JP4728010B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image of a laser printer, a digital copying machine, or the like that forms an image by transferring a plurality of color toner images onto a recording medium using a moving body such as a conveyance belt or an image carrier belt (intermediate transfer belt). More particularly, the present invention relates to an image forming apparatus having a function of correcting the image forming position of a toner image.

In recent years, image forming apparatuses that form high-quality color images have been widely put into practical use. One of the image forming methods used in an image forming apparatus that forms a color image is a tandem method in which a plurality of image forming units are arranged in parallel along a transport unit. By using this tandem method, image forming processing can be realized at high speed.
In a tandem color image forming apparatus, light beams emitted from a plurality of light sources are irradiated onto a plurality of image carriers arranged in parallel in the apparatus to form an electrostatic latent image.

Then, different colors of developer (for example, toner of four colors including yellow (Y), magenta (M), cyan (C) or black (K)) are attached to the formed electrostatic latent image. Thus, a toner image to be a real image is formed.
A recording material such as a recording sheet carrying the formed toner image on a moving body such as a conveyance belt is sequentially conveyed to a transfer position of each image carrier.
Thereafter, the toner image formed on each image carrier is transferred onto the recording material in an overlapping manner, and the transferred toner image is fixed on the transfer paper recording medium to form a multicolor image.

In such an image forming apparatus that forms an image by superimposing a plurality of color toner images, the toner image is transferred at a high speed onto a recording medium that moves in the transport direction.
Further, if the position of the toner image to be superimposed on the recording medium is shifted, the quality of the formed image may be deteriorated. Therefore, in such an image forming apparatus, the alignment accuracy of each color is stabilized. It is equipped with a function for correcting misalignment.
Conventionally, various image forming apparatuses equipped with such a positional deviation correction function have been proposed including the following patent documents.
Japanese Patent Laid-Open No. 5-100556 Japanese Patent Laid-Open No. 6-1002

Patent Document 1 proposes a technique for detecting an image forming position of a pattern image formed on a photoconductor using a compact and inexpensive position detecting means and adjusting the image forming position based on the position detection signal. Has been.
Patent Document 2 proposes a technique for detecting a toner image pattern on an image carrier using an optical sensor and adjusting a positional deviation of the toner image based on an output signal of the sensor.

As proposed in the above-mentioned patent documents, the conventional misregistration correction function supports a plurality of toner patterns based on the reference color and the non-reference color in order to detect a color shift between the reference color and the non-reference color. Adhere to the body.
The image forming apparatus irradiates the toner pattern with light using an optical sensor and stores the reflected light as data.
The positional deviation correction is performed by integrating the reflected light data of all the toner patterns and calculating the amount of color deviation between the reference color and the non-reference color.

However, the above-described misregistration correction function in the prior art requires time for forming all the plurality of toner patterns on the image carrier in order to detect the misregistration amount.
For this reason, when performing misregistration correction for each image forming process, such as when forming a plurality of images, the image forming process is interrupted for a long time until the amount of color misregistration between the reference color and the non-reference color is calculated ( Had to be stopped).
SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of correcting the image forming position of a toner image without stopping the image forming process.

According to the first aspect of the present invention, the latent image generating means for generating a toner image for each color, the transport means for transporting the recording medium on a moving body, the recording medium transported by the transport means, A transfer unit that transfers the toner image generated by the latent image generation unit, and a pattern forming unit that forms a toner pattern of a reference color and a non-reference color between the recording media that are continuously conveyed on the moving body; A detection unit that detects the toner pattern formed by the pattern formation unit; and a positional deviation amount of the non-reference color with respect to the reference color is calculated based on a detection result of the detection unit, and a calculated positional deviation amount And a correcting unit that corrects a deviation in the image forming position of the toner image between the reference color and the non-reference color, and is formed between the recording media by the pattern forming unit. The toner pattern is one group that is different from each other in which a pattern group composed of a plurality of toner patterns is divided into a plurality of groups, and the detecting means detects all the toner patterns constituting the pattern group. The number of groups of the toner pattern groups detected and formed between the recording media by the pattern forming means can be changed based on the temperature change rate of the image forming apparatus, and the number of groups of the toner pattern groups can be changed. When the change is made based on the temperature change rate of the image forming apparatus, the temperature change rate of the image forming apparatus is large, and the change rate or change amount of the color shift amount between the reference color and the non-reference color is large. If it is supposed in advance to reduce the number of groups of the toner pattern group, to increase the number of toner patterns included in one group Temperature change rate is rather small, the case where the change rate or variation of the color shift amount between the reference color and the non-reference color that is reduced is previously assumed, by increasing the number of groups of the toner pattern group, 1 The object is achieved by reducing the number of toner patterns included in one group .

