Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to a thermal
recording system.
Along with the development and popularity of data
processing apparatus such as personal computers and
word processors, recording apparatus have increased in
importance as output terminal devices7 Various types
of recording or printing apparatus such as wire-dot,
ink-jet and thermosensitivs recording apparatus have
been developed. Among these, a thermal recording
apparatus is receiving most attention these days.
The thermal recording apparatus has advantages in
that a normal paper sheet can be used for recording,
a noise level at the time of recording is low, a
recording mechanism is simple, easy maintenance can
be performed, and alteration of recorded data is
impossible. Furthermore, along with the development
of color output terminal devices such as a color CRT
display, there arises a demand Eor a color recording
apparatus. A color thermal recording apparatus can
be easily arranged to perform good color reproduction.
The color thermal recording apparatus is the most
promising apparatus among various types of color
recording apparatus.
In the conventional thermal recording apparatus,
a number of thermal heating resistive elements are
aligned in line, and the thermal heating resistive
elements are selectively supplied with current in
,''~
~z~
accordance with a recording slgnal. This energizing
cycle is then repeated to heat the resistive elements,
so that an ink carried on an ink ribbon is melted by
the heated resistive element The ink is then
transferred to the paper sheet so as to record an
image on the sheet. Although the thermal recording
apparatus has the above advantages, it has a drawback
in that the recorded image becomes poor due to a heat
retention or storage effect of the resistive elements
as the recordin0 speed increases. In order to increase
the recording speed, an interval between energizing
cycles is shortened. When a resistive element which
was energized in the immediately preceding energizing
cycle is reenergized after a short time interval, heat
cannot be sufficiently lost. Therefore, when the same
resistive element is successively energized at a short
interval after the immediately preceding energizing
cycle, the temperature of this resistive element
continues to increase~ In this manner, when the
energizing cycles are repeated at short intervals,
the present temperatures of the individual resistive
elements difEer due to their thermal history. When
resistive elements having different temperatures are
simultaneously energized, areas at which inks are
melted differ, thereby resulting in an image having
a nonuniform density. In particular, when characters
are recorded, the ink is often transferred to a narrow
.. ~
~2~ 8~
space which does not correspond to the image data, thus
degrading legibility.
In order to solve the abovè problem, a system is
proposed in Japanese Patent Publication No. 55-48631 of
Nippon Telegraph & Telephone Public Corporation for "Dot-
Type Printing System", published December 6, 1980, wherein
an energizing time of each thermal heating resistive ele-
ment when mark data as recording data are continuously
supplied is set to be shorter than that when the mark data
follows space data. The energizlng time of the subse~uent
energizing cycle of a given thermal heating resistive
element is switched in a two-step manner in accordance
with whether or not the given resistive element was ener-
gized in the immediately preceding enargizing cycle. With
this system, the above drawback ~an be eliminated to some
extent. In practice, however, this system cannot elimin-
ate the nonuniform density of the recorded image since
the thermal histories o~ the resistive elements still
differ from each other, especially in high speed recording,
dua to insu~ficient controllability.
It is an ob~ect o the present invention to provide
a thermal recording system capable of recording an image
at a stable recording density.
It is another object o~ the present invention to
provide a thermal recording system arranged to control
supply energy to be supplied to thermal heating resistive
elements for recoxding image data at the .....
q,~
present time in consideration of a previous thermal
history thereof.
A thermal recording system according to the
present invention comprises a thermal head having a
number of thermal heating resistive elements aligned
in line, and drive circuit means for selectively
energizing the thermal heating resistive elemen-ts,
by current supply, in accordance with image data to
print the image data on a line. The thermal recording
apparatus has a calculai:ion circuit means for calcu-
lating, from storage energy which would be stored in
each thermal heating resistive element after image
data of one line has been recorded and image data of
the next line, supp]y energy to be supplied to each
resistive element to record the image data of the next
line and storage energy stored in each resistive element
after the image data of the next line has been recorded.
A control circuit means causes the drive circuit means
of the thermal head to control energy supplied to each
thermal heating resistive element in response to the
supply energy data from the calculation circuit means.
The storage energy data is stored in a memory and is
used for calculating the next supply and storage energy.
