U.S. patent number 3,781,548 [Application Number 05/131,114] was granted by the patent office on 1973-12-25 for control system.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Robert E. Gerace.
United States Patent |
3,781,548 |
Gerace |
December 25, 1973 |
CONTROL SYSTEM
Abstract
A control system for regulating the performance of predetermined
sequences of operations by an operating device upon sheets of
material having variable lengths is disclosed in accordance with
the teachings of the present invention wherein photoelectric
sensing means are utilized to sense the leading and trailing edges
of a sheet of material upon which the device operates. Pulse
generating means generates first and second pulses when the
photoelectric sensing means senses the leading and trailing edges
respectively, of a sheet of material. First and second switch means
respond to the generated first and second pulses for initiating
first and second predetermined sequences of operations
respectively, to be performed by the operating device.
Inventors: |
Gerace; Robert E. (Fairport,
NY) |
Assignee: |
Xerox Corporation (Stamford,
CT)
|
Family
ID: |
22447938 |
Appl.
No.: |
05/131,114 |
Filed: |
April 5, 1971 |
Current U.S.
Class: |
250/559.26;
250/223R; 250/559.36 |
Current CPC
Class: |
G05B
19/063 (20130101); G03G 21/14 (20130101) |
Current International
Class: |
G05B
19/04 (20060101); G05B 19/06 (20060101); G03G
21/14 (20060101); H01j 039/12 () |
Field of
Search: |
;250/221,214,222,223,219DC,219DR,219,26D ;209/111.7 ;317/124
;235/61.11E ;355/14 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lawrence; James W.
Assistant Examiner: Nelms; D. C.
Claims
What is claimed is:
1. A control system for regulating the performance of predetermined
sequences of operations by an electrophotographic reproducing
device wherein said predetermined sequences are performed in time
delayed relationship, said time delay being defined by the length
of a document to be reproduced, comprising:
photoelectric sensing means for sensing the leading and trailing
edges of a document to be reproduced;
pulse generating means coupled to said photoelectric sensing means
for generating a first pulse when said photoelectric sensing means
senses the leading edges of a document and for generating a second
pulse when said photoelectric sensing means senses the trailing
edge of a document, said pulse generating means comprising
triggerable bistable means adapted to assume a first stable state
when a signal applied thereto exceeds a predetermined threshold
level and to assume a second stable state when a signal applied
thereto is less than said predetermined threshold level; and
transition detecting means coupled to said triggerable bistable
means for detecting each transition in the state assumed by said
triggerable bistable means whereby said first pulse is generated
when said triggerable bistable means assumes said first state and
said second pulse is generated when said triggerable bistable means
assumes said second state;
first switch means coupled to said pulse generating means and
responsive to said first pulse for initiating a first predetermined
sequence of operations, said first switch means including first
bistate means coupled to said pulse generating means and adapted to
assume a first state in response to said first pulse, and first
electromagnetic means coupled to said first bistate means and
adapted to be energized when said first bistate means assumes said
first state, whereby the energization of said first electromagnetic
means enables first mechanical means to establish said first
predetermined sequence of operation, and
second switch means coupled to said pulse generating means and
responsive to said second pulse for initiating a second
predetermined sequence of operations, said second switch means
comprising,
second bistate means coupled to said pulse generating means and
adapted to assume a first state in response to said second pulse,
and
second electromagnetic means coupled to said second bistate means
and adapted to be energized when said second bistate means assumes
said first state, whereby the energization of said second
electromagnetic means enables second mechanical means to establish
said second predetermined sequence of operations.
2. A control system in accordance with claim 1 wherein said
triggerable bistable means comprises Schmitt trigger means whereby
said first stable state is represented by a signal admitting of a
first level and said second stable state is represented by a signal
admitting of a second level.
3. A control system in accordance with claim 2 wherein said
transition detecting means comprises differentiating means
responsive to transitions in the level of a signal applied
thereto.
4. A control system in accordance with claim 3 wherein said first
and second bistate means comprise first and second monostable
multivibrator means, respectively, each of said monostable
multivibrator means being adapted to assume the quasistable output
state thereof in response to a pulse applied thereto.
5. A control system in accordance with claim 4 wherein said first
and second electromagnetic means comprise:
first and second relay means, respectively, each of said first and
second relay means including an energizing coil and a moveable
contact, said moveable contact being adapted to complete a series
circuit; and
first and second solenoid means including first and second
activating coils serially connectable to a source of energy via
said first and second moveable contacts, respectively.
6. A control system in accordance with claim 2 wherein said
transition detecting means comprises:
bistable circuit means having first and second stable output states
and adapted to assume the first stable output state thereof in
response to an applied signal admitting of a first level and to
assume the second stable output state thereof in response to an
applied signal admitting of a second level; and
differentiating means responsive to transitions in the output state
assumed by said bistable circuit means.
7. A control system in accordance with claim 6 wherein said first
and second bistate means comprise:
first and second relay means, respectively, each of said first and
second relay means including an energizing coil and a moveable
armature, said moveable armature being adapted to complete a series
circuit; and
first and second switch means coupled to said differentiating means
and responsive to pulses applied thereto for energizing said first
and second energizing coils, respectively.
8. A control system in accordance with claim 7 wherein said first
and second electromagnetic means comprise first and second solenoid
means including first and second activating coils serially
connectable to a source of energy via said first and second
moveable armatures, respectively.
9. A control system in accordance with claim 8 wherein said
bistable circuit means comprises:
a relay coil;
a switch having a control terminal for selectively energizing said
relay coil when a signal admitting of a first level is applied to
said control terminal; and
a relay armature connected to a voltage source and adapted to
contact a first relay contact when said relay coil is energized and
to contact a second relay contact when said relay coil is
de-energized.
10. A control system in accordance with claim 9 wherein said
differentiating means comprises:
a first differentiator coupled to said first relay contact for
generating said first pulse when said relay armature contacts said
first relay contact; and
a second differentiator coupled to said second relay contact for
generating said second pulse when said relay armature contacts said
second relay contact.
11. In a device for performing operations upon sheets of material
having variable lengths wherein said operations are sequentially
performed under the control of mechanical controlling means,
apparatus for activating the mechanical controlling means,
comprising:
photocell means for sensing the leading and trailing edges of a
sheet of material upon which said device operates, said photocell
means being spaced from and in optical communication with a source
of light for producing a signal in accordance with the intensity of
light communicated thereto, the space defined by said photocell
means and said source of light being adapted to receive said sheet
of material;
Schmitt trigger means coupled to said photocell means for
generating a signal admitting of a first level when said signal
produced by said photocell means exceeds a threshold level and for
generating a signal admitting of a second level when said signal
produced by said photocell means is less than said threshold
level;
pulse generating means having an input terminal coupled to said
Schmitt trigger means and first and second output terminals for
generating a first pulse at said first output terminal when the
signal generated by said Schmitt trigger admits of a transition
from said second level to said first level and for generating a
second pulse at said second output terminal when the signal
generated by said Schmitt trigger admits of a transition from said
first level to said second level;
first switch means coupled to said first output terminal and
responsive to said first pulse for completing a first series
circuit;
second switch means coupled to said second output terminal and
responsive to said second pulse for completing a second series
circuit;
first solenoid means including an energizing coil serially
connected to a source of energy via said first series circuit
whereby said first solenoid means enables first clutch means to
activate said mechanical controlling means, and
second solenoid means including an energizing coil serially
connectable to a source of energy via said second series circuit
whereby said second solenoid means enables second clutch means to
activate said mechanical controlling means.
