Image recording apparatus and method for maintaining image quality after recording interruption

An image recording apparatus has a stand-by mode in which a recording operation is interrupted during recording for stand-by. The apparatus includes a recording head for recording on a recording medium, a head temperature detecting device for detecting the temperature of the recording head, a memory device for storing temperature information detected by the head temperature detecting device when recording in the stand-by mode is interrupted, a stand-by time counting device for counting an interruption time for recording operation in the stand-by mode, and a head driving controlling device for transmitting a driving signal to the recording head. The controlling device is responsive to a temperature stored in the temperature memory device and an interruption time calculated by the stand-by time counting device on resumption of a recording operation after it is interrupted and the apparatus is placed in the stand-by mode.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a recording apparatus for recording using a 
recording head and more particularly to a recording apparatus having a 
stand-by mode which interrupts and resumes recording during recording. 
2. Related Background Art 
As this type of recording apparatus, digital recording devices such as an 
ink jet recording type and a thermal transfer recording type have been 
well known so far. 
Especially, an ink jet recording apparatus has merits such as easy 
coloring, and prevails as, for example, an output device, etc. for 
computer graphics. 
FIG. 7 is a block diagram showing the constitution when the ink jet 
recording apparatus is used as an output device for computer graphics. In 
FIG. 7, numeral 101 is a host computer, numerals 102 and 104 are image 
signals, numeral 103 is an interface, and numeral 105 is an ink jet 
printer. Image data, which the host computer 101 has therein, is 
transmitted to the interface 103 as an image signal 102, and is once 
stored in a memory (not shown) in the interface 103. 
The interface 103 converts the image data within the memory into such a 
form that can be processed by an ink jet printer, and then transfers it to 
the ink jet printer 105 as an image signal 104. The ink jet printer 105 
records in accordance with the transferred image signal 104. 
In the above constitution, the capacity of the memory, in the interface 
103, is generally several megabytes to several tens of megabytes, but the 
amount of image data which the host computer 101 has may exceed this 
capacity sometimes. In such a case, the host computer 101 is capable of 
transferring data only for the capacity of the memory in the interface 103 
and after finishing recording based on these data, further transferring 
the remaining data for recording based thereon. 
At this time, the printer 105 records on the basis of the data from the 
interface 103, and interrupts carrying of the recording sheet and driving 
of the recording head to stand by until the next data is transferred. This 
enables the system with the above-mentioned constitution for recording an 
image to cope with a larger amount of image data than the memory capacity 
of the interface 103 for recording on the basis thereof. 
The recording apparatus having a stand-by mode for interrupting such a 
recording operation had the following problem. That is, the density of an 
image to be recorded may be discontinuously different before and after the 
stand-by. This is undesirable from the stability point of view in 
recording, and the image quality will be noticeably impaired especially 
when the above-mentioned change in density occurs on the same recording 
sheet. 
FIG. 8 is a diagram of a typical recording sheet when the above-mentioned 
stand-by state occurs while a sheet of recording sheet is being recorded. 
In FIG. 8, it is assumed that the recording width of a recording head, 
that is, the length of the range in which discharging orifices are 
arranged, is d in the ink jet type recording head, and the recording head 
records images by scanning in the X direction in FIG. 8. Although an image 
for 14 scans in total can be recorded on a sheet of the recording sheet 
shown in FIG. 8, the memory capacity of the interface 103 is assumed to 
have only five scans. 
In such a case, recording is first continuously performed on a portion 
shown by A in FIG. 8, and thereafter the recording head enters a stand-by 
state until image data for a portion shown by B is transferred. After this 
transfer is finished, recording is continuously performed on the B 
portion, and thereafter the recording head enters the stand-by state again 
until the image data for a C portion is transferred. After this transfer 
is finished, recording is continuously performed on the C portion to 
finish recording on a sheet of recording sheet. 
When the recording head continuously records, its temperature generally 
rises. For example, in the ink jet type recording head, a discharge energy 
generating element to discharge ink generates heat energy with discharging 
to raise the head temperature. Also in the thermal transfer type recording 
head, the heat generated by the heating element raises the head 
temperature. When the temperature thus rises, the ink viscosity lowers and 
the ink discharge increases to increase the recording density, for 
example, in the ink jet type recording head. Also in the thermal transfer 
type, the amount of ink to be transferred onto the surface increases to 
increase the density in the same manner. 
However, once the recording head enters a stand-by state for recording, the 
temperature lowers, and the recording density may lower in recording 
immediately thereafter. This phenomenon is seen with different types of 
recording heads, and is noticeable especially in the ink jet type 
recording head in which a heater is caused to generate heat to boil ink 
and ink is discharged by the pressure of bubbles generated thereby. 
Changes in the recording density when such an image as shown in FIG. 8 is 
recorded are shown in FIG. 9. 
Since when recording is continuously performed as shown in FIG. 9, the 
temperature of the recording head rises little by little and the density 
increases as the temperature rises, the change in density is not 
noticeable. When, however, the recording stand-by state shown by points of 
time D and E in FIG. 9 intervenes, a change in density abruptly occurs 
with lowered temperature of the recording head. As a result, a problem 
occurs in the image to be recorded that the difference in density between 
portions recorded before and after such a stand-by state is very 
noticeable. 
To reduce the above-mentioned change in density by keeping the head 
temperature before and after such a stand-by state within a fixed range, a 
method has been well known so far in which the recording head is provided 
with temperature detecting means such as a thermistor and a heat 
insulating heater and the heat insulating heater is driven in accordance 
with the heat temperature detected by the temperature detecting means to 
control the temperature. In addition to this, another method was also well 
known in which a fan is provided and is driven if the head temperature is 
higher than the preset temperature. 
