JP2002103606A - Ink jet recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of an ink jet recorder that high frequency driving is impossible. SOLUTION: A rectangular driving waveform is applied to the electrode 55 of a head 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording apparatus, and more particularly, to an ink jet recording apparatus equipped with an electrostatic ink jet head.

[0002]

2. Description of the Related Art As an ink jet recording apparatus used as an image recording apparatus (image forming apparatus) such as a printer, a facsimile, a copying apparatus, and a plotter, a nozzle for discharging ink droplets and a discharge chamber (ink flow path, A pressure chamber, a pressurized liquid chamber, a liquid chamber, etc.), a vibrating plate forming a wall surface of the ink flow path, and an electrode opposed to the vibrating plate. 2. Description of the Related Art There is known an ink jet head equipped with an electrostatic ink jet head that ejects ink droplets from nozzles by deforming and displacing.

As a head driving device in such an ink jet recording apparatus, for example, Japanese Patent Laid-Open No. 7-1325
As disclosed in Japanese Patent Publication No. 98, there is provided a timing pulse generator and a charging circuit and a discharging circuit using a charging resistor and a discharging resistor, and the like. In some cases, a drive pulse waveform is applied such that charges between the two are charged and discharged exponentially. Also, Japanese Patent Application Laid-Open
As disclosed in JP-A-214770, there is also known a device in which a timer circuit and a three-phase switching element are used to adjust the timing at which ink droplets are ejected.

[0004]

However, a head driving apparatus for applying a driving pulse waveform such that charges are charged and discharged exponentially between a diaphragm and an electrode using the above-described charging / discharging circuit is provided. If the repetition frequency of the drive pulse waveform is increased to increase the printing speed, the charge time of the electric charge between the diaphragm and the electrode (time for displacing the diaphragm toward the electrode) becomes shorter. When the charging time is shortened as described above, bubbles may be mixed in from the nozzles due to the generation of a sudden negative pressure in the ink flow path, which may result in defective ejection of ink droplets or impossibility of ejection.

[0005] Therefore, in order to discharge ink droplets stably, a sufficient charge is charged between the diaphragm and the electrode, and the diaphragm is slowly deformed (bent), so that the ink flow path in the ink flow path is reduced. It is necessary to prevent air bubbles from being mixed due to the generation of a sudden negative pressure. For this purpose, it is necessary to secure a charging time of several tens of μs or more per discharge of one ink droplet, and the repetition frequency of the drive pulse waveform that can be applied to the inkjet head is limited. It is relatively difficult to increase the speed to increase the speed.

In addition, by using the above-described driving circuit having a charging circuit and a discharging circuit using a charging / discharging resistor, the charging time and discharging time of the electric charge between the diaphragm and the electrode are adjusted to discharge the ink droplet. In order to control the resistance, it is necessary to adjust each resistance value of the charging resistance and the discharging resistance used in the charging circuit and the discharging circuit, but the adjustment of each resistance value is very troublesome, and the circuit configuration is also complicated. The circuit becomes complicated and complicated, which increases the circuit cost.

Further, when a drive pulse waveform is used such that the electric charge between the diaphragm and the electrode is charged and discharged exponentially, the actuator portion (diaphragm, electrode, gap) of the ink jet head is used. The influence of waveform distortion is likely to occur due to manufacturing variations, and the effect of waveform distortion is also likely to occur due to variations in resistance values, because the driving circuit uses resistors in the charging circuit and the discharging circuit. Therefore, it is relatively difficult to apply a drive pulse waveform having a fixed shape for each head, and it is relatively difficult to reduce the variation of the ejection characteristic value of the ink droplet for each head and keep it constant. Issues.

In the case of adjusting the timing of ejecting ink droplets by a timer circuit and a three-phase switching element as in the above-described head driving device, the adjustment of the timing is very troublesome. In addition, the configuration of the driving circuit becomes complicated. In addition, since the same drive pulse waveform as that of the above-described head drive device is used, there are also problems unique to the drive pulse waveform and its waveform generation circuit, as described above.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an ink jet recording apparatus capable of high-frequency driving with a simple structure and capable of obtaining stable ink droplet ejection characteristics.

[0010]

In order to solve the above-mentioned problems, an ink jet recording apparatus according to the present invention is provided with means for applying a trapezoidal drive waveform to an ink jet head. .

[0011] The ink jet recording apparatus according to the present invention comprises:
In this configuration, a means for applying a rectangular drive waveform to the inkjet head is provided.

In the ink jet recording apparatus according to the present invention, it is preferable that the drive waveform is a waveform that does not exceed 5 μs from the initial voltage value to the desired voltage value. Further, it is preferable that the drive waveform is a waveform in which the time required to return from the desired voltage value to the initial voltage value does not exceed 6 μs. Further, it is preferable that the drive waveform is a waveform in which the time required to return from the desired voltage value to the initial voltage value does not exceed 2 μs.

The nozzle hole of the ink jet head has a discharge volume of 30 pl when a driving waveform is applied.
It is preferable that the size is such that an ink droplet that does not exceed the size is ejected. Further, it is preferable that the drive waveform is generated by the D / A conversion means.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic perspective explanatory view of a mechanism of an ink jet recording apparatus according to the present invention, and FIG. 2 is a side explanatory view of the mechanism.

