JP7119511B2 - Device for ejecting liquid and method for detecting abnormality in device for ejecting liquid - Google Patents

Description

The present invention relates to an apparatus for ejecting liquid and an abnormality detection method for the apparatus for ejecting liquid.

2. Description of the Related Art In an inkjet type image forming apparatus, air bubbles may be generated inside a nozzle for ejecting ink droplets, and the ink droplets may not be ejected at a desired speed and volume, resulting in an abnormal image.

On the other hand, there is a technique of measuring the residual vibration inside the nozzle using a piezoelectric element (piezo element), detecting the presence or absence of bubble generation, and leading to a recovery operation. For example, in Japanese Patent Application Laid-Open No. 2002-100002, pressure vibration of ink in an ink jet recording head is detected using a detection piezoelectric element that is different from a piezoelectric element (piezo element) during driving, and based on the frequency spectrum obtained from the frequency characteristics of the vibration, Detecting an abnormal condition inside the head is disclosed.

However, in Patent Document 1, the pressure fluctuation due to the residual vibration after the change of the piezoelectric element propagates from the pressure chamber to the liquid surface (meniscus) of the nozzle, and further propagates from the liquid surface to the pressure chamber and returns. Since the voltage change in the piezoelectric element is detected, the signal-to-noise ratio (SN ratio) is small, and the presence or absence of air bubbles in the pressure chamber cannot be detected with high accuracy. In addition, if the drive voltage used for detection is increased in order to increase the SN ratio, ink droplets will be ejected, making it difficult to implement.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a liquid ejecting apparatus capable of accurately detecting abnormal occurrences such as air bubbles generated in pressure chambers or nozzles.

In order to solve the above problems, in one aspect of the present invention,
a nozzle;
a pressure chamber communicating with the nozzle and containing a liquid;
a pressure generating element that applies pressure to the liquid in the pressure chamber;
a drive waveform generator for inputting a single-cycle voltage to the pressure generating element as a detection waveform;
a liquid surface vibration detection unit for irradiating the liquid surface of the liquid in the nozzle with light and detecting vibration of the liquid surface in the nozzle caused by the detection waveform;
a determination unit that determines an abnormality in the pressure chamber or the nozzle based on the detected vibration waveform of the liquid surface and the single-cycle voltage ;
The determination unit uses the single-cycle voltage input to the pressure generating element and the output waveform of the liquid surface vibration detected by the liquid surface vibration detection unit to determine the transfer function of the pressure chamber. derive,
Abnormal occurrence such as entrapment of air bubbles in the pressure chamber or the nozzle is detected according to the difference between the derived transfer function and its normal value.
An apparatus for dispensing liquid is provided.

According to one aspect, in a device that ejects liquid, it is possible to accurately detect the occurrence of abnormalities such as air bubbles generated in pressure chambers or nozzles.

1 is a plan view of an image forming apparatus according to an embodiment of the invention; FIG. FIG. 2 is a bottom view of one recording head mounted in the image forming apparatus of FIG. 1; FIG. 2 is a longitudinal sectional view of the liquid chamber of the recording head of the present invention; 4A and 4B are schematic diagrams of vibration detection by a recording head and a liquid surface vibration detection unit according to an embodiment of the present invention; FIG. 3 is a block diagram relating to droplet ejection and vibration detection of the present invention; FIG. 6 is a functional block diagram of a transfer function analysis unit in FIG. 5; FIG. 6 is a hardware block diagram of the controller, drive control board, and detection board shown in FIG. 5; FIG. 4 shows waveforms used in liquid surface vibration detection according to the present invention, including (a) a diagram showing a detection waveform input to a piezoelectric element and (b) a diagram showing an output waveform detected by a laser Doppler vibrometer. Schematic diagram showing vibration propagation in a liquid chamber in detection of liquid surface vibration in a comparative example. 8A and 8B are diagrams showing a waveform for detection input to a piezoelectric element, and FIG. 4B showing an output waveform of residual vibration detected by the piezoelectric element, which are used for liquid surface vibration detection in a comparative example; An output example of a transfer function calculated by the present invention when a bubble is included in the liquid chamber or nozzle. 4 is a flow chart showing control of inspection/recovery of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, the form for implementing this invention is demonstrated with reference to drawings. Hereinafter, in each drawing, the same components are denoted by the same reference numerals, and redundant description may be omitted.

