JP2014006470A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve print quality by stabilizing the quantity of heat which is applied from a fixing belt to a printing medium.SOLUTION: An image forming device includes a fixing part that fixes a developer image on a printing medium, and control means for controlling the fixing part. The fixing part includes a rotatable rotating member, a rotatable pressure member arranged in contact with the rotating member to pressurize the printing medium held together with the rotating member, a heating part for heating the rotating member, and temperature detection means for detecting a temperature of an inner peripheral surface of the rotating member. The control means includes: a distance calculation part that calculates the amount of rotation of the rotating member; and a temperature control part that controls the heating part on the basis of the temperature detected by the temperature detection means and controls the temperature of the rotating member to be the target temperature. The temperature control part acquires a temperature just before starting of rotation of the rotating member from the temperature detection means, to set the target temperature according to the temperature just before starting of rotation and the amount of rotation calculated by the distance calculation part.

Description

  The present invention relates to an image forming apparatus having a fixing device for fixing a developer image on a printing medium.

In a conventional image forming apparatus, toner as a developer image corresponding to a print image is transferred to a print medium, and the toner is fixed to the print medium with heat and pressure by a fixing device.
This fixing device heats the fixing belt by stretching a fixing belt on a heating body, an upper pressure roller, and a belt support member, and fixes even when dust adheres to the surface of the fixing belt and a printing medium is wound around the fixing belt. In order to accurately detect the temperature of the belt, temperature detection is performed on the inner peripheral surface of the fixing belt, and driving of the heater of the heating body is controlled so that the temperature becomes a predetermined temperature and a constant temperature. Further, the lower pressure roller is pressed against the upper pressure roller via the fixing belt, and the toner is transferred by heat and pressure by passing the print medium onto which the toner has been transferred between the fixing belt and the lower pressure roller. It is made to fix to a printing medium (for example, refer patent document 1).

JP 2010-134389 A (paragraphs “0020” to “0029”, FIGS. 1, 2, 3, 4, and 5)

However, in the conventional technique, when the temperature detecting means is brought into contact with the inner peripheral surface of the fixing belt, a heat flow is generated due to the presence of the members that come into contact with the fixing belt and the heated fixing belt. A temperature difference occurs between the surface and the back surface. For this reason, if the target temperature is not corrected, there is a problem that the amount of heat applied to the print medium by the fixing belt becomes insufficient or excessive, and so-called cold offset or hot offset occurs, resulting in a decrease in print quality. .
An object of the present invention is to solve such a problem, and an object of the present invention is to stabilize the amount of heat given to a print medium by a fixing belt and improve the print quality.

  Therefore, the present invention includes a fixing unit that fixes a developer image on a print medium, and a control unit that controls the fixing unit. The fixing unit contacts a rotatable rotating member and the rotating member. A rotatable pressure member that sandwiches and pressurizes the print medium together with the rotation member, a heating unit that heats the rotation member, and a temperature detection unit that detects the temperature of the inner peripheral surface of the rotation member The control means controls the heating part based on the temperature detected by the temperature detection means and the distance calculation part for calculating the rotation amount of the rotary member, and sets the temperature of the rotary member to the target temperature. A temperature control unit for controlling, the temperature control unit obtains the temperature immediately before the start of rotation of the rotating member from the temperature detecting means, and the temperature immediately before the start of rotation and the rotation amount calculated by the distance calculation unit The target temperature is set according to Characterized in that it.

  According to the present invention as described above, it is possible to stabilize the amount of heat given to the print medium by the fixing belt and to improve the print quality.

1 is a block diagram showing a control configuration of an image forming apparatus according to a first embodiment. 1 is a schematic side sectional view showing a configuration of an image forming apparatus in a first embodiment. Explanatory drawing which shows the structure of the fixing device in 1st Example. Explanatory drawing which shows the structure of the belt thermistor in 1st Example. The graph which shows the temperature transition of the front surface and back surface of the fixing belt in a 1st Example The graph which shows the relationship between the moving amount | distance of a fixing belt, and front and back temperature difference in a 1st Example The graph which shows the relationship between the moving amount | distance of a fixing belt, and front and back temperature difference in a 1st Example The graph which shows the maximum relationship between the detected temperature of the belt thermistor just before rotation of the fixing belt and the front and back temperature difference in the first embodiment. The flowchart which shows the flow of the temperature control process in a 1st Example. The flowchart which shows the flow of the target temperature setting process in a 1st Example. FIG. 3 is a block diagram illustrating a control configuration of an image forming apparatus according to a second embodiment. Graph showing the maximum relationship between the rotation stop time of the fixing belt and the front and back temperature difference in the second embodiment The graph which shows the relationship between the front-back temperature difference at the time of a fixing belt rotation stop in a 2nd Example, and a coefficient. The flowchart which shows the flow of the temperature control process in 2nd Example. The flowchart which shows the flow of the target temperature correction process in 2nd Example.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic sectional side view showing the configuration of the image forming apparatus in the first embodiment.
In FIG. 2, an image forming apparatus 1 is, for example, an electrophotographic printer, and includes a paper feed cassette 2 that stores paper as a print medium, and a paper transport unit 4 that transports paper fed from the paper feed cassette 2. A light emitting diode (LED) head 3 as a recording light exposure member, and a toner image corresponding to the recording light emitted from the LED head 3 is formed, and the toner image is formed on the paper conveyed from the paper feed cassette 2 The image forming apparatus includes a toner image forming unit 5 to be transferred and a fixing device 6 for fixing the toner image transferred onto the paper by the toner image forming unit 5. The LED head 3 is disposed adjacent to the toner image forming unit 5.

