GB2277394A - Ink jet recording apparatus - Google Patents

Abstract

In an ink jet recording apparatus, relative timing of drop information and charging is adjusted in a test mode in accordance with an intergrated current valve from a drop catcher 8. <IMAGE>

Description

DESCRIPTION OF INVENTION Title: "Ink Jet Recording Apparatus" THIS INVENTION relates to an ink jet recording apparatus, and more particularly to an ink jet recording apparatus of the continuous jet type wherein ink is jetted continuously from a nozzle of an ink jet recording head.

Various ink jet recording apparatus are conventionally known and practically used. One of such conventional ink jet recording apparatus is of the continuous jet type wherein ink is jetted continuously from an ink jet recording head. An exemplary one of such conventional continuous jet type ink jet recording head is shown in Figure 8.Referring to Figure 8 the continuous jet type ink jet recording head shown includes an ink bottle 91 in which ink is accommodated, an ink pump 92 for applying a pressure to ink from the ink bottle 91 and sending out the thus pressurized ink, an ink tube 93 for supplying ink from the ink pump 92 therethrough, a nozzle 94 having a circular orifice of a very small diameter, an ink electrode 95 for holding the potential of ink in the nozzle 94 at a ground level, a vibrating element 96 in the form of a piezoelectric vibrating element mounted on the nczzle 4, a vbrating element driving vibrator 97 or applying an exciting signal to the vibrating element 96. a controlling electrode 98 having a circular opening or a sit-like opening coaxial with the nozzle 94 for receiving a controlling signal to control charging of a jet of ink.

a grounding electrode 9 disposed in front of the controlling electrode 98 and grounded itself. a knife edge 100 mounted on the grounding electrode 99, a deflecting high voltage dc power source Chereinafter referred to as deflecting power source) 101, and a deflecting electrode 102 connected to the deflecting power source 101 for cooperating with the grounding electrode 99 to produce therebetween an intense electric field perpendicular to an ink jet flying axls to deflect a charged ink drop to the grounding electrode 99 side.

The thus deleted charged ink drop is flown to a record medium 104 wrapped around a rotary drum 103.

In such conventional continuous jet type ink jet recording apparatus. ink pressurized by the ink pump 92 is introduced by way of the ink tube 93 into the nozzle 94, at which a Jet of the ink is formed fro3 the orifice thereof. The ink jet 18 is disintegrated into a train of ink drops with a spontaneous disintegrating frequency which depends upon a diameter and a flow rate of the ink jet and physical propertie of the Ink.In this instance if the exciting frequency of the vibrating element 96 mounted on the nozzle 94 is set to a value at or around the spontaneous disintegrating frequency, then disintegration will be synchronized with exci-ation of the vibrating element 96. and consequently, ink drops of a very uniform size are produced in accordance with the exciting frequency.

Ink drops disintegrated in this manner are charged. upon separation from the ink jet. by electrostatic induction by way of an integrating circuit composed of an electric resistance Rj of the ink jet and an electrostatic capacitance between the ink jet and the controlling electrode 98. Thus, if the controlling signal is a rectangular wave having an amplitude çc.

then a potential of an ink drop immediately before @ disintegration is given by #j - #c (1 - exp (-t/CjRj)) t the uniform ik drops separated from the ink jet are charge modulated in accordance with a controlling signal (recording pulse signal synchronized in phase Hirh h an exciting signal. then such charged ink drops will be deflected to the grounding electrode 99 side by an act con f he deflecting electr@c field and cut by the knife edge 100 while only non-charged ink drops are allowed to advance straightforwardly and pass by the knife edge 100 so that they form dots of ink on the record medium 104 rapped around the rotary drum 103.

Now, if the exciting frequency (disintegrating frequency) is set to T-d and an ink jet is pulse width modulated by a frequency of fd/n. then a picture image of n gradations with a controlled dot diameter can be recorded at the frequency of fs/n.

In the conventional continuous Jet type ink jet recording apparatus described above, the exciting signal to the vibrating element 96 and the controlling signal (recording pulse) to the controlling electrode 98 must be synchronized with each other maintaining a certain optical phase relationship. In particular, while an ink - dot is produced in synchronism with an exciting signal.

a timing at which an ink j et disintegrates into an ink drop is varied deli@ately during one period of an exciting signal by a variation of parameters such as a temperature, an ink pressure and physical propertits of ink. If such timing of disintegration and the controlling signal (recording pulse ee displaced in phase fro eac other, tn the electric resistance RJ of an ink Jet presents a very high value immediately before disintegration. and consequently. an edge of the controlling signal (recording pulse) comes within a region (hereinafter referred to as forbidden region) where the resistance is very high.Accordingly, charging of an ink drop takes place but incompletely.

and an incompletely charged ink drop is produced. If an incompletely charged ink drop is produced, then it is impossible to individually control ink drops accurately.

As a result. a spot-like noise is produced mainly at a highlight portion of a recorded picture image.

A technique of merely synchronizing an exciting signal and a controlling signal (recording pulse) with each other is disclosed. for example, in Japanese Patent Laid-Open Application No. 62-225363, Japanese Patent Lald-Open Application No. 63-264361 and so forth.

Meanwhile, a method cf determining an optimum phase between an exciting signal and a controlling signal (reoording pulee) ie disclosed. for example. in U.S. Patent No. 4, 839, 665, wherein an ink jet is charged either in accordance with a probe pulse having a smaller width than a period (1/f@) of an exciting signal or another probe pulse having a pair cf pulses having an equal amplitude and an equal pulse width within one period of suc exciting signal but having the opposite polarities to each other while changing the phase of the probe pulse. and a current which flows together with an ink Jet (such current will be hereinafter referred to as Jet current) is successively measured to find out an optimum phase from measured values of the Jet current.

However, such jet current is a very low current (10 to 100 nA) and a current source is exposed to various noises. With an actual machine, it is difficult to shield such current source from external noises.

Particularly. noises (hums) from a commercial power supply of. for example. ac 100 V matter.

