JPS58201667A - Deflection control type ink jet recorder - Google Patents

Abstract

PURPOSE:To provide the titled recorder having a wide operating range wherein satellite droplets are not generated, wherein of a vibration applied to ink, the amplitude in such a direction as to raise the ink pressure is enlarged, and the amplitude is regulated in accordance with the viscosity of the ink. CONSTITUTION:A half-wave rectifying and adding circuit 19b is constituted of an operational amplifying circuit (OPO), diodes D1, D2, resistors R1, R2, a thermistor TH and the like. The thermistor TH has a negative temperature characteristic of resistance, and a signal having a predetermined amplitude determined by the resistors R1, R2 and the thermistor TH appears at an output terminal of the circuit OPO. The resistance of the thermistor TH is relatively high, so that the level of a half-wave rectified signal of an output from the circuit OPO becomes high, and the amplitude in such as direction as to lower the pressure of the vibration applied to the ink is enlarged.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention jets vibrated ink from a nozzle, selectively charges the jetted ink at a position where it separates into ink particles using a charging electrode, and deflects the charged ink particles using a deflection electrode. The present invention relates to an inkjet recording apparatus that deflects and collides with a predetermined position on recording paper, and particularly relates to control of pressurized ink to become particles.

In this type of inkjet recording, ink that is continuously ejected from a nozzle is separated into ink particles of a predetermined size while in flight, so-called particleization. The second particle formation is performed by applying high-frequency vibration at a constant period to the pressurized ink within the ink jet head. One or more electrostrictive vibrators are generally used as means for applying vibration. When each ink droplet is selectively charged with a predetermined charge according to the recorded data and the ink droplets are passed through a predetermined deflection electric field, the ink droplets are charged depending on the presence or absence of charge or the level of charge. The flight trajectory is deflected, and each ink droplet collides with a predetermined position on the recording medium or with an ink receiver (cater) for collection according to recording data, thereby performing a prescribed recording. The principle of charging in inkjet recording is based on the fact that the ink is broken at predetermined intervals while the ink tip is charged by electrostatic induction in the electric field generated by the charging electrode, leaving a charge in the separated ink. .

By the way, in the second type of inkjet recording, minute ink particles, that is, satellite particles, may be generated between a predetermined ink particle and another ink particle during particle formation. After separation, these satellite particles may fly alone, may recombine with the original ink particles that have been separated, or may bond with ink particles different from (before or after) the original separated particles. In the case of a second party, there is no problem as it will not affect the records. However, the first
In the case of the first person and the third person, a part of the charge of a given ink droplet is transferred to the satellite particles, which affects the recording. For example, in the case of the first person, the charge of a given ink droplet decreases and The amount of deflection of the ink particles changes, causing a deviation in the recording position, and moreover, the charged satellite particles are deflected and collide with undesirable positions on the recording paper, causing stains.

In addition, in the case of a third party, charge movement occurs due to satellite particles, the charge of the ink particles to be charged decreases, and the amount of deflection becomes smaller, and the uncharged ink particles are charged by that amount and deflected, and recording is performed. Misalignment and staining occur due to ink particles that should collide with the cutter colliding with the recording paper.

As a technique to eliminate the inconvenience of inkjet recording caused by these satellite particles,
No. 79 (inkjet printer) and Special Publication No. 1979
No. 43713 (inkjet head) is known. The former uses a plurality of oscillators so that the vibrations synthesized by the fundamental wave applied thereto and its predetermined harmonics form a triangular wave, so as to prevent the generation of satellite particles. The latter also uses a sine wave of a predetermined frequency and its second waveform to prevent the generated satellite particles from recombining with the original ink particles and affecting recording.
The vibrator is driven by a composite wave of harmonics. However, in harmonic drive as shown in these conventional examples, if the frequency of the fundamental wave is high (that is, the rate of atomization is fast), the movement of the ink does not follow the movement of the vibrator at the harmonics, resulting in insufficient The disadvantage is that no effects can be obtained, and in order to obtain these effects, the frequency of the fundamental wave must be lowered and the recording speed must be slowed down. Moreover, these effects improve recording quality only at low temperatures, where the viscosity of the ink is relatively high and satellite particles are likely to occur; on the other hand, at temperatures above room temperature, particle formation does not occur. This results in the phenomenon of appeasement.

