JPH01150549A - Bubble detecting device for ink flow path in ink jet printer - Google Patents

Abstract

PURPOSE:To enable the detection of bubbles present in an ink flow path without disposing sensors between an ink supply path and a nozzle of an ink drip producing mechanism by deciding the presence of bubbles on the basis of the response signals from an ink drip producing piezo-electric element in the ink drip producing mechanism. CONSTITUTION:A bubble detecting apparatus of the present invention has a response extracting means 5 for extracting the response signals from a piezo-electric element 3 representing the changes in the ink liquid pressure at the time when an ink supply valve 1 is opened or closed and a deciding means 6 for deciding the presence of bubbles on the basis of the ink liquid pressure changes represented by the response signals. When the ink supply valve 1 is opened or closed under pressure, the response extracting means 5 extracts the response signal of the piezo-electric element 3 representing the liquid pressure change caused following the operation of the ink supply valve 1. The deciding means 6 then decides the presence of bubbles on the basis of the change represented by the response signal so extracted. Generally, the deciding means 6 decide that bubbles are present the change represented by the response signal is dull, and when the presence of bubbles is decided, a bubble releasing operation or the like is performed, while when the presence of bubbles is not decided, the preparation for a normal printing operation is then made.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is particularly directed to a continuous jet type in which pressurized ink is supplied through an ink supply flow path when an ink supply valve is open to a piezoelectric element. The present invention relates to an ink flow path bubble detection device for an inkjet printer having an ink droplet generation mechanism that ejects ink droplets from a nozzle by photographing.

[Prior Art] A continuous jet inkjet printer sends ink pressurized by a pump through an ink supply channel to an ink droplet generation mechanism. Vibrations of piezoelectric elements such as the controlled based on The flight path of the ink drop is controlled, for example, in a charge control type ink droplet, by controlling the amount of charge of the ink drop, which is caused to pass through a constant deflection electric field at a constant speed, based on image information.

In such an inkjet printer, in order to prevent ink dripping, it is necessary to sharply increase the ink liquid pressure from the ink supply channel to the nozzle of the ink droplet generation mechanism when ejecting the ink drops. Therefore, when ink drops are ejected, the ink supply valve provided downstream of the pump in the ink supply flow path is normally opened all at once while the pump action continues.

As mentioned above, in an inkjet printer that requires a steep rise in ink liquid pressure from the ink supply channel to the nozzle of the ink droplet generation mechanism, air bubbles entering the ink flow path may cause the rise in liquid pressure to This makes the ink drop dull and causes ink dripping when the ink drop starts ejecting. Therefore, it is necessary to detect that air bubbles have entered the flow path from the ink supply flow path to the nozzle of the ink droplet generation mechanism.

Therefore, in conventional ink flow path bubble detection devices, a pressure sensor is provided in the ink droplet generation mechanism, and based on the pressure detected by this pressure sensor, the ink liquid pressure increases when the ink droplet is ejected, or the ink droplet The downward change in ink liquid pressure when ejection is stopped is measured, and if this change is slow, it is determined that air bubbles are mixed in.

[Problems to be Solved by the Invention] However, in the conventional ink flow path bubble detection device as described above, when an attempt is made to downsize the ink droplet generation mechanism, accurate bubble detection becomes difficult.

This is because the mounting space for the pressure sensor is limited due to the miniaturization of the ink droplet generation mechanism, making it difficult to install the pressure sensor under optimal conditions. This is because it becomes difficult to install the pressure sensor without adversely affecting the atomization characteristics of the ink drop.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to enable air bubbles to be detected in an ink flow path without particularly providing any separate sensors between the ink supply flow path and the nozzle of the ink droplet generation mechanism.

[Means for solving the problems] As shown in FIG. The object is an inkjet printer that has an ink droplet generation mechanism 4 that ejects ink droplets in the form of droplets from a nozzle 4a by vibrations of 3.The above problem is solved by a bubble detection device in an ink flow path in this type of inkjet printer. Technical means for solving the problem include a response extracting means 5 for extracting a response signal of the piezoelectric element 3 in response to fluctuations in ink liquid pressure when the ink supply valve 1 is opened or closed in a pressurized state, and a response extracting means 5. The apparatus is equipped with a determining means 6 for determining the presence or absence of bubbles based on the state of change of the response signal of the piezoelectric element 3 extracted in the step.

