US 3233781 A
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Feb. 8, 1966 w. J. GRUBBS TONER CONTROL SYSTEM 2 Sheets-Sheet 1 Filed May 8, 1963 INVENTOR. WILLIAM J. 620555 QTTOEWEYS Feb. 8, 1966 w. J. GRUBBS 3,233,781
TONER CONTROL SYSTEM Filed May 8, 1963 2 Sheets-Sheet 2 /Z0 INVENTOR.
' WILL/HM J. 620555 HT TOPNEYS United States Patent O 3,233,781 TONER CONTROL SYSTEM, William J. Grubbs, New Brunswick, N.J., assignor to Savin Business Machines Corporation, New York, N.Y., a corporation of New York Filed May 8, 1963, Ser. No. 278,815 6 Claims. (Cl. 222-57) My invention relates to a toner control system and more particularly to a system for accurately regulating the proportion of toner to carrier in an electrostatic copying machine.
There are known in the prior art machines which operate on an electrostatic principle for producing copies of documents and the like. In these machines a uniform electrostatic charge is placed on a coating of photoconductive material carried by the surface on which the copy is to be produced. This may be achieved in any suitable manner known to the art as by passing the coating carrier over a charged surface. After the coating has been charged, it is exposed to a light pattern corresponding to the image to be produced. Usually this is to be a positiveto-positive photographic reproduction of the original so that the pattern can be a reflected image projected by a suitable optical system from a line drawing or continuous tone original.
As the charged surfaceisexposed to the light pattern, the electrical charge flows from the photoconductive surface in proportion to the light incident upon a given area. The result of this action is a latent electrostatic image on the surface which carries the photoconductive coating.
In order to develop the latent electrostatic image, suitably charged particles are applied to the surface. The. particles are so charged as to electrostatically adhere to the latent charged image on the carrier. This powdered material or toner is so pigmented as to contrast with the material of the coating to produce the desired visible image.
In the prior art in order to cause the toner particles to acquire the desired charge and to prevent them from pilling or balling in such a manner as wouldcause the image to be smeared or streaked, these toner particles are continuously mixed with a suitable granular material or carrier.
After'the toner has been applied to the latent electrostatice image, the image can be set by the action of heat, for example, to cause the toner particles to fuse into the coating material.
From the foregoing it will readily be appreciated that each time a copy is made, some toner is depleted from the supply. It will readily be understood further that as the proportion of toner in the mixture of toner and carrier becomes less and less, the image produced on subsequent copies will be fainter and fainter. It is thus apparent that if any satisfactory copies are to be produced, at least periodically the supply of toner in the mixture must be replenished.
I have discovered that in order to produce copies of the same quality over a relatively long period of time, the proportion of toner to carrier must be closely regulated. If there is too great a proportion of toner to carrier the resultant copy Will be smudged and unclear. If, on the other hand, too little toner is present the image is dim and it may even occur that some particles of carrier material are picked up. It has been demonstrated that if there is either too great a percentage or too small a percentage of toner to carrier, in both cases contrast disappears.
One suggestion which has been advanced in the prior art is that a predetermined amount of toner be added to the mixture on each operation of the machine. This procedure has proved to be entirely unsatisfactory. It will readily be apparent that the same amount of toner is not used in making each and every copy to be made on the machine. Thus if copies requiring a very large amount of toner are being made, the percentage of toner to carrier quickly becomes too small to make satisfactory copies. On the other hand, if a number of copies requiring only a relatively small amount of toner are made in succession, then the percentage of toner to carrier becomes too great so that the copies are smudged and contrast disappears.
I have invented a toner control system for electrostatic copying machines which overcomes the defects of machines of the prior art. My toner control system permits the relative percentage of toner to carrier to be controlled with a high degree of accuracy. My system permits the percentage of toner to carrier to be maintained at a relatively constant value. A machine incorporating my] toner control system is able to produce excellent copies with a high degree of accuracy over a relatively long period of time. My system is relatively simple for the desirable result achieved thereby.
One object of my invention is to provide a toner control system for controlling with a high degree of accuracy the percentage of toner to carrier in an electrostatic copying machine.
Another object of my invention is to provide a toner control system which maintains the percentage of tone to carrier in an electrostatic copying machine at a relatively constant value.
A further object of my invention is to provide a toner control system for an electrostatic copying machine which permits the machine to make copies of goodquality with a high degree of accuracy over a relatively long period of time.
