JP7306187B2 - Image forming apparatus and image forming method - Google Patents

Description

The present invention relates to an image forming apparatus and an image forming method.

2. Description of the Related Art Conventionally, image forming apparatuses such as electrophotographic printers, copiers, facsimiles, and multifunction machines, for example, printers, are provided with image forming units for respective colors of black, yellow, magenta, and cyan, each of which has a photosensitive member. A drum, a charging roller, a developing roller, a toner supply roller, etc. are provided. In each image forming unit, the surface of the photosensitive drum uniformly charged by the charging roller is exposed by the LED head to form an electrostatic latent image, and the electrostatic latent image is developed by the developing roller. A toner image is formed as a developer image, and the toner images of each color are superimposed and transferred onto paper as a medium by a transfer roller to form a color toner image, and the color toner image is fixed on the paper by a fixing device. A color image is formed by being caused to do so.

By the way, the fixing device is, for example, a heating unit having a heater and a fixing belt disposed movably surrounding the heater, and the fixing belt is brought into contact with the heater so as to be rotatable. A backup roller is provided, and the toner image on the paper is heated by the heating unit when passing through the nip portion between the fixing belt and the backup roller, is pressed by the backup roller, and is fixed to the paper. Let me.

However, if the temperature in the longitudinal direction of the backup roller is uneven, or if the paper transport speed is uneven in the longitudinal direction of the nip portion, the paper will wrinkle.

Therefore, in order to prevent the paper from wrinkling, there is provided a printer provided with a fixing device provided with a backup roller having an inverted crown whose diameter increases from the central portion to both ends in the longitudinal direction. (See Patent Document 1, for example).

In the fixing device, since the peripheral speed of both ends of the backup roller is higher than the peripheral speed of the central portion, the paper is pulled toward the both ends, and slackness does not occur in the vicinity of the central portion of the paper. As a result, it is possible to prevent the paper from wrinkling.

JP 2017-3945 A

However, in the conventional printer, the paper transport speed differs depending on whether narrow paper is used or wide paper. If the conveying speed is uniformly controlled, depending on the width of the paper, the color toner image before being fixed may be rubbed, or color shift may occur between the toner images of each color, resulting in deterioration of the image quality. end up

The present invention solves the problems of the conventional printer described above, and enables image formation capable of improving the image quality without rubbing the developer image or causing color shift, etc., even if the width of the medium is different. An object of the present invention is to provide an apparatus and an image forming method.

For this purpose, in the image forming apparatus of the present invention, there are provided an image forming section for forming a developer image on a medium, a first fixing member in which a heating member is disposed, and from the central portion to both ends in the longitudinal direction. A second fixing member having a shape with an increased diameter and brought into contact with the heating member via the first fixing member is provided, and the fixing member is conveyed at a nip portion between the first and second fixing members. a fixing device for fixing the developer image on the medium to the medium; a fixing drive unit for conveying the medium in the nip; When the width of the medium is less than a predetermined value, the driving speed of the driving unit for fixing is set based on the temperature of the central portion, and when the width of the medium is greater than or equal to the predetermined value. and a drive processing unit for setting the drive speed of the fixing drive unit based on the temperature of the both ends.

According to the present invention, in the image forming apparatus, there are provided an image forming section for forming a developer image on a medium, a first fixing member in which a heating member is disposed, and from the central portion to both ends in the longitudinal direction. A second fixing member having a shape with an increased diameter and brought into contact with the heating member via the first fixing member is provided, and the fixing member is conveyed at a nip portion between the first and second fixing members. a fixing device for fixing the developer image on the medium to the medium; a fixing drive unit for conveying the medium in the nip; When the width of the medium is less than a predetermined value, the driving speed of the driving unit for fixing is set based on the temperature of the central portion, and when the width of the medium is greater than or equal to the predetermined value. and a drive processing unit for setting the drive speed of the fixing drive unit based on the temperature of the both ends.

In this case, the temperature of the central portion and the temperature of both ends in the longitudinal direction of the fixing device are detected, and the temperature of the driving portion for fixing is determined according to the width of the medium based on the temperature of the central portion and the temperature of both ends. Since the driving speed is set, even if the width of the medium is different, the developer image is not rubbed, the color shift is not generated, and the image quality can be improved.

In addition, by setting the driving speed of the driving unit for fixing based on the temperature of the central portion and the temperature of both ends, it is possible to form appropriate slack in the medium between the image forming unit and the fixing device. , the image forming apparatus can be miniaturized because there is no need to dispose a slackness sensor. As a result, the cost of the image forming apparatus can be reduced.

3 is a control block diagram of the printer according to the first embodiment of the invention; FIG. 1 is a conceptual diagram of a printer according to a first embodiment of the invention; FIG. 1 is a schematic diagram of a fixing device according to a first embodiment of the invention; FIG. It is a figure which shows the heater control circuit in the 1st Embodiment of this invention. It is a figure which shows the example of the drive signal pattern table in the 1st Embodiment of this invention. It is a figure which shows the example of the duty-ratio correction value table in the 1st Embodiment of this invention. FIG. 4 is a diagram showing a state in which slack is formed in the paper according to the first embodiment of the present invention; FIG. 4 is a diagram showing the relationship between the width of a sheet and the ratio of transport speeds according to the first embodiment of the present invention; It is a figure which shows the example of the rotational speed correction value table in the 1st Embodiment of this invention. 4 is a first flow chart showing operations of a print control unit and a fixing control unit according to the first embodiment of the present invention; 8 is a second flow chart showing operations of the print control section and the fixing control section according to the first embodiment of the present invention; FIG. 4 is a diagram showing a subroutine of heat treatment according to the first embodiment of the present invention; It is a figure which shows the example of the reference value table in the 1st Embodiment of this invention. FIG. 7 is a diagram for explaining the state of the fixing device when the duty ratio is set to 0[%] in the duty ratio correction control according to the first embodiment of the present invention; FIG. 10 is a diagram for explaining the state of the fixing device when PID control is performed based on the temperature deviation regardless of whether the paper is narrow or wide; FIG. 10 is a diagram showing a subroutine of heat treatment according to the second embodiment of the present invention; FIG. 10 is a diagram for explaining the state of the fixing device when heat treatment is performed in the second embodiment of the present invention;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this case, a printer as an image forming apparatus will be described.

FIG. 2 is a conceptual diagram of a printer according to the first embodiment of the invention.

In the figure, 10 is a printer, Cs is a housing of the printer 10, Bd is a main body of the printer 10, that is, a device main body, and a paper cassette 11 as a medium storage section is arranged at the bottom of the device main body Bd, A stacker St1 arranged in the paper cassette 11 is loaded with paper P as a medium. Adjacent to the front end of the paper cassette 11, a paper feeding mechanism for separating and feeding the paper P one by one is arranged.

The paper feed mechanism consists of a hopping roller 12 that rotates to feed out the paper P, and a separating member 13 that prevents double feeding of the paper P. The paper P is separated one by one by the paper feed mechanism to convey the medium. The paper is fed to the paper transport path Rt1 as a path, sent to the registration roller pair 14 disposed above the hopping roller 12, and after the skew is corrected by the registration roller pair 14, the transport rollers at a predetermined timing. 15 and supplied to the image forming section Q1 for forming a color image.

The image forming section Q1 includes image forming units 16Bk, 16Y, 16M, and 16C for black, yellow, magenta, and cyan, which are detachably attached to the apparatus main body Bd, and image forming units 16Bk, 16Y. , 16M, and 16C above the photoreceptor drums 31 as image carriers, facing the photoreceptor drums 31, LED heads 22 as exposure devices, and image forming units 16Bk, 16Y, 16M, and 16C. It consists of a transfer unit u1 arranged below.

