Donor rolls with modular commutation

A donor roll for transporting marking particles to an electrostatic latent image recorded on a surface is provided. The donor roll is adaptable for use with a commutator for applying an electrical field to the roll to assist in transporting the marking particles. The donor roll includes a rotatably mounted body and an electrode member mounted on the body. The donor roll further includes a connector operably associated with the body, electrically connected to the electrode member, and rotatable with the body. The connector is adapted to be removably connectable to the commutator.

The present invention relates to a developer apparatus for 
electrophotographic printing. More specifically, the invention relates to 
a donor roll as part of a scavengeless development process. 
Cross reference is made to the following applications filed concurrently 
herewith: U.S. application Ser No. 08/533,627, filed Sep. 25, 1995, 
entitled "Donor Rolls with Magnetically Coupled (Transformer) 
Commutation", by Steven C. Hart et al.; and U.S. application Ser. No. 
08/533,108, filed Sep. 25, 1995, entitled "Donor Rolls with Exterior 
Commutation", by Steven C. Hart et al. 
In the well-known process of electrophotographic printing, a charge 
retentive surface, typically known as a photoreceptor, is 
electrostatically charged, and then exposed to a light pattern of an 
original image to selectively discharge the surface in accordance 
therewith. The resulting pattern of charged and discharged areas on the 
photoreceptor form an electrostatic charge pattern, known as a latent 
image, conforming to the original image. The latent image is developed by 
contacting it with a finely divided electrostatically attractable powder 
known as "toner." Toner is held on the image areas by the electrostatic 
charge on the photoreceptor surface. Thus, a toner image is produced in 
conformity with a light image of the original being reproduced. The toner 
image may then be transferred to a substrate or support member (e.g., 
paper), and the image affixed thereto to form a permanent record of the 
image to be reproduced. Subsequent to development, excess toner left on 
the charge retentive surface is cleaned from the surface. The process is 
useful for light lens copying from an original or printing electronically 
generated or stored originals such as with a raster output scanner (ROS), 
where a charged surface may be imagewise discharged in a variety of ways. 
In the process of electrophotographic printing, the step of conveying toner 
to the latent image on the photoreceptor is known as "development." The 
object of effective development of a latent image on the photoreceptor is 
to convey toner particles to the latent image at a controlled rate so that 
the toner particles effectively adhere electrostatically to the charged 
areas on the latent image. A commonly used technique for development is 
the use of a two-component developer material, which comprises, in 
addition to the toner particles which are intended to adhere to the 
photoreceptor, a quantity of magnetic carrier beads. The toner particles 
adhere triboelectrically to the relatively large carrier beads, which are 
typically made of steel. When the developer material is placed in a 
magnetic field, the carrier beads with the toner particles thereon form 
what is known as a magnetic brush, wherein the carrier beads form 
relatively long chains which resemble the fibers of a brush. This magnetic 
brush is typically created by means of a "developer roll." The developer 
roll is typically in the form of a cylindrical sleeve rotating around a 
fixed assembly of permanent magnets. The carrier beads form chains 
extending from the surface of the developer roll, and the toner particles 
are electrostatically attracted to the chains of carrier beads. When the 
magnetic brush is introduced into a development zone adjacent the 
electrostatic latent image on a photoreceptor, the electrostatic charge on 
the photoreceptor will cause the toner particles to be pulled off the 
carrier beads and onto the photoreceptor. Another known development 
technique involves a single-component developer, that is, a developer 
which consists entirely of toner. In a common type of single-component 
system, each toner particle has both an electrostatic charge (to enable 
the particles to adhere to the photoreceptor) and magnetic properties (to 
allow the particles to be magnetically conveyed to the photoreceptor). 
Instead of using magnetic carrier beads to form a magnetic brush, the 
magnetized toner particles are caused to adhere directly to a developer 
roll. In the development zone adjacent the electrostatic latent image on a 
photoreceptor, the electrostatic charge on the photoreceptor will cause 
the toner particles to be attracted from the developer roll to the 
photoreceptor. 
An important variation to the general principle of development is the 
concept of "scavengeless" development. The purpose and function of 
scavengeless development are described more fully in, for example, U.S. 
Pat. No. 4,868,600 to Hays et al., which is hereby incorporated by 
reference. In a scavengeless development system, toner is detached from 
the donor roll by applying AC electric field to self-spaced electrode 
structures, commonly in the form of wires positioned in the nip between a 
donor roll and photoreceptor. This forms a toner powder cloud in the nip 
and the latent image attracts toner from the powder cloud thereto. Because 
there is no physical contact between the development apparatus and the 
photoreceptor, scavengeless development is useful for devices in which 
different types of toner are supplied onto the same photoreceptor such as 
in "tri-level"; "recharge, expose and develop"; "highlight"; or "image on 
image" color xerography. 
