CA1281763C - Liquid developer charge director control - Google Patents
Liquid developer charge director controlInfo
- Publication number
- CA1281763C CA1281763C CA000529691A CA529691A CA1281763C CA 1281763 C CA1281763 C CA 1281763C CA 000529691 A CA000529691 A CA 000529691A CA 529691 A CA529691 A CA 529691A CA 1281763 C CA1281763 C CA 1281763C
- Authority
- CA
- Canada
- Prior art keywords
- toner
- charge director
- liquid developer
- source
- liquid
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/06—Apparatus for electrographic processes using a charge pattern for developing
- G03G15/10—Apparatus for electrographic processes using a charge pattern for developing using a liquid developer
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/06—Apparatus for electrographic processes using a charge pattern for developing
- G03G15/10—Apparatus for electrographic processes using a charge pattern for developing using a liquid developer
- G03G15/104—Preparing, mixing, transporting or dispensing developer
- G03G15/105—Detection or control means for the toner concentration
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/06—Apparatus for electrographic processes using a charge pattern for developing
- G03G15/10—Apparatus for electrographic processes using a charge pattern for developing using a liquid developer
- G03G15/104—Preparing, mixing, transporting or dispensing developer
Abstract
Abstract of the Disclosure A copier wherein charge director is supplied to a liquid developer in response to a conductivity measurement thereof. The toner concentrate is deficient in charge director and is supplied to the liquid developer in response to an optical transmissivity measurement thereof.
Conductivity is measured by a pair of spaced electrodes immersed in the developer and excited by a variable alternating voltage source through a fixed resistor.
The effects of inherent capacitance between electrodes are neutralized by a variable capacitor. A
phase sensitive detector is provided with a reference voltage having the same phase shift as occasioned by capacitive effects. The copier is disabled if developer conductivity decreases appreciably below the desired value or if the developer temperature becomes excessive.
The developer conductivity measurement is corrected by a developer temperature measurement.
Conductivity is measured by a pair of spaced electrodes immersed in the developer and excited by a variable alternating voltage source through a fixed resistor.
The effects of inherent capacitance between electrodes are neutralized by a variable capacitor. A
phase sensitive detector is provided with a reference voltage having the same phase shift as occasioned by capacitive effects. The copier is disabled if developer conductivity decreases appreciably below the desired value or if the developer temperature becomes excessive.
The developer conductivity measurement is corrected by a developer temperature measurement.
Description
Title of the Invention LIQUID DEVELOPER CHARGE DIRECTOR CONTROL
Background of the Invention Liquid developers generally include a liquid phase, comprising an insulating carrier liquid such as an isoparaf-finic hydrocarbon, and a solid phase, comprising toner particles composed of a pigment and a binder. The solid phase toner is dispersed or suspended in the liquid phase carrier.
Liquid developers further include a minor amount of charge director which insures that the toner particles are uniformly charged with the same polarity, which may be either positive orl negative depending upon the particular application. The liquid, eveloper is used to develop a latent image formed on a photo-onductive imaging surface. Usually the photoconductive urface is charged with one polarity; and the toner particles re charged with an opposite polarity. If the liquid developer ontains exces~ive charge director, then the images developed ill tend to be somewhat faint because of loss of image charge ue to leakage in the higher conductivity liquid developer.
n the other hand if the liquid developer contains insufficient harge director, then the images developed will also tend to be omewhat faint since toner particles having reduced charge move ith reduced velocity through the developer liquid to the maging surface;
A more serious problem with liquid developers having nsufficient charge director is that the toner tends to drop ut of suspension, forming sludge deposits which continually ~81763 grow until operation o~ the electrostatic copier must be interrupted for cleaning. It is the maintenance of the ' charge on the toner particles by the charg~ director which Il causes the toner particles to repel one another, maintaining ~! them dispersed, and preventing them from agglomerating and ! forming sludge deposits li Summary of the Invention Il In general our invention contemplates a liquid il developer control system wherein a liquid carrier, such as 10 1, isodecane, from a first container is added to a diluted working developer suspension to maintain the volume of such I, working developer constant. The optical transmissivity ;~ of the working developer is measured; and toner concentrate I frorn a second container is added to the working developer to maintain its optical transmissivity at a predetermined ! value. The conductivity of the working developer is also 'I measured and charge director concentrate from a third container is added to the working developer to maintain I, its conductivity at a predetermined value.
20 ! In the making of a copy with a liquid developer, a constant amount of carrier liquid is deposited over the entire surface of the copy sheet. This carrier liguid from ! the working suspen~ion contains an associated amount of l liquid phase charge director. There is further deposited 25 ¦ upon the copy sheet an amount of toner proportional to the ¦ extent of printing on the copy sheet. This toner includes ¦ an associated amount of solid phase charge director.
¦ Accordingly, during the making of a copy, there is lost lX81763 from the working developer a first constant quantity of charge director associated with the carrier liquid and a second variable quantity of charge director associated with the toner solids. The toner concentrate in the second container is preferably provided with a total amount of charge director not appreciably exceeding that associated with the solid phase toner. This prevents detectable sludging of the toner concentrate and insures that the toner concentrate can not cause the conductivity of the working developer to exceed its desired value. The charge director concentrate from the third container effectively supplies the charge director lost by transfer of carrier liquid to each copy sheet.
One object of our invention is to provide a liquid developer control system wherein a charge director concentrate is supplied to the working developer suspension in response to a conductivity measurement thereof.
Another object of our invention is to provide a liquid developer control system wherein a toner concentrate is added to the working suspension in response to a transmissivity measurement thereof.
Still another object of our invention is to provide a liquid developer control system wherein the toner concentrate contains a total amount of charge director not appreciably exceeding that associated with the solid phase toner.
A further object of our invention is to disable an electrophotocopier if the temperature of the liquid developer becomes excessive in order to prevent sludging.
~8~7~3 A further ob~ect of our invention is to ~isable an electrophotocopier if the conduotivity of the liquid developer drops appreciably below its proper value in order to prevent sludging.
Other and further objects of our inventlon will appear from the following description.
The Prior Art Gardiner et al 3,981,267 (Re. 30,477) uses a conductivity measurement of the liquid developer to control a constant current source providing biasing current to the development ele~trode.
Mochizuki et al 4,310,238 shows a liquid developer transmissivity control system, wherein the desired transmis6ivity value is modified by a measurement of the onductivity of the working suspension. More particularly, as the conductivity of the working suspension gradually increases during the making of many copies, the resulting "fatigue" of the developer is compensated for by adding more toner concentrate to decrease the transmissivity of the working developer.
¦ Brief Description of the Drawing ¦ The accompanying drawing, which forms part of the instant specification and is to be read in conjunction ¦therewith, is a schematic view of a preferred embodiment ¦of our liquid developer charge director control.
~281763 Description of Preferred Embodiment Referring now to the drawing, the working suspension is contained within a tank 10. A first container 12 having a neck 24 is provided with a supply of carrier liquid such as Isopar-G (a trademark of Exxon Corporation) which is a mixture of isoparaffinic hydrocarbons, lar~ely isodecane, having a extremely low bulk conductivity. Container 12 is held inverted; and carrier liquid issues from neck 24 until the height of the working suspension in tank lO covers the lower end of neck 24. The working developer is relatively dilute and typically might be 1~ toner solids and 99~ carrier liquid by weight.
Within a second container 14 we provided a supply of toner concentrate. Typically the concentrate might be 10~ toner solids by weight and 90~ carrier liquid such as Isopar. The rate of sludging depends upon the temperature and the amount of charge director. Sludging is increased by temperature and is decreased by charge director. The sludging of the toner concentrate in container 14 is 2Q negligible compared with that of the working suspension in tank 10 because the concentrate is substantially at or only slightly above ambient or room temperature while the working suspension in tank 10 may approach temperatures as high as 100F. Any local hot spots within tan~ 10 form sludging sites.
~28~763 To further reduce any minimal sludging of the toner concentrate in the second container 14, we further provide the toner concentrate with a relatively large amount of charge director which, however, does not appreciabily exceed that associated with the solid phase. Bo,th toner solids and charge director associated therewith are removed from the system by transfer to copy paper and by sludging as well. Carrier liquid may be removed from the system both by transfer to copy paper and by evaporation. Both carrier liquid and charge director associated therewith are removed from the system by transfer to copy paper. However, evaporation of carrier liquid produces no loss in charge director. If the copier is maintained at operating temperature for an extended period of time and the sludging and evaporation rates are made up solely by toner concentrate from the second container 14, the amount of charge director within tank 10 will continually increase if the toner concentrate contains any charge director in excess of that a6sociated with the toner solids. We ensure that the charge director control system will not lose control due to excessive charge director in tank 10 by ensuring that the charge director in the toner concentrate does not appreciably exceed thatassociated with the toner solids.
