Patent Description:
A liquid ejection head that supplies a predetermined amount of a liquid to a predetermined position is known. Such a liquid ejection head can be mounted in an inkjet printer, a 3D printer, a liquid dispensing device, or the like. An inkjet printer ejects ink droplets from an inkjet head to form an image on a surface of a recording medium. A 3D printer ejects droplets of a molding material from a molding material ejection head and the droplets are cured to form a three-dimensional molded object. A dispensing device ejects droplets of a sample liquid or solution to supply a predetermined amount of the sample liquid or solution to a plurality of different containers (e.g., wells of a well plate or the like).

A liquid ejection head typically includes a plurality of channels for ejecting liquid. Each channel includes a nozzle, a pressure chamber connected to the nozzle, and an actuator that changes a volume of the pressure chamber to eject liquid from the nozzle. The liquid ejection head selects a channel from among the available channels, and applies a drive signal to the actuator of the selected channel to drive the actuator. When the actuator is driven, the volume of the pressure chamber changes, and the liquid in the pressure chamber is ejected from the nozzle of the selected channel.

One terminal of the actuator is connected to an individual wiring that applies the drive voltage. The other terminal of the actuator is connected to a common wiring that applies a common potential to every actuator. It is desirable that the common potential be kept constant for every actuator. However, in reality, the applied common potential may not be constant across every actuator due to resistance in the common wiring. If the potential on the common wiring varies, ejection characteristics of the liquid may be adversely affected. Therefore, it can be necessary to measure the resistance of the common wiring so that the resistance of the common wiring can be kept to a low value.

<CIT> discloses a liquid ejection head with individual, common and monitoring wirings. The monitoring wirings can be used to check the output waveforms of the drive IC when the ink jet head is developed or malfunction thereof is analysed.

To this end, there is provided a liquid ejection head, liquid ejection apparatus and a method for producing thereof according to appended claims.

In general, a liquid ejection head in which resistance of a common wiring used to apply a common potential to a plurality of actuators can be measured is described.

According to one embodiment, a liquid ejection head includes a plurality of actuators on a substrate spaced from one another along a first direction. The actuators are between a first edge side of the substrate and a second edge side of the substrate in a second direction. A plurality of individual wirings is provided. Each individual wiring is connected to a first terminal of an actuator in the plurality of actuators and has a terminal portion at the first edge side of the substrate. A common wiring is provided with a first portion and a plurality of second portions. Each second portion is branched from the first portion in the second direction and individually connected to a second terminal of an actuator in the plurality of actuators. The first portion extends along the first direction on the second edge side of the substrate and has a first end terminal and a second end terminal spaced from each other in the first direction. A monitor terminal is provided at a position between the first and second end terminals of the first portion in the first direction. The monitor terminal extends in the second direction from the first edge side of the substrate toward the first portion. The monitor terminal is electrically connected to the first portion.

Hereinafter, a liquid ejection head according to certain example embodiments will be described with reference to the accompanying drawings. In the drawings, the same elements, aspects, or components are denoted by the same reference symbols.

An inkjet printer <NUM> that can be equipped with a liquid ejection head according to an embodiment will be described as an example. <FIG> illustrates a schematic configuration of the inkjet printer <NUM>. In the inkjet printer <NUM>, a cassette <NUM> in which a sheet S can be stored, an upstream conveyance path <NUM> of the sheet S, a conveyance belt <NUM> that conveys the sheet S from the cassette <NUM>, a plurality of inkjet heads (<NUM>, <NUM>, <NUM>,<NUM>) that eject ink droplets toward the sheet S on the conveyance belt <NUM>, a downstream conveyance path <NUM> of the sheet S, and a control board <NUM> are disposed inside a housing <NUM>. A discharge tray <NUM> is also provided. An operation unit <NUM>, which is a user interface, is provided at an upper portion side of the housing <NUM>.

Image data to be printed on the sheet S is generated by, for example, a computer <NUM> that is an externally connected device. The image data generated by the computer <NUM> is transmitted to the control board <NUM> of the inkjet printer <NUM> through a cable <NUM> and connectors <NUM> and <NUM>.

