JP3577685B2 - Power transmission device for electrophotographic image forming apparatus - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power transmission device that transmits power of a driving source to smoothly rotate a drum-shaped photoconductor (hereinafter, also simply referred to as a photoconductor) of an electrophotographic image forming apparatus.
[0002]
[Prior art]
In recent years, for example, the image quality of digital image devices has been remarkably improved, and in order to realize image quality at a high level of 300 to 400 dpi to 600 to 1200 dpi, it is required to pursue the precision of the photoconductor drive system to the utmost. . In particular, many electrophotographic image forming apparatuses integrally connect a gear to which rotation is transmitted from a drive source and a photoreceptor, and the integrated drum gear receives fluctuations of various loads connected to the same drive source. There is a problem that the rotation speed unevenness is transmitted, and an image formed on the photosensitive member is likely to have unevenness and a defect called small pitch banding.
[0003]
In order to solve the above-mentioned problem, in a transmission device for transmitting the power of a drive source to a moving member of a driven body, a transmission using an elastic joint for transmitting a rotational force to a part of a transmission system via a rubber member. The apparatus is disclosed in JP-A-51-60532, JP-A-60-49550, JP-A-4-156473, JP-A-5-188671, JP-A-6-193680, JP-A-6-202240, JP-A-6-249321, and JP-A-6-249321. No. 6,294,453. However, even in the transmission devices described in these publications, the driving accuracy of the photosensitive member, which is a moving member, cannot be improved due to various causes, and there is a problem that defects such as unevenness of an image due to uneven rotation speed of the photosensitive member occur. Is not completely eliminated.
[0004]
Therefore, the natural frequency f _N expressed by f _N = (1 / 2π) (K / I) ^1/2 (where K is the torsional stiffness of the drive system and I is the moment of inertia) of the photoconductor drive system, By interposing an elastic member connecting the photosensitive member and the coaxially rotatable drum gear to each other to reduce the torsional rigidity K, the frequency of the rotation fluctuation power spectrum of the drive system, that is, the drive system For example, the frequency is lower than a frequency such as a harmonic of 44 Hz of 22 Hz for one rotation of the motor gear, a harmonic of 64 Hz for one tooth of the second shaft gear or a harmonic of 50 Hz of 25 Hz for one tooth of the drum gear, thereby driving. Japanese Patent Application Laid-Open No. 7-140842 discloses a driving device for a rotating body in which the gain of the transfer function of the system is reduced to make the rotation of the photosensitive member smooth. However, it has been found that even with this driving device, it is difficult to sufficiently eliminate the unevenness in the rotational speed of the photoconductor, and it is sometimes impossible to completely eliminate the problem of the occurrence of defects such as unevenness in the image.
[0005]
[Problems to be solved by the invention]
SUMMARY An advantage of some aspects of the invention is to solve the above-described problem, and to transmit a power of a driving source to a smooth rotation of a moving member and to use the photosensitive member when rotating the photosensitive member of an image forming apparatus. The object of the present invention is to provide a power transmission device that facilitates formation of a transferred image without defects such as unevenness in the photoreceptor by smoothly rotating the photoconductor.
[0006]
[Means for Solving the Problems]
The object of the present invention can be achieved by the following configurations.
(1) having a drum-shaped photoconductor and a drive gear provided on a shaft of the drum-shaped photoconductor,
Via a connection between a projection member provided on one of the drum-shaped photoreceptor and the drive gear, and a working portion comprising a hole provided on the other,
A power transmission device of an electrophotographic image forming apparatus configured to transmit a rotational force from a drive source applied to the drive gear to the drum-shaped photoconductor,
The action section,
An elastic member comprising an elastic bending portion or an elastic bending member,
A viscous member provided adjacent to the elastic member,
The projecting member is opposed to a surface of the viscous member opposite to a surface on which the elastic member is disposed so as to be able to contact the viscous member.
A power transmission device for an electrophotographic image forming apparatus.
(2) One end of the elastic member is fixed to the surface of the drum-shaped photoreceptor or the drive gear having the hole of the action portion, and the other end is joined to a viscous member made of a rubber plate via a seat plate. The power transmission device for an electrophotographic image forming apparatus according to (1), wherein the power transmission device is a coil spring.
[0007]
The elastic member according to the present invention is made of an elastic material in which elastic properties that generate a stress that is linearly proportional to strain at the time of deformation are dominant, and in particular, a longitudinal elastic coefficient of 200 to 500 kgf / cm ² as a physical property value. And a member made of an elastic material having a viscosity damping coefficient ratio η in the range of 0.01 to 0.1. As an elastic material forming the elastic member, a resin material such as polyacetal is used. As a specific elastic member, a plate-shaped member in a cantilever or double-supported beam state, or a coil spring member having one end fixed is used.
