JP4403724B2 - Image forming apparatus and toner adhesion amount detection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention irradiates light on the surface of an image carrier, detects light emitted from the surface, and determines the toner adhesion amount on the image carrier based on the detection result, and detection of the toner adhesion amount It is about the method.
[0002]
[Prior art]
In an electrophotographic image forming apparatus such as a printer, a copying machine, and a facsimile machine, a small test image (patch image) having a predetermined image pattern is formed as needed, and the amount of toner constituting the patch image By adjusting various image forming conditions based on the measurement results, a predetermined image density can be stably obtained.
[0003]
For example, in the image forming apparatus previously proposed by the applicant of the present application, the toner adhesion amount of the patch image is obtained as follows (see Patent Document 1). That is, the image carrier is irradiated with light, and the reflected light is divided into p-polarized light and s-polarized light, and the respective light amounts are detected, and the toner adhesion amount on the image carrier is obtained based on the light amount ratio. Yes.
[0004]
In this way, by detecting a plurality of light components contained in the light emitted from the image carrier individually and using the detection results, the effects of noise and fluctuations in the amount of light applied to the image carrier are affected. It is difficult to measure the amount of adhered toner with high accuracy.
[0005]
[Patent Document 1]
JP 2002-116614 A (FIG. 1)
[0006]
[Problems to be solved by the invention]
In the technique of individually detecting a plurality of light components included in the light emitted from the image carrier, the level of the detected light amount and the amount of change are different for each light component. Therefore, the dynamic range of the light amount detection value of each light component varies. Further, measurement errors are inevitably included in the light amount detection values of the respective light components.
[0007]
When the toner adhesion amount is calculated based on the light amount detection values of a plurality of light components as in the conventional technique described above, the accuracy may be reduced due to the difference in the dynamic range and the measurement error. In some cases, the toner adhesion amount may be difficult to calculate.
[0008]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of appropriately determining the toner adhesion amount based on the light amount detection values of a plurality of light components.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to the present invention is configured such that an irradiating unit that irradiates light toward the surface of an image carrier and a light component included in outgoing light emitted from the image carrier. Light amount detecting means for receiving different first and second light components and outputting first and second output signals corresponding to the received light amounts respectively, and one of the first and second output signals Control means for determining the amount of toner adhering to the image carrier on the basis of the level and a value obtained by multiplying the other signal level of the first and second output signals by a predetermined weighting coefficient. The image carrier is an intermediate transfer member that temporarily carries a toner image, and the light amount detecting means includes a beam splitter provided on an optical path of reflected light from the image carrier, and the beam splitter. Each p-polarized light component and s-polarized light component as the first and second light components divided by receiving outputs said first and second output signals by,
The control means calculates a difference between one signal level of the first and second output signals and a value obtained by multiplying the other signal level of the first and second output signals by a predetermined weighting factor. Based on the amount of toner adhered to the image carrier. The difference becomes zero when the weighting coefficient is a predetermined maximum toner adhesion amount on the image carrier, while the smaller the toner adhesion amount on the image carrier, the more the difference becomes. Is set to be large It is characterized by that.
[0010]
In the invention configured as described above, On the reflected light path from the intermediate transfer member as the image carrier Two light components contained in the emitted light (P-polarized component, s-polarized component) A value obtained by applying a predetermined weight to the light quantity detection result of one of the light quantity detection results and the other light quantity detection result Difference Therefore, the toner adhesion amount on the image carrier can be obtained with high accuracy even when the dynamic ranges of the light quantity changes of the two components are different.
[0012]
In this case, for example, when the toner adhesion amount on the image carrier is a predetermined maximum toner adhesion amount, the difference becomes zero while the toner adhesion amount on the image carrier is It can be set so that the smaller the number, the larger the difference. By doing so, the difference and the toner adhesion amount have a one-to-one correspondence, and the toner adhesion amount can be uniquely determined from the value of the difference. Further, since the difference is a value of zero or more, the calculation is easy.
[0013]
The “maximum toner adhesion amount” is a toner adhesion amount that can provide an image with a high density necessary and sufficient in accordance with the specifications of the apparatus. In other words, in the correspondence relationship between the toner adhesion amount and the image density, the toner adhesion amount corresponding to the image density that is determined to require no higher density image, or the image density even if the toner adhesion amount is increased further. This is the toner adhesion amount that is judged to hardly change.
