[0001] The present invention relates to a color image forming apparatus such as a color
printer, a color copier and the like. The present invention especially relates to
a color image forming apparatus which can form a color image of stable quality, be
made compact, and meet the demand of forming a black and white image. Furthermore,
the present invention relates to a color image forming apparatus which enables to
stably form a black and white.
[0002] A copier with a process cartridge has been disclosed in Japanese Patent Publication
Open to Public Inspection No. 163276/1982, wherein the process cartridge is integrally
composed of a photoreceptor drum, a charger, a cleaning unit and a black and white
developing unit, and the process cartridge can be easily attached to and removed from
the apparatus.
[0003] In this type of copier, the above-described process cartridge is replaced before
parts and materials to be used to form an image have worn out beyond limits in order
to avoid overworking the copier and to obtain a stable image quality.
[0004] In the copying machine industry, there is now an increased demand for a color image
instead of a black and white image because a color image has much information. In
order to meet the demand, a color copier has been disclosed in Japanese Patent Publication
Open to Public Inspection No. 72159/1983, wherein the color copier is provided with
a color copy process cartridge which has a photoreceptor drum, a charger, a color
developing device composed of a plurality of developing units, a cleaning unit and
the like, and is provided with a black and white copy process cartridge with a black
(BK) developing device so that the black and white copy process cartridge can be used
as the spare of the color copy process cartridge.
[0005] However, the above-described color copy process cartridge has a complicated structure
and is expensive since a plurality of developing devices are installed in it. In order
to put the color copy process cartridge into practical use in terms of cost reduction,
it is preferable that the above-described cartridge is replaced and discarded after
its photoreceptor with long life has been used to its limits or the carrier in the
developer has been used to its limits. The life of the above-described photoreceptor
drum is usually 50000 to 80000 color copies and the life of the carrier contained
in the developer is 20000 to 30000 color copies. Accordingly, toner is needed to be
supplied from a toner supply unit provided to each of the plural apparatus, wherein
each toner supply unit is corresponding to a developing unit. The toner supply unit
is provided to the outside portion of the outer wall of the process cartridge and
connected with the process cartridge at the connecting portion which has an opening
to supply toner to the developing chamber of the developing unit.
[0006] However, in the case of the color image forming apparatus disclosed in the above-described
official report, the process cartridge must be replaced when the image forming mode
is changed from the color image forming mode to the black and white image forming
mode, or from the black and white image forming mode to the colour image forming mode.
Accordingly, it has the disadvantages of complicated operation, high cost, and waste
of time.
[0007] There is a demand for a compact and light image forming apparatus as a printer and
copier have become popular, Since the black and white image forming apparatus has
been replaced with the colour image forming apparatus, it has become very important
to make the apparatus compact. However, in the case of the above-described colour
image forming apparatus disclosed in the official report, a plurality of developing
units, a transfer means, and other image forming units are not arranged properly.
Therefore, it has been difficult to make the above-described apparatus compact and
to obtain a colour image of stable quality.
[0008] EP-A-0,293,597 discloses a developing device in which the colour developing means
are constructed into a single unit and the black developing means comprises a second,
independently arranged unit. EP-A-0,228,062 discloses a photoreceptor cartridge unit
which includes a frame on which a photoreceptor drum, a corona charger, a cleaner
unit and a separator unit are integrally mounted.
[0009] Furthermore, in some prior image forming apparatus there has been the disadvantage,
that the apparatus is stained by the toner which leaks out and dispersed when the
toner supply unit is connected with the process cartridge at the connecting portion.
In order to eliminate this disadvantage, a complicated sealing member to seal the
connecting portion becomes necessary, wherein the sealing member is opened and closed
when the toner supply unit is connected with and disconnected from the process cartridge.
Especially, in the case of a colour image forming apparatus, it is necessary to supply
a plural kinds of toner to a plurality of developing units. Accordingly, the structure
becomes further complicated and even when a small amount of toner leaks out and disperses,
the image quality is lowered because of colour mixture caused by mixed toner.
