JP2007240687A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which outputs a high-quality image by reducing the rotation variation of a photoreceptor drum in all the frequency bands from low frequency to high frequency even when printing speed gets higher. <P>SOLUTION: The image forming apparatus includes: a supporting member 74 supporting the motor rotary shaft 75 of a driving motor 73 for driving the photoreceptor drum so that a driving motor body 76 can turn with the motor rotary shaft 75 as center; vibration absorbing members 83 and 84 coupled with the driving motor body 76 so as to regulate the turning of the driving motor body 76; a detection means detecting the rotational speed of the driving shaft of the photoreceptor drum; and a control means for controlling the rotational speed of the motor rotary shaft 75 of the driving motor 73. The control means controls the rotational speed of the motor rotary shaft 75 based on the result of detection by the detection means so that the rotation variation of the driving shaft may be reduced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a composite machine thereof, and more particularly to an image forming apparatus provided with a photosensitive drum.

2. Description of the Related Art Conventionally, image forming apparatuses such as copying machines and printers often use a photosensitive drum as an image carrier (see, for example, Patent Document 1).
Specifically, a latent image is formed by laser scanning on the surface of the photosensitive drum that is rotationally driven by a drive motor, and the latent image is developed by a developing unit (a toner image is formed). The toner image formed on the photosensitive drum is transferred to a recording medium (sometimes through a transfer process to an intermediate transfer belt). Then, the recording medium onto which the toner image has been transferred reaches the fixing unit, and the toner image on the recording medium is fixed.

  In such an image forming apparatus, it is known that image unevenness such as banding in the sub-scanning direction occurs due to rotational fluctuation of the photosensitive drum. That is, since the laser scanning described above is performed at regular time intervals, when the photosensitive drum undergoes rotational fluctuation, the interval (scanning interval) in the sub-scanning direction on the photosensitive drum varies. Then, the fluctuation in the scanning interval when forming the latent image becomes the density fluctuation of the toner image as it is, and image deterioration due to image unevenness occurs.

On the other hand, in Patent Document 1 and the like, the drive gear of the photosensitive drum is connected to the drive shaft of the photosensitive drum via an elastic body (or viscoelastic body) for the purpose of suppressing the occurrence of image unevenness. Techniques to do this are disclosed.
Patent Document 2 and the like disclose a technique of attaching a drive motor for driving a drive shaft of a photosensitive drum to a frame body via an elastic member for the purpose of suppressing rotation unevenness of the photosensitive drum. .

Further, in Patent Document 3, etc., for the purpose of eliminating banding that occurs in the photosensitive drum, the detection value by the rotation speed sensor (detecting means) that detects the rotation of the photosensitive drum (driving shaft) is brought close to the ideal value. Thus, a technique for correcting and controlling the drive motor is disclosed.
Further, Patent Document 4 and the like disclose a technique in which a flywheel is installed on a drive shaft of a photosensitive drum via a viscoelastic member for the purpose of reducing the rotational fluctuation of the photosensitive drum.

Japanese Patent Laid-Open No. 7-140842 JP 2002-207330 A Japanese Patent Laid-Open No. 2002-247872 JP 2001-50249 A

  In the conventional image forming apparatus, in the drive system for driving the photosensitive drum to rotate, the rotational fluctuation (unevenness of rotation) of the photosensitive drum cannot be reduced in all frequency bands from a low frequency to a high frequency.

The main frequencies of rotation fluctuations that occur in the photosensitive drum are as follows: one rotation component of the drive motor (motor rotation shaft), one rotation component of the drive gear of the photosensitive drum, one gear tooth component (one tooth component) of the motor gear and the drive gear. It is. One rotation component of the drive motor is a rotation variation of the drive motor itself and an eccentric component of the motor gear, and is caused by a meshing error or a tooth groove shake. One rotation component of the drive gear is an eccentric component of the gear, and is caused by a meshing error of the drive gear itself or a tooth groove shake. One tooth component of the motor gear and the drive gear is mainly caused by a single pitch error of each gear.
The fluctuating frequency is, in descending order, a gear tooth component of the motor gear and the drive gear, a rotation component of the drive motor, and a rotation component of the drive gear. The one rotation component of the drive motor and the one rotation component of the drive gear have a low frequency and a long period on the image (toner image), and therefore are not visually noticeable. However, the gear 1 tooth component of the motor gear and the drive gear is visually most noticeable because the pitch of the image density fluctuation is about 0.5 to 2 mm, depending on the printing speed.

