JP7567641B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming device.

Conventionally, in image forming devices such as printers, copiers, facsimile machines, and multifunction machines, for example electrophotographic printers, a toner image is formed on the surface of a photoconductor drum in the image forming section, the toner image is transferred to paper as a medium, and then fixed to the paper in a fixing device as a fixing device to form an image and perform printing.

A belt-type fixing device includes a heating unit that is arranged to be free to move and has a fixing belt with a heater arranged inside, and a pressure roller that is arranged to be free to rotate and is pressed against the heater via the fixing belt. In the fixing device, the temperature of the fixing belt is detected by a fixing thermistor arranged opposite the outer circumferential surface of the fixing belt, and the temperature of the heater is detected by a heater thermistor arranged in contact with the heater, and the heater is controlled based on the temperature of the fixing belt and the temperature of the heater (see, for example, Patent Document 1).

JP 2020-71325 A

However, in the conventional fixing device, it is not possible to appropriately control the heater according to various printing conditions, such as the transport speed of the paper transported through the fixing section between the fixing belt and the pressure roller, and the thickness of the paper, resulting in a decrease in image quality.

The present invention aims to provide an image forming device that solves the problems of the conventional fixing unit, can appropriately control the heater according to various printing conditions, and can improve image quality.

To this end, the image forming apparatus of the present invention includes a belt member, a heater disposed within the belt member for heating the belt member, a first temperature detection unit disposed within the belt member on the rear side of the heater, a second temperature detection unit disposed outside the belt member facing the outer peripheral surface of the belt member, and a heating control processing unit for controlling the heater based on the temperatures detected by the first and second temperature detection units.

The heating control processing unit then controls the heater by changing the weights of the detected temperatures detected by the first temperature detection unit and the second temperature detection unit according to the transport speed and thickness of the medium transported through the fixing unit.

According to the present invention, the image forming device includes a belt member, a heater disposed within the belt member for heating the belt member, a first temperature detection unit disposed within the belt member on the rear side of the heater, a second temperature detection unit disposed outside the belt member facing the outer peripheral surface of the belt member, and a heating control processing unit for controlling the heater based on the temperatures detected by the first and second temperature detection units.

The heating control processing unit then controls the heater by changing the weights of the detected temperatures detected by the first temperature detection unit and the second temperature detection unit according to the transport speed and thickness of the medium transported through the fixing unit.

In this case, the weights of the detected temperatures detected by the first temperature detection unit and the second temperature detection unit are changed according to the transport speed and thickness of the medium transported through the fixing unit, so the heater can be appropriately controlled to accommodate a variety of printing conditions. As a result, image quality can be improved.

FIG. 2 is a control block diagram of the printer according to the embodiment of the present invention. 1 is a conceptual diagram of a printer according to an embodiment of the present invention. FIG. 2 is a detailed diagram of a fixing unit according to the embodiment of the present invention. 6 is a flowchart showing the operation of a control unit in the printer of the reference example. 5 is a time chart for explaining image quality when printing is performed in a first printing mode in the printer of the reference example. 10 is a time chart for explaining image quality when printing is performed in a second printing mode in the printer of the reference example. 10 is a time chart for explaining image quality when printing is performed in a third printing mode in the printer of the reference example. 5 is a flowchart showing an operation of a control unit in the embodiment of the present invention. FIG. 4 is a diagram showing an example of a heating control table according to the embodiment of the present invention. 5 is a time chart for explaining image quality when printing is performed in a first printing mode according to the embodiment of the present invention. 6 is a time chart for explaining image quality when printing is performed in a second printing mode in the embodiment of the present invention. 10 is a time chart for explaining image quality when printing is performed in a third printing mode in the embodiment of the present invention.

The following describes in detail an embodiment of the present invention with reference to the drawings. In this case, a printer will be described as an image forming device.

Figure 2 is a conceptual diagram of a printer according to an embodiment of the present invention, and Figure 3 is a detailed diagram of a fixing unit according to an embodiment of the present invention.

In FIG. 2, 10 is the printer, Cs is the housing that is the exterior of the printer 10, Wt is the top wall, and Bd is the main body of the printer 10, i.e., the device main body.

A paper cassette 11 is disposed at the bottom of the device body Bd as a medium storage section, and paper P is stored in the paper cassette 11. A hopping roller 13 is disposed at the front end of the paper cassette 11 as a feeding member. When the hopping roller 13 is rotated, the paper P is separated one by one and fed out to the paper transport path Rt1 as the medium transport path.

