JP2012187810A - Detection method for ink deterioration in inkjet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect ink deterioration based on the magnitude of a load current value in order to avoid damage of a circuit in a share mode type inkjet head in which ink directly comes in contact with electrodes of piezoelectric elements.SOLUTION: In the share mode type inkjet head 1, a predetermined inspection drive waveform is imparted from a driving source 7 to the electrodes 8 for each of nozzles 5, then, a current measuring device 10 converts the current value to a voltage value and measure the voltage value. A reference value obtained by measuring a reference ink is compared with a detection value obtained by measuring the ink being the detection object, and if the inspection value is beyond the extent of the reference value, it is determined as the ink deterioration, and purging, alarming or the like is performed for each of the nozzles.

Description

  The present invention is a shear mode type inkjet head that discharges ink from a nozzle by applying an electric field perpendicular to the polarization direction to a piezoelectric element, thereby causing ink alteration from the magnitude of the load current. The present invention relates to an ink alteration detection method to be detected.

  One structural example of the share mode type ink jet head will be described. The invention disclosed in Patent Document 1 below is an example. That is, two piezoelectric elements polarized in opposite directions in the plate thickness direction are bonded with an adhesive to form a two-layer plate member. A large number of grooves are cut from one plate surface of the plate member at regular intervals so that the grooves pass through the bonding surface of the piezoelectric element and the front ends of the grooves are not opened at the front end of the plate material. Create a tooth-like structure. Then, one surface of the piezoelectric element in which these grooves are opened is closed with another plate material. The rear end of each groove communicates with a common ink chamber, and an orifice plate having a nozzle at the position of each groove is provided at the opening of the front end. A driving electrode is provided on the inner surface of the groove communicating with the ink chamber and filled with ink.

  In the above configuration, if an electric field perpendicular to the polarization direction is applied to the electrode with respect to the piezoelectric element, a shear mode displacement is generated in the piezoelectric member, and the ink in the groove is pressurized by this displacement, and is applied to the groove. Ink droplets are ejected from the communicating nozzles.

  In an image forming apparatus using an inkjet head having the above-described configuration, generally, an inkjet head is provided at a predetermined position so that a plurality of nozzles are arranged in a direction orthogonal to the conveyance direction of the paper, and conveyed with respect thereto. The paper is transported by the mechanism, and the inkjet head is driven at an appropriate timing in synchronization with the transport of the paper, whereby the ejected ink droplets are attached to the paper to form a desired image.

  In the share mode type ink-jet head, as described above, since the electrode is provided on the inner surface of the groove formed in the piezoelectric element, the ink filling the groove directly touches the electrode. Therefore, in such a share mode type ink jet head, oil-based ink having a relatively low dielectric constant and a high resistance value is usually used in order to avoid short-circuit between electrodes. However, if it is necessary to use an ink with a low electrical resistance value (for example, water-based ink) for various reasons, an insulating coating must be applied to the electrode in the groove in contact with the ink. It must be.

JP 2000-135787 A

  As described above, in the shear mode type ink jet head in which the ink is in direct contact with the electrode of the piezoelectric element, generally only oil-based ink having a low dielectric constant and a high resistance value can be used. However, even if oil-based ink is used, water is mixed into the oil-based ink due to condensation in the ink path or water mixing into the inkjet head, and water-based ink is mixed into the oil-based ink by mistake. For this reason, the quality of the oil-based ink is changed, the electric resistance is lowered, the load on the drive circuit of the inkjet head is increased, and thermal damage may occur.

  In addition, when a special ink such as an emulsion ink has to be used for a special application, the components may be separated to lower the electrical resistance, resulting in the same inconvenience.

The present invention has been made in view of the above problems, and in the share mode type ink jet head in which the ink is in direct contact with the electrode of the piezoelectric element, the electric resistance is reduced when the ink is deteriorated, and the driving circuit is formed. It is an object of the present invention to be able to avoid a problem when using ink that may cause electrical damage with a simple configuration.

An ink alteration detection method for an ink jet head according to claim 1,
Electricity is applied to the electrodes provided in the piezoelectric elements constituting the ink storage space, and an electric field perpendicular to the polarization direction is applied to the piezoelectric elements to cause shear mode displacement, and the ink is pressurized by the displacement to the storage space. In the ink alteration detection method of an ink jet head that discharges ink from a communicating nozzle,
In a state where there is a reference material in the storage space, a current value obtained by giving a predetermined inspection driving waveform to the electrode is stored as a reference current value,
In a state where there is ink in the storage space, a current value obtained by giving a predetermined inspection driving waveform to the electrode is acquired as an inspection current value,
The reference current value and the inspection current value are compared, and when the inspection current value is larger than a predetermined setting value than the reference current value, it is determined that the ink has deteriorated.

An ink alteration detection method for an ink jet head according to claim 2, wherein the ink alteration detection method for an ink jet head according to claim 1,
The reference substance is one substance selected from the group consisting of air or reference ink.
Here, the reference ink means an ink having an electrical resistance within a range acceptable as a product, particularly an ink whose electrical resistance falls within a predetermined range including the median value of the allowable range. is doing.

  According to the ink alteration detection method of the present invention, when special ink whose electrical resistance may decrease due to alteration is to be used for special applications, moisture in the IJ head due to condensation in the ink path. It is possible to detect that the electrical resistance of the ink has decreased due to some trouble such as contamination of the ink as an increase in the load current of the drive circuit, and to detect the degree of the trouble for each nozzle. If an abnormality due to ink deterioration is detected, the nozzles are forcibly ejected according to the degree of failure, or recovery operation such as purging is performed for all nozzles, and then the drive current waveform is re-measured to re-measure the ink deterioration. You can check the recovery status. If it does not recover, it can issue a warning of failure.

It is a figure which shows the equivalent circuit schematic of the inkjet head and ink which concerns on embodiment of this invention, and the circuit diagram of a drive circuit. 1 is a schematic configuration diagram of an inkjet head device according to an embodiment of the present invention. It is a circuit diagram of the voltage detection part in the inkjet head device which concerns on embodiment of this invention. It is a wave form diagram which shows the inspection drive waveform measured by the current detection part of the ink jet head device concerning the embodiment of the present invention, and the detection current waveform by reference ink. It is a wave form diagram which shows the test drive waveform measured by the current detection part of the ink jet head device concerning the embodiment of the present invention, and the detection current waveform by the ink which is the measuring object. It is a functional block diagram of the inspection part in the ink jet head device concerning the embodiment of the present invention. 4 is a flowchart showing an ink alteration detection procedure performed by an inspection unit in the inkjet head device according to the embodiment of the present invention.

  An inkjet head device according to an embodiment of the present invention will be described with reference to FIGS. The ink jet head device according to the present embodiment applies an electric field perpendicular to the polarization direction to a piezoelectric element to generate a shear mode displacement, thereby electrically changing the ink in a shear mode type ink jet head that ejects ink from a nozzle. A function to detect from a change in resistance value is added.

  FIG. 1 shows an equivalent circuit diagram of a share mode type inkjet head 1 composed of piezoelectric elements, an ink 2 included in the inkjet head 1, and a drive circuit 3 that drives the inkjet head 1.

  As shown in the equivalent circuit diagram of FIG. 1, the share mode type inkjet head 1 is an equivalent circuit in which a resistor R, a coil L, a capacitor C connected in series and another capacitor C are connected in parallel. expressed. Although not shown in FIG. 1, as shown in FIG. 2 as a schematic structure, the inkjet head 1 has two piezoelectric elements polarized in opposite directions with respect to the plate thickness direction. The nozzle 5 is provided in the opening of the groove formed so as to pass through the bonding surface of the piezoelectric element and open at the front end. A driving electrode 8 is provided on the inner surface of the groove, and ink is supplied from the ink supply device 6 to the groove. In the schematic diagram of FIG. 2, only one nozzle 5 is shown, but in reality, a large number of grooves and nozzles are formed in a row in two piezoelectric elements 4 and 4 polarized in opposite directions. An electrode 8 is provided on the inner surface of each groove so that each nozzle 5 can be driven.

  As shown in the equivalent circuit diagram of FIG. 1, the drive circuit 3 is configured so that when one of the three switching elements S1, S2, S3 (for example, a transistor) is turned on, the other two switching elements are turned off. It is configured to operate. The drive circuit 3 includes an inkjet head 1 (IJ) drive signal source 7 as shown in FIG. 2, and a drive signal having a predetermined current required for discharging ink supplied therefrom is supplied to the switching element S1. , S2 and S3 to the electrodes 8 of the nozzles 5 of the inkjet head 1. As a result, positive (for example, +20 V), ground (0 V), and negative (−20 V) potentials are selectively applied to the electrodes 8 of the nozzles 5 of the inkjet head 1, and driving is controlled for each nozzle 5. can do.

As shown in the equivalent circuit diagram of FIG. 1, the ink 2 used in the inkjet head 1 is represented by an equivalent circuit in which a capacitor C and a resistor R are connected in parallel. In the ink 2 in a favorable state under a favorable environment, the component of the resistance R is as close to ∞ as possible, but when the quality is changed, the component of the resistance R decreases and the impedance of the capacitor C and the resistance R approaches.
In general, the ink used in an inkjet head has a range of acceptable electrical resistance for each product, and the ink is manufactured to meet such standards. Depending on the state, it may be out of this range. In order to detect such a change in ink quality or a change in ink quality that appears due to a change in load current, it is necessary to determine a reference for comparing the electrical resistance or load current. In the present embodiment, among the inks having an electrical resistance within a range acceptable as a product, an ink whose electrical resistance falls within a predetermined range including the median value of the allowable range is referred to as a reference ink, This is used as a reference for comparison of ink quality change. Specifically, the upper limit and lower limit of the load current that flows when the inkjet head 1 filled with the reference ink is driven by the drive circuit 3 with a predetermined inspection drive waveform to be described later, or the upper limit of the voltage value converted from the load current and Use the lower limit as the reference value. In general, the reference value varies depending on the type of ink (for example, the type of ink for each color such as C, M, Y, and K).

  The ink jet head drive signal source 7 shown in FIG. 2 is provided in the drive circuit 3 (FIG. 1) for driving the ink jet head 1 and is driven at the time of inspection for measuring the resistance of the ink 2 or at the time of preparation. A test drive waveform with a load current that is low enough not to eject ink 2 is applied to the electrode 8 of the inkjet head 1 via the switching elements S1, S2, S3 of the drive circuit 3 (FIG. 1). As a result, each electrode 8 of each nozzle 5 of the ink jet head 1 has three stages of positive, ground, and negative (or three stages of H, 0, and L) as shown in each upper stage of FIGS. A test drive waveform is provided.

  As shown in FIG. 2, a current detection unit 10 is provided between the inkjet head drive signal source 7 included in the drive circuit 3 (FIG. 1) and the electrode 8 of the inkjet head 1. FIG. 3 is a circuit diagram showing the structure of the current detection unit 10. The voltage difference between both ends of the resistor 11 is amplified by the operational amplifier 12 and then A / D converted by the A / D converter 13, and the load current is converted into a voltage value. The detection value that is the value converted to is output.

  FIG. 6 is a functional block diagram of the inspection unit 20 that uses the detection value output from the current detection unit 10 shown in FIG. 3 to detect ink alteration from a change in voltage value corresponding to a change in load current. Although not shown, the inkjet head device of the present embodiment includes a control unit that controls and controls the entire device, and the inspection unit 20 shown in FIG. 6 may be configured as a part thereof. Alternatively, the controller may be configured as a separate body. The inspection unit 20 includes a primary storage unit 21 that temporarily stores a detection value from the current detection unit 10 and a reference value storage memory 22 that stores the reference value (upper limit value and lower limit value) of the reference ink described above. ing. The inspection unit 20 is an inspection target based on the comparison value of the comparison unit 23 that compares the detection value stored in the primary storage unit 21 with the reference value stored in the reference value storage memory 22 and the comparison unit 23. A normal / abnormal determination unit 24 that determines whether the ink is normal or abnormal is provided. That is, when the energized ink changes in quality and the electrical resistance decreases, the load current increases, but the normal / abnormal determination unit determines whether or not the increase corresponds to the ink deterioration. , A detection value (data in the primary storage unit 21) that is a voltage value corresponding to the load current of the ink to be inspected as a determination target, and a voltage value corresponding to the load current obtained in the case of the reference ink under the same conditions. The reference value (data in the reference value storage memory 22) is compared by the comparison unit 23. If the detected value is between the upper limit value and the lower limit value of the reference value, it is determined to be normal, and if not, it is determined to be abnormal. To do. The normal / abnormal determination unit 24 can transmit the determination result (test result) to the main body control means. The inspection unit 20 has a test signal generation unit 25. The test signal generator 25 outputs an inspection drive waveform having a predetermined current value to the inkjet head 1 (IJ) drive signal source 7 to the drive circuit 3 in response to an inspection instruction input from the input means of the main body control means. A test drive waveform output instruction signal to be output is output, a start signal that is a trigger signal for instructing the current detection unit 10 to start voltage measurement is output at a predetermined timing, and the normal / abnormality determination unit 24 is further output at a predetermined timing. It is possible to output a determination operation instruction signal.

Next, in the ink jet head device of the present embodiment, a method for detecting ink alteration from a change in load current or a change in voltage value converted therefrom will be described focusing on the operation of the control means and the drive circuit 3.
First, an operation for taking a reference value to be compared with a detected value is performed. That is, in a state where the ink jet head device is filled with reference ink as a reference material, a predetermined inspection drive waveform as shown in the upper part of FIG. 4 is applied to each electrode of each nozzle 5 via the drive circuit 3. At this time, a detected current value having a waveform as shown in the lower part of FIG. Here, among the detected current values, the peak value is referred to as a detected current value I1p, and the average value is referred to as a detected current value I1a. The current detection unit 10 converts these current values into voltage values and outputs them as detection values. Specifically, a voltage value converted from the detected current value I1p that is a peak value is used as an upper limit value of the detected value, and a voltage value converted from the detected current value I1a that is an average value is used as the lower limit value of the detected value. Are stored in the reference value storage memory.

Next, the control procedure of the ink alteration detection in the inkjet head device of the present embodiment will be described with reference to the flowchart of the control procedure (FIG. 7) and the functional block diagram (FIG. 6).
When the power of the ink jet head device is turned on (S1), the inspection unit 20 performs an ink alteration detection operation according to an inspection program (S4) at every predetermined ink inspection interval (S2). The inspection program (S4) is automatically executed at predetermined time intervals as described above, and can also be started when the user of the apparatus determines that the image formation result is defective (S3).

  In the inspection program (S4), an ink deterioration inspection is first performed (S5). First, the test signal generator 25 generates a test signal in response to an inspection instruction from the control means. Here, the test signal includes a test drive waveform output instruction signal, a start signal, and a determination operation instruction signal as shown in FIG. As a result, the inkjet head 1 (IJ) drive signal source 7 outputs an inspection drive waveform to the drive circuit 3, and the current detection unit 10 performs voltage measurement by converting the load current value into a voltage value at a predetermined timing. The normal / abnormal determination unit 24 is caused to execute a determination operation at a predetermined timing.

  The current detection unit 10 performs signal detection of a detection value obtained by converting the load current value into a voltage value as described above (S52). This detected value is stored in the primary storage unit 21 of the inspection unit 20. The comparison unit 23 compares the reference value in the reference value storage memory 22 with the detection value of the primary storage unit 21 (S53, S55), and the normal / abnormality determination unit 24 determines whether the ink is normal or abnormal from the comparison result. (S54, S56, S57). That is, the comparison unit 23 first compares the detected value with the upper limit value of the reference value (for example, + 20% when viewed from the median value) (S53), and if the detected value exceeds the upper limit value (S53, or higher), The normal / abnormal determination unit 24 determines that the ink is defective (S54). If the detected value does not exceed the upper limit value (S53, hereinafter), the normal / abnormality determination unit 24 determines that the upper limit is within the range, and then determines the lower limit value. The comparison unit 23 compares the lower limit value of the reference value (for example, −20% as viewed from the median value) with the detected value (S55), and when the detected value is lower than the lower limit value (S55, below), normal / The abnormality determination unit 24 determines that the ink is defective (S56). If the detected value exceeds the lower limit value (S55, or higher), the normal / abnormality determination unit 24 determines that the lower limit as well as the upper limit is within the range, and finally determines that the ink is normal. (S54).

  The above inspection by the inspection unit 20 is performed in units of nozzles. As shown in FIGS. 4 to 5, in this embodiment, the test current value of the ink to be inspected is higher than the reference current value, and the electric resistance value of the ink is reduced. Yes. This is because, for example, the water dispersed in the ink aggregates into large particles, which are connected to each other to break the insulation. As a result, the load current increases in the process of transition from the insulated state to the conductive state. It is thought that it is showing. Other causes may be considered, but from the degree of increase in the load current, whether or not the ink is in a denatured state that cannot be overlooked can be determined for each nozzle by the procedure described above.

  Since the normality / abnormality determination unit 24 of the inspection unit 20 transmits the inspection result to the control unit, the control unit performs various control operations for each nozzle 5 on the inkjet head device based on the inspection result for each nozzle 5. Can be done. For example, the nozzle 5 determined to be defective can be forcibly ejected, or the recovery operation such as purging can be performed not only for the nozzle 5 determined to be defective, but also for all the nozzles 5. When such a recovery operation is performed, the recovery state of the ink alteration can be confirmed for each nozzle 5 by re-measurement of the drive current waveform thereafter. Further, a defect warning may be issued when a defect is first detected, or a defect warning may be issued again when recovery is not performed and recovery is performed. Alternatively, the reference value may be prepared in a plurality of stages, the degree of decrease in the ink resistance may be evaluated in a plurality of stages, and the strength of the purge force may be adjusted according to the degree of the defective state.

In the above-described embodiment, a new ink that is properly manufactured, has a good storage condition, and has a predetermined electric resistance is used as a reference ink. When the ink is charged, the first measurement is performed to determine the change in the electric resistance of the ink. had obtained a reference value as a detection criteria, no ink jet head 1, may be obtained a reference value between the electrodes 8, 8 perform the first measured while only air.

DESCRIPTION OF SYMBOLS 1 ... Inkjet head 2 ... Ink 3 ... Drive circuit 4 ... Piezoelectric element 5 ... Nozzle 6 ... Ink supply device 7 ... Inkjet head (IJ) drive signal source 8 ... Electrode 10 ... Current detection part 20 ... Inspection part 21 ... Primary storage part 22 ... Reference value storage memory 23 ... Comparison unit 24 ... Normal / abnormal judgment unit

Claims (2)

Electricity is applied to the electrodes provided in the piezoelectric elements constituting the ink storage space, and an electric field perpendicular to the polarization direction is applied to the piezoelectric elements to cause shear mode displacement, and the ink is pressurized by the displacement to the storage space. In the ink alteration detection method of an ink jet head that discharges ink from a communicating nozzle,
In a state where there is a reference material in the storage space, a current value obtained by giving a predetermined inspection driving waveform to the electrode is stored as a reference current value,
In a state where there is ink in the storage space, a current value obtained by giving a predetermined inspection driving waveform to the electrode is acquired as an inspection current value,
The reference current value and the inspection current value are compared, and when the inspection current value is larger than a predetermined set value than the reference current value, it is determined that the ink has deteriorated. Ink alteration detection method. 2. The ink alteration detection method for an ink jet head according to claim 1, wherein the reference substance is one substance selected from the group consisting of air and reference ink.

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