BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus
which forms an image on the rotating photoreceptor through a digital system.
In an electrophotographic copying machine or printer, an
electrostatic latent image is formed on the surface of a rotating cylindrical photoreceptor
or of a running belt-shaped photoreceptor, then, the formed electrostatic latent
image is developed with toner, and the toner image thus developed is transferred
onto and fixed on a recording sheet to obtain an image.
Now, let it be assumed that a driving roller which makes
the cylindrical photoreceptor of the apparatus representing a photoreceptor drum
to rotate and makes the belt-shaped photoreceptor to run is called a rotational
When there is caused speed variation (speed fluctuation)
on a photoreceptor which is supposed to rotate at a constant speed, small pitch
banding phenomenon takes place, and the jitters and image irregularities are caused
on the outputted image. This appears especially conspicuously in an electrophotographic
technology of a digital system wherein writing on a photoreceptor is conducted through
scanning by a semiconductor laser, and speed variation in the sub-scanning direction
in the writing system is caused by the speed variation of rotation of the photoreceptor,
causing delicate deviation of writing lines in their intervals, resulting in a factor
to lower image quality sharply.
With regard to technologies for improving accuracy in driving
a rotational body which is supposed to rotate at a constant speed, there are many
proposals which are roughly divided into the following two categories.
One of the two categories is one wherein a flywheel is
incorporated in the driving system, and TOKKAIHEI
disclose those wherein a conventional flywheel is easily mounted or dismounted.
disclose technologies wherein a flywheel is provided in a rotational body.
In addition, TOKKAIHEI
disclose technologies wherein frequency response of a rotational body
are detected and thereby, moment of inertia of a flywheel is normalized in connection
with vibrating frequency.
The other of the two categories is one wherein vibration
in the rotational direction of the drive transmitting system is absorbed by using
gears and timing belt pulleys in which elastic members are provided on the half
way of the rotational body driving system. Concrete examples are shown in TOKKAIHEI
As stated above, in prior art, use of a flywheel has been
the most effective technical means for improving accuracy in driving a rotational
body, but there has been a theoretical problem that a large apparatus is required
and large torque is also required in the rise of rotation. Further, since the flywheel
itself is one to reduce rotational vibration by its rotational kinetic energy, when
obtaining its effect in the case of low speed rotation of a rotational body, it
is necessary to use a flywheel having a larger diameter compared with the rotational
body. Therefore, for the purpose of avoiding a large-sized apparatus, one has had
to be contented with a functional limit even when providing a flywheel in the rotational
It has become popular recently to obtain a natural frequency
of a driving system for a rotational body and thereby to design the driving system
taking the relation with vibrating frequency into consideration, and to obtain frequency
response of a rotational system focusing on a natural frequency and thereby to change
a form of frequency response, namely a form of transfer functions by the design
of inertial quantity to change the peak position so that the driving system may
be optimum. The most serious problem in this case is that a diameter of the flywheel
is required to be large or the flywheel is required to be heavy in weight, naturally
in the case of a single rotational body driving system, when considering to move
a natural frequency to a low frequency area. This means that, when natural frequency
f of basic frequency is represented by
the value of natural frequency f is made small by making moment of inertia I of
the rotational body to be large. (K in this case represents torsional rigidity of
the driving system.)
On the other hand, improving the driving accuracy by providing
elastic members on the half way of the driving system means that a vibration component
in the rotational direction generated in the driving system is converted into heat
in the elastic members to be diffused. Since there are no concepts of frequency
response and transfer function in this case, effects of the elastic members can
not be predicted depending upon vibrating frequency of the generated vibration and
the structure of the driving system, resulting in different levels of effects.
However, in development of an image forming apparatus of
a digital system, reproducibility of one dot line by laser writing is required strictly
as performances are improved and accuracy required for the driving system has become
strict rapidly. The accuracy required in this case is on the level wherein uniformity
of laser writing in the sub-scanning direction can be guaranteed in connection with
visual sensitivity of a visual system, and with the trend of high density recording
such as 600 dpi - 2400 dpi, there is required highly accurate driving of a rotational
body having no speed fluctuation and satisfying a high level in which a human being
can not recognize small pitch banding.
