JP7592973B2 - Fixing device, image forming apparatus, and method for controlling temperature of fixing device - Google Patents

Description

The present invention relates to a fixing device, an image forming device, and a method for controlling the temperature of the fixing device.

A known fixing device used in image forming devices such as copiers, printers, facsimiles, and all-in-one machines is one that passes a recording medium such as paper or an overhead projector through a fixing nip formed by contact between a fixing member heated by a heat source and an opposing pressure member, and fixes a toner image on the recording medium by heat and pressure. In the fixing device, the fixing member is controlled to reach a predetermined target temperature (fixing temperature).

In recent years, in order to save energy, fixing devices that enable rapid heating by reducing the thermal capacity of the fixing member, significantly shorten the preheating time, and reduce unnecessary heat dissipation into the atmosphere have become mainstream. In such fixing devices, feedback control is performed based on temperature information from a temperature detection means for the fixing member to ensure stable fixing performance.

However, conventional feedback control using PID control or the like cannot compensate for the loss of heat from the fixing member caused by the passage of the recording medium, resulting in a shortage of heat required to melt the toner, resulting in problems such as image offset.
The amount of heat dissipated by the fixing member varies depending on the type (size, thickness, etc.) of the recording member being passed through, so it is necessary to set and control an appropriate target temperature based on information about the recording member.

In response to this, a control method has been disclosed that combines feedforward control, which controls the heating of the fixing member before the recording medium is passed through the fixing nip, based on previously acquired information about the recording medium, in order to prevent a rapid drop in temperature of the fixing member due to the passage of the recording medium (see, for example, Patent Document 1).

However, when a recording medium of a different type than the one preset is fed through the printer, the temperature of the corresponding fixing member is not properly controlled, which may result in a decrease in image quality, such as insufficient heat causing image offset or excessive heat causing wrinkles or curling on the recording medium.

The present invention aims to provide a fixing device that can appropriately control the temperature during fixing and prevent deterioration of the quality of the printed image, even when a recording medium of a different type than the one previously set is passed through.

In order to solve the above problem, the fixing device of the present invention comprises a fixing member heated by a heat source and a pressure member forming a fixing nip between the fixing member and the pressure member, and fixes an image on the recording medium by passing the recording medium through the fixing nip. The fixing device further comprises a heat disturbance estimation means for predicting a heat disturbance based on the amount of heat dissipated from the fixing member and the pressure member when the recording medium passes through the fixing nip during a past fixing operation, a heat disturbance acquisition means for acquiring the heat disturbance, and a preview control means for determining a feedforward signal for suppressing temperature fluctuations of the fixing member based on the acquired heat disturbance, and is characterized in that during continuous printing, the heat disturbance estimation means predicts the heat disturbance based on the amount of heat dissipated by a preceding recording medium, and the preview control means inputs the feedforward signal to the heating source before the following recording medium passes through the fixing nip .

According to the present invention, it is possible to provide a fixing device that can appropriately control the temperature during fixing and prevent deterioration of the quality of the printed image even when a recording medium of a different type than the one that has been preset is passed through.

1 is an explanatory diagram of a configuration of a main part of an image forming apparatus according to an embodiment of the present invention; 1 is a cross-sectional view of a first fixing device according to an embodiment of the present invention. FIG. 2 is a perspective view illustrating an example of a fixing device. FIG. 4 is an exploded perspective view of the fixing device shown in FIG. 3 . FIG. 2 is a perspective view of the appearance of the fixing belt module; FIG. 6 is an exploded perspective view of the fuser belt module of FIG. 5 . FIG. 2 is a side view illustrating an example of a fixing device. FIG. 2 is an explanatory diagram showing the positional relationship in the longitudinal direction of main components of the fixing device. FIG. 4 is a plan view showing an example of a heat generation pattern of a heat source. FIG. 4 is a cross-sectional view of a second fixing device according to an embodiment of the present invention. FIG. 11 is a cross-sectional view of a third fixing device according to an embodiment of the present invention. FIG. 11 is a cross-sectional view of a fourth fixing device according to an embodiment of the present invention. FIG. 2 is a block diagram of control relating to a temperature control method of a fixing device of the present invention. 5 is a flowchart showing an example of a temperature control method for the fixing device of the present invention. (A) is a table showing an evaluation of the printing results of Example 1 and Comparative Example 1, (B) is a graph showing the thermal disturbance of Example 1, and (C) is a graph showing the feedforward signal (C) of Example 1. (A) is a table showing an evaluation of the printing results of Example 2 and Comparative Example 2, (B) is a graph showing the thermal disturbance of Example 2, and (C) is a graph showing the feedforward signal (C) of Example 2. (A) is a table showing an evaluation of the printing results of Example 3 and Comparative Example 3, (B) is a graph showing the thermal disturbance of Example 3, and (C) is a graph showing the feedforward signal (C) of Example 3. (A) is a table showing an evaluation of the printing results of Example 4 and Comparative Example 4, (B) is a graph showing the thermal disturbance of Example 4, and (C) is a graph showing the feedforward signal (C) of Example 4.

The fixing device, image forming device, and temperature control method for the fixing device according to the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the embodiments shown below, and can be modified within the scope of what a person skilled in the art can imagine, including other embodiments, additions, modifications, deletions, etc., and any aspect is within the scope of the present invention as long as it achieves the functions and effects of the present invention.

[Image forming apparatus]
FIG. 1 is an explanatory diagram of the essential structure of a laser printer as one embodiment of an image forming apparatus equipped with a fixing device according to the present invention, which will be described later, and illustrates the principle in a simplified manner.
As shown in FIG. 1, the image forming apparatus according to this embodiment includes a paper feed unit 4, a pair of registration rollers 6, a photosensitive drum 8 as an image carrier, a transfer unit 10, and a fixing device 1.

The paper feed means 4 has a paper feed tray 14 in which recording media (hereinafter also referred to as "paper") S is stored in a stacked state, and a paper feed roller 16 that separates and sends out the papers S stored in the paper feed tray 14 one by one, starting from the top one.
The paper S sent out by the paper feed roller 16 is temporarily stopped by the pair of registration rollers 6, where any misalignment is corrected, and then the paper S is sent to the transfer location T by the pair of registration rollers 6 at a timing synchronized with the rotation of the photosensitive drum 8, that is, at a timing when the leading edge of the toner image formed on the photosensitive drum 8 coincides with a predetermined position of the leading edge of the paper S in the transport direction.

