JPS5968259A - Deflection controlled ink jet recording apparatus - Google Patents

Abstract

PURPOSE:To make it possible to stably perform charge detection, by a method wherein a recessed space is formed to the upper end of an insulating holder for supporting a conductive gutter for capturing non-printing ink particles and the gutter potential is amplified by a charge detect circuit to detect charge. CONSTITUTION:Ink droplets injected from a head 5a are passed through a charging electrode 6 and deflection electrodes 71, 72 and non-charged particles are collided with a gutter 9 to be recovered therein. This gutter 9 comprises a conductor and secured to an insulating gutter holder 13 while connected to a charge detect circuit 20 through a shield wire 15. A recessed space 13a is formed to the upper end of this insulating holder 13 so as to surround the side wall of the gutter 9 and a projection 13b is further formed thereto in order to prolong the distance with an earth shield SH. By this mechanism, the ink invaded between the outer surface of the gutter 9 and the holder 13 is raised by a capillary phenomenon but not raised from the lower end of the recessed space 13a and the leak during charge detection is reduced and detection is stably performed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves ejecting ink subjected to ultrasonic vibration from a nozzle, selectively charging the ejected ink at a position where it separates into ink particles with a charging electrode, and deflecting the charged ink particles with an electrode. This invention relates to inkjet recording in which the ink particles are deflected and collided with the recording paper, and in particular, it relates to the detection of the charge of ink particles, such as searching for an appropriate charging voltage application phase with respect to the separation phase of ink particles, and detecting charged ink particles in the adjustment setting of the deflection amount. .

To give an overview of this type of inkjet recording, ink is sucked into a pump from an ink tank through a filter.
It is discharged into an accumulator which smoothes pressure fluctuations. Pressurized ink is applied to the inkjet head from an accumulator, and vibration at a constant frequency is applied to the pressurized ink by excitation of an electrostrictive vibrator within the head. The pressurized ink, which is vibrated in this way, is ejected from the nozzles of the head. This ejected ink is regularly separated into ink particles at a position a certain distance from the nozzle. This separation period is equal to the period of the vibration. A charging electrode is arranged at a position where the ink particles are separated, and a charging voltage is applied to the charging electrode. The level of the charging voltage changes in stages, and when not recording (image signal: low level L), it is at 0 level (
For example, earth potential). It is necessary to apply the charging voltage in a pulsed manner, and moreover, it is necessary to apply the charging voltage at each stage in accordance with a certain phase in which ink particles are formed. The charging voltage pulse phase is set. This is because the output clock of the clock pulse generator is applied to the excitation voltage generator, which generates a sine wave synchronized with the clock and applies it to the electrostrictive vibrator of the head. The output clock is given to a phase setting circuit to create a charging clock with a constant pulse width that has a certain set phase difference from the phase of the clock. A search charge pulse of a constant level is generated by a search signal generator and applied to the charge electrode via a gate and an amplifier, and the charge of the ink particles is detected by the charge detection electrode to generate a predetermined number of ink particles. During this time, the charge detection circuit monitors whether a charge detection signal is generated or not, and when it is issued, the phase search is terminated. If it is not issued, the phase setting circuit is commanded to shift the phase by one step, and the charge clock pulse is output. This is done in each circuit operation of shifting the phase by a predetermined phase from the previous one.

After setting the appropriate charging phase of the charging clock with respect to the output clock of the clock pulse generator in this way, the charging signal whose level changes stepwise, which is created by the charging signal generator with reference to the charging clock, controls the gate and amplifier. A charge is applied to the charged electrode through the charge electrode, and a printing/recording operation is performed. In other words, when a charging voltage whose level changes stepwise in synchronization with the charging clock is applied to the charging electrode, the ink particles become charged corresponding to the charging voltage level, and are deflected by the electric field of the deflection electrode according to the amount of charge. Ru.

When the image signal is at a low level L, the charging voltage is set to O level, and since the ink particles are not charged at this time, they are captured by the gutter.

Conventionally, charge detection electrodes include cylindrical or U-shaped electrostatic induction type electrodes, and electrodes in which two flat plate electrodes are arranged adjacently or facing each other, as well as a gutter for capturing ink particles (for example, in Japanese Patent Application Laid-Open No. 49-107142 and JP-A-55-84680).

