Note: Descriptions are shown in the official language in which they were submitted.
5~77
8ackground of the Invention
_ _
The present inventlon relates to an apparatus and
method for printing a dot matrix of characters on a record
member and, more particularly, to an apparatus and method for
substantially increasing the speed of such printing without
reduction in the quality of the printed characters.
In a printer for printing a dot matrix on a record
member, print or output ends of wires are held in a printhead
in a fixed array. The printhead is fixed to a carriage which
typically moves within a limited range along a track to
suocessive printing stations. At each printing station, a
predetermined number of wires are actuated to strike the
record member through an inking ribbon to form a portion of a
dot matrix of a character on the member. To actuate the print
wires, electricaL signals are generated to energize a
determined number of electromagnets which control hammers or
"clappers" which propel the wires to move them towards the
record member. Both the wires and their electromagnets are
embodied in the printhead, known as a matrix printhead, which
typically has a single column of, for example, 7 or 9 wires,
; facing the record member.
It is, of course, desirable to design a wire
printing system which can form characters as quickly as
possible. In the present state of the art, the frequency of
impact of a wire on a record member is about 1,000 impacts per
second, which produces about 200 characters per second. This
- operating speed is limited by the minimum interval allowable
between successive impacts of each wire, with such minimum
interval being limited for a number of reasons. First, a
; sufficiently efficient electromagnetic material is not
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presently available to move the clapper fa~t enough to propel
its associated wire to cause an impact rate significantly
hi~her than about l,OOO cycles per second. Second, even if
such material were presently available, the dynamics of the
wire and clapper would impose upon the design of the printhead
severe constraints such as allowable settling time, material
strengths and wear characteristics of the wire and clapper.
Alternately, to generate a strong magnetic field without an
efficient magnetic material would impo~e severe restrictions
on the design of the drive circuit for the clapper, power
consumption, reliability and the economics of the printing
system.
One system for increasing the rate of character
formation includes operating the printhead wires at the
present limit of about 1,000 impacts per second~ but which
provides two separate printheads, each printing half a line,
thereby doubling the rate of character formation. In such a
system, the two printheads, each having a single column of
wires and movable together, are operated simultaneously so .r
that while one printhead is printing the first half of a line,
the other printhead is printing the second half of the line.
This two printhead system has a number of disadvantages as
will now be described.
In many instances, a dot matrix printer may not be
printing a full line on a record member such as a sheet of
paper. In this case, in the two printhead system the left
printhead, for example, will be performing more work than the
right printhead, the percentage of more work depending on the
percentage of a full line being printed. If only half a line
is to be printed, the right printhead will move along the
record member, but will not perform any printing.
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Consequently, it i9 not unlikely that the left printhead will
wear out much faster than the right printhead, thereby
requiring significant time and cost in providing a new
printhead and readjusting the machine for this new head.
Also, the use of two separate printheads requires additional
manufacturing cost for hardware and additional physical space
on the dot matrix printer, thereby adding additional design
constraints. Perhaps even more importantly, the throughput or
character formation of this machine when printing, for
example, half a line, is still only that of the single head
machine described above.
Furthermore, with a two printhead printer, line
buffering is necessary in order to print a full line. That
is, data incoming to the dot matrix printer and representing a
full line of characters must be stored in two separate half-
line buffers before the printer can be activa~ed to print such
a line. This is because the data for the first part of the
left half of the line must be sent to the left printhead when
data for the first part of the right half of the line is sent
to the right printhead since the two printheads must be
activated simultaneously to print both halves of the line
simultaneously. Also, thè dot matrix printer having the two
separate printheads is relatively more difficult to control
when it is responding to character at a time key-board data
entry. To key in a whole line o~ information, the left
printhead moves right to record the left half of the line,
then the two printheads are returned to their original left
position, printhead selection is then switched to the right
printhead, and then keyed in data will be printed on the right
half of the line with the right printhead.
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ln addition, in a dot matrix printer, the gap
between the ends of the printhead wires and the record member
must be accurately adjusted to achieve suitable print density.