In the paper transport path Rt1, a pair of paper feed rollers m1 serving as a first transport member is disposed adjacent to the hopping roller, and downstream of the pair of paper feed rollers m1, a writing sensor s1 serving as a first medium detection unit that detects the position of the paper P before an image is formed is disposed, and downstream of the writing sensor s1, a pair of registration rollers m2 serving as a second transport member is disposed. Then, downstream of the pair of registration rollers m2 in the paper transport path Rt1, an image forming unit Q1 is disposed.

The image forming section Q1 is composed of an image forming unit 16, an LED head Hd as an exposure device, a transfer roller 18 as a transfer member, etc., and in the image forming unit 16, a toner cartridge Ct as a developer container that contains toner as a developer, a photosensitive drum 21 as an image carrier, a charging roller 22 (FIG. 1) as a charging device described below, a developing roller 23 as a developer carrier described below, etc. are arranged.

A fixing device, 31, is disposed downstream of the image forming section Q1 on the paper transport path Rt1. The fixing device 31 includes a heating unit 34 as a first fixing member, and a pressure roller 35 as a second fixing member disposed opposite the heating unit 34, and fixes the toner image, which is a developer image on the paper P sent from the image forming section Q1, to the paper P.

In addition, an entrance sensor s2 serving as a second medium detection unit is disposed adjacent to the fixing unit 31 upstream of the fixing unit 31 on the paper transport path Rt1, and an exit sensor s3 serving as a third medium detection unit is disposed adjacent to the fixing unit 31 downstream of the fixing unit 31. The entrance sensor s2 detects the position of the leading edge of the paper P immediately before the toner image is fixed in the fixing unit 31, and the exit sensor s3 detects the position of the trailing edge of the paper P immediately after the toner image is fixed in the fixing unit 31.

A transport roller pair m3 serving as a third transport member is disposed downstream of the exit sensor s3 on the paper transport path Rt1, and a discharge roller pair m4 serving as a fourth transport member for discharging the paper P outside the device body Bd is disposed downstream of the transport roller pair m3. A discharge port h1 is formed adjacent to the discharge roller pair m4, and a stacker sk for stacking the paper P discharged from the discharge port h1 is formed on the top wall Wt.

Next, we will explain the fixing unit 31.

In FIG. 3, 31 is a fixing unit, 34 is a heating unit fixedly arranged within the device body Bd, 35 is a pressure roller rotatably arranged within the device body Bd, and 50 is a control unit that controls the entire printer 10.

The heating unit 34 includes a heater (flat heater) Ht as a heating element, a heat diffusion member 31 disposed in contact with a surface Sa of the heater Ht on the pressure roller 35 side of the heater Ht, and a heat diffusion member 32 disposed on the pressure roller 35 side of the heater Ht.
7, a heater thermistor s4 as a first temperature detection unit disposed on the back surface Sb side of the heater Ht, and a fixing belt 32 as a belt member disposed so as to be freely movable and surrounding the heater Ht, the heat diffusion member 37 and the heater thermistor s4.

The heater Ht is composed of a planar heating element arranged to extend in the width direction of the paper P within the fixing belt 32, and is formed by laminating an electrical insulating layer, a resistive heating element, electrodes, and a protective layer in that order on a stainless steel substrate. A power source 49 is connected to the electrodes, and a predetermined amount of power is supplied from the power source 49 to the resistive heating element, causing the heating portion of the resistive heating element to heat up. The longitudinal dimension of the heating portion is 224 mm so that it can print on paper P of Letter vertical size (width 215.9 mm).

The heat diffusion member 37 is made of stainless steel and is made of a plate material arranged to extend in the width direction of the paper P within the fixing belt 32, and transmits the heat generated by the heater Ht to the fixing belt 32 with minimal unevenness in the longitudinal direction.

The fixing belt 32 is made of a resin film material having a cylindrical shape, both ends of which are supported by predetermined support members (not shown), and is caused to rotate as the pressure roller 35 rotates. In this embodiment, the fixing belt 32 is made of a film material, but the fixing belt 32 can also be made of a rubber material, SUS (stainless steel), or the like. As the fixing belt 32 runs, friction occurs between the heat diffusion member 37 and the inner surface of the fixing belt 32, so that grease (not shown) is applied to the surface of the heat diffusion member 37 to improve the sliding properties between the heat diffusion member 37 and the fixing belt 32.