Here, since the techniques such as Patent Document 1 and Patent Document 2 described above support a part of the components of the drive system that drives the photosensitive drum via an elastic member, the spring constant of the drive system is low. As a result, it is possible to expect the effect that the rotational fluctuation of the high frequency in the photosensitive drum is reduced.
However, when the spring constant of the drive system is lowered, the low-frequency rotation fluctuation in the photosensitive drum increases. Further, in Patent Document 1 and the like, since it is necessary to rotatably support the drive gear on the drive shaft of the photosensitive drum, the inclination of the tooth trace occurs due to the fall of the drive gear due to the backlash of the bearing portion. There was a possibility that the rotational fluctuation would increase.
Similarly, the techniques of Patent Literature 3, Patent Literature 4 and the like cannot be expected to reduce the rotational fluctuation of the photosensitive drum in all frequency bands from low frequencies to high frequencies.

In order to solve such a problem, a measure using a traction drive in which a gear 1 tooth does not fundamentally change due to friction drive can be considered. However, in that case, since the torque that can be transmitted relatively becomes smaller than the method of using the gear to reduce and transmit the rotational driving force of the drive motor, it is relatively difficult to transmit a large torque. The drive system will be enlarged.
In an electrophotographic image forming apparatus, due to the characteristics of the photosensitive drum, a certain time is required from the exposure process to the development process. Therefore, the faster the printing speed, the longer the distance from the exposure position to the development position in order to ensure the time between both processes. As a result, the diameter of the photosensitive drum increases, and the load torque of the drive system that drives the photosensitive drum also increases. Therefore, particularly in a high-speed image forming apparatus, a gear drive system having a large transmission torque is used without using the traction drive described above.

  The present invention has been made to solve the above-described problems. Even when the printing speed is increased, the rotational fluctuation of the photosensitive drum is varied in all frequency bands from a low frequency to a high frequency. An object of the present invention is to provide an image forming apparatus that outputs a high-quality image that is reduced.

  An image forming apparatus according to a first aspect of the present invention includes a drive shaft on which a drive gear is installed, a photosensitive drum on which a toner image is formed, and the drive shaft of the photosensitive drum on the drive shaft. A drive motor that transmits a rotational driving force via a drive gear, a support member that supports the drive motor main body so that the drive motor main body can rotate about the motor rotation shaft of the drive motor, and the rotation of the drive motor main body are restricted. A vibration absorbing member connected to the drive motor main body, a detecting means for detecting the rotation speed of the drive shaft of the photosensitive drum, and a control means for controlling the rotation speed of the motor rotation shaft of the drive motor. And the control means controls the rotational speed of the motor rotation shaft so as to reduce the rotational fluctuation of the drive shaft based on the detection result of the detection means.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the drive motor is formed such that the motor rotation shaft protrudes from both sides of the drive motor main body, The support member supports both ends of the motor rotation shaft so as to be rotatable.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the vibration absorbing member is a damper member and an elastic member.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect of the present invention, the vibration absorbing member is an actuator that electrically expands and contracts.

  An image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to any one of the first to fourth aspects, wherein a flywheel is installed on the drive shaft of the photosensitive drum.

  An image forming apparatus according to a sixth aspect of the present invention is the image forming apparatus according to the fifth aspect, wherein the flywheel is supported by the drive shaft via a damper member and an elastic member.

  An image forming apparatus according to a seventh aspect of the present invention is the image forming apparatus according to any one of the first to sixth aspects, wherein the drive gear meshes with a motor gear installed on the motor rotation shaft. The rotational driving force by the drive motor is configured to be transmitted to the drive shaft at a reduced speed.

