at 300
cycles per minute.
The illustrated type of slider drive was chosen because of its
simplicity and low moving mass. Other drives are of course also
possible, however. A crank drive, or a pin-chain type drive, for
example, could also be used. Some of these drives may drive the
slider in a linear fashion as opposed to the sinusoidal fashion as
in the present embodiment.
The mechanical drive for the various portions of the high speed
printer illustrated in FIGS. 1 and 2 of the drawings is shown in
FIG. 3. Paper tractors 23 are driven through gears by stepper motor
83 for stepping the web 11 past the print heads 17 in slider 19.
The pause between each step must be long enough for the print heads
17 to traverse the web 11 once and the stepping speed must be fast
enough to advance the web by one line in the turn-around time of
the slider 19. In the illustrated embodiment the web 11 may be
advanced at a speed on the order of 600 lines per minute or
more.
As explained above, the slider 19 is driven by means of disc 73
through the cable 71 (FIG. 2). The disc 73 is driven through a
magnetic clutch/brake mechanism 83 by a drive motor 87. During
printing the drive motor 87 is operated at a constant speed so that
the slider 19 traverses the web 11 at the desired frequency. For
instance, if the printer is to operate at a 600 line per minute
rate, the slider 19 must operate at 300 cycles per minute.
As will be explained in more detail later, means are provided for
synchronizing the operation of stepper motor 85 and the slider 19
so that the web 11 remains still while the slider 19 traverses it.
The magnetic clutch/brake mechanism 83 is provided so that, if it
is desired to leave portions of the web 11 blank, the slider can be
held immobile while the stepper motor 85 moves the web 11 at a
faster rate.
The drive for the transport rollers of the processor portion 25 of
the printer is provided by the processor motor 89 through a slip
clutch 91. The slip clutch 91 is coupled by means of belt 93 to the
transport roller 55 and to belt 95. Belt 95 in turn drives roller
45 and belt 97. Belt 97 is used to drive roller 43. the processor
motor 89 operates at a speed which slightly overdrives the rollers
of the processor 25 in order to keep the web 11 tensioned over
roller 31. The slip clutch 91 prevents the rollers of the processor
25 from damaging the web 11 by insuring that they do not exert too
much tensioning force on it.
The toning roller 27 is driven by the motor 99. The roller 55 of
the "0" ring conveyor drives roller 53 through gears 58 by means of
the motor 89.
The structure of the slider 19 and print head 17 is illustrated in
more detail in FIG. 4 of the drawings. The slider 19 is of
trapezoidal cross section and slides in the ways 20 on either side
of the slider. Each of the ways 20 consists of a lower portion 105
having a part cut out to allow the passage of the print heads 17
and a flat upper surface on which the base of the slider 19 rests.
Each of the ways 20 also has an upper portion 107 attached to the
lower portion 105 by means of bolts 109. The upper portion 107
includes an angled surface 111 which bears against the angled face
of the slider 19 and holds it against both vertical and horizontal
movements. This slider construction has the advantage of allowing
the adjustment of both the horizontal and vertical forces on the
slider 19 by the adjustment of only the bolts 109.
Various structures may be used for the print head 17 (FIG. 1) and
several embodiments are illustrated in FIG. 5 through FIG. 11 in
the drawings. An embodiment of a print head 17 which may be made by
printed circuit techniques is illustrated in FIG. 5 of the
drawings. According to this embodiment, the conductors 111 which
form the seven styli of the printing head are etched on a printed
circuit backing board 113 which may be formed of a polyphenylene
oxide base material marketed under the trade name Z-tron by
Polypenco Inc., or on a polyester such as Mylar (trademark). The
conductors 111 which form the seven styli run from the printing
face 115 of the printing head 17 back to the interconnection
portion 117 of the printing head 17. Here a series of seven
individual interconnection pads 119 are formed for connecting the
individual styli 111 to the drive circuitry.
