JPS5842833B2 - charging voltage generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charge-controlled inkjet printing device in which ink droplets ejected from a nozzle are charged in accordance with an image signal and deflected by a deflection electrode to form an image on recording paper. This invention relates to a charging voltage generator that provides a charging voltage to a charging voltage generator.

In this type of inkjet printing device, ink is ejected from a nozzle by excitation at a predetermined frequency, and becomes an ink droplet at a position a certain distance from the tip of the nozzle.

The rate of formation of this ink droplet is determined by the excitation frequency of the ink jet.

In order for the charging electrode to apply a charge to the ink droplet in accordance with the image signal (representing the position of the printed pixel), the voltage application to the charging electrode in accordance with the image signal must be set in a certain synchronous relationship with the formation of the ink droplet. Must be.

Since this synchronization setting is extremely difficult, conventionally, prior to printing or when the inkjet head returns, a voltage for charging phase search is applied to the charging electrode to detect the charging phase of the ink droplet. This sets the charge phase during photo recording.

To prevent ink droplets from colliding with the recording paper during charging phase search, that is, to prevent ink droplets from hitting the recording paper when detecting the charging phase during recording operation, such as when the inkjet head returns. During charging phase retrieval, a voltage of opposite polarity to that during application is applied to the charging electrode to collect both charged and uncharged ink droplets in the gutter.

Therefore, in this case, a charging voltage generator that applies a charging voltage to a charging electrode is conventionally composed of two sets of amplifier circuits that generate a charging voltage of positive polarity and a charging voltage of negative polarity. The output voltage is selectively applied to the charging electrodes by a mechanical switch such as a mercury relay that switches in response to a search command signal.

(For example, Japanese Patent Application Laid-Open No. 52-2123).

The use of two sets of amplifier circuits and expensive mercury relays increases the cost of the circuit, and the switching operation speed is slow, which poses a problem in speeding up the phase search.

Furthermore, there is a limit to the lifespan of the mechanical switch means.

The present invention has been made for the purpose of reducing the number of amplifier circuits that amplify input pulses to the charging voltage level and omitting mechanical switch means in a charging voltage generator that selectively outputs charging voltages of positive and negative polarity. It is something that

First, an example of the configuration of a charge control type inkjet printing apparatus equipped with the charge voltage generator of the present invention is shown in FIGS. 1 and 2.

In FIG. 1, 1 is an ink tank, 2 is an ink jet nozzle, 3 is a charging electrode, 4 is a deflection electrode, 5 is a gutter, and 6 is a recording paper.

Vibration is applied to the nozzle 2 or the ink liquid in the nozzle by an electrostrictive vibrator, and the electrostrictive vibrator is excited and energized based on the output pulse of the excitation signal generator 7 via the amplifier AMP1.

This excitation signal generator 7 can be of a conventionally known type, or, for example, divides a clock pulse to obtain a pulse with a certain period, and uses this to energize a mono-multi-by-break to generate an excitation signal with a constant period and a constant pulse width. It is also possible to have a configuration that generates.

The charging electrode 3 is connected to a bipolar amplifier AMP 2, that is, a charging voltage generator, which switches the output between positive polarity and reverse polarity according to the input signal. Further, during printing and recording, a charging voltage is applied based on the output pulse of the charging signal generator 9.

This charge signal generator 9 may be of a conventionally known type, and is equipped with a mono multi-bi break and an analog gate, and generates a pulse with a constant width by energizing the mono multi-bi break with a charge reference signal. It may also be configured to output an image signal (the level of which represents the printing pixel position) by opening (turning on) the analog gate.

A charging phase reference signal is applied to search signal generator 8 and charging signal generator 9 from phase setting circuit 10 through AND gates AND1 and AND2, respectively.

For example, as an example of optical charge detection, during a phase search, when the charge phase is appropriate and the charged ink droplets in flight coalesce, for example, the ink droplet detection means is used as an ink droplet detection means at a flying position where three ink droplets are integrated. The used photosensor 1 is installed, and its ink droplet detection signal is amplified by an amplifier AMP3 and given to a frequency discrimination circuit 12.

The general operation of the apparatus shown in FIG. 1 will be explained as follows.

When the frequency of the output pulse a of the clock pulse generator CLG is fa and its period is Ta, the excitation signal generator 7 generates an excitation pulse b having a frequency of fa/8 and a pulse width of 4Ta in this example.

As a result, ink is ejected from the nozzle 2, and ink droplets are formed at a speed of fa/8 after the ejection column is cut off.