According to a second aspect of the present invention, in the first aspect of the present invention, the exposure unit that irradiates the photosensitive drum with the laser beam modulated by the image data, and the temperature of the apparatus is measured inside the exposure unit. A temperature sensor, and a temperature change rate of the image forming apparatus is measured by the temperature sensor.

  According to the present invention, correction can be performed at an appropriate timing by changing the number of groups of toner pattern groups formed between the recording media based on the temperature change rate of the image forming apparatus.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS.
In the present exemplary embodiment, a tandem (type) color image forming apparatus in which image forming units are arranged along the conveyor belt 21 will be described as an example.
In the image forming apparatus according to the present embodiment, the case where the toner pattern is fixed on the conveyance belt 21 will be described. However, the same applies to the case where the toner pattern is fixed on the image carrier belt (intermediate transfer belt). It shall have a configuration.
FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to the present embodiment.
As shown in FIG. 1, the image forming apparatus according to the present exemplary embodiment is arranged in parallel in the apparatus casing along the paper feeding unit 10, the transport unit 20, and the transport unit 20 (yellow (Y), The image forming unit 30 includes a magenta (M), cyan (C), and black (K) image, a fixing unit 40, and a detection unit 50. Each configuration will be described below.

The paper feed unit 10 includes a paper feed tray 11, a paper feed roller 12, a separation roller 13, a registration roller pair 14, and the like.
In the paper supply unit 10, the recording paper (transfer paper) in the paper supply tray 11 is separated one by one by the paper supply roller 12 and the separation roller 13, and sent to the registration roller pair 14.
Then, the timing adjustment of the recording paper sent out from the paper feed tray 11 is performed by the registration roller pair 14 and the registration sensor 60, and the recording paper is sent out to the transport unit 20 at a predetermined timing.

The transport unit 20 includes a transport belt 21, a driving roller 22, a driven roller 23, a cleaning unit 24, a transfer unit 25, and the like.
In the transport unit 20, the driving roller 22 and the driven roller 23 are rotationally driven in the counterclockwise direction by drive control of a motor or the like, and the transport belt 21 stretched between the driving roller 22 and the driven roller 23 is in the transport direction. It is rotated toward.
As a result, the recording paper delivered from the paper supply unit 10 is sequentially conveyed to the image forming unit 30 that transfers the toner images of the respective colors.
Then, a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image are sequentially transferred onto the recording paper conveyed to the image forming unit 30.

The image forming unit 30 includes a photosensitive drum 31 for each color arranged in parallel along the conveyance direction of the conveyance belt 21, a charging unit 32 provided in a peripheral portion of each photosensitive drum 31, and an exposure unit. 33, a developing unit 34, a cleaning unit 35, a charge eliminating unit 36, and the like.
In the image forming unit 30, the photosensitive drum 31 is rotated in the clockwise direction by drive control, and static electricity is uniformly charged on the surface of the photosensitive drum 31 by the charging unit 32.
Laser light modulated by the image data is irradiated onto the photosensitive drum 31 from the exposure unit 33, whereby an electrostatic latent image is formed on the photosensitive drum 31.
Next, a toner image is formed on the photosensitive drum 31 by attaching toner to the photosensitive drum 31 on which the electrostatic latent image is formed using the developing unit 34.
When the recording paper is transported to the image forming unit 30, a transfer potential is applied to the transport belt 21 by the transfer unit 25 disposed on the back surface of the transport belt 21, and the recording paper is formed on the photosensitive drum 31. Yellow (Y), magenta (M), cyan (C), and black (K) toner images are sequentially superimposed and transferred onto a recording sheet.