A method of measuring a jet current is also disclosed in U.S. Patent No. 4.835.665 mentioned above wherein a current detecting resistor is interposed between an ink electrode and the ground to convert a jet current into a voltage. Another method wherein an ink electrode is connected to a virtual grounding point of an operational amplifier constituting a current to voltage converter is disclosed in No. PCT/US88/03311.

The two method: are advantageous in that. whore a @ontinuous jet type ink jet recording apparatus includes a plurality of nozzles like a color ink Jet printer. a jet current can be detected independently for each of the nozzles. However. in order to irtroduce all of Jet currents t a current detector, entire ink supplying systems from ink bottles to nozzles including ink pumps must be kept in an electrically isolated condition.

Further, each of such ink supplying systems includes a very long ink tube and so forth and accordingly makes a very harmful noise source. Accordingly. it is difficult to measure a jet current at a high S/N ratio.

A further method of detecting a jet current flowing between a grounding electrode and a deflecting electrode is disclosed in U.S. Patent No. 4, 839, 665 mentioned hereinabove. The method is superior to the method which makes use of an ink electrode in that a jet current can be measured at a high S/N ratio with low noises. However it has the following problems that: (1) while seasurement is easier on The grounding - electrode slde to which no high voltage is applied, in euch instance, the grounding electrode. which is soiled with waste liquid, must be kept in an @ isolated condition; and (2) even in a continuous jet type ink Jet recording apparatus such as a color ink jet printer which includes a plurality of nozzles. only one deflecting electrode and o: one grounding elecTrode are provided. and in this instance. since waste liquid from the nozzles come to the single grounding electrode. a jet current cannot be measured independently for each of the nozzles.

Also a method is disclosed in U.S. Patent No.

4, 839, 665 mentioned hereinabove wherein an electrically isolated conductive ink catcher is provided in front of a grounding electrode and a deflecting electrode. and a current detecting resistor is interposed between te, conductive ink catcher and the ground to detect a jet current. While the method is better then the two methods described above. since a signal source has a high impedance of 10@ to 101@ #, also the current detecting resistor must be high in resistance. which makes it easy to admit noises. Consequently.

measurement of a jet current at a high S/N ratio cannot be achieved. Thus. an alternative measuring method using an ac technique, that is, a method wherein a probe pulse is amplitude modulated and a jet current is detected by means of a narrow-band amplifier, is disclosed in U.S. Patent No. 4, 839, 665 mentioned above.

This method, however. still ha: a problem that a circuit system is complicated and expensive and the stability is low because an amplitude modulated probe pulse is used.

As described above. an .nk Jet printer such as s color ink jet printer normally includes a plurality of nozzles. In particular. where the conventional continuous set type ink jet recording apparatus described hereinabove with reference to FIG. 19 is constructed as such ink Jet printer. It ; includes a plurality of such continuous jet type ink jet recording heads as described above. In this instance, the continuous jet type ink jet recording heads are provided independently of each other while the grounding electrode 99. knife edge 100, deflecting power source 101 and deflecting electrode 102 are provided commonly to the ink jet recording heads. In such ink jet printer. the nozzles 94 of the ink jet recording heads are disposed in line either in an axial direction (hereinafter referred to as drum axial direction) or in a circumferential direction (hereinafter referred to as drum circumferential direction) of the rotary drum 103.

By the way. @i @ince the nozzles 94 are different in directions or axes of ink jets therefrom (nozzle axes) and in flying speeds of such ink jets, they must be adjustable in registration. However, where flying speeds 0:' ink jets are different, even if a controlling signal is received simultaneously by the controlling electrodes 98, times required for ink jets to reach a surface cf the rotary drum 104 are different fom each other. Consequently, the ink jets will be flown to displaced positions.

Adjustment in alignment of such nozzles 94 where they are arranged in line in an axial direction of the rotary drum 103 includes. as adjustment in a drum axial direction, mechanical leftward and rightward adjustment (in the drum axial direction) of the nozzles 94 and time lag adjustment of of recording picture element data for the nozzles 94 (by a distance between the nozzles 94).

and includes. as adjustment in a drum circumferentlal direction, time lag adjustment of recording picture element data for the nozzles 94.

Adjustment in registration in a drum circumferential direction is conventionally achieved by either of the following two registration adjusting mechanisms: (1) Accerding to such registration adjusting mechanism ae disclosed. fcr example. in Kent Bladh. Report 1.

Dept. Electr. Meas. , I Lund Inst. Tech. . 1982. pp. 112-114 or in Japanese Patent Lald-Open Application No. 62- 225969, del@y circuits having delay times adjustable independently of each other are provided for nozzle for four different colors (C (cyan), M (magenta), Y (yellow) and BK (black)). each of the delay circuits is composed of a serial-in/serial-out type shift register and an oscillator having a variable vibration frequency and having an output to be supplied zs a shift clock signal to the shut register.A time required until picture image data are outputted from the shift register after having been inputted to the shift register, that is. a delay time, can be adjusted by varying an output frequency of the oscillator.

(2) According to the other registration adjusting mechanism disclosed in Japanese Patent Laid-Open Application No. 62-33647. Japanese Patent Laid-Open Application No. 62-68761 and so forth. buffer memories (line buffers) are provided into which picture image data can be written at different addresses variable independently for four colors (C. M, Y and BK). Four color data are written into the buffer memories at different addresses which are displaced from each other by distances corresponding to distances between them.

and reading out (printing) of data from the buffer mDmorles is performed simultaneously for the four colors to compensate for the displacements of the nozzles.

With the first registration adjusting mechanism described above. f it is intended to raise the resoluion for registration adjustment to assure a wide range of adjustment. then the oscillator frequency of the oscillator must be raised and the number of bits must be increased. Accordingly. a shift register which is high in number of bits and can operate at a high speed (for example. a several hundreds to several kilobits shift register which operates by several megahertz) is required. However. such shift register is expensive and is not readily available. Accordingly. a plurality of shift registers which do not have a sufficiently large number of bits must be connected in series in use.

Further. since the resolution in time ls a reciprocal number to an oscillation frequency of the oscillator if such frequency varies. then the resolution in registration adjustment is varied.

Accord'ngly, in case registration adjustment is performed with a higher oscillation frequency so that a resolution for registration adjustment necessary at 2 minimum frequency may be assured. the resolution in registration adjustment may be unnecessarily high.