[0014]
At this time, when the difference is a negative value, the control unit can determine that the toner adhesion amount on the image carrier is the maximum toner adhesion amount. This is because this value becomes negative when the actual toner adhesion amount exceeds the maximum toner adhesion amount or when the difference was originally supposed to be zero or a positive value close to this, but the measurement error This is because the calculation results in a negative value due to an error in the process of obtaining the difference, and in any case, it may be determined that a necessary and sufficient amount of toner is attached. By doing so, it is easy to perform arithmetic processing in a region where the toner adhesion amount is large, and the processing efficiency can be improved.
[0015]
In addition, the light amount detection unit is configured to multiply a value obtained by multiplying a received light amount of the first light component by a first gain coefficient set in advance corresponding to a dynamic range of the light amount change of the first light component. A first output signal and a value obtained by multiplying the received light amount of the second light component by a second gain coefficient set in advance corresponding to the dynamic range of the light amount change of the second light component. You may make it output as 2 output signals.
[0016]
That is, if a gain corresponding to the dynamic range of the light quantity change of each light component is given to the light quantity detection result itself of the two light components, the dynamic range of the first and second output signals corresponding to each light component can be widened. can do. For this reason, even when the dynamic ranges of the light quantity changes of the two light components are greatly different, it becomes difficult to be affected by noise or the like in the processing process, and the toner adhesion amount can be obtained with high accuracy.
[0017]
The dynamic range of each light quantity can be estimated in advance based on these values if the light quantity to be irradiated, its wavelength, the optical properties of the toner, the sensitivity of the light quantity detection means, etc. are known. Value.
[0018]
In this case, it is preferable that the weighting coefficient is set corresponding to a ratio of the first and second gain coefficients. For example, if the light amount detection means outputs a light amount detection result with a gain larger than the other, if the weighting coefficient is determined so as to cancel this gain ratio, the influence of noise or the like can be suppressed and widened. It is possible to detect the amount of light in the dynamic range, and to obtain the toner adhesion amount using the original light amount difference in the calculation process.
[0019]
In the present invention, the irradiation unit is configured to irradiate the image carrier with light having a single polarization component, while the light amount detection unit emits light emitted from the image carrier. The same polarization component as the light emitted from the irradiation means is received as the first light component, and the polarization component different from the light emitted from the irradiation means is received as the second light component. It is suitable for the apparatus made. This is because, in such an apparatus, of the two light components included in the emitted light, a first light component that is the same polarization component as the irradiation light, and a second light component that is a polarization component different from this, This is because there is a large difference in the amount of light detected and a large difference in the dynamic range.
[0020]
In order to achieve the above object, the toner adhesion amount detection method according to the present invention irradiates light toward the surface of an intermediate transfer member serving as an image carrier, and on the optical path of reflected light from the image carrier. The light emitted from the image carrier is divided into p-polarized component and s-polarized component as first and second light components which are different from each other by a beam splitter, and the respective light amounts are detected, and according to the respective light amounts. First and second output signals, and a predetermined weighting factor is applied to one of the first and second output signals and to the other of the first and second output signals. Based on the difference from the multiplied value, the amount of toner adhering to the image carrier is obtained. The difference becomes zero when the toner adhesion amount on the image carrier is a predetermined maximum toner adhesion amount, while the smaller the toner adhesion amount on the image carrier is, Is set to be larger It is characterized by that.
[0021]
In the invention configured as described above, similarly to the above-described image forming apparatus, it is possible to appropriately determine the toner adhesion amount on the image carrier based on the light amount detection results of the two light components.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a view 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. This apparatus 1 forms a full color image by superposing four color toners (developers) of yellow (Y), cyan (C), magenta (M), and black (K), or black (K) toner. This is an image forming apparatus that forms a monochrome image using only the image forming apparatus. In this image forming apparatus 1, when an image signal is given to the main controller 11 from an external device such as a host computer, the CPU 101 provided in the engine controller 10 controls each part of the engine unit EG in response to a command from the main controller 11. Then, a predetermined image forming operation is executed, and an image corresponding to the image signal is formed on the sheet S.
[0023]
In the engine unit EG, the photosensitive member 22 is provided to be rotatable in the arrow direction D1 in FIG. A charging unit 23, a rotary developing unit 4 and a cleaning unit 25 are arranged around the photosensitive member 22 along the rotation direction D1. The charging unit 23 is applied with a predetermined charging bias, and uniformly charges the outer peripheral surface of the photoconductor 22 to a predetermined surface potential. The cleaning unit 25 removes the toner remaining on the surface of the photosensitive member 22 after the primary transfer, and collects it in a waste toner tank provided inside. The photosensitive member 22, the charging unit 23, and the cleaning unit 25 integrally constitute the photosensitive member cartridge 2, and this photosensitive member cartridge 2 is detachably attached to the main body of the apparatus 1 as a whole.
