JP2006018007A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which the shift of a patch pattern detection position is detected, and image density is detected without forming the image of a patch pattern which leads to increase of downtime. <P>SOLUTION: In the image forming apparatus provided with a control means 150, when the image density of a plurality of continuous patch patterns formed on an image carrying member 8 is detected, an area larger than the area required to calculate image density is detected with an image density sensor 40; its patch pattern results are stored in a memory 150b; on the basis of positional information of the patch patterns detected with a subsequently formed patch pattern, the positional deviation of the patch patterns is calculated; according to the obtained the positional deviation, only patch pattern detection results of the area required to calculate image density are selected from the patch pattern detection results stored in the memory 150b; and the image density of the patch patterns is calculated under control of the control device 150. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a complex machine thereof, and more particularly to an image density detection technique.

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, a technique for testing image forming performance such as image forming performance at a predetermined timing using an image density sensor is known for the purpose of stabilizing image quality. Specifically, first, a patch pattern is formed on an intermediate transfer belt as an image carrier. After the patch pattern is formed, the toner adhesion amount on the patch pattern is measured by an image density sensor.
A pattern larger than the detection range of the image density sensor is created as the patch pattern, and the portion where the sensor output is saturated (the portion where the patch pattern is formed in the entire detection range of the image density sensor) is measured and detected. The toner adhesion amount is calculated based on the result. The image forming performance is discriminated based on the calculated toner adhesion amount, and the result is fed back to change the image forming condition and control the image density to be constant.
Here, there is a problem that the patch pattern detection position varies greatly due to variations in the exposure position and variations in the positional relationship between the intermediate transfer member and the image density sensor. In order to solve this, a large patch pattern that absorbs variation in positional relationship is imaged, and the center portion is detected by an image density sensor. For example, as shown in Patent Document 1, position information is provided at the tip. There is known a technique for measuring a patch pattern to be obtained, measuring a deviation amount of a detection position, and correcting a detection timing of a patch pattern created thereafter.
JP-A-11-143147

However, in the method of forming a large patch pattern and detecting the central portion thereof with the image density sensor, it is necessary to increase the size of the patch pattern beyond the maximum expected shift amount, so it takes time to form the patch pattern. There was a problem that. In addition, since normal image formation cannot be performed during patch pattern creation, it is downtime for the user and the convenience is greatly reduced.
Further, the image forming performance test often measures a plurality of patch patterns, and in this case, the downtime is further increased, which is often a complaint of the user. Also, the method of measuring the patch pattern that obtains position information at the tip, measuring the amount of deviation of the detection position, and correcting the detection timing of the patch pattern that is created after that, increases the number of patch patterns to be imaged by one. Increase downtime.
SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of detecting an image density by detecting a shift of a patch pattern detection position without forming a patch pattern that leads to an increase in downtime.

In order to achieve the above object, an image density sensor for detecting the image density of a patch pattern, storage means for storing a patch pattern result detected by the image density sensor, and a position for calculating the positional deviation amount of the patch pattern A deviation amount calculating means and a density calculating means for calculating the image density of the patch pattern are provided, and the image density is calculated when detecting the image density of a plurality of continuous patch patterns created on the image carrier. The image density sensor detects an area wider than the area required for the image, stores the patch pattern result in the storage means, and also includes position information of the patch pattern to be detected by the patch pattern created subsequently. The positional deviation amount of the patch pattern is calculated by the positional deviation amount calculating means, and the patch pattern stored in the storage means is calculated from the obtained positional deviation amount. Select down detection results patch pattern detection result of the area required to calculate the image density of only, and calculates the image density of the patch pattern by said density calculation means.
The invention described in claim 2 is characterized in that, in the image forming apparatus described in claim 1, an image forming apparatus that creates a subsequent patch pattern with a darker image density than the preceding patch pattern.
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, an image forming apparatus in which a patch pattern for detecting a position has the highest image density is a main feature.
According to a fourth aspect of the present invention, the image forming apparatus according to the first aspect is mainly characterized by an image forming apparatus having a plurality of patch patterns for detecting positions.

