Fuser control circuit for copying apparatus
United States Patent [1 1 Traister l FUSER CONTROL CIRCUIT FOR COPYING APPARATUS [75] Inventor: Robert L. Traister, Webster. NY.  
 [73] Assignee: Xerox Corporation, Stamford.  
 Conn.  
 [22] Filed: July 29. 1973 [2]] Appl. No.: 382.638  
  Related US. Application Data [63] Continuation of Ser. No. 312.557. Dec. 6. I972.  
 [ Apr. 29, 1975 3.475.593 l0/l969 Olofsson et al. 219/501 3.496.339 2/1970 Portas et al 2l9/50l 3.532.855 l0/l970 Van Cleave 2l9/2l6 3.783.235 l/l974 Sprague 2l9/2l6 Primary Examiner-C. L. Albritton [57] ABSTRACT A circuit for controlling power to the fuser of an electrostatic type reproduction machine in response to voltage levels across the fuser heat source as monitored by a transformer-rectifier combination. The transformer signal output is applied to an R/C circuit which controls a switching means in the fuser power line. When a preset power level is reached. the switching means triggers to interrupt power to the fuser heating source. A second R/C control circuit serves. following a time interval. to reset the switching means and resume power to the fuser heater.  
 6 Claims, 3 Drawing Figures 64 66 5 a l H 6 PxJENTEnAPazsisrs 3.881.085  
 sum 2 OF 2 F/GI 3 F USER CONTROL CIRCUIT FOR COPYING APPARATUS This is a continuation, of application Ser. No. 312,557, filed Dec. 6, 1972, now abandoned.  
  This invention relates to a control for the fuser of electrostatic type reproduction machines, and more particularly to a control designed to provide a preset power input to the fuser heater irrespective of changes in line voltage.  
  In electrostatic type reproduction machines, a toner delineated image of the original document being copied is electrostatically formed on the copy material. In order to render the image permanent, the image is fused by passing&#39;copy material through a heated oven, conventionally called a fuser. There, a combination of heat and pressure melts, i.e., fuses. the toner onto the copy material to form a permanent image.  
  In machines of this type, correct fuser temperatures are critical. If the fuser temperature is too low, fusing may be incomplete. This is most often evidenced by smearing or loss of image, particularly when the copy material is handled. If the fuser temperature is too high,  
 there is danger that the copy material may burn or char.  
  Most fusers employ some type of electric heater, for example, a quartz lamp, as a heat source. One obvious factor in the performance of this type of fuser and in the operating temperatures obtained by the fuser is line voltage. Where line voltages differ from the optimum voltages for which the fuser heater is designed, fuser temperatures may change which may result in improperly fused copies.  
  It is a principal object of the present invention to provide a new and improved fuser control.  
  It is a further object of the present invention to provide an improved current level control for the fuser heat source of a copying machine.  
  It is an object of the present invention to provide a circuit for controlling line power to the heater of a copying machine fuser designed to provide substantially constant power to the heater irrespective of changes in line voltage.  
  It is an object of the present invention to provide an improved fuser power controller effective to limit power input to the fuser heater to that required for efficient fuser operation.  
  It is an object of the present invention to provide a power controller for fusers permitting the fuser to be designed for minimum anticipated line voltages with the assurance that line voltages over and above the minimum line voltage will be accomodated without adverse effect on the fuser or fuser operation.  
 I The invention relates to an apparatus for producing copies of documents, comprising, in combination: a fuser for fixing images produced on the copies; a heater for heating the fuser; switching means to control power to the fuser heater adapted when in a first switching state to provide power to the fuser heater and when in a second switching state to interrupt power to the fuser heater; and control means for operating the switching means including first capacitance means effective on a predetermined charge to switch the switching means to the second state whereby power to the heater is interrupted, means to charge the first capacitance means in proportion to line voltages across the heater, second capacitance means effective on a predetermined charge to switch the switching means to the first switching state and provide power to the heater, and means for charging the second capacitance means in response to switching of the switch means to the second switching state.  
  Other objects and advantages will be apparent from the following description and drawings in which:  
  FIG. 1 is a schematic sectional view of an electrostatic type reproduction machine embodying the principles of the present invention;  
  FIG. 2 is an enlarged cross sectional view showing the fusing apparatus of the reproduction machine shown in FIG. 1; and  
  FIG. 3 is a schematic circuit representation of the fuser control arrangement of the present invention.  
  Referring particularly to FIGS. I and 2 of the drawings, an exemplary copier/reproduction machine, designated generally by the numeral 10 and incorporating the fuser control arrangement of the present invention, is there shown. As in all electrostatic systems such as the xerographic type machine illustrated, a light image of a document to be reproduced is projected onto the sensitized surface of a xerographic plate to form an electrostatic latent image thereon. Thereafter. the latent image is developed with an oppositely charged developing material to form a xerographic powder or&#39; toner image, corresponding to the latent image on the plate surface. The toner image is then electrostatically transferred to a support surface where it is fused by a fusing device so that the toner image is permanently adhered to the support surface.  