A pickup roller <NUM> supplies the sheets S one by one from the cassette <NUM> to the upstream conveyance path <NUM>. The upstream conveyance path <NUM> includes feed roller pairs <NUM> and <NUM>, and sheet guide plates <NUM> and <NUM>. The sheet S is conveyed to an upper surface of the conveyance belt <NUM> via the upstream conveyance path <NUM>. An arrow <NUM> in the drawing indicates a conveyance path of the sheet S from the cassette <NUM> to the conveyance belt <NUM>.

The conveyance belt <NUM> is a mesh-like endless belt having a large number of through holes formed on a surface thereof. Three rollers, that is, a drive roller <NUM> and driven rollers <NUM> and <NUM>, rotatably support the conveyance belt <NUM>. A motor <NUM> rotates the conveyance belt <NUM> by rotating the drive roller <NUM>. In the drawing, an arrow <NUM> indicates a rotation direction of the conveyance belt <NUM>. A negative pressure container <NUM> is disposed on a back surface side of the conveyance belt <NUM>. The negative pressure container <NUM> is connected to a pressure reducing fan <NUM>. The fan <NUM> produces an airflow to cause an inside of the negative pressure container <NUM> to have a negative pressure relative to atmospheric pressure and causes the sheet S to be held on the upper surface of the conveyance belt <NUM> by a suction force. In the drawing, an arrow <NUM> denotes a flow of the airflow.

The inkjet heads <NUM> to <NUM>, each of which is an example of a liquid ejection head, are disposed so as to face the sheet S on the conveyance belt <NUM> with a slight gap of, for example, <NUM> therebetween. The inkjet heads <NUM> to <NUM> each eject ink droplets toward the sheet S. The inkjet heads <NUM> to <NUM> can thus print an image on the sheet S when the sheet S passes below. The inkjet heads <NUM> to <NUM> have the same structure with the difference being that respective inks to be ejected by each have different colors from one another. The colors of the inks are, for example, cyan, magenta, yellow, and black.

The inkjet heads <NUM> to <NUM> are connected to ink tanks (<NUM>, <NUM>, <NUM>, <NUM>) and ink supply pressure adjusting devices (<NUM>, <NUM>, <NUM>, <NUM>) via ink flow paths (<NUM>, <NUM>, <NUM>,<NUM>). The ink tanks <NUM> to <NUM> are disposed above the inkjet heads <NUM> to <NUM>, respectively. During standby, in order to prevent ink from leaking from nozzles <NUM> (see <FIG>) of the inkjet heads <NUM> to <NUM>, the ink supply pressure adjusting devices <NUM> to <NUM> respectively adjust pressure inside of the inkjet heads <NUM> to <NUM> to a negative pressure (with respect to atmospheric pressure), for example, -<NUM> kPa. At the time of image formation processes, the ink in the respective ink tanks <NUM> to <NUM> are supplied to the respective inkjet heads <NUM> to <NUM> by the respective ink supply pressure adjusting devices <NUM> to <NUM>.

After the image formation, the sheet S is fed from the conveyance belt <NUM> to the downstream conveyance path <NUM>. The downstream conveyance path <NUM> includes feed roller pairs <NUM>, <NUM>, <NUM>, and <NUM>, and sheet guide plates <NUM> and <NUM> that define a conveyance path of the sheet S. The sheet S passes through the downstream conveyance path <NUM> and is fed from a discharge port <NUM> to the discharge tray <NUM>. An arrow <NUM> in the drawing indicates a conveyance path of the sheet S.

Next, a configuration of the inkjet heads <NUM> to <NUM> will be described. The inkjet head <NUM> is described with reference to <FIG>, the inkjet heads <NUM> to <NUM> have the same structure as the inkjet head <NUM>.

