JP7516127B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus that forms an image on a recording material.

Wide color gamut printing technology is known for color laser printers. This technology expands the color gamut, mainly in the high density range, by increasing the amount of toner on the photosensitive drum, thereby achieving a wider color gamut than normal printing. Increasing the amount of toner on the photosensitive drum is achieved by making the peripheral speed ratio between the developing roller and the photosensitive drum larger than normal (developing roller peripheral speed > photosensitive drum peripheral speed) and by increasing the potential contrast on the photosensitive drum. Regarding this wide color gamut print mode, Patent Documents 1 and 2 disclose a technology for predicting the results of density correction in wide color gamut print mode (called wide color gamut density correction) from the results of density correction not in wide color gamut print mode (called normal density correction).

JP 2019-020521 A JP 2019-095522 A

However, there was room for improvement in the accuracy of this prediction in wide gamut print modes.

The objective of the present invention is to provide a technology that can reduce the consumption of developer due to correction operations and improve the accuracy of correction.

In order to achieve the above object, an image forming apparatus according to the present invention comprises:
An image forming apparatus that forms a toner image as an output image on a recording material based on input image data,
An image carrier;
a developer carrier for developing the electrostatic image formed on the image carrier with toner;
an intermediate transfer member onto which the toner image formed on the image carrier is transferred;
a transfer means for transferring the toner image from the intermediate transfer body to the recording material;
a control unit capable of executing a normal mode and a wide color gamut mode in which the color gamut of the image formed on the recording material is expanded to a larger value than that in the normal mode;
a positional deviation correction unit that corrects input position information included in the input image data to output position information used for forming the toner image so that the position of the toner image formed on the recording material is a predetermined position;
a density correction unit that corrects input density information included in the input image data to output density information used for forming the toner image in accordance with predetermined density condition data that defines a relationship between the density of the input image and the density of the output image, so that the density of the toner image formed on the recording material becomes a predetermined density;
Equipped with
In the normal mode, a first correction operation can be executed by the position deviation correction means and the density correction means to correct the input position information and the first input density information to the output position information and the first output density information,
In the image forming apparatus, a second correction operation can be executed in which, in the wide color gamut mode, the density corrector corrects second input density information in the wide color gamut mode to second output density information,
The present invention is characterized in that image formation is performed in the wide color gamut mode based on the output position information obtained by the first correction operation performed in the normal mode and the second output density information obtained by the second correction operation performed in the wide color gamut mode.
In order to achieve the above object, an image forming apparatus according to the present invention comprises:
An image forming apparatus that forms a toner image as an output image on a recording material based on input image data,
An image carrier;
a developer carrier for developing the electrostatic image formed on the image carrier with toner;
a transfer unit that transfers the toner image formed on the image carrier onto the recording material;
a control unit capable of executing a normal mode and a wide color gamut mode in which the color gamut of the image formed on the recording material is expanded to a larger value than that in the normal mode;
a positional deviation correction unit that corrects input position information included in the input image data to output position information used for forming the toner image so that the position of the toner image formed on the recording material is a predetermined position;
a density correction unit that corrects input density information included in the input image data to output density information used for forming the toner image in accordance with predetermined density condition data that defines a relationship between the density of the input image and the density of the output image, so that the density of the toner image formed on the recording material becomes a predetermined density;
Equipped with
In the normal mode, a first correction operation can be executed by the position deviation correction means and the density correction means to correct the input position information and the first input density information to the output position information and the first output density information,
In the image forming apparatus, a second correction operation can be executed in which, in the wide color gamut mode, the density corrector corrects second input density information in the wide color gamut mode to second output density information,
The present invention is characterized in that image formation is performed in the wide color gamut mode based on the output position information obtained by the first correction operation performed in the normal mode and the second output density information obtained by the second correction operation performed in the wide color gamut mode.

As described above, the present invention can reduce the consumption of developer due to the correction operation and improve the accuracy of the correction.

Schematic diagram of an image forming apparatus Configuration diagram of a positional deviation correction sensor and a density correction sensor unit of an image forming apparatus System configuration diagram of an image forming apparatus System configuration diagram of the controller of the image forming apparatus FIG. 1 is a diagram for explaining a gamma correction process of an image forming apparatus. FIG. 1 is a diagram showing the relationship between environmental changes in an image forming apparatus and the validity period of density conditions. A flowchart showing a process for updating the validity period of a density condition in an image forming apparatus. 1 is a timing chart showing control in the first embodiment; 1 is a flowchart showing control in the first embodiment. 11 is a timing chart showing a control according to another embodiment of the first embodiment. 11 is a timing chart showing control in the second embodiment. 1 is a flowchart showing a control process according to a second embodiment of the present invention;

The following describes in detail the embodiments of the present invention with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the embodiments should be changed as appropriate depending on the configuration and various conditions of the device to which the invention is applied. In other words, it is not intended to limit the scope of the present invention to the embodiments described below.

(Embodiment 1)
[Description of Image Forming Apparatus]
1 is a schematic diagram of an image forming apparatus. In the following description, the letters a, b, c, and d at the end of the reference symbols indicate that the corresponding members are related to the formation of yellow (Y), magenta (M), cyan (C), and black (Bk) toner images, respectively. In the following description, when it is not necessary to distinguish between colors, the reference symbols may be used without the letters a, b, c, and d at the end.

(Image forming section)
First, an image forming section (hereinafter also referred to as a station) as an image forming means for forming a yellow (Y) toner image will be described. The photosensitive drum 1a as a photosensitive member (image carrier) is a metal cylinder on which a functional organic material is laminated in multiple layers, including a carrier generation layer that is photosensitive to light and generates charges, and a charge transport layer that transports the generated charges, and the outermost layer has low electrical conductivity and is almost insulated. The charging roller 2a as a charging means (charging member) is in contact with the photosensitive drum 1a and uniformly charges the surface of the photosensitive drum 1a while rotating in accordance with the rotation of the photosensitive drum 1a. A DC voltage or a voltage obtained by superimposing an AC voltage is applied to the charging roller 2a, and the photosensitive drum 1a is charged by discharging in a small air gap on the upstream and downstream sides from the contact nip between the charging roller 2a and the surface of the photosensitive drum 1a.

