JPH045054A - Ink jet printer - Google Patents

Abstract

PURPOSE:To correct irregularity in density of a recording image by a method wherein after ordinarily recording an image, a same image is repetitively recorded by thining out, a low density nozzle is made to record comparatively many image data, and a high density nozzle is made hardly to record the image data. CONSTITUTION:An image clock 9 is inputted to a timing generator 10, output of the generator 10 is inputted to a write address counter 11 and a read address counter 12, and either output of counters 11, 12 accesses an address of a memory 6 via a selector 13. The read image data which is stored in the memory 6, since a switching signal is generally '0', is sent as a printing data 16 as it is to a next stage. A correction data of each nozzle is stored in a memory 14, and is read in synchronization with the image clock. When the switching signal is selected as '1', the correction data is selected. At that time, a logical product (AND) of the image data and the correction data is sent as the printing data 16 to the next stage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inkjet printer having a plurality of nozzles, and particularly to a printer that corrects density unevenness.

[Prior Art] The operating principle of a bubble jet printer, which is one type of ink jet printer, is briefly shown in FIG.

In the figure (■), ink is exposed to the outside through a narrow passage. A heater is arranged on one side of the passage, and when printing is desired, current can be passed through the heater to heat it. Then, as shown from ■ to ■, bubbles are generated in the ink, and this force causes the ink to be ejected to the outside.

The current problem when generating highly accurate printed images using a bubble jet printer is that the amount of ink ejected from each nozzle must be uniform. For example, the average amount of ink ejected from each nozzle is 25p1
In this case, if there is a difference in ejection amount of about a few percent, density unevenness becomes noticeable. However, since it is extremely difficult to make the amount of ejected ink uniform, conventional methods have been taken to correct density unevenness at the image processing stage. FIG. 7 shows an example of a circuit for this purpose.

Correction data for the bubble jet head is stored in the ROM10I, and expanded to the SRAM 104 via the CPU 102 and the RAM peripheral circuit 103. The data in the SRAM 104 is read out by an image clock 106 synchronized with the image data 105 and connected to an upper address of the ROM 107. In other words, ROM1 is synchronized with the image data.
By switching the upper address of 07, data 108 can be obtained via an independent r table for each image.

E Problems to be Solved by the Invention] However, in the conventional example described above, each nozzle has 6 to 8 bits of γ selection data, and a plurality of r values for density unevenness correction, for example, 64 types, are required.

Taking FIG. 7 as an example, the r selection data is: 128 nozzles * 4 colors = 512 Bytes The density unevenness data for γ correction is.

256Byte * 64 * 4 heads = 65.53
6 Bytes If peripheral hardware circuits are included in these, the cost will be considerable. That is, there are problems of increased costs due to increased circuit scale and increased equipment size. Furthermore, in systems such as copying machines that include image processing circuits,
Although a configuration similar to the above-mentioned conventional example can be used, the conventional example cannot support this because printers usually do not include such a function.

An object of the present invention is to provide an inkjet printer that solves the above problems.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an inkjet head having a plurality of ejection nozzles that ejects ink based on image data, and an inkjet head that ejects ink based on image data, and an inkjet head that ejects ink based on image data. and a control means for repeatedly recording the density unevenness correction data generated by the thinning means by the ejection nozzle.

[Function] According to the present invention, with the above configuration, after normal image recording, the same image is thinned out and repeatedly recorded, so that the nozzles with low density record a relatively large amount of image data, and the nozzles with high density record almost no image data. to correct density unevenness in recorded images.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

First, an outline of a bubble jet printer to which the present invention is applied will be explained.

FIG. 8 is a schematic diagram thereof, and 81 is a carriage which is scan-driven in the direction shown by arrow S in the figure. Reference numeral 82 denotes a wire to which the carriage 81 is attached and is stretched around pulleys 83 provided at both ends of its movement range. 8
A motor 4 is coupled to one pulley 83 and serves as a drive source for scanning and driving the carriage 81 in the S direction.

Reference numerals 85 denote first and second guardrails extending in the S direction to guide the carriage 81.

Reference numeral 86 denotes a platen roller for regulating the recording surface of a recording medium such as paper, film, etc. and for conveying the recording medium. Reference numeral 87 denotes a motor that is combined with the platen roller 86 and rotates the platen roller when conveying the recording medium. Also, 88 is
This is a cable for transmitting control signals, and one end is connected to the carriage 8.
1, and the other end is connected to control means (not shown) to transmit image data, control signals, etc. between the control means and the carriage. This cable 88 is connected to the carriage 8
1 (in the form of a flexible cable).

The internal structure of the carriage 81 is shown in FIG.

It incorporates bubble jet writing heads in four colors: cyan, magenta, yellow, and black, each color in this example having 128 ink outlets, each spaced at Ll, L2, . It has L3 and is lined up in - column. That is, 128 dots of each of the four colors can be printed in one scan in the S direction. Now, when considering a printer with a print density of 400 DPI, the LO is approximately 8 mm for this print head with 128 dots per line.

With the above configuration, a specific example of the present invention is shown in FIGS. 1 and 2.
This will be explained using Figures 3 and 3.

First, FIG. 2 shows the flow of electrical signals within the printer.

CPL121 is a memory control gate array (GA) 2
2. Controls the head control GA 23, the motor driver 24 for paper feeding and carriage movement, and the like. Image signal 25
is once passed through the memory control gate array (GA) 22.
The data is stored in the memory 26, and is normally delayed according to the carriage structure described above and sent to the next stage head control GA 23.

Normally, a bubble jet head is dynamically driven to simplify the drive circuit, and this is also the case in this embodiment, and the head control GA 23 performs the initial processing related to head driving.