As illustrated in <FIG>, the inkjet head <NUM> includes a head portion <NUM> that is an example of a liquid ejection portion. The head portion <NUM> includes a nozzle plate <NUM>, an actuator substrate <NUM>, and an ink supply portion <NUM>. The ink supply portion <NUM> is connected to the ink supply pressure adjusting device <NUM> (see <FIG>) via the ink flow path <NUM>. The actuator substrate <NUM> of the head portion <NUM> is connected to a flexible printed wiring board <NUM> that is, for example, a film-based wiring board. The flexible printed wiring board <NUM> in this example is connected to a printed circuit board <NUM>, which may serve as a relay board.

On the flexible printed wiring board <NUM> an integrated circuit (IC) <NUM> is mounted. IC <NUM> is used for driving of ink ejections and may be referred to as a driver chip <NUM> or a driving IC <NUM>. In other examples, the driving IC <NUM> may be mounted on a substrate different from the flexible printed wiring board <NUM> and connected to the flexible printed wiring board <NUM> rather than directly mounted thereon. The driving IC <NUM> temporarily stores print data from the control board <NUM> of the inkjet printer <NUM> that has been sent via the printed circuit board <NUM>. The driving IC <NUM> functions as a control unit and gives a drive signal to each channel so as to eject an ink at a predetermined timing in manner corresponding to the print (image) data or the like.

The nozzle plate <NUM>, which is an example of a nozzle portion, is a rectangular plate formed of, for example, a resin such as polyimide or a metal such as stainless steel. The nozzles <NUM> of the channels are arranged along a longitudinal direction (X direction) of the nozzle plate <NUM>. A nozzle density is set within a range of, for example, <NUM> dpi to <NUM> dpi.

The actuator substrate <NUM> is, for example, a rectangular substrate made of insulating ceramics. As illustrated in <FIG>, pressure chambers <NUM> and air chambers <NUM> are alternately formed with one another in the actuator substrate <NUM> along a first direction, for example, the X direction. Each pressure chamber <NUM> communicates with a corresponding nozzle <NUM>. Each pressure chamber <NUM> communicates with the ink supply portion <NUM> via a common ink chamber formed in the actuator substrate <NUM>, for example. The air chambers <NUM> disposed adjacently to the pressure chambers <NUM> are, for example, closed spaces that do not communicate with a nozzle <NUM> or the common ink chamber. The pressure chambers <NUM> and the air chambers <NUM> are formed by cutting out portions of two piezoelectric members <NUM> stacked on the actuator substrate <NUM> with opposite polarization directions (for example, facing directions), in a rectangular groove shape extending lengthwise in a second direction such as a Z direction. That is, the pressure chamber <NUM> and the air chamber <NUM> are partitioned from each other by remaining portions of the two piezoelectric members <NUM>. The two piezoelectric members <NUM> are stacked on each other in a third direction, for example, a Y direction. The remaining portions of the two piezoelectric members <NUM> left after the cutting out of the rectangular groove shapes which may be referred to as side walls in some instances.

An electrode <NUM> is formed on a bottom surface and both side surfaces of the groove-shaped pressure chamber <NUM>. The electrode <NUM> of each pressure chamber <NUM> is connected to an individual wiring <NUM> (also referred to as a wiring electrode <NUM>). The electrode <NUM> is formed on a bottom surface and both side surfaces of the groove-shaped air chamber <NUM>. The electrode <NUM> of each air chamber <NUM> is connected to a common wiring <NUM> (also referred to as a wiring electrode <NUM>). That is, a connection point between an electrode <NUM> of a pressure chamber <NUM> and individual wiring <NUM> is one terminal of one actuator <NUM>. A connection point between the electrode <NUM> of the air chamber <NUM> and the common wiring <NUM> is the other terminal of the actuator <NUM>. The individual wiring <NUM> is connected to a drive circuit D ("driver D") of the driving IC <NUM>. The driver D for each channel applies a drive voltage V1 as a drive signal to the corresponding actuator <NUM> of the channel to independently drive the actuator <NUM>. The common wiring <NUM> is connected to, for example, the ground (GND). With this configuration, an electric field is applied in a direction intersecting (desirably, orthogonal to) a polarization axis of the piezoelectric member <NUM> in the actuator <NUM>, and the piezoelectric member <NUM> portion that is a side wall of the pressure chamber <NUM> is deformed symmetrically in the X direction in a shear mode.