Still another object of my invention is to provide a toner control system which is relatively simple for the result achieved thereby.
Other and further objects of my invention will appear from the following description. I
In general my invention contemplates the provision of a toner control system including means for continuously monitoring the mixture of toner and carrier in an electrostatic copying machine to determine the relative proportion of toner and carrier. Means responsive to the monitoring system adds toner to the mixture in proportion to the amount which has been withdrawn from the supply in the course of making copies.
In the accompanying drawings which form part of the instant specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:
FIGURE 1 is a schematic view illustrating one form of my toner control system.
FIGURE 2 is a schematic view of an alternate form of my toner control system.
FIGURE 3 is a schematic view of an alternate form of the electrical circuit of my toner control system.
Referring now to FIGURE 1 of the drawings, one form of my toner control system is adapted to be applied to an electrostatic copying machine (not shown) of a suitable type known to the art including a reservoir 10 holding a supply 12 of a mixture of powdered toner and powdered carrier. Suitable materials for use as toners and carriers are known in the art. In themachine either a direct or a reversed image can be obtained either by using the same carrier and choosing toner powder to give the image desired or by using the same toner and varying the carrier so as to give the desired image. Examples of toners which can be employed are asphaltum, dragons blood, zein powder, vinsol powder, resin powder and other powders which are known as electroscopic powders. In general, they are finely divided resinous materials capable of beingattracted and held by electrical charges. The carriers employed are generally magnetic materials. Alternatively, they may be granular materials having a cubic, rhombic, hexagonal or tetragonal crystalline structure. Some specific materials which have been found suitable are sodium chloride, ammonium chloride, aluminum potassium chloride, rochelle salt, sodium nitrate, aluminum nitrate, potassium chlorate, methyl methacrylate resin, granular zircon and other such materials. The particle size of the carriers can vary from '50 to +325 mesh with the optimum size being within the range from 100 to +140 mesh. The surfaces of the carriers can be left as is or they may be chemically treated to produce a desired triboelectric relationship with the particular toner used.
In general the toners which are dyed or pigmented resinaceous powders are so chosen as to maintain a specific triboelectric relationship with the particular carrier being employed. The particle size range of the toners may vary from 1 to 50 microns with the optimum range being from 5 to 20 microns. It will readily be understood that the percentage by weight of toner to carrier will vary from machine to machine. However, in any given machine there exists an optimum range which will .produce the best picture with the least background. Generally speaking, the toner may vary from about 1.5% to 12.5% by weight to carrier with the optimum range being from about 1.5 by weight to about 4% by weight.
It is to be understood the terms positive and negative as aplied to toners which are used to develop elec trostatic latent images created through an electrophotographic or electrostatic process have come to mean that a positive toner is a material which in combination with a carrier will give an exact or direct copy of the original item. A negative toner in combination with a particular carrier will give a reversed copy of the original item. Positive and negative toners are chosen with reference to a particular carrier. If an attempt is being made to develop an electrostatic image of negative charge so as to obtain a direct copy of the original item, a toner-carrier combination would be chosen which will produce a posi-' tive charge on the toner so as to be attracted to the image areas. If on the other hand it is desired to obtain a re-' versed copy of the original, a toner-carrier combination would be chosen which will develop a negative charge on the toner so as to be repelled from the image to the nonimage areas. Consequently, where the electrostatic image is negative a positive toner has a positive charge whereas a negative toner has a negative charge. However, where the electrostatic image is positively charged then a positive toner has a negative charge and a negative toner has a positive charge. It will readily be appreciated from the following explanation that my toner control system operates with any combination of toner and carrier without regard to the fact of whether a positive toner or a negative toner is being used. If the latent electrostatic image is negative, the carrier and toner must be so related on the triboelectric scale that the toner acquires a positive charge when the particles are tumbled. The potential difference in the charges developed by two contacting dielectrics is proportional to the difference between their dielectric constants, the material having a greater constant becoming positive.
The mixture 12 may be applied to the latent electrostatieimage in any suitable manner. Where a magnetic carried is employed, a roller and a magnet may be employed to pick up particles from the mixture and, at the point of contact between the roller and the image, the toner particles will be transferred to the image while the carrier particles remain on the roller. Any suitable means is employed to agitate the mixture 12 constantly so that the carrier and toner particles are thoroughly mixed at all points throughout the reservoir.
