U.S. patent number 3,690,760 [Application Number 05/131,311] was granted by the patent office on 1972-09-12 for electrostatic printing system.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Willard K. Banks, James L. Lyon.
United States Patent |
3,690,760 |
Banks , et al. |
September 12, 1972 |
ELECTROSTATIC PRINTING SYSTEM
Abstract
An electrostatic printing apparatus wherein photoconductive
elements are individually movable through process stations for
charging, exposing and developing an electrostatic image, and
wherein the photoconductive element is fed through a process buffer
means between each of the stations so that asynchronous operation
results. A plurality of the photoconductive elements with the
electrostatic image are cycled a predetermined number of times
through the development and transfer stations at a higher rate so
that multiple copies can be printed from a single image deposition
for each of the photoconductive elements without slowing the
operation of the other parts of the system.
Inventors: |
Banks; Willard K. (Cupertino,
CA), Lyon; James L. (Los Gatos, CA) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
22448873 |
Appl.
No.: |
05/131,311 |
Filed: |
April 5, 1971 |
Current U.S.
Class: |
399/76;
399/361 |
Current CPC
Class: |
G03G
15/266 (20130101); G03G 21/14 (20130101); G03G
2215/00966 (20130101) |
Current International
Class: |
G03G
15/26 (20060101); G03G 21/14 (20060101); G03G
15/00 (20060101); G03g 015/00 () |
Field of
Search: |
;355/3,14,16,17 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Horan; John M.
Assistant Examiner: Mathews; Alan A.
Claims
What is claimed is:
1. An electrophotographic reproducing apparatus wherein a plurality
of resilient recording members are passed through a series of
process stations for producing and transferring an image for
reproduction on a copy sheet comprising:
a plurality of feeding means and a plurality of processing stations
arranged to form a first and a second separate processing path;
a plurality of means selectively actuable at each of said
processing stations for controlling said feeding means in moving
the recording members through said processing stations;
a plurality of recording member position sensing means;
program means for providing a series of signals indicative of
operations to be performed on said recording members in said
machine; and
electronic control means operable under coincident control of said
signals from said program means and said recording member sensing
means to generate signals to selectively actuate certain of said
controlling means to move said recording members along the selected
processing path to perform the operations specified by said program
means on said recording members at the selected ones of said
processing stations.
2. The apparatus according to claim 1 wherein said first separate
processing path includes a charging station and an exposure station
and said second separate processing path includes a developing
station and a transfer station.
3. The apparatus according to claim 2 wherein said charging and
said exposure operations are performed asynchronously at a first
speed and said developing and transfer operations are performed
continuously at a second speed which is a substantially greater
speed than said first speed.
4. The apparatus according to claim 2 wherein said recording
members are processed through said first processing path one at a
time and said recording members are processed concurrently a
predetermined number of operations through said second processing
path.
5. An electrophotographic reproducing apparatus wherein a resilient
recording member is passed through a series of process stations for
producing and transferring an image for reproduction on a copy
sheet comprising:
a plurality of feeding means and a plurality of processing stations
arranged to form a first and a second separate processing path;
a plurality of means selectively actuable at each of said
processing stations for controlling said feeding means in moving
the recording members through said processing stations;
a plurality of recording member position sensing means;
program means for providing a series of signals indicative of
operations to be performed on said recording members in said
machine; and
electronic control means operable under coincident control of said
signals from said program means and said recording member sensing
means to generate signals to selectively actuate certain of said
controlling means to sequentially move a plurality of said
recording members along said first processing path to produce a
predetermined electrostatic image to be copied on said recording
members; and
electronic control means operable under coincident control of said
signals from said program means and said recording member sensing
means to generate signals to move a plurality of said recording
members continuously through said second processing path a
plurality of times to produce one copy of said image each time said
recording member is moved through said second processing path.
6. The apparatus according to claim 5 additionally comprising
signals from said program means for specifying the number of
reproductions to be made of the image produced on each of said
recording members;
means for recording the number of reproductions produced for each
of said recording members moving through said second processing
path; and
means for ejecting said recording member from said second
processing path when said specified number of reproductions has
been produced.
7. The apparatus according to claim 6 additionally comprising means
for moving a recording member ejected from said second processing
path to said first processing path.
8. The apparatus according to claim 7 additionally comprising means
for moving the ejected recording member through a cleaning station
and an erase station as said member is moved from said second to
said first processing path.
