JP2014219538A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove the influence of ripple noise from a value detected by a toner concentration sensor.SOLUTION: An image forming apparatus includes: an image forming unit 5 for forming a toner image; an image carrier 6 which carries the toner image; and a toner concentration sensor 15 which detects toner concentration of the toner image formed on the image carrier 6 at a predetermined sampling period. The image forming apparatus also includes: a ripple noise period calculation unit 113 which calculates a ripple noise period generated from one or more AC component generation sources 8, 9 located near the toner concentration sensor 15, from AC component frequency information of the AC component generation sources 8, 9; a sampling period control unit 114 which varies the sampling period according to the calculated ripple noise period; and an averaging process unit 100 which averages a plurality of sampling values output from the toner concentration sensor 15, according to the varied sampling period.

Description

  The present invention relates to an image forming apparatus including a toner density sensor that detects the density of toner on an image carrier.

  In an electrophotographic image forming apparatus, a patch image having a predetermined image pattern is formed, the amount of toner is measured by a toner density sensor, and various image forming conditions are adjusted based on the measurement result. Image density can be obtained stably.

  By the way, ripple noise due to an AC bias is generated in the output of the toner concentration sensor due to unnecessary radiation from an AC component generated by an AC component generation source such as a discharge electrode existing in the vicinity of the toner concentration sensor.

  As a means for removing noise, for example, when data that may contain noise is detected in the output of the toner density sensor, a noise component is calculated from adjacent data, and the noise component is offset to obtain an accurate output. An image forming apparatus to be obtained is known (see Patent Document 1). Specifically, an accurate sensor output is obtained by replacing data having a value more than a certain distance from an average value of sampling data obtained by reading a certain area of the patch image with an average value of adjacent data.

Japanese Patent Laid-Open No. 2004-361871

  However, with the technique described in Patent Document 1, although specific noise can be removed, ripple noise cannot be removed. Hereinafter, the reason will be described with reference to FIGS.

FIG. 13 is an explanatory diagram showing a conventional noise removal processing method. FIG. 14 is an explanatory diagram when a conventional noise removal processing method is performed when ripple noise occurs. 13 and 14, the horizontal axis indicates the position of the sampling point, and the vertical axis indicates the detection value (sampling value) detected by the toner density sensor.
As shown in FIG. 13, the sampling value 202 of the patch image Ip attached along the driving direction of the intermediate transfer belt 6 is far away from the value (average value) obtained by averaging the sampling values of other sampling points. And contains noise. When the sampling value 202 including noise is detected, the sampling value at the sampling point is replaced with the average value 202 ′ of the sampling values of the two adjacent sampling points 201 and 203.

  However, as shown in FIG. 14, due to the influence of ripple noise 210 having an AC waveform, depending on the sampling position, the sampling value is an average value (broken line) offset by an arrow from a normal value (solid line) when there is no ripple noise 210. ) Is output. That is, when a conventional noise removal processing method is performed when ripple noise occurs, ripple noise is not detected, and image forming conditions cannot be adjusted appropriately.

  From the above situation, a technique for removing the influence of ripple noise from the detection value of the toner density sensor has been desired.

  An image forming apparatus according to one aspect of the present invention includes an image forming unit that forms a toner image, an image carrier that carries the toner image formed by the image forming unit, and a toner density of the toner image that is formed on the image carrier. And a toner density sensor that outputs a sampling value by sampling at a predetermined sampling period. Further, a ripple noise cycle calculation unit that calculates a ripple noise cycle generated from one or more AC component generation sources existing in the vicinity of the toner density sensor from AC component frequency information of the AC component generation source, and a ripple noise cycle calculation unit A sampling period control unit that performs control to vary the sampling period in accordance with the ripple noise period calculated in (1) is provided. Furthermore, an averaging processing unit is provided that averages a plurality of sampling values output from the toner density sensor in accordance with the sampling cycle varied by the sampling cycle control unit.

In the above configuration, the ripple noise period is N, the sampling period is n, the length of detecting the toner image in the driving direction of the image carrier is L, the driving speed of the image carrier is V, and the sampling number is P (2 or more). It is more desirable that the following condition is satisfied.
Sampling period n is n ≦ L / (2V) and n ≠ N,
Sampling number P is P ≦ (N / n) × a (a is a natural number)
It is the largest natural number that satisfies

  In the above configuration, an appropriate sampling period is set according to the frequency of the AC component output from the AC component generation source in the vicinity of the toner concentration sensor. The toner density sensor outputs a sampling value of the toner density according to the sampling cycle. Then, the sampling value output from the toner density sensor is averaged according to the set sampling cycle. As a result, the normal value of the toner density sensor can be obtained by removing the influence of ripple noise.

  According to the present invention, it is possible to remove the influence of ripple noise from the detection value of the toner density sensor and appropriately correct the image.

