JP2020116936A - Liquid discharge device and control method of drive waveform - Google Patents

Abstract

To improve image quality by reducing stepped density unevenness when switching a drive waveform according to a detected temperature in a liquid discharge device.SOLUTION: A liquid discharge device includes: a recording head which has a plurality of nozzles for discharging liquid and forms an image by discharging liquid while performing a plurality of times of scanning to a discharge object surface; moving means which moves the recording head in a main scanning direction while discharging liquid and moves the recording head in a sub-scanning direction after the recording head discharges liquid; drive waveform application means which applies each drive waveform to the plurality of nozzles; temperature detection means which detects a temperature in the vicinity of the recording head; correction means which corrects the drive waveform on the basis of the detected temperature; and control means which performs control so that a use ratio of a second drive waveform corresponding to a second temperature is gradually increased to a use ratio of a first drive waveform corresponding to a first temperature during the plurality of times of scanning when a temperature changes from a first temperature to a second temperature.SELECTED DRAWING: Figure 9

Description

The present invention relates to a liquid ejection device and a drive waveform control method.

Conventionally, as a liquid ejecting apparatus, a drive waveform is applied to a piezoelectric element, and the pressure in the ink chamber is increased or decreased by the deformation of the piezoelectric element to raise or lower the pressure in the ink chamber, thereby causing an ink droplet as a liquid to reach an object such as paper. Ink jet recording apparatuses that eject ink toward a target are known.

In such an ink jet recording apparatus, since the viscosity of the ejected ink changes depending on the ambient temperature, the temperature is detected by means such as a thermistor provided at a predetermined position in the apparatus, and the detected temperature is assumed. A technique for outputting a drive waveform corresponding to the ink viscosity is already known.

Then, in order to suppress image quality variation due to temperature change and realize high image quality, a drive waveform control method is disclosed in which the drive waveform is changed according to the temperature change of the ink to maintain an optimum ejection speed.

However, in the conventional drive waveform control method, while the temperature change of ink is continuous, the drive waveform is switched discontinuously at predetermined temperature intervals. Therefore, the volume of the ejected droplets in the drive waveform before the switching and the volume of the ejected droplets in the drive waveform after the switching relatively vary greatly, which causes density unevenness of the printed image. .. Further, the inkjet head generally has variations in ejection characteristics due to variations in manufacturing (resonance period of individual liquid chambers, etc.), and density unevenness may become significant depending on the degree of this variation. In particular, in a serial printer in which the head scans the surface of the paper, there is a problem that unevenness in density occurs in steps and the image quality deteriorates.

The present invention has been made in view of the above, and in the control for changing the drive waveform of the piezoelectric element, which is performed in response to the change in the characteristics such as the viscosity of the ejected liquid depending on the environmental temperature, the It is an object of the present invention to provide a liquid ejection apparatus and a drive waveform control method capable of suppressing the occurrence of liquid concentration unevenness on an ejection target surface.

In order to solve the above-mentioned problems and achieve the object, a liquid ejecting apparatus according to the present invention has a plurality of nozzles for ejecting a liquid, and the liquid is ejected while performing a plurality of scans on an ejection target surface. A recording head that ejects onto the ejection target surface to form an image on the ejection target surface, and moves the recording head in the main scanning direction while ejecting liquid from the recording head, and after the recording head ejects liquid Moving means for moving the recording head in the sub-scanning direction, driving waveform applying means for applying a driving waveform to each of the plurality of nozzles, temperature detecting means for detecting a temperature in the vicinity of the recording head, and the temperature When the temperature near the recording head changes from the first temperature to the second temperature based on the temperature detected by the detection unit and the temperature near the recording head changes, during the plurality of scans, Control means for controlling the usage ratio of the second drive waveform corresponding to the second temperature to gradually increase with respect to the usage ratio of the first drive waveform corresponding to the first temperature. ..

According to the present invention, in the liquid ejection device, it is possible to improve the image quality by reducing unevenness in density when switching the drive waveform according to the detected temperature.

FIG. 1 is an external perspective view showing a configuration of an example of an inkjet recording apparatus, which is an example of a liquid ejection apparatus according to an embodiment, as seen through. FIG. 2 is a side view of the apparatus for explaining the internal mechanism of the inkjet recording apparatus. FIG. 3 is a block diagram showing a hardware configuration of a control unit of the inkjet recording apparatus. FIG. 4 is a block diagram showing an example of the configuration of the print control unit and the head driver. FIG. 5 is an explanatory diagram of an image forming method by the inkjet recording apparatus. FIG. 6 is an explanatory diagram of waveforms for driving the recording head. FIG. 7 is a block diagram showing the functional arrangement of the print control unit. FIG. 8 is an explanatory diagram of an example of drive waveform correction. FIG. 9 is an explanatory diagram of a drive waveform control method. FIG. 10 is a flowchart showing the flow of an example of drive waveform control according to the first embodiment. FIG. 11 is an explanatory diagram of an example of drive waveform switching control according to the first embodiment. FIG. 12 is an explanatory diagram of another example of drive waveform switching control according to the first embodiment. FIG. 13 is an explanatory diagram of an example of drive waveform switching control according to the second embodiment. FIG. 14 is a flowchart showing the flow of an example of drive waveform control according to the second embodiment. FIG. 15 is a diagram illustrating another example of the configurations of the print control unit and the head driver.

Embodiments of a liquid ejection device and a drive waveform control method according to the present invention will be described in detail below with reference to the accompanying drawings. An example of an inkjet recording apparatus as an example of the liquid ejection apparatus according to this embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective explanatory view illustrating an inkjet recording apparatus, and shows an internal mechanism in a see-through manner. Further, FIG. 2 is a side view of the apparatus for explaining the internal mechanism of the recording apparatus.