For the reasons mentioned above, there are generally employed
highly accurate gears, exclusive driving, and a large-sized flywheel in the scope
of prior art. However, when employing a flywheel, there is no way to avoid heavy
weight and a large apparatus. For providing a printer of an electrophotographic
system, too, there has been proposed a structure to transmit gear driving force
to a rotational body such as a photoreceptor drum through elastic members because
of necessity to materialize the highly accurate driving structure which is light
in weight, compact in size and low in cost. However, this technology which employs
only elastic members has had a problem that a gain in a resonance area is large,
and speed fluctuation in the vicinity of the resonance area and load variation adversely
affect to a great extent to worsen small pitch banding although the technology has
shown great effects to reduce speed fluctuation which is higher than a natural frequency.
JP 07 042773 A
discloses a damping device for a rotating drum of an electrophotographic
printer or the like comprising a structure where a silicon oil is held in a clearance
between a side face of a rotating drum and a fixed plate opposed thereto and between
concentric and radially spaced O-rings. A torsion elastic part made up of a section
with reduced torsional rigidity is provided at a driving torque introduction side
of a turning shaft for the rotating drum.
JP 07 210032 A
discloses a driving device for a rotating image forming body of an electrophotographic
image forming apparatus and compriser as the drive transmission section a side surface
member having an elastically deformable part having plural radially extending ribs
attached to an end face of a photoreceptor drum. An engaging hole is provided on
three of the ribs and the holes are respectively engaged with an engaging pin fixed
to a side face of a driving gear. By driving the gear the side surface member is
elastically deformed by the interaction with the pins and the drum is rotated by
the reaction of the elastic deformation of the side surface member.
JP 07 140842 A
discloses a further driving device for a rotatable photoreceptor drum
of an image forming apparatus comprising an inertial load installed on the flange
of the photoreceptor drum and rotated integrally therewith. Pins are provided on
the inertial load on the one hand and also on a driving gear and are mutually connected
via coil springs, thereby reducing the rigidity of the driving system constituted
by the photoreceptor drum and the driving gear.
discloses a driving apparatus for a cylindrical rotary body in an image
forming apparatus having elastic material connected inside the photoreceptor drum
to the internal surface of the photoreceptor drum on the one side and to a ring-shaped
core member connected to the drive shaft of an axis extending through the photoreceptor
drum on the other side.
SUMMARY OF THE INVENTION
An object of the invention is to attain, with the novel
structure solving the problems mentioned above, the highly accurate driving structure
which is light in weight, compact in size and low in cost and is hardly affected
adversely by an external disturbance, and thereby to provide an image forming apparatus
with a rotational body driving apparatus which can output images with high image
With respect to this object the present invention provides
an image forming apparatus as defined in claim 1. Preferred embodiments are defined
in the dependent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
DETAILED DESCRIPTION OF THE INVENTION
- Figs. 1(a) and 1(b) show respectively a perspective view and a sectional view
each showing a rotational body driving mechanism.
- Each of Figs. 2 (a) - 2 (c) represents an illustration showing an example of
a drive-transmitting section related to the invention.
- Each of Figs. 3 (a) - 3 (d) represents an illustration showing an example of
installation of a viscoelastic body in drive-transmitting section.
- Each of Figs. 4 (a) and 4 (b) represents measurement data of acceleration response
in the case of a beam alone.
- Each of Figs. 5 (a) and 5 (b) represents measurement data of acceleration response
in the case where a viscoelastic body is added to a beam.
- Each of Figs. 6 (a) and 6 (b) represents measurement data of speed unevenness
of a photoreceptor drum in the case of a beam alone.
- Each of Figs. 7 (a) and 7 (b) represents measurement data of speed unevenness
of a photoreceptor drum in the case where a viscoelastic body is added to a beam
- Each of Figs. 8 (a) and 8 (b) represents measurement data of speed fluctuation
of a photoreceptor drum in the case where moment of inertia are added to a viscoelastic
- Each of Figs. 9 (a) and 9 (b) represents speed fluctuation data of a photoreceptor
drum obtained in the case where a viscoelastic body is replaced under the condition
in Figs. 8 (a) and 8 (b).
- Each of Figs. 10 (a) and 10 (b) represents an illustration showing another embodiment
of the drive-transmitting section related to the invention.
- Each of Figs. 11 (a) and 11 (b) represents an illustration related to the control
of frequency response.
