JP2003186350A - Image forming apparatus and method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately measure an image density of a toner image transferred to a transfer medium in an image forming apparatus and an image forming method for transferring the toner image formed on a photoconductor to the transfer medium as the transfer medium such as a transfer belt, a transfer drum, etc., is driven to rotate. <P>SOLUTION: Before a patch image is transferred to an intermediate transfer belt, a sampling data for correction referred to a vertical synchronization signal Vsync is sampled and an eccentric component E (x) and a period profile F(x) as correction information are found based on the sampling data. After the patch image is transferred to the intermediate transfer belt, a sampling data DD(x) for measurement referred to the vertical synchronization signal Vsync is sampled, the eccentric component E(x) and the period profile F(x) are subtracted from the sampling data DD(x), a correction value C(x) is found, and the image density of the patch image is found based on the correction value C(x). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and an image forming method for transferring a toner image formed on a photoconductor onto a transfer medium while rotating a transfer medium such as a transfer belt or a transfer drum. In particular, the present invention relates to a technique for measuring the image density of a toner image formed on a transfer medium with high accuracy.

[0002]

2. Description of the Related Art In electrophotographic image forming apparatuses such as printers, copying machines and facsimile machines, there are some which transfer a toner image formed on a photosensitive member onto a transfer medium such as a transfer belt or a transfer drum. For example, Japanese Patent Laid-Open No. 11-2
In the apparatus described in Japanese Patent No. 58872, four process units are arranged along a transfer belt that is stretched around two rollers. Each process unit forms a latent image on the photoconductor and develops the latent image with toner to form a toner image. The toner images formed by these process units have different toner colors (yellow, cyan, magenta, and black), and the toner images are transferred to the transfer belt so as to overlap each other. In this way, a color image is formed on the transfer belt.

Further, in this apparatus, in order to adjust the image density of the toner image and form an image of stable density, a toner image (patch image) of a predetermined pattern is formed on the transfer belt, and the density is set to the density. Measuring with a sensor. This density sensor includes a light emitting element that irradiates the transfer belt with light and a light receiving element that receives the light reflected from the transfer belt, and calculates the amount of toner adhering to the transfer belt based on the output from the light receiving element. Therefore, the image density of the toner image is measured.

Based on the image density of the patch image thus measured, density control factors that affect the image density such as the developing bias, the charging bias and the exposure energy are controlled to stabilize the image density.

[0005]

By the way, when the image density of the toner image formed on the transfer medium such as the transfer belt is measured by the density sensor as described above, the measurement result is simply attached to the transfer medium. The measurement result may vary depending on not only the toner amount but also the surface condition of the transfer medium, such as the reflectance and the surface roughness.
For example, the surface color of the transfer medium changes with the increase in the cumulative number of prints of the image forming apparatus, and as a result, even if the toner adhesion amount is the same, the output from the density sensor changes according to the change of the surface color. As a result, accurate concentration measurement becomes difficult. Further, when the surface condition of the transfer medium is non-uniform, the influence of the surface condition cannot be ignored.

Further, in the conventional apparatus using the transfer belt as the transfer medium, since the density sensor is arranged at a position relatively distant from the roller, there is the following problem. First, at the position away from the roller as described above, the transfer belt flaps in a direction substantially orthogonal to the belt moving direction, and the distance from the density sensor to the transfer belt (hereinafter referred to as “sensing distance”) is random. Or, it fluctuates unstablely, and the sensor output becomes unstable due to the distance fluctuation. As a result, accurate measurement is difficult.

Further, the transfer belt is stretched over a plurality of rollers, and some rollers are eccentric to some extent. Therefore, the transfer belt further flaps due to the rotation of the eccentric roller, which makes the sensor output unstable and makes accurate measurement difficult.

Further, the thickness of the transfer belt is not uniform over the entire circumference of the transfer belt, and thickness unevenness may be present, which is one of the factors of variation in the sensing distance.

The present invention has been made in view of the above problems, and an image forming apparatus for transferring a toner image formed on a photoconductor to a transfer medium such as a transfer belt or a transfer drum while rotating the transfer medium. Another object of the present invention is to accurately measure the image density of the toner image transferred to the transfer medium in the image forming method.

[0010]

SUMMARY OF THE INVENTION The present invention provides an image forming apparatus and an image forming method for transferring a toner image formed on a photoconductor onto a transfer medium while rotating the transfer medium. To achieve this, we have the following structure. That is, an image forming apparatus according to the present invention has a light emitting element and a light receiving element, irradiates a rotating transfer medium with light from the light emitting element, and receives light from the transfer medium with the light receiving element and receives the light. A density sensor that outputs a signal according to the amount and a control unit that determines the image density of the toner image formed on the transfer medium based on the output from the density sensor are provided, and the control unit transfers the toner image to the transfer medium. Previously, the output signal from the light receiving element was sampled with reference to the synchronization signal output in relation to the rotational drive of the transfer medium to obtain the correction sampling output, and information on the transfer medium was obtained based on this correction sampling output. This is obtained as correction information, and when obtaining the image density of the toner image on the transfer medium, the output signal from the light receiving element is sampled based on the synchronization signal. Grayed and with obtaining the measurement sampling output, the measurement sampling output is corrected by the correction information, and configured to determine the image density of the toner image based on the correction value.