In the form of my toner control system illustrated in FIGURE 1, the casing holding the mixture 12 has a window 14 in a wall 16 thereof so that particles of the mixture 12 are visible from outside the casing. I connect a lamp 18 across the terminals 20 and 22 of a suitable source of voltage to light the lamp to produce a beam 24 of light which travels from the lamp and through the window 14 so as to impinge on the mixture 12 within the reservoir 10. From the explanation given hereinabove, it will readily be appreciated that the toner particles are darker than are the carrier particles. Thus the amount of light from the beam 24 which is reflected from the mixture 12 will be a measure of the reflectivity of the mixture. I have represented the reflected light schematically by the beam 26. It will readily be understood that when the proportion of toner to carrier in the mixture 12 becomes less, more of the light from beam 24 will be reflected so that the beam 26 becomes more intense.
I provide my system with a means for measuring any change in intensity of the beam 26. I connect respective resistors 28 and '50 and two light-sensitive elements 32 and 34 in a Wheatstone bridge. I select the resistors 28 and 30 to be of substantially the same value and select the devices 32 and 34 to be as nearly identical as is possible. These devices 32 and 34 may for example be suitable semiconductor photoconductive elements. As is known in the art, these devices become more conductive as the amount of light impinging thereon increases. I connect a suitable source of potential such as a battery 36 across the input terminals 38 and 40 of the Wheatstone bridge. As is known in the art, when the bridge is unbalanced a potential difference exists across the output terminals 42 and 44 of the bridge.
I position the device 32 within a housing or shield 46 to prevent any of the reflected light of beam 26 from reaching this device while permitting light represented by a beam 48 from lamp 18 to impinge on the device. I connect a resistor 50 across the device 34 and provide a brush 52 which can be positioned to balance the bridge including resistors 28 and 30 and devices 32 and 34 when the mixture 12 has the desired proportion of toner to carrier. As is known in the art, when the bridge is balanced there is no difference in potential across the output terminals 42 and 44 of the bridge. j
My toner control system includes a transistor 54 having a base 56 connected to terminal 44, an emitter 58 connected to terminal 42 and a collector 60. Transistor 54 is a p-n-p transistor which will conduct when the base 56 is at a lower potential than is the emitter 58. This condition results when the output terminal 44 of the bridge is at a lower potential than is the output terminal 42.
I connect a battery 62 and a relay winding 64 in the collector circuit of the transistor 54. When the transistor conducts, win-ding 64 is energized to cause its armature 66 to close a normally open switch 68 to complete the circuit of a solenoid 70 to a source having terminals 72 and 74.
My toner control system includes a hopper 76 containing a supply of toner. A guide 78 carries a bracket 80 which supports a plug 82 which fits into a seat formed by beveling the lower end of the outlet 84 of the hopper 76. A spring 86 normally positions the guide 78 at a location at which the plug 82 closes the outlet 84.
Solenoid 70 has an armature 88 pivotally connected to a lever 90 rotatably supported on a pin 92 carried by a bracket 94 on the hopper. The other end of lever 9tl'is forked to provide arms having slotted ends which engage pins 96 on the guide 78. When the solenoid 70' is energized, it draws its armature upwardly as viewed in FIGURE 1 to rotate the lever 90 in a counterclockwise direction to move the plug 82 and the guide 78'- downwardly. In this position of the parts, toner is per-- mitted to flow out of the hopper 76 and through the guide 78 into the casing 10. It will be seen that the guide 78 extends through an opening 98 in casing 10.
I provide my control system with means for changing the relative proportion of toner to carrier in the mixture 12. I accomplish this by connecting a variable resistor having a resistance winding 100 and a brush 102 across the resistor 28. It will readily be seen that as I decrease the amount of resistance of winding 100 in the circuit, I add more toner to the mixture 12. Once this value has been set and the light balancing resistor 50 has been adjusted, then this system operates to maintain the average proportion of toner to carrier at a relatively constant value over a long period of operation of the machine.
There are known in the art electrostatic copying machines which employ liquid developers. For example, the developer may be an emulsion consisting of immiscible fiuid carrier and toner phases, the latter being composed of a suspension of developer particles in an insulating liquid. The toner particles are carried on the surface of globules of the fluid carrier phase. The liquid developer may be adispersion of finely divided opaque particles such, for example, as carbon, colored resins and glass in an insulating liquid. The developer may also be a suspension of carbon black in kerosene or another suitable dielectric liquid. It has also been suggested that nonflammable, nontoxic developers be provided. For example, trichloromonofluoromethane or trichlorotrifluoroethane are used with a coloring matter such as phthalocyanine blue and a fixative such as an alkyd resin. These are merely examples of some liquid developers which can be used. As is pointed out hereinabove, my toner control system is applicable to any suitable liquid developer as well as to solid phases.