This ink jet recording apparatus comprises a carriage movable in the main scanning direction inside the recording apparatus main body 1, an ink jet head including an ink jet head mounted on the carriage, an ink cartridge for supplying ink to the ink jet head, and the like. The paper feed cassette 4 or the manual feed tray 5 takes in the paper 3, and records the required image by the print mechanism 2, and then the output tray mounted on the rear side. 6 is discharged.

The printing mechanism 2 slides the carriage 13 in a main scanning direction (a direction perpendicular to the paper surface of FIG. 2) by a main guide rod 11 and a sub guide rod 12 which are guide members which are laterally mounted on left and right side plates (not shown). This carriage 1
Reference numeral 3 denotes a head (recording head) 1 including an inkjet head that ejects ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (Bk).
4 is mounted with the ink droplet ejection direction facing downward, and an ink tank (ink cartridge) 15 for supplying each color ink to the head 14 is exchangeably mounted on the upper side of the carriage 13.

Here, the carriage 13 is slidably fitted on the main guide rod 11 on the rear side (downstream side in the paper transport direction), and the front guide rod 1 on the front side (upstream side in the paper transport direction).
2 slidably mounted. The main scanning motor 1 is moved to scan the carriage 13 in the main scanning direction.
A timing belt 20 is stretched between a driving pulley 18 and a driven pulley 19, which are driven to rotate by 7, and the timing belt 20 is fixed to the carriage 13.

Although the heads 14 of each color are used here as the ink jet head, a single head having nozzles for ejecting ink droplets of each color may be used. Further, the head 14 is an electrostatic ink jet head that presses ink by displacing the vibration plate with an electrostatic force between a vibration plate forming an ink flow path wall surface and an electrode facing the vibration plate.

On the other hand, the paper 3 set in the paper feed cassette 4
Roller 21 and a friction pad 22 for separating and feeding the paper 3 from the paper feed cassette 4 and a guide member 23 for guiding the paper 3
A transport roller 24 that reverses and transports the fed paper 3, a transport roller 25 that is pressed against the peripheral surface of the transport roller 24, and a tip roller 26 that defines an angle at which the paper 3 is fed from the transport roller 24. Is provided. The transport roller 24 is driven to rotate by a sub-scanning motor 27 via a gear train.

Further, there is provided a printing receiving member 29 which is a paper guide member for guiding the paper 3 fed from the transport roller 24 below the head 14 in accordance with the moving range of the carriage 13 in the main scanning direction. . This print receiving member 2
9, a transport roller 31 and a spur 32, which are rotatably driven to send the sheet 3 in the sheet ejection direction, are provided on the downstream side in the sheet conveying direction, and further, a sheet ejection roller 33 and a spur 34 for sending the sheet 3 to the sheet ejection tray 6. And a guide member 3 forming a paper discharge path
5 and 36 are provided.

A reliability maintenance / recovery mechanism (hereinafter, referred to as a "subsystem") 37 for maintaining and recovering the reliability of the head 14 is disposed on the right end side in the moving direction of the carriage 13. The carriage 13 is moved to the subsystem 37 side during printing standby, and the head 14 is capped by capping means or the like.

Next, an ink jet head constituting the head 14 of the ink jet recording apparatus will be described with reference to FIGS. 3 is an explanatory cross-sectional view of the inkjet head in the longitudinal direction of the diaphragm, and FIG. 4 is an enlarged cross-sectional view of a main part of the head in the lateral direction of the diaphragm.

This ink jet head includes a first substrate 41 which is a diaphragm / liquid chamber substrate, a second substrate 42 which is an electrode substrate provided below the first substrate 41, and a first substrate 41.
And a third substrate 43 which is a lid member provided on the upper side of the nozzle groove 44, and a plurality of nozzle grooves 44 for discharging a plurality of ink droplets.
A pressurized chamber (also referred to as a discharge chamber) 46 is an ink flow path communicating with each other, and a common liquid chamber flow path 48 communicates with each pressurized chamber 46 via a fluid resistance part 47 also serving as an ink supply path. are doing.

As the first substrate 41, a single crystal silicon substrate is used, a nozzle groove 44 is formed at one end, and a pressurizing chamber 46 communicating with the nozzle groove 44 and a bottom portion which is a wall surface of the pressurizing chamber 46 are formed. , A groove forming the fluid resistance portion 47, and a recess forming the common liquid chamber flow path 48.

The use of a single-crystal silicon substrate as the first substrate 41 facilitates the processing when the thin diaphragm 50 having a thickness of about several μm is formed by etching, and has a small size of about several μm. The gap can be formed with high accuracy by anodic bonding with the second substrate 42. Further, when the diaphragm 50 is vibrated, it is necessary to apply a voltage to the electrode to generate an electrostatic force. However, since silicon is semiconductive, the diaphragm 50 can also serve as an electrode. Therefore, there is an advantage that there is no need to provide a separate electrode on the diaphragm 50 side.