The image forming method according to the present invention is
Before transferring the toner image to the transfer medium, the rotating transfer medium is irradiated with light based on the synchronization signal output in association with the rotational drive of the transfer medium, and the amount of light from the transfer medium is changed. The step of obtaining the correction sampling output by sampling the corresponding signal, and obtaining the information about the transfer medium as the correction information based on the correction sampling output, and the synchronization signal for obtaining the image density of the toner image on the transfer medium. As a reference, the step of irradiating the rotating transfer medium with light and sampling a signal according to the light amount of the light from the transfer medium to obtain a measurement sampling output, and correcting the measurement sampling output with the correction information And a step of obtaining the image density of the toner image based on the correction value.

In the invention thus constructed, the information regarding the transfer medium is obtained as the correction information based on the correction sampling output before the image density of the toner image on the transfer medium is obtained. Then, the measurement sampling output obtained for obtaining the image density of the toner image is not used as it is to obtain the image density, but the measurement sampling output is corrected by the correction information, thereby affecting the transfer medium ( For example, the surface state of the transfer medium, thickness unevenness, etc.) are canceled and a correction value reflecting only the image density of the toner image is obtained. Therefore, by obtaining the image density of the toner image based on this correction value, the image density of the toner image can be measured with high accuracy, and the image can be formed with a stable density based on the measurement result. .

Further, both the correction sampling output and the measurement sampling output are obtained with reference to the synchronization signal output in association with the rotational driving of the transfer medium.
Since both are synchronized, it is possible to easily and satisfactorily correct the measurement sampling output based on the correction information.

By the way, when the transfer medium is a transfer belt which is stretched over a plurality of rollers, the light emitting element is arranged so as to face one of the plurality of rollers so as to sandwich the transfer belt, and transfer is performed. It is desirable to irradiate the light on the area wound around the sensor facing roller in the surface area of the belt. This is because by doing so, unstable fluttering of the transfer medium (transfer belt) in the direction substantially orthogonal to the belt movement direction is suppressed, and therefore the distance (sensing distance) between the density sensor and the transfer medium fluctuates. Is effectively suppressed. In addition,
The sensor facing roller is fixed at a predetermined position,
It is desirable to select a roller that is rotatable at the predetermined position. This is because, when the density sensor is arranged so as to face the roller rotatably fixed at a predetermined position, the distance between the roller and the density sensor is constant.

When the transfer medium is composed of the transfer belt as described above, the eccentricity component of the roller is obtained as the correction information based on the correction sampling output.
Further, it is useful to remove the eccentric component from the correction sampling output and obtain the periodic profile indicating the surface state of the transfer belt as the correction information. That is, since the eccentricity component becomes a variation component of the sensing distance, this eccentricity component is accurately obtained as information (correction information) related to the transfer belt, the measurement sampling output is corrected by the eccentricity component, and the correction value is obtained. If the image density of the toner image is obtained based on this, the image density of the toner image can be accurately measured regardless of the variation in the sensing distance.

Further, the periodic profile of the transfer belt can be obtained by subtracting the eccentric component from the correction sampling output. Since this periodic profile reflects information (correction information) on the transfer belt such as the surface condition of the transfer medium and uneven belt thickness, the sampling output for measurement is used when determining the image density of the toner image on the transfer belt. If the correction is made by the periodic profile and the image density of the toner image is obtained based on the correction value, the measurement accuracy of the toner amount can be further improved.

The medium cycle required for the transfer medium to make one round is an integral multiple of the roller cycle required for the sensor facing roller to make one round, and is also an integral multiple of the sampling interval for sampling the output signal from the light receiving element. With this configuration, the correction information and the measurement sampling output are completely synchronized, and the correction of the measurement sampling output based on the correction information can be performed easily and satisfactorily.

On the other hand, when the medium cycle is a non-integer multiple of the sampling interval or a non-integer multiple of the roller cycle, a deviation occurs between the eccentric component and the measurement sampling output. However, the eccentricity component may be corrected according to the amount of deviation. Specifically, in the former case (a non-integer multiple of the sampling interval), the eccentric component is determined according to the amount of deviation between the sampling timing when the correction sampling output is obtained and the sampling timing when the measurement sampling output is obtained. Is corrected, and the corrected eccentricity component may be used as correction information. In the latter case (a non-integer multiple of the roller cycle), the eccentricity component is corrected according to the difference between the peripheral length of the transfer belt and the peripheral length of the sensor facing roller, and the corrected eccentricity component is used as correction information. Good.

[0019]

FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. 2 is shown in FIG.
3 is a block diagram showing an electrical configuration of the image forming apparatus of FIG.
This image forming apparatus is provided with black (K), cyan (C),
Four color toners of magenta (M) and yellow (Y) are overlaid to form a full color image, or black (K)
This is a device that forms a monochrome image using only the toner of the above. In this image forming apparatus, when an image signal is given to the main controller 11 of the control unit 1 from an external device such as a host computer, the main controller 1
The engine controller 12 controls each part of the engine part EG in response to a command from the control unit 1 to form an image corresponding to the image signal on the sheet S.

In the engine section EG, the photoconductor 2 is rotatably provided in the direction of arrow D1 in the figure. Further, a charging unit 3 as a charging unit, a rotary developing unit 4 as a developing unit, and a cleaning unit 5 are arranged around the photoconductor 2 along the rotation direction D1 thereof. The charging unit 3 is the charging bias generator 1
A charging bias is applied from 21 to uniformly charge the outer peripheral surface of the photoconductor 2.

