JP5262809B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the productivity of a monochrome image by making larger the outer diameter of a black photoreceptor, and to suppress a color smear between the monochrome image and a color image with comparatively simple control. <P>SOLUTION: The image forming apparatus 11, which includes a first driving means 42 driving color photoreceptors 15Y, 15M and 15C and a second driving means 43 driving the black photoreceptor 15K different in diameter from that of each of color photoreceptors, includes: a first detection means 49 detecting the rotational speed fluctuations of the color photoreceptors 15; a second detection means 52 detecting the rotational speed fluctuations of the black photoreceptor 15K; and a control means 57 which Fourier-transforms a detection value, to calculate a frequency, an amplitude and a phase, calculates correction wave data based on the frequency, amplitude and phase of the color photoreceptors 15 and the black photoreceptor 15K after the Fourier transformation and changes the rotational speed of the color photoreceptors 15, so as to superimpose the positional deviation of the color photoreceptors 15 on the positional deviation of the black photoreceptor 15K, based on the correction wave data. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus to which an electrophotographic method is applied, such as a recording device or a display device such as a copier, FAX, or printer, regardless of color or monochrome.

  Conventionally, in an electrophotographic full-color image forming apparatus in which a plurality of photosensitive drums are juxtaposed in tandem, the outer diameter (peripheral length) of each photosensitive drum is the same, and the rotational drive system of each drum is the same. The color shift in the sub-scanning direction has been suppressed to a minimum by controlling the phase of rotation unevenness due to the eccentricity of the gear.

  In recent full-color image forming apparatuses, there is a tendency to emphasize the productivity of monochrome images. For this reason, the outer diameter (outer peripheral length) of the photosensitive drum for forming a monochrome image is set large.

  However, as shown in FIG. 12, when the outer diameter (peripheral length) of the black photosensitive drum 81 for monochrome image formation is larger than that of the photosensitive drum 82 for color image formation, the black photosensitive drum 81 and Since the phase and amplitude of the rotation unevenness of the color photoconductive drum 82 are not matched, color misregistration between monochrome and color cannot be suppressed.

  Hereinafter, the color shift will be described. In order to cause color misregistration, first, misregistration occurs. The positional deviation means that the position of the electrostatic latent image actually written on the photosensitive member is shifted from the original writing position due to uneven rotation speed of the motor that drives the photosensitive member. For example, writing is performed from the original writing position 83 on the black photosensitive drum 81 to a position 84 shifted in the direction of the arrow r1 due to uneven rotation speed of a motor (not shown) that drives the photosensitive drum 81. Misalignment occurs. The amount of displacement at this time is represented by the amplitude of the graph a in FIG. 13, and is assumed to be about 7 μm as indicated by the point p. Similarly, writing is performed at a position 86 shifted in the direction of the arrow r2 from the original writing position 85 on the color photosensitive drum 82, thereby causing a positional shift. The amount of positional deviation at this time is similarly represented by the amplitude of the graph b, and is assumed to be about −3 μm as indicated by the point p. Due to this misregistration, black is transferred to the position 88 on the intermediate transfer belt 87, while the color is transferred to the position 89. As a result, color misregistration occurs. The color misregistration amount at this time is represented by the amplitude of the graph c, and as indicated by a point p, a value obtained by subtracting the black color misregistration amount from the color misregistration amount, that is, −3 μm− (7 μm) = − 10 μm. . Due to the color shift, the originally assumed color is not created.

  In order to prevent color misregistration, as shown in FIG. 14, for example, only monochrome driving is controlled so as to eliminate rotation unevenness. As a result, the black misregistration (graph d) can be significantly reduced, but the color misregistration (graph f) cannot be suppressed because the color (graph e) causes misregistration.

  Next, in order to prevent color misregistration, as shown in FIG. 15, the driving of both black and color is controlled to control the rotation unevenness of all colors. As a result, the black misregistration (graph g) and the color misregistration (graph h) can be greatly reduced, and the color misregistration (graph i) can be suppressed. For example, Patent Documents 1 and 2 describe an image forming apparatus that controls a driving unit for each color by transmitting a signal for correcting a rotation speed to each driving unit that drives a photosensitive drum of each color. .

  However, in any of the image forming apparatuses described in the patent documents, there is a problem in that the load on the CPU and the memory serving as the control unit increases because the driving units of the photosensitive drums of the respective colors are controlled.

JP 2007-304558 A JP 2008-90278 A

  The present invention has been made in view of the above-described conventional problems. The outer diameter (peripheral length) of the black photosensitive member is increased to increase the productivity of the monochrome image, and the color of the monochrome image and the color image is increased. It is an object of the present invention to provide an image forming apparatus capable of suppressing the shift by relatively simple control.

