JP2001199055A - Ink jet image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet image forming apparatus capable of executing accurate adjustment of head alignment. SOLUTION: A first printing pattern having a line with a predetermined width is printed on a printing medium by each head and the width of the line is read by an optical sensor. A difference 83 in the width between the lines printed by a head to be a reference and the other head is stored as a read tolerance due to a color of the optical sensor. When executing the adjustment of alignment for the head, a second printing pattern is printed by using the reference head and the other head and a gap between the lines printed by the reference head and the other head is read by using the optical sensor. The read gap is corrected based on the read tolerance and then a position shift of the other head with respect to the reference head is obtained, thereby executing the adjustment of alignment for the other head with respect to the reference head based on the position shift.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet image forming apparatus such as a plotter for forming an image by discharging ink onto a print medium, and more particularly to a head alignment adjustment thereof.

[0002]

2. Description of the Related Art Conventionally, an ink-jet plotter that forms a color image by discharging ink onto a print medium such as paper uses a plurality of heads corresponding to a plurality of inks. Each head has a plurality of ink ejection nozzles arranged in one or more rows in a direction perpendicular to the print scanning direction. As the color inks, usually four types of inks of cyan, magenta, yellow, and black (black) are used.

FIG. 1 shows a configuration around a carriage on which four heads for these four inks are mounted. In the figure,
Reference numeral 11 denotes a black (K) ink head, 12 denotes a cyan (C) ink head, 13 denotes a magenta (M) ink head, and 14 denotes a yellow (Y) ink head. Reference numeral 15 denotes a carriage that holds each color head and scans in a direction perpendicular to the medium transport direction. Reference numeral 16 denotes a reference scale for detecting the position of the carriage 15 (and, consequently, the position of each head) in the carriage scanning direction perpendicular to the medium transport direction. This is generally called a linear scale. Reference numeral 17 denotes a sensor unit having a built-in optical sensor having a light emitting unit and a light receiving unit for reading a line segment formed on a print medium.

FIG. 2 shows a specific configuration example (a) of the linear scale 16 and a specific configuration example (b) of the optical linear scale sensor 24. The linear scale method is generally of an optical type and a magnetic type, but the optical type is shown here. The linear scale 16 is provided with slits 22 at regular intervals. The linear scale sensor 24 includes the carriage 15
It is mounted on (FIG. 1) and moves along the linear scale 16 as if it straddles the linear scale 16. A flexible cable 23 for electric signal is connected to the linear scale sensor 24 in order to cope with the movable configuration. The rear scale sensor 24 generates an electric pulse signal by detecting light transmitted through the slit 22 of the linear scale 16. The current position of the head can be detected by counting the pulse signals. Although the slit interval of the linear scale is various such as 1/300 inch, 1/360 inch, here, 1/360 inch is shown. Since the ejection timing of the ink is determined in synchronization with the slit interval, the ejection accuracy is simply determined by the slit interval. However, it is possible to adjust the ejection timing smaller than the slit interval.

[0005] In order to perform printing, the heads of each color must be able to eject ink droplets to target positions on a print medium. Normally, only one sensor 24 is provided for a plurality of heads due to problems such as complicated mounting and cost. Therefore, in the above example, one of the four heads is used as the reference head, and the other heads are ejected at positions offset by the physical mounting position with respect to the reference head. Therefore, in the carriage scanning direction, each head must be exactly a distance of an integral multiple of the linear scale slit interval, and in the paper transport direction, the nozzle start positions of all heads must be exactly aligned with the reference line in the carriage scanning direction. . Therefore, as a factor for determining the ejection accuracy, the physical mounting position of each head occupies a large factor other than the slit interval.

[0006] However, it is extremely difficult to keep the head mounting accuracy below the slit interval of the linear scale. In addition, since the carriage ejects ink droplets while moving on the print medium at a constant speed in a direction perpendicular to the medium transport direction, the ejected ink droplets are not ejected directly below by the inertia force in the carriage movement direction, and the carriage is ejected. Landing on the print medium is shifted from the discharge point in the moving direction.
Since the shift due to the inertial force changes depending on the time from the ejection point to the position above the print medium, the shift amount also changes depending on the distance between the carriage and the print medium.