In the conventional example where this gutter is used as a charge detection electrode, the gutter is insulated from the ink that has flowed down and has proceeded to the ink recovery system, and a capacitor for charge integration and a switch for discharging the capacitor are connected to the gutter, and the capacitor voltage is The ink droplet is determined to be charged when the ink droplet increases to a predetermined level or higher within a predetermined time.

In such charge detection using an insulating gutter.

Ink splashes caused by the impact of ink particles on the gutter stain the inner and outer surfaces of the insulator holder that supports the gutter,
There is a problem that dirt on the outer surface causes leakage between the gutter and the collected ink, making the capacitor voltage unstable and charge detection unstable. In particular, if the outer surface is heavily contaminated, it is determined that the battery is not charged even if it is properly charged.

Further, the conductive gutter 9 is usually inserted into the insulator holder 13 and fixed, as shown in FIG. 1a (longitudinal sectional view) and FIG. However, the ink that collided with the gutter 9 was damaged by the insulator holder 13.
and the gutter 9, rises along the outer surface of the gutter through capillary development, reaches the upper surface of the holder 13, is absorbed by the fine dust, and is bonded to the hygroscopic shield SH (earth shield). Leaks are likely to occur between the two.

To solve this problem, it is necessary to keep a part of the rattle clean at all times, which is difficult to manage.

The first purpose of the present invention is to reduce the instability of charge detection due to ink stains, and the second purpose is to perform charge detection that can shorten the flight distance of ink particles and has high detection reliability. It is.

In order to achieve the above object, in the present invention, a concave space surrounding the conductive gutter is formed at the upper end of the insulator holder that supports the conductive gutter that captures non-imprinted ink particles,
Further, the gutter includes a resistor for grounding the gutter, and the charge on the ink particles is detected by a charge detection circuit that amplifies the potential of the gutter.

By doing this, firstly, the charge is detected through direct contact (collision) with the ink particles, resulting in high stability, and secondly, the presence of the concave space at the upper end of the holder reduces leakage due to ink stains. Thirdly, due to the resistor of the charge detection circuit, variations in gutter potential due to the size of ink stains are small, so the charge detection potential is stabilized. There is no increase in flight distance due to the placement of electrostatic induction type detection electrodes.

In a preferred embodiment of the present invention, in charge detection during phase search, charging voltage pulses are intermittent at a period of two or more periods of the ink droplet separation excitation frequency, so that continuously flying ink particles are separated from a plurality of successive droplets. A charge is activated, and subsequent successive drops are uncharged to form a periodic charge pattern. By doing this, a sinusoidal voltage with a period corresponding to the intermittent period appears at the input terminal of the amplifier circuit due to the stray capacitance of the lead connecting the gutter and the amplifier circuit and the RC smoothing by the resistor. This sine wave voltage is
This can be obtained by blocking the noise with a filter circuit whose passband is that period.

The sinusoidal voltage passed through the filter is smoothed by an integrating circuit and converted into a stable (less level fluctuation) DC voltage, which can be compared with a reference voltage to determine charge. That is, a stable AC waveform is obtained and the determination process is stabilized.

FIG. 2 shows one apparatus configuration for implementing the present invention. Second
In the figure, the ink in the ink car 1-ridge 1 is pumped 2.
The pressure is fed to the accumulator 3, and the pressure vibrations are absorbed by the accumulator 3. Ink at a constant pressure is supplied to the ink jet head 5 through the filter 4. In the head 5, constant frequency pressure vibration is applied to the ink by constant frequency excitation of the cylindrical electrostrictive vibrator 5a. As a result, the ink ejected from the head 5a separates into ink particles at a predetermined distance from the nozzle. A charging electrode 6 is placed at this separated position.
is arranged, and when a charging voltage is applied to the electrode 6 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 71s72 and collide with the recording paper 8. The uncharged ink particles collide with the gutter 9, travel from the gutter 9 to the filter 10, are sucked by the pump 11, reach the ink recovery tank 12 and the ink tank 13, are sucked by the pump 2, and are sent to the accumulator 3.

