JP2021005015A - Image forming apparatus - Google Patents

Abstract

To solve the problem in which: when an intermediate transfer belt is stopped at the same position for a long period, elastic deformation occurs at bent portions of the intermediate transfer belt; and therefore, the elastic deformation portions may be erroneously detected during pattern detection for color shift correction.SOLUTION: In a result of detection in color shift correction, when abnormalities are detected at a plurality of portions in a main scanning direction, the distance between reading pattern sets is increased, and determination of the end of pattern set detection is changed from the basis of the number of edge count to the basis of timer count, so as to achieve stable reading. When no abnormality is detected, pattern formation is continued while maintaining the short distance between the reading pattern sets, so as to reduce downtime.SELECTED DRAWING: Figure 13

Description

The present invention minimizes a decrease in productivity when controlling an image forming apparatus that sequentially superimposes images of a plurality of colors to form a color image and transfers the image onto a recording paper to prevent deterioration of image quality due to color shift. This is to limit the number.

Conventionally, in an electrophotographic copying machine that forms a multicolor image, a color image is formed by superimposing images of a plurality of colors such as yellow, magenta, cyan, and black. Therefore, if the image formation position of each color shifts, the color shifts on the paper to be image-formed.

In an electrophotographic copying machine, the image formation position of each color is the expansion / contraction of a member due to a temperature change of a laser scanner that forms an electrostatic latent image, and the deviation of a driving part such as a photosensitive drum that secures a visible toner image. It is known that it is an element that can be sequentially changed due to uneven rotation of the intermediate transfer belt formed by superimposing the toner images of each color.

For this reason, self-correction has been realized by the airframe itself by forming a predetermined color shift amount detection pattern and reading it with an optical sensor in order to sequentially correct the color shift.
Therefore, even if the image formation characteristics change due to parts replacement or the image characteristics change due to expansion or contraction of the parts due to changes in the ambient temperature, there are many colors today that automatically correct the image characteristics. It is used in copiers.

If the electrophotographic color copier has been used for a long period of time, the deterioration of each component will progress, and the intermediate transfer belt formed by superimposing the toner images of each color will be dented or scratched, resulting in failure to read the detection pattern. May be done.

Conventionally, when reading a color shift amount detection pattern, yellow, magenta, cyan, and black 4 are prepared in case of dents or scratches on the intermediate transfer belt that is the target of forming the color shift amount detection pattern. A detection pattern consisting of colors is divided into fixed sizes, a plurality of reflected light amount sensors arranged in the main scanning direction count the number of edges of the reflected light amount, and the plurality of sensors detect when the predetermined number of edges is reached. By reading the interval between patterns, repeating this multiple times and using the averaged value, and excluding the pattern set that deviates from the normal value, even if the detection pattern cannot be read correctly due to various disturbance factors, it is mistakenly read. A process has been performed that does not perform an inappropriate amount of color shift correction (Patent Document 1).

Japanese Unexamined Patent Publication No. 2003-215001

However, the intermediate transfer belt used for forming a color image in an electrophotographic copying machine has a configuration in which it is stretched and bent by rollers at a plurality of locations, and also has a configuration in which it is stopped while being sandwiched by a secondary transfer roller. Therefore, if the intermediate transfer belt is stopped at a specific position for a long period of time, elastic deformation may occur in the intermediate transfer belt. In such a case, since the reflected light is scattered and the amount of reflected light is reduced as in the detection pattern, it may be erroneously detected as a detection pattern.

These elastic deformations occur in the entire longitudinal direction of the intermediate transfer belt. Therefore, since any of the sensors arranged in the longitudinal direction may be erroneously detected, unlike the dents that occur in the intermediate transfer belt, the number of edges of the reflected light of the correction pattern is counted by a predetermined number of the multiple sensors. The pattern set could not be determined under the AND condition.

In addition, in order to deal with these problems, if the color shift correction pattern is to be detected and completed for each pattern set in the time consisting of the theoretical distance in the pattern set unit, the timer error is calculated between the pattern sets. It is necessary to take an extra interval for adjustment.

Therefore, when viewed as a whole, it becomes longer by the amount of the pattern set interval in proportion to the number of pattern sets. Therefore, color shift correction is performed between pages during the print job in the electrophotographic color image forming apparatus. This causes an increase in downtime, which causes a problem of productivity reduction for the user.

Due to the above problems, it has not been possible to achieve both improvement in productivity by shortening the pattern for color shift correction and false detection of pattern detection due to elastic deformation of the intermediate transfer belt.

In order to solve the above problems, the image forming apparatus according to the present invention is
An image forming means for forming toner images of different colors on a plurality of photoconductors, an intermediate transfer body that is rotationally driven and the toner images on the plurality of photoconductors are transferred, and an intermediate transfer body that is transferred to the intermediate transfer body. A detection means that detects the toner image, and a control means that causes the image forming means to form a pattern image, causes the detection means to detect the pattern image, and controls color shift based on the detection result of the pattern image. The control means causes the image forming means to form a first pattern image, causes the detecting means to detect the first pattern, and relates to the number of edges included in the detection result of the first pattern. The first mode for controlling the detection of the detection means when one condition is satisfied, the image forming means for forming a second pattern image, the detecting means for detecting the second pattern, and the second pattern. It is characterized in that a second mode for controlling the detection of the detection means is selectively executed when the second condition regarding the detection time of the above is satisfied.