However, this type of temperature control is slow in response while the 
temperature is abruptly changing, and it is difficult to precisely control 
the temperature when the temperature comparatively abruptly changes as 
shown by the points of time D and E in FIG. 9. Especially when one 
recording head is provided with one each of thermistor and heater to 
control the entire recording head to a fixed temperature, the ink 
temperature in the liquid channel, where the discharge energy generating 
element is disposed and the discharge energy is applied to ink, does not 
reach the predetermined temperature even if a temperature to be detected 
by the thermistor reaches a predetermined temperature. Recording in this 
state frequently leaves a difference in density. For this reason, in order 
to overcome this phenomenon, it is regarded as necessary to heat the ink 
in the liquid channel, which directly relates to discharging, to the 
predetermined temperature as fast as possible. 
In the above-mentioned conventional image recording apparatus, however, 
when the recording head continuously prints, the head temperature mostly 
exceeds the predetermined temperature even if the fan is driven. When the 
head interrupts the recording and enters the stand-by state in this state, 
such a change in density as mentioned above still occurs because the 
recording head temperature continues lowering until the predetermined 
temperature is reached. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an image recording 
apparatus capable of obtaining an image whose density is less changed by 
interruption of recording. 
It is a further object of the present invention to provide an image 
recording apparatus capable of obtaining a uniform image free from change 
in density even if the head temperature lowers during stand-by. 
It is another object of the present invention to provide an image recording 
apparatus capable of obtaining a uniform image free from change in density 
in the actual picture by correcting the image signal even if the head 
temperature lowers during the stand-by. 
It is an additional object of the present invention to provide a recording 
apparatus having a mode in which the recording head is placed in a 
stand-by state by interrupting the recording while an image is being 
recorded, capable of raising the recording element temperature to suppress 
the difference in density occurring before and after the interruption by 
driving the recording element for the recording head beforehand in 
accordance with the recording head temperature immediately before 
interrupting the recording, a duration for which the recording has been 
interrupted, etc. before resuming the recording after interrupting the 
recording. 
In order to accomplish the above-mentioned object, an image recording 
apparatus having a stand-by mode, in which recording operation is 
interrupted during recording for stand-by, according to the present 
invention comprises, a recording head for recording on a recording medium, 
head temperature detecting means for detecting the temperature of the 
recording head, memory means for storing temperature information detected 
by the head temperature detecting means when recording in the stand-by 
mode is interrupted, stand-by time counting means for counting an 
interruption time for recording operation in the stand-by mode, and head 
driving controlling means for transmitting a driving signal, to the 
recording head, adapted to a temperature stored in the temperature memory 
means and an interruption time calculated by the stand-by time counting 
means on resuming after recording operation is interrupted in the stand-by 
mode. 
Also in order to accomplish the above-mentioned object, an image recording 
apparatus capable of appropriately interrupting and resuming recording 
when driving a recording head to record an image, according to the present 
invention comprises temperature detecting means for detecting the 
temperature of the recording head on interrupting the recording, 
interruption time detecting means for detecting the record interruption 
time, and correcting means for correcting an image signal to be 
transmitted to the recording head in accordance with the detection results 
of the temperature detecting means and the interruption time detecting 
means on resting recording. 
Also in order to accomplish the above-mentioned object, an image recording 
apparatus for interrupting and resuming the recording operation using a 
recording head in accordance with the input state of an image signal, 
according to the present invention comprises head temperature detecting 
means for detecting the temperature of the recording head, and controlling 
means for detecting the temperature of the recording head on interrupting 
and resuming the recording operation by means of the head temperature 
detecting means, and when resuming the recording operation, for correcting 
the input image signal in accordance with a difference in temperature of 
the recording head between on interrupting and on resuming the recording 
operation. 
Further in order to accomplish the above-mentioned object, an image 
recording apparatus equipped with a recording head for recording an image 
and temperature controlling means for detecting the temperature of the 
recording head and controlling the temperature within a predetermined 
range, according to the present invention comprises memory means for 
storing the temperature of the recording head on interrupting the 
recording, and resuming means for controlling the temperature controlling 
means so that the temperature of the recording head is almost equal to a 
temperature of the recording head when the record, which has been stored 
in the memory means, is interrupted on resuming after the recording is 
interrupted.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will hereinafter be described in detail with respect 
to embodiments thereof shown in the drawings. 
FIG. 1 is a block diagram for a system consisting of a recording apparatus 
according to the first embodiment of the present invention and its host 
computer. 
In FIG. 1, numerals 101 and 103 are the same host computer and interface as 
described in FIG. 7 respectively. Numeral 105 is an ink jet printer, and 
the constitution thereof in this embodiment is described below. 
A driver 110 drives a recording head 112 on the basis of driving data 
(image signal) 104 to be transferred from an interface 103. A CPU 111 
controls each portion of a printer 105. A RAM 111A has an area to be used 
as a work area, etc. for control process by CPU 111, a counter area for 
counting a stand-by time as mentioned later, and a register for storing 
detected temperature. A ROM 111B has stored a procedure as mentioned later 
in FIG. 5, a table as mentioned later in FIG. 4, etc. 
Numeral 112 is an ink jet type recording head for discharging ink by heat 
energy, and numeral 113 is head temperature detecting means such as a 
thermistor. A carriage driving motor 114 drives a carriage which carries a 
recording head 112 and scans for recording, and also performs a 
predetermined drive during dry ejection at a predetermined position as 
mentioned later. Numeral 102 is an image data signal, numeral 104 is a 
driving data signal, numeral 120 is a state indication signal from the 
interface, numeral 121 is a head driving signal, numeral 122 is a 
discharge indication signal, numeral 123 is a head temperature signal and 
numeral 124 is a carriage movement signal. 
