JP2939457B2 - Bubble detector for inkjet recording head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air bubble detecting device for an ink jet recording head of an ink jet printer which ejects ink droplets when printing dots are obtained, and more particularly to a bubble detecting device for an ink jet recording head which detects air bubbles in an ink flow path. Related to the device.

[0002]

2. Description of the Related Art Generally, in an on-demand type ink jet printer in which the volume of an ink flow path is changed by an electrostrictive vibrator and ink droplets are obtained only when necessary, when air bubbles enter a flow path filled with ink, The change in the internal volume of the flow channel generated by the electrostrictive vibrator is limited to the change in the air pressure of the bubble, and there is a drawback that it is not possible to obtain an appropriate ink droplet ejection.

For this reason, various means for detecting bubbles in the ink flow path, such as Japanese Utility Model Publication No. 59-5570, Japanese Patent Application Laid-Open No. 60-262655, and Japanese Patent Application Laid-Open No.
No. 41750 has been proposed.

[0004]

However, these means require a special selection of parts to be used, a part having a special structure, and a complicated discriminating method in the manufacturing method as described below.

According to Japanese Utility Model Publication No. 59-5570, a resistor is inserted into one of the electrostrictive vibrators, and a voltage generated at an end point of the resistor and a capacitor resistor driven similarly to the electrostrictive vibrator are connected. The voltage at the end point of the resistor in the series connection state is compared. In this method, when preparing a plurality of ejection heads, it is necessary to insert a resistor for each electrostrictive vibrator, which requires a complicated manufacturing method.

According to Japanese Patent Publication No. 60-262655, a voltage waveform appearing at an end point of an electrostrictive vibrator is divided by a Zener diode and a resistor to detect an oscillating voltage efficiently. In order for the Zener diode to be in a certain voltage range, a sufficient reverse current is required. Usually, the voltage of the electrostrictive vibrator generated by mechanical strain does not have a sufficient ability to supply this current, and the oscillating voltage to be obtained is attenuated, so that a sufficient amplitude cannot be supplied to the voltage comparator.

According to Japanese Patent Application Laid-Open No. 63-141750, the period of vibration is measured to detect the presence or absence of bubbles, but a counter or a timer is required for period measurement. This is based on the above-mentioned Jiko 59-5570.
In the case of driving a plurality of ejection heads at the same time, as in the case of Japanese Patent Application Laid-Open Publication No. H11-209, there is a disadvantage that the circuit becomes enormous.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and is an ink jet apparatus which can detect bubbles efficiently at a low cost and in a short time even for a plurality of nozzles, while having a simple and sufficient decomposition ability. An object of the present invention is to provide a bubble detecting device for a recording head.

[0009]

According to a first aspect of the present invention, there is provided an air bubble detecting apparatus for an ink jet recording head according to the present invention, wherein an electrostrictive vibrator is provided in each of ink paths of a plurality of nozzles. A driving voltage is applied to the electrostrictive vibrator to discharge ink droplets. In the ink jet recording head, a voltage generated in the electrostrictive vibrator due to a change in the volume of the ink flow path is equal to the drive voltage value. It is characterized in that a bubble detecting means is provided for always detecting whether or not the above-mentioned excessive voltage is reached during the printing operation to detect the presence or absence of bubbles in the ink flow path.

[0010]

According to the present invention, the detection of bubbles is completed only by detecting whether or not the voltage generated in the electrostrictive vibrator is an excessive voltage equal to or higher than the drive voltage value. Therefore, according to the present invention, it is possible to detect bubbles efficiently at a low cost and in a short time even for a plurality of nozzles, while having sufficient decomposition ability easily and easily. This reliably prevents abnormal printing,
In addition, this means for eliminating bubbles can be operated. That is, starting printing, detecting bubbles, stopping driving, removing bubbles,
The restoration of the unprinted portion can be realized continuously as a series of processes, and a normal printing operation accompanied by automatic restoration can be realized for a long time.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a mechanical structure of an ink jet recording head used in the present invention, FIG. 2 shows a bubble detecting circuit and a driving circuit used in the present invention, and FIG. 3 shows a waveform of each part of the circuit in FIG. .