As described above, when the transfer of the toner image is completed in each image forming unit 30, the residual toner attached on the photosensitive drum 31 is cleaned by the cleaning unit 35.
Then, the surface of the photosensitive drum 31 is neutralized by the light applied to the photosensitive drum 31 by the static eliminating unit 36 to prepare for the formation of the next electrostatic latent image. Again, the charging unit 32 charges the surface of the photosensitive drum 31 to execute an image forming processing operation.
The recording paper on which the toner images of the respective colors are transferred moves along the conveyance direction while being adsorbed on the conveyance belt 21, is peeled (separated) from the conveyance belt 21, and is conveyed to the fixing unit 40. The

The fixing unit 40 includes a fixing roller and a pressure roller.
The fixing roller and the pressure roller are configured such that when one of the rollers is rotationally driven, the other roller is also rotated with a predetermined force.
The fixing roller is controlled to be heated to a predetermined fixing temperature by a built-in heater. By this heating control, the recording paper conveyed along the conveying belt 21 is heated and pressurized by the fixing roller and the pressure roller, thereby fixing the toner images of the respective colors on the recording paper.
The fixing unit 40 is provided with a temperature sensor that detects the fixing temperature.
After the toner image is fixed on the recording paper in the fixing unit 40, the recording paper is discharged from the image forming apparatus.

The detection unit 50 includes a pattern detection sensor 51 disposed on the downstream side in the transport direction of the black (K) image forming unit 30 on the transfer paper.
The pattern detection sensor 51 is a sensor that detects a toner pattern formed on the conveyance belt 21 that is disposed in the main scanning direction of the conveyance belt 21. The pattern detection sensor 51 is constituted by a charge coupled device such as a CCD.
In the image forming apparatus according to the present embodiment, the pattern detection sensor 51 detects each color toner pattern formed on the conveyance belt 21, and based on the detected toner pattern data, the reference color and the non-reference color are detected. The amount of color misregistration is calculated, and image correction and position misalignment correction are performed based on the calculation result.

Next, a toner pattern formed on the conveyance belt 21 will be described.
FIG. 2 is a diagram showing one type of toner pattern group formed on the conveyance belt in the image forming apparatus according to the present embodiment.
As shown in FIG. 2, a plurality of toner patterns P <b> 1 to P <b> 10 are formed on the transport belt 21 side by side at positions that can be detected by the pattern detection sensor 51.
In the image forming apparatus according to the present embodiment, black (K) is set as a reference color, and other yellow (Y), magenta (M), and cyan (C) are set as non-reference colors.
The toner patterns P1 to P10 are formed for each color of yellow (Y), magenta (M), cyan (C), and black (K).
That is, one group of toner patterns P1 to P10 is required for each combination of the reference color and each non-reference color. Therefore, when the correction process is performed on all colors, three types of toner patterns P1 to P10 are required.

Here, in order to avoid complication of explanation, for example, the amount of color misregistration between black (K) and yellow (Y) in a combination of one set of reference color and non-reference color is detected, and positional deviation correction is performed. The case where it performs is demonstrated.
Then, by comparing the toner patterns P1 to P10 of the color set as the reference color with the toner patterns P1 to P10 of the color that is the non-reference color, the color shift amount between the reference color and the non-reference color is calculated. Based on the calculation result, image correction and positional deviation correction are performed.
The number of toner patterns constituting the toner pattern group can be arbitrarily changed according to the image quality accuracy of the image to be formed.