[0024]
Then, the light beam L is irradiated from the exposure unit 6 toward the outer peripheral surface of the photosensitive member 22 charged by the charging unit 23. The exposure unit 6 exposes the light beam L onto the photosensitive member 22 in accordance with an image signal given from an external device, and forms an electrostatic latent image corresponding to the image signal.
[0025]
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 configured as a support frame 40 that is rotatably provided about a rotation axis center orthogonal to the paper surface of FIG. A yellow developing device 4Y, a cyan developing device 4C, a magenta developing device 4M, and a black developing device 4K are provided. The developing unit 4 is controlled by the engine controller 10. Based on the control command from the engine controller 10, the developing unit 4 is driven to rotate, and the developing units 4Y, 4C, 4M, and 4K are selectively brought into contact with the photoreceptor 22 or have a predetermined gap. When positioned at a predetermined development position opposed to each other, toner is applied to the surface of the photosensitive member 22 from a developing roller 44 provided in the developing unit and carrying toner of a selected color. As a result, the electrostatic latent image on the photosensitive member 22 is visualized with the selected toner color.
[0026]
The toner image developed by the developing unit 4 as described above is primarily transferred onto the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer region TR1. The transfer unit 7 includes an intermediate transfer belt 71 stretched between a plurality of rollers 72 to 75, and a drive unit (not shown) that rotates the intermediate transfer belt 71 in a predetermined rotation direction D2 by rotationally driving the roller 73. It has. When a color image is transferred to the sheet S, each color toner image formed on the photosensitive member 22 is superimposed on the intermediate transfer belt 71 to form a color image and taken out from the cassette 8 one by one. The color image is secondarily transferred onto the sheet S conveyed to the secondary transfer region TR2 along the conveyance path F.
[0027]
At this time, in order to correctly transfer the image on the intermediate transfer belt 71 to a predetermined position on the sheet S, the timing of feeding the sheet S to the secondary transfer region TR2 is managed. Specifically, a gate roller 81 is provided on the transport path F on the front side of the secondary transfer region TR2, and the gate roller 81 rotates in accordance with the timing of the circumferential movement of the intermediate transfer belt 71. S is sent to the secondary transfer region TR2 at a predetermined timing.
[0028]
Further, the sheet S on which the color image is thus formed is conveyed to the discharge tray portion 89 provided on the upper surface portion of the apparatus main body via the fixing unit 9, the pre-discharge roller 82 and the discharge roller 83. Further, when images are formed on both sides of the sheet S, when the rear end portion of the sheet S on which the image is formed on one side as described above is conveyed to the reversal position PR behind the pre-discharge roller 82. The rotation direction of the discharge roller 83 is reversed, whereby the sheet S is conveyed in the direction of the arrow D3 along the reverse conveyance path FR. Then, the sheet is again placed on the transport path F before the gate roller 81. At this time, the surface of the sheet S to which the image is transferred by contacting the intermediate transfer belt 71 in the secondary transfer region TR2 is first transferred. It is the opposite surface. In this way, images can be formed on both sides of the sheet S.
[0029]
In addition, the apparatus 1 includes a display unit 12 controlled by the CPU 111 of the main controller 11 as shown in FIG. The display unit 12 is constituted by, for example, a liquid crystal display, and in accordance with a control command from the CPU 111, the operation guidance to the user, the progress of the image forming operation, the occurrence of an abnormality in the apparatus, the replacement timing of any unit, etc. A predetermined message for notification is displayed.
[0030]
In FIG. 2, reference numeral 113 denotes an image memory provided in the main controller 11 for storing an image given from an external device such as a host computer via the interface 112. Reference numeral 106 is a ROM for storing a calculation program executed by the CPU 101, control data for controlling the engine unit EG, and the like. Reference numeral 107 is a RAM for temporarily storing calculation results in the CPU 101 and other data. is there.
[0031]
A cleaner 76 is disposed in the vicinity of the roller 75. The cleaner 76 can be moved toward and away from the roller 75 by an electromagnetic clutch (not shown). Then, the blade of the cleaner 76 abuts on the surface of the intermediate transfer belt 71 that is stretched over the roller 75 while moving to the roller 75 side, and the toner that remains on the outer peripheral surface of the intermediate transfer belt 71 after the secondary transfer. Remove.