12. The apparatus of claim 11 further including first monostable
multivibrator means interposed between said first switch means and
said first output terminal for controlling said first switch means
whereby said first series circuit is completed for a period of time
determined by the time constant of said first monostable
multivibrator means; and second monostable multivibrator means
interposed between said second switch means and said second output
terminal for controlling said second switch means whereby said
second series circuit is completed for a period of time determined
by the time constant of said second monostable multivibrator means.
Description
This invention relates to a control system for regulating the
performance of predetermined sequences of operations by an
operating device and more particularly, to a control system for
controlling the operation of a device in accordance with the length
of a sheet of material upon which said device operates.
Many devices that perform operations upon sheets of material
require that such operations be executed in a predetermined
sequence. Exemplary devices include industrial assembly machines
wherein sheets of material are transported to various mechanisms
for manufacturing a completed product, data card readers and
perforators, and document reproducing machines. In each of the
aforementioned devices the operations performed on the sheet of
material, i.e., a sheet of industrial material, a data card or a
document, are usually performed in a predetermined timed sequence.
Unfortunately a variation in the length of the material upon which
the operations are performed, or a variation in the operating speed
of the machine results in an improperly timed operation. Although
the prior art has attempted to minimize variations in machine
operating speed by rigid synchronization thereof, variations in the
length of the sheet of material have heretofore required
corresponding manual adjustments of the device to facilitate proper
performance of each sequence of operations.
To facilitate the explanation thereof the present invention will be
described with reference to its application in an
electrophotographic reproducing device. However, it will be
understood that the subject matter of the present invention is
readily applicable to other devices such as the exemplary devices
mentioned hereinabove.
The disclosure of electrophotographic reproduction in U. S. Pat.
No. 2,297,691 which issued to C. F. Carlson has resulted in a
variety of commercially available reproducing devices. Most of
these devices produce a copy of an original document by depositing
an electrostatic charge on the surface of a photoreceptor,
advancing the charged photoreceptor to an exposure station whereat
the charged photoreceptor is exposed to an image of said original
document, advancing the exposed photoreceptor to a developing
station whereat the electrostatic latent image of the original
document is developed by depositing toner particles thereon,
advancing the developed photoreceptor to a transfer station whereat
the developed image is transferred to a support surface, advancing
the support surface through a fusing station whereat the
transferred developed image is fused to the support surface thereby
forming a copy of the original document, and advancing the copy to
an external location. The aforementioned steps are performed
sequentially under the control of pre-set programming means. The
pre-set programming means may comprise electrical apparatus such as
a well-known digital computer, or the pre-set programming means may
comprise mechanical apparatus such as rotatable cam assemblies
which are described in U. S. Pat. No. 3,301,126 which issued to R.
F. Osborne et al. on Jan. 31, 1967 and assigned to Xerox
Corporation. The electrophotographic reproducing device disclosed
in the last-mentioned patent includes a transportable exposure
station adapted to scan a stationary document. In addition the
developed electrostatic latent image is transferred to individual
sheets of paper. An alternative embodiment of an
electrophotographic reproducing device is disclosed in U. S. Pat.
No. 3,401,613 which issued to M. Davis on Sept. 17, 1968 and
assigned to Xerox Corporation wherein an original document is
transported past a fixedly disposed exposure station and the
developed electrostatic latent image is transferred to a web of
paper. The Davis patent discloses means for cutting a support
surface web in spaced relation to the leading and trailing edges of
the original document being reproduced. However the essential
operations described hereinabove are executed independently of the
length of the document.
The prior art has attempted to regulate the operations of an
electrophotographic reproducing device in accordance with the
length of a document to be reproduced by disposing microswitches in
the transport path of the document. The microswitches are adapted
to energize appropriate circuits when the document is in contact
therewith. An attendant disadvantage however is the unreliability
of micro-switch operation. Repeated actuation of the micro-switch
results in frequent failure thereof. In addition physical contact
between the micro-switch and the document to be reproduced often
results in deformation of the document which may mutilate the
document and obstruct the machine.
Therefore, it is an object of the present invention to provide a
control system for regulating the performance of predetermined
sequences of operations by an electrophotographic reproducing
machine in accordance with the length of the document to be
reproduced.
It is another object of this invention to provide apparatus for
activating the mechanical programmers of an electrophotographic
reproducing device such that a first sequence of operations is
performed upon sensing the leading edge of document to be
reproduced and a second sequence of operations is performed upon
detecting the trailing edge of a document to be reproduced.
It is a further object of this invention to provide a control
system including photoelectric sensing means for sensing the
leading and trailing edges of a document to be reproduced, for
regulating the performance of predetermined sequences of
operations.
Yet another object of this invention is to provide apparatus for
activating the mechanical controlling means of a device wherein
said device performs sequential operations upon sheets of material
having variable lengths.
A still further object of this invention is to provide a control
system for creating delays in the performance of sequential
operations by an electrophotographic reproducing machine wherein
said delays correspond to the length of the document to be
reproduced.
An additional object of this invention is to provide a control
system for regulating delayed operation of an electrophotographic
reproducing machine wherein said control system is operable
independent of the mechanical drive speed of said machine, and said
drive speed need not be constant.
Another object of this invention is to initiate the operation of a
device upon sensing the leading edge of a sheet of material upon
which said device operates and to terminate the operation of said
device upon detecting the trailing edge of said sheet of
material.
Various other objects and advantages of the invention will become
clear from the following detailed description of exemplary
embodiments thereof, and the novel features will be particularly
pointed out in connection with the appended claims.
In accordance with this invention a control system for regulating
the performance of predetermined sequences of operation by an
electrophotographic reproducing machine in accordance with the
length of a document to be reproduced is provided wherein
photoelectric sensing means senses the leading and trailing edges
respectively, of the document to be reproduced; pulse generating
means coupled to said photoelectric sensing means generates first
and second pulses in response to the sensing of the leading and
trailing edges respectively; first switch means responds to a
generated first pulse for activating a mechanical programming means
to control a first predetermined sequence of operations; and second
switch means responds to a generated second pulse for activating
the mechanical programming means to control a second predetermined
sequence of operations .
The invention will be more clearly understood by reference to the
following detailed description of exemplary embodiments thereof in
conjunction with the accompanying drawings in which:
FIG. 1 is a block diagram of a first embodiment of the control
system of the present invention;
FIG. 2 is a schematic diagram of a portion of the apparatus of FIG.
1;
FIG. 3 is a block diagram of another embodiment of the control
system of the present invention; and
FIG. 4 is a schematic diagram of a portion of the apparatus of FIG.
3.
Referring now to the drawings wherein like reference numerals are
used throughout, and in particular to FIG. 1, there is illustrated
a block diagram of an embodiment of the control system of the
present invention which comprises photoelectric sensing means 10,
Schmitt trigger means 13, pulse generating means 14, monostable
multivibrator means 16 and 17, clutch means 18 and 19, mechanical
programming means 21 and 22 and device 23. As noted hereinabove,
the present invention will be described with reference to an
electrophotographic reproducing device. Accordingly, device 23 may
comprise a conventional electrophotographic device. It is
understood however that device 23 may comprise a data card reader,
a data card perforator, an industrial assembly machine or any other
device adapted to perform operations on sheets of material.
