Head unit and liquid ejection device

Abstract

The present application provides a head unit and a liquid ejection device that improve the detection accuracy of residual vibrations. The head unit includes: a piezoelectric element that displaces in accordance with a drive signal and causes a liquid to be ejected; a drive signal generation section that generates the drive signal; a residual vibration signal generation circuit that detects a change in the electromotive force of the piezoelectric element that occurs due to a residual vibration in a pressure chamber that communicates with a nozzle after the supply of the drive signal, and outputs the change 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 demodulation signal; an A / D converter that converts the demodulation signal into a digital signal; and a determination section that determines a state in the pressure chamber based on the digital signal.

Description

Technical Field

[0001] This invention relates to a head unit and a liquid ejection device. Background Technology

[0002] As a method for determining the nozzle state of a printing apparatus, a method for detecting residual vibration is known (see Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Publication No. 2005-211873

[0004] In the technology described in Patent Document 1, when transmitting the residual vibration signal, which is an analog waveform detected in the head, to the control unit, it is necessary to transmit the residual vibration signal from the head to the AD converter. However, during this transmission, noise may be superimposed on the analog waveform of the residual vibration signal. Summary of the Invention

[0005] To address the aforementioned issues, one approach is a head unit comprising: a piezoelectric element that is displaced according to a drive signal and causes liquid to be ejected; a drive signal generation unit that generates the drive signal; a residual vibration signal generation circuit that detects changes in the electromotive force of the piezoelectric element in a pressure chamber connected to the nozzle caused by the supply of the drive signal, and outputs this 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 the state of the pressure chamber based on the digital signal.

[0006] To address the aforementioned issues, one approach is a liquid ejection device comprising a conveying mechanism and a head unit, wherein the head unit includes: a piezoelectric element that is displaced according to a drive signal and ejects liquid; a drive signal generation unit that generates the drive signal; a residual vibration signal generation circuit that detects the change in the electromotive force of the piezoelectric element in a pressure chamber connected to the nozzle caused by the supply of the drive signal, and outputs it 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 the state of the pressure chamber based on the digital signal. Attached Figure Description

[0007] Figure 1 This is a schematic diagram showing the structure of an inkjet printer, which is one of the liquid ejection devices according to an embodiment.

[0008] Figure 2 To indicate the implementation method Figure 1 An exploded schematic perspective view of an example structure of the head unit 35 in the inkjet printer shown.

[0009] Figure 3 A block diagram illustrating the main components of the inkjet printer according to the embodiment.

[0010] Figure 4 To indicate the implementation method Figure 1 A schematic cross-sectional view of an example head unit in an inkjet printer, as shown.

[0011] Figure 5 This is a state diagram showing the various states of the head unit when a drive signal is input according to the implementation method.

[0012] Figure 6 To illustrate the proposed implementation method Figure 4 The circuit diagram of the calculation model for the residual vibration of the vibrating plate in a single vibration.

[0013] Figure 7 This is a diagram illustrating an example of the circuitry of a head unit having the residual vibration detection section according to the embodiment.

[0014] Figure 8 This is a diagram illustrating another example of the circuitry of a head unit having the residual vibration detection section according to the embodiment.

[0015] Figure 9 This is a diagram illustrating an example of the structure of a substrate having a head unit with a residual vibration detection section according to the embodiment.

[0016] Figure 10 This diagram illustrates an example of the circuitry for a head unit with an existing residual vibration detection section.

[0017] Explanation of reference numerals in the attached figures

[0018] 1…Inkjet printer, 2…Main unit, 3…Printing section, 4…Printing unit, 5…Paper feeding unit, 6…Control unit, 7…Operation panel, 8…Main unit, 9…Interface unit, 10…Ejection anomaly detection unit, 21…Pattern, 22…Paper outlet, 24…Recovery mechanism, 25…Flow path substrate, 26…Common liquid chamber substrate, 26a…Through-through section, 26b…Wiring section, 27…Moldable substrate, 27a…Ink inlet, 27b…Through-through section, 27c…Flexible section, 28…Unit housing, 28a…Section, 28b…Ink inlet path, 29…Flexible cable, 29a…One end, 29b…Main unit, 29c…End, 30 …elastic film, 31…cartridge, 32…carriage, 33…drive signal generation unit, 35, 35A…header unit, 41…carriage motor, 42…reciprocating movement mechanism, 43…carriage motor driver, 51…paper feed motor, 52…paper feed roller, 52a…driven roller, 52b…drive roller, 53…paper feed motor driver, 100…inkjet head, 200…piezoelectric element, 240…nozzle plate, 241…nozzle, 248…external electrode, 249…internal electrode, 251…connecting cavity, 252…nozzle plate, 253…nozzle, 254…metal plate, 255…adhesive film, 256…connecting port forming plate, 257…cavity 258…Cavity, 259…Reservoir, 260…Ink supply port, 261…Port, 262…Vibrating plate, 263…Lower electrode, 264…Upper electrode, 301…First head unit, 301A…First A head unit, 311…First piezoelectric element, 312…Upper electrode, 313…Lower electrode, 321a, 321b…Drive switches, 321n…Detection switch, 322a…Bias switch, 322b…Bias switch, 331…Detection resistor, 341…First amplifier, 342…Second amplifier, 346…Amplifier, 347…Differential output, 351…Demodulation circuit, 361…A D converter, 421…synchronous belt, 422…carrier guide shaft, 501…headboard, 502…extension cable, 503…drive board, 601…residual vibration signal generation circuit, 602…analog differential residual vibration signal generation circuit, 603…drive circuit, 604…demodulation circuit, 605…AD converter, 901A…existing head unit, 941…amplifier, 951…AD converter, Cm…flexibility, COMA, COMB…drive signals, L1…conveyor mechanism, N1…first node, N2…second node, N3…third node, P…recording paper, VBS…fixed potential, W1…ejector section. Detailed Implementation

[0019] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0020] The embodiments of the liquid ejection device disclosed herein will be described in detail below.

[0021] This embodiment is given by way of example and should not be interpreted in a limiting way.

[0022] In this embodiment, an inkjet printer that prints images on recording paper using ejected ink will be described as an example of a liquid ejection device. Ink is an example of a liquid material. Recording paper is an example of a droplet receiver.

