Patent Description:
The present disclosure relates to a head unit and a liquid ejection apparatus.

As a method of discriminating a nozzle state of a printing apparatus, a method of detecting residual vibration has been known (see <CIT>).

In the technique described in <CIT>, when a residual vibration signal as an analog waveform detected in a head is transmitted to a control unit, the residual vibration signal needs to be transmitted from the head to an AD converter. However, in a process of the transmission, noise may be superimposed on the analog waveform of the residual vibration signal.

To solve the above-described problem, a head unit according to an aspect includes a piezoelectric element displaced according to a driving signal to cause a liquid to be ejected, a driving signal generation unit that generates the driving signal, a residual vibration signal generation circuit that outputs a change in an electromotive force of the piezoelectric element according to residual vibration, in a pressure chamber in communication with a nozzle, that occurs after supply of the driving signal, as a residual vibration signal, an analog differential residual vibration signal generation circuit that converts the residual vibration signal into an analog differential residual vibration signal, a demodulation circuit that demodulates the analog differential residual vibration signal and outputs a demodulated signal, an AD converter that converts the demodulated signal into a digital signal, and a determination unit that determines, based on the digital signal, a state in the pressure chamber.

To solve the above-described problem, a liquid ejection apparatus according to an aspect includes a transport mechanism and the above head unit.

Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings.

Hereinafter, a liquid ejection apparatus of the embodiment of the present disclosure will be described in detail. The present embodiment is merely an example and should not limit the interpretation of the contents of the present disclosure. Hereinafter, the present embodiment will be described by using an ink jet printer that ejects ink to print an image on recording paper, as an example of a liquid ejection apparatus. Ink is an example of a liquid material. Recording paper is an example of a droplet receiving body.

<FIG> is a schematic view illustrating a configuration of an ink jet printer <NUM>, which is a type of a liquid ejection apparatus, in the embodiment. Note that in the following description, in <FIG>, an upper side is referred to as an upper portion and a lower side is referred to as a lower portion. First, the configuration of the ink jet printer <NUM> will be described. The ink jet printer <NUM> illustrated in <FIG> includes an apparatus main body <NUM> and is provided with a tray <NUM> on which recording paper P is installed on a rear side of an upper portion, a paper discharge port <NUM> to which the recording paper P is discharged on a front side of a lower portion, and an operation panel <NUM> on an upper surface.

The operation panel <NUM> is configured with, for example, a liquid crystal display, an organic electroluminescence (EL) display, a light emitting diode (LED) lamp, or the like and includes a display portion (not illustrated) that displays an error message or the like and an operation portion (not illustrated) configured with various switches. The display portion of the operation panel <NUM> functions as a notification unit. In addition, the apparatus main body <NUM> mainly includes thereinside a printing apparatus <NUM> including a printing unit <NUM> that is a moving body configured to reciprocate, a paper feeding apparatus <NUM> that feeds and discharges the recording paper P to and from the printing apparatus <NUM>, and a control unit <NUM> that controls the printing apparatus <NUM> and the paper feeding apparatus <NUM>.

The paper feeding apparatus <NUM> intermittently sends the recording paper P one by one by control of the control unit <NUM>. The recording paper P passes near an area under the printing unit <NUM>. At this time, the printing unit <NUM> reciprocates in a direction substantially orthogonal to a direction of sending the recording paper P and performs printing on the recording paper P. That is, the reciprocating of the printing unit <NUM> and the intermittent sending of the recording paper P are main scanning and sub-scanning during printing so as to perform ink jet-type printing.

The printing apparatus <NUM> includes the printing unit <NUM>, a carriage motor <NUM> serving as a driving source that causes the printing unit <NUM> to move such that the printing unit <NUM> reciprocates in the main scanning direction, and a reciprocating mechanism <NUM> that causes the printing unit <NUM> to reciprocate upon receiving rotation of the carriage motor <NUM>. The printing unit <NUM> includes a plurality of head units <NUM>, ink cartridges (I/C) <NUM> that supply ink to the respective head units <NUM>, and a carriage <NUM> on which the head units <NUM> and the ink cartridges <NUM> are mounted. Note that in the case of an ink jet printer that consumes a large amount of ink, the ink cartridges <NUM> may not be mounted on the carriage <NUM> and may be installed in other locations and configured to be in communication with the head units <NUM> via tubes so that the ink is supplied (not illustrated).

Note that full color printing is made possible through using of cartridges filled with four colors of ink of yellow, cyan, magenta, and black, as the ink cartridge <NUM>. In this case, the head units <NUM> corresponding to the respective colors are provided in the printing unit <NUM>. Here, four ink cartridges <NUM> corresponding to four colors of ink are illustrated in <FIG>, but the printing unit <NUM> may be configured to further include the ink cartridges <NUM> for other colors such as light cyan, light magenta, dark yellow, and special colors, for example.

<FIG> is an exploded schematic perspective view illustrating the configuration of each head unit <NUM>. As illustrated in <FIG>, the head unit <NUM> in the embodiment is schematically configured with a nozzle plate <NUM>, a flow channel substrate <NUM>, a common liquid chamber substrate <NUM>, a compliance substrate <NUM>, and the like and is attached to a unit case <NUM> in a state in which the members described above are laminated.

The nozzle plate <NUM> is a plate-shaped member in which a plurality of nozzles <NUM> are arranged in rows at a pitch corresponding to a dot forming density. For example, a nozzle row is formed of three hundred nozzles <NUM> arranged in rows at a pitch corresponding to <NUM> dpi. In the embodiment, two nozzle rows are formed in the nozzle plate <NUM>. Here, the two nozzle rows are formed while being shifted by a half of a pitch between the nozzles <NUM> in a direction in which the nozzles <NUM> are arranged. The nozzle plate <NUM> is formed of, for example, a glass ceramic material, a silicon single crystal substrate, stainless steel, or the like.