The heater thermistor s4 is a contact-type temperature detection unit that is disposed in contact with the back surface Sb of the heater Ht at a predetermined location in the longitudinal direction of the heater Ht within the fixing belt 32, and detects the temperature of the heater Ht.

The pressure roller 35 is driven by a fixing motor M3 (FIG. 1) (described later) as a drive unit for fixing, and rotates in the direction of arrow A. The pressure roller 35 is also pressed against the heater Ht and the heat diffusion member 37 via the fixing belt 32 by a pressure mechanism (not shown), forming a nip portion Np as a fixing portion between the pressure roller 35 and the fixing belt 32.

The fixing unit 31 is provided with a fixing thermistor s5 as a second temperature detection unit that is disposed upstream of the fixing unit 31 on the paper transport path Rt1, i.e., on the entrance side of the fixing unit 31, facing the outer circumferential surface of the fixing belt 32, and detects the temperature of the surface of the fixing belt 32. The fixing thermistor s5 is a non-contact temperature detection unit that is disposed outside the fixing belt 32 at a predetermined distance from the outer circumferential surface of the fixing belt 32, receives infrared rays emitted from the surface of the fixing belt 32, and converts the amount of infrared light into temperature.

If the fixing thermistor s5 is disposed in contact with the back surface Sb of the heater Ht within the fixing belt 32, the thermal conductivity from the front surface Sa to the back surface Sb of the heater Ht is low, making it difficult to accurately detect the temperature of the surface of the fixing belt 32. Furthermore, if the fixing thermistor s5 is disposed in contact with the inner surface of the fixing belt 32 within the fixing belt 32, contact between the fixing thermistor s5 and the inner surface of the fixing belt 32 can cause unevenness in the grease applied to the inner surface of the fixing belt 32 or contact marks on the inner surface of the fixing belt 32, resulting in band-like unevenness in the image.

Furthermore, if the fixing thermistor s5 is disposed downstream of the fixing device 31 in the transport direction of the paper P, water vapor generated from the paper P during fixing may adhere to the fixing belt 32. In that case, the amount of infrared light emitted from the outer surface of the fixing belt 32 changes, making it impossible to accurately detect the temperature of the outer surface of the fixing belt 32.

Next, the operation of the printer 10 will be described.

When the transport motor M2, which serves as a drive unit for transport and will be described later, is driven and the hopping roller 13 is rotated, the paper P is separated one by one and fed to the paper transport path Rt1.

The fed paper P is transported by the paper feed roller pair m1, and after skew is corrected by the registration roller pair m2, it is sent to the image forming unit Q1.

At this time, when the writing sensor s1 detects the position of the paper P, the drive motor M1 (described later) serving as a drive unit for image formation is driven, and in the image forming unit Q1, the photoconductor drum 21 is rotated, and the charging roller 22 uniformly charges the surface of the photoconductor drum 21. Then, when the LED head Hd exposes the photoconductor drum 21 according to the image data, an electrostatic latent image is formed as a latent image on the surface of the photoconductor drum 21, and the developing roller 23 attaches toner to the electrostatic latent image, developing the electrostatic latent image and forming a toner image.

Next, the paper P is transported between the photoconductor drum 21 and the transfer roller 18, during which the toner image is transferred onto the paper P.

Then, the paper P onto which the toner image has been transferred is sent to the fixing device 31, and while being transported through the nip portion Np between the fixing belt 32 and the pressure roller 35, the toner image that has been attached to the paper P by weak electrostatic force is heated and melted by the fixing belt 32, and is then pressed by the pressure roller 35 to be fixed to the paper P. In this way, an image is formed on the paper P.

The paper P on which the image has been formed is transported by the transport roller pair m3, and is discharged from the device body Bd through the discharge port h1 by the discharge roller pair m4, and is then loaded onto the stacker sk.

Next, we will explain the control device of the printer 10.

Figure 1 is a control block diagram of a printer in an embodiment of the present invention.

In the figure, 10 is a printer, and the PC is a host computer as a higher-level device connected to the printer 10 via a wired or wireless LAN or the like.

50 is a control unit, IF is an interface unit as a communication unit that connects the printer 10 to the host computer PC and receives print data from the host computer PC to accept print requests and transmits printer 10 status information to the host computer PC, 53 is a ROM as a first storage unit, and 54 is a RAM as a second storage unit. In this embodiment, a rewritable flash ROM or the like is used as the ROM 53.

