TONER DISPENSER CONTROL SYSTEM

Abstract: An apparatus in which the dispensation of toner particles used to form a highlight colour document is controlled. The percentage of the document arranged to have highlight colour portions thereon is determined, and a first signal corresponding thereto generated. A second signal corresponding to the rate of toner particle usage per document is transmitted. A third signal corresponding to the total number of documents being reproduced is produced. The first, second and third signals are multiplied to generate a control signal corresponding to the required dispense rate for the toner particles to form the highlight colour portions of the copies of the document.

Description: This invention relates generally to apparatus for controlling the concentration of toner particles used to highlight documents. Generally, the process of electrophotographic printing includes charging a photoconductive member to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive surface is exposed to a light image of an original document being reproduced. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer mixture into contact therewith. This forms a powder image on the photoconductive member which is subsequently transferred to a copy sheet. Finally, the powder image is heated to fix it permanently to the copy sheet. A common type of developer mixture frequently used in electrophotographic printing machines comprises carrier granules having toner particles adhering triboelectrically thereto. This two-component mixture is brought into contact with the photoconductive surface. The toner particles are attracted from the carrier granules to the latent image. During usage, toner particles are depleted from the developer mixture, which must be periodically replenished. Concentration of the toner particles within the developer mixture has heretofore been controlled by devices which form a sample electrostatic latent image on the photoconductive surface and subsequently develop this latent image. The density of the toner powder image is then detected by the utilization of a an infrared light source which transmits light rays on to the toner powder image developed on the sample electrostatic latent image. The intensity of the light rays reflected from the powder image is detected. This information is then processed and utilized to regulate the discharge of toner particles into the development system. Previously, systems of this type have been used with black toner particles. Attempts to employ this system with toner particles of a colour other than black have proven to be difficult and expensive because of the different reflectivities of the colour toner particles and the narrow bandwidth associated with their reflectivity. Additional hardware is necessary to adjust the gain compensation, and special algorithms are required. The capability of maintaining the concentration of colour toner particles, as well as black toner particles, at optimum levels has increased in importance with the advent of colour highlighting and multi-colour electrophotographic printing machines. In a colour highlighting electrophotographic printing machine, selected portions of the document are reproduced in a highlight colour, such as red. The remainder of the document is reproduced with black toner particles. This may be achieved by several different techniques. In one technique, selected areas of the original document are masked during the first cycle. The non-masked areas are then reproduced with black toner particles. During the next cycle, the masked areas are unmasked and the unmasked areas are masked. During this cycle, the unmasked areas are reproduced with highlight colour toner particles, e.g. red toner particles. Both the red and black toner particles are transferred to a common copy sheet. Thereafter, the copy sheet passes through the fusing device so as to affix both the red and black toner particles thereto. This forms a colour highlight copy. Alternatively, during one cycle, the portions selected to be reproduced with the colour highlight copy may be erased from the electrostatic latent image. The remainder of the electrostatic latent image is then developed with black toner particles which are subsequently transferred to the copy sheet. During the next cycle, the other portion of the electrostatic latent image is erased, the remaining portion thereon being developed with red or colour highlighting toner particles. These toner particles are then transferred to the same copy sheet. Again, this results in a copy having selected portions thereof reproduced with highlight colour toner particles. Still another approach employs a laser beam to record one electrostatic latent image corresponding to the black text regions, and another electrostatic latent image corresponding to the highlight colour text regions. These latent images are then developed with the appropriately-coloured toner particles. In any case, it is evident that at least two development systems are employed. One of the development systems may use black toner particles, with the other development system using the colour highlighting toner particles. It is, thus, necessary to maintain the concentration of not only the black toner particles at the optimum level, but also of the colour highlighting toner particles. Various techniques have hereinbefore been devised for controlling the concentration