JP6107507B2 - Liquid ejection device and short circuit detection method - Google Patents

Description

  The present invention relates to a liquid ejection device and a method for detecting a short circuit in a power feeding unit connected to a ejection driving unit of the liquid ejection device.

  Patent Document 1 discloses a liquid ejection device (inkjet head) including a piezoelectric element for ejecting liquid from a nozzle. The ink jet head disclosed in Patent Document 1 includes a power feeding unit (head driving device) that drives a piezoelectric element by applying a voltage to two electrodes of the piezoelectric element. The power supply unit supplies a drive signal to one electrode of the piezoelectric element and applies a constant voltage to the other electrode on the ground side.

  Conventionally, a configuration in which the other electrode of the piezoelectric element is connected to the ground is well known. However, in Patent Document 1, a bias voltage higher than the ground is applied to the other electrode on the ground side. A configuration is disclosed. That is, the power supply unit of Patent Document 1 includes a bias power supply circuit that applies a bias voltage to the other electrode on the ground side.

  The bias power supply circuit generates a bias voltage using a head drive power supply for generating a drive signal. Specifically, the bias power supply circuit has a Zener diode provided between the head driving power supply and the ground, and generates a bias voltage (for example, 6 V) slightly higher than the ground by the Zener diode.

JP2003-72069A (FIG. 1)

  In the power feeding unit (head driving device) of Patent Document 1, between a power supply line that connects one electrode of the piezoelectric element and a power source, and a ground line that connects the other electrode of the piezoelectric element and the ground, In the unlikely event that a short circuit occurs, a large leakage current may flow between the two lines, so it is desirable to reliably detect the short circuit. In order to detect the short circuit, for example, it is conceivable to monitor the voltage fluctuation of the power supply line caused by the leakage current at the short circuit location.

  However, in Patent Document 1, the power supply line and the ground line are connected by a bias power supply circuit. A constant amount of current always flows through the Zener diode of the bias power supply circuit regardless of the driving of the piezoelectric element. For this reason, if the leakage current flowing through the short-circuited portion is smaller than the current flowing through the Zener diode, it is difficult to detect a voltage change caused by the leakage current. Therefore, the detection accuracy of the leakage current between the two lines is lowered, and there is a possibility that the short circuit cannot be detected until a considerably large leakage current flows.

  An object of the present invention is to improve the detection accuracy of a short circuit between two voltage supply lines in a power feeding unit that can generate an intermediate voltage from two types of voltages and supply the intermediate voltage to a discharge driving unit.

A liquid discharge apparatus according to a first aspect of the present invention includes a flow path structure in which a liquid flow path including a nozzle is formed, a discharge drive unit that is provided in the flow path structure and discharges liquid from the nozzle, and the discharge drive A power supply unit connected to the unit,
The power supply unit includes: a first line to which a predetermined first voltage is applied; a second line to which a predetermined second voltage lower than the first voltage is applied; and the first line and the second line. An intermediate voltage generation unit that is connected to each other and generates a third voltage between the first voltage and the second voltage to be supplied to the ejection driving unit;
A determination unit for determining whether a short circuit has occurred between the first line and the second line;
The power supply unit is provided in a conduction path between the first line and the second line via the intermediate voltage generation unit, and the determination unit is between the first line and the second line. It has a path cut-off switch that can cut off the conduction path when determining a short circuit.

  In this invention, the path | route cutoff switch which can interrupt | block this conduction | electrical_connection path is provided in the conduction | electrical_connection path | route via the intermediate voltage production | generation part between a 1st line and a 2nd line. When detecting whether or not a short circuit has occurred between the first line and the second line, the current can be prevented from flowing through the conduction path by blocking the conduction path with the path cutoff switch. Thereby, by eliminating the influence of the current flowing through the conduction path, it becomes easy to grasp even if the leakage current at the short-circuited portion is very small, so that the short-circuit detection accuracy is improved.

A liquid ejection device according to a second aspect of the present invention includes, in the first aspect, a voltage detection unit that detects a voltage of the first line, and a control unit that controls the operation of the path cutoff switch.
The determination unit controls the first line and the first line based on a voltage change of the first line detected by the voltage detection unit after the control unit controls the path cutoff switch to cut off the conduction path. A short circuit between the second lines is determined.

  In the present invention, the voltage change of the first line due to the leakage current at the short-circuit location when there is a short circuit is detected by detecting the voltage change of the first line after the conduction path is cut off by the path cut-off switch. It becomes easy to detect. Accordingly, the short circuit detection accuracy is improved.

  According to a third aspect of the present invention, in the liquid ejecting apparatus according to the second aspect of the present invention, the liquid discharge device further includes a supply cutoff switch that cuts off the supply of the first voltage to the first line from the voltage generation unit that generates the first voltage. The control unit controls the operation of the supply cutoff switch, and the determination unit controls the path cutoff switch to cut off the conduction path, and then controls the supply cutoff switch. Then, after the voltage supply from the voltage generation unit is cut off, a determination of a short circuit between the first line and the second line is made based on the voltage change of the first line detected by the voltage detection unit. It is characterized by doing.

  When the conduction path is cut off by the path cut-off switch, and then the voltage supply from the voltage generation unit to the first line is cut off by the supply cut-off switch, the voltage of the first line drops due to the presence or absence of a short circuit (presence of leakage current). Will be different. Therefore, the presence or absence of a short circuit between the first line and the second line can be detected from the voltage change of the first line after the conduction path is interrupted by the supply cutoff switch.