- Fig. 12 is a sectional structure diagram of an image forming apparatus showing
an embodiment of the invention.
- Fig. 13 is a perspective view showing a layout of each component in the aforesaid
- Fig. 14 is a sectional view of an image forming apparatus having a belt-shaped
The greatest differences between a rotational body driving
apparatus of the invention stated below and that in prior art are the following
- 1. The invention is theoretically different from those wherein a form of a transfer
function in frequency response is changed by a flywheel, and it is one capable of
controlling frequency response with an extremely simple structure without using
a flywheel. Namely, natural frequency f has been changed by changing moment of inertia
I in the prior art (see Fig. 11 (a)), but in the invention, frequency response can
be controlled by changing torsional rigidity K of a substantial driving system.
- 2. The invention not only can control frequency response by changing the peak
position of the frequency characteristic but also can reduce freely a magnitude
of the frequency characteristic, namely, a level of a gain of the transfer function.
This corresponds to the occasion wherein the peak of the transfer function is not
only moved in parallel but also moved in the size direction so that the height of
the transfer function is lowered (see Fig. 11 (b)).
Owing to the foregoing, there is offered an effect that
an absolute value of a vibration in the rotational direction existing in the corresponding
frequency area is sharply lowered.
Next, the structure and functions of a color image forming
apparatus to which the rotational body driving apparatus of the invention is applied
will be explained with reference to Figs. 12-14.
In Fig. 12, the numeral 10 is a photoreceptor drum representing
an image carrier having OPC photoreceptor coated on its drum which is grounded and
is driven to rotate clockwise. The numeral 12 is a scrorotron charging unit which
applies uniform charging VH to the circumferential surface of photoreceptor
drum 10 by means of corona discharging conducted by a grid kept to voltage VG
and a corona discharge wire. Prior to the charging conducted by scrorotron charging
unit 12, the circumferential surface of the photoreceptor is neutralized by means
of exposure conducted by PCL 11 in which a light emitting diode is used, so that
hysteresis remaining on the photoreceptor up to the moment of the previous printing
may be eliminated.
After uniform charging on the photoreceptor, imagewise
exposure is conducted by imagewise exposure means 13 based on image signals. The
imagewise exposure means 13 having therein an unillustrated laser diode serving
as a light source for emission, rotary polygon,mirror 131, f &thgr; lens and reflecting
mirror 132 which deflects a light path, conducts scanning to form a latent image
on the photoreceptor 10 through the rotation (sub-scanning) of the photoreceptor
10. In the present example, exposure is applied on the area for characters to form
a reversal latent image wherein the area for characters shows lower voltage VL.
Around the photoreceptor drum 10, there are provided developing
units 14 each housing therein developing agents composed of carrier and toner representing
each of yellow (Y), magenta (M), cyan (C) and black (K), and development for the
first color is conducted first by developing sleeve 141 which houses therein magnets
and rotates while holding a developer. The developer is composed of a carrier having
therein a core of ferrite that is coated with insulating resins and of toner whose
main material is polyester to which dyes depending on a color, charge control agents,
silica and titanium oxide are added, and the developer is regulated by a layer forming
means to be in layer thickness (developer) of 100 - 600 µm on developing sleeve
141, and is conveyed to a developing area.
A clearance between the developing sleeve 141 and the photoreceptor
drum 10 in the developing area is made to be 0.2 - 1.0 mm which is greater than
the layer thickness (developer), and AC bias voltage of VAC and DC bias
voltage of VDC are impressed on the clearance to be superimposed. Since
VDC and charge of VH toner are in the same polarity, toner
urged by VAC to leave a carrier is not stuck to the area of VH
which is higher than VDC in terms of voltage but is stuck to the area
of VL which is lower than VDC in terms of voltage so that
image-visualization (reversal development) is conducted.
After completion of image-visualization for the first color,
there is started an image forming process for the second color wherein uniform charging
by scorotron charging unit 12 is conducted again, and a latent image based on image
data for the second color is formed by imagewise exposure means 13. In this case,
neutralizing carried out by PCL 11 in the image forming process for the first color
is not conducted because toner sticking to the image area for the first color scatters
due to a sudden fall of surrounding voltage.