Around the photosensitive drum 8, in the order of the rotation direction indicated by the arrow, there are arranged a charging roller 18 as a charging means, a mirror 20 constituting part of an exposure means (not shown), a developing means 22 equipped with a developing roller 22a, a transfer means 10, and a cleaning means 24 equipped with a cleaning blade 24a.

Between the charging roller 18 and the developing means 22, the exposure light Lb is irradiated onto an exposure portion 26 on the photosensitive drum 8 via a mirror 20, and is scanned.
The image forming operation in the printer is carried out in the same manner as in the conventional printer.
That is, when the photosensitive drum 8 starts to rotate, the surface of the photosensitive drum 8 is uniformly charged by the charging roller 18, and the exposure light Lb is irradiated onto the exposure section 26 based on the image information, and scanned to form an electrostatic latent image corresponding to the image to be created.
This electrostatic latent image is moved to the developing means 22 by the rotation of the photosensitive drum 8, where toner is supplied and the image is made visible, forming a toner image.

The toner image formed on the photosensitive drum 8 is transferred onto the sheet S which has entered the transfer region T at a predetermined timing by the application of a transfer bias by the transfer means 10 .
The paper S carrying the toner image is transported toward the fixing device 1, where the toner image is fixed, and then discharged and stacked on a paper discharge tray (not shown).

Residual toner remaining on the photosensitive drum 8 without being transferred at the transfer site T reaches the cleaning means 24 as the photosensitive drum 8 rotates, and is scraped off and cleaned by the cleaning blade 24a while passing through the cleaning means 24.
Thereafter, the residual potential on the photosensitive drum 8 is removed by a discharging means (not shown) to prepare for the next image forming process.

[Fixing device]
FIG. 2 is a cross-sectional view of the fixing device (first fixing device) according to the embodiment of the present invention.
In the fixing device of this embodiment, the temperature of the fixing member is controlled by a temperature control method according to the present invention, which will be described later.

As shown in FIG. 2, the fixing device of this embodiment includes a fixing member (hereinafter also referred to as a "fixing belt") 28 that is heated by a heater 50, which is a heat source, and a pressure member (hereinafter also referred to as a "pressure roller") 30 that forms a fixing nip N between the fixing member 28.
The fixing device fixes the image on the recording medium S by passing the recording medium S through the fixing nip N.

The fixing belt 28 has a polyimide (PI) base having an outer diameter of 25 mm and a thickness of 40 to 120 μm. A release layer having a thickness of 5 to 50 μm and made of a fluorine-based resin such as PFA or PTFE is formed on the outermost layer of the fixing belt 28 in order to increase durability and ensure releasability. An elastic layer having a thickness of 50 to 500 μm and made of rubber or the like may be provided between the base and the release layer.
The base material of the fixing belt 28 is not limited to polyimide, but may be a heat-resistant resin such as PEEK, or a metal base material such as nickel (Ni) or SUS. The inner peripheral surface may be coated with a sliding layer such as polyimide or PTFE.

The pressure roller 30 has an outer diameter of, for example, 25 mm, and is composed of a solid iron core 30a, an elastic layer 30b formed on the surface of the core 30a, and a release layer 30c formed on the outside of the elastic layer 30b. The elastic layer 30b is made of silicone rubber and has a thickness of, for example, 3.5 mm. In order to improve the release property of the surface of the elastic layer 30b, it is desirable to form the release layer 30c made of a fluororesin layer having a thickness of, for example, about 40 μm.
The pressure roller 30 is in pressure contact with the fixing belt 28 by a biasing means.

A stay 61 and a heater holder 53 are arranged in the axial direction inside the fixing belt 28. The stay 61 is made of a metal channel material, and both ends are supported by both side plates of the heating device. The stay 61 reliably receives the pressing force of the pressure roller 30 to stably form the fixing nip N.

The heater holder 53 is for holding the base material 50b of the heater 50, which is a heat source, and is supported by a stay 61. The heater holder 53 can be preferably formed of a heat-resistant resin with low thermal conductivity, such as LCP, which reduces heat transfer and enables the fixing belt 28 to be heated efficiently.
The heater holder 53 is shaped to support only two points near both ends of the base material 50b in the short direction in order to avoid contact with the heating resistor 50a. This further reduces the amount of heat flowing to the heater holder 53, and allows the fixing belt 28 to be heated efficiently.

3 and 4 are perspective views of the fixing device (fixing unit) of the present embodiment. Fig. 4 is an exploded perspective view of Fig. 3.
The fixing device has a fixing belt module 29 including a pressure roller 30 and a fixing belt 28 disposed inside a frame formed by joining a first frame member 71 and a second frame member 72 .

The first frame member 71 is formed of a U-shaped metal sheet. In this embodiment, the first frame member 71 is formed by bending a single piece of metal sheet, but it may be formed by fastening two or three members, such as a side plate and a bridging plate, with screws or the like.
The first frame member 71 has two U-shaped notches, and a pressure bearing 73 made of a sliding bearing is provided at one end. The core metal 30a of the pressure roller 30 is fitted into the pressure bearing 73 to rotatably hold the pressure roller 30. The pressure bearing 73 may be a ball bearing.
A pressure gear 39 is provided at one end of the pressure roller 30, and rotates in conjunction with a gear provided on the main body of the image forming apparatus.

The fixing belt module 29 is slidably inserted into a notch in the first frame member 71. A pressure spring (compression spring) 76 is provided between the fixing belt module 29 and a second frame member 72 fastened to the first frame member 71. The pressure spring 76 biases the fixing belt module 29 against the pressure roller 30 to form a fixing nip N.
The pressure spring 76 may directly urge the fixing belt module 29, or may have a lever member or the like interposed therebetween. By using a lever member, a large pressure force can be obtained with a weak spring by the principle of leverage.

5 and 6 are perspective views of the fixing belt module 29. FIG. 6 is an exploded perspective view of FIG.
The fixing belt module 29 includes a heater 50, a heater holder 53, a left flange 74, a right flange 75, and the fixing belt 28 whose inner circumferential surface is supported by these.