On the other hand, with the second registration adjusting mechanism described above. four color (C, M. Y and BK) picture data are written into the buffer memories at different addresses, field they are read out, upon printing, in synchronism with a picture element recording clock. Accordingly, a resolution in registration adjustment is a reciprocal number to a frequency of a picture element recording clock signal and is very low on a recording face because it is provided by recording dots on the recording face. Accordingly, the second registration adjusting mechanism is very low in resolution in registration adjustment and accordingly is not suitable for a high resolution printer.

In our co-pending U.K. Patent Application No.

9125474.8 (GB 2251710) there is described and claimed an ink jet recording apparatus, characterised in that it comprises: a plurality of nozzles for jetting therefrom ink jets; exciting means provided for each of said nozzles for causing an ink jet from the nozzle to disintegrate into drops of ink in response to an exciting clock signal; charging means provided for each of said nozzles for selectively charging such drops of ink from the nozzle in accordance with a controlling signal; said nozzles being arranged such that drops of ink formed from ink jets therefrom may impinge in an overlapping relationship at a location on a record medium supported on a rotary drum when all of said charging means for said nozzles are controlled by a same controlling signal; and a registration adjusting system including dot clock generating means for producing a first picture element recording clock signal from a rotary drum position signal representative of a rotational position of said rotary drum, said registration adjusting system further including registration adjusting means provided for each of said nozzles, each of the registration adjusting means including frequency multiplying means for multiplying a frequency of the first picture element recording clock signal to produce a first registration adjusting clock signal, start position delaying means for producing, from the first registration adjusting clock signal, a second registration adjusting clock signal which is delayed by a time corresponding to external variable instruction data from an original position pulse signal representative of an original position of said rotary drum, synchronizing means for producing, from the first picture element recording clock signal, a second picture element recording clock signal synchronized with the second registration adjusting clock signal and the exciting clock signal, a line buffer for storing picture image data therein and for being controlled in accordance with the second picture element recording clock signal to recall the stored data therefrom, controlling signal generating means for generating, from the second picture element recording clock signal, a loading signal delayed by a predetermined time, pulse width modulating means for receiving picture element data read out from said line buffer in response to the loading signal to output a pulse width modulating signal having a pulse width corresponding to the thus received picture image data, and high voltage switching means for voltage controlling the pulse width modulating signal to produce a controlling signal for the corresponding charging means.

It is an object of the present invention to provide an ink jet recording apparatus of the continuous jet type wherein an optimum phase between disintegration of a jet of ink and a recording pulse signal is automatically adjusted to assure high quality printing.

According to one aspect of the present invention, there is provided an ink jet recording apparatus of the continuous jet type, which comprises an electrically isolated conductive drop catcher, a current detector connected to the conductive drop catcher for detecting a jet current, and optimum phase determining means for determining an optimum phase relationship between disintegration of an ink jet and a recording pulse signal in accordance with a value of a jet current detected by the current detector.

In the ink jet recording apparatus of the continuous jet type, the current detector is connected to the electrically isolated conductive drop catcher and detects a jet current, and the optimum phase determining means determines an optimum phase relationship between disintegration of an ink jet and a recording pulse signal in accordance with a value of a jet current detected by the current detector.

With the ink jet recording apparatus of the continuous jet type, noises can be removed with ~~~~~~~~~~ certainty -rorn a jet current wit a very simple construction. and the jet current can be measured with a high degree of accuracy. Then, the optimum phase relationship between disintegration of an ink Jet and a recording pulse signal is automatically adjusted in accordance with a result of such measurement of the jet current. Consequently. ink drops can be controlled individually with certainty.Accordingly. drop noises which may otherwise be caused principally et a highlight portion of a recorded picture image by incompletely charged ink drops can be eliminated.

According to a further aspect of the present invention. there is provided an ink jet recording apparatus of the continuous jet type. which comprises jet forming means including a nozzle for pressurizing ink to form a Jet of such ink. oscillating means having an oscillation frequency at or around a spontaneous disintegrating frequency of an ink jet.

delay and exciting means for variably delaying an output of the oscillating means and exciting a vibrating element counted on the nozzle in response to the delayed signal to cause an ink jet to be diintegrated into ink drops in synchronism with such excitation, charging means for selectively charging an ink drop. deflecting means for selectively producing a deflecting electric field and deflecting a charged ink drop when a deflecting electric field is produced but allowing a charged ink drop TO advance straightforwardly when no deflecting electric field is produced. an electrically isolated conductive drop catcher, a current detector connected to the electrically isolated conductive drop catcher for detecting a jet current. and optimum phase determining means for determining an optimum phase of the delaying and exciting means in response to a value of a Set current detected by the current detector.

In the ink jet recording apparatus of the continuous jet type, the jet forming means pressurizes ink to form a jet of such ink from the nozzle. and the delaying and exciting means variably delays an output of the oscillating means having an oscillation frequency at or around a spontaneous disintegrating frequency of an ink Jet and excites the vibrating element mounted on the nozzle in response to the delayed signal to cause an ink jet to be disintegrated into ink drop; in syncnrcnism with such excitawion. The charging means selectively charges an ink drop. and the deflecting means selectively produces a deflecting electric field and deflects a charged ink drop when a deflecting electric field is produced but allows a charged ink drop to advance straightforwardly when no deflecting electrio rield is produced. The current detector connected to the electrically isolated conductive drop catcher detects a jet current. and the optimum phase determining means determines an optimum phase of the delaying and exciting means in response to a value of a jet current detected by the current detector.

Also with the ink jet recording apparatus of the continuous Jet type, noises can be removed with certainty from a jet current with a very simple construct.'=n. and the jet current can be measured with e hlgh degree of accuracy. Then. the optimum phase relationship between disintegration of an ink Jet and a recording pulse signal is automatically adjusted in accordance with a result of such measurement of the jet current. Consequently. ink drops can be controlled individually with certainty. Accordingly. drop noises which may otherwise be caused principally at a highlight portion of a recorded picture image by incompletely charged Ink drops can be eliminated.

According to a yet further aspect of the present invention -here is provided an nk jet recording apparatus of the continuous jet type. which comprises jet orming means including a nozzle or pressurizing ink to form a jet of such ink. osciliating means having an oscillatIon frequency at or around a spontaneous disintegrating frequency of an ink jet, exciting means for exciting a vibrating element mounted on te nozzle in response to an output of the oscillating means to cause an ink jet formed from the jet forming means to be disintegrated into ink drops in synchronism with such excitation. delaying and charging means for variably delaying an output signal of the oscillating means and selectively charging an ink drop with the thus delayed signal. deflecting means for select.vely producing a deflecting electric field and deflecting a charged ink drop when a deflecting electric field is produced but allowing a charged ink drop to advance straightforwardly when no deflecting electric field is produced. an electrically Isolated conductive drop catcher, a current detector connected to the electrically isolated conductive drop catcher for detecting a jet current. and optimum phase deter=ining means for determining an optimum phase of the delaying and charging means in response to a value of a jet current detected by the current detector.

In the an @ ink et recording apparatus of the continuous et type. the jet forming means pressurizes ink to form a Jet of such ink from the nozzle. and the exciting means ex@ites the vibrating element mounted on te nozzle in response to an output of the oscillating means having an oscillation frequency at or around a spontaneous disintegrating frequency of an ink jet to cause an ink jet forked from the jet forming means to be disintegrated into ink drops in synchronism with such excitation.The delaying and charging means variably delays an output signal of the oscillating means and selectively charges an ink drop with the thus delayed signal, and the deflecting means selectively produces a deflecting electric field and deflects a charged ink drop when a deflecting electric field is produced but allow a charged inx drop to advance straightforwardly when no deflecting electric field is produced. The current detector connected to the electrically isolated conductive drop catcher detects a jet current, and the optimum phase determining means dete-rmines an optimum phase of the delaying and charging means in response to a value of a jet current detected by the current detector.

Also with the ink jet recording apparatus of the continuous jet type. noises can be removed with certainty rom Z Jet current with a very sample construction, ad the jet current can be measured with a high degree of accuracy. Then the optimum phase relationship between disintegration of an ink jet and a recording pulse signal is automatically adjusted in accordance with a result of such measurement of the jet current. Consequently, Ink drops can be controlled Individually with certainty.Accordingly. drop norses which may otherwise be caused principally at a highlight portion of a recorded picture image by incompletely charged ink drops can be eliminated.

According to a yet further aspect of the present invention. there is provided an optimum phase determining method for an ink jet recording apparatus of the continuous jet type. which comprises the steps of jetting a jet of ink from a nozzle and thereafter holding a steady condition wherein such ink jet is jetted fr== the nozzle. the ink Jet dIsintegrating into ink drops. successively applying probe pulses of successively displaced phases to a controlling electrode for controlling charging of the individual ink drops while successively measuring a jet current for such phases. letting he ink drops paee by a deflecting electrode while no deflecting electric field is formed by the deflecting electrode. a::A determining, based on thus measured values of t:e jet current, an optimum phase between dlsintegraticn of an ink jet and a recording pulse to be applied to the deflecting electrode for formation of a deflecting electric field.

In the optimum phase determining method for an ink jet recording apparatus of the conTinuous Jet type.

a jet of ink is jetted from a nozzle. and thereafter a steady condition whereon such ink Jet is jetted from the nozzle is held. The ink jet disintegrates into ink drops. Probe pulses of successively displaced phases are successively applied to a controlling electrode for controlling charging of the individual ink drops while a jet current is successively measured for such phases.

The ink drops are let pass by a deflecting electrode while no deflecting electric field is formed by the deflecting electrode and an optimum phase between dieintegration of an ink jet and a recording pulse to be applied to the deflecting electrode for formation of a deflecting electric field is determined based on thus -measured values of the Jet current.

With the optimum phase determining method a jet current is measured with a high degree of accuracy, and he optimum phase relationship between dlsintegration of an ink jet and a recording pulse signal is automatically adjusted in accordance with a result of such measurement of the jet current. Consequently, ink drops can be controlled individually with certainty. Accordingly, drop noises which may otherwise be caused principally at a highlight portion of a recorded picture image by incompletely charged ink drops in an ink jet recording apparatus can be eliminated.

Embodiments of the invention are described below by way of example with reference to the accompanying drawings, in which: FIGURE 1 is a block diagram of an ink jet recording apparatus embodying the present invention; FIGURE 2 is a block diagram of a synchronizing signal generating circuit for generating a synchronizing signal for the synchronous control of a current detector of the ink jet recording apparatus of Figure 1; FIGURE 3 is a time chart illustrating operation of the synchronizing signal generating circuit of Figure 2; FIGURE 4 is a time chart illustrating a relationship among production of ink drops, an exciting signal and a controlling signal (probe pulse signal) in the ink jet recording apparatus of figure 2;; FIGURE 5 is a time chart illustrating a phase relationship between a probe pulse signal and an exciting signal in the ink jet recording apparatus of Figure 2; FIGURE 6 is a graph showing a result of measurement of a relationship between an exciting signal and a jet current in the ink jet recording apparatus of Figure 2, FIGURE 7 is a block diagram similar to Figure 1 but showing a modification of the apparatus of Figure 1, and FIGURE 8 is a block diagram showing a conventional continuous jet type ink jet recording apparatus.

Referring to Figure 1 there is shown another continuous jet type ink jet recording apparatus to which the present invention is applied. The ink jet recording apparatus includes a nozzle 1 having a circular orifice (not shown) of a very small diameter, an ink electrode 2 for holding the potential of ink in the nozzle 1 at a ground level, a vibrating element 3 in the form of a piezoelectric vibrating element mounted on the nozzle 1, a controlling electrode 4 having a circular opening or a slit-like opening coaxial with the nozzle 1 for receiving a controlling signal to control charging of a jet of ink in response to picture image data, a grounding electrode 5 disposed in front of the controlling electrode 4 and grounded itself, a knife edge 6 mounted on the grounding electrode 5, a deflecting power source El, a deflecting electrode 7 connected to the deflecting power source El for cooperating with the grounding electrode 5 to produce therebetween an intense electric field perpendicular to an ink jet flying axis to deflect a charged ink drop to ~~~ the grounding electrode 5 side, a switch SW1 for alternatively connecting the deflecting electrode 7 to te deflecting power scarce El or he ground. a reference cscillstor CG for generating a reference clock signal CLK, a frequency divider FD for frequency dividing such reference clock signal CLK into one N-th (N is a positive integer) to produce an exciting clock signal PCLK. a delay puse generator DG for successivey delaying the exciting clock signal PCLK to N stages in response to the reference clock signal CLK to produce a train of pulses #@, #1. #2, ... and #N-1, a multiplexer (2) for selecting one of the delayed pulses #@, , #1, #2, ... and #N-1. a vibrating element driver VD for driving the vibrator 3 in response to a pulse seiected by the multiplexer (2) MP2, a pulse width modulator PWM for converting picture image data into a pulse width corresponding to a density gradation. a probe pulse generator PG for producing, in synchronism with a rising or falling edge of the exciting clock signal PCLK, a probe pulse having a sufficiently small pulse width comparing wIth a period of the exciting clock signal PCLK, a synchronizing circuit SC for synchronizing a rising or falling edge of an output of te pulse width modulator PWM with a rising or falling edge of the exciting clock signal PCLK. another multiplexer (1) MP1 for selecting one of a probe pulse from the probe pulse generator PG and an output of te synchronizing circuit SC. a high voltage switch HVS for voltage amplifying an output of the multiplexer (1) P1 to produce a controlling signal to be applied to the controlling electrode 4. a conductive drop catcher 8 disposed at a location Chereinafter referred to as home position) forwardly of the grounding electrode 5 and deflecting electrode 7 and serving also as a detecting electrode, a shield line 9 having an end connected to the conductive drop catcher 8. a current detector or current to voltage converter composed of three switches SW2, SW3 and SW4, an integrating capacitor C and an integrator OP, and an analog to digital (A/D) converter ADC for converting an output of the current detector from an analog signal into a digital signal.

The delay pulse generator DG is constructed. for example. from a serial-in narallel-out type N-bit shift register.

The probe pulse generator PG is constructed. for example. from a monoctable. multivibrator which 1; triggered by an edge of an exciting clock signal PCLK.

The ilitegrating capacitor C suitably has a capacitance of 1 to 10 ?..- or so and preferably has h high insulation resistance suon as a polystyrol or polypropylene capacitor.

line integrator OP is constructed from an operational amplifier of an FET (field effect transistor) Input with which a leak current (less than 1 nA) can be ignored comparlng with a jet current Ij. and the input thereof is connected to a virtual grounding point thereof.

Also the switches SW2. SW3 and SW4 are each constructed from an FET with which a leak current can be ignored comparing with the jet current Ij.

Referring now to FIG. 2 , there is shown a synchronizing signal generating circuit for generating a synchronizing signal to cause the switches SW2. S3 and SW4 to operate In synchronism with commercial power supply of. for example. ac 100 V. The synchronizing signal generating circuit is composed of a transformer T. a resistor R. a pair of diodes D1 and D2. a preset counter PSC. and a pair of fli@-flo@s FF1 and FF2.

The preset counter PSC can be set to a variable preset value by way of a route not shown, and the int@gration time of the integrator OP can be arbitrarily set to * value an integral number of times the period of the commercial power supply or. ac 100 V by changing such preset value of the preset counter PSC. In the present continuous jet type ink jet recording apparatus. the integration time is set To three times the period of the commercial power supply ef ac 100 V as seen from FIG. 3.

A reset signal RESET. an integration starting signal HOLD and an integration ending signal HOLD are produced from the synchronizing signal generating circuit. Such reset signal RESET. integration starting signal HOLD and integration ending signal HOLD are fluxed to one period of the commercial power supply of ac 100 V, and when they present a high ("H') level, the switches SS4, SW3 and SW2 are closed, but when they present a low ("L") level, the switches SW4, SW3 and SW2 are open. respectively.

In operation. when power is made available to the continuous jet type ink Jet recording apparatus. an operating voltage is supplied to the circuit system shown in FIGS. 1 and 2, whereupon the circuit system starts its operation. First. a phase adjusting operation is performed. It is to be noted that such phase adjusting operation ir normally performed when a carriage (not shown) on which thQ nozzle 1 is carried is positioned at its home position and immediately before a recording operation is swatted. Where the continuous jet type l::k jet record nag apparatus is constructed as a color ink jet printer. it includes four or three such nozzles 1 fcr four colors (C (cyan), M (magenta). Y (yellow) and BK (black)) or three colors (C.M and Y) and a phase adjusting operation is performed parallelly for the four or three nozzles 1.

First, ink is pressurized by an ink pump (not shown) and introduced into the nozzle 1 by way of an ink tube (not shown). Consequently. an ink jet is jetted from the nozzle 1, and the nozzle 1 Is thereafter kept in suoh steady condition wherein an ink jet is being jetted. Meanwhile. an MPU (not shown) changes over the switch SW1 to the grounding side to change the level of te deflecting electrode 7 to a ground level.

Consequently, the deflecting electric field between the grounding electrode 5 and deflecting electrode 7 disappears. Consequently. also a charged ink drop can pass by the knife edge 6. Further, the MPU controls the multiplexer (1) MP1 to select an output of the probe pulse generator PG. Furthermore, the carriage on which the nozzle 1 le carried is set to the home position by a carriage motor (not shown).

Meanwhile. the reference oscillator CG develops a reference clock signal C K. and sch reference clock signal CLX is divided in frequency into one N-th (1/N) by the frequency divider FD thereby to fora an exciting pulse signal PCLK. Such exciting pulse signal PCLK has an exciting frequency PCLK (in the following description, a signal and a frequency of such signal are denoted by a same reference character) given by CLK/N.

For example, when the reference clock frequency CLK is CLK x 16 MHz and the dividing ratio N of the frequency divider FD Is N = 16. the exciting signal frequency PCLK is PCLK - 1 MHz (= 16/16). The exciting pulse signal PCLK outputted from the frequency divider FD is inputted to the delay pulse generator DG, probe pulse generator PG and synchronizing circuit SC.

The delay pulse generator DG receives the exciting clock signal PCLK as data and the reference clock signal CLK as a shift clock signal and outputs a train of N pulses #@, #@, #2, ... and #N-i having a same period as the exciting clock signal PCLK but having phases delayed successively by 2#/N from the exciting clock eignal PCLK. One of the N pulses ee, St. #2, ...

and #N-@ is selected by the MPU by way of the multiplexer (2) MP2 and transmitted to the vibrating element driver VD. The vibrating element driver VD excites the vibrating element 3 in response to an output signal of the multiplexer (2) MP2. Consequently. a jet of ink jetted from the nozzle 1 is disintegrated into ink drops n synchronism with such excitation of the vibrating element 3.

The probe pulse generator P5 generates. in a synchronized relationship with a rising or falling edge (which is same as that upon recording) of the exciting clock signal PCLK, such a probe pulse having a pulse width sufficiently short comparing with a period of the exciting clock signal PCLK as seen in FIG. 3. For example. when the exciting clock signal PCLK has a period of 1 psec (oscillated at 1 MHz), the pulse width of the Probe pulse from the probe pulse generator PG is 0 1 to 0.3 sec.

The probe pulse outputted from the probe pulse generator PG is inputted by way of the multiplexer (1) MP1 to the high voltage switch HVS. at which it is voltage amplified to form a controlling signal. and such controlling signal is applied to the controlling electrode 8. Accordingly, a drop of ink disintegrated in synchronism with excitation of the vibrating element 3 im charged in reeponee to such probe pulse. When the continuous jet type ink jet recording apparatus operates in such a manner as illustrated in FIG. 3 an ink drop is always charged. but a charging voltage is removed only while a probe pulse is applied as a controlling signal to the controlling electrode 4 (for example, for 0.1 to 0.3 sec).

Since the deflecting electric field is not present. even a charged ink is not deflected and passes by the knife edge 6 so that it is caught by te conductive drop catcher 8 located at the home position and electrically isolated from the other electric components.

Charge of charged ink drops caught by the conductive drop catcher 8 is lnputted as a Jet current Ij to the current detector, which is composed of the switches SW2. SW3 and SW4. integrating capacItor C and integrator OP. by way of the shield line 9. so that it is integrated for a fixed period of time by the integrator OP. The thus integrated charge appears as a voltage across the integrating capacitor C.

The switches SW2. SW3 and SW4 operate in synchronism with the commercial power supply of ac 100 V in cider to remove noises included in the commercial power supply of ac 100 V and any other noises from an input current to the integrator OP sc that only the jet current Ij may be integrated by the integrator OP and transmitted to the A/D converter ADC.

More particularly, in the synohronizing signal generating circuit shown in FIG. 2, the commercial power supply of ac 100 V is stepped down by the transformer T and clasped at O V and 5 V by the diodes D1 and D2, and a thus clamped signal is supplied to a Schmitt gate SG. at which a clock signal CX of a TTL (transistor-transistor logic) level synchronized with the commercial power supply of ac 100 V is produced.

From the clock signal CK. such an integration ending sIgnal HOLD. an integration starting signal HOLD and a reset signal RESET as shown in FIG.3 are produced by the preset counter PSC and flip-flops FF1 and FF2.

When the reset signal RESET changes fom a low level to a high level. the switch SW4 is closed to short-circuit the integrating capacitor C.

Consequently. the output of the integrator 0? is reset to O V.

When the reset signal RESET changes from a high level to a low level after one period of the commercial power supply of ac 100 V, the switch SW4 is opened.

Since the integration ending signal HOLD ic a a low level (the switch SW2 is open) and the integration staring signal HOLD is at a hgh level (the switch SW3 is closed) then. the jet current Ij will thereafter flow into a virtual grounded point of the operational amplifier constituting the integrator OP. thereby starting an integrating operation of the integrator OP.

When an interval of time equal to the predetermined integral number of times (three times in the case shown in FIG. 3 ) the period of the commercial power supply of ac 100 V elapses afttr starting of such integrating operation. the integration ending signal HOLD changes from a low level to a high level so that the switch SW2 is closed while the integration starting signal HOLD changes from a high level to a low level so that the switch SW3 is opened. Consequently, the jet current Ij is interrupted. and the jet current Ij which has been integrated by the Integrat:ng capacitor C till then is thereafter held as a voltage output of the integrator OP.Now, since an ink jet is charged in accordance with a controlling signal (probe pulse) applied to the controlling electrode so that it may have a negative charge. the jet current j flows in the direction indicated by an arrow mark in FIG. 1 into the integrating capacitor C. and the output of the integraTor OP presents a hh voltage.

By the way. 1= is almost impossible with an actual machine to perfectly shield a route between the conductive drop catcher 8 to the integrator OP from noises. Therefore. during an integrating operation.

noises included in the commercial power supply of ac 100 V and high frequency noises produced from peripheral electronic appliances are overlapped in an output of te Integrator OP. Among such noises, high frequency noises are averaged and do not matter because the integrating time is longer than one period of the commercial power supply of ac 100 V and sufficiently long. Meanwhile.

noises of the commercial power supply of ac 100 V are averaged during an integrating period and accordingly are removed automatically since the integrating time is set to an integral number of times the period cf the commercial power supply of ac 100 V.

After an integrating operation is completed. the integration starting signal HOLD changes from a high level to a low level so that the switch SWS is opened.

and consequently, simultaneously when the Jet current Ij is interrupted. also noises coming to the integrator OP from the i nput side are interrupted. Accordingly. if only the integrator OP is interrupted sufficiently, then noises which may matter are only those wiz are generated in the Inside of the integrator OP. and consequently. the jet current Ij can be measured with a very high degree of accuracy. In this manner, a current detector having a very high performance can be constructed using simple and inexpensive devices.

The Jet current IJ converted into a voltage by the integrator OP is then converted into digital data by the A/D converter ADC and outputted into a data bus (nct shown) to the MPU. It is to be noted that. though not shown. the integration ending signal HOLD is supplied to the MPU. and the MPU instructs the A/D converter ADC to perform an analog to digital converting operation in synchronism with the integration ending signal HOLD.

Such measurement of a jet current Ij described above is performed for each of the pulses #@. #1 #2, ... and #N-1, which are successively displaced in phase by 2#n/N (n = 0. 1, 2 ..., N-1) from the exciting clock signal PCLK. by successively changing over the multiplexer (2) NP2 so that the vibrator s may be successively driven in response to the pulses #2, #1, #2. ... and #N-@ to excite the nozzle 1 as seen from FIG. 5 A value of the jet current Ij measured for each of the phases is converted -rom an analog value to a data value by the /D converter ADC and stored into a RAM (random access memcry) (not shown) of the MPU.

FIG. 6 shows a result of plotting of values of the jet current IJ measured for the individual phases using test picture image data. Presence or absence of an incompletely charged ink drop is determined by observaticn on a stroboscope using a microscope and a small mark 0 represents absence of an incompletely charged Ink drop while another small mark # represents presence of an incompletely charged ink drop.The fact that the result of measurement indicates such a tendency as shown in FIG. 6 can be understood because such forbidden region as mentioned hereinabove appears in synchronism with an exciting signal and the jet current IJ is low when incompletely charged ink drops are present. but is high when no incompletely charged ink drop is present (refer to U.S. Patent No. 4, 839, 665 and C. H. Hertz and B. A. Samuelsson. J. Imag. Tech.. 15.

141. 1989).

The MPU determines, in accordance with algorism In the form of software, an optimum phase (#1@ or #@ @ in FIG. 6) with which charged ink drope and non-charged ink drops are separated completely from each other wi-h respect to a rising or falling edge of a controlling signal against a variation in phase and no incompletely charged ink drop is produced. Then, the MPU controls the multiplexer (2) MP2 to select the phase #12 or eia.

In the case of N = 16. the Jet current Ij is successively measured while the phase 6 is varied in the direction indicated by an arrow mark in FIG. 6 . and preferably the optimum phase is set to a phase prior by three phase distances or so to another phase at which the jet current IJ presents a maximum value, that is, to a phase prior by amount 3 2v/16 @ 3#/8 (67.5 degrees) to such phase. It is to be noted that an optimum phase set once in this nanner will not be changed during recording on one page of a record medium.Consequently. recording on one page of a record medium is performed in a same phase After completion of such phase adjustment, the MPU changes over the switch SW1 to the deflectIng power source El side to apply a deflecting voltage to the deflecting electrode 7 in order to perform recording on a record medIum. Consequently. a deflecting electric field is produced so that a charged ink drop pasting between the grounding electrode 5 and the deflecting electrode 7 will be deflected to the grounding electrode side and cut by the knife edge 6. Further. the MPU changes over the multiplexer (1) MP1 so as to select an output of the synchronizing circuit SC.Consequently. a pulse width modulating signal for picture element data will be inputted to the high voltage switch HVS.

On the other hand, upon recording. picture element data, which are synchronized with a picture element. recording instruction signal DCLK produced from an output of a shaft encoder (not shown) directly coupled to a rotary drum (not shown), are transmitted from a line buffer (not shown; a line memory in which picture image data for one full rotation of the rotary drum are stored) to the pulse width modulator PWM. at which each picture image data are converted into a pulse width corresponding to a gradation in density thereof.

An output of the pulse width modulator PWM is transmitted to the synchron:zing circuit SC.

The synchronizing circuit SC synchronizes a rising or falling edne of the output of the pulse width modulator PWM with a rising or falling edge of an exciting clock sIgnal PCLK.

An output of the synchronizing circuit SC is inputted by way of the multiplexer (1) MP1 to the high voltage switch HVS. at which it is voltage amplified to a potentIal necessary for charging of an ink jet to produce a controlling signal. Such controlling signal @@ applied to.the controlling electrode 4. A jet of ink is thus induction charged in response to such controlling signal. and a drop of the thus charged ink is deflected to the grounding electrode 5 side by an action of the deflecting electric field and ct by the knife edge 6 while only a non-charged ink drop is allowed to advance straightforwardly so that it passes by the knife edge 6 and forms a dot on a record medium wrapped on the rotary drum. Consequently, recording on one page of the record medium can be performed while picture image data (output of the pulse width modulator PWM) are synchronized with the exciting signal FCLK and besides held in an optimum phase relationship with disintegration of an ink jet.

It is to be noted that, when an ink jet is interrupted once. particularly when such interrution of an ink jet continues for a long time. an optimum phase condition 16 varied delicately by a variation cf physical property values of ink by variation of the temperature or by a variation of jetting condItions, and accordingly. it is desirable to perform a phase adjusting operation immediately before startling of each record operation.

Further. in case the integration time is set to three times the period of the commercIal power supply of ac 100 V as in the continuous jet type ink jet recording apparatus described above. a resetting sectlon and a holding section must be added, and consequently, a total of 5 periods of the commercial power supply of ac 100 V, that is. in the case of a 50 Hz area, a total of 0.1 sec, is required for measurement of a jet current Ij of one phase. Accordingly. even if measurement is performed for a total of 16 phases (N = 16). a total time required for phase adjustment is only 1.6 seconds (the processing time of the MPU can be ignored because it operates at a very high speed). Even in the case of a color ink jet printer, since measurement is performed parallelly for four colors (C, M.Y and BK) or three colors (C, M and Y), a time required for phase adjustment is equal to that of a continuous jet type Ink jet recording apparatus for a single color.

Referring now to FIG. 7, there is shown a modification to the continuous jet type ink jet recording apparatus of FIG. 1 . The modified continuous jct type ink jet recording apparatus is constructed such that, while the continuous jet type ink jet recording apparatus of FIG. 1 is constructed such that. in order to determine an optimum phase between disintegration of an ink jet and a recording pulse. an exciting clock signal PCLX is delayed to find out an optimum phase, a recording pulse is delayed to find out an optimum phase.

In particular, the present continuous jet type ink jet recording apparatus is modified such that an exciting clock signal PCLK outputted from the frequency divider FD is lnputted directly to the vibrating element driver VD, and an output of the multiplexer (2) MP2 is inputted to the probe pulse generator PG and the synchronizing circuit SC.

