[0001] The present invention relates to an electrophotographic image forming apparatus such
as a copying machine, a facsimile machine, a printer or the like.
[0002] There is known an image forming apparatus as an apparatus in which a toner image
formed on a photoconductive drum is transferred to a sheet of recording paper so as
to form an image on the sheet of recording paper. Conventionally, an image forming
apparatus capable of obtaining high quality printed image is desired.
[0003] Fig. 6A and Fig. 6B show part of an image forming apparatus 1 in accordance with
the conventional technique. Fig. 6A is a cross sectional view and Fig. 6B shows a
simplified model. As shown in Fig. 6A, a photoconductive drum 2 is composed of a hollow
cylindrical photoconductive drum elementary pipe portion 43 and a pair of drum flanges
6 which cover openings at both ends of the photoreceptor drum elementary pipe portion
43. Further, a drum shaft 8, which penetrates the photoconductive drum 2 in the axial
direction, is provided on the same shaft as that of the photoconductive drum 2. Then,
the drum shaft 8 is rotatably supported by a pair of shaft bearings 41 provided at
both ends of the drum shaft.
[0004] A transfer roller 3 has a cylindrical shape, and an axis A2 thereof is arranged in
parallel with an axis A1 of the photoconductive drum 2. Further, a roller shaft 7,
which penetrates the transfer roller 3 in the axial direction, is provided on the
same shaft as that of the transfer roller 3, and is rotatably supported by a pair
of shaft bearings 42 provided at both ends of the roller shaft. Further, the roller
shaft 7 comes in contact with a pair of spring members 5 having elasticity in the
axial direction, a pair of tracking rolls 4, which are a control means according to
the invention, are provided. The roller shaft 7 is pressed against the drum shaft
8 with the spring members 5. The gap H is made between the photoconductive drum 2
and the transfer roller 3 at a proper value by allowing each tracking roll 4 to come
in contact with the photoconductive drum 2. Such conventional image forming apparatus
1 is disclosed in JP-A 9-218549 (1997).
[0005] Such an image forming apparatus 1 is configured to make the gap between a circumferential
surface of the photoconductive drum and a circumferential surface of the transfer
roller. Accordingly, the photoconductive drum and the transfer roller can move without
friction, so that abrasion and peeling of the photoreceptive layer in the circumferential
surface of the photoreceptor drum can be prevented. Consequently, the toner image
can be finely transferred to the recording paper, thereby preventing fluctuation of
image.
[0006] Further, in addition to the above mentioned image forming apparatus which is configured
to keep the gap between a circumferential surface of the photoconductive drum and
a circumferential surface of the transfer roller at a proper value by the controlling
means such as a tracking roll, there is another image forming apparatus, which is
configured so as to press the circumferential surface of the photoconductive drum
and the circumferential surface of the transfer roller with a specific pressure by
the controlling means. Such conventional technique is disclosed in Japanese Unexamined
Patent Publication JP-A 2-165173 (1990).
[0007] According to the image forming apparatus, by bringing the circumferential surface
of the photoconductive drum into contact with the circumferential surface of the transfer
roller, and by pressing them at a steady specific pressure, there is no need to further
increase the transfer electric field (or potential difference) which functions between
the circumferential surface of the photoconductive drum and the circumferential surface
of the transfer drum. Further, problems such that letters are missing in the middle
part due to high pressure is not raised. Consequently, the toner image can be finely
transferred to the recording paper.
[0008] The foregoing conventional technique has the following problems, in which the positional
relationship between the outer circumference of an image carrier which supports a
toner image, such as a photoconductive drum, a photoconductor belt, and an intermediate
transfer, and the circumferential surface of the transfer roller which transfers the
toner image on the image carrier to the recording paper, is controlled to be a predetermined
positional relationship by spring members and the controlling means.
[0009] When inserting a sheet of recording paper between the surface of the image carrier
and the surface of the transfer roller, the interval between the photoconductive drum
and the transfer roller further increases in comparison with the case where sheets
of recording paper are not housed in the space between the surface of the image carrier
and the surface of the transfer roller. After discharging the recording paper from
the space between the surface of image carrier and the surface of the transfer roller,
the positional relationship is reset to its original position by the spring member's.
At the time, an impact caused by insertion and withdrawal of the recording paper,
is transmitted to the image carrier. In particular, when inserting a recording paper
having a certain thickness and unevenness, the impact is increased.
[0010] An impact is transmitted to the image carrier, thereby causing displacement of the
image carrier in a short time and creating vibrations on the toner image supported
on the image carrier and unfixed toner image which is transferred to the recording
paper. Consequently, there is problems that blot and blur of image are generated due
to vibrations and high quality image cannot be obtained. In a particular case where
the image carrier and the transfer roller have a hollow, when an impact is transmitted
to the outer circumference of the portion having a hollow inside, vibrations created
by the image carrier is further increased.
[0011] Further, according to the copying machine, which is one example of the image forming
apparatus, after fixing an image of a developing material such as a toner on the circumferential
surface of the photoconductive drum, which is one example of the image carrier, the
toner image is transferred to transfer materials such as a transfer sheet, thereby
printing the image. At the time, in the periphery of the photoconductive drum, rotating
bodies are provided, namely, a charging roller which applies static charges to the
photoconductive drum, a developing roller which forms a toner image on the circumferential
surface of the photoconductive drum, and a transfer roller which transfers the toner
image by pressing against the circumference of the photoconductive drum. At this time,
to obtain an image having a certain quality, these rotating bodies provided in the
periphery are required to keep the interval between shafts or the interval between
circumferential surfaces with regard to the photoconductive drum with high accuracy.
[0012] In response to the needs, the following technique is proposed in, for example, JP-A
2-165173 and JP-A 8-63043 (1996). A guide portion is provided on the peripheral rotating
body such as the transfer roller and the circumference or the rotation axis of the
image carrier such as the photoconductive drum, and the guide portion comes in contact
with the circumference of the image carrier or the peripheral rotating body, thereby
keeping the interval between shafts of the image carrier and the peripheral rotating
body and the interval between the circumferences to a proper value.
[0013] Further, according to the technique disclosed in JP-A 4-175779 (1992), a ring-shaped
spacer roller provided on the peripheral rotating body are brought into contact with
support members of the image carrier, thereby the interval between shafts of the image
carrier and the peripheral rotating body and the interval between the circumferences
can be kept to a proper value.
[0014] In JP-A 2-165173 and JP-A 8-63043, the following technique is disclosed. The guide
portion or the like comes in contact with the opposing material while rotating around
the periphery of each rotating shaft in accordance with the rotation of the image
carrier and the peripheral rotating body. In JP-A 4-175779, the spacer roller are
brought in contact with a supporting portion of the image carrier while rotating in
accordance with the rotation of the support member of the image carrier and the peripheral
rotating body.
[0015] Then, in the periphery of the image carrier, fine particles made of the developing
material such as a toner, and the transfer material such as a transfer sheet, are
suspended in general. In such environment, there is a problem in accordance with the
technique disclosed in JP-A 2-165173 and JP-A 8-63043. Because the guide portion comes
in contact with the opposing material while rotating, the particles bite the contact
surface, thereby creating vibrations on the image carrier and the peripheral rotating
body, or causing the abrasion on the contact surface. Consequently, it becomes difficult
to keep the interval between the image carrier and the peripheral rotating body to
a proper value, in some cases. Further, according to JP-A4-175779, since the support
member of the image carrier to be contacted with the spacer roller is generally charged,
it can relieve adhesion of the toner or the like, however, it is impossible to solve
the problem of the abrasion. Moreover, the guide portion disclosed in JP-A 2-165173
and JP-A 8-63043, and the spacer roller disclosed in JP-A 4-175779, the whole circumferences
become the contact surface. Therefore, there is necessity to process the whole circumferences
of the guide portion and the spacer in high accuracy, so that the cost of processing
rises.
[0016] Further, according to the copying machine, which is one example of the image forming
apparatus, to transfer a toner image formed on the circumference of the photoconductive
drum (an example of an image carrier), to a paper or the like (an example of a transfer
material) , the paper is guided to the predetermined transfer position by a paper
guide (an example of a guide member) in close proximity to the transfer roller (an
example of a transfer member) . The paper or the like is pressed against part of the
circumferential surface of rotating photoreceptor drum by the transfer roller, thereby
transferring the toner image. At the time, to keep a certain image quality of the
transferring image transferred to the paper or the like, the transfer roller and the
paper guide should be arranged with respect to the photoreceptor drum with high accuracy.
[0017] Then, when a paper jam is caused between the transfer roller and the photoreceptor
drum or the paper guide, or when a stain is found on the circumferential surface of
the transfer roller, it is necessary to remove the jammed paper or perform maintenance
such as cleaning of the circumferential surface of the transfer roller. Because of
this, the transfer roller and the paper guide, which is formed in close proximity
thereto, should be supported to be separated. Also, it is desirable to perform the
separation easily. To meet the needs, the following technique is disclosed in JP-A
11-93940 (1999). As a method of supporting the transfer roller so as to facilitate
a work top mount and demount, mounting and demounting of the transfer roller can be
easily carried out by providing a collar, a handle part, and the like provided with
a small-diameter part in a non-circular shape in cross section, at the end portion
of the rotation axis of the transfer roller, and rotating the small-diameter part
in the direction capable of mounting and demounting through operation of the handle
part.
[0018] According to JP-A 11-93940, however, when mounting and demounting the transfer roller
at the time of performing maintenance, the paper guide should be mounted and demounted
with a screw and the like, so that there is a problem that it takes much time to perform
maintenance operation. Moreover, there arises another problem that the extent of screwing
causes displacement of the positional relationship between the transfer roller and
the paper guide.
[0019] According to the copying machine and the like, which is one example of the image
forming apparatus, to transfer a toner image formed on the circumferential surface
of the photoconductive drum (an example of an image carrier), to a paper or the like
(an example of a transfer material), the paper is guided to the predetermined transfer
position by a paper guide (an example of a guide member) in close proximity to the
transfer roller (an example of a transfer member). The paper is pressed against part
of the circumferential surface of rotating photoconductive drum by the transfer roller,
thereby transferring the toner image. Further, the paper which is stuck to the photoconductive
drum due to static electricity, is peeled off by removing static electricity from
the transferred paper, with a means for removing static. At the time, to keep a certain
image quality of the transferring image transferred to the paper, the interval between
the transfer roller or the paper guide and the means for removing static should be
arranged with respect to the photoreceptor drum with high accuracy. In addition to
this, the intense of pressing the transfer member against the photoconductive drum
should be kept consistently. To meet the needs, the following technique is disclosed
in Japanese Examined Patent Publication JP-B2 2710996. By supporting the paper guide
with a shaft of the transfer roller, the paper guide is arranged with respect to the
transfer roller with high accuracy.
[0020] In general, the transfer member such as a transfer roller is pressed against the
image carrier with a spring or the like so as to keep consistent intense of pressing
against the image carrier. Accordingly, when the surface of the transfer member deteriorates
with time, the position of the rotation axis of the transfer member with respect to
the image carrier is deviated. At the time, since the paper guide is supported with
the shaft of the transfer roller according to JP-B2 2710996, there is a problem that
the position of the paper guide with respect to the image carrier is also deviated.
Further, when performing maintenance on the transfer roller at paper jam, it is necessary
to remove the paper guide from the shaft of the transfer roller. However, the function
of facilitating the removal is not indicated, so that there is a problem that maintenance
operation is difficult.
[0021] Moreover, the function for positioning of the means for removing static electricity
is not particularly disclosed in JP-B2 2710996. It can be considered to support the
means for removing static electricity with a shaft of the transfer roller, as in the
case of supporting the paper guide disclosed in JP-B2 2710996, however, there is a
problem that the position is deviated when the surface of the transfer roller deteriorates
with time.
[0022] It is an object of the invention to provide an image forming apparatus in which fine
transfer can be carried out without transmitting vibrations to an image carrier and
a recording paper even if an impact is caused when inserting and discharging the recording
paper.
[0023] It is an object of the invention to provide an image forming apparatus at low cost,
in which proper positioning can be carried out without causing vibrations due to a
bite of suspended particles such as a toner or the abrasion of the members for positioning.
[0024] It is an object of the invention to provide an image forming apparatus in which positioning
of the transfer member and the guide member which guides a transfer material to the
transfer position, can be carried out with respect to the image carrier with high
accuracy, and the guide members, which are arranged in close proximity to the transfer
member, can be easily separated so as to perform maintenance on the transfer member.
[0025] It is an object of the invention to provide an image forming apparatus which facilitates
the positioning of the transfer member, the guide member, the means for removing static
electricity, and the like, with respect to the image carrier with high accuracy.
[0026] The invention provides an image forming apparatus comprising:
an image carrier for carrying a toner image; and
a transfer roller which is loaded with a force that tends to move the transfer roller
toward the image carrier, the transfer roller being arranged in a predetermined positional
relation to the image carrier by control means,
wherein the control means is disposed between an axis of the transfer roller and
an axis of the image carrier so as to be located outwardly away from an axial end
portion of the image carrier.
[0027] The invention provides an image forming apparatus comprising:
an image carrier, rotatably supported, for carrying a toner image;
a peripheral rotary body involved in image formation, which is rotatably supported
in a periphery of the image carrier; and
control means for controlling displacement of the peripheral rotary body in a direction
proximate to the image carrier so as to maintain a predetermined positional relationship
between the image carrier and the peripheral rotary body, the control means being
so configured that an acting point of impacting force, which is generated in between
the image carrier and the peripheral rotary body at a time of image formation, is
located on an axis of the image carrier between a position of an axial end portion
of the image carrier and a position nearby in which the image carrier is supported.
[0028] According to the invention, the image carrier and the peripheral rotary body, for
example a transfer roller, are arranged in a predetermined positional relationship
by the control means. The control means is arranged axially outwardly relative to
the image carrier. This arrangement helps reduce the amount of displacement of the
image carrier resulting from impacting force caused by insertion and ejection of a
recording paper sheet.
[0029] According to the invention, when impacting force is generated due to the passage
of the recording paper sheet, the amount of displacement of the image carrier, as
well as vibrations developed in the image carrier per se, can be reduced. This makes
it possible to prevent a blurred image from occurring at the time of insertion and
ejection of a recording paper sheet, thereby obtaining high-quality images.
[0030] Besides, in the image forming apparatus embodying the invention, there is no need
to increase an axial dimension of the image carrier for the sake of abutment of the
control means, and therefore the image carrier can be made small in the axial dimension.
This contributes to reduction in cost associated with the image carrier which is consumable
yet expensive.
[0031] In the invention, it is preferable that the control means is made of a material having
shock absorbency.
[0032] According to the invention, since the control means is made of a shock-absorbing
material, an impact caused by insertion and ejection of a recording paper sheet can
be absorbed by the control means, thereby alleviating the impact on the image carrier
and the recording paper sheet during image transfer process.
[0033] Further, according to the invention, the control means is capable of absorbing an
impact. Thus, the impact on the image carrier and the recording paper sheet during
image transfer process can be further alleviated, thereby attaining more satisfactory
image quality.
[0034] In the invention, it is preferable that the control means includes a first control
member loosely fitted to a shaft of the image carrier and a second control member
loosely fitted to a shaft of the peripheral rotary body, the first and second control
means abutting against each other.
[0035] According to the invention, the first and second control members are loosely fitted
to the shafts of the image carrier and the peripheral rotary body, for example, a
transfer roller, respectively. In this arrangement, even if the image carrier and
the transfer roller are rotated, the first and second control members can be constantly
kept at rest in an abutting state without rotating. Consequently, the control members
are each inhibited from rotating concurrently with the image carrier and the transfer
roller, thereby preventing the wearing away of the abutment surfaces of the control
members. Moreover, since the abutment surfaces of the control members are made less
prone to adhesion of foreign matters such as toner, a predetermined positional relationship
can be established between the image carrier and the transfer roller with high accuracy.
[0036] Further, according to the invention, the wearing away of the abutment surfaces of
the first and second control members, as well as adhesion of foreign matters, can
be successfully prevented, and thereby a certain gap can be secured between the image
carrier and the transfer roller with accuracy. This makes it possible to impart steady
contact pressure force to a recording paper sheet during image transfer process, thus
allowing the toner image to be transferred onto the recording paper sheet without
causing unevenness.
[0037] In the invention, it is preferable that the control means is arranged outwardly away
from the axial end portion of the peripheral rotary body.
[0038] According to the invention, the control means is arranged away from the end portion
of the peripheral rotary body, for example, a transfer roller. This arrangement helps
reduce the amount of displacement of the transfer roller caused by impacting force
resulting from insertion and ejection of a recording paper sheet.
[0039] Further, according to the invention, since the control means is arranged away from
the end portion of the transfer roller, the amount of displacement of the transfer
roller caused by impacting force can be reduced. This further decreases the possibility
of a blurred image being created during insertion and ejection of a recording paper
sheet.
[0040] In the invention, it is preferable that the image forming apparatus further comprises
oscillation control means for controlling oscillation of each of the first and second
control members.
[0041] According to the invention, the first and second control members are inhibited from
oscillation and kept in an abutting state. Thus, it never occurs that the fine particles
are bitten into the abutment portions or that the abutment portions rub and wear.
Moreover, by not processing the entire circumferential surfaces of the first and second
control members but only their abutment portions with high accuracy, the processing
operation can be carried out at relatively low cost.
[0042] In the invention, it is preferable that the oscillation control means is so configured
as to inhibit rotation of the first and second control members.
[0043] According to the invention, the first and second control members can be disposed
so as not to rotate in synchronism with the rotary shaft.
[0044] In the invention, it is preferable that the abutment portion of the first control
member, which abuts against the second control member, is so configured as to protrude
outwardly relative to the other non-abutting portions.
[0045] According to the invention, the first control member can be made lighter in weight
and occupies less space than in a case of adopting a disc shape.
[0046] In the invention, it is preferable that a helical gear is additionally provided as
driving means for rotatably driving at least one of the image carrier and the peripheral
rotary body.
[0047] According to the invention, vibrations resulting from a bite of suspended particles
such as toner, as well as abrasion of the positioning members, can be successfully
prevented. This allows highly accurate positioning of the rotatably-supported image
carrier and the peripheral rotary body involved in image formation rotatably arranged
in the periphery of the image carrier, such as a charge body or transfer member.
[0048] The invention provides an image forming apparatus comprising:
an image carrier for carrying a toner image;
image carrier supporting means for supporting the image carrier in such a way that
the image carrier is rotatable about a first rotary shaft which is arranged substantially
horizontally;
a transfer member for transferring the toner image carried on the image carrier onto
a transfer material;
transfer member supporting means for supporting the transfer member in such a way
that the transfer member is rotatable about a second rotary shaft which is arranged
substantially parallel to the first rotary shaft; and
a guide member, arranged in close proximity to the transfer member, for guiding the
transfer material to a transfer position in the transfer member, the guide member
being supported by the transfer member supporting means.
[0049] According to the invention, since the guide member is supported by the transfer member
supporting means for supporting the transfer member, positioning of the guide member
with respect to the transfer member can be achieved with high accuracy. This allows
the transfer material to be guided to the transfer position with improved accuracy.
[0050] In the invention, it is preferable that the transfer member supporting means and
the guide member are each designed to be positioned with respect to the image carrier
supporting means by abutting against the image carrier supporting means.
[0051] According to the invention, the transfer member supporting means and the guide member
can be positioned with respect to the image carrier supporting means with high accuracy.
This allows the transfer member and the guide member to be positioned with respect
to the image carrier with high accuracy, so that the quality of the transferred image
is maintained at a predetermined level.
[0052] In the invention, it is preferable that the guide member is supported by the transfer
member supporting means so as to be oscillatable within a predetermined range of oscillation,
and that, when the transfer member supporting means is moved away from the image carrier
supporting means, the guide member oscillates so as to be located in a position distant
from the transfer member.
[0053] According to the invention, prior to performing maintenance on a path through which
the transfer material passes, the transfer member supporting means and the image carrier
supporting means are moved away from each other. This allows the guide member to move
away from the'transfer member, thereby facilitating the maintenance of the transfer
position.
[0054] According to the invention, the transfer member and the guide member for guiding
the transfer material to the transfer position can be positioned with respect to the
image carrier with high accuracy. This makes it possible to maintain the quality of
the image transferred onto the transfer material at a predetermined level. Moreover,
the guide member can be easily moved away from the transfer roller arranged in close
proximity thereto, thereby facilitating maintenance such as cleaning of the transfer
roller.
[0055] The invention provides an image forming apparatus comprising:
an image carrier for carrying a toner image;
image carrier supporting means for supporting the image carrier in such a way that
the image carrier is rotatable about a first rotary shaft which is arranged substantially
horizontally;
a transfer member for transferring the toner image carried on the image carrier onto
a transfer material;
transfer member supporting means for supporting the transfer member in such a way
that the transfer member is rotatable about a second rotary shaft which is arranged
substantially parallel to the first rotary shaft;
a cover member, arranged so as to be freely movable close to and away from the image
carrier supporting means, for supporting the transfer member supporting means in such
a way that the transfer member supporting means is kept in a floating state in a substantially
horizontal direction;
a guide member, arranged in close proximity to the transfer member, for guiding the
transfer material to a transfer position in the transfer member;
a transfer member supporting means urging mechanism, disposed in the cover member,
for resiliently urging the transfer member supporting means toward the image carrier
supporting means; and
first positioning means, disposed in part of the transfer member supporting means,
for positioning the transfer member supporting means with respect to the image carrier
supporting means by abutting against the image carrier supporting means.
[0056] According to the invention, so long as the transfer member supporting means and the
image carrier supporting means can be prevented from moving away from each other by
the transfer member supporting means urging mechanism, the transfer member supporting
means can be positioned with respect to the image carrier supporting means with high
accuracy. As a result, the transfer member is positioned with respect to the image
carrier with high accuracy.
[0057] In the invention, it is preferable that the transfer member supporting means is additionally
provided with a transfer member urging mechanism for resiliently urging the transfer
member toward the image carrier.
[0058] According to the invention, even if, for example, the surface of the transfer member
deteriorates with time, by the transfer member urging mechanism, the contact pressure
force of the transfer member with respect to the image carrier can be kept constant.
[0059] In the invention, it is preferable that a first urging pressure, which is exerted
by the transfer member supporting means urging mechanism in a direction of the image
carrier supporting means, is set to be greater than a second urging pressure exerted
by the transfer member urging mechanism in the same direction.
[0060] According to the invention, the transfer member supporting means is prevented from
moving away from the image carrier supporting means by a reaction force exerted by
the transfer member urging mechanism. At this time, in order to keep these supporting
means closer to each other under a state where vibrations take place in the image
forming apparatus, the first urging pressure should preferably be set to be 1.5 times
or above greater than the second urging pressure.
[0061] In the invention, it is preferable that there are additionally provided guide member
supporting means for supporting the guide member on the transfer member supporting
means; and second positioning means, disposed in part of the guide member, for positioning
the guide member with respect to the image carrier supporting means by abutting against
the image carrier supporting means.
[0062] According to the invention, the guide member is supported by the transfer member
supporting means which is arranged in a predetermined position with respect to the
image carrier supporting means. Thus, similarly, the guide member is positioned with
respect to the image carrier with a predetermined distance secured therebetween.
[0063] In the invention, it is preferable that an urging position in the transfer member
supporting means urging mechanism is located in between the first positioning means
and the second positioning means.
[0064] According to the invention, it never occurs that the urging pressure of the transfer
member supporting means urging mechanism is lopsidedly exerted on one of the first
and second positioning means, thereby making the positioning state more stable.
[0065] In the invention, it is preferable that there is provided charge removal means for
removing charges remaining on the transfer material after the transfer process, and
the charge removal means is supported by the transfer member supporting means.
[0066] According to the invention, the charge removal means is supported by the transfer
member supporting means which is arranged in a predetermined position with respect
to the image carrier supporting means. Thus, similarly, the charge removal means can
be positioned with respect to the image carrier with a predetermined distance secured
therebetween.
[0067] According to the invention, the transfer member, the guide member, the charge removal
means, and the like can be easily positioned with respect to the image carrier with
high accuracy, thereby keeping the quality of the image transferred onto the transfer
material at a predetermined level.
[0068] Other and further objects, features, and advantages of the invention will be more
explicit from the following detailed description taken with reference to the drawings
wherein:
Fig. 1 is a cross sectional view showing a principal configuration of an image forming
apparatus 10 of a first embodiment according to the invention;
Fig. 2 is a cross sectional view showing the vicinity of a transfer roller of the
image forming apparatus 10;
Fig. 3 is a front view showing part of the image forming apparatus shown in Fig. 2;
Fig. 4A-4B are side views of Fig. 3;
Fig. 5A-5B show part of the image forming apparatus 10 in accordance with the first
embodiment of the invention, and Fig. 5A is a cross sectional view and Fig. 5B is
a simplified model;
Fig. 6A-6B show part of a conventional image forming apparatus 1, and Fig. 6A is a
cross sectional view and Fig. 6B is a simplified model;
Fig. 7 is a plan view showing an image forming apparatus of a second embodiment of
the invention in which part of a principal part thereof is cross-sectionally shown;
Fig. 8 is a schematic front view showing the principal part of the image forming apparatus
of the second embodiment of the invention;
Fig. 9 is a schematic plan view showing the image forming apparatus of the second
embodiment in which part of the principal part is enlargedly shown;
Fig. 10 is a cross sectional view showing the image forming apparatus of the second
embodiment of the invention;
Fig. 11 is a cross sectional view showing a principal part of an image forming apparatus
of a third embodiment of the invention in a state that a cover portion is opened;
Fig. 12 is a cross sectional view showing the principal part of the image forming
apparatus of the third embodiment in a state that a cover portion is closed;
Fig. 13 is a perspective view showing a transfer device of the image forming apparatus
of the third embodiment in a state that a paper guide is opened;
Fig. 14 is a perspective view showing the transfer device of the image forming apparatus
of the third embodiment in a state that a paper guide is closed;
Fig. 15 is a cross sectional view showing the image forming apparatus of the third
embodiment in a state that the cover portion is opened; and
Fig. 16 is a cross sectional view showing the image forming apparatus of the third
embodiment in a state that the cover portion is closed.
[0069] Now referring to the drawings, preferred embodiments of the invention are described
below.
[0070] Now, embodiments of the present invention will be described and will be offered for
understanding of the present invention with reference to the accompanying drawings.
Incidentally, the ensuing embodiments are mere practicable examples of the present
invention, and they are not of characters restricting the technical scope of the present
invention.
[0071] Fig. 1 is a sectional view showing the principal construction of an image forming
apparatus 10 in this embodiment. The image forming apparatus 10 is an apparatus, such
as copying machine or printer, in which an image is formed on recording paper by electrophotography,
and in which a mechanism for forming the image on the recording paper is disposed
around a photoconductive drum 12 being an image carrier. Arrayed successively from
the upstream side of the photoconductive drum 12 in the rotating direction thereof
are a charging mechanism 13 which charges the surface of the photoconductive drum
12 uniformly, an exposure mechanism 14 which irradiates the photoconductive drum surface
with light for forming an electrostatic latent image, a development mechanism 15 which
forms a toner image by supplying toner to the electrostatic latent image formed on
the photoconductive drum surface, a transfer roller 16 which is a peripheral rotary
member for transferring the toner image formed on the photoconductive drum surface
onto the recording paper 19 being a recording medium, a cleaning blade 17 which cleans
the photoconductive drum surface, and a charge removal lamp 18 which removes residual
charges on the photoconductive drum surface.
[0072] In the image forming apparatus 10, image formation proceeds in such a way that the
surface of the photoconductive drum 12 is first charged uniformly by the charging
mechanism 13, that the charged photoconductive drum surface is irradiated with a laser
beam by the exposure mechanism 14 so as to form an electrostatic latent image, that
the electrostatic latent image is supplied with the toner by the development mechanism
15 so as to form a toner image, that the toner image is transferred onto the recording
paper which is sent in between the transfer roller 16 and the photoconductive drum
12, and that the recording paper is heated by a thermal fixation mechanism, not shown,
so as to fix the toner image onto the recording paper.
[0073] The toner which remains on the photoconductive drum surface after the image transfer
is removed by the cleaning blade 17, and charges which similarly remain on the photoconductive
drum surface are removed by the charge removal lamp 18, whereby the image forming
apparatus 10 gets ready for the next image formation.
[0074] Fig. 2 shows the vicinity of the transfer roller 16 of the image forming apparatus
10, and is a sectional view seen from a side on which the recording paper is inserted.
As shown in Fig. 2 and Fig. 5A to be referred to later, the image forming apparatus
10 includes the photoconductive drum 12, flanges 20, the transfer roller 16, first
control members 22, second control members 23 and urging members 24.
[0075] Referring to Fig. 5A to be described later, the photoconductive drum 12 is formed
of a photoconductive drum elementary pipe 12a which is in the shape of a hollow cylinder,
and the pair of drum flanges 20 which cover the open parts of the photoconductive
drum elementary pipe 12a at both the ends thereof. Besides, a drum shaft 21 which
penetrates through the photoconductive drum 12 in the axial direction thereof is formed
so as to be coaxial with this photoconductive drum 12, and the drum shaft 21 is rotatably
supported by a pair of drum side bearings 28 which are disposed at both the end parts
of this drum shaft 21.
[0076] The transfer roller 16 is formed in the shape of a column, and its axis A4 is arranged
in parallel with the axis A3 of the photoconductive drum 12. Besides, a roller shaft
25 which penetrates through the transfer roller 16 in the axial direction thereof
is formed so as to be coaxial with this transfer roller 16. The roller shaft 25 is
rotatably supported by a pair of roller side bearings 29 which are disposed at both
the end parts of this roller shaft 25. As shown in Fig. 2, the roller side bearings
29 are fitted in corresponding slots 30 which are provided in the frame 27 of the
image forming apparatus 10. The roller side bearings 29 are displaceable toward the
drum shaft 21 owing to the slots 30, whereby the roller shaft 25 which these roller
side bearings 29 support is supported so as to be capable of coming near to and away
from the drum shaft 21. In this embodiment, accordingly, the transfer roller 16 is
arranged under the photoconductive drum 12 and is supported so as to be capable of
moving up and down.
[0077] Further, a gear b is fixed to one end part of the drum shaft 21, and it meshes with
a gear a to which a turning force is transmitted from a rotation transmission mechanism
not shown. Thus, the turning force from the rotation transmission mechanism is transmitted
to the photoconductive drum 12 through the gear a, gear b and drum shaft 21. Besides,
gear grooves 40 are formed in the peripheral surface of one flange 20 mounted on the
photoconductive drum 12, that is, the flange 20 on a side on which the gear b is formed.
[0078] A gear d is fixed to one end part of the roller shaft 25. The gear d meshes with
the gear grooves 40 formed in the above flange 20. Thus, the rotation of the photoconductive
drum 12 is transmitted to the transfer roller 16. Accordingly, the transfer roller
16 can be rotated in synchronism with the photoconductive drum 12 so as to hold the
inserted recording paper between it and this drum 12 and to eject the recording paper.
[0079] The pair of bearings 29 on the roller shaft side are respectively furnished with
the urging members 24. The urging members 24 have elasticity, and they are made of,
for example, springs. Thus, the urging members 24 press the transfer roller 16 toward
the photoconductive drum 12.
[0080] Fig. 3 is a front view showing part of the image forming apparatus 10 in Fig. 2.
The first control members 22 and second control members 23 which constitute control
means 50 are formed in the shape of discs, and such control members in one pair are
respectively disposed on both the sides of each of the photoconductive drum 12 and
transfer roller 16. The roller shaft 25 is urged toward the drum shaft 21 by the urging
members 24 until the first control members 22 and the second control members 23 abut
against each other, whereby a predetermined gap H is defined between the photoconductive
drum 12 and the transfer roller 16. The predetermined gap H is set to be less than
the thickness of the recording paper. In this way, the first and second control members
22, 23 regulate the displacement of the transfer roller 16 in the direction of coming
near to the photoconductive drum 12.
[0081] The first control members 22 are loosely fitted at positions spaced from the photoconductive
drum 12 in a state where they are rotatable with respect to the drum shaft 21. More
specifically, each of the first control members 22 is arranged on the drum shaft 21
between the position of the axial end part of the photoconductive drum 12 and the
position of the drum side bearing 28 nearby. Likewise, the second control members
23 are loosely fitted at positions spaced from the transfer roller 16 in a state where
they are rotatable with respect to the roller shaft 25. More specifically, each of
the second control members 23 is arranged on the roller shaft 25 between the position
of the axial end part of the transfer roller 16 and the position of the roller side
bearing 29 nearby. Besides, the first control members 22 and the second control members
23 have shock absorption means, and they are formed of an elastic, shock-absorbingmaterial
such as resin or hard rubber.
[0082] Figs. 4A and 4B are side views corresponding to Fig. 3. Fig. 4A shows a state before
the recording paper 19 is inserted, while Fig. 4B shows a state where the recording
paper 19 has been inserted. The recording paper 19 is conveyed toward the gap H between
the photoconductive drum 12 and the transfer roller 16 as shown in Fig. 4A, and it
is inserted between the photoconductive drum 12 and the transfer roller 16 as shown
in Fig. 4B. On this occasion, since the thickness of the recording paper 19 is greater
than the gap H between the photoconductive drum 12 and the transfer roller 16, the
transfer roller 16 is brought away from the photoconductive drum 12, and the distance
between the photoconductive drum 12 and the transfer roller 16 increases, so that
the first control members 22 and the second control members 23 come away from each
other. The transfer roller 16 is pressed by the urging members 24 so as to come near
to the photoconductive drum 12, and the recording paper 19 passes between the photoconductive
drum 12 and the transfer roller 16 against the pressing forces of the urging members
24. When the recording paper 19 has been ejected, the first control members 22 and
the second control members 23 are brought into abutment again by the spring forces
of the urging members 24, and the distance between the photoconductive drum 12 and
the transfer roller 16 is restored to the predetermined gap size H.
[0083] Herein, impulses appear at the insertion and ejection of the recording paper 19.
Since, however, the first control members 22 and the second control members 23 are
mounted at the positions respectively spaced from the photoconductive drum 12 and
the transfer roller 16, moments acting due to the forces of the impulses can be lessened
to mitigate the deflections of the photoconductive drum 12 and the transfer roller
16. This will be elucidated with reference to Figs. 5A, 5B, 6A and 6B.
[0084] Figs. 5A and 5B show part of the image forming apparatus 10 in the embodiment of
the present invention, and Fig. 5A is a sectional view, while Fig. 5B is a simplified
model diagram. On the other hand, Figs. 6A and 6B show part of an image forming apparatus
1 in the prior art, and Fig. 6A is a sectional view, while Fig. 6B is a simplified
model diagram.
[0085] As shown in Fig. 5A and Fig. 6A, in order to compare the prior-art apparatus 1 and
the apparatus 10 of the invention, they are assumed to be the same in, for example,
the dimensions of photoconductive drums 2, 12, the positions of bearings 41, 28, the
characteristics of urging means 5, 24, the dimensions of drum shafts 8, 21 and the
materials of various members, except the positions of control means 4, 50 arranged
round the axes of the photoconductive drums 2, 12 being image carriers. In the prior-art
apparatus 1, the control means 4 abut against the outer periphery of the photoconductive
drum 2, and they are respectively disposed at predetermined lengths L1, L2 from the
drum side bearings 41. In contrast, in the apparatus 10 of the invention, the control
means 50 are spaced from the photoconductive drum 12, and they are respectively disposed
at predetermined lengths L3, L4 from the drum side bearings 28. As the lengths between
the drum side bearings 41, 28 and the control means 4, 50, accordingly, the lengths
L3, L4 in the apparatus 10 of the invention are less than the lengths L1, L2 in the
prior-art apparatus 1.
[0086] The magnitudes of the impulsive forces which arise in inserting and ejecting the
recording paper, depend upon how much the transfer roller is displaced from the axis
of the photoconductive drum. Accordingly, in a case where the thicknesses of recording
sheets of paper are equal, the image forming apparatuses 1, 10 in the prior art and
of the invention undergo equal impulsive force magnitudes. Since, however, the impulsive
forces appear at the positions of the control means for regulating the relative position
between the photoconductive drum and the transfer roller, the acting positions of
the impulsive forces differ between in the prior art and in the invention. More specifically,
in the prior-art apparatus 1, the acting points of the impulsive forces are located
at both the axial end parts of the photoconductive drum 2. In the apparatus 10 of
the present invention, the acting points of the impulsive forces are located on the
drum shaft 21 between the positions of the axial end parts of the photoconductive
drum 12 and the positions of the corresponding drum side bearings 28 nearby.
[0087] As shown in Fig. 5B and Fig. 6B, accordingly, moments around the bearings 28, 41
based on the impulsive forces F become less in the invention than in the prior art
for the reason that the lengths L3, L4 between the bearings 28 and the control means
50 in the case of the invention are less than the lengths L1, L2 between the bearings
41 and the control means 4 in the case of the prior art. Consequently, the deflections
of the drum shafts attributed to the impulsive forces F become less in the invention
than in the prior art, and the displacement magnitudes and vibrations of the surfaces
of the photoconductive drums bearing toner images become less in the invention than
in the prior art.
[0088] As described above, according to the invention, when the impulse forces have acted
due to the passage of the recording paper, the displacement magnitudes and vibrations
of the image carrier can be relieved, and the toner image on the image carrier can
be favorably transferred onto the recording paper.
[0089] Further, the first and second control members are formed of the shock absorbing material,
so that the impulsive forces and the vibrations ascribable thereto are absorbed. The
vibrations to be imparted to the photoconductive drum 12 and the recording paper 19
are relived in this way, whereby the toner image formed on the photoconductive drum
12, and the toner image transferred onto the recording paper and not fixed yet are
not vibrated, a picture is prevented from blurring or oscillating, and a good picture
can be formed.
[0090] Moreover, the first control members 22 and the second control members 23 are loosely
fitted on the drum shaft 21 and the roller shaft 25, respectively, so that even when
the drum shaft 21 and the roller shaft 25 have been rotated, the first control members
22 and the second control members 23 can be at rest in an abutting state without rotating.
Accordingly, the first control members 22 and the second control members 23 are not
rotated together with the photoconductive drum 12 and the transfer roller 16, and
the abutment surfaces of the first control members 22 and second control members 23
are prevented from wearing off. Besides, a foreign matter such as the toner does not
adhere onto the abutment surfaces, and the exact constant gap H can be defined between
the photoconductive drum 12 and the transfer roller 16.
[0091] The above embodiment merely exemplifies the invention, and the construction can be
altered within the scope of the invention. By way of example, in the embodiment, the
control means are employed so as to define the predetermined gap H between the photoconductive
drum being the image carrier and the transfer roller. However, the invention is not
restricted only to the aspect, but it shall cover also, for example, an image forming
apparatus in which control means regulate the image carrier and the transfer roller
so that the transfer roller may be held in pressed contact with the image carrier
under a predetermined pressure.
[0092] Besides, in this embodiment, the photoconductive drum and the transfer roller are
regulated into the predetermined positional relationship by causing the first control
members and the second control members to abut against each other, but the predetermined
positional relationship may well be established by employing one sort of control members.
By way of example, the photoconductive drum and the transfer roller may well be regulated
into the predetermined positional relationship by causing the first control members
and the shaft of the transfer roller to abut against each other, or by causing the
second control members and the shaft of the image carrier to abut against each other.
[0093] Further, at least either the first control members or the second control members
need not be disposed directly on the shaft, and they may be arranged between the respective
axes A3 and A4 of the photoconductive drum 12 and transfer roller 16. By way of example,
it is also allowed to dispose other members coaxial with the axis A3 and to dispose
at least either the first or the second control members between the axes A3 and A4
through the other members. Moreover, the first and second control members need not
always be disc-shaped, but they may well be in any other shapes.
[0094] Still further, the image carrier is exemplified as the photoconductive drum in the
foregoing, but it may alternatively be a photosensitive belt or an intermediate transfer
member. In case of the photosensitive belt, the control means are disposed between
the axis of a shaft opposing to the transfer roller, among a plurality of shafts for
rotating the photosensitive belt tightly, and the axis of the transfer roller.
[0095] Here, Fig. 7 is a partially-sectional plan view of the principal portions of an image
forming apparatus 60 according to the second embodiment of the invention, Fig. 8 is
a schematic front view of the principal portions of the image forming apparatus 60
according to the second embodiment of the invention, Fig. 9 is a partially-enlarged
schematic plan view of the principal portions of the image forming apparatus 60 according
to the second embodiment of the invention, and Fig. 10 is a sectional view of the
image forming apparatus 60 according to the second embodiment of the invention.
[0096] The image forming apparatus 60 is a copying machine which is an example of an image
forming apparatus embodying the invention.
[0097] First, the arrangement of the principal portions, etc. in the image forming apparatus
60 will be described with reference to Fig. 10. Fig. 10 is a front sectional view
of the apparatus 60. A photoconductive drum 70 (being an example of an image carrier)
which is one of the principal portions is arranged near the left side of the apparatus
60 substantially centrally in the vertical direction thereof, and it is surrounded
with a charging roller 80, a development roller 90 and a transfer roller 100 (being
examples of peripheral rotary members, respectively) . Transfer paper or the like
for forming a picture thereon is fed from a paper supply unit 61 located at the lower
part of the apparatus 60, to the touching parts of the peripheral surfaces of the
photoconductive drum 70 and the transfer roller 100, by feed rolls 62. The transfer
paper or the like onto which a toner image on the photoconductive drum 70 has been
transferred by the transfer roller 100, has its toner image fixed by a fixation device
63 located at the upper part of the apparatus 60 and is ejected onto the top surface
of the apparatus 60 by paper ejection rolls 64.
[0098] Next, the principal portions of the image forming apparatus 60 will be described
with reference to Figs. 7, 8 and 9. As shown in Fig. 7, the photoconductive drum 70
is a columnar member of hollow structure, and it is rotatably supported by two drum
shafts 70a which are, in turn, supported by a supporting member 103. Besides, the
development roller 90 and the transfer roller 100 which are arranged around the photoconductive
drum 70 are respectively supported by the supporting members 103 through rotary shafts
90a and 100a. Photosensitive collars 71 (being an example of first control members),
and development collars 91 and transfer collars 101 (being examples of second control
members, respectively) are snugly supported at both the end parts of the corresponding
rotary shafts 70a, 90a and 100a of the photoconductive drum 70, development roller
90 and transfer roller 100, respectively. The collars 71, 91 and 101 are respectively
provided with openings which are substantially equal in diameter to the corresponding
rotary shafts 70a, 90a and 100a, and the rotary shafts 70a, 90a and 100a are respectively
supported in states where they are inserted through the corresponding openings. Regarding
the charging roller 80 not shown in Fig. 7, charging collars 81 (being an example
of the second control members) (refer to Fig. 8) are supported likewise to the development
collars 91 and the transfer collars 101. The photosensitive collars 71 are pressed
articles of metal, molded articles of resin, or the likes, and the charging collars
81, development collars 91 and transfer collars 101 are molded articles of resin,
or the likes.
[0099] One of the photosensitive collars 71 is provided with a pin 71a (being an example
of oscillation control means) protruding in parallel with the corresponding drum shaft
70a, and it is so constructed that the pin 71a engages part of the supporting member
103. Besides, the charging collars 81, development collars 91 and transfer collars
101 are respectively provided with ribs 81a, 91a and 101a (being examples of the oscillation
control means, respectively) rising in parallel with the corresponding rotary shafts
80a, 90a and 100a, and they are so constructed that the ribs 81a, 91a and 101a engage
parts of the supporting member 103. Shown in Fig. 9 is a state where the rib 101a
with which the transfer collar 101 is provided engages the part 103a of the supporting
member 103.
[0100] Owing to the engagements of the pin 71a and the ribs 81a, 91a and 101a, the collars
71, 81, 91 and 101 are respectively held so as not to rotate even when the photoconductive
drum 70, charging roller 80, development roller 90 and transfer roller 100 are rotated.
[0101] As shown in Fig. 8, the charging collars 81, development collars 91, and transfer
collars 101 abut against the photosensitive collars 71 at abutment parts 71b and 81b,
71c and 91c, and 71d and 101d, respectively. Thus, the interaxial distances of the
respective rotary shafts 80a, 90a and 100a of the charging roller 80, development
roller 90 and transfer roller 100 with respect to the drum shafts 70a are held constant.
The collars 71, 81 have their dimensions from the corresponding rotary shafts 70a,
90a to the abutment parts 71c, 91c machined within predetermined errors in order that
the gap between the peripheral surfaces of the development roller 90 and photoconductive
drum 70 may become a value appropriate for development, for example, about 0.5 mm.
Besides, the transfer roller 100 has its peripheral surface made of a conductive elastic
material such as urethane rubber, while the charging roller 80 has its peripheral
surface made of a brush of conductive fibers of, for example, rayon, the conductive
elastic material, or the like. Further, the rotary shafts 100a, 80a of the respective
rollers 100, 80 are pressed toward the drum shafts 70a by springs 104, etc.
[0102] Owing to the construction as stated above, the transfer collars 101 and charging
collars 81 abut against the corresponding photosensitive collars 71, so that the respective
interaxial distances are held constant and that the peripheral surfaces of the transfer
roller 100 and charging roller 80 are held in a predetermined pressed contact state.
Besides, since the collars 71, 81 and 101 have their outside diameters machined within
predetermined errors, the precisions of the interaxial distances are kept high.
[0103] In this manner, the collars 71, 81, 91 and 101 which hold constant the interaxial
distances of the charging roller 80, development roller 90 and transfer roller 100
with respect to the photoconductive drum 70 are held in the state where they abut
at the abutment parts 71b, 71c, 71d, 81b, 91c and 101d without rotating. Therefore,
toner or any other powder of paper pieces or the likes is not bitten into the abutment
parts 71b, 71c, 71d, 81b, 91c and 101d, and the abutment parts 71b, 71c, 71d, 81b,
91c and 101d do not rub and wear, either. Further, the collars 71, 81, 91 and 101
may have only their dimensions from the corresponding rotary shafts 70a, 80a, 90a
and 100a to the abutment parts 71b, 71c, 71d, 81b, 91c and 101d machined at high precisions,
so that they can be fabricated at comparatively low cost.
[0104] Further, the photosensitive collar 71 is in a wasteless shape in which the abutment
parts 71b, 71c and 71d thereof jut out more than the other non-abutting parts, so
that it can be made lighter in weight and smaller in space than in case of a discshape.
By way of example, in a case where the photoconductive drum 70 and the peripheral
devices, such as the charging roller 80, acting thereon are unitarily supported by
the supporting member 103 so as to construct a process unit, the process unit can
be compacted in such a way that reinforcement parts for reinforcing the process unit
are formed in the recesses defined between the respectively adjacent abutment parts
71b, 71c and 71d of the photosensitive collar 71.
[0105] Besides, as shown in Fig. 7, helical gears 72, 102 for smoothly transmitting to the
transfer roller 100 the turning force of the photoconductive drum 70 rotated by a
driver not shown are respectively disposed on one end part of one of the drum shafts
70a and one end part of the rotary shaft 100a of the transfer roller 100, whereby
the transfer roller 100 is smoothly driven to rotate.
[0106] Here, as shown in Fig. 9, a thrust load ascribable to the helical gears 72, 102 acts
on the rotary shaft 100a of the transfer roller 100 in a direction toward one of the
transfer collars 101, and the transfer collar 101 is about to rotate following the
helical gear 102 on account of the friction of its contact surface with the helical
gear 102. However, the rib 101a with which the transfer collar 101 is provided comes
into engagement with the part 103a of the support member 103, and the rotation of
the transfer collar 101 is checked.
[0107] While, in the image forming apparatus 60, the photosensitive collar 71 is so configured
that the abutment parts 71b, 71c and 71d jut out more than the other parts thereof,
it may alternatively be disc-shaped or take any other shape.
[0108] While, in the image forming apparatus 60, a helical gear is employed as means for
transmitting a turning driving force to the transfer roller 100, a rubber belt or
the like may be employed instead.
[0109] While the image forming apparatus 60 is embodied as an example of copying machines,
an image forming apparatus to which the invention is applicable may include a laser
printer, a facsimile machine, or the like.
[0110] Fig. 11 is a sectional view illustrating principal portions of an image forming apparatus
110, with its cover portion kept in an opened state, in accordance with a third embodiment
of the invention; Fig. 12 is a sectional view illustrating the principal portions
of the image forming apparatus 110 of the third embodiment, with its cover portion
kept in a closed state; Fig. 13 is a perspective view illustrating a transfer device
of the image forming apparatus 110 of the third embodiment, with its paper guide kept
in an opened state; Fig. 14 is a perspective view illustrating the transfer device
of the image forming apparatus 110 of the third embodiment, with its paper guide kept
in a closed state; Fig. 15 is a sectional view illustrating the image forming apparatus
110 of the third embodiment, with its cover portion kept in an opened state; and Fig.
16 is a sectional view illustrating the image forming apparatus 110 of the third embodiment,
with its cover portion kept in a closed state.
[0111] The image forming apparatus 110 is a copying machine which is an example of an image
forming apparatus embodying the invention.
[0112] First, the schematic structure of the image forming apparatus 110 will be described
with reference to Fig. 15. Fig. 15 shows the image forming apparatus 110 when viewed
from the left-hand side. The image forming apparatus 110 is roughly composed of a
main body 111 and a cover portion 170. The cover portion 170 (being an example of
the cover member) is provided with a rail 171 which is supported by the main body
111, and is thereby horizontally supported so as to be freely movable from the front
side of the image forming apparatus 110 toward the main body 111 (in the mutually
approaching or departing direction) . By pressing the cover portion 170 against the
main body 111, a retaining lever 172, which is rotatably supported by the cover portion
170, is brought into engagement with a retaining pin 112 disposed in the main body
111, whereby, as shown in Fig. 16, the cover portion 170 is held in engagement with
the main body 111, i.e. is brought into a closed state. Moreover, by detaching the
retaining lever 172 from the retaining pin 112, the cover portion 170 is disengaged
from the main body 111, so that the cover portion 170 is moved away from the main
body 111, i.e. is brought into an opened state.
[0113] Next, with reference to Fig. 11, the structures of the principal portions of the
image forming apparatus 110 will be described. The main body 111 includes: a photoconductive
drum 121 for forming a toner image on the circumferential surface thereof (an example
of the image carrier); a charging device 201 for applying static charges to the photoconductive
drum 121; a development device 202 for forming a toner image on the circumferential
surface of the photoconductive drum 121; a cleaning device 203 for removing the toner
remaining on the photoconductive drum 121 after the transferring of the toner image
onto a paper sheet (an example of the transfer material) or the like; a paper supply
roller 204 for feeding a paper sheet or the like from below upward to a transfer position;
and a main body frame 120 which is a member for supporting the photoconductive drum
121 and other components (an example of the image carrier supporting means).
[0114] Moreover, the cover portion 170 loosely supports a transfer device frame 130 (an
example of the transfer member supporting means) for supporting specific devices involved
in image transfer, and is provided with a first spring 141 (an example of the transfer
member supporting means urging mechanism) for urging the transfer device frame 130
to be pressed against the main body 111 in said mutually approaching or departing
direction. Further, the transfer device frame 130 supports a transfer roller 131 (an
example of the transfer member) for transferring a toner image onto a paper sheet
or the like by being brought into pressed contact with the circumferential surface
of the photoconductive drum 121; a paper guide 150 (an example of the guide member)
for guiding the paper sheet or the like fed from the paper supply roller 204 to the
transfer position; and a charge removal device 160 (an example of the charge removal
means) for removing charges remaining on the paper sheet or the like after the toner
image transfer. In addition, the transfer device frame 130 is provided with a second
spring 142 (an example of the transfer member urging mechanism) for urging a rotary
shaft 131a of the transfer roller 131 to be pressed in a predetermined direction.
In this way, an image transfer device 132 is constructed.
[0115] The photoconductive drum 121 is horizontally supported by the main body frame 120
so as to be rotatable about a rotary shaft 121a (a first rotary shaft) which is perpendicular
to the mutually approaching or departing direction. In the vicinity thereof are disposed
the charging device 201, the development device 202, the cleaning device 203, and
other components. Moreover, below the photoconductive drum 121 is disposed the paper
supply roller 204.
[0116] The transfer device frame 130 has a fitting pin 130c formed so as to protrude toward
the main body 111, and the main body frame 120 has a fitting hole 120c in which the
fitting pin 130c is fitted. The fitting hole 120c is so configured that, when receiving
the fitting pin 130c, upper and lower surfaces of the fitting pin 130c are brought
into contact with the inner surface thereof.
[0117] The transfer device frame 130 has a hemispherical abutment part 130a (an example
of the first positioning means) which abuts against a first abutment surface 120a
constituting a part of the main body 111 in a state where the cover portion is closed.
Likewise, the paper guide 150 has an abutment part 150b (an example of the second
positioning means) which abuts against an abutment surface 120b of the main body 111.
[0118] The transfer device frame 130 is supported by the cover portion 170 so as to be slidable
in the mutually approaching or departing direction. The first spring 141 is disposed
between the abutment parts 130a and 150b, as viewed in the vertical direction, and
has its one end supported by the cover portion 170, and has its other end arranged
so as to urge the transfer device frame 130 to be pressed against the main body 111
in the mutually approaching or departing direction.
[0119] The transfer roller 131 has, on its circumferential surface, a formed material, such
as urethane rubber, for bringing a paper sheet or the like into intimate contact with
the circumferential surface of the photoconductive drum 121.
[0120] The transfer roller 131 has a rotary shaft 131a (a second rotary shaft) arranged
parallel to the rotary shaft 121a of the photoconductive drum 121. The second rotary
shaft 131a is rotatably supported by a groove portion 130d so as to be slidable obliquely
upwardly. The groove portion 130d has a width which is substantially equal to the
diameter of the second rotary shaft 131a. The second spring 142 has its one end supported
by the groove portion 130d, and has its other end configured so as to push the second
rotary shaft 131a obliquely upwardly. The sliding direction of the rotary shaft 131a
is so determined that the rotary shaft 131a slides toward the rotary shaft 121a of
the photoconductive drum 121 in a state where the cover portion is closed. Moreover,
the relationship between the first and second springs 141 and 142 is such that the
latter is smaller in pressing force in the mutually approaching or departing direction
than the former.
[0121] The paper guide 150 is supported by the transfer device frame 130 so as to be vertically
rotatable about a shaft 150a, arranged parallel to the rotary shaft 121a of the photoconductive
drum 121, within a predetermined range of rotation.
[0122] The charge removal device 160, which is supported in close proximity to the upper
part of the transfer roller 131, is constituted by a point discharge electrode or
the like, and is supported by the transfer device frame 130.
[0123] As shown in Fig. 13, the transfer device frame 130, the paper guide 150, and the
charge removal device 160 are so formed as to extend along the direction of the rotary
shaft 131a of the transfer roller 131 to each end of the transfer roller 131. The
fitting pin 130c and the abutment part 130a, 150b are each arranged in twos at each
end of the transfer roller 131.
[0124] The paper guide 150 is rotatably supported by the transfer device frame 130 in such
a way that, when the cover portion 170 is pulled to be brought into an opened state,
the paper guide 150 rotates under its own weight downwardly within the predetermined
range of rotation, and is thereby held away from the transfer roller 131 (the paper
guide 150 is in an opened state). Fig. 13 is a perspective view illustrating the transfer
device 132 composed of the transfer device frame 130, the transfer roller 131 supported
thereby, and others, with the paper guide kept in an opened state.
[0125] In this way, when the cover portion 170 is opened, the transfer roller 131, the photoconductive
drum 121, and the paper guide 150 are moved away from the main body 111, and thereby
the circumferential surface of the transfer roller 131 is widely exposed. This helps
facilitate maintenance operations such as removal of jammed paper or cleaning of the
circumferential surface of the transfer roller 131.
[0126] Moreover, when the cover portion 170 is pushed to come near the main body 111, the
fitting pin 130c is fitted in the fitting hole 120c, and simultaneously part of the
paper guide 150 abuts on the abutment surface 120b of the main body 111. This causes
the paper guide 150 to rotate upwardly within the predetermined range of rotation.
Further, when the cover portion 170 is pushed to be brought into the closed state,
as shown in Fig. 12, by the pressing action of the second spring 142, part of the
circumferential surface of the transfer roller 131 comes in pressed contact with part
of the circumferential surface of the photoconductive drum 121, and the abutment part
130a abuts against the first abutment surface 120a. At the same time, the abutment
part 150b abuts against the second abutment surface 120b, thereby determining the
inclination of the paper guide 150. Moreover, the paper guide 150 is pressed to rotate
upwardly within the predetermined range of rotation so as to be supported in close
proximity to the transfer roller 131 (the paper guide 150 is in a closed state) .
Fig. 14 is a perspective view illustrating the transfer device 132, with the paper
guide kept in a closed state. In this state, the paper guide 150 is able to, with
high accuracy, guide a paper sheet or the like fed from the paper supply roller 204
to a position where the transfer roller 131 and the photoconductive drum 121 make
pressed contact with each other.
[0127] In this way, the fitting pin 130c is constrained to vertical movement, thereby positioning
the transfer device frame 130 with respect to the main body frame 120 in the vertical
direction. At the same time, by the pressing action of the first spring 141, the abutment
parts 130a and 150b are respectively kept in contact with the abutment surfaces 120a
and 120b of the main body frame 120, thereby positioning the transfer device frame
130 with respect to the main body frame 120 in the mutually approaching or departing
direction.
[0128] Incidentally, the second spring 142 is smaller in pressing force in the mutually
approaching or departing direction than the first spring 141. In this configuration,
the reaction force of the pressing action of the second spring 142 prevents the transfer
device frame 130 from moving away from the main body frame 120. Moreover, the photoconductive
drum 121 is supported by the main body frame 120, and the transfer roller 131, the
paper guide 150, and the charge removal device 160 are respectively supported by the
transfer device frame 130. Therefore, the transfer roller 131, the paper guide 150,
and the charge removal device 160 are positioned with respect to the photoconductive
drum 121 so that the distance therebetween is kept constant. Moreover, the contact
pressure force of the transfer roller 131 with respect to the photoconductive drum
121 can be kept constant by the pressing action of the second spring 142. Further,
since the pressing position of the first spring 141 is located between the abutment
parts 130a and 150b, as viewed in the vertical direction, the pressing action of the
first spring 141 is stabilized without being lopsidedly exerted on one of the abutment
parts.
[0129] As described thus far, the transfer roller 131 and the paper guide 150 can be easily
moved away from the photoconductive drum 121 simply by pulling the cover portion 170
out of the main body 111 without extra operations such as screwing. This helps facilitate
maintenance operations such as removal of jammed paper or cleaning of the transfer
roller 131.
[0130] Moreover, the positions of the transfer roller 131, the paper guide 150, and the
charge removal device 160, as well as the inclination of the paper guide 150, with
respect to the photoconductive drum 121 can be kept constant at all times simply by
pressing the cover portion 170 against the main body 111. Further, even if, for example,
the surface of the transfer roller 131 deteriorates with time, the transfer roller
131 and the photoconductive drum 121 can be held in a predetermined pressed contact
state. This makes it possible to keep the quality of the image transferred onto a
paper sheet or the like at a predetermined level.
