JPS58201666A - Deflection control type ink jet recorder - Google Patents

Abstract

PURPOSE:To provide the titled recorder capable of eliminating affects of satellite droplets on recording without reducing recording speed, wherein the amplitude of a vibration in such as direction as to lower ink pressure is set to be larger than that of a vibration in such a direction as to raise the ink pressure. CONSTITUTION:An exciting voltage generator 19 is constituted of a sine wave converting circuit 19a, a half-wave rectifying and adding circuit 19b and an amplifying circuit 19c. The circuit 19a eliminates harmonic components of an input signal, while the circuit 19b adds the input signal and a half-wave rectified signal thereof to each other. Accordingly, the change in the ink pressure can be enlarged in such as direction as to lower the pressure, and a large velocity change is obtained at a position in proximity to a part of the ink jetted when the ink pressure is minimum, resulting in that the ink is easily broken and the dropletization is stabilized.

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. This particle formation is performed by applying regular high frequency vibrations to the pressurized ink within the ink ejecting head. Generally, one or more electrostrictive vibrators are 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 particle moves to a predetermined position on the recording medium or to an ink receiver (gutter) for collection depending on the recording data.
A predetermined recording is performed by colliding with the object. 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 created by the charging electrode, which leaves a charge in the ink after one separation. .

By the way, in this type of inkjet recording, during particle formation, minute ink particles, that is, satellite particles, may be generated between certain ink particles and other ink particles. After separation, the satellite particles may fly alone, may recombine with the original ink particles that were separated by two, 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 third parties, 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 electric charge of a given ink droplet decreases and the amount of deflection of that ink droplet changes, causing a shift in the recording position, and the charged satellite particles are deflected, causing an undesirable result on the recording paper. It collides with the position and causes dirt.

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. Contamination occurs due to misalignment and the fact that ink particles that should have hit the gutter hit the recording paper.

As a technique to eliminate the inconvenience of inkjet recording caused by these satellite particles,
No. 79 (inkjet printer).

and Japanese Patent Publication No. 55-43713 (inkjet head) are 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. In addition, the latter is designed to drive the vibrator with a composite wave of a sine wave of a predetermined frequency and its second harmonic, so that the generated satellite particles do not recombine with the original ink particles and affect recording. This is what I did. However, in high shoulder wave driving as shown in these conventional examples, if the frequency of the fundamental wave is high (that is, the atomization speed is fast), the movement of the ink does not follow the movement of the vibrator at harmonics, and it is not sufficient. However, in order to obtain these effects, the frequency of the fundamental wave must be lowered and the recording speed must be slowed down.

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 object of the present invention is to eliminate the influence of satellite particles on recording, which would otherwise slow down the recording speed, and the second object is to provide an inkjet recording device that is simple in construction, compact, and inexpensive. That's true.

In order to achieve the above object, in the present invention, the amplitude of the vibration in the direction of decreasing the ink pressure is made larger than the amplitude of the vibration in the direction of increasing the ink pressure. This allows the ink to break at points where satellite particles may occur.
It has become clear that satellite particles are less likely to be formed when vibrations larger than the predetermined ink particle formation position are applied. According to this, the movement of the ink can sufficiently follow the vibration without lowering the vibration frequency, so 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 also 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 one 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 gutter 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 in the home position, the flight line of the ejected ink droplets leaves the edge of the recording paper 26 and the charged ink droplets are captured by the gutter 12. The ink in the blade gutter 11 is sucked by a 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 shuts off between the accumulator 4 and the filter 6 by deenergizing the solenoid.
Also, the ink tank 1 and the filter 6 are communicated with each other. gutter 1
Inside 2, there is a plate-shaped charge detection electrode 13 that is insulated and supported.

A shield wire 14 is connected to the second 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 I9 in this embodiment includes a sine wave conversion circuit 19a, a half-wave rectification and summation circuit 19b and an amplifier j! It is composed of I 19 c. The sine wave conversion circuit 19a is a circuit that removes harmonic components of an input signal. The sine wave conversion circuit m19a receives a pulse signal Vp input to the base end of the transistor Q1, and converts the fundamental wave of the signal from the pulse signal Vp into a parallel resonant circuit of an electric coil L and a capacitor C connected to the collector of the transistor Q1. The frequency component is extracted and output via the emitter follower circuit of transistor Q2. The half-wave rectification adder circuit 19b is
Roughly speaking, it is a circuit that adds an input signal and a signal obtained by half-wave rectification of that signal. Operational amplifier opo, diode D1゜D2. Resistor R1, R2, thermistor TH
A circuit consisting of the following is a half-wave rectifier circuit. The thermistor TH has a characteristic of causing a negative resistance value change with respect to temperature, and in this embodiment, the temperature of the ink is detected by the thermistor TH.

