US3756192A

US3756192A - Automatic toner concentration control system

Info

Publication number: US3756192A
Application number: US00209042A
Authority: US
Inventors: H Locklar; D Tao; L Tarver
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1971-12-17
Filing date: 1971-12-17
Publication date: 1973-09-04
Anticipated expiration: 1990-09-04
Also published as: CA1013806A; DE2257033A1; FR2165421A5; JPS4869527A; DE2257033C3; GB1376359A; IT967829B; JPS5213935B2; DE2257033B2

Abstract

A toner concentration control system for an electrostatic copier wherein light is alternately reflected from multicomponent developer material containing toner and from a calibrated reflector to a photosensor. An imbalance of toner in the developer material results in a difference in reflected light intensity from the developer and reflector which is converted into an electrical signal having an AC component. A phase sensing circuit detects the position of the peak of the AC signal component with reference to the position of the calibrated reflector and provides a control signal to a toner replenishing device. Developer flow past the photosensor is intermittently halted during concentration sensing to reduce noise effects. A plurality of selectable calibrated reflectors provide different concentration settings. Additional concentration settings are obtained by varying the light spectrum emitted by the light source.

Description

United States Patent [1 1 .Locklar et al.

1451 Sept. 4, 1973 AUTOMATIC TONER CONCENTRATION CONTROL SYSTEM [73] Assignee: International Business Machines Corporation, Armonk, NY.

22 Filed: Dec. 17, 1971 21 Appl. 190.; 209,042

Marlow 356/205 Little 356/183 Primary Examiner-Mervin Stein Assistant Examiner-Leo Millstein Att0rneyJohn W. Girvin, Jr. et .al.

[5 7 ABSTRACT A toner concentration control system for an electrostatic copier wherein light is alternately reflected from rnulticomponent developer material containing toner and from a calibrated reflector to a photosensor. An imbalance of toner in the developer material results in a difference in reflected light intensity from the developer and reflector which is converted into an electrical signal having an AC component. A phase sensing circuit detects the position of the peak of the AC signal component with reference to the position of the calibrated reflector and provides a control signal to a toner replenishing device. Developer flow past the photosensor is intermittently halted during concentration sensing to reduce noise effects. A plurality of selectable calibrated reflectors provide different concentration settings. Additional concentration settings are obtained by varying the light spectrum emitted by the light source.

8 Claims, 8 Drawing Figures PATENTEDSEP 4 ms 3356; 192

sum 1 or 4 INVENTORS HENRY C. LOCKLAR DEH C. TAO

'LOYD E. TARVER JR.

BY g whlw gq ATTORNEY.

PATENTED SEP 4 I973 SHEET 2 DP 4 FIG. 2

FIG. 8

ADD -s TONER R 7 T W m V N 5 R n E (l T R E V N D 5 V M 4 L W V t L;

INVERTER 5 V5 REPLENISH MOTOR MAGNET DRIVER SHEEI 3 [IF 4 FIG. 3

F ulalllll Vcc FIG. 5

PATENTEDSEI 4191s SHEET t (If 4 POSITIVE AMPLIFIED SIGNAL NEGATIVE AMPLIFIED SIGNAL POSITIVE AMPLIFIED SIGNAL NEGATIVE AMPLIFIED SIGNAL AUTOMATIC TONER CONCENTRATION CONTROL SYSTEM CROSS-REFERENCE TO RELATED APPLICATION The following application is assigned to the same assignee as the present application:

U. S. Pat. application Ser. No. 1 10,725, entitled Coated Carrier Particles with Polarity and/or Magnitude of Triboelectric Charge Controlled, Method of Making Same, and Improved Electrophotographic Process, William J. Kukla and Howard Everett Munzel, inventors, filed Jan. 28, 1971.

BRIEF BACKGROUND OF INVENTION 1. Field This invention relates to a toner concentration control system for an electrostatic reproduction apparatus and more particularly to an improved optical sensing apparatus for maintaining constant image density of an electrostatic printer which utilizes a multicomponent developer material containing toner.

2. Description of the Prior Art In well-known electrostatic printing processes, a surface bearing a latent electrostatic image is developed by applying a developer material comprising toner and a carrier material to the surface. A portion of the applied toner is selectively attracted to the image areas of the surface and the remainder of the developer material is removed and allowed to recirculate to form subsequent images. In order to assure that there is a sufficient and proper amount of toner in the developer material, it is necessary to add quantities of toner material to the developer material to replace that which has been used for imaging.