1 is an overall configuration diagram of an image forming system including an image forming apparatus according to a first embodiment of the present invention. 2 is a block diagram illustrating a hardware configuration of each unit of the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. FIG. 3 is an explanatory diagram illustrating an internal configuration of a main part and a ripple noise removing unit of the image forming apparatus according to the first embodiment of the present invention. 3 is a flowchart showing ripple noise removal processing by the image forming apparatus according to the first embodiment of the present invention. 6 is a graph showing an example of sampling data (two points) output by the toner density sensor when there is one AC component generation source according to the first embodiment of the present invention. 6 is a graph showing an example of sampling data (eight points) output by the toner density sensor when there is one AC component generation source according to the first embodiment of the present invention. 6 is a graph showing an example of sampling data (10 points) output by the toner density sensor when there is one AC component generation source according to the first embodiment of the present invention. It is explanatory drawing which shows an example of the alternating current waveform output from a removal electrode and a separation pole. 6 is a graph showing an example of sampling data (four points) output by the toner density sensor when there are two AC component generation sources according to the first embodiment of the present invention. It is explanatory drawing which shows the internal structure of the principal part and ripple noise removal part of the image forming apparatus which concern on the 2nd Embodiment of this invention. 6 is a flowchart illustrating a ripple noise removal process by an image forming apparatus according to a second embodiment of the present invention. It is explanatory drawing which shows the determination method of the presence or absence of the ripple noise by the dark current which concerns on the 2nd Embodiment of this invention. It is explanatory drawing which shows the conventional noise removal processing method. It is explanatory drawing at the time of implementing the conventional noise removal processing method at the time of ripple noise generation | occurrence | production.

  Hereinafter, an example of an embodiment for carrying out the present invention will be described with reference to the accompanying drawings. In the drawings, common components are denoted by the same reference numerals, and redundant description is omitted.

<First Embodiment>
[Example of overall configuration of image forming system]
FIG. 1 is an overall configuration diagram of an image forming system including an image forming apparatus according to a first embodiment of the present invention. In FIG. 1, the portion considered necessary for the description of the present invention in the configuration of the image forming system is mainly described.

  As shown in FIG. 1, the image forming system 1 includes a paper feeding device 20, an image forming device 10, and a fixing device 30.

  The paper feeding device 20 is provided with a plurality of paper storage portions 20a according to the paper size and type. In the paper feeding device 20, the corresponding paper storage unit 20 a is selected based on an instruction from the image forming device 10, the paper S is taken out by a paper feeding unit (not shown), and is sent to the conveyance path C of the image forming device 10. .

  The image forming apparatus 10 employs an electrophotographic system that forms an image using static electricity. For example, toner images of four colors of yellow (Y), magenta (M), cyan (C), and black (K) are used. Is a tandem type color image forming apparatus. The image forming apparatus 10 includes an operation display unit 105, an image forming unit 5, an intermediate transfer belt 6 (image carrier), and a secondary transfer unit 7.

  The image forming unit 5 includes four image forming units 5Y, 5M, 5C, and 5K in order to form toner images of colors of yellow, magenta, cyan, and black. Further, the image forming apparatus 10 includes a plurality of rollers (conveying rollers) 11, 12, and 13 for conveying paper. The rollers 11, 12, and 13 are usually constituted by a pair of rollers. Each roller described below has the same configuration. The operation display unit 105 has a function as an operation unit that instructs the start of a job such as image forming processing.

  In the image forming mode, the image forming apparatus 10 charges the photosensitive member 51 included in the image forming units 5Y, 5M, 5C, and 5K, erases the electric charge according to the original image, and exposes the photosensitive member 51 to the electrostatic latent image. Form an image. Then, toner is attached to the electrostatic latent images of the photoreceptors 51 of yellow, magenta, cyan, and black using a developing unit to form toner images of each color. Next, the toner images formed on the yellow, magenta, cyan, and black photoconductors 51 are sequentially primary-transferred onto the surface of the intermediate transfer belt 6 that rotates in the direction of the arrow.

  Next, a sheet of toner image of each color primarily transferred onto the intermediate transfer belt 6 by the secondary transfer unit 7 (secondary transfer roller) is supplied from the sheet feeding device 20 and is conveyed by the rollers 11 and 12. Secondary transfer to S. The toner images of the respective colors on the intermediate transfer belt 6 are secondarily transferred to the paper S, whereby a color image is formed. The image forming apparatus 10 discharges the sheet S on which the color toner image is formed to the fixing device 30 by the roller 13.

  A toner density sensor 15 is disposed downstream of the primary transfer nip portion formed by the intermediate transfer belt 6 and the photosensitive member 51 of the image forming unit and upstream of the secondary transfer portion 7 in the sheet conveyance direction. Yes. The toner density sensor 15 detects the toner density of each color toner image transferred to the intermediate transfer belt 6 before being secondarily transferred by the secondary transfer unit 7 and outputs the detection result to the control unit 100 described later.

  As the toner density sensor 15, for example, a transmissive photosensor in which a light emitting member and a light receiving member are arranged to face each other, or a reflective photosensor that detects reflected light from an emitted light object is used. Alternatively, a line sensor in which a light emitting member and a plurality of photoelectric conversion elements are arranged linearly over a part or the entire area in the paper width direction, or an image sensor in which photoelectric conversion elements are arranged in a matrix form is used. As the line sensor and the image sensor, a CCD type image sensor or a CMOS type (including MOS type) image sensor can be used.