That is, this gap must be adjusted so that the wires will
strike the record member through the inking ribbon with
appropriate force to place a pronounced dark dot on the
member. When two separate printheads are used, their gaps
should be precisely the same; otherwise, for example, the left
printhead might print characterq which are darker than those
printed by the right printhead, resulting in an overall
appearance which is not pleasing. Since these gaps may be,
for example, as small as .014 inches with tolerances of only
I .001 incheq, it is oftentimes difficult to match accurately
the gap distances of both printheads.
Yet another disadvantage of the dot matrix printer ~`~
having two printheads is that the width of the record member
on which it can print is limited if advantage is to be taken
of the increased rate of character ~ormation which such
printer can provide. If a sufficiently wide paper is not
used, then, for example, on}y the left printhead will be
useful while the right printhead will not be energized. Thus,
again the rate of character formation of the two printhead
machine will be reduced, for example, to that of a single
printhead machine described above.
Furthermore, as indicated above, the two separate
printheads must be operated simultaneously to print
respectively one half of a line. This means that the wires in
both printheads will be energized simultaneously, thereby
increasing the peak power requirements of the machine.
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Summary of the Invention
It is an object of an aspect of the present
invention to provide a novel apparatus and method for
printing characters on a record member.
It is an object of an aspect of the present
invention to provide an apparatus and method which over-
come the above-mentioned disadvantages of a two print-
head dot matrix printer.
It is an object of an aspect of the present
invention to provide a novel dot matrix printer and ;
method of operating the same.
An object o~ an aspect of the present
invention is to increase significantly the operating
speed of a dot matrix printer without reducing the
quality of the printed matter produced by relatively low
speed printers.
In accordance with one aspect of this
invention there is provided a single, movable printhead
for use in a high speed printer for printing a dot -
.:,
matrix of characters on a record member, the matrix
including odd- and even-numbered columns of dots, a dot
col~nn being a series of dots aligned so that a straight ~;; ;
line extending through the centerpoints of the dots is
at a fixed angle to the direction of movement of the -
printhead, comprising:
a. a first column of a predetermined number -
of means for printing only odd-numbered dot columns on ;
the record member; and
b. a second column of a predetermined number ~f
of means for printing only even-numbered dot columns of -
the record member, said second column being spaced from -
said first column by a predetermined distance equal to
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an odd multiple of the space between two ad~acent dot ;-
columns, center-to-center.
By way of added explanation, the foregoing `;
and other objects of the invention are obtained with a
single printhead having a predetermined number of print
wires arranged in two spaced columns and energizers for
the wires. Each column has, for example, 9 wires, and
the wires in a column are moved to impact only alter- ;~
nate dot columns on the record member. The wires in
one column are energized to print only odd-numbered dot
columns on the record member, while the wires in the
other column are energized to print only even-numbered
dot columns on the recording member. While the minimum
interval between impacts of wires in a given printhead :
column is the same as in the present state of the art,
for example l,000/second, the two columns of wires -
reduces by one half the minimum required interval for
printing two adjacent dot columns on the record member, ~ -~
thereby doubling the rate of character formation.
In one embodiment the columns of wires are
spaced apart a distance equal to an even number multiple
of the space
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between two adjacent dot columns on the record member, center-
to-center. In this embodiment, ~he wires of the respective
columns are energized alternately to print, respectively, odd
and even dot columns on the record member. In an alternative
embodiment, the two multi-wire columns are spaced apart a
distance equal to an odd number multiple of the space between
two adjacent dot columns, center-to~center. In this latter
embodiment, the wires of the respective columns are energized
~imultaneously to print, respectively, odd and even dot
columns on the record member.
Brief Description of the Drawing~
Fig. 1 is a perspective view of the single printhead
of the present invention.
Fig. 2 is a cross-sectional view taken through lines
2-2 of Fig. 1.
Fig. 3 is a bottom plan view of an armature retainer
taken along lines 3-3 of Fig. 2 with one armature mounted
therein.
