Development apparatus having an improved developer feeder roll

A development apparatus includes a housing defining a chamber holding a supply of two-component developer material consisting of toner, and magnetizable carrier beads. The development apparatus also includes an extended life, increased reliability magnetic roll assembly within the housing for repeatably transporting a desired quantity of attracted developer material, fed from the chamber, for movement through the development zone. The improved magnetic roll assembly includes a rotatable non-conductive shell or substrate surrounding a magnetic member so as to prevent the creation of eddy currents in the substrate during its rotation. The substrate has an elastomeric coating layer formed over it. The elastomeric coating layer has a mechanically deformable smooth surface for effectively holding, even at relatively high rates of speed, the quantity of attracted developer material thereon being transported. The smooth surface is deformable by magnetized carrier beads acting under the influence of the magnetic member.

This invention relates generally to electrostatographic reproduction 
machines, and more particularly concerns a development apparatus having an 
improved developer feeder roll. 
Generally, the process of electrostatographic reproduction includes 
uniformly charging a photoconductive member, or photoreceptor, to a 
substantially uniform potential, and imagewise discharging it or imagewise 
exposing it to light reflected from an original image being reproduced. 
The result is an electrostatically formed latent image on the 
photoconductive member. The latent image so formed is developed by 
bringing a charged developer material into contact therewith. 
Two-component and single-component developer materials are commonly used. 
A typical two-component developer material comprises magnetic carrier 
particles, also known as "carrier beads," having charged toner particles 
adhering triboelectrically thereto. A single component developer material 
typically comprises charged toner particles only. In either case, the 
charged toner particles when brought into contact with the latent image, 
are attracted to such image, thus forming a toner image on the 
photoconductive member. The toner image is subsequently transferred to a 
receiver sheet which is then passed through a fuser apparatus where the 
toner image is heated and permanently fused to the sheet forming a copy of 
the original image. 
To develop a latent image in an electrostatographic reproduction machine, 
charged toner particles are brought, by a development apparatus, into 
contact with the latent image formed as described above. For such 
development using two-component developer material, the development 
apparatus typically includes a housing defining a chamber within which the 
developer material is mixed and charged. Moving and mixing two-component 
developer material triboelectrically and oppositely charges the "carrier 
beads" and the toner particles causing the toner particles to adhere to 
the carrier beads. 
As disclosed for example in U.S. Pat. No. 5,245,392, and U.S. Ser. No. 
07/091858 both assigned to the assignee of the present application, one 
type of a two-component development apparatus includes a housing, a mixing 
chamber, a development zone, and a donor member for transporting charged 
toner particles from the mixing chamber to the development zone. A 
plurality of electrode wires are closely spaced relative to the donor 
member within the development zone. An AC voltage is applied to the 
electrode wires for forming a toner cloud in the development zone. 
Electrostatic fields generated by an adjacent latent image serve to 
attract charged toner particles from the toner cloud, thus developing the 
latent image. 
As also disclosed, it is conventional to provide in such an apparatus, a 
conductive, usually metallic magnetic roll for transporting developer 
material from the mixing chamber to the donor member. The magnetic roll is 
mounted rotatably between the mixing chamber and the donor member, and 
serves to magnetically attract and hold magnetizable carrier beads (which 
have charged toner particles triboelectrically adhering thereto) onto its 
toughened or knurled surface. The charged toner particles are then 
electrostatically attracted from the carrier beads on the roughened or 
knurled surface of the magnetic roll onto the donor member for 
transporting to the development zone. 
The uniformity and quality of latent images developed in the development 
zone depend significantly on the quantity and uniformity of developer 
material repeatably transported by the magnetic roll to the donor member. 
As disclosed for example in each of the following references, the quantity 
and uniformity of developer material transported by such a magnetic roll 
are determined primarily by the surface roughness of the magnetic roll. 
For example, in this regard U.S. Pat. No. 4,034,709 (issued Jul. 12, 1977 
to Fraser et al.) discusses the importance of, and several ways of, 
roughening the surfaces of magnetic developer rolls. In particular, it 
discloses such a magnetic developer roll that includes a rough 
styrene-butadiene surface-coating for holding and directly transporting 
developer material through a development zone. 
