U.S. patent number 3,874,493 [Application Number 05/424,513] was granted by the patent office on 1975-04-01 for electronic page printer.
This patent grant is currently assigned to Texas Instruments Incorporated. Invention is credited to A. Kent Boyd.
United States Patent |
3,874,493 |
Boyd |
April 1, 1975 |
Electronic page printer
Abstract
An electronic printer is disclosed which has a printhead
comprised of a matrix of selectively heatable semiconductor mesas
controlled by an MOS decoding matrix which converts binary data to
dot matrix characters. A temperature compensating circuit samples
the temperature of the printhead prior to each print cycle and
adjusts the power to the heated mesas to a level to achieve uniform
print quality. The printhead is moved across a page by a cable
system indexed by a stepping motor. A pressure pad presses the
thermally sensitive paper against the printhead and is also moved
across the page by the cable system in synchronism with the
printhead. A control circuit is provided to store upper case and
lower case signals, and perform the functions of carriage return,
new line, back space, and print-and-step. The printer includes a
simplified paper feed for a continuous sheet and other unique
mechanical features.
Inventors: |
Boyd; A. Kent (Houston,
TX) |
Assignee: |
Texas Instruments Incorporated
(Dallas, TX)
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Family
ID: |
26973720 |
Appl.
No.: |
05/424,513 |
Filed: |
December 13, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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303915 |
Nov 6, 1972 |
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161983 |
Jul 12, 1971 |
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788137 |
Dec 31, 1968 |
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Current U.S.
Class: |
400/120.14;
347/197; 347/210; 400/48 |
Current CPC
Class: |
B41J
2/365 (20130101); B41J 2/36 (20130101) |
Current International
Class: |
B41J
2/36 (20060101); B41J 2/365 (20060101); B41j
001/24 () |
Field of
Search: |
;197/133,49,1R,144,148
;346/76 ;101/93C ;340/172.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Burr; Edgar S.
Assistant Examiner: Rader; R. T.
Attorney, Agent or Firm: Levine; Harold Grossman; Rene
Devine; Thomas G.
Parent Case Text
This is a continuation of application Ser. No. 303,915 filed Nov.
6, 1972, now abandoned, which is a continuation of application Ser.
No. 161,983 filed July 12, 1971, now abandoned, which is itself a
continuation of application Ser. No. 788,137 filed Dec. 31, 1968,
now abandoned.
Claims
What is claimed is:
1. An electronic page printer for printing on a sheet of recording
medium, comprising:
a. an electronic thermal printhead, said thermal printhead having a
support chip and a character matrix of semiconductor elements
mounted on said support chip in thermally separated relationship
for printing characters on the sheet of recording medium,
b. stationary means for supporting the sheet of recording medium in
front of the printing surface of the electronic printhead,
c. means for moving said electronic printhead to a plurality of
printing positions across the width of said sheet of recording
medium, and
d. engagement means for moving said sheet of recording medium into
engagement with said electronic printhead, said engagement means
including a moveable member having a flat resilient pressure pad
for moving a selected portion of the sheet of recording medium into
contact with the said electronic printhead, said pressure pad
comprising a thin, hard metal plate connected to said moveable
member by a resilient block, for providing uniform contact of said
printhead against said recording medium.
2. The combination according to claim 1 wherein the means for
moving the electronic printhead and the pressure pad across the
width of the sheet of the recording medium comprises a cable system
connected both to the printhead and to the pressure pad.
3. The combination according to claim 2 wherein the cable system is
driven by a stepping motor which operates through the cable system
to step the electronic printhead and pressure pad into alignment
with each printing position across the width of the sheet of
recording medium.
4. The combination according to claim 3 wherein the cable system
includes a drum driven by the stepping motor, a length of cable
wound helically around the drum for supplying cable to and for
accumulating cable from the cable system.
5. The combination according to claim 1 further including a pair of
rollers positioned in engagement with the edges of the sheet of
recording medium at the ends of the path of travel of the
electronic printhead and means for selectively rotating the rollers
a predetermined amount to effect line feeding for the sheet of
recording medium.
6. The combination according to claim 5 wherein the means for
rotating the rollers comprises a stepping motor.
7. The combination according to claim 6 further including a
stationary recording medium guide member extending between the
rollers and having a curved recording medium supporting
surface.
8. The combination according to claim 7 further including a shaft
extending from the stepping motor and a spring connected to the
shaft for opposing movement of the electronic printhead across the
width of the sheet of recording medium and for returning the
printhead upon de-energization of the stepping motor.
9. The combination according to claim 2 further comprising:
e. circuit means diffused into each of the semiconductor elements,
including a resistive heating element and switch means for
controlling current flow through the resistive heating element,
f. an integrated circuit chip mounted on the support chip adjacent
the matrix semiconductor elements, the integrated circuit
comprising a buffer stage for each semiconductor element the output
of which is coupled to drive the base of the transistor switch
means of the respective semiconductor elements,
g. character generation means comprised of MOS transistors for
decoding parallel binary character data and driving the buffer
stages in a combination to graphically produce the character by
heated elements of the matrix, at least a plurality of the MOS
transistors being formed on a monolithac semiconductor chip,
and
h. supply voltage means for supplying power to the buffer stages
and circuit means including means for sensing the temperature of
the matrix and adjusting the supply voltage to a level such as to
heat the selected mesas to a preselected temperature range.
Description
This invention relates generally to electronic printers, and more
particularly relates to such a device for printing in the format of
a typewritten page by means of an electronically controlled matrix
of thermal elements.
A number of different devices have been proposed and are presently
being used to print out data presented in the form of electrical
signals. The most prevalently used may be classed as impact
printers and are characterized in that an ink ribbon is placed over
the page and impacted with a mechanical reproduction of the symbol
such as an alphanumeric character to be printed. These systems
inherently have many mechanical parts, are noisy and require
frequent maintenance and repairs. In addition, these systems are
inherently limited in speed by their relatively large mass.
