Patent Grant
7054572
The present invention is in the field of electrophotographic printers and copiers. More specifically this invention relates to the fuser apparatus used to fuse an image on a receiving sheet.
Most heated roller fusing systems for fixing toner images to a receiving sheet heat a roller called the fusing roller. An unheated pressure roller forms a nip with the fusing roller. The receiving sheet is fed into the nip with an unfixed toner image contacting the fusing roller. The heated fusing roller then ‘fuses’ the image to the receiving sheet.
As heat is removed from the fuser roller by several sheets of paper, the temperature sensor tells the heater to turn on full, and the fuser roller end temperatures rise slightly higher than the temperature of the fuser roller at its center. This is because more heat is being removed from the center of the fuser roller (by the receiving sheets) than from the ends. This results in greater thermal expansion at the ends of the fuser roller than at its center. This in turn produces a tentering force that keeps the trail edges of the sheets in tension and prevents wrinkling.
After a fuser has been idle for approximately 5 minutes or more, the end temperatures of the fuser roller are slightly lower than the temperature of the middle portion of the fuser roller, due to heat dissipation at the ends. The effect of this temperature profile is that the first few copies (or prints) made have a greater tendency to become wrinkled as they go through the nip because the desired tentering force is insufficient. Tentering is a force that keeps the trail edge of the sheets in cross-track tension as they pass through the fuser in order to minimize wrinkling, i.e. outwardly opposing forces on the sheet in a direction transverse to the direction of motion of the sheet and in the same plane as the sheet. This may be accomplished by providing differential overdrive in the fuser nip. In a prior art device a tentering force is generated with a fuser roll that has a larger outside diameter on the ends than at the center (a “flared” profile).
Further, after a fuser has been idle for a few minutes, the first few sheets experience a ‘temperature droop’. That is, the fuser roller temperature decreases as a function of time due to the first few sheets removing heat faster than it can be replenished. This reduces the effectiveness of the image fusing on these first sheets. An apparatus for mitigating thermal droop is disclosed in U.S. Pat. No. 4,963,943, the contents of which are fully incorporated by reference as if set forth herein.
Previous fuser roller temperature control devices have focused on maintaining a relatively constant temperature along the axis of the fuser roller. U.S. Pat. No. 5,787,321, by Nishikawa et al discloses a Temperature Controlling Device for a Fixing Unit. The purpose of this device is to prevent overheating of any portions of the fixing (fusing) roller. The control is based on a differential temperature between two sections of the roller, when the differential becomes too great, the cooling fans are either turned on or off.
In U.S. Pat. No. 6,532,348, by Allmendinger discloses a Method and Device for Generating and Adjusting Temperature Values in a Fixing Roller of a Toner Image Fixing Unit. The purpose of this device is to allow for homogeneous warming of the fixing roller along its axial length as determined on the basis of a determined core temperature of the fixing roller.
A fuser apparatus and method is desired which would create a non-homogeneous temperature along a fuser roller axial length, thus allowing the first sheets passing through to see the same tentering force as the later sheets passing through, thus preventing wrinkling on all the sheets. A method is also desired which would prevent temperature droop, thus allowing the first few sheets to be exposed to the same fuser roller temperature as the later sheets, thereby improving the quality of image fusing.
Various aspects of the invention are presented in
According to an aspect of the invention, an improved method of operation of a fuser 5 for fixing toner images to a receiving sheet 50 comprises cooling the fuser roller 10 during or after the idle condition, prior to the first receiving sheet 50 entering the fuser 5, such that the fuser roller 10 is cooled enough to cause the logic and control system 40 to activate the fuser roller heater 12. By cooling the fuser roller 10, and activating the fuser roller heater 12 prior to the arrival of the first receiver sheet 50, the fuser run condition is simulated. This helps prevent thermal droop because it eliminates the lag time between the arrival of the first receiving sheet 50 and the activation of the fuser roller heater 12.