9. An electrophotographic reproducing apparatus wherein a resilient
recording member is passed through a series of process stations for
producing and transferring an image for reproduction on a copy
sheet comprising:
a plurality of temporary storage means each capable of storing a
plurality of said recording members;
a first feeding means for moving a recording member from the first
of said temporary storage means through a charge station to the
second of said temporary storage means to produce a uniform charge
on said recording member;
a second feeding means for moving a recording member from said
second storage means through an exposure station to the third of
said temporary storage means to produce an electrostatic image on
said recording member;
a third feeding means for moving a recording member from said third
temporary storage means through a developing and a transfer station
to produce a reproduction of said image on a copy sheet;
a plurality of recording member position sensing means mounted
adjacent to said temporary storage means;
program means for providing a series of signals indicative of
operations to be performed on said recording members in said
machine; and
electronic control means operable under coincident control of said
signals from said program means and said record member position
sensing means to generate signals to selectively actuate certain of
said feeding means to move said recording members through the
selected processing stations to perform the operations specified by
said program means.
10. The apparatus according to claim 9 wherein said third feeding
means comprises means for simultaneously mounting a plurality of
recording members for movement through a continuous processing
path.
11. The apparatus according to claim 10 additionally comprising
means for separately sensing each of said recording members being
moved by said third feeding means.
12. The apparatus according to claim 9 wherein said third feeding
means comprises a continuously rotatably drum member.
13. The apparatus according to claim 11 additionally
comprising:
means for receiving signals from said program means indicating the
number of reproductions to be made from each of said recording
members;
means for counting the number of reproductions produced from each
of said recording members moved by said third feeding means;
and
means for ejecting a recording member from said third feeding means
when the predetermined number of reproductions has been
produced.
14. The apparatus according to claim 13 additionally comprising
means for moving said ejected recording member to said first
temporary storage means.
15. The apparatus according to claim 14 additionally
comprising:
a cleaning station;
an erase station; and
means for moving said ejected recording member through said
cleaning station and said erase station when said recording member
is being moved to said first temporary storage means.
16. The apparatus according to claim 9 additionally comprising:
timing means for timing the elapsed interval since a recording
member has been moved through the charge station by said first
feeding means;
means responsive to the passage of a predetermined interval, after
charging a recording member, to generate a time expired signal;
an eject mechanism; and
means responsive to said time expired signal to energize both said
second feeding means and said eject mechanism to move said
recording member from said second to said first temporary storage
means.
17. The apparatus according to claim 9 wherein said recording
members comprise:
a resilient photoconductive sheet member;
a top support member extending laterally beyond said sheet member,
said top support member being terminated in enlarged end
portions.
18. The apparatus according to claim 17 wherein said temporary
storage means comprises a pair of rail members, said rail members
being spaced so that said enlarged end portions of said sheet
support member laterally position the recording member in said
temporary storage means.
Description
BACKGROUND OF THE INVENTION
This invention relates to electrostatic printing apparatus and more
particularly to apparatus for asynchronously moving a
photoconductive element through processing stations so that
multiple copies can be printed from a single image deposition.
Prior art printing and copying apparatus normally uses continuous
photoconductors in the form of drums or belts with the processing
stations spaced along the surfaces of the photoconductors. The
process by nature is continuous and synchronous and this operation
produces one copy per cycle. Due to the synchronous operation, this
apparatus does not permit individual process speeds within the
total process to be tailored for optimum operation. In addition,
the photoconductor has a limited life due to the continuous cycle
of charging and cleaning the photoconductive surface. It is
therefore the major object of this invention to provide apparatus
which utilizes individually movable photoconductive elements in its
operation.
It is another object of this invention to provide apparatus in
which the station-to-station operation is asynchronous so that
individual process stations can be tailored for optimum
operation.
SUMMARY OF THE INVENTION
Briefly, according to the invention, there is provided
electrostatic printing apparatus which utilizes individually
movable photoconductive elements which are moved through the
process stations on an asynchronous basis to charge, expose and
develop an electrostatic image on the photosensitive member with
each of these operations being separated by process buffer means
wherein the photosensitive member can be temporarily stored. A
plurality of the photosensitive members with the electrostatic
image can be processed multiple cycles at a higher speed through
the developing and transfer stations to provide multiple copies of
the image without slowing the throughput of the system.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic view showing the possible paths of the
photosensitive element through the printing apparatus;
FIG. 2 is a side diagrammatic view of the printing apparatus
comprising the invention;
FIG. 3 is a schematic block diagram of control means 100 of the
machine of FIG. 2;
FIG. 4 is a view showing the apparatus for pickup of the
photosensitive element from one of the process buffer means;
FIG. 5 is a view showing in greater detail the means for moving the
photosensitive elements along the transport path; and
FIG. 6 is a perspective view of drum member 62 showing the mounting
of control members;
FIG. 7 is an enlarged view of the means for loading and retaining a
sheet on drum member 62;
FIG. 8 is an alternate embodiment for the exposure station
utilizing flash exposure;
FIG. 9 is a schematic block diagram of the controls circuits for
the printing apparatus;
FIG. 10 is a schematic block diagram of the control circuits for
shift register 138;
FIG. 11 is a schematic block diagram of the control circuits for
timing means 136;
FIG. 12 is a schematic block diagram of the control circuits for
counting means 140.