According to the image forming apparatus according to the present invention, it is possible to increase productivity without extending downtime while maintaining the accuracy of color shift correction of an electrophotographic color printer apparatus.

Sectional drawing of an Example explaining the present invention Block diagram for controlling an embodiment for explaining the present invention Intermediate transfer belt and color shift correction pattern formation diagram for explaining the subject of the present invention. The relationship diagram of the intermediate transfer belt and the reflected light amount sensor explaining the subject of this invention. Overall view of the color shift correction pattern for explaining the subject of the present invention. Color shift correction pattern and reflected light waveform for explaining the subject of the present invention Color shift correction pattern for explaining the subject of the present invention and waveform at the time of dent occurrence Elastic deformation and color shift correction pattern formation diagram of the intermediate transfer belt for explaining the subject of the present invention. Detection waveform of elastic deformation and color shift correction pattern of intermediate transfer belt for explaining the subject of the present invention Elastic deformation of the intermediate transfer belt and reading control of the color shift correction pattern for explaining the subject of the present invention Flow chart of color shift correction control for explaining the present invention Timing chart of normal time of color shift correction control for explaining the present invention Timing chart when the color shift correction control for explaining the present invention is abnormal Flow chart of color shift correction control for explaining the present invention Flow chart of color shift correction pattern control for explaining the present invention

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

FIG. 1 is an internal configuration diagram of a printer engine of a copying machine to which the present invention is applied.

The 101y to 101k are yellow, magenta, cyan, and black process units, respectively, and are composed of a photosensitive drum, a developing device, a charging roller, and the like. A photosensitive drum 102k is housed in the central portion of the process unit 101k, and is rotationally driven by a drum motor (not shown). Reference numeral 103k is a charging roller, which uniformly charges the surface of the photosensitive drum 102k by applying a high voltage. The 104k is a laser scanner unit that scans a laser modulated and output from a laser diode in the longitudinal direction using a polygon mirror rotating body, and performs laser exposure on a uniformly charged photosensitive drum 102k according to input image information. , Form an electrostatic latent image. Reference numeral 105k is a developer, and a visible toner image corresponding to an electrostatic latent image is formed on a photosensitive drum 102k by a two-component developer composed of toner and a carrier. Reference numeral 106k is a toner bottle filled with toner, which supplies toner to the developer 105k. Reference numeral 107k is a primary transfer roller for primary transfer from the photosensitive drum 102k to the intermediate transfer belt 108 which is an endless belt-shaped member for sequentially superimposing the colors Y, M, C, and K. Reference numeral 109k is an auxiliary charging brush, which charges the transfer residual toner that cannot be completely transferred by the primary transfer roller 107k so as to have a uniform charge.

Regarding the photosensitive drum 102k, the charging roller 103k, the developing device 105k, and the auxiliary charging brush 109k included in the process unit 101y to 101k, only black is described, but yellow, magenta, and cyan are also common. Hereinafter, when the description includes the photosensitive drum 102, the charging roller 103, the developing device 105, and the auxiliary charging brush 109, each color of yellow, magenta, cyan, and black is included.

The toner image primaryly transferred to the intermediate transfer belt 108 is secondarily transferred onto the paper by the secondary transfer roller shown in 110. The residual toner that could not be transferred by the secondary transfer roller 110 and the toner image for adjustment that is not intended to be transferred on the paper are collected by the cleaning blade 111. Reference numeral 112 denotes a reflected light amount sensor that detects the edge of the shading change of the pattern imaged on the intermediate transfer belt.

The paper P is stored in the paper cassette 113, is conveyed by the paper feed roller 114, is skewed by the resist roller 115, and is then sent to the secondary transfer roller 110. After the toner image is transferred by the secondary transfer roller 110, the toner is heat-fixed by the fixing roller 117 and the pressure roller 118, and is conveyed to the paper ejection tray 120 or the in-body output tray 121 by the paper ejection flapper 119.

Next, the load control circuit configuration of the image forming apparatus will be described with reference to the block diagram of FIG.

Reference numeral 201 denotes a CPU, which controls the printer engine shown in FIG. Reference numeral 202 denotes a ROM, which stores a program for operating the CPU 201. Reference numeral 203 denotes a RAM, which is used by the CPU 201 to temporarily store data.

Reference numeral 204 denotes an EEPROM, which is a non-volatile memory for enabling the information set in the operation of the copier to be recorded even when the power is turned off, and can be rewritten by a predetermined procedure. ..

Reference numeral 205 denotes an input / output port of the CPU 201, which is via a device connected to the CPU 201.