When the image forming apparatus 1 receives the print instruction, the sheet conveying unit 4 conveys the sheet to the toner image forming unit 5 in accordance with the image formation timing. The LED head 3 irradiates the toner image forming unit 5 with recording light corresponding to the printing information, and the toner image forming unit 5 forms a toner image corresponding to the irradiated recording light on the paper.
Thereafter, the paper on which the toner image is formed is conveyed to the fixing device 6, and after the toner on the paper is fixed by the heat and pressure of the fixing device 6, the paper is discharged out of the apparatus.

FIG. 1 is a block diagram showing a control configuration of the image forming apparatus in the first embodiment.
In FIG. 1, the control configuration of the image forming apparatus 1 is that the above-described LED head 3 and toner image forming unit 5, a paper transport motor 17 for transporting paper, and the upper pressure roller of the fixing device 6 are rotated to fix the fixing belt. Controls the operation of the entire image forming apparatus 1 including the fixing motor 18 that rotates the fixing belt 61, the fixing heater 61 that heats the fixing belt, the belt thermistor 67 that detects the temperature of the fixing device 6, and the fixing device (fixing unit) 6. It consists of the control part 10 as a control means.

The control unit 10 includes an LED head control unit 11 that controls the LED head 3, a toner image formation processing unit 12 that controls the toner image forming unit 5, a paper conveyance motor control unit 13 that controls the paper conveyance motor 17, and fixing. The fixing motor control unit 14 that controls the motor 18, the distance calculation unit 15 that calculates the rotation amount of the fixing belt, and the heating and cooling control of the fixing heater 61 based on the temperature detected by the belt thermistor 67, And a temperature controller 16 for controlling the temperature of the fixing belt to a target temperature.
The control unit 10 includes control means such as a CPU (Central Processing Unit), and controls the operation of the entire image forming apparatus 1 based on a control program (software) stored in a storage unit such as a memory.

3A and 3B are explanatory views showing the structure of the fixing device in the first embodiment, FIG. 3A is a sectional view of the fixing device 6, and FIG. 3B is a diagram of the fixing device 6 shown in FIG. FIG. 6 is a diagram viewed from the sheet conveyance direction indicated by a middle arrow A.
In FIG. 3, the fixing device 6 includes a fixing belt 64 as an endless rotatable rotating member for conveying and heating a sheet, a fixing heater 61 as a heating unit for heating the fixing belt 64, and a fixing belt 64. An upper pressure roller (first pressure member) 63 as a rotatable pressure member that is disposed so as to be in contact with the inner peripheral surface of the paper and that presses the paper together with the fixing belt 64 and presses the fixing belt 64. The lower pressure roller (second pressure member) 65 disposed so as to be in contact with the outer peripheral surface of the upper pressure roller 63 and the inner peripheral surface of the fixing belt 64 to support the fixing belt 64. A belt support member 69 serving as a member to be operated, and a belt thermistor 67 serving as a temperature detecting means provided on the belt support member 69 for detecting the temperature of the inner peripheral surface of the fixing belt 64. In this embodiment, the fixing device 6 as a fixing unit for fixing the developer image on the print medium includes the distance calculation unit 15 and the temperature control unit 16 shown in FIG.

The fixing heater 61 and the belt thermistor 67 are connected to the temperature control unit 16 shown in FIG. 1 and controlled by the temperature control unit 16.
The upper pressure roller 63 has an outer diameter of 40 mm, a cored bar 63a as a base made of an iron metal solid shaft, and a 4 mm thick heat-resistant porous sponge covering the cored bar 63a. It has an elastic body layer 63b.

Since the material of the elastic body layer 63b is a heat-resistant porous elastic body having a low thermal conductivity and a heat insulating action, the heat loss of the fixing belt 64 is reduced, and the fixing belt 64 is rotated for temperature recovery. Pre-rotation time is shortened.
Further, since the elastic layer 63b has a relatively low hardness, the width in the direction indicated by the arrow A in FIG. 3A of the region 66 (hereinafter referred to as “nip portion”) where the sheet and the fixing belt 64 are in contact with each other. A sufficient nip width can be obtained.
The upper pressure roller 63 has a gear (not shown), and rotates when the gear is rotationally driven by the fixing motor 18 (paper transport unit 4) shown in FIG.