Within a third container 16 we provide a charge director concentrate which may contain ~5 % by weight of charge director and 95~ carrier liquid such as Isopar.
lZ1~176~3 i Electrophotocopiers employ a photoconductive sur~ace which may be charged either positively or negatively. The charge ¦director imparts a charge to the toner particles which is ¦ordinarily opposite to that with which the photoconductive ¦surface is charged. For example if the surface is char~ed ¦positivcly, then a negative charge director would be employed ¦both in the toner concentrate container 14 and in the charge director concentrate container 16. Such negative charge directors include metal salts of fatty acids such as calcium 1(~ palmitate and metal salts of naphthenic acid such as barium petronate. If the photoconductive surface is negatively oharged, then a positive charge director would be employed.
Such positive charge directors include transition metal salts of fatty acids such as aluminum stearate and transition ¦metal salts of naphthenic acid such as cobalt naphthanate.
¦Furthcr charge directors known to the prior art include ¦sodium dioctyl sulfosuccinate, lecithin and calcium petronate, ¦sometimes known as "mahogany soap". Generally we prefer ¦charge directors which are soluble in the carrier liquid.
¦ A shaded pole induction motor 18 drives a stirrer 19 within tank 10 to prevent settling of toner in the working suspension. A further shaded pole induction motor 20 drives a stirrer 21 which extends through a hole 26 in the top of the second container 14 to prevent settling of the toner ~s in the conc trate, The char irect~r conc ntrate con~ainer 1~8~763 , ~ ~
,~, 16 is provided with an air hole 28 in the top thereo~. The l second container 14 is provided with a short outlet pipe 30 1, which is coupled by flexible tubing 34 to the inlet of a ~, positive displacement pump 38 having an eccentric shaft 39 1i 5~l which is driven by a direct current motor 40. The outlet of ,l pump 38 is connected by flexible tubing 46 to a short inlet pipe 50 ~f tank 10. The third container lÇ is provided with ,1 a short outlet pipe 32 which is coupled by flexible tubing 36 Il to the inlet of a positive displacement pump 42 having an 10¦¦ eccentric shaft 43 which is driven by DC motor 44. The ¦ outlet of pump 42 is coupled by flexlble tubing 48 to a short inlet pipe 52 o~ tank 10. Positive displacement pumps 38 and 42 may be of the flexible vane type; and both the rotors thereof and motors 40 and 44 rotate counterclockwise in the direction of the arrows. Excitation of motor 40 drives pump 38, supplying toner concentrate from container 14 to tank 10.
Excitation of motor 44 supplies charge director concentrate ~rom container 16 to tank 10.
One wall o~ tank 10 is provided with a tran~par~nt plate 62, which permits light ~rom an incandescent lamp 60 to pase therethrough to a photosensitive device 66 mounted within tank 10. Device 66 may comprise a photoconductor such a~ cadmium sulfide. The toner control may be substantially as shown in U.S. Patent 4,579,253, issued April 1, 1986 to Shenier for Toner Control System. Light rom lamp 60 is also directed through a variable or adjustable aperture 64 to a reference photosensitive device 68 which is similar to device 66. The primary winding 56 of a transformer indicated generally by the reference numeral 54 is excited lZ81763 ¦ by an alternating current source of, for example, 115 volts.
Transformer 54 is provided with a secondary winding 58 ¦ having a center tap which is grounded. Terminals 57 and 59 ¦ of winding 58 respectively pro~-ide +10 and -10 volts AC.
¦ Lamp 60 is connected between terminals 57 and 59. Terminal ¦ 57 is connected through device 68 to one terminal of a potentiometer 67, the other terminal of which is connected through devlce 66 to terminal 59. The slider of potentiometer 67 is connected through an AC amplifier 80 to the input of a phase sensitive detector 84 which receives a reference input from terminal 59. Positive outputs of detector 84 actuate a trigger circuit 86 which enables a free running power multivibrator 88. Multivibrator 88 is coupled to one terminal of motor 40, the other terminal of which is grounded.¦
Terminal 57 is connected to one electrode 70 of a pair of spaced electrodes 70 and 71 disposed within tank lO.
Electrode 71 is connected through a 50 megohm resistor 74 to the slider of a 200 kilohm potentiometer 73 connected botween terminal 59 and ground. Terminal 59 is connected through an adjustable capacitor 72 having a nominal value of 35 picofarads to electrode 71. Terminal 59 is further connected serially through a rheostat 76 having a nominal value of 33 kilohms and a .07 microfarad capacitor 77 to ground. Electrode 71 is connected to the gate of an insulated-gate field-effect transistor amplifier 81, which may comprise a source follower having a voltage amplification of substantially unity with an extremely high input impedance lZ81~63 and a low output impedance. The source output of field effect transistor amplifier 81 is connected through an AC amplifier 82 to a phase sensitive detector 83, the reference input of which is supplied by a conduct~r 78 connected to the ~unction of rheostat 76 and capacitor 77.
Detector 83 drives the positive input of a unity gain Il differential amplifier 85. Positive o~tputs of amplifier ¦1 85 actuate a trigger circuit 87 which enables a free running ¦ power multivibrator 90. Multivibrator 90 is connected to ¦ one terminal of motor 44, the other terminal of which is ¦ grounded.
A wall plug 92 provides a source of 115 volts AC
at 60 Hertz. Conductor 93 of plu~ 92 i5 connected to one Il terminal of primary winding 56 and to the armature of a !¦ normally closed relay switch 105 which may be opened by ¦¦ energization of a DC relay winding 104. Conductor 93 is jl further connected to one terminal of each of stirring motors ¦l 18 and 20. Conductor 91 of plug 92 is connected to the ~' armature of a normally open relay switch 99 which may be ¦ closed by energization of an AC relay winding 98. The fixed ¦ contact of relay switch 99 is connected to the other terminal of each of stirring motors 18 and 20, to the other terminal of primary winding 56, and through a resistor 102 to one terminal of relay winding 98. The other terminal of winding 98 is connected to the fixed contact of relay switch 105.
Conductor 91 is connected to one contact of a spring-loaded normally-open "on" switch 94. The other contact of switch 94 is connected through a resistor 96 to the first terminal of winding 98. The fixed contact of relay switch 99 also 30 1 provides power to the copier as is well-known to the art.
' ~ 10-lZ81763 Ter~inal 59 is c~nnected to one contact of a ¦ spring-loaded, normally-open "off" switch 108. The other contact of switch 108 is connected through a resistor 110 I and forwardly through a diode 112 to a first terminal of ¦ relay winding 104 the other terminal of which is grounded.
¦ The output of amplifier 8S is connected through a normally-¦ closed, manually-operable switch 114 and forwardly through ¦ a diode 115 to the input of a trig~er circ~lit 116. The ¦ output of trigger circuit 116 is connected to the first ¦ terminal of relay winding 104. Upon the making of each j copy, an output is provided by circuit 118which is coupled to the resetting input of a one minute timer 120. The output of timer is connected to the first terminal of relay winding 1lo4.
¦ The temperature of the working suspension is measured by a sensor 122 providing an electrical output scaled, for example, in degrees Pahrenheit. The output of temperature sensor 122 is applied to the negative input of a unity gain differential amplifier 128 and to the positive input of a unity gaindifferential amplifier 130. A source of a fixed voltage 124 scaled to represent ambient or room temperature of 70F. is applied to the positive input of differential amplifier 128, A source of a fixed voltage 126 scaled to ¦ represent a temperature of 100F. is applied to the negative ¦ input of differential amplifier 130. The output of differential amplifier 128 is applied to the negative input ¦ of differential amplifier 85. The output of differential ¦ amplifier 13~ is appl~ed through an amplifier 132 to a trigger ¦ circuit 134, the output of which is connected to the first terminal of relay winding 104.
1 ~281763 In operation of our invention, the "on" switch 94 ! is momentarily closed which, through resistor 96, energizes ¦ relay winding 98, the circuit being completed through switch j 105. Relay switch 99 closes, applying power from conductor 1¦ 91 through resistor~102 to winding 98, maintaining it energ-~¦ zed. The closing of switch 99 also excites stirring motors ¦¦ 18 and 20, energizes primary winding 56, and provides power to the copier through other connections not shown.
I In operation of the toner control system, adjustable ¦ aperture 64 causes the amount of light falling on device 68 ~o be equal to that passing through window 62 and falling upon device 66 when the working suspension has the desired transmissivity. In such event, equal voltage drops occur 11 across devices66 and 68; and the input of amplifier 80 is ll at ground potential. Potentiometer 67 is adjusted to compensate or slight mismatch in devices 66 and 68. As the transmissivity o~ the working developer increases due to depletion of toner, more light falls upon device 66, reducing its resistance. An AC voltage appears at the ~ input of amplifier 80 which is in phase with that at terminal 59. Phase sensitive detector 84 now provides a positive output. When such output exceeds +0.5 volt, for example, trigger circuit 86 is actuated, causing multivibrator 88 1 to excite motor 40 with a duty cycle of, for example, one second "on" and four seconds "off". During each one second ¦ interval that motor 44 is excited, it rotates counterclockwise correspondingly driving pump 38 and supplying toner concentrate from container 14 to tank 10. The four second 1 - .
