US3682132A

US3682132A - Automatic developer controller

Info

Publication number: US3682132A
Application number: US803773A
Authority: US
Inventors: Roman C Kamola
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1969-03-03
Filing date: 1969-03-03
Publication date: 1972-08-08
Anticipated expiration: 1989-08-08

Abstract

Apparatus for monitoring the density of electroscopic toner powder images wherein an electrically conductive light transmissive probe is utilized as a xerographic photoreceptor simulator for cyclically developing and cleaning a toner powder image on the probe surface. The density of the electroscopic toner image on the probe surface is sensed at a predetermined time by passing a light beam from a lamp through the probe and developer material into a photosensor. The photosensor and light source are supported in a protective sealed housing to eliminate contamination of these components by the ambient conditions of the xerographic developing apparatus. The photosensor is coupled to a threshold or level detector to generate a control signal when the density of the image developed on the probe surface is less than a predetermined amount.

Description

Kamola [451 Aug. 8, 1972 AUTOMATIC DEVELOPER CONTROLLER [72] Inventor: Roman C. Kamola, North Rose,

, NY. [73] Assignee: Xerox Corporation, Rochester, NY. [22] Filed: March 3, 1969 [21 Appl. No.: 803,773

Primary Examiner-Peter Feldman Attorney-Paul M. Enlow, Donald F. Daley, James J. Ralabate, Norman E. Schrader, Ronald Zibelli and August E. Roehrig, Jr.

[57] ABSTRACT Apparatus for monitoring the density of eiectroscopic toner powder images wherein an electrically conductive light transmissive probe is utilized as a xerographic photoreceptor simulator for cyclically developing and cleaning a toner powder image on the probe surface. The density of the electroscopic toner image on the probe surface is sensed at a predetermined time by passing a light beam from a lamp through the probe and developer material into a photosensor. The photosensor and light source are supported in a protective sealed housing to eliminate contamination of these components by the ambient conditions of the xerographic developing apparatus. The photosensor is coupled to a threshold or level detector to generate a control signal when the density of the image developed on the probe surface is less than a predetermined amount.

9 Clains, 6 Drawing figures PATENTEDMIB elm 3,682,132

' SHEET 1 OF 5 INVENTOR. ROMAN OKAMOLA W ATTORNE v PmENTE-Dws wn 3,682,132

SHEEI 3 OF 5 PATENTED 3 I972 SHEET t 0F 5 FIG 6 PATENTED 81972 I 3.682.132

sum 5 or 5 I I I I I I I I I I //5v ac AUTOMATIC DEVELOPER CONTROLLER BACKGROUND OF THE INVENTION This invention relates to the monitoring and control of latent electrostatic image development and in particular to a novel xerographic image development sensor adapted to monitor the density of electroscopic toner powder images in a xerographic developing system for controlling the amount of toner powder in a xerographic developer mixture.

More specifically, the invention relates to a pho toreceptor simulator utilizing an electrically conductive light transmissive probe for monitoring the toner powder in a dynamic xerographic development system. The probe is utilized for cyclically developing and cleaning a toner powder image on the probe surface to sense the density of an electroscopic toner powder image formed thereon by means of a light beam passed through the image bearing probe into a photosensor. The light source and photosensor are supported in a housing to eliminate spurious deposition of toner powder on these elements.

In the process of xerography, a xerographic plate comprising a layer of photoconductive material on a conductive backing is given a uniform electrical charge over its surface and then exposed to the subject matter to be reproduced by various projection techniques. This exposure discharges the plate in accordance with the light intensity reaching it, thereby creating a latent electrostatic image on or in the plate.

Development of the image is effected by developers which comprise, in general, a mixture of suitable pigmented or dyed resin-based powder, hereinafter referred to as toner, and a granular carrier material which functions to generate triboelectric charges on, and to carry the toner. More specifically, the function of the carrier material is to provide mechanical control of the toner,'or to carry the toner to an image surface and simultaneously provide almost complete homogeneity of charge polarity. In the development of the image, the toner powder is brought into surface contact with the photoconductive coating and is held thereon electrostatically in a pattern corresponding to the latent electrostatic image. Thereafter, the developed xerographic image may be transferred to a support material to which it may be fixed by any suitable means such as heat fusing.

