JP3033601B2 - Continuous jet type inkjet recording device - Google Patents

Description

The present invention relates to a continuous jet type ink jet recording apparatus,
In particular, the present invention relates to a technique for controlling a phase relationship between a timing at which an ink column is divided into ink particles and a rising or falling of a control signal (recording pulse) in a continuous jet type ink jet recording apparatus in an optimum state.

[Conventional technology]

For example, as shown in FIG. 6, a conventional continuous jet type ink jet recording apparatus has an ink bottle 61 for storing ink.
An ink pump 62 that pressurizes and sends ink, an ink tube 63 that supplies ink, a nozzle 64 having a very small diameter circular orifice, and an ink electrode 65 that sets the potential of the ink in the nozzle 64 to the ground level. A vibrator 66 composed of a piezo vibrator mounted on the nozzle 64, a vibrator driving transmitter 67 for giving an excitation signal to the vibrator 66, and a circular or slit-shaped opening concentric with the nozzle 64 and image data A control electrode 68 to which a control signal for controlling the charging of the ink jet is applied correspondingly, a ground electrode 69 disposed in front of the control electrode 68 and grounded, and a knife edge 70 attached to the ground electrode 69, A strong electric field perpendicular to the jet flight axis is created between the high voltage DC power supply for deflection (hereinafter simply referred to as deflection power supply) 71 and the deflection power supply 71 and the ground electrode 69 to deflect the charged ink particles to the ground electrode 69 side. Deflection for The electrode 72 was provided. Reference numeral 73 denotes a rotating drum around which a recording medium is wound.

In such a conventional continuous jet type ink jet recording apparatus, the ink pressurized by the ink pump 62 is guided to the nozzle 64 through the ink tube 63, and the ink jet is formed from the orifice. At the spontaneous particle formation frequency. At this time, if the excitation frequency of the vibrator 66 attached to the nozzle 64 is set near the spontaneous particle generation frequency, the particle formation is synchronized with the excitation of the vibrator 66, and the ink particles of a very uniform size match the excitation frequency. Occur.

The ink particles thus be granulated in the, when split from the ink column, and the electric resistance R _j of the ink column, the integration circuit consisting of the capacitance C _j between the ink column and the control electrode 68 Is charged by electrostatic induction through the control signal, and the control signal has an amplitude φ _c
, The potential of the ink particles immediately before the formation of the particles becomes φ _j = φ _c (1−exp (−t / C _j R _j )).

When a uniform row of ink particles split from the ink column is charged and modulated by a control signal (recording pulse) corresponding to the density of the image and synchronized in phase with the excitation signal, the charged ink particles are moved to the ground electrode 69 by the action of the deflection electric field. Deflected by the knife edge
Cut at 70, only the uncharged ink particles go straight and pass through the knife edge 70 to form dots on the recording medium wound around the rotating drum 73.

Now, assuming that the excitation frequency (particleization frequency) is _fd and the ink jet is pulse width modulated at a frequency of _fd / n, an n-gradation image with a controlled dot diameter is recorded at a frequency of _fd / n. be able to.

[Problems to be solved by the invention]

In the above-described conventional continuous ejection type ink jet recording apparatus, the excitation signal to the vibrator 66 and the control signal (recording pulse) to the control electrode 68 must be synchronized while maintaining a certain optimal phase relationship. That is, the ink particles are generated in synchronization with the excitation signal, but the timing of splitting (breaking) from the ink column into the ink particles depends on the temperature, ink pressure,
Due to a change in a parameter such as an ink physical property value, the value slightly changes during one cycle of the excitation signal. When the phase of the timing and control signals granulation (recording pulse) is shifted, the electric resistance R _j of the ink column becomes very large value with particles of just before the edge of the control signal (recording pulse) is the resistance Since the ink particles enter an extremely large region (hereinafter referred to as a forbidden region), the charging of the ink particles becomes incomplete, and halfway charged ink particles are generated. When halfway charged ink particles are generated, precise control of the ink particles one by one becomes impossible, and as a result, granular noise mainly occurs in a highlight portion of an image.

A technique for simply synchronizing an excitation signal and a control signal (recording pulse) is disclosed in JP-A-62-225363 and JP-A-63-225363.
No. 264361, and the like.

On the other hand, as a method of searching for the optimum phase between the excitation signal and the control signal (recording pulse), the amplitude of the probe pulse or the amplitude of the excitation signal during one period is narrower than the period (1 / f _d ) of the excitation signal. Charges the inkjet while changing the phase with a probe pulse that has a pair of pulses with the same pulse width and different polarity, and measures the current flowing with the inkjet (hereinafter referred to as the jet current) to optimize from the value of the jet current US Patent No.
No. 4,839,665. However, the jet current is a very small current (10 to 100 nA) and the current source is exposed to various noises, and it is difficult to shield it in a real machine (especially, a commercial AC power supply of 100 V (hereinafter, AC 100 V) Is a problem).