Each of the LED heads 22 exposes the surface of the photosensitive drum 31 to form an electrostatic latent image as a latent image.

The transfer unit u1 includes a drive roller R1 as a first transfer roller, a driven roller R2 as a second transfer roller, and stretched between the drive roller R1 and the driven roller R2 so as to be free to travel. and a transfer belt 17 as a belt member, and a transfer member that is rotatably arranged to face the photosensitive drum 31 via the transfer belt 17 and forms a transfer portion between the photosensitive drum 31 and the transfer belt 17 . of transfer rollers 21 are provided.

The paper P supplied to the image forming section Q1 is conveyed as the transfer belt 17 is run, passes through the transfer section between each photosensitive drum 31 and each transfer roller 21, and at this time , toner images as developer images of respective colors formed on the respective photosensitive drums 31 in the image forming units 16Bk, 16Y, 16M, and 16C are sequentially superimposed and transferred onto the paper P by the respective transfer rollers 21 to transfer color images. A toner image is formed.

Then, the paper P onto which the color toner image has been transferred is sent to a fixing device 18 as a fixing device.

The fixing device 18 includes a fixing belt 45 as a first fixing member that is arranged to run freely, a heater Ht (FIG. 3) as a heating member that is arranged in the fixing belt 45 and will be described later, and A backup roller 47 as a second fixing member and as a fixing driving roller, which is rotatably arranged in contact with the heater Ht via the fixing belt 45, is provided, and a color toner image on the paper P is provided. is heated by the fixing belt 45 and pressed by the backup roller 47 to form the paper P to form a color image. A heating unit 46 is configured by the fixing belt 45 and the heater Ht.

Then, the paper P on which the color image is formed is ejected from the fixing device 18, transported by the pair of transport rollers 19, and then ejected outside the apparatus body Bd by the pair of ejection rollers 20 to be formed on the top of the housing Cs. are stacked on the stacked stacker St2.

Next, the image forming units 16Bk, 16Y, 16M and 16C will be described. Since the image forming units 16Bk, 16Y, 16M, and 16C all have the same structure, the image forming unit 16Bk will be explained, and the explanation of the image forming units 16Y, 16M, and 16C will be omitted.

The image forming unit 16Bk includes a body of the image forming unit 16Bk extending in the width direction of the paper P, that is, a unit body 37, and a developing device detachably attached to the unit body 37. A toner cartridge 41 is provided as a developer reservoir, and toner (not shown) as a black developer is accommodated in the toner cartridge 41 .

The image forming unit 16Bk is rotatably arranged in the unit main body 37 in contact with the photosensitive drum 31 and the photosensitive drum 31, and the photosensitive drum 31 is rotated clockwise. As a result, the charging roller 32 as a charging device that uniformly charges the surface of the photosensitive drum 31 is rotated in the direction opposite to the rotation direction of the photosensitive drum 31, that is, in the counterclockwise direction. A developer carrier is rotatably disposed in contact with the body drum 31 and is rotated counterclockwise to attach toner to the electrostatic latent image on the photosensitive drum 31 to develop the electrostatic latent image. It includes a developing roller 33 as a body, a cleaning device 36 for scraping off toner remaining on the photosensitive drum 31 after the transfer of the toner image, and removing the toner as waste toner.

A writing sensor s1 is arranged between the conveying roller pair 15 and the image forming section Q1, and the writing sensor s1 detects the presence or absence of the sheet P in the sheet conveying path Rt1. The detection signal of the writing sensor s1 serves as a reference for the timing for exposing the photosensitive drum 31 by the LED head 22 and the timing for applying a high voltage to the transfer roller 21. FIG.

An exit sensor s2 is provided between the fixing device 18 and the transport roller pair 19, and the exit sensor s2 detects the presence or absence of the paper P in the paper transport path Rt1. Based on the detection signal of the exit sensor s2, it is determined whether or not all the image forming processes for the paper P have been completed, that is, whether or not printing has been completed.

Next, the fixing device 18 will be described.

FIG. 3 is a schematic diagram of a fixing device according to the first embodiment of the invention. In the figure, the horizontal axis represents the longitudinal position of the backup roller 47, and the vertical axis represents the roller diameter (radius) of the backup roller 47. As shown in FIG.

In the figure, 18 is a fixing device, 46 is a heating unit, 47 is a backup roller, and the heating unit 46 has a heater Ht and a fixing belt 45 .

The fixing belt 45 is formed of a cylindrical film having a multi-layered structure, and includes a metal substrate such as polyimide (PI) or stainless steel (SUS), an elastic layer made of silicone rubber covering the substrate, and a coating layer (or tubular surface layer) made of a fluororesin such as polytetrafluoroethylene (PTFE) or perfluoroalkoxyalkane (PFA) covering the elastic layer.

The backup roller 47 has an outermost layer formed of a metal core, an elastic layer made of a rubber material covering the metal core, and a tube made of a fluorine resin such as perfluoroalkoxyalkane (PFA) covering the elastic layer. release layers, each layer being adhered to one another.

When the paper P is conveyed through the nip portion Np between the fixing belt 45 and the backup roller 47 , the color toner image transferred in the transfer portion and adhered to the paper P by weak electrostatic force is transferred to the fixing belt 45 . is heated and melted by the heat of the backup roller 47 and fixed to the paper P by the pressure of the backup roller 47 .

By the way, as the paper P, not only plain paper with a basis weight of about 70 to 80 [gsm] but also thin paper, envelopes, etc. with a basis weight of 60 [gsm] or less are used. , wrinkles occur in the paper P when the transport speed of the paper P in the longitudinal direction of the nip portion Np is uneven.

Therefore, in the present embodiment, in order to prevent the paper P from being wrinkled, the backup roller 47 has a different diameter at the central portion and at both ends in the longitudinal direction, and the diameter is different from the central portion to both ends. The backup roller 47 is formed in a shape with a larger diameter, ie, an inverted crown shape, so that when the backup roller 47 is rotated, the peripheral speed of both ends of the backup roller 47 is higher than the peripheral speed of the central portion. As a result, the transport speed of the paper P at both ends of the nip portion Np becomes higher than the transport speed of the paper P at the center, and the paper P is pulled toward both ends, so that the paper P near the center becomes loose. , and wrinkles on the paper P can be prevented.

In this embodiment, the diameter of the backup roller 47 increases at a constant rate of change from the central portion to both ends in the longitudinal direction, and the outer peripheral surface Sa of the backup roller 47 is at a predetermined angle with respect to the axis of the backup roller 47. be tilted.

Further, in the present embodiment, the speed ratio γ of the transport speed of the paper P in the nip portion Np differs by approximately 0.2% between the minimum value and the maximum width of the paper P used. A reverse crown amount Aq of the backup roller 47 is set. For example, when the diameter of both ends of the backup roller 47 is r1, the diameter of the central portion is r2, and the value obtained by subtracting the diameter r2 from the diameter r1 is the reverse crown amount Aq, the reverse crown amount Aq is
Aq=r1-r2
= 0.2 [mm]
be made.

As the heater Ht, a planar heater composed of a planar heating element extending in the longitudinal direction is used. The heater Ht is formed by sequentially laminating an electrical insulating layer, a resistive heating layer, an electrode and a protective layer on a substrate made of stainless steel or ceramic, and generates heat by supplying electric power through the electrodes. In order to suppress temperature unevenness in the longitudinal direction of the fixing belt 45 heated by the heater Ht, a metal heat diffusion member with high thermal conductivity is arranged between the heater Ht and the fixing belt 45 . can be set.

