Photographic processing roller having a surface roughened by electric discharge machining

An improved cylindrical processing roller is provided for use in a motor driven photographic processing apparatus of the type which spreads a fluid processing composition in a thin, substantially uniform layer between selected layers of integral type self-processable film units while advancing a film unit to the exterior of a camera after photoexposure. The improvement in the roller resides in a novel circumferential roller surface roughened by electrical discharge machining techniques to provide the roller with a high-friction characteristic for transporting the film units while being insufficiently rough to leave any visually perceptible marks on a film unit.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention in general relates to photographic apparatus and in 
particular to improved cylindrical processing rollers for use in motor 
driven photographic processing apparatus of the type which spread a fluid 
processing composition in a thin, substantially uniform layer between 
selected layers of integral type, self-processable film units while 
advancing a film unit to the exterior of a camera after photoexposure. 
2. Description of the Prior Art 
Fully automatic photographic cameras which utilize integral type 
self-processable film units are well-known in the photographic field, 
having been extensively described in the patent literature and in public 
use for several years now. These cameras, such as Polaroid Corporation's 
"SX-70" and "Pronto!" and Eastman Kodak Company's "EK-6" and "EK-8" 
cameras, are designed to automatically produce furnished, waste-free color 
prints with virtually no operator involvement other than to compose the 
picture, perhaps focus, and then actuate the camera by depressing its 
cycle "start" button. 
They accomplish this task through the use of specially designed 
interdependent function providing subsystems that are organized to carry 
out a programmed series of sequential operations which produce the 
finished print. 
Once actuated, the order of camera operations begins with exposure of a 
film unit. Afterwards, the exposed film unit is advanced from its exposure 
location into engagement with a film processing subsystem or apparatus 
which initiates a diffusion transfer process for developing and forming a 
visible image in the film unit while transporting it to the exterior of 
the camera where it becomes accessible to the photographer. 
The film units, as for example those described in considerable detail in 
U.S. Pat. Nos. 3,415,644; 3,594,165; and 3,761,268, normally contain all 
the photographic components necessary for the diffusion transfer process. 
Typically, the film units comprise, in general terms, a pair of superposed 
sheet elements, at least one being transparent, which serve to support 
layers of photochemical substances which may comprise photosensitive and 
image-receiving layers; and, as well, include a rupturable container of 
viscous processing fluid positioned adjacent a leading edge of the film 
unit and adapted to have its processing fluid released between the sheet 
elements to begin the diffusion transfer process. Release of the 
processing fluid is effected by the processing apparatus which first 
operates to rupture the container and thereafter causes the released mass 
of processing fluid to flow between the sheet elements, opposite the 
direction of travel of the film unit, so that the processing fluid is 
progressively deposited between the sheet elements as a thin, uniform 
layer generally coextensive with the exposed area of the film unit. Upon 
completion of the diffusion transfer process, the final image is viewable 
through the sheet element which is transparent. 
Photographic processing apparatus having the capability of performing the 
film advancing and fluid spreading operations outlined above are 
well-known in the art. Generally, such apparatus comprise a pair of 
rollers rotatably mounted in juxtaposed relation and resiliently urged 
toward one another to exert a pressure on the film unit as it is advanced 
between them in response to rotation of at least one of the rollers by a 
motor drive. The rollers typically are manufactured to precision 
tolerances so that the fluid layer thickness is properly sized for optimum 
photographic image quality and at least one of them is provided with a 
high-friction, sheet-contacting surface to provide a high traction force 
to transport the film unit to the outside of the camera without slippage 
and without visably damaging the surfaces of the film unit. 
In addition to the precision tolerances and the high-friction, low-abrasion 
surface characteristic, these rollers must also possess high strength so 
that they either won't deform under the pressures generated during 
processing or deform only in a predictable manner, have high corrosion 
resistance, and be capable of retaining their original geometry after 
having processed a number of film units related to their expected useful 
life. 
Changes in initial roller geometry can occur by a build up of particulate 
matter from the film units which is picked up by the roller's surfaces. 
Thus, a further design requirement on these type of rollers is that they 
do not pick up particulate matter. 
One prior art device which satisfies the functional criteria for such film 
processing apparatus is described in considerable detail in U.S. Pat. No. 