All other types of printers are generally classified as nonimpact
printers. One such printer is the Teletype Inktronic which sprays
ink onto the paper in controlled droplets deflected by an
electrostatic field in much the same manner as a cathode ray tube.
This system is very expensive and large. Another system utilizes a
cathode ray tube display which is projected onto special
photographic paper which must then be developed. This system is
extremely fast, but is also very complex and expensive. Another
system passes electric current through paper causing the paper to
change color. Although relatively fast, this system must use the
time required to print an entire line even if only one character is
printed on the line. Thus, all of the nonimpact printers are
characterized not only by high printing speeds, but also high
costs.
This invention is concerned with a relatively high speed nonimpact
printer which is very compact, lightweight, simple, relatively
inexpensive, and has a high printing rate when compared with
systems of similar costs. The printer utilizes an electronically
controlled thermal printing matrix which is mounted on a
lightweight carriage. The carriage is stepped across the page to
print a line of characters, then returned and the paper advanced
one line. The claims are directed to both the electrical and
mechanical aspects of the device in various combinations and
subcombinations.
The novel features believed characteristic of this invention are
set forth in the appended claims. The invention itself, however, as
well as other objects and advantages thereof, may best be
understood by reference to the following detailed description of an
illustrative embodiment, when read in conjunction with the
accompanying drawings, wherein:
FIG. 1 is a schematic logic diagram of an inputoutput station in
accordance with the present invention;
FIG. 2 is a simplified sectional view of an inputoutput station in
accordance with the present invention;
FIG. 3 is an end view of the electronic printer of the input-output
terminal of FIG. 2;
FIG. 4 is a front elevational view of the electronic printer of
FIG. 3;
FIG. 5 is a schematic diagram illustrating the cable system of the
electronic printer of FIG. 3;
FIG. 6 is a plan view of the electronic printer of FIG. 3;
FIG. 7 is a partial vertical sectional view of a portion of the
paper advance mechanism of the electronic printer of FIG. 3;
FIG. 8 is a transverse sectional view of the electronic printer of
FIG. 3 looking toward the left-hand end of the device with a
carriage at the left-hand margin;
FIG. 9 is a schematic circuit diagram of the electronic controls of
the electronic printer;
FIG. 10 is a schematic logic diagram of the control logic shown in
FIG. 9;
FIG. 11 is an isometric view of the rear face of the printhead and
heat sink of the electronic printer of FIG. 3;
FIG. 12 is an enlarged view of the printhead shown in FIG. 11;
FIG. 13 is a sectional view taken substantially on lines 13--13 of
FIG. 12; and
FIG. 14 is a schematic circuit diagram of the temperature
compensation circuit of FIG. 9.
DESCRIPTION OF FIG. 1 LOGIC
Referring now to the drawings, an input-output station in
accordance with the present invention is indicated generally by the
reference numeral 10 in the schematic logic diagram of FIG. 1. The
input-output station 10 is adapted to operate with a conventional
data set 12 used to transmit serial-by-bit data by existing
telephone data link. For example, the data set may be a Bell
Telephone System type 103F2 and may be linked by telephone line
with an IBM 360 Model 30 computer utilizing an IBM 2702
transmission control unit. Utilizing such a system, a rate of
fifteen characters per second can be achieved, the limiting factor
being the telephone line data link.
The system 10 includes a data set interface 14 which is adapted to
convert serial-by-bit character codes to the necessary logic levels
of "request to send," "clear to send," "data terminal ready," "data
set ready," and "carrier data" in the conventional manner. In
addition, serial-by-bit data is transmitted from interface 14 over
line 16, and the same type of data is received over line 18. The
serial-by-bit data is transmitted from the interface 14 to a
converter 20 by way of line 22, and serial-by-bit data is received
from the converter 20 by way of line 24.
The converter 20 is a shift register having parallel data inputs on
channel 26 and parallel data outputs on channel 28 in addition to
the serial input 22 and serial output 24. The converter thus
performs serial-to-parallel conversion of data received from the
data set interface 14, and performs parallel-to-serial conversion
of data output to the data set interface 14.
The parallel-by-bit data from the converter 20 is passed through a
selectively enabled switching network represented by OR gate 30 to
a single character buffer 32. The parallel data in buffer 32 is
continuously available to an electronic printer 34, which will
hereafter be described in detail, by way of channel 36, and to an
auxiliary output device 37 of any desired type by way of channel
38. The electronic printer 34 has the capability of printing
character data at the maximum transmission rate.
The parallel-by-bit data produced by a conventional keyboard and
encoder device 40 and the data encoded by the auxiliary input
device 39 may be selectively, in the alternative, passed through
gate 30 by way of channels 42 and 44, respectively, and stored in
buffer 32. This data is printed out by the electronic printer 34 as
it is encoded to permit the operator of the keyboard to read what
is being encoded. The character in the buffer 32 is also stored in
an accumulator register 48 by way of channel 50. The accumulator
register 48 is comprised of a number of shift registers equal to
the number of parallel bits contained in the data, each MOS shift
register having a number of bits corresponding to a complete line
of data produced by the electronic printer 34. For example, if the
electronic printer 34 is capable of printing a fifty character
line, the shift registers of the accumulator 48 would include at
least fifty bits plus end of address and new line code characters
at the beginning and end of the block of data. The output from the
accumulator register 48 is passed through level converters 54 and
gated out by way of channel 56, gate 58, channel 60, and gate 62 to
the converter 20 at the appropriate time as will hereafter be
described.
All data passing through gate 30, whether from the converter 20,
keyboard encoder 40, or output of the auxiliary device 37, is
continually applied to a static command decode circuit 64 by way of
channel 63. The command decode circuit 64 produces eight logic
signals on lines 65-72 which are indicative, respectively, of the
end of transmission (HOT), poll character for station (POLL),
keyboard address, auxiliary input address, electronic printer
address, auxiliary output address, end of address (EOA) received,
and "yes" received.