-lZ81763 ¦ interval between successive excitations of motor 40 permits j stirrer 19 to circulate the toner concentrate throughout the ~ working suspension. As the transmissivity of the working ¦ suspension decreases due to increase in amount of toner, ¦ the output of detector 84 decreases; and at zero volts, ¦ for example, trigger circuit 84 is turned "off", disabling ¦ multivibrator 88 and motor 40.
Charge director in the working suspension is depleted l not only by transfer of carrier liquid to a copy sheet ¦ but also by loss of toner due either to transfer thereof to a copy sheet or to sludging thereof withln tank 10. Electrodes 70 and 71 may be formed as parallel plates or as concentric cylinders having respective diameters of .55 inch and .45 inch l with len~ths of approximately 2.5 inches. The spacing ', between the cylinders may thus be approximately .05 inch.
The area bctween spaced electrodes 70 and 71 is approximately i ¦ 3.9 square inches. The working suspension may have optimum ¦ performance with a bulk conductivity of 50 picohos per I centimeter, for example. This produces a resistance between ¦ electrodes 70 and 71 of approximately 100 megohms. The input to amplifier 81 will be at ground potential with the slider ¦ of potentiometer 73 positioned substantially at its midpoint and providing -5 VAC. Potentiometer 73 acts as a variable potential source having a maximum internal resistance, when ~ ¦ positioned at its midpoint, of 50 kilohms which is one-thousandth the 50 megohms resistance of fixed resistor 74.
¦ The conductance betweer, the parallel plates or concentric cylinders 70 and 71 is proportional to the surface ~.28'1763 area and inversely proportional to the spacing therebetween.
The same relationship also prevails for the capacitance between the plates or cylinders 70 and 71. Isopar-G has a dielectric constant of 2.0; and the capacitance between plates 70 and 71 is approximately 35 picofarads. At a frequency of 60 Hertz, the capacitive reactance bet~een plates 70 and 71 is 7S megohms. Capacitor 72, having a nominal value of 35 picofarads, is adjusted to equality l with the capacitance of plates 70 and 71, so that the input ¦ to amplifier 81 can have zero quadrature comDonent. The eqùivalent capacitance of plates 70 and 71 and capacitor ¦72 is 70 picofarads which at a frequency of 60 Hertz has i a capacitive reactance of 37.5 megohms. This is shunted ¦by the 33.3 megohms equivalent resistance of resistor 74 1 and plates 70-71.
lZ81763 As the conductivity of the w~rking suspension in tank 10 decreases due to the depletion of charge director, ¦ the re~istance between plates 70 and 71 increases. In ¦ the absence of capacitive effects, this would produce an ¦ AC voltage at the input of amplifier 81 which is in phase with that of the -10 VAC potential at terminal 59.
¦ Because of the capacitive effect of plates 70~71 and ¦ neutralizing capacitor 72, the voltage at the input of ¦ amplifier 81 lags that at terminal 59 by arctan (33.3/37.5) ¦ = tan 1,89 - 41,6. Capacitor 77 has a value which is approximately a thousand times the 70 picofarad equivalent capacitance of plates 70-71 and capacitor 72; and resistor 76 has a nominal resistance which is one-thousandth that of the 33.3 megohm equivalent resistance of plates 70-71 and resistor 74, Resistor 76 is adjusted so that the reference voltage on conductor 78 lags that at terminal S9 by 41.6.
Small errors in the adjustment of capacitor 72 produce at the input of amplifier 81 only voltage components in quadrature with the reference signal on conductor 78 provided to detector 83, Accordingly, detector 83 will produce no voltage output. However, increase in the resistance between plates 70 and 71, due to decrease in the conductivity of the working suspension, produces at the input of amplifier 81 a voltage component in phase with the reference signal provided to detector B3 on conductor 78. Phase sensitive detector 83 now produces positive output. We prefer AC conductance measurement, lZ81763 despite capacitive effects, to prevent any net deposition of toner on electrodes 70 and 71, as would occur if DC potentials ¦
ere applied thereto. I
The working suspension has a positive temperature coefficient of bulk conductivity which may, for example, be +O,S picomho per centimeter per degree Fahrenheit. At a temperature of 100F. the same optimum performance working ',suspension m~y thus have an increased bulk conductivity of 1150 ~ 0.5 (100-70) = 65 picomhos per centimeter. As the ~Itemperature of the working suspension increases above 70F., jlthe output of differential amplifier 128 becomes negative.
The increased bulk conductivity of the working suspension produces a negative output from detector 83. The gradient in Ivolts per F. of sensor 122 and the gain of amplifier 82 should be such that the negative outputs of both amplifier 128 and detector 83 are substantially equal, so that no output is produced from differential amplifier 85 as long as thè composition oP the working suspension does not change, lirrespective of changes in its temperature. The conductivity ilmeasurement is thus modified by correcting for changes in ¦¦conductivity caused by variations in developer temperature llfrom 70F. As the amount of charge director in the working ,¦developer composition gradually decreases, the output of ¦ amplifier 85 gradually increases.
When the output of amplifier 85 exceeds ~0.5 volt, for example, trigger circuit 87 is actuated, causing multivibrator 90 to excite motor 44 with a duty cycle of, for example, one-quarter second "on" and five seconds "off".
; -16-lZ81763 Pump 42 may have one-fifth the volume or displacement of pump 38. ~he amount of charge director concentrate to be added is extremely small. The five seconds "off" interval permits stirrer 19 to thoroughly mix the added charge director with the working suspension. During each one-quarter second interval that motor 44 is excited, it drives pump 42 counterclockwise, supplying charge director from the third container 16 to tank 10. As the conductivity of the working developer increases, the output of amplifier 85 decreases;
I and at zero volts, for example, trigger circuit 87 is turned "off", disabling multivibrator 90 and motor 44.
~he following examples of working developer and toner concentrate are given by way of illustration and not by way of limitation. A 1% w~rking developer suspens on ¦ may comprise 990 grams of Isopar G and 10 grams of toner solids including pigment and binder. Optimum performance Il may be at a conductivity of 50picomhos per centimeter ¦¦ at 70F. which may require 238 millig.ams of a given charge ~I director. The loss of each gram of toner solids, whether ~ by transfer to a copy sheet or by sludging within tank 10, 1~ e~v~ gr~ cb~9 ~r~
P 6t~
~ -17-~ lZ81763 Each gram of carrier liquid transferred to a copy sheet may remove 0.2 milligram of charge director. The 10 grams of toner solids requires 4 x 10 = 40 milligrams of charge 1 director; the Isopar carrier requires 990 x 0.2 - 198 ¦ milligrams of charge director; and the total amount of charge director is 40 ~ 198 = 238 milligrams. A 10% toner ¦ concentrate may contain 100 grams of toner solids, including ¦ pigment and binder, and 900 grams of Isopar-G. The toner ¦ concentrate preferably further includes 4 milligrams of ¦ charge director associated with each gram of toner solids, ¦ or 4 x 100 - 400 milligrams of charge director, to prevent sludging. However, the toner concentrate preferably ¦ contains little or no further charge director associated with the 900 grams of Isopar. The toner concentrate is thus deficient by 900 x 0.2 ~ 180 milligrams of charge director to ~nsure that the system cannot lose control. The carrier liquid in the first container 12 is also deficient in charge director since preferably little or none is provided therein. All further charge director needs are supplied from the charge director concentrate in the third container 16.
To turn the copier off, the spring-loaded, manually-operable "off" switch 108 is momentarily depressed, supplying DC current through resistor 110 and rectifier 112 to winding 104. Engerization of winding 104 opens switch 105, disabling the circuit for winding 98. Switch 99 thus opens, removing power from the copier. The copier also turns itself off automati 11y if no copies are made for a period of one minut~.
1'~81763 ¦ As long as copies are being made more frequently than once ¦ each minute, the copy sensor 118 will reset the one minute timer 120 before it provides an output. ~owever, if no copy is made for a period-exceeding one minute, then the copy sensor 118 will not reset timer 120 before its timing interval has expired. When the one minute timing interval of timer 120 expires, an output signal is produced which energizes winding 104, opening switch 105 and disabling the circuit for winding 98. Switch 99 now opens, removing power from the copier.
