JP2004009501A - Inkjet printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for detecting defective ejection of ink caused by generation of a fault of a piezoelectric element and generation of bubbles in a pressure chamber before and during printing, in an inkjet head. <P>SOLUTION: The inkjet printer has a resonant frequency measuring part 52 for measuring a resonant frequency by oscillation of an electric current when the piezoelectric element 14 is driven, a storing part 53 for storing reference resonant frequency data and the measured result, and an operation part 54 for comparing the measured result with the resonant frequency data. The defective ejection of the ink cuased by the generation of the fault of the piezoelectric element 14 and the generation of the bubbles in the pressure chamber 3 is detected by measuring change in the resonant frequency when the piezoelectric element 14 is driven. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ink jet printer that deforms a piezoelectric element by applying an electric signal to the piezoelectric element and causes ink droplets to fly by a generated pressure to form an ink image on a recording medium.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there has been known an ink jet head in which a pressure chamber is pressed by a piezoelectric element to discharge ink from a nozzle. FIG. 1 shows an example of an ink jet head using a piezoelectric element. The piezoelectric element has a ceramic member on an end face, the vibrating surface of the piezoelectric element is arranged so as to face the inlet opening of the nozzle, and is adhered and fixed to the housing.
[0003]
In order to eject ink droplets from the inkjet head, an electric signal is applied to the individual electrodes and the common electrode from an external drive power supply to deform the piezoelectric element. This deformation changes the volume of the pressure chamber via the vibration plate, and changes the pressure of the ink filled in the pressure chamber. This pressure change causes the ink to be ejected from the nozzles as ink droplets.
[0004]
In the ink jet head, the size of the print medium and the speed of printing have been increased, and the number of nozzles tends to increase. As the number of nozzles increases, the number of nozzles that cause non-ejection of ink also increases. Causes of non-ejection include foreign matter that separates from the atmosphere or the recording medium adheres to the nozzle and blocks the nozzle, solidifies the ink itself and causes the nozzle to be clogged, A case where the displacement of the element is not transmitted to the pressure chamber, and a case where a failure of the piezoelectric element itself occurs. In particular, when the ink cartridge is replaced, air bubbles easily flow into the flow path, and the flowed air bubbles are accumulated in the pressure chamber, and a non-discharge nozzle is easily generated.
[0005]
In inkjet printing, non-ejection of ink degrades print quality, so it is necessary to detect non-ejection of ink. As disclosed in Japanese Patent Application Laid-Open No. H11-334102, there has been proposed a method of determining whether air bubbles are attached to a pressure chamber based on the frequency characteristics of the impedance of a piezoelectric element.
[0006]
When non-ejection is detected, maintenance operations such as suction purge from the nozzle side, pressure purge from the ink supply side, and cleaning of the nozzle surface with silicon rubber or the like are performed. Foreign matter, clogging, and bubbles are removed by the maintenance operation, and non-discharge is eliminated.
[0007]
Regarding the failure of the piezoelectric element, as disclosed in JP-A-11-64175 and JP-A-2000-138514, the frequency characteristic of the impedance of the piezoelectric element is measured at the time of manufacturing, and the failure of the piezoelectric element is detected. A method of doing so has been proposed.
[0008]
[Problems to be solved by the invention]
However, in the conventional bubble detection for measuring the impedance characteristics of the piezoelectric element, it is not possible to drive the piezoelectric element to eject ink during the measurement of the impedance. Further, since it takes time to measure the impedance, it has been necessary to perform the measurement before starting the printing or by interrupting the printing.
[0009]
Further, if the recovery is not performed even after the maintenance operation is repeated, it is estimated that a defect has occurred in the piezoelectric element. However, since the bubble detecting means does not judge the failure of the piezoelectric element, the piezoelectric element is finally determined. In order to determine that the body element is defective, it was necessary to remove the ink jet head from the printer and perform an inspection.
