US3487978A - Automatic toner concentrate detector - Google Patents

Description

Jam 6 1970 s. A. GAwRoN AUTOMATIC TONER CONCENTRATE DETECTOR Original Filed June 14, 1967 2 Sheets-Sheet 1 Jan. 6, 1970 s. A. GAwRoN 3,487,978

AUTOMATIC TONER CONCENTRATE DETECTOR Original Filed June 14, 1967 2 Sheets-Sheet 2 United States Patent O Int. Cl. G01f 11/00 U.S. Cl. 222-1 1 Claim ABSTRACT F THE DISCLOSURE A rotating reflective disc located directly in a developer mix containing toner is electrically biased so that it will attract toner from the mix. The amount of toner attracted to the surface of the disc is a function of the concentration of toner in the mix. A light beam is directed to reflect off the surface onto a photoelectric unit, with the intensity of the light striking the unit being controlled by the amount of toner on the surface. The photoelectric unit and source of light are mounted in a protective housing in order to render them free of toner dust. The unit is calibrated to signal a dispensing apparatus to operate when the intensity of the reflected light indicates a less than optimum toner concentration.

This application is a division of copending application, Ser. No. 646,056, filed June 14, 1967, now Patent No. 3,399,652.

BACKGROUND OF THE INVENTION This invention relates to an apparatus which monitors and controls the feeding of toller to a mass of developer mix in accordance with the concentration of toner in said mix. More particularly, this invention relates to `an apparatus for continuously measuring the concentration of toner in the developer mix by optically sensing the amount of toner that is triboelectrically attracted to a sampling medium. In accordance with the well known electrostatic printing process, a surface bearing a latent electrostatic image is developed by selectively applying a developer mix comprising toner and a carrier medium to the image. With repeated use of the mix toner is gradually consumed until there is no longer a suicient concent1-ation of toner in the mix to develop high quality, dense images.

The prior art systems of monitoring toner concentration follow two general schemes of measurement, electrical and optical. Electrical systems depend on measuring the changes in resistance of the mix as the high resistivity toner component varies in relation to the conductive carrier component, and the optical systems depend on measuring the density of a calibrated toner test pattern. In the latter system the test pattern is established in accordance wih the concentration of toner in the mix provinding a graduated visible scale correlated to the toner concentration as determined yby an optical sensing device.

The prior art systems are somewhat deficient in that variations in the toner formulation in the case of the electrical systems require frequent calibration checks to account for any changes in resistance of the thermoplastic resin. Optical systems are confronted with the interference due to the airborne particles falling on the optical sensing components which result in false readings and in general require frequent cleaning maintenance of all the components in order to be sure that no erroneous measurements occur.

3,487,978 Patented Jan. 6, 1970 ice lt is the general object of this invention to provide an improved automatic toner feed control device that is accurate, reliable and free of frequent cleaning maintenance.

It is a further object of this invention to provide an automatic toner feed control that monitors the concentration directly at the point of addition of the toner so that there is little time-lag between the generation of the monitoring signal and the activation of the dispensing device in either starting or stopping.

It is still another object of this invention to provide an automatic toner feed control in which the toner sampling device is self-cleaning.

It is still another object of this invention to provide an automatic toner feed control in which optical components used to measure the amount of toner deposition are protected against the accumulation of the toner from out the optical path.

It is a specific object of this invention to provide an automatic toner feed control `which is capable of operating under changing temperature conditions. A related object is to provide a temperature responsive control operatively associated with the photoelectric instru ments which compensate for fluctuation of the temperature.

It is still another specific object of this invention to provide a toner feed control device which is particularly well adapted to be used in conjunction with conventional magnetic brush developing assemblies.

The present invention comprises a conductive probe having a reflective or transparent light transmitting specular surface, a reflective surface being preferred, means for bringing the probe and mix into Contact to collect a sample of toner on the specular surface, means for photoelectically measuring the amount of toner on the surface, and dispensing means for adding toner to the mix in accordance with the amount of toner attracted to and retained on the probe. The term light transmitting as used herein refers either to the light reflective property of the probe or its transparent property. The probe is connected to a DC potential imparting to the specular surface a toner-attracting electrostatic charge which is uniformly distributed over the surface to establish an electrical field of uniform intensity. The range of voltage to be applied can vary widely depending on the nature of the mix formulation and, in particular, the type of resin toner employed. In a typical magnetic brush arrangement where the resistivity of the toner is in the range of from 1010-1012 ohm centimeters and the carrier is iron, the applied voltage can range from 25-200 volts, preferably in the range of from 40-60 volts. It has been found that, if the biasing potential applied to the probe is Within the range of from about 40-60 volts DC, the probe is selfcleaning. It is realized that this device can be biased at higher levels, but as the biasing potential increases, the toner on the disc becomes more difficult to remove and reversing the polarity of the biasing potential or other measures must be taken to clean the probe. The electrical eld attracts toner from the mix and deposits the micron-size particles over the probe surface in a uniform manner to provide a horogeneous toner Vformation thereon. It will be appreciated that the action of the probe is to simulate the'developing step of the apparatus so that there is close correlation between the monitoring device and the actual imaging process that takes place in a copying machine.