The lower pressure roller 65 is pressed in a direction in contact with the outer peripheral surface of the upper pressure roller 63 by an elastic body (not shown) such as a spring. The lower pressure roller 65 is in contact with the upper pressure roller 63 at a position facing the upper pressure roller 63 via the fixing belt 64, and thereby the upper pressure roller 63 in contact with the fixing belt 64. The nip part 66 is formed between the two.
The fixing belt 64 is a highly heat-resistant polyimide resin in which a release layer made of silicon rubber having a thickness of 200 μm is formed on a surface layer of a substrate having a thickness of 100 μm, and has a small heat capacity and good thermal responsiveness. Yes. The base may be metallic or rubber made of stainless steel or nickel.

The fixing heater 61 is obtained by forming a resistance heating element, an electrical insulating layer, an electrode, a protective layer made of a fluorine-based resin, etc. on a substrate such as SUS430. The fixing heater 61 is connected to the temperature controller 16 shown in FIG. 1 and generates heat when a voltage is applied from a power source (not shown) to heat the fixing belt 64. The temperature control unit 16 shown in FIG. 1 controls the heat generation timing of the fixing heater 61.
The voltage applied to the fixing heater 61 is, for example, 100 V, and the output of the fixing heater 61 is, for example, 1200 W.

  The belt support member 69 is made of high heat-resistant PPS (polyphenylene sulfide resin), and its shape is rounded so as not to hinder the movement of the rotating fixing belt 64. It is disposed upstream of the nip portion 66 and downstream of the fixing heater 61 in the rotational direction shown. The belt support member 69 also supports a belt thermistor 67.

As shown in FIG. 3B, the belt thermistor 67 is held at the center in the longitudinal direction (width direction) of the belt support member 69 and is disposed so as to contact the inner peripheral surface of the fixing belt 64. Details of the belt thermistor 67 will be described later.
The fixing belt 64 is stretched around a fixing heater 61, an upper pressure roller 63, and a belt support member 69, and is driven by the upper pressure roller 63 that rotates in a direction indicated by an arrow B in the drawing by driving the fixing motor 18 shown in FIG. Along with the rotation, it rotates in the direction indicated by arrow C in the figure.

A sensor 68 that detects the number of rotations of the fixing belt 64 is disposed in the vicinity of the fixing belt 64. The distance calculation unit 15 illustrated in FIG. 1 calculates the rotation amount of the fixing belt 64, that is, the movement amount, from the rotation number of the fixing belt 64 detected by the sensor 68.
Further, the lower pressure roller 65 is pressed in the direction of the upper pressure roller 63 disposed so as to face the outer pressure surface of the upper pressure roller 63 via the fixing belt 64, and the upper pressure roller 63 is rotated. It follows and rotates in the direction shown by arrow D in the figure.

The sheet on which the toner image is formed in the toner image forming unit is conveyed in the direction indicated by the arrow A in the drawing, and is heated by the fixing belt 64 in contact with the outer peripheral surface of the fixing belt 64 at the nip 66. The toner is fixed by the pressure of the pressure roller 63 and the lower pressure roller 65.
In this embodiment, the inner peripheral surface of the fixing belt 64 that contacts the fixing heater 61, the upper pressure roller 63, and the belt support member 69 is referred to as the back surface, and the outer peripheral surface of the fixing belt 64 that is the opposite surface is mainly used. It is called the surface.

FIG. 4 is an explanatory diagram showing the configuration of the belt thermistor in the first embodiment.
In FIG. 4, a belt thermistor 67 includes a thermistor element 673 as a member for detecting temperature, a thermistor wiring 674 as a member for transmitting a detection result of the thermistor element 673 to the temperature controller 16 shown in FIG. 1, and a thermistor element. A heat insulating member 672 for fixing the 673 to the fixing belt 64 as a part to be measured and a fixing member 671 for fixing the thermistor element 673 are provided.
The thermistor element 673 is an element whose resistance value changes according to temperature, and the temperature controller 16 shown in FIG. 1 detects the temperature of the thermistor element 673 by detecting the resistance value. In this embodiment, an element having a characteristic that the resistance value decreases as the temperature rises is used.

In order to prevent the temperature detection of the thermistor element 673 from causing an error, the heat insulating member 672 uses a silicon sponge having a high heat insulating property such as a sponge, and the thermistor element 673 is fixed as a measured part via the fixing member 671. The belt 64 is pressed against and brought into contact.
The thermistor wiring 674 has one end connected to both poles of the thermistor element 673 and the other end connected to the temperature controller 16 shown in FIG. The temperature controller 16 shown in FIG. 1 detects a change in the resistance value of the thermistor element 673 via the thermistor wiring 674.

The operation of the above configuration will be described.
First, FIG. 1, FIG. 4, FIG. 5 and FIG. 6 show the time course of the temperature difference between the front surface (outer peripheral surface) and the back surface (inner peripheral surface) of the fixing belt (hereinafter referred to as “front / back temperature difference”). This will be described with reference to FIG.