  The fixing device 30 is a device that performs a fixing process on the paper S on which a color toner image is formed, which is supplied from the image forming apparatus 10. The fixing device 30 includes, for example, a fixing unit 31, a roller 32 near the carry-in port, and a roller 33 near the discharge port.

  The fixing unit 31 provided in the fixing device 30 pressurizes and heats the conveyed paper S, and fixes the transferred toner image on the paper S. The fixing unit 31 includes, for example, a fixing upper roller and a fixing lower roller which are a pair of fixing members. The upper fixing roller and the lower fixing roller are arranged in pressure contact with each other, and a fixing nip portion is formed as a pressing portion between the upper fixing roller and the lower fixing roller.

  A heating unit is provided inside the fixing upper roller. The roller part at the outer peripheral part of the fixing upper roller is heated by the radiant heat from the heating part. Then, the heat of the roller portion of the fixing upper roller is transmitted to the sheet, whereby the toner image on the sheet is thermally fixed.

  The sheet S is conveyed so that the surface on which the toner image is transferred by the secondary transfer unit 7 (surface to be fixed) faces the fixing upper roller, and passes through the fixing nip portion. Accordingly, the sheet passing through the fixing nip is subjected to pressure by the upper fixing roller and the lower fixing roller and heating by the heat of the upper fixing roller. The sheet S on which the fixing process has been performed by the fixing unit 31 is discharged to the discharge tray 50 by the roller 33.

[Configuration of control system of image forming system]
Next, a control system of the image forming apparatus 10 provided in the image forming system 1 will be described.
FIG. 2 is a block diagram illustrating a hardware configuration of each unit of the image forming apparatus 10.

  As shown in FIG. 2, the image forming apparatus 10 includes a control unit 100. The control unit 100 includes, for example, a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102 for storing programs and data executed by the CPU 101, and a RAM (Random Access) used as a work area of the CPU 101. Memory) 103. The ROM 102 stores, for example, control programs for various jobs, setting value data used for ripple noise removal processing, and the like. As the ROM 102, for example, an electrically erasable programmable ROM is used. The control unit 100 controls each block, that is, controls the entire apparatus.

  The control unit 100 is connected to an HDD (Hard disk drive) 104 and an operation display unit 105 via a system bus 107, respectively. The control unit 100 is connected to the image reading unit 4, the image processing unit 106, the image forming unit 5, and the secondary transfer unit 7 via the system bus 107. Further, the control unit 100 is connected to the toner density sensor 15 and the ripple noise removal unit 111 via the system bus 107, respectively.

  The HDD 104 is a large-capacity storage device that stores image data of an original image obtained by reading by the image reading unit 4 and stores output image data and the like. The operation display unit 105 is a touch panel including a display such as a liquid crystal display (LCD) or an organic ELD (Electro Luminescence Display) and a touch sensor (an example of an operation unit). The operation display unit 105 displays an instruction menu for the user, information about the acquired image data, and the like. Furthermore, the operation display unit 105 includes a plurality of keys, receives input of various instructions, data such as characters and numbers by user key operations, generates an input signal, and outputs the input signal to the control unit 100.

  Image data generated by the image reading unit 4 and image data transmitted from a PC (personal computer) 120 which is an example of an external device connected to the image forming apparatus 10 are sent to the image processing unit 106 for image processing. Is done. The image processing unit 106 performs processes such as analog processing, A / D conversion, shading correction, and image compression on the received image data.

  The communication unit 108 receives job information transmitted from the PC 120 which is an external information processing apparatus via a communication line. The received job information is sent to the control unit 100 via the system bus 107.

  The control unit 100 controls driving of the image forming unit 5 and the secondary transfer unit 7 based on the job information. The control unit 100 may be configured to control the fixing process of the fixing unit 31 disposed in the fixing device 30.

  Under the control of the control unit 100, the toner density sensor 15 lights the light emitting member with a preset reference light emission setting value, receives the reflected light from the intermediate transfer belt 6 on which the toner image has been primarily transferred, The detection value (detection signal) is output to the control unit 100 at a sampling period of. The control unit 100 calculates the toner adhesion amount (toner concentration) of the toner image transferred to the intermediate transfer belt 6 based on the toner adhesion amount characteristic information that associates the detection value of the toner density sensor 15 with the toner adhesion amount. . Then, the control unit 100 applies the calculated toner density to a determination unit such as a determination table or a conversion formula, and controls the toner amount of the toner image transferred to the intermediate transfer belt 6 in the image forming unit 5. The toner adhesion amount characteristic information and the data relating to the determination unit are stored in the ROM 102 or the HDD 104 in advance.

  As control factors for the amount of toner adhered to the intermediate transfer belt 6, for example, the toner density in the developing unit of the image forming unit 5, the developing bias, the amount of exposure to the photosensitive member by the exposing unit, and the charging of the photosensitive unit by the charging unit The voltage, the content of the image data, etc. are mentioned. The ROM 102 holds a table for associating the toner adhesion amount with its control factor, and the control unit 100 controls the toner adhesion amount as an image forming condition with reference to the table.