Also, the surface of the heater Ht is coated with grease to enhance the slidability between the heater Ht and the fixing belt 45 .

Further, the heater Ht is divided into three parts along the fixing belt 45 in the longitudinal direction. It consists of a side heater LH as a first edge heating section located and a side heater RH as a second edge heating section located on the right side when looking at the downstream side in the conveying direction of the paper P. Note that the side heaters LH and RH constitute both end heating portions.

The main heater MH and the side heaters LH and RH are independently driven to be turned on and off, and the side heaters LH and RH are driven to be turned on and off simultaneously.

The dimensions of the main heater MH and the side heaters LH and RH are arbitrarily determined according to the specifications of the printer 10, operator's requests, and the like. In this embodiment, the distance between the left end of the side heater LH and the right end of the side heater RH is set so that the distance between both ends of the main heater MH is equal to the width of A4 size paper (210 [mm]). is determined to be equal to the length of A4 size paper (297 mm), which is the maximum printable width of the printer 10 .

When the paper P whose width is equal to or less than the width of the A4 size paper is used, only the main heater MH is turned on and off, and the width is greater than the width of the A4 size paper and the length of the A4 size paper. When the following paper P is used, the main heater MH is turned on/off, and the side heaters LH and RH are turned on/off according to the width of the paper P.

For this purpose, a main thermistor Ms as a first detection unit on the heating side is provided at the longitudinal center of the back surface of the main heater MH. Side thermistors Ls and Rs are provided as a second detection unit, and the temperatures of the main heater MH and the side heaters LH and RH are detected by the main thermistor Ms and the side thermistors Ls and Rs.

Further, outside the fixing belt 45, an infrared temperature sensor Is is arranged as a third detecting section on the heating side for detecting the temperature of the surface of the fixing belt 45. As shown in FIG. The infrared temperature sensor Is is a non-contact temperature sensor, and is arranged so as to face the fixing belt 45 and be positioned at the center of the main heater MH on the inlet side of the fixing device 18 in the paper P transport direction. Receives infrared rays radiated from the surface of the fixing belt 45 and converts the amount of light into temperature.

Further, in order to detect the temperature of the surface of the backup roller 47, a main thermistor Mt as a pressure-side first detection unit is installed at the center of the backup roller 47 in the longitudinal direction. Side thermistors Lt and Rt as a second detection unit on the pressurizing side are arranged in the vicinity.

The main thermistor Mt and the side thermistors Lt and Rt indirectly detect the surface temperature of the fixing belt 45 . Therefore, when continuous printing is performed on narrow paper P, it is possible to monitor an increase in the temperature of the portion of the surface of the fixing belt 45 that does not contact the paper P, that is, the non-paper-passing portion.

Side thermistors Ls and Rs arranged on the back surface of the heater Ht may be used to detect the temperature of the surface of the fixing belt 45 and monitor the increase in the temperature of the non-paper passing portion. In this case, the surface temperature of the fixing belt 45 detected by the side thermistors Ls and Rs may fluctuate depending on the thickness of the paper P conveyed through the nip portion Np, and the temperature of the non-paper-passing portion may rise. cannot be monitored accurately. Therefore, by detecting the surface temperature of the fixing belt 45 not only by the side thermistors Ls and Rs but also by the main thermistor Ms, the surface temperature detected by the side thermistors Ls and Rs and the surface temperature detected by the main thermistor Ms Based on the temperature difference from the surface temperature, it is possible to monitor the increase in the temperature of the non-sheet-passing area. That is, by monitoring whether the temperature difference between the surface temperature detected by the side thermistors Ls and Rs and the surface temperature detected by the main thermistor Ms increases, the temperature rise in the non-sheet-passing area can be prevented. can be monitored.

Next, a control device for the printer 10 will be described.

FIG. 1 is a control block diagram of a printer according to the first embodiment of the invention.

In the figure, reference numeral 50 denotes a print control unit as a first control unit; 51, a fixing control unit as a second control unit that controls the fixing device 18 (FIG. 2); A ROM 52 as a first storage section consisting of a volatile memory, a RAM 53 as a second storage section consisting of a volatile memory, an operation panel 54, a paper feed motor 55 as a drive section for paper feed, and a drive section for transfer. belt motor 56, an ID motor 57 as a driving unit for image formation, a fixing motor 58 as a driving unit for fixing, an LED head 22, a high voltage circuit 59, etc., and the backup roller 47 is connected to the fixing motor 58. be done.

The print control unit 50 includes a CPU as an arithmetic unit (not shown), an input/output port, etc., and performs various processes based on programs recorded in the ROM 52 .

In the ROM 52, in addition to recording the programs and various setting values, a paper size table in which the paper size of each paper P accommodated in the paper cassette 11, that is, the length and width of the paper P is recorded, A drive signal pattern table in which pattern data for generating drive signals SG1 and SG2 (FIG. 4), which will be described later, is recorded, and a duty ratio correction value for correcting the center reference duty ratio Duty1(n), which will be described later. A duty ratio correction value table in which α is recorded, and a rotation speed correction value table and a reference value table for setting the rotation speed, which is the driving speed of the fixing motor 58, are provided.

Upon receiving print data from a host computer (not shown) as a host device, the print control unit 50 drives the image forming unit Q1 based on the print data to form a color toner image on the paper P. FIG.

Then, the fixing control section 51 drives the fixing device 18 to fix the color toner image on the paper P to the paper P. As shown in FIG.

For this purpose, the fixing control section 51 includes a heat processing section Pr1 and a drive processing section Pr2. The heat processing unit Pr1 controls the temperature of the fixing device 18, which is the surface temperature of the fixing belt 45 in the present embodiment, so as to reach a target temperature according to the printing conditions such as the thickness and width of the paper P. . Further, the drive processing unit Pr2 controls the rotational speed of the fixing motor 58 based on the width of the paper P, the temperature of the surface of the fixing belt 45, and the like.

The operation panel 54 includes a display unit (not shown) composed of an LED screen or the like for displaying the status of the printer 10, and an operation unit (not shown) composed of switches, keys, etc. for the operator to input instructions to the printer 10.

The paper feed motor 55 is composed of a stepping motor, a DC motor, or the like, and rotates the hopping roller 12 to feed the paper P from the paper cassette 11, and rotates the registration roller pair 14 and the transport roller pair 15 to transport the paper P. do.

The belt motor 56 is composed of a stepping motor, a DC motor, or the like, and rotates the driving roller R1 to cause the transfer belt 17 to run.

The ID motor 57 is a DC motor, and rotates the photosensitive drum 31, charging roller 32, developing roller 33, etc. in each of the image forming units 16Bk, 16Y, 16M, and 16C.

The fixing motor 58 consists of a DC motor, rotates the backup roller 47, runs the fixing belt 45 of the fixing device 18, conveys the paper P in the nip portion Np (FIG. 3), and rotates the conveying roller pair 19. to convey the paper P, and rotate the discharge roller pair 20 to discharge the paper P to the outside of the apparatus main body Bd. In the fixing device 18, the rotation of the fixing motor 58 is transmitted to the backup roller 47 after being decelerated through a gear train (not shown).

The high voltage circuit 59 applies high voltage to the charging roller 32, developing roller 33, etc. in each of the image forming units 16Bk, 16Y, 16M, and 16C, and applies high voltage to the transfer roller 21 in the transfer unit u1.