Fig. 4 is an end elevation showing print wires and
taken along lines 4-4 of Fig. 1.
Fig. 5 illustrates dot columns on a record member.
Fig. 6 is a schematic diagram of the electrical
circuitry for energizing print wires in the printhead of
Fig. 1.
Fig. 7 is an alternative embodiment of dot columns
on a record member.
Detailed Description of the Drawings
With reference to Figs. 1-3, there is shown a single
printhead 10 comprising an odd side assembly 12 and an even
side assembly 1~, together with a common stylus guide assembly
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16 for guiding a plurality of impact wire~ or styli 18 along
predetermined paths. While Figs. 2 and 3 include sections of
assembly 12, it is to be noted that assembly 14 is the same as
section 12 and, therefore, need not be separately shown in
section.
Each assembly 12, 14 includes a support plate 20
having 9 electromagnets 22 supported on the support plate 20.
Each electromagnet includes an inner pole piece 24 upstanding
from the surface of the support plate 20 and a coil 26
disposed about the inner pole piece 22. Each coil 26 is
electrically connected to a driver circuit (see Fig. 6) which
selectively applies a predetermined current flow through the
coil. Each electromagnet 22 also comprises an outer pole
piece 28 upstanding from the top surface of the support plate
20 adjacent the associated coil 26.
Each a~sembly 12, 14 also comprises nine armatures
or clappers 30 respectively associated with the nine
electromagnets 22. Each clapper 30 forms with its associated
electromagnet 22 an electromagnetic actuator for converting
electrical energy into mechanical energy to move an associated
one of the print wires 18. Each armature 30 has an inner end
32 and an outer end 3~ extending outwardly from the outer pole
piece 28 by a predetermined distance.
An armature retainer 35 for retaining each of the
25 nine armatures 30 includes a relatively rigid disk 36 having
a central opening 38 for receiving a screw 40 which is screwed
into a cylindrical post 42 of the guide assembly 16 to connect
the retainer 35 to the assembly 16. The disk 36 also includes
a peripheral portion 44 having, as shown in Fig. 3, depending
posts 46 for receiving a pair of notches 48, 50 of each
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cl~pper 30 ~or engagement by two ad~acent posts 46, thereby
restraining radial movement of the clapper 30 relative to the
disk 36.
The retainer 34 also comprises a shock-absorbing
member, such as an 0-ring 52, together with a relatively
resilient biasing member, such as a rubber 0-ring 54, mounted
to the peripheral portion 4~ of the disk 36 between two
adjacent circumferential walls 56, 58. The posts 46 are
dependent from the wall 58.
As shown in Fig. 2, the cross-sectional diameter of
the 0-ring 54 is such as to compress normally when the
retainer 35 is mounted to the guide assembly 16 with the
electromagnet 22 de-energized. The diameter of the 0-ring 54
and those of the walls 56, 58 are predetermined relative to
15 the location of the clappers 30 and outer pole pieces 28. The
axis 60 of the 0-ring 54 is preferably slightly offset
outwardly`of the piYot line of each clapper 30, this pivot
line being at the outermost edge 62 of the associated outer
pole piece 28.
The retainer 35 has the primary function o~
retaining the clappers 30 engaged with their associated outer
pole pieces 28. Additionally, and preferably, the retainer 35
also functions to apply a moment of force to each clapper 30
tending to cause the inner end 32 to rotate about the
associated outer pole piece 28 to hold normally this inner
edge in engagement with the 0-ring 52.
As shown in Fig. 2, the disk 36 also includes a pair
of walls 64, 66 depending from a central portion of the disk
36 and mounting the 0-ring 52 therebetween. The wall 64 has
nine spaced grooves 65 formed therein for accommodating
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re~pectively the clappers 30 at locations adjacent the inner
ends 32. The grooves 65, in cooperation with the posts 46 and
notches 48, 50 in each clapper suitably restrain any movement
of the clappers in a plane perpendicular to the longltudinal
axis 68 of the head 10.