Reference numeral 206 denotes a timer, and the CPU 201 can acquire the current time and the elapsed time in clock units, and can notify the CPU 201 with a signal that a predetermined number of clocks have elapsed.

Reference numeral 207 is an RTC (RealTime Clock), and the CPU 201 can acquire the elapsed time including when the power is turned off by a power supply means (not shown).

Reference numeral 208 denotes a network I / F, which is an interface for accepting a print job from a PC connected to the LAN.

Reference numerals 211 to 223 are control units connected to the input / output port 205. Reference numeral 211 denotes a laser driver, which controls the laser scanner units 104y to 104k. Reference numeral 212 denotes a motor driver, which controls the rotation of the photosensitive drum 102, the intermediate transfer belt 108, the paper feed roller 114, the resist roller 115, and the like.

Reference numeral 213 is a high-voltage control unit that controls the high-voltage output of the charging roller 103 and the developing device 105, the primary transfer roller 107, the secondary transfer roller 110, and the like included in the process unit 101.

Reference numeral 214 denotes a transport sensor, which is a sensor that is arranged on a paper transport path in the printer device and can detect the paper position.

Reference numeral 221 denotes a front side reflected light amount sensor included in the reflected light amount sensor 112, which is a sensor located on the front side when viewed from the front surface of the main body. Reference numeral 222 denotes a central reflected light amount sensor included in the reflected light amount sensor 112. Reference numeral 223 is a back-side reflected light amount sensor included in the reflected light amount sensor 112.

FIG. 3 is a diagram in which a detection pattern for the amount of color shift correction is formed on the intermediate transfer belt 108 of the image forming apparatus.

The intermediate transfer belt 108 is rotated by a drive roller that is rotationally driven by a DC brushless motor (not shown). The detection pattern of the color shift correction amount formed on this is detected by the reflected light amount sensor 112.

The detected reflected light is read by the reflected light amount sensor 221 on the front side, the reflected light amount sensor 222 in the center, and the reflected light amount sensor 223 on the back side at three positions in the longitudinal direction.

The reflected light amount sensor 112 will be described with reference to FIG.

The reflected light amount sensor 112 is composed of a light emitting unit 301 composed of an infrared LED or the like and a light receiving unit 303 composed of a phototransistor or the like.

The light emitting unit 301 and the light receiving unit 303 are attached at an angle such that the infrared light emitted by the light emitting unit 301 is reflected by the intermediate transfer belt 108 and the reflected light is incident on the light receiving unit 303. When the color shift detection pattern 302 is formed on the intermediate transfer belt 108 by toner, the light receiving unit 303 receives the reflected light.

The reflected light received by the light receiving unit 303 is converted into an electric signal according to the amount of reflected light. The output electric signal voltage has a low voltage when the amount of reflected light is small, and a high voltage when the amount of reflected light is large.

Generally, the larger the amount of toner on the intermediate transfer belt 108, the smaller the amount of reflected light. Therefore, the higher the output signal voltage of the reflected light amount sensor 112, the lower the imaged toner concentration, and the lower the output signal voltage. The lower the value, the higher the toner concentration, and the output signal voltage and the toner concentration are in a proportional relationship.

The positional relationship between the reflected light amount sensor 112, the intermediate transfer belt 108, and the color shift detection pattern 302 is as shown in FIG. 3, and the reflected light amount sensor 112 is rotated by the rotation of the intermediate transfer belt 108. The image of the color shift detection pattern 302 formed long in the direction can be continuously read.

The detection pattern of the color shift correction amount will be described with reference to FIG.

FIG. 5 is a pattern formed on the intermediate transfer belt 108.

601 is a pattern imaged with yellow toner, 602 is a pattern imaged with magenta, 603 is cyan, and 604 is a pattern imaged with black toner, and they are arranged 300 pixels apart from each other. As for the interval between patterns, the interval is measured with this as one set. The patterns of 601 to 604 are sequentially detected by the back side reflected light amount sensor 223 according to the rotation of the intermediate transfer belt 108.

Similarly, 611 to 614 are pattern sets imaged with yellow, magenta, cyan, and black toners, respectively, and are sequentially detected by the back side reflected light amount sensor 223 following the pattern sets 601 to 604. The pattern sets 601 to 604 and 611 to 614 are spaced longer than each color in order to identify when the positions of the colors are displaced.

701 to 704 and 711 to 714 are pattern sets also imaged with yellow, magenta, cyan, and black toners, and are sequentially detected by the central reflected light amount sensor 222.

801 to 804 and 81 to 814 are also pattern sets imaged with yellow, magenta, cyan, and black toners, and are sequentially detected by the front side reflected light amount sensor 221.

The pattern sets 601 to 604, 611 to 614, 701 to 704, 711 to 714, 801 to 804, and 81 to 814 mainly determine the color shift between the colors in the rotation direction of the photosensitive drum 102 and the intermediate transfer belt 108. It is a thing, and the pattern set is repeated multiple times to create and read. Although only two sets are shown in FIG. 5, in some cases, the intermediate transfer belt 108 may be repeatedly formed for one week.