The ink jet recording head has a substrate 1 and a vibration plate 2 joined together, an ink flow path 3 connected to the ink supply side between the two, and a nozzle portion 4 at the tip end for discharging the ink inside. And an electrostrictive vibrator 5 made of a piezoelectric element or the like is fixed to the surface of the vibration plate 2 by an appropriate method.

As shown in FIG. 2, the electrostrictive vibrator 5 is driven by a drive circuit 6 and is formed so that the generation of bubbles is detected by a bubble detection circuit 7.

In one drive circuit 6, a transistor 8 for reducing the voltage across the electrostrictive vibrator 5;
A transistor 9 for increasing the voltage at both ends of the electrostrictive vibrator 5 is connected in series between the drive voltage V0 and the ground. That is, both transistors 8 and 9 are connected via two resistors 10 and 11 having both collectors connected in series, and one transistor 9 has an emitter connected to the drive voltage V
0, and the emitter of the other transistor 8 is grounded. The driving point 5a of the electrostrictive vibrator 5 has two resistors 10,
11 and the other ground point 5b is grounded. The base of the transistor 8 is formed so that a low-potential drive timing signal input from an input terminal 12 is input via bias resistors 13 and 14. The base of the transistor 9 is formed such that a high-potential drive timing signal input from the input terminal 15 is input via the transistor 16. That is, the bias resistor 1 is connected to the base of the transistor 16.
A high-potential drive timing signal is input via the gates 7 and 18, the emitter is grounded, and the collector is connected to the base of the transistor 9 via a resistor 19. Further, a resistor 20 is connected between the emitter and the base of the transistor 9.

In the other bubble detecting circuit 7, a diode 22 is connected between the other end of the resistor 21 having one end connected to the driving point 5a of the electrostrictive vibrator 5 and the driving voltage V0. From the cathode of the diode 22 to the capacitor 23
And the resistor 24 are connected in series and grounded. The connection point between the capacitor 23 and the resistor 24 is connected to the + input terminal of the voltage comparator 25. A battery 26 for comparison voltage is connected to a negative input terminal of the voltage comparator 25.

Next, the operation of this embodiment will be described.

When ink is ejected from the ink jet recording head, the high potential drive timing signal and the low electric drive timing signal are supplied to the input terminals 15 and 12 at timings as shown in FIGS. To input. As a result, the voltage applied between the driving point 5a and the ground point 5b of the electrostrictive vibrator 5 by the driving circuit 6 is changed.

When the voltage at both ends of the electrostrictive vibrator 5 is changed as described above, the electrostrictive vibrator 5 generates mechanical distortion. Due to this mechanical distortion, the driving voltage V0
Is present, and an attempt is made to maintain an equilibrium state with the drive voltage V0. Further, the diaphragm 2 is also mechanically distorted in accordance with the mechanical distortion of the electrostrictive vibrator 5, whereby
The volume of the ink flow path 3 changes, and as a result, the ink in the ink flow path 3 protrudes outside the surface of the nozzle portion 4. The ink that has once started moving tends to continue moving due to inertial force while following the drive. However, due to the bulk elasticity of the ink, a stress that causes the ink to return to its original state acts, so that the ink protrudes from the surface of the nozzle portion 4 and then attempts to return to the opposite direction. In this process, the surface tension of the ink acts to partially separate the ink as droplets. The separated ink droplet flies toward the recording paper by inertia and is used for printing.

On the other hand, the ink remaining in the nozzle section 4 tends to return to its original state due to volume elasticity. This force is applied to the electrostrictive vibrator 5 via the vibration plate 2, and a stress in a direction opposite to the mechanical strain obtained from the drive circuit 6 is applied. That is, the charge distribution in the electrostrictive vibrator 5 leads to a change in the charge distribution opposite to that at the time of the original driving. The change in the charge inside the electrostrictive vibrator 5 causes an excess voltage at the driving point 5a which is higher than the voltage given by the driving voltage V0. The action and reaction with the electrostrictive vibrator 5 in the ink flow path 3 are periodically repeated by the mechanical structure of the ink jet recording head and the vibration system such as the volume elasticity of the ink. The driving point 5a of the electrostrictive vibrator 5 at this time
Are as shown in FIG. 3 (c).