The control unit 50 includes a CPU as a calculation device (not shown), an input/output port, a timer, etc., and controls the entire printer 10 at a predetermined control period, which in this embodiment is 0.1 seconds, and performs various processes based on a program recorded in ROM 53. In addition to the program, the ROM 53 also records settings, thresholds, etc. required for the control unit 50 to perform the various processes. In this embodiment, the ROM 53 also stores a heating control table Tb1 (FIG. 9) for calculating the on-duty Dty described below.

In addition to image data generated based on the print data and used for printing, various control data is temporarily stored in the RAM 54. The RAM 54 functions as a work area when the CPU performs calculations.

43 is a power source for applying a charging voltage to the charging roller 22, 44 is a power source for applying a developing voltage to the developing roller 23, 45 is a power source for applying a transfer voltage to the transfer roller 18, M1 is a drive motor for rotating the photosensitive drum 21, the developing roller 23, etc., 46 is a power source for driving the drive motor M1, M2 is a conveying motor for rotating the paper feed roller pair m1, the registration roller pair m2, the conveying roller pair m3, the discharge roller pair m4, etc., 47 is a power source for driving the conveying motor M2, M3 is a fixing motor for rotating the pressure roller 35, 48 is a power source for driving the fixing motor M3, 49 is a power source for supplying power to the heater Ht, and Hd is an LED head.

In addition, s1 is the writing sensor, s2 is the entrance sensor, s3 is the exit sensor, s4 is the heater thermistor, and s5 is the fixing thermistor.

The control unit 50 has a print processing unit Pr1, a heating control processing unit Pr2, etc.

The print processing unit Pr1 performs the print process, receives print data from the host computer PC, and when a print request is received, converts the print data into image data, drives the LED head Hd based on the image data, forms an image on the paper P, and performs printing.

The heating control processing unit Pr2 performs heating control processing and controls the heater Ht based on the temperature detected by the heater thermistor s4, i.e., the detected temperature Ts1, and the temperature detected by the fixing thermistor s5, i.e., the detected temperature Ts2. To achieve this, the heating control processing unit Pr2 changes the weights of the detected temperatures Ts1 and Ts2, in this embodiment the first and second coefficients ε1 and ε2 described below, in accordance with the printing conditions of the transport speed and thickness of the paper P transported through the nip portion Np, calculates the on-duty Dty, and turns the heater Ht on and off.

Next, we will explain the images that are printed in different printing conditions using the printer 10 of the reference example.

First, we will explain the operation of the printer 10 in the reference example.

Figure 4 is a flowchart showing the operation of the control unit in the reference example printer.

In the printer 10 of the reference example, when the power supply (not shown) is turned on, the heating control processing unit Pr2 drives the fixing motor M3, rotates the pressure roller 35, and runs the fixing belt 32, and starts controlling the heater Ht by setting the target temperature Te of the fixing belt 32 to, for example, 160°C (step S1).

To achieve this, the heating control processing unit Pr2 receives print data from the host computer PC and waits for a print request (step S2). When a print request is received, it reads the detection temperature Ts2 detected by the fixing thermistor s5 and controls the heater Ht so that the detection temperature Ts2 becomes the target temperature Te.

Then, the heating control processing unit Pr2 waits for the detected temperature Ts2 to fall within the printable temperature range (step S3). The printable temperature range is a temperature range set so that printing can be performed satisfactorily; for example, if the target temperature Te is 160°C, the printable temperature range is set to a range of ±10°C from the target temperature Te, that is, 150 to 170°C.

The heating control processing unit Pr2 turns on the heater Ht when the detected temperature Ts2 is lower than the printable temperature range, and turns off the heater Ht when the detected temperature Ts2 is higher than the printable temperature range.

When the detected temperature Ts2 falls within the printable temperature range, the print processing unit Pr1 starts printing (step S4). To do this, the print processing unit Pr1 drives the transport motor M2, rotates the hopping roller 13 to feed the paper, rotates the paper feed roller pair m1, the registration roller pair m2, etc. to feed the paper P to the image forming unit Q1, and transfers the toner image onto the paper P in the image forming unit Q1.

Next, the heating control processing unit Pr2 calculates the deviation ΔT2 between the target temperature Te and the detected temperature Ts2 for each control period of the control unit 50, performs a PID calculation, and calculates the on-duty Dy for turning the heater Ht on and off (step S5). The on-duty Dy represents the proportion of the time that the heater Ht is on during the control period, and is larger the larger the deviation ΔT2 is, and is smaller the smaller the deviation ΔT2 is.

