JP2938934B2 - 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, and more particularly to an image forming apparatus that forms an image using a recording head having a plurality of recording elements arranged.

In particular, the present invention relates to an apparatus having a mechanism for automatically adjusting the print characteristics of a recording head of an ink jet recording apparatus, and is particularly effective for an apparatus for forming a color image at a high gradation by overlapping ink droplets.

[Background Art] With the spread of information processing devices such as copying machines, word processors and computers, and communication devices, digital images are formed by using a recording head of an ink jet system or a thermal transfer system as an image forming (recording) device of these devices. Recorders are rapidly becoming popular. In such a printing apparatus, in order to improve the printing speed, it is common to use a printing head in which a plurality of printing elements are integrated and arranged (hereinafter, referred to as a multi-head in this section).

For example, in an ink jet recording head, a so-called multi-nozzle head in which a plurality of ink ejection ports and liquid paths are integrated is generally used, and a plurality of heaters are generally integrated in a thermal transfer type or a thermal type thermal head. .

However, it is difficult to uniformly manufacture the recording elements of the multi-head due to the characteristic variation due to the manufacturing process, the characteristic variation of the head constituent material, and the like, and a certain degree of variation occurs in the characteristic of each recording element. For example, in the above-described multi-nozzle head, variations occur in the shape of the ejection ports and liquid paths, and in the thermal head, variations also occur in the shape, resistance, and the like of the heater. Such non-uniformity of characteristics among the recording elements appears as non-uniformity in the size and density of dots recorded by each recording element,
Eventually, density unevenness occurs in the recorded image.

To cope with this problem, various methods have been proposed for visually detecting the density unevenness or visually inspecting the adjusted image and manually correcting the signal applied to each recording element to obtain a uniform image. .

For example, in a multi-head 330 in which the recording elements 31 are arranged as shown in FIG. 20A, when the input signal to each recording element is made uniform as shown in FIG. 20B, uneven density is visually found as shown in FIG. 20C. In this case, as shown in Fig. 20D, it is common to correct the input signal and give a large input signal to the recording element in the low density part and a small input signal to the recording element in the high density part. Also known as

It is known that in the case of a recording method capable of modulating a dot diameter or a dot density, gradation recording is achieved by modulating a dot diameter to be recorded by each recording element according to an input.
For example, in the case of an inkjet recording head using a piezo method or a bubble jet method, the driving voltage or pulse width applied to each ejection energy generating element such as a piezo element or an electrothermal conversion element is used. In the thermal head, the driving voltage or pulse width applied to each heater is used. Is modulated according to an input signal, it is considered that the dot diameter or dot density of each recording element can be made uniform, and the density distribution can be made uniform as shown in FIG. 20E. Also, when it is difficult or difficult to modulate the drive voltage or pulse width, or when it is difficult to adjust the concentration over a wide range even if they are modulated,
For example, when one pixel is composed of a plurality of dots,
The number of dots to be recorded is modulated according to the input signal, so that a large number of dots can be recorded in a low density portion and a small number of dots can be recorded in a high density portion. In the case where one pixel is composed of one dot, the dot diameter can be changed by modulating the number of ink ejections (the number of ejections) for one pixel in the ink jet recording apparatus. As a result, the concentration distribution can be made uniform as shown in FIG. 20E.

Japanese Patent Application Laid-Open No. 57-41965 filed by the present applicant discloses that a color image is automatically read by an optical sensor and a correction signal is given to each color ink jet recording head to form a desired color image. I have. This publication discloses basic automatic adjustment, and discloses important technical disclosures. However, various problems become evident in application to various device configurations in the course of practical application, but the technical problem of the present invention is not recognized in this publication.

On the other hand, other than the concentration detection method, JP-A-60-206660, U.S. Patent No. 4,328,504, JP-A-50-147
As disclosed in JP-A-241-241 and JP-A-54-27728, there is known an apparatus in which a landing position of a droplet is automatically read and corrected so that the droplet lands at an accurate position. These methods are also common as automatic adjustment techniques, but do not recognize the technical problem of the present invention.

[Problem to be Solved by the Invention] In order to cope with such a problem, a density unevenness reading unit is provided in the image forming apparatus, and the density unevenness distribution in the printing element array range is periodically read to obtain density unevenness correction data. It is effective to recreate it. According to this, even if the density unevenness distribution of the head changes, the correction data is created again in accordance with the change, so that a uniform image without unevenness can be always maintained.

On the other hand, when the recording head and the reading unit are provided in the same device, the recording head may have an undesirable effect on the reading unit. For example, in the case of an ink jet recording apparatus, ink mist, water droplets, and the like generated from a recording head adhere to a reading sensor, a light source, and the like of a reading unit, and the reading accuracy is reduced, and accurate unevenness correction may not be performed. Generally, there is also a possibility that paper dust and other dust of the recording paper may adhere to the reading unit.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of executing an accurate and stable reading operation without increasing the size of the apparatus.

[Means for Solving the Problems] For this purpose, an image forming apparatus according to the present invention includes a recording head in which a plurality of recording elements are arranged to form an image on a recording medium, and a carriage or a carriage on which the recording head is mounted. A reading unit provided on a member that moves in conjunction with the reading unit, a housing that protects the reading unit inside when the reading unit is not reading, and an optical path of the reading unit that can be opened when reading by the reading unit. And a shutter provided on the housing.

According to the present invention, in an image forming apparatus for forming an image on a recording medium using a recording head in which a plurality of recording elements are arranged, a carriage on which the recording head is mounted or a member that moves in conjunction with the carriage is provided. A reading unit, a housing for internally protecting the reading unit when the reading unit is not reading, and a shutter provided in the housing so that an optical path of the reading unit can be opened when reading by the reading unit. It is characterized by having.

[Operation] According to the present invention, a reading unit is provided on a carriage or a member (a head or the like) that is moved in conjunction with the carriage so that an image formed by the head can be compactly read. By providing a housing that protects the reading means inside when not reading, and by providing a shutter for opening the optical path when reading the reading means with respect to the housing, when the reading means is not reading, the reading means can be made of paper dust or the like. It is effectively protected from dirt caused by sneaking in of water droplets, ink mist, etc., and enables accurate reading.