However, when air bubbles enter the ink flow path 3, the electrostrictive vibrator 5 generated by the drive circuit 6
The change in the volume in the ink flow path 3 due to the mechanical distortion of the ink is absorbed by the change in the air pressure of the bubble, and the movement of the ink is reduced or no longer occurs. At this time, an appropriate ink droplet cannot be obtained. Also, since there is no movement of the ink, no distortion is generated in the electrostrictive vibrator 5 beyond the distortion generated by the driving circuit 6, so that the driving circuit 5
No voltage higher than the voltage obtained from is generated.

In the present embodiment, the presence or absence of bubbles in the ink flow path 3 is detected by monitoring the voltage at the driving point 5a of the electrostrictive vibrator 5 by the bubble detection circuit 7.

Immediately, when there are no bubbles, proper ink movement occurs, and accordingly, an excessive voltage equal to or higher than the drive voltage V0 is applied to the electrostrictive vibrator at a time according to the structure of the ink jet recording head and the physical properties of the ink. 5 appears at the driving point 5a,
When a bubble is generated, the presence or absence of the bubble is detected based on the fact that a voltage equal to or higher than the driving voltage V0 does not appear at the driving point 5a.

The bubble detection by the bubble detection circuit 7 is performed as follows.

When the electrostrictive vibrator 5 is electrically driven to a low voltage by the drive circuit 6, the diode 22 is biased in the forward direction and a forward current flows. When the voltage at both ends of the diode 22 exceeds the threshold value of the diode 22, the forward current sharply increases. As a result, most of the driving voltage received by the electrostrictive vibrator 5 is divided by the resistor 21. Is set to a sufficiently large value, the driving circuit 6 is not affected. On the other hand, since the voltage generated by the mechanical distortion reaches a voltage higher than the drive voltage V0, the diode 22 is reversely biased. At this time, since the reverse current of the diode 22 is smaller by three digits or more than the forward current, the voltage of the electrostrictive vibrator 5 is almost divided by the diode 22. Therefore, as shown in FIG. 3D, the cathode terminal voltage almost caused by the mechanical strain of the electrostrictive vibrator 5 is directly taken out from the cathode terminal of the diode 22. The voltage amplitude of the cathode terminal voltage is AC-coupled by a capacitor 23, and FIG.
(E) is taken out as the AC voltage shown in FIG.
And applied to the + input terminal of the voltage comparator 25. This input voltage is compared by the voltage comparator 25 with a reference voltage value, for example, 1 V, for distinguishing the presence / absence of a bubble formed by the voltage value of the battery 26.

If there are no air bubbles in the ink flow path 3, the AC voltage shown in FIG. 3E changes beyond the reference voltage value. When there is no excess voltage, it is determined that there is an excessive voltage caused by mechanical distortion, and a pulse shown in FIG. 3F is output to detect that there is no bubble.

On the other hand, when air bubbles are present in the ink flow path 3, despite the fact that the ink jet recording head is driven,
Since the input voltage to the voltage comparator 25 is 0 volt,
No pulse is generated at the output terminal 27, and it is determined that there are bubbles in the ink flow path 3.

According to the present embodiment, the bubble detection is completed only by detecting whether or not the voltage generated in the electrostrictive vibrator 5 becomes an excessive voltage equal to or higher than the drive voltage value V0. When a plurality of the electrostrictive vibrators 5 are provided, the circuit shown in FIG. 6 can be reliably detected (see FIG. 6).
reference). Therefore, according to the present embodiment, it is possible to detect bubbles with high efficiency at a low cost and in a short time even for a plurality of nozzles while having a sufficient decomposition ability easily and sufficiently.

FIGS. 4 to 8 show a more accurate detection and operation control of bubbles by using the embodiment constructed as shown in FIG.

FIGS. 4 and 5 show the timing of the bubble detection.