In the image forming apparatus according to the present embodiment, a pattern detection sensor 51 is provided in the center of the transport belt 21 as shown in FIG. Therefore, the toner patterns P <b> 1 to P <b> 10 are formed at the center in the width direction of the transport belt 21 so as to be arranged along the traveling direction of the transport belt 21.
In order to calculate the color misregistration amount between the reference color and the non-reference color, a plurality of patterns having different shapes are required.
The individual toner patterns P1 to P10 of the toner pattern group are configured by patterns having different shapes that are shifted little by little (for example, one dot at a time) in the main scanning direction and the sub-scanning direction.
In the image forming apparatus according to the present embodiment, a case where positional deviation correction is performed using ten different toner patterns in the main scanning direction and the sub-scanning direction will be described.

Then, as shown in FIG. 2, the ten toner patterns P1 to P10 are divided into five groups, that is, divided into two toner patterns per group.
For example, when forming and outputting an image on a plurality of recording media (transfer sheets), when performing misregistration correction using the grouped toner patterns P1 to P10, as shown in FIG. The patterns P1 to P10 are distributed.
Specifically, one group of toner patterns P1 to P10, that is, two toner patterns are formed in order in front of the top recording medium and between each recording medium.

The image forming apparatus sequentially reads the toner patterns of each group by the pattern detection sensor 51 when performing a series of image forming processes.
Then, when all the toner patterns P1 to P10 (all groups) have been read, the amount of misregistration between the reference color and the non-reference color is calculated based on the detected data of the toner patterns P1 to P10 of each color. Start.
After the calculation process of the color misregistration amount between the reference color and the non-reference color is completed, the image forming apparatus performs a correction process of the image formation position of the toner image based on the calculated color misregistration quantity, that is, a misregistration correction.
After this correction process is performed, the image forming apparatus performs the image forming process again from the recording media after the last group.
In the image forming process performed after the correction process, an appropriate image subjected to the positional deviation correction is formed.

In addition, when the change rate of the apparatus temperature (machine temperature) in the image forming apparatus is large and the change rate or change amount of the color misregistration amount between the reference color and the non-reference color is assumed to be large (predicted). In such a case, it is desirable to perform misalignment correction as follows.
For example, as shown in FIG. 4, the toner patterns P1 to P10 are divided into three groups. Specifically, the toner pattern P1 to P4 constitutes a first group, the toner patterns P5 to P7 constitute a second group, and the toner patterns P8 to P10 constitute a third group.

Then, a first group (toner patterns P1 to P4) is formed in front of the top recording medium, and a second group (toner pattern) is provided between the top recording medium and the next recording medium and behind the next recording medium, respectively. P5 to P7) and the third group (toner patterns P8 to P10) are formed.
When all the toner patterns P1 to P10 (all groups) have been read, calculation of the color misregistration amount between the reference color and the non-reference color is started based on the detected data of the toner patterns P1 to P10 of each color. .
After the calculation process of the color misregistration amount between the reference color and the non-reference color is completed, the image forming apparatus performs a correction process of the image formation position of the toner image based on the calculated color misregistration quantity, that is, a misregistration correction.
After this correction process is performed, the image forming apparatus performs the image forming process again from the recording media after the last group.

As described above, when the positional deviation correction is performed by dividing the toner patterns P1 to P10 into three groups, all the toner patterns P1 are compared with the case where the positional deviation correction is performed by dividing the toner patterns P1 to P10 into five groups. ˜P10 is read when the pattern detection sensor 51 reads, that is, the number of recording media conveyed when all the toner patterns P1 to P10 are read by the pattern detection sensor 51 is reduced.
Therefore, compared with the case where the positional deviation correction is performed by dividing the toner patterns P1 to P10 into five groups, the conveyance period in the conveyance belt 21 that can reflect the positional deviation correction can be set smaller (finely). it can.
Therefore, even when it is assumed in advance that the change rate or change amount of the color misregistration amount between the reference color and the non-reference color is large, the misregistration correction corresponding to the change rate or change amount is appropriately performed. It can be carried out.
As a result, an image in which color misregistration is appropriately suppressed can be formed at an early stage, that is, an initial stage of the image forming process.