Then, the light beam L is emitted from the exposure unit 6 toward the outer peripheral surface of the photoconductor 2 charged by the charging unit 3. As shown in FIG. 2, the exposure unit 6 is electrically connected to the image signal switching unit 122, and the exposure power control unit 123 exposes the image signal according to the image signal given through the image signal switching unit 122. The unit 6 is controlled to scan and expose the photoconductor 2 with the light beam L to form an electrostatic latent image corresponding to an image signal on the photoconductor 2.
For example, based on a command from the CPU 124 of the engine controller 12, when the image signal switching unit 122 is in conduction with the patch creation module 125, the patch image signal output from the patch creation module 125 is sent to the exposure power control unit 123. Given a patch latent image is formed.
On the other hand, the image signal switching unit 122 is the main controller 11
When conducting with the CPU 111, the light beam L is scanned and exposed on the photoconductor 2 according to the image signal given from the external device such as the host computer via the interface 112, and the light beam L corresponding to the image signal is exposed. An electrostatic latent image is formed on the photoconductor 2.

The electrostatic latent image thus formed is developed with toner by the developing unit 4. That is, in this embodiment, the developing unit 4 is the developing unit 4 for black.
K, cyan developing unit 4C, magenta developing unit 4M,
Further, a yellow developing device 4Y is provided rotatably around the axis. Then, these developing devices 4K, 4C, 4
M and 4Y are rotationally positioned, and are selectively abutted on or separated from the photoconductor 2,
A developing bias is applied by the developing bias generator 126 to apply the toner of the selected color to the surface of the photoconductor 2. As a result, the electrostatic latent image on the photoconductor 2 is visualized in the selected toner color.

The toner image developed by the developing unit 4 as described above is transferred to the transfer unit 7 in the primary transfer region TR1.
Is primarily transferred onto the intermediate transfer belt 71. As shown in FIG. 1, the transfer unit 7 includes an intermediate transfer belt 71 that is wound around a plurality of rollers 72 to 75, and a drive unit (not shown) that rotates the roller 73 to rotate the intermediate transfer belt 71. It has and. When the color image is transferred to the sheet S, the toner images of the respective colors formed on the photoconductor 2 are superposed on the intermediate transfer belt 71 to form a color image, and a predetermined secondary transfer region TR is formed.
In 2, the color image is secondarily transferred onto the sheet S taken out from the cassette 8. Further, the sheet S on which the color image is thus formed is conveyed to the discharge tray portion provided on the upper surface of the apparatus main body via the fixing unit 9.

As shown in FIG. 1, a cleaning unit 76, a density sensor 60 and a vertical synchronization sensor 77 are arranged near the roller 75. Of these, the cleaning unit 76 can be moved toward and away from the roller 75 by a cleaner driving unit (not shown). Then, the blade of the cleaning unit 76 contacts the surface of the intermediate transfer belt 71 stretched over the roller 75 while moving to the roller 75 side, and remains attached to the outer peripheral surface of the intermediate transfer belt 71 after the secondary transfer. Remove toner. Further, the vertical synchronization sensor 77 uses the intermediate transfer belt 71.
Is a sensor for detecting the reference position, and functions as a vertical synchronization sensor for obtaining a synchronization signal output in association with the rotational driving of the intermediate transfer belt 71, that is, a vertical synchronization signal Vsync. Further, the density sensor 60 is provided so as to face the surface of the intermediate transfer belt 71, and is configured as described below to measure the optical density of the patch image formed on the outer peripheral surface of the intermediate transfer belt 71.

In FIG. 2, reference numeral 113 indicates an interface 11 from an external device such as a host computer.
2 is an image memory provided in the main controller 11 for storing an image given via
7 is a calculation program executed by the CPU 124,
Is a memory (storing means) for storing the calculation result in, the control data for controlling the engine EG, and the like.

FIG. 3 is a diagram showing the structure of the density sensor.
The density sensor 60 includes a winding area 71 a wound around the roller 75 in the surface area of the intermediate transfer belt 71.
It has a light emitting element 601 such as an LED for irradiating light to the inside. Further, the density sensor 60 is provided with a polarization beam splitter 603, an irradiation light amount monitor light-receiving unit 604, and an irradiation light amount adjustment unit 605 for adjusting the irradiation light amount of the irradiation light.

The polarization beam splitter 603, as shown in the figure, has a light emitting element 601 and an intermediate transfer belt 71.
And p-polarized light having a polarization direction parallel to the incident surface of the irradiation light on the intermediate transfer belt 71,
It is divided into s-polarized light having a vertical polarization direction. Then, while the p-polarized light is incident on the intermediate transfer belt 71 as it is, the s-polarized light is extracted from the polarization beam splitter 603 and then incident on the light receiving unit 604 for monitoring the irradiation light amount, and the irradiation light amount is changed from the light receiving unit 604. The proportional signal is the irradiation light amount adjustment unit 605.
Is output to.

The irradiation light amount adjusting unit 605 is provided with a signal from the light receiving unit 604 and the engine controller 1.
The light emitting element 601 is feedback-controlled based on the light amount control signal Slc from the second CPU 124.
Then, the irradiation light amount applied to the intermediate transfer belt 71 is adjusted to a value corresponding to the light amount control signal Slc. As described above, in this embodiment, it is possible to appropriately change and adjust the irradiation light amount in a wide range.