In the inkjet recording apparatus 1, a printing mechanism including a carriage movable in the main scanning direction inside the recording apparatus main body 1A, a recording head including an inkjet head mounted on the carriage, an ink cartridge that supplies ink to the recording head, and the like. Contains the parts 2 and so on. In the lower part of the recording apparatus main body 1A, a paper feed cassette 4 capable of stacking a large number of sheets 3 can be detachably attached from the front side. Further, a manual feed tray 5 for manually feeding the paper 3 is attached so as to be openable and retractable. The paper 3 fed from the paper feed cassette 4 or the manual feed tray 5 is taken into the recording apparatus main body 1A, a desired image is recorded by the printing mechanism unit 2, and then the discharged paper mounted on the rear surface side of the recording apparatus main body 1A. The paper is discharged to the tray 6.

In the printing mechanism unit 2, a carriage 13 is slidably held in the main scanning direction by a main guide rod 11 and a sub guide rod 12 which are guide members which are horizontally mounted on left and right side plates (not shown). A recording head 14 that ejects ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (Bk) is mounted on the carriage 13. The recording head 14 has a plurality of ink ejection ports (nozzles) arranged in a direction intersecting the main scanning direction. The recording head 14 is mounted so that the ink droplet ejection direction is downward. Further, the carriage 13 is replaceably mounted with an ink cartridge 15 of each color for supplying each color ink to the recording head 14.

The ink cartridge 15 has an atmosphere port communicating with the atmosphere at the upper part, a supply port supplying the ink to the recording head 14 at the lower part, and contains a porous body filled with the ink inside. The ink stored inside and supplied to the recording head 14 is maintained at a slight negative pressure by the capillary force of the porous body. Further, although a plurality of recording heads 14 for each color are used here as the recording heads, one recording head having a plurality of nozzles for ejecting ink droplets of each color may be used.

Here, the carriage 13 has a rear side (downstream side in the sheet conveyance direction) slidably fitted to the main guide rod 11, and a front side (upstream side in the sheet conveyance direction) slidably attached to the sub guide rod 12. It is placed in. Then, in order to move and scan the carriage 13 in the main scanning direction, a timing belt 20 is stretched between a drive pulley 18 and a driven pulley 19 which are rotationally driven by the main scanning motor 17, and the timing belt 20 is mounted on the carriage 13. It is fixed to. Therefore, the carriage 13 is reciprocally driven by the forward and reverse rotations of the main scanning motor 17.

On the other hand, in order to convey the paper 3 set in the paper feed cassette 4 to the lower side of the recording head 14, the paper feed roller 21 and the friction pad 22 for separately feeding the paper 3 from the paper feed cassette 4 and the paper 3 are guided. The guide member 23, the transport roller 24 that reverses and transports the fed paper 3, the transport roller 25 that is pressed against the peripheral surface of the transport roller 24, and the delivery angle of the paper 3 from the transport roller 24 are defined. And a tip roller 26 for The conveying roller 24 is rotationally driven by the sub-scanning motor 49 (see FIG. 2) via the gear train 27.

Further, there is provided a print receiving member 29 which is a paper guide member for guiding the paper 3 delivered from the transport roller 24 below the recording head 14 in correspondence with the movement range of the carriage 13 in the main scanning direction. A transport roller 31 and a spur 32, which are driven to rotate in order to send out the paper 3 in the paper discharge direction, are provided on the downstream side of the print receiving member 29 in the paper transport direction, and further, the paper 3 is sent to the paper discharge tray 6 A roller 33, a spur 34, and guide members 35 and 36 that form a paper discharge path are provided.

At the time of recording, the recording head 14 is driven according to an image signal while moving the carriage 13 to eject ink to the stopped paper 3 to record one line, and after the paper 3 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the sheet 3 has reached the recording area, the recording operation is terminated and the sheet 3 is ejected.

A recovery device 37 for recovering the ejection failure of the head 14 is arranged at a position outside the recording area on the right end side of the carriage 13 in the moving direction. The recovery device 37 has a cap means, a suction means, and a cleaning means. The carriage 13 is moved to the recovery device 37 side while waiting for printing. Then, the recording head 14 is capped by the capping means. By this capping, the ejection opening portion of the recording head 14 is kept in a wet state, so that ejection failure of the recording head 14 due to ink drying can be prevented. In addition, the recovery device 37 sucks ink that is not related to printing from the ejection openings of the recording head 14 during recording, thereby making the ink viscosity of all the ejection openings constant and maintaining stable ejection performance.

When liquid ejection failure occurs, the ejection port (nozzle) of the head 14 is sealed by the capping unit, and the bubbles and the like are sucked out from the ejection port by the suction unit through the tube and the ink or dust attached to the ejection port surface is sealed. Etc. are removed by the cleaning means. As a result, the ejection failure of the recording head 14 is recovered. Further, the sucked ink is discharged to the waste ink reservoir installed in the lower portion of the main body and absorbed and held by the ink absorber inside the waste ink reservoir.

Next, the outline of the control unit of the inkjet recording apparatus 1 will be described with reference to the block diagram of FIG. The control unit 40 includes a CPU (Central Processing Unit) 41 that controls the entire apparatus, a ROM (Read Only Memory) 42 that stores programs executed by the CPU 41 and other fixed data, and temporarily stores image data and the like. RAM (Random Access Memory) 43, a rewritable non-volatile memory 44 for retaining data even when the power of the apparatus is cut off, image processing for performing various signal processing, rearrangement, etc. on image data, Other components include an ASIC (Application Specific Integrated Circuit) 45 that processes an input/output signal for controlling the entire device.

