JP2016165819A - Liquid droplet discharge device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid droplet discharge device capable of improving drive efficiency when applying different driving signals to a piezoelectric element in the liquid droplet discharge device using the piezoelectric element as liquid droplet discharge control means.SOLUTION: A liquid droplet discharge device includes a nozzle for discharging liquid droplets. The liquid droplet discharge device further includes: a piezoelectric element 161 for generating discharge force to discharge liquid droplets from the nozzle; a prevention drive signal generation section for driving the piezoelectric element 161 to generate a prevention drive signal which is a drive signal to prevent discharge defectives of the liquid droplets from the nozzle; a drive waveform generation section 201 for driving the piezoelectric element 161 to generate a droplet discharge drive signal which is a drive signal to discharge liquid droplets from the nozzle for a purpose other than the prevention of the discharge defectives; and drive signal changeover sections 215, 216, and 217 for switching the droplet discharge drive signal and the prevention drive signal as the drive signals to drive the piezoelectric element 161.SELECTED DRAWING: Figure 10

Description

  The present invention relates to a droplet discharge device and an image forming apparatus.

  In recent years, there has been a tendency to digitize information, and image processing apparatuses such as printers and facsimiles used for outputting digitized information and scanners used for digitizing documents have become indispensable devices. Such an image processing apparatus is often configured as a multifunction machine that can be used as a printer, a facsimile, a scanner, or a copier by providing an imaging function, an image forming function, a communication function, and the like.

  Among such image processing apparatuses, as an aspect of a printer that is used for outputting digitized information, there is a printer that employs an inkjet method (hereinafter referred to as an inkjet printer). In an inkjet printer, an image is formed by a recording head ejecting ink onto a recording medium such as paper.

  As a mode for controlling ink ejection in the recording head, there are a method using a piezoelectric element, a method in which ink is heated to generate bubbles and ink is ejected by the pressure, and a method using electrostatic force. In a recording head using such an ejection control means, a high-density multi-nozzle can be realized relatively easily, and a high-definition image can be formed on a recording medium.

  For example, in a recording head using a piezoelectric element as an ejection control unit, ink is ejected from each nozzle by applying a driving signal that constitutes a predetermined driving waveform to the piezoelectric element. In addition, the generated drive waveform is common for each gradation, but by selectively applying a drive pulse constituting the drive waveform to the piezoelectric element, ink dots of different sizes can be divided, The piezoelectric element can be driven differently, such as preventing ink ejection failure. Prevention of ink ejection failure is, for example, adjusting the ink viscosity by finely driving the nozzles.

  For the purpose of accurately controlling the load of such a piezoelectric element, it has been proposed to increase the types of voltage values that can be output and to increase the accuracy of the voltage waveform while suppressing an increase in circuit scale. (For example, see Patent Document 1).

  As described above, a common drive waveform for one printing cycle (hereinafter referred to as “common drive waveform”) is generated by a drive signal for ejecting ink (hereinafter referred to as “droplet ejection drive signal”) and fine drive. It is composed of drive signals (hereinafter referred to as “fine drive signals”) for preventing ink ejection defects. Therefore, even when only the fine drive signal is selected from the drive pulses constituting the drive waveform and applied to the piezoelectric element, it takes extra time for the droplet ejection drive signal. Similarly, even when only the droplet ejection drive signal is selected from the drive pulses constituting the drive waveform and applied to the piezoelectric element, it takes extra time for the fine drive signal.

  In this way, when the common drive waveform is composed of a plurality of drive signals that cause the piezoelectric elements to perform different operations, it takes longer than the time required to drive the piezoelectric elements, and the drive efficiency of the piezoelectric elements deteriorates. Further, in the technique disclosed in Patent Document 1, in the control of the voltage waveform applied to the load, the drive pulse that constitutes the common drive waveform is not selectively applied to the piezoelectric element. The premise in control is different.

  Such a problem is not limited to an image forming apparatus using an ink jet method, and may occur in the same manner as long as it is a liquid droplet ejection apparatus that ejects liquid droplets from a nozzle.

  The present invention has been made to solve such problems, and in a droplet ejection apparatus using a piezoelectric element as a droplet ejection control means, driving efficiency when different driving signals are applied to the piezoelectric element. It aims at improving.

  In order to solve the above problems, an aspect of the present invention is a droplet discharge device having a nozzle that discharges a droplet, and an actuator element that generates a discharge force for discharging a droplet from the nozzle; A prevention drive signal generation unit that generates a prevention drive signal that is a drive signal for driving the actuator element to prevent a droplet ejection failure from the nozzle, and preventing the ejection failure by driving the actuator element. A droplet discharge drive signal generation unit that generates a droplet discharge drive signal that is a drive signal for discharging droplets from the nozzle for purposes other than the above, and the droplet discharge drive signal as a drive signal for driving the actuator element And a drive signal switching unit that switches between the prevention drive signals.