Here, a pulse is generated at a mechanical distortion time unique to each ink jet recording head based on the drive timing to the drive circuit 6, and at this time, the output state (pulse) of the voltage comparator 25 is generated. The presence or absence of air bubbles in the ink jet recording head is reliably determined by monitoring the level of the ink jet recording head.

That is, the ink jet recording head has a built-in variation at the time of manufacture. As a result, the time at which the voltage peak occurs due to the mechanical strain appearing in the electrostrictive vibrator 5 differs for each nozzle of each ink jet recording head.

Therefore, prior to printing or at an appropriate time, a time for determining the output of the voltage comparator 25 for each nozzle of the ink jet recording head is determined.

FIG. 4 shows the inspection time determination circuit. The inspection time determination circuit includes a delay pulse generation circuit 28 that generates a pulse at a variable time based on a drive pulse output from the drive circuit 6, and a voltage comparison circuit that generates a pulse at a time when the delay pulse generation circuit 28 generates a pulse. Circuit 29 which samples the output of the comparator 25 and outputs the result as a comparison result 30
And a control circuit 31 that supplies a pulse generation time setting signal 32 to the delay pulse generation circuit 28 and determines a comparison result 30.

Next, the operation of the inspection time determination circuit will be described.

Prior to printing or at an appropriate time,
The control circuit 31 outputs the pulse generation time setting signal 32 to the delay pulse generation circuit 28 while sequentially delaying the pulse generation time setting signal by Δt time. As a result, the delay pulse generating circuit 28 that has received the high-potential drive timing signal from the input terminal 15 generates the first pulse when the high-potential drive timing signal rises, as shown in FIG. Thereafter, the second and subsequent pulses are generated while being sequentially delayed by Δt time. The latch circuit 29 receiving the pulse from the delay pulse generating circuit 28 outputs the output from the detection circuit 7 for each pulse, that is, the electrostrictive vibrator shown as pulses a, b, c,. It is determined whether or not an excessive voltage of 5 has occurred, and the result is output to the control circuit 31 as a comparison result 30.
In this example, when the pulses a, b, c,... Shown in FIG. 5C are generated, the comparison result 30 indicating that there is a pulse is output from the Q terminal of the latch circuit 29. Specifically, the pulse a indicating the occurrence of the first excess voltage of the electrostrictive vibrator 5 will be described.
Is the rising time of the n-th pulse, and the falling of the pulse a is the falling time of the m-th pulse of the delay pulse generating circuit 28. The comparison result 30 with the pulse a is output to the control circuit 31 throughout. In this control circuit 31, the generation time of the pulse a is when n × Δt time has elapsed from the rise of the high-potential drive timing signal, and the disappearance time of the pulse a is m × t from the rise of the high-potential drive timing signal. It is detected that the time Δt has elapsed, and further, the intermediate time (n + m) × Δt /
2 is calculated.

Therefore, when printing and air bubble detection are continuously performed thereafter, the intermediate time is set to the control circuit 31.
Thus, the delay pulse generation circuit 28 is set with the pulse generation time setting signal 32, and the output of the bubble detection circuit 7 is continuously sampled by the latch circuit 29 to determine the presence or absence of bubbles.

Thus, the presence or absence of bubbles can be detected in a reliable manner in response to the first occurrence of an excessive voltage of the electrostrictive vibrator 5 unique to each ink jet recording head.

FIG. 6 shows a case in which a plurality of nozzles are individually driven by a plurality of electrostrictive vibrators 5, 5,... In some cases in which one of the electrostrictive vibrators 5 is driven and the other is not. . At this time, in the electrostrictive vibrator 5 that is not driven, the bubble detection determination is not performed.

FIG. 6 is a circuit diagram thereof, and the same parts as those in FIG. 2 are denoted by the same reference numerals.