DETAILED DESCRIPTION OF THE EMBODIMENT
The electrostatic printing apparatus comprising the invention
utilizes individually movable photosensitive elements. The movement
of the sheets through the machine is controlled by a plurality of
electromagnetic control means which are selectively energizable to
select the proper mechanical device to perform the programmed
printing function in the machine. A control means is provided to
develop electrical signals to selectively actuate the
electromagnetic control means according to both programmed
functions and control signals from the mechanical devices.
Referring to FIG. 1 of the drawings, the printer comprises supply
buffer A which holds a sufficient supply of sheets. Upon demand, a
sheet or sheets are withdrawn and passed through a sensitizing
station, CHARGE, at a relatively constant velocity to produce a
uniform charge on the sheet, then to a holding station at buffer B.
Subsequently a charged sheet is brought to the EXPOSE station for
exposure to selectively discharge areas of the sheet to form a
latent electrostatic image on the sheet of the image to be printed.
The exposure operation may be either continuous or incremented as
the application requires. Once through the EXPOSE station, the
sheet with the latent image proceeds either to a holding station at
buffer C, or is recycled back along the recharge loop to supply
buffer A if required for any reason. From buffer C the exposed
photoconductor proceeds to the DEVELOP and TRANSFER stations. Here
the latent image is developed and transferred to a copy sheet after
which the image is permanently fixed to the sheet at the FUSE
station. At this point multiple copies can be made by recycling the
exposed photoconductor back through the DEVELOP-TRANSFER station as
many times as there are copies required. The process speed at this
station may be faster than that at the previous or subsequent
stations. Once the desired number of copies are produced, the
photoconductive sheet is transferred through the CLEAN and ERASE
stations back to the supply buffer A for subsequent reuse.
A plurality of electrical signals is generated in the machine and
sent to control means 100 to permit the electrical control signals
to be synchronized with the mechanical movement of the sheets
through the machine. Control means 100 may comprise any suitable
device for supplying control signals to perform the desired
functions in accordance with the desired printing functions and the
output from the sensing means located throughout the processing
stations of the machine. Control means 100 may comprise the
processor of an electronic data processing system if desired. The
printer may also be operated as a stand-alone unit, in which case
the machine would have its own control circuitry built in to cycle
the machine through the desired steps to perform the processing
function of the machine.
Referring to the embodiment of the invention shown in the drawings,
the electrostatic printing apparatus utilizes individually movable
photosensitive element 20, a plurality of which are mounted in a
supply process buffer means 22. The process buffer means 22 and
other components of the printer are mounted on suitable support
means 21, 23 at either side to provide a relatively open central
area to facilitate the unimpeded movement of photosensitive
elements 20 through the process stations of the printer. A
selectively operable transport means 24 is utilized for moving the
photosensitive element 20 from the supply buffer through a charging
station 26 to place a uniform charge on the photosensitive member
as it moves through the charging station to a second process buffer
means 28. Transport means 24 as well as other transport means in
the system is provided motive power from a drive means 25 such as a
motor, For example, through suitable belts or gears (shown by
dashed lines in the drawings). A second selectively actuable
transport means 30 is provided to move the photosensitive element
through an exposure station 32 to expose the photosensitive element
to a light image to produce a latent electrostatic image on the
photosensitive element 20. Transport means 30 is disposed to
deposit photosensitive element 20 in a third process buffer means
34 preparatory to developing the electrostatic image. In the event
that the photosensitive element is not to be used for the
production of an image, a reject buffer means 36 is provided to
temporarily store the photosensitive element 20 preparatory to
moving element 20 through an erase station 38 by return transport
means 48 to supply process buffer means 22 for reuse in the
printing apparatus. A third transport means 40 is provided to move
photosensitive element 20 through a predetermined number of cycles
through a developing station 42 and a transfer station 44 to
produce the predetermined number of copies. At each of these cycles
the electrostatic image is made visible by the deposition of a
development material commonly called toner which adheres to the
photosensitive element 20 and an electric field is provided at
transfer station 44 which facilitates the transfer of the developer
material to a printing sheet 46 upon which the finished copy is
produced. After the predetermined number of copies have been
produced, photosensitive element 20 is moved by an eject transport
means 47 for temporary storage in return buffer means 49. Sheets
are positioned for movement by return transport means 48 through a
cleaning station 50 where any remaining particles of the developer
material is removed. The sheet is then moved through the erase
station 38 where any remaining electrostatic charge is discharged,
and the sheet is then returned to supply process buffer means 22
for reuse in the printing apparatus.