This invention can be more fully understood from
the following detailed description when taken in con-
junction with the accompanying drawings, in whicho
Fig. 1 is a block diagram of a thermal recording
-- 5
system embodying the present invention;
Fig. 2 is a data format used for calculating the
storage energy of the ith thermal heating resistive
element of the thermal head;
Fig. 3 is a block diagram of a storage energy
memory shown in Fig. l;
Figs. 4A and 4B are respectively timing charts
for explaining the operation of the storage energy
memory shown in FigO 3;
Fig. 5 is a block diagram of a supply energy
control section shown in Fig. l;
Figs. 6A and 6B are diagrams Eor explaining the
control of the supply energy;
Fig. 7 is a block diagram of drive circuits of
the thermal head; and
Fig. 8 is a detailed diagram of one of the drive
circuits shown in Fig~ 7.
~ig. 1 shows the schematic con~iguration o~ a
thermal recording or printing system embodying the
present invention. Input image data or recording
data 1 is supplied to an input buffer 2 and is properly
processed therein. An output signal of the input
buffer becomes an input signal 4 of a calculator 3
for calculating supply energy and storage energy of
each thermal heat resistive element. The calculator
3 calculates the supply enregy to each thermal heating
resistive element and storage energy ~hich would be
stored therein after energization, in accordance with
output data 4 of the input buffer 2 and output data 6
of a storage energy memory 5, and outputs calculated
supply ener~y data 7 and storage energy data 8 to a
supply energy control 9 and the storage energy memory
5, respectively. The storage energy memory 5 stores
storage energy data of each resistive element calculated
~rom the beginning of printing up to the present moment.
Storage ene~gy data 6 read out from the storage energy
memory 5 is supplied as the input signal 6 to the
calculator 3. The storage energy data stored in the
storage energy memory 5 are sequentially updated in
units of thermal heating resistive elements every
time new storage energy data are calculated by the
calculator 3, so that the memory 5 holds the present
storage energy data of the resistive elements. The
supply energy control ~ temporarily stores supply
energy data 7. The supply energy data 7 is read out
in response to a readout signal and is supplied as
input data 11 ~o a thermal head 10, The circuits of
the thermal recording apparatus are controlled by a
timing controller 12. The above description illustrates
the overall configuration of the thermal recording
apparatus of the present invention. The functions of
the individual parts will be described in detail below.
In this embodiment, the supply energy to be
supplied to each resistive element and the storage
~ ..
~z:a~9~
-- 7 --
energy stored in each resistive element after energiza-
tion are calculated in accordance with the input image
data and the storage energy data stored in the memory
5. The relationship between the input image data and
the storage energy data i5 shown in Fig. 2.
Assume that supply energy data and corresponding
storage energy data are calculated for the ith thermal
heating resistive element of the thermal head, that
the thermal heating resistive elements aligned to the
right of the ith element are the (i-l~th, (i-2)thl ... r
elementsl and that the thermal heating resistive
elements aligned to the left of the ith element are
the (i~l)th, (i~2)th, ..., elements. In this embodi-
ment, the thermal head has an A4 width and comprises
a line head of 12 dots/rnm. Therefore, 1 ~ i ~ 2592.
The supply energy to be supplied to the ith resistive
element is calculated from the input image data Di,
Di~l~ and Di~2 respectively to the ith, (i~l)th and
(i~2)th resistive elements`, and storage energy data
Qii Qi+l and Qi-~2 thereof. Similarly, the storage
energy of the ith resistive element after energization
is calculated from the input image data Di, Di~l, and
Di~2 respectively supplied to the ith, (i~l)th and
(i~2)th resistive elements, and storage energy data
Qi' Qi~l and Qi-~2 thereof. The energy data for each
resistive element is represented by 4~bit data.
Fig. 3 shows the configuration of the input buffer
-- 8
2 and the storage energy memorv 5. In this embodiment,
the image data are stored in an image memory 20. The
image data is read out as the 8 bit parallel input
image signal 1 from an image memory 20 in response to
a signal MR generated from the timing controller 12,
and is loaded into a shift register 21 in response
to a signal LD. I'he shift register 21 performs
parallel-to-serial conversion. The image data 1 is
loaded into the ne~t shift register 22 in a serial
manner in response to a signal SRCLK generated after
loading of image data into the shift register 21. When
the 8-bit data is read out from the shift register 21
in response to the signal SRCLK, the timing controller
12 stops generating the signal .SRCL~ and starts
generating the signal MR so that the next image data
is read out from the image memory 20. The above opera-
tion is repeated until the image data corresponding to
one line are read out from the image memory 20. Each
bit of the image signal corresponds to a resistive
element for one-clot display.