A typical "hybrid" scavengeless development apparatus includes, within a 
developer housing, a transport roll, a donor roll, and an electrode 
structure. The transport roll advances carrier and toner to a loading zone 
adjacent the donor roll. The transport roll is electrically biased 
relative to the donor roll, so that the toner is attracted from the 
carrier to the donor roll. The donor roll advances toner from the loading 
zone to the development zone adjacent the photoreceptor. In the 
development zone, i.e., the nip between the donor roll and the 
photoreceptor, are the wires forming the electrode structure. During 
development of the latent image on the photoreceptor, the electrode wires 
are AC-biased relative to the donor roll to detach toner therefrom so as 
to form a toner powder cloud in the gap between the donor roll and the 
photoreceptor. The latent image on the photoreceptor attracts toner 
particles from the powder cloud forming a toner powder image thereon. 
Another variation on scavengeless development uses a single-component 
developer material. In a single component scavengeless development, the 
donor roll and the electrode structure create a toner powder cloud in the 
same manner as the above-described scavengeless development, but instead 
of using carrier and toner, only toner is used. 
It has been found that for some toner materials, the tensioned electrically 
biased wires in self-spaced contact with the donor roll tend to vibrate 
which causes non-uniform solid area development. Furthermore, there is a 
possibility that debris can momentarily lodge on the wire to cause 
streaking. Thus, it would appear to be advantageous to replace the 
externally located electrode wires with electrodes integral to the donor 
roll. 
In U.S. Pat. No. 5,172,170 to Hays et al., there is disclosed an apparatus 
for developing a latent image recorded on a surface, including a housing 
defining a chamber storing at least a supply of toner therein a moving 
donor member spaced from the surface and adapted to transport toner from 
the chamber of said housing to a development zone adjacent the surface, 
and an electrode member integral with the donor member and adapted to move 
therewith. The electrode member is electrically biased to detach toner 
from said donor member to form a cloud of toner in the space between the 
electrode member and the surface with toner developing the latent image. 
The biasing of the electrodes is typically accomplished by using a 
conductive brush which is placed in a stationary position in contact with 
the electrodes on the periphery of the donor member. U.S. Pat. No. 
5,172,170 is herein incorporated by reference. The conductive brush is 
electrically connected with a electrically biasing source. The brush is 
typically a conductive fiber brush made of protruded fibers or a solid 
graphite brush. Typically only the electrode in the nip between the donor 
member and the developing surface is electrically biased. As the donor 
member rotates the electrode that now is in the nip needs to contact the 
brush. Since the distance between the nip and the developing surface is 
very small it is impractical to position the conductive brush in the nip. 
To accomplish the biasing of the donor member, the member must be extended 
beyond the developing surface. The donor member is typically an expensive 
complicated component that is very long and slender. 
Donor members are long to accommodate sufficiently wide copy substrates and 
slender to minimize developer housing size. Donor members require 
extremely accurate dimensions to meet copy quality requirements. The 
critical dimensions of a donor roll include the outside diameter, surface 
finish and runout of the donor member periphery. The added length of the 
donor member required to accommodate the commutation of the donor roll 
electrodes makes the maintaining of these critical dimensions even more 
difficult. Donor members are thus very expensive. 
The use of a stationary position conductive brush in contact with the 
electrodes on the periphery of the donor member as a commutation method 
has many problems. Many materials for the contact brush have been 
considered including metal and non-metal materials. A carbon fiber brush 
and a solid graphite brush have been found to be most successful. The use 
of rubbing contact in the brush causes commutation electrode wear which 
reduces the life of the donor roll. The abrupt connection and 
disconnection of the brush with the respective electrode creates 
electrical noise and arcing between the brush and the electrode and may 
further reduce the life of the donor roll. 
The following disclosures related to scavengeless and electroded rolls may 
be relevant to various aspects of the present invention: 
U.S. patent application Ser. No. 08/376,585 
Applicant: Rommelmann et al. 
Filing Date: Jan. 23, 1995 
U.S. patent application Ser. No. 08/339,614 
Applicant: Rommelmann 
Filing Date: Nov. 15, 1994 
U.S. Pat. No. 5,394,225 
Patentee: Parker (Prker) 
Issue Date: Feb. 28, 1995 
U.S. Pat. No. 5,289,240 
Patentee: Wayman 
Issue Date: Feb. 22, 1994 
U.S. Pat. No. 5,268,259 
Patentee: Sypula 
Issue Date Dec. 7, 1993 
U.S. Pat. No. 5,172,170 
Patentee: Hays et al. 
Issue Date: Dec. 15, 1992 
U.S. Pat. No. 4,868,600 
Patentee: Hays et al. 
Issue Date: Sep. 19, 1989 
U.S. Pat. No. 3,996,892 
Patentee: Parker et al. 
Issue Date: Dec. 14, 1976 
U.S. Pat. No. 3,980,541 
Patentee: Aine 
Issue Date: Sep. 14, 1976 
U.S. Pat. No. 3,257,224 
Patentee: Jons et al. 
Issue Date: Jun. 21, 1966 
Ser. No. 08/376,585 discloses an apparatus for transporting marking 
particles. The apparatus includes a donor roll and an electrode member. 
The electrode member includes a plurality of electrical conductors mounted 
on the surface of donor roll with adjacent electrical conductors being 
spaced from one another. The electrode member further includes a 
connecting member fixedly secured to the donor roll. The connecting member 
electrically interconnects at least two electrical conductors. 
Ser. No. 08/339,614 discloses a donor roll for transporting marking 
particles to an electrostatic latent image recorded on a surface. The 
donor roll includes a body rotatable about a longitudinal axis and an 
electrode member. The electrode member includes a plurality of electrical 
conductors mounted on the body with adjacent electrical conductors being 
spaced from one another having at least a portion thereof extending in a 
direction transverse to the longitudinal axis of the body. 
U.S. Pat. No. 5,394,225 discloses a donor roll which has two sets of 
interdigitized embedded electrodes in the surface. An optical switching 
arrangement is located between a slip ring commutated by a brush and one 
set of interdigitated electrodes. The optical switching arrangement 
includes a photoconductive strip. 
U.S. Pat. No. 5,289,240 discloses a donor roll which has two distinct sets 
of electrodes along the periphery of the donor roll. The roll has a first 
set of electrodes that extend axially the length of the roll. The first 
set of electrodes includes groups of 1 to 6 electrodes which are 
electrically interconnected to each other and are commutated by contacting 
the filaments of a brush which is electrically interconnected to a biasing 
source. The roll also has a second set of electrodes that extend axially 
the length of the roll, are interconnected to each other, do not contact 
the brush, and are grounded. 
U.S. Pat. No. 5,268,259 discloses a process for preparing a toner donor 
roll which has an integral electrode pattern. The process includes coating 
a cylindrical insulating member with a photoresistive surface, pattern 
exposing the photoresistive surface to light to form an electrode pattern 
and depositing conductive metal on the portion of the member exposed to 
light to form the electrode pattern. 
U.S. Pat. No. 5,172,170 discloses a donor roll with a plurality of 
electrical conductors spaced from one another with one of the conductors 
located in one of the grooves in the donor roll. A dielectric layer is 
disposed in at least the grooves of the roll interposed between the roll 
and the conductors and may cover the region between the grooves. The 
dielectric layer may be fabricated of anodized aluminum or a polymer and 
may be applied by spraying, dipping or powder spraying. The roll is made 
from a conductive material such as aluminum and the dielectric layer is 
disposed about the circumferential surface of the roll between adjacent 
grooves. The conductive material is applied to the grooves by a coater to 
form the electrical conductors. A charge relaxable layer is applied over 
the donor roll surface. 
U.S. Pat. No. 4,868,600 discloses a scavengeless development system in 
which toner detachment from a donor and the concomitant generation of a 
controlled powder cloud is obtained by AC electrical fields supplied by 
self-spaced electrode structures positioned within the development nip. 
The electrode structure is placed in close proximity to the toned donor 
within the gap between toned donor and image receiver, self-spacing being 
effected via the toner on the donor. 
U.S. Pat. No. 3,996,892 discloses a donor roll having an electrically 
insulative core made of a phenolic resin. The donor roll core is coated 
with conductive rubber doped with carbon black. Conductor strips are 
formed on the rubber by a copper cladding process followed by a 
photo-resist-type etching technique. 
U.S. Pat. No. 3,980,541 discloses composite electrode structures including 
mutually opposed electrodes spaced apart to define a fluid treatment 
region. Resistive electrodes serve to localize the effects of electrical 
shorts between electrodes. Non-uniform sheet and filamentary electrodes 
are disclosed for producing a substantially non uniform electric field. 
U.S. Pat. No. 3,257,224 discloses a developing apparatus including a trough 
to contain magnetizable developer and a magnetic roller. The roller 
transports the developer to an electrophotographic material and includes 
plates having a number of windings. The plates and windings are located 
inside the roll. The plates and windings serve as electromagnets to 
magnetically attract the developer so that it may be transported to the 
material. 
SUMMARY OF THE INVENTION 
According to the present invention there is provided a donor roll for 
transporting marking particles to an electrostatic latent image recorded 
on a surface. The donor roll is adaptable for use with a commutator for 
applying an electrical field to the roll to assist in transporting the 
marking particles. The donor roll includes a rotatably mounted body and an 
electrode member mounted on the body. The donor roll further includes a 
connector operably associated with the body, electrically connected to the 
electrode member, and rotatable with the body. The connector is adapted to 
be removably connectable to the commutator. 
According to the present invention, there is also provided a developer unit 
for developing a latent image recorded on the surface of an image 
receiving member to form a developed image. The developer unit includes a 
housing defining a chamber for storing at least a supply of marking 
particles therein and a movably mounted donor member. The member is spaced 
from the surface and adapted to transport marking particles from the 
chamber of the housing to a development zone adjacent the surface. The 
donor member includes a body and an electrode member mounted on the body. 
The developer unit further includes a commutation member removably 
electrically connected to the electrode member. 
According to the present invention, there is further provided an 
electrophotographic printing machine of the type having a developer unit 
adapted to develop with marking particles an electrostatic latent image 
recorded on a surface of an image receiving member. The improvement 
includes a housing defining a chamber for storing at least a supply of 
marking particles therein and a movably mounted donor member. The member 
is spaced from the surface and adapted to transport marking particles from 
the chamber of the housing to a development zone adjacent the surface. The 
donor member includes a body and an electrode member mounted on the body. 
The developer unit further includes a commutation member removably 
electrically connected to the electrode member.

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. 
Inasmuch as the art of electrophotographic printing is well known, the 
various processing stations employed in the FIG. 2 printing machine will 
be shown hereinafter schematically and their operation described briefly 
with reference thereto. 
Referring initially to FIG. 2, there s shown an illustrative 
electrophotographic printing machine incorporating the development 
apparatus of the present invention therein. The printing machine 
incorporates a photoreceptor 10 in the form of a belt having a 
photoconductive surface layer 12 on an electroconductive substrate 14. 
Preferably the surface 12 is made from a selenium alloy or a suitable 
photosensitive organic compound. The substrate 14 is preferably made from 
a polyester film such as Mylar.RTM. (a trademark of Dupont (UK) Ltd.) 
which has been coated with a thin layer of aluminum alloy which is 
electrically grounded. The belt is driven by means of motor 24 along a 
path defined by rollers 18, 20 and 22, the direction of movement being 
counterclockwise as viewed and as shown by arrow 16. Initially a portion 
of the belt 10 passes through a charge station A at which a corona 
generator 26 charges surface 12 to a relatively high, substantially 
uniform, potential. A high voltage power supply 28 is coupled to device 
26. 
Next, the charged portion of photoconductive surface 12 is advanced through 
exposure station B. At exposure station B, ROS 36 lays out the image in a 
series of horizontal scan lines with each line having a specified number 
of pixels per inch. The ROS includes a laser having a rotating polygon 
mirror block associated therewith. The ROS exposes the charged 
photoconductive surface of the printer. 
After the electrostatic latent image has been recorded on photoconductive 
surface 12, belt 10 advances the latent image to development station C as 
shown in FIG. 2. At development station C, a development system 38, 
develops the latent image recorded on the photoconductive surface. 
Preferably, development system 38 includes a donor roll or roller 40 and 
electrical conductors in the form of embedded electrode wires or 
electrodes 42 embedded on the periphery of the donor roll 40. Electrodes 
42 are electrically biased relative to donor roll 40 to detach toner 
therefrom so as to form a toner powder cloud in the gap between the donor 
roll and photoconductive surface. The latent image attracts toner 
particles from the toner powder cloud forming a toner powder image 
thereon. Donor roll 40 is mounted, at least partially, in the chamber of 
developer housing 44. The chamber in developer housing 44 stores a supply 
of developer material 45. The developer material is a two component 
developer material of at least magnetic carrier granules having toner 
particles adhering triboelectrically thereto. A transport roll or roller 
46 disposed interiorly of the chamber of housing 44 conveys the developer 
material to the donor roll 40. The transport roll 46 is electrically 
biased relative to the donor roll 40 so that the toner particles are 
attracted from the transport roller to the donor roller. 
Again referring to FIG. 2, after the electrostatic latent image has been 
developed, belt 10 advances the developed image to transfer station D, at 
which a copy sheet 54 is advanced by roll 52 and guides 56 into contact 
with the developed image on belt 10. A corona generator 58 is used to 
spray ions on to the back of the sheet so as to attract the toner image 
from belt 10 the sheet. As the belt turns around roller 18, the sheet is 
stripped therefrom with the toner image thereon. 
After transfer, the sheet is advanced by a conveyor (not shown) to fusing 
station E. Fusing station E includes a heated fuser roller 64 and a 
back-up roller 66. The sheet passes between fuser roller 64 and back-up 
roller 66 with the toner powder image contacting fuser roller 64. In this 
way, the toner powder image is permanently affixed to the sheet. After 
fusing, the sheet advances through chute 70 to catch tray 72 for 
subsequent removal from the printing machine by the operator. 
After the sheet is separated from photoconductive surface 12 of belt 10, 
the residual toner particles adhering to photoconductive surface 12 are 
removed therefrom at cleaning station F by a rotatably mounted fibrous 
brush 74 in contact with photoconductive surface 12. Subsequent to 
cleaning, a discharge lamp (not shown) floods photoconductive surface 12 
with light to dissipate any residual electrostatic charge remaining 
thereon prior to the charging thereof for the next successive imaging 
cycle. 
It is believed that the foregoing description is sufficient for purposes of 
the present application to illustrate the general operation of an 
electrophotographic printing machine incorporating the development 
apparatus of the present invention therein. 
Referring now to FIG. 3, there is shown development system 38 in greater 
detail. Housing 44 defines the chamber for storing the supply of developer 
material 45 therein. The developer material 45 includes carrier granules 
76 having toner particles 78 adhering triboelectrically thereto. 
Positioned in the bottom of housing 44 are horizontal augers 80 and 82 
which distributes developer material 45 uniformly along the length of 
transport roll 46 in the chamber of housing 44. 
Transport roll 46 comprises a stationary multi-pole magnet 84 having a 
closely spaced sleeve 86 of non-magnetic material designed to be rotated 
about the magnet 84 in a direction indicated by arrow 85. The toner 
particles 78 are attached triboelectrically to the magnetic carrier 
granules 76 to form the developer material 45. The magnetic field of the 
stationary multi-pole magnet 84 draws the magnetic carrier granules 76, 
toward the roll and along with the granules 76, the toner particles 78. 
The developer material 45 then impinges on the exterior of the sleeve 86. 
As the sleeve 86 turns, the magnetic fields provide a frictional force to 
cause the developer material 45 including the carrier granules 76 to 
rotate with the rotating sleeve 86. This in turn enables a doctor blade 88 
to meter the quantity of developer adhering to sleeve 86 as it rotates to 
a loading zone 90, the nip between transport roll 46 and donor roll 40. 
This developer material adhering to the sleeve 86 is commonly referred to 
as a magnetic brush. 
The donor roll 40 includes the electrodes 42 in the form of electrical 
conductors positioned about the peripheral circumferential surface 
thereof. The electrodes are preferably positioned near the circumferential 
surface and may be applied by any suitable process such as plating, 
overcoating or silk screening. It should be appreciated that the 
electrodes may alternatively be located in grooves (not shown) formed in 
the periphery of the roll 40. The electrical conductors 42 are 
substantially spaced from one another and insulated from the body of donor 
roll 40 which may be electrically conductive. Half of the electrodes, 
every other one, are electrically connected together. Collectively these 
electrodes are referred to as common electrode members 114. The remaining 
electrodes are referred to as active electrode members 112. These may be 
single electrodes or they may be electrically connected together into 
small groups. Each group is typically on the order of 1 to 4 electrodes; 
all groups within the donor roll having the same number of electrodes. 
Either the whole of the donor roll 40, or at least a layer 111 thereof, is 
preferably of a material which has sufficiently low electrical 
conductivity. This material must be sufficiently conductive so as to 
prevent any long term build up of electrical charge. Yet, the conductivity 
of this layer must be sufficiently low so as to form a blocking layer to 
prevent shorting or arcing of the magnet brush to the donor roll electrode 
members and/or donor roll core itself. 
Embedded within the low conductivity layer 111 are the donor roll 
electrodes 42. As earlier stated these electrodes may be classified as 
common electrode members 114 or as active electrode members 112. The 
common electrode members 114 are all electrically connected together. The 
active electrode members 112 may be electrically connected into small 
groups of 1 to 4 electrodes. 
The donor roll 40 and common electrode members 114 are kept at a specific 
voltage with respect to ground by a direct current (DC) voltage source 92. 
An alternating current (AC) voltage source 93 may also be connected to the 
donor roll 40 and the commons. 
The transport roll 46 is also kept at a specific voltage with respect to 
ground by a DC voltage source 94. An AC voltage source 95 may also be 
connected to the transport roll 46. 
By controlling the magnitudes of the DC voltage sources 92 and 94 one can 
control the DC electrical field created across the magnetic brush, i.e. 
between the donor roll surface and the surface of the rotating sleeve 86. 
When the electric field between these members is of the correct polarity 
and of sufficient magnitude, it will cause toner particles 78 to develop 
from the magnetic brush and form a layer of toner particles on the surface 
of the donor roll 40. This development will occur in what is denoted as 
the loading zone 90 
By controlling the magnitude and frequencies and phases of the AC voltage 
sources 93 and 95 one can control the of the AC electrical field created 
across the magnetic brush, i.e. between the donor roll surface and the 
surface of the rotating sleeve 86 of magnetic roll 46. The application of 
the AC electrical field across the magnetic brush is known to enhance the 
rate at which the toner layer develops onto the surface of the donor roll 
40. 
It is believed that the effect of the AC electrical field applied across 
the magnetic brush in the loading zone between the surface of the donor 
roll 40 and the rotating sleeve 86 is to loosen the adhesive and 
triboelectric bonds of the toner particles to the carrier beads. This in 
turn makes it easier for the DC electrical field to cause the migration of 
the toner particles from the magnetic brush to donor roll surface. 
In the loading zone, it is also desirable to connect the active electrode 
members 112 to the same DC voltage source as the one to which the common 
electrode members 114 are connected. In this case the connection in the 
loading zone would be to DC voltage source 92. This has been demonstrated 
to improve the efficiency with which the donor roll is loaded. 
Additionally, it has been demonstrated that the application of AC 
electrical voltage to the active electrode members 112 can enhance the 
development efficiency. 
While the development system 38 as shown in FIG. 3 utilizes donor roller DC 
voltage source 92 and AC voltage source 93 as well as transport roller DC 
voltage source 94 and AC voltage source 95, the invention may be 
practiced, with merely DC voltage source 92 on the donor roller. 
It has been found that a value of about 200 V rms applied across the 
magnetic brush between the surface of the donor roll 40 and the sleeve 86 
is sufficient to maximize the loading/reloading/development efficiency. 
That is the delivery rate of toner particles to the donor roll surface is 
maximized. The actual value can be adjusted empirically. In theory, the 
values can be any value up to the point at which arcing occurs within the 
magnetic brush. For typical developer materials and donor roll to 
transport roll spacings and material packing fractions, this maximum value 
is on the order of 400 V rms. The source should be at a frequency of about 
2 kHz. If the frequency is too low, e.g. less than 200 Hz, banding will 
appear on the copies. If the frequency is too high, e.g. more than 15 kHz, 
the system would probably work but the electronics may become expensive 
because of capacitive loading losses. 
Donor roll 40 rotates in the direction of arrow 91. The relative voltages 
between the donor roll 40, common electrode members 114, and active 
electrode members 112, and the sleeve 86 of magnetic roll 46 are selected 
to provide efficient loading of toner from the magnetic brush onto the 
surface of the donor roll 40. Furthermore, reloading of developer material 
on magnetic roll 46 is also enhanced. In the development zone, AC and DC 
electrode voltage sources 96 and 97, respectively, electrically bias 
electrical conductors 42 to a DC voltage having an AC voltage superimposed 
thereon. Electrode voltage sources 96 and 97 are electrically connectable 
with isolated electrodes 42. As donor roll 40 rotates in the direction of 
arrow 91, successive electrodes 42 advance into development nip 98, the 
nip between the donor roll 40 and the photoreceptor belt 10, and are 
electrically biased by voltage sources 96 and 97. 
The construction and geometry of a segmented donor roll is described in 
detail in U.S. Pat. No. 5,172,259 to Hays et al., U.S. Pat. No. 5,289,240 
to Wayman, and U.S. Pat. No. 5,413,807 to Duggan the relative portions 
thereof incorporated by reference herein. 
According to the present invention and referring to FIG. 1, a modular 
commutator 120 is shown. The modular commutator includes the donor member 
40. The donor member 40 may be in any suitable form, for example, in the 
form of an endless belt or a generally cylindrically shaped roll. As shown 
in FIG. 1, the donor member 40 is in the form of a donor roll. The donor 
roll 40 includes a rotatably mounted body 122. 
Typically the body 122 includes a core 132 over which an overlaid material 
134 is placed. The overlaid material 134 may be applied in any suitable 
manner, for example, the material 134 may be a molded material, molded 
onto the core 132. The core 132 may be electrically conductive or 
non-conductive and may be made of a durable high strength, electrically 
conductive material, for example, aluminum. The molded material 134 may be 
made from any suitable material and is explained more fully in earlier 
mentioned patents which have been incorporated by reference. 
The active electrode members 112 are preferably equally spaced and axially 
positioned along the periphery of the body 122 and are applied over the 
molded material 134. Equally spaced and located between the active 
electrode members 112 are the common electrode members 114. If the core 
132 is made of a conductive material, the electrode members 114 may be 
electrically connected to the core 132 to provide a grounding path for the 
common electrode members 114. 
The donor member 40 further includes a connector 136. The connector 136 is 
electrically connected to the electrode member 112. Preferably for a donor 
roll 40 having a plurality of active electrode members 112, the connector 
136 includes a plurality of connecting members 138. Each of the connecting 
members 138 are separably electrically connected to the active electrode 
members 112. 
To simplify the commutating of the donor roll 40, preferably, more than one 
of the active electrode members 112, for example, 2, 3 or 4 of the active 
electrode members are commonly electrically connected to a connector 
member 138. Doing so correspondingly decreases the total number of 
connector members and the associated number of commutations during each 
revolution of the donor roll 40. 
The connector members 138 may have any suitable shape or configuration. The 
connector members 138 may either include positive material, such as in the 
form of either a protrusion or negative material, such as in the form of 
an aperture or cavity. As shown in FIG. 1, the connector members 138 are 
in the form of apertures. The connector members are electrically connected 
to the active electrode members 112 and in order to conduct electricity, 
the commutator members 138 are made of an electrically conductive 
material, for example, a metal, for example, copper. 
The connector 136 may be located anywhere along the periphery of the donor 
member 40, but preferably the connector 136 is located at a first end 144 
of the body 122 of the donor member 40. 
A commutation member 146 is removably electrically connected to the 
electrode member 42. The commutation member 146 may have any suitable 
shape or configuration and may for example include brushes which contact 
pads or may include non-contact type of commutations, such as magnetic, 
capacitive, or resistive types of commutation. The commutation member 146 
may be secured in any suitable fashion to the donor member 40. For 
example, the commutation member 146 may be secured to the first end 144 of 
the body 122 or may alternatively, or in addition to, be connected to 
first journal 150 of the donor member 40. 
The donor member 40 preferably includes the first journal 150 and second 
journal 152 which serve to support the donor member 40. The first journal 
150 and second journal 152 are preferably supported by first bearing 154 
and second bearing 156, respectively. The first and second bearings 154 
and 156 are secured to developer housing 44. To provide the necessary 
strength and accuracy, typically the bearings 154 and 156 are rolling 
element bearings, for example, ball type bearings. It should be 
appreciated, however, that the invention may be practiced where the 
bearings 154 and 156 are sleeve type or other type of bearings. Outer race 
160 of the bearings 154 and 156 are mounted into housing 44. Bearing balls 
162 separate inner race 164 from the outer race 160. 
Typically, the inner race 164 of the bearings 154 and 156 are fitted over 
the journals 150 and 152, respectively. The fit between the inner race 164 
and the journals 150 and 152 as well as the fit between the outer race 160 
and the housing 44 may be selected for optimum performance. The races 160 
and 164 may be secured respectively to the housing 44 and the journals 150 
and 152 by any suitable means such as slip fit, press fit, glue or any 
other suitable means. 
As shown in FIG. 1, the commutation member 146 includes an opening 166 
through which the first journal 150 slidably fits. The first journal 150 
may assist in the support of the commutation member 146 or the opening 166 
may merely be a clearance between the commutation member 146 and the first 
journal 150. Extending inwardly from inner face 168 of the commutation 
member 146 are commutation connectors 170. The commutation connectors 170 
mate with the respective connecting members 138 of the donor member 40. 
As shown in FIG. 1, the commutation connectors 170 are in the form of pins 
which point axially inward from the inner face 168 of the commutation 
member 146. The commutation connectors 170 are designed to contact and 
electrically interconnect with the connecting members 138. The commutation 
connectors 170 may likewise support or assist in supporting the 
commutation member 146 on to the donor roll 40. It should be appreciated 
that while, as shown, the connecting members 138 are in the form of 
apertures into which the commutation connectors 170 in the form of pins 
fit, however, the commutation connector 170 and the connector members 138 
may take any suitable pair of mating forms such as bars and slots, concave 
and convex mating arcs, springs and pads, or any suitable pair of 
electrical connectors. 
The commutation member 146 is electrically connected to a power supply 172. 
The power supply 172 preferably includes an A.C. power source 174 as well 
as a D.C. power source 175. 
Referring now to FIG. 4, the commutation member 146 and the connector 136 
are shown in greater detail. As shown in FIG. 4, the commutator connector 
170 is in the form of a set of pins 176. The pins 176 have a length 
L.sub.p and a diameter D.sub.p. The connector 136 includes connecting 
members 138 in the form of sockets 138. One socket 138 corresponds and is 
positioned coaxially with a corresponding pin 176 in the commutation 
member 146. 
As the commutation member 146 is assembled onto the donor roll 40, the 
commutation member 146 is moved in the direction of arrow 178 toward first 
end 144 of the body 122. The sockets 138 have a diameter D.sub.S which is 
so sized to allow the pins 176 to be inserted thereinto. The sockets 138 
have a length L.sub.S which is slightly longer than the length L.sub.P of 
the pins 176 in order that the pins 176 may be fully inserted into the 
sockets 138. The pins 176 and the sockets 138 are made of any suitable 
durable electrically conductive material, for example, a metal, preferably 
copper, silver or gold. 
Referring now to FIG. 5, the connecting members 138 are shown electrically 
connected to the active electrode members 112. Electrical leads 180 
interconnect the connecting members 138 to the active electrode members 
112. The electrical leads 180 may be any suitable durable electrically 
conductive material, for example, copper, aluminum, gold or silver. The 
electrical leads 180, as well as the connecting members 138 and the 
commutation connectors 170 may be applied in any suitable fashion for 
example, by electroplating, soldering, coating or any suitable process. A 
separate electrical lead 180 may be used to separably connect each 
connecting member 138 with an individual active electrode member 112, or 
as shown in FIG. 5, the electrical lead 180 may be used to connect two 
adjoining active electrode members 112 with a common connecting member 
138. 
Referring now to FIG. 6, an alternate embodiment of the modular commutation 
system of the present invention is shown in modular commutator. Modular 
commutator 220 is similar to modular commutator 120 of FIG. 1 except that 
first bearing 254 unlike first bearing 154 of FIG. 1 is slip fitted onto 
the periphery of body 222 of donor roll 240. The first bearing 254 thereby 
divides the body 222 of the donor roll 240 into a particle transportation 
portion 282, a support portion 284, and an external portion 286. The 
particle transportation portion 282 of the donor roll 240 receives the 
toner particles from the transport roll (see FIG. 3). The particle 
transportation portion 282 includes active electrode members 212 which 
assists in removing the toner particles from the roll to form the powder 
cloud. The particle transportation 282 is thus adjacent the 
photoconductive belt 10 so that the powder cloud may develop the latent 
image on the belt 10. 
