CA1128114A - Test cycle quality control system for an electrophotographic machine - Google Patents

Abstract

TEST CYCLE QUALITY CONTROL SYSTEM FOR AN
ELECTROPHOTOGRAPHIC MACHINE
Abstract of the Disclosure A system for checking copy quality variables within the image area of an electrophotographic machine. During a test cycle, quality is checked by producing sample test areas within the photoconductor image area ordinarily used for producing copies. Reflectance measurements are made on sample test areas and compared to a dynamically floating reference achieved by a reflectance measurement from a cleaned portion of the photoconductor within the image area.
The testing circuit is balanced so that the same reflectance voltage should be generated whether the single reflectivity-sensing device is viewing a sample test area or a cleaned reference area. The system can be used to check for quality variables such as toner concentration, image voltage and an abnormally low reflectance photoconductor and provides a check on its own fault-free condition during periods when it is not in use.

Description

1 TEST CYCLE QUALITY CONTROL S~STEM FOR ~N
ELECTROPHOTOGRAPHIC MACHINE
This invention relates to electrophotographic machines and more particularly to a machine system in which a test cycle is provided.
Related Patent Applications Applications numbered 317,955, 321,243 and 321,24 relate to inventions utilizing the test cycle described herein.
Background of the Invention In document copier machines of the electrophoto-graphic type, charged latent images are produced on a photo-receptive material and then developed through the application of a developer mix. Where the photoreceptive material is separate from the copy paper itself, a transfer of the developed image to the copy paper takes place with subsequent fusing of the developed image to the paper. ~ common type of developer mix currently in use in such machines is com-prised of a carrier material, such as a magnetic bead, coated with a colored powdery substance called toner. It is the toner which is attracted to the charged, latent image to develop that image and it is the toner which is then trans-ferred from the latent image to the copy paper (where the copy paper is separate from the photoreceptive material).
Finally, it is the toner which is then fused to the copy paper to produce the finished copy.

' ~`'``'`

~L~2~

1 I-t is apparent from the procedure outlined above

2 that toner is a supply item which must be periodically

3 replenished in the developer mix since the toner is carried

4 out of the machine on the copy paper as a reproduced image.
It is also apparent that the concentration of toner particles 6 in the developer mix i5 significant to good development of 7 the latent image since too light a toner concentration will result in too light a developed image and too heavy a toner 9 concentration will result in too dark a developed image.
Other variables which seriously affect copy quality 11 include the image voltage of the photoconductor and the bias 12 voltage on the developer. Many other variables factor into 13 these basic quantities, for example, the quality of the 14 original, the cleanliness of the optical system, and the condition of the photoconductor.
16 The present invention relates to a system wherein 17 a test cycle is provided in which quality-related variables 18 such as toner density and image voltage can be controlled.
19 A control scheme for image voltage is fully disclosed in one of the related patent applications, named above; the inventive ~1 test cycle will be described herein primarily in terms of 22 its application to toner concentration control. Regardless, 23 however, of the quality variable to be controlled, accurate 2~ control cannot be attained withou-t the test cycle of this invention wherein the area of the photoconductor ordinarily 26 used for producing document copies is the area used for the 27 quality control test. The most pertinent prior art known to 28 the inventor is in the area of toner concentration control, 29 that ar~ is discussed below.