  When the image forming apparatus of the present invention detects the image density of a plurality of continuous patch patterns created on the image carrier, an image density larger than the area required for calculating the image density is detected. Detected by the sensor, the patch pattern result is stored in the memory, the amount of positional deviation of the patch pattern is calculated based on the positional information of the patch pattern detected by the patch pattern that is created subsequently, and the obtained positional deviation Control means for selecting only the patch pattern detection result of an area required for calculating the image density from the patch pattern detection result stored in the memory from the quantity and performing control for calculating the image density of the patch pattern So you can achieve the intended purpose.

Hereinafter, an electrophotographic printer (hereinafter simply referred to as a printer) will be described as an example of an embodiment of an image forming apparatus to which the present invention is applied. First, the basic configuration of the printer will be described. FIG. 1 is a schematic configuration diagram of the printer.
In the figure, the printer 100 includes four process cartridges (toner image forming units) 6Y, 6M, and 6 for generating toner images of yellow, magenta, cyan, and black (hereinafter referred to as Y, M, C, and K). 6C, 6K. These use Y, M, C, and K toners of different colors as the image forming material, but the other configurations are the same and are replaced when the lifetime is reached. For example, the process cartridge 6Y for generating a Y toner image includes a drum-shaped photoreceptor 1Y, a drum cleaning device, a charge eliminating device, a charging device, and a developing device.
The process cartridge 6Y can be attached to and detached from the main body of the printer 100 so that consumable parts can be replaced at a time. The charging device uniformly charges the surface of the photoreceptor 1Y that is rotated clockwise in the drawing by a driving unit (not shown). The uniformly charged surface of the photoreceptor 1Y is exposed and scanned with a laser beam to carry a Y electrostatic latent image.
The Y electrostatic latent image is developed into a Y toner image by a developing device using Y toner. Then, intermediate transfer is performed on the intermediate transfer belt 8. The drum cleaning device removes the toner remaining on the surface of the photoreceptor 1Y after the intermediate transfer process. Further, the static eliminator neutralizes residual charges on the photoreceptor 1Y after cleaning. By this charge removal, the surface of the photoreceptor 1Y is initialized and prepared for the next image formation. In the other process cartridges 6M, 6C, and 6K, M, C, and K toner images are similarly formed on the photoreceptors 1M, 1C, and 1K, and are intermediately transferred onto the intermediate transfer belt 8.

An optical writing unit 7 is disposed below the process cartridges 6Y, 6M, 6C, and 6K in the drawing. The optical writing unit 7 serving as a latent image forming unit irradiates the respective photoconductors in the process cartridges 6Y, 6M, 6C, and 6K with laser light emitted based on the image information. By this exposure, electrostatic latent images for Y, M, C, and K are formed on the photoreceptors 1Y, 1M, 1C, and 1K.
The optical writing unit 7 irradiates the photosensitive member through a plurality of optical lenses and mirrors while scanning a laser beam emitted from a light source with a polygon mirror rotated by a motor. On the lower side of the optical writing unit 7 in the figure, a sheet feeding means having a sheet feeding cassette 26, a sheet feeding roller 27 incorporated therein, a registration roller pair 28, and the like are disposed. The paper feed cassette 26 stores a plurality of transfer papers P, which are recording media, and a paper feed roller 27 is in contact with each uppermost transfer paper P.
When the paper feeding roller 27 is rotated counterclockwise in the drawing by a driving means (not shown), the uppermost transfer paper P is fed toward the rollers of the registration roller pair 28. The registration roller pair 28 rotationally drives both rollers to sandwich the transfer paper P, but temporarily stops rotating immediately after sandwiching. Then, the transfer paper P is sent out toward a later-described secondary transfer nip at an appropriate timing.
In the sheet feeding unit having such a configuration, a conveying unit is configured by a combination of the sheet feeding roller 27 and the registration roller pair 28 corresponding to the timing roller. This transport means transports the transfer paper P from a paper feed cassette 26 serving as a storage means to a secondary transfer nip described later. Above the process cartridges 6Y, 6M, 6C, and 6K in the drawing, an intermediate transfer unit 15 that moves the intermediate transfer belt 8 that is an intermediate transfer member endlessly while stretching is disposed.
In addition to the intermediate transfer belt 8, the intermediate transfer unit 15 includes four primary transfer bias rollers 9Y, 9M, 9C, and 9K, a cleaning device 10, and the like. A secondary transfer backup roller 12, a cleaning backup roller 13, a tension roller 14 and the like are also provided. The intermediate transfer belt 8 is endlessly moved in the counterclockwise direction in the figure by the rotational drive of at least one of the rollers while being stretched around these three rollers.
The primary transfer bias rollers 9Y, 9M, 9C, and 9K sandwich the intermediate transfer belt 8 that is moved endlessly in this manner from the photoreceptors 1Y, 1M, 1C, and 1K to form primary transfer nips, respectively. Yes. In these methods, a transfer bias having a polarity opposite to that of toner (for example, plus) is applied to the back surface (loop inner peripheral surface) of the intermediate transfer belt 8.