[0032]
Further, a density sensor 60 is disposed in the vicinity of the roller 75. The density sensor 60 is provided so as to face the surface of the intermediate transfer belt 71, and if necessary, the density of the toner image formed on the outer peripheral surface of the intermediate transfer belt 71, more specifically, the toner constituting the toner image. Measure the amount. Based on the measurement result, the apparatus 1 adjusts the operating conditions of each part of the apparatus that affects the image quality, for example, the developing bias applied to each developing device, the intensity of the exposure beam L, and the like.
[0033]
FIG. 3 is a diagram showing the configuration of the density sensor. The density sensor 60 includes a light emitting element 601 such as an LED that irradiates light to a winding area 71 a that is wound around the roller 75 in the surface area of the intermediate transfer belt 71. Further, the density sensor 60 includes a polarization beam splitter 603, an irradiation light amount monitoring light receiving unit 604, and an irradiation light amount in order to adjust the irradiation light amount of the irradiation light in accordance with the light amount control signal Slc provided from the CPU 101 as will be described later. An adjustment unit 605 is provided.
[0034]
As shown in FIG. 3, the polarization beam splitter 603 is disposed between the light emitting element 601 and the intermediate transfer belt 71, and the light emitted from the light emitting element 601 is incident on the intermediate transfer belt 71. It is divided into p-polarized light having a polarization direction parallel to the plane and s-polarized light having a perpendicular polarization direction. The p-polarized light enters the intermediate transfer belt 71 as it is, while the s-polarized light is extracted from the polarization beam splitter 603 and then incident on the light receiving unit 604 for monitoring the amount of irradiation light. The light receiving element 642 of the light receiving unit 604 A signal proportional to the irradiation light amount is output to the irradiation light amount adjustment unit 605.
[0035]
This irradiation light amount adjustment unit 605 feedback-controls the light emitting element 601 based on the signal from the light receiving unit 604 and the light amount control signal Slc from the CPU 101, and the amount of irradiation light irradiated onto the intermediate transfer belt 71 from the light emitting element 601 The value is adjusted to a value corresponding to the control signal Slc. As described above, in this embodiment, the amount of irradiation light can be appropriately changed and adjusted in a wide range by the output signal from the CPU 101.
[0036]
Further, in this embodiment, the input offset voltage 641 is applied to the output side of the light receiving element 642 provided in the light receiving unit 604 for monitoring the irradiation light quantity, and the light emitting element as long as the light quantity control signal Slc does not exceed a certain signal level. 601 is configured to be kept off.
[0037]
When a predetermined level light amount control signal Slc is given to the irradiation light amount adjustment unit 605, 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 among the light components of the reflected light, and a signal corresponding to each light amount is sent to the CPU 101. Is output.
[0038]
As shown in FIG. 2, the reflected light amount detection unit 607 receives the polarization beam splitter 671 disposed on the optical path of the reflected light and the p-polarized light passing through the polarization beam splitter 671, and corresponds to the light amount of the p-polarized light. And a light receiving unit 670s that receives the s-polarized light divided by the polarization beam splitter 671 and outputs a signal corresponding to the light quantity of the s-polarized light.
[0039]
In the light receiving unit 670p, the light receiving element 672p receives the p-polarized light from the polarization beam splitter 671, and the output from the light receiving element 672p is amplified by the amplifier circuit 673p, and then the amplified signal is a signal corresponding to the amount of p-polarized light. Is output from the light receiving unit 670p. Similarly to the light receiving unit 670p, the light receiving unit 670s includes a light receiving element 672s and an amplifier circuit 673s. For this reason, the light quantity of two different component light (p polarized light and s polarized light) among the light components of reflected light can be calculated | required independently.
[0040]
In this embodiment, output offset voltages 674p and 674s are applied to the output sides of the light receiving elements 672p and 672s, respectively, and the output voltages Vp and Vs of the signals given from the amplifier circuits 673p and 673s to the CPU 101 are on the plus side. It is offset.
[0041]
FIG. 4 is a diagram illustrating an example of output characteristics of the light receiving element. Since the irradiation light from the density sensor 60 is absorbed and scattered by the toner, as shown in FIG. 4, the output voltage of the light receiving element 672p corresponding to the p-polarization component that is the same polarization component as the irradiation light is the intermediate transfer belt. As the amount of toner adhering to the surface region 71a of the toner increases, it decreases.
