Sheet film buffer station

In an electrographic copier, a buffer station for storing discrete sheets, adapted to have transferable images formed respectively thereon, and for distribution of such sheets into a track assembly where such sheets are transported into operative relation with electrographic process stations of such copier. The buffer station safely stores a plurality of sheets in spaced relation to prevent contact between adjacent sheets. The buffer station is indexable relative to the track assembly for alignment with such track assembly so as to receive a sheet from or distribute a sheet to the track assembly. The stored sheets are selectively released from the buffer station when respectively aligned with the track assembly.

BACKGROUND OF THE INVENTION 
This invention relates generally to electrographic copier apparatus 
utilizing a plurality of discrete film sheets, and more particularly to a 
sheet film buffer station for such apparatus. 
In copending U.S. patent application Ser. No. 427,238 filed Sept. 29, 1982 
in the name of Kindt, an electrophotographic copier is described which 
utilizes a plurality of discrete sheets of photoconductive film. The film 
sheets are transported seriatim about a continuous path track assembly 
into operative relation with electrographic process stations. In the 
reproduction process, in order, each film sheet is uniformly charged, 
exposed to a light image of a document to be reproduced to form a charge 
pattern on such sheet, and developed with pigmented thermoplastic marking 
particles electrostatically attracted to the charge pattern to form a 
transferable image corresponding to the document image. The transferable 
image is then transferred to a receiver member to form the document 
reproduction and the sheet is cleaned for reuse. An advantage to using the 
plurality of discrete film sheets, as contrasted to the use of a 
continuous photoconductive web or drum, is that the rate of movement of 
the respective film sheets through the process stations can be varied to 
optimize the operation of each process station on the film sheets. 
The path length of the track assembly is desirably long enough to 
accommodate the total number of film sheets between the last station of 
the reproduction process and the first station. The reason for having such 
path length is so that, after completion of a reproduction run, no sheet 
remains in intimate relation with any process station where damage to that 
sheet by remaining in such station could occur. Alternatively, the track 
assembly may include a storage chamber, or buffer station, to hold the 
film sheets between reproduction runs. The employment of a buffer station 
has significant advantages over the continuous path track assembly in that 
it shortens the overall path length of the track assembly. That is, the 
distance between the last process station and the first station, required 
to accommodate the total number of film sheets, is reduced. Further, the 
buffer station can store film sheets for a time sufficient to compensate 
for any variation in the time it takes for individual sheets to complete 
their travel through a cycle of the reproduction process. By selectively 
holding individual sheets in the buffer station for an appropriate length 
of time, the sheets are prevented from bumping into one another due to a 
cummulative effect of different travel speeds of respective sheets. 
A buffer station for rigid photoconductive film plates is shown in U.S. 
Pat. No. 3,698,602, issued Oct. 17, 1972, in the name of Gnage. In the 
buffer station of this patent, the film plates, with integral spacers, are 
in contact with one another and progress seriatim from an entrance 
location to an exit location. Accordingly, such station would not be 
suitable for use with non-rigid film sheets. Such plates must be 
maintained separated by the spacers to prevent damage to the plate 
surfaces, such as by rubbing contact between the surfaces of adjacent 
plates. Moreover the travel path of the plates through such buffer station 
elongates the total plate travel path (when the distance necessary to 
travel between entrance and exit location of the buffer station is 
included). Additionally, such buffer station only allows distribution of 
the plates from the station into the travel path in the same order in 
which they are received in the station (first plate in is first plate 
out). 
SUMMARY OF THE INVENTION 
This invention is directed to a buffer station for discrete sheets, adapted 
to have transferable images formed respectively thereon, and employed for 
making reproductions in an electrographic copier. The buffer station 
safely stores such film sheets without damage to the sheet surfaces and 
distributes such sheets into a track assembly where such sheets are 
transported into operative relation with electrographic process stations 
of such copier. A plurality of sheets are stored in the buffer station in 
spaced relation to prevent contact between adjacent sheets. The buffer 
station is indexable relative to the track assembly for alignment with 
such track assembly so as to receive a sheet from or distribute a sheet to 
the track assembly. The stored sheets are selectively released from the 
buffer station when respectively aligned with the track assembly. 