Referring now to FIGURE 2, I have shown a form of my toner control system which is particularly adapted to controlling the amount of toner in a liquid developer. In this case the tank It) contains a liquid developer 194 of the type mentioned hereinabove. Any suitable apparatus similar to that discussed hereinabove in connection with the form of my invention shown in FIGURE 1 and adapted to dispense the toner can be employed with the apparatus shown in FIGURE 2. Suitable liquid agitating apparatus is used to keep the developer 104 uniformly mixed throughout the tank Where I employ a liquid developer, rather than relying on the refiectivity of the developer as in the form of my invention shown in FIGURE 1, I rely on the light transmitting properties of the developer. For this reason I dispose a mirror 106 within the tank 10 at a short distance behind the window 14. In this case the amount of light represented by the beam 26 is a measure of the light transmission through the liquid 104. Since all the other parts of the form of my device adapted to handle a liquid developer are substantially the same as those shown in FIGURE 1, they have not been illustrated in detail in FIGURE 2.
Referring now to FIGURE 3, I have shown an alternate form of my invention which is somewhat simpler and less expensive than is the particular arrangement illustrated in FIGURE 1. It will readily be apparent that in the form of my invention shown in FIGURE 3, I replace the battery 36 with a transformer winding 108 having a capacitor 116 connected thereacross for supplying potential to the bridge through a rectifier 112. A similar arrangement of a winding 114, a rectifier 116 and a capacitor 118 replaces the battery 62 while a winding 120 supplies potential to the lamp 18. This arrangement requires less space, weighs less and has a longer life without servicing than does the form of my invention shown in FIGURE 1.
In operation of the form of my invention shown in FIGURE 1, I first adjust the resistor 50 to balance the two devices 32 and 34. I then set brush 102 to a position corresponding to the desired percentage by weight of toner to carrier in the mixture 12. With the bridge in balance, transistor 54 does not conduct and relay winding 64 is deenergized. Now in the course of operation of the machine the supply of toner is depleted. When the proportion of toner falls below that corresponding to the setting of brush 102, more light is reflected onto the device 34 so that its conductivity increases and the potential at output terminal 44 drops. Thus the base of transistor 54 is at a lower potential than is the emitter 58 so that the transistor conducts to energize winding 64 to close switch 63 to energize solenoid 70 to rock lever to move plug 82 away from its seat to permit toner to fall into the reservoir 10. As soon as this additional toner falls into the reservoir, it is immediately mixed with the carrier so that the amount of light refiected as represented by beam 26 is reduced and the conductivity of the device 34 decreases. Owing to this decrease in conductivity of the device 34, the potential at point 44 rises until transistor 54 cuts off to deenergize winding 64 to cause switch 68 to open so that solenoid 70 is deenergized and spring 86 moves the plug 82 back into engagement with its seat. It will readily be seen that my system adds to the mixture 12 substantially as much toner as has been taken away in the course of operation of the machine.
If for any reason I desire to increase the proportion of toner in the mixture, I reduce the amount of resistance introduced into the circuit by resistor so that the potential of the emitter 58 rises to turn the transistor on to increase the amount of toner in the mixture until the resistance of the device 34 increases to a point at which the transistor 54 cuts off. To decrease the proportion of toner I increase the amount of resistance introduced into the circuit by resistor 100 and allow normal operation of the machine to reduce the proportion of toner.
The operation of the form of my invention shown in FIGURE 3 is substantially the same as that outlined above in connection with the form of my invention shown in FIGURE 1. The diiference between the two arrangements is that where my system is used on a machine which operates with liquid developer then I prefer to rely on the transmissivity of the developer rather than on its reflectivity. Preferably I employ a circuit of the type shown in FIGURE 3 owing to practical considerations.
It will be seen that I have accomplished the objects of my invention. I have provided a toner control system which permits an electrostatic copying machine to make good copies with a high degree of consistency over a relatively long period of time in use. My system maintains the proportion of toner to carrier substantially constant. My system is simple for the result achieved thereby. I can readily change the proportion of toner to carrier as desired.