  According to the present invention, in a droplet discharge device using a piezoelectric element as droplet discharge control means, it is possible to improve the driving efficiency when different drive signals are applied to the piezoelectric element.

1 is a diagram illustrating an overall configuration of an inkjet printer according to an embodiment of the present invention. 1 is a block diagram illustrating a functional configuration of an inkjet printer according to an embodiment of the invention. FIG. 2 is a diagram schematically illustrating a configuration of a recording head according to an embodiment of the invention. FIG. 2 is a cross-sectional view of a recording head according to an embodiment of the invention. 3 is a block diagram illustrating a functional configuration of a print control unit and a head driver according to the embodiment of the invention. FIG. It is a figure which illustrates the drive signal of the head driver which concerns on embodiment of this invention. It is a figure which illustrates the drive signal of the head driver which concerns on embodiment of this invention. It is a figure which illustrates the conventional drive circuit for the comparison with the drive circuit which concerns on embodiment of this invention. It is a figure which illustrates the common drive waveform produced | generated when driving each piezoelectric element in the drive circuit for the comparison with the drive circuit which concerns on embodiment of this invention. It is a figure which illustrates the drive circuit which concerns on embodiment of this invention. It is a figure which illustrates the drive circuit which concerns on embodiment of this invention. It is a figure which illustrates the droplet discharge drive waveform and fine drive waveform in the operation state of the drive circuit which concerns on embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, an ink jet printer including a multi-channel ink jet recording head will be described as an example of a droplet discharge device. The ink jet printer is also an image forming apparatus that forms an image by ejecting ink with a droplet ejecting apparatus.

  1A and 1B are diagrams schematically showing the overall configuration of the ink jet printer 1 according to the present embodiment. FIG. 1A is a perspective view of the ink jet printer 1, and FIG. FIG. 3 is a perspective side view of the inkjet printer 1.

  As shown in FIGS. 1A and 1B, the ink jet printer 1 according to the present embodiment includes a carriage 101 that can move in the main scanning direction inside the apparatus main body, a recording head 102 mounted on the carriage 101, and recording. It includes a printing mechanism section and the like configured by an ink cartridge 103 that supplies ink to the head 102. A paper feed cassette (or a paper feed tray) 104 on which a recording medium such as a large number of sheets P can be loaded from the front side of the apparatus main body of the inkjet printer 1 can be detachably mounted. Further, in the inkjet printer 1, the manual feed tray 105 for manually feeding the paper P can be opened.

  The ink jet printer 1 takes in the paper P fed from the paper feed cassette 104 or the manual feed tray 105, records a required image by the printing mechanism described above, and then discharges the paper onto a paper discharge tray 106 mounted on the rear side. To do. In the following description, the recording medium is a sheet. However, the recording medium is not only a sheet but also a sheet-like material such as a film or plastic, as long as it is an object for image formation output. It can be adopted.

  In addition, the printing mechanism unit holds the carriage 101 slidably in the main scanning direction (the direction perpendicular to the paper surface) with a main guide rod 107 and a sub guide rod 108 which are guide members horizontally mounted on left and right side plates (not shown). ing. The recording head 102 mounted on the carriage 101 ejects ink droplets of each color of yellow (Yellow), cyan (Cyan), magenta (Magenda), and black (blackK). The plurality of ink discharge ports that discharge these color inks are arranged in a direction crossing the main scanning direction, and the ink discharge ports are directed downward.

  Each ink cartridge 103 for supplying ink of each color to the recording head 102 is replaceably mounted on the carriage 101. In addition, the ink cartridge 103 has an air port communicating with the standby on the upper side, a supply port for supplying ink to the recording head 102 on the lower side, and a porous body filled with ink inside. The ink supplied to the recording head 102 is maintained at a slight negative pressure by the capillary force of the porous body. In this embodiment, the recording head 102 is provided for each color. However, a single head having nozzles for ejecting ink of each color may be used.

  The carriage 101 is slidably attached to the main guide rod 107 on the rear side (downstream side in the paper conveyance direction), and slidably attached to the sub guide rod 108 on the front side (upstream side in the paper conveyance direction). In order to move and scan the carriage 101 in the main scanning direction, a timing belt 112 is stretched between a driving pulley 110 and a driven pulley 111 that are rotationally driven by a main scanning motor 109. The timing belt 112 and the carriage 101 are fixed, and the carriage 101 is reciprocated by forward and reverse rotation of the main scanning motor 109.