  In the liquid ejection device according to a fourth aspect of the present invention, in the third aspect of the present invention, the power feeding unit is parallel to the conduction path passing through the intermediate voltage generation unit between the first line and the second line. The voltage detection unit includes a capacitor for voltage stabilization, and the voltage detection unit is configured to discharge the capacitor when the supply of the voltage to the first line is interrupted by the supply cutoff switch. A voltage drop from the first voltage of one line is detected.

  The capacitor provided between the first line and the second line suppresses fluctuations in the voltages of the first line and the second line even when a large current instantaneously flows to the piezoelectric actuator. In the present invention, the capacitor for stabilizing the voltage is used for determining a short circuit between the first line and the second line. That is, when the voltage supply is cut off by the supply cut-off switch, the voltage of the first line gradually decreases as the capacitor is discharged. Therefore, it becomes easy to distinguish the difference in voltage change between when there is a short circuit and when there is no short circuit, and it is possible to easily detect the presence or absence of a short circuit between the first line and the second line.

  In any one of the first to fourth inventions, the liquid ejection device according to a fifth aspect of the present invention is configured to shut off the conduction path by the path cutoff switch when the ejection driving unit does not eject liquid from the nozzle. The determination of the short circuit is performed by the determination unit.

  If the conduction path is cut off by the path cut-off switch, the intermediate voltage generator cannot generate the third voltage. Therefore, a short circuit is detected when the ejection drive unit does not eject liquid from the nozzle.

  A short-circuit detection method according to a sixth aspect of the present invention is the method for detecting a short-circuit between the first line and the second line of the power feeding unit in the liquid ejection device according to the first aspect, wherein the path cutoff switch And determining whether or not a short circuit has occurred between the first line and the second line based on a voltage change of the first line after the conduction path is interrupted. is there.

  In the present invention, by detecting the voltage change of the first line after the conduction path is cut off by the path cutoff switch, it becomes easier to detect the voltage change caused by the leakage current at the short-circuited location, and the short-circuit detection accuracy is improved. To do.

  According to the present invention, when detecting whether or not a short circuit has occurred between the first line and the second line, the current is prevented from flowing through the conduction path by blocking the conduction path with the path cutoff switch. As a result, the influence of the current flowing through the conduction path is eliminated, and even when the leakage current at the short-circuited portion is very small, it is easy to grasp, so that the short-circuit detection accuracy is improved.

1 is a schematic plan view of an ink jet printer according to an embodiment. It is a top view of an inkjet head. It is the A section enlarged view of FIG. FIG. 4 is a sectional view taken along line IV-IV in FIG. 3. It is the VV sectional view taken on the line of FIG. It is a figure which shows schematically the electric structure of a control apparatus, a power supply device, and an inkjet head. It is an equivalent circuit diagram of a piezoelectric actuator and a power feeding unit. It is operation | movement explanatory drawing of a piezoelectric actuator. It is an equivalent circuit diagram of a piezoelectric actuator and a power feeding unit when a short circuit is detected. It is a flowchart of a short circuit detection process. It is a figure which shows the voltage fall of the 1st line when a voltage supply is interrupted | blocked. It is sectional drawing equivalent to FIG. 5 of the piezoelectric actuator of a change form. FIG. 13 is an equivalent circuit diagram of the piezoelectric actuator of FIG. 12 and its power feeding unit.

  Next, an embodiment of the present invention will be described. FIG. 1 is a schematic plan view of the ink jet printer of the present embodiment. First, a schematic configuration of the inkjet printer 1 will be described with reference to FIG. In the following, the front side in FIG. 1 is defined as the upper side, and the other side of the page is defined as the lower side, and the explanation will be made using direction words “up” and “down” as appropriate.

(Schematic configuration of the printer)
As shown in FIG. 1, an ink jet printer 1 (liquid ejection device of the present invention) includes a platen 2, a carriage 3, an ink jet head 4, a transport mechanism 5, a control device 6, and the like.

  On the upper surface of the platen 2, a recording sheet 100 as a recording medium is placed. The carriage 3 is configured to reciprocate in the scanning direction along the two guide rails 10 and 11 in a region facing the platen 2. An endless belt 14 is connected to the carriage 3, and the endless belt 14 is driven by a carriage drive motor 15, whereby the carriage 3 moves in the scanning direction.

  The inkjet head 4 is attached to the carriage 3 and moves in the scanning direction together with the carriage 3. The inkjet head 4 is connected to ink cartridges 17 of four colors (for example, black, yellow, cyan, and magenta) mounted on the printer 1 by a tube (not shown). A plurality of nozzles 25 are formed on the lower surface of the inkjet head 4 (the surface on the opposite side of the paper surface in FIG. 1). The inkjet head 4 ejects the four colors of ink supplied from the ink cartridge 17 to the recording paper 100 placed on the platen 2 from the plurality of nozzles 25.

  The transport mechanism 5 includes two transport rollers 18 and 19 disposed so as to sandwich the platen 2 in the transport direction. The transport mechanism 5 transports the recording paper 100 placed on the platen 2 in the transport direction by two transport rollers 18 and 19.

  As shown in FIG. 6, which will be described later, the control device 6 includes a CPU (Central Processing Unit) 70, a ROM (Read Only Memory) 71, a RAM (Random Access Memory) 72, and an ASIC including various control circuits. Application Specific Integrated Circuit) 73 and the like. The control device 6 is connected to an external device such as a PC (not shown) so that data communication is possible.

