JPS5919160A - Image-forming device - Google Patents

Abstract

PURPOSE:To provide the titled device capable of covering a wide range of density with a simple construction and particularly performing tone reproduction, wherein a plurality of recording heads having different density characteristics are used, and the heads are aligned on the same main scanning line. CONSTITUTION:Video signals from R, G, B are inputted into sample-and-hold circuits SHR, SHG, SHB, and a synchronizing signal SYNC is inputted into a system controller to sample and hold the video signals. Outputs of respective color video signals are stored in line memories MR, MG, MB. This information is subjected to a masking treatment and a ground color removing treatment by a matrix circuit MX, and respective signals of cyan C, magenta M, yellow Y and black BL are outputted. The signals thus outputted are stored in latch memories MC, MM, MY, MBL and are inputted into head-controlling matrix circuits MXC, MXM, MXY, MXBL. The signals thus inputted are converted into code signals, which are inputted into digital-to-analog converters DAC, DAM, DAY, DABL, and are inputted into a head-driving circuit DRC to control the ejected quantity of ink droplets.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming apparatus that forms images using dots, and more particularly to an image forming apparatus that is capable of reproducing 5'1 tonality.

Various devices capable of reproducing υ gradation have been proposed in the past, and the present invention will be described in detail below using an inkjet printer as an example.

The following methods have been conventionally proposed for reproducing gradation.

The first method is to express gradations by controlling the amount of liquid ejected from an inkjet head to vary the diameter of the dots printed.

The second method is to use an IJ matrix in which one pixel is made up of, for example, 4 x 4 micropixels without changing the dot diameter, and use a dither method on this matrix to reproduce rIVI tonality. There is. However, in the first method, it is difficult to increase the range from the minimum dot diameter to the maximum dot diameter that can be printed, and it is possible to reproduce only a few gradations. Therefore, printing out television images or photographic images is unsatisfactory.

The second method improves the shortcomings of the first method, but for example, if one pixel is made up of five 4x4 matrices, it is impossible to reproduce 17 gradations. is possible. However, compared to the first method, one pixel is 4X4-16 (H
By doing so, the print speed will be reduced to 1/16, or the number of print heads must be increased by 16 to increase the print speed. However, doing this does not only complicate the configuration of the print head, but also requires an enormous electrical circuit for image processing using the dither method, resulting in a significant overall cost increase. Ta.

SUMMARY OF THE INVENTION In view of the above drawbacks of the prior art, it is an object of the present invention to provide an image forming apparatus that has a simple configuration and can cover a wide density range.

Specifically, for example, an image forming apparatus uses multiple heads with different dot diameters and different recording densities, that is, multiple heads with different density characteristics, and arranges these multiple heads on the same main scanning line. The purpose is to provide

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1(IL) is a cross-sectional view of the inkjet head shown in this embodiment, and FIG. 1(b) is a cross-sectional view showing the structure of the piezo vibrator 2. In FIG. In the figure, 1 is a glass tube with a tapered tip, and 2 is a piezo vibrator circumscribing the glass tube 1. 6 is a tubular piezo element, 4.5 are electrodes, and by applying a pulsed voltage between the electrodes 4 and 5, the tube contracts and recovers in the inner diameter direction. At this time, by supplying ink from the direction of arrow A, ink droplets can be ejected from the rounded end (orifice portion) of the glass tube. Furthermore, it is possible to change the size of the ejected ink droplets by changing the magnitude of the voltage applied to the piezo element 6, and in our experiments we were able to vary the print dot diameter by about three times as much. However, it is unsatisfactory.

However, the ink dot diameter changes not only by changing the voltage applied to the piezo element but also by changing the orifice diameter DO.

Actually, by changing the ink density, it is possible to change the optical density without changing the orifice diameter.

By using two heads 6.7 with different orifice diameters as inkjet heads in Fig. 2! We have shown an inkjet printer that is capable of reproducing multiple gradations.

Further, FIG. 3 shows an inkjet printer having an inkjet head unit 20 consisting of two heads 16.17 and an inkjet head unit 20 consisting of ink tanks 71B and 19 filled with ink of different densities, respectively. 17 are arranged as shown in FIG. In the figure, arrow C indicates the moving direction of the head, that is, the main scanning line direction.

Further, the distance between the heads is determined by ε, rubit, where the distance between the formed dots is one dot. Of course, n is determined by the size of the head and the number of pixels to be formed, and if it is a positive integer, then t/(, but it is advantageous to make the number as small as possible because the memory capacity will be smaller.0 6 is a configuration diagram of the mechanical parts of the printer equipped with the head unit 10.20 shown in FIG. This is a head-feeding pulse motor that scans the carriage 24 using a guide 25 and a screw 26.

Figure 6 shows flilJ 1 when the printer in Figure 5 is applied to a printer that prints out color video signals.
FIG. 11 is a block diagram of an 1111 circuit. The operation will be explained according to the diagram.

First, the image signals from R, G, and B are input to the sample and hold circuits 5) IFI, SHG, and SHB, respectively, and the synchronization signal 5YNC is input to the system controller 5YSOO.
It is input to N. The video signal is sampled and held according to the timing signal from this 5YS (3ON).The sample output of each color video signal is passed through the signal changeover switch SW and the AD converter ADO to the line memory MR,
They are stored in MG and MB, respectively. Next, line memory M
R.

The information in MG and MB is subjected to a strip masking process 1 and an under color removal process by w) RIX circuit MX, and outputs a cyan signal C, a magenta signal M, a yellow signal Y, and a black signal BL.

Now, 0. The output signals of M, Y, and BL are from the latch memory MO,
It is stored in MM, MY, and MBL, and its output is also head controlled! Trix circuit MXO, MXM, MXY
, MX, and BLK are input.

