BACKGROUND OF THE INVENTION
[0001] The present invention relates to the improvement of the magnetic brush development
process applicable to the electrophotography and the electrostatic recording characterized
by developing the electrostatic latent image formed on the image carrier into the
visible image.
[0002] Conventionally, as far as the development process using the developer consisting
of a single-component developer including the magnetic substance or a two-component
developer consisting of the mixture of the toner and the carrier which is the magnetic
substance is concerned, the development process using the magnetic brush developing
device as shown in Fig. 10 is used. In said figure, numeral notation 71 denotes an
electrostatic latent image carrier (hereinafter referred to simply as image carrier)
that is to turn in the direction of an arrow and is also a photosensitive layer comprising,
for example, ZnO, Se, OPC and so on, and 72 is a developer conveyance sleeve (hereinafter
referred to simply as the sleeve) consisting of a non-magnetic cylindrical body that
is to turn in the direction of an arrow to convey the developer D to the developing
area E. 73 is a magnetic roll that is disposed inside the developing sleeve 72 and
consists of the plural number of magnets having different polarities arranged radially
and alternately so that said developer D is not only caused to be deposited on sail
sleeve 72 but also caused to form the brush due to the magnetic force. 74 is a brushformation
controller that is provided on the upstream side of the development area E and controls
the thickness of the developer layer to the predetermined value so that the electrostatic
latent image can be developed with the brush formed at its best condition. 5 is a
power source of the bias such as the DC bias to be applied to the developing sleeve
72 to prevent the scattering of the toner and the foggy development. 75a is a protective
resistor.
[0003] The development process using the magnetic developing device can be divided into
a process using a stationary magnetic roll 73 and rotary developing sleeve 72 and
another process rotating the magnetic roll 73. In any of said processes, the layer
of the developing agent controlled by the brush-formation controller 74 forms the
flow of the developing agent, is adsorbed on the developing sleeve and conveyed to
the development area E for the development.
[0004] Conventionally, the space, DSD, (hereinafter referred to as the space in development
area) between the image carrier 71 and the developing sleeve 72 in the development
area and the space, DH, (hereinafter referred to as the developing agent controlling
space) between the brush-formation controller 74 and the developing sleeve 72 are
kept constant in controlling the quantity of the developing agent to be conveyed for
development. In this case, as one of the conditions necessary for accomplishing the
development satisfactorily, there is the correlation between the DSD, the space in
the development area, and the DH, the developing agent controlling space, and the
accuracies of these spaces are required to be maintained at adequately high levels.
[0005] In the conventional system, the center of rotation of the image carrier 71 and the
center of the rotation of the developing sleeve 72 are in a fixed relationship with
each other as far as their relative positions are concerned. In such a fixed relationship,
an example of the conditions for accomplishing satisfactory development including
the values of DSD, the space in development area, and DH, the developing agent controlling
space are as follows:
Value of DSD: 0.40 ±0.04 mm
Value of DH : 0.40 ±0.03 mm
[0006] Another condition to be satisfied simultaneously with the above condition is as follows:
Value of DSD - Value of DH = -0.02 - +0.3 mm
[0007] These conditions are required to be satisfied throughout the whole range werein the
image on the image carrier 71 is formed with the toner at the time the development.
Both the image carrier 71 and the developing sleeve 72 are of cylindrical form. In
the case of the ordinary electrophotographic duplicating machine, the image carrier
and the developing sleeve take the form of a cyliner about 30 cm long in its axial
direction in many instances. Thus, in order to maintain the developing agent controlling
space DH within said range, it is essential for the axis of the developing sleeve
72 and the brush-formation controller 74 to be parallel to each other at highest possible
accuracy. Also, in order to maintain the space DSD in the development area within
said range, it is also essential not only that the axis of the developing sleeve 72
and the axis of the drum of the image carrier 71 are kept parallel to each other highest
possible accuracy but also that the cross-sectional forms of said developing sleeve
and said drum are completely circular. Furthermore, the drum of the image carrier
71 and the developing sleeve are to be free from eccentricity, but it is difficult
either from the machining technique or machine assembly technique to eliminate the
eccentricity. For instance, where the axis of the developing sleeve 72 is fixed, said
space DSD in the development area varies as the drum rotates, thereby causing the
uneveness of the development. According to the conventional way of solving this problem,
the sleeve is pressed against the drum through a spacer in order to keep said space
constant all times. In the case of such conventional system, however, said space varies
when the foreign matter such as the developing agent is deposited on the surfaces
of the drum, spacer or the sleeve, this causes the change in the space and the uneveness
of the development as the result. Besides, as the surface of the spacer wears out,
the space DSD cannot be maintained constant as one of the disadvantages of the conventional
system. In addition, the conventional system requiring the precision construction
including the highly accurate spacer cause another disadvantage such as the high manufacturing
cost.
[0008] Furthermore, the conventional system also causes what is called the blocking phenomenon
characterized by the oversupply of the developing agent for the space DSD in the development
area due to the variation of the developing agent controlling space DH. This phenomenon
is especially conspicuous where the single-component developing agent is used, and
this phenomenon causes the extreme deterioration of the image quality. On this understanding,
a system wherein the space DSD in the development area is set so that it can be enlarged
when the development agent is supplied exceeding the predetermined quantity has been
proposed in the specification of Japanese Patent Publication No. 61-28989. Such proposal,
however, cannot be the solution to said problem of the conventional system, since
the proposed system also relies on the stop member in setting the space DSD in the
development area at the time of the development like the case of the conventional
system.
SUMMARY OF THE INVENTION
[0009] The present invention relates to a development process for developing the electrostatic
latent image on the image carrier using te single-component or the two-component developing
agent and is intended to provide a development process enabling the satisfactory and
stable development of the image without relying on the conventional machanism requiring
the high-precision machined parts and highly accurate adjustment of the parts.
[0010] Said object of the present invention can be accomplished by the development process
characterized in that the electrostatic latent image carrier and the magnetic brush
supporter are disposed opposite to each other so as to be able to change their relative
positions freely and that the development of the image is accomplished by bringing
the magnetic brush and said electrostatic latent image carrier to be pressed against
each other.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011]
Figs. 1 through 5 are respectively the partial side views showing the outline of the
image-forming system using the developing system embodying the development process
according to the present invention.
Fig. 6 shows the composition of the developing system as one of the embodiments of
the present invention.
Fig. 7 is a cross-sectional view of the magnetic roll.
Fig. 8 is a graphical illustration of the relationship between the developing agent
controlling space DH and the space DSD in the development area.
Fig. 9 is a diagram showing the relationship between the line pressure and the space
in the development area and the range of the line pressure wherein the satisfactory
development can be accomplished.
Fig. 10 is a drawing showing the composition of the conventional developing system.
Figs. 11 through 18 are respectively the cross-sectional views of the improved developing
systems as the embodiments of the present invention.
Fig. 19 is a cross-sectional view of another embodiment of the present invention.
Fig. 20 is a cross-sectional view of the developing roller shown in the above Fig.
19.
Fig. 21 is a cross-sectional view of further another embodiment of the present invention.
Fig. 22 is an oblique view of the developing roller according to the present invention.
Fig. 23 is a lateral cross-sectional view of said developing roller including the
view of its axis.
Fig. 24 shows the driving system and power transmission gear system provided to the
aforementioned system.
Fig. 25 is a diagram showing the relationship between the depressing load and the
space in the development area in the aforementioned system.
Fig. 26 the gear system for the transmission of driving force provided to the aforementioned
system.
Fig. 27 shows the relationship between the depressing load and the space in the development
area in the aforementioned system shown in Fig. 26.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The photosensitive material as the image carrier to be used in the developing process
according to the present invention can be, for example, the selenium-based photosensitive
material (selenium photosensitive material, selenium-tellurium photosensitive material,
selenium-arsenic photosensitive material), or the photoconductive inorganic pigment
dispersed type photosensitive material (zinc oxide photosensitive material, cadmium
sulfide photosensitive material), or the amorphous silicon type photosensitive material
(function separation type, single-layer type), or the organic photoconductive photosensitive
material (single-layer type, function separation type), or the composite type photosensitive
material (photosensitive material consisting of the upper layer of selenium-based
material and the lower layer of organic photosensitive material or photosensitive
material consisting of the selenium and polyvinyl carbazole). The image carrier can
be of non-photosensitive material. For the non-photosensitive image carrier, the synthetic
resin film such as the polyester film may be used.
[0013] Any of the aforementioned image carriers is adaptable to the developing process according
to the present invention, but the organic photoconductive photosensitive material
and the amorphous silicon are especially preferable. Said photosensitive materials
can preferably be used in the developing process according to the present invention,
wherein the development takes place at a relatively low electric potential, to provide
stable and high-quality developed image.
[0014] The organic pigments usable as the charge-generating materials to consitute the organic
photosensitive material are as follows:
Monoazo pigment, polyazo pigment, metal complex salt pigment, pyrazolone azo pigment
and azo-based pigments such as stilbene azo pigment and thiazole azo pigment.
(2) Perylene pigments such as the perylenic acid anhydride and perylenic acid imide.
(3) Anthraquinone or polycyclic quinone pigments such as the anthraquinone derivative,
anthoanthrone derivative, diben divenzpyrenequinone derivative, pyranethoron derivative,
violanthoron derivative and isobiolanthrone derivative.
(4) Indigoid pigments such as the indigo derivative and thioindigo derivative.
(5) Phthalocyanine pigments such as the metal phthalocyanine and non-mental phthalocyanine.
(6) Carbonium pigments such as the diphenylmethane pigment, tripherylmethane pigment,
xanthene pigment and acridine pigment.
(7) Quinoimine pigments such as azine pigment, oxazine pigment and thiazine pigment.
(8) Methine pigments such as cyanine pigment and azomethine pigment.
(9) Quinoline pigments.
(10) Nitro pigments.
(11) Nitroso pigments.
(12) Benzoquinone and naphthoquinone pigments.
(13) Naphthal-imide pigments.
(14) Perinone pigments such as bis benzimidazole derivative.
[0015] The polycyclic quinone pigments and azo pigments are preferable. As the charge transport
materials, the triphenylamine compounds or the hydrazone compounds are preferable.
[0016] As for the developing agents to be used in the developing process according to the
resent invention, any generally available one-component or two-component developing
agent may be used and they are not limited to any apecified ones. As the one-component
developing agent, the magnetic toner may be used.
[0017] The two-component developing agent consists of the toner and the carrier. The resins
as the binders of the one-component developing agents and the two-component developing
agents may be any publicly known resins and are not limited to any specified ones.
As the resins suitable for the fixing process by heating, there are, for example,
the styrene resin, styrene-acylic resin,, styrene-butadiene resin, polyester resin,
epoxy resin, polymide resin and polyurethane resin. As the resins suitable for the
pressure fixing process, there are the polyolefin compounds such as the polyethylene,
polypropylene and polytetrafluoride-ethylene; polyethylene copolymers such as the
ethylene-vinyl acetate copolymer, ethylene-ester acrylate copolymer and polyethylene-ester
methacrylate copolymer; polyester; styrene-butadiene copolymer; the waxes such as
the beewax, carnauba wax and microcrystalline wax; the higher fatty acids such as
the stearic acid and palmitic acid and their chlorides and esters; epoxy resin; the
rubbers such as the isobutylene rubber, cyclized rubber and nitrile rubber; polyamide;
chloro-indene resin; maleic acid modified resin; phenol modified terpene resin; sillicon
resin and so on.
[0018] The polyester resin preferred as the binder of the toner is obtained through the
condensation polymerization of the alcohol monomer and the carboxylic acid monomer.
As the alcohol monomers to be used for this purpose, there are, for example, the diol
compounds such as the ethylene glycol, diethylene glycol, triethylene glycol, 1, 2-propylent
glycol, 1, 3-propylene glycol, 1, 4-butanediol, enopentyl glycol and 1, 4-butanediol
and the etherified bisphenols such as the 1,4-bis (hydroxymethyl) cyclohexane, bisphenol-A,
hydrogenated bisphenol-A and polyoxyethylene bisphenol-A; and other bivalent alcohol
monomers. As the preferred carboxylic acid type monomers, there are, for example,
the maleic acid, fumaric acid, mesaconic acid, citraconic acid, itaconic acid, glutaconic
acid, phtalic acid, cyclohexane dicabonic acid, succinic acid, adipic acid, sebasic
acid, malonic acid and the anhydrides of thesee acids; the dimer of lower alkylester
and linolenic acid; and other bivalent organic acid monomers.
[0019] Besides said bivalent monomers, the polymonomers higher than the trivalent monomers
may be used when necessary. As the preferred polyalchol monomers higher than trivalent
monomers, there are, for example, the sorbitol, 1, 2, 3, 6-hexane-tetrol, 1, 4-sorbitan,
pentaerythritol, dipentaerythritol, tripentaerythritol, cane suger, 1, 2, 4-butanetriol,
1, 2, 5-petanetriol, glycol, 1, 2-methylpropanetriol, 2-methyl-1, 2, 4-butanetriol,
trimethylethane, trimethylpropane, 1, 3, 5-trihy-droxymethylbenzene and others. Also,
as the preferred polycarboxylic acid monomers higher than the trivalent monomers,
there are, for example, 1, 2, 4-benzenetricarboxylic acid, 1, 3, 5-benzenetricarboxylic
acid, 1, 2, 4-cyclohexanetricarboxylic acid, 2, 5, 7-naphalenetricarboxylic acid,
1, 2, 4-naphthalenetricarboxylic acid, 1, 2, 4-butanetricarboxylic acid, 1, 2, 5-hexanetricarboxylic
acid, 1, 3-dicarboxyl-2-methylenecarboxy-propane, tetra (methylenecarboxy) methane,
1, 2, 7, 8-octanetetracarboxylic acid, empol trimer acid, their anhydrides and others.
[0020] The styrene-acrylic resin preferred as the binder of the toner can be obtained through
the copolymerization of the styrene monomer and acrylic monomer. As the styrene monomers,
there are, for example, the syrene, O-methylstyrene, m-methylstyrene, p-methylstyrene,
α-methylstyrene, p-ethylstyrene, 2, 4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene,
p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-methoxystyrene,
p-phenylstyrene, p-chlorstyrene and 3, 4-dichlorstyrene. These monomers may be used
either singly or in combination of plural kinds. As the preferred acrylic monomers,
there are, for example, the acrylic acid compounds such as the acrylic acid, methly
acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl
acrylate, dodecyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, stearyl acrylate,
2-chlorolethyl acrylate, phenyl acrylate, α-chlor acrylate methy or ester acrylate;
the methacrylic acid compounds such as the methacrylic acid, methyl methacrylate,
ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate,
n-octyl methacrylate, dodecyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate,
stearyl methacrylate, phenyl mathacrylate, dimethylaminoethyl methacrylate and diethyl
diethyl aminoethyl methacrylate or ester methacrylates and others. These monomers
may be used either singly or in combination of plural kinds.
[0021] In obtaining the resin particle powder, besides said binder resins, as the additives
to be used whenever necessary, there are, for example, coloring agents, charge controlling
agents and mold releasing agents.
[0022] As the preferred coloring agents, there are, for example, the carbon black, nigrosine
dye (C.I.No. 50415B), aniline blue (C.I. No. 50405), chalco oil blue (C.I.No. uzoic
blue 3), chrome yellow (C.I. No. 14090), ultramarine blue (C.I.No. 77103), Du Pont
oil red (C.I.No. 26105), quinoline yellow (C.I.No. 47005), methyleneblue chloride
(C.I.No. 52015), phthalocyanine blue (C.I.No. 74160), malachite green oxalate (C.I.No.
42000), lamp black (C.I.No. 77266), Rose bengal (C.I.No. 45435), their mixtures and
others. The content of the coloring agent should preferably range 0.1 - 20% in weight
to 100% of binder resin in weight, most preferably 0.5 - 10% in weight.
[0023] For the charge controlling agent, various pigments or dyes may be used. More specifically,
the negosine, azo, quaternary ammonium salt, thiourea pigments or dyes may be used.
These charge controlling agents may be used in combination. The content of the charge
controlling agent should preferably range 0.1% - 10% in weight to 100% of the binder
resing in weight, most preferably 0.5% - 5% in weight.
[0024] As the preferred mold releasing agents, there are, for example, the polyelefin, fatty
acid metallic salt, fatty acid ester, partially saponified fatty acid ester, higher
fatty acid, higher alcohol, fluid or solid paraffin wax, amide wax, polyhydric alcohol
sster, silicon varnish, aliphatic phlorocarbon, etc. Especially, the polyolefin such
as the polyethylene and polypropylene whose softening points range 80 - 180°C is preferable,
70 - 160°C most preferably when measured by the ring and ball method. These mold releasing
agents may be used in combination. The content of the mold releasing agent is preferred
to range 1 - 10% in weight to 100% of the binder resin in weight.
[0025] The toner to constitute the two-component developing agent to be used according to
the present invention may be one consisting of the resin particle powder formed into
spheres and mixed with the external additive such as one for improving the adaptability
to cleaning.
[0026] As the preferred agents for improving the adaptability to the cleaning, there are,
for example, the fatty acid metallic salts such as the stearate and calcium stearate.
For example, the fine grains of the polymers such as the polymethyl methacrylate,
the fine grains of polystyrene and polyvinylidene fluoride may be used.
[0027] The toner to constitute the two-component developing agent may be manufactured, for
example, by the following process. That is, the binder resin and the additive, which
is to be used whenever necessary, are kneaded, for example, with the extruder as the
mixture is being melted. Then, the mixture is cooled, crushed into rough pieces, for
example, with the hammer mill or wiley type crusher, further crushed into fine grains
using, for example, the jet mill and sorted into the resin grains of desired size.
[0028] Then, said resin grains are subjected to the repetitive impact of the mechanical
energy in the gaseous phase so that the grains are shaped into spherical grains to
obtain the desired toner without being crushed further.
[0029] The sphering treatment of the resin grains may be conducted either at the room temperature
or at the heated condition for some softening. Too much heating, however, causes the
increase in the viscosity of the binder resin, which furhter causes the aggregation
of the resin grains leading to the formation of the lumps and the serious hindrance
to the production of the toner with ideal distribution of grain sizes.
[0030] The carrier to constitute the two-component developing agent according to the present
invention is not limitted to special one but it may be preferred to use the carrier
of magnetic particles, the resing-coated carrier consisting of the magentic particles
whose surfaces are coated with the resin and the magnetic substance dispersion type
carrier consisting of the binder resin containing dispersed magnetic substance.
[0031] As the preferred magnetic substances to be used in the carrier may be, for example,
the substances which are conspicuously magnetized in the direction of the magnetic
field such as the iron, ferrite and magentite; the metals such as the iron, nickel
and cobalt which are highly magnetizable or the alloys and chemical compounds containing
these metals; and the alloys not containing the highly magnetic elements but highly
magnetizable when subjected to the appropriate heat treatment such as the kinds of
the alloys called the Heusler alloys including the manganess-copper-aluminum alloy,
manganess-copper-tin alloy and chromium dioxide.
[0032] The preferred resins usable in obtaining the resin-coated carrier or the magnetic
substance dispersion type carrier are not specified but may be, for example, the styrene
resin, acrylic resin, styrene-acrylic resin, vinyl resin, ethylene resin, rosin modified
resin, polyamide resin, polyester resin and so on. These resins may be used in combination.
[0033] The present invention relates to the development process characterized by that the
magnetic brush whereon said single-component or two-component developing agent is
deposited is made to contact said image carrier for the development of the image,
and said image carrier and the magnetic brush are disposed opposite to each other
so that said magnetic brush and said image carrier are able to change their relative
positions freely when said magnetic brush comes to contact the image carrier for the
development of the image.
[0034] As described previously, the development using the magnetic brush is accomplished
when the developing agent is conveyed to the development area for the purpose of the
development by the developing sleeve and its built-in roller. The development using
the magnetic brush according to the present invention is accomplished by causing both
or either one of the developing sleeve and the magnetic roll to rotate.
[0035] Changing the relative positions of the image carrier and the magnetic brush according
to the present invention may be acomplished either by changing both the position of
the drum axis of the image carrier and the position of developing sleeve axis to cause
said DSD in the development area to change or by fixing the position of the axis of
the image carrier drum whereas the position of the developing sleeve axis is left
changeable to enable the DSD in the development area to change.
[0036] The means for enabling the developing agent to be pressed against the image carrier
between the magnetic brush supporter and the image carrier according to the present
invention may be either the pressure of the loaded spring or the gravitational pressure
or the pressure deriving from the combiantion of the both. Besides, the pressurizing
means driven by the solenoid may equally be used. As described here, according to
the present invention, the image carrier and the magnetic brush supporter are disposed
opposite to each other but so as to be able to change their relative positions when
they come into contact under pressure for accomplishing the desired development, and
thus the magnetic brush can always be pressed against the image carrier under a constant
pressure to ensure the development of the uniform and high-quality visible images.
[0037] Furthermore, the development process according to the present invention is applicable
to both the normal development and the reversed development.
[0038] The present inventor has conducted the study on the relationship between the pressure
to cause both said magentic brush and the image carrier to be pressed agaist each
other and the space DSD in the development area and on the range of the appropriate
compressive pressure, and then reached the conclusions discussed in the following.
[0039] In said study, in considering the compressive pressure, the total compressive pressure
should be considered in terms of the pressure (gf/cm²) divided by the area of the
developing agent present in the development area between the drum with the photosensitive
material as the image carrier and the developing sleeve as the magnetic brush supporter,
but, actually, the value (gf/cm) (hereinafter referred to as the "linear pressure")
obtained by dividing the total compressive pressure by the lateral length of the development
area is considered, since it is difficult to measure the area of the development area.
[0040] When the total compressive pressure is considered in terms of the linear pressure,
however, it seem to vary depending on the diameter D(PH) of the drim with the photosensitive
material and the diameter D(DV) of the developing sleeve.
[0041] Thus, as for the D(PH), four different diameters were prepared, that is 50 mm, 80
mm, 150 mm and 200 mm and as for the D(DV), three different were prepared, that is
20 mm, 30 mm and 40 mm, then the experiment was conducted as to various combinations
of PH and DV.
[0042] The result of the experiment concerning the relationship between the space DSD in
the development area and the linear pressure (gf/cm), however, indicates that there
is no significant difference depending on the difference in said diameters. Thus,
in said experiments, the diameter of 80 mm is used for the D(PH), and the diameter
of 30 mm for the D (DV).
[0043] Fig. 9 shows the relationship between the linear pressure and the space in the development
area, and the range within which the high-quality development can be accomplished.
[0044] In the experiment, a drum of 80 mm in diameter whose surface was covered with a layer
of OPC photosensitive material was used as the image carrier; a developing sleeve
of 30 mm in diameter with a magnetic roll fixed inside said sleeve was used as the
magnetic brush supporter; the magnetic flux density in the development area was set
within 800 to 900 Gauss; and the toner of within 9 to 13 µm in average grain size
was used.
[0045] The space DSD in the development area varies depending on the developing agent controlling
space DH. Said Fig. 9 shows the cases under two different conditions, that is, DH
= 0.5 mm and DH = 0.40 mm.
[0046] As shown in said diagram, the space DSD in the development area is almost equal to
the developing agent controlling space DH where the linear pressure is 5 gf/cm or
less but the space DSD decreases as the linear pressure increases where the linear
pressure is above 5 gf/cm.
[0047] In any of the cases where DH = 0.05 mm or DH = 0.40 mm, fairly satisfactory development
can be accomplished when the liner pressure is within the range (A) of 5 - 200 gf/cm,
but the poor development almost close to the whitening can occur when the linear pressure
is less than 5 gf/cm, and the uneven development occurs when the linear pressure is
higher than 200 gf/cm. Thus, the latter two linear pressure ranges are ranges of poor
development.
[0048] Besides, when the linear pressure is within the range (C1) of 5 - 15 gf/cm and the
range (C2) of 80 - 200 gf/cm, the frequency of the poor development tends to increase
depending on the environmental condition, especially when the temperature is realtively
high, and so these ranges would be considered to be unstable ranges.
[0049] Thus, it has been clarified that the desirable linear pressure range (B) is within
15 - 80 gf/cm.
[0050] The preferred embodiments of the present invention will be explained in the following.
[0051] Figs. 1 through 3 are respectively the partial side views of the image forming units
using the developing units embodying the development process according to the present
invention, each representing the case where the position of the image carrier drum
is fixed, whereas the position of the developing sleeve axis is left movable to keep
the space DSD in the development area variable.
[0052] In these figures, 1 denotes a photosensitive drum using the photosensitive material
such as the OPC as the image carrier, and 2 a developing unit with the magnetic brush
using the two-component developing agent consisting of the mixture of the toner and
the carrier. The photosensitive drum 1 rotates in the direction indicated with an
arrow and forms the electrostatic latent image thereon by the latent image forming
device, which is not shown in the drawing, provided on the upstream side of the developing
unit 2. Then, said photosensitive drum is brushed with the magnetic brush of the two-component
developing agent D that is conveyed on the developing sleeve 3 of the developing unit
2. The developing sleeve 3 of the developing unit 2 shown in the drawing may be either
fixed or left to be able to rotate counterclockwise so that the magnetic brush can
be conveyed towards the direction indicated by anarrow as is shown in Fig. 1 as the
internal magnetic roll 4 haveing the N and S magnetic poles rotates clockwise (the
roll may be fixed where the developing sleeve 3 is set to rotate).
[0053] In Fig. 1, the developing unit 2 indicates an embodiment using the component of the
gravity as the means for pressing. Said developing unit 2 is supported, like a pendulum,
at a supporting point 5 provided on the frame of the image forming unit. The center
of gravity of said developing unit 2 locates at right side of the vertical line passing
the supporting point 5 so that said developing unit comes to contact the photosensitive
drum 1 when the magnetic brush is not on the developing sleeve 3. Then, said contact
pressure can be adjusted by changing the engaging position of the engaging base 6
of the developing unit 2 engaging with the supporting point 5. By using this contact
pressure adjusting system, the contact pressure can be controlled and stabilized;
furthermore, the space DSD in the development area can be determined automatically
corresponding to the clearance between the developing sleeve 3 and the brush formation
controller 7, that is, the value of the controlling space for the developing agent
D, so that the toner image with adequate density and free of vertical and lateral
unevenness can be formed not only when the photosensitive material such as Se is used
for the photosensitive drum 1 but also even when the photosensitive materials which
form the low-potential electrostatic image such as the OPC is used. The contact pressure
can be varied continuously by adjustably setting the position of the supporting point
5 or the engaging base 6. Note that 8 denotes a stirrer for agitating developing agent,
and 9 a toner feeder for the toner hopper.
[0054] Figs. 2 and 3 show the embodiments using a spring as the contact pressure provider.
In the embodiment shown in Fig. 2, the developing unit 2 is supported with the supporting
point 5 and a spring 10 and differs from the developing unit 2 described in Fig. 1
in that the contact pressure of the developing sleeve 3 against the photosensitive
drum 1 can be adjusted by adjusting the pressing force of the spring 10. This embodiment
is also capable of accomplishing desired development as well as the developing unit
2 shown in Fig. 1.
[0055] In the embodiment shown in Fig. 3, the developing unit 2 moves on the frame of the
image formation unit by means of wheels 11, and the contact pressure of the developing
sleeve 3 against the photosensitive drum 1 is adjustable by the spring 10, thereby
differentiating from the developing units shown in Figs. 1 and 2, but this embodiment
is capable of accomplishing the desired development as well as the development unit
shown in Figs. 1 and 2.
[0056] Figs. 4 and 5 respectively show the partial side views of the image formation unit
embodying the development process according to the present invention. In each of these
cases, the developing sleeve axis is fixed whereas the position of the image carrier
is left movable so that the space DSD in the development area can be kept vaiable.
[0057] In the embodiment shown in Fig. 4, the developing unit 2 is fixed to the frame 12
of the main unit, and the toner supplied from the toner feeder 9 is mixed with other
developing agent with the stirrer 8 in order to prepare the developing agent of appropriate
mixing ratio, which is to be supplied as the developing agent D to the internally
located developing sleeve 3. The brush formation controller 7 controls the layer thickness
of the magnetic brush. On the other hand, the drum axis 1a of the photosensitive drum
1 is disposed so as to be able to move along a long groove 14 provided on the frame
13 of the main unit, and thus the space DSD in the development area can be changed
depending on the position of said drum axis. The spring 10 is a compression-loaded
spring disposed between the frame 13 of the main unit and the drum axis 1a and exerts
the pressing force to cause the surface of the photosensitive drum to press against
the magnetic brush to effect the desired development of the image.
[0058] In contrast with the embodiment shown in Fig. 4 characterized by making only the
photosensitive drum to be movable, the embodiment shown in Fig. 5 is characterized
by making the whole body of the image carrier in the form of the drum unit to be movable.
More particularly, in the embodiment shown in Fig. 5, the photosensitive drum 1 and
the peripherally located cleaning member 16 and the charged electrode 17 are arranged
so as to constitute the drum unit 15; the wheels 11 permit said drum unit to move
along the long groove 14; and the space DSD in the development area can be varied
depending on the position of said drum unit. The spring 10 compressed between the
frame 13 of the main unit and the drum unit 15 is loated with the force to cause the
surface of the photosensitive drum to be pressed against the magnetic brush for acomplishing
desired development of the image.
[0059] The datails of the embodiments of the present invention will be explained in the
following.
(Embodiment 1)
[0061] In the unit shown in Fig. 3, the photosensitive drum 1, 80 mm⌀ in diameter and 330
mm long, has a layer of OPC photosensitive material on its surface and is designed
to be charged with the surface potential of -600 V (black part potential) as the drum
rotates at a peripheral speed of 150 mm/sec. The developing sleeve 3, 30 mm in diameter
and 320 mm long, of the developing unit 2 is designed so as to be able to rotate at
a peripheral speed faster 2.9 times that of the photosensitive drum, in the direction
indicated with an arrow in Fig. 1, wherein the internal magentic body 4 is fixed.
The layer thichness controlling gap between the sleeve 3 and the brush formation controller
7 is set to 0.4 mm. In preparing the developing agent, the toner with the average
size ranging 9 - 13 µm is prepared by adding the coloring agent into polyester resin,
the carrier consisting of the ferrite cores coated with the fluororesin of 2 µm thick
is made to form the particles with the average particle size of 70 µm, and the toner
and the carrier are then mixed with the silica, titanium oxide and stearic acid to
prepare the two-component developing agent. The developing unit 2 is pressed towards
the photosensitive drum 1 by means of the two spring exerting the spring pressure
of 575 gf, equivalent to 35.9 gf/cm in terms of the linear pressure.
[0062] The result of the experiment conducted under the above- mentioned conditions indicates
that the toner image with adequate stability and density can be developed without
uneveness.
[0063] In the above embodiment, a series of experiments for the development were conducted
under varied conditions such as the peripheral speed of the photosensitive drum varied
within 105 - 150 mm/sec., the surface potential varies within -500 V to -700 V, the
rotating speed (peripheral speed) of the sleeve varied within 2 to 3.5 times that
of the photosensitive drum, the layer thichness controlling gas varied within 0.25
to 1.0 mm, the thichness of resin coating for the carrier particles varies within
1 to 4 µm, the average particle size of the carrier particles varied with 70 to 100
µm, the average particle size of the toner varied within 9 to 13 µm, the spring pressure
varied within 400 to 700 g or the liner pressure varied within 25 to 43.8 gf/cm, and
it has been clarified that the stable image with adequate density can be developed
even under these conditions.
(Embodiment 2)
[0064] More detailed study was conducted as to the embodiment shown in Fig. 3, and the result
of this study will be discussed in the following in reference to Fig. 6.
[0065] In Fig. 6, 21 denotes the image carrier of 80 mm in diameter and 320 mm in length
whose circumferential surface is coated with the OPC photosensitive material, which
rotates in the direction (clockwise direction) indicated with an arrow at a peripheral
speed vP of 110 mm/sec. Said image carrier is negatively charged with a corona charger
not shown in the drawing; said negative charge potential decreases depending the degree
of the exposure that takes place following said negative charging process; and the
electrostatic latent image is formed on said image carrier 21. The relationship between
the density of original image and the surface potentiality of the photosensitive material
exposed to the original image according to the results of the actual measurements
are as follows:
V
1.3 (Density of original image: 1.3) = -590 to -700 V
V
0.2 (Density of original image: 0.2) = -200 to -240 V
V
0.0 (Density of original image: 0.0) = -50 to -80 V
[0066] As for this embodiment, the development process concerned with the development of
the electrostatic latent image and developing unit will be explained, but the image
carrier need not be limited to the OPC photosensitive material nor is the charging
to the negative charging. The surface potential of the image carrier also need not
be limited within said range. Thus, in applying this embodiment, said development
bias may be adjusted depending on the surface potential.
[0067] The developing agents applicable to the development process according to the present
invention are as described in the foregoing, but the following developing agents are
used in this embodiment.
[0068] The toner used in this embodiment is of the particle size of 11 µm (by average weight)
and prepared by replacing the polyester of the toner used in the embodiment 1 with
the atyrene-acrylic resin and by addings 3 weight % of the polypropylene to the total
weight of the toner. The magnetic carrier is of the spherical carriers with particle
size of 70 µm whose surfaces are coated with the fluororesin, and the toner can be
positively charged when stirred together with the magnetic carrier. The toner consumed
during the development process is replenished in the developing unit which will be
explained later, and the toner density is controlled within 3 to 6 w%. The developing
agent controlled within said condition maintains desirable fluidity.
[0069] In Fig. 6, 30 denotes the developing unit, which is contained in a development casing
31 of polycarbonate and the like, and the following members are contained in said
casing. That is the developing sleeve 32, which contains the magnetic roll 33 consiting
of a group of magnets installed stationarily inside said sleeve. The magnetic roll
33 comprises a main magnet N1 disposed opposite to the image carrier 21 and the six
pieces of auxiliary magnets S4, N3, S3, S2, N2 and S1 arranged on the internal circumferential
surface of said sleeve in the counterclockwise order so that said auxiliary magnets
maintain their anular positions as are shown in Fig. 7 and exert the magnetic flux
densities as are listed in Table 1 on the circumferential surface of the developing
sleeve 32.
[0070] The main magnet N1 disposed opposite to the image carrier 21 is slightly (5°) inclined
against the line drawin between the drum axis of the image carrier 21 and the axis
of the developing sleeve 32 so that its maximum magnetic flux density is present in
the upstream direction (clockwise direction.) All the auxiliary magnets their magnetic
forces so as to cause the developing agent to be adsorbed on the developing sleeve
32. The auxiliary magnets S3 and S2, which are of the same polarity, are disposed
adjacent to each other and thus the repulsive magnetic field is formed between them,
and the developing agent which has been deposited on the circumferential surface of
the developing sleeve 32, conveyed to the development area and used for the development
is changed with the newly stirred developing agent in this respulsive magnetic field.
In this embodiment, the magnetic roll 33 is of the stationary type, but the present
invention is applicable to the rotary type magnetic roll too.
[0071] The developing sleeve 32 consists of a aluminium or a stainless steel cylinder with
relatively small wall thichness having the outside diameter of 30 mm and the length
of 300 mm. The external circumferential surface of said developing sleeve is of sandblast-finish
(using #30 sand), and the roughness of the surface after the sandblasting treatment
range within Ra = 3 - 8 µm. Said developing sleeve 32 rotates counterclockwise (in
following direction in the development area) at a peripheral speed vs of 336 mm/sec.
(Number of revolution: 214 rpm) in the development process. Thus, the development
in the case of this embodiment is accomplished in the following relationship of the
speeds:
Speed ratio (vs/vp) = 3.05
[0072] As one of the conditions for the satisfactory development of the image, it is considered
that the speed ratio (vs/vp) should be at least 2 though it is dependent on the quantity
of the developing agent to be conveyed, but the value in this embodiment is not necessarily
limited.
[0073] The brush formation controller 34 is disposed parallel to the axis of the developing
sleeve 32 and fixed to the point on the upsteam side at about 140° from the position
of the main magnetic pole in the development area E leaving the developing agent controlling
space D to the developing sleeve 32. The space DH is not required to be maintained
so accurately as the space in the case of the conventional developing unit or the
development process. The space DH should be set to about 0.5 mm though the reason
for this will explained in details. 35A is a main stirring blade. 35B is an auxiliary
stirring blade. 36 is a toner replenishing roller. 37 is a toner stirring plate.
38 is a remainder quantity detection sensor. 39 is a toner cartridge holder. When
the toner cartridge containing the toner which is cylindrical in form is set in the
toner cartridge holder 39, a port of the cartridge is opened by the port opening mechanis
not shown in the drawing to cause the toner to drop due to the gravity, and the toner
accumulates on the toner replenishing roller 36. The toner stirring plate 37 turns
slowly to prevent the accumulated toner from hardening.
[0074] When the toner accumulated on the toner replenishing roller 36 is consumed, the remainder
quantity detection sensor 38 detects the quantity of the remainder and give an alarm
requiring the toner cartridge to be refilled. Also, when the density of the toner
in the developing unit 30 is found to be not enough the separately installed toner
density detector, this causes the toner replenishing roller 36 to rotate to replenish
the developing agent pool with the toner.
[0075] The developing agent remaining in the developing agent pool is stirred together with
the newly replenished toner by the auxiliary stirring blade 35B and the main stirring
blade 35A in order to prepare the developing agent in which the toner is distributed
uniformly, and, simultaneously, the toner is charged by the friction occurring while
being stirred.
[0076] The stirred developing agent is deposited on the developing sleeve 32, and its quantity
to be conveyed to the development area E is controlled by the brush formation controller
34. Then, the toner is electrostatically deposited on the electrostatically charged
latent image on the image carrier 21 to accomplish the development of the image.
[0077] The developing unit incorporating the aforementioned system and capable of operating
in the aforementioned manner is designed so as to be movable and has it's weight of
3.5 kgf including the weight of the developing agent. Said developing unit is pressed
by the spring so as to come close to the drum of image carrier 21. On the side of
the recording unit, two rails 51 are installed parallelly to each other on both the
near side and the far side, viewing Fig. 6 from front side. Said rails 51 are made
from the material with relatively small coefficient of friction and provide the smooth
surfaces with adequate rigidity.
[0078] On the other hand, the developing unit 30 is provided with two pairs of the rollers
41A and 41B for the movement of said unit, each located on both the near side and
the far side. Said two pairs of rollers 41A and 41B for the movement are designed
to move on the rails 51, but, in this embodiment, said rollers are provided with the
ball bearings for minimising the resistances at the time of the movement. Of course,
the roller bearings may be used instead of the beall bearings.
[0079] On the side of the recording unit, a compression supporting shafts 52 are provided
on both the near side and the far side. The two pressure springs 53 with one end supported
by the compression supporting shaft 52 are encorporated so that the compressed and
forced two pressure springs 53 press the side wall 31A through a pressure shoe 54,
thereby causing the developing unit 30 to be pressed against the circumferential surface
of the drum of the image carrier 21. As a result, the developing agent deposited and
held on the surface of the developing sleeve 32 causes the electrostatic latent image
on the image carrier to be developed. In this embodiment, for the pressure springs
53, the two pressure springs with the pressure load F ranging 200 gf to 600 gf are
used to provide the linear pressure ranging 13.3 gf/cm to 40 gf/cm. Consequently,
the poor development having the whitening condition was observed in a few cases where
the linear pressure was 13.3 gf/cm, but the satisfactory development was obtained
where the linear presure was 16 fg/cm or more.
[0080] The present invention is represented by the foregoing embodiments. The result of
the study on the developing unit shown in Fig. 6 will be explained in the following.
[0081] Fig. 8 is a graphical illustration indicating the change in the space DSD in the
development area where the developing agent controlling space DH is changed within
about 0.4 mm to 0.6 mm. For the pressing force, an experiment was conducted using
the two pressure springs 35 whose pressing forces F are set to 575 gf respectively
to produce the linear pressure of 38.3 gf/cm and using a same reference image as an
original image to be copied.
[0082] According to the result of the experiment, satisfactory developments can be obtained
in all the cases as far as the DSD and DH are within the graphically shown ranges.
This means that the system, according to the present invention characterized by that
the space DSD in the development area is variable depending on the quantity of the
developing agent to be supplied during the development process, automatically corrects
the space DSD even when the set value of the space DH has varied or deviated for desirable
development.
[0083] More strictly, however, the space DSD in the development area is primarily not dependent
only on the above-mentioned two conditions but also dependent on many other conditions
to some extent. For example, the DSD is also dependent to some extent on the surface
potential and line speed of image carrier, the fluidity of developing agent, the density
and electric charge intensity of the toner and the density of the original image (the
potential of electrostatic latent image). The result of the study by the present inventor
indicates that there is the following relationship between the condition of the original
image (Black solid printed matter or blank white paper) and the space DSD in the development:
DSD (Black solid printed matter) = DSD (Blank paper) + 0.02 mm.
[0084] In the foregoing, the content of the present invention is explained in reference
to its embodiments. The content of the present invention, however, is not limited
to that represented by above embodiments. For example, in said embodiment, the pressure
spring 53 are used as the means for providing the pressing force that cause the circumferential
surface of the developing sleeve 32 to be pressed against the surface of the image
carrier 21. Instead of said kind of pressure-producing means, however, the means for
obtaining the necessary pressing force from the component of the weight of the developing
unit 30 by inclining the rails 51 for the movement of said developing unit 30 may
be employed. Besides, the direction of the movement of the developing unit 30 may
be conveted into the pressing force by means of the dead weight. Furthermore, in the
embodiment described in the foregoing, the surface position of the image carrier 21
is fixed, and the developing unit 30 is pressed so as to be brought close to said
developing unit, but the development process according to the present invention permits
the developing unit 30 to be fixed while the image carrier 11 is pressed so as to
be brought close to said developing unit 30, and such development process is also
included in the concept of the present invention.
[0085] The development process according to the present invention is characterized by the
variable space in the development area that permits the image carrier and the magnetic
brush to be pressed against each other during the development process, so that a stable
brusing force is produced between the image carrier and the developing agent to develop
the high-quality image stably.
[0086] Furthermore, the space in the development area can be varied depending on the quantity
of the developing agent deposited on the developing sleeve for conveyance, so that
the developing agent can flow smoothly without causing the ecattering of the developing
agent.
[0087] Also, according to the development process of the present invention, it is not necessary
to rise up the toner concentration in the two-component type developing agent even
when the OPC is used for the photosensitive material of the photosensitive drum, so
that the toner of adequate concentration which will not cause uneven development can
be obtained stably, and this one of the outstanding features of this development process.
[0088] Further, the development process and the developing unit according to the present
invention is provided with the function to enable the automatic control of the space
in the development area, and this permits the accuracy and the allowance of the brush
formation controlling member and the allowances of the deflections of the image carrier
drum and the developing sleeve due to their eccentricities to be set broader than
those of the conventional developing unit, so that the manufacturing costs of the
parts and the number of steps of assembly work can be reduced.
[0089] The improvement of the conventional developing unit through the introduction of the
aforementioned development process will be explained in the following.
[0090] With respect to the aforementioned development process, as the means for keeping
the developing sleeve pressed against the image carrier at a constant intensity, the
means for pressing the whole developing unit elastically by the separately provided
spring member and the system for pressing the developing unit by utilizing its own
weight as the dead weight have been explained.
[0091] Said systems, however, may cause the hardening of the developing agent that ends
up with the formation the depressed marks on the surface of the image carrier or the
crystallization of the photosensitive material such as one containing Se, since, with
said systems, the developing sleeve is left pressed against the image carrier even
after the developing unit comes to rest, thereby causing the developing agent layer
to be left compressed for a long period of time to promote the packing and the hardening
of the developing agent.
[0092] The packing of the developing agent can cause the scattering of the image carrier
or cause unnecessary developing agent to be deposited on the image carrier when the
developing unit is started, thereby causing deteriora tion of the developed image.
[0093] The present inventors have taken into account said short-comings of aforementioned
systems and improved said systems to prevent the packing of the developing agent layer
that occurs when the developing agent layer is left compressed for a long period of
time.
[0094] More specifically, the developing unit comprising the electrostatic latent image
carrier and the magnetic brush supporter which are disposed opposite to each other
and to be able to change their realative positions freely so that the magnetic brush
can be pressed against said electrostatic latent image carrier to accomplish the desired
development is improved by providing the means for separating said magnetic brush
and said electrostatic latent image carrier from each while the development process
is not in progress.
[0095] The embodiment of the present invention comprising the above-mentioned improved system
is shown in Figs. 1 though 18.
[0096] Figs. 11 and 12 show the improved version of the developing unit shown in Fig. 6.
This improved developing unit has a rotary shaft 152 with a pair of elliptical cams
151 set to the same angular phase fixed on the front and the rear end of said shaft
is disposed parallelly to said depressing shaft 142.
[0097] On the other hand, each of the side walls 121 at the front and the back of said developing
unit housing 121 is provided with a square notch 121B so that said cams 151 can respectively
fit into the openings of said notches 121B.
[0098] While the developing unit 120 is in operation, the rotation of said rotary shaft
152 is controlled by the signal from the controller of the recording unit to set the
rotary angle of said rotary shaft to the point at which said cams 151 rise as illustrated
in Fig. 11, and so some gap can be formed between the edge side 121C of the member
with said notch 121B and said cam 151.
[0099] Thus, said developing unit 20 is pressed towards the left by the elastic force of
said pressure spring 143 to cause the developing sleeve 122 with the developing agent
deposited and carried on its surface to be pressed against the surface of said image
carrier 111 to effect the development of the electrostatic latent image.
[0100] When the developing unit 120 has stopped to operate, said rotary shaft 152 is caused
to rotate clockwise by about 90° starting from the angle indicated in Fig. 11 according
to the signal issued from said controller and kept at the position indicated in Fig.
12.
[0101] During the course in which said can 151 reaches the angle indicated in Fig. 12, the
edge side 121C of said notch 121B is depressed by the circumferential surface of the
cam 151, so that said edge side 121C is caused to move on said rail 141 towards the
right agaist the elastic force of said pressure spring 143 as said rollers 131A and
131B for the movement rotates and stop at the position indicated in Fig. 12.
[0102] Consequently, the developing unit 120 is caused to retreat towards the left to open
the development area E between the developing sleeve 122 and the image carrier 111,
so that the compressive force acting on the developing agent on the developing sleeve
122 can be removed.
[0103] With respect to each of the following embodiments, the systems such as those for
bringing said developing unit 120 to be pressed against the image carrier 111 or bringing
it to be released from the pressure will be explained.
[0104] Fig. 13 and 14 show the second embodiment of the present invention, in which the
developing unit 120 is pressed against the image carrier 111 or released from the
pressure by the pressing system as is explained in the following.
[0105] The pressure spring 243 is installed in compressed condition between the pressing
shoe 244 and the guide cylinder 245 that containes said pressing shoe 244 so that
the sliding stroke of said pressing shoe 244 is suppressed.
[0106] Said guide cylinder 245 in supported slidably in horizontal direction to the body
of the developing unit, and the pressure pin 245A is linked to the slot cam 246A of
the cam plate 246.
[0107] The cam plate 246 with said slot cam 246A is fixed to the rotary shaft 247 installed
on the main unit and has the radius with the curvature that gradually diminishes in
counterclockwise direction so as to enable said guide cylinder 245 to slide horizontally
through said pin 245A as said rotary shaft 247 rotates.
[0108] Fig. 13 shows that the cam plate 246 is at the angular position where said cam plate
came to rest after rotating counterclockwise due to the rotation of said rotary shaft
247, and that the guide cylinder 245 is at the leftmost position after being caused
to slide towards the side of the developing unit by said slot cam 246A.
[0109] In the couse of the displacement of said guide cylinder 245, the end of the presing
shoe 244 comes to contact the side wall 121A of the developing unit 120 to cause said
developing unit 120 to be pushed towards the side of the image carrier 111 and kept
pushed even after the operation of the developing unit is stopped, and so the pressure
said pressure spring 243 increases to cause said developing unit 120 to be pushed
further thereby causing the developing sleeve 122 to be pressed slidably against the
surface to the image carrier 111 to effect the development of the electrostatic latent
image.
[0110] On the other hand, to cancell the contact pressure of the developing sleeve 122 to
the image carrier 111, the cam plate 246 is caused to rotate counterclockwise and
stop by the rotation of said rotary shaft 247, so that, as shown in Fig. 14, the guide
cylinder 245, while suppressing the pressing shoe 244, is caused to move towards the
right due to the change of the curvature radius of said slot cam 246A, whereby the
pressure acting on the developing unit 120 can be cancelled.
[0111] Consequently, the developing unit 120 is set free on the rails 141 thereby opening
the development area E as shown in Fig. 14.
[0112] Figs. 15 and 16 show the third embodiment. In this embodiment, the rails 241 are
fixed at a predetermined declination against the image carrier 111 so that the developing
unit 120 on said rails 241 is caused to move towards the image carrier 111 due to
the component of the dead weight of the developing unit itself.
[0113] That is, where the total weight of said developing unit 120 including the weight
of the developing agent is assumed to be 3.5 kgf, and said declination to be 6°, the
component of the total gravity can be determined as
3.5 kgf x sin 6° = 0.36 kgf
Thus, the developing sleeve 122 is pressed against the surface of the image carrier
111 with the force given above to provide a desirable condition for the development
of the image.
[0114] Thus, this embodiment can dispense with the pressure spring 143 or 243 which is required
in the first and the second embodiments, and the pressure to bring the developing
sleeve 122 to contact the image carrier 111 can be cancelled by the rotation of the
cam 151 like the case of the first embodiment; however, in this embodiment, the development
area E can be opened by simply resisting the dead weight of said developing unit 20
as shown in Fig. 16.
[0115] Figs. 17 and 18 show the fourth embodiment, wherein the rails 341 are installed so
as to be able to oscillate freely on the axis 342 to serve as the supporting point,
and said rails are supported with the cam 343 located beneath said rails 341.
[0116] When said cam 343 makes the angle at which said cam rises as illustrated in Fig.
17, said rails 341 are declined at a predetermined angle, whereby said developing
unit 120 on said rails 341 is caused to move towards the image carrier 111 due to
the force deriving from the component of the dead weight of said developing unit itself.
[0117] Thus, the pressure spring 143 or 243 which is required in the first and the second
embodiments is not required in this embodiment, since the developing sleeve 122 can
be brought to be pressed against the surface of the image carrier 111 to effect the
desired development of the image owing to the force deriving from the component of
the dead weight of the developing unit 120 like the case of the third embodiment.
[0118] To cancell the pressure to cause the developing sleeve 122 to be brought to be pressed
against the image carrier 111, as illustrated in Fig. 18, said cam 343 is caused to
rotate clockwise by about 90° so that said rails 341 is brought to be horizontal or
declined slightly to the image carrier 111, whereby the component deriving from the
dead weight of the developing unit 120 can be cancelled to release the development
area E as illustrated in Fig. 18.
[0119] An object of the present invention is to provide an electrostatic recording system
wherein the gap between the developing sleeve and the image carrier of the developing
unit can be adjusted automatically while the development process is in progress, whereas
the gap can be kept larger than the adjustable range while the developing unit is
at rest, so that the developing agent can be brought to slidably contact the image
carrier while producing adequate brushing effect between the developing agent and
the image carrier, and the packing of the developing agent that may occur while the
developing unit is at rest can be prevented, whereby the developing unit capable of
constantly developing the highquality images can be provided.
[0120] In the development system designed so that the relative positions of said developing
unit comprising the magnetic brush supporter and electrostatic latent image carrier
can be varied freely, and the magnetic brush that has passed the developing agent
controller is pressed against said electrostatic latent image carrier to effect the
desired development of the image, the packing or hardening of the developing agen
that may occur when left unused for a long period of time can also be prevented where
the rollers having the outside diameters larger than the outside diameter of the magnetic
brush supporter and not coming into contact with the electrostatic latent image carrier
during the development process are installed on the same axis as that of the magnetic
brush supporter.
[0121] The embodiment wherein the developing unit incorporating said rollers will be explained
in the following in reference to Figs. 19 through 23.
[0122] In said developing unit, the set position of the brush formation controller 407 is
normally adjusted so that the developing agent controlling space DH range within 0.4
to 0.6 mm, and the pressing force (gf) is adjusted so that the linear pressure (gf/cm)
to be determined by dividing the pressing force by the axial length (cm) of the developing
sleeve in the development area E ranges within 15 to 80 gf/cm where the development
can be effected satisfactorily.
[0123] When said linear pressure is set to 38.3 gf/cm, the relationship between said developing
agent controlling space DH and the space DSD in the development area can be expressed
graphically as in shown in Fig. 18, according to the result of the experiment.
[0124] Where the recording unit has been left unused over a long period of time, the developing
agent D in the development area E is subjected to the compressive force, and said
space DSD in the development area will be reduced gradually to cause the developing
agent D to be packed and hardened, which adversely affect the later development process.
According to the present invention, however, the rollers 404 having the outside diameter
larger by 0.4 to 0.5 mm than the outside diameter of the developing sleeve 433 of
the development roller 403 as the supporter of the magnetic brush are installed on
both ends of the development roller, so that said space DSD in the development area
will not becomes smaller than the values ranging within 0.2 to 0.25 mm, whereby the
packing and hardening of the developing agent D can be prevented.
[0125] Fig. 21 is a cross-sectional view showing another embodiment of the present invention.
In this embodiment, the photosensitive drum 401 as the electrostatic latent image
carrier is movable in the form of the drum unit, whereas the developing unit 422 is
stationary. That is, the photosensitive drum 401 rotably supported by the drum unit
425 through the shaft 401a and peripherally located cleaner 426 and the charged electrode
427 are integrated into the drum unit, and the wheels 428 installed on the drum unit
425 move along the longitudinal groove 429 provided on the frame 423 of the body of
the recording unit, whereby the space DSD in the development area can be varied according
to the position of the drum unit. The pressure spring 424 is compressed between the
frame 423 of the main unit and the drum unit 425 and exerts its pressure so as to
cause the surface of the photosensitive body to be pressed against the magnetic brush
to effect the desired development of the image.
[0126] The developing unit 422 comprises the development roll 403 with the rollers 404 installed
on its both ends, the brush formation controller 417, stirring blade 418 and toner
replenisher 419.
[0127] The development rollers 403 used in the foregoing two embodiments will be explained
in details in the following.
[0128] Fig. 22 is an oblique perspective view showing the development rollers according
to the present invention. Fig. 23 is a lateral cross-sectional view showing said development
rollers including their shaft. As shown in Fig. 23, the rollers 404 are installed
rotably to the rotary shaft 433a of the developing sleeve 433 and to the stationary
shaft 434a of the magnetic roller 434 through the ball bearing 436A. The bearing 436B
is a bearing installed between the magnetic roll 434 and the rotary shaft 433a. The
bearing 436C is a bearing installed between the developing sleeve 433 and the stationary
shaft 434a.
[0129] The magnetic roll 343 is provided with the main magnet and the auxiliary magnets
which have already been explained in reference to Fig. 7.
[0130] As discussed previously, the outside diameters of rollers 404 being set larger by
0.4 - 0.5 mm than the outside diameter of the developing sleeve 433, even when the
recording unit is left unused for a long period of time not only leaving the developing
agent in the development area subjected to compressive force but also causing the
space DSD in the development area to be reduced, the circumferential surfaces of the
rollers 404 contact the ends of the circumferential surfaces of the photosensitive
drum 401 to prevent the space DSD in the development area from reducing below 0.2
- 0.25 mm. Thus, the compaction and hardening of the developing agent can be prevented.
[0131] As discussed in the foregoing, the developing unit according to the present invention
is movable to the image carrier within the recording system, and said developing unit
comprises the rotary parts such as the developing sleeve as the means for accomplishing
the desired development. The present inventors have studied from various angles the
means for transmitting the rotation and the driving force of the drive motor to the
movable developing unit.
[0132] The developing unit according to the present invention is designed to accomplish
the desired development by causing the magnetic brush to be pressed against the image
carrier by providing almost constant pressure, but it is no easy matter to provide
a developing unit that is capable of performing the development operation at stable
condition without having said contact pressure hindered or varied excessively due
to the transmission of the driving force to the developing unit from the drive system.
More particularly, in transmitting the electric power to the developing unit from
the main system, depending on the construction of the transmission system, the torque
to be transmitted may include the component of the force that acts against the force
required for the developing unit to be pushed, or the vibration due to the transmission
of the electric power may reduce the necessary contact pressure, and thus it is not
easy to provide a system capable of keeping the developing unit pressed against the
image carrier at a constant contact pressure.
[0133] Thus, it is another object of the present invention to overcome the above-mentioned
difficulties and provide a developing unit capable of receiving the transmission of
the electric power without adversely affecting the contact pressure of the developing
unit to the image carrier so that the developing process can be operated stably and
efficiently at all times.
[0134] The above objective of the present invention can be attained by providing a development
system featuring that the developing unit comprising the magnetic brush suppor is
designed movable and that the developing unit designed to accomplish the desired development
by bringing the magnetic brush to be pressed against the electrostatic latent image
carrier is driven by the drive motor installed on said movable developing unit.
[0135] The electric power to drive said developing unit according to the present invention
is provided by the drive mechanism described in the following.
[0136] Fig. 24 shows the gear system of said developing unit 120 located on the back of
the side wall 121A at the innermost side of the housing 121 of said developing unit.
The shafts S1, S2, S3, S4 and S5 are the shafts as the axis of rotation of said developing
sleeve 122, main stirring blade 125A, auxiliary stirring blace 125B, toner replenishing
roller 126 and toner stirring plate 127 which are extended through said side wall
121A.
[0137] The spur gears G1, G2 and G3, the intermediate gear G6 meshing with said spur gear
G3 and the spur gears G4 and G5 meshing parallelly with said intermediate gear G6
are fixed to each of said shafts respectively so that when the drive power is transmitted
to said spur gear G1, all said spur gears or all said shafts start to turn simultaneously
to drive various parts within said developing unit 120 in the directions indicated
by arrows respectively for operating the development process.
[0138] The stepped gear consisting of the drive gear G0 meshing with said spur gear G1 and
the worm gear WG which are combined into a unit is rotably supported with the shaft
S0 installed at the back of said side wall 121A, and said worm gear WG meshes with
the worm gear W on the shaft of the drive motor M supported with the bracket B installed
on the back of said side wall 121A.
[0139] Said drive motor M is supplied with the power from the power source of the recording
unit through a cable and causes said spur gear G1 to rotate counterclockwise at the
rate of 214 revolutions per minute through said worm gear system and the drive gear
G0.
[0140] As described in the foregoing, the developing unit 120 according to the present invention
contains the power source to drive various parts and all the power transmission systems,
so that the operations of various parts are not affected at all by the position of
the developing unit 120. Consequently, the elastic action of said pressure spring
143 can be utilized fully, and this enables the space DSD in the developing area to
be maintained stably and accurately.
[0141] Fig. 25 is a diagram showing the relationship between the pressure load by the pressure
spring 143 and the value of the space DSD in the development area as to the Case I
where the developing agent controlling space DH is set to 0.55 mm and the Case II
where the same is set to 0.40 mm. This diagram indicates that, in each of said cases,
the elastic action of the said pressure spring 143 enables the near side and the far
side of said developing unit 120 to be subjected to uniform pressure load, so that
the space DSD in the development area can be maintained uniform throughout the full
length of the developing sleeve.
[0142] The developing unit according to the present invention is designed so that the space
in the development area formed between the image carrier and the developing unit can
be varied automatically depending on the quantity of the developing agent by means
of the pressing force acting to cause the developing unit to be pushed towards the
image carrier, and whereby the brushing force produced between the image carrier and
the developing agent can be stabilized; furthermore, the power source to drive said
developing unit and the rela-power transmission systems are all contained in the developing
unit, so that the zigzag motion of the developing unit caused by the component of
the drive force occurring in transmitting the power from the drive system can be eliminated;
consequently, almost uniform space in the development area can be provided covering
the full length of the developing sleeve corresponding to the pressure given from
the back; as a result, a developing unit featuring the freedom form the unnecessary
vibration during the development process and the extremely reliable performance to
promise the stable and efficient development operation can be provided.
[0143] The transmission of the power to the developing unit according to the present invention,
however, can also be accomplished even when the power transmission system that causes
the component of the force from the power transmission system provided on the side
of the main system to be exerted in the direction of said compact pressure.
[0144] Fig. 26 shows the gear system of said developing unit provided on the back of the
innermost side wall 121 of the housing 121 of the developing unit.
[0145] The part of the power from the power source of themain unit of the recording system
is transmitted to the shaft S0 supported with the bearing on the base of the main
unit through the power transmission system not shown in the drawing and said image
carrier 111 to cause the drive gear G0 fixed to said shaft S0 to turn clockwise.
[0146] Said drive gear G0 is installed on the fixed location on the main unit, but, as explained
previously, when the developing unit is pressed leftward to cause the developing sleeve
122 to be pressed against the image carrier 111, said drive gear is meshed with the
said spur gear G1 to cause the drive power of the main unit of the recording system
to be transmitted to the developing unit 120.
[0147] According to the present invention, the center of rotation of said drive gear G0
or the position of said shaft S0 is set so as to make an angle ϑ with the horizontal
line passing the center of rotation of said spur gear G1 as illustrated in Fig. 26,
whereby the angular moment F of said drive gear G0 to be transmitted to said spur
gear G1 comprises the component of force F1 in vertical direction and the component
of force F2 in horizontal direction that is to cause said spur gear G1 to be pushed
towards the image carrier 111.
[0148] Consequently, the developing unit 120 is subjected not only to the elastic action
of the pressure spring 143 but also to the pressure deriving from the component of
the force F2 occuring in transmitting the power from said drive gear G0 so that said
developing unit can be pressed more surely against the image carrier 111 to ensuer
the stable and accurate development operation at all times.
[0149] Besides, said angle ϑ should not be too small nor too large in order to expect the
aforementioned effect, and so the angle should preferably range within 20° to 35°.
If the component of force F2 causes the negative pressure, the drive power cannot
be transmitted adequately, thereby causing the vibration and unstable operation of
the developing unit 120.
[0150] Thus, in the developing unit 120 according to the present invention, the space DSD
in the development area is dependent on the pressure load consisting of the pressure
from said two pressure springs 143 and said component of force F2 deriving from the
drive gear G0. The result of the actual measurement of the relationship between DSD
and the pressure load indicates that the DSS varies almost linearly.
[0151] In Fig. 27, Case I represents the relationship between the pressure of the pressure
spring 143 and the space DSD in the development area where the developing agent controlling
space DH is set to 0.55 mm, and Case II represents the same where the developing agent
controlling space DH is set to 0.40 mm. In each of these cases, the added pressure
acts on the far side of the developing sleeve 122 due to the reason that the said
component of force F2 acts only on the far side, and the space DSD in the development
area is relatively small for the far side of the developing sleeve, whereas the same
is slightly large for the near side, thereby producing slight difference in the value
of DSD. Such slight difference, however, scarcely affect the actual image processing
as far as the development process according to the present invention is applied, so
that the difference can scarcely be recognized as far as the developed images are
concerned.
[0152] The developing unit according to the present invention is designed so that the space
in the development area formed between the developing unit and the image carrier can
be varied automatically depending on the quantity of the developing agent by the pressing
force to cause the developing unit to be pushed towards the image carrier in order
to stabilize the brushing force produced between the image carrier and the developing
agent. Furthermore, said developing unit is designed so that the component of the
force deriving from the power transmission system can be used positively together
with said pressure to ensure the developing unit to be pushed more securely ot prevent
undesirable condition such as the vibration during the development operation. Thus,
the pressing force acting on said developing unit can always be maintained at an appropriate
level, and so the developing unit promising high-quality development through stable
operation can be provided.