When an end of transmission signal EOT is received, a reset
flip-flop 74 is set, which in turn resets the entire system. When
the station poll character is received, the poll flip-flop 76 is
set which in turn enables the keyboard flip-flop 78, the auxiliary
input flip-flop 80, the printer flip-flop 82, and the auxiliary
output flip-flop 84. Then when a keyboard address, an auxiliary
input address, a printer address, or an auxiliary output address is
decoded, the respective flip-flops are set.
When the keyboard flip-flop 78 is set, gates 86 and 88 are enabled.
If the MOS accumulator register 48 is full, as detected by the MOS
full detector 90, gate 86 enables gate 58 through OR gate 96 so
that data stored in register 52 is gated out. If the MOS storage 48
is not full, gate 88 produces an output which triggers the "No"
flip-flop 92 through OR gate 94. Then when the MOS accumulator 48
is filled, the output from gate 88 ceases, the "No" flip-flop 92 is
reset, and the data from the MOS accumulation register 52 is gated
out as a result of the signal through gates 86, 96, and 58. The
same procedure is followed when the auxiliary input rather than the
keyboard is addressed by the computer as the result of the
operation of AND gates 98 and 100. Thus, the input from either the
keyboard or the auxiliary device is selected by the central
processing unit of the computer.
When the printer is addressed, the printer flip-flop 82 is set,
thus enabling gates 102, 104 and 106. Then if the electronic
printer 34 is not ready, as indicated by a low state on line 105,
gate 104 sets "No" flip-flop 92 through gate 94. When the
electronic printer is ready, gate 102 sets "Yes" flip-flop 108
through OR gate 110 and gate 106 is enabled by line 114 if the text
flip-flop 112 is high as a result of receiving an end of address
record over channel 71. This gates out a print strobe when a timing
pulse is applied to gate 106 by the timing circuit 116.
When the auxiliary output device is addressed on line 70, the
auxiliary output flip-flop 84 is set, thus enabling gates 117, 118
and 120. These three gates then function in the same manner as
gates 102, 104 and 106, dependent upon the status of the ready line
122 from the auxiliary device 37, and line 114 from the text
flip-flop 112.
A "Yes" flip-flop 124 is set whenever the printer is addressed and
ready, whenever the auxiliary output is addressed and ready, or
whenever a longitudinal redundancy check is satisfactory as will
presently be described. An end of block flip-flop 126 is set by
line 127 whenever a line shift is detected in the last storage
space of the accumulation register 48. A command encoder 128
produces an appropriate character whenever the flip-flops 124 and
126 are set and this character is transferred by channel 130
through gate 62 and channel 26 to the converter 20.
The content of the buffer 32 is also continually applied to a
longitudinal redundancy check (LRC) circuit 132. The circuit 132
performs a conventional longitudinal redundancy check on all
incoming data received from the central processing unit and then
compares the locally generated LRC number with the LRC number
received from the central processing unit immediately following the
receipt of an end of block decode signal from the command decode 64
which sets end of block (EOB) flip-flop 133. In addition, the LRC
circuit 132 generates an LRC number for all outgoing data. The LRC
number is transmitted by way of channel 134, gate 136, channel 138
and gate 62 after an end of block character (EOB) has been sent
from encoder 128. This results from the detection of a line shift
character in the last storage space of the accumulation register 52
and the setting of EOB flip-flop 126 by line 127, to in turn set
the enable LRC flip-flop 139 and gate out the LRC number through
gate 136.
OPERATION OF FIG. 1 LOGIC
In operation, assume that data is to be transmitted to the central
processing unit. The operator of the keyboard 40 first presses the
clear button which resets all flip-flops and puts an end of address
(EOA) code in the first character of the MOS accumulation register
48. The operator then proceeds to enter data from the keyboard into
the accumulation register 48 by way of gate 30 and buffer 32. When
the operator has either filled the line, or entered all of the
data, the return carriage button is pushed which generates a new
line code which is also entered in the accumulation register
48.
As soon as the new line character is received by the first-in
storage space of the accumulation register, all characters are
stepped through the register until the end of address (EOA)
character is detected at the first-out storage space, indicating
that the MOS register is full. This resets the text flip-flop 112
by way of channel 113 to disable print strobes through gate 106,
and sets the MOS full flip-flop 90 to enable gates 86 and 98 by way
of line 93. Then when the central processing unit polls the
station, poll flip-flop 76 is set, thus enabling flip-flops 78, 80,
82 and 84. Then when the keyboard is polled, keyboard flip-flop 78
is set, thus enabling gate 58 through gate 96. Data is then sent
from accumulation register 52 to the computer over channel 60, gate
62 and converter 20 at the maximum rate permitted by the data link,
the rate being clocked ty the timing circuit 116.
When the new line character is detected in the first-out storage
space of the accumulator register 48, the end of block flip-flop
126 is set by line 127 so that an end of block character is
transmitted on channel 130 following the new line character. The
output from the end of block flip-flop 126 also sets the enable LRC
flip-flop 139 which in turn enables gate 136 so that the LRC number
is transmitted following the end of block character. After the
central processing unit has performed the longitudinal redundancy
check, a "yes" is transmitted by the central processing unit. When
the "yes" code is decoded by the command decode 64, the station 10
goes into the idle state.
If an end of address EOA character is received from the computer,
text flip-flop 112 is set by line 71, thus enabling either gate 106
or 120. The central processing unit may then send data which will
be printed out without further addressing the station or electronic
printer.