The flow channel substrate <NUM> is formed through thermal oxidation of a very thin elastic film <NUM> made of silicon dioxide on a surface on a common liquid chamber substrate <NUM> side, which is an upper surface of the flow channel substrate <NUM>. In the flow channel substrate <NUM>, a plurality of cavities <NUM>, which are defined by a plurality of partition walls by an anisotropic etching process, are formed correspondingly to the respective nozzles <NUM>. The cavities <NUM> are illustrated in <FIG>. Therefore, the cavities <NUM> are also formed in rows and are shifted by a half of a pitch between the nozzles <NUM> in the direction in which the nozzles <NUM> are arranged. A communication hollow portion <NUM> is formed outside a row of the cavities <NUM> in the flow channel substrate <NUM>. The communication hollow portion <NUM> is in communication with the cavities <NUM>.

In addition, for each cavity <NUM> in the flow channel substrate <NUM>, a piezoelectric element <NUM> for deforming the elastic film <NUM> to pressurize ink in the cavity <NUM> is formed.

On the flow channel substrate <NUM> in which the piezoelectric element <NUM> is formed, the common liquid chamber substrate <NUM> having a penetrating hollow portion 26a that penetrates the common liquid chamber substrate <NUM> in a thickness direction is disposed. Examples of the material of the common liquid chamber substrate <NUM> include glass, a ceramic material, metal, resin, or the like, and for example, the common liquid chamber substrate <NUM> may be formed of a material having substantially the same thermal expansion coefficient as the flow channel substrate <NUM>. For example, the common liquid chamber substrate <NUM> may be formed by using a silicon single crystal substrate made of the same material as the material of the flow channel substrate <NUM> made of a silicon single crystal substrate.

In addition, the penetrating hollow portion 26a in the common liquid chamber substrate <NUM> is in communication with the communication hollow portion <NUM> of the flow channel substrate <NUM>. In addition, in the common liquid chamber substrate <NUM>, a wiring hollow portion 26b that penetrates the common liquid chamber substrate <NUM> in a substrate thickness direction is formed between the adjacent piezoelectric element rows. In addition, on an upper surface side of the common liquid chamber substrate <NUM>, the compliance substrate <NUM> is disposed. In a region in the compliance substrate <NUM> facing the penetrating hollow portion 26a of the common liquid chamber substrate <NUM>, an ink inlet 27a for supplying ink from an ink introduction needle side to a common liquid chamber is formed and penetrates the compliance substrate <NUM> in a thickness direction. In addition, a region other than the ink inlet 27a, in the region of the compliance substrate <NUM> facing the penetrating hollow portion 26a, and a penetrating port 27b is a flexible portion 27c that is formed very thin, and the flexible portion 27c seals an opening of the penetrating hollow portion 26a on an upper portion side so as to define and form the common liquid chamber. In addition, the flexible portion 27c functions as a compliance portion that absorbs pressure fluctuation of ink in the common liquid chamber. Moreover, the penetrating port 27b is formed in a central portion of the compliance substrate <NUM>. The penetrating port 27b is in communication with a hollow portion 28a of the unit case <NUM>.

The unit case <NUM> is a member in which an ink introduction path 28b that is in communication with the ink inlet 27a and supplies ink introduced from the ink introduction needle side to a common liquid chamber side is formed, and in which a recessed portion that allows expansion of the flexible portion 27c is formed in a region facing the flexible portion 27c. In a central portion of the unit case <NUM>, the hollow portion 28a that penetrates the unit case <NUM> in a thickness direction is provided, and one end side of a flexible cable <NUM> is inserted into the hollow portion 28a in an insertion direction indicated by the void arrow, coupled to a terminal led out from the piezoelectric element <NUM>, and fixed by an adhesive. Examples of the material of the unit case <NUM> include, for example, a metal material such as stainless steel.

In the flexible cable <NUM>, a control integrated circuit (IC) 29d for controlling application of a driving voltage to the piezoelectric element <NUM> is mounted on one surface of a rectangular base film made of polyimide or the like, and a pattern of individual electrode wiring to be coupled to the control IC 29d is also formed. In addition, one end portion of the flexible cable <NUM> is provided with a plurality of rows of coupling terminals (not illustrated) corresponding respective external electrodes led out from the piezoelectric element <NUM>, and another end portion is provided with a plurality of rows of another terminal side coupling terminals to be coupled to a substrate terminal portion of a substrate that relays a signal from a main body side of the ink jet printer <NUM>. In addition, in the flexible cable <NUM>, wiring patterns other than the coupling terminals at each end portion and a surface of the control IC 29d are covered with a resist. The external electrodes correspond to a lower electrode <NUM> and an upper electrode <NUM> illustrated in <FIG>.

One end side 29a of the flexible cable <NUM> coupled to the external electrodes is folded so as to project. More specifically, the flexible cable <NUM> is folded from a main body 29b of the flexible cable <NUM> and formed into a mountain shape so that a leading end of the one end side 29a becomes a ridgeline, and an end 29c is folded back in a reverse direction of the insertion direction of the flexible cable <NUM>.

The nozzle plate <NUM>, the flow channel substrate <NUM>, the common liquid chamber substrate <NUM>, the compliance substrate <NUM>, and the unit case <NUM> are mutually joined by being heated while being laminated with an adhesive, a thermal welding film, or the like interposed therebetween.

The description will be returned to <FIG>. The reciprocating mechanism <NUM> includes a carriage guide shaft <NUM> each end of which is supported by a frame (not illustrated), and a timing belt <NUM> that extends in parallel to the carriage guide shaft <NUM>. The carriage <NUM> is supported by the carriage guide shaft <NUM> of the reciprocating mechanism <NUM> so as to freely reciprocate and is also fixed to a part of the timing belt <NUM>.

When the timing belt <NUM> is caused to travel normally or reversely via a pulley by operation of the carriage motor <NUM>, the printing unit <NUM> is guided by the carriage guide shaft <NUM> and reciprocates. In addition, when the printing unit <NUM> reciprocates, ink droplets are appropriately ejected from respective ink jet heads <NUM> of the head units <NUM> correspondingly to image data to be printed, and printing is performed on the recording paper P. Note that the image data may be called printing data or the like.