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

(1) Mechanical configuration of the apparatus (FIGS. 1 to 5) (2) Control system (FIGS. 6 to 8) (3) Unevenness correction sequence (FIGS. 9 to 16) (4) ) Other Embodiments (FIGS. 17 to 19) (5) Others (1) Mechanical Configuration of Apparatus, etc. FIG. 1A schematically shows a serial printer type ink jet recording apparatus according to an embodiment of the present invention. The recording heads 201C, 201M, 201Y, and 201BK are supplied with inks of cyan, magenta, yellow, and black from ink tanks (not shown) via ink tubes.
The ink supplied to the recording heads 201C, 201M, 201Y, and 201BK is driven by a recording head driver or the like in accordance with a recording signal corresponding to recording information from a main control unit described later with reference to FIG. Ink droplets are ejected from each recording head and recorded on the recording medium 202.

A conveyance motor 208 is a drive source for intermittently feeding the recording medium 202, and a main scanning motor 206 for driving the feed roller 204 and the conveyance roller 205 is a main scanning carriage 203 for driving the main scanning belt.
It is a driving source for scanning in the directions of arrows A and B via 210. In this embodiment, a pulse motor is used for the paper feed motor 208 and the main scanning motor 206 because accurate paper feed control is required.

When the recording medium 202 reaches the feed roller 205, the feed roller clutch 211 and the conveying motor 208 are turned on, and the recording medium 20
2 is transported on the platen 207 until it reaches the transport roller 204. The recording medium 202 is detected by a detection sensor 212 provided on a platen 207, and the sensor information is used for position control, jam control, and the like. When the recording medium 202 reaches the conveyance roller 204, the feeding roller clutch 211 and the conveyance motor 208 are turned off, and a suction operation is performed from inside the platen 207 by a suction motor (not shown), so that the recording medium 202 is moved to the image recording area. To the platen 207. Recording medium 2
Prior to the image recording operation on 02, the scanning carriage 203 is moved to the position of the home position sensor 209, and then forward scanning is performed in the direction of arrow A, and cyan, magenta, yellow, and black inks are moved from a predetermined position. The recording head 201C
The image recording is performed by ejecting from # 201BK to # 201BK. When the image recording for the predetermined length is completed, the scanning carriage 203 is stopped, and conversely,
The backward scanning is started in the direction of arrow B, and the scanning carriage 203 is returned to the position of the home position sensor 209. During the backward scanning, the paper is fed in the direction of the arrow C by driving the transport roller 204 by the transport motor 208 to feed the paper by the length recorded by the recording heads 201C to 201BK.

In this embodiment, the recording heads 201C to 201BK are ink jet recording heads of a type in which bubbles are formed by heat and ink droplets are ejected at the pressure, and four ink jet heads each having 256 ejection ports are used. doing.

When the scanning carriage 203 stops at the home position detected by the home position sensor 209, the recovery device 290
Performs the recovery operation of the recording head 1. This is a process for performing a stable printing operation. In order to prevent unevenness at the time of the start of the discharge caused by a change in the viscosity of the ink remaining in the discharge port of the print head 201, the pause time, the temperature in the apparatus, the discharge This is a process of performing a suction operation on the recording head 201 by the recovery device 290, a preliminary ejection operation of ink, and the like according to pre-programmed conditions such as time.

By repeating the above operation, image recording is performed on the entire surface of the recording medium.

In the figure, reference numeral 214 denotes each of the recording heads 201C to 201C by the control circuit 215.
A density unevenness reading unit that reads a test pattern printed on the recording medium 202 by giving a uniform image signal to 201BK and outputs a reading signal.In this example, the reading unit is fixed to the main scanning belt 210 via a holder 244. The reading operation is performed on the platen 207. Therefore, the recording head and the reading unit are linked when moving.

In this example, the recording medium 202 on which the test pattern is recorded is illuminated by the light source 218, and the recording density of the test pattern recorded on the recording paper by each recording head is read by the reading sensors 217C, 217M, 217Y, 217BK. A / D converter 236 converts a read signal of the test pattern recording read by each read sensor read by each read sensor into a digital signal, and then temporarily stores the read signal in RAM 219.

Reference numeral 250 denotes an opening / closing unit that opens and closes a shutter as protection means of the reading unit 214 described with reference to FIG. 1B. The opening / closing unit 250 opens the shutter only when a test pattern is read. The opening / closing unit 250 is manually operated by an operator or the like, has a mechanism for opening and closing the shutter sequentially with engagement with the shutter, and has a reading mechanism. An appropriate form, such as one that issues an opening / closing command to a shutter opening / closing drive unit provided in the unit 214, may be used.

FIG. 1B is a side sectional view showing a configuration example of the reading unit according to the first embodiment of the present invention. Since the reading unit 214 is connected to the main scanning belt 210 via the holder 244, the reading unit 214 repeats reciprocation in the main scanning direction together with the carriage 203 during normal recording. Reading sensor 217 (each sensor 217C
The light receiving element 232, the lamp 233, and the filter 220 are respectively provided in a housing to prevent the light source 218 including the light receiving element 232, the lamp 233, and the filter 220 from being contaminated by ink mist. The shutters 245b and 246b are provided in the optical path portions of the housings.

245b and 246b are in a closed state as shown by a two-dot chain line in FIG. 1B, thereby preventing intrusion of ink mist and the like.
On the other hand, immediately before the reading unit 214 moves to the test pattern position and the uneven reading operation is performed, the shutter opening / closing unit
The shutters 245b and 246b are opened by the 250, and reading is performed. Then, immediately after the reading is performed, the shutter 245
b, 246b is closed.

With the above operation, it is possible to prevent contamination of the optical system due to ink mist, paper dust, water droplets, and the like in the apparatus, and to prevent deterioration of the density unevenness reading unit over time.

In the figure, the shutter is shown as a shutter that opens and closes inside the housing by rotating as shown by a dashed line in the figure. However, the shutter may be inserted or detached in other forms, for example, by sliding in a predetermined direction. It may open and close.

In a preferred embodiment, the shutter may be a sliding type, and a cleaner may be attached to a portion that slides on the reading mechanism to perform a cleaning action accompanying the opening / closing operation. The member may be shared.

FIG. 2 is a schematic diagram for explaining the reading unit of the present example.
In order to improve the read density of the density unevenness of the test pattern by the recording head recorded on the recording medium 202, color filters 220R, 220G, 220B are provided on the recording medium side of the illumination light source 18.
L is provided to irradiate C, M, and Y test patterns recorded on the recording medium 202 with R, G, and BL lights. Then, by irradiating the complementary color light to the test pattern of each color of C, M, Y in this way, the spectral sensitivity of each reading sensor 217C, 217M, 217Y, 217BK is different for each color of the test pattern. It is not necessary to read the density unevenness of each color while using the same sensor with the same spectral sensitivity for each sensor.

The image signal read in this manner is sent to the image forming unit, where it is used for correcting the driving conditions of the recording head as described later.