A concave portion 54 is formed in the second substrate 42 by using Pyrex (registered trademark) glass (borosilicate glass), and an individual portion facing the diaphragm 50 with a gap 56 is formed on the bottom surface of the concave portion 54. The electrode 55 is formed by, for example, sputtering gold or the like, and an actuator section is constituted by the diaphragm 50 and the electrode 55. Note that the electrode 55 extends outside to integrally form an electrode terminal portion 55a. Further, the use of Pyrex glass for the second substrate 42 facilitates anodic bonding with the silicon substrate.

The surface of the electrode 55 is formed of a dielectric insulating layer (oxide film-based insulating film) such as a SiO ₂ film or a nitride film-based insulating film such as a Si ₃ N ₄ film in order to improve the durability of the electrode 55. Although the electrode protection film 57 is formed, the electrode protection film 57 is not formed on the surface of the electrode 55, or the electrode protection film 57 is formed on the surface of the electrode 55 and the insulating film is formed on the diaphragm 50 side. Can also.

As the third substrate 43, a stainless steel substrate is used, and is joined to the first substrate 41 with an adhesive. The joining of the third substrate 43 forms a nozzle groove 44, a discharge chamber 46, a fluid resistance part 47, and a common liquid chamber flow path 48. Also,
An ink supply port 61 for supplying ink from outside to the common liquid chamber flow path 48 is formed in the third substrate 43, and the ink cartridge 15 described above is connected via an ink supply pipe 62 connected to the ink supply port 61. Supplies ink.

Next, a method of joining the first substrate 41 and the second substrate 42 will be described. A small gap of about several μm is formed with high precision like an electrostatic inkjet head,
As a method of assembling (joining), it is preferable to use an anodic bonding method. This anodic bonding method can be expected to ensure the dimensional accuracy of the gap more than other bonding methods (brazing, fusion welding, etc.), and a voltage is applied between the first substrate 41 and the second substrate 42 (− By applying about 300 V to -500 V), precise bonding can be performed at a relatively low temperature (300 to 400 ° C.).

In order to reliably perform such anodic bonding, the first substrate 41 or the second substrate 42 is so formed that covalent bonding between the substrates occurs at the bonding interface between the first substrate 41 and the second substrate 42. Either must be a substrate that contains a large amount of alkali ions, and when anodic bonding, a material whose coefficient of thermal expansion is relatively consistent between substrates so that distortion between the substrates due to thermal stress is reduced. It is preferable to select.

In this embodiment, as described above, a single-crystal silicon substrate is used for the first substrate 41, and the second substrate 42 contains a large amount of alkali ions such as Na, and has a coefficient of thermal expansion relatively equal to that of the silicon substrate. Since a Pyrex glass (borosilicate glass) substrate is used, reliable bonding with little thermal distortion between the substrates can be obtained.

Next, an outline of a control section of the ink jet recording apparatus will be described with reference to FIG. The control unit includes a microcomputer (hereinafter, referred to as a “CPU”) 80 for controlling the entire recording apparatus, a ROM 81 storing required fixed information, a RAM 82 used as a working memory, and the like. An image memory 83 for storing data obtained by processing the transferred image data;
A parallel input / output (PIO) port 84, an input buffer 85, a parallel input / output (PIO) port 86, a waveform generation circuit 87, a head drive circuit 88, and a driver 89
Etc. are provided.

Here, various information such as image data from the host, various instruction information from an operation panel (not shown), a detection signal from a paper presence / absence sensor for detecting the start and end of the paper, and a signal Signals from various sensors such as a home position sensor for detecting a home position (reference position) are input.
Required information is transmitted to the host and the operation panel via the port 84.

The waveform generation circuit 87 generates a drive waveform between the vibration plate 50 and the electrode 55 of the head 14 such that the vibration plate 50 is displaced toward the electrode 55 with a displacement amount for ejecting ink droplets and timing. appear. By using a D / A converter for D / A converting the drive waveform data from the CPU 80 as the waveform generation circuit 87, a required drive waveform can be generated and output with a simple configuration.

The head drive circuit 88 includes a PIO port 86
The driving waveform is applied to the energy generating means (diaphragm 50 and electrode 55) corresponding to each nozzle groove 44 of the head 14 based on various data and signals given via the. Further, the driver 89 moves and scans the carriage 13 in the main scanning direction by controlling the driving of the main scanning motor 17 and the sub-scanning motor 27 in accordance with the driving data supplied via the PIO port 86, respectively. Is rotated to convey the sheet 3 by a predetermined amount.

Next, a part related to the head drive control unit in this control unit will be described with reference to the block diagram of FIG. The head drive control unit is provided with the CPU 8 described above.
0, a main control unit 91 including a ROM 81, a RAM 82, peripheral circuits, and the like, a waveform generation circuit 87, an amplifier 92, a drive circuit (driver IC) 93, and the like.

The main control section 91 supplies data for generating a drive waveform to be applied to the electrode 55 of the head to the waveform generation circuit 87 and print signals (serial data) SD, shift signals to the driver IC 93. Clock CL
K, a latch signal LAT, and the like. Waveform generation circuit 87
As described above, a drive waveform that generates energy for ejecting ink droplets from the nozzles 44 to the actuator section of the inkjet head is generated in time series. That is, the main control unit 91 and the waveform generation circuit 87 constitute a means for generating and outputting a drive waveform.