The most rudimentary prior art system for controlling the toner concentration of a developer material included a manually settable device for controlling the amount of toner metered to the developer material during each printing cycle. This method of control was based upon guess work by the operator who observed the output copy quality and made a judgment as to whether more or less toner should be dispensed in order to improve the print quality. Such systems necessarily depend upon the judgment of the operator and further require the constant presence of the operator.

Various prior art systems have been proposed for automatically controlling the toner concentration of developer material. These systems rely on measuring a physical characteristic of the developer material such as its electrical resistance, inductance, or capacitance, or an optical characteristic. These prior systems which measure an optical characteristic fall into two general categories: Those which incorporate a probe which electrostatically attracts toner material over a fixed period of time and is optically sensed to determine the amount of toner attracted and those which measure the light reflected from the multiple component developer material to obtain a measurement of the amount of toner present within the mixture.

With each of these optical systems, it is necessary to assure uniformity of the measuring apparatus since minor discrepancies within such apparatus results in poor quality reproductions. Accordingly, most of these devices take the form of a first photosensing device responsive to light reflected from the material to be measured which originates at a light source and a second photosensing device responsive to light from the same light source. The photosensing devices are precisely matched and each form a portion of a bridge circuit. Thus, variations in the light source are compensated for by the action of the two photosensing elements. However, it is necessary that each of the photosensing elements be precisely matched and that each such device age in the same manner. It is further necessary that noise effects generated by moving toner particles be eliminated in such prior devices. Thus, the bridge circuit generally has a threshold circuit associated therewith to prevent actuating the toner dispenser with a noise signal. Since the threshold must be relatively high, a great degree of latitude in toner concentration must be allowed for in the developing system. Further, the small magnitude of reflectance variation to be sensed and the drift effects associated with requisite amplification devices make such devices impracticable.

SUMMARY In order to overcome the above-noted shortcomings of the prior art and to provide an optical toner concentration sensing system which consistently and accurately detects the concentration of toner in a multicomponent developer material mixture, the present invention incorporates a calibrated reference which is periodically interposed between the sensing apparatus and the developer material to be sensed thereby effecting the generation of an electrical signal having an AC component whenever there is a difference in the intensity of light reflected from the reference and that reflected from the developer material. A phase sensing circuit is provided to detect the position of the peak of the AC signal component with reference to the position of the calibrated reflector thereby avoiding effects of component drift inherent in amplitude detection systems. Utilization of a single sensing device assures uniformity of system operation. The surface of the light reflecting device is given a predetermined value of reflectance thereby providing for continual recalibration of the electrical signal assuring a high degree of accuracy within the system. Movement of the developer material is periodically halted to prevent unwanted noise signals effected by the moving material.

A plurality of selectable reference devices are incorporated into the system thereby providing a wide latitude of selectable, controllable toner concentrations and/or developer material components. An additional control of the light source spectral emission provides additional concentration settings.

Accordingly, it is the principle object of the invention to automatically and precisely control toner dispensing in an electrostatic processing system. A further object of the invention is to maintain consistency in image quality of an electrostatic printing device. Such consistency is obtained by maintaining the proper ratio of toner in a multicomponent developing material. It is a further object of the invention to accurately optically sense the toner concentration of the developer material.

The foregoing objects, features, and advantages of the invention will be apparent from the following more particular description of the preferred embodiment of the invention as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a schematic pictorial illustration of a conventional electrostatic reproduction apparatus incorporating the toner concentration control system of the present invention.

FIG. 2 is a crosssectional view of the developer material flow path and optical sensing elements of the toner concentration control system.

FIG. 3 is a circuit diagram of the threshold detection logic of the toner concentration control system.

FIG. 4 is a circuit diagram of the phase indicator logic of the toner concentration control system.

FIG. 5 is a circuit diagram of the flow indicator logic of the toner concentration control system.

FIGS. 6 and 7 are wave form diagrams of various signals of the circuits of the toner concentration control system.

FIG. 8 is a logic block diagram of the replenisher motor control logic of the toner concentration control system.

DESCRIPTION Referring now to the drawings, and more particularly to FIG. 1 thereof, a schematic pictorial illustration of a conventional electrostatic reproduction apparatus incorporating the toner concentration control system of the present invention is depicted.

