Note: Descriptions are shown in the official language in which they were submitted.
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Background and Summary of the Invention
The prior art alphanumeric impact line printer described in U.S.
patent No. 3,782,278 issued January 1, 1974, David L. Barnett et al, forms
characters by printing dots at selected dot positions within a dot matrix.
A horizontal character line comprises a plurality of adjacent character
positions and a fixed blank space horizontally adjacent to each character
position to provide a space between printed characters. In addition, a
fixed vertical space is provided between lines of printed characters. It
is oftentimes desirable to perform graphics plotting functions with impact
printers of this type either separately or intermixed with alphanumeric
character printing. Plotting with these printers can only be accomplished
in a very rudimentary fashion by printing a selected alphanumeric character
(for example, the letter "X") at the character position along a horizontal
` character line which is closest to the actual location of the data point to
be plotted. This method of plotting is generally unsatisfactory because of
the lack of resolution. Resolution is understood in the art to be the number
of data points which can be plotted per inch.
It is therefore an obiect of an aspect of this invention to provide
an alphanumeric impact line printer in which the user may select either a
printing mode or a graphics plotting mode of operation and in which signif-
icantly enhanced resolution is provided in the plotting mode.
This object is accomplished in accordance with the illustrated
preferred embodiment of this invention by providing logic circuitry responsive
to selection of the graphics plotting mode of operation for increasing the
number of available dot positions at which dots may be printed to include the
space
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between character positions of a horizontal character line
as well as the vertical space between adjacent character
lines.
By way of added explanation, in accordance with one
aspect of this invention there is provided an improved
impact printer for printing alphanumeric characters on a
flexible print medium, each of said alphanumeric characters
being formed at discrete spaced character positions along a
- plurality of discrete spaced horizontal character lines by
lQ printing dots at selected dot positions within a dot
matrix of rows and columns at each desired character position,
the impact printer being of the type having a frame; a
plurality of aligned print hammers mounted on a hammer
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support, each print hammer being associated with a character.
: position along a horizontal character line and each carry-
ing a striking means for printing a dot; means movably
securing the hammer support to the frame with the print
hammers adjacent the flexible print medium; a stationary
platen positioned opposite the print hammers and on the
opposite side of.the flexible print medium; horizontal
stepping means connected to the hammer support for stepping
the hammer support and print hammers a discrete number of
horizontal step positions across the flexible print medium
to align each print hammer with successive adjacent ones
of the matrix columns, the discrete number of horizontal
step positions being equal to the number of columns
within the dot matrix; a plurality of electromagnets
immovably secured to the frame, each associated with a
single one of the print hammers and each positioned to
actuate, when energized, its associated print hammer when
that print hammer is in any one of the discrete step
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positions; and vertical stepping means for vertically
advancing the flexible print medium a discrete number of
vertical step positions to align the print hammer striking
means with successive adjacent ones of the matrix rows of
a horizontal character line and for vertically advancing
the flexible print medium an increased increment between
the last matrix row and the first matrix row respectively ~
of adjacent character lines to create a space therebetween, :
wherein the improvement comprises: input/output control
means for receiving ASCII-coded character information and
graphics dot data from an external source, said input/
output control means.including mode select means for
designating a graphics plotting mode of operation and for
issuing a signal indicative of the type of information being ~
received from the external source; character generation and ~ .
storage means, including read-only memory means for storing
matrix row and column information relating to an alpha-
numeric character set employed by the printer, said character
generation and storage means being connected to said input/
output control means for storing ASCII-coded character
information and graphics dot data to be printed on a given
horizontal character line; and operation sequence control-
ling means connected to said input/output control means and
to said character generation and storage means, said
operation sequence controlling means being responsive to the
signal issued by said input/output control means indicating
that graphics dot data is being received from the external
source for increasing the number of horizontal step posi-
tions to which the print hammers are stepped and for
addressing said character generation and storage means on a
dot row basis and for receiving therefrom dot information
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pertaining to all the dots to be printed on a current
horizontal dot row, said operation sequence controlling
means thereupon being operative for selectively energizing
the electromagnets for printing that dot information.