[0010] The above-described colour image forming apparatus has the further disadvantages,
that colour mixture tends to occur, and that it is difficult to maintain stability
of the apparatus to acquire balance because a plurality of developing units stacked
horizontally in the process cartridge are horizontally provided close to the photoreceptor
drum. The above-described colour image forming apparatus has the further disadvantage,
that the transfer and conveyance mans of transfer paper tends to be stained by the
toner which leaked out and dispersed because the means is located below the photoreceptor
drum.
[0011] Conventionally, various types of electrostatic image forming apparatuses have been
used. One has the features that; a photoreceptor drum and a developing unit are provided
to a unit which can be rapidly attached to and removed from the apparatus. Another
has the features that; a unit including a photoreceptor drum and a unit including
a developing unit are individually provided to the apparatus, wherein both units can
be rapidly attached to and removed from the apparatus. The above-mentioned electrostatic
image forming apparatuses are formed in such a manner that the inspection of the inside
of the apparatus, the exchange of parts, and the cleaning of the inside of the apparatus
can be easily and positively conducted.
[0012] The life of a photoreceptor which is repeatedly used to form images, is limited.
For example, the photoreceptor is generally replaced with a new one when it has been
used to the limit defined as the number of times in which the photoreceptor has been
used to form images, wherein the number of times can be 10000, 30000 or 50000 times.
The life of a developing unit is limited in the same way as the photoreceptor. The
photoreceptor is commonly replaced with a new one when it has been used to the limit.
[0013] The photoreceptor and the developing unit have the endurance limit within which an
image of good quality can be formed. The endurance limit is determined by the number
of times in which images have been formed. When the photoreceptor is used to the limit,
it is suddenly degraded. For that reason, the photoreceptor must be replaced with
a new one before is has been worn beyond the limit. In the case of the developing
unit, although the endurance limits of Y, M, C, and BL developing units are the same,
the frequency of use of each developing unit is different when multicolour image forming
is conducted. Accordingly, each developing unit reaches the limit of use at different
times. In many cases, the frequence of use of the black developing unit is high and
the frequency of use of the colour developing unit is not so high. In the case described
above, if each colour developing unit is discarded on the assumption that each colour
unit has worn out synchronously with the black developing unit, it will amount to
discarding colour developing units which still have enough capacity, which can be
considered enormous losses from the view point of economical use of colour developer
and colour developing units.
[0014] In the case of multicolour image forming, the frequency of use of Y, M, and C developers
or of B, G, and R developers can be regarded as almost the same.
[0015] According to the present invention there is provided a colour image forming apparatus
for forming a colour image comprising:
an image retainer for carrying said colour image,
a charging means for charging a surface of said image retainer,
a means for forming a latent image on the charged surface of said image retainer,
a multicolour developing means for developing said latent image,
a black developing means for developing said latent image,
a means for conveying a transfer sheet and transferring said developed latent image
onto said transfer sheet, and
a cleaning means for cleaning a residual developer on the surface of said image
retainer,
characterised in that wherein at least said image retainer, said cleaning means
and one of said developing means are formed in a detachable processing cartridge,
and wherein the other said developing means is detachably attached to a body means
of said colour image forming apparatus.
[0016] In a colour image forming apparatus according to the present invention in which a
colour image forming process cartridge is adopted, there are the advantages that:
a colour image of stable quality is obtained; the apparatus is made compact by the
proper arrangement and composition of image forming units; and the image forming mode
is easily converted from colour image forming to black and white image forming without
being restricted by a cartridge.
[0017] In a colour image forming apparatus according to the present invention in which a
black and white image forming process cartridge is adopted, there are the advantages
that: the quality of a black and white image is stabilized by adopting a black and
white process cartridge; the image quality is improved and the apparatus is made compact
by a proper arrangement and composition of image forming units; and by providing colour
developing units to the apparatus the image forming mode is easily converted from
the black and white copying mode to the colour copying mode without restrictions of
the process cartridge.