In FIG. 6, two electrostrictive vibrators 5-1 and
For 5-2, high potential driving is performed by a common transistor 9 and low potential driving is performed by a separate transistor 8, and separate bubble detection circuits 7-1 and 7-2 are provided. . AND gates 33 and 34 are connected to the input terminals of the low-potential drive units, respectively, and a print determination signal is input to one input terminal of each of the AND gates 33 and 34 through input terminals 35 and 36, respectively. It has become. In addition, each AND gate 33, 3
A low-potential drive timing signal is input to the other input terminal of each of the four through an input terminal 12. Each low-potential drive unit includes a latch circuit 37 that stores print determination data at a low-potential drive timing.
38 are provided. Each of the latch circuits 37 and 38 functions as a nozzle determination unit that detects that the nozzle is a nozzle from which an ink droplet is ejected. A print determination signal is input to the D terminal of each of the latch circuits 37 and 38 through each of the input terminals 35 and 36, and the input terminal 12 is input to the C terminal of each of the latch circuits 37 and 38.
, A low-potential drive timing signal is input. In the output section of each of the bubble detection circuits 7-1 and 7-2,
When the print determination data stored by the respective latch circuits 37 and 38 indicate printing, logic gates 39 and 40 are provided for outputting bubble detection as true. One input terminal of each of the logic gates 39 and 40 has a bubble detection circuit 7
-1 and 7-2 are input, and the outputs of the Q terminals of the latch circuits 37 and 38 are input to the other input terminals. Further, each of the logic gates 39 and 40 samples the output of each of the logic gates 39 and 40 at a time determined based on the high potential drive timing signal, respectively.
Latch circuit 2 of the above embodiment for determining and holding the presence or absence of bubbles
Latch circuits 41 and 42 similar to 9 are provided. A pulse from the delay pulse generating circuit 28 is input to a C terminal of each of the latch circuits 41 and 42, and an output of each of the logic gates 39 and 40 is input to a D terminal.

Next, the operation of the system shown in the circuit diagram of FIG. 6 will be described.

First, at the time of high-potential driving, a high-potential driving timing signal is inputted through the input terminal 15, and the electrostrictive vibrators of all nozzles (in this example, two electrostrictive vibrators 5-1 and 5-1) are used.
Apply a high potential to 5-2). Next, for the nozzles that need to be printed, a print decision signal prepared for each nozzle and a low-potential drive timing signal common to all nozzles are input through AND gates 33 and 34 to respond to electrostrictive vibration. A low potential is applied to the terminals 5-1 and 5-2. At this time, the print decision data is stored in the latch circuits 37 and 38 for each nozzle by the low potential drive timing signal. The outputs of the latch circuits 37 and 38 are logically operated by the outputs of the individual bubble detection circuits 7-1 and 7-2 and the respective logic gates 39 and 40. Each logic gate 3
The logical operation outputs 9 and 40 are latched by the latch circuits 41 and 42 by the pulse generated by the delay pulse generation circuit 28 based on the high potential drive timing signal. As a result, it is possible to determine the presence or absence of bubbles in the nozzles that are driven to a low potential and eject ink droplets.

FIG. 7 shows a further application example of the present invention, and is a circuit diagram for stopping the subsequent ink droplet drive simultaneously with the detection of a bubble.

When ejecting ink droplets while moving the ink jet recording head in the printing direction, bubbles may be generated in the ink flow path 3 during the movement. When the bubbles generated in this process gradually increase, the size of the ink droplets gradually decreases after the detection of the bubbles, or the ejection direction becomes an inappropriate direction, which may lower the printing quality. For this reason, it is desired to stop the subsequent ink ejection operation upon the occurrence of bubbles. In this embodiment, the ink ejection is stopped at the same time as the detection of the bubble generation.

In FIG. 7, the same parts as those in FIG. 6 are denoted by the same reference numerals.

In the present embodiment, the circuit for one electrostrictive vibrator 5 shown in FIG. 6 has a bubble between the logic gate 39 and the latch circuit 41 which is continuously detected for each high potential drive. In the determination of presence / absence, when a bubble is detected once, a logic gate 43 for providing a logic structure for continuously holding the bubble is provided. That is, the inverted output of the Q bar terminal of the latch circuit 41 is input to one input terminal of the logic gate 43, and the output of the logic gate 39 is input to the other input terminal. The inverted output of the Q-bar terminal of the latch circuit 41 is also input to the AND gate 33 of the low-potential drive unit of the drive circuit 6. Accordingly, the AND gate 33 performs low-potential driving at the time of the low-potential drive timing according to the print determination data when no bubble is detected, based on the print determination data, the low-potential drive timing signal, and the inverted output of the latch circuit 41 for bubble detection determination, When air bubbles are detected, the low potential driving is stopped without depending on the state of the print determination data. The reset terminal of the latch circuit 41 is formed so that a reset signal is input through an input terminal 44.