~L2~i4 1 Th~ prior art includes U.S. Patents 2,956,487 and 2 3,348,522. U.S. Pa-tent 2,956,~87 provides a toner concentra-3 tion control system where the reflectivity of the document 4 image to be reproduced is used as a measure of toner density.
This sys-tem appears subject to difficulty since reflectivity 6 readings will change dependen-t upon the quality of the 7 original. U.S. Patent 3,348,522 discloses a toner concentra-8 tion control scheme in which a special test image is developed 9 outside the image area used Eor reproducing document cQpies.
In this latter patent separate reflectivity-sensing devices 11 are used to simultaneously sense light reflected from a 12 single light source, one sensing device to establish a 13 voltage indicative of clear photoconductor outside the image 14 area and the other to establish a voltage indicative of the test area which, as noted above, is also outside the image 16 area. U.S. Patent 3,348,523 is essentially similar to U.S.
17 Patent 3,348,522.
18 ~.S. Patent 3,926,338 discloses a circuit for use 19 in a toner concentration control scheme. In this patent thermally insensitive photodetectors must be used since the 21 large amount of heat generated during machine operation 22 affects the accuracy of toner concentration control readings.
23 Similarly, this patent says that a stable amplifying circuit, 24 stable referring to temperature~stability, must be used in order to avoid destruction of the validity of the sensed 26 signal.
27 The inventor herein has found a better way. He 28 has discovered that it is superior to provide a test cycle ~976~37 ~3-1 and place the test area wit~in the image area, i.e., the 2 part of the photoconductor used for document reproduction.
3 In that manner, the advantages of testing a developed image ~ are combined with the advan-tages of using -the very same photoconductor that is used for document reproduction. The 6 inve/ltor found that on sho--t runs, the -test cycle could be 7 made -to correspond to a run-out cycle after the last copy had been produced. However, he found that it may be necessary g to skip an occasional copy during long, multi-copy runs in order to provide the test cycle of this invention. The 11 inventor found -that machines can be engineered wherein a 12 special test cycle need be run only once every 10 copies, or 13 even less frequently, and thus reduce the impact of -the special 14 cycle on copy reproduction rates. In relation to toner concentration control, the inventor discovered that the use 16 Of the image area as a test area pr~duced signiEicant advan~
17 tages in accuracy. Some reasons for this include the fact 18 that as photoconductor ages wi-th use, there is a tendency 19 for toner to build up on the image area; that -the photocon-ductor surface characteristics of the image area change with 21 use, thus affecting development; and that the image area 22 suffers alectrostatic degradation with use. A result of 23 these factors is that the image area itself becomes darkened ~ as compared to the areas of the photoconductor which are not used for image impressions. The inventor noted that when 26 the test area is positioned outside the image area these 27 degrading factors are much less present in the density test.
28 However, in the inventor's system wherein a test cycle is BO976037 -~-8~1~

1 provided thus allowing the -toner concentration control test 2 area or the image voltage tes-t area to be within the image 3 area any results of -toner ~ilming, aging, use, etc., are 4 present in the quality test. Consequently, the absolute quantity of toner in the developer mix can be adjusted as the photoconductor changes and the value of developing bias 7 voltage can be changed to provide compensating factors for 8 these effects. Such resul-ts are not possible unless the 9 quality tests are taken within the image area. Even if the tests are taken within the image area, there is s-till no 11 assurance that the results will be accurate unless the 12 testing circuit is able to compare the tested quantities to ~3 a meaningful reference and unless the quantities are devoid 1~ of circuit-ind~lced non-linearities.
1~ In addition to providing the toned test areà
16 within the image area, it was determined that the test cycle 17 enables the viewing of a cleaned, uncharged area of the 13 photoconductor within the image area in order to provide a 19 reference voltage. The ~rior art schemes used a reference ~o voltage obtained from outside the image area and consequently 21 not subject to the variables named above. Additionally, it 22 was discovered that various elemental factors such as tempera-23 ture as well as component non-linearities prevented accurate 24 comparisons of reference voltage and sensed voltage unless the identical sensor is used for both measurements and 26 unless it is excited to similar levels during both measurements.
27 In this regard, it was discovered that the amount of light 28 received for both sample and reference measurements by the , ~&~

1 sensor must be made equal (at the correct quality level) to 2 avoid photodetec-tor non~linearities and an ingenious circuit 3 arrangement to provide this property was invented.
4 In the system described herein a reference voltage is allowed to vary from test to test by viewing a "bare"
6 area of the actual photoconductor used for producing copies.
i The fact that the reference voltage is sensed each time a 8 test is made by the same photodetector used to sense the 9 developed image provides an extremely important advantage in that the variables associated with temperature, such as the 11 effect of shifts in the magnitude of the dark voltage of the 12 photodetector and shifts in the light output of the light 13 source are minimized. O-ther factors such as changes in the 14 optical characteristics of the photoconductor due to oxidation and surface changes are also minimized. As a consequence o~
16 this dynamism the system becomes insensitive to temperature, 17 becomes insensitive to variations in comp~nent qualities, 18 and insensitive to other variables as noted. In the systems 19 described in the prior art, few of these variables were ever compensated, most of them were not even considered.
21 Moreover, by sensing the reference voltage during 22 a test cycle from a bare photoconductor area that is used 23 for the production of copies, additional quality-sensing 24 capabilities are provided such as the sensing of an abnor-mally low reflectance photoconductor, i.e., a pho-toconductor 26 on which toner buildup has produced a darkened condition or 27 where the cleaning station or erase means has malfunctioned 28 such that an area of the photoconductor that should be clean 29 is instead producing low reflectance.