The heater 50 is attached to a heater holder 53 .
The surface of the heater holder 53 on which the heater 50 is not disposed is supported by a stay 61 made of sheet metal having higher rigidity than the heater holder 53. Flanges (a left flange 74 and a right flange 75) are provided at both longitudinal ends of the heater holder 53. The flanges abut against the inner circumferential surface of the fixing belt 28 to guide its rotation, and also restrict it to prevent meandering by abutting against the end of the fixing belt.

The heater 50 and the heater holder 53 have a longitudinal positioning shape P1, and the heater holder 53 and the left flange 74 have a longitudinal positioning shape P2. The positioning shapes P1 and P2 are provided only on one longitudinal end side (the left side in this embodiment), thereby making it possible to mitigate the effects of deformation due to thermal expansion.
The stay 61 is fitted to the left flange 74 and the right flange 75 with some play.

FIG. 10 is a side view of the fixing device (fixing unit) of this embodiment.
The pressure roller 30 rotates in the direction of the arrow D1 in the figure as a result of a pressure gear 39 (not shown) meshing with a gear of the image forming apparatus main body and rotating.
The fixing belt (not shown) 28 rotates in the direction of the arrow D2, following the pressure roller 30. The sliding property of the fixing belt 28 can be improved by applying grease, oil, or the like to the inner peripheral surface of the fixing belt 28 that slides against the members constituting the fixing belt module 29.

9 shows a schematic configuration of a heater 50 which is a heat source. Fig. 9(A) and Fig. 9(B) show examples of different heating element patterns.
The heater 50 has a heating element 50a (elements 501 to 508) arranged on a heater substrate 50b, and further has a conductor pattern 50d having a smaller resistance than the heating element 50a, and electrode portions (50e, 50f), with an insulating layer 52 formed to cover them.

The material of the heater substrate 50b is preferably one having excellent heat resistance and insulating properties, such as ceramics such as alumina and aluminum nitride, glass, mica, etc. Also, an insulating material may be laminated on a conductive material such as a metal.
Among these, from the viewpoint of cost, low-cost aluminum, stainless steel, etc. are preferable. On the other hand, from the viewpoint of improving the thermal uniformity of the fixing member and improving image quality, materials with high thermal conductivity, such as copper, graphite, graphene, etc., are preferable.
The heater substrate 50b in this embodiment is an alumina base material having a short side width of 8 mm, a long side width of 270 mm, and a thickness of 1.0 mm.

The heating element 50a can be formed by applying a paste made of a mixture of silver palladium (AgPd) and glass powder to the heater substrate 50b by screen printing or the like, and then firing the paste.
The heating elements 501 to 508 of the heating element 50a of this embodiment each have a resistance value of 80 Ω at room temperature.
The material of the heating element 50a may be a resistive material such as silver alloy (AgPt) or ruthenium oxide (RuO ₂ ) in addition to the above examples.

The conductive pattern 50d and the electrode portions (50e, 50f) are formed by screen printing silver (Ag) or silver palladium (AgPd).

The insulating layer 52 is made of heat-resistant glass having a thickness of 75 μm.
The insulating layer 52 is formed so as to cover the heating element 50a and the conductive pattern 50d on the heater substrate 50b, and ensures the sliding property with the inner circumferential surface of the fixing belt 28 as well as the insulation property.
The heater 50 contacts the fixing belt 28 on the insulating layer 52 side, and increases the temperature of the fixing belt 28 by heat transfer, thereby heating an unfixed image on the paper S transported to the fixing nip N.

The heating element 50a has a pattern consisting of a plurality of heating element elements 501 to 508 divided in the longitudinal direction, and each of the heating element elements 501 to 508 is electrically connected in parallel.
The heating element 50a is made of a material having a PTC (positive temperature coefficient of resistance) characteristic, and has the characteristic that the resistance value increases (heater output decreases) as the temperature increases.
As a result, when printing on paper S narrower than the width of the heating element 50a, the temperature and resistance of the heating elements outside the paper width of the paper S rise because the heat is not absorbed by the paper S. Since the voltage applied to each of the heating elements 501 to 508 is constant, the output of the heating elements outside the paper width relatively decreases, suppressing the temperature rise.
When the heating elements are connected in series, it is necessary to slow down the printing speed during continuous printing in order to suppress the temperature rise of the heating elements outside the paper width, but when the heating elements are connected in parallel as in this embodiment, there is no need to slow down the printing speed.

When the heating elements 501 to 508 are arranged in parallel in the longitudinal direction, spaces are created between the elements to ensure insulation, resulting in a decrease in the amount of heat generated.
For this reason, in this embodiment, the ends of each heating element are arranged to overlap in the longitudinal direction as shown in Figs. 9(A) and 9(B), thereby suppressing the effect of a decrease in the amount of heat generated.
In FIG. 9A, a step portion is formed by an L-shaped notch at the end of each of the heating elements 501 to 508, and the step portion is made to overlap a step portion at the end of the adjacent resistive heating element.
In FIG. 9B, inclined portions are formed by obliquely cutting the ends of the heating elements 501 to 508, and the inclined portions are made to overlap the inclined portions of the ends of the adjacent resistive heating elements.
Moreover, the heating elements 501 to 508 may be formed by folding back the heating material so as to obtain the desired output (resistance value).

FIG. 8 is an explanatory diagram showing the positional relationship in the longitudinal direction of the main components of the fixing device.
It is preferable that the heat generating region of the heater 50 in the longitudinal direction is longer than the width of the paper S.
In the figure, the portion longer than the paper S is indicated by "L." Specifically, for a letter size of 216 mm width, which is the maximum size of paper that can be passed through the fixing device of this embodiment, L is preferably 0.5 to 7 mm (the length of the heat generating element 50a is 217 to 230 mm), and more preferably L is 1.0 to 5 mm (the length of the heat generating element 50a is 219 to 226 mm).
This makes it possible to prevent a drop in temperature at the longitudinal ends immediately after starting up the apparatus, and to prevent an excessive rise in temperature outside the paper width when paper is being fed continuously.