Next, the operation of the system shown in the circuit diagram of FIG. 7 will be described.

First, the latch circuit 41 is initialized to a logical value 0 by a reset signal input from the input terminal 44 before the movement of the ink jet recording head starts.

Thereafter, while printing is continuously performed, bubbles are generated in the ink flow path 3 and detected by the bubble detection circuit 7, and the logical value 1 indicating the bubble detection is stored in the latch circuit 41. Then, an inverted output is output from the Q bar terminal to the AND gate 33 and the logic gate 43. The AND gate 33 receiving the inverted output stops the low-potential drive regardless of the state of the print determination data signal. on the other hand,
When the logic gate 43 receives the inverted output indicating the detection of bubble generation even once during continuous printing, the logic gate 43 sets the latch circuit 41 to the logic value 1
Is performed to hold the data. As a result, the subsequent ink ejection is stopped at the same time as the generation of bubbles.

In the case of a configuration in which a plurality of nozzles can be ejected simultaneously, each of the nozzles has a latch configuration shown in FIG. 7, and its inverted output is supplied to an AND gate provided in the low potential drive section of each nozzle. By additionally inputting (33, 34 in FIG. 6), the driving can be stopped for each nozzle. It is also possible to generate the logical sum of the outputs of all the latches and stop the ejection of all the nozzles at the same time. In particular, when the injection of all the nozzles is stopped at the same time, the AND gate 33 that determines the low potential drive of each nozzle,
Instead of giving the stop signal to 34, the low-potential drive timing signal may be stopped.

FIG. 8 is a diagram for storing the moving position of the ink jet recording head when bubbles in the ink flow path 3 of the ink jet recording head are detected.

When performing printing while moving the ink jet recording head, when performing the bubble detection operation, the driving of the electrostrictive vibrator 5 is stopped simultaneously with the bubble detection so as not to lower the printing quality as shown in FIG. Has been described.

On the other hand, stopping the movement of the ink jet recording head at the same time as the driving stop of the ink droplet ejection requires a mechanical drive circuit that overcomes the inertial force of the ink jet recording head, and the accuracy of the ink jet recording head moving at high speed is reduced. It is difficult to stop well.

Therefore, in this embodiment, even if bubbles in the ink flow path 3 are detected, the movement of the ink jet recording head is not stopped, and only the driving of the ink droplet ejection is stopped. Is stored.

Thereafter, the ink jet recording head moved for printing is gently stopped after passing through the area to be printed, and then the bubble detecting circuit 7 moves the ink jet recording head while performing printing while moving. It is determined whether or not is detected. When air bubbles are detected, the discharging operation of the air bubbles is started, and the inside of the ink jet recording head is recovered in preparation for the subsequent printing. After the recovery in the ink jet recording head, printing is restarted. At this time, the ink jet recording head moves slowly without driving the ink droplets to the position where the bubble is detected. Printing is started on an unprinted portion as soon as the bubble detection position is reached. Accordingly, the ink droplet driving stopped by the bubble detection coincides with the start point of the restart printing after the discharge of the bubbles in the head, and the printing interrupted by the bubble detection can be smoothly restored.

FIG. 8 for enabling such an operation is to store the moving position of the ink jet recording head when bubbles in the ink flow path 3 of the ink jet recording head are detected. The counter circuit 45 is added to the circuit of FIG.

The counter circuit 45 counts the number of printing units from the start of movement of the ink jet recording head to the bubble detection position. A high-potential drive timing signal is input to a C terminal, and a latch is input to an EN terminal. Circuit 41
The inverted output from the Q bar terminal is input. When no bubble is detected, the counter circuit 45 increases the count by one according to the high-potential drive timing signal. When there is a bubble detection, the counter circuit 45 holds the count value regardless of the state of the high-potential drive timing signal.