  On the other hand, in order to convey the sheet set in the sheet feeding cassette 104 to the lower side of the recording head 102, a sheet feeding roller 113, a friction pad 114, a guide member 115, a conveying roller 116, a conveying roller 117, and a leading end roller 118 are provided. It has been. The paper feed roller 113 and the friction pad 114 separate and feed the paper P from the paper feed cassette 104, and the guide member 115 guides the paper P separated and fed.

  The transport roller 116 reverses and transports the fed paper P. The conveyance roller 117 is pressed against the circumferential surface of the conveyance roller 116, and the leading end roller 118 defines the feeding angle of the paper P from the conveyance roller. Further, the transport roller 116 is rotationally driven through a gear train by a sub scanning motor (not shown).

  A printing receiving member 119 is provided as a paper guide member that guides the paper P fed from the transport roller 116 on the lower side of the recording head 102 corresponding to the range of movement of the carriage 101 in the main scanning direction. On the downstream side of the printing receiving member 119 in the paper conveyance direction, a conveyance roller 120 and a spur 121 that are rotationally driven to send the paper P in the paper discharge direction are provided. Further, a paper discharge roller 122 and a spur 123 that send the paper P to the paper discharge tray 106, and guide members 124 and 125 that form a paper discharge path are arranged.

  At the time of image recording on the paper P, the controller of the ink jet printer 1 drives the recording head 102 in accordance with the image signal while moving the carriage 101, thereby ejecting ink onto the stopped paper P to perform one scan. Record. Then, the controller of the ink jet printer 1 records the next line after conveying the paper P by a predetermined amount. When the controller of the inkjet printer 1 receives a recording end signal or a signal that the trailing edge of the paper P reaches the recording area, the controller ends the recording operation and discharges the paper P.

  The recording head 102 includes a piezoelectric element as a driving element for driving a plurality of nozzles provided as described above. That is, in the inkjet printer 1 according to the present embodiment, a piezoelectric element is used as an actuator element that generates an ejection force for ejecting ink (droplets) from each of a plurality of nozzles. By applying a predetermined drive waveform to the piezoelectric element, ink is ejected from each nozzle.

  A maintenance / recovery device 126 for recovering the ejection failure of the recording head 102 is disposed at a position outside the recording area on the right end side in the movement direction of the carriage 101. The maintenance / recovery device 126 includes a cap unit, a suction unit, and a cleaning unit. The carriage 101 is moved to the maintenance / recovery device 126 side during printing standby, and the recording head 102 is capped by the capping means. Thereby, the discharge port part is kept in a wet state, and discharge failure due to ink drying is prevented.

  Further, the recording head 102 discharges ink not related to recording to the maintenance / recovery device 126 (empty discharge) during recording or the like, thereby making the ink viscosity of all the discharge ports constant and maintaining stable discharge performance. Specifically, when a discharge failure occurs, the capping unit seals the discharge port (nozzle) of the recording head 102, and the suction unit sucks out bubbles and the like from the discharge port through the tube. Then, ink or dust adhering to the ejection port surface is removed by the cleaning means, and the ejection failure is recovered. Further, the sucked ink is discharged to a waste ink reservoir (not shown) installed at the lower part of the main body and absorbed and held by an ink absorber inside the waste ink reservoir.

  Next, the functional configuration of the inkjet printer 1 according to the present embodiment will be described. FIG. 2 is a block diagram illustrating a functional configuration of the inkjet printer 1 according to this embodiment. As shown in FIG. 2, the inkjet printer 1 according to this embodiment includes a controller 100, a carriage 101, a main scanning motor 109, a sensor group 133, a conveyance belt 135, a maintenance / recovery motor 136, a charging roller 137, and an operation panel 138. . In the following, the same components as those shown in FIG. 1 are denoted by the same reference numerals as those in FIG.

  The operation panel 138 is a user interface that functions as an operation unit and a display unit for inputting and displaying information necessary for the inkjet printer 1. The carriage 101 is mounted with a recording head 102 that ejects ink and a head driver 131 that drives the recording head 102. Further, the carriage 101 is moved in the main scanning direction, which is a direction perpendicular to the sub-scanning direction, which is the conveyance direction of the sheet, with respect to the sheet conveyed by the conveyance belt 135, so that ink is applied to the front surface of the sheet. Discharge to perform image formation output.

  The main scanning motor 109 is a motor that supplies power for moving the carriage 101 in the main scanning direction. The sub-scanning motor 134 is a motor that supplies power to a conveyance belt 135 that conveys a sheet that is an image output target. The maintenance / recovery motor 136 is a motor that drives the maintenance / recovery device 126.

  The sensor group 133 is various sensors that detect various information in the inkjet printer 1. Specifically, for example, the sensor group 133 monitors a rotation detection sensor for detecting the rotation of the main scanning motor 109 and the sub scanning motor 134, an optical sensor for detecting the position of the paper, and a temperature in the apparatus. A thermistor, a sensor for monitoring the voltage of the charging belt, an interlock switch for detecting opening and closing of the cover, and the like. The charging roller 137 charges the conveyance belt 135 to generate an electrostatic force for attracting the sheet, which is an image output target, to the conveyance belt 135.