Xerox Disclosure Journal (Vol. 4, No. 3 May/June 1979) discloses a magnetic 
roll in which desired surface roughness is obtained by covering the roll 
with a netting material such as nylon stockings. Xerox Disclosure Journal 
(Vol. 4, No. 4 July/August 1979) on the other hand discloses a similar 
magnetic roll that is roughened by forming a multiplicity of small, 
shallow depressions in its surface. As a further example, U.S. Pat. No. 
4,558,943 (issued Dec. 17, 1985 to Patz) discloses a similar magnetic roll 
that is roughened by forming valleys in its surface which are then filled 
with a polymeric material. 
As can be expected, when such rolls are used to transport two-component 
developer material containing carrier beads which can be abrasive, the 
carrier beads tend to wear out the desired roughness of their surfaces 
over time. Such wearing out of the surface roughness of a roll 
disadvantageously and eventually reduces the frictional characteristics of 
the surface, and hence its ability to repeatably transport desired 
quantities of developer material. This particular disadvantage is further 
aggravated in development apparatus that are required to operate at 
substantially high rates of speed. In such an apparatus, the magnetic roll 
is accordingly required to rotate at a substantially high number of 
revolutions per unit time. As can be expected, at such high rates of 
rotation, centrifugal forces, for example, make it increasingly difficult 
for the rotating roll to hold onto developer material on its worn out 
surface. There is therefore a need for an improved magnetic roll with a 
surface that substantially resists wear and tear from carrier beads in 
two-component developer, and that continues to exhibit acceptable holding 
ability at high speeds on developer material being transported thereby. 
Conventionally too, such magnetic rolls typically include a conductive 
substrate or shell, such as an aluminum shell, that is coated variously. 
It has been found that the rotation of the conductive shell of such a roll 
through a magnetic field, of the magnet within its core induces eddy 
currents through out the conductive shell. Such eddy currents as is well 
known, result in power losses as well as in reductions in the magnetic 
flux of the magnetic field. Such power losses for a high speed roll have 
been found to be as much as 19% of the free-space power required for 
driving the roll. Such losses also undesirably cause eddy current heating 
within the housing of the loss development apparatus. There is therefore 
also a need for an improved magnetic roll that overcomes such eddy current 
related disadvantages. 
SUMMARY OF THE INVENTION 
In accordance with one aspect of the present invention, there is provided a 
development apparatus for developing a latent image recorded on an image 
bearing surface. The development apparatus includes a housing that defines 
a chamber holding a supply of magnetizable developer material. The 
magnetizable developer material is comprised of toner particles and 
magnetic carrier beads. The development apparatus also includes a 
rotatable magnetic roll assembly mounted within the housing. The rotatable 
magnetic roll assembly has a path of rotation for moving a quantity of the 
developer material therealong, includes a magnetic member that generates a 
strong magnetic field at a first point along the path of rotation. The 
rotatable magnetic roll assembly also includes a rotatable cylindrical 
shell surrounding the magnetic member. The cylindrical shell has an outer 
surface that moves along the path of rotation, and an elastomeric coating 
that is formed onto the outer surface. The elastomeric coating so formed 
has a smooth surface for holding a quantity of the developer material that 
is magnetically attracted thereonto by the magnetic member. The smooth 
surface has a durometer hardness within a range of 60a to 70d, thereby 
enabling magnetic carrier beads in the quantity of developer material 
being held magnetically thereon to form temporary decompressions into the 
smooth surface for frictionally holding the quantity of developer material 
thereon even at substantially high rates of speed. 
In accordance with another aspect of the present invention, there is 
provided a high speed development apparatus for developing latent images 
recorded on an image bearing surface. The apparatus includes a housing 
defining a mixing chamber for holding and mixing a supply of magnetizable 
two-component developer material that includes toner particles and 
magnetizable carrier beads. A moving donor member, for positioning spaced 
from the image bearing surface, transports toner particles to a 
development zone adjacent the image bearing surface. A plurality of biased 
electrode wires, located within the development zone, creates a 
powder-cloud of the toner particles which are then attracted by a latent 
image on the image bearing member for image development. A movable feeder 
member is positioned adjacent a magnetic device and so as to be between 
the mixing chamber and donor member. A desired quantity of the 
magnetizable developer material from the mixing chamber is attracted by 
the magnetic device onto the feeder member for holding and transportation 
to the donor member. For preventing such a desired quantity of 
magnetizable developer material from slipping off the moving feeder member 
when it is rotated at a substantially high rate of speed, the feeder 
member includes a smooth surface outer layer that is mechanically 
deformable by magnetizable carrier beads thereon acting under the magnetic 
influence of the magnetic device.

While the present invention will be described in connection with a 
preferred embodiment thereof, it will be understood that it is not 
intended to limit the invention to that embodiment. On the contrary, it is 
intended to cover all alternatives, modifications, and equivalents as may 
be included within the spirit and scope of the invention as defined by the 
appended claims. 
DETAILED DESCRIPTION OF THE INVENTION 
Inasmuch as the art of electrostatographic reproduction is well known, the 
various processing stations employed in an exemplary electrostatographic 
reproduction machine will be shown hereinafter schematically, and their 
operations described only briefly. 
Referring initially to FIG. 5, there is shown an exemplary 
electrostatographic reproduction machine 10 incorporating the development 
apparatus of the present invention. The electrostatographic reproduction 
machine 10 for example employs a belt type image bearing member 12 having 
a photoconductive surface 14 formed over an electrically grounded 
conductive substrate 16. One skilled in the art, however, will appreciate 
that another suitable arrangement of a photoconductive image bearing 
member may be used. As shown, belt 12 moves in the direction of arrow 18 
to advance successive portions of photoconductive surface 14 sequentially 
through the various processing stations disposed about the path of 
movement thereof. Belt 12 is entrained about stripping roller 20, 
tensioning roller 22, and drive roller 24. Drive roller 24 is mounted 
rotatably in engagement with belt 12. Motor 26 is coupled to, and rotates 
roller 24 in order to advance belt 12 in the direction of arrow 18. Belt 
12 is maintained in tension by a suitable pair of springs (not shown) 
resiliently urging tensioning roller 22 against belt 12 with a desired 
spring force. Stripping finger 20 and tensioning roller 22 are mounted to 
rotate freely. 
Initially, a portion of belt 12 passes through charging station SA where a 
corona generating device, indicated generally by the reference numeral 28, 
charges photoconductive surface 14 to a relatively high, and substantially 
uniform potential. High voltage power supply 30 is coupled to corona 
generating device 28, and excitation of the power supply 30 causes corona 
generating device 28 to charge a portion of the photoconductive surface 14 
of belt 12. After such charging, the charged portion is advanced, as belt 
12 is moved, to exposure station SB. 
At exposure station SB, lamps 36 flash light rays for reflection onto an 
original document 32 that is placed face down upon a transparent platen 
34. The light rays reflected imagewise from the original image of document 
32 are transmitted through lens 38 to form a light image thereof. Lens 38 
focuses the imagewise light rays onto the charged portion of 
photoconductive surface 14 at exposure station SB and thus selectively 
dissipates the charge thereon to form a latent image. The latent image 
thus formed on photoconductive surface 14 corresponds to the informational 
areas contained within the original image of document 32. For such image 
wise exposure of photoconductive surface 14, a raster output scanner (ROS) 
(not shown) may alternatively be used in lieu of the lamps and light lens 
system previously described. As is well known, the ROS can be used as such 
to layout an image in a series of horizontal scan lines with each line 
having a specified number of pixels per inch. 
After the electrostatic latent image has been formed thus on 
photoconductive surface 14, belt 12 advances the latent image to 
development station SC. At development station SC, the development 
apparatus of the present invention, indicated generally by the reference 
numeral 40, (to be described in detail below) develops the latent image 
recorded on the photoconductive surface 14 to form a toner image. Belt 12 
then advances the toner image to transfer station SD where a copy sheet 54 
is advanced by sheet feeding apparatus 56 into a transfer relation with 
the toner image. Preferably, sheet feeding apparatus 56 includes a feed 
roll 58 contacting the uppermost sheet of a stack 60 of such sheets. 
Transfer station SD also includes a corona generating device 64 which 
sprays ions onto the back side of sheet 54 to attract the toner image from 
photoconductive surface 14 onto sheet 54. After such image transfer, sheet 
54 is separated from the belt 12 and moved in the direction of arrow 66 
onto a conveyor (not shown) which advances sheet 54 to fusing station SE. 
As shown, fusing station SE includes a fuser assembly indicated generally 
by the reference numeral 68 that has a pair of fusing rolls. The fusing 
assembly rolls 68 preferably include a heated fuser roller 70 and a 
back-up pressure roller 72. Sheet 54 is passed between fuser roller 70 and 
back-up roller 72 so that the toner image thereon contacts heated fuser 
roller 70. In this manner, the toner image is heated, fused and 
permanently affixed to sheet 54 forming a sheet copy of the original image 
of document 32. The sheet copy now on sheet 54 is then advanced through a 
chute 74 to a catch tray 76 for subsequent removal from the reproduction 
machine 10. 
Meanwhile, belt 12 next moves the portion of the surface 14 from which the 
image had been transferred to the copy sheet 54 to a cleaning station SF 
where residual toner particles are cleaned or removed. Cleaning station 
SF, for example, includes a rotatably mounted fibrous brush 78 that 
rotates in contact with photoconductive surface 14 for cleaning by 
removing the residual toner particles. Subsequent to such cleaning, a 
discharge lamp (not shown) floods photoconductive surface 14 with light in 
order to dissipate any residual electrostatic charge remaining thereon 
from the prior imaging cycle. 
It is believed that the foregoing description is sufficient for purposes of 
the present application to illustrate the general operation of an 
electrostatographic reproduction machine incorporating the development 
apparatus of the present invention. Typically, the speed of such 
electrostatographic reproduction machines is measured in terms of a number 
of sheet copies produced per unit time. Among different families of such 
machines, speed therefore varies significantly from a low between 10 and 
20 copies per minute to a high of greater than 100 copies per minute. For 
such machines to produce high quality copies or reproductions of original 
images, the processing stations (including the development station SC), 
must be designed so as to function effectively at a desired speed of the 
machine. For example, the development station SC therefore must be capable 
of functioning as such, even at substantially high machine speeds, to 
repeatably deliver a uniform, desired quantity of toner particles to the 
development zone for latent image development. 
Referring now to FIG. 1A, there is shown one embodiment of the development 
apparatus 40 of the present invention. The development apparatus 40 
includes improved elements that enable an extended life, and the 
repeatable delivery of a uniform, desired quantity of toner for high speed 
latent image development. As shown, development apparatus 40 includes a 
movable donor member shown as a roll 42 that is mounted, at least 
partially, within a mixing chamber 46. Mixing chamber 46 is defined by 
housing 48, and holds a supply QS of developer material consisting of 
toner particles and carrier beads. The donor member 42 is moved to 
transport toner particles fed from the chamber 46 into contact with cloud 
producing electrode wires 44 within a development zone DZ for latent image 
development. The developer material QS typically is a two-component 
developer material comprising at least magnetizable carrier beads and the 
toner particles. As is well known, the developer material is moved and 
mixed within the mixing chamber 46 by a mixing device 49 in order to 
oppositely and triboelectrically charge such carrier beads and toner 
particles respectively. As a consequence of such charging, the oppositely 
charged toner particles adhere triboelectrically to the charged 
magnetizable carrier beads. Importantly, the development apparatus 40 
includes the developer feeder assembly or magnetic roll 50 of the present 
invention (to be described in detail below). As shown, the feeder assembly 
50 is shown disposed interiorly of the chamber 46 for feeding a quantity 
QF of developer material from the chamber 46 to the donor member 42. The 
magnetic roller 50 and the donor member 42 are electrically biased 
relative to each other so that charged toner particles within the quantity 
QF of developer material fed to the donor member 42 are attracted from the 
magnetic roll 50 to such donor member 42. Positioned within the mixing 
chamber 46 in the bottom of housing 48 is the mixing device 49, such as a 
horizontal auger, which distributes developer material uniformly along the 
length of magnetic roll 50, so that the lowermost part of magnetic roll 50 
is always substantially immersed in a body of developer material QS. 
As further shown in FIG. 1A, the donor member 42 is biased to a specific 
voltage, by a DC power supply 80 in order to enable the donor member 42 to 
attract charged toner particles off of magnetic roll 50 in a nip 82. To 
enhance the attraction of charged toner particles from the chamber 46, 
magnetic roll 50 is also biased by a DC voltage source 84. It is also 
biased by a AC voltage source 86 that functions to temporarily loosen the 
charged toner particles thereon from their adhesive and triboelectric 
bonds to the charged, magnetized carrier beads. Loosened as such, they can 
be attracted more easily to the donor member 42. AC voltage source 86 can 
be applied either to a conductive layer of the magnetic roll 50 as shown 
in FIG. 1, or directly to the donor roll in series with the DC supply 80. 
Similarly as shown, an AC bias is also applied to the electrode wires 44 
by an AC voltage source 88 and serves to loosen charged toner particles 
from the donor member 42, as well as to form a toner cloud within the 
development zone DZ. 
Referring now to FIG. 1 B, there is shown another embodiment 40A of the 
development apparatus of the present invention. In this embodiment, like 
elements as in FIG. 1A are shown with like reference numerals. 
Importantly, the development apparatus 40A also includes the improved 
elements that enable an extended life, as well as the repeatable delivery 
of a uniform, desired quantity of toner for high speed latent image 
development. In FIG. 1B, because of its longer life and increased 
developer material moving capability, the feeder assembly 50 is being used 
effectively, in a magnetic brush development apparatus housing 48A as a 
magnetic brush developer roll. As is well known, a magnetic brush 
developer roll as such receives developer material from the mixing chamber 
46 and transports it directly into and through the development zone DZ for 
image development. It should be noted that although the improved developer 
feeder assembly 50 of the present invention (FIGS. 1A, 1B) is shown as a 
roll, the improvement design concepts therein are equally applicable to a 
belt type feeder assembly. 
Referring now to FIGS. 2 and 3, details of the magnetic roll or developer 
feeder assembly 50 of the present invention are illustrated. In accordance 
with the objectives of the present invention, the developer feeder 
assembly or roll 50 is designed so as to have a substantially longer life 
relative to conventional roughened surface metallic rolls. It is also 
designed so as to be able to maintain a high level of high speed developer 
feeding reliability over such life. It is further designed so as to 
significantly reduce or eliminate the occurrence of eddy currents and eddy 
current related disadvantages such as power losses and undesirable eddy 
current heating. 
Returning now to FIGS. 2 and 3, the developer feeder assembly or roll 50 of 
the present invention includes a movable substrate or shell 90 that has a 
first surface 92, a second surface 94 and a path of movement or rotation 
96 (shown by the arrow 98) defined substantially by the second surface 94. 
The feeder assembly 50 also includes at least a magnetic member such as 
the magnetic members M1, M2, M3, M4 positioned interiorly of the first 
surface 92 of the substrate or shell 90, as well as adjacent the path of 
movement 96 thereof. The path of movement 96 is continuous and surrounds 
the position of the magnetic members. As positioned, each magnetic member 
M1 to M4 generates a strong magnetic field about a point along the path of 
movement 96, for example, about a first point P1 which is the pick up or 
loading point for the feeder assembly 50 within the chamber 46. As also 
shown, the feeder assembly 50 further includes a thin elastomeric coating 
or layer 100 that is formed onto the second surface 94 of the movable 
shell 90. The elastomeric coating 100 importantly has a mechanically 
deformable smooth surface 102 for holding, during transportation, a 
quantity QF of magnetic or magnetized developer material (FIG. 3) that is 
attracted thereonto by the magnetic members M1 to M4 as positioned on the 
opposite side of the movable substrate or shell 90. 
Referring in particular to FIG. 2, magnetic members M1 to M4 are stationary 
permanent magnets, for example, that are each coextensive in length with, 
and are positioned closely spaced from, the first or interior surface 92 
of the movable shell 90. The shell 90 preferably is non-magnetic (to be 
described further below), and is designed to be rotated about the magnetic 
members M1 to M4 in a direction indicated by the arrow 98. Because the 
two-component developer material QS in the chamber 46 includes magnetic or 
magnetizable carrier beads, the effect of the shell 90 rotating through 
the strong stationary magnetic fields of M1 to M4 is to cause the quantity 
QF of such developer material to be attracted to the exterior of the shell 
90. As also shown, a doctor blade 104 may be used to limit the radial 
depth of developer on the surface 102 as it rotates through a 
toner-transfer nip 82 (FIG. 1A) with the donor member 42. 
The field strength of the peak radial field of the magnetic members around 
the pick up or loading point P1 of the feeder assembly or magnetic roll 50 
preferably is about 600 gauss. As also shown, other points, for example 
point P2, along the path of movement of the movable shell 90 include no, 
or at best a weak magnetic field. The surface of the magnetic roll 50 
should be about 2.5 mm away from the top of the magnetic members. The 
radial field of each magnetic member is commonly the component of the 
magnetic field thereof that is directed radially outward relative to the 
axis of the magnetic member. The tangential component of each magnetic 
field is tangent to the circumference of the roll 50, and will often be 
defined when all the radial peaks are defined and specified. The polarity 
of each magnetic field can be North or South, but preferably should be 
alternating from magnetic member to magnetic member as shown. The magnetic 
force generated by the gradient of the resulting magnetic field together 
with the inventive characteristics of the elastomeric coating 72 (to be 
detailed below) are particularly important for the functioning of the 
present invention. This magnetic force, which acts on magnetized developer 
material QF on the surface of the elastomeric coating, effectively enables 
reliable high speed, and extended life, feeding of developer material QF 
from the chamber 46 of the apparatus 10. In accordance with the present 
invention, the permeability (.mu.) of the developer material is preferably 
within a range of 4 to 6, and the magnetic force acting on a mass of such 
developer material is typically 40-80 times larger than a force that would 
be generated by gravity on the same mass of developer material. 
Still referring to FIGS. 2 and 3, when the feeder assembly 50 is a roll as 
shown, its cylindrical substrate or shell 90, for example, is usually 
about 475 mm long in the development apparatus 10. At such a length, the 
beam strength requirements are such that the Modulus of Elasticity (E) 
thereof should be at least 300,000 pounds per square inch. Furthermore, 
because the thickness of the shell affects the magnetic field strength 
therethrough, the shell 90 preferably has an inner diameter of 38.6 mm, 
and an outside diameter of 42.0 mm. As such, the roll 50 advantageously 
should have an allowable center deflection of about 0.0016 inch when the 
roll is fully loaded with developer material QF. 
In order to meet these various requirements, the substrate or shell 90, for 
example, can be made out of a general purpose polycarbonate. An important 
consideration for selecting shell material is that the selected material 
has to be compatible with elastomeric coating 100. Compatibility results 
in good adhesion which is important for the desired long, or extended 
service life of the feeder assembly. As such, other materials that can be 
used are, for example, phenolics having a Modulus of elasticity (E) of 
about 900,000 psi, and polyesters having a Modulus of elasticity (E) of 
about 400,000 psi. Thermo plastics materials as well as thermo setting 
materials of the sort that are compatible with the elastomeric coating 100 
can be used. It has been found that the higher the (E) value of the 
material used for the shell, the thinner the walls of the shell can be 
made. Thinner walls can advantageously lead to increased magnetic field 
strength at the outside surface of the shell. They can also simplify 
manufacturing by allowing for larger clearances between the magnetic 
members and the inside surface 92 of the shell. More importantly, the 
shell 90 can be made out of a high strength urethane based polyester which 
would eliminate the need for an elastomeric coating 100 thereover. The 
modulus of elasticity E for such a urethane based polyester shell is about 
300,000 psi with a durometer value of about 70d, which would result in a 
roll shell capable of receiving small magnetic force induced 
decompressions 110. The roll 50 as a whole when made as such would have a 
volume resistivity of 10.sup.8 ohm-cm throughout. 
In accordance with another objective of the present invention, the movable 
substrate or shell 90 is advantageously made electrically non-conductive 
in order to eliminate or prevent the occurrence of eddy currents that 
would be generated within a movable electrically conductive shell due to 
the presence of the magnetic members M1 to M4 within its core. An eddy 
current is an electric current that is induced within the body of a 
conductor when that conductor either moves through a non-uniform magnetic 
field, or is in a region where there is a changing magnetic field. The 
movement of the shell 90 about magnetic members M1 to M4 represents such a 
set up if the shell 90 is conductive. 
Referring to FIG. 4 for example, a chart showing eddy current losses is 
illustrated. The chart shows two lines 106, and 108, each representing the 
total power needed to drive the development apparatus 10 under eddy 
current, and non-eddy current conditions, respectively. To generate the 
top line 106, a test was conducted using a conventional feeder assembly 
50A (not shown) that included a conventional conductive aluminum shell, 
along with magnetic members positioned within its core. The conductive 
shell was driven, and its surface speed was measurably varied from 40 IPS 
(inches per second) to 65 IPS. This test represented eddy current 
generating conditions. The total power required to run the apparatus 10 
was recorded at the various speeds (see top line 106). 