Next, the heating control processor Pr2 turns the heater Ht on and off based on the on-duty Dy (step S6).

The print processing unit Pr1 then determines whether printing of the print data has been completed (step S7), and if printing has been completed, ends the process. If printing has not been completed, the heating control processing unit Pr2 calculates the on-duty Dy again to print the remaining print data (step S5). Note that if an abnormality occurs, such as the paper P sticking to the fixing belt 32, the print processing unit Pr1 also ends the process.

Next, the flowchart will be described.
Step S1: The heating control processor Pr2 starts controlling the heater Ht.
In step S2, the heating control processor Pr2 waits for a print request to be received, and if a print request is received, the process proceeds to step S3.
Step S3: The heating control processor Pr2 waits until the detected temperature Ts2 falls within the printable temperature range. If the detected temperature Ts2 falls within the printable temperature range, the process proceeds to step S4.
In step S4, the print processing unit Pr1 starts printing.
Step S5: The heating control processor Pr2 calculates an on-duty Dy for turning the heater Ht on and off.
In step S6, the heating control processor Pr2 turns the heater Ht on and off based on the on-duty Dy.
In step S7, the print processing unit Pr1 judges whether printing has been completed or not. If printing has been completed, the process ends, and if printing has not been completed, the process returns to step S5.

However, when the paper P passes through the nip portion Np, heat is absorbed from the fixing belt 32 by the paper P, and the actual temperature Tr, which is the actual temperature of the fixing belt 32, changes and drops. However, until the part where the actual temperature Tr has dropped moves to a position opposite the fixing thermistor s5, the fixing thermistor s5 cannot detect the dropped actual temperature Tr, resulting in a detection delay.

For example, if the outer diameter of the fixing belt 32 is 30 mm, and the fixing thermistor s5 is disposed facing the fixing belt 32 at a position 63 mm downstream in the running direction of the fixing belt 32 from the downstream end (exit end) of the nip portion Np, when the paper P is transported at a high speed such as 210 mm/s, the detection delay is short, about 0.3 seconds, whereas when the paper P is transported at a low speed such as 72 mm/s, the detection delay is long, about 0.9 seconds.

Furthermore, when considering the thermal response time of the fixing thermistor s5 itself, the amount of heat dissipated from the fixing belt 32, the amount of heat diffusion of the fixing belt 32, etc., the fixing thermistor s5 becomes even less able to detect the reduced actual temperature Tr.

That is, the detected temperature Ts2 of the fixing thermistor s5 differs depending on the transport speed of the paper P.
In addition, when the paper P is thin paper, the heat capacity of the paper P is small and the heat absorbed by the paper P is small, so the amount by which the actual temperature Tr of the fixing belt 32 drops is small. Conversely, when the paper P is thick paper, the heat capacity of the paper P is large and the heat absorbed by the paper P is large, so the amount by which the actual temperature Tr of the fixing belt 32 drops is large.

Therefore, the detected temperature Ts2 of the fixing thermistor s5 also differs depending on the thickness of the paper P.
As such, since the detection temperature Ts2 of the fixing thermistor s5 varies depending on the printing conditions, such as the transport speed and thickness of the paper P, if the temperature of the outer surface of the fixing belt 32 is uniformly detected by the fixing thermistor s5, the actual temperature Tr of the fixing belt 32 cannot be detected with high accuracy.

Next, we will explain the image quality when images are formed in different printing formats under different printing conditions using the printer 10 of the reference example.

Figure 5 is a time chart for explaining the image quality when printing in the first print mode on the printer of the reference example, Figure 6 is a time chart for explaining the image quality when printing in the second print mode on the printer of the reference example, and Figure 7 is a time chart for explaining the image quality when printing in the third print mode on the printer of the reference example.

In this case, in the first printing mode, thin paper P was transported at high speed to print, in the second printing mode, thick paper P was transported at low speed to print, and in the third printing mode, thin paper P was transported at low speed to print. Each time chart also shows the detected temperature Ts1 detected by the heater thermistor s4, the detected temperature Ts2 detected by the fixing thermistor s5, the on/off indicating the presence or absence of paper P detected by the exit sensor s3 for each control cycle, the gloss value indicating the glossiness of the image formed on the paper P, and the transition of the on-duty Dy calculated for each control cycle.