<Image forming apparatus>
First, a configuration in which the liquid ejecting apparatus of the present invention is applied to a serial image forming apparatus will be described. FIG. 1 is an explanatory plan view of the image forming apparatus 100. FIG.

In FIG. 1, the carriage 6 is mainly driven by a guide rod 122 as a main guide member horizontally mounted between main side plates 121A and 121B constituting the frame members of the apparatus main body and subordinate guide members (guide rods, guide stays, etc.) (not shown). It is held slidably in the scanning direction (longitudinal direction of the guide rod). The carriage 6 is composed of a main scanning motor, a drive pulley, a driven pulley and a timing belt. be done. The carriage 6 functions as a moving section that moves together with the recording head 2 .

The carriage 6 is provided with 4 integrated sub-tanks each comprising a liquid ejection head as image forming means for ejecting ink droplets of, for example, yellow (Y), magenta (M), cyan (C), and black (K) colors. recording heads 2 are mounted. The recording head 2 is mounted with a nozzle array having a plurality of nozzles arranged in a sub-scanning direction perpendicular to the main scanning direction, with the droplet ejection direction facing downward.

On the other hand, below the carriage 6, a transport belt 141 is arranged as transport means for transporting the paper 1 fed from the paper feed cassette in the sub-scanning direction. The conveying belt 141 is an endless belt, and is stretched between a conveying roller 142 and a tension roller 143 rotatably held between sub-side plates, and the conveying roller 142 is rotationally driven by a sub-scanning motor. As a result, it is circulated in the arrow direction (belt conveying direction). With this configuration, the carriage 6 can move in the transport belt moving direction, that is, in the direction perpendicular to the recording medium transport direction.

A maintenance/recovery means 8 is arranged at one end of the carriage 6 outside the printing area in the main scanning direction.

The maintenance/recovery means 8 is provided in a portion different from the transported paper 1 in the moving range of the carriage 6 . The maintenance/recovery means 8 is a blank ejection receiver and/or a cap for recovering the ink ejected as blank ejection when ink is not ejected onto the paper 1, and suction means for sucking from below is provided below them. may be provided.

A mirror 10 and a Laser Doppler Vibrometer (LDV) 9 are provided at the other end of the carriage 6 outside the printing area in the main scanning direction (below, the Laser Doppler Vibrometer is abbreviated as LDV). (sometimes described as

In the present invention, in order to check the state of the ink in the nozzles of the recording head 2, the meniscus, which is the surface of the nozzle, is vibrated, the laser beam refracted by the mirror 10 is irradiated, and the vibration of the meniscus is measured by the LDV 9. is detected.

FIG. 2 shows an enlarged bottom view of the recording head 2K. As shown in FIG. 2, a plurality of nozzles (nozzle holes) 104 are formed in each recording head 2, and two nozzle rows LA and LB are formed along the belt conveying direction shown in FIG. there is

In the nozzle rows LA and LB, a plurality of nozzles 104 are arranged at intervals p, and the nozzles of the nozzle row LA and the nozzles of the nozzle row LB are arranged at positions shifted by 2/1·p from each other. , the resolution of the image can be increased.

<Head>
Next, an example of the recording head 2 (31) functioning as a liquid ejection head will be described with reference to FIG. FIG. 3 is a cross-sectional explanatory view along the longitudinal direction of the liquid chambers of the recording head 2 (direction orthogonal to the nozzle arrangement direction).

In this recording head 2, a channel plate 101, a vibration plate member 102, and a nozzle plate 103 are joined together. As a result, an individual liquid chamber 106 through which a nozzle 104 for ejecting droplets communicates through a through hole 105, a fluid resistance section 107 for supplying liquid to the individual liquid chamber 106, and a liquid introduction section 108 are formed.

Ink is introduced from the common liquid chamber 110 formed in the frame member 117 into the liquid introduction section 108 via the filter section 109 formed in the vibration plate member 102 , and then from the liquid introduction section 108 through the fluid resistance section 107 . Ink is supplied to the liquid chamber 106 . The term "individual liquid chamber" includes what is called a liquid chamber, a pressurized chamber, a pressurized liquid chamber, a pressure chamber, an individual channel, a pressure generation chamber, and the like.