As means for solving the above-mentioned problems, an image forming apparatus according to the present invention includes a plurality of color photoreceptors for forming a color image, first drive means for driving the color photoreceptor, and the diameter of the color photoreceptor. A black photosensitive member that forms a monochrome image, and a second driving unit that drives the black photosensitive member.
First detecting means for detecting a rotational speed variation of the color photoconductor;
Second detection means for detecting a rotation speed fluctuation of the black photosensitive member;
The detected value is Fourier transformed to calculate the frequency, amplitude and phase, the frequency, amplitude and phase of the color photoreceptor after the Fourier transform, and the frequency, amplitude and phase of the black photoreceptor after the Fourier transform. And a control means for calculating a correction wave data from the control unit and changing a rotational speed of the color photoconductor so that a positional deviation of the color photosensitive member and a positional deviation of the black photosensitive member overlap with each other based on the correction wave data. ,
Equipped with a,
The correction wave data is obtained by adding the waveform of the phase opposite to the phase of the color photoconductor after Fourier transform and the waveform of the black photoconductor after Fourier transform .

  The control means changes the rotational speed of the color photosensitive member so that the positional deviation of the color photosensitive member and the black photosensitive member overlap, so that the positional deviation of the color photosensitive member and the positional deviation of the black photosensitive member are And the color misregistration between color and black can be reduced.

  Further, since the color shift between the color and the block can be reduced only by changing the rotation speed of the color photoconductor, the color shift can be reduced by simple control.

As other means, a plurality of color photoreceptors for forming a color image, a first drive means for driving the color photoreceptor, a single black photoreceptor for forming a monochrome image having a diameter different from that of the color photoreceptor, An image forming apparatus comprising: a second driving unit that drives the black photosensitive member;
First detecting means for detecting a rotational speed variation of the color photoconductor;
Second detection means for detecting a rotation speed fluctuation of the black photosensitive member;
The detected value is Fourier transformed to calculate the frequency, amplitude and phase, the frequency, amplitude and phase of the color photoreceptor after the Fourier transform, and the frequency, amplitude and phase of the black photoreceptor after the Fourier transform. And a control means for calculating a rotation speed of the black photosensitive member based on the correction wave data so that the positional deviation of the black photosensitive member and the positional deviation of the color photosensitive member overlap with each other. ,
Equipped with a,
It is preferable that the correction wave data is a sum of a waveform having a phase opposite to the phase of the black photoconductor after Fourier transform and a waveform of the color photoconductor after Fourier transform .

  The control means changes the rotation speed of the black photoconductor so that the position shift of the black photoconductor and the position shift of the color photoconductor overlap, so that the position shift of the black photoconductor and the position shift of the color photoconductor And the color shift between black and color can be reduced.

  Further, since the color shift between the color and the block can be reduced only by changing the rotation speed of the black photosensitive member, the color shift can be reduced by simple control.

  Color shift between color and black can be reduced only by changing the rotational speed of either the color photoconductor or the black photoconductor. This also makes it possible to reduce color misregistration with simple control.

1 is a schematic view of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an overall perspective view of the photosensitive drum driving mechanism in FIG. 1. FIG. 3 is a rear view of the photosensitive drum driving mechanism of FIG. 2. FIG. 4 is an enlarged perspective view of the rotation detection device of FIG. 3. FIG. 4 is a block diagram for controlling the photosensitive drum driving mechanism of FIG. 3. 4 is a flowchart for controlling the photosensitive drum driving mechanism of FIG. 3. It is a figure which shows the pulse signal of the gear which the sensor of FIG. 4 detected. It is a figure which shows the amount of position shift and color shift of a color photoconductor and a black photoconductor obtained by Fourier-transforming a pulse signal. It is a figure which shows the waveform of the correction wave data which the main control part computed. FIG. 10 is a diagram illustrating a waveform of a color photosensitive drum after correction obtained by superimposing the waveform of the color photosensitive drum in FIG. 8 and the correction wave data in FIG. 9; It is a figure which shows that color misregistration decreased by controlling the color photoconductive drum. FIG. 4 is a diagram illustrating a positional shift and a color shift that occur in a photosensitive drum and a secondary transfer belt. FIG. 6 is a diagram illustrating a positional shift amount and a color shift amount between a color photoconductor and a black photoconductor. It is a figure which shows the result of having controlled the conventional photosensitive drum drive mechanism. It is a figure which shows the other result which controlled the conventional photoconductor drum drive mechanism.

  Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows an image forming apparatus 11 according to an embodiment of the present invention. First, a schematic configuration of the image forming apparatus 11 will be described. The image forming apparatus 11 includes an intermediate transfer belt 12 as an image carrier at a substantially central portion inside the image forming apparatus main body 11a. The intermediate transfer belt 12 is supported by the outer peripheral portions of the rollers 13a and 13b and is driven to rotate in the direction of arrow A. Below the lower horizontal portion of the intermediate transfer belt 12, four print units 14Y, 14M, 14C, and 14K respectively corresponding to yellow (Y), magenta (M), cyan (C), and black (K) colors are intermediate. They are arranged side by side along the transfer belt 12. Each of the print units 14Y, 14M, 14C, and 14K includes the photosensitive drums 15Y, 15M, 15C, and 15K, the developing devices 16Y, 16M, 16C, and 16K, and the intermediate transfer belt 12, and the photosensitive drums 15Y, 15M, and 15C, respectively. Primary transfer rollers 17Y, 17M, 17C, and 17K that face 15K are provided. The developing devices 16Y, 16M, 16C, and 16K communicate with toner cartridges 18Y, 18M, 18C, and 18K disposed above the intermediate transfer belt 12, respectively. A portion of the intermediate transfer belt 12 supported by the driving roller 13 a is in pressure contact with the secondary transfer roller 19, and a nip portion between the secondary transfer roller 19 and the intermediate transfer belt 12 serves as a transfer portion 21. . A pressure roller 25 connected to the fixing roller driving unit 24 and a fixing roller 26 facing the pressure roller 25 are disposed further downstream of the sheet passing path 22a. The pressure contact portion serves as a fixing nip region 27. It has become.

  In the lower part of the image forming apparatus 11, a first paper feed unit 28a and a second paper feed unit 28b are arranged vertically. The sheets S stacked and accommodated in each of the sheet feeding units 28a and 28b are sent out one by one from the uppermost one to the sheet passing path 22b. A circulation path 31 is provided on the side of the image forming apparatus 11. The single-sided printed paper that is switched back by the paper discharge roller 32 is conveyed downward through the circulation path 31, and is again conveyed upward through the paper passing path 22c with the unprinted surface facing the intermediate transfer belt 12 side. It has become so. A manual paper feeder 33 is provided below the circulation path 31. A paper feed roller 34 for feeding the paper S is disposed in the paper feed path 22b from the manual paper feed device 33 and the paper feed units 28a and 28b as representatively shown in FIG. Reference numeral 35 denotes an exposure unit 35 that exposes the print units 14Y, 14M, 14C, and 14K based on image signals.

  Next, a schematic operation of the image forming apparatus 11 having the above configuration will be described. Color print data obtained by reading an image with the image reading unit 37 or image data output from a personal computer or the like is subjected to predetermined signal processing, and then yellow (Y), magenta (M), cyan ( C) and black (K) are supplied to the exposure unit 35 as image signals of respective colors. In each of the print units 14Y, 14M, 14C, and 14K, the laser light modulated by the image signal is projected onto the respective photosensitive drums 15Y, 15M, 15C, and 15K, and an electrostatic latent image is formed. Yellow, magenta, cyan, and black toner images are formed on the photosensitive drums 15Y, 15M, 15C, and 15K developed by the developing devices 16Y, 16M, 16C, and 16K. The formed yellow, magenta, cyan, and black toner images are primarily transferred onto the moving intermediate transfer belt 12 in sequence by the action of the primary transfer rollers 17Y, 17M, 17C, and 17K. The superimposed toner image formed on the intermediate transfer belt 12 in this way reaches the transfer unit 21 as the intermediate transfer belt 12 moves. In the transfer unit 21, the superimposed toner images are secondarily transferred collectively onto the paper S supplied from the paper supply units 28 a and 28 b or the manual paper supply device 33 by the action of the secondary transfer roller 19. Next, the sheet S on which the toner image is secondarily transferred reaches the fixing nip region 27. In the fixing nip region 27, the toner image is fixed on the paper S by the action of the fixing roller 26 and the pressure roller 25. The paper S on which the toner image has been fixed is discharged to the paper discharge tray 38 via the paper discharge roller 32.

  As shown in FIG. 2, the photosensitive drums 15 </ b> Y, 15 </ b> M, 15 </ b> C, and 15 </ b> K are driven by the photosensitive drum driving mechanism 41. The photosensitive drum driving mechanism 41 includes a first driving unit 42 that is a first driving unit that drives the yellow, magenta, and cyan photosensitive drums 15Y, 15M, and 15C that form a color image, and a black that forms a monochrome image. The second driving unit 43 is a second driving unit that drives the photosensitive drum 15K.