Each assembly 12, 14 has its respective support
plate 20 resting on a base plate 70 and is connected thereto
by a screw 72 extending through the base plate 70 and support
plate 20. As shown in Fig. 2, each wire 18 extends through
the guide assembly 16 including plate 70 and into the assembly
12 or 14 through pla~e 20. A cap 74 is mounted on upper end
18a of the wire 18. A suitable compression spring 76 is
coupled between the cap 74 and an upper surface 78 of a hollow
extension 79 of plate 70 to force normally the aap 74 into
engagement with the lower surface of the clapper 30 adjacent
its inner end 32.
Each wire 18 follows a generally curvilinear path as
it is guided through the guide assembly 16. The caps 74 of
~ each assembly 12, 14 are arranged in a horseshoe type array,
whereas the lower ends 18b of the wires 1~, as shown in Fig.
4, are arranged in two vertical columns in a substantially
linear array. This is accomplished by providing a plurality
of guide members 80, 82 and 84 having holes for each
respective wire 18. These hole patterns in the guide members
progressively constrict the horseshoe type array down to the
linear array shown in Fig. 4. The guide member 84 preferably
includes a conventional ruby bearing plate of the variety
commonly employed in matrix printheads of this type.
In the operation of this printhead, each wire 18 can
be propelled to impact a record member (not shown) through an
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inking ribbon (not shown) adiacent the lower end 18b of each
wire to form one dot of the desired dot matrix. To propel
each wire, an associated electromagnet 22 is energized by
applying current through the coil 26. This produces a
magnetic flux path through the electromagnet in a well-known
manner causing the armature or clapper 30 to be attracted to
the inner pole piece 24. When this occurs, the inner end 32
of the armature pushes the cap 74, and thus the wire 18,
downwardly, as viewed in Fig. 2, causing the wire to be
propelled through the guide assembly 16 until printing end 18b
impacts the record member via the ribbon. During the latter
portion of this action, the armature 30 bottoms on the inner
pole piece 24 and the print wire 18 goes into free flight.
During the time the wire is in free flight, the electromagnet
22 will be de-energized, so that no magnetic force then exists
to hold armature 30 to the inner pole piece 24.
The rebound force on the wire 18, after it strikes
the record member, causes the return flight of such wire.
When the wire 18 returns, the cap 74 impacts the clapper 30
and both return together to their initial position. The shock
absorbing characteristics of the 0-rings 52,54 contribute to
the desired damping of the clapper 30.
Fig. 4 discloses the alignment of the ends 18b of
the print wires 18 to print a dot matrix on the record member.
These ends are aligned in two parallel columns 9 A and B,
respectively. Column A comprises nine print wires 18 which
are coupled to the assembly 12 and responsive to respective
electromagnets 22 in that assembly, while column B comprises
nine wires 18 which are coupled to the assembly 14 and
responsive to respective electromagnets 22 in the latter
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assembly. The center-to-center spacing d between the two
columns A, B of print wires is predetermined and equal to one
of two distances in acc~rdance with the two embodiments of the
present invention, as will be more fully described.
Fig. 5 illustrates the relationship of the various
print positions on a record member for printing, ~or example,
an upper case letter D or M by the printhead of the present
invention. As one example, the printhead of the present
invention may be used to print characters which are 10 pitch,
i.e., there are 10 characters, such as the letter D, per one
inch. Furthermore, as one example, such printhead is used to
print a 9 by 5 dot matrix in which there are 9 print wires per
dot column and 5 dot spaces or 6 dot columns per character.
This is shown in Fig. 5 in which there are numbered six dot
columns Cl-C6 comprising 5 dot spac~s between the columns and
9 dots Dl-Dg per column. For upper case letters, only dots Dl-
D7 are used whereas for lower case letters having descenders,
such as g and j, the last two dots D8-Dg are used to form the
characters.
As may be appreciated, a dot column may be de~ined
as a series of dots aligned so that a ~traight line extending
through the centerpoints of the dots is at a fixed angle to
the direction of movement of the printhead.