When the conductivity control system is operating normally, the output from amplifier 85 will gradually increase from zero volts to approximately 0.5 volt, whereupon charge director concentrate is added until the output of amplifier 85 drops back to zero volts again. If the third container 16 i8 empty of charge director concentrate, or if there is a failurein trigger circuit 87, multivibrator 90, motor 44, or pump 42, then the output from I amplifier 85 will gradually increase beyond 0.5 volt. Diode 115 may be formed of silicon and requires approximately 0.5 ¦ volt of forward bias for conduction. The input of trigger ¦ circuit 116 now begins to rise from ground potential. When the output of amplifier 85 exceeds t 1.0 volt, the input of trigger circuit 116 exceeds l0.5 volt, thereby actuating it ¦ and energizing winding 104. Relay switch 105 opens, disabling the circuit for winding 98. This opens switch 99,, removing power from the copier. While the copier may be momentarily turned "on" by depressing switch 94, it will immediatëly thereafter be turned "off" by amplifier 85 1'~81763 through switch 114, diode 115, trigger circuit 116, and winding 104, which opens switch 105. It is desired that the copier not be permitted to operate with significantly less charge director in the working developer than that required to bring the system to optimum performance. Significantly reduced amounts of charge director would lead to more rapid sludging of toner in tank 10, resulting not only in loss of t~er material but also more frequent maintenance.
~ Generally operation of the copier can be restored 10 ¦ by providing a fresh supply of charge director concentrate ¦ in container 16. However, the output of amplifier 85 still ¦ exceeds ~1.0 volt. To prevent this output of amplifier 85 from turning "off" the copier, switch 11~ is opened. The input of trigger circuit 116 drops to ground potential, turning "off" trigger 116, and disabling relay winding 104.
Motor 44 now causes charge director concentrate to be pumped ¦ from container 16 into tank 10. When the output of amplifier ¦ ~5 drops below +1.0 volt, switch 114 may be closed. Trigger ¦ circuit 116 will not be turned "onN, since its input i8 less ¦ than +0.5 volt. Charge director concentrate will continue to ¦ be pumped until the output of amplifier 85 drops to ground ¦ potential, turning noff" trigger circuit 87.
¦ The copier normally operates with developer ¦ temperatures Iess than 100F., where the sludging rate is acceptably small. If, for example, a cooling fan fails, then the developer temperature will rise above 100F. The output of differenti~l amplifier 130 will become positive and~through amplifier 132, actuate trigger circuit 134. This energizes winding 104, turning "off" the copier and preventing 1~81~63 ¦ any further rise in developer temperature or increase in ¦ sludging rate.
¦ It will be seen that we have accomplished the objects ¦ of our invention. We have provided a system for independently 1 controiling the quantity of carrier liquid, the quantity of ¦ of toner solids and the quantity of charge director in a ¦ workin~ liquid developer. The height or volume of carrier , liquid is controlled by the neck 24 of container 12. The ¦ quantity of toner concentrate is governed by a balanced 1 transmissivity measuring system wherein equal amounts of ¦ light fall upon matched photosensitive devices. The ¦ guantity of charge director concentrate is governed by an ¦ alternating current conductivity measurement wherein the !¦ inherent capacitance between the conductivity measuring I electrodes is compensated for by a balanced circuit employing ¦ a phase sensitive detector. To prevent either sludging of the toner concentrate or loss of control of the charge director control system, the toner concentrate contains a total amount of charge director which does not appreciably exceed that associated with the toner solids and contains little or no charge director associated with the carrier li~uid component. Our system exhibits none of the so called "fatigue" effects of prior art systems which supply excessive charge director with the toner concentrate. In such systems, the conductivity of the working developer gradually increases, causing an excessive discharge rate of the photoconductive surface and the latent image thereon. To prevent excessive sludging of the working suspension when the charge director l concentrate is exhausted or the control system fails, the ¦ copier is automatically turned off; and further operation is inhibited. The copier ls further disabled if the temperature ~81763 of the working suspension rises above a point where the sludging rate is still acceptably small. The conductivity ¦measurement is modified by correcting for changes in ¦developer conductivity caused by changes in its temperature.
¦ It will be understood that certain features and Isubcombinations are of utility and may be employed without ! reference to other features and subcombinations. This is contemplated by and is within the scope of our claims. It is further obvious that various changes may be made in " details within the scope of our claims without departing from the spirit of our invention. It is therefore to be understood that our invention is not to be limited to the ,specific details shown and described.
Having thus described our invention, what we claim iss i!
,1 !¦ .
,
Background of the Invention Liquid developers generally include a liquid phase, comprising an insulating carrier liquid such as an isoparaf-finic hydrocarbon, and a solid phase, comprising toner particles composed of a pigment and a binder. The solid phase toner is dispersed or suspended in the liquid phase carrier.
Liquid developers further include a minor amount of charge director which insures that the toner particles are uniformly charged with the same polarity, which may be either positive orl negative depending upon the particular application. The liquid, eveloper is used to develop a latent image formed on a photo-onductive imaging surface. Usually the photoconductive urface is charged with one polarity; and the toner particles re charged with an opposite polarity. If the liquid developer ontains exces~ive charge director, then the images developed ill tend to be somewhat faint because of loss of image charge ue to leakage in the higher conductivity liquid developer.
n the other hand if the liquid developer contains insufficient harge director, then the images developed will also tend to be omewhat faint since toner particles having reduced charge move ith reduced velocity through the developer liquid to the maging surface;
A more serious problem with liquid developers having nsufficient charge director is that the toner tends to drop ut of suspension, forming sludge deposits which continually ~81763 grow until operation o~ the electrostatic copier must be interrupted for cleaning. It is the maintenance of the ' charge on the toner particles by the charg~ director which Il causes the toner particles to repel one another, maintaining ~! them dispersed, and preventing them from agglomerating and ! forming sludge deposits li Summary of the Invention Il In general our invention contemplates a liquid il developer control system wherein a liquid carrier, such as 10 1, isodecane, from a first container is added to a diluted working developer suspension to maintain the volume of such I, working developer constant. The optical transmissivity ;~ of the working developer is measured; and toner concentrate I frorn a second container is added to the working developer to maintain its optical transmissivity at a predetermined ! value. The conductivity of the working developer is also 'I measured and charge director concentrate from a third container is added to the working developer to maintain I, its conductivity at a predetermined value.
20 ! In the making of a copy with a liquid developer, a constant amount of carrier liquid is deposited over the entire surface of the copy sheet. This carrier liguid from ! the working suspen~ion contains an associated amount of l liquid phase charge director. There is further deposited 25 ¦ upon the copy sheet an amount of toner proportional to the ¦ extent of printing on the copy sheet. This toner includes ¦ an associated amount of solid phase charge director.
¦ Accordingly, during the making of a copy, there is lost lX81763 from the working developer a first constant quantity of charge director associated with the carrier liquid and a second variable quantity of charge director associated with the toner solids. The toner concentrate in the second container is preferably provided with a total amount of charge director not appreciably exceeding that associated with the solid phase toner. This prevents detectable sludging of the toner concentrate and insures that the toner concentrate can not cause the conductivity of the working developer to exceed its desired value. The charge director concentrate from the third container effectively supplies the charge director lost by transfer of carrier liquid to each copy sheet.
One object of our invention is to provide a liquid developer control system wherein a charge director concentrate is supplied to the working developer suspension in response to a conductivity measurement thereof.
Another object of our invention is to provide a liquid developer control system wherein a toner concentrate is added to the working suspension in response to a transmissivity measurement thereof.
Still another object of our invention is to provide a liquid developer control system wherein the toner concentrate contains a total amount of charge director not appreciably exceeding that associated with the solid phase toner.
A further object of our invention is to disable an electrophotocopier if the temperature of the liquid developer becomes excessive in order to prevent sludging.
~8~7~3 A further ob~ect of our invention is to ~isable an electrophotocopier if the conduotivity of the liquid developer drops appreciably below its proper value in order to prevent sludging.
Other and further objects of our inventlon will appear from the following description.
The Prior Art Gardiner et al 3,981,267 (Re. 30,477) uses a conductivity measurement of the liquid developer to control a constant current source providing biasing current to the development ele~trode.
Mochizuki et al 4,310,238 shows a liquid developer transmissivity control system, wherein the desired transmis6ivity value is modified by a measurement of the onductivity of the working suspension. More particularly, as the conductivity of the working suspension gradually increases during the making of many copies, the resulting "fatigue" of the developer is compensated for by adding more toner concentrate to decrease the transmissivity of the working developer.
¦ Brief Description of the Drawing ¦ The accompanying drawing, which forms part of the instant specification and is to be read in conjunction ¦therewith, is a schematic view of a preferred embodiment ¦of our liquid developer charge director control.
~281763 Description of Preferred Embodiment Referring now to the drawing, the working suspension is contained within a tank 10. A first container 12 having a neck 24 is provided with a supply of carrier liquid such as Isopar-G (a trademark of Exxon Corporation) which is a mixture of isoparaffinic hydrocarbons, lar~ely isodecane, having a extremely low bulk conductivity. Container 12 is held inverted; and carrier liquid issues from neck 24 until the height of the working suspension in tank lO covers the lower end of neck 24. The working developer is relatively dilute and typically might be 1~ toner solids and 99~ carrier liquid by weight.