The correspondence between the detection pattern of the color shift correction amount and the reflected light amount and the detection information will be described with reference to FIG.

As described above, 601 to 604 are imaged on the front side of the intermediate transfer belt 108, and 601 is a pattern image formed of toner composed of yellow, 602 is magenta, 603 is cyan, and 604 is black. Of the reflected light amount sensors 112, the waveform showing the reflected light amount when they are incident on the reflected light amount sensor 223 on the back side is 521, and as described above, the reflected light amount is scattered in the pattern portion because the incident light is scattered. Since the amount of light returning to the sensor decreases, the voltage value becomes low, and the portion without the pattern has a high voltage value because the rate of incident light returning to the reflected light amount sensor is high.

The waveform obtained by comparing this signal with the predetermined threshold voltage by a comparator and binarizing it is 522. By measuring the distance between the edges of this waveform, the distance 523 between yellow and magenta, the distance 524 between magenta and cyan, and the distance 525 between cyan and black can be obtained.

The detection method is the same for 701 to 704 imaged in the center of the intermediate transfer belt 108 and 801 to 804 imaged in the back side.

By calculating the distance value between each color, the distance between yellow and magenta, the distance between yellow and cyan, and the distance between yellow and black can be obtained. A visible toner image without color shift can be formed by comparing these values with the theoretical distance, calculating the correction value, and shifting the image by the correction value at the next image formation.

As described above, these patterns are detected by three positions in the longitudinal direction, a reflected light amount sensor 221 on the front side, a reflected light amount sensor 222 in the center, and a reflected light amount sensor 223 on the back side.

For the color shift in the rotation direction of the intermediate transfer belt, use the average value of the intercolor distances of the front, center, and back sensors, and for the color shift in the longitudinal direction of the intermediate transfer belt, form a diagonal pattern. The amount of deviation is detected from the detection timing of each color of the front side, center, and back side sensors.

With respect to the formation of such a pattern for color shift correction, as shown in FIG. 7, when a dent 661 on the intermediate transfer belt 108 is generated between the pattern 603 and the pattern 604, the formed visible toner image Since the reflected light is scattered in the same manner as the pattern, the change in the reflected light may be in the form of a change in the amount of reflected light between the pattern 603 and the pattern 604 as shown in 531.

At this time, if the output signal of the reflected light amount sensor is binarized at a predetermined threshold value by a circuit including a comparator, it can be detected as if the pattern by the toner image is located between the pattern 603 and the pattern 604. is there.

In such a case, if the color shift correction pattern is read in order from the beginning, the pattern shifts. That is, in the example of FIG. 7, the distance 535 between yellow and magenta and the distance 536 between magenta and cyan are correct, but the distance 537 between cyan and black is not correct because the dented portion is misrecognized, and continues as it is. If the distance between the patterns is measured in sequence, the correspondence between the colors and the patterns will shift.

However, since the dents on the intermediate transfer belt 108 do not occur at the same time in each of the plurality of reflected light amount sensors arranged in the longitudinal direction, even if the edge is erroneously detected by the front side reflected light amount sensor 221 for example, the other center It is rare that the reflected light amount sensor 222 and the back side reflected light amount sensor 223 erroneously detect in the same pattern set.

Therefore, when the front side reflected light amount sensor 221, the center reflected light amount sensor 222, and the back side reflected light amount sensor 223 determine the predetermined number of edges corresponding to one pattern set under the AND condition, the correspondence between the reading pattern and the color is deviated. It was possible to prevent it from happening.

However, here, not only the case where the intermediate transfer belt is partially dented but also the case where the elastic deformation of the intermediate transfer belt 108 is generated in the entire longitudinal direction will be described.

FIG. 8 is a diagram in which elastic deformation occurs in the intermediate transfer belt 108. These elastic deformations occur when the intermediate transfer belt is in a stopped state for a long period of time at a bent portion, particularly at a position where the intermediate transfer belt is bent and the other roller faces the outside of the opposing position.

Reference numeral 311 is an elastic deformation portion, and the elastic deformation portion moves according to the rotation of the intermediate transfer belt 108. Since there is no difference in the elastically deformed portion from the viewpoint of electrical resistance, the efficiency of primary transfer of the visible toner image from the photosensitive drum 102 does not decrease.

Therefore, there is no problem in the toner image formed on the paper as the final product, and the formation of the color shift correction pattern described above is not affected, but the reading of the color shift correction pattern is affected.

This phenomenon will be described with reference to FIG.

In FIG. 9, 601,701,801 are images of yellow toner, 602,702,802 are magenta, 603,703,803 are cyan, and 604,704,804 are black toner. , They are arranged 300 pixels apart from each other.

901 is a signal indicating that the edge timing for each pattern set is being detected, and indicates that the edge detection is stopped at the High level and the edge is detected at the Low level. Reference numeral 911 is a signal indicating that the pattern set detection results are being read collectively, and indicates that the pattern set detection results are being read at the High level and being read at the Low level.