Further, in this embodiment, the input offset voltage 641 is applied to the output side of the light receiving element 642 provided in the irradiation light amount monitor light receiving unit 604, so long as the light amount control signal Slc does not exceed a certain signal level. The light emitting element 601 is configured to be maintained in the off state. The specific electrical configuration is as shown in FIG.
FIG. 4 is a diagram showing an electrical configuration of the light receiving unit 604 adopted in the density sensor 60 of FIG. In the light receiving unit 604, the light receiving element P such as a photodiode is used.
The anode terminal of S is connected to the non-inverting input terminal of the operational amplifier OP that constitutes the current-voltage (I / V) conversion circuit, and is also connected to the ground potential via the offset voltage 641. The cathode terminal of the light receiving element PS is connected to the inverting input terminal of the operational amplifier OP, and is also connected to the output terminal of the operational amplifier OP via the resistor R. Therefore, light is incident on the light receiving element PS, and the photocurrent i
, The output voltage V0 from the output terminal of the operational amplifier OP becomes V0 = i · R + Voff (where Voff is an offset voltage value),
A signal corresponding to the amount of reflected light is output from the light receiving unit 604. The reason for such a configuration will be described below.

When the input offset voltage 641 is not applied, the light quantity characteristic shown by the broken line in FIG. 5 is exhibited. In other words, when the light amount control signal Slc (0) is given from the CPU 124 to the irradiation light amount adjusting unit 605, the light emitting element 601 is turned off, and when the signal level of the light amount control signal Slc is increased, the light emitting element 601 is turned on and the intermediate transfer belt is turned on. The amount of light irradiated onto 71 also increases almost in proportion to the signal level. However, the light amount characteristic may be parallel-shifted like the one-dot chain line and two-dot chain line shown in FIG. 5 due to the influence of the ambient temperature and the configuration of the irradiation light amount adjustment unit 605. If so, the CPU 124
The light-emitting element 601 may be turned on even though the turn-off instruction, that is, the light amount control signal Slc (0) is given from the.

On the other hand, as in the present embodiment, when the input offset voltage 641 is applied and preliminarily shifted to the right hand side in the figure to provide the dead zone (signal levels Slc (0) to Slc (1)). In (solid line in the figure), a light-off command, that is, a light amount control signal Slc (0) is given from the CPU 124, so that the light-emitting element 601 can be surely turned off, and malfunction of the device can be prevented in advance. .

On the other hand, the light amount control signal Slc exceeding the signal level Slc (1) is transmitted from the CPU 124 to the irradiation light amount adjusting unit 6
When the light is applied to the light source 05, the light emitting element 601 is turned on and the intermediate transfer belt 71 is irradiated with p-polarized light as irradiation light. Then, the p-polarized light is reflected by the intermediate transfer belt 71, and the reflected light amount detection unit 607 detects the p-polarized light amount and the s-polarized light amount of the reflected light components, and the CPU 124 outputs a signal corresponding to each light amount. Is output.

This reflected light amount detection unit 607 is shown in FIG.
, A polarization beam splitter 671 arranged on the optical path of the reflected light, and a polarization beam splitter 671
The light receiving unit 670p which receives the p-polarized light passing through and outputs the signal corresponding to the light amount of the p-polarized light, and the s-polarized light split by the polarization beam splitter 671 are received, and the signal corresponding to the light amount of the s-polarized light is received. Output light receiving unit 6
It is equipped with 70s. In this light receiving unit 670p, the light receiving element 672p has a polarization beam splitter 671.
From the light receiving element 672p is amplified by the amplifier circuit 673p, and the amplified signal is used as a signal corresponding to the light amount of the p polarized light.
It outputs from p. The light receiving unit 670s has a light receiving element 672s and an amplifier circuit 673s, like the light receiving unit 670p. Therefore, the amounts of two different component lights (p-polarized light and s-polarized light) of the reflected light components can be independently obtained.

Further, in this embodiment, the light receiving element 672 is used.
output offset voltage 674p, on the output side of p, 672s,
674s are applied respectively, and the amplifier circuit 673
The output voltages Vp and Vs of the signals given to the CPU 124 from p and 673s are offset to the plus side as shown in FIG. The specific electrical configuration of each of the light receiving units 670p and 70s is the same as that of the light receiving unit 604, and therefore the illustration and description thereof will be omitted here. Also in the light receiving units 670p and 670s configured as above,
Similar to the light receiving unit 604, each output voltage Vp, Vs has a value of zero or more even when the reflected light amount is zero, and the output voltage Vp, Vs is proportional to the increase of the reflected light amount.
Also increases. In this way, the output offset voltage 674p,
By applying 674 s, the influence of the dead zone in FIG. 5 can be reliably eliminated, and an output voltage according to the amount of reflected light can be output.

The signals of these output voltages Vp and Vs are input to the CPU 124 via an A / D conversion circuit (not shown). And at the right time,
For example, optimization processing of density control factors that affect image density such as development bias, charging bias and exposure energy at timings such as when the apparatus power is turned on and when the cumulative count value of the number of printed sheets reaches a predetermined value. By doing so, the image density is stabilized. Hereinafter, the optimization process of the concentration control factor will be described in detail with reference to FIGS. 7 to 11.

FIG. 7 is a flow chart showing the density control factor optimizing process executed in the image forming apparatus of FIG. In this image forming apparatus, C at the above timing
The PU 124 controls each part of the apparatus according to a program stored in advance in the memory 127 to determine the optimum value of the concentration control factor. In addition, here, the intermediate transfer belt 7
The circumference of 1 is an integral multiple of the circumference of the sensor facing roller 75, and the medium cycle P71 required for the intermediate transfer belt 71 to make one round is the roller cycle P75 required for the sensor facing roller 75 to make one round. Is an integer multiple (“5” times as shown in FIG. 9 later), and the optimization processing is performed on the assumption that the CPU 124 is an integer multiple of the sampling interval for sampling the output voltages Vp and Vs from the density sensor 60. Will be described.