A general discrimination criterion for the discrimination means 6 is to discriminate the presence of bubbles when the change in the response signal is relatively slow.

Specific aspects of the above-mentioned discriminating means include, for example, a peak time measuring means for measuring the time until the fluctuation peak of the extracted response signal is reached, and a predetermined time measured by the peak time measuring means. Comparison and determination means for determining the presence of bubbles when the reference time is exceeded. In this case, the reference time is determined based on the time until the fluctuation peak of the response signal extracted in the absence of bubbles is reached.

[Operation] Opens or closes the ink supply valve 1 in a pressurized state. At this time, the response extracting means 5 extracts a response signal of the piezoelectric element 3 in response to fluctuations in ink fluid pressure caused by the operation of the ink valve 1. Then, the determination means 6 regarding the extracted response signal.
The presence or absence of bubbles is determined based on the state of change. Generally, the determining means 6 determines the presence of bubbles when the change in the response signal is relatively slow.

[Example] Embodiments of the present invention will be described below based on the drawings.

FIG. 2 is a diagram showing an example of the basic structure of the target inkjet printer.

In the figure, an ink supply channel 20 is formed from a tank 11 in which ink I is stored to a drop generator 12 (ink droplet generating device) that ejects ink droplets. A pump 15 for supplying ink I in 11 to the drop generator 12 side, a pre-stage filter 16, an ink supply valve 17, and a post-stage filter 18 are provided, respectively. A piezoelectric element 14 for applying ultrasonic vibration is provided on the back side of the liquid chamber 12a of the drop generator 12, and a nozzle 13 from which an ink droplet is ejected is formed on the opposite side, and the ink supply flow is The vibration of the piezoelectric element 14 during the supply of ink I via the channel 20 causes an ink droplet to be ejected from the nozzle 13 in the form of a droplet.

Then, the ink drop ejected from the nozzle 13 is charged and deflected based on the image information, reaches the paper 10, and a visible image corresponding to the image information is reproduced on the paper 10.

Note that an ink discharge channel 22 is formed from the drop generator 12 to the tank 11 for returning the ink (2) in the drop generator 12, and this ink discharge channel 22 is provided with a discharge valve 19. In addition, in this type of continuous jet inkjet printer, the ink drop is deflected to the gutter 23 position when not printing, and from this gutter 23 there is a return flow that returns the collected ink I to the tank 11. A channel 24 is formed.

The basic configuration of the bubble detection system in the ink flow path is, for example, the third
It is as shown in the figure.

In the figure, an oscillation signal from an oscillator 31 is transmitted to an amplifier 32.
, the drop generator 12 via the changeover switch 33
The current is applied to a piezoelectric element 14 provided on the back side of the liquid chamber 12a, and the connection to the piezoelectric element 14 is switched to the bubble detection system described above using a changeover switch 33. This bubble detection system detects and responds to the time until the response signal of the piezoelectric cable 14 reaches a fluctuation peak due to fluctuations in ink liquid pressure from the ink supply channel 20 to the nozzle 13 of the drop generator 12. A peak time detection circuit 34 that outputs a pulse signal with a time width, and a piezoelectric cable 1
A waveform shaping circuit 35 detects the rising edge of the response signal No. 4 and outputs a predetermined pulse signal, and a reference pulse generation circuit 36 triggers by the pulse signal from the waveform shaping circuit 35 and outputs a signal with a reference pulse width. , compares the reference pulse signal from the reference pulse generation circuit 36 and the detection pulse signal from the peak time detection circuit 34, and raises the output when the pulse width of the detection pulse signal becomes larger than the pulse width of the reference pulse signal. It is equipped with a comparison circuit 37. Specifically, the peak time detection 34 raises the output when the response signal from the piezoelectric element 14 changes (rising or falling), and when the response signal reaches a fluctuation peak and changes in the opposite direction. When the output is turned down (falling down or rising), the corresponding output is turned down.

