JP3422114B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to a banding method by suppressing a change in a resonance frequency of a photosensitive member driving system when the photosensitive member is driven. Horizontal stripes)
The present invention relates to an image forming apparatus that prevents image quality deterioration such as the above. 2. Description of the Related Art In a conventional image forming apparatus, a photosensitive member drive system for transmitting a drive torque from a drive motor to a photosensitive member via a gear, a belt, or the like has a frequency response characteristic based on its configuration. It is designed so that the meshing frequency and rotation frequency of gears and belts do not match the resonance frequency of the photoconductor drive system. When the resonance frequency of the photoconductor drive system matches the meshing frequency or rotation frequency of the gear or belt, the drive system becomes a resonance system. In such a state, the aforementioned frequency components are amplified, and the amplified frequency components are transmitted to the photoconductor via the drive system, so that the rotation speed of the photoconductor is varied. When the rotation speed of the photoconductor changes as described above, the dot position of the electrostatic latent image formed on the photoconductor is shifted, which causes image quality deterioration such as banding. FIG. 7 shows a configuration of a conventional image forming apparatus. This image forming apparatus includes a document reading unit 1, a laser scanning unit 6, an electrostatic recording unit 12, and a paper conveying unit 21. The original reading section 1 has a lamp 3 for irradiating the original on a platen 2 and a fixed image pickup device 5 for receiving the reflected light of the original via an optical system 4. A laser light source 7 that emits a laser beam 7A modulated according to a signal, a rotary polygon mirror 8 driven by a scanner motor 8A to scan the laser beam 7A in the main scanning direction, and a laser beam that enters through a lens 9 7A to photosensitive drum 1
The electrostatic recording unit 12 includes a photosensitive drum 10 driven by a photosensitive member drive system, and a charger 13 that charges the photosensitive drum 10.
A developing device 14 for developing the electrostatic latent image formed on the photosensitive drum 10 with toner; a transfer device 15 for transferring the toner image on the photosensitive drum to paper supplied from paper feed cassettes 18 to 20; A cleaning device 16 that removes toner remaining on the body drum 10; and a static eliminator 17 that removes electricity from the photoconductor drum 10. The paper transport unit 21 supplies a paper at a predetermined timing. The fixing device 23 includes a fixing device 23 for fixing a transfer image transferred to a sheet, and a discharge tray 24 from which the sheet on which the image is recorded is discharged. FIG. 8 shows a photoreceptor drive system of the image forming apparatus shown in FIG. 7, in which a photoreceptor drum rotary shaft 10A is driven via a gear 27 from a gear 26 provided on a rotary shaft 25A of a drive motor 25. As a result, the photosensitive drum 10 rotates. A cleaning device 16 is configured to be connected to / disconnected from the surface of the photosensitive drum 10. Further, a fixing device 23 is connected to the photosensitive drum drive shaft 10A, and the fuser roll 23A is connected / disconnected. FIG. 9 shows a change in load in the photosensitive member drive system of the image forming apparatus described above. When the photosensitive drum 10 is driven, a steady load A is generated in the photosensitive member drive system.
At time t ₁ , when the cleaning device 16 is connected to the surface of the photoconductor drum 10, a load B is generated, and the load B is added to the steady load A, so that the driving load of the photoconductor drive system increases. The torque (load torque) for driving the photoconductor drive system from the drive motor 25 to the photoconductor drum 10 changes based on the increased drive load, so that the torsional rigidity of the photoconductor drive system changes. FIG. 10 shows a meshing portion of the gear 26 and the gear 27.
When it is connected to zero, the load torque due to the friction between the photosensitive drum 10 and the cleaning device 16 increases, so that the engagement of the gears 26 and 27 changes. When the load torque is small, the meshing width between the gear 26 and the gear 27 is small as shown in FIG. 10A, and when the load torque is large, the driven side as shown in FIG. When the gear 27 is elastically deformed from the shape shown by the dotted line to the shape shown by the solid line, the engagement with the gear 26 is expanded, and the torsional rigidity of the photoconductor drive system is increased accordingly. FIG. 11 shows the relationship between the torsional stiffness of the photosensitive member drive system and the load torque. The torsional stiffness increases with an increase in the load torque, and saturates when a load torque of a certain value or more is applied. It will be constant. Such a change in torsional rigidity changes the resonance frequency of the photoconductor drive system. FIG. 12 shows a change in the resonance frequency of the photosensitive member drive system due to a change in torsional rigidity.