Next, a heater control circuit for driving the heater Ht and turning it on and off will be described.

FIG. 4 is a diagram showing a heater control circuit according to the first embodiment of the invention.

In the figure, 60 is a heater control circuit, 51 is a fixing control section, 61 is a triac drive circuit, 63 is a commercial power supply that is an AC power supply, Ht is a heater, MH is a main heater, LH and RH are side heaters, Ms and Mt are Main thermistor, Ls, Rs, Lt, and Rt are side thermistors, Is is an infrared temperature sensor, TR1 is a triac as a main switching element that turns on/off the main heater MH, and TR2 is a secondary that turns on/off the side heaters LH and RH. A triac as a switching element.

Sensor outputs of the main thermistors Ms, Mt, the side thermistors Ls, Rs, Lt, Rt, and the infrared temperature sensor Is are sent to the fixing controller 51 .

One terminal of the commercial power supply 63 is connected to one electrode of each of the main heater MH and the side heaters LH and RH. It is connected to each other electrode of LH and RH.

The triac drive circuit 61 is composed of a photo-triac (not shown), is insulated between the primary side and the secondary side, is connected to the fixing control section 51 on the primary side, and is connected to the gate terminals of the triacs TR1 and TR2 on the secondary side. be done.

When the drive signal SG1 for the main heater MH and the drive signal SG2 for the side heaters LH and RH are sent from the fixing control section 51 to the triac drive circuit 61, the triac drive circuit 61 sets the duty ratio representing the pulse width of the drive signals SG1 and SG2. The triacs TR1 and TR2 are driven according to the ratios Duty1 and Duty2 to change the ON time and the power supplied to the main heater MH and the side heaters LH and RH. The drive signals SG1 and SG2 are composed of signals of "1" (high level) or "0" (low level) set every 10 [ms] when one control cycle is 100 [ms]. .

Next, the operation of the heat processing section Pr1 of the fixing control section 51 will be described.

FIG. 5 is a diagram showing an example of a drive signal pattern table according to the first embodiment of the invention, and FIG. 6 is a diagram showing an example of a duty ratio correction value table according to the first embodiment of the invention. In FIG. 6, the horizontal axis represents the width of the paper P, and the vertical axis represents the duty ratio correction value α.

First, when the temperature of the surface of the fixing belt 45 detected by the infrared temperature sensor Is is defined as a detection temperature Ts, the detection temperature Ts is the temperature of the surface of the fixing belt 45 determined by the printing conditions such as the thickness and width of the paper P. The heat treatment performed so as to reach the target temperature Te will be described.

In this case, the heat processing section Pr1 (FIG. 1) determines the difference between the target temperature Te and the detected temperature Ts, that is, the temperature deviation ε
ε=Te−Ts
PID control based on is performed every 100 [ms] which is a control cycle, and the central reference duty ratio Duty1(n) in n control cycles for turning on/off the main heater MH
Duty1(n)=Kp*ε+Ki*Σε+Kd*dε/dt
+DutyMod1 (n-1) [%] ……(1)
Calculate

Note that in equation (1), Kp is a proportional gain, Ki is an integral gain, and Kd is a differential gain. DutyMod1(n-1) is the remainder of the central reference duty ratio Duty1(n-1) that was not consumed in the previous control cycle, ie, the n-1 control cycle.

Subsequently, the heat processing unit Pr1 refers to the drive signal pattern table provided in the ROM 52 as shown in FIG. A driving signal SG1 is generated based on the pattern data and sent to the triac driving circuit 61 (FIG. 4).

The drive signal pattern table defines a duty ratio Duty1 of 1 [%] to 100 [%] as 0 [%] or more and less than 10 [%], 10 [%] or more and less than 20 [%], 20 [%] or more and less than 30 [%], 30 [%] or more and less than 40 [%], 40 [%] or more and less than 50 [%], 50 [%] or more, and Less than 60 [%], 60 [%] or more and less than 70 [%], 70 [%] or more and less than 80 [%], 80 [%] or more and less than 90 [%], 90 [ %] or more and less than 100 [%] and No. divided into 100 [%]. 1 to No. Each pattern is formed by dividing one control cycle into 10 patterns, and each pattern consists of 10 "1" or "0" set every 10 [ms]. ] signals.

For example, when the duty ratio Duty1(n) is 100[%], No. Since all of the 10 signals set every 10 [ms] of the 11 patterns are "1", the drive signals SG1 and SG2 are continuously high for 100 [ms], which is one control period. leveled.

Further, when the duty ratio Duty1(n) is 25[%], No. 10 signals set every 10 [ms] of 3 patterns are "1", "0", "0", "0", "0", "1", "0", " 0”, “0”, and “0”, the drive signals SG1 and SG2 are given by
0 [ms] ≤ τ < 10 [ms]
is held high during
10 [ms] ≤ τ < 50 [ms]
is held low during
50 [ms] ≤ τ < 60 [ms]
is held high during
60 [ms] ≤ τ < 100 [ms]
is held low during

And no. In pattern 3, a common signal is set for any duty ratio Duty1(n) of 20% or more and less than 30%, so 20% of 25% is consumed to generate the drive signals SG1 and SG2, and 5[%] is added as the remainder DutyMod1(n) in the calculation of the duty ratio Duty1(n+1) in the next n+1 control cycles.

That is, No. 1 to No. In each pattern of 10, 0 [%], 10 [%], 20 [%], 30 [%], 40 [%], 50 [%], 60 [%], 70 [%], 80 [%] And the portion exceeding 90[%] is taken as the remainder DutyMod1(n) and added to the calculation of the next control cycle.

Further, the heat processing unit Pr1 performs duty ratio correction control according to the width of the paper P to be used, and generates a duty ratio Duty2(n) based on both ends for turning on/off the side heaters LH and RH. do.

For this purpose, the heat processing unit Pr1 refers to the paper size table to read the width of the paper P to be used, and also refers to the duty ratio correction value table as shown in FIG. Based on the duty ratio correction value α, the center reference duty ratio Duty1(n) is corrected, and both end reference duties for turning on/off the side heaters LH and RH are read out. Ratio Duty2(n)
Duty2(n)=(Duty1(n)-DutyMod1(n-1))*α
+Duty Mod2 (n-1) [%] ……(2)
Calculate

In formula (2), DutyMod1(n-1) and DutyMod2(n-1) are the duty ratios Duty1(n-1) and Duty2(n-1) that were not consumed in n-1 control cycles. It's left over.

Subsequently, the heat processing unit Pr1 refers to the drive signal pattern table, reads pattern data corresponding to the duty ratio Duty2(n) based on both ends, generates a drive signal SG2 based on the pattern data, and generates a triac. It is sent to the drive circuit 61 .

As shown in the duty ratio correction value table in FIG. 6, when the width of the paper P is less than 210 [mm], which is the width of the A4 size paper, the duty ratio correction value α is set to 0 [%]. When the width of the paper P is 210 [mm] or more, the duty ratio correction value α is increased in proportion to the width of the paper P. The paper P having a width of less than 220 [mm] is defined as a narrow paper, and the paper P having a width of 220 [mm] or more is defined as a wide paper.

Therefore, the narrower the width of the paper P, the smaller the duty ratio correction value α and the duty ratio Duty2(n) based on both ends. When the drive signal SG2 is generated, the time during which the drive signal SG2 is high level is shortened.