  The ripple noise removing unit 111 appropriately changes the sampling period of the toner density sensor 15 under the control of the control unit 100 and removes the influence of ripple noise from the detection value of the toner density sensor 15. The sampling period of the toner concentration sensor 15 is determined based on the frequency of the AC component output from the AC component generation source existing in the vicinity of the toner concentration sensor 15. The control unit 100 functions as an averaging processing unit that averages a plurality of sampling values output from the toner density sensor 15 according to a set sampling cycle. The averaging process may be performed by, for example, addition averaging.

  In this embodiment, an example in which the personal computer 120 is applied as an external device has been described. However, the present invention is not limited to this, and various other devices such as a facsimile device can be applied as the external device. it can.

[Internal configuration of ripple noise elimination unit]
Hereinafter, the ripple noise removing unit 111 will be described in detail.
FIG. 3 is an explanatory diagram illustrating an internal configuration of a main part of the image forming apparatus 10 and the ripple noise removing unit 111.
Each of the image forming units 5Y, 5M, 5C, and 5K includes photoreceptors 51Y, 51M, 51C, and 51K. On the downstream side of the nip portion between the intermediate transfer belt 6 and each photoconductor 51, the electrode removal electrode 8 is disposed. Here, the photoconductor 51K will be described as a representative. The removal electrode 8 erases the charge remaining on the photoconductor 51 under the control of the control unit 100. A separation pole 9 is disposed on the downstream side of the secondary transfer unit 7. The separation pole 9 erases the charge remaining on the sheet S after the secondary transfer under the control of the control unit 100 and separates the sheet S from the intermediate transfer belt 6. The removal electrode 8 and the separation electrode 9 are an example of an AC component generation source located near the toner concentration sensor 15.
In the example of FIG. 3, the toner density sensor 15 is disposed on the downstream side of the removal electrode 8 and on the upstream side of the secondary transfer unit 7.

  The ripple noise removal unit 111 includes an AC frequency storage unit 112, a ripple noise cycle calculation unit 113, and a sampling cycle control unit 114.

  The AC frequency storage unit 112 is a storage unit that stores AC frequency information of AC components output from AC component generation sources such as the electrode removal 8 and the separation electrode 9. Since the frequency of the AC component generated by the AC component generation source such as the electrode removal electrode 8 or the separation electrode 9 is set in advance, the set value is stored. For the AC frequency storage unit 112, a rewritable storage unit such as the RAM 103 or the HDD 104 may be used.

  The ripple noise cycle calculation unit 113 is a calculation unit that calculates a ripple noise cycle from the AC frequency information stored in the AC frequency storage unit 112.

  The sampling cycle control unit 114 is a control unit that sets (varies) the sampling cycle of the toner density sensor 15 according to the ripple noise cycle calculated by the ripple noise cycle calculation unit 113.

Since the image quality deterioration level changes depending on the charge amount of the toner and the like, the optimum output value of the deelectrode 8 is varied. Further, since the separation property between the intermediate transfer belt 6 and the paper changes depending on the paper type, the output value of the separation pole 9 after the secondary transfer is variable. For example, the output value of the removal electrode 8 and the output value of the separation electrode 9 can be varied within the following range as an example. These output values change, for example, when the user operates the operation display unit 105 to set the image quality of the toner image.
Output of the electrode removal electrode AC: 1 to 10 kV, DC: −5 to 1 kV, frequency: 500 Hz to 3 kHz
-Output of separation pole 9 AC: 1 to 10 kV, DC: -5 to 0 kV, frequency: 100 Hz to 1 kHz

  When the ripple noise period is N, the sampling period n and the sampling number P are varied as in the following conditional expression, and a plurality of obtained sampling values are averaged. By such processing, the influence of ripple noise is removed from the detection value of the toner density sensor 15. Here, L is a length for detecting a toner image in the driving direction of the intermediate transfer belt 6 (hereinafter referred to as “detection distance”), and V is a process speed (driving speed of the intermediate transfer belt 6). Note that P is a natural number of 2 or more, and a is a natural number.

The conditional expression related to the sampling period n in Expression (1) indicates a condition for setting the sampling period n to a period smaller than the Nyquist period when the detection distance L and the process speed V are given.
In addition, the conditional expression that functions on the sampling number P in Expression (1) indicates a condition for obtaining a large value and a small value (see FIGS. 5 to 7 to be described later) as sampling point values. . N / n is the number of times that sampling can be performed during one period of ripple noise, and the sampling number P is more preferably set to the largest natural number among a times (N / n). By setting the sampling number P in this way, various values corresponding to the ripple noise are mixed at the sampling points of the set sampling number. Therefore, normal values are obtained by averaging these multiple sampling values.

  The ripple noise removing unit 111 described above can be configured using hardware or software. When configured using software, the CPU 101 in the control unit 100 reads and executes a ripple noise removal program stored in the ROM 102, thereby realizing its function.

[Ripple noise elimination processing]
FIG. 4 is a flowchart showing ripple noise removal processing by the ripple noise removal unit 111 of the image forming apparatus 10.
First, the control unit 100 of the image forming apparatus 10 detects the start of a job based on an operation signal input from the operation display unit 105 or job information input via the communication unit 108. When the control unit 100 detects the start of a job, it starts ripple noise removal processing.

