[0001] The present invention relates to a magnetic brush developing apparatus for developing
an electrostatic latent image, which is used in an electrophotographic recording apparatus
or the like.
[0002] Widely known as a developing method applicable to a developing apparatus is a two-component
magnetic brush developing method using a toner or a colored powder, and a carrier
or a magnetic powder as a developer.
[0003] The carrier used therein imparts an electrostatic charge to the toner through a triboelectrification
or the like thereof, and the toner is held by the electrostatic force for conveyance.
[0004] Also, the developing roller functions to convey the developer to the developing section
and holds the carrier by the magnetic force for conveyance, and thus the magnetic
properties of the developing roller have a great influence on the image quality.
[0005] The principle of the two-component magnetic brush developing method relevant to the
present invention, will now be described with reference to Fig. 18.
[0006] A developing roller 1 is constituted of a magnet 1b having a plurality of magnetic
poles, and a rotational sleeve 1a which rotatably covers the surface of the magnet
1b.
[0007] The magnet 1b is usually fixed, and a developer 4 is caught on the surface of the
rotational sleeve 1a, through the magnetic force exerted by the magnet 1b, and carried
to a developing section 9 in which a photosensitive drum 3 confronts the developing
roller 1a, through the rotation of the rotational sleeve 1a.
[0008] The developer restriction member 2, i.e., a blade is arranged opposite to the developing
roller 1 (rotational sleeve 1a) to restrict the amount of the developer 4 to be carried
to the developing section 9.
[0009] The amount of the developer 4 passing through the developer restriction member 2
is determined by the interval (a blade gap) between the developing roller 1 and the
developer restriction member 2, and the amount by which the developer head has been
raised. Accordingly, the amount of the developer 4 which has passed through the developer
restriction member 2 is determined by the height of the developer head. The developer
head is the height of the developer brush carried on the surface of the sleeve 1a.
[0010] The image quality is also influenced by the height of the developer head. Namely
if the height of the developer is comparatively low and the amount of the developer
to be carried to the developing section 9 is thus reduced, sufficient toner for a
development is not supplied, which results in a deterioration of the image density.
Conversely, if an excessive amount of toner is supplied, the image is unstable.
[0011] Namely, a variation in the height of the developer head may cause an instability
of the image and a deterioration of the image quality. Accordingly, to eliminate any
unevenness of the image quality, it is necessary to maintain the quantity of developer
4 passing through the blade gap of a constant value.
[0012] Moreover, even though the blade gap is constant, the quantity of the developer 4
passing through the blade gap is determined by the amount by which the developer resting
on the developing roller 1 is raised in the developer restriction member facing section
6.
[0013] Therefore, to obtain a firm image quality without unevenness, that condition of the
raising of developer head on the developing roller 1 in the developer restriction
member facing section 6 should be always the same.
[0014] The condition of the raising of the developer is determined by the vertical magnetic
flux density at a position opposite to the developer restriction member 2 on the developing
roller 1, and as a result, the vertical magnetic flux density at the opposing position
must be constant.
[0015] Figure 19 shows the distribution of the vertical component (normal to the sleeve
surface) of the magnetic flux density of the conventional developing roller 1. Note,
in this specification, the "vertical component of the magnetic flux density" will
be hereinafter referred to as "magnetic flux density". The peak portion of the magnetic
flux density in the magnetic flux density distribution will be designated as a magnetic
pole. This embodiment has five magnetic poles as shown in Fig. 19. The magnetic pole
A confronts the photosensitive drum 3, the magnetic poles B, C, and E are mainly used
for conveying the developer 4b, and a magnetic pole D is mainly used for applying
the developer 4 to the developing roller 1. Also, the developer restriction member
facing section 6 is positioned between the magnetic poles B and C.
[0016] Figure 20 shows, on an enlarged scale, the distribution of the magnetic flux density
of the conventional developer restriction member facing section 6. As clearly shown
by the drawing, the conventional developing apparatus suffered from a large change
in the vertical component of the magnetic flux density on the developing roller 1
in the developer restriction member facing section 6.
[0017] Note, the parts to be mounted in the developing apparatus have respective mounting
precision errors which must be allowed for in the fabrication. Namely, if the mounting
precision for the developer restriction member 2 is ±0.5 degrees, if the precision
in the magnetized position for the magnet 1b is ±3 degrees, if the fixing precision
for the magnet 1b ±0.5 degrees, and if the processing precision of the other parts
is ±1 degree, the position of the developer restriction member 2 relative to the magnetic
flux density distribution has a precision as shown by the positional precision range
Q. The positional precision range Q is generally within the range of ±5 degrees of
the above-mentioned precision, and becomes 10 degrees in total.
[0018] In the conventional developing roller 1, the magnetic flux density in the developer
restriction member facing section 6 differs depending on the developing apparatus
used, due to the large variation in the magnetic flux density within the positional
precision range Q.
[0019] An example is US Patent No. 4 851 872. A developing device is disclosed therein which
includes a developing sleeve provided rotatably at a side of an electrostatic latent
image support member, a supply member for supplying developer to the developing sleeve,
a bristle height regulating member which confronts an upper portion of the developing
sleeve so as to adjust an amount of the developer transported to a developing region
and a plurality of magnets provided in the developing sleeve. The magnetic poles of
the magnets not only extend in an axial direction of the developing sleeve but are
arranged in a circumferential direction of the developing sleeve. The magnetic poles
include a weak magnetic pole disposed adjacent to the upper portion of the developing
sleeve and two strong magnetic poles between which the weak magnetic pole is interposed.
The strong magnetic poles have a polarity different from that of the weak magnetic
pole.
[0020] In connection with this, US Patent No. 4,825,241 discloses an electrostatic latent
image developing apparatus including a rotatable developing sleeve, multiple fixed
magnets in the developing sleeve and a brush height regulating member positioned opposite
one of the multiple magnets is magnetised so that the region corresponding to 80%
plus of the peak value of magnetic force has a spread which subtends an angle of 20°
or more at the exterior surface of the developing sleeve.
[0021] As described hereinbefore, the difference in the magnetic flux density causes a variation
in the amount of the developer 4 to be carried to the developing section, which has
a large affect on the image quality. Accordingly, many different problems arise such
as a remarkable difference in the image density depending on the developing apparatus
used, a solid, a thin line, missing out of half toning dots, and the adherence of
the carrier to the photosensitive body.
[0022] JP-A-1-154 182 discloses the use of a third pole placed between the first two for
the purpose of reducing the variation in the amount of developer to be carried.
[0023] An object of the invention is to overcome the conventional disadvantages and to provide
a magnetic brush developing apparatus which prevents unevenness in the image quality
resulting from a substitution of different developing apparatus, thus leading to an
improvement in the image quality, and which has a wider assembly precision range enabling
an easy installment of the apparatus.
[0024] In accordance with the invention there is thus provided a magnetic brush developing
apparatus, comprising: a development container for containing a developer; a developing
roller including a shaft and a magnet stationarily located in said development container
and having a plurality of magnetic poles at points on its circumference; a rotational
sleeve arranged so as to cover the outer circumference of said magnet and rotatably
driven to carry the developer of said development container; and a developer restriction
member arranged opposite said rotational sleeve to restrict the amount of the developer
carried by said rotational sleeve; wherein at the position facing said developer restriction
member, and in its vicinity, there is formed a uniform magnetic flux density section
having a magnetic flux density whose radial component is uniform to a predetermined
tolerance on the periphery of the said rotational sleeve; wherein a first two of said
magnetic poles are positioned so that a distance between said two magnetic poles is
such that magnetic flux flows from one magnetic pole toward the other magnetic pole
past a third magnetic pole which is placed between the said two magnetic poles at
a position substantially opposite the developer restriction member, such that the
uniform magnetic flux density section is formed between said first two of said poles,
wherein said first two of said magnetic poles are different from each other, characterised
in that the third magnetic pole has a weaker magnetic flux than said first two poles,
an angle between center lines of said two magnetic poles is not less than twice an
average width of said first two magnetic poles, and wherein the third magnetic pole
has a width being about a half that of either of said first two magnetic poles and
has a strength of magnetization of approximately 5 to 50% of that of at least one
of said first two magnetic poles.
[0025] Further, in an embodiment said uniform magnetic density section may include a distribution
of a magnetic flux density having a vertical component which is substantially uniform
in a wider range than that of any of a precision in a magnetized position for said
magnet, a precision in a mounting of said magnet to said developing apparatus, and
a precision in a mounting of said developer restriction member to said developing
apparatus. Further, said uniform magnetic flux density section may include a distribution
of a magnetic flux density having a vertical component which is substantially uniform
in a wider range than that of a precision of a relative mounting position of said
uniform magnetic flux density section and of said developer restriction member.
[0026] Moreover, said uniform magnetic flux density sections may be provided on both sides
of said developer restriction member facing position, to thus extend by an angle of
at least 3 degrees, preferably at least 5 degrees, more preferably at least 10 degrees,
in terms of the rotational angle of said rotational sleeve.
[0027] Furthermore, said uniform magnetic flux density section may have a vertical magnetic
flux density within the range of ±20%, preferably ±15%, more preferably ±10% with
respect to the preset value for said developer restriction member facing position.
[0028] To illustrate the functions of the present invention, Figure 17 shows the variation
in the developer head based on the magnetic flux density distribution of the developer
restriction member facing section 6.
[0029] Fig. 17(a) shows the state of the developer head in the developer restriction member
facing section 6.
[0030] In the embodiment, the magnetic flux density has a substantially uniform vertical
component in the developer restriction facing section 6, so that the condition of
raising of the head in this section is substantially uniform.
[0031] As a result, even if the mounting position of the developer restriction member with
respect to the magnetic flux density distribution is diverged, the condition of raising
of the developer is uniform in the developer restriction member facing section 6,
so that the amount of the developer 4 to be carried to the developing section 9 passing
through the developer restriction member 2 remains unchanged.
[0032] Fig. 17(b) shows the state of the developer head in the developer restriction facing
section 6 of the prior art. In the conventional techniques, the vertical component
of the magnetic flux density is changed in the developer restriction member facing
section 6, which causes the variation in the state of the head raising in this section.
[0033] Consequently, if the mounting position of the developer restriction member 2 with
respect to the magnetic flux density distribution is diverged from the design center
value 6a due to the processing precision of the parts and the like, the head raising
of the developer 4 is different in the developer restriction member facing section
6, and thus the amount of the developer 4 to be carried to the developing section
passing through the developer restriction member 2 differs depending on the developing
apparatus used.
[0034] Then, as described earlier, the variation in the amount of the developer 4 influences
the image quality, resulting in a different image quality depending on the developing
apparatus used.
[0035] As described above, a constant uniform image quality can be obtained in an individual
developing apparatus, effectively resulting in an improvement in the image quality
and a reduction of the processing precision of the parts.
[0036] According to the embodiments described the magnetic flux density in the developer
restriction member facing section may thus be almost unchanged even though the relative
mounting position diverges between the magnetic flux density distribution and the
developer restriction member, thereby rendering the supply of the developer uniform
among different developing devices. As a result, despite the substitution of the developing
apparatus, a uniform image quality may be obtained without unevenness, leading to
an improvement in the image quality, and a developing apparatus having a wider processing
and assembly precision range can be obtained.
[0037] For a better understanding of the invention and to show how the same may be carried
into effect, reference will now be made, purely by way of example, to the accompanying
drawings in which:-
Fig. 1 is a schematic side sectional view of the printer of the principle embodiment;
Fig. 2 shows a side sectional view of the developing apparatus of one embodiment;
Fig. 3 is a perspective view of the developing roller of the embodiment;
Fig. 4 shows a distribution of the magnetic flux density of the developing roller
of the embodiment;
Fig. 5 is a partially enlarged view showing the distribution of the magnetic flux
density of the developing roller of the embodiment;
Fig. 6 is a graph showing a relationship between the position of the developer restriction
member and the printing density;
Fig. 7 is a graph showing a relative position of the developer restriction member
with regard to the magnetic flux density distribution;
Fig. 8 is a chart showing results of the image evaluation;
Fig. 9 is an explanatory drawing showing the magnetization principle;
Fig. 10 is a lateral view of the developing roller of another embodiment;
Fig. 11 shows the relationship between the blade and the magnetic poles B and C;
Fig. 12 shows a developing roller and the distribution of the magnetic flux density;
Fig. 13 illustratesa method of forming a uniform magnetic flux density section by
a balance control between the two magnetic poles B and C. This method is not covered
by the present claims.
Fig. 14 illustrates another method of forming uniform magnetic flux density section
by providing a new magnetic pole C';
Fig. 15 shows a distribution of the magnetic flux density in the embodiment of Fig.
13;
Fig. 16 shows a distribution of the magnetic flux density in the embodiment of Fig.
14;
Fig. 17 is a partially enlarged view showing the state of the developer head;
Fig. 18 is an explanatory drawing of the principle of the developing apparatus;
Fig. 19 shows a distribution of the magnetic flux density of the developing roller
of the conventional example; and
Fig. 20 is a partially enlarged view of the magnetic flux density distribution of
the developing roller of the conventional example.
[0038] Embodiments of the present invention will now be described with reference to the
drawings.
[0039] Figure 1 shows an electrophotographic printer. The present invention is widely applicable
to not only printers but also copying machines and the like.
[0040] In Fig. 1, reference numeral 3 denotes a photosensitive drum rotatable around a shaft
thereof, 11 denotes a preelectrostatic charger for electrifying the photosensitive
drum 3, 12 represents a light exposure device for exposing the photosensitive drum
3 by a scanned laser beam, to form an electrostatic latent image on the surface of
the photosensitive drum 3.
[0041] Also, reference numeral 10 represents a magnetic brush developing apparatus for developing
the electrostatic latent image formed on the photosensitive drum 3, to form a toner
image, 13 designates a transfer device for transferring the toner image onto a printing
sheet, 14 designates a cleaner for removing residual toner on the surface of the photosensitive
drum 3, and 15 shows a fixing roller for thermally fixing the toner image onto the
sheet.
[0042] Figure 2 shows the developing apparatus 10.
[0043] Contained within a development container 7 is a two component developer 4 composed
of a toner 4a, a colored powder, and a carrier 4b, i.e., a magnetic powder. The toner
4a is supplied into the development container 7 from a toner hopper 21 provided on
the upper portion through a toner supply roller 22.
[0044] The toner used in this embodiment is made of styrene acrylic series or polyester
series resin and has an average particle diameter of 11 to 12 µm. The carrier, which
is a resin-coated magnetic material such as magnetite or ferrite has an average particle
diameter of about 100 µm. A saturation magnetization of the carrier is 80 emu/g.
[0045] Reference numeral 23 stands for a stirring device for stirring the developer within
the development container 7, to produce an electrostatic charge therein. 24 signifies
a flow restriction member for returning the developer 4 held back by a developer restriction
member 2, to the stirring device 23, and 25 signifies a toner density sensor for detecting
a toner density in the developer 4 through a measurement of a permeability of the
developer 4, to thereby determine the toner replenishment timing.
[0046] The development container 7 has at its left end portion an opening which defines
a developing section 9 for developing the surface of the photosensitive drum 3, in
which there is provided a developing roller 1 constituted of a cylindrical magnet
1b made of a magnetized magnetic material, and a tubular rotational sleeve 1a rotatably
driven and arranged so as to cover the surface of the magnet 1b.
[0047] In this embodiment, the magnet 1b is made of ferrite and has a shaft made of a non-magnetic
material such as aluminum alloy, for example. Also, the rotational sleeve 1a is made
of the non-magnetic material such as aluminum alloy, for example.
[0048] Figure 3 is a perspective view showing the partially cut-away developing roller 1.
The magnet 1b shown in Fig. 3 includes a plurality of radially alternately magnetized
lines (five lines).
[0049] The developer 4 held on the surface of the rotational sleeve 1a through a magnetic
force exerted by the magnet 1b, is carried to the developing section 9 by the rotation
of the rotational sleeve 1a.
[0050] As shown in Fig. 2, a developer restriction member or blade 2 made of a non-magnetized
material is rigidly fixed to the development container 7 so as to be parallel to the
axial direction of the rotational sleeve 1a. Provided between the developer restriction
member 2 and the rotational sleeve 1a is a predetermined small gap (1.0 mm in this
embodiment), and as a result, the height of the developer 4 (the height of the head)
carried by the rotation of the rotational sleeve 1a is restricted to a predetermined
value by the developer restriction member 2.
[0051] Then, only the toner which develops the electrostatic latent image formed on the
surface of the photosensitive drum 3 is transmitted to the photosensitive drum 3,
and the remaining developer 4 is returned to the development container 7 by the developing
roller 1.
[0052] Figure 4 shows a distribution of the magnetic flux density, in which reference numeral
6 denotes a developer restriction member facing section arranged opposite to the developer
restriction member 2.
[0053] A magnetic pole A is an N pole confronting the photosensitive drum 3. Magnetic poles
B, C, and E are mainly utilized to carry the developer 4, and a magnetic pole D is
mainly used to apply the developer 4 to the developing roller 1. Further, the magnetic
poles E and D have the same polarity, and therebetween the developer is removed from
the developing roller 1. Further, the developer 4 that has been removed is stirred
by the stirring device 23 for re-use.
[0054] As shown in the enlarged view of Fig. 5, between the magnetic poles B and C the developer
restriction member facing section 6 has a substantially uniform magnetic flux density
of, for example, 80 to 90 gauss, due to the magnetic pole C. (10
4 gauss = 1 Tesla).
[0055] That magnetic flux density lying between 80 to 90 gauss is suitable to obtain a satisfactory
image in the apparatus of this embodiment, the magnitude of which may be appropriately
selected depending on the properties of the apparatus.
[0056] The uniform magnetic flux density section Z is made to extend across 10 degrees or
more and is 20 degrees in total at both sides of the developer restriction member
facing the position 6a therebetween.
[0057] Methods of forming the thus widely spread uniform magnetic flux density section Z
will be described later in detail.
[0058] As described earlier, the parts mounted in the apparatus have respective mounting
precisions (errors permissible in the manufacture) and the like. Accordingly, when
the mounting precision of the developer restriction member 2 is ±0.5 degrees, the
magnetized positional precision of the magnet 1b is ±3 degrees, the fixing precision
of the magnet 1b is ±0.5 degrees, and the processing precision of the other parts
is ±1 degree, the position of the developer restriction member 2 relative to the magnetic
flux density distribution of the developing roller 1 includes a precision shown by
a positional precision range Q.
[0059] Q is on the order of 10 degrees (±5 degrees), and the uniform magnetic flux density
section Z is formed so as to be substantially double the range Q in this embodiment.
[0060] As a result, the magnetic flux density of the developer restriction member facing
section 6 is almost unchanged, and accordingly, even if a different developing apparatus
is used, the amount of developer 4 supplied to the developing section 9 is unchanged
in each developing apparatus.
[0061] Figure 6 is a graph showing the relationship between the relative positional variation
of the developer restriction member 2 with respect to the magnetic flux density distribution
of the developing roller 1, and the printing density (developing density). Figure
7 shows the + or - direction of the graph. The variation in the relative position
of the developer restriction member with respect to the magnetic flux density distribution
of the magnet, toward the directions as shown in the drawing, are designated by +
and -, respectively.
[0062] A solid line in Fig. 6 shows the apparatus of this embodiment, and a broken line
shows the conventional apparatus. As can be seen, this embodiment apparatus is subjected
to very little change in the printing density regardless of the position of the developer
restriction member 2 within the positional precision range Q.
[0063] Therefore, each developing apparatus can present a similar uniform image quality
within a predetermined range, with respect to the image density, fogging, skip, carrier
adhesion and the like.
[0064] Figure 8 shows the angle range for the uniform magnetic flux density section Z of
the developing roller used in the developing apparatus, and the ratio of the developing
apparatus by which a satisfactory printing can be obtained when the variation range
of the magnetic flux density is changed. The image density of a 4 mm square solid
of an output image was judged to be satisfactory at 1.2 or over.
[0065] In the drawing, ⓞ means that the ratio (good ratio of the apparatus) of the developing
apparatus at which a satisfactory printing can be obtained is approximately 100%,
o means that the ratio (good ratio of the apparatus) of the developing apparatus at
which a satisfactory printing can be obtained is 80% or more, △ signifies that the
ratio (good ratio of the apparatus) of the developing apparatus at which a satisfactory
printing can be obtained is 60% or more, and x signifies that the ratio (good ratio
of the apparatus) of the apparatus at which a satisfactory printing can be obtained
is 50% or less. It will be appreciated from Fig. 8 that the developing apparatus using
a developing roller having a uniform magnetic flux density section Z with a wider
angle range, and having a narrower variation angle of the magnetic flux density within
the foregoing angle range, is able to obtain a satisfactory printing with a 1.2 or
more image density.
[0066] For example, for the developing apparatus using a developing roller (as used in the
embodiment in Fig. 6) having an angle range of ±10 degrees or more and having a variation
range of the magnetic flux density of ±10 or less, the good ratio of the apparatus
was almost 100%, which is an ideal result.
[0067] On the contrary, for the developing apparatus using a developing roller having an
angle range of + 5 degrees or more, and the variation range of the magnetic flux density
of ±15% or less, the good ratio of the apparatus was 80% or more, and for the developing
apparatus using a developing roller having an angle range of ±3 degrees and the variation
range of the magnetic flux density of ±20%, the good ratio of the apparatus was 60%
or more.
[0068] For the developing apparatus using a developing roller having an angle range of ±2
degree or less and the variation range of the magnetic flux density of ±25%, or more,
the good ratio of the apparatus was 50% or less, which is unusable in practice.
[0069] Also, in the case of the developing apparatus using a developing roller having an
angle range of ±2 degrees or less, and the variation range of the magnetic flux density
of + 10 or less, as well as the developing apparatus using a developing roller having
an angle range of ±10 degrees or more and an variation range of the magnetic flux
density of ±25% or more, the good ratio of the apparatus was not less than 60%.
[0070] From the above experimental results, it is understood that the uniform magnetic flux
density section Z should be formed to extend by 3 degrees, preferably by 5 degrees,
more preferably 10 degrees in terms of angle range on both sides of the developer
restriction member facing section 6 therebetween, more preferably, a 5 degrees angle
range or more, most preferably a 10 degrees angle range or more.
[0071] It is also understood that the vertical magnetic flux density of the uniform magnetic
flux density section Z should lie within a range of ±20%, preferably ±15%, more preferably
±10% with respect to the preset value at the developer restriction member facing section
6.
[0072] In these experiments, 16 kinds of developing rollers were used to make 20 measurements
each.
[0073] A description is now given of a method of fabricating a developing roller lying within
the angle range and the variation range of the magnetic flux density as described
above.
[0074] First, the magnetizing of the magnet 1b will be described with reference to Fig.
9.
[0075] As shown in the drawing, an electromagnet 30 is arranged surrounding a magnet raw
material 1c. A coil (not shown) of the electromagnet 30 is then energized to exert
a magnetic force on the electromagnet 30, to thereby magnetize the magnet raw material
1c to form a magnet 1b. In this case, the range of the angular position of each magnetic
pole is determined by the angular positional arrangement of the electromagnet 30,
and the magnitude of the magnetic flux density of each magnetic pole is determined
by the current supplied to the coil of the electromagnet 30.
[0076] Figure 10 shows a developing roller of another embodiment in accordance with the
present invention. In the drawing, the magnet 1b has a shaft having planes to which
magnets are attached, and through an appropriate magnetic flux density and the angle
arrangement, a satisfactory distribution of the magnetic flux density can be obtained.
[0077] Methods of forming a uniform magnetic flux density section Z will now be described
with reference to Figs. 11 to 16.
[0078] Figure 11 shows the relationship between the positions of the developer restriction
member or blade 2 and the two magnetic poles B and C located on the circumference
of the developing roller 1 and between these magnetic poles B and C. There are two
methods of forming the uniform magnetic flux density section Z, one being attained
by a balance control between the two magnetic poles B and C located between these
magnetic poles B and C, and the other being attained by providing a new magnetic pole
C' in the vicinity of the developer restriction member (blade) 2.
[0079] In Fig. 12(a) shows a structure of the developing roller and Fig. 12(b) shows the
vertical component of the magnetic flux density distribution on the rotational sleeve
la of the developing roller 1. As mentioned hereinbefore, the developing roller 1
comprises the rotational sleeve la and the magnet 1b. An isotropic ferrite magnet
is used as a material of the magnet 1b. As shown in Fig. 12(a), if an external magnetic
field is exerted on such a magnet material, the magnetic poles (A, B, C, ...) are
formed. Figure 12(b) shows the results of the measurements of the magnetic flux density
distribution on the rotational sleeve la. The positions of the magnetic poles B and
C are shown at the bottom of the drawing. In Fig. 12(b), the abscissa indicates an
angle θ.
(1) Balance Control of Magnetic Poles
[0080] Although not covered by the present claims the method of forming a uniform magnetic
flux density section Z by a balance control between the two magnetic poles B and C,
between which the developer restriction member or blade 2 is arranged is now described.
If the distance between the two magnetic poles B and C is increased, as shown in Fig.
13(a), not only does the magnetic flux flow from the magnetic pole C (N-pole) toward
the magnetic pole B (S-pole), but also the magnetic flux flows toward the inner magnetic
poles located at the side of a shaft of the developing roller, as shown by broken
lines in Fig. 13(a), and thus, both magnetic fluxes are mutually balanced so that
a flat portion is formed. If the strength of magnetization and the width of these
two magnetic poles B and C are the same, the flat portion is located at a zero line
of the magnetic flux density, but if the strength of magnetization of one of the magnetic
poles B and C is smaller than that of the other, or if the width of one is narrower
than that of the other, the flat portion is not located at the zero line. For example,
if the width of the magnetic pole C (N-pole) is narrower, the amount of the magnetic
flux around the magnetic pole B (S-pole) is increased, and therefore, the flat portion
is moved to the side of N-pole, and thus a uniform magnetic flux density section Z
is formed at the side of N-pole, as shown in Fig. 13(c).
[0081] Therefore, in a method of obtaining a balance control between the two magnetic poles
B and C, a uniform magnetic flux density section (flat portion) Z can be advantageously
formed if the angle θ
0 (Fig. 12(a)) between the center lines of the two magnetic poles B and C is not less
than three times the average width of these magnetic poles B and C, and if the width
of one of the magnetic poles B and C is smaller (not more than 80%) than that of the
other, or the magnetic flux density of one is smaller than that of the other.
(2) Provision of a New Magnetic Pole C'
[0082] A method of forming a uniform magnetic flux density section Z by providing a new
magnetic pole C' will now be described with reference to Fig. 14. As mentioned above
(1), if the distance between the two magnetic poles B and C is increased, the uniformity
of the magnetic flux density will be lost as shown in Fig. 14(a). Therefore, a new
magnetic pole C' is arranged between the two magnetic poles B and C and opposite the
developer restriction member or blade 2. The distance between the magnetic poles B
and C' is a little bit shorter than the distance between the magnetic poles C' and
C. The width of the magnetic pole C' is about one half that of the magnetic pole B
or C and the strength of magnetization of the magnetic pole C' is about 5 to 50% that
of the magnetic pole B or C. Figure 14(b) shows a distribution of magnetic flux density
of this magnetic pole C' on the rotational sleeve 1a. The distribution of magnetic
flux density between the magnetic poles B and C is represented as a combination of
both, and thus a uniform magnetic flux density section Z is formed, as shown in Fig.
14(c).
[0083] Therefore, a uniform magnetic flux density section (flat portion) Z can be advantageously
formed by providing a new magnetic pole C', the width of which is about a half that
of the magnetic pole B or C and a strength of magnetization thereof is about 5 to
50% of that of the magnetic pole B or C, at a position between the developer restriction
member or blade 2 and the two magnetic poles B and C. In this case, the angle θ, (Fig.
12(a)) between the center lines of the two magnetic poles B and C is not less than
twice the average width of these magnetic poles B and C.
[0084] Figures 15 and 16 show a distribution of the magnetic flux density in the above-mentioned
embodiments (1) and (2), respectively. In Fig. 15, the strength of magnetization of
the magnetic poles A, B, C, D and E is the same, but the width thereof is changed
as follows. Also the positions of these magnetic poles A, B, C, D and E are set as
follows.
Magnetic pole |
Pole |
Magnetization strength |
Width |
Position |
A |
N |
1.8 (KG) |
60° |
0 |
B |
S |
same |
30° |
75° |
C |
N |
same |
25° |
167.5° |
D |
S |
same |
35° |
212.5° |
E |
S |
same |
40° |
300.0° |
[0085] In Fig. 16, the strength of magnetization and the width of the magnetic poles A,
B, C, C', D and E are set as follows. Also the positions of these magnetic poles are
set as follows.
Magnetic pole |
Pole |
Magnetization strength |
Width |
Position |
A |
N |
1.8 (KG) |
60° |
0 |
B |
S |
1.8 (KG) |
30° |
80° |
C |
N |
0.2 (KG) |
15° |
117.5° |
C' |
N |
1.8 (KG) |
25° |
157.5° |
D |
S |
1.8 (KG) |
35° |
212.5° |
E |
N |
1.8 (KG) |
40° |
300.0° |
[0086] It should be noted that the present invention is not confined to the above embodiments.
With respect to the uniform magnetic flux density section Z, providing there exists
an appropriate magnetic flux density (for example, 80 to 90 gauss) within the range
of at least 5 degrees or more, and 10 degrees or more in total on the both sides of
the designed developer restriction member facing point 6a therebetween, the image
quality among the apparatuses can be made largely uniform compared to the conventional
apparatuses.
[0087] Also, the above angle may be made at least 3 degrees or more on both sides thereof,
and 6 degrees or more in total, to obtain a better effect.
1. A magnetic brush developing apparatus, comprising:
a development container for containing a developer (4);
a developing roller including a shaft and a magnet (1b) stationarily located in said
development container (7) and having a plurality of magnetic poles at points on its
circumference;
a rotational sleeve (1a) arranged so as to cover the outer circumference of said magnet
(1b) and rotatably driven to carry the developer (4) of said development container
(7); and
a developer restriction member (2) arranged opposite said rotational sleeve (1a) to
restrict the amount of the developer (4) carried by said rotational sleeve (1a);
wherein at the position (6a) facing said developer restriction member (2), and in
its vicinity (6), there is formed a uniform magnetic flux density section (Z) having
a magnetic flux density whose radial component is uniform to a predetermined tolerance
on the periphery of the said rotational sleeve (1a); wherein a first two of said magnetic
poles are positioned so that a distance between said two magnetic poles is such that
magnetic flux flows from one magnetic pole toward the other magnetic pole past a third
magnetic pole (C') which is placed between the said two magnetic poles at a position
substantially opposite the developer restriction member (2), such that the uniform
magnetic flux density section is formed between said first two of said poles, wherein
said first two of said magnetic poles are different from each other, characterised
in that the third magnetic pole has a weaker magnetic flux than said first two poles,
an angle (Θo) between center lines of said two magnetic poles (B, C) is not less than
twice an average width of said first two magnetic poles (B, C), and wherein the third
magnetic pole (C') has a width being about a half that of either of said first two
magnetic poles (B or C) and has a strength of magnetization of approximately 5 to
50% of that of at least one of said first two magnetic poles (B or C).
2. A magnetic brush developing apparatus according to claim 1, wherein said uniform magnetic
flux density section (Z) includes a distribution of magnetic flux density whose component
normal to the sleeve (1a) is substantially uniform in a wider range than that of any
of a magnetized positional precision for said magnet (1b), a mounting precision of
said magnet (1b) to said development container (7), and a mounting precision of said
developer restriction member (2) to said development container (7).
3. A magnetic brush developing apparatus according to claim 1, wherein said uniform magnetic
flux density section (Z) includes a distribution of magnetic flux density whose component
normal to the sleeve (1a) is substantially uniform in a wider range than that of a
relative mounting positional precision between said uniform magnetic flux density
section (Z) and said developer restriction member (2).
4. A magnetic brush developing apparatus according to any of claims 1 to 3, wherein said
uniform magnetic flux density sections (Z) are provided on both sides of said developer
restriction member facing point (6a) therebetween so as to extend by an angle of at
least 10 degrees each in terms of a rotational angle of said rotational sleeve (1a).
5. A magnetic brush developing apparatus according to any preceeding claim, wherein said
uniform magnetic flux density section (Z) has a magnetic flux density normal to the
sleeve (1a) lying within the range of ±10% with respect to a preset value for said
developer restriction member facing point (6a).
6. A magnetic brush developing apparatus according to any one of claims 1 to 4, wherein
said uniform magnetic flux density section (Z) is provided on both sides of said developer
restriction member facing point (6a) therebetween so as to extend by an angle of at
least 3 degrees in terms of a rotational angle of said rotational sleeve (1a), and
said uniform magnetic flux density sections (Z) has a magnetic flux density normal
to the sleeve (1a) lying within the range of ±20% with respect to a preset value for
said developer restriction member facing point (6a).
7. A magnetic brush developing apparatus according to any one of claims 1 to 3, wherein
said uniform magnetic flux density section (Z) is provided on both sides of said developer
restriction member facing point (6a) therebetween so as to extend by an angle of at
least 3 degrees in terms of a rotational angle of said rotational sleeve (1a), and
said uniform magnetic flux density section (Z) has a magnetic flux density normal
to the sleeve (1a) lying within the range of ±10% with respect to a preset value for
said developer restriction member facing point (6a).
8. A magnetic brush developing apparatus according to any one of claims 1 to 3, wherein
said uniform magnetic flux density section (Z) is provided on both sides of said developer
restriction member facing point (6a) therebetween so as to extend by an angle of at
least 10 degrees in terms of a rotational angle of said rotational sleeve (1a), and
said uniform magnetic flux density section (Z) has a magnetic flux density normal
to the sleeve (1a) lying within the range of ±20% with respect to a preset value for
said developer restriction member facing point (6a).
9. A magnetic brush developing apparatus according to any one of claims 1 to 3, wherein
said uniform magnetic flux density section (Z) is provided on both sides of said developer
restriction member facing point (6a) therebetween so as to extend by an angle of at
least 5 degrees in terms of a rotational angle of said rotational sleeve (1a), and
said uniform magnetic flux density section (Z) has a magnetic flux density normal
to the sleeve (1a) lying within the range of ±10% with respect to a preset value for
said developer restriction member facing point (6a).
10. A magnetic brush developing apparatus according to any preceding claim, wherein said
developer restriction member (2) is arranged between two (B, C) of said plurality
of magnetic poles, an angle (Θo) between center lines of said two magnetic poles (B,
C) is not less than three times an average width of said two magnetic poles (B, C),
and a width of one of said two magnetic poles (B, C) is smaller than that of the other.
11. A magnetic brush developing apparatus according to any preceding claim, wherein said
developer restriction member (2) is arranged between two (B, C) of said plurality
of magnetic poles, an angle (Θo) between center lines of said two magnetic poles (B,
C) is not less than three times an average width of said two magnetic poles (B, C),
and a magnetic flux density of one is smaller than that of the other.
1. Magnetbürsten-Entwicklungsgerät, umfassend:
einen Entwicklungsbehälter zum Aufnehmen eines Entwicklers (4);
eine eine Welle und einen Magneten (1b) umfassende Entwicklungswalze, die stationär
in dem Entwicklungsbehälter (7) angeordnet ist und eine Vielzahl von Magnetpolen an
Punkten auf ihrem Umfang hat;
eine drehbare Hülse (1a), die so eingerichtet ist, daß sie den äußeren Umfang des
Magneten (1b) überdeckt, und die drehangetrieben wird, um den Entwickler (4) vom Entwicklungsbehälter
(7) zu transportieren; und
ein Entwicklerbegrenzungsglied (2), welches der drehbaren Hülse (1a) gegenüberliegend
eingerichtet ist, um die Menge des von der drehbaren Hülse (1a) transportierten Entwicklers
(4) zu begrenzen;
wobei in der dem Entwicklerbegrenzungsglied (2) zugewandten Position (6a) und in deren
Nachbarschaft (6) auf der Peripherie der drehbaren Hülse (1a) eine Sektion (Z) mit
einer gleichförmigen Magnetflußdichte ausgebildet ist mit einer Magnetflußdichte,
deren radiale Komponente gleichförmig bis zu einer vorgegebenen Toleranz ist;
wobei zwei erste der Magnetpole so positioniert sind, daß ein Abstand zwischen diesen
beiden Magnetpolen derart ist, daß ein Magnetfluß von einem Magnetpol zu dem anderen
Magnetpol über einen dritten Magnetpol (C') fließt, welcher zwischen den beiden Magnetpolen
in einer Position angeordnet ist, die im wesentlichen dem Klingenbegrenzungsglied
(2) gegenüberliegt, derart, daß die Sektion einheitlicher Magnetflußdichte zwischen
diesen ersten beiden dieser Pole ausgebildet ist, wobei die ersten beiden dieser Magnetpole
voneinander verschieden sind, dadurch gekennzeichnet, daß der dritte Magnetpol einen schwächeren Magnetfluß hat als die ersten beiden Pole,
daß ein Winkel (θ0) zwischen Mittellinien dieser beiden Magnetpole (B, C) nicht kleiner als das Zweifache
einer mittleren Breite der ersten beiden Magnetpole (B, C) ist, und wobei der dritte
Magnetpol (C') eine Breite hat, die etwa die Hälfte derjenigen von jedem der beiden
ersten Magnetpole (B oder C) ist, sowie eine Magnetisierungsstärke von annähernd 5
bis 50% derjenigen von wenigstens einem der beiden ersten Magnetpole (B oder C).
2. Magnetbürsten-Entwicklungsgerät nach Anspruch 1, bei welchem die Sektion (Z) gleichförmiger
Magnetflußdichte eine Verteilung der Magnetflußdichte aufweist, deren zur Hülse (1a)
normale Komponente im wesentlichen gleichförmig in einem Bereich ist, der breiter
als derjenige irgendeiner magnetisierten Positioniergenauigkeit für diesen Magnet
(1b), einer Montagegenauigkeit dieses Magneten (1b) an dem Entwicklungsbehälter (7)
und eine Montagegenauigkeit des Entwicklerbegrenzungsgliedes (2) an dem Entwicklungsbehälter
(7) ist.
3. Magnetbürsten-Entwicklungsgerät nach Anspruch 1, bei welchem die Sektion (Z) gleichförmiger
Magnetflußdichte eine Verteilung der Magnetflußdichte aufweist, deren zur Hülse (1a)
normale Komponente im wesentlichen gleichförmig in einem Bereich ist, der breiter
als derjenige einer relativen Montage-Positioniergenauigkeit zwischen der Sektion
(Z) mit gleichförmiger Magnetflußdichte und dem Entwicklerbegrenzungsglied (2) ist.
4. Magnetbürsten-Entwicklungsgerät nach einem der Ansprüche 1 bis 3, bei welchem die
Sektionen (Z) gleichförmiger Magnetflußdichte auf beiden Seiten des dazwischen liegenden,
dem Entwicklerbegrenzungsglied zugewandten Punktes (6a) vorgesehen sind derart, daß
sie sich jeweils in einem Winkel von wenigstens 10 Grad bezogen auf einen Drehwinkel
der Drehhülse (1a) erstrecken.
5. Magnetbürsten-Entwicklungsgerät nach einem der vorangehenden Ansprüche, bei welchem
die Sektion (Z) gleichförmiger Magnetflußdichte eine zu der Hülse (1a) normale Magnetflußdichte
hat, die innerhalb des Bereiches von ± 10% bezogen auf einen vorgegebenen Wert für
den dem Entwicklerbegrenzungsglied zugewandten Punkt (6a) liegt.
6. Magnetbürsten-Entwicklungsgerät nach einem der Ansprüche 1 bis 4, bei welchem die
Sektion (Z) gleichförmiger Magnetflußdichte auf beiden Seiten des dazwischen liegenden,
dem Entwicklerbegrenzungsglied zugewandten Punktes (6a) vorgesehen ist derart, daß
sie sich in einem Winkel von wenigstens 3 Grad bezogen auf einen Drehwinkel der Drehhülse
(1a) erstreckt, und bei welchem die Sektionen (Z) gleichförmiger Magnetflußdichte
eine zu der Hülse (1a) normale Magnetflußdichte haben, die innerhalb des Bereiches
von ± 20% bezogen auf einen vorgegebenen Wert für den dem Entwicklerbegrenzungsglied
zugewandten Punkt (6a) liegt.
7. Magnetbürsten-Entwicklungsgerät nach einem der Ansprüche 1 bis 3, bei welchem die
Sektion (Z) gleichförmiger Magnetflußdichte auf beiden Seiten des dazwischen liegenden,
dem Entwicklerbegrenzungsglied zugewandten Punktes (6a) vorgesehen ist derart, daß
sie sich in einem Winkel von wenigstens 3 Grad bezogen auf einen Drehwinkel der Drehhülse
(1a) erstreckt, und bei welchem die Sektion (Z) gleichförmiger Magnetflußdichte eine
zu der Hülse (1a) normale Magnetflußdichte hat, die innerhalb des Bereiches von ±
10% bezogen auf einen vorgegebenen Wert für den dem Entwicklerbegrenzungsglied zugewandten
Punkt (6a) liegt.
8. Magnetbürsten-Entwicklungsgerät nach einem der Ansprüche 1 bis 3, bei welchem die
Sektion (Z) gleichförmiger Magnetflußdichte auf beiden Seiten des dazwischen liegenden,
dem Entwicklerbegrenzungsglied zugewandten Punktes (6a) vorgesehen ist derart, daß
sie sich in einem Winkel von.wenigstens 10 Grad bezogen auf einen Drehwinkel der Drehhülse
(1a) erstreckt, und bei welchem die Sektion (Z) gleichförmiger Magnetflußdichte eine
zu der Hülse (1a) normale Magnetflußdichte hat, die innerhalb des Bereiches von ±
20% bezogen auf einen vorgegebenen Wert für den dem Entwicklerbegrenzungsglied zugewandten
Punkt (6a) liegt.
9. Magnetbürsten-Entwicklungsgerät nach einem der Ansprüche 1 bis 3, bei welchem die
Sektion (Z) gleichförmiger Magnetflußdichte auf beiden Seiten des dazwischen liegenden,
dem Entwicklerbegrenzungsglied zugewandten Punktes (6a) liegt derart, daß sie sich
in einem Winkel von wenigstens 5 Grad bezogen auf einen Drehwinkel der Drehhülse (1a)
erstreckt, und bei welchem die Sektion (Z) gleichförmiger Magnetflußdichte eine zu
der Hülse (1a) normale Magnetflußdichte hat, die innerhalb des Bereiches von ± 10%
bezogen auf einen vorgegebenen Wert für den dem Entwicklerbegrenzungsglied zugewandten
Punkt (6a) liegt.
10. Magnetbürsten-Entwicklungsgerät nach einem der vorangehenden Ansprüche, bei welchem
das Entwicklerbegrenzungsglied (2) zwischen zwei (B, C) aus der Vielzahl von Magnetpolen
angeordnet ist, wobei ein Winkel (θ0) zwischen Mittellinien der beiden Magnetpole (B, C) nicht kleiner als das Dreifache
einer mittleren Breite der beiden Magnetpole (B, C) ist, und bei welchem eine Breite
von einem der beiden Magnetpole (B, C) geringer als die des anderen ist.
11. Magnetbürsten-Entwicklungsgerät nach einem der vorangehenden Ansprüche, bei welchem
das Entwicklerbegrenzungsglied (2) zwischen zwei (B, C) aus der Vielzahl von Magnetpolen
angeordnet ist, bei welchem ein Winkel (θ0) zwischen Mittellinien der beiden Magnetpole (B, C) nicht kleiner als das Dreifache
einer mittleren Breite der beiden Magnetpole (B, C) ist, und bei welchem eine Magnetflußdichte
von einem geringer als die des anderen ist.
1. Appareil de développement à balai magnétique, comprenant :
un récipient de développement destiné à contenir un agent de développement (4),
un rouleau de développement comprenant un arbre et un aimant (1b) placé en position
fixe dans le récipient (7) de développement et ayant plusieurs pôles magnétiques en
des points de sa circonférence,
un manchon rotatif (1a) disposé afin qu'il recouvre la circonférence externe de l'aimant
(1b) et entraîné en rotation afin qu'il entraîne l'agent de développement (4) du récipient
de développement (7), et
un organe (2) de restriction d'agent de développement disposé en face du manchon rotatif
(1a) afin qu'il limite la quantité d'agent de développement (4) transportée par le
manchon rotatif (1a),
dans lequel, à la position (6a) tournée vers l'organe (2) de restriction d'agent de
développement et à son voisinage (6), une section (Z) à densité uniforme de flux magnétique
est formée avec une densité de flux magnétique dont la composante radiale est uniforme,
avec une tolérance prédéterminée, à la périphérie du manchon rotatif (1a), dans lequel
deux premiers pôles magnétiques sont disposés afin que la distance comprise entre
les deux pôles magnétiques soit telle que le flux magnétique s'écoule d'un pôle magnétique
vers l'autre pôle magnétique en face d'un troisième pôle magnétique (C') qui est placé
entre les deux pôles magnétiques précités pratiquement en face de l'organe (2) de
restriction à lame, si bien que la section de densité uniforme de flux magnétique
est formée entre les deux premiers pôles, et dans lequel les deux premiers pôles magnétiques
sont différents l'un de l'autre, caractérisé en ce que le troisième pôle magnétique
a un flux magnétique inférieur à celui des deux premiers pôles, l'angle (θo) formé
par les axes centraux des deux pôles magnétiques (B, C) n'est pas inférieur au double
de la largeur moyenne des deux premiers pôles magnétiques (B, C), et dans lequel le
troisième pôle magnétique (C') a une largeur à peu près égale à la moitié de celle
de l'un ou l'autre des deux premiers pôles magnétiques (B ou C) et a une intensité
d'aimantation comprise entre environ 5 et 50 % de celle de l'un au moins des deux
premiers pôles magnétiques (B ou C).
2. Appareil de développement à balai magnétique selon la revendication 1, dans lequel
la section (Z) de densité uniforme de flux magnétique comprend une distribution de
la densité de flux magnétique dont une composante normale au manchon (1a) est pratiquement
uniforme sur une étendue plus grande que celles de la précision de position d'aimantation
de l'aimant (1b), de la précision de montage de l'aimant (1b) sur le récipient de
développement (7), et de la précision de montage de l'organe (2) de restriction d'agent
de développement sur le récipient de développement (7).
3. Appareil de développement à balai magnétique selon la revendication 1, dans lequel
la section (Z) à densité uniforme de flux magnétique comprend une distribution de
densité de flux magnétique dont la composante normale au manchon (1a) est pratiquement
uniforme sur une plage plus large que celle de la précision relative de position de
montage existant entre la section (Z) de densité uniforme de flux magnétique et l'organe
(2) de restriction d'agent de développement.
4. Appareil de développement à balai magnétique selon l'une quelconque des revendications
1 à 3, dans lequel les sections (Z) de densité uniforme de flux magnétique sont placées
des deux côtés d'un point intermédiaire (6a) tourné vers l'organe de restriction d'agent
de développement afin qu'elles recouvrent un angle d'au moins 10° chacune, représenté
par l'angle de rotation du manchon rotatif (1a).
5. Appareil de développement à balai magnétique selon l'une quelconque des revendications
précédentes, dans lequel la section (Z) de densité uniforme de flux magnétique a une
densité de flux magnétique perpendiculaire au manchon (1a) qui est comprise dans une
plage égale à ±10 % autour de la valeur préréglée pour l'organe de restriction d'agent
de développement tourné vers le point (6a).
6. Appareil de développement à balai magnétique selon l'une quelconque des revendications
1 à 4, dans lequel la section (Z) de densité uniforme de flux magnétique est placée
des deux côtés d'un point intermédiaire (6a) tourné vers l'organe de restriction d'agent
de développement afin qu'elle couvre un angle d'au moins 3° correspondant à l'angle
de rotation du manchon rotatif (1a), et les sections (Z) de densité uniforme de flux
magnétique ont une densité de flux magnétique perpendiculaire au manchon (1a) qui
est comprise dans une plage égale à ±20 % autour d'une valeur préréglée pour l'organe
de restriction d'agent de développement tourné vers le point (6a).
7. Appareil de développement à balai magnétique selon l'une quelconque des revendications
1 à 3, dans lequel la section (Z) de densité uniforme de flux magnétique est placée
des deux côtés d'un point intermédiaire (6a) tourné vers l'organe de restriction d'agent
de développement afin qu'elle couvre un angle d'au moins 3° par rapport à l'angle
de rotation des manchons rotatifs (1a), et la section (Z) de densité uniforme de flux
magnétique a une densité de flux magnétique perpendiculaire au manchon (1a) qui est
comprise dans une plage égale à ±10 % autour de la valeur préréglée de l'organe de
restriction d'agent de développement tourné vers le point (6a).
8. Appareil de développement à balai magnétique selon l'une quelconque des revendications
1 à 3, dans lequel la section (Z) de densité uniforme de flux magnétique est placée
des deux côtés d'un point intermédiaire (6a) tourné vers l'organe de restriction d'agent
de développement afin qu'elle recouvre un angle d'au moins 10°, représenté par l'angle
de rotation du manchon rotatif (1a), et la section (Z) de densité uniforme de flux
magnétique a une densité de flux magnétique perpendiculaire au manchon (1a) qui est
comprise dans une plage égale ±20 % autour d'une valeur préréglée de l'organe de restriction
d'agent de développement tourné vers le point (6a).
9. Appareil de développement à balai magnétique selon l'une quelconque des revendications
1 à 3, dans lequel la section (Z) de densité uniforme de flux magnétique est placée
des deux côtés d'un point intermédiaire (6a) tourné vers l'organe de restriction d'agent
de développement afin qu'elle couvre un angle d'au moins 5° représenté par l'angle
de rotation du manchon rotatif (1a), et la section (Z) de densité uniforme de flux
magnétique a une densité de flux magnétique perpendiculairement au manchon (1a) qui
est comprise dans une plage de ± 10 % par rapport à la valeur préréglée de l'organe
de restriction d'agent de développement tourné vers le point (6a).
10. Appareil de développement à balai magnétique selon l'une quelconque des revendications
précédentes, dans lequel l'organe (2) de restriction d'agent de développement est
placé entre deux (B, C) des pôles magnétiques, l'angle (θo) des axes centraux des
deux pôles magnétiques (B, C) n'est pas inférieur au triple de la largeur moyenne
des deux pôles magnétiques (B, C), et la largeur de l'un des deux pôles magnétiques
(B, C) est inférieure à celle de l'autre.
11. Appareil de développement à balai magnétique selon l'une quelconque des revendications
précédentes, dans lequel l'organe (2) de restriction d'agent de développement est
placé entre deux (B, C) des pôles magnétiques, l'angle (θo) des axes centraux des
deux pôles magnétiques (B, C) n'est pas inférieur au triple de la largeur moyenne
des deux pôles magnétiques (B, C), et la densité de flux magnétique de l'un est inférieure
à celle de l'autre.