As a method of measuring the jet current, a method of inserting a current detection resistor between the ink electrode 65 and the ground and converting the jet current into a voltage is disclosed in the aforementioned US Pat. No. 4,839,665. In addition, a method of connecting the ink electrode 65 to a virtual ground point of an operational amplifier constituting a current / voltage converter is described in PCT /
It is disclosed in US88 / 03311. These methods have the advantage that a continuous jet type ink jet recording apparatus using a plurality of nozzles 64, such as a color ink jet printer, can independently detect a jet current for each nozzle 64. The ink pump 62 from the ink bottle 61 to the nozzle 64
The entire ink supply system must be kept in an insulated state, and the ink supply system has a long ink tube 63 etc., which is a very harmful noise source. There is a problem that it is difficult.

A method of detecting a jet current flowing between the ground electrode 69 and the deflection electrode 72 is disclosed in the aforementioned U.S. Pat. No. 4,839,665. This method can measure a jet current with a low noise and a high S / N ratio as compared with the method using the ink electrode 65, but the measurement at the ground electrode 69 side where no high voltage is applied is possible. Easy, but in that case, the ground electrode contaminated with waste liquid
Multiple nozzles, such as color inkjet printers, that must keep 69 insulated
Even with a continuous jet type ink jet recording device using 64,
Since only one pair of the deflection electrode 72 and the ground electrode 69 is provided, and the waste liquid from each nozzle 64 collects on one ground electrode 69, the jet current cannot be measured independently for each nozzle 64. There is.

Further, a method of providing a conductive ink catcher insulated from the other in front of the ground electrode 69 and the deflection electrode 72, and inserting a current detection resistor between the conductive ink catcher and the ground to detect a jet current, U.S. Pat.No. 4,839,66
No. 5 discloses it. This method is the best method as compared with the above two methods, but since the impedance of the signal source is as high as 10 ⁹ to 10 ¹⁰ Ω, a large value of the current detection resistor is required, and noise is likely to enter. There is a problem that it is difficult to measure a jet current having a high S / N ratio. Therefore, an alternating measurement method, that is, a method in which a probe pulse is amplitude-modulated and a jet current is detected by a narrow-band amplifier is disclosed in the above-mentioned US Pat. No. 4,839,665. However, in this method, since the amplitude-modulated probe pulse is used, the circuit system is complicated and expensive, and the stability is poor.

In view of the above points, an object of the present invention is to measure a jet current with a very simple configuration with high accuracy, and automatically adjust an optimal phase between ink jetting and recording pulses based on the result. Accordingly, an object of the present invention is to provide a continuous jet type ink jet recording apparatus capable of surely controlling ink particles one by one.

[Means for solving the problem]

The continuous ejection type ink jet recording apparatus of the present invention comprises: a jet forming means for forming an ink jet from a nozzle by pressurizing ink; an oscillation means for outputting an excitation signal having an oscillation frequency near a spontaneous particleization frequency of the ink jet; The excitation signal from the means is delayed by N (positive integer) number of phases 2πn / N (n = 0, 1, 2,..., N−1), and the delayed signal excites the vibrator attached to the nozzle. A delay excitation unit for splitting the ink jet into ink particles in synchronization with the excitation; and charging the ink particles by a probe pulse having a time width shorter than one cycle of the excitation signal in synchronization with an excitation signal from the oscillation unit. A charging unit, a conductive particle catcher that is electrically insulated from others and catches ink particles charged by the charging unit, A current detector for detecting the charge of the charged charged ink particles as a jet current at predetermined time intervals, and the current detector detects N phases 2πn / N (n = 0, 1, 2,..., N) of the delay signal. An optimal phase determining means for detecting the jet current in N-1) and determining a middle phase of a phase range in which no halfway charged ink particles are generated in the resulting jet current curve as an optimal phase of the delay exciting means; It is characterized by having.

Further, the continuous jet ink jet recording apparatus of the present invention is a jet forming means for forming an ink jet from a nozzle by pressurizing the ink, an oscillating means for outputting an excitation signal having an oscillation frequency near the spontaneous particleization frequency of the ink jet, Exciting means for exciting the vibrator attached to the nozzle with an excitation signal from the oscillating means to split the ink jet into ink particles in synchronization with the excitation, and for the excitation signal in synchronization with the excitation signal from the oscillating means. On the other hand, the phase of the rising or falling edge is delayed by N (positive integer) number of phases 2πn / N (n = 0, 1, 2,..., N−1) from one cycle of the excitation signal. A delay charging means for charging the ink particles by a probe pulse having a short time width, and catching the ink particles electrically insulated from others and charged by the delay charging means. A conductive particle catcher;
A current detector for detecting the charge of the charged ink particles caught by the conductive particle catcher as a jet current at predetermined time intervals; and the current detector detects N phases 2πn / N (n = 0) of the probe pulse. , 1, 2,..., N−1), and a phase in the middle of a phase range in which no halfway charged ink particles are generated in the resulting jet current curve is set as an optimal phase of the delay charging means. And an optimal phase determining means for determining.