~2~

1 Still another capability of the test apparatus is 2 the means to check itself for proper functioning during 3 periods when it is not in use. Therefore, when its use is 4 needed, the machine is at least partially assured that it will receive correct indications of the measured qualities.
6 Summary of the Invention 7 This invention involves the provision of a test 8 cycle wherein various quality tests are performed within the 9 image area ordinarily used for document reproduction in order to assure copy quality in an electrophotographic 11 machine~ Among these tests are toner concentration control 12 in which a test area is produced within the document reproduc-13 tion image area of the photoconductor. During long, multi-14 copy reproduction runs, when a test cycle is performed the lS reproduct.ion of a copy is either skipped or the test is made 16 on a portion of the photoconductor not in use for that 17 specific copy; for shorter runs, the tests are perormed 18 during a run-out cycle. The erase means already provided in 19 the machine is used for production of the test area, thus 2~ combining special test function with Qperating function in 21 the single erase means.
22 Brief Description of the Drawings 23 The above-mentioned and other ~eatures and objects 24 of this invention and the manner of attaining them will`
25 ` become more apparent and the invention itself will best be 26 understood by reference to the following description of 27 embodiments of the invention taken in conjunction with the 28 accompanying drawings, the descri~tion of which follows.

l FIGURE 1 shows a schema-tic layout of an electrophoto-graphic machine utilizin~ the instant invention.
FIGURE 2 shows the optical system and a photoconductive drum in the machine of FIGURE 1.
FIGURE 3 is an idealized perspective view of components in the paper path of the machine.
FIGURE 4 shows the reflectivity-sensing elements of the toner concentration control device.
FIGURE 5 which appears on the second sheet of drawings, sho~s the layout of the photoconductor with the loeation of the bare reference area and the developed test area within the document reproduction image area.
FIGURE 6 shows the circuit for processing the referenee and test information.
FIGURE 7 which appears on the second sheet of drawings, shows the layout of the photoconductor for minimiæing the need for special cycles in long, multi-copy runs.
Detailed Deseription a. In General FIGURE l shows a typical eleetrophotographie maehine of the transfer type. Copy paper is fed from either paper bin lQ or paper bin 11 along guides 12 in the paper path to a transfex station 13A located just above transfer corona 13.
At tha~ station an image is placed upon the copy paper. The copy paper continues through the fusing rolls 15 and 16 where the image i$ firmly attached to the copy paper. The paper continues along path 17 into a movable deflector 18 and from there into one of the collator bins 19.
BO9-76~037 -~-DLM~W14 1 In order to produce an image on the photoconductive 2 surface 26 a document to be copied is placed upon a glass 3 platen 50. An image of tha-t document is transferred to the 4 pho-toconductive sur~ace 26 through an optics module 25 producing that image on the photoconductive surface 26 at 6 exposure station 27. As the drum 20 continues to rotate in 7 the direction A, developer 23 develops the image which is ~ then transferred -to the copy paper. As the photoconductor 9 continues -to rotate it comes under the influence of preclean corona 22 and erase lamp 24 which discharge all of the 11 remaining charged areas on the photoconductor. The photocon-12 ductor continues to pass around and through the developing i3 statioil 23 (which is also a cleaning station in this embodi-14 men-t) until it reaches the charge corona 21 where the photo-conductor 26 is again charged prior to receiving another 16 image at exposure station 27.