  Next, under the control of the control unit 100, the ripple noise period calculation unit 113 of the ripple noise removal unit 111 reads AC frequency information from the AC frequency storage unit 112 (step S1), and whether there is a plurality of AC frequency information. Is determined (step S2).

When there is only one AC frequency information (NO in step S2), the ripple noise cycle calculation unit 113 employs the AC cycle of the AC frequency information as the ripple noise cycle (step S3).
In addition, when there is a plurality of AC frequency information (YES in Step S2), the ripple noise period calculation unit 113 calculates a ripple noise period from the plurality of AC frequency information (Step S4).

  After the process of step S3 or step S4 is completed, the sampling period control unit 114 performs a process of changing the sampling period of the toner density sensor 15 according to the ripple noise period according to the equation (1) (step S5). For example, the changed sampling cycle is stored in the RAM 103 (or HDD 104). After this process ends, the ripple noise removal method ends.

  Thereafter, the toner density sensor 15 performs sampling in the changed sampling cycle, and the control unit 100 calculates an average value of a plurality of sampling values output from the toner density sensor 15. Then, the control unit 100 changes the image forming conditions by using the average value of the plurality of sampling values as the detection value of the toner density sensor 15, and creates a toner image.

  This ripple noise removal processing may be performed at the start of the job or before the start of the job as described above, or may be performed during execution of image formation. For example, when the set value of the AC component changes for some reason during image formation based on a certain job, ripple noise removal processing is performed between sheets, and the sampling period of the toner density sensor 15 is changed. Good.

[When there is only one AC component source: electrode removal only]
As described above, since the ripple noise frequency changes according to the user setting, the sampling period and the number of samplings must be changed each time. Hereinafter, an example of the ripple noise removal process when one AC component generation source exists in the vicinity of the toner concentration sensor 15 will be described. In this example, an example of changing an appropriate sampling period and the number of samplings with respect to a set value of the electrode removal electrode 8 as an AC component generation source is shown.

(Example of 2 sampling points)
FIG. 5 is a graph showing an example of sampling data (two points) output from the toner concentration sensor 15 when there is one AC component generation source. The horizontal axis indicates the position (msec) of the sampling point (indicated by a white circle), and the vertical axis indicates the detection value (sampling value) detected by the toner density sensor 15. The patch image Ip is formed on the surface of the intermediate transfer belt 6 along the driving direction of the intermediate transfer belt 6. The scanning direction of the patch image Ip is opposite to the driving direction of the intermediate transfer belt 6. As an example, the output value of the electrode removal 8 and the correction conditions are set as follows. These can be set by the user operating the operation display unit 105.
-Output value of the electrode removal electrode AC: 4 kV, DC: -2 kV, frequency f: 1 kHz
Correction conditions: Patch image detection length (detection distance) L: 5 mm, process speed V: 460 mm / s

  When the frequency f of the output value of the discharge electrode 8 is 1 kHz, the period N of the ripple noise 121 is 1 msec (= 1 / f). According to Equation 1 described above, the sampling period n can be set within a range of about 5.4 msec or less, for example, 5.4 msec. Here, the sampling number P within the detection distance L (5 mm) is set to two points, and the two sampling values are averaged. One sampling value is larger than the normal value (located at the peak of the waveform), and the other sampling value is smaller than the normal value (located at the valley of the waveform), so it is canceled out by calculating the average value of the two sampling values To obtain the desired normal value. The timing at which the toner concentration sensor 15 starts measurement may start from an arbitrary phase of the ripple noise waveform.

  Thus, in this example, an appropriate sampling period and the number of samplings (two points in this example) are set according to the frequency of the AC component output from the AC component generation source (in this example, the electrode removal electrode 8). Then, two sampling values output from the toner density sensor 15 are averaged according to the sampling cycle. Thereby, a normal value obtained by removing the influence of ripple noise from the detection value of the toner density sensor 15 can be obtained. As a result, the image forming conditions can be changed based on the normal value of the toner density sensor 15, and the formed toner image can be corrected appropriately.

  In general, when the patch image Ip is read by the toner density sensor 15 and the toner image is corrected, a certain distance or more is measured in order to ensure correction accuracy. In the present embodiment, the detection distance L is 5 mm. However, it is only necessary to obtain the set sampling number. For example, the detection distance L may be 2.5 mm or more, which is a length corresponding to 5.4 cycles of ripple noise. That's fine.

(Example of 8 sampling points)
FIG. 6 is a graph showing an example of sampling data (eight points) output from the toner concentration sensor 15 when there is one AC component generation source. The setting of the output value of the electrode removal 8 is the same as in the example of FIG.
-Output value of the electrode removal electrode AC: 4 kV, DC: -2 kV, frequency f: 1 kHz
Correction conditions: Patch image detection length (detection distance) L: 4.6 mm, process speed V: 460 mm / s

  As described above, the period N of the ripple noise 121 of the discharge electrode 8 is 1 msec (= 1 / f). According to Equation 1 described above, the sampling period n can be set within a range of 5 msec or less, for example, 0.5 msec. Here, the sampling number P within the detection distance L (4.6 mm) is set to 8 points, and the 8 sampling values are averaged.