Further, in the method for determining an optimum phase in the continuous jet type ink jet recording apparatus of the present invention, the step of jetting the ink jet from a nozzle to maintain a steady state and the step of applying an excitation signal to the nozzle to split the ink jet into ink particles Turning off the deflection electric field; applying a probe pulse having a time width shorter than one cycle of the excitation signal to the control electrode in synchronization with the excitation signal; and sequentially switching the phase of the probe pulse. Measuring a jet current in each of N (positive integer) phases 2πn / N (n = 0, 1, 2,..., N−1), and an intermediate charge in a jet current curve obtained from the measured jet current Determining a phase in the middle of the phase range in which no ink particles are generated as an optimal phase between the inkjetting and the recording pulse. I do.

[Action]

In the continuous ejection type ink jet recording apparatus of the present invention, the jet forming means pressurizes the ink to form an ink jet from the nozzle, and the oscillation means outputs an excitation signal having an oscillation frequency near the spontaneous particleization frequency of the ink jet,
The delay excitation means converts the excitation signal from the oscillation means to N (positive integer)
Each phase is delayed by 2πn / N (n = 0, 1, 2, ..., N-1), and the vibrator attached to the nozzle is excited by the delayed signal, and the ink jet is divided into ink particles in synchronization with the excitation. The charging means charges the ink particles with a probe pulse having a time width shorter than one cycle of the excitation signal in synchronization with the excitation signal from the oscillating means, and a conductive particle catcher electrically insulated from the others. The current detector detects the charged ink particles caught by the conductive particle catcher as a jet current at predetermined time intervals, catching the ink particles charged by the charging means, and the optimum phase determining means is delayed by the current detector. Each of the N phases 2πn / N of the signal (n = 0, 1, 2,...,
The jet current in N-1) is detected, and the phase in the middle of the phase range in which the intermediately charged ink particles do not occur in the resulting jet current curve is determined as the optimal phase of the delay excitation means.

Further, in the continuous jet ink jet recording apparatus of the present invention, the jet forming means pressurizes the ink to form an ink jet from the nozzle, the oscillation means outputs an excitation signal having an oscillation frequency near the spontaneous particleization frequency of the ink jet, Exciting means excites a vibrator mounted on the nozzle with an excitation signal from the oscillating means to divide the ink jet into ink particles in synchronization with the excitation, and delay charging means in synchronization with the excitation signal from the oscillating means. , One cycle of the excitation signal obtained by delaying the phase of the rising or falling edge by N (positive integer) number of phases 2πn / N (n = 0, 1, 2,..., N−1) Ink particles are charged by a probe pulse having a shorter time width, and an electrically insulated conductive particle catcher catches the charged ink particles by the delay charging means, and charges the ink particles. The flow detector detects the charge of the charged ink particles caught by the conductive particle catcher as a jet current at predetermined time intervals, and the optimum phase determination means uses the current detector to detect each of N phases 2πn / N of the probe pulse.
(N = 0, 1, 2,..., N−1), and the phase in the middle of the phase range in which no halfway charged ink particles are generated in the resulting jet current curve is determined by the delay charging means. Determine the optimal phase.

Further, in the method for determining an optimum phase in the continuous jet type ink jet recording apparatus of the present invention, the ink jet is ejected from the nozzle to maintain a steady state, an excitation signal is applied to the nozzle to split the ink jet into ink particles, and the deflection electric field is changed. Is turned off, a probe pulse having a time width shorter than one cycle of the excitation signal is applied to the control electrode in synchronization with the excitation signal, and the phases of the probe pulse are sequentially switched to obtain N (positive integer) number of phases 2πn / The jet current at N (n = 0, 1, 2,..., N−1) is measured, and the phase in the middle of the phase range in which no halfway charged ink particles are generated in the jet current curve obtained from the measured jet current is calculated. It is determined as the optimal phase between the inkjet particleization and the recording pulse.

