JP2863267B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a color image recording apparatus that forms an image using a plurality of recording heads. The present invention relates to a color ink-jet recording apparatus for forming an image.

2. Description of the Related Art Conventionally, in an apparatus of this type, for example, an ink jet recording apparatus, ink is ejected from a plurality of ink ejection ports formed in a recording head based on a data signal, and ink droplets are attached to a recording medium for recording. It is carried out. This recording method has been widely used in, for example, printers, facsimile machines, and copiers.

As a recording type of the ink jet recording apparatus, a recording head is mounted on a carriage moving along a recording medium and scanning is performed in the width direction of the recording medium to perform recording for each line as in the other recording methods. There are a serial type and a line type in which printing is performed using a so-called full multi-head in which ink ejection openings for one line are arranged in a print head.

By the way, in recent serial printers,
Increasingly, a recording head body or a cartridge in which this and an ink tank serving as an ink supply source are integrated can be replaced when a user of the recording apparatus fails or the ink becomes exhausted.

[Problems to be Solved by the Invention] However, in the above-described conventional recording apparatus,
Due to the replacement of the recording head or the cartridge, the recording dot position of each color deviates from the ideal position due to the manufacturing accuracy of the apparatus main body and the recording head, and the quality of the recorded image is reduced due to the color deviation or the decrease in resolution. There's a problem.

To prevent this, after replacing the head, the user records an image from which the recording dot position of each color can be determined, and manually adjusts the head fixing position so that the recording dot is printed at the optimum position while viewing the image. Correction of the recording dot position has been performed by making a correction or by switching an external selection switch to electrically change the ink ejection timing.

However, this method is very time-consuming, and it becomes very difficult for the user to visually determine the optimum recording dot position as the recording apparatus has a higher resolution.

Of course, changes in landing accuracy and the like can occur due to aging and the like, and such problems are fixed recording heads and full multi-type recording heads that do not require replacement, and even other than the inkjet method. This also occurs in a recording head of the system.

An object of the present invention is to solve such a problem and to provide an image forming apparatus capable of always performing good image recording.

[Means for Solving the Problems] For this purpose, the invention according to claim 1 is an image forming apparatus that forms an image on a recording medium by using a plurality of recording heads, so that the image is superimposed on the same reference dot position. Driving means for driving a first recording head and a second recording head among the plurality of recording heads to form first and second dots; and an overlap of the first dot and the second dot. A control means for controlling the drive timing of the first print head and the second print head according to the state is provided.

According to a second aspect of the present invention, there is provided an image forming apparatus according to the first aspect, further comprising a reading unit for optically reading an image formed on the recording medium, wherein the control unit controls the first unit by the reading unit.
The drive timing of the first print head and the second print head is controlled based on the result of reading the overlapping state of the dot and the second dot.

According to a third aspect of the present invention, in the first or second aspect, the driving unit is configured to control the first recording head and the second recording head at a plurality of reference dot positions arranged at predetermined intervals in a predetermined area. And the control means controls the drive timing of the first print head and the second print head based on the ink coverage of the predetermined area. Features.

A fourth aspect of the present invention is characterized in that, in any one of the first to third aspects, the plurality of recording heads respectively correspond to recording materials of different colors.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the recording head is an inkjet recording head that forms an image by discharging ink on a recording medium.

A sixth aspect of the present invention is characterized in that, in the fifth aspect, the ink jet recording head has an electrothermal conversion element used for causing ink to eject the ink by causing film boiling.

According to the present invention, in an image forming apparatus that forms an image by ejecting ink according to an image density signal by a plurality of recording heads, each head is disposed within a predetermined area at a predetermined interval. Multiple reference dot states (for example,
Based on a test pattern image obtained by driving under the conditions corresponding to the first and second dots, the dot recording state (for example, recording dot position) of each head is changed to the optimum reference dot state (for example, the first and second dots). Correction to the state where the second dot is hit at the same position) makes it possible to print at a more optimal recording dot position without the trouble of a user manually compensating for color shift, And the resolution can be prevented, and the printing quality can be improved.

