JP4568966B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus using an inkjet method.
[0002]
[Prior art]
Conventionally, as an image forming apparatus, as shown in FIG. 9, there is an apparatus in which a print head, that is, an ink ejecting apparatus 600 is mounted on a carriage 100 and scanned in parallel with a print medium 700. The carriage 100 is slidably supported on the guide bars 110 and 120 and is reciprocated along the guide bar by a belt 140 driven by a motor 37. A tank 150 containing ink to be supplied to the head unit 600 is detachably mounted on the carriage 100. The print medium 700 is held in parallel with the scanning direction of the head unit 600 by the conveying rollers 160 and 170 and is conveyed in a direction perpendicular to the scanning direction.
[0003]
As the ink ejecting apparatus 600, a piezoelectric ceramic or electrostatic force or the like is used as an actuator to deform the wall surface of the ink flow path and the ink in the ink flow path is ejected as droplets from the nozzle, or a heater is used as the ink flow path. There are known ones that locally boil the ink inside and eject ink droplets by the pressure, and a printing pattern is represented by dots landed on the printing medium. As an example of the former, the ink ejecting apparatus 600 is a shear mode type using a piezoelectric material as disclosed in Japanese Patent Laid-Open No. 63-247051. An example is shown in FIG. The ink ejecting apparatus 600 includes an actuator substrate 601 in which a plurality of slender groove-shaped ink flow paths 613 extending in the thickness direction of the print medium surface and a space 615 that does not contain ink are arranged with a side wall 617 interposed therebetween, and a cover plate 602. The side wall 617 is composed of a lower wall 611 polarized in the arrow P1 direction in the lower half and an upper wall 609 polarized in the arrow P2 direction in the upper half. Each ink flow path 613 has a nozzle 618 at one end and a manifold (not shown) for supplying ink to the other end. The end of the space 615 on the manifold side is closed so that ink does not enter. Electrodes 619 and 621 are provided as metallization layers on both side surfaces of each side wall 617. Specifically, an in-channel electrode 619 is provided on the surface of the side wall 617 on the ink channel 613 side, and an in-space electrode 621 is provided on the surface of the side wall 617 on the space 615 side. The in-space electrodes 621 facing each other in the same space 615 are insulated from each other.
[0004]
Ink is ejected using a pair of side walls 617 sandwiching one ink flow path 613 as one actuator. For example, as shown in FIG. 7, when driving the ink flow path 613b, when all the in-flow path electrodes 619 are grounded and the voltage E (V) is applied to the space electrodes 621c, d on both outer sides of the flow path, An electric field in the direction of arrow E perpendicular to the polarization direction is generated on the side walls 617c, d, and the upper and lower portions of the side walls 617c, d are each subjected to piezoelectric thickness slip deformation in the direction of increasing the volume of the ink flow path 613b. At this time, the pressure in the ink flow path 613b including the vicinity of the nozzle 618b decreases. This state is maintained for a one-way propagation time T in the pressure wave ink channel 613.
In the meantime, ink is supplied from a manifold (not shown).
[0005]
The one-way propagation time T is a time required for the pressure wave in the ink flow path 613 to propagate in the longitudinal direction of the ink flow path 613. The length L of the ink flow path 613 and the ink flow path 613 T = L / a is determined by the speed of sound a in the ink inside. According to the pressure wave propagation theory, the pressure in the ink flow path 613 is reversed and turned to a positive pressure just after T time has elapsed from the application of the voltage, but applied to the space electrodes 621c and d in accordance with this timing. The applied voltage is returned to 0 (V).
[0006]
Then, the side walls 617c and d return to the state before deformation (FIG. 6), and pressure is applied to the ink. At that time, the pressure turned positive and the pressure generated when the side walls 617c and d return to the state before deformation are added together, and a relatively high pressure is generated in a portion near the nozzle 618b of the ink flow path 613b. Ink droplets are ejected from the nozzle 618b.
[0007]
More specifically, if the time from the application of the voltage to the return of the voltage to 0 (V) deviates from the one-way propagation time T, the ink efficiency is lowered because the ink droplet is ejected. Since the injection is not performed at all when it becomes almost an even multiple, normally, when it is desired to increase the energy efficiency, for example, when it is desired to drive at a voltage as low as possible, the application of the voltage until the voltage is returned to 0 (V). It is desirable that the time is equal to the one-way propagation time T or at least approximately an odd multiple.