〔Example〕

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

FIG. 1 is a configuration diagram showing a main part of a continuous ejection type ink jet recording apparatus according to one embodiment of the present invention. The continuous ejection type ink jet recording apparatus according to the present embodiment includes a nozzle 1 having a very small diameter circular orifice, an ink electrode 2 for setting the potential of the ink in the nozzle 1 to the ground level, and a piezoelectric vibrator mounted on the nozzle 1. A control electrode 4 having a circular opening or a slit-like opening concentric with the nozzle 1 and having a control signal applied thereto for controlling the charging of the ink jet corresponding to the image data; A ground electrode 5, which is grounded, a knife edge 6 attached to the ground electrode 5, a deflecting electrode E1, and a strong electric field orthogonal to the jet flight axis between the deflecting power source E1 and the ground electrode 5. A deflecting electrode 7 for deflecting the charged ink particles toward the ground electrode 5, a switch SW1 for switching whether the deflecting electrode 7 is connected to a deflecting power source E1 or grounding, and a reference generator for generating a reference clock CLK. Vessels CG and the reference clock CLK and N (positive integer) frequency divider 1 frequency-divided to create an excitation signal PCLK of partial FD
, A delay pulse generator DG that outputs a pulse train θ ₀ , θ ₁ , θ ₂ ,..., Θ _{N−1 in} which the excitation signal PCLK is delayed in N stages according to the reference clock CLK, and a delayed pulse train θ ₀ , θ ₁ , θ ₂ ,
..., θ _N-1 Multiplexer (2) M
P2, a vibrator driver VD for driving the vibrator 3 with a pulse selected by the multiplexer (2) MP2, a pulse width modulator PM for converting image data into a pulse width corresponding to a density gradation, and an excitation signal PCLK Pulse generator that generates a probe pulse whose pulse width is sufficiently shorter than the period of the excitation signal PCLK in synchronization with the rising or falling edge of the
PG, a synchronization circuit SC for synchronizing the rising or falling edge of the output of the pulse width modulator PM with the rising or falling edge of the excitation signal PCLK, and a probe pulse and synchronization circuit from the probe pulse generator PG A multiplexer (1) MP1 for selecting one of the outputs from the SC, a high-voltage switch HVS for amplifying the voltage of the output of the multiplexer (1) MP1 and applying it to the control electrode 4 as a control signal, and a ground electrode 5
A conductive particle catcher 8 also serving as a detection electrode disposed in a region not related to recording (hereinafter, referred to as a home position) in front of the deflection electrode 7, a shield wire 9 having one end connected to the conductive particle catcher 8, Switch SW2,
A current detector (current / voltage converter) composed of SW3, SW4, integrating capacitor C and integrator OP, and the output of the current detector
An A / D converter ADC for D-conversion constitutes the main part.

The delay pulse generator DG is, for example, a serial-in parallel
It is composed of an ll-Out type N-bit shift register.

The probe pulse generator PG is composed of, for example, a monostable multivibrator triggered by an edge of the excitation signal PCLK.

The integration capacitor C suitably has a capacity of about 1 to 10 nF, and desirably a high insulation resistance such as a polystyrene or polypropylene capacitor.

The integrator OP has negligible leakage current (1 nA or less) compared to the jet current I _j (Field Effect Transistor)
It consists of an input operational amplifier, whose input is connected to its virtual ground.

Switches SW2, SW3 and SW4 are also leakage current than the jet current I _j is an FET negligible.

FIG. 2A shows that the switches SW2, SW3 and SW4 are set to AC100V.
FIG. 3 is a circuit diagram showing an example of a synchronization signal generation circuit for operating in synchronization with the circuit. This synchronization signal generation circuit includes a transformer T, a resistor R, diodes D1 and D2, a preset counter PSC, and flip-flops FF1 and FF2.

The preset counter PSC can set the preset value variably (the path is not shown), and by changing the preset value, the integration time can be arbitrarily set to an integral multiple of the cycle of 100 VAC. . In the present embodiment, as shown in the timing chart of FIG. 2B, it is assumed that the integration time is set to be three times the cycle of 100 V AC.

The reset signal RESET, the integration start signal ▲ ▼, and the integration end signal HOLD are each fixed to one cycle of 100 VAC, and when each is at the “H” level, the switches SW4 and SW
3 and SW2 are closed, and open when it is at “L” level.

Next, the operation of the thus-configured continuous ejection type ink jet recording apparatus of the present embodiment will be described.

When the power is turned on to the continuous ejection type ink jet recording apparatus, the operating voltage is supplied to the circuit system shown in FIGS. 1 and 2A, and the phase adjustment operation is started. In general, the phase adjustment operation is executed immediately before the start of a recording operation in which a carriage (not shown) on which the nozzle 1 is mounted is waiting at a home position. In the case of a color inkjet printer, the phase adjustment operation is performed in parallel for four colors (C (cyan), M (magenta), Y (yellow), BK (black)) (or three colors excluding BK).