The gutter 9 is a conductor and is fixed to an insulating gutter holder 13 , and an insulating tube 14 connects the gutter holder 13 to the filter 10 . One end of the core wire of the shield wire 15 is connected to the conductor gutter 9, the other end is connected to the charge detection circuit 20, and the shield jacket is grounded.

An enlarged vertical cross-sectional view of the gutter 9 and the gutter holder 13 is shown in FIG. 3a, and a cross-sectional view taken along the line nB-nB is shown in FIG. 3b.

In this embodiment, a recessed space 13a is formed at the upper end of the insulating holder 13 so as to surround the side wall of the gutter 9, and the distance between the lower end of the inner surface of the holder in contact with the recessed space 13a and the earth shield SH is further increased. , holder 1
A protrusion 13b protruding from the upper surface of 3 is formed. ,
This protrusion 13b causes the concave space 13a to extend further upward. The ink that has entered the minute gap between the outer surface of the gutter 9 and the holder 13 rises through the gap due to capillary development, but since the distance between the outer surface of the gutter 9 and the inner surface of the holder 13 is long in the space 13a, the lower end of the space 13a It does not rise above. Therefore, the insulation on the upper surface of the holder 13 is high, and leakage is less likely to occur.

FIG. 4 shows the configuration of the charge detection circuit 20. The charge detection circuit 20 has a resistance value R smaller than Rg in order to prevent instability of the grounding resistance on the gutter 9 side due to fluctuations in the ink resistance Rg between the gutter 9 and the ground of the filter 10 (FIG. 1).
resistor R for voltage conversion, field effect type 1 to transistor FET for impedance conversion, and operational amplifier 21.
Bypass filter 22. It is composed of an integrating circuit 24 and a comparator 24 for DC smoothing.

The configuration of the phase control circuit 30 is shown in FIG. 5, and the input/output timing of each part thereof is shown in FIG. Referring also to FIG. 6, a 1.6 MHz clock pulse ○P is applied to the phase control circuit 30, and the counter 31 clocks it. Each bit of the output code of the counter 31, A
The A bit of -D (A=first to D=fourth) is applied to the serial-in/parallel-out shift register 32 as a shift activation pulse, and the D bit is applied as an input signal. As a result, the output terminals 0 to 0 of the shift register 32
7, pulses having a pulse width of D whose phase is shifted by A period appear one after another, one of which is output from the data selector 37 as an electrostrictive vibrator excitation pulse Vp and applied to the excitation amplifier circuit 4I.

The output bits B-D of the counter 31 are applied to a decoder 34, and the output pulses at the first output terminal 0 and the fifth output terminal 4 of the decoder 34 are applied to a frequency divider 36 and a T-flip-flop 35, respectively. The Q output of the T-flip-flop 35 is applied to the printing signal generation circuit 45 as a charging timing signal CP. The pulse whose frequency is divided to 1/16 by the frequency divider 36 and shaped to the output pulse width of the decoder 34 by the AND gate AN2 is applied to the charge amplifier 44 as a phase search charge signal pulse pp.

Please refer to FIG. The charging signal PP has 16 consecutive pulses, followed by a pause period of 16 pulses, and has a duration of 320 μs.
It is intermittent with a period of c. On the other hand, the printing charge timing signal Cp is a continuous pulse, and has a pulse width (high level H) eight times that of the pulse pp, with the pulse pp approximately at the center.

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 determined by the data selector 37 using the count code A- of the counter 33. It is shifted or changed depending on which of the shift register outputs O to 7 is output according to C.

In other words, the charging voltage pulse phase is fixed and the ink droplet separation phase is shifted.

Next, phase search will be explained with reference to FIGS. 2 to 6.