In the photoreceptor charged again to be at voltage of
VH on the entire circumferential surface of the photoreceptor drum 10,
the area having thereon no image for the first color is subjected to formation of
a latent image similar to that for the first color which is then developed, but
the area which has thereon the image for the first color and is developed again
is subjected to formation of a latent image at VM' caused by adhering
toner for the first color serving as light-shielding and by charges owned by toner
itself, thus, development in accordance with voltage difference between VDC
and VM' is conducted. In the area where an image for the second color
is superposed on that for the first color, intermediate voltage satisfying the relation
of VH > VM > VL is sometimes used because
if development for the first color is conducted after forming a latent image at
VL, the balance between the first color and the second color is lost.
For each of the third and fourth colors too, the same image
forming process as for the second color is conducted, and visual images for four
colors are formed on the circumferential surface of photoreceptor drum 10.
On the other hand, recording sheet P fed out of sheet-feeding
cassette 15 through Woodruff roller 16 stops momentarily, and is conveyed by rotational
action of sheet-feeding roller 17 to a transfer area when transfer timing is adjusted.
In the transfer area, transfer roller 18 is brought into
pressure contact with the circumferential surface of the photoreceptor drum 10 in
synchronization with transfer timing to nip the conveyed recording sheet P so that
images of multiple colors are collectively transferred onto the recording sheet
Then, the recording sheet P is neutralized almost simultaneously
with the foregoing by separation brush 19 which is in pressure contact, and then
is separated from the circumferential surface of the photoreceptor drum 10 to be
conveyed to fixing unit 20 where toner is melted and fixed by heating and pressuring
respectively of heat roller 201 and pressure roller 202, and then is ejected out
of the apparatus through sheet-ejection roller 21. Incidentally, the transfer roller
18 and the separation brush 19 are retreated from the circumferential surface of
the photoreceptor drum 10 after the recording sheet P has passed through them to
be ready for the following formation of toner images.
On the other hand, the photoreceptor drum 10 from which
the recording sheet P has been separated is subjected to removing of remaining toner
and cleaning both conducted through pressure contact of blade 221 of cleaning unit
22, and is further subjected to neutralizing conducted by PCL 11 and charging conducted
by charging unit 12 to enter the following image forming process. Incidentally,
the blade 221 is retreated from the circumferential surface of the photoreceptor
drum 10 by moving immediately after the cleaning of the photoreceptor surface.
Fig. 13 shows a layout on a plane for each unit constituting
the aforesaid apparatus, and the side shown with arrow mark A is a front side of
the apparatus which corresponds to the side on the operation side.
A main body of the apparatus has two erected side panels
1 and 2, and between these side panels, there are incorporated a writing unit representing
the imagewise exposure means 13, photoreceptor drum 10, a developing unit housing
therein plural developing units 14, fixing unit 20 and a DC power supply unit. Outside
the side panel 1, on the other hand, there are provided a driving system, a formatter
which decodes printer command, and a control board for controlling operation sequence
of a machine, and outside the side panel 2, there is arranged a toner box communicated
with each developing unit 14 in a developing module.
Since the photoreceptor drum 10 and the developing module
are located in the vicinity of the operation side of the apparatus, they can be
drawn out to the front side of the apparatus with a simple operation in a certain
structure, and when the upper portion of the main body is arranged to be opened,
jam clearance in the transfer position can be done by taking out a drum carriage
to its take-out position without taking the photoreceptor drum 10 and the developing
module out of the main body.
Further, jam clearance at the sheet-feeding section can
be done by taking the photoreceptor drum 10 and sheet-feeding cassette 15 loaded
in the lower portion of the developing module out of the apparatus, and jam clearance
at the sheet-ejection section can be realized by employing the structure wherein
the rear and side surfaces are opened.
Next, an embodiment of a driving apparatus for photoreceptor
drum 10 which is a rotary body will be explained.
Fig. 1 (a) shows photoreceptor drum 10 and driving mechanism
30. The driving mechanism 30 is composed of driving motor 31 such as a pulse motor
and of gear train 32 linked with the driving motor 31, and final gear 33 of the
gear train 32 is engaged with driving gear 34 provided rotatably and coaxially with
the photoreceptor drum 10.