First, ink is pressurized by an ink pump (not shown) and guided to the nozzle 1 through an ink tube (not shown), and an ink jet is ejected from the nozzle 1 to be kept in a steady state. The MPU (not shown) is connected to the switch SW1
Is switched to the ground side to set the deflection electrode 7 to the ground level.
As a result, the deflection electric field between the ground electrode 5 and the deflection electrode 7 is turned off, and the charged ink particles pass through the knife edge 6. Further, the MPU includes a multiplexer (1) M
Let P1 select the output of the probe pulse generator PG. Furthermore, the nozzle 1 is driven by a carriage motor (not shown).
Is set to the home position.

On the other hand, the reference oscillator CG outputs the reference clock CLK,
The frequency of the reference clock CLK is divided by a frequency divider 1 / N by a frequency divider FD.
The excitation signal PCLK is input to the delay pulse generator DG, the probe pulse generator PG, and the synchronization circuit SC. That is, the excitation frequency PCLK of the excitation signal PCLK (hereinafter, the signal and the frequency of the signal are denoted by the same reference numerals) is CLK /
N (eg, CLK = 16 MHz, N = 16, PCLK = 1 MHz).

The delay pulse generator DG receives an excitation signal PCLK as data, a reference clock CLK as a shift clock, and N sets of pulse trains θ ₀ , θ ₁ , θ ₂ in which one cycle of the excitation signal PCLK is sequentially delayed by 2π / N. , ..., θN _-1 are output. One of the N sets of pulse trains θ ₀ , θ ₁ , θ ₂ ,..., Θ _{N -1} is selected by the MPU via the multiplexer (2) MP2 and output to the transducer driver VD. The transducer driver VD excites the transducer 3 according to the output from the multiplexer (2) MP2. Thereby, the ink jet ejected from the nozzle 1 is turned into particles in synchronization with the excitation by the vibrator 3, as shown in FIG.

The probe pulse generator PG synchronizes with the rising or falling edge of the excitation signal PCLK (same as at the time of recording), and as shown in FIG. 3, the pulse width is sufficiently smaller than the period of the excitation signal PCLK. (For example, 0.1 to 0.3 μsec when the period of the excitation signal PCLK = 1 μsec (1 MHz oscillation)).

The probe pulse output from the probe pulse generator PG is supplied to the high-voltage switch H via the multiplexer (1) MP1.
The voltage is input to the VS, amplified by the high voltage switch HVS, and applied to the control electrode 4 as a control signal. Therefore, the ink particles that are converted into particles in synchronization with the excitation of the vibrator 3 are charged according to the probe pulse. Now, in the example shown in FIG. 3, since the polarity of the probe pulse is negative, the ink particles are always charged, and the time (for example, 0.1 to 10) when the probe pulse is applied to the control electrode 4 as a control signal.
The charging voltage is turned off for 0.3 μsec).

Since the deflection electric field is turned off, the charged ink particles pass through the knife edge 6 without being deflected and are captured by the conductive particle catcher 8 which is insulated from others at the home position.

Charge of the conductive particles catcher 8 captured charged ink particles, switches SW2, SW3 and SW4 which operates in conjunction via shielded wires 9 as a jet current I _j, the integrating capacitor C, and current consisting integrator OP It is input to the detector, integrated for a certain time, and appears as a voltage across the integration capacitor C.

Switches SW2, SW3 and SW4 is to remove noise and other noise due AC100V integrator OP is integrated by a jet current I _j, operating in synchronization with AC100V to transmit the A / D converter ADC .

In detail, in the synchronization signal generation circuit, 100V AC is stepped down by transformer T, clamped to 0V and 5V by diodes D1 and D2, and TTL (Tra) synchronized to 100V AC by Schmitt gate SG.
nsistor-Transistor Logic) level clock signal CK
make. This is set by a preset counter PSC and two flip-flops FF1 and FF2 by an integration end signal HOLD and an integration start signal shown in the timing chart of FIG. 2 (b).
▼ and make a reset signal RESET.

When the reset signal RESET becomes "H", the switch SW4 is closed, the integration capacitor C is short-circuited, and the output of the integrator OP is reset to 0V.

After one cycle of 100 V AC, when the reset signal RESET becomes “L”, the switch SW4 is opened. At this time, the integration end signal H
Since OLD is “L” (SW2: open) and the integration start signal ▲ ▼ is “H” (SW3: closed), the jet current I _j is
Flows into the virtual grounding point of the operational amplifier constituting, and integration is started.

When an integral multiple (3 times in the figure) of the AC100V cycle has elapsed since the start of integration, the integration end signal HOLD changes to "H" (switch
SW2 is closed), the integration start signal ▲ ▼ becomes an "L" (the switch SW3 is opened), the jet current I _j is cut off, so far into the integrating capacitor C to the integrated jet current I _j
Is held as the voltage output of the integrator OP. Now, the ink jet is charged so as to have a negative charge by the control signal (probe pulse) applied to the control electrode 4, so that the integrating capacitor C has the jet current I _{j in the} direction of the arrow.
Flows, and the output of the integrator OP becomes a positive voltage.