The control unit 40 also includes a host I/F 46 for transmitting and receiving data and signals to and from the host side, a data transfer unit for driving and controlling the recording head 14, and a drive waveform generating unit for generating a drive waveform. A print control unit 47 including the above, a head driver (driver IC (Integrated Circuit)) 48 for driving the recording head 14 provided on the carriage 13 side, and a motor drive for driving the main scanning motor 17 and the sub scanning motor 49. Unit 50, AC bias supply unit 52 that supplies an AC (Alternating Current) bias to charging roller 51, detection signals from encoder sensors 53 and 54, and detection signals from various sensors such as a temperature sensor that detects environmental temperature. An I/O (Input/Output) 55 for inputting is input.

An operation panel 56 for inputting and displaying information necessary for the inkjet recording apparatus 1 is connected to the control section 40. Here, the control unit 40 transmits image data and the like from a host side such as an information processing device such as a personal computer, an image reading device such as an image scanner, and an imaging device such as a digital camera to a cable or a LAN (Local Area Network). It is received by the host I/F 46 via the network. Then, the CPU 41 of the control unit 40 reads out and analyzes the print data in the reception buffer included in the host I/F 46, performs necessary image processing and data rearrangement processing in the ASIC 45, and prints this image data. The data is transferred from the control unit 47 to the head driver 48. The generation of dot pattern data for image output is performed by a printer driver on the host side as described later.

The print control unit 47 transfers the above-described image data as serial data to the head driver 48. Further, the print control unit 47 outputs to the head driver 48 a transfer clock, a latch signal, a droplet control signal (mask signal), etc. which are necessary for the transfer of the image data and the confirmation of the transfer. Further, the print control unit 47 supplies the drive waveform generation unit and the head driver, which are composed of a D/A converter for performing D/A conversion of the pattern data of the drive signal stored in the ROM 42, a voltage amplifier, a current amplifier, and the like. Includes drive waveform selection means.

Then, the print controller 47 generates a drive waveform composed of one drive pulse (drive signal) or a plurality of drive pulses (drive signals), and outputs the drive waveform to the head driver 48. The head driver 48 selectively ejects the liquid droplets of the recording head 14 based on the image data corresponding to one row of the recording head 14 which is serially input, based on the drive signal that forms the drive waveform provided from the print controller 48. The recording head 14 is driven by applying the ejection energy to a drive element (for example, the piezoelectric element as described above) that generates the energy. At this time, by selecting the drive pulse forming the drive waveform, for example, dots of different sizes such as large drops (large dots), medium drops (medium dots), and small drops (small dots) can be ejected. it can.

The CPU 41 also detects the speed detection value and the position detection value obtained by sampling the detection pulse from the encoder sensor 54 forming the linear encoder, and the speed target value and the position target value obtained from the speed/position profile stored in advance. The drive output value (control value) for the main scanning motor 17 is calculated based on the above, and the main scanning motor 17 is driven via the motor drive unit 50.

Similarly, based on the speed detection value and the position detection value obtained by sampling the detection pulse from the encoder sensor 53 forming the rotary encoder, and the speed target value and the position target value obtained from the speed/position profile stored in advance. The drive output value (control value) for the sub-scanning motor 49 is calculated. This drive output value is output from the motor drive unit 50 to the motor driver, and the sub-scanning motor 49 is driven via the motor driver.

Next, an example of the print controller 47 and the head driver 48 will be described with reference to FIG.

As described above, the print control unit 47 includes a drive waveform generation unit 61 that generates and outputs a drive waveform composed of a plurality of drive pulses (drive signals) in one printing cycle, and an image corresponding to a print image. It is provided with data, a clock signal, a latch signal (LAT), and a data transfer unit 62 that outputs the droplet control signals M0 to M3. The drive waveform generator 61 is provided for each piezoelectric element 14a. Further, the droplet control signal is a 2-bit signal for instructing opening and closing of an analog switch 63, which is a switch unit described later of the head driver 48, for each droplet, and is a H-level waveform that should be selected according to the printing cycle of the drive waveform. The state transitions to (ON) and to the L level (OFF) when not selected.

The head driver 48 inputs a transfer clock (shift clock) and serial image data (gradation data: 2 bits/CH) from the data transfer unit 62, and each register value of the shift register 64 by a latch signal. A latch circuit 65 for latching, a decoder 66 for decoding grayscale data and control signals M0 to M3 and outputting the result, and a level conversion of a logic level voltage signal of the decoder 66 to a level at which the analog switch 63 can operate. A level shifter 67 for turning on and off, and an analog switch 63 that is turned on/off (opened/closed) by the output of the decoder 66 given through the level shifter 67.

The analog switch 63 is connected to the selection electrode (individual electrode) of each piezoelectric element 14a, and receives the drive waveform from the drive waveform generation unit 61 provided for each piezoelectric element 14a. Therefore, by turning on the analog switch 63 in accordance with the result of decoding the droplet control signals M0 to M3 and the image data (gradation data) transferred serially, the required drive signal forming the drive waveform can be generated. It is passed (selected) and applied to the piezoelectric element 14a.

With the above configuration and control method, ink is ejected from the recording head 14 to form an image.

Next, a method of forming an image by the inkjet recording apparatus which is an example of the present embodiment will be described with reference to FIG.

There are a plurality of modes of image forming resolution depending on the image quality, output speed, paper type, and the like. Here, as an example, a mode in which image quality is prioritized will be described. The image forming resolution in the mode giving priority to the image quality is 1200 dpi (dot per inch)×1200 dpi (dpi is a unit indicating the resolution of how many dots are formed in 1 inch).