The paper feeding apparatus <NUM> has a paper feeding motor <NUM> serving as a driving source of the paper feeding apparatus <NUM>, and a paper feeding roller <NUM> that rotates by operation of the paper feeding motor <NUM>. The paper feeding roller <NUM> is composed of a driven roller 52a and a driving roller 52b that face each other in an up-down direction with a transport path of the recording paper P interposed therebetween and pinch the recording paper P, and the driving roller 52b is coupled to the paper feeding motor <NUM>. As a result, the paper feeding roller <NUM> is configured to send many sheets of the recording paper P installed on the tray <NUM> one by one toward the printing apparatus <NUM> or discharge the recording paper P one by one from the printing apparatus <NUM>. Note that in place of the tray <NUM>, a configuration in which a paper feeding cassette that stores the recording paper P can be detachably attached may be adopted. Moreover, the paper feeding motor <NUM> also sends the recording paper P according to the image resolution interlocking with the reciprocating operation of the printing unit <NUM>. The paper feeding operation and the paper sending operation can be performed by respective separate motors or alternatively can be performed by the same motor with a component such as an electromagnetic clutch that switches torque transmission. In the present embodiment, the paper feeding motor <NUM> and the paper feeding roller <NUM> constitute a transport mechanism L1.

The control unit <NUM> performs printing processing on the recording paper P by controlling the printing apparatus <NUM>, the paper feeding apparatus <NUM>, and the like based on, for example, printing data input from a host computer <NUM> such as a personal computer, or a digital camera. In addition, the control unit <NUM> displays an error message or the like in the display portion of the operation panel <NUM>, or turns on or blinks an LED lamp or the like, and at the same time, causes each unit to perform corresponding processing based on a signal generated by pressing of various switches input from the operation portion. Moreover, the control unit <NUM> transfers an error message or information on abnormal ejection or the like to the host computer <NUM> where necessary. The host computer <NUM> is illustrated in <FIG>.

<FIG> is a block diagram schematically illustrating a main portion of the ink jet printer of the present disclosure. In <FIG>, the ink jet printer <NUM> of the present disclosure includes an interface portion <NUM> that receives printing data or the like input from the host computer <NUM>, the control unit <NUM>, the carriage motor <NUM>, a carriage motor driver <NUM> that drives and controls the carriage motor <NUM>, the paper feeding motor <NUM>, a paper feeding motor driver <NUM> that drives and controls the paper feeding motor <NUM>, the head unit <NUM>, a driving signal generation unit <NUM> that drives and controls the head unit <NUM>, an abnormal ejection detection unit <NUM>, a recovery mechanism <NUM>, and the operation panel <NUM>. The recovery mechanism <NUM> is a mechanism that recovers a function so that the head unit <NUM> normally operates when ink droplets cannot be ejected from the head unit <NUM>. Specifically, the recovery mechanism <NUM> performs flushing operation and wiping operation. The flushing operation is head cleaning operation in which ink droplets are ejected from all or target nozzles <NUM> of the head unit <NUM> when a cap is attached to the head unit <NUM> or at a location where ink droplets do not splash on the recording paper. In addition, during the wiping operation, substances such as paper dust or dust adhering to a head surface is wiped off by a wiper to clean a nozzle plate. At this time, the inside of the nozzles <NUM> may have a negative pressure and suck ink of other colors. Therefore, after the wiping operation, a fixed amount of ink droplets is ejected from all the nozzles <NUM> of the head unit <NUM> so that the flushing operation is performed. Note that the details of the abnormal ejection detection unit <NUM> and the driving signal generation unit <NUM> will be described later.

In <FIG>, the control unit <NUM> includes a field programmable gate array (FPGA) <NUM>. The FPGA <NUM> performs various kinds of processing such as printing processing and abnormal ejection detection processing. Note that the control unit <NUM> may include, in place of the FPGA <NUM>, a central processing unit (CPU) and a storage unit composed of a nonvolatile semiconductor memory or the like.

As described above, the printing unit <NUM> includes the plurality of head units <NUM> corresponding to the respective colors of ink. In addition, each head unit <NUM> includes the plurality of nozzles <NUM> and the piezoelectric elements <NUM> corresponding to the respective nozzles <NUM>. That is, the head unit <NUM> includes the plurality of ink jet heads <NUM> having a pair of the nozzle <NUM> and the piezoelectric element <NUM>. The respective ink jet heads <NUM> are a droplet ejection head.

In addition, to the control unit <NUM>, although not illustrated, for example, various sensors that can detect the ink remaining amount of the ink cartridge <NUM>, the position of the printing unit <NUM>, and the printing environment such as the temperature and humidity are electrically coupled. The control unit <NUM> acquires printing data from the host computer <NUM> via the interface portion <NUM> and then stores the printing data in the FPGA <NUM>. Then, the FPGA <NUM> performs predetermined processing on the printing data, and based on the processing data and input data from the various sensors, outputs control signals to the driving signal generation unit <NUM>, each of the carriage motor driver <NUM> and the paper feeding motor driver <NUM>, and the head unit <NUM>. When the control signals are input via the carriage motor driver <NUM> and the paper feeding motor driver <NUM>, the carriage motor <NUM> of the printing apparatus <NUM> and the paper feeding motor <NUM> of the paper feeding apparatus <NUM> each operate. As a result, printing processing is performed on the recording paper P.

Next, a structure of each head unit <NUM> will be described. <FIG> is a schematic sectional view of the head unit <NUM> illustrated in <FIG>. A head unit 35A illustrated in <FIG> corresponds to the ink jet head <NUM>. In addition, the head unit 35A corresponds to the head unit <NUM> illustrated in <FIG>. According to the configuration portion illustrated in <FIG>, an ejection portion W1 is configured. <FIG> are plan views illustrating an example of a nozzle surface of the printing unit <NUM> in which the head unit 35A illustrated in <FIG> is adopted. Note that a nozzle plate <NUM> and a nozzle <NUM> illustrated in <FIG> correspond to the nozzle plate <NUM> and the nozzle <NUM> in the examples of <FIG> and <FIG>, respectively.

