JPS59220378A - Detector for electric charge on ink particle - Google Patents

Abstract

PURPOSE:To prevent misdetection from occurring in detecting electric charges by a nozzle from the exterior and perform favorable ink jet recording, by a method wherein a gutter is formed of an insulator, and an electric charge detecting electrode is provided in an ink passage provided directly below the gutter. CONSTITUTION:An ink jetted from an ink jet head 5 is split into ink particles at a position spaced by a predetermined distance from the head 5, and are electrically charged by an electrode 6. The electrically charged ink particles are deflected, and impinges on a recording paper 8, while non-charged ink particles impinges on the gutter 9, fall along the gutter 9, are led to an ink-recovering tank 12 and to an ink tank 13 by being sucked by a pump 11, and is fed into an accumulator 3 by being sucked by a pump 2. Directly below the gutter 9, the electric charge detecting electrode is fixed along the inside wall of an ink guide, and is connected with a shield wire 15 the other end of which is connected to an electric charge detecting circuit 20.

Description

Detailed Description of the Invention ■Technical Field The present invention jets ink to which ultrasonic vibrations have been applied from a nozzle, and selectively charges the jetted ink at a position where it separates into ink particles using a charging electrode. The present invention relates to inkjet recording in which particles are deflected by a deflection electrode and collides with a recording paper, and particularly relates to charge detection of ink particles for searching for an appropriate charging voltage application phase with respect to the separation phase of the ink particles.

■Prior art 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. The ejected ink regularly separates into ink particles at a certain distance from the nozzle. This separation period is
Equal to the period of the above 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 stepwise, and is set to O level (for example, ground potential) when not recording (image signal: roJ). 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 done by applying the output clock of the clock pulse generator to the excitation voltage generator, generating a sine wave synchronized with the clock, and applying it to the electrostrictive vibrator of the head. The output clock of the device is fed to a phase setting circuit to create a charging clock with a partial pulse width that has a certain set phase difference from the clock phase, and a charging clock that has exactly the same phase as this charging clock and has the same or opposite polarity as the charging voltage. A search signal generator generates a search charge pulse at a constant level and applies it to the charge electrode via a gate and an amplifier, and a charge detection electrode detects the charge on the ink particles, and a predetermined number of ink particles are detected. During the generation of particles, the charge detection circuit monitors whether or not a charge detection signal is emitted, and when it is emitted, the phase search is terminated, and when it is not emitted, the phase setting circuit is commanded to shift the phase by one step. This is done in each circuit operation of shifting the charging clock by a predetermined phase from the previous one.

After setting the proper 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, is used to control 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 the electric field of the deflection electrode corresponds to the amount of charge. Deflected. When the image signal is at the "0" level, the charging voltage is at the 0 level, and at this time, the ink particles are not charged and are collected by the gutter.

One method of charge detection is to detect the charge on an ink droplet impinging on the gutter or the resulting current flowing through a predetermined resistor.

In this case, the ink collection gutter is made of a metal electrode, an integrator, an amplifier, etc. are connected to the electrode to amplify the signal level, and the output level is compared with a predetermined reference level to determine whether charged or uncharged. Judgment is being made.

By the way, the gutter of an inkjet recording device is set at an angle of 15 mm with respect to the flight axis of ink particles (generally horizontal) to prevent ink mist from being generated by ink particles colliding with the gutter.
It is relatively large, with a head that is inclined at a slight angle and a vertically disposed base that guides the ink to the ink collection system. However, discharge, electric field fluctuation, etc. due to the high deflection voltage used in this type of inkjet recording may induce noise signals in the gutter electrode, resulting in erroneous charge detection.

Although noise induction can be avoided by making the electrode smaller and providing electrostatic shielding, it is impossible to electrostatically shield the entire gutter electrode so as not to impede the flight of ink particles toward the gutter.

(2) Purpose The present invention aims to prevent erroneous charge detection due to external noise.

(2) Structure To detect the charge of non-printed ink particles, an electrode may be placed in a portion of the ink flow path of the ink recovery system where the ink charge is not affected. That is, since ink particles captured by the gutter flow below the gutter, a portion of the ink passageway below the gutter may be provided with a conductive material. However, the position where the conductive material is placed must be upstream of the position where the ink contacts the ground metal or the like.

In addition, it is preferable to perform charge detection as soon as the charge on the ink particles does not change due to leakage, etc. From this point of view, it is preferable to use the gutter as the detection electrode, but the gutter does not induce noise as described above. be. Therefore, for example, if the gutter is made of an insulator such as polycarbonate or polyacetal resin, and a charge detection electrode is placed in the ink passage directly under the gutter, the size of the charge detection electrode itself can be reduced.
By electrostatically shielding most of its surroundings, the effects of induced noise can be reduced.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1a shows the configuration of one type of inkjet recording apparatus embodying the present invention. In FIG. 1, ink in an ink cartridge 1 is pumped to an accumulator 3 by a pump 2, and pressure vibrations are absorbed by the accumulator 3. The constant pressure ink passes through a filter 4 to an ink jet head 5.
supplied to In the head 5, a 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 disposed on the separation position side, 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 that of the charging voltage. The charged ink particles are deflected by the deflection electric field between the deflection electrodes 71 and 72 and collide with the recording paper 8 .

