Method and apparatus for copier quality monitoring and control

Data correlated to the light reflectance of a maximum toned area and a minimum toned area is recorded to establish standards for monitoring and controlling subsequent copier operation. A test pattern is imaged onto the photoconductor by controlled illumination levels in a series of steps with the detection of light reflectance from that test pattern being subsequently compared to establish the maximum black and maximum white criteria for storage. Light reflected from cleaned photoconductor areas and subsequently established toner patches then are used to compare against the original test pattern reflectance data. Toner replenishment, controls and machine function monitoring (e.g.: white copy background, developer operation, etc.) are based on these recorded standards from the test pattern.

TECHNICAL FIELD 
The present invention relates to methods and apparatus for monitoring the 
quality of operation of a copier. More particularly, the present invention 
relates to methods and apparatus for monitoring the amount of toner 
applied to a photoconductor surface and for providing control responses 
based upon the monitored data. The invention is particularly useful for 
controlling such copier functions as toner level in the developer, toner 
replenishment to the developer, adjustment of illumination lamp levels, 
adjustment of biasing voltage levels and the like, based upon dynamic 
standards. 
BACKGROUND ART 
Contemporary xerographic copiers often employ so-called patch sensing 
techniques for monitoring the level of toner in the developer. These 
systems establish a test pattern by discharging the photoconductor 
everywhere except in a discrete path or stripe and thereafter monitoring 
the light reflectivity of both the cleaned photoconductor and the patch. 
Such patches are either placed in the area of the photoconductor outside 
of the image areas so as not to delay copying operations or are performed 
by a special cycle to establish the patch in the image area and to test 
its reflectivity. An unsatisfactory light reflectivity of the patch area 
causes a response in the form of increased toner introduction or 
replenishment from a reservoir to a developer sump. A system for 
performing such an operation is shown in U.S. Pat. No. 4,178,095 by J. R. 
Champion and S. D. Seigal which issued on Dec. 11, 1979 and is assigned to 
the same assignee as the present application. 
Another process for monitoring machine operation is suggested in the IBM 
Technical Disclosure Bulletin of January 1980 (Vol. 22 No. 8B) at pages 
3606-3608 in the article entitled "Copier Adjustment" by B. A. Nilsson. 
This article suggests controlled introduction of gray to white transition 
bands on a copier during servicing so that the servicing user can compare 
these bands as transferred and fused on a copy sheet against a standard 
for a satisfactorily operating machine. The service person can then make 
appropriate adjustments based upon the result. 
However, the prior art has not suggested that the operation of a copier is 
monitorable by establishing a series of light to dark transition bands on 
the photoconductor upon initialization of the machine, and subsequently 
comparing toned patches from the photoconductor with those bands so as to 
dynamically determine the status and appropriate responses to the machine 
operation. 
DISCLOSURE OF THE INVENTION 
The present invention relates to methods and apparatus for establishing 
toner level standards for a copier. Such copiers employ a moving 
photoconductor which is charged for receiving an electrostatic image of an 
original document or the like. A lamp illuminates the photoconductor and a 
developer applies toner to the photoconductor. In its preferred 
embodiments, the present invention is particularly well suited for use in 
conjunction with reflected light measuring devices associated with the 
photoconductor. 
In the copier environment mentioned above, the process in accordance with 
the present invention includes charging the photoconductor to a normal 
level for accepting images. The lamp and developer are controlled for 
selectively creating sequential areas on the photoconductor ranging from 
an area of maximum toner application to an area of minimum toner 
application. The output of the measuring device is sensed where this 
output indicates light reflected from the photoconductor sequential areas 
mentioned above as they pass the measuring device. Signals are then stored 
corresponding to the reflected light measurement output correlated to the 
sequential areas of toner application on the photoconductor. This process 
makes it possible to at least partially determine the operation of the 
copier by subsequent comparisons of the reflected light output with the 
stored signals. 