First, prior to transferring the patch image to the intermediate transfer belt 71, steps S1 to S3 are executed to obtain information on the intermediate transfer belt 71 (roller 7 which will be described later).
The eccentricity component of 5 and the periodic profile) are obtained as correction information. That is, in the first step S1, the dark output voltages Vp0 and Vs0 are detected and they are stored in the memory 127.
Remember. Here, "dark output voltage Vp0, Vs0" means
A light amount control signal Slc (0) corresponding to a turn-off command is output to the irradiation light amount adjusting unit 605 to turn off the light emitting element 601.
It means the output voltage that indicates the amount of p- and s-polarized light in this off state. Then, as will be described later, the output voltage V
By subtracting the output voltages Vp0 and Vs0 from p and Vs, the adverse effects of the dark output voltages Vp0 and Vs0 can be eliminated, and more accurate measurement can be performed.

Next, a signal Slc (2) having a signal level exceeding the dead zone is set as the light amount control signal Slc, and this light amount control signal Slc (2) is supplied to the irradiation light amount adjusting unit 605 to turn on the light emitting element 601 ( Step S2). Then,
The light from the light emitting element 601 is irradiated onto the intermediate transfer belt 71, and p of the light reflected by the intermediate transfer belt 71 is emitted.
The amount of polarized light and the amount of s-polarized light are reflected light amount detection unit 607.
Output voltage V corresponding to each received light amount detected by
p and Vs are input to the CPU 124. And CPU1
24 calculates the correction information based on the output voltages Vp and Vs, and stores it in the memory 127 (step S3).

FIG. 8 is a flowchart showing the correction information calculation process, and FIG. 9 is a diagram showing the correction information calculation process. In this correction information calculation process (step S3), when a predetermined time ΔT has elapsed since the vertical synchronization signal Vsync was output (step S31), sampling of the output voltages Vp and Vs is started (step S32). Then, the output voltage Vp0 when the light is turned off is subtracted from the output voltage Vp at each sampling position x, and this light amount signal SigP (= Vp-Vp
0) and subtracting the output voltage Vs0 at the time of extinction from the output voltage Vs at each sampling position x to obtain the light amount signal SigS (= Vs-Vs0), and then the light amount signal ratio (= SigP / SigS ) At each sampling position x
It is stored in the memory 127 as the sampling data D (x) in step S33. The sampling data D (x) obtained for the intermediate transfer belt 71 before the patch image is thus transferred corresponds to the “correction sampling output” of the present invention.

In this apparatus, since the peripheral length of the intermediate transfer belt 71 is 5 times the peripheral length of the sensor facing roller 75 as described above, the sampling data D (x) obtained as described above is used. When n consecutive sampling data, for example, 60 sampling data are taken out, a component for one cycle (roller cycle P75) of the sensor facing roller 75 is included in these 60 sampling data. Focusing on the eccentricity component of the roller 75, it is not necessary to consider the eccentricity component by taking the average value of one cycle of the roller 75. This is because the sensor facing roller 75
Includes a case where the sensing distance becomes far and a case where the sensing distance becomes close due to the eccentricity, and each effect cancels each other out by taking the average value. This is because they can be considered almost equivalent.

Therefore, for example, 60 (= P71 / P75) sections are defined by defining 60 continuous sampling data from the sampling data D (x) shown in FIG. 9 as one section, and sampling positions forming each section. x (x = 30,
The average value AV (x) for one round of the roller 75 centering around 31 ,. That is, AV (30) = (D (0) + ... + D (30) + ... + D (59)) / 60 AV (31) = (D (1) + ... + D (31) + ... + D (60)) / 60 AV (32) = (D (2) + ... + D (32) + ... + D (61)) / 60 ... AV (210) = (D (180) + ... + D (210) + ... + D (239) ) /
60 is required. In the above equation, sampling positions “0” to “5
The center of 60 pieces of sampling data of "9" is set to 30, but the center is strictly between "29" and "30", and the above equation is: AV (29) = (D (0) + ... + D (30 ) + ... + D (59)) / 60 (same as below).

The average value AV (x) thus obtained
Is the eccentric component of the roller 75 canceled,
The eccentricity component E (x) of the roller 75 at each sampling position x can be obtained by subtracting the average value AV (x) from the sampling data D (x). That is, the eccentricity component E (x) of the roller 75 can be obtained by E (x) = D (x) -AV (x). However, here, the eccentricity components of five rounds of the roller 75 during one round of the intermediate transfer belt 71 are obtained.

Here, each section is one of the rollers 75.
Since it corresponds to the circumference, the eccentricity component E (x) should show the same value if the phase is the same. Therefore, the average value Eav (a) of the eccentricity components in each phase in the five sections is expressed by the following equation: Eav (a) = {D (30 + a) −AV (30 + a)} + {D (90+ a) -AV (90 + a)} + {D (120 + a) -AV (120 + a)} / 3 (1) (where a = 0, 1, ... 59),
The data is stored in the memory 127 (step S34). As described above, in this embodiment, a plurality of eccentricity components are obtained while the intermediate transfer belt 71 makes one revolution, and the average value thereof is obtained. Therefore, the eccentricity component E (x) that is the correction information is obtained with high accuracy. It is possible (Fig. 9). Of course, the intermediate transfer belt 71
The number of rotations of the roller 75 per one round is not limited to "5", and if the number of rotations is two or more, the eccentricity component of the roller 75 can be obtained in the same manner as described above.