Photoelectric sensing means 10 may comprise a conventional
photocell such as a phototransistor, a photodiode or the like, or a
phototube adapted to produce an output signal having a magnitude
proportional to the intensity of radiation impinging thereon.
Accordingly photoelectric sensing means 10 is spaced from and in
optical communication with a source of light 11. The source of
light 11 may comprise a conventional light emissive element such as
an incandescent lamp for emitting light having a substantially
constant intensity. The sapce defined by the photoelectric sensing
means 10 and the source of light 11 is adapted to receive a sheet
of material 12 which, for purposes of explanation, may comprise a
document to be reproduced. The sheet 12 may be transported by
conventional means such as roller means, endless belt means or the
like, not shown, in the direction indicated by the arrow A so as to
intercept the optical path between the source of light 11 and the
photoelectric sensing means 10.
Photoelectric sensing means 10 is coupled to pulse generating means
14 via Schmitt trigger means 13. The Schmitt trigger means 13 is a
well-known triggerable bistable circuit adapted to provide an
indication of the relative magnitude of an input signal supplied
thereto. Accordingly, Schmitt trigger means 13 is capable of
assuming a first stable state represented by a signal admitting of
a first level when the output signal supplied thereto by
photoelectric sensing means 10 exceeds a predetermined threshold
level and a second stable state represented by a signal admitting
of a second level when the output signal supplied thereto by the
photoelectric sensing means 10 is less than the predetermined
threshold level. Schmitt trigger means 13 may be replaced by other
conventional level detecting circuits, such as an amplitude
comparator or a unijunction transistor circuit, adapted to indicate
whether the magnitude of the signal produced by photoelectric
sensing means 10 exceeds a predetermined threshold level. Pulse
generating means 14 includes a first output terminal coupled to
monostable multivibrator means 16 via inverting circuit 15 and a
second output terminal coupled to monostable multivibrator means
17. The pulse generating means 14 is adapted to detect a change in
the stable state assumed by Schmitt trigger means 13. Accordingly,
pulse generating means 14 is responsive to a transition in the
level of the signal applied thereto by Schmitt trigger means 13.
One embodiment of pulse generating means 14 may comprise a
conventional differentiating circuit whereby a pulse is produced at
a first output terminal thereof in response to a transition from
the second level to the first level in the signal supplied thereto
and a pulse is produced at a second output terminal thereof in
response to a transition from the first level to the second level
in the signal supplied thereto. Alternatively, pulse generating
means 14 may include a single output terminal whereat a positively
poled pulse is produced in response to a positive transition in the
signal supplied thereto and a negatively poled pulse is produced in
response to a negative transition in the signal supplied thereto.
Another embodiment of pulse generating means 14 may comprise a
conventional univibrator circuit. It should be understood by those
skilled in the art that Schmitt trigger means 13 and pulse
generating means 14 may be combined in a single circuit such as a
unijunction transistor circuit or the like whereby a first pulse is
generated when the magnitude of the signal produced by
photoelectric sensing means 10 exceeds a predetermined threshold
level and a second pulse is generated when the magnitude of the
signal produced by photoelectric sensing means 10 is less than said
predetermined threshold level.
Monostable multivibrator means 16 is a conventional bistate device
exhibiting a stable output state and a quasi-stable output state.
The monostable multivibrator means 16 may be triggered into the
quasi-stable output state thereof upon applying a pulse thereto. As
is understood by those skilled in the art, the monostable
multivibrator means 16 assumes its quasi-stable output state for a
period of time determined by the time constant thereof.
Accordingly, the monostable multivibrator means 16 serves to
provide an output pulse of uniform pulse width in response to each
input pulse applied thereto. It will be seen hereinafter that
monostable multivibrator means 16 may be triggered into its
quasistable state by applying a negative going pulse thereto.
However pulse generating means 14 is adapted to provide a
positively poled pulse at the first output terminal thereof in
response to a positive transition in the signal supplied thereto.
Accordingly, inverting circuit 15 is interposed between pulse
generating means 14 and monostable multivibrator means 16 to invert
the polarity of the triggering pulse. Inverting circuit 15 may
comprise a conventional inverting amplifier, a phase inverter or a
logic negation circuit, well known to those of ordinary skill in
the art. It is of course recognized that if monostable
multivibrator means 16 is adapted to be triggered into its
quasi-stable state by a positively poled triggering pulse,
inverting circuit 15 may be omitted. Monostable multivibrator means
17 is coupled to the second output terminal of pulse generating
means 14 and is identical to the aforementioned monostable
multivibrator means 16. Accordingly, further description of
monostable multivibrator means 17 need not be set forth herein.
Since a negatively poled triggering pulse is provided at the second
output terminal of pulse generating means 14 in response to a
negative transition in the signal supplied thereto, it is not
necessary to interpose an additional inverting circuit between the
pulse generating means 14 and the monostable multivibrator means
17.
Monostable multivibrator means 16 is coupled to clutch means 18 and
is adapted to activate the latter upon assuming its quasi-stable
output state. Accordingly clutch means 18 may include
electromagnetic means such as solenoid means, relay means, a
combination thereof, or the like. Activation of clutch means 18 is
effective to couple mechanical programming means 21 to the motor
drive system 20 of device 23. Mechanical programming means 21 may
comprise a first rotatable cam assembly such as described in U. S.
Pat. No. 3,301,126 which issued on Jan. 31, 1967 to R. F. Osborne.
Coupling of the first cam assembly 21 to the motor drive system 20
enables each of the cams therein to rotate in synchronism with the
motor to thereby control a first sequence of operations performed
by device 23.
Clutch means 19 is coupled to monostable multivibrator means 17 and
is adapted to be activated upon the assumption of the quasi-state
output state thereof by monostable multivibrator means 17. Clutch
means 19 is similar to aforementioned clutch means 18 and
therefore, need not be described in great detail. The activation of
clutch means 19 is effective to couple mechanical programming means
22 to the motor drive system 20. Mechanical programming means 22 is
similar to aforedescribed mechanical programming means 21 and may
comprise a second rotatable cam assembly for controlling a second
sequence of operations performed by device 23.
The operation of the control system illustrated in FIG. 1 will now
be described with reference to a conventional electrophotographic
reproducing device. It is recalled however that the present
invention finds ready application with any device capable of
performing operations upon sheets of material having variable
lengths. Initially photoelectric sensing means 10 receives a beam
of light of substantially constant intensity communicated thereto
from the source of light 11. If it is assumed there is no
obstruction in the light path defined by the photoelectric sensing
means 10 and the source of light 11, the photoelectric sensing
means responds to the relatively high intensity of impinging light
to produce a signal that is less than a predetermined threshold
level. This signal is applied to Schmitt trigger means 13 whereby
the Schmitt trigger means assumes a second stable state which is
represented by a signal admitting of a second level. As is
understood by those of ordinary skill in the art, the signal
representative of the state of Schmitt trigger means 13 is a d.c.
signal.