  The controller 100 is a control unit that controls the operation of the inkjet printer 1, and as shown in FIG. 2, a CPU (Central Processing Unit) 11, a ROM (Read Only Memory) 12, a RAM (Random Access Memory) 13, an NVRAM ( A non-volatile RAM (Non Volatile RAM) 14, an Application Specific Integrated Circuit (ASIC) 15, a host I / F 16, a print control unit 17, a motor drive unit 18, an AC bias supply unit 19, and an I / O 20;

  The CPU 11 is a calculation means and controls the operation of each part of the controller 100. The ROM 12 is a read-only nonvolatile storage medium, and stores programs such as firmware. The RAM 13 is a volatile storage medium capable of reading and writing information at high speed, and is used as a work area when the CPU 11 processes information. The NVRAM 14 is a nonvolatile storage medium capable of reading and writing information, and stores a control program and control parameters.

  The ASIC 15 is a hardware circuit that executes image processing necessary for image formation output. The host I / F 16 is an interface for receiving drawing data from a host device such as a PC (Personal Computer), and uses an Ethernet (registered trademark) or a USB (Universal Serial Bus) interface. The I / O 20 is a port for inputting a detection signal from the sensor group 133 to the controller 100.

  The print control unit 17 includes data transfer means for driving and controlling the recording head 102 included in the carriage 101, and drive waveform generation means for generating a drive waveform. The motor driving unit 18 drives the main scanning motor 109 and the sub scanning motor 134. The AC bias supply unit 19 supplies an AC bias to the charging roller 137.

  Drawing data from the host side, such as an information processing device such as a PC, an image reading device such as an image scanner, and an imaging device such as a digital camera, is input to the host I / F 16 by the controller 100 and stored in a reception buffer in the host I / F 16. Stored. The CPU 11 performs an operation according to the program loaded in the RAM 13 to read and analyze the print data in the reception buffer included in the host I / F 16, and controls the ASIC 15 to perform necessary image processing and data rearrangement processing. Etc. Thereafter, the CPU 11 controls the print control unit 17 to transfer the drawing data processed in the ASIC 15 to the head driver 131.

  The print control unit 17 transfers the drawing data described above to the head driver 131 as serial data, and transmits a transfer clock, a latch signal, a droplet control signal (mask signal), and the like necessary for transferring the drawing data and confirming the transfer. Output to the head driver 131. The print control unit 17 also includes a drive waveform generation unit and a head driver 131 configured by a D / A converter, a voltage amplifier, a current amplifier, and the like that perform D / A conversion on the drive signal pattern data stored in the ROM 12. Drive waveform selection means to be applied is included. In addition, the print control unit 17 generates a drive waveform including one drive pulse (drive signal) or a plurality of drive pulses (drive signal) and outputs the drive waveform to the head driver 131.

  The head driver 131 drives the recording head 102 based on one line of drawing data input serially. Specifically, the head driver 131 discharges droplets from the recording head 102 with a drive signal constituting a drive waveform supplied from the print control unit 17 based on drawing data for one line input serially. This is selectively applied to the drive element that generates the energy. At this time, the head driver 131 selects a driving pulse constituting the driving waveform, for example, large droplets (large dots), medium droplets (medium dots), small droplets (small dots), and so on. Can be sorted out.

  Here, the configuration of the recording head 102 in the carriage 101 will be described. FIG. 3 is a diagram schematically illustrating the configuration of the recording head 102 in the carriage 101 according to the present embodiment. As illustrated in FIG. 3, the carriage 101 according to the present embodiment includes recording heads 102 </ b> K, 102 </ b> C, 102 </ b> M, and 102 </ b> Y for each color of CMYK (Cyan, Magenta, Yellow, blackK) as the recording head 102. ing.

  4A is a cross-sectional view of the recording head 102 taken along the cutting line AA ′ in FIG. 3, and FIG. 4B is a cross-sectional view of the recording head 102 taken along the cutting line BB ′ in FIG. As shown in FIGS. 4A and 4B, the recording head 102 according to this embodiment includes a flow path plate 151 formed by, for example, anisotropic etching of a single crystal silicon substrate, and the flow path plate 151. A diaphragm 152 formed by nickel electroforming, for example, bonded to the lower surface and a nozzle plate 153 bonded to the upper surface of the flow path plate 151 are bonded and stacked. As a result, ink is supplied to the nozzle communication path 155 that is a flow path through which the nozzle 154 that discharges droplets (ink drops) communicates, the liquid chamber 156 that is a pressure generation chamber, and the liquid chamber 156 through the fluid resistance portion (supply path) 157. An ink supply port 159 communicating with the common liquid chamber 158 is formed.

