U.S. patent number 3,643,629 [Application Number 04/867,768] was granted by the patent office on 1972-02-22 for magnetic powder applicator.
This patent grant is currently assigned to Minnesota Mining & Manufacturing. Invention is credited to Larry G. Kangas, Robert J. Kline.
United States Patent |
3,643,629 |
Kangas , et al. |
February 22, 1972 |
MAGNETIC POWDER APPLICATOR
Abstract
An applicator for uniformly applying magnetically responsive dry
particulate material to broad areas on a web moved past the
applicator to deposit the material in pattern areas attracting the
material thereto. The applicator comprises an applicating roller
having a plurality of magnetic members arranged about a shaft
within a rotatable nonmagnetic sleeve to provide a magnetic field
around the roller having a feed zone with a radial field changing
to a tangential field, an applicating zone with a stronger radial
field following the feed zone and a return zone extending from the
applicating zone to the feed zone and having a stronger tangential
field immediately following the applicating zone. A scavenging
roller has a plurality of magnetic members arranged about a
rotatable shaft within a nonmagnetic sleeve to carry any free
particulate material applied by the applicating roller away from
the web surface and back to a tray.
Inventors: |
Kangas; Larry G. (St. Joseph
Township, Saint Croix County, WI), Kline; Robert J. (Grant
Township, Washington County, MN) |
Assignee: |
Minnesota Mining &
Manufacturing (St. Paul, MN)
|
Family
ID: |
25350430 |
Appl.
No.: |
04/867,768 |
Filed: |
October 20, 1969 |
Current U.S.
Class: |
399/269; 399/273;
399/276; 277/345; 335/303 |
Current CPC
Class: |
G03G
15/09 (20130101) |
Current International
Class: |
G03G
15/09 (20060101); G03g 013/00 () |
Field of
Search: |
;118/637 ;117/17.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Stein; Mervin
Assistant Examiner: Millstein; Leo
Claims
We claim:
1. An applicating roller for placing a uniform layer of
magnetically responsive dry particulate material in contact with a
surface moved past the peripheral surface of said roller, said
applicating roller comprising:
a stationary shaft of high magnetic permeability material,
magnetic means for producing a magnetic field about said peripheral
surface of said roller having a feed zone with a generally radial
field changing to a generally tangential field, an applicating zone
following said feed zone with a generally radial field stronger
than that of said feed zone and extending to both sides of the
portion of said peripheral surface of said roller past which a said
surface may be moved, and a return zone following said applicating
zone and extending about said array to said feed zone, said return
zone having a generally tangential field stronger than that of said
feed zone immediately following said applicating zone, said
magnetic means comprising a plurality of elongated generally
sector-shaped in cross section strips of magnetic material formed
of fine grain permanent magnetic material dispersed in a
nonmagnetic immobilizing matrix, said strips being arranged in a
circular array about said shaft with the edges of said strips
generally radial and in side-by-side relation to form at least a
partial cylinder, each said strip being radially polarized with
constant polarity along its length and adjacent strips being
oppositely polarized along their adjacent edges, and
a nonmagnetic hollow cylindrical sleeve fit over said arranged
magnetic strips, extending axially of said shaft and supported for
rotation about said magnetic strips to carry a quantity of said
particulate material on the outer surface thereof.
2. An applicating roller as recited in claim 1 wherein said sleeve
is electrically conductive.
3. An applicating roller as recited in claim 1 wherein each of said
magnetic strips has an axial length of between 8 and 15 inches.
4. A magnetically responsive dry particulate material applicator
comprising:
an applicating roller for placing a uniform layer of a said
material in contact with a surface moved past the peripheral
surface of said roller, comprising:
a stationary shaft of high magnetic permeability material,
magnetic means for producing a magnetic field about said peripheral
surface of said roller having a feed zone with a generally radial
field changing to a generally tangential field, an applicating zone
following said feed zone with a generally radial field stronger
than that of said feed zone and extending to both sides of the
portion of said peripheral surface of said roller past which a said
surface may be moved, and a return zone following said applicating
zone and extending about said array to said feed zone, said return
zone having a generally tangential field stronger than that of said
feed zone immediately following said applicating zone, said
magnetic means comprising a plurality of elongated generally
sector-shaped in cross section strips of magnetic material formed
of fine grain permanent magnetic material dispersed in a
nonmagnetic immobilizing matrix, said strips being arranged in a
circular array about said shaft with the edges of said strips
generally radial and in side-by-side relation to form at least a
partial cylinder, each said strip being radially polarized with
constant polarity along its length and adjacent strips being
oppositely polarized along their adjacent edges, and
a nonmagnetic hollow cylindrical sleeve fit over said arranged
magnetic strips, extending axially of said shaft and supported for
rotation about said magnetic strips to carry a quantity of said
particulate material on the outer surface thereof,
means for supplying a said particulate material to said sleeve in
said generally radial field of said feed zone, and
a doctor blade adjacent the periphery of said sleeve in said
generally radial field of said feed zone for limiting the amount of
said particulate material which may be carried from said supply
means to said applicating zone.
5. An applicating roller as recited in claim 4 wherein said sleeve
is electrically conductive.
6. An applicating roller as recited in claim 4 wherein each of said
magnetic strips has an axial length of between 8 and 15 inches.
Description
This invention relates to an applicator for applying a uniform
layer of magnetically responsive dry particulate material to
particle-attractive areas on a moving, differentially
particle-attractive surface.
The present invention is particularly useful in applying pigmented
particulate material to an article to develop an image thereon. One
example of such use is in developing imagewise a differentially
conductive pattern formed by projecting a light image on a
photoconductive web. The photoconductive web being positioned
between an insulative layer, backed by an electrode, and a second
electrode contacting the particulate or powder which is in
electrically conductive contact between the second electrode and
the photoconductive web.
The prior art is replete with magnetically responsive powder
applicators in which permanent magnets are arranged about a shaft
within a nonmagnetic outer sleeve, and the shaft and the sleeve are
mounted for relative rotation. Recently, as illustrated by U.S.
Pat. No. 3,455,276, it has been found advantageous in such devices
to utilize magnetic members formed of fine grain permanent magnet
material dispersed in a nonmagnetic immobilizing matrix. With such
magnetic members it is possible to present an even deposition of
particulate material or developer powder to an image-bearing member
with a width of 81/2 to 13 inches since the magnetic field along
the magnetic members can be made constant for such length unlike
other permanent magnets. While such an applicator does present a
uniform layer of particulate material to a photoconductive web the
desired uniform layer of particulate material on the particle
attractive areas of the web has not been achieved. As the
particulate material is transferred from the sleeve of the
applicating roller to the photoconductive web where the attractive
force on the web overcomes the magnetic attraction of the
applicating roll, the powder extends between the web and the
sleeve. As the web is advanced, the particulate material separates
from the sleeve and forms treelike piles on the web with the
particles in the uppermost portion of the piles weakly attracted or
free on the web. As the web continues to move along, these free
particles may then become dislodged and come to rest on the
nonattractive (e.g., background) areas of the web. Furthermore,
upon transferring the particulate material from the photoconductive
web to a sheet of copy paper to form an image thereon the
nonattracted particles may be dispersed onto areas of the copy
paper where they are not desired. In either case these dislodged
particles will darken or change the image resolution on a sheet of
copy paper which is highly undesirable.
According to the present invention, an improved applicating roller
utilizing magnetic members formed of fine grain permanent magnet
material dispersed in an immobilizing matrix is provided. The
present invention also provides an apparatus for applying a uniform
layer of magnetically responsive particulate material to
particle-attractive areas on a moving differentially
particle-attractive web such that the particles applied to the web
are all attracted thereto. The present invention further provides
an applicator for presenting a dimensionally uniform coating of
magnetically responsive particulate material to a wide,
differentially particle-attractive surface to deposit the
particulate material in the particle-attractive areas.
The apparatus illustrated is adapted for applying a layer of
magnetically responsive dry particulate material to particle
attractive areas on a moving differentially particle attractive
surface and comprises an applicating roller and a scavenging
roller, each roller comprising a magnetically permeable shaft, a
plurality of generally sector-shaped strips of magnetic material,
said strips being magnetized to create axially extending areas of
alternating polarity in adjacent circumferential position about
said shaft, and a nonmagnetic sleeve fitted over the magnetic
strips, means for mounting the sleeve and the shaft of the
applicating roller for relative rotation to carry particulate
material on the sleeve to a said moving surface, and means for
mounting the sleeve and the shaft of the scavenging roller to carry
any nonattracted or free particulate material around the sleeve
away from a said surface.
The novel features and advantages of the present invention will
become apparent after reading the following description which
refers to the accompanying drawing wherein:
FIG. 1 is a longitudinal elevational view of a particulate material
applicator made in accordance with the present invention;
FIG. 2 is an end elevational view of the applicator of FIG. 1;
FIG. 3 is a diagrammatic vertical sectional view of the operation
of the applicator of FIG. 1;
FIG. 4 is a cross-sectional view taken along line 4--4 of FIG. 1;
and
FIG. 5 is a perspective view illustrating one magnetic member.
A magnetically responsive dry particulate material applicator made
in accordance with the present invention and generally designated
10, is illustrated in FIG. 1 and comprises an applicating roller 12
and a scavenging roller 14 supported with their peripheral surfaces
adjacent a moving surface 16 having areas differentially attractive
to the particulate material. In the illustrated embodiment, the
rollers 12 and 14 are supported by frame members 17 comprising a
pair of end plates 18 and 19, a developer powder tray 21 extending
between the rollers 12 and 14, and a developer powder hopper 23
extending between the end plates 18 and 19 above the powder tray
21.
The applicating roller 12 comprises a shaft 25 formed of a material
having a high magnetic permeability, such as soft iron,
stationarily supported at opposite ends in the frame members 17.
Positioned above the shaft 25 are four generally sector-shaped
strips of magnetic material 27, which will be described in greater
detail hereinafter. Rotatably mounted relative to the shaft 25
coaxially therewith, as by bearing mounted end caps 32 is a
nonmagnetic cylindrical sleeve 33 formed of a material (e.g.,
glass, aluminum, or polymeric material) which will not shield the
magnetic field from the magnetic strips 27. At one end the sleeve
33 is formed with a pulley 34 about which a drive belt 36 passes to
rotate the sleeve 33 about the magnetic strips 27. The drive belt
36 also passes around an idler roller 38, a bail shaft pulley 39
and a drive pulley 40. The drive pulley 40 is suitably driven from
a drive motor 42 through gears in a gear box 41.
As desired in some copying applications, the applicating roller 12
serves as an electrode; therefore, it is desired to connect the
sleeve 33 to a source of electrical potential; and in the
illustrated embodiment a connector 43 is attached to the shaft 25,
to which a lead from a source of a potential may be coupled. The
sleeve 33 is electrically connected to the shaft 86 25 by sliding
leaf 44 (FIG. 5) of resilient conductive material. The sleeve 33 in
this example is preferably formed of aluminum, but could be formed
of another nonmagnetic material such as glass with an electrically
conductive, nonmagnetic surface coating.
The applicating roller 12 is positioned adjacent the tray 21 in
parallel aligned spaced relation to the moving differentially
particle-attractive surface 16, defined by the surface of a web
comprising, for example a differentially light-struck
photoconductive coating 46 carried on an insulative backing 48
supported in turn on an electrically conductive surface 47. In any
instance, if the moving surface of the web 16 is to be coated, it
carries an undeveloped differential image pattern to which is to be
applied an even coating of particulate image-forming magnetically
responsive material hereinafter referred to as developer powder 49,
which may be supplied by the applicating roller 12 from a supply
disposed in the tray 21.
Along the edge adjacent the applicating roller 12, the tray 21 is
formed with an inclined surface defining a doctor blade 51 spaced
from the sleeve 33 of the applicating roller 12 to define a doctor
gap with the sleeve 33 across the width of the moving surface 16
through which the developer powder 49 must pass to be applied to
the moving surface 16.
Like the applicator roller 12, the scavenging roller 14 comprises a
shaft 54 formed of a material having a high magnetic permeability,
such as soft iron, supported at opposite ends in the frame members
17. Positioned about the shaft 54 are similar generally
sector-shaped strips of magnetic material 55, which will be
described in greater detail hereinafter. A nonmagnetic cylindrical
sleeve 57 formed of a material which will not shield the magnetic
field from the magnetic strips 55 is supported coaxially with the
shaft 54. Like the applicating roller 12 the sleeve 57 and the
shaft 54 of the scavenging roller 14 are relatively rotatable,
however, unlike the applicating roller 12 the sleeve 57 of the
scavenging roller 14 is fixed while the shaft 54 is rotatable. The
sleeve 57 of the scavenging roller 14 has an insulating extension
58 secured along its length to mate with the edge of the tray 21
opposite the doctor blade 51. This forms a continuous surface along
the base of the tray 21 around the scavenging roller sleeve 57 and
into the tray 21. The scavenging roller shaft 54 is suitably
bearinged in end caps 59 (only one of which is shown) of the sleeve
57. At one end the shaft 54 extends through an end cap 59 and
supports a roller 61 which is suitably driven, such as by a roller
63 that contacts an extension of the moving surface 16 and the
roller 61, to provide rotation of the shaft 54 and the magnetic
strips 55 in a counterclockwise direction as viewed in FIG. 3.
The magnetic strips 27 and 55 are generally shaped as sectors of a
hollow cylinder having radially inner faces concavely curved and
convex radially outer surfaces joined by radially extending edge
walls. In each roller 12 or 14 the magnetic strips 27 or 55 are
arranged in a circular array about their associated shaft 25 or 54
with their edges generally radial and in side-by-side relation. The
strips 27 and 55 are formed by extrusion of a nonmagnetic matrix
which may be a resinous or plastic composition, and an elastomeric
semisolid, or viscous liquid, capable of hardening, setting or
being cured to a solid state in which is evenly dispersed
anisotropic ferrite domain-sized particles, which particles are
capable of achieving physical orientation when acted upon by
internal shear stresses. Examples of the particles are certain
fine-grained, permanent magnet materials, particularly the ferrites
of barium, lead, and strontium which are easily magnetized to
saturation. The matrix may be natural rubber with compound agents,
plasticizers, vulcanizing agents, and the like to provide the
hardness of the matrix desired, or may be a thermoplastic of
thermosetting material, as for example, polyvinyl chloride.
Preferably the ferrite particles are oriented such that each
particle (as illustrated diagrammatically in FIG. 5 at 65) is
positioned with its magnetic poles positioned radially relative to
each other.
In the applicating roller 12, since the shaft 25 is fixed, the
magnetic strips 27 are constantly positioned as schematically
illustrated in FIG. 3. The strips 27 are arranged about the shaft
25 with the edges thereof generally radial and in side-by-side
relation to substantially form a cylinder and they are magnetized
to provide peripheral circumferential areas of constant polarity
extending the lengths of the strips with adjacent areas oppositely
polarized. Two such peripheral areas provided by a single magnetic
strip 31 are illustrated in FIG. 5. The magnetic strips 27 produce
the relative magnetic field component strengths illustrated in FIG.
4 where the radial field component is illustrated in dotted lines
and the tangential field component is illustrated in full lines.
The magnetic field just prior to and at the doctor blade 51 is
generally exclusively radial thereby tending to align the developer
powder particles in rows standing out perpendicularly from the
surface of the sleeve 33. As the sleeve 33 rotates the doctor blade
may then trim these rows of particles to pass particles through the
doctor gap. A stronger tangential field is developed immediately
past the doctor blade 51 to draw the powder passing the doctor gap
against the sleeve 33 to improve the powder flow toward the moving
surface 16. The radial field at the doctor blade together with the
tangential field immediately thereafter define a powder feed
zone.
Along the line nearest the moving surface 16 and to both sides
thereof is an applicating zone. In the applicating zone the
magnetic field is nearly exclusively radially oriented, thereby
tending to align the developer powder particles in rows extending
outward radially from the sleeve 33 to increase the density of
powder contacting the moving surface 16. A uniform layer of
developer powder is thereby presented to the photoconductive
surface 46. The web 46 may then selectively attract developer
powder from the applicator sleeve 33 according to the image pattern
thereon while maintaining a space between the sleeve 33 and the web
46 to prevent powder from being pressed onto nonattractive areas of
the web.
Moving about the sleeve 33 counterclockwise (as viewed in FIG. 3 or
4) away from the moving surface 16 is a powder return zone in which
the magnetic field is rapidly changed to a dominant tangential
field stronger than that in the feed zone to lay the rows of
developer powder particles against the sleeve 33 to aid in moving
any nonattracted particles away from the moving surface. Continuing
in a counterclockwise direction about the applicating roller 12 the
return zone extends to the feed zone and the magnetic field has a
sufficient strength to carry the remaining nonattracted developer
powder on the sleeve 33 back into the tray 21.
The unique magnetic field about the applicating roller 12 is
accomplished by the size, polarization and positioning of the four
magnetic strips 28, 29, 30 and 31. The weak radial field of the
feed zone at the doctor blade 51 is generally provided by a
four-pole approximately 35.degree. sector magnet 28. The weak
tangential field of the feed zone is provided by the 35.degree.
four-pole magnet 28 and a first two-pole 90.degree. sector magnet
29 abutting the 35.degree. four-pole magnet 28. Due to its mass the
first two-pole 90.degree. sector magnet 29 also generally provides
the strong radial field in the applicating zone and cooperates with
a second two-pole 90.degree. magnet 30, that is adjacent and spaced
from it, to provide the strong tangential field of the return zone.