[0023] Figure 1 This is a schematic diagram showing the structure of an inkjet printer 1, which is one of the liquid ejection devices in the embodiment.

[0024] Furthermore, in the following explanation, Figure 1 The upper side is referred to as the upper part, and the lower side as the lower part. First, the structure of the inkjet printer 1 will be described.

[0025] Figure 1 The inkjet printer 1 shown has a main body 2, a tray 21 for holding recording paper P is provided at the upper rear, a paper discharge port 22 for discharging recording paper P is provided at the lower front, and an operation panel 7 is provided on the upper surface.

[0026] The operation panel 7 may be composed of, for example, a liquid crystal display, an organic EL (Electroluminescence) display, or an LED (Light Emitting Diode) lamp, and includes a display section (not shown) for displaying error messages and an operation section (not shown) composed of various switches. The display section of the operation panel 7 functions as a notification unit.

[0027] In addition, the main body 2 of the device mainly includes: a printing device 4, which has a printing part 3 that is a reciprocating moving part; a paper feeding device 5 that supplies and discharges recording paper P relative to the printing device 4; and a control unit 6 that controls the printing device 4 and the paper feeding device 5.

[0028] Under the control of the control unit 6, the paper feeding device 5 intermittently feeds recording paper P one sheet at a time. The recording paper P passes near the lower part of the printing unit 3. At this time, the printing unit 3 reciprocates in a direction approximately orthogonal to the feeding direction of the recording paper P, printing onto the recording paper P. That is, the reciprocating movement of the printing unit 3 and the intermittent feeding of the recording paper P constitute the main scan and sub-scan in the printing process, performing inkjet printing.

[0029] The printing apparatus 4 includes: a printing unit 3; a carriage motor 41, which is a drive source for moving the printing unit 3 in a reciprocating manner in the main scanning direction; and a reciprocating movement mechanism 42, which receives the rotation of the carriage motor 41 to move the printing unit 3 reciprocally.

[0030] The printing section 3 includes: multiple printhead units 35, ink cartridges (I / C) 31 that supply ink to each printhead unit 35; and a carriage 32 that mounts each printhead unit 35 and the ink cartridges 31. Alternatively, in the case of inkjet printers with high ink consumption, the ink cartridges 31 may be configured not to be mounted on the carriage 32 but to be located in another part, connected to the printhead unit 35 via a tube and supplied with ink, but this is not shown in the figure.

[0031] Furthermore, as ink cartridge 31, full-color printing is possible by using an ink cartridge filled with four colors of ink: yellow, cyan, magenta, and black. In this case, a header unit 35 corresponding to each color is provided in the printing section 3. Here, in Figure 1 The image shows four ink cartridges 31 corresponding to four colors of ink, but the printing section 3 can also be configured to have ink cartridges 31 with other colors, such as light cyan, light magenta, dark yellow, and specific colors of ink.

[0032] Figure 2 An exploded perspective view showing the structure of head unit 35.

[0033] like Figure 2 As shown, the head unit 35 in the embodiment is roughly composed of a nozzle plate 240, a flow path substrate 25, a common liquid chamber substrate 26, a plastic substrate 27, etc., and is installed on the unit housing 28 in a stacked state.

[0034] The nozzle plate 240 is a plate-shaped component in which a plurality of nozzles 241 are arranged in rows at a spacing corresponding to the dot formation density. For example, a nozzle array is formed by arranging 300 nozzles 241 at a spacing corresponding to 300 dpi. In an embodiment, two nozzle arrays are formed on the nozzle plate 240. Here, the two nozzle arrays are formed by offsetting the distance between the nozzles 241 by half in the arrangement direction of the nozzles 241. The nozzle plate 240 can be formed, for example, from glass ceramic, a single-crystal silicon substrate, or stainless steel.

[0035] On the upper surface of the flow path substrate 25, i.e., on the side of the common liquid chamber substrate 26, an extremely thin elastic film 30 made of silicon dioxide is formed by thermal oxidation. On the flow path substrate 25, a plurality of cavities 258, divided by multiple partitions through anisotropic etching, are formed corresponding to each nozzle 241. Regarding the cavities 258, as... Figure 4 As shown.

[0036] Therefore, the cavities 258 are also formed in a row, offset by half the spacing between the nozzles 241 in the direction in which the nozzles 241 are arranged. A communicating space 251 is formed on the outer side of the row of cavities 258 on the flow path substrate 25. This communicating space 251 communicates with each cavity 258.

[0037] In addition, for each cavity 258 on the flow path substrate 25, a piezoelectric element 200 is formed to deform the elastic membrane 30 and pressurize the ink in the cavity 258.

[0038] A common liquid chamber substrate 26 having a through-hole 26a extending through the thickness direction is disposed on the flow path substrate 25 on which the piezoelectric element 200 is formed. Examples of materials for the common liquid chamber substrate 26 include glass, ceramic materials, metals, and resins. For example, it can also be formed from a material with a coefficient of thermal expansion approximately the same as that of the flow path substrate 25. For example, a monocrystalline silicon substrate made of the same material as the flow path substrate 25 (if it is a monocrystalline silicon substrate) can be used to form the common liquid chamber substrate 26.

[0039] Furthermore, the through-hole 26a on the common liquid chamber substrate 26 communicates with the through-hole 251 of the flow path substrate 25. In addition, wiring holes 26b extending through the thickness direction of the substrate are formed on the common liquid chamber substrate 26 between adjacent rows of piezoelectric elements.

[0040] Additionally, a malleable substrate 27 is disposed on the upper surface side of the common liquid chamber substrate 26. In the region of the malleable substrate 27 opposite to the through-hole 26a of the common liquid chamber substrate 26, an ink inlet 27a is formed through in the thickness direction for supplying ink from the ink inlet needle side to the common liquid chamber.