On the other hand, since the nozzle density formed in one head unit is 300 dpi, in order to obtain a resolution of 1200 dpi in the nozzle row direction, at least four times of head scanning is performed while shifting the cycle corresponding to 1200 dpi in the nozzle row direction. Need to repeat. Further, the image formation in the head scanning direction is also performed twice in order to disperse the image formation error. That is, in order to complete the image formation of a certain area (unit cell), it is necessary to repeat the head scanning “4 times in the nozzle row direction×2 times in the main scanning direction=8 times”.

In an actual operation, the unit cells of FIG. 5 are not printed by the same nozzle array in order to diffuse the variation of discharge for each nozzle. When one scan is completed, the head moves in the nozzle row direction by a predetermined amount. It will be printed.

Next, the waveform for driving the recording head will be described with reference to FIG.

The drive waveform is generated by the drive waveform generation unit 61 (provided for each piezoelectric element 14a) of the print control unit 47 shown in FIG. 4, the nozzles to be ejected and the waveform type are selected by the head driver 48, and recording is performed. It is supplied to the piezoelectric element 14a inside the head 14 (see FIG. 3). Further, the control unit selects the type of drive waveform according to the temperature detected by the temperature sensor 57 (see FIG. 3). For example, as shown in FIG. 6, generally, in a low temperature environment, the viscosity of the ink becomes high, and therefore, a means for increasing the voltage to the piezoelectric element is taken, so that the voltage becomes higher than the waveform at high temperature.

As described above, since the viscosity of the ink changes due to the influence of the ambient temperature, it is necessary to change the drive waveform for driving the piezoelectric element in response to the change in the ambient temperature. In other words, it is necessary to correct the drive waveform of the piezoelectric element according to the change in environmental temperature. By performing such a correction, it is possible to keep the ejection amount and the ejection speed of the ink constant, and suppress the deterioration of the image recorded on the paper surface.

More specifically, in the present embodiment, the print controller 47 corrects the waveform of the drive waveform signal Vcomx to suppress variations in the ink ejection speed and the ink ejection amount.

FIG. 7 is a functional configuration block diagram of the print control unit 47. The print control unit 47 stores the drive waveform data serving as a reference in advance, holds the drive waveform table 71 to be output, and the image data DD-1 to DD-4 to be output in the next cycle, and outputs this image data. A data transfer unit 62, and a pixel/Vcom count unit that outputs a combination of the number of drive nozzles in the next cycle and drive waveform signals Vcom1 to Vcom4 output in the next cycle based on the input image data DD-1 to DD-4. 72, a drive waveform correction value calculation unit 73 that calculates and outputs a drive waveform magnification correction value based on the input value of the temperature detected by the temperature sensor 57 (see FIG. 3), and an input reference drive waveform. A drive waveform correction unit 74 that corrects the drive waveform magnification correction value that has been input, and outputs drive waveform control data DW1 to DW4 based on a combination of the number of drive nozzles and drive waveform signals Vcom1 to Vcom4 to the head driver 48, respectively. I have it. The drive waveform table 71, the pixel/Vcom count unit 72, the drive waveform correction value calculation unit 73, and the drive waveform correction unit 74 constitute the drive waveform generation unit (provided for each piezoelectric element 14a) 61. ing.

Specifically, the drive waveform correction value calculation unit 73 includes a temperature information acquisition unit 731, a correction determination unit 732, and a calculation unit 733. The RAM 43 holds a drive waveform correction table in which a drive waveform magnification correction value corresponding to each drive waveform is set.

The temperature information acquisition unit 731 acquires the temperature information near the head by inputting the temperature value output by the temperature sensor 57.

The correction determination unit 732 compares the temperature value near the head acquired as the initial value by the temperature information acquisition unit 731 with the temperature value near the head acquired by the temperature information acquisition unit 731 after one scan for each scanning of the head. Then, when the temperature difference exceeds the threshold value (for example, 1° C.), the correction of the drive waveform is determined.

When the correction is determined by the correction determination unit 732, the calculation unit 733 calculates and outputs the drive waveform correction value for each remaining scan of the scan region (for example, the unit cell being scanned). Image formation is completed by performing head scanning a plurality of times on each unit cell as in the mode described with reference to FIG. Therefore, the calculation unit 733 uses a predetermined algorithm to indicate the piezoelectric element that corrects the drive waveform among the piezoelectric elements of the plurality of nozzles that form the recording head for each remaining scan of the scan area (for example, the unit cell being scanned). The values are gradually increased in order, and the drive waveform magnification correction values are acquired from the drive waveform correction table and output to the drive waveform correction unit 74. It should be noted that the unit cell number, information indicating the number of times of scanning in each unit cell, and the like are determined by the pixel/Vcom count unit 72 based on the image data output from the data transfer unit 62. The combination is output to the drive waveform correction value calculation unit 73.

Next, the drive waveform correction operation of the print controller 47 having the above configuration will be described. It should be noted that, for ease of understanding, repetitive description is omitted here as appropriate.
The data transfer unit 62 outputs the held image data DD-1 to DD-4 to be output in the next cycle to the pixel/Vcom counting unit 72.

The pixel/Vcom counting unit 72 calculates a drive waveform correction value based on a combination of the number of drive nozzles in the next cycle and the drive waveform signals Vcom1 to Vcom4 output in the next cycle, based on the input image data DD-1 to DD-4. It is output to the unit 73. Further, the pixel/Vcom counting unit 72 outputs a unit cell number, information indicating the number of scans in each unit cell, and the like based on the image data output from the data transfer unit 62.

The drive waveform correction value calculation unit 73 outputs the number of drive nozzles and the drive waveform signals Vcom1 to Vcom4 to the drive waveform correction unit 74. Further, the drive waveform correction value calculation unit 73 outputs the drive waveform magnification correction value to the drive waveform correction unit 74. When the temperature in the vicinity of the head exceeds a threshold value, the drive waveform correction value calculation unit 73 corrects the drive waveforms of the piezoelectric elements of the plurality of nozzles forming the print head as the number of scans increases in the remaining scans thereafter. Increase the number (the number at which the drive waveform magnification exceeds 1).