  According to the present invention, a vibration absorbing member is installed so as to restrict the rotation of the drive motor main body that is rotatably supported, and the rotation of the motor rotation shaft is based on the detection result of the rotation speed of the drive shaft of the photosensitive drum. The speed is controlled. As a result, even when the printing speed is increased, the image forming apparatus can output a high-quality image by reducing the rotational fluctuation of the photosensitive drum in all frequency bands from a low frequency to a high frequency. Can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
A first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is an apparatus main body of a color copying machine as an image forming apparatus, 2 is a writing section (exposure section) that emits laser light based on input image information, and 20Y, 20M, 20C, and 20BK are colors (yellow, magenta). , Cyan, black), 21 is a photosensitive drum (image carrier) accommodated in each of the process cartridges 20Y, 20M, 20C, and 20BK, 22 is a charging unit that charges the photosensitive drum 21, Reference numerals 23Y, 23M, 23C, and 23BK denote developing devices (developing units) that develop the electrostatic latent image formed on the photosensitive drum 21, and 24 denotes a toner image formed on the photosensitive drum 21 to the intermediate transfer belt 27. A transfer bias roller 25 for transferring and a cleaning unit for collecting untransferred toner on the photosensitive drum 21 are shown.

  In addition, 27 is an intermediate transfer belt on which toner images of a plurality of colors are transferred in an overlapping manner, 28 is a second transfer bias roller for transferring the toner image formed on the intermediate transfer belt 27 to the recording medium P, and 29 is an intermediate transfer belt. 27 is an intermediate transfer belt cleaning unit that collects untransferred toner, 30 is a conveyance belt that conveys a recording medium P on which a four-color toner image is transferred, and 32Y, 32M, 32C, and 32BK are developing devices 23Y and 23M. , 23C, 23BK, a toner replenishing unit that replenishes toner of each color, 51 a document conveying unit that conveys the document D to the document reading unit 55, and 55 a document reading unit (scanner) that reads image information of the document D, 61 Indicates a paper feeding unit in which a recording medium P such as transfer paper is accommodated, and 66 indicates a fixing unit for fixing an unfixed image on the recording medium P.

Here, each of the process cartridges 20Y, 20M, 20C, and 20BK is obtained by integrating the photosensitive drum 21, the charging unit 22, and the cleaning unit 25, respectively. Image formation of each color (yellow, magenta, cyan, black) is performed on the photosensitive drum 21 in each of the process cartridges 20Y, 20M, 20C, and 20BK.
In the first embodiment, the photosensitive drum 21 is mounted on the process cartridge. However, the photosensitive drum 21 may be a single unit without configuring the process cartridge.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described.
First, the document D is transported from the document table in the direction of the arrow in the drawing by the transport roller of the document transport unit 51 and placed on the contact glass 53 of the document reading unit 55. Then, the document reading unit 55 optically reads the image information of the document D placed on the contact glass 53.

  Specifically, the document reading unit 55 scans the image of the document D on the contact glass 53 while irradiating light emitted from the illumination lamp. Then, the light reflected by the document D is imaged on the color sensor via the mirror group and the lens. The color image information of the document D is read for each color separation light of RGB (red, green, blue) by the color sensor, and then converted into an electrical image signal. Further, the image processing unit (not shown) performs color conversion processing, color correction processing, spatial frequency correction processing, and the like based on the RGB color separation image signals, and performs yellow, magenta, cyan, and black processing. Get color image information.

  Then, the image information of each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. Then, laser light (exposure light) based on the image information of each color is emitted from the writing unit 2 toward the photosensitive drums 21 of the corresponding process cartridges 20Y, 20M, 20C, and 20BK.

On the other hand, each of the four photosensitive drums 21 is rotationally driven in the clockwise direction in FIG. 1 by a drive system described later. First, the surface of the photosensitive drum 21 is uniformly charged at a position facing the charging unit 22 (a charging process). Thus, a charged potential is formed on the photosensitive drum 21. Thereafter, the surface of the charged photosensitive drum 21 reaches the irradiation position of each laser beam.
In the writing unit 2, laser light corresponding to the image signal is emitted from the light source corresponding to each color. The laser light is incident on the polygon mirror 3 and reflected, and then passes through the lenses 4 and 5. The laser light after passing through the lenses 4 and 5 passes through different optical paths for each of the yellow, magenta, cyan, and black color components (this is an exposure process).

  The laser beam corresponding to the yellow component is reflected by the mirrors 6 to 8 and then irradiated onto the surface of the photosensitive drum 21 of the first process cartridge 20Y from the left side of the drawing. At this time, the yellow component laser light is scanned in the rotation axis direction (main scanning direction) of the photosensitive drum 21 by the polygon mirror 3 that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 21 charged by the charging unit 22.

