Note: Descriptions are shown in the official language in which they were submitted.
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SEI.ECTlVE DENSII'Y PRINTING USING DOT
MATRIX PRINT ~-IEADS IN FIXED SPATIAL RELATION
Technical Field
This invention relates to dot ma-trix printers and,
more particularly, to selectively varying the dot
density and print quality.
Background
In order to achieve quality or "pretty" printed
characters, one relies upon a relatively smooth
character contour in addition to a hiyh contrast
(black/white) ratio between character and the recording
medium. Where a character is formed on a medium ~rom a
matrix of dots produced by a wire matrix print head
through a ribbon, the contrast ratio is a functi.on of
the dot density. In this regard, character contour or
smoothness is a function of the overlap relationship
among the dots especially in the vertical direction.
Martin, et al., USP 4,010,835 issued 8 March 1977,
describes a wire matrix print head arranged to provide
two different printing arrays. In a first embodiment,
the print wires are contained in two guides, one of
which can be translationally displaced in a vertical
direction from the other guide which is held in a fixed
position. In a second embodiment, the wires are
arranged in a single wire guide rotatable about an axis
which is perpendicular to the document and parallel to
the print wires. Further, in Martin the print head is
translated horizontally from left to right to print
across a line on
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a document. Printing i.s e:Efected by the impact of
se1ectkd plura]ities of print wires, each of which is
provided with a separate actuator arranged so that when
the actuator is eneryiæed, -the associated print wi.re is
driven forwared to impact the paper. An inlced rihbon
is interposed between the document (recordinc~ medium)
and the print wires. The impact oF the print wi.re on
the ribbon causes a do-t to be printed at a selected
point on the document. By energizing combinations of
actuators, combinations of print wires can be imprinted
corresponding to a selected character.
In the prior art, it has been customary to
fabricate a single vertical wire column print head with
wires bent along a portion of their extent. This bend
creates a long wire path subjec-t to breakage and
friction. Replacement of wires in such a head is not
feasi~le. In contrast, a relatively never-fail print
head may be fashioned from wires being laid in a
diagonal rather than column array.
Reference should be made to Leontiades, USP
4,284,001, issued 18 August 1981 showing a wire matrix
printer having a plurality of print heads in which the
wires are positioned in slanted relationship. In this
arrangement, it is possible for a slant head to be
involved with two or more characters. The overlapping
of the slant heads and dotted character matrices
creates a complex mapping relationship between both the
data points and the print wire matrix.
Choberka, et al., USP 4,284,363, issued 18 August
1981, describes a dot matrix tilting print head
assembly in which the print head is rotatably mounted
and framed. The dot matrix print head has its wires
actuated to cause dots to be printed on the recordiny
medium while the
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print head is :Iaterally moved across the medium, the
centers o~ the dots being separa-tecl by a given
dlstance. In order to :i~prove print quality, there i.s
involved the insertion of dots between previously
printed dots by controlling the rotation.
The Invention
The -technical problem solved by this invention is
to vary the density within prin-ted dot matrix
characters by selectively overstriking the same mediurn
position with the same character or a portion thereof
positionally offset in at least one direction without
requiring that the medium be moved or complex
rotational head motion be involved. The solution
involves partitioning each print line extent into
several zones and assigning print heads to the
counterpart zones; positioning the heads in fixed
verti.cal offset relation to each other, and selectively
causing each head to imprint the mediurn wi-thin its zone
for low density and to overstrike a designated position
within ano-ther zone with a predetermined character or
portion thereof for high density.
Significantly, the printer includes a plurality of
print heads, each posltioned to print a portion of the
line and each including a plurality of wires which
print dots separated by a given distance.
Corresponding wires of one of the alterna-te print heads
is horizontally aligned to print dots between printed
dots of the other of the alternate print heads. A
vertical displacement or offset of one-half character
dot between overstrik.ing pairs of heads yields
aesthetically pleasing dot matrix characters. For low
density, the half character dot displacement between
the characters in the zones is not readily discernible
to the eye. Advantageously, the
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only mechallical mot:i.on ls the horizonta]. di..spl.acement
of the preferably ganged print heads.
Brie:E Summary of the Drawings
FIG. 1 is a simplifled system diagram for a dot
matrix printer system of the type within which the
inven-tion is contained;
FIG. 2 illustrates the printer conso].e inclucling
the recording medium propagation path in relation to
the print head mechanism;
FIG. 3 is a frontal view of the printer unit in
the console shown in FIG. 2;
FIG. 4 illustrates four heads of nine-wire per
head printing bloc~;
FIG. 5 depicts the recording medium partiti~ned
into prin-t zones;
FIGS. 6 and 7 show the dot distribution in low and
high density printing.
Description of the Preferred Embodiment and Industrial
Applicability
The wire matrix printer is substantially of the
type described in Leontiades, USP 4,284,001 issued
August 18, 1981.
Referring now to FIG. 1, there is shown a
represen~ative system configuration including a host
system 1, and a printer system 2. The printer system
includes a
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con-trol uni-t 3 and an attachment logic 4. Command and
da-ta signals are provldecl by the host system to printer
control unit 3 by way of bus 5. Command and control
signals are obtalned from printer control unit 3 over
the printer adapter 4 by way of bus 6. Status signals
are supplled by the printer control unit 3 to host
system 1 over bus 5. Typically, the host system
applies sequences of commands and data to the printer
and monitors status in return. Control unit 3 receives
the eommands, decodes them, checks for errors, and
generates status information. Control unit 3 further
regulates printing and spacing and includes local
diagnostics. The adapter 4 executes decoded control
unit commands, monitors all printer operations,
actuates print wires, drives motors, senses printer
emitters, and controls operator panel lights and
switching circuitry. Also, the adapter controls the
traetors, the ribbon drive, the print head carrier, the
operator panel, and the printer sensors. It should be
appreciated that the printer control unit 3 and adapter
4 incorporate one or more mieroprocessors for analyzing
eommands and data and to regulate operations.