After being formed on the intermediate transfer belt 108, they are irradiated to the reflected light amount sensor 112, and the signal indicated by the reflected light becomes 681,781,881. When elastic deformation occurs in the intermediate transfer belt, it is detected by the reflected light amount sensor 112 as if a pattern is formed, as in 671, 771, 871.

When reading these color shift correction patterns in units of one set consisting of yellow, magenta, cyan, and black, the reading end judgment for one set is determined by the number of falling edges and rising edges of changes in the amount of reflected light. , The edge of the reflected light was started to be detected at the timing 902, but the edge was detected at the wrong position by the elastic deformation points 671, 771, 871 on the intermediate transfer belt 108.

Therefore, the elastically deformed portion of the intermediate transfer belt is also counted indistinguishable from the correction pattern, and the reading end determination position for one set shifts, and the rising edge of the cyan pattern 603,703,803 is formed. At the time of detection, it may be erroneously determined that the reading of one pattern set is completed as in the timing 905.

Further, if the reading end determination position for one set shifts, as shown in timing 906, the reading start position for the next set also shifts, which affects the subsequent reading of the pattern, and the second pattern. Since the read end determination portion of the set is also shifted as in the timing 907, there is a problem that only the pattern set of the abnormality determination portion can be excluded and the color shift correction cannot be performed correctly.

Further, as shown in FIG. 10, the reading end determination for one set is not determined by the number of falling edges and rising edges of the change in the amount of reflected light, but the rotation speed of the intermediate transfer belt 108 is determined from the distance between the sets. A method of calculating and judging on a time basis is also conceivable.

As an example, the connection timer 206 is used for the CPU 201, the timer counts up as shown in 921, and the reading end determination for one set is performed at the timing when the predetermined time is reached. The change in the counter value of the timer at this time is as shown in 931.

Specifically, the timer of the section 922 is set from the timing 932 before the arrival of the pattern for one set, and it is determined that the end is completed at the timing 933 when the count value reaches the value corresponding to the time for one set, and the time is set to 915. As shown, the reading result for one set is acquired.

In order to continuously read the next pattern 1 set, the timer of the section 923 is set from the timing 936, and it is judged that the end is completed at the timing 937 when the count value reaches the value corresponding to the time for one set, and as shown in 917. Acquire the reading result for one set.

When determining the end of each pattern set by this method, the problem that the reading position of the subsequent pattern set shifts due to the influence of the elastic deformation points 871, 771, 871 of the intermediate transfer belt 108 can be avoided, but the actual pattern There is a slight error between the read timing and the timer provided in the microprocessor, so there must be a gap between the pattern set being read and the next pattern set, resulting in increased downtime overall. There was a problem of doing.

In order to solve the above problems, as an application example of the present invention, a determination when the CPU 201 forms and reads a color shift correction pattern will be described with reference to the flowchart of FIG.

First, the CPU 201 forms a color shift correction amount on the intermediate transfer belt 108 (step 2001), and the number of rising edges and falling edges reaches a predetermined number in each of the front side, center, and back side pattern sensors. This is used as a criterion for determining the end of one pattern set, and the pattern set is read (step 2002).

The CPU 201 sequentially reads a plurality of pattern sets, but deviates from the theoretical positions of yellow, magenta, cyan, and black at the same position by a plurality of sensors on the front side, the center, and the back side for each pattern set reading. It is determined whether there is an edge-to-edge distance of the interval (step 2003).

Here, if there is no edge-to-edge distance deviating from the theoretical position of each color, it is determined that the intermediate transfer belt 108 does not have an erroneous edge detection due to elastic deformation, and the same applies to the subsequent pattern sets. The pattern formation is continued (step 2004), and the reading method is similarly the end of one pattern set when the number of rising edges and falling edges reaches a predetermined number for each of the front side, center, and back side pattern sensors. Continue reading as a criterion (step 2005).

If the distance between the edges deviating from the theoretical position of each color in step 2003 is present in the front, center, and back sensors, the intermediate transfer belt 108 has a pattern caused by elastic deformation. It is determined that an edge false detection has occurred, and the subsequent pattern set is switched so as to form a longer interval between the pattern sets (step 2006), and a timer is set from the timing before the pattern is reached for one set. , The method is changed to the method of determining the end when the count value reaches the value corresponding to the time for one set, and the reading is continued (step 2007).

FIG. 12 is a timing chart showing the color shift correction pattern formation and the reading timing in the cases of steps 2004 and 2005 in the flowchart described above, that is, in the case where the intermediate transfer belt 108 is not elastically deformed.

601 to 604, 611 to 614, 621 to 624, and 631 to 634 are pattern sets imaged with yellow, magenta, cyan, and black toners, respectively, and are created at positions that are sequentially read by the back side reflected light amount sensor 223. Be imaged.