In the specific example shown in Fig. 5, a straight
line extending through a dot column is at an angle of 90 in
relation to the direction of movement of the printhead. This
will be provided when the wire columns A and B are at 90 in
relation to printhead movement, as shown in Fig. 4. These
wire columns A and B could be placed at any suitable angle to
produce a corresponding dot column at such angle; obviously,
though, for example, an angle of 0 would not be suitable.
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With reference to Fig. 4, again, in either of the
two embodiments the wire~ in column A are used to print only
the odd dot columns Cl, C3, C5 while the wires in column B are
used to print only the even dot columns C2, C4, C6. Thus, the
printhead has to move a distance equal to two dot spaces,
e.g., the distance between three dot columns Cl C3 or C2-C4,
center-to-center before print wires in column A or B may have
to be energized again to print dots on a dot column. This
means that the printhead of the present invention can move
twice as fast as when wires in a printhead having only a
single column have to be activated at adjacent dot columns
Cl-C6 to print the desired character.
In one embodiment of the present invention, the
spacing d between columns A and B of print wires is equal to
an even number multiple of the space between two adjacent dot
columns, center-to-center. For example, if this even number
multiple is 2, the distance d is equal to the distance between
three dot columns, center-to-center, such as columns Cl-C3.
Thus, this spacing d is equal to the distance t between
columns Cl and C3, as shown in Fig. 5. In this first
embodiment, and with reference to Fig. 5, the wires in columns
A and B are energized alternately to print the dot matrix. As
the printhead moves across the dot column Cl, wires in column
A will be selectively energized to print a predetermined
number of dots for the letter D since this is an odd-numbered
column. When the printhead next moves column A over dot
column C2, none of the wires in columns A and B will be
energized since column A is across an even-numbered dot column
and column B has not yet crossed any dot column (assuming C
is the first dot column of a line; while column B is not
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"energized" in this condition because no dots are to be
printed, it may be considered "energized" so that the above
stated rule of alternately energizing the columns A and B is
satisfied; the reason for this will become more apparent when
the energizing circuit of Fig. 6 is discussed.). In the next
instance when column A moves across dot column C3, selected
w~res in column A will be energized to continue printing the
letter D since column A will be across an odd-numbered column;
however, the wires in column B, which is now across odd-
numbered dot column C1, will not be energized. In the verynext instance, column A will be located across even-numbered
dot ,column C4 and, there~ore, the wires in this column will
not be energized, but column B will now be across even-
numbered column C2 and there~ore the wires in this column B
will be selectively energized to print the required dots for
this dot column. This process continues until the matrix for
the letter D and similarly letter M is completed. Thus, in
this first embodiment, wires in columns A and B are energized
alternately since both columns are simultaneously either
- across an odd- or even-numbered dot column and column A is
used only for the odd-numbered dot columns while column B is
used only for the even-numbered dot columns.
In a second embodiment, the distance d between the
columns A and B of print wires is equal to an odd number
multiple of the space between two adjacent dot columns, center-
to~center. For example, if this odd number multiple is 1, the
distance d is equal to the distance t' between two dot
columns, center-to-center, as shown in Fig. 5, i.e., one dot
column space. In this second embodiment, while the wires in
column A are used to print only odd-numbered dot columns and
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3S~77
the wires in column B are used to print only even-numbered dot
columns, as in the first embodiment, the wires in the two dot
columns are selectively energized simultaneously to print the
character. For example, to print the letter D, when column A
is across dot column Cl, its wires will be selectively
energized to print the dots in this column (as~uming C1 is the
first column in the line, then column B wires would not be
"energized" because no dots are required; however, the column
B wires may be considered "energized" 90 that the above stated
rule of ~imultaneous energizat.ion is satisfied; the reason for
this also will become more apparent when Fig. 6 i3 di~cussed).