One step for establishing the sequential areas of toner application on the 
photoconductor is to vary the power to the illumination lamp from a 
maximum brightness to a lamp-off condition. In addition, subsequent 
reflected light output signals are comparable with the stored signals and 
the copier operation is adjustable in accordance with the difference 
between those signals. One application of this adjustment is to add toner 
to the developer in proportion to the difference between the compared 
signals. It is also possible to control operation of the reflecting or 
measuring means output for subsequent signal determinations so as to 
accommodate changes in the photoconductor reflectance as occurs from 
usage. Yet another application of the results of the comparison of 
subsequent signals is to control the intensity of the illumination lamp in 
accordance with the difference between the signals. 
Apparatus for implementing the present invention includes circuitry having 
a comparator with the reflected light sensing output coupled to one input 
and a power source responsive to an input for appplying selectable power 
levels to the illumination lamp. The circuitry includes a controller with 
means for producing first and second output signals of selectable 
magnitudes, the first output being used to control the power source at its 
input and the second output providing the second input to the comparator. 
The control further includes means for storing data correlated to signals 
at the comparator output terminal and a sequencer which further includes 
means energizing the controller first output to cause the lamp to produce 
light in a sequence between a maximum intensity and a reduced or off 
condition so as to place an image test pattern on the photoconductor. The 
sequencer further includes means operable in response to the output signal 
of the reflected light responsive means caused by the photoconductor test 
pattern for varying the second output signal until the comparator output 
indicates a favorable comparison result. The sequencer then is able to use 
means to enable the storing means to store data correlated to at least the 
maximum and minimum levels of the favorable comparison results. 
The sequencer can further include means operable subsequent to the storage 
of the data in the storing means relating to the test pattern for 
actuating the first and second output producing means and means for 
comparing the signal from the comparator output terminal with the data 
stored in the storing means. The apparatus can further include means to 
adjust the first signal output of the controller to the power source for 
the illumination lamp to accommodate changes in reflectivity of the 
photoconductor. The apparatus is adaptable to employ the response from the 
comparing means output indicating that inadequate toner is present on the 
photoconductor to cause toner replenishment in the developer. Other 
utilizations of the comparison result are readily apparent, such as for 
the purpose of controlling various bias voltage levels associated with the 
developers and/or coronas, flagging out-of-tolerance conditions to the 
operator, accelerated toner replenishment when a highly reduced toner 
level is determined and so forth. 
The foregoing and other objects, features, advantages and applications of 
the present invention are readily apparent to those having normal skill in 
the art from the following more detailed description of the preferred 
embodiments as illustrated in the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The general organization of elements associated with the xerographic 
processing of copies in a contemporary copier is shown in the side view of 
FIG. 1. A continuing concern relative to such copiers is the insurance of 
copy quality in the form of clear differentiation between black and white 
areas of the documents being copied. The original documents serially 
introduced at entryway 20 are driven by roller pairs 21 and 22 past the 
scan window where they are illuminated by lamps 30 and 31 so that a fiber 
optic bundle 35 can direct the image onto a photoconductive belt around 
capstan 40. The upper cover 50 is shown pivotable to allow passage of 
large documents, books or objects over the scan window. Copy sheets from a 
supply (not shown) are introduced at 60 and receive their image at 
transfer station 70. These copy sheets are subsequently passed through 
fuser 80 and are delivered at exit 90. 
The basic operation of the copier is such that the precharge corona 101 
charges the photoconductor belt on capstan 40 to about -1200 volts. Charge 
corona 102 drives the photoconductor positive to about -870 volts. The 
optic system 103 introduces a latent electrostatic image on the 
photoconductor where the black areas on the photoconductor are about -850 
volts and the white areas are about -225 volts. Developer 104 adheres 
toner particles to the highly negative areas on the photoconductor. 
On the second revolution, corona 101 acts as a transfer corona causing 
toner to be removed from the photoconductor to the copy paper introduced 
at 60. 
Next corona 102 acts as a clean corona to drive the photoconductor voltage 
to about zero and to ensure all residual tone particles are positive. 