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

FIG. 1 shows a main part of a serial printer type color ink jet recording apparatus according to an embodiment of the present invention.
A recording head 1a that ejects yellow Y color ink, a recording head 1b that ejects magenta M color ink, a recording head 1C that ejects cyan C color ink, and a recording head 1d that ejects black Bk color ink, It is installed on the carriage 2 at a distance D as shown in FIG. FIG. 2 is a plan view of the ejection openings 8 of the recording heads as viewed from the front, and is arranged side by side for Bk, C, M, and Y from the left. An element (e.g., an electrothermal converter) that generates energy (e.g., thermal energy) used for ink ejection is disposed in the liquid path inside each ejection port.

In FIG. 1, the carriage 2 moves right and left along a guide shaft 3 at a speed V. Further, the recording medium 4
The recording head is kept horizontal with respect to the ink discharge port forming surface of the recording head by a pair of conveying rollers 5 installed vertically. And
Ink droplets adhere to the recording medium 4 in the order of black Bk, cyan C, magenta M, and yellow Y, and a multicolor image is formed. Reference numeral 6 denotes an encoder, which is read by an optical sensor provided in the carriage 2, and controls the ink ejection timing according to the scanning position of the recording head. Reference numeral 7 denotes a reflection type optical sensor mounted on the carriage 2 similarly to the recording head, and is used for detecting a recording dot position.

Reference numeral 10 denotes a recovery device, which is disposed at the home position of the recording heads 1a to 1d and can cover the discharge port forming surface of the head, a pump disposed behind the cap, or further a discharge port forming surface. A cleaning member may be provided. By using such a recovery device, for example, the following recovery process for stabilizing the ejection state can be performed. That is, when dust or bubbles enter the liquid path inside the discharge port, or when the ink in the liquid path thickens and becomes unsuitable for discharge, the cap is brought into contact with the recording head, The suction force is applied by the pump to forcibly discharge the ink from the discharge port, and the cause of the discharge failure can be removed together with the ink. In addition, ink ejection (preliminary ejection) can be performed by driving the recording head in a state where the cap faces the recording head in the same manner as during normal driving. Further, after such processing, the cleaning member can be cleaned by engaging the cleaning member with the discharge port forming surface. In addition, the cap can be kept in contact with the ejection port forming surface during non-printing to protect the cap.

 Next, a control system of the present example apparatus will be described.

FIG. 3 shows one configuration example of the control system. Here, H is a host device that supplies image data and various commands related to recording to the device of this example, and has a computer, an image reader, and other forms. Reference numeral 101 denotes a CPU serving as a main control unit of the apparatus of the present example, which has a microcomputer form,
Each unit is controlled in accordance with a processing procedure described later. 102 is a ROM storing a program and other fixed data corresponding to the processing procedure, and 219 is a RAM having a temporary storage area for image data and an area used for work during various control processes.

Reference numeral 106 denotes an instruction input unit for giving an on-line switch with the host device, a command input for recording start, a command input for test pattern recording for dot deviation correction, and the like.
108 is the presence or absence of the recording medium, the transport state, the presence or absence of
Sensors for detecting other operation states. Reference numeral 110 denotes a display unit, which is used to notify the operation state, setting state, and presence / absence of an abnormality of the apparatus. An image processing unit 111 performs logarithmic conversion, masking, UCR, and color balance adjustment on image data to be recorded.

Reference numeral 112 denotes a head driver for driving an ink ejection energy generating element of the recording head 1 (the heads 1a to 1d are collectively shown). Reference numeral 120 denotes a head control unit described later with reference to FIG. Reference numeral 113 denotes a temperature adjusting unit for adjusting the temperature of the recording head 1, and specifically, may include, for example, a heater for heating and a cooling fan provided for the head 1. 111 is a drive mechanism of the recovery device, 115 is a mechanism including a motor for scanning the print head and the reading unit, and 116 is a drive unit of a motor for driving the print medium transport system.

 FIG. 4 shows a configuration example of the head control unit 120.