In the next instant, column A is across dot column C2 and
column B is across dot column Cl, at which time none of the
wires in either column will be energized since column A is
across an even-numbered dot column and column B i3 across an
odd-numbered dot column. In the next instant, column A will
be across dot column C3 and column B will be across dot column
C2, in which event wires in both columns A and B will be
selectively energized simultaneously to print the dots in
these two columns. Thus, it can be appreciated that as the
columns A and B cross the dot columns Cl-C6 to print letters D
or M, the wires in columns A and B will either not be
energized or selectively energized simultaneously. It will,
therefore, also be appreciated that in the two embodiments
described, wires in a given column are moved the distance t
before such wires may have to be again energized.
Fig. 6 illustrates, schematically, a diagram of a
circuit for energizing the wires in columns A and B in
accordance with the two embodiments described above. A
position transducer 88 generates a signal each time a column A
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or column B of print wires traverses a dot column on a record
member. Transducer 88 includes a light ~ource 90 and a
phototransistor assembly 92 which are attached to a movable
carriage (not shown) supporting the printhead, and a scale 94,
fixed to a frame (not shown) which interrupts the light path
from the source to the phototransistor. The scale 94 is so
constructed that each time the carriage crosses a dot column,
the light path from source 90 to the transistor 94 is
interrupted. Such on and oYf interruptions of the light path
will, when suitably amplified through an amplifier 96, produce
a train of square pulses having one cycle per dot column, as
shown at the output of amplifier 96.
A microprocessor 98 or other similar logic unit is
connected to the output o~ amplifier 96. Microprocessor 98
stores data representing the dot patter~ of the characters
desired to be printed, and feeds data for the odd-numbered dot
columns to a buffer 100 and the data for the even-numbered dot
columns to a buffer 102. The microprocessor 98 also OlltpUtS
an odd column fire select pulse on line 104 and an even column
fire select pulse on line 106. The microprocessor 98 is
programmable to output the fire select pulses on lines 104,106
alternately for purposes of the first embodiment described
above, or simultaneously for purposes of the second embodiment
described above. A more detailed description of the structure
and operation of the microprocessor 98 will be given below.
~ach buffer 100,102 has nine outputs identified in
Fig. 6 as pin 1 - pin 9 corresponding to each of the print
wires 18 in a respective column A or column B on the
printhead. The nine outputs pin 1 - pin 9 for odd column
buffer 100 are connected as one input, respectively, to nine
NAND gates 108, only two of which are specifically shown.
,
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Each o~ the nine outputs pin 1 - pin 9 of the even column
buffer 102 is connected as one input to nine NAND gates 110,
only two of which are specifically shown. The NAND gates 108
receive as a second input the odd column firing qelect pulse
on line 104 from microprocessor 98, while the NAND gates 110
have a second input receiving the even column firing select
pulses on line 106 from the mioroprocessor 98. A one-shot
multivibrator 112 outputs a firing pulse of predetermined
duration as a third input to each of the NAND gates 108 and
110. Multivibrator 112 outputs its firing pulse in response
to each square wave ~ignal from amplifier 96, the firing pulse
duration being smaller than one dot column square wave period
from the amplifier.
The output of each NAND gate 108,110 is fed through
a resistor Rl to the base of a respective transistor 114,120
whose emitter is connected to a voltage source V and whose
emitter and base are coupled through a resistor R2. The
collector of each transistor 114,120 is con~ected respectively
to the base of another transistor 116,122 through a resistor
R3. The collector of transistor 116,122 is coupled to the
voltage source V through the coil 26 for each of the
electromagnets 24 and the emitter is coupled to ground through
a resistor R4. A resistor R5 is connected across the base and
emitter of each transistor 116,122, and diode 118,124 is
connected across the coil 26 as shown.
In operation, assume that the first embodiment,
which is preferred, is to be used in which the columns A and B
of print wires are spaced apart a distance equal to two dot
column spaces. Consequently, the microprocessor 98 will be
programmed to output alternately an odd column fire select
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pulse on line 104 upon recelpt of one waveform from amplifier
96 followed by an even column firing select pulse on line 106
when the microprocessor 98 receives the next waveform from
amplifier 96.