Since the GA 23 cannot directly drive the head, the head 28 is driven via a head driver circuit 27 for current amplification and voltage conversion.

Next, a block diagram related to the present invention is shown in FIG.

FIG. 1 picks up the parts related to the present invention and explains them in detail.

In Figure 2, the circuit in Figure 1 is the memory control GA22.
include.

As shown in FIG. 1, the image clock 9 is input to a timing generator 10, the output of the generator 10 is input to a write address counter 11 and a read address counter 12, and one of the outputs of both counters 11 and 12 is input to a selector. The address of memory 6 is accessed via 13.

Since the switching signal 15 is normally "O", the image data stored in the memory 6 and read out is sent as is to the next stage as print data 16. Correction data for each nozzle is stored in the memory 14 and read out in synchronization with the one-image clock 9. When the switching signal is selected to be "1", the correction data is selected. At this time, the logical product (AND) of the image data and the correction data is sent to the next stage as print data 16. FIG. 3 shows the timing when generating correction data.

In this example, one period has 16 pixels.

For example, if the density of the nozzle with the highest density is 1 and the data of the thinnest nozzle is 0.75, if the printing rate of the thinnest nozzle is increased by 25%, the density should be the same as that of the darkest nozzle.

For example, if we consider correction data generation as one cycle of 16 pixels, the thinnest nozzle will generate 4 times per 16 pixels, then 3 times, 2 times, 1 time, 0 times, etc. depending on the nozzle density.
Step-by-step correction can be achieved.

In Figure 3, 4/16DUTY is 1 as shown in the figure.
It has a timing that allows printing at a rate of 4 times per 6 pixels.

An example of thinned-out printing is shown at the bottom of FIG.

Taking the case of DUTY 4/16 as an example, if there is image data as shown in the figure, the print data is an AND of the two, so the print data is as shown at the bottom.

3/16.22/16. The same applies to l/16DYTY.

Other SF1 Examples (1) In FIG. 4, the read address counter 52 has an OP/DOWN configuration compared to FIG. 1 (other configurations are the same as in FIG. 1). This configuration is based on the case where the carriage shown in FIG. 8 performs normal printing on the forward pass and corrective printing on the return pass.

Since the counter 52 normally reads out the image data stored in the memory 46 in the order in which it was input, the counter 52 is OP.
/DOWN*=output up counter, and when performing correction printing on the return trip, data needs to be read from the reverse, so OP/DOWN*=O and down counter. With such a configuration, it is possible to prevent a decrease in printing speed.

(2) FIG. 5 shows an example in which the correction data generation timing (4/16 to 1/16 DUTY) in FIG. 3 is generated using random numbers.

An example of the printing pattern in that case is shown at the bottom of FIG.

In the example shown in Figure 3, we tried to shift the phase of the generation timing of each correction data so that vertical streaks would not occur due to correction.
When considering the case of printing a periodic repeating pattern, it is conceivable that, for example, the way the correction is applied will be different for even number printing and odd number printing. In order to correct this, the generation timing of 4/16DUTY-1/16DUTY in FIG. 5 is determined by random numbers.

(3) In FIGS. 3 and 5, correction is applied at a cycle of every 16 pixels, but this cycle may be increased in order to further improve precision or to avoid unevenness caused by correction. On the other hand, if low cost is desired, the period may be made small, such as a 10-pixel period.

As described above, (A) After normal image recording, the same image data is thinned out and recorded repeatedly. That is, density complementary recording is performed in which the nozzles with low density record a relatively large amount of image data, and the nozzles with high density record almost none.

(B) In order to suppress a decrease in recording speed, density supplementary recording is performed when the printer carriage is reversed.

(C) Recording data for one main scan is stored in a memory, and has two functions: density supplementary recording at the time of inversion and correction of the distance between the heads of each color.

(D) Give the correction data a phase difference or use random numbers so that streaks do not appear in the correction recording.

[Effects of the Invention] As described above, according to the present invention, it is possible to realize high-quality head recording density correction at low cost.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a block diagram of an electrical system of a printer explaining the present invention, and Fig. 3 is a diagram showing a timing chart to supplement the detailed explanation of the present invention. , Fig. 4 is a block diagram of another embodiment of the present invention, Fig. 5 is a diagram showing a timing chart of the embodiment of the present invention, Fig. 6 is a diagram showing the bubble jet discharge principle, and Fig. 7 is a diagram showing the conventional embodiment. FIG. 8 is a block diagram of a density correction circuit, FIG. 8 is a schematic diagram of a bubble jet printer, and FIG. 9 is a configuration diagram of a bubble jet head in a carriage. (-7atm) No. buff "Ruzoe, t=#裡"

Claims (1)

[Scope of Claims] 1) An inkjet head having a plurality of ejection nozzles that eject ink based on image data, and a device for generating density unevenness correction data by thinning the image data according to the recording density of each of the ejection nozzles. An inkjet printer comprising: a drawing means; and a control means for repeatedly recording density unevenness correction data generated by the thinning means using the ejection nozzle. 2) The inkjet printer according to claim 1, wherein the inkjet head records a normal image on an outward pass and records density unevenness correction data on a return pass. 3) The inkjet printer according to claim 1, wherein the density unevenness correction data is generated with a predetermined phase difference. 4) The inkjet printer according to claim 1, wherein the density unevenness correction data is generated by random number generation. 5) In claim 2, the inkjet head has a plurality of heads, and the thinning means stores image data for one scan in a memory, and eliminates density unevenness on the return path based on the data stored in the memory. An ink jet printer, wherein correction data is generated, and the control means uses the memory to correct the distance between each of the heads.