The scanner unit 11a as a light irradiation means is configured to scan laser light using a polygon mirror or to irradiate light using an LED array. The scanner unit 11a forms an electrostatic latent image (electrostatic image) on the photosensitive drum 1a as an image carrier by irradiating the photosensitive drum 1a with a beam 12a modulated based on an image signal. The development unit 8a as a development means is composed of a development roller 4a as a developer carrier, a non-magnetic one-component developer 5a, and a developer coating blade 7a. The development roller 4a is abutted against the photosensitive drum 1a. The electrostatic latent image formed on the photosensitive drum 1a is developed into a toner image (developer image) by the development roller 4a. The rotation of the development roller 4a during development is controlled by a rotation speed control means such as a development motor (not shown). The developed toner image is primarily transferred onto the intermediate transfer belt 80 as a transferee by applying a primary transfer bias to the primary transfer roller 81a. After the primary transfer, any residual toner remaining on the photosensitive drum 1a is cleaned by the cleaning unit 3a.

The charging roller 2a is connected to a charging bias power source 20a, which is a voltage supply means (charging voltage application section) to the charging roller 2a, and is supplied with power. The developing roller 4a is connected to a developing bias power source 21a, which is a voltage supply means (developing voltage application section) to the developing roller 4a, and is supplied with power. The primary transfer roller 81a, which serves as a primary transfer means, is connected to a primary transfer bias power source 84a, which is a voltage supply means to the primary transfer roller 81a, and is supplied with power. The above-mentioned photosensitive drum 1a, charging roller 2a, cleaning unit 3a, developing roller 4a, non-magnetic one-component developer 5a, developer application blade 7a, and developing unit 8a can be made into an integrated process cartridge 9a that is detachable from the image forming apparatus. However, the configuration of the cartridge is not limited to this, and the photosensitive drum 1a, etc. can be made into one cartridge, and the developing unit 8a, etc. can be made into a separate developing cartridge.

The above is the configuration of the station corresponding to the color yellow. The stations (image forming means) corresponding to magenta, cyan, and black have the same device configuration, except that the toner colors used are different. Each part is given the same reference number followed by the letters b, c, and d, and detailed explanations are omitted here. In the following, the station for forming a toner image of yellow (Y) color is also called the first station. Similarly, the station for forming a toner image of magenta (M) color is also called the second station, the station for forming a toner image of cyan (C) color is also called the third station, and the station for forming a toner image of black (K) color is also called the fourth station. In the direction of movement of the intermediate transfer belt 80, the first station is located at the most upstream position, followed by the second station, the third station, and the fourth station in that order.

The intermediate transfer belt 80 is supported by three rollers, a secondary transfer opposing roller 86 as a tension member, a drive roller 14, and a tension roller 15, so that an appropriate tension is maintained. By driving the drive roller 14, the intermediate transfer belt 80 rotates and moves in the forward direction relative to the photosensitive drums 1a to 1d at approximately the same speed. In addition, primary transfer rollers 81a to 81d that abut against the intermediate transfer belt 80 are arranged on the inside of the intermediate transfer belt 80, facing the photosensitive drums 1a to 1d. The primary transfer rollers 81a to 81d are connected to primary transfer bias power sources 84a to 84d. The primary transfer rollers 81a to 81d sequentially transfer the respective color toner images formed on the photosensitive drums 1a to 1d onto the intermediate transfer belt 80, thereby forming a color image. In addition, charge removal members 23a to 23d are arranged downstream of the primary transfer rollers 81a to 81d in the rotation direction of the intermediate transfer belt 80. The drive roller 14, tension roller 15, charge removal members 23a-23d, and secondary transfer opposing roller 86 are electrically grounded by wiring (not shown).

When feeding a recording material (recording medium) P, such as paper, from the paper feed cassette 16, the pickup roller 17 is driven by a stepping motor (not shown) (hereinafter also referred to as the paper feed motor). As a result, the bottom plate 29 rises and pushes up the recording materials P stacked in the paper feed cassette 16. The top sheet of the pushed-up recording material P comes into contact with the pickup roller 17, and the recording material P is fed by the rotation of the pickup roller 17. The fed recording material P is transported to the registration roller 18, and when the leading edge of the recording material P is detected by the registration sensor 35, the drive of the paper feed motor is stopped and the transport of the recording material P is temporarily stopped. The recording material P that has been temporarily stopped by the registration roller 18 is re-transported at a predetermined timing in accordance with the movement of the toner image transferred onto the intermediate transfer belt 80, and is transported to the secondary transfer section.

The toner images formed on the photosensitive drums 1a to 1d are transferred, and the color image formed on the intermediate transfer belt 80 is moved to the secondary transfer position, which is a secondary transfer section consisting of the secondary transfer roller 82 and the intermediate transfer belt 80. By applying a secondary transfer bias to the secondary transfer roller 82 as a secondary transfer means, the color image on the intermediate transfer belt 80 is secondarily transferred onto the recording material P.

The fixing unit 19, which is composed of a heating member, such as a fixing film, and a pressure member, such as a pressure roller, applies heat and pressure to the color image that has been secondarily transferred onto the recording material P, fixing the toner image to the recording material P. The recording material P with the toner image fixed by the fixing unit 19 is discharged onto the discharge tray 36, and the series of image forming operations is completed.

[Configuration of optical sensor]
The positional deviation correction sensor/density correction sensor unit 60 is a sensor that detects positional deviation correction patterns for detecting the amount of positional deviation of each color image transferred onto the intermediate transfer belt, and also detects density correction patterns for detecting density.