The photoreceptor drum 10 is made of a cylindrical aluminum
basic material, and the drum circumferental surface is coated with the OPC photoreceptor
stated above. Flanges 101 attached to both ends of the photoreceptor drum 10 are
engaged with shaft 103. Thus, a side of the flange 101 on one side and a side of
the driving gear 34 are positioned to be away from each other by a prescribed distance,
and drive transmission section 35 provided between both sides transmits driving
force of the driving motor 31 to the photoreceptor drum 10.
Fig. 1 (b) shows a partial section of the photoreceptor
drum 10 and the driving gear 34. In the embodiment illustrated, shaft 103 is supported
to be fixed on the image forming apparatus main body, and driving gear 34 is engaged
with the shaft 103 through an unillustrated bearing such as, for example, an oilless
bearing, and the flange 101 attached on the photoreceptor drum 10 is engaged, in
the same way as in the foregoing, with the shaft 103 through bearing B. Incidentally,
there can be also employed a constitution wherein the shaft 103 is supported to
be rotatable in the image forming apparatus main body, and the photoreceptor drum
10 is fixed on the shaft 103.
Fig. 2 (a) is an exploded perspective view showing constitution
of an embodiment of drive transmission section 35. In the drive transmission section
35 which conducts drive transmission between the driving gear 34 and the flange
101 of the photoreceptor drum 10, beam-shaped elastic body 351 having beam section
351A is provided on the end face of the driving gear 34, beam section 351A is provided
to be fixed at the position which is almost in the direction of a radius of driving
gear 35, and drive linking protrusion 352 which is bar-shaped and rigid is fixed
on an end face of the flange 101. In the assembled state, the drive linking protrusion
352 is in contact with the position which is almost the center of the beam section
351A of the beam-shaped elastic body 351 as shown in Fig. 2 (b), and the drive linking
protrusion 352 is pushed in the arrowed direction through the beam section 351A
as the driving gear 34 rotates, thus, drive transmission to the photoreceptor drum
10 is carried out.
In the drive transmission section 35, there is provided
viscoelastic body 353 which comes in surface contact with a point on beam section
351A which is opposite to the point where the drive linking protrusion 352 touches
the beam section 351A, while being deformed with a constant compressibility. In
the invention, there are provided in the drive transmission section a first elastic
member (beam section 351A) which determines, through elastic deformation behavior,
a natural frequency of a driving system composed of a rotational body and a driving
source and a second elastic member (viscoelastic body 353) which acts on elastic
behavior of the first elastic member and increases its damping characteristic, which
will be explained in detail as follows.
The beam-shaped elastic body 351 in the present embodiment
is a resin molding made of polyacetal (POM), and it is fixed firmly on the driving
gear 34 by three screws, for example. The beam section 351A is a both-end supported
beam which is fixed at its both ends and has a thickness of 1.8 mm and a length
of 35 mm, and it determines natural frequency. As a material for the beam-shaped
elastic body 351, there may be used selectively the elastic resin materials and
metallic materials both for industrial use such as ABS resins (ABS), SUS alloys,
zinc-coated steel plate (SECC-C-20/20) and aluminum alloys, in addition to those
mentioned above. Further, the beam-shaped section may also be of a cantilever type
shown in Fig. 2 (c), though it is in a form of a both-end supported beam in the
For viscoelastic body 353 in the present embodiment, there
are used chloroprene rubber (CR), ethylenepropyrene rubber (EPDM), silicone gel,
oil-impregnated porous rubber, butyl rubber, thermoplastic elastomer, and high-function
material wherein high vibration absorbing capability is added to thermoplastic resin.
The viscoelastic body 353 is an elastic body whose JIS rubber hardness is in a range
from 20 degrees to 100 degrees, and preferably is in a range from 40 degrees to
80 degrees, and viscoelastic bodies preferably used represent one whose dynamic
dissipation factor tan &dgr; is 0.3 or more, and preferably is 0.5 or more. The
viscoelastic body 353 having the characteristics mentioned above is in surface contact,
under its condition to be compressed in advance with compressibility of 1% - 15%,
with a certain area on the beam section 351A that is opposite to the point where
drive linking protrusion 352 touches the beam section 351A.