The parallel~to-serial conversion is performed by
the shift register 21 to calculate the supply energy
and the storage energy in units of resistive elements.
However, where the image data is serially received,
it may be directly loaded into the shift register 22.
The shift register 22 serves to extract the image
data Di, Di~l and Di~2 (to be supplied to the calculator
_ 9 _
3) from the serial image data taken from the shift
register 21.
In this embodiment, as shown in Fig. 2, the data
supplied to the calculator 3 comprise input image data
5 to the ith, (i+l)th and li}2)th resistive elements.
Therefore, among the ou-tputs of the shift register 22,
the 5-bit image data corresponding to the ith, (i~13th
and (i~ 2)th resistive elements is supplied to the
calculator 3.
A random access memory (RAMA) 23, latches 24,
25, 26, 27 and 28, adders 29 and 30, a write address
counter 31, a read address counter 32 and a selector
33 constitute the storage energy memory 5 shown in
Fig. 1. The RAMA 23 stores storage energy data of the
resistive elements. Addresses of the RAMA 23 correspond
to the respective resistive elements of the thermal
head. In this embodiment, the address coun~ers 31 and
32 designate 2592 addresses. The storage energy data
8 calculated by the calculator 3 has four bits. The
20 4-bit storage energy data 8 is supplied to a terminal
DIN of the RAMA 23 and is written at an address
specified by the writa address counter 31 in response
to a signal WR generated from the timing controller 12.
When the signal WR is not supplied to a terminal WR of
25 the RAMA 23, the 4-bit storage energy data stored at the
address designated by the read address counter 32 is
read out to a terminal DoUT of the RAMA 23. Each of
. . .
- ~%~6~9~
-- 10 --
the latches 24 to 28 comprises a 4-bit latch which
latches a 4-bit input signal in response to a signal
__
LATCH generated by the timing controller 12, and holds
the latched data until the next signal LATCH is supplied
thereto. The latches 24 to 28 are connected in cascade
to constitute a shift register so that 4-bit data is
sequentially shifted toward the output stage every time
the signal LATCH is supplied thereto.
The storage energy data of a first resistive
element which is specified by the read address counter
32 is read out from the terminal DouT of the RAMA 23
and is latched by the latch 24 in response to a first
:
LATCH signal. The count of the read address counter
32 is incremented by one in response to the first
1~ LATCH signal, so that the storage energy data of a
second resistive element is read out from the terminal
DoUT. In response to the next LATCH signal, the storage
energy data of the second resistive element is latched
by the latch 24. At th~ same time, the storage energy
data of the first resistive element is latched by the
latch 25.
In this manner, each time the LATCH signal is
issued, the storage energy data from the RAMA are
sequentially shifted. When the storage energy data
Qi of the ith resistive element is latched by the
latch 26, storage energy data of the (i+l)th, (i+23th,
(i-l)th and (i-2)th resistive elements are latched by
-
the latches 25, 24, 27 and 28~ respectively.
As previously described, the supply energy data oE
the ith reslstive element and the storage energy data
after energization thereof are calculated in accordance
with the input image data to the ith, (i~l)th and
(i~2)th resistive elements, and with storage energy
data thereof ob-tained to date. In other words, the
supply energy data and the storage energy data can be
calculated in accordance with data having a total of
25 bits (i.e., 5-bit data from the shift register 22
and the 20-bit (4 bits x 5) storage energy data from
the latches 24 to 28).
However, a calculation with 25 bits becomes
complicated, so that the following simple operation is
performed in practice.
The calculation process is based on a well-known
equation of heat conduction as follows:
aT/at = a(a2T/ax2 + a2T/ay2 + a2T/az2) -~ q/pC
~ (1)
where
T : temperature
a : heat diffusion ratio
q : heat energy per unit volume and unit time
p : density
C : specific heat
In order to control the supply energy for the
. .:
- 12 -
thermal head in accordance ~ith a digital calculation,
a solution to equation (1) must have a format which is
readily applicable to calculation by a digital circuitO
Assume -that the printing period is defined as a
time increment QT, and that the pitch of the array of
thermal heating resistive elements, the width of the
resistive elemen~ along the direction perpendicular
to the array, and the thickness of a glass layer
immediately under the resistive element are defined
as spatial increments Qx, Qy and Q z. Also assume that
the temperature in the vicinity of the ith resistive
element in a given printing period n is defined as Tin.