When the paper P was transported at high speed, the transport speed was 210 [mm/s] and the paper interval was 60 [mm], and when the paper P was transported at low speed, the transport speed was 72 [mm/s] and the paper interval was 200 [mm]. When thin paper was used as the paper P, the basis weight was 80 [g/ ^m2 ], and when thick paper was used, the basis weight was 250 [g/ ^m2 ].

When evaluating image quality based on the image gloss value, it can be seen that in the first printing format, the gloss value of an image of one page is almost stable, but in the second and third printing formats, as the detection temperatures Ts1 and Ts2 fluctuate, the gloss value of an image of one page fluctuates in the same cycle.

As mentioned above, this indicates that the fixing thermistor s5 is not detecting the actual temperature Tr of the fixing belt 32 with high accuracy.

It is possible to control the heater Ht based only on the detected temperature Ts1 detected by the heater thermistor s4, but since the heater thermistor s4 is disposed on the side opposite the paper feed side and detects the temperature of the fixing belt 32 via the heater Ht, it takes a long time for the heater thermistor s4 to detect the actual temperature Tr of the fixing belt 32, resulting in a detection delay. In addition, a detection delay occurs due to the thermal response time of the heater thermistor s4 itself. Therefore, the actual temperature Tr of the fixing belt 32 cannot be detected accurately by the heater thermistor s4 alone.

Next, we will explain the operation of the control device of the printer 10 in this embodiment.

Figure 8 is a flowchart showing the operation of the control unit in an embodiment of the present invention, and Figure 9 is a diagram showing an example of a heating control table in an embodiment of the present invention.

When the printer 10 is turned on, the print processing unit Pr1 waits for print data to be sent from the host computer PC, and when the print data is sent, the heating control processing unit Pr2 reads the printing conditions, such as the transport speed and thickness of the paper P, from the print data.

Next, the heating control processing unit Pr2 drives the fixing motor M3, rotates the pressure roller 35, and runs the fixing belt 32. It also references the heating control table Tb1 in the ROM 53 shown in FIG. 9 to set a target temperature Te2 of the fixing belt 32 corresponding to the transport speed and thickness of the paper P, and starts controlling the heater Ht (step S11). For example, if the paper P to be printed is thin paper and the transport speed is 210 mm/s, the target temperature Te2 of the fixing belt 32 is set to 160°C. The heater Ht is kept on continuously until the detected temperature Ts2 of the fixing belt 32 reaches the target temperature Te.

Next, the heating control processing unit Pr2 waits to receive a print request from the host computer PC (step S12), and when it receives the print request, it waits for the detected temperature Ts2 to fall within the printable temperature range (step S13). The printable temperature range is set to a range of ±10°C with respect to the target temperature Te2, and when the target temperature Te2 is 160°C, the printable temperature range is set to 150 to 170°C. When the detected temperature Ts2 is lower than the printable temperature range, the heating control processing unit Pr2 turns on the heater Ht, and when the detected temperature Ts2 is higher than the printable temperature range, it turns off the heater Ht.

When the detected temperature Ts2 falls within the printable temperature range, the print processing unit Pr1 starts printing (step S14). To do this, the print processing unit Pr1 reads the transport speed, drives the transport motor M2, rotates the hopping roller 13 to feed the paper P from the paper cassette 11, rotates the paper feed roller pair m1, the registration roller pair m2, etc. to feed the paper P to the image forming unit Q1, and transfers the toner image onto the paper P in the image forming unit Q1.

Then, the heating control processing unit Pr2 refers to the heating control table Tb1, reads out the target temperature Te1 of the heater Ht corresponding to whether the paper P is thin paper or thick paper and the transport speed of the paper P, reads the detected temperature Ts1 detected by the heater thermistor s4, and calculates the deviation ΔT1 between the target temperature Te1 and the detected temperature Ts1 for each control period of the control unit 50 based on the detected temperature Ts1, performs a PID calculation, and calculates a first duty value Dy1 (step S15). The first duty value Dy1 represents the proportion of the time that the heater Ht is on during the control period, calculated based on the temperature detected by the heater thermistor s4, and is set to be larger as the deviation ΔT1 is larger and smaller as the deviation ΔT1 is smaller.