[0041] Furthermore, the area of ​​the malleable substrate 27 opposite to the through-hole 26a, excluding the ink inlet 27a and the through-hole 27b, forms an extremely thin flexible portion 27c. This flexible portion 27c seals the upper opening of the through-hole 26a, thus dividing and forming a common liquid chamber. Moreover, this flexible portion 27c functions as a malleable portion that absorbs pressure fluctuations of the ink within the common liquid chamber. Additionally, a through-hole 27b is formed in the center of the malleable substrate 27. This through-hole 27b communicates with the hollow portion 28a of the unit housing 28.

[0042] The unit housing 28 is a component having an ink inlet path 28b that communicates with the ink inlet 27a for supplying ink introduced from the ink inlet needle side to the common liquid chamber side, and a recessed portion that allows the flexible portion 27c to expand in the region opposite to the flexible portion 27c. A hollow portion 28a extending along the thickness direction is provided in the center of the unit housing 28. One end of the flexible cable 29 is inserted into this hollow portion 28a in the insertion direction indicated by the hollow arrow, and connected to a terminal leading from the piezoelectric element 200, and fixed with adhesive. Examples of materials for the unit housing 28 include stainless steel and other metal materials.

[0043] The flexible cable 29 has a control IC (Integrated Circuit) 29d mounted on one side of a rectangular base film such as polyimide for controlling the application of driving voltage to the piezoelectric element 200, and a pattern of individual electrode wiring connected to the control IC 29d is formed therein. Furthermore, at one end of the flexible cable 29, a plurality of connection terminals (not shown) are arranged corresponding to the external electrodes extending from the piezoelectric element 200, and at the other end, a plurality of other-end connection terminals are arranged to connect to the substrate terminal portion of a substrate that relays signals from the main body of the inkjet printer 1. The wiring pattern at both ends of the flexible cable 29, excluding the connection terminals, and the surface of the control IC 29d are covered with resist. External electrodes and Figure 4 The lower electrode 263 and the upper electrode 264 shown correspond to each other.

[0044] One end 29a of the flexible cable 29 connected to the external electrode is bent in a convex manner. More specifically, the body 29b of the flexible cable 29 is bent into a mountain shape with the front end of one end 29a forming a ridge, and the end 29c is folded back in the opposite direction to the insertion direction of the flexible cable 29.

[0045] The nozzle plate 240, flow path substrate 25, common liquid chamber substrate 26, plastic substrate 27, and unit housing 28 are joined together by heating while an adhesive or hot melt film is placed in the middle and stacked.

[0046] return Figure 1 Description. The reciprocating movement mechanism 42 has: a carriage guide shaft 422, both ends of which are supported on a frame (not shown); and a timing belt 421 extending parallel to the carriage guide shaft 422.

[0047] The carriage 32 is freely supported on the carriage guide shaft 422 of the reciprocating mechanism 42 and fixed to a part of the timing belt 421.

[0048] The printing unit 3 reciprocates as the carriage motor 41 moves forward and backward via the pulley, guided by the carriage guide shaft 422. During this reciprocating motion, ink droplets are appropriately ejected from each inkjet head 100 of the print head unit 35 corresponding to the image data to be printed, and then printed onto the recording paper P. This image data may also be referred to as print data, etc.

[0049] The paper feeding device 5 has a paper feeding motor 51 as its drive source and a paper feeding roller 52 that rotates due to the operation of the paper feeding motor 51. The paper feeding roller 52 consists of a driven roller 52a and a drive roller 52b that sandwich the recording paper P vertically across the transport path of the recording paper P. The drive roller 52b is connected to the paper feeding motor 51. Thus, the paper feeding roller 52 feeds or discharges multiple sheets of recording paper P, which are placed on the tray 21, one by one into or from the printing device 4. Alternatively, it can be configured to house a paper feeding box that can be easily installed and removed from the recording paper P in place of the tray 21.

[0050] Furthermore, the paper feed motor 51, in conjunction with the reciprocating motion of the printing unit 3, also feeds the recording paper P, which corresponds to the resolution of the image. The paper feed and paper delivery actions can be performed by different motors, or they can be performed by the same motor via a torque transmission switching component such as an electromagnetic clutch.

[0051] In this embodiment, the paper feeding motor 51 and the paper feeding roller 52 constitute the conveying mechanism L1.

[0052] The control unit 6, for example, controls the printing apparatus 4 and the paper feeding device 5, etc., based on printing data input from the host computer 8 such as a personal computer or digital camera, thereby performing printing processing on the recording paper P. Furthermore, the control unit 6 causes the display unit of the operation panel 7 to display error messages, or to illuminate / flash LEDs, and causes each unit to perform corresponding processing based on various switch press signals input from the operation unit. Moreover, the control unit 6 transmits error messages or printing abnormality information to the host computer 8 as needed. The host computer 8, for example... Figure 3 As shown.

[0053] Figure 3 A block diagram illustrating the main components of the inkjet printer disclosed herein. Figure 3 The inkjet printer 1 disclosed herein includes: an interface unit 9 for receiving printing data input from a host 8; a control unit 6; a carriage motor 41; a carriage motor driver 43 for driving and controlling the carriage motor 41; a paper feed motor 51; a paper feed motor driver 53 for driving and controlling the paper feed motor 51; a head unit 35; a drive signal generation unit 33 for driving and controlling the head unit 35; an ejection abnormality detection unit 10; a recovery mechanism 24; and an operation panel 7.

[0054] The recovery mechanism 24 is a mechanism for restoring the normal operation of the head unit 35 when ink droplets cannot be ejected from the head unit 35. Specifically, the recovery mechanism 24 performs a rinsing action and a wiping action. The rinsing action is a head cleaning action that ejects ink droplets from all or all of the nozzles 241 of the head unit 35 when the cover of the head unit 35 is installed or in a location where ink droplets are not applied to the recording paper. In addition, during the wiping action, paper dust or other adhering substances on the head surface are wiped away with a scraper to clean the nozzle plate. At this time, negative pressure is created inside the nozzles 241, which may introduce ink of other colors. Therefore, after the wiping action, a certain amount of ink droplets are ejected from all the nozzles 241 of the head unit 35 to perform the rinsing action.

[0055] Furthermore, the ejection anomaly detection unit 10 and the drive signal generation unit 33 will be described in detail later.

