Development apparatus with magnetically rotated skive

A compact and less costly development apparatus includes a first magnetic field generated by a driven magnetic development roller, and a second magnetic field generated by a magnetic skive for effectively removing spent developer material from the development roller. The magnetic skive which consists of a stationary non-magnetic shell and a rotatable multiple pole magnetic core, is rotatably driven by a magnetic coupling formed by such first and second magnetic fields.

BACKGROUND OF THE INVENTION 
This invention relates to electrostatographic copiers and printers, and 
more particularly to a compact and less expensive development apparatus 
therein for producing high quality toner developed images. 
In such a copier or printer, especially one for producing high-resolution 
images, a development apparatus, of the type including a magnetic 
development roller, utilizes very fine toner particles that are contained 
in a magnetic developer material. The developer material is carried, at a 
desired velocity, by the magnetic development roller for developing 
electrostatic latent images on an image-bearing member. Such developer 
material consists, for example, of a mixture of ferromagnetic carrier 
particles and such toner particles, at a desired concentration. The 
concentration or level of toner particles in the mix, as expected, is 
usually depleted each time an image is developed. 
Ordinarily, such depletion will result in poor quality development of 
subsequently produced images. Therefore to ensure quality development of 
such subsequently developed images, the depleted spent developer must, for 
example, be effectively removed from each portion of the development 
roller, before such portion again carries fresh developer (of the desired 
concentration) for development. 
Conventional devices for skiving or removing spent developer from the 
surface of development rollers are disclosed, for example, in U.S. Pat. 
Nos. 2,975,758; 4,660,504 and 3,982,498. These devices include, 
respectively, an eccentric shell about a magnetic development roller, a 
mechanical skive, and a magnetic brush roll. 
The eccentric shell type device operates by directing the spent developer 
further and further away from the magnetic influence of the magnetic core 
of the development roller until the spent developer passively falls off 
gravitationally from the surface of such shell. Ordinarily, the 
effectiveness of such eccentric shell devices is limited because the spent 
developer is removed passively, and because there is a contradictory and 
competing need on the other hand for the same surface of the eccentric 
shell to be within the magnetic influence of its magnetic core so as to 
enable the development roller to magnetically attract fresh developer 
thereto from an adjacent developer feed roller. 
Mechanical skive devices are often also ineffective. They typically include 
a mechanical edge located in skiving or scraping engagement with the 
developer-carrying outside surface of a development roller shell, for 
scraping spent developer therefrom. The spent developer so scraped off is 
thereafter allowed to gravitationally fall off the mechanical skive. Such 
mechanical skives, however, are particularly ineffective in development 
apparatus which utilize very fine toner particles for high resolution 
image development. In such development apparatus, the shell and the core 
of the development roller normally are being rotated in the same direction 
such that the net forward velocity of the spent developer is imparted by 
the shell. Such a net velocity, of course, will be opposite in direction 
to the component velocity being imparted by the magnetic core of such 
development roller. 
The mechanical skive is particularly ineffective here because when the 
spent developer is still within the magnetic influence of the core of the 
development roller, and loses its shell-imparted forward velocity due to 
being scraped or skived from such shell, the magnetic tendency of the core 
will be to move the spent developer backwards away from the mechanical 
skive. The results often are undesirable bridging, and flaking of the 
toner component of such developer. 
On the other hand, although it is well known to use a magnetic device such 
as a development roller or magnetic brush roll to move 
developer-containing magnetic carrier particles, the effectiveness of such 
a roll, when used as a skive for a magnetic development roller, is 
significantly limited if it must work against, and must overcome the 
magnetic influence of the magnetic core of the development roller in order 
to remove spent developer from such development roller. Furthermore, 
because such rolls normally include a driven shell and hence separate 
drive means, the tendency is for them to be bulky and expensive. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide in a development 
apparatus having a development roller, a skiving device for actively 
skiving spent developer from such development roller. 
It is another object of the present invention to provide in such a 
development apparatus, a skiving device which does not adversely affect 
the ability of the development roller to magnetically pick up fresh 
developer from a development supply roller. 
It is still another object of the present invention to provide a skiving 
device that is effective in skiving spent developer from the development 
roller of a high-resolution development apparatus in which the shell and 
core of the development roller are being rotated in the same direction, 
and in which the net forward velocity of the developer is imparted by the 
shell, oppositely to that being imparted by the core. 
A further object of the present invention is to provide a development 
apparatus that includes such a skiving device, and that is compact and 
inexpensive. 
In accordance with the present invention, a development apparatus, in an 
electrostatographic copier or printer, includes a drivable magnetic 
development roller generating a first magnetic field for picking up and 
carrying fresh developer material within the apparatus. The apparatus 
further includes a rotatable magnetic skiving device, generating a second 
magnetic field, for effectively skiving and removing developer material 
from such development roller, and a magnetic coupling formed by such first 
and second magnetic fields for rotating such a skiving device within the 
apparatus.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to the drawings, FIG. 1 illustrates a portion of a 
development apparatus, in an electrostatographic copier or printer, that 
includes a development zone generally designated 10, and that is suitable 
for high-resolution image development. The development zone 10 includes 
part of an image-bearing member 12 carrying electrostatic latent images 
14, and part of a development roller 16 carrying fresh developer material 
18 for developing the latent images 14, turning them into visible toner 
images 20. 
As illustrated, the image-bearing member 12 is moved in the direction of 
arrow 22 at a given, slow velocity V.sub.1. The development roller 16, 
which consists of a non-magnetic shell 24 and a magnetic core 26, is moved 
so that its shell 24 and its core 26 are both traveling rotatably in the 
same direction, for example, clockwise as illustrated, and so that the 
development roller 16 imparts a net linear velocity V.sub.2 to the 
developer material thereon. As is well known, when the magnetic core 26 is 
being rotated, for example, in the clockwise direction as shown, it will 
magnetically tend to impart a linear velocity V.sub.3 to the magnetized 
developer material 18 such that V.sub.3 is opposite in direction to the 
rotational direction of the core 26. On the other hand, the non-magnetic 
shell 24 on which the developer material 18 actually rides, will impart a 
velocity V.sub.4 to the developer 18 such that V.sub.4 is in the same 
direction as the rotation of the shell 24, and therefore against V.sub.3, 
as shown. As such, if V.sub.4 is made greater than V.sub.3, the net 
velocity V.sub.2 of the developer 18 will be in the same direction as the 
rotation of the shell 24 and core 26, and can thus be made as small, that 
is, as slow as is desired, even to the point where V.sub.4 -V.sub.3 is 
practically zero. 
Accordingly, the fresh developer material 18 which is comprised of a mix of 
small magnetic carrier particles and pigmented toner particles at a 
desired concentration or level, can be picked up and carried on a portion 
of the outside surface 28 of the shell 26 at the high counteracting linear 
velocities V.sub.3 and V.sub.4 (which result in the net velocity V.sub.2) 
for high resolution development of the latent images 14. 
For such development, a development apparatus 40, as shown in FIG. 2, is 
located within the copier or printer so that during rotation of the shell 
24 and core 26 of the development roller, as described above, the 
developer material 18 (on the surface 28 of the shell) will come into 
brushing contact with the latent images 14. During such brushing contact, 
some of the toner particles in the fresh developer 18 on each portion of 
the surface 28, are spent or used up in development, thereby leaving spent 
developer 30 on such portion. Such spent developer 30, as expected, has a 
reduced and less than desired concentration or level of toner particles 
therein, and should therefore be effectively removed from such portion in 
order to prevent poor image development resulting from undesirable 
dilution of other fresh developer 18 subsequently picked up by such 
portion. 
FIG. 2 fully illustrates the development apparatus 40 of the type forming 
the development zone 10 of FIG. 1. The development apparatus 40 as 
illustrated includes the development roller 16, as well as, skiving means 
for effectively removing such spent developer 30 from the development 
roller 16. As shown, the development apparatus 40 comprises a housing 42 
in which is located a mixing device 44 for mixing and blending the 
developer material 18, a developer material feed roller 46, the 
development roller 16, and a skiving device 60. 
The mixing device 44 is located in a sump portion 48 of the housing 42, and 
rotates to blend or mix the toner and carrier particles that constitute 
the developer mix 18. The blended developer 18 is pulled into the feed 
roller 46 through a first aperture 50 in a hollow non-magnetic shell 51, 
by means of a stationary magnet 52. Inside the shell 51, a non-magnetic 
fluted core 54 mechanically carries the developer 18 passed a second 
aperture 56 that is adjacent the development roller 16. 
The development roller 16 includes the rotatable non-magnetic shell 24, and 
the rotatable magnetic core 26 which consists of a plurality e.g. (6) of 
single, alternating N and S pole magnets. Each of these magnets is strong 
enough to generate a magnetic field of a first strength about the shell 
24. As shown, the shell 24 is eccentric with the core 26, but it can also 
be concentric. As described above, the shell 24 and core 26 are rotatably 
driven in the same direction (clockwise as shown), with the core being 
rotated fast enough to induce the high linear velocity V.sub.3, and the 
shell 24 being simultaneously rotated fast enough at a counteracting 
linear velocity V.sub.4, thereby resulting in a net linear velocity 
V.sub.2 (for the developer material 18). 
The development roller 16 and the feed roller 46 are located so that 
developer material 18 being carried by the fluted core 54, passed the 
second aperture 56, will be within the influence of each magnetic field of 
the core 26 as such field is moved with the core 26 passed the aperture 
56. As such, a quantity of the developer 18 will be magnetically attracted 
by the passing magnetic field of the core 26 through the aperture 56, and 
onto a portion of the outside surface 28 of the non-magnetic shell 24. 
Then with the shell 24 and core 26 of the development roller rotating as 
illustrated in FIG. 1, the attracted developer 18 on such portion of the 
surface 28 will be carried at the high counteracting linear velocities 
V.sub.3, V.sub.4, the net linear velocity V.sub.2 into, and passed, the 
development zone and hence at 10 for developing the latent images 14. Such 
development results in spent developer material 30 which, for the reasons 
discussed above, should be removed. 
Accordingly, for removing such spent developer 30 from the surface 28 of 
the development roller, the apparatus 40 further includes the magnetic 
skive device 60. As shown, the skive device 60 includes a stationary 
non-magnetic shell 62 and a rotatable magnetic core 64 consisting of a 
plurality e.g. (6) of single, alternating N and S pole magnets. Each of 
such magnets is strong enough to generate a second magnetic field of a 
second strength about the shell 62, and into an overlapping relationship 
with the first magnetic field of the closest magnet of the development 
roller core 26. The magnets, and hence the magnetic fields of the skive 
60, are made so that they are stronger than those of the development 
roller 16, as measured for example, within the area B where such magnetic 
fields overlap between the shell 24 of the development roller, and the 
shell 62 of the skive device 60. 
In cases where the shell 24 of the development roller 16 and the shell 62 
of the skive are spaced a distance of about 0.025", within this area B, 
magnetic field strengths of 400 Gauss for each development roller magnet, 
and 900 Gauss for each skive device magnet, have been found to be 
operatively very satisfactory in affecting the skiving of spent developer 
from the development roller of the apparatus of the present invention. 
FIG. 2 further illustrates a magnetic coupling 66 formed by the magnetic 
field of each magnet of the development roller overlapping with the 
magnetic field of the closest magnet of the skive device 60. Coupling 66 
is formed as such when the shell 24 and core 26 of the development roller 
16 are rotatably driven, for example, clockwise passed the area B. By 
means of the coupling 66, the momentum of the driven core 26 is 
transmitted to the rotatable core 64 of the skive device 60, thereby 
rotatably moving the core 64 in the opposite or counterclockwise direction 
as illustrated. Utilization of the magnetic coupling 66 instead of a 
separate drive means for moving the core 64 in this manner, allows the 
development apparatus 40 to be compact and less costly. 
When the core 64 of the skive device 60 is rotatably moved as such by the 
coupling 66, the skive device 60 effectively operates to skive off and 
remove spent developer 30 from the surface 28 of the shell 24, as follows. 
First, the magnetic field of each magnet of the skive device 60, because 
it is stronger than that of the development roller magnet closest to it, 
within the area B, will attract the spent developer material 30 away from 
the surface 28 of the development roller shell 24, and onto the surface of 
the skive shell 62. As described above, the rotational, counterclockwise 
movement of the core 64 of the skive 60, and hence of its magnets as 
caused by the coupling 66, will cause the attracted spent developer 30 on 
the shell 62 to move in the opposite, that is, clockwise direction as 
shown by the arrow 68. In effect therefore, the combined impacts of the 
greater strength, and of such rotation, of the magnets of the core 64 on 
the spent developer 30, is to move such spent developer away from, and 
against the movement of, the portion of the surface 28 carrying it. Such 
away-and-against movement of the spent developer is very effective in 
skiving off and removing such spent developer from the surface 28. 
Additionally, it is important to note that within the area B, the direction 
of the velocity V.sub.3 being induced in the spent developer 30 by the 
rotating core 26 of the development roller 16 is also against the movement 
of the surface 28, and hence operates additively with the movement of the 
same developer being induced in the same direction (arrow 68) by the core 
64 of skive device 60. As such, the skiving off and removal of the spent 
developer 30 within the area B is substantially enhanced by the action 
therein of the rotating magnets of the core 26 of the development roller 
16 moving the spent developer 30 additively in the same direction against 
the movement of the surface 28, as are the magnets of the skive device 60. 
Following such removal from the surface 28, the spent developer 30, as 
illustrated, is held magnetically onto the surface of the shell 62 and 
there travels, as shown, until it is removed, for example, by means of a 
secondary conventional mechanical skive 69. Alternatively, it can also be 
removed by means of a conventional eccentric shell type skive device, and 
thereafter allowed to fall back into the sump 48 for remixing by the 
device 44. 
Unlike in the case of a development roller as discussed above, the use of 
conventional skiving devices to secondarily remove the spent developer 30 
from the surface of the skive device 60 as suggested here, is acceptable 
because, with the device 60, there is no need on the other hand for it to 
magnetically pick up developer material. Furthermore, any ineffectiveness 
of such secondary conventional skiving device in removing the spent 
developer 30 from the skive 60 will not result in poor image quality, and 
so the use of such conventional skives here is not as critical as it would 
be in the case of the development roller. 
As can be seen, by utilizing the magnetic coupling 66 instead of separate 
drive means to rotatably move the core 64 of the skive device 60, the 
development apparatus 40 of the present invention can be made compact and 
less costly. The skive device 60 also actively and effectively skives and 
removes spent developer from the development roller 16, and can do so even 
in a high resolution development apparatus in which the shell and core of 
the development roller tend to move the spent developer in opposite 
directions. Finally, such skiving and removal of the spent developer is 
substantially enhanced by the additive, not oppositive, tendencies of the 
magnetic cores of the development roller and skive device in moving the 
spent developer 30 from the surface 28 of the development roller. 
Although the description of the invention has been made with particular 
reference to a preferred embodiment, it is understood that modifications 
and variations can be effected within the spirit and scope of the 
invention.