In the present invention, the meaning of adjusting so that density unevenness does not occur at the time of image formation means that the image density due to droplets from a plurality of liquid ejection ports of the recording head is made uniform by the recording head itself, or for each of the plurality of heads. At least one of the following: uniforming the image density of the image, or performing homogenization in order to obtain a desired color or a desired density by mixing a plurality of liquids.
And preferably satisfies a plurality of these.

As a means for correcting the density uniformity, it is preferable to automatically read a reference print giving the correction conditions and automatically determine the correction conditions, and add a manual adjustment device for fine adjustment and user adjustment to this. I do not deny that.

The purpose of correction determined by the correction conditions may be not only the optimum printing conditions, but also adjustment within a predetermined range including an allowable range, or a reference density that changes according to a desired image, and all of the purposes included in the purpose of correction are applied. You can do it.

As an example, a description will be given of a case of correcting density unevenness of a multi-head with a recording element number N in which the print output of each element is made to converge to an average density value for the purpose of correction.

It is assumed that the density distribution when each element (1 to N) is driven and printed by a certain uniform image signal S is as shown in FIG. First measuring the concentration OD ₁ ~OD _N in the portion corresponding to each recording element an average density as the correction object Ask for. The average density is not limited to each element, and may be obtained by a method of integrating the amount of reflected light to obtain an average value or a known method.

If the relationship between the value of the image signal and the output density of a certain element or element group is as shown in FIG. 4, the signal actually given to this element or this element group corrects the signal S to obtain the target density ▲ ▼. What is necessary is just to determine the resulting correction coefficient α. That is, the correction signal S obtained by correcting the signal S to α × S = (（/ OD _n ) × S may be given to this element or group according to the input signal S. More specifically, the fifth
This is performed by performing a table conversion as shown in the figure. Fifth
In the figure, the straight line A is a straight line of slope 1.0, although the input signal is a table which outputs without completely converting, line B is the gradient is linear in α = ▲ ▼ / OD _n input signals S
Is a table for converting the output signal into α · S.
Therefore, the correction coefficient α _n for each table as shown by the straight line B in FIG. 5 for the image signal corresponding to the n-th recording element
When the head is driven after performing the table conversion in which is determined, the densities of the portions recorded by the N recording elements become ▲
It becomes equal to ▼. If such processing is performed on all recording elements, density unevenness is corrected, and a uniform image is obtained. That is, unevenness can be corrected by previously obtaining data indicating what table conversion should be performed on an image signal corresponding to which recording element.

Needless to say, this objective correction may be performed by comparing the densities of the nozzle groups (in units of 3 to 5 nozzles) to perform an approximate uniform processing.

Although it is possible to correct the density unevenness by such a method, the density unevenness occurs later due to a change in the density unevenness state before correction or a change over time of the correction circuit depending on a use state of the apparatus or an environmental change. Therefore, in order to deal with such a situation, it is necessary to change the correction amount of the input signal. As a cause of this, it is conceivable that, as the ink jet recording head is used, a precipitate from the ink adheres to the vicinity of the ink ejection port or a foreign substance adheres to the vicinity of the ink ejection port, and the concentration distribution changes. . This is also predicted from the fact that the density distribution may change due to deterioration or deterioration of each heater in the thermal head. In such a case, for example, since the density unevenness correction is not sufficiently performed with the input correction amount set at the beginning of manufacturing or the like, the problem that the density unevenness gradually becomes conspicuous with use is also a problem in long-term use. This is a problem to be solved.

By the way, the interval between the reading unit and the recording medium on which the test pattern is recorded differs depending on the reading accuracy, but it is desirable that the interval is kept constant. However, in this example, since the reading unit is scanned on the platen 207, the interval is maintained. can do.

Also, the reflected light from the recording medium is incident on each reading sensor, and this incident light is light in a predetermined range on the test pattern by arranging an appropriate aperture member on the front surface of each sensor. Then, the average of the unevenness in the range is detected. According to our experiments, the aperture diameter is
About 0.2 to 1 mm was good. Then, if unevenness is corrected in accordance with the detection result, a uniform image can be obtained.

(2) Configuration of Control System Next, a description will be given of a control system of the apparatus of the present example configured by combining the above-described units.

FIG. 6 shows a 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 1 denotes a CPU serving as a main control unit of the apparatus of the present embodiment, which has a form of a microcomputer, and controls each unit according to 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 providing an on-line switch with the host device, inputting a command for starting recording, inputting a command for recording a test pattern for correcting density unevenness, and inputting information on the type of recording medium. Reference numeral 108 denotes sensors for detecting the presence or absence of a recording medium, the conveyance state, the presence or absence of the remaining amount of ink, and other operation states. Reference numeral 110 denotes a display unit, which is used to notify the operation state, setting state, and presence / absence of 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 201 (the heads 201Y, 201M, 201C, and 201BK are collectively shown). 113 is a temperature adjustment unit for adjusting the temperature of the recording head 201,
Specifically, it may include, for example, a heating heater 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 206 for scanning the print head and the reading unit, and 116 is a drive unit of a motor 208 for driving a print medium transport system.

FIG. 7 shows in detail a system for correcting density unevenness in the above configuration. Here, 121C, 121M, 121Y and 121BK are cyan, magenta, yellow and black image signals processed by the image processing unit 111, respectively. Reference numerals 122C, 122M, 122Y, and 122BK denote unevenness correction tables for the respective colors, which can be provided in the area of the ROM 102. 123C, 123M, 123Y and 123BK are image signals after the correction. 130C to 130BK are gradation correction tables for each color, and 131C to 131BK are binarization circuits using a dither method, an error diffusion method, or the like.
(Not shown in FIG. 7) to the respective color heads 1C to 1BK.

126C, 126M, 126Y and 126BK are the respective color signals read by the reading unit 214 via the respective color filters shown in FIGS. 1 and 2, and are input to the A / D converter 236.
Reference numeral 119 denotes a RAM area for temporarily storing the digital output signal, and the area of the RAM 219 can be used. 128C, 128
M, 128Y and 128BK are CPU based on the stored signal.
Reference numeral 101 denotes the calculated correction data. Reference numerals 129C to 129BK denote unevenness correction RAMs for the respective colors, and the area of the RAM 219 can be used. Then, the output of the non-uniformity correction signal 13 for each color is output.
0C to 130BK are the unevenness correction tables 122C to 122BK, respectively.
And the image signals 121C-121BK are supplied to the heads 201C-201BK.
Is converted so as to correct the unevenness.

