Dry process developing apparatus

A dry process developing apparatus of a type in which, by supplying toner contained in a toner replenishing tank with respect to magnetic carrier magnetically attracted onto an outer peripheral surface of a developing sleeve, a magnetic developing material composed of the magnetic carrier and toner is prepared on the outer peripheral surface of the developing sleeve for developing an electrostatic latent image supported on the surface of an electrostatic latent image support member by the use of this developing material. The developing apparatus includes a space chamber defined between a bristle height restricting member and a front restricting member so as to open towards the outer peripheral surface of the developing sleeve, and preliminarily loaded with the magnetic carrier, and a toner supplying section for supplying the toner with respect to the outer peripheral surface of the developing sleeve at the upstream side of the front restricting member.

BACKGROUND OF THE INVENTION 
The present invention generally relates to a developing apparatus and more 
particularly, to a dry process developing apparatus for use in a copying 
process such as electrographic copying or the like. 
Dry developing processes which have already been put into actual 
applications at present may be broadly divided into the dual-component or 
two-component developing process which employs a developing material in a 
powder form composed of a mixture of toner and magnetic carrier, and the 
mono-component or one-component developing process which employs a 
developing material in a powder form composed of only magnetic toner. In 
the above two-component developing process, although developing and 
transfer characteristics of the toner itself are superior, there are some 
problems related to deterioration of carrier and stability of the mixing 
ratio of the toner to the carrier. Meanwhile, since the one-component 
developing process is free from any problem due to employment of carrier, 
it has been a recent tendency for this process to be adopted in many 
copying apparatuses. 
However, with respect to toner, there is a difficult problem in that 
conditions incompatible with each other, i.e. conditions for electrical 
conductivity during the development and conditions for electrical 
insulation during the transfer are required. At the present stage, it is 
intended to improve the developing characteristics through adoption of 
various countermeasures by employing electrically insulative magnetic 
toner having favorable transfer characteristics, without imposing 
excessive loads on the copying process. 
Subsequently, a comparative study will be made between a process in which 
toner is formed into a thin layer for effecting the developing and another 
process in which toner is formed into a layer having a thickness to a 
certain extent through employment of a charging type magnetic toner for 
the toner. 
In the latter thick layer process, if there are no differences between 
toner particles in the physical properties and surface condition of the 
toner, the toner can favorably effect triboelectrical charging with 
respect to a developing sleeve, but part of the toner at the upper part of 
the layer is hardly charged triboelectrically, thus resulting in a faulty 
developing. However, if there is a predetermined distribution in the 
physical properties and/or the surface condition of the toner, the toner 
at the upper part of the layer can be subjected to the triboelectric 
charging between the toner particles. In other words, the toner is 
provided with stable charging characteristics when there is a difference 
in a triboelectric series, which makes it possible to effect a favorable 
development. On the other hand, in the former thin layer process, a 
favorable development may be achieved only if the toner has a difference 
in the triboelectric series with respect to the developing sleeve, but 
there is such a disadvantage that the developed images are substantially 
low in density since the toner layer is thin. 
Incidentally, when developing experiments are actually carried out using 
the thick layer process as described above, it is possible to effect a 
stable development. The reasons are such that, since the amount of 
magnetic powder exposed to surfaces of toner particles and amounts of 
exposed additives such as dye, carbon black, etc. are different according 
to dispersion, classification, aftertreatment process, etc. during 
manufacture of toner, there is produced a difference in the triboelectric 
series between the toner particles, thus resulting in the triboelectric 
charging of the toner particles to each other. However, when the ratio of 
inversely charged toner (it is to be noted that originally, individual 
toner particles are negatively charged by the triboelectric charging 
thereof with respect to the developing sleeve) in the developing material 
becomes high, probability of contact between the inversely charged toner 
and the developing sleeve is increased, with a consequent transfer of the 
charging polarity to the original negative polarity. In connection with 
the above, upon separation of only the inversely charged toner, it has 
been found that the magnetic powder content is high. Since the toner as 
described above is poor in charge retaining characteristic, and tends to 
produce a leakage of charge during transportation thereof along a 
peripheral surface of the developing sleeve, it may be considered that 
transfer of the charging polarity is easily effected. 
Even the thick layer process as described so far has such disadvantages 
that the developing gap and the magnetic brush bristle height restricting 
gap employed therein are generally narrow, with a high accuracy being 
required therefor, while the bristle height restricting gap tends to be 
clogged by the toner. Moreover, the charging mechanism depends on the 
state of manufacture of the toner in terms of probability, and it is 
difficult to reproduce such a state of manufacture of the toner in exactly 
the same manner. Furthermore, since the toner concentration is at 100%, 
variation of the toner amount at the developing region is likely to become 
conspicuous. 
In order to overcome the drawbacks as described in the foregoing, it has 
been considered by the present inventors to mix magnetic carrier into the 
toner layer on the outer peripheral surface of the developing sleeve. 
In FIG. 1, there is shown a basic construction of a conventional developing 
apparatus employed for the one-component developing process, which 
generally includes a cylindrical developing sleeve 1 rotatably provided 
adjacent to a photosensitive surface 5a of a photosensitive or 
photoreceptor drum 5, for rotation in a direction indicated by an arrow b, 
a magnet roller 2 sequentially magnetized with S and N poles at its outer 
peripheral surface and rotatably accommodated in the developing sleeve 1 
for rotation in a direction indicated by an arrow a, a bristle height 
restricting plate 3 fixedly provided above and adjacent to the peripheral 
surface of the developing sleeve 1, and a toner tank 4 in which toner is 
contained. By the rotation of the magnet roller 2 in the direction of 
arrow a and the rotation of the developing sleeve 1 in the direction of 
arrow b, the toner is transported for circulation along the peripheral 
surface of the developing sleeve 1 in the direction of arrow b so as to be 
rubbed against an electrostatic latent image preliminarily formed on the 
photosensitive surface 5a of the photoreceptor drum 5 driven for rotation 
in a direction indicated by an arrow c, thereby to develop said 
electrostatic latent image. In the above case, the amount of toner 
transported to the developing region A is restricted by the bristle height 
restricting plate 3. 
In the developing apparatus as described above, when the developing is 
effected by mixing magnetic carrier into the toner layer on the outer 
peripheral surface of the developing sleeve 1, there was observed by the 
present inventors a phenomenon that part of the carrier was collected at 
the upstream side B of the bristle height restricting plate 3 in the 
direction for transporting the developing material and thereafter, 
dispersed into the toner contained in the toner tank 4 as shown by an 
arrow d upon application of the toner transporting force, etc. thereto. In 
other words, as the developing proceeds, the amount of carrier transported 
to the developing region A is reduced, with a variation (rising) of toner 
concentration, or the triboelectric charging between the toner and carrier 
becomes insufficient, thus making it impossible to obtain developed images 
of high quality. This also means that the toner concentration can not be 
set at a predetermined value. Moreover, there is a disadvantage that, if 
irregularity of the toner concentration takes place in the axial direction 
of the developing sleeve 1, such an irregular toner concentration is not 
readily eliminated, since it is difficult to subject the toner and carrier 
positively to a moving force in the axial direction. 
SUMMARY OF THE INVENTION 
Accordingly, an essential object of the present invention is to provide a 
dry process developing apparatus for use in a copy process such as 
electrographic copying, which is suited to a developing process employing 
sham monocomponent developing material having a small amount of starter 
carrier mixed thereinto, and capable of stabilizing toner concentration, 
achieving a sufficient triboelectric charging between the toner and 
carrier, and also effectively eliminating the irregular toner 
concentration in the axial direction of a developing sleeve. 
Another important object of the present invention is to provide a dry 
process developing apparatus of the above described type, in which 
magnetic carrier in the magnetic developing material transported for 
circulation in one direction along the outer peripheral surface of the 
developing sleeve is positively prevented from being dispersed into the 
toner contained in a toner replenishing tank during operation of the 
apparatus. 
A further object of the present invention is to provide a dry process 
developing apparatus of the above described type, which has a simple 
construction and is stable in functioning, and can be readily incorporated 
into electrographic copying apparatuses and the like at low cost. 
In accomplishing these and other objects, according to one preferred 
embodiment of the present invention, there is provided a dry process 
developing apparatus for use in a copying process, which includes a 
developing sleeve having a magnet member provided therein, a driving means 
for driving and rotating the developing sleeve and/or the magnet member so 
as to transport a developing material along the outer peripheral surface 
of the developing sleeve, a bristle height restricting member provided at 
an upstream side of a developing region in the direction of transportation 
of the developing material for restricting the height of magnetic brush 
bristles, a front restricting member provided at an upstream side of the 
bristle height restricting member, a chamber for carrier accommodation 
which is opened towards the outer peripheral surface of the developing 
sleeve, in a position between the bristle height restricting member and 
the front restricting member and in wich the magnetic carrier is 
preliminarily loaded, and a toner supplying means for supplying the toner 
with respect to the outer peripheral surface of the developing sleeve at 
an upstream side of the front restricting member, so that the magnetic 
developing material composed of a mixture of the magnetic carrier and 
toner is prepared on the outer peripheral surface of the developing sleeve 
by supplying the toner contained in a toner replenishing tank with respect 
to the magnetic carrier magnetically attracted onto the outer peripheral 
surface of the developing sleeve, thereby to develop an electrostatic 
latent image supported on surface of an electrostatic latent image support 
member by using the magnetic developing material. 
By the above arrangement and further modifications thereof to be described 
later according to the present invention, an improved dry process 
developing apparatus has been advantageously provided, with substantial 
elimination of disadvantages inherent in the conventional arrangement of 
this kind.

DETAILED DESCRIPTION OF THE INVENTION 
Before the description of the present invention proceeds, it is to be noted 
that like arts are designated by like reference numerals throughout the 
accompanying drawings. 
Referring now to the drawings, there is shown in FIGS. 2 and 3 a dry 
process developing apparatus according to one preferred embodiment of the 
present invention. 
In the first place, the general construction of a copying machine, to which 
the dry process developing appratus of the present invention may be 
applied, will be described hereinbelow with reference to FIG. 2. The 
copying machine generally includes a photosensitive or photoreceptor drum 
10 having a photosensitive surface 10a and arranged to be driven for 
rotation at a constant speed in a direction indicated by arrow c, and 
various processing devices such as a corona charger 11, an image exposing 
means 12, the dry process developing apparatus 20 according to the present 
invention, a transfer charger 13, a cleaning blade 14 for removing 
remaining toner from the photosensitive surface 10a, and an eraser lamp 15 
for erasing residual charge, etc. sequentially disposed around the 
photoreceptor drum 10 as illustrated. As shown by a two-dotted chain line 
in FIG. 2, a copy paper sheet is arranged to be fed from the right side 
towards the left side, and after the transfer process, discharged out of 
the copying apparatus through a fixing device (not shown). 
On the other hand, the dry process developing apparatus 20 according to the 
present invention includes a developing sleeve 21 of an electrically 
conductive non-magnetic material formed into a cylindrical configuration 
and provided adjacent to the photosensitive surface 10a of the 
photoreceptor drum 10 for rotation in the direction of arrow b, a magnet 
roller 22 sequentially magnetized with S and N poles at the outer 
peripheral surface thereof and coaxially provided in the developing sleeve 
21 for rotation in the direction of arrow a, with a bristle height 
restricting plate 23 being disposed above and adjacent to the surface of 
the developing sleeve 21. By the rotation of the magnet roller 22 in the 
direction of arrow a and the rotation of the developing sleeve 21 in the 
direction of arrow b, the developing material is transported for 
circulation along the outer peripheral surface of the developing sleeve 21 
in the direction of arrow b. At an upstream side of the bristle height 
restricting plate 23, there is further provided a front restricting plate 
24 for the developing material, which is integrally formed with a housing 
or side wall 25a of a toner replenishing tank 25, with the forward edge of 
said front restricting plate 24 confronting the outer peripheral surface 
of the developing sleeve 21. A chamber 26 is formed between the bristle 
height restricting plate 23 and the front restricting plate 24. The upper 
portion of the above chamber 26 is covered by a covering plate 27 for 
selective opening or closing, and the chamber 26 is opened, at its lower 
portion, only towards the outer peripheral surface of the developing 
sleeve 21. 
Meanwhile, the lower portion of the toner replenishing tank 25 defined by 
the housing including the side wall 25a, another side wall 25b, and a lid 
member 25c, etc. is formed into a toner supplying section 28 open towards 
the upstream side of the front restricting plate 24, while a plate member 
29 for forming a bottom portion of the toner replenishing tank 25 is 
provided on the wall 25b at the lower part of the toner supplying section 
28, with a scraper 30 having a hole 30a formed therein being further 
provided in a position below the plate member 29 so as to contact under 
pressure the outer peripheral surface of the developing sleeve 21 in a 
so-called forward direction. There are also provided developing material 
scattering preventing plates 31 and 32 in position at the lower edge of 
the toner replenishing tank 25 and below a developing region A. 
Using the above arrangement, the present inventors have carried out various 
developing experiments through variations of such conditions as the gap d1 
between the photosensitive surface 10a of the photoreceptor drum 10 and 
the outer peripheral surface of the developing sleeve 21 at the developing 
region A, the gap d2 between the bristle height restricting plate 23 and 
the outer peripheral surface of the developing sleeve 21, and the gap d3 
between the front restricting plate 24 and the outer peripheral surface of 
said developing sleeve 21, etc. or by altering the kind of toner and 
carrier, with favorable results being obtained respectively. 
Some of the above experiments will be described hereinbelow for the purpose 
of illustrating the present invention, without any intention of limiting 
the scope thereof. 
(EXPERIMENT I) 
Gap d1=0.60 mm 
Gap d2=0.40 mm 
Gap d3=1.20 mm 
Magnet roller: 
Magnetic force: 750 G 
No. of poles: 8 
Revolutions: 800 rpm (in the direction of arrow a) 
Developing sleeve: 
Outer diameter: 31 mm 
Revolutions: 80 rpm (in the direction of arrow b) 
Processing speed (circumferential speed of photoreceptor drum): 130 mm/sec 
Carrier: manufactured by Nippon Iron Powder Co., Ltd. 
Name used in trade: F-182 
Average particle dia.: 65-70 .mu.m 
Loading amount: 40 g 
Toner: charging type magnetic toner 
Magnetic powder content: 40 wt% 
Electrostatic latent image potential: +400 V (max. potential) 
Developing bias: 
DC +100 V 
AC 600 Hz, 500 Vrms 
In the above Experiment I, 60,000 copy paper sheets were subjected to 
copying, but consumption of the carrier on the outer peripheral surface of 
the developing sleeve 21 was hardly noticed, nor was there any 
deterioration of the carrier itself. 
(EXPERIMENT II) 
Magnet roller: Fixed 
Developing sleeve Revolutions: 80 rpm (in the direction of arrow b) 
Carrier: manufactured by Nippon Iron Powder Co., Ltd. 
Name used in trade: F-182 
Average particle dia.: 65-70 .mu.m 
Loading amount: 40 g 
Toner: charging type magnetic toner 
Magnetic powder content: 15 wt% 
Other conditions were generally the same as in Experiment I. 
In the above Experiment II, trial products of sepia toner in which the 
amount of magnetic powder was reduced, and green toner in which 5 to 10 
wt% of TiO+ pigment was contained, were employed to replace the toner 
referred to above, and both of such trial products of color toner also 
provided favorable copied images. 
(EXPERIMENT III) 
Gap d1=0.50 mm 
Gap d2=0.30 mm 
Gap d3=1.00 mm 
Carrier: manufactured by Fuji Electrochemical Co., Ltd. 
Name used in trade: X-012 
Average particle dia.: 45 .mu.m 
Loading amount: 80 g 
Toner: charging type non-magnetic toner 
Electrostatic latent image potential: +400 V (max. potential) 
Developing bias: DC +150 V 
Subsequently, behavior of the carrier and toner, and mechanism of the 
developing will be explained. 
The carrier is first loaded into the chamber 26 by opening the covering 
plate 27, and upon actuation of the developing apparatus, is placed on the 
outer peripheral surface of the developing sleeve 21. In the above case, 
the toner may be preliminarily mixed to a certain extent in the carrier. 
Thereafter, the toner is loaded in the toner replenishing tank 25 and fed 
onto the outer peripheral surface of the developing sleeve 21 from the 
toner supplying section 28. By the rotation of the magnet roller 22 in the 
direction of arrow a and the rotation of the developing sleeve 21 in the 
direction of arrow b, the toner is transported for circulation in the 
direction of arrow b along the outer peripheral surface of the developing 
sleeve 21, and stirred and mixed with the carrier while passing through 
the chamber 26 so as to be charged to a negative polarity by the 
triboelectric charging with respect to the carrier and/or triboelectric 
charging with respect to the developing sleeve 21. In the actual practice, 
the developing is effected in a state where the toner and carrier are 
sufficiently mixed with each other for developing an electrostatic latent 
image formed, in a positive polarity, on the photosensitive surface 10a of 
the photoreceptor drum 10 at the developing region A. 
After the developing, the toner is further transported through a hole 30a 
of the scraper 30 in the direction of arrow b together with the carrier, 
and at the toner supplying section 28, is supplied with fresh toner, and 
then, remains in the chamber 26 for a while so as to be stirred and mixed 
thereat for again being transported to the developing region A 
subsequently. 
In the above case, although the amount of the developing material 
transported to the developing region A is restricted by the gap d2 at the 
bristle height restricting plate 23, since the gap d3 at the front 
restricting plate 24 is set to be larger than the gap d2, all the carrier 
reaches the chamber 26 through the gap d3. Here, the carrier and toner 
restricted by the bristle height restricting plate 23 stay within the 
chamber 26 so as to be stirred and mixed also in the axial direction of 
the developing sleeve 21, but such carrier and toner, especially the 
carrier, is stirred only within the chamber 26, without being dispersed or 
diffused into the toner contained in the toner replenishing tank 25 
through the toner supplying section 28. Thus, the toner concentration at 
the developing region A is determined by the amount of the carrier loaded 
in the chamber 26. Accordingly, the toner concentration of the developing 
material at the developing region A is maintained at a constant value at 
all times. Moreover, by preliminarily adjusting the amount of carrier to 
be loaded into the chamber 26, it is possible to set the toner 
concentration accurately and as desired. 
In the above case, it is necessary for the gap d3 at the front restricting 
plate 24 to allow to pass therethrough, a greater amount of the developing 
material than the gap d2 at the bristle height restricting plate 23. In 
other words, the gap d3 is required to have a size sufficient to allow all 
the developing material including the carrier to pass therethrough, and 
the front restricting plate 24 partitions between the chamber 26 and the 
toner replenishing tank 25 so as to prevent the carrier staying in the 
chamber 26 from dispersing or diffusing into the toner contained in the 
toner replenishing tank 25. Moreover, not only is the triboelectric 
charging between the toner and carrier sufficiently effected during 
passage of the developing material through the chamber 26, but also the 
uneven toner concentration in the axial direction may be effectively 
eliminated. If the gap d3 is narrow, permitting less amount of the 
developing material to pass therethrough than the gap d2, the carrier 
tends to stay at the portion of the front restricting plate 24, and 
dispersion or diffusion of the carrier can not be prevented. 
It is to be noted here that, in order to improve the transporting force of 
the developing material by the developing sleeve 21, the outer peripheral 
surface of the developing sleeve 21 may be formed with minor undulations 
or concave and convex portions by a blast processing, etc. 
On the other hand, for the magnetic carrier, there may be employed iron 
carrier, ferrite carrier and resin coated carrier thereof, and further, 
binder carrier, etc. which is prepared by bonding together fine magnetic 
powder with a resin. Meanwhile, for the toner, it is possible to employ 
magnetic toner or non-magnetic toner, and the content of the magnetic 
powder should preferably be less than 40 wt%, since the fixing property of 
the toner deteriorates as the magnetic powder content becomes high, and 
upon exceeding 40 wt%, the toner concentration at the developing region 
tends to be lowered. As described above, in the case where the magnetic 
powder is contained in the toner, coloring is difficult as compared with 
the case of the non-magnetic toner, although soiling of the apparatus does 
not easily take place due to scattering of the developing material, etc. 
even if the toner is not sufficiently triboelectrically charged with 
respect to the carrier. More specifically, in the above case, it is 
necessary to add TiO.sub.2, etc. to eliminate the color of the magnetic 
powder, with further addition thereto of a dye, pigment or the like, and 
the addition of TiO.sub.2, etc. adversely affects the mutual triboelectric 
charging between the toner particles. However, in the case of the magnetic 
toner, there is an advantage that the image quality may be improved 
through impression of an AC developing bias. 
In the case where the non-magnetic toner is employed, since the 
triboelectric charging between the toner particles can not be utilized, 
the toner tends to be scattered unless the triboelectric charging thereof 
with respect to the carrier is sufficiently effected, and thus, it is 
necessary to suppress the toner concentration (at the developing region) 
so that it is low as compared with the case where the magnetic toner is 
employed. For this purpose, the front restricting plate 24 can be made of 
a magnetic material to form a so-called carrier curtain at the portion 
where the front restricting plate 24 is provided for suppressing the 
amount of toner to be supplied from the toner supplying portion 28. 
Meanwhile, in order to guarantee still more sufficient triboelectric 
charging between the toner and carrier, the circumferential length of the 
chamber 26 may be increased so as to increase the amount of carrier 
staying in the chamber 26. 
Subsequently, the function of the carrier with respect to the toner will be 
explained. 
In the first place, the carrier has the function to achieve a positive 
triboelectric charging of the toner. In addition to the above function, 
the carrier also electrostatically attracts the toner triboelectrically 
charged with respect to the carrier and/or the developing sleeve 
transportation thereof to the developing region A under the state where 
the toner charge is retained. In the conventional case where the toner 
layer is thick, the toner at the upper part of the layer can hardly retain 
a charge although provided with a counter charge, but mixing the carrier 
into the toner layer guarantees such retaining of charge, while 
functioning to increase the transporting force by improving the 
permeability. In other words, by the presence of the carrier, the 
substantial magnetic field intensity at the developing region A is 
increased, and this is effective for removal of fogging in the case of the 
magnetic toner. Furthermore, by the rising of the dielectric constant at 
the developing region A, the substantial magnetic field intensity is 
increased, i.e., it becomes possible to lower the substantial toner 
concentration, with the toner layer being kept as it is in a thick layer, 
without the necessity for forming the toner layer into a thin layer. 
For example, in the case of the charging type magnetic toner, inversely 
charged toner having the function of a carrier is present in such toner, 
and is subjected to developing (i.e., adhesion) on the developing sleeve 
21 during the development. Therefore, it is necessary to scrape off this 
inversely charged toner by a scraper and return it again onto the outer 
peripheral surface of the developing sleeve 21. In the case where carrier 
is mixed into the toner as in the present invention, the carrier is 
assumed to be subjected to developing (i.e, adhesion) on the developing 
sleeve 21, but owing to the strong magnetic force, it is favorably 
transported without being kept adhered onto the developing sleeve 21. 
Accordingly, in the foregoing embodiment, although the scraper 30 with the 
hole 30a is provided at the downstream of the developing region A for 
scraping off the developing material from the developing sleeve 21, such 
scraper is not necessarily required to be provided. However, by the 
provision of said scraper 30 with the hole 30a, the stirring and mixing 
efficiency may be improved. 
Hereinbelow, the characteristic (charging characteristic) required for the 
toner will be described. 
Toner is required to have a triboelectric charging property with respect to 
the carrier, developing sleeve, etc., and to be provided with such 
characteristics that the amount of adhesion thereof to the electrostatic 
latent image at the side of the toner polarity to be charged by the 
friction with respect to the carrier when the toner is used alone for 
developing, is more than two times the amount of adhesion thereof at the 
opposite polarity. In other words, as shown in FIG. 4, this means that, in 
the case of negatively charged toner having a larger amount of adhesion to 
the electrostatic latent image at the side of positive polarity, the 
relation is represented by tan .theta.1/tan .theta.2.gtoreq.2. By the 
above relation, it is meant that the toner itself has a charging 
characteristic, and since the toner with the charging characteristic is 
subjected to triboelectric charging also between toner particles thereof 
although it is triboelectrically charged with respect to the carrier, 
developing sleeve, etc., upon comparison of developing characteristics 
between single toners, the charging characteristic is varied according to 
the chargeability of the respective single toners, with a consequent 
variation of the amount of adhesion. 
In other words, the toner has a selectivity for the polarities. By 
imparting such charging characteristic to the toner, it becomes possible 
to obtain a developing material having a high mixing ratio of the 
effective toner. 
However, in the case where tan .theta.1/tan .theta.2 is smaller than 2, it 
is impossible to achieve a high ratio of the effective toner, because in 
the above case, since the number of toner particles inversely charged is 
large, it becomes difficult to bring polarities of toner into agreement by 
causing all the toner to be triboelectrically charged with respect to the 
carrier. Accordingly, the amount of toner having a sufficient charge is 
decreased, with a reduction in the image density. 
Referring back to FIGS. 2 and 3, the cover plate 27 provided at the upper 
portion of the chamber 26 is intended not only to permit loading of a 
predetermined amount of carrier in the chamber 26 at the start, but also 
to take out or replenish the carrier in the case where the deterioration 
or consumption of the carrier takes place for some reason. 
As shown in the modification of FIG. 5, the bristle height restricting 
plate 23', the front restricting plate 24' and the cover plate 27' may be 
integrally molded into one unit, for example, of a resin material, if a 
replenishing and taking out portion (not particularly shown) for the 
carrier is separately provided. Moreover, when a proper radius of 
curvature is provided at each of the corner portions 26a and 26b, a smooth 
flow or circulation of the developing material within the chamber 26 may 
be achieved, and entry of an excessive amount of toner from the toner 
replenishing tank 25 can be prevented still more positively, although in 
the foregoing experiments, the entry of an execessive amount of toner 
which may invite a problem, has not actually taken place. Meanwhile, in 
order to prevent the entry of an excessive amount of toner as referred to 
above, it is also effective, in the case of a magnet roller fixed type 
developing apparatus, to cause one of the magnetic poles of the magnet 
roller 22 and the front restricting plate 24' to confront each other. In 
the above case, not only can the gap d3 be increased owing to rising of 
the developing material at the forward edge of the front restricting plate 
24' confronting said one magnetic pole by the action of the magnetic 
field, but the entry of an excessive amount of toner from the toner 
supplying section 28 can be advantageously prevented. 
Referring to FIG. 6, there is shown a dry process developing apparatus 20B 
according to a second embodiment of the present invention, in which a 
bristle height restricting plate 23B, and a front restricting plate 24B 
are provided below the developing sleeve 21, with a chamber 26B being 
formed by a cartridge 35 of a receiving dish type adapted to be inserted 
or withdrawn in the axial direction of the developing sleeve 21, and thus, 
the initial loading or replacement of the carrier, etc. may be effected by 
the selective insertion or withdrawal of the cartridge 35. By the rotation 
of the magnet roller 22 in the direction of arrow a' and the rotation of 
the developing sleeve 21 in the direction of arrow b', the developing 
material is circulated for transportation over the outer peripheral 
surface of the developing sleeve 21 in the direction of arrow b', while 
the photoreceptor drum 10 is adapted to be driven for rotation in the 
direction of arrow c'. Meanwhile, a toner supplying section 28B is defined 
by a partition plate 33 extending downwardly from the side wall 25a of the 
toner replenishing tank 25 and the front restricting plate 24B, with a 
toner stirring member 34 arranged to be pivotable in a direction indicated 
by an arrow e being provided adjacent to the toner supplying section 28 as 
shown. Although not particularly shown, the toner replenishing tank 25 is 
extended towards the right in FIG. 6 so that pressure due to the weight of 
the toner within the toner replenishing tank 25 will not be applied onto 
the developing sleeve 21 directly. 
Since other parts and effects of the developing apparatus 20B of FIG. 6 are 
generally similar to those of the developing apparatus 20 of FIGS. 2 and 
3, a detailed description thereof is abbreviated here for brevity, with 
like parts being designated by like reference numerals. 
As is seen from the foregoing description, according to the first and 
second embodiments of the present invention, since the chamber is formed 
between the bristle height restricting member and the front restricting 
member provided at the upstream side thereof, the developing material 
transported to the developing region stays in the chamber so as to be 
stirred and mixed, whereby the undesirable dispersion or diffusion of the 
carrier into the toner contained in the toner replenishing tank is 
prevented, thus making it possible to maintain a constant toner 
concentration at the developing region at all times. In other words, it 
becomes possible to set the toner concentration correctly as desired by 
preliminarily adjusting the amount of carrier supplied. Furthermore, 
during passage of the developing material through the chamber, the toner 
and carrier are subjected to a sufficient triboelectric charging, and 
moreover, a so-called filter effect, by which the irregular toner 
concentration in the axial direction of the developing sleeve can be 
rapidly eliminated, can be achieved. 
Referring further to FIG. 7, there is shown a dry process developing 
apparatus 20C according to a third embodiment of the present invention, 
which is intended to eliminate a phenomenon still present in the 
arrangement of FIGS. 2 and 3, that the magnetic carrier tends to be 
dispersed into the toner contained in the toner replenishing tank 25 from 
the outer peripheral surface of the developing sleeve 21 particularly when 
the developing apparatus of FIGS. 2 and 3 is operated for a long period of 
time. The dispersion of the magnetic carrier as described above may result 
in an inconvenience in that the toner concentration of the magnetic 
developing material prepared on the outer peripheral surface of the 
developing sleeve is raised more than necessarily, and the axial 
irregularity in the toner concentration is caused if the dispersion of the 
carrier is not uniform in the axial direction. 
In the developing apparatus 20 of FIG. 3, the problems as described above 
are considered to result from the following causes. 
(i) The toner supplied at a position X1 is mixed and stirred with the 
magnetic carrier before it is transported up to a position X2, and the 
magnetic carrier slightly raised on the outer peripheral surface of the 
developing sleeve 21 may be restricted at the forward edge of the front 
restricting plate 24. 
(ii) The position and direction in which the toner is supplied are as 
indicated by an arrow Y1 while the position and direction in which the 
magnetic carrier may be dispersed are as shown by an arrow Y2, and it is 
rather difficult to effectively prevent the magnetic carrier from 
dispersing. Therefore, a small amount of magnetic carrier is gradually 
dispersed into the toner replenishing tank 25. 
In the dry process developing apparatus 20C in FIG. 7, a bristle height 
restricting plate 23C is integrally formed with the inner face of the 
inclined upper wall 25Ca of the toner replenishing tank 25b in a position 
upstream of the developing region A in the developing material 
transporting direction, while a front restricting plate 24C is fixed, at 
its upper portion, to a ceiling of the toner replenishing tank 25b, with 
the lower portion of the plate 24C confronting the outer peripheral 
surface of the developing sleeve 21 at the upstream side of the bristle 
height restricting plate 23C. This front restricting plate 24C functions 
as a partition plate for dividing the interior of the toner replenishing 
tank 25b into a developing section and a toner containing section h, and 
also forms a toner supply passage p between its lower horizontal portion 
24Ca and the bottom of the tank 25b. The above passage p communicates the 
toner containing section h with the outer peripheral surface of the 
developing sleeve 21, and is provided with a supply restricting plate t 
disposed at the inlet side thereof. 
Moreover, between the bristle height restricting plate 23C and the front 
restricting plate 24C, a chamber 26C for being loaded the magnetic carrier 
therein is formed so as to open only towards the outer peripheral surface 
of the developing sleeve 21. The front restricting plate 24C is provided, 
on its portion located within the chamber 26C, with many fins f which are 
attached thereto so as to be inclined in the axial direction of the 
developing sleeve 21 and which function for stirring the magnetic 
developing material in the axial direction of the developing sleeve 21 
within the chamber 26C. The developing material scattering preventing 
plates 31C and 32C provided on the lower edge of the toner replenishing 
tank 25b and below the developing region A are made of magnetic material 
for magnetically attracting thereto the magnetic toner scattering from the 
developing region A. 
On the other hand, at the bottom portion of the toner containing section h 
of the toner replenishing tank 25b, there are provided a toner send-out 
vane V and a toner-empty detecting plate D. The toner send-out vane V is 
arranged to be driven for rotation about a support shaft Va at a constant 
speed in the direction indicated by an arrow d, and by the above rotation, 
supplies the toner, through the passage p, to the magnetic developing 
material circulated for transportation over the outer peripheral surface 
of the developing sleeve 21. Meanwhile, the toner empty detecting plate D 
is pivotally supported about a pivotal shaft Da, and is adapted to be 
moved upwardly when the toner send-out vane V rotating in the direction of 
arrow d is brought into contact therewith, and to be moved downwardly by 
its weight when released from contact with said vane V. The time required 
for this downward movement varies according to the amount of toner 
contained in the tank 25b, i.e., the time becomes short as the amount of 
toner is decreased due to reduction of resistance. Therefore, the toner 
amount is detected by measuring the above time for the downward movement 
of the plate D with a proper switching means for external display when the 
tank 25b becomes empty. 
Moreover, at the upper portion of the toner replenishing tank 25b, there is 
detachably mounted a cartridge R for toner replenishment. The toner 
preliminarily contained in the cartridge R is fed into the toner 
containing section h by withdrawing a cartridge lid Ra together with the 
lid member 25Cc of the tank 25b. 
The function of the dry process developing apparatus 20C having the 
construction as described so far will be explained hereinbelow. 
In the first place, the magnetic carrier prepared, for example, by 
preliminarily mixing strong magnetic particles with binder type particles 
is loaded into the chamber 26C, and after this developing apparatus is 
operated for preparation, toner is loaded into the toner containing 
section h. In the above case, the magnetic carrier loaded into the chamber 
26C may be a magnetic carrier composed only of strong magnetic particles 
or that prepared by preliminarily mixing toner into the magnetic carrier. 
Thus, in the above state, it becomes possible to effect the development of 
electrostatic latent images by this developing apparatus. 
Here, by the rotation of the magnet roller 22 in the direction of arrow a 
and also, the rotation of the developing sleeve 21 in the direction of 
arrow b, the toner is transported along the outer peripheral surface of 
the developing sleeve 21 in the direction of arrow b, and during passage 
through the chamber 26C, is stirred and mixed with the magnetic carrier, 
and thus the toner and the magnetic carrier are respectively subjected to 
triboelectric charging. As a result of the above mixing and stirring, the 
toner and the magnetic carrier, which are the respective compositions of 
the magnetic developing material, are combined at this timepoint, into one 
developing material at a constant mixing ratio at all times, and at the 
developing region A, magnetic brush bristles made of the magnetic 
developing material are positively formed. The magnetic brush bristles 
thus formed rub against the photosensitive surface 10a of the 
photoreceptor drum 10 for developing the electrostatic latent image formed 
on the surface 10a into a visible toner image. After being used for the 
developing, the magnetic developing material remaining on the outer 
peripheral surface of the developing sleeve 21 reaches the outlet side of 
the toner supply passage p, where it is supplied with the toner through 
the pivotal movement of the toner send-out vane V so as to be subsequently 
employed for the developing again. 
For the developing bias, DC voltage is applied to the developing sleeve 21 
based on ordinary practice, but such DC voltage have superposed therein an 
AC voltage or the developing sleeve 21 may be suitably grounded for this 
purpose. 
Incidentally, when the developing apparatus 20C described so far is 
employed, there is no tendency that the magnetic carrier is dispersed into 
the toner contained in the toner containing section h even during 
operation for a long period of time, and such favorable effect is 
considered to be due to the reasons as described below. 
(i) Although the transported amount of the magnetic developing material 
reaching the developing region A is restricted by the bristle height 
restricting plate 23C, the front restricting gap formed between the front 
restricting plate 24C and the developing sleeve 21 is set to be larger 
than the bristle height restricting gap formed between the bristle height 
restricting plate 23C and the developing sleeve 21, whereby in principle, 
all the magnetic carrier reaches the chamber 26C through the front 
restricting gap. 
(ii) Toner is supplied through the toner supply passage p to the magnetic 
developing material in the course of transportation, and simultaneously 
with the supply of toner, the restriction by the front restricting plate 
24C is effected. 
In other words, the toner supplied to the developing material and the 
magnetic carrier are not mixed and stirred into each other by the time 
when the restriction by the front restricting plate 24C is effected after 
supply of the toner, and thus, there is no tendency that the layer 
thickness of the magnetic developing material is increased. More 
specifically, when the toner is consumed by the developing, the layer 
thickness of the magnetic developing material is reduced by the amount of 
consumption, and even if the toner is supplied thereto, it is located 
radially outwardly of the magnetic developing material if there is no 
mixing and stirring, and thus, only the toner thus supplied is restricted 
by the front restricting plate 24C. Accordingly, the magnetic developing 
material itself is not restricted by the front restricting plate 24C, and 
there is no such inconvenience that the magnetic carrier raised off the 
sleeve 21 by the increase of the layer thickness is restricted by the 
front restricting plate 24C so as to be dispersed. 
(iii) The toner is supplied with respect to the place and direction in 
which the magnetic carrier tends to be dispersed into the toner contained 
in the toner containing section h, and furthermore, the toner is imparted 
with transporting force by the rotation of the toner send-out vane V. 
More specifically, the developing material located in the passage p moves 
towards the right in FIG. 7 through said passage p by the restricting 
action of the front restricting plate 24C and the transporting force with 
respect to the developing material in the direction indicated by arrow b, 
and tends to leave the outer peripheral surface of the developing sleeve 
21. However, in the passage p, the toner is supplied with the 
transportation force towards the left in FIG. 7 by the rotation of the 
toner send-out vane V in the direction of arrow d, thus suppressing the 
dispersion of the magnetic carrier. 
On the other hand, in the chamber 26C, the magnetic carrier and toner 
restricted by the bristle height restricting plate 23C stay so as to be 
mixed and stirred, and particularly, are sufficiently stirred also in the 
axial direction of the developing sleeve 21 by the fins f described 
earlier. Thus, the toner concentration of the magnetic developing material 
which forms the magnetic brush at the developing region A is determined by 
the amount of the magnetic carrier staying in the chamber 26C. 
Accordingly, the toner concentration at the developing region A is 
maintained at a constant value at all times, and it is possible to adjust 
such toner concentration according to the amount of magnetic carrier 
preliminarily loaded in the chamber 26C. 
Hereinbelow, there is shown one example of data obtained by experiments 
carried out by the present inventors through employment of the dry process 
developing apparatus 20C as described in the foregoing. The experiments 
were effected through alterations of kinds or mixing ratios of toner and 
magnetic carrier or through variations of developing conditions such as 
the developing gap, bristle height restricting gap, front restricting gap, 
etc. respectively giving favorable results. 
(EXPERIMENT IV) 
Magnetic carrier: prepared by mixing 25 g of ferrite carrier F-141 (name 
used in trade and manufactured by Nippon Iron Powder Co., Ltd. Average 
particle diameter 50 .mu.m) with 25 g of binder type carrier (average 
particle diameter 37 .mu.m, magnetic powder content 66 wt%) made by 
dispersing magnetic powder into a resin. 
Toner: charging type magnetic toner 
Magnetic powder content: 30 wt% 
Developing conditions 
Developing sleeve: 
Outer diameter: 24.5 mm 
Revolutions: 79 rpm (in the direction of arrow b) 
Magnet roller: 
Magnetic force: 750 G 
No. of poles: 8 
Revolutions: 900 rpm (in the direction of arrow a) 
Developing gap (d1): 0.45 mm 
Bristle height restricting gap (d2): 0.35 mm 
Front restricting gap (d3): 1.5 mm 
Supply passage length (d4): 5.5 mm 
Supply passage height (d5): 3.5 mm 
Processing speed (circumferential speed of photoreceptor drum): 112 mm/sec 
Electrostatic latent image potential: +500 V (max. potential) 
Developing bias: 
DC +200 V 
AC 600 Hz, 350 Vrms 
Toner supply vane: 
Revolutions: 60 rpm (in the direction of arrow d) 
In the above experiment, although 100,000 copy paper sheets were subjected 
to copying, no dispersion of the magnetic carrier into the toner contained 
in the toner containing section h was observed and copied images were 
favorable to the last sheet, without any deterioration of the magnetic 
carrier itself. 
Meanwhile, the toner concentration at the developing region A was 
maintained at 25 wt%, and it was possible to alter the toner concentration 
within the range of 15 to 50 wt% upon variation of the amount of magnetic 
carrier to 30 to 60 g. 
The length of the toner supply passage d4 should preferably be longer than 
3 mm, and was favorable in the range between about 4 and 10 mm. If the 
length d4 is too short, dispersion of the magnetic carrier is noticed, 
while when it is too long, supply of the toner becomes insufficient. The 
toner supply passage height d5 should preferably be lower than 8 mm, and 
was favorable at about 2 to 7 mm. If the passage was too narrow, supply of 
the toner became insufficient, while when it was too wide, dispersion of 
the magnetic carrier was noticed, and thus, the function as the toner 
supply passage p can not be achieved if the dimensions are out of the 
above range. It is to be noted here, however, that the values of this kind 
and the toner concentration, etc. are to be properly determined by the 
magnetic force of the magnet roller 22, and kinds of the magnetic carrier 
and toner, etc., and can not be solely decided by one factor. 
It should be noted here that the supply restricting plate t provided at the 
inlet side of the toner supply passage p is not necessarily required in 
the present invention, but has an effect to reduce the pessure of the 
toner within the toner supply passage p. Since the toner supply passage p 
is narrow, there is a possibility that toner is hardened by the pressure 
if the toner employed is not very good in fluidity, and the plate t has 
for its object to prevent such undesirable hardening. Accordingly, the 
supply restricting plate t may be replaced by another member having a 
function to reduce the direct pressure from the toner send-out vane V. For 
example, a wire mesh or the like can be provided at the inlet side of the 
toner supply passage p or a permanent magnet or magnetic plate can be 
embedded in the bottom portion of the passage p. However, since such a 
magnetic plate is adapted to reduce the supply pressure by being 
magnetized through the magnetic force of the magnet roller 22, it may be 
used only for an apparatus of a stationary magnet roller type. 
Moreover, the fins f provided in the space chamber 26C are not necessarily 
required for the present invention, but these fins f have an effect to 
improve stirring of the magnetic developing material within the chamber 
26C. Therefore, to obtain a similar effect, the fins f may be replaced, 
for example, by rod-like members made of a magnetic material and axially 
provided in the chamber 26C. In the above case, the magnetic rod-like 
members are magnetized by the magnetic force of the magnet roller 22, and 
from therearound the magnetic field for the stirring. Accordingly, such 
rod-like members are particularly effective for the developing apparatus 
of the magnetic roller rotating type as in the present embodiment. 
On the other hand, the toner supply passage p is not necessarily required 
to be formed by the front restricting plate 24C itself, and the 
configuration of the front restricting plate 24C itself may be suitably 
determined as desired so long as the object of the present invention can 
be achieved thereby. For example, the lower horizontal portion 24Ca of the 
front restricting plate 24C may be folded in a direction opposite to that 
in FIG. 7. 
As is clear from the foregoing description, according to the third 
embodiment of the present invention, since the toner supply passage is 
formed at the upstream side of the front restricting member in the state 
for communication of the toner replenishing tank with the outer peripheral 
surface of the developing sleeve, while the toner supplying means for 
feeding out the toner in the direction towards the outer peripheral 
surface of the developing sleeve through the toner supply passage is 
provided in the toner replenishing tank, the undesirable dispersion of the 
magnetic carrier in the magnetic developing material circulated for 
transportation in one direction over the outer peripheral surface of the 
developing sleeve, into the toner contained in the toner replenishing tank 
during operation of the developing apparatus, may be positively prevented, 
and thus, it becomes possible to obtain developed image of a good image 
quality over a long period. 
Although the present invention has been fully described by way of example 
with reference to the accompanying drawings, it is to be noted here that 
various changes and modifications will be apparent to those skilled in the 
art. Therefore, unless otherwise such changes and modifications depart 
from the scope of the present invention, they should be construed as being 
included therein.