As a result, when continuous printing is performed on narrow paper, it is possible to suppress an increase in the temperature of the non-paper passing portion of the backup roller 47 .

In this embodiment, the width of the paper P is read from the paper size table of the ROM 52, but the operator operates the operation section of the operation panel 54 to change the width of the paper cassette 11 (FIG. 2). The width of the sheet P accommodated in can be directly input. Further, a sensor (for example, a line sensor) for detecting the width of the paper P is arranged on the paper transport path Rt1, the width of the paper P detected by the sensor is read, and the paper P is guided to the paper cassette 11. A sensor for detecting the width of the paper P can be arranged based on the position of the guide, and the width of the paper P detected by the sensor can be read.

In the present embodiment, since the main thermistor Ms and the side thermistors Ls, Rs are arranged on the rear surfaces of the main heater MH and the side heaters LH, RH, the main heater MH and the side heaters LH, RH are turned on/off. Although it is possible to directly control the off state, the proper temperatures of the main heater MH and the side heaters LH and RH differ depending on the paper size, thickness, etc. of the paper P used. The on/off of the side heaters LH and RH cannot be optimally controlled.

Therefore, in the present embodiment, on/off of the side heaters LH and RH is controlled based on the duty ratio correction value α.

By the way, the backup roller 47 is formed with the elastic layer so that it can press the paper P with a sufficient pressure even when the color toner image on the paper P conveyed through the nip portion Np is thick. It has become so.

Further, the elastic layer has a sponge structure so that the heat of the main heater MH is sufficiently transferred to the paper P without being absorbed by the elastic layer.

However, if the elastic layer has a sponge structure, the coefficient of thermal expansion increases, so the thermal expansion of the backup roller 47 itself changes the transport speed of the paper P in the fixing device 18 . That is, when the temperature of the surface of the backup roller 47 is low, the diameter of the backup roller 47 becomes small, and the conveying speed of the paper P in the fixing device 18 becomes low. The diameter of the fixing device 47 is increased, and the conveying speed of the paper P in the fixing device 18 is increased.

In this case, in the paper transport path Rt1, the paper P is transported while being nipped between the photosensitive drum 31 and the transfer belt 17 in the image forming section Q1 and between the fixing belt 45 and the backup roller 47 in the fixing device 18. Therefore, when the temperature of the surface of the backup roller 47 is high and the conveying speed of the paper P in the fixing device 18 is high, tension is applied to the paper P, and the color toner image before being fixed may be rubbed or the color toner image may be rubbed. Color misregistration occurs between toner images, and the image quality is degraded.

Therefore, in the present embodiment, between the image forming section Q1 and the fixing device 18, the paper P is appropriately slackened.

FIG. 7 is a diagram showing a state in which slack is formed in the paper according to the first embodiment of the present invention.

In the figure, Rt1 is a paper transport path, P is paper, Q1 is an image forming section, R1 is a driving roller, 18 is a fixing device, 45 is a fixing belt, and 47 is a backup roller.

In this case, when the temperature of the surface of the backup roller 47 is low and the conveying speed of the paper P in the fixing device 18 increases, slack is formed in the paper P at the slack forming portion Ar1 between the image forming portion Q1 and the fixing device 18. be.

Therefore, it is possible to prevent tension from being applied to the paper P, and the color toner images before being fixed are not rubbed, and the toner images of the respective colors are prevented from being out of alignment. Quality can be improved.

By the way, in the present embodiment, the backup roller 47 is formed in an inverted crown shape in which the diameter increases from the central portion to both ends in the longitudinal direction. becomes higher.

FIG. 8 is a diagram showing the relationship between the width of the sheet and the speed ratio of the transport speed in the first embodiment of the present invention. In the figure, the horizontal axis represents the width of the paper P, and the vertical axis represents the speed ratio γ of the transport speed.

The figure shows the speed ratio γ when the transport speed when the width of the paper P is set to the minimum value is Vmin and the transport speed when the width of the paper P is changed is V.
γ=100.000*(V/Vmin) [%]
represents

As can be seen from the figure, as the width of the paper P increases, the speed ratio γ increases proportionally. The diameter of both ends of the backup roller 47 is r1, the diameter of the central portion is r2, and the value obtained by subtracting the diameter r2 from the diameter r1 or the value obtained by dividing the diameter r1 by the diameter r2 is the inverse crown amount Aq.
Aq=r1−r2 (or r1/r2)
, in this embodiment, the reverse crown amount Aq is set.

Therefore, according to the surface temperature of the backup roller 47, the rotation speed of the fixing motor 58 (FIG. 1) is uniformly changed. If the amount of slack is optimized based on the transport speed, the amount of slack becomes excessive when narrow paper is used as the paper P, and when the narrow paper is used as the paper P, the backup roller 47 If the amount of slack is set to an optimum value based on the transport speed of the central portion of the sheet P, the amount of slack becomes too small when wide paper is used.

Therefore, in the present embodiment, the drive processor Pr2 sets the rotation speed of the fixing motor 58 according to the temperature of the surface of the backup roller 47 in the longitudinal direction.

Therefore, the fixing control unit 51 switches the main thermistor Mt and the side thermistors Lt, Rt in order to set the rotational speed of the fixing motor 58 according to the width of the paper P used.

FIG. 9 is a diagram showing an example of a rotational speed correction value table according to the first embodiment of the invention. In the figure, the horizontal axis represents the surface temperature of the backup roller 47, and the vertical axis represents the rotation speed correction value β.

That is, when wide paper is used as the paper P, the fixing controller 51 reads the temperature of the surface of the both ends of the backup roller 47 detected by the side thermistors Lt and Rt, and stores the temperature in the ROM 52 as shown in the figure. By referring to the rotation speed correction value table provided, the rotation speed correction value β corresponding to the surface temperature at both ends is read, and the rotation speed of the fixing motor 58 is set based on the rotation speed correction value β. Further, when narrow paper is used as the paper P, the fixing controller 51 reads the surface temperature of the central portion of the backup roller 47 detected by the main thermistor Mt, refers to the rotation speed correction value table, A rotation speed correction value β corresponding to the surface temperature of the central portion is read, and the rotation speed of the fixing motor 58 is set based on the rotation speed correction value β.

Therefore, when wide paper is used as the paper P, the rotation speed of the fixing motor 58 is set based on the rotation speed correction value β corresponding to the temperature of the surface at both ends of the backup roller 47, and the narrow width paper is used as the paper P. When paper is used, the rotation speed of the fixing motor 58 is set based on the rotation speed correction value β corresponding to the temperature of the surface of the central portion of the backup roller 47. Therefore, the amount of slack in the paper P can be adjusted appropriately. can do.

Next, operations of the print control unit 50 and the fixing control unit 51 when setting the rotational speed of the fixing motor 58 will be described.

FIG. 10 is a first flowchart showing the operation of the print control section and the fixing control section according to the first embodiment of the present invention, and FIG. FIG. 12 is a second flowchart showing the operation, FIG. 12 is a diagram showing a heat treatment subroutine in the first embodiment of the present invention, and FIG. 13 is a diagram showing an example of a reference value table in the first embodiment of the present invention. is.

The print control unit 50 waits for a print request to be sent from the host computer to the printer 10 .

When the print request is transmitted, the fixing control section 51 determines whether the width of the paper P used for printing is less than a predetermined value. In the present embodiment, the predetermined value is set to 220 [mm], which is the width at which the duty ratio correction value α is 20 [%] in the duty ratio correction value table (FIG. 6). Therefore, the fixing control section 51 determines whether the width of the paper P used for printing is less than 220 [mm], that is, whether the paper P is narrow paper.