FIG. 8 shows an example of the unevenness correction table.
There are 61 correction straight lines whose inclinations from = 0.70X to Y = 1.30X are different from each other by 0.01, and the correction straight lines are switched according to the unevenness correction signals 130C to 130BK. For example, when a signal of a pixel to be recorded at an ejection port having a large dot diameter is input, a correction straight line having a small inclination is selected, and when an ejection port having a small dot diameter is selected, a correction straight line having a large inclination is selected. to correct.

The non-uniformity correction RAMs 129C to 129BK record a correction straight line selection signal necessary for correcting non-uniformity of each head. That is, the unevenness correction signals having 61 types of values from 0 to 60 are stored for the number of ejection ports, and the unevenness correction signals 130C to 130BK are output in synchronization with the input of the image signals. Then, the signals 123C to 123BK whose unevenness has been corrected by the γ straight line selected by the unevenness correction signal are input to the tone correction tables 130C to 130BK, where the tone characteristics of each head are corrected and output. The signal is then converted to binary signals by the binarization circuits 131C to 131BK.
Valued, head 201C-201BK via head driver
, A color image is formed.

(3) Sequence of Unevenness Correction Under the above configuration, in this example, the following process is performed so that unevenness correction can be performed more accurately.

By performing the unevenness correction processing, the ejection energy generating element corresponding to the ejection port in the portion where the density of the head is high reduces the driving energy (for example, the drive duty), and conversely, the ejection energy generating element corresponding to the ejection port in the thin portion does not. Increase drive energy. As a result, density unevenness of the recording head is corrected and a uniform image is obtained.However, if the density unevenness pattern of the head changes during use, the unevenness correction signal used becomes improper and unevenness appears on the image. Occurs. In such a case, the following procedure is started by operating the unevenness correction signal rewriting mode instruction switch provided in the instruction input unit 106 to instruct to rewrite the unevenness correction data.

 FIG. 9 shows an example of an unevenness correction processing procedure according to this example.

When this procedure is started, first, in step S1, an input of the type of the recording medium is received. In this case, for example, a message “Please input the type of recording paper currently used” is displayed on the display unit 110 such as a liquid crystal panel. Upon seeing this, the operator designates the type of the recording medium currently used by using a switch or the like provided in the instruction input unit 106.
In step S3, a determination is made based on this, and if the type of the input recording paper is not optimal for density unevenness detection, such as an OHP sheet or a small amount of coated paper, the display unit 110 is displayed in step S5. For example, a message such as "Please use the specified paper" is displayed. As a result, if the specified paper is replaced again and the specified paper type is entered,
Alternatively, when the type of the input recording medium is a designated one from the beginning, the procedure proceeds to the following procedure.

In this embodiment, the type of the recording medium is re-inputted each time the mode enters the non-uniformity correction data rewriting mode, and based on the result, it is determined whether to rewrite the non-uniformity correction data.
However, information on the type of recording medium used is usually
It is often already specified at the time of recording. For example,
Since the tint of the recording output often differs depending on the type of recording medium, an image processing apparatus that changes image processing such as a masking coefficient according to the type of recording medium used is known.

Therefore, in a modified example of the present embodiment, the type of the recording medium used during normal recording is input, optimal image processing is performed in accordance with the input, and when entering the unevenness correction data rewriting mode, the input is performed in advance. It is determined whether or not the unevenness correction data is to be rewritten according to the type of the recording medium.
Therefore, there is an effect that it is not necessary to input the type of the recording medium again.

Further, in this embodiment, it is necessary to specify the recording medium by pressing a switch, but in still another modification of this embodiment, it is unnecessary.

FIG. 10 shows a recording medium 2 'used in the example. Here, reference numeral 20 denotes a recorded pattern for correcting unevenness of each color, and reference numeral 25 denotes a recording medium identification mark. An identification mark having a density corresponding to the type is provided in the leading end margin of the recording medium. Then, at the time of reading the uneven density, prior to reading the unevenness correction pattern, the density unevenness reading unit 214 reads the pattern.

If it is determined that the paper is the designated paper, the rewriting of the unevenness correction data is started as it is, and if not, the display is performed so that the recording medium is changed to the specified paper, and the work of rewriting the unevenness correction data may be prohibited. .

By doing so, it is possible to save the trouble of inputting the type of the recording medium.

In still another modification of the present embodiment, a similar effect is obtained without using an identification mark. For this purpose, a sensor unit for detecting the type of recording medium can be provided separately from the density unevenness reading unit 214. This sensor uses an ultraviolet lamp as a lamp and a sensor having sensitivity in an ultraviolet region as a sensor. Then, the type of the recording medium is determined from the reflected light amount of the margin itself of the recording medium. In general, many coated papers for ink jet recording contain a fluorescent agent to make the paper look whiter. Therefore, if an ultraviolet lamp is used as the lamp, the type of the recording medium can be determined from the reflected light. That is, when the amount of reflected light is large, it can be determined that the paper has a thick coat layer, when the amount of reflected light is medium, the paper has a thin coat layer, and when there is almost no reflection, it is determined that the paper is an OHP film. Only when it is determined that the designated paper is suitable for density unevenness detection due to a large amount of reflected light, reading of uneven density and rewriting of unevenness correction data are performed. In other cases, the same display as above is performed and the same display is performed. Can be banned. This allows
In particular, the same effect as described above can be obtained without the operator inputting the type of the recording medium or providing the identification mark.

In this example, the test pattern is recorded only when the recording medium is a specific recording medium. However, by appropriately setting a range for averaging unevenness in reading, various types of recording media can be handled. You can also.

Referring again to FIG. 9, if the recording medium is suitable for the unevenness correction processing, the process proceeds to step S7 to perform temperature adjustment.
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. Therefore, for example, when this procedure is started and a test pattern is recorded, as shown in the area a in FIG. 18, the recording head temperature is the first temperature adjustment reference.
Recording will be performed in a state at ° C. On the other hand, when images are actually continuously recorded, the temperature of the head is increased as shown in a region b in FIG. 11, and recording is performed at a maximum temperature of 50 ° C., which is the second temperature adjustment reference. There is also.

By the way, from the results of the experiment, as shown in FIG. 12A,
It is known that the density (OD value) varies in accordance with the temperature of the recording head. Therefore, in this case, as shown in FIG. 12B, when the unevenness correction for 40 ° C. is performed, a uniform image with a uniform head temperature of 40 ° C. can be obtained. The image may still be uneven.