Mirror 105 in housing 50 allows light from the optic system 103 to act as 
an erase system. Residual toner on the photoconductor is then 
preconditioned so the developer 104 acts as a cleaner. The machine is thus 
ready to make another copy. The operation described is known as the 
two-cycle copy process although the present invention is also useful in 
other copier environments. 
The necessary conditions for ensuring control of the electrophotographic 
process are next considered. It is necessary that a fixed amount of toner 
is applied to the photoconductor when the photoconductor is at its maximum 
negative potential. It is also important to ensure minimum amount of toner 
is applied in the minimum negative potential areas. To help perform this 
function, sensor 106 is added. FIG. 3 shows diagrammatically the elements 
of sensor 106 which is comprised of a light emitting diode 120 which is 
directed towards the photoconductor belt 121 and thus produces light 
reflected towards a photodetector or solar cell 102. FIG. 4 shows the 
electronics associated with operation of the sensor 106. 
When the machine is initially turned on, the microcontroller 201 determines 
the output voltage of operational amplifier 204 when sensor 106 is 
detecting light reflected from a clean photoconductor and current through 
the LED 120 in sensor 106 is determined by resistors 202 and 203. 
Microcontroller 201, operational amplifier 205, operational amplifier 212 
and associated resistors 206, 207, 208, 209, 210 and 211 are connected as 
an analog-to-digital converter to perform the function of converting the 
output voltage of operational amplifier 204 to digital information for 
storage in microcontroller 201 memory. In a typical operating environment, 
microcontroller 201 is a conventional 4-bit product like the Nippon 
Electric Co. Ltd. (NEC) MPD 546C. 
While the fuser is warming up in response to an intialization start by the 
operator, the machine performs the necessary functions to optimize its 
electrophotographic parameters as described below. The microcontroller 201 
starts the main drive motor, and turns the high voltage power supplies on 
which drive coronas 101 and 102. The voltage on the photoconductor between 
coronas 101 and 102 is driven to about -1200 volts. The charge corona 102 
with its grid at about -870 volts drives the photoconductor potential to 
about -870 volts. When the photoconductor leading edge of the image area 
is at optic station 103, microcontroller 201 turns the illumination lamp 
250 off by causing the output of operational amplifier 205 to become 
greater than the reference voltage (REF) established by adjustable 
resistance network 255. 
Next microcontroller 201 produces an electrostatic image as shown in FIG. 2 
by decreasing the voltage output of operational amplifier 205 in equal 
steps when mirror 105 is in position. The reason the pattern of FIG. 2 is 
developed is because photodiode 301 is monitoring the illumination lamp 
level and as the voltage input to the positive terminal of operational 
amplifier 303 decreases (becomes more negative), the output of the 
illumination lamp 250 increases by a proportional amount since the 
photodiode 301 output current is proportional to light energy. Note that 
the illumination lamp 250 shown in FIG. 4 is the equivalent of both lamps 
30 and 31 shown in FIG. 1. Note also that, as shown in FIG. 2, the odd 
numbered stripes (1, 3, 5, 7 . . . 19) are transition zones and are not at 
any defined level. 
As the photoconductor passes through developer 104, a gray scale is 
produced on the photoconductor starting from an all-black and going 
through an all-white. As the photoconductor continues, corona 101 is off 
since paper is not being picked and also it is desirable not to change the 
polarity of the toner charge. Next the charge corona grid is at ground 
potential to help discharge the photoconductor and ensure the toner 
particles are positive. 
The microcontroller 201 produces as an output the digital information 
concerning the clean photoconductor reference level on lines 401, 402, 
403, 404 and 405 to produce the proper potential as an output of 
operational amplifier 205. The microcontroller turns transistor 215 on, 
increasing the current in the sensor 106 LED about the expected change in 
photoconductor reflectance which is about 10 volts. As the black stripe 
passes under sensor 106, the photoconductor reflectance level is compared 
with the stored level using operational amplifier 212 as a comparator. If 
the output of operational amplifier 212 is negative (i.e.: output of 
operational amplifier 204 more negative than output of operational 
amplifier 205), microcontroller 201 instructs the machine to add toner to 
the developer. Examples of metering roller operations and the like for 
introducing toner from a reservoir to a toner sump are shown in U.S. Pat. 