Thus, when the eccentricity component Eav (a) of the roller 75 at each phase is obtained according to the equation (1), the eccentricity component is subtracted from the sampling data D (x) to obtain the surface condition of the intermediate transfer belt 71. A periodic profile F (x) that reflects is obtained (FIG. 9). That is, the periodic profile F (x) is F (0) = D (0) -Eav (30) F (1) = D (1) -Eav (31) ... F (29) = D (29) -Eav (59) F (30) = D (30) −Eav (0) F (31) = D (31) −Eav (1). Then, the periodic profile F (x) that is the correction information
Is also stored in the memory 127 (step S3).
5).

When the correction information is obtained in this way, the process proceeds to step S4 in FIG. 7 to perform the patch sensing process. Figure 1
0 is a flowchart showing the patch sensing process, and FIG. 11 is a diagram showing the patch sensing process. In this patch sensing process (step S4), while changing the density control factor in multiple steps, a patch image corresponding to the patch image signal output from the patch creation module 125 is formed on the photoconductor 21, and the patch image is formed. The image is transferred onto the intermediate transfer belt 71 (step S41).

Then, the correction information calculation process (step S
Similar to the case of 3), after a predetermined time ΔT has passed since the vertical synchronization signal Vsync was output (step S42),
Sampling of the output voltages Vp and Vs is started (step S43). Then, the output voltage Vp0 when the light is turned off is subtracted from the output voltage Vp at each sampling position x to obtain the light amount signal SigP (= Vp-Vp0), and the output voltage Vs when the light is turned off is output from the output voltage Vs at each sampling position x. Vs
After subtracting 0, the light quantity signal SigS (= Vs-Vs0) is obtained, and then the light quantity signal ratio (= SigP / SigS) is stored in the memory 127 as sampling data DD (x) at each sampling position x ( Step S44). The intermediate transfer belt 71 after the patch image is transferred in this way
The sampling data DD (x) obtained with respect to "corresponding to" corresponds to the "measurement sampling output" of the present invention.

In the next step S45, the correction information previously obtained in step S3 from the sampling data DD (x), that is, the eccentric component E (x) and the periodic profile F
By subtracting (x), sampling data DD
(x) to the eccentric component of the roller 75 and the intermediate transfer belt 7
The influence of the surface condition of 1 is removed, and the correction value C (x) that reflects only the image density of the patch image is obtained (step S
45).

When the patch sensing process (step S4) is completed in this way, the image density of each patch image is calculated based on the correction value C (x) (step S5), and then the optimum value of the density control factor is calculated based on these image densities. Is determined (step S6).

As described above, according to this embodiment, the surface area of the intermediate transfer belt wound around the roller 75, that is, the winding area 71a is irradiated with light and reflected by the winding area 71a. The light is received by the light receiving element 672.
The image density is measured on the basis of the signal received at p, 672s and output from the density sensor 60. In this winding area 71a, there is no unstable fluttering of the intermediate transfer belt 71 in a direction substantially orthogonal to the belt moving direction, and fluctuations in the distance (sensing distance) between the density sensor 60 and the intermediate transfer belt 71 are eccentric to the roller. It is possible to suppress only the variation caused by the above, and it is possible to improve the measurement accuracy.

Further, according to this embodiment, the roller 75
The image density of the patch image is calculated based on the correction value C (x) removed from the sampling data DD (x) due to the influence of the eccentricity component of the roller and the surface state of the intermediate transfer belt 71. The image density of each patch image can be measured with high accuracy without being affected by the eccentric component and the surface condition of the intermediate transfer belt 71. Moreover, since the density control factor is optimized based on the image density, it is possible to form an image with stable density.

Further, sampling outputs D (x) and DD (x)
Are acquired with reference to the vertical synchronization signal Vsync output in association with the rotational drive of the intermediate transfer belt 71, both are in synchronization, and the measurement sampling output based on the correction information can be easily corrected. Moreover, it becomes possible to perform the operation satisfactorily. Further, particularly in this embodiment, the medium period P
Since 71 is an integral multiple of the roller cycle P75 and an integral multiple of the sampling interval, a phase shift occurs between the rotation cycle of the intermediate transfer belt 71, the rotation cycle of the sensor facing roller 75, and the sampling cycle. Since it does not exist, the influence of the eccentricity component can be corrected by subtracting the eccentricity component E (x) from the sampling data DD (x) as it is.

On the other hand, the following devices, (1) the medium period P71 is a non-integer multiple of the roller period P75 and is also a non-integer multiple of the sampling interval, (2) the medium period P71 is a roller. For an apparatus that is an integer multiple of the cycle P75 and is a non-integer multiple of the sampling interval, and (3) an apparatus that is a non-integer multiple of the roller cycle P75 and the media cycle P71 is an integer multiple of the sampling interval, Intermediate transfer belt 71
, A rotation cycle of the sensor facing roller 75, and a sampling cycle, a phase shift occurs. Therefore, the eccentricity component E (x) is corrected by the phase shift and the corrected eccentricity component is corrected. And it is sufficient.