In the mixture of toner particles and carrier material, the toner particles, which are many times smaller than the carrier material, adhere to and coat the surface of carrier material due to the triboelectric attrac' therebetween. During development, as the tonercoated carrier material rolls or tumbles over the xerographic plate carrying a latent electrostatic image of a polarity opposite to the charge on'the toner, toner particles are pulled away from the carrier by the latent electrostatic image and deposited on the plate to form a developed toner-powder image. As toner-powder images are formed, additional toner powder must be supplied to the developer mixture to replenish the toner deposited on the xerographic plate. The toner material may be of the type disclosed in Carlson US. Pat. No. 2,940,934, wherein the toner particles comprise a finely divided pigmented resin having a particle size less than 20 microns and preferably an average particle size between about 5 and microns and comprising a finely divided uniform mixture of pigment in a non-tacky, low-melting resin. Desirably, the pigment will be a black pigment such as carbon black or other minutely divided carbonaceous pigment.

As the toner powder in the developer mixture is depleted during the development of the latent image on the xerographic plate, more toner powder must be added to maintain a desirable level of copy density. In the event that too much toner powder is added to the developer mixture, heavy deposits of toner in the image areas, in combination with an undesirable deposit of toner in the non-image or background areas, results in producing prints of poor contrast with blotchy images or poor resolution.

In addition, overtoning by the operator adds to the severity of toner powder accumulation on critical machine components such as the corotrons, illumination system, optical system, fuser and transport system, as well as necessitating more frequent replacement of filter bags and cleaning brushes. Thus, with an automatic development control system incorporated in an automatic xerographic reproducing machine to sense the density of toner powder images and thereby regulate the amount of the toner powder in the developer mixture, fewer service calls are necessary to'keep the quality of the xerographic reproductions ata high level.

In automatic reproducing machines such as shown in FIG. 1 a moving xerographic plate, which may be in the form of a cylinder, is exposed to a light source to create a latent electrostatic image to be developed by appropriate means such as a continuous flow of developer material over the plate surface. It is necessary, in order to produce prints of consistently good copy density, to vary thetoner dispensing rate in accordance with the rate of consumption which is a function of the type and frequency of copy being reproduced. The dispensing of toner in prior art devices has been dependent upon the machine operator visually inspecting the finished copy and manually regulating the toner concentration by appropriate changes in a machine setting. It is readily apparent that dispensing by this means results in image densities largely dependent on the alertness and ability of the operator to visually evaluate the density of the copy image. Not only must the operator detect the need for a setting change, but the operator must be able to accurately effect the proper ,degree of change through the dispenser setting. In the event that the operator oversets the dispensing rate and excess toner is added to the developer mixture, the only method whereby the toner concentration may again become acceptable is by the reproduction of a sufficient number of additional copies. Considerable waste of material and time usually occurs when the proper setting of toner concentration has to be determined by an operator, since setting changes are made only after copy deterioration has become apparent.

Various attempts have been made to develop a sensor which would control the development of a toner powder image on the photoreceptive surface of the xerographic plate or drum. It has been found that control systems which expose and develop a toner powder test image on a portion of the xerographic drum, which is sensed by reflecting a light beam from the test image into a photosensor, cause fatigue of the photoreceptive material and eventually give erroneous determinations.

Another attempt to solve this problem was the use of a sensor to simulate the photoreceptive surface of the xerographic drum. Such an apparatus is disclosed in U.S. Pat. No. 3,094,049 issued June 18, 1963, to Christopher Snelling. The apparatus disclosed in the aforementioned patent utilizes a xerographic drum simulator having electrically isolated portions with a series of graduated reference indicia calibrated to correspond with toner deposition patterns of known concentration when the simulator (electrode) is biased with a predetermined voltage. A light beam is passed through the calibrated simulator into a photosensor to control the amount of toner powder in the developer mixture in response to the toner concentration determined by the simulator. This apparatus of the aforementioned patent senses the concentration of the toner powder in the developer mixture by correlating the amount of light passing to the photosensor through the portions of the simulator which do not have a toner powder image formed thereon. As more or less toner powder is attracted to the simulator, the light transmitting portion of the electrode changes, thereby, varying the output of the photosensor.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to improve the development of latent electrostatic charge patterns.