As can be better seen by FIG. 6 in conjunction with FIG. 5, the end
portion 121 of writing head 17 consists of a laminate of several
layers. The styli 111 are covered with a covering layer 123 which
may be made of the same material as the substrate 113. The covering
layer 123 may be glued to the styli 111 and substrate 113 by an
epoxy-type glue, which glue also fills in the interstices between
the adjacent styli 111. Metal plates 125, which may be formed of
stainless steel, ceramic or glass-filled plastic, are attached to
either side of the end portion 121 of the writing head 17. These
plates 125 act to increase the mechanical strength and stability of
the end portion 121, and also make for an extremely low wear, low
friction printing face 115. The plates 125 may be attached to the
end portion 121 by means of an epoxy glue or by bolts.
After the end portion 121 is laminated, the printing face 115 is
ground in order to provide a very smooth flush face. Preferably the
edges of the plate 125 are beveled in order to allow the printing
head 17 to cam over the edge of the paper web 11 when the printing
is being performed on a narrow web 11.
One problem encountered with the printer of the invention is the
tendency of the writing head 17 to clog with particles from the
dielectric coating on the paper web 11 if the stylus design is not
correct. These particles are thought to result from the sliding
contact between the printing heads 17 and the paper. The stylus
designs described in relation to FIGS. 5 and 6 has been found to
minimize this flaking tendency and thereby give good results.
The printing head 17 may be fixedly mounted in the sliders 19 as
indicated schematically in FIG. 1. In this case it has been found
preferable to have the printing head 17 extending slightly (0.005
inch has been found suitable) from the slider 19. This is
preferable both to decrease the frictional contact between the
slider and print head assembly and also because, if they were
mounted flush with the slider 19, any particles from the coating of
the web 11 getting between the slider 19 and the web 11 might bring
the printing heat 17 out of contact with the paper and thereby
cause a malfunction.
Although, as stated above, the writing head 17 may be fixedly
mounted in the slider 19, it has been found preferable to
spring-mount them as shown in FIGS. 7 and 8 of the drawings.
According to this embodiment, the end portion 121 of the writing
head 17 is slidably mounted in a close fitting aperture in the
slider 19. A spring 127 is connected between an extension 129
attached to the printing head 17 and a mounting piece 131 attached
to the slider 19 for forwardly biasing the writing head 17.
The use of the spring-mounted writing head 17 has been found to
improve printing quality. It is thought that this is because it
insures good contact between the writing face 115 and the web 111.
The strength of the spring 127 is chosen so that, during printing,
the printing face 115 extends about 0.005 inch from the surface of
the slider 19.
Another embodiment of a spring-mounted writing head is illustrated
in FIGS. 9 and 10 of the drawings. According to this embodiment,
the writing head 133 is formed of a slug of plastic material having
a rectangular cross section which is slidably mounted in a close
fitting aperture in the slider 19. A mounting member 135 which may
be bolted to the slider 19 holds one end of a compressed spring
137, and the other end of the spring 137 bears against a plate 139
which may be formed as part of the writing head 133. The spring 137
biases the writing head 133 in the forward direction so that it
extends slightly from the surface of the slider 19. According to
this embodiment the writing head 133 and the bearing plate 139 may
be formed as a single piece by injection molding technique out of a
suitable plastic material. In order to be suitable, the plastic
material must wear very slowly when in contact with the paper and
have a very low coefficient of friction. One material which has
been found to be suitable is Delrin AF, which is a teflon-filled
Delrin marketed by DuPont.
Holes for the styli 141 may be drilled in the head. The styli are
then inserted in the holes and potted. An extension 143 of the
printing head 133 may be provided to carry the styli 141 back
through an aperture 145 in the mounting bracket 135. Connections
are made to the styli at the back face of the extension 143. Good
results have been achieved with printing heads constructed
according to the embodiment illustrated in FIGS. 9 and 10. This
embodiment has the advantage of being somewhat simpler and cheaper
to make than that described in relation to FIGS. 5 through 8.
It is also possible to form a printing head such as shown in FIGS.
9 and 10 in two halves split at the line A -- A in FIG. 10. In
making the printing head according to this method seven parallel
axial channels for receiving the seven styli 141 are formed in
one-half of the writing head in the face A -- A which is then
coated with copper of such a thickness that the channels are filled
in. The face A -- A is then ground down to remove the copper plated
on the face, thereby leaving only the seven individual styli in the
channels. The two halves of the writing head may then be attached
together, for instance by means of an epoxy glue.
In FIG. 11 there is shown still another embodiment in which the
need for a separate writing head is eliminated altogether.