Conventionally, in order to prevent deterioration of printing accuracy on a print medium due to a mounting error of the head or the like, alignment adjustment of the head is performed after replacing the head. This adjustment is simple, prints multiple line segments by delaying the ejection timing of heads other than the reference head by a few minute distances from the linear scale pulse, and aligns them straight with the line segments printed by the reference head The user adjusts the alignment by recognizing the line segment and setting it on the inkjet plotter. The reading of these line segments can be automatically read and adjusted by providing an optical sensor on a carriage or the like.

FIG. 3 shows an example of a print pattern (test pattern) printed when a black head is used as a reference head when performing alignment adjustment in the carriage scanning direction and FIG. 4 performs alignment adjustment in the paper transport direction. In this pattern, it can be seen that the alignment adjustment point in the carriage scanning direction in FIG. 3 matches the reference head with the fourth in cyan, the second in magenta, and the first in yellow. Further, it can be seen that the alignment adjustment points in the paper transport direction in FIG. 4 correspond to the reference head at No. 3 for cyan, No. 4 for magenta, and No. 2 for yellow. When these numbers are set by the user on the ink-jet plotter, or when the adjustment values are automatically set by reading line segments with an optical sensor, the set alignment adjustment values are used during normal printing.

[0009]

Conventionally, in the case where head alignment is automatically adjusted by an optical sensor, it is necessary to adjust the sensor reading determination threshold for each color on average in order to absorb a reading error due to the color of the optical sensor. The alignment accuracy has been improved by correcting the read value with an experimentally obtained value of a position reading error from the reference color that occurs when another color is read from the reference color.

However, this method cannot correct an error caused by a deviation in the distance between the head and the print medium as described in the prior art. The reading error also changed due to a change in the reflectance of light from the light emitting unit when the print medium was changed.

Further, even if the head alignment can be adjusted accurately, the deterioration of the printed image cannot be avoided when the head is mounted at an angle.

The present invention has been made in view of such a conventional problem, and an object of the present invention is to provide an ink-jet image forming apparatus capable of performing more accurate head alignment adjustment.

Another object of the present invention is to adjust the head alignment in such a manner that a reading error of the optical sensor due to a change in the distance between the head and the printing medium and a reading error of the optical sensor due to a change in the type of the printing medium are also included. An object of the present invention is to provide an ink-jet image forming apparatus which can be used.

[0014]

An ink jet image forming apparatus according to the present invention is an ink jet image forming apparatus for forming an image by discharging ink onto a print medium, comprising a plurality of nozzles each for discharging ink droplets. A plurality of heads, means for transporting the print medium in a direction perpendicular to the head scanning direction, means for printing a first print pattern having a line segment of a predetermined width on the print medium by each head, An optical sensor having a light-emitting unit for projecting light into the light and a light-receiving unit for receiving the reflected light, and a width of a line segment of the first print pattern printed by each of the heads based on an output of the optical sensor. Means for storing the difference between the widths of the line segments printed by the reading and reference heads and the other heads as reading errors due to the color of the optical sensor. And butterflies.

By using this reading error for head alignment adjustment, it is possible to cancel the reading error due to the color of the optical sensor and read the line segment position accurately. In addition, the correction is performed in a form including the reading error of the optical sensor due to a change in the distance between the head and the printing medium, and the correction is also performed in a manner including the reading error of the optical sensor due to a change in the type of the printing medium.

For example, in the alignment adjustment in the head scanning direction, means for printing a second printing pattern having a line segment extending in a direction perpendicular to the head scanning direction using a reference head and another head, By using an optical sensor to read the interval between line segments printed by the reference head and the other head, and correcting the read interval based on the reading error, the misalignment of the other head with respect to the reference head in the head scanning direction is obtained. And a means for adjusting the alignment of the other head with respect to the reference head in the head scanning direction based on the displacement.