As a result, when the drive waveform data serving as the reference is input from the drive waveform table 71, the drive waveform correction unit 74 corrects the drive waveform data by the input drive waveform magnification correction value and outputs the drive waveform control data DW1 to DW4 to the head driver 48, respectively. Output.

FIG. 8 is an explanatory diagram of an example of drive waveform correction. As shown in FIG. 8, when the reference drive waveform data (=drive waveform magnification=1) is input from the drive waveform table 71, the drive waveform magnification correction is performed on a portion other than the intermediate potential while keeping the intermediate potential constant. The values are multiplied to obtain drive waveform control data DW1 to DW4. In the case of the example of FIG. 8, the drive waveform data serving as the reference is multiplied by the drive waveform magnification correction value=1.2 to obtain drive waveform control data DW1 to DW4. As a result, the voltage fluctuation is suppressed and the fluctuation of the ink ejection speed and the ink ejection amount is suppressed.

In this embodiment, a predetermined process is set after the change of the drive waveform is determined and before the change of the drive waveform is completed. This process of changing the drive waveform contributes to suppressing unevenness in image density that occurs when the drive waveform is corrected.

In the conventional correction of the drive waveform, the change of the drive waveform is decided when the change of the environmental temperature exceeds a predetermined threshold value (for example, 1° C.), and the drive waveforms of the drive piezoelectric elements of all the nozzles of the recording head are determined. It is changed all at once. As a result, as shown in FIG. 9, there is a visible density difference between the adhering ink density in the printed image before the drive waveform is changed and the adhering ink density in the printed image after the drive waveform is changed.

As described above with reference to FIG. 5, when ink is ejected from the nozzles of the recording head onto the paper surface to form an image, for example, the paper surface is divided into several areas called unit cells (in FIG. Area: unit cells 1 to 8) are divided, and the recording scan by the recording head is performed 8 times for each unit cell to complete the image formation. The number of unit cells and the number of print scans are determined from the relationship between the resolution of the image to be printed (for example, 1200 dpi) and the nozzle density of the print head used for printing (for example, 300 dpi). The print scan means an operation of ejecting liquid from a plurality of nozzles of the print head while scanning the print head with respect to the target paper surface.

In the present embodiment, in the recording scan by the recording head after determining the change of the drive waveform of the piezoelectric element of the nozzle of the recording head, the recording is performed from the first recording scan to the last eighth recording scan. The drive waveforms of the piezoelectric elements of the plurality of nozzles forming the head are controlled so that the number of changes from the first drive waveform before the change determination to the second drive waveform after the correction is gradually increased, and the last eight times. At the time of print scan, the change to a new drive waveform is completed for all piezoelectric elements. As a result, as shown in FIG. 9, in the present embodiment, it is possible to suppress the density difference of the adhered ink in the image created after the change of the drive waveform is determined to a level that is not visible.

In the present embodiment, the drive waveforms of the drive elements (piezoelectric elements) of the plurality of nozzles of the print head corresponding to changes in the ambient temperature are gradually changed in proportion to a plurality of print scans performed during image formation. As a general configuration, two examples (Embodiment 1 and Embodiment 2) are proposed.

(Embodiment 1)
The first embodiment of the drive waveform changing process will be described with reference to FIG. In the example of FIG. 5, the paper surface to be printed is divided into areas 1 to 8 (unit cells 1 to 8), and each unit cell is printed and scanned eight times by the print head. In this embodiment, each unit cell is divided into eight regions (cells). Then, in the first scan, the drive waveform of the piezoelectric element of the nozzle that scans the cell 1 in each unit cell is driven with a new drive waveform. In the subsequent second scan, the drive waveform of the piezoelectric element of the nozzle that scans cell 2 is changed in addition to the change of the drive waveform of the piezoelectric element of the nozzle that scans cell 1 the previous time. In the subsequent third scan, the drive waveform of the piezoelectric element of the nozzle that further scans the cell 3 is changed. In this way, in the eighth scan, the drive waveform of the piezoelectric element that scans all eight cells 1-8 of each unit cell 1-8 is changed to a new drive waveform. As a result, as shown in FIG. 9, in the image formed on the paper surface, the density of the recording ink changes gradually with the number of scans due to the change of the driving waveform, and therefore the step of the ink density cannot be visually recognized. Suppressed to level. In the first embodiment, the drive waveform of the piezoelectric element of the nozzle that scans the cells is changed in the order of cell 1 to cell 8. However, the number of cells scanned by the second drive waveform does not increase. The cell numbers may be in ascending order as well as descending order, and may be in any order. In short, from the first scan to the eighth scan, if the drive waveforms of the plurality of nozzles can be gradually shifted from the state in which all of them are driven by the first drive waveform to the state in which all of them are driven by the second waveform, Good.

FIG. 10 is a flow chart showing the flow of the drive waveform control of the first embodiment. In FIG. 10, N indicates the number of unit cells, i indicates the current unit cell, and j indicates the scan number in each unit.

When the printing operation is started, the temperature near the recording head is measured (step S1). Then, the detected temperature is set (step S2). Next, the printing operation for one scan is executed (step S3). Then, the temperature in the vicinity of the recording head is measured, and it is determined whether the temperature is the same as or different from the previously detected temperature (step S4). The determination as to whether they are the same or different is made based on whether the temperature difference is less than 1° C. or 1° C. or more, for example.

When the measured temperature is the same as the previously detected temperature, the process returns to step S1. If the measured temperature is different from the previously detected temperature, it is determined whether the current unit cell exceeds N (i>N) or is N or less (i≦N) (step S5). When the current unit cell exceeds N (i>N), it is determined whether or not there is print residue (step S6). If there is no print residue, the printing operation is terminated, and if there is print residue, the process returns to step S1.

