JPH02151447A - Ink jet recording apparatus - Google Patents

Abstract

PURPOSE:To perform stable recording by providing a current detection means for detecting the current flowing to conductive ink when jetting action without ink is performed and a driving control means for controlling a voltage pulse on the basis of the detection result of said current detection means. CONSTITUTION:When a voltage pulse is applied to one of electrodes 2, 3 in an initial state, a current passes through conductive ink 1 to flow between the electrodes 2, 3. Since the surface in contact with the conductive ink other than the electrodes 2, 3 of a recording head is insulating and the electrodes 2, 3 are connected to a drive circuit, the density of the current flowing to the conductive ink 1 becomes max. in the vicinity of the electrode 2 and the ink generated heat on the surface of the electrode 2 to generate an air bubble. The conductive ink 1 is emitted from an emitting orifice 4 by the pressure change at this time. By setting a pulse width between t1-t2 in the waveform of the drive voltage pulse applied to the electrode 2 or 3 and that of the current flowing to the conductive ink 1 between the electrodes 2, 3, the ink can be emitted by the generation/elimination of an air bubble of one time. Therefore, stable recording can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inkjet recording apparatus, and more particularly to a vibration control device in an inkjet recording apparatus.

L! i! L逢4 Conventional techniques related to the present invention include the following. US Pat. No. 3,179,042 describes that the ink is preheated by ejecting the ink using Joule heat (I"R loss) when electricity is applied to the conductive ink. Japanese Unexamined Patent Publication No. 61-242850 describes that energy adjustment is performed by detecting head temperature.In an inkjet method, ink droplets are ejected by heating (or generating heat) the ink.

The ejection state differs depending on the initial ink temperature. For this,
In the conventional example described above, the temperature of the ink or the head (or the vicinity of the head) is detected, and the heating is controlled to keep them within a certain temperature range, or the drive voltage pulse is controlled based on the detected temperature. In the former method, the heat generating part (
It is difficult to keep the temperature of the ink in the heating section and the temperature of the supplied ink constant, and the warm-up time is also long. In the latter case, since an average driving voltage pulse determined through experiments is applied, it is difficult to correct variations between heads or between nozzles.

1-Ikketsu The present invention was made in view of the above-mentioned circumstances.
In this method, conductive ink is energized to generate heat and bubbles, and the resulting pressure change causes ink droplets to be ejected.

The purpose of this invention is to provide an inkjet recording apparatus that detects a current waveform and applies an appropriate drive voltage pulse so as to generate stable bubbles (stable ejection).

In order to achieve the above-mentioned object, the present invention provides an inkjet recording apparatus that jets and records conductive ink from an ejection port by applying a voltage pulse to at least one of a pair of electrodes in contact with the conductive ink. The present invention is characterized by having a current detection means (16) for detecting the current flowing through the conductive ink at the time of dry ejection, and a drive control means (12) for controlling the voltage pulse based on the detection result. be. Hereinafter, the present invention will be explained based on examples.

FIGS. 1(a) to 1(c) are diagrams showing the state of bubble generation in the recording head of the inkjet recording apparatus according to the present invention. In FIG. 1, 1 is conductive ink, 2 and 3 are electrodes, and electrode 2 has a sufficiently smaller contact area with conductive ink 1 than electrode 3. In FIG.

Further, 4 is an ink ejection port. FIG. 1(a) shows the initial state, and by applying a voltage pulse to one of the electrodes 2 and 3, a current flows between the electrodes 2 and 3 through the conductive ink 1. The surface of the recording head other than electrodes 2 and 3 that contacts the conductive ink 1 is insulative, and the electrodes 2 and 3 are connected to a drive circuit (not shown). In (b), the current density flowing through the conductive ink 1 is at its maximum near the electrode 2, the ink generates heat on the surface of the electrode 2, and bubbles 8 are generated (I"R loss). (C) shows at this time. Conductive ink 1 due to pressure change
is discharged from the discharge port 4.

FIGS. 2(a) to 2(c) are diagrams showing other embodiments of the recording head and the bubble generation state thereof. FIG. 2 is similar to FIG. 1, but has a narrow passage 7 provided between electrodes 2 and 3, and the cross-sectional area (plane perpendicular to the current direction) of the narrow passage 7 is the same as the electrode 2.
By making the surface area sufficiently smaller than the surface areas of and 3, the current density in the narrow passage portion 7 increases, generating heat and generating bubbles 8.

FIG. 3 is a diagram showing the driving voltage pulse applied to the electrode 2 or 3 and the current waveform flowing through the conductive ink 1 between the electrodes 2 and 3, where (,) is the driving voltage pulse, and (b) is the current. Waveform,
(C) is a diagram showing the comparator output of FIG. 4. Set the pulse width between 10 and 11 in the current waveform in Figure 3 (
That is, between t□ and t2), ink can be ejected by generating and extinguishing bubbles once. When a driving voltage pulse (peak value vp, pulse width tw) is applied to one of the electrodes 2.3, a current flows through the conductive ink 1 between the electrodes 2 and 3, gradually generating heat and increasing the conductive bottom of the ink. At 9 in FIG. 3(b), where the current value increases as the current increases, the current path narrows and the current decreases due to the generation of air bubbles. It is cut off at 10 in Figure (b) (Figure 1 (b), Figure 2 (b)
(equivalent to), but the bubbles become even larger due to the heat storage up to that point (equivalent to Fig. 1 (C) and Fig. 2 (Q)). Eventually, the bubbles are cooled by the surrounding ink and the wall surface of the channel and shrink (at this time, the meniscus shown in FIGS. 1 and 2(c) is cut and ejected as droplets). During the shrinking process, the size of the bubbles changes to
When the current waveform in Figure 3 (b) reaches the same size as in Figure (b) and Figure 2 (b), the current waveform in Figure 3 (b) is 11, and as it is further reduced, a current begins to flow between electrodes 2 and 3. . After that, the current waveform and bubble repeat the same thing.