The uncharged ink particles collide with the gutter 9, fall downward along the gutter 9, 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. It will be done.

FIG. 1i) shows the vicinity of the gutter 9 viewed from the deflection electrodes 71+72 side, and FIG. 1c shows a cross section taken along line 1c-Ic in FIG. 1b. This will be explained with reference to FIGS. 1b and 1c. Gutter 9 is made of a non-conductive material (polycarbonate in this example).

It consists of a head 9a that is inclined at 15 degrees with respect to the ink ejection axis and has a sharp tip, and a perpendicular base 9b that is continuous with the head 9a. The base portion 9b is provided with a large number of longitudinal linear irregularities to adjust the flow of ink.

The base 9b of the gutter has an ink guide 16 formed hollow.
It is fixed to the inner wall of the Like the gutter 9, the ink guide 16 is made of a non-conductive material.

Directly below the gutter 9, a ring-shaped charge detection electrode 17 is fixed along the inner wall of the ink guide 16.

In this example, stainless steel is used for the charge detection electrode 17. The charge detection electrode 17 has a charge detection circuit 20 at the other end.
This is done by connecting the shielded wire 15 connected to the .

A grounded metal plate 18 is attached to the outer periphery of the ink guide I6. An ink recovery tube 19 is connected below the ink guide 16 via a grounded filter 10. An ink mist absorption plate 50 is arranged so as to surround the gutter 9. The ink mist absorption plate 50 is made of a conductive material made of sintered stainless steel, and is grounded. 50a is a slit through which deflected ink particles used for printing pass. The ink mist absorption plate 5o is fixed to the same carriage as the gutter 9° ink guide 16 and the like.

The configuration of the charge detection circuit 20 is shown in FIG. The charge detection circuit 20 has a resistance value Rc smaller than Rg in order to prevent instability of the ground resistance of the charge detection electrode 17 due to fluctuations in the ink resistance Rg between the charge detection electrode 17 and the grounded filter lO. A resistor R for voltage conversion, a field effect transistor FET for impedance conversion, an operational amplifier 21, and a bypass filter 22. It consists of a product circuit 23 and a comparator 24 for DC smoothing.

The configuration of the phase control circuit 30 is shown in FIG. 3, and the input/output timing of each part thereof is shown in FIG. Referring to Figure 3,
A 1.6 MHz clock pulse Op is applied to the phase control circuit 30 and counted by the counter 31. Callan 1 of counter 31 - each bit A of the code output
A pin 1- of D (A=1st to D=4th) outputs 0 to the serial-in/parallel-out shift register 32.
7, pulses with a pulse width of D whose phase is shifted by A cycle appear sequentially, one of which is outputted from the data selector 37 as the electrostrictive vibrator excitation pulse Vp and sent to the excitation amplifier circuit 41.
is applied to

The output bits B-D of the counter 31 are applied to the decoder 34, and the first output faO and the fifth output terminal 4 of the decoder 34 are applied to the decoder 34.
output pulses are applied to frequency divider 36 and T flip-flop 35, respectively. T flip prop 35 Q
The output is applied to the printing signal generation circuit 45 as a charging timing signal Cp.

The pulse whose frequency is divided by 1/36 by the frequency divider 36 and shaped into the output pulse width by the decoder 34 by the AND gate AN2 is applied to the charge amplifier 44 as a phase search charge signal pulse. As shown in FIG. 4, the charge signal PP has 16 consecutive pulses, followed by a rest period of 16 pulses, and has a length of 320 μm.
Intermittent at a cycle of seC. On the other hand, the printing charge timing signal Cp is a continuous pulse, and is a pulse ppp.
is approximately in the center and the pulse width is 8 times that (high level "1")
has.

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 37 to the count code A of the counter 33. -C, it is shifted or changed depending on which of the shift register outputs 0 to 7 is output. 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. 1a to 4. During phase search, the search instruction signal is set to a high level "1", and the switching circuit (or relay) 4 is activated accordingly.
7 becomes a 44-6 connection, and the deflection voltage power supply circuit 42
is deenergized (switched off). In this state, 320
A negative constant level charging pulse synchronized with a phase search charging pulse Pp having a period of 10 μsec and intermittent at a μsec period is applied from the amplifier 44 to the charging electrode 6 via the switching circuit 47 .

On the other hand, the counter 33's callan 1 code is ro on the gold plate.
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 Vp, and the ink particles are separated at a phase corresponding to the period and phase of this VP (phase with respect to Pp). do. When the separation of the ink droplets coincides with the pulse P-p, the ink droplets become positively charged and collide with the gutter 9. That is, the ink particles that are separated at the period of the pulse pp produce a charge pattern with a period of 320 μsec, in which 16 successive particles are negatively charged and the next 16 particles are uncharged, and all the ink particles collide with the gutter 9.