The reproduction apparatus depicted comprises a plurality of processing stations located about a cylindrically shaped electrostatic photosensitive plate 11. The cylindrical plate comprises a layer of photoconductive material superimposed over a conductive backing. A suitable photoconductive material is disclosed in U. S. Pat. No. 3,484,237 issued Dec. 16, 1969. The photoconductive material is sensitized by a corona generating device 13 as it rotates therepast in the direction of arrow 15. A light image of the copy 17 to be reproduced is projected onto the sensitized surface. of the electrostatic photosensitive plate 11 rotating thereunder to form an electrostatic latent image thereon. The rotating plate thereafter passes a developer station 19 where multicomponent developer material including electrostatically charged toner is applied to the surface of the electrostatic photosensitive plate 11 containing the latent electrostatic image thereon. The toner particles are preferentially attracted to the latent image on the plate 11 and are subsequently transferred to a support surface 21 by conventional electrostatic transfer or by heat transfer. The plate continues to rotate past a cleaning station 25 which removes residual toner from the surface thereof.

The developer station 19 comprises a sump portion 31 containing multicomponent developer material 33. The principle components of the developer material are electroscopic toner and a carrier. Suitable materials for use as toners are well known in the art and generally comprise finely divided resinous materials capable of being attracted and held by electrical charges. Examples of toners which can be employed are commercially marketed by the International Business Machines Corporation as IBM part No. 1162057 and IBM part No. 1 162051. The IBM part No. 1 162057 toner comprises a copolymer of styrene/n-butyl methacrylate resin, maleic anhydride modified polyester, polyvinyl stearate plasticizer and carbon black pigment. The IBM part No. I 162051 toner comprises a copolymer of n-butyl methacrylate/methymethacrylate resin, maleic anhydride modified polyester, polyvinyl butyral plasticizer, carbon black pigment, and a fumed silica physically mixed in the toner after compounding. Many wellknown suitable carrier materials can be utilized, the carrier particles generally being between 50 and 1,000 microns in size. Often, the carrier is manufactured by coating sand, glass beads, or metallic beads with a material which triboelectrically interacts with the selected toner to produce the desired charge on the toner to provide good imaging quality. An example of such a carrier and the control of its triboelectric charge characteristic is disclosed in the aforereferenced copending application of William .I. Kukla, et al.

A toner dispenser 35 is provided to dispense toner particles into the multicomponent developer material 33 located in the sump portion 31 of the developer unit 19. A rotating auger 39 stirs the freshly added toner with the developer material to assure complete mixing thereof.

The small toner particles of the developer material 33 are held onto the surfaces of the relatively large carrier particles by electrostatic forces, which develop from the contact between the toner and carrier particles producing triboelectric charging of the toner and carrier to opposite polarities.

A bucket conveyor 41 rotates through the sump portion 31 of the developer station 19 and scoops up quantities of developer material 33 for delivery to the upper portion of the rotating electrostatic photosensitive plate 11.

The thus delivered developer material cascades downwardly over the rotating plate 11 and the triboelectrically charged toner particles adhere to the electrostatic latent image on the plate 11. The carrier material and toner material not adhering to the plate fall back into the sump portion 31 for subsequent mixing with toner particles 37. As discussed above, the toned latent image is transferred to a support surface 21 as the plate 11 continues its rotational motion.

In order to assure high quality images, it is necessary that the proper ratio of toner to carrier in the developer material be maintained. By varying this ratio, for example, by having excessive toner, dark blurred overdeveloped images are obtained. When too little toner is present in the developer material, light underdeveloped images are obtained. In order to automatically control the ratio of toner and carrier and maintain it at a desired level, a sample of the developer material is obtained and optically sensed to determine its light reflectance characteristic. Since the reflectance characteristic of the toner particles differs from that of the carrier particles, a properly proportioned mixture of the developer material will have a predetermined light reflectance characteristic. This characteristic would, of course, differ for each different toner or carrier which may be selected for a system. Since the toner particles are generally darker than the carrier particles, the amount of light reflected becomes greater as the proportion of toner to carrier in the mixture becomes less and, conversely, less light is reflected from the mixture as the ratio of toner to carrier increases.

In order to obtain a sample of the developer material as it is delivered to the electrostatic photosensitive plate 11, a diverter 51 is positioned in the flow path of the developer material as it tumbles from the bucket conveyor 41 toward the plate 11 and continually captures a portion of the developer material as it is delivered from the bucket conveyor. The developer material is delivered from the diverter 51 to a chute member 53 containing a viewing window 55 therein. The developer material flows through the chute member 53 and exits therefrom into the sump portion 31 of the developer station 19. An actuable shutter member 57 halts developer flow through the exit of the chute member 53 thereby causing the developer material to halt within the chute member and thus remain stationary at the viewing window 55.