The channel plate 101 is formed by laminating metal plates such as SUS, and forming openings and grooves such as through holes 105, individual liquid chambers 106, fluid resistance portions 107, and liquid introduction portions 108, respectively. The vibration plate member 102 is a wall surface member that forms the walls of the liquid chambers 106 , the fluid resistance section 107 , the liquid introduction section 108 , and the like, and is also a member that forms the filter section 109 . The channel plate 101 is not limited to a metal plate such as SUS, and can be formed by anisotropically etching a silicon substrate.

Then, a columnar lamination as actuator means (pressure generating means) for generating energy for ejecting droplets from the nozzles 104 by pressurizing the ink in the individual liquid chambers 106 on the surface of the vibration plate member 102 opposite to the liquid chambers 106 . A piezoelectric element 112 of the mold is bonded. One end of the piezoelectric element 112 is joined to the base member 113, and the piezoelectric element 112 is connected to an FPC 115 for transmitting a drive waveform. These components constitute the piezoelectric actuator 111 .

In this example, the piezoelectric element 112 is used in the d33 mode in which it expands and contracts in the stacking direction, but may be used in the d31 mode in which it expands and contracts in the direction orthogonal to the stacking direction.

In the recording head 2 configured as described above, for example, by lowering the voltage applied to the piezoelectric element 112 from the reference potential, the piezoelectric element 112 contracts as shown in FIG. The volume of the individual liquid chamber 106 expands as it deforms. As a result, ink flows into the individual liquid chamber 106 .

After that, by increasing the voltage applied to the piezoelectric element 112, as shown in FIG. shrink the volume of As a result, the ink in the individual liquid chamber 106 is pressurized, and droplets L are ejected from the nozzle 104 .

By returning the voltage applied to the piezoelectric element 112 to the reference potential, the diaphragm member 102 is restored to its initial position and the liquid chamber 106 expands to generate a negative pressure. The chamber 106 is filled with ink. Therefore, after the vibration of the meniscus surface of the nozzle 104 is attenuated and stabilized, the operation for ejecting the next droplet is started.

<Liquid surface vibration detection>
FIG. 4 is a schematic diagram of vibration detection by the recording head and the liquid surface vibration detection unit according to the embodiment of the present invention.

In one embodiment of the present invention, a laser Doppler vibrometer (LDV) 9 is used as a liquid surface vibration detector that measures the vibration of the liquid surface in the nozzle caused by the detection waveform applied to the piezoelectric element 112 . A laser Doppler vibrometer divides a laser into two and irradiates it on an object, detects the phase shift frequency-modulated by the Doppler transition after the reflection, and quantifies the speed of vibration.

As shown in FIG. 4, a mirror 10 is provided at a position that can face the nozzles 104 of the recording head 2 . In order to check the state of the ink in the nozzles of the recording head 2, the meniscus (liquid surface), which is the surface of the nozzle, is vibrated, the laser beam refracted by the mirror 10 is irradiated, and the meniscus vibration is measured by the LDV 9. is detected as the output waveform Vout. In this example, a mirror is used as an example of a member that reflects and bends laser light, but other members may be used as long as they are optical members that can bend and reflect laser light.

In the present invention, the piezoelectric element is cyclically deformed (contracted or expanded) by applying the single-cycle waveform Vin as the detection waveform, thereby applying a cyclic pressure to the ink in the liquid chamber 106 . Occur. The pressure propagates through the liquid chamber 106 and the nozzle 104 (P), as shown in the schematic diagram of the print head 2 in FIG.

Then, a laser beam emitted from a laser Doppler vibrometer (LDV) 9 is irradiated to the ink meniscus (liquid surface) of the nozzle 104, and an output waveform (response output signal) Vout obtained by detecting the vibration state of the liquid surface is measured. do. That is, vibration propagates from the piezoelectric element 112 that continues to expand and contract in response to the applied single-period signal Vin, and the laser Doppler vibrometer 9 measures the ink meniscus of the vibrating nozzle.

Laser Doppler vibrometers are characterized by their high signal-to-noise ratio because they can be converted into electrical signals and amplified, and because they are non-contact measurements, there is little noise. Therefore, in the present invention, by performing detection using the laser Doppler vibrometer 9, the meniscus vibration (liquid surface vibration) of the ink in the liquid chamber and the nozzle can be measured with high precision using the output waveform Vout.