17 FIGURE 2 is a perspective of the optics system 18 showing the document glass 50 upon which the document to be 19 copied is placed. An illumination lamp 40 is housed in a re~lector 41. Sample light rays 42 and ~3 emanate from lamp 21 40 and are directed from dichroic mirror 44 to the document 22 glass 50 whereat a line of light 45 is produced. Sample 23 light rays 42 and 43 are reflected from the document placed 24 on the document glass to refleetive surface 46; from there to refleetive surface 47 to reflective surfaee 48 and thenee 26 through lens 9 to another refleetive surface 49. ~rom 27 mirror 49 the ligh-t rays are finally reflected throu~h 28 opening 51 in wall 52 to reach photoconduetor 26 whereat a 1 line of ligh-t 45' is produced. In -that manner a replica of 2 ~he information contained in the l:ine of light 45 on the 3 glass platen 50 is produced on the photoconductor 26 at 451.
4 The entire length of a document placed on document glass 50 is scanned by motion of lamp 40 and the mirrors 44, 46, 47 6 and 4g. By traversing the line of light 45 across the 7 document at the same speed at which the line of light 45' is 8 moved across photoconductor 26 by rotation of drum 20, a 1:1 9 copy of the document can be produced on the photoconductor 26.
11 E'IGURE 3 shows the various elements in the paper 12 path in perspective. Here a copy sheet 31 is shown with its 13 -trailiny edge 31A in the paper pa-th at guides 12. The copy 14 paper is receiving an image at transfer station 13A and is in the process of having -that image fused to itself by fuser 16 rolls 15 and 16. The leading edge llB of the copy paper is 17 about to leave the document copier and proceed into the 18 collator 19 which is represented in simplified form.
19 After an image is transferred to the copy paper, the photoconauctor 26 continues to rotate until it comes-21 under the influence of preclean corona 22 which applies a 22 charge to the photoconductive surface to neutralize the 23 remaining charge -thereon. Photoconductor 26 continues to 24 rotate until the photoconductor comes under the influence of Z5 an erase light 24' in housing 24. The erase light produces 26 illumination across the entirety of the photoconductor 26 in 27 order to complete the discharge of any remaining areas on 28 the photoconductive surface which have not been neutralized sO976037 -10-1 by the preclean corona 22. After passing under erase lamp 24', the photoconductor continues through the cleaning 3 station of developer/cleaner 23, wherein any remaining toner powder not transferred to copy paper is cleaned from the photoconductor prior to the beginning oE the next copy 6 cycle.
7 In the ne~t copy cycle the charge corona 21 lays ~ down a uniform charge across photoconductor 26 which charge 9 is variably removed when the image of the document is placed on the photoconductor at the exposure sta-tion 27 shown in 11 FIGURE 1. Preclean corona 32 and erase lamp 24' are ofE
12 during this cycle.
13 When the toner concentration control cycle i5 run, 1~ and if the result indicates a need to add toner to the developer, a signal is sent to replenisher 35 which holds a 16 supply of toner and operates to dump a measured amount into 17 the developer~ In tllat manner, the toner density of the 18 developer mix is replenished. Any suitable replenisher 19 mechanism may be used including the replenisher described in IBM Techni~al ~isclosure Bulletin, Vol. 17, No. 12, pp.
21 3516, 3S17.
22 b. The Test Cycle 23 FIGURE 3 shows a housing 32 containin~ the toner 24 concentration control sensing system shown in FIGURES 4 and 6. When it is desired to sense for the concentration of 26 toner in the developer mix the photoconductor is charged as 27 usual at the charge ~orona 21, but no image is placed on the 28 charged photoconductor at e~posure station 27. Instead, on ~:L28~