_scription of the Drawings
Figure 1 is a plot of the parabolic curve Y =
7.45-X made with a prior art printer.
Figure 2 is a plot of the parabolic curve Y =
7.45-X made with a printer/plotter constructed according
to the present invention.
Figure 3 is a diagram illustrating the dot position
matrices associated with three adjacent character positions
along a horizontal character line when the printer is
operating in the alphanumeric printing mode.
Figure 4 is a diagram illustrating how the number
of dot positions associated with the three character
positions illustrated in Figure 3 is increased when the
graphics plotting mode of operation is selected.
Figure 5 is a detailed block diagram of logic
circuitry for controlling operation of the printer/plotter
in accordance with the present invention.
Description of the Preferred Embodiment
Operation of the present printer/plotter in the
printing mode is basically the same as described in the
referenced patent. As illustrated
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in Figure 3 of the present application, each discrete character position
along a horizontal character line comprises a dot matrix of rows and
columns, a 5 x 7 dot matrix being shown as exemplary. A space is provided
between ad~jacent horizontal character rositions. hs shown and described
in the referenced patent, a horizontal bank of print hammers is employed
` for printing dots at selected dot positions of each dot matrix. Each
character position is associated with just one of the print hammers com-
prising the bank. The print hammers are simultaneously stepped horizontally ~ -
to sequentially align each hammer with each of the matrix columns of the
character position associated with that hammer. In the case of a 5-column
dot matrix, the print hammer bank is stepped five times. The total horizon-
tal excursion of the print hammer bank in the printing mode is shown in
Figure 3 hereof. The hammers are selectively actuated at each step to print
the appropriate dots. After the hammer bank has completed stepping through
each matrix column position, a paper feed motor steps the paper an incre-
mental distance corresponding to the distance between adjacent rows of the
dot matrices. The print hammers are again stepped through each matrix column
position to facilitate printing of dots at the appropriate dot matrix column
positions of the new row. This procedure is repeated for all dot matrix
rows until all the dots associated with a line of characters have been
printed. At this point the paper feed motor steps the paper an incremental
distance greater than the distance between dot matrix rows to create a
space between printed lines, and the next line of printed characters is
constructed in the manner just described.
An attempt to plot graphics data points using the printer described
in the referenced pat~ent by printing an alphanumeric character at the
character position closest to the actual location of each graphics data point
results in the plot illustrated in Figure 1. Such a plot is quite unsatis-
factory for most plotting operations because of the discontinuities resulting
from the inability of the printer to print a single dot at or very close to
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the actual location of each graphics data point to be plotted. This serious
drawback is overcome by the present invention which facilitates plots of the
type illustrated in Figure 2.
Referring now to Figure 4 of the prese~t application, there is shown
a diagram of how the dot matrices representing the two character positions
illustrated in Figure 3 are expanded, when the graphics plotting mode of
operation is selected, to provide dot positions at which dots may be printed
within the horizontal space between character positions and within the vertical
space between character lines. By means of logic circuitry descrihed in detail
hereinafter these additional dot positions, as well as the dot positions
within the 5 x 7 dot matrix at each character position, are each separately
addressable in the graphics plotting mode of operation to provide greatly
enhanced resolution such that a given data point can be plotted within a
few thousandths of an inch of its actual location. If desired, the dot
position density of the basic character position matrix~nlay be increased,
and the horizontal space between character positions, as well as the vertical
space between character lines, may be arranged to include additional dot
positions to provide an even greater degree of resolution in the graphics
plotting mode of operation. For purposes of illustration, as indicated by
Fi~ures 3 and 4, a 5 x 7 dot matrix has been chosen, and the horizont;al
space between adjacent character positions has been divided to include
two additional dot columns. The total horizontal excursion oF the print
hammer bank is increased in the graphics plotting mode of operatlon, as
shown in Figure 4, to allow dots to be printed at the selected dot positions
within these two additional dot columns The vertical space between adjacent
character lines has been divided to include three additional dot rows, also
as illustrated in Figure 4.