In the head unit 35A illustrated in <FIG>, a vibration plate <NUM> vibrates by driving of the piezoelectric element <NUM>, and ink, which is a liquid, in the cavity <NUM> is ejected from the nozzle <NUM>. A metal plate <NUM> made of stainless steel is bonded via an adhesive film <NUM> to the nozzle plate <NUM> made of stainless steel through which the nozzle <NUM>, which is a hole, is formed, and the similar metal plate <NUM> made of stainless steel is bonded via the adhesive film <NUM> further thereon. In addition, a communication port formation plate <NUM> and a cavity plate <NUM> are sequentially bonded further thereon.

The nozzle plate <NUM>, the metal plate <NUM>, the adhesive film <NUM>, the communication port formation plate <NUM>, and the cavity plate <NUM> are each formed into a predetermined shape and are overlapped to form the cavity <NUM> and a reservoir <NUM>. The predetermined shape is a shape that forms a recessed portion. The cavity <NUM> and the reservoir <NUM> are in communication with each other via an ink supply port <NUM>. In addition, the reservoir <NUM> is in communication with an ink intake port <NUM>.

The vibration plate <NUM> is installed on an upper surface opening portion of the cavity plate <NUM>, and the piezoelectric element <NUM> is bonded to the vibration plate <NUM> with the lower electrode <NUM> interposed therebetween. In addition, the upper electrode <NUM> is bonded on a side of the piezoelectric element <NUM> opposite from the lower electrode <NUM>. The driving signal generation unit <NUM> applies and supplies a driving voltage waveform between the upper electrode <NUM> and the lower electrode <NUM>, so that the piezoelectric element <NUM> vibrates and the vibration plate <NUM> bonded thereto vibrates. The vibration of the vibration plate <NUM> changes the volume of the cavity <NUM>, the pressure in the cavity <NUM> changes, and ink, which is a liquid filling the inside of the cavity <NUM>, is ejected as droplets from the nozzle <NUM>. That is, the piezoelectric element <NUM> is displaced according to a driving signal and causes a liquid to be ejected.

The liquid is replenished by the amount that is reduced in the cavity <NUM> due to ejection of droplets when ink is supplied from the reservoir <NUM>. In addition, ink is supplied from the ink intake port <NUM> to the reservoir <NUM>.

Next, ejection of ink droplets will be described with reference to <FIG> are state diagrams illustrating respective states of the head unit according to the embodiment when a driving signal is input. When a driving voltage is applied from the driving signal generation unit <NUM> to the piezoelectric element <NUM> illustrated in <FIG>, a mechanical power such as expansion and contraction or a warp may occur in the piezoelectric element <NUM>. Therefore, the vibration plate <NUM> is bent in an up direction in <FIG> with respect to an initial state illustrated in <FIG>, and as illustrated in <FIG>, the volume of the cavity <NUM> expands. In this state, when the driving voltage is changed by control of the driving signal generation unit <NUM>, the vibration plate <NUM> is restored by an elastic restoring force thereof, moves further in a down direction than is the position of the vibration plate <NUM> in the initial state, and the volume of the cavity <NUM> is suddenly contracted as illustrated in <FIG>. At this time, by a compression pressure generated in the cavity <NUM>, part of ink, which is a liquid material, filling the cavity <NUM> is ejected as ink droplets from the nozzle <NUM> that is in communication with the cavity <NUM>.

The vibration plate <NUM> of each cavity <NUM> performs attenuation vibration by ink ejection operation by a driving signal of the driving signal generation unit <NUM>, which is a series of the actions described above, until a driving voltage is input by the next driving signal so that ink droplets are ejected again. Hereinafter, the attenuation vibration is also referred to as residual vibration. The residual vibration of the vibration plate <NUM> is assumed to have a natural vibration frequency determined by the shapes of the nozzle <NUM> and the ink supply port <NUM>, or acoustic resistance r according to ink viscosity or the like, inertance m according to an ink weight in a flow channel, and compliance Cm of the vibration plate <NUM>.

A calculation model of the residual vibration of the vibration plate <NUM> based on the above-described assumption will be described. <FIG> is a circuit diagram illustrating a calculation model of simple vibration, assuming the residual vibration of the vibration plate <NUM>. In this manner, the calculation model of the residual vibration of the vibration plate <NUM> can be expressed by a sound pressure p, the inertance m, the compliance Cm, and the acoustic resistance r described above. In addition, when a step response, in a case in which the sound pressure p is applied to the circuit in <FIG>, is calculated for a volume speed u, the following formulae are obtained. <MAT> <MAT> <MAT>.

<FIG> is a diagram illustrating an example of a configuration of a circuit of a first head unit <NUM> according to the present embodiment. The first head unit <NUM> has a function of detecting residual vibration.

The first head unit <NUM> includes a first piezoelectric element <NUM>, an upper electrode <NUM>, and a lower electrode <NUM>. The first piezoelectric element <NUM> corresponds to the piezoelectric element <NUM> illustrated in <FIG>. The upper electrode <NUM> and the lower electrode <NUM> are disposed on and below the first piezoelectric element <NUM>, respectively. The upper electrode <NUM> and the lower electrode <NUM> are each in contact with the first piezoelectric element <NUM>. The upper electrode <NUM> is coupled to the driving signal generation unit <NUM>. The lower electrode <NUM> is coupled to a constant voltage signal generation circuit (not illustrated). The constant voltage signal generation circuit generates and supplies a signal having a constant voltage. The constant voltage corresponds to a fixed voltage VBS.