During the phase search, the search instruction signal is set to a high level 11, and accordingly, the switching circuit (or relay) 47 is connected to 44-6, and the deflection voltage power supply circuit 42 is deenergized (switched off). In this state, 320μs
A negative constant level charging pulse synchronized with a phase search charging pulse PP having a period of 10 μsec and intermittent with an ec period is applied to the charging electrode 6 from the amplifier 44 via the switching circuit 47 . On the other hand, the ring 1- on the counter 33 is plated with gold.
Assuming that the code is ro 00J, the pulse at the output terminal 0 of the shift register 32 is applied to the excitation amplifier circuit 41 as an excitation pulse ■p, and the phase corresponds to the period and phase of this VP (phase with respect to Pp). Ink particles separate. When the separation of the ink particles is timed with the pulse Pp, the ink particles become positively charged and collide with the gutter 9. In other words, 16 consecutive ink particles separated at the period of the pulse PP are negatively charged, and the next 16 are negatively charged.
Six particles are uncharged, creating a charging pattern with a period of 320 μsec, and all the ink particles collide with the gutter 9. Therefore, in this case, the gutter potential causes potential fluctuations similar to the charging pattern. The FE of the circuit 20 is
The base potential of T produces a sinusoidal or envelope-like potential fluctuation with a period of 320 μsec. Such a sine wave voltage is inverted by the FET, further inverted and amplified by the operational amplifier ftM unit 21, and is outputted at a positive level.
2. Haino (Sfilter 22 has a period of 32
Blocks noise of less than 0 μsec.

The integrating circuit 23 smoothes the sine wave with a period of 3201 Lsec and stabilizes it to a constant DC level. This DC voltage is compared with a reference voltage by a comparator 24, and when the DC voltage is higher than the reference voltage, that is, when the ink particles are charged,
The output of the comparator 24 is at a low level L, and when the ink droplets are uncharged or incompletely charged, the output of the comparator 24 is at a high level H.

The output of this comparator 24 is output from the printing control unit (
(not shown) and is also applied to the analog gate hANl of the phase control circuit 30. The printing control unit 1- sets the phase search signal to high level 1] and then
When the search determination pulse Pdk is applied to the Antogae-I-ANl of the circuit 30 at m5ec cycles, and the output Pok of the comparator 24 becomes L (ink particle charged detection), Pdk becomes 1.0.
Stop the output every m5ec and move on to printing charge control. Therefore, while the output of the comparator 24 is H (ink not charged), one pulse is given to the counter 33 from the anti-game hANl every 10 m5ec, the counter 33 counts up by one, and the output Vp of the data selector 37 is shifted. The pulse at the output terminal i of the register 32 changes to the pulse at the output terminal i+1 (the phase is shifted by I step by 1)6
The counter 33 carries out circular counting, and when the pulse of any one of the output terminals 0 to 7 of the shift register 32 is applied as vp to the excitation amplifier circuit 41, the ink particles are charged, and the output of the comparator 24 becomes L. Become.

When the output of the comparator 24 changes from H to L during the phase search, the printing control unit sets the phase search instruction signal to 1 and performs printing. During printing, the switching circuit 47 connects the amplifier 43 and the charging electrode 6, and the deflection power supply circuit 42 is energized, so that a constant high voltage of positive or negative voltage is applied to the deflection electrode 72. The printing signal generation circuit 45 generates a voltage whose level changes step by step.
This is applied to the amplifier 43 during the L interval of the pulse Cp and when the printing data is L indicating recording.

In the above embodiment, when the gutter holder 13 and the pipe 14 are wet with ink, the resistance between the gutter 9 and the filter 10 (ground) is IOMΩ to 100MΩ, and even if a large amount of ink is left intentionally, the resistance is more than IMΩ. It is. The stray capacitance of the shield wire 15 is 100 to 1000p
F, and the input resistance R was 100KΩ.

7a and 7b show the output waveform of the bypass filter 22 of the charge detection circuit 20. FIG. Figure 7a shows the measured waveform when the gutter holder 13 and pipe 14 are empty.
FIG. 7b shows the measured waveform when both are filled with ink. There is a small difference in the amplified voltage level when the ink is empty and full, and in normal usage, the ink is sucked by the pump 11 while the inner surface of the gutter holder 13 and the inner surface of the pipe 14 are wet, so the amplified voltage level fluctuates. There are few. 1st a
As shown in the figure and FIG. 1b, when the gutter 9 is in contact with the upper end of the holder 13, ink enters the gap between the holder 13 and the gutter 9 and rises along the outer surface of the gutter. When the top surface of the holder 13 contacts the earth shield SH, the distance between the gutter 9 and the shield SH is extremely short, so the resistance between them is extremely lower than 100Ω, and the amplified voltage level is quite high. Significant decline. However, in the present invention, as shown in FIGS. 3a and 3b, a space 13a is formed at the upper end of the holder 13 to block the ink from rising due to capillary development of the ink. There are no short circuits, and as mentioned above, fluctuations in the amplified voltage level are extremely small.