Any time that data is to be transmitted by the computer to station
10, the station is polled to set POLL flip-flop 76 and either the
electronic printer 34 is addressed to set flip-flop 82, or the
auxiliary output device 37 is addressed to set flip-flop 84. Then
when an end of address signal is transmitted, text flip-flop 112 is
set by channel 71 to enable gate 106 or 120. If the printer is
addressed and is ready, the output of gate 102 sets the "Yes"
flip-flop 124 and a "yes" is transmitted to the computer indicating
that the printer is ready. If the auxiliary output device is
addressed and is ready, then a "yes" is transmitted to the
computer. The data is then printed out by the addressed output
device at the rate received from the computer. When the end of
block (EOB) character is received from the computer, the end of
block flip-flop 133 is set, thus enabling the longitudinal
redundancy check circuit 132. The next character from the computer
is the longitudinal redundancy check number which is compared with
the longitudinal redundancy check number generated locally during
receipt of the last data block. If the LRC numbers agree, "Yes"
flip-flop 124 is set by channel 135 and a "yes" is transmitted to
the computer. If the LRC numbers do not agree, the "No" flip-flop
92 is set by line 137 and a "no" transmitted to the computer. If a
"yes" is transmitted to the computer, additional data may be sent
by preceding the data with an end of address (EOA) character. If an
end of transmission character (EOT) is sent instead, the reset
flip-flop 74 is set through line 65 and the entire station 10 is
cleared.
DESCRIPTION OF FIGS. 2- 8
The input-output station 10 is shown in the simplified longitudinal
sectional view of FIG. 2 and is comprised of a keyboard and encoder
section 40, an electronic printer 34, and an electronic circuitry
package 140 which includes all of the circuitry of FIGS. 1, 9, 10
and 14. As previously mentioned, the keyboard and encoder 40 is of
conventional design and includes the electronics necessary to
produce the seven parallel bit binary code representative of the
characters on the conventional typewriter keyboard, together with
the necessary control codes. The mechanical aspects of the
electronic printer 34 are shown in the detailed views of FIGS. 3-8.
The electronic circuitry is illustrated in FIGS. 9-14.
Referring now to FIGS. 3-8, the electronic printer 34 has a support
comprised of a base plate 150 to which are attached right-hand and
left-hand end plates 152 and 154, respectively. As can best be seen
in FIGS. 4 and 8, a carriage indicated generally by the reference
numeral 156 is slidably mounted on a pair of cylindrical rods 158
and 160. The upper rod 158 is pivotally journaled in the end plates
152 and 154. The lower rod 160 is connected to the upper rod 158 by
right- and left-hand arms 162 and 164. The left-hand arm 164 has a
bell crank portion 166 which is connected by a spring 168 to the
base plate 150.
The carriage 156 includes a channel portion 170 which has apertures
in the flange portions receiving the rods 158 and 160, and a heat
sink 172 which is connected to the channel 170 by a pair of
standoffs 174 (see FIG. 8). An electronically controlled thermal
printing matrix 176, which will hereafter be described in greater
detail, is bonded to the interior face of the heat sink 172. An
extension 160a of the rod 160 extends to the left of the arm 164. A
metal tab 178 is connected to the end of the extension 160a. A
magnet 180 is mounted on the left-hand face of the left-hand
upright support plate 154 in a position to hold the tab 178 when
the lower rod 160 is pivoted inwardly. The rod 160 is also
connected to the piston rod 182 of the dash pot 184 which is also
mounted on the left-hand face of the left-hand upright support
plate 154. When the tab 178 is pushed inwardly against the magnet
180, the upper end of the heat sink 172 and thus the printhead 176
is pivoted outwardly and held so as to permit loading of the paper
as will presently be described. The dash pot 184 prevents the
spring 168 from damaging the printhead 176 as it is returned by
physically breaking the hold of the magnet 180.
A third rod 186 and a paper advance drive shaft 188 (see FIG. 8)
extend between the upright support plates 152 and 154 and form a
track upon which a pressure pad carriage 190 is slidably mounted.
The pressure pad carriage supports a pressure pad 192 which is
substantially the same size as the printing matrix of the printhead
176 in mating contact with the printing matrix. The pressure pad
192 includes a thin hard metal plate connected to the pressure pad
carriage 190 by a resilient block. The hard metal plate provides an
abrasive resistant surface, while the resilient block provides
self-alignment to assure uniform contact over the face of the flat
matrix.
Both the printhead carriage 156 and the pressure pad carriage 190
are moved from left to right across the respective tracks 158-160
and 186-188 by a carriage stepping motor 194 and cable system. The
cable system includes a drum 196 mounted directly on the shaft of
the stepping motor 194. The opposite ends of a cable 198 are
secured in grooves 200 and 202 in drum 196 to form an endless loop.
A length of the cable 198 greater than the distance of travel of
the carriage 156 is wound around drum 196 at each end. As
illustrated in the schematic diagram of FIG. 5, the cable 198
extends around a pulley 204 journaled on the right-hand upright 152
to a second pulley 206 mounted on the left-hand upright 154 to form
a first reach 198a. The cable continues around pulley 208 journaled
on the right-hand upright 152, pulley 210 journaled on the
left-hand upright 154, and back around pulley 212 mounted on the
right-hand upright 152 to form reaches 198b, 198c and 198d. The
cable 198 is wound on the drum 196 in such a manner as to unwind
and pass around pulley 204 as it is wound onto the drum from around
pulley 212 at the same point on the drum. The printhead carriage
156 is connected to reach 198a, and the pressure pad carriage 190
is connected to reach 198c so that the two carriages are always
moved in the same direction and in synchronism by the cable
system.
An electrical cable takeup carriage 214 is comprised of a U-shaped
plate having a base portion 216 extending parallel to the rod 160
and right-hand and left-hand arm portions 218 and 220 having
sliding bearings 222 which ride on the print carriage rods 158 and
160. A pair of pulleys 224 and 226 are journaled on the base
portion 216. A second cable 228 (see FIG. 5) extends from the
right-hand upright 152 around the left-hand pulley 226, back around
the right-hand pulley 224 and then is anchored at the left-hand
upright 154. The cable 228 is not shown in FIGS. 4 or 6 to simplify
the drawings. A spool 230 is also journaled on the takeup carriage
214 and a flat multiple wire electrical cable 232 extends from an
anchor bracket 234 on the left-hand upright 154 around the spool
230 to the carriage 156. As the carriage 156 moves between the
left-hand position 156a shown in dotted outline in FIG. 5 and the
right-hand position shown in solid outline, the spool 230 is moved
one-half the distance as represented by the dotted position 230a as
a result of the cable 228, thus keeping a slack out of the
multilead electrical cable 232.