Here, in the present embodiment, a configuration in which a driving signal COMA and a driving signal COMB each having a different waveform, as a driving signal, can be switched and used is illustrated, but the number of driving signals that can be switched is not particularly limited. For example, one kind of driving signal may be used. That is, in the present embodiment, two switches of a driving switch 321a and a driving switch 321b are illustrated, but one of the driving switch 321a and the driving switch 321b may be used. In addition, in another example, three kinds of driving switches may be used.

One end of the driving switch 321a is coupled to a terminal of the driving signal COMA. One end of the driving switch 321b is coupled to a terminal of the driving signal COMB. Another end of the driving switch 321a, another end of the driving switch 321b, one end of a detection switch 321n, and the upper electrode <NUM> are electrically coupled in a first node N1.

One end of a bias switch 322a is coupled to a terminal of the driving signal COMA. One end of a bias switch 322b is coupled to a terminal of the driving signal COMB. Another end of the detection switch 321n, one end of a detection resistance <NUM>, a negative input terminal of a first amplifier <NUM>, and a positive input terminal of a second amplifier <NUM> are electrically coupled in a third node N3. Another end of the detection resistance <NUM>, another end of the bias switch 322a, another end of the bias switch 322b, a positive input terminal of the first amplifier <NUM>, and a negative input terminal of the second amplifier <NUM> are electrically coupled in a second node N2.

The driving switch 321a switches a coupling state of the driving signal COMA and the first node N1 between ON and OFF. The driving switch 321b switches a coupling state of the driving signal COMB and the first node N1 between ON and OFF. The driving switch 321a and the driving switch 321b are switches used to selectively apply the driving signal COMA and the driving signal COMB to the first node N1, respectively. Here, two driving signals of the driving signal COMA and the driving signal COMB are generated by the driving signal generation unit <NUM> illustrated in <FIG>. The driving signal generation unit <NUM> is controlled by the control unit <NUM>.

The first head unit <NUM> includes the detection switch 321n. The detection switch 321n switches a coupling state of the first node N1 and the third node N3 and a coupling state of the first node N1 and the second node N2 between ON and OFF. The detection switch 321n is a switch that switches the coupling state of the first node N1 and the third node N3 between ON and OFF so as to switch between a state in which a residual vibration signal can be supplied to a residual vibration signal generation circuit and a state in which a residual vibration signal cannot be supplied to the residual vibration signal generation circuit. Here, the driving switch 321a, the driving switch 321b, and the detection switch 321n are controlled by the control unit <NUM> illustrated in <FIG>.

Here, the driving switch 321a, the driving switch 321b, and the detection switch 321n may be configured by using a transmission gate (TG), for example. Note that the transmission gate includes a P channel transistor and an N channel transistor that are coupled in parallel, for example, but may be configured with a transistor of either one of the channels.

The first head unit <NUM> includes the bias switch 322a and the bias switch 322b corresponding to the driving signal COMA and the driving signal COMB, respectively.

Here, the bias switch 322a and the bias switch 322b correspond to the driving switch 321a and the driving switch 321b, respectively. When one of the driving switch 321a and the driving switch 321b is not included, corresponding one of the bias switch 322a and the bias switch 322b is not included in the same manner.

The bias switch 322a switches a coupling state of the second node N2 and the driving signal COMA between ON and OFF. The bias switch 322b switches a coupling state of the second node N2 and the driving signal COMB between ON and OFF. The bias switch 322a and the bias switch 322b are switches to selectively apply the driving signal COMA and the driving signal COMB to the second node N2, respectively. Here, the bias switch 322a and the bias switch 322b are controlled by the control unit <NUM> illustrated in <FIG>.

Here, the bias switch 322a and the bias switch 322b may be configured by using, for example, a transmission gate.

The first head unit <NUM> includes a residual vibration signal generation circuit, an analog differential residual vibration signal generation circuit, a demodulation circuit <NUM>, an AD converter <NUM>, and an FPGA <NUM>. The residual vibration signal generation circuit includes the upper electrode <NUM>, the detection switch 321n, and the detection resistance <NUM>. The residual vibration signal generation circuit outputs a change in an electromotive force of the first piezoelectric element <NUM> according to the residual vibration, in a pressure chamber in communication with a nozzle, that occurs after a driving signal is supplied, as a residual vibration signal. That is, the residual vibration signal generation circuit acquires a waveform of the residual vibration signal. The residual vibration signal is acquired as an analog signal. Note that the residual vibration signal generation circuit may be called a residual vibration detection unit that outputs the residual vibration signal as a waveform of an analog signal. The pressure chamber is the cavity <NUM> illustrated in <FIG>.

The detection resistance <NUM> functions as a bias resistance that supplies a voltage of the driving signal COMA or the driving signal COMB. When at least one of the coupling state of the second node N2 and the driving signal COMA and the coupling state of the second node N2 and the driving signal COMB is turned ON by corresponding one of the bias switch 322a and the bias switch 322b, and the coupling state of the first node N1 and the third node N3 is turned ON by the detection switch 321n, a potential difference is generated by the residual vibration between both ends of the detection resistance <NUM>. In the first head unit <NUM>, the potential difference, a delay time of the residual vibration, and a cycle of the residual vibration are detected so that the state of the nozzle is discriminated.

The analog differential residual vibration signal generation circuit converts the residual vibration signal output by the residual vibration signal generation circuit into an analog differential residual vibration signal. The residual vibration signal, whose waveform is acquired by the residual vibration signal generation circuit, is amplified as a differential signal by the analog differential residual vibration signal generation circuit. The differential signal is also referred to as an analog differential residual vibration signal.

The analog differential residual vibration signal generation circuit includes the first amplifier <NUM> and the second amplifier <NUM>. In the present embodiment, as an example, the first amplifier <NUM> and the second amplifier <NUM> are each a discrete component. Therefore, in the present embodiment, as an example, the analog differential residual vibration signal generation circuit is composed of discrete components. The first amplifier <NUM> and the second amplifier <NUM> are each disposed at a different position on a head substrate.