Within a second container 14 we provided a supply of toner concentrate. Typically the concentrate might be 10~ toner solids by weight and 90~ carrier liquid such as Isopar. The rate of sludging depends upon the temperature and the amount of charge director. Sludging is increased by temperature and is decreased by charge director. The sludging of the toner concentrate in container 14 is 2Q negligible compared with that of the working suspension in tank 10 because the concentrate is substantially at or only slightly above ambient or room temperature while the working suspension in tank 10 may approach temperatures as high as 100F. Any local hot spots within tan~ 10 form sludging sites.
~28~763 To further reduce any minimal sludging of the toner concentrate in the second container 14, we further provide the toner concentrate with a relatively large amount of charge director which, however, does not appreciabily exceed that associated with the solid phase. Bo,th toner solids and charge director associated therewith are removed from the system by transfer to copy paper and by sludging as well. Carrier liquid may be removed from the system both by transfer to copy paper and by evaporation. Both carrier liquid and charge director associated therewith are removed from the system by transfer to copy paper. However, evaporation of carrier liquid produces no loss in charge director. If the copier is maintained at operating temperature for an extended period of time and the sludging and evaporation rates are made up solely by toner concentrate from the second container 14, the amount of charge director within tank 10 will continually increase if the toner concentrate contains any charge director in excess of that a6sociated with the toner solids. We ensure that the charge director control system will not lose control due to excessive charge director in tank 10 by ensuring that the charge director in the toner concentrate does not appreciably exceed thatassociated with the toner solids.
Within a third container 16 we provide a charge director concentrate which may contain ~5 % by weight of charge director and 95~ carrier liquid such as Isopar.
lZ1~176~3 i Electrophotocopiers employ a photoconductive sur~ace which may be charged either positively or negatively. The charge ¦director imparts a charge to the toner particles which is ¦ordinarily opposite to that with which the photoconductive ¦surface is charged. For example if the surface is char~ed ¦positivcly, then a negative charge director would be employed ¦both in the toner concentrate container 14 and in the charge director concentrate container 16. Such negative charge directors include metal salts of fatty acids such as calcium 1(~ palmitate and metal salts of naphthenic acid such as barium petronate. If the photoconductive surface is negatively oharged, then a positive charge director would be employed.
Such positive charge directors include transition metal salts of fatty acids such as aluminum stearate and transition ¦metal salts of naphthenic acid such as cobalt naphthanate.
¦Furthcr charge directors known to the prior art include ¦sodium dioctyl sulfosuccinate, lecithin and calcium petronate, ¦sometimes known as "mahogany soap". Generally we prefer ¦charge directors which are soluble in the carrier liquid.
¦ A shaded pole induction motor 18 drives a stirrer 19 within tank 10 to prevent settling of toner in the working suspension. A further shaded pole induction motor 20 drives a stirrer 21 which extends through a hole 26 in the top of the second container 14 to prevent settling of the toner ~s in the conc trate, The char irect~r conc ntrate con~ainer 1~8~763 , ~ ~
,~, 16 is provided with an air hole 28 in the top thereo~. The l second container 14 is provided with a short outlet pipe 30 1, which is coupled by flexible tubing 34 to the inlet of a ~, positive displacement pump 38 having an eccentric shaft 39 1i 5~l which is driven by a direct current motor 40. The outlet of ,l pump 38 is connected by flexible tubing 46 to a short inlet pipe 50 ~f tank 10. The third container lÇ is provided with ,1 a short outlet pipe 32 which is coupled by flexible tubing 36 Il to the inlet of a positive displacement pump 42 having an 10¦¦ eccentric shaft 43 which is driven by DC motor 44. The ¦ outlet of pump 42 is coupled by flexlble tubing 48 to a short inlet pipe 52 o~ tank 10. Positive displacement pumps 38 and 42 may be of the flexible vane type; and both the rotors thereof and motors 40 and 44 rotate counterclockwise in the direction of the arrows. Excitation of motor 40 drives pump 38, supplying toner concentrate from container 14 to tank 10.
Excitation of motor 44 supplies charge director concentrate ~rom container 16 to tank 10.
One wall o~ tank 10 is provided with a tran~par~nt plate 62, which permits light ~rom an incandescent lamp 60 to pase therethrough to a photosensitive device 66 mounted within tank 10. Device 66 may comprise a photoconductor such a~ cadmium sulfide. The toner control may be substantially as shown in U.S. Patent 4,579,253, issued April 1, 1986 to Shenier for Toner Control System. Light rom lamp 60 is also directed through a variable or adjustable aperture 64 to a reference photosensitive device 68 which is similar to device 66. The primary winding 56 of a transformer indicated generally by the reference numeral 54 is excited lZ81763 ¦ by an alternating current source of, for example, 115 volts.
Transformer 54 is provided with a secondary winding 58 ¦ having a center tap which is grounded. Terminals 57 and 59 ¦ of winding 58 respectively pro~-ide +10 and -10 volts AC.
¦ Lamp 60 is connected between terminals 57 and 59. Terminal ¦ 57 is connected through device 68 to one terminal of a potentiometer 67, the other terminal of which is connected through devlce 66 to terminal 59. The slider of potentiometer 67 is connected through an AC amplifier 80 to the input of a phase sensitive detector 84 which receives a reference input from terminal 59. Positive outputs of detector 84 actuate a trigger circuit 86 which enables a free running power multivibrator 88. Multivibrator 88 is coupled to one terminal of motor 40, the other terminal of which is grounded.¦
Terminal 57 is connected to one electrode 70 of a pair of spaced electrodes 70 and 71 disposed within tank lO.
Electrode 71 is connected through a 50 megohm resistor 74 to the slider of a 200 kilohm potentiometer 73 connected botween terminal 59 and ground. Terminal 59 is connected through an adjustable capacitor 72 having a nominal value of 35 picofarads to electrode 71. Terminal 59 is further connected serially through a rheostat 76 having a nominal value of 33 kilohms and a .07 microfarad capacitor 77 to ground. Electrode 71 is connected to the gate of an insulated-gate field-effect transistor amplifier 81, which may comprise a source follower having a voltage amplification of substantially unity with an extremely high input impedance lZ81~63 and a low output impedance. The source output of field effect transistor amplifier 81 is connected through an AC amplifier 82 to a phase sensitive detector 83, the reference input of which is supplied by a conduct~r 78 connected to the ~unction of rheostat 76 and capacitor 77.
Detector 83 drives the positive input of a unity gain Il differential amplifier 85. Positive o~tputs of amplifier ¦1 85 actuate a trigger circuit 87 which enables a free running ¦ power multivibrator 90. Multivibrator 90 is connected to ¦ one terminal of motor 44, the other terminal of which is ¦ grounded.
A wall plug 92 provides a source of 115 volts AC
at 60 Hertz. Conductor 93 of plu~ 92 i5 connected to one Il terminal of primary winding 56 and to the armature of a !¦ normally closed relay switch 105 which may be opened by ¦¦ energization of a DC relay winding 104. Conductor 93 is jl further connected to one terminal of each of stirring motors ¦l 18 and 20. Conductor 91 of plug 92 is connected to the ~' armature of a normally open relay switch 99 which may be ¦ closed by energization of an AC relay winding 98. The fixed ¦ contact of relay switch 99 is connected to the other terminal of each of stirring motors 18 and 20, to the other terminal of primary winding 56, and through a resistor 102 to one terminal of relay winding 98. The other terminal of winding 98 is connected to the fixed contact of relay switch 105.
Conductor 91 is connected to one contact of a spring-loaded normally-open "on" switch 94. The other contact of switch 94 is connected through a resistor 96 to the first terminal of winding 98. The fixed contact of relay switch 99 also 30 1 provides power to the copier as is well-known to the art.
' ~ 10-lZ81763 Ter~inal 59 is c~nnected to one contact of a ¦ spring-loaded, normally-open "off" switch 108. The other contact of switch 108 is connected through a resistor 110 I and forwardly through a diode 112 to a first terminal of ¦ relay winding 104 the other terminal of which is grounded.
¦ The output of amplifier 8S is connected through a normally-¦ closed, manually-operable switch 114 and forwardly through ¦ a diode 115 to the input of a trig~er circ~lit 116. The ¦ output of trigger circuit 116 is connected to the first ¦ terminal of relay winding 104. Upon the making of each j copy, an output is provided by circuit 118which is coupled to the resetting input of a one minute timer 120. The output of timer is connected to the first terminal of relay winding 1lo4.