[0131] While, in the image forming apparatus 110, the transfer roller 131 is designed to
be slidably supported, it may be simply rotatablysupported. To achieve this, for example,
the transfer device frame 130 is provided with a supporting portion having an opening
whose inner diameter is substantially equal to the diameter of the rotary shaft 131a,
and the rotary shaft 131a is inserted through the opening. Also in this case, the
transfer roller 131 can be correctly positioned with respect to the photoconductive
drum 121.
[0132] Moreover, in the image forming apparatus 110, the second spring 142 is smaller in
pressing force in the mutually approaching or departing direction than the first spring
141. In this connection, according to the result of the test conducted, the pressing
force of the first spring 141 in said direction should preferably be set to be 1.5
times or more greater than that of the second spring 142. By doing so, even though
vibrations take place in the apparatus, the abutment parts 130a and 150b can be inhibited
from moving away from the main body frame 120.
[0133] Further, while, in the image forming apparatus 110, the pressing position of the
first spring 141 is located between the abutment parts 130a and 150b as viewed in
the vertical direction, it may be located, for example, in the same position as the
abutment part 130a as viewed in the vertical direction. To achieve this, for example,
the abutment part 130a is cylindrically shaped so as to secure a sufficiently wide
contact area between the main body frame 120 and the abutment part 120a.
[0134] Still further, while the image forming apparatus 110 is embodied as a copying machine,
image forming apparatuses to which the invention is applicable may include a printer,
a facsimile machine, or the like.
[0135] The invention may be embodied in other specific forms without departing from the
spirit or essential characteristics thereof. The present embodiments are therefore
to be considered in all respects as illustrative and not restrictive, the scope of
the invention being indicated by the appended claims rather than by the foregoing
description and all changes which come within the meaning and the range of equivalency
of the claims are therefore intended to be embraced therein.
1. An image forming apparatus (10) comprising:
an image carrier (12) for carrying a toner image; and
a transfer roller (16) which is loaded with a force that tends to move the transfer
roller (16) toward the image carrier (12), the transfer roller (16) being arranged
in a predetermined positional relation to the image carrier (12) by control means
(50),
wherein the control means (50) is disposed between an axis of the transfer roller
(16) and an axis of the image carrier (12) so as to be located outwardly away from
an axial end portion of the image carrier (12).
2. An image forming apparatus (10, 60) comprising:
an image carrier (12, 70), rotatably supported, for carrying a toner image;
a peripheral rotary body (16, 80, 90, 100) involved in image formation, which is rotatably
supported in a periphery of the image carrier (12, 70); and
control means (50) for controlling displacement of the peripheral rotary body (16,
80, 90, 100) in a direction proximate to the image carrier (12, 70) so as to maintain
a predetermined positional relationship between the image carrier (12, 70) and the
peripheral rotary body (16, 80, 90, 100), the control means (50) being so configured
that an acting point of impacting force, which is generated in between the image carrier
(12, 70) and the peripheral rotary body (16, 80, 90, 100) at a time of image formation,
is located on an axis of the image carrier (12, 70) between a position of an axial
end portion of the image carrier (12, 70) and a position nearby in which the image
carrier (12, 70) is supported.
3. The image forming apparatus of claim 1 or 2, wherein the control means (50) is made
of a material having shock absorbency.
4. The apparatus of claim 1, 2, or 3, wherein the control means (50) includes:
a first control member (22, 71) loosely fitted to a shaft (21, 70a) of the image carrier
(12, 70); and
a second control member (23, 81, 91, 101) loosely fitted to a shaft (25, 80a, 90a,
100a) of the peripheral rotary body (16, 80, 90, 100), the first and second control
means (22, 71; 23, 81, 91, 101) abutting against each other.
5. The apparatus of claim 1, 2, 3, or 4, wherein the control means (50) is arranged outwardly
away from the axial end portion of the peripheral rotary body (16, 80, 90, 100).
6. The apparatus of any one of claims 1 to 5, futher comprising:
oscillation control means (71a, 81a, 91a, 101a) for controlling oscillation of each
of the first and second control members (71, 81, 91, 101).
7. The image forming apparatus (60) of claim 6, wherein the oscillation control means
(71a, 81a, 91a, 101a) is so configured as to inhibit rotation of the first and second
control members (71, 81, 91, 101).
8. The apparatus of claim 6 or 7, wherein the abutment portion of the first control member
(71), which abuts against the second control member (81, 91, 101), is so configured
as to protrude outwardly relative to the other non-abutting portions.
9. The apparatus of claim 6, 7, or 8, wherein a helical gear (102) is provided as driving
force transmitting means for rotatably driving at least one of the image carrier (70)
and the peripheral rotary body (80, 90, 100).
10. An image forming apparatus (110) comprising:
an image carrier (121) for carrying a toner image;
image carrier supporting means (120) for supporting the image carrier (121) in such
a way that the image carrier (121) is rotatable about a first rotary shaft (121a)
which is arranged substantially horizontally;
a transfer member (131) for transferring the toner image carried on the image carrier
(121) onto a transfer material;
transfer member supporting means (130) for supporting the transfer member (131) in
such a way that the transfer member (131) is rotatable about a second rotary shaft
(131a) which is arranged substantially parallel to the first rotary shaft (121a);
and
a guide member (150), arranged in close proximity to the transfer member (131), for
guiding the transfer material to a transfer position in the transfer member (131),
the guide member (150) being supported by the transfer member supporting means (130).
11. The image forming apparatus (110) of claim 10, wherein the transfer member supporting
means (130) and the guide member (150) are each designed to be positioned with respect
to the image carrier supporting means (120) by abutting against the image carrier
supporting means (120).
12. The image forming apparatus (110) of claim 10 or 11,
wherein the guide member (150) is supported by the transfer member supporting means
(130) so as to be oscillatable within a predetermined range of oscillation,
and wherein, when the transfer member supporting means (130) is moved away from
the image carrier supporting means (120), the guide member (150) oscillates so as
to be located in a position distant from the transfer member (131).
13. An image forming apparatus (110) comprising:
an image carrier (121) for carrying a toner image;
image carrier supporting means (120) for supporting the image carrier (121) in such
a way that the image carrier (121) is rotatable about a first rotary shaft (121a)
which is arranged substantially horizontally;
a transfer member (131) for transferring the toner image carried on the image carrier
(121) onto a transfer material;
transfer member supporting means (130) for supporting the transfer member (131) in
such a way that the transfer member (131) is rotatable about a second rotary shaft
(131a) which is arranged substantially parallel to the first rotary shaft (121a);
a cover member (170), arranged so as to be freely movable close to and away from the
image carrier supporting means (120), for supporting the transfer member supporting
means (130) in such a way that the transfer member supporting means (130) is kept
in a floating state in a substantially horizontal direction;
a guide member (150), arranged in close proximity to the transfer member (131), for
guiding the transfer material to a transfer position in the transfer member (131);
a transfer member supporting means urging mechanism (141), disposed in the cover member
(170), for resiliently urging the transfer member supporting means (130) toward the
image carrier supporting means (120); and
first positioning means (130a), disposed in part of the transfer member supporting
means (130), for positioning the transfer member supporting means (130) with respect
to the image carrier supporting means (120) by abutting against the image carrier
supporting means (120).
14. The image forming apparatus (110) of claim 13, wherein, in the transfer member supporting
means (130) is disposed a transfer member urging mechanism (142) for resiliently urging
the transfer member (131) toward the image carrier (121).
15. The image forming apparatus (110) of claim 14, wherein a first urging pressure, which
is exerted by the transfer member supporting means urging mechanism (141) in a direction
of the image carrier supporting means (120), is set to be greater than a second urging
pressure exerted by the transfer member urging mechanism (142) in the same direction.
16. The image forming apparatus (110) of claim 15, wherein the first urging pressure is
set to be 1.5 times or above greater than the second urging pressure.
17. The apparatus of claim 13, 14, 15, or 16, further comprising:
guide member supporting means (150a) for supporting the guide member (150) on the
transfer member supporting means (130); and
second positioning means (150b), disposed in part of the guide member (150), for positioning
the guide member (150) with respect to the image carrier supporting means (120) by
abutting against the image carrier supporting means (120).
18. The image forming apparatus (110) of claim 17, wherein an urging position in the transfer
member supporting means urging mechanism (141) is located in between the first positioning
means (130a) and the second positioning means (150b).
19. The apparatus of any one of claims 13 to 18, further comprising:
charge removal means (160) for removing charges remaining on the transfer material
after the transfer process, the charge removal means (160) being supported by the
transfer member supporting means (130).