[0010]
The present invention solves such a problem, and an object of the present invention is to provide a means for detecting occurrence of a failure of a piezoelectric element during printing or non-ejection of ink due to bubbles in a pressure chamber. is there.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, in the present invention, a pressure chamber for storing ink, a piezoelectric element for generating pressure fluctuation in the pressure chamber by application of an electric signal, and at least a part of a wall surface of the pressure chamber are formed. A diaphragm connected to the piezoelectric element by an elastic material, a restrictor serving as a flow path for supplying ink to the pressure chamber, a housing having a common ink passage for supplying ink to the restrictor, and a pressure chamber. Inkjet printer having an inkjet head having nozzles for ejecting ink from the apparatus, a resonance frequency measuring means for measuring a resonance frequency for each of the piezoelectric elements, and a storage means for storing reference resonance frequency data and reference result data And, comparing the measurement result of the resonance frequency measurement means and the resonance frequency data, the occurrence of failure of the piezoelectric element and the And having a computation means for determining the power chamber of the bubble generating. This makes it possible to measure a change in the resonance frequency of the piezoelectric element and detect ink non-ejection.
[0012]
Further, the resonance frequency measuring means, when discharging ink from the inkjet head, a current measuring means for measuring the current of the piezoelectric element, and a calculating means for frequency-decomposing the current value and selecting a peak frequency. It is characterized by having. Thus, the resonance frequency of the piezoelectric element can be measured during ink ejection.
[0013]
The resonance frequency of the piezoelectric element when the pressure chamber is empty of ink is f1, the reference value having a certain allowable value is f2, and the resonance frequency of the piezoelectric element measured by the resonance frequency measuring means is f2. When the resonance frequency is f3 and the relationship of f3 <f2 or f1 <f3 is satisfied, it is determined that the piezoelectric element is defective. This makes it possible to detect the occurrence of a defect in the piezoelectric element.
[0014]
The resonance frequency of the piezoelectric element in a state where the pressure chamber is empty of ink is f1, the reference value having a certain tolerance is f2, and the resonance frequency of the piezoelectric element measured by the resonance frequency measuring unit is f1. When f3 <f3 ≦ f1 holds, it is determined that bubbles exist in the pressure chamber. Thus, the presence or absence of bubbles in the pressure chamber can be determined.
[0015]
Further, the reference value f2 is in a range of ± 3% of the median value.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described based on examples with reference to the drawings.
[0017]
FIG. 1 is a perspective view illustrating the structure of a main part of an inkjet head 10 according to the present invention. In the nozzle plate 2 in which the plurality of nozzles 1 are formed, the processing accuracy of the opening shape of the nozzles 1 has a great influence on the ink ejection characteristics of the inkjet head 10. In order to suppress these nozzle accuracy variations among a plurality of nozzles 1, a high processing accuracy is required for the method of manufacturing the nozzle plate 2. Therefore, the nozzle plate 2 is formed by a precision press method of stainless steel, a laser processing method, electroforming of nickel, or the like.
[0018]
The nozzle plate 2 has a chamber plate 4 in which a pressure chamber 3 is formed, and a restrictor plate in which a common ink passage 12 and the pressure chamber 3 are connected to form a restrictor 5 for controlling the flow of ink into the pressure chamber 3. 6 is positioned and joined.
[0019]
Further, the diaphragm plate 9 includes a vibrating plate 7 for efficiently transmitting the pressure of the piezoelectric element to the pressure chamber 3 and a filter unit 8 for removing dust and the like in the ink flowing from the common ink passage 12 into the restrictor 5. Having. The diaphragm plate 9 and the housing 11 in which the common ink passage 12 is formed are similarly positioned and joined.
[0020]
The chamber plate 4, restrictor plate 6, and diaphragm plate 9 are made by a stainless steel etching method or a nickel material electroforming method. The housing 11 is formed by cutting stainless steel or the like, and is joined to an ink introduction pipe 20 that guides ink from the ink cartridge 31 to the common ink passage 12.