As described above, the heater 50 and the heater holder 53 have positioning shapes P1 and P2 on the left side in the figure.
The positioning shape P1 is configured so that the convex portion of the heater holder 53 fits into the concave portion of the heater 50 .
The positioning shape P2 is configured such that the heater holder 53 sandwiches a groove formed in the left flange 74 .
The positioning shape P3 is configured so that a convex portion of the image forming apparatus main body fits into an opening portion formed in the second frame 72 .
Furthermore, the convex shape of the first frame member 71 is fitted into a hole in the second frame member 72 and fixed thereto.
By providing these positioning means, the positioning accuracy of the heater 50 is improved.

The power supply connector 54 is preferably provided on the side where the positioning shapes P1 and P2 are provided (the left side in the longitudinal direction in the drawing) so that the positional relationship with the heater 50 does not change due to deformation caused by thermal expansion.
In order to prevent the temperature from rising due to heat generated by the meshing of the pressure gear 39, it is preferable to provide the pressure gear 39 on the side where the power supply connector 54 is not provided (the right side in the longitudinal direction in the drawing). This arrangement allows the pressure gear 39 to be closer to the frame side plate, and the core metal 30a can be made thinner due to increased rigidity, thereby achieving weight reduction and cost reduction. (It is fixed to the pressure bearing 73, and a force is applied to the pressure gear 39 in a cantilever state.)

The fixing device has a temperature detection means (thermistor) 34 that measures, by contact or non-contact, the temperature of any of the heater 50, the fixing belt 28, and the pressure roller 30. In order to improve positional accuracy, the thermistor 34 is preferably provided on the side where the positioning shapes P1 and P2 are provided (the left side in the longitudinal direction in the drawing).
When the thermistor 34 is brought into contact with or close to the rear surface of the heater 50, a separate insulating member made of glass, ceramic, or the like may be provided on the rear surface of the heater 50.

The temperature detected by the thermistor 34 is input to the power control unit. The power control unit controls the current supplied to the electrode units (50e, 50f) based on the detected temperature so that each of the heating elements 501 to 508 reaches a predetermined target temperature.
The power control unit can be configured with a microcomputer including a CPU, ROM, RAM, an I/O interface, and the like.
When paper S is passed through the fixing nip N, heat is dissipated (heat transferred to the paper) by the paper passing through, so by controlling the supply current taking into account the amount of heat dissipation, the temperature of the fixing belt 28 can be controlled to the desired temperature.
The temperature control method for the fixing device according to the present invention will be described in detail later.

(Another embodiment of the fixing device)
The fixing device 1 is not limited to the above-described embodiment, but may be configured as second to fourth embodiments shown in FIGS.

As shown in FIG. 10, the second fixing device has a pressure roller 40 on the opposite side to the pressure roller 30, and the fixing belt 28 is sandwiched between the pressure roller 40 and a heater 50 to be heated.
A nip forming member 32 is provided on the inner side of the fixing belt 28 .
The nip forming member 32 contacts the pressure roller 30 via the fixing belt 28 to form a fixing nip N.

As shown in FIG. 11, the third fixing device uses a heater 50 to heat areas other than the fixing nip N. Also, unlike the second fixing device described above, the third fixing device does not have a pressure roller 40. For this reason, the heater 50 arranged inside the fixing belt 28 is curved to match the curvature of the fixing belt 28, and the contact area between the heater 50 and the fixing belt 28 in the circumferential direction is lengthened to ensure a heated area.

As shown in FIG. 12, the fourth fixing device is provided with a first nip N1 which is a fixing nip, and a second nip N2 which is a heating nip.
That is, the nip forming member 32 and the stay 61 are disposed on the opposite side of the pressure roller 30 from the contact portion with the fixing belt 28, and the pressure belt 31 is disposed so as to be able to rotate so as to contain them. A sheet S is passed through the fixing nip N1 between the pressure belt 31 and the pressure roller 30, and the toner image on the sheet S is heated and fixed.

[Method for controlling temperature of fixing device]
(Device configuration)
The fixing device of the present invention includes a means for acquiring the amount of heat dissipated from the fixing member (fixing belt) 28 and the pressure member (pressure roller) 30 when the recording medium S passes through the fixing nip N as a heat disturbance, a heat disturbance estimation means for predicting the heat disturbance based on the amount of heat dissipated by the recording medium S during past fixing, and a predictive control means for determining a feedforward signal for suppressing temperature fluctuations of the fixing member (fixing belt) 28 based on the heat disturbance predicted by the heat disturbance estimation means.

The temperature control according to this embodiment performs feedforward control and includes a means for detecting a heat quantity disturbance, a means for predicting the heat quantity disturbance, and a means for determining the manipulated variable based on the predicted heat quantity disturbance. Since the signal flow of the feedforward control is a one-way control method from detecting the heat quantity disturbance to determining the manipulated variable, it is used in conjunction with feedback control to maintain the target temperature.

FIG. 13 shows an outline of the temperature control of the fixing device according to the present invention.
The control means according to this embodiment, shown in the block diagram of FIG. 13, includes a fixing system 80, an FB (feedback) controller 81, and an FF (feedforward) controller 82, and as the FF controller, includes a heat disturbance estimation means 83, a heat disturbance acquisition means 84, and a prediction control means 85.
Before the recording medium S is passed through the fixing nip N, a heat disturbance estimation means 83 estimates a heat disturbance, and a heater power is input from a prediction control means 85 to suppress temperature fluctuations (temperature ripples and temperature drops) of the fixing belt 28.

A disturbance observer is used to estimate the heat disturbance of the recording medium S.
The heat disturbance acquiring means 84 acquires the heat disturbance predicted by the disturbance observer.
The disturbance observer estimates the thermal disturbance entering the fixing system 80 to be controlled as part of the state of the controlled object, monitors the input and output of the controlled object, measures the thermal disturbance, and provides feedback to the control of the fixing system 80.
The heat disturbance estimation unit 83 makes a prediction based on the input (operation amount) input to the fixing system 80 and the temperature output (control amount) of each member. This prediction information is used at the time of the next printing.

In this embodiment, a feedforward signal (power, which is a manipulated variable) for minimizing the thermal disturbance applied to the fixing system 80 is determined based on the thermal disturbance of the predicted information.
By minimizing thermal disturbance, it is possible to suppress temperature fluctuations (ripples and temperature drops) in the fixing belt 28 when paper passes through it, reduce the deviation between the target temperature and the predicted temperature, and reduce energy consumption during the fixing operation.
This makes it possible to realize stable fixing and prevent deterioration in the quality of the printed image.

