JPH0254226B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charge control type inkjet recording device, and in particular, it is possible to accurately control the timing of charging of ink droplets ejected from a nozzle of an inkjet head to the printing start point of a recording paper. The dot misalignment is corrected by aligning the dots.

FIG. 1 is a schematic overall configuration diagram for explaining an example of an ink jet recording apparatus to which the present invention is applied. In the figure, 1 is an ink jet head body, 2 is an orifice (nozzle), and 3 is an electrostrictive vibrator. , 4 is a charge signal generator, 5 is a charging electrode, 6 is a charge amount detection electrode, 7a and 7b are deflection electrodes, 8 is an unnecessary ink drop collection gutter, 9 is a rotating drum, 10 is an ink tank, 11 is a filter, 12 is an ink pressure pump,
Reference numeral 13 denotes a pressure regulating valve, which, as is well known, pressurizes and excites the ink in the head body 1 to eject it from the orifice 2, and the ink liquid column 1 ejected from the orifice 2.
4 is separated into ink droplets at the charging electrode 5, and a charge corresponding to the printing information signal is given to the separated ink droplets by the charge signal generator 4, and the charged ink droplets 15 are then separated at the deflection electrodes 7a and 7b. The information is reproduced on the recording paper on the rotating drum 9 by deflecting it according to the amount of charge, while the non-charged ink droplets 16 that are not used for printing are captured by the gutter 8 and collected into the ink tank 10, and again. It is intended for use by

Then, as described above, the drum 9 is rotated,
In an inkjet recording apparatus that prints while moving the head body 1 in a direction perpendicular to the direction of rotation of the drum 9, a signal is generated every time the drum 9 rotates, and printing is started in response to this signal. However, in practice, it is difficult to completely synchronize the rotation of the drum with the excitation frequency, and due to uneven rotation of the drum, a one-dot printing deviation occurs at the start of printing. To solve this problem, for example, it is possible to shorten the interval between dots and reduce dot misalignment by increasing the excitation frequency above the actually required frequency, but there is also a limit to the excitation frequency. This is undesirable because the printing speed decreases. On the other hand, as mentioned above,
In an inkjet printing device that controls the presence or absence of printed dots depending on the presence or absence of electrical charge, so-called charge distortion and deflection distortion occur in which subsequent ink droplets are not printed at predetermined positions due to the influence of preceding charged droplets. There is a problem, and in order to solve this problem, conventionally,
It has been proposed to provide two or more uncharged ink drops (guard drops) between charged ink drops.

In view of the above-mentioned circumstances, the present applicant first made it possible to charge all the ink droplets, that is, the guard drops, and made the chargeable state active when the one-rotation signal of the drum was generated. By using the signal as a printing charge signal, it is possible to synchronize the rotation of the drum and the start of printing, thereby synchronizing the rotation of the drum with the charge signal every revolution, for example, when the guard drop is 2. In this case, we proposed an inkjet recording device that can reduce dot misalignment to one-third.

