JP2017191232A - Development device, and image formation device equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a development device capable of suppressing a collision sound which is emitted by a swing gear accompanying switching between monochrome and color modes, without hindering a reduction in size and an increase in speed of an image formation device.SOLUTION: A swing gear (810) changes its posture to a first position during the forward rotation of a drive motor (700) and to a second position during the inverse rotation. A first transmission system transmits torque from the swing gear at the first position and a second transmission system transmits torque from the swing gear at the second position. A first development roller (28K) is rotated by the torque from either of the transmission systems, and attaches a monochrome toner to a photoreceptor (21K). A second development roller is rotated by the torque from the first transmission system, and attaches toners in three colors to different photoreceptors (21Y, 21M, 21C). A control part (286), at switching between color and monochrome modes, makes a drive motor perform precursor rotation. The drive motor, at the precursor rotation, decelerates after acceleration to a rotational speed lower than normal. During the deceleration, the swing gear completes posture change.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an electrophotographic image forming apparatus, and more particularly to a developing roller driving mechanism.

  In electrophotographic image forming devices such as laser printers and multifunction peripherals (MFPs), actuators are implemented for each of the various functions required mainly for the purpose of maintaining high image quality, high speed, and high reliability. Is done. For example, different drive motors are installed for each transport roller for the purpose of achieving both high speed and high accuracy of sheet transport, and developing devices with different toner colors are driven by different motors in order to reduce color misregistration errors. Is done.

  In recent years, with the progress of downsizing and height reduction of image forming apparatuses, demand for use in SOHO, retail stores, etc. is increasing. In order to meet this demand, it is required to further reduce the size and height of medium- and small-sized models such as desktop models, and to realize multi-functions such as a combination of a printer and a scanner at a lower cost. Yes. An idea for achieving both a reduction in size and a reduction in cost without reducing the function is to reduce the total number of motors by realizing a plurality of operations with a common motor. In this case, switching between different operations is realized by switching a transmission mechanism of torque from the same motor between different systems.

For example, the four-cycle color printer disclosed in Patent Document 1 rotates the entire rotary unit that holds four color developing cartridges to alternately bring these cartridges closer to a single photoconductor. As a result, the motor and the pressure member for pressing each cartridge against the photosensitive member are shared.
The tandem type color printer disclosed in Patent Document 2 uses a one-way clutch to transmit the torque of a single drive motor to different gear trains during forward rotation and reverse rotation. Thus, the torque rotates both the cyan (C) toner developing roller and the black (K) toner developing roller during normal rotation of the motor, and rotates only the K toner developing roller during reverse rotation.

  Patent Document 3 discloses a technique for realizing switching of a transmission mechanism between different gear trains using a swing gear. The color printer disclosed in Patent Document 4 uses a swing gear to transmit the torque of a single drive motor to different gear trains during forward rotation and reverse rotation. As a result, the torque rotates both the fixing roller and the paper discharge roller when the motor rotates forward, and separates the pressure member from the fixing roller when the motor rotates in the reverse direction.

Japanese Patent Laid-Open No. 06-317980 JP 2010-044158 A Japanese Patent Laid-Open No. 2004-225761 Japanese Patent Laying-Open No. 2015-066451

  As for tandem color printers, it is considered promising that sharing the drive motor for the four color toner developing rollers is effective in reducing the size and cost of the printer. In this standardization, it is particularly desirable to use a rocking gear. This is because, as described in Patent Document 4, it is difficult to use a one-way clutch to reduce the size of the transmission system and reduce the number of parts.

On the other hand, there is a known problem that it is difficult to suppress the operation sound of the printer when using the swing gear. When the swing gear collides with a fixing member such as a boss that prevents the swing, generally a high and sharp sound is generated. Such a collision sound not only has a high sound pressure, but also the sound quality tends to make the user uncomfortable, so it is not preferable for using the printer in a quiet environment such as SOHO.
As a device for the purpose of suppressing the collision noise generated by the swing gear, for example, a technique of causing the drive motor to slow down the swing gear when the swing gear collides with the fixed member (see, for example, Patent Document 1). And the technique (for example, refer patent document 3) which installs a shock absorbing material or protrusion in the contact part with a fixing member is known. However, in either technique, it is difficult to sufficiently reduce the speed of the oscillating gear without hindering speeding up and downsizing of the printer. Actually, since the rotational speed or torque of the drive motor is set to be high so as to meet the high processing speed of the printer, the amount of deceleration of the oscillating gear necessary for sufficiently reducing the collision noise is excessive. Furthermore, since the swing range of the swing gear is designed to be small so as to meet the small size of the printer, it is difficult to decelerate the swing gear by a necessary amount within the range.

  An object of the present invention is to solve the above-described problems, and in particular, the swing gear is generated in accordance with the switching between the monochrome mode and the color mode without hindering both the downsizing and speeding up of the image forming apparatus. An object of the present invention is to provide a developing device capable of suppressing a collision sound.

  A developing device according to an aspect of the present invention is a developing device that is mounted on an electrophotographic image forming apparatus that includes a tandem type image forming unit and can operate in both a monochrome mode and a color mode. A drive motor that can rotate in both directions, and swings with a torque from the drive motor. When the drive motor rotates in the first direction, it moves to the first position, and when it rotates in the second direction, it moves to the second position. An oscillation gear that switches the transmission destination of the torque by changing, a first transmission system that transmits torque from the oscillation gear at the first position, and a second transmission system that transmits torque from the oscillation gear at the second position The first developing system rotates with torque from either the first transmission system or the second transmission system, rotates with the torque from the first transmission system, and the first developing roller for adhering the monochromatic toner to the photosensitive member. The roller includes a plurality of second developing rollers that adhere toners of different colors to different photoreceptors and a control unit that controls the rotation of the drive motor. The control unit includes the drive motor and the first in the color mode. Rotate in the direction, rotate in the second direction in monochrome mode, and when switching from one mode to the other in both modes, the precursor is temporarily accelerated from the stationary state to a rotational speed lower than the normal rotational speed in each mode and then decelerated. The rotation is executed, and the change of posture of the swinging gear is completed during the deceleration period in the precursor rotation.

  The developing device may further include a chassis that includes at least one boss projecting within the swing range of the swing gear and supports the swing gear so as to be swingable. The oscillating gear may be prevented from oscillating by contacting one of the at least one boss at each of the first position and the second position. The control unit may control the drive motor such that the swing gear collides with any one of the at least one boss during the deceleration period in the precursor rotation. When the control unit causes the drive motor to perform the pre-rotation, the control unit may decelerate the drive motor by stop control for the drive motor. When the control unit causes the drive motor to perform the pre-rotation, the control unit may suppress the rotation speed to be lower than the normal rotation speed by reducing the torque of the drive motor. In this case, the control unit may lower the torque of the drive motor by limiting the amount of current supplied to the drive motor.

  The control unit may skip execution of the precursor rotation by the drive motor according to the operation mode of the image forming apparatus. The control unit may evaluate the degree of deterioration of the swing gear, and may select the speed or time of the precursor rotation according to the degree of deterioration. In this case, the control unit may evaluate the degree of deterioration of the swing gear by the number of sheets processed by the image forming apparatus, the number of rotations of the drive motor, or the energization time. The control unit may select the speed or time of the precursor rotation depending on whether the mode is switching from the color mode or the monochrome mode. The drive motor may be a brushless DC motor.

  An image forming apparatus according to one aspect of the present invention is an electrophotographic image forming apparatus, and includes an exposure unit that forms an electrostatic latent image on a photosensitive member with modulated light based on image data, and a developing device. A developing unit that develops the electrostatic latent image with toner and a transfer unit that transfers the toner image from the photoreceptor to the sheet are provided.

  The developing device according to one aspect of the present invention causes the drive motor to perform a pre-rotation when switching from one of the color mode and the monochrome mode to the other. In the pre-rotation, the drive motor temporarily accelerates from a stationary state to a rotational speed lower than the normal rotational speed in each mode and then decelerates. During the deceleration period in the precursor rotation, the developing device causes the swing gear to complete the posture change. As a result, the developing device can suppress the collision sound generated by the rocking gear when the mode is switched between monochrome and color without hindering the reduction in size and speed of the image forming apparatus.