  Referring to FIG. 3, the first drive unit 42 meshes with the first motor 45, and the gear 47 </ b> C connected to the cyan photosensitive drum 15 </ b> C rotating around the shaft 46 </ b> C, and the gear 47 </ b> C between the first motor 45. Is engaged with the first motor 45 at a position opposed to the gear 47M, and is engaged with a gear 47M connected to a magenta photosensitive drum 15M rotating around a shaft 46M, and an intermediate gear 48 engaged with the gear 47M. A gear 47Y connected to 15Y, and a first rotation detecting device 49 serving as a first detecting means for detecting the rotation speed of the gear 47C, that is, the rotation speed of the cyan photosensitive drum 15C. Since the first motor 45 drives the first drive unit 42, the rotational speeds of the yellow, magenta, and cyan photosensitive drums 15Y, 15M, and 15C are the same, and no color shift occurs between these colors. . Further, in order to detect the rotation speed of the photoconductive drums 15Y, 15M, and 15C that form a color image, the first gear is selected from any one of the yellow gear 47Y, the magenta gear 47M, and the cyan gear 47C. A single rotation detection device 49 may be provided.

  The second drive unit 43 meshes with the second motor 51 and is connected to a black photosensitive drum 15K that rotates about the shaft 46K, and the rotational speed of the gear 47K, that is, the black photosensitive drum 15K. And a second rotation detection device 52 as second detection means for detecting the rotation speed.

  As shown in FIG. 4, the first and second rotation detecting devices 49 and 52 provided on the gears 47C and 47K are on the opposite side of the respective photosensitive drums 15 (15C and 15K) of the gear 47 (47C and 47K). A disk-shaped encoder disk 54 that is fixed to the surface and rotates around the shaft 46 (46C, 46K) together with the gear 47, and light that passes through a slit 55 formed in the encoder disk 54 is detected to detect the gear 47. And two sensors 56 for detecting the rotational speed.

  As for the number of sensors 56, if the rotation center of the encoder disk 54 is deviated from the rotation center of the gear 47, the detection signal is shifted even if the rotation speed of the gear 47 is not changed. A change in one rotation cycle is detected. Therefore, by arranging the two sensors 56 so that the shaft 46 is symmetric between the two, it is possible to detect a signal having a phase opposite to that of the shift, so that correction for canceling the fluctuation of the eccentric component due to the shift is performed. The rotational speed of the gear 47 can be detected accurately.

  As shown in FIG. 5, the rotational speeds of the gears 47C and 47K detected by the first and second rotation detecting devices 49 and 52 are inputted to the main control unit 57 as control means. The main control unit 57 is connected to a motor control unit 58, and the motor control unit 58 is connected to the motors 45 and 51 via a driver 59.

  Next, driving control of the photosensitive drum 15 in the photosensitive drum driving mechanism 41 having the above-described configuration will be described in detail with reference to the flowchart of FIG.

  In step S1, the second rotation detection device 52 detects a pulse signal of the black photosensitive drum 15K shown in FIG. 7, for example. In step S2, the first rotation detector 49 similarly detects the pulse signal of the cyan photosensitive drum 15C. In step S3, the main control unit 57 performs Fourier transform on the pulse signal of the black photosensitive drum 15K, thereby calculating the frequency, amplitude, and phase of the black photosensitive drum 15K shown in FIG. 8 (graph A). . In step S4, the main control unit 57 similarly performs Fourier transform on the pulse signal of the cyan photosensitive drum 15C, so that the frequency and amplitude of the color photosensitive drum 15 (15Y, 15M, 15C) shown in the graph B are obtained. The phase is calculated. When unevenness in rotational speed occurs in the motors 45 and 51 of the photosensitive drum driving mechanism 41, the pulse signal detected from the photosensitive drum 15 is disturbed, and the amplitude of each frequency obtained by Fourier-transforming this changes. This amplitude indicates the amount of misregistration, and the difference between the amplitude of the black photoconductor drum 15K and the amplitude of the color photoconductor drum 15 is the color shift indicated by the amplitude of the graph C.