Figure 2 shows an example of the misalignment correction and density correction sensor configuration of the image forming apparatus. The misalignment correction and density correction sensor unit 60 has misalignment correction and density correction sensors 201 and 202 at a position perpendicular to the transport direction of the intermediate transfer belt 80. The misalignment correction and density correction sensors 201 and 202 share the sensor by reading the misalignment correction pattern 206 as a toner image for position detection and the density correction pattern 207 as a toner image for density detection at different times. In other words, the misalignment correction and density correction sensors 201 and 202 function as a density detection means for detecting the density of the toner image for detection, and also function as a position detection means for detecting the formation position of the toner image for detection on the intermediate transfer belt 80 as the transferee. By arranging two or more misalignment correction and density correction sensors 201 and 202 at a position perpendicular to the transport direction of the intermediate transfer belt 80, the main scanning direction magnification of the image and the sub-scanning direction inclination are detected. Moreover, density detection is performed by one or more misalignment correction/density correction sensors 201 and 202. The misalignment correction/density correction common sensors 201 and 202 have a light emitting element 203 that emits light toward the intermediate transfer belt 80 and the misalignment correction pattern 206. Furthermore, the misalignment correction/density correction common sensors 201 and 202 are composed of a sensor 204 that detects diffuse reflected light from the intermediate transfer belt 80 and the misalignment correction pattern 206, and a sensor 205 that detects regular reflected light. The light emitting element 203 is disposed so as to have an irradiation angle of 15° with respect to the perpendicular direction of the intermediate transfer belt 80. The diffuse reflected light detection sensor 204 is disposed so as to have a light receiving angle of 45° in order to detect the diffuse reflected light from the intermediate transfer belt 80. The regular reflected light detection sensor 205 is disposed so as to have a light receiving angle of 15° in order to detect the regular reflected light from the intermediate transfer belt 80. The infrared light emitted from the light emitting element 203 is irradiated onto the intermediate transfer belt 80 itself, the misalignment correction patterns 206 for each color on the intermediate transfer belt 80, and the density correction patterns 207. The position of the misalignment correction patterns 206 is detected by receiving diffuse reflected light from the intermediate transfer belt 80 and the misalignment correction patterns 206 on the intermediate transfer belt 80 with a diffuse reflected light detection sensor 204, which is a light receiving element. In addition, the density of the density correction patterns 207 is detected by receiving specular reflected light and diffuse reflected light from the intermediate transfer belt 80 and the density correction patterns 207 on the intermediate transfer belt 80 with a diffuse reflected light detection sensor 204 and a specular reflected light detection sensor 205, which are light receiving elements.

[System configuration for positional deviation correction and density correction]
3A is a block diagram for explaining the overall system configuration of the image forming apparatus. The controller unit 301 can communicate with the host computer 300 and the engine control unit 302. When performing positional deviation correction and density correction, the controller unit 301 sends a positional deviation correction and density correction start command and a video signal to the CPU 311 and the image processing GA 312. In addition, the engine control unit 302 includes a control unit 314 for a positional correction and density correction detection sensor, a fixing control unit 315 for controlling the fixing unit, and a paper control unit 316 for controlling the conveyance of the recording material in the image forming apparatus. Furthermore, the engine control unit 302 includes a motor and a driving gear train as a driving source, and includes a photosensitive drum/driving roller driving unit 333 as a driving means for rotating and driving the photosensitive drum 1 and the developing roller 4 so that the circumferential speeds of the photosensitive drum 1 and the developing roller 4 can be individually controlled. The image control unit 313 controls the photosensitive drum/driving roller driving unit 333 so as to appropriately change the circumferential speed settings of the photosensitive drum 1 and the developing roller 4 according to the operation mode of the image formation. Details will be described later.

When the CPU 311 receives the position misalignment correction and density correction start command, it instructs the image control unit 313 to start image formation with position misalignment correction and density correction.

When the image control unit 313 receives the start of positional deviation correction and density correction, it applies various biases and prepares for toner image formation. When the CPU 311 is ready for various biases, it transmits a video signal output start command to the controller unit 301. When the controller unit 301 receives the video signal output start command from the CPU 311, it outputs the video signal. Image processing GA 312
Upon receiving a video signal from the controller unit 301, the image control unit 313 transmits image formation data to the image control unit 313. The image control unit 313 starts a latent image based on the image formation data received from the image processing GA 312, forms a toner image on the photosensitive drum 1, and transfers the toner image on the photosensitive drum 1 to the intermediate transfer belt 80.

The CPU 311 obtains a voltage value corresponding to the toner density from the toner image on the intermediate transfer belt using a position correction/density correction detection sensor. From the detected voltage result, the CPU 311 calculates the positional deviation correction amount of each color toner image in the main scanning and sub-scanning directions between each color, and the density correction amount of each color toner image. The CPU 311 notifies the controller of the positional deviation correction amount and the density correction amount via the video interface unit 310. The positional deviation correction in this embodiment will be described in detail later, but in order to make the position of the toner image actually formed on the transfer body a desired position, the input position information included in the input image data is corrected to output position information used to form the toner image. Then, the image forming means corrects (converts) it to output position information used to form the toner image. In the following description, various configurations of the image forming device related to the correction of the output position information correspond to the positional deviation correction means of the present invention.

[Details of Density Correction]
In the present invention, in order to perform characteristic control regarding the density correction, the density correction process will be described in more detail. In short, density correction is a process of correcting the relationship between the (here, reflective) density of the density correction pattern formed on the intermediate transfer belt 80 of the image forming device 36 and the gradation density of the image information input from the host computer 300. That is, in order to make the density of the toner image actually formed a desired density, the input density information included in the input data is used with predetermined density condition data that specifies the relationship between the density of the input image and the density of the output image. Then, the image forming means corrects (converts) it to output density information used for forming the toner image. In addition, in the following description, various configurations of the image forming device related to the correction of density information correspond to the density correction means (density information conversion means) of the present invention. In addition, various configurations of the image forming device related to the acquisition of density condition data ((i) reference color gamut data, (ii) actual measured wide color gamut data, (iii) predicted wide color gamut data) used for the correction of density information correspond to the acquisition means of the present invention. Details will be described below.

First, we will explain how the color information obtained by the density correction sensor is used for correction. Figure 4 is a block diagram showing an overview of the correction process performed inside the controller 301. A print job written in a page description language (PDL) such as PCL or PostScript is generally sent from the host PC 300 to the controller 301. The controller 301 sends YMCK bitmap information to the engine control unit 302 mainly via a RIP (Raster Image Processor) unit 317, a color conversion unit 318, a gamma correction unit 319, and a halftoning unit 320.

Specifically, the RIP unit 317 performs file analysis (interpretation) of the print job written in PDL sent from the host PC 300, and performs RGB bitmapping according to the resolution of the image forming device. In general, the color reproduction range of an electrophotographic image forming device is narrower than that of an LCD display. Therefore, the next color conversion unit 318 performs color matching to match the colors as much as possible, taking into account the difference in color reproduction range between devices. The color conversion unit 318 also performs conversion from RGB data to YMCK data. After that, the gamma correction unit 319 performs gamma correction, and the halftoning unit 320 performs gradation expression processing such as dithering. The detection result obtained by the density correction sensor is used by the gamma correction unit 319 to select appropriate image data.