FIG. 1A is a perspective view illustrating an appearance of an image forming apparatus according to an embodiment of the present invention. (B) is a schematic cross-sectional view of the image forming apparatus along a straight line Ib-Ib shown in (a). FIG. 2A is an enlarged view of a black toner photoconductor unit shown in FIG. FIG. 2B is a partial cross-sectional view of the image forming apparatus along a straight line IIb-IIb shown in FIG. (A) is a schematic diagram which shows a transmission mechanism when the attitude | position of the rocking | fluctuation gear shown in FIG. 2 is a 1st position. (B) is a schematic diagram showing the transmission mechanism when the swing gear is in the second position. FIG. 2 is a block diagram illustrating a configuration of an electronic control system of the image forming apparatus illustrated in FIG. 1. (A) is a graph showing the relationship between the rotational speed of the drive motor and the sound pressure of the collision sound immediately before the swing gear shown in FIG. 2 is stopped by the boss. (B) is a graph which shows the relationship between the torque which a drive motor applies with respect to the rocking gear just before being stopped by a boss | hub, and the sound pressure of a collision sound. (A) is a graph showing the time-dependent change of the rotational speed of the drive motor ranging from a precursor rotation to a normal starting sequence. (B) is a graph showing the time-dependent change of the rocking | fluctuation angle of the rocking | fluctuation gear accompanying the precursor rotation of a drive motor. It is a flowchart of control of the drive motor by the control part shown in FIG. (A) is a table | surface which shows the relationship between the number of sheets which the image forming apparatus processed, the magnitude | size of the load which a rocking | fluctuation gear receives, and the time of precursor rotation. (B) is a graph showing the time-dependent change of the rotational speed of the drive motor in precursor rotation. (C) is a graph showing the time-dependent change of the swing angle of the swing gear accompanying the precursor rotation. (A) is a table | surface which shows the relationship between the change direction of the rocking | swiveling angle of a rocking | fluctuation gear, the magnitude | size of the load which it receives, and the time of precursor rotation. (B) is a graph showing the time-dependent change of the rotational speed of the drive motor in precursor rotation. (C) is a graph showing the time-dependent change of the swing angle of the swing gear accompanying the precursor rotation.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Appearance of image forming apparatus]
FIG. 1A is a perspective view showing an external appearance of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus 100 is an electrophotographic color printer, that is, a color laser printer. A paper discharge tray 41 is provided on the upper surface of the printer 100 casing, and accommodates sheets discharged from a paper discharge port 42 opened in the back thereof. An operation panel 51 is attached in front of the paper discharge tray 41. On the operation panel 51, a display with a built-in touch panel is arranged in addition to various mechanical push buttons. The display displays a graphics user interface (GUI) screen such as an operation screen and an input screen for various information. The touch panel accepts user input operations through gadgets including GUI screens such as icons, virtual buttons, menus, and toolbars. A sheet feeding cassette 11 is removably attached to the bottom of the printer 100, and a bundle of sheets is accommodated therein. “Sheet” refers to a thin film or thin plate material, article, or printed material made of paper or resin. The type of sheet that can be stored in the paper feed cassette 11, that is, the paper type, is plain paper, high-quality paper, color paper, or coated paper, and the size is A3, A4, A5, or B4. Furthermore, the posture of the sheet can be set to either vertical or horizontal.

[Internal structure of image forming apparatus]
FIG. 1B is a schematic cross-sectional view of the printer 100 along the straight line Ib-Ib shown in FIG. As shown in the figure, the printer 100 includes a feeding unit 10, an image forming unit 20, a fixing unit 30, and a paper discharge unit 40.
The feeding unit 10 feeds the sheet SH1 from the paper feeding cassette 11 to the image forming unit 20 one by one using the paper feeding roller 12.

  The image forming unit 20 is a tandem type, and forms a color or monochrome toner image on the sheet SH2 sent from the feeding unit 10. Specifically, each of the four photoconductor (PC) units 20Y, 20M, 20C, and 20K first charges the surface of the photoconductor (PC) drums 21Y, 21M, 21C, and 21K, and the charged portion exposes the exposure unit 22. Shed light from Since these lights are modulated according to the gradation value distribution of yellow (Y), magenta (M), cyan (C), and black (K) indicated by the image data, each surface of the PC drum 21Y,. An electrostatic latent image of each color is formed. Next, the PC units 20Y,... Develop the electrostatic latent image with Y, M, C, and K toners. Thereafter, the four-color toner images are sequentially transferred from the surface of the PC drum 21Y,... To the surface of the intermediate transfer belt 24 by the electric field between the primary transfer rollers 23Y, 23M, 23C, 23K and the PC drum 21Y,. Transferred to the same position. Thus, one color toner image is formed at that position. Thereafter, when this color toner image passes through the nip between the drive pulley 24R of the intermediate transfer belt 24 and the secondary transfer roller 25, the sheet is simultaneously fed to the same nip by the electric field between the both 24R and 25. Transferred to the surface of SH2. The sheet SH2 is peeled off from the secondary transfer roller 25 and then sent out to the fixing unit 30.

  The fixing unit 30 thermally fixes the toner image on the sheet SH <b> 3 sent out from the image forming unit 20. Specifically, when the sheet SH3 is passed through the nip between the fixing roller 31 and the pressure roller 32, the fixing roller 31 applies heat of a built-in heater to the surface of the sheet SH3, and the pressure roller No. 32 applies pressure to the heated portion of the sheet SH3 and presses it against the fixing roller 31. The toner is welded onto the surface of the sheet SH3 by the heat from the fixing roller 31 and the pressure from the pressure roller 32. Thereafter, the fixing roller 31 and the pressure roller 32 send the sheet SH3 from the fixing unit 30.

The paper discharge unit 40 conveys the sheet SH3 sent from the fixing unit 30 to the paper discharge tray 41. Specifically, when the leading end of the sheet SH3 reaches the nip between the fixing unit 30 and the discharge roller 43, the discharge roller 43 pulls the leading end into the discharge port 42. As a result, the sheets SH3 sequentially pass through the discharge outlet 42 from the leading edge and are stacked on the discharge tray 41.
[Photosensitive unit structure]
FIG. 2A is an enlarged view of the PC unit 20K for K toner shown in FIG. The PC units 20Y, 20M, and 20C for other color toners also have a substantial structure in common with the PC unit for K toner 20K. The PC unit 20K includes a charger 26, an exposure port 27, a developing unit 28, and a cleaning blade 29 in addition to the PC drum 21K. These are arranged around the PC drum 21K.

-Photosensitive drum-
The PC drum 21K is a cylindrical member made of a conductor such as aluminum whose outer peripheral surface is covered with a photoconductor. The photoreceptor is a material whose charge amount changes according to the exposure amount, and includes, for example, an inorganic material such as amorphous selenium, selenium alloy, amorphous silicon, or a stacked structure (OPC) of a plurality of organic materials. Although (a) in FIG. 2 is not shown, the PC drum 21K can rotate around a central axis (in FIG. 2A, the axis passing through the center of the circular cross section of the PC drum 21K perpendicular to the paper surface). It is supported by. The central shaft is connected to the drive motor through a torque transmission mechanism such as a gear and a belt. When the PC drum 21K rotates once by the torque from the drive motor (clockwise in FIG. 2A), the surface of the photoconductor faces the surrounding elements 26, 27, 28, 23K, and 29 in order. To do.

-Charging part-
The charging unit 26 includes a charging roller 261. The charging roller 261 is a cylindrical member whose core is surrounded by a conductive flexible resin. In FIG. 2, (a), the axis passing through the center of the circular cross section of the charging roller 261 perpendicular to the paper surface. ) Is supported for rotation around. Since the outer circumferential surface of the charging roller 261 is in contact with the outer circumferential surface of the PC drum 21K, the charging roller 261 rotates following the rotation of the PC drum 21K. For example, a negative high voltage (about several hundred to several thousand volts, hereinafter referred to as “charging bias”) is applied to the core of the charging roller 261. As a result, a discharge is generated in the vicinity of the nip between the charging roller 261 and the PC drum 21K. This discharge negatively charges the surface portion of the photoreceptor located near the nip.

-Exposure part-
The charged portion on the surface of the photosensitive member passes through the exposure port 27 as the PC drum 21K rotates. The exposure port 27 is an elongated slit opened in the bottom surface of the casing of the PC unit 20K ((a) of FIG. 2 is not shown), and extends in the axial direction of the PC drum 21K to extend the charging unit 26 and the developing unit. 28 is communicated with the exit of the exposure unit 25 (see FIG. 1B). Light emitted from the exposure unit 25 is applied to the charged portion on the surface of the photoreceptor through the exposure port 27.