[0021]
Finally, a plurality of piezoelectric elements 14 and a piezoelectric actuator 13 including a support substrate 15 for fixing the piezoelectric elements 14 are positioned and joined. The piezoelectric actuator 13 includes a plurality of piezoelectric elements 14, each of which corresponds to one of the pressure chambers 3. Further, the support substrate 15 is formed with individual electrodes 16 for sending electric signals independent of the external drive circuit 21 to the respective piezoelectric elements 14. When a selective electric signal is applied to the piezoelectric element 14 from the external drive circuit 21, the piezoelectric element 14 is distorted. Since the piezoelectric element 14 is bonded to the support substrate 15 having high rigidity, the piezoelectric element 14 is preferentially displaced to the vibration plate 7 to increase the pressure in the pressure chamber 3. The ink jet head 10 described in the present embodiment is used in an apparatus that forms an ink image on a recording medium 36 by discharging ink from the nozzles 1 based on such a principle.
[0022]
FIG. 2 shows a serial inkjet printer as an example using the present invention.
[0023]
A recording unit 32 on which the ink jet head 10 and an ink cartridge 31 for supplying ink to the ink jet head 10 are mounted is slidably supported on a guide shaft 33 and connected to a power transmission member 34. The reciprocating motion is carried out along the guide shaft 33 by 35. On the other hand, the recording medium 36 faces the nozzle surface 37 of the inkjet head 10 and is transported by the transport roll 38 in a direction perpendicular to the direction in which the recording unit 32 moves. Ink is ejected onto the recording medium 36 from the nozzles 1 of the inkjet head 10 in accordance with a recording signal to form an image. A control board 22 for controlling the inkjet head is connected to the inkjet head 10 by a cable 23. In the control board 22, circuits related to control of the inkjet head 10, such as the external drive circuit 21, the head control unit 55, the resonance frequency measurement unit 52, and the calculation unit 54 shown in FIG.
[0024]
The purge cap 39 provided outside the recording area is made of an elastic material such as rubber. At the time of non-recording, the recording unit 32 moves to above the purge cap 39, and the purge cap 39 caps the nozzle surface 37 by a power source (not shown). In many cases, the cap is provided with an ink absorbing sheet 40 for facilitating suction at the time of suctioning ink, moistening the atmosphere in the cap, and the like. Also, one end of a tube 41 is connected to the bottom surface of the purge cap 39, and the tube 41 can make the inside of the cap a negative pressure via a suction pump 42, and the ink sucked from the inkjet head 10 The ink is discharged to a discharge ink chamber 43 provided at the other end of the tube 41. The wiper 44 is made of an elastic material such as rubber, and when the recording unit 32 passes through the wiper 44, the wiper 44 comes into contact with the nozzle surface 37 to remove ink and foreign matters accumulated on the nozzle surface 37.
[0025]
In this example, a serial type recording apparatus is described. However, even in a line head type recording apparatus in which the head is held at a fixed position (stops) at the time of printing, a fixed position at the time of printing at the time of wiping and capping. , The nozzle can be maintained in the same manner as in the serial method.
[0026]
FIG. 3 shows the configuration of the present invention.
[0027]
In FIG. 3, an external drive circuit 21 and a resonance frequency measuring unit 52 are connected to the piezoelectric element 14 via a switching unit 51. In the resonance frequency measuring unit 52, the ammeter 60 measures a current flowing from the external drive circuit 21 to the piezoelectric element 14. The FFT calculation unit 61 performs frequency decomposition by performing a Fourier transform on the current value from the ammeter 60, and outputs a peak frequency as a resonance frequency. The storage unit 53 stores reference data of the resonance frequency. The resonance frequency measurement unit 52 and the storage unit 53 are connected to the calculation unit 54, and the measured resonance frequency data is compared with the reference data to determine the presence or absence of bubbles. The above components are controlled by the head control unit 55. The main controller 56 sends commands to each part of the printer (not shown) such as a transport mechanism and a maintenance mechanism.
[0028]
One end of the piezoelectric element 14 is fixed to the support substrate 15, and the tip is bonded to the diaphragm 7. The vibration of the piezoelectric element 14 can be considered as a fixed end on the fixed plate side and a vibration of the free end with mass in the spring mass system on the vibrating plate 7 side. The resonance frequency has a unique value depending on the length, rigidity, and mass of the piezoelectric element 14. The mechanical resonance can be electrically measured, for example, as a frequency-impedance characteristic of the piezoelectric element 14 or a vibration period of a current due to residual vibration when the piezoelectric element 14 is driven.