3,776,118 issued to John J. Driscoll et. al. on Dec. 4, 1973 and entitled 
"Photographic Film Processing Apparatus". Here the processing apparatus 
includes a roller assembly having first and second rotatably mounted 
juxtaposed elongated rollers which are resiliently urged toward one 
another. A pair of annular collars are provided on the first roller to 
define a minimum gap between the rollers to facilitate the initial 
introduction of the leading edge of a film unit between the rollers. The 
first roller is adapted to be selectively driven by a motor of the camera 
and, when so driven, its annular collars impart a rotary motion to the 
second roller. At least those portions of the two rollers adapted to 
contact one another are formed of a relatively low friction, impact 
resistant material, such as stainless steel, while at least the 
sheet-contacting facing surface of the first roller is formed of a 
relatively high friction material such as urethane. The urethane which is 
coated on the first roller operates to provide the relatively high 
traction force between the first roller and the film unit to transport the 
film unit outside of the camera and the stainless steel provides the 
strength necessary to withstand the pressures generated during the 
transport and fluid spreading phases. In addition to its strength, the 
stainless steel also possesses desirable corrosion resistant 
characteristics. 
Although the performance of this type device is more than adequate as 
evidenced by its success in Polaroid Corporation's "SX-70" and "Pronto!" 
cameras, it is, as one would expect from its design criteria, relatively 
expensive to manufacture. The urethane coating coupled with the precision 
tolerances in particular represent a major portion of its cost. 
Another motor driven processing apparatus is that used in Eastman Kodak 
Company's "EK-6" and "EK-8" cameras. Here both rollers, which appear to be 
surfacehardened steel, are motor driven and each has a roughened surface 
to provide the high traction force necessary for film transport. It 
appears that the roughened surfaces of these rollers may be achieved by 
conventional crush grinding techniques and may afterwards be plated for 
corrosion protection and wear resistance. The roughened surfaces of these 
rollers would also appear to be relatively expensive to manufacture. 
Consequently, there is a need for an improved, less expensive, photographic 
processing roller which can be used with integral type, self-processable 
film units. Thus, it is a primary object of the present invention to 
provide such a roller by using electrical discharge machining (EDM) 
techniques to texture its surface to achieve the high-friction, 
low-abrasion surface required of these type rollers. 
It is recognized that EDM textured roller surfaces have been used 
extensively in the steel industry for the purpose of texturing sheet steel 
(U.S. Pat. Nos. 3,878,353; 3,800,117; and Re 28,027) and that EDM also has 
been used to increase the friction of rolls used to feed strip stock (U.S. 
Pat. No. 3,941,970). However, the EDM textured rollers disclosed above are 
not appropriate for use with self-processable film. Therefore, it is 
another object of the present invention to provide an improved 
photographic processing roller having a particular EDM surface which is 
suitable for use with self-processable film units. 
Other objects of the invention will in part be obvious and will in part 
appear hereinafter. The invention accordingly comprises the apparatus 
possessing the construction, combination of elements and arrangement of 
parts which are exemplified in the following detailed disclosure. 
SUMMARY OF THE INVENTION 
This invention, in general, relates to photographic apparatus and in 
particular to an improved cylindrical processing roller for use in a motor 
driven photographic processing apparatus of the type for advancing an 
integral type self-processable film unit to the exterior of a camera while 
simultaneously spreading a fluid processing composition between selected 
layers of the film unit and of the type having a circumferential surface 
of given length machined to a precision diameter to facilitate spreading 
the fluid processing composition in a substantially uniform thin layer 
between the film unit's selected layers. The improvement comprises a 
plurality of generally spaced apart, substantially uniform sized and 
shaped microscopic craters formed along a predetermined length of the 
roller's surface by electrical discharge machining. The craters cover no 
more than 50 percent of the area of the predetermined surface length and 
each is surrounded by a substantially uniform annular lip which extends 
above the surface by an amount insufficient to mark the film unit's 
surfaces. Each annular lip has a volume which generally equals the volume 
of the depressed portion of the crater which is below the surface. The 
roller surface is thus configured to provide the roller with a 
high-friction characteristic for transporting a film unit while being 
insufficiently rough to leave any visually perceptible marks on a film 
unit's surfaces, to minimize pickup of particulate matter from the film 
unit which would otherwise build up and reduce the high-friction 
characteristic, and to maintain the effectiveness of the roller's 
precision diameter so that substantially no change in its fluid spreading 
performance results from the presence of the craters. 
In the illustrated embodiment of the improved roller, the mean diameter of 
the microscopic craters is 0.0014 inches and the mean height of each 
crater's annular lip, above the surface, is 0.00016 inches. Also, the mean 
number of microscopic craters per square inch is 80,000 so that the 
craters cover between 10 and 20 percent of the area of the predetermined 
surface length.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, there is shown a fully automatic camera 10 of the 
type which uses integral, self-processable film units and in which the 
improved photographic processing roller of the present invention is 
incorporated. 
The camera 10 comprises a body 12, a front cover 14, and a door 16 which 
interconnect to define its outward appearance and serve as a protective 
enclosure for housing the camera's interior components. 
Located in a vertical forward wall 18 of the front cover 14 is an objective 
taking lens 20 having an optical axis, OA, therethrough. The objective 
taking lens 20 may be a Cooke Triplet or similar multi-element type of 
lens which can have its focal length changed by adjusting the axial air 
spacing between its optical elements. This may be accomplished in a 
well-known manner by rotating a bezel, such as that designated at 21, 
which extends through an opening in the front cover 14 and is coupled with 
a screw-threaded lens mount (not shown). 
Formed in the base of the body 12 is a well-known film cassette receiving 
chamber 30 which is adapted to releasably hold a film cassette such as 
that designated at 32. The cassette 32 comprises a generally rectangular 
parallelepiped housing 36 which has an upwardly facing wall 37 having a 
generally rectangular aperture 39 therein. Mounted in registration with 
and biased toward the aperture 39 is a stacked array of integral type 
self-processable film units generally designated at 34. Underneath the 
stacked array of film units 34 is a flat, thin battery (not shown) which 
may be used to supply power to the various electrical components of the 
camera 10. 
Each film unit 34 comprises a pair of superposed sheet elements including a 
top transparent sheet 44, preferably formed of mylar, beneath which is a 
bottom sheet that is not shown. Positioned adjacent the leading edges of 
the film unit's sheet elements is a rupturable container of viscous 
processing fluid or composition (not shown) adapted to have its contents 
spread between the film unit's sheet elements to effect a diffusion 
transfer process after photoexposure. 
Each film unit's sheet elements, and the rupturable container are bound 
together by a binding element 42 which overlaps their lateral edges and 
has portions adhered to their outwardly facing surfaces. The peripheral 
edges of the binding element 42 which terminate on the outer surfaces of 
the transparent sheet 44 are generally coextensive with the aperture 39 of 
the film cassette 32 and as such define the area of each film unit 34 
which may be exposed through the top transparent sheet 44. Also the 
longitudinal edges of the film unit's sheet elements which are bound by 
the element 42 operate in a well-known manner to at least in part define 
the thickness of the layer of processing fluid which can be spread between 
the film unit's sheet elements. 
An example of such a film cassette is described in considerable detail in 
U.S. Pat. No. 3,872,487 issued to Nicholas Gold on March 18, 1975 and 
entitled "Photographic Film Assemblage and Apparatus" and of such film 
units in previously mentioned U.S. Pat. Nos. 3,415,644; 3,594,165; and 
3,761,268. 
The body 12 also includes a generally planar rear wall 13 slanted at a 
predetermined angle with respect to both the film cassette 32 and the 
optical axis, OA, of the objective taking lens 20. Attached to the 
interior of the rear wall 13, but not shown, is a trapezoidalshaped mirror 
positioned along the optical axis, OA, intersecting it at a predetermined 
angle, to provide a folded optical path between the objective taking lens 
20 and the forwardmost one of the stacked array of film units 34. With 
this optical arrangement, rays from a scene which emerge from the 
objective taking lens 20 are reflected from the mirror toward the film 
units 34. 
Exposure of the film units 34 is regulated automatically by a well-known 
exposure control system which is located, but not shown, behind the front 
cover's vertical forward wall 18. 
Located to the right of the objective taking lens 20 in an optical system 
22 which is used to direct scene light to a photodetector (not shown) 
which forms part of the camera's exposure control system. 
To the left of the objective taking lens 20 is a camera start button 24 
which, when actuated, initiates, in a well-known manner, a camera 
operating cycle. 
Once a camera operating cycle is initiated, photoexposure of a forwardmost 
one of the film units 34 is effected in the manner previously outlined. 
The photoexposed film unit is then advanced toward the forward end of the 
camera 10 where it is brought into engagement with a film processing 
apparatus 46 which includes improved rollers according to the present 
invention. 
Advancement of a photoexposed film unit 34 is accomplished via a pick 
member 40 which fits a slot 38 of the film cassette housing 36 and engages 
a portion of the film unit's trailing edge. The pick member 34 is actuated 
by a well-known film advancing apparatus to which it is attached to move 
toward the processing apparatus 46 a predetermined distance while pulling 
a photoexposed film unit 34 along with it. 
Such a film advancing arrangement is described in considerable detail in, 
for example, U.S. Pat. No. 3,047,192 issued to Bruce K. Johnson et. al. on 
Sept. 6, 1977 and entitled "Photographic Apparatus With Sequencing 
System". 
The film processing apparatus 46 is mounted in a well-known manner on the 
door 16 to pivot downwardly thereby providing access to the film cassette 
receiving chamber 30 so that the film cassette 32 can be loaded or removed 
therefrom. As an example of this arrangement, reference may be had to U.S. 
Pat. No. 3,974,510 issued to Andrew S. Ivester on Aug. 10, 1976 and 
entitled "Mounting Apparatus for a Spreader Roller Assembly". 
The processing apparatus 46 comprises a "U"-shaped support bracket 48 which 
includes a base 54 attached to the door 16. The base 54 has two spaced 
apart vertical legs, 50 and 52, depending upwardly therefrom. Formed in 
each vertical leg, 50 and 52, are vertically oriented slots, 56 and 58, 
respectively. Slidably disposed in each vertical slot, 56 and 58, are 
complementary configured bearing blocks, 60 and 62, respectively, in which 
are mounted for rotation the journals of a cylindrical bottom roller 66. 
The bottom roller 66 thus arranged can rotate with respect to the bearing 
blocks, 60 and 62, while the bearing blocks, 60 and 62, can slide up or 
down in their respective slots, 56 and 58. 
Opposed end portions of a bow-shaped spring 68 engage, respectively, the 
bottoms of the bearing blocks, 60 and 62, to resiliently urge the roller 
66 upwardly. 
Rotatably mounted above the bottom roller 66 is a top roller 64 whose 
journals fit complementary shaped bearings (not shown) which are pressed 
into the upper end of the vertical legs 50 and 52. In this manner, the 
rollers 64 and 66 are rotatably mounted in juxtaposed relationship to 
define a pressure generating gap between them through which a film unit 34 
can be advanced by rotating the rollers, 64 and 66, in a manner to be 
described. 
Fixedly mounted on a journal 69 of the top roller 64 is a compound spur 
gear comprising a gear 70 meshed with a pinion gear 76 and a gear 72 
meshed with a gear 74 which is fixedly attached to a journal 71 of the 
bottom roller 66. 
The pinion gear 76 is driven by a well-known motor powered gear train (not 
shown) to cause the rollers 64 and 66 to rotate, via the gearing 
arrangement outlined, to advance a photoexposed film unit 34 to the 
exterior of the camera 10 while spreading its self-contained processing 
fluid in a substantially uniform thin layer between its sheet elements. 
Such a gearing arrangement is described in detail, for example, in U.S. 
Pat. No. 4,051,492 issued to Irving Laskin et. al. on Sept. 27, 1977 and 
entitled "Photographic Apparatus Gear Train Having a Unique Set of Gears". 
The cylindrical processing rollers, 64 and 66, are preferably formed of 
stainless steel and have their circumferential surfaces machined to a 
precision diameter (tolerances held to a few tenths of a mil) to 
facilitate spreading of the film unit's processing fluid. 
As seen in FIG. 1, the circumferential surfaces of each roller, 64 and 66, 
are provided with the invention's improved roughened surfaces, 78 and 80, 
respectively, to provide them with a high-friction characteristic for 
transporting film units 34 without leaving any visually perceptible marks 
on them, particularly their transparent mylar top sheets 44. 
The improved roughened surfaces, 78 and 80, as best seen in FIGS. 2 and 3, 
comprise a plurality of generally spaced apart, substantially uniform 
sized and shaped microscopic craters formed along a predetermined length 
of each roller's circumferential surface by electrical discharge machining 
in a manner to be described. 
The top roller's improved surface 78 is centrally disposed along its full 
length leaving a pair of spaced apart smooth end sections, 82 and 84, 
which are unroughened (no craters) so as to reduce the possibility of 
picking up particulate matter from the film units 34, particularly from 
their masked longitudinal edges over which the end sections, 82 and 84, 
ride while the film units 34 are transported between the rollers, 64 and 
66. 
However, the bottom roller's roughened surface 80 extends across the entire 
length of the bottom roller's circumferential surface. 
The craters, as can be seen in FIG. 2, preferably cover between 10 and 20 
percent of the area corresponding to the predetermined length of the 
roller's circumferential surfaces over which they extend. However, the 
craters may cover a higher percentage of area and still be operative but 
should not exceed 50 percent area coverage. 