When the width of the paper P is less than 220 mm and the width of the paper P is narrow, the fixing control unit 51 adjusts the temperature of the surface of the central portion of the fixing belt 45 when heating the fixing belt 45. Set the center reference as the reference. Further, when the width of the paper P is 220 mm or more and the paper P is wide paper, the fixing control unit 51 heats the fixing belt 45 based on the temperature of the surface of both ends of the fixing belt 45 . Set the end criteria to be .

Next, the fixing controller 51 starts heating the heater Ht and starts warming up the fixing device 18 .

Subsequently, the fixing control unit 51 performs heat processing by the heat processing unit Pr1 and driving processing by the drive processing unit Pr2 in parallel.

The heat processing part Pr1 determines whether or not the center reference is set, and if the center reference is set, the duty ratio of the center reference is determined based on the temperature deviation ε between the target temperature Te and the detected temperature Ts. Duty1(n) is calculated, and based on the central reference duty ratio Duty1(n), a drive signal SG1 is generated to turn on/off the main heater MH.

When the center reference is not set and both end references are set, the heat processing unit Pr1 sets the center reference duty ratio Duty1(n ) is calculated, and based on the central reference duty ratio Duty1(n), the driving signal SG1 is generated to turn on/off the main heater MH. Subsequently, the heat processing section Pr1 performs duty ratio correction control according to the width of the paper P to be used, refers to the paper size table, reads out the width of the paper P to be used, and adjusts the duty ratio correction value. By referring to the table, the duty ratio correction value α corresponding to the width of the paper P is read, and based on the duty ratio correction value α, the duty ratio Duty2(n) in n control cycles based on both ends is calculated. Based on the reference duty ratio Duty2(n), the drive signal SG2 is generated to turn on/off the side heaters LH and RH.

During this time, the drive processing unit Pr2 performs drive processing to drive the fixing motor 58, and the print control unit 50 performs print control to print on the paper P. FIG.

Therefore, the drive processing unit Pr2 waits until the driving conditions for the fixing motor 58 are satisfied, and starts driving the fixing motor 58 when the driving conditions are satisfied. In this case, the fixing unit 18 has finished warming up, and the temperature of the main heater MH detected by the main thermistor Ms and the temperature of the side heaters LH and RH detected by the side thermistors Ls and Rs are The surface of the heater Ht is coated with the temperature of the main heater MH, which is detected by the main thermistor Ms, whether the print data received from the host computer has been edited, and whether a predetermined temperature has been reached. When the temperature of the main heater MH and the temperatures of the side heaters LH and RH reach the predetermined temperatures, editing of print data is completed, and the temperature of the main heater MH is determined. becomes the temperature at which the grease melts or higher, the drive condition for the fixing motor 58 is established, and the drive processing unit Pr2 starts driving the fixing motor 58. FIG.

When the host computer sends a subsequent print request after the print request is completed, the heating of the heater Ht and the driving of the fixing motor 58 are automatically skipped in the flow chart of FIG.

Subsequently, the print control unit 50 waits until the print start condition is satisfied, and starts printing when the print start condition is satisfied.

In this case, it is determined whether or not the surface temperature of the fixing belt 45, which is the temperature Ts detected by the infrared temperature sensor Is (FIG. 3), has reached the target temperature Te. When the detected temperature Ts reaches the target temperature Te, printing is started. Condition is met. It is also possible to determine that the print start condition is met when the detected temperature Ts reaches a temperature several degrees lower than the target temperature Te.

Subsequently, the drive processing unit Pr2 performs rotation speed setting processing to set the rotation speed of the fixing motor 58 .

Therefore, when the paper P is narrow paper and the central portion reference is set, the fixing control section 51 reads the surface temperature Tcenter of the central portion of the backup roller 47 detected by the main thermistor Mt, and By referring to the rotation speed correction value table (FIG. 9), the rotation speed correction value β corresponding to the temperature Tcenter is read. Read out the speed reference value N1 of the rotation speed for.

Subsequently, the drive processing unit Pr2 determines the rotation speed Nn of the fixing motor 58 when the paper P is narrow paper and the central portion reference is set.
Nn=N1*(1+β)
set.

Further, when the paper P is wide paper and the both-ends reference is set, the fixing controller 51 reads the surface temperatures TLside, TRside of the both ends of the backup roller 47 detected by the side thermistors Lt, Rt. , the average value Tside of the temperatures TLside and TRside
Tside=(TLside+TRside)/2
is calculated, the rotational speed correction value table is referenced to read the rotational speed correction value β corresponding to the average value Tside, and the reference value table is referenced to read the speed reference value N2 of the rotational speed for wide paper.

Subsequently, the drive processing unit Pr2 determines the rotation speed Nw of the fixing motor 58 when the paper P is wide paper.
Nw=N2*(1+β)
set.

In this embodiment, since the backup roller 47 is formed in an inverted crown shape, the transport speed when a narrow paper is transported in the nip portion Np is higher than the transport speed when a wide paper is transported. low. Therefore, the speed reference value N1 of the rotation speed of the fixing motor 58 is made higher than the speed reference value N2.

Further, in the present embodiment, when the paper P is narrow paper, the rotation speed correction value table and the reference value table are referred to, and the rotational speed corresponding to the temperature Tcenter of the surface of the central portion of the backup roller 47 is determined. When the speed correction value β and the speed reference value N1 for narrow paper are read, the rotation speed Nn of the fixing motor 58 is set, and the paper P is wide paper, the rotation speed correction value table is referred to, The rotation speed correction value β corresponding to the average value Tside of the surface temperatures TLside and TRside of both ends of the backup roller 47 and the speed reference value N2 for wide paper are read out, and the rotation speed Nw of the fixing roller 58 is set. However, the rotation speeds Nn and Nw can be set without referring to the rotation speed correction value table.

In that case, when the paper P is narrow paper, the reference temperature of the surface of the central portion of the backup roller 47 is set to the reference temperature T1, and when the paper P is wide paper, the temperature of both ends of the backup roller 47 is set to the reference temperature T1. Assuming that the reference value of the surface temperature is the reference temperature T2, and the coefficient that is the adjustment value due to the thermal expansion of the backup roller 47 is δ, the paper P is a narrow paper, and fixing is performed when the central portion reference is set. The rotation speed Nn of the motor 58 is
Nn=N1*(1+δ*(T1-Tcenter))
, and the rotation speed Nw of the fixing motor 58 when the paper P is wide paper and the both-ends reference is set is
Nw=N2*(1+δ*(T2-Tside))
become.

In this embodiment, the reference temperature T2 for wide paper is set lower than the reference temperature T1 for narrow paper, but the reference temperature T2 and the reference temperature T1 can be made equal.

Next, the print control unit 50 reads the detection signal from the exit sensor s2 (FIG. 2) and determines whether printing has ended based on the detection signal. In this embodiment, the presence or absence of the paper P in the paper transport path Rt1 is detected based on the detection signal, and the print control unit 50 detects that there is no paper P in the paper transport path Rt1. When a predetermined time has passed since the detection, it is determined that printing has ended.

Subsequently, the print control unit 50 determines whether or not a subsequent print request has been transmitted from the host computer. is less than 220 [mm], that is, whether the paper P is narrow paper.

On the other hand, when the host computer does not send a subsequent print request, the fixing control section 51 stops the heating of the heater Ht and stops the driving of the fixing motor 58 .