¦ The temperature of the working suspension is measured by a sensor 122 providing an electrical output scaled, for example, in degrees Pahrenheit. The output of temperature sensor 122 is applied to the negative input of a unity gain differential amplifier 128 and to the positive input of a unity gaindifferential amplifier 130. A source of a fixed voltage 124 scaled to represent ambient or room temperature of 70F. is applied to the positive input of differential amplifier 128, A source of a fixed voltage 126 scaled to ¦ represent a temperature of 100F. is applied to the negative ¦ input of differential amplifier 130. The output of differential amplifier 128 is applied to the negative input ¦ of differential amplifier 85. The output of differential ¦ amplifier 13~ is appl~ed through an amplifier 132 to a trigger ¦ circuit 134, the output of which is connected to the first terminal of relay winding 104.
1 ~281763 In operation of our invention, the "on" switch 94 ! is momentarily closed which, through resistor 96, energizes ¦ relay winding 98, the circuit being completed through switch j 105. Relay switch 99 closes, applying power from conductor 1¦ 91 through resistor~102 to winding 98, maintaining it energ-~¦ zed. The closing of switch 99 also excites stirring motors ¦¦ 18 and 20, energizes primary winding 56, and provides power to the copier through other connections not shown.
I In operation of the toner control system, adjustable ¦ aperture 64 causes the amount of light falling on device 68 ~o be equal to that passing through window 62 and falling upon device 66 when the working suspension has the desired transmissivity. In such event, equal voltage drops occur 11 across devices66 and 68; and the input of amplifier 80 is ll at ground potential. Potentiometer 67 is adjusted to compensate or slight mismatch in devices 66 and 68. As the transmissivity o~ the working developer increases due to depletion of toner, more light falls upon device 66, reducing its resistance. An AC voltage appears at the ~ input of amplifier 80 which is in phase with that at terminal 59. Phase sensitive detector 84 now provides a positive output. When such output exceeds +0.5 volt, for example, trigger circuit 86 is actuated, causing multivibrator 88 1 to excite motor 40 with a duty cycle of, for example, one second "on" and four seconds "off". During each one second ¦ interval that motor 44 is excited, it rotates counterclockwise correspondingly driving pump 38 and supplying toner concentrate from container 14 to tank 10. The four second 1 - .
-lZ81763 ¦ interval between successive excitations of motor 40 permits j stirrer 19 to circulate the toner concentrate throughout the ~ working suspension. As the transmissivity of the working ¦ suspension decreases due to increase in amount of toner, ¦ the output of detector 84 decreases; and at zero volts, ¦ for example, trigger circuit 84 is turned "off", disabling ¦ multivibrator 88 and motor 40.
Charge director in the working suspension is depleted l not only by transfer of carrier liquid to a copy sheet ¦ but also by loss of toner due either to transfer thereof to a copy sheet or to sludging thereof withln tank 10. Electrodes 70 and 71 may be formed as parallel plates or as concentric cylinders having respective diameters of .55 inch and .45 inch l with len~ths of approximately 2.5 inches. The spacing ', between the cylinders may thus be approximately .05 inch.
The area bctween spaced electrodes 70 and 71 is approximately i ¦ 3.9 square inches. The working suspension may have optimum ¦ performance with a bulk conductivity of 50 picohos per I centimeter, for example. This produces a resistance between ¦ electrodes 70 and 71 of approximately 100 megohms. The input to amplifier 81 will be at ground potential with the slider ¦ of potentiometer 73 positioned substantially at its midpoint and providing -5 VAC. Potentiometer 73 acts as a variable potential source having a maximum internal resistance, when ~ ¦ positioned at its midpoint, of 50 kilohms which is one-thousandth the 50 megohms resistance of fixed resistor 74.
¦ The conductance betweer, the parallel plates or concentric cylinders 70 and 71 is proportional to the surface ~.28'1763 area and inversely proportional to the spacing therebetween.
The same relationship also prevails for the capacitance between the plates or cylinders 70 and 71. Isopar-G has a dielectric constant of 2.0; and the capacitance between plates 70 and 71 is approximately 35 picofarads. At a frequency of 60 Hertz, the capacitive reactance bet~een plates 70 and 71 is 7S megohms. Capacitor 72, having a nominal value of 35 picofarads, is adjusted to equality l with the capacitance of plates 70 and 71, so that the input ¦ to amplifier 81 can have zero quadrature comDonent. The eqùivalent capacitance of plates 70 and 71 and capacitor ¦72 is 70 picofarads which at a frequency of 60 Hertz has i a capacitive reactance of 37.5 megohms. This is shunted ¦by the 33.3 megohms equivalent resistance of resistor 74 1 and plates 70-71.
lZ81763 As the conductivity of the w~rking suspension in tank 10 decreases due to the depletion of charge director, ¦ the re~istance between plates 70 and 71 increases. In ¦ the absence of capacitive effects, this would produce an ¦ AC voltage at the input of amplifier 81 which is in phase with that of the -10 VAC potential at terminal 59.
¦ Because of the capacitive effect of plates 70~71 and ¦ neutralizing capacitor 72, the voltage at the input of ¦ amplifier 81 lags that at terminal 59 by arctan (33.3/37.5) ¦ = tan 1,89 - 41,6. Capacitor 77 has a value which is approximately a thousand times the 70 picofarad equivalent capacitance of plates 70-71 and capacitor 72; and resistor 76 has a nominal resistance which is one-thousandth that of the 33.3 megohm equivalent resistance of plates 70-71 and resistor 74, Resistor 76 is adjusted so that the reference voltage on conductor 78 lags that at terminal S9 by 41.6.
Small errors in the adjustment of capacitor 72 produce at the input of amplifier 81 only voltage components in quadrature with the reference signal on conductor 78 provided to detector 83, Accordingly, detector 83 will produce no voltage output. However, increase in the resistance between plates 70 and 71, due to decrease in the conductivity of the working suspension, produces at the input of amplifier 81 a voltage component in phase with the reference signal provided to detector B3 on conductor 78. Phase sensitive detector 83 now produces positive output. We prefer AC conductance measurement, lZ81763 despite capacitive effects, to prevent any net deposition of toner on electrodes 70 and 71, as would occur if DC potentials ¦
ere applied thereto. I
The working suspension has a positive temperature coefficient of bulk conductivity which may, for example, be +O,S picomho per centimeter per degree Fahrenheit. At a temperature of 100F. the same optimum performance working ',suspension m~y thus have an increased bulk conductivity of 1150 ~ 0.5 (100-70) = 65 picomhos per centimeter. As the ~Itemperature of the working suspension increases above 70F., jlthe output of differential amplifier 128 becomes negative.
The increased bulk conductivity of the working suspension produces a negative output from detector 83. The gradient in Ivolts per F. of sensor 122 and the gain of amplifier 82 should be such that the negative outputs of both amplifier 128 and detector 83 are substantially equal, so that no output is produced from differential amplifier 85 as long as thè composition oP the working suspension does not change, lirrespective of changes in its temperature. The conductivity ilmeasurement is thus modified by correcting for changes in ¦¦conductivity caused by variations in developer temperature llfrom 70F. As the amount of charge director in the working ,¦developer composition gradually decreases, the output of ¦ amplifier 85 gradually increases.
When the output of amplifier 85 exceeds ~0.5 volt, for example, trigger circuit 87 is actuated, causing multivibrator 90 to excite motor 44 with a duty cycle of, for example, one-quarter second "on" and five seconds "off".
; -16-lZ81763 Pump 42 may have one-fifth the volume or displacement of pump 38. ~he amount of charge director concentrate to be added is extremely small. The five seconds "off" interval permits stirrer 19 to thoroughly mix the added charge director with the working suspension. During each one-quarter second interval that motor 44 is excited, it drives pump 42 counterclockwise, supplying charge director from the third container 16 to tank 10. As the conductivity of the working developer increases, the output of amplifier 85 decreases;
I and at zero volts, for example, trigger circuit 87 is turned "off", disabling multivibrator 90 and motor 44.
~he following examples of working developer and toner concentrate are given by way of illustration and not by way of limitation. A 1% w~rking developer suspens on ¦ may comprise 990 grams of Isopar G and 10 grams of toner solids including pigment and binder. Optimum performance Il may be at a conductivity of 50picomhos per centimeter ¦¦ at 70F. which may require 238 millig.ams of a given charge ~I director. The loss of each gram of toner solids, whether ~ by transfer to a copy sheet or by sludging within tank 10, 1~ e~v~ gr~ cb~9 ~r~
P 6t~
~ -17-~ lZ81763 Each gram of carrier liquid transferred to a copy sheet may remove 0.2 milligram of charge director. The 10 grams of toner solids requires 4 x 10 = 40 milligrams of charge 1 director; the Isopar carrier requires 990 x 0.2 - 198 ¦ milligrams of charge director; and the total amount of charge director is 40 ~ 198 = 238 milligrams. A 10% toner ¦ concentrate may contain 100 grams of toner solids, including ¦ pigment and binder, and 900 grams of Isopar-G. The toner ¦ concentrate preferably further includes 4 milligrams of ¦ charge director associated with each gram of toner solids, ¦ or 4 x 100 - 400 milligrams of charge director, to prevent sludging. However, the toner concentrate preferably ¦ contains little or no further charge director associated with the 900 grams of Isopar. The toner concentrate is thus deficient by 900 x 0.2 ~ 180 milligrams of charge director to ~nsure that the system cannot lose control. The carrier liquid in the first container 12 is also deficient in charge director since preferably little or none is provided therein. All further charge director needs are supplied from the charge director concentrate in the third container 16.