When it is determined in step S5 that the current unit cell is N or less (i≦N), the scan number in the unit cell is j or more (i≧j) or less than j (i<j). It is determined whether there is any (step S7).

When the scan number in the unit cell is larger than i (i<j), the first drive waveform after the drive waveform change decision is set to the drive waveform (step S8). After setting, the process returns to step S5. On the other hand, when the scan number in the unit cell is i or less (i≧j), the second drive waveform before the change determination of the drive waveform is set as the drive waveform (step S9). After setting, the process returns to step S5.

According to the control flow of FIG. 10, the drive waveform switching control shown in FIG. 11 is performed. The item of “scan order” in FIG. 11 represents the order of scanning in time, and the first drive waveform before the drive waveform change determination is used in each scan or the second drive after the drive waveform change determination is performed. The gray cell on the right indicates whether to use the waveform. The item “number of units after determination of drive waveform change” indicates the number of eight unit scans after determination of drive waveform change. After the drive waveform change is determined, the frequency of occurrence of the first drive waveform before the drive waveform change determination in the unit scan and after the drive waveform change determination is gradually reduced. The control flow shown in FIG. 10 is an example, and the control flow is not limited to this as long as it is a control flow in which the occurrence probability of the second drive waveform before and after the drive waveform change determination is gradually increased.

FIG. 12 is a diagram illustrating another control flow. In this control flow, after the drive waveform change is determined, the frequency of occurrence of the first drive waveform in the unit scan before the drive waveform change determination and after the drive waveform change determination is gradually reduced. An example in which the first drive waveform and the changed second drive waveform are temporally dispersed is shown. By doing so, the density variation in the density step portion can be made smoother.

(Embodiment 2)
In the second embodiment of the drive waveform changing process, for example, the paper surface to be ejected is divided into regions 1 to 8 (unit cells 1 to 8), and each unit cell is scanned eight times by the recording head. In the first scan, the drive waveform of 1/8 of all the nozzles used when scanning from unit cell 1 to unit cell 8 is changed to the second drive waveform. In the second scan, the drive waveform of 2/8 of all the used nozzles when scanning the unit cells 1 to 8 is changed to the second drive waveform. Then, in the third scan, the drive waveform of 3/8 of all the used nozzles when scanning the unit cell 1 to the unit cell 8 is changed to the second drive waveform. In this manner, in the eighth scan, the drive waveforms of all the used nozzles when scanning all the unit cells of the unit cells 1 to 8 are changed to the second drive waveforms to perform the scan.

The example shown in FIG. 13 shows the control of the drive waveform when the change of the drive waveform based on the temperature measurement in the vicinity of the head is determined when the second scan of the eight scans is completed. In this case, the number of nozzles driven by the second drive waveform of all the used nozzles starts to be increased from the third scan, and all nozzles are driven by the second drive waveform in the final eighth scan. To control. The order of the nozzles for changing the drive waveform may be the nozzle arrangement order (ascending order and descending order) or may be random. In short, from the first scan to the eighth scan, if the drive waveforms of the plurality of nozzles can be gradually shifted from the state in which all of them are driven by the first drive waveform to the state in which all of them are driven by the second waveform, Good.

FIG. 14 is a flowchart showing the flow of drive waveform control of the second embodiment. In FIG. 14, N indicates the total number of scans required to complete the image formation, and i indicates the current scan number.

When the printing operation is started, the temperature near the recording head is measured (step S10). Then, the detected temperature is set (step S11). Next, the printing operation for one scan is executed (step S12). Then, the temperature near the recording head is measured, and it is determined whether the temperature is the same as or different from the previously detected temperature (step S13). The determination as to whether they are the same or different is made based on whether the temperature difference is less than 1° C. or 1° C. or more, for example.

If the measured temperature is the same as the previously detected temperature, the process returns to step S10. If the measured temperature is different from the previous detected temperature, it is determined whether the current scan i (number of times) exceeds N (i>N) or is less than N (i≦N) (step S14). ). If the current scan i exceeds N (i>N), then it is determined whether there is any print residue (step S15). If there is no print residue, the printing operation is terminated, and if there is print residue, the process returns to step S10.

When it is determined in step S14 that the current scan i (number of scans) is N or less (i≦N), the second drive waveform is set for the i/N nozzle (step S16), and the remaining nozzles are set. The first drive waveform remains set (step S17). Next, the print operation for one scan is executed (step S18), and it is determined whether or not there is any print residue (step S19). If there is no print remaining, the printing operation is ended, and if there is print remaining, the scan number is incremented by one (i=i+1) and the process returns to step S14.

The drive waveform control method of the second embodiment can also obtain the same effect as the drive waveform control method of the first embodiment described above.

(Other Examples of Print Controller and Head Driver)
FIG. 15 is a diagram illustrating another example of the configurations of the print control unit and the head driver. The controller 90 and the head drive unit 80 shown in FIG. 15 correspond to a print control unit and a head driver.

The head drive unit 80 is configured to drive the N piezoelectric elements 5 (5-1 to 5-N) corresponding to the N nozzles provided in the recording head. The head driving unit 80 drives the piezoelectric elements 5 for one nozzle row of the recording head.

One electrode of each piezoelectric element 5 is connected to a common potential (for example, ground) together with the other piezoelectric element 5 via the FPC board that transmits a driving waveform, and the other electrode is connected to the head drive unit 80. It

The head drive unit 80 is composed of one or a plurality of integrated circuits, and at least a portion connected to the piezoelectric element 5 is installed on the FPC board. Based on the data transferred from the controller 90, the head drive unit 80 individually generates an optimum drive waveform for the piezoelectric element corresponding to each nozzle so that the ink droplets are ejected from each nozzle in an appropriate state. Then, each piezoelectric element 5 is driven.

