U.S. patent number 3,734,604 [Application Number 05/181,374] was granted by the patent office on 1973-05-22 for failsafe system for electrostatic copying apparatus.
This patent grant is currently assigned to Afga-Gevaert Aktiengesellschaft. Invention is credited to Karl Hartwig, Gunter Maurischat, Roland Szostak.
United States Patent |
3,734,604 |
Szostak , et al. |
May 22, 1973 |
FAILSAFE SYSTEM FOR ELECTROSTATIC COPYING APPARATUS
Abstract
An electrostatic copying apparatus wherein a photoelectric
detector scans the path for transfer sheets which receive powder
images from a drum-shaped xerographic surface. The detector
cooperates with two timers the first of which is actuated by the
latent image producing device to furnish signals at intervals when
the detector normally should not detect sheets and the second of
which is also actuated by the latent image producing device but at
such intervals that it furnishes signals when the detector normally
should detect transfer sheets. The operation of the apparatus is
terminated if a signal from the detector coincides with the signal
from the first timer because this indicates a pileup of sheets, and
also if a signal from the detector does not coincide with a signal
from the second timer because this indicates the exhaustion of the
supply of sheets in the apparatus. The detector scans the path for
the sheets upstream of a fusing station wherein the powder images
are fixed to respective sheets.
Inventors: |
Szostak; Roland (Grunwald,
DT), Hartwig; Karl (Unterhaching, DT),
Maurischat; Gunter (Munich, DT) |
Assignee: |
Afga-Gevaert Aktiengesellschaft
(Leverkusen, DT)
|
Family
ID: |
5783087 |
Appl.
No.: |
05/181,374 |
Filed: |
September 17, 1971 |
Foreign Application Priority Data
|
|
|
|
|
Sep 22, 1970 [DT] |
|
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P 20 46 681.3 |
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Current U.S.
Class: |
399/33; 271/259;
340/675; 399/166 |
Current CPC
Class: |
G03G
15/70 (20130101) |
Current International
Class: |
G03G
15/00 (20060101); G03g 015/00 () |
Field of
Search: |
;355/14,3,8 ;271/57
;340/259 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Moses; Richard L.
Claims
We claim:
1. In an electrostatic copying apparatus, a combination comprising
a driven xerographic surface; means for producing on said surface a
series of electrostatic latent images by imaging successive
portions of at least one original onto successive portions of said
surface; means for converting said latent images into powder
images; feeding means for transferring successive powder images
onto successive sheets of transfer material -- which are normally
separated from each other by gaps each extending between the
trailing edge of a preceding sheet and the leading edge of the
next-following sheet -- by conveying such sheets into a
predetermined path wherein the leading edge of each sheet contacts
said surface at a first point and the trailing edge of each sheet
moves away from contact with said surface at a second point; fusing
means adjacent to said path downstream of said second point and
arranged to fix the powder images to the respective sheets; sheet
advancing means adjacent to said path downstream of said fusing
means; photoelectric detector means adjacent to a predetermined
portion of said path intermediate said second point and said
advancing means to produce first signals in response to detection
of sheets in said portion of said path; and timer means actuatable
by said means for producing said latent images to produce second
signals at such intervals that, while said timer means is being
actuated, one of said gaps is located in said predetermined portion
of said path in the normal course of transport of sheets into the
range of said advancing means so that the generation of first
signals by said detector means normally does not coincide with the
generation of second signals by said timer means.
2. A combination as defined in claim 1, further comprising drive
means for continuously moving said surface at a predetermined
speed, said feeding means being arranged to convey said sheets into
said path at said predetermined speed and said advancing means
comprising a pair of rotary members located at the opposite sides
of said path and means for rotating at least one of said rotary
members.
3. A combination as defined in claim 1, further comprising drive
means for continuously moving said surface at a predetermined
speed, said feeding means being arranged to convey said sheets into
said path at said predetermined speed and said means for producing
said latent images comprising a carriage arranged to move originals
with reference to said surface and means for imaging successive
portions of the thus moved original onto successive portions of
said surface, said carriage comprising means for actuating said
timer means.
4. A combination as defined in claim 3, wherein said timer means
comprises electric switch means and said means for actuating said
switch means includes a projection provided on said carriage.
5. A combination as defined in claim 1, further comprising means
for terminating the operation of said apparatus in response to
simultaneous generation of first and second signals by said
detector means and said timer means.
6. A combination as defined in claim 5, wherein said operation
terminating means comprises means for terminating the movement of
said surface and for deactivating said fusing means and said
feeding means.
7. A combination as defined in claim 1, further comprising second
timer means for generating third signals at such intervals that,
during the generation of third signals, said detector means
produces first signals in response to detection of successive
sheets in said predetermined portion of said path in the normal
course of transport of sheets along said path, and means for
terminating the operation of said apparatus in response to the
absence of simultaneous generation of first and third signals by
said detector means and said second timer means.
8. A combination as defined in claim 7, wherein the means for
terminating the operation of said apparatus in response to the
absence of simultaneous generation of first and third signals by
said detector means and said second timer means comprising an
electric circuit.
9. In an electrostatic copying apparatus, a combination comprising
a driven xerographic surface; means for producing on said surface a
series of electrostatic latent images by imaging successive
portions of at least one original onto successive portions of said
surface; means for converting said latent images into powder
images; feeding means for transferring successive powder images
onto successive sheets of transfer material -- which are normally
separated from each other by gaps each extending between the
trailing edge of a preceding sheet and the leading edge of the
next-following sheet -- by conveying such sheets into a
predetermined path wherein the leading edge of each sheet contacts
said surface at a first point and the trailing edge of each sheet
moves away from contact with said surface at a second point; fusing
means adjacent to said path downstream of said second point and
arranged to fix the powder images to the respective sheets, said
fusing means comprising heat generating means; sheet advancing
means adjacent to said path downstream of said fusing means;
photoelectric detector means adjacent to a predetermined portion of
said path intermediate said second point and said advancing means
to produce first signals in response to detection of sheets in said
portion of said path; timer means actuatable to produce second
signals at such intervals that, while said timer means is being
actuated, one of said gaps is located in said predetermined portion
of said path in the normal course of transport of sheets into the
range of said advancing means so that the generation of first
signals by said detector means normally does not coincide with the
generation of second signals by said timer means; means for
terminating the operation of said apparatus in response to
simultaneous generation of first and second signals by said
detector means and said timer means, said operation terminating
means comprising means for terminating the movement of said surface
and for deactivating said fusing means and said feeding means; and
cooling means arranged to cool said fusing means irrespective of
the simultaneous generation of first and second signals by said
detector means and said timer means.
10. In an electrostatic copying apparatus, a combination comprising
a driven xerographic surface; means for producing on said surface a
series of electrostatic latent images by imaging successive
portions of at least one original onto successive portions of said
surface; means for converting said latent images into powder
images; feeding means for transferring successive powder images
onto successive sheets of transfer material -- which are normally
separated from each other by gaps each extending between the
trailing edge of a preceding sheet and the leading edge of the
next-following sheet -- by conveying such sheets into a
predetermined path wherein the leading edge of each sheet contacts
said surface at a first point and the trailing edge of each sheet
moves away from contact with said surface at a second point; fusing
means adjacent to said path downstream of said second point and
arranged to fix the powder images to the respective sheets; sheet
advancing means adjacent to said path downstream of said fusing
means; photoelectric detector means adjacent to a predetermined
portion of said path intermediate said second point and said
advancing means to produce first signals in response to detection
of sheets in said portion of said path; said detector means
comprising a signal emitting element; timer means actuatable to
produce second signals at such intervals that, while said timer
means is being actuated, one of said gaps is located in said
predetermined portion of said path in the normal course of
transport of sheets into the range of said advancing means so that
the generation of first signals by said detector means normally
does not coincide with the generation of second signals by said
timer means, said timer means comprising switch means which is
actuated periodically by said means for producing said latent
images; amplifier means for amplifying the first signals from said
element; a logical circuit having a first input connected with said
amplifier means, a second input arranged to receive second signals
on closing of said switch means, and an output arranged to emit
signals in response to simultaneous reception of first and second
signals at said first and second inputs; and means for terminating
the operation of said apparatus in response to signals from the
output of said logical circuit.
11. A combination as defined in claim 10, wherein said means for
terminating the operation of said apparatus comprises relay means
arranged to change its condition of energization in response to
signals from the output of said logical circuit and to thus
immediately terminate the operation of said apparatus.
12. In an electrostatic copying apparatus, a combination comprising
a driven xerographic surface; means for producing on said surface a
series of electrostatic latent images by imaging successive
portions of at least one original onto successive portions of said
surface; means for converting said latent images into powder
images; feeding means for transferring successive powder images
onto successive sheets of transfer material -- which are normally
separated from each other by gaps each extending between the
trailing edge of a preceding sheet and the leading edge of the
next-following sheet -- by conveying such sheets into a
predetermined path wherein the leading edge of each sheet contacts
said surface at a first point and the trailing edge of each sheet
moves away from contact with said surface at a second point; fusing
means adjacent to said path downstream of said second point and
arranged to fix the powder images to the respective sheets; sheet
advancing means adjacent to said path downstream of said fusing
means; photoelectric detector means adjacent to a predetermined
portion of said path intermediate said second point and said
advancing means to produce first signals in response to detection
of sheets in said portion of said path, said detector means
comprising a signal emitting element; first timer means actuatable
to produce second signals at such intervals that, while said timer
means is being actuated, one of said gaps is located in said
predetermined portion of said path in the normal course of
transport of sheets into the range of said advancing means so that
the generation of first signals by said detector means normally
does not coincide with the generation of second signals by said
timer means; second timer means actuatable by said means for
producing said latent images at such intervals that said
predetermined portion of said path contains successive sheets
during successive actuations of said second timer means in the
course of normal transport of sheets along said path, said second
timer means comprising electric switch means which is actuated
periodically by said means for producing said latent images to
produce third signals in response to actuation thereof; amplifier
means arranged to amplify the first signals emitted by said
element; a logical circuit having a first input connected with said
amplifier means, a second input connected with said switch means
and an output arranged to transmit signals in response to
simultaneous reception of first and third signals at said first and
second inputs thereof; and means for terminating the operation of
said apparatus in response to signals from the output of said
logical circuit.
Description
BACKGROUND OF THE INVENTION
The present invention relates to improvements in electrostatic
copying apparatus of the type wherein successive strip-shaped
portions of originals are imaged onto a xerographic surface which
is in continuous motion and moves at the exact speed of the
original as well as at the exact speed of sheet-like transfer
material which is to receive a powder image from the xerographic
surface. The freshly transferred powder image is thereupon caused
to pass through a fusing station to insure that it is permanently
affixed to transfer material.
A drawback of the presently known electrostatic copying apparatus
of the just outlined character is that the sheets of transfer
material, which normally consist of paper, are likely to pile up in
front of or at the fusing station and to be heated to kindling
temperature whereby the entire apparatus can go up in flames. Such
damage to or complete destruction of the copying apparatus is
likely to occur if the feeder for sheets of transfer material
continues to operate after a sheet has been caught in the apparatus
in close or immediate proximity of heated parts at the fusing
station.
SUMMARY OF THE INVENTION
An object of the invention is to provide an electrostatic copying
apparatus with a novel safety device or failsafe system which can
automatically terminate the operation of at least some units in
response to stoppage of a single sheet of transfer material or in
response to a pileup of two or more sheets at a point where such
pileup of several sheets or the stoppage of a single sheet could
result in minor or major damage to or total destruction of the
apparatus.
Another object of the invention is to provide the copying apparatus
with an additional safety device which insures automatic stoppage
of the apparatus (or at least all important component parts of the
apparatus) in response to exhaustion of the supply of sheets of
transfer material.
A further object of the invention is to provide the electrostatic
copying apparatus with a novel electric circuit which embodies the
just discussed safety devices.
An additional object of the invention is to provide the copying
apparatus with a single detector for sheets of transfer material
which can be used to initiate the operation of either safety
device.
Still another object of the invention is to provide an
electrostatic copying apparatus which can be utilized to furnish
any desired number of copies of a single original and wherein such
versatility of the apparatus can be achieved by a device which
performs at least one additional important function.
The invention is embodied in an electrostatic copying apparatus
having a driven xerographic surface which is preferably a
cylindrical surface and is moved at a predetermined speed, means
for producing on the xerographic surface a series of electrostatic
latent images by imaging successive portions of at least one
original onto successive portions of such surface, means for
converting the latent images into powder images, for example, by
spraying the latent images with a suitably colored toner, feeding
means for transferring successive powder images onto successive
sheets of transfer material (which are normally separated from each
other by gaps each extending the trailing edge of a preceding sheet
and the leading edge of the next-following sheet) by conveying such
sheets into a predetermined path wherein the leading edge of each
sheet contacts the xerographic surface at a first point and moves
out of contact with such surface at a second point, fusing means
adjacent to the path downstream of the second point and having
means for fixing the powder images to respective sheets (preferably
by heating the toner to melting temperature but below the kindling
temperature of the sheets), sheet advancing means adjacent to the
path downstream of the fusing means, photoelectric detector means
adjacent to a predetermined portion of the path intermediate the
second point and the advancing means (preferably between the second
point and the fusing means) and serving to produce signals in
response to detection of sheets in the predetermined portion of the
path, and signal generating timer means which is actuable
(preferably by the means for producing latent images on the
xerographic surface) at such intervals that, while the timer means
is being actuated, the detector means does not produce a signal
because the actuation of the timer means should take place whenever
a gap is located in the predetermined portion of the path in the
course of normal transport of sheets along the path and into the
range of the advancing means so that the detector means then
normally fails to detect sheets in the predetermined portion of the
path. Simultaneously generation of signals by the detector means
and by the timer means indicates the likelihood of a pileup of
sheets, and such simultaneous signals are used to bring about at
least partial stoppage of the copying apparatus.
The stoppage of the apparatus may involve turning off or arresting
all movable parts, such as the xerographic surface, the components
of the latent image forming means, the component or components of
the converting means, the component or components of the feeding
means, and the heating device of the fusing means.
The novel features which are considered as characteristic of the
invention are set forth in particular in the appended claims. The
improved copying apparatus itself, however, both as to its
construction and its mode of operation, together with additional
features and advantages thereof, will be best understood upon
perusal of the following detailed description of certain specific
embodiments with reference to the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic representation, in partial section, of a
presently preferred embodiment of the copying apparatus; and
FIG. 2 is a circuit diagram of the apparatus shown in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG. 1, there is shown an electrostatic copying
apparatus, also called xerographer development apparatus, which
comprises a drum-shaped xerographic surface 1 (hereinafter called
drum) which is connected with the ground by way of its drive shaft
1a. The periphery of the drum 1 is provided with the customary
photoconductive layer of selenium successive increments of which
travel along a charging station 101 accommodating a corona
discharge device 2. The shaft 1a receives torque from a main prime
mover 58 (FIG. 2) and drives the drum 1 in a counterclockwise
direction as indicated by the arrow A so that the increments on
which a uniform electrostatic charge is deposited by the corona
discharge device 2 move past an exposure station 102 accommodating
the objective lens 3 which images on the drum 1 successive strips
of an original 4, e.g., a copy to be reproduced. The original 4 is
illuminated by two tubular lamps 5, 6 and is supported by a
carriage 7 which is reciprocable by a drive including a cord or
cable 8 and a helical resetting spring 21. The cord 8 moves the
carriage 7 (and the original 4 thereon) forwardly (arrow B) at the
exact peripheral speed of the drum 1. It will be noted that the
direction of forward movement of the carriage 7 (arrow B) is
counter to the direction of rotation of the drum 1 (arrow A). The
forward end of the cord 8 is connected to a pulley (not shown)
which is coupled to the drum 1 in response to energization of an
electromagnetic clutch (not shown) which can be energized by a
starter switch accessible to the operator of the copying apparatus.
The circuit of the electromagnetic clutch is opened by the carriage
7 when the latter completes a forward stroke (arrow B) of
predetermined length whereby the resetting spring 21 returns the
carriage 7 to a starting position (to the left of the position
shown in FIG. 1) in which the carriage abuts against a fixed stop
20. Such clutches are well known from the art of electrostatic
copying apparatus. The parts 3, 5, 6, 7 and the drive for the
carriage 7 together constitute a means for producing on the drum a
series of electrostatic latent images by repeatedly imaging
successive portions of a single original 4 or by imaging successive
portions of several discrete originals, one after the other.
The electrostatic latent images of one or more originals 4 are
transported past a development station 103 accommodating a
conventional dispenser 19 for pulverulent developing material of
the type known as toner. The dispenser 19 constitutes a means for
converting latent images into powder images which adhere to the
drum 1. The toner is normally a pigmented resin which is held on
the drum 1 electrostatically to form thereon a powder image pattern
which is thereupon transferred onto a sheet-like transfer material
10a (hereinafter called sheets) at a transfer station 104. The
sheets 10a normally consist of paper and are removed seriatim from
a stack 10 on a table 10A by a feeder 9 having a roller 9d which
engages the topmost sheet of the stack 10 while moving in a forward
direction (arrow C). The feeder 9 is connected with a cable or cord
9a which can be driven by the drum 1 in the same way as the cord 8,
i.e., by an electromagnetic clutch (not shown) which can drive a
pulley or sheave attached to the forward end of the cord 9a. A
helical resetting spring 9b returns the feeder 9 to a starting
position, in which a projection of the feeder abuts against a stop
9c, as soon as the clutch is deenergized so that the pulley for the
cord 9a ceases to share the angular movement of the drum 1. The
clutch for the pulley of the cord 9a is energized by a switch (not
shown) which is actuated by the carriage 7 in such a way that the
leading edge of a freshly withdrawn sheet 10a enters the transfer
station 104 simultaneously with the powder image on the
photoconductive layer of the drum 1. The switch for the just
discussed electromagnetic clutch is opened by the carriage 7 to
deenergize the clutch and to permit return movement of the feeder 9
under the action of the resetting spring 9b when the leading edge
of the freshly delivered sheet 10a contacts the periphery of the
drum 1. The carriage 7 can be provided with lobes, cams, arms or
analogous actuating means for the switches which control the
electromagnetic clutches for the cords 8 and 9a. The leading edge
of a freshly withdrawn sheet 10a enters the transfer station 104 to
contact the drum 1 at a first point P1 of a predetermined path 110
and the trailing edge of such sheet leaves the transfer station 104
and thus moves out of contact with the drum 1 at a second point P2
of the path 110.
The transfer station 104 accommodates a second corona discharge
device 11 which provides the rear side of the sheet 10a with an
electrostatic charge corresponding to that of the drum 1. This
causes the particles of the negatively charged toner to adhere to
the adjacent surface of the sheet 10a to form thereon an image of
the original 4. The electrostatically transferred powder image is
thereupon permanently fixed to the sheet 10a at a fusing or fixing
station 106 which is adjacent to the path 110 but is not adjacent
to the peripheral surface of the drum 1. Prior to reaching the
fusing station 106, successive increments of each sheet 10a pass
through a separating station 105 which accommodates a corona
discharge device 13. The purpose of the corona discharge device 13
is to neutralize the charge which is applied to the rear side of
the sheet 10a by the corona discharge device 11 at the transfer
station 104. The separating station 105 may further accommodate a
blower nozzle 16 having one or more orifices 16a which discharge
one or more streams of slightly compressed air to further promote
the separation of successive sheets 10a from the drum 1. The nozzle
16 constitutes a desirable but optional feature at the separating
station 105; the source of compressed gas for this nozzle is not
shown in FIG. 1. Such compressed gas can be furnished by the blower
61 (FIG. 2) of a cooling device for the copying apparatus,
especially for the parts at the fusing station 106. The separating
station 105 can be said to form the rightmost part of the transfer
station 104 and is adjacent to that portion of the path 110 which
includes the point P.sub.2.
The parts at the fusing station 106 include a heat radiating device
15 above and a metallic plate-like guide 18 below the path 110 for
successive sheets 10a. The heat which is generated by the device 15
causes the particles of toner to melt and to be absorbed by the
material of the respective sheets 10a. The fusing station 106 is
located immediately upstream of two sheet advancing rolls 17a, 17b
at least one of which is driven by the prime mover 58 or by the
drum 1 to move the sheets 10a into an intercepting receptacle which
is accessible from without the copying apparatus.
After moving beyond the separating station 105, successive
increments of the drum 1 travel past a cleaning station 107 which
accommodates a rotary brush 14 serving to remove the remnants of
toner before the thus cleaned increments of the photoconductive
layer reenter the charging station 101.
In accordance with a feature of the present invention, the
electrostatic copying apparatus further comprises a photoelectric
detector PD including a light source 24 which emits a beam of light
against the dark peripheral surface of the drum 1 or against a
sheet 10a which travels along the path 110 between the separating
station 105 (point P.sub.2) and the advancing rolls 17a, 17b. In
the illustrated embodiment, the photoelectric detector PD is
disposed between the point P.sub.2 and the fusing station 106. The
light source 24 is partially surrounded by a suitably configurated
reflector 24a and the light sensitive signal generating element 23
of the photoelectric detector PD is adjacent to a shield 22 which
insures that the light-sensitive surface of the element 23 is
exposed only or mainly to light which issues from the source 24 and
is reflected on the drum 1 or on a passing sheet 10a.
As shown in FIG. 2, the light sensitive element 23 of the
photoelectric detector PD is connected in series with a resistor 27
and by a conductor 25 to the negative pole of a source of 12 volt
current. A second conductor 26 connects the resistor 27 with the
positive pole of a source of 12 volt current. The resistance of the
resistor 27 is much smaller then the resistance of the light
sensitive element 23 when the latter receives light which is
emitted by the light source 24 and is reflected on the dark
peripheral surface of the drum 1. Thus, the potential at the
junction 28 between the resistor 27 and the light sensitive element
23 is then a positive potential. However, when the light sensitive
element 23 is exposed to light which issues from the source 24 and
is reflected on the normally white surface of a passing sheet 10a,
its resistance is much smaller than that of the resistor 27, i.e.,
the potential at the junction 28 is then a negative potential. The
sheets 10a (or at least those sides of the sheets which face away
from the drum 1) need not be white, as long as their opacity is
sufficiently less than the opacity of the peripheral surface on the
drum 1 to thus insure that the resistance of the light sensitive
element 23 is less than the resistance of the resistor 27 when the
element 23 is exposed to light which is reflected on a sheet 10a.
It will be noted that the just described components of the electric
circuit which is shown in FIG. 2 act not unlike a switch which
applies to the junction 28 a positive potential in the absence of a
sheet 10a between the stations 105, 106 and a negative potential
when the photoelectric detector PD detects a sheet 10a.
The junction 28 is connected with a conductor 29 which is connected
with two differential amplifiers 32, 33 by way of conductors 30,
31. The output of the amplifier 32 is connected with one input of a
first logical circuit here shown as an AND-gate 36 by a conductor
34, and the output of the amplifier 33 is connected with one input
of a second logical circuit or AND-gate 37 by a conductor 35. The
other inputs of the AND-gates 36, 37 can be connected with the
conductor 26 by conductors 38, 42 and 39, 43. The conductors 39, 43
are connected to the contacts of a first timer here shown as a
microswitch 41, and the conductors 38, 42 are connected with the
contacts of a second timer or microswitch 40. As shown in FIG. 1,
the microswitches 40, 41 are respectively provided with trips 40a,
41a which can be displaced by a projection 142 of the carriage 7
for originals 4. The microswitch 41 is positioned in such a way
that it is closed by the projection 142 in the very moment when the
trailing edge of a sheet 10a has moved beyond the detector PD in
the course of normal operation of the copying apparatus. The
microswitch 41 can cause the output of the AND-gate 37 to transmit
a signal in the event of a pileup of sheets 10a in the copying
apparatus, namely, between the stations 105 and 106.
The projection 142 of the carriage 7 causes the trip 40a to close
the microswitch 40 at such intervals that when, if the copying
apparatus operates normally, the light sensitive surface of the
element 23 must be exposed to light which is reflected on a sheet
10a. Thus, the microswitch 40 can cause the output of the AND-gate
36 to transmit a signal which indicates the absence of sheets in
the path 110 of the copying apparatus, and more particularly the
absence of a sheet 10a in the space between the stations 105 and
106 at a time when the corresponding portion of the path 110 for
the sheets 10a should have accommodated a passing sheet.
The differential amplifier 32 is connected in the circuit of FIG. 2
in such a way that it transmits a signal via conductor 34 when the
potential at the junction 28 is a positive potential, i.e., when
the light sensitive element 23 of the detector is exposed to light
which is reflected on the opaque surface of the drum 1. Since the
microswitch 40 closes at a time when the portion of the path 110
between the stations 105 and 106 should accommodate a sheet 10a,
the two inputs of the AND-gate 36 receive signals at the same time
only when the operation is improper because a sheet 10a fails to
advance toward the fusing station 106 at a time when the fusing
station should receive a sheet. The differential amplifier 33
transmits to the corresponding input of the AND-gate 37 a signal
when the potential at the junction 28 is a negative potential.
Since the switch 41 closes at a time when the detector PD should
not detect a sheet between the stations 105, 106 (and more
particularly in that portion of the path 110 for sheets 10a which
is traversed by the light beam issuing from the light source 24),
the output of the AND-gate 37 will transmit a signal only when a
sheet 10a has become stuck in or ahead of the fusing station 106 or
in the event of a pileup of two or more sheets between the stations
105 and 106. The microswitch 41 is held by the projection 142 of
the carriage 7 in closed position for an interval of time which
normally elapses between the movement of the trailing edge of a
preceeding sheet 10a beyond the beam issuing from the light source
24 and the movement of the leading edge of the next following sheet
10a into such light beam, i.e., while a gap between two successive
sheets moves past the detector PD.
The outputs of the AND-gates 36, 37 are respectively connected with
pulse transformers 47, 46. These transformers amplify the incoming
signals and convert such signals into constant signals of proper
polarity. The pulse transformer 46 is connected with a relay 49 by
way of a conductor 48. The switch 55 of the relay 49 is connected
in one power lead 56 of the main energy source for the
current-consuming parts of the copying apparatus. Such current
consuming parts include one or more lamps one of which is shown at
60, the main prime mover 58 which is an electric motor, the coils
59 of the radiation heater 15 at the fusing station 106, and the
aforementioned blower 61 of the means for cooling the parts at the
station 106.
The pulse transformer 47 is connected with a second relay 53 by way
of conductors 50, 51 and a time-delay element 52. The switch 54 of
the second relay 53 is also connected in the power lead 56 of the
main energy source which later further includes a second power lead
57. It will be noted that the opening of relay switch 54 results in
stoppage of the motor 58 and in opening of the circuit of the lamp
or lamps 60. The opening of switch 55 entails stoppage of the motor
58, opening of the circuit of the lamp or lamps 60, and opening of
the circuit of the coil 59 in the readiation heater 15. The motor
for the blower 61 is connected with the power leads 56, 57 in such
a way that the blower 61 continues to cool the parts 15, 18 at the
fusing station 106 even if the relays 49, 53 cause simultaneous
opening of the switches 54 and 55. The operation of the copying
apparatus is terminated in response to opening of the switch 54 or
motor 58 which drives drum 1 (and hence the carriage 7 and feeder
9) as well as the wheel 19a of the dispenser 19, the brush 14, and
the advancing rolls 17a, 17b.
THE OPERATION:
The switches 54, 55 are assumed to be closed so that the motor 58
drives the drum 1 (by way of the shaft 1a), the brush 14, the wheel
19a of the dispenser 19, and the advancing rolls 17a, 17b. The
circuit of the coil 59 and lamp or lamps 60 is also completed and
the blower 61 cools the parts 15, 18 at the fusing station 106. If
the operator wishes to obtain a copy of an original 4 which has
been placed onto the carriage 7, it is necessary to close a master
switch (not shown) which energizes the electromagnet for the pulley
of the cord 8 so that the carriage 7 begins to move in the
direction indicated by the arrow B at the exact peripheral speed of
the drum 1. The lens 3 images the original 4 on the drum 1 to form
thereon an electrostatic latent image. As the carriage 7 moves in a
direction to the right, as viewed in FIG. 1, it closes a switch
(not shown) which energizes the electromagnet for the pulley of the
cord 9a so that the feeder 9 begins to advance the topmost sheet
10a of the stack 10 in the direction indicated by the arrow C. When
the carriage 7 has covered such a distance that, in the course of
normal operation of the copying apparatus the leading edge of the
freshly supplied sheet 10a would have to be located in front of the
light source 24, the projection 142 closes the microswitch 40 by
way of the trip 40a. The output of the AND-gate 36 transmits a
signal to the pulse transformer 47 only if the detector PD detects
the absence of a sheet 10a between the stations 105 and 106. The
signal from the pulse transformer 47 is delayed by the element 52
which opens the switch 54 of the relay 53 after elapse of an
interval which corresponds to that required for completion of a
working cycle. The opening of switch 54 results in stoppage of the
motor 58 and in opening of the circuit of the lamp or lamps 60. The
circuit of the coil 59 in the radiation heater 15 remains completed
and the blower 61 continues to cool the parts 15, 18 at the fusing
station 106. The operation of the copying apparatus can begin as
soon as the supply of sheets 10a is replenished.
The microswitch 41 is open during the just described stage of
operation so that the output of the AND-gate 37 cannot transmit a
signal to the pulse transformer 46 and the switch 55 of the relay
49 remains closed. The trip 41a for the microswitch 41 is actuated
by the projection 142 only when the trailing edge of a sheet 10a is
supposed to have advanced beyond the light beam which is emitted by
the light source 24 of the detector PD between the stations 105 and
106. If the detector detects the presence of a sheet 10a between
such stations, the corresponding input of the AND-gate 37 receives
a signal from the amplifier 33 and the pulse transformer 46 causes
the relay 49 to immediately open the switch 55 and to this arrest
the motor 58 simultaneously with opening of the circuit for the
lamp or lamps 60 and coil 59. The blower 61 is not affected by the
opening of switch 55 so that it can continue to cool those parts of
the apparatus which are normally heated to an elevated
temperature.
It will be noted that the photoelectric detector PD normally fails
to produce such signals which cause immediate opening of the switch
55 and the resulting termination of operation of the copying
apparatus. This is due to the fact that, in the course of normal
operation, the light sensitive element 23 fails to produce signals
simultaneously with those signals which are produced in response to
closing of the timer or microswitch 41 because the microswitch 41
is closed at such intervals and for such periods of time that its
closing coincides with the passage of a gap between two successive
sheets 10a past that portion of the path 110 which is scanned by
the detector PD. However, if a sheet 10a happens to be located in
the space between the stations 105, 106 at a time when this portion
of the path 110 should not contain a sheet, the light sensitive
element 23 causes the amplifier 33 to transmit a signal to the
corresponding input of the AND-gate 37 at the exact moment when the
other input of the AND-gate 37 receives a signal because the
microswitch 41 is closed; the relay 49 is then energized without
delay and immediately opens the switch 54 to terminate the
operation of the copying apparatus.
On the other hand, the amplifier 32 transmits to the corresponding
input of the AND-gate 36 a signal only when the light sensitive
element 23 does not produce a signal which is indicative of the
presence of a sheet 10a in that portion of the path 110 which
extends between the stations 105, 106. Since the timer or
microswitch 40 is closed at a time when, in the course of normal
operation of the copying apparatus, the just mentioned portion of
the path 110 should contain a sheet 10a, the signal from the output
of the AND-gate 36 indicates the absence of sheets 10a in the path
110, and such signals cause a stoppage of the apparatus (by way of
the relay 53 and switch 54) with a delay which is determined by the
element 52.
The just discussed timers 40, 41 for the logical circuits 36, 37
cooperate with the light sensitive element 23 of the photoelectric
detector PD to insure automatic stoppage of the copying apparatus
in response to a pileup of sheets 10a in that portion of the path
110 which extends between the advancing rolls 17a, 17b and the
point P2 as well as in response to unwarranted absence of sheets
10a in such portion of the path 110. The pileup could cause heating
of the arrested sheets to kindling temperature and the resulting
fire could caused serious damage to or total destruction of the
apparatus. The absence of sheets 10a can indicate the exhaustion of
the supply of sheets 10a on the table 10A, and this warrants a
stoppage of the apparatus. Furthermore, the operator can rely on
the microswitch 40 to produce a desired number of copies of a
single original 4. For example, an original can be placed onto the
carriage 7 and a predetermined number of sheets 10a is then placed
onto the table 10A. The copying apparatus is started and the
microswitch 40 will cooperate with the light sensitive element 23
to automatically arrest the apparatus when the supply of sheets 10a
on the table 10A is exhausted, i.e., when the apparatus has
completed the making of a predetermined number of copies of a
single original. This renders its unnecessary to equip the copying
apparatus with a conventional selector knob which can be moved to
several positions in each of which the apparatus produces a
different number of copies of the same original, or the selector
knob can be designed to serve as a means for preparing the
apparatus for the making of one, two, three or four copies
only.
Each of the switches 54, 55 can actuate a device which produces a
visible or audible signal when the switch 54 or 55 opens. The lamp
or lamps 60 can be said to constitute a device for generating
visible signals (absence of illumination) in response to opening of
the switch 54 or 55.
The operation of the light sensitive element 23 and microswitch 41
is in contrast to operation of safety devices in presently known
electrostatic copying apparatus. As explained above, these parts
will cooperate to cause the switch 55 to open without any delay if
the portion of the path 110 which is scanned by the photoelectric
detector PD does not accommodate a gap between a pair of successive
sheets 10a at a time when the light beam issuing from the light
source 24 should normally impinge on the dark surface of the drum
1. Such cooperation of the element 23 with the microswitch 41 is of
advantage because the detector PD scans a portion of the path 110
wherein the accumulation of sheets 10a or unforeseen stoppage of a
single sheet 10a could result in damage of the copying apparatus
because the arrested sheet or sheets could be heated to kindling
temperature. If the operator fails to immediately remove a single
sheet which is stuck at the fusing station 106, the burning of such
single sheet is not likely to cause serious damage to the copying
apparatus. The next-following sheets are unable to reach the fusing
station 106 because the switch 55 opens in response to stoppage of
a single or foremost sheet 10a in the space between the stations
105 and 106.
The microswitch 40 and the associated parts 36, 32, 47, 52, 53, 54
constitute a desirable optional feature of the copying apparatus.
As explained above, these parts insure a delayed stoppage of the
apparatus in response to detection of the absence of sheets 10a in
a predetermined portion of the path 110 (between the advancing
rolls 17a, 17b and the point P2). Savings in space and material are
achieved due to the fact that the photoelectric detector PD can
cooperate with the microswitch 41 to indicate a pileup of sheets
10a as well as will the microswitch 40 to indicate the absence of
sheets 10a. In each instance, the main prime mover 58 of the
copying apparatus is arrested, either immediately or with a certain
delay. As explained above, the provision of the microswitch 40
renders it possible to dispense with the customary knob which
determines the number of copies to be made from a single original,
or to simplify the controls for such selection by using a selector
knob with a relatively small number of settings and by relying on
the microswitch 40 to arrest the apparatus upon completion of a
desired number of copies of a single original 4 (by placing a
corresponding number of sheets 10a onto the table 10A and by
allowing the apparatus to run until the supply of sheets on the
table 10A is exhausted).
Without further analysis, the foregoing will so fully reveal the
gist of the present invention that others can, by applying current
knowledge, readily adapt it for various applications without
omitting features which fairly constitute essential characteristics
of the generic and specific aspects of our contribution to the art
and, therefore, such adaptations should and are intended to be
comprehended within the meaning and range of equivalence of the
claims.
What is claimed as new and desired to be protected by Letters
Patent is set forth in the appended claims.
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