  Although neither (b) of FIG. 1 nor (a) of FIG. 2 is shown, the exposure unit 25 includes, for example, an LED array. The LED array includes one or more LED rows arranged in one direction, extends in the axial direction of the PC drum 21K at an interval from the exposure port 27, and extends linearly in the axial direction of the PC drum 21K on the surface of the photoreceptor. At the same time, light is irradiated to the area. In particular, the exposure unit 25 modulates the emitted light amount of each LED or its blinking timing according to the correspondence between the position of the irradiation target of each LED and the K gradation value distribution represented by the image data. Due to this modulation, the amount of exposure generally varies from place to place in the linear area on the surface of the photoreceptor. Since the charge amount of the photoreceptor decreases with the exposure amount, a charge amount distribution corresponding to the K gradation value distribution, that is, one line of the electrostatic latent image is formed in this linear region.

-Development part-
The surface of the photosensitive member including the electrostatic latent image faces the developing unit 28 as the PC drum 21 rotates. The developing unit 28 includes two auger screws 281 and a developing roller 28K in a housing 280. The inside of the housing 280 is immersed in the developer. This developer is a two-component developer and includes a toner and a carrier. The toner is non-magnetic fine particles and is colored K. The carrier is a magnetic powder, the particle diameter of which is larger than that of the toner, and a large number of toner particles are adsorbed on the surface. The developer is supplied from a toner bottle (not shown in FIGS. 1 and 2) installed inside the printer 100. The auger screw 281 is supported by the housing 280 so as to be rotatable around the central axis. As the auger screw 281 rotates, the developer circulates inside the housing 280 while being stirred. During this circulation, the toner is negatively charged by friction with the carrier.

  The developing roller 28K is a cylindrical member made of a non-magnetic material such as aluminum or stainless steel, and is rotatably supported by a fixed shaft 282 that penetrates the developing roller 28K. The developing roller 28K is connected to a drive motor through a torque transmission mechanism (see FIG. 2B) described later. The fixed shaft 282 is fixed to the housing 280 of the developing unit 28. The outer periphery of the fixed shaft 280 is surrounded by a permanent magnet, and the carrier (magnetic material) in the developer is attracted to the outer peripheral surface of the developing roller 28K by the magnetic force. Although (a) in FIG. 2 is not shown, since a fine groove is formed on the outer peripheral surface, when the developing roller 28K rotates in a state where the developer is adsorbed, the developer is outer peripheral surface of the developing roller 28K. Move while being caught by Thus, the developing roller 28K conveys the developer adsorbed on the bottom of the outer peripheral surface from the inside of the housing 280 of the developing unit 28 to the nip between the developing roller 28K and the PC drum 21K.

  The developing unit 28 further applies a negative high voltage (hereinafter referred to as “developing bias”) to the developing roller 28K. The development bias includes, for example, a DC component of −several hundred to several thousand V and an AC component having a frequency of several kHz and an amplitude (Vpp) of several kV. By applying the developing bias, a portion having a higher potential than the developing roller 28K appears in the electrostatic latent image. The electrostatic force acting between each of these portions and the developing roller 28K separates the toner from the developer covering the outer peripheral surface of the developing roller 28K and attaches it to those portions of the electrostatic latent image. The higher the potential with respect to the developing roller 28K, the higher the concentration of toner attached to that portion. Since the potential distribution represented by the electrostatic latent image corresponds to the gradation value distribution represented by the image data, the distribution of the toner density attached to the electrostatic latent image corresponds to the density of the image represented by the image data. Thus, the image is reproduced on the surface of the photoreceptor as a toner image visualized from the electrostatic latent image.

-Transcription part-
The toner image moves to the nip between the PC drum 21K and the primary transfer roller 23K as the PC drum 21K rotates. The primary transfer roller 23K is a metal cylindrical member, and is rotatable around a central axis (in FIG. 2A, an axis passing through the center of the circular cross section of the primary transfer roller 23K perpendicularly to the paper surface). It is supported. Since the outer peripheral surface of the primary transfer roller 23K is in contact with the outer peripheral surface of the PC drum 21K, it is driven to rotate by the rotation of the PC drum 21K. A positive high voltage (several hundred to several thousand volts, hereinafter referred to as “primary transfer bias”) is applied to the core of the primary transfer roller 23K. As a result, the negatively charged toner image is transferred from the surface of the PC drum 21K to the surface of the intermediate transfer belt 24.

  The secondary transfer roller 25 (see FIG. 1B) also has the same structure as the primary transfer roller 23K, and has a positive high voltage (several hundred to several thousand V with respect to its core). "Secondary transfer bias") is applied. As a result, the negatively charged toner image is transferred from the surface of the intermediate transfer belt 24 to the surface of the sheet SH2 that passes through the nip between the drive pulley 24R of the intermediate transfer belt 24 and the secondary transfer roller 25.

-Cleaning blade-
The surface of the photoreceptor including the trace of the toner image transferred to the sheet SH2 comes into contact with the cleaning blade 29 as the PC drum 21K rotates. The cleaning blade 29 is, for example, an elongated plate-like member made of a thermosetting resin such as polyurethane rubber, the longitudinal direction is parallel to the axial direction of the PC drum 21K, and the plate surface is inclined with respect to the radial direction of the PC drum 21K. One of the long sides (edges) facing the outer peripheral surface of the PC drum 21K is in contact with the outer peripheral surface of the PC drum 21K. The length of the blade 29 is substantially equal to the portion of the outer peripheral surface of the PC drum 21K covered with the photoconductor. The blade 29 scrapes off the toner from the surface of the photoreceptor at the edge.

[Torque transmission mechanism to developing roller]
FIG. 2B is a partial cross-sectional view of the printer 100 along the line IIb-IIb shown in FIG. This cross section includes a drive motor 700 and a torque transmission mechanism 800 from the motor 700 to four developing rollers included in the four PC units 20Y,. The transmission mechanism 800 includes a swing gear 810 and a chassis 820.

-Oscillating gear-
The swing gear 810 includes a main body 801, a main gear 811, and auxiliary gears 812 and 813. The main body 801 is a flat plate-like member such as a baseball base, for example, and is supported by a rotating shaft 802 so as to be able to swing around it. Although not shown in FIG. 2B, the rotating shaft 802 is connected to the shaft of the drive motor 700. The drive motor 700 is, for example, a direct current brushless (BLDC) motor, and can rotate in both forward and reverse directions. The torque from the drive motor 700 causes the rotary shaft 802 to rotate about its own central axis, and the main body 801 swings and changes its posture accordingly. The postures of the main body 801 at both ends of the swing range are referred to as “first position” and “second position”, respectively. In FIG. 2B, the first position is indicated by a solid line, and the second position is indicated by a one-dot chain line. In particular, the posture of the main body 801 is changed from the second position to the first position by the rotation of the rotating shaft 802 accompanying the normal rotation of the drive motor 700 (clockwise in FIG. 2B), and the rotation accompanying the reverse rotation (FIG. 2). (B) counterclockwise), the first position changes to the second position.

  A notch 814 that is elongated in the swinging direction (left-right direction in FIG. 2B) is opened at the center of the main body 801, and a boss 825 projects from the chassis 820 through the notch. As the main body 801 swings, the boss 825 is displaced with respect to the notch 814. When the posture of the main body 801 reaches the first position or the second position, the boss 825 collides with the inner surface of the notch 814 located at the end in the longitudinal direction to prevent the main body 801 from swinging. Although (b) of FIG. 2 is not shown, the rotating shaft 802 is connected to the main body 801 via a torque limiter. The torque limiter transmits torque from the rotating shaft 802 to the main body 801 while the posture of the main body 801 is intermediate between the first position and the second position. When the posture of the main body 801 reaches the first position or the second position, the torque received by the rotary shaft 802 from the main body 801 increases suddenly due to the impact of the boss 825 on the inner surface of the notch 814. In response to this, the torque limiter cuts off the transmission of torque from the rotary shaft 802 to the main body 801 and thereafter causes the rotary shaft 802 to idle with respect to the main body 801.