According to this embodiment, the slider 19 is itself the writing
head. For each of the four writing heads a line of seven holes is
drilled in the slider 19, as is illustrated in FIG. 11. The styli
147 are then inserted into the holes and fixedly mounted therein,
preferably by means of an epoxy type glue. The face 149 of the
slider 19 is then ground so that it provides a very flat, smooth
surface with the tips of the styli being flush therewith.
In this embodiment the material of the slider 19 must have a very
low coefficient of friction so that it does not cause the
generation of particles from the coating on the web 11. Delrin AF
mentioned above has been found to be a suitable material for the
slider 19 in this embodiment.
With this embodiment of the writing head and slider assembly, it is
preferable that the grounding bar 21 (FIG. 1) have a flexible
resilient surface facing toward the web 11 in order to insure good
contact between the styli 147 and the web 11.
An eighth stylus 150 may also be included in the printing head of
FIG. 11, or for that matter in any of the printing head
configurations illustrated in FIGS. 4 through 10. This eighth
stylus 150 may be used for underlining selected portions of the
information being printed.
Print heads similar to that illustrated in FIGS. 9 and 10 of the
drawings may be constructed using a flat wire cable which is
assembled with supporting metal or plastic side pieces. The
printing face of the printing head should be ground so that the
conductors are flush with the face.
An important feature of the printer according to the invention is
that the dots of the characters are printed while the print heads
17 are moving across the web 11 rather than while stopped. As a
result of this, the problem of the tendency of prior art printers
to print "doughnuts" is solved since the edges of the styli are
wiped across the web 11 during the time they are energized for
depositing charge and thus deposit dots having a uniform charge
distribution which, when developed, appear dark and solid.
In order to maximize the uniformity of the charge distribution, it
is preferable to use styli with a thin rectangular cross section as
opposed to ones with a round cross section.
Since, during printing, the motion of the slider 19 is
approximately sinusoidal, it is not possible to time the enabling
of the print heads for printing the dots of the successive columns
with a free-running clock signal. Rather, an optical position
encoder illustrated in FIGS. 12 and 13 of the drawings, is used in
conjunction with the slider 19 for generating timing pulses to
enable the printing of the successive columns of dots by the print
head 17.
In the illustrated embodiment of the invention each print head 17
prints 32 characters. Each character position contains seven
columns positions, five columns positions of which are used to form
the 5 .times. 7-dot character matrix and the other two serving as
the intercharacter spaces. It is necessary to generate 224 position
signals each time the slider 19 traverses the web 11. FIG. 13,
which is a sectional view of FIG. 12, along the line A -- A shows
the circuitry which may be used to sense the position of the slider
19. Light from the bulb 151 is collected by a bundle of glass
fibers 153 and passed through a slit 155 in housing 157. The slit
155 may, for instance, be 150 microns wide by 0.5 inch high. Light
from the slit 155 is interrupted by a transparent mask 159, which
is fixedly attached to the slider 19. The mask 159 has 224 parallel
black lines 161 ruled on it, each of which may be 175 microns wide
by 0.5 inch high. The lines may be spaced from each other by 175
microns.
The light passing through the mask 159 passes through a slit in
housing 163 which may be identical to the slit 155 in housing 157,
and which must be directly opposite slit 155. The light is then
collected by a fiber optic bundle 165 which may be substantially
identical to the bundle 153, and fed to the input of a
phototransistor 167. This output is amplified by amplifier 169. The
output amplifier 169 may then be used to enable the printing of the
successive columns of dots by the printing heads 17.
Each time the light source 151 is interrupted by one of the lines
161 a voltage pulse appears at the output of the amplifier 169.
This pulse may then be used to enable the printing heads 17 for
printing the successive columns of dots.
The phototransistor 167 may, for instance, be a Fairchild type
FPT-100.
If the drive used for the slider imparts a uniform speed to it,the
position encoder would not be necessary.
An embodiment of circuitry which may be used to control the printer
according to the illustrated embodiment of the invention is
illustrated in FIG. 14 of the drawings. The data to be printed is
received in a serial-by-bit fashion from a computer and fed into
the six-bit serial-to-parallel converter 171. From the converter
171 the data is transferred one six-bit character at a time to the
one-line buffer 173. The one-line buffer 173 holds a full line of
128 six-bit characters to be printed on a single sweep of the print
head 17 across the web 11. The six-bit code for the successive
characters to be printed by the print heads 17 are sent by the
buffer 173 to the individual character decoders 175. Four of these
character decoders are provided, one for each of the print heads
17.