FIGS. 2A and 2B are respectively a schematic sectional view and a principal 
portion perspective view of conventional aspects of the above-mentioned 
ink jet printer respectively. 
In FIG. 2A, numeral 105 is a printer, numeral 2 is roll paper, numerals 3 
and 4 are paper feed rollers, numeral 5 is a cutter, numeral 6 is a 
carriage, numeral 112 is an ink jet head, numeral 8 is a subscan roller, 
numeral 9 is a platen, and numerals 10 and 11 are paper guides. 
In FIGS. 2A and 2B, a recording head 112 is carried on a carriage 6 to scan 
for recording, and is capable of moving to a predetermined position for 
dry ejection as mentioned later. The carriage 6 moves driven by the 
carriage motor (not shown) through a belt 6B while being guided along the 
moving path by a guide 6A in these movements. The recording head 112 
consists of four recording heads corresponding to each ink of yellow, 
magenta, cyan and black as shown in FIG. 2B, and each recording head has, 
for example, 64 discharging orifices in the subscan direction (a direction 
perpendicular to the scanning direction). 
An ink receiver 160 is provided in an area adjacent to the recording area 
for the recording head 112 so that it may be opposite to each discharging 
orifice thereof. A portion, which receives ink discharged from the 
recording head 112, is made of, for example, an ink absorber, and further 
the ink received together therewith can be designed to be led into a waste 
ink tank (not shown). The recording head 112 performs so-called dry 
ejection at a position opposite to the ink receiver 112 after stand-by for 
recording as mentioned later to heat the ink in each liquid channel. 
During the dry ejection, a capping member, etc. relating to discharge 
recovery can be used instead of using the exclusive ink receiver 160 as 
mentioned above. 
In a range, which may be opposite to the discharging orifice forming 
surface of the recording head 112, a platen 9 extends to control the 
recording surface on recording sheet 2. The recording sheet 2 is cut into 
a single sheet state after a predetermined amount thereof is carried, but 
is housed in the form of roll paper 20 at a predetermined position of the 
printer 105 before it is recorded. One end of the roll paper 20 is fed to 
the recording area by a paper feed roller 3 in accordance to the recording 
operation, and is carried in the recording area while its recording 
surface is being controlled by a pair each of upstream side carrying 
roller 4 and downstream side carrying roller 8. 
By successively repeating this carrying and scanning by a carriage 6, the 
recording head 112 discharges ink to record on the recording sheet 2. When 
a portion corresponding to the rear end of the first page of the recording 
paper 2 is carried to the position of a cutter 5, the recording paper 2 is 
cut by rotating this cutter. When recording for one page in this recording 
paper is finished thereafter, it is exhausted at a predetermined position 
of an exhaust paper tray, etc. through paper guides 10 and 11. 
The recording head used in the above embodiment is an ink type recording 
head taking advantage of heat energy as mentioned above. A portion 
corresponding to one of the discharging orifices of this recording head is 
shown in FIGS. 3A and 3B. 
FIG. 3A is a sectional view of the discharging orifice and liquid channel 
in communication therewith. A heater (electricity-heat converter) 150 
consists of a heating resistors, and an electrode 151 supplies power to 
the heater 150. The heater 150 and electrode 151 are formed on a substrate 
made of Si, etc. Numeral 152 is a discharging orifice, and numeral 153 is 
ink filled in the liquid channel. 
FIG. 3B is a constitution diagram showing the above recording head. 
In the recording head 112, a heater (electricity heat converter) 150, which 
generates heat energy for supplying an applied voltage, is disposed in 
each liquid channel to allow a plurality of discharging orifices 152 
provided in rows to discharge the recording liquid. By applying a driving 
signal, the heater 150 is allowed to generate heat energy, causing film 
boiling of the ink to form a bubble in the ink liquid channel. The growth 
of this bubble discharges an ink droplet through the discharging orifice 
152. 
When discharging using such a head, the ink temperature in the liquid 
channel, where the heat of the heater 150 is directly applied to the ink 
to be discharged, rises comparatively fast. Since dry ejection is 
performed beforehand to prevent occurrence of a difference in recording 
density after such a recording stand-by as mentioned above, it is possible 
to reduce a difference between the ink temperature in the liquid channel 
and the temperature before the stand-by state as far as possible. 
FIG. 4 is a diagram showing a number of pulses for dry ejection to be 
output in accordance with the temperature before stand-by and the stand-by 
time. A curve F shows when the recording head temperature is 45.degree. C. 
immediately before a stand-by state, a curve G for 50.degree. C., and a 
curve H for 40.degree. C. respectively. When the temperature immediately 
before the stand-by is higher, and the stand-by time is longer, the ink 
temperature in the liquid channel can be immediately brought close to the 
temperature before the stand-by state by performing dry ejection with more 
pulses, and it becomes possible to suppress the change in density as far 
as possible. Since the diagram shown in FIG. 4 differs with the 
construction of the head, it is desirable to obtain it by experiment 
beforehand. 
FIG. 5 is a flow chart showing the procedure of recording according to this 
embodiment. The recording process of this embodiment will be described 
referring to FIG. 5. 
When the recording process is started, stand by in step S501 while a 
predetermined amount of image data adapted to the memory capacity of the 
interface 103, for example, image data for five scans as described in FIG. 
8 is transferred from the host computer 101 to the interface 103. 
The transferred image data is stored in the memory of the interface 103, 
and is converted into driving data. When transfer of this predetermined 
amount is finished, it is judged through a flag in step S503 whether or 
not the above predetermined amount has been recorded after this procedure 
was started. That is, it is judged here whether or not it is the first 
recording out of recording for one page shown in FIG. 8. If the flag is 
"L", it is regarded as the first recording on the first page to proceed to 
step S505 for recording for one scan. 