A helical spring 236 is fixed to the left-hand end of the shaft of
the stepping motor 194 and to the left-hand upright 154 by the
bracket 238. The spring 236 preloads the shaft of the stepping
motor 194 with sufficient torque to maintain the carriage 156 at
its full left-hand position when the windings of motor 194 are
open-circuited, and the torque of the spring is increased as the
motor 194 steps the carriage from left to right. However, since the
spring 236 has a substantial length, the torque loading on the
motor shaft is not significantly increased from a percentage
standpoint, particularly since the shaft rotates only about three
and one-half revolutions. When the windings of the stepping motor
194 are open-circuited, the torque of spring 236 drives the drum
196 in a direction to very rapidly move the printhead carriage 156
and the pressure pad carriage 190 to the left-hand margin
position.
A system for supporting and feeding thermally sensitive paper 240
form a large roll is comprised of a right-hand support 242 which is
connected to the right-hand upright by standoffs 243 and a
left-hand support 244 which is connected to the left-hand upright
154. The supports 242 and 244 have identical V-shaped grooves 246
and 248 at the upper end for receiving the stub axles 250 and 252
projecting from the support for the roll of paper. The sheet of
paper 240 proceeds upwardly from the periphery of the roll around a
buffer roller 254 which is journaled on arms 256 and 258, see FIG.
6, which in turn are journaled on the supports 242 and 244,
respectively, at pivot points lying on axis 260. The arms 256 and
258 are biased upwardly by the straps 261 wound around drums 263
and urged downwardly by springs 265. The arms pivot against the
force of the spring between the upper position shown in solid
outline in FIG. 3 and the position shown in dotted outline. The
paper 240 then proceeds around a fixed, cylindrical, lower shelf
262, up between the printhead 176 and the pressure pad 192, and
over a fixed, cylindrical, upper shelf 264 which terminates in an
upwardly extending flange portion 266. A guide trough 268 is
disposed beneath the lower shelf 262 to assist in causing the paper
to pass upwardly in front of the lower shelf 262.
From FIGS. 4, 6 and 8, it will be noted that the lower shelf 262
and the upper shelf 264 are spaced apart to provide a
longitudinally extending groove 270. The pressure pad 192 projects
through the groove 270 to a point slightly beyond the cylindrical
curvature of the lower and upper shelves 262 and 264, as can best
be seen in FIG. 8. The lower and upper shelves 262 and 264 are
mounted on a pair of slotted sleeves 272 (see FIG. 7) and 274 which
are journaled on the line feed drive shaft 188 by bearings 278.
Paper drive rollers 280 and 282 are splined to the drive shaft 188
at each end of the shelves 262 and 264 and have resilient rims with
radii very slightly larger than the radii of curvature of the
cylindrical shelves 262 and 264. A drive sheave 284 is splined to
the shaft 188. Shaft 188 is rotatably journaled in the right-hand
and left-hand uprights 152 and 154. A pair of idler rollers 286 and
288 are journaled on a shaft 289 which extends between the ends of
arms 290 and 292 which in turn are pivotally mounted on a rod 294
which extends between the right-hand and left-hand uprights 152 and
154. The arms 290 and 292 are connected to helical springs 296 and
298, respectively, which are disposed around the rod 294 and
anchored by clamps 300 and 302 so as to continually urge the
rollers 286 and 288 toward the respective drive rollers 280 and
282, to clamp the edges of the paper 240 between the idler rollers
286 and 288 and drive rollers. A roller 303 is also journaled on
the center of shaft 289 to assist in guiding the paper. A second
stepping motor 304 is mounted on the outer face of the right-hand
upright support 152 and has a shaft extending leftward into a
rotary dash pot 306. A drive sheave 308 is mounted on the housing
of the dash pot 306 and drives a toothed belt 310 which passes
around sheave 284 on the feed roller shaft 188. Thus, as the motor
304 is stepped as will hereafter be described, the continuous sheet
of paper 240 from the roll is advanced, one line at a time, by the
rollers 280 and 282.
DESCRIPTION OF ELECTRONIC PRINTER CONTROL CIRCUITRY
The circuitry for operating the electronic printer 34 is shown in
the schematic block diagram in FIG. 9. The data output from the
buffer 32 is fed both to a control logic circuit 320 and to an MOS
array character generator circuit 322. The control logic 320
decodes control characters from the data to provide a data bit on
line 324 representative of whether an upper case or lower case
character (i.e., upshift or downshift) is to be printed. The
control logic 320 also prevents operation of the printer if a
parity check is not satisfactory, and provides a print and step
cycle, a back space cycle, a carriage return and line feed cycle,
and a line feed only cycle. During the print and step cycle, the
control logic 322 also produces a positive-going print pulse on
line 326, a negative-going print pulse on line 327, and a printer
not ready signal on line 105. The character generator circuit
decodes seven parallel bits, plus complements, to selectively turn
the buffer stage 420 and heater element transistor 424 "on" during
the print cycle to produce the proper character. A temperature
compensation circuit 450 senses the temperature of printhead 176 by
means of diode 452 prior to the print cycle, and then sets the
supply voltage to the printhead at a level to produce a
predetermined temperature during the print cycle.
Referring now to the detailed logic diagram of FIG. 10, the
printhead carriage stepping motor 194 has four windings, each of
which moves the shaft of the motor to a predetermined position when
energized. A reversible counter 318 is reset to a count of one when
the printhead carriage 156 returns to the left-hand margin by a
logic 0 on line 338. The counter is then incremented one count at
the end of each print pulse by line 336 going from a logic 1 to a
logic 0. A decoder 328 decodes the count of counter 318 and
energizes the outputs 330-333 by operating the appropriate
transistor switches during counts one through four, respectively,
to step the printhead carriage from left to right across the page.
One of the outputs 330-333 is always energized so as to maintain
the printhead carriage in position against the force of the
carriage return spring 236. When a carriage return signal is
received on line 334, indicated by a logic 0, the count decoder is
disabled so that all power is removed from winding circuits
330-333, thus permitting the motor to be freely driven by the
carriage return spring 236 without back EMF. The counter 316 counts
in the reverse mode whenever line 340 is at a logic 0 level.
The paper feed stepping motor 304 has two windings which are
energized from outputs 342 and 343 which are controlled by the
transistor switches operated by the outputs of NAND gates 344 and
345, respectively. Neither of the windings of the paper feed
stepping motor 304 is energized except while stepping the motor.
However, the motor has a high holding torque when deenergized to
hold the paper in position.
The incoming control characters are decoded by the decoder 346
which produces a logic 1 level on the appropriate output line
348-352, respectively, whenever a "back space," "upper case,"
"lower case," "carriage return" or "new line only" character is
received. In addition, the paper is rapidly advanced by repeated
carriage return cycles as long as line 354 goes to a logic 1 level
on command from the keyboard.
An upper case latch UC comprised of NAND gates 356 and 357 is set
to the logic 1 state to produce a logic 1 at the top output 324
whenever upper case line 349 goes to a logic 1 level, and is set to
a logic 0 state whenever lower case line 350 goes to a logic 1
level.
A carriage return latch CR comprised of NAND gates 358 and 359 is
set to a logic 1 state in response to a logic 1 level on line 351
and a print strobe on line 336, and allows the carriage to return
to the left margin position closing a left limit switch which
produces a logic 0 on input 360. The carriage return latch CR is
reset by the first print strobe after the printhead carriage closes
the limit switch.
A new line latch NL comprised of NAND gates 362 and 363 is set to a
logic 1 state in response to a logic 1 level on line 352, and a
print strobe on line 336, and is reset to a logic 0 state in
response to line 364 from NAND gate 394 going to a logic 0
state.
A master timing latch MT comprised of NAND gates 366 and 367 is set
to a logic 1 state whenever lines 350, 354, 351 and 352 are at a
logic 0 level and a print strobe is gated through gate 368. The
master timing latch MT is reset to a logic 0 level in response to
the output of NAND gate 394 going to a logic 0 level.
A print cycle latch PC comprised of NAND gates 370 and 371 is set
to the logic 1 level whenever the output of NAND gate 368 goes to a
logic 0 level in response to a print strobe, and is reset to a
logic 0 level whenever line 372, which is the output of NAND gate
374, goes to a logic 0 level.
The logic 1 output from the master timing latch MT and the output
from the carriage return latch CR are ORed through NOR gate 376 to
disable NAND gate 368 and prevent the passage of a print strobe
during either a carriage return cycle or a print cycle. The logic 0
output of the master timing latch MT turns an oscillator circuit
378 "on" to clock a two-stage counter comprised of J-K flip-flops
380 and 381.
During a print cycle, or a back space cycle, signified by the
carriage return latch CR and new line latch NL both being in the
logic 0 level so that the output of NOR gate 382 is a logic 1, gate
374 produces a logic 0 on line 372 when flip-flop 380 complements
to the logic 1 state on the first pulse from oscillator 378. The
logic 0 at the output of gate 374 causes the output of gate 390 to
go to a logic 1 level which is stored on capacitor 392. Then when
flip-flop 380 complements to the logic 0 state on the second pulse
from oscillator 378, the output from gate 384 goes back to a logic
1 which results in a logic 0 pulse out from gate 394 to reset the
flip-flops 380 and 381 and the master timing latch MT. In the event
either carriage return latch CR or new line latch NL is in the
logic 1 state, the logic 0 output of NOR gate 382 will disable NAND
gate 374, thus preventing the resetting of flip-flops 380 and 381
and master timing latch MT after the second count. Instead, the
flip-flops 380 and 381 and master timing latch MT are reset on the
fourth count when the outputs of gates 374, 384 and 390 are all at
a logic 1 level and the output of gate 394 goes to a logic 0
level.
In the operation of the circuit of FIG. 10, the application of
power to the circuit automatically sets upper case latch UC to the
lower case mode, resets new line latch NL, resets the print cycle
latch PC, and institutes a carriage return cycle by setting
carriage return latch CR as a result of applying a logic 0 to reset
input 390 by logic circuitry that is not illustrated. When the
carriage return latch is set, the logic 0 on line 334 de-energizes
the printhead carriage stepping motor so that spring 236 returns
the carriage to the left margin and closes the left limit switch,
thus applying a logic 1 to the input of the NAND gate 361 to enable
the gate to reset the CR latch on the next strobe pulse. The true
output of the CR latch also disables gate 368 through the circuit
including NAND gate 375 and NOR gate 376. The output of gate 376
also produces a "printer not ready" indication on output 105. The
true output of the CR latch also resets the counter 318 to the
reference count through NAND gate 383. Then on the next print
strobe on line 336, the carriage return latch CR is reset and the
system is ready for operation with the printhead carriage at the
left-hand margin and the counter 318 at the count of one and the
carriage stepping motor 194 energized.
The upper case UC is initially set to the lower case state and this
information fed to the character generator. Any time that an upper
case character is decoded, latch UC is set to the logic 1 state and
all subsequent characters will be upper case until such time as a
lower case code is again received. During the presence of either an
upper case or a lower case signal, the print strobe is blocked from
the master timing latch MT at gate 368 through NOR gate 341.