  The control device 6 executes various processes such as printing on the recording paper 100 by the CPU 70 and the ASIC 73 in accordance with the program stored in the ROM 71. For example, in the printing process, the control device 6 controls the inkjet head 4, the carriage drive motor 15, and the like based on a print command input from an external device such as a PC, and prints an image or the like on the recording paper 100. . Specifically, an ink discharge operation for discharging ink while moving the inkjet head 4 in the scanning direction together with the carriage 3 and a transport operation for transporting the recording paper 100 in the transport direction by the transport rollers 18 and 19 alternately. Let me do it. In the above description, the control device 6 performs various processing by the CPU 70 and the ASIC 73. However, the present invention is not limited to this, and the control device 6 may be realized by any hardware configuration. Good. For example, the processing may be performed by only the CPU or only the ASIC. The functions may be shared by two or more CPUs or two or more ASICs.

(Inkjet head)
Next, the inkjet head 4 will be described. FIG. 2 is a plan view of the inkjet head. FIG. 3 is an enlarged view of a portion A in FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. FIG. 5 is a cross-sectional view taken along line VV in FIG. 2 and 4, the COF 63 connected to the piezoelectric actuator 21 is schematically shown by a two-dot chain line. In FIG. 5, the flow path structure below the pressure chamber 26 shown in FIG. 4 is not shown. As shown in FIGS. 2 to 5, the inkjet head 4 includes a flow path unit 20 and a piezoelectric actuator 21.

(Configuration of flow path unit)
As shown in FIG. 4, the flow path unit 20 (the flow path structure of the present invention) is formed by stacking five plates 31 to 35 each having a flow path forming hole. When these five plates 31 to 35 are stacked, the respective flow path forming holes communicate with each other, whereby the flow path unit 20 is formed with an ink flow path as described below.

  As shown in FIG. 2, four ink supply holes 23 connected to the four ink cartridges 17 (see FIG. 1) are formed on the upper surface of the flow path unit 20. In the flow path unit 20, four manifolds 24 connected to the four ink supply holes 23 are formed. Four inks of four ink cartridges 17 are supplied to the four manifolds 24 through the four ink supply holes 23, respectively. The four manifolds 24 extend in the transport direction.

  The flow path unit 20 has a plurality of nozzles 25 formed on the lowermost plate 35 and a plurality of pressure chambers 26 formed on the uppermost plate 31. As shown in FIG. 2, a plurality of nozzles 25 are arranged along the transport direction on the lower surface of the flow path unit 20 (the surface on the other side of the paper in FIG. 3), and four rows each corresponding to the four manifolds 24. A nozzle row is configured. Each pressure chamber 26 is a hole having a substantially rectangular planar shape that is long in the scanning direction.

  The plurality of pressure chambers 26 are arranged in a plane along the upper surface of the flow path unit 20. The plurality of pressure chambers 26 are covered from above by the piezoelectric body 40 of the piezoelectric actuator 21 joined to the upper surface of the flow path unit 20. The plurality of pressure chambers 26 are arranged in four rows corresponding to the four manifolds 24 and the four nozzle rows. Each pressure chamber 26 has a substantially elliptical planar shape that is long in the scanning direction. Further, one end portion in the longitudinal direction of each pressure chamber 26 communicates with the manifold 24, and the other end portion in the longitudinal direction communicates with the nozzle 25. As a result, as shown in FIG. 4, the flow path unit 20 is formed with a plurality of individual ink flow paths that branch from the manifold 24 and reach the nozzles 25 through the pressure chambers 26.

(Configuration of piezoelectric actuator)
The piezoelectric actuator 21 (the ejection drive unit of the present invention) is joined to the upper surface of the flow path unit 20 so as to cover the plurality of pressure chambers 26. As shown in FIGS. 2 to 5, the piezoelectric actuator 21 includes an ink sealing film 43, a piezoelectric body 40 including two piezoelectric layers 41 to 43, a plurality of individual electrodes 44, and a common electrode 45. I have.

  The ink sealing film 43 is a thin film formed of a material with low ink permeability, for example, a metal material such as stainless steel. The ink sealing film 43 is bonded to the upper surface of the flow path unit 20 so as to cover the plurality of pressure chambers 26.

  The two piezoelectric layers 41 and 42 constituting the piezoelectric body 40 are each made of a piezoelectric material mainly composed of lead zirconate titanate, which is a mixed crystal of lead titanate and lead zirconate. The piezoelectric layers 41 and 42 are disposed on the upper surface of the ink sealing film 43 in a state where they are laminated.

  The plurality of individual electrodes 44 are disposed on the upper surface of the upper piezoelectric layer 41. More specifically, as shown in FIGS. 2 to 5, each individual electrode 44 is disposed in a region of the upper surface of the piezoelectric layer 41 facing the central portion of the pressure chamber 26. The plurality of individual electrodes 44 are arranged along the transport direction so as to correspond to the plurality of pressure chambers 26 and constitute four individual electrode rows. An individual terminal 49 is drawn out from each individual electrode 44, and a bump 57 made of a conductive material such as gold is provided at the end of the individual terminal 49. As shown in FIG. 4, a COF 63 that is a wiring member is pressed against and bonded to the bump 57. Thereby, the individual terminal 49 is electrically connected to the wiring formed in the COF 63 via the bump 57.