The driver IC 93 is a control means for selecting a drive waveform input in a time series in accordance with a print signal and controlling the selection of the drive waveform applied to each individual electrode 55 of the ink jet head constituting the head 14. That is, the driver IC 9
Reference numeral 3 denotes a shift register 95 for inputting a serial clock CLK and a serial signal SD as a print signal from the main control unit 91, and a latch circuit 96 for latching a register value of the shift register 95 with a latch signal LAT from the main control unit 91. A level conversion circuit 97 for changing the level of the output value of the latch circuit 96;
And an analog switch array 98 whose turning-off is controlled. The analog switch array 98 includes analog switches AS1 to ASm connected to m individual electrodes 55 of the inkjet head 40 (the number of nozzles is m). The diaphragm 50 serving as a common electrode of the ink jet head is grounded.

Then, serial data (print signal) SD is fetched into the shift register 95 in accordance with the shift clock, and the serial data SD fetched into the shift register circuit 95 by the latch signal LAT in the latch circuit 96.
Is latched and input to the level conversion circuit 98. The level conversion circuit 98 turns on / off the analog switch ASm (m = 1 to m) connected to the individual electrode 55 of each actuator according to the content of the data.

This analog switch ASm (m = 1 to
m) is supplied with a drive waveform from the waveform generation circuit 87 via the amplifier 92, so that the analog switch ASm (m = m)
1 to m) are turned on, the drive waveform is selectively applied to the individual electrodes 55.

Next, the operation of the ink jet head will be described with reference to FIGS. When a positive pulse voltage is applied to the electrode 55 from the head drive circuit 88, the surface of the electrode 55 is charged to a positive potential, and the lower surface of the diaphragm 50 facing the electrode 55 is charged to a negative potential. I do. Therefore, as shown by the arrow in FIG. 7A, the diaphragm 50 is caused to act on the electrode 55 facing the diaphragm 50 by an electrostatic attraction function (electrostatic attraction force).
Deflection in the direction. Here, the magnitude of the electrostatic attraction force P generated on the diaphragm 50 is expressed as in equation (1).

[0042]

(Equation 1)

In the equation (1), ε is the permittivity of the air existing between the diaphragm 50 and the electrode 55, S is the effective area of the electrostatic force acting between the diaphragm 50 and the electrode 55,
V indicates a drive voltage value applied to the electrode 55, and d indicates an effective gap distance between the diaphragm 50 and the electrode 55.

Here, the effective gap distance d is expressed by equation (2) when a substance having a dielectric constant other than air is interposed between the diaphragm 50 and the electrode portion 55.

[0045]

(Equation 2)

[0046] However, in the equation (2), a dielectric insulating layer between the d _a diaphragm 50 and the distance of the gap existing between the electrodes 55, the d _epsilon diaphragm 50 and the electrode portion 55 5
The thickness of 7 and ε _r indicate the relative permittivity of the dielectric insulating layer 57.

That is, when a substance having a certain dielectric constant is interposed between the diaphragm 50 and the electrode 55, as shown in the equation (2), the thickness d _{ε of the} interposed dielectric substance and the dielectric substance By changing the relative permittivity ε _r of
Electric field intensity E (E (E) generated between diaphragm 50 and electrode 55
= V / d), and the magnitude of the electrostatic attraction force P generated thereby changes.

Therefore, as shown in the equation (1), the magnitude of the electrostatic attraction force P is such that the smaller the effective gap distance d between the diaphragm 50 and the electrode 55 is, the larger the electrostatic attraction force is applied to the diaphragm 50. Works. Further, as the drive voltage value V to the electrode 55 is increased, the diaphragm 50 bends toward the electrode 55, and as shown in FIGS.
Side is in contact via a dielectric insulating layer 57. The state where the diaphragm 50 is in contact with the electrode 55 in this manner is referred to as a contact state.

When the application of the pulse voltage, which is a pulse-like voltage to the electrode 55, is turned off, FIGS.
As shown in (1), since the restoring force P1 is acting on the flexed (deformed) diaphragm 50, the diaphragm 50 is restored by the restoring force P1, and the pressure in the pressurizing chamber 46 rises rapidly. To do
Ink droplets 65 are formed from the nozzle holes 44 and are ejected toward the paper 3. When a pulse voltage is applied to the electrode 55 (ON), the diaphragm 50 bends again in the direction of the electrode section 55, so that the ink flows from the common liquid chamber flow path 48 through the fluid resistance section 47 to the pressure chamber 46. Will be replenished within.

Next, a first embodiment of the head drive control in the ink jet recording apparatus thus configured will be described with reference to FIGS. First, FIG.
When the voltage V1 is applied to the electrode 55 in the form of a pulse as shown in (a), the non-ejection nozzles (meaning the nozzles that do not eject ink droplets) at the time points t0 to t7 of the pulsed voltage V1 The meniscus vibrates as shown in FIG. Further, between the diaphragm 50 and the electrode 55, while in the contact state (the diaphragm 50
(During contact with the electrode 55), it is observed that a charge / discharge current in which the current value oscillates positively and negatively as shown in FIG. Further, the pressure in the pressurizing chamber 46 is observed to fluctuate in the positive and negative directions as shown in FIG.