[Lookup table]
FIG. 5A shows a lookup table (LUT). In FIG. 5A, the first quadrant shows a graph of the lookup table, with the horizontal axis showing the input image data expressed in hexadecimal (Hex), and the vertical axis showing the image data to be used expressed in hexadecimal. The second quadrant shows a gamma curve before correction (hereinafter also referred to as a gamma curve before correction), with the horizontal axis showing the reflection density, and the vertical axis showing the image data to be used as in the first quadrant. Note that the reflection density is also simply called density. The gamma curve is a curve showing the relationship between the input image data and the actual output image density corresponding to the input image data. The third quadrant shows a gamma curve after correction (hereinafter also referred to as a gamma curve after correction), with the horizontal axis showing the reflection density (density output) as in the second quadrant, and the vertical axis showing the input image data (Hex).

The graph shown in the second quadrant in Figure 5(a) is the pre-correction gamma curve. Usually, the pre-correction gamma curve is not linear. Therefore, the input image data is not used as is, but is converted into image data that maintains linearity before use. A table that shows the correlation between this input image data and the image data that is actually used is called a lookup table. Recreating a lookup table to match the characteristics of the current image forming device body is called gamma correction (hereinafter referred to as gamma correction). In this embodiment, performing the gamma correction is also called density correction.

As shown in the third quadrant of Figure 5(a), ideally the relationship between input image data and reflection density is linear. Note that this graph shows the general relationship between input image data and reflection density. The data in this graph is obtained, for example, based on the results of measuring the density of an image printed on a recording material such as paper after fixing using an external measuring device. For example, in this example, when considering the characteristics of the current image forming device main body (pre-correction gamma curve) shown in the second quadrant of Figure 5(a), it can be seen that in order to obtain the ideal density for input image data of 80h, it is actually necessary to use image data of C0h.

In this embodiment, multiple density correction patterns with different densities are measured (density detection) to obtain data for multiple points that constitute the pre-correction gamma curve, i.e., data that represents the relationship between input image data and output density (called density condition data). Then, performing gamma correction using the pre-correction gamma curve obtained from this data is called density correction.

[Changes in gamma curve in wide color gamut print mode]
The pre-correction gamma curve is a characteristic of the current image forming apparatus itself, and changes under various conditions such as the cartridge and the usage environment as described below. This is the same for different print modes such as a normal print mode as a reference mode for forming a toner image in a reference color gamut and a wide color gamut print mode as a wide color gamut mode for forming a toner image in a color gamut wider than the reference color gamut. In this embodiment, the image forming operation modes include a normal mode for office use and a wide color gamut mode for increasing density and color. Compared to the normal mode, the wide color gamut mode can increase the amount of toner supply by increasing the peripheral speed ratio between the photosensitive drum and the developing roller. Specifically, the peripheral speed ratio (first peripheral speed ratio) of the normal mode is 120%, and the peripheral speed ratio (second peripheral speed ratio) of the wide color gamut mode is 240%.

The peripheral speeds of the photosensitive drum and the developing roller may be set by changing the rotation speed of the developing roller, or the rotation speed of the developing roller may be fixed and the rotation speed of the photosensitive drum may be changed to make the peripheral speed ratio variable. Alternatively, the rotation speed of the developing roller and the rotation speed of the photosensitive drum may both be changed individually to variably control the peripheral speed ratio. In this case, the peripheral speed ratio may be changed by lowering both the rotation speed of the developing roller and the rotation speed of the photosensitive drum and setting a difference in the extent of the reduction.

The wide color gamut mode can also be achieved by increasing the development contrast, which is the potential difference between the photosensitive drum surface potential and the development bias (development voltage or development potential), compared to the normal mode. Here, the development contrast is formed by the light area potential constituting the electrostatic latent image formed on the photosensitive drum and the development bias applied to the development roller. This development contrast causes the toner on the development roller to move to the photosensitive drum and develop the electrostatic image. The dark area potential after charging in the normal mode is set to -500V, and the light area potential after exposure is set to -100V. In this embodiment, the value of the light area potential refers to the value measured by a surface potentiometer on the photosensitive drum when forming an image pattern in which the entire paper, such as a solid black image, is developed with toner. The development potential (development bias) applied to the development roller is set to -300V, and the development contrast is set to 200V. In the normal mode, the dark area potential after charging is −650 V, the light area potential after exposure is −100 V, the development bias applied to the development roller is −450 V, and in the wide color gamut mode, the development contrast is 350 V, so that the color gamut can be expanded in the wide color gamut mode.

The graph in FIG. 5(b) is the same as that in FIG. 5(a), and the explanation of the horizontal and vertical axes is omitted. FIG. 5(b) shows the deviation of the reflection density from linearity when printing is performed in the wide color gamut print mode using the LUT optimized for the normal print mode. In FIG. 5(b), the dashed line in the second quadrant shows the characteristics of the image forming device body in the normal print mode, and this dashed line graph is the same as the graph in the second quadrant of FIG. 5(a). Also, in FIG. 5(b), the solid line in the second quadrant shows the characteristics (uncorrected gamma curve) of the image forming device body in the wide color gamut print mode. The wide color gamut print mode is a print mode in which the amount of toner per unit area supplied from the development roller 4 to the photosensitive drum 1 is increased compared to that in the normal print mode by increasing the difference in peripheral speed of the development roller 4 relative to the photosensitive drum 1. Therefore, in the wide color gamut print mode, the reflection density is higher than that in the normal print mode over the entire image data range. When an image is formed using input image data of 80h, the reflection density is about 0.6 in normal print mode, but in wide color gamut print mode the reflection density increases to 1.0. In other words, when the LUT in normal print mode is used for input image data of 80h, the image data used becomes C0h. As a result, the density in wide color gamut print mode becomes 1.0, which is darker than the density of 0.6 that should be achieved.

As a result, as shown in the third quadrant of FIG. 5B, while the corrected gamma curve (dashed line) in the normal print mode is linear, the corrected gamma curve (solid line) in the wide gamut print mode is not linear and has a distorted shape. Therefore, normally, in the wide gamut print mode, as in the normal print mode, it is necessary to obtain an LUT for the wide gamut print mode after grasping the gamma using the density sensor 218. However, in order to obtain an LUT for the wide gamut print mode, even in the wide gamut print mode, a process is required in which a detection toner image (detection image) is formed on the intermediate transfer belt 80 and the density of the detection toner image is measured by the density sensor 60.

