Photoconductive drum having expandable mount

A photoconductive drum has a flexible photoconductive loop and an expandable mount. The mount includes a shell with a slit allowing the shell to expand. A pair of wedges are moved toward each other on a shaft. Cam surfaces on the wedges push against chamfered corners on ribs extending inward from the shell to expand both ends of the shell. The shell assumes the shape of the loop even though loop is slightly conical.

TECHNICAL FIELD 
This invention relates to electrophotography and more specifically to a 
photoconductive drum of the type including a photoconductive loop mounted 
on an expandable mount. 
BACKGROUND ART 
U.S. Pat. No. 3,536,485, Roth et al is illustrative of a number of 
references which show a photoconductive drum in which the photoconductive 
surface is part of a flexible web. The web is first formed into an endless 
loop. The loop is mounted on a mandrel which has a natural size larger 
than the interior of the loop but which is contracted for purposes of 
mounting. The mandrel is allowed to expand to hold the loop and form a 
photoconductive drum. 
Drums formed in this manner are less expensive than the traditional 
photoconductive drum in which the photoconductive layers are coated on the 
exterior of a continuous cylinder. The loops can be formed by traditional 
web coating and finishing operations in which extremely high quality is 
obtainable at low cost. When the photoconductive surface has worn out, the 
loop is replaced. This has an obvious advantage over reconditioning a 
coated drum which requires grinding and/or solvent treating the sensitive 
surface, finishing and recoating. 
Photoconductive loops are cut from a larger web. They include a suitable 
support, for example, polyester, with the necessary electrophotographic 
layers coated thereon, for example, a conductive layer and one or more 
photoconductive and other layers that make up a modern photoconductive 
plate or web. After cutting to the desired size the loops are formed by 
connecting two opposite ends together at a seam, which may be 
ultrasonically formed. The seaming process itself is extremely well 
developed. However, at present, it is not possible to consistently 
eliminate meaningful amounts of conicalness from the final loop. That is, 
in general, the circumference of the loop at one end will be slightly 
different from the circumference at the other end. The loop, rather than 
being a perfect cylinder is slightly conical in shape. 
Some conicalness in the final drum can be absorbed in the system by 
mounting components against the drum. That is, if the left side of a 
development station is maintained the same distance from the drum that the 
right side of the development station is maintained, the conicalness in 
the drum itself will not show up as an image defect in the final print or 
copy. However, if the mandrel for a loop is a perfect cylinder, and the 
loop itself is conical there will necessarily be some looseness of the 
loop at the larger circumference end. Such looseness permits dirt to get 
under the loop, which can cause image defects of a far more serious nature 
than conicalness of the drum itself. The looser edge acts differently to 
hard and soft backed stations than does the tight edge. In color systems, 
image registration can vary between the loose and tight edge. 
DISCLOSURE OF THE INVENTION 
It is an object of the invention to provide a photoconductive drum 
generally of the type including an expandable mount supporting a 
photoconductive loop in which the tendency toward looseness of the loop at 
one of the opposing ends is lessened or eliminated. 
This and other objects are accomplished by an expandable mount for the loop 
which mount includes a generally cylindrically-shaped shell having opposed 
open ends and an axial slit permitting expansion of the shell. A pair of 
wedges are positioned inside the shell, which wedges are movable toward or 
away from each other. Cam surfaces associated with the shell and the 
wedges convert force applied changing the distance between the wedges to a 
pair of forces expanding opposite ends of the shell. 
With such structure comparable forces expanding the shell at essentially 
each end of the shell will cause the shell to generally assume the shape 
of the loop. Since any loop has some stretch to it, a portion of the 
conicalness will be removed by the mandrel causing somewhat more stretch 
to the smaller circumference end of the loop. The rest of the conicalness 
will be conformed to by the mandrel leaving no looseness at the larger end 
of the resulting photoconductive drum. 
According to a preferred embodiment the shell is formed of a single casting 
which includes a cylindrically shaped outer surface and ribs projecting 
from the inside of the shell toward its center. The ribs have chamfered 
edges which form shell cam surfaces. A pair of cylindrical wedges are 
mounted on a shaft. The wedges have cam surfaces which mate with the 
chamfered surfaces. The shaft has clamp threads upon which a suitable 
clamp nut can be turned to move the wedges closer together. As the nut is 
tightened the wedges move closer together and the cam surfaces expand 
opposite ends of the shell with generally equal forces. These forces are 
resisted by the loop causing the shell to generally assume the shape of 
the loop, with some stretching.

