BACKGROUND OF THE INVENTION
Field of the Invention
[0001] This invention relates to an image forming apparatus of the transverse transfer type
in which toner images are transferred to a printing paper in a direction perpendicular
to a direction of feed of the printing paper.
Description of the Related Art
[0002] Recently, image forming apparatuses of the toner type, capable of forming a clear
image with a high resolution, have been extensively used, and a representative example
of such apparatuses is a laser beam printer. Among such image forming apparatuses
of the toner type, an image forming apparatus of the transverse transfer type (disclosed,
for example, in Japanese Patent Unexamined Publication No. 4-69254), in which a toner
image-carrying member is rubbed or pressed against a printing paper in a direction
perpendicular to a direction of feed of the printing paper to thereby transfer toner
images bit by bit (or step by step) to the printing paper, is very suitable for achieving
a small-size design of the apparatus.
[0003] Such a conventional image forming apparatus of the transverse transfer type will
be described below.
[0004] Fig. 24 is a schematic view showing an image forming process in a conventional image
forming apparatus, and Fig. 25 is a schematic view showing a transfer process in a
conventional image forming apparatus.
[0005] The image forming process will be first described with reference to Fig. 24. A belt-like
toner image-carrying member 1, comprising a non-photosensitive material, is extended
by a plurality of rollers and so on to be disposed in a direction perpendicular to
a direction of feed of printing paper 2, and when forming an image, this toner image-carrying
member 1 is revolved in a direction indicated by arrows, so that toner images are
formed on the surface of the toner image-carrying member 1. The plurality of rollers
and so on, which extend the toner image-carrying member 1, include support rollers
3 and 4 (serving also as end rollers as described later), a displacement roller 5
suitably displaceable for adjusting the tension of the toner image-carrying member
1, and electrostatic latent image-forming means 6 for forming an electrostatic latent
image. The electrostatic latent image-forming means 6 comprises a photosensitive drum
6a, and exposure means (LED chip) for forming an electrostatic latent image on the
surface of the photosensitive drum 6a. A toner is not caused to adhere directly to
this electrostatic latent image, but the electrostatic latent image is used to form
a pseudo electrostatic latent image on the toner image-carrying member 1. By electric
lines of force produced by the electrostatic latent image, a pseudo electrostatic
latent image is formed on a surface of the toner image-carrying member 1 made in contact
with the photosensitive drum 6a, and developing means 7 is brought into contact with
this pseudo electrostatic latent image, thereby causing a toner to adhere to the pseudo
electrostatic latent image to form a toner image. This image forming method is much
like a method in which a magnet is put on a reverse surface of a paper sheet, and
iron powder is distributed over an obverse surface of the paper sheet, thereby forming
an image on the paper sheet.
[0006] Next, the transfer process will be described with reference to Fig. 25. When the
image forming operation for one step is finished in the image forming process, toner
images, formed on the toner image-carrying member 1, are brought to a region which
faces the printing paper 2 as the toner image-carrying member 1 revolves and extends
between the support rollers 3 and 4. During the image formation, a transfer opposed
roller 8 is kept retracted inwardly from the toner image-carrying member 1, and when
transferring the toner images to the printing paper 2, the transfer opposed roller
8 is pressed toward the printing paper 2 to come into contact with the toner image-carrying
member 1, and also the displacement roller 5 for adjusting the tension of the toner
image-carrying member 1 is moved toward the printing paper 2. The transfer opposed
roller 8, pressing the toner image-carrying member 1 against the printing paper 2,
is reciprocally movable in a direction perpendicular to the direction (that is, direction
perpendicular to the sheet of Fig. 25) of feed of the printing paper 2, and a transfer
region P is determined by the longest path of movement of the transfer opposed roller
8. This longest movement path is obtained when selecting the printing paper 2 having
the maximum printable width. Those rollers, which come closest to the transfer opposed
roller 8 respectively at the starting end and the terminal end of the longest movement
path, are the above-mentioned end rollers. Namely, the two end rollers are provided
respectively at the starting end and terminal end of the longest movement path, and
in this conventional construction, the support rollers 3 and 4 serve as the end rollers,
respectively.
[0007] In the transfer process of Fig. 25, the rotating transfer opposed roller 8 rotatingly
moves from left to right in the transfer region P between the support rollers 3 and
4 to transfer the toner images, formed on the toner image-carrying member 1, onto
the printing paper 2. At this time, a transfer finish surface Z of the toner image-carrying
member 1 where the transfer of the toner images has been finished is gradually moved
away from the printing paper 2 as the transfer opposed roller 8 passes the transfer
finish surface Z. In this conventional construction, the process of transferring the
toner images to the printing paper 2 and the process of fixing the toner images thus
transferred to the printing paper 2 are carried out simultaneously, and toner particles
on the printing paper 2 are fused by a heat source, provided either on the transfer
opposed roller 8 or a platen 9, to be fixed. After the transfer for one step is finished,
the transfer opposed roller 8 is again retracted inwardly from the toner image-carrying
member 1, and the above-mentioned image forming process is effected, and also the
printing paper 2 is fed by an amount corresponding to an effective transfer width
of the toner image-carrying member 1.
[0008] In the above conventional image forming apparatus, however, as shown in Fig. 25,
the transfer opposed roller 8 is brought into contact with the support rollers (end
rollers) 3 and 4 to be thus limited in movement, and therefore the transfer opposed
roller 8 can reciprocally move only in the transfer region P extending between the
support rollers 3 and 4. Thus non-transfer regions R where the transfer opposed roller
8 can not move are formed in a region corresponding to a longitudinal width Q of the
toner image-carrying member 1 determined by the arrangement of the support rollers
3 and 4. Therefore, when arranging the support rollers (end rollers) 3 and 4 which
determine the longitudinal width Q of the tone image-carrying member 1, not only the
transfer region P but also the right and left non-transfer regions R must be taken
into consideration, and there has been encountered a problem that these non-transfer
regions R hinder achievement of a compact design of the image forming apparatus.
SUMMARY OF THE INVENTION
[0009] It is therefore an object of this invention to provide an image forming apparatus
in which non-transfer regions where a transfer opposed roller can not move are eliminated
or reduced, thereby achieving a compact (small-size) design of an apparatus body.
[0010] To attain the above object, the invention provides an image forming apparatus of
transverse transfer type for transferring toner images, which are carried by a toner
image carrying member stretched around a plurality of rollers in a direction perpendicular
to a feeding direction of a printing paper, to the printing paper by means of a transfer
opposed roller to fix the toner images transferred to the printing paper, and wherein
at least one of rollers, which are among said rollers stretching said toner image
carrying member therearound but other than said transfer opposed roller and come closest
to said transfer opposed roller at starting and terminal ends of a longest movement
path of said transfer opposed roller, is spaced a greater distance than a diameter
of said transfer opposed roller from a surface of the printing paper, to which toner
images are transferred. With the above arrangement, a non-transfer region, in which
the transfer opposed roller cannot move, within a longitudinal width of the toner
image carrying member can be reduced, which makes a body of the image forming apparatus
small in size.
[0011] Also, the invention provides an image forming apparatus of transverse transfer type
for transferring toner images, which are carried by a toner image carrying member
stretched around a plurality of rollers in a direction perpendicular to a feeding
direction of a printing paper, to the printing paper by means of a transfer opposed
roller to fix the toner images transferred to the printing paper, and wherein while
said transfer opposed roller performs transfer of the toner images, that surface of
said toner image carrying member, on which transfer has finished, is not moved away
from the printing paper. With the above arrangement, the transfer finished surface
will not be loosened, so that tension of the toner image carrying member is kept constant
before and behind the transfer opposed roller to improve a transfer accuracy.
[0012] In an aspect of the invention, at least one of rollers, which are among the rollers
stretching said toner image carrying member therearound but other than the transfer
opposed roller and come closest to said transfer opposed roller at the starting and
terminal ends of the longest movement path of the transfer opposed roller, comprises
a displacement roller which is displaced following movements of the transfer opposed
roller. With the above arrangement, the displacement roller is improved in followability
with respect to the transfer opposed roller, and looseness of the toner image carrying
member caused by movements of the transfer opposed roller can be efficiently eliminated.
[0013] In another aspect of the invention, the toner image carrying member comprises a photosensitive
belt, and further comprising exposure means for exposing the toner image carrying
member in accordance with image signals, and developing means for developing the toner
image carrying member. With the above arrangement, a non-transfer region, in which
the transfer opposed roller cannot move, within a longitudinal width of the toner
image carrying member can be reduced, which makes a body of the image forming apparatus
small in size.