Due to the structure mentioned above, it is possible for
the viscoelastic body 353 to control the damping coefficient extremely effectively
and freely on a dominant basis. In the embodiment, the viscoelastic body 353 is
in contact with a portion on the beam section 351A that is opposite to the point
where the drive linking protrusion 352 touches the beam section 351A as shown in
Fig. 2 (b). However, it is also possible to arrange so that the viscoelastic body
353 comes in contact with a portion on the beam section 351A that is on the same
side as the point where the drive linking protrusion 352 touches the beam section
351A as shown in Fig. 3 (a). It is further possible to arrange so that the viscoelastic
body 353 comes in contact with a side on the side where the drive linking protrusion
352 touches the beam section 351A as shown in Fig. 3 (b). The position where the
viscoelastic body 353 comes in contact with the beam section 351A is not limited
to one point, but it is possible to arrange so that the viscoelastic body 353 comes
in contact with the beam section 351A at two points one of which is the same as,
and the other of which is opposite to a point where the drive linking protrusion
352 touches the beam section 351A as shown in Fig. 3 (c), for example.
Though the viscoelastic body 353 which is compressed in
advance by 1% - 15% is brought into contact with beam section 351A, it is also possible
to make an arrangement wherein pressing member 354 capable of adjusting finely the
distance from beam section 351A is provided separately from the beam-shaped elastic
body 351 as shown in Fig. 3 (d), and the viscoelastic body 353 is set between them
after obtaining appropriate compressibility of the viscoelastic body 353.
The inventors of the invention made an arrangement wherein
viscoelastic body 353 made of material of CR rubber having rubber hardness of 61
degrees is used to be in contact with a reverse side of beam section 351A at compressibility
of 10% with regard to photoreceptor drum 10 having moment of inertia of 27000 gcm2,
and whereby lowered the natural frequency of the beam section 351A from 25 Hz to
15 Hz by making the viscoelastic body 353 to touch to make the reduction of gain
of transfer coefficient possible.
Figs. 4 - 9 represent data showing the conditions stated
Fig. 4 represents data obtained through an arrangement
wherein viscoelastic body 353 was removed, and a portion of a beam of beam section
351A was shaken and the acceleration response of the beam was measured, in which
(a) shows data whose axis of abscissa represents time, while (b) shows data whose
axis of abscissa represents frequency.
Fig. 5 shows data obtained through an arrangement wherein
viscoelastic body 353 was attached on beam section 351A and a portion of the beam
of the beam section 351A was shaken, in which (a) shows data whose axis of abscissa
represents time, while (b) shows data whose axis of abscissa represents frequency.
When Fig. 4 is compared with Fig. 5, it is observed that the gain of natural frequency
is lowered in frequency area data by attachment of the viscoelastic body 353, while
vibration is promptly attenuated in the time axis area data and thereby vibration
characteristics are improved.
Figs. 6 - 9 represent data obtained by measuring speed
unevenness of photoreceptor drum 10 by a laser Doppler after applying the foregoing
actually on drive transmission section 35 of an image forming apparatus. Fig. 6
represents data obtained by removing the viscoelastic body 353. In the actual driving
system, there are various factors for load variation for photoreceptor drum 10 and
they are causing speed unevenness of the photoreceptor drum 10. Therefore, in the
case of beam section 351A alone in Fig. 6, load variation affects adversely to make
the gain in the vicinity of torsion natural frequency (approx. 25 Hz) to be great,
and a p - p value of time axis area data is also great.
Fig. 7 represents data obtained through an arrangement
wherein viscoelastic body 353 was attached on beam section 351A. When Fig. 7 is
compared with Fig. 6, it is understood that when the viscoelastic body 353 is attached,
the gain of resonance in a frequency area is controlled to be low in spite of load
variation, a p - p value of time axis area data is kept to be small stably, and
driving accuracy is improved. Data shown in Fig. 8 represent those obtained through
an arrangement wherein moment of inertia of photoreceptor drum 10 in Fig. 7 was
increased further by 12000 gcm2, and when Fig. 8 is compared with Fig.
7, it is understood that speed unevenness is further lowered.
Fig. 9 shows data obtained in an arrangement wherein the
viscoelastic body 353 employing CR rubber in Fig. 8 was replaced with viscoelastic
body 353 employing thermoplastic elastomer having dissipation factor tan &dgr;
of 1.9 (manufacturer (Toso) ED 1920N). It is observed that the gain in the vicinity
of 25 Hz is further lowered and speed evenness is improved by using the viscoelastic
body whose dissipation factor is considerably great compared with that of CR rubber.