For non-eddy current conditions, a second test was conducted under 
conditions where the magnetic members were removed from the core of the 
conductive shell. This was equivalent to removing the conductive shell 
instead, and mounting an electrically non-conductive shell around the 
magnetic members. In either case, no eddy currents (generated or not) 
would flow in the shell under these conditions. The shell and the rest of 
the apparatus 10 were again driven, and the surface speed thereof was 
measurably varied the same as above. The total power required to run the 
apparatus 10 was again recorded at such speeds (see the lower line 108). 
It is quite clear from these plots of the lines 106, 108 that more total 
power was required under the first test (eddy current) conditions than 
under the second (non-eddy current) conditions to run the apparatus 10. At 
each plotted point, the difference in required total power amounts to an 
eddy current power loss at that speed for the apparatus 10. As measured 
and plotted, these losses for example were 2.7 watts at 40 ips, and 6.4 
watts at 65 ips, which are losses ranging from 15% to 19%. The use of an 
electrically non-conductive shell around the magnetic members M1 to M4, (a 
condition under which no eddy currents will flow through the shell), would 
therefore be significantly advantageous. 
Referring still to FIGS. 2 and 3, the elastomeric coating 100 is a thin 
coating made for example from electrically conductive urethane material 
that has a thickness within a range of 0.040 to 0.060 inch. The smooth 
surface 102 thereof has a preferred durometer hardness within a range of 
60a to 70d. As such, the smooth surface 102 can be magnetically deformed 
temporarily and easily, by a magnetic force (not shown) of any of the 
strong magnetic fields of M1 to M4 acting on magnetized carrier beads of 
the developer material QF on such smooth surface. Such deformation results 
in decompressions 110 (FIG. 3) that reliably provide a frictional 
structure for holding the attracted developer material QF onto the surface 
of the rotating shell, even when the shell is being rotated at 
substantially high rates of speed. Given such impact of the magnetic 
forces on the smooth surface 102, it is clear that when being rotated with 
the shell 90, the smooth surface 102 will be temporarily decompressed for 
example when at the first point P1 along the path of movement, but would 
resiliently reform and become smooth again when at the no, or weak, 
magnetic field point P2. Unlike conventional developer transporting 
surfaces with roughness formations that wear out over time, the smooth 
surface 102 advantageously results in a substantially improved extended 
life for the developer feeder assembly or roll 50 of the present 
invention. 
As can be seen, an improved development apparatus 10 for developing a 
latent image recorded on an image bearing surface 14, has been provided 
and includes a housing 48 defining a chamber 46 that holds a supply of 
two-component developer material QS. The two-component developer material 
consists of toner and magnetizable carrier beads. The improved development 
apparatus 10 also includes a development zone DZ adjacent the image 
bearing surface 14, and a movable donor member 42 for moving toner fed 
from the chamber 46 through the development zone for image development. 
The improvement comprises a magnetic roll assembly 50 for moving a 
quantity QF of magnetically attracted developer material from the chamber 
into toner-transfer relation 54 with the donor member. The magnetic roll 
assembly 50 includes a rotatable non-conductive shell 90 surrounding the 
magnetic members M1 to M4 so as to prevent the creation of eddy currents 
during rotation of the shell about the magnetic members. An elastomeric 
coating layer 100 having a desired durometer hardness within a range of 
60a to 70d is formed over the non-conductive shell and has a smooth 
surface 102 for holding the quantity of attracted developer material 
thereon. The smooth surface 102 as such, is magnetically deformable 
temporarily by magnetic forces of the strong magnetic fields of the 
magnetic members acting on magnetized carrier beads on the smooth surface 
102. 
The magnetic roll assembly as disclosed is also suitable for use generally 
in a development apparatus for moving magnetic or magnetizable developer 
material including toner particles and magnetizable carrier beads, along a 
desired path, for example, along a direct image development path between 
the mixing chamber and the development zone for image development. As 
illustrated, it is also particularly suitable for use in a donor type 
apparatus as a feeder assembly for feeding developer material from a 
mixing chamber to a donor member. 
While this invention has been described in conjunction with various 
embodiments, it is evident that many alternatives, modifications, and 
variations will be apparent to those skilled in the art. Accordingly, it 
is intended to embrace all such alternatives, modifications, and 
variations as fall within the spirit and broad scope of the appended 
claims.