The energy balance at the point i is given by the
following general equation in the form of a forward
difference equation:
n - Tin~/Rj ~ qin _ qo
= Ci(Tin+l - Tin~/Q~ .. (2
2~ where
Tln = Ti_ln, Rl = (Ax/QyQ z~- (l/k)
T2n = Ti+ln, R2 = Rl
T3n = TUinl R3 = (Qy/QzQx)- (l/k)
T4n = TDin, R4 = R3
Tsn = To, R5 = (Qz/QxAy)- ~l/k)
To is the room temperature, k is the heat conductivity,
qO is the energy used for activating a coloring agent,
- 13 -
and qin is the energy supplied from a resistive element.
The energy qO must be kept constant to obtain the
optimum printing quality by means of the thermal head.
The energy qO is determined by a time integral of the
temperature gradient in the direction toward the
coloring agent. If a pulse width tin of a pulse
applied to a thermal heating resistive element to
determine the energizing time is a controllable
factor, the energy qO depends on Tin indicating the
storage state and the energy qin~V~/R)-tin) which is
a function of Tin.
In order to keep the energy qO constant, such
tin, a function of Tin, as to keep qO constant must
be ohtained, A distance between the thermal heating
resistive element and the coloring agent is shorter
than the dimensions of the resistive element, so that
the equation can be dealt with as a matter of one-
dimensional nonsteady heat conduction. The present
inventors obtained the following solution:
~0
tin = KEl~Din[[l ~ KE2(1-~in)}/{1 - KE3(1-~?in)}]2
-- (3)
where KEl, KE2 and KE3 are constants, respectively,
Din is printing data which indicates ~ (mark) or "O"
(blank) and ~in = Tin/(TC To) (Tin < Tc - a constant
normalized temperature). The supply energy qin is
determlned by equation (3). As a result, Tin+l, that
- ~4 -
is, the temperature during the next prlnting period
can be predicted from equation (2).
Tin+l is in practice a function of not only Tin
and Ti+ln but also TUin and TDin. However, the
following equation can be obtained in consideration
of the heat conduction and the recording or printing
speed:
Qin+l = KQl{Qin + RQ2(1 - Qin)J~}
+ KQ3{ tQ1_ln + Qi+1n)/2}
+ KQ2(~ti-ln + ~ ){1 - IQi-ln + Qi+ln)/2}
where KQl, KQ2 and KQ3 are constants.
Equations (3) and (4) may be rewritten as follows:
tin = f(Qin,Din) ~- (5)
n+l = g(Qin9Qi~ln~Din~Di+l ) ... (6)
The width tin of the pulse applied to the resistive
element can be understood to be calculated from the
storage energy Qin and the input image data Din.
Similarly, the storage energy data Qin+l during the
next printing period can be derived from the present
storage energy distribution Qi+mn and the data stream
Di+mn (where m = -1, 0, +1) in accordance with
equation (6).
The storage energies of the (i-~l)th resistive
elements ((Ri-~l)) which influence the ith resistive
- 15 -
element (Ri~ are assumed to be substantially idenkical
to each other. Therefore, the arithmetic mean of the
storage energy of the (i-l~th and (i+l)th resistive
elements is used in equation (~).
In order that the solution of the difference
equation (2~ converges, the printing period must be
shorter than about 3.8 msec when the resolution of the
thermal head is 12 dots/mm; and the printing period
must be shorter than about 2~1 msec when the resolution
is 16 dots/mm. As the resolution is increased, heat
tends to be conducted further than the adjacent volume
unit consisting of one resistive elemen-t and glass
layer immediately thereunder within a printing periodO
In view of such a phenomenon, the heat conduction from
the volume units associated with the two adjacent
resistive elements (Ri+], Ri~2~ on the right and left
sides of the volume unit associated with the ith
resistive element (~i~ is considered.
Equation (3~ is of a form which can be easily
handled in this embodiment. Various types of equations
can be derived in accordance with: physical canditions
such as the printing period, the head resolution, the
head construction and the head material; the properties
of the material; and an approximation method to obtain
a solution.
The adders 29 and 3~ are provided in Fig. 3 in
consideration of thermal conduction from the adjacent
. ~ .
A~ Z~ )~8 ~
- 16 -
volume units.