The character decoders 175 also receive five inputs from the
seven-bit shift register 177. Shift register 177 is controlled by
the slider position sensor whose operation is described in relation
to FIGS. 12 and 13. The pulse output of the amplifier 169 is first
shaped by the square wave shaper circuit 179 and then used to
control a monostable multivibrator 181. Monostable multivibrator
181 in turn controls the seven-bit shift register 177.
The seven-bit shift register 177 therefore shifts each time the
print heads 17 come into position for printing the next column of
dots. The outputs 2 through 6 of the shift register 177 correspond
to the five columns of the 5 .times. 7 character matrix. The
outputs 1 and 7 correspond to the intercharacter spaces.
The outputs 2 through 6 of the shift register 177 are fed to the
character decoders 175. The decoders 175, on the basis of the
six-bit character code from the buffer 173 and the activated column
input from the shift register 177, generate drive pulses to
selected ones of the corresponding set of seven high-voltage
amplifiers 183. The outputs of the seven high-voltage amplifiers
are used directly to activate the seven styli of the print heads
17.
The web advance stepper motor 85 (FIGS. 1 and 14) is controlled
through the stepper driver circuitry 185. The web 11 is line-spaced
by the stepper motor 85 during the time that the stylus and print
head assembly is changing direction at the end of a sweep across
the web 11. When a portion of the web 11 is to be left blank, the
slider 19 is stopped at one end of its sweep by the clutch/brake
mechanism 83 (FIGS. 1 and 2) and the driver circuitry 185 pulses
the stepper motor 85 at a high rate so that the web 11 is moved
quickly past the slider 19 for that portion which is to be left
blank.
The control and timing signals for the stepper motor driving
circuitry 185, the clutch/brake 83, and the character data handling
circuitry are provided by the control unit 187. The control unit
187 receives control signals from the computer to which the printer
is coupled and in turn controls the flow of data received by the
printer from the serial-to-parallel converter 171 to the printing
head driver circuitry 183. The control unit 187 also controls the
motion of the slider 19 through the clutch/brake 83 and the
movement of the web 11 through the stepper motor 85 and the
associated drive circuitry 185.
The slider and printing head assembly sweeps across the web 11
alternately from right-to-left and left-to-right. It is therefore
necessary for the control unit 187 to control the data handling
circuitry in such a manner that the data signals de-livered to the
high voltage amplifiers 183 cause the print heads 17 to print the
successive lines of characters on the web 11 alternately forwards
and backwards. In the illustrated embodiment of the invention, the
data input from the computer to the converter 171 is in the
left-to-right reading mode.
Therefore the control unit 187 must invert alternate lines of data
signals supplied to the high voltage amplifiers 183. This is
accomplished by inverting the order of character readout from the
buffer 173 to the character decoders 175 and by inverting the order
of energization of the output by the seven-bit shift register 177,
thereby inverting the order in which the columns of dots for each
character are printed by the print heads 17.
A more detailed diagram of portions of the control unit 187 and the
buffer 173 is illustrated in FIG. 15 of the drawings. The buffer
173 may include four sets 189 of six 32-bit end around shift
registers 191. Each set 191 is associated with one of the character
decoders 175 and print heads 19. The bits of the six-bit character
code for each character to be printed are stored in the
corresponding bit location in the shift registers 191. Thus the
bits of the six-bit code for a particular character to be printed
may be stored, for instance, in the first, or third, or 32-bit
location of each of the six shift registers 191 of a set 189. The
following character to be printed would be stored in an adjacent
bit location of each of the shift registers 191.
When the printer is turned on by closing switch 193 (FIG. 16), the
high voltage power supply 281, the low voltage power supply 283,
the slider drive motor 87, the developer roller motor 99, the
processor motor 89, the developer pump 39 and the blower 63, shown
in FIG. 16, are actuated. After a predetermined delay to allow
these components to get over any transient conditions the control
logic 195 sends a ready signal to the computer on line 197 which
tells the computer that the computer is ready to print and
essentially turns over the control of the operation of the printer
to the computer.