FIG. 5 is a graph showing the temperature transition of the front surface and the back surface of the fixing belt in the first embodiment. The fixing heater 61 is driven from the time when the detected value by the belt thermistor 67 of the fixing belt 64 is 30 ° C. When the belt thermistor 67 is maintained at 170 ° C., the temperature of the back surface (inner peripheral surface) of the fixing belt 64 detected by the belt thermistor 67 and a thermistor of the same type (not shown) disposed opposite the belt thermistor 67 are detected. The transition of the temperature of the front surface (outer peripheral surface) of the fixing belt 64 is shown.
Note that the horizontal (x) axis in FIG. 5 indicates the rotation amount (mm × 1000) that is the movement amount due to the rotation of the fixing belt 64, and the vertical (y) axis indicates the temperature (° C.) of the fixing belt 64.

FIG. 6 is a graph showing the relationship between the amount of movement of the fixing belt and the difference between the front and back temperatures in the first embodiment. The fixing heater 61 is driven from the time point when the detected value of the fixing belt 64 by the belt thermistor 67 is 30 ° C. The transition of the temperature difference between the front and back surfaces of the fixing belt 64 when the thermistor 67 maintains 170 ° C. is shown.
In FIG. 6, the horizontal (x) axis indicates the rotation amount (mm × 1000) that is the movement amount due to the rotation of the fixing belt 64, and the vertical (y) axis indicates the temperature difference (° C.) of the fixing belt 64. Yes.

When the fixing belt 64 repeats the rotation operation, the temperature difference between the front and back sides disappears as the movement amount due to the rotation of the fixing belt 64 increases as shown in FIG. 5, and the movement amount due to the rotation of the fixing belt 64 as shown in FIG. As the temperature increases, the temperature difference between the front and back surfaces attenuates to 0 ° C.
This is warmed by the fixing belt 64 in which the belt support member 69 and the upper pressure roller 63 rotate, and the temperature difference between the fixing belt 64 and the belt support member 69 and the upper pressure roller 63 is reduced. This shows that the temperature difference between the front and back surfaces of the fixing belt 64 is reduced because the heat transfer to the belt support member 69 and the upper pressure roller 63 is reduced.

FIG. 7 is a graph showing the relationship between the movement amount of the fixing belt and the front and back temperature difference in the first embodiment. The fixing heater 61 is driven when the detected value of the fixing belt 64 by the belt thermistor 67 is 115 ° C. The transition of the temperature difference between the front and back surfaces of the fixing belt 64 when the thermistor 67 maintains 170 ° C. is shown.
In FIG. 7, the horizontal (x) axis indicates a rotation amount (mm × 1000) that is a movement amount due to the rotation of the fixing belt 64, and the vertical (y) axis indicates a front-back temperature difference (° C.) of the fixing belt 64. Yes.

The maximum value of the front-back temperature difference shown in FIG. 7 is the front-back temperature difference in which the movement amount due to the rotation of the fixing belt 64 is substantially zero, and the detection value by the belt thermistor 67 of the fixing belt 64 shown in FIG. It can be seen that it is lower than the maximum value of the temperature difference between the front and back when the fixing heater 61 is driven.
As can be seen from the fact that the temperature detected by the belt thermistor 67 is high, the temperature of the belt support member 69 and the upper pressure roller 63 is higher than the case where the value detected by the belt thermistor 67 is 30 ° C. The temperature difference between the fixing belt 64 and the belt support member 69 and the upper pressure roller 63 is reduced, and the heat transfer from the fixing belt 64 to the belt support member 69 and the upper pressure roller 63 is reduced. It shows that the maximum value of the temperature difference decreases compared to the case where the detected value by the belt thermistor 67 is 30 ° C.

FIG. 8 is a graph showing the maximum relationship between the detected temperature of the belt thermistor immediately before the rotation of the fixing belt and the front-back temperature difference in the first embodiment, and the detected temperature by the belt thermistor 67 of the fixing belt 64 immediately before the rotation driving described above. And shows the maximum characteristics of the front and back temperatures.
In FIG. 8, the horizontal (x) axis indicates the temperature (° C.) detected by the belt thermistor 67 of the fixing belt 64 immediately before the rotational driving, and the vertical (y) axis indicates the maximum front-back temperature difference (° C.). For example, y = −0 .0776x + 12.113 relationship.
Based on the temperature detected by the belt thermistor 67 disposed so as to come into contact with the back surface of the fixing belt 64 from the maximum relationship between the detected temperature of the belt thermistor immediately before the rotation of the fixing belt shown in FIG. The temperature control unit 16 controls the temperature of the fixing belt 64.

Next, the operation of the fixing device will be described with reference to FIGS.
When the control unit 10 receives the print instruction, the control unit 10 sets a set temperature for fixing the toner on the paper based on the print information (paper thickness, size, type) included in the print instruction, The fixing motor control unit 14 drives the fixing motor 18 to rotate the upper pressure roller 63 shown in FIG. 3 in a direction indicated by an arrow B through a gear (not shown), and the fixing belt 64 is indicated by an arrow C in the figure. Rotate in the direction.