[0018] In one case, the colour image forming apparatus of the present invention has the
advantages that: the charger, multi-colour developer unit for example the Y, M and
C (Yellow, Magenta and Cyan) developing units, the cleaning unit, and the waste toner
collecting container are provided around the photoreceptor drum and they are integrally
built in the process cartridge; the process cartridge is provided to the apparatus,
wherein the cartridge can be easily attached to and removed from the apparatus; and
the BK (black) developing unit is singly provided to the apparatus, wherein the BK
developing unit can be easily attached to and removed directly from the apparatus.
The above-described composition in which the process cartridge is adopted, offers
advantages as follows: the stabilization of colour image quality can be ensured; the
apparatus can be made compact; the BK developing unit can be easily replaced when
the toner has been consumed or the developer has been worn out without being restricted
by the process cartridge; and not only colour image forming but also a large amount
of black and white images can be stably formed.
[0019] Furthermore in this first case, the composition of the apparatus acquires balance,
maintains stability and is made compact, and furthermore the quality of a colour image
and a black and white image is improved by locating the Y, M, C, and BK developing
units below the photoreceptor drum, and by locating the transfer and conveyance means
of transfer paper above the photoreceptor.
[0020] In this first cast, it is preferable that the above-described developing units are
vertically provided around the photoreceptor drum and the Y, M and C colour developing
units share some portions of walls which separate the developing units so that the
developing units are integrally composed. The developer used in the developing units
may be either one-component developer mainly composed of magnetic toner or two-component
developer composed of nonmagnetic toner and magnetic carrier. However, it is preferable
to use the two-component developer so that clear image tone of colouring agents can
be obtained.
[0021] In this first case, the cartridge is continuously used to form an image until the
carrier in the developer or the photoreceptor has been used out to its limits. When
one of them reaches its limits, it is removed from the apparatus, to be replaced.
Since there is not enough room in the developing chamber of the colour developing
unit located in the process cartridge, it is preferable that toner is supplied to
the colour developing unit from the toner supply unit located on the front side or
on the rear side of the apparatus. As far as the BK developing unit provided to the
apparatus is concerned, the toner chamber may be provided in the developing unit and
toner may be supplied from the toner chamber (toner hopper) to the developing chamber,
and when the toner has been consumed, the developer may be replaced. A toner container
which is filled with toner may be attached to or removed from the developing chamber
in order to supply toner, and the developing unit may be replaced when the developer,
especially the carrier, has been worn out. Furthermore, a toner supply hopper may
be provided so that the toner can be supplied to the developing chamber from the outside
of the apparatus.
[0022] As the developing units have the structure and arrangement described above, the process
cartridge may be made more compact and its arrangement may become stable.
[0023] Furthermore, as the developer is sufficiently charged by triboelectric charging when
the developer is stirred and mixed, excellent development occurs and the colour image
of high quality may be obtained. Since the transfer and conveyance means of transfer
paper is located above the photoreceptor drum, the means is not stained by toner which
leaks out from the developing units.
[0024] In this first case, in order to efficiently obtain fine colour images or fine black
and white images over long periods of time, it is preferable that: a waste toner collecting
container is provided in the process cartridge; the residual toner on the surface
of the photoreceptor drum is scraped off; and he collected waste toner is put into
the waste toner collecting container by waste toner conveyance pipe which has a screw
conveyor or coil spring. Instead of the above-described waste toner collecting container,
the inside of the photoreceptor drum can be used as the room to put the waste toner
into.
[0025] The colour image forming process and the black and white image forming process are
stored beforehand in the program memory, and when image forming is conducted, one
of the image forming processes is selected by operating the program operation key
provided to the apparatus in order to form an image according to the image forming
process selected through the control unit.
[0026] Alternatively, in the other case the colour image forming apparatus of the present
invention has the advantages that: the charger, the BK developing unit, the cleaning
unit, and the waste toner collecting container, if necessary, are integrally located
around the photoreceptor and built in the process cartridge; the process cartridge
is easily attached to and removed from the apparatus; and the colour developing unit
if yellow (Y), magenta (M), and cyan (C) is provided to the apparatus directly. Since
the image forming apparatus of the present example has such a structure as described
above, an inexpensive disposable process cartridge for use in forming a black and
white image is realized. As a colour developing unit is installed as an optional unit
in this example, the black and white image forming mode is rapidly converted to the
colour image forming mode and the colour mode is rapidly converted to the black and
white mode without replacing the process cartridge.
[0027] Since in this second case the colour developing unit is provided to the apparatus,
it has the advantage that the developing unit can be replaced, when this is needed,
without interfering with the process cartridge, and that the toner supply unit is
easily provided to the colour developing unit.
[0028] In this second case the apparatus is composed to acquire balance to maintain stability,
the apparatus is made compact, and furthermore the quality of a black and white image
and a colour image is improved by locating a group of developing units including the
colour developing unit and the BK developing unit below the photoreceptor, and by
locating the transfer and conveyance means of transfer paper above the photoreceptor.
[0029] A toner supply chamber is provided to the BK developing unit in the process cartridge.
When the toner in the toner supply chamber has been consumed, the process cartridge
is replaced. Otherwise, a toner supply unit may be added to the above-described developing
unit and the toner may be supplied to the developing unit from the toner supply chamber
until the carrier in the developer has been worn out to its limits, and when the carrier
has been worn out beyond its limits, the process cartridge may be replaced. Alternatively,
the BK developing unit in the process cartridge may be made replaceable, and when
the photoreceptor ha been worn out to limits, the process cartridge may be replaced.
[0030] In this second case in order to effectively continue forming black and white images
which are in great demand, it is preferable that: a waste toner collecting container
is provided in the process cartridge; the residual toner on the surface of the photoreceptor
is scraped off; and the collected waste toner is conveyed to the waste toner collecting
container by a waste toner conveyance pipe to which a screw conveyor or a coil spring
is provided. The waste toner may be put into the inside of the photoreceptor drum
instead of the waste toner collecting container. It is preferable that the toner is
supplied to the Y, M, and C colour developing units from toner supply hoppers which
are provided on the front side of the apparatus or on the rear side of the apparatus.
When the toner has been consumed or the carrier has been worn out to limits, the colour
developing unit may be replaced individually or as a unit as necessary. When an image
is formed by the colour image forming apparatus of the present invention, the process
to form a black and white image and that to form a colour image are stored beforehand
in the program memory. One of the processes is selected by operating a key to be used
for program operation so that the desired image forming process can be performed through
a control unit.
[0031] The invention will be better understood from the following description, given by
way of example only, with reference to the accompanying drawings in which:-
Fig. 1 is a sectional view of the colour printer of the first example.
Fig. 2 is a perspective view of the colour printer illustrated in Fig. 1.
Fig. 3 is a sectional view of the colour printer of the second example.
Fig. 4 is a perspective view of the colour printer illustrated in Fig. 3.
[0032] Fig. 1 is a sectional view of the color printer of the first example. The numeral
1 is a process cartridge in which the photoreceptor 2, the charger 3, the color developing
unit 4, the cleaning unit 10, and the waste toner collecting container 15 are provided.
The developing unit 4 comprises the Y developing unit 5, the M developing unit 6,
and the C developing unit 7, wherein the above developing units share some portions
of the walls of the developing unit 4, and are integrally composed. The developing
rollers 5a, 6a, and 7a, the stirring rollers 5b, 5c, 6b, 6c, 7b, and 7c, and the layer
thickness regulating rollers 5d, 6d, and 7d, are provided in the above-described developing
units. The developing rollers and the stirring rollers are vertically located in the
developing units. The developing units are located below the photoreceptor drum 2
so that the developing units surround the circumferential surface of the photoreceptor
2. The cleaning unit 10 has the waste toner collecting tube 10a, the waste toner collecting
film 10b, the cleaning blade 10c, and the discharge lamp 10d used before cleaning.
The waste toner scraped off from the surface of the photoreceptor by the blade 10c,
is collected to the toner collecting tube 10a through the waste toner collecting film
10b. The toner collecting tube 10a is connected with one end of the waste toner conveyance
tube 12 and the other end of the waste toner conveyance tube 12 is connected with
the waste toner recovery tube 15a in the waste toner recovery container 15. Accordingly,
the waste toner which has been scraped off is collected to the toner recovery container
15 through the waste toner conveyance tube 12.
[0033] The BK developing unit 8 is separated from the process cartridge 1, wherein the developing
unit can be rapidly attached to and removed from the apparatus without being restricted
by the process cartridge. Therefore, the BK developing unit 8 can meet the demand
to form a plurality of black and white images, which is the important characteristics
of the present invention.
[0034] The numeral 20 is an optical unit for laser beams to expose an image. The optical
unit 20 for laser beams has the polygon mirror 20a, the collimator lens 20b, the reflection
mirror 20c, 20d, and 20e, the f-ϑ lens 20f, and the dustproof type glass 20g. The
letter L is an exposure light beam. The semiconductor laser beams modulated by the
video signal sent from the outside of the apparatus, are introduced to the optical
unit 20, and the surface of the photoreceptor drum is exposed to the image exposing
light L to form an electrostatic latent image.
[0035] The numeral 30 is a transfer paper feed cassette. Transfer paper P which was sent
by the feed roller 31 from the paper feed cassette 30, is conveyed to the transfer
region through the conveyance passage 32 and the upper conveyance roller 33a and the
lower conveyance roller 33b of the conveyance rollers 33.
[0036] The numeral 40 is a transfer and conveyance unit. The numeral 40a is a transfer and
conveyance belt. The numeral 40b and the numeral 40c are drive rollers to drive the
belt 40a. The numeral 40d is a belt tension roller. The numeral 40e is a transfer
pole. The numeral 41 is a fixing unit which is composed of the press roller 41a and
the heat roller 41b. A fixed transfer paper is delivered to the delivery tray 43 by
the upper delivery roller 42a and the lower delivery roller 42b of the delivery rollers
42.
[0037] The apparatus is composed of the upper box unit K₂ and the lower box unit K₁, and
the boundary between K₂ and K₁ is the line P₁ - P₂. The upper box unit K₂ can be opened
with regard to the line P₁ - P₂, wherein the upper box unit K₂ comprises the upper
transfer paper conveyance roller 33a, the transfer and conveyance unit 40, the press
roller 41a of the fixing unit 41, and the upper delivery roller 42a, wherein the lower
box unit K₁ comprises the process cartridge 1, so that a transfer paper jam which
occurs in the transfer and conveyance system can be recovered.
[0038] When the side lid K₃ including the delivery tray 43 is opened with regard to the
boundary P₃ - P₄, the transfer paper feed cassette 30 can be attached to and removed
from the apparatus. A transfer paper jam which occur in the transfer paper conveyance
process, can be treated by opening the side lid K₄, which includes one side of the
conveyance passage, with regard to the boundary P₅ - P₆.
[0039] Referring to Fig. 1 and Fig. 2, the way how the process cartridge 1 is attached to
and removed from the apparatus, will be explained. In Fig. 1, the upper box unit K₂
is opened around the shaft Q₁ as a center and the upper box unit K₂ is opened from
the lower box unit K₁, which includes the process cartridge 1, with regard to the
boundary P₁ - P₂. Then, the front door A is opened toward the viewer's side by pulling
the handle M and the front side of the apparatus is opened. After that, the lower
protrusions 11a and 11b of the process cartridge 1 are slid along the guide rails
12a and 12b. In this way, the process cartridge 1 is pulled out toward the viewer's
side to be replaced. In the case of the BK developing unit 8 which is one of the characteristics
of the present invention, the front door A is opened to the viewer's side in the same
way as described above, and the sliding members 13a and 13b, which engage with the
guide rails 14a and 14b, are slid so that the BK developer 8 can be pulled out.
[0040] The developing roller 8a, the stirring rollers 8b and 8c, and the layer thickness
restricting rollers 8d and 8e are included in the above-described BK developer 8.
Toner is supplied to the color developing units 5, 6, and 7 of Y, M, and C from the
toner supply units 5e, 6e, and 7e which are provided at the rear of the apparatus.
[0041] Image forming of the present example was carried out by the above-described color
image forming apparatus as follows. The color process stored in the memory 45 was
read out beforehand by operating the color process designation key 48 in the process
designation keys 47, and the color process was designated through the CPU 46. According
to a color video signal, an image was formed by the color developing units of Y, M,
and C in the process cartridge and by the BK developing unit provided to the apparatus.
[0042] First of all, the cleaning unit was released and at the first rotation of the photoreceptor
drum 2 the circumferential surface of the photoreceptor drum 2 was uniformly charged
by the charger 3 so that the drum 2 was charged to the electrical potential -700V.
Then, the laser beams emitted from the semiconductor laser unit 22 were modulated
by the signal Y which was the first video signal, and the surface of the photoreceptor
drum 2 was exposed to the obtained modulated laser beams to form an electrostatic
latent image. Then the latent image was developed by the Y developing unit 5 containing
two-component developer on which the developing bias of D.C component -600V and A.C
component 3KHz, 500V, was impressed, wherein the development was conducted by the
method of noncontact reversal development. In this way, a Y toner image was formed
on the photoreceptor drum.
[0043] At the next stage, the photoreceptor drum 2 was rotated and charged by the charger
3 to the electrical potential -700V again. Then the photoreceptor was exposed to the
laser beams modulated by M signals and the latent image was developed by the M developing
unit 6. In this way, a M toner image was superimposed on the Y toner image previously
formed on the photoreceptor. In the same way, at the third revolution and the fourth
revolution of the photoreceptor drum 2, the photoreceptor drum was exposed to the
laser beams modulated by C signals and BK signals. Then, reversal development by the
C developing unit 7 and the BK developing unit 8 was conducted in order to superimpose
the C toner image and the BK toner images onto the previously formed Y and M toner
image. The color toner image was formed in this way. Image forming of the M toner
image, the C toner image, and the BK toner image was carried out under the same condition
as image forming of the Y toner image.
[0044] Then, a transfer paper was sent out by the paper feed roller 31 from the paper supply
cassette 30 according to the predetermined image forming program. Then the transfer
paper was conveyed by the transfer belt 40a to the transfer region T through the conveyance
passage 32. The color toner image on the photoreceptor 2 was transferred onto the
above-described transfer paper by the transfer pole 40e in the transfer region T.
The transferred image on the paper was fixed by the heat roll 41b of the fixing unit
41. Then the transfer paper was delivered onto the delivery tray 43 by the delivery
rollers 42, wherein the transfer paper was delivered face down. After the color toner
image was transferred onto the transfer paper, the above-described cleaning unit was
turned on and the residual toner on the photoreceptor 2 was removed from the surface
of the photoreceptor so that the photoreceptor 2 was ready for the next image formation.
The above-described operation was repeated 1000 times so as to form color images:
The color toner was successively supplied to the developing unit 4 from the toner
supply units 5e(Y), 6e(M), and 7e(C) and the BK toner was stably supplied from the
toner chamber 8e in the BK developing unit 8 during the image forming. Accordingly,
clear images of high density could be obtained from the beginning of the operation
to the end.
[0045] Then the image forming process was changed to the black and white image forming process
by operating the monochrome (black) process designation key 49 of the process designation
key 47, and images were formed with the BK developing unit 8 according to the black
and white video signal.
[0046] The electrical potential of -700V was uniformly impressed on the surface of the photoreceptor
drum 2 by the charger 3 while the cleaning blade 10c came into contact with the photoreceptor
2. Then, the laser beams modulated according to the BK video signal, were emitted
from the laser unit 22 and the surface of the photoreceptor drum 2 was exposed to
the modulated laser beams through the optical laser unit 20 so that an electrostatic
latent image could be formed. This electrostatic latent image was developed by the
BK developing unit 8 which contained two-component-developer and on which the bias
of D.C component -600V and A.C component 3KHz, 500V was impressed, wherein noncontact
reversal development was conducted. A BK toner image was formed on the surface of
the photoreceptor 2 in this way. This BK toner image was transferred and fixed onto
the transfer paper sent from the paper supply cassette 30 so that the BK image could
be formed. After the image was transferred onto the transfer paper, the photoreceptor
drum was cleaned by the cleaning unit 10. The above-described operation was repeated
5000 times to form black and white images. While the operation was repeated, the BK
developing unit was replaced, wherein the replacement was conducted having no relation
with the process cartridge 1, to continue image forming. As a result, clean images
of high density could be obtained.
[0047] In this example, image formation could be conducted over long periods of time by
putting the waste toner scraped off from the surface of the photoreceptor 2 by the
cleaning unit to the waste toner collecting container 15.
[0048] In the above-described example, the present invention was applied to a color printer.
If the color printer is combined with a color scanner, the apparatus can be a color
copier. The present invention includes the color copier described above.
[0049] It is clear from the above explanations that in the color image forming apparatus
of the present invention the apparatus can be made compact; the arrangement of image
forming units can be made stable; the conversion between a color image and a black
and white image can be rapidly conducted without being restricted by the process cartridge;
and furthermore the image of stable quality can be obtained.
[0050] Fig. 3 is a sectional view which explains the color printer of the second example
of the present invention. In Fig. 3, the numeral 1 is a process cartridge. The photoreceptor
drum 2, the charger 3, the BK developing unit 8, the cleaning unit 10, and the waste
toner collecting container 15 are provided in the process cartridge 1. The developing
roller 8a, the stirring rollers 8b, 8c, the layer thickness restricting roller 8d,
the developer scraping member 8e (the scraper) used for scraping the developer from
the photoreceptor after development, and the toner supply cylindrical member 8f are
provided in the above described BK developing unit 8. A plurality of black and white
images can be printed as the toner is successively supplied from the toner supply
cylindrical member 8f.
[0051] The cleaning unit 10 has the waste toner collecting tube 10a, the waste toner collecting
film 10b, the cleaning blade 10c, and the discharge lamp 10d used before cleaning.
The wasted toner scraped off from the surface of the photoreceptor 2 is collected
to the waste toner collecting tube 10a through the waste toner collecting film 10b.
The waste toner collecting tube 10a is connected with one end of the waste toner conveyance
tube 12 which is provided on the front side of the apparatus, and the other end of
the waste toner conveyance tube 12 is connected with the waste toner recovery tube
15a of the waste toner recovery container 15. The scraped waste toner is recovered
into the waste toner recovery container 15 through the waste toner conveyance tube
12.