Next, the flow charts of FIGS. 10 and 11 will be described.
Step S1 The print control unit 50 waits for a print request to be sent from the host computer, and proceeds to step S2 when the print request is sent.
Step S2 The fixing control section 51 determines whether the width of the paper P is less than a predetermined value. If the width of the paper P is less than the predetermined value, the process proceeds to step S3, and if the width of the paper P is greater than or equal to the predetermined value, the process proceeds to step S4.
Step S3 The fixing control section 51 sets the center reference.
Step S4 The fixing control section 51 sets both end reference.
Step S5 The fixing controller 51 starts heating the heater Ht.
Step S6 The heat processing unit Pr1 performs heat processing, and the process proceeds to step S14.
Step S7 The driving processing section Pr2 waits until the driving conditions for the fixing motor 58 are established. If the conditions for driving the fixing motor 58 are satisfied, the process proceeds to step S8.
Step S8 The driving processing section Pr2 starts driving the fixing motor 58. FIG.
Step S9 The print control unit 50 waits for the print start condition to be satisfied. If the print start condition is met, the process proceeds to step S10.
Step S10 The print control unit 50 starts printing.
Step S11 The drive processing unit Pr2 performs rotation speed setting processing.
Step S12 The print control unit 50 determines whether printing has ended. If the printing is completed, the process proceeds to step S13, and if the printing is not completed, the process returns to step S11.
Step S13 The print control unit 50 determines whether a subsequent print request has been sent from the host computer. If the subsequent print request has been transmitted, the process returns to step S2, and if the subsequent print request has not been transmitted, the process proceeds to step S14.
Step S14 The fixing controller 51 stops the heating of the heater Ht, stops the driving of the fixing motor 58, and ends the process.

Next, the flowchart of FIG. 12 will be described.
Step S6-1 The heat processing section Pr1 determines whether or not the center reference is set. If the center reference is set, the process proceeds to step S6-2, and if the center reference is not set, the process proceeds to step S6-3.
Step S6-2 The heat processing section Pr1 turns on/off the main heater MH based on the central reference duty ratio Duty1(n), and returns.
Step S6-3 The heat processing section Pr1 turns on/off the main heater MH based on the central reference duty ratio Duty1(n).
Step S6-4 The heat processing section Pr1 turns on/off the side heaters LH and RH based on the duty ratio Duty2(n) based on both ends, and returns.

As described above, in the present embodiment, the temperature Tcenter of the surface of the central portion of the backup roller 47 and the temperatures TLside and TRside of the surfaces of both ends of the backup roller 47 are detected. Since the rotation speeds Nn and Nw of the fixing motor 58 are set based on the temperature Tcenter and the surface temperatures TLside and TRside at both ends, even if the width of the paper P is different, the speed of the paper P in the longitudinal direction of the nip portion Np is reduced. There is no unevenness in the conveying speed, and the color toner image is not rubbed or color misregistration occurs. As a result, image quality can be improved.

In addition, since the paper P can be properly slackened between the image forming section Q1 and the fixing device 18, there is no need to provide a slackness sensor, and the size of the printer 10 can be reduced. can lower the cost of

By the way, since the heater Ht is divided in the longitudinal direction, from the viewpoint of fixing the toner image on the paper P, when the paper P having a narrow width, for example, the width of the A4 size paper or less is used. , duty ratio correction control can be performed in the heating process, and the duty ratio Duty2(n) of the drive signal SG2 for turning on/off the side heaters LH and RH can be set to 0 [%].

However, when the duty ratio Duty2(n) of the driving signal SG2 is set to 0%, the conveying speed of the paper P in the longitudinal direction of the nip portion Np becomes uneven, and a twisting force is applied to the fixing belt 45. The load applied to the base material accumulates, and the fixing belt 45 may break.

FIG. 14 is a diagram for explaining the state of the fixing device when the duty ratio is set to 0[%] in the duty ratio correction control according to the first embodiment of the present invention.

In the figure, 18 is a fixing unit, 45 is a fixing belt, 47 is a backup roller, Np is a nip portion, MH is a main heater, LH and RH are side heaters, Mt is a main thermistor, Lt and Rt are side thermistors, and Mv1 is a nip. The transport speeds Lv1 and Rv1 of the paper P at the central portion of the portion Np are the transport speeds of the paper P at both ends of the nip portion Np.

In the present embodiment, when the duty ratio Duty2(n) of the drive signal SG2 is set to 0 [%] in the heating process, the portion of the backup roller 47 facing the main heater MH is heated and the temperature rises. Since the diameter is increased by thermal expansion, the conveying speed Mv1 of the paper P in the nip portion Np is increased, whereas the portions of the backup roller 47 facing the side heaters LH and RH are not heated and the temperature is low. Since the diameter cannot be increased up to now, the transport speeds Lv1 and Rv1 of the paper P at the nip portion Np do not increase.

As a result, the conveying speeds Mv1, Lv1, and Rv1 of the paper P in the longitudinal direction of the nip portion Np become uneven, a force in the twisting direction is applied to the fixing belt 45, and the load applied to the base material accumulates. may break in the regions ArL and ArR.

On the other hand, even if the PID control is performed based on the temperature deviation ε between the target temperature Te and the detected temperature Ts regardless of the width of the paper P without performing the duty ratio correction control in the heating process, the paper in the longitudinal direction of the nip portion Np The transport speed of P is uneven, a force in the twisting direction is applied to the fixing belt 45, and the load applied to the base material is accumulated, and the fixing belt 45 may break.

FIG. 15 is a diagram for explaining the state of the fixing device when PID control is performed based on the temperature deviation regardless of whether the paper is narrow or wide.

In the figure, 18 is a fixing device, 45 is a fixing belt, 47 is a backup roller, Np is a nip portion, MH is a main heater, LH and RH are side heaters, Mt is a main thermistor, Lt and Rt are side thermistors, and Mv2 is a nip. The transport speeds Lv2 and Rv2 of the paper P at the central portion of the portion Np are the transport speeds of the paper P at both ends of the nip portion Np.

In this case, if PID control is performed based on the temperature deviation ε regardless of the width of the paper P in the heating process, the portions of the backup roller 47 facing the side heaters LH and RH are heated from the portions facing the main heater MH. , and the conveying speeds Lv2 and Rv2 of the paper P at the nip portion Np become higher than the conveying speed Mv2.

As a result, the conveying speeds Mv2, Lv2, and Rv2 of the paper P in the longitudinal direction of the nip portion Np become uneven, a force in the twisting direction is applied to the fixing belt 45, and the load applied to the base material accumulates. may break in the regions ArL and ArR.

Therefore, a second embodiment of the present invention that can prevent the force in the twisting direction from being applied to the fixing belt 45 will be described. The same reference numerals are assigned to components having the same structure as in the first embodiment, and the effects of the same embodiment are used for the effects of the invention due to having the same structure.

FIG. 16 is a diagram showing a heat processing subroutine in the second embodiment of the present invention, and FIG. 17 is a diagram for explaining the state of the fixing device when heat processing is performed in the second embodiment of the present invention. It is a diagram.

17, 18 is a fixing device as a fixing device, 45 is a fixing belt as a first fixing member, 47 is a backup roller as a second fixing member and a fixing drive roller, Np is a nip portion, MH is the main heater as the central heating part, LH and RH are the side heaters as the first and second end heating parts, Mt is the main thermistor as the first detection part on the pressure side, Lt and Rt are the pressure side. Mv3 is the transport speed of the paper P (FIG. 2) as a medium in the central portion of the nip portion Np, and Lv3 and Rv3 are the transport speeds of the paper P at both ends of the nip portion Np. be.