[0042]
On the other hand, the output voltage of the light receiving element 672s corresponding to the s-polarized light component is only a part of the light component generated by scattering of the irradiation light, and the level is lower than the output of the light receiving element 672p. The amount of change relative to the amount is small. That is, for the s-polarized component, the dynamic range DR1 of the output signal of the light receiving element 672s with respect to the toner amount change is narrow. In addition, the output voltages of the two light receiving elements 672p and 672s are substantially the same level near the toner adhesion amount Tmax.
[0043]
In this embodiment, the gain ratio Sg of the amplifier circuit 673s to the amplifier circuit 673p is set to Sg = 3. That is, by setting the gain for the s-polarized component to be three times the gain for the p-polarized component, the level of the light receiving element 672s is increased and the dynamic range is expanded to DR2 as shown by the dotted line in FIG. Further, by doing so, the level of the output voltage Vs output from the density sensor 60 becomes high, so that it can be made less susceptible to the influence of electrical noise mixed from the peripheral circuit.
[0044]
Returning to FIG. 3, the description of the density sensor 60 will be continued. In the light receiving units 670p and 670s configured as described above, the output voltages Vp and Vs have values of zero or more and are reflected even when the amount of reflected light is zero, similarly to the light receiving unit 604. The output voltages Vp and Vs also increase in proportion to the increase in the amount of light. By applying the output offset voltages 674p and 674s in this way, the influence of the dead band of the amplifier circuits 673p and 673s operating with a single power supply (region where the input voltage and output voltage are not proportional when the input voltage is near zero) is assured. The output voltage according to the amount of reflected light can be output.
[0045]
In the image forming apparatus 1 having the density sensor 60 configured as described above, the adhesion amount of toner constituting the toner image formed on the intermediate transfer belt 71 can be detected as follows. The toner adhesion amount is detected by the CPU 101 controlling each part of the apparatus as necessary, for example, when a patch image is formed and image forming conditions are controlled based on the density.
[0046]
FIG. 5 is a flowchart showing toner adhesion amount detection processing. First, in order to grasp the surface state of the intermediate transfer belt 71, base sampling is performed (step S1). That is, before the toner image is formed, the surface area 71a is irradiated with light from the density sensor 60 while the intermediate transfer belt 71 is moved, and the output voltages Vp and Vs of the density sensor 60 at that time are set at regular time intervals. And sampled data is stored. By doing so, information such as dirt and discoloration of the intermediate transfer belt 71 which is the base of the toner image can be obtained.
[0047]
The temporal and spatial intervals of sampling are appropriately determined according to the size of the detection spot of the density sensor 60 (the size of the surface area of the intermediate transfer belt 71 expected by the reflected light amount detection unit 607) and the moving speed of the intermediate transfer belt 71. You just have to decide. As for the number of samples, for example, the length of one round of the intermediate transfer belt 71 may be sampled, or sampling may be performed only for a region where a toner image to be described later is formed.
[0048]
Next, the engine unit EG is controlled to form a toner image having a predetermined pattern and transferred to the surface of the intermediate transfer belt 71 (step S2). Here, as an example, it is assumed that the toner image to be formed is a solid image.
[0049]
Then, for the formed toner image, the output voltages Vp and Vs of the density sensor 60 are sampled (step S3), and the sampling result is stored. The result should be the same no matter where the sampling is performed in the solid image, but here sampling is performed at a plurality of positions in the solid image in consideration of density unevenness and measurement error that occur during image formation. By doing and averaging them, the effect of such fluctuations is suppressed. The same applies to the ground sampling results. Hereinafter, the average values of the sensor output voltages Vp and Vs sampled for the toner image are represented as Vdp_ave and Vds_ave, respectively. Further, the average values of the sensor output voltages Vp and Vs sampled on the base (the surface of the intermediate transfer belt 71 before forming the toner image) are represented as Vtp_ave and Vts_ave, respectively.
[0050]
The next steps S4 and S5 will be described later. Predetermined calculations are performed based on the sampling results for the background and toner image thus obtained, and the resulting evaluation value Gt of the toner image is obtained (step S6).
[0051]
The evaluation value Gt has a one-to-one correspondence with the toner adhesion amount in the toner image on the intermediate transfer belt 71, and is a value serving as an index of the image density of the toner image. That is, the evaluation value Gt is zero when no toner adheres to the intermediate transfer belt 71, while the evaluation value Gt also increases as the toner adhesion amount increases, and it is necessary to adhere more toner than that in the design. The evaluation value Gt is defined so that the evaluation value Gt becomes 1 when the maximum toner adhesion amount is “No”. Specifically, the following formula:
Gt = 1- {Sg. (Vdp_ave-Vp0)-(Vds_ave-Vs0)} / {Sg. (Vtp_ave-Vp0)-(Vts_ave-Vs0)} (Equation 1)
Thus, an evaluation value Gt is obtained.