It is possible to prevent satellite particles from being generated without special harmonic drive, but in order to do so, it is necessary to adjust the temperature of the ink, the moisture content of the ink, the amplitude of vibration, the ink pressure, etc. must be maintained within a certain range. However, its range is very narrow and difficult to control.

The first objective of the present invention is to eliminate the influence of satellite particles on recording without slowing down the recording speed, and the second objective is to provide an inkjet recording apparatus that can perform good recording over a wide temperature range. It is to provide.

In order to achieve the above object, the present invention.

Increasing the amplitude of the vibration in the direction of lowering the ink pressure compared to the amplitude of the vibration in the direction of increasing the ink pressure,
The amplitude of at least one of them is changed depending on at least one of the following conditions: ambient temperature, ink temperature, and ink conductivity. It has been revealed that this applies a larger vibration to the ink rupture point where satellite particles may occur than at the predetermined ink particle formation position, widening the operating range in which recording quality does not deteriorate due to satellite particles. Ta. Further, according to this, even if the viscosity of the ink changes due to temperature changes, evaporation of water, etc., the amplitude of the peaks or troughs of vibration is corrected accordingly.

Particle formation does not become unstable at room temperature or high temperature,
Since the ink movement sufficiently follows the vibrations without lowering the vibration frequency, there is no need to slow down the recording speed. Further, since harmonic drive is not required, there is no need for a plurality of vibrating bodies, and the inkjet head can be made smaller and the number of components can be reduced. However, it is possible to use a plurality of vibrating bodies.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 shows the main mechanical elements of one embodiment of the invention, and FIG. 2 shows the main electrical elements. First, refer to FIG. In FIG. 1, ink in an ink tank 1 is sucked by a pump 3 through a filter 2 and is pumped to an accumulator 4. In the accumulator 4, pressure fluctuations due to suction and discharge of the pump 3 are absorbed. For constant pressure ink, use a solenoid valve 5. The ink is supplied to the ink jet head 8 through the filter 6 and heater 7. In the head 8, constant frequency pressure fluctuations are applied to the ink by constant frequency excitation of an electrostrictive vibrator. As a result, the ink ejected from the nozzle of the ink ejecting head 8 separates into ink particles at a predetermined distance from the nozzle. A charging electrode 9 is disposed at this separation position, and when a charging voltage is applied to the electrode 9 at the time of separation, the ink particles are charged to a polarity opposite to the polarity of the charging voltage. The charged ink particles are deflected by the deflection electric field between the deflection electrodes 10a and 10b, and collide with the recording paper 26 when the head is in the recording position, and toward the gutter 12 when the head is in the home position. Uncharged ink particles are directed toward the gutter 11 both when the head is in the recording position and when the head is in the home position. In other words, the filters 6 to 11 surrounded by two-dot chain lines are mounted on the scanning carriage.

Gutter 12 is positioned to capture charged ink particles when the carriage is in the home position. When the carriage is at the home position, the flight line of one ejected ink droplet leaves the edge of the recording paper 26, and the charged ink particles are captured by the gutter 12. The ink in the gutter 11 is sucked by the pump 27 and returned to the ink tank 1, and the ink in the gutter 12 returns to the ink tank 1 by its own weight. When ink ejection is stopped, first the pump 3 and the heater 7 are deenergized, then the solenoid of the solenoid valve 5 is deenergized, and then the pump 27 is deenergized. The solenoid valve 5 disconnects the accumulator 4 and the filter 6 and connects the ink tank 1 and the filter 6 by deenergizing the solenoid. Inside the gutter 12 is a plate-shaped charge detection electrode 13 that is insulated and supported. A shield wire 14 is connected to this electrode 13.