Each crater, as best seen in FIG. 3, is surrounded by a substantially 
uniform annular lip which extends above its corresponding roller's smooth 
(uncratered or untextured) surface. The volume of each crater's annular 
lip generally equals the volume of the "bowl" shaped portion of the crater 
which is below the roller's smooth surface. Thus, each crater's annular 
lip represents a mass of stainless steel formed generally by displacing 
material with a minimum stock removal. 
The height to which each annular lip extends above the smooth roller 
surface is chosen so that it provides an increase in friction compared to 
the unroughened roller. However, the lip height is not so high as to cause 
visually percetible marks in the film units 32. 
For Polaroid Corporation's "SX-70 Land" type film, it has been found that 
the lip height should not exceed 0.00035 inches. However, the preferred 
mean lip height for the embodiment illustrated is 0.00016 inches with a 
standard deviation of 0.00006 inches. 
The mean diameter of the craters of the illustrated embodiment is 0.0014 
inches with a standard deviation of 0.0004 inches, the mean number of 
craters per square inch of surface area of the illustrated embodiment is 
80,000 and its surface roughness as measured with a standardized 
profilometer (Bendix Model S-48 Proficorder) is between 40 and 60 
microinches/inch (AA). 
Structured in this manner, the improved roughened surfaces, 78 and 80, of 
the rollers, 64 and 66, respectively not only are provided with a 
high-friction, low-abrasion characteristic but, as well, are configured to 
minimize pick up of particulate matter from the film units 34 and to 
maintain the effectiveness of each roller's precision diameter so that 
substantially no change in its fluid spreading performance results from 
the presence of the craters. 
It is important that the craters be generally spaced apart to minimize 
pickup of particulate matter from the film units. If build up of 
particulate matter were to occur, the high-friction characteristic gained 
by the addition of the craters would be reduced thereby defeating their 
purpose. An additional problem caused by build up is a change in the 
roller's precision diameter causing it to have an effective diameter 
larger than intended. The effective diameter can also change if too many 
craters are applied to the roller's surface, i.e. more than 50% by area 
coverage, and are spaced too close together. 
An electrical discharge machining apparatus 86 by which the craters can be 
formed in the roller's circumferential surfaces according to the criteria 
outlined above is diagrammatically illustrated in FIG. 4 to which 
reference is now made. 
A roller 94 is mounted for rotation at a controlled angular speed. The 
roller is coupled to the positive end of a D.C. source 88 via a 
conventional EDM pulse control circuit 90 while the negative end of the 
D.C. source is coupled to an electrode 92. The electrode 92 is mounted for 
controllable movement along the length of the roller 94 and toward its 
surface to establish a gap between the electrode and roller surface. This 
may be accomplished in a well-known manner as, for example, by using a 
servomechanism designed for this purpose. The electrode 92 as shown is 
shaped to the roller's surface covering only a fraction of its 
circumference and is also substantially narrow compared to the roller's 
length. As is well-known the roller 94 and electrode 92 are immersed in a 
suitable dielectric fluid to effect the EDM process. 
With the apparatus 86, the roller is rotated at a fixed angular speed after 
which the electrode 92 is moved along its length at a fixed linear 
velocity in the direction, X, traversing the roller's length from end to 
end just once. 
During the electrode traverse, the craters are randomly formed on the 
roller's surface in a generally spaced apart relationship. The actual 
size, depth and distribution of the craters depends, of course, on such 
parameters as electrode to surface gap, power transferred during arc 
discharge, duration of arc discharge, polarity of the electrode and 
roller, and the relative movement of the electrode with respect to the 
roller surface. 
The surface of the illustrated embodiment, for example, was achieved by 
rotating the roller (approximately 1/4 inch diameter) at 1850 RPM while 
moving a 1/16" wide electrode across its length at a rate of 0.9 
inches/second. Power was set at 7.5 amp. .mu.sec. and pulsed on and off 
every 10.0 microseconds--5 microseconds on and then -5.0 microseconds off. 
The initial surface finish of the uncratered roller was generally less 
than 16 microinches/inch (AA). 
Certain changes may be made in the above described embodiment without 
departing from the scope of the invention, and those skilled in the art 
may make still other changes according to the teachings of the disclosure. 
Therefore, it is intended that all matter contained in the above 
description or shown in the accompanying drawings shall be interpreted as 
illustrative and not in a limiting sense.