Another object of this invention is to improve xerographic developing by automatically adjusting the amount of toner powder in the developer mixture in response to the density of an electroscopic toner powder image.

A further object of this invention is to improve xerographic developing by cyclically developing and cleaning an electroscopic toner powder image on a xerographic drum simulator and sensing the density of the image developed thereon.

Still another object of this invention is to prevent erroneous determination of image density by protecting the sensor components from spurious deposition of toner powder due to ambient conditions of the developer apparatus.

These and other objects are attained in accordance with the present invention wherein there is provided a xerographic drum simulator including a transparent electrically conductive probe having a substantially uniform electrical charge on its surface and positioned in cooperative relationship with the developer mixture of a xerographic reproducing machine. The probe is electrically charged to cyclically develop and clean an electroscopic toner powder image by means of the quantity of developer material moving relative thereto. The sensor apparatus disclosed herein is adapted to generate a control signal in response to image density and is effectively sealed in a housing structure to prevent spurious toner powder accumulation on the sensor components.

DESCRIPTION OF THE DRAWINGS Further objects of this invention together with additional features contributing thereto and advantages accruing therefrom, will be apparent from the following description of one embodiment of the invention when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a front elevational view of an automatic xerographic reproducing machine utilizing the invention of this application;

FIG. 2 is an enlarged front elevation of the developer apparatus of the automatic xerographic reproducing machine with parts broken away to better illustrate the sensor apparatus of this invention;

FIG. 3 is a front perspective view of the sensor to better illustrate the components thereof;

FIG. 4 is a partial sectional view of the sensor taken along lines 4-4 of FIG. 3;

FIG. 5 is a partial sectional view of the sensor taken along lines'S-S of FIG. 3; and

FIG. 6 is a mechanical schematic of the sensor apparatus.

FIG. 7 is an electrical schematic of the sensor apparatus.

Referring now to the drawings, there is shown in FIG. 1 an embodiment of the subject invention in a suitable environment such as an automatic xerographic reproducing machine, although it should be noted that the invention is not intended to be limited thereto.

The automatic xerographic reproducing machine includes a xerographic plate 14 including a photoconductive layer or light receiving surface on a conductive backing, journaled in a frame to rotate in the direction indicated by the arrow to cause the plate surface to sequentially pass a series of xerographic processing stations.

For the purpose of the present disclosure, the several xerographic processing stations in the path of movement of the plate surface may be described functionally, as follows:

A charging station 15 at which a uniform electrostatic charge is deposited on or in the photoconductive plate;

an exposure station 13 at which a light or radiation pattern of copy to be reproduced is projected onto the plate surface to dissipate the charge in the exposed areas thereof to thereby form a latent electrostatic image of the copy to be reproduced;

a developing station A at which the xerographic developing material, including toner particles having an electrostatic charge opposite to that of the latent electrostatic image, is cascaded over the plate surface whereby the toner particles adhere to the latent electrostatic image to form a toner powder image in configuration of the copy being reproduced;

a transfer station B at which the toner powder image is electrostatically transferred from the plate surface to a transfer material or a support surface; and

a drum cleaning and discharge station C at which the plate surface is brushed to remove residual toner particles remaining thereon after image transfer, and exposed to a relatively bright light source to effect sub- 5. stantially complete discharge of any residual electrostatic charge remaining thereon or therein.