The heating control processing unit Pr2 also reads the detected temperature Ts2 detected by the fixing thermistor s5, calculates the deviation ΔT2 between the target temperature Te2 and the detected temperature Ts2 for each control period of the control unit 50 based on the detected temperature Ts2, performs a PID calculation, and calculates a second duty value Dy2 (step S16). The second duty value Dy2 represents the proportion of the time during which the heater Ht is on in the control period calculated based on the temperature detected by the fixing thermistor s5, and is larger the larger the deviation ΔT2 is, and is smaller the smaller the deviation ΔT2 is.

In this embodiment, the conveying speed when conveying the paper P at high speed is 210 [mm/s] and the paper interval is 60 [mm], and the conveying speed when conveying the paper P at low speed is 72 [mm/s] and the paper interval is 200 [mm]. When thin paper is used as the paper P, the basis weight is 80 [g/ ^m2 ], and when thick paper is used, the basis weight is 250 [g/ ^m2 ].

Furthermore, the target temperature Te1 of the heater Ht when thin paper P is transported at high speed is set to 205 [°C], the target temperature Te1 when thick paper P is transported at high speed is set to 230 [°C], the target temperature Te1 when thin paper P is transported at low speed is set to 155 [°C], and the target temperature Te1 when thick paper P is transported at low speed is set to 180 [°C]. Furthermore, the target temperature Te2 of the fixing belt 32 when thin paper P is transported at high speed is set to 160 [°C], the target temperature Te2 when thick paper P is transported at high speed is set to 175 [°C], the target temperature Te2 when thin paper P is transported at low speed is set to 135 [°C], and the target temperature Te2 when thick paper P is transported at low speed is set to 145 [°C].

Next, the heating control processor Pr2 weights the first and second duty values Dy1, Dy2 based on the printing mode in the printer 10, and calculates an on-duty Dty for turning the heater Ht on and off (step S17). To this end, the heating control processor Pr2 refers to the heating control table Tb1, reads out the weights of the detected temperatures Ts1, Ts2 corresponding to the transport speed and thickness of the paper P, i.e., the first and second coefficients ε1, ε2, and adds the value obtained by multiplying the first duty value Dy1 by the first coefficient ε1 and the value obtained by multiplying the second duty value Dy2 by the second coefficient ε2 to calculate the on-duty Dty.
Dty=Dy1×ε1+Dy2×ε2
(step S17).

In this embodiment, the sum of the first and second coefficients ε1 and ε2 is set to 1 so that the amount of heat generated is not insufficient or excessive when the heater Ht is turned on and off. However, once the detection temperatures Ts1 and Ts2 have stabilized and image quality can be maintained, it is no longer necessary to set the sum of the first and second coefficients ε1 and ε2 to 1.

Then, the heating control processing unit Pr2 turns the heater Ht on and off based on the on-duty Dty (step S18).

Next, the print processing unit Pr1 determines whether printing of the print data has been completed, and if so, ends the process; if not, the heating control processing unit Pr2 calculates the on-duty Dty again to print the remaining print data (step S15).

Next, the flowchart will be described.
In step S11, the heating control processor Pr2 starts controlling the heater Ht.
In step S12, the heating control processor Pr2 waits for a print request to be received, and if a print request is received, the process proceeds to step S13.
Step S13: The heating control processor Pr2 waits until the detected temperature Ts2 falls within the printable temperature range. If the detected temperature Ts2 falls within the printable temperature range, the process proceeds to step S14.
In step S14, the print processing unit Pr1 starts printing.
Step S15: The heating control processor Pr2 calculates the first duty value Dy1 based on the detected temperature Ts1 detected by the heater thermistor s4, and the process proceeds to step S17.
In step S16, the heating control processor Pr2 calculates the second duty value Dy2 based on the detected temperature Ts2 detected by the fixing thermistor s5.
In step S17, the heating control processor Pr2 calculates the on-duty Dty.
In step S18, the heating control processor Pr2 turns on and off the heater Ht based on the on-duty Dty.
In step S19, the print processing unit Pr1 judges whether printing has been completed or not. If printing has been completed, the process ends, and if printing has not been completed, the process returns to step S15.

Next, we will explain the image quality when an image is formed in a printing format with different printing conditions using the printer 10 of this embodiment.

Figure 10 is a time chart for explaining the image quality when printing in a first printing mode in an embodiment of the present invention, Figure 11 is a time chart for explaining the image quality when printing in a second printing mode in an embodiment of the present invention, and Figure 12 is a time chart for explaining the image quality when printing in a third printing mode in an embodiment of the present invention.