Here, 11a is a recording head and a driver that ejects yellow Y color ink, 11b is a recording head and a driver that ejects magenta M color ink, 11c is a recording head and a driver that ejects cyan C color ink, and 11d is a A recording head and a driver that eject black Bk color ink.

12a, 12b, 12c and 12d are image density signals of yellow Y, magenta M, cyan C and black Bk, respectively, 14a,
14b, 14c and 14d are signals of yellow Y, magenta M, cyan C and black Bk, respectively, which have been binarized by the binarization processing unit 13.

Reference numerals 15a, 15b, 15c and 15d denote buffers for controlling the ink ejection timing. Reference numerals 17a, 17b, 17c, and 17d are signals of yellow Y, magenta M, cyan C, and black Bk, which are distributed to elements for causing each recording head to perform ink discharge by the shift registers 16a, 16b, 16c, and 16d. The number of stages of each shift register of the shift registers 16a, 16b, 16c, 16d is configured to be the same as the number of each head. Reference numeral 18 denotes a recording dot position detection circuit, and the ejection timing is controlled by an ejection timing setting / control circuit 19 based on a signal from this circuit.

 The outline of the correction method in this example is shown below.

When the recording dot position correction is activated by the instruction input unit 106 of the apparatus, the test pattern shown in FIG. 5 is printed. The test pattern is printed in a combination of Bk + C, Bk + M, and Bk + Y based on the recording dot position of black Bk. Here, the case of Bk + C is shown.

FIG. 5 (A) shows a case where the recording dot positions of black Bk and cyan C completely match, and FIG. 5 (B) shows that the ejection timing of cyan C is later than black Bk.
This shows the case where both recording dot positions are shifted,
FIG. 5 (C) shows a case where the ejection timing of cyan C is earlier than that of black Bk, and there is a shift between the recording dot positions of both.

FIG. 6 shows an output signal waveform when the optical sensor 7 reads a test pattern.

In this example, the test pattern on the recording medium surface is read by the optical sensor 7 and the recording dot position matching accuracy is determined based on the change in reflected light intensity. In this case, it is desirable that the optical sensor 7 has no spectral sensitivity for each color.

The reflected light intensity change is output as a voltage or current value change. FIG. 6 (A) shows a case where the recording dot positions are completely coincident as shown in FIG. 5 (A), and FIG. 6 (B) shows a case where the reference color black Bk is used as shown in FIG. 5 (B). 6C shows a case where the ejection timing of the other color is late and the recording dot positions of both colors are shifted, and FIG. This shows the case where the color ejection timing is fast and the recording dot positions of both colors are shifted.

In this embodiment, a detection method based on a change in current value is described. The coincidence accuracy of the recording dot positions is determined by the time t in FIG. 6, and the shorter the time t, the higher the coincidence accuracy. Therefore, by controlling the ejection timing of the other head with respect to the black Bk head in accordance with the time t, it is possible to correct the displacement of the recording dots.

FIG. 7 shows an example of an ejection timing correction processing procedure according to this example.

When this procedure is started, first, the temperature of each head is adjusted in step S100A. This is due to the following reasons.

In an ink jet recording apparatus, the recording head is usually kept in a predetermined temperature range (for example, about 40 ° C., which is a first temperature adjustment reference), for suppressing fluctuations in image density and stabilizing ejection. On the other hand, when images are actually continuously recorded, the temperature of the head may be increased, and recording may be performed at a maximum temperature of 50 ° C., which is the second temperature adjustment reference.

Therefore, when this procedure is started immediately after image formation, if the used amount of each recording dot varies depending on the content of the image being formed, the ink viscosity changes according to the temperature, and thus each head has The ink ejection amount, that is, the dot diameter varies, and in this example in which the overlapping state of the dots is determined at the time t, there is a possibility that the displacement cannot be accurately detected. Further, even when the recording head is not yet controlled within a temperature range adjusted during normal recording, such as immediately after the apparatus is turned on or in a bad environment, it is also conceivable that accurate detection of a position shift may not be performed similarly. .

Therefore, as in this example, the temperature of each head is adjusted in advance, each head is controlled to a temperature adjustment range performed during normal recording, a test pattern is formed, and correction is performed based on the test pattern. Can be prevented.