Phase setting circuit 10E, frequency is fa/8 and pulse width is T.
Eight sets of pulses having phases of Ta are generated, and one set k of them is applied to a search signal generator 8 and a charge signal generator 9 through AND gates AND1 and AND2, respectively.

The search signal generator 8 successively extracts two adjacent pulses at the period of droplets continuously formed with the pulse k of that phase, deletes one pulse, and then extracts the next pulse. By repeating extraction and deletion of pulses such as extracting two pulses, a Ta pulse width search signal (phase search pulse) is created in which every second pulse is deleted.

The charge signal generator 9 generates a printing charge signal (printing charge pulse) centered on the phase of the pulse, with a pulse width of, for example, 4Ta, and a pulse height of an image signal level (representing a pixel position).

Now, the search command signal Z (low level "O" during printing and recording,
When the high level "1" at the time of retrieval) is "1", the amplifier AMP2 is switched to the output mode with the opposite polarity to that at the time of printing, and the output k of the phase setting circuit 10 is outputted by the AND gate AND.
1 to the search signal generator 8, and if the phase of this output is in a certain proper phase relationship with the excitation signal, the ink droplets exiting through the charging electrode 3 will have two adjacent ink droplets at the time of printing. A positive charge is the opposite of the charge, the next one is uncharged, the next two are positively charged, and so on, resulting in intermittent charging, and the repulsion between positively charged ink particles and the charged ink particles and uncharged ink particles. Due to the suction force, the three ink droplets quickly merge into one, and when they pass just in front of the photo sensor 1, the number of ink droplets becomes fa/24.

If the phase of the output of the phase setting circuit 10 is inappropriate, the ink droplets will not be charged, and therefore the number N of ink droplets passing just in front of the photosensor 1 will be fa/24〈N≦f
It becomes a/8.

When fa/24, the frequency discrimination circuit 12 outputs a significant signal and fixes the phase of the output pulse of the phase setting circuit 10 as it is, and when fa/24<N≦fa/8, the phase setting circuit 10 automatically outputs a significant signal. The phase of the output pulse is sequentially advanced or delayed at each time.

This is done by sequentially switching and outputting the aforementioned eight sets of fa/8 pulses to form pulses.

In this way, when a certain set of eight pulses is being output, the detection frequency becomes fa/24, and the phase shift operation of the phase setting circuit 10 is stopped.

In this state, the printing and recording operation begins, and the AND gate AMD
1 is closed (off) and AND2 is opened, the amplifier AMP2 accordingly changes the output voltage polarity (positive polarity) during printing.
Then, the inkjet printing is performed with the number of ink droplets of fa/8, and the ink liquid travels as shown by the dotted line in FIG. 1 in accordance with the image signal and hits the recording paper 6 or the gutter 5.

If the search signal generator 8 generates intermittent pulses by outputting two consecutive output pulses from the phase setting circuit 10, deleting the next two pulses, and outputting the next two pulses, it will not work normally. When the ink droplets are charged, the two ink droplets coalesce into one ink droplet, and the ink droplet detection frequency of the photosensor 11 is the frequency fa of the excitation signal.
/8 becomes fa/16.

In this case as well, the presence or absence of charge is determined by the frequency determination circuit 12 as in the case described above.

The photosensor 11 may be placed at a position 11F immediately in front of the gutter 5.

In addition, instead of the photosensor 11, a mechanical-electrical conversion means such as a piezo element for detecting the collision of ink droplets is installed in the gutter 5.
It may be installed in the inner space.

In the inkjet printing apparatus shown in FIG. 2, the charge detection circuit 14 is energized when detecting the charge phase, and detects the potential change between each electrode of the charge detection electrode 13. Ink droplet is charged on detection electrode 1
3, a charge detection signal is given to the search signal generator 8.

The search signal generator 8 is activated by the search command signal Z and synchronized with the output clock a of the clock pulse generator CLG, and generates a plurality of sets (for example, 8 sets of pulses c-J) are generated.

Then, for the excitation signal, one of c--3 (for example, C) is applied to the amplifier AMP2 for a certain period of time, and the next one of c = j (for example, d) is applied to the amplifier AMP2 for the next certain period of time. Similarly, other values (for example, e-'-J) are sequentially given at regular intervals.

As a result, a charging voltage whose phase is shifted by 2π/n is applied to the charging electrode 3 at regular intervals in synchronization with the period of the excitation signal, and during this period, the charging detection circuit 14 detects the charging of the ink droplet. It is detected and notified to the search signal generator 8.