, When the cleaning device 16 is connected to the photosensitive member drive system having the resonance frequency f ₁ of the photosensitive drum 10 indicated by A and the resonance frequency f ₂ of the drive motor 25 indicated by B, the torsional rigidity of the photosensitive member drive system There was increased, the resonant frequency of the photosensitive drum 10 as shown in a ₁ is, and FIG. 12 (b)
As shown in FIG. 7, the frequency changes to a frequency f _1a higher than f ₁ . Next, referring to FIG. 8, when the fuser roll 23A is connected to the photosensitive drum drive shaft 10A, the inertia weight of the photosensitive drum drive shaft 10A increases to increase the moment of inertia of the photosensitive member drive system. . FIG. 13 shows a change in the resonance frequency of the photosensitive member drive system due to a change in the moment of inertia.
(A), the the fuser roll 23A to the photoreceptor driving system having a resonant frequency f ₂ of the drive motor 25 shown at the resonance frequency f ₁ and B of the photoreceptor drum 10 as indicated by A is connected, the moment of inertia is increased When the resonance frequency of the photosensitive drum 10 is f, as shown in FIG.
It changes to a frequency f _1b lower than ₁ . As described above, when the resonance frequency changes due to the change in the torsional rigidity and the moment of inertia of the photosensitive member drive system, for example, the meshing frequency and the rotation frequency of the gears 26 and 27 match the resonance frequency of the photosensitive member drive system. As a result, a resonance system is formed, and there is a possibility that the rotation speed of the photosensitive member fluctuates. In order to solve such inconvenience, the resonance frequency of the drive system is set low in advance by lowering the torsional rigidity of the photoconductor drive system or increasing the moment of inertia, and the frequency of the speed fluctuation transmitted to the drive system is reduced. The resonance frequency is changed by controlling the excitation current of the motor or the driving device of the rotating body disclosed in Japanese Patent Application Laid-Open No. 6-95564 so that the vibration frequency does not coincide with the excitation frequency accompanying the change in the process speed of the driving system. There is an image forming apparatus proposed in Japanese Patent Application No. 6-232686 which prevents the coincidence of the image forming apparatus. [0015] However, according to the conventional image forming apparatus, the torsional rigidity of the photosensitive member drive system is reduced.
Alternatively, even if the moment of inertia is increased, the torsional stiffness changes due to the change in the load torque, which causes a change in the resonance frequency, and may match the frequency component that causes the rotation speed change of the photoconductor. In order to suppress the change in the resonance frequency, for example, a method of extremely increasing the machining accuracy of the photoconductor drive system or setting a large inertia moment of the photoconductor drive system in advance can be considered. However, the method described below has the disadvantage of increasing the size of the apparatus and increasing power consumption. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an image forming apparatus capable of suppressing a change in resonance frequency even when the torsional rigidity and the moment of inertia of the photoconductor driving system change when the photoconductor is driven. Another object of the present invention is to provide an image forming apparatus which realizes high image quality by suppressing a change in the resonance frequency of the photosensitive member driving system. According to the present invention, there is provided an image forming apparatus having a photosensitive member drive system for transmitting a driving force generated by a drive motor to a photosensitive member. Braking means for increasing or decreasing the braking load on the body drive system;
An operation is performed in which the torsional rigidity of the photoconductor moving system is increased.
That time, the reduces the braking load by the braking means
An operation is performed in which the torsional rigidity of the photoconductor drive system does not change, and the moment of inertia of the photoconductor drive system increases.
That time, so does not change the moment of inertia of the photoreceptor driving system increases the braking load by the braking means
Accordingly, there is provided an image forming apparatus having a resonance frequency change suppressing unit for suppressing the photosensitive member drive system from becoming a resonance system. According to the image forming apparatus of the present invention, when the load torque of the photoconductor drive system changes when the photoconductor is driven, the torsional rigidity of the photoconductor drive system changes. On the other hand, when the inertia weight of the photoconductor drive system changes when the photoconductor is driven, the moment of inertia changes. The resonance frequency change suppression means suppresses the change in resonance frequency due to the change in torsional rigidity and moment of inertia.
The photoreceptor drive system is controlled by increasing or decreasing the braking load on the photoreceptor drive system, and the photoreceptor drive system becomes a resonant system by matching the resonance frequency with the frequency component that affects the rotation speed of the photoreceptor. To prevent Hereinafter, an image forming apparatus according to the present invention will be described in detail with reference to the drawings. Portions having the same configuration and function as those of the prior art are denoted by the same reference numerals, and duplicate description will be omitted. FIG. 1 shows an embodiment of a photosensitive member drive system in an image forming apparatus according to the present invention, and a photosensitive drum to which drive torque is transmitted from a rotation shaft 25A of a drive motor 25 via gears 26 and 27. A rotating shaft 10A, a brake 30 provided on the photosensitive drum rotating shaft 10A, and a photosensitive drum 10 driven by the photosensitive drum rotating shaft 10A.