[0052]
In the above equation, Vp0 and Vs0 are voltages Vp and Vs sampled with the light emitting element 601 of the density sensor 60 turned off, respectively. As shown in FIG. 3, since offset voltages 674p and 674s are applied to the output side of the light receiving elements 672p and 672s, the density sensor 60 outputs a predetermined positive voltage even when the light emitting element 601 is turned off. Vp and Vs are output. The values Vp0 and Vs0 are the output voltages at this time, and by subtracting these values Vp0 and Vs0 from each sampling data (or their average value), the change in the output voltage corresponding to the detected light amount is obtained. It can be taken out.
[0053]
Further, the difference between the gains of the amplifier circuits 673p and 673s constituting the density sensor 60 is compensated by multiplying the term corresponding to the p-polarized component by the value Sg. In this way, the following calculation can be performed based on the original light amount difference between the two light components.
[0054]
In this case, when the toner adhesion amount is large, as shown in FIG. 4, the two outputs Vp and Vs of the density sensor 60 are smaller than when the toner adhesion amount is small. This means that the larger the toner adhesion amount, the numerator in the second term on the right side of (Equation 1):
Sg · (Vdp_ave−Vp0) − (Vds_ave−Vs0) (Equation 2)
Means approaching zero.
[0055]
In this embodiment, as described above, the evaluation value Gt = 0 when the toner adhesion amount on the intermediate transfer belt 71 is minimum, and the evaluation value Gt = 1 when the toner adhesion amount is maximum. This is because the density sensor 60 having the characteristics shown in FIG. 4 is used. That is, as shown in FIG. 4, the difference between the light receiving element outputs corresponding to the light components of p-polarized light and s-polarized light becomes maximum when the toner adhesion amount is zero, while the difference decreases as the toner adhesion amount increases. Eventually, when the toner adhesion amount Tmax, the difference becomes zero. In this embodiment, the density sensor 60 is employed such that the toner adhesion amount Tmax at which the light receiving element outputs corresponding to both polarization components are substantially equal is substantially equal to the maximum toner adhesion amount required in the image forming apparatus. More generally, the maximum toner adhesion amount in the apparatus does not necessarily match the toner adhesion amount at which the value of (Equation 2) becomes zero. Therefore, the evaluation value Gt obtained based on (Equation 1) may exceed 1 or be a negative value.
[0056]
As described above, if the evaluation value Gt indicating the toner adhesion amount is too large or can take both positive and negative values, the subsequent processing is complicated. Therefore, as a result of using another density sensor, if the maximum toner adhesion amount in the apparatus and the toner adhesion amount at which the value of (Equation 2) becomes zero greatly deviate, The coefficient of the term, that is, the “weighting coefficient” of the present invention may be a value different from the gain ratio Sg for both polarization components in the density sensor 60.
[0057]
FIG. 6 is a diagram showing the relationship between the weighting coefficient and the sensor output. Here, a description will be given assuming that a weighting coefficient is applied to the output corresponding to the s-polarized component. As shown in FIG. 6, for example, when the weighting coefficient Ka (> 0), the value of (Expression 2) becomes zero when the toner adhesion amount Ta shown in FIG. On the other hand, for example, when the weighting coefficient Kb (<Kb <Ka), the value of (Expression 2) becomes zero when the toner adhesion amount Tb shown in FIG.
[0058]
That is, if the “weighting coefficient” of the present invention is changed, the toner adhesion amount value at which the value of (Equation 2) becomes zero also changes. Therefore, if the weighting coefficient in (Equation 2) is set so that the toner adhesion amount when the value of (Equation 2) becomes zero becomes the maximum toner adhesion amount in the apparatus, the value of (Equation 2) is usually It becomes zero or positive, and as a result, the evaluation value Gt shown in (Expression 1) is a value between 0 and 1.
[0059]
In this embodiment, since the maximum toner amount in the apparatus substantially coincides with the toner amount Tmax in the density sensor 60, the “weighting coefficient” of the present invention is the gain ratio Sg for both polarization components in the density sensor 60. I was able to.
[0060]
Despite this, if the sampling result is substituted into (Equation 2), this value becomes negative due to the sensitivity variation of the light receiving element and the measurement error inevitably included in each sampling data. Sometimes. As a result, the evaluation value Gt shown in (Expression 1) exceeds 1. Although the evaluation value Gt is defined to be a value between 0 and 1, it is inconvenient to obtain such a result. In particular, when a calculation is performed using a fixed-point processor, an abnormal result may be obtained if an operation with an operation result exceeding 1 is performed.