The comparison and determination signal from the comparison circuit 45 is input to the control circuit 45, and the control circuit 45 determines the presence or absence of bubbles based on this comparison and determination signal.

When it is determined that air bubbles are present, the control circuit 45 instructs air bubble removal processing such as replacing the ink (2). This control circuit 45 also controls the generation of the oscillator 31, and controls the ink circulation system (IH3) whose specific configuration is shown in FIG.
Drivers for pumps, various solenoid valves, etc. in 40 (I) I
In addition to controlling the drive of the s driver) 41, it also has functions such as switching control of the changeover switch 33.

In the above embodiment, the changeover control function of the changeover switch 33 and the control circuit 45 constitutes a response extraction means for extracting the response signal of the piezoelectric element 14, and the peak time detection circuit 34 and the waveform shaping circuit 35, reference pulse generation circuit 36, comparison circuit 37,
The bubble discrimination function based on the output of the comparison circuit 37 in the control circuit 45 constitutes the discrimination means according to the present invention.

Next, the specific operation will be explained.

When replacing the ink I or before actually starting printing, the basic detection mode is set (depending on the user's setting operation input), the control circuit 45 sends a drive signal to the IHS driver 41 and an oscillation signal to the oscillator 31. While keeping the command signal etc. in the off state, the changeover switch 33 is switched to the bubble detection system side.

Further, the pump 15 is driven with the ink supply valve 17 closed, and the ink upstream of the ink supply valve 17 is pressurized. In this state, when the ink supply valve 17 is instantaneously opened (closed on the atmospheric side), the ink liquid pressure in the flow path from the ink supply valve 17 to the downstream drop generator 12 changes to, for example, as shown in FIG. 4(a). As shown, the pressure rises rapidly from atmospheric pressure PO and reaches a predetermined hydraulic pressure P1 (for example, 3 kg/ci) after an overshoot. At this time, the pressure fluctuation within the liquid chamber 12a of the drop generator 12 is also similar, and a response signal to the pressure fluctuation is outputted from the piezoelectric element 14, for example, in a waveform as shown in FIG. 4(C). . The timings of the peak of this response signal and the peak of the above-mentioned pressure fluctuation normally coincide with each other. When such a response signal from the piezoelectric element 14 is input to the peak time detection circuit 34 via the changeover switch 33, the peak time detection circuit 34 detects a pulse width corresponding to the time tSu until the response signal reaches its fluctuation peak. A detection signal is output, and this detection signal is compared with a reference pulse signal from a reference pulse generation circuit 36 in a comparison circuit 37.

Here, the ink supply path 20 from the ink supply valve 17
If there are no bubbles between the point and the nozzle 13 of the drop generator 12, the time required for the ink liquid pressure to reach the predetermined liquid pressure P1 is short, so that the peak of the response signal of the corresponding piezoelectric element 14 Time to reach tSu
also becomes shorter than the reference pulse signal width, and the comparison determination signal from the comparison circuit 37 maintains the 1-level. On the other hand, if air bubbles exist in the same ink flow path, the pressure propagation becomes slow and the time required for the ink liquid pressure to reach the predetermined liquid pressure P1 becomes longer, so that the response signal of the corresponding piezoelectric element 14 peaks. The time it takes to reach tsuG becomes longer than the reference pulse signal width. As a result, the comparison determination signal from the comparison circuit 37 rises to the H level, and the control circuit 45 recognizes that a bubble exists in the ink flow path. Then, air bubble removal processing and the like are performed.

If it is determined that there are no bubbles in the above judgment, the changeover switch 33 is activated by the command from the control circuit 45.
to the side and preparations are made for normal printing operation.

The pulse width of the reference pulse signal output from the reference pulse signal generation circuit 36 is determined based on the time taken for the response signal to reach its peak in the absence of bubbles, and is determined based on the time taken for the response signal to reach its peak in the absence of bubbles, and is The ink volume t1 varies depending on the material of the ink flow path, the responsiveness of the ink supply valve (electromagnetic valve), etc. Specifically, it is determined in the following range, 10fflSf3C.