  Similarly, the laser beam corresponding to the magenta component is reflected by the mirrors 9 to 11 and then irradiated to the surface of the photosensitive drum 21 of the second process cartridge 20M from the left side of the paper, thereby causing an electrostatic latent image corresponding to the magenta component. An image is formed. The cyan component laser light is reflected by the mirrors 12 to 14 and then irradiated to the surface of the photosensitive drum 12 of the third process cartridge 20C from the left side of the drawing to form a cyan component electrostatic latent image. The black component laser light is reflected by the mirror 15 and then irradiated on the surface of the photosensitive drum 21 of the fourth process cartridge 20BK from the left side of the paper, thereby forming an electrostatic latent image of black component.

Thereafter, the surface of the photosensitive drum 21 on which the electrostatic latent images of the respective colors are formed reaches positions facing the developing devices 23Y, 23M, 23C, and 23BK, respectively. Then, the respective color toners are supplied from the developing devices 23Y, 23M, 23C, and 23BK onto the photosensitive drum 21, and the latent image on the photosensitive drum 21 is developed (this is a developing step).
Thereafter, the surface of the photosensitive drum 21 after the development process reaches a position facing the intermediate transfer belt 27. Here, the transfer bias roller 24 is installed at each facing position so as to contact the inner peripheral surface of the intermediate transfer belt 27. Then, at the position of the transfer bias roller 24, the images of the respective colors formed on the photosensitive drum 21 are sequentially superimposed and transferred onto the intermediate transfer belt 27 (first transfer step).

Then, the surface of the photosensitive drum 21 after the first transfer process reaches a position facing the cleaning unit 25. The untransferred toner remaining on the photosensitive drum 21 is collected by the cleaning unit 25 (this is a cleaning process).
Thereafter, the surface of the photosensitive drum 21 passes through a static elimination unit (not shown), and a series of image forming processes on the photosensitive drum 21 is completed.

On the other hand, the surface of the intermediate transfer belt 27 on which the images of the respective colors on the photosensitive drum 21 are transferred in an overlapping manner travels in the direction of the arrow in the drawing and reaches the position of the second transfer bias roller 28. Then, the full-color image on the intermediate transfer belt 27 is secondarily transferred onto the recording medium P at the position of the second transfer bias roller 28 (second transfer step).
Thereafter, the surface of the intermediate transfer belt 27 reaches the position of the intermediate transfer belt cleaning unit 29. Then, the untransferred toner on the intermediate transfer belt 27 is collected by the intermediate transfer belt cleaning unit 29, and a series of transfer processes on the intermediate transfer belt 27 is completed.

Here, the recording medium P at the position of the second transfer bias roller 28 is transported from the paper feeding unit 61 via the transport guide 63, the registration roller 64, and the like.
Specifically, the transfer paper P fed by the paper feed roller 62 from the paper feed unit 61 that stores the recording medium P passes through the conveyance guide 63 and is guided to the registration roller 64. The recording medium P that has reached the registration roller 64 is conveyed toward the position of the second transfer bias roller 28 in synchronization with the toner image on the intermediate transfer belt 27.

Thereafter, the recording medium P on which the full-color image is transferred is guided to the fixing unit 66 by the conveyance belt 30. In the fixing unit 66, the color image is fixed on the recording medium P at the nip between the heating roller 67 and the pressure roller 68.
Then, the recording medium P after the fixing process is discharged as an output image by the paper discharge roller 69 to the outside of the apparatus main body 1, and a series of image forming processes is completed.

Next, the image forming unit of the image forming apparatus will be described in detail with reference to FIG. FIG. 2 is a cross-sectional view showing the image forming unit.
The four image forming units installed in the apparatus main body 1 have substantially the same structure except that the color of the toner T used in the image forming process is different. Therefore, the alphabet of reference numerals in the process cartridge, the developing device, and the toner replenishing unit. (Y, M, C, BK) is omitted for illustration.

As shown in FIG. 2, a photosensitive drum 21, a charging unit 22, and a cleaning unit 25 are integrally stored in the process cartridge 20.
The cleaning unit 25 is provided with a cleaning blade 25 a that contacts the photosensitive drum 21. The cleaning blade 25a is made of a rubber material such as polyurethane rubber, and the tip thereof is in contact with the photosensitive drum 1 at an optimal angle and pressure. In the casing of the cleaning unit 25, a transport screw 26a for transporting untransferred toner accommodated (collected) in the cleaning unit 25 toward a waste toner container (not shown) is installed.