The optical characteristic of the developer material at the viewing window 55 is detected by illuminating the developer material with light from the light source 59 which is reflected to the photosensing device 61. The reflected light is converted into an electrical signal and is applied by AC coupling means to the threshold detection logic 63. The AC coupling eliminates the effects of long-term component drift in the system. The photosensing device 61 is also responsive to light reflected from the teeth 65 of the rotating chopper wheel 67 as the teeth rotate in front of the viewing window 55. The level of reflectance of each chopper wheel tooth is such that it has a value of reflectance equal to that of the developer material of a desired toner concentration as it is viewed through the viewing window 55. Consequently, any toner-carrier mixture having a value of toner concentration less than the desired value appears lighter than the corresponding chopper wheel tooth and vice versa. In the device depicted, the chopper wheel 67 has four teeth 65, each of which may have a different reflectance value corresponding to a desired toner concentration setting of the same or of different developer materials. Each such reflectance value modities the light incident thereon by a differing amount. The chopper wheel 67 is pinned to a shaft 69 which, in turn, is driven by the pulley 71. The pulley 71 has a magnetic actuator 73 attached thereto which actuates the reed switch 75 upon each revolution of the pulley wheel. The signal from the reed switch 75 actuates a single shot 77 which in turn provides a logic signal input to the delay unit 78. The logic signal is delayed by a selectable amount in accordance with the desired image density and, hence, the tooth 65 selected as a reference. The delayed signal is provided as an input to the replenisher motor control logic 79.

As the chopper wheel 67 rotates, the photosensing device 61 is presented with light which is alternately reflected from the teeth 65 and from the developer materiallocated in the viewing window 55. The electrical signal obtained from the photosensing device will contain an AC component when the intensity of the light reflected from the developer material differs from that of the light reflected from the teeth 65. If the teeth all have the same reflectance value, no AC signal would be present when the reflectance from the developer material is the same as that from the teeth. The AC component will have either a maximum value or a minimum .value when the photosensing device 61 is viewing a tooth 65 depending upon whether the developer material in the viewing window 55 is darker or lighter than the tooth. As noted above, when the developer material is lighter than the tooth, the mixture is lean in toner, and it is necessary to add additional toner to the mixture. In order to accomplish this, the toner dispenser can be turned on in a manner to be described and caused to remain on until the developer material becomes darker than the tooth. Thus, with the disclosed arrangement, it is necessary only to determine if the peak of the AC signal component is generated by a tooth 65 of the chopper wheel 67 or by the developer material located within the viewing window 55. Accordingly, a simple phase detection circuit can be utilized to provide an indication of the position of the tooth with respect to the peak of the AC signal. The magnetic actuator 73 and reed switch provide the necessary synchronizing signal to determine whether the photodetector is viewing a tooth 65 or the developer material in the viewing window 55.

When the developer material appearing in the viewing window 55 is lighter than the tooth 65 utilized as a reference, the replenisher motor control logic 79 generates a signal which actuates the replenisher motor 81. The replenisher motor 81 drives a toner replenishing drum 83. The toner replenishing drum 83 has slots located in the surface thereof which carry toner particles from the resevoir 85 to a position where they fall into the sump portion 31. Such a toner dispensing apparatus is described in U. S. Pat. No. 3,572,555 issued Mar. 30, 1971, assigned to the assignee of this invention.

In order to prevent an unwanted noise signal resulting from the motion of the developer material past the viewing window during the time that it is desired to measure the toner concentration, the shutter member 57 is actuated by a cam 87 to prevent developer flow through the chute member 53. When the shutter member 57 is thus actuated, the sample switch 89 is closed providing an input signal to the replenisher motor con trol logic 79. This input signal prevents the threshold detection logic 63 from actuating the replenisher motor 81 during those time periods when developer material is flowing through the chute member 53.

Referring now to FIG. 2 of the drawings, a crosssectional view of the developer material flow path and the optical sensing elements of the toner concentration control system are depicted. The developer material enters the chute member 53 from the diverter 51 of FIG. 1. The chute member 53 is formed to create an upper pocket 91 which collects a funnel-shaped quantity of developer material therein. The stagnant pocket of developer material thus created prevents newly added developer material from scrapping against the side walls of the chute member 53 prior to optical sensing thereby providing a minimum disturbance to the toner-carrier ratio of the developer material from the state in which it exists prior to entering the chute member 53. A grounded plate 93 formed of NESA" glass, a trademark of the Pittsburg Plate Glass Company, which is generally tin-oxide coated glass that is transparent to white light is mounted adjacent the viewing window 55. The grounded glass member prevents toner particle buildup due to electrostatic charging adjacent the viewing window thereby insuring accurate measurement of the developer material. When the cam 87 rotates causing the shutter member 57 to open, developer material flows past the plate 93 and scrubs the plate keeping it free of excess toner particles. The exit of chute 53 is small enough to cause packed flow of the developer material.