By the way, in an actual machine, it is almost impossible to completely shield the space from the conductive particle catcher 8 to the integrator OP from noise. Therefore, during integration operation, AC10
0V noise is superimposed on high frequency noise generated from other peripheral electronic devices. Among them, the high frequency noise is averaged and poses no problem because the integration time is sufficiently long as one cycle of 100 VAC or more. Further, since the integration time of the AC100V noise is set to an integral multiple of the cycle of the AC100V, the noise is averaged during the integration period and automatically removed.

When the integration is completed, the integration start signal ▲ ▼
Becomes "L" and the switch SW3 is opened, so that the jet current _Ij is turned off and, at the same time, the noise entering the integrator OP from the input side is cut off. Therefore, if only the integrator OP is sufficiently shielded, the noise is only noise generated internally, and the jet current _Ij can be measured with extremely high accuracy. As described above, in this embodiment, a very high-performance current detector can be configured with simple and inexpensive elements.

Jet current I converted to voltage by integrator OP
_j is converted into digital data by the A / D converter ADC and output to the data bus (not shown) of the MPU. Although not shown, the integration end signal HOLD is output to the MPU,
PU sends A / D to A / D converter ADC in synchronization with integration end signal HOLD.
Command the conversion operation.

Measurements of the jet current I _j described above, as shown in FIG. 4 (a), MPU is sequentially switches the multiplexer (2) MP2, 2πn / N (n = 0,1,2 respect excitation signal PCLK ,…, N
-1) pulse train theta ₀ with shifted _{phase, θ 1, θ 2, ...} , by driving the vibrator 3 sequentially exciting the nozzle 1 at theta _N-1, are performed for each phase.

The value of the jet current _Ij measured for each phase is A / D-converted by an A / D converter ADC, and the MPU RAM (not shown)
Are stored respectively.

FIG. 4B is a diagram showing an example of a result of plotting the values of the jet current _Ij measured for each phase using the test image data. The presence or absence of the half-charged ink particles is determined by observing with a microscope using a strobe light. ○ indicates that there is no half-charged ink particle, and ● indicates that there is a half-charged ink particle. The measurement result shows a tendency as shown in FIG. 4 (b) because the forbidden region appears in synchronization with the excitation signal, and when there is an intermediately charged ink particle, the jet current _Ij is small and the If no charged ink particles can be understood from the fact that the greater the jet current I _j (the U.S. Patent 4,839,665 and No. CHHertz and B.
A. Samuelsson, J. Imag. Tech. 15 , 141 (1989)).

The MPU uses a firmware algorithm to determine the optimal phase at which rising and falling edges of the control signal for phase fluctuations are completely separated into charged and uncharged ink particles and no midway charged ink particles are generated. (In the case of FIG. 4 (b), θ ₁₂ or θ ₁₃ ) is determined,
A multiplexer (2) MP2 is set to select theta ₁₂ or theta _13. In the case of N = 16, the jet current _Ij is measured while the phase θ is advanced in the direction of the arrow, and about three points before the phase giving the maximum value, that is, about 3.2π / 16
= 3π / 8 (67.5 °). The optimum phase is set by returning the phase to about three points before the phase of the peak value of the jet current curve, because the optimum phase is set in the middle of the phase range where the intermediately charged ink particles are not generated, and the jet current I _j This is to cope with the detection error of, the fluctuation of the value of the jet current _Ij after detection, and the like. Note that the optimal phase once set is not changed during recording of one recording medium, and recording of one recording medium is performed at the same phase.

When the phase adjustment is completed, the MPU switches the switch SW1 to the deflection power supply E1 side and applies a deflection voltage to the deflection electrode 7 in order to perform recording on the recording medium. Therefore, the deflection electric field is turned on, and the charged ink particles passing between the ground electrode 5 and the deflection electrode 7 are deflected toward the ground electrode 5 and cut by the knife edge 6. Also, the MPU
The multiplexer (1) switches MP1 to a state in which the output of the synchronization circuit SC is selected. This enables the high-voltage switch HVS
Is in a state where a pulse width modulation signal of image data is input.

On the other hand, during recording, image data synchronized with a pixel recording command signal DCLK generated from an output of a shaft encoder (not shown) directly connected to a rotating drum (not shown) is stored in a line buffer (not shown; rotating drum). From the line memory storing the image data for one rotation) to the pulse width modulator PM, where each image data is converted into a pulse width corresponding to the density gradation and sent to the synchronization circuit SC.