Then, the transfer function analysis unit (judgment unit) 12 obtains the transfer function H(s) (=Vout/Vin) of the liquid chamber 106 from the single period signal Vin used for input and the detected output waveform Vout. , whether or not an abnormality such as air bubbles has occurred in the liquid chamber 106 or the nozzle 104 .

A control configuration for realizing the liquid surface vibration detection shown in FIG. 4 will be described below.

<Liquid Ejection/Liquid Surface Vibration Detection Control>
FIG. 5 is an overall block diagram relating to image formation control according to the embodiment of the present invention.

The image forming apparatus 100 has a controller 4, a drive control board 3K, a recording head 2K, an LDV 9, and a detection board 11 as a configuration related to image formation control. FIG. 5 shows the configuration related to the control of the nozzle row L1 of the black head 2K, but the nozzle row L2 and the other color heads 2M, 2C, and 2Y have the same control configuration. shall be

The controller 4 is a main control unit of the image forming apparatus 100 and controls the entire system. The controller 4 is a higher control section of the drive control board 3K.

The drive control board 3 and the recording head 2 are provided in the recording head 2 or the carriage 6 shown in FIG. A cable 29 electrically connects the drive control board 3K and the recording head 2K.

The drive control board 3 is a rigid board on which a driving waveform for driving the piezoelectric element 112 in the recording head 2K and a circuit for generating an image data signal are mounted.

The recording head 2K incorporates a piezoelectric element 112, and ejects ink droplets onto the paper 1 by driving the piezoelectric element according to the drive waveform and the image data signal transmitted from the drive control board 3K.

The drive control board 3 has a control section 31 and a drive waveform generation section 32 .

The control unit 31 generates timing control signals and drive waveform data based on image data.

The drive waveform generator 32 DA-converts the generated drive waveform data, and amplifies the voltage and current.

The recording head 2</b>K has a head substrate 21 , a piezoelectric element support substrate 23 and piezoelectric elements 112 . A control unit 22 is provided on the head substrate 21 , and a piezoelectric element driving IC 24 is provided on the piezoelectric element support substrate 23 .

A digital signal such as a timing control signal generated by the control unit 31 of the drive control board 3 is transmitted to the recording head 2 by serial communication via the cable 29 . Then, it is deserialized by the control unit 22 on the head substrate 21 and input to the piezoelectric element driving IC 24 on the piezoelectric element supporting substrate 23 .

The drive waveform generated by the drive waveform generator 32 is input to the piezoelectric element 112 via the cable 29 by turning ON/OFF the piezoelectric element drive IC 24 in response to the timing control signal.

The control section 31 of the drive control board 3 has an image processing section 33 . The image processing unit 33 performs image processing and correction based on the image data received from the controller 4 and the line synchronization signal LS that serves as a reference for printing.

Note that the image processing unit 33 has been described as a function of the control unit 31 of the drive control board 3 in FIG. may be set to

Further, in the present invention, a laser Doppler vibrometer (LDV) 9 and a detection substrate 11 are provided separately from the carriage 6 . The LDV 9 has a laser light source 91 , a light receiving section 92 and a processing section 93 . The detection substrate 11 has a transfer function analysis section 12 .

The LDV9 irradiates an object with a laser beam amplitude-modulated at the fundamental frequency, measures the phase difference between the reflected light from the object and the time, and multiplies the time by the speed of light. Find the distance of

The processing unit 93 is provided with, for example, a CPU 94 for instructing light emission and light reception, a driver 95 for driving the laser light source 91 , and an amplifier 96 for amplifying the light received by the light receiving unit 92 .

The transfer function analysis unit 12 of the detection substrate 11 analyzes the output waveform Vout detected by the LDV 9 and determines whether or not an abnormality has occurred in the liquid chamber 106 or nozzle 104 .

When the transfer function analysis unit 12 determines that the recovery operation is necessary, the controller 4 instructs the carriage 6 or the maintenance/recovery means 8 to perform the maintenance/recovery operation. For example, when performing recovery by flushing, the ink is idle ejected from the nozzles 104 of the print head 2K. When suction recovery is performed, the recording head 2K is moved by the carriage 6 to a position facing the maintenance and recovery means 8, and suction is performed from below while the cap of the maintenance and recovery means 8 is fitted on the recording head 2K. , a negative pressure is applied to the nozzle 104 to suck out the ink in the nozzle 104 and the liquid chamber 106 .