FIG. 3a shows a specific configuration of the excitation voltage generator 19 for driving the electrostrictive vibrator of the ink jet head 8. As shown in FIG. Referring to FIG. 3a, the excitation voltage generator 19 in this embodiment is comprised of a sine wave conversion circuit 19a, a half-wave rectification and addition circuit 19b, and an amplification circuit H119c. Sine wave conversion times! l
19a is a circuit for removing harmonic components of the input signal. The sine wave conversion circuit Is19a is a transistor Ql
receives a pulse signal Vp input to the base end of the transistor Q1, extracts the frequency component of the fundamental wave of Vp from the signal in a parallel resonant circuit consisting of an electric coil r connected to the collector of the transistor Q1 and a capacitor C, and extracts the frequency component of the fundamental wave of the transistor Q2. Output via emitter follower circuit. Half-wave rectification addition port 51
Roughly speaking, 9b is a circuit that adds an input signal and a signal obtained by half-wave rectification of that signal. Operational amplifier ○P
O, diode ■) 1°D2. A circuit consisting of resistors R1, R2, thermistor T+ (etc.) is a half-wave rectifier circuit. In the example, the temperature of the ink is detected by the thermistor TH.During the negative half cycle of the signal input to the OPO, the diode D1 becomes forward biased and D2 becomes reverse biased, so that the OPO When the amplification degree is low and the input signal has a positive half cycle, diode D1 is reverse biased and D2 is forward biased, so a signal with a predetermined amplitude determined by resistors R1 and R2 and thermistor TH is output from the OPO. If the resistance values of resistors R1, R2 and thermistor TH are rl, r2, and rt, respectively, then the amplification G for the positive polarity signal of OPO is
is expressed by the following equation.

G=-(r2+rt)/r]...(
I) Since rt changes depending on the ink temperature, when the ink temperature changes, the amplitude of the half-wave rectified signal of the OPO output changes. The rectified signal is applied to transistor Q3 via variable resistor VR for amplitude adjustment. ]
- A signal (sine wave) that is not rectified by inverting the inverting amplifier OPI is applied to the base end of the run transistor Q4.

The collectors of transistors Q3 and Q4 are both connected to one resistor R3, and when the voltage of resistor R3 is F, that is, the amplitude of the output signal is 1. It is determined by the current sum of the current of Q/I. In other words, the output signal has a signal waveform obtained by adding a sine wave signal and a signal obtained by half-wave rectification of the sine wave signal. FIG. 3b shows signal waveforms at various parts in FIG. 3a. The signal output from the half-wave rectifying and adding circuit 19b has a waveform in which the positive half-wave and the negative half-wave have different amplitudes, as shown in FIG. 3b. The amplifier circuit 19c is a class A amplifier using one transistor Q5, and amplifies the signal outputted from the half-wave rectifying and adding circuit +9b to a level necessary for driving an electrostrictive vibrator that vibrates the ink.

FIG. 3c shows the relationship between the change in ink pressure corresponding to the voltage applied to the electrostrictive vibrator and the ink ejected from the nozzle. To explain with reference to Fig. 3c, the ejected ink undergoes minute velocity modulation according to the pressure change caused by the electrostrictive vibrator when it is ejected, and the ink is ejected when the ink pressure is at its maximum during flight. The part of the ink collected at the position of the molecule ix is broken and becomes particles at the position of 1 mn of the ink ejected when the ink pressure is the lowest. During this particle formation, the ink velocity change is small near Imn, so the ink fracture is unstable, especially when the ink viscosity is relatively high.
Fractures occur at two positions near 2, and satellite particles are likely to form. However, as shown in this example, when the change in ink pressure is increased in the direction of decreasing pressure, a large velocity change is obtained at a position of around 1 mm, which makes the ink easy to break, resulting in stable particle formation, and no satellite particles are generated. The range of motion becomes wider.

This will be explained with reference also to FIG. 3a. When the ink temperature is relatively low and the ink viscosity is high, satellite particles are likely to be generated, but since the resistance value rt of the thermistor TH is relatively large, the level of the half-wave rectified signal output from the OPO becomes high. The amplitude of the vibration applied to the ink increases in the direction of lowering the pressure. Therefore, as described above, the generation of satellite particles is automatically controlled so as to be difficult to generate. Even when the ink temperature is normal or relatively high, the thermistor TH adds a half-wave rectified signal with an amplitude corresponding to each temperature to the sine wave signal, adjusting the level of the signal applied to the electrostrictive vibrator. Therefore, even if the viscosity of the ink becomes relatively low due to temperature changes, particle formation will not become unstable.