Alternatively, in the alignment adjustment in a direction perpendicular to the head scanning direction, means for printing a line extending in a direction parallel to the head scanning direction using a reference head and another head, and the optical sensor By reading the interval between the line segments printed by the reference head and the other head using the reference head, and correcting the read interval by the reading error, the misalignment of the other head with respect to the reference head in the direction perpendicular to the head scanning direction. And means for adjusting the alignment of the other head with respect to the reference head in a direction perpendicular to the head scanning direction based on the positional deviation.

Another ink jet image forming apparatus according to the present invention is an ink jet image forming apparatus for forming an image by discharging ink onto a print medium, comprising a plurality of heads each having a plurality of nozzles for discharging ink droplets. ,
Means for transporting the print medium in a direction perpendicular to the head scanning direction, means for printing a first print pattern having a line segment of a predetermined width on the print medium by each head, and projecting light on the line segment An optical sensor having a light emitting unit and a light receiving unit that receives the reflected light of the optical sensor, a unit that changes a reading determination threshold level of the optical sensor, and reading and determining the output of the optical sensor at the threshold level, whereby the plurality of light sensors are read. The width of a plurality of line segments printed by the head is determined, the reading determination threshold level of the optical sensor is changed so that these widths become a predetermined width, and the reading determination threshold level of each line segment is changed by the optical sensor. Means for storing for each color.

The stored judgment threshold level is used as follows.

That is, means for printing a second print pattern having a line segment extending in a direction perpendicular to the head scanning direction using a reference head and another head, and for each head using the optical sensor The interval between line segments printed by the reference head and the other head is read using the corresponding read determination threshold level, and the displacement of the other head relative to the reference head in the head scanning direction is determined based on the read interval. And means for adjusting the alignment of the other head with respect to the reference head in the head scanning direction based on the displacement.

Alternatively, means for printing a line segment extending in a direction parallel to the head scanning direction using a reference head and another head, and the reading determination threshold level corresponding to each head using the optical sensor. Means for reading the interval of the line segment printed by the reference head and the other head using, based on the read interval, a means for determining the displacement of the other head relative to the reference head in a direction perpendicular to the head scanning direction, Means for adjusting the alignment of the other head with respect to the reference head in a direction perpendicular to the head scanning direction based on the displacement.

Using the optical sensor, the position of one end and the other end of the line segment is detected for each head, and the amount of deviation of the position is determined. It may have means for determining. In this case, when it is determined that the tilt of the head is abnormal, it is preferable to have means for notifying the user of the determination.

The head inclination detection can be performed before the head alignment adjustment. By doing so, the deterioration of the image due to the head inclination can be cancelled, and the careless head alignment adjustment can be prevented.

[0024]

Embodiments of the present invention will be described below in detail with reference to the drawings.

First, FIG. 5 shows a schematic configuration of a main part of an image forming apparatus used in the present embodiment. Elements similar to those in FIG. 1 are given the same reference numerals. The carriage 15 is
The linear scale 16 is moved by the carriage moving belt 55.
Reciprocate in the direction crossing the print medium 53 along the arrow. The print medium 53 is conveyed on a medium conveyance holding platen 52 by rotation of a platen roller 54. As before,
The slit interval of the linear scale 16 in the present embodiment is 1/360 inch. However, the present invention is not limited to this.

Although a driving source for driving the platen roller 54 and the belt 55 is not particularly shown, a pulse motor or the like can be used.

The carriage 15 has the same configuration as that shown in FIG. 1, and in this embodiment, the head for ejecting ink uses black (black), cyan, magenta,
Installed in the order of yellow. The optical sensor unit 17 is located to the left of the black head when viewed from the front side of the carriage in FIG.