[0056] In Figure 3 In this unit, the control unit 6 includes an FPGA (Field Programmable Gate Array) 61. The FPGA 61 performs various processes such as printing processing and ejection anomaly detection. Alternatively, the control unit 6 may replace the FPGA 61 with a CPU (Central Processing Unit) and a storage unit composed of non-volatile semiconductor memory.

[0057] As described above, the printing section 3 includes multiple head units 35 corresponding to inks of various colors. Furthermore, each head unit 35 includes multiple nozzles 241 and piezoelectric elements 200 corresponding to each of these nozzles 241. That is, the head unit 35 has a structure comprising multiple inkjet heads 100 each having a set of nozzles 241 and a piezoelectric element 200. The inkjet head 100 is a droplet ejection head.

[0058] In addition, although not shown in the figure, the control unit 6 is electrically connected to various sensors that can detect the ink level of the ink cartridge 31, the position of the printing section 3, the printing environment such as temperature and humidity.

[0059] When the control unit 6 receives printing data from the host 8 via the interface unit 9, it stores the printing data in the FPGA 61. Then, the FPGA 61 performs prescribed processing on the printing data and, based on the processed data and input data from various sensors, outputs control signals to the drive signal generation unit 33, the carriage motor driver 43, the paper feed motor driver 53, and the head unit 35. When these control signals are input via the carriage motor driver 43 and the paper feed motor driver 53, the carriage motor 41 and the paper feed device 5 of the printing apparatus 4 operate respectively. Thus, printing processing is performed on the recording paper P.

[0060] Next, the structure of each head unit 35 will be described.

[0061] Figure 4 yes Figure 1 A schematic cross-sectional view of the head unit 35 shown. Figure 4 The head unit 35A shown is equivalent to the inkjet head 100. Furthermore, the head unit 35A and... Figure 3 This corresponds to the head unit 35 shown.

[0062] pass Figure 4 The components shown are used to form the ejection section W1.

[0063] Figure 5 To indicate that it has been applied Figure 4 A top view of an example of the nozzle surface of the printing section 3 of the head unit 35A shown. Furthermore, Figure 4 The nozzle plate 252 and nozzle 253 shown are respectively in Figure 2 as well as Figure 5 In the example, it corresponds to nozzle plate 240 and nozzle 241.

[0064] Figure 4 The head unit 35A shown is driven by the piezoelectric element 200 to vibrate the vibrating plate 262, thereby ejecting the ink from the liquid in the cavity 258 from the nozzle 253. A stainless steel metal plate 254 is bonded to the stainless steel nozzle plate 252, which has the nozzle 253 forming an orifice, via an adhesive film 255, and then another stainless steel metal plate 254 is bonded to it via an adhesive film 255. Furthermore, a communication port forming plate 256 and a cavity plate 257 are sequentially bonded to it.

[0065] Nozzle plate 252, metal plate 254, adhesive film 255, connecting port forming plate 256, and cavity plate 257 are each formed into a predetermined shape. By overlapping them, a cavity 258 and a reservoir 259 are formed. The predetermined shape is a recessed shape. The cavity 258 and the reservoir 259 are connected via an ink supply port 260. In addition, the reservoir 259 is connected to an ink intake port 261.

[0066] A vibrating plate 262 is provided at the opening on the upper surface of the cavity plate 257, and a piezoelectric element 200 is connected to the vibrating plate 262 via a lower electrode 263. An upper electrode 264 is connected to the piezoelectric element 200 on the side opposite to the lower electrode 263. The drive signal generation unit 33 applies and supplies a drive voltage waveform between the upper electrode 264 and the lower electrode 263, causing the piezoelectric element 200 to vibrate, and the vibrating plate 262 connected to it to vibrate. The vibration of the vibrating plate 262 causes a change in the volume of the cavity 258, resulting in a change in the pressure within the cavity 258, and causing the liquid ink filling the cavity 258 to be ejected as droplets from the nozzle 253. In other words, the piezoelectric element 200 is displaced according to the drive signal, causing the liquid to be ejected.

[0067] The amount of liquid reduced in cavity 258 by the ejection of droplets is replenished by supplying ink from reservoir 259. In addition, ink is supplied to reservoir 259 from ink inlet 261.

[0068] Next, refer to Figure 5 The ejection of ink droplets is explained.

[0069] Figure 5 This is a state diagram showing the various states of the head unit when a drive signal is input according to the implementation method.

[0070] When from the drive signal generation unit 33 to Figure 4 When a driving voltage is applied to the piezoelectric element 200, mechanical forces such as stretching or warping are generated within the piezoelectric element 200. Therefore, the vibrating plate 262 relative to... Figure 5 The initial state shown in (a) is towards Figure 4 The upper part of the flex is bent, such as Figure 5 As shown in (b), the volume of cavity 258 expands. In this state, when the drive voltage changes under the control of the drive signal generation unit 33, the vibrating plate 262 recovers through its elastic restoring force and moves downward past its initial position, thereby... Figure 5 As shown in (c), the volume of cavity 258 contracts rapidly. At this time, due to the compressive pressure generated within cavity 258, a portion of the liquid material filling cavity 258, i.e., ink, is ejected as ink droplets from nozzle 253, which is connected to cavity 258.

[0071] The vibrating plate 262 of each cavity 258 vibrates damped during the ink ejection operation based on the drive signal generated by the drive signal generation unit 33, which is part of this series of actions, until the drive voltage is input by the next drive signal and ink droplets are ejected again. Hereinafter, this damped vibration will also be referred to as residual vibration. It is assumed that the residual vibration of the vibrating plate 262 has an inherent vibration frequency determined by the acoustic resistance r caused by the shape of the nozzle 253 and the ink supply port 260 or the ink viscosity, the inertia m caused by the weight of the ink in the flow path, and the compliance Cm of the vibrating plate 262.

[0072] The calculation model for the residual vibration of the vibrating plate 262 based on the above assumption is explained.

[0073] Figure 6 This is a circuit diagram representing a calculation model of the residual vibration of the vibrating plate 262. Thus, the calculation model of the residual vibration of the vibrating plate 262 is represented by the sound pressure p, the aforementioned inertia m, compliance Cm, and acoustic impedance r. Furthermore, if the volume velocity u is calculated... Figure 6 The circuit provides a step response to the sound pressure p, which gives the following equation.