It is recalled that the pulse generating means 14 is responsive to
transitions in the signal supplied thereto. However the signal
presently supplied by Schmitt trigger means 13 admits of a constant
d.c. second level. Accordingly trigger pulses are not provided at
the first and second output terminals of pulse generating means 14
and monostable multivibrator means 16 and 17 maintain their
respective stable output states. Thus, neither clutch means 18 nor
clutch means 19 is activated and neither mechanical programming
means 21 nor mechanical programming means 22 is coupled to motor
drive system 20. Consequently, device 23 will not execute the
sequences of operations that are controlled by the mechanical
programming means 21 and 22 respectively, and device 23 will
maintain a quiescent condition.
It will now be assumed that a document to be reproduced 12 is
introduced into the space defined by photoelectric sensing means 10
and the source of light 11. It is recognized that the document 12
may be transported in the direction indicated by the arrow A by
conventional transport means such as a conveyor belt, drive rollers
or the like. Alternatively, the document 12 may assume a stationary
relationship and an exposure mechanism including the photoelectric
sensing means 10 and source of light 11 may be displaced in a
direction opposite to that indicated by the arrow A to scan the
surface of the document. In either event when the leading edge of
document 12 intercepts the optical path between the source of light
11 and photoelectric sensing means 10, the obstruction presented
thereby reduces the intensity of light impinging on the
photoelectric sensing means 10 to a substantially zero value.
Accordingly, the signal applied by the photoelectric sensing means
10 to Schmitt trigger means 13 increases to exceed the
predetermined threshold level. Schmitt trigger means 13 responds to
the signal applied thereto to assume the first stable state
thereof, which state is represented by a signal admitting of a
first level. Thus, the d.c. signal supplied to pulse generating
means 14 is now characterized by a transition from a second level
to a first level. If it is assumed that the first level of the d.c.
signal supplied to pulse generating means 14 is greater than the
second level thereof, pulse generating means 14 is actuated to
generate a positive pulse at the first output terminal thereof in
response to the positive transition. The polarity of the positive
pulse is inverted by inverting means 15 thereby applying a negative
triggering pulse to the input terminal of monostable multivibrator
means 16. It is of course recognized that if monostable
multivibrator means 16 is operable in response to positively poled
triggering pulses inverting circuit 15 may be omitted and the first
output terminal of pulse generating means 14 may be directly
coupled to the input terminal of monostable multivibrator means
16.
When monostable multivibrator means 16 is triggered into the
quasi-state output state thereof in response to the triggering
pulse applied thereto, a pulse of predetermined width is applied to
clutch means 18. If the clutch means 18 includes an electromagnetic
member, such as a solenoid, the pulse applied thereto enables the
solenoid to be energized, thereby releasing a mechanical clutch
member such as a spring clutch. It is clear then that when
monostable multivibrator means 16 returns to the stable output
state thereof, the resulting de-energization of the solenoid will
have no effect upon the released clutch member. Release of the
mechanical clutch member couples the mechanical programming means
21 to motor drive system 20 whereby the cam assembly includable in
the mechanical programming means 21 now rotates in synchronism with
the motor. As the cam assembly rotates, a first sequence of
operations is performed by the device 23. Typical of these
operations are: the charging of a photoreceptor initiated by the
rotation of a first cam; exposure of the charged photoreceptor to a
light image of the document 12 to form an electrostatic latent
image, initiated by the rotation of a second cam; development of
the electrostatic latent image, initiated by the rotation of a
third cam; transfer of the developed image to a web, initiated by
the rotation of a fourth cam; and movement of the web, initiated by
the rotation of a fifth cam. It is recognized that the foregoing
operations are merely exemplary of some of the operations performed
by a conventional electrophotographic reproducing device, and are
not to be interpreted as limiting the present invention thereto. In
addition the sequence of performance of the foregoing operations is
not limited to the sequence just described and is determinable by
the particular mechanical programming means utilized.
As the document 12 continues to be transported in a direction
indicated by the arrow A, the intensity of the light impinging upon
photoelectric sensing means 10 is substantially constant.
Accordingly Schmitt trigger means 13 is supplied with a signal that
is maintained above the predetermined threshold level and the
Schmitt trigger means retains the first stable state thereof.
Consequently pulse generating means 14 does not detect further
transitions in the d.c. signal supplied thereto and additional
triggering pulses are not generated thereby. Hence monostable
multivibrator means 16 and 17 assume their respective stable output
states and clutch means 18 and 19 are not activated. The normal
operation of mechanical programming means 21, once initiated, is
therefore not affected and device 23 performs a first sequence of
operations. When the trailing edge of document 12 is transported
past the optical path defined by the source of light 11 and
photoelectric sensing means 10, the intensity of the light
impinging upon photoelectric sensing means 10 is increased such
that the signal supplied to Schmitt trigger means 13 falls below
the predetermined threshold level. Consequently Schmitt trigger
means 13 assumes the second stable state thereof and the d.c.
signal now supplied to pulse generating means 14 is characterized
by a negative transition from the aforementioned first level to the
second level. Pulse generating means 14 responds to the negative
transition to generate a negatively poled triggering pulse at the
second output terminal thereof, which pulse is applied to
monostable multivibrator means 17. Application of the triggering
pulse to monostable multivibrator means 17 triggers the monostable
multivibrator means into the quasi-stable output state thereof,
thereby applying a pulse of predetermined width to clutch means 19.
As is now understood, clutch means 19 is thus activated to couple
mechanical programming means 22 to motor drive system 20. The
ensuing rotation of the cam assembly comprising mechanical
programming means 22 controls a second sequence of operations
executed by device 23. Typical of these operations are: fixing of
the transferred image to the web, initiated by the rotation of a
first cam; cutting of the web, initiated by the rotation of a
second cam; delivery of the copy to a location external of the
electrophotographic reproducing device, initiated by the rotation
of a third cam; and preparing the device for subsequent operation,
initiated by the rotation of a fourth cam. The foregoing operations
and sequence of execution thereof are merely exemplary and are not
intended to limit the use of device 23 or the application of the
present invention. Other operations may be performed and in a
sequence determined by the particular programming means
utilized.
It is to be understood that when the programs determined by
mechanical programming means 21 and 22 respectively, are completed,
clutch means 18 and 19 are restrained from further rotation,
thereby decoupling the respective mechanical programming means from
motor drive system 20.
The control system illustrated in FIG. 1 is subject to various
modifications and changes. For example, the photoelectric sensing
means 10 may produce a signal that is less than a predetermined
threshold level when document 12 is interposed in the optical path
defined by the source of light 11 and the photoelectric sensing
means 10, whereupon Schmitt trigger means 13 assumes its first
stable state. In addition, the d.c. signal supplied to pulse
generating means 14 by Schmitt trigger means 13 may be
characterized by a negative transition when photoelectric sensing
means 10 detects the leading edge of document 12. Furthermore, the
pulse generating means 14 may be provided with a single output
terminal connected in common relationship to inverting circuit 15
and monostable multivibrator means 17 to which are provided
positively and negatively poled pulses. Although the foregoing and
various other modifications are readily attained, it is manifest
that mechanical programming means 21 be activated upon detection of
the leading edge of document 12 and mechanical programming means 22
to be activated upon detection of the trailing edge of document
12.
Referring now to FIG. 2 there is illustrated a schematic diagram of
a portion of the control system of FIG. 1 comprising photoelectric
sensing means 10, Schmitt trigger means 13, pulse generating means
14, inverting circuit 15, monostable multivibrator means 16 and 17,
and clutch means 18 and 19. Photoelectric sensing means 10 is
illustrated as a variable impedence means having an impedance that
varies as a function of the intensity of light impinging thereon.