FIG. 6 shows a functional block diagram of the transfer function analysis section 12 of the present invention.

The transfer function analysis unit 12 has a transfer function calculation unit 201, a transfer function change calculation unit 202, a normal state storage unit 203, and a comparison determination unit 204 in an executable manner.

The transfer function calculation unit 201, the transfer function change calculation unit 202, and the comparison determination unit 204 are implemented by the FPGA 71 in FIG. Normal state storage unit 203 is implemented by ROM 72 .

The transfer function calculator 201 obtains the transfer function H(s) of the ink chamber from the detection waveform Vin input to the piezoelectric element 112 and the detected output waveform Vout. Specifically, the transfer function H(s) is obtained by dividing the output waveform Vout by the applied detection waveform Vin (H(s)=Vout/Vin)).

Based on the frequency characteristics of the nozzle, the transfer function change calculator 202 calculates the transfer function H(s) as [H(s)_amplitude], which is the change in the transfer function with respect to the amplitude, and [H(s)_amplitude], which is the change in the transfer function with respect to the phase. Calculate [H(s)_phase]. The frequency characteristic of the nozzle corresponds to the natural vibration frequency of the nozzle and is determined at the manufacturing stage.

The normal state storage unit 203 stores in advance H(s)_amplitude, which is the change in the transfer function with respect to amplitude, and/or H(s)_phase, which is the change in the transfer function with respect to the phase, in the normal state. Keep

The comparison determination unit 204 compares the detected transfer function change H(s)_amplitude and/or transfer function change H(s)_phase with respect to the amplitude and the normal state stored in the normal state storage unit 203. The H(s)_amplitude of the state and/or the H(s)_phase of the normal value are compared to determine whether the state of the liquid chamber or nozzle is abnormal. Then, the comparison/determination unit 204 inputs a signal indicating the presence/absence of abnormality to the controller 4 .

When the transfer function analysis unit 12 transmits a signal indicating that there is an abnormality, the controller 4 instructs the maintenance/recovery means 8 or the recording head 2 to perform the maintenance/recovery operation.

Although FIG. 6 shows an example in which the transfer function analysis unit 12 is provided on the detection substrate 11 different from the controller 4 , the function of the transfer function analysis unit 12 may be provided inside the controller 4 .

Next, hardware configurations of the controller 4, the drive control board 3, and the detection board 11 will be described with reference to FIG. FIG. 7 is a hardware block diagram of the controller 4, drive control board 3, and detection board 11 of the image forming apparatus 100. As shown in FIG.

As shown in FIG. 7, the controller 4 includes a CPU (Central Processing Unit) 61, a ROM (Read Only Memory) 62, a RAM (Random Access Memory) 63, an NV (Non Volatile) RAM 64, an interface (I/F) 65 and IO interface 66 are connected via memory bus 67 . Note that the memory bus 67 may be separated into a plurality of buses.

In the drive control board 3 , the FPGA 51 , ROM 52 , RAM 53 , NVRAM 54 and IO interface 55 are connected via a bus 56 .

In the controller 4 , the CPU 61 controls the entire image forming apparatus 100 . The ROM 62 stores various information, control programs, and the like. The RAM 63 is used as a work area when various processes are executed.

For example, the CPU 61 uses the RAM 63 as a work area to execute various control programs stored in the ROM 62 and output control commands for controlling various operations in the image forming apparatus 100 . At this time, the CPU 61 performs various operational controls in the image forming apparatus 1 in cooperation with the FPGA 51 while communicating with the FPGA 51 .

The NVRAM 64 stores device-specific information, updatable information, and the like.

The interface 65 mediates exchange of information with an external device such as a host computer. The IO interface 66 mediates exchange of information with each unit in the device. The IO interface 66 is also connected to the IO interface 55 of the drive control board 3, the IO interface 75 of the detection board 11, input/output devices such as an operation panel, various sensors, and the like. The various sensors include, for example, a home position sensor of the carriage 6, a paper position detection sensor that detects the position of the paper 1, and sensors that detect internal environments such as temperature and humidity. It should be noted that the NVRAM 64 may be configured to be removable.