Therefore, in the apparatus of the present embodiment, during normal recording or during recording standby, the temperature adjustment unit is controlled according to the temperature of the recording head 1.
Turn on / off 113 (heater and fan) appropriately,
As shown in the figure, the temperature of the recording head is kept within a predetermined temperature range (about 40 ° C.). In contrast, in the temperature non-uniformity correction process, the set temperature is raised to 45 ° C., that is, the temperature adjustment standard is increased during test pattern printing with respect to the temperature adjustment standard for normal recording, and the heater and the fan are appropriately adjusted. By turning on / off, the head temperature is raised to about 45 ° C., and then a test pattern for checking uneven density is recorded, and uneven density correction is performed based on the test pattern. As described above, the recording operation of the recording head is stabilized by adjusting the temperature, that is, for example, when the head temperature is 45 ° C.
By forming a test pattern as described above and performing density unevenness correction based on the test pattern, it becomes possible to perform substantially uniform density unevenness correction over the entire temperature control range as shown in FIG. 11C.

In this example, the head temperature is the first temperature in this example.
Test patterns are printed at a temperature of 40 ° C., which is the temperature adjustment standard, and at 50 ° C., which is the maximum heating temperature during recording (second temperature adjustment standard), and the density unevenness of these two types of test patterns is determined. Detection may be performed, and correction may be performed based on a value obtained by averaging the density unevenness (first and second density data).

In addition, in order to reduce the time required for the correction of the density unevenness, in order to increase the head temperature from, for example, 40 ° C. to 45 ° C., in addition to the temperature adjusting heater, the recording element (electrothermal conversion element) is used. By applying an electric pulse to the extent that ink is not ejected, it is possible to shorten the time required for raising the head temperature, thereby shortening the time required for performing density unevenness correction.

In addition, in order to record the density unevenness correction test pattern as described below and reduce the head temperature to the normal recording state after the correction (45 ° C. → 40 ° C.), the fan is driven and the recovery device 220 If ink refresh is performed by using, it is possible to shorten the time until the recording becomes possible.

Further, it is needless to say that the adjustment temperature at the time of test pattern recording can be appropriately determined in relation to the temperature adjustment range at the time of normal recording.

Referring again to FIG. 9, in this example, the ejection stabilizing operation is performed in step S9. This is because if the density unevenness correction processing is performed as it is in a case where the recording head does not have a normal ejection characteristic due to thickening of ink, mixing of dust bubbles, etc., faithful head characteristics (density unevenness)
May not be able to be confirmed.

During the ejection stabilization process, the recording heads 201C to 201BK
And the recovery device 290 are opposed to each other, and the above-described suction processing is performed to forcibly discharge the ink from the discharge port. 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 recording head in the same manner as during normal recording to perform preliminary ejection. However, the driving energy at the time of preliminary ejection does not necessarily have to be the same as at the time of 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.

FIG. 13 shows an example of recording these patterns. In the figure, a pattern for stabilizing the ejection is shown, and an inspection image pattern for inspecting the presence or absence of non-ejection (in FIG. Is a test pattern for detecting density unevenness. The ejection stabilization pattern used here was one with a printing ratio of 100% duty performed by driving all ejection ports of all recording heads.
By recording this stable ejection pattern, the temperature of the head is stabilized, the ink supply system is also in a steady state, the conditions for performing normal recording are set, and the presence or absence of a defective ejection in the actual recording state And uneven density can be accurately grasped.

By the way, in the present example, when the recordable width of the recording head 201 is slightly larger than the image recording width to prepare for registration adjustment between the heads, the recording width at the time of test pattern recording is made larger than the normal image recording width. Is preferred. Therefore, in such a case, it is strongly desirable to perform inspection over the width of the ejection port arrangement range, and a test pattern of that width is printed.

FIG. 14 shows an example of the configuration of a circuit for performing such an operation. Reference numeral 141 denotes a selector for selecting a usable ejection port range of the print head, and 143 and 145 store image data and a test pattern to be printed, respectively. The memory 145 is used to select a discharge port range used during an actual printing operation.
This is a counter used to make 1 select.

When the above-described discharge stabilization processing is completed, step
In S11, a predetermined test pattern is recorded by the recording heads 201C to 201BK, and density unevenness is read from this.
The operation at the time of recording a test pattern or reading uneven density in this example will be described with reference to the timing chart of FIG.

FIG. 15 is a timing chart showing the operation of the apparatus of this embodiment. The density unevenness correction processing procedure is started at timing a in the figure, and after the above-described processing, the recording medium 202 is moved to the image recording area at timing b. After being conveyed, the main scanning motor is driven at the timing c, and the cyan, magenta, yellow, and black recording heads 20 are driven at the timings d, e, f, and g.
1C, 201M, 201Y, 201BK drivers are driven to
The test pattern is recorded on 2. This test pattern is used for density unevenness reading. At this time, all the unevenness correction tables are straight lines with a slope of 1.0, and no unevenness correction is performed. The pattern may be a uniform halftone, and the printing ratio may be about 30 to 75%.

By the way, when the test pattern is recorded on the recording medium 202 by each recording head in this manner, the ink recorded from each recording head is not instantaneously absorbed depending on the type of the recording medium, and is recorded on the recording medium 2. In some cases, the state of the uneven density of the test pattern is not immediately stabilized.

Accordingly, in the present embodiment, in order to prevent the density unevenness reading unit 214 from reading the density unevenness of the test pattern until the state of the density unevenness of the test pattern recorded by each recording head is reduced to a stable state. After the recording of the test pattern by the recording head,
During a predetermined time t, the recording paper is stopped without being transported (step S13 in FIG. 9). After the density unevenness of the test pattern is stabilized, the recording medium is conveyed at the timing i, and the test turn is performed by the reading unit 214.
When the scanning range is reached, the reading sensor is driven after the timing j to read the density unevenness of the test pattern of each color by the reading unit 214.

According to the experiments of the present inventors, when a test pattern was recorded at a printing ratio of 50% on a coated ink jet recording paper with a recording head having a resolution of 400 dpi, the above-mentioned recording paper stop time was about 3 to 10 seconds, which was sufficient. Met.

FIG. 16 is a timing chart showing another operation example of the device of this example. In this operation example, the recording medium 202 with respect to the transport speed v ₁ at the time of conveyance with respect to the recording position, the test pattern recording is completed by the recording head (point g '), the recording medium to a density unevenness reading unit 14 decelerating the sheet conveyance speed v ₂ when conveyed v _1> v is obtained by the ₂ so as, this same effect as Figure 15 can be obtained by.