And a cleaning device 16 provided so as to be connected to / disconnected from the photosensitive drum 10. The brake 30 is configured to adjust the braking force applied to the photosensitive drum rotating shaft 10A in accordance with the connection / disconnection of the cleaning device 16, and the photosensitive drum is not connected when the cleaning device 16 is not connected. A predetermined brake load is generated in the photoconductor drive system by braking the rotating shaft 10A with a predetermined force. In the above-described photoconductor driving system, when the cleaning device 16 is connected while the photoconductor drum 10 is being driven, a driving load on the photoconductor drum rotating shaft 10A is generated due to friction. At this time, the brake 30 is connected to the cleaning device 16.
The braking force is reduced in accordance with the driving load generated by the connection. FIG. 2 shows a change in load of the photoconductor drive system. When the photoconductor drum 10 is driven, a brake load C ₁ by the brake 30 is applied to the photoconductor drive system in addition to the steady load A.
At time t ₁ , the photosensitive drum 1
When the cleaning device 16 is connected to the surface of the zero, a load B is generated by friction. The brake 30 reduces the sum of the steady load A, the load B due to the connection of the cleaning device 16 and the brake load C ₂ by reducing the braking force from C ₁ to C ₂ based on the generation of the load B. The brake load is reduced so as to be the same as before the connection of the device 16. By reducing the brake load from C ₁ to C ₂ in this manner, the load torque of the photosensitive member drive system is kept constant without fluctuating, and even if the cleaning device 16 is connected / disconnected, the photosensitive drum is exposed to light. Since the torsional rigidity of the body drive system is kept constant, a change in the resonance frequency is suppressed. FIG. 3 shows another embodiment of the photosensitive member driving system in the image forming apparatus of the present invention. The photosensitive member driving system is provided between a rotating shaft 25A of a driving motor 25 and a photosensitive drum rotating shaft 10A. An intermediate shaft 31 having a gear 33;
And a fixing device 23 having a fuser roll 23A connected to and disconnected from the photosensitive drum rotating shaft 10A. The shaft 10A is configured to transmit a driving torque from the driving motor 25 via the gears 26, 32, 33, and 27, and the brake 30 is mounted on the photosensitive drum rotating shaft 10A in a predetermined size in advance. The brake load is given. In the above-described photoconductor driving system, when the fuser roll 23A is connected to the photoconductor drum rotation shaft 10A while the photoconductor drum is being driven, the photoconductor drum rotation shaft 10A
The moment of inertia increases due to an increase in the inertial weight of. As described above, when the moment of inertia of the photosensitive drum rotating shaft 10A increases, the photosensitive drum rotating shaft 10A
The resonance frequency of A decreases. At this time, the brake 30 is connected to the photosensitive drum rotating shaft 1 increased by the connection of the fuser roll 23A.
Increase the brake load according to the inertial weight of 0A. When the torsional rigidity of the photosensitive member drive system is increased by the brake 30, the resonance frequency of the photosensitive member increases. That is, the resonance frequency f ₁ indicated by C by increasing the torsional stiffness in accordance with an increase in the moment of inertia as shown in FIG. 4 proceeds to a high frequency high frequency f _1a than that. Thus, the moment of inertia of the photoconductor drive system is increased, as indicated by B, it cancels the resonance frequency f _1b to be migrated to a lower frequency to match the resonance frequency f ₁ C set in advance as shown in C be able to. FIG. 5 shows still another embodiment of the photoconductor driving system in the image forming apparatus of the present invention. The photoconductor drum 10 is driven by a gear 26 provided on a rotating shaft 25A of a driving motor 25 via a gear 27. Drum rotating shaft 10A that transmits a driving torque to the photosensitive drum 10, a bias transfer roll 28 provided so as to be connected to / disconnected from the photosensitive drum 10, an encoder 34 that detects the rotating speed of the photosensitive drum rotating shaft 10A, and an encoder 34 The control unit 35 sets an input frequency to the drive motor 25 based on the detection result of the rotation speed by the control unit 35, and a motor drive unit 36 that generates the input frequency set by the control unit 35 and outputs the input frequency to the drive motor 25. ing. FIG. 6 shows the transfer function of the photosensitive member drive system shown in FIG.
(S), the transfer function of the photoconductor drive system for which the resonance frequency is set is G ₀ (s), the rotation angle of the photoconductor drum 10 as an output is θ (s), and the feedback gain by the control unit 35 is H.