[0008]
An example of specific dimensions of the conventional ink droplet ejecting apparatus 600 will be described. The length L of the ink chamber 613 is 12.0 mm. The nozzle 618 is a tapered type having a diameter of 32 μm or 26 μm on the ink droplet ejection side and a diameter of 40 μm on the ink chamber 613 side, and has a length of 75 μm. The viscosity of the ink used in the experiment at 25 ° C. is about 2 mPa · s, and the surface tension is 30 mN / m. The ratio L / a (= T) of the speed of sound a in the ink in the ink chamber 613 to L was 12.0 μsec.
[0009]
A conventional image forming method using the image forming apparatus having such a configuration when the print resolution in the moving direction of the carriage has a plurality of modes such as 360 dpi (dot / inch) and 720 dpi will be described.
The first conventional example is a method using the same drive waveform for both 360 dpi and 720 dpi. The higher the printing resolution, the smaller the volume of the ejected ink droplets. Therefore, in the 720 dpi mode, it is necessary to eject at a lower driving voltage than in the 360 dpi mode. An example of the drive waveform is shown in FIG. The number given to the drive waveform 20 is the ratio of the length of time to the one-way propagation time T of the pressure wave in the ink flow path 613. It comprises an ejection pulse F5 for ejecting ink droplets and an ejection stabilization pulse S3 for suppressing residual vibration generated by the ejection pulse F5 and stopping excess ink ejection. The peak value (voltage value) of all the pulses is the same. As shown in FIG. 5, when the length L of the ink flow path 613 is 12.0 mm and the emission diameter of the nozzle 618 is φ32 μm, a droplet volume ejected when a driving voltage of 20 (V) is applied. Is 25 pl when a driving voltage of 35 pl (picoliter) and 15 (V) is applied, the former was used in the 360 dpi mode and the latter was used in the 720 dpi mode.
[0010]
It is known from experiments that the maximum drive frequency at which the drive waveform 20 can be stably ejected is 10800 (Hz). Since the same drive waveform 20 is used, the maximum drive frequency is common to 10800 (Hz) in both the 360 dpi mode and the 720 dpi mode. become.
[0011]
Therefore, as shown in FIG. 3A, the moving speed of the carriage during image formation is 10800/360 = 30.0 (inches / sec. Hereinafter abbreviated as IPS) in the 360 dpi mode, and 10800 in the 720 dpi mode. /720=15.0 (IPS), which requires two carriage speeds. Note that the minimum dot interval in the carriage movement direction in each mode is the reciprocal 1 / H of the resolution H, 360 dpi, and 720 dpi.
[0012]
In order to further improve the print quality, the second conventional example is a method of using different drive waveforms for 360 dpi and 720 dpi for the purpose of increasing the difference in ink droplet volume between the low resolution mode and the high resolution mode. An example of the drive waveform is shown in FIG. The drive waveform 30 is a drive waveform for 360 dpi, and the number attached is the ratio of the length of time to the one-way propagation time T of the pressure wave in the ink flow path 613. It comprises two ejection pulses F6 and F7 for ejecting ink droplets and an ejection stabilization pulse S4 for suppressing residual vibration of the ejection pulses F6 and F7. The peak value (voltage value) of all the pulses is the same. The drive waveform for 720 dpi is the same as the drive waveform 20 used in the first conventional example. As shown in FIG. 5, when the length L of the ink flow path 613 is 12.0 mm and the emission diameter of the nozzle 618 is φ26 μm, when a drive waveform 30 with a drive voltage of 18 (V) is applied, ejection is performed. The applied ink drop volume is 20 pl when a drive waveform 20 with a drive voltage of 40 pl and 16 (V) is applied, and the ink droplet volume difference between modes is larger than that of the first conventional example, and a good print image quality is obtained.
[0013]
It is known from experiments that the maximum drive frequency at which the drive waveform 30 can be stably ejected is 13000 (Hz), and the maximum drive frequency at which the drive waveform 20 can be stably ejected is 16000 (Hz). As shown in FIG. 4, the carriage movement speed during image formation is 13000/360 = 36.1 (IPS) in the 360 dpi mode, and 16000/720 = 22.2 (IPS) in the 720 dpi mode. In some cases, two carriage speeds are required.