In the negative half cycle of the signal input to the OPO,
Diode D1 is forward biased and D2 is reverse biased, so the amplification degree of OPO is low.During the positive half cycle of the input signal, diode DI is reverse biased and D2 is forward biased, so the resistor R-1, R2
and a signal with a predetermined amplitude determined by the thermistor TH is oPO
appears at the output end of When the resistance values of the resistors @R1, R2 and thermistor TH are rl, r2, and rt, respectively, the amplification degree G for the positive polarity signal of the OPO is expressed by the following equation.

G=-(r2+rt)/rl"...' (1) rt changes according to the ink temperature, so when the ink temperature changes, the amplitude of the half-wave rectified signal of the OPO output changes. The rectified signal is through the variable resistor VR for amplitude adjustment,
It is applied to transistor Q3. Transistor Q4
A non-rectified signal (sine wave) is applied to the base end of the inverting amplifier OPI. The collectors of transistors Q3 and Q4 are both connected to one resistor R3, and the voltage drop across resistor R3, ie the amplitude of the output signal, is the same as that of transistors Q3. It is determined by the current added to the current of Q4.

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 jl 19 c is a class A amplifier using one transistor Q5, and amplifies the signal output from the half-wave rectifying and adding circuit 19b to a level necessary for driving the 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 in accordance with the pressure change caused by the electrostrictive vibrator at the time of ejecting.

During flight, the ink collects at a position of 1 mx in the part of the ink jetted when the ink pressure is at its maximum, and breaks and becomes particles at a position of 1 mn in the part of the ink jetted when the ink pressure is at its lowest.

During this particle formation, the ink velocity change is small near Imn, so the ink breaks are unstable, and especially when the ink has a relatively high viscosity, breaks occur at two positions in this vicinity. Satellite particles are likely to occur. However, as shown in this example, when the change in ink pressure is increased in the direction of decreasing pressure, a large speed change is obtained at a position near Imn, which makes the ink easy to break and stabilizes particle formation.
The operating range in which satellite particles are not generated 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 occur, 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.

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 to adjust the level of the signal applied to the electrostrictive vibrator. Therefore, even if the viscosity of the ink becomes relatively low due to a temperature change, the 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 circuit @23
is connected. The second circuit 23 is a high input impedance field effect transistor FET and an operational amplifier OP.
1. Bypass filter HPF, integral circuit I for DC smoothing
It consists of GR and comparator C○'M.

FIG. 5 shows the configuration of the phase setting circuit 24. A clock pulse ○p of 1,6 M)lz is applied to the phase setting circuit 24, and this is counted by the counter Cot. Each bit A-D of the count code output of counter CO1 (
The A bits (A=1st to D=4th) are serial in.
The D bit is applied to the parallel-out shift register SR as a shift activation pulse and as an input signal.

As a result, pulses with a pulse width of D whose phase is shifted by A period appear sequentially at output terminals 0 to 7 of the shift register SR, and one of the pulses is outputted from the data selector D'S as the excitation pulse VP of the electrostrictive resonator. It is 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 FDl 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 by 1/16 by the frequency divider FDI and shaped by the AND gate AN2 to the output pulse width of the output terminal O of the decoder DE is applied to the search charge voltage generator 21 as a phase search charge signal pulse pp. The charging 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 the pulse Pp
(high level "1").

In the second embodiment, the phases of both the phase search charge signal pulse pp and the impression charge timing pulse Cp are fixed, and the phase of the electrostrictive vibrator excitation pulse Vp is determined by the data selector DS and the count code A- of the counter CO2. It is shifted or changed depending on which of the shift register outputs 0 to 7 is output according to C. 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, this 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 amplifier $19c described above.

The sine wave conversion circuit 130b includes a coil L and two capacitors C.
This is an amplifier using a π-type low-pass filter composed of 1, , and C2. This low-pass filter is the frequency of the fundamental wave component of the input signal, which is +0
Passes signal components below 0 KHz and blocks frequency components above that. The signal input to the 22 is a pulse signal with a fundamental frequency (1/signal period) of 100 K II z and contains harmonics, but the signal that has passed through this filter has the harmonic components attenuated and becomes a sine wave. 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 this circuit 30b are determined by 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(+)” (r 3/ r 1) ・ ・ ・
・ ・ ・ ・(2) G()=(r2+rt)/r
l...(3) However, rl, r2. r3 and rt are resistance values of resistors R1, R2, R3 and thermistor TH, respectively.