DESCRIPTION OF THE PREFERRED EMBODIMENT It is felt that the preceding description of the xerographic process is sufficient for a better understanding of this invention. Referring now to the subject matter of the invention as best shown in FIGS. 2-5, the developing station A which effects development of the latent electrostatic image of the cylindrical xerographic plate, comprises a developer apparatus 16 which coacts with the cylindrical plate 14 to develop the latent electrostatic'image on or in the plate surface by means of the xerographic toner powder. Mounted within the developer housing is a driven bucket-type conveyor 18 used to convey developer material from the reservoir portion of the developer housing to the upper portion of the developer housing from where it is cascaded over a hopper chute onto the xerographic drum. As shown, the conveyor includes a series of parallel spaced buckets 19 secured to a suitable pair of conveyor belts passing around a conveyor drive pulley and a conveyor idler pulley secured on appropriate drive and idler shafts to rotate therewith. As the developer material cascades over the drum, toner particles of the developer material adhere electrostatically to the previously formed latent electrostatic image areas on the drum 14, the remaining developer material falling off the peripheral surface of the drum to be deflected by a baffle plate into the bottom of the developer housing. Toner particles consumed during the developing operation to form the visible powder images are replenished by a toner dispenser 17 mounted within the developer housing. For further details concerning the specific details of construction for a suitable developer apparatus reference is made to W. G. Lewis et a]. U.S. Pat. No. 3,067,720.

As the developing mixture is cascaded over the xerographic drum, toner particles are pulled away from the carrier and deposited on the drum to form toner powder images, while the partially denuded carrier particles pass off the drum into the reservoir. As toner powder images are formed, additional toner particles must be supplied to the developing mixture in proportion to the amount of toner deposited on the drum. To supply additional toner particles to the developing mixture, the toner dispenser 17 is used to accurately meter toner to the developer mixture. Although any one of a number of well-known powder or granulated material dispensers may be used, the toner dispenser shown (FIGS. 1 and 2) is of the type disclosed in R. A. Hunt U.S. Pat. No. 3,013,703.

The toner dispenser 17 dispenses a uniform quantity of toner for a given stroke of the dispensing plate and, therefore, it is apparent that the quantity of toner delivered by the toner dispenser may be altered by varying the number of strokes per unit of time. Reciprocation of the dispensing plate is effected by means of an eccentric secured to the end of a shaft coacting with a bifurcated lever arm secured to the dispensing plate. It is felt that the preceding description of the toner dispenser 17 is sufficient for an un derstanding of its function in relation to the subject matter of this invention. For further details relative to the specific construction of this device, reference is made to the aforementioned Hunt Patent.

In order to control the dispensing of toner from the toner dispenser 17, there is shown in FIGS. 2-7 the details of an electroscopic toner powder image density sensor 40 which ultimately efie'ctuates actuation of the dispenser by energization of the dispensing motor M in accordance with the density of an image developed on the surface of a probe 44.

The xerographic image density sensor 40, to be hereinafter described in detail, is secured within the developer housing 16 by a suitable bracket 26 appropriately fixed to a side wall of the developer housing which electrically insulates the sensor from the surrounding structure. A collecting hopper 41 having side portions adapted to contain a quantity of xerographic developer material is secured to a support member 27 of the sensor for maintaining the collecting hopper beneath the moving buckets 19 of the conveyor system to receive the overflow of developer material falling from each bucket as it progresses to cascade the developer material onto the xerographic plate. Although the overflow of developer material is usually of a sufficient quantity, it is sometimes desirable to provide small holes 29 in the bottom of the buckets 19 to increase the amount of developer material passed to the sensor. The collecting hopper 41, as shown in FIG. 2, is positioned at an angle of approximately 20 relative to the vertical in such a way as to catch the falling developer material and to guide the material into the sensor apparatus 40. The front wall 25 of the hopper 41 is slidably secured to the side portions of the hopper to permit adjustment of the throat 24 formed between the front wall and the support member 27 to set the flow rate of the developer material through the sensor.

- The sensor apparatus 40 (FIGS. 2-5) includes a photoelectric sensor P-l positioned in the path of light emanating from lamp L-l to vary the resistance of the photosensor P-l in proportion to the light intensity impinging thereon. The photosensor P-l is electrically connected in a conventional circuit whereby the change in resistance of the photosensor is interpreted as a change in voltage. The light source L1 is supported within the upper portion 40 a of sensor housing 40 by a set screw in a position to direct a light beam into the photosensor P-l. Interposed in this light path emanating from lamp L-l to the photosensor P-l, are a pair of electrically conductive

transparent electrodes

42 and 43. A suitable type of electrode is a tin oxide coated glass plate manufactured by Pittsburgh Plate Glass Inc. under the trade name of NESA Glass. As shown, the lamp L-l and photosensor P-l are positioned such that the light beam is passed directly from the light source through the probe 44 into the photosensor. However, it is obvious that a mirror surface would be utilized, if desired, to form a folded optical path such that the light beam would be reflected through the image on the probe surface and into the photosensor. The transparent light transmitting surface of the probe 44 is intended to include either the transparent property of the probe or its reflective property as heretofore discussed.