At the time of printing, ink droplets are ejected from each head to a target position on the print medium 53 in synchronization with a pulse generated based on the linear scale 16 as the carriage 15 moves. The ejection position for four heads must be determined by one pulse generation. In order to eject the ink of each head to the same position in the carriage scanning direction for one pulse, the ejection timing is delayed by the physical head mounting position in the carriage scanning direction.

The movement of the carriage 15 causes the head width (1
Band), and then the print medium 53
Is moved by one band, and the carriage 15 forms an image portion for the next one band. By repeating such operations, the entire image can be formed.

In order to perform the automatic alignment adjustment in this embodiment, the test pattern (first print pattern) shown in FIG. 6 is printed. In the present embodiment, the width 61 of each print line segment depends on the sensitivity of the optical sensor, but corresponds to the width of 4 counts of the linear scale, that is, the width of 4 dots of ink droplets. The printing interval 62 for each line is 12 dot intervals,
The number of line segments is 16 for each color. However, the configuration of the test pattern in the present invention is not limited to this.

When the line segments of all colors of the test pattern are printed, first, in order to determine the reference value of the optical sensor, the rightmost position from the left side position 63 of the line group printed in black so as to penetrate the line group. The optical sensor unit 17 is moved up to 64 at a predetermined speed (for example, 10 mm / sec). Meanwhile, the light emitting unit of the sensor unit 17 is turned on to read the width of each line printed in black.

FIG. 7 shows the configuration of the processing of the sense signal and the signal flow when the line segment of the test pattern is scanned by the optical sensor. The light 7 from the light emitting section 71 of the optical sensor is applied to the print medium 53 on which the test pattern is printed.
2, the light receiving unit 74 receives the reflected light 73 and the light receiving unit 74 generates a light receiving signal. This signal is input to the reading circuit 75 at the subsequent stage. In the reading circuit 75, the light receiving signal is binarized. The binarized determination output is sampled at minute time intervals by the CPU 70, and the width of the line segment is obtained. The sampling interval of the CPU 70 depends on the line segment scanning speed of the carriage, and may be any speed that is sufficiently faster than the scanning speed.
In the present embodiment, the time is set to 100 μsec, but is not limited to this.

In this embodiment, the moving speed of the carriage 15 is 1
CPU sampling interval 1 for 0.0 mm / sec
Since it is 00 μsec, the line segment detection resolution, that is, the line segment minimum detection width Wmin is

Wmin [mm] = 10.0 [mm / sec] × 100
× (10 −6) [sec]. The linear scale 1 of the minimum detection width of this line segment
The resolution R for / 360 inches is: R = (25.4 / 360) × (1 / Wmini) ≒ 70.555 This means that the time between one count of the linear scale is about 7
This means that a line segment width can be detected with a resolution of 0.555.

The integrated reading value of the plurality of line widths by the black ink read as described above is represented by 1 which is the number of line segments.
The number divided by 6 is stored as the reference line width (average line width). Next, the line segment width of each color is read in the same manner as the line segment reading with black ink. The difference between the read line segment width of each color and the black line segment width by the reference head is obtained, and each difference is stored as an optical sensor reading error for each color other than black.

The reading result of the above operation will be described with reference to a graph. FIG. 8 shows a waveform of an optical sensor output at the time of reading a line segment. 84 is the threshold level of the reading circuit, 81 is the binarization active time in reading black ink, 82 is the binarization active time in cyan ink reading, and 83 is the difference between the two binarization active times, that is, with respect to the black reference head. This shows the reading correction value of the cyan head. Therefore, the binarization active time 81 (the number of samplings) in reading black ink
Is Tk, the binarization active time 82 in cyan ink reading (the sampling number thereof) is Tc, and the cyan ink reading correction value Scyan is:

Scyan = (Tk−Tc) / 2. Here, only the optical sensor reading level with cyan ink is shown, but the same applies to other inks except black ink.