Each time the carriage i9 returned to the leftmost
dot column of a line to be printed, a reset pulse is generated
in a well-known manner (not shown) to reset the microprocessor
98 generating the column fire select pulses. Then, as the
carriage and printhead move across the first or odd dot
column, amplifier 96 generates a first waveform which is acted
on by the microprocessor 98 to provide an odd column fire
select pulse on line 104, which is fed to the NAND gates 108.
In addition, multivibrator 112 generates a firing pulse of
predetermined duration to enable the NAND gates 108 for a
corresponding period of time. At this time, buffer 100
provides output data on pins 1 - 9 depending upon which of the
nine dots of the first odd dot column Cl are to be printed on
the record member. Consequently, the NAND gates 108 receiving
print dot data from pins 1 - 9 will gate this data for the
duration of the firing period of the pulse from multivibrator
112 to turn on transistors 114. With transistors 114 turned
on, transistors 116 will be turned on so that current will
flow through coils 26 to energize the corresponding wires 18
in odd side assembly 12 to print the first odd column.
When the carriage next moves the printhead one dot
column space, column A is across even numbered dot c~lumn C2,
but column B is not yet across dot column Cl. Therefore,
microprocessor 98 will produce an even column fire select
pulse on line 106 which is fed to the NAND gates 110 and
multivibrator 112 sends a firing period pulse to NAND gates
.
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110 to enable them. However, at this time column B will not
be over any dot column in the line and, therefore, buffer 102
will output logic data indicating that the nine print wires 18
in column B are not to be activated. When the carriage next
moves one dot column space so that column A is across dot
column C3 and column B is across dot column Cl, the
transistors 116 again will be closed in the manner indicated
above so that dots will be printed on the odd dot column C3 in
accordance with the data from buffer 100 for thiq dot column.
When the carriage next moves a fourth dot column space, column
A will be across even dot column C4 and column B will be
opposite even dot column C2. At this time, microprocessor 98
will generate the even column fire select pulse on line 106
which, together with the firing period pulse from
multivibrator 112, will enable NAND gates 110.
Consequently, the even column data from buffer 102 for this
column C2 will be gated through gates 110 to turn on
transistors 120 which turn on transistors 122. Therefore,
coils 26 in the even side assembly 14 will be energized in
accordance with this data for column C2, thereby printing the
appropriate dots on the record member. The above operation
continues for the entire length of the line to be printed and
then the carriage is returned to the leftmost position where
the circuits in microprocessor 98 are reset to print another
line of characters.
If it is desired to print characters in accordance
with the second embodiment described above, then the
microprocessor 98 is programmed to output simultaneously an
odd column firing select pulse on line 104 and an even column
firing select pulse on line 106 for each waveform generated by
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amplifier 96. When column A is opposite the first or leftmost
dot column Cl, all the NAND gates 108 and 110 will be enabled.
However, at this time only buffer 100 will output data causing
selected solenoids 26 in odd assembly 12 to be activated,
while the data from buffer 102 will be such as to not energize
coils 26 in the even side assembly 14. Then, when column A is
opposite the second column C2 and column B i9 opposite the
first column Cl, gates 108 and 110 will again be enabled;
however, buffers 100 and 102 will output data which will not
cause any of the coils 26 to be energized. Upon the next
movement of the carriage, column A will be across dot column
C3 and column B will be across dot column C2. Consequently,
all the NAND gates 108 and 110 again will be enabled and
buffer 100 will output data to energize coils 26 to print the
odd column while buffer 102 will output data to energize coils
26 for printing dots on even column C2. It can therefore be
appreciated from the foregoing that as amplifier 96 outputs a
waveform for each dot column, the print wires in columns A and
B will either both be activated or both not be activated as
the carriage moves across a line.