  The controller 10 that has rotated the upper pressure roller 63 and the fixing belt 64 determines whether or not the temperature detected by the belt thermistor 67 of the fixing device 6 by the temperature controller 16 is within a predetermined printable temperature range. Determine whether. When the control unit 10 determines that the temperature is within the printable temperature range, the sheet conveyance motor control unit 13 drives the sheet conveyance motor 17 to start sheet conveyance in order to start sheet conveyance.

  The printable temperature range is a temperature range in which the toner can be fixed to the paper, and is determined by TD1 as the lower allowable temperature and TD2 as the upper allowable temperature. The lower allowable temperature TD1 is, for example, a set temperature −20 ° C. for fixing the toner on the paper, and the upper allowable temperature TD2 is, for example, a set temperature + 20 ° C. for fixing the toner on the paper.

When the median value of the lower allowable temperature TD1 and the upper allowable temperature TD2 is the target temperature T_ctl, the lower control allowable temperature T1 and the upper control allowable temperature T2 for performing fixing temperature control are:
Lower allowable temperature TD1 <lower control allowable temperature T1 <target temperature T_ctl
Target temperature T_ctl <Upper control allowable temperature T2 <Upper allowable temperature TD2
The value is set to satisfy the relationship.
In this embodiment, the lower control allowable temperature T1 is the target temperature T_ctl-10 ° C., and the upper control allowable temperature T2 is the target temperature T_ctl + 10 ° C.

Next, referring to FIG. 1, FIG. 2 and FIG. 3, the temperature control processing performed by the temperature control unit will be described in accordance with the step represented by S in the flow chart showing the flow of the temperature control processing in the first embodiment of FIG. explain.
S101: When the control unit 10 receives the print instruction, the control unit 10 drives the fixing motor 18 by the fixing motor control unit 14, and rotates the upper pressure roller 63 shown in FIG. 3 in the direction indicated by the arrow B in the drawing. Then, the fixing belt 64 is rotated in the direction indicated by the arrow C in the drawing. When the fixing belt 64 starts rotating, the temperature control unit 16 acquires the initial belt temperature of the fixing belt 64 detected by the belt thermistor 67 of the fixing device 6.

In the present embodiment, hereinafter, the time interval at which the temperature control unit 16 detects the temperature of the fixing belt 64 by the belt thermistor 67 is, for example, 100 milliseconds. Further, the temperature control unit 16 detects the temperature of the fixing belt 64 by background processing.
S102: The temperature control unit 16 sets a target temperature T_ctl. Details of the target temperature T_ctl setting process will be described later.
S103: The temperature control unit 16 that has set the target temperature T_ctl acquires the temperature detected by the belt thermistor 67 of the fixing device 6.

S104: The temperature control unit 16 determines whether the detected temperature of the belt thermistor 67 is equal to or higher than the temperature obtained by subtracting the lower control allowable temperature T1 with the target temperature T_ctl as a reference.
Detection temperature of belt thermistor 67 ≧ (target temperature T_ctl−lower control allowable temperature T1)
If it is determined that it is satisfied, printing is started as described below, and the process proceeds to S106. If it is determined that it is not satisfied, the process proceeds to S105.

If the temperature control unit 16 determines that the detected temperature of the belt thermistor 67 is equal to or higher than “target temperature T_ctl−lower control allowable temperature T <b> 1”, the control unit 10 starts printing and the paper transport motor control unit 13. Thus, the paper transport motor 17 is driven to start paper feeding and transport.
The paper transport unit 4 transports the paper to the toner image forming unit 5 in accordance with the image formation timing, and the LED head 3 irradiates the toner image forming unit 5 with recording light corresponding to the printing information, and the toner image forming unit. 5 forms a toner image corresponding to the irradiated recording light on the paper.

The sheet on which the toner image is formed is conveyed to the fixing unit 6 by the sheet conveying unit 4, and after the toner image on the sheet is fixed by the heat and pressure of the fixing unit 6, the sheet is discharged out of the apparatus.
S105: The temperature control unit 16 that has determined that the detected temperature of the belt thermistor 67 is lower than “target temperature T_ctl−lower control allowable temperature T1” applies voltage to the fixing heater 61 to generate heat, and the process proceeds to S102. .

S106: The temperature control unit 16 that has determined that the detected temperature of the belt thermistor 67 is equal to or higher than “target temperature T_ctl−lower control allowable temperature T1”, the acquired detected temperature of the belt thermistor 67 is based on the target temperature T_ctl. It is below the temperature obtained by adding the upper control allowable temperature T2, that is,
Detection temperature of belt thermistor 67 ≦ (target temperature T_ctl + upper control allowable temperature T2)
If satisfied, the process proceeds to S108, and if not satisfied, the process proceeds to S107.

S107: The temperature control unit 16 that has determined that the detected temperature of the belt thermistor 67 is higher than “target temperature T_ctl + upper control allowable temperature T2” stops the power supply to the fixing heater 61, stops the heat generation, and the process proceeds to S102. Transition.
S108: When the temperature control unit 16 determines that the detected temperature of the belt thermistor 67 is equal to or lower than “target temperature T_ctl + upper control allowable temperature T2”, the control unit 10 gives an instruction to stop the rotation of the fixing belt 64 such as the end of printing. If there is no instruction, the process proceeds to S102 and the processes of S102 to S108 are repeated, whereby the temperature of the fixing belt 64 of the fixing device 6 can be maintained at the target temperature. On the other hand, when the control unit 10 determines that there is an instruction to stop the rotation of the fixing belt 64, the process ends.