Here, the device (1) will be described in detail. In this device (1), as shown in FIGS. 12 and 13, since there is a phase shift between the rotation cycle of the intermediate transfer belt 71 and the sampling cycle, the density after the vertical synchronization signal Vsync is output. The timing of sampling the output signal from the sensor 60 may differ between the correction information calculation process (step S3) and the patch sensing process (step S4). That is, in the correction information calculation process (step S3), it is time Δ from the output of the vertical synchronization signal Vsync.
While the sampling is started after T1, the sampling is started in the patch sensing process (step S4) after a time ΔT2 from the output of the vertical synchronizing signal Vsync. Further, since there is a phase shift between the rotation period P71 of the intermediate transfer belt 71 and the rotation period P75 of the sensor facing roller 75, the correction information calculation process (step S3) and the patch sensing process (step S4) are performed. Therefore, the phase of the sensor facing roller 75 is different. Thus, the device
In the case of (1), two types of shift amounts are inherent.

Therefore, in the case of the device (1), the above two types of shift amounts are obtained based on the rotation cycle of the intermediate transfer belt 71, the rotation cycle of the sensor facing roller 75, and the sampling cycle, and the correction information is obtained. The corrected eccentricity component EE (x) is obtained by shifting the eccentricity component E (x) obtained in the calculation process (step S3) of FIG.
Sampling data DD for measurement using this as correction information
The eccentricity component EE (x) may be subtracted from (x).

The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, the eccentricity components E (x), EE (x) and the periodic profile F (x) are used as the correction information, but the correction information is not limited to these, and the intermediate transfer belt 71 is used. Any information that includes information about For example, the sampling data D (x) obtained in step S3 is directly used as the correction information in the memory 12
7, and the sampling data for measurement DD (x) may be corrected based on this sampling data D (x).

In the above embodiment, the density sensor 60 is arranged facing the roller 75, but the density sensor 60 may be arranged facing the other roller around which the intermediate transfer belt 71 is stretched. You may However, it is desirable to provide the density sensor 60 for a roller that is fixedly arranged in advance with respect to the apparatus main body and is rotatable at the fixed position among the plurality of rollers 72 to 74. This is because, when the density sensor 60 is arranged so as to face a roller rotatably fixed at a predetermined position, the distance between the roller and the density sensor 60 is constant.

Further, in the above embodiment, the light quantity signal ratio (= SigP / SigS) is used as the correction sampling output and the measurement sampling output, but in addition to this, the output voltages Vp, Vs, the light quantity signals SigP, SigS, Light intensity signal sum (= SigP + SigS) and light intensity signal difference (= SigP-Sig)
S) or the like can be used.

Further, in the above embodiment, as shown in FIG. 3, the light emitting element 601 is arranged so that the incident surface (the paper surface in the figure) containing the irradiation light and the reflected light is substantially orthogonal to the rotation axis of the sensor facing roller 75. Although the light receiving elements 672p and 672s are arranged, the arrangement relationship between them is not limited to this. For example, even if the density sensor 60 is configured so that the incident surface is substantially parallel to the roller rotation axis. Good. Also,
If the incident surface and the roller rotation axis are not parallel, not only will the sensing distance fluctuate due to eccentricity of the roller, but also the amount of reflected light will change due to changes in the angle of the roller surface (reflection surface). By making them parallel,
The angle of the reflecting surface can be made more stable. For the same reason, in order to stabilize the angle of the reflecting surface, the entrance surface and the roller rotation axis may be arranged in the same plane.

Further, in the above embodiment, the present invention is applied to the image forming apparatus using the intermediate transfer belt 71 as a transfer medium, but the application target of the present invention is not limited to this. The present invention can also be applied to an image forming apparatus using a transfer drum, and the present invention can be applied to all image forming apparatuses that transfer a toner image formed on a photoconductor onto a transfer medium.

In the above embodiment, the vertical synchronizing signal Vsync output from the vertical synchronizing sensor 77 is used as the synchronizing signal output in association with the rotational drive of the intermediate transfer belt 71. Is not limited to the vertical synchronization signal Vsync, and for example, a signal output in association with the rotational drive of the photoconductor 2 or the intermediate transfer belt 71.
It is possible to use a signal or the like output from a driving unit that rotationally drives.

Further, in the above embodiment, the image forming apparatus is capable of forming a color image using four color toners, but the application of the present invention is not limited to this, and a monochrome image is formed. Of course, the present invention can be applied to an image forming apparatus that forms only an image. The image forming apparatus according to the above embodiment is a printer that forms an image provided from an external device such as a host computer on a copy paper, a transfer paper, a paper, and a sheet S such as an OHP transparent sheet. Can be applied to all electrophotographic image forming apparatuses such as copiers and facsimile machines.

[0062]

As described above, according to the present invention, before the image density of the toner image on the transfer medium is obtained, the information about the transfer medium is obtained as the correction information based on the correction sampling output. Since the measurement sampling output is corrected by the correction information and the image density of the toner image is obtained based on the correction value, the measurement sampling output has an influence on the transfer medium (for example, the surface state of the transfer medium). And thickness unevenness) are removed, and a correction value that reflects only the image density of the toner image can be obtained. Then, by obtaining the image density of the toner image based on this correction value, the image density of the toner image can be measured with high accuracy, and the image can be formed with a stable density based on the measurement result. .

Further, since both the correction sampling output and the measurement sampling output are configured to be acquired on the basis of the synchronization signal output in association with the rotational driving of the transfer medium, they should be synchronized. Therefore, it becomes possible to easily and satisfactorily correct the measurement sampling output based on the correction information.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG.

FIG. 3 is a diagram showing a configuration of a density sensor.