As described above, the pulse voltage V1 is applied to the electrode 5
The vibration phenomenon occurs in the meniscus, the diaphragm-electrode current (charge / discharge current) and the pressure in the pressurizing chamber when applied to the diaphragm 5 as described with reference to FIGS.
0 is bent in the direction of the electrode 55 to be in a contact state, and at the same time, ink flows into the pressurizing chamber 46 from the nozzle groove 44 side and the fluid resistance part 47 side, and the flow of each ink causes the vibration plate 50 to contact. Experiments have shown that a strong pressure wave is generated in the pressurizing chamber 46 in the state.

Further, the pulse width (voltage application time) of the pulse-like voltage is set at times t1 to t7 with reference to time t0 in FIG.
When it is changed to the above, the discharge characteristic value of the ink droplet (the discharge speed Vj and the discharge amount of the ink droplet = drop volume Mj) changes as shown in FIG. That is, it has been confirmed by experiments that the ejection characteristic value of the ink droplet fluctuates greatly by changing the pulse width.

Here, it was experimentally confirmed that the oscillation cycle of the ink droplet ejection characteristic value corresponds to the oscillation cycle of the pressure fluctuation in the pressurizing chamber 46. That is, as shown in the pressure fluctuation waveform of the pressurized chamber shown in FIG.
From time t1 to time t1, the inside of the pressurizing chamber 46 is in a negative pressure state. In this case, as shown in FIG.
Is canceled by the negative pressure P2 generated in the pressurizing chamber 46, and acts in a direction in which the ink flow velocity in the direction of the nozzle hole 44 decreases, so that the negative pressure P2 is in a stronger time region (time t0 to t0). During t1), a state occurs in which no ink droplet is ejected.

Also, since the diaphragm 50 is in the contact state at the time point t1, a positive current generated at the time of the contact at the time point ta flows as shown in the charge / discharge current waveform shown in FIG. In addition, since the pressure fluctuation value (negative pressure P2) becomes zero, ink droplet ejection is started. Further, the pressure chamber 46 is in a positive pressure state from the time point t1 to the time point t3. In this case, as shown in FIG.
A state occurs in which the positive pressure P3 generated in the pressurizing chamber 46 is superimposed, and the ink flow speed in the direction of the nozzle hole 44 is increased.

Therefore, in this ink jet head, after the diaphragm 50 is in the contact state (after the contact).
The discharge characteristic value of the ink droplet fluctuates in accordance with the magnitude of the positive and negative pressure fluctuations generated in the pressurizing chamber 46, and the positive pressure P3 in the pressurizing chamber 46 peaks (maximum) at time t2. The ejection characteristic value of the ink droplet reaches a peak (maximum) corresponding to t6, and the negative pressure P2 in the pressurizing chamber 46 peaks (minimum).
It has been found that the discharge characteristic value of the ink droplet has a peak (minimum value) corresponding to the time point t4 when

Next, the shape of the drive waveform applied to the ink jet head will be described. First, a conventionally used driving waveform (for example, a driving pulse waveform described in JP-A-7-132598) will be described with reference to FIG. This drive waveform is, as shown in FIG.
This is a waveform in which charges between the diaphragm and the electrodes are charged and discharged exponentially. Experiments have shown that when this drive waveform is applied to the electrode 55 of the head, the diaphragm 50 in the discharge chamber 46 exhibits a displacement behavior as shown in FIG. This shows the behavior of the displacement of the diaphragm 50 peculiar to the actuator of the ink jet head using the electrostatic force.

That is, in the case of the electrostatic actuator, when a positive pulse voltage V1 as shown in FIG. 7A is applied to the electrode 55, it corresponds to a distance of １ ／ of the effective gap distance d described above. (The diaphragm 50 is shown in FIG.
The inflection point a or the inflection point b of the displacement waveform of FIG. ) Until
The state where the magnitude of the electrostatic attraction force P generated between the diaphragm 50 and the electrode 55 is balanced with the restoring force P1 held by the diaphragm 50 itself (equilibrium state). Accordingly, during the period from the point where the displacement of the diaphragm 50 is 0 to the inflection point a or the inflection point b, the displacement of the diaphragm 50 follows the magnitude of the voltage value of the pulse voltage V1. The displacement of the diaphragm 50 can be controlled.

However, when the displacement of the diaphragm 50 passes the inflection point a or the inflection point b, the diaphragm 50
When approaching in the direction, the electrostatic attraction force P suddenly becomes stronger than the restoring force P1, and the displacement of the diaphragm 50 becomes non-equilibrium. Therefore, the voltage value of the pulse voltage V1 applied to the electrode 55 Irrespective of this, the diaphragm 50 is suddenly bent in the direction of the electrode 55 and deformed, and finally the diaphragm 50 is deformed toward the electrode 55 as described above, that is, as shown in FIG.
The electrode 55 is deformed until it reaches the distance da of the gap between the electrode 55 and the electrode 55, and comes into contact with the electrode 55.