The computer continually sends clock pulses on line 199 to the
control logic 195 for controlling the loading of the characters to
be printed into the buffer 173. While the computer is sending data
to the printer, it also generates a voltage level on line 201 to
the control logic 195. While this voltage level is present on line
201, the control logic 195 transmits the clock signals received on
line 199 to the six-bit serial-to-parallel converter 171 for
enabling the serial-to-parallel converter 171 to receive and store
the contemporaneously received data bits from the computer. The
frequency of the enabling pulses being sent to the
serial-to-parallel converter 171 is divided by six by the frequency
divider circuit 203 whose output is transmitted through OR gate 205
to shifting line 207, which causes the contents of the shift
register 191 to shift one place to the right. This causes the
contents of the serial-to-parallel converter 171 to be transmitted
through the gating circuit 209 to the first bit place of the six
registers 191 of a set of registers 189 selected by the gating
circuit 209.
Thus, each time the serial-to-parallel converter 171 is filled with
a six-bit character code, its contents are transmitted through
gating circuit 209 to the first bit place of a set 89 of shift
registers 191.
The gating circuit 209 is controlled by the output of the frequency
divider circuit 211, which divides the frequency of the shift
pulses received from the frequency divider 203 through OR gate 205
on line 207 by 32. In this way the first 32 six-bit character codes
received from the computer are successively loaded into the shift
registers 191 of the set 189 which controls the leftmost print head
19. Therefore, when the 32nd character is loaded into the first set
189 of shift registers 191, the six-bit code of the character to be
printed in the leftmost character position on the web 11 on the
next sweep of the print head and slider assembly across the web 11
is located in the 32nd bit place of the registers 191 of the first
set 189.
When the divider 211 signals the gating circuit 209 that the 32nd
character code is loaded into the first set 189 of shift registers
191, the gating circuit 209 switches so that the following
characters are loaded in an identical manner into the second set
189 of shift registers 191 which may be identical with the first
set 189. The second set 189 of shift registers 191 hold the
information to be printed by the second writing head 19.
This process continues with the divider 211 signalling the gating
circuit 209 on every 32nd six-bit character code received so that
the gating circuit 209 loads successive groups of 32 characters
into the successive sets 189 of shift registers 191 until all four
sets 189 are filled with 32 characters each.
When the computer has sent the 128 character field to the printer,
the voltage level on line 201 to the control logic 195 drops,
thereby causing the control logic 195 to cease send-ing the
enabling signals to the serial-to-parallel converter 171.
If the slider 19 is beginning its sweep across the web 11 from the
left-hand side of the web 11, the multivibrator 213 has its output
which is connected to AND gate set, thus enabling the AND gate 215
to transmit pulses generated on line 7 of the seven-bit shift
register 177 (FIG. 14) to the OR gate 205 to act as shift pulses on
the line 207 to the shift registers 191.
The output from the shift registers 191 is taken from the 32nd bit
place of each of the registers which, at the end of the loading
operation described above, stores the bits of the characters to be
printed in the leftmost printing position of each of the print
heads 19. Thus, the six-bit codes of the first, thirty-third,
sixty-fifth, and ninety-seventh characters to be printed on the
128-character line are present on the input line of the character
decoders 175 from the buffer 173.
The operation of the printer electronics will first be described in
relation to the situation when the slider 19 is traversing the web
11 from left to right. When the print heads 19 reach the position
where they are to begin printing, the first line ruled on the
transparent mask 159 passes between the lamp 151 and the photodiode
167 causing a pulse output from the photo transistor 167. This
pulse is amplified by amplifier 169 shaped by square wave shaper
179 and then used to trigger the monostable multivibrator 181. The
output of the monostable multivibrator 181 activates the line
number 1 of the seven-bit shift register 177. Since the printing of
the characters takes place in columns 2 through 6 of the
seven-column matrix provided for each character, the output number
1 of the shift register 177 is not connected to the character
decoders 175 but may be used for housekeeping functions. When the
next line on the mask 159 passes between the lamp 151 and the
photodiode 167, the pulse output of the phototransistor 167 is
coupled to the seven-bit shift register 177 through the
aforementioned circuitry and causes the shift register 177 to
shift, thereby activating output line number 2. This line
corresponds to the leftmost column position of the character to be
printed and is coupled to column input number 1 of each of the
character decoders 175.