[0014]
[Problems to be solved by the invention]
As described in the above-described conventional technology, when increasing the resolution in the carriage movement direction, some new carriage movement speeds must be prepared for the slower speed in accordance with the resolution.
[0015]
In general, the carriage is driven by a stepping motor or DC motor in a serial image forming apparatus, and the repetition drive frequency of the ink ejecting apparatus is fixed to the maximum possible frequency in order to achieve the maximum printing speed and various resolutions. The moving speed of the carriage is changed in accordance with the resolution to be realized. Usually, it is designed so that three to four moving speeds can be selected. When the moving speed changes, motor drive system change, motor drive current value change, acceleration / deceleration sequence parameter change, etc. are performed with respect to motor control. Further, in an inkjet image forming apparatus, when printing is performed while the carriage is reciprocating, the dot position is shifted depending on the printing direction, and is further shifted depending on the moving speed. Therefore, it is necessary to change parameters for dot position adjustment. For this purpose, the print control means stores all the above parameters and uses them appropriately. Further, when there is a possibility that the current value or the driving method is changed, hardware having a function that can realize them is required.
[0016]
In many cases, a stepping motor is used to drive the carriage. In the case of a stepping motor, in addition to the above-described problems, vibration is a problem with respect to the movement of the carriage. The vibration of the carriage becomes more problematic as the rotation speed range of the motor becomes wider, and adding a slower speed greatly expands the rotation speed range of the motor.
[0017]
Thus, the addition of the carriage speed has many problems, such as parameter storage, hardware function improvement, and carriage vibration.
[0018]
Accordingly, the present invention solves such problems, and an object of the present invention is to provide an image forming apparatus having a print mode capable of executing a plurality of resolutions without increasing the types of carriage moving speeds. It is in.
[0019]
[Means for Solving the Problems]
In order to achieve the above object, according to a first aspect of the present invention, there is provided an ink ejecting apparatus that ejects ink filled in an ink chamber as droplets by applying an ejection pulse signal to an actuator along a print medium. In an image forming apparatus that is mounted on a moving carriage, ejects ink droplets while the ink ejecting device moves along the print medium, and expresses a print pattern by dots formed by ink droplets landed on the print medium . A first print mode for printing an image at a print resolution; and a second print mode for printing an image at a print resolution higher than the predetermined print resolution. In the first print mode, ink droplets are ejected. A plurality of ejection pulses to be applied, a first drive waveform having a predetermined length is applied to the actuator at a first drive frequency, and a predetermined drive signal is applied to the print medium. Ink droplets that form dots of the size are ejected, and in the second print mode, the number of ejection pulses is smaller than the number of ejection pulses of the first drive waveform, and the length of the first drive waveform is longer Applying a short second drive waveform to the actuator at a second drive frequency higher than the first drive frequency, the dots of the predetermined size formed on the print medium in the first print mode Ejecting ink droplets that form smaller dots, wherein the first drive waveform includes at least one ejection pulse during the passage of the length of the second drive waveform from the beginning of the waveform. And at least one ejection pulse after the time of the length of the second drive waveform has elapsed, and in the first print mode and the second print mode, the moving speed of the carriage is set. Characterized in that it is an.
[0020]
[0021]
Thereby, each printing mode of a plurality of resolutions can be executed at the same carriage speed.
[0022]
[0023]
Further, since the number of ejection pulses is small at high resolution, the maximum repetition drive frequency of the ink ejection means can be increased, and the difference in dot size between the resolutions can be clarified.
[0024]
Invention according to claim 2, in the image forming apparatus according to claim 1, wherein the first driving frequency, when the first driving waveform is applied, the actuator of the predetermined size It is the highest drive frequency that can stably eject ink droplets that form dots, and the second drive frequency is an ink droplet that causes the actuator to form the small dots when the second drive waveform is applied. It is the highest drive frequency that can stably inject fuel . Thus, since each drive frequency is the highest drive frequency that can be stably ejected, it is possible to stably realize printing at each resolution at high speed.