Therefore, during the time when the diaphragm 50 is in contact (between the inflection points a and b), if the voltage value of the pulse voltage V1 is equal to or more than the predetermined voltage value, The displacement and displacement amount of the diaphragm 50 cannot be controlled by the value. The moment when the restoring force P1 of the diaphragm 50 becomes the maximum as the ejection pressure of the ink droplet, the contact point da to the inflection point b
It is clear from experiments that the vibration displacement from the inflection point b to the displacement of the diaphragm 50 becomes zero hardly contributes to the ejection pressure of the ink droplet.

From these facts, in this ink jet head, the time region that contributes relatively effectively as the ejection pressure of the ink droplets is between the inflection points a and b (while the diaphragm 50 is in contact with it). ), That is, the time of the time width Td shown in FIG.

Accordingly, in the case of the drive waveform of FIG. 7A, the time width Td that effectively contributes to ink ejection is shorter than the pulse width Ta applied to the electrode 55. It is considered that the drive waveform a) exponentially changes has a uselessly long pulse width Ta.
Therefore, even if it is desired to increase the printing speed by applying a drive waveform to the electrode 55 at a higher drive frequency, the length of the pulse width Ta is limited in the drive waveform shown in FIG. It becomes difficult to apply a drive waveform at a repetition cycle shorter than the width Ta.

Therefore, in the present invention, the driving waveform applied to the electrode 55 is effective as the ejection pressure of the ink droplet by utilizing the characteristic of the displacement behavior of the vibration plate 50 peculiar to the ink jet head utilizing the electrostatic force. In addition, in order to contribute effectively, a trapezoidal driving waveform as shown in FIG. 14 or a rectangular (or square) as shown in FIG.
Drive waveform is generated to form an electrode 5 of the ink jet head.
5 to enable printing at a higher driving frequency.

That is, when the trapezoidal driving waveform shown in FIG. 14A is applied, the displacement of the diaphragm 50 is shown in FIG.
And the pulse width Tb of the drive waveform and the diaphragm 5
0 is in contact with and effectively contributes to the ejection of ink droplets.
Since d is substantially equal, the drive waveform can be applied to the electrode 55 at a higher drive frequency, and the printing speed can be further increased.

The displacement of the diaphragm 50 when the rectangular drive waveform shown in FIG. 15A is applied is as shown in FIG. 15B, and the pulse width of the drive waveform is also the same as described above. Since Tc and the time width Td in which the diaphragm 50 abuts and effectively contributes to ink droplet ejection are substantially equal, a higher driving frequency can be applied to the electrode 55 with a simpler driving waveform, and a higher printing speed can be achieved. Can be increased.

According to an experiment, when a drive waveform as shown in FIG. 13A is applied to the electrode 55 of the head in order to obtain the same constant ink droplet ejection characteristics, the drive frequency is about 8 kHz at the maximum. While it could only be raised up to
When a trapezoidal driving waveform as shown in FIG. 14A is applied to the electrode 55 of the head, the driving frequency is set to 1 at the maximum.
The printing speed could be increased to about 6 kHz, and the printing speed could be doubled with the same image quality.

Here, the nozzle holes of the ink jet head when applying these trapezoidal or rectangular drive waveforms will be described. When a drive waveform such as a trapezoidal or rectangular drive waveform is applied to the electrode 55 such that the diaphragm 50 rapidly bends and deforms, the inside of the discharge chamber 46 becomes a sudden negative pressure state. There is a possibility that bubbles may be mixed into the ejection chamber 46 and the ejection of ink droplets may become unstable.

However, in the case of an ink jet head, as shown in FIG. 16A, even when a rectangular drive waveform is applied to the electrode 55, the nozzle hole is not affected by a phenomenon peculiar to the actuator utilizing electrostatic force. By gradually changing the size, the diaphragm 5 is affected by the fluid resistance in the discharge chamber 46 as shown in FIG.
The displacement behavior of 0 changes as δ1 → δ2 → δ3, and the manner of deformation of the diaphragm 50 becomes gradually slower.

Therefore, the influence of the sudden generation of the negative pressure in the discharge chamber 46 is reduced, and the influence of the bubbles mixed from the nozzle holes 44 is reduced. In addition, by reducing the size of the nozzle hole, the area of the nozzle surface that comes into contact with air is reduced, and the entry of air bubbles from the nozzle hole 44 can be further suppressed.

Here, a rectangular drive waveform shown in FIG. 15A is applied to the electrode 55 of the ink jet head, and the ink droplet ejection when the size of the nozzle hole and the ejection volume of one ink droplet is changed. The state stability was evaluated. Table 1 shows the evaluation results. In the table, "○"
Indicates that the ejection state is stable, "△" indicates that the ejection state is unstable, and "-" indicates that the ink droplet of the droplet volume cannot be ejected from the nozzle hole.

[0070]

[Table 1]

As can be seen from Table 1, when the ejection volume of one ink droplet is 30 pl or less, the ink droplet can be stably ejected into the ejection chamber 46 without bubbles.