Hence the impedance of photoelectric sensing means 10 tends to
decrease as the intensity of light communicated thereto increases
and conversely, the impedence thereof tends to increase as the
intensity of light decreases. A first terminal of the photoelectric
sensing means 10 is coupled to terminal 103 via adjustable contact
102 of potentiometer 101. Another terminal of the photoelectric
sensing means 10 is coupled to a common conducting lead 105 adapted
to be supplied with a reference potential such as ground potential.
Terminal 103 is supplied with an operating potential represented as
+V. Adjustable contact 102 is additionally coupled to the Schmitt
trigger means 13 via current limiting resistance 104. The Schmitt
trigger means 13 is comprised of transistors 131 and 136 which are
adapted for regenerative operation. The emitter electrodes of
transistors 131 and 136 are connected in common to common
conducting lead 105 via resistance 138. The collector electrode of
transistor 131 is connected to the base electrode of transistor 136
via the parallel circuit comprised of resistance 133 and
capacitance 134. The base electrode of transistor 136 is
additionally connected to common conducting lead 105 via resistance
135. The collector electrodes of transistors 131 and 136 are
connected to resistances 132 and 137 respectively, which in turn
are supplied with operating potential +V. One of ordinary skill in
the art will recognize that Schmitt trigger means 13 as herein
illustrated is of conventional design and is described in the sixth
edition of the transistor manual published in 1962 by the General
Electric Company. If desired other conventional circuits may be
utilized to form the Schmitt trigger means 13.
The collector electrode of transistor 136 is connected to pulse
generating means 14 which comprises first and second
differentiating circuits. A first differentiating circuit is
comprised of the series connections of capacitance 141, capacitance
145, and resistance 150 which is coupled to common conducting lead
105. The common junction of capacitance 141 and capacitance 145 is
connected to common conducting lead 105 via positively poled diode
143. The second differentiating circuit is comprised of the series
connections of capacitance 142, capacitance 146 and resistance 147
which is coupled to common conducting lead 105. The common junction
of capacitance 142 and capacitance 146 is coupled to the common
conducting lead 105 via negatively poled diode 144. As is
understood by those of ordinary skill in the art, the presence of
positively poled diode 143 limits the operation of the first
differentiating circuit such that positive pulses are generated
across resistance 150 whereas negative pulses are inhibited.
Conversely the presence of negatively poled diode 144 limits the
operation of the second differentiating circuit such that negative
pulses are generated across resistance 147 and positive pulses are
inhibited. It is recognized that the combination of capacitance 141
and diode 143 and the combination of capacitance 142 and diode 144
comprise conventional clamping circuits.
The common junction of capacitance 145 and resistance 150, which
corresponds to the aforementioned first output terminal of pulse
generating means 14, is coupled to inverting means 15. Inverting
circuit 15 is comprised of transistor 151, arranged in emitter
follower configuration, having an emitter electrode connected to
the base electrode of transistor 156 via a.c. coupling capacitor
153. Transistor 156 is arranged in conventional inverting amplifier
configuration for amplifying the magnitude of and inverting the
sense of a pulse applied to the base electrode thereof. Resistances
154 and 155 comprise conventional biassing resistances for the
transistor 156. The collector electrode of transistor 156 is
coupled to monostable multivibrator means 16 via diode 161. The
diode 161 is suitably poled so that monostable multivibrator 16 is
triggered to its quasi-stable output state by the application of
negative pulses.
Monostable multivibrator means 16 is comprised of a conventional
circuit including transistors 162 and 166 wherein the collector
electrode of transistor 166 is capacitively coupled to the base
electrode of transistor 162 and the collector electrode of
transistor 162 is resistively coupled to the base electrode of
transistor 166. It is apparent therefore, that the stable output
state of monostable multivibrator means 16 is attained when
transistor 162 assumes its conducting state and conversely, the
quasi-state output state is attained when transistor 166 assumes
its conducting state. The collector electrode of transistor 166 is
additionally coupled to one end of an energizing coil 169 of a
first relay circuit, the other end of which is supplied with
operating voltage +V. A moveable armature 170 of the relay circuit
is magnetically controlled by the energizing coil 169 in the
well-known manner. It is understood by those of ordinary skill in
the art that the inductance of energizing coil 169 may contribute
to the generation of injurious voltage transients capable of
damaging transistor 166. Accordingly, diode 168 is connected in
shunt relationship with energizing coil 169 to absorb the
transients.
The common junction of capacitance 146 and resistance 147 is
coupled to monostable multivibrator 17 via diode 171 suitably poled
so that the monostable multivibrator means is triggered to the
quasi-stable output state thereof by the application of negative
triggering pulses. The monostable multivibrator means 17 is
comprised of transistors 172 and 176 wherein the collector
electrode of transistor 176 is capacitively coupled to the base
electrode of transistor 172 and the collector electrode of
transistor 172 is resistively coupled to the base electrode of
transistor 176. It is observed that the circuit comprising
monostable multivibrator means 17 is identical to the circuit
comprising monostable multivibrator means 16. Hence, the stable
output state of monostable multivibrator means 17 is attained when
transistor 172 assumes its conducting state and conversely, the
quasistable output state is attained when transistor 176 assumes
its conducting state. The collector electrode of transistor 176 is
additionally coupled to one end of an energizing coil 179 of a
second relay circuit, the other end of which is supplied with
operating voltage +V. A moveable armature 180 of the relay circuit
is magnetically controlled by the energizing coil 179 in the
well-known manner. Diode 178 is connected in shunt relationship
with energizing coil 179 to absorb harmful transients that may be
produced.
Clutch means 18 is herein illustrated as including a solenoid
having an energizing coil 182 that is serially connectable to
terminal 181 via moveable armature 170. Likewise clutch means 19 is
illustrated as including a solenoid having an energizing coil 191
that is connectable to terminal 181 via moveable armature 180. The
terminal 181 is adapted to be supplied with a source of energizing
voltage whereby coils 182 and 191 may be selectively energized to
thereby activate an associated clutch means.
Operation of the schematic diagram of FIG. 2 will now be described.
If no obstruction is present to prevent light from impinging upon
photoelectric sensing means 10, the intensity of the light received
tends to reduce the impedance of the photoelectric sensing means to
a minimal value. Accordingly the voltage drop from terminal 103 to
moveable contact 102 is much greater than the voltage drop across
the low impedance of photoelectric sensing means 10. Hence moveable
contact 102 applies a voltage less than the predetermined threshold
level to the base electrode transistor 131 of Schmitt trigger means
13. Consequently transistor 131 assumes its nonconducting state
thereby providing the collector electrode of transistor 131 with a
high voltage potential. The high voltage potential is applied to
the base electrode of transistor 136 whereby the latter transistor
assumes its conducting state. Hence the collector electrode of
transistor 136 is provided with a d.c. voltage determined by the
voltage divider network comprised of resistances 137 and 138. The
d.c. voltage is effectively blocked by capacitances 141 and 142 of
pulse generating means 14 and the remaining circuitry of FIG. 2
maintains its quiescent state.