The preferred construction of the probe is that of a rotatable member, such as, for example, a disc. In accordance with the preferred embodiment of this invention, a rotating disc formed into a plurality of radially extending iin portions is partially immersed in a mass of developer mix. It is preferred that the finned disc be located in the mix directly where the toneris dispensed. As the disc rotates, toner is attracted from the mass onto the surface of the fins and withdrawn to a viewing zone where the change in reflectivity on each of the fins, due to the attraction of the toner, is measured. Since the disc is conductive, preferably formed of metal, the charge is uniformly distributed over the n surface. It has been found that, for optimum results, the n surface should provide a greater area than the viewing area of the photocell. However, it is understood that the continuous rotation of the disc provides continuous sampling of the mix which is monitored by the photocell and provides a system which, in effect, integrates a large number of lsamplings so as to provide a fairly accurate control.

This device has been found to be particularly well adapted for use with conventional magnetic brush developing assemblies, although it is contemplated that this device is equally Well adapted for use with other types of developing apparatus, such as cascade developers.

The optical measuring means include a light source, a photodiode which functions as a light-responsive switch in this control, and a temperature control device which is operatively associated with the photodiode to compensate for changing temperature conditions which affect the response characteristics of the photodiode.

To avoid deposition of the airborne toner on the light source, it is enclosed in a protective housing having a light access opening. The housing is formed of materials which 'are triboelectrically similar to the triboelectric characteristic of the toner. Housings formed of plastics, such as acrylic resins or polyvinyl acetate resins, tend to be tribolectrically positive and, hence, they will repel the positively charged toner. However, it should be understood that other materials of construction may be used which are conductive in which case an external field may be applied to the housing to create the equivalent effect of using triboelectrically oriented plastic materials.

To further reduce the likelihood of toner deposition on the sensing device, the housing construction provides for a pair of light conducting channels which converge at a common opening in the front of the housing juxtaposed the face of the fin portions. The light source and the photodiode are each received in one of the channels at points remote from the common opening. The common opening at which the channels converge serves as an exit way for the light rays which are directed onto the ns from the light source, and at the same time act as an entry way to -the other channel in which is mounted the photodiode for ,sensing the lightrays reflected fromthe n surface. Accordingly, the light source is mounted at the head of one of the channels and the photocell is `locatedat the end'of the second channel, Thisitype of an arrangement serves to protect the emission source and the' sensing element from the interfering effects of toner dust which may tend to accumulate thereon.

BRIEF DESCRIPTIONv E vDRAWING Other objects and features of this invention will become apparent from the; following description takenv in' connection with the accompanying drawingsY in which:

FIGURE 1 is a perspective view of a portion of a con- `ventonal magnetic brush developing'apparatus showing DESCRIPTION 0E PREFERRED EMBODIMENT According to FIGURES 1 and 2, there is shown a magnetic brush assembly, indicated generally as 10, and the toner feed control of this invention, indicated generally 'The assembly 10 is a conventional magnetic brush assembly such as disclosed in detail in U.S. Patent No. 3,- 003,462, which includes `a rotatably mounted cylinder 14, (FIGURE 2), having magnetic pole pieces 1 6 disposed .within and"v along the longitudinal axis rof the cylinder,

"and a pair of augers 18 and 20 which, working in con- "ce'rt, serve'to circulate the vmix 22 laterally through the trough 24.v As se'en from FIGURE 2,'the auger 18 isY ro- `tateclin ac'ounterclockwise direction 4moving a portion 'of' the mix'22 from'the trough 24 to the assembly 10. Simultaneously/g the auger '20 'is being rotated in a clocks'e direction to return the mixl from th'e'assembly 10 vto afthe "'trough 2(4'for `replenishment with fresh toner. The .'vc'ylin'der 14 is rotated in acou'nterclockwise direction, "and aslit rotates,v it' collects on its outer surface developer mix Being fed by the auger 18. Under the influence of lt'liel'magnetic *field produced bythe magnetic pole piece 16, the magentic mix 22 is formed in the configuration of a magnetic brush 26 on the periphery/'of'r the cylinder '14.By vbringing a sheet bearing a latent electrostatic image intotangentialcontact with/the brush 26, the image lis Iselectively developed. Y L.