That is, while allowing the recording head 112 to be opposite to the 
recording area of recording sheet 2, the recording head 112 is once 
reciprocated within this range to perform recording for one scan by 
discharging ink in accordance with the going action or the reciprocation 
during this duration. 
Then it is judged in step S507 from, for example, the content of a counter 
for number of scanning times stored in the CPU 111 whether or not 
recording for one page has been finished. If it is judged that the 
recording is not finished, it is judged in step S509 whether or not 
recording of a predetermined amount stored in the memory within the 
interface 103 is finished through driving data. 
For example, in an embodiment shown in FIG. 8, it can be judged from the 
content of the counter stored in the CPU 111 whether or not recording for 
five scans is finished. If negatively judged here, the process in step 
S505 and after is repeated. 
If it is judged in step S509 that recording for the driving data stored in 
the memory of the interface 103 is finished, a flag showing that scanning 
of the above predetermined amount has been finished is regarded as flag 
"H" in step S511, the recording head 112 is moved to the stand-by position 
such as a home position in step S513, and at the same time, counting of 
the stand-by time is started in step S515. 
This counting can be performed by counting the period of a signal showing 
the stand-by state to be fed from the interface 103. Together with this 
process, the recording head temperature when scanning of the above 
predetermined amount is finished is detected in step S517, and after it is 
stored in the RAM 111A, the step returns to step S501 to enter a stand-by 
state. 
In step S501, it is judged that transfer of the image data to the interface 
103 has been finished. When it is further judged in step S503 that the 
content of the flag, which has been set in step S511, is "H", that is, 
when it is judged that the recording has been interrupted into a stand-by 
state, the step proceeds to step S519. The stand-by time, which has been 
counted so far, is detected and this counting time is reset. Then in step 
S521, the recording head 112 is moved to the position of the ink receiver 
160 for dry ejection. 
To perform this dry ejection, a number of ejections for dry ejection is 
determined by referring to the table, stored in the ROM 111B, having such 
a relationship as shown in FIG. 4, and on the basis of the stand-by time 
detected in step S519 and the recording head temperature before the 
stand-by, detected in step S517. After the completion of the dry ejection, 
the process proceeds to step S505 to start recording operation again. 
In the above first embodiment, ink has been actually discharged to raise 
the temperature of the ink within the liquid channel after the stand-by. 
In the second embodiment, however, a driving pulse with a voltage, current 
or pulse width to such a degree that no ink is discharged is applied. 
In the case of an ink jet type using heat energy, the heater may be damaged 
due to cavitation, etc. attendant upon formation and disappearance of a 
bubble during ink ejection. For this reason, an attempt is made to prevent 
the shortened life of the recording head as far as possible by trying to 
avoid unnecessary ink ejection as much as possible. Also the first 
embodiment requires means to collect ink discharged at the dry ejection 
position, possibly leading to a more bulky apparatus constitution. 
In the above embodiment, the ink temperature within the liquid channel is 
allowed to rise fast by applying a driving pulse to such a degree that no 
ink ejection is performed to the heater within each liquid channel in 
order to suppress the change in density before and after the stand-by. 
In addition, in the above first and second embodiments, the applied pulse 
of the discharge heater has been determined in accordance with the 
stand-by time and the head temperature before the stand-by. In the third 
embodiment, however, the applied pulse is determined taking the 
environmental temperature into consideration in addition to these two. 
In the third embodiment, environmental temperature detecting means 115 is 
separately provided as shown in FIG. 6 to input the environmental 
temperature into the CPU 111, and at the same time, to prepare a table 
having such a relationship as shown in FIG. 4 beforehand for each 
environmental temperature to be detected. When the environmental 
temperature is low, it is thereby possible to use more discharge pulses 
because the lowered head temperature during stand-by is great, and when 
the environmental temperature is high, it is possible to use less 
discharge pulses. As a result, it becomes possible to suppress the change 
in density more precisely. 
For the driving pulse applied to head, not only its number of pulses but 
also the voltage and pulse width of the driving pulse may be made variable 
in accordance with the stand-by time. 
As can be seen from the above description, according to the present 
invention, a recording head driving signal to control the temperature when 
resuming recording is determined in accordance with the recording head 
temperature when the recording is interrupted and the interruption time. 
Since the recording head is driven through this signal beforehand, the 
higher the temperature during interruption, and the longer the 
interruption time in, for example, the ink jet type recording head, it is 
possible to immediately return the recording head temperature to the 
temperature during interruption through a driving signal with more 
ejection pulses or a larger pulse width. 
As a result, it is possible to suppress the difference in density of image, 
etc. to be recorded before and after the recording stand-by as far as 
possible, and to prevent the image quality from lowering due to the 
recording stand-by. 
The fourth embodiment of the present invention will be described referring 
to the drawings. 
FIG. 10 is a block diagram showing the fourth embodiment of the present 
invention, and portions with the same function as in FIG. 1 are affixed 
with the same symbols. FIG. 11 is a graph showing a table stored in the 
look-up table 110A in the embodiment in FIG. 10. FIG. 12 is a graph 
showing the data stored in the memory 116 in the embodiment in FIG. 10. 
In FIG. 10, numeral 110A is a look-up table (LUT) , numeral 116 is a 
memory, numeral 121 is an output image signal from the look-up table 110A, 
and numeral 122a is a look-up table selection signal of discharge command 
signals 122. 
An 8-bit image signal transferred from the host computer 101 is once stored 
in the memory within the interface 103, and then is input into a look-up 
table 110A (hereinafter called "LUT 110A") after being rearranged. In the 
LUT 110A, straight lines 0.01 each different in gradient from Y=0.69X to 
Y=1.32X are prepared as 64 tables as shown in FIG. 11, and the input 
signal is converted in accordance with a table selected through a 
selection signal 122A. 