The support portion 284 is that portion of the roll 240 that supports the 
roll 240. The particle transportation portion 282 and the support portion 
284 may have the same diameter as shown in FIG. 1, or the support portion 
284 may be larger or smaller than the particle transportation portion 282. 
When the support portion 284 and the particle transportation portion 282 
have different diameters, for example, the support portion being smaller 
to minimize the size of the donor roll 40, a neck down region (not shown) 
is located between the particle transportation portion 282 and the support 
portion 284 of the body 222 of the roll 240. Extending outwardly from the 
support portion 284 of the body 22 of the donor roll 240 is the external 
portion 286. The external portion 286 includes connector 236 to which 
commutation member 246 is connected. 
Referring now to FIG. 7, a third embodiment of the modular commutator of 
the present invention is shown in modular commutator 320. The modular 
commutator 320 is similar to the modular commutator 120 of FIG. 1. Donor 
roll 340 is similar to donor roll 40 of FIG. 1 except that unlike donor 
roll 40 which has a constant diameter, donor roll 340 includes body 322 
having three separate areas. These areas include a particle transportation 
portion 382 similar to particle transportation portion 282 of the donor 
roll 240 of FIG. 6, a neck down portion 390 connected to the particle 
transportation portion 382 and a commutating portion 392 connected to the 
neck down region 390. Connector 336 is located in the commutating portion 
392. Connector 336 includes connecting members 338 which are in the form 
of axially extending pads located on the periphery of the connecting 
portion 392 and equally spaced from each other. 
The modular commutator 320 includes commutation member 346 which is similar 
to commutation member 146 of FIG. 1 and may include any suitable type of 
commutation system. The commutation member 346 includes a cavity 396. 
Commutation connectors 370 are located on the periphery of the cavity 396. 
Commutation connectors 370 are similar to commutation connectors 170 of 
FIG. 1, except that the commutation connectors 370 include longitudinally 
extending pads 376 which correspond in the axial position with the 
connecting members 338 located in the commutation portion 392 of the body 
322 of the donor roll 340. As the commutation member 346 is positioned 
axially in the direction of arrow 378, the commutation connectors 370 of 
the commutation member 346 slide over the connecting members 338 of the 
connector 336. 
Referring now to FIG. 8, the commutation member 346 and the connector 336 
are shown in greater detail. The connector 336 has a diameter D.sub.CO 
which is slightly smaller than diameter D.sub.A of the cavity 396 of the 
commutation member 346 in order that the connector 336 may slidably fit 
into the commutation member 346. As shown in FIG. 8, diameter D.sub.R, the 
diameter of the roll 340, is smaller than diameter D.sub.C of the 
commutation member 346. It should be appreciated, however, that the 
diameter D.sub.C may be made equal to, smaller than or larger than the 
diameter D.sub.R of the roll. The diameter D.sub.CO of the connector 336 
may be either smaller or larger than the diameter D.sub.R of the roll 340. 
Electrical leads 380 interconnect the connecting members 338 to active 
electrode members 312. Since preferably more than one electrode 312 is 
connected to a connecting member 338, the number of connecting members 338 
is less than the number of electrode members 112. Therefore, the diameter 
D.sub.C of the commutation member 346 may be substantially smaller than 
the diameter D.sub.R of the roll 340. 
To assist in making a more robust commutating member 346, the commutation 
member 346 may have the diameter D.sub.C significantly larger than the 
diameter D.sub.R of the roll 340. Conversely, the commutation member 346 
may have a diameter D.sub.C substantially smaller than the diameter 
D.sub.R of the roll 340 in order to minimize space and cost. 
By providing a modular commutation system, updated commutation technologies 
may be incorporated into the donor roll without a complete reconstruction 
of the entire roll assembly. 
By providing a modular commutation system to a donor roll, a change from 
single to double, triple or quadruple groupings of the active electrode 
members can be handled within the commutation module with the same donor 
roll. 
By providing a modular commutation system to a donor roll, the engineering 
improvements of the donor roll and the commutator may proceed in parallel 
and upgrades in the commutation technology can be more easily implemented 
both in the development of new products and in the field in the 
retrofitting of existing products. 
By providing a modular commutating donor roll, the replacement of damaged 
rolls in the field may be accomplished without throwing away the expensive 
donor roll. 
By providing a modular donor roll commutator, during manufacturing any 
defective donor roll portions and commutation portions may be separately 
removed from the production line, thereby improving the overall yields of 
the assemblies. 
By providing a modular commutating donor roll, the diameter of the 
commutation region is no longer dictated by the diameter of the donor roll 
itself. Indeed it may be advantageous to have the commutation module whose 
diameter is different, most likely larger, than the diameter of the donor 
roll. 
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.