The invention, and its objects and advantages, will become more apparent in 
the detailed description of the preferred embodiment presented below.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the accompanying drawing, an electrographic copier 10 
employing discrete film sheets S transported about a track assembly 12 is 
schematically shown in FIG. 1. The track assembly 12 is arranged in a 
closed loop path associated with typical electrographic process stations. 
Film sheets, transported about the track assembly 12 in the direction of 
arrow A, are successively brought seriatim into operative relation with 
such electrographic process stations to enable copies of input information 
(e.g. documents) to be reproduced on such sheets respectively. That is, 
one film sheet is employed for making one reproduction. The discrete film 
sheets are formed, for example, from material including a photoconductive 
layer such as described in U.S. Pat. No. 3,615,414 issued Oct. 26, 1971 in 
the name of Light. A buffer station 14 according to this invention, for 
safely storing and selectively distributing film sheets, is located in a 
portion of the path of the track assembly 12 between the last station of 
the reproduction process cycle (cleaning station) and the first station 
(charger). 
Control of the copier 10 is accomplished by a logic and control unit L 
including a microprocessor for example. The microprocessor receives 
operator input signals from an input panel P and timing signals, for 
example from sensors (not shown) detecting transport of the film sheets 
about the track assembly. Based on such signals and a program for the 
microprocessor, the unit L produces signals to control the transport of 
the film sheets and the timing of operation of the various electrographic 
process stations for carrying out the reproduction process. The production 
of a program for a number of commerically available microprocessors such 
as INTEL model 8080 or model 8085 microprocessor (which along with others 
are suitable for use with the invention), is a conventional skill well 
understood in the art. Programmer having ordinary skill in the art to the 
particular details of any such program would, of course, depend on the 
architecture of the designated microprocessor. 
The buffer station 14 includes a housing 16 and a support member 30 for 
such housing (see FIGS. 2 through 4). The housing 16 is defined by a pair 
of side walls 18a, 18b maintained in a fixed spacial relation by brace 
members 22. A plurality of parallel ribs 20a, 20b are connected to and 
extend perpendicularly from the side walls 18a, 18b respectively. The ribs 
20a, 20b form opposed cavities 24 for receiving the marginal edge portions 
of discrete film sheets S, and divide the housing 16 into a plurality of 
chambers for storing the discrete film sheets respectively in spaced 
relation. The dimension of the ribs 20a, 20b, measured from the side walls 
18a, 18b respectively is selected to be of an extent where only that 
portion of the marginal edges of the film sheets outside the respective 
image-receiving surface areas is contacted by such ribs. The spaced 
relation of the film sheets in the chambers prevents the sheets from 
rubbing against one another and scratching or otherwise damaging an 
image-receiving surface of a film sheet. A pair of arms 26a, 26b are 
attached to the outboard sides of brace members 22 respectively and extend 
laterally therefrom. 
The support member 30 is of a generally U-shaped configuration having a 
base plate 30a and upstanding side walls 30b. Roller bearings 28a, 28b, 
carried by the side walls 30b support the arms 26a, 26b for ready movement 
of the housing 16 relative to the support member 30. The support member 30 
is mounted on parallel, substantially horizontal guide rails 31 located in 
the apparatus 10 transverse to the track assembly 12. The support member 
is selectively movable along the rails 31 to locate the housing 16 in an 
operative position in line with the track assembly 12 between an upstream 
portion 12a of such assembly and a downstream portion 12b, or at a 
position accessible from the exterior of the copier 10. When the housing 
16 is located in such accessible position, an operator may preload 
discrete sheets S into the chambers or may replace any one of the sheets. 