The head drive unit 80 can be provided integrally with the recording head.

The controller 90 separates the image data to be printed into image data corresponding to each recording head and nozzle row, and transfers the image data to the head drive unit 80. Further, the controller 90 has a function of transferring the basic drive waveform information and drive waveform correction information used when the drive waveform is generated by the head drive unit 80 to the head drive unit 80 and setting the same, and various controls for the head drive unit 80. Has the function of supplying signals.

As shown in FIG. 15, the head drive unit 80 includes a shift register 81, a latch 82, drive waveform generation units 83 (83-1 to 83-N), a basic drive waveform information holding unit 84, and a drive waveform correction information holding unit 85. , And a control unit 86.

From the controller 90 to the head drive unit 80, N pieces of image data SDI corresponding to one row of data of the recording head are serially input in synchronization with the transfer clock SCK. The N pieces of image data serially input are sequentially held in the shift register 81. Here, if it is assumed that ink droplets corresponding to dots having different four-value sizes of large droplets, medium droplets, small droplets, and no ejection are ejected from the nozzles of the recording head, then one image data has 2 bits. The data.

The latches 82 are N latches that hold the N image data once held in the shift register 81 by the input of the latch enable signal LEN, and each hold 2-bit data (D1 to DN). , To the corresponding drive waveform generators 83.

The drive waveform generation unit 83 generates drive waveforms for individually driving the N piezoelectric elements 5-1 to 5-N, and makes them correspond to the piezoelectric elements 5-1 to 5-N, respectively. Further, N driving waveform generation units 83-1 to 83-N are provided. When the 2-bit image data Di is supplied from the latch 82 in synchronization with the latch enable signal LEN, the drive waveform generation unit 83-i, which is the i-th (here, i is 1 to N) channel, receives the basic drive waveform. The basic drive waveform information held in the information holding unit 84 and the correction information held in the drive waveform correction information holding unit 85 are referred to, a drive waveform is generated with the latch enable signal LEN as a start reference, and the piezoelectric element is generated. Supply to 5-i.

The basic drive waveform information storage unit 84 stores basic drive waveform information, which is information of a basic drive waveform that does not include correction information for each nozzle (for each channel), such as a large droplet, a medium droplet, a small droplet, and no ejection. Is held as a drive waveform for each different dot. The drive waveform generation unit 83-i of the basic drive waveform information held by the basic drive waveform information holding unit 84 has basic drive waveform information (for example, image data Di corresponding to the image data Di supplied from the latch 82). If it is data representing a large droplet, basic driving waveform information for the large droplet) is acquired. The details of the basic drive waveform information will be described later.

Further, the drive waveform correction information holding unit 85 holds correction information for correcting the basic drive waveform information for each nozzle (for each channel). The drive waveform generation unit 83-i acquires the correction information corresponding to the i-th channel from the correction information held by the drive waveform correction information holding unit 85. Then, the drive waveform generation unit 83-i corrects the basic drive waveform information acquired from the basic drive waveform information holding unit 84 by using the correction information acquired from the drive waveform correction information holding unit 85, and thereby the i-th A drive waveform most suitable for driving the channel is generated and supplied to the piezoelectric element 5-i.

The control unit 86 controls the entire head drive unit 80. The control unit 86 has a function of communicating with the controller 90. For example, the control unit 86 receives the basic drive waveform information and the correction information described above from the controller 90, and then the basic drive waveform information holding unit 84 and the drive waveform. Processing such as setting in the correction information holding unit 85 and updating information is performed. The correction information held for each nozzle is set by the controller 90 or the control unit 36 by appropriately calculating the drive waveform magnification correction value for each scanning number.

Next, the detailed configuration of the drive waveform generation unit 83 will be described. The drive waveform generation unit 83 (83-1 to 83-N) includes a charge/discharge signal generation unit 91 and a driver unit 92, as shown in FIG. 15.

The charge/discharge signal generation unit 91 uses the image data Di, the basic drive waveform information, the correction information, and the latch enable signal LEN as the waveform generation start reference, and the charge signal up for controlling the timing and time of charging the piezoelectric element 5. , And generates a discharge signal dn for controlling the timing and time of discharge for the piezoelectric element 5.

The driver unit 92 charges the piezoelectric element 5 according to the charge signal up generated by the charge/discharge signal generation unit 91, and discharges the piezoelectric element 5 according to the discharge signal dn generated by the charge/discharge signal generation unit 91. ..

By configuring the driver unit 92 as described above, the voltage Vp (that is, the drive waveform) applied to the piezoelectric element 5 is arbitrarily controlled by controlling the timing and the period when the charge signal up and the discharge signal dn become active. It is possible to control the waveform shape. Here, the drive waveform generation unit 83 (83-1 to 83-N) is provided individually for each of the N piezoelectric elements 5-1 to 5-N, and therefore, for each piezoelectric element 5. Each can be driven with an optimum drive waveform. That is, even if variations in the ink droplet amount and landing position occur due to variations in the nozzle shape of each nozzle, the ink flow path structure, piezoelectric element characteristics, switching element characteristics, temperature characteristics, etc., these variations should be reduced. The drive waveforms can be corrected respectively, and the deterioration of image quality can be suppressed.