Electrode 43 has a portion through which the light beam from lamp L-l passes electrically charged to a polarity the same as that of the charge on the toner powder to repel the toner powder from the electrode surface for keeping the transparent surface clear of ambient toner powder. Alternatively, the entire surface of electrode 43 may be charged to repel the toner powder. This electrode is secured in the sensor housing 40 a by means of any suitable commercially available sealant, such as G.E. RTV adhesive sealant, to preclude the normal toner powder dust atmosphere within the developer housing 16 from depositing on the lamp L-l. The sealing of the lamp L-l in the upper housing 40 a prevents erroneous measurements of the image density as a result of spurious deposition of toner powder on the light source.

As best shown in FIGS. 3 and 5, the upper sensor housing 40 a is slidably supported on bar 21 which is fixedly secured to the lower sensor housing 40 b at its opposite end to permit adjustment of the spacing between the

electrodes

42 and 43 to allow the quantity of developer material passing through the throat 24 and across probe 44 from being constricted by the electrode surfaces.

The electrode 42 is supported in the lower housing portion 40 b of sensor 40 and sealed in this position by a suitable sealant, such as that previously described, to preclude the normal toner powder dust atmosphere within the developer housing 16 from depositing on the photosensor P-l. The sealing of the photosensor in the housing prevents interference with the measurement of the density of the toner powder image as a result of spurious deposition of toner powder on the photosensor. Electrode 42 is formed with a light transmitting surface or probe 44 carrying a toner attracting charge of one polarity which is uniformly distributed over the probe surface. The light .transmitting probe 44 is electrically connected by means of suitable contacts 20 which electrically couple the probe to first and second switch contacts 47 and 48, respectively. A portion 45 of the electrode 42 adjacent to the probe 44 is connected by means of contacts 20 which electrically couple portion 45 to

terminals

49 and 50. The contacts are part of a double pole single throw switch having a first switch arm 51 movable between the

contacts

48 and 49 and a second switch arm 52 movable between the contacts 47 and 50.

To provide a more accurate determination of the image density developed on the surface of probe 44, and to minimize the response time required to add the desired amount of toner powder to the developer mixture, the electrical charge on the probe surface is cyclically varied to attract toner powder to and repel toner powder from the probe surface. When the polarity of the probe 44 is reversed to repel the toner powder, the continuous cascade of developer material over the probe surface erases the previously formed image. In operation, each of the

switch arms

51 and 52 are connected to a pole of a source 53 of direct current for energizing portion 45 of the electrode 42, probe 44, the light source L-l and to continuously maintain the toner repelling charge on electrode 43. These connections are shown in FIG. 6 with the positive pole of source 53 being connected to the arm 52 thereby providing the probe 44 with a toner attracting charge which is uniformly distributed over its entire surface. The negative pole is connected to the switch arm 51 thereby providing the electrically isolated portion 45 with a negative potential. This electrical configuration is merely illustrative and has been chosen for descriptive purposes because of the particular charge chosen for the toner particles, which for purposes of illustration, is negative. The electrical coupling of the

switch arms

51 and 52 is such that toner particles will be attracted to the probe 44 and repelled from the upper electrode 43 and the portion 45 of the electrode 42. The electrical charge on the probe 44 and the surrounding portion 45 of the electrode 42 is cyclically alternated to attract and repel toner powder from the probe surface. During the portion of the cycle in which the probe 44 is charged positively, toner powder is attracted from the developer mixture to create a toner powder image over the probe surface and the density of the image so formed is sensed by means of the change of resistance of the photocell due to the variation in the amount of light impinging thereon. When the polarity of the electrical charge on the probe 44 is reversed, the toner powder will be repelled from the probe surface and the probe thereby cleaned by means of the continuous cascade of developer material across the electrode surface. The photosensor is deactuated during this portion of the cycle.