Alternatively, a plurality of V-shaped rectifying grooves may be formed vertically on the lower surface of the ink flow inside the gutter holder 13, and a grounding plate may be disposed below the grooves. According to this, the ink from the gutter 9 to the ground plate forms a resistance Rg, and the ink distribution is adjusted in the rectifying groove, so that Rg is stabilized. In addition, various other modifications may be made. For example, the ink may be grounded through an additional resistor, or the gutter 9 may be grounded through an additional resistor. In any case, gutter 9
By grounding through a resistor, the charge detection voltage becomes stable.

FIG. 8 shows a modification of the charge detection circuit 20. In this case, the shield wire 9 and the field effect transistor FET1
The charge detection circuit 20 is AC-coupled to the shielded wire 15 by inserting a coil capacitor C1 between them, and then the resistor R1 is connected. The output of amplifier 21 is connected to capacitor C2 and resistor R.
It is applied to the base of FET 2 through a low-pass filter consisting of FET 2, and then applied to bypass filter 22. In this charge detection circuit 20, DC bias signals such as frictional charging when injecting from the nozzle and charging when colliding with the gutter are blocked by the coidenser CI, and the discharge current of the charge charged by the charge signal is inputted in a pulsed manner. The voltage flows through the resistor 1, and the output of the amplifier 21 becomes a pulse-like signal corresponding to the charge of each droplet.

Note that when using this charge detection circuit 20, the gutter 9
The connection wire between and capacitor C1 should be short, and the stray capacitance should be 20
It should be a small value of ~30 pF or less.

The time constant T of the low-pass filter (C2, R2) is preferably set to the following value for the interruption and continuation of 16 pulses of the phase search charge signal pp.

10 μsec<T<10×16 μsec As a result, a signal with a 16-pulse cycle is applied to the bypass filter 22. The bypass filter 22 filters out low-frequency noise from the signal and shapes it into a sine wave, and the integration circuit 23 converts it into a DC level.

[Brief explanation of the drawing]

FIG. 1a and FIG. ib are longitudinal cross-sectional views showing how a conventional gutter is installed. FIG. 2 is a block diagram showing one embodiment of the present invention. 3a and 3b are enlarged longitudinal cross-sectional views of the gutter 9 shown in FIG. 2, FIG. 4 is an electric circuit diagram showing the configuration of the charge detection circuit 20, and FIG. 5 is a diagram showing the configuration of the phase control device 30. The block diagram, FIG. 6 is a time chart showing the input and output of the phase control device, and FIGS. 7a and 7b are graphs showing the output waveform of the bypass filter 22 of the charge detection circuit 20. FIG. 8 is a circuit diagram showing another embodiment of the charge detection circuit 20. 1: Ink force -1 to ridge 5: Ink jet head 5a: Electrostrictive vibrator 6: Charge electrode 71+
72: Deflection electrode 8: Recording paper 9: Conductive gutter 10 = Filter 12; Recovery ink tank 13 Ni gutter holder 14 = Pipe 15: Shield wire Patent applicant Ricoh Co., Ltd. Figure 1a Figure 38 TIT'1 Figure 1b Ni-komi figure 3b

Claims (1)

[Scope of Claims] Pressurized ink is supplied to an ink ejection head, the pressurized ink is subjected to regular vibrations in the ink ejection head, and ejected from a nozzle of the head, and the point at which the ink ejected from the nozzle separates into particles. In a deflection control inkjet recording device that charges ink particles by applying a charging voltage to a charging electrode and deflects the charged ink particles with a deflection electric field; a conductive gutter that captures non-imprinted ink particles; an insulator holder supporting the gutter and having a concave space formed at its upper end to surround the gutter; and a charge detection circuit having a resistor connected to the gutter and grounding the gutter, and amplifying the voltage appearing on the resistor. A deflection control inkjet recording device comprising;