  As described above, in this example, as in the example of FIG. 5, it is possible to obtain the normal value of the toner density sensor 15 by removing the influence of the ripple noise and to appropriately correct the toner image. can get. In addition, since the normal value of the toner density sensor 15 can be obtained more accurately by increasing the number of samplings than in the example of FIG. 5, the correction accuracy of the toner image is improved.

  In the example of FIG. 6, the detection distance L is 4.6 mm. However, it is only necessary to obtain the set sampling number, and the detection distance L is about 1.84 mm, which is a length corresponding to, for example, four periods of ripple noise. That is all you need.

(Example of 10 sampling points)
FIG. 7 is a graph showing an example of sampling data (10 points) output from the toner concentration sensor 15 when there is one AC component generation source. The setting of the output value of the electrode removal 8 is the same as in the example of FIG.
-Output value of the electrode removal electrode AC: 4 kV, DC: -2 kV, frequency f: 1 kHz
Correction conditions: Patch image detection length (detection distance) L: 4.6 mm, process speed V: 460 mm / s

  As described above, the period N of the ripple noise 121 of the discharge electrode 8 is 1 msec (= 1 / f). According to Equation 1 described above, the sampling period n can be set within a range of about 4.4 msec or less, for example, 0.3 msec. Here, the sampling number P within the detection distance L (4 mm) is set to 10 points, and 10 sampling values are averaged.

  As described above, in this example, as in the example of FIG. 6, the influence of ripple noise can be removed to obtain the normal value of the toner density sensor 15, and the toner image can be appropriately corrected. can get. In addition, since the normal value of the toner density sensor 15 with higher accuracy can be obtained by increasing the number of samplings than in the example of FIG. 6, the correction accuracy of the toner image is further improved.

  In the example of FIG. 7, the detection distance L is 4.6 mm, but it is only necessary to obtain the set number of samplings. The detection distance L is about 1.38 mm, which is a length corresponding to, for example, three periods of ripple noise. That is all you need.

  5 to 7 show examples in which the sampling value is an even number, but may be an odd number as long as the ripple noise can be canceled.

[When there are two AC component generation sources: electrode removal and separation electrode]
FIG. 8 is an explanatory diagram showing an example of an AC waveform output from the removal electrode 8 and the separation electrode 9. FIG. 9 is a graph showing an example of sampling data (four points) output from the toner concentration sensor 15 when there are two AC component generation sources. The output values and correction conditions of the electrode removal electrode 8 and the separation electrode 9 are set as follows. These can be set by the user operating the operation display unit 105.
-Output value of electrode removal electrode AC: 4 kV, DC: -2 kV, frequency f: 500 Hz
-Output value of separation pole 9 AC: 2 kV, DC: -1 kV, frequency f: 200 Hz
Correction conditions: Patch image detection length (detection distance) L: 5 mm, process speed V: 460 mm / s

  As shown in FIG. 8, when the frequency f of the output value of the discharge electrode 8 is 500 Hz, the period N of the ripple noise 122a by the discharge electrode 8 is 2 msec (= 1 / f). Similarly, the period N of the ripple noise 122b due to the separation pole 9 is 5 msec. Therefore, the period N of the combined waveform 122 (see FIG. 9) of the ripple noise 122a and the ripple noise 122b output from the removal electrode 8 and the separation pole 9 is 5 msec. According to Equation 1 described above, the sampling period n can be set within a range of about 5.4 msec or less, for example, 2.5 msec. Here, as shown in FIG. 9, the sampling number P within the detection distance L (5 mm) is set to four points, and the four sampling values are averaged. The timing at which the toner density sensor 15 starts measurement may start from an arbitrary phase of the combined ripple noise waveform.

  As described above, in this example, an appropriate sampling period and the number of samplings (in this case, depending on the frequency of the AC component obtained by synthesizing the AC components output from a plurality of AC component generation sources (in this example, the removal electrode 8 and the separation electrode 9). Adjust 4 points in the example. Then, by averaging the plurality of sampling values output from the toner density sensor 15, the normal value of the toner density sensor 15 can be obtained by removing the influence of ripple noise. Therefore, it is possible to change the image forming condition based on the normal value of the toner density sensor 15 and appropriately correct the toner image to be formed.

  According to the first embodiment described above, an appropriate sampling period and sampling number are set according to the frequency of the AC component output from the AC component generation source in the vicinity of the toner concentration sensor 15. Then, the sampling values of a predetermined number of sampling points output from the toner density sensor 15 according to the sampling cycle are averaged. Thereby, even when there are two or more AC component generation sources, a normal value obtained by removing the influence of ripple noise from the detection value of the toner density sensor 15 can be obtained. As a result, the image forming conditions can be changed based on the normal value of the toner density sensor 15, and the formed toner image can be corrected appropriately.