  The recording head 102 includes two rows of stacked piezoelectric elements 161 as electromechanical conversion elements that are pressure generating means (actuator means) for deforming the diaphragm 152 to pressurize the ink in the liquid chamber 156, and And a base substrate 162 to which the piezoelectric element 161 is bonded and fixed. A strut portion 163 is provided between the piezoelectric elements 161. The column portion 163 is a portion formed at the same time as the piezoelectric element 161 by dividing the piezoelectric element member. However, since the drive voltage is not applied, the column portion 163 becomes a simple column.

  Further, an FPC (Flexible Printed Circuit) cable 164 equipped with a drive IC (not shown) is connected to the piezoelectric element 161. The periphery of the diaphragm 152 is joined to a frame member 165, and the frame member 165 serves as a through-hole 166 and a common liquid chamber 158 that house an actuator unit composed of the piezoelectric element 161 and the base substrate 162. A recess and an ink supply hole 167 for supplying ink from the outside to the common liquid chamber 158 are formed.

  The nozzle plate 153 forms a nozzle 154 having a diameter of 10 to 30 μm corresponding to each liquid chamber 156 and is bonded to the flow path plate 151 with an adhesive. The nozzle plate 153 is obtained by forming a water repellent layer on the outermost surface through a required layer on the surface of a nozzle forming member made of a metal member.

  The piezoelectric element 161 is a stacked piezoelectric element in which piezoelectric materials 168 and internal electrodes 169 are alternately stacked, and is a PZT (PbZrO3-PbTiO3) element here. The individual electrodes 170 and the common electrode 171 are connected to the internal electrodes 169 drawn to the alternately different end faces of the piezoelectric element 161. In this embodiment, the ink in the liquid chamber 156 is pressurized using the upward displacement in the drawing as the piezoelectric direction of the piezoelectric element 161. Alternatively, a structure in which one row of piezoelectric elements 161 is provided on one substrate 162 may be employed.

  In the liquid discharge head configured as described above, for example, the voltage applied to the piezoelectric element 161 is lowered from the reference potential, the piezoelectric element 161 is contracted, and the diaphragm 152 is lowered to expand the volume of the liquid chamber 156. Ink flows into the liquid chamber 156. Thereafter, by increasing the voltage applied to the piezoelectric element 161, the piezoelectric element 161 extends in the stacking direction, the diaphragm 152 deforms in the nozzle 154 direction, and the volume / volume of the liquid chamber 156 contracts. Thereby, the recording liquid in the liquid chamber 156 is pressurized, and droplets of the recording liquid are ejected (jetted) from the nozzle 154.

  Then, by returning the voltage applied to the piezoelectric element 161 to the reference potential, the diaphragm 152 is restored to the initial position, and the liquid chamber 156 expands to generate a negative pressure. Is filled with recording liquid. Therefore, after the vibration of the meniscus surface of the nozzle 154 is attenuated and stabilized, the operation moves to the next droplet discharge.

  Next, details of the print control unit 17 and the head driver 131 will be described. FIG. 5 is a block diagram illustrating the functional configuration of the print control unit 17 and the head driver 131. As shown in FIG. 5, the print control unit 17 includes a drive waveform generation unit 201 and a data transfer unit 202. As described above, the drive waveform generation unit 201 generates and outputs a drive waveform (common drive signal) composed of a plurality of drive pulses (drive signals) within one printing cycle. The data transfer unit 202 outputs 2-bit print data (gradation signals 0 and 1) corresponding to the print image, a clock signal, a latch signal (LAT), and droplet control signals M0 to M3.

  The droplet control signal is a 2-bit signal that instructs each droplet to open and close an analog switch 215 that is a switch unit of the head driver 131 described later. Specifically, for example, the droplet control signal transitions to the H level (ON) with a waveform to be selected in accordance with the printing cycle of the common drive waveform, and transitions to the L level (OFF) when not selected.

  The head driver 131 includes a shift register 211, a latch circuit 212, a decoder 213, a level shifter 214, and an analog switch 215. The shift register 211 inputs the transfer clock (shift clock) and serial print data (gradation data: 2 bits / CH) from the data transfer unit 202. The latch circuit 212 latches each resist value of the shift register 211 with a latch signal.

  The decoder 213 decodes the gradation data and the droplet control signals M0 to M3 and outputs the result. The level shifter 214 converts the logic level voltage signal of the decoder 213 to a level at which the analog switch 215 can operate. The analog switch 215 is turned on / off (opened / closed) by the output of the decoder 213 given through the level shifter 214.