  In machine 10, an original document 12 to be copied is placed upon a transparent support platen l4 fixedly arranged in an illumination assembly generally indicated by the reference numeral 15 and disposed at the left end of the machine. While upon the platen, the document 12 is illuminated, thereby producing image rays corresponding to the informational areas on the original. The image rays are projected by means of an optical system onto the photosensitive surface of a xerographic plate. In the exemplary copier/reproduction machine 10, the xerographic plate is in the form of a flexible photoconductive belt 17 supported in a belt assembly 18.  
  The support assembly 18 for photoconductive belt 17 includes three rollers 20, 21 and 22 located with parallel axes at approximately the apices of a triangle. The upper roller 22 is rotatably supported on shaft 23 which in turn is rotatably driven by a suitable motor and drive means (not shown) to drive&#39;belt 17 in the direction shown by the arrow in FIG. 1. During this movement of the belt, the reflected light image of the original document 12 on platen 14 is flashed upon the photoreceptor surface of belt 17 at an exposure station 25 to produce an electrostatic latent image thereon.  
  The continued movement of photoconductive belt 17 carries the electrostatic image through a developing station 26 in which there is positioned a developer assembly generally indicated by the reference numeral &#39;28. There the latent electrostatic image is developed by means of toner through the use of a multiple magnetic brush system 29.  
  The developed electrostatic image is carried by belt 17 to the transfer station 30 where the developed image is transferred to a support surface, normally a sheet of copy paper 31, brought forward between transfer roller 32 and belt 17. In order to accomplish transfer of the developed image solely by means of the electrical bias on transfer roller 32, the copy sheet 31 is moved at substantially the same speed as belt 17. A sheet transport mechanism generally indicated at 34 is provided to advance copy sheets 31 from a paper handling mechanism generally indicated by the reference numeral 35 to transfer station 30.  
  Following transfer, the copy sheet 31 is stripped from belt 17 and conveyed through fuser 38 wherein the toner image is permanently fused or affixed thereto. Following fusing, the finished copy is discharged into output tray 39.  
  Photoconductive belt 17 comprises a photoconductive layer of selenium. which is the light receiving surface and imaging medium for the apparatus, on a conductive backing. Further details regarding the structure of the belt assembly 12 and its relationship with the machine and support therefor may be found in the copending application Ser. No. 102,312, filed Dec. 29,  
 1970, and assigned to the same assignee, now US. Pat. No. 3,730,623, issued May I, 1973.  
  Referring now to FIG. 2, fuser 38 includes a suitable housing 40 within which is disposed a lower heated fuser roll 41 and an upper pressure roll 42, rolls 41, 42 cooperating to form a nip through which the copy sheets 31 pass. Rolls 41, 42 are suitably supported for rotation and driven in unison by a suitable drive means (not shown). Pressure roll 42 is comprised of a rela tively soft material such as Teflon, Neoprene, and the like with the result that pressure contact between the rolls 41, 42 deforms the surface of pressure roll 42. In  
 .this way, an increased contact arc between the copy sheet and the heated fuser roll 41 is obtained.  
  In the exemplary arrangement illustrated, fuser roll 41 is hollow, the roll 41 being formed from a suitable heat conductive material. A source of heat such as lamp 44 is disposed therewithin. A suitable temperature variable resistor, i.e., thermistor 45 is supported on a fuser housing 40 in heat exchange relation therewith to sense temperature conditions within the fuser housing 40.  
  Referring particularly to FIG. 3 of the drawing, a control circuit is there shown schematically for controlling power input to heating lamp 44 of fuser 40 irrespective of variations in line voltage. Referring thereto, fuser heating lamp 44 is connected to a source of power, shown here as line terminals L1, L2, by suitable switching means, represented in exemplary fashion by silicon controlled rectifier SCR 46.  
  A transformer 51 has primary winding 52 thereof tapped across heating lamp 44. The secondary or output winding 53 of transformer 51 is connected to the input terminals of a suitable full wave rectifier 55. A suitable source of dc. bias or reference voltage, represented by line 58, is provided, one terminal 56 of rectifier being connected to voltage line 58. The other output terminal 57 of rectifier 55 is connected by line 64 to the control gate 65 of switching amplifier 66 as will appear.  
  A control capacitor 60 is connected in parallel with terminals 56, 57,of rectifier 55 across lines 58, 64, a suitable capacitor charging resistor 61 being provided in line 64 between rectifier terminal 57 and capacitor 60. Discharge resistor 62 parallels capacitor 60.  
  A suitable controller, such as switching amplifier 66, is provided for controlling operation of SCR 46, the output terminal of amplifier 66 being connected to the control terminal of SCR 46 by line 69. Gate 67 of amplifier 60 is set to a suitable d.c. reference voltage level from line 58, a suitable voltage controlling resistor 63 being provided therein.  
  A capacitor is connected through a suitable charging resistor 71 with line 69. Suitable voltage level resistors 74, are connected across amplifier 66 and between line 64 and ground respectively. Discharge resistor 78 is provided between amplifier gate 67 and ground, diode 79 providing a path from capacitor 70 to resistor 78.  
  During operation of copier 10, line voltages across heating lamp 44 of fuser 40 are constantly monitored by the control circuit transformer 51. The output of winding 53 of transformer 51 is rectified by rectifier 55, the resulting d.c. signal voltage serving to charge control capacitor 60 through resistor 61. When the charge on capacitor 60 reaches a predetermined level, the signal voltage in line 64 to gate 65 of amplifier 66 switches amplifier 66 to a conductive state. The resulting control signal in line 69 triggers SCR 46 to a blocking condition thereby interrupting power to fuser lamp 44.  
  It will be understood that with power to lamp 44&#34; terminated, the signal voltage generated by transformer 51 falls and control capacitor 60 discharges through resistor 62.  
  With switching amplifier 66 conductive, the signal voltage in line 69 charges capacitor 70 through resistor 71. When the charge on capacitor 70 reaches the predetermined level as determined by resistors 74, 75, amplifier 66 is switched back to a non-conductive state. With the loss of control signal in line 69, SCR 46 is reset to a conductive state and power input to heating lamp 44 is restored. As will be understood, capacitor 70, on switching of amplifier 66 to a non-conductive state, will discharge through resistor 78 in preparation for the next cycle.  
  While the invention has been described with reference to the structure disclosed, it is not confined to the details set forth, but is intended to cover such modifications or changes as may come within the scope of the following claims.  
  What is claimed is: 1. In an apparatus for producing copies of documents having a fuser for fixing images produced on the copies together with a heater for heating the fuser, the combination of: t  
 switching means to control power to said fuser heater adapted when in a first switching state to provide power to said heater and when in a second switching state to interrupt power to said heater; and  
 control means for operating said switching means including first capacitance means adapted on a predetermined charge to switch said switching means to said second state whereby power to said heater is interrupted,  
 means to charge saidfirst capacitance means in proportion to line voltages across said heater,  
 second capacitance means adapted on a predetermined charge to switch said switching means to said first state and provide power to said heater, and  
 means for charging said second capacitance means in response to switching of said switching means to said second state.  
  2. In a reproduction apparatus for producing copies of original documents, said apparatus including a fuser for permanently fixing the images produced and a heater for heating said fuser, the combination of:  
 switching means in the power circuit to said heater switchable on a predetermined control signal to a blocking condition whereby power to said heater is interrupted;  
 control switch means adapted in a first switch condition to provide said control signal and in a second switch condition to terminate said control signal; and  
 circuit means for operating said control switch means including a first control capacitor,  
 means to charge said first capacitor in proportion to the power supplied to said heater, said circuit means being adapted on a predetermined first capacitor charge to trigger said control switch means to said first switch condition whereby said switching means is switched to a blocking condition and power to said heater is interrupted, and  
 a second control capacitor chargeable upon switching of said control switch means to said first switch condition, said circuit means being adapted on a predetermined second capacitor charge to trigger said control switch means to said second switch condition whereby said switching means is switched to a conducting condition and power is provided to said heater.  
  3. A power controller for the fuser of a copying machine adapted to maintain a predetermined power input to the fuser despite variations in line voltage, comprising, in combination:  
 means monitoring power input to said fuser adapted when said predetermined power level is reached to cut off power to said fuser; and  
 means adapted following a preset timed interval to restore power to said fuser.  
  4. A power controller for the fuser of a copying machine adapted to maintain a predetermined power input to the fuser despite variations in line voltage, comprising, in combination:  
 means to cut off said fuser from the power source whenever power input to said fuser exceeds a predetermined level; and  
 means to prevent restoration of power to said fuser for a preset interval. 5. A power controller to protect the fuser of a copying machine from excessive line voltage, comprising:  
 signal generating means for monitoring power levels across said fuser adapted on a predetermined power level to generate a preset control signal;  
 means responsive to said control signal to interrupt said line voltage and terminate power to said fuser; and  
 timing means adapted following a timed interval to restore said line voltage. 6. in an apparatus for producing copies of documents having a fuser for fixing images produced on the copies together with a heater for heating the fuser, the combination of:  
 switching means to control power to said fuser heater adapted when in a first switching state to provide power to said heater and when in a second switching state to interrupt power to said heater; and  
 control means for operating said switching means including means responding to power input to said heater adapted on a preset power input to switch said switching means to said second state whereby power to said heater is interrupted; and  
 means for switching said switch means to said first state following a predetermined interval whereby to restore power to said fuser.