The character decoders, on the basis of the six-bit character code
signal present at their inputs from the buffer 173 and the column
select input present at one of the input lines from the seven-bit
shift register 177, activate selected ones of their outputs to the
corresponding groups of seven high voltage amplifiers 183, which,
in turn, activate the corresponding styli on the corresponding
print heads 19. In this manner charge dots are deposited on the web
11 for forming the latent image of the first column of the first
character to be printed. The passage of the successive third
through sixth lines on the mask 159 between the light source 151
and the phototransistor 167 cause the seven-bit shift register 177
to activate successively its third through sixth lines, which in
turn cause the character decoders 175 to energize the proper styli
on the corresponding print heads 19 through the corresponding group
of high voltage amplifiers 183 for printing the latent image of the
characters present on the output of the one-line buffer 173.
When the seventh line on the mask 159 passes between the lamp 151
and the phototransistor 167, the shift register 177 energizes line
number 7 which is connected through AND gate 215 (FIG. 15) to OR
gate 205 to act as a shift pulse for the shift registers 191 of all
four groups 189. The AND gate 215 is enabled to pass the input from
line 7 of the shift register 177 since its other input is activated
by the multivibrator 213 because the slider 19 is moving from left
to right.
The shift pulse on line 207 causes the shift registers to shift
their contents end around one place to the right thereby shifting
the bits of the second character to be printed by each of the print
heads into the 32nd bit place. This makes the bits of the second
character to be printed present on the inputs of the character
decoders 175. This process continues as the successive lines on the
mask 159 pass between the lamp 151 and the phototransistor 167
causing the shift register 177 to shift on each line and the shift
register 191 of the buffer 173 to shift on every seventh line. In
this way each of the print heads are controlled through the high
voltage amplifiers 183 to latently image the web 11 with a 32-bit
character portion of the 128-character line being printed.
When the print heads 17 have printed their 32nd charac-ter an
end-of-line pulse is generated. This may be done, for instance, in
the manner illustrated in FIG. 17 of the drawings by using a pair
of magnetically operated reed switches 217 and 219 which are
actuated by the magnetic pole piece 221 mounted on the slider 19.
The reed switches 217 and 219 are positioned so that when the
slider 19 reaches the left-hand margin of the printed area, switch
217 is closed by the action of the magnet 221 and when the slider
19 reaches the right-hand margin (i.e., when each of the print
heads 17 have printed their 32-character segment of the line to be
printed), the switch 219 is closed by the magnet 221. One side of
the reed switches 217 is connected to a voltage source V, while the
other sides are connected to opposite sides of the multivibrator
213 (FIG. 15). Therefore, when the slider 19 reaches the lefthand
margin of the area to be printed, indicating that the subsequent
line is to be printed from left to right, the switch 217 sets the
multivibrator 213 so that the output of the multivibrator 213
connected to the AND gate 215 is actuated. When the slider reaches
the righthand margin, it actuates switch 219 which resets
multivibrator 213 and actuates its output which is connected to the
AND gate 223.
The output pulses from the end-of-line signalling switches 217 and
219 are also connected through OR gate 225 to the control logic 195
as an end-of-line signal. This end-of-line signal is sent to the
computer on request line 227 as a request for the computer to send
the next line of data to be printed. The computer then sends the
next line in the same manner as was described previously, thereby
loading the buffer 173 with the next line of characters to be
printed. After printing a line from left to right the next line
printed is printed from right to left. Thus the 32nd, 64th, 96th
and 128th characters are printed first by the respective print
heads 19. Also each of the printed characters is printed
backwards.
Since the output of the shift registers 191 in the illustrated
embodiment is taken from the 32nd bit place which, at the beginning
of the sweep, holds the character to be printed last by the print
heads when they are printing from right to left, it is necessary to
shift the characters in the shift registers 191 to supply them to
the character decoders 175 in the correct order. It is also
necessary that the inputs to the character decoders 175 from the
seven-bit shift register 177 be activated in the reverse order from
the way in which they are activated in printing from left to
right.