The synchronization circuit SC synchronizes (coincides) the rising or falling edge of the output of the pulse width modulator PM with the rising or falling edge of the excitation signal PCLK.

The output of the synchronization circuit SC is input to the high-voltage switch HVS via the multiplexer (1) MP1, and the high-voltage switch HVS amplifies the voltage to a potential required for ink-jet charging and applies the amplified signal to the control electrode 4 as a control signal. By this control signal, the ink jet is inductively charged, and the charged ink particles are deflected to the ground electrode 5 side by the action of the deflecting electric field and cut by the knife edge 6, and only the non-charged ink particles go straight and pass through the knife edge 6. Then, dots are formed on the recording medium wound around the rotating drum. As a result, the image data (the output of the pulse width modulator PM) is synchronized with the excitation signal PCLK, and the recording of one recording medium can be performed while maintaining the optimal phase relationship with the dropletization of the inkjet.

Note that once the ink jet is turned off, especially when the ink jet is turned off for a long time, the optimum phase state is slightly changed due to fluctuations in ink physical properties and fluctuations in ejection conditions due to temperature changes. It is desirable to perform a phase adjustment operation.

When the integration time is set to three times the cycle of 100 V AC as in the present embodiment, the reset section and the hold section are added to measure the jet current _Ij of one phase.
In the case of an area of 50 Hz, that is, 50 Hz, 0.1 sec is required. Therefore, even if 16 phases (N = 16) are measured, the time required for the phase adjustment is only 1.6 seconds (the processing time of the MPU is high and can be ignored). Even in the case of a color ink jet printer, four colors (C, M, Y, BK) (or three colors excluding BK) are processed in parallel, so the phase adjustment time is the same as in the case of a single color continuous jet type ink jet recording device. .

FIG. 5 is a configuration diagram showing a main part of a continuous jet ink jet recording apparatus according to another embodiment of the present invention. The continuous ejection type ink jet recording apparatus of the present invention delays the excitation signal PCLK when the continuous ejection type ink jet recording apparatus of the embodiment shown in FIG. 1 determines the optimal phase between the ink dropletization and the recording pulse. While the optimum phase is found by making the recording pulse delayed, the optimum phase is found by delaying the recording pulse. That is, in the continuous ejection type ink jet recording apparatus of this embodiment, the excitation signal PCLK is directly input to the oscillator driver VD, and the output of the multiplexer (2) MP2 is input to the probe pulse generator PG and the synchronization circuit SC. Is entered. Therefore, since all parts correspond to the parts in the continuous ejection type ink jet recording apparatus of the embodiment shown in FIG. 1, the corresponding parts are denoted by the same reference numerals and their detailed description is omitted.

Also in continuous jet type ink jet recording apparatus of this embodiment thus constructed, the control signal only in that the measurement of the jet electrode I _j by shifting the phase of (the probe pulse) by 2 [pi / N is different, the first It goes without saying that the phase between the excitation signal and the recording pulse is automatically and optimally adjusted in the same manner as in the continuous ejection type ink jet recording apparatus of the embodiment shown in the figure.

The present inventor conducted various experiments using the continuous jet type ink jet recording apparatus of the present invention. As a result, the jet current with a sufficiently high S / N ratio under the condition of 1 to 10 cycles of AC100V was obtained. It was confirmed that I _j could be measured.

〔The invention's effect〕

As described above, according to the present invention, the jet current is measured with high accuracy by reliably removing noise with an extremely simple configuration, and the time between the ink dropletization and the recording pulse is determined based on the measurement result. By automatically adjusting the optimum phase, the ink particles can be reliably controlled one by one, and the effect of eliminating the particle noise generated mainly in the highlight portion of the image due to the intermediately charged ink particles can be eliminated. is there.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main part of a continuous jet type ink jet recording apparatus according to an embodiment of the present invention, and FIG. 2 (a) generates a synchronization signal for synchronously controlling a current detector in FIG. FIG. 2 (b) is a circuit diagram showing a synchronous signal generating circuit, FIG. 2 (b) is a timing chart showing the operation of the synchronous signal generating circuit shown in FIG. 2 (a), and FIG. 3 is a continuous ejection type ink jet recording apparatus of this embodiment. 4A is a timing chart showing the relationship between the generation of the ink particles, the excitation signal, and the control signal (probe pulse) in FIG. 4. FIG. 4A shows the phase relationship between the probe pulse and the excitation signal in the continuous ejection type ink jet recording apparatus of this embodiment. FIG. 4 (b) is a timing chart, FIG. 4 (b) is a diagram showing an example of a measurement result of a relationship between a phase of an excitation signal and a jet current in the continuous ejection type ink jet recording apparatus of this embodiment, FIG. Block diagram showing the configuration of a continuous jet type ink jet recording apparatus according to another embodiment of the present invention, FIG. 6 is a block diagram showing an example of a conventional continuous jet type ink jet recording apparatus. In the figure, 1 ... nozzle, 2 ... ink electrode, 3 ... vibrator, 4 ... control electrode, 5 ... ground electrode, 6 ... knife edge, 7 ... deflection electrode, 8 ... conductive particles Catcher, 9 Shield wire, ADC A / D converter, C integration capacitor, CG reference oscillator, DG delay pulse generator, E1 deflection power supply, FD frequency divider, FF1, FF2… flip-flop, MP1… multiplexer (1), MP2… multiplexer (2), OP… integrator, PSC… preset counter, PG… probe pulse generator, PM… pulse width modulation SC, synchronization circuit, SW1 to SW4, switch, VD, vibrator driver.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-217256 (JP, A) JP-A-2-60752 (JP, A) JP-A-2-80947 (JP, A) JP-A 57-217 188379 (JP, A) JP-A-60-46259 (JP, A) U.S. Pat. No. 4,839,965 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 3/04