l As the cylinder 14 continues to rotate, Iand the brush "'26-whichiscarried thereon is moved'beyond the influence fof themagnet'icfux lield established by the pole pieces 4 16. The mix -is'the'nvreleased from the surface-'of the 'cylinder 14 and-falls back into the `main body' of the mix being circulated by the auger 20. The toner concentration vmonitoring assembly," identified generally as 28, is disposed in` the`tr`ough424 which serves as-the terminal point Afor the usedlmix before it is recirculated by the auger `18.

It is at this station that fresh toner 30 is dispensed into `the trough 2'4'fror'n 'a dispensinghopper- 32. A detailed lchrome-plating or similar' surface treatment in order to provide a specularly reflective surface. The disc member 34 "is mounted on a shaft 40 coupled to a drive motor 42,-It will be observed that the disc member 34 is situated between the 'angers 18 and 20 rotating in a plane normal to the lplane passing through the axes of rotation of the respective augers. The disc 34 is partially immersed in the developer mix 22 Where it is exposed to a representative sampling ofthe mixture to be analyzed Vfor the con- "Ic'entration of toner therein. vImmediately adjacent the specularly reflective'face -portion 38 of the disc member .'34 is a light'reflect'ance sensing unit 44 encased in ardust- :protective housing 46 attached by means of a bracket 48 to the trough 24. The housing 46 construction provides for' a pair of converging channels 50 and 52 (FIGURE 3) which converge to a common opening 54 atthe front portion of the housing juxtaposed thedisc 34 immediaterthe face portions 38. Itwwill hefapparent that vthe'rotation of the discmember 34 causesI a good deal of toner powder in the mix to become airborne, particularly inthe; immediate vicinity 'of the sensing unit 44.

At the head of channel 52 is a light source '56 operating inconjunction 'with ailens element 58y directing the light through the opening 54 which serves as an exit Way for the light rays to be impinged on the face portions 38 of the-tins 36.=The..light Irays impinge upon the face portion 38 at an angle of incidence and are reflectedtherefrom into the opening -54 `vat any'angle of reection from the surface which is equalto the angle of incidencefromthe light source 56. The light proceeds into `the channel 52 .at'theend of Which'is alight-responsive photodiode 60 and afocusing lens 62. This photodiode 60 may be a conventional photocell or a silicon-duodiode. The vangular relationship of the channels is such as to conform to the angle of incidence and the angle of reflection of the light rays impinging and being reflected from the face surface 38 of the fins 36. It will be appreciated that the location of the light source and the photocell inside their respective channels at a location remote from the opening 54 protects these elements from becoming coated with the toner dust. In this manner the all-important transmission and reception of the light rays vital to the operation of the sensing unit is not impaired.

It has 'been found desirable for the material of construction of the housing 46 to have triboelectric characteristics the same or similar to the toner. The similarity of triboelectric characteristics prevents the attraction of toner to the housing. A wide variety of plastic materials may be used, such as acrylic ester polymers and poly-Vinyl acetates, which have been found to be particularly suitable for the application. lt is to be understood that, while the preferred materials of construction are plastic, other materials of construction may be used, such as metals, which may be electrically blased by an external source in order to create the necessary charge relationship to the toner particles and thereby obtain the equivalent result as using a triboelectrically oriented plastic material.

In order to achieve consistant and invariant measurement, the light-responsive photodiode 60 includes a temperature-sensing element 66 such as a thermistor located adjacent the photodiode 60. An increase in temperature of the photodiode 60 environment will affect its response because of its inherent characteristic to undergo a decrease in resistance. Accordingly, an increase in temperature Would result in an erroneous output lowering the resistance beyond what is attributable to reflected energy which is the significant energy toY be measured. The thermistor control 66 serves to shunt off a proportional amount of the output current due to a change in the operating temperature in the environment of the diode 60 so that the control portion of the mechanism receives a signal primarily based on the quantity of radiation being reflected from the specularly reflective face portions 38.

To further reduce the possibility of occluding the photodiode 60 or the light source 56 with toner particles, the housing 46 is mounted at an oblique angle with the opening 54 at a lower elevation than the photodiode or the light source. To accommodate this angular position of the housing 46, the face portions 38 of the fins 36 may be formed at an angle so that the light rays from the light source are directed along a line normal to the face portion. This technique of positioning the housing 46 in relation to the disc 34 keeps out the larger particles which are heavy enough to be prevented by the gravitational forces from moving up into the respective channels 50 and 52.