The output signals of these matrix circuit latch memories are converted into code signals indicating the head to be selected and the voltage value to be applied. This code signal is transmitted to the DA converter DAC, DA
It is input to M, DAY, and DABL and converted into an analog voltage value. This voltage is input to the head drive circuit DRO (in the case of cyan), and the head selected by the head select signal H8 is driven by a desired timing signal TP,
Controls the amount of ink droplets ejected.

Also, the signal from 5YSOON is sent to driver DR1゜DR2.
Via the pulse motor HM for head feeding.

It is added to the paper feed shimotor LF to control head feed and paper feed υ, respectively. In particular, the head feed pulse generator HM is controlled by a signal synchronized with the head ejection timing pulse TP.

FIG. 7 is a detailed circuit diagram of the head drive section of FIG. 6.

Referring to FIG. 6, the control of an inkjet head will be explained in a physical way by taking digital signal processing as an example. As shown in the fifth diagram!
The 8-bit digital signal from the trick circuit MXC is
Gate circuit GTI.

Input to GT2. The head selection signal flAH8 is
When the signal is at the high level, the gate circuit GTI opens and the signal is input to the parallel input/parallel output shift register SR1. The shift register SRI is shifted one bit at a time from the timing signal TPIK.The shift register SRI is set to one stage because the two heads are separated by n bits.

Therefore, when nine timing pulses are generated, the output of MXC is output to D/A converter DA1, and an analog signal corresponding to the digital value is obtained. is input to the drive circuit AMP2.

Similarly, the head selection signal H8 is also input to the two-stage shift register SR2 that is shifted by timing/curse, so when there is an output from the D/A connector (-ta) DAl, an output is also obtained from the simultaneous AND gate G6. In this way, the head H2 with the large orifice diameter is driven with a delay of l timing pulses TP after the output from the MXC.

On the other hand, when the head selection signal H8 is at a low level, the gate circuit GT2 opens and the output digital signal of 5MX0 is directly input to the D/A converter DA2.The head selection signal H8 is also directly input to the AND gate G2. The head H1 having such a small orifice diameter is driven almost simultaneously with the output of the MXO.

The driving of the head H1 when the minute signal H8 is at a low level will be explained. Antgame) One end of G2 is a noirepel, so
When the timing pulse TD reaches /S, the output of the AND gate G2 becomes NO. Here head H1
A voltage vH is applied through a resistor R6. As a result, the piezoelectric vibrator contracts in the direction of the inner diameter of the glass tube, and colored droplets are ejected. The amount of colored droplets ejected is controlled by voltage vH.

Also, at this time, the transistor Tr2 is off because the output of the inverter G6 is at p- level.Next, when the pulse becomes low, the transistor Trl turns off, and Tr2 turns off. By turning on the head H1, the charge charged in the head H1 is discharged through the resistor B4, and the piezo element is restored to its original state.Ink droplet ejection is controlled in the above manner.

Although the heads H1 and H2 have been described using heads with different orifice diameters, a similar control circuit can be constructed even when inks of different densities are used. Further, although two examples have been shown, it is of course possible to use six or more heads.

Although only cyan ink has been described above, a control circuit can be similarly constructed for magenta, yellow, and black.

Further, although a shift register is used as a head interval compensating means for compensating the interval between heads, a simple delay circuit may be used. All of the heads for each color may be arranged on the same main scanning line, but it is sufficient if a plurality of heads with different density characteristics of the next color are arranged on the same main scanning line.

As described above, in this embodiment, one pixel is represented by one dot,
The dot spacing is constant. Since a plurality of recording heads with different density characteristics are arranged on the same main scanning line, no memory is required to store recording signals. - It is sufficient to simply provide a delay circuit that delays the recording signal.

Also, in terms of manufacturing, it is only necessary to specify the accuracy in each direction of main travel. Furthermore, it becomes possible to make the printer device thinner.

In this embodiment, the head spacing is set to 1/2 bit, but by setting it to exactly 1/2 bit, head feeding can be precisely controlled by the pulse motor. Further, by using the rubit interval, both heads can be driven with the same timing pulse, which further simplifies the circuit.

Although the present specification has been described using an inkjet printer as an example, the invention is not limited to this, and can be applied to any dot printer capable of expressing dots with varying density characteristics, such as electrostatic printers, thermal printers, and thermal transfer printers.

Of course, it goes without saying that the present invention is also fully applicable to the recording methods and devices disclosed in Japanese Patent Application Laid-open No. 54-59956 and Japanese Patent Application Laid-open No. 55-27282, filed by the present applicant. . Further, although circular dots are used, the present invention is not limited to this, and the present invention can be applied to dots of various shapes.

[Brief explanation of drawings]

FIG. 1(1) is a sectional view of an inkjet head to which the present invention can be applied, FIG. 1(b) is a sectional view of a piezo vibrator, FIG. 2 is a configuration diagram of the head of the first embodiment, and FIG. The figure is a configuration diagram of the head of the second embodiment, Figure 4) (b) is a diagram showing the arrangement of the heads, Figure 5 is a configuration diagram of the mechanical part of the printer, and Figure 6 is the printer of Figure 5. Control block diagram of 7th
This figure is a detailed circuit diagram of the head driving section of FIG. 6. In the figure, 6, 7, 1 (S, 17 are inkjet heads using piezo vibrators, HM is a pulse motor for moving the head, and TP is a timing pulse, respectively.

Claims (1)

[Claims] An image forming apparatus that forms an image using a recording head that forms dots, characterized in that a plurality of recording heads having different density characteristics are used and the plurality of recording heads are arranged on the same main scanning line. Image forming device.