No. Re. 28,589 by A. H. Knight and M. J. Miller which is assigned to the 
same assignee as this application and also in the October 1968 IBM 
Technical Disclosure Bulletin in the article entitled "Toner Dispenser" by 
J. A. Machmer at pages 497- 498. Also, the toner replenishment rate is 
controllable in proportion to the test patch reflectivity displacement as 
compared to the prior recorded gray zones. 
Next microcontroller 201 turns transistor 215 off and turns transistor 219 
on causing an increase in LED current of about 15% above the clean level. 
Microcontroller 201 looks at the developed gray stripes (the even numbered 
stripes in FIG. 2 of 2, 4, 8, 10 . . . 20). When controller 201 finds the 
first stripe which has a reflectance causing the output of operational 
amplifier 201 to be more negative than operational amplifier 205 output, 
microcontroller 201 records in memory the stripe number. By using a 
look-up table in memory, microcontroller 201 determines what the states of 
lines 401, 402, 403, 404 and 405 were on a previous cycle when the stripe 
was produced by optic system 103 in its controlled circuit of operational 
amplifiers 302, 303, 304 and associated components. The digital 
information is useful as a reference level to control various machine 
operations such as the light intensity of the illumination lamp 30 or 250. 
The photoconductor now continues around the proper number of times to 
remove all the toner from the surface of the photoconductor. The copier is 
then turned off and continues waiting until the fuser finishes warming up. 
When an operator wants to improve the copy quality of the machine, the only 
adjustment is potentiometer 216. The only reason this is required is due 
to the fact that background of the original is not of the proper 
reflectance for optimum copy quality. The actual function of potentiometer 
216 is a memory element to instruct the machine of the difference in its 
reflectance standard (mirror 105) and the reflectance of the original. 
Note when the machine is putting the electrostatic image on the 
photoconductor, transistor 214 is on. At all other times, transistor 214 
is off, allowing the machine illumination to default to its clean level 
(light intensity to drive the photoconductor from black level to a voltage 
level corresponding to 15% background on the photoconductor with the 
mirror). 
As the machine is used, it is necessary to update the electrophotographic 
parameters at the end of most jobs. This can be done after running a 
predetermined number of copies after the previous sample such as after 
more than 5 but less than 100 copies. It is suggested that, if a copy 
count goes to 100 without sampling, machine interruption to take a sample 
is mandatory. Instead of going through a detailed setup as described 
earlier, a similar process is used except the pattern is with a reduced 
number of gray stripes instead of the number shown in FIG. 2. The number 
of gray stripes included in the reduced sample includes the optimum gray 
stripe area and one or more additional stripes on either side thereof. The 
machine then updates its data accordingly. 
If the machine does not include a separate button for initializing the 
parameter recording, the process described is performable automatically 
with the very first copy after the machine has turned on. One having 
normal skill in the art will realize there are many different 
implementations of the above concept which may appear to the casual 
operator totally different. For example, assume it is desirable to use 
some other substrate as determined by the casual operator for the 
reflectance standard instead of mirror 105. This is easily done by adding 
the circuitry shown in block 411. The purpose is to inform the machine of 
use of a different reflectance standard. The casual operator positions the 
potentiometer 216 in the center and closes switch 413. The microcontroller 
turns transistor 214 on and repeats the setup procedure described earlier. 
The microcontroller is controlled by an emitter switch 213 associated with 
operation of the belt drive system. That is, these emitter pulses are used 
for synchronization purposes in a well-known manner. The output signal at 
terminal 275 is connected to the driving mechanism for the toner metering 
arrangement in the replenishing system. 
Although the present invention has been described with particularity 
relative to the foregoing detailed description of the exemplary preferred 
embodiment, various modifications, changes, additions and applications of 
the present invention in addition to those mentioned herein will be 
readily apparent to those having normal skill in the art without departing 
from the spirit of this invention.