When the shutter member 57 closes, developer material halts within the opening 95 of the chute member 53 including that portion of the opening 95 adjacent the plate 93. As described heretofore, switch 89 is closed thereby providing an electrical signal which enables the output signal of the photosensing device 61 to be utilized to control the toner replenisher motor 81 of FIG. 1. That is, although the chopper wheel 67 and the magnetic actuator 73 are in operation at all times,.when the reproduction machine is in operation, the signal from the photosensing device 61 is sampled only when the shutter member 57 has stopped the fiow of developer material through the opening 95. It has been found that, for the device disclosed, by allowing developer to flow for a period of seconds and by halting such flow for a period of 2 seconds, an accurate measurement can be obtained and utilized to control the tonercarrier ratio of the developer material within a fine tolerance.

Referring now to FIG. 3 of the drawings, a circuit diagram of the threshold detection logic of the toner concentration control system is depicted. This logic is responsive to the photosensing device 61 which, by way of example, could comprise an RCA 93 1A photo multiplier tube and comprises

threshold circuits

101 and 103 and a differential amplifier. The AC component of the signal from the photosensing device 61 is supplied to the differential amplifier transistor 105 which, along with transistor 107, differentially amplifies the signal and applies the thus amplified signal to the

threshold circuits

101 and 103 so that the positively amplified signal will drive one threshold circuit while the negatively amplified signal drives the other circuit. The threshold circuits yield output signals V1 and V2 which are pulses occurring at the positive and negative peaks, respectively, of the differentially amplified signal when the magnitude of this AC signal is above the threshold values. The combination of

resistors

109 and 111 and resistors 113 and 115 determine the peak magnitudes necessary to yield the output pulses V1 and V2. The

threshold circuits

101 and 103 thus prevent a noise signal supplied by the photosensing device 61 from effecting output pulses which would drive the replenisher motor control logic and further provide for adjustment in the setting of the desired toner concentration. Since two threshold levels are involved, by properly adjusting the resistor combination, levels can be set which will give a voltage signal V1 when the mixture is too lean in toner and will give a voltage signal V2 when the mixture is too rich in toner. This double set point arrangement allows for a latch type circuit to provide the necessary signal to the replenisher motor.

Referring once again to FIG. 1 of the drawings, it has been described that the magnetic actuator 73 actuates the reed switch 75 upon each revolution of the pulley 71 and corresponding revolution of the chopper wheel 67. The magnetic actuator 73 is placed so that the photosensing device 61 is viewing a tooth 65 when the read switch 75 is actuated.

Referring now to FIG. 4 of the drawings, a circuit diagram of the phase indicator logic of the toner concentration and control system is depicted. Closure of the reed switch 75 by the magnetic actuator 73 of FIG. 1 actuates a single shot circuit consisting of

transistors

121 and 123 and their associated resistive and capacitive elements. The resistive and capacitive elements are sized so that the width of the output signal pulse V3 is less than the length of time that the photosensing device 61 views a tooth 65 (FIG. 1).

Referring once again to FIG. 1 of the drawings, it has been described how the sample switch 89 provides an electrical signal input to the replenisher motor control logic 79 when the shutter member 57 blocks flow of developer material through the chute member 53. It has been further described that during this period of time, that the output signals of the threshold detection logic 63 and the single shot 77 are utilized. With reference to FIG. 5 of the drawings, a circuit diagram of the flow indicator logic of the toner concentration control system is depicted. When contact 890 of the switch 89 of FIG. 1 is closed, transistor 127 provides an output signal V4.

Referring now to FIG. 6 of the drawings, wave form diagrams of various signals of the circuits of the toner concentration control system are depicted. These wave forms occur when a lean mixture is detected. Wave form 141 is representative of the V3 output signal of the phase indicator logic depicted in FIG. 4. It will be recalled that the single shot provides an output pulse for each revolution of the chopper wheel 67 of FIG. 1, the output pulse corresponding to the time during which the photosensing device 61 is viewing a tooth 65 of the chopper wheel. Because the light reflected from the tooth 65 of the chopper wheel is less than that reflected from a lean mixture, the photosensing device 63 will provide a peak signal when sensing the tooth (the more intense light signal producing a more negative electrical signal).