An output signal 121 from the LUT 110A is input into the recording head 
112. The recording head 112 has a head driving circuit (not shown), which 
drives the recording head 112 through a driving pulse adapted to the input 
image data to discharge ink. The amount of discharged ink is ensured to be 
almost in proportion to the magnitude of the driving pulse. 
When usual printing is started, a state indication signal 120 showing the 
usual printing state is transmitted to the CPU 111 from the interface 103. 
At this time, the CPU 111 selects one with a gradient of 1.0 from the LUT 
110. 
When recording of image for the memory capacity of the interface 103 is 
finished, the interface 103 transmits a signal showing a stand-by state to 
the CPU 111. On receipt of this signal, the CPU 111 detects a temperature 
T of the recording head 112 to once store it in a memory (not shown), and 
counts a time t until it receives a signal showing the usual printing 
state. When transfer of the data is finished to enter the next printing 
state, the CPU 111 determines a table to be selected from the LUT 110A in 
accordance with the head temperature T immediately before the interruption 
and the interruption time t when resuming the recording. 
FIG. 12 is a graph showing conditions for deciding the graph gradient on 
the basis of the table of the LUT 110A, stored in the memory 116, to be 
selected when resuming printing. 
When the head temperature immediately before the interruption is 25.degree. 
C. or less, the head has the same temperature as the room temperature, and 
it is judged that there is no lowered temperature due to the interruption. 
Therefore, the graph gradient according to the table of LUT 110A remains 
at 1.0. 
If, however, the head temperature immediately before the interruption is 
25.degree. C. or more, judging that the head temperature will lower due to 
the interruption, the same image density as that immediately before the 
interruption is ensured to be obtained by making the graph gradient, 
larger than 1.0, according to the table of LUT 110A on resuming. The 
longer the interruption time, and the higher the head temperature 
immediately before the interruption, the change in density during the 
interruption is compensated by making the graph gradient according to the 
table of LUT 110A the larger. 
After resuming printing, the coefficient is gradually returned to the 
original. When, for example, a table corresponding to a graph with a 
gradient of 1.10 is selected from the LUT 110A on resuming and the 
interface memory has a capacity for 10 scans, an image is recorded on the 
basis of the table of the LUT 110A corresponding to a graph with a 
gradient of 1.01 on the 10th scan by continuing to decrease the gradient 
at a rate of 0.01 each for every scanning. When resuming recording after 
the next stand-by, correction is performed with a table with a gradient of 
1.0 as a reference in the same manner. 
Even if the head temperature lowers during stand-by, an uniform image free 
from any change in density in the real picture can be obtained by thus 
correcting the image signal. 
In a color image forming apparatus, the above control may be independently 
provided for each color recording head. 
On decreasing a graph gradient according to the table after resuming the 
recording, not only a number of scanning but also the recording time, 
number of recording pulses, etc. may be counted to return the coefficient 
accordingly. 
FIG. 13 is a block diagram showing the fifth embodiment of the present 
invention. 
In the above embodiment, environmental temperature detecting means 115 is 
added to the embodiment in FIG. 10, and a table determination condition of 
the LUT 110A has been prepared in the memory 116 for each environmental 
temperature. 
The environmental temperature detecting means 115 is composed of a 
thermistor, etc., and detects the environmental temperature where the 
apparatus is placed to transmit an environmental temperature signal 125 to 
the CPU 111. 
The CPU 111 selects a condition determination curve (not shown) in 
accordance with the environmental temperature, and further determines the 
graph gradient based on the table of LUT 110A in accordance with the head 
temperature before the interruption and the interruption time. The 
condition determination curve is stored in the ROM as the LUT 110A, and 
with each of the environmental temperature, the head temperature before 
interruption, and the interruption time as an address, the gradient is 
output. 
For the condition determination curve to select the graph according to the 
LUT 110A, when the environmental temperature is low, a graph with more 
gradient should be selected because the head temperature drop is great 
during interruption, and when the environmental temperature is high, a 
graph with less gradient should be selected. 
This enables suppressing the change in density more exactly. 
FIG. 14 is a block diagram showing the sixth embodiment of the present 
invention. Those affixed with the same number as those in FIG. 10 show the 
same component elements. 
In the above embodiment, a binarization circuit 130 is inserted between the 
LUT 110A in the embodiment in FIG. 10 and the recording head 112 for 
connection. 
In the embodiment in FIG. 10, a recording head, in which the size of the 
dot can be changed in accordance with the magnitude of an input image 
signal, is used. In the above embodiment, however, the present invention 
applies to a head in which the size of the dot cannot be changed or is 
difficult to be changed. 
A binarization circuit 130 converts a multi-value image signal into a 
binary signal through the binarization method such as the dither method 
and the error diffusion method. The recording head prints dots with a 
predetermined size in accordance with a binary signal for image recording. 
Other functions are the same as in the embodiment in FIG. 10. 
In such a constitution, it is possible to compensate the lowered density by 
printing more dots per unit area in order to obtain an uniform image free 
from any change in density in the actual picture when resuming recording 
even if the temperature lowers during stand-by. 
As mentioned above, the present invention has such an effect that the 
change in image density due to interruption is compensated and an uniform 
image free from any change in density can be obtained by correcting the 
image signal to be applied to the image recording head on the basis of the 
image recording head temperature when the recording is interrupted and the 
time until recording is resumed since interrupted on resuming the 
recording. 
The seventh embodiment will be described referring to the drawings. 
FIG. 15 is a block diagram showing a constitution of the seventh embodiment 
of the present invention, and portions having the same function as in FIG. 