Reference numeral 681 is a waveform obtained by binarizing the detection waveform of the back-side reflected light amount sensor 223 with a predetermined voltage threshold value by a comparator.

701 to 704, 711 to 714, 721 to 724, and 731 to 734 are pattern sets similarly imaged with yellow, magenta, cyan, and black toners, and are created at positions that are sequentially read by the central reflected light amount sensor 222. Be imaged.

Reference numeral 781 is a waveform obtained by binarizing the detection waveform of the central reflected light amount sensor 222 with a predetermined voltage threshold value by a comparator.

801 to 804, 81 to 814, 821 to 824, and 831 to 834 are pattern sets similarly imaged with yellow, magenta, cyan, and black toners, and are positioned so as to be sequentially read by the front side reflected light amount sensor 221. It is imaged.

Reference numeral 881 is a waveform obtained by binarizing the detection waveform of the front side reflected light amount sensor 221 with a predetermined voltage threshold value by a comparator.

Now, when the CPU 201 starts counting the rising edge and the falling edge with respect to the first pattern sets 601 to 604, 701 to 704, and 801 to 804 at the timing 952, the front side reflected light amount sensor 221 and the center at the timing 953. Regarding the number of edges of the reflected light amount sensor 222 and the back side reflected light amount sensor 223, 8 edges are aligned under the AND condition.

In response to this, the CPU 201 acquires the time interval between the edges of the waveform 681, the waveform 781, and the waveform 881 at the timing 962, and when the acquisition is completed, the CPU 201 acquires the next pattern set 611-614, 711-714, 811 at the timing 954. Edge detection is started for ~ 814. When the 8 edges of the reflected light amount sensors 221 to 223 on the front, center, and back sides are aligned again under the AND condition at the timing 955, the CPU 201 is between the edges of the waveform 681, the waveform 781, and the waveform 881 with respect to the second pattern set at the timing 963. Get the time interval of.

Similarly, for the third pattern set, 621-624, 721-724, 821-824, edge detection is started from timing 956, and when 8 edges are aligned again under the AND condition at timing 957, at timing 964. Get the time interval between edges.

Similarly, for the fourth pattern set, 631-634, 731-734, and 831-834, edge detection is started from timing 958, and when 8 edges are aligned again under AND conditions at timing 959, edges are aligned at timing 965. Get the time interval between.

In this way, if there is no effect of elastic deformation on the intermediate transfer belt 108, each pattern set can be set under the AND conditions of the front, center, and back sensors based on the counts of the falling edge and rising edge. Judge the end of reading.

On the other hand, FIG. 13 shows the color shift in the case of steps 2006 and 2007 in the flowchart described above, that is, the case where the intermediate transfer belt 108 is elastically deformed and is erroneously detected as a color shift correction pattern. It is a timing chart which showed the correction pattern formation and the reading timing.

Similar to FIG. 12, 601 to 604, 611 to 614, 621 to 624, and 631 to 634 are pattern sets imaged with yellow, magenta, cyan, and black toners, respectively. 701 to 704, 711 to 714, 721 to 724, and 731 to 734 are pattern sets that are sequentially read by the central reflected light amount sensor 222. 801 to 804, 81 to 814, 821 to 824, and 831 to 834 are pattern sets that are imaged at positions that are sequentially read by the front side reflected light amount sensor 221.

921 is a diagram showing a section in which a timer is used, and 931 is a diagram showing a value of a timer counter.

Now, the CPU 201 starts counting the rising edge and the falling edge for the first pattern sets 601-604, 701-704, and 801-804 at the timing 962, but the edge error due to the elastic deformation of the intermediate transfer belt is started. The detection is 671 for the back side reflected light amount sensor 223, 771 for the central reflected light amount sensor 222, and 871 for the front side reflected light amount sensor 221.

In this case, the number of edges of the front side reflected light amount sensor 221 and the center reflected light amount sensor 222 and the back side reflected light amount sensor 223 at the timing 963 when the rising edges of the cyan patterns 603, 703, and 803 are detected are 8 edges, respectively. Are aligned under the AND condition.

In response to this, the CPU 201 acquires the time interval between the edges of the waveform 681, the waveform 781, and the waveform 881 at the timing 962, but the cyan pattern should be originally detected from the magenta pattern 602,702,802. False edge detection due to elastic deformation detected instead of timing The values up to 671, 771, and 871 are significantly different, and are detected by all the front, center, and back sensors, so the first pattern set is elastic. It can be determined that false edge detection due to deformation has occurred.

If the detection of the color shift correction pattern is continued as it is, it is considered that the correspondence between the color and the edge of the pattern set is shifted and that elastic deformation on the intermediate transfer belt 108 occurs at other bending points. As described in 2006 and step 2007, the pattern set formation interval and the pattern set end determination condition are changed.

However, since there is a certain distance between the photosensitive drum 102 that forms yellow, magenta, cyan, and black color images and the reflected light amount sensor 112 that detects patterns, the formation interval should be switched immediately from the pattern set to be read next. Therefore, after determining that there is elastic deformation, the pattern set for which the pattern of the first color is formed is switched.