FIG. 2 is an electrical block diagram for explaining an example of a dot misalignment correction device previously proposed by the present applicant, in which a clock pulse generation circuit 21 generates a clock pulse having a frequency eight times the excitation frequency, for example. This clock pulse is down-done to 1/8 by the frequency dividing circuit 22 and supplied to the phase shift circuit 23, where the ink is detected by the signal from the charge amount detection electrode 6 sent through the amplifier 25. A phase matching the timing at which the liquid column 14 separates into ink droplets is selected, and an excitation signal having a phase matching the droplet separation timing is supplied to the electrostrictive vibrator 3 through the amplifier 24. Note that when searching for an excitation signal phase that matches the droplet separation timing, the output signal from the frequency dividing circuit 22 is searched by the search pulse generating circuit 26.
The output signal of the search pulse generation circuit 26 controls the charge control circuit 30 to apply a charge signal to the charge electrode 5, and the charge amount detection electrode 6
The phase shift circuit 23 is controlled to shift the phase of the excitation signal by 1/8 phase until an output signal appears on the charge amount detection electrode, that is, until the ink droplet is charged. When the ink droplet is charged, the phase shift operation of the phase shift circuit 23 is stopped, and the electrostrictive vibrator is excited with the excitation phase at that time, so that the ink droplet is charged with the optimum excitation phase. However, as mentioned above, in the type of inkjet recording device provided with guard drops, there is no need to charge the guard drops, and therefore, the charged droplets during printing are more sensitive to the ink droplets ejected from the inkjet head 1. For example, when two guard drops are provided, the charging frequency becomes 1/3 of the excitation frequency. Second
In the figure, 27 is a frequency dividing circuit for this purpose. For example, when two guard drops are provided, the search pulse is stepped down to 1/3, and the inkjet head 1
It charges every second ink droplet ejected from the ink droplet. In this case, if the timing is exactly when the charged ink droplets are ejected at the start of printing, there will be no misalignment of the printing dots, but as mentioned above, due to uneven rotation of the drum, etc., the printing start timing may not always be the same. The charging timings do not match, resulting in printing deviation of one dot interval at most. In order to correct the above-mentioned printing deviation, the present applicant first lowered the load power signal by, for example, 1/3 using a frequency dividing circuit 27, as shown in FIG. 3rd each for a to c
Three chargeable pulses as shown in Figures a to c are obtained and supplied to the synchronization circuit 29, and in the synchronization circuit 29, they are synchronized with the printing start signal (see Figure 3d) from the drum one rotation signal generation circuit 28. The chargeable pulse (pulse a in the example of FIG. 3) that is active when this printing start signal is generated, that is, the charging timing, is sent as a charging pulse to the charging control circuit 30. Charge control circuit 30
proposed an inkjet recording device in which a charge code (see Fig. 3 f) is obtained by performing logical processing with the print data, and this charge code is applied to the charge electrode 5 through an amplifier 31 to perform printing. .

However, in the above-mentioned inkjet recording device, synchronization is achieved only once per rotation of the rotating drum, so there is a difference in printing quality between the leading edge and trailing edge of the rotating drum, and this difference is due to synchronization. Since a motor is used, fluctuations in the AC power supply become noticeable. In order to solve this problem, a method was proposed that uses an encoder that generates 384 pulses per rotation of the rotating drum and synchronizes with the pulses from this encoder. Since the charging pulse is synchronized with the charging pulse (see FIG. 4b), there is a disadvantage that a difference occurs in the interval between charged droplets (see FIG. 4a), resulting in a striped pattern in the printing result.

In order to solve the above-mentioned drawbacks, the present invention excites the ink jet head with an excitation signal, and converts the ink droplets used for printing among the plurality of ink droplets ejected from the nozzles of the ink jet head into charge signals. In an inkjet recording apparatus that charges the charged droplets accordingly and deflects the charged charged droplets to print on a recording paper on a rotating drum, the rotating drum includes a rotation signal generating means for the rotating drum, and a charging device that is synchronized with the rotation signal generating means. a signal generating means; a charging means for converting the ink droplet into a charged droplet using a charging signal from the charging signal generating means; a determining means for determining a change in the interval between the charged droplets when the interval between the charged droplets changes; and a correction means for correcting the amount of charge of the ink droplets charged by the charging means in accordance with the output output. Hereinafter, the present invention will be explained based on examples.

FIG. 5 is a block diagram of the main part of the electric circuit used in the inkjet recording apparatus according to the present invention, and FIG.
The figure is a flowchart for explaining the operation of the circuit of FIG. The DQ flip-flop circuit of the frequency dividing circuit 27 divides the frequency into 1/3 to obtain chargeable pulses a to c, while converting the encoder pulse into a charge pulse with a frequency three times the charging period or a period 1/3. Thus, a charging pulse (one of chargeable pulses a to c) which is quantized and synchronized with the rising edge of the quantized signal is obtained, and the printing data is sampled by the gate circuit 40 using this charging pulse. The output is supplied to a shift register 41 and delayed. In the shift register 41, the output delayed by 1 bit becomes charge data and is sent to the charge amplification section.