1 this cycle, the erase lamp 2~' remains on discharging all of 2 the charge which has been laid down by charge corona 21 in 3 order to provide bare pho-toconductor for a reference test 4 area. However, the erase lamp 24' is momentarily interrupted to produce a charged striye -toned sample for a test area.
6 If the lamp 24' is comprised of an array of light-emitting 7 diodes, the array can be segmented such that only a few of 8 the LEDs are momentari].y turned off and therefore only a 9 small "patch" of charge remains on the photoconductor at the conclusion of this part of the cycle. If a fluorescent tube 11 is used as the erase lamp 24', momentarily reducing its l2 energization to a low level will produce a "stripe" of 13 charge remaining on the photoconductor at the conclusion of 14 this part of the cycle.
Whether a stripe of charge or a patch of charge is ]6 produced, the charged test area continues to rotate in the 17 direction A until it reach~s the developer 23 where toner is L8 placed onto the charged area to produce a toned sample test 19 area. No copy paper need be present at transfer station 13A
in the test cycle, thus allowing the developed test area to 21~ continue its rotation in direction A until it approaches the 22 toner concentration control housing 32. At this point, 23 referring now to FIGURE 4, a light-emitting diode (LED) or 24 other suitable light source 33 is energized to produce li~ht rays which reflect off the toned sample test area 35 and are 26 reflected to a photosensor 34. It should be noted that the 27 toned image could be transferred to copy paper, if desired.
28 The reflectance of the developed and trans~erred stripe (ox ~0976037 -12-1 patch) would -therl be sensed by locating sensors on the paper 2 path. It should also be noted that the principles of this 3 system work well with photosensitive paper, i.e., electrophoto-4 graphic machines in which the image is exposed directly onto the copy paper rather than through a transfer station.
6 FIGURE 5 shows the layout of-the photoconductor 26 7 with an image area 28 outlined therein. A developed patch 30 has been produced within the image area 28. FIGUR~ 2 9 shows apparatus for producing patch 30. As described above, erase lamp 24' is momentarily interrupted to produce a 11 stripe of charge. While the above description designated 12 45' as a line of light producing an image on photoconductor 13 26, suppose now that during the test cycle the line or 14 stripe 45' is used to designate a stripe of charge produced by momentarily interrupting lamp 24'. Suppose also that 16 document lamp 40 is turned on during the test cycle so that 17 light from lamp 40 wi.ll erase the stripe of charge ~5' 18 unless it is interrupted. Such an interruption is made 19 possible by the provision of shutter 36 which is shown in FIGURE 2 as dropping across slot 51 in wall 52. Shutter 36 21 is actuated by solenoid 38. As a result, light from lamp ~0 22 is blocked away from photoconductor 26 by shutter 36, thus 23 producing a stripe of charge 37. Of course, erase lamp 24' 24 will erase all of stripe 37 e~cept for patch 30. In that manner, a patch instead of a stripe can be produced. Note 26 that slot 51 should be positioned close to the photoconductive 27 surface 26.

, 1 AS FIGURE 5 demonstrates, placing the test area 30 2 within image area 28 necessitates skipping the production of 3 a copy during a long, multi-copy run since a density test 4 should be taken periodically, for example, after 20 copies.
On short runs the test is taken on the run-out cycle at the 6 conclusion of document reproduction. FIGURE 7 shows the 7 layout of photoconductor 26 illustrating a technique for 8 avoiding the need for skipping copies even when operating a 9 long, multi-copy run. If the machine has the capability of producing two different size copies, for example, 8.5 x 11 11 inches and 8.5 x 14 inches, the extra 3-inch part of the 12 image area 28 can be used for the density test without 13 skipping a copy. FIGURE 7 shows the timing considerations 14 needed for the erase lamp, the document lamp, and the shutter 1~ 36 of FIG~RE 2.
16 If a segmented LED array is used for the erase 17 lamp, or if a stripe of charge is produced instead of a 18 patch 30, the production of the test area is obtained by 19 turning off the document lamp at the conclusion of viewing the ll-inch document and momentarily interrupting the erase 21 lamp as shown on EIGURE 7. Of course, no shutter is used in 22 that case.
23 c. The Circuit - FIGURE 6 24 In order to produce a reference voltage, when the proper time in the sequential operation of the machine has 26 arrived, the logic control of the machine provides a signal 27 to trigger the viewing of a reference sample. This is 28 accomplished by energizing LE~ 33 in the following manner.

~28~1~

1 The logic signal results in -triggering a transistor switch 2 (not shown) which connects the reference sample input line 3 60 to ground. As a consequence, the voltage on the negative 4 input of OP AMP 61 is dropped from approximately 8 volts to about ground potential. This causes the negative input of 6 oP AMP 61 to switch from a value higher than the positive 7 input to one that is lower resulting in an inversion of OP
8 AMP output from low to high on line 62. That output is then 9 ~ed back to the positive input to lock the OP AMP 61 in a high output condition avoiding oscillations. The output 11 voltage on line 62 is applied to transistor Q2 to turn that 12 transistor on, thus closing a circuit from the 24-volt 13 source th.rough the light-emitting diode 33 and transistor Q2 14 to ground. The result is to provide light from the LED 33 to the photocell 34 at the precise ti.me in the machine cycle 16 to reflect light rays from the bare photoconductor to photo-17 cell 34.
18 In order to produce a sensed toned sample voltage, 19 when the proper time in the machine cycle is reached to direct light upon the toned sample a logic signal is provided 21 to turn on a transistor switch, not shown, to connect the 22 toned sample input line to ground. This results in lowering 23 the negative input on OP AMP 63 from approximately 8 volts 24 to ground potential and causes the output on line 64 to go high. The signal on line 64 turns on the transistor Ql, 26 causing the light-emitting diode to conduct through the 27 transistor Ql to ground. Note that the resistance levels 28 connected with the transistor Ql are significantly lower BO976037 -lS