In this case, the heat processing part Pr1 (FIG. 1) determines whether or not the center reference is set, and if the center reference is set, based on the temperature deviation ε between the target temperature Te and the detected temperature Ts Then, based on the central reference duty ratio Duty1(n), the drive signal SG1 is generated to turn on/off the main heater MH.

Further, the heat processing part Pr1 measures the temperatures of the surfaces of the central portion and both ends, in this embodiment, the temperature Tcenter of the surface of the central portion of the backup roller 47 detected by the main thermistor Mt, the side thermistor Lt, The side heaters LH and RH are turned on/off based on the surface temperatures TLside and TRside of the both ends of the backup roller 47 detected by Rt.

For this purpose, the heat processing section Pr1 reads the temperature Tcenter of the surface of the central portion of the backup roller 47, reads the temperatures TLside and TRside of the surfaces of both ends of the backup roller 47, and obtains the average value Tside of the temperatures TLside and TRside.
Tside=(TLside+TRside)/2
is calculated, and the difference between the central surface temperature Tcenter and the average value Tside, that is, the detected temperature difference μ
μ = T center - T side
is the set temperature μth, and the side heaters LH and RH are turned on and off.

Based on experimental results, the set temperature μth is set so that the transport speed Mv3 of the paper P at the central portion of the nip portion Np and the transport speeds Lv3 and Rv3 of the paper P at both ends of the nip portion Np are equal. That is, the outer diameter difference between the diameter of the center portion of the backup roller 47 and the diameter of both ends of the backup roller 47 in the inverted crown shape is set to cancel out.

In the present embodiment, the conveying speeds Mv3, Lv3, and Rv3 of the paper P at the nip portion Np are uniform in the longitudinal direction, and the force in the twisting direction is not applied to the fixing belt 45, so that the fixing belt 45 breaks. can be prevented.

Next, the flowchart of FIG. 16 will be described.
Step S6-11 The heat processing section Pr1 determines whether or not the center reference is set. If the center reference is set, the process proceeds to step S6-12, and if the center reference is not set, the process proceeds to step S6-14.
Step S6-12 The heat processing section Pr1 turns on/off the main heater MH based on the central reference duty ratio Duty1(n).
Step S6-13 The heat processing section Pr1 turns on/off the side heaters LH and RH based on the detected temperature difference μ, and returns.
Step S6-14 The heat processing section Pr1 turns on/off the main heater MH based on the center reference duty ratio Duty1(n).
Step S6-15 The heat processing part Pr1 turns on/off the side heaters LH and RH based on the duty ratio Duty2(n) based on both ends, and returns.

As described above, in the present embodiment, PID control is performed so that the detected temperature difference μ becomes the set temperature μth. can do. As a result, no twisting force is applied to the fixing belt 45, so that the fixing belt 45 is not broken.

In the present embodiment, PID control is performed so that the detected temperature difference μ becomes the set temperature μth, but it is also possible to perform PID control so that the detected temperature difference μ becomes zero.

In each of the above-described embodiments, the backup roller 47 is formed in an inverted crown shape, but the backup roller 47 may be formed in a crown shape in which the diameter decreases from the central portion to both ends in the longitudinal direction. can also

Note that even when the backup roller 47 has a straight shape in which the diameters are equal at the central portion and at both end portions in the longitudinal direction, heat treatment is performed by the fixing control section 51 as in each of the above-described embodiments, and the surface of the central portion is The side heaters LH and RH are turned on and off so that the detected temperature difference μ between the temperature Tcenter and the average value Tside becomes the set temperature μth, and the conveying speed of the paper P in the longitudinal direction of the nip portion Np is not uneven. can be made

Although the printer 10 has been described in each of the above-described embodiments, the present invention can be applied to image forming apparatuses such as copiers, facsimiles, and multi-function machines.

It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made based on the gist of the present invention, and they are not excluded from the scope of the present invention.

10 Printer 18 Fixing device 45 Fixing belt 47 Backup roller 58 Fixing motor Ht Heater Is Infrared temperature sensor Lt, Rt Side thermistor Mt Main thermistor Nn, Nw Rotation speed Np Nip part P Paper Pr2 Drive processing part Q1 Image forming part Tcenter Central part Surface temperature TLside, TRside Surface temperature at both ends

Claims (12)

(a) an image forming unit that forms a developer image on a medium;
(b) a first fixing member in which a heating member is disposed; a fixing device that includes a second fixing member that is brought into contact with the fixing device, and fixes the developer image on the conveyed medium to the medium at a nip portion between the first and second fixing members;
(c) a fusing drive for transporting media in the nip;
(d) a detection unit that detects the temperature at the central portion and the temperature at both ends in the longitudinal direction of the fixing device;
(e) when the width of the medium is less than a predetermined value, setting the driving speed of the driving unit for fixing based on the temperature of the central portion; and a drive processor that sets the drive speed of the drive unit for fixing based on the temperature of the drive unit. 2. The image forming apparatus according to claim 1, wherein the temperature of the central portion and the temperature of the both ends are temperatures of the surface of the second fixing member. 3. The image forming apparatus according to claim 1, wherein the heating member is divided in the longitudinal direction along the first fixing member, and includes a central heating section located in the center and both end heating sections located at both ends. . 4. The image forming apparatus according to claim 3, further comprising a heat processing section that drives the central heating section of the heating member based on a temperature deviation between a target temperature and a detected temperature of the central section of the fixing device. 5. The image forming apparatus according to claim 4, wherein the target temperature of the central portion is the temperature of the surface of the first fixing member. 6. The image forming apparatus according to claim 4, wherein the heat processing section calculates a duty ratio based on the temperature deviation, and drives the central heating section based on the duty ratio. The heating processing section corrects the duty ratio for driving the central heating section based on a duty ratio correction value corresponding to the width of the medium, and drives both end heating sections based on the corrected duty ratio. Item 7. The image forming apparatus according to item 6 . 8. The image forming apparatus according to claim 7 , wherein, when the width of the medium is less than a predetermined value, the heat processing section drives both end heating sections based on a detected temperature difference between the temperature of the center portion and the temperature of both end portions. . 9. The image forming apparatus according to claim 8, wherein the temperature of the central portion and the temperature of the both ends are temperatures of the surface of the second fixing member. When the width of the medium is less than a predetermined value, the heat processing section heats both ends so that the detected temperature difference becomes a set temperature that cancels out the outer diameter difference between the diameter of the central portion and the diameter of the both ends. 10. The image forming apparatus according to claim 8, wherein the image forming apparatus is driven. 10. The image forming apparatus according to claim 8, wherein when the width of the medium is less than a predetermined value, the heat processing section drives the both-end heating section so that the detected temperature difference becomes zero. An image forming portion for forming a developer image on a medium, a first fixing member in which a heating member is disposed, and a shape with a diameter increasing from a central portion to both ends in a longitudinal direction, the first fixing member a second fixing member that is brought into contact with the heating member via the fixing member, and fixes the developer image on the conveyed medium to the medium at the nip portion between the first and second fixing members. In an image forming method for an image forming apparatus having a device and a fixing drive section for conveying a medium in the nip section,
(a) detecting the temperature at the central portion and the temperatures at both ends in the longitudinal direction of the fixing device;
(b) when the width of the medium is less than a predetermined value, setting the driving speed of the drive unit for fixing based on the temperature of the central portion; An image forming method, wherein the driving speed of the driving unit for fixing is set based on the temperature of the fixing unit.

Images