In FIG. 13, switching is performed from the third pattern set, 621 to 624, 721 to 724, 821 to 824 and later. That is, the interval from the last pattern 624, 724, 824 of the third pattern set to the next fourth pattern set is the first that the reading end of one pattern set is determined by the count of the falling edge and the rising edge. -Longer than the interval of the second pattern set (624 to 631, 724 to 731, 824 to 831).

Further, at the detection start timing 964 of the third pattern set, the timer 206 starts the time measurement corresponding to the section 925. The section 925 is a section indicating the time from the start of the third pattern set to the end of the third pattern set and the center of the fourth pattern set.

The timer counting up from timing 932 to timing 933 with respect to the timer 206 that started counting at timing 964 reached the end of the third pattern set and the center of the fourth pattern set when the time corresponding to the interval 925 was reached. Is determined, the reading of the pattern set is completed (timing 965), and the edge spacing of the pattern set is acquired (timing 985).

When the acquisition of the edge spacing of the pattern set is completed, the reading of the next fourth pattern set is started.

When edge detection is performed for the fourth pattern set 631 to 634, 731-734, and 813 to 834, the timer 206 measures the time corresponding to the section 926 to measure the edge, as in the case of the third pattern set. Judges the end of edge reading of the pattern set.

When the edge-to-edge distance measurement of the pattern set is started at the timing 965, the timer count-up is started at the timing 9036, and when the time corresponding to the interval 926 is reached, the end of the fourth pattern set and the next fifth pattern are reached. It is determined that the center of the set has been reached, the reading of the pattern set is finished (timing 967), and the edge interval of the pattern set is acquired (timing 987).

As described above, when forming a pattern for color shift correction and determining the reading end for each pattern set consisting of each color, at first, in order to shorten the overall pattern forming / reading time in order to increase productivity as much as possible. In addition, the reading end determination for each pattern set is performed by counting the number of falling and rising edges of the color shift correction pattern.

In addition, the value of the pattern interval is referred to at each end of reading for each pattern set, and if multiple sensors provided in the longitudinal direction include edge-to-edge distance information different from the theoretical value at the same location at multiple locations, the intermediate value is used. It is judged that an erroneous edge detection has occurred due to elastic deformation of the transfer belt, and the color and edge judgment of each color pattern does not deviate in the subsequent pattern sets. The interval between the pattern sets is widened so that the reading independence is maintained, and the reading end judgment of each pattern set is switched to the time reference using a timer.

Based on these judgments, in the electrophotographic color image forming apparatus, when the intermediate transfer belt is not elastically deformed, the intermediate transfer belt is elastically deformed by forming and reading a pattern image as short as possible to increase productivity. If this is the case, it is possible to prevent erroneous detection of the color shift correction pattern and elastic deformation, and to maintain image quality at the same time.

In the first embodiment, the pattern for color shift correction is read in units of pattern sets, the distance between the read patterns is determined, and the distance between the patterns deviates from the theoretical value of each color pattern position of yellow, magenta, cyan, and black. When information was included, a method was adopted in which the formation interval of the pattern set for color shift correction and the end determination were switched from the middle.

This method is suitable for minimizing the pattern formation time for color shift correction, but for reading a pattern set consisting of yellow, magenta, cyan, and black, and then actually reflecting it in the next pattern formation, A delay of the distance from the reflected light amount sensor 112 to the farthest photosensitive drum 102 occurs.

Therefore, when the pattern for color shift correction is short, or when an erroneous detection occurs due to elastic deformation of the intermediate transfer belt in the latter half of a plurality of pattern sets, the image formation interval of the pattern set may not be changed in time. In such a case, the judgment of FIG. 14 is performed.

FIG. 14 is a determination flow when the CPU 201 performs color shift correction control.

The CPU 201 forms a color shift amount detection pattern on the intermediate transfer belt 108 (step 2101), and the number of rising edges and falling edges reaches a predetermined number in each of the front side, center, and back side pattern sensors. A pattern set is read as a criterion for determining the end of one pattern set (step 2102).

The CPU 201 sequentially reads a plurality of pattern sets, but deviates from the theoretical positions of yellow, magenta, cyan, and black at the same position by a plurality of sensors on the front side, the center, and the back side for each pattern set reading. It is determined whether there is an edge-to-edge distance of the interval (step 2103).

Here, if there is no edge-to-edge distance deviating from the theoretical position of each color, it is determined that the intermediate transfer belt 108 does not have an erroneous edge detection due to elastic deformation, and the same applies to the subsequent pattern sets. The pattern formation is continued (step 2004), and the reading method is similarly the end of one pattern set when the number of rising edges and falling edges reaches a predetermined number for each of the front side, center, and back side pattern sensors. Continue reading as a criterion (step 2005).

If the distance between the edges deviating from the theoretical position of each color in step 2003 is present in the front, center, and back side sensors, the intermediate transfer belt 108 has a pattern caused by elastic deformation. If it is determined that an edge false detection has occurred, but the distance to the subsequent pattern set is shorter than the distance from the yellow photosensitive drum 102y, which is the leading color, to the reflected light amount sensor 112, the pattern formation is retried from the beginning. (Step 2106).

When retrying pattern formation from the beginning, the image is formed so that the interval between the pattern sets is wide from the first pattern set, and the end judgment condition is also the next pattern from the pattern set being read by the timer 206. The reading end determination for each pattern is performed by the determination method using the time between sets (step 2107).

As a result, regardless of the length of the color shift correction pattern or the timing when the elastic deformation of the intermediate transfer belt is detected on the color shift correction pattern, the downtime is limited to the case where the elastic deformation of the intermediate transfer belt has an effect. It is possible to provide a color image forming apparatus that minimizes the influence of the above.

In Examples 1 and 2, it is determined whether or not an erroneous detection of an edge due to elastic deformation has occurred in the intermediate transfer belt 108 based on the distance between the edges obtained from the detection result of the intermediate transfer belt 108. In this embodiment, the correction pattern detection method is switched based on the period during which the rotational drive of the intermediate transfer belt 108 is stopped, regardless of whether or not an erroneous edge detection has occurred.

In this embodiment, the determination when the CPU 201 forms and reads the color shift correction pattern will be described with reference to the flowchart of FIG.

First, the CPU 201 measures the time using the RTC207 and determines whether or not the intermediate transfer belt 108 has been stopped for a long period of time (step 3001). That is, if 7 days have not passed since the intermediate transfer belt 108 stopped the rotational drive, it is determined that the intermediate transfer belt 108 has not been elastically deformed.

If it is determined that 7 days have not passed, a color shift correction amount is formed on the intermediate transfer belt 108 (step 3002), and this is applied to the rising edge and the falling edge by the pattern sensors on the front side, the center, and the back side, respectively. The pattern set is read with the fact that the number of the above reaches a predetermined number as the end determination criterion of one pattern set (step 3003).

If it is determined that 7 days have passed, the interval between the pattern sets is lengthened (step 3004), the timer is set from the timing before the pattern is reached for one set, and the count value is set to the time for one set. It is read by a method of determining the end when the corresponding value is reached (step 3005).

As described above, in forming the color shift correction pattern and determining the reading end for each pattern set consisting of each color, if the stop time of the intermediate transfer belt is shorter than the predetermined time, the productivity should be increased as much as possible. In order to shorten the overall pattern formation / reading time in order to increase the number, the number of falling and rising edges of the color shift correction pattern is counted to determine the reading end for each pattern set.

If the stop time of the intermediate transfer belt is longer than the predetermined time, it is determined that the intermediate transfer belt is elastically deformed, the interval between the pattern sets is widened, and the reading end determination of each pattern set is determined by the timer. Switch to the time standard using.

Based on these judgments, in an electrophotographic color image forming apparatus, when the intermediate transfer belt is not elastically deformed, the intermediate transfer belt is elastically deformed by forming and reading a pattern image as short as possible to increase productivity. If so, it is possible to prevent erroneous detection of the color shift correction pattern and elastic deformation, and to maintain the image quality at the same time.

101 process unit, 102 photosensitive drum, 103 charging roller,
104 Laser Scanner Unit, 105 Developer, 106 Toner Bottle,
107 Primary transfer roller, 108 Intermediate transfer belt, 109 Auxiliary charging brush,
110 secondary transfer roller, 111 cleaning blade,
112 reflected light sensor, 113 paper cassette, 114 paper feed roller,
115 resist rollers, 116 manual feed trays, 117 fixing rollers,
118 Pressurized roller, 119 paper ejection flapper, 120 paper ejection tray,
121 In-cylinder output tray, 201 CPU, 202 ROM,
203 RAM, 204 EEPROM, 205 I / O ports,
206 timer, 207 RealTimeLock,
211 laser driver, 212 motor driver,
213 High-voltage unit, 214 transport sensor, 221 front-side reflected light amount sensor,
222 Central reflected light amount sensor, 223 Back side reflected light amount sensor

Claims (1)

An image forming means for forming toner images of different colors on a plurality of photoconductors,
An intermediate transfer body that is rotationally driven and transfers the toner image on the plurality of photoconductors,
A detection means for detecting the toner image transferred to the intermediate transfer body, and
A control means that causes the image forming means to form a pattern image, causes the detecting means to detect the pattern image, and controls color shift based on the detection result of the pattern image.
Have,
The control means
The detection means when the image forming means forms a first pattern image, the detecting means detects the first pattern, and the first condition regarding the number of edges included in the detection result of the first pattern is satisfied. The first mode to control the detection of means and
The image forming means is made to form a second pattern image, the detecting means is made to detect the second pattern, and the detection of the detecting means is controlled when the second condition regarding the detection time of the second pattern is satisfied. Second mode and
An image forming apparatus characterized in that the image is selectively executed.