[0074] u={p / (ω·m)}e -ωt ·sinωt,

[0075] ω={1 / (m·Cm)-α 2} 1 / 2 ,

[0076] α = r / 2m.

[0077] Figure 7 This diagram illustrates an example of the circuit structure of the first head unit 301 according to this embodiment. The first head unit 301 has the function of detecting residual vibration.

[0078] The first head unit 301 includes a first piezoelectric element 311, an upper electrode 312, and a lower electrode 313. The first piezoelectric element 311 and... Figure 4 Corresponding to the piezoelectric element 200 shown. The upper electrode 312 and the lower electrode 313 are respectively disposed above and below the first piezoelectric element 311. The upper electrode 312 and the lower electrode 313 are in contact with the first piezoelectric element 311.

[0079] The upper electrode 312 is connected to the drive signal generation unit 33. The lower electrode 313 is connected to a constant voltage signal generation circuit (not shown). The constant voltage signal generation circuit generates and supplies a signal with a constant voltage. This constant voltage is equivalent to a fixed potential VBS.

[0080] In this embodiment, a structure is shown that allows switching between drive signals COMA and COMB, each with a different waveform, but the number of drive signals that can be switched is not particularly limited. For example, a single drive signal can also be used. That is, in this embodiment, two switches, drive switch 321a and drive switch 321b, are shown, but one of them can also be used. In another example, three drive signals can also be used.

[0081] One end of the drive switch 321a is connected to the terminal of the drive signal COMA.

[0082] One end of the drive switch 321b is connected to the terminal of the drive signal COMB.

[0083] The other end of drive switch 321a, the other end of drive switch 321b, the other end of detection switch 321n, and upper electrode 312 are electrically connected to the first node N1.

[0084] One end of the bias switch 322a is connected to the terminal of the drive signal COMA.

[0085] One end of the bias switch 322b is connected to the terminal of the drive signal COMB.

[0086] The other end of the detection switch 321n, one end of the detection resistor 331, the - input terminal of the first amplifier 341, and the + input terminal of the second amplifier 342 are electrically connected at the third node N3.

[0087] The other end of the sensing resistor 331, the other end of the bias switch 322a, the other end of the bias switch 322b, the + input terminal of the first amplifier 341, and the - input terminal of the second amplifier 342 are electrically connected to the second node N2.

[0088] Drive switch 321a switches the connection state of drive signal COMA with the first node N1 between on and off states. Drive switch 321b switches the connection state of drive signal COMB with the first node N1 between on and off states. Drive switches 321a and 321b are switches used to selectively apply drive signal COMA and drive signal COMB to the first node N1, respectively.

[0089] Here, the two drive signals COMA and COMB are generated by... Figure 3 The drive signal generation unit 33 shown generates the signal. The drive signal generation unit 33 is controlled by the control unit 6.

[0090] The first head unit 301 includes a detection switch 321n. The detection switch 321n switches the connection state between the first node N1 and the third node N3, and the connection state between the first node N1 and the second node N2, respectively, between being on and off. The detection switch 321n is a switch used to switch between a state where a residual vibration signal can be supplied to the residual vibration signal generation circuit and a state where it cannot be supplied, by switching the connection state between the first node N1 and the third node N3 between being on and off.

[0091] Here, drive switch 321a, drive switch 321b and detection switch 321n are... Figure 3 The control unit 6 shown is used for control.

[0092] Here, the drive switch 321a, drive switch 321b and detection switch 321n can also be constructed using a transmission gate (TG).

[0093] Furthermore, the transmission gate may have, for example, a P-channel transistor and an N-channel transistor connected in parallel, but it may also be composed of transistors from either channel.

[0094] The first head unit 301 has a bias switch 322a and a bias switch 322b corresponding to the drive signal COMA and the drive signal COMB, respectively.

[0095] Here, bias switches 322a and 322b correspond to drive switches 321a and 321b respectively, and are not present if a part of drive switches 321a and 321b is not present.

[0096] Bias switch 322a switches the connection state between the second node N2 and the drive signal COMA between on and off. Bias switch 322b switches the connection state between the second node N2 and the drive signal COMB between on and off. Bias switches 322a and 322b are used to selectively apply drive signal COMA and drive signal COMB to the second node N2, respectively.

[0097] Here, bias switches 322a and 322b are... Figure 3 The control unit 6 shown is used for control.

[0098] Here, bias switches 322a and 322b can also be constructed using transmission gates, for example.

[0099] The first head unit 301 includes a residual vibration signal generation circuit, an analog differential residual vibration signal generation circuit, a demodulation circuit 351, an AD converter 361, and an FPGA 371. The residual vibration signal generation circuit includes an upper electrode 312, a detection switch 321n, and a detection resistor 331. The residual vibration signal generation circuit detects the change in the electromotive force of the first piezoelectric element 311 caused by residual vibration within the pressure chamber connected to the nozzle after the supply of a drive signal, and outputs this as a residual vibration signal. That is, the residual vibration signal generation circuit acquires the waveform of the residual vibration signal. The residual vibration signal is acquired as an analog signal. Alternatively, the residual vibration signal generation circuit can also be referred to as a residual vibration detection unit that detects the residual vibration signal as a waveform of an analog signal. The pressure chamber refers to... Figure 4 Cavity 258 is shown.

[0100] The detection resistor 331 functions as a bias resistor for supplying the voltage to the drive signal COMA or the drive signal COMB. When at least one of the connection states of the second node N2 and the drive signal COMA or the second node N2 and the drive signal COMB is turned on via bias switch 322a or bias switch 322b, and the connection state of the first node N1 and the third node N3 is turned on via detection switch 321n, a potential difference is generated across the detection resistor 331 due to residual vibration. In the first head unit 301, the state of the nozzle is determined by detecting this potential difference, the delay time of the residual vibration, and the period of the residual vibration.

[0101] 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 was obtained by the residual vibration signal generation circuit, is amplified into a differential signal by the analog differential residual vibration signal generation circuit. This differential signal is also called the analog differential residual vibration signal.