- Referring now to Figure 5 of the present application, t:here is shown
a block diagram of logic circuitry for controlling the printer in both the
alphanumeric printing and graphics plotting modes of operation. The illus-
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trated logic blocks may be constructed in accordance with any of the
techniques well known to those persons skil1ed in the art of logic
implementation. An input/output control unit 100 receives print ;~
commands5 ASCII-coded character infornlation to be printed9 and graphics
dot data to be plotted via a multi-bit bus 116. The source of such informa-
` tion is typically a computer or a desk-top calculator. A mode select line
118 is provided for signalling the input/output control unit 100 on a char-
acter-by-character basis whether the information received on bus 116 is ASCII-
coded character information or graphics dot data. hn alternative method of
distinguishing between ASCII-coded character information and graphics dot
data is to provide an ASCII control code to specify that all information
subsequently received will be graphics dot data. Receipt of a second ASCIJ
control code would then signal the end of graphics dot data and the beginning
of ASCII-coded character information. A multi-bit bus 108 is provided to
transmit ASCII-coded character information and graphics dot data from input/
output control unit 100 to a character generation and storage unit 300.
Character generation and storage unit 300 includes a storage register fol^
storing information relative to a full character line which may comprise
alphanumeric characters and/or graphics dot data. A graphics bit line 110
is set by input/output control unit 100 to indicate to character generation
and storage unit 300 that information being transmitted on bus 10~ is graphics
dot data.
A multi-bit command bus 102 transmits hardware commands to an
operation sequence controller 200. In response to such commands operation
sequence controller 200 appropriately actuates a bank of hammer solenoids
21, a paper feed motor 23, and a hammer stepper 22, all of which are shown
and described in detail in the referenced patent. A multi-l)it status blls
104 provides an indication of the current operational status of the various
components of the printer system to input/output control unit 100. A graphics
control line 106 carries a signal from input/output control unit 100 to oper-
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ation sequence controller 200 indicating whether the current dot row
(i.e. the dot row about to be printed) contains graphics dot data. If
it does, operation sequence controller 200 serves to increase 1:he excursion
of the hammer bank provided by hammer stepper 22 as descril)ed above. This
facilitates selectively printing graphics dot data within the horizontal
space between adjacent character positions. The two extra columns of dot
positions provided by the increased excurs'on of the hammer bank are ignored
at those character positions along a horizontal character line at which
alphanumeric characters are to be printed. This results in printing
alphanumeric characters within the normal 5 x 7 dot matrix at the desired
character positions while permitting graphics dot data to be printed within
an expanded dot matrix at other character positions along the same hori-
zontal character line. Alphanumeric characters may be printed at locations
offset from the discrete character positions by selecting the graphics
plotting mode of operation, in which dot data is supplied for each
individual dot position at which dots must be printed to form the desired
offset character. In the event it is desired to print graphics dot data
on one or more of the three dot rows provided within the vertical space
between a given two adjacent character lines, a signal on graphics control
line 106 indicates to operation sequence controller 200 tha1; paper feed
mctor 23 is to be stepped in dot row increments between those two character
lines.
Character generation and storage circuil; 300 incl~des a read-only
memory which contains the matrix row and column dot information relating
to each character of a chosen alphanumeric character set employed by the
printer. When printing the dots associated with a given alphanumeric
character, the read-only memory is addressed via a mull;i-bit address line
112 on a dot row basis by operation seguence controller 200 to extract the
dot information pertaining to all five of the dot columns of the character
position at which the character is to be printed. This information is trans-
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mitted on a dot data line 114 back to operation sequence controller 200,
which then appropriately actuates hammer stepper 22 and the hammer solenoids
21. Graphics dot data to be printed on a particular dot row is similarly
supplied by character generation and storage unit 200 to operal:ion sequence
controller 200, except that the dot data is not retrieved from the read- :-
only memory but rather from the storage register contained within character
generation and storage unit 300. All the dot information relative to the
current dot row is transmitted via dot data line 114 for accumulat.ion hy
operation sequence controller 200 prior to being printed.
While the present 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 various changes in form and details may he
made therein without departing from the spirit and scope of the invention.
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