  In this embodiment, the set target temperature T_ctl is corrected by the rotation amount of the fixing belt 64. The target temperature T_ctl is determined according to each paper setting by reading the target temperature from a ROM (Read Only Memory), which is a storage unit (not shown), according to the print setting received by the control unit 10 and the thickness and size of the paper. The target temperature can be set.

The target temperature setting process performed by the temperature controller 16 in S102 described above is shown in FIG. 1, FIG. 2, and FIG. 3 according to the step represented by S in the flowchart of the target temperature setting process in the first embodiment of FIG. Will be described with reference to FIG.
S111: The temperature control unit 16 reads a target reference temperature T_def (for example, T_def = 170 ° C.) that is a target temperature of the front surface of the fixing belt 64 from the storage unit.

S112: The temperature control unit 16 calculates an initial temperature difference Ts (for example, Ts = 10 ° C.) from the belt temperature (for example, 30 ° C.) measured in S101 of FIG.
The initial temperature difference Ts is a correction value calculated from the detected temperature of the belt thermistor 67 of the fixing belt 64 immediately before the rotational driving described in FIG.

As the initial temperature difference Ts, a function as shown in FIG. 8 obtained in advance is stored in the storage unit, and the temperature control unit 16 uses the temperature detected by the belt thermistor 67 of the fixing belt 64 immediately before the rotational drive. To calculate.
In this manner, the temperature control unit 16 determines the temperature difference between the inner peripheral surface (back surface) and the outer peripheral surface (front surface) of the fixing belt 64 from the temperature immediately before the rotation of the fixing belt 64 acquired from the belt thermistor 67. An initial temperature difference Ts is derived.

S113: The distance calculation unit 15 detects the rotation speed of the fixing belt 64 from the start of belt rotation by the sensor 68, and calculates the rotation amount (movement amount) X of the fixing belt 64.
S114: The temperature control unit 16 sets the correction value Tk according to the rotation amount X of the fixing belt 64 calculated by the distance calculation unit 15 (for example, the correction value Tk≈4 ° C. when the rotation amount X is 5000 mm × 1000). calculate.

  As described with reference to FIGS. 6 and 7, the correction value Tk is the initial temperature difference Ts calculated in S112 in consideration of the fact that the front-back temperature difference decreases as the rotation amount of the fixing belt 64 increases. A function in which the temperature difference between the front and back surfaces decreases with an increase in the rotation amount of the fixing belt 64, that is, a function similar to FIGS. 6 and 7, is stored in the storage unit, and the rotation amount X of the fixing belt 64 is determined based on the rotation amount X. Is calculated by the temperature control unit 16.

The temperature control unit 16 calculates and sets the target temperature T_ctl according to the following Equation 1 (for example, target temperature T_ctl = 170 ° C.−4 ° C. = 166 ° C.).
Target temperature T_ctl = target reference temperature T_def−correction value Tk (Expression 1)
In this embodiment, the value of the correction value Tk is obtained by an approximate function. As the approximation function, a function that is logarithmically approximated according to the characteristics of the temperature change is used.

  In this way, the temperature control unit 16 acquires the temperature immediately before the rotation of the fixing belt 64 by the belt thermistor 67, and uses the temperature immediately before the rotation of the fixing belt 64 and the rotation amount calculated by the distance calculation unit 15. Accordingly, the target temperature T_ctl is calculated, the present process is terminated, the process returns to S102 in FIG. 9, and the target temperature T_ctl is set.

By controlling the temperature of the fixing belt 64 as described above, the target temperature is corrected according to the back surface detection temperature of the fixing belt 64 and the rotation amount of the fixing belt 64, and the temperature of the front surface of the fixing belt 64 is adjusted. Since the target temperature is kept constant, the amount of heat applied to the print medium is stabilized and the print quality is improved.
Even when the pressure roller is equipped with a heater, an approximate function can be obtained by experiment as described above. Therefore, if the temperature control similar to the above-described temperature control is performed using the approximate function, printing can be performed. The amount of heat applied to the medium is stabilized, and the print quality is improved.

  As described above, in the first embodiment, the temperature control unit acquires the temperature immediately before the start of rotation of the fixing belt from the belt thermistor, and the temperature immediately before the start of rotation of the fixing belt and the distance calculation unit of the control unit By setting the target temperature according to the calculated amount of rotation and controlling the temperature of the fixing belt, the amount of heat given to the print medium by the fixing belt can be stabilized and the print quality can be improved. can get.