  The analog switch 215 is connected to the selection electrode (individual electrode) 170 of each piezoelectric element 161, and the common drive waveform from the drive waveform generation unit 201 is input thereto. Therefore, when the analog switch 215 is turned on according to the result of decoding the serially transferred gradation data and the droplet control signals M0 to M3 by the decoder 213, a required drive signal constituting the common drive waveform passes. Applied to the piezoelectric element 161 (selected).

  Next, an example of the drive waveform will be described. 6 and 7 are diagrams illustrating driving signals of the head driver 131. As shown in FIG. 6, the drive waveform generation unit 201 generates and outputs drive signals (drive waveforms) including, for example, five drive pulses P1 to P5 within one printing cycle (one drive cycle). As shown in FIG. 6, the drive pulses P1 to P5 are composed of a waveform element that falls from the reference potential Ve, a waveform element that rises from the state after the fall, and the like. One printing cycle is determined by the maximum driving frequency.

  On the other hand, the head driver 131 selects a driving pulse to be used from the driving pulses (driving signals) constituting the driving waveform shown in FIG. 6 according to the droplet control signals M0 to M3 from the data transfer unit 202. The head driver 131 selects the drive pulse P3 as shown in FIG. 7B when forming small droplets (small dots) according to the droplet control signals M0 to M3 from the data transfer unit 202. The head driver 131 selects drive pulses P2 and P4 as shown in FIG. 7C when forming a medium drop (medium dot), and forms a large drop (large dot) as shown in FIG. As shown in d), the drive pulses P2 to P5 are selected.

  Further, in the case of fine driving, the head driver 131 selects the driving pulse P1 as shown in FIG. As described above, the nozzles perform idle ejection by fine driving, and adjust the ink viscosity to be constant. That is, the drive pulse P1 is a fine drive signal for finely driving the nozzle, and a prevention drive signal for preventing defective ejection of droplets from the nozzle. On the other hand, the drive pulses P2 to P5 are drive signals for causing droplets to be ejected from the nozzles for purposes other than prevention of ejection failure. The head driver 131 applies the drive pulse selected by each to the piezoelectric element 161 of the recording head 102.

  As described above, the recording head 102 drives the driving pulses (hereinafter referred to as “droplet ejection drive signal”) such as P2 to P5 for ejecting droplets other than the idle ejection and the driving of P1 for idle ejection. It is driven by different drive pulses such as pulses (hereinafter referred to as “fine drive signal”). In the inkjet printer 1 in which the recording head 102 is driven by such different driving pulses, the configuration of a driving circuit for efficiently driving the recording head 102 is the gist of the present embodiment.

  Here, a conventional drive circuit will be described for comparison with the configuration of the drive circuit according to the present embodiment. FIG. 8 is a diagram illustrating a conventional drive circuit for comparison with the configuration of the drive circuit according to the present embodiment. As shown in FIG. 8, the conventional drive circuit includes a controller side substrate and a carriage side substrate of the inkjet printer 1.

  The controller-side board is a board of the controller 100 shown in FIG. 2, and includes the drive waveform generation unit 201 and the resistor R of the print control unit 17 shown in FIG. The carriage side substrate is the substrate of the recording head 102 shown in FIG. 2, and includes the analog switch 215 and the piezoelectric element 161 shown in FIG.

  As shown in FIG. 8, the carriage side substrate has a plurality of piezoelectric elements 161-1 to 161-n (n is an integer of 1 or more and is not always the same number) and signals to each piezoelectric element. Switches 215-1 to 215-n for switching the application state are included. That is, in the example of the drive circuit shown in FIG. 8, the recording head 102 is composed of n nozzles for each color.

  As shown in FIG. 8, the drive waveform generation unit 201 generates a common drive waveform for the piezoelectric element 161 connected to the switch 215 that is turned on among the switches 215-1 to 215-n on the carriage side substrate. A drive signal to be configured is selectively applied. FIG. 9 is a diagram illustrating a common drive waveform generated by the drive waveform generation unit 201 when each piezoelectric element 161 is driven in the drive circuit shown in FIG.

  As shown in FIG. 9, in the common drive waveform, a fine drive signal and a droplet discharge drive signal are arranged in one printing cycle. For example, as shown in FIG. 9, the signal from the start time T0 to the time T1 of one printing cycle is the fine drive signal, and the signal from the time T1 to the end time T2 of the one printing cycle is the droplet discharge driving signal.

  The fine drive signal and the droplet ejection drive signal that constitute the common drive waveform shown in FIG. 9 are output to the carriage side substrate and selectively applied to each piezoelectric element 161 by turning on / off the switch 215. For example, it is assumed that the switch 215-1 is turned off in the fine drive signal output period (time T0 to T1) and the switch 215-1 is turned on in the droplet discharge drive signal output period (time T1 to T2). In this case, the piezoelectric element 161-1 is driven so that ink is ejected onto the paper.