In these examples, since the scanning range of the recording head and the scanning range of the reading unit in FIG. 1 are different on the platen, a fixing stabilization time is provided for the conveyance of the recording medium. The operation may be stopped for a predetermined time. This is effective when the scanning range of the recording head matches the scanning range of the reading unit. However, if the fixing stability until reading is not a problem, the above processing is unnecessary.

After fixing stabilization as described above, step S15 in FIG.
In this example, the unevenness reading process is performed by the shutter opening / closing unit 250.
45b and 246b are opened (step S14), and immediately after reading, the shutters 245b and 246b are closed (step S16). That is, the insides of the housings 245a and 246a are opened only at the time of reading, so that contamination by ink mist of the light receiving element, the lamp, the filter, and the like is effectively prevented.

Based on the above, unevenness correction is performed in step S17 in FIG. That is, from the signal obtained by reading the density unevenness,
Signals for the number of discharge ports are sampled, and these are used as data corresponding to each discharge port. Assuming that these are R ₁ , R ₂ ,... R _N (N is the number of discharge ports), these are temporarily stored in the RAM 119 and then the CPU 101 performs the following calculation.

These data are converted into a density signal by performing an operation of C _n = −log (R _n / R ₀ ) (R ₀ is a constant satisfying R ₀ ≧ R _n ; 1 ≦ n ≦ N).

Next, average density Is calculated.

Subsequently, the degree to which the density corresponding to each ejection port deviates from the average density is calculated as follows.

ΔC _n = / C _n Next, a signal correction amount (ΔS) _n corresponding to (ΔC) _n is obtained by ΔS _n = A × ΔC _n .

Here, A is a coefficient determined by the gradation characteristics of the head.

Subsequently, a selection signal of a correction straight line to be selected according to ΔS _n is obtained, and the non-uniformity correction signals having 61 kinds of values “0” to “60” are stored in the non-uniformity correction RAMs 129C to 129BK for the number of ejection ports. A different γ straight line is selected for each ejection port based on the unevenness correction data created in this way, density unevenness is corrected, and the unevenness correction data is rewritten.

Then, through the judgment step S19 in FIG. 9, a test pattern is recorded again by each recording head based on the correction data, and the test pattern of each recording head is read again by the density unevenness reading unit 14 to calculate density unevenness correction data. After repeating this operation several times, the density unevenness correction operation is terminated.

As described above, the test pattern recording of each recording head, the reading by the density unevenness reading unit 14, and the calculation of the density unevenness correction data can be repeatedly performed automatically plural times or more in one processing for one printing medium. This makes it possible to improve the density unevenness correction accuracy of each print head even for a print head in which the density unevenness is not sufficiently corrected even by a single density unevenness correction operation, and to shorten the correction time as a whole. become able to.

In the above-described embodiment of the present invention, if at least a density inspection print such as a test turn is performed, if one pixel is composed of a plurality of dots, the print duty, that is, the print setting is within the number of constituent dots. Can be performed by modulating the number of recording dots. The printing duty in this case is
Not 100%, preferably 75% or less 25% or more,
Optimally, it is preferable to form a test pattern with a print duty of 50%. This is because it is most suitable for a system for optically obtaining a reflection density, and a minute change in density can be obtained as being suitable for the printing characteristics of the recording head.

However, the printing ratio can be set by modulating the driving voltage and / or the driving pulse width, or by modulating the number of ink ejections per dot. These also correspond to the case where one pixel is composed of one dot. You can do it. In other words, it goes without saying that the present invention can be applied to whatever printing ratio is set by performing any kind of modulation.

Although the above embodiment of the present invention is an optimum embodiment in which the obtained correction processing is performed for each of the ejection energy generating elements, practically, in consideration of the convergence state and the processing time of the density uniformization processing, a predetermined value is obtained. It is preferable to perform correction so as to apply a common correction to a plurality of adjacent ejection energy generating elements.
From this point of view, it is preferable that the optimal configuration is such that the multiple ejection energy generating elements of the print head apply a common correction to each block drive group in which a plurality of elements are grouped. The block drive itself may be any of a well-known or known one, or a specific block drive method. However, a drive condition capable of implementing a corrected uniform density after determining the density unevenness of the present invention is given. Needless to say, this is a premise.

Further, the data relating to the test pattern may be provided from the host device for the configuration of FIG.
It may be provided by the configuration shown in the drawing or by test pattern data generating means integrated with the recording head 1.

As described above, in this example, since the density unevenness reading unit is provided on the carriage or the member that moves in conjunction with the carriage, the reading operation of the test pattern is performed on the platen for regulating the recording surface flat. In addition, the recording medium can be kept flat and the distance between the recording media of the reading units can be kept constant, and the sub-scanning of the recording medium can be performed accurately, so that accurate density reading can be performed. In addition, a special configuration for maintaining the above distance for reading is not required in the configuration of the apparatus, so that the apparatus can be downsized. Also,
Since the recording head and the reading unit maintain a predetermined distance, the reading sensor can be protected from inconvenience caused when the two come close to each other, for example, the influence of ink mist or heat. Furthermore, by using a monocular sensor without using a line sensor such as a CCD, and by accurately feeding the recording medium and moving the reading unit, it is easy to detect the density over the printing width. As compared with the case of using the sensor, the sensor is inexpensive, no shading correction is required, and a simple light source can be used, and the accuracy degradation when the sensor or the light source becomes dirty can be reduced.

Further, since the recording medium in the printed state can be read without being ejected outside the apparatus, there are few error factors in density detection at the time of reading, and high-precision density detection can be realized in combination with high-precision reading position accuracy.

(4) Other Embodiment FIG. 17 is a schematic view of another embodiment, in which each recording head 20
Provide uniform image signal to 1C, 201M, 201Y, 201BK and record media
Reading a test pattern recorded on 202 and outputting a read signal is the same as in the above example. In this example, the density unevenness reading unit 214 is connected to a linear reading sensor 232.
And a light source 233. Further, the configuration of fixing them to the main scanning belt 210 via the holder 244 or an appropriate modification thereof is the same as that described with reference to FIG. 1, and the same effects can be obtained. Also,
Since only one reading sensor is required, the size of the apparatus can be reduced.

Also, as shown in FIG. 18, on the reading surface side of the reading line sensor 232, the color filters 234R, R, G, and BL of the respective colors are adjusted in accordance with the position of the test pattern by each recording head recorded on the recording medium 202. By providing 234G and 234BL, the reading accuracy of the reading sensor 232 for each color of the print pattern can be improved.