Conventionally, as means for removing ripple noise, (1) shield the toner density sensor, (2) remove noise by circuit processing of the toner density sensor, and (3) turn off the AC bias output during the detection operation of the toner density sensor. And so on. However, the removal means (1) increases the installation space and costs. Further, the removing means (2) causes an increase in cost and an increase in circuit area. Furthermore, since the removal means (3) stops the AC bias output that is originally required for image formation, the productivity and the image quality are degraded.
On the other hand, according to the configuration of the present embodiment, an accurate output of the toner density sensor 15 can be obtained by varying the sampling period in consideration of the ripple noise period, which reduces productivity and increases costs. High quality image quality can be obtained without degrading correction accuracy.

<Second Embodiment>
As described above, since the toner concentration sensor 15 is composed of a semiconductor device such as a photo sensor, a line sensor, or an image sensor, an electric charge (dark current) is generated in a state where light is blocked. When an AC component generation source exists in the vicinity of the toner concentration sensor 15, this dark current varies depending on the AC component output from the AC component generation source. Therefore, an embodiment will be described in which the dark current of the toner density sensor 15 is analyzed and the influence of ripple noise included in the output of the toner density sensor 15 is removed.

  FIG. 10 is an explanatory diagram showing an internal configuration of a main part and a ripple noise removing unit of the image forming apparatus according to the second embodiment of the present invention. 10, parts corresponding to those in FIG. 3 are denoted by the same reference numerals, and detailed description thereof is omitted.

  An image forming apparatus 10A illustrated in FIG. 10 includes a ripple noise removing unit 111A in place of the ripple noise removing unit 111 of the image forming apparatus 10 illustrated in FIG. The ripple noise removal unit 111A includes a dark current detection unit 131, a ripple noise determination unit 132, a frequency analysis unit 133, a ripple noise cycle calculation unit 113, and a sampling cycle control unit 114.

  The dark current detection unit 131 detects a dark current based on a sampling value output by the toner density sensor 15 during a predetermined sampling period when the light is blocked, and outputs the detection result to the ripple noise determination unit 132.

  The ripple noise determination unit 132 determines whether or not the ripple noise that needs to remove the influence on the dark current is included based on the detection result of the dark current input from the dark current detection unit 131, and the determination result is determined. The frequency analysis unit 133 is notified.

  The frequency analysis unit 133 analyzes the frequency of the ripple noise included in the dark current and outputs the analysis result (AC frequency information) to the ripple noise period calculation unit 113. As the frequency analysis unit 133, for example, a Fast Fourier Transform (FFT) device can be used.

FIG. 11 is a flowchart showing ripple noise removal processing by the ripple noise removal unit 111A of the image forming apparatus 10A according to the second embodiment of the present invention.
First, under the control of the control unit 100, the dark current detection unit 131 of the ripple noise removal unit 111A has a toner concentration in a state where the AC component generation source generates an AC component (hereinafter referred to as “AC output ON”). The dark current of the sensor 15 is detected at an arbitrary sampling period, and the detected dark current sampling value is averaged (step S11). When the AC output is on, the control unit 100 causes the AC electrode generation source, for example, the electrode removal 8 and the separation electrode 9 to generate an AC component based on the set value as described above. Normally, since AC output is off except during image formation, control is performed to turn on AC output when dark current is detected.

  Next, the ripple noise determination unit 132 compares the dark current value of the toner density sensor 15 when the AC output is on with the dark current value determined for each device of the toner density sensor 15, and the dark current when the AC output is on. It is determined whether or not the value is within a predetermined range (−b ≦ x ≦ b x: toner density sensor output value) (step S12). The dark current value determined for each device of the toner density sensor 15 is stored in advance in the ROM 102 or the like.

  Here, FIG. 12 is an explanatory diagram showing a method for determining the presence or absence of ripple noise due to dark current. In the figure, the horizontal axis indicates the position of the sampling point, and the vertical axis indicates the detection value (dark current value) detected by the toner density sensor 15. The dark current is measured, for example, at a time T other than the detection time of the toner density sensor 15 used for correcting the toner image, that is, when the toner density sensor 15 is in an off state.

As shown in FIG. 12, when the dark current value of the toner density sensor 15 is within the ripple noise generation threshold (−b ≦ x ≦ b) (YES in step S12), the ripple noise determination unit 132 It is determined that no ripple noise has occurred, and the ripple noise removal process is terminated.
On the other hand, when the dark current value of the toner density sensor 15 is outside the range of the ripple noise occurrence threshold (−b ≦ x ≦ b) (NO in step S12), the ripple noise determination unit 132 determines that the ripple noise 125 to be removed is It determines with having generate | occur | produced, and the determination result is output to the frequency analysis part 133. FIG.

  When there is the ripple noise 125, the frequency analysis unit 133 analyzes the frequency component included in the ripple noise 125, and outputs the analysis result to the ripple noise period calculation unit 113 as AC frequency information (step S13).

  Next, the ripple noise cycle calculation unit 113 calculates a ripple noise cycle from the AC frequency information input from the frequency analysis unit 133. When the ripple noise 125 includes a plurality of AC frequency information (a plurality of AC components), the ripple noise cycle is calculated following step S4 in FIG. Finally, the sampling period control unit 114 changes the sampling period of the toner density sensor 15 according to the ripple noise period according to the equation (1) (step S14). Then, using the sampling value output from the toner density sensor 15 based on this sampling period, the image forming conditions are changed to create a toner image.