[0052] The charger 3 is a scorotron charger with a grid and its discharging wire can be
cleaned by a manually operated cleaning means. The color developing unit 4 comprises
the Y developing unit 5, the M developing unit 6, the C developing unit 7, wherein
the developing units are integrally assembled sharing some portions of the walls located
between them, and each developing unit can be easily attached to and removed from
the apparatus. The developing units have the developing rollers 5a, 6a, 7a, the stirring
rollers 5b, 6b, 7b, 5c, 6c, 7c, the layer thickness restricting rollers 5d, 6d, 7d,
and the scrapers 5e, 6e, 7e. This color image developing unit 4 can be replaced according
to the demand of a user without being restricted by the process cartridge 1. In the
present example, toner hoppers to supply the toner are provided to the Y, M, and C
developing units so that color images can be successively formed until the carrier
in the developer is worn out to its limits.
[0053] As the developing rollers and the stirring rollers of the BK developing unit 8 and
the color developing unit 4 are vertically located, the efficiency of stirring and
mixing is high enough that sufficient triboelectric charging can be conducted to the
developer.
[0054] The above-described developing units are located below the photoreceptor drum 2,
wherein the developing units surround the circumferential surface of the photoreceptor.
Accordingly, the apparatus can be made further compact.
[0055] Referring to Fig. 3 and Fig. 4, the way how to attach the process cartridge 1 and
the color developing unit 4 to the lower box unit K₁ and how to remove them from it,
will be explained as follows. First of all, in order to remove the process cartridge
1 and the color developing unit 4 from the lower box unit K₁, the upper box unit K₂
is opened around the shaft Q₁ as a center with regard to the lower box unit K₁. Then,
the handle M located on the front side of the cartridge and the handle M' located
on the rear side of the cartridge are held and the process cartridge 1 is drawn up
to remove the cartridge from the apparatus. Successively, the color developing unit
4 located below the process cartridge 1 is drawn up in the same way.
[0056] In order to attach the process cartridge 1 and the color developing unit 4 to the
lower box unit K₁, the color developing unit 4 is forced to engage with the unit receivers
4a, 4b, and then the process cartridge 1 is forced to engage with the cartridge receivers
1a, 1b provided to the lower box unit K₁. After that, the upper box unit K₂ is closed
to the lower box unit K₁ so that the apparatus becomes ready to form an image. When
the upper box unit K₂ is closed, the protrusion N (N') provided to the process cartridge
1 is pressed downward by the protrusion L (L') provided to the upper box unit K₂ so
that the process cartridge can be fixed to the cartridge receivers 1a, 1b. The gap
between the photoreceptor drum 2 and the color developing unit 4 is maintained by
a bumping member which is not shown in the drawings. When the upper box unit is closed,
the color developing unit is also fixed to the unit receivers 4a, 4b through the above-described
bumping member.
[0057] The image forming process in the second example is the same as that in the first
example. The BK toner image in the second example was transferred and fixed onto the
transfer paper sent from the transfer paper supply cassette 30 and the BK image was
formed. After transferring, the photoreceptor drum 2 was cleaned by the cleaning unit
10. When image forming was conducted 25000 times while toner was supplied to the developing
unit from the cylindrical toner supply member 8f, the process cartridge was replaced
in case the carrier was worn out, and image forming was successively carried out.
As a result, a clear black and white image of high density could be obtained. Other
characteristics of the obtained images were the same as those in the first example.
[0058] It is clear from the above explanations that according to the image forming apparatus
of the present example; the apparatus can be made compact; the image forming units
can be arranged stable; the conversion between color image forming and black and white
image forming can be rapidly carried out without being restricted by the process cartridge;
black and white images which are in great demand can be stably printed; and additionally
color images can be printed.
[0059] When an image forming means formed in a detachable cartridge has been used and worn
out to the limit, the old cartridge can be immediately replaced with a new one so
that the function can be recovered. Furthermore, the operation to recover the function
is only to replace a cartridge, which is so simple and positive that not an expert
but an ordinary operator who does not have specific expertise can easily replace it.
As the cartridges can be replaced according to the frequency of use, it is not necessary
to use expensive materials and the cartridges can be reasonably replaced with new
ones