of toner particles within a developer mixture. The following patents appear to be relevant: US-A-3 409 901, 4 111 151, 4 466 731, 4 468 112 and 4 492 179. The relevant portions of the foregoing patents may be briefly summarized as follows: US-A- 3,409,901 teaches an electrophotographic printing machine for reproducing copies from a cathode ray tube. A control system integrates the control signal provided to the cathode ray tube and actuates a toner supplier to add more toner to the developer material when the sump reaches a predetermined level. The system is then zeroed and the integration restarted. US-A- 4,111,151 adds differently-coloured toner particles to a common sump, based upon the percentage of colour in the copies being made and on the copy transmissivity. After determining the transmissivity, the percentage of a particular colour is calculated to determine the number of milligrams of each colour toner used per copy. US-A- 4,466,731 describes a toner concentration control system wherein the optical reflector of a developed test area is determined and the result used to replenish with the development system toner particles. US-A- 4,468,112 describes a system which measures and integrates the total charge on a photoconductive drum. The signal is then used to control the addition of toner particles to the developer material. US-A- 4,492,179 senses the total charge on the electrostatic latent image and uses this sensed signal to control the addition of toner particles to the developer material. US-A-3,914,043 discloses a xerographic copier which is designed to have manually-selected areas of monochromatic originals reproduced in toner of a different colour, to produce highlighted copies. JP-A-6159458 discloses a polychromatic copier adapted to calculate the amount of toner of each colour necessary for each copy, and to replenish each developing unit with that amount of toner. The present invention aims at providing apparatus which calculates in advance the amount of coloured toner needed to highlight a specified area of a document, and to control the rate at which coloured toner is dispensed, to keep the amount needed in balance with that available. Accordingly the present invention provides toner dispenser control apparatus which is as claimed in the appended claims. The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic elevational view of an illustrative electrophotographic printing machine incorporating the apparatus of the present invention therein; and Figure 2 is a diagram of a control system for regulating the concentration of toner particles in the development units employed in the Figure 1 printing machine. While the present invention will hereinafter be described in connection with a preferred embodiment and method of use thereof, it is not intended to limit the invention to that embodiment or method of use. In as much as the art of electrophotographic printing is well known, the various processing stations employed in the Figure 1 printing machine will be shown hereinafter schematically and their operation described briefly with reference thereto. Referring now to Figure 1, the electrophotographic printing machine employs a belt 10 having a photoconductive surface 12 deposited on a conductive substrate 14. Photoconductive surface 12 is made from a selenium alloy with conductive substrate 14 of an aluminum alloy which is electrically grounded. The photoconductive surface 12 and conductive substrate 14 may be made from any suitable materials, and are not limited to selenium and aluminum alloys. Belt 10 moves in the direction of arrow 16 to advance successive portions of photoconductive surface 12 sequentially through the various processing stations disposed about the path of movement thereof. Belt 10 is entrained about stripping roller 18, tensioning roller 20 and drive roller 22. Drive roller 22 is mounted rotatably in engagement with belt 10. Motor 24 rotates roller 22 to advance belt 10 in the direction of arrow 16. Roller 22 is coupled to motor 24 by suitable means such as a belt drive. Belt 10 is maintained in tension by a pair of springs (not shown) resiliently urging tensioning roller 20 against belt 10 with the required spring force. Both stripping roller 18 and tensioning roller 20 are mounted to rotate freely. Initially, a portion of belt 10 passes through charging station A. At charging station A, a corona-generating device 26 charges photoconductive surface 12 to a relatively-high, substantially-uniform potential. High voltage power supply 28 is coupled to device 26. Excitation of power supply 28 causes device 26 to charge photoconductive surface 12 of belt 10. After photoconductive surface 12 of belt 10 is charged, the charged portion thereof is advanced through writing station B At writing station B, a laser system 30 includes a laser device which generates a laser beam modulated by a modulator in response to a signal from central processing unit 32 corresponding to the information for printing stored in a page memory 34. The modulated laser beam is reflected by a prism rotated in a direction for effecting scanning, then focused by a lens and guided by deflecting mirrors onto the charged portion of photoconductive surface 12. Exposure of the charged portion of the photoconductive surface by the modulated laser beam records the desired electrostatic latent image thereon. An edit control 36 also transmits a signal to the centralized processing unit which defines the portions of the page to be reproduced in a highlight colour. By way of example, the centralized processing unit 32 can be composed of a microprocessor 8080, supplied by Intel Corporation, and the related control units associated therewith. Thus, in operation, the page memory 34 transmits an electrical signal to centralized processing unit 32 indicating the information to be recorded on photoconductive surface 12. Similarly, edit control 36 transmits a signal to centralized processing unit 32 indicating those portions of the page to be reproduced in a highlight colour. The centralized processing unit controls laser system 30 so that a first electrostatic latent image is formed on photoconductive surface 12 which corresponds to the information to be reproduced in black. Thereafter, a second electrostatic latent image is recorded on the photoconductive surface corresponding to the information to be reproduced in the highlight colour. After the electrostatic latent images have been recorded on photoconductive surface 12, belt 10 advances the latent images to development station C. Development station C includes developer units 38 and 40. Developer unit 38 is adapted to develop the electrostatic latent image with highlight colour toner particles, e.g. red toner particles. Developer unit 40 is adapted to develop the electrostatic latent image with black toner particles. Each developer unit has a toner particle dispenser associated therewith. Thus, developer unit 38 includes a red toner particle dispenser, whereas developer unit 40 includes a black toner particle dispenser. Actuation of the respective toner particle dispensers is controlled by central processing unit 32. In addition, central processing unit 32 selectively actuates either developer unit 38 or developer unit 40. Thus, when the electrostatic latent image corresponding to those portions of the document to be reproduced with black toner particles is advanced to development station C, developer unit 40 is moved from an inoperative position spaced from photoconductive surface 12 to an operative position closely adjacent thereto. At this time, developer unit 40, which includes a developer roller forming a magnetic brush of developer material, develops the electrostatic latent image with black toner particles. Thereafter, centralized processing units 32 de-energizes developer unit 40 by moving it to its inoperative position. Substantially simultaneously, developer unit 38 is actuated and moved from its inoperative position spaced from photoconductive surface 12 to the operative position closely adjacent to photoconductive surface 12. Developer unit 38 includes a developer roller which forms a magnetic brush of developer material. The brush of developer material is arranged to be in contact with the photoconductive surface so that the next electrostatic latent image, i.e., electrostatic latent image adapted to be developed with red toner particles, is developed. It is apparent that, depending upon the quantity of toner particles employed to develop successive electrostatic latent images, both red and black toner particles must be furnished to the respective developer units. After the electrostatic latent images are developed, belt 10 advances the toner powder images to transfer station D. A sheet of support material 42 is advanced to transfer station D by sheet-feeding apparatus 44 including a feed roll 46 contacting the uppermost sheet of stack 48. Feed roller 46 rotates to advance the uppermost sheet from stack 48 into chute 50. Chute 50 directs the advancing sheet of support material into contact with photoconductive surface 12 of belt 10 in a timed sequence so that successive toner powder images formed thereon contact the advancing sheet of support material at transfer station D. Transfer station D includes a corona-generating device 52 which sprays ions onto the back of sheet 42. This attracts both toner powder images from photoconductive surface 12 to sheet 42. After transfer, sheet 42 continues to move in the direction of arrow 54 onto a conveyor (not shown) which advances sheet 42 to fusing station E. Fusing station E includes a fuser assembly indicated generally by the reference numeral 56, which permanently affixes the transferred powder images to sheet 42. Preferably, fuser assembly 56 comprises a heated fuser roller 58 and a back-up roller 60. Sheet 42 passes between fuser roller 58 and back-up roller 60 with the toner powder images contacting fuser roller 58. In this manner, the toner powder images are permanently affixed to sheet 42. After fusing, chute 62 advances sheet 42 to catch tray 64 for subsequent removal from the printing machine by the operator. After the sheet of support material is separated from photoconductive surface 12 of belt 10, the residual toner particles adhering to photoconductive surface 12 are removed therefrom at cleaning station F. Cleaning station F includes a rotatably mounted fibrous brush 66 in contact with photoconductive surface 12. The particles are cleaned from photoconductive surface 12 by the rotation of brush 66 in contact therewith. Subsequent to cleaning, a discharge lamp (not shown) floods photoconductive surface 12 with light to dissipate any residual electrostatic charge remaining thereon prior to the charging thereof for the next successive imaging cycle. It is believed that the foregoing description is sufficient for the purposes of the present invention to illustrate the general operation of an electrophotographic printing machine incorporating the features of the present invention therein. Referring now to Figure 2, there is shown the manner in which the concentration of toner particles within the respective developer units is regulated. As shown thereat, page memory 34 transmits an electrical signal to the central processing unit 32 which defines the text to be reproduced. Edit control 36 transmits an electrical signal to central processing unit 32 which defines the selected portion of the text which is to be in a highlight colour. Central processing unit 32 develops a signal which is a function of the percentage of area of the document to be highlighted in a colour other than black. This is achieved by dividing the signal from edit control 36 by the signal from page memory 34. The resultant signal is a function of the percentage of the document adapted to be reproduced in a highlight colour. The central processing unit 32 also determines the amount of toner required to reproduce in black toner the entire document transmitted from page memory 34. This, in turn, permits the central processing unit 32 to define the required rate of toner particle usage per document. The key operator actuates the printing machine control panel to select the total number of documents to be reproduced. In addition, the key operator can also select the portions of the copy to be reproduced in the highlight colour by selecting the coordinates of the highlight colour portion on the key pad on the control panel. The signal from the control panel corresponding to the selected colour highlight coordinates is transmitted to edit control 36 and the signal corresponding to the number of copies to be made is transmitted to central processing unit 32. The central processing unit 32 generates a third signal corresponding to the total number of documents being reproduced. Thereafter, the central processing unit 32 multiplies the first signal, corresponding to the percentage of the document colour highlighted, with the second signal, corresponding to the rate of toner particle usage per document, and the third signal, corresponding to the total number of documents being produced, to generate a control signal, corresponding to the required dispense rate for the highlight colour toner particles. This control signal is employed to regulate the discharge of toner particles from a toner dispenser, indicated generally by the reference numeral 68, associated with developer unit 38 (Figure 1). As shown in Figure 2, the centralized processing unit 32 transmits the control signal to voltage source 70. The control signal from centralized processing unit 32 regulates the output voltage from voltage source 70 so as to control the furnishing of additional toner particles to developer unit 38. Toner dispenser 68 is disposed in development unit 38. Toner dispenser 68 includes a container 72 storing a supply of toner particles therein. A suitable roller 74 is disposed in chamber 76 coupled to container 72 for dispensing toner particles into auger 78. By way of example, auger 78 comprises a helical spring mounted in a tube having a plurality of apertures therein. Motor 80 rotates the helical member of auger 78 so as to advance the toner particles through the tube. The toner particles are then dispensed from the apertures thereof into the chamber of the development system housing for use by the developer roller of developer unit 38. Energization of motor 80 is controlled by voltage source 70 connected to central processing unit 32. In this way, the amount of toner particles being dispensed into the highlight colour developer unit corresponds to the amount of toner particles being used to develop the colour highlight portion of the electrostatic latent images. This ensures that the overall concentration of the toner particles within developer unit 38 is maintained substantially constant. Central processing unit 32 also develops a fourth signal as a function of the product of the second signal, corresponding to the rate of toner particle usage per document, and the third signal, corresponding to the total number of documents being reproduced. The control signal is subtracted from the fourth signal to generate a regulating signal corresponding to the required dispense rate for the toner particles used to form the unhighlighted portions of the document, e.g. the black toner particles. This regulating signal is utilized to control the dispensing of toner particles into developer unit 40. Central processing unit 32 transmits the regulating signal to voltage source 82. The regulating signal from central processing unit 32 regulates the output voltage from voltage source 82 so as to control the furnishing of additional toner particles to developer unit 40. The toner dispenser 84 is disposed in developer unit 40. Toner dispenser 84 includes a container 86 storing a supply of toner particles therein. A suitable roller 88 is disposed in chamber 90 coupled to container 86 for dispensing toner particles into auger 92. Auger 92 is substantially identical to auger 78 and comprises a helical spring mounted in a tube having a plurality of apertures therein. Motor 94 rotates the helical element of auger 92 so as to advance the toner particles through the tube. The toner particles are then dispensed from the aperture thereof into the chamber of developer unit 40 for use by the developer roller thereof. Energization of motor 94 is controlled by voltage source 82. As previously noted, voltage source 82 is connected to central processing unit 32 and is controlled by the regulating signal generated therefrom. In recapitulation, it is evident that the system of the present invention controls the dispensing of colour highlight toner particles and black toner particles. In both cases, the rate of dispensing the toner particles into the respective developer units corresponds to the usage rate. Thus, the rate of toner particles being dispensed into the respective developer units is equal to the rate that the toner particles are being used. In this way, the toner particle concentration within each of the developer units remains substantially constant. Thus, the dispense rate for both the colour highlight toner particles and the black toner particles is regulated to maintain the concentration thereof substantially in equilibrium. The apparatus of the present invention pre-dispenses toner particles to meet the requirements for higher colour concentration documents. Known toner dispenser systems react to signals indicating the need for additional toner particles to maintain the developer material at the desired concentration, i.e. they act after the fact. This apparatus is a feed-forward system, i.e. a type of artificial intelligence, which anticipates the need for additional toner particles and supplies only enough additional toner particles to meet this need. Thus, the apparatus of the present invention minimizes contamination and material usage rates, while optimizing material life.

Claims: Toner control apparatus for controlling the rate of replenishment of coloured toner particles used to form a copy from a monochromatic original, on which copy selected portions of the original are to be reproduced in a highlight colour, characterised by: means (36) for determining the proportional areas of those portions of each monochromatic original which are to be reproduced in a highlight colour, and for generating a first signal corresponding thereto; means (32) for generating a second signal corresponding to the rate of toner particle usage per copy; means for producing a third signal corresponding to the total number of highlighted copies to be produced, and means for multiplying together the first, second and third signals to generate a control signal corresponding to the required dispense rate for the coloured toner particles to form the highlighted portions of the selected number of copies. An apparatus according to claim 1, including means (38), responsive to the control signal, for dispensing coloured toner particles. An apparatus according to claim 2, including means for generating a fourth signal as a function of the product of the second signal and the third signal, and means for subtracting the control signal from the fourth signal to generate a regulating signal corresponding to the required dispense rate for the toner particles used to form the unhighlighted portions of the document. An apparatus according to any preceding claim, including: means for generating a fifth signal corresponding to the size of the document; and means for generating a sixth signal corresponding to the size of the portions of the document which are to be reproduced in a highlight colour, with the first signal being a function of the sixth signal divided by the fifth signal. A method of controlling the rate of replenishment of coloured toner particles used to form a copy from a monochromatic original, on which copy selected portions of the original are to be reproduced in a highlight colour, characterised by: generating a first signal corresponding to the percentage of each monochromatic original which is to be reproduced in a highlight colour generating a second signal corresponding to the rate of toner particle usage per copy; generating a third signal corresponding to the total number of highlighted copies to be reproduced; and multiplying the first, second and third signals with one another to generate a control signal corresponding to the required dispense rate for the toner particles forming the highlight colour portions of the document. A method according to claim 5, including the step of generating a fourth signal as a function of the product of the second signal and the third signal, and subtracting the control signal from the fourth signal to generate a regulating signal corresponding to the required dispense rate for the toner particles used to form the unhighlighted portions of the document. A method according to claim 6, wherein said step of generating a first signal includes the steps of: generating a fifth signal corresponding to the size of the document; and generating a sixth signal corresponding to the size of the portions of the document which are to be reproduced in a highlight colour, with the first signal being a function of the sixth signal divided by the fifth signal. An electrophotographic printing machine of the type having at least two developer units with developer materials comprising different colour toner particles therein so that the document being printed has highlight colour portions, including the apparatus as claimed in any of claims 1 to 4.

Inventors: HERLEY, JAMES A.
Applicants: XEROX CORPORATION
Application year: 1987
Main classification: G03G15
IPC codes: G03G15