  In step S5, the main control unit 57 calculates correction wave data. Here, the correction wave data is, for example, when correcting the rotational speed of the color photoconductor drum 15, and a waveform (graph E in FIG. 9) having a phase opposite to the phase of the color photoconductor drum 15 after Fourier transform. FIG. 6 is a graph (graph D) obtained by adding the waveform (graph A) of the black photosensitive drum 15K after Fourier transform. Further, as shown in FIG. 10, the correction wave data (graph D) is superimposed on the waveform (graph B) of the color photosensitive drum 15 so that it substantially matches the waveform of the black photosensitive drum 15K. The waveform shown in F is obtained.

  In step S6, the main control unit 57 performs inverse Fourier transform on the correction wave data into a pulse signal. In step S <b> 7, the main control unit 57 transmits the pulse signal after the inverse Fourier transform to the motor control unit 58 of the color photosensitive drum 15 and outputs the pulse signal to the first motor 45 through the driver 59. ing. Thus, the first motor 45 drives the color photosensitive drum 15 based on the pulse signal of the correction wave data. Therefore, the positional deviation amount is substantially matched by reducing the rotational speed of the color photoconductive drum 15 to the rotational speed of the black photoconductive drum 15K, and the color misregistration is reduced. Specifically, as shown in FIG. 11, since the positional deviation amount (graph A) of the black photosensitive drum 15K and the positional deviation amount (graph F) of the color photosensitive drum 15 substantially coincide, Color shift (graph G) from the color can be suppressed.

  Thereby, the drive control of the photosensitive drums 15Y, 15M, 15C, and 15K in the photosensitive drum drive mechanism 41 is completed.

  As described above, according to this embodiment, the first motor 45 can reduce the color misregistration between color and black only by controlling the rotation speed of the color photoconductor drum 15. Color shift can be reduced by control.

  In the above embodiment, the rotational speed of the color photosensitive drum 15 is controlled. However, the same effect can be obtained by controlling the rotational speed of the black photosensitive drum 15K. When the rotation speed of the black photosensitive drum 15K is controlled, the correction wave data in Step 5 is converted to the waveform of the phase opposite to the phase of the black photosensitive drum 15K after the Fourier transformation, and the color photosensitivity after the Fourier transformation. Calculation is performed by adding the waveform of the body drum 15 together.

  In step S <b> 6, the main control unit 57 transmits the correction wave data to the motor control unit 58 of the black photosensitive drum 15 </ b> K and outputs the correction wave data to the second motor 45 through the driver 59.

DESCRIPTION OF SYMBOLS 11 Image forming apparatus 15 Photosensitive drum 49 1st rotation detection apparatus (1st detection means)
52 Second rotation detection device (second detection means)
57 Main control unit (control means)

Claims (2)

A plurality of color photoreceptors for forming a color image, a first driving means for driving the color photoreceptor, one black photoreceptor for forming a monochrome image having a diameter different from that of the color photoreceptor, and the black photoreceptor An image forming apparatus comprising: a second driving unit that drives
First detecting means for detecting a rotational speed variation of the color photoconductor;
Second detection means for detecting a rotation speed fluctuation of the black photosensitive member;
The detected value is Fourier transformed to calculate the frequency, amplitude and phase, the frequency, amplitude and phase of the color photoreceptor after the Fourier transform, and the frequency, amplitude and phase of the black photoreceptor after the Fourier transform. And a control means for calculating a correction wave data from the control unit and changing a rotational speed of the color photoconductor so that a positional deviation of the color photosensitive member and a positional deviation of the black photosensitive member overlap with each other based on the correction wave data. ,
Equipped with a,
2. The image forming apparatus according to claim 1, wherein the correction wave data is obtained by adding a waveform having a phase opposite to the phase of the color photoconductor after Fourier transform and a waveform of the black photoconductor after Fourier transform . A plurality of color photoreceptors for forming a color image, a first driving means for driving the color photoreceptor, one black photoreceptor for forming a monochrome image having a diameter different from that of the color photoreceptor, and the black photoreceptor An image forming apparatus comprising: a second driving unit that drives
First detecting means for detecting a rotational speed variation of the color photoconductor;
Second detection means for detecting a rotation speed fluctuation of the black photosensitive member;
The detected value is Fourier transformed to calculate the frequency, amplitude and phase, the frequency, amplitude and phase of the color photoreceptor after the Fourier transform, and the frequency, amplitude and phase of the black photoreceptor after the Fourier transform. And a control means for calculating a rotation speed of the black photosensitive member based on the correction wave data so that the positional deviation of the black photosensitive member and the positional deviation of the color photosensitive member overlap with each other. ,
Equipped with a,
2. The image forming apparatus according to claim 1, wherein the correction wave data is obtained by adding a waveform having a phase opposite to the phase of the black photoconductor after Fourier transform and a waveform of the color photoconductor after Fourier transform .

Images