10 are affixed with the same symbols. 
In FIG. 15, numeral 112 is an ink jet recording head with a constitution 
shown in FIG. 3, numeral 113 is head temperature detecting means such as a 
thermistor, numeral 123 is a head temperature signal, and controlling 
means is composed of a CPU 111 and an LUT 110A. The ink jet recording head 
112 consists of a plurality of recording heads, and recording liquids with 
different colors are discharged from the respective recording heads. 
An 8-bit image signal 102 transferred from the host computer 101 is once 
stored in the memory within the interface 103, and then is input into LUT 
110A after being rearranged. 
In the LUT 110A, 64 sets of tables consisting of straight lines 0.01 each 
different in gradient from Y=0.69X to Y=1.32X are stored as shown in the 
above FIG. 11, and the magnitude of the pulse of the input image signal is 
converted in accordance with a table selected through an LUT selection 
signal 122A. 
When usual printing is started, a state indication signal 120 to be output 
from the interface 103 shows an usual printing state. At this time, the 
CPU 111 outputs an LUT selection signal 122A showing that a table with a 
gradient of 1.0 is selected to the LUT 110A. 
Then when recording of image for the memory capacity of the interface 103 
is finished, the interface 103 transmits a signal showing a stand-by state 
to the CPU 111. On receipt of this signal, the CPU 111 detects a 
temperature T.sub.1 of the ink jet recording head 112 through a head 
temperature signal 123 to be output by the head temperature detecting 
means 113 to once store it in a built-in memory (not shown). Then the CPU 
111 stands by until the host computer 101 finishes transmitting the next 
image data to the interface 103. 
Thereafter transmitting of the data is finished, and immediately before the 
next printing begins, the CPU 111 detects a temperature T.sub.2 of the ink 
jet recording head 112 again to calculate (T.sub.1 -T.sub.2), that is, the 
temperature difference between before and after the recording 
interruption. Then the CPU 111 selects a table of the LUT 110A in 
accordance with the value of the difference in temperature (T.sub.1 
-T.sub.2) when resuming recording. 
FIG. 16 shows a relationship between the value of the difference in 
temperature (T.sub.1 -T.sub.2) and the gradient of a table of LUT 110A to 
be selected in accordance with this value. As shown therein, the larger 
(T.sub.1 -T.sub.2), a table with a larger coefficient is selected on 
resuming. This is because the lowered recording density is compensated by 
raising the image signal level even if the recording density lowers due to 
lowered temperature during stand-by. The above coefficient is gradually 
returned to the original after printing is resumed. 
When, for example, a table with a gradient of 1.10 is selected on resuming 
and the memory of the interface 103 has a capacity for 10 scans, an image 
is recorded using a table with a gradient of 1.01 on the 10th scan by 
continuing to decrease the gradient at a rate of 0.01 each for every 
scanning. When resuming recording after the next stand-by, a table of LUT 
110A is selected with a table with a gradient of 1.0 as a reference in the 
same manner for correction. Even if the head temperature lowers during 
stand-by, an uniform image free from any change in density in the real 
picture can be obtained because the image signal is to be corrected in 
accordance with this lowered temperature. 
In a color image forming apparatus, the above control may be independently 
performed for each color recording head. 
On returning the table gradient after resuming the recording, not only a 
number of scannings but also the recording time, number of recording 
pulses, etc. may be counted to return the coefficient to the original 
accordingly. 
The eighth embodiment of the present invention will be described. 
In the embodiment in FIG. 17, a recording head, in which the size of the 
dot can be changed according to the magnitude of an input image signal, is 
used. In the above embodiment, however, the present invention applies to a 
head in which the size of the dot cannot be changed or is difficult to be 
changed. 
FIG. 17 is a block diagram showing the constitution of the above 
embodiment, and those affixed with the same numbers as in FIG. 15 have the 
same component elements. 
In FIG. 17, a binarization circuit 130 converts an output image signal 121 
to be transmitted from a LUT 110A into a binary signal by the binarization 
method such as the dither method and the error diffusion method. The ink 
jet recording head 112 prints dots with a predetermined size in accordance 
with a binary signal 124 to be transmitted by the binarization circuit 130 
for image recording. Other functions are the same as in the seventh 
embodiment. 
In such a constitution, it is possible to compensate the lowered density by 
printing more dots when resuming recording even if the temperature lowers 
during stand-by in order to obtain an uniform image free from any change 
in density in the actual picture. 
The ninth embodiment will be described. In the abovementioned seventh and 
eighth embodiments, the table gradient is returned to the original a 
predetermined amount each for every scanning after recording is resumed. 
In this embodiment, however, while detecting the head temperature, the 
gradient is returned in accordance with the amount of detection. 
For example, it is assumed that a difference in temperature between before 
and after stand-by is .DELTA.T=(T.sub.1 -T.sub.2), a table with a gradient 
of K is selected in accordance with the difference in temperature 
.DELTA.T, and the head temperature when recording on the n-th scan begins 
after recording is resumed is t. In this case, a table with a gradient of 
1+(T.sub.1 -t)/(T.sub.1 -T.sub.2).times.(K-1) is selected as a table in 
this scanning. 
It is assumed that when a table with K=1.2 is selected at, for example, 
.DELTA.T=10.degree., the temperature has been considerably returned and is 
only 4.degree. C. lower than T.sub.1 when recording on the second line 
begins. In this case, the gradient of the second line is as follows: 
EQU 1+4/10.times.(1.2-1)=1.08 
By doing as mentioned above, the gradient of the table to be used at a 
temperature closer to the actual ink jet recording head temperature can be 
brought near to the original value. 
In the above embodiment, there are instances where the gradient immediately 
before the next interruption does not return to 1.0. In this case, 
assuming the gradient immediately before the next interruption to be K', a 
table with a gradient obtained by multiplying the gradient obtained from 
FIG. 16 by K' may be used as a table on the next resuming. 
The present invention has such an effect that the recording density can be 
prevented from changing on resuming recording and an uniform image can be 
obtained on interrupting and resting recording because on resuming 
recording, the image signal is corrected in accordance with a difference 
between a recording head temperature at that time and a recording head 
temperature on interrupting recording. Also since the image signal after 
resuming recording is recorrected in accordance with the state of use or 
the temperature of the recording head, the image after resuming recording 
can be made uniform. 
FIG. 18 is a block diagram showing the tenth embodiment when the present 
invention is applied to the output for computer graphics. 
In FIG. 18, numeral 105 is an ink jet printer, numeral 112 is an ink jet 
recording head, numeral 101 is a host computer, numeral 102 is an image 
signal, numeral 103 is an interface, numeral 104 is an image signal, 
numeral 111 is a CPU (Central Processing Unit), numeral 113 is head 
temperature detecting means such as a thermistor, numeral 116 is a fan, 
numeral 117 is a head temperature controlling heater, numeral 120 is a 
state indication signal from the interface, numeral 123 is a head 
temperature signal, numeral 126 is a fan driving signal, numeral 127 is a 
head heater driving signal and numeral 128 is an inhibit signal. 
The temperature controlling means is composed of the CPU 111, head 
temperature detecting means 113 and a head heater 117. The CPU 111 also 
constitutes memory means and resuming means. 
The control in the tenth embodiment shown in FIG. 18 will be described 
referring to FIG. 19. 
It is first checked whether or not it is in usual printing (step S1). If in 
usual printing, an image signal 102, which is an image data from the host 
computer 111, is once stored in a memory (not shown) within the interface 
103. The interface 103 rearranges the stored image data so that it is 
received by an ink jet head 112 to transmit it to the ink jet head 112 as 
an image signal 104. The ink jet head 112 prints in accordance with the 
image signal 104. 
During this period, the interface 103 transmits an interface state 
indication signal 120 showing an usual printing state to the CPU 111. 
While this interface state indication signal 120 is being transmitted, the 
CPU 111 sets a present temperature for controlling temperature to an usual 
value, for example, 35.degree. C. A head temperature signal 123 from the 
head temperature detecting means 113 is input into the CPU 111, and if it 
is higher than 35.degree. C., the CPU 111 outputs a fan driving signal 126 
to drive a fan 116. If lower than 35.degree. C., the CPU 111 outputs a 
head heater driving signal 127 to drive a head heater 117 to maintain the 
temperature (hereinafter called "head temperature") of the ink jet head 
112 within a predetermined range (for example, 34.degree. C. to 36.degree. 
C.) (steps S2, S3, S4). 
When recording of an image for the memory capacity of the interface 103 is 
finished, the interface 103 transmits an interface state indication signal 
120 showing a stand-by state, in which recording is being interrupted, to 
the CPU 111. On receipt of this interface state indication signal 120, the 
CPU 111 once stores the head temperature (T.degree. C.) at the time to set 
it to a preset temperature for controlling temperature (step S5). 
Thereafter, the CPU 111 inputs a head temperature signal 123 from the head 
temperature detecting means 113 again to check the head temperature (step 
S6). If the head temperature is equal to the preset temperature (T.degree. 
C.) left stored in the CPU 111, printing is enabled as soon as the 
stand-by state is finished (step S11). However, if the head temperature is 
not equal to the preset temperature (T.degree. C.), the CPU 111 transmits 
an inhibit signal 128 to the interface 103 to inhibit the ink jet head 112 
from transmitting an image signal 104 even if transfer of data from the 
host computer 101 to the interface 103 is finished (step S7). 
If the head temperature is lower than the preset temperature (T.degree. 
C.), a head heater 115 is driven, and if higher than the preset 
temperature, a fan 114 is driven to lower the head temperature so that it 
is equal to the preset temperature (T.degree. C.) (steps S8, S9, S10). If 
the head temperature is equal to the preset temperature (T.degree. C.), 
the state is returned to a printable state to resume recording of an image 
(step S11). 
Since recording is resumed after the head temperature is returned to that 
immediately before recording interruption, even if recording is thus 
interrupted into a stand-by state and the head temperature changes, it is 
possible to obtain an uniform image free from any change in image density. 
The eleventh embodiment will be described. FIG. 20 shows the control of the 
eleventh embodiment, and the eleventh embodiment is different from the 
tenth embodiment in that printing is not enabled immediately even if the 
head temperature reaches the preset temperature (T.degree. C.), but it is 
enabled five seconds later on resuming recording from the stand-by state. 
This is for the following reason: 
A thermistor as head temperature detecting means, which detects the head 
temperature, is generally mounted to the substrate of the recording head. 
For example, in the case of an ink jet head, when the temperature of ink 
within the nozzle does not reach the predetermined temperature even if a 
temperature to be detected by this thermistor reaches the predetermined 
temperature, a difference in printing density still remains. 
For this reason, by waiting five seconds after the thermistor detection 
temperature reaches the preset temperature (T.degree. C.) (step S12) in 
the eleventh embodiment, it is ensured that the temperature of ink within 
the ink jet head nozzle reaches the preset temperature (T.degree. C.). As 
a result, change in density can be securely suppressed. For other than the 
above step 12, the description is omitted because those are the same as in 
FIG. 19. 
In the above-mentioned tenth and eleventh embodiments, when an ink jet head 
using heat energy composed of such head elements as shown in FIG. 3 is 
used for ejection, the temperature of ink within the nozzle rises 
abruptly, and therefore, it is possible to return the temperature of ink 
within the nozzle to a temperature immediately before recording 
interruption in a very short time. 