To provide this cyclic operation, the

switch arms

51 and 52 are mechanically connected together and to the armature of a solenoid 54. A switchable timing device 55 is connected to the solenoid for periodically energizing the solenoid to effect movement of its plunger. With the

switch arms

51 and 52 positioned in contact with terminals 49 and 47, respectively, toner particles are attracted from the developer mixture to the probe 44. After a predetermined period of time has elapsed, preferably 10 seconds, the timer will energize the solenoid 54 for switching the

arms

51 and 52 to the

terminals

48 and 50, respectively, and to open a switch, not shown, to inactivate the photosensor P-l to preclude sensing during the cleaning cycle. This reversing of the charge on the probe 44 repels the accumulated toner powder and the developer material passing over the probe surface during this cycle cleans the probe to thereby condition the probe surface for another attract cycle. As previously stated, the upper electrode 43 is continuously charged with a negative polarity to repel toner powder from the electrode surface to insure an accurate determination of the density of the image formed on the probe 44.

Within the sensor 40, photosensor P-l is positioned directly below probe 44 and supported in the light path passing directly from lamp L-l through the probe 44. Due to the conventional electrical connection, the output from the photosensor, therefore, is controlled by the density of the toner powder image developed on the surface of probe 44. The output from the photosensor is coupled to a suitable threshold detector, such as a conventional Schmidt trigger 66, connected to an amplifier 67 which is utilized to amplify the signal produced by the threshold detector and to energize a solenoid 68 for actuating a normally open switch S-l connected in series with a normally closed switch 8-2. When the output from the photosensor P-l, coupled to the threshold detector 66, is of a predetermined magnitude, the detector will provide an electrical signal which will result in additional toner powder being added to the developer mixture.

and are connected to a suitable source of electrical power. Upon energization of the solenoid 68, the switch S-l closesto cause energization of the motor M. The motor shaft, or a mechanical device 32, may be provided with a cam arrangement (not shown) adapted to actuate the normally closed limit switch -2 to an open position during a portion of each revolution of the motor shaft. With solenoid 68 being continuously energized during an under-toned condition of the developer mixture, the motor will intermittently actuate the mechanical device 32.

During normal operation of the automatic toner dispensing apparatus, the sensor light source L-l is continuously energized for passing a light beam through the probe 44. This light is transmitted through the image on the probe 44 and sensed by the photocell P-l. The firing level of the threshold detector 66 is adjusted so that there is an output from the detector as determined by the desired density of the image that is formed on the probe 44. As the toner supply in the developer housing 16 depletes during normal xerographic processing, the density of the toner image that is formed on the probe 44 will lessen. With an image density lower than the predetermined level the Schmidt trigger, which in effect is a level or threshold detector, will produce an electrical pulse causing a momentary energization of the solenoid and closing the contact S- 1. For each electrical pulse produced in this manner, the motor shaft for motor M will rotate one complete revolution to actuate the dispensing of toner powder into the developer mixture.

As the density of the toner image on the probe 44 increases, the output from the level detector 66 will become restored thereby terminating further actuation of the toner dispenser. The sensitivity of the sensing circuit can be varied by adjusting the firing level of the threshold detector 66 and the strength of the D. C. source 65. These components will determine the output to the solenoid and may be varied so that a high unbalance must be present before a level can be detected by the Schmidt trigger thereby obtaining a relatively wide density range for xerographic reproductions. If high quality contrast is needed in the reproductions, then a very'sensitive level may be preset whereby the slightest unbalance will demand toner dispensing and replenishment.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teaching of the invention without departing from its essential teachings.