[Predicted Density Correction]
As described above, when density measurements are performed to obtain an LUT in the wide color gamut print mode, the accuracy of the LUT is good, but downtime occurs for the density measurements. To solve this problem, a process that is often performed in the wide color gamut print mode is predictive density correction. Predictive density correction is a process in which an LUT in the wide color gamut print mode is created based on density information in the normal print mode and predetermined information, and gamma correction is performed. Examples of the predetermined information include the difference in peripheral speed of the developing roller 4 relative to the photosensitive drum 1, the degree of use of the drum unit, the degree of toner consumption, and the like. By using predictive density correction, it is possible to reduce downtime caused by normal density correction, but the accuracy of gamma correction is inferior to that of normal density correction.

In the predicted density correction, a correlation table of density information in the normal print mode and the wide color gamut print mode for each of the above-mentioned predetermined information is prepared in advance. The correlation table is created from a gamma curve in which the conditions of each of the above-mentioned predetermined information are changed in some ways. Specifically, the density ratio of the print image in both of the above-mentioned modes under each condition is calculated, and the density ratio that best suits the current conditions of the image forming apparatus is predicted from the data. Based on this correlation table, the density information obtained by measuring the density correction pattern 207 is converted to a density in the wide color gamut mode. The correlation table is stored in a storage unit (not shown) of the engine control unit 302. A more specific and detailed method using actual data is described in paragraph 0037 and subsequent paragraphs of JP-A-2019-95522 of Patent Document 2.

In this embodiment, the correlation table is a correlation table when the peripheral speed difference of the developing roller 4 with respect to the photosensitive drum 1 is 280%, and is created from a gamma curve obtained by changing the usage rate (number of prints) of each drum unit and developing unit under several conditions. Then, by using the obtained predicted density correction, a curve using the predicted density of the LUT in the wide color gamut print mode can be obtained.

[Correction of image forming conditions in normal print mode and wide color gamut print mode]
The image forming apparatus in this embodiment performs the above-mentioned positional deviation correction and density correction (the two are collectively called image forming condition correction) in the following manner.

In the normal mode, the image forming conditions are corrected (called normal image forming conditions correction) by performing both the positional deviation correction and the density correction in one correction, and is performed when the valid period of the density conditions (= density condition data) expires. A correction operation in which both the positional deviation correction and the density correction are performed in one correction is called integrated calibration. Integrated calibration refers to performing both corrections in the same sequence. Specifically, it refers to a correction operation in which the density correction pattern 207 is formed immediately after the positional deviation correction pattern 206 is formed on the intermediate transfer belt 80, and the positional deviation correction and the density correction are performed in a series of operations. More specifically, after the positional deviation correction is performed, the density correction pattern 207 is formed without cleaning the positional deviation correction pattern 206. Therefore, the integrated calibration can be performed during one rotation of the intermediate transfer belt 80. When the integrated calibration is performed, the light emission amount of the light emitting element 203 for performing the positional deviation correction and the density correction in succession is determined.

At this time, the engine control unit 302 notifies the controller 301 of the expiration date as a request to execute image formation condition correction. The controller 301 corrects the image formation conditions at the notified timing, thereby always guaranteeing density. The above correction is performed in the wide color gamut print mode at the same timing as in the normal print mode.

On the other hand, image formation condition correction in wide color gamut mode (called wide color gamut density correction) does not perform positional deviation correction, but only density correction. Therefore, instead of performing positional deviation correction in wide color gamut mode, the positional deviation correction result performed by normal image formation condition correction is reflected in wide color gamut mode. Furthermore, the timing of execution is not necessarily when the validity period expires in wide color gamut print mode. Because wide color gamut print mode is a special mode, in this embodiment, the user decides whether or not to execute during wide color gamut print mode. Therefore, even if the validity period of the density conditions performed last time expires, a request to execute a new correction is not issued. Furthermore, the validity period of the density conditions itself is not constantly managed in that print mode.

[Validity period of concentration conditions]
The timing for correcting the image forming conditions will be described below.

Corrections to image formation conditions while the image forming device is in operation are made when the validity period of the density conditions expires. The validity period here is determined by the following criteria:

After a predetermined number of pages have been printed As printing continues, the toner state changes from time to time. Therefore, the image forming apparatus corrects the image forming conditions every time a predetermined number of pages have been printed. In this embodiment, the predetermined number of pages is 200 pages.

When the environment changes, the toner state changes depending on the amount of moisture in the air. Therefore, the image forming apparatus corrects the image forming conditions when the amount of moisture changes beyond the allowable range. The allowable range conditions in this embodiment are shown in FIG. 6.

Figure 6 is a graph showing the relationship between the amount of moisture at the time of the previous image formation condition correction and the amount of moisture constantly detected by the image forming device. 601 shows the upper limit of the allowable moisture amount, 602 the lower limit, and if the relationship between the moisture amount at the time of the previous correction and the currently detected moisture amount is within the area of 603, it is considered to be within the allowable range. When the amount of moisture constantly detected falls outside this range, the image forming device corrects the image formation conditions.

After a Predetermined Time Has Elapsed Even if printing has not been performed, if a certain amount of time has elapsed since printing, the toner state will have changed. Therefore, the image forming apparatus corrects the image forming conditions after the predetermined time has elapsed. In this embodiment, the predetermined time is 30 minutes.

The above describes the method of determining the effective period of the image formation conditions for three cases. In the image forming device of this embodiment, in order to determine the effective period, the above three conditions are constantly detected in parallel. Then, when it is determined that the effective period has expired for any one of the conditions, the image forming device corrects the image formation conditions. Therefore, the effective period is usually not constant, but varies depending on the environment in which the image forming device is placed and the usage conditions.

The above conditions also apply to the expiration date of actual measurement condition 1 in wide color gamut mode, which will be described later. In this embodiment, the expiration date of the density condition in normal mode and the expiration date of the actual measurement condition in wide color gamut mode are the same. The expiration date of the actual measurement condition in wide color gamut mode is not limited to the above conditions, and may be set longer or shorter than the expiration date of the density condition in normal mode, as appropriate.