[0029]
In order to measure the resonance frequency of the piezoelectric element 14, in the present invention, the vibration of the current due to the residual vibration when driving the piezoelectric element 14 is measured.
[0030]
FIG. 4 shows an example of the voltage and current of the piezoelectric element 14 when the ink is filled.
[0031]
The vibration of the cycle of the resonance frequency appears as the residual vibration of the piezoelectric element 14 and electrically becomes the vibration of the current. In the figure, the oscillation cycle of the current after driving the piezoelectric element 14 is about 3.1 μs, and the resonance frequency is 325 kHz.
[0032]
In the ink jet head used as the present embodiment, the resonance frequency is about 200 to 500 kHz, and other frequencies such as the driving frequency of the piezoelectric element 14 and the Helmholtz frequency of the ink which peak at a frequency other than the resonance frequency in the frequency decomposition by Fourier transform are It is 100 kHz or less, and can be easily separated from the resonance frequency. The advantage of this example over the conventional method of measuring the resonance frequency by measuring the frequency characteristic of impedance is that the resonance frequency can be measured even during ink ejection.
[0033]
Next, a method of detecting non-ejection due to occurrence of a defect in the piezoelectric actuator 13 according to the present invention will be described.
[0034]
The occurrence of failure of the piezoelectric actuator 13 in the ink jet head 10 can be roughly classified into two patterns: peeling between the piezoelectric element 14 and the vibration plate 7 and damage due to breakage or cracking of the piezoelectric element 14.
[0035]
When the piezoelectric element 14 is peeled off from the diaphragm 7, the mass of the free end of the piezoelectric element 14 decreases, which can be detected as an increase in the resonance frequency. Further, when the piezoelectric element 14 is damaged, the resonance frequency shows an abnormal value, and the failure of the piezoelectric actuator 13 can be detected.
[0036]
In the experiment of the present embodiment, when the piezoelectric element 14 exhibiting an average resonance frequency of 325 kHz peels off in a normal state, the resonance frequency becomes close to 370 kHz which is a value before the piezoelectric element 14 is bonded to the diaphragm 7. Increased. Further, when the piezoelectric element was damaged, no current flowed and the resonance frequency could not be measured.
[0037]
When the above-described failure of the piezoelectric actuator 13 occurs, the resonance frequency is outside the interval between the resonance frequency of the piezoelectric element 14 in a state where the ink is empty in the pressure chamber 3 and the resonance frequency in a state where the ink is filled.
[0038]
Next, a method of detecting non-ejection due to bubbles in the pressure chamber 3 of the present invention will be described. The resonance frequency measuring section 52 detects the generation of bubbles in the pressure chamber 3 as a change in the resonance frequency of the piezoelectric element 14.
[0039]
The mass on the vibration plate 7 side increases or decreases depending on the presence or absence of ink and bubbles in the pressure chamber 3, and the resonance frequency also changes accordingly. If there are no bubbles in the pressure chamber 3, the mass of the free end of the piezoelectric element 14 increases, and the resonance frequency decreases. When the ink is completely filled, the mass of the free end is also constant, and the resonance frequency is constant. However, when there are bubbles, the mass of the free end of the piezoelectric element 14 decreases, and the resonance frequency increases.
[0040]
As an example, FIG. 5 shows a current caused by residual vibration when the piezoelectric element 14 is driven when there is a bubble in the pressure chamber 3 and when there is no bubble. When there were no bubbles in the pressure chamber 3, the oscillation frequency of the current was 325 kHz, and when there were bubbles, it was 340 kHz. The storage unit 53 stores resonance frequency data when the pressure chamber 3 is empty and resonance frequency data when the ink is filled when the inkjet head 10 is manufactured. The stored resonance frequency data may be individual data measured at the time of manufacture for each inkjet head 10, or may be a calculated value or an average value. When bubbles are expected to be mixed in the ink jet head 10 such as when the ink is filled in the head or when the ink cartridge 31 is replaced, or before the start of printing and during the printing, the resonance frequency is measured and compared. It is possible to detect a failure of the nozzle 14 or a non-ejection due to bubbles in the pressure chamber 3.