The temperature to be adjusted may be uniform for each head, or may be determined for each head according to the ejection conditions and the frequency of use of each head. However, the test is performed at an appropriate adjustment temperature during normal recording. Preferably, a pattern is recorded.

Next, in this example, an ejection stabilizing operation is performed in step S100B. This is because if the test pattern formation processing is performed as it is in a case where the recording head does not have normal ejection characteristics due to thickening of ink, mixing of dust or air bubbles, faithful head characteristics are recognized. This is because there is a possibility that the operation cannot be performed.

At the time of the ejection stabilization process, the recording heads 1a to 1d and the recovery device 220 are opposed to each other, and the above-described suction process is performed to forcibly eject ink from the ejection ports.
Further, it is also possible to clean the discharge port forming surface by abutting the ink absorber disposed on the cap unit with the discharge port forming surface, or by blowing air or wiping. Further, it is also possible to drive the print head in the same manner as during normal printing to perform preliminary ejection (however, the driving energy at the time of preliminary ejection is not necessarily the same as during printing). That is, the same processing as the so-called ejection recovery operation performed in the inkjet recording apparatus may be performed.

Note that, instead of or after the above-described processing, a pattern for stabilizing ejection can be recorded on a recording medium. Then, a test pattern or the like for density unevenness correction may be recorded thereafter.

Next, print the test pattern shown in FIG. 5 in step S101, performs the test pattern read by the optical sensor 7 at step S102, stores the time t as t ₀ in the waveform shown in Figure 6 at step S103 .

In step S104, the discharge timing of the control target head is advanced by one step with respect to the reference color head (Bk head in this example), the test pattern is printed again in step S105, and the test pattern is read in step S106. the time t in the waveform shown in FIG. 6 at S107 t ₁
To be stored.

Step S108 compares the t ₀ and t ₁ and time, when the paddle short towards the time the changed ejection timing t ₁ is the step S1
Storing time t ₁ as t ₀ at 16, again in 1 Sutebbu faster the discharge timing of the control target head at step S117, the test pattern printed in step S118, S119, S120, reading,
It performs an operation of storing the time t of a waveform change portion as t _1.

The time t at step S121 compared to t _1, t ₁ is the case longer than t ₀ slowed 1 Step ejection timing of the control target head at step S122, and terminates the correction as the state before the re-correction. On the other hand, if the t ₁ is applied shorter than t ₀ at step S121 the operation from step S116 to step S121
Repeat until t ₁ > t ₀ is satisfied.

If the time t ₁ is longer than t ₀ Step S108, the ejection timing of the controlled head by one step late in step S109, the printing of the test pattern at step S110, S 111, S112, read, and read waveform change storing the time t of the part as t _1.

Step S113 compares the t ₀ and t ₁ in, it terminates the correcting ejection timing of the controlled head as a state before the re-correction by one step quickly. Step S113 in t ₁ is the From step S109 if it takes shorter than t ₀ to step S113 t ₁
Repeat until t> ₀ is satisfied.

It is desirable that the one-step correction amount of the ejection timing can be corrected by an amount equal to or less than the recording dot pitch.

As shown in FIG. 8 (A), when the recording dot positions of the reference head and the control target head are separated from each other by a recording dot pitch or more, there are two waveform changes in the output corresponding to the read light intensity. .

In this case, reference is made to the counter pulse having the same pulse waveform as the black Bk ejection timing in FIG. 8B, and if there are two test pattern reading waveform changes between each pulse, the change time t is changed. By setting as shown in FIG. 8 (A), erroneous detection can be eliminated.

The sequence for determining and correcting the recording dot position accuracy described above is performed for each combination of black Bk vs. cyan C, black Bk vs. magenta M, black Bk vs. yellow Y,
The correction is performed until the correction of all combinations is completed. In addition, the corrected ejection timing correction condition is written in a nonvolatile RAM or the like, and the power supply of the apparatus is turned on unless the correction is performed again.
Even if it is turned off, it can be made to be stored.