Figure 7 is a flowchart of the effective period determination process. This process starts after the effective period of the image formation conditions has expired and the correction of the image formation conditions has been completed. Then, three monitoring processes S702, S703, and S704 constantly monitor whether the three conditions for determining the effective period are met. Furthermore, as described above, if any one of the three conditions is met, the engine control unit 302 considers the expiration date to have expired, and in S705 notifies the controller 301 of a request to correct the image formation conditions. Note that the time lapse detection process S702 is only performed after printing, so it is started after waiting for the end of printing in S701. After the request to correct the image formation conditions has been notified in S705 and the correction has been performed, a new effective period determination process starts again.

[Control of the First Embodiment]
As described above, the normal image formation condition correction determines the validity period by the above method even when printing in the wide color gamut print mode. Therefore, the normal image formation condition correction is performed even in the wide color gamut print mode. That is, the reference color gamut data is newly acquired (updated) every time the validity period expires. However, since the print mode is the wide color gamut print mode, the density correction in this case uses the predicted density correction described above. On the other hand, the wide color gamut density correction is performed according to the user's request as described above, and is performed completely independently of the normal image formation condition correction. That is, the reacquisition (updating) of the measured wide color gamut data is not performed automatically even when the validity period expires, but is performed at the user's (the user of the image forming device) discretionary timing.

The control employed in this embodiment is described below. Figure 8 is a timing chart showing the control of image formation condition correction in this embodiment, and shows the correction process of image formation conditions (here, only density conditions) in wide color gamut mode.

801 indicates normal image formation condition correction, and 802 indicates the validity period of the density conditions determined at that time. 803 and 804 indicate wide color gamut density correction and the validity period of the corrected image formation conditions, respectively. 805 indicates the density conditions used by the image forming device, and printing is performed using those density conditions.

Figure 8 shows the density conditions used by the image forming device when the user performs wide color gamut density correction while normal image formation condition correction is being performed all the time. When the first normal image formation condition correction (acquisition of first reference color gamut data) is performed, predicted density correction (correction using predicted wide color gamut data acquired based on the reference color gamut data) is performed. Therefore, the density conditions of the image forming device (density condition data used in wide color gamut mode) become predicted condition 1 (first predicted wide color gamut data). When the user then performs wide color gamut density correction (acquisition of first actual wide color gamut data), the density conditions of the image forming device at that point (density condition data used in wide color gamut mode) use the obtained actual condition 1 (first actual wide color gamut data).

There are two characteristic controls in this embodiment. First, the effective period of the wide color gamut density correction (correction using the first measured wide color gamut data) that the user selects to execute is also managed. The above management is performed using a method similar to that used to manage the effective period of the image formation conditions in normal print mode. Conventionally, such management has not been performed in wide color gamut density correction. However, in wide color gamut density correction, even if the effective period of the density conditions has expired, no notification of a request to correct the image formation conditions (705 in FIG. 7) is made. Only the effective period of the density conditions in wide color gamut mode is managed.

The second step is to make a judgment to select appropriate density conditions in consideration of the validity period in the second normal image formation condition correction (acquisition of second reference gamut data (update from first reference gamut data)). In this embodiment, since the density conditions in wide gamut mode (actual measurement conditions 1 in the figure) are still valid at the time of the second normal image formation condition correction, the actual measurement conditions 1 are continued to be used based on the result of this judgment process. Even after the validity period of the actual measurement conditions 1 has expired, if the validity period of the second normal image formation conditions has not expired, the actual measurement conditions 1 are continued to be used. Then, in the third normal image formation condition correction (acquisition of third reference gamut data (update from second reference gamut data)) when the validity period has expired, the density conditions obtained by the correction (predicted conditions 3 in the figure) are used. In other words, a correction is made using the third predicted wide gamut data acquired based on the third reference gamut data. In this way, more appropriate density conditions can be used in the image forming device.

Next, the control in this embodiment will be described with reference to the flowchart in FIG. 9. When a normal image forming condition correction command is notified from the controller 301, image position deviation correction is performed in S901. After that, before entering density correction, the process enters step S902, in which it is determined whether the density condition in the current wide color gamut print mode is within the valid period. Here, if the density condition is within the valid period as described above, the current density condition is updated without performing new density correction (S903) (the density condition in the wide color gamut print mode is normally set without updating, but is updated here just to be safe). If it is outside the valid period in S902, normal image forming condition correction processing is performed in S904, and density condition data is obtained from the density detection result. Next, the above-mentioned density correction processing is performed on the pre-correction gamma curve obtained from the density condition data in S905, and the density condition (predicted density) of the wide color gamut print mode is obtained. Then, the image forming condition is updated in S906. In FIG. 8, the second and third normal image forming condition corrections correspond to the processing within the valid period and outside the valid period in S902, respectively.

The basic processing method is the same even if image formation condition correction in normal print mode is performed manually, i.e., at the user's request. In this case, the usage conditions are determined by the validity period of the density conditions in the wide color gamut print mode. Therefore, the only difference from the above control is that the normal image formation condition correction command is issued manually, so the judgment flowchart in Figure 10 will be the same. The timing chart in Figure 8 will differ, so this will be explained using Figure 10.

Figure 10 is a timing chart for when all image formation conditions are manually corrected by the user. It is assumed that normal image formation condition correction is performed first, followed by wide color gamut density correction, and then normal image formation condition correction is performed twice. In this figure, the second and third corrections in normal print mode are performed after the validity period of the density conditions in normal print mode has expired, since they are performed manually by the user. However, even in this case, the density conditions to be used are determined in the same judgment process as when the above correction command expires, so if the density conditions in wide color gamut print mode are within the validity period, the actual measured conditions are used, and if they are outside the validity period, the predicted conditions are used.

By performing the control of this embodiment, it is possible to obtain image formation conditions that are closer to the desired conditions while maintaining the benefit of reducing downtime obtained by density prediction control in wide color gamut mode.