Next, the operation of the system shown in the circuit diagram of FIG. 8 will be described.

First, before starting the movement of the ink jet recording head, a reset signal is inputted at least once from the input terminal 44 to set the counter circuit 45 and the latch circuit 41 to the initial value 0.

Thereafter, the movement of the ink jet recording head for printing is started, and a high potential drive timing signal is generated. In the case of printing, a low-potential drive timing signal is generated as needed in synchronization with the high-potential drive timing, and ink droplets are ejected. At this time, the presence or absence of bubbles is determined. If no bubble is detected, the counter 45
Is increased by 1 according to the high potential drive timing signal.
When an air bubble is detected, the latch circuit 41 becomes true, and therefore, even if a high-potential drive timing occurs, the counter circuit 45 holds and stores the previous value.

When the printing is resumed thereafter, the position where the bubble is detected during the movement of the stored ink jet recording head is output as the value of the counter, so that the printing after the interruption of the printing can be performed satisfactorily. .

It should be noted that the present invention is not limited to the above-described embodiment, and can be changed as needed.

[0064]

As described above, since the bubble detecting device for an ink jet recording head according to the present invention is constructed and operates, it is determined whether or not the voltage generated in the electrostrictive vibrator becomes an excessive voltage equal to or higher than the driving voltage value. The bubble detection is completed only by the detection.
Therefore, according to the present invention, an on-demand type ink jet printer is capable of detecting bubbles easily and inexpensively and in a short time even with a plurality of nozzles, while having a simple and sufficient decomposition capability continuously. Can be. As a result, abnormal printing can be reliably prevented, and the air bubble discharging means can be operated. In other words, starting printing, detecting bubbles, stopping driving, discharging bubbles, and restoring unprinted parts can be realized continuously as a series of processes, realizing normal printing operation with automatic repair for a long time. It has the effect that it can be done.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of an ink jet recording head used in the present invention.

FIG. 2 shows an embodiment of a bubble detecting device for an ink jet recording head according to the present invention, and is a circuit diagram of a bubble detecting circuit for detecting an excessive voltage.

FIG. 3 is a diagram showing a voltage waveform state of each part in FIG. 3;

FIG. 4 is a configuration diagram of an inspection time determination circuit.

FIG. 5 is a diagram showing a waveform state of each part in a test time determination process in FIG. 4;

FIG. 6 is a circuit diagram for performing bubble detection for each ejection nozzle when driving a plurality of nozzles.

FIG. 7 is a circuit diagram for stopping the subsequent ink droplet drive simultaneously with the bubble detection.

FIG. 8 is a circuit diagram for storing a bubble detection position in the ink head.

[Explanation of symbols]

 3 Ink flow path 5, 5-1 and 5-2 Electrostrictive vibrator 6 Drive circuit 7 Bubble detection circuit 25 Voltage comparator 28 Delay pulse generation circuit 29, 41, 42 Latch circuit 31 Control circuit 45 Counter circuit

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akihiko Miyashita 1-7 Yukitani Otsukacho, Ota-ku, Tokyo Inside Alps Electric Co., Ltd. (72) Inventor Nakatoshi 1-7 Yukitani Otsuka-cho, Ota-ku, Tokyo (56) References JP-A-58-18275 (JP, A) JP-A-63-141750 (JP, A) JP-A-3-246056 (JP, A) (58) Fields investigated (Int.Cl. ⁶ , DB name) B41J 2/125 B41J 2/045 B41J 2/055 B41J 2/175

Claims (1)

(57) [Claims] 1. An ink jet recording head for providing an electrostrictive vibrator in each of ink flow paths of a plurality of nozzles and applying a drive voltage to the electrostrictive vibrator to discharge ink droplets. Whether or not the voltage generated in the electrostrictive vibrator due to the change in the volume of the passage is an excess voltage equal to or higher than the drive voltage value is constantly detected during the printing operation to detect the presence or absence of bubbles in the ink flow path. A bubble detecting device for an ink jet recording head, comprising: