Ink jet misdischarge recovery by simultaneously driving an ink jet head and exhausting ink therefrom

A method is used for recovering misdischarge of liquid in an on-demand type liquid jet recording apparatus. The apparatus comprises a recording head having a discharge port for discharging liquid, a liquid path communicating with the discharge port and energy generating means provided in response to the liquid path so as to generate energy utilized for discharging liquid, and exhausting means for exhausting liquid in the liquid path. Drive of the energy generating means is performed in synchronism with drive of the exhaust means at least in a predetermined time period.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method for recovering misdischarge is an 
ink jet recorder which eliminates non-discharge or misdischarge of ink to 
permit stable discharge of ink, and an ink jet recording apparatus using 
the same. 
2. Related Background Art 
In a prior art ink jet recorder such as that disclosed in U.S. Pat. No. 
4,045,802, capping means for closing a periphery of an discharge orifice 
of a record head is provided to close the periphery in a non-record mode 
so that the record head is isolated from surrounding atmosphere while the 
record head is capped, and air layer in the capping means is filled with 
vapor of ink to keep a saturated vapor pressure so that drying and 
increase of viscosity of the ink in the discharge orifice are prevented. 
However, in such a recorder, in a low humidity environment or when 
recording is paused for a long time it is not possible to sufficiently 
prevent the increase of viscosity of ink even if drying is prevented by 
the capping means, and hence it is difficult to completely prevent 
non-discharge or misdischarge of the ink from the nozzle in a record mode. 
When a fine air bubble or dust is present in the ink in the discharge 
orifice, it causes disturbance of discharge of the ink in the record mode 
and it significantly deteriorates an image quality. 
In order to solve such a problem, U.S. Pat. No. 4,600,931 discloses an ink 
jet recorder which renders the air layer in the capping means to be of low 
pressure so that the ink in the discharge orifice of the record head is 
sucked. U.S. Pat. No. 4,123,761 disclosed an ink jet recorder which has 
pumping means for an ink supply system including the record head and it is 
automatically or manually activated to pressurize the ink so that the ink 
is discharged from all nozzles of the record head. U.S. Pat. No. 4,176,363 
discloses an ink jet recorder which effects pre-discharge in order to 
prevent non-discharge of the ink. 
However, even such ink jet recorders are not always sufficient in that the 
recorders are always operable in a best condition regardless of a 
surrounding environment or recording condition. It is particularly 
difficult to completely eliminate fine air bubbles in the ink. Even if 
there is no fine air bubble at the start of recording, fine air bubbles 
may be generated and grown by cavitation during continuous recording 
operation, or ink droplets including air bubbles therein may be discharged 
from the discharge orifice to cause disturbance in the discharge of the 
ink. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method for recovering 
misdischarge in an ink jet recording apparatus which allows recording at a 
best condition in any circumstance. 
It is another object of the present invention to provide an ink jet 
recording apparatus which can remove air bubbles of any size with a simple 
construction and enable high quality recording. 
Still another object of the invention is to provide an ink jet recording 
apparatus comprising a recording head having energy generating means for 
generating energy to be used to discharge ink, exhaust means for 
exhausting ink in said recording head; drive means for applying a drive 
signal to said energy generating means to drive said recording head in 
response to the drive of said exhausting means and means for varying the 
drive signal applied to said energy generating means in response to the 
drive of said exhausting means. 
Still another object of the invention is to provide a method for recovering 
misdischarge of liquid in an on-demand type liquid jet recording 
apparatus, said apparatus comprising a recording head having a discharge 
port for discharging liquid, a liquid path communicating with said 
discharge port and energy generating means provided in response to said 
liquid path so as to generate energy utilized for discharging liquid and 
exhausting means for exhausting liquid in said liquid path, wherein drive 
of said energy generating means is performed in synchronism with drive of 
said exhaust means at least in a predetermined time period. 
Still another object of the invention is to provide a method for recovering 
misdischarge of liquid in a liquid jet recording apparatus, said apparatus 
comprising a recording head having a discharge port for discharging 
liquid, a liquid path communicating with said discharge port and energy 
generating member provided in response to said liquid path so as to 
generate energy utilized for discharging liquid and suction means for 
sucking liquid from said discharge port, wherein said recording head is 
driven by changing a signal to be applied to said energy generating means 
in response to drive of said suction means. 
Still another object of the invention is to provide a ink jet recording 
apparatus comprising a recording head having a discharge port for 
discharging ink, a liquid path communicating with said discharge port and 
energy generating means provided in response to said liquid path so as to 
generate energy utilized for discharging liquid, driving means for driving 
said recording head, exhausting means for exhausting liquid in said liquid 
path during non-operation period, and detecting means for detecting drive 
of said exhausting means, wherein said driving means is driven by a 
detection signal of said detecting means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiment 1 
FIG. 1 shows a schematic top view of an ink jet recording apparatus of the 
present invention. 
In FIG. 1, numeral 1 denotes a platen which is rotated by a line feed motor 
7 which is a pulse motor to feed a record sheet (not shown). The presence 
or absence of the record sheet is detected by a sheet sensor 9. Numeral 2 
denotes an ink jet recording head which has a plurality discharge ports 30 
through which ink is to be discharged. It is mounted on a carriage which 
is slidable on a guide bar (not shown) and movable along the platen 1 by 
drive by a carriage motor 8 which is a DC motor, through a belt 14. In 
order to detect the position of the recording head 2, a linear encoder 12 
and an encoder sensor 13 are provided, and in order to detect a home 
position, a home position sensor 11 is provided. In order to recover 
misdischarge of ink from the discharge ports 30 of the recording head 2, a 
cap 3 which is used to protect the discharge ports and to suck the ink and 
which is driven by an auto-cap motor 6 is provided. The operational 
position of the cap 3 is detected by a cap sensor 10. 
The cap 3 is connected to a pump 31 through a tube 112 and the pump 31 can 
suck the ink from the nozzle by reducing a pressure. 
The ink jet recording apparatus thus constructed is controlled by a control 
unit shown in FIG. 2 which uses a known CPU 20. The CPU 20 operates in 
accordance with inputs entered by switches provided on a console panel 
(not shown). It refers the inputs from the encoder sensor 13 and the home 
position sensor 11, controls the drive of the carriage motor 8 through a 
DC servo reversible circuit 22, controls the drive of the line feed motor 
7 through a pulse motor drive circuit 23, and supplies record data D to a 
head driver 24, which drives the recording head 2 to discharge the ink. It 
also controls other mechanisms (not shown) in accordance with inputs from 
other sensors 25. 
When a print switch of the switches 21 is depressed, the record operation 
is started. After the presence of the record sheet has been detected by 
the sheet sensor 9, the line feed motor 7 is driven by several steps, the 
platen 1 is rotated and the record sheet is set to a start of record 
position. Then, the carriage motor 8 is driven to reciprocally move the 
recording head 2, and the line feed motor 7 is driven in synchronism 
therewith to feed the record sheet one line at a time. On the other hand, 
a drive signal (drive pulse) representing the record data is applied from 
the head driver 24 to energy generating means of the recording head 2 so 
that the recording head 2 is driven and the ink is discharged from the 
discharge ports 30 to record characters or image. 
If the recording is not properly done due to misdischarge of the ink, a 
recovery switch of the switches 21 is depressed for recovery. FIG. 3 shows 
a flow chart thereof, and FIG. 4 shows a schematic sectional view of ink 
suction recovery means as ink exhausting means. FIG. 5 shows a timing 
chart of the drive of the pump and the recording head. 
In a step 1001, the home position sensor 11 detects if the head 2 is at the 
home position. If it is not at the home position, the recording head 2 is 
returned to the home position by the carriage motor 8 (step 1002). In a 
step 1003, the cap sensor 10 detects if the discharge ports are capped, 
and if they are not capped, the auto-cap motor 6 is energized to cap the 
discharge ports (step 1004). In a step 1005, a piston 153 of the pump 31 
is driven downward by a motor (not shown). As a result, a volume in a 
cylinder 150 above the piston increases and a negative pressure is 
generated. In a step 1006, a lowermost point sensor 125 provided on the 
suction pump detects that the piston reaches its bottom point, the motor 
is deenergized and a flow-in valve 160 is opened (step 1007). The negative 
pressure of the pump is applied to the ink in the liquid path of the ink 
jet recording head 2 through the tube 112, and the ink in the liquid path 
is sucked by the pump. As the ink is sucked, a signal is applied to the 
head driver in a step 1008 and the head is driven in a manner described 
below. As a result, the ink vibrates and fine air bubbles which deposit to 
an inner wall of the liquid path of the record head 2 and which are hardly 
removed merely by the suction pump are easily removed (FIG. 5). 
In steps 1009 and 1010, the piston 153 is returned upward by a spring 165 
so that the pressures in the pump and the cap are returned to their 
initial states. In a step 1101, the capping is released and the record 
operation is ready to start. 
In the present embodiment, the diameter of the air bubbles 36 in the liquid 
path 35 of FIG. 6 is 10.about.500 .mu.m. In FIG. 6, numeral 32 denotes a 
piezoelectric element which is electromechanical transducer means as 
energy generation means, and numeral 34 denotes a filter for removing 
foreign materials such as dust. In the present embodiment, the drive 
frequency of the recording head varies between 300 Hz and 10 KHz. 
In the present embodiment, as shown in FIG. 2, signal varying means 26 for 
varying the drive signal (drive pulse) applied to the recording head when 
the ink is sucked from the discharge port. The signal varying means is 
driven on basis of a signal generated from sensor 125. 
A voltage of the drive pulse is varied to change the drive force of the 
recording head by the pulse varying means 26. 
As shown in FIGS. 7 and 8, the voltage of the drive pulse is continuously 
varied between 30 V and 80 V for two seconds at the driving frequency of 
500 Hz as the ink is sucked from the discharge port. 
In this manner, by driving the ink suction pump while the drive force of 
the recording head is varied, fine air bubbles which could not be removed 
merely by the suction pump are substantially perfectly removed. 
FIG. 9 shows a modification of the drive pulse shown in FIG. 7. In the 
present modification, a pulse of the opposite polarity is applied prior to 
a pulse for pressurizing the ink. 
In FIGS. 7 and 9, the voltage of the drive pulse voltage is varied to 
change the drive force of the recording head. In FIGS. 10 and 11, a width 
of the pulse is varied by the signal varying means. In FIGS. 12, 13, 14, 
15, 16, 17 and 18, the drive force of the recording head is varied in a 
predetermined time period timed with the suction through the discharge 
port. The time period .vertline.t.sub.2 -t.sub.1 .vertline. during which 
the drive force is varied is preferably 0.5.about.3 seconds, while taking 
a lifetime of the energy generation member and a size of the liquid path 
in the record head into account. Power minimum (Pmin) indicates a minimum 
drive force to allow normal discharge of the ink, and power maximum (Pmax) 
indicates a maximum drive force to allow normal discharge of the ink. 
In the present invention, the range of variation of the drive force of the 
recording head is preferably between Pmin and Pmax, as shown in FIGS. 8 
and 12.about.18, while taking an effect to the energy generating means and 
an efficiency of removal of air bubbles into consideration, although other 
range of drive force may be used. 
In the present embodiment, in order to vary the drive force of the record 
head in the range between Pmin and Pmax, the voltage of the drive pulse is 
changed in the range between 30 V and 80 V, or the pulse width is varied 
in the range between 5 .mu.sec and 30 .mu.sec. 
In this manner, by repeatedly varying the drive force of the recording head 
once to several times and driving the ink suction pump to suck the ink 
from the discharge port, fine air bubbles which were left if only the 
suction pump wee used can be substantially perfectly removed. By varying 
the drive force of the record head, the displacement of the air bubbles in 
the liquid path varies. Thus, by varying the drive force of the record 
head simultaneously with the forcive discharge of the ink, air bubbles of 
any size can be discharged from the liquid path. 
It should be noted that both the voltage and the width of the drive pulse 
may be varied. 
Additionally, ink flow reaches its peak (maximum) and air bubbles are more 
effectively removed since drive timing of said recording head is in 
synchronism with application of entire negative pressure in the cylinder 
at a time. 
The drive pulse is not limited to the square wave used in the embodiment 
but it may have a waveform having a fall time of 200.about.300 .mu.sec 
during the last transition of the drive pulse. 
In the present invention, the voltage of the drive pulse is defined by a 
peak value of the drive pulse, and the pulse width is defined by a pulse 
width at one half of the peak value. 
Embodiment 2 
In the present embodiment, when the ink is sucked from the discharge port 
by the signal varying means and in response to the signal of the lowermost 
sensor, the frequency of the drive signal (drive pulse) applied to the 
record head is varied. 
As shown in FIG. 19, in the recovery operation of the recording head, the 
ink is forcibly discharged from the discharge port and the frequency (F) 
of the drive pulse (50 V) applied to the energy generation means of the 
record head is changed in the range between 300 Hz and 10 kHz. As a 
result, air bubbles of any size in the liquid path of the record head 
resonate and are removed by repeatedly and continuously varying the drive 
frequency of the recording head as shown in FIG. 19 to forcibly suck the 
ink. 
FIGS. 20 to 27 show other examples for varying the frequency of the drive 
pulse. For example, as shown in FIGS. 20(a) and 20(b), the drive is 
started from a low frequency and the frequency is gradually increased to 
sequentially match to resonance frequencies of the fine air bubbles. An 
upper limit fmax of the frequency is preferably that which does not 
adversely affect to the head (for example, does not cause break in the 
piezoelectric element which is the energy generating means), e.g., 10 kHz. 