The base plate 30a of the support member 30 is in juxtaposition with the 
bottom of housing 16. A slotted opening 32 is formed in the base plate 30a 
at a position whereby when the support member 30 is moved to locate the 
housing 16 in its operative position, the opening is adjacent to and 
aligned with the downstream portion 12b of track assembly 12. The base 
plate 30a thus serves to retain discrete film sheets S in their respective 
chambers, with the exception of the chamber aligned with the opening 32. 
A gate 34 is associated with the opening 32. The gate 34 selectively blocks 
the opening 32 to retain a film sheet in the chamber aligned with the 
opening, or clears the opening to enable the sheet in such aligned chamber 
to drop into the portion 12b of track assembly 12 under the influence of 
gravity. Of course, a suitable mechanism could be provided to positively 
feed the sheet from such chamber. The gate 34 is, for example, a compliant 
roller 36 mounted on pivotable interconnected linkage arms 38 and 40. When 
the arm 40 moves in a clockwise direction (as viewed in FIG. 2), arm 38 
moves the roller 36 to the right away from the opening 32; conversely, 
when the arm 40 moves in a counterclockwise direction, arm 38 moves the 
roller to the left to block the opening 32. The compliant nature of the 
roller 36 causes a portion of the roller to enter the opening and form a 
substantially planar surface with the sheet supporting surface of plate 
30a. In this manner a film sheet aligned with opening 32 is prevented from 
prematurely entering the opening. 
Movement of the housing 16 to align the film sheets in the chambers 
respectively with the track assembly 12 is effected, for example, by a 
reversible indexing motor M controlled by the logic and control unit L. 
The motor M rotatably drives a gear 42 supported to mesh with a rack 44 
fixed on arm 26a. The gear 42 is rotated by the motor M through a 
preselected angular displacement (either clockwise or counterclockwise as 
viewed in FIG. 2) to move the rack, and thus the housing 16, transversely 
through a distance substantially equal to the distance between 
longitudinal centerlines of adjacent chambers. Accordingly, the actuation 
of the motor M selectively indexes the chambers for the desired alignment 
of such chambers respectively with the track assembly. 
In operation, with a desired number of discrete film sheets S preloaded in 
respective housing chambers, and with the housing in its operative 
position relative to track assembly 12, the motor M is energized to move 
the housing to its rightmost position against a first limit switch 46a. 
The switch 46a produces a signal indicative of the housing being in such 
position, and in response to such signal the motor M is energized to index 
the housing 16 until the first chamber containing a film sheet is aligned 
with track assembly portion 12b. Such alignment is sensed by a sheet 
detection switch 48 mounted on the base plate 30a adjacent to the opening 
32 (see FIG. 2). When the film sheet in the left-most chamber containing a 
film sheet engages the switch 48, the switch produces a signal indicating 
such chamber (and its film sheet) is aligned with track assembly portion 
12b. The motor M is then deenergized in response to such signal. 
Thereafter, when a film sheet is called for by the copier 10 for 
reproduction of input information, the gate 34 is actuated for movement 
away from its position where it blocks the opening 32. The aligned film 
sheet then drops, under the influence of gravity, into track assembly 
portion 12b for transport through the electrographic process stations of 
copier 10. The switch 48 detects the exit of the sheet from the chamber 
and produces a signal indicative thereof. In response to such signal, and 
after a preselected time to allow the film sheet to fully enter the track 
assembly portion 12b, the gate 34 is actuated to return to its opening 
blocking position. When more than one sheet is called for, such as for 
example upon making of multiple reproductions of the input information, 
the motor M is energized in response to the sheet exit signal to index the 
housing 16 for alignment of subsequent chambers respectively with the 
track assembly portion 12b. The gate 34 is similarly actuated at timed 
intervals so that the film sheets contained in aligned chambers 
respectively drop from such chambers into track assembly portion 12b. When 
a discrete film sheet has completed its travel about the operative path 
through track assembly 12, it is returned to the housing 16 from track 
assembly portion 12a and received in an aligned (empty) chamber. 