If the light path to photoelectric sensing means 10 is now
interrupted by the leading edge of a document, the impedance of the
photoelectric sensing means tends to increase and the voltage drop
thereacross rises above the predetermined threshold level. If
desired, the photoelectric sensing means 10 may alternatively
comprise a photodiode, a phototransistor, or the like, serially
interposed between moveable contact 102 and resistance 104, and
adapted to produce an increased output voltage in response to a
decrease in the intensity of light impinging thereon. Application
of the increased voltage to the base electrode of transistor 131
drives the transistor into its conducting state thereby diminishing
the voltage at the collector electrode thereof. Accordingly,
transistor 136 is urged to its nonconducting state and the
collector electrode thereof is provided with a d.c. voltage
substantially equal to the operating voltage +V. The positive d.c.
voltage transition produced at the collector electrode of
transistor 136 is coupled to diodes 143 and 144 by capacitances 141
and 142 respectively. The positive transition provides a forward
bias on diode 144 and is shunted thereby to common conducting lead
105. However, the positive transition provides a reverse bias on
diode 143. Accordingly, capacitance 145 and resistance 150 function
in the well-known manner to differentiate the positive transition
and transistor 151 is supplied with a positive pulse 148 at the
base electrode thereof. The emitter follower configuration of
transistor 151 applies a positive pulse to the base electrode of
transistor 156. Transistor 156 is arranged as a conventional
inverting amplifier however, whereby the magnitude of the positive
pulse applied to the base electrode thereof is amplified and the
polarity of the pulse is inverted. Consequently a negative pulse
159 is provided at the collector electrode of transistor 156.
Negative pulse 159 is coupled to diode 161 and applied thereby as a
triggering pulse to the base electrode of transistor 162 of
monostable multivibrator means 16.
If it is assumed that the circuit parameters of the monostable
multivibrator means 16 are suitably chosen, transistor 162 will
assume its conducting state and transistor 166 will be cut off
prior to the application of a triggering pulse thereto. This, it is
understood, corresponds to the stable output state of monostable
multivibrator means 16 wherein a low voltage substantially equal to
ground potential is provided at the collector electrode of
transistor 162 and a high voltage substantially equal to the
operating voltage +V is provided at the collector electrode of
transistor 166. Application of the negative pulse 159 to the base
electrode of transistor 162 drives transistor 162 completely below
cutoff and the voltage provided at the collector electrode of
transistor 162 increases. The voltage provided at the collector
electrode of transistor 162 is supplied to the base electrode of
transistor 166 by resistance 165. Hence, when the aforementioned
voltage obtains the proper magnitude, transistor 166 is driven to
its conducting state and the collector electrode thereof is
provided with a voltage substantially equal to ground potential.
Consequently, a series circuit is now provided from terminal 103
through energizing coil 169 through transistor 166 to the common
conducting lead 105. The flow of current through coil 169 results
in energization thereof causing moveable armature 170 to close.
Closure of moveable armature 170 completes a series circuit from
terminal 181 through the energization coil 182 of the solenoid
included in clutch means 18. It is understood that transistor 166
will remain in its conducting state, i.e., monostable multivibrator
means 16 will assume the quasi-stable output state thereof, for
only a finite time because the base electrode of transistor 162 is
connected to terminal 103 through resistance 164. Therefore, the
voltage applied to the base electrode of transistor 162 will
increase at a rate determined by the time constant of the
monostable multivibrator means 16 which is a function of resistance
164 and capacitance 167, and when the applied voltage obtains the
proper magnitude the monostable multivibrator means 16 will resume
the stable output state thereof. Accordingly, current will no
longer flow through coil 169, the moveable armature 170 will be
opened and coil 182 will be de-energized. However, as has been
previously described with reference to FIG. 1, if clutch means 18
includes a mechanical spring clutch member, energization of coil
182 will enable the clutch member to effect a complete rotation
irrespective of the subsequent de-energization of the coil 182.
Obstruction of the light path to photoelectric sensing means 10 by
the document to be reproduced maintains the impedance of the
photoelectric sensing at a relatively high value. Accordingly the
voltage applied to the base electrode of transistor 131 sustains
the transistor 131 in its conducting state. Hence the d.c. signal
provided at the collector electrode of transistor 136 is
characterized by a constant value substantially equal to the
operating potential +V, to which pulse generating means 14 does not
respond.
When the trailing edge of the document 12 is transported past the
photoelectric sensing means 10, the impedance of the photoelectric
sensing means is decreased in response to light impinging thereon.
Accordingly the voltage supplied to the base electrode of
transistor 131 by moveable contact 102 is less than the
predetermined threshold level required to maintain the transistor
in its conducting state. It is here noted that the predetermined
threshold level may be adjusted by a corresponding adjustment of
the moveable contact 102 of potentiometer 101 in the well-known
manner. When transistor 131 assumes its nonconducting state, the
voltage provided at the collector electrode thereof is
substantially equal to the operating voltage +V, sufficient to
drive transistor 136 into its conducting state. Consequently the
d.c. signal provided at the collector electrode of transistor 136
is decreased from the aforementioned first valve thereof to a
second value thereof. This negative transition is coupled to diode
143 by capacitance 141 and to diode 144 by capacitance 142. The
negative transition results in a forward bias of diode of 143 and
is shunted thereby to common conducting lead 105. However, the
negative transition provides a reverse bias on diode 144 whereupon
the negative transition is differentiated to produce negative pulse
149 at the common junction of capacitance 146 and resistance 147.
It should be understood that the diode 143 effectively inhibits the
differentiating circuit comprised of capacitance 145 and resistance
146.
Negative pulse 149 is applied to the base electrode of transistor
172 of monostable multivibrator means 17 by diode 171. The
monostable multivibrator means 17 is triggered thereby into its
quasi-stable output state. The manner of operation of the
monostable multivibrator means 17 is identical to that described
hereinabove with respect to monostable multivibrator means 16 and
therefore need not be set forth in detail herein. It is observed
that when monostable multivibrator means 17 assumes the quasistable
output state thereof, a series circuit is completed from terminal
103 through coil 179 through transistor 176 to the common
conducting lead 105 thereby energizing coil 179 to close moveable
armature 180. The closure of moveable armature 180 completes a
series circuit from terminal 181 through the closed armature 180 to
energizing coil 191 of a solenoid included in clutch means 19.
Accordingly, the clutch means 19, which may include a mechanical
spring clutch member, is activated. The subsequent return of
monostable multivibrator means 17 to the stable output state
thereof interrupts the flow of current through coil 179 to thereby
open moveable armature 180, resulting in de-energization of the
coil 191. At this time the schematic diagram of FIG. 2 is now
prepared to respond to the leading and trailing edges of a
subsequently transported document. It is clear from the foregoing
explanation thereof, that monostable multivibrator means 16 and 17
cooperate with moveable armatures 170 and 180 and function as
switch means which may be closed for predetermined periods of time
to selectively connect coils 182 and 191 to the source of energy
provided at terminal 181.