There are many ways in which the fuser roller may be cooled. One such way is blowing a gas, such as air, onto the fuser roller 10, or drawing a gas, such as air, over the fuser 10. Another way would be to have a cooling or heat sink roller 15 in contact with the fuser roller 10 (see
In a further aspect of the invention, the fuser roller 10 is cooled for a predetermined amount of time. According to a further aspect of the invention, the fuser roller or just the middle portion 16 is cooled after the run condition, for example to prevent an over-temperature condition. In any of the embodiments of the invention, only the middle portion 16 may be cooled, although both the end portions 11 and the middle portion 16 are cooled.
Referring now
A cross-sectional view of another embodiment, nozzle 200, is presented in
The adjustable element 104 and deflecting element 206 may be independently controlled by any suitable means, for example screws, cams, levers, pneumatics, hydraulics, and electromechanical devices (including solenoids, motors and stepper motors). An array of such control elements may be provided to control a lengthwise array of elements 104 and 206.
Several temperature sensors 14 may be provided along the length of the fuser roller 10. These various temperatures give a temperature profile of the fuser roller 10.
In various aspects of the invention, the amount of heat drawn from the fuser roll is varied to achieve a desired result, including minimizing thermal droop and/or maintaining sheet tentering force. For example, receiving sheets 50 can be of various weights. Lighter weight sheets are more likely to wrinkle than heavier weight sheets. Thus lighter weight sheets need the fuser roller ends 11 hotter than do heavier weight sheets to prevent wrinkling. Thus, in a further embodiment of the invention, the heat absorbing capacity of the receiving sheet may be input to the logic and control system 40, and the logic and control system 40 adjusts the predetermined amount of time that the fuser roller 10 is cooled according to the receiver sheet 50 heat absorbing capacity. According to further embodiments, the heat absorbing capacity of the receiving sheet may be input manually, or by using a look-up table, or by sensing with a sensor, or by sensing the power being drawn by the fuser heat source. For example, heavier-weight sheets and sheets having a higher heat capacity absorb more heat during the fusing process, which could be determined in advance, and be compiled in a look-up table. Depending on the weight of the receiving sheet, the logic and control system 40 can delay the feeding of a first receiving sheet 50 until the predetermined amount of time has passed. According to a further aspect of the invention, the intensity of the fluid flow could be varied as a function of the sheet heat absorbing capacity. In further embodiments, the predetermined time could remain unchanged, and the flow intensity varied as a function of sheet heat absorbing capacity. Further, the temperature of the cooling fluid could also be modulated as a function of sheet heat absorbing capacity. Variations and combinations of these concepts are evident in light of the description provided herein.
According to another aspect of the invention, a fuser 5 for fixing toner images to a receiving sheet 50 comprises a fuser roller 10, wherein the fuser roller 10 has opposing end portions 11, and a middle portion 16, a fuser roller heater 12, a logic and control system 40, a fuser roller temperature sensor 14, a source of cooling fluid 60, and a cooling device 70 for cooling the fuser roller 10, wherein the cooling device 70 cools the fuser roller middle portion 16.
In a preferred embodiment, the cooling device 70 further comprises a separate cooling device 71 for cooling the end portions 11, such that the cooling device 70 can cool either the middle portion 16 and/or the end portions 11. To more effectively simulate the run condition, according to an aspect of the invention, the length of the middle portion 16 is related to the width of the receiving sheet 50. For example, it may be approximately equal to, less than, or greater than the width of the receiving sheet, the ideal relationship being determined empirically. In a preferred embodiment, the cooling device 70 is adjustable such that as the receiver sheet 50 width changes, the cooling device 70 adjusts to cool the corresponding fuser middle portion 16. Thus, for 11 inch paper, the middle portion would equal 11 inches, and for 14 inch paper, the middle portion would be 14 inches. This adjustment could be done on the cooling device 70 for example by having various ports available for fluid flow, and closing or opening these port according to the width needing cooling.
In a further embodiment, the fluid directing device 70 further comprises a fluid directing device for directing the fluid onto the middle portion 76, and a separate fluid directing device for directing the fluid onto the end portions 71, such that the fluid directing device 70 can direct the fluid either at the middle portion 16 or at the end portions 11. This aspect is shown in
In a steady state run condition, the fuser roller end 11 temperature is greater than the fuser roller middle 16 temperature. This results in greater thermal expansion at the ends 11 of the fuser roller 10. The expanded, hotter ends 11 of the fuser roller 10 create differential overdrive with respect to the cooler smaller center of the fuser roller 10, this results in a differential ‘tentering’ force on the receiving sheets 50. According to a further aspect of the invention, a method of creating a desired tentering force on a receiving sheet 50 in a fuser 5 for fixing toner images to a receiving sheet 50, comprises cooling the middle portion 16 of the fuser roller 10 prior to the run condition, such that the end portions 11 are hotter than the middle portion 16. This may be controlled and maintained while sheets are being fed through the fuser, for example during steady state sheet feeding. In a preferred embodiment, the middle portion 16 is approximately equal to the receiver sheet 50 width. This tentering force could further be improved by grinding the fuser roller 10 to the desired optimum shape, such that the ends 11 are slightly expanded with respect to the middle portion 16, for example in a fusing system having a pressure roll and a fuser roll, by slightly modifying the shape of the fuser roller and/or pressure roller. The variance of pressure, in the form of a gradient of pressure that changes along the direction through the nip that is parallel to the axes of the rolls, can be established, for example, by continuously varying the overall diameter of the fuser and/or pressure roller along the direction of its axis such that the diameter is smallest at the midpoint of the axis and largest at the ends of the axis, in order to give the fuser roller and/or pressure roll a subtle “bow tie” or “hourglass” shape. This causes the pair of rolls to exert more pressure on the receiver sheet in the nip in the areas near the ends of the rolls than in the area about the midpoint of the rolls. This gradient of pressure helps to prevent wrinkles and cockle in the receiver sheet as it passes through the nip. A fuser roller is disclosed in United Patent Application Publication US 2004/0023144 A1, filed Aug. 4, 2003, in the names of Jerry A. Pickering and Alan R. Priebe, the contents of which are incorporated by reference as if fully set forth herein. Alternatively or in combination, the tentering force may also be improved by varying the degree of fuser roller and/or pressure roller bending.
According to further aspects of the invention, a roller 10 shape is provided to generate a tentering force for all sheet sizes. A constant temperature may be maintained along the length of the roller 10 by selective cooling along the length of the roller 10. In addition, a center portion of the roller 10 may receive greater cooling (heat removal) than end portions of the roller 10 prior to sheet feeding, and/or the end portions of the roller 10 may receive greater cooling (heat removal) than the center portion during sheet feeding).
According to further aspects of the invention, a desired temperature gradient along the length of the roller 10 is controlled and maintained by controlling cooling (heat removal) along the length of the roller 10. This temperature gradient may be chosen, in combination with the roller 10 profile, to provide a desired tentering force on the sheets. This temperature gradient may be controlled during feeding of sheets to maintain the desired tentering force on the sheet. Alone or in combination, the temperature gradient, and thus the cooling, may be varied as a function of time to vary from one sheet to the next in order to compensate for the various sheet variables previously described herein.
The logic and control 40 may be constructed and programmed according to methods and practices know in the relevant art. In this regard, it is contemplated that those skilled in the art having reference to this specification will be readily able to derive the specific computer program instructions suitable for a given logic and control to carry out the operations described herein, in the appropriate computer language.
The concepts disclosed herein may also be applied to the pressure roll 20, as an alternative, or in combination with applying them to the fuser roll 10.
The various aspects disclosed herein may be used alone or in combination, the invention not being limited to the specific examples presented herein, including the drawings. Numerous variations are possible, and may be evident to persons of ordinary skill in the relevant art, all of which are considered to fall within the purview of the invention.
This application claims the benefit of prior provisional application Ser. No. 60/459,110 filed Mar. 31, 2003.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4963943 | Tamary | Oct 1990 | A |
| 5787321 | Nishikawa et al. | Jul 1998 | A |
| 5991565 | Hanyu et al. | Nov 1999 | A |
| 6532348 | Allmendinger | Mar 2003 | B1 |
| 6539185 | Hanyu et al. | Mar 2003 | B1 |
| 6636718 | Yura et al. | Oct 2003 | B1 |
| Number | Date | Country | |
|---|---|---|---|
| 20040190925 A1 | Sep 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60459110 | Mar 2003 | US |