That is, the pressure chamber <NUM> for ink is formed sandwiched between a pair of columnar actuators <NUM>. A potential difference is applied to both walls of the columnar actuator <NUM>, that is, an inner wall and an outer wall of the pressure chamber <NUM>, and the actuator <NUM> is deformed by being charged. Accordingly, a volume of the pressure chamber <NUM> is changed, and as a result, an ink pressure in the pressure chamber <NUM> is changed. By adjusting a magnitude and a timing of this pressure/volume change, ink can be ejected from the nozzle <NUM>.

<FIG> is a plan view of the actuator substrate <NUM>, the flexible printed wiring board <NUM>, and the printed circuit board <NUM> before being connected to each other. <FIG> is a partially enlarged view of the actuator substrate <NUM>. <FIG> is a plan view illustrating the substrates <NUM>, <NUM>, and <NUM> connected to each other. <FIG> is a side view illustrating the substrates <NUM>, <NUM>, and <NUM> when connected to each other.

The actuator substrate <NUM> and the flexible printed wiring board <NUM> are connected such that respective terminal portions <NUM> and <NUM> overlap each other. The flexible printed wiring board <NUM> and the printed circuit board <NUM> are connected such that respective terminal portions <NUM> and <NUM> overlap each other.

As described above, an actuator <NUM> has an individual wiring <NUM> (wire) connected to one terminal thereof. A plurality of individual wirings <NUM> (wires) thus are led out from the respective actuators <NUM> and formed up (gathered together) at the terminal portion <NUM> at one edge of the actuator substrate <NUM>. The one edge of the actuator substrate <NUM> is the edge of the substrate on a side to which the flexible printed wiring board <NUM> is connected. In the terminal portion <NUM>, the individual wirings <NUM> are formed in parallel at equal intervals, for example.

The common wiring <NUM> in this example includes a first wiring portion <NUM> and several second wiring portions <NUM>. The first wiring portion <NUM> and the second wiring portion <NUM> are disposed on a side opposite to the terminal portion <NUM> as viewed from the actuator <NUM> so as not to intersect with the individual wiring <NUM>. The first wiring portion <NUM> is formed along an arrangement direction of the actuators <NUM> on the other edge side of the actuator substrate <NUM> and is formed up at the terminal portion <NUM> by folding back both sides, for example, both end portions in the arrangement direction of the actuators <NUM> in a direction intersecting the arrangement direction of the actuators <NUM>. Therefore, in the terminal portion <NUM>, a pair of terminals led out from both end portions of the first wiring portion <NUM> are positioned symmetrically at both sides of the substrate. The direction intersecting the arrangement direction of the actuators <NUM> is, for example, a direction orthogonal to the arrangement direction of the actuators <NUM>. The plurality of second wiring portions <NUM> branched from the first wiring portion <NUM> are formed along the direction intersecting the arrangement direction of the actuators <NUM>, and each second wiring portion <NUM> is connected to the other terminal of the corresponding actuator <NUM>.

A monitor terminal <NUM> is disposed on the side to which the flexible printed wiring board <NUM> is connected. The monitor terminal <NUM> is connected to the first wiring portion <NUM> of the common wiring <NUM> and is used when measuring resistance of the first wiring portion <NUM>. As an example, the monitor terminal <NUM> is formed in a wire shape and passes between a pair of otherwise adjacent individual wirings <NUM>. The monitor terminal <NUM> is connected to the first wiring portion <NUM> at a position between adjacent actuators <NUM>. In the illustrated example, a portion of the monitor terminal <NUM> is formed by an electrode <NUM> (see <FIG>) of an air chamber <NUM> and another portion is formed by a second wiring portion <NUM>. That is, the monitor terminal <NUM> is led out by using the electrode <NUM> of an air chamber <NUM> to be connected to the first wiring portion <NUM> across the arrangement of the actuators <NUM> without intersecting with other wirings such as the individual wirings <NUM> and the second wiring portion <NUM> of another channel. In a case of a head structure in which the air chambers <NUM> are not provided, the monitor terminal <NUM> may be an independent wiring connected to the first wiring portion <NUM>.

The monitor terminal <NUM> is formed at a position corresponding to a midpoint or the like along a length direction of the first wiring portion <NUM> extending along the arrangement direction of the actuators <NUM>. Preferably, the position is where the first wiring portion <NUM> is symmetrically divided into two different parts. The number of monitor terminals <NUM> is not necessarily limited to just one at the midpoint position, and a plurality of monitor terminals <NUM> may be provided using electrodes of a plurality of air chambers <NUM>. By increasing the number of monitor terminals <NUM>, electrode resistance can be managed or tracked more finely. Further, as a preferable example, an interval between individual wirings <NUM> adjacent to the monitor terminal <NUM> and the interval between adjacent individual wirings <NUM> is adjusted so that pitches P of the terminals in the terminal portion <NUM> are equal (see <FIG>). With this arrangement, the monitor terminal <NUM> and an electrostatic capacitance measurement terminal, which will be described later, are arranged at equal intervals, and thus there is an advantage that batch probing can be facilitated.

The individual wirings <NUM>, the first wiring portion <NUM>, the second wiring portions <NUM>, and the monitor terminal(s) <NUM> are formed of, for example, nickel, aluminum, gold, or an alloy thereof in a thin film shape. A wiring width of the individual wirings <NUM>, the second wiring portions <NUM>, and the monitor terminal(s) <NUM> can be selected from a range of, for example, <NUM> to <NUM>. Since the first wiring portion <NUM> needs to supply charging and discharging currents to all the actuators <NUM>, a wiring width of the first wiring portion <NUM> is larger than that of the individual second wiring portions <NUM>. The wiring width of the first wiring portion <NUM> is, for example, <NUM>. A thickness of the individual wirings <NUM>, the first wiring portion <NUM>, the second wiring portions <NUM>, and the monitor terminal(s) <NUM> is, for example, <NUM>. In order to ensure electrical insulation (separation), an insulating layer, an insulating material, or the like may be provided in regions outside the terminal portion <NUM>.

The flexible printed wiring board <NUM> is a flexible printed wiring board comprising, for example, a synthetic resin film of polyimide. The driving IC <NUM> is, for example, a driver chip formed on a silicon semiconductor substrate. Output wirings <NUM>, input wirings <NUM>, a power supply wiring <NUM> for the voltage V1, a ground wiring <NUM>, and common passing wirings <NUM> are formed on the flexible printed wiring board <NUM>. The wirings <NUM> to <NUM> and the driving IC <NUM> are preferably formed on one surface of the flexible printed wiring board <NUM>. As an example, the flexible printed wiring board <NUM> is formed using a chip on film (COF) technique. The output wirings <NUM> led out from the driving IC <NUM> are formed up at the terminal portion <NUM>. The output wirings <NUM> are individual wirings formed on the flexible printed wiring board <NUM>. The number of output wirings <NUM> is, for example, the same as the number of the individual wirings <NUM> on the actuator substrate <NUM> side.

The common passing wiring <NUM> is formed from the terminal portion <NUM> on a side to which the actuator substrate <NUM> is connected, to the terminal portion <NUM> on a side to which the printed circuit board <NUM> is connected. The common passing wirings <NUM> are formed in pairs on both sides of the substrate to reduce a voltage drop occurring in the first wiring portion <NUM> during driving. The common passing wirings <NUM> are respectively connected to terminals of the first wiring portion <NUM> that are formed in a pair on the terminal portion <NUM> of the actuator substrate <NUM>.

The input wirings <NUM> led out from the driving IC <NUM> are formed up at the terminal portion <NUM> on a side to which the printed circuit board <NUM> is connected. Since the driving IC <NUM> can be controlled by serial communication, the number of the input wirings <NUM> can be less than the number of the output wirings <NUM>.

The power supply wiring <NUM> and the ground wiring <NUM> are connected to the driving IC <NUM>. The power supply wiring <NUM> and the ground wiring <NUM> are formed up at the terminal portion <NUM> on the side to which the printed circuit board <NUM> is connected. The output wirings <NUM>, the input wirings <NUM>, the power supply wiring <NUM>, the ground wiring <NUM>, and the common passing wiring <NUM> are formed of, for example, copper thin film.

The printed circuit board <NUM> is a hard substrate (e.g., inflexible substrate). The printed circuit board <NUM> in this example permits through holes to be formed in the substrate material. The substrate material in this example comprises one or more epoxy resin layer containing glass fibers with one or more copper wiring layers laminated together in multiple layers. Output wirings <NUM>, a power supply wiring <NUM>, and a ground wiring <NUM> are formed in a terminal portion <NUM>. The output wirings <NUM> are connected to the input wirings <NUM> of the flexible printed wiring board <NUM>. The power supply wiring <NUM> is connected to the power supply wiring <NUM> of the flexible printed wiring board <NUM>. The ground wiring <NUM> is connected to the ground wiring <NUM> and the common passing wiring <NUM> of the flexible printed wiring board <NUM>. Signals for selectively driving the actuators <NUM>, which are sent from the control board <NUM> of the inkjet printer <NUM>, are supplied to the output wirings <NUM>. The drive voltage V1 is applied to the power supply wiring <NUM>. The ground wiring <NUM> is connected to the ground (GND) by, for example, the control board <NUM> of the inkjet printer <NUM>.

In particular, as illustrated in <FIG>, the terminal portion <NUM> of the actuator substrate <NUM> and the terminal portion <NUM> of the flexible printed wiring board <NUM> can be connected via an anisotropic conductive film (ACF) <NUM>. That is, the terminal portion <NUM> of the actuator substrate <NUM> and the terminal portion <NUM> of the flexible printed wiring board <NUM> are arranged so as to face each other, the ACF <NUM> is interposed therebetween, and the wirings of the terminal portions <NUM> and <NUM> are collectively connected by thermocompression bonding using, for example, a thermocompression bonding tool. Accordingly, the individual wirings <NUM> and the output wirings <NUM>, and the common wiring <NUM> and the common passing wiring <NUM> can be electrically connected to each other. The flexible printed wiring board <NUM> and the printed circuit board <NUM> are connected in the same manner.

<FIG> is a configuration diagram of a resistance measurement circuit <NUM> that measures the resistance of the first wiring portion <NUM> of the common wiring <NUM>. The measurement of the resistance is performed on the actuator substrate <NUM> before the flexible printed wiring board <NUM> is connected, for example, during a manufacturing process of the inkjet head <NUM>. As illustrated in <FIG>, probes <NUM> are used to measure the resistance of the first wiring portion <NUM>. A plurality of probes <NUM> can be used to measure resistance at the first wiring portion <NUM>, and one or more of the monitor terminal <NUM> arranged in the terminal portion <NUM>.

The resistance of the first wiring portion <NUM> can be measured using a four-terminal method. In the resistance measurement circuit <NUM>, the probes <NUM> connected to a current source <NUM> are connected to different ends of the first wiring portion <NUM> as the "Terminal <NUM>" and the "Terminal <NUM>", respectively. A voltage detection circuit <NUM> is connected to "Terminal <NUM>" of the first wiring portion <NUM> and the monitor terminal <NUM>. A voltage detection circuit <NUM> is connected to "Terminal <NUM>" of the first wiring portion <NUM> and the monitor terminal <NUM>. In <FIG>, two probes <NUM> connected to the current source <NUM> are used as a set to cause a predetermined current to flow.

In the measurement of the resistance of the first wiring portion <NUM>, a predetermined current from the current source <NUM> is caused to flow from "Terminal <NUM>" to the "Terminal <NUM>" of the first wiring portion <NUM>, and the current is measured. The "Terminal <NUM>" and "Terminal <NUM>" are led out from opposite ends of the first wiring portion <NUM> in order to prevent a voltage drop that can be caused by current concentration when many actuators <NUM> are simultaneously driven during printing, and this configuration is also used in the measurement of the resistance.

At the same time, a voltage (first detection voltage) between the "Terminal <NUM>" and the "Terminal <NUM>" is measured. "Terminal <NUM>" connects to the first wiring portion <NUM> in close proximity to the "Terminal <NUM>", and "Terminal <NUM>" connects to the monitor terminal <NUM>. Terminal <NUM> and Terminal <NUM>" are current-supplying terminals of a four terminal method. "Terminal <NUM> and "Terminal <NUM>" are voltage detection terminals. At the same time, a voltage (second detection voltage) between the "Terminal <NUM>" and the "Terminal <NUM>" of the first wiring portion <NUM> is measured. The "Terminal <NUM>" is connected to the wiring <NUM> in proximity to the Terminal <NUM>. "Terminal <NUM>" and "Terminal <NUM>" are current-supply terminals of the four terminal method. "Terminal <NUM>" and "Terminal <NUM>" are voltage detection terminals. In accordance with Ohm's law, a value obtained by dividing the detection first detection voltage by the current flow value is equal to the resistance value of a half of the first wiring portion <NUM> (on the left side of the drawing), a value obtained by dividing the second detection voltage by the current flow value is the resistance value of a half of the first wiring portion <NUM> (on the right side of the drawing), and a value obtained by dividing a sum of the first detection voltage and the second detection voltage by the current flow value is the resistance value of the entire first wiring portion <NUM>. If the number of available monitor terminals <NUM> is increased, the distribution of the wiring resistances along the first wiring portion <NUM> can be determined in more detail. It is preferable to manage the wiring forming processes in the manufacturing process so that these resistance values for different portions of the first wiring portion <NUM> fall within some predetermined range of values.

As described with reference to <FIG>, one terminal of each actuator <NUM> is connected to the individual wiring <NUM>, and each actuator <NUM> is independently driven by the corresponding driver D of the driving IC <NUM>. The other terminal of each actuator <NUM> is connected to a common potential via the common wiring <NUM> (<NUM>, <NUM>). When the common potential is constant for each actuator <NUM>, a net voltage applied to each actuator <NUM> can be individually controlled for each channel according to an output waveform of each driver D connected to the individual wiring <NUM> without adjustment/compensation.

However, in reality, since the common wiring <NUM> (or sub-portions <NUM> thereof) unavoidably has resistance, the current flow through the common wiring <NUM> varies when driving different actuators <NUM>. In particular, the resistance of the first wiring portion <NUM> causes a voltage drop when charging and discharging currents from the actuators <NUM> are concentrated. Since the voltage drop changes depending on which channel is being driven, a phenomenon called crosstalk in which ejection characteristics of each channel change depending on a printing pattern may occur in the inkjet head <NUM>, and the printing quality deteriorates. In order to prevent this, it is generally necessary to keep the resistance of the first wiring portion <NUM> to a low value. For the management of this phenomenon, it is generally necessary to measure certain resistance values in the inkjet head <NUM>.

In addition, the resistance of the first wiring portion <NUM> may not be formed uniformly due to manufacturing issues along its length or at each position. For example, when the common wiring <NUM> (<NUM>, <NUM>) is formed by wet chemical plating, depending on a state of a plating layer, there may be a place where the plating is thicker and the resistance is lower and a place where the plating is thinner and the resistance is higher. Therefore, it is desirable to understand or measure the actual distribution of the resistances within or along the first wiring portion <NUM>.

The monitor terminal <NUM> is prepared to be connectable. By measuring a voltage waveform at the monitor terminal <NUM> during driving, it is possible to confirm how much the voltage drop is caused by the resistance of the first wiring portion <NUM>, which affects a net waveform applied to an actuator <NUM>.

Further, as illustrated in <FIG>, a monitor terminal <NUM> and a monitor pad <NUM> may be provided on the flexible printed wiring board <NUM>, and the monitor terminal <NUM> of the actuator substrate <NUM> and the monitor terminal <NUM> may be connected by the ACF <NUM>. This is because if the monitor pad <NUM> is provided on the flexible printed wiring board <NUM>, probing for confirming the net waveform is easier. In order to prevent a short circuit in a normal state, the monitor pad <NUM> may be normally covered with a resist material (insulating material) formed on the flexible printed wiring board <NUM>. In this case, when confirming the net waveform, the resist material may be peeled off to achieve contact with the monitor pad <NUM>. In addition, it is possible to track aspects related to the process of manufacturing the inkjet head <NUM>.