Another embodiment of the control system in accordance with the
present invention is illustrated in FIG. 3 which comprises
photoelectric sensing means 10, Schmitt trigger means 13, bistable
means 31, pulse generating means 32 and 33, solenoid means 34 and
35, clutch means 18 and 19, and first and second mechanical
programming means 21 and 22. Photoelectric sensing means 10 is in
optical communication with a source of light 11 as described
hereinbefore with reference to FIG. 1 and is adapted to detect the
leading and the trailing edges of a document 12 transported in the
direction indicated by the arrow A. Photoelectric sensing means 10
is coupled to Schmitt trigger means 13, previously described, which
in turn is coupled to bistable means 31. Bistable means 31 is
characterized by first and second stable output states and is
adapted to detect transitions in the signal supplied thereto by
Schmitt trigger means 13. More specifically bistable means 31 is
capable of assuming the first stable output state thereof, when the
signal supplied thereto admits of a first level and to assume the
second stable output state thereof when the signal supplied thereto
admits of a second level. Hence bistable means 31 may comprise a
conventional bistable multivibrator circuit, a flip-flop circuit, a
two-position switch, a conventional relay circuit or the like.
Bistable means 31 is provided with first and second output
terminals wherein a signal is provided at the first output terminal
thereof in response to a detected positive transition in the signal
supplied thereto; and a signal is provided at the second output
terminal thereof in response to a detected negative transition in
the signal supplied thereto.
Pulse generating means 32 is coupled to the first output terminal
of bistable means 31 and is adapted to provide a pulse in response
to a signal supplied thereto. Pulse generating means 32 may be
similar to the aforedescribed pulse generating means 14 and
therefore may comprise a conventional differentiating circuit, a
unijunction transistor circuit, a univibrator, or the like. The
second output terminal of bistable means 31 is coupled to pulse
generating means 33 which is similar to just mentioned pulse
generating means 32. The pulse generating means 32 and 33 are
coupled to solenoid means 34 and 35, respectively, each of which
solenoid means is adapted to be energized in response to a pulse
generated by an associated pulse generating means. Solenoid means
34 and 35 are coupled to clutch means 18 and 19 which are adapted
to supply mechanical programming means 21 and 22 with the motor
power derived from motor drive system 20 in the now understood
manner previously described with respect to FIG. 1.
Operation of the apparatus represented by the block diagram of FIG.
3 will now be described. In the interest of brevity however, those
components corresponding to previously described components of FIG.
1 will not be explained in detail. Photoelectric sensing means 10
supplies a signal that exceeds a predetermined threshold level to
Schmitt trigger means 13 upon detecting the leading edge of
document 12. Schmitt trigger means 13 is triggered to its first
stable state in response to the signal supplied thereto thereby
applying a d.c. signal admitting of a first level to bistable means
31. The signal supplied to bistable means 31 is characterized by a
positive transition whereby bistable means 31 provides the first
output terminal thereof with a signal. As will be described
hereinafter the signal provided at the first output terminal of
bistable means 31 is preferably a d.c. signal having a
predetermined magnitude.
The signal provided at the first output terminal of bistable means
31 activates pulse generating means 32 to generate a positive pulse
in response thereto. The generated pulse energizes solenoid means
34, such as by enabling the energizing coil of the solenoid means
to be supplied with energy, thereby releasing the clutch means 18
to couple mechanical programming means 21 to motor drive system 20.
Upon termination of the pulse generated by pulse generating means
32, solenoid means 34 is de-energized and the coupling between
mechanical programming means 21 and motor drive system 20 is thence
removed after one complete rotation of the cam assembly includable
in the mechanical programming means.
Bistable means 31 provides a constant signal at the first output
terminal thereof until photoelectric sensing means 10 detects the
trailing edge of document 12. Photoelectric sensing means 10
responds to the passing of the trailing edge of document 12 through
the optical path defined by source of light 11 and the
photoelectric sensing means 10 by providing a signal of magnitude
less than the predetermined threshold level to Schmitt trigger
means 13. Accordingly Schmitt trigger means 13 assumes its second
state whereupon bistable means 31 is provided with a signal
admitting of a second level. Bistable means 31 assumes the second
stable output state thereof in response to the negative transition
in the signal supplied thereto. Consequently the signal provided at
the first output terminal of bistable means 31 is terminated and
the second output terminal thereof is provided with a d.c. signal
of predetermined magnitude. The signal provided at the second
output terminal of bistable means 31 is applied to pulse generating
means 33 whereupon a positive pulse is generated. The generated
pulse is effective to energize solenoid means 35, such as by
enabling the energizing coil of the solenoid means to be supplied
with energy, such that clutch means 19 is released to couple
mechanical programming means 22 to motor drive system 20. Solenoid
means 35 is de-energized when the pulse generated by pulse
generating means 33 terminates and the cam assembly includable in
mechanical programming means 32 effects one complete rotation. It
is readily apparent that if desired, pulse generating means 32 and
33 may be replaced by a single conventional pulsing circuit having
first and second output terminals coupled to solenoid means 34 and
35 respectively. In addition the combination comprising bistable
means 31, pulse generating means 32, and pulse generating means 33
may be replaced by a single conventional circuit adapted to
generate pulses in response to transitions in the signal applied
thereto. An exemplary circuit is disclosed at page 18 of the first
edition of Electronics Handbook of Circuit Design published by
McGraw-Hill, Inc. New York, New York.
A schematic diagram of a portion of the apparatus represented in
FIG. 3 is illustrated in FIG. 4 and comprises photoelectric sensing
means 10, Schmitt trigger means 13, bistable means 31, pulse
generating means 32 and 33, and solenoid means 34 and 35. The
photoelectric sensing means 10 and Schmitt trigger means 13 have
been described in detail hereinabove. Accordingly, further
description thereof is not deemed necessary for a complete
understanding of the schematic illustration of FIG. 4. The
collector electrode of transistor 136 of Schmitt trigger means 13
is coupled to the base electrode of transistor 312 of bistable
means 31 by resistance 310. A biassing potential is applied to the
base electrode of transistor 312 by resistance 311. Transistor 312
is arranged in a conventional relay driving circuit having a relay
coil 313 in the collector circuit thereof. As is understood
transistor 312 may comprise a conventional switching transistor,
well known to those of ordinary skill in the art. Relay coil 313 is
magnetically coupled to a conventional relay armature 314 which, in
turn, is connected to terminal 103. Relay armature 314 is adapted
to contact first and second relay contacts 315 and 316
respectively, in accordance with the energization of relay coil
313. More specifically, energization of coil 313 enables relay
armature 314 to complete a circuit from terminal 103 to relay
contact 315. Conversely, de-energization of relay coil 313 enables
relay armature 314 to complete a series circuit from terminal 103
to relay contact 316.
Relay contact 315 is connected to capacitance 322 of pulse
generating means 32. A d.c. current path from relay contact 315 to
common conducting lead 105 is provided by resistance 321.
Capacitance 322 is connected in series relationship with
resistances 324 and 325 thereby forming a conventional
differentiating circuit. Diode 323 is coupled from the common
junction of capacitance 322 and resistance 324 to the common
conducting lead 105 and is suitably poled to inhibit the production
of negative pulses. The common junction of resistances 324 and 325,
which corresponds to the output terminal of a conventional
differentiating circuit, is coupled to the base electrode of
transistor 326. Transistor 326 is arranged in conventional relay
driving configuration, similar to the configuration previously
described with respect to transistor 312, and includes an
energizing coil 327 of a relay circuit connected to the collector
electrode thereof. Energizing coil 327 is magnetically coupled to
moveable armature 328 which, in turn, is capable of completing a
series circuit from terminal 341 to the activating coil 342 of a
conventional solenoid means 34.
The second relay contact 316 of bistable means 31 is connected to
capacitance 332 of pulse generating means 33. Pulse generating
means 33 is similar to the aforementioned pulse generating means 32
and therefore includes a conventional differentiating circuit
comprised of capacitance 332, resistance 334 and resistance 335
connected in series relationship. Diode 333 is connected from the
common junction of capacitance 332 and resistance 334 to the common
conducting lead 105 and is suitably poled to inhibit the production
of negative pulses. The common junction of resistances 334 and 335
is connected to the base electrode of transistor 336 arranged in
conventional relay driving configuration and including energizing
coil 337 connected to the collector electrode thereof. Energizing
coil 337 is magnetically coupled to moveable armature 338 which is
adapted to complete a series circuit from terminal 341 to
activating coil 351 of the conventional solenoid means 35.
The operation of the apparatus represented by the schematic diagram
illustrated in FIG. 4 will now be described. As is now understood
detection of the leading edge of a document results in an increase
in the impedance of photoelectric sensing means 10 and a
corresponding increase in the voltage provided at the collector
electrode of transistor 136. Hence Schmitt trigger means 13 assumes
its first stable state and a signal admitting of a first level is
provided at the collector electrode of transistor 137. One of
ordinary skill in the art will recognize that photoelectric sensing
means 10 may alternatively comprise a photodiode, a phototransistor
or the like, interposed in series relationship between resistance
104 and moveable contact 102.
The signal provided at the collector electrode of transistor 136 is
applied to the base electrode of transistor 312 and is of a
magnitude sufficient to drive the latter transistor into its
conducting state. Accordingly a series circuit is completed from
terminal 103 through relay coil 313 through transistor 312 to the
common conducting lead 105. Current flowing in the completed series
circuit energizes the relay coil 313 to urge relay armature 314
into contact with relay contact 315. As a consequence thereof a
series circuit is completed from terminal 103 through relay
armature 314 to relay contact 315 to the common junction of
resistance 321 and capacitance 322. Hence the voltage at said
common junction rapidly increases to a value equal to +V whereby
the differentiating circuit produces a positive pulse 329. It is
observed that the positive pulse 329 provides a reverse bias on the
diode 323 which, in turn, corresponds to an open circuit. The
positive pulse 329 is applied to the base electrode of transistor
326 thereby driving the transistor into its conducting state. When
transistor 326 assumes its conducting state, a series circuit is
completed from terminal 103 through energizing coil 327 through
transistor 326 to the common conducting lead 105. The flow of
current through the completed circuit energizes the energizing coil
327 to close moveable armature 328. The closure of armature 328
enables the activating coil 342 of solenoid means 34 to be supplied
with energy applied to terminal 341. Solenoid means 34 is thus
activated to release clutch means 18 as hereinabove described.
Pulse 329 terminates after a brief duration thereof, whereupon
transistor 326 returns to its non-conducting state. Accordingly,
coil 327 is de-energized, moveable armature 328 is opened and
solenoid means 34 is de-activated. It is recognized however, that
the solenoid means 34 need be activated for only a brief interval
of time to enable clutch means 18 to release.
Subsequent to the detection of the leading edge of a document,
light communication to photoelectric sensing means 10 is
interrupted and transistor 312 is maintained in its conducting
state by the application of a signal admitting of a first level to
the base electrode thereof. Hence, relay armature 314 remains in
contact with relay contact 315 and capacitance 322 retains a
constant voltage substantially equal to +V. Consequently, pulse
generating means 32 does not provide further pulses. Upon detecting
the trailing edge of a document however, the base electrode of
transistor 131 is supplied with a signal that is less than the
predetermined threshold level. Accordingly, Schmitt trigger means
13 assumes its second stable state and the signal provided at the
collector electrode of transistor 136 is characterized by a
negative transition from the first level to a second level. The
decrease in magnitude of the voltage applied to the base electrode
of transistor 312 is effective to switch said transistor into its
non-conducting state. Hence current ceases to flow through relay
coil 313 thereby de-energizing the coil and relay armature 314 is
urged into contact with relay contact 316.
When relay armature 314 is removed from relay contact 315, the
voltage stored by capacitance 322 discharges through resistance 321
and rapidly decreases to provide a forward bias on diode 323. The
diode thus provides a short circuit in shunt relationship with the
differentiating circuit of pulse generating means 32, thereby
inhibiting the generation of a negative pulse. The completed series
circuit from terminal 103 through relay armature 314 to relay
contact 316 provides a rapidly increasing voltage at the common
junction of resistance 331 and capacitance 332. This rapidly
increasing voltage is differentiated by the differentiating circuit
comprising pulse generating means 33 and a positive pulse 339 is
applied to the base electrode of transistor 336. It is recognized
that the positive pulse 339 applies a reverse bias on diode 333
which diode is now equivalent to an open circuit. Pulse 339, which
admits of short duration, drives transistor 336 into its conducting
state thereby completing a series circuit from terminal 103 through
energizing coil 337 through transistor 336 to the common conducting
lead 105. The energization of coil 337 closes moveable armature 338
whereby activating coil 351 of solenoid means 35 is supplied with
energy from terminal 341. The termination of pulse 339 returns
transistor 336 to the nonconducting state thereof, and coil 337 is
de-energized. Accordingly moveable armature 338 is opened to
interrupt the supply of energy to activating coil 351. The relay
armature 314 ramains in contact with relay contact 316 and
capacitance 332 retains a constant voltage substantially equal to
+V. Consequently, pulse generating means 33 does not provide
further pulses.
It is readily apparent from the foregoing explanation that moveable
armature 328 and 338 of FIG. 4 correspond to the aforedescribed
armatures 170 and 180 of FIG. 2. In addition, activating coils 342
and 351 correspond to aforedescribed coils 182 and 191. One of
ordinary skill in the art will recognize that transistors 326 and
336 may be replaced by other conventional switching devices, such
as silicon control switches or the like, adapted to selectively
energize coils 327 and 337. Likewise, transistor 312 may be
replaced by a conventional switching device for energizing coil 313
in accordance with the level of the signal produced by Schmitt
trigger means 13. It is further recognized that the differentiating
circuits illustrated in FIG. 2 and in FIG. 4 may be replaced by
conventional operational amplifier differentiating means well known
to those of ordinary skill in the art. Furthermore the Schmitt
trigger means 13 and other conventional circuits illustrated herein
may be comprised of conventional discrete components or of
integrated circuits. Moreover the transistor elements utilized in
the present invention are not limited to the n-p-n configurations
illustrated but may include other conventional transistors such as
p-n-p transistors, field effect transistors or the like.
While the invention has been particularly shown and described with
reference to a plurality of embodiments thereof and a particular
application thereof, it will be obvious to those of ordinary skill
in the art that the present invention admits of general application
with a device for performing operations upon sheets of material
having variable length. The operations executed by the device may
be individually performed or sequentially performed as described
hereinabove. Moreover execution of the operations may be controlled
by conventional controlling means such as the mechanical
controlling means aforedescribed, or electrical controlling means
well known to those skilled in the art. Therefore the foregoing and
various other changes and modifications in form and details may be
made without departing from the spirit and scope of the invention.
Consequently, it is intended that the appended claims be
interpreted as including all such changes and modifications.
* * * * *