However, in the case of this example, although the unevenness reading sensor 232 is single, the reading output of the sensor generally changes depending on the color. For example, in the case of using a sensor whose spectral sensitivity is close to visual sensitivity, which is generally used, the output density to be read is largest for BK and decreases in the order of C, M, and Y. For example, the output ratio of BK: C: M: Y is 1: 0.8: 0.75: 0.25.

When the density unevenness correction amount is obtained from the ratio between the average density in the head and the density of the ejection port of interest, this difference in output does not matter. For example, the output for the C is to become a K ₁ times the output for BK. The average density in the head 1BK is ▲ ▼, the density of the target outlet is OD _BKn , and the head 1
It is assumed that the average density in C is ▲ ▼ and the density of the target ejection port of the head 1C is OD _Cn . Assuming that the unevenness of the target outlet of head 1BK is the same as that of head 1C, the sensor output is D _Cn = K ₁ × OD _BKn . At this time, the correction value of C is And matches BK. Therefore, the output difference between the colors does not matter.

However, when the density unevenness correction amount is obtained from the absolute value of the density of the target outlet or the difference between the average density and the target outlet density, a difference in sensor output between the colors becomes a problem.

For example, when calculating a correction value from the difference between the average density and the target outlet density, , And this value is, the direction of C is K ₁ times the BK. The correction data for the target ejection port is calculated based on this value. However, although the density unevenness of the head is equal, the final correction amount differs between BK and C. Occur.

Therefore, in this embodiment, the ratio of the sensor output between the colors is determined in advance, and the CPU 101 performs the unevenness reading process.
This problem is solved by multiplying the sensor output by the reciprocal of this ratio, and correcting unevenness based on the multiplied value.

For example, BK, C, M, the output ratio of _{Y 1: K 1: K 2} : When the K _3, multiplied by "1" in the output when reading the BK, when C is
Multiplied by 1 / K _1, when the M multiplied by 1 / K _2, when the Y multiplied by 1 / K _3.

Thus, for example, in the above example, Thus, the optimum correction can be performed without being affected by the sensor output ratio between the colors.

It is to be noted that such correction of the sensor output can be performed not in the calculation by the CPU 101 but in the preceding stage.

This is, for example, when the A / D converter 127 is configured with 8 bits,
Since the output value of each color must be converted into digital data within the 8-bit width of the dynamic range,
This is effective in reducing the resolution of the read data of each color.

That is, for example, as shown in FIG. 18, amplifiers 235C, 235M, 235Y, and 235BK for amplifying read signals of respective colors are provided.
The sensor output value of the read signal of each color as shown in FIG.
By adjusting them so that they are substantially equal as shown in FIG. 19B, the width of the read signal when the read signal is A / D-converted can be set narrower as a whole. Therefore, the resolution of the read data in 8 bits can be increased, and the reading accuracy can be further improved.

The present invention is not limited to the examples described above, but can be appropriately modified. For example, each recording head 201C, 201
When the test pattern is recorded on the recording medium 202 by scanning in the directions of the carriages A and B on which the M, 201Y, and 201BK are mounted, each time the carriage 203 is scanned once, the test pattern is recorded by the recording head of one color. After the reading line sensor 232 reads the test pattern recorded on the recording medium 202, the carriage 203 is again scanned, and the next recording head performs the test pattern recording on the recording medium 202. Can also.

That is, by reading the test pattern recorded on the recording medium by each recording head for each color as in this example, the capacity of the RAM 219 for storing the test pattern read data can be reduced to 1/4. As a result, the device configuration can be reduced.

In each of the embodiments described above, the present invention is applied to a serial printer type image forming apparatus.However, the present invention is applied to a line printer type image forming apparatus, for example, an ink discharge port over a range corresponding to the width of a recording medium. It is needless to say that the present invention can also be applied to an ink jet recording apparatus having a so-called full multi-type recording head in which are aligned.

Further, the configuration of the reading system is not limited to the above example with respect to, for example, the type and size of the reading sensor and the relative scanning with the test pattern. For example, the sensor may be a monocular sensor that reads reflected light in a predetermined range, or a sensor in which reading elements such as CCDs are arranged over a range corresponding to the arrangement range of recording elements. In the latter case, it is preferable that a plurality of reading elements be caused to react with one ejection port, and the average value of the read values be associated with one ejection port.

In addition, the configuration of the means for protecting the light source, the sensor, and the like from contamination by ink mist and the like does not necessarily need to include each of the separate housings and the shutter combined with the housings as described above. Can be adopted. For example, special protection means may be provided for the lamp (at least the light-emitting portion), the sensor (at least the light-receiving portion), and the filter (at least the light-transmitting portion) so that they can be simultaneously opened and closed before and after reading. If contamination of the member does not pose a problem, the member may be omitted from the protection means. Alternatively, the entire reading unit may be housed in an integrated housing, and a single shutter or other protection means may be provided.

(5) Others The present invention can be applied to an image forming apparatus using various recording methods in which density unevenness may be a problem (for example, a thermal printer), but when applied to an ink jet recording method, among them, Canon Inc. This provides an excellent effect in the proposed bubble jet type recording apparatus. According to such a method, it is possible to achieve a higher density and a higher definition of the recording, and it is more effective to prevent the occurrence of the density unevenness.

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 both the so-called on-demand type and the continuous type. In particular, in the case of the on-demand type, it is arranged corresponding to a sheet or a liquid path holding a liquid (ink). Applying at least one drive signal corresponding to the recording information and providing a rapid temperature rise exceeding nucleate boiling to the electrothermal transducer, thereby causing the electrothermal transducer to generate thermal 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 the specification of 63359 and the equivalent of 4435262 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. 59-23670 discloses a configuration in which a common slit is used as a discharge section of an electrothermal converter for a plurality of electrothermal converters, and an aperture for absorbing a pressure wave of thermal energy is provided. The effect of the present invention is effective even if the configuration is based on 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, the present invention can be effectively applied to a full-line type recording head having a length corresponding to the maximum width of a recording medium on which a recording apparatus can record. 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.

Also, in a serial type device, a printhead fixed to the device main body or a replaceable chip that is attached to the device main body to enable electrical connection with the device main body and supply of ink from the device main body. The present invention is also effective when a recording head of a type or a cartridge type recording head in which an ink tank is provided integrally with the recording head itself is used.

Further, it is preferable to add a preliminary auxiliary means and the like in addition to the recovery means for the print head provided as a configuration of the printing apparatus in the present invention since the effect of the present invention can be further stabilized. If you list these specifically,
Capping means, cleaning means, preheating means using an electrothermal transducer or another heating element or a combination thereof for the recording head, and preliminary ejection mode for performing ejection different from printing are also stable. This is effective for performing recorded data.

Regarding the type or number of print heads to be mounted, for example, in addition to one provided for single color ink, a plurality of print heads are provided corresponding to a plurality of inks having different print colors and densities. May be used. That is, for example, the printing mode of the printing apparatus is not limited to the printing mode of only the mainstream color such as black, but may be any of integrally forming the printing head or a combination of a plurality of printing heads. The present invention is also extremely effective for an apparatus provided with at least one of full colors by color mixture.

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 a solid state to a liquid state, or ink that solidifies in a standing state to prevent evaporation of the ink can be used. In any 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
No. -56847 or JP-A-60-71260, while being held as a liquid or solid substance in a porous sheet recess or through hole, facing the electrothermal converter. It is good also as a form. In the present invention,
The most effective one for the above-mentioned ink is one that executes the above-mentioned film boiling method.

In addition, the image forming apparatus 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 a facsimile apparatus having a transmission / reception function. It may be. In particular, in a device such as a copying machine or a facsimile provided with an image reading means (reader) as a document reading system, it can also be used as a reading means for reading density unevenness of a recorded image.

Although the above-described embodiments show various configurations taking up a number of technical problems, all of the above-described configurations are not essential to the present invention, and the designed device configuration and setting of a desired concentration uniformization level are not necessary. This indicates that it is more preferable to arbitrarily require a configuration by using one or more of the above configurations.

[Effects of the Invention] As described above, according to the present invention, a reading unit is provided on a carriage or a member (a head or the like) that is moved in conjunction with the carriage, so that reading an image formed by the head can be made compact. In a configuration that can be performed, by providing a housing that protects the reading unit inside when not reading, and by providing a shutter that can open the optical path when reading the reading unit with respect to the housing, when reading is not performed, The reading means is effectively protected from contamination by paper dust and the like (water droplets, ink mist, etc.) wrapping around, and enables accurate reading.

[Brief description of the drawings]

FIG. 1A is a schematic perspective view of an ink jet recording apparatus according to an embodiment of the image forming apparatus of the present invention, FIG. 1B is a sectional side view showing a configuration example of a reading unit and a protection means, and FIG. FIGS. 3 to 5 are explanatory diagrams for explaining an aspect of density unevenness correction in a multi-nozzle head, and FIG. 6 is a block diagram showing a configuration example of a control system of an ink jet recording apparatus according to the present embodiment. FIG. 7 is a block diagram showing in detail a system for correcting density unevenness, FIG. 8 is an explanatory view for explaining an unevenness correction table used in this example, and FIG. 9 is an unevenness correction process according to this example. FIG. 10 is a flowchart showing an example of a procedure. FIG. 10 is a schematic diagram showing a state in which an identification mark is attached to a recording medium in order to perform density unevenness correction according to the type of the recording medium. FIGS. 12A, 12B, and 12C are explanatory diagrams for explaining a mode of performing stable density unevenness correction regardless of temperature, and FIG. 13 is a diagram for stabilizing ejection. FIG. 14 is an explanatory diagram showing an example in which a pattern, an ejection failure detection pattern, and a test pattern for density unevenness correction are recorded on a recording medium. FIG. 14 shows the density over all ejection ports in a full multi-type print head according to this example. FIG. 15 is a block diagram showing an example of the configuration of a main part of a control system for performing unevenness correction. FIG. 15 and FIG. 16 are timing charts showing two operation examples of the present apparatus from recording of a test pattern to reading density unevenness. FIG. 18 is a schematic perspective view of an ink jet recording apparatus according to another embodiment of the present invention. FIG. 18 is a block diagram showing a configuration example for correcting a difference in output magnitude depending on the color of a reading sensor in the embodiment. , FIGS. 19A and 19B are explanatory diagrams of the correction mode, and FIGS. 20A to 20E are explanatory diagrams for describing general density unevenness correction in a multi-nozzle head. 101: CPU, 102: ROM, 106: Instruction input unit, 113: Head temperature adjustment unit, 219: RAM, 122C, 122M, 122Y, 122Bk: Unevenness correction table, 236: A / D conversion 129C, 129M, 129Y, 129Bk ... Unevenness correction RAM, 235C, 235M, 235Y, 235C ... Amplifier, 201, 201C, 201M, 201Y, 201Bk ... Recording head, 202 ... Recording medium, 203 ... Carriage, 206: motor, 210: main scanning belt, 214: reading unit, 217C, 217M, 217Y, 217Bk: sensor, 218: light source, 220: filter, 232: light receiving element, 233: lamp, 245a, 246a ... housing, 245b, 246b ... shutter, 250 ... shutter opening and closing unit.

Claims (9)

(57) [Claims] A recording head on which a plurality of recording elements are arranged for forming an image on a recording medium; a carriage on which the recording head is mounted or a reading means provided on a member which moves in conjunction with the carriage; When the reading means is not reading, a housing for protecting the reading means inside; and a shutter provided in the housing so that an optical path of the reading means can be opened when reading by the reading means. Characteristic image forming apparatus. 2. The image forming apparatus according to claim 1, wherein said reading means reads an image formed on a recording medium by said recording head. 3. The reading means reads a test pattern formed on a recording medium by the recording head, and corrects data for correcting an image formed by the recording head based on a result of the reading by the reading means. The image forming apparatus according to claim 2, further comprising a creating unit that creates the image. 4. An image forming apparatus according to claim 1, wherein a plurality of said recording heads are provided corresponding to recording agents having different colors for performing multi-color recording. 5. The recording head according to claim 1, wherein the recording head is of an ink jet type, and has an electrothermal conversion element used to cause the ink to eject the ink by causing film boiling. Image forming apparatus. 6. An image forming apparatus for forming an image on a recording medium using a recording head in which a plurality of recording elements are arranged, comprising: a carriage on which the recording head is mounted or a reading member provided on a member which moves in conjunction with the carriage. Means; a housing for protecting the reading means inside when the reading means is not reading; and a shutter provided on the housing so that an optical path of the reading means can be opened when reading by the reading means. An image forming apparatus characterized in that: 7. An image forming apparatus according to claim 6, wherein said reading means reads an image formed on a recording medium by said recording head. 8. A reading means for reading a test pattern formed on a recording medium by the recording head, and correction data for correcting an image formed by the recording head based on a result of the reading by the reading means. The image forming apparatus according to claim 7, further comprising a creating unit that creates the image. 9. The image according to claim 6, wherein said recording head is of an ink jet type, and has an electrothermal conversion element used for causing ink to eject by causing a film boiling in the ink. Forming equipment.