The main gear 811 is supported by a rotating shaft 802 so as to be rotatable around the rotating shaft 802. The auxiliary gears 812 and 813 are rotatably supported by the main body 801 around each central axis,
The main gear 811 is engaged. Therefore, when the main gear 811 rotates with the rotation of the rotating shaft 802, the sub gears 812 and 813 rotate in a driven manner.
-Chassis-
The chassis 820 is a member that supports one end in the longitudinal direction of the four developing rollers. The chassis 820 further supports four drive gears 82Y, 82M, 82C, and 82K and three relay gears 821, 822, and 823 so as to be rotatable around each central axis. Each drive gear 82Y is connected coaxially to a different developing roller. The first relay gear 821 is connected to a drive gear (hereinafter, abbreviated as “C drive gear”) 82C connected to the developing roller of the C toner PC unit 20C and to the developing roller of the M toner PC unit 20M. It is arranged between the drive gear 82M (hereinafter abbreviated as “M drive gear”) and meshed with both gears 82C and 82M. The second relay gear 822 is disposed between the M drive gear 82M and a drive gear (hereinafter abbreviated as “Y drive gear”) 82Y connected to the developing roller of the Y toner PC unit 20Y. It is engaged with 82M and 82Y. The third relay gear 823 is arranged next to a drive gear (hereinafter abbreviated as “K drive gear”) 82K connected to the developing roller of the K toner PC unit 20K, and meshed with the gear 82K.

-First transmission system-
FIG. 3A is a schematic diagram showing the transmission mechanism 800 when the posture of the swing gear 810 is the first position. In the swing gear 810 at the first position, the swing of the main body 801 is stopped by the boss 825 that contacts one end of the notch 814, the first sub gear 812 is engaged with the C drive gear 82C, and the second sub gear 813 is K. Engages with the drive gear 82K. Further, since the torque limiter causes the rotating shaft 802 to idle with respect to the main body 801, the rotating shaft 802 rotates only the main gear 811. The rotation of the main gear 811 rotates the sub gears 812 and 813. The rotation of the first sub gear 812 rotates the C drive gear 82C, and the rotation further rotates the first relay gear 821, the M drive gear 82M, the second relay gear 822, and the Y drive gear 82Y in order. The rotation of the second sub gear 813 rotates the K drive gear 82K. By interlocking these gears, the torque of the drive motor 700 is transmitted to all of the four drive gears 82C, 82M, 82Y, and 82K, so that all of the four developing rollers rotate. The torque propagation path at this time is indicated by broken line arrows TM, L1,..., L6, R1,. That is, in the chassis 820, all of the gears 82C,..., 82K, 821, and 822 except for the third relay gear 823 that only rotates idly transmits torque from the swing gear 810 at the first position, that is, the first Configure the transmission system.

-Second transmission system-
FIG. 3B is a schematic diagram showing the transmission mechanism 800 when the swing gear 810 is in the second position. In the swing gear 810 in the second position, the swing of the main body 801 is stopped by the boss 825 contacting the other end of the notch 814, and the first sub gear 812 is separated from the C drive gear 82C, while the second sub gear 813 meshes with the third relay gear 823. Further, since the torque limiter causes the rotating shaft 802 to idle with respect to the main body 801, the rotating shaft 802 rotates only the main gear 811. The rotation of the main gear 811 rotates the sub gears 812 and 813. The first sub gear 812 idles, and the C drive gear 82C, the first relay gear 821, the M drive gear 82M, the second relay gear 822, and the Y drive gear 82Y are stopped. The rotation of the second sub gear 813 rotates the third relay gear 823, and the rotation rotates the K drive gear 82K. Since the torque of the drive motor 700 is transmitted only to the K drive gear 82K by interlocking these gears, only the developing roller 28K of the K toner PC unit 20K rotates. The torque propagation path at this time is represented by broken line arrows TM, K1,..., K3 in FIG. That is, in the chassis 820, the third relay gear 823 and the K drive gear 82K constitute a system for transmitting torque from the swing gear 810 at the second position, that is, a second transmission system.

[Electronic control system of image forming apparatus]
FIG. 4 is a block diagram illustrating the configuration of the electronic control system of the printer 100. In this control system, in addition to the elements 10, 20, 30, and 40 of the printer 100, the operation unit 50 and the main control unit 60 are connected to each other through a bus 90 so as to communicate with each other.
−Driver−
Each element 10,..., 40 of the printer 100 includes drive units 10D, 20D, 30D, 40D. Although not shown in FIG. 4, each drive unit 10 </ b> D includes actuators, control circuits, and the like for movable members such as transport rollers 12, 21, 24 </ b> R, 25, 31, 32, 43, PC drums 21 </ b> Y,. Includes a combination of drive circuits. The actuator is, for example, a BLDC motor. The control circuit is an electronic circuit such as a microprocessor (MPU / CPU), an application specific integrated circuit (ASIC), or a programmable integrated circuit (FPGA), and is an actual control amount fed back from an actuator, for example, a motor. If there is, the target value of the voltage applied to the actuator is instructed to the drive circuit based on the rotational speed. The drive circuit is an inverter and applies a voltage to the actuator using a switching element such as a power transistor (FET). By using feedback control by these control circuits and drive circuits, each drive unit 10D,... Controls the control amount of the actuator to a target value instructed from the main control unit 60.

-Operation part-
The operation unit 50 is an entire interface between a user mounted on the printer 100 and an external electronic device, and accepts a job processing request and image data to be printed through a user operation or communication with the external electronic device. These are transmitted to the main controller 60. As shown in FIG. 4, the operation unit 50 includes an operation panel 51 and an external interface (I / F) 52. As shown in FIG. 1A, the operation panel 51 includes a push button, a touch panel, and a display. The operation panel 51 displays a GUI screen on this display. The operation panel 51 also identifies what is pressed by the user from among the push buttons, or detects the position touched by the user from the touch panel, and transmits information related to the identification or detection to the main control unit 60 as operation information. . In particular, when the print job input screen is displayed on the display, the operation panel 51 displays the size, sheet type, orientation (separately between portrait and landscape), the number of copies, image quality, high-speed mode, and quietness of the print target sheet. It accepts printing-related conditions such as mode selection from the user, and incorporates items indicating these conditions into the operation information. The external I / F 52 includes a USB port or a memory card slot, through which image data to be printed is taken directly from an external storage device such as a USB memory or a hard disk drive (HDD). The external I / F 52 further includes a communication port connected to the external network NTW by wire or wireless, and receives image data to be printed from another electronic device through the network NTW.

−Main control unit−
The main controller 60 is an integrated circuit mounted on a single printed circuit board installed inside the printer 100. As shown in FIG. 4, the main control unit 60 includes a CPU 61, a RAM 62, and a ROM 63. The CPU 61 is composed of one MPU and executes various firmware. The RAM 62 is a volatile semiconductor memory device such as a DRAM or an SRAM, and provides a work area when the CPU 61 executes firmware to the CPU 61 and stores image data to be printed received by the operation unit 50. The ROM 63 is configured by a combination of a non-writable nonvolatile storage device and a rewritable nonvolatile storage device. The former stores firmware, and the latter includes a semiconductor memory device such as an EEPROM, flash memory, and SSD, or an HDD, and provides a storage area for environment variables and the like to the CPU 61.

The main control unit 60 implements various functions as a control subject for the other elements 10, 20,... According to various firmware executed by the CPU 61. For example, the main control unit 60 displays a GUI screen on the operation unit 50 to accept a user input operation. Further, the main control unit 60 determines the operation mode of the printer 100 according to the operation information from the operation unit 50.
The operation mode of the printer 100 includes, for example, “operation”, “standby (low power)”, and “sleep”.

  “Operation mode” refers to an operation mode in which the printer 100 processes a print job. For example, the feeding unit 10 continuously feeds the number of sheets indicated by the operation information, the image forming unit 20 repeats the formation of the toner image and the transfer to the sheet, and the fixing unit 30 heats and heats the sheet. Continue with pressure. The operation mode is further divided into various sub modes according to the operation conditions of the printer 100 indicated by the job processing request. For example, it is divided into two types, “color” and “monochrome”, depending on whether the printing condition is color or monochrome, and “standard” and “silent” depending on the processing speed setting value of the printer 100. And can be divided into two types. In “standard mode”, the processing speed is set to a standard value, for example, the highest value within a range in which stable operation of the printer 100 is guaranteed. In the “silent mode”, the processing speed is kept lower than the standard value so that the operation sound of the printer 100 is reduced as compared with the standard mode. The main operation sound sources of the printer 100 include movable members such as a conveyance roller, actuators thereof, sheets conveyed by them, and a fan for cooling the main control unit 60 and a power source. In order to reduce the operating sound pressure generated by these sound sources, in the silent mode, the rotation speed of the conveyance roller, the rotation speed of the drive motor, the conveyance speed of the sheet, and the rotation speed of the cooling fan are set lower than their standard values. .

“Standby mode” refers to an operation mode in which the printer 100 stands by in a state where a job can be executed. Specifically, the feeding unit 10 and the image forming unit 20 are stopped, and the fixing unit 30 preheats the fixing roller 31 to keep it at an appropriate temperature.
“Sleep mode” refers to an operation mode in which the printer 100 minimizes power consumption. For example, in addition to the feeding unit 10 and the image forming unit 20, the fixing unit 30 is also stopped, and in particular, power supply to the heater built in the fixing roller 31 is shut off.

  The main control unit 60 responds to various events occurring in the printer 100, for example, completion of job processing, pressing of a stop button or a power button, detection of a gesture by a touch panel, reception of a job processing request or a stop command from the network. To switch the operation mode of the printer 100. The main control unit 60 further provides information necessary for the switching to each element 10 of the printer 100. For example, when the operation mode is instructed, the main control unit 60 designates the paper type and number of sheets to be fed, the timing of rotation of the respective conveying rollers 12,. The image forming unit 20 is provided with image data and image forming timing, and the fixing unit 30 is designated with a target temperature of the fixing roller 31 and a heat generation amount of the heater.

-Image forming part-
The control system of the image forming unit 20 is an integrated circuit such as an MPU / CPU, ASIC, or FPGA mounted on a printed circuit board different from the main control unit 60. This control system includes control modules for the driving unit 20D, the exposure unit 22, the charging unit 26, and the developing unit 28, and the transfer unit 230. The control module of the development unit 28 includes a development bias generation unit 285 and a control unit 286.

  The transfer unit 230 includes a primary transfer bias generation unit and a secondary transfer bias generation unit. The generation unit, the charging bias generation unit included in the charging unit 26, and the development bias generation unit 285 included in the development unit 28 include a booster circuit such as a switching converter and its control circuit. These control circuits are electronic circuits such as MPU / CPU, ASIC, and FPGA, and are integrated into a single chip. Each control circuit controls the booster circuit to generate each bias voltage from the output of a commercial power source or the like.

  The control unit 286 is an electronic circuit such as an MPU / CPU, an ASIC, or an FPGA, and controls the rotation of the common drive motor 700 for the four developing rollers. Specifically, the control unit 286 includes a combination of a control circuit and a drive circuit for the drive motor 700. The control circuit instructs the drive circuit of a target value of the voltage applied to the motor 700 based on the actual rotational speed fed back from the drive motor 700. For example, an optical or magnetic encoder is mounted on the main body of the drive motor 700, and the control unit 286 measures the rotational speed of the drive motor 700 from the frequency of the AC signal generated by the encoder. The drive circuit is an inverter, and applies a pulse voltage to the drive motor 700 using a switching element such as an FET. In particular, the drive circuit matches the average value per unit time of the voltage actually applied to the drive motor 700 to the target value by pulse width modulation (PWM) control for the pulse voltage.

  In particular, the control unit 286 causes the drive motor 700 to rotate forward in the color mode and reverse in the monochrome mode. The target value of the rotational speed in each mode is set to a standard value in the standard mode, and is set lower than the standard value in the silent mode. Further, in the silent mode, the control unit 286 first confirms whether switching from the color mode to the monochrome mode or vice versa is necessary before starting the drive motor 700 in the normal sequence. For example, when both the new job and the immediately preceding job are processed in the color mode or the monochrome mode, or after the initialization of the setting, the job processing request received first by the printer 100 is the same color mode or the same as the initial setting. When the monochrome mode is designated, there is no need to switch between color / monochrome mode. If any switching is necessary, the control unit 286 causes the drive motor 700 to perform the precursor rotation. “Precursor rotation” refers to the operation of the drive motor 700 for the purpose of changing the posture of the swing gear 810 from the first position to the second position or vice versa. In the pre-rotation, the drive motor 700 temporarily accelerates from a stationary state to a rotational speed lower than the normal rotational speed in any of the color and monochrome modes and then decelerates. In particular, the control unit 286 controls the drive motor 700 so that the swing gear 810 completes the posture change during the deceleration period. Details of the control of the precursor rotation will be described later.

[Collision sound between rocking gear and boss]
Whenever the swing gear 810 changes its posture from the first position to the second position or vice versa, the boss 825 collides with the end of the notch 814 of the swing gear 810, and generally a high and sharp sound is produced. . Since the sound quality of this collision sound is likely to make the user uncomfortable, in order to adapt the printer 100 to use in a quiet environment such as SOHO, it is necessary to have a function for suppressing the sound pressure of this collision sound as low as possible. is there.

  FIG. 5A is a graph showing the relationship between the rotational speed of the drive motor 700 and the sound pressure of the collision sound immediately before the swing gear 810 is stopped by the boss 825. When the drive motor 700 is activated in a normal sequence, the rotational speed of the drive motor 700 has already reached the target value when the swing gear 810 is stopped by the boss 825. The standard value of the rotation speed of the drive motor 700 is set to several thousand rpm, and the target value of the rotation speed is 1000 rpm or more even in the silent mode. As a result, the difference in rotational speed between the developing roller and the PC drum is kept sufficiently small, and the printer 100 speeds up the processing without impairing the high image quality. On the other hand, as shown in FIG. 5A, the sound pressure of the collision sound increases to 55 dB or more at a rotational speed of 1000 rpm or more. This sound pressure has reached a level that is regarded as noise in residential areas (see “Environmental Standards” based on the provisions of Article 16, Paragraph 1 of the Basic Environment Law). In order to reduce the sound pressure of the collision sound to less than 55 dB, the rotational speed of the drive motor 700 must be reduced to less than 1000 rpm. However, since the difference in rotational speed between the developing roller and the PC drum is too wide, it is difficult to move a sufficiently large amount of toner from the developing roller to the PC drum.

  FIG. 5B is a graph showing the relationship between the torque applied by the drive motor 700 to the rocking gear 810 immediately before being stopped by the boss 825 and the sound pressure of the collision sound. When the drive motor 700 is started in a normal sequence, the drive motor 700 is accelerating when the swing gear 810 is stopped by the boss 825, and its torque is maintained considerably higher than the standard value. The standard value of the torque of the drive motor 700 is set to hundreds of tens mNm. As a result, the drive motor 700 can maintain the rotation speed of the developing roller constant regardless of the fluctuation of the load torque received from the developing roller, so that the printer 100 speeds up the processing without impairing the image quality. However, as shown in FIG. 5B, on the other hand, the sound pressure of the collision sound rises to 55 dB or more at a torque of 150 mNm or more. In order to reduce the sound pressure of the collision sound to less than 55 dB, the torque of the drive motor 700 must be reduced to less than 150 mNm. However, it is difficult to stabilize the rotation of the developing roller with a torque within that range.

  From the above, both the rotational speed and torque that can reduce the sound pressure of the collision sound between the rocking gear 810 and the boss 825 to an acceptable level are realized in the normal control of the drive motor 700 in the operation mode. Is difficult. Accordingly, the control unit 286 causes the drive motor 700 to perform the pre-rotation before the normal startup sequence, particularly when switching between the color mode and the monochrome mode is necessary in the silent mode.

[Precursor rotation of drive motor]
FIG. 6A is a graph showing the change over time of the rotational speed of the drive motor 700 from the precursor rotation to the normal startup sequence. As this figure shows, the graph is divided into two curved sections. The front-stage parts PP1 and PP2 represent the precursor rotation, and the rear-stage parts PN1 and PN2 represent a normal startup sequence.

The precursor rotation is divided into an acceleration period PP1 and a deceleration period PP2. The control unit 286 sets the time length of each of the periods PP1 and PP2 to a predetermined value, for example, tens of milliseconds to hundreds of tens of milliseconds.
In the acceleration period PP1, the control unit 286 activates the drive motor 700 and then increases the rotation speed to a target value NP, for example, several hundred rpm. Specifically, for example, control unit 286 maintains the target value of the rotational speed at a constant value NP from start time T0 to end time T1 of acceleration period PP1. The control circuit of the drive motor 700 sets the target value of the applied voltage to the drive motor 700 higher as the difference between the measured value of the rotational speed of the drive motor 700 and the target value NP increases. The drive circuit matches the average height per unit time of the pulse voltage applied to the drive motor 700 to the voltage target value by PWM control. Since the difference between the measured value of the rotational speed and the target value NP is large at the initial stage of the acceleration period PP1, the applied voltage to the drive motor 700 is high. Due to the large amount of inrush current accompanying this, a strong torque is generated in the drive motor 700, and this torque starts to rotate the rotating shaft 802 and the swinging gear 810. As the rotational speed of the drive motor 700 increases, the difference between the actually measured value and the target value NP narrows, so that the control circuit decreases the target value of the applied voltage. Therefore, the average value of the applied voltage from the drive circuit is lowered, and the current amount of the drive motor 700 is reduced. As a result, the torque generated by the drive motor 700 is weakened, and the acceleration of the rotating shaft 802 and the swing gear 810 is relaxed. Thus, in the latter period of the acceleration period PP1, the rotational speed of the drive motor 700 is maintained at the target value NP.

  In the deceleration period PP2, the control unit 286 causes the drive motor 700 to lower the rotational speed from the target value NP. In particular, the control unit 286 performs stop control for the drive motor 700. This stop control is a normal stop sequence for the drive motor 700. Specifically, for example, the control unit 286 changes the target value of the rotation speed to “0” at the start time T1 of the deceleration period PP2. As a result, the control circuit of the drive motor 700 sets the target value of the applied voltage to “0”, so that the drive circuit stops supplying power to the drive motor 700. Thereafter, the drive motor 700 continues to rotate with inertia. Further, since inertial force, frictional force, stress, and the like generated in the torque transmission path from the drive motor 700 to the swing gear 810 act on the drive motor 700 as a braking force, the rotational speed thereof is a target value NP in the acceleration period PP1. It begins to descend from and eventually reaches “0”. That is, the swing of the swing gear 810 stops. The start time T1 of the deceleration period PP2 and its time length T3-T1 are set so that this oscillation stops in the deceleration period PP2.

  The control unit 286 starts a normal startup sequence for the drive motor 700 at the end time T3 of the precursor rotation. This activation sequence is divided into an acceleration period PN1 and a constant speed period PN2. During the acceleration period PP1, the rotational speed of the drive motor 700 increases to a target value NN, for example, several thousand rpm, and during the constant speed period PN2, the rotational speed is maintained at the target value NN. The time length of the acceleration period PN1 is set to a predetermined value, for example, several hundred milliseconds. The time length of the constant speed period PN2 varies depending on the progress of job processing. The control of the drive motor 700 in the acceleration period PN1 is the same as the control in the acceleration period PP1 of the precursor rotation.

  In the pre-rotation, the target value NP of the rotational speed of the drive motor 700 in the acceleration period PP1 is suppressed to a value sufficiently lower than the target value NN = several thousand rpm in the acceleration period PN1 of the startup sequence, which is several hundred rpm. Since the speed at which the rocking gear 810 reaches the first position or the second position is lower than the target value NP, the sound of the collision sound between the rocking gear 810 and the boss 825 is shown in FIG. The pressure is reduced to less than 55 dB.

  FIG. 6B is a graph showing the change over time of the swing angle of the swing gear 810 accompanying the precursor rotation of the drive motor 700. The “swing angle” means the rotation angle of the main body 801 around the rotation axis 802. In FIG. 6B, “color” represents the swing angle of the main body 801 at the first position, and “monochrome” represents the swing angle of the main body 801 at the second position. As shown in this graph, the swing angle starts changing from, for example, “color” at the start time T0 of the pre-rotation, and reaches “monochrome” at time T2. This represents that the swing gear 810 starts swinging by the torque generated by the drive motor 700 at the start time T0, leaves the first position, and reaches the second position at time T2. In this case, the time length of the acceleration period PP1 and the target value NP of the rotation speed are set so that the time T2 is later than the end time T1 of the acceleration period PP1. Accordingly, the swing angle reaches “monochrome” in the deceleration period PP2 of the precursor rotation, that is, the swing gear 810 reaches the second position. Since the drive motor 700 does not substantially generate torque during the deceleration period PP2, the drive motor 700, the rotation shaft 802, and the swing gear 810 continue to rotate with inertia but are decelerated by a braking force from a load such as a developing roller. To do. Therefore, as indicated by the inclination of the graph, the speed of the rocking gear 810 when the rocking angle reaches “monochrome” is lower than the peak value in the acceleration period PP1.

  FIG. 6B further shows a change with time in the swing angle when the swing gear 810 changes its posture in a normal startup sequence by a broken line. The swing angle starts changing from, for example, “color” at the start time T3 of the acceleration period PN1 of the activation sequence, and reaches “monochrome” at time T4. This represents that the swing gear 810 starts swinging by the torque generated by the drive motor 700 at the start time T3, leaves the first position, and reaches the second position at time T4. As is apparent from a comparison of the slope of the broken line at the arrival time T4 in the startup sequence and the slope of the solid line at the arrival time T2 in the precursor rotation, the swing gear 810 at the time when the swing angle reaches “monochrome”. The speed is lower in the pre-rotation than in the startup sequence.

Further, unlike the acceleration period PN1 of the startup sequence, the drive motor 700 does not generate torque in the deceleration period PP2 of the precursor rotation. Therefore, the impulse received by the boss 825 due to the collision with the swing gear 810 does not include a component due to the torque.
As described above, in the pre-rotation, the impact generated between the swing gear 810 and the boss 825 is weaker than in the normal startup sequence. As a result, the sound pressure of the collision sound between the rocking gear 810 and the boss 825 in the precursor rotation is sufficiently lower than the sound of the collision in the startup sequence.

In the pre-rotation, the time length of the acceleration period PP1 is suppressed to a value shorter than the time length of the acceleration period PN1 of the activation sequence = several hundred milliseconds, that is, ten to several hundred milliseconds. Therefore, the delay in the start-up time associated with the pre-rotation is not a substantial problem unless the processing is particularly urgent.
[Control flow of drive motor]
FIG. 7 is a flowchart of control of the drive motor 700 by the control unit 286. This control is started in response to a job processing start instruction from the main control unit 60.

In step S101, the control unit 286 confirms whether the silent mode is set. If it is the silent mode, the process proceeds to step S102, and if not, the process proceeds to step S104.
In step S102, since the silent mode is set, the control unit 286 further checks whether switching from the color mode to the monochrome mode or vice versa is necessary. If switching is necessary, the process proceeds to step S103, and if not necessary, the process proceeds to step S104.

In step S103, since it is necessary to switch between the color mode and the monochrome mode, the control unit 286 causes the drive motor 700 to perform the precursor rotation. Thereafter, the process proceeds to step S104.
In step S104, any of the following three conditions (1), (2), and (3) is satisfied. (1) Standard mode, not silent mode. (2) Silent mode, but mode switching between color / monochrome is not required. In conditions (1) and (2), step S103, that is, execution of the precursor rotation is skipped. (3) Since the mode is silent and the mode switching between color / monochrome is necessary, the precursor rotation is executed. Further, the elapsed time from the start time T0 of the precursor rotation reaches the sum of the time lengths of the acceleration period PP1 and the deceleration period PP2, that is, the precursor rotation end time T3 has arrived.

  Therefore, the control unit 286 starts a normal startup sequence for the drive motor 700. At this time, the target value NN of the rotational speed of the drive motor 700 is set to a standard value in the standard mode, and is set to a value lower than the standard value in the silent mode. With this activation sequence, the rotational speed of the drive motor 700 is maintained at the target value NN. As a result, the rotation speed of each of the four developing rollers is maintained at a predetermined value in the color mode, and the rotation speed of the developing roller of the K toner PC drum 21K is maintained at a predetermined value in the monochrome mode. Thereafter, the process proceeds to step S105.

In step S105, the control unit 286 confirms whether the main control unit 60 has notified the end of job processing. If notified, the process proceeds to step S106, and if not notified, the process repeats step S105.
In step S <b> 106, the end of the job process is notified from the main control unit 60, so the control unit 286 starts a stop sequence for the drive motor 700. That is, the control unit 286 changes the target value of the rotation speed of the drive motor 700 to “0” and stops the power supply to the drive motor 700. Thereafter, the drive motor 700 continues to rotate due to inertia, but eventually stops due to the braking force from the load. Thereafter, the process ends.

[Advantages of the embodiment]
In the printer 100 according to the above-described embodiment of the present invention, the developing unit 28 causes the drive motor 700 to perform the precursor rotation when switching from one of the color mode and the monochrome mode to the other. In the pre-rotation, the drive motor 700 once accelerates from a stationary state to a rotational speed NP that is lower than the normal rotational speed NN in each mode, and then decelerates. During the deceleration period PP2 in the precursor rotation, the developing unit 28 changes the posture of the swing gear 810 from one of the first position and the second position to the other. Thus, in the pre-rotation, the impact generated between the swing gear 810 and the boss 825 is weaker than in the normal startup sequence for the drive motor 700. As a result, the sound pressure of the collision sound between the rocking gear 810 and the boss 825 in the precursor rotation is sufficiently lower than the sound of the collision in the startup sequence. In this way, the developing unit 28 can suppress the collision sound generated by the rocking gear 810 when the mode is switched between monochrome and color without hindering the reduction in size and speed of the printer 100.

[Modification]
(A) The image forming apparatus according to the embodiment of the present invention is a color laser printer 100. The image forming apparatus according to the embodiment of the present invention may be any of a facsimile, a copier, and a multifunction machine as long as it is a color compatible machine including a tandem type image forming unit.
(B) The torque transmission mechanism 800 shown in FIG. 2B is configured by a gear train. In addition, the torque transmission mechanism from the drive motor 700 to the developing roller may include an element other than a gear such as a belt. Further, in this transmission mechanism 800, there is one boss 825 that stops the swing of the swing gear 810. In addition, a plurality of notches may be provided in the main body 801 of the swing gear 810, and the swing of the main body 801 may be stopped by one boss per notch. Different bosses may contact the main body 801 at the first position and the second position.

(C) In the precursor rotation acceleration period PP1 shown in FIG. 6, the control unit 286 maintains the target value NP of the rotational speed of the drive motor 700 constant from the start time T0 to the end time T1. In addition, the control unit 286 may gradually increase the target value of the rotation speed from the initial value at the start time T0 to the final value NP.
At the start time T1 of the precursor rotation deceleration period PP2 shown in FIG. 6, the control unit 286 changes the target value of the rotational speed of the drive motor 700 to “0”. Thereafter, the drive motor 700 continues to rotate with inertia and stops with the braking force from the load. In addition, the control unit 286 may gradually reduce the target value of the rotation speed from the initial value NP at the start time T1 to “0”. Further, the control unit 286 may cause the drive motor 700 itself to generate a braking force by short-circuit braking.

  (D) The control unit 286 performs speed control on the drive motor 700. In addition, the control unit may perform torque control on the drive motor 700. Specifically, for example, the control circuit first measures the current amount of the drive motor 700, and estimates the torque actually generated by the drive motor 700 from the measured value. Next, the control circuit instructs the drive circuit of the target value of the amount of current supplied to the drive motor 700 based on the error between the estimated value of the torque and the target value. The drive circuit matches the average value per unit time of the amount of current actually supplied to the drive motor 700 to the target value by PWM control. In this case, when causing the drive motor 700 to perform the pre-rotation, the control unit may reduce the torque of the drive motor 700 so that the rotation speed NP is lower than the rotation speed NN in the normal startup sequence. . Specifically, the control unit may lower the torque target value below the target value in the normal startup sequence. As a result, the amount of current supplied to the drive motor 700 is limited in the pre-rotation than in the normal startup sequence, so the torque of the drive motor 700 is reduced.

(E) The order of the steps shown in FIG. 7 is not fixed and can be changed. For example, the confirmation of the silent mode in step S101 and the necessity confirmation of the mode switching between color / monochrome in step S102 may be reversed.
(F) The load that the swing gear 810 receives during swing generally increases with the aging of both members, such as the wear of the connecting portion between the main body 801 and the rotating shaft 802. Regardless of this increase in load, the control unit 286 evaluates the degree of deterioration of the swing gear 810 for the purpose of reliably changing the posture of the swing gear 810 by the precursor rotation, and the precursor rotation according to the degree of deterioration is evaluated. Speed or time may be selected.

  FIG. 8A is a table showing the relationship between the number of sheets processed by the printer 100, the magnitude of the load received by the rocking gear 810, and the time of precursor rotation. As shown in this table, as the number of processed sheets increases to 0, 100k, and 1000k (the letter k represents a unit of 1000 sheets), the load that the swing gear 810 receives when swinging is 50 mNm, 100 mNm, and 200 mNm. And increase.

  FIG. 8B is a graph showing the change over time of the rotation speed of the drive motor 700 in the precursor rotation, and FIG. 8C is a graph showing the change over time in the swing angle of the swing gear 810 accompanying the precursor rotation. It is. In these graphs, the alternate long and short dash line represents the rotational speed of the drive motor 700 and the swing angle of the swing gear 810 when the number of processed sheets is 100 k. In this case, the drive motor 700 can still increase the rotational speed to the initial target value NP against the load received by the swing gear 810. That is, the swing angle of the swing gear 810 can change from “color” to “monochrome”, for example. On the other hand, the broken line represents the rotational speed of the drive motor 700 and the swing angle of the swing gear 810 when the number of processed sheets is 1000 k. In this case, since the load received by the oscillating gear 810 is excessive, as long as the pre-rotation is performed with the same target value NP and the acceleration period PP1 having the same length as before, the drive motor 700 changes the rotational speed to the initial value. It can be increased only to a value NQ lower than the target value NP. That is, the pre-rotation is completed while the swing angle of the swing gear 810 is moving from “color” to “monochrome”, for example, and the swing angle cannot reach “monochrome”.

  The control unit 286 monitors the number of processed sheets of the printer 100, and when the value reaches 1000k, extends the time for the pre-rotation, particularly the acceleration period. For example, as shown in FIG. 8A, if the time length of the precursor rotation is 200 milliseconds when the number of printed sheets is less than 1000k, the control unit 286 increases the time length to 400 milliseconds when the number of printed sheets is 1000k or more. These time length values are determined in advance based on experiments or simulations, and are stored in a nonvolatile memory element built in the control unit 286. By extending the time of the precursor rotation, as shown in FIG. 8B, the area surrounded by the graph representing the rotational speed of the drive motor 700 in the precursor rotations PE1 and PE2 and the horizontal axis increases. Since this area corresponds to the change amount of the swing angle, an increase in the area means that the swing angle changes from “color” to “monochrome” as shown in FIG. On the other hand, the peak value of the rotational speed does not exceed the initial target value NP, and the rotational speed drops to “0” before the end time TE3 of the post-extension deceleration period PE2. Accordingly, the sound pressure of the collision sound between the swing gear 810 and the boss 825 remains low.

In this manner, the control unit 286 evaluates the degree of deterioration of the swing gear 810 based on the number of processed printers 100, and extends the time of the precursor rotation according to the degree of deterioration. As a result, even if the load on the swing gear 810 increases as the main body 801 and the rotating shaft 802 deteriorate with time, the posture of the swing gear 810 can be reliably changed regardless of the increase.
The control unit 286 may increase the target value of the precursor rotation speed from the original value NP instead of extending the precursor rotation time. The target value after the increase is within a rotational speed range (see FIG. 5A) where the sound pressure of the collision sound between the rocking gear 810 and the boss 825 is less than a threshold value such as 55 dB, and deceleration. The rotation speed of the drive motor 700 may be set so that it can be lowered from the target value to “0” by the end time TE3 of the period PE2. Further, the control unit 286 may evaluate the degree of deterioration of the swing gear 810 by the number of rotations of the drive motor 700 or the energization time instead of the number of sheets processed by the printer 100.

  (G) As shown in FIG. 2B, the shape of the main body 801 of the swing gear 810 is generally asymmetric with respect to a vertical plane including the rotation shaft 802. Alternatively, as shown in FIG. 3, the posture of the swing gear 810 is generally asymmetric with respect to the vertical plane including the rotation shaft 802 between the first position and the second position. Therefore, generally, there is a difference in the magnitude of the load received by the rocking gear 810 between when the rocking gear 810 changes its posture from the first position to the second position and vice versa. Regardless of this difference, for the purpose of reliably changing the posture of the swing gear 810 by the precursor rotation, the control unit 286 determines the speed of the precursor rotation depending on whether the switching is between the color mode or the monochrome mode. Or you may choose time.

FIG. 9A is a table showing the relationship between the change direction of the swing angle of the swing gear 810, the magnitude of the load received by it, and the time of the pre-rotation. As shown in this table, the load applied to the rocking gear 810 differs between 50 mNm and 100 mNm when the rocking angle changes from “color” to “monochrome” and vice versa.
FIG. 9B is a graph showing the change over time of the rotational speed of the drive motor 700 in the precursor rotation, and FIG. 9C is a graph showing the change over time in the swing angle of the swing gear 810 accompanying the precursor rotation. It is. Of these graphs, the portion from time T0 to time T3 represents a case where the swing angle changes from “color” to “monochrome”, and the portion from time TQ0 to time TQ3 has a swing angle of “monochrome”. This represents the case of changing from “color” to “color”. In the former case, the magnitude of the load received by the rocking gear 810 is relatively small, 50 mNm, as shown in FIG. Therefore, the drive motor 700 can increase the rotational speed to the initial target value NP against this load. That is, the swing angle of the swing gear 810 can change from “color” to “monochrome”. Conversely, when the swing angle changes from “monochrome” to “color”, the load received by the swing gear 810 is excessively 100 mNm as shown in FIG. As long as the acceleration period PP1 has the same length as the target value NP, the drive motor 700 increases the rotational speed only to a value NR lower than the initial target value NP, as shown in FIG. I can't let you. That is, the pre-rotation is completed while the swing angle of the swing gear 810 is moving from “monochrome” to “color”, for example, and the swing angle cannot reach “color”.

  The control unit 286 distinguishes between the color mode and the monochrome mode, and when switching from the monochrome mode to the color mode is necessary, the time for the pre-rotation, particularly the acceleration period, is extended as compared with the reverse case. For example, as shown in FIG. 9A, if the time length of the precursor rotation is 200 msec in the switching from the color mode to the monochrome mode, the control unit 286 increases the time length to 400 msec in the reverse switching. . These time length values are determined in advance based on experiments or simulations, and are stored in a nonvolatile memory element built in the control unit 286. By extending the time of the precursor rotation, as shown in FIG. 9B, the area surrounded by the graph representing the rotational speed of the drive motor 700 in the precursor rotations PQ1 and PQ2 and the horizontal axis is increased. ), The swing angle changes from “monochrome” to “color”. On the other hand, the peak value of the rotational speed does not exceed the initial target value NP, and the rotational speed drops to “0” before the end time TQ3 of the post-extension deceleration period PQ2. Accordingly, the sound pressure of the collision sound between the swing gear 810 and the boss 825 remains low.

  As described above, the control unit 286 extends the time of the precursor rotation depending on whether the color mode or the monochrome mode is switched. Accordingly, even if the load received by the rocking gear 810 varies depending on the rocking direction due to the shape of the rocking gear 810 or the asymmetry of the posture between the first position and the second position, the difference between the two is different. Regardless, the posture of the rocking gear 810 can be changed reliably.

  The control unit 286 may increase the target value of the precursor rotation speed from the original value NP instead of extending the precursor rotation time. The target value after the increase is within a rotational speed range (see FIG. 5A) where the sound pressure of the collision sound between the rocking gear 810 and the boss 825 is less than a threshold value such as 55 dB, and deceleration. The rotational speed of the drive motor 700 may be set so that it can be lowered from the target value to “0” by the end time TQ3 of the period PQ2.

  The present invention relates to a developing roller driving mechanism in an electrophotographic image forming apparatus. As described above, when switching between a color mode and a monochrome mode, the driving motor is caused to perform a pre-rotation before a normal start-up sequence, and thereby swing. Complete the posture change of the dynamic gear. Thus, the present invention is clearly industrially applicable.

100 color laser printer 20Y, 20M, 20C, 20K photoconductor unit 21Y, 21M, 21C, 21K photoconductor drum 22Y, 22M, 22C, 22K exposure unit 23Y, 23M, 23C, 23K primary transfer roller 24 intermediate transfer belt 24R intermediate Transfer belt drive pulley 25 Secondary transfer roller 26 Charger 27 Exposure port 28 Developing unit 280 Developing unit casing 281 Auger screw 282 Fixed shaft 28K Developing roller 29 Cleaning blade 800 Torque transmission mechanism 810 Oscillating gear 801 Oscillating gear Main body 802 Rotating shaft 811 Main gear 812, 813 Sub gear 814 Notch in main body 820 Chassis 821, 822, 823 Relay gear 82Y, 22M, 82C, 82K Drive gear connected to developing roller 825 Boss P 1 precursor rotation of the acceleration period PP2 precursor rotation deceleration period PN1 startup sequence of acceleration period PN2 rotational speed target value in the target value NN startup sequence of rotational speed in the deceleration period NP precursor rotation of the startup sequence

Claims (11)

It is a developing device mounted on an electrophotographic image forming apparatus having a tandem type image forming unit and capable of operating in both monochrome mode and color mode.
A drive motor that can rotate in both forward and reverse directions;
The torque is oscillated by the torque from the drive motor, and the torque is transmitted by changing the posture to the first position when the drive motor rotates in the first direction and to the second position when the drive motor rotates in the second direction. A rocking gear to switch the destination,
A first transmission system for transmitting torque from the rocking gear at the first position;
A second transmission system for transmitting torque from the swing gear at the second position;
A first developing roller that rotates by torque from any of the first transmission system and the second transmission system and adheres a single color toner to the photosensitive member;
A plurality of second developing rollers that rotate with torque from the first transmission system and adhere toners of different colors to different photoreceptors with the first developing roller;
A control unit for controlling rotation of the drive motor;
With
The controller rotates the drive motor in the first direction in the color mode, rotates in the second direction in the monochrome mode, and switches the drive motor to the drive motor when switching from one mode to the other. A developing device characterized in that a pre-rotation that decelerates once after accelerating to a rotational speed lower than a normal rotational speed in a mode is executed, and a change in posture of the swinging gear is completed during a deceleration period in the pre-rotation . A chassis that includes at least one boss projecting within a swing range of the swing gear and supports the swing gear in a swingable manner;
The swinging gear is prevented from swinging by contacting any one of the at least one boss at each of the first position and the second position,
The developing device according to claim 1, wherein the control unit controls the drive motor such that the swing gear collides with one of the at least one boss during a deceleration period in the precursor rotation. .   The developing device according to claim 1, wherein the control unit decelerates the drive motor by a stop control for the drive motor when the drive motor performs the precursor rotation.   The said control part suppresses the rotational speed of the said drive motor lower than the said normal rotational speed by making the said drive motor reduce a torque, when performing the said precursor rotation, The Claim 1 or Claim characterized by the above-mentioned. 2. The developing device according to 2.   The developing device according to claim 4, wherein the control unit causes the drive motor to reduce torque by limiting an amount of current supplied to the drive motor.   The developing device according to claim 1, wherein the control unit skips execution of the precursor rotation by the drive motor in accordance with an operation mode of the image forming apparatus.   The said control part evaluates the deterioration degree of the said rocking | fluctuation gear, The speed or time of the said pre-rotation rotation is selected according to the said deterioration degree, The Claim 1-6 characterized by the above-mentioned. Development device.   8. The development according to claim 7, wherein the control unit evaluates the degree of deterioration of the swing gear by the number of sheets processed by the image forming apparatus, the number of rotations of the drive motor, or the energization time. apparatus.   9. The control unit according to claim 1, wherein the control unit selects the speed or time of the precursor rotation according to whether the switching is performed between a color mode and a monochrome mode. 10. Development device.   The developing device according to claim 1, wherein the drive motor is a brushless DC motor. An electrophotographic image forming apparatus,
An exposure unit that forms an electrostatic latent image on a photoconductor with modulated light based on image data; and
A developing unit that develops the electrostatic latent image with toner using the developing device according to claim 1;
A transfer portion for transferring a toner image from the photoreceptor to a sheet;
An image forming apparatus.

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