Referring to FIGURE 4, there is shown the control circuit 68 connected by feed lines to a 11S-volt AC power supply controlled by a double-pull, single-throw switch 72. The control circuit 68 includes the drive motor 42 which drives the disc 34., a vibrating coil 74 for vibrating,

the hopper dispenser 32 and the toner sampling circuit and monitoring circuit, identified generally as 76 and 78, respectively. The constant voltage transformer 82 is connected across the 11S-volt line which powers the primary winding 83 of the transformer 82. The toner sampling and toner monitoring circuits are connected to the secondary windings 85, 86 and 88 of the transformer 82.

The light source 56 is connected across the winding 8S in series with a l0 ohm variable resistor 87 used to adjust the intensity of the light source in accordance with the characteristics of the photodiode 60.

A biasing potential of about 50 volts DC is applied to the disc 34 from the winding 86 which feeds the input to a full-wave rectifier 92 which is, in turn, connected through resistors 94 and 96 arranged in parallel connection. The resistors 94 and 96 are rated at 820 kiloohms. When the toner employed is positively charged, the disc is connected as shown so that a negative charge is applied thereto. When the toner employed is of a negative polarity,

the connections between the disc 34 and the rectifier 92 are reversed so that the disc is charged to a positive polarity.

Winding 88 supplies power to the toner monitoring circuit 78. The winding 88 is connected to the input terminals of a full-wave rectifier 98. Across the output terminals of the rectifier 98 is connected a filter network consisting of a pair of 50 microfarad condensors 100 and 104 across a 33-ohm resistor 102. The output of the filter network is connected to the input line of the photodiode 60. The negative output terminal of the rectifier 98 leads to the thermistor 66. Variable resistor 108 is in series connection with the variable resistor 110 leading to the output side of photodiode 60. As a result of the constant illumination of the photodiode 60 and its proximate location to the light source 56 (FIGURE 3), the temperature of the photodiode gradually increases with use. Since the only variable factor in the monitoring system should be the amount of toner deposited on the fins 36, the temperature control device, such as the thermistor 66, serves to draw off a proportional amount of the output of the diode attributable to the increased heat of the system.

As the environment heats up, the photodiode 60 increases in the temperature causing the drop in resistance, and hence, resulting in a greater current output to the transistors 114 and 116 which function as a high-gain amplifier control. In order to control the current output caused by heat, the thermistor 66, in close proximity to the photodiode 60, also undergoes a decrease in resistance and, hence, serves to shunt that portion of the heatproduced current around the transistor network. The resistors 108 and 110 serve to modify the response characteristics of the thermistor so that it is compatible withy the diode characteristics at the given temperature of operation so that only that portion of the output due to heat is shunted off.

The diode 60 is at its high impedance level when the light being cast on it is at a low intensity level. Since the fin portions 36 are spaced apart as the disc rotates, it produces a discontinuous refiected light pattern. To negate the effect of this intermittent illumination of the photodiode, there is provided a condenser 112 to even out the output signal of the photodiode 60.

When the output signal from the photodiode 60 reaches a predetermined level, it will fire the transistor 114 which will permit current to fiow to the base of transistor 116- Which, in turn, at the predetermined level will also fire causing current to flow through resistor 120 to the predriver transistor .122. The firing level of the pre-driver transistor 122 is controlled by the variable resistor 124.A

Upon reaching the firing level 0f the transistor 122, it

supplies current to the lbase of the output driver transistor 126 which energizes the coil of the main relay 130A pulling in its contacts 13'2 energizing the vibrating solenoid 74 to dispense the toner into the trough 24. The 20-microfarad condenser 134 in parallel relation to the coil 130 protects the driver transistor 126 against lock when the coil is de-energized. The resistors 136, 138 and are current limiting resistors; resistor 144 (l0 kiloohms) sets the level of voltage response for transistor 122 with the unsaturated range of the high gain amplifier circuit of transistors 114 and 116. Resistor 142 assures that the base of transistor 122 does not reach ground potential.

