Patent Grant
9354567
This patent application claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Applications Nos. 2010-230419 and 2011-106196, filed on Oct. 13, 2010 and May 11, 2011, respectively, the entire disclosure of each of which is hereby incorporated by reference herein.
1. Field of the Invention
The present invention relates to a fixing device, a fixing device control method, and an image forming apparatus, and more particularly, to a fixing device that fixes a toner image in place on a recording medium with heat and pressure, a control method for use in such a fixing device, and an electrophotographic image forming apparatus, such as a photocopier, facsimile machine, printer, plotter, or multifunctional machine incorporating several of those imaging functions, which employs a fixing device with a heating control capability.
2. Description of the Background Art
In electrophotographic image forming apparatuses, such as photocopiers, facsimile machines, printers, plotters, or multifunctional machines incorporating several of those imaging functions, an image is formed by attracting toner particles to a photoconductive surface for subsequent transfer to a recording medium such as a sheet of paper. After transfer, the imaging process is followed by a fixing process using a fixing device, which permanently fixes the toner image in place on the recording medium by melting and setting the toner with heat and pressure.
Various types of fixing devices are known in the art, most of which employ a pair of generally cylindrical looped belts or rollers, one being heated for fusing toner (“fuser member”) and the other being pressed against the heated one (“pressure member”), which together form a heated area of contact called a fixing nip through which a recording medium is passed to fix a toner image onto the medium under heat and pressure.
Those types of fixing devices may be operated with different types of recording media varying in terms of basis weight or mass per unit area, surface properties imparted, for example, by coating material, etc., depending on specific requirements of print jobs being processed. Also, the fixing device can experience varying operational conditions depending on specific applications of an image forming system in which the process is installed. For example, some printers execute print jobs at a low processing speed with an elongated period of deactivation between consecutive print jobs, and others execute a large number of print jobs at a high processing speed sequentially and continuously.
The inventors have recognized that such variations in operational conditions can result in variations in the amount of heat applied through the fixing nip. This is particularly true with a today's power-efficient fixing device that has a heater for heating a fuser member to a regulated heating temperature but no dedicated heater for a pressure member, wherein the pressure member exhibits a relatively low heat capacity and therefore is susceptible to variations in operational temperature. Variations in the amount of heat applied through the fixing nip often take place due to variations in operational temperature of the pressure member, which can result in excessive amounts of heat applied to the recording medium. Inconsistent heating through the fixing nip, if not corrected, would adversely affect quality of the toner image processed through the fixing device, since good fixing performance depends on the ability to heat a recording medium to a consistent, desired temperature sufficient for fusing and melting toner particles through the fixing nip.
To date, various methods have been proposed to provide a fixing process controllable against variations in environmental and operational conditions.
For example, an image forming apparatus may be given a controller that modifies a control parameter of an electrophotographic imaging process based on user-specified information representing properties of a recording medium in use. Alternatively, an image forming apparatus may employ a controller that controls operation of a fixing process based on physical properties of a recording medium, such as surface texture, thickness, moisture content, etc., detected during operation.
Exemplary aspects of the present invention are put forward in view of the above-described circumstances, and provide a novel fixing device for fixing a toner image printed on a recording medium having a specific heat capacity.
In one exemplary embodiment, the fixing device includes a rotatable fuser member a heater, a rotatable pressure member, a thermometer, and a feedback controller. The rotatable fuser member is subjected to heating. The heater heats the fuser member to a heating temperature. The rotatable pressure member is disposed opposite the fuser member. The fuser member and the pressure member are pressed against each other to form a fixing nip therebetween, through which the recording medium is conveyed with a first, printed surface thereof facing the fuser member and a second, non-printed surface thereof facing the pressure member, so as to fix the toner image in place under heat and pressure as the fuser and pressure members rotate together. The thermometer is disposed adjacent to the pressure member to detect an operational temperature of the pressure member. The feedback controller is operatively connected with the thermometer to control the heating temperature according to the detected operational temperature, so that the recording medium exhibits a substantially constant post-fixing temperature downstream from the fixing nip regardless of the heat capacity of the recording medium.
Other exemplary aspects of the present invention are put forward in view of the above-described circumstances, and provide a novel method for use in a fixing device.
In one exemplary embodiment, the fixing device that fixes a toner image printed on a recording medium having a specific heat capacity, and includes a rotatable fuser member subjected to heating to a heating temperature, and a rotatable pressure member disposed opposite the fuser member. The fuser member and the pressure member are pressed against each other to form a fixing nip therebetween. The method includes the steps of conveyance, detection, and control. The conveyance step conveys the recording medium under heat and pressure through the fixing nip. The detection step detects an operational temperature of the pressure member during passage of the recording medium through the fixing nip. The control step controls the heating temperature according to the detected operational temperature, so that the recording medium exhibits a substantially constant post-fixing temperature downstream from the fixing nip regardless of the heat capacity of the recording medium.
Still other exemplary aspects of the present invention are put forward in view of the above-described circumstances, and provide an image forming apparatus incorporating a fixing device.
A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
In describing exemplary embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve a similar result.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, exemplary embodiments of the present patent application are described.
As shown in
The image forming apparatus 100 comprises a tandem color printer that forms a color image by combining images of yellow, magenta, and cyan (i.e., the complements of three subtractive primary colors) as well as black, consisting of four electrophotographic imaging stations 12C, 12M, 12Y, and 12K arranged in series substantially laterally along the length of an intermediate transfer belt 11, each forming an image with toner particles of a particular primary color, as designated by the suffixes “C” for cyan, “M” for magenta, “Y” for yellow, and “K” for black.
Each imaging station 12 includes a drum-shaped photoconductor rotatable counterclockwise in the drawing, facing a laser exposure device 13 therebelow, while surrounded by various pieces of imaging equipment, such as a charging device, a development device, a transfer device incorporating an electrically biased, primary transfer roller 25, a cleaning device for the photoconductive surface, etc., which work in cooperation to form a primary toner image on the photoconductor 3 for subsequent transfer to the intermediate transfer belt 11 at a primary transfer nip defined between the photoconductive drum and the primary transfer roller 25.
The intermediate transfer belt 11 is trained around multiple support rollers to rotate counterclockwise in the drawing, passing through the four primary transfer nips sequentially to carry thereon a multi-color toner image toward a secondary transfer nip defined between a secondary transfer roller 21 and a belt support roller.
Below the laser exposure device 13 is a sheet conveyance mechanism 14 including one or more input sheet trays 15 each accommodating a stock of recording media such as paper sheets S and equipped with a feed roller 17. The sheet conveyance mechanism 14 also includes a pair of registration rollers 19, an output unit formed of a pair of output rollers 23, an in-body, output sheet tray 18 located underneath the image scanner 200, and other guide rollers or plates disposed between the input and output trays 15 and 18, which together define a primary, sheet conveyance path P for conveying a recording sheet S from the input tray 15, between the registration rollers 19, then through the secondary transfer nip, then through the fixing device 20, and then between the output rollers 23 to the output tray 18. A pair of secondary, sheet conveyance paths P1 and P2 are also defined in connection with the primary path P, the former for re-introducing a sheet S into the primary path P after processing through the reversal unit 300 or upon input in a manual input tray 36, and the latter for introducing a sheet S from the primary path P into the reversal unit 300 downstream from the fixing device 20.
During operation, the image forming apparatus 100 can perform printing in various print modes, including a monochrome print mode and a full-color print mode, as specified by a print job received from a user.
In full-color printing, each imaging station 12 rotates the photoconductor drum clockwise in the drawing to forward its outer, photoconductive surface to a series of electrophotographic processes, including charging, exposure, development, transfer, and cleaning, in one rotation of the photoconductor drum.
First, the photoconductive surface is uniformly charged by the charging roller and subsequently exposed to a modulated laser beam emitted from the exposure device 13. The laser exposure selectively dissipates the charge on the photoconductive surface to form an electrostatic latent image thereon according to image data representing a particular primary color. Then, the latent image enters the development device which renders the incoming image visible using toner. The toner image thus obtained is forwarded to the primary transfer nip at which the incoming image is transferred to the intermediate transfer belt 11 with an electrical bias applied to the primary transfer roller 25.
As the multiple imaging stations 12 sequentially produce toner images of different colors at the four transfer nips along the belt travel path, the primary toner images are superimposed one atop another to form a single multicolor image on the moving surface of the intermediate transfer belt 11 for subsequent entry to the secondary transfer nip between the secondary transfer roller 21 and the belt support roller.
Meanwhile, the sheet conveyance mechanism 14 picks up a recording sheet S from atop the sheet stack in the sheet tray 15 to introduce it between the pair of registration rollers 19 being rotated. Upon receiving the incoming sheet S, the registration rollers 19 stop rotation to hold the sheet S therebetween, and then advance it in sync with the movement of the intermediate transfer belt 11 to the secondary transfer nip at which the multicolor image is transferred from the belt 11 to the recording sheet S with an electrical bias applied to the secondary transfer roller.
After secondary transfer, the recording sheet S is introduced into the fixing device 20 to fix the toner image in place under heat and pressure. The recording sheet S, thus having its first side printed, is forwarded to a sheet diverter, which directs the incoming sheet S to an output roller pair 23 for output to the in-body output tray 18 along the primary path P when simplex printing is intended, or alternatively, to the media reversal unit 300 along the secondary path P2 when duplex printing is intended.
For duplex printing, the reversal unit 300 turns over the incoming sheet S for reentry to the sheet conveyance path P along the secondary path P1, wherein the reversed sheet S again undergoes electrophotographic imaging processes including registration through the registration roller pair 19, secondary transfer through the secondary transfer nip, and fixing through the fixing device 100 to form another print on its second side opposite the first side.
Upon completion of simplex or duplex printing, the recording sheet S is output to the in-body output tray 18 for stacking inside the apparatus body, which completes one operational cycle of the image forming apparatus 100.
As shown in
At least one of the opposing rollers 1 and 2 forming the fixing nip N is stationary or fixed in position with its rotational axis secured in position to a frame or enclosure of the apparatus body, whereas the other can be positioned with its rotational axis movable while elastically biased against the opposite roller, so that moving the positionable roller relative to the stationary roller allows adjustment of a width w of contact between the fuser and pressure members, across which the fixing nip N extends in a direction X of conveyance of a recording sheet S.
In the present embodiment, the heat roller 4 comprises a hollow cylindrical body of thermally conductive material within which the heater 5 is accommodated. The heater 5 may be any suitable heat source, including electrical resistance heater, such as a halogen lamp or a ceramic heater, as well as electromagnetic induction heater (IH), which produces heat according to a duty cycle or power supply being input per unit of time. The heat roller 4 in conjunction with the internal heater 5 serves to heat the fuser belt 3 as the belt 3 rotates around the internally heated roller 4.
The pressure roller 2 comprises a cylindrical body of sponged material that has relatively low thermal capacity, with no dedicated heater disposed adjacent to the pressure roller 2. Alternatively, instead, the pressure roller 2 may have a dedicated heater, in which case the heater serves to maintain the pressure roller 2 at a sufficiently high temperature to allow immediate activation of the fixing device after an extended period of deactivation.
During operation, the fuser roller 1 rotates in a given rotational direction (i.e., counterclockwise in the drawing) to rotate the fuser belt 3 in the same rotational direction, which in turn rotates the pressure roller 2 in the opposite rotational direction (i.e., clockwise in the drawing). The heat roller 4 is internally heated by the heater 5 to heat a length of the rotating belt 3 to a heating temperature Theat, so as to sufficiently heat and melt toner particles through the fixing nip N.
As the rotary fixing members rotate together, a recording sheet S bearing an unfixed, powder toner image passes through the fixing nip N in the sheet conveyance direction X to fix the toner image in place, wherein heat from the fuser belt 3 causes toner particles to fuse and melt, while pressure from the pressure roller 2 causes the molten toner to settle onto the sheet surface.
Throughout the fixing process, the recording sheet S moves at a given conveyance speed V, and resides in the fixing nip N during a period of nip dwell time t depending on the conveyance speed V and the width w of the fixing nip N. The recording sheet S after fixing exits the fixing nip N to reach a post-fixing position PF downstream from the fixing nip N where the sheet S exhibits a post-fixing temperature Tpf depending on the amount of heat applied through the fixing nip N.
As used herein, the term “post-fixing temperature” describes a temperature of a recording medium at a post-fixing position adjacent to and immediately downstream from an exit of a fixing nip, which can be obtained through measurement using a thermometer detecting temperature of the recording medium at the post-fixing position, or through estimation based on readings of a thermometer detecting temperature outside the fixing nip as well as one or more operational parameters related to heating of the recording medium. Also, the term “nip dwell time” herein denotes a period of time during which a particular imaginary point in the recording medium conveyed at a particular conveyance speed passes across the entire width of the fixing nip, which may be obtained by dividing the width of the fixing nip by the conveyance speed of the recording medium.
Quality of a toner image fixed on a recording medium is dictated by various factors, such as adhesion of toner to the recording medium, which determines resistance against undesired transfer or flaking of toner off the printed surface, as well as surface texture or glossiness of toner fused and solidified on the recording medium. The inventors have recognized that such quality factors of the fixing process is highly correlated with the post-fixing temperature, which well reflects an amount of heat applied to the recording medium through the fixing nip to cause toner to exhibit adhesion and gloss after completion of the fixing process.
Experiments I and II
Experiments have been conducted to investigate a relation between post-fixing temperature and imaging quality of a fixing process as dictated by adhesion and glossiness exhibited by toner fixed onto a recording medium, using experimental equipment as shown in
As shown in
Downstream from the fixing nip N is a thermometer 107, comprising a thermal radiation, non-contact temperature sensor with laser sighting, model FT-H20, commercially available and manufactured by Keyence Corporation, which can measure temperature by sensing thermal radiation from an object aimed at with a laser beam L.
The thermometer 107 was used to measure a post-fixing temperature of the recording sheet S with its laser beam L directed to a post-fixing position PF at a distance d from a downstream end of the fixing nip N. The distance d was sufficiently short, so as to precisely measure the temperature immediately after exiting the fixing nip N, for example, ranging from approximately 10 mm to approximately 30 mm, which was equivalent to a time interval of approximately 50 msec to approximately 300 msec during which the recording sheet S proceeded at a typical conveyance speed through the fixing process.
With additional reference to
As shown in
In Experiment I, the experimental equipment depicted in
Specifically, the recording sheet S was first marked with a centerline CL (
Multiple image samples were prepared in a similar manner, each of which was subjected to visual inspection, in which the toner image was evaluated in terms of adhesion of toner to the recording sheet through comparison with patches of reference images, numerically rated and ranked from “1” having significant flake-off of toner, denoting a lowest level of toner adhesion, to “5” with substantially no toner flaking, denoting a highest level of toner adhesion, as shown in
As shown in
In Experiment II, the experimental equipment depicted in
Multiple image samples were prepared in a similar manner, each of which was subjected to visual inspection, in which the toner image was evaluated in terms of glossiness measured using a commercially available glossmeter.
As shown in
The Experiments I and II demonstrate that there is a strong linear correlation between the post-fixing temperature Tpf and the imaging quality dictated by toner adhesion and image glossiness. Such experimental results indicate that the post-fixing temperature Tpf can be used to precisely indicate, measure, or control an amount of heat applied through the fixing nip N, which causes toner to exhibit adhesion and gloss after completion of the fixing process.
That is, variations in the post-fixing temperature Tpf indicate variations in the amount of heat applied through the fixing nip N, leading to inconsistent imaging quality as well as excessive heat and power wasted during operation, where an undue amount of heat is applied to a recording medium which then exhibits a post-fixing temperature higher than that originally designed. Maintaining the post-fixing temperature Tpf to a desired, constant temperature is therefore required not only to maintain a consistent imaging performance but also to provide an energy-efficient thermal fixing process.
As shown in
As shown in
By contrast, as shown in
Variations in the post-fixing temperature Tpf with the operational temperature Tpress of the pressure member depicted above indicate that the amount of heat applied through the fixing nip N largely depends on the operational temperature Tpress of the pressure member as it does on the operational temperature of the fuser member. Such dependency may be explained by the fact that the recording medium passing through the fixing nip derives heat not only from the fuser member but also, to a certain extent, from the pressure member, so that changes in the pressure member temperature are well reflected in changes in the amount of heat applied through the fixing nip, and thus in the post-fixing temperature.
Inconsistent heating through the fixing nip caused by variations in operational temperature of the pressure member, if not corrected, would cause adverse effects on imaging quality of the fixing process as well as undue energy waste or heating through the fixing nip.
The problem is particularly pronounced in today's energy-efficient systems which have no heater or heating control provided to the pressure member during printing, wherein a heater is designed to selectively heat the fuser member that directly contacts the printed face of a recording medium, while leaving the opposed, pressure member free of excessive accumulated heat, thereby saving energy. In such a fixing device, the pressure member is typically formed of material of a relatively low heat capacity, and therefore is prone to variations in operational temperature due to changes in operational conditions, such as upon entry into a standby or sleep mode, or during sequential processing of multiple recording media.
In particular, the operational temperature of the pressure member tends to vary where the fixing device is employed with different types of recording media, each of which has a specific heat capacity depending on physical and thermal properties of the material, such as thickness, basis weight, density, thermal conductivity, or the like. Using recording media of varying heat capacities can result in a varying operational temperature of the pressure member due to a varying amount of heat dissipated in the recording medium from the pressure member at the fixing nip. Such variations in operational temperature of the pressure member can be significant where the fixing device sequentially processes recording media of a specific type that exhibits a heat capacity different from that originally designed for the fixing process.
As shown in
Such difference in the rate of increase in operational temperature Tpress indicates that the operational temperature Tpress of the pressure member varies depending not only on the number of recording media sequentially processed during operation, but also on the type, or more precisely in this case, the heat capacity of recording media being processed.
According to this patent specification, the fixing device 20 can adjust the heating temperature of the fuser member according to an operational temperature of the pressure member detected during operation, so as to process a recording medium with a substantially constant post-fixing temperature regardless of the type of recording medium in use, leading to a consistent and consistently good imaging performance and high energy-efficiency of the fixing process.
Referring back to
Specifically, the feedback controller 10 includes a central processing unit (CPU) that controls overall operation of the apparatus, as well as its associated memory devices, such as a read-only memory (ROM) storing program codes for execution by the CPU and other types of fixed data, a random-access memory (RAM) for temporarily storing data, and a rewritable, non-volatile random-access memory (NVRAM) for storing data during power-off. Such a control system may also include a rotary drive for driving a motor-driven rotary member included in the apparatus, such as a photoconductive drum, a fixing roller, or the like.
The controller 10 incorporates feedback control, or feedback control in conjunction with feed-forward control, for power supply control in the fixing device 20, which serves to control power supply to the heater 5 of the heat roller 4 by controlling the PWM drive circuit 9 to adjust a duty cycle (i.e., the duration per unit of time in which a driving voltage is supplied to the heater 5) according to a differential between a specified setpoint temperature and an operational temperature detected in the fixing device 20, so that the fuser belt 3 heated by the internally heated roller 4 imparts a sufficient amount of heat to the incoming sheet S for fixing the toner image through the fixing nip N.
During operation, a recording sheet S having a specific heat capacity enters the fixing process, absorbing a certain amount of heat from the pressure roller 2 during passage through the fixing nip N. Upon entry of the recording sheet S, the thermometer 7 measures an operational temperature Tpress of the pressure roller 2, and communicates the measured temperature Tpress to the controller 10. The controller 10 receives the measured operational temperature Tpress of the pressure member 2 from the thermometer 7, which reflects the amount of heat dissipated from the pressure roller 2, and thus indicates the heat capacity of the recording sheet S in use.
Based on the measured temperature Tpress, the controller 10 determines an optimal heating temperature Theat to which the fuser belt 3 is to be heated to adjust the post-fixing temperature Tpf to a desired, setpoint temperature Tset for the particular type of recording sheet S being processed. The controller 10 then directs the PWM driver 9 to adjust power supply to the heater 5, so as to heat the fuser belt 3 to the optimized heating temperature Theat, resulting in a substantially constant post-fixing temperature of the recording sheet S at the post-fixing position PF regardless of the heat capacity of the recording sheet S in use.
Optimization of the heating temperature Theat according to the measured operational temperature Tpress may be accomplished, for example, based on a predefined correlation in the form of a lookup table or mathematical formula stored in an appropriate memory such as ROM or the like, which associates a specific operational temperature of the pressure roller 2 with an optimal heating temperature Theat for maintaining the post-fixing temperature Tpf at a desired setpoint temperature Tset. Such correlation may be determined theoretically through calculation, or empirically from raw data obtained through experimentation.
Additionally, the operational temperature Tfuse of the fuser belt 3 detected by the first thermometer 6 may also be involved as input variables in the control of the heating temperature Theat, in which case the controller 10 manipulates the heating temperature Theat based on the multiple input temperatures to obtain the desired post-fixing temperature Tpf.
As shown in
In feedback heating control according to this patent specification, the post-fixing temperature of a recording sheet S may be determined through simulation of thermal conduction among fixing members at the fixing nip N. An example of such is illustrated below with reference to
As shown in
where “θ” represents temperature, “ρ” represents density, “c” represents specific heat capacity, “λ” represents thermal conductivity of the fixing member, and “t” represents time.
The equation Eq. 1 above may be used to simulate thermal conduction among adjoining members, including the fuser member, the pressure member, and the recording medium, during fixing process, wherein temperature distribution at the upstream end point x1 is given as an initial condition, based on which the amount of heat applied at the intermediate point x2 and the downstream end point x3, respectively, are determined. For simplicity of calculation, the nonlinear original function Eq. 1 may be transformed into a finite difference equation to obtain an approximated numerical solution, of which a detailed description is omitted herein.
As shown in
Initially, the thermometer 7 measures an operational temperature Tpress of the pressure roller 2 during passage through the fixing nip N, and communicates the measured temperature Tpress to the controller 10 (step S110). Based on the operational temperature Tpress, which reflects the amount of heat dissipated from the pressure roller 2, and thus indicates the heat capacity of the recording sheet S in use, the controller 10 determines an optimal heating temperature Theat to which the fuser belt 3 is to be heated to adjust the post-fixing temperature Tpf to a desired, setpoint temperature Tset for the particular type of recording sheet S being processed (step S120).
Optionally, the controller 10 may acquire one or more operational parameters such as physical properties of the recording sheet S in use, including nip dwell time, basis weight, thermal conductivity, specific heat capacity, moisture content, and any combination thereof, which may be obtained through measurement with a sensor, or derived from user-specified information stored in an appropriate memory (step S130), so as to accordingly correct the heating temperature Theat based on the acquired information of the recording sheet S (step S240). Such correction to the heating temperature Theat may be accomplished, for example, by modifying the predefined correlation between the optimal heating temperature Theat and the operational temperature Tpress, as will be described later in more detail.
With the heating temperature Theat thus determined, the controller 10 then directs the PWM driver 9 to adjust power supply to the heater 5, so as to heat the fuser belt 3 to the optimized heating temperature Theat, resulting in a substantially constant post-fixing temperature of the recording sheet S at the post-fixing position PF regardless of the heat capacity of the recording sheet S in use (step S150).
The feedback heating control described in steps S110 through S150 may be performed repeatedly or continuously during processing of a single print job, and terminate upon completion of fixing on the recording sheet S through the fixing nip N.
As shown in
As shown in
The graphs of
Also indicated is that the feedback heating control according to this patent specification can process different types of recording media with a consistent and consistently high imaging quality of the fixing process, wherein controlling the heating temperature Theat according to the operational temperature Tpress reflecting the amount of heat dissipated from the pressure member in the recording medium results in a substantially constant post-fixing temperature Tpf of the recording medium regardless of the heat capacity of each specific type of recording medium.
Hence, the fixing device 20 according to this patent specification can process a recording sheet S with consistent and consistently good imaging quality and high thermal efficiency, wherein the controller 10, operatively connected with the thermometer 7 disposed outside the fixing nip N to measure an operational temperature Tpress of the pressure roller 2 indicative of a heat capacity of a recording medium S in use, optimizes a heating temperature Theat to which the fuser belt 3 is heated according to the detected temperature Tpress for the specific type of recording sheet S being processed, so that the recording sheet S exhibits a substantially constant post-fixing temperature Tpf downstream from the fixing nip N regardless of the heat capacity of the recording sheet S in use.
In particular, the fixing device 20 can perform feedback heating control based on an operational temperature of the pressure member detected outside the fixing nip N, instead of a measured post-fixing temperature of the recording medium. Feedback heating control based on the detected operational temperature of the pressure member is less costly to implement, while allowing for good control with a fast and reliable response to changes in the post-fixing temperature, compared to feedback control involving measurement of post-fixing temperature with a relatively expensive, laser-based thermometer.
Also, the fixing device 20 can control heating through the fixing nip N by adjusting the heating temperature Theat of the fuser belt 3 according to the operational temperature Tpress of the pressure roller 2. Compared to heating control through adjustment of the nip dwell time, heating control through adjustment of the heating temperature Theat is superior in terms of responsiveness and controllability to obtain a desired, constant post-fixing temperature regardless of the heat capacity of recording sheet S in use.
According to one or more embodiments of this patent specification, the controller 10 performs feedback heating control so as to maintain the post-fixing temperature at an adjustable, setpoint temperature Tset. The setpoint temperature Tset may fall in a range from approximately 120° C. to approximately 140° C., and preferably, from approximately 125° C. to approximately 135° C. The controller can perform feedback heating control to maintain the post-fixing temperature within 5° C. from the setpoint temperature Tset.
Specifically, the fixing device 20 maintains the post-fixing temperature Tpf within an optimal range of approximately 5° C., resulting in a consistent imaging quality with uniform gloss of the resulting prints. Such optimal range is consistently attained where the fixing device 20 processes different sets of ten recording sheets sequentially through the fixing nip N, each sheet set being made of paper material with a basis weight ranging from 55 g/m2 to 100 g/m2 as is frequently used in a typical office environment.
Experiment III
Experiments have been conducted to evaluate criticality of having the 5-degree optimal range for variations in the post-fixing temperature Tpf in terms of its effects on imaging quality dictated by image glossiness.
In the experiments, three pairs of sample images were prepared employing a fixing device that incorporated a fuser member having its circumferential surface formed of PFA. Before printing, the fuser member was heated to a specified temperature, and then was left idle for approximately 15 minutes to allow the entire assembly to accumulate sufficient heat therein. Printing was conducted using a recording media of enamel paper, weighing 180 g/m2, and polyester polymerization black toner, under an ambient temperature of 23° C., with a nip dwell time of 45 msec.
Each pair of sample images prepared included a reference image having a standard level of gloss and a comparative image having another level of gloss, so that there was a difference in gloss between the reference and comparative image samples: Sample A with a gloss difference of 5%; Sample B with a gloss difference of 7.5%; and Sample C with a gloss difference of 10%. The glossiness of each image sample was determined by a commercially available, specular glossmeter, model Uni Gloss 60 manufactured by Konica Minolta Sensing, Inc., which measures specular reflection of light illuminating a surface at an incident angle of 60°, as is typically applied in measuring glossiness of printed materials, such as those for office use.
The sample images were presented side by side to human evaluators, who were then asked whether there was any difference in appearance between the standard and comparative image samples. Perceptibility of gloss difference was determined as a percentage of evaluators who answered that they perceived a difference in gloss between the paired images, so that the gloss difference detracted from the appearance or visual quality of the image sample.
As shown in
The experimental results indicate that a gloss difference of 5% or 7.5% across a single image is substantially imperceptible to human eyes, whereas a gloss difference of 10% across a single image is noticeable and can significantly detract from the image quality. Considering the threshold level for perceptibility of gloss difference, keeping the gloss difference within 7.5% can ensure good imaging quality of the fixing device in terms of uniformity in gloss across an image.
With additional reference to
As shown in
In such a configuration, the controller 10 may access to the memory 11 to acquire one or more operational parameters such as physical properties of a recording sheet S to accordingly correct the amount of heat applied through the fixing nip N based on the acquired information of the recording sheet S. Such operational parameters include, for example, a nip dwell time t which changes as the width w of fixing nip changes due to thermal expansion or contraction of the fixing members accumulating heat during operation, as well as basis weight w, thermal conductivity λ, specific heat capacity c, and moisture content θ of a recording sheet in use, each of which may be obtained through measurement with a sensor, or derived from user-specified information stored in an appropriate memory.
Such arrangement enables the controller 10 to properly determine an optimal heating temperature Theat based on a measured operational temperature Tpress of the pressure member 2, even where the amount of heat applied through the fixing nip N changes as variations in operational parameters affect conduction of heat from the pressure member across the fixing nip N. Several such embodiments are depicted hereinbelow with reference to
As shown in
Theat=m*Tpress+b Eq. 2
where “m” and “b” are the slope and the y-intercept, respectively, of the linear function. Note that the lines t1 through t3 represent linear functions having different negative slopes m and different y-intercepts b, indicating dependency of these constants on the nip dwell time t of a recording sheet S. In particular, the slope m of the linear function, in absolute value, is largest for the nip dwell time of 100 msec and smallest for the nip dwell time of 30 msec.
As shown in 22A, the absolute value of the slope m linearly increases with increasing nip dwell time t. In the present example, the relation between the variables m and t is represented by the following approximate equation:
m=m(t)=−0.0027*t−0.1812 Eq. 3
Since the magnitude of slope m represents a degree to which the heating temperature Theat depends on the operational temperature Tpress of the pressure roller 2, the equation Eq. 3 above indicates that the longer the nip dwell time t, the greater the effect of the pressure roller temperature Tpress on the heating temperature Theat, and the resulting post-fixing temperature Tpf. Such a relation between the nip dwell time t and the effect of the pressure roller temperature Tpress is attributable to the fact that a prolonged nip dwell time t results in a greater amount of heat conducted from the pressure roller 2 to the recording sheet S through the fixing nip N.
As shown in
b=b(t)=0.1282*t+176.7 Eq. 4
Thus, the slope and the y-intercept of the linear function Eq. 2 can be represented by the t-dependent functions m(t) and b(t), respectively, the value of each of which is determined by the nip dwell time t of a recording sheet S.
In the feedback heating control according to this patent specification, specific t-dependent functions m(t) and b(t), or coefficients of these equations, determined experimentally or through simulation are stored in the memory for later retrieval. Specific values of nip dwell time t may be derived, for example, through estimation from thermal conditions of the fixing members expanding or contracting with varying operational temperatures or through measurement using an appropriate sensor. Substituting a nip dwell time t into the functions m(t) and b(t) gives specific values of m and b, which in turn are substituted into the equation Eq. 2 to yield a correlation between the temperatures Theat and Tpress modified for the specific nip dwell time t, as follows:
Theat=m(t)*Tpress+b(t) Eq. 2.1
Applying the equation Eq. 2.1 above gives a corrected optimal heating temperature Theat for a specific nip dwell time t with which a recording sheet S in use is processed through the fixing nip N. Such modification to the correlation between the optimal heating temperature Theat and the operational temperature Tpress based on the nip dwell time t allows for adjusting the amount of heat applied through the fixing nip N as the fixing device 20 processes different recording sheets S with different nip dwell times t, resulting in an effective feedback heating control to maintain a constant post-fixing temperature regardless of changes in the operational conditions.
As shown in
Note that, as is the case with the lines t1 through t3 of
In particular, the magnitude of slope m of the linear function Eq. 2 is negatively associated with the basis weight w, wherein the slope m of the linear function, in absolute value, is largest for the basis weight of 54 g/m2 and smallest for the basis weight of 150 g/m2, which indicates that the smaller the basis weight w, the greater the effect of the pressure roller temperature Tpress on the heating temperature Theat, and the resulting post-fixing temperature Tpf. Such a relation between the basis weight w and the effect of the pressure roller temperature Tpress is attributable to the fact that a reduced basis weight w of recording sheet results in accelerated conduction of heat from the pressure roller 2 to the recording sheet S through the fixing nip N.
Thus, the slope and the y-intercept of the linear function Eq. 2 can be represented by w-dependent functions m(w) and b(w), respectively, the value of each of which is determined by the basis weigh w of a recording sheet S.
In the feedback heating control according to this patent specification, specific w-dependent functions m(w) and b(w), or coefficients of these equations, determined experimentally or through simulation are stored in the memory for later retrieval. Specific values of basis weight w may be derived, for example, from user-specified information or through measurement using an appropriate sensor. Substituting a basis weight w into these functions m(w) and b(w) gives specific values of m and b, which in turn are substituted into the equation Eq. 2 to yield a correlation between the temperatures Theat and Tpress modified for the specific basis weight w, as follows:
Theat=m(w)*Tpress+b(w) Eq. 2.2
Applying the equation Eq. 2.2 above gives a corrected heating temperature Theat for a specific basis weight w of a recording sheet S in use. Such modification to the correlation between the optimal heating temperature Theat and the operational temperature Tpress based on the basis weigh w allows for adjusting the amount of heat applied through the fixing nip N as the fixing device 20 processes different recording sheets S of different basis weights w, resulting in an effective feedback heating control to maintain a constant post-fixing temperature regardless of changes in the operational conditions.
As shown in
Note that, as is the case with the lines t1 through t3 of
In particular, the magnitude of slope m of the linear function Eq. 2 is positively associated with the thermal conductivity λ, wherein the slope m of the linear function, in absolute value, is largest for the thermal conductivity of 0.25 W/(m*K) and smallest for the thermal conductivity of 0.1 W/(m*K), which indicates that the greater the thermal conductivity λ, the greater the effect of the pressure roller temperature Tpress on the heating temperature Theat, and the resulting post-fixing temperature Tpf. Such a relation between the thermal conductivity λ and the effect of the pressure roller temperature Tpress is attributable to the fact that an increased thermal conductivity λ of recording sheet results in accelerated conduction of heat from the pressure roller 2 to the recording sheet S through the fixing nip N.
Thus, the slope and the y-intercept of the linear function Eq. 2 can be represented by λ-dependent functions m(λ) and b(λ), respectively, the value of each of which is determined by the thermal conductivity λ of a recording sheet S.
In the feedback heating control according to this patent specification, specific λL-dependent functions m(λ) and b(λ), or coefficients of these equations, determined experimentally or through simulation are stored in the memory for later retrieval. Specific values of thermal conductivity λ may be derived, for example, from user-specified information or through measurement using an appropriate sensor. Substituting a thermal conductivity λ, into these functions m(λ) and b(λ) gives specific values of m and b, which in turn are substituted into the equation Eq. 2 to yield a correlation between the temperatures Theat and Tpress modified for the specific thermal conductivity λ, as follows:
Theat=m(k)*Tpress+b(X) Eq. 2.3
Applying the equation Eq. 2.3 above gives a corrected heating temperature Theat for a specific thermal conductivity λ of a recording sheet S in use. Such modification to the correlation between the optimal heating temperature Theat and the operational temperature Tpress based on the thermal conductivity λ allows for adjusting the amount of heat applied through the fixing nip N as the fixing device 20 processes different recording sheets S of different thermal conductivities λ, resulting in an effective feedback heating control to maintain a constant post-fixing temperature regardless of changes in the operational conditions.
As shown in
Note that, as is the case with the lines t1 through t3 of
In particular, the magnitude of slope m of the linear function Eq. 2 is negatively, if slightly, associated with the specific heat capacity c, wherein the slope m of the linear function, in absolute value, is largest for the specific heat capacity of 760 kJ(m3*K) and smallest for the specific heat capacity of 1,440 kJ(m3*K), which indicates that the smaller the specific heat capacity c, the greater the effect of the pressure roller temperature Tpress on the heating temperature Theat, and the resulting post-fixing temperature Tpf. Such a relation between the specific heat capacity c and the effect of the pressure roller temperature Tpress is attributable to the fact that a reduced specific heat capacity c of recording sheet results in accelerated conduction of heat from the pressure roller 2 to the recording sheet S through the fixing nip N.
Thus, the slope and the y-intercept of the linear function Eq. 2 can be represented by c-dependent functions m(c) and b(c), respectively, the value of each of which is determined by the specific heat capacity c of a recording sheet S.
In the feedback heating control according to this patent specification, specific c-dependent functions m(c) and b(c), or coefficients of these equations, determined experimentally or through simulation are stored in the memory for later retrieval. Specific values of heat capacity c may be derived, for example, from user-specified information or through measurement using an appropriate sensor. Substituting a specific heat capacity c into these functions m(c) and b(c) gives specific values of m and b, which in turn are substituted into the equation Eq. 2 to yield a correlation between the temperatures Theat and Tpress modified for the specific heat capacity c, as follows:
Theat=m(c)*Tpress+b(c) Eq. 2.4
Applying the equation Eq. 2.4 above gives a corrected heating temperature Theat for a specific heat capacity c of a recording sheet S in use. Such modification to the correlation between the optimal heating temperature Theat and the operational temperature Tpress based on the specific heat capacity c allows for adjusting the amount of heat applied through the fixing nip N as the fixing device 20 processes different recording sheets S of different heat capacities c, resulting in an effective feedback heating control to maintain a constant post-fixing temperature regardless of changes in the operational conditions.
As shown in
Note that, as is the case with the lines t1 through t3 of
In particular, the magnitude of slope m of the linear function Eq. 2 is negatively, if slightly, associated with the moisture content θ, wherein the slope m of the linear function, in absolute value, is largest for the moisture content of 3% and smallest for the moisture content of 9%, which indicates that the smaller the moisture content θ, the greater the effect of the pressure roller temperature Tpress on the heating temperature Theat, and the resulting post-fixing temperature Tpf. Such a relation between the moisture content θ and the effect of the pressure roller temperature Tpress is attributable to the fact that a reduced moisture content θ of recording sheet results in an increased apparent conductivity of the recording sheet S, leading to an accelerated conduction of heat from the pressure roller 2 to the recording sheet S through the fixing nip N.
Thus, the slope and the y-intercept of the linear function Eq. 2 can be represented by θ-dependent functions m(θ) and b(θ), respectively, the value of each of which is determined by the moisture content θ of a recording sheet S.
In the feedback heating control according to this patent specification, specific O-dependent functions m(θ) and b(θ), or coefficients of these equations, determined experimentally or through simulation are stored in the memory for later retrieval. Specific values of moisture content θ may be derived, for example, from user-specified information or through measurement using an appropriate sensor. Substituting a moisture content θ into these functions m(θ) and b(θ) gives specific values of m and b, which in turn are substituted into the equation Eq. 2 to yield a correlation between the temperatures Theat and Tpress modified for the moisture content θ, as follows:
Theat=m(θ)*Tpress+b(θ) Eq. 2.5
Applying the equation Eq. 2.5 above gives a corrected heating temperature Theat for a specific moisture content θ of a recording sheet S in use. Such modification to the correlation between the optimal heating temperature Theat and the operational temperature Tpress based on the moisture content θ allows for adjusting the amount of heat applied through the fixing nip N as the fixing device 20 processes different recording sheets S of different moisture contents θ, resulting in an effective feedback heating control to maintain a constant post-fixing temperature regardless of changes in the operational conditions.
In further embodiments, in stead of using a single operational parameter, the fixing device 20 according to this patent specification may adjust the heating temperature Theat based on a composite operational parameter α obtained by combining two or more operational parameters including, for example, a nip dwell time t, basis weight w, thermal conductivity λ, specific heat capacity c, and moisture content θ of a recording sheet in use, each of which may be obtained through measurement with a sensor, or derived from user-specified information stored in an appropriate memory.
The composite parameter α may be any arithmetic combination of operational parameters, which is determined to be significantly associated with each of the magnitude of the slope m and the y-intercept m of the linear function Eq. 2, as shown in
Specifically, one example of composite operational parameter α is obtained by dividing the thermal conductivity λ by the basis weight w of a recording sheet S in use, as follows:
α=λ/w Eq. 5
As shown in
As is the case with each specific operational parameter, the absolute value of the slope m linearly increases with increasing composite operational parameter λ/w (
Thus, the slope and the y-intercept of the linear function Eq. 2 can be represented by a-dependent functions m(α) and b(α), the value of each of which is determined by the operational parameter α being an arithmetic combination of the thermal conductivity λ and the basis weight w of the recording medium in use.
In the feedback heating control according to this patent specification, specific α-dependent functions m(α) and b(α), or coefficients of these equations, determined experimentally or through simulation are stored in the memory for later retrieval. Substituting a operational parameter α into the functions m(α) and b(α) gives specific values of m and b, which in turn are substituted into the equation Eq. 2 to yield a correlation between the temperatures Theat and Tpress modified for the specific parameter α, as follows:
Theat=m(a)*Tpress+b(a) Eq. 2.6
Applying the equation Eq. 2.6 gives a corrected heating temperature Theat for a specific composite operational parameter α with which a recording sheet S in use is processed through the fixing nip N. Such modification to the correlation between the optimal heating temperature Theat and the operational temperature Tpress based on the composite parameter α allows for adjusting the amount of heat applied through the fixing nip N as the fixing device 20 processes different recording sheets S of different thermal conductivities λ and different basis weights w, resulting in an effective feedback heating control to maintain a constant post-fixing temperature regardless of changes in the operational conditions.
Although in several embodiments described above, the controller adjusts the amount of heat applied through the fixing nip by modifying the correlation between the optimal heating temperature Theat and the post-fixing temperature Tpf, such adjustment may also be accomplished by modifying the correlation between the optimal conveyance speed V and the post-fixing temperature Tpf based on one or more operational parameters.
Also, although in the embodiments described above with reference to
To recapitulate, the fixing device 20 according to this patent specification can control heat application through the fixing nip N so as to process a recording medium S with consistent and consistently good imaging quality and high thermal efficiency, wherein the controller 10, operatively connected with the thermometer 7 disposed outside the fixing nip N to measure an operational temperature Tpress of the pressure member 2 indicative of a heat capacity of a recording medium S in use, optimizes a heating temperature Theat to which the fuser member 3 is heated according to the detected temperature Tpress for the specific type of recording medium S being processed, so that the recording medium S exhibits a substantially constant post-fixing temperature Tpf downstream from the fixing nip N regardless of the heat capacity of the recording medium S in use. The image forming apparatus 100 incorporating the fixing device 20 also benefits from feedback heating control according to this patent specification.
Although in several embodiments depicted above, the image forming apparatus is configured as a tandem color printer that employs four imaging stations arranged sequentially along an intermediate transfer belt, alternatively, instead, the feedback heating control according to this patent specification may be applicable to any type of imaging system that includes a pair of opposed rotary members disposed opposite to each other to form a nip therebetween, in particular, one that incorporates a fixing capability to fix a toner image in place on a recording medium conveyed thorough a fixing nip.
For example, the printer section may employ any number of imaging stations or primary colors associated therewith, e.g., a full-color process with three primary colors, a bi-color process with two primary colors, or a monochrome process with a single primary color. Further, instead of a tandem printing system, the printing section may employ any suitable imaging process for producing a toner image on a recording medium, such as one that employs a single photoconductor surrounded by multiple development devices for different primary colors, or one that employs a photoconductor in conjunction with a rotary or revolver development system rotatable relative to the photoconductive surface. Furthermore, the image forming apparatus according to this patent specification may be applicable to any type of electrophotographic imaging systems, such as photocopiers, printers, facsimiles, and multifunctional machines incorporating several of such imaging functions.
Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-230419 | Oct 2010 | JP | national |
| 2011-106196 | May 2011 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5742865 | Yajima et al. | Apr 1998 | A |
| 7912392 | Yoshinaga et al. | Mar 2011 | B2 |
| 20070217803 | Nakayama | Sep 2007 | A1 |
| 20090169232 | Kunii et al. | Jul 2009 | A1 |
| 20090297199 | Yamashina et al. | Dec 2009 | A1 |
| 20100061754 | Ishigaya et al. | Mar 2010 | A1 |
| 20100092220 | Hasegawa et al. | Apr 2010 | A1 |
| 20100092221 | Shinshi et al. | Apr 2010 | A1 |
| 20110052224 | Yamashina et al. | Mar 2011 | A1 |
| 20110064437 | Yamashina et al. | Mar 2011 | A1 |
| 20110091226 | Ishigaya et al. | Apr 2011 | A1 |
| 20110182634 | Ishigaya et al. | Jul 2011 | A1 |
| 20110206402 | Yamashina | Aug 2011 | A1 |
| 20110217057 | Yoshinaga et al. | Sep 2011 | A1 |
| 20110222927 | Yamashina | Sep 2011 | A1 |
| Number | Date | Country |
|---|---|---|
| 60-150075 | Aug 1985 | JP |
| 62-144177 | Jun 1987 | JP |
| 6-308854 | Nov 1994 | JP |
| 7-230231 | Aug 1995 | JP |
| 10-198216 | Jul 1998 | JP |
| 11030928 | Feb 1999 | JP |
| 11-338289 | Dec 1999 | JP |
| 3535587 | Mar 2004 | JP |
| 2004-258654 | Sep 2004 | JP |
| 2005-84419 | Mar 2005 | JP |
| 2006-195422 | Jul 2006 | JP |
| 2009-187020 | Aug 2009 | JP |
| Entry |
|---|
| Computer translation of Kimura et al., filed Feb. 1999, JP11-030928A. |
| U.S. Appl. No. 13/109,346, filed May 17, 2011, Yasunori Ishigaya, et al. |
| U.S. Appl. No. 13/252,543, filed Oct. 4, 2011, Yasunori Ishigaya, et al. |
| Office Action issued Feb. 24, 2015 in Japanese Application No. 2011-106196. |
| Extended European Search Report issued Feb. 1, 2012 in patent application No. 11185036.8. |
| Number | Date | Country | |
|---|---|---|---|
| 20120093534 A1 | Apr 2012 | US |