Also with the present continuous Jet type ink jet recording apparatus constructed in this manner, a phase between an exciting clock signal and a recording pulse is automatically adjusted to an optimum one similarly as with the continuous jet type ink jet recording apparatus of FIG. 1 while it is only different that a phase of a controlling signal (probe pulse) is successively displaced by 2n/N to different stages when measurement of the Jet current Ij is proceeded, It is to be notcd that several exarinatione have been conducted using a continuous jet type ink jet recording apparatus manufactured in accordance with the present invention, and it has been confirmed from the examinations that a jet current Ij can be measured at a sufficiently high S/N ratio so far as the integrating time ranges from 1 to 10 periods of the commercial power supply of ac lOOV.

Claims (10)

1. An ink jet recording apparatus of the continuous jet type, characterised in that it comprises: an electrically isolated conductive drop catcher (8); a current detector (SW2, SW3, SW4, C, OP) connected to said conductive drop catcher (8) for detecting a jet current (Ij); and optimum phase determining means (MPU) for determining an optimum phase relationship between disintegration of an ink jet and a recording pulse signal in accordance with a value of a jet current (Ij) detected by said current detector (SW2, SW3, SW4, C, OP).

2. An ink jet recording apparatus of the continuous jet type as set forth in claim 1, characterised in that said current detector (SW2, SW3, SW4, C, OP) includes an Integrator (OP). and a plurality of switches (SW2. SW3.

SW4) for controlling starting and ending of an integrating operation and resetting of said integrator (OP).

3. An ink jet recording apparatus of the continuous jet type as set forth in claim 2, characterized in that said switches (SW2, SW3, SW4) operate in synchronism with a frequency of an available commercial ac power supply

4. An ink jet recording apparatus of the continuous jet type. characterized in that it comprises: jet forming means (1) including a nozzle (1) for pressurizing ink to form a Jet of such ink: oscillating means (CG) having an oscillation frequency at or around a spontaneous disintegrating frequency of an ink jet; delaying and exciting means (FD.DG. MP2. VO) for variably delaying an output of said oscillating means (CG) and exciting a vibrating element (3) mounted on said nozzle (1) in response to the delayed signal to cause an ink jet to be disintegrated into ink drops in synchronism with such excitation; charging means (4) tor selectively charging an ine drop; @ @@ deflecting means (5, 7) for selectively producing a deflecting electric field and deflecting a charged ink drop when a deflecting electric field is produced but allowing a charged ink drop to advance straightforwardly when no deflecting electric field is produced; an electrically isolated conductive drop catcher (8); a current detector (SW2, SW3. SW4, C.OP) connected to said electrically isolated conductive drop catcher (8) for detecting a jet current (Ij): and optimum phase determining means (MPU) for determining an optimum phase of said delaying and exciting means (FD. DG. MP2. VD) in response to a value of a jet current (Ij) detected by said current detector (SW2, SW3, SW4. C, OP).

5. An ink jet recording apparatus of the continuous jet type as set forth in claim 4@ characterized in that said current detector (SW2. SW3. SW4. C. OP) includes an integrator (OP), and a plurality of switches (SW2, SW3.

SW4) for controlling starting and ending of an integrating operation and resetting of said integrator (OP).

6. An ink Jet recording apparatus of the continuous jet type as set forth in claim 5, characterized in that said switches (SW2, SW3. SW4) operate in synchronism with a frequency of an available commercial ac power supply.

7 An Ink Jet recording apparatus of the continuous jet type, characterized in that it comprises: jet forming means (1) including a nozzle (1) for pressurizing ink to form a jet of such ink; oscillating means (CG) having an oscillationfrequency at or around a spontaneous disintegrating frequency of an ink jet; exciting means (VD) for exciting a vibrating element (3) mounted on said nozzle (1) in response to an output of said oscillating means (CG) to cause an ink jet formed from said jet forming means (1) to be disintegrated into ink drops in synchronism with such excitation: delaying and charging means (FD. DG.MP2) for variably delaying an output eignal of said oscillating mean: CCG) and selectively charging an ink drop with the thus delayed signal; deflecting means (7) for selectively producing a deflecting electric field and deflecting a charged ink drop when a deflecting electric field is produced but allowing a charged ink drop to advance straightforwardly when no deflecting electric field is produced; an electrically isolated conductive drop catcher (8); a current detector (SW2. SW3, SW4, C, OP) connected to said electrically isolated conductive drop catcher (8) for detecting a jet current (Ij) ; and optimum phase determining means (MPU) for determining an optimum phase of said delaying and charging means (FD. DG.MP2) in response to a value of a jet current (Ij) detected by said current detector (SW2, SW3, SW4, C, P).

8. An ink jet recording apparatus of the continuous jet type as set forth in claim 7 characterized in that said current detector (SW2. SW3, SW4. C, OP) includes an integrator (OP), and a plurality of switches (SW2, SW3.

SW) for controlling starting and ending of an integrating operation and resetting of said integrator (OP).

9. An ink jet recording apparatus of the continuous Jet type as set forth in claim 12, characterized in that said switches CSW2. SW3 SW4) operate in synchronism with a frequency of an available commercial ac power supply.

10. An optimum phase determining method tor an ink Jet recording apparatus of the continuous jet type, characterised in that it comprises the steps of: jetting a jet of ink from a nozzle (1) and thereafter holding a steady condition wherein such ink jet is jetted from said nozzle (1), the ink jet disintegrating into ink drops; successively applying probe pulses of successively displaced phases to a controlling electrode (4) for controlling charging of the individual ink drops while successively measuring a jet current (Ij) for such phases; letting the ink drops pass by a deflecting electrode (7) while no deflecting electric field is formed by said deflecting electrode (7); and determining, based on thus measured values of the jet current (Ij), an optimum phase between disintegration of an ink jet and a recording pulse to be applied to said deflecting electrode (7) for formation of a deflecting electric field.

il. An ink jet recording apparatus substantially as hereinbefore described with reference to, and as shown in, Figures 1 to 6 of the accompanying drawings.