FIG. 4 shows the configuration of the charge detection circuit 23 shown in FIG. 2. Referring to FIG. 4, there is a gap between the core wire of the shield wire 14 and the ground due to ink stains on the inner wall of the gutter 12.
3 - Resistance Rc smaller than Rg to prevent instability in charge detection due to fluctuations in insulation resistance Rg between ground
A resistor R for voltage conversion with = 100KΩ is connected. The core wire of the shield wire 14 has a charge detection gap @23
is connected. This circuit 23 consists of a high input impedance field effect transistor FET, an operational amplifier OP
I, bypass filter HPF, integral circuit I for DC smoothing
It consists of GR and comparator COM.

FIG. 5 shows the configuration of the phase setting circuit 24. A clock pulse Op of 1.6 MIIz is applied to the phase setting circuit 24, and this is counted by the counter C○1. Each bit A-D (A
The A bits (=1st to D=4th) are applied as shift activation pulses to the serial-in/parallel-out shift register SR, and the D bits are applied as input signals, thereby causing the output terminal of the shift register SR to 0 to 7, pulses having a pulse width of D whose phase is shifted by A cycle appear in sequence, one of which is outputted from the data selector DS as an excitation pulse Vp of the electrostrictive vibrator and applied to the excitation voltage generator 19.

The output bits B-D of the counter COI are applied to the decoder DE, the first output 0 and the fifth output 4 of the decoder DE.
output pulses are applied to frequency divider FDI and T flip-prop FF, respectively.

The Q output of the T flip-flop FF is applied to the applied charging voltage generator 20 as a charging timing signal Cp. The pulse whose frequency is divided to 1/16 by the frequency divider FDI and shaped by the AND gate AN2 to the output pulse width of the output terminal 0 of the decoder DE is applied to the search charge voltage generator 21 as a phase search charge signal pulse Pp. The charge signal Pp has 16 consecutive pulses, followed by a pause period of 16 pulses, and has a length of 320μ.
It is intermittent at a period of sec. On the other hand, the printing charge timing signal Cp is a continuous pulse, and is a pulse ppp.
(high level "1").

In this embodiment, the phases of both the phase search charging signal pulse pp and the printing charging timing pulse Cp are fixed, and the phase of the electrostrictive vibrator excitation pulse Vp is set by the data selector DS and the count code A-C of the counter CO2. It is shifted or changed depending on which of the shift register outputs 0 to 7 is to be output. In other words, the charging voltage pulse phase is fixed and the separation phase of the ink particles is shifted.

FIG. 6 shows another embodiment of the excitation voltage generator 30. To explain with reference to FIG. 6, the second excitation voltage generator 3
0 is a sine wave conversion circuit 30a, an asymmetric gain amplifier 30
b and an amplifier circuit 30c. Amplifier circuit 3
0c has the same configuration as the aforementioned amplifier circuit 19c.

The sine wave conversion circuit 30b includes a coil L and two capacitors C.
This is an amplifier using a π-type low-pass filter composed of I and C2. This low-pass filter passes signal components having a frequency of the fundamental wave component of the input signal, that is, 100 KHz or less, and blocks frequency components higher than that. The signal input to this filter is a pulse signal with a fundamental frequency (1/signal period) of 100 K II z and contains harmonics, but the signal that passes through this filter has the harmonic components attenuated and becomes a sine signal. Become a wave. In other words, this circuit 30a operates in the same manner as the sine wave conversion circuit 19a described above.

The asymmetric gain amplifier 30b has substantially the same function as the half-wave rectifying and adding circuit 19b, and the amplification degree for the positive polarity component of the input signal is different from the amplification degree for the negative polarity component of the signal. In other words, when inputting a sine wave signal in which the amplitude of the positive polarity component is equal to the amplitude of the negative polarity component, a pseudo sine wave signal in which the amplitude of the positive polarity component and the amplitude of the negative polarity component are different is output at the output terminal. can get. The amplification degree G(+) for the positive polarity component and the amplification degree G(-) for the negative polarity component of the second circuit 30b are the diode DI.

Ignoring the effects of the forward impedance of D2 and the coupling capacitor Cc, each is expressed by the following equations.