  On the other hand, for example, it is assumed that the switch 215-2 is turned on in the output period of the fine drive signal and the switch 215-2 is turned off in the output period of the droplet discharge drive signal. In this case, the piezoelectric element 161-2 is finely driven to adjust the ink viscosity.

  As described above, in the drive circuit shown in FIG. 8, when each piezoelectric element 161 is driven by the common drive waveform shown in FIG. 9, even when driven by either the fine drive signal or the droplet discharge drive signal, It is necessary to wait for the output period of one drive signal. Therefore, it takes longer than the time required to drive each piezoelectric element 161, and the driving efficiency of each piezoelectric element 161 is poor.

  Next, the drive circuit according to the present embodiment will be described. FIG. 10 is a diagram illustrating a drive circuit according to this embodiment. As shown in FIG. 10, the drive circuit according to this embodiment has a configuration in which a charge pump circuit and analog switches 216-1 to 216-n are added to the drive circuit shown in FIG. The charge pump circuit accumulates charges by the capacitors 218-1 and 218-2 that are power storage elements, and discharges the accumulated charges to the piezoelectric elements 161 via the switches 216-1 to 216-n.

  In the present embodiment, the fine drive signal is generated based on the electric charge released by the charge pump circuit. That is, the charge pump circuit according to the present embodiment functions as a prevention drive signal generation unit that generates a prevention drive signal (fine drive signal) by discharging from the storage element. On the other hand, the drive waveform generation unit 201 according to the present embodiment generates a drive waveform composed only of droplet ejection drive signals. That is, the drive waveform generation unit 201 according to the present embodiment functions as a droplet discharge drive signal generation unit that generates a droplet discharge drive signal.

  The switches 216-1 to 216-n switch the application state of the fine drive signal generated by the charge pump circuit to the plurality of piezoelectric elements 161-1 to 161-n. The analog switches 217-1 to 217-7 switch a current flow in order to control charging / discharging by the capacitors 218-1 and 218-2. Hereinafter, analog switches 216-1 to 216-n, 217-1 to 217-1 to 217-7, and capacitors 218-1 and 218-2 may be referred to as switches 216, 217, and capacitors 218, respectively. .

  Specifically, when the switches 217-1, 217-4, and 217-7 are turned on, the capacitors 218-1 and 218-2 are charged, and the voltage V <b> 1 = V <b> 0 at the capacitor 218-1 is obtained. At this time, the voltage V2 = V0. Then, when the switches 217-1, 217-4, and 217-7 are turned off, for example, when the switch 215-1, the switch 216-2, and the switch 217-4 are turned on, the electric charge accumulated in the capacitor 218-1 is changed. Released.

  FIG. 11 is a diagram illustrating a drive circuit illustrating a current flow when the switch 215-1, the switch 216-2, and the switch 217-4 are turned on. As shown in FIG. 11, when the switch 216-2 and the switch 217-4 are turned on, the electric charge accumulated in the capacitor 218-1 is discharged to the piezoelectric element 161-2 at the voltage V0.

  FIG. 12 is a diagram illustrating a droplet discharge drive waveform and a fine drive waveform in the operation state of the drive circuit shown in FIG. When the switch 215-1 is turned on, a drive signal constituting the droplet discharge drive waveform shown in FIG. 12A is applied to the piezoelectric element 161-1. Further, when the switch 216-2 and the switch 217-4 are turned on, a fine drive signal constituting the fine drive waveform shown in FIG. 12B is applied to the piezoelectric element 161-2.

  That is, the switches 215, 216, and 217 function as a drive signal switching unit that switches between a droplet discharge drive signal and a prevention drive signal as a drive signal for driving the piezoelectric element 161 that is an actuator element. The drive signal switching unit switches to discharging from the capacitor 218 to the piezoelectric element 161 when switching to the prevention drive signal as a drive signal for driving the electrically capacitive piezoelectric element 161.

  In the case described with reference to FIG. 12, the electric charge charged in the capacitor 218-1 is discharged to the piezoelectric element 161, so that the piezoelectric element 161 is changed by the fine drive signal changed from the reference voltage Ve to V0. The case of driving has been described as an example. In addition, the switches 217-2, 217-5, and 217-7 may be further turned on to discharge the charge charged in the capacitor 218-2 to the piezoelectric element 161. In this case, the piezoelectric element 161 is driven by the fine drive signal changed from the reference voltage Ve to 2V0 (2V0> Ve).

  As described above, the inkjet printer 1 according to the present embodiment includes the charge pump circuit that generates the fine drive signal, in addition to the drive waveform generation unit 201 that generates the droplet discharge drive signal. Then, the inkjet printer 1 controls the switch 215 to selectively apply a droplet ejection drive signal to the piezoelectric element 161, and controls the switch 216 to selectively apply a fine drive signal to the piezoelectric element 161. To do.