Therefore, when a rectangular or trapezoidal drive waveform is applied, the ejection volume of one ink droplet becomes 3
The size of the nozzle hole is set so as to be 0 pl or less.
As a result, ink droplets can be stably ejected even at a high drive frequency, and high-quality images can be printed at high speed.

Next, the rise and fall times of a rectangular or trapezoidal drive waveform will be described with reference to FIG. As shown in FIG.
5, the ink meniscus in the nozzle hole 44 is displaced as shown in FIG. 4B, and the pressure in the discharge chamber 46 is varied as shown in FIG.

Here, the drive waveform shown in FIG. 9A is, as described above, the time during which the pressure fluctuation generated in the pressurizing chamber 46 after the diaphragm 50 contacts the electrode 55 becomes positive pressure. Correspondingly, the pulse widths T2 and T6 are set in advance. In the case of this ink jet head, the vibration period of the pressure fluctuation generated in the pressurizing chamber 46 after the vibration plate 50 abuts is usually 10 to 10.
The cycle is very short, about 20 μsec. If the drive waveform can follow the oscillation cycle of the short pressure fluctuation, it is possible to form ink droplets at a higher drive frequency.

In order to follow such a short pressure fluctuation oscillation cycle, a trapezoidal or rectangular drive waveform is used.
Here, when the rising time T1 and the falling time T3 are changed while keeping the pulse width T2 of the driving waveform constant, the rising time T1 (from the initial voltage value to the desired voltage value) is changed as shown in FIGS. The discharge characteristic values (discharge speed Vj and discharge amount Mj) of the ink droplets gradually decrease as the time until the discharge reaches the predetermined time and the fall time T3 (the time until the voltage returns from the desired voltage value to the initial voltage value) increase. Tend to.

Accordingly, the rise time T1 and fall time T3 of the trapezoidal drive waveform as shown in FIG.
When the rising time T1 is set to approximately 5 μs or less as shown in FIG. 18, the ejection characteristic value of the ink droplet can be kept relatively high and constant, and the higher driving frequency can be maintained. It is easy to adapt to ink droplet ejection in

By setting the fall time T3 to about 6 μs or less as shown in FIG. 19, the ejection amount of ink droplets can be kept relatively high and constant, and stable ejection can be obtained. More preferably, the fall time T3 is 2
By setting the value to μs or less, both the ejection speed and the ejection amount of the ink droplet can be kept constant at a high value, and a stable ejection can be obtained, and the ink droplet ejection at a higher driving frequency can be more easily adapted. Therefore, it is more advantageous.

Next, another example of the head drive control unit for generating the above-described trapezoidal or rectangular drive waveform and applying the same to the head will be described with reference to FIGS. 20 and 21. FIG. A head drive control unit 1 shown in FIG. 20 outputs a timing pulse corresponding to a print signal.
00, a drive pulse from the head drive control circuit unit 100 is input via the buffer 101, a rectangular drive pulse corresponding to the timing pulse is generated, and the resistors R1 to R3 and the transistor Tr1 are supplied to the electrode 55 of the head. ~
And an output circuit comprising Tr3.

A head drive control circuit using such a resistor circuit can also generate and output a rectangular drive waveform. However, in this circuit, the pulse width of the driving waveform varies due to the variation in the resistance value of the resistance element, and the droplet discharge characteristics may become unstable.

The head drive control section shown in FIG. 21 supplies voltage data corresponding to the drive waveform to the counter 111 from the head drive control circuit section 110, and stores the count value of the counter 111 in the memory 112. The D / A converter 113 converts the voltage data value stored and held in the D / A converter 113 into an output circuit including the transistors Tr1 and Tr2 via the buffer 114, and applies it to the electrode 55 of the head.

By generating a drive waveform using a D / A converter in this manner, a highly accurate drive waveform can be generated, and variations in the ejection characteristic values of ink droplets can be reduced.

In the above embodiment, the shapes, arrangements, and forming methods of the nozzles, pressurizing chambers, fluid resistance portions, and common channel liquid chambers of the ink jet head can be appropriately changed. For example, in the above-described embodiment, the edge shooter type inkjet head is formed such that the nozzles eject the ink droplets in a direction intersecting the displacement direction of the diaphragm. A side shooter type inkjet head formed to discharge may be used.

[0083]

As described above, according to the ink jet recording apparatus of the present invention, since a means for applying a trapezoidal drive waveform to the ink jet head is provided, the ink jet recording apparatus is stable with a simple configuration even in high frequency driving. Ink droplet ejection can be performed, and high-quality recording can be performed at higher speed.

Further, according to the ink jet recording apparatus of the present invention, since means for applying a rectangular drive waveform to the ink jet head is provided, stable ink droplet discharge is possible with a simple configuration even in high frequency driving. And high-quality recording can be performed at higher speed.

Here, the drive waveform is a waveform in which the time from the initial voltage value to the desired voltage value does not exceed 5 μs, so that ink droplets can be ejected at a relatively efficient timing with substantially constant ejection characteristics. It can be ejected, and high-speed printing can be performed with high image quality. In addition, since the drive waveform does not exceed 6 μs from the desired voltage value to the initial voltage value, ink droplets can be ejected at relatively efficient timing with substantially constant ejection characteristics, High-speed recording with high image quality can be performed. In this case, the drive waveform does not exceed 2 μs until returning from the desired voltage value to the initial voltage value.
Ink droplets can be ejected with high droplet ejection characteristics at more efficient timing, and more stable print quality can be obtained.