The first amplifier <NUM> outputs a first signal that is obtained through amplifying of a residual vibration signal. The second amplifier <NUM> outputs a second signal that is obtained through inverting of the residual vibration signal that is amplified with the same magnification as the first amplifier <NUM>. The first signal and the second signal have reverse polarities and equal amplitudes. Therefore, the first signal and the second signal constitute an analog differential residual vibration signal. In the present embodiment, as an example, the first amplifier <NUM> and the second amplifier <NUM> are each configured with a negative feedback type amplifier using an operational amplifier, and the amplitude of an output signal can be adjusted by a variable resistor that divides the voltage of the output signal.

The first signal output from the first amplifier <NUM> and the second signal output from the second amplifier <NUM> are each input into the demodulation circuit <NUM>. That is, the analog differential residual vibration signal generated by the analog differential residual vibration signal generation circuit is input into the demodulation circuit <NUM>.

The demodulation circuit <NUM> demodulates the first signal input from the first amplifier <NUM> and the second signal input from the second amplifier <NUM> and outputs a demodulated signal. That is, the demodulation circuit <NUM> demodulates an analog differential residual vibration signal and outputs a demodulated signal. The demodulated signal is an analog signal. Note that the waveform of the demodulated signal and the waveform of the residual vibration signal are the same, as an example. The demodulation circuit <NUM> includes a differential input amplifier, as an example. The demodulation circuit <NUM> suppresses or removes noise while amplifying the analog differential residual vibration signal.

The demodulated signal that is demodulated by the demodulation circuit <NUM> is input into the AD converter <NUM>. The AD converter <NUM> converts the demodulated signal output from the demodulation circuit <NUM> into a digital signal. The AD converter <NUM> outputs the converted digital signal to the FPGA <NUM>. The FPGA <NUM> determines the state in the pressure chamber based on the digital signal output from the AD converter <NUM>. The FPGA <NUM> corresponds to the FPGA <NUM> illustrated in <FIG>. The FPGA <NUM> is an example of a determination unit.

Here, in the present embodiment, a driving signal for testing is applied to the first piezoelectric element <NUM> during the printing operation, and residual vibration, which is a pressure change in the cavity <NUM> that occurs due to the application of the driving signal, is detected as a change in an electromotive force of the first piezoelectric element <NUM> by the residual vibration signal generation circuit. Based on a control signal output from the control unit <NUM>, the driving signal generation unit <NUM> supplies the driving signal for testing to the first piezoelectric element <NUM>. On the other hand, the control unit <NUM> supplies the electromotive force of the first piezoelectric element <NUM> to the residual vibration signal generation circuit when the residual vibration is detected. The residual vibration signal generation circuit outputs a signal that indicates a change in the electromotive force of the first piezoelectric element <NUM> as a residual vibration signal.

In the example of <FIG>, detailed illustration is omitted, but the first head unit <NUM> includes a plurality of piezoelectric element portions corresponding to a plurality of respective nozzles. Each of the piezoelectric element portions are composed of one or more piezoelectric elements. In the example of <FIG>, a case in which the first piezoelectric element <NUM>, which is one piezoelectric element, is used as the piezoelectric element portion is illustrated, but the configuration is not limited thereto. For example, a combination of a plurality of piezoelectric elements can be used as the piezoelectric element portion.

Here, the AD converter <NUM> is mounted on a driving substrate <NUM>. The first amplifier <NUM> and the second amplifier <NUM> as the residual vibration signal generation circuit are mounted on a head substrate <NUM>. In the first head unit <NUM>, the residual vibration signal acquired by the residual vibration signal generation circuit is converted into an analog differential residual vibration signal by the analog differential residual vibration signal generation circuit, and transmitted to the AD converter <NUM> via the demodulation circuit <NUM>. That is, in the first head unit <NUM>, the distance between the head substrate <NUM> and the driving substrate <NUM> is greater than a predetermined distance. In the first head unit <NUM>, differential transmission is used to transmit a residual vibration signal from the residual vibration signal generation circuit to the AD converter <NUM>. In the first head unit <NUM>, noise immunity is enhanced by the differential transmission.

As described above, the demodulated signal that is input from the demodulation circuit <NUM> into the AD converter <NUM> is an analog signal. Therefore, the demodulation circuit <NUM> and the AD converter <NUM> are preferably disposed as close to each other as possible.

Here, with reference to <FIG>, another configuration of the first head unit will be described. A first A head unit 301A illustrated in <FIG> includes a residual vibration signal generation circuit, an analog differential residual vibration signal generation circuit, the demodulation circuit <NUM>, the AD converter <NUM>, and the FPGA <NUM>. When the first A head unit 301A illustrated in <FIG> is compared with the first head unit <NUM> illustrated in <FIG>, the configuration of the residual vibration signal generation circuit is different.

In the first A head unit 301A, the analog differential residual vibration signal generation circuit includes an amplifier <NUM> and a differential output unit <NUM>. As an example, the amplifier <NUM> and the differential output unit <NUM> are each mounted as a portion of a single IC component. As an example, the amplifier <NUM> is an operational amplifier as an IC component. The differential output unit <NUM> is a differential output amplifier as an IC component. Therefore, in the first A head unit 301A, the analog differential residual vibration signal generation circuit is composed of IC components. In the analog differential residual vibration signal generation circuit that is composed of IC components, the size of the circuit can be reduced compared to a case in which the analog differential residual vibration signal generation circuit is composed of discrete components.

A positive input terminal of the amplifier <NUM> is electrically coupled to the second node N2. A negative input terminal of the amplifier <NUM> is electrically coupled to the third node N3. The amplifier <NUM> amplifies a residual vibration signal. The differential output unit <NUM> generates an analog differential residual vibration signal from the residual vibration signal amplified by the amplifier <NUM> and outputs the analog differential residual vibration signal. That is, the differential output unit <NUM> outputs the first signal and the second signal that are obtained through amplifying of the residual vibration signal. The first signal and the second signal output from the differential output unit <NUM> are each input into the demodulation circuit <NUM>.