In this example, the sequence is performed in response to an instruction input by the operator. However, the sequence may be started at an appropriate timing, such as every predetermined period or every time the apparatus is turned on.

FIG. 9 is an enlarged view of a test pattern for recording dot position detection according to another embodiment of the present invention.

Each of the colors is printed by thinning out one dot or two dots. FIG. 9A shows a reference color head (black B).
k) and the recording dot position of the control target head (here, cyan C) match. FIG. 9 (B)
Indicates that the recording dot positions of the reference color head and the control target color head are shifted.

The optical sensor used in this embodiment has a lower resolution than that of the sensor shown in the previous embodiment, and can measure an average of the portion within the dotted line in FIG. 9A.

FIG. 10 shows an output current value from the optical sensor according to the present example.

Output current value when the recording dots with the print head control target head match indicates I _0, if there is a deviation in the recording dot positions of the output color by the reference color and the controlled object head output current value It is the I _1. Here I ₁ <I ₀ ,
This is because, when there is a shift in the recording dot position, the output current from the optical sensor decreases due to a decrease in the whiteness of the paper, that is, a decrease in the amount of reflected light, due to a large amount of ink coverage per unit area. is there.

When the actual correction is performed, the initial output current value is compared with the output current value obtained when the discharge timing of the control target color is corrected by the same method as the sequence shown in FIG. The ejection timing can be corrected so that the value becomes maximum. Incidentally, in this case, the value of I ₀ by the color combinations are different is, to change the value of I ₀ is a reference value in accordance with the combination is preferred.

Further, when a test pattern is recorded by a recording head, depending on the type of recording medium, ink recorded from each recording head is not instantaneously absorbed, and the state of the test pattern recorded on the recording medium is not immediately stabilized. If there is a possibility that accurate dot misalignment may not be detected,
A standby process is performed until the test pattern recorded by each recording head has settled down to a stable state, so that the test pattern cannot be read.

In the above description, a case is described in which a correction is performed to obtain a state in which there is no recording dot position shift between recording heads as a recording dot state to be formed, and a test pattern used for the correction is recorded. Although it has been described that the recording dots of the control target recording head are formed so as to be overlaid on the recording dots of the head, the present invention is not necessarily limited to such an embodiment.

For example, dots may be simultaneously formed on the reference recording head and the control target head at a certain scanning position of the carriage, instead of being formed under driving conditions under which a test pattern is overprinted. In this case, the distance between the two heads is obtained based on the output obtained by scanning them with the reading sensor (for example, by measuring the peak-to-peak), and this is determined by the predetermined distance (that is, the ejection defined for the control target head). (A standard distance that does not cause dot misalignment when driven with the timing adjustment value.)
If not, the correction may be performed on the assumption that a dot position shift occurs.

Further, by comparing the density distribution pattern obtained by the scanning scan of such a test pattern with a density distribution pattern that is a reference in terms of shape and size, the density of recording dots, that is, the ink ejection amount is also controlled.
That is, the density may be corrected not only by correcting the recording dot position as the reference dot state to be formed but also by adjusting the ejection amount between the heads.

Further, the reference dot state is, specifically, an overlap of dots recorded by a plurality of heads, and the overlapping state is to match the dot centers or to further match the radius (size). For example, a state determined to obtain an optimal formed image can be obtained.

(Others) The present invention is not limited to the ink jet recording method, and is applied to a recording apparatus using various recording methods such as a thermal printer. This provides an excellent effect in the recording apparatus. This is because according to such a method, it is possible to achieve higher density and higher definition of recording.