[0025]
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the ink ejecting device changes a volume of the ink chamber by an operation of the actuator, and a pressure wave is generated in the ink chamber. Is generated, and ink droplets are ejected. As described above, in the case of generating a pressure wave, it is possible to effectively realize the configurations of the above claims by associating the drive waveform with the propagation time of the pressure wave.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0027]
The mechanical configuration of the image forming apparatus and the ink ejecting apparatus of the present embodiment is the same as the conventional configuration described with reference to FIGS.
[0028]
An example of specific dimensions of the ink droplet ejecting apparatus 600 will be described. The length L of the ink chamber 613 is 8.0 mm. The nozzle 618 was 26 μm in diameter on the ink droplet ejection side, and the ratio L / a (= T) of the sound velocity a in the ink in the ink chamber 613 to L was 8.0 μsec.
[0029]
An image forming method according to the present embodiment will be described in the case where there are a plurality of modes such as 300 dpi and 600 dpi for printing resolution in the carriage movement direction using the ink ejecting apparatus having such a configuration.
[0030]
An example of the drive waveform is shown in FIG. The drive waveform 10 is a drive waveform for 300 dpi, and the number attached is the ratio of the length of time to the one-way propagation time T of the pressure wave in the ink flow path 613. Two ejection pulses F1 and F2 for ejecting ink droplets, an ejection stabilization pulse S1 for suppressing residual vibration of the ejection pulses F1 and F2, and two ejection pulses F3 and F4 for ejecting ink droplets again And an injection stabilization pulse S2 for suppressing residual vibration of the injection pulses F3 and F4. The peak value (voltage value) of all the pulses is the same.
[0031]
The drive waveform 20 is a drive waveform for 600 dpi, and is the same as that described with reference to FIG.
[0032]
As shown in FIG. 5, when the length L of the ink flow path 613 is 8.0 mm and the emission diameter of the nozzle 618 is φ26 μm, ejection is performed when a driving waveform 10 of a driving voltage of 17 (V) is applied. The ink droplet volume is 60 pl, and 15 pl when a drive waveform 20 with a drive voltage of 15 (V) is applied. The ink droplet volume difference between the modes is larger than in the conventional example, and a good print image quality is obtained.
[0033]
It is known from experiments that the maximum drive frequency at which the drive waveform 10 can be stably injected is 7500 (Hz), and the maximum drive frequency at which the drive waveform 20 can be stably injected is 15000 (Hz).
[0034]
Therefore, as shown in FIG. 1, the carriage moving speed during image formation is 7500/300 = 25.0 (IPS) in the 300 dpi mode, and 15000/600 = 25.0 (IPS) in the 600 dpi mode. In this case, only one carriage speed is required.
[0035]
FIG. 8 is a block diagram illustrating an electrical configuration of the image forming apparatus. The control system of this embodiment includes a microcomputer 41, a ROM 42, and a RAM 43 having a one-chip configuration. The microcomputer 41 drives an operation panel 14 for a user to give a printing instruction, a motor drive circuit 35 for driving a print medium transport motor 38, and a carriage moving motor 37 equipped with an ink ejecting apparatus. A motor drive circuit 36 and the like are connected.
[0036]
The ink ejecting apparatus 600 is driven by the drive circuit 21, and the drive circuit 21 is controlled by the control circuit 22. That is, as shown in FIG. 6, the electrodes 619 and 621 provided in the ink flow paths 613 of the head unit 600 are connected to the drive circuit 21. The drive circuit 21 generates various pulse signals based on the control of the control circuit 22 and applies them to the ink ejecting apparatus.
[0037]
The microcomputer 41, the ROM 42, the RAM 43, and the control circuit 22 are connected via an address bus 23 and a data bus 24. The microcomputer 41 generates a print timing signal TS and a control signal RS according to a program stored in advance in the ROM 42 and transfers it to the control circuit 22.
[0038]
The control circuit 22 includes a gate array, and print data DATA for forming the image data on a print medium based on the image data stored in the image memory 25 according to the print timing signal TS and the control signal RS. A transfer clock TCK, a strobe signal STB, and a print clock CLK that are synchronized with the print data DATA are generated and transferred to the drive circuit 21.
[0039]
The control circuit 22 also stores in the image memory 25 image data transferred from an external device such as a personal computer 26 via the Centronics interface 27. Then, the control circuit 22 generates a Centronics data reception interrupt signal WS based on the Centronics data transferred from the external device via the Centronics interface 27, and transfers it to the microcomputer 41. The signals DATA, TCK, STB, and CLK are transferred through a harness cable 28 that connects the drive circuit 21 and the control circuit 22.