Now, if an encoder pulse is generated in synchronization with the signal a, the output of the gate 29a will be obtained. Next, when the encoder pulses are generated in a shifted manner and synchronized with the signal b, the output of the gate 29b is obtained. Gate 29d with its two inputs
The output is as shown in the timing chart shown in FIG. The output of the gate 29d is set to 1 by a charging pulse.
The data is delayed by a certain amount of bits, then ANDed with the inverted signal of the signal that is not delayed, and the data is determined to be “present”.
, the output of the gate 40 will be as shown in FIG. Outputs S ₁ to _{S 6} of shift register 41
is as shown in FIG. 6, and first, an AND output of S ₁ and S ₄ (output of gate 44) is obtained. When the period changes due to a change in the encoder pulse and synchronization with b is achieved, the drop interval becomes 4λ, so the outputs of S ₁ and S ₅ become HIGH, and the output of the gate 45 is obtained. The output of the gate 45 changes the gain code, making it possible to eliminate white streaks. That is, when the interval between charged droplets changes from 3λ to 4λ, there is no output from the gate circuit 44 shown in FIG. 5, but an output from the gate circuit 45 is obtained. The fact that there is no output from the gate circuit 44 means that the interval between the charged droplets has changed, and this change results in a striped pattern (white streaks). Therefore, the output of the gate circuit 45 obtained by changing the interval between charged droplets is input to the gain control so that the interval between charged droplets is narrowed when the interval between charged droplets is wide, and the output is widened when the interval between charged droplets is narrow. By changing the output of the gain control so that the ink droplet is preferably located between the front and rear charged droplets, the amount of charge charged to the ink droplet (charge amount) can be controlled, and the dot misalignment can be corrected.

As is clear from the above description, according to the present invention, striped patterns due to changes in droplet spacing are eliminated, and printing quality can be improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic overall configuration diagram for explaining an example of an inkjet recording device to which the present invention is applied, and FIG. 2 is an electric circuit diagram for explaining an example of a dot misalignment correction device in a conventional inkjet recording device. Figure 3 is a time chart for explaining the operation of the electric circuit in Figure 2, and Figure 4 is a time chart for explaining the operation of the electric circuit in Figure 2.
FIG. 5 is a time chart for explaining the drawbacks of the prior art, FIG. 5 is a main part electrical circuit diagram for explaining an embodiment of the dot misalignment correction device according to the present invention, and FIG. 6 is a timing chart. DESCRIPTION OF SYMBOLS 1... Ink jet head, 3... Electrostrictive vibrator, 5... Charging electrode, 6... Charge amount detection electrode, 7
a, 7b... Deflection electrode, 9... Drum, 21...
Clock pulse generation circuit, 22... Frequency division circuit, 2
3... phase shift circuit, 24, 25... amplifier,
26... Search pulse generation circuit, 27... Frequency division circuit, 28... Drum 1 rotation signal generation circuit, 29...
... Synchronous circuit, 30 ... Charge control circuit, 31 ... Amplifier, 40 ... Gate circuit, 41 ... Shift register, 42 to 46 ... Gate circuit.

Claims (1)

[Claims] 1 The ink jet head is excited by an excitation signal, and among the plurality of ink droplets ejected from the nozzles of the ink jet head, the ink droplets used for printing are charged according to the charging signal, and the charged droplets are charged. In an inkjet recording device that deflects and prints on recording paper on a rotating drum, a rotation signal generating means for the rotating drum, a charge signal generating means synchronized with the rotation signal generating means, and a charge signal generating means generated by the charge signal generating means. a charging device that converts the ink droplets into charged droplets using a selected charging signal; a determining device that determines a change in the interval between the charged droplets when the interval between the charged droplets changes; 1. A dot misalignment correction device for an inkjet recording apparatus, comprising a correction means for correcting the amount of charge of an ink droplet to be charged next by the means.