A more detailed description of the structure and
operation of microprocessor 98 or other similar logic unit
will now be given. The output of the amplifier 96, the
- position signal, is used as an interrupt signal to the
microprocessor 98. The microprocessor 98 can be pre-
programmed in such a fashion that each time a position signal
arrives, it will execute a specified segment of a program
previously stored in a memory device such as a Read Only
Memory. The character fonts are stored also in such a memory
device in a series of data words, each data word corresponding
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1~13S67~7
to a dot column and the presence or absence of a bit in a word
denoting the presence or absence of a dot in a dot column.
Typically, 5 such words will ~e necessary to store a 7 x 5
matrix character. To print a particular character, the
microprocessor 98 will be programmed to present the data words
to its output ports in a specified sequence. The data signals
at the microprocessor output ports are normally bu~fered in
bu~fers`100 and 102 to provide a steady continuous signal for
the duration of the energization of coils 26.
To print a 7 x 5 dot matrix character, for instance,
the program is ~o structured that the data word for the first
column (column l) is presented to the odd column information
buffer 100 while the data word for the even column (column 0)
i9 stored on the even column buffer 102, which in this first
instance happens to be a blank word. Then, in the embodiment
that energizes the odd and even column coils 26 alternately, a
signal is presented to a third output port which enables only
the odd column coils 26 to be energized for the duration
controlled by the one-shot multivibrator 112. The next
position signal from amplifier 96 would cause a signal to be
presented to the third output port which would enable only the
even column coils 26 to be energized for the duration
controlled by the one-shot multivibrator 112. In the second
embodiment, the odd and even fire-enable signals are presented
to the third output port simultaneously, causing both odd and
even column coils 26 to be energized simultaneously. Such
signal will then need to be presented to the third output port
only every other position signal arrival. The process then
repeats for both embodiments with the data word for columns 3
and 2 presented to the odd and even column information buffer
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respectively and then the data words for 5 and 4 will likewise
be presented. A microprocessor 98 which can be easily
programmed by one skilled in the art to carry out the above
operation is the Intel 8080 manufactured by the Intel Corp.,
Santa Clara, California.
Thus far, the description of the invention has been
given in relation to the printing of what i3 known in the art
as full dot column matrix printing. However, the invention
can also be employed to print at half spaces in-between the
full dot column positions, such half-space printing also being
known in the art. This half-space printing is used since it
allows for a more eye-pleasing structuring of the printed
characters.
Fig 7 illustrates the character D printed with dots
at the half-spaces; it will be apparent that the matrix format
shown in Fig. 7 is restructured in relation to the matrix
format of Fig. 5. ~-
To carry out the present invention, the character
structuring of Fig. 7 is predetermined such that no printing
on two consecutive half dot spaces is required of a particular
coil 26; thus, the frequency requirement on the printhead 10
is no different from the two embodiments already described
where full dot columns only are printed. The information
stored in the Read Only Memory of microprocessor 98 for each 7
x 5 character would require 4 extra data words for the 4 half
P ( 2A~ C3A~ C4A~ C5A) in between the 5 full dot
positions (Cl, C2, C3, C4, C5), making a total of 9 data words
necessary to store the pattern for a character. Such
character structure is commonly known as the 7 x 9 or 9 x 9
font style depending on the number of wires 18 used. The
sequencing of the wires is quite obvious with the half-spaces
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labelled C2~, C3A~ C4A, C5A as shown in Fig. 7, with C2A being
the half-space between Cl and C2, C3A being the half-space
between C2 and C3, etc., and de~ining C2A and C4A as being
even and C3A and C5A as being odd. As before, the program
stored in the Read Only Memory of microprocessor 98 will be so
structured that the column A of wires will print only the odd-
labelled dot columns (i.e., columns 1, 3A, 3, 5A, 5) and the
column B of wires will print only the even-labelled dot
columns (2A, 2, 4A, 4). It is to be noted that in this hal~-
space dot matrix printing embodiment, the spacing d betweencolumns A and B would still be the same as in the two
embodiments described above in printing full dot columns.
While the invention has been particularly shown and
described with reference to a preferred embodiment thereof, it
will be understood by those skilled in the art that the
foregoing and other changes in ~orm and details may be made
therein without departlng from the spirit and scope o~ the
invention.
.