Next, with reference to <FIG>, the configuration of a substrate of the first head unit <NUM> will be described. <FIG> is a schematic view illustrating an example of the configuration of a substrate of the first head unit <NUM> according to the present embodiment.

The first head unit <NUM> includes the head substrate <NUM>, an extension cable <NUM>, and the driving substrate <NUM>. The head substrate <NUM> and the driving substrate <NUM> are coupled via the extension cable <NUM>.

A residual vibration signal generation circuit <NUM> and an analog differential residual vibration signal generation circuit <NUM> are mounted on the head substrate <NUM>. The residual vibration signal generation circuit <NUM> is disposed further on a piezoelectric element <NUM> side than is the analog differential residual vibration signal generation circuit <NUM>.

A driving circuit <NUM>, a demodulation circuit <NUM>, an AD converter <NUM>, and an FPGA <NUM> are mounted on the driving substrate <NUM>. The driving circuit <NUM>, the demodulation circuit <NUM>, the AD converter <NUM>, and the FPGA <NUM> are disposed at positions close to the head substrate <NUM> in this order on the driving substrate <NUM>.

The head substrate <NUM> is an example of a first substrate on which the analog differential residual vibration signal generation circuit is mounted. The driving substrate <NUM> is an example of a second substrate on which the demodulation circuit is mounted. The first substrate and the second substrate are configured as different substrates.

The residual vibration signal generation circuit <NUM> illustrated in <FIG> corresponds to the residual vibration signal generation circuit illustrated in <FIG>. That is, the residual vibration signal generation circuit <NUM> corresponds to the upper electrode <NUM>, the detection switch 321n, and the detection resistance <NUM>. The analog differential residual vibration signal generation circuit <NUM> illustrated in <FIG> corresponds to the analog differential residual vibration signal generation circuit illustrated in <FIG>. That is, the analog differential residual vibration signal generation circuit <NUM> corresponds to the first amplifier <NUM> and the second amplifier <NUM>. Note that the analog differential residual vibration signal generation circuit <NUM> may correspond to the analog differential residual vibration signal generation circuit illustrated in <FIG>. In this case, the analog differential residual vibration signal generation circuit <NUM> corresponds to the amplifier <NUM> and the differential output unit <NUM>. The driving circuit <NUM> illustrated in <FIG> corresponds to the driving signal generation unit <NUM> illustrated in <FIG>. The demodulation circuit <NUM>, the AD converter <NUM>, and the FPGA <NUM> illustrated in <FIG> correspond to the demodulation circuit <NUM>, the AD converter <NUM>, and the FPGA <NUM> illustrated in <FIG>, respectively.

The residual vibration signal generation circuit <NUM> and the AD converter <NUM> are mounted on different substrates, which are the head substrate <NUM> and the driving substrate <NUM>, respectively. Therefore, the distance from the residual vibration signal generation circuit <NUM> to the AD converter <NUM> is longer than that in a case in which the residual vibration signal generation circuit <NUM> and the AD converter <NUM> are mounted on the same substrate.

Moreover, in the first head unit <NUM>, the head substrate <NUM> and the driving substrate <NUM> are coupled via the extension cable <NUM>. Therefore, the distance between the residual vibration signal generation circuit <NUM> to the AD converter <NUM> is made long at least by the length of the extension cable <NUM>.

In addition, as illustrated in <FIG>, in the driving substrate <NUM>, the driving circuit <NUM> is mounted on a side closer to the head substrate <NUM> than is the AD converter <NUM>. That is, the driving circuit <NUM> is mounted between the residual vibration signal generation circuit <NUM> and the AD converter <NUM>. The distance from residual vibration signal generation circuit <NUM> to the AD converter <NUM> is made long at least by the size of the driving circuit <NUM>.

Therefore, in the first head unit <NUM>, the residual vibration signal, which is an analog signal, needs to be transmitted by the distance from the residual vibration signal generation circuit <NUM> to the AD converter <NUM>. In the first head unit <NUM>, as described above, the residual vibration signal is converted into an analog differential residual vibration signal and transmitted from the analog differential residual vibration signal generation circuit <NUM> to the demodulation circuit <NUM>. Therefore, in the first head unit <NUM>, the noise immunity can be enhanced during transmission of the residual vibration signal.

Note that the analog differential residual vibration signal generation circuit <NUM> and the demodulation circuit <NUM> may be mounted on the same substrate.

In addition, the AD converter <NUM> may be mounted on a substrate different from the driving substrate <NUM>. However, as in the present embodiment, when the AD converter <NUM> is mounted on the driving substrate <NUM> on which the demodulation circuit <NUM> is mounted, the distance between the demodulation circuit <NUM> and the AD converter <NUM> can be made shorter. The shorter the distance is, the shorter the distance, in which the analog signal demodulated by the demodulation circuit <NUM> is transmitted from the demodulation circuit <NUM> to the AD converter <NUM>, is, whereby the noise immunity can be enhanced during transmission of the residual vibration signal.

In addition, the residual vibration signal generation circuit <NUM> may be mounted on a substrate different from the head substrate <NUM>. However, as in the present embodiment, when the residual vibration signal generation circuit <NUM> is mounted on the head substrate <NUM> on which the analog differential residual vibration signal generation circuit <NUM> is mounted, the distance between the residual vibration signal generation circuit <NUM> and the analog differential residual vibration signal generation circuit <NUM> can be made shorter. The shorter the distance is, the shorter the distance, in which the residual vibration signal detected by the residual vibration signal generation circuit <NUM> is transmitted from the residual vibration signal generation circuit <NUM> to the analog differential residual vibration signal generation circuit <NUM>, is, whereby the noise immunity can be enhanced during transmission of the residual vibration signal.