All the rollers except the primary transfer bias rollers 9Y, 9M, 9C, and 9K are electrically grounded. The intermediate transfer belt 8 sequentially passes through the primary transfer nips for Y, M, C, and K along with the endless movement thereof, and Y, M, and C on the photoreceptors 1Y, 1M, 1C, and 1K. , K toner images are superimposed and primarily transferred. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the intermediate transfer belt 8.
The secondary transfer backup roller 12 sandwiches the intermediate transfer belt 8 between the secondary transfer roller 19 and forms a secondary transfer nip. The four-color toner image formed on the intermediate transfer belt 8 is transferred to the transfer paper P at the secondary transfer nip. Untransferred toner that has not been transferred onto the transfer paper P adheres to the intermediate transfer belt 8 after passing through the secondary transfer nip. This is cleaned by the cleaning device 10.
In the secondary transfer nip, the transfer paper P is sandwiched between the intermediate transfer belt 8 and the secondary transfer roller 19 whose surfaces move in the forward direction, and is conveyed in the opposite direction to the registration roller pair 28 side. . When the transfer paper P sent out from the secondary transfer nip passes between the rollers of the fixing device 20, the four-color toner image transferred to the surface is fixed by heat and pressure. Thereafter, the transfer paper P is discharged out of the apparatus through a pair of paper discharge rollers 29.
A stack unit 30 is formed on the upper surface of the printer body, and the transfer paper P discharged outside the apparatus by the discharge roller pair 29 is sequentially stacked on the stack unit 30. Above the secondary transfer roller 19, a reflection type photosensor 40 as an image density detection unit is disposed and configured to output a signal corresponding to the light reflectance on the intermediate transfer belt 8.
In this reflection type photosensor 40, the difference between the amount of reflected light on the surface of the intermediate transfer belt 8 and the amount of reflected light of a reference pattern image to be described later can be set to a sufficient value between the diffuse light detection type and the regular reflection light detection type. Is used. The role of the reflective photosensor 40 will be described later.