Further, the FPGA 51 of the drive control board 3 performs image data processing, timing control, etc. related to image formation. For example, the FPGA 51 uses the RAM 63 as a work area, selects the driving waveform stored in the ROM 62 , and outputs a control command for instructing meniscus oscillation of the ink in the individual liquid chamber 106 . At this time, the FPGA 51 communicates with the CPU 61 of the controller 4 and cooperates with the CPU 61 to control various operations in the image forming apparatus 1 .

In the ROM 52 of the drive control board 3, a common drive waveform and a single-cycle waveform Vin, which is a detection waveform, are stored in advance.

In the detection board 11 , the FPGA 71 , ROM 72 , RAM 73 , NVRAM 74 and IO interface 75 are connected via a bus 76 .

The FPGA 71 of the detection board 11 uses the RAM 73 as a work area to perform calculations related to the transfer function and determination of the presence or absence of an abnormality shown in FIG. Run.

6 and 7, an example in which the controller 4 is provided in the image forming apparatus 100 has been described. good too.

<Detected waveform>
FIG. 8 shows the applied input waveform and the detected output waveform used in the vibration detection of the present invention. In FIG. 8, (a) shows the detection waveform input to the piezoelectric element 112, and (b) shows the output waveform detected by the Doppler device 9. FIG. In FIG. 8, the horizontal axis indicates time [μs], and the vertical axis indicates potential [V].

As shown in FIG. 8A, in the present invention, a single period signal Vin is applied to the piezoelectric element 112 as a detection waveform. This single period signal Vin is also applied to the transfer function analysis section 12 . A single period signal is, for example, a sine wave signal. FIG. 8A shows an example of a sine wave signal, but a triangular wave or rectangular wave may be used as long as the waveform has a single period.

The application of this single-cycle waveform Vin causes the piezoelectric element 112 to cyclically deform (contract or expand), thereby generating a cyclical pressure on the ink in the ink liquid chamber 106 .

FIG. 8(b) shows the output waveform measured by the laser Doppler vibrometer 9. FIG. Since FIG. 8 shows waveforms in a laser Doppler device using a phase difference detection method, the detected output waveform Vout shown in FIG. A phase difference is generated with respect to the voltage Vin of , resulting in a periodic waveform.

In FIG. 8B, since the output waveform Vout shows a periodic waveform, it corresponds to the detection result of a normal state in which noise or the like is not generated.

<Comparative example>
9 and 10, a method of measuring meniscus vibration according to a comparative example, in which the method of detecting vibration is different, will be described. FIG. 9 is a schematic diagram showing vibration propagation in the liquid chamber in the liquid level vibration detection of the comparative example.

In the comparative example, the response in the ink liquid chamber to the piezo drive voltage Vin is measured using the same piezo element or another piezo element. Therefore, during measurement, the vibration generated by the piezoelectric element 112 is propagated to the meniscus of the ink (P1), and the vibration propagated from the meniscus of the ink to the piezoelectric element 112 (P2) is measured. Become.

10A and 10B show waveforms used for liquid surface vibration detection in a comparative example, in which FIG. 10A is a diagram showing a detection waveform input to a piezoelectric element, and FIG. It is a figure which shows the output waveform of a vibration.

In the comparative example, as shown in FIG. 10A, a non-periodic single-shot pulse is input to the piezoelectric element 112, and then ink is generated due to one-time expansion and contraction of the piezoelectric element due to the single-shot pulse. Measuring the residual vibration waveform. Further, as shown in FIG. 9, since the amount propagated and converted to the piezoelectric element as an electromotive force is measured, the state of the meniscus is detected by the return propagation. As shown in FIG. 10(b), there is much noise and the noise SN ratio is small.

Further, if the drive voltage is increased to increase the SN ratio, ink will be ejected, which is difficult to implement during printing.

In contrast, in the present invention, the laser Doppler vibrometer 9 is used to directly measure the meniscus of the ink. It can be measured directly without propagating back to the internal ink.

<Abnormality detection by the transfer function of the present invention>
FIG. 11 is an output example of the transfer function when air bubbles are included, detected by the Doppler vibrometer 9 of the present invention.

Specifically, FIG. 11 shows numerical values obtained by varying the frequencies of the input single-period waveform Vin and the output detection waveform Vout measured in FIG.

In FIG. 11, the change in transfer function with respect to amplitude is "H(s)_amplitude", and the change in transfer function with respect to phase is "H(s)_phase".

As shown in FIG. 4, when a bubble B is generated inside the ink liquid chamber or nozzle, the amplitude and phase of the detected output waveform Vout change. As a result, as shown in FIG. 11, the portion in which the transfer function H(s) changes, which stands out from the amount of change in other portions, corresponds to "change due to bubble generation".

This calculation result and the transfer function H(s) in a normal state without bubble generation are measured in advance, and by comparing and verifying this normal H(s), it is possible to determine whether bubbles are generated. determine whether Comparing FIG. 11 with FIG. 10B, it can be seen that the noise generation position is clear.

Therefore, the size and position of air bubbles generated in the ink chambers and nozzles change, and the frequency at which air bubbles can be detected with high accuracy also changes. Therefore, when the values change as shown in FIG. 11, it is determined that bubbles are generated.

Thus, in the present invention, since the transfer function H(s) is derived as the frequency characteristic, it is possible to accurately detect the occurrence of bubbles regardless of the size and position of the bubbles.

If it is determined that air bubbles are contained in the image, the air bubbles are eliminated by performing maintenance such as a recovery operation called flushing or a suction operation using a maintenance/recovery means, thereby avoiding the occurrence of abnormal images due to air bubbles. can do

<Inspection/recovery flow>
Next, the inspection and recovery flow of the present invention will be described with reference to FIG. FIG. 12 is a control flow of print head inspection and recovery in the image forming apparatus of the present invention.

In S<b>1 (Step 1 ), the drive waveform generator 32 applies a single-cycle waveform Vin as a detection waveform to the piezoelectric element 112 . This application expands and contracts the piezoelectric element 112, which propagates and vibrates the meniscus of the ink.

In S2, the laser Doppler vibrometer 9 detects meniscus vibration of the ink.

In S3, the transfer function analysis unit 12 calculates a transfer function H(s) based on the detected output waveform Vout of the meniscus vibration and the input single period waveform Vin.

In S4, using the frequency characteristics for the transfer function H(s), H(s)_amplitude, which is the change in the transfer function with respect to amplitude, and H(s)_phase, which is the change in the transfer function with respect to the phase, are calculated. do.

In S5, if the amount of deviation in change of H(s)_amplitude and H(s)_phase compared with the normal state is smaller than the threshold (NO), it is determined that the ejection state is normal (S6).

In S5, if the amount of deviation in change of H(s)_amplitude and H(s)_phase compared to the normal state is equal to or greater than the threshold value (Yes), it is determined that air bubbles are present (S7).

Then, in S8, the recovery operation is appropriately performed, and the flow ends.

As described above, according to the present invention, it is possible to accurately detect the occurrence of abnormalities such as bubbles generated inside the ink chamber or nozzle. Then, the maintenance/recovery operation can be performed appropriately by using the detection result detected with high accuracy.

Although the preferred embodiment has been described in detail above, it is not limited to the above-described embodiment, and various modifications and substitutions can be made to the above-described embodiment without departing from the scope of the claims. can be added.

In the above example, the liquid droplet ejecting apparatus of the present invention is used as a serial image forming apparatus, but the configuration of the present invention may be applied to a line image forming apparatus.

For example, in the above embodiment, an image forming apparatus equipped with a recording head according to the present invention has been described. can do.

In the present application, a "device that ejects liquid" is a device that includes a liquid ejection head or a liquid ejection unit, drives the liquid ejection head, and ejects liquid. Devices that eject liquid include not only devices that can eject liquid onto an object to which liquid can adhere, but also devices that eject liquid into air or liquid.

The "liquid ejecting device" can include means for feeding, transporting, and ejecting an object to which liquid can adhere, as well as a pre-processing device, a post-processing device, and the like.

For example, as a "device that ejects liquid", an image forming device that ejects ink to form an image on paper, and powder is formed in layers to form a three-dimensional object (three-dimensional object). There is a three-dimensional modeling apparatus (three-dimensional modeling apparatus) that ejects a modeling liquid onto a formed powder layer.