[0102] The analog differential residual vibration signal generation circuit includes a first amplifier 341 and a second amplifier 342. In this embodiment, as an example, the first amplifier 341 and the second amplifier 342 are discrete components. Therefore, in this embodiment, as an example, the analog differential residual vibration signal generation circuit is composed of discrete components. The first amplifier 341 and the second amplifier 342 are respectively disposed at different positions on the head substrate.

[0103] The first amplifier 341 outputs a first signal amplified from the residual vibration signal. The second amplifier 342 amplifies the residual vibration signal at the same magnification as the first amplifier 341 and outputs a second signal inverted from it. The first and second signals have opposite polarities and equal amplitudes. Therefore, the first and second signals constitute an analog differential residual vibration signal.

[0104] In this embodiment, as an example, the first amplifier 341 and the second amplifier 342 are each composed of a negative feedback type amplifier using an operational amplifier, and the amplitude of the output signal can be adjusted by a variable resistor that divides the voltage of its output signal.

[0105] The first signal output from the first amplifier 341 and the second signal output from the second amplifier 342 are respectively input to the demodulation circuit 351. That is, the analog differential residual vibration signal generated by the analog differential residual vibration signal generation circuit is input to the demodulation circuit 351.

[0106] Demodulation circuit 351 demodulates the first signal input from first amplifier 341 and the second signal input from second amplifier 342, and outputs a demodulated signal. That is, demodulation circuit 351 demodulates the analog differential residual vibration signal and outputs a demodulated signal. The demodulated signal is an analog signal. Furthermore, the waveform of the demodulated signal and the waveform of the residual vibration signal are, for example, identical.

[0107] As an example, demodulation circuit 351 features a differential input amplifier. Demodulation circuit 351 amplifies the analog differential residual vibration signal while suppressing or removing noise.

[0108] The demodulated signal demodulated by demodulation circuit 351 is input to AD converter 361.

[0109] The AD converter 361 converts the demodulated signal output from the demodulation circuit 351 into a digital signal. The AD converter 361 then outputs the converted digital signal to the FPGA 371.

[0110] The FPGA 371 determines the state within the pressure chamber based on the digital signal output from the AD converter 361. The FPGA 371 is equivalent to... Figure 3 The FPGA 61 shown is an example. FPGA 371 is an example of a decision unit.

[0111] In this embodiment, during the printing operation, a test drive signal is applied to the first piezoelectric element 311, and the resulting pressure change within the cavity 258, i.e., the residual vibration, is detected by the residual vibration signal generation circuit as a change in the electromotive force of the first piezoelectric element 311. The drive signal generation unit 33 supplies the test drive signal to the first piezoelectric element 311 based on the control signal output from the control unit 6. On the other hand, when detecting residual vibration, the control unit 6 supplies the electromotive force of the first piezoelectric element 311 to the residual vibration signal generation circuit.

[0112] The residual vibration signal generation circuit detects the signal representing the change in electromotive force of the first piezoelectric element 311 as the residual vibration signal.

[0113] Although Figure 7 Detailed illustrations are omitted in the example, but the first head unit 301 and the plurality of nozzles each have a plurality of piezoelectric element sections. Each piezoelectric element section is composed of one or more piezoelectric elements.

[0114] exist Figure 7 The example shows a case where a single piezoelectric element, namely the first piezoelectric element 311, is used as the piezoelectric element section, but it is not limited to this. For example, a combination of multiple piezoelectric elements can also be used as the piezoelectric element section.

[0115] Here, the AD converter 361 is mounted on the drive substrate 503. The first amplifier 341 and the second amplifier 342, serving as the residual vibration signal generation circuit, are mounted on the head substrate 501. In the first head unit 301, the residual vibration signal obtained 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 361 via the demodulation circuit 351. That is, in the first head unit 301, the distance from the head substrate 501 to the drive substrate 503 is greater than a predetermined distance. In the first head unit 301, differential transmission is used to transmit the residual vibration signal from the residual vibration signal generation circuit to the AD converter 361. In the first head unit 301, noise immunity is improved through this differential transmission.

[0116] As described above, the demodulated signal input from the demodulation circuit 351 to the AD converter 361 is an analog signal. Therefore, the demodulation circuit 351 and the AD converter 361 are preferably located as close as possible to each other.

[0117] Here, refer to Figure 8 The other structures of the first head unit will be described. Figure 8 The first A-head unit 301A shown includes a residual vibration signal generation circuit, an analog differential residual vibration signal generation circuit, a demodulation circuit 351, an AD converter 361, and an FPGA 371. When... Figure 8 The first A-head unit 301A shown is... Figure 7 When comparing the first head unit 301 shown, the structures of the residual vibration signal generation circuits are different.

[0118] In the first A-head unit 301A, the analog differential residual vibration signal generation circuit includes an amplifier 346 and a differential output unit 347. As an example, the amplifier 346 and the differential output unit 347 are mounted as part of a single IC component. As an example, the amplifier 346 is an operational amplifier as an IC component. The differential output unit 347 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 constructed from an IC component. Compared to the case where it is constructed from discrete components, constructing the analog differential residual vibration signal generation circuit from an IC component reduces the circuit size.

[0119] The positive input terminal of amplifier 346 is electrically connected to the second node N2. The negative input terminal of amplifier 346 is electrically connected to the third node N3. Amplifier 346 amplifies the residual vibration signal.

[0120] Differential output 347 generates and outputs an analog differential residual vibration signal based on the residual vibration signal amplified by amplifier 346. That is, differential output 347 outputs a first signal and a second signal after amplifying the residual vibration signal. The first signal output from differential output 347 and the second signal output from second amplifier 342 are respectively input to demodulation circuit 351.

[0121] Next, refer to Figure 9 The structure of the substrate of the first head unit 301 will be described. Figure 9 This is a schematic diagram illustrating an example of the structure of the substrate of the first head unit 301 according to this embodiment.

[0122] The first head unit 301 includes a head substrate 501, an extension cable 502, and a drive substrate 503. The head substrate 501 and the drive substrate 503 are connected by the extension cable 502.

[0123] The residual vibration signal generation circuit 601 and the analog differential residual vibration signal generation circuit 602 are mounted on the head substrate 501. The residual vibration signal generation circuit 601 is positioned on the side closer to the piezoelectric element 200 than the analog differential residual vibration signal generation circuit 602.