The measurement circuit depicted in <FIG> can also measures or detect whether each actuator <NUM> is normal. For example, a capacitance measurement circuit <NUM> can be used to measure a capacitance of each actuator <NUM> by measuring a waveform of a current flowing through each probe <NUM> when a predetermined voltage waveform is being applied via the probe <NUM>-<NUM>. The probe <NUM>-<NUM> connects each the individual wirings <NUM> individually to the capacitance measurement circuit <NUM>. Then, based on the measured capacitances, it can be determined whether each actuator <NUM> is normal and/or whether a wiring pattern for each individual wiring <NUM> is normal. If the probe <NUM>-<NUM> and the probes <NUM>-<NUM> to <NUM>-<NUM> are integrally configured so that probing can be performed collectively, both the resistance measurement of the first wiring portion <NUM> and the capacitance measurement of the actuators <NUM> can be performed by switching tested circuits during probing or changing positioning of probes <NUM>, and inspection time can be shortened. In this case, the monitor terminal <NUM> of the first wiring portion <NUM> is used in measuring the resistance of the first wiring portion <NUM>, and the capacitance of an actuator <NUM> can be measured between each individual wiring <NUM> and at least one of "Terminal <NUM>" or "Terminal <NUM>" of the first wiring portion <NUM> or the monitor terminal <NUM>. When the resistance measurement of the first wiring portion <NUM> and the capacitance measurements of the actuators <NUM> are performed at the same time, the measurement time can be further shortened. But when the resistance measurement and the capacitance measurement are separately performed by switching circuits, a measurement results are typically more accurate.

According to the above-described embodiment, by providing the monitor terminal <NUM> on the actuator substrate <NUM>, it is possible to measure the resistance of the first wiring portion <NUM> that applies a common potential to the plurality of actuators <NUM>.

The inkjet head <NUM> is not limited to a inkjet head with a single row of actuators. For example, as shown in <FIG>, the inkjet head <NUM> may have two rows of actuators. In the case of the inkjet head <NUM> including two rows of actuators, the first wiring portion <NUM> is between the two rows of actuators.

The inkjet head <NUM> is not limited to the shear-mode actuator <NUM> in which the pressure chamber <NUM> and the air chamber <NUM> are alternately arranged. For example, a plurality of nozzles <NUM> and a plurality of actuators <NUM> may be arranged on a surface of the nozzle plate <NUM>. In addition, an actuator <NUM> of a drop-on-demand piezo type may be used.

In an embodiment, the inkjet head <NUM> of the inkjet printer <NUM> is described as an example of a liquid ejection device, in other examples the liquid ejection device of the present disclosure may be a molding material ejection head of a 3D printer or a sample ejection head of a dispensing device.

Claim 1:
A liquid ejection head, comprising:
a plurality of actuators (<NUM>) on a substrate (<NUM>) spaced from one another along a first direction, the plurality of actuators being between a first edge side of the substrate and a second edge side of the substrate in a second direction;
a plurality of individual wirings (<NUM>), each individual wiring being connected to a first terminal of an actuator in the plurality of actuators and having a terminal portion at the first edge side of the substrate;
a common wiring (<NUM>) including a first portion (<NUM>) and a plurality of second portions (<NUM>), each second portion being branched from the first portion in the second direction and individually connected to a second terminal of an actuator in the plurality of actuators, the first portion extending along the first direction on the second edge side of the substrate and having a first end terminal and a second end terminal spaced from each other in the first direction; and
a monitor terminal (<NUM>) at a position between the first and second end terminals of the first portion in the first direction, the monitor terminal extending in the second direction from the first edge side of the substrate toward the first portion;
characterised by the monitor terminal being electrically connected to the first portion.