[0008]
The viscous member according to the present invention is made of an elastic material in which a viscous force that relieves an impact force is dominant. In particular, the viscous damping coefficient ratio η is in the range of 0.3 to 0.8 as a physical property value, A member made of an elastic material having a coefficient in the range of 0.1 to 1 kgf / cm ² . As an elastic material forming the viscous member, a rubber material, for example, CR rubber, silicon rubber, butyl rubber, silicon gel, or the like is used. As a specific viscous member, a plate-shaped or block-shaped rubber member is used, and is provided on the elastic member.
[0009]
The elastic modulus of the elastic material in the definition of the elastic member and the viscous member described above is, of course, the Young's modulus. In addition, the viscous damping coefficient ratio η of the elastic material is, for example, adjacent to the vibration when the elastic material vibrates to recover the strain by instantaneously removing the load from the state where the rod-shaped elastic material is expanded or compressed by applying a load. that mountain height _is a value obtained by _{x i,} x i = _{+ 1} logarithmic i.e. logarithmic decrement of the ratio _{δ log (x i / x i} + 1) from ^{η = δ / (4π 2 +} δ 2) 1/2.
[0010]
Further, the elastic member and the inherent frequency of the torsional in all member integrally rotated, for example Ono Sokki Co. piezoelectric type FFT analyzer made dual-channel of the impact hammer and the acceleration sensor and the respective amplifiers By attaching a receiving member receiving the tangential impact force to the outer periphery of the moving member, for example, the photoreceptor, and the acceleration sensor for detecting the tangential acceleration, and applying the impact force to the receiving member with the hammer. , A value obtained as a frequency corresponding to the peak value of the transfer function graph output from the FFT analyzer. In addition, the frequency of the vibration source applied to the transmission system refers to the fluctuation corresponding to one rotation of the motor related to the shaft accuracy such as the vibration of the shaft of the motor of the drive source, the fluctuation related to the accuracy of the magnet arrangement and the accuracy of the rotor / stator, the gear And the frequency corresponding to one rotation of the gear or the timing belt / pulley relating to the eccentricity of the timing belt / pulley, and the fluctuation corresponding to one tooth of the gear or the timing belt. It refers to a theoretically derived frequency of the periodic fluctuation as described above that can be considered in the system.
[0011]
The present inventors have conducted intensive studies and found that the main cause of lowering the driving accuracy of the moving member by the power transmission device is a transfer function of the drive system, and among them, a natural frequency of torsion of the drive system which particularly corresponds to a peak value. It has been found that the frequency region where the gain is high and the frequency region where the frequencies of the excitation sources of the drive system are relatively densely overlapped. In order to improve the drive characteristics and obtain high-precision rotation accuracy, it is important to appropriately set the natural frequency of the torsion of the drive system with respect to the predicted vibration source frequency. The present invention has been accomplished as a solution means.
[0012]
As a specific method of appropriately setting the natural frequency of the torsion of the photoconductor drive system with respect to the frequency of the excitation source, the shape of the drive shaft, that is, the shaft diameter is changed, or a part of the shaft is made thinner. However, as the shaft diameter is reduced, there is a problem in the shaft strength such that the torsional strength of the shaft is weakened, and there is a limit. Therefore, in the power transmission device of the present invention, by providing an elastic member whose elastic characteristic is dominant in a part of the drive system, the natural frequency of the torsion of the photosensitive member drive system can be set freely. The transmitted vibration can be reduced by setting the natural frequency to be outside the frequency of the excitation source of the drive system. Further in the apparatus of the present invention, by the viscosity characteristics provided dominant elastic member to a part of the drive system, to reduce the gain of the transfer function in the natural frequency of the twist of the driving system, in a wide frequency range Therefore, the fluctuation level of the vibration source existing in the region is reduced, and smooth rotation can be transmitted to the photoconductor.
[0013]
When the effects of the elastic member and the viscous member in the apparatus of the present invention are schematically shown, the transfer function of the drive system can be changed as shown in the graphs of FIGS. 6 and 7, curves A are transfer functions of a conventional power transmission device in which a photoconductor and a drum gear are integrated, and curves B and C are inventions disclosed in JP-A-7-140842 in which only an elastic member is interposed in a drive system. And D and E show the transfer functions of the power transmission device of the present invention in which a viscous member is also interposed in the drive system of the devices of curves B and C.