The twelfth embodiment will be described. In this embodiment, the present 
invention applies to an ink jet printer shown in the above FIG. 2B. In the 
above embodiment, when recording of recording image for one line is 
finished, recording for one line is repeated again after subscanning roll 
paper 2 by a subscan roller 8. 
This twelfth embodiment utilizes heat energy for ejection of the 
above-mentioned ink jet head using heat energy, and if the temperature of 
the ink jet head 112 is lower than the preset temperature (T.degree. C.), 
ink is ejected at a dry ejection position 160 provided in a non-image area 
at the left end of the platen 9 in addition to driving of a head heater 
(not shown). By means of heat generated at this time, the temperature of 
the ink jet head 112 has been designed to reach the preset temperature 
(T.degree. C.) earlier. 
This enables the temperature of ink within the nozzle of the ink jet head 
112 to immediately return to a temperature before the recording 
interruption, reducing some loss in time. 
As mentioned above, the present invention is able to compensate any change 
in image density due to recording interruption and obtain an uniform image 
with less change in density by controlling the recording head temperature 
so that it is almost equal to a temperature when recording was interrupted 
on resuming after interrupting recording. 
Although an ink jet recording apparatus using a serial type recording head 
has been described in the above embodiments, one using a full line type 
recording head may be used. 
In addition, the present invention can be applied to not only an ink jet 
recording head using heat energy, etc., but also to others, such as 
thermal transfer, in which the temperature of the recording head rises 
during driving. 
Further, the stand-by state is not always limited to time to receive 
transfer data. The present invention can apply even when a stand-by state 
occurs during printing for other objects including head recovery operation 
such as sucking of ink during printing and wiping of the ejection surface. 
The present invention brings about excellent effects particularly in an ink 
jet system using heat energy among the ink jet recording system. 
As to its representative constitution and principle, for example, one 
practiced by use of the basic principle disclosed in, for example, U.S. 
Pat. Nos. 4,723,129 and 4,740,796 is preferred. This system is applicable 
to either of the so called on-demand type and the continuous type. 
Particularly, the case of the on-demand type is effective because, by 
applying at least one driving signal which gives rapid temperature 
elevation exceeding nucleate boiling corresponding to the recording 
information on an electricity-heat converters arranged corresponding to 
the sheets or liquid channels holding liquid (ink), heat energy is 
generated at the electricity-heat converters to effect film boiling at the 
heat acting surface of the recording head, and consequently the bubbles 
within the liquid (ink) can be formed corresponding one by one to the 
driving signals. 
By discharging the liquid (ink) through an opening for discharging by 
growth and shrinkage of the bubble, at least one droplet is formed. By 
making the driving signals into pulse shapes, growth and shrinkage of the 
bubble can be effected instantly and adequately to accomplish more 
preferably discharging of the liquid (ink) particularly excellent in 
response characteristic. 
As the driving signals of such pulse shape, those as disclosed in U.S. Pat. 
Nos. 4,463,359 and 4,345,262 are suitable. Further excellent recording can 
be performed by employment of the conditions described in U.S. Pat. No. 
4,313,124 of the invention concerning the temperature elevation rate of 
the above-mentioned heat acting surface. 
As the constitution of the recording head, in addition to the combination 
constitutions of discharging orifice, liquid channel, electricity-heat 
converter (linear liquid channel or right angle liquid channel) as 
disclosed in the above-mentioned respective specifications, the 
constitution by use of U.S. Pat. No. 4,558,333, or 4,459,600 disclosing 
the constitution having the heat acting portion arranged in the flexed 
region is also included in the present invention. In addition, the present 
invention can be also effectively made the constitution as disclosed in 
Japanese Patent Laid-Open Application No. 59-123670 which discloses the 
constitution using a slit common to a plurality of electricity-heat 
converters as the discharging portion of the electricity-heat converter or 
Japanese Patent Laid-Open Application No. 59-138461 which discloses the 
constitution having the opening for absorbing pressure wave of heat energy 
corespondent to the discharging portion. 
Further, as the recording head of the full line type having a length 
corresponding to the maximum width of recording medium which can be 
recorded by the recording device, either the constitution which satisfies 
its length by combination of a plurality of recording heads as disclosed 
in the above-mentioned specifications or the constitution as one recording 
head integrally formed may be used, and the present invention can exhibit 
the effects as described above further effectively. 
In addition, the present invention is effective for a recording head of the 
freely exchangeable chip type which enables electrical connection to the 
main device or supply of ink from the main device by being mounted on the 
main device, or for the case by use of a recording head of the cartridge 
type provided integrally on the recording head itself. 
Also, addition of a restoration means for the recording head, a preliminary 
auxiliary means, etc. provided as the constitution of the recording device 
of the present invention is preferable, because the effect of the present 
invention can be further stabilized. Specific examples of these may 
include, for the recording head, capping means, cleaning means, 
pressurization or aspiration means, electricity-heat converters or another 
heating element or preliminary heating means according to a combination of 
these, and it is also effective for performing stable recording to perform 
preliminary mode which performs discharging separate from recording. 
Further, as the recording mode of the recording device, the present 
invention is extremely effective for not only the recording mode only of a 
primary color such as black etc., but also a device equipped with at least 
one of plural different colors or full color by color mixing, whether the 
recording head may be either integrally constituted or combined in plural 
number. 
Further in addition to those used as an image output terminal for 
information processing equipment such as computers, as a form of an ink 
jet recording apparatus of the present invention, copying apparatus 
combined with a reader, etc., and those which assume the form of a 
facsimile equipment having transmitting and receiving functions may be 
used.