There are three basic operative cycles for the buffer station 14 which are 
dependent on respective modes of operation of the copier 10. In the first 
mode, only one discrete film sheet is called for by the copier 10, such as 
when only one reproduction of input information is to be made. Such one 
film sheet is released from its chamber aligned with the track assembly 
portion 12b into such portion by movement of the gate 34 away from opening 
32. After such sheet is released, the gate 34 returns to its opening 
blocking position and indexing of the housing 16 is inhibited. Therefore, 
after the released sheet completes transport about the track assembly 12, 
such film sheet returns to the same chamber from which it was released, 
and it is retained in such chamber for subsequent use. 
In a second mode, a particular number of film sheets (equal to or less than 
the total number of available film sheets) are called for by the copier 10 
corresponding, for example, to the number of reproductions to be made. The 
film sheets are sequentially released from their respective chambers into 
track assembly portion 12b by selective movement of the gate 34 in timed 
relation with indexing of the housing 16 to the left (as viewed in FIG. 2) 
to respectively align the chambers with such track assembly portion. Such 
indexing of the housing is effected by the motor M in the above described 
manner. After the release of the last of the particular number of film 
sheets from its respective chamber, indexing of the housing 16 is 
inhibited and the housing remains in the position where such chamber is in 
alignment with the track assembly portion 12a to receive the first of the 
film sheets returning to the buffer station 14. The first returning film 
sheet (first film sheet released from the buffer station) is returned to 
such chamber, and such return is sensed by switch 48. Switch 48 produces a 
signal indicative of the return of such film sheet, and in response to 
such signal the housing is indexed to the right to align the adjacent 
chamber with portion 12a to receive the next returning film sheet. This 
sequential indexing of the housing 16 is repeated as the remaining sheets 
are returned to respective chambers. 
It is apparent that in this second operative cycle of the buffer station 
14, the film sheets are shuffled on return to chambers; that is, the 
sheets are returned to respective chambers in a reverse order from the 
order in which they were originally stored in the chambers. Thus the last 
film sheet returned to the buffer station during an operative cycle of the 
buffer station becomes the first sheet used in a subsequent operative 
cycle. This reversal of the order of the film sheets in the chambers of 
the buffer station assures that the sheets are statistically used 
substantially equally. Equalization of the use of the film sheets serves 
to prolong the useful life of the sheets. 
In a third mode of operation of the copier 10, a number of reproductions 
greater than the number of available film sheets are called for. During 
this mode of operation (reproduction run), the film sheets are 
sequentially released from their respective chambers into track assembly 
portion 12b by selective movement of the gate 34 in timed relation with 
indexing of the housing 16 to the left, as described with reference to the 
second mode of operation, until the housing engages limit switch 46b and 
the sheet in the last (right-most) chamber is released. After release of 
the last film sheet, indexing of the housing 16 is inhibited and the 
housing remaining in its left-most position with the right-most chamber 
aligned with the track assembly portions 12a, 12b. The film sheets are 
then continuously transported about the track assembly (and through such 
aligned chamber). The gate 34 is held out of its opening blocking position 
during this continuous transport for free passage of the film sheets 
through the buffer station. Alternatively, the gate may be moved into its 
opening blocking position in timed relation with return of a film sheet to 
the aligned chamber (momentarily stopping such sheet) and then moved to 
its position away from the opening to insure that each film sheet leaves 
the chamber at a preselected time. At the end of the reproduction run, the 
film sheets are returned for storage in respective chambers in a similar 
manner to that described with reference to the second mode of operation. 
During the continuous portion of this reproduction run, the path length 
about the track assembly 12 through right-most chamber is the same for 
each film sheet and is the minimum distance of sheet travel for each cycle 
about the track assembly. While the travel speed of individual sheets may 
vary during transport through selected electrographic process stations, 
the average speed for each film sheet is substantially the same for its 
complete cycle about the track assembly. Therefore, the respective film 
sheets travel over the same path length, and the travel time about such 
path during one cycle is substantially the same for each sheet. Such equal 
path length and travel time facilitates timing and control of the 
electrographic process stations of the copier 10, and improves 
productivity by providing a minimum distance of travel and travel time for 
each film sheet about the track assembly 12. 
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.