As described above, the head unit according to the present embodiment includes a piezoelectric element, the driving signal generation unit <NUM>, a residual vibration signal generation circuit, an analog differential residual vibration signal generation circuit, a demodulation circuit, an AD converter, and a determination unit. The piezoelectric element is displaced according to a driving signal to cause a liquid to be ejected. The driving signal generation unit <NUM> generates the driving signal. The residual vibration signal generation circuit outputs a change in an electromotive force of the piezoelectric element according to residual vibration, in a pressure chamber in communication with a nozzle, that occurs after supply of the driving signal, as a residual vibration signal. The analog differential residual vibration signal generation circuit converts the residual vibration signal into an analog differential residual vibration signal. The demodulation circuit demodulates the analog differential residual vibration signal and outputs a demodulated signal. The AD converter converts the demodulated signal into a digital signal. The determination unit determines, based on the digital signal, a state in the pressure chamber.

In the present embodiment, the head unit <NUM> or the first head unit <NUM> is an example of the head unit. In the present embodiment, the driving signal COMA and the driving signal COMB are examples of the driving signal. In the present embodiment, the piezoelectric element <NUM> or the first piezoelectric element <NUM> is an example of the piezoelectric element. In the present embodiment, the cavity <NUM> is an example of the pressure chamber. In the present embodiment, the upper electrode <NUM>, the detection switch 321n, and the detection resistance <NUM>, or the residual vibration signal generation circuit <NUM> is an example of the residual vibration signal generation circuit. In the present embodiment, the first amplifier <NUM> and the second amplifier <NUM>, the amplifier <NUM> and the differential output unit <NUM>, or the analog differential residual vibration signal generation circuit <NUM> is an example of the analog differential residual vibration signal generation circuit. In the present embodiment, the demodulation circuit <NUM> or the demodulation circuit <NUM> is an example of the demodulation circuit. In the present embodiment, the AD converter <NUM> or the AD converter <NUM> is an example of the AD converter. In the present embodiment, the FPGA <NUM>, the FPGA <NUM>, or the FPGA <NUM> is an example of the determination unit.

According to this configuration, in the head unit (the first head unit <NUM> in the present embodiment) according to the present embodiment, a residual vibration signal, which is an analog signal, is transmitted by differential transmission, and noise superimposition during transmission can be removed by demodulation before the residual vibration signal is input into the AD converter <NUM>. That is, in the head unit according to the present embodiment, through differentially transmitting of the residual vibration signal, the noise immunity can be enhanced. Therefore, in the head unit according to the present embodiment, the detection accuracy of residual vibration can be enhanced. In the head unit according to the present embodiment, for example, a four-direction ground (GND) guard ring is not necessary.

Here, for the purpose of comparison with the head unit according to the present embodiment, with reference to <FIG>, the configuration of a circuit of a head unit 901A of the related art will be described. The head unit 901A of the related art includes a residual vibration signal generation circuit, an amplifier <NUM>, an AD converter <NUM>, and an FPGA <NUM>. When the head unit 901A of the related art illustrated in <FIG> is compared with the first head unit <NUM> illustrated in <FIG>, the head unit 901A of the related art is different in that the head unit 901A of the related art includes the amplifier <NUM> in place of an analog differential residual vibration signal generation circuit.

In the head unit 901A of the related art, after the residual vibration signal, which is an analog signal, is amplified by the amplifier <NUM> mounted inside the head substrate, the residual vibration signal is input into the AD converter <NUM> by a single-end transmission system. Then, based on a signal that is digitized by the AD converter <NUM>, the nozzle state is determined by the FPGA <NUM>.

According to the configuration of the head unit 901A of the related art, the residual vibration signal is transmitted as an analog signal from the amplifier <NUM> to the AD converter <NUM>. Here, the AD converter <NUM> is mounted on a driving circuit substrate. This is because an AD converter such as the AD converter <NUM> has a large circuit size and cannot be mounted inside the head substrate.

In a printing apparatus for industrial use, the distance from the head substrate to the driving circuit substrate may be great. Therefore, according to the configuration of the head unit 901A of the related art, the residual vibration signal, which is an analog signal, needs to be transmitted over a long distance from the amplifier <NUM> mounted on the head substrate to the AD converter <NUM> mounted on the driving circuit substrate by a single-end method. In a process of transmission from the amplifier <NUM> to the AD converter <NUM>, noise is likely to be superimposed on the residual vibration signal, which is an analog signal, from a peripheral device. When noise is superimposed on the residual vibration signal, the AD converter performs digital processing with a waveform on which noise is superimposed. The waveform on which noise is superimposed may be largely different from the original residual vibration waveform. As a result, in the head unit 901A of the related art, the nozzle state may be falsely determined.

In addition, in recent years, in a substrate included in a liquid ejection apparatus, many semiconductor devices are aggregated near the head, and the density has been increased. On the other hand, in order to transmit the residual vibration signal, which is an analog signal, a wiring layout that improves the noise immunity needs to be employed. As a result, wiring distances of other signals are extended, or wiring layouts of other signals are made complicated, and the signal quality may be deteriorated.

On the other hand, in the head unit according to the present embodiment, since the noise immunity can be enhanced through differential transmission of the residual vibration signal, restrictions on the wiring layout of the substrate for transmitting the residual vibration signal can be mitigated, and the degree of freedom in wiring can be improved.

Claim 1:
A head unit (<NUM>) comprising:
a piezoelectric element (<NUM>) displaced according to a driving signal to cause a liquid to be ejected; and
a driving signal generation unit (<NUM>) that generates the driving signal; and
a residual vibration signal generation circuit (<NUM>) that outputs a change in an electromotive force of the piezoelectric element (<NUM>) according to residual vibration, in a pressure chamber in communication with a nozzle, that occurs after supply of the driving signal, as a residual vibration signal;
an analog differential residual vibration signal generation circuit (<NUM>) that converts the residual vibration signal into an analog differential residual vibration signal;
a demodulation circuit (<NUM>) that demodulates the analog differential residual vibration signal and outputs a demodulated signal;
an AD converter (<NUM>) that converts the demodulated signal into a digital signal; and
a determination unit (<NUM>) that determines, based on the digital signal, a state in the pressure chamber.