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

2 Another embodiment is shown in Figures 7a and 7b. FIG. 7a is a block diagram of the ink vibration system, and FIG. 7b is a side view of the ink jet head 8 shown in FIG. 7a. 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. The second ink jet head 8 includes two electrostrictive vibrators 8a.
, 8b are provided, and driving forces are applied to the electrostrictive vibrators 8a and 8b from separate drive systems, respectively. That is, the sine wave signal obtained from the sine wave conversion circuit M@31a having the same configuration as 19a is divided into two systems, one of which is rectified by a 16-wave rectifier circuit mainly composed of the operational amplifier OPO, The voltage is applied to the electrostrictive resonator 8a through an amplifier, and the other side is applied to the electrostrictive resonator 8b through an inverting amplifier consisting of an operational amplifier OPl, and an amplifier connected to its output.
is applied to

The vibration applied to the ink, which is a composite of the vibrations generated by the electrostrictive vibrators 8a and 8b, is the same as in the previous embodiment, with the amplitude of the vibration in the direction of increasing the ink pressure being greater than the amplitude of the vibration in the direction of decreasing the ink pressure. The vibration becomes a sinusoidal wave with a large amplitude. The magnitude of the amplitude in the direction of lowering the ink pressure is the half-wave rectification circuit F.
It changes depending on the ink temperature detected by the thermistor I113 lb. Note that even when a multi-nozzle head is used as in this 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. Good too.

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 32b are attached to the inner wall of the ink tank 1 to detect the electrical conductivity of the ink inside the ink tank. The water contained in 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. Half-wave rectification adder circuit 3 shown in FIG. 8b
3 is a circuit modified from the half-wave rectifying and adding circuit 19a shown in FIG. 3a, and includes operational amplifiers OP4. A viscosity detection circuit composed of a transistor Q6 and the like is added. Although this circuit does not include a thermistor, it may be inserted at the same position as +9a. A predetermined voltage 2 obtained by dividing the shoulder voltage Vcc by resistors R9 and RIO is applied to the non-inverting input terminal of the operational amplifier ○P4, and V is applied to the inverting input terminal of OF2.
cc is the resistance R4 and resistor R8 between the electrodes 32a and 32b.
A divided voltage is applied. Therefore, 0L)
A voltage 3 is generated at the output of 4 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 the resistance value R between the collector and emitter of transistor Q6 is
ce changes according to voltage v3. That is, when the ink viscosity changes, the resistance Rce changes accordingly, and the output signal level of the half-wave rectifier circuit (OPO) changes.

For example, 1. When the water content of the ink decreases due to evaporation, the resistance R+ increases and becomes Vl<V2, so VI=
The output voltage v3 increases to V2, the voltage applied to the transistor Q6 increases, and the resistance Rce decreases. The amplification degree G of the half-wave rectifier circuit (OPO) for negative polarity signals is: G = R12/ (R1+・Rce/ R11+ R
ce)·”·(4) Therefore, as Rce becomes smaller, the amplitude of the output signal of the half-wave rectifier circuit increases, and the amplitude in the direction of lowering the pressure of the vibration applied to the ink increases.

In the above embodiments, the amplitude of the electrostrictive vibrator driving voltage in the direction of lowering the ink pressure was changed according to the temperature or the electrical conductivity of the ink, but the driving voltage amplitude in the direction of increasing the ink pressure was changed. may be changed simultaneously.

As described above, according to the present invention, the amplitude of the vibration applied to the ink in the direction of increasing the pressure of the ink is increased, so that the operating range in which satellite particles are not generated is widened.

[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 port 823 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, 8b: 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, 30
a, 31a: Sine wave conversion circuit 19b, 33: Half-wave rectification and addition circuit 19c, 30c: Amplification circuit 30b: Asymmetric gain amplification circuit 32a, 32b: Electrode patent applicant Ricoh Co., Ltd.

Claims (6)

[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 charges ink particles by applying a charging voltage to t and deflects the charged ink particles using a deflection electric field, t is an amplitude in the direction of increasing the pressure of the pressurized ink, while an amplitude in the direction of decreasing the pressure A deflection control inkjet recording device comprising: a vibration excitation unit that applies vibration with large amplitude to ink. (2) The deflection control inkjet recording apparatus according to claim (1), wherein the vibrating means has a single vibrating body. (3) The deflection control inkjet according to claim (2), wherein the excitation means includes means for rectifying the sine wave signal and means for adding the sine wave signal and a signal obtained by rectifying the sine wave signal. Recording device. (4) The excitation means includes an amplification means that has different amplification degrees for the positive potential and the negative potential of the hexagonal signal. A deflection control inkjet recording apparatus according to claim (2). (5) The vibrating means includes a plurality of vibrating bodies. A deflection control inkjet recording apparatus according to claim (1). (6) The vibrating 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. A deflection control inkjet recording apparatus according to claim (5).