As described above, when the misregistration correction is performed using the toner patterns P1 to P10 divided into three or five groups, a plurality of toner patterns are formed between the conveyed recording media.
Therefore, it is necessary to intentionally provide a region for forming a toner pattern between the recording media. As the number of toner patterns per group, that is, the number of toner patterns written between the recording media increases, the interval between the recording media is increased. Will increase.
As described above, when the interval between the recording media on the conveyance belt 21 is increased, there is a possibility that the speed of the image forming process is decreased, that is, the processing speed is decreased.

Therefore, for example, in the second half of the image forming process after a certain driving time, the apparatus temperature (machine temperature) in the image forming apparatus is saturated and constant, the rate of change of the apparatus temperature (machine temperature) is small, and the reference color is not If it is assumed in advance (when predicted) that the rate of change or the amount of change in the amount of color deviation from the reference color will be small, it is desirable to perform positional deviation correction as follows.
For example, as shown in FIG. 5, the toner patterns P1 to P10 are divided into 10 groups. Specifically, one group is constituted by one toner pattern.

Then, one group of toner patterns P1 to P10, that is, one toner pattern is sequentially formed in front of the top recording medium and between each recording medium.
When all the toner patterns P1 to P10 (all groups) have been read, calculation of the color misregistration amount between the reference color and the non-reference color is started based on the detected data of the toner patterns P1 to P10 of each color. .
After the calculation process of the color misregistration amount between the reference color and the non-reference color is completed, the image forming apparatus performs a correction process of the image formation position of the toner image based on the calculated color misregistration quantity, that is, a misregistration correction.
After this correction process is performed, the image forming apparatus performs the image forming process again from the recording media after the last group.

As described above, when the positional deviation correction is performed by dividing the toner patterns P1 to P10 into 10 groups, all the toners are compared with the case where the positional deviation correction is performed by dividing the toner patterns P1 to P10 into 3 or 5 groups. The number of recording media conveyed when the patterns P1 to P10 are read by the pattern detection sensor 51 increases, that is, the number of recording media when all the toner patterns P1 to P10 are read by the pattern detection sensor 51 increases.
Therefore, compared with the case where the positional deviation correction is performed by dividing the toner patterns P1 to P10 into three or five groups, the conveyance period in the conveyance belt 21 that can reflect the positional deviation correction can be set larger. .
As a result, it is possible to perform image formation without reducing the speed of the image forming process, that is, without reducing the processing speed, even while performing misregistration correction.

  As described above, color misregistration correction (position misregistration correction) is performed by changing the number of groups into which the toner patterns P1 to P10 are divided in accordance with the rate of change or amount of color misregistration between the predicted reference color and the non-reference color. ), That is, the conveyance period in the conveyance belt 21 that can reflect the positional deviation correction, can suppress the decrease in the image forming speed while appropriately suppressing the color deviation. That is, it is possible to efficiently perform misalignment correction corresponding to the state of the image forming apparatus.

The adjustment of the color misregistration correction (position misalignment correction) interval may be performed in real time by providing a temperature sensor for measuring the apparatus temperature (machine temperature) in the image forming apparatus and based on the measured value of the temperature sensor.
Specifically, the change rate of the apparatus temperature (air temperature), that is, the change rate or change amount of the color misregistration amount between the reference color and the non-reference color is calculated based on the measurement result of the temperature sensor, and the color is calculated based on the calculation result. Adjust the gap for deviation correction (positional deviation correction).
The part where the temperature sensor for measuring the apparatus temperature (machine temperature) is disposed is preferably, for example, the inside of the exposure unit 33 (shown in FIG. 1) including elements that greatly affect the color shift.