In the above embodiment, the presence or absence of air bubbles was determined based on the response signal of the piezoelectric element 14 when the pressure of the ink flow path increases. The same determination can be made even if the ink supply valve 16 is suddenly opened to the atmosphere by closing the flow path while the ink supply valve 16 is in a pressurized state. Specifically, when the ink supply valve 16 is opened to the atmosphere, the ink liquid pressure rapidly decreases from a predetermined liquid pressure P1 to atmospheric pressure PO, for example, as shown in FIG. 4(b).

Correspondingly, the response signal of the piezoelectric element 14 is also shown in FIG.
The peak position approximately coincides with the hydraulic pressure fluctuation peak. The pressure fluctuation in this case also changes in mode depending on the presence or absence of bubbles, as described above. Therefore, the presence or absence of bubbles can be determined in the same way as above based on the time tSD until the response signal reaches its peak.

According to the above embodiment, when the ink liquid pressure between the ink supply channel 20 and the nozzle 13 of the drop generator 12 is suddenly changed, the response signal output from the piezoelectric element 14 for ink drop generation is Since the presence or absence of air bubbles in the ink flow path is determined based on the above, it is possible to determine whether air bubbles are present anywhere in the ink supply flow path 20 or the drop generator 12 without particularly providing a sensor. becomes.

Note that the configuration of the bubble detection system is not limited to the configuration of the above embodiment, and other aspects may be used, such as determining the presence or absence of bubbles based on the signal level after a predetermined time elapses from the start of fluctuation in the response signal of the piezoelectric element 14. It is possible to configure the following.

[Effects of the Invention] As described above, according to the present invention, the presence or absence of air bubbles is determined based on the response signal from the piezoelectric element for ink droplet generation in the ink droplet generation mechanism.
It is possible to detect air bubbles in the ink flow path from the ink supply flow path to the nozzle of the ink droplet generation mechanism without providing any special sensors. Therefore, even if the ink droplet generation mechanism is miniaturized, the installation position of the sensors does not have to be a particular problem, and there is no need to consider the effects of vibration propagation from the piezoelectric element when ejecting ink drops. Good bubble detection can be easily achieved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of the present invention, FIG. 2 is a diagram showing an example of the basic structure of an inkjet printer to which the ink flow path bubble detection device according to the present invention is applied, and FIG. FIG. 4 is a diagram illustrating an example of a bubble detection device in a flow path, and is a diagram illustrating the relationship between ink liquid pressure fluctuation and a response signal of a piezoelectric element. [Explanation of symbols] 1.17... Ink supply valve 2.20... Ink supply channel 3.14... Piezoelectric element 4... Ink droplet generation mechanism 5... Response extraction means 6...・Discrimination means 12...Drop generator 13...Nozzle 15...Pump 34...Peak time detection circuit 35...Waveform shaping circuit 36...Reference pulse generation circuit 45...Control circuit Patent application Person Representative of Fuji Xerox Co., Ltd. Person
Patent attorney Kosei Nakamura (2 others) Figure 1 Figure 2 Figure 4 (a) j: (() (b)

Claims (1)

[Claims] 1) When the ink supply valve (1) is open, the pressurized ink (I) supplied through the ink supply channel (2) is caused to drop from the nozzle by the vibration of the piezoelectric element (3). A bubble detection device in an ink flow path in an inkjet printer having an ink droplet generation mechanism (4) that ejects ink droplets in a pressurized state, the ink liquid pressure when the ink supply valve (1) is opened or closed in a pressurized state. The presence or absence of air bubbles is determined based on the state of change of the response signal of the piezoelectric element (3) extracted by the response extraction means (5) for extracting the response signal of the piezoelectric element (3) to the fluctuation and the response detection means (5). An apparatus for detecting air bubbles in an ink flow path in an inkjet printer, characterized by comprising a discriminating means (6) for discriminating. 2) The discriminating means (6) includes a peak time measuring means for measuring the time until the fluctuation peak of the extracted response signal is reached, and the time measured by the peak time measuring means is a predetermined reference time. 2. A bubble detection device in an ink flow path in an inkjet printer according to claim 1, further comprising a comparison and determination means for determining the presence of bubbles when the bubble exceeds the limit.