In the embodiment shown in FIG. 3 the control means 100 for the
machine comprises a storage means 102, a program decoder 104, clock
and cycle control means 106 and control circuitry 108 to develop
electrical signals to control electromagnets in the machine to
perform the desired function. In the case where the processor of an
electronic data processing system is used to control the machine,
the first three stated elements of the control means are normally
present and the instructions are included as part of the stored
program. In the case where the machine is operated as a stand-alone
unit, the storage device may comprise any suitable device capable
of exhibiting two stable states such as a magnetic core storage
system, an array of electronic bistable devices or any other memory
device having the operating speed and capability necessary for the
described operations. One type of control device suitable for use
with the system is the type known as a read only memory. This
device is designed for programming in a predetermined manner
dependent upon the control manifestations entered into the memory
at the start of operations. Cycling means are provided to read out
sequential program steps to an external temporary storage device
such as a register wherein a bit position of the register is
coupled to control a particular electromagnet.
To make the printer ready to process data, a manually actuated
start key is depressed to energize the start-up circuits. During
start-up all sheets are returned to the supply buffer and all
devices which require a specified time for reaching operating
condition are made ready for operation. At the end of this time a
sufficient number of sheets are charged so that the machine is then
ready to run. Further operations of the machine are then controlled
by program instructions which specify the operations to be
performed on the sheets as they are moved through the process
stations of the machine. The basic instructions for controlling the
machine are CHARGE A SHEET, EXPOSE A SHEET, EXPOSE A LINE and PRINT
N COPIES. In a CHARGE A SHEET instruction, a sheet from the supply
buffer is moved past a charging device such as a corona discharge
device so that a uniform charge is provided over the surface of the
sheet. In an EXPOSE A SHEET instruction, a charged sheet is removed
from the charge buffer and moved into position to expose an image
on the sheet and the sheet is moved from the expose transport to
the develop buffer. In an EXPOSE A LINE instruction, the expose
drive is energized to move the sheet in position for having a line
exposed. This operation is continued until a sheet is completed, at
which time the sheet is ejected to the develop buffer. In a PRINT N
COPIES instruction, the sheet is placed on a device which takes the
sheets successively past a develop station and a transfer station
at which point the developed image is transferred to a copy sheet
to which the image is permanently fused as it is moved through a
fusing station. The sheet is moved repetitively through these steps
for N-cycles and the sheet is then ejected to the return transport.
The sheet is then moved through the erase and cleaning stations as
the sheet is moved in the return transport back to the supply
buffer for further use in the machine.
Photosensitive element 20 may be any suitable device which can be
selectively moved through stations of the process. In the
embodiment of the invention shown in the drawings, the
photosensitive element 20 comprises a flexible sheet of
photoconductive material the length and width of which is somewhat
greater than the maximum size of the desired output copy image. The
element has fixed across one end an elongated support member 54
which extends outward from the edge of the sheet and terminates in
enlarged end portions 56. A support member 58 is fixed to the
bottom of the sheet and extends a relatively small distance beyond
the edges of the sheet. Support 58 produces substantial rigidity in
the lateral direction and also provides enough mass to the
photosensitive sheet so that the sheets hang substantially
vertically in the process buffer means.
The process buffer means has a capacity for storing a plurality of
photosensitive elements 20. Any suitable device can be utilized
which is operable to store the photosensitive elements and permit
the selection of one photosensitive element at a time on demand
from the process control circuits. In the embodiment of the
invention shown in the drawings, the process buffer means comprises
a pair of spaced inclined rail members 52. Rail members 52 are
spaced a distance sufficient for end portions 56 of support member
54 to extend outside the rail members thereby laterally positioning
the photosensitive sheet so that the sheet can be moved throughout
the process stations without interference from the apparatus
comprising the process buffer means or the associated transport
means.
To insure that a sufficient quantity of the photosensitive sheets
are present in the machine before the start of an operation, a
sensing means 65 is provided. In the embodiment shown in the
drawings, sensing means 65 comprises a micro switch which is
attached to side rail 52 of buffer means 22 so that end portion 56
of photosensitive element 20 contacts the operative portion of the
micro switch to generate an electrical signal which denotes to the
control circuit that buffer 22 is loaded with a sufficient number
of sheets.
Transport means 24 is provided for transporting the photosensitive
sheet from supply buffer 22 past the charging station 26. The
embodiment of transport means 24 shown in the drawings comprises a
chain and sprocket drive which has suitable placed gripper means
for engaging support member 54 of the lowermost sheet in buffer
means 22 and moving the sheet past the charging station to buffer
means 28. A charging operation is initiated by an electrical signal
CHARGE A SHEET which is coupled to energize a single revolution
clutch 66 to transmit power from the device motor to sprocket 67
which is meshed with chain 68. Two sets of gripper means 69 are
mounted at opposite points on chain 68 and these gripper means are
operative to engage support means 54 of the sheet. At the start of
a cycle of driving motion of clutch 66 one of the gripper means 69
is positioned to pick up a sheet from buffer means 22 and the other
gripper means 69 is positioned to discharge a sheet into buffer
means 28. A fixed cam means 70 is provided which cams movable
gripper jaw 71 from stationary gripper bar 72 so that gripper jaw
71 extends in the hopper means to engage the sheet (shown as full
line position in FIGS. 4 and 5). As the gripper means moves past
the lower end of the buffer, the sheet is engaged by the gripper
means to move the sheet in a vertical path past charging station 26
so that uniform charge is produced across the surface of the
photosensitive sheet due to the constant velocity drive provided by
transport means 24. A second fixed cam means 70 is provided at the
upper end of the transport so that the gripper means releases the
charged sheet and gravity moves the sheet into buffer means 28.