G(+)=-(r3/r1)・・・・・・(2)G(
-)=-(r2+rt)/r1...(3)
However, rl, r2. r3 and rt are each resistance R1
, R2, R3 and the resistance value of the thermistor TH.

The thermistor TH detects the temperature of the ink as in the previous embodiment. Therefore, when the ink temperature changes, the resistance value rt changes accordingly, and the amplification degree G(-) changes,
Since the amplitude of the positive polarity component of the output signal is changed, the vibration amplitude of the electrostrictive vibrator in one direction is automatically adjusted so that particle formation is performed appropriately.

Another embodiment is shown in Figures 7a and 7b. Figure 7a is a block diagram of the ink vibration system, and Figure 7b is the block diagram of the ink vibration system.
FIG. 3 is a side view of the ink jet head 8 shown in the figure. In this embodiment, the ink jet head 8 is a multi-nozzle head that includes a large number of nozzles 8C for one liquid chamber. This ink jet head 8 includes two electrostrictive vibrators 8a and 8.
The electrostrictive vibrators 8a and 8b are each provided with a driving force from a separate driving system. That is, the above 19
The sine wave signal obtained from the sine wave conversion circuit 31a having the same configuration as a is divided into two systems, one of which is connected to the operational amplifier O.
Rectified by a half-wave rectifier circuit centered around PO,
One is applied to the electrostrictive vibrator 8a through an amplifier, and the other is applied to the electrostrictive vibrator 8b through an inverting amplifier consisting of an operational amplifier OP1 and an amplifier connected to its output.

The vibrations applied to the ink, which are a combination of the vibrations generated by the electrostrictive vibrators 8a and 8b, are vibrations that lower the ink pressure compared to the amplitude of the vibrations that increase the ink pressure, as in the previous embodiment. becomes a sinusoidal vibration with a large amplitude.

The magnitude of the amplitude in the direction of lowering the ink pressure changes depending on the ink temperature detected by the thermistor of the half-wave rectifier circuit 31b. Note that even when a multi-nozzle head is used as in the second embodiment, AC voltages with different amplitudes for the positive half-wave and the negative half-wave are applied to each electrostrictive vibrator as in the previous embodiment. It's okay.

Another embodiment is shown in Figures 8a and 8b. This will be explained with reference to FIGS. 8a and 8b. In this embodiment, two electrodes 32a and 3 are provided on the inner wall of the ink tank 1.
2b is attached to detect the conductivity of the ink in the ink tank 1. The water contained in the ink decreases over time due to evaporation.

As the water content of the ink decreases, the viscosity of the ink increases and the conductivity of the ink decreases. Therefore, by detecting the conductivity of the ink, a signal corresponding to the viscosity of the ink can be obtained. The half-wave rectifying and adding circuit 33 shown in FIG. 8b is a modified half-wave rectifying and adding circuit 19a shown in FIG. There is. Although this circuit does not include a thermistor, it may be inserted at the same position as 19a. The non-inverting input terminal of the operational amplifier OP4 is connected to the power supply voltage Vcc.
A predetermined voltage (■2) divided by resistors R9 and R10 is applied, and Vcc is applied to the inverting input terminal of ○P4, and the voltage is applied to the electrode 32.
A voltage divided by a resistor Ri and a resistor sR8 between a and 32b is applied. Therefore, a voltage v3 is generated at the output of ○P4 that makes the voltage v1 at the inverting input terminal equal to v2. When the conductivity of the ink changes, the resistance Ri changes and the output voltage (3) changes. Voltage ■3 is applied to transistor Q6 via a resistor, and transistor Q6
The collector-emitter resistance value Rce changes depending on the voltage V3. In other words, when the ink viscosity changes, the resistance Rce changes accordingly, and the half-wave rectifier circuit (OPO)
output signal level changes. For example, when the water content of the ink decreases due to evaporation.

Since the resistance Ri increases and becomes Vl<V2, this is changed to V1.
= V2, the output voltage v3 increases, the voltage applied to the transistor Q6 increases, and the resistance Rce decreases. The amplification degree G for the negative polarity signal of the half-wave rectifier HI (OPO) is: G = R12/ (R11・Rce/ R11+Rc
e)" (4), when Rce becomes smaller, the amplitude of the output signal of the half-wave rectifier circuit becomes larger, and the amplitude in the direction of lowering the pressure of the vibration applied to the ink becomes larger.