What is claimed is:

1. An electroscopic toner powder image sensor to monitor the amount of toner powder in an electroscopic developer mixture including a light transmissive probe having a toner attracting charge which is uniformly distributed over the surface, said charge being capable of attracting a uniformly deposited toner powder image on said surface from a mixture of electroscopic developer material in a quantity indicative of the amount of toner powder in the developer mixture,

means for moving the electroscopic developer mixture and probe relative to one another to attract and retain the toner powder on said probe surface,

sensing means for detecting the amount of toner retained on said surface to monitor the amount of toner powder in the developer mixture for producing a control signal, and

a housing enclosing said sensing means, said housing including a light transmissive conductive member electrically biased to prevent electroscopic toner powder from being deposited on a surface thereof through which light is transmitted.

2. An electroscopic toner powder image sensor including means defining a flow path for passing electroscopic developer material comprising toner particles and carrier material therethrough,

a light transmissive probe positioned adjacent said flow path and in contact with passing developer material,

means operatively connected to said probe for forming toner particle image on the probe surface,

sensing means responsive to the toner particle image formed on the probe surface for producing an electrical control signal, and

housing means enclosing said sensing means, said housing means including a light transmissive conductive member biased to prevent electroscopic developer material from being deposited on a surface thereof through which light is transmitted.

3. The apparatus of claim 2 wherein said sensing means is responsive to the density of the toner particle image formed on the probe surface.

4. The apparatus of claim 3 wherein said control signal is coupled to means for adding toner particles into the developer material.

5. The apparatus of claim 3 wherein said means operatively connected to said probe for forming a toner particle image on the probe surface is cyclically operable to form and erase a toner particle image from the probe surface.

6. The apparatus of claim 3 wherein an electrode is positioned to intercept the passing developer material to effect a cascading of the developer material over the electrode surface.

7. The apparatus of claim 3 including means to retain an amount of developer material for passing over said light transmissive probe at a predetermined flow rate.

8. The apparatus of claim 3 wherein said sensing means includes illuminating means positioned to pass a light beam through said probe, and passing developer material, and

a photosensor positioned in the light beam of said illuminating means with the probe and passing developer material therebetween.

9. An electroscopic toner powder image sensor including means defining a flow path for passing electroscopic developer material comprising toner particles and carrier material therethrough,

a first member positioned adjacent said flow path and in contact with passing developer material,

housing means enclosing said sensing means including a light transmissive conductive member electrically biased to prevent electroscopic developer material from being deposited on a surface thereof through which light is transmitted.

Claims

1. An electroscopic toner powder image sensor to monitor the amount of toner powder in an electroscopic developer mixture including a light transmissive probe having a toner attracting charge which is uniformly distributed over the surface, said charge being capable of attracting a uniformly deposited toner powder image on said surface from a mixture of electroscopic developer material in a quantity indicative of the amount of toner powder in the developer mixture, means for moving the electroscopic developer mixture and probe relative to one another to attract and retain the toner powder on said probe surface, sensing means for detecting the amount of toner retained on said surface to monitor the amount of toner powder in the developer mixture for producing a control signal, and a housing enclosing said sensing means, said housing including a light transmissive conductive member electrically biased to prevent electroscopic toner powdEr from being deposited on a surface thereof through which light is transmitted.

2. An electroscopic toner powder image sensor including means defining a flow path for passing electroscopic developer material comprising toner particles and carrier material therethrough, a light transmissive probe positioned adjacent said flow path and in contact with passing developer material, means operatively connected to said probe for forming toner particle image on the probe surface, sensing means responsive to the toner particle image formed on the probe surface for producing an electrical control signal, and housing means enclosing said sensing means, said housing means including a light transmissive conductive member biased to prevent electroscopic developer material from being deposited on a surface thereof through which light is transmitted.

8. The apparatus of claim 3 wherein said sensing means includes illuminating means positioned to pass a light beam through said probe, and passing developer material, and a photosensor positioned in the light beam of said illuminating means with the probe and passing developer material therebetween.

9. An electroscopic toner powder image sensor including means defining a flow path for passing electroscopic developer material comprising toner particles and carrier material therethrough, a first member positioned adjacent said flow path and in contact with passing developer material, means operatively connected to said member for forming a toner particle image on a surface thereof, sensing means responsive to the toner particle image formed on the surface for producing an electrical control signal, and housing means enclosing said sensing means including a light transmissive conductive member electrically biased to prevent electroscopic developer material from being deposited on a surface thereof through which light is transmitted.