The adder 29 serves to calculate an a~erage of
4-bit storage energy data of the (i+l)th and (i-l)th
resistive elements obtained from the latches 25 and 27.
Namely, the four more significant bits of the a~der 29
are used as the storage energy data to be supplied to
: the calculator 3. Similarly, the adder 30 calculates
the average value o the 4-bit storage energy data
of the (i~2)th and (i-2)th resistive elements which
are respectively obtained from the latches 24 and 28.
The three more signiElcant bits of the adder 30 are
used as the storage energy data of the (i+2)th resistive
elements to be supplied to the calculator 3.
The 5-bit lmage data from the shift register 22,
the 4-bit data of the ith resistive element from the
latch 26, the 4-bit storage data of the (i+l)th
resistive elements from the adder 29, and the 3-bit
storage energy data of the (i+2)th resistive elements
from the adder 30 are applied to the calculator 3.
In other words, 16 bits in total are used.
The calculator 3 calculates the supply energy
Ein to be injected in the ith resistive element,
and the storage energy Qin+1 which will be stored in
the ith resistive element until the ith element is
again energized after the supply energy Ein has been
injected in the ith element, in accordance with the
input image data Di_2r Di_1~ Di~ Di+1 and Di+2 and
the storage energy data i~2n, i-tln and Qin obtained
to date.
The calculator 3 simulates the equation of heat
conduction in accordance with equations (3) and (4) to
provide prediction values of the proper supply energy,
and storage energy in the next printing period. The
supply energy data is applied to the thermal head 10
through the supply energy control 9. The storage
energy prediction data is stored in the storage energy
memory 5 and is used as input data to the calculator
3 in the next printing period. The contents of the
storage energy memory 5 are updated every printing
period.
In this embodiment, the calculator comprises a
ROM. The supply energy data and the storage energy
data which have been calculated by a computer in
advance are stored in the ROM. The 5-bit i~age data
and the ll-bit storage energy data are used as 16-bit
address data of the ROMo The 4-bit supply energy data
7 and the 4-bit storage energy data 8 are read out from
the ROM. I'he upper four bits of one-byte output of the
ROM are assigned to the supply energy data, and the
lower four bits thereof to the storage energy data.
Therefore, the capacity of the ROM of the calculator
3 is 64 K bytes.
The operation of the circuit shown in Fig. 3 will
be described with reference to the timing charts in
9~
- 18 -
Figs~ 4A and 4B~ The 8-bit image data is read out
from the image memory 20 in response to the signal MR
and is loaded in the shift register 21 in response to
the falling edge of the signal LD~ The 8-bit data
loaded in the shift regis-ter 21 are serially loaded
into the shift register 22 in response to the rising
edges of the signal SRCLK. When the 8-bit data shift
is completed, the signal MR is issued again from the
timing controller 12 to load the ne~t 8~bit data into
the shift register 21. Thereafter, the above operation
is repeated u~til data (324 bytes) on one line are
shiftedO
The timing controller 12 generates the signal
LATCH together with the signal SRCLK so as to shift
the storage energy data from the RAMA 23 from ~he
lower latches to the upper latchesO The count of the
read address counter 32 is incremented by one every
time the signal LATCH is applied to the latches, so
that the storage energy data are sequentially read
out fro~ the terminal DouT of the RAMA 23. The
storage energy data calculated by the calculator 12
are sequentlally stored in the RAMA 23 in response to
the signal WR. The count of the write address counter
31 is incremented every time the data is stored in the
RAMA 23.
The read address differs from the write address
in Fig. 4A or 4B, since the image data of the first
resistive element must be shifted to the 3rd bit from
the LSB of the shift register 22 and the storage energy
data o~ the first resistive element must be shifted to
the latch 26 in order to calculate the supply energy
and the storage energy of the first resistive element.
The selector 33 is used to switch between the read
address signal and the write address signal. When
data calculation for one line is completed, all the
signals are made off until a read synchronizing signal
for the next line is issued. When the synchronizing
signal is issued, data readout is performed for the
next line. The above operations are repeated until
the data processing of all lines is completed.
Fig. 5 shows the detailed configuration of the
supply energy control 9 of Fig. 1. In this embodiment,
since the thermal head has a resolution of 12 dots/mm
and an A4 width, the number of thermal heating resistive
elements is 2592. In order to shorten the time of data
transfer to the thermal head, the thermal head of this
embodiment has nine input data ports SINl to SIN3
each adap~ed to receive data in a serial manner. Each
data port receives data corresponding to 288 resistive
elements~
The arrangement of the thermal head 10 will be
described with reterence to Figs~ 7 and 8. In this
embodiment, thermal heating resistive element drive
ICs are used to drive the elements in units of 32 dots.
~ .
- 20 -
Each port thus requires 9 drive circuits, so that
81 drive circuits 611 to 6181 are arranged in the
thermal head 10~ As shown in Fig. 8, each drive
circuit comprises a 32-bit shift register 62, a latch
circuit 63, an enable gate circuit 64 and, a driver
65 for driving thermal heating resistive elements Rl
to ~32~
Referring back to Fig. 5, the supply energy data
7 calculated by the calculator 3 are applied to the
a RAMB(ll) 4~ to a RAMB(l9) 46 or a RAM~(21) 45 to a
RAMB(29) ~7 through a buffer(ll) 40 to buffer(l9) 42 or
a buffer(21) ~1 to buffer(29) 43, respectively. Nine
buffers (i.e., buffer(l) to buffer(9)) and nine RAMBs
(i.e., RAMB(l) to RAMB(9)) respectively correspond to
nine ports SINl to SIN9. If the thermal head has one
input port, one set of a buffer and a RAM suffice.
Furthermore, two sets each having nine buffers and
nine RAMBs are prepared for a high speed recording.
For example, while data are written in the RAMB(ll)
to RAMB(l9), data are read out from the RAMB(21) to
RAMB(29). In this manner, the write and read operations
can be simultaneously performed. If no high speed
operation is required, a set of nine buffers and nine
RAMBs may be used.
Assume that a timing signal Gl is issued from
the timing controller 12. The timing signal Gl and a
timing signal G2 are applied to terminals CSl of the
9~
- 21 -
buffer(ll) to buffer(l9) and of the buffer(21) to
buffer(29), respectively. When the timing signal Gl
is issued, the timing signal G2 is not issued and
vice versa. Each buffer is enabled only when a signal
of logic "0" is supplied to the terminals CSl and CS2
thereof so as to supply the supply energy data Erom
the calculator 3 to the corresponding P~MBo Otherwise,
the data line of the supply energy data is disconnected
from the corresponding RAMB.
The data is written at an address of RAMBs which is
accessed by an address counter 48 or 49 when a signal is
applied to its terminal WR. Otherwise, da~a is read out
from an address accessed by the corresponding address
count0~. The address counter 48 is commonly used for
RAMB(ll) to RAMB(l9), and the address counter 49 is
commonly used for the RAMB(21) to RAMB(29). The same
address data are supplied to the RAMB(ll) to RAMB(l9)
or RAMB(21) to RAM~(29).
The number of address data is equal to the number
of resistive elements for one port r SO that the number
of address data is 288 in the case of nine ports.
Since the timing signal Gl is issued from the tlming
controller 12, the RAMB(21) to RAMB(29) are disconnected
from the supply energy data lines. When the supply
energy of the first resistive element is calculated,
a signal RAMB(ll)WR is generaged from the timing
controller 12. In this case, the buffer(ll) 40 is
- 22
enabled, so that the supply energy data is coupled to
the data line of the RAMB(ll).
The supply energy data is written at an address
accessed by the address counter 48. Signals RAMs(ll )WR
to RAMB(19)WR have a period 288 times the period of
the signal WR shown i.n Figs. 4A and 4B. The data is
written in the RAMB(ll) in response to the signal
RAMB(ll)WR. The next signal RAMB(12)WR is used to
write the data in the RAMB(12). Similarly~ the data
is written in the RAMB(lg) in response to the last
signal RAMB(l9 )WR. Each buffer is enabled only when
the signal WR is supplied to the corresponding RAMB
so as to write the supply energy data in this RAMB.