[0061]
Therefore, prior to the calculation of (Equation 1) in step S6, the value of (Equation 2) described above is calculated to determine the sign (steps S4 and S5). It is not necessary to calculate (Equation 1), and the evaluation value Gt is set to 1 assuming that a sufficient amount of toner is attached (step S7). The reason why this may be done will be described with reference to FIG.
[0062]
FIG. 7 is a diagram illustrating an example of the relationship between the evaluation value of a toner image and its optical density. As described above, the evaluation value Gt is a value indicating the toner adhesion amount on the intermediate transfer belt 71. The image density (optical density OD) of the toner image depends on the amount of toner adhesion. When the relationship between the two is plotted, as shown in FIG. 7, the evaluation value Gt is large, that is, the amount of toner adhesion. In the large area, the inclination is smaller than in the area where the toner amount is small. In other words, in a region where the toner adhesion amount is large, fluctuations in the toner adhesion amount are less noticeable as changes in toner image density.
[0063]
Further, as shown in FIG. 4, the amount of the s-polarized component contained in the scattered light from the toner image does not decrease monotonously with the increase in the toner adhesion amount, but may increase. Therefore, when toner exceeding a certain toner amount Tmax adheres, the output signal corresponding to the s-polarized component becomes larger, and as a result, the value of (Expression 2) becomes negative.
[0064]
In any case, it can be said that a sufficient amount of toner is adhered to obtain a necessary image density, and there is not much practical advantage in calculating the toner adhesion amount more finely than necessary. Therefore, when the result of (Equation 2) is negative, it is possible to determine that sufficient toner has adhered without performing subsequent calculations. Note that, when the result of (Expression 2) is zero, the result is the evaluation value Gt = 1 even if the next processing step is either step S6 or step S7, so that the calculation can be omitted in this embodiment. The process proceeds to step S7.
[0065]
As described above, the toner adhesion amount as a toner image on the intermediate transfer belt 71 can be obtained. Then, by using the result, adjustment of a bias voltage, a gradation correction characteristic, and the like given to each part of the apparatus can be performed to maintain stable image quality.
[0066]
As described above, in this embodiment, light having a single p-polarized component is irradiated onto the surface region 71a of the intermediate transfer belt 71, and the p-polarized component having the same polarization as the irradiated light out of the light emitted therefrom. The s-polarized component orthogonal to this is detected individually. At this time, since the gains for the output signals of the light receiving elements 672p and 672s corresponding to the light amounts of both polarization components are made different according to the respective signal levels, the dynamic range of the output signal is ensured.
[0067]
Also, if it is determined that a sufficient amount of toner is attached during the calculation, it is assumed that the toner amount is sufficient by omitting the subsequent calculations. Can be requested.
[0068]
As described above, in this embodiment, the intermediate transfer belt 71 and the CPU 101 function as the “image carrier” and the “control unit” of the present invention, respectively, and the density sensor 60 is the “irradiation unit” of the present invention. And “light quantity detection means”. The output voltages Vp and Vs of the concentration sensor 60 correspond to the “first output signal” and the “second output signal” of the present invention, respectively.
[0069]
In this embodiment, the p-polarized light component and the s-polarized light component received by the light receiving units 670p and 670s correspond to “first light component” and “second light component”, respectively. Therefore, the output voltages Vp and Vs of the density sensor 60 correspond to “first and second output signals”, respectively. Furthermore, since the gain ratio Sg when detecting each of the two light components is 3, in this embodiment, when the “first gain coefficient” is 1, the “second gain coefficient” is 3.
[0070]
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-described embodiment, the light having only the p-polarized component is irradiated, and as two light components to be received, the p-polarized light having the same polarization plane and the s-polarized light having a polarization plane perpendicular thereto are used. However, you may make it irradiate and receive the light which has a property other than this. For example, all the light components other than the p-polarized component that is the first light component may be used as the second light component.
[0071]
For example, in the above-described embodiment, the evaluation value Gt is introduced as a value indicating the toner adhesion amount. However, any other value, for example, on the intermediate transfer belt 71, may be used as long as it is a value indicating the toner adhesion amount. The toner density or the numerical value converted into the image density may be used. The above-described calculation formula for the evaluation value Gt is merely an example, and other appropriate calculation formulas may be introduced according to the purpose.