To place the apparatus in operation, the switch 72 is closed energizing the drive motor 42 and the primary coil 83 of the constant voltage transformer 82. The disc member 34 begins to rotate at a speed not in excess of 50 r.p.m. It will be appreciated that the particular speed at which the disc 34 is rotated may -be varied over a wide range, the only limitation being that its speed =be adjusted so as not to stir up the developer mix to the point where it Ibegins throwing out the particles from the trough 24. Insulating spacers 136 and 138 (FIGURE 1) are provided between the motor and the trough wall, and for the shaft 40, in order to electrically insulate the disc 34 from ground so that the disc is electrically oating. AS the disc member 34 moves through the developer miX 22, toner is attracted to the ns, and in particular to the specularly reflective face portions 38 in accordance with the concentration of toner on the mix. It will be appreciated that the disc member 34, being of a different material than the developer mix, will generate triboelectric forces such that the powder will be attracted to the specularly reflective surface. However, it is perferred that a biased charge be applied to the disc as provided -by the secondary winding 86 through the rectier 92. The voltage applied is in the range of from 40-60 volts causing the attraction of the electroscopic powder.

Simultaneously, the light source 56 is energized causing radiation in the visible range f the spectrum to be directed on the face portions 38 of which has been attracted a certain amount of toner. The intensity of reected light from the specularly reective surface 38 may be correlated to the toner concentration in the mix, since the amount which is attracted to the surface is directly dependent on the concentration present in the mix. By adjusting the variable resistor 110, the output current level at which the transistor 114 is to be red may be preset. The variable resistor 110 operating in conjunction with the diode 60 determines the current level at which the transistor 114 will re causing current to flow to the base of transistor 116 leading to the pre-driver transistor 122. In the circumstance that the current level is insufficient to fire the transistor 114, it returns to the input side of the photo diode through the resistor (1.5 kiloohms) 138. The high-gain amplication achieved through the transistors 114 and 116 directs the signal to the pre-driver transistor 122 controlled yby the variable resistor (l5 kiloohms) 124.

When the pre-driver transistor 122 res, it permits the passage of current through resistor kiloohms) 127 to the base of the transistor 1'26 which then energizes the relay 130 which pulls in its contacts 132 energizing the vibrator mechanism 74 of the hopper 32, which then ybegins the vibrator mechanism 74 of the hopper 32, which then Ibegins the dispensing of fresh toner into the trough 24.

The calibration of the device will depend on the nature of the material, but in general the operator will determine the concentration in the mix which results in the optimum quality reproduction, and itis this concentration for which the toner sampling circuit 7-6 and the toner monitoring circuit 78 are adjusted to maintain.

As the fresh toner is dispensed from the hopper 32, it falls directly into the trough 24 and there is intermixed with the existing developer mix by the augers A18 and 20, and the disc member 34 immediately samples the replenished developer mix which in turn is immediately monitored by the toner monitoring circuit 78 so that an instantaneous reading is obtained without any undue delay or lag between the addition ofv toner and the readout,

Although the present invention has been described with reference to an illustrative embodiment thereof, it should be understood that numerous other embodiments and modifications can be devised `by those skilled in the art that would fail within the spirit and scope of this invention.

What is claimed is: l

1. The method for automatically controlling the concentration of toner in a developer mix to a predetermined level as measured by using photoelectric detection means and a probe in conjunction with toner dispensing means preset to dispense toner responsive to said detecting means upon detecting an amount of toner less than said predetermined concentration comprising the steps of (l) inserting the probe into the developer mix for attracting a first quantity of toner thereon dependent on the concentration of toner in the mix;

(2) withdrawing said probe from the developer mix to a viewing position;

(3) irradiating the probe with a beam of radiant energy;

(4) detecting the amount of radiant energy transmitted from the probe and generating a signal correlated to the toner concentration in the mix;

(5) dispensing fresh toner into said mix when said signal level is below that set for the predetermined concentration level;

(6) 'reinserting said probe into the mass whereup said iirst quantity is released an a second quality of toner adheres;

(7) repeating steps 2-5 until the signal level correlates to the predetermined concentration level.

References Cited UNITED STATES PATENTS y3,224,649 12/1965 Gum@ zzz- 199 3,300,091 l/1967 Wondrak et al. 222-76 3,419,188 12/1968 Mrchen 2224-76 XR ROBERT B. REEVES, Primary Examiner U.s. c1. X.R. 222-52 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,487,978 January 6 1970 Stanley A. Gawron It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 63, "horogeneous" should read homo eneous Column 4, line 37, "3,224,468" should read 3,224, 49 line 73, "This" should read The Column 7, lines 4l and 4 cancel "the Vibrator mechanism 74 of the hopper 32, which then begins". Column 8, line l2 "fail" should read fall line "thereon" should read therein line 35 "whereup" should r` whereupon line 36 "an" should read and same line "quality" should read quantity Signed and sealed this 3rd day of November 1970.

(SEAL) Attest: A

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents

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