In this embodiment, both image misalignment correction and density correction are performed in the normal image formation condition correction, and only density correction is performed in the image formation condition correction in the wide color gamut print mode (called wide color gamut image condition correction). That is, in the normal mode, a first correction operation is performed to correct the input position information to the output position information and the first input density information to the first output density information, and in the wide color gamut mode, a second correction operation is performed to correct the second input density information in the wide color gamut mode to the second output density information. Then, based on the output position information obtained by the first correction operation performed in the normal mode and the second output image information obtained by the second correction operation performed in the wide color gamut mode, image formation is performed in the wide color gamut mode. However, it is possible to perform only density correction in the normal image formation condition correction, not only in such a case. In addition, it is also possible to perform both position misalignment correction and density correction in both the normal image formation condition correction and the wide color gamut image condition correction.

(Embodiment 2)
A second embodiment of the present invention will be described below with reference to the timing chart of Fig. 11. Note that a description of the same configuration and control as in the first embodiment will be omitted.

This embodiment differs from the first embodiment in the method of determining the density conditions to be used when normal image formation condition correction is performed when the density conditions in the wide color gamut print mode are outside of their validity period. In the first embodiment, when the validity period has expired, a predicted density (predicted condition 3 in the figure) based on the density detection results in the normal image formation condition correction is used. In this embodiment, in order to further optimize the density conditions to be used, a process is provided for determining and selecting the density conditions to be used. Therefore, as shown in FIG. 11, in the third normal image formation condition correction, either predicted condition 3 or actual condition 1 is used after going through the results of the above determination process.

The above-mentioned determination process will be described below. First, in FIG. 11, at the timing when the first wide color gamut density correction is performed, the engine control unit 302 stores the density conditions (density condition data) in the normal print mode during the valid period at that time in a storage unit (not shown). The density conditions are stored in association with each other as the density conditions of the normal print mode during the first wide color gamut print mode. Then, outside the valid period, the third normal image forming condition correction (acquisition of third reference color gamut data (updating from the second reference color gamut data)) is performed. Then, the engine control unit 302 compares the density conditions obtained by the correction with the density conditions in the storage unit (=the density conditions of the normal print mode associated with the first wide color gamut density correction) (first reference color gamut data). Then, if the difference between the two is small, the density conditions are used, assuming that the density conditions obtained by the first wide color gamut density correction have not changed significantly in the toner state. As described above, since the predicted density correction is less accurate than the density correction using the actually measured density, it may be possible to obtain more desirable image forming conditions by reusing density conditions that are out of their validity period, if possible. In other words, in this embodiment, image forming conditions that are out of their validity period are reevaluated and reused depending on the results. The reevaluation method will be specifically described below.

Each density detected data in the normal print mode associated with the first wide color gamut density correction is defined as Dγw_detect(i), and each data obtained in the third normal image forming condition correction is defined as Dγ_detect(i) (i=1, 2, . . . N: N is the number of density condition data). At this time, the difference ΔDγ between the two is defined as the following formula.

When ΔDγ is equal to or smaller than a predetermined threshold, the density condition actually measured in the first wide color gamut density correction is used in this embodiment. The predetermined threshold is, for example, a value that is 5% of Dγwtotal defined by the following formula:

The threshold value to be set varies depending on the configuration of the individual image forming device and the image forming conditions. Therefore, it is preferable to compare the density conditions actually measured in the wide color gamut print mode in advance for each value of ΔDγ/Dγtotal and determine the allowable value. The above comparison may also be determined by comparing images actually printed under both density conditions. In the wide color gamut print mode, the γ curve in the low- to medium-density region is relatively prone to change. Therefore, in the above judgment, it is possible to evaluate the difference value in the low- to medium-density region by assigning a specific weight to it. Alternatively, it is possible to narrow the evaluation down to the above density region.

Next, the control in this embodiment will be described using the flowchart of FIG. 12. In FIG. 12, the validity period of the density conditions in the wide color gamut print mode in S1202 is determined, and the control is the same as in FIG. 9 except when it is outside the validity period (N in S1202), so the description will be omitted. After it is determined that the validity period is outside the validity period in S1202, normal density correction processing is performed in S1204, and density data in the normal print mode is obtained from density detection (Dγ_detect(i) described above). Then, in S1205, the difference value between the Dγ_detect(i) and the actual measurement data of the normal print mode density conditions associated with the density conditions in the wide color gamut print mode (Dγw_detect(i) described above) is evaluated by the above-mentioned method, and the change in the density conditions is evaluated. If the change in the density conditions is within the threshold (within the threshold range) as described above, the process proceeds to step S1203 in order to use the density conditions actually measured in the wide color gamut print mode. If it is outside the threshold (outside the threshold range), in S1206, the density is predicted using the density condition data for the normal print mode to obtain the predicted density for the wide color gamut print mode. The subsequent steps are the same as those in FIG. 9.

By carrying out the control of this embodiment, even if the density conditions actually measured in the wide color gamut print mode in the first embodiment are outside the valid period, it is possible to obtain image forming conditions closer to the desired conditions.

In FIG. 11, the density condition to be used after the expiration of the validity period of the density condition (actual condition 1) in the wide color gamut print mode remains as actual condition 1 in this embodiment (even in embodiment 1 (FIGS. 8, 10)). It is also possible to insert a process of determining which of the two conditions to select at this point. The determination process at that time can use the method adopted in this embodiment (the method performed in FIG. 12 S1205). If the difference value between the first reference color gamut data (original data of predicted condition 1) set when the first actual measured wide color gamut data was acquired and the second reference color gamut data (original data of predicted condition 2) exceeds a predetermined threshold value, the reliability of the first actual measured wide color gamut data is no longer guaranteed. In that case, density correction using the second predicted wide color gamut data (predicted condition 2) acquired based on the second reference color gamut data that reflects the current device status in a more timely manner is adopted until the validity period of the second reference color gamut data expires. If the difference value is within the threshold, the change in the device status is small, and the reliability of the first measured wide color gamut data can be considered to remain high, so density correction using the first measured wide color gamut data (measurement condition 1) is adopted until the expiration date of the second reference color gamut data. After the expiration date of the second reference color gamut data, the control is the same as above.

In this embodiment, the control to evaluate changes in image formation conditions is performed outside the valid period of the image formation conditions actually measured in the wide color gamut print mode, but it is not limited to this and may be performed within the valid period.