[0072]
Further, for example, in the above embodiment, the toner adhesion amount of the toner image formed on the intermediate transfer belt 71 is detected by the density sensor 60. That is, in this embodiment, the intermediate transfer belt 71 functions as an “image carrier”, but other than this, for example, the toner adhesion amount of a toner image formed on the surface of the photosensitive member 22 may be detected. .
[0073]
In the above-described embodiment, the present invention is applied to an apparatus that forms an image using four color toners of yellow, magenta, cyan, and black. However, the types and number of toner colors are limited to those described above. It is not a thing but arbitrary. In addition to the rotary development type apparatus as in the present invention, the so-called tandem type image forming apparatus in which developing units corresponding to the respective toner colors are arranged in a line along the sheet conveying direction. The present invention is also applicable. Furthermore, the present invention is not limited to the electrophotographic apparatus as in the above embodiment, but can be applied to all image forming apparatuses.
[Brief description of the 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 illustrating a configuration of a density sensor.
FIG. 4 is a diagram illustrating an example of output characteristics of a light receiving element.
FIG. 5 is a flowchart showing toner adhesion amount detection processing;
FIG. 6 is a diagram illustrating a relationship between a weighting coefficient and a sensor output.
FIG. 7 is a diagram illustrating an example of a relationship between a toner image evaluation value and its optical density.
[Explanation of symbols]
60 ... density sensor (irradiation means, light quantity detection means) 71 ... intermediate transfer belt (image carrier) 101 ... CPU (control means), p-polarized light, s-polarized light ... first light component, second light component, Vp, Vs (output of concentration sensor 60) (first output signal, second output signal), Ka, Kb ... weighting factor, Sg ... gain ratio (weighting factor)

Claims (5)

Irradiation means for irradiating light toward the surface of the image carrier;
Amount of light that receives first and second light components different from each other among the light components included in the emitted light emitted from the image carrier and outputs first and second output signals corresponding to the respective amounts of received light. Detection means;
The image carrier based on one signal level of the first and second output signals and a value obtained by multiplying the other signal level of the first and second output signals by a predetermined weighting factor. Control means for determining the amount of toner adhered to the top,
The image carrier is an intermediate transfer member that temporarily carries a toner image;
The light amount detecting means has a beam splitter provided on the optical path of the reflected light from the image carrier, and the p-polarized component and the s-polarized light as the first and second light components divided by the beam splitter. Receiving each component and outputting the first and second output signals;
The control means calculates a difference between one signal level of the first and second output signals and a value obtained by multiplying the other signal level of the first and second output signals by a predetermined weighting factor. Based on the amount of toner adhered to the image carrier ,
The difference is zero when the weighting coefficient is a predetermined maximum toner adhesion amount on the image carrier, while the smaller the toner adhesion amount on the image carrier is, the smaller the difference is. An image forming apparatus that is set to be large . The image forming apparatus according to claim 1 , wherein the control unit determines that the toner adhesion amount on the image carrier is the maximum toner adhesion amount when the difference is a negative value. The light amount detecting means is configured to multiply a value obtained by multiplying a received light amount of the first light component by a first gain coefficient set in advance corresponding to a dynamic range of a light amount change of the first light component. The second output is a value obtained by multiplying the received light amount of the second light component by a second gain coefficient set in advance corresponding to the dynamic range of the light amount change of the second light component. and outputs as a signal, the weighting factors, the image forming apparatus according to claim 1 or 2 is set to correspond to the ratio of the first and second gain coefficients. While the irradiation means is configured to irradiate light having a single polarization component toward the image carrier,
The light amount detection means receives, as the first light component, the same polarized light component emitted from the image carrier as the first light component, and the light emitted from the irradiation means. the image forming apparatus according to any one of 3 claims 1 configured to receive different polarization components as said second optical component. Light is emitted toward the surface of an intermediate transfer member serving as an image carrier, and light beams emitted from the image carrier on the optical path of reflected light from the image carrier are different from each other by a beam splitter. And a p-polarized component and a s-polarized component as second light components to detect respective light amounts, and generate first and second output signals corresponding to the respective light amounts,
Based on a difference between one signal level of the first and second output signals and a value obtained by multiplying the other signal level of the first and second output signals by a predetermined weighting factor, the image Find the amount of toner adhering to the carrier ,
The difference is zero when the toner adhesion amount on the image carrier is a predetermined maximum toner adhesion amount, while the weight coefficient is such that the smaller the toner adhesion amount on the image carrier, the smaller the difference. A toner adhesion amount detection method, wherein the toner adhesion amount detection method is set to be large .

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