[0040]
The microcomputer 41 determines the resolution of the image data transferred from the external device according to the program stored in the ROM 42, outputs a control signal RS corresponding to the resolution, and the control circuit 22 outputs the control signal RS corresponding to the resolution. The print clock CLK having the highest drive frequency is output. The microcomputer 41 designates the rotational speed of the carriage moving motor 37 to the drive circuit 35 in accordance with a program stored in the ROM 42. In addition, data of the driving waveforms 10 and 20 is stored in a predetermined area of the ROM 42, and the microcomputer 41 reads out driving waveform data corresponding to the determined resolution and outputs the driving waveform data to the driving circuit via the control circuit 22. . The resolution can also be designated from the operation panel 44. That is, the microcomputer 41, the ROM 42, the RAM 43, and the control circuit 22 have means for determining the resolution, setting the print mode according to the resolution, setting the repetition drive frequency of the ink ejecting apparatus, setting the moving speed of the carriage, and the like. Constitute.
[0041]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, since the carriage movement speed is the same in the print modes of a plurality of resolutions, it is not necessary to increase the types of carriage movement speeds. Therefore, it is not necessary to store many parameters for changing the moving speed, or to add hardware, and the problem of carriage vibration can be solved.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a combination of print resolution and drive frequency according to an embodiment of the present invention.
FIG. 2 is a diagram showing drive waveforms according to the embodiment of the present invention.
FIG. 3 is a diagram illustrating a combination of conventional print resolution and drive frequency.
FIG. 4 is a diagram showing drive waveforms according to a conventional example.
FIG. 5 is a diagram illustrating a relationship between dimensions of an ink ejecting apparatus according to an embodiment of the present invention and a conventional example and an ink droplet volume.
FIG. 6 is a diagram illustrating an ink ejecting apparatus according to an embodiment of the invention.
FIG. 7 is a diagram illustrating the operation of the ink ejecting apparatus according to the embodiment of the invention.
FIG. 8 is a diagram showing an electrical control configuration of the image forming apparatus according to the embodiment of the present invention.
FIG. 9 is a diagram illustrating a structure of an image forming apparatus according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Drive waveform 20 Drive waveform 600 Ink ejection apparatus 613 Ink flow path 618 Nozzle

Claims (3)

An ink ejecting device that ejects ink filled in the ink chamber as droplets by applying an ejection pulse signal to an actuator is mounted on a carriage that moves along the print medium, and the ink ejector follows the print medium. In an image forming apparatus that ejects ink droplets while moving and expresses a print pattern by dots formed by ink droplets landed on a print medium,
A first print mode for printing an image at a predetermined print resolution, and a second print mode for printing an image at a print resolution higher than the predetermined print resolution;
In the first print mode, a plurality of ejection pulses for ejecting ink droplets are provided, a first drive waveform having a predetermined length is applied to the actuator at a first drive frequency, and a predetermined drive Ink droplets that form dots of size,
In the second print mode, a second drive waveform having fewer ejection pulses than the number of ejection pulses of the first drive waveform and shorter than the length of the first drive waveform is the first drive frequency. An ink droplet that is applied to the actuator at a second driving frequency higher than that to form dots smaller than the predetermined size dots formed in the first print mode on a print medium;
The first drive waveform has a duration of at least one of the ejection pulses and a length of the second drive waveform while the time of the length of the second drive waveform has elapsed from the beginning of the waveform. After elapse, comprising at least one said injection pulse;
An image forming apparatus, wherein the carriage movement speed is the same in the first print mode and the second print mode . The first drive frequency is the highest drive frequency at which the actuator can stably eject ink droplets that form the predetermined size dots when the first drive waveform is applied,
The second drive frequency is a maximum drive frequency at which the actuator can stably eject ink droplets forming the small dots when the second drive waveform is applied. 2. The image forming apparatus according to 1. 3. The ink ejecting apparatus according to claim 1, wherein the ink ejecting device ejects ink droplets by generating a pressure wave in the ink chamber by changing a volume of the ink chamber by an operation of the actuator. The image forming apparatus described in 1.

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