In addition, in the fixing device of this embodiment, during continuous printing, the heat disturbance estimation means 83 predicts heat disturbance based on the amount of heat dissipated by the preceding recording medium S, and the prediction control means 85 inputs a feedforward signal to the heater 50, which is the heat source, before the following recording medium S passes through the fixing nip N.

If the information of the recording medium S that has passed through the fixing nip N differs from the previously set information of the recording medium S, the predictive control means 85 changes the feedforward signal based on the heat disturbance predicted from the amount of heat dissipated by the recording medium S that has passed through the fixing nip N.
Here, the information on the recording medium S refers to factors that affect the amount of heat dissipation during fixing, such as the thickness of the recording medium S, the length of the recording medium S, and the like.

Furthermore, when the power supply voltage during fixing is lower than the rated voltage, it is preferable to advance the timing of the feedforward control by the preview control means 85 .
Furthermore, when the power supply voltage during fixing is lower than the rated voltage, it is preferable to suppress the power as the feedforward output by the preview control means 85 .

(Temperature Control Method)
The temperature control method of the fixing device according to the present invention includes a step of acquiring the amount of heat dissipated from the fixing member (fixing belt) 28 and the pressure member (pressure roller) 30 when passing through the fixing nip N as a heat disturbance, a step of predicting the heat disturbance based on the amount of heat dissipated by the recording medium S during past fixing, and a step of determining a feedforward signal for suppressing temperature fluctuations of the fixing member 28 based on the heat disturbance predicted by the heat disturbance estimation means 83.

The flowchart in FIG. 14 shows a control flow during continuous printing as an example of the flow of the temperature control method of this embodiment.
First, information (such as thickness and size) of the recording medium S is set in the device (step S001), and continuous printing is started (step S002).
In printing on the recording medium S that is passed first, fixing is performed by a fixing device whose temperature is controlled based on the thermal disturbance predicted based on the information set in step S001 (steps S003 and S004).

The heat disturbance during printing of the first sheet (n=1) in step S004 is obtained (step S005), and the heat disturbance for the second sheet (n+1, n=1) is predicted based on this heat disturbance (step S006). A feedforward signal is determined based on the predicted heat disturbance (step S007), and the determined feedforward signal is input to the heat source before the second sheet of recording medium S passes through the fixing nip N.

It is determined whether or not to continue continuous printing (step S009). If printing is to continue, the process returns to step S005. Thereafter, step S006 is performed to predict a heat disturbance based on the amount of heat dissipated by the preceding recording medium (the nth sheet), and step S007 is performed to predict a heat disturbance for the subsequent recording medium (the n+1th sheet).
If printing is not to be continued, printing is terminated.

Thus, the temperature control method of this embodiment includes a step of predicting a heat disturbance based on the amount of heat dissipated by the preceding recording medium S during continuous printing, and a step of inputting a feedforward signal determined based on the predicted heat disturbance to the heater 50, which is a heating source, before the following recording medium passes through the fixing nip N.
Here, when the information of the preceding recording medium S that has passed through the fixing nip N differs from the preset information of the recording medium S, the method includes a step of changing the feedforward signal based on the heat disturbance predicted from the amount of heat dissipated by the recording medium S that has actually passed through the fixing nip N.

The above-mentioned configuration allows proper temperature control during fixing even when a recording medium of a different type than the one previously set is fed through, preventing deterioration in the quality of the printed image, such as insufficient heat causing image offset, or excessive heat causing wrinkles or curling on the recording medium.

[Example]
Example 1
An image forming apparatus equipped with the fixing device according to the present invention was used to continuously print on 10 sheets of recording medium.
As information on the recording medium used for printing, the paper thickness category "thin paper (recording medium having a basis weight of 59 g/m ² or less)" was selected and set in the image forming apparatus.
On the other hand, a recording medium having a basis weight of 105 g/m ² or more, which corresponds to “thick paper” in the paper thickness classification, was set in the paper feed tray.

At the start of printing, the fixing member was controlled to a temperature suitable for fixing "thin paper" (for example, 120°C) based on the set information.
In reality, the "thick paper" was fed, and the amount of heat dissipated was different from the predicted heat disturbance, resulting in a shortage of heat for fixing, and a cold offset image was generated on the first sheet.
When printing the second sheet, the heat disturbance estimation means predicted the heat disturbance with high accuracy from the heat dissipation amount of the first sheet and inputted the feedforward signal optimal for fixing "thick paper" to the heater, so no cold offset image occurred. Similarly, no cold offset image occurred when printing the third sheet and thereafter.
The evaluation results of the print image quality of the first to third, fifth, seventh, and tenth sheets are shown in Fig. 15 (A). In the table, "x" indicates the occurrence of a cold offset image, and "o" indicates that no cold offset image occurred and that the image quality was good.

The feedforward signal is easy to detect when the temperature of the fixing belt 28 or the pressure roller 30 is sufficiently increased and reaches a temperature saturation state. This is because, in the temperature saturation state, power equivalent to the amount of heat dissipation is input to the heater 50.
In this example, the above-mentioned continuous printing was performed after performing continuous printing for 10 minutes that was not included in the evaluation and the fixing device was brought to a temperature saturated state.

The thermal disturbance used during printing of the first to third sheets is shown in FIG.
When printing the first sheet, the thermal disturbance predicted based on the set information is used.
When printing the second sheet, a heat quantity disturbance predicted based on the heat quantity disturbance obtained when printing the first sheet is used. Similarly, when printing the third sheet, a heat quantity disturbance predicted based on the heat quantity disturbance obtained when printing the second sheet is used.

The feedforward signal input during printing of the first to third sheets is shown in FIG.
The feedforward signal is a signal for suppressing temperature fluctuations of the fixing belt 28 , specifically, for controlling the temperature drop to be minimized, and is input to the heater 50 .
The signal during printing of the first sheet is determined from the thermal disturbance predicted based on the set information.
The signal when printing the second sheet is a signal determined from the thermal disturbance predicted based on the printing of the first sheet, and the signal when printing the third sheet is a signal determined from the thermal disturbance predicted based on the printing of the second sheet.