[0014] In further aspect of the invention, there are further provided exposure means for
simultaneously exposing the toner image carrying member at one line in accordance
with image signals for respective four primary colors, and developing means for providing
toners of respective four primary colors and forming toner layers on the same developing
roller for respective four primary colors. With the above arrangement, a non-transfer
region, in which the transfer opposed roller cannot move, within a longitudinal width
of the toner image carrying member can be reduced, which makes a body of the image
forming apparatus small in size.
[0015] In still another aspect of the invention, while the transfer opposed roller performs
transfer of the toner images, that surface of the toner image carrying member, on
which transfer has finished, is sequentially moved away from the printing paper. With
the above arrangement, a non-transfer region, in which the transfer opposed roller
cannot move, within a longitudinal width of the toner image carrying member can be
reduced, which makes a body of the image forming apparatus small in size.
[0016] In still further aspect of the invention, while transfer of the toner images is performed,
the rollers except for the transfer opposed roller and the displacement roller which
is displaced following movements of the transfer opposed roller to impart tension
to the toner image carrying member are rotated. With the above arrangement, looseness
of the transfer finished surface of the toner image carrying member during the transfer
of the toner images is actively taken to enable keeping tension of the toner image
carrying member before and behind the transfer opposed roller constant, so that slippage
of the transfer opposed roller is eliminated to improve a transfer accuracy.
[0017] In another aspect of the invention, while transfer of the toner images is performed,
the rollers except for the transfer opposed roller and the displacement roller which
is displaced following movements of the transfer opposed roller to impart tension
to the toner image carrying member are enabled to be rotated. With the above arrangement,
looseness of the transfer finished surface of the toner image carrying member during
the transfer of the toner images is actively taken to enable keeping tension of the
toner image carrying member before and behind the transfer opposed roller constant,
so that slippage of the transfer opposed roller is eliminated to improve a transfer
accuracy.
[0018] In further aspect of the invention, while the transfer opposed roller performs transfer
of the toner images, that surface of the toner image carrying member, on which transfer
has finished, is not moved away from the printing paper. With the above arrangement,
looseness of the transfer finished surface during the transfer of the toner images
is not produced, so that tension of the toner image carrying member is kept constant
before and behind the transfer opposed roller constant to improve a transfer accuracy.
[0019] In still another aspect of the invention, three or more rollers including the transfer
opposed roller and the displacement roller which is displaced following movements
of the transfer opposed roller revolve the toner image carrying member to form toner
images. With the above arrangement, a non-transfer region, in which the transfer opposed
roller cannot move, within a longitudinal width of the toner image carrying member
can be reduced, which makes a body of the image forming apparatus small in size.
[0020] In still further aspect of the invention, two or more rollers including the displacement
roller, which is displaced following movements of the transfer opposed roller, but
not including the transfer opposed roller revolve the toner image carrying member
to form toner images. With the above arrangement, the transfer opposed roller does
not revolve the toner image carrying member during the formation of images, so that
tension of the toner image carrying member is made more stable to improve an accuracy
of image formation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021]
Fig. 1 is a schematic view showing a construction of an image forming apparatus according
to a first embodiment of the invention;
Fig. 2 is a perspective view showing a transfer process performed in the image forming
apparatus of the first embodiment;
Figs. 3 and 4 are schematic views showing displacement of a toner image-carrying member
in the image forming apparatus of the first embodiment;
Fig. 5 is a schematic view showing fixing means of the image forming apparatus of
the first embodiment;
Fig. 6 is a schematic view showing a construction of an image forming apparatus according
to a second embodiment of the invention;
Fig. 7 is a perspective view showing a transfer process performed in the image forming
apparatus of the second embodiment;
Figs. 8 to 11 are schematic views showing displacement of a toner image-carrying member
in the image forming apparatus of the second embodiment;
Fig. 12 is a schematic view showing a construction of an image forming apparatus according
to a third embodiment of the invention;
Fig. 13 is a perspective view showing a transfer process performed in the image forming
apparatus of the third embodiment;
Figs. 14 to 17 are schematic views showing displacement of a toner image-carrying
member in the image forming apparatus of the third embodiment;
Fig. 18 is a schematic view showing a construction of an image forming apparatus according
to a fourth embodiment of the invention;
Fig. 19 is a perspective view showing a transfer process performed in the image forming
apparatus of the fourth embodiment;
Figs. 20 to 23 are schematic views showing the transfer process performed in the image
forming apparatus of the fourth embodiment;
Fig. 24 is a schematic view showing an image forming process performed in a conventional
image forming apparatus; and
Fig. 25 is a schematic view showing a transfer process performed in the conventional
image forming apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] Preferred embodiments of the present invention will now be described with reference
to Figs. 1 to 23, and those portions identical, respectively, to those of a conventional
construction will be designated by identical reference numerals, respectively.
[0023] In the present invention, those rollers, which come closest to a transfer opposed
roller at respective starting and terminal ends of a longest path of movement of the
transfer opposed roller (obtained when selecting a printing paper having a maximum
printable width) during an image transfer operation, will be called "end rollers",
respectively.
[0024] In a first embodiment of the present invention, left and right end rollers (disposed
at the starting end and the terminal end of the longest movement path) are provided
at such a height or level that the transfer opposed roller will not contact the left
and right end rollers, and with this arrangement limitations imposed on the end rollers
are eliminated, thereby totally eliminating non-transfer regions where the transfer
opposed roller can not move. The first embodiment of the present invention will now
be described in detail with reference to Figs. 1 to 5.
[0025] Fig. 1 is a schematic view showing a construction of an image forming apparatus according
to the first embodiment of the invention, and Fig. 2 is a perspective view showing
a transfer process performed in the image forming apparatus of the first embodiment.
Figs. 3 and 4 are schematic views showing displacement of a toner image-carrying member
in the image forming apparatus of the first embodiment, and Fig. 5 is a schematic
view showing fixing means of the image forming apparatus of the first embodiment.
[0026] In Figs. 1 and 2, the toner image-carrying member 10 is in the form of a photosensitive
belt having a surface coated with an organic photoconductive material, and is extended
by a plurality of rollers in a direction perpendicular to a direction of feed of printing
paper 2, and when forming images, this toner image-carrying member 10 is revolved
in a direction indicated by arrows, so that toner images are formed on the surface
of the toner image-carrying member 10. Static charging means 11, developing means
12, cleaning means 13, static eliminating means 14 and so on are provided around the
toner image-carrying member 10, and exposure means 15 for radiation of a laser beam
is provided above the toner image-carrying member 10. In this first embodiment, although
the exposure means 15 is described as typically using a laser, LED or LCD may be used
in the exposure means 15. When the toner image-carrying member 10 is revolved in the
direction (indicated by the arrows in Fig. 1) perpendicular to the direction of feed
of the printing paper 2, that portion of the toner image-carrying member 10 which
has passed past the static charging means 11 is electrically charged uniformly at
about -600 V, and a potential of that portion of the toner image-carrying member 10,
to which a laser beam is radiated from the exposure means 15 in accordance with an
image signal, rises to about -100 V, so that an electrostatic latent image is formed
on this portion. When a toner 12a is applied by a developing roller 12b to this portion
having the electrostatic latent image thereon, a toner image (visible image) 12c appears
on the toner image-carrying member 10. Thus, during the revolution of the toner image-carrying
member 10, the toner images 12c successively appear on the toner image-carrying member
10.
[0027] As shown in Fig. 1, during the image forming operation, the toner image-carrying
member 10 is extended by at least three rollers, that is, support roller 16, displacement
roller 17 and transfer opposed roller 18 in the direction perpendicular to the direction
of feed of the printing paper 2. A longest path of movement of the transfer opposed
roller 18 is obtained when selecting the printing paper 2 having a maximum printable
width, and those rollers, which come closest to the transfer opposed roller 18 at
respective starting and the terminal ends (i.e., left end and right end in Fig. 1)
of the longest movement path, are made the end rollers. In this first embodiment,
the support roller 16 and the displacement roller 17, which are provided respectively
at the left and right ends of the longest movement path, correspond to the end rollers,
respectively. The displacement roller 17 is suitably displaceable so as to adjust
tension of the toner image-carrying member 10, and the transfer opposed roller 18
rolls in opposed relation to a transfer plate 19 to transfer to the printing paper
2 the toner images 12c on the toner image-carrying member 10. In this first embodiment,
since the support roller 16 and the displacement roller 17, serving also as the end
rollers, are arranged at such a height as not to contact with the transfer opposed
roller 18, the non-transfer regions R, which have been problematic with the conventional
construction of Figs. 24 and 25 and in which the transfer opposed roller 18 can not
move, are eliminated. Therefore, the transfer opposed roller 18 can move between the
left end roller 16 and the right end roller 17, that is, over an entire longitudinal
width Q of the toner image-carrying member 10, so that a transfer region P where the
transfer opposed roller 18 can move is greatly increased.