[0041]
A series of non-ejection inspection processes in the above-described inkjet printer will be described with reference to the flowchart shown in FIG.
[0042]
The non-discharge inspection process shown in FIG. 6 is performed when the power of the printer is turned on, after the ink cartridge 31 is replaced, before printing is started, during the maintenance operation, and during the printing operation. In each of the above operations other than the printing operation, the inkjet head 10 may perform inspection by ejecting ink with the purge cap 39 capped.
[0043]
There are two types of resonance frequency data stored in the storage unit 53, a resonance frequency f1 when the pressure chamber 3 is empty of ink and a resonance frequency f2 when ink is normally filled. Here, since the resonance frequency is lower in the state where ink is filled, f2 <f1.
[0044]
In the example of the ink jet head of this embodiment, the resonance frequency f1 when the ink chamber is empty is 350 kHz, and the resonance frequency when the ink is filled is 325 kHz.
(Step S1)
The switching unit 51 is switched in synchronization with the ink ejection cycle, and the nozzle 1 for measuring the resonance frequency is selected. The nozzle 1 to be selected is the nozzle 1 that drives the piezoelectric element 14.
(Step S2)
Perform resonance frequency measurement. The resonance frequency of the piezoelectric element 14 selected in step S1 is measured by the resonance frequency measurement unit 52. The obtained measurement result is stored in the storage unit 53 as f3.
(Step S3)
This is compared with the data f2 stored in the storage unit 53 and in a state where the ink is completely filled.
| F2-f3 | <δ
If so, it is determined that the piezoelectric element 14 is normal and that there is no bubble in the pressure chamber 3 and discharge is possible, and the process proceeds to step S7. If not, the process proceeds to step S4.
[0045]
In the experiment of the present embodiment, when the resonance frequency f1 when the pressure chamber 3 is empty of ink is 350 kHz on average and the resonance frequency after ink filling is about 325 kHz, normal ejection was obtained. Further, when δ = 10 kHz, that is, within a range of 3% variation of f2, normal ejection was obtained.
(Step S4)
It is determined whether the cause of the out-of-criterion in step S3 is the occurrence of a defect in the piezoelectric element 14 or the occurrence of bubbles in the pressure chamber 3.
f3 <f2 or f1 <f3
When it becomes, it is determined that the piezoelectric element 14 is defective, and the process proceeds to step S5. Also,
f2 <f3 ≦ f1
If so, it is determined that bubbles have occurred in the pressure chamber 3, and the process proceeds to step S6.
(Step S5)
An error is displayed as a defect of the piezoelectric element 14, that is, an abnormality of the inkjet head 10, and the process ends. If the printing operation is being performed, the printing operation is stopped.
(Step S6)
A maintenance operation for discharging bubbles in the pressure chamber 3 is performed. If the printing operation is being performed, the printing is temporarily stopped. In the maintenance operation, the ink and bubbles are forcibly discharged by the purge cap 39 by suction from the nozzle 1 side or pressurization from the ink cartridge 31 side. Purging may be performed on the entire inkjet head 10 or may be performed on the nozzles 1 that have detected bubbles. After performing the maintenance operation, the resonance frequency of the corresponding piezoelectric element 14 is measured again in step S1, and the discharge of air bubbles is confirmed.
(Step S7)
If it is determined in step S3 that ejection is possible, it is determined in step S7 whether the measurement has been completed. If the measurement has not been completed, the process returns to step S1. The measurement may be completed when all the nozzles have completed one round or when the printing operation has been completed.
[0046]
In the case of the inspection other than the time of the printing operation, the inspection may be performed at least once for all the nozzles 1. In the inspection during the printing operation, the measurement may be performed a plurality of times while changing the nozzle 1 to be measured until the printing operation is completed.
[0047]
The resonance frequency of the piezoelectric element 14 is a value that varies depending on the specifications of the piezoelectric element 14, such as length and mass, and the value and range of the criterion in the present invention are determined by the resonance frequency of the piezoelectric element 14 as a specific example. It is not limited to the value of the frequency. The value of the criterion actually used is a value determined by the above experiment.
[0048]
【The invention's effect】
The present invention makes it possible to detect the occurrence of a defect in a piezoelectric element and the non-ejection due to the generation of bubbles in a pressure chamber from a change in the resonance frequency of the piezoelectric element before printing or during a printing operation. Thus, it is possible to prevent the occurrence of non-ejection of ink during printing and a decrease in print quality.
[0049]
Further, since the removal of air bubbles in the pressure chamber can be confirmed, it is possible to perform the minimum maintenance operation.
[0050]
Further, since the occurrence of a failure of the piezoelectric element can be known, it is not necessary to repeat unnecessary maintenance operations when the failure of the piezoelectric element occurs. This saves time and ink, and the need to replace the ink jet head can be known. It becomes possible.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an ink jet head.
FIG. 2 is a schematic view showing an embodiment of an ink jet printer.
FIG. 3 is a block diagram showing an embodiment of the present invention.
FIG. 4 is a graph showing a driving voltage and a driving current.
FIG. 5 is a graph showing a difference in drive current depending on the presence or absence of bubbles.
FIG. 6 is a flowchart showing an embodiment of the present invention.
[Explanation of symbols]
1 is a nozzle, 2 is a nozzle plate, 3 is a pressure chamber, 5 is a restrictor, 7 is a diaphragm, 9 is a diaphragm plate, 10 is an ink jet head, 11 is a housing, 13 is a piezoelectric actuator, 14 is a piezoelectric element, 15 Is a support substrate, 21 is an external drive circuit, 22 is a control substrate, 39 is a purge cap, 44 is a wiper, 51 is a switching unit, 52 is a resonance frequency measuring unit, 53 is a storage unit, 54 arithmetic unit, and 55 is a head control unit. , 56 are a main controller, 60 is an ammeter, and 61 is an FFT operation unit.

Claims (5)

A pressure chamber for storing ink, a piezoelectric element for generating pressure fluctuation in the pressure chamber by application of an electric signal, and at least a part of a wall surface of the pressure chamber is formed and connected to the piezoelectric element by an elastic material. An ink jet head including a vibration plate, a restrictor serving as a flow path for supplying ink to the pressure chamber, a housing having a common ink path for supplying ink to the restrictor, and a nozzle for discharging ink from the pressure chamber In an inkjet printer having
Resonance frequency measurement means for measuring a resonance frequency for each piezoelectric element, storage means for storing reference resonance frequency data and measurement result data, and comparing the measurement result of the resonance frequency measurement means with the resonance frequency data And an arithmetic means for determining occurrence of a defect in the piezoelectric element or occurrence of bubbles in the pressure chamber. The resonance frequency measuring means includes a current measuring means for measuring a current of the piezoelectric element at the time of ink ejection of the ink jet head, and a calculating means for frequency-decomposing the current value and selecting a peak frequency. The ink jet printer according to claim 1, wherein: The resonance frequency of the piezoelectric element when the pressure chamber is empty of ink is f1, the reference value having a certain allowable value is f2, and the resonance frequency of the piezoelectric element measured by the resonance frequency measuring means. Is f3,
f3 <f2 or f1 <f3
The ink jet printer according to claim 1, wherein when the relationship is satisfied, it is determined that the piezoelectric element is defective. The resonance frequency of the piezoelectric element when the pressure chamber is empty of ink is f1, the reference value having a certain tolerance is f2, and the resonance frequency of the piezoelectric element measured by the resonance frequency measuring means is f3. And when
f2 <f3 ≦ f1
4. The ink jet printer according to claim 1, wherein when the following relationship is satisfied, it is determined that air bubbles are present in the pressure chamber. 5. The ink jet printer according to claim 3, wherein the reference value f2 is in a range of ± 3% with respect to a median value.

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