Accordingly, the out-of-phase or negatively amplified signal output of the differential amplifier of FIG. 3 depicted by wave form 143 has a negative peak 145 which occurs at the same time as the pulse V3 of wave form 141. When this peak is below the threshold detection level indicated by line 147, an output pulse V1 as indicated by wave form 149 is supplied by the threshold detection circuit of FIG. 3. The next negative peak 151 of the wave form 143 corresponds to the light reflected from a nonselected tooth 65 of FIG. 1 which may or may not be below the threshold as indicated by line 147. As depicted, the wave form is above the threshold.

The in-phase or positively amplified signal from the photosensing device is indicated by wave form 153. The negative peaks of this wave form, 155 and 157, correspond to the time during which the developer material is being viewed and produce pulses V2 denoted by wave form 159 when they exceed the threshold value denoted by line 161. As noted heretofore, the threshold levels denoted by

lines

147 and 161 are independent of one another thereby providing double set point control.

Referring now to FIG. 7 of the drawings, a wave form diagram of the various signals of the circuits of the toner concentration control system is depicted. These wave forms occur when a rich mixture is detected. When a rich mixture is detected, the negative peak of the out-of-phase or negatively amplified photosensing device signal, as indicated by wave form 163, occurs out of phase with the single shot pulse depicted by wave form 165. Conversely, the negative peaks of the wave form 167 corresponding to the in-phase amplified sig-- nal overlap the output pulse of the single shot. Thus, pulses V1, denoted by wave form 169, are out of phase with the single shot, and the pulses V2, denoted by wave form 171, are in phase with the single shot.

Referring now to FIG. 8 of the drawings, a logic block diagram of the replenisher motor control logic of the toner concentration control system is depicted. It will be recalled from the description immediately preceding that a lean mixture causes pulses V1 to overlap with the single shot pulses V3. Thus, when the flow indicator logic provides an output signal V4 indicating that sampling is to be effected, the logic inverter units and 177 provide an output signal, ADD. The ADD signal drives the magnet driver 179 which, in turn, actuates the replenisher motor 81. As described heretofore, the replenisher motor effects the dispensing of additional quantities of toner into the developer mix. This motor continues to operate until the ADD signal is dropped.

As noted heretofore, the out-of-phase output V2 of the differential amplifier does not overlap with the signal .V3 until a rich mixture is detected. Accordingly, the inverter 181 provides an output signal V5 until a rich mixture is detected. This singal, V5, along with the ADD signal provide an input to the inverter 175 which keeps the ADD signal on until the V5 signal is dropped when a rich mixture is detected. This double set point control thus enables the threshold at which the replenisher motor 81 is actuated to be controlled as well as controlling the threshold level at which the replenisher motor 81 is turned off.

Referring once again to FIG. 1 of the drawings, it has been further found that by varying the spectral emission of the light source 59, the toner concentration of the developer material can be maintained at different levels within the range dictated by the gray scale on the selected tooth 65 of the chopper wheel 67. This is because the viewing window 55 has a non-uniform transmission spectrum causing light reflected from the developer material to be dependent upon both incident light intensity and the incident light spectrum. The spectral emission of the light source can be varied by varying the filament voltage by control 182 of FIG. 2. In the particular device depicted, a General Electric lamp N o. 253 was utilized and a gray scale was selected with its reflectance equivalent to a toner concentration of 0.48-0.50 percent for a lamp voltage of 1.80 volts. By varying the lamp voltage between 1.75 volts and 2.0 volts, the nominal toner concentration is maintained at different levels between 0.38 percent and 0.60 percent (:':0.05 percent). Accordingly, a simple control on the lamp voltage can provide a wide range of toner concentration selectivity.

A further selectable means of controlling the toner concentration within a selectable desired range is to provide differing gray scales on each of the teeth 65 of the chopper wheel 67. A delay control 78 delays the output signal of the single shot 77 by the amount of time that it takes for the desired tooth to rotate to the viewing position. Thus, if it were desirous to compare the intensity of light reflected from the developer material with the gray scale on tooth 65a, a delay would be selected corresponding to the amount of time that it takes for the chopper wheel to rotate one half of a revolution. A simple operator control 183 can be utilized to select the desired delay network.