A lower limit fmin of the frequency is preferably that which effectively 
causes the resonation of the air bubbles in the liquid path, e.g., 300 Hz. 
The time period .vertline.t.sub.2 -t.sub.1 .vertline. during which the 
drive frequency is varied as shown in FIGS. 20.about.27 may be preferably 
0.5.about.3 seconds. By repeating the change of the frequency once to 
several times in the time period .vertline.t.sub.2 -t.sub.1 .vertline., 
the air bubbles can be more effectively removed from the recording head. 
In the present embodiment, the range of the change of the drive frequency 
is 300.about.10,000 Hz. It may be preferably 1/10.about.5 times of a 
reference drive frequency which allows normal discharge of the ink from 
the recording head. 
The size of the air bubbles in the liquid path of the record head includes 
variation, and a resonance frequency of the air bubbles in the liquid path 
also includes variation. On an assumption that it is more effective to 
drive the head at a varying frequency than at a constant frequency, the 
recovery of the recording head having a liquid path of 0.5 mm in inner 
diameter including air bubbles of different sizes is observed as shown in 
FIG. 28. When only the ink suction pump is used, several tens air bubbles 
of 10.about.200 .mu.m in diameter are left in the liquid path as shown in 
FIG. 29. When the ink suction pump is activated while the record head is 
driven (at a constant drive frequency), only several air bubbles are left 
as shown in FIG. 30. By activating the ink suction pump while varying the 
head drive frequency, the air bubbles are completely removed as shown in 
FIG. 31. 
In the present invention, the drive frequency is defined as a reciprocal of 
a time from the beginning of first transition of a drive pulse to the 
beginning of first transition of the next drive pulse. 
By varying the drive frequency of the recording head simultaneously with 
varying the drive force, a better result is obtained and this method is 
applicable to any size of liquid path. 
In the present invention, the timing of the drive of the recording head is 
not critical so long as the recording head is synchronously driven during 
the operation of the exhausting means. 
For example, the exhausting means may be driven before driving the 
recording head and also a reverse order may be allowed. 
Driving of the exhausting means is terminated before termination of driving 
of the recording head and also a reverse order may be allowed. 
The timing signal may be not supplied only from the lowermost sensor but 
also from elements engaging the exhausting means, such as a cap sensor, 
pump driving sensor. 
In the Embodiments 1 and 2, means for varying the drive signal (signal 
varying means) applied to the recording head during the suction operation 
is provided separately from the head driver, although it may be integral 
with the head driver or the CPU may has a corresponding function. 
In the above embodiments, suction means for sucking the ink from the 
discharge port through the cap is provided as the exhaust means to 
discharge the ink in the recording head. Alternatively, it may be effected 
by pressurizing means for pressurizing the ink by a pump arranged on an 
ink supply side. 
The present invention is applicable to any ink jet recorder which records 
by discharging ink to a recording plane, whatever configuration and 
recording system are. It is applicable not only to the ink jet recorders 
shown in the embodiments but also to a full-multiple type recorder in 
which recording heads are arranged over an entire width of the record 
sheet. The discharge energy generation means is not limited to the 
electro-mechanical transducer but an ink jet recorder which uses an 
electro-thermal transducer as shown in FIG. 32 may be used. 
FIG. 32 shows a full-multiple type recording head 200 which uses an 
electro-thermal transducer. Numeral 201 denotes the electro-thermal 
transducer which is energy generating means for generating an energy to be 
used for discharging the ink, numeral 202 denotes a liquid path, numeral 
203 denotes a common liquid chamber, and numeral 204 denotes a discharge 
port. 
FIG. 33 shows a schematic drive circuit for the head shown in FIG. 32. In 
this circuit, a drive signal for driving the electro-thermal transducer 
201 varies in response to a capping signal and a signal for recovery 
operation. In this arrangement, the recording head may be driven during 
ink exhausting operation. 
In accordance with the present invention, means for forcibly exhausting the 
ink in the recording head and the recording head are simultaneously driven 
and the ink is forcibly discharged while the drive force of the recording 
head is varied and/or the drive frequency of the recording head is varied. 
Accordingly, the air bubbles and dusts of any size in the head are 
effectively removed and the optimum discharge condition is achieved under 
any environmental condition or recording condition. Thus, the safety, 
continuous recording durability and image recording quality of the ink jet 
recorder are significantly enhanced.