When no sheet is in gripper means 69 the movable jaw 71 is spring
biased to the dotted position shown in FIG. 5. Solenoid actuated
cam means 70' are located in the inoperative position shown dotted
in FIG. 5 when the solenoid is not energized. When the solenoid is
actuated the cam means 70' is moved to the operative position which
is shown in full line in FIG. 5.
Process buffer means 28 is similar in construction to process
buffer means 22; however, since photosensitive sheets 20 are
utilized on demand, the capacity of this buffer is not as great
since it is usually necessary to store only a few charged
photosensitive elements at a time to meet the demands of the
process. A large number of photosensitive materials are known which
are suitable for use in constructing sheets 20. The characteristics
of the materials vary widely and the characteristics are subject to
trade-offs to obtain the best combination of characteristics for
the particular application. One limitation in the characteristics
which may be present is a decay with time of the electrostatic
charge, the rate of which depends upon the construction of the
photosensitive sheet. To provide control over the number of charged
sheets and the elapsed time that the sheets have been charged, a
sensing means is provided. In the embodiment of the invention shown
in the drawing, the sensing means comprises a micro switch 73
mounted on the side of the rails of buffer means 28 adjacent each
of the sheets and positioned so that end portion 56 of the sheets
will energize the switches to generate an electrical signal which
designates to the control circuit that the corresponding sheet is
present. To provide control over the time the sheet has been
charged, a shift register is provided with a number of stages equal
to the number of sensing switches 73 provided. Each time one of
switches 73 is actuated the shift register is actuated to shift one
position and a timing device is provided for each sheet to
determine the time that the sheet has been charged. In the event
that the predetermined time elapses before the sheet is exposed,
transport means 30 is actuated along with eject means 84 to
transport the sheet to reject buffer means 36 for return to the
supply buffer 22 for reuse in the printer.
Transport means 30 is provided for moving a charged sheet through
the exposure station to produce a light image on the sheet which is
operable to selectively discharge the electrostatic charge on the
photosensitive element to produce an electrostatic image. In the
embodiment of the invention shown in the drawings, transport means
30 comprises a chain and sprocket drive which is selectively
controllable to provide either continuous or incremental motion of
the photosensitive sheet past the exposure station. This control is
provided by a stepping motor drive. The stepping motor drive is
operable to produce one increment of motion in response to an
electrical signal or to produce continuous drive in response to a
continuous series of electrical signals. The type of driving motion
past the exposure station is dependent upon the type of exposure
desired. The exposure station shown in FIG. 2 comprises a lens
coupled cathode ray tube 33. In this case, it is desired to expose
the sheet to successive images of lines of printing coupled from
the cathode ray tube 33 so that in this case an incremental drive
is utilized. The embodiment of the exposure station shown in FIG. 8
comprises a flash exposure station. In this case, the sheet is
moved to the proper exposure position and then stopped. The
exposure is made by a suitable light source 89 such as a flash lamp
which is directed through condenser lens 90 to the micro image
means 91 such as a microfilm slide for example. The image is
projected by projection lens 92 and mirror 93 to the sheet 20 being
held at the exposure station. The sheet is removed through the
remainder of the exposure station where the sheet is ejected into
buffer means 34.
Transport means 40 is provided to selectively move the sheet from
process buffer means 34 through developing station 42 and transfer
station 44. Developing station 42 may comprise any suitable means
for rendering the latent image on sheet 20 visible. One suitable
developing apparatus is a magnetic brush developer apparatus. A
finely divided colored material commonly called toner is intermixed
with and deposited on more coarsely divided iron filings. The toner
and iron filings are electrostatically charged with respect to each
other by triboelectric charging. The iron filings coated with toner
are placed in a magnetic field and the filing form streamers
extending along the magnetic lines of force constituting a
brush-like mass. By rotating the magnet field producing means near
the surface of the sheet 20, the magnetic brush is placed in
contact with and drawn across the surface bearing the electrostatic
image. As the brush crosses an area of the image surface having an
electrostatic charge, the charge on the surface exerts a greater
attraction for the toner than the iron filings, thereby retaining a
portion of the toner and separating it from the iron filings. As
portions of the toner are electrostatically withdrawn from the
brush, means are provided for replenishing the toner or for
constantly exchanging the used iron filings for fresh filings
coated with toner.