[0014]
That is, in the device of the present invention, the elastic member interposed in the drive system mainly changes the natural frequency which is the frequency giving the peak value of the transfer function, and the viscous member mainly lowers the gain of the peak value of the transfer function. Since the function and effect of the elastic member and the viscous member are separated, a smooth rotation of the moving member can be achieved more easily than in the rotation transmitting device of the invention disclosed in Japanese Patent Application Laid-Open No. Hei 7-140842. Can be.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0016]
1 and 2 are an exploded perspective view and a front view of a main part of a power transmission device of the present invention showing an example applied to rotation of a photoreceptor, and FIGS. 3, 4 and 5 show other examples, respectively. FIG. 3 is a front view of an essential part of an assembled state similar to FIG. 2, wherein reference numeral 1 in the figure denotes an electrophotographic photosensitive member which is rotated clockwise to form a toner image of a transfer image to be transferred onto a transfer material or the like on a peripheral surface thereof The image forming body 2 is a driving gear coaxial with the image forming body 1 that rotates the image forming body 1 by being rotated clockwise by a gear train of a power transmission system from a motor of a driving source (not shown).
[0017]
The image forming body 1 and the driving gear 2 in the illustrated example have the shaft 1a and the passive projection 1b provided integrally with the image forming body 1, and the driving gear 2 includes a shaft hole 2a and an elastic bending portion or an elastic bending member. There is provided an operating portion 2b in which an elastic member 3 and a viscous member 4 made of an elastic compressing member are joined. The shaft 1a is rotatably fitted in the shaft hole 2a, and the passive projection 1b is connected to the viscous member of the operating portion 2b. The members 4 are connected so as to come into contact with the surface on the opposite side of the joining surface and receive the rotational force from the action portion 2b. Here, the elastic member 3 is made of a resin material such as polyacetal, polycarbonate, or ABS resin having a longitudinal elastic modulus in a range of 200 to 500 kgf / cm ² , and preferably a viscous damping coefficient η in a range of 0.01 to 0.1. Alternatively, the viscous member 4 is formed of a metal material such as aluminum or a copper alloy, and has a viscous damping coefficient η in a range of 0.3 to 0.8 and a longitudinal elastic coefficient in a range of 0.1 to 1 kgf / cm ² . Formed from synthetic rubber or natural rubber such as CR rubber, silicon rubber, butyl rubber, and silicon gel.
[0018]
Specifically, the action portion 2b in the example of FIGS. 1 and 2 is formed by arranging two square holes as illustrated in parallel on the main body of the resin-made image forming gear 2, for example. A doubly-supported elastic member 3 extending in the radial direction is formed between the square holes, and a viscous member 4 made of a rubber plate of synthetic rubber or natural rubber is attached to an upstream surface in the rotation direction of the elastic member 3 with an adhesive or the like. It is formed by joining. The working portion 2b in the example of FIG. 3 is a cantilevered elastic member 31 in which the doubly supported elastic member 3 of the working portion 2b in the example of FIGS. Things. In this example, the cantilever-like elastic member 31 has the free end on the shaft hole 2a side, but may have the free end on the opposite side. The operating portion 2b in the example of FIG. 4 is a leaf spring elastic member 32 provided by inserting the cantilever elastic member 31 of the operating portion 2b in the example of FIG. Things. Also in this example, the free end of the elastic member 32 may be on the opposite side to the illustrated example.
[0019]
In contrast to the action portion 2b using the elastic members 3, 31, and 32 that undergo only the bending deformation, the action portion 2b in the example of FIG. 5 includes the elastic member 33 of the coil spring that receives not only the bending deformation but also the torsional deformation. This embodiment differs from the action section 2b of the example shown in FIGS. 1 to 4 in that it is used. One end of the elastic member 33 of the coil spring is fixed to a surface of the square hole of the driving gear 2 facing upstream in the rotation direction by insert or bonding, and the seat plate 5 is fixed to the other end by bonding or the like. A viscous member 4 made of a rubber plate is joined to the seat plate 5 with an adhesive or the like to form the action portion 2b of FIG.