FIG. 4 is a block diagram of detection control of the inkjet recording apparatus according to the present invention, and FIG. 5 is a flowchart thereof. In the figure, 1 is conductive ink, 2.3 is an electrode, 12
is a control device (ml! dynamic control means) including a reference clock generation circuit, POM, and PAM.

MPU, i10. Includes timers, counters, etc. 1
3 is a programmable power supply, 14 is a switch control circuit, 1
5 is a switching circuit, 16 is a current detection circuit, 17 is a reference value generation circuit, and 18 is a comparator. For empty discharge, turn off the power
This is performed in various ways depending on the system, such as at N time, when a recording signal is input, or at fixed time intervals, but the current detection/drive control of the present invention performs a dry ejection immediately before recording when a recording signal is input. It is best to perform detection control using In that case, an appropriate drive waveform can be obtained.

Furthermore, if the peak value of the driving voltage pulse shown in FIG. 3(a) is made variable, El in FIG.

When E, E, the peak value is increased and the dry ejection is performed again to obtain an appropriate driving voltage pulse.

In Fig. 5, E□, E, ,E are the cases where bubbles remain in the flow path (recovery operation is sufficient)
, or when it is impossible to print due to extremely low temperatures (an abnormality is displayed, etc.). In FIG. 5, idle ejection is performed with Vps as the lowest voltage, and in the case of E, , E, , E, the peak value may be gradually increased from VPS and repeated as shown by the broken line.

Summer - End As is clear from the above explanation, according to the present invention, by utilizing the characteristic that the current is cut off by the bubbles generated by the heat generation of ink, the maximum ejection frequency and ejection stability allowable during dry ejection. The above t□ and t2 can be known by applying the dynamic voltage pulse of the maximum pulse lltws, and the appropriate pulse width (t□(t
u<t z ) can be selected. If tw is between 1 and t□, there is no change in the state of bubble generation and disappearance. Further, even when the environmental temperature is low or high, it is possible to obtain almost the same bubble generation and disappearance conditions, and stable recording can be performed. Furthermore, by making the peak value of the driving voltage pulse variable, it becomes possible to record in a wide environmental temperature range, and
More appropriate driving conditions can be selected. In other words, if tw is too long or too short, ejection becomes unstable, so when the environmental temperature is high (the ink conductivity is high), a voltage pulse with a low peak value is used, and when the environmental temperature is low, the voltage pulse is high. This can be achieved by applying a voltage pulse with a peak value.

In addition, in the inkjet recording apparatus of the present invention, as described above, since it is sufficient to select tw between t and t2, even if there is some variation between nozzles in the case of a multi-nozzle head, It is also possible to set the selection conditions based on the detection/control flow for one nozzle as the conditions for all nozzles.

[Brief explanation of the drawing]

FIGS. 1(a) to (Q) are diagrams showing the state of bubble generation in the recording head of the inkjet recording apparatus according to the present invention;
Figures 2 (a) to (c) are diagrams showing other embodiments of the recording head and their bubble generation states; Figure 3 is the current flowing through the conductive ink when a driving voltage pulse is applied between the electrodes; FIG. 4, a diagram showing waveforms, is a block diagram of detection and control of the inkjet recording apparatus according to the present invention. 1... Conductive ink, 2, 3... Electrode, 4... Discharge port. 12...Control device (IQM dynamic control means), 13...Programmable source, 16...Current detection circuit, 17.
...Reference value generation circuit, 18...Comparator. Figure 1 (a) Section 2 (a) (b) (b) (C) (C) Procedural amendment (bin) 1. Indication of the case 1986 Patent Application No. 306717 2, Name of the invention Inkjet recording device 3, Relationship with multiple amendments Patent applicant address 1-3-6 Nakamagome, Ota-ku, Tokyo Name (Name) ) (674) Ricoh Co., Ltd. Representative Hama
1) 1001 Chuo Dai-6 Kannai Building, 1-2-1 Furo-cho, Naka-ku, Yokohama 231, Japan 6. Brief description of the drawings in the specification subject to amendment No. 1: Core, Contents of amendment "This is a block diagram of detection and control." written on page 9, line 10 of the specification. This is a flowchart for

Claims (1)

[Claims] 1. In an inkjet recording device that ejects and records conductive ink from an ejection port by applying a voltage pulse to at least one of a pair of electrodes that are in contact with conductive ink, a blank discharge is performed to cause the conductive ink to flow at that time. An inkjet recording apparatus characterized by having a current detection means for detecting a current, and a drive control means for controlling a voltage pulse based on the detection result.