  The developing device 23 mainly includes a developing roller 23a facing the photosensitive drum 21, a first transport screw 23b facing the developing roller 23a, and a second transport screw facing the first transport screw 23b via a partition member 23e. 23c and a doctor blade 23d facing the developing roller 23a.

  Further, the developing device 23 is provided with a first developer containing portion 23g and a second developer containing portion 23h separated by a partition member 23e. The first developer accommodating portion 23g and the second developer accommodating portion 23h communicate with each other at both ends in the longitudinal direction (in a range where no partition member 23e is interposed) to form a developer circulation path. A developing roller 23a, a first conveying screw 23b, and a doctor blade 23d are disposed in the first developer accommodating portion 23g. A second transport screw 23c and a magnetic sensor 40 are disposed in the second developer accommodating portion 23h.

  The developing roller 23a includes a magnet that is fixed inside and forms a magnetic pole on the circumferential surface of the roller, and a sleeve that is made of a nonmagnetic material and rotates around the magnet. A plurality of magnetic poles (main pole, transport pole, pumping pole, agent cutting pole, etc.) are formed on the developing roller 23a (sleeve) by the magnet.

The developing roller 23a (sleeve) is connected to a driving source installed in the apparatus main body 1 and is driven to rotate by the driving source. Although not shown, the developing roller 23a, the first transport screw 23b, and the second transport screw 23c are drivingly connected by a gear train. Thereby, as the developing roller 23a is rotationally driven by the drive source, the first transport screw 23b and the second transport screw 23c are also rotationally driven following the development roller 23a.
In the developing device 23, a two-component developer G composed of toner T and carrier C is accommodated.

Hereinafter, the image forming process described above will be described in more detail.
The developing roller 23a rotates in the direction of the arrow in FIG. The developer G in the developing device 23 is supplied from the toner replenishing portion 32 to the toner replenishing port by the rotation of the first conveying screw 23b and the second conveying screw 23c arranged with the partition member 23e interposed therebetween. It circulates in the longitudinal direction while being agitated and mixed with the toner T supplied through 23f.

  Then, the toner T that is frictionally charged and adsorbed on the carrier C is carried on the developing roller 23 a together with the carrier C. The developer G carried on the developing roller 23a then reaches the position of the doctor blade 23d. The developer G on the developing roller 23a is adjusted to an appropriate amount at the position of the doctor blade 23d, and then reaches a position facing the photosensitive drum 21 (developing area).

  Thereafter, in the development area, the toner T in the developer G adheres to the electrostatic latent image formed on the surface of the photosensitive drum 21. Specifically, the toner T is latently exposed by the electric field formed by the potential difference (development potential) between the latent image potential (exposure potential) of the image area irradiated with the laser light L and the development bias applied to the development roller 23a. Adhere to the image.

Thereafter, most of the toner T adhering to the photosensitive drum 21 in the developing process is transferred onto the intermediate transfer belt 27. Then, the untransferred toner T remaining on the photosensitive drum 21 is mechanically scraped by the cleaning blade 25a and collected in the cleaning unit 25.
On the other hand, the developer on the developing roller 23a that has passed through the developing region (the toner density is lowered) is released from the developing roller 23a at the position of the first developer containing portion 23g. The developer G released from the developing roller 23a is conveyed toward the second developer accommodating portion 23h by the first conveying screw 23b, and a circulation cycle in which the developer G is mixed and stirred is repeated.

  Here, the toner replenishing unit 32 provided in the developing device 23 includes a toner container 33 configured to be replaceable, and a toner hopper unit that holds and rotates the toner container 33 and replenishes the developing device 23 with fresh toner T. 34. The toner container 33 contains toner T (any one of yellow, magenta, cyan, and black). A spiral protrusion is formed on the inner peripheral surface of the toner container 33.

  The toner T in the toner container 33 is appropriately supplied into the developing device 23 from the toner supply port 23f as the toner T in the developing device 23 is consumed. That is, new toner (replenishment toner) is appropriately replenished into the developing device 23 from the toner replenishing port 23f so that the toner concentration (TC) of the developer circulating in the developing device 23 is within a predetermined range. Consumption of the toner T in the developing device 23 is detected by a magnetic sensor 40 installed below the second conveying screw 23c of the developing device 23 and a photo sensor 45 facing the photosensitive drum 21.