(S), and the proportional constant to the input is k. In the above configuration, the connection of the bias transfer roll 28 increases the load torque and the moment of inertia of the photoconductor drive system. The relationship between the input and output of the photoconductor driving system at this time is expressed by equation (1). θ (s) / F (s) = kG ₁ (s) / (1 + kG ₁ (s) H (s)) (1) G ₁ (s) is the inertia due to the connection of the bias transfer roll 28. This is the transfer function of the photoconductor drive system when the moment is increased. The control unit 35 controls the input of the drive motor 25 so that the transfer function of the photoconductor drive system shown in the equation (1) becomes equivalent to G ₀ (s). Since the frequency may be set, the feedback gain H (s) is set as shown in equation (2). H (s) = (kG ₁ (s) −G ₀ (s)) / kG ₁ (s) G ₀ (s) (2) From the equation (2), the feedback gain H (s) is satisfied. The input frequency F ₁ (s) is represented by equation (3). F ₁ (s) = F (s) + H (s) θ (s) (3) As described above, the feedback gain is set by the control unit 35 according to the change in the resonance frequency, and the motor drive unit 36 is set. By setting the input frequency, it is possible to suppress the change in the resonance frequency due to the change in the torsional rigidity and the moment of inertia of the photosensitive member drive system, and it is possible to prevent image quality deterioration such as banding. As described above, according to the image forming apparatus of the present invention, the change in the resonance frequency based on the change in the torsional rigidity of the photoconductor drive system or the change in the moment of inertia of the photoconductor drive system. Because of having the resonance frequency change suppression means to suppress, even if the torsional rigidity or moment of inertia of the photoconductor drive system changes at the time of driving the photoconductor, it is possible to suppress the change of the resonance frequency and prevent image quality deterioration such as banding High image quality can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram showing one embodiment of a photoconductor driving system in an image forming apparatus of the present invention. FIG. 2 is an explanatory diagram showing a change in load of a photoconductor driving system in the present invention. FIG. 3 is an explanatory view showing another embodiment of the photoconductor driving system in the image forming apparatus of the present invention. FIG. 4 is an explanatory diagram showing a change in a resonance frequency of a photoconductor driving system in the present invention. FIG. 5 is an explanatory view showing still another embodiment of the photoconductor driving system in the image forming apparatus of the present invention. FIG. 6 is an explanatory diagram showing a transfer function of the photoconductor driving system of FIG. 5; FIG. 7 is an explanatory diagram illustrating a configuration of a conventional image forming apparatus. FIG. 8 is an explanatory diagram illustrating a photoconductor driving system of the image forming apparatus of FIG. 7; FIG. 9 is an explanatory diagram illustrating a change in load in a photoconductor driving system of a conventional image forming apparatus. FIG. 10 is an explanatory diagram showing a meshing portion of a gear 26 and a gear 27 in a photoconductor driving system of a conventional image forming apparatus. FIG. 11 is an explanatory diagram illustrating a relationship between torsional rigidity and load torque of a photosensitive member drive system of a conventional image forming apparatus. FIG. 12 is an explanatory diagram showing a change in the resonance frequency of the photosensitive member drive system due to a change in torsional rigidity. FIG. 13 is an explanatory diagram showing a change in the resonance frequency of the photoconductor drive system with a change in the moment of inertia. [Description of References] 1, document reading unit 2, platen 3, lamp 4, optical system 5, fixed image sensor 6, laser scanning unit 7, laser beam 7A, laser light source 8, rotating polygon mirror 8A, scanner motor 9, lens 10, photoconductor drum 10A, photoconductor drum rotating shaft 11, reflection mirror 12, electrostatic recording unit 13, charger 14, developing unit 15, transfer unit 16, cleaning device 17, static eliminator 18, paper feed cassette 19, Paper cassette 20, paper feed cassette 21, paper transport unit 22, registration roll 23, fuser 23A, fuser roll 24, discharge tray 25, drive motor 25A, rotating shaft 26, gear 27, gear 28, bias transfer roll 30, brake 31, intermediate shaft 32, gear 33, gear 34, encoder 35, control unit 36, motor drive unit

──────────────────────────────────────────────────続 き Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 21/00 350 G03G 15/00 550 G03G 21/00 370-540 G03G 21/14

Claims (1)

(57) An image forming apparatus provided with a photoconductor drive system for transmitting a driving force generated by a drive motor to a photoconductor, wherein a braking load on the photoconductor drive system is increased or decreased. and braking means for the operation is performed in which the torsional rigidity of the photoreceptor mobility system is increased
That time, the reduces the braking load by the braking means
An operation is performed in which the torsional rigidity of the photoconductor drive system does not change, and the moment of inertia of the photoconductor drive system increases.
That time, so does not change the moment of inertia of the photoreceptor driving system increases the braking load by the braking means
The image forming apparatus further includes a resonance frequency change suppression unit that suppresses the photosensitive member drive system from becoming a resonance system.