Claims (6)

(57) [Claims] 1. A jet forming means for forming an ink jet from a nozzle by pressurizing ink, an oscillating means for outputting an excitation signal having an oscillation frequency near a spontaneous particleization frequency of the ink jet, and an excitation signal from the oscillating means. The N (positive integer) phases are each delayed by 2πn / N (n = 0, 1, 2,..., N−1), and the vibrator mounted on the nozzle is excited by the delayed signal and synchronized with the excitation. Delay excitation means for dividing the ink jet into ink particles, and one of the excitation signals synchronized with the excitation signal from the oscillation means.
A charging means for charging the ink particles by a probe pulse having a time width shorter than a cycle; a conductive particle catcher electrically insulated from others to catch the ink particles charged by the charging means; A current detector for detecting the electric charge of the charged ink particles caught by the catcher as a jet current at predetermined time intervals; and N phases 2π of the delay signal by the current detector.
The jet current at n / N (n = 0, 1, 2,..., N−1) is detected, and the phase in the middle of the phase range in which no halfway charged ink particles are generated in the resulting jet current curve is delayed by the delay. And an optimal phase determining means for determining an optimal phase of the exciting means. 2. A jet forming means for forming an ink jet from a nozzle by pressurizing ink, an oscillating means for outputting an excitation signal having an oscillation frequency near a spontaneous particle formation frequency of the ink jet, and an excitation signal from the oscillating means. An exciting unit that excites the vibrator mounted on the nozzle and splits the inkjet into ink particles in synchronization with the excitation; and a rising or falling edge of the excitation signal in synchronization with the excitation signal from the oscillation unit. The probe phase is delayed by N (positive integer) number of phases 2πn / N (n = 0, 1, 2,..., N−1), and is shorter than one period of the excitation signal. A delay charging means for charging the ink particles; a conductive particle catcher electrically insulated from the others and catching the ink particles charged by the delay charging means; A current detector for detecting the charge of the charged ink particles caught by the child catcher as a jet current at predetermined time intervals; and the current detector detects N phases 2πn / N (n = 0, 1, 1) of the probe pulse. 2,..., N-1) is detected, and a phase in the middle of a phase range in which no halfway charged ink particles are generated in the resulting jet current curve is determined as an optimum phase of the delay charging means. A continuous ejection type ink jet recording apparatus comprising: a phase determination unit. 3. A deflecting electric field can be switched on / off. The deflecting means is provided with a deflecting means for deflecting the charged ink particles when on and turning the charged ink particles straight when off, and turning off the deflecting means when detecting the jet current. Claim 1 or 2
A continuous jet ink jet recording apparatus as described in the above. 4. The continuous jet ink jet according to claim 1, wherein said current detector comprises an integrator, and a plurality of switches for controlling the integration start, integration stop and reset operations of said integrator. Recording device. 5. The switch according to claim 1, wherein said plurality of switches are a commercial AC power supply of 100V.
5. The device operates in synchronization with the frequency of
A continuous jet ink jet recording apparatus as described in the above. 6. A step of injecting an ink jet from a nozzle to maintain a steady state, a step of applying an excitation signal to the nozzle to split the ink jet into ink particles, a step of turning off a deflection electric field, and a control electrode. Applying a probe pulse having a time width shorter than one cycle of the excitation signal in synchronization with the excitation signal, and sequentially switching the phase of the probe pulse to obtain N (positive integer) number of phases 2πn / N ( measuring the jet current at n = 0, 1, 2,..., N−1), and determining the phase in the middle of the phase range where no halfway charged ink particles are generated in the jet current curve obtained from the measured jet current. Determining the optimum phase between the ink dropletization and the recording pulse in the continuous jet ink jet recording apparatus. .