It is to be understood that while I have shown and described my system as employing a relatively dark toner which is to be picked up by the surface on which the copy is produced and a relatively lighter carrier, I could as well arrange my system to operate with a relatively lighter material which is picked up to make a copy on a dark surface in combination with a relatively dark carrier.
It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.
Having thus described my invention, what I claim is:
1. Apparatus for regulating the relative proportion of mixed materials having divergent optical characteristics including in combination a container for holding a supply of a mixture of said materials in a predetermined relative proportion, a bridge comprising a pair of light-sensitive arms, a source of light positioned adjacent said container to direct light toward said supply, means comprising a shield disposed between said arms to direct light from said source directly to one of said arms and from said material to the other of said arms, means normally balancing said bridge when said materials are in said predetermined relative proportion and means responsive to unbalance of said bridge for regulating said mixture to said predetermined portion.
2. Apparatus for regulating the relative proportion of mixed materials having divergent optical characteristics including in combination a container holding a supply of a mixture of said materials in a predetermined relative proportion, a bridge circuit comprising a light-responsive arm, means for directing light to said mixture and from said mixture to said light-responsive arm, means for balancing said bridge when the light directed to said element corresponds to said predetermined relative proportion and means responsive to unbalance of said bridge when light directed to said light-responsive arm deviates from that corresponding to said predetermined relative proportion for regulating said mixture to said predetermined proportion.
3. Apparatus for regulating the relative proportion of mixed materials having divergent optical characteristics including in combination a container holding a supply of a mixture of said materials in a predetermined relative proportion, a bridge comprising a light-responsive arm and a variable control arm, means for directing light to said mixture and from said mixture to said light-responsive arm, means comprising said control arm for balancing said bridge when the light directed from said mixture to said light-responsive arm corresponds to said predetermined relative proportion and means responsive to unbalance of said bridge for regulating said mixture to said predetermined proportion, said control arm being adapted to be varied to change said predetermined proportion.
4. Apparatus for regulating the relative proportion of mixed materials having divergent optical characteristics including in combination a container holding a supply of a mixture of said materials in a predetermined relative proportion, a bridge comprising a pair of respective lightsensitive arms, a source of light, means for directing light from said source directly to one of said light-sensitive arms and from said source to said mixture and from said mixture to said other light-sensitive arm, means comprising a light-balancing resistor for normally balancing said bridge when the light from said mixture to said other arm corresponds to said predetermined proportion and means responsive to an unbalance of said bridge for regulating said mixture to said predetermined proportion.
5. Apparatus for regulating the relative proportion of a mixture of a relatively light carrier material and a relatively dark toner material including in combination a container holding a supply of a mixture of said materials in a predetermined relative proportion, a bridge comprising a photoconductive element in one of the arms of said bridge, a light source, means for directing light from said source to said mixture, means mounting said photoconductive element in a position to receive reflected light from said mixture, means normally balancing said bridge when the reflected light from said mixture corresponds to said predetermined proportion and means responsive to unbalance of said bridge for regulating said mixture to said predetermined proportion.
6. Apparatus for regulating the relative proportion of mixed materials having divergent optical characteristics including in combination a container holding a supply of a mixture of said materials in a predetermined relative proportion, a bridge including a first arm comprising variable control impedance, a second arm comprising a first light-sensitive element and a third arm comprising a second light-sensitive element and a light-balancing impedance, a source of light, means for directing light from said source directly to one of said light-sensitive elements and for directing light from said source to said mixture and from said mixture to the other light-sensitive element, means comprising said variable control impedance and said light-balancing impedance for normally balancing said bridge when said mixture is in said predetermined proportion and means responsive to unbalance of said bridge for regulating said mixture to said predetermined proportion, said variable control resistor being adapted to be varied to change said predetermined proportion.
References Cited by the Examiner UNITED STATES PATENTS 1,002,635 9/1911 Bratkowski 2502l8 X 1,678,884 7/1928 Sweet 250218 X 1,943,684 1/1934 Martin et a1. 250218 X 3,094,049 6/1963 Snelling 1.7
OTHER REFERENCES Textile Worl-d, Dec. 1948, vol. 98, No. 12, pages 103 to 106 (copy in Scientific Library). 7
CHARLES A. WILLMUTI-I, Primary Examiner.
WILLIAM D. MARTIN, Examiner.