If a line of data is to be printed, the next print strobe received
on line 336 is passed through gate 368 to set the master timing
latch MT and the print cycle latch PC. The complement output of the
print cycle latch is gated out by gate 339 and inverted on line 326
to produce a positive print pulse which results in the energization
of the character generator, and a complementary negative pulse on
line 327 to operate the temperature compensation circuit to print a
character. The true output of the master timing latch MT is gated
through NOR gate 376 to disable gate 368 and produce a printer not
ready indication on line 105. The complement output of the master
timing latch MT sets the oscillator 378 in operation. As soon as
the first flip-flop 380 is complemented by the first pulse from the
oscillator 378, the output of NAND gate 374 goes to zero, thus
resetting the print cycle latch PC. This terminates the print cycle
pulse on lines 326 and 327, and increments the counter 326 as line
336 falls to a logic 0. The zero output from gate 374 causes the
output from gate 390 to be a logic 1 which is stored on capacitor
392. Then when the output of gate 374 goes back to a logic 1 when
flip-flop 381 complements on the next pulse from the oscillator
378, the output of gate 394 goes to a logic 0 which resets
flip-flops 380 and 381 and the master timing latch MT, thus
terminating the print cycle. Thus, a character has been printed and
the printhead carriage stepped one space to the right immediately
after the counter 326 was incremented at the end of the print
pulse. This procedure is repeated to print characters across the
line.
If a back space signal is decoded at any time prior to a print
strobe on line 336, the logic 0 level on line 340 causes the
counter 326 to be conditioned to count in the reverse mode, while
line 341 disables gate 339 so that no output print strobe is
produced on lines 326 and 327 during the back space.
In the event a carriage return character is decoded, the gate 368
is disabled through NOR gate 337. Then the next print strobe sets
the carriage return latch CR and the master timing latch MT to the
logic 1 states through gate 335. When the master timing latch is
set at a logic 1 state, the print ready line 105 goes to logic 0
and gate 368 is disabled by gate 376, and oscillator 378 is set in
operation. Also, when the carriage return latch CR is set at the
logic 1 state, gate 374 is disabled through gate 382 and the output
of gate 329 goes to a logic 0, thus enabling gate 327. The
complement output of the carriage return latch CR is then at a
logic 0 which open circuits all of the windings to the carriage
stepping motor 194, thus permitting the spring 236 to return the
carriage to the left-hand margin and close the left limit switch.
The true output of the CR latch also resets the counter 318 through
gate 383. Since gate 374 is disabled, the counter comprised of
flip-flops 380 and 381 proceeds to the count of four before being
reset by the output of gate 366. As flip-flop 380 goes through the
second and fourth counts, the logic 1 level on the complement
output of flip-flop 380 complements flip-flop 325. The true output
of flip-flop 325 in conjunction with the output of gate 327 is
decoded by gates 344 and 345 to cause the paper drive stepping
motor 304 to advance two steps, which corresponds to a single line
advance of the paper. When the output of gate 394 goes to zero at
the count of four, the cycle is ended by resetting flip-flops 380
and 381 and the master timing latch MT. The next print strobe then
resets the carriage return latch through gate 361 to complete the
carriage return cycle during which the carriage was returned to the
left margin, and the paper advanced ready to print a new line.
In the event a new line only character is decoded, gate 368 is
again disabled through gate 337. Then on the next print strobe, the
new line latch NL and the master timing latch MT are both set as a
result of the output of gate 325 going to a logic 0 level. The true
output of the new line latch NL then enables gate 327 through gate
329, and disables gate 374 through gate 382. The true output of the
master timing latch MT causes the print ready line 105 to go to a
logic 0 and disables gate 368, and the complement output sets the
oscillator 378 in operation. The flip-flops 380 and 381 again
proceed to a count of four before being reset by the output of gate
394, and the paper drive stepping motor is stepped on the counts of
two and four as previously described. The logic 0 output from gate
394 resets the master timing MT and new line NL latches to end the
cycle.
The MOS character generator 322 is of the type described in
copending U.S. application, Ser. No. 567,459, filed on July 25,
1966, entitled "Binary Decoder," and assigned to the assignee of
the present invention. The character generator 322 receives a total
of seven parallel bits of information including the back space
information on line 324 from the control logic 320 and the
complement of each. Six bits of the information plus their
complements are received on inputs 400 and an additional bit and
its complement are input on lines 402 and 403. The twelve inputs
400 are arranged in parallel relationship and extend normal to a
number of parallel character output lines 404. There is one output
line 404 for each character to be generated, typically 80. Each of
the lines 404 is connected to ground through an MOS transistor 406.
The gates of MOS transistors 406 are connected to a negative
voltage source so that the transistors function as load resistors.
The input lines 400 are connected to the gates of input decoding
MOS transistors 408. The sources of the input decoding transistors
408 are connectable to a positive voltage source through a bipolar
switching transistor 410, and the drains are connected to the
character output lines 404. Fifty output lines 412 (two outputs for
each element of the electronic printhead) extend normal to the
character lines 404. An MOS transistor 414 is provided to connect
each of the outputs 412 that is required to generate the character
in the matrix represented by the character line 404 to ground. The
data inputs 402 control MOS transistors 416, and inputs 403 control
MOS transistors 417 so as to select which of a pair of output lines
412 are to be connected to the gate of an MOS output buffer 418
which controls current supplied through bipolar transistor 410 to
the base of bipolar transistor 420 used to drive the bipolar
transistor 424 which controls current through the heater resistor
426 of each element of the electronic printhead during the print
cycle. The MOS circuit 322 is enabled by the print pulse on line
326 from the control logic 320 which turns bipolar transistors 422
and 410 "on" to connect the positive voltage terminal to the
sources of MOS transistors 408 and 418.
Thus, during a print cycle when transistor 410 is turned "on," the
character lines 404 are normally at a positive potential determined
by the values of the load resistances 406 so long as any one of the
transistors 408 connected to the particular character line 404 is
"on." This results in the transistor 414 controlled by the
particular output line 404 being turned "off" and the element
controlled by output line 412 being "off." If, however, all of the
transistors 408 connecting the positive voltage supply to the
particular character line 404 are turned "off," as will be the case
only when the particular combination of logic inputs designates the
character represented by the particular character line 404, then
the output line 404 is at ground potential and all of the output
lines 412 necessary to form that character will be connected to
ground by an MOS transistor 414. The information on lines 402
finally selects between two differently coded output lines 412 to
ultimately turn "on" the output transistor 418 for the particular
elements necessary to generate the character. The MOS circuit 322
is an integrated circuit contained in a single package.