  As described above, in the second embodiment, an effect similar to that in the first embodiment can be obtained, in which the normal value of the toner density sensor 15 can be obtained by removing the influence of the ripple noise. In addition to this, the following effects are obtained in the present embodiment. In the present embodiment, the AC frequency information is obtained based on the dark current output from the toner density sensor 15 when the AC output is on, instead of the AC frequency information stored in the AC frequency storage unit 112 in advance. Therefore, the normal value of the toner density sensor 15 can be obtained by removing the influence of the ripple noise output from the AC component generation source existing in the vicinity of the toner density sensor 15.

  In the configuration described above, the ripple noise determination unit 132 detects the dark current value output from the toner density sensor 15 when the AC output is on, and determines whether or not an AC component (ripple noise) of a predetermined level or higher is included. However, this determination process may be omitted. In this case, since all AC components included in the dark current value output from the toner density sensor 15 are processed as ripple noise, it is possible to obtain a detection value from which the influence of the ripple noise is further removed from the toner density sensor 15.

<Modification>
The embodiment to which the invention made by the present inventor is applied has been described above. However, the present invention is not limited by the description and drawings which form part of the disclosure of the invention according to the above-described embodiments, and various modifications may be made without departing from the spirit of the invention described in the claims. Is possible.

  For example, in the first and second embodiments described above, the example in which the image forming unit 5 is provided with the four image forming units 5Y, 5M, 5C, and 5K to form a color image has been described. You may apply to the image forming apparatus which forms the monochrome image provided only one.

  In the first and second embodiments described above, the toner image formed on the photoreceptor 51 (photoreceptor drum) is transferred to the intermediate transfer belt 6, and the toner image is transferred from the intermediate transfer belt 6 onto the sheet. Although the example of the next transfer has been described, the present invention may be applied to an image forming apparatus that directly transfers a toner image from the photoreceptor 51 to a sheet as an image carrier.

  In the first and second embodiments described above, the configuration in which the ripple noise removing unit 111, 111A executes the ripple noise removing process has been described. However, the control unit 100 may perform a part or all of the configuration. May be.

  In the second embodiment described above, when there are a plurality of ripple noise frequencies, the frequency of the ripple noise outside the threshold range is specified, and only the ripple noise of the specified frequency is removed. Also good.

  DESCRIPTION OF SYMBOLS 5 ... Image formation part, 6 ... Intermediate transfer belt, 7 ... Secondary transfer part, 10, 10A ... Image formation apparatus, 15 ... Toner density sensor, 111, 111A ... Ripple noise removal part, 112 ... AC frequency storage part, 113 ... Ripple noise cycle calculation unit, 114 ... Sampling cycle control unit, 131 ... Dark current detection unit, 132 ... Ripple noise determination unit, 133 ... Frequency analysis unit

Claims (6)

An image forming unit for forming a toner image;
An image carrier that carries the toner image formed by the image forming unit;
A toner density sensor that samples a toner density of a toner image formed on the image carrier at a predetermined sampling period and outputs a sampling value;
A ripple noise period calculation unit that calculates a ripple noise period due to an AC component generated from one or more AC component generation sources existing in the vicinity of the toner concentration sensor from AC component frequency information of the AC component generation source;
A sampling period control unit that performs control to vary the sampling period according to the ripple noise period calculated by the ripple noise period calculation unit;
An image forming apparatus comprising: an averaging processing unit that averages a plurality of sampling values output from the toner density sensor in accordance with the sampling cycle varied by the sampling cycle control unit. The ripple noise period is N, the sampling period is n, the length for detecting a toner image in the driving direction of the image carrier is L, the driving speed of the image carrier is V, and the sampling number is P (a natural number of 2 or more) ), The sampling period n is
n ≦ L / (2V) and n ≠ N
And the sampling number P is P ≦ (N / n) × a (a is a natural number)
The image forming apparatus according to claim 1, wherein the image forming apparatus is a maximum natural number satisfying the condition. The image forming apparatus according to claim 2, further comprising a storage unit that stores the AC component frequency information of the AC component generation source. A dark current detection unit that detects a dark current of the toner concentration sensor in a state where an AC component is generated from the AC component generation source;
The image forming apparatus according to claim 2, further comprising: a frequency analysis unit that analyzes a frequency of the AC component included in the dark current detected by the dark current detection unit and outputs the analysis result as the AC component frequency information. apparatus. It is determined whether or not the dark current value of the toner density sensor in a state where an alternating current component is generated from the alternating current component generation source is within a set threshold range, and the dark current value is outside the threshold range. The image forming apparatus according to claim 4, further comprising: a ripple noise determination unit that determines that ripple noise is generated. The ripple noise period calculation unit, when the AC component frequency information is one, calculates the ripple noise period from the frequency included in the AC component frequency information,
The image according to any one of claims 1 to 5, wherein when the AC component frequency information is plural, the ripple noise period is calculated based on a smallest frequency among plural frequencies included in the AC component frequency information. Forming equipment.

Images