[0124] The driving circuit 603, demodulation circuit 604, AD converter 605, and FPGA 606 are mounted on the driving substrate 503. The driving circuit 603, demodulation circuit 604, AD converter 605, and FPGA 606 are arranged sequentially in the driving substrate 503 near the head substrate 501.

[0125] Head substrate 501 is an example of a first substrate on which an analog differential residual vibration signal generation circuit is mounted. Drive substrate 503 is an example of a second substrate on which a demodulation circuit is mounted. The first substrate and the second substrate are configured as different substrates.

[0126] Figure 9 The residual vibration signal generation circuit 601 shown is... Figure 7 The residual vibration signal generation circuit shown corresponds to this. That is, the residual vibration signal generation circuit 601 corresponds to the upper electrode 312, the detection switch 321n, and the detection resistor 331. Figure 9 The analog differential residual vibration signal generation circuit 602 shown is... Figure 7 The analog differential residual vibration signal generation circuit 602 corresponds to the first amplifier 341 and the second amplifier 342. Furthermore, the analog differential residual vibration signal generation circuit 602 can also be used with... Figure 8 The analog differential residual vibration signal generation circuit shown corresponds to this. In this case, the analog differential residual vibration signal generation circuit 602 corresponds to the amplifier 346 and the differential output 347.

[0127] Figure 9 The driving circuit 603 shown is Figure 3 This corresponds to the drive signal generation unit 33 shown.

[0128] Figure 9 The demodulation circuit 604, AD converter 605, and FPGA 606 shown are respectively connected to... Figure 7 The demodulation circuit 351, AD converter 361, and FPGA 371 shown correspond to each other.

[0129] The residual vibration signal generation circuit 601 and the AD converter 605 are mounted on different substrates, namely the head substrate 501 and the drive substrate 503, respectively. Therefore, compared with the case where the residual vibration signal generation circuit 601 and the AD converter 605 are mounted on the same substrate, the distance from the residual vibration signal generation circuit 601 to the AD converter 605 becomes longer.

[0130] Furthermore, in the first head unit 301, the head substrate 501 and the drive substrate 503 are connected by an extension cable 502. Therefore, the distance from the residual vibration signal generation circuit 601 to the AD converter 605 is at least longer than the length of the extension cable 502.

[0131] In addition, such as Figure 9As shown, in the drive substrate 503, the drive circuit 603 is mounted on the side closer to the head substrate 501 than the AD converter 605. That is, the drive circuit 603 is mounted between the residual vibration signal generation circuit 601 and the AD converter 605. The distance from the residual vibration signal generation circuit 601 to the AD converter 605 is at least an amount greater than the size of the drive substrate 503.

[0132] Therefore, in the first head unit 301, a residual vibration signal, which is an analog signal, needs to be transmitted over the distance from the residual vibration signal generation circuit 601 to the AD converter 605. In the first head unit 301, 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 602 to the demodulation circuit 604. Therefore, in the first head unit 301, noise immunity during the transmission of the residual vibration signal can be improved.

[0133] In addition, the analog differential residual vibration signal generation circuit 602 and the demodulation circuit 604 can also be mounted on the same substrate.

[0134] Alternatively, the AD converter 605 can be mounted on a different substrate than the drive substrate 503. However, as in this embodiment, mounting the AD converter 605 on the drive substrate 503, where the demodulation circuit 604 is mounted, shortens the distance between the demodulation circuit 604 and the AD converter 605. The shorter this distance, the shorter the distance the demodulated analog signal travels from the demodulation circuit 604 to the AD converter 605, thus improving the noise immunity during the transmission of residual vibration signals.

[0135] Alternatively, the residual vibration signal generation circuit 601 can be mounted on a different substrate than the head substrate 501. However, as in this embodiment, mounting the residual vibration signal generation circuit 601 on the head substrate 501 on which the analog differential residual vibration signal generation circuit 602 is mounted can shorten the distance between the residual vibration signal generation circuit 601 and the analog differential residual vibration signal generation circuit 602. The shorter this distance, the shorter the distance the residual vibration signal detected by the residual vibration signal generation circuit 601 travels from the residual vibration signal generation circuit 601 to the analog differential residual vibration signal generation circuit 602, thus improving the noise immunity during the transmission of the residual vibration signal.

[0136] As described above, the head unit according to this embodiment includes a piezoelectric element, a drive signal generation unit 33, a residual vibration signal generation circuit, an analog differential residual vibration signal generation circuit, a demodulation circuit, an AD converter, and a determination unit.

[0137] The piezoelectric element is displaced according to the drive signal, causing the liquid to be ejected.

[0138] The drive signal generation unit 33 generates drive signals.

[0139] The residual vibration signal generation circuit detects the change in the electromotive force of the piezoelectric element caused by the residual vibration in the pressure chamber connected to the nozzle after the drive signal is supplied, and outputs it as a residual vibration signal.

[0140] The analog differential residual vibration signal generation circuit converts the residual vibration signal into an analog differential residual vibration signal.

[0141] The demodulation circuit demodulates the analog differential residual vibration signal and outputs the demodulated signal.

[0142] An AD converter converts a demodulated signal into a digital signal.

[0143] The judgment unit determines the state of the pressure chamber based on digital signals.

[0144] In this embodiment, head unit 35 or first head unit 301 is an example of a head unit.

[0145] In this embodiment, drive signal COMA and drive signal COMB are examples of drive signals.

[0146] In this embodiment, piezoelectric element 200 or first piezoelectric element 311 is an example of a piezoelectric element.

[0147] In this embodiment, cavity 258 is an example of a pressure chamber.

[0148] In this embodiment, the upper electrode 312, the detection switch 321n, and the detection resistor 331, or the residual vibration signal generation circuit 601, is an example of a residual vibration signal generation circuit.

[0149] In this embodiment, the first amplifier 341, the second amplifier 342, the amplifier 346, and the differential output 347, or the analog differential residual vibration signal generation circuit 602, are examples of analog differential residual vibration signal generation circuits.