A four-pole 90.degree. sector magnet 31 abuts the second 90.degree.
two-pole magnet 30 and is adjacent and spaced from the 35.degree.
four-pole magnet 28 to complete the array of magnets. The magnet 31
provides a sharply varying magnetic field near the end of the
return zone to promote increased tumbling action as the returned
powder mixes in the tray with the supply powder.
As in the applicating roller 12, the magnetic strips 55 of the
scavenging roller 14 are arranged about the shaft 54 with the edges
thereof generally radial and side-by-side relation to form a
cylinder and they are magnetized to provide peripheral
circumferential areas of constant polarity extending the length of
the strips 55 with adjacent areas oppositely polarized. However,
unlike the applicating roller 12, the magnetic strips 55 are all
similar, 90.degree. sectors each of which is magnetized to provide
a north pole and a south pole, generally of equal strength, on its
peripheral surface. These strips 55 have sufficient magnetic
strength to pull any free powder particles on the photoconductive
web 46 against the sleeve 57.
A bail shaft 67 is rotatably supported above the developer powder
tray 21 and extends parallel to the rollers 12 and 14. The bail
shaft 67 is bearinged in the frame members 17 and extends through
one end thereof to carry the bail pulley 39 so as to be suitably
driven by the motor 42. Two helical springs 68 extend
perpendicularly from the bail shaft 67, one generally at each end
of the tray 21, and a wire bail 69 is supported at the free ends of
the springs 68 to normally lie parallel to the bail shaft 67.
In use, a differentially exposed photoconductive web 46 is moved
first past the applicating roller 12. As it does so, the developer
powder 49 is moved from the tray 21 through the doctor gap and into
contact with the web 46 on the applicating roller sleeve 33.
Developer powder is transferred to the particle-attractive areas on
the web 46 corresponding to the images carried thereon. As the
developer powder on the sleeve 33 separates from the powder applied
to the web 46 treelike piles of developer powder are formed at the
imaged areas on the web. Any powder carried into contact with
nonattractive areas of the web continues to be carried on the
sleeve 33 around the applicating roller 23 and back into the tray
21.
As the web 46 continues to be moved, it passes under the scavenging
roller 14. As the treelike piles of developer powder on the image
areas of the web 46 pass under the scavenging roller 14 any weakly
attracted powder at the tops of the trees or free powder on
nonattractive areas of the web is attracted to the sleeve 57 of the
scavenging roller 14 by the magnetic strips 55. While the shaft 54,
and therefore, the magnetic strips 55 are rotated counterclockwise,
as illustrated in FIG. 1, the powder attracted to the surface of
the sleeve 57 progresses in a tumbling fashion around the sleeve in
a clockwise direction (opposite the direction of rotation of the
magnets) and thereby into the tray 21. Any powder returned to the
tray by the scavenging roller 14 again becomes available as supply
for the applicating roller 12, powder supplied adjacent the
scavenging roller 14 being moved toward the applicating roller 12
by rotation of the bail shaft 67 and the bail 69.
In one specific operative embodiment the applicating roller sleeve
33 is aluminum with a wall thickness of 0.025 inch and an inside
diameter to provide an air gap of about 0.012 inch between its
inner surface and the periphery of the magnets 27. The sleeve 33 is
spaced from the photoconductive web 46 0.013 inch with a tolerance
of plus or minus 0.002 inch. The gap at the doctor blade 51 is made
0.010 inch with a tolerance of plus or minus 0.002 inch and the
center of the doctor blade is spaced about 60.degree. (clockwise as
viewed in FIGS. 3 and 4) from a vertical plane intersecting the
axis of the applicating roller 12.
The strength of the radial field component in the applicating zone
when measured on the outside of the aluminum sleeve 33 is about 400
gauss provided primarily by the first two-pole 90.degree. sector
magnet 29. This radial field strength will produce an applicating
zone on the planar photoconductive web 46 which extends across the
web 46 and which is between 0.75 and 1.0 inch wide when the sleeve
33 is rotated at one-tenth the web speed in a direction opposite to
the movement of the web 46.
The sleeve 57 of the scavenging roller 14 is preferably spaced from
the web surface about 0.125 to 0.150 inch. The scavenging roller
magnets 55 are rotated by rotation of their shaft 54 at a speed
between 100 and 500 r.p.m., preferably about 300 r.p.m.
* * * * *