OPERATION OF THE INVENTION Developer material is delivered from the sump portion 31 to the electrostatic photosensitive plate 11 containing a latent electrostatic image thereon. The developer material cascades over the latent image causing toner particles to be attracted thereto. The density of the toner particles attracted to the image depend upon the ratio of toner to carrier in the developer material. In order to maintain a desired ratio, a portion of the developer material is diverted by diverter 51 into the chute member 53. Cam 87 is periodically rotated to close shutter member 57 causing the developer material to halt within the chute member 53 so that it is stationary in front of the viewing window 55. Light from the light source 59 is alternately reflected from the teeth of the rotating chopper wheel 67 and from the developer material located within the viewing window 55 and is presented to the photosensing device 61. The teeth 65 each have a calibrated gray scale thereon corresponding to a desired toner concentration. When the light reflected from the developer material differs from that reflected from a selected tooth, the photosensing device 61 provides an AC signal output to the threshold detection logic 63. Additionally, a phase pulse is generated by the coaction of the magnetic actuator 73 and the reed switch 75 which electronically indicates that a tooth 65 is being viewed at the time of occurrence of the phase pulse. The replenisher motor control logic 79 is responsive to the threshold detection logic 63 and to the phase pulse to determine whether the developer material is overly lean or overly rich. If the developer material is overly lean, the replenisher motor control logic 79 provides an actuating signal to the replenisher motor 81 which causes toner material 37 to be dispensed into the sump portion 31 of the developing station 19.

In order to produce extremely dense copy or extremely light copy, differing gray scales are provided on each of the teeth 65. Operator selection of a desired density selects the tooth 65 which will be utilized in controlling the developer material concentration. The operator selection effects an appropriate delay of the signal generated by the reed switch 75 so that the tooth corresponding to the desired setting is adjacent the viewing station at the time the gating signal is provided by the delay unit 78 to the replenisher motor control logic 79. Further, by providing a simple control to the lamp filament voltage of the light source 59, additional settings may be selected for a given tooth setting.

While the above description has related to the utilization of a chopper wheel or light shutter which interrupts the light reflected from the developer material to provide an unvarying reference, it is recognized by those skilled in the art that relative motion between the reference and the developer material could instead be effected by movement of the light source-photosensing device from a first viewing position wherein the developer material is viewed to a second viewing position wherein a reference is viewed. Further, the reference could comprise a filter arrangement through which the light is passed to obtain a desired light intensity striking the photosensing device for comparison purposes. That is, it is only necessary that light reflected or refracted through the developer material be alternately presented to the photosensing device with light generated at the same source and reflected or refracted through a fixed reference. Accordingly, various devices for presenting the light in such an alternate manner can be devised without departing from the spirit and scope of this invention.

It is further recognized by those skilled in the art that various circuits can be utilized to detect the output of the photosensing device and convert the AC signal output thereof into a logical signal indicative of the toner concentration within the developer material. Further, various well-known dispensing devices can be utilized including those which dispense a measured quantity of toner material for each actuation thereof. Additionally, various forms of developing stations such as a magnetic brush developing station can be utilized.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it should be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. Apparatus for controlling the concentration of multicomponent developer material including toner for use in an electrostatic reproduction apparatus including:

actuatable means for dispensing toner into the developer material;

a light source;

a developer unit fixedly mounted and having a viewing window for presenting developer material illuminated by said light source;

at least one calibrated light reflector movable from a first position to a second position, said light reflector being illuminated by said light source when in said second position;

photosensing means alternately responsive to light reflected from said illuminated developer material presented by said viewing window and to light reflected from said light reflector when said light reflector is in said second position for converting light into an electrical signal having an AC component when the intensity of light from the light reflector differs from the intensity of light from the developer material, said light reflector being interposed between said viewing window and said photosensing means when in said second position for preventing light from said developer material from striking said photosensing means;

control means responsive to said electrical signal for actuating said actuatable means for dispensing toner.

2. The toner concentration control system set forth in claim 1 further comprising means for effecting motion of said developer material past the viewing window;

actuatable halting means for halting the motion of said developer material at the viewing window;

means for actuating said halting means and for providing a halting signal;

said control means being further responsive to the halting signal for actuating said actuatable means.

3. The toner concentration control system set forth in claim 1 wherein said calibrated light reflector reflects light of an intensity equal to that reflected by a desired developer material concentration and wherein said control means being responsive whenever the intensity of the reflected light from the light modifying means is greater than the intensity of the reflected light from the developer material.