Hereinafter, the configuration and operation of the drive system for driving the photosensitive drum 21, which is characteristic in the first embodiment, will be described with reference to FIGS. 3 to 5.
FIG. 3 is a schematic diagram showing a drive system of the photosensitive drum 21. 4 is a view of the drive motor 73 in the drive system of FIG. FIG. 5A is a side view showing the flywheel 77 installed on the drive shaft 21 a of the photosensitive drum 21, and FIG. 5B is a front view showing the flywheel 77.

  As shown in FIG. 3, the photosensitive drum 21 is provided with a drive shaft 21 a that rotates together with the photosensitive drum 21. A drive gear 70 that transmits the rotational driving force of the drive motor 73 to the drive shaft 21a is installed on the drive shaft 21a. Specifically, the drive gear 70 meshes with a motor gear 75a formed on the motor rotation shaft 75 of the drive motor 73, and the rotational drive force by the drive motor 73 is decelerated and transmitted to the drive shaft 21a. As a result, the photosensitive drum 21 is rotationally driven in a predetermined direction at a predetermined rotation speed.

  An encoder wheel 71 is provided on the drive shaft 21 a of the photosensitive drum 21. On the surface of the encoder wheel 71, dark portions and bright portions are alternately formed radially (or holes are formed radially). And the detection sensor 72 is installed so that the encoder wheel 71 may be pinched | interposed. The detection sensor 72 is an optical sensor including a light emitting element and a light receiving element, and optically detects a dark part and a bright part (or a hole part) formed on the encoder wheel 71. Thus, the encoder wheel 71 and the detection sensor 72 function as detection means for detecting the rotation speed (or rotation fluctuation) of the rotation shaft 21a.

  And the control means 80 and 81 control the rotational speed of the motor rotating shaft 75 so that the rotation fluctuation | variation of the drive shaft 21a reduces based on the detection result of the detection sensor 72 (detection means). Specifically, based on the rotation speed detected by the detection sensor 72, the rotation control unit 80 controls the motor control unit 81 so as to reduce the rotational fluctuation of the drive shaft 21a.

Referring to FIG. 3, drive motor 73 is supported by bearing 74 (support member) so that drive motor main body 76 (motor box) can rotate about motor rotation shaft 75.
Specifically, the drive motor 73 is formed such that the motor rotation shaft 75 protrudes from both sides of the drive motor main body 76. Then, both ends of the motor rotating shaft 75 are rotatably supported by a bearing 74 installed on a side plate (not shown). With such a configuration, the drive motor main body 76 is rotatably supported with respect to the support member (bearing 74).

  Here, the drive motor main body 76 is connected to the vibration absorbing members 83 and 84, and the rotation of the drive motor main body 76 that is rotatably supported is restricted. Specifically, referring to FIG. 4, a support arm 79 is fixed to the drive motor main body 76. The support arm 79 (drive motor main body 76) is supported by a support portion 85 (main body side support portion) on the apparatus main body 1 side through an elastic member 84 and a damper member 83 that function as a vibration absorbing member.

  Thus, by supporting the drive motor main body 76 via the elastic member 84 and the damper member 83 that function as a vibration absorbing member, the motor rotation shaft 75 ( The rotational driving force is transmitted from the motor gear 75a) to the drive shaft 21a via the drive gear 70. Therefore, the fluctuation of one gear tooth of the motor gear 75a and the drive gear 70 is absorbed, and the rotation fluctuation of one gear tooth component on the drive shaft 21a of the photosensitive drum 21 is reduced.

  With reference to FIGS. 3 and 5, a flywheel 77 is installed on the drive shaft 21 a of the photosensitive drum 21. Specifically, the fly hole 77 is supported on a rotation support plate 78 integrally installed on the drive shaft 21a via an elastic support member 87. Here, the elastic support member 87 is made of a rubber material having elasticity and vibration damping properties, and functions as an elastic member and a damper member.

  In this way, by installing the flywheel 77, the resonance frequency of the entire drive system is lowered, and high-frequency rotation fluctuations are less likely to occur. Therefore, high-frequency rotation fluctuations such as a gear 1 tooth component are reduced. Furthermore, by installing the flywheel 77 on the drive shaft 21a via the elastic support member 87, minute vibrations are converted into heat and reduced, so that the rotational fluctuation of the drive shaft 21a is further reduced.

The effects when using the drive system of the photosensitive drum 21 in the first embodiment will be summarized below.
First, in the first embodiment, the drive motor main body 76 is rotatably supported and the rotation is restricted via the vibration absorbing members 83 and 84. As a result, the spring constant as the drive system of the photosensitive drum 21 is lowered, and the gear 1 tooth component of the drive gear 70 and the motor gear 75a is not transmitted to the photosensitive drum 21 (drive shaft 21a). In addition, by installing the damper member 83, resonance at a specific frequency is prevented and vibration is converted into heat, so that vibration is reduced over a wide range of frequencies.
In addition, as a vibration absorption member, you may use the member which has both elasticity and damping property like a rubber material, and functions as an elastic member and a damper member.

  In the first embodiment, since both ends of the motor rotation shaft 75 of the drive motor 73 are supported by the bearings 74, the parallelism between the drive gear 70 (drive shaft 21a) and the motor rotation shaft 75 is highly accurate. Can be set. Thereby, the rotation fluctuation | variation by the meshing error of the drive gear 70 and the motor gear 75a is reduced.

  Although the spring constant as the drive system of the photosensitive drum 21 is reduced by the above-described configuration, the low-frequency rotation fluctuation is increased. However, in the first embodiment, the encoder wheel 71 and the detection sensor 72 installed on the drive shaft 21a of the photosensitive drum 21 including the frequency of one rotation component of the drive gear 70 and one rotation component of the drive motor 73 are included. Thus, the rotation fluctuation is detected, and the drive motor 73 is controlled by the rotation control unit 80 and the motor control unit 81 so as to cancel the rotation fluctuation. As a result, it is possible to reduce the rotational fluctuation of the low frequency component that increases due to the decrease in the spring constant as the drive system.

  Further, in the first embodiment, since the flywheel 77 is installed on the drive shaft 21a via the elastic support member 87, the rotational inertia force of the drive shaft 21a is increased, and the rotational fluctuation of the drive shaft 21a is further reduced. Will do.

  Therefore, according to the configuration of the first embodiment, in all frequency bands of the drive system, from the high frequency of one tooth component of the gears 70 and 75a to the low frequency of one rotation component of the gears 70 and 75a. The rotational fluctuation can be reduced. In addition, since the drive system of the photosensitive drum 21 in the first embodiment uses a gear drive system with a large transmission torque, good driving can be achieved even when the diameter of the photosensitive drum 21 is large and the load is high. This makes it possible to increase the printing speed with little rotational fluctuation.

  As described above, in the first embodiment, the vibration absorbing members 83 and 84 are installed so as to restrict the rotation of the drive motor main body 76 that is rotatably supported, and the drive shaft of the photosensitive drum 21. The rotation speed of the motor rotation shaft 75 is controlled based on the detection result of the rotation speed 21a. As a result, even when the printing speed is increased, the rotational fluctuation of the photosensitive drum 21 is reduced in all frequency bands from a low frequency to a high frequency, and a high-quality image without image unevenness is output. can do.

Embodiment 2. FIG.
6 and 7, the second embodiment of the present invention will be described in detail.
FIG. 6 is a schematic diagram showing a drive system of the photosensitive drum in the second embodiment, and corresponds to FIG. 3 in the first embodiment. 7 is a view of the drive motor in the drive system of FIG. 6 as viewed from the direction A, and corresponds to FIG. 4 in the first embodiment.
The second embodiment is different from the first embodiment in which the elastic member 84 and the damper member 83 are used as the vibration absorbing member in that the actuator 93 that electrically expands and contracts is used as the vibration absorbing member. To do.

  Referring to FIGS. 6 and 7, in the drive system in the second embodiment, the drive motor body 76 of the drive motor 73 rotates with respect to the support member (bearing 74) as in the first embodiment. It is supported movably. In the second embodiment, the drive motor main body 76 is connected to an actuator 93 as a vibration absorbing member, and the rotation of the drive motor main body 76 that is rotatably supported is restricted.

Specifically, a support arm 79 is fixed to the drive motor main body 76. The support arm 79 (drive motor main body 76) is supported by the main body side support portion 85 via an actuator 93 that functions as a vibration absorbing member.
Here, the actuator 93 is a piezoelectric element, a voice coil, or the like, and its length changes according to an electric signal. The actuator control unit 90 controls the change frequency and change amount (expansion / contraction amount) of the length of the actuator 93.

  In the drive system configured as described above, first, rotation fluctuation of the drive shaft 21a is detected by the encoder wheel 71 and the detection sensor 72 installed on the drive shaft 21a of the photosensitive drum 21. Then, the one rotation component of the drive motor 73 and the one rotation component of the gears 70 and 75a that can be handled by the control of only the drive motor 73 are reduced by the rotation control unit 80 and the motor control unit 81. On the other hand, the actuator 93 is controlled by the actuator control unit 90 so as to cancel the rotational fluctuation detected by the detecting means 71 and 72 for high-frequency rotational fluctuations such as the gear 1 tooth component of the drive gear 70 and the motor gear 75a. I will respond. That is, the fluctuation of the rotation of the drive shaft 21a of the photosensitive drum 21 is reduced by extending and contracting the actuator 93 as a vibration absorbing member.

  As described above, in the second embodiment, as in the first embodiment, the actuator (vibration absorbing member) 93 is installed so as to restrict the rotation of the drive motor main body 76 that is rotatably supported. The rotation speed of the motor rotation shaft 75 is controlled based on the detection result of the rotation speed of the drive shaft 21a of the photosensitive drum 21. As a result, even when the printing speed is increased, the rotational fluctuation of the photosensitive drum 21 is reduced in all frequency bands from a low frequency to a high frequency, and a high-quality image without image unevenness is output. can do.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the embodiments can be modified as appropriate in addition to those suggested in the embodiments. Is clear. In addition, the number, position, shape, and the like of the constituent members are not limited to the above embodiments, and can be set to a number, position, shape, and the like that are suitable for carrying out the present invention.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view illustrating an image forming unit in the image forming apparatus of FIG. 1. It is the schematic which shows the drive system of a photosensitive drum. It is the figure which looked at the drive motor in the drive system of FIG. 3 from the A viewing direction. It is a figure which shows the flywheel installed in the drive shaft of a photoconductor drum. It is the schematic which shows the drive system of the photosensitive drum in Embodiment 2 of this invention. It is the figure which looked at the drive motor in the drive system of FIG. 6 from the A viewing direction.

Explanation of symbols

1 image forming apparatus body (apparatus body),
21 photosensitive drum, 21a drive shaft,
70 Drive gear,
71 Encoder wheel (detection means), 72 Detection sensor (detection means),
73 drive motor, 74 bearing,
75 motor rotation shaft, 75a motor gear,
76 drive motor body,
77 flywheel, 78 rotating support plate,
80 rotation control part (control means), 81 motor control part (control means),
83 damper member (vibration absorbing member), 84 elastic member (vibration absorbing member),
87 elastic support member (damper member, elastic member), 90 actuator control unit,
93 Actuator (vibration absorbing member).

Claims (7)

A photosensitive drum having a drive shaft on which a drive gear is installed and on which a toner image is formed;
A drive motor that transmits a rotational driving force to the drive shaft of the photosensitive drum via the drive gear;
A support member that supports the drive motor main body so that the drive motor main body can rotate about the motor rotation shaft of the drive motor;
A vibration absorbing member coupled to the drive motor body so as to restrict rotation of the drive motor body;
Detecting means for detecting the rotational speed of the drive shaft of the photosensitive drum;
Control means for controlling the rotational speed of the motor rotation shaft of the drive motor,
The image forming apparatus according to claim 1, wherein the control unit controls a rotation speed of the motor rotation shaft so as to reduce a rotation fluctuation of the drive shaft based on a detection result of the detection unit. The drive motor is formed such that the motor rotation shaft protrudes from both sides of the drive motor body,
The image forming apparatus according to claim 1, wherein the support member rotatably supports both ends of the motor rotation shaft. The image forming apparatus according to claim 1, wherein the vibration absorbing member is a damper member and an elastic member. The image forming apparatus according to claim 1, wherein the vibration absorbing member is an actuator that electrically expands and contracts. The image forming apparatus according to claim 1, wherein a flywheel is installed on the drive shaft of the photosensitive drum. The image forming apparatus according to claim 5, wherein the flywheel is supported by the drive shaft via a damper member and an elastic member. 2. The drive gear is configured to mesh with a motor gear installed on the motor rotation shaft so that the rotational drive force by the drive motor is transmitted to the drive shaft at a reduced speed. The image forming apparatus according to claim 6.

Images