Patent Publication Number: US-6041208-A

Title: Method and arrangement for retrieving/supplying developing material in electrophotography forming apparatus

Description:
CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for METHOD FOR RETRIEVING/SUPPLYING DEVELOPING MATERIAL IN ELECTROPHOTOGRAPHY FORMING APPARATUS earlier filed in the Korean Industrial Property Office on the 17 th  of Apr. 1997 and there duly assigned Serial No. 12638/1997. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a developing device of an output apparatus using an electrophotography processor and, more specifically, to a method and arrangement for separately retrieving used developing material on a developing roller and supplying new developing material while balancing the retrieval of the used developing material with the supply of the new developing material in accordance with an increase in the number of papers being printed. 
     2. Related Art 
     Typically, a cleanerless developing system has a supply roller connected to a developing roller for performing the retrieval of used toner, as well as supply and friction-charging of the new toner. In such systems, the functions of retrieving used toner, supplying new toner and friction-charging the toner are simultaneously performed. 
     However, in such a system, there is a problem in that it is difficult to properly set the level of the power supply which supplies power to the supply roller of such a system, the supply roller being made of semiconductive elastic sponge. Furthermore, such systems have a limited design in that they cannot achieve a balance between the supply of the toner and retrieval of the toner while varying the resistance of the roller in accordance with an increase in the number of papers being printed. As a result, such systems are incapable of obtaining a stable image. 
     Therefore, there is a need for the development of a method for retrieving/supplying developing material in an electrophotography forming apparatus, and in particular, there is a need to provide a method for separately retrieving used developing material on a developing roller and supplying new developing material, while at the same time balancing the retrieval of the used developing material with the supplying of a new developing material in accordance with an increase in the number of pages or papers being printed. 
     The following patents are considered to be representative of the prior art relative to the present invention, and are burdened by the disadvantage discussed above: U.S. Pat. No. 5,729,267 to Shimada et al., entitled Image Forming Apparatus Having Image Transfer With Toner Cleaning Function, U.S. Pat. No. 5,726,695 to Ueda, entitled Developing Device, U.S. Pat. No. 5,717,981 to Yamanaka, entitled Developing Device For Electrophotographic Image Forming Apparatus, U.S. Pat. No. 5,678,143 to Nagahara et al., entitled Image Forming Apparatus For Collecting Residual Toner From A Drum Using An AC Voltage, U.S. Pat. No. 5,671,465 to Kimura et al., entitled Image Forming Apparatus Having A Revolver Type Developing Device, U.S. Pat. No. 5,526,099 to Katakabe, entitled Developing Device And An Image Forming Apparatus Using The Same, U.S. Pat. No. 5,473,417 to Hirano, entitled Developing Apparatus Having Toner Supply Roller Applied With Bias Voltage Varied In Accordance With Changes In Physical Properties Thereof, U.S. Pat. No. 5,420,668 to Okano, entitled Image Forming Apparatus, U.S. Pat. No. 5,333,040 to Imamiya, entitled Developing Device Having Improved Toner Transport Capacity For Use In An Image Forming Apparatus, U.S. Pat. No. 5,032,872 to Folkins et al., entitled Developing Device With Dual Donor Rollers Including Electrically Biased Electrodes For Each Donor Roller, U.S. Pat. No. 4,947,212 to Ikegawa et al, entitled Developing Apparatus With Color Dependent Toner Supply Voltage, U.S. Pat. No. 4,912,513 to Oka et al., entitled Developing Apparatus With Variable Developing Bias Voltage, U.S. Pat. No. 4,714,942 to Nakanishi, entitled Reversal Image Development Type Electrophotographic Printing System, U.S. Pat. No. 4,878,088 to Nakanishi entitled Developing Unit Of Electrophotographic Apparatus, U.S. Pat. No. 4,811,686 to Yamane, entitled Developing Device Of An Electrophotographic Machine, U.S. Pat. No. 4,545,669 to Hays et al., entitled Low Voltage Electrophotography With Simultaneous Photoreceptor Charging, Exposure And Development, U.S. Pat. No. 4,522,481 to Imai et al., entitled Toner Supply Control Method For Electrophotographic Copier, U.S. Pat. No. 4,480,911 to Itaya et al., entitled Developing Apparatus And A Developing Method Of An Electrostatic Image, and U.S. Pat. No. 4,277,003 to Tabuchi et al., entitled Developing Material Supplying Device. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method and arrangement for separately retrieving used developing material on a developing roller and supplying new developing material, while balancing the retrieval of the used developing material with the supply of the new developing material in accordance with an increase in the number of papers being printed. 
     In order to achieve the above object, the present invention is provided with a method for retrieving/supplying developing material in an electrophotography forming apparatus including a developing roller, a retrieval roller and a supply roller, the method including the steps of: rotating the retrieval roller connected with the developing roller in the same direction as the rotating direction of the developing roller; and applying voltages to the developing roller, the retrieval roller and the supply roller according to the following expression 1. 
     
         Vr&gt;Vd&gt;Vs                                                   [Expression 1] 
    
     Vr: voltage applied the retrieval roller 
     Vd: voltage applied to the developing roller 
     Vs: voltage applied to the supply roller 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of this invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which like reference symbols indicate the same or similar components, wherein: 
     FIG. 1 is a diagram showing a cleanerless developing system; and 
     FIG. 2 is a diagram showing the state where the used toner of the developing roller is retrieved and the new toner is supplied according to a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Hereinafter, a preferred embodiment of the present invention will be concretely explained with reference with accompanying drawings. Most of all, throughout the drawings, it is noted that the same reference numerals of letter will be used to designate like or equivalent elements having the same function. Further, the detailed description on known function and constructions unnecessarily obscuring the subject matter of the present invention will be avoided in the present invention. 
     FIG. 1 is a diagram showing a cleanerless developing system, wherein a supply roller 104 is connected to a developing roller 102 performing the retrieval of the used toner, and supplies and friction-charges the new toner, that is, simultaneously performs the functions of retrieving the used toner on the developing roller 102, supplying the new toner, and friction-charging the toner. However, there is a problem in that it is difficult to properly set the level of the power supply to the supply roller 104, which is made of semiconductive elastic sponge. That is why the positive (+) potential applied to the supply roller 104 to retrieve the negative (-) toner used on the developing roller 102 should be higher than the potential applied to the developing roller 102, and the negative (-) potential applied thereto should be lower than the potential applied to the supply roller 104 to supply and friction-charge the toner. However, the system of FIG. 1 has a limited design and cannot balance the supply of toner with the retrieval of toner while varying the resistance of the roller in accordance with an increase in the number of papers being printed, and is thereby incapable of obtaining a stable image. 
     FIG. 2 is a diagram showing the state where the used toner of the developing roller is retrieved and the new toner is supplied according to a preferred embodiment of the present invention. The arrangement of FIG. 2 includes a photosensitive unit 101 for forming an electrostatic latent image, a charge roller 107 for charging the photosensitive unit 101, a developing roller 102 for developing the toner at an exposing unit (at the latent image), a doctor blade 106 for doctoring the toner layer on the developing roller 102, a retrieval roller 203 for retrieving the used toner on the developing roller 102, a supply roller toner hopper for supplying and friction-charging the new toner on the developing roller 102, and an agitator 105 for supplying the toner. 
     A detailed embodiment of the present invention will now be concretely explained with reference to FIG. 2. 
     The toner on the developing roller 102, as formed by means of the doctor blade 106 of FIG. 2, is developed at a nip of the photosensitive unit 101. The remaining toner is retrieved at a nip of the supply roller 104. In order to ensure separation of the retrieval of the toner from the supply of the new toner, the retrieval roller 203 only retrieves the used toner formed on the developing roller 102, and the supply roller 104 supplies and friction-charges the new toner. 
     Meanwhile, the retrieval roller 203 has a voltage Vr of higher potential than the bias voltage Vd applied at a power supply terminal Vref2 of the developing roller 102, while rotating (counterclockwise) in the same direction as the rotating direction of the developing roller 102, thereby improving the capacity of retrieving the negative (-) toner. The supply roller 104 friction-charges the toner and applies a bias voltage Vs of lower potential than the developing bias voltage Vd so as to supply new toner while rotating (counterclockwise) in the same direction as the rotating direction of the developing roller 102, thereby improving the capacity to supply the toner. 
     Accordingly, the relationship of the developing bias voltage Vd applied to the power supply terminal Vref2 of the developing roller 102, the supply bias voltage Vs applied to the power supply terminal Vref4 of the supply roller 104, and the retrieval bias voltage Vr applied to the power supply terminal Vref3 of the retrieval roller 203 will be given in following expression 1. 
     
         Vr&gt;Vd&gt;Vs                                                   [Expression 1] 
    
     Vr: voltage applied the retrieval roller 
     Vd: voltage applied to the developing roller 
     Vs: voltage applied to the supply roller 
     For instance, when the developing bias voltage Vd is -300V, the bias voltage Vr of the retrieval roller 203 should be -200V and the supply bias voltage Vs of the supply roller 104 should be -400V to satisfy the above expression 1. 
     As is apparent from the foregoing, the present invention can constantly obtain an image of high quality owing to improvement in the capacity to retrieve used toner and supply new toner. That is why the toner is easily deteriorated and the image quality is deteriorated by the friction of the blade or the supply roller if the used toner continuously remains on the developing roller. 
     Therefore, it should be understood that the present invention is not limited to the particular embodiment disclosed herein as the best mode contemplated for carrying out the present invention, but rather that the present invention is not limited to the specific embodiments described in this specification, except as defined in the appended claims.