When the supply energy data of the first resistive
element is written in the RAMB(ll), the signal WRl is
issued from the timing controller 12, and the count of
the address counter 48 is incremented by one. The
signal WRl is issued every time one of the RAMB(ll)
to RAMB(l9) receives the signal WR. The supply energy
data of the second resistive element i5 wri-tten in the
same manner as in the RAMB(ll). The above operation
is then repeated to write the first 288 supply energy
data in the RAMB(ll)~
Af ter the supply energy data of the 288 th
resistive element is written in the RAMB(ll), the
address counter 48 designates the same address as in
the case wherein the supply energy data of the first
- 23 -
resistive element is writtenO The supply energy data
of the 289th resistive element is written in the
RAMB(12) in response to the signal RAMB(12)WR generated
from the timing controller 12. The data line of the
RAMB(ll) is disconnected from the supply energy data
line. In the same manner as in the RAMB(ll), after
the supply energy data of 289th to 577th resistive
elements are written in the RAMB(12), the RAMB(12) is
disconnected ~rom the supply energy data line. The
above operation is repeated to write the supply energy
data of the 230~th to 2592th resis-tive elements in the
RAMB(19). Thus, the calculation for one line is
completed.
While the supply energy data for one line are
written in the RAMB(11) 44 to RAMB(l9) 46, the previous
supply energy data are read out from the RAMB(21) 45
to RAMB~29) 47 and are supplied to the thermal head
through a multiplexer(l) 50 to a multiplexer(9) 51,
thereby energizing the resistive elements to record
image data. At this time, the RAMB(21) to the RAMB(29)
are disconnected from the supply energy data lines,
respectively.
Since the signal Gl is generated from the timing
controller 12, the signals RAMB(21)WR to RAMB(29)WR
are not issued. In other words, the RAMB(21) to
RAMB(29) are kept in the read mode so that the supply
energy data accessed by the address counter ~9 is read
-~ ~z~9~
- 24 -
out onto the data line. In response to control
signals 51 from the timing controller 12, one bit of
the 4-bit data from each of the RAMB(ll) to RAMB(l9)
or of the RAMB(21) to RAMB(29) is selected by the
multiplexer(l) 50 to multiplexer(9) 51 and is
supplied to the corresponding port. At the present
time, the RAMB(21) to RAMB(29) are set in the read
mode, so that the selected one-bit data of data read
out from the RAMB(21) to RAMB(29) are issued from the
multiplexer(l) to multiplexer(9)~ respectively. The
data supplied to the input ports SINl to SIN9 of the
thermal head 10 are written in the corresponding shift
registers in response to the signal CLK generaged from
the tlming controller 12. At the same time, the timing
controller 12 generages the signal CLK2 to increment
the addr0ss counter ~9 of the RAMB(21) to RAMB(29).
As a result, supply energy data corrasponding to the
next resistive elements~in the respective groups are
read out from the RAMB(21) to RA~B(29)~ One-bit data
of the same order as the previous one-bit data are
supplied to the corresponding terminals SIN through
the multiplexer(l) to mu]tiplexer(9). This one-bit
data is written in the corresponding shift register
in response to the signal CLK. At this time, the
immediately preceding one-bit data is shifted by
one bit. This operation is repeated by 288 times,
so that the same order bits of all the 4-bit data of
19l~
- 25 -
the RAMB(21) to RAMB(29) are written in all the
eighty-one shift registers 62 in the thermal head 10.
The data written in the shift registers 62 is latched
by the latch circuits 63 in response to a signal
ALATCH. Output data of the latch circuits 63 is
supplied to the drivers 65 through the enable gate
circuits 64 which are enabled by one of enable signals
M~N-l to MEN-4 from the timing controller 12. The
resistive elements Rl to R32 are heated or are not
heated in accordance with the corresponding data "0"
or "1". The enable signals MEN-l to MEN-4 supplied to
the gate circuits 64 have different pulsewidths to be
descrihed later.
Fig. 6A shows the relationship between the 4-bit
supply energy data 7 and the enable signals MEN-l to
MEN-4. In this embodiment, a voltage applied to the
resistive elements of the thermal head is constant, so
that a current flowing therethrough is also constant~
In order to change the supply energy of the resistive
elements, the energizing time must change in accordance
with the supply energy. The 4-bi-t supply energy data
generated from the calculator represents an energizing
time of a resistive element. However, the energizing
time cannot vary in units of resistive elements because
of the structural restriction of the thermal head. In
practice, the energizing times of the resistive elements
have the same length of period. In order to vary the
9B15~
- 26 -
energizing times of the resistive elements, the
energization of each resistive element may be repeated
several times in accordance with the corresponding
supply energy data.