[0028] In Figs. 3 and 4, the displacement roller 17 is displaced as the transfer opposed
roller 18 moves, and is displaced left and right so as to remove looseness of the
toner image-carrying member 10 due to the movement of the transfer opposed roller
18. For example, when the transfer opposed roller 18 moves from a left end A to an
intermediate point B as shown in Fig. 3, the displacement roller 17 moves from a left
end D to a right end E. When the transfer opposed roller 18 moves from the intermediate
point B to a right end C as shown in Fig. 4, the displacement roller 17 returns from
the right end E to the left end D. When forming the toner images on the toner image-carrying
member 10, the transfer opposed roller 18 is fixed at the left end A (Fig. 3) or the
right end C (Fig. 4), and the toner image-carrying member 10 is kept in a floating
condition as indicated by a solid line to be revolved without displacement, so that
the toner images 12c thereon are brought into opposed relation to the printing paper
2.
[0029] It is to be noted that the toner image-carrying member 10 is revolved when the transfer
opposed roller 18 is located at either the left end A or the right end C, and that
the toner image-carrying member 10 is stopped while the transfer opposed roller 18
moves over the printing paper 2. Namely, the revolution of the toner image-carrying
member 10 and the movement of the transfer opposed roller 18 are exclusive events
with respect to each other, and do not occur at the same time.
[0030] However, the exclusive events are theoretical, and actually in order to keep the
tension of the toner image-carrying member 10 at a constant level on the opposite
(front and rear) sides of the transfer opposed roller 18, the support roller 16 is,
in some cases, minutely rotated (almost slided), and strictly a slight discordance
occurs. A method of keeping the tension of the toner image-carrying member 10 at a
constant level before and behind the transfer opposed roller 18 will be described
in detail.
[0031] When the transfer opposed roller 18 moves from the left end A to the right end C
in the going path (or the going stroke) as shown in Figs. 3 and 4, a transfer finish
surface Z of the toner image-carrying member 10 develops on the left side (rear side)
of the transfer opposed roller 18 as the transfer opposed roller 18 moves. This transfer
finish surface Z is kept spaced from the printing paper 2 to be extended tense by
the transfer opposed roller 18 and the support roller 16. However, since the transfer
opposed roller 18 moves while being rotated, a forward portion (which has not yet
undergone transfer) of the toner image-carrying member 10 disposed in the direction
of advance of the transfer opposed roller 18 is pulled by the transfer opposed roller
18 to be increased in tension whereas the transfer finish surface Z, disposed rearwardly
of the transfer opposed roller 18 in the direction of advance, tends to be slightly
loosened to be reduced in tension. When a tension difference thus develops between
the forward and rearward portions of the toner image-carrying member 10 disposed,
respectively, before and behind the transfer opposed roller 18, the transfer opposed
roller 18 is liable to slip, so that the precision of transfer of the toner images
to the printing paper 2 is lowered. In order to prevent the transfer precision from
being lowered, the tension of the toner image-carrying member 10 need to be kept at
a constant level before and behind the transfer opposed roller 18 as much as possible,
and therefore the support roller 16, which is one of the two rollers for applying
a tension to the transfer finish surface Z, is minutely rotated in a direction (i.e.,
a clockwise direction indicated by an arrow in Figs. 3 and 4) to eliminate looseness
on the transfer finish surface Z, thereby increasing the tension of the transfer finish
surface Z. There are two methods of minutely rotating the support roller 16, and one
method (active method) is to rotate the support roller 16 by a drive force, and in
the other method (passive method), the support roller 16 affords a play to be made
rotatable in a direction to eliminate looseness of the transfer finish surface Z.
By adopting one of the two methods, the support roller 16 can be minutely rotated
to eliminate the looseness of the transfer finish surface Z, and therefore the tension
of the toner image-carrying member 10 can be kept at a constant level before and behind
the transfer opposed roller 18.
[0032] For transferring the toner images to the printing paper 2, as shown in Fig. 2, the
feed of the printing paper 2 is temporarily stopped to keep the printing paper 2 stationary
on the transfer plate 19 (see Fig. 1), and also the revolution of the toner image-carrying
member 10 is stopped. Then, those portions of the toner image-carrying member 10 on
which the toner images 12c (Fig. 1) are formed, respectively, are sequentially pressed
or rubbed against the printing paper 2 by rolling the transfer opposed roller 18 on
the reverse side of the toner image-carrying member 10, thereby transferring the toner
images 12c to the printing paper 2, and at this time the toner image-carrying member
10 is displaced from the left end to the right end or vice versa by an amount corresponding
to the transfer operation for one step. At this time, the transfer finish surface
Z of the toner image-carrying member 10 where the transfer of the toner images 12c
has been finished is gradually moved away from the printing paper 2 as the transfer
opposed roller 18 moves. During the transfer operation, the transfer plate 19, supporting
the printing paper 2 thereon, is applied with positive voltage to attract and separate
the negatively-charged toner images 12c from the surface of the toner image-carrying
member 10 to have the images transferred to the printing paper 2. The transfer operation
by the toner image-carrying member 10 can be effected not only in the going path,
but also in the return path (or the return stroke) as described above. At this time,
when viewing the direction of movement of the toner image-carrying member 10 from
the side of the printing paper 2, the toner image-carrying member 10 is displaced
on the printing paper 2 in a direction perpendicular to the direction of feed of the
printing paper 2.
[0033] Each time the transfer operation for one step is finished, the transfer opposed roller
18 passes over the printing paper 2, and moves to a region outside the printing paper
2, so that the toner image-carrying member 10 is spaced apart from the printing paper
2. Then, the feed of the printing paper 2 is started, and at this time the printing
paper 2 is fed in an amount corresponding to an effective transfer width M (see Fig.
2) of the toner image-carrying member 10.
[0034] The cleaning means 13 removes the residual toner on the surface of the toner image-carrying
member 10 by means of a cleaning blade or a cleaning brush, and the thus removed toner
is recovered as waste toner. Thus, the cleaning means 13 physically cleans the surface
of the toner image-carrying member 10. The static eliminating means 14 neutralizes
the negative charge remaining on the surface of the toner image-carrying member 10
from which the residual toner has been removed, thus electrically cleaning the surface
of the toner image-carrying member 10. The provision of the static eliminating means
14 is not essential.
[0035] After the above steps are repeated, the printing paper 2 is gradually fed to the
fixing means 20 as shown in Fig. 2. In the fixing means 20, the printing paper 2,
having the transferred images thereon, is held between a pressure roller 21 and a
heating roller 22 containing a heat source therein, and the toner particles are fused
by the heating roller 22 to be fixed to the printing paper 2. If this fixing operation
is effected after all the images are transferred to the printing paper 2, the printing
paper 2 is discharged without being stopped, and therefore the heat source of the
heating roller 22 may be kept turned on. However, if the images are in the course
of transfer to the printing paper 2, the printing paper 2 is in a stopped condition,
and therefore the heat source of the heating roller 22 need to be temporarily turned
off, or the heating roller 22 need to be moved away from the printing paper 2. Another
fixing method as shown in Fig. 5 may be used, in which fixing means 23 comprises a
heat source 24 and a reflection plate 25, and a reflection plate 26 is provided below
the fixing means 23 so as to enhance a thermal efficiency, thereby effecting fixation
without contacting with the toner. In the manner described above, a series of image
forming steps are finished.
[0036] As described above, in this first embodiment, the left and right end rollers (i.e.,
the support roller 16 and the displacement roller 17) are arranged at such a height
as not to contact with the transfer opposed roller 18, and with this arrangement the
non-transfer regions R, which has been problematic with the conventional construction
and in which the transfer opposed roller 18 can not move, is completely eliminated.
As a result, the longitudinal width Q of the tone image-carrying member 10 can be
reduced to a limit, so that the body of the image forming apparatus can be made small
in size.
[0037] In a second embodiment of the present invention, one end roller is provided at such
a height as not to contact with a transfer opposed roller, and with this arrangement
a limitation imposed on the one end roller is eliminated, thereby eliminating a non-transfer
region, in which the transfer opposed roller can not move, at one end of a path of
movement of the transfer opposed roller. In contrast with the conventional construction,
a transfer finish surface of a toner image-carrying member, for which the transfer
of toner images has been finished, is not moved away from printing paper even after
the transfer opposed roller passes the transfer finish surface, and therefore the
tension of the toner image-carrying member is kept constant before and behind the
transfer opposed roller, thereby enhancing the transfer precision. The second embodiment
of the present invention will now be described with reference to Fig. 6 to 11 and
Fig. 5.
[0038] Fig. 6 is a schematic view showing a construction of an image forming apparatus according
to the second embodiment of the invention, and Fig. 7 is a perspective view showing
a transfer process performed in the image forming apparatus of the second embodiment.
Figs. 8 to 11 are schematic views showing displacement of a toner image-carrying member
in the image forming apparatus of the second embodiment.
[0039] In Figs. 6 to 7, the toner image-carrying member 10 comprising a photosensitive belt
having a surface coated with an organic photoconductive material is extended by a
plurality of rollers in a direction perpendicular to a direction of feed of printing
paper 2, and when forming images, this toner image-carrying member 10 is revolved
in a direction indicated by arrows, so that toner images are formed on the surface
of the toner image-carrying member 10. This second embodiment differs from the first
embodiment in that the toner image-carrying member 10 is extended obliquely (that
is, in a slanting manner), and with this arrangement the transfer finish surface Z
(see Fig. 7) is not moved away from the printing paper 2 as described later. Static
charging means 11, developing means 12, cleaning means 13, static eliminating means
14 and so on are provided around the toner image-carrying member 10, and exposure
means 15 for radiation of a laser beam is provided above the toner image-carrying
member 10. In this second embodiment, the exposure means 15 typically uses a laser,
while LED or LCD may be used in the exposure means 15. When the toner image-carrying
member 10 is revolved in the direction (indicated by the arrows in Fig. 6) perpendicular
to the direction of feed of the printing paper 2, that portion of the toner image-carrying
member 10, which has passed past the static charging means 11, is electrically charged
uniformly at about -600 V, and a potential of that portion of the toner image-carrying
member 10, to which a laser beam is radiated from the exposure means 15 in accordance
with an image signal, rises to about -100 V to cause an electrostatic latent image
to be formed on this portion. When a toner 12a is applied by a developing roller 12b
to this portion having the electrostatic latent image thereon, a toner image (visible
image) 12c appears on the toner image-carrying member 10. Thus, during the revolution
of the toner image-carrying member 10, the toner images 12c successively appear on
the toner image-carrying member 10.
[0040] As shown in Fig. 6, during the image forming operation, the toner image-carrying
member 10 is extended by at least three rollers, that is, support roller 16, displacement
roller 17 and transfer opposed roller 18, in the direction perpendicular to the direction
of feed of the printing paper 2. A longest path of movement of the transfer opposed
roller 18 is obtained when selecting the printing paper 2 having a maximum printable
width, and those rollers, which come closest to the transfer opposed roller 18 at
respective starting and terminal ends (i.e., left end and right end in Fig. 6) of
the longest movement path, are made the end rollers. In this second embodiment, the
support roller 16 and the displacement roller 17, which are provided respectively
at the left and right ends of the longest movement path, serve as the end rollers,
respectively. The displacement roller 17 is suitably displaceable so as to adjust
tension of the toner image-carrying member 10, and the transfer opposed roller 18
rolls in opposed relation to a transfer plate 19 to transfer the toner images 12c
to the printing paper 2. In this second embodiment, since one of the end rollers,
i.e., the support roller 16 and the displacement roller 17, that is, the displacement
roller 17, is arranged at such a height as not to contact with the transfer opposed
roller 18, one (that is, the right non-transfer region) of the non-transfer regions
R (which have been problematic with the conventional construction of Figs. 24 and
25), in which the transfer opposed roller 18 can not move, is removed. Therefore,
the transfer opposed roller 18 can move beyond the displacement roller (end roller)
17, that is, to the right end of the entire longitudinal width Q of the toner image-carrying
member 10, so that a transfer region P, in which the transfer opposed roller 18 can
move is greatly increased.
[0041] In Figs. 8 and 9, the displacement roller 17 is displaced in accordance with the
movement of the transfer opposed roller 18, and is displaced obliquely so as to eliminate
the looseness of the toner image-carrying member 10 caused due to the movement of
the transfer opposed roller 18, thereby keeping the tension of the toner image-carrying
member 10 at a constant level. For example, when the transfer opposed roller 18 moves
from a left end A to an intermediate point B as shown in Fig. 8, the displacement
roller 17 moves obliquely from a right end F to an intermediate point G. When the
transfer opposed roller 18 moves from the intermediate point B to a right end C as
shown in Fig. 9, the displacement roller 17 moves obliquely from the intermediate
point G to a left end H.
[0042] When the transfer opposed roller 18 moves from the left end A to the right end C,
the image transfer operation for one step is finished, and therefore the transfer
opposed roller 18 is returned to the position shown in a solid line in Fig. 8 so that
the image formation operation can be effected. This returning movement of the transfer
opposed roller 18 will be described with reference to Figs. 10 and 11. As indicated
in solid lines in Fig. 10, the displacement roller 17 moves right obliquely from the
left end H, and also the transfer opposed roller 18 floats off the right end C, so
that the transfer finished surface Z of the toner image-carrying member 10, held in
intimate contact with the printing paper 2, is moved away from the printing paper
2 in a manner to form an angle between the transfer finish surface Z and the printing
paper 2. The displacement roller 17 further approaches the right end F, and also the
transfer opposed roller 18 approaches the left end A in parallel relation to the printing
paper 2, and at this time the transfer finished surface Z of the toner image-carrying
member 10 never contacts the printing paper 2. The transfer opposed roller 18 is moved
parallel to the printing paper 2 until it reaches a position indicated by a broken
line in Fig. 11, and after the transfer opposed roller 18 reaches this position indicated
by the broken line, it moves downward to return to a position indicated by a solid
line in Fig. 11 and also in Fig. 8. The transfer opposed roller 18 is moved along
the path shown in Figs. 8 to 11 when the transfer operation for one step is effected,
and in this second embodiment, the transfer of the images is effected only in the
going path (or the going stroke) of the transfer opposed roller 18 shown in Figs.
8 and 9, and is not effected in the return path (or the return stroke) shown in Figs.
10 and 11. The second embodiment differs in this respect from the first embodiment.
[0043] The second embodiment further differs from the first embodiment in that the transfer
finished surface Z is held in intimate contact with the printing paper 2 during the
transfer of the toner images to the printing surface 2, as shown in Figs. 8 and 9.
Therefore, that portion (which has not yet been transferred) of the toner image-carrying
member 10 disposed forwardly of the transfer opposed roller 18 in the direction of
advance of the transfer opposed roller 18 is pulled by the transfer opposed roller
18 to have an increased tension, and the transfer finished surface Z, extended between
the transfer opposed roller 18 and the support roller 16 and held in intimate contact
with the printing paper 2, is also pulled by the transfer opposed roller 18 to have
an increased tension. Namely, the toner image-carrying member 10 is pulled by the
transfer opposed roller 18 before and behind the transfer opposed roller 18, so that
the tension of the toner image-carrying member 10 is kept at the constant level. Therefore,
unlike (the first embodiment) it is not necessary to minutely rotate the support roller
16 so as to eliminate the looseness of the transfer finished surface Z.
[0044] In the second embodiment, when forming the toner images on the toner image-carrying
member 10, the transfer opposed roller 18 is fixed at the left end A as shown in Fig.
8, and the toner image-carrying member 10 is kept in a floated condition as indicated
in a solid line, and is revolved without displacement, so that the toner images 12c
thereon are brought into opposed relation to the printing paper 2.
[0045] It is to be noted that the toner image-carrying member 10 is revolved only when the
transfer opposed roller 18 is fixed at the left end A, and the toner image-carrying
member 10 is completely out of contact with the printing paper 2. When the transfer
opposed roller 18 moves over the printing paper 2 to form the transfer finish surface
Z on the toner image-carrying member 10 (and when the transfer opposed roller 18 has
finished its going stroke, and is fixed at the right end C), the revolution of the
toner image-carrying member 10 is stopped. Namely, the revolution of the toner image-carrying
member 10 and the formation of the transfer finished surface Z are exclusive events
with respect to each other, and do not occur at the same time.
[0046] For transferring the toner images to the printing paper 2, as shown in Fig. 7, the
feed of the printing paper 2 is temporarily stopped to keep the printing paper 2 stationary
on the transfer plate 19 (see Fig. 6), and also the revolution of the toner image-carrying
member 10 is stopped. Then, those portions of the toner image-carrying member 10,
on which the toner images 12c are formed, respectively, are sequentially pressed or
rubbed against the printing paper 2 by rolling the transfer opposed roller 18 on the
reverse side of the toner image-carrying member 10, thereby transferring the toner
images 12c to the printing paper 2, and at this time the toner image-carrying member
10 is displaced from the left end to the right end to effect the transfer operation
for one step. At this time, the transfer finished surface Z of the toner image-carrying
member 10 having finished the transfer of the toner images 12c is not moved away from
the printing paper 2, but is held in intimate contact with the printing paper 2 even
after the transfer opposed roller 18 passes the transfer finished surface Z. During
the transfer operation, the transfer plate 19, supporting the printing paper 2 thereon,
is applied with positive voltage, and attracts the negatively-charged toner images
12c, so that the toner images 12c are separated from the surface of the toner image-carrying
member 10, and are transferred to the printing paper 2. In this second embodiment,
the transfer operation performed by the toner image-carrying member 10 can be effected
only in the going path as described above. At this time, when viewing the direction
of movement of the toner image-carrying member 10 from the side of the printing paper
2, the toner image-carrying member 10 is displaced on the printing paper 2 in a direction
perpendicular to the direction of feed of the printing paper 2.
[0047] Each time the transfer opposed roller 18 is returned to the position indicated by
the solid line in Fig. 11 after the transfer operation for one step is finished, the
feed of the printing paper 2 is started, and at this time the printing paper 2 is
fed a distance corresponding to an effective transfer width M (see Fig. 7) of the
toner image-carrying member 10.
[0048] The cleaning means 13 removes the residual toner on the surface of the toner image-carrying
member 10 by a cleaning blade or a cleaning brush, and the thus removed toner is recovered
as waste toner. Thus, the cleaning means 13 physically cleans the surface of the toner
image-carrying member 10. The static eliminating means 14 neutralizes the negative
charge residing on the surface of the toner image-carrying member 10, from which the
residual toner has been removed, thus electrically cleaning the surface of the toner
image-carrying member 10. The provision of the static eliminating means 14 is not
essential.
[0049] After the above steps are repeated, the printing paper 2 is gradually fed to the
fixing means 20 as shown in Fig. 7. In the fixing means 20, the printing paper 2,
having the transferred images thereon, is held between a pressure roller 21 and a
heating roller 22 containing a heat source therein, and the toner particles are fused
by the heating roller 22 to be fixed to the printing paper 2. If this fixing operation
is effected after all the images are transferred to the printing paper 2, the printing
paper 2 is discharged without being stopped, and therefore the heat source of the
heating roller 22 is kept turned on. However, if the images are in the process of
being transferred to the printing paper 2, the printing paper 2 is in a stopped condition,
and therefore the heat source of the heating roller 22 needs to be temporarily turned
off, or the heating roller 22 needs to be moved away from the printing paper 2. Another
fixing method as shown in Fig. 5 may be used, in which fixing means 23 comprises the
heat source 24 and the reflection plate 25, and the reflection plate 26 is provided
below the fixing means 23 so as to enhance a heat efficiency, thereby fixing the toner
without contact with the toner. In the manner described above, a sequence of image
forming steps are finished.
[0050] As described above, in this second embodiment, one of the two end rollers (i.e.,
the support roller 16 and the displacement roller 17), that is, the displacement roller
17, is arranged at such a height as not to contact with the transfer opposed roller
18, and with this arrangement the non-transfer region R, which has been problematic
with the conventional construction and in which the transfer opposed roller 18 can
not move, can be reduced at that side of the displacement roller 17. As a result,
the longitudinal width Q of the tone image-carrying member 10 can be considerably
reduced, so that the body of the image forming apparatus can be of a smaller size.
And besides, during the transfer operation, the transfer finished surface Z of the
toner image-carrying member 10 is not separated from the printing surface 2, but is
held in intimate contact with the printing paper 2, and therefore the transfer finished
surface Z will not be loosened, so that the tension of the toner image-carrying member
10 is kept at the constant level before and behind the transfer opposed roller 18,
thereby enhancing the transfer precision.
[0051] A third embodiment of the present invention is generally similar to the second embodiment,
and in the third embodiment, one of end rollers is provided at such a height as not
to contact a transfer opposed roller, and with this arrangement a limitation imposed
on the one of end rollers is eliminated, thereby eliminating a non-transfer region,
in which the transfer opposed roller can not move, at one end of a path of movement
of the transfer opposed roller. Unlike the conventional construction, a transfer finished
surface of a toner image-carrying member where the transfer of toner images has been
finished is not moved away from printing paper even after the transfer opposed roller
passes the transfer finished surface, and therefore the tension of the toner image-carrying
member is kept constant before and behind the transfer opposed roller, thereby enhancing
the transfer precision. However, the third embodiment differs from the second embodiment
in that the toner image-carrying member is revolved by at least two rollers including
the displacement roller but not including the transfer opposed roller, so as to form
toner images. When forming the images, the transfer opposed roller is not used, and
therefore the tension of the toner image-carrying member is stabilized, thereby further
enhancing the image forming precision. The third embodiment of the present invention
will now be described with reference to Fig. 12 to 17 and Fig. 5.
[0052] Fig. 12 is a schematic view showing the construction of an image forming apparatus
according to the third embodiment of the invention, and Fig. 13 is a perspective view
showing a transfer process by the image forming apparatus of the third embodiment.
Figs. 14 to 17 are schematic views showing displacement of a toner image-carrying
member in the image forming apparatus of the third embodiment.
[0053] In Figs. 12 to 13, the toner image-carrying member 10 in the form of a photosensitive
belt having a surface coated with an organic photoconductive material, is extended
by a plurality of rollers in a direction perpendicular to a direction of feed of printing
paper 2, and when forming images, this toner image-carrying member 10 is revolved
in a direction indicated by arrows, so that toner images are formed on the surface
of the toner image-carrying member 10. This third embodiment differs from the first
embodiment in that the toner image-carrying member 10 is extended obliquely (that
is, in a slanting manner), and with this arrangement the transfer finished surface
Z (see Fig. 13) is not moved away from the printing paper 2 as described later. Static
charging means 11, developing means 12, cleaning means 13, static eliminating means
14 and so on are provided around the toner image-carrying member 10, and exposure
means 15 for applying a laser beam is provided above the toner image-carrying member
10. In this third embodiment, the exposure means 15 uses a laser while LED or LCD
may be used for the exposure means 15. When the toner image-carrying member 10 is
revolved in the direction (indicated by the arrows in Fig. 12) perpendicular to the
direction of feed of the printing paper 2, that portion of the toner image-carrying
member 10 passed past the static charging means 11 is electrically charged uniformly
at about -600 V, and the potential of that portion of the toner image-carrying member
10, to which a laser beam is applied from the exposure means 15 in accordance with
an image signal, rises to about -100 V, so that an electrostatic latent image is formed
on this portion. When a toner 12a is applied by a developing roller 12b to a portion
having the electrostatic latent image thereon, a toner image (visible image) 12c appears
on the toner image-carrying member 10. Thus, during the revolution of the toner image-carrying
member 10, the toner images 12c successively appear on the toner image-carrying member
10.
[0054] As shown in Fig. 12, during the image forming operation, the toner image-carrying
member 10 is extended by at least two rollers (that is, support roller 16 and displacement
roller 17) in the direction perpendicular to the direction of feed of the printing
paper 2. The third embodiment is different from the first embodiment in that during
the image forming operation, the transfer opposed roller 18 is retracted inside the
toner image-carrying member 10, and does not serve as a roller for extending the toner
image-carrying member 10. The longest path of movement of the transfer opposed roller
18 is obtained when selecting the printing paper 2 having a maximum printable width,
and those rollers, which come closest to the transfer opposed roller 18 respectively
at the starting and terminal ends (i.e., left end and right end in Fig. 12) of the
longest movement path, serve as end rollers. In the third embodiment, the support
roller 16 and the displacement roller 17, which are provided respectively at the left
and right ends of the longest movement path, serve as the end rollers, respectively.
The displacement roller 17 is suitably displaceable during the transfer operation
so as to adjust the tension of the toner image-carrying member 10, and the transfer
opposed roller 18 rolls in opposed relation to a transfer plate 19 to transfer the
toner images 12c from the toner image-carrying member 10 to the printing paper 2.
In the third embodiment, since one of the end rollers (i.e., the support roller 16
and the displacement roller 17), that is, the displacement roller 17, is arranged
at such a height as not to contact the transfer opposed roller 18, one (that is, the
right non-transfer region) of the non-transfer regions R, which have been problematic
with the conventional construction of Figs. 24 and 25 and in which the transfer opposed
roller 18 can not move is eliminated. Therefore, the transfer opposed roller 18 can
move beyond the displacement roller (end roller) 17, that is, to the right end of
the entire longitudinal width Q of the toner image-carrying member 10, so that a transfer
region P, in which the transfer opposed roller 18 can move, is greatly increased.
[0055] In Figs. 14 and 15, the displacement roller 17 is displaced in accordance with the
movement of the transfer opposed roller 18, and is displaced obliquely so as to eliminate
looseness of the toner image-carrying member 10 due to the movement of the transfer
opposed roller 18, thereby keeping the tension of the toner image-carrying member
10 at a constant level. For example, when the transfer opposed roller 18 moves downward
to a left end A from a retracted position inside the toner image-carrying member 10,
and further moves from the left end A to an intermediate point B as shown in Fig.
14, the displacement roller 17 moves obliquely from a right end F to an intermediate
point G. When the transfer opposed roller 18 moves from the intermediate point B to
a right end C as shown in Fig. 15, the displacement roller 17 moves obliquely from
the intermediate point G to a left end H.
[0056] When the transfer opposed roller 18 moves from the left end A to the right end C,
the image transfer operation for one step is finished, and therefore the transfer
opposed roller 18 is returned to the retracted position inside the toner image-carrying
member 10, as indicated in a solid line in Fig. 14, so that the image formation operation
can be effected. This returning movement of the transfer opposed roller 18 will be
described with reference to Figs. 16 and 17. As indicated in solid lines in Fig. 16,
the displacement roller 17 moves right obliquely from the left end H, and also the
transfer opposed roller 18 floats off the right end C, so that the transfer finished
surface Z of the toner image-carrying member 10, having been held in intimate contact
with the printing paper 2, is moved away from the printing paper 2 in a manner to
form an angle between the transfer finished surface Z and the printing paper 2. The
displacement roller 17 further approaches the right end F, and also the transfer opposed
roller 18 approaches the left end A in parallel relation to the printing paper 2,
and at this time the transfer finished surface Z of the toner image-carrying member
10 never contacts the printing paper 2. The transfer opposed roller 18 is moved parallel
to the printing paper 2 as indicated by a broken line in Fig. 17, and is returned
to the retracted position inside the toner image-carrying member 10 as indicated in
a solid line in Fig. 17 and also in Fig. 14. The transfer opposed roller 18 is moved
along the path shown in Figs. 14 and 17 when the transfer operation for one step is
effected, and in the third embodiment, the transfer of the images is effected only
in the going path (or the going stroke) of the transfer opposed roller 18 shown in
Figs. 14 and 15, and is not effected in the return path (or the return stroke) shown
in Figs. 16 and 17. The third embodiment differs in this respect from the first embodiment.
[0057] The third embodiment further differs from the first embodiment in that the transfer
finished surface Z is held in intimate contact with the printing paper 2 during the
transfer of the toner images to the printing surface 2, as shown in Figs. 14 and 15.
Therefore, that portion (which has not yet undergone transfer) of the toner image-carrying
member 10 disposed forwardly of the transfer opposed roller 18 in the direction of
advance of the transfer opposed roller 18 is pulled by the transfer opposed roller
18 to have an increased tension, and the transfer finished surface Z, extended between
the transfer opposed roller 18 and the support roller 16 and held in intimate contact
with the printing paper 2, is also pulled by the transfer opposed roller 18 to have
an increased tension. Namely, the toner image-carrying member 10 is pulled by the
transfer opposed roller 18 before and behind the transfer opposed roller 18, so that
the tension of the toner image-carrying member 10 is kept at the constant level. Therefore,
it is not necessary to minutely rotate the support roller 16 so as to eliminate looseness
of the transfer finished surface Z as in the first embodiment.
[0058] In the third embodiment, when forming the toner images on the toner image-carrying
member 10, the transfer opposed roller 18 is held in the retracted position inside
the toner image-carrying member 10 as shown in Fig. 14, and the toner image-carrying
member 10 is kept in a floated condition as indicated in a solid line, and is revolved
without displacement, so that the toner images 12c thereon are taken to the opposed
surface of the printing paper 2.
[0059] It is to be noted that the toner image-carrying member 10 is revolved only when the
transfer opposed roller 18 is disposed in the retracted position inside the toner
image-carrying member 10, and the toner image-carrying member 10 is completely out
of contact with the printing paper 2. When the transfer opposed roller 18 moves over
the printing paper 2 and the transfer finished surface Z is formed on the toner image-carrying
member 10 (and when the transfer opposed roller 18 has finished its going stroke,
and is fixed at the right end C), the revolution of the toner image-carrying member
10 is stopped. Namely, the revolution of the toner image-carrying member 10 and the
formation of the transfer finished surface Z are exclusive events with respect to
each other, and do not occur at the same time.
[0060] For transferring the toner images to the printing paper 2, as shown in Fig. 13, the
feed of the printing paper 2 is temporarily stopped to keep the printing paper 2 stationary
on the transfer plate 19 (see Fig. 12), and also the revolution of the toner image-carrying
member 10 is stopped. Then, those portions of the toner image-carrying member 10 on
which the toner images 12c are formed, respectively, are sequentially pressed or rubbed
against the printing paper 2 by rolling the transfer opposed roller 18 on the reverse
side of the toner image-carrying member 10, thereby transferring the toner images
12c to the printing paper 2, and at this time the toner image-carrying member 10 is
displaced from the left end to the right end to effect the transfer operation for
one step. At this time, the transfer finished surface Z of the toner image-carrying
member 10, on which the transfer of the toner images 12c has been finished, is not
moved away from the printing paper 2, but is held in intimate contact with the printing
paper 2 even after the transfer opposed roller 18 passes the transfer finished surface
Z. During the transfer operation, the transfer plate 19, supporting the printing paper
2 thereon, is applied with positive voltage, and attracts and separates the negatively-charged
toner images 12c from the surface of the toner image-carrying member 10 to have the
images transferred to the printing paper 2. In the third embodiment, the transfer
operation by the toner image-carrying member 10 can be effected only in the going
path of the transfer opposed roller 18 as described above. At this time, when viewing
the direction of movement of the toner image-carrying member 10 from the side of the
printing paper 2, the toner image-carrying member 10 is displaced on the printing
paper 2 in a direction perpendicular to the direction of feed of the printing paper
2.
[0061] Each time the transfer opposed roller 18 is returned to the position indicated by
the solid line in Fig. 17 after the transfer operation for one step is finished, the
feed of the printing paper 2 is started, and at this time the printing paper 2 is
fed a distance corresponding to an effective transfer width M (see Fig. 13) of the
toner image-carrying member 10.
[0062] The cleaning means 13 removes the residual toner on the surface of the toner image-carrying
member 10 by a cleaning blade or a cleaning brush, and the thus removed toner is recovered
as waste toner. Thus, the cleaning means 13 physically cleans the surface of the toner
image-carrying member 10. The static eliminating means 14 neutralizes the negative
charge residing on the surface of the toner image-carrying member 10 from which the
residual toner has been removed, thus electrically cleaning the surface of the toner
image-carrying member 10. The provision of the static eliminating means 14 is not
essential.
[0063] After the above steps are repeated, the printing paper 2 is gradually fed to the
fixing means 20 as shown in Fig. 13. In the fixing means 20, the printing paper 2,
having the transferred images thereon, is interposed between a pressure roller 21
and a heating roller 22 containing a heat source therein, and the toner particles
are fused by the heating roller 22 to be fixed to the printing paper 2. If this fixing
operation is effected after all the images are transferred to the printing paper 2,
the printing paper 2 is discharged without being stopped, and therefore the heat source
of the heating roller 22 is kept turned on. However, if the images are in the process
of being transferred to the printing paper 2, the printing paper 2 is in a stopped
condition, and therefore the heat source of the heating roller 22 needs to be temporarily
turned off, or the heating roller 22 needs to be moved away from the printing paper
2. Another fixing method as shown in Fig. 5 may be used, in which fixing means 23
comprises the heat source 24 and the reflection plate 25 which is provided below the
fixing means 23, so as to enhance a heat efficiency, thereby fixing the toner in non-contact
manner. In the manner described above, a sequence of image forming steps are finished.
[0064] As described above, in the third embodiment, one of the two end rollers (i.e., the
support roller 16 and the displacement roller 17), that is, the displacement roller
17, is arranged at such a height as not to contact the transfer opposed roller 18,
and with this arrangement the non-transfer region R which has been problematic with
the conventional construction and in which the transfer opposed roller 18 can not
move, is eliminated on that side where the displacement roller 17 is provided, as
in the second embodiment. As a result, the longitudinal width Q of the tone image-carrying
member 10 can be considerably reduced, so that the body of the image forming apparatus
can be made smaller is size. And besides, during the transfer operation, the transfer
finished surface Z of the toner image-carrying member 10 is not separated from the
printing surface 2, but is held in intimate contact with the printing paper 2, and
therefore the transfer finished surface Z will not be loosened, so that the tension
of the toner image-carrying member 10 is kept at the constant level before and behind
the transfer opposed roller 18, thereby enhancing the transfer precision.
[0065] The third embodiment differs from the second embodiment in that the toner image-carrying
member 10 is revolved by at least two rollers including the displacement roller 17
but not including the transfer opposed roller 18, so as to form toner images. When
forming the images, the transfer opposed roller 18 is not used, and therefore the
tension of the toner image-carrying member 10 is stabilized, thereby further enhancing
the image forming precision.
[0066] A fourth embodiment of the invention is outlined as follows: The developing means,
used in the first to third embodiments, is divided into four portions so as to accommodate
color images. A basic construction of the fourth embodiment is similar to those of
the first to third embodiments, and therefore as a specific example, there is provided
a construction in which the developing means of the first embodiment is divided into
four portions for accommodating color images, and only the color image-processing
portions will be described in detail, and remaining portions will not be described
in detail since these will be easily appreciated from the first to third embodiments.
The fourth embodiment of the present invention will now be described with reference
to Figs. 18 to 23 and Fig. 5.
[0067] Fig. 18 is a schematic view showing a construction of an image forming apparatus
according to the fourth embodiment of the invention, and Fig. 19 is a perspective
view showing a transfer process in the image forming apparatus of the fourth embodiment.
Figs. 20 to 23 are schematic views showing the transfer process in the image forming
apparatus of the fourth embodiment.
[0068] In Figs. 18 and 19, a toner image-carrying member 10 in the form of a photosensitive
belt having a surface coated with an organic photoconductive material, is extended
by a plurality of rollers in a direction perpendicular to a direction of feed of printing
paper 2, and when forming images, this toner image-carrying member 10 is revolved
in a direction indicated by arrows to permit toner images to be formed on the surface
of the toner image-carrying member 10. Static charging means 11, developing means
27, cleaning means 13, static eliminating means 14 and so on are provided around the
toner image-carrying member 10, and exposure means 15 for radiating a laser beam is
provided above the toner image-carrying member 10. In this fourth embodiment, the
exposure means 15 typically uses a laser while LED or LCD may be used for the exposure
means 15. When the toner image-carrying member 10 is revolved in the direction, indicated
by the arrows in Fig. 18, perpendicular to the direction of feed of the printing paper
2, that portion of the toner image-carrying member 10 having passed past the static
charging means 11 is electrically charged uniformly at about -600 V. In accordance
with image signals, respectively, corresponding to four primary colors including cyan,
magenta, yellow and black, laser beams, respectively, corresponding respectively to
the four primary colors, are radiated in a line to the surface of the toner image-carrying
member 10. Potential of that portion of the toner image-carrying member 10, to which
the laser beams have been radiated, rises to about -100 V, so that electrostatic latent
images, distinguished from one another in accordance with the four primary colors,
are formed simultaneously on the surface of the toner image-carrying member 10. When
toners of four primary colors are applied by a developing roller 28 to the portion
having the electrostatic latent images formed thereon, a color toner image (visible
image) appears on the toner image-carrying member 10, and in this manner the color
toner images successively appear on the toner image-carrying member 10.
[0069] The developing means 27 comprises four sections, respectively, corresponding to the
four primary colors, and four developing means 27C, 27M, 27Y and 27B contain a cyan
toner, a magenta toner, a yellow toner and a black toner, respectively, to form four
separate toner layers of the four primary colors (cyan, magenta, yellow and black),
respectively, on the common developing roller 28. Actually, a gap is formed between
two adjacent ones of the four separate toner layers of the four primary colors, and
a ratio of a width of each toner layer to the gap is, for example, 1:1, 2:1 or 3:1.
However, for simplifying the description, it is assume that the four separate toner
layers of the four primary colors are formed ideally without any gap between two adjacent
toner layers. The printing paper 2 is fed a distant corresponding to a width of one
color toner layer.
[0070] In the fourth embodiment, the four primary colors are developed at the same time
by the common developing roller 28 having the four separate toner layers of the four
primary colors formed thereon. In the developing operation, in order to convert the
electrostatic latent images, respectively, corresponding to the four primary colors,
into respective visible images, the developing roller 28, having the negatively-charged
four toner layers of the four primary colors adhered thereto, is pressed against the
toner image-carrying member 10, so that the four primary color toners are transferred
to the electrostatic latent images distinguished from one another for the four primary
colors, thereby forming the toner images of the four primary colors (cyan, magenta,
yellow and black) distinguished from one another for the four primary colors.
[0071] In transferring the toner images to the printing paper 2, as shown in Fig. 19, the
feed of the printing paper 2 is temporarily stopped to keep the printing paper 2 stationary
on a transfer plate 19 (see Fig. 18), and also the revolution of the toner image-carrying
member 10 is stopped. Then, those portions of the toner image-carrying member 10,
on which the color toner images are formed, are sequentially pressed or rubbed against
the printing paper 2 by rolling a transfer opposed roller 18 on the reverse side of
the toner image-carrying member 10, thereby transferring the color toner images to
the printing paper 2, and at this time the toner image-carrying member 10 is displaced
from the left end to the right end or vice versa a distance corresponding to one step.
At this time, a transfer finished surface Z of the toner image-carrying member 10,
for which the transfer of the color toner images has been finished, is gradually moved
away from the printing paper 2 as the transfer opposed roller 18 passes. During the
transfer operation, the transfer plate 19, supporting the printing paper 2 thereon,
is applied with positive voltage, and attracts and separates the negatively-charged
color toner images from the surface of the toner image-carrying member 10 to have
the images transferred to the printing paper 2. The transfer operation by the toner
image-carrying member 10 can be effected not only in the going path, but also in the
return path (or the return stroke) as described above. At this time, when viewing
the direction of movement of the toner image-carrying member 10 from the side of the
printing paper 2, the toner image-carrying member 10 is displaced on the printing
paper 2 in a direction perpendicular to the direction of feed of the printing paper
2.
[0072] Each time the transfer operation for one step is finished, the transfer opposed roller
18 passes over the printing paper 2 to a region outside the printing paper 2, so that
the toner image-carrying member 10 is spaced apart from the printing paper 2. Then,
the feed of the printing paper 2 is started, and at this time the printing paper 2
is fed a distance corresponding to a width of one color toner layer.
[0073] In the method of forming color toner images in the fourth embodiment, first, only
the black toner image is transferred in one step as shown in Fig. 20. In the next
step shown in Fig. 21, the black and yellow toner images are transferred such that
the black and yellow toner layers are superimposed in a first row. Similarly, in the
next step shown in Fig. 22, the black, yellow and magenta toner images are transferred
such that the black, yellow and magenta toner images are superimposed in the first
row, and the black and yellow toner images are superimposed in a second row. In the
next step shown in Fig. 23, the black, yellow, magenta and cyan toner images are transferred
such that a color (multi-color) image is formed in the first row by the superimposed
black, yellow, magenta and cyan toner images, the black, yellow and magenta toner
images are superimposed in the second row, and the black and yellow toner images are
superimposed in a third row. At subsequent steps, the transfer operation is carried
out in a reverse manner. More specifically, in the next step, the yellow, magenta
and cyan toner images except for the black toner image are transferred, and in the
next step, the magenta and cyan toner images (further except for the yellow toner
image) are transferred, and finally only the cyan toner image is transferred.