The sheet bearing the toned image is moved to the transfer station
where suitable transfer apparatus is utilized to transfer the toned
image to a copy member. In the embodiment shown, the transfer
apparatus comprises a conductive roll 59 which feeds printing sheet
46 adjacent to sheet 20. A charge is placed on roll 59 by power
supply V of sufficient magnitude and of a sign opposite to the
charge holding the toned image to sheet 20 so that the toned image
is attracted to printing sheet 46. As is known in the art, the
voltage V on roll 59 is chosen to prevent distortion of the
electrostatic image pattern on sheet 20 so that multiple copies of
the image can be obtained. The image is then fused to printing
sheet 46 (by means not shown) and the printed output is fed to
output hopper means 57.
In the embodiment of the invention shown in the drawings, transport
means 40 comprises a drum member 62 which is utilized to remove the
photosensitive sheet from process buffer means 34 under control of
a proper electrical signal from the control circuits. Drum member
62 is provided with a slot 74 to receive the leading edge of
photosensitive element 20 and a second slot 75 to receive the
trailing edge of element 20.
In the embodiment shown in FIGS. 2 and 7, the apparatus for loading
a sheet on drum member 62 comprises an electromagnet 41 on each
side of the sheet positioned to push support member 54 of the sheet
into leading edge slot 74 when electromagnet 41 is energized so
that the support member 54 is retained in slot 74 by a spring
retainer means 39. The remainder of the sheet is drawn along by the
drum and the trailing edge of the sheet follows guide members 37
which are spaced so that any contact with sheet 20 is in the
non-image areas. The trailing edge of the sheet follows the
curvature of guide 37 so that the bottom support member 58 is
forced into trailing end slot 75 and retained there by spring
retainer means 43.
In the embodiment shown, four sets of slots 74a-d, 75a-d are
provided so that four photosensitive elements 20 can be mounted on
drum 62 simultaneously to produce a predetermined number of copies
of the image stored upon photosensitive element 20. A sensing means
is provided to determine whether a particular slot is filled as the
slot approaches the sheets in buffer means 34. In the embodiment
shown, the sensing means comprises a plurality of microswitches
suitably mounted to the support means 21, 23. Microswitch 63 is
mounted to sense the presence of end portions 56 of photosensitive
element 20 in a slot 74 of drum member 62. When an element 20 is
not present the switch remains open and an open switch at the
sensing time causes an electrical signal SLOT OPEN to be generated.
A set of microswitches 76a-d is mounted on the support means in a
position to be operated by projections 77. In the embodiment shown,
each of projections 77a-d is radially positioned on drum 62 aligned
with one of the switches 76 so that the designation of the
approaching slot can be determined. In this manner, a particular
sheet can be identified as being in a particular slot.
One counter is provided for each slot and when it is determined
that, for example, sheet Y is in slot A, the number of copies of
sheet Y is set in the counter associated with slot A. The count can
be maintained in a hardware counter or the count can be maintained
by the associated computer when the printer is operated as part of
a data processing system. In the embodiment shown, each time the
microswitch 76 is energized for a particular slot, the associated
counter is decremented by one count. When the count reaches one, a
signal is generated which is operable to eject the photosensitive
element 20 after the next transfer operation is completed for that
slot. Photosensitive element 20 is then picked up by eject
transport means 47 which is operative to move the sheet to return
buffer means 49.
The apparatus for ejecting a sheet from drum member 62 comprises
eject means 84' which is actuated by a rotary solenoid 45. When
solenoid 45 is deenergized, eject means 84 is in the lower dotted
position (FIG. 2). When solenoid 45 is energized, eject means is
moved from the lower dotted position to the upper dotted position
and eject means 84 is returned to its original position when
solenoid 45 is deenergized. The energization of solenoid 45 is
timed so that eject means 84' reaches the upper position when a
gripper means is in position to receive the sheet.
Eject transport means 47 is similar in construction to the other
transport means; however, the speed of transport means 47 is
synchronized with the speed of drum 62 so that sheets can be
removed from the drum without slowing the overall operation of the
printer. The speed of drum 62 is normally greater than the
transport speeds up to that point due to the requirement for
producing multiple copies. The speed chosen for drum 62 is
dependent on the projected number of copies to be produced, the
characteristics of the materials to be used, and the number of
sheets that can be mounted on drum 62 at the same time. In a
particular application the speed of drum 62 was chosen at three
times the average transport rate for the charge and expose
transport means so that the average number of multiple copies can
be made without appreciably slowing the overall process.
Return transport means 48 is provided to move photosensitive
elements 20 from return buffer means 49 and reject buffer means 36
to supply process buffer means 22 for reuse in the system. In the
embodiment of the invention shown in the drawings, return transport
means comprises a chain and sprocket drive which utilizes a
plurality of gripper means 69 spaced on the chain member for
picking up sheets from return buffer means 49 and reject buffer
means 36. Return buffer means 49 comprises a pair of rail members
51 spaced to receive sheets 20. A spring member 53 is mounted over
rail member 51 and spaced to permit free movement of the support
members 54 to a position at which curved end portion 55 of spring
member 53 stops the sheet. The sheet is then in position to be
picked up by gripper means 69 on transport means 48. Cam means 70
is mounted to open gripper means 69 so that a sheet is picked up as
end portion 55 is deflected out of the path of the sheet. End
portion 55 then retains the next sheet in a position to be picked
up by the next gripper means on transport means 48. The sheets
which are picked up from buffer means 49 are moved through cleaning
station 50 to remove any remaining developer particles. In the
embodiment shown, cleaning station 50 comprises a rotating brush
which is operative to remove the developer particles since guide
means 78 functions to position the sheet close to the rotating
brush. The developer particles removed in the cleaning station are
collected for disposal.
To insure that sheets in the buffer means 36 do not interfere with
sheets already being returned by transport means 48, a sensing
means is provided to sense whether approaching gripper means
already carry a sheet 20. When an empty gripper approaches, the
loading means is actuated to permit one sheet 20 to move to
position to be picked up by the approaching gripper means. In the
embodiment shown, the sensing means comprises a microswitch means
85 mounted in a position so that the switch is operated by an end
portion 56 of the sheet to close one contact and to close a second
contact by the presence of the gripper means. Thus, loading means
86 is activated when only the gripper contact is closed to move one
sheet 20 to the position to be picked up by the approaching
gripper. A cam means is moved into position to open the gripper
means to pick up the sheet. In the embodiment of the invention
shown in the drawings, loading means 86 comprises a pivoted arm 79
mounted for movement by solenoid 83. A sheet 20 is retained in
position by spring member 87, and the sheet is moved into position
to be picked up by a gripper means. The end portion of arm 79
prevents a second sheet 20 in buffer means 36 from interfering with
the pick-up of the sheet. The sheet is transported through erase
station 38, and guide means 81 positions the sheet for movement
through the erase station 38. The erase station may comprise a
fluorescent lamp and this lamp is operable to remove any remaining
electrostatic charge from the photosensitive sheet prior to the
sheet being returned to supply process buffer 22 for reuse in the
system. An eject means 84" and a fixed cam means are utilized to
eject the sheets into return guides 61 for return to supply process
buffer means 22 for reuse in the system.
The control circuitry 108 comprises a start latch 110 which is
energized by the electrical signal produced by depressing the START
button of the machine. The start latch is combined in AND circuit
112 with the output of OR circuit 114 to actuate through driver 116
the stepping motor drive 118 to eject previously charged sheets
from the charge buffer. This is accomplished by sensing the state
of switches which form the inputs to OR circuit 114. Deflector
means 120 is also energized at this time to move the sheets to the
reject buffer for return to supply buffer means 22. AND circuit 125
is utilized to position gripper means 69 in a position to pick up a
sheet 20. When the start latch is on and a sheet is in the
pre-develop process buffer means 34, switch 88 is actuated which
conditions AND circuit 157 to actuate drum load magnets 41 through
OR circuit 158 and driver 159 to place the sheet in the first open
slot on drum member 62. The sheet is then ejected from drum member
62 by the signal generated by AND circuit 160 and OR circuit 161.
The sheets are then returned to the supply buffer means 22. When
the sheets have been returned to the supply buffer means 22, the
RUN signal is generated. When the initial conditions which relate
to placing the components in a status ready for operation, AND
circuit 122 is actuated. The output of AND circuit 122 and OR
circuit 124 provide the inputs to AND circuit 126 to actuate,
through driver 128, the single revolution clutch 66 to energize the
drive to charge a sheet. When all of the sheets are charged as
sensed by OR circuit 124, AND circuit 126 is deconditioned and this
output through inverter 130 conditions AND circuit 132 to turn on
RUN latch 134. The machine then has a supply of charged sheets and
is ready to execute instructions to produce a specified image.
The production of quality images is influenced by the uniformity
and the level of the charge existing on the sheet 20 at the time of
exposure to the image to be produced. The characteristics of the
materials comprising sheets 20 are such that charge is dissipated
over a period of time. For this reason it is desirable to sense the
time which has elapsed since a particular sheet was charged. This
is accomplished by providing a timing means 136 for each of the
sheets in the charge buffer. In the embodiment shown in the
drawings a supply of four charged sheets is maintained at charge
buffer 28. In this case timing means 136a-d are provided to account
for the time which has elapsed since the sheet was charged. The
means for sensing the time comprises a shift register 138 which has
a number of stages equal to the number of sheets to be charged
which in the embodiment shown is four. When the first sheet is
charged a 1-bit is set into the first stage of the shift register
by the SET signal which is generated by AND circuit 144. A clock
pulse generator is provided to step timing means 136 and the timing
means 136a is started when the first sheet is charged. In the event
that the sheet is not exposed prior to the expiration of the
predetermined time set for timing means 136-a, the sheet is ejected
from the charge buffer since the charge may have deteriorated to
the point that images of the desired quality can no longer be
produced from that level of charge on sheet 20. When the second
sheet is charged, a SHIFT signal is coupled to shift register 138
so that the one bit is present in stage 2 of the shift register.
The SHIFT signal is generated during start operations by AND
circuit 146 and coupled through OR circuit 147. This shift signal
is connected to shift register 138 to shift the one bit by one
position. The one bit signal is combined in AND circuit 135b with a
clock pulse signal to start timing means 136b and the same
operation is provided by AND circuits 137 and 139 with respect to
the third and fourth sheets as the 1-bit in shift register 138 is
shifted through the register. Shift register 138 is provided with
an end around carry so that a ring is produced; therefore, when the
one-bit is shifted from stage 4 the 1-bit is next shifted to the
first stage of the shift register. During RUN operations the SHIFT
signal is generated by AND circuit 133.
To execute a PRINT N COPIES instruction, the sheet is placed on a
transport means which moves the sheet past develop and transfer
stations to produce a copy on a suitable copy receiving means such
as plain paper. If one copy is produced per cycle as in
conventional systems, then the total throughput of the system would
be dependent on the number of copies required. To eliminate this
dependence the speed of the printing transport means is faster than
the other transport means and in addition the transport means
functions to process several sheets at the same time for a printing
operation. In the embodiment shown, the drum member 62 has
provision for four sheets and the drum speed is three times the
speed of the other transport means. The number of copies is
included in the instruction and a counter 140 is provided to record
the number of copies of each of the sheets on drum member 62. The
sheet 20 is placed on drum member 62 by drum load magnet 41 and
this magnet is energized by sensing whether a slot is open as the
drum approaches the buffer. When a SLOT OPEN signal is received,
the drum load mechanism 41 is actuated. At the same time the signal
which designates the number of slot is sensed and a coded signal
representing the count is gated to line 141. The SLOT OPEN signal
and the corresponding slot signal condition the corresponding AND
circuit 143a-d so that the count on line 141 is gated to the
corresponding counter 140a-d by gate 145a-d so that the number of
copies can be monitored. Counters 140a-d comprise count down
counters so that a count signal is provided through AND circuit
149a-d each time a slot reaches the monitoring position. When the
value in the counter reaches 1, this designates that the last copy
is to be made on the following cycle so that the eject mechanism 45
is actuated at the time when the appropriate slot is opposite the
eject transport means 47. The sheet is then ejected and returned to
the supply buffer means for reuse in the machine. In the embodiment
shown this control is provided by AND circuits 150-153 which sense
counts in counters 140a-d respectively. When a counter reaches 1
the corresponding AND circuit is conditioned and a delay 154 is
timed to provide a signal through OR circuit 155 and driver 156 to
operate eject magnet 45 at the time when the support means of the
sheet is opposite eject transport means 47.
In the embodiment shown the control means for keeping track of the
elapsed time since a sheet was charged comprises a shift register
138 which has a number of stages equal to the number of sheets to
be charged. In the embodiment shown, four sheets are charged at one
time; however, it will be recognized that the number could be
different depending upon the process requirements and the
characteristics of the materials being used. A timing means 136 is
also required for each of the sheets. A clock pulse supplied by
control means 106 is utilized to step timing means 136 at any
suitable rate to provide a time interval of the required accuracy
for the process. Both the shift register 138 and timing means 136
are reset to zero at the start of operations by a RESET signal
which is generated from AND circuit 142. A 1-bit is set into the
first stage of shift register 138 concurrently with the first sheet
being charged by the output from AND circuit 144. The output from
the first stage is combined with a clock pulse in AND circuit 135A
to produce a signal to start timing means 136A. The subsequent
clock pulse signals timing means 136A is stepped in response to the
output of AND circuit 148A which senses when timing means 136A
stands at a count other than zero. In the event that the time
expires before the sheet is used a TIME EXPIRED signal is operative
to actuate through OR circuit 163 the drive means 118 to reject the
sheet. In the event that the sheet is used before the expiration of
the time the corresponding timing means 136 is reset by means of
AND circuits 162a-d.
While the invention has been particularly shown and described with
reference to a preferred embodiment thereof, it will be understood
by those skilled in the art that various changes in the form and
details may be made therein without departing from the spirit and
scope of the invention.
* * * * *