Further, of the head drive unit 80, the only circuit that needs to be configured in a high breakdown voltage process and that operates by being connected to the power supply (voltage value Vh) is the driver unit 92 (in the portion A surrounded by the one-dot chain line in FIG. 15). Others can be configured by a low withstand voltage process such as a core voltage of 1V. Further, the conventionally used drive waveform generation circuit requires a DA converter and a voltage or current amplifier in order to generate and drive the drive waveform, and even if they are integrated, their size becomes very large. On the other hand, in the present embodiment, the piezoelectric element 5 can be driven with a very simple configuration as shown in FIG. 15, and therefore, even if a plurality of drive waveform generation units 83 are provided for each nozzle, the recording head It can be realized as an integrated circuit with a chip size sufficient to be installed in. In the conventional recording head as well, at least one pair of bidirectional switching elements is provided for each piezoelectric element, and the direction of the current flowing through the bidirectional switching elements is bidirectional, so normally at least two or more transistors It is composed of. That is, even with the configuration in which the plurality of drive waveform generation units 83 corresponding to the respective piezoelectric elements 5 are provided as in the present embodiment, the chip size does not increase as compared with the conventional recording head. Therefore, the size of the device is not increased, the power consumption is not increased, and the cost is not increased.

The program executed by the liquid ejecting apparatus of each embodiment is a file in an installable format or an executable format in a computer such as a CD-ROM, a flexible disk (FD), a CD-R, a DVD (Digital Versatile Disk). It is provided by being recorded in a readable recording medium.
Further, the program executed by the liquid ejecting apparatus of each embodiment may be stored in a computer connected to a network such as the Internet and provided by being downloaded via the network. In addition, the program executed by the liquid ejection device of each embodiment may be provided or distributed via a network such as the Internet.
Further, the program of the liquid ejection device of each embodiment may be configured to be provided by being pre-installed in a ROM or the like.
The liquid ejecting apparatus of each embodiment may be applied to a multifunction machine having at least two functions of a copy function, a printer function, a scanner function, and a facsimile function, or an image of a copying machine, a printer, a facsimile apparatus, or the like. It may be applied to any of the forming devices.

11 Main guide rod (moving means)
12 Secondary guide rod (moving means)
13 Carriage (moving means)
14 recording head 41 CPU (control means)
48 head driver (driving waveform applying means)
56 Temperature sensor (temperature detection means)
71 Drive waveform table (correction means)
73 Drive Waveform Correction Value Calculation Unit (Correction Means)
74 Drive waveform correction unit (correction means)

JP, 2004-106253, A JP, 2011-131429, A Japanese Patent No. 2887012

Claims (8)

A recording head having a plurality of nozzles for ejecting a liquid, ejecting a liquid onto the ejection target surface while performing a plurality of scans on the ejection target surface to form an image on the ejection target surface,
Moving means for moving the recording head in the main scanning direction while ejecting liquid from the recording head, and moving the recording head in the sub scanning direction after the recording head ejects liquid;
Drive waveform applying means for applying a drive waveform to each of the plurality of nozzles,
Temperature detecting means for detecting the temperature in the vicinity of the recording head,
Correction means for correcting the drive waveform based on the temperature detected by the temperature detection means,
When the temperature in the vicinity of the recording head changes from the first temperature to the second temperature, the usage ratio of the second drive waveform corresponding to the second temperature during the plurality of scans is the second. Control means for gradually increasing the usage rate of the first drive waveform corresponding to the temperature of 1;
A liquid ejecting apparatus comprising: The control unit divides the ejection target surface into a plurality of scan regions, further divides each scan region into a plurality of cell regions, and the liquid is ejected with the second drive waveform during the plurality of scans. The liquid ejecting apparatus according to claim 1, wherein the change of the drive waveforms for the plurality of nozzles is controlled so that the cell area of the plurality of nozzles gradually increases. The liquid ejecting apparatus according to claim 2, wherein the control unit determines the number of the plurality of scan areas and the number of the plurality of cell areas based on the resolution of the image and the nozzle density of the recording head. The control unit divides the ejection target surface into a plurality of scan regions, and scans the plurality of scan regions a plurality of times, the first of all nozzles used in proportion to an increase in the number of scans. The liquid ejection device according to claim 1, wherein the change of the drive waveform for the plurality of nozzles is controlled so that the ratio of the nozzles driven by the drive waveform of 2 is gradually increased. A step of forming an image on the ejection target surface by ejecting the liquid onto the ejection target surface while performing a plurality of scans on the ejection target surface using a recording head having a plurality of nozzles for ejecting the liquid; ,
Moving the recording head in the main scanning direction while ejecting liquid from the recording head, and moving the recording head in the sub scanning direction after the recording head ejects liquid;
Applying a drive waveform to each of the plurality of nozzles,
Detecting the temperature in the vicinity of the recording head,
Correcting the drive waveform based on the detected temperature,
When the temperature in the vicinity of the recording head changes from the first temperature to the second temperature, the usage ratio of the second drive waveform corresponding to the second temperature during the plurality of scans is the second. Controlling to gradually increase the usage ratio of the first drive waveform corresponding to the temperature of 1;
A method of controlling a drive waveform including a. In the controlling step, the ejection target surface is divided into a plurality of scan regions, each scan region is further divided into a plurality of cell regions, and the liquid is ejected with the second drive waveform during the plurality of scans. 6. The drive waveform control method according to claim 5, wherein the change of the drive waveform for the plurality of nozzles is controlled so that the cell area to be gradually increased. 7. The drive waveform control method according to claim 6, wherein the controlling step determines the number of the plurality of scan areas and the number of the plurality of cell areas based on the resolution of the image and the nozzle density of the recording head. .. The controlling step divides the ejection target surface into a plurality of scan areas, and scans the plurality of scan areas a plurality of times, in which all of the nozzles used in proportion to an increase in the number of scans are used. The drive waveform control method according to claim 5, wherein the change of the drive waveform for the plurality of nozzles is controlled so as to gradually increase the ratio of the nozzles driven by the second drive waveform.