The search signal generator 8 detects the charging phase by determining the charging phase of the ink from the phase of the search signal from which the charging detection signal has arrived, and sets the phase of the output pulse of the charging signal generator 9 as the charging phase.

As mentioned above, the amplifier AMP used as a charging voltage generator
2, it is required to output a voltage of a certain polarity during printing and recording, and to output a voltage of the opposite polarity during charge phase retrieval.

FIG. 3a shows an embodiment of the charging voltage generator of the present invention used as the amplifier AMP2, and FIG. 3b shows input and output waveforms of each part thereof.

The configuration and operation of the charged voltage generator shown in FIG. 3a will be explained below with reference to the waveforms shown in FIG. A charge pulse and a phase search pulse are input.

Transistor Tr1 corresponds to the level of these pulses.
The conductivity of is determined, and a pulse with a charging voltage level corresponding to the pulse level is obtained.

In response to the output of the amplifier circuit, a time constant circuit is formed with a capacitor C1 and a resistor R8, and diodes D1 and D2 are connected in antiparallel with switching transistors T, 2 and T, 3 to a resistor R3 whose one end is grounded. A positive polarity and a negative polarity clamp circuit CLP are configured.

The transistor Tr2 is "off" when the printing command signal Z is at the positive level "1" and the "charged phase search" is commanded, and opens the short-circuit path by the diode D1. Transistor Tr3 is "on" via a switching circuit made up of transistors Tr4 and Tr5, closing the short circuit created by diode D2.

Therefore, when Z = rlJ, that is, "when searching for a charged phase," transistor Tr3 is on, and therefore diode D2 is on, and its bottom is clamped to the zero voltage level with respect to the output voltage pulse of the amplifier circuit. A voltage pulse of positive polarity (plus with respect to ground) is applied to the charging electrode 3.

When the printing command signal Z is at the low level "0" (printing record), the transistor T is on and T3 is off, so the diode D2 is on, and in response to the output voltage pulse of the amplifier circuit, Its top will be clamped to the zero voltage level, and a negative pulse voltage will be applied to the charging electrode 3.

The voltage level of this negative pulse voltage is the voltage level of the transistor Tr.
This value corresponds to the conductivity of l, that is, the pulse height of the printing charge pulse.

In this way, as the input signal Vi switches between the printing charge pulse and the phase search pulse in response to changes in the phase search command signal Z, the voltage polarity changes as shown by o in FIG. 3b. Opposite imprint charging voltage and phase search charging voltage are output.

In addition, when the polarity of the printing charging voltage and the phase search charging voltage are set to be opposite, it is necessary to set the phase search signal Z to be "0" and "1" as the "imprint charging command" on the phase search command. good.

As described above, in the present invention, the impression and drop charge voltage and the reverse polarity voltage for phase search can be obtained by one set of amplifier circuits.

In addition, since no mechanical switch means such as a mercury relay is used, ink droplets are alternately charged during phase search charging.
Or, its applicability in cases where high-speed polarity switching is required, such as when carrying out a phase search method in which ink droplets are quickly combined by forming a set of two consecutive ink droplets and charging each set with opposite polarity, alternately positive and negative. is a dog.

[Brief explanation of the drawing]

FIGS. 1 and 2 are block diagrams showing an inkjet printing apparatus using the charging voltage generating device of the present invention. FIG. 3a is a circuit diagram showing one embodiment of the present invention, and FIG. 3b is a waveform diagram showing its input and output. 1... Ink tank, 2... Nozzle, 3.
...Charging electrode, 4...Deflection electrode, 5...
... Gutter, 6 ... Recording paper, 11 ...
... Photosensor, 13... Charge detection electrode, A
MC...Amplification circuit, CLP...Clamp circuit, Ti2s'rr3..."" Transistor (
switching element).

Claims (1)

[Scope of Claims] 1. An inkjet printing device in which ink droplets ejected from a nozzle are charged by a charging electrode, and a deflection electrode deflects the ink droplets according to the amount of charge to print the ink on recording paper. In a charging voltage generator that applies charging voltages having mutually different polarities to charging electrodes during phase search charging and printing recording charging according to both the phase search pulse and the printing charging pulse as well as the search command signal; An amplifier circuit that generates a voltage pulse of a charge level in response to a phase search pulse and an imprinted charge pulse, and a semiconductor switching element that is turned on or off according to a search command signal, and when the search command signal instructs a search, the amplification circuit It is equipped with a clamp circuit that aligns the top and bottom of the output voltage pulse of the circuit to zero voltage level, and the other to zero voltage level when no search is instructed. A charging voltage generator characterized by being configured to generate a charging voltage.