DISCLOSURE OF THE PREFERRED EMBODIMENTS 
According to FIG. 2 a photoconductive drum 1 includes a photoconductive 
loop 2 and an expandable mount 3 therefor. The mount 3 includes a shell 4, 
shown best in FIG. 1. The shell 4 is cast out of aluminum or other 
suitable material as a complete cylinder. After casting, a slit 9 is cut 
axially to permit the shell to be expanded. In its unstressed condition, 
it is enough smaller than the inside of loop 2 that loop 2 may be fit over 
it. Cast to the inside of shell 4 are ribs 5 which have chamfered corners 
6 at each end. 
A shaft 10 runs the length of the shell and includes a fixed wedge 11 at 
one end. Wedge 11 can be machined integrally with shaft 10 or it can be 
held on shaft 10 by a pair of nuts or the like. It is shown in FIG. 2 
formed integrally with shaft 10. A second wedge 13 of substantially the 
same shape as wedge 11 is positioned on shaft 10 and is movable axially 
thereon. The left end of shaft 10 as seen in FIG. 2 has a sleeve 20 with 
clamp threads on which second wedge 13 is mounted. A clamp nut 21 has 
interior threads mating with the clamp threads on sleeve 20. 
In assembly, shell 4 in its contracted and relaxed condition receives loop 
2 as shown in FIG. 2. Shaft 10 with wedge 11 fixed thereon is inserted 
from the right end of shell 4. Wedge 13 and nut 21 are positioned on the 
left end of shaft 10. 
Wedges 11 and 13 have cam surfaces 14 and 15 respectively which mate with 
the chamfered corners 6 of ribs 5. Ideally, each of these surfaces are at 
45 degree angles so that any reduction in the distance between wedges 11 
and 13 will increase the forces on the ribs forcing the shell to expand. 
As nut 21 is tightened, the wedges 11 and 13 move closer together applying 
substantially equal forces on chamfered corners 6 forcing the end portions 
of the shell to expand with substantially equal force. As the loop begins 
to restrict the expansion of the shell, its smallest circumference end 
both tends to stretch slightly and also tends to resist the movement of 
wedge associated with that end thereby causing the other end of shell 4 to 
expand more than the end of the shell at the narrower end of the loop. The 
shell thus tends to take the conical shape of the loop as stretched. The 
final product is a photoconductive drum that has somewhat less conicalness 
than the unstretched loop but also has a shell which is slightly conical 
to match it. The slit 9, of course, is slightly different width at one end 
than the other. 
The chamfered ribs 5 are shown as a preferred embodiment. With well 
machined parts, the wedges could actually rest against the outside edges 
of the inner wall of the shell, the direction of the expanding force 
coming entirely from the shape of the wedges. Similarly the wedges could 
lack the slanted surfaces 14 and 15 relying totally on the slanted 
surfaces 6 for the change in direction of the force from nut 21. The 
surfaces 6, 14 and 15 are shown at generally 45 degrees to the axis. 
Obviously, these surfaces could be at other inclines depending on the 
mechanical advantage desired from their contact. Note that substantial 
mechanical advantage is added to this system by the pitch of the threads 
of nut 21. 
FIG. 3 shows an embodiment in which the shell 4 has inclined surfaces 30 
which respond to curved surfaces 31 on wedges 11 and 13. 
The invention has been described in detail with particular reference to a 
preferred embodiment thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention as described hereinabove and as defined in the appended claims.