In the configuration of the second embodiment, a timer is added to the control unit in the configuration of the first embodiment shown in FIG. The configuration of the second embodiment will be described based on the block diagram showing the control configuration of the image forming apparatus in the second embodiment of FIG. Note that parts similar to those of the first embodiment described above are denoted by the same reference numerals and description thereof is omitted. Further, since the configuration of the image forming apparatus is the same as that of the first embodiment, the description thereof is omitted.
In FIG. 11, the control unit 10 of the image forming apparatus 1 includes an LED head control unit 11, a toner image formation processing unit 12, a paper transport motor control unit 13, a fixing motor control unit 14, a distance calculation unit 15, It consists of a temperature control unit 16 and a timer 21.
The timer 21 as the time measuring means measures the passage of time, and in this embodiment, measures the time when the fixing belt stops rotating.

The operation of the above configuration will be described.
First, when there is a temperature difference between the front and back of the fixing belt, the rotation of the fixing belt is stopped, and after a predetermined time has elapsed, the driving is restarted. The change of the difference will be described with reference to FIGS.

FIG. 12 is a graph showing the maximum relationship between the rotation stop time of the fixing belt and the front-back temperature difference in the second embodiment. In FIG. 12, the horizontal (x) axis shows the rotation stop time (seconds) of the fixing belt, and the vertical (y) axis shows the maximum (° C.) of the front-back temperature difference.
In FIG. 12, when the initial front and back temperature difference is 15 ° C., 8 ° C., and 2 ° C., the maximum y (° C.) of the front and back temperature difference is approximated by the following function, for example.
When the initial front / back temperature difference is 15 ° C., y = 14.716e ^−0.1376x
When the initial front / back temperature difference is 8 ° C., y = 7.3578e ^−0.1376x
When the initial front / back temperature difference is 2 ° C, y = 1.8395e ^-0.1376x

As shown in FIG. 12, the larger the front / back temperature difference when rotation is stopped, the more the front / back temperature difference of the fixing belt 64 is attenuated to 0 ° C. When the fixing belt 64 stops, the amount of heat from the fixing heater 61 is not transmitted, so the fixing belt 64 only dissipates heat, and the amount of heat dissipated depends on the members contacting the fixing belt 64 and the internal temperature of the fixing device 6. Due to the temperature difference, the greater the difference between the front and back temperature of the fixing belt 64 when stopped, the greater the temperature drop until a predetermined time elapses.
In addition, since the heat capacity of the fixing belt 64 is small, the time until the front-back temperature difference becomes around 0 ° C. is about 20 seconds.

FIG. 13 is a graph showing the relationship between the front and back temperature difference and the coefficient when rotation of the fixing belt is stopped in the second embodiment. Assuming that the coefficient of the approximate function shown in FIG. 12 is A, a linear characteristic (for example, y = 0.9197x + 0.6131) exists between the front and back temperature difference x when the rotation of the fixing belt 64 is stopped and the coefficient A (y). There is.
In this embodiment, in FIG. 12, the approximate function is a logarithmically approximated function according to the temperature change characteristic, but may be a linearly approximated function.

  Based on what has been described above, in a state where there is a difference in temperature between the front and back of the fixing belt, the temperature that the temperature control unit 16 performs when the rotation driving of the fixing belt is stopped and restarted after a predetermined time has elapsed. The control process will be described with reference to FIGS. 2, 3 and 11 in accordance with the step represented by S in the flowchart showing the flow of the temperature control process in the second embodiment of FIG.

S201, S202: The processing is the same as S101, S102 shown in FIG. Note that the target temperature setting process in S202 is the same process as in the first embodiment shown in FIG.
S203: The temperature control unit 16 performs a target temperature correction process. Details of the target temperature correction process will be described later.
S204 to S209: The processing is the same as S103 to S108 shown in FIG.

S210: The temperature control unit 16 stores the correction value Tk calculated in S114 shown in FIG. 10 in the storage unit as the temperature difference Tsl at the time of rotation stop, and ends this process.
The temperature difference Tsl at the time of rotation stop is the temperature difference between the inner peripheral surface and the outer peripheral surface of the fixing belt 64 derived from the temperature immediately before the rotation of the fixing belt 64 starts, and the rotation amount until the rotation stop calculated by the distance calculation unit 15. The temperature difference between the front and back when the rotation of the fixing belt 64 is derived.

Next, the target temperature correction processing performed by the temperature control unit 16 is shown in FIGS. 2, 3 and 11 according to the step indicated by S in the flowchart showing the flow of the target temperature correction processing in the second embodiment of FIG. Will be described with reference to FIG.
S211: The temperature control unit 16 reads a target reference temperature T_def (for example, T_def = 170 ° C.) from the storage unit.

S212: The temperature control unit 16 reads the temperature difference Tsl during rotation stop (for example, Tsl = 4 ° C.) from the storage unit.
S213: The temperature control unit 16 acquires the elapsed time from when the fixing belt 64 is stopped by using the timer 21, and sets it as the rotation stop time of the fixing belt 64. For example, the rotation stop time of the fixing belt 64 acquired by the timer 21 is 5 seconds.