To turn the copier off, the spring-loaded, manually-operable "off" switch 108 is momentarily depressed, supplying DC current through resistor 110 and rectifier 112 to winding 104. Engerization of winding 104 opens switch 105, disabling the circuit for winding 98. Switch 99 thus opens, removing power from the copier. The copier also turns itself off automati 11y if no copies are made for a period of one minut~.
1'~81763 ¦ As long as copies are being made more frequently than once ¦ each minute, the copy sensor 118 will reset the one minute timer 120 before it provides an output. ~owever, if no copy is made for a period-exceeding one minute, then the copy sensor 118 will not reset timer 120 before its timing interval has expired. When the one minute timing interval of timer 120 expires, an output signal is produced which energizes winding 104, opening switch 105 and disabling the circuit for winding 98. Switch 99 now opens, removing power from the copier.
When the conductivity control system is operating normally, the output from amplifier 85 will gradually increase from zero volts to approximately 0.5 volt, whereupon charge director concentrate is added until the output of amplifier 85 drops back to zero volts again. If the third container 16 i8 empty of charge director concentrate, or if there is a failurein trigger circuit 87, multivibrator 90, motor 44, or pump 42, then the output from I amplifier 85 will gradually increase beyond 0.5 volt. Diode 115 may be formed of silicon and requires approximately 0.5 ¦ volt of forward bias for conduction. The input of trigger ¦ circuit 116 now begins to rise from ground potential. When the output of amplifier 85 exceeds t 1.0 volt, the input of trigger circuit 116 exceeds l0.5 volt, thereby actuating it ¦ and energizing winding 104. Relay switch 105 opens, disabling the circuit for winding 98. This opens switch 99,, removing power from the copier. While the copier may be momentarily turned "on" by depressing switch 94, it will immediatëly thereafter be turned "off" by amplifier 85 1'~81763 through switch 114, diode 115, trigger circuit 116, and winding 104, which opens switch 105. It is desired that the copier not be permitted to operate with significantly less charge director in the working developer than that required to bring the system to optimum performance. Significantly reduced amounts of charge director would lead to more rapid sludging of toner in tank 10, resulting not only in loss of t~er material but also more frequent maintenance.
~ Generally operation of the copier can be restored 10 ¦ by providing a fresh supply of charge director concentrate ¦ in container 16. However, the output of amplifier 85 still ¦ exceeds ~1.0 volt. To prevent this output of amplifier 85 from turning "off" the copier, switch 11~ is opened. The input of trigger circuit 116 drops to ground potential, turning "off" trigger 116, and disabling relay winding 104.
Motor 44 now causes charge director concentrate to be pumped ¦ from container 16 into tank 10. When the output of amplifier ¦ ~5 drops below +1.0 volt, switch 114 may be closed. Trigger ¦ circuit 116 will not be turned "onN, since its input i8 less ¦ than +0.5 volt. Charge director concentrate will continue to ¦ be pumped until the output of amplifier 85 drops to ground ¦ potential, turning noff" trigger circuit 87.
¦ The copier normally operates with developer ¦ temperatures Iess than 100F., where the sludging rate is acceptably small. If, for example, a cooling fan fails, then the developer temperature will rise above 100F. The output of differenti~l amplifier 130 will become positive and~through amplifier 132, actuate trigger circuit 134. This energizes winding 104, turning "off" the copier and preventing 1~81~63 ¦ any further rise in developer temperature or increase in ¦ sludging rate.
¦ It will be seen that we have accomplished the objects ¦ of our invention. We have provided a system for independently 1 controiling the quantity of carrier liquid, the quantity of ¦ of toner solids and the quantity of charge director in a ¦ workin~ liquid developer. The height or volume of carrier , liquid is controlled by the neck 24 of container 12. The ¦ quantity of toner concentrate is governed by a balanced 1 transmissivity measuring system wherein equal amounts of ¦ light fall upon matched photosensitive devices. The ¦ guantity of charge director concentrate is governed by an ¦ alternating current conductivity measurement wherein the !¦ inherent capacitance between the conductivity measuring I electrodes is compensated for by a balanced circuit employing ¦ a phase sensitive detector. To prevent either sludging of the toner concentrate or loss of control of the charge director control system, the toner concentrate contains a total amount of charge director which does not appreciably exceed that associated with the toner solids and contains little or no charge director associated with the carrier li~uid component. Our system exhibits none of the so called "fatigue" effects of prior art systems which supply excessive charge director with the toner concentrate. In such systems, the conductivity of the working developer gradually increases, causing an excessive discharge rate of the photoconductive surface and the latent image thereon. To prevent excessive sludging of the working suspension when the charge director l concentrate is exhausted or the control system fails, the ¦ copier is automatically turned off; and further operation is inhibited. The copier ls further disabled if the temperature ~81763 of the working suspension rises above a point where the sludging rate is still acceptably small. The conductivity ¦measurement is modified by correcting for changes in ¦developer conductivity caused by changes in its temperature.
¦ It will be understood that certain features and Isubcombinations are of utility and may be employed without ! reference to other features and subcombinations. This is contemplated by and is within the scope of our claims. It is further obvious that various changes may be made in " details within the scope of our claims without departing from the spirit of our invention. It is therefore to be understood that our invention is not to be limited to the ,specific details shown and described.
Having thus described our invention, what we claim iss i!
,1 !¦ .
,
Claims (22)
1. A liquid developer control system including in combination a first source of carrier liquid, a second source of toner, a third source of charge director, means for supplying carrier liquid from the first source to the liquid developer, first means for measuring the optical transmissivity of the liquid developer, means responsive to the first means for supplying toner from the second source to the liquid developer, second means for measuring the conductivity of the liquid developer, and means responsive to the second means for supplying charge director from the third source to the liquid developer.
2. A system as in Claim 1 wherein the first means includes a pair of matched photosensitive devices receiving substantially equal amounts of light from a common light source when the developer liquid has the desired transmissivity, one device responding to source light transmitted through the liquid developer.
3. A system as in Claim 1 further including means for agitating the liquid developer.
4. A system as in Claim 1 wherein the third source includes a charge director concentrate comprising charge director and carrier liquid, the concentration of charge director in the charge director concentrate being much greater than the concentration of charge director in the liquid developer.
5. A system as in Claim 1 wherein the second source includes a toner concentrate comprising toner dispersed in carrier liquid, the concentration of toner in the toner concentrate being much greater than the concentration of toner in the liquid developer.
6. A system as in Claim 5 wherein the liquid developer includes a first amount of charge director associated with the toner and a second amount of charge director associated with the carrier liquid, and wherein the toner concentrate includes a total amount of charge director not appreciably in excess of that amount of charge director associated with the toner.
7. A system as in Claim 5 further including means for agitating the toner concentrate.
8. A control system for a liquid developer comprising carrier liquid and toner and charge director components including in combination means for measuring the conductivity of the liquid developer and means responsive to the measuring means for controlling the charge director component of the liquid developer independently of the toner component.
9. A system as in Claim 8 wherein the charge director component is soluble in the carrier liquid component.
10. A control system for a liquid developer comprising carrier liquid and toner and charge director components including in combination a pair of spaced electrodes, the space therebetween being filled with liquid developer, a variable alternating voltage source, means connecting one terminal of the source to one electrode, a resistor, means including the resistor for connecting the other electrode to the other terminal of the source, and means responsive to the voltage at said other electrode for controlling one of said components.
11. A system as in Claim 10 wherein the resistor is fixed.
12. A control system for a liquid developer compris-ing carrier liquid and toner and charge director components including in combination a pair of spaced electrodes, the space therebetween being filled with liquid developer, said electrode having a certain conductance and a certain capacitance there-between, an alternating voltage source, means connecting one terminal of the source to one electrode, a capacitor having a value approximately equal to said certain capacitance, means including the capacitor for connecting the other electrode to the other terminal of the source, and means responsive to the voltage at said other electrode for controlling one of said components.