Therefore, in this case, the potential of the charge detection electrode 17 below the gutter 9 causes potential fluctuations similar to the charge pattern. However, the stray capacitance of the shield wire 15 and the charge detection electrode 1
Due to the time constant determined by the ink resistance Rg between 7 and ground (10) and the input resistance R of the charge search circuit wt20, the potential of the FET of the charge detection circuit 20 fluctuates in the form of a sine wave or an envelope with a period of 320 μsecC. will occur.

Such a sine wave voltage is inverted by the FET, further inverted and amplified by the operational amplifier 21, and then applied to the bypass filter 22 at a positive level. The bypass filter 22 blocks noise with a period of less than 320 μSec. The integrating circuit 23 smoothes the sine wave with a period of 320 μsecC and stabilizes it to a DC level. This DC voltage is compared with a reference voltage in a comparator 24, and when the DC voltage is higher than the reference voltage, that is, when the ink particles are charged, the comparator 24
The output of the comparator 24 is rOJ, and when the ink droplet is uncharged or incompletely charged, the output of the comparator 24 is a high level rlJ.

The output of this comparator 24 is output from the printing control unit (
(not shown) and is also applied to the AND gate ANI of the phase control circuit 30. The printing control unit 1~ sets the phase search signal to "1" and then prints 10m5e.
The search determination pulse Pdk is applied to the AND gate ANI of the circuit 30 at period c, and the output Pok of the comparator 24 becomes "OJ
(detection of charged ink particles), 10m5 of Pdk
One pulse is given to the counter 33 from the antigame hAN for each ec, the counter 33 counts up by one, and the output VP of the data selector 37 changes from the pulse at the output terminal i of the shift register 32 to the pulse at the output terminal i+1 ( In other words, the phase is shifted by one step.)

The counter 33 repeatedly counts and the shift register 3
When a pulse from any one of the output terminals 0 to 7 of 2 is applied to the excitation amplifier circuit 41 as VP, the ink particles are charged,
The output of the comparator 24 becomes rOJ.

When the output of the comparator 24 changes from "1" to "0" during the phase search, the printing controller 1-roll unit sets the phase search instruction signal to "0" and performs printing recording.

In printing, the switching circuit 47 is the amplifier 43.
- The charging electrode 6 is connected, the deflection power supply circuit 42 is energized, and a constant positive or negative high voltage is applied to the deflection electrode 72. The printing signal generation circuit 45 generates a voltage whose level changes step by step, and this
It is applied to the amplifier 43 when the printing data is [1] instructing recording in the "0" section.

In the above embodiment, the gutter 9 is made of a non-conductive material, but the gutter 9 is made of a conductive material, and an insulating material is interposed between the gutter 9 and the charge detection electrode 17. You can also use it as However, in that case, the gutter 9 cannot be grounded, so the gutter 9 and the charge detection electrode 17
In addition, the collected ink flow deteriorates the insulation between the gutter 9 and the charge detection electrode 17, and the noise voltage induced in the gutter 9 adversely affects the charge detection of the charge detection electrode. Therefore, it is preferable to use the above configuration.

(2) Effects As described above, according to the present invention, shielding of the charge detection section is simplified, so malfunction of charge detection due to induction of external noise can be prevented, and good inkjet recording can be performed.

[Brief explanation of the drawing]

FIG. 1a is a block diagram showing the configuration of one type of inkjet recording apparatus that implements the present invention. Fig. 1b is a front view showing the vicinity of the gutter 9, and Fig. 1c is a front view showing the vicinity of the gutter 9.
It is a sectional view taken along the Ie-Ie line in figure b. FIG. 2 is a block diagram showing the charge detection circuit of FIG. 1a. FIG. 3 is a block diagram showing the phase control circuit of FIG. 1a. FIG. 4 is a timing chart showing the signal timing of each part of the circuit. l: Ink cartridge 5: Ink jet head 5a:
Electrostrictive vibrator 6: Charge electrode 71.72: Deflection electrode 8: Recording paper 9 nigator lo: Filter 12: Recovery ink tank 15: Shield wire 16: Ink guide
17: Charge detection electrode 18: Metal plate 19: Ink collection tube 20: i-charge detection circuit 50:
Ink mist absorption plate 50a: ink passage slit 423

Claims (3)

[Claims] (1) In a charge detection device of a charge deflection type inkjet printing device: a gutter that captures non-imprinted ink particles; a charge detection electrode insulated from the gutter and placed below the gutter; and a charge detection electrode connected to the charge detection electrode. An ink particle charge detection device comprising: a detection circuit. (2) The gutter is made of a non-conductive material, and the charge detection electrode is disposed directly under the gutter.
The ink particle charge detection device described in 2. (3) The charge detection device for ink particles according to claim 1 or 2, further comprising a grounded conductive material around the charge detection electrode.