(Comparative Example 1)
Continuous printing was carried out on 10 sheets of recording medium (plain paper) using an image forming apparatus equipped with a conventional fixing device that does not have the means for performing the temperature control according to the present invention.
As in the first embodiment, the paper thickness category of the recording medium to be used for printing was selected as "thin paper" and set in the image forming apparatus. A recording medium corresponding to the paper thickness category of "thick paper" was set in the paper feed tray.
At the start of printing, the fixing member was controlled to a temperature suitable for fixing "thin paper" (for example, 120°C) based on the set information.
In reality, the "cardboard" was fed, and the amount of heat dissipated differed from the predicted heat disturbance, resulting in a shortage of heat for fixing, and cold offset images occurred in all printed images.
The evaluation results of the print image quality for the first to third, fifth, seventh, and tenth sheets are shown in Fig. 15A. In the table, "x" indicates the occurrence of cold offset images.

Example 2
An image forming apparatus equipped with the fixing device according to the present invention was used to continuously print on 10 sheets of recording medium.
As information on the recording medium used for printing, the paper thickness category "heavy paper (recording medium having a basis weight of 105 g/m ² or more)" was selected and set in the image forming apparatus.
On the other hand, a recording medium having a basis weight of 59 g/m ² or less, which corresponds to the category of "thin paper" in terms of paper thickness, was set in the paper feed tray.

At the start of printing, the fixing member was controlled to a temperature suitable for fixing "cardboard" (for example, 150° C.) based on the set information.
In reality, the amount of heat was excessive due to the "thin paper" being fed through, and the first sheet of paper showed the occurrence of hot offset images and curls and wrinkles in the recording medium.
When printing the second sheet, the heat disturbance estimation means predicted the heat disturbance with high accuracy from the heat dissipation amount of the first sheet and inputted a feedforward signal that was optimal for fixing the "thin paper" to the heater, so no hot offset image or curling or wrinkling of the recording medium occurred. The same was true for printing the third sheet and onwards.
The evaluation results of the print image quality of the first to third, fifth, seventh, and tenth sheets are shown in Fig. 16 (A). In the table, "△" indicates the occurrence of hot offset images and the occurrence of curling or wrinkling of the recording medium, and "◯" indicates good image quality.

The thermal disturbance used during printing of the first to third sheets is shown in FIG.
When printing the first sheet, the thermal disturbance predicted based on the set information is used.
When printing the second sheet, a heat quantity disturbance predicted based on the heat quantity disturbance obtained when printing the first sheet is used. Similarly, when printing the third sheet, a heat quantity disturbance predicted based on the heat quantity disturbance obtained when printing the second sheet is used.

The feedforward signal input during printing of the first to third sheets is shown in FIG.
The feedforward signal is a signal for suppressing temperature fluctuations of the fixing belt 28 , specifically, for controlling the temperature drop to be minimized, and is input to the heater 50 .
The signal during printing of the first sheet is determined from the thermal disturbance predicted based on the set information.
The signal when the second sheet is printed is a signal determined from the thermal disturbance predicted based on the printing of the first sheet, and the signal when the third sheet is printed is a signal determined from the thermal disturbance predicted based on the printing of the second sheet.

(Comparative Example 2)
An image forming apparatus equipped with a conventional fixing device not having the means for performing the temperature control according to the present invention was used to continuously print 10 sheets of recording medium (plain paper).
As in the second embodiment, the paper thickness category of the recording medium to be used for printing was selected as "thick paper" and set in the image forming apparatus. A recording medium corresponding to the paper thickness category of "thin paper" was set in the paper feed tray.
At the start of printing, the fixing member was controlled to a temperature suitable for fixing "cardboard" (for example, 150° C.) based on the set information.
In reality, the fact that the "thin paper" was passed through the printer resulted in an excessive amount of heat being dissipated during fixing due to a heat disturbance that differed from the predicted heat disturbance, resulting in hot offset images in all printed images and curling and wrinkling of the recording media.
The evaluation results of the print image quality for the first to third, fifth, seventh and tenth sheets are shown in Fig. 16A. In the table, "△" indicates the occurrence of hot offset images and the occurrence of curls or wrinkles in the recording medium.

Example 3
An image forming apparatus equipped with the fixing device according to the present invention was used to continuously print on 10 sheets of recording medium.
As information on the recording medium used for printing, the paper thickness category "thin paper (recording medium having a basis weight of 59 g/m ² or less)" was selected and set in the image forming apparatus.
On the other hand, a recording medium having a basis weight of 105 g/m ² or more, which corresponds to “thick paper” in the paper thickness classification, was set in the paper feed tray.
The power supply voltage was set to a voltage lower than the rated voltage. Specifically, printing was performed at about 80 V in an image forming apparatus with a 100 V specification.

At the start of printing, the fixing member was controlled based on the set information so that the temperature was suitable for fixing "thin paper" (for example, 120°C). The maximum power of the heater was reduced from 1000W to about 640W.
In reality, the "thick paper" was fed, and the amount of heat dissipated was different from the predicted heat disturbance, resulting in a shortage of heat for fixing, and a cold offset image was generated on the first sheet.
When printing the second sheet, the heat disturbance estimation means predicted the heat disturbance with high accuracy from the amount of heat dissipated from the first sheet and input a feedforward signal to the heater that was optimal for fixing to "thick paper," so that no cold offset image occurred.
In addition, in order to input an optimal feedforward signal to the heater when thin paper is passed through under low voltage conditions, feedforward control was started earlier than in Example 1, and the feedforward output (power) was lower than in Example 1.
Similarly, no cold offset images were observed in the third and subsequent prints.
The evaluation results of the print image quality of the first to third, fifth, seventh, and tenth sheets are shown in Fig. 17A. In the table, "x" indicates the occurrence of a cold offset image, and "o" indicates that no cold offset image occurred and that the image quality was good.

The thermal disturbance used during printing of the first to third sheets is shown in FIG.
When printing the first sheet, the thermal disturbance predicted based on the set information is used.
When printing the second sheet, a heat quantity disturbance predicted based on the heat quantity disturbance obtained when printing the first sheet is used. Similarly, when printing the third sheet, a heat quantity disturbance predicted based on the heat quantity disturbance obtained when printing the second sheet is used.

The feedforward signal input during printing of the first to third sheets is shown in FIG.
The feedforward signal is a signal for suppressing temperature fluctuations of the fixing belt 28 , specifically, for controlling the temperature drop to be minimized, and is input to the heater 50 .
The signal during printing of the first sheet is determined from the thermal disturbance predicted based on the set information.
The signal when printing the second sheet is a signal determined from the thermal disturbance predicted based on the printing of the first sheet, and the signal when printing the third sheet is a signal determined from the thermal disturbance predicted based on the printing of the second sheet.
Compared to the first embodiment, the timing of the signal input is earlier and the feedforward output (power) is lower.

(Comparative Example 3)
Continuous printing was carried out on 10 sheets of recording medium (plain paper) using an image forming apparatus equipped with a conventional fixing device that does not have the means for performing the temperature control according to the present invention.
As in the third embodiment, the paper thickness category of the recording medium to be used for printing was selected as "thin paper" and set in the image forming apparatus. A recording medium corresponding to the paper thickness category of "thick paper" was set in the paper feed tray.
At the start of printing, the fixing member was controlled to a temperature suitable for fixing "thin paper" (for example, 120°C) based on the set information.
The power supply voltage was set to a voltage lower than the rated voltage. Specifically, printing was performed at about 80 V in an image forming apparatus with a 100 V specification.
In reality, the "cardboard" was fed, and the amount of heat dissipated differed from the predicted heat disturbance, resulting in a shortage of heat for fixing, and cold offset images occurred in all printed images.
The evaluation results of the print image quality of the first to third, fifth, seventh, and tenth sheets are shown in Fig. 17(A). In the table, "x" indicates the occurrence of cold offset images. The degree of cold offset was more significant than in Example 1.

Example 4
An image forming apparatus equipped with the fixing device according to the present invention was used to continuously print on 10 sheets of recording medium.
As information on the recording medium to be used for printing, the paper thickness category was selected as "thin paper (recording medium with a basis weight of 59 g/ ^m2 or less)." In addition, the paper size category was selected as "irregular size," and the length value was input as "200 mm" from the setting means.
A recording medium corresponding to "thin paper" and having a length of 150 mm, which is shorter than the above-mentioned set value, was set in the paper feed tray.

At the start of printing, the fixing member was controlled to a temperature suitable for fixing "thin paper" (for example, 120°C) based on the set information.
In reality, a recording medium having a length of "150 mm" was passed through, and therefore there was a heater input for heating the difference of 50 mm even after the trailing edge of the first recording medium had passed.
When printing the second sheet, the heat disturbance estimation means predicted the heat disturbance with high accuracy from the heat dissipation amount of the first sheet, and inputted a feedforward signal that was optimal for fixing the recording medium with a length of "150 mm" to the heater, so that unnecessary heating was not performed. Similarly, the heating time was appropriate for printing the third sheet and thereafter.
The evaluation results of the heating times for the first to third, fifth, seventh, and tenth sheets are shown in Fig. 18(A). In the table, "△" indicates that heater input was observed after the recording medium passed, and "◯" indicates that the heater input was appropriate and ended after the recording medium passed, and no unnecessary heating was performed.

The thermal disturbance used during printing of the first to third sheets is shown in FIG.
When printing the first sheet, the thermal disturbance predicted based on the set information is used.
When printing the second sheet, a heat quantity disturbance predicted based on the heat quantity disturbance obtained when printing the first sheet is used. Similarly, when printing the third sheet, a heat quantity disturbance predicted based on the heat quantity disturbance obtained when printing the second sheet is used.

The feedforward signal input during printing of the first to third sheets is shown in FIG.
The feedforward signal is a signal for suppressing temperature fluctuations in the fixing belt, specifically, for controlling power consumption to be minimized while paper is passing, and is input to the heater.
The signal during printing of the first sheet is determined from the thermal disturbance predicted based on the set information.
The signal when printing the second sheet is a signal determined from the thermal disturbance predicted based on the printing of the first sheet, and the signal when printing the third sheet is a signal determined from the thermal disturbance predicted based on the printing of the second sheet.

(Comparative Example 4)
Continuous printing was carried out on 10 sheets of recording medium (plain paper) using an image forming apparatus equipped with a conventional fixing device that does not have the means for performing the temperature control according to the present invention.
As in Example 4, the paper thickness category of the recording medium to be used for printing was selected as "thin paper" and the length was set to "200 mm" in the image forming apparatus. A recording medium that was classified as "thin paper" in terms of paper thickness and had a length of "150 mm" was set in the paper feed tray.
At the start of printing, the fixing member was controlled to a temperature suitable for fixing "thin paper" (for example, 120°C) based on the set information.
In reality, a recording medium having a length of "150 mm" was passed through, and therefore there was a heater input for heating the difference of 50 mm even after the trailing end of the recording medium had passed.
The evaluation results of the heating times for the first to third, fifth, seventh, and tenth sheets are shown in Fig. 18A. In the table, "△" indicates that heater input was observed even after the recording medium had passed, resulting in unnecessary heating.

As described above, the fixing device according to the present invention can appropriately control the temperature during fixing even when a recording medium of a type different from the one preset is fed through, and can prevent a decrease in the quality of printed images in an image forming apparatus equipped with the fixing device. It can also prevent unnecessary heating during the fixing operation and reduce power consumption during the fixing operation.

1 Fixing device 28 Fixing member (fixing belt)
29 Fixing belt module 30 Pressure member (pressure roller)
30a: core metal; 30b: elastic layer; 30c: release layer; 34: temperature detection means (thermistor)
50 Heat source (heater)
50a Heating element 50b Heater substrate 50d Conductive pattern 50e, 50f Electrode portion 52 Insulating layer 53 Heater holder 61 Stay 83 Heat quantity disturbance estimating means 85 Prediction control means N Fixing nip S Recording medium

JP 2011-90300 A

Claims (14)