In this embodiment, as shown in Fig. 6, four
energizing times Tl to T4 are set in accordance wi-th
the four enable signals MEN-l to MEN-4. The four
energizing times and the four bits of the supply energy
data have a one-to-one correspondence. For example,
the MSB Ei l corresponds to energizing time Tl; Ei 2,
to T2; Ei 3, to T3; and Ei 4, to T41 The energizing
time of each resistive element is selected by a bit
or bits of "l" of the supply energy data. For example,
if Ei l - Ei 3 = Ei 4 = l and Ei 2 = o, the energizing
t-mes Tl, T3 and T4 are selected as shown in Fig. 6B.
The corresponding resistive element is energized during
a time of Tl + T3 + T4. In this embodiment, the
energizing time of each resistive element is changed
in such a manner as described above.
Furthermore, according to this embodiment, the
times Tl, T2, T3 and T4 can be freely set in accordance
with the enable signals MEN-l to MEN-4. When
Tl = T2 = T3 = T4, a maximum of four steps of the
energizing time intervals can be obtained. When the
pulsewidths of the enable signals MEN-l to MEN-4
(corresponding to the times Tl to T4~ differ from each
other, a maximum of lÇ steps of the energizing time
- ~7 -
interva].s can be obtained. Furthermore, if the number
of bits of the supply energy data is increased, or
the supply order of enable pulses having clifferent
pulsewidths is changed, then the more precise control
of the energizing time would be enabled.
The operation of the thermal recording system
will be repeated.
The multiplexer(l) to multiple~er(9) selec-t, for
example, the MSB Ei 1 of the 4-bit supply energy data
read out from the RAMB(21) to RAMB(29) to feed the
thermal head 10. As previously described, when the
readout of one-bit data is performed 288 times, all
the MSB data Ei 1 of the supply energy for all the
resistive elements are written in the shift registers
of the thermal head 10. The MSs data are latched by
the latch circuits in response to the signal ALATC~
generated from the timing controller 12. Next, the
latched data are supplied to the drivers through the
gate circuits in response to the enable signal MEN-l
for setting the energizing time Tl. As a result,
a current is supplied to the resistive elements
corresponding to data of "1" for the energizing
time Tl.
When the MSB data Ei 1 are latched by the latch
circuits, data readout from the RAMB(21) to RAL~B(29)
is restarted from address 1. At this time, the
multiplexer(l) to multiplexer(9) select the bit Ei 2
~2~1"3~3~
~ 28 -
(next to the MSB) of the 4-bit supply energy data read
out from each of the RAMBt21~ to RAMB(29). In the
same manner as in the ~SB data, the resistive elements
are selectively energi~ed in accordance with the data
Ei 2 of the 4-bit supply energy data for the time T2
set by the enable signal MEN-2.
Data readout from the RAMB(21) to RAMB(29) is
restarted from address 1 thereof. In thi.s case, the
multiplexer(l) to multiplexer(9) select the one-bit
data Ein3. The timin~ controller 12 generates the
enable signal MEN-3, SG that the resistive elements
are selectively energized -Eor the time T3 set by the
enable signal MEN-3. Finally, the fourth time data
readout operation is performed with respect to the
RAMB(2I) to RAMB(29). The multiplexer(l) to
multiplexer(9) select the LS~ data Ein4 of the 4-bit
supply energy data. The timing controller 12 supplies
the enable signal MEN-4 to the enable gate circuit 64.
As a result, the resistive elements are selectively
energized for the time T4 set by the enable signal
MEN-4. In this manner, the four-time data readout
operations from the R~MBs and the four-time selective
energizations of the resistive elements in accordance
with the readout data are performed to print the image
data corresponding to one line.
The supply energy must be preset to cause the
resistive element to reach a predetermined temperature,
J5~38
- 29 -
since the transfer factor of ink to a sheet depends
solely on the temperature of the resistive element, as
has been found according to experiments.
The features of the present inven-tion described
above will be summarized as follows:
(1) The storage energies are determined in
accordance with input image data to be recorded and
the storage energies resulting from the recording
operation of the previous image data;
(2) The supply energy is determined in accordance
with this storage energy and the input image data; and
~ (3) Time and space factors are considered with
respect to the thermal conduction.
~ The present invention is not limited to the
particular embodiment. Various changes and modifica-
tions may be made within the spirit and scope of the
present invention~ For example, the content of the
ROM of the calculator 3 may be obtained theoretically
or empirically. Alternatively, the calculator 3 may
be comprised of a CPU or -the likeO
. ..