8 1~ ~

l than the resistances associated with transistor Q2. As a 2 result, the current level through transistor Ql is signifi-3 cantly higher than the current level through Q2, thus creating a more intense light from ~ED 33 when the toned sample is viewed. The reason ~or this is that the bare photoconductor 6 will reflect a higher light level than the toned photoconduc-7 tor. It was xecognized that the reflected light intensities 8 exciting the photocell must be kept at a nearly equal level ~ whether viewing a bare sample or a toned sample. The reason for this is to avoid the non-linearities which occur in ll photocell excitations from reception of different light 12 levels to avoi.d the non-linearities in circuit response and l~ to guarantee high signal levels whether viewing the bright 14 reference sample or the dark toned sample in order to improve noise immunity. In a system which is designed to be relatively 16 free from variations in component sensitivities, this is an 17 important feature.
18 Referring now to the circult of photocell 34, note 19 that OP AMP 65 is connected as a transconductance ampli~ier.
With photocell 34 off only a small dark current flow exists 2~ between the output of OP AMP 65 and the negative input.
22 However, when the photocell is excited, the current flow is 23 substantially increased causing a significant voltage drop 24 across resistors Rl6 and Rl7 creating a voltage level at line 66 of perhaps 1 or 2 volts. Zener diode 67 limits the 2~ voltage level which can occur at line 66 to 8.5 volts, i.e., 27 a swing of 8.5 volts from the photocell unexcited value.
28 Assuming a photocell excited voltage level of 2 volts at ~28~