13. A system as in Claim 12 wherein the capacitor is adjustable.
14. A control system for a liquid developer comprising carrier liquid and toner and charge director components including in combination a pair of spaced electrodes, the space therebetween being filled with liquid developer, a first alternating voltage source, means connecting one terminal of the first source to one electrode, a capacitor, means including the capacitor for connecting the other electrode to the other terminal of the first source, a variable alternating voltage source, a resistor, means including the resistor for connecting said other electrode to one terminal of the variable source, means connecting the other terminal of the variable source to said other terminal of the first source, and means responsive to the voltage at said other electrode for controlling one of said components.
15. A system as in Claim 14 wherein the resistor is fixed.
16. A system as in Claim 14 wherein the capacitor is adjustable.
17. A control system for a liquid developer comprising carrier liquid and toner and charge director components including in combination a pair of spaced electrodes, the space therebetween being filled with liquid developer, an alternating voltage source, means connecting the source to one electrode, a phase sensitive detector having a signal input and a reference input, means connecting the other electrode to the signal input, means for providing a voltage having a predetermined phase shift other than 0° or 180° relative to said source, means applying said voltage to the reference input, and means responsive to the phase sensitive detector for controlling one of said components.
18. A control system for an electrostatic copier having a liquid developer comprising carrier liquid and toner and charge director components including in combination means for measuring the conductivity of the liquid developer and providing a first signal when the conductivity is slightly less than a desired value and a second signal when the conductivity is appreciably less than said value, means responsive to the first signal for increasing the charge director component, and means responsive to the second signal for disabling the copier.
19. A control system for a liquid devleoper comprising carrier liquid and toner and charge director components including in combination means responsive to the optical transmissivity of the developer for controlling the toner component and means responsive to the conductivity of the developer for controlling the charge director component independently of the toner component.
20. In a control system for a liquid developer comprising carrier liquid and toner and charge director wherein a first amount of charge director is associated with the toner and a second amount of charge director is associated with the carrier liquid, a toner concentrate including toner dispersed in carrier liquid, the concentration of toner in the toner concentrate being much greater than the concentration of toner in the liquid developer, the toner concentrate further including a total amount of charge director not appreciably in excess of that amount of charge director associated with the toner, whereby said toner concentrate is deficient in charge director.
21. A control system for an electrostatic copier having a liquid developer comprising carrier liquid and toner and charge director components including in combination means for measuring the temperature of the liquid developer, means responsive to the measuring means for providing a signal when the temperature exceeds a predetermined value, and means responsive to said signal for disabling the copier.
22. A control system for a liquid developer comprising carrier liquid and toner and charge director components including in combination means for providing a conductivity measurement of the liquid developer, means for providing a temperature measurement of the liquid developer, means responsive to the temperature measurement for modifying the conductivity measurement, and means responsive to the modified conductivity measurement for controlling one of said components.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US82961886A | 1986-02-14 | 1986-02-14 | |
| US829,618 | 1986-02-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1281763C true CA1281763C (en) | 1991-03-19 |
Family
ID=25255024
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000529691A Expired - Fee Related CA1281763C (en) | 1986-02-14 | 1987-02-13 | Liquid developer charge director control |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP0259448B1 (en) |
| JP (1) | JPH0830921B2 (en) |
| KR (1) | KR950011878B1 (en) |
| AU (1) | AU7083687A (en) |
| CA (1) | CA1281763C (en) |
| DE (1) | DE3788833T2 (en) |
| DK (1) | DK534487A (en) |
| HK (1) | HK179395A (en) |
| WO (1) | WO1987005128A1 (en) |
Families Citing this family (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0306217A3 (en) * | 1987-08-31 | 1989-08-23 | Savin Corporation | Concentrated toner solution and pressurized toner dispensing mechanism |
| US4785327A (en) * | 1987-09-03 | 1988-11-15 | Savin Corporation | Pneumatic charge director dispensing apparatus |
| DE68926393T2 (en) * | 1988-06-06 | 1996-11-21 | Indigo Nv | DOUBLE COLOR IMAGE METHOD AND DEVICE |
| US4947201A (en) * | 1988-06-06 | 1990-08-07 | Spectrum Sciences | Imaging system |
| US5108866A (en) * | 1988-06-06 | 1992-04-28 | Spectrum Sciences B.V. | Process for preparing liquid toner composition |
| DE3836465A1 (en) * | 1988-10-26 | 1990-05-03 | Lang Apparatebau Gmbh | METHOD FOR MONITORING AND / OR DIFFERENTIATING LIQUIDS USED IN BREWERY |
| JPH02176674A (en) * | 1988-12-28 | 1990-07-09 | Ricoh Co Ltd | Standby condition controller for wet copying machine |
| US4980259A (en) * | 1989-01-26 | 1990-12-25 | Savin Corporation | Liquid developer formulation |
| EP0462174B1 (en) * | 1989-03-06 | 1994-09-28 | Indigo N.V. | Liquid developer systems with self-replenishment of bulk conductivity |
| US5585900A (en) * | 1989-05-15 | 1996-12-17 | Indigo N.V. | Developer for liquid toner imager |
| US5208130A (en) * | 1989-07-31 | 1993-05-04 | Spectrum Sciences B.V. | Charge director compositions for liquid developer |
| US5003352A (en) * | 1989-10-24 | 1991-03-26 | Am International, Inc. | Liquid toner supply system and method |
| IL112731A0 (en) * | 1995-02-21 | 1995-05-26 | Indigo Nv | Imaging apparatus with temperature control |
| US5832334A (en) * | 1997-05-15 | 1998-11-03 | Minnesota Mining And Manufacturing Company | Color control system for electrographic printer |
| US6088560A (en) * | 1998-07-07 | 2000-07-11 | Imation Corp. | Liquid ink replenishment system for liquid electrographic imaging devices |
| WO2013107498A1 (en) * | 2012-01-16 | 2013-07-25 | Hewlett-Packard Indigo B.V. | Electrostatic printing |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3233781A (en) * | 1963-05-08 | 1966-02-08 | Savin Business Machines Corp | Toner control system |
| PL79948B1 (en) * | 1968-01-31 | 1975-08-30 | Mitsubishi Jukogyo Kabushiki Kaisha | |
| US3981267A (en) * | 1975-05-20 | 1976-09-21 | Savin Business Machines Corporation | Electrophotographic liquid developing system |
| JPS6040025B2 (en) * | 1975-08-06 | 1985-09-09 | キヤノン株式会社 | Surplus developer removal device |
| US4579253A (en) * | 1977-05-17 | 1986-04-01 | Savin Corporation | Toner control system |
| JPS55103570A (en) * | 1979-02-01 | 1980-08-07 | Canon Inc | Method and device for controlling of developing solution temperature |
| JPS55121459A (en) * | 1979-03-14 | 1980-09-18 | Hitachi Ltd | Developer supervising device |
| US4310238A (en) * | 1979-09-08 | 1982-01-12 | Ricoh Company, Ltd. | Electrostatic copying apparatus |
| JPS56102874A (en) * | 1980-01-19 | 1981-08-17 | Canon Inc | Developer replenishing device |
| JPS5915956A (en) * | 1982-07-20 | 1984-01-27 | Ricoh Co Ltd | Electrostatic latent image developing device |
| US4515292A (en) * | 1983-05-19 | 1985-05-07 | Burroughs Corporation | Digital implementation of toner concentration sensing apparatus |
-
1987
- 1987-02-13 WO PCT/US1987/000351 patent/WO1987005128A1/en active IP Right Grant
- 1987-02-13 AU AU70836/87A patent/AU7083687A/en not_active Abandoned
- 1987-02-13 DE DE87901903T patent/DE3788833T2/en not_active Expired - Lifetime
- 1987-02-13 CA CA000529691A patent/CA1281763C/en not_active Expired - Fee Related
- 1987-02-13 EP EP87901903A patent/EP0259448B1/en not_active Expired - Lifetime
- 1987-02-13 JP JP62501431A patent/JPH0830921B2/en not_active Expired - Lifetime
- 1987-02-13 KR KR1019870700925A patent/KR950011878B1/en not_active IP Right Cessation
- 1987-10-13 DK DK534487A patent/DK534487A/en not_active Application Discontinuation
-
1995
- 1995-11-23 HK HK179395A patent/HK179395A/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| DE3788833T2 (en) | 1994-05-11 |
| EP0259448B1 (en) | 1994-01-19 |
| WO1987005128A1 (en) | 1987-08-27 |
| KR950011878B1 (en) | 1995-10-11 |
| EP0259448A4 (en) | 1988-07-04 |
| AU7083687A (en) | 1987-09-09 |
| KR880700955A (en) | 1988-04-13 |
| DK534487D0 (en) | 1987-10-13 |
| EP0259448A1 (en) | 1988-03-16 |
| DK534487A (en) | 1987-12-09 |
| JPH0830921B2 (en) | 1996-03-27 |
| HK179395A (en) | 1995-12-01 |
| DE3788833D1 (en) | 1994-03-03 |
| JPS63502855A (en) | 1988-10-20 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |