U.S. patent number 3,928,772 [Application Number 05/450,959] was granted by the patent office on 1975-12-23 for time dependent fault detector.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Thomas J. Mooney.
United States Patent |
3,928,772 |
Mooney |
December 23, 1975 |
Time dependent fault detector
Abstract
The RC time constant of a timer in a time dependent fault
detector is automatically varied so that the timer may be used to
monitor a plurality of mutually exclusive routines to which
different maximum permissible periods of time are alloted. For
example, the detector may be advantageously used to interrupt the
operation of a xerographic copier if any one of a plurality of
operating sequences of the copier is not completed on a timely
basis.
Inventors: |
Mooney; Thomas J. (Fairport,
NY) |
Assignee: |
Xerox Corporation (Stamford,
CT)
|
Family
ID: |
23790220 |
Appl.
No.: |
05/450,959 |
Filed: |
March 14, 1974 |
Current U.S.
Class: |
307/116; 399/76;
399/9 |
Current CPC
Class: |
G03G
15/55 (20130101) |
Current International
Class: |
G03G
15/00 (20060101); G03G 015/00 () |
Field of
Search: |
;340/309.1,309.6
;307/94,116 ;355/14 ;271/57 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hohauser; Herman J.
Claims
What is claimed is:
1. In combination with a xerographic copier having a plurality of
mutually exclusive routines each alloted a different amount of
time, a time dependent fault detector for interrupting the
operation of said copier whenever any one of said routines fails to
be completed within the time alloted thereto; said detector
comprising a timing capacitor, a resistive path for supplying
charging current for said capacitor, a shunt path coupled in
parallel with said capacitor for bypassing said charging current
around said capacitor until one of said routines is initiated,
means responsive to the initiation of any one of said routines for
disabling said shunt path to thereby trigger said timer into
operation, and means for selectively bypassing a portion of the
resistance in said path to thereby adjust the time out period of
said timer to match the time alloted to said one routine.
2. The combination of claim 1 wherein said timer further includes a
thyristor which switches from one state to another when said
capacitor charges to a predetermined voltage level, thereby marking
time out of said timer.
3. The combination of claim 2 wherein said thyristor is a
programmable unijunction transistor having an anodecathode circuit
and a gate-cathode circuit, and said capacitor is coupled across
said anode-cathode circuit; and further including means for
applying a bias voltage to said gatecathode circuit, whereby said
programmable unijunction transistor switches from a non-conductive
state to a conductive state when said timer times out.
4. The combination of claim 3 wherein said bypass means includes a
transistor having a collector-emitter circuit connected in parallel
with said resistance, whereby the time out period of said timer is
adjusted by switching said transistor into and out of conduction.
Description
BACKGROUND OF THE INVENTION
This invention relates to failure detectors and, more particularly,
to time dependent failure detectors.
As is known, time dependent failure detection is a relatively
straightforward technique for monitoring any routine which normally
advances from one identifiable point to another within a
predetermined amount of time. To carry it out, there typically is a
timer having a time out period selected to equal the maximum time
period required by a particular routine under normal operating
conditions, means for triggering the timer into operation when the
routine reaches the first or reference point, and means for
resetting the timer when the routine reaches the other or
termination point. Thus, if the timer times out, it indicates that
there has been a departure from nominal conditions or, in other
words, that a failure has occured.
On occasion, several different time dependent fault detectors are
used in the same machine or process to monitor mutually exclusive
routines, especially when those routines are alloted different
amounts of time. As will be seen, this invention eliminates the
need for resorting to that wasteful practice.
SUMMARY OF THE INVENTION
More particularly, one of the important objects of the present
invention is to provide a time dependent fault detector which may
be utilized to monitor a plurality of mutually exclusive routines,
even if those routines are alloted different amounts of time.
Another object of this invention is to provide a method and means
for automatically adjusting the time out period of a time dependent
fault detector to match the maximum amount of time alloted to any
one of a plurality of mutually exclusive routines.
A further object of this invention is to provide a time dependent
fault detector for automatically interrupting the operation of a
xerographic copier if any one of a plurality of mutually exclusive
operating sequences is not completed on a timely basis.
Still another object of the present invention is to provide a
reliable and economical time dependent fault detector having the
above-mentioned characteristics and capabilities.
In keeping with these and other objects, means are provided in
accordance with this invention for automatically adjusting the time
out period of a timer in a time dependent fault detector. Mutually
exclusive routines to which different maximum time periods are
alloted can, therefore, be monitored by a single detector since the
time out period of the timer may be adjusted to match any one of
them. Adjustment of the time out period is conveniently
accomplished by switching a transistor into and out of conduction
to thereby vary the RC time constant of the timer.
BRIEF DESCRIPTION OF THE DRAWINGS
Still further objects and advantages of the present invention will
become apparent when the following detailed description is read in
conjunction with the attached drawings, in which:
FIG. 1 is a perspective view of a xerographic copier with which the
present invention may be advantageously utilized;
FIG. 2 is a simplified schematic of the processor section of the
copier shown in FIG. 1; and
FIG. 3 is a schematic of a time dependent fault detector
constructed in accordance with the present invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
While the invention is described in some detail hereinafter with
reference to a specific embodiment, it is to be understood that
there is no intent to limit it to that embodiment. On the contrary,
the intent is to cover all modifications, alternatives, and
equivalents falling within the spirit and scope of the invention as
defined by the appended claims.
Turning now to the drawings, and at this point especially to FIGS.
1 and 2, there is a xerographic copier 10 having a charging station
11, an exposure station 12, a development station 13, a transfer
station 14 and a cleaning station 15 disposed about the periphery
of a drum 16 which is coated with a photoreceptor 17. In operation,
an original document is placed image side down on a transparent
platen 18, a dial 19 is set to the desired number of copies, and a
print button 21 is depressed to initiate the copying process.
Copying starts with the energization of a corona generator 22 at
the charging station 11 to uniformly charge the photoreceptor 17.
The original document is flood illuminated by a suitable lamp (not
shown) and is then scanned by a moving optics system 23 so that
light reflected from the document is focused on the photoreceptor
17 at the exposure station 12. The reflected light discharges the
photoreceptor 17 in an imagewise configuration to thereby provide a
latent electrostatic image. The latent image is developed at the
development station 13 by the application of an electroscopic toner
powder, and the developed image is then transferred at the transfer
station 14 to a copy sheet 24 which is fed from a cassette-type
supply tray 25. Finally, to complete the process, the toner image
is permanently affixed to the copy sheet 24 at a fuser station 26
and residual toner is removed from the photoreceptor 17 at the
cleaning station 15.
As will be appreciated, there are a number of routines which must
be successfully completed on a timely basis to make a satisfactory
copy, and some of those routines are mutually exclusive. For
example, in the optics system 23 there is a full rate scanning
mirror 27 which is mounted on a carriage (not shown) to be
reciprocatingly driven between a home positioned beneath the
left-hand margin of the platen 18 (as viewed in FIG. 2) and an end
of scan position beneath the opposite or right-hand margin of the
platen 18, as described in more detail in a copending and commonly
assigned application of W. F. Hoppner, which was filed June 6, 1973
under Ser. No. 367,996 on an "Exposure Apparatus." In the ordinary
course, the scanning mirror 27 returns to its home position at the
outset of each copy cycle and then moves towards its end of scan
position to scan the original document. Jam detection and copy
quantity control are, therefore, provided for this particular
copier through the use of a microswitch 28 which is positioned to
be actuated when the scanning mirror 27 is in its home position and
deactuated when the mirror 27 is in any other position.
Specifically, the jam detection and copy quantity logic are
dependent on the successful and repeated actuation of the
microswitch 28, as more fully explained in a copending and commonly
assigned application of L. J. Fantozzi, which was filed Apr. 6,
1973 under Ser. No. 348,828 for "Control Circuitry for Trouble
Detection and Recovery System in a Copier/Duplicator." Accordingly,
if there is a failure within the drive mechanism (not shown) for
the optics system 23 or of the microswitch 28, jam detection and
copy quantity control are lost, thereby creating the risk of a run
away machine condition and of smoke and odor from undetected
jams.
Analysis of this particular copier reveals that a failure of the
drives for the optics 23 or of the microswitch 28 is indicated
whenever that switch (1) is not actuated within six seconds or so
after the print button 21 is depressed or (2) remains actuated
during the copying cycle for more than about six tenths of a
second. Time dependent failure detection may, therefore, be
advantageously utilized. But there are a pair of mutually exclusive
routines to be monitored, and those routines are alloted different
amounts of time.
Referring to FIG. 3, there is a time dependent fault detector 31
which is capable of monitoring mutually exclusive routines, even if
they are alloted different amounts of time. The capabilities of the
detector 31 have been synergistically extended in accordance with
this invention by including a timer 32 having an automatically
adjustable time out period. To that end, as shown, the timer 32
comprises a three terminal thyristor 33 which is switched from one
state of conduction to the other when a timing capacitor 34 charges
to a predetermined voltage level. The charging time constant for
the capacitor 34 is adjusted under the control of a transistor 35
to thereby match the time out period of the timer 32 to the
particular routine being monitored, and the timer 32 is triggered
into operation and reset under the control of an inverter 36.
More particularly, in the illustrated embodiment, current is drawn
from a dc. power supply through a resistor 37 and the parallel
combination of collector-emitter circuit of the transistor 35 and
another resistor 38. The output of the inverter 36 is connected in
parallel with the series combination of the timing capacitor 34 and
a further resistor 39 in the ground return path for that current
flow. Thus, the current drawn from the dc. power supply is returned
to ground through the timing capacitor 34 and it series resistor 39
or through the output of the inverter 36 depending on the logic
level of the input signal applied to the input of the inverter 36.
Specifically, if that signal is at a high (1) logic level, the
timer 32 is triggered into operation because the current is routed
through the timing capacitor 34 to charge it toward the critical
voltage level. If, on the other hand, a low (0) logic level signal
is applied to the inverter 36, its output provides a relatively low
impedance shunt path to ground for the current drawn from the dc.
power supply and for any discharge current drawn by the capacitor
34.
Now, when the timer 32 is triggered into operation, its time out
period depends on the state of conduction of the transistor 35. If
that transistor is in a nonconductive state, the RC charging time
constant for the timing capacitor 34 is relatively long and the
time out period of the timer 32 is, therefore, relatively long.
But, if the transistor 35 is in a conductive state, the resistor 37
is effectively bypassed and, consequently, the charging time
constant for the capacitor 34 is reduced to thereby reduce the time
out period of the timer 32.
To ensure that the timer 32 is relatively insensitive to ordinary
fluctuations in the output current of the dc. supply source, the
thyristor 33 is a programmable unijunction transistor (PUT). As
shown, the PUT 33 has its anode-cathode circuit coupled across the
timing capacitor 34 and the resistor 39 and its gate coupled to a
junction between a pair of voltage dividing resistors 41 and 42
which, in turn, are connected across the dc. supply source. As a
result, there is a gate-cathode bias voltage which holds the PUT 33
in a non-conductive state until the timer 32 times out. When that
occurs, however, the PUT 33 switches into conduction because there
then is sufficient voltage across the timing capacitor 34 to cause
the anode-cathode voltage on the PUT 33 to exceed its gate-cathode
bias voltage. In other words, time out of the timer 32 is marked by
a significant drop in the gate-cathode voltage of the PUT 33.
The input and output interfaces 43 and 44, respectively, for the
detector 31 are more or less tailored to its particular application
to the copier 10 (FIGS. 1 and 2). That is, they are selected,
together with the values of the capacitor 34 and of the resistors
37-39 and 41-42, to interrupt the operation of the copier 10 if the
microswitch 28 (1) is not actuated within six seconds or so after
the print button 21 is depressed or (2) remains actuated for more
than about six tenths of a second at any time during a copying
cycle. Indeed, to accomplish that, the input interface relies on
certain signals that are supplied by the copier 10 -- viz., (a) an
initializing signal (INIT) which drops from a high (1) logic level
to a low (0) logic level approximately 20 milliseconds after the
print button 21 is depressed, (b) a scan signal (SCAN) which is at
a high (1) or a low (0) logic level depending on whether the
microswitch 28 is actuated or not, and (c) a run signal (INIT +
BJAMF) which is herein assumed to simply be the complement of the
initializing signal (INIT). For a description of the provision made
in the copier 10 to supply those signals, reference may be had to
the aforementioned application Ser. No. 348,828.
Inasmuch as the interfaces 43 and 44 form no part of the present
invention, other than to mate the detector 31 with the copier 10,
there is no reason to burden this disclosure with a detailed
discussion of them. Indeed, the drawings provide sufficient detail
to make their operation self-evident.
CONCLUSION
In view of the foregoing, it will now be appreciated that the
present invention provides a time dependent fault detector suitable
for monitoring a plurality of mutually exclusive routines, even if
different amounts of time are alloted to those routines.
* * * * *