[0150] In this embodiment, demodulation circuit 351 or demodulation circuit 604 is an example of a demodulation circuit.

[0151] In this embodiment, AD converter 361 or AD converter 605 is an example of an AD converter.

[0152] In this embodiment, FPGA61, FPGA371, or FPGA606 is an example of a decision unit.

[0153] According to this structure, in the head unit (first head unit 301 in this embodiment), the residual vibration signal, as an analog signal, is transmitted via differential transmission, and noise overlap during transmission can be removed by demodulation before the residual vibration signal is input to the AD converter 361. That is, in the head unit of this embodiment, by performing differential transmission on the residual vibration signal, noise immunity can be improved. Therefore, in the head unit of this embodiment, the detection accuracy of residual vibration can be improved. In the head unit of this embodiment, for example, four-directional GND guard rings are not required.

[0154] Here, for comparison with the head unit involved in this embodiment, refer to Figure 10 The circuit structure of the existing head unit 901A is described below. The existing head unit 901A includes a residual vibration signal generation circuit, an amplifier 941, an AD converter 951, and an FPGA 971. When... Figure 10 The existing head unit 901A shown is... Figure 7 When compared with the first head unit 301 shown, the existing head unit 901A differs in that it has an amplifier 941 instead of an analog differential residual vibration signal generation circuit.

[0155] In the existing head unit 901A, the residual vibration signal, which is an analog signal, is amplified by the amplifier 941 installed inside the head substrate and then input to the AD converter 951 in a single-ended transmission mode. Subsequently, based on the signal digitized by the AD converter 951, the FPGA 971 determines the state of the nozzle.

[0156] Based on the existing head unit 901A structure, the residual vibration signal is transmitted as an analog signal from amplifier 941 to AD converter 951. Here, AD converter 951 is mounted on the drive circuit board. This is because the circuit size of an AD converter like AD converter 951 is too large to be installed inside the head unit board.

[0157] In industrial printing apparatuses, the distance from the head substrate to the drive circuit board is sometimes significant. Therefore, according to the existing head unit 901A structure, the residual vibration signal, which is an analog signal, needs to be transmitted over a long distance from an amplifier 941 mounted on the head substrate to an AD converter 951 mounted on the drive circuit board. During this transmission from the amplifier 941 to the AD converter 951, noise from peripheral devices can easily be superimposed on the residual vibration signal, which is an analog signal. When noise superimposed on the residual vibration signal, the AD converter performs digitization with the noisy waveform. This noisy waveform sometimes differs significantly from the original residual vibration waveform. As a result, in the existing head unit 901A, the nozzle state is sometimes incorrectly determined.

[0158] Furthermore, in recent years, the substrates of liquid ejection devices have seen an increase in semiconductor density, with more semiconductor devices clustered around the head. On the other hand, to transmit residual vibration signals as analog signals, wiring layouts with improved noise immunity are necessary. As a result, wiring distances for other signals are extended, or wiring layouts for other signals become more complex, leading to a decrease in signal quality.

[0159] On the other hand, in the head unit according to this embodiment, the noise resistance can be improved by differentially transmitting the residual vibration signal, thereby alleviating the constraints of the wiring layout of the substrate used to transmit the residual vibration signal and thus increasing the degree of freedom of wiring.

[0160] The above description, with reference to the accompanying drawings, details one embodiment of the present disclosure. However, the specific structure is not limited to the structure described above, and various design changes can be made without departing from the spirit of the present disclosure.

Claims

1. A head unit, characterized in that, have: The piezoelectric element is displaced according to the driving signal, causing the liquid to be ejected; A drive signal generation unit generates the drive signal; The residual vibration signal generation circuit detects the change in the electromotive force of the piezoelectric element in the residual vibration in the pressure chamber connected to the nozzle after the driving signal is supplied, and outputs it as a residual vibration signal. A circuit for generating analog differential residual vibration signals converts the residual vibration signals into analog differential residual vibration signals. The demodulation circuit demodulates the analog differential residual vibration signal and outputs a demodulated signal. An AD converter converts the demodulated signal into a digital signal. The determination unit determines the state of the pressure chamber based on the digital signal; The first substrate is equipped with the analog differential residual vibration signal generation circuit; as well as The second substrate is equipped with the demodulation circuit. The first substrate is different from the second substrate. The first substrate and the second substrate are connected by an extension cable.

2. The head unit according to claim 1, characterized in that, The analog differential residual vibration signal generation circuit is composed of discrete components.

3. The head unit according to claim 1, characterized in that, The analog differential residual vibration signal generation circuit is composed of IC components.

4. The head unit according to claim 1, characterized in that, The second substrate is equipped with the AD converter.

5. The head unit according to claim 1, characterized in that, The first substrate is equipped with a residual vibration signal generation circuit.

6. A liquid ejection device, comprising a conveying mechanism and a head unit, characterized in that, The head unit includes: The piezoelectric element is displaced according to the driving signal, causing the liquid to be ejected; A drive signal generation unit generates the drive signal; The residual vibration signal generation circuit detects the change in the electromotive force of the piezoelectric element in the residual vibration in the pressure chamber connected to the nozzle after the driving signal is supplied, and outputs it as a residual vibration signal. A circuit for generating analog differential residual vibration signals converts the residual vibration signals into analog differential residual vibration signals. The demodulation circuit demodulates the analog differential residual vibration signal and outputs a demodulated signal. An AD converter converts the demodulated signal into a digital signal. The determination unit determines the state of the pressure chamber based on the digital signal; The first substrate is equipped with the analog differential residual vibration signal generation circuit; as well as The second substrate is equipped with the demodulation circuit. The first substrate is different from the second substrate. The first substrate and the second substrate are connected by an extension cable.

7. The liquid ejection device according to claim 6, characterized in that, The analog differential residual vibration signal generation circuit is composed of discrete components.

8. The liquid ejection device according to claim 6, characterized in that, The analog differential residual vibration signal generation circuit is composed of IC components.

9. The liquid ejection device according to claim 6, characterized in that, The second substrate is equipped with the AD converter.

10. The liquid ejection device according to claim 6, characterized in that, The first substrate is equipped with a residual vibration signal generation circuit.

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