The interval of color misregistration correction (position misalignment correction) may be adjusted based on the elapsed time from the start of image formation or the number of output recording media.
For example, immediately after the start of image formation, it is assumed in advance that the rate of change of the apparatus temperature (machine temperature) in the image forming apparatus is large, and the rate of change or the amount of change in the color misregistration amount between the reference color and the non-reference color is large. Therefore, the conveyance period in the conveyance belt 21 that can reduce the number of groups to be divided and reflect the positional deviation correction is set to be short (short).
On the other hand, when a certain amount of processing time has elapsed since the start of image formation, for example, when the number of recording media output from the start of image formation exceeds 50, the apparatus temperature (machine temperature) in the image forming apparatus is saturated and becomes constant. Because the change rate of the device temperature (air temperature) is small and the change rate or change amount of the color shift amount between the reference color and the non-reference color is assumed to be small in advance, the number of groups to be divided is increased and the position shift The conveyance period in the conveyance belt 21 that can reflect the correction is set to be long (long).

  In this way, by adjusting the interval of color misregistration correction (position misalignment correction) based on the elapsed time from the start of image formation and the number of output recording media, color misregistration correction (position misregistration) can be performed at an appropriate timing. Correction) interval can be adjusted. In addition, since the color misregistration correction (position misalignment correction) interval can be adjusted without using a temperature sensor, the cost of the image forming apparatus can be reduced.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an exemplary embodiment. FIG. 4 is a diagram illustrating one type of toner pattern group formed on a conveyance belt in the image forming apparatus according to the present embodiment. FIG. 6 is a diagram illustrating an example of a toner pattern formed on a conveyance belt. FIG. 6 is a diagram illustrating an example of a toner pattern formed on a conveyance belt. FIG. 6 is a diagram illustrating an example of a toner pattern formed on a conveyance belt.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Paper feed part 11 Paper feed tray 12 Paper feed roller 13 Separation roller 14 Registration roller pair 20 Carrying unit 21 Carrying belt 22 Drive roller 23 Driven roller 24 Cleaning part 25 Transfer part 30 Image forming unit 31 Photosensitive drum 32 Charging part 33 Exposure Section 34 Developing section 35 Cleaning section 36 Static elimination section 40 Fixing section 50 Detection section 51 Pattern detection sensor 60 Registration sensor

Claims (2)

Latent image generating means for generating a toner image for each color;
Transport means for transporting the recording medium on a moving body;
Transfer means for transferring the toner image generated by the latent image generation means to a recording medium conveyed by the conveyance means;
A pattern forming unit for forming a toner pattern of a reference color and a non-reference color between the recording media continuously conveyed in the moving body;
Detecting means for detecting the toner pattern formed by the pattern forming means;
Based on the detection result of the detection means, a positional deviation of the non-reference color with respect to the reference color is calculated, and based on the calculated positional deviation amount, a toner image between the reference color and the non-reference color is calculated. Correction means for correcting the deviation of the image forming position;
With
The toner pattern formed between the recording media by the pattern forming unit is a group that is different from each other in which a pattern group composed of a plurality of toner patterns is divided into a plurality of groups,
The detecting means detects all the toner patterns constituting the pattern group,
The number of groups of the toner pattern group formed between the recording media by the pattern forming unit can be changed based on the temperature change rate of the image forming apparatus,
When changing the number of groups of the toner pattern group based on the temperature change rate of the image forming apparatus, the temperature change rate of the image forming apparatus is large, and the change in the amount of color shift between the reference color and the non-reference color If the rate or amount of change that is larger is assumed in advance, to reduce the number of groups of the toner pattern group, to increase the number of toner patterns included in one group, the temperature change rate is rather low, the reference When it is assumed in advance that the change rate or change amount of the color misregistration amount between the color and the non-reference color is small , the number of toner pattern groups is increased, and the number of toner patterns included in one group An image forming apparatus characterized in that An exposure unit that irradiates a photosensitive drum with laser light modulated by image data; and
A temperature sensor for measuring the temperature of the apparatus inside the exposure unit;
The image forming apparatus according to claim 1, wherein a temperature change rate of the image forming apparatus is measured by the temperature sensor.

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