4 is a diagram showing an electrical configuration of a light receiving unit adopted in the concentration sensor of FIG.

5 is a diagram showing a light amount control characteristic in the density sensor of FIG.

6 is a graph showing how the output voltage changes with the amount of reflected light in the density sensor of FIG.

7 is a flowchart showing an optimization process of a density control factor executed in the image forming apparatus of FIG.

FIG. 8 is a flowchart showing a correction information calculation process.

FIG. 9 is a diagram showing a process of calculating correction information.

FIG. 10 is a flowchart showing patch sensing processing.

FIG. 11 is a diagram showing a patch sensing process.

FIG. 12 is a diagram showing a process of calculating correction information.

FIG. 13 is a diagram showing a patch sensing process.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Control unit (control means) 2 ... Photoconductor 12 ... Engine controller (control means) 60 ... Density sensor 71 ... Intermediate transfer belt (transfer medium) 71a ... Wrapping area area 74 ... Sensor facing roller 76 ... Vertical synchronization sensor 124 ... CPU (control means) 127 ... Memory 601 ... Light emitting element 642, 672p, 672s, PS ... Light receiving element D (x) ... Sampling data (correction sampling output) DD (x) ... Sampling data (measurement sampling output) E (x), EE (x) ... Polarization component (correction information) F (x) ... Period profile (correction information) P71 ... Medium cycle P75 ... Roller cycle Vsync ... Vertical sync signal

Continued front page    F term (reference) 2G059 AA01 AA05 BB10 EE02 EE05                       EE13 GG02 GG04 JJ19 JJ22                       KK01 KK03 MM01 MM05 MM09                       MM10 MM14                 2H027 DA09 DE02 DE07 DE10 EB04                       EE02                 2H077 DA05 DA49 DA63 DB03 GA03                       GA13                 2H200 FA02 GA23 GA34 GA47 GB12                       GB25 GB44 HA03 HA12 HB03                       HB12 JA02 JC04 JC09 JC12                       JC20 PB13 PB17 PB39

Claims (8)

[Claims] 1. An image forming apparatus for transferring a toner image formed on a photoconductor onto a transfer medium while rotating the transfer medium, wherein the transfer medium has a light emitting element and a light receiving element and is rotating. And a density sensor that receives light from the transfer medium by the light receiving element and outputs a signal according to the amount of light received, and the transfer medium based on the output from the density sensor. And a control unit for determining the image density of the toner image formed on the transfer medium, wherein the control unit outputs a synchronization signal output in association with rotational driving of the transfer medium before transferring the toner image to the transfer medium. While sampling the output signal from the light receiving element as a reference to obtain a correction sampling output,
Information regarding the transfer medium is obtained as correction information based on the correction sampling output, and when obtaining the image density of the toner image on the transfer medium,
The output signal from the light receiving element is sampled based on the synchronization signal to obtain a sampling output for measurement, the sampling output for measurement is corrected by the correction information, and the image density of the toner image is calculated based on the correction value. An image forming apparatus characterized in that it is required. 2. The transfer medium is a transfer belt stretched over a plurality of rollers, and the light emitting element faces one of the plurality of rollers so as to sandwich the transfer belt. The image forming apparatus according to claim 1, wherein the image forming apparatus is arranged and irradiates light on a winding area wound around the sensor facing roller in a surface area of the transfer belt. 3. The image forming apparatus according to claim 2, wherein the control unit obtains an eccentric component of the roller as the correction information based on the correction sampling output. 4. The image forming apparatus according to claim 3, wherein the control unit further removes the eccentric component from the correction sampling output to further obtain a periodic profile indicating a surface state of the transfer belt as the correction information. 5. A medium cycle required for the transfer medium to make one round is an integral multiple of a roller cycle required for the sensor facing roller to make one round, and a sampling interval for sampling an output signal from the light receiving element. The image forming apparatus according to any one of claims 2 to 4, which is an integral multiple of. 6. The image forming apparatus according to claim 3, wherein a medium cycle required for the transfer medium to make one round is a non-integer multiple of a sampling interval for sampling an output signal from the light receiving element. The control means corrects the eccentric component according to the amount of deviation between the sampling timing when the correction sampling output is obtained and the sampling timing when the measurement sampling output is obtained, and after the correction, An image forming apparatus using an eccentric component as the correction information. 7. The medium cycle required for the transfer medium to make one round is a non-integer multiple of the roller cycle required for the sensor facing roller to make one round. In the image forming apparatus, the control unit corrects the eccentric component according to the difference between the peripheral length of the transfer medium and the peripheral length of the sensor facing roller,
An image forming apparatus using the corrected eccentricity component as the correction information. 8. An image forming method for transferring a toner image formed on a photoconductor onto a transfer medium while rotating the transfer medium, wherein the toner image on the transfer medium is transferred before the toner image is transferred onto the transfer medium. Light is applied to the rotating transfer medium on the basis of a synchronization signal output in association with the rotation drive, and a signal corresponding to the amount of light from the transfer medium is sampled to obtain a correction sampling output. Asking for
A step of obtaining information on the transfer medium as correction information based on the correction sampling output; and an optical signal on the rotating transfer medium based on the synchronization signal in order to obtain the image density of the toner image on the transfer medium. A step of obtaining a measurement sampling output by sampling a signal corresponding to the light amount of the light from the transfer medium while irradiating the toner, and correcting the measurement sampling output with the correction information, and the toner based on the correction value. An image forming method comprising: a step of obtaining an image density of an image.