JPS6021068B2 - Dot misalignment correction device for inkjet printing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an inkjet printing machine, and more particularly to an apparatus for correcting dot misalignment in inkjet printing.

■ Conventional technology In inkjet printing, the inkjet head is moved relative to the printing paper, or the printing paper is moved relative to the inkjet head (hereinafter referred to as scanning), and the printing paper is moved from the inkjet head to the printing paper. A dot distribution is formed on the printing paper by colliding ink in the form of dots, thereby forming an image.

The speed of relative movement, that is, the scanning speed, is usually set constant. However, the speed fluctuates due to errors or fluctuations in the mechanical or electrical system. Furthermore, it is desirable to increase the scanning speed in printed areas where the image signal density is low. If the scanning speed is varied or changed as described above, the ink dots will shift from their predetermined positions on the printing paper.

This will be explained with reference to FIG. FIG. 1 is a vector diagram showing the relationship between scanning speed and ink dot position on printing paper.

Now, it is assumed that the printing strip A is stationary, the inkjet head is moved along the scanning line SL parallel to it, and the ink is jetted perpendicularly to the printing paper PA. It is also assumed that ink is ejected at point A at a speed of VE, and the inkjet head scans at a speed of Vs. In this case, the ink jetted from the inkjet head collides with point B on the printing paper PA at a speed of VB. If V6 and Vs are always constant,
By ejecting ink at regular intervals, ink dots are printed at equal intervals (pixel intervals) on the printing fine PA. Therefore, if VE and Vs are always constant, by ejecting ink at a constant cycle, it will be possible to spray the printing paper PA at equal intervals (
Ink dots are printed at pixel intervals). However, V.E.
When Vs is kept constant, for example, if Vs becomes low as shown by the dotted line, the dot position becomes B and deviates from the predetermined position B. Thus, variations or changes in scanning speed cause dot misalignment. The inkjet head is equipped with a diaphragm in which a diaphragm is formed on a distortion element plate.

In this inkjet head, a full amount of ink is ejected by applying a pulse voltage to the box distortion element plate.
The size of the ink droplet corresponds to the applied voltage, and increases as the voltage increases. Therefore, printing density is controlled by controlling the pulse voltage wave height.
FIG. 2 shows the relationship between the pulse voltage wave height and the printing density.

Varying the level of pulse voltage applied to such a tortoise-distortion plate changes the velocity of the ejected ink droplets. Therefore, when performing such concentration control, the velocity of the ink droplet V
E changes, resulting in dot misalignment. This will be explained using FIG. Print paper at ink droplet velocity VE and scanning velocity VE? Ink fill occurs at point B at point A, but if the ink droplet velocity VE changes without changing the scanning speed VB, for example, if it becomes lower as shown by the dotted line, the ink dot position changes from B to B.

In other words, dot misalignment occurs. (1) Purpose It is an object of the present invention to prevent printing misalignment of ink dots due to changes in scanning speed and ink droplet ejection speed.

■Configuration When the scanning speed changes, for example, when the scanning speed Vs decreases as shown by dots and lines in Figure 1, the inkjet bias is shifted by the resulting dot shift D, so that the predetermined position can be adjusted. Ink dots can be formed on B.

In the case shown in FIG. 1, when the scanning speed decreases, the inkjet energization may be slowed down, and conversely, when the scanning speed increases, the inkjet energization may be made faster. Furthermore, when the ink droplet ejection speed changes in response to a change in recording density, for example, when the ink droplet speed VE is lowered as shown by the dotted line in FIG. By shifting the bias, an ink dot can be formed at a predetermined position B. In the case shown in FIG. 3, when the ink droplet velocity VB is increased, the inkjet energization may be made slower, and when it is lowered, the inkjet energization may be made faster. - Even when both the scanning speed Vs and the ink bran speed V8 change, dot misalignment can be prevented by adjusting the inkjet energization point in the same manner as described above.

Accordingly, the present invention includes a storage means for outputting time data corresponding to both the relative movement speed data between the printing paper and the inkjet head and the image signal data that determines the ink ejection speed, and the latch means for holding the image signal data. image signal output timing control means for outputting the image signal data held by the latch means with a time delay indicated by the time data;
Equipped with

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on embodiments of the present invention shown in the drawings.

FIG. 4 is a block diagram showing one embodiment of the present invention.

This embodiment is applied to an inkjet printing apparatus that receives an image signal indicating recording density and prints dots with an area corresponding to the image signal. In this case, a diaphragm is used. Since the inkjet head has an energizing voltage (pulse voltage) of a value corresponding to an image signal, the ink speed varies in accordance with the image signal. Therefore, the configuration is such that dot misalignment can be corrected in response to the scanning speed and image signal. In Figure 4, 1,
and 12 are analog-to-digital converters that receive analog speed signals and analog image signals, respectively; 2 and 22 are gate circuits; 3 is a storage device; 4 is a preset counter; 5 is a clock pulse oscillator; and 6 is a count value detection circuit. , MMB is a monostaple multipipulator, FFI is a flip-flop, and ANDI is an AND gate.

The analog-to-digital converters 1 and 12 convert the input analog voltage signal into an 8-bit digital code signal in this example.

The gate circuits 2 and 22 each consist of eight AND gates, and each AND gate is connected to each line of the 8-bit digital code output of the converters 1 and 12.