Referring now to FIGS. 11-13, the printhead 176 which is mounted
upon the heat sink 172 is of the type described and claimed in its
various aspects in copending U.S. applications, Ser. No. 650,821,
filed July 3, 1967, entitled "Thermal Displays Using Air Isolated
Integrated Circuits and Methods of Making Same," and Ser. No.
671,821, filed Sept. 29, 1967, entitled "Integrated Heater Element
Array and Drive Matrix and Method of Making Same," and each
assigned to the assignee of the present invention. The printhead
176 is comprised of a 5 .times. 5 matrix of semiconductor mesas 428
which are thermally isolated one from the other by air gaps as best
seen in FIG. 13, and which are bonded to a ceramic chip 432 by a
thermally insulating epoxy layer 434. The transistor 424 (see FIG.
9) and resistor 426 for each mesa is diffused in the interior face
adjacent the epoxy layer. The transistor 420 for each of the 25
mesas is formed in the face of a semiconductor chip 436 generally
in the area designated by the dotted outline 438 in FIG. 12 and the
circuits completed by thin metallic film leads formed on the
surface of the semiconductor mesas 428 and chip 436 adjacent the
epoxy layer 434. The ceramic chip 432 is then bonded to the
metallic heat sink 172. The leads to the driver circuit for the
mesas terminate around the periphery of the semiconductor chip 436
and are bonded to leads formed on a printed circuit template 440
mounted on the heat sink 172. The leads on the printed circuit 440
are soldered to the leads carried by the multilead strap cable
232.
Referring now to FIG. 14, the temperature compensation circuit 450
includes a temperature sensing diode 452 which is located on the
chip 436 adjacent to the matrix of thermal elements 428 generally
in the position indicated in FIGS. 12 and 13. A constant voltage is
established at point 454 by a Zener diode 456 so that current flows
through resistor 458, the temperature sensing diode 452, and the
common return line from all of the transistors 420 and 424 on the
printhead 176. The resistance of the common return is represented
by resistor 460.
The voltage at point 462 is sampled through switch 464 and stored
on capacitor 466 except during each negative going print cycle.
Thus, whenever input 327 from the control logic 320 is at a
positive voltage level so that transistors 470 and 472 are turned
"on" and point 474 is positive, switch 464 is turned "on." Then
during the negative going print cycle on line 327, the switch 464
is turned "off."
The voltage on capacitor 466 is applied to the noninverting input
of an operational amplifier 476. The output of amplifier 476 is
passed through a pair of output stages 478 and 480 to an output 482
which is connected to provide collector current to all of the
transistors 420 and 424 of the printhead. Resistor 485 provides a
load when all elements of the printhead are turned "off" during a
print cycle, such as would be required to produce a space. A
feedback resistor 484 connects the output 482 back to the inverting
input of amplifier 476. The inverting input is also connected
through a variable resistance 486 to the sliding contact of a
voltage divider 488 which is connected across the reference Zener
456. The inverting input is also connected through a resistor 490
and a second switch 492 to ground, and alternatively through a
variable resistance 494 to a voltage supply of about 9.0 volts at
point 496, as established by the Zener diode 498 and the negative
voltage at terminal 500. The switch 492 is also controlled by
transistors 470 and 472 and thus is turned "off" during the print
cycle, and "on" during the sample cycle.
Prior to operation of the temperature compensation circuit 450, the
sliding contact of voltage divider 488 is first adjusted to that
the voltage at the sliding contact is equal to the voltage at the
sample point 462 when the diode 452 is at ambient temperature. This
voltage is typically +0.7 volt. Next, the print pulse is activated
at a slow rate and variable resistor 494 is adjusted until the
output voltage at point 482 is at the level necessary to achieve
the desired darkness of print. Next, the print rate is increased to
the maximum anticipated rate and variable resistor 486 adjusted to
achieve the same print quality, thus producing approximately the
same output voltage at 482.
In the operation of the circuit 450, the average temperature of the
printhead is sensed by means of the voltage drop across diode 452
prior to each print cycle, and the power applied to the printhead
during the print cycle is then adjusted according to the previously
sensed temperature. For example, when the printing rate is slow,
the offset potential voltage across the diode 452 is approximately
0.7 volt so that 0.7 volt is stored on capacitor 466 during the
sampling period when switch 464 is open. Switch 492 is also open
during this sampling period so that point 493 is essentially
shorted to ground. This configuration results in an output voltage
of approximately +3.0 volts at 482 to keep the amplifier from going
into saturation, but not sufficiently high to produce printing. In
addition, all of the printheads are "off" so that no printing can
result. During the print cycle, switches 464 and 492 are closed and
at least part of the elements of the printhead will usually be
turned "on." Closing sampling switch 464 prevents voltage surges at
point 462 due to increased IR drop across resistor 460 and heating
of the printhead from being applied to the amplifier 476 with
resulting inaccuracies and instabilities. Closing of switch 492
pulls point 493 more negative, requiring a higher voltage at the
output 482 to balance the amplifier. However, as the temperature of
the diode 452 increases, due to an increase in printing rate or the
nature of the characters being printed, or to a lesser extent due
to an increase in the ambient temperature, the offset voltage
across the diode 452 decreases, thus decreasing the voltage stored
on capacitor 466 and applied to the input of amplifier 476 during
the print cycle. For example, an increase in the temperature in the
printhead of 50.degree. C results in a lowering of the voltage by
0.1 volt to about 0.6 volt. The inverting input is then maintained
only at approximately 0.6 volt during the print cycle so that the
output voltage at 482 need not be as high as would otherwise be
necessary to balance the amplifier 476. The output voltage required
to balance the amplifier is further reduced by the current that
then passes through resistor 486, which compensates for the
increased cooling rate at higher printhead temperatures.
Although a preferred embodiment of the invention has been described
in detail, it is to be understood that various changes,
substitutions, and alterations can be made therein without
departing from the spirit and scope of the invention as defined by
the appended claims.
* * * * *