FIG. 2 is a block diagram showing a part of the electric circuit of the printer. In the figure, a control unit 150 includes electrically connected toner image forming units (process cartridges) 6Y, 6M, 6C, and 6K, an optical writing unit 7, a paper feed cassette 26, a registration roller pair 28, a transfer unit 15, and a reflection unit. The mold photosensor 40 and the like are controlled. The control unit 150 includes a CPU 150a that controls the arithmetic unit and the like, and a RAM 150b that stores data.
The control unit 150 is configured so that each toner image forming unit 6 has a predetermined timing such as when a main power supply (not shown) is turned on, when waiting after a predetermined time has elapsed, or when waiting for a predetermined number of prints to be output. It is configured to test image forming performance such as image forming performance.
Specifically, when this predetermined timing comes, first, the photosensitive drums 1Y, 1M, 1C, and 1K are uniformly charged while rotating. With respect to this charging, unlike the uniform charging (for example, −700 V) during normal printing, the potential is gradually increased. Then, development is performed by the developing unit while forming an electrostatic latent image for the reference pattern image by scanning with the laser beam.
By this development, bias development pattern images of the respective colors are formed on the photosensitive drums 1Y, 1M, 1C, and 1K. During development, the control unit 150 performs control so that the value of the developing bias applied to the developing roller of each developing unit is gradually increased.
In this way, an image is formed from a pattern having a low image density, and a gradually dark pattern is formed. Conversely, if both the charging and developing bias are gradually lowered, an image is formed from a pattern having a high image density and a thin pattern is gradually formed. However, in general, a high-voltage power supply has a lower voltage than a lower voltage. Since it takes time, there is a drawback that the pattern image forming time becomes long.
The bias development pattern images of these colors are transferred so as to be arranged on the intermediate transfer belt 8 without overlapping. When each of the pattern images passes through a position facing the reflection type photosensor 40 as the intermediate transfer belt 8 moves endlessly, the amount of reflected light is detected and output to the control unit 150 as an electrical signal.
The control unit 150 calculates the light reflectance of each reference image based on the output signals sequentially sent from the reflective photosensor 40, and stores it in the RAM 150b as density pattern data. The pattern that has passed the position facing the reflective photosensor 40 is cleaned by the cleaning device 10.

FIG. 3 is a schematic diagram showing the reference pattern image P (Py, Pm, Pc, Pk). In the figure, the reference pattern image P is composed of ten reference images arranged at intervals of 13 mm. In this laser printer, each reference image 101 is 13 mm long × 15 mm wide and is formed through a 13 mm gap.
Therefore, the lengths of the reference pattern images Pk, Pm, Pc, and Py on the intermediate transfer belt 8 are L2 = 247 mm, respectively. Unlike the toner images of the respective colors formed during the printing process, the reference pattern images Pk, Pm, Pc, and Py are not overlapped on the intermediate transfer belt 8 and are arranged in order of Py, Pm, Pc, and Pk. Are formed and transferred to the intermediate transfer belt 8.
FIG. 4 is a diagram showing a state in which each reference pattern image on the intermediate transfer belt is detected by a reflective photosensor. On the upper right side of the transfer belt 8 in the figure, a reflective photosensor 40 as an image detecting means is disposed. Each reference pattern image on the intermediate transfer belt 8 is moved with endless movement and detected by the reflective photosensor 40, and then removed by the transfer unit cleaning device 10.
The reflective photosensor 40 detects the amount of reflected light in the following order from the front end of the first pattern Py1 to the rear end of Pk10. That is, detection is performed in the order of ten reference images of the reference pattern image Pk, ten reference images 101 of the reference image Pm, ten reference images 101 of the reference image Pc, and ten reference images 101 of the reference image Pk. (See FIG. 3). At this time, a voltage signal corresponding to the light reflection amount of each reference image 101 is detected by a method described later and sequentially output to the control unit 150. The control unit 150 stores the voltage signals sequentially sent from the reflective photosensor 40 in the RAM 150b.

The details of the detection method of the 10 reference pattern images Pk will be described. FIG. 5 shows the pattern image density detection range and the RAM 150b storage range. The image density detection range for calculating the image density of the patch pattern uses only the central part of the patch pattern where the output of the normal reflection type photosensor 40 is saturated. When an image is formed with no pattern displacement, only the image density detection range may be stored in the RAM 150b. However, in practice, there is a displacement as shown in FIG. 6, and the entire image density detection range is stored. There are many things that cannot be done.
Therefore, the voltage signal of the reflective photosensor 40 is stored in the RAM 150b in a range wider than the image density detection range as shown in FIG. 5 so that the entire image density detection range can be stored even if there is a positional deviation. . This operation is repeated for the patterns Pk1 to Pk10, and the signal of the reflective photosensor 40 of each pattern is stored. In addition, the pattern position is detected in parallel with the voltage signal storing operation of the reflective photosensor 40 in the RAM 150b.
For pattern position detection, a high-density pattern, that is, Pk10, which is the pattern with the highest density of the last image formed, is used. The pattern position detection method uses a method of detecting the position from the rising edge because the sensor voltage signal rises abruptly when the vicinity of the pattern edge is detected by the reflection type photosensor 40. You may detect the position where a voltage signal falls suddenly.
The pattern having the highest image density has an advantage that it can be easily determined because the difference between the rising and falling voltage signals is large. It should be noted that a pattern with a low image density is not desirable as a pattern for detecting a position because it does not rise so rapidly that a voltage signal at the back end of the front end can be detected.
Therefore, the position of the head pattern cannot be detected because the image density is too thin, and the position needs to be detected by the subsequent pattern. In this way, the voltage signal data of the reflective photosensor 40 including the image density detection range from the patterns Pk1 to Pk10 and the pattern position information can be obtained.