The storage device 3 is a MOSIC read-only memory (RO
M) is used which receives the 8-bit code signal of converter 1 through a gate circuit 2, and the 8-bit code signal of converter 12 through a similar gate circuit 22.

The storage device 3 has, for example, 2S×2S memories, and each memory has an X address designated by the speed signal digital code and a Y address designated by the image signal digital code.

That is, each memory is divided into, for example, 2S groups for each speed signal digital code, the groups are specified by the speed signal digital code, and the memories in each group are specified by the image signal digital code.
Therefore, a certain scanning speed Vs', a certain image density V8j
A certain memory M;j is specified for reading. Each memo in each group is determined by adding the scanning speed Vs to the delay time necessary to make the dot misalignment zero when the ink droplet velocity VE changes to high or low depending on the image density at that scanning speed.
A delay time CLj, which is the sum of the delay time corresponding to i, is stored, and this delay time CLj is the delay time C for a certain scanning speed Vsm and a certain density VEs.
This is the delay time required to print at the same dot position as when Lsm and E' are given.

Therefore, by inputting the speed signal and the digital code signal of the image signal (density signal) to the address end of the storage device 3, the inkjet activation delay time required to make the dot misalignment zero is displayed at the output end. A digital signal representing . . . appears and is applied to the preset input of the counter 4.

Counter 4 is set to subtraction mode. converter 1,
A speed signal arrives at the converter 12, and an image signal arrives at the converter 12.
A position pulse with a period inversely proportional to the speed is applied to the flip-flop FFI.

This position pulse is emitted every time the inkjet head moves a unit pixel distance when the printing paper PA is in a stationary state, and the pulse interval indicates time. As the scanning speed increases, the pulse interval of the position pulses becomes shorter.
However, the inkjet head only advances a certain distance between each pulse. The image signal, which is a printing signal, arrives in synchronization with the position pulse, and its value indicates the recording density (excitation voltage).

The clock pulse oscillator 5 continuously oscillates pulses with a constant period that is extremely short relative to the position pulse, and supplies the pulses to the AND gate ANDI. Now, speed Vs
The arrival of a speed signal representing i produces at the output of converter 1 a digital signal representing Vsi.

When the position pulse and the image signal VEj arrive there, the gate 2 and the gate 22 are opened, and the memory M of the recording device 3 is
CLij is read from ij and the counter 4 is preset to that value. On the other hand, the position pulse sets the flip-flop FFI, and its Q output (high level 1)
is given to the AND gate ANDI, and the AND gate A
NDI provides the clock pulses of clock pulse oscillator 5 to the count pulse input of counter 4. counter 4
is sequentially subtracted from the preset value CLj. In this way, when the number of clock pulses that arrive through the AND gate ANDI reaches CLj, the output of the counter 4 becomes a code indicating 0. This code is detected and a pulse-like output is generated. At the rising point of the pulse output of the detector 6, a mono-multivibrator MMB is triggered to produce a constant width pulse. The gate circuit 7 is opened during the output pulse width of the MMB, and the image signal (digital data) held in the latch circuit 9 in synchronization with the position pulse is given to the D/A converter 8 and converted into an analog signal. is applied to a printhead energization circuit (not shown). At the rising point of the output of the mono multivibrator MMB, the flip-flop FFI is reset and its Q output returns to the low level 0,
The AND gate ANDI is turned off (gate closed). With the above operation, the image signal given to the printing head energizing circuit appears after counting CLj clock pulses (5 outputs) after the arrival of the position pulse, and printing is performed in synchronization with this image signal. Synchronous pulse indicating energization timing (
MMB output) is applied to the printing head energizing circuit together with the image signal.

This count time of CLij becomes the delay time. In the case of this embodiment, the shortest delay time C at the maximum possible scanning speed Vsm and maximum density VEs is given by m, ES,
Based on this printing dot position, its maximum scanning speed V
At a speed lower than Sm, the maximum density VEs, and a lower recording density, a delay time greater than that of CLsm and ES is given so that printing is performed at the same dot positions as at the maximum scanning speed VSm and the maximum density V83. ■EffectsAs understood from the above explanation, in the present invention,
Since the printing signal is issued at a timing when printing dot deviation due to changes in recording density and scanning speed is reduced to zero, dot deviation is prevented and accurate inkjet printing can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a vector diagram to explain that fluctuations in scanning speed cause printed dots to fade, Fig. 2 is a graph showing the relationship between inkjet energizing voltage, printing density, and ink full speed, and Fig. 3 is a vector diagram for explaining that a change in ink full speed causes dot misalignment. FIG. 4 is a block diagram showing the configuration of an embodiment of the present invention. SL...Scanning line, PA...Print paper, 1,,12...Analog-digital converter,
2,,22,7... gate circuit, 3...
Storage device, 4... Counter, 5... Clock pulse oscillator, 6... Count value detector, 8... Digital-to-analog converter, 9 ...
...Latch circuit. Figure 1 Tsutomu Figure 2 Figure 3 Gap

Claims (1)

[Claims] 1. A storage means for outputting time data corresponding to both the relative movement speed data between the printing paper and the inkjet head and the image signal data that determines the ink ejection speed, the latch means for holding the image signal data, and the time data. an image signal output timing control means for outputting the image signal data held by the latch means with a time delay shown in FIG.