As for the representative configuration and principle, it is preferable to use the basic principle disclosed in, for example, US Pat. Nos. 4,723,129 and 4,740,796. This method can be applied to any of the so-called on-demand type and continuous type. In particular, in the case of the on-demand type, it is arranged corresponding to the sheet or liquid path holding the liquid (ink). Applying at least one drive signal corresponding to recording information and providing a rapid temperature rise exceeding nucleate boiling to the electrothermal transducer, thereby causing the electrothermal transducer to generate heat energy, and This is effective because a film in the liquid (ink) corresponding to the driving signal can be formed one by one by causing film boiling on the heat acting surface. The liquid (ink) is ejected through the ejection opening by the growth and contraction of the bubble to form at least one droplet. When the drive signal is formed into a pulse shape, the growth and shrinkage of the bubble are performed immediately and appropriately, so that the ejection of a liquid (ink) having particularly excellent responsiveness can be achieved, which is more preferable. U.S. Pat. No. 44
Those described in JP-A-63359 and JP-A-4345262 are suitable. Further, if the conditions described in US Pat. No. 4,313,124 relating to the invention relating to the temperature rise rate of the heat acting surface are employed, more excellent recording can be performed.

As a configuration of the recording head, in addition to a combination configuration (a linear liquid flow path or a right-angled liquid flow path) of a discharge port, a liquid path, and an electrothermal converter as disclosed in the above-mentioned specifications, A configuration using U.S. Pat. No. 4,558,333 and U.S. Pat. No. 4,459,600, which disclose a configuration in which is disposed in a bending region, is also included in the present invention. In addition, Japanese Unexamined Patent Publication No. 59-123670 discloses a configuration in which a common slit is used as a discharge portion of an electrothermal converter for a plurality of electrothermal converters, and an opening for absorbing a pressure wave of thermal energy is provided. The effect of the present invention is also effective when used in JP-A-59-138461, which discloses a configuration corresponding to a discharge unit. That is, according to the present invention, recording can be reliably and efficiently performed regardless of the form of the recording head.

Further, even with respect to a full line type recording head having a length corresponding to the maximum width of a recording medium that can be recorded by the recording apparatus, the dot position shift due to a temporal change of the head itself and its surrounding mounting members, etc. Therefore, the present invention can be effectively applied. Such a recording head may have a configuration that satisfies the length by a combination of a plurality of recording heads, or a configuration as one integrally formed recording head.

In addition, the serial type as described above and the recording head fixed to the apparatus main body are also effective for coping with the above-mentioned aging. In addition, a replaceable chip-type recording head that can be electrically connected to the apparatus main body or supplied with ink from the apparatus main body by being attached to the apparatus main body, or an ink tank integrated with the recording head itself The use of the provided recording head of the cartridge type is particularly effective in coping with dimensional errors and the like in addition to the above-mentioned aging.

Further, it is preferable to add recovery means for the print head, preliminary auxiliary means, and the like provided as a configuration of the printing apparatus in the present invention since the effects of the present invention can be further stabilized. If these are specifically mentioned, capping means for the recording head, cleaning means, pressurizing or suction means, preheating means using an electrothermal transducer or another heating element or a combination thereof, Performing a preliminary ejection mode in which ejection is performed separately from printing is also effective for performing stable printing.

Regarding the type or number of print heads to be mounted, a plurality of print heads may be provided corresponding to a plurality of inks having different densities in addition to those having different print colors. That is, for example, as a printing mode of the printing apparatus, a printing mode using dark and light ink of only a mainstream color such as black,
The present invention is also very effective for an apparatus provided with at least one of multi-colors of different colors or full-colors of mixed colors, although the recording head may be formed integrally or by a combination of a plurality of print heads.

In addition, in the embodiments of the present invention described above, the ink is described as a liquid. However, an ink that solidifies at or below room temperature and softens or liquefies at room temperature, or the ink itself in an inkjet method. In general, the temperature is controlled within a range of 30 ° C. or more and 70 ° C. or less to control the temperature so that the viscosity of the ink is in a stable ejection range. I just need. In addition, the temperature rise due to thermal energy can be positively prevented by using it as energy for changing the state of the ink from the solid state to the liquid state, or ink that solidifies in the notification state to prevent evaporation of the ink can be used. In either case, the ink is liquefied by the application of the thermal energy according to the recording signal, and the ink is liquefied, and the liquid ink is discharged. The present invention is also applicable to a case where an ink that liquefies for the first time by energy is used. The ink in such a case is disclosed in
As described in JP-A-56847 or JP-A-60-71260, a form in which the porous sheet is opposed to the electrothermal converter while being held as a liquid or solid substance in the concave portions or through holes of the porous sheet. It may be. In the present invention, the most effective one for each of the above-mentioned inks is to execute the above-mentioned film boiling method.