The nozzle hole of the ink jet head has a discharge volume of 30 pl when a drive waveform is applied.
By setting the size to eject ink droplets not exceeding, smaller ink droplets can be ejected stably by high-frequency driving, and the image quality can be further improved.

Further, by generating the drive waveform by the D / A conversion means, it is possible to stably maintain the ejection characteristics of ink droplets more accurately and stably, and to use a relatively simple structure for each head. Variation in image quality can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic perspective explanatory view of a mechanism section of an ink jet recording apparatus according to the present invention.

FIG. 2 is an explanatory side view of the mechanism.

FIG. 3 is an explanatory cross-sectional view in the longitudinal direction of a diaphragm showing an example of a head of the recording apparatus.

FIG. 4 is an enlarged sectional explanatory view of a main part of the head in the transverse direction of the diaphragm.

FIG. 5 is a block diagram illustrating an example of a control unit of the recording apparatus.

FIG. 6 is a block diagram of a part related to a head drive control unit of the recording apparatus.

FIG. 7 is an explanatory diagram for explaining an operation of the head up to contact with the diaphragm;

FIG. 8 is an explanatory diagram for explaining an operation of the head from a diaphragm restoration;

FIG. 9 shows a first example relating to head drive control in the recording apparatus.
Explanatory drawing for explanation of embodiment

FIG. 10 is an explanatory diagram for explaining a pulse width of a driving waveform and an ink droplet ejection characteristic value.

FIG. 11 is an explanatory diagram for explaining pressure fluctuation of the head.

FIG. 12 is an explanatory diagram for explaining pressure fluctuation of the head.

FIG. 13 is an explanatory diagram for explaining a diaphragm displacement caused by application of the same drive waveform as a conventional drive waveform;

FIG. 14 is an explanatory diagram for explaining an example of a drive waveform according to the present invention and a displacement of a diaphragm caused by application of the same drive waveform.

FIG. 15 is an explanatory diagram for explaining another example of the driving waveform according to the present invention and the displacement of the diaphragm due to the application of the same driving waveform.

FIG. 16 is an explanatory diagram for explaining the same driving waveform and the displacement of the diaphragm and the nozzle hole by applying the same driving waveform;

FIG. 17 is an explanatory diagram for explaining parameters of a driving waveform according to the present invention;

FIG. 18 is an explanatory diagram illustrating a relationship between a rising time of the driving waveform and an ink droplet ejection characteristic value.

FIG. 19 is an explanatory diagram illustrating the relationship between the fall time of the drive waveform and the ink droplet ejection characteristic value.

FIG. 20 is a block circuit diagram illustrating another example of the head drive control unit.

FIG. 21 is a block circuit diagram illustrating still another example of the head drive control unit.

[Explanation of symbols]

13: carriage, 14: head, 24: transport roller,
33: paper ejection roller, 40: ink jet head, 41
... first substrate, 42 ... second substrate, 43 ... third substrate, 44 ...
Nozzle groove, 46 pressurizing chamber, 47 fluid resistance part, 48 common flow path liquid chamber, 50 diaphragm, 55 electrode, 87 waveform generating circuit, 88 head drive circuit, 113 D / A converter

Claims (7)

[Claims] A nozzle for discharging ink droplets, an ink flow path communicating with the nozzle, a vibration plate provided in a part of the ink flow path, and an electrode facing the vibration plate; An ink jet recording apparatus having an ink jet head for discharging a droplet of ink from the nozzle by deforming a vibration plate by electrostatic force, comprising: means for applying a trapezoidal drive waveform to the ink jet head. Inkjet recording device. A nozzle for discharging ink droplets, an ink flow path communicating with the nozzle, a vibration plate provided in a part of the ink flow path, and an electrode facing the vibration plate; An ink jet recording apparatus having an ink jet head for ejecting ink droplets from the nozzles by deforming a vibration plate by electrostatic force, comprising means for applying a rectangular drive waveform to the ink jet head. Inkjet recording device. 3. The ink jet recording apparatus according to claim 1, wherein the drive waveform is a waveform that does not exceed 5 μs from the initial voltage value to a desired voltage value. apparatus. 4. The ink-jet recording apparatus according to claim 1, wherein said drive waveform does not exceed 6 μs in time from a desired voltage value to return to an initial voltage value. Recording device. 5. The ink-jet recording apparatus according to claim 1, wherein a time required for the drive waveform to return from a desired voltage value to an initial voltage value does not exceed 2 μs. Recording device. 6. The ink jet recording apparatus according to claim 1, wherein the nozzle hole of the ink jet head is provided with an ink droplet whose ejection volume does not exceed 30 pl when the driving waveform is applied. An ink jet recording apparatus having a size for discharging. 7. An ink jet recording apparatus according to claim 1, wherein said drive waveform is generated by a D / A converter.