  S214: The temperature control unit 16 uses the characteristic shown in FIG. 13 based on the rotation stop temperature difference Tsl read from the storage unit (for example, if the rotation stop temperature difference Tsl = 4 ° C., the coefficient A = 4). And a post-stop correction value Tkl is calculated based on the rotation stop time of the fixing belt 64 using a function similar to the graph shown in FIG. For example, the post-stop correction value Tkl is 2 ° C. according to FIG. 12, since the rotation stop time of the fixing belt 64 when the rotation stop temperature difference Tsl = 4 ° C. is 5 seconds.

Further, the temperature control unit 16 calculates and sets the target temperature T_ctl using the standard reference temperature T_def, the correction value Tk, and the post-stop correction value Tkl according to the following equation (for example, the target temperature T_ctl = 170 ° C.− 4 ° C-2 ° C = 164 ° C).
Target temperature T_ctl = target reference temperature T_def−correction value Tk−post-stop correction value Tkl (Expression 2)
The correction value Tk is a value calculated by the target temperature setting process shown in FIG.

Thus, the temperature control unit 16 corrects the post-stop correction calculated according to the rotation stop time of the fixing belt 64 measured by the timer 21 with respect to the target temperature T_ctl set in the target temperature setting process shown in FIG. Correction is made with the value Tkl, and the target temperature T_ctl after the rotation of the fixing belt 64 is stopped is calculated and set. Then, the present process is terminated and the process returns to S203 in FIG.
By controlling the temperature of the fixing belt 64 as described above, when the temperature difference between the front and back surfaces of the fixing belt 64 exists, the rotation driving of the fixing belt 64 is stopped, and after a predetermined time has elapsed, the driving is restarted. Even if it exists, since the temperature of the front surface of the fixing belt 64 is kept constant at the target temperature, the amount of heat given to the printing medium is stabilized and the printing quality is improved.

As described above, in the second embodiment, in addition to the effects of the first embodiment, the temperature control unit corrects the target temperature according to the rotation stop time of the fixing belt measured by the timer. Thus, in the state where there is a temperature difference between the front and back surfaces of the fixing belt, even if the rotation driving of the fixing belt is stopped and the driving is restarted after a predetermined time has elapsed, the amount of heat given to the printing medium is stabilized, and the printed product The effect that the position can be improved is obtained.
In the first and second embodiments, the image forming apparatus has been described as a printer. However, the image forming apparatus is not limited thereto, and may be a facsimile machine, a copier, a multifunction peripheral (MFP), or the like.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Paper feed cassette 3 LED head 4 Paper conveyance part 5 Toner image formation part 6 Fixing device 10 Control part 11 LED head control part 12 Toner image formation process part 13 Paper conveyance motor control part 14 Fixing motor control part 15 Distance Calculation unit 16 Temperature control unit 17 Paper transport motor 18 Fixing motor 21 Timer 61 Fixing heater 63 Upper pressure roller 64 Fixing belt 65 Lower pressure roller 67 Belt thermistor 68 Sensor 69 Belt support member

Claims (5)

A fixing unit that fixes the developer image on the print medium, and a control unit that controls the fixing unit;
The fixing unit is
A rotatable rotating member;
A rotatable pressing member that is disposed in contact with the rotating member and presses the print medium together with the rotating member;
A heating unit for heating the rotating member;
Temperature detecting means for detecting the temperature of the inner peripheral surface of the rotating member,
The control means includes
A distance calculation unit for calculating a rotation amount of the rotating member;
A temperature control unit that controls the heating unit based on the temperature detected by the temperature detection unit and controls the temperature of the rotating member to a target temperature;
The temperature control unit acquires a temperature immediately before the rotation of the rotating member from the temperature detection unit, and sets the target temperature according to the temperature immediately before the rotation starts and the rotation amount calculated by the distance calculation unit. An image forming apparatus. The image forming apparatus according to claim 1.
The image forming apparatus, wherein the rotating member is a belt. The image forming apparatus according to claim 1, wherein:
The temperature control unit derives a temperature difference between the inner peripheral surface and the outer peripheral surface of the rotating member from the temperature immediately before the rotation of the rotating member acquired from the temperature detecting unit, and the temperature difference and the distance calculating unit An image forming apparatus, wherein the target temperature is set according to the calculated rotation amount. The image forming apparatus according to any one of claims 1 to 3,
Comprising time measuring means for measuring the time when the rotating member stopped rotating,
The temperature control unit obtains the temperature immediately before the rotation of the rotating member from the temperature detection unit, and sets the target temperature according to the temperature immediately before the rotation start and the rotation amount calculated by the distance calculation unit. On the other hand, the target temperature is corrected according to the rotation stop time of the rotating member measured by the time measuring means. The image forming apparatus according to claim 4.
The temperature control unit is based on the temperature difference between the inner peripheral surface and the outer peripheral surface of the rotating member derived from the temperature immediately before the rotation of the rotating member starts, and the rotation amount until the rotation stop calculated by the distance calculating unit. The temperature difference between the inner peripheral surface and the outer peripheral surface when the rotation of the rotating member is stopped is derived, and the temperature difference between the inner peripheral surface and the outer peripheral surface at the time of the previous rotation stop and the rotation stop time of the rotating member are An image forming apparatus that corrects a target temperature.

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