[0074] The cleaning means 13 removes the residual toner on the surface of the toner image-carrying
member 10 by a cleaning blade or a cleaning brush to recover the same as waste toner.
Thus, the cleaning means 13 physically cleans the surface of the toner image-carrying
member 10. The static eliminating means 14 neutralizes the negative charge residing
on the surface of the toner image-carrying member 10, from which the residual toner
has been removed, thus electrically cleaning the surface of the toner image-carrying
member 10. The provision of the static eliminating means 14 is not essential.
[0075] After the above steps are repeated, the printing paper 2 is gradually fed toward
fixing means 20 as shown in Fig. 19. In the fixing means 20, the printing paper 2,
having the transferred images thereon, is interposed between a pressure roller 21
and a heating roller 22 containing a heat source therein, and the toner particles
are fused by the heating roller 22 to be fixed to the printing paper 2. If such fixing
operation is effected after all the images are transferred to the printing paper 2,
the printing paper 2 is discharged without being stopped, and therefore the heat source
of the heating roller 22 is kept turned on. However, if the images are in the process
of being transferred to the printing paper 2, the printing paper 2 is in a stopped
condition, and therefore the heat source of the heating roller 22 needs to be temporarily
turned off, or the heating roller 22 needs to be moved away from the printing paper
2. Another fixing method as shown in Fig. 5 may be used, in which fixing means 23
comprises the heat source 24 and the reflection plate 25, and the reflection plate
26 is provided below the fixing means 23 so as to enhance a heat efficiency, thereby
fixing the toner in non-contact manner. In the manner described above, a sequence
of image forming steps are finished.
[0076] As described above, in the fourth embodiment, at least one of the two end rollers
(i.e., the support roller 16 and the displacement roller 17) is arranged at such a
height as not to contact the transfer opposed roller 18, and with this arrangement
the non-transfer region R, which has been problematic with the conventional construction
and in which the transfer opposed roller 18 can not move, is eliminated on at least
one of the left and right sides. As a result, the longitudinal width Q of the tone
image-carrying member 10 can be considerably reduced, so that the body of the image
forming apparatus can be made smaller in size.
[0077] Finally, briefly describing the present invention as set forth in claim 1, the toner
image-carrying member does not always need to comprise a photosensitive member, and
in some cases the exposure means is not needed. For example, a toner image can be
formed by forming an electrostatic latent image by means of a heat source to develop
the same. Alternatively, toner coated all over the surface of the toner image-carrying
member is blown off the surface by a jet of air to enable forming a toner image as
in carving or engraving.
[0078] As described above, in the image forming apparatus of the transverse transfer type
according to the present invention, the toner images, carried by the toner-image carrying
member extended by the plurality of rollers in the direction perpendicular to the
direction of feed of the printing paper, are transferred by the transfer opposed roller
to the printing paper in the direction perpendicular to the direction of feed of the
printing paper, and the toner images thus transferred to the printing paper are fixed.
Among the rollers extending the toner image-carrying member, at least one of those
rollers except for the transfer opposed roller, which come closest to the transfer
opposed roller at the starting and terminal ends, respectively, of the longest path
of movement of the transfer opposed roller, is provided at such a height as not to
contact the transfer opposed roller. With this construction, the non-transfer region,
in which the transfer opposed roller can not move, is reduced, and therefore the body
of the image forming apparatus can be made smaller in size.
1. In an image forming apparatus of transverse transfer type for transferring toner images,
which are carried by a toner image carrying member stretched around a plurality of
rollers in a direction perpendicular to a feeding direction of a printing paper, to
the printing paper by means of a transfer opposed roller to fix the toner images transferred
to the printing paper, the improvement wherein at least one of rollers, which are
among said rollers stretching said toner image carrying member therearound but other
than said transfer opposed roller and come closest to said transfer opposed roller
at starting and terminal ends of a longest movement path of said transfer opposed
roller, is spaced a greater distance than a diameter of said transfer opposed roller
from a surface of the printing paper, to which toner images are transferred.
2. In an image forming apparatus of transverse transfer type for transferring toner images,
which are carried by a toner image carrying member stretched around a plurality of
rollers in a direction perpendicular to a feeding direction of a printing paper, to
the printing paper by means of a transfer opposed roller to fix the toner images transferred
to the printing paper, the improvement wherein while said transfer opposed roller
performs transfer of the toner images, that surface of said toner image carrying member,
on which transfer has finished, is not moved away from the printing paper.
3. Apparatus according to claim 1, wherein at least one of rollers, which are among said
rollers stretching said toner image carrying member therearound but other than said
transfer opposed roller and come closest to said transfer opposed roller at the starting
and terminal ends of the longest movement path of said transfer opposed roller, comprises
a displacement roller which is displaced following movements of said transfer opposed
roller.
4. Apparatus according to claim 2, wherein at least one of rollers, which are among said
rollers stretching said toner image carrying member therearound but other than said
transfer opposed roller and come closest to said transfer opposed roller at the starting
and terminal ends of the longest movement path of said transfer opposed roller, comprises
a displacement roller which is displaced following movements of said transfer opposed
roller.
5. Apparatus according to claim 1, wherein said toner image carrying member comprises
a photosensitive belt, and further comprising exposure means for exposing said toner
image carrying member in accordance with image signals, and developing means for developing
said toner image carrying member.
6. Apparatus according to claim 2, wherein said toner image carrying member comprises
a photosensitive belt, and further comprising exposure means for exposing said toner
image carrying member in accordance with image signals, and developing means for developing
said toner image carrying member.
7. Apparatus according to claim 5, further comprising exposure means for simultaneously
exposing said toner image carrying member at one line in accordance with image signals
for respective four primary colors, and developing means for providing toners of respective
four primary colors and forming toner layers on the same developing roller for respective
four primary colors.
8. Apparatus according to claim 6, further comprising exposure means for simultaneously
exposing said toner image carrying member at one line in accordance with image signals
for respective four primary colors, and developing means for providing toners of respective
four primary colors and forming toner layers on the same developing roller for respective
four primary colors.
9. Apparatus according to claim 1, wherein while said transfer opposed roller performs
transfer of the toner images, that surface of said toner image carrying member, on
which transfer has finished, is sequentially moved away from the printing paper.
10. Apparatus according to claim 1, wherein while transfer of the toner images is performed,
said rollers except for said transfer opposed roller and said displacement roller
which is displaced following movements of said transfer opposed roller to impart tension
to said toner image carrying member are rotated.
11. Apparatus according to claim 2, wherein while transfer of the toner images is performed,
said rollers except for said transfer opposed roller and said displacement roller
which is displaced following movements of said transfer opposed roller to impart tension
to said toner image carrying member are rotated.
12. Apparatus according to claim 1, wherein while transfer of the toner images is performed,
said rollers except for said transfer opposed roller and said displacement roller
which is displaced following movements of said transfer opposed roller to impart tension
to said toner image carrying member are enabled to be rotated.
13. Apparatus according to claim 2, wherein while transfer of the toner images is performed,
said rollers except for said transfer opposed roller and said displacement roller
which is displaced following movements of said transfer opposed roller to impart tension
to said toner image carrying member are enabled to be rotated.
14. Apparatus according to claim 1, wherein while said transfer opposed roller performs
transfer of the toner images, that surface of said toner image carrying member, on
which transfer has finished, is not moved away from the printing paper.
15. Apparatus according to claim 1, wherein three or more rollers including said transfer
opposed roller and said displacement roller which is displaced following movements
of said transfer opposed roller revolve said toner image carrying member to form toner
images.
16. Apparatus according to claim 9, wherein three or more rollers including said transfer
opposed roller and said displacement roller which is displaced following movements
of said transfer opposed roller revolve said toner image carrying member to form toner
images.
17. Apparatus according to claim 2, wherein two or more rollers including said displacement
roller, which is displaced following movements of said transfer opposed roller, but
not including said transfer opposed roller revolve said toner image carrying member
to form toner images.
18. Apparatus according to claim 14, wherein two or more rollers including said displacement
roller, which is displaced following movements of said transfer opposed roller, but
not including said transfer opposed roller revolve said toner image carrying member
to form toner images.