  Thereby, since the droplet discharge drive signal and the fine drive signal can be applied to the piezoelectric element 161 by different systems, the droplet discharge drive signal and the fine drive signal can be output without waiting for the output period of the unnecessary drive signal within one printing cycle. The piezoelectric element 161 can be driven by the fine drive signal. Therefore, according to the present embodiment, in the inkjet printer 1, it is possible to improve the driving efficiency when different driving signals are applied to the piezoelectric elements.

  In the present embodiment, the case where the charge pump circuit generates a fine drive signal has been described as an example. Since the charge pump circuit includes the switch 217 and the capacitor 218, such a configuration can suppress an increase in circuit scale. However, instead of the charge pump circuit, a generation circuit that generates a fine drive signal different from the drive waveform generation unit 201 may be provided.

  In the present embodiment, the case where the voltage charged in the capacitor 218 is V0 is described as an example. However, the voltage charged in the capacitor 218 is varied by resistance division or the like to be an arbitrary voltage. Also good.

  The present embodiment is not limited to the serial type image forming apparatus which is the ink jet printer 1 shown in FIG. 1, and can be similarly applied to other types of image forming apparatuses. As another type of image forming apparatus, for example, a line type in which overlap processing is performed in which the end nozzles of adjacent heads are arranged in an overlapping manner and the overlapping portion image is formed by overlapping dots with overlapping nozzles is formed. An image forming apparatus is mentioned. In addition, for example, there is a serial type image forming apparatus having a connection head configuration. In addition, the present embodiment is not limited to an image forming apparatus using an inkjet method, and can be similarly applied to a droplet discharge device that discharges droplets from nozzles.

1 Inkjet printer 11 CPU
12 ROM
13 RAM
14 NVRAM
15 ASIC
16 Host I / F
17 Print Control Unit 18 Motor Drive Unit 19 AC Bias Supply Unit 20 I / O
DESCRIPTION OF SYMBOLS 100 Controller 101 Carriage 102 Inkjet head 103 Ink cartridge 104 Paper feed cassette 105 Manual feed tray 106 Paper discharge tray 107 Main guide rod 108 Subordinate guide rod 109 Main scanning motor 110 Drive pulley 111 Follow pulley 112 Timing belt 113 Feed roller 114 Friction pad 115 Guide member 116 Conveying roller 117 Conveying roller 118 Leading end roller 119 Printing receiving member 120 Conveying roller 121 Spur 122 Discharge roller 123 Spur 124 Guide member 126 Maintenance and recovery device 131 Head driver 133 Sensor group 134 Sub-scanning motor 135 Conveying belt 136 Maintenance and recovery Motor 137 Charging roller 138 Operation panel 151 Flow path plate 152 Vibration plate 153 Nozzle plate 154 Noz 155 Communication path 156 Liquid chamber 157 Fluid resistance portion 158 Common liquid chamber 159 Ink supply port 161 Piezoelectric element 162 Base substrate 163 Supporting portion 164 FPC cable 165 Frame member 166 Through portion 167 Ink supply hole 168 Piezoelectric material 169 Internal electrode 170 Individual electrode 171 Common electrode 201 Drive waveform generation unit 202 Data transfer unit 211 Shift register 212 Latch circuit 213 Decoder 214 Level shifter 215, 216, 217 Analog switch 218 Capacitor

Japanese Patent No. 4775482

Claims (4)

A droplet discharge device having a nozzle for discharging a droplet,
An actuator element for generating a discharge force for discharging a droplet from the nozzle;
A preventive drive signal generating unit that generates a preventive drive signal that is a drive signal for driving the actuator element to prevent defective ejection of droplets from the nozzle;
A droplet discharge drive signal generation unit that generates a droplet discharge drive signal that is a drive signal for driving the actuator element to discharge droplets from the nozzle for purposes other than prevention of the discharge failure;
A droplet discharge device comprising: a drive signal switching unit that switches between the droplet discharge drive signal and the prevention drive signal as a drive signal for driving the actuator element. The prevention drive signal generation unit includes a storage element, generates the prevention drive signal by charging / discharging from the storage element,
The drive signal switching unit switches to discharging from the power storage element to the electrically capacitive actuator element when switching to the prevention drive signal as a drive signal for driving the actuator element. The droplet discharge device according to claim 1. The droplet ejection apparatus according to claim 1, wherein the prevention drive signal generation unit generates the prevention drive signal for adjusting the viscosity of the droplet by driving the actuator element.   An image forming apparatus, wherein a droplet is ejected by the droplet ejecting apparatus according to claim 1 to form an image.