Further, the "apparatus for ejecting liquid" is not limited to one that visualizes significant images such as characters and figures with the ejected liquid. For example, it includes those that form patterns that have no meaning per se, and those that form three-dimensional images.

The above-mentioned "substance to which a liquid can adhere" means a substance to which a liquid can adhere at least temporarily, such as a substance to which a liquid adheres and adheres, a substance which adheres and permeates, and the like. Specific examples include media such as recording media such as paper, recording paper, recording paper, film, and cloth, electronic components such as electronic substrates and piezoelectric elements, powder layers (powder layers), organ models, and test cells. Yes, and unless otherwise specified, includes anything that has liquid on it.

The material of the above-mentioned "thing to which a liquid can adhere" may be paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, etc., as long as the liquid can adhere even temporarily.

Also, the "liquid ejection head" is not limited to the pressure generating means to be used. For example, a piezoelectric actuator (which may use a laminated piezoelectric element), a thermal actuator using an electrothermal conversion element such as a heating resistor, or an electrostatic actuator consisting of a diaphragm and a counter electrode can be used.

Further, the terms used in the present application, such as image formation, recording, printing, printing, printing, modeling, etc., are synonymous.

1 Paper (recording medium)
2 Recording head (droplet ejection head)
9 Doppler vibrometer (liquid surface vibration detector)
11 detection substrate 12 transfer function analysis unit (judgment unit)
104 nozzle 106 liquid chamber (pressure chamber)
112 piezoelectric element (pressure generating element)
B bubbles

JP-A-2006-051700

Claims (7)

a nozzle;
a pressure chamber communicating with the nozzle and containing a liquid;
a pressure generating element that applies pressure to the liquid in the pressure chamber;
a drive waveform generator for inputting a single-cycle voltage to the pressure generating element as a detection waveform;
a liquid surface vibration detection unit for irradiating the liquid surface of the liquid in the nozzle with light and detecting vibration of the liquid surface in the nozzle caused by the detection waveform;
a determination unit that determines an abnormality in the pressure chamber or the nozzle based on the detected vibration waveform of the liquid surface and the single-cycle voltage ;
The determination unit uses the single-cycle voltage input to the pressure generating element and the output waveform of the liquid surface vibration detected by the liquid surface vibration detection unit to determine the transfer function of the pressure chamber. derive,
Abnormal occurrence such as entrapment of air bubbles in the pressure chamber or the nozzle is detected according to the difference between the derived transfer function and its normal value.
A device that dispenses liquid. The device for ejecting liquid according to claim 1, wherein the liquid surface vibration detector is a laser Doppler vibrometer. 3. The apparatus for ejecting liquid according to claim 1, wherein the transfer function includes frequency characteristics. 4. The apparatus for ejecting liquid according to claim 3 , wherein the determination unit compares a change in transfer function with respect to amplitude with a normal state to determine whether or not an abnormality has occurred. 4. The apparatus for ejecting liquid according to claim 3 , wherein the determination unit compares a change in the transfer function with respect to the phase with a normal state to determine whether or not an abnormality has occurred. The apparatus for ejecting liquid according to any one of claims 1 to 5 , further comprising a control section that performs an abnormal state recovery operation on the liquid surface of the nozzle when the determination section determines that there is an abnormality. A method for detecting an abnormality in a liquid ejection device, comprising: a nozzle; a pressure chamber communicating with the nozzle and containing liquid; a pressure generating element for applying pressure to the liquid in the pressure chamber; hand,
inputting a single cycle of voltage to expand and contract the pressure-generating element;
a vibration detection step of irradiating the liquid surface of the liquid in the nozzle with light by a liquid surface vibration detection unit and detecting vibration of the liquid surface in the nozzle caused by the detection waveform;
determining an abnormality in the pressure chamber or the nozzle based on the detected vibration waveform of the liquid surface and the input single-cycle voltage;
In the determining step, the transfer function of the pressure chamber is determined using the single-cycle voltage input to the pressure generating element and the output waveform of the liquid surface vibration detected by the liquid surface vibration detection unit. and derive
Abnormal occurrence such as entrapment of air bubbles in the pressure chamber or the nozzle is detected according to the difference between the derived transfer function and its normal value.
An abnormality detection method for a device that ejects liquid.

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