FIGS. 2 and 3 illustrate eomponents of the printer
housed in console 10. Aecess panels or covers 11, 12,
13 keep a relatively clean industry environment. Top
cover 11 has a window 14 enabling an operator to
observe paper path movement during operation of the
printer whenever the cover is closed. The recording
medium is paper 15. It is obtained from a stored stack
16 and is fed into an upwardly or downwardly
transversing paper path as seen in FIGSo 2 and 3 by way
of a mechanical assembly 20 which includes one or more
sets of tractors 90 and 91. A guide 28 moves the paper
after printing to a takeup stack ~not shown) positioned
below the printing mechanism and to the rear of the
console. The printer incorporates a print assembly 30
which is positioned in a horizontal
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relationslli~ with respect to the mecliuln ~5 at;a prillt
station 32. The printer ribbon drive assembly 40 is
located in closer proximity to the front of the printer.
The printer control unit 3 and its associated micro-
processors are situated behind the side cover 13.
A ribbon ~1 is provided on one of the spools ~2 or43. Each ribbon box preferably contains a disposable
ribbon shoe ~6 mounted on spring attachment members 130
and 13l between print assembly 30 and the medium 15 in
order to maintain rib~on 41 in proper alignment and to
minimize ink smudging on the medium. The ribbon moves on
a path in front of the print head around posts 125, 126,
127, and 128. Two motors drive ribbon ~1 back an~ forth
between spools 42 and 43. *he printer control unit 3
detects ribbon jams and end of ribbon condition. A ribbon
jam turns on an error indicator and stops printing.
The printer includes an operator panel 26 that
consists of several operator control keys, two indicator
lights, a power on/off switch, an operator panel
display, and a density display.
Referring now to FIC. 4, print block 50 includes
four groups of nine print wires 52 and associated
actuator (not shown). Print block 50, print wires 52,
and the print actuators are described in detail in
Canadian Patent Application No. 358,503, filed Augus-t 19,
1980, by W.W. Boynton et al entitled "PrinteriSubsystem
Wi-th Microprocessor Control". Each
group of nine print wires 52 is referred to as a print
head and is respectively designated heads 1 through 4.
Each of the print wires 52 is, in turn, respectively
numbered 1 through 9, vertically from top to bottom with
wires 1 through 5 being on a first slanted path, such
- that adjacent wires 52 are separated horizontally by
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0.40 inches allcl vertieally by 0.01~7 inches. Ally number
of print heacis may be used, sucll as Eor-example two, four
or seven.
As shown in EIG. 5, a verticcll or slallt matrix printer
having two heads 54 in gang relatlollslli~) eaeh of whieh are
normally assigned to a predetermined zone along a print line
extent. In low density printing, the garlc3 heads 5~ would
be positionecl to the left of the first: eharacter to be
printed and inerementally movecl left to rigllt until the
heads were positioned just to the rigllt of the last char-
ac-ter to be ~rinted upon that line. I~t thls point, -the
medium would be advanced so -that the gang heads eould be
aetuated for printing purposes in a riyll-t to left direetion
for the next print line. 'l`he use of multiple heads and
zones increases print speed beeause the heads are driven in
parallel over a shorter distanee.
Referring now to FIG. ~, thcre is shown the detail
of -the normal low vertieal clensity priilting within the
zonal boundaries. Typieally, a head will print dot
matrix eharacters haviny .020 illC}l spacinCI t}lerebetWeell
horizontally and .0167 inehes vertieall~. Tlle other head
is vertically offset. The amount of vertlcal oEfset is
.00833 inehes. This is a half a dot eharaeter spaeing.
FIG. 7 shows the detail of high c~uality printing in whieh
the horizontal dot spaeing is .010 inehes and the
vertieal dot spaeing in any vertieal row is .00833 inches.
Where it is desired to write a line of c3uality prlnting
left to right, the ganged heacls are positionecl sueh that
the right most head is to the left of the irst
eharaeter. Assuming the riclht most heacl is vertically
displaeed lower tllan the left head, a character as shown
in the right most E in FIG. 7 would be first laid O~lt all
along the print extent whilc? the second or left most head
would overs-trike each eharaeter position with the same
character in the same order but offset vertieally
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upwards to a~hleve tlle vert.ical anclllori~onLa:L print
density shc)wll in ~'IG. 7. Tlle gancJecl print head movement
would contillue ulltil. t:he .l.ef t IllOSt head was positioned to
the rigtlt of the last character at thc right end of the
line to be prlllted. The print rate for quality prilltillg
is l~n of the draEt printing, wllere n i.s the number of
ganged heads.
Si(.~nLficclntly, the ganged relationship arnong the
heads is not malldatory, althoucJh it does obviate
problems of maintaining synchronism of data and . ~.
position. It will be further understood by those skilled
in the art that the alternate print heads are _ _ ~
horizontally aligned with respect to one another so that
the dots of one of the two alternate print heads imprints
dots between previously printed dots of the other of the
alternate print heads. The heads are COIl trolled in the
quality print mode to print over two portions of the line
whereby quality printed dot matrix characters result. By
controllably printing in the draft mode, -the print
quality is of sparse density.
It will be further understood by those skilled in
this art that various other changes in the form and
details may be made therein without departing from -the
spirit and scope of the invention.