A method for extracting the voltage signal data of the reflective photosensor 40 in the image density detection range from Pk1 to Pk10 using these two pieces of information will be described. As an example, the image density detection range data extraction method of this method will be described on the assumption that the pattern position information is shifted to the rear end side by 1 mm as shown in FIG.
In this case, since the image density detection range at the center of the pattern is similarly shifted to the rear end side of 1 mm, the image density detection range is 3 mm to 7 mm from the data storage start point in the data stored in the RAM 150b shown in FIG. The part will be extracted. Therefore, the first 3 mm portion of the stored data and the 1 mm portion at the rear end are used as the data invalid range and the remaining portion is used as the valid range for image density detection. This operation is repeated from Pk1 to Pk10, the positional deviation is corrected in each pattern, and the voltage signal of the reflective photosensor 40 only at the pattern center is extracted.
Similarly, Py, Pm, and Pc can accurately extract voltage signal data of the reflective photosensor 40 in the image density detection range by repeating pattern imaging, data storage, pattern position deviation detection, and data extraction. . Furthermore, the position information is detected not only with one pattern but with a plurality of patterns, and the average of the positional deviation amount of each pattern further improves the accuracy of the positional deviation amount detection. In this way, after obtaining the reflection type photosensor voltage signal in the image density detection range of each pattern, the image density is calculated based on the result of averaging the voltage signals.

1 is a configuration diagram of an image forming apparatus according to an embodiment of the present invention. 1 is a control block diagram of an image forming apparatus according to an embodiment of the present invention. The schematic diagram which shows the reference | standard pattern image P (Py, Pm, Pc, Pk). FIG. 6 is a diagram illustrating a state in which each reference pattern image on the intermediate transfer belt is detected by a reflective photosensor. The figure which shows the pattern image density detection range and RAM storage range. The figure which shows the reference pattern without a position shift, and the reference pattern with a position shift.

Explanation of symbols

8 intermediate transfer belt (image carrier), 40 reflective photosensor (image density sensor), 150 control unit (control means), 150b RAM (memory)

Claims (4)

An image density sensor for detecting the image density of the patch pattern, a storage means for storing the patch pattern result detected by the image density sensor, a positional deviation amount calculating means for calculating the positional deviation amount of the patch pattern, and a patch pattern Density calculating means for calculating the image density of
When detecting the image density of a plurality of continuous patch patterns created on the image carrier, the image density sensor detects an area wider than the area required to calculate the image density, and the patch The pattern result is stored in the storage means, and the positional deviation amount of the patch pattern is calculated by the positional deviation amount calculation means based on the positional information of the patch pattern to be detected by the patch pattern created subsequently, and obtained. From the patch pattern detection results stored in the storage means, only the patch pattern detection results in the area required for calculating the image density are selected from the positional deviation amount, and the image density of the patch pattern is calculated by the density calculation means. An image forming apparatus.   2. The image forming apparatus according to claim 1, wherein the succeeding patch pattern is created with a darker image density than the preceding patch pattern.   2. The image forming apparatus according to claim 1, wherein the patch pattern for detecting the position has the highest image density. 2. The image forming apparatus according to claim 1, comprising a plurality of patch patterns for detecting positions.

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