[0020]
As described above, the driving gear 2 having any of the above-mentioned working portions 2b pushes the passive projection 1b of the image forming body 1 in the circumferential direction by the viscous member 4 of the working portion 2b, and causes the image forming body 1 to vibrate the natural vibration of the driving system and the like. It transmits a smooth rotation that absorbs the vibration caused by the load fluctuation. The power transmission device of the present invention for transmitting rotation to the image forming body 1 is not limited to the illustrated example, and a passive unit having the same structure as the above-described working unit is provided on the image forming body 1 side, and the driving gear 2 side May be provided so that the image forming body 1 is rotated by pressing the viscous member of the passive unit. Needless to say, the drive gear 2 is not limited to a resin gear. Further, the power transmission device of the present invention is not limited to the one that rotates the image forming body, and may be one that drives another rotating body that requires smooth rotation.
[0021]
1 and 2, the elastic member 3 of the working portion 2b of the drive gear 2 shown in FIGS. 1 and 2 has a longitudinal elastic modulus of 350 kgf / cm ² and a viscous damping coefficient ratio η of 0. And the viscous member 4 is made of a rubber plate having a η of 0.6 and a longitudinal elastic coefficient of 0.6 kgf / cm ² . The power spectrum of the speed fluctuation by the FFT analyzer has a low level on the low frequency side as shown in FIG. 8, and the time waveform of the speed fluctuation recorded by the FFT analyzer during the rotation of the image forming body 1 is shown in FIG. As shown, the amplitude is small. On the other hand, the power spectrum of the same speed fluctuation that drives the image forming body 1 of the rotation transmitting device, which is different only by removing the viscous member 4 of the rubber plate, is higher than that of FIG. 8 as shown in FIG. On the frequency side, the level is nearly twice as large, and the time waveform of the same speed fluctuation due to the rotation of the image forming body 1 has a large amplitude as shown in FIG. The ratio of the integral values on the plus side of the average value of 0 in the speed fluctuation graphs of FIGS. 9 and 11, ie, the ratio of the average amplitude, was 41:69. It is clear from this that the device of the present invention can transmit a smooth motion.
[0022]
【The invention's effect】
As described in detail above, the power transmission device of the present invention can transmit the power of the drive source to the smooth movement of the moving member, and when used for rotation of the photosensitive member of the image forming apparatus, the rotation of the photosensitive member Is performed smoothly, and a remarkable effect that a transfer image free from defects such as uneven speed on the photoreceptor can be formed can be obtained.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of a main part of a power transmission device of the present invention showing an example applied to rotation of a photoconductor.
FIG. 2 is a front view of a main part of an assembled state of the power transmission device of FIG. 1;
FIG. 3 is a front view similar to FIG. 2, showing another example of the power transmission device of the present invention in an assembled state.
FIG. 4 is a front view of a main part of an assembled state similar to FIG. 2, showing another example of the power transmission device of the present invention.
FIG. 5 is a front view of a main part of an assembled state similar to FIG. 2, showing another example of the power transmission device of the present invention.
FIG. 6 is a graph showing a change in a transfer function of a power transmission device using an elastic member interposed in a drive system.
FIG. 7 is a graph showing a change in a transfer function of a power transmission device due to a viscous member interposed in a drive system.
FIG. 8 is a power spectrum of the speed fluctuation of the photoconductor of the example of FIG. 1;
FIG. 9 is a time waveform of the rotation speed fluctuation of the photoconductor of FIG. 6;
FIG. 10 is a power spectrum of speed fluctuation when the rubber member of the photoconductor of FIG. 6 is removed.
FIG. 11 is a time waveform of the rotation speed fluctuation of the photoconductor of FIG. 8;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Image forming body 1a Shaft 1b Passive protrusion 2 Drive gear 2a Shaft hole 2b Working part 3, 31, 32, 33 Elastic member 4 Viscous member 5 Seat plate

Claims (2)

Having a drum-shaped photoreceptor and a drive gear provided on a shaft of the drum-shaped photoreceptor,
Via a connection between a projection member provided on one of the drum-shaped photoreceptor and the drive gear, and a working portion comprising a hole provided on the other,
A power transmission device of an electrophotographic image forming apparatus configured to transmit a rotational force from a drive source applied to the drive gear to the drum-shaped photoconductor,
The action section,
An elastic member comprising an elastic bending portion or an elastic bending member,
A viscous member provided adjacent to the elastic member,
The projecting member is opposed to a surface of the viscous member opposite to a surface on which the elastic member is disposed so as to be able to contact the viscous member.
A power transmission device for an electrophotographic image forming apparatus. The elastic member is a coil spring having one end fixed to the surface of the drum-shaped photoreceptor or the drive gear having the hole of the action portion, and the other end connected to a viscous member made of a rubber plate via a seat plate. The power transmission device for an electrophotographic image forming apparatus according to claim 1, wherein

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