In order to cause the shift register 177 to activate its output in
reverse order, it is possible to include gating in the register
controlled by the output of the multivibrator 213 to reverse the
order of counting, or to include two shift registers, one of which
is used when printing from left to right and the other which is
used when printing from right to left. Either of these alternatives
would be well within the skill of one skilled in the art, and
therefore will not be described in greater detail here.
In order to bring the bits of the correct character to be printed
to the 32nd bit place of the registers 191, it is possible to shift
the contents of the register 31 places to the right each time a new
character is to be printed. As illustrated in FIG. 15, this may be
accomplished by using a clock circuit 227 which is turned on by
output 7 of shift register 177 through the AND gate 223 to generate
31 shift pulses to the OR gate 205. In this way the 31 shift pulses
are passed to line 207 and shift the contents of the shift
registers 191 by the required amount. The AND gate 223 is enabled
to pass the pulse on its input from line 7 of shift register 177
since its input from multivibrator 215 is actuated. The clock
circuit 227 should have a high enough frequency, (e.g. 1 mhz) in
order that the shift registers 191 may be shifted the requisite 31
places between each character to be printed.
Counter 229 and AND gate 231 are provided to turn off the clock 227
each time after it has generated the required 31 shift pulses to
the shift registers 191. The counter 229 may, for instance, be a
standard five-stage binary counter which counts the pulses from the
clock circuit 227. The outputs of all five stages are connected to
the AND gate 231. When all five stages are actuated, (i.e., when
the counter 229 has counted 31 pulses), the output of AND gate 231
goes high which turns off the clock 227 and clears the counter
229.
The operation of the electronics is then essentially identical to
that described above in regard to printing from left to right with
the exceptions that the shift register 177 counts in the reverse
direction and the contents of the shift registers 191 are shifted
31 places between each character place in order to bring the proper
character to be printed to the 32nd bit place of the shift
registers 191.
If the computer wants to leave some lines blank instead of
printing, it merely sends a line step signal to the control logic
195 on line 233 which causes the control logic to operate the brake
portion of the clutch/brake 83 for stopping the slider 19 at the
end of its travel and actuates the stepper motor 85 for line
spacing the paper. If several lines are to be left blank, the
computer sends the required number of blank space pulses to the
control logic 195 for stepping the paper the required amount. The
slider 19 is kept at one end of its travel for the entire
procedure.
Other signals which may pass between the computer and the control
logic 195 includes an end-of-print signal on line 237 from the
computer to the control logic 195 which tells the printer that the
printing is finished. The control logic 195 may also send an error
signal on line 239 to the computer when an error condition occurs
such as when a paper jam occurs or when the paper is exhausted.
An example of a high-voltage amplifier circuit which may be used to
drive a stylus on a print head 19 is illustrated in FIG. 18 of the
drawings. Normally high voltage transistor 241 is turned off so
that voltage source V.sub.B charges capacitor 243 through resistor
245 and diode 247 up to approximately V.sub.B. When the character
decoder 175 energizes the input at the base of the transistor 241
with a positive going pulse, the transistor 241 turns on, thereby
causing its collector potential to drop to a voltage level slightly
above ground. Since the voltage across capacitor 243 cannot change
instantaneously, the voltage at the anode of diode 247 is driven
negatively to a voltage near minus V.sub.B, thereby shutting off
diode 247. This negative voltage pulse also appears at the stylus
251 causing a voltage difference of approximately V.sub.B between
the diode 247. This negative voltage pulse also appears at the
stylus 251 causing a voltage difference of approximately V.sub.B
between the stylus and the grounded platen 251 thereby causing a
dot of negative charge to be deposited on the dielectric coating of
web 11. A V.sub.B voltage on the order of between 500 and 800 volts
has been found to be suitable for the amplifier. Resistor 253 is
provided in order to protect the transistor 241 from high current
should there be a puncture in the web 11 that would short the
stylus 249 to ground.
Although the printer, according to the invention, has been
described in relation to a line printer, it should be apparent that
with minor modifications the printer could find many other uses.
For instance, the printer could equally well be used for printing
graphics if the paper stepping distance were adjusted so that each
step was equal to the character height of a character printed by
seven styli. In this case some changes would have to be made in the
electronics also in the decoding of the input and in order to
eliminate the intercharacter spaces.
* * * * *