In addition, the density conditions of the normal print mode that are valid at that time are associated with the wide color gamut density correction, but the following may also be done. That is, the density conditions of the normal print mode (density conditions obtained by the second normal image formation condition correction in FIG. 11) that are valid during the period in which the density conditions in the wide color gamut print mode are valid may also be associated. When the first measured wide color gamut data (actual condition 1) has expired and the second reference color gamut data (original data of predicted condition 2) that was set at the time of the expiration has been updated to the third reference color gamut data, the change in the reference color gamut data before and after the update is observed. In other words, when the difference value between the second reference color gamut data and the third reference color gamut data exceeds a predetermined threshold value, the density correction is adopted using the third predicted wide color gamut data (predicted condition 3) obtained based on the third reference color gamut data that reflects the current device status in a more timely manner. If the difference value is within the threshold, the change in the device status is small, and the reliability of the first measured wide color gamut data can be considered to remain high, so density correction using the first measured wide color gamut data (measurement condition 1) is adopted.

In the above embodiment, a configuration in which a detection toner image is formed on an intermediate transfer belt (intermediate transfer body) as a transferee and various corrections are performed is exemplified, but the present invention is not limited to the above configuration of an image forming device to which it is applicable. For example, in a device configuration in which a toner image is directly transferred from a photosensitive drum to a recording material, the recording material or a conveying belt as a conveying body that conveys the recording material corresponds to the transferee. In such a configuration, a transfer means having a configuration similar to the above-mentioned primary transfer roller and primary transfer bias power supply is provided, and the toner image is transferred from the photosensitive drum to the recording material or the conveying belt by the transfer means.

3...photosensitive drum, 4...developing roller, 80...intermediate transfer belt, 201, 202...positional deviation correction/density correction sensor, 301...controller, 302...engine control unit, 311...CPU, 312...image processing GA, 313...image control unit, 317...RIP unit, 318...color conversion unit, γ319...correction unit, 320...halftoning unit

Claims (8)

An image forming apparatus that forms a toner image as an output image on a recording material based on input image data,
An image carrier;
a developer carrier for developing the electrostatic image formed on the image carrier with toner;
an intermediate transfer member onto which the toner image formed on the image carrier is transferred;
a transfer means for transferring the toner image from the intermediate transfer body to the recording material;
a control unit capable of executing a normal mode and a wide color gamut mode in which the color gamut of the image formed on the recording material is expanded to a larger value than that in the normal mode;
a positional deviation correction unit that corrects input position information included in the input image data to output position information used for forming the toner image so that the position of the toner image formed on the recording material is a predetermined position;
a density correction unit that corrects input density information included in the input image data to output density information used for forming the toner image in accordance with predetermined density condition data that defines a relationship between the density of the input image and the density of the output image, so that the density of the toner image formed on the recording material becomes a predetermined density;
Equipped with
In the normal mode, a first correction operation can be executed by the position deviation correction means and the density correction means to correct the input position information and the first input density information to the output position information and the first output density information,
In the image forming apparatus, a second correction operation can be executed in which, in the wide color gamut mode, the density corrector corrects second input density information in the wide color gamut mode to second output density information,
An image forming apparatus characterized in that image formation is performed in the wide color gamut mode based on the output position information obtained by the first correction operation performed in the normal mode and the second output density information obtained by the second correction operation performed in the wide color gamut mode. An image forming apparatus that forms a toner image as an output image on a recording material based on input image data,
An image carrier;
a developer carrier for developing the electrostatic image formed on the image carrier with toner;
a transfer unit that transfers the toner image formed on the image carrier onto the recording material;
a control unit capable of executing a normal mode and a wide color gamut mode in which the color gamut of the image formed on the recording material is expanded to a larger value than that in the normal mode;
a positional deviation correction unit that corrects input position information included in the input image data to output position information used for forming the toner image so that the position of the toner image formed on the recording material is a predetermined position;
a density correction unit that corrects input density information included in the input image data to output density information used for forming the toner image in accordance with predetermined density condition data that defines a relationship between the density of the input image and the density of the output image, so that the density of the toner image formed on the recording material becomes a predetermined density;
Equipped with
In the normal mode, a first correction operation can be executed by the position deviation correction means and the density correction means to correct the input position information and the first input density information to the output position information and the first output density information,
In the image forming apparatus, a second correction operation can be executed in which, in the wide color gamut mode, the density corrector corrects second input density information in the wide color gamut mode to second output density information,
An image forming apparatus characterized in that image formation is performed in the wide color gamut mode based on the output position information obtained by the first correction operation performed in the normal mode and the second output density information obtained by the second correction operation performed in the wide color gamut mode. The image forming apparatus according to claim 2, further comprising a conveyor belt for conveying the recording material. The image forming apparatus according to any one of claims 1 to 3, characterized in that if the first correction operation is performed in the normal mode before the expiration date of the wide color gamut mode, actual measurement conditions based on the second output density information obtained by the second correction operation in the wide color gamut mode are used in image formation in the wide color gamut mode. The image forming apparatus according to any one of claims 1 to 3, characterized in that when the first correction operation is performed in the normal mode after the expiration date of the wide color gamut mode, in forming an image in the wide color gamut mode, either the actual measurement conditions based on the second output density information obtained by the second correction operation in the wide color gamut mode or the predicted conditions predicted from the first output density information obtained by the first correction operation in the normal mode are used. The image forming apparatus according to claim 5, wherein, based on a result of comparing a first density condition data set before the first correction operation is performed in the normal mode with a second density condition data set after the first correction operation is performed, either the actual measurement condition or the predicted condition is used in image formation in the wide color gamut mode. a driving means for driving the image carrier and the developer carrier to rotate at different peripheral speeds,
the normal mode is a mode in which a peripheral speed ratio of the developer carrier to the image carrier is set to a first peripheral speed ratio, and the electrostatic image is developed with the toner,
6. An image forming apparatus according to claim 1, wherein the wide color gamut mode is a mode in which a color gamut of an image formed on the recording material is expanded more than that in the normal mode by setting a circumferential speed ratio between the image carrier and the developer carrier to a second circumferential speed ratio that is greater than the first circumferential speed ratio in the normal mode. a charging member for charging the surface of the image bearing member;
an exposure unit that exposes the surface of the image carrier charged by the charging member to form an electrostatic image;
a charging voltage application unit that applies a charging voltage to the charging member;
a developing voltage applying section that applies a developing voltage to the developer carrying member,
7. The image forming apparatus according to claim 1, wherein in the wide color gamut mode, a potential difference between the surface of the image carrier exposed by the exposure unit and the developing voltage is made larger than that in the normal mode.

Images