1 line 66, the change from 0 volts to 2 volts is coupled 2 through capacitor 68 to an integra-ting circuit comprised of 3 OP AMP 69, capacitor 70, field e~fect -transistor (EET) Q5 4 and the associated resistances. Under ordinary conditions 16 volts is placed on the input of OP AMP 69 resulting in an 6 output of 16 volts at line 71. When a light source excites 7 the photocell, resulting in a voltage of, for example, 2 8 volts on line 66, a two-volt swing appears across the capacitor 9 68 and is placed on the capacitor 70, resulting in a ramping down of the voltage on liné 71 from 16 volts to 14 volts.
11 If a bare (reference) sample is being taken the output of OP
12 AMP 61 biases diode 72 to turn on FET Q6 during the bare 13 sample period. Thus the 14 volts on line 71 passes through 14 FET Q6 and is placed on capacitor 73~ That voltage is stored until such time as the toned ~sample is taken by 16 photocell 34.
17 When the toned sample is taken, there should again lg be a 2-volt potential produced on line 66 if the density of 19 the toned sample is approximate`ly correct. This is true hecause of the balancing of current flow in photocell 34 21 regardless of whether a reference sample or a toned sample 22 is be.ing taken ~due to the different current levels through 23 LED 33 as explained above). Thus a 2-volt swing again 24 appears across capacitor 68 resulting in a 2-volt potential drop across capacitor 70, causing the voltage of line 71 to 26 ramp down from 16 to 14 volts. During the toned sample 27 input period FET Q7 is turned on and FET Q6 remains off.
28 Thus the 14 volts present on capacitor 73, that is, the 1 reference voltage, is placed on the positive inputs of OP
2 AMPS 74 and 75, while the toned sample input present on line 3 71 is connec~ed directly to the negative input of OP AMP 74, 4 and is connected through a voltage divider network to the S negative input of OP ~MP 75. If, for example, resistance 6 levels R21 and R22 were equal, the potential at the negative 7 input of OP AMP 75 would be the difference of 14 volts o~
8 line 71 and the 16 volts input, that is, 15 volts.
9 At OP AMP 74, the 14-volt reference signal is placed on the posi-tive input while the 14-volt toned sample 11 signal is placed on the negative input. Since there is no 12 differential, the output of OP AMP 74 indicates that the 13 toner concentration condition is correct and the toner low 14 signal remains off. Similarly, at OP AMP 75, the bare sample input is 14 volts, the toned sample input is 15 16 volts, and therefore the toner extra low signal remains off.
17 Suppose, however, that the toner density of the 18 toned patch was too light. ~he resu].t would be an excessive 19 reflection of light from that patch, causing a high excitation of photocell 34 and resulting in a potential at line 66 of, 21 for example, 4 volts. In this example a 4-volt swing would 22 appear across capacitor 68, thus causing a ramping of the 23 voltage at line 71 from 16 volts to 12 volts. Now the 12 24 volts appears directly on the negative input of OP AMP 74 and is compared to the 14 volts on the positive input, 26 creating a high output, thus turning on the "toner low"
27 signal. OP AMP 16 is designed to register when a 30 milli 2~ volt difference appears, and thus the low output signal will ,~
BO~76037 -18-1 now be eneryized. At OP AMP 75, the toned sample signal of 2 12 volts on line 71 is divided against 16 volts and if the 3 resistances R21 and R22 were equal, would cause 14 volts to 4 appear at the negative input of oP AMP 75. Since both inputs are 14 volts, the toner extra low signal remains off.
6 Suppose now that the toned sample was so light 7 that the photocell excited to such a degree that a 6-volt -8 swing was experienced on line 66, thus sending the voltage g on line 66 from 0 volts to 6 volts. That 6-volt swing causes a ramping of the voltage on line 71 from 16 volts to 11 10 volts. When the 10 volts is divided with the 16 volts 12 (again assuming equal R21 and R22 values) a voltage of 13 13 volts is placed on the negative input of OP AMP 75. When 1~ this 13-volt signal is compared to the 14-volt reference, lS the toner ex-tra low output signal is turned on.
16 During regular operation of the machine, i.e., 17 when there is no interruption for a test cycle, it is desir-18 able to provide a checking signal in order to determine that 19 the test network is in operating order. That is provided by the portion of the circuit including transistor 08. Note 21 that when transistor Q8 is turned on the negative input to 22 OP AMP 75 is grounded and thus turns high the output of OP
23 AMP 75. As a consequence, the toner extra low signal is 24 turned on~ At the same time the voltage levels at OP AMP 74 keep the toner low output signal off. This creates an 2~ unusual condition of having the toner extra low signal on 27 while the toner low signal is off. This condition is forced 2~ by the operation of transistor Q8, and thus any change in .

1 this condition during the operation of the machine will 2 siynify to the machine logic that something is wrong in the 3 test circuit. Note that transistor Q8 is turned on by a 4 high output from OP AMP 76. A high output from OP AMP 76 is present whenever the output of OP AMP 77 is high ~neglecting 6 the ~C time delay). OP AMP 77 is high when the negative 7 input is lower than the input on the positive side. Note 8 that since line 66 is at 0 volts during regular operation, ~ the voltage at the negative inpu-t of OP AMP 77 is lower than the positive side under normal conditions. Note, however, 11 that when a bare or toned sample is taken, voltage on line 12 66 rises, thus turning off the high output from OP AMP 77, 13 turning off the high output from OP AMP 76 and thus opening 1~ the circuit of transistor Q8.
Another quality test available through this circuit 16 is that if the photoconductor has become so coated with 17 toner that when the bare sample is taken it actually is a 1~ darkened sample, there will be only a small amount of light 19 from LED 33 appearing at the photocell 34. It will be a much lower photocell excitation than expected, consequently, 21 the voltage on line 66 does not change significantly, and 22 thus even though a bare sample is being taken, transistor Q8 23 is not turned off since line 66 does not change significantly 24 higher from its regular value. Therefore the output of OP
AMP 77 remains high and transistor Q8 remains on. In this 2G situation, the logic senses the ~act that the toner extra 27 low output signal from OP AMP 75 has remained on even 1 though it should have gone off when entering the test sequence.
2 This inorms the logic that a darkened photoconductor condition 3 is present and that remedial steps are needed. Consequently, 4 the circuit o~ transistor Q8 performs a darkened pho-toconductor

5 check as well as indicating -the presence of problems in the

6 test circuit itself.