In addition, the form of the ink jet recording apparatus of the present invention may be used as an image output terminal of an information processing apparatus such as a computer, a copying apparatus combined with a reader or the like, or a facsimile apparatus having a transmission / reception function. Or the like.

[Effects of the Invention] As described above, according to the present invention, in an image forming apparatus that forms an image by ejecting ink in accordance with an image density signal by a plurality of recording heads, each head is positioned within a predetermined area. The state of dot recording of each head based on a test pattern image obtained by driving under a condition corresponding to a plurality of reference dot states (for example, a state where the first and second dots coincide with each other) arranged at predetermined intervals. (For example, a recording dot position) is corrected to an optimum reference dot state (for example, a state in which the first and second dots are hit at the same position), thereby causing a trouble of manual correction by a user. Print at the most suitable recording dot position,
It has become possible to prevent color misregistration and reduction in resolution, and to improve print quality.

In addition, since the recording dot positions of the other heads are corrected with reference to one of the heads, the positional deviation between the heads can be reliably and easily corrected.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram of a serial printer type color ink jet recording apparatus according to an embodiment of the present invention, FIG. 2 is a front view showing an example of a head configuration in the color ink jet recording apparatus shown in FIG. FIG. 4 is a block diagram showing a configuration example of a control system of the apparatus shown in FIG. 1, FIG. 4 is a block diagram showing a configuration example of a dot misregistration correction unit in this example, and FIGS. FIGS. 6A to 6C are explanatory diagrams showing test pattern images used in an example, and FIGS. 6A to 6C are waveform diagrams showing output signal waveforms obtained by reading the test pattern images of FIGS. 5A to 5C with an optical sensor. FIG. 7 is a flowchart showing an example of a sequence for determining and correcting the recording dot position in the present embodiment. FIGS. 8A and 8B are output signal waveforms obtained by reading a test pattern image with an optical sensor, respectively. of 9 (A) and 9 (B) are explanatory diagrams showing test pattern images used in another embodiment of the present invention, and FIG. 10 is an explanatory diagram showing an example of a counter pulse waveform. FIG. 4 is an explanatory diagram showing an output current value when a test pattern image is read by an optical sensor. 1, 1a to 1d: recording head, 2: carriage, 3: guide shaft, 4: recording paper, 5: transport roller, 6: encoder, 7: optical sensor, 8: ink ejection port, 10: recovery device,
11 print head and driver, 12 image density signal, 13
... Binarization processing section, 14... Binarized signal, 15 .buffer, 16... Shift register.

Claims (6)

(57) [Claims] An image forming apparatus for forming an image on a recording medium by using a plurality of recording heads, wherein the first recording head and the second recording head of the plurality of recording heads are overlapped at the same reference dot position. Driving means for driving a recording head to form a first dot and a second dot; and the first recording head and the second dot in accordance with an overlapping state of the first dot and the second dot. And a control means for controlling the drive timing of the recording head. 2. A reading means for optically reading an image formed on the recording medium, wherein the control means reads the overlapping state of the first dot and the second dot by the reading means. And controlling the driving timing of the first recording head and the second recording head based on the result.
An image forming apparatus according to claim 1. 3. The printing device according to claim 1, wherein the driving unit is configured to overlap the plurality of reference dot positions arranged at predetermined intervals in a predetermined area by the first recording head and the second recording head. 3. The method according to claim 1, wherein the control unit controls a drive timing of the first print head and the second print head based on an amount of ink coverage in the predetermined area. The image forming apparatus as described in the above. 4. An image forming apparatus according to claim 1, wherein said plurality of recording heads correspond to recording materials of different colors, respectively. 5. The image forming apparatus according to claim 1, wherein said recording head is an ink jet recording head which forms an image by discharging ink on a recording medium. 6. An image forming apparatus according to claim 5, wherein said ink jet recording head has an electrothermal conversion element used to cause ink to eject the ink by causing film boiling.