In order to perform alignment correction using this correction value, the head-to-head alignment is corrected by printing the line segments shown in FIG. 9 and reading the line segment intervals. In FIG. 9, reference numeral 91 denotes a line segment width to be printed, 92 denotes a line segment interval, 93 denotes a line segment by black ink, and 94 denotes a line segment by cyan ink. Here, the line segment interval 92 and the line segment width 9
The value of 1 is the same as those of the print pattern of FIG. That is, the line segment interval is 12 dots and the line segment width is 4 dots.

The interval between the line segment of black ink and the line segment of cyan ink of this pattern is read by an optical sensor, and the read value is defined as Dcyan. This reading D
As described in FIG. 8, cyan is larger than the actual value by the error value Scyan. Therefore, the determined cyan ink alignment correction value Adjcyan is: Adjcyan [mm] = (Dcyan−Scyan) × Wmin [mm] Automatic alignment correction is performed based on this correction value Adjcyan.

Here, only the correction of the cyan head is shown, but the same applies to heads of other colors.

The alignment adjustment in the direction perpendicular to the carriage scanning direction is performed in the same manner as described above. However, in the case of the present embodiment, alignment adjustment is not performed by moving each head in a direction perpendicular to the carriage scanning direction.
As shown in FIG. 0, alignment adjustment in a direction perpendicular to the carriage scanning direction is performed by masking several nozzles at the upper end and the lower end of the head nozzle. In FIG. 10, 10
1 is a black head, 102 is a cyan head, 103 is a magenta head, 104 is a yellow head, 105a,
106a, 107a, 108a are the number of upper end mask nozzles,
Reference numerals 105b, 106b, 107b, and 108b indicate the number of lower end mask nozzles. When the alignment is adjusted by this method, the minimum correction unit is the nozzle unit, but the physical alignment in the direction perpendicular to the carriage scanning direction for each head must be adjusted more accurately than the alignment in the carriage scanning direction. Therefore, such a configuration is sufficient.

However, it is technically possible to correct each head to move in the direction perpendicular to the carriage scanning direction. The head is moved by the calculated correction amount to align the head in the direction perpendicular to the carriage scanning direction. In addition, better printing quality can be obtained.

In this manner, the readings of the optical sensors of the other heads are corrected for each alignment adjustment so as to match the readings of the optical sensors of the reference head, thereby causing variations in the optical sensors, deterioration, and printing media. It is possible to eliminate an alignment adjustment error due to a change in light reflectivity due to light, a difference in sensor sensitivity due to color, and the like.

Next, a second embodiment of the present invention will be described. The configuration of the carriage and the like is the same as in the first embodiment. The concept of the alignment adjustment method in the present embodiment is basically the same as in the first embodiment. However,
In the first embodiment, when the optical sensor input value is binarized, binarization is performed using the same threshold level (threshold) regardless of which color is read, and the line width reading value of each head is calculated. The correction value is determined by using the difference. On the other hand, in the second embodiment, the threshold level at the time of binarization is changed so that the line width becomes the same as the reference head at the stage of the line width reading value.

The test pattern for performing the automatic alignment adjustment of the threshold level change may be the pattern shown in FIG. 6 as in the first embodiment.

FIG. 11 shows the configuration of signal processing and the flow of signals when a line segment is scanned by an optical sensor. Although similar to the configuration of the first embodiment shown in FIG. 7, the difference is that the threshold level 114 of binarization in the reading circuit 75 is variably controlled by the CPU 70. That is, in the reading circuit 75, the CPU
The light receiving signal is binarized by a threshold level 114 set by a D / A converter built in the 70. The binarized determination output is sampled at minute time intervals by the CPU 70, and the width of the line segment is determined. In the same manner as described above, a value obtained by dividing the integrated reading value of the line segment width by black ink by 16 which is the number of line segments is stored as the reference line segment width. Next, when the line segments of other colors are read in the same manner, the binarization threshold of the reading circuit 75 is set so that the line width of each color is the same as the line width of black ink for each color. Change level.

The flow of the process for reading the line segment width other than the black ink will be described with reference to the flowchart of FIG.

First, the light emitting section is turned on to obtain reflected light from the optical sensor (S11). Next, the carriage is moved to read a line segment (S12), and wait until reading is completed (S13). When the reading is completed, a comparison is made with the line segment reading width of the black ink serving as the reference head (S14).
If the comparison result is equal to or less than a predetermined reference value (S1
5, Yes), it is determined that the binarization threshold level of the line segment of the color being read is optimal for obtaining the same sensitivity as that of the reference head, and the light emitting unit is turned off (S16), followed by terminating the present process. .

If the comparison result exceeds the reference value in step S15, the number of readings is checked (S17). If the number of readings is equal to or more than the predetermined maximum value, the light emitting unit is turned off (S19), and then a reading error is notified to the user. If the number of readings is less than the maximum value, the threshold level is changed (S18), and the process returns to step S12.

Such an operation is performed for all the line segments written by the heads other than the reference head, and the reading threshold levels suitable for all the heads are stored.

The reading result of the above operation will be described with reference to a graph. FIG. 13 shows a waveform of an optical sensor output at the time of reading a line segment. 8, 84 is a threshold level for black ink, 81 is a binarization active time for reading black ink, 82 is a binarization active time for reading cyan ink using the black ink threshold level 84, and 135 is cyan. The optimum threshold level 133 in ink reading is a binarization active time when cyan ink is read using the optimum threshold level 135.

When the optimum threshold level can be set, the binarization active time 81 in reading black ink is Tk, and the binarization active time when cyan ink is read using the optimum threshold level 135 is Tc. Then, Tc = Tk.

In practice, it is rare that Tk = Tc, so if the absolute value of the difference between the two times is less than a predetermined range, the threshold level is considered to be optimal.

Here, only the optical sensor reading level with cyan ink is shown, but the same applies to other inks except black ink.

In order to perform the alignment correction using this correction value, the line segments of the second print pattern shown in FIG. 9 are printed and the line segments of the respective inks are printed in the same manner as in the first embodiment. By performing the binarization at the corresponding threshold level, the line segment interval is read. As a result, an accurate line segment interval is obtained, and head-to-head alignment is performed based on the line segment interval.

As described above, by changing the threshold level at the time of binarization so that the line width becomes the same as the reference head at the stage of reading the line width, an accurate line can be obtained. By obtaining the minute intervals, it is possible to eliminate alignment adjustment errors due to variations and deterioration of the optical sensor, changes in light reflectance due to the print medium, differences in sensor sensitivity due to colors, and the like.

Next, a third embodiment according to the present invention will be described. The configuration of the carriage in this embodiment is the same as that of the first embodiment. However, as shown in FIG. 14, a display panel 147 (for example, a liquid crystal panel) is provided as notification means for notifying the user of information. Of course, the display panel 147 can be provided in the other embodiments described above. The notification means is not limited to the display panel.

In the first and second embodiments, the head is attached to the carriage at an angle to the carriage (rotated in a plane parallel to the print medium), and the arrangement direction of the print nozzles is If it is inclined with respect to the direction, an error occurs in the alignment correction value itself obtained as described above, and good print quality cannot be obtained even if the alignment is adjusted.

Therefore, in the present embodiment, in order to eliminate unnecessary alignment adjustment in such a case, the positions of one end (upper end) and the other end (lower end) of the print line are read before performing the alignment adjustment. The shift amount is obtained, and when the shift amount is equal to or larger than the predetermined shift amount, the user is notified using the display panel 147 or the like in FIG. 14 to urge the user to perform the work of removing the inclination.

More specifically, a pattern as shown in FIG. 15 is printed. This pattern is similar to the pattern shown in FIG. 6, but the length of each line segment is set to a length corresponding to the entire nozzle width of the head (here, 128 nozzles). To detect the inclination of the line segment of each color, first, at the position of one end (upper end) of the line group to be inspected (here, around the eighth nozzle inward from the uppermost nozzle), the left position of the line segment group 151
Starts moving the optical sensor at a constant speed (10mm / se
Scan the group of line segments in c). At this time, sampling is started from a predetermined position 152 before the first line segment, and the number of samples until the first line segment is detected is obtained. With respect to the second line segment, sampling is started from a predetermined position 153 between the first and second line segments, and the number of samples until the second line segment is detected is obtained. Next, such processing is performed on the position of the other end (lower end) of the line segment group (here, around the eighth nozzle inward from the lowermost nozzle). The position information of the obtained one end position and the other end position of the line segment are compared with each other. The difference is a predetermined value (for example, 2 dots, that is, 70.5
If it is 55 × 2) or more, it is regarded as a head inclination error of the head of the line segment group. In this case, for example, the display panel 14
7 is notified to the user, such as "Head Notes".

When the user is informed of such a warning, the head is removed once and the head is surely mounted again. A special mechanism for correcting the tilt of the head may be provided for cases where this cannot be dealt with. For example, in the mounting portion of the head with respect to the carriage, the upper end of the head is rotatably supported in a plane parallel to the print medium, one side of the lower end of the head is supported by a spring, and the other side is subjected to spring force. Against this, hold down with a fastening member such as a screw. With such a mechanism, the tilt angle of the head can be adjusted.

While the preferred embodiment of the present invention has been described above, various modifications and changes are possible.

[0063]

According to the present invention, the difference or threshold level of the other heads is corrected for each alignment adjustment in accordance with the reference head, thereby causing variations and deterioration of the optical sensor, changes in the light reflectance due to the print medium, and the like. It is possible to eliminate an alignment adjustment error due to a difference in sensor sensitivity due to a color or the like. In addition, it is possible to avoid in advance the deterioration of print quality and the poor alignment adjustment caused by the inclination of the print nozzle array itself when the head is inclined in the rotation direction parallel to the print medium.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating four inks 4 of an ink-jet image forming apparatus.
FIG. 3 is a diagram illustrating a configuration around a carriage on which a head is mounted.

FIG. 2 is a diagram illustrating a specific configuration example (a) of a linear scale of the image forming apparatus of FIG. 1 and a specific configuration example (b) of an optical linear scale sensor.

FIG. 3 is a diagram illustrating an example of a manual head alignment print pattern in a carriage scanning direction.

FIG. 4 is a diagram illustrating an example of a head alignment print pattern in a direction perpendicular to a manual carriage scanning direction.

FIG. 5 is a diagram illustrating a schematic configuration of a main part of the image forming apparatus used in the embodiment of the present invention.

FIG. 6 is a diagram showing an example of a test pattern for reading an optical sensor correction value according to the present invention.

7 is a block diagram showing a configuration of a process of a sense signal and a signal flow when a line segment of the test pattern of FIG. 6 is scanned by an optical sensor.

8 is a waveform diagram of an optical sensor output at the time of reading a line segment in the block diagram of FIG. 7;

FIG. 9 is a diagram showing an example of a head alignment adjustment pattern according to the present invention.

FIG. 10 is a diagram illustrating an example of a head alignment adjustment method in a direction perpendicular to the carriage scanning direction.

FIG. 11 is a block diagram illustrating a configuration of a sense signal process and a signal flow when a line segment is scanned by an optical sensor according to the second embodiment of the present invention.

FIG. 12 is a flowchart illustrating a flow of processing for reading a line segment width other than black ink according to the second embodiment of the present invention.

FIG. 13 is a waveform diagram of an optical sensor output at the time of reading a line segment according to the second embodiment of the present invention.

FIG. 14 is a diagram illustrating a configuration around a carriage according to a third embodiment of the present invention.

FIG. 15 is a diagram showing a print pattern according to the third embodiment of the present invention.

[Explanation of symbols]

 11, 12, 13, 14 Ink head 15 Carriage 16 Linear scale 24 Optical linear scale sensor 52 Platen 53 Print medium 54 Platen roller 55 Belt 70 CPU 71 Light emitting unit 74 Light receiving unit 75 Reading circuit

Claims (8)

[Claims] 1. An ink jet image forming apparatus for forming an image by discharging ink onto a print medium, comprising: a plurality of heads each having a plurality of nozzles for discharging ink droplets; Means for transporting a print medium, means for printing a first print pattern having a line segment of a predetermined width on the print medium by each head, a light emitting unit for projecting light to the line segment, and reflected light An optical sensor having a light receiving portion for receiving, based on an output of the optical sensor, reading a width of a line segment of the first print pattern printed by each head, and printing by a reference head and another head. Means for storing the difference between the widths of the line segments as a reading error due to the color of the optical sensor. 2. A means for printing a second print pattern having a line segment extending in a direction perpendicular to the head scanning direction by using a reference head and another head; Means for reading the interval of the line segment printed by the head, and correcting the read interval based on the reading error to obtain a displacement of the other head relative to the reference head in the head scanning direction. 2. An inkjet image forming apparatus according to claim 1, further comprising: means for adjusting the alignment of said another head with respect to said reference head in a head scanning direction. 3. A means for printing a line segment extending in a direction parallel to the head scanning direction using a reference head and another head, and a line printed by the reference head and another head using the optical sensor. Means for reading a minute interval and correcting the read interval based on the reading error to obtain a positional deviation of the other head relative to the reference head in a direction perpendicular to the head scanning direction. 2. The inkjet image forming apparatus according to claim 1, further comprising: a unit that performs alignment adjustment of the other head with respect to the reference head in a direction perpendicular to a direction. 4. An ink-jet image forming apparatus for forming an image by discharging ink onto a print medium, comprising: a plurality of heads each having a plurality of nozzles for discharging ink droplets; Means for transporting a print medium, means for printing a first print pattern having a line segment of a predetermined width on the print medium by each head, a light emitting unit for projecting light to the line segment, and reflected light An optical sensor having a light receiving unit for receiving the light; a means for changing a reading determination threshold level of the optical sensor; and a plurality of lines printed by the plurality of heads by reading and determining the output of the optical sensor at the threshold level. The width of the minute is determined, and the reading determination threshold level of the optical sensor is set so that these widths become a predetermined width. Owl, read judgment threshold level in each line segment, an inkjet image forming apparatus characterized by comprising: means for storing for each of the optical sensors color, the. 5. A means for printing a second print pattern having a line segment extending in a direction perpendicular to the head scanning direction using a reference head and another head, and for each head using the optical sensor. The interval between line segments printed by the reference head and the other head is read using the corresponding read determination threshold level, and the displacement of the other head relative to the reference head in the head scanning direction is determined based on the read interval. 5. The inkjet image forming apparatus according to claim 4, further comprising: means for adjusting the alignment of the other head with respect to the reference head in the head scanning direction based on the positional deviation. 6. A means for printing a line segment extending in a direction parallel to the head scanning direction by using a reference head and another head, and said read determination threshold level corresponding to each head by using said optical sensor. Means for reading the interval of the line segment printed by the reference head and the other head using, based on the read interval, a means for determining the displacement of the other head relative to the reference head in a direction perpendicular to the head scanning direction, The inkjet image forming apparatus according to claim 4, further comprising: means for performing alignment adjustment of the other head with respect to the reference head in a direction perpendicular to the head scanning direction based on the positional shift. 7. The position of one end and the other end of a line segment for each head is detected by using the optical sensor, the amount of deviation of the position is obtained, and when the amount of deviation of a certain amount or more is detected, the inclination of the head is detected. The inkjet image forming apparatus according to claim 2, further comprising a unit that determines an abnormality. 8. When it is determined that the tilt of the head is abnormal,
8. The ink-jet image forming apparatus according to claim 7, further comprising means for notifying the user of the fact.