7 Upon testing for toner density, if the tonér low

8 signal is activated, the toner replenisher 35 (FIGURE 3)

9 operates to dump a quantity of toner into developer 23. If both the toner low and the toner extra low signals are 11 activated, a variety of possibilities for further action are 12 present, depending on machine design. For example, the l3 first subseguent action would probably be to check a "cartridge 14 empty" signal from the toner replenisher 35. If it is ~5 empty, a call for the key operator oE the machine is in 1~ order. However, if the replenisher has an adequate toner 17 supply, the next action might be to shut the machine down.
1~ Alternatively, there might be repeated toner density checks 19 after a few more copies until the toner extra low signal is 2~ no longer active. At some point, if the extra low sign~1 21 remains activated, the machine would be shut down.
22 As stated above, a test cycle can be run on the 23 shut-down cycle when only small numbers of reproductions are 24 called for during a reproduction run. Special test cycles with reproductions skipped may be used only during long, 26 multi-copy runs. Providing the specific control circuitry ?7 for interrupting machine operation to provide special test 28 cycles at the proper time is dependent upon the requirements 1 of a particular machine. Such circuit design is well within 2 the skill of the art and does not comprise a part of the 3 instant invention. Similarly, control apparatus for receiving 4 -the toner low and toner extra low signals to actuate the replenisher are well within the skill of the art and not a 6 part of the invention herein.
7 While this invention has been described within the ~ framework of a par-ticular embodiment, i.e., a transfer type 9 machine of the -two-cycle type, it can be equally well used in conventional single-cycle machines and it will be under-11 stood by those skilled in the art that the foregoing and 12 other changes in form and details may be made without depart-13 ing~from the spirit and scope of the invention.

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of determining the condition of copy quality variables of an electrophotographic machine of the transfer type having a photoconductor, a charge corona for producing a relatively uniform charge on the photoconductor, an exposure station for producing a latent image upon the charged photoconductor, a developer with a supply of toner for applying said toner to the latent image whereby a toned image is produced, a transfer corona station to transfer the developed latent image to a receiving member, an erase lamp for neutralizing remaining charge on the photoconductor after transfer, and a cleaning station for cleaning away residual toner remaining on the photoconductor after transfer, comprising utilizing a test cycle during which a copy is not reproduced and in which the condition of copy quality variables within the area of the photoconductor ordinarily used for document reproduction is determined.

2. The method of Claim 1 during which a toner density concentration control test method is performed comprising the steps of:
1) charging the photoconductor;
2) erasing or discharging the charge on the photoconductor but leaving a charged test area located in an area of the photoconductor used for copy reproductions;
3) developing the test area;
4) taking a reflectance measurement of the developed test area; and 5) comparing the results of the reflectance measurement to a reference in order to determine whether additional toner needs to be added to the developer supply.

3. The method of Claim 2 further including the step of passing the photoconductor through the exposure station without producing a complete latent image of a document to be reproduced.

4. The method of claim 3 further including the step of passing the photoconductor through the transfer station with the transfer corona off and thereby not transfer-ring the developed latent test area to a receiving member.

5. The method of Claim 4 wherein said erase lamp is used for said step of erasing the charge on the photocon-ductor but leaving a charged test area by momentarily inter-rupting the erasing light beams.

6. The method of Claim 5 wherein said machine further includes a document lamp and a shutter and wherein said charged test area is limited in extent by turning on said document lamp, thus exposing said photoconductor at said exposure station, but limiting the extent of said exposing by a shutter.

7. The method of Claim 6 wherein said test cycle is run upon the completion of copy production when the number of copies produced on a single run is less than n copies.

8. The method of Claim 6 wherein said test cycle is run during the middle of a single run of more than n copies by interrupting the production of copies in order to make the test cycle.

9. The method of Claim 2 wherein the erased area and the test area are produced within the image area used for producing large copies but not used for producing small copies.

10. The method of Claim 9 wherein said erase lamp is used for said step of erasing the charge on the photocon-ductor but leaving a charged test area by momentarily inter-rupting the erasing light beams.

11. The method of Claim 10 wherein said machine further includes a document lamp and a shutter and wherein said charged test area is limited in extent by turning on said document lamp, thus exposing said photoconductor at said exposure station, but limiting the extent of said exposing by a shutter.