A fixing device including a fixing member heated by a heat source and a pressure member forming a fixing nip between the fixing member and the pressure member, and fixing an image on a recording medium by passing the recording medium through the fixing nip,
a heat quantity disturbance estimating means for predicting a heat quantity disturbance based on an amount of heat dissipated from the fixing member and the pressure member when a recording medium passes through the fixing nip during past fixing;
A heat quantity disturbance acquisition means for acquiring the heat quantity disturbance;
a predictive control unit that determines a feedforward signal for suppressing a temperature fluctuation of the fixing member based on the acquired heat quantity disturbance ,
During continuous printing,
the heat quantity disturbance estimation means predicts a heat quantity disturbance based on a heat quantity dissipated by a preceding recording medium;
The fixing device according to claim 1, wherein the preview control means inputs a feedforward signal to the heat source before a succeeding recording medium passes through the fixing nip . A fixing device including a fixing member heated by a heat source and a pressure member forming a fixing nip between the fixing member and the pressure member, and fixing an image on a recording medium by passing the recording medium through the fixing nip,
a heat quantity disturbance estimating unit for predicting a heat quantity disturbance based on an amount of heat dissipated from the fixing member and the pressure member when a recording medium passes through the fixing nip during past fixing;
A heat quantity disturbance acquisition means for acquiring the heat quantity disturbance;
a predictive control unit that determines a feedforward signal for suppressing a temperature fluctuation of the fixing member based on the acquired heat quantity disturbance,
When the information of the recording medium that has passed through the fixing nip is different from the information of the recording medium that has been preset,
The fixing device according to claim 1, wherein the predictive control means changes a feedforward signal based on a heat quantity disturbance predicted from a heat quantity dissipated by a recording medium passing through the fixing nip. During continuous printing,
the heat quantity disturbance estimation means predicts a heat quantity disturbance based on a heat quantity dissipated by a preceding recording medium;
3. The fixing device according to claim 2 , wherein the preview control means inputs a feedforward signal to the heat source before a succeeding recording medium passes through the fixing nip. When the information of the recording medium that has passed through the fixing nip is different from the information of the recording medium that has been preset,
2. The fixing device according to claim 1 , wherein the predictive control means changes the feedforward signal based on a heat quantity disturbance predicted from a heat quantity dissipated by the recording medium passing through the fixing nip. 5. The fixing device according to claim 2 , wherein the information about the recording medium is either a thickness or a length of the recording medium. 6. An image forming apparatus comprising the fixing device according to claim 1. In a temperature control of a fixing device, the fixing device includes a fixing member that is heated by a heat source and a pressure member that forms a fixing nip between the fixing member and the pressure member, and fixes an image on a recording medium by passing the recording medium through the fixing nip,
a heat quantity disturbance estimating step of predicting a heat quantity disturbance based on an amount of heat removed from the fixing member and the pressure member when a recording medium passes through the fixing nip during past fixing;
a heat quantity disturbance acquiring step of acquiring the heat quantity disturbance;
and a predictive control step of determining a feedforward signal for suppressing a temperature fluctuation of the fixing member based on the acquired heat quantity disturbance ,
During continuous printing,
A step of predicting a heat disturbance based on a heat dissipation amount by a preceding recording medium;
and inputting a feedforward signal determined based on a predicted heat quantity disturbance to the heat source before a subsequent recording medium passes through the fixing nip . In a temperature control of a fixing device, the fixing device includes a fixing member that is heated by a heat source and a pressure member that forms a fixing nip between the fixing member and the pressure member, and fixes an image on a recording medium by passing the recording medium through the fixing nip,
a heat quantity disturbance estimating step of predicting a heat quantity disturbance based on an amount of heat removed from the fixing member and the pressure member when a recording medium passes through the fixing nip during past fixing;
a heat quantity disturbance acquiring step of acquiring the heat quantity disturbance;
and a predictive control step of determining a feedforward signal for suppressing a temperature fluctuation of the fixing member based on the acquired heat quantity disturbance,
When the information of the recording medium that has passed through the fixing nip is different from the information of the recording medium that has been preset,
A temperature control method for a fixing device, comprising the step of changing a feedforward signal based on a heat quantity disturbance predicted from a heat quantity dissipated by a recording medium passing through the fixing nip. In a temperature control of a fixing device, the fixing device includes a fixing member that is heated by a heat source and a pressure member that forms a fixing nip between the fixing member and the pressure member, and fixes an image on a recording medium by passing the recording medium through the fixing nip,
a heat quantity disturbance estimating step of predicting a heat quantity disturbance based on an amount of heat removed from the fixing member and the pressure member when a recording medium passes through the fixing nip during past fixing;
a heat quantity disturbance acquiring step of acquiring the heat quantity disturbance;
and a predictive control step of determining a feedforward signal for suppressing a temperature fluctuation of the fixing member based on the acquired heat quantity disturbance,
If the power supply voltage is lower than the rated voltage,
and advancing the timing of the feedforward control by the predictive control step. In a temperature control of a fixing device, the fixing device includes a fixing member that is heated by a heat source and a pressure member that forms a fixing nip between the fixing member and the pressure member, and fixes an image on a recording medium by passing the recording medium through the fixing nip,
a heat quantity disturbance estimating step of predicting a heat quantity disturbance based on an amount of heat removed from the fixing member and the pressure member when a recording medium passes through the fixing nip during past fixing;
a heat quantity disturbance acquiring step of acquiring the heat quantity disturbance;
and a predictive control step of determining a feedforward signal for suppressing a temperature fluctuation of the fixing member based on the acquired heat quantity disturbance,
If the power supply voltage is lower than the rated voltage,
The temperature control method for a fixing device, comprising : suppressing a feedforward output by the preview control step. During continuous printing,
A step of predicting a heat disturbance based on a heat dissipation amount by a preceding recording medium;
11. The temperature control method of a fixing device according to claim 8 , further comprising a step of inputting a feedforward signal determined based on a predicted heat quantity disturbance to the heat source before a succeeding recording medium passes through the fixing nip. When the information of the recording medium that has passed through the fixing nip is different from the information of the recording medium that has been preset,
11. The temperature control method for a fixing device according to claim 7, further comprising a step of changing a feedforward signal based on a heat quantity disturbance predicted from a heat quantity dissipated by a recording medium passing through the fixing nip. If the power supply voltage is lower than the rated voltage,
11. The temperature control method for a fixing device according to claim 7, 8 or 10 , wherein a timing of the feedforward control in the preview control step is advanced. If the power supply voltage is lower than the rated voltage,
10. The temperature control method for a fixing device according to claim 7, wherein a feedforward output by the preview control step is suppressed.

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