JPH0132783B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a particle phase detection method for a so-called charge-controlled inkjet printer, in which the charge of ink droplets ejected and generated from a nozzle is controlled and an image is obtained by deflection.

Droplet charging methods for inkjet printers generally include a two-value charging method, which forms charged and uncharged droplets according to a charged/uncharged signal, and a deflection method, which gives the droplet an amount of charge that corresponds to the position of the image. Two types of molds are known.

In both of the above two methods, if the timing at which the droplets are charged is not constant, in the case of the deflection type, the print position of the droplets will change, and in the case of the charged binary type, the droplets that should be non-printed will become non-printed droplets. Due to a charging error, the paper was not charged and was printed through the gutter, both of which caused print distortion.

Therefore, the printing timing at which the printing droplets are charged is
This plays a large role in the accuracy of the prints obtained.

This printing timing, that is, the particle formation phase, can be detected by applying voltage pulses of different phases to the ink droplets and comparing which phase has the largest amount of charge, or by collecting the ink droplets to determine the amount of charge. Two methods are known: one method is to place an electrode close to the flight path of an ink droplet, and the other is to compare the magnitude of the amount of induction caused by a charged ink droplet.

However, in any of these methods, there are significant restrictions on the placement of containers or electrodes as additional means, and the device cannot be made smaller. It also has the disadvantage that the circuit configuration becomes complicated.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method capable of determining the atomization phase of an ink droplet without adding any detection components.

The above purpose is achieved by providing a capacitor in parallel with the charged electrode, and after charging the capacitor to a constant voltage from the outside, the capacitor and the charged electrode are brought into contact and separated at a fixed period and with a fixed phase shift with respect to the period. This can be achieved by inducing a charging electrode in a part of the capacitor's container and then separating it, and measuring the residual capacity of the capacitor to measure the timing of droplet separation.

The present invention will be explained in detail below using the accompanying drawings.

First, let's consider the charging state. As shown in FIG. 1a, charging of the droplets is generally accomplished by applying a voltage to the charging electrode 13 when the liquid column 11 or separated droplet 12 is at ground potential through the nozzle. The thus charged droplets are separated and, in the case of the charged binary type, pass through a deflection electrode (not shown) and are collected by a gutter. The droplets, which are not charged, collide with the printing paper without being deflected and print is printed.

At this time, if the charging timing and the droplet separation timing match, the droplet 12 that is about to be separated is supplied with a charge corresponding to the charging electrode via the liquid column (from the ground). As this timing continues, a plurality of droplets (14 to 16) are charged and separated.

Figure 1a shows an example when the timing of the ink droplets matches (in phase) and is _well charged. The capacitance between the droplet 12 and the electrode is C ₁₁ ', and the capacitance between each separated ink drop and the electrode is C ₁₂ , C ₁₃ , C ₁₄ , and C ₁₅ .

The charge on the droplet side of the illustrated capacitance C ₁₂ to _{C 15} between these charged droplets and the charged electrode 13 is retained even if the charge on the charged electrode disappears, and when the charge is applied to the charged electrode again, form a capacity.

On the other hand, FIG. 1b shows a case where the charging timings do not match, and the droplet 12 is connected to the liquid column 11.
A charging voltage is applied to the charging electrode immediately after separation from the liquid column 11, and only the liquid column 11 is charged. Furthermore, since the charge in the liquid column is not distributed to the separated droplets, the charge remains constant and is neutralized through the nozzle when the charging voltage disappears.

Therefore, the separated droplet is not charged and the capacitance formed between the droplet and the charged electrode is only C ₁₁ .

Therefore, in FIGS. 1a and 1b, when a charging voltage is applied, the capacitance formed between the charging electrode and the droplet (liquid column and separated droplet) differs greatly.

That is, as shown in FIGS. 2a and 2b, a capacitor _C1 is provided in parallel with the power supply E for applying the charged electrode, and after the capacitor _C1 is charged by closing the switch A, the switch A is opened.

Next, this capacitor is connected to the charged electrode via the capacitor _C1 and the switch B which connects and disconnects the ground contact in synchronization with the timing of voltage application to the charged electrode.

At this time, the charge induced from the capacitor _C1 to the charging electrode in synchronization with the voltage application timing to the charging electrode of the ink droplets is the same as that shown in Fig. 2a, when the timing of the droplet formation coincides with the particle formation timing. There is a big difference when they are not aligned [Figure 2b].

The present invention focuses on this difference in capacitance, and a capacitor is provided in parallel with the charged electrode, and after the capacitor is once charged to a constant voltage from the outside, the capacitor and the charged electrode are connected at a fixed cycle and at a fixed voltage with respect to the cycle. By contacting and separating with a phase shift, a part of the capacitance of the capacitor is induced in the charged electrode and then separated, and the timing of droplet separation is measured by measuring the residual capacitance of the capacitor.

The present invention will be explained using the equivalent circuit shown in FIG. In the figure, _C1 is an external capacitor.
C ₂ is a capacitance formed by a plurality of ink droplets and a charging electrode. Walks you through the detection process.

1 Close switch A and charge capacitor _C1 to a constant voltage.

2 Open switch A and connect capacitor C ₁ and power supply E.
Separate.

3 Turn down switch B to discharge the remaining capacity C ₂ from the previous cycle of this process.

4 Fold down switch B and distribute the charge of C ₁ to C ₂ .

5 Push down switch B and discharge _C2 .

6 The input to the detection element V is only C ₁ , and C ₁
Measure the voltage.

Since the voltage appearing at V at this time varies greatly depending on whether the timing of charging the droplet is good or bad, this voltage is compared with a pre-calculated value to judge whether the timing is good or bad.