In the above embodiments, the amplitude of the electrostrictive vibrator driving voltage in the direction of lowering the ink pressure was changed depending on the temperature or the conductivity of the ink, and the driving voltage amplitude in the direction of increasing the ink pressure was also changed. They may be changed at the same time.

As described above, according to the present invention, the amplitude of the vibration applied to the ink is increased in the direction of increasing the pressure of the ink, and the amplitude is adjusted according to the viscosity of the ink, so that the operating range that does not generate satellite particles is widened. It becomes wider and the particle formation becomes stable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main parts of the mechanism of an embodiment of the present invention, FIG. 2 is a block diagram showing main electrical elements, and FIG. 3a is a specific configuration of the excitation voltage generator 19 shown in FIG. 2. FIG. 3b is a time chart showing the signal waveform of the circuit in FIG. 3a, FIG. 3c is a side view showing the relationship between the ink pressure and the ink ejected from the nozzle, and FIG. 4 is the diagram shown in FIG. FIG. 5 is a block diagram of the charge detection circuit 23 shown in FIG. 2, and FIG. 5 is a block diagram of the phase setting port @24 shown in FIG. Fig. 6 is a circuit diagram of an excitation voltage generator showing another embodiment of the present invention, Fig. 7a is a block diagram of the main part showing another embodiment, and Fig. 7b is the ink jet head of Fig. 7a. FIG. 3 is a side view seen from the recording paper side. FIG. 8a is a block diagram of the main mechanical parts showing another embodiment, and FIG. 8b is a circuit diagram of the excitation voltage generator of the embodiment. 2.6: Filter 5: Solenoid valve 8: Ink jet head 8a, Bb: Electrostrictive vibrator 9: Charge electrode 10a, 10b: Deflection electrode 11.
12 Nigator 13: Plate-shaped charge detection electrode 14: Shield wire 19, 30: Excitation voltage generator 19a, 30a
, 31a: Sine wave conversion circuit 19b, 33: Half-wave rectification and addition circuit 19c, 30c: Amplification circuit 30b: Asymmetric gain amplification circuit 32a, 32b: ft Pole Patent applicant Ricoh Co., Ltd.

Claims (8)

[Claims] (1) Pressurized ink is supplied to the ink ejection head, and in the ink ejection head, the pressurized ink is ejected from the nozzle of the head with regular vibration, and at the point when the ink ejected from the nozzle separates into particles, the charged electrode In a deflection control inkjet recording device that applies a charging voltage to charge ink particles and deflects the charged ink particles with a deflection electric field; a detection means that detects at least one of ambient temperature, ink temperature, and ink conductivity; pressurization; an excitation means for applying to the ink a vibration having a larger amplitude in a direction to lower the pressure than an amplitude in a direction to increase the pressure of the ink; and a vibration means to increase the ink pressure according to a signal from the detection means; A deflection control inkjet recording apparatus comprising: a control means for changing at least one of the amplitude in the direction of increasing the ink pressure and the amplitude in the direction of decreasing the ink pressure. (2) The deflection control inkjet recording apparatus according to claim (1), wherein the vibrating means has a single vibrating body. (3) The excitation means is means for rectifying the sine wave signal. The deflection control inkjet recording apparatus according to claim 2, further comprising means for adding a sine wave signal and a signal obtained by rectifying the sine wave signal. (4) The deflection control inkjet recording apparatus according to claim (3), wherein the means for adding the signals includes a temperature sensing element. (5) The deflection control inkjet recording apparatus according to claim (2), wherein the vibration excitation means includes amplification means having different amplification degrees for positive and negative potentials of the input signal. (6) The deflection control inkjet recording apparatus according to claim (5), wherein the amplifying means includes a temperature-sensitive element. (7) The deflection control inkjet recording apparatus according to claim (1), wherein the vibration excitation means includes a plurality of vibrating bodies. (8) The excitation means includes means for applying a sine wave signal to one of the vibrating bodies and applying a rectified sine wave signal to the other vibrating body, Deflection control inkjet recording device as described in 2.