  The common electrode 45 is disposed between the two piezoelectric layers 41 and 42. The common electrode 45 faces the plurality of individual electrodes 44 in common across the piezoelectric layer 41. As shown in FIG. 2, two extraction electrodes 47 are provided at both ends in the scanning direction on the upper surface of the upper piezoelectric layer 41, and the two extraction electrodes 47 are a plurality of the plurality of extraction electrodes 47 formed on the piezoelectric layer 41. It is electrically connected to the common electrode 45 through a through hole (not shown). The extraction electrode 47 is provided with a plurality of bumps 58. The two extraction electrodes 47 are electrically connected to the wiring formed on the COF 63 through the plurality of bumps 58.

  A portion of the piezoelectric layer 41 sandwiched between the individual electrode 44 and the common electrode 45 is particularly referred to as an active portion 51. As indicated by the white arrow a in FIG. 5, the active portion 51 is polarized downward in the thickness direction, that is, in a direction from the individual electrode 44 toward the common electrode 45.

(Configuration of the power feeding unit)
Next, the power feeding unit 61 that applies voltages to the electrodes 44 and 45 of the piezoelectric actuator 21 will be described. FIG. 6 is a diagram schematically illustrating an electrical configuration of the control device, the power supply device, and the inkjet head. The power supply unit 61 includes a head substrate 62, a driver IC 64, and the like. In addition, although illustration is abbreviate | omitted, the head board | substrate 62 of the electric power feeding part 61 is connected with the power supply device 55 and the control apparatus 6 by wiring members, such as a flexible flat cable (FFC).

  The power supply unit 61 is connected to the first line 66a connected to the VDD terminal of the power supply device 55 (the voltage generation unit of the present invention) formed on a wiring member such as FFC, and to the GND terminal of the power supply device 55. Second line 66b. The first line 66a is maintained at the power supply voltage, and the second line 66b is maintained at the ground. In the following description, the power supply voltage applied to the first line 66a is also referred to as “first voltage V1”, and the ground is also referred to as “second voltage V2”. The “voltage” here means a potential difference with respect to the ground. That is, the second voltage V2 = 0V.

  Further, the head substrate 62 of the power feeding unit 61 is connected to the control device 6 by a plurality of signal wirings 66c formed on a wiring member such as FFC. The ASIC 73 of the control device 6 generates a control signal for controlling the driver IC 64 based on print data input from an external device such as a PC (not shown). The control signal generated by the ASIC 73 is sent to the head substrate 62 through a plurality of signal wirings 66c.

  The head substrate 62 is connected to the piezoelectric actuator 21 by a COF 63 on which a driver IC 64 is mounted as shown in FIGS. As shown in FIGS. 2 and 4, the COF 63 is disposed so as to cover the piezoelectric body 40 of the piezoelectric actuator 21 from above. A plurality of terminals (not shown) are provided on the back surface of the COF 63. The plurality of terminals of these COFs 63 are formed on the upper surface of the piezoelectric body 40, a plurality of individual terminals 49 led out from the plurality of individual electrodes 44, two lead electrodes 47 electrically connected to the common electrode 45, and bumps They are electrically connected via 57 and 58, respectively.

  Based on the control signal transmitted from the control device 6 via the head substrate 62, the driver IC 64 applies the voltage applied to the individual electrode 44 to the first voltage V1 (power supply voltage) applied to the first line 66a. Switching is made between the second voltage V2 (ground) applied to the second line 66b. FIG. 7 is an equivalent circuit diagram of the piezoelectric actuator and the power feeding unit. Note that the active portion 51 of the piezoelectric actuator 21 formed of a piezoelectric material that is a ferroelectric material stores a charge (charge) when a potential difference occurs between the electrodes 44 and 45 sandwiching the active portion 51, and the potential difference is eliminated. The stored charge is discharged (discharge). That is, as shown in FIG. 7, the active part 51 can be regarded as a capacitor C having a certain capacitance.

  As shown in FIG. 7, the driver IC 64 is a kind of switching circuit composed of transistors. The driver IC 64 switches ON / OFF of the two switches SW1 and SW2 shown in FIG. 7 based on the control signal transmitted from the control device 6, whereby the voltage at the point A in FIG. Is switched between the first voltage V1 and the second voltage V2.

  As shown in FIGS. 6 and 7, the head substrate 62 incorporates a capacitor C0, a voltage detection circuit 67, a supply cutoff switch SWb, an intermediate voltage generation circuit 65, and the like.

  The capacitor C0 is provided between the first line 66a and the second line 66b. The capacitor C0 is provided to stabilize the voltage of the first line 66a and the second line 66b. Further, a discharge path 69 for discharging the charge stored in the capacitor C0 is also provided between the first line 66a and the second line 66b. The discharge path 69 is provided with resistors Rx and Ry connected in series. The resistance value of the resistor Rx is, for example, several tens of kΩ, and the resistance value of the resistor Ry is, for example, several kΩ. Even when a large current momentarily flows through the power supply unit 61 when the active unit 51 is driven (during charging / discharging of the capacitor C), voltage fluctuations of the first line 66a and the second line 66b are caused by charging / discharging of the capacitor C0. Is suppressed.

  The voltage detection circuit 67 (the voltage detection unit of the present invention) detects the voltage fluctuation of the first line 66 a and sends the detected signal to the control device 6. In the present embodiment, a voltage detection circuit 67 is connected to the discharge path 69 described above. The voltage detection circuit 67 is provided to constantly monitor the voltage of the first line 66a. However, as will be described later, the voltage detection circuit 67 also detects a short circuit between the first line 66a and the second line 66b. Used.

  The supply cutoff switch SWb is provided on the upstream side (power supply device 55 side) of the first line 66a with respect to the connection point with the voltage detection circuit 67. The opening / closing operation of the supply cut-off switch SWb is controlled by a control signal from the ASIC 73 of the control device 6 and can cut off the voltage supply from the power supply device 55 to the power supply unit 61 (first line 66a).

  A conduction path 68 that connects the first line 66a and the second line 66b is provided in parallel with the capacitor C0 on the downstream side (piezoelectric actuator 21 side) of the capacitor C0. This conduction path 68 is provided with an intermediate voltage generation circuit 65 (intermediate voltage generation unit of the present invention) that generates an intermediate third voltage V3 between the first voltage V1 and the second voltage V2. As shown in FIG. 7, the intermediate voltage generating circuit 65 has two resistors R1 and R2 connected in series. The resistance values of the resistors R1 and R2 are, for example, about several kΩ. The voltage between the first line 66a and the second line 66b is divided by the two resistors R1 and R2, thereby generating a third voltage V3 intermediate between the first voltage V1 and the second voltage V2. For example, when the first voltage V1 = 28V and the second voltage V2 = 0V, the third voltage V3 of about 5V is generated. The output of the intermediate voltage generation circuit 65 is connected to the point B in FIG. That is, the third voltage V <b> 3 that is an intermediate voltage is always applied to the common electrode 45 that sandwiches the active portion 51 with the individual electrode 44.

  Further, the intermediate voltage generation circuit 65 includes a path cutoff switch SWa that blocks the conduction path 68. In FIG. 7, the path cutoff switch SWa is provided between the two resistors R1 and R2. As will be described later, this path cut-off switch SWa cuts off the conduction path 68 when detecting a short circuit between the first line 66a and the second line 66b. The opening / closing operation of the path cutoff switch SWa is controlled by a control signal from the ASIC 73 of the control device 6, and the state of the conduction path 68 is switched between the conduction state and the cutoff state by the path cutoff switch SWa. The position where the path cutoff switch SWa is provided is not limited to between the resistors R1 and R2, and may be any position in the conduction path 68.

  The capacitor C0, the voltage detection circuit 67, the supply cut-off switch SWb, and the intermediate voltage generation circuit 65 are not necessarily incorporated in the head substrate 62, and are provided in a wiring member such as an FFC, a driver IC, or the like. May be. For example, the capacitor C0 may be provided on a wiring member such as an FFC that connects the head substrate 62 and the control device 6. FIG. 6 is a diagram in which the control device 6 and the power supply device 55 are separately connected to the head substrate 62 of the inkjet head 4, but the first line 66 a connected to the power supply device 55 and the first line 66 a are connected. A configuration in which the two lines 66b are connected to the head substrate 62 via the control device 6 can also be adopted. In that case, the voltage detection circuit 67 may be incorporated in the ASIC 73 of the control device 6. Further, the intermediate voltage generation circuit 65 may be provided in the control device 6.

(Operation of piezoelectric actuator)
Next, the operation of the piezoelectric actuator 21 when the voltage of the individual electrode 44 is switched by the driver IC 64 of the power feeding unit 61 will be described. FIG. 8 is an explanatory view of the operation of the piezoelectric actuator 21. In FIG. 8, the thick vertical arrow b indicates the direction of the electric field acting on the active part 51, and the solid horizontal arrow c indicates the deformation direction (extension or contraction) in the surface direction of the active part 51. .

(A) When First Voltage is Applied FIG. 8A shows a state in which the first voltage V <b> 1 that is the power supply voltage is applied to the individual electrode 44. At this time, a voltage difference is generated between the individual electrode 44 to which the first voltage V1 is applied and the common electrode 45 to which the third voltage V3 is applied. A downward electric field from the electrode 44 toward the common electrode 45 acts. Further, as indicated by an arrow a, the polarization direction of the active portion 51 is also downward. Accordingly, since the direction of the electric field acting on the active portion 51 is the same as the polarization direction, the active portion 51 contracts in the surface direction as indicated by an arrow c. When the active portion 51 facing the central portion of the pressure chamber 26 contracts in the surface direction, the piezoelectric body 40 bends so as to be convex toward the pressure chamber 26 (lower side), and the central portion is displaced downward. .

  Here, the third voltage V3 applied to the common electrode 45 is an intermediate voltage between the first voltage V1 and the second voltage V2. Therefore, compared with the case where the second voltage V1 (ground) is applied to the common electrode 45 as it is, the potential difference between the individual electrode 44 and the common electrode 45 is reduced, and the strength of the electric field acting on the active portion 51 is reduced. Thereby, generation | occurrence | production of the dielectric breakdown by a high intensity | strength electric field acting on the active part 51 is prevented. As described above, when the electric field acting on the active portion 51 is reduced, the piezoelectric deformation (shrinkage amount) of the active portion 51 is naturally reduced, and the piezoelectric body 40 is opposed to the central portion of the pressure chamber 26. The downward displacement of the part is also reduced. However, as will be described later, the decrease in the displacement amount of the piezoelectric body 40 is compensated when the second voltage V2 is applied to the individual electrode 44 described below.

(B) When Second Voltage is Applied FIG. 8B shows a state where the second voltage V <b> 2 that is the ground is applied to the individual electrode 44. Even in this case, a voltage difference is generated between the individual electrode 44 to which the second voltage V2 is applied and the common electrode 45 to which the third voltage V3 is applied. However, in this case, the voltage of the common electrode 45 is higher than the voltage of the individual electrode 44. Therefore, as shown by the arrow b, an upward electric field acting from the common electrode 45 toward the individual electrode 44 acts on the active portion 51, contrary to FIG. 8A. This electric field is opposite to the polarization direction of the active part 51 indicated by the arrow a. Therefore, as indicated by the arrow c, the active part 51 extends in the surface direction. As described above, the active portion 51 facing the central portion of the pressure chamber 26 extends in the surface direction, so that the piezoelectric body 40 bends so as to protrude toward the opposite side (upper side) from the pressure chamber 26, and the center The part is displaced upward.

  As described above, when the second voltage V2 is applied to the individual electrode 44, the piezoelectric body 40 is deformed in the direction opposite to the previous application of the first voltage V1. That is, when the third voltage V3 higher than the second voltage V2 is applied to the common electrode 45, the piezoelectric body when the first voltage V1 is applied to the individual electrode 44 of FIG. Although the displacement amount of 40 decreases, the decrease in the displacement amount is compensated by the displacement of the piezoelectric body 40 in the reverse direction when the second voltage V2 is applied to the individual electrode 44 in FIG. 8B.

  As described above, when the voltage of the individual electrode 44 is switched between the first voltage V <b> 1 and the second voltage V <b> 2, the piezoelectric body 40 is displaced up and down in a region facing the pressure chamber 26, and thus the volume of the pressure chamber 26. Changes. Due to this volume change, pressure (discharge energy) is applied to the ink in the pressure chamber 26, and the ink is discharged from the nozzle 25 communicating with the pressure chamber 26.

(Short-circuit detection)
Next, detection of a short circuit between the first line 66a and the second line 66b of the power feeding unit 61 will be described. FIG. 9 is an equivalent circuit diagram of the piezoelectric actuator 21 and the power feeding unit 61 when a short circuit is detected. As indicated by a two-dot chain line in FIG. 9, if a short circuit occurs between the first line 66 a and the second line 66 b, a large leakage current may flow in the shorted part 75. Note that the short circuit may occur in the driver IC 64 by, for example, destroying a circuit in the driver IC 64 due to static electricity, lightning, or the like. It can also occur when conductive foreign matter adheres to the FFC, FPC 63, head substrate 62, and the like. Therefore, the printer 1 of the present embodiment detects a short circuit between the first line 66a and the second line 66b as follows.

  FIG. 10 is a flowchart of the short circuit detection process. In FIG. 10, Si (i = 10, 11, 12, 13) indicates a step number. The short circuit detection process in FIG. 10 is executed by the CPU 70 and the ASIC 73 of the control device 6. Further, this short-circuit detection process is executed at an appropriate timing when the piezoelectric actuator 21 is not driven, that is, when ink is not ejected from the nozzle 25. For example, it may be performed every time a predetermined time has elapsed since the previous detection, or may be performed when a signal for detecting a short circuit is input from the outside.

  As shown in FIG. 10, first, the control device 6 controls the path cutoff switch SWa to block the conduction path 68 provided with the intermediate voltage generation circuit 65 (S10). This prevents a current from flowing through the conduction path 68 when a short circuit is detected. When the conduction path 68 is interrupted, the intermediate voltage generation circuit 65 cannot generate the third voltage V3. However, as described above, the short-circuit detection process is executed when the piezoelectric actuator 21 is not driven. Therefore, even if the intermediate voltage generation circuit 65 cannot generate the third voltage V3, no particular problem occurs.

  Next, the control device 6 controls the supply cutoff switch SWb to cut off the voltage supply from the power supply device 55 to the first line 66a (S11). That is, power supply from the power supply device 55 to the power supply unit 61 is interrupted. In a state where the first voltage V1 is applied from the power supply device 55 to the first line 66a, the capacitor C0 is in a charged state. When the voltage supply (power supply) from the power supply device 55 is cut off by the supply cut-off switch SWb, the discharge of the capacitor C0 is started, the discharge current Ia flows through the discharge path 69, and the voltage of the first line 66a decreases. To do. The control device 6 checks the voltage drop of the first line 66a detected by the voltage detection circuit 67 after being cut off by the supply cut-off switch SWb (S12).

  Here, consider a case where a short circuit occurs between the first line 66a and the second line 66b as indicated by a two-dot chain line in FIG. FIG. 11 is a diagram illustrating a voltage drop in the first line 66a when the voltage supply is cut off. FIG. 11 shows the voltage change when the voltage supply is cut off (OFF) by the supply cut-off switch SWb at time t1, and the curve A shown by the solid line is the voltage change when there is no short circuit, the curve shown by the two-dot chain line B is a voltage change when there is a short circuit. When the voltage supply is cut off, the voltage of the first line 66a decreases in a curved manner due to the discharge of the capacitor C0. Furthermore, when there is a short circuit, the leakage current Ib flows through the short circuit point 75 when the capacitor C0 is discharged. Therefore, as shown in FIG. (Voltage drop speed) increases.

  Therefore, the control device 6 determines whether or not a short circuit has occurred between the first line 66a and the second line 66b based on the result of the voltage drop check of the first line 66a (S13). In the present embodiment, the control device 6 also serves as a “control unit” of the present invention that controls the switches SWa and SWb and a “determination unit” that determines the presence or absence of a short circuit.

  Hereinafter, examples of the determination method will be given. It is assumed that the data of the voltage drop curve A in FIG. 11 when there is no short circuit is stored in the ROM 71 of the control device 6 in advance. Then, the voltage detection value actually detected by the voltage detection circuit 67 is compared with the value of the voltage drop curve A, and if the difference is greater than or equal to a certain value, it is determined that a short circuit exists. Note that the voltage detection circuit 67 may detect the voltage a plurality of times within a predetermined time after the time t1, and use the voltage detection values for the plurality of times to determine the short circuit.

  Here, as described above, in the present embodiment, the path cut-off switch that can cut off the conduction path 68 to the conduction path 68 between the first line 66a and the second line 66b via the intermediate voltage generation circuit 65. SWa is provided. When a short circuit is detected between the first line 66a and the second line 66b, the conduction path 68 is blocked by the path cutoff switch SWa so that no current flows through the conduction path 68. As a result, the influence of the current flowing through the conduction path 68 can be eliminated, and even if the leakage current Ib flowing through the short-circuited point 75 is very small, the influence of the leakage current Ib (specifically, the leakage current) in the short-circuit determination of S13. It becomes easier to grasp the voltage drop due to Ib. Accordingly, the short circuit detection accuracy is improved.

  In the present embodiment, the presence / absence of a short circuit is detected based on the voltage drop of the first line 66a after the supply of the voltage of the first line 66a is cut off by the supply cut-off switch SWb. Further, in the present embodiment, the capacitor C0 for voltage stabilization is used for determining a short circuit between the first line 66a and the second line 66b. That is, when the voltage supply is cut off by the supply cut-off switch SWb, the voltage of the first line 66a gradually decreases as the capacitor C0 is discharged. Therefore, it becomes easy to discriminate the difference in voltage change between when there is a short circuit and when there is no short circuit, and the presence or absence of a short circuit can be easily detected.

  In S13, when the control device 6 determines that there is a short circuit between the first line 66a and the second line 66b, the control device 6 may, for example, Process. That is, the control device 6 displays the fact on the display device (not shown) of the printer 1. Alternatively, a signal indicating the occurrence of an abnormality is transmitted to an external device such as a PC.

  Next, modified embodiments in which various modifications are made to the embodiment will be described. However, components having the same configuration as in the above embodiment are given the same reference numerals and description thereof is omitted as appropriate.

1] The circuit configuration of the intermediate voltage generation circuit 65 is not limited to the configuration of FIG. For example, a third voltage may be generated using a Zener diode instead of the resistor R2 of FIG.

2] In the embodiment, the presence or absence of a short circuit is detected based on the voltage change of the first line 66a when the voltage supply from the power supply device 55 is cut off. On the other hand, it is also possible to detect the presence or absence of a short circuit based on the current change when the voltage supply from the power supply device 55 is interrupted. For example, in FIG. 9, when there is a short circuit between the first line 66a and the second line 66b, the leakage current Ib flows through the short-circuited portion 75, so that the discharge current Ia from the capacitor C0 is increased accordingly. Become. Accordingly, the current value of the discharge current Ia may be detected, and a short circuit may be determined based on the change over time.

3] In the above-described embodiment, the voltage supply from the power supply device 55 to the first line 66a is cut off by the supply cut-off switch SWb at the time of short circuit detection (S11 in FIG. 10), but the voltage supply is not cut off. Both can detect short circuits. For example, the current flowing through the first line 66a differs depending on whether or not there is a short circuit between the first line 66a and the second line 66b. Therefore, a current detection circuit using a Hall element, a resistor and an amplifier circuit is provided in the first line 66a, and the current flowing through the first line 66a is monitored by this current detection circuit, so that a short circuit can be prevented. The presence or absence can also be detected.

4] The configurations of the piezoelectric actuator 21 and the power feeding unit 61 are not limited to those of the above embodiment. That is, the present invention can be applied to any configuration in which the piezoelectric actuator 21 is supplied with an intermediate voltage between the first voltage V1 and the second voltage V2.

(A) For example, two or more types of intermediate voltages may be supplied from the intermediate voltage generation circuit to the piezoelectric actuator. The piezoelectric actuator 21A shown in FIG. 12 includes a piezoelectric body 40A composed of three piezoelectric layers 41A, 42A, and 43A, an individual electrode 44A, a first common electrode 45A, and a second common electrode 46A. The individual electrode 44A is disposed on the upper surface of the uppermost piezoelectric layer 41A. The first common electrode 45A is disposed between the uppermost piezoelectric layer 41A and the intermediate piezoelectric layer 42A. The second common electrode 46A is disposed between the intermediate piezoelectric layer 42A and the lowermost piezoelectric layer 43A. The individual electrode 44A and the first common electrode 45A are opposed to each other with the piezoelectric layer 41A (first active portion 51A) interposed therebetween. The individual electrode 44A and the second common electrode 46A are opposed to each other with the two piezoelectric layers 41A and 42A (second active portion 52A) interposed therebetween. The voltage of the individual electrode 44A is switched between the first voltage V1 and the second voltage V2. Further, a third voltage V3 and a fourth voltage V4, which are intermediate voltages between the first voltage V1 and the second voltage V2, are respectively applied to the first common electrode 45A and the second common electrode 46A (the voltage of the voltage). Large / small relationship: V1> V3> V4> V2).

  FIG. 13 is an equivalent circuit diagram of the piezoelectric actuator 21A of FIG. 12 and its power feeding unit 61A. The first active part 51A and the second active part 52A are equivalent to the capacitors C1 and C2, respectively. The intermediate voltage generation circuit 65A includes three resistors Ra, Rb, and Rc connected in series. The intermediate voltage generation circuit 65A divides the voltage between the first line 66a and the second line 66b, and outputs the third voltage V3 and the fourth voltage. A voltage V4 is generated. Note that a path cutoff switch SWa capable of blocking the conduction path 68A is provided between the resistance Rb and the resistance Rc. The point C voltage in FIG. 13, that is, the voltage of the individual electrode 44A is switched between the first voltage V1 and the second voltage V2 by the switches SW1 and SW2 of the driver IC 64A. The third voltage V3 generated by the intermediate voltage generation circuit 65A is applied to the point D in FIG. 13, that is, the first common electrode 45A. The fourth voltage V4 generated by the intermediate voltage generation circuit 65A is applied to the point E in FIG. 13, that is, the second common electrode 46A.

  In this configuration, when a short circuit between the first line 66a and the second line 66b is detected, the conduction path 68A passing through the intermediate voltage generation circuit 65A is blocked by the path cutoff switch SWa. This prevents current from flowing through the conduction path 68A and eliminates the influence on short circuit detection.

(B) In the embodiment, the first voltage V1 is the power supply voltage of the power supply device 55 and the second voltage V2 is the ground. However, the first voltage V1 and the second voltage V2 are the power supply voltage and the ground. Other voltages may be used.

(C) Further, the ejection drive unit that ejects ink from the nozzles 25 of the inkjet head 4 is not limited to the piezoelectric actuator. For example, the present invention can be applied to a system in which ink is heated by a heating element to give ejection energy to the ink.

5] In the above embodiment, the ASIC 73 of the control device 6 that controls the path cutoff switch SWa is configured to determine whether or not there is a short circuit. That is, the control device 6 also serves as a “control unit” and a “determination unit” of the present invention. On the other hand, the determination part which determines a short circuit may be provided separately from the control part. For example, in addition to the circuit board on which the switch control circuit for the path cutoff switch SWa is mounted, a circuit board on which a determination circuit for determining a short circuit is mounted may be provided.

6] The determination of a short circuit is not limited to the form performed in the printer. For example, in the embodiment, the information on the voltage change of the first line 66a detected by the voltage detection circuit 67 is sent to an external device such as a PC, and based on this information, the external device is connected to the first line 66a. You may determine the presence or absence of the short circuit between the 2nd lines 66b. In this case, it is not necessary to provide a short circuit determination circuit or the like in the printer. This form is particularly suitable for performing a short circuit determination by connecting the printer to a PC or the like in which a short circuit determination program is installed in a pre-shipment inspection of the printer.

  In the above-described embodiment and its modifications, the present invention is applied to an inkjet head that prints an image or the like by ejecting ink onto a recording sheet. The present invention can also be applied to a liquid ejection apparatus that is used. For example, the present invention can also be applied to a liquid ejection device that ejects a conductive liquid onto a substrate to form a conductive pattern on the substrate surface.

DESCRIPTION OF SYMBOLS 1 Inkjet printer 4 Inkjet head 6 Control apparatus 20 Flow path unit 21,21A Piezoelectric actuator 25 Nozzle 55 Power supply device 61, 61A Power supply part 65, 65A Intermediate voltage generation circuit 66a First line 66b Second line 67 Voltage detection circuit 68, 68A Conduction path C0 Capacitor SWa Path cutoff switch SWb Supply cutoff switch

Claims (6)

A channel structure in which a liquid channel including a nozzle is formed;
A discharge driving unit that is provided in the flow channel structure and discharges liquid from the nozzle;
A power feeding unit connected to the ejection driving unit,
The power feeding unit is
A first line to which a predetermined first voltage is applied;
A second line to which a predetermined second voltage lower than the first voltage is applied;
An intermediate voltage generator connected to the first line and the second line, respectively, for generating a third voltage between the first voltage and the second voltage to be supplied to the ejection driver; Have
A determination unit for determining whether a short circuit has occurred between the first line and the second line;
The power feeding unit is
When the determination unit determines a short circuit between the first line and the second line, provided in a conduction path between the first line and the second line via the intermediate voltage generation unit. A liquid discharge apparatus having a path cutoff switch capable of interrupting the conduction path. A voltage detector for detecting the voltage of the first line;
A control unit for controlling the operation of the path cutoff switch,
The determination unit is configured to control the path cutoff switch to cut off the conduction path, and then determine the first line and the first line based on a voltage change of the first line detected by the voltage detection unit. The liquid ejection apparatus according to claim 1, wherein a short circuit between the second lines is determined. A supply cut-off switch that cuts off the supply of the first voltage to the first line from the voltage generator that generates the first voltage;
The control unit controls the operation of the supply cutoff switch,
The determination unit
The control unit controls the path cut-off switch to cut off the conduction path, and then controls the supply cut-off switch to cut off the voltage supply from the voltage generation unit, and then detected by the voltage detection unit. The liquid ejection device according to claim 2, wherein a short circuit between the first line and the second line is determined based on a voltage change of the first line. The power supply unit includes a capacitor for voltage stabilization provided in parallel with the conduction path via the intermediate voltage generation unit between the first line and the second line.
The voltage detection unit detects a voltage drop from the first voltage of the first line when the supply of voltage to the first line is interrupted by the supply cutoff switch and the capacitor is discharged. The liquid ejection apparatus according to claim 3, wherein the liquid ejection apparatus is a liquid ejection device.   5. The short circuit determination by the determination unit is performed by blocking the conduction path by the path cut-off switch when the discharge driving unit does not discharge liquid from the nozzle. A liquid ejection apparatus according to claim 1. The liquid ejection apparatus according to claim 1, wherein a short circuit between the first line and the second line of the power feeding unit is detected.
It is determined whether or not a short circuit has occurred between the first line and the second line based on a voltage change of the first line after the conduction path is interrupted by the path cutoff switch. A short-circuit detection method.

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