The drive transmission section 35 in the embodiment explained
above is of structure (see Fig. 2) wherein beam-shaped elastic body 351 is fixed
on the end face of driving gear 34, drive linking protrusion 352 is fixed on the
end face of flange 101, beam section 351A of the beam-shaped elastic body 351 is
brought into contact with the drive linking protrusion 352, and thereby rotation
of the driving gear 34 is transmitted to the drive linking protrusion 352 through
the beam section 351A. However, it is also possible to obtain the same effect through
the structure which is utterly opposite to the foregoing. Fig. 10 shows the structure
of drive transmission section 35' in the present embodiment, and beam-shaped elastic
body 351' having thereon beam section 351A' is provided on the end face of flange
101', and the beam section 351A' is fixed to be almost in the direction of a radius
of the flange 101' in terms of positional relation. On the beam section 351A', there
is provided viscoelastic body 353' in a way that the viscoelastic body 353' is in
contact with the beam section 351A'. On the end face of driving gear 34', there
is fixed bar-shaped and rigid drive linking protrusion 352' which is in contact
mostly with the central position of the beam section 351A' in the assembled state
as shown in Fig. 10 (b) and it pushes the beam section 351A' in the arrowed direction
as the driving gear 34' rotates, thus drive transmission to photoreceptor drum 10
is carried out.
Further, though the rotational body itself is represented
by photoreceptor drum 10 in the rotational body driving apparatus explained above,
the rotational body is not limited to the photoreceptor drum 10, and it is also
possible to employ an image outputting apparatus wherein belt-shaped photoreceptor
110 is provided and the rotational body of the invention is represented by driving
roller 111 which drives the photoreceptor 10. Even in this case, the driving roller
111 can be rotated without its speed fluctuation by applying the driving apparatus
in the above-mentioned embodiment to the driving roller 111, thus, it is possible
to move the photoreceptor 110 at a constant speed and thereby to improve remarkably
quality of images to be outputted.
The rotational body driving apparatus of the invention
further offers an excellent effect even when it is applied to a recording apparatus
for recording images on a light-sensitive film with a laser beam wherein, for example,
a light-sensitive film is wound around a drum-shaped rotational body and is scanned
by a polygon mirror while the rotational body is rotated at a constant speed.
Further, in the rotational body driving apparatus of the
invention explained above, the rotational body itself is an image carrier such as
photoreceptor drum 10. However, the rotational body driving apparatus can be applied
also to a rotational body employed in image forming apparatuses of other types.
For example, when the invention is applied to a conveyance roller for conveying
an image recording sheet, the image recording sheet can be conveyed at high conveyance
accuracy and quality of images formed on the image recording sheet can be improved.
Due to the invention, natural frequency in torsion of a
rotational body can be controlled freely and dominantly by the first elastic member
(beam section), and an damping coefficient can be controlled freely and dominantly
by the second elastic member (viscoelastic body), which improves markedly the degree
of freedom in designing. Both a natural frequency of a rotational body driving system
and an damping coefficient which can be set freely result in a concrete effect that
speed fluctuation is lowered because of a gain of the transfer function which is
in an area where the gain is originally lowered, in the area of the frequency higher
than the natural frequency and the gain of the transfer function itself is lowered
by the effect of an damping member, and thereby result in an effect that a resonance
level in the vicinity of the natural frequency is lowered, which makes it possible
to obtain an effect that speed fluctuation related to driving of a rotational body
is wholly lowered efficiently and accuracy of driving a rotational body is markedly
As a result, there is obtained a stable driving system
which is highly resistant against speed fluctuation in the vicinity of a resonance
area, vibration from a driving section for development in the case of an image forming
apparatus, and against external disturbances such as variations of loads including
a blade and a transfer roller.
Since the invention makes an influence of load variation
and speed fluctuation to be extremely small, a rotational body and a photoreceptor
drum on which an image is formed can constantly be rotated highly accurately and
As a result, in an image forming apparatus, small pitch
banding which is a primary image trouble caused by speed fluctuation of a photoreceptor
is made small extremely, and images with high image quality can be provided stably
by making small pitch banding to be at a level which can not be recognized by human