7 Repeat steps 4-6. (Although not necessarily necessary.
In order to improve measurement accuracy, it is desirable to repeat the measurement a certain number of times before measuring. ) Next, we will explain using experimental results.

When the length of the charging electrode 13 is 2 mm and the particle formation point is located at the center of the electrode in the longitudinal direction, the amount of charge induced in the charging electrodes with matching and mismatching particle formation phases is 2:1.
When the capacitance C ₂ of the charged electrode portion was measured when they matched, it was approximately 5×10 ⁻¹⁴ . charging capacitor
Since C ₁ is coupled in parallel with the input capacitance of the voltage detection element, it can be calculated to be approximately 100p.

C ₁ , C ₂ when switch B is shorted to the side
Since the voltages at both ends of are equal, if the charges charged in C ₁ and C ₂ are Q ₁ and _Q 2, then Q ₁ /C ₁ = Q ₂ /C ₂ Substituting the above values from this equation, Q ₂ can be When calculated, Q ₂ =C ₂ /C ₁・Q ₁ =5×10 ⁻¹⁴・/100×10 ⁻¹²・Q ₁ =5×10 ⁻⁴・Q ₁ . Therefore, the voltage drop due to N times of charging and discharging is V=V ₀ (1-5×10 ⁻⁴ ) ^N .

When N=1000, V=0.606V ₀ .

Since the particle formation frequency is approximately 100KHz, the time required for N=1000 is 0.01 seconds.

Therefore, when the timing of particle formation matches, the output voltage V of the detector is 0.606 of the initially applied voltage.
It will be doubled. On the other hand, when the particle formation timings do not match, this residual voltage output is almost equal to the applied voltage, so it can be compared with the capacitance using a known simple means.

Further, if desired, the angle of phase lead/lag can be determined by comparing this output voltage V with a reference voltage corresponding to the angle of phase shift.

In the configuration described above, by arranging an external capacitor in parallel with the charging electrode and applying the voltage of the capacitor to the charging electrode after charging the capacitor, it is not necessary to provide a capacitor near the print head. Further, by using any other voltage detecting means in the inkjet printer as the detector, there is no need to provide a separate detecting means.

FIG. 4 shows an example in which the timing of opening and closing of each switch is favorable according to the embodiment of the present invention. a) is the phase of particle formation. In b), when the switch A is opened and closed, the high level is set. As a result, switch A is closed before switch B is pushed to one side, charging _C1 to a constant charge. c)
is shown at a high level when it falls to the side at the timing of opening and closing switch B.

When the timing of charging and the timing of particle formation match, the capacitance of C ₁ decreases step by step as shown in d). Here, for example, when a pulse is sent to V to instruct sampling at position e), V samples and holds the voltage at this point, and displays the voltage value at f). Next, compare these with the pre-calculated values, and if they match the charge (voltage) of _C1 at the sample hold position in d) (T position in Figure 5), the timing of particleization is judged to be good. do.

That is, FIG. 4a shows the phase of particle formation, in which particle formation is performed at a constant period. Also, Figure 4c shows the fourth
Figure a shows the timing of bringing the charging electrode 13 and the capacitor _C1 into contact and separating at the same period as the phase of particle formation.

If good timing between charging timing and particle formation timing is detected, change the charging timing of a certain period (that is, shift the phase).
This is done by measuring the residual capacitance of capacitor _C1 and finding the best point.

If the opening/closing timing of switch B does not coincide with the particle formation, _C1 will hardly discharge, so the value of f) will be large, and as a result, it can be determined that the timing of particle formation is poor.

FIG. 5 shows the charge state of C ₁ when the particle formation phases match and do not match, with the vertical axis representing voltage and the horizontal axis representing time.

In the embodiments described above, a case has been described in which the particulate phase is detected with respect to one jet and a charging electrode, but the present invention can also be applied to the case where the jet has a plurality of multi-nozzles.

A known circuit configuration can be used to carry out the above method, and there is no need to provide any additional parts around the print head (the capacitor itself is located a certain distance from the charging electrode). It is possible to miniaturize the device (which can be provided within the power source for the charging electrode).

[Brief explanation of drawings]

1, 2a and 2b are diagrams for explaining the charging state, FIG. 3 is a diagram showing an equivalent circuit of the circuit according to the present invention, and FIG. 4 is a timing chart. FIG. 5 is a diagram showing the charge state of C ₁ when the particle formation phases match and when they do not match. Symbols in the figure, A, B: Switch, C ₁ : Capacitor, C ₂ : Capacity of ink droplet and charged electrode, 11
(11') 13-15: Droplet, _C11 ( _C11 ')- _C15 :
Charge capacity, 13: Charged electrode.

Claims (1)

[Claims] 1. A capacitor is provided in parallel with the charged electrode, and after the capacitor is once charged to a constant voltage from the outside, the capacitor and the charged electrode are brought into contact and separated at a fixed period and with a fixed phase shift with respect to the period, thereby changing the capacitance of the capacitor. A particulate phase detection method for an inkjet printer, characterized in that the timing of droplet separation is measured by inducing a part of the droplet in a charged electrode, separating the droplet, and measuring the residual capacity of the capacitor.