4. The apparatus for controlling the concentration of multicomponent developer material set forth in claim 8 comprising a plurality of calibrated light reflectors having differing light reflectance characteristics;

selection means for selecting one of said plurality of light reflectors;

motion means for moving said selected one of said light reflectors to said second position;

and wherein said photosensing means is responsive to light reflected from said selected light reflector when said selected light reflector is in said second position.

5. The apparatus for controlling the concentration of multicomponent developer material set forth in claim 9 wherein said plurality of light reflectors are mounted on a rotary means and wherein said motion means effects rotation of said rotary means thereby presenting each light reflector at said second position.

6. Apparatus for controlling the concentration of multicomponent developer material set forth in claim 8 further comprising:

means for varying the light spectrum of said light source by a controlled amount;

said viewing window having a nonuniform light transmission spectrum;

said photosensing means being responsive to reflected light to provide an output signal, the magnitude of which is dependent on the spectrum of light incident thereon;

and wherein said control means being responsive to a predetermined magnitude of said electrical signal for actuating said actuatable means.

7. Apparatus for controlling the concentration of multicomponent developer material set forth in claim 8 further comprising:

phase signal generating means for generating a phase signal identifying the position of the light reflector; said control means being further responsive to said phase signal for actuating said actuatable means when the intensity of the light from the light reflector is less than that from the developer material.

8. Apparatus for controlling the concentration of multicomponent developer material set forth in claim 7 wherein said control means being responsive to a predetermined magnitude of said electrical signal in phase with said phase signal for actuating said actuable means and responsive to a second predetermined magnitude of said electrical signal to deactuate said actuable means.

23313" UNTTED STATES PATENT OFFICE CTER'TEIMCATE CF CQRRECTION Patent No. 3,755,192 Dated September- 4, 1973 Inventor) Henry C, Locklar; Den C. Tao; and Loyd E. Tarver, J1".

7 It is: certified that error appears in the above-identified patent and the: said Letters Patent are hereby corrected as shown below:

, In the Claims Column 12 a line 5 delete "8" and insert --1 Column 12 line 17 delete "9" and insert 4-. Column 12, line 23 delete "8" and insert -l- Column 12 line 37 delete "8" and insert Signed and sealed this 18th day of December-197 3.

(SEAL) Attest:

EDWARD Mn FLETCHER, JRo RENE D. TEGTME YER Attesting Officer Acting Commissioner of Patents

Claims

1. Apparatus for controlling the concentration of multicomponent developer material including toner for use in an electrostatic reproduction apparatus including: actuatable means for dispensing toner into the developer material; a light source; a developer unit fixedly mounted and having a viewing window for presenting developer material illuminated by said light source; at least one calibrated light reflector movable from a first position to a second position, said light reflector being illuminated by said light source when in said second position; photosensing means alternately responsive to light reflected from said illuminated developer material presented by said viewing window and to light reflected from said light reflector when said light reflector is in said second position for converting light into an electrical signal having an AC component when the intensity of light from the light reflector differs from the intensity of light from the developer material, said light reflector being interposed between said viewing window and said photosensing means when in said second position for preventing light from said developer material from striking said photosensing means; control means responsive to said electrical signal for actuating said actuatable means for dispensing toner.

2. The toner concentration control system set forth in claim 1 further comprising means for effecting motion of said developer material past the viewing window; actuatable halting means for halting the motion of said developer material at the viewing window; means for actuating said halting means and for providing a halting signal; said control means being further responsive to the halting signal for actuating said actuatable means.

4. The apparatus for controlling the concentration of multicomponent developer material set forth in claim 8 comprising a plurality of calibrated light reflectors having differing light reflectance characteristics; selection means for selecting one of said plurality of light reflectors; motion means for moving said selected one of said light reflectors to said second position; and wherein said photosensing means is responsive to light reflected from said selected light reflector when said selected light reflector is in said second position.

6. Apparatus for controlling the concentration of multicomponent developer material set forth in claim 8 further comprising: means for varying the light spectrum of said light source by a controlled amount; said viewing window having a nonuniform light transmission spectrum; said photosensing means being responsive to reflected light to provide an output signal, the magnitude of which is dependent on the spectrum of light incident thereon; and wherein said control means being responsive to a predetermined magnitude of said electrical signal for actuating said actuatable means.

7. Apparatus for controlling the concentration of multicomponent developer material set forth in claim 8 further comprising: phase signal generating means for generating a phase signal identifying the position of the light reflector; said control means being further responsive to said phase signal for actuating said actuatable means when the intensity of the light from the light reflector is less than that from the developer material.