In this case, in the first printing mode, thin paper P was transported at high speed to print, in the second printing mode, thick paper P was transported at low speed to print, and in the third printing mode, thin paper P was transported at low speed to print. Each time chart also shows the detected temperature Ts1 detected by the heater thermistor s4, the detected temperature Ts2 detected by the fixing thermistor s5, the on/off indicating the presence or absence of paper P detected by the exit sensor s3 for each control cycle, the gloss value of the image formed on the paper P, and the transition of the on-duty Dty calculated for each control cycle.

When evaluating image quality based on gloss value, it can be seen that the gloss value of an image per page is stable in all three printing formats.

In this manner, in this embodiment, the weights of the detected temperature Ts1 detected by the heater thermistor s4 and the detected temperature Ts2 detected by the fixing thermistor s5 are changed according to the transport speed and thickness of the paper P transported through the nip portion Np, so that the heater Ht can be appropriately controlled in response to various printing conditions. As a result, the image quality can be improved.

In this embodiment, the heater thermistor s4 serving as the first temperature detection unit is disposed in contact with the heater Ht. However, if the temperature of the heater Ht can be detected in the vicinity of the heater Ht, it is not necessary to dispose the first temperature detection unit in contact with the heater Ht.

In this embodiment, the printer 10 has been described, but the present invention can also be applied to image forming devices such as copiers, facsimile machines, and multifunction machines.

The present invention is not limited to the above-described embodiment, and various modifications are possible based on the spirit of the present invention, and are not excluded from the scope of the present invention.

10 Printer 32 Fixing belt Ht Heater Np Nip P Paper Pr2 Heating control processing section Sb Back surface s4 Heater thermistor s5 Fixing thermistors Ts1 and Ts2 Detected temperature

Claims (11)

(a) a belt member;
(b) a heater disposed within the belt member for heating the belt member;
(c) a first temperature detection unit disposed on a rear side of the heater within the belt member;
(d) a second temperature detection unit disposed outside the belt member so as to face an outer circumferential surface of the belt member; and
(e) a heating control processing unit that controls the heater based on the detected temperatures detected by the first and second temperature detection units,
(f) An image forming apparatus characterized in that the heating control processing unit controls the heater by changing the weights of the detected temperatures detected by the first temperature detection unit and the second temperature detection unit in accordance with the transport speed and thickness of the medium transported through the fixing unit. The image forming apparatus according to claim 1, wherein the heating control processing unit controls the heater based on the deviation between the target temperature of the heater and the detected temperature detected by the first temperature detection unit, and the deviation between the target temperature of the belt member and the detected temperature detected by the second temperature detection unit. (a) a weight of the detected temperature detected by the first temperature detection unit is a first coefficient by which a first duty value calculated based on a deviation between a target temperature of the heater and the detected temperature detected by the first temperature detection unit is multiplied;
(b) an image forming apparatus according to claim 2, wherein the weight of the detected temperature detected by the second temperature detection unit is a second coefficient multiplied by a second duty value calculated based on the deviation between a target temperature of the belt member and the detected temperature detected by the second temperature detection unit. The image forming device according to claim 3, wherein the heating control processing unit calculates an on-duty for turning the heater on and off by adding a value obtained by multiplying the first duty value by a first coefficient and a value obtained by multiplying the second duty value by a second coefficient. (a) the first coefficient is small when the medium is transported at a high speed and is large when the medium is transported at a low speed;
5. The image forming apparatus according to claim 3, wherein the second coefficient is set to be large when the medium is transported at a high speed and set to be small when the medium is transported at a low speed. (a) the first coefficient is set to be large when thin paper is used as the medium and set to be small when thick paper is used as the medium;
(b) The image forming apparatus according to any one of claims 3 to 5, wherein the second coefficient is small when thin paper is used as the medium, and is large when thick paper is used as the medium. The image forming apparatus according to claim 3, wherein the target temperature of the heater is high when the medium is transported at a high speed and low when the medium is transported at a low speed. The image forming device according to claim 3 or 7, wherein the target temperature of the heater is high when thick paper is used as the medium and low when thin paper is used as the medium. The image forming apparatus according to claim 3, wherein the target temperature of the belt member is high when the medium is transported at a high speed and low when the medium is transported at a low speed. The image forming apparatus according to claim 3 or 9, wherein the target temperature of the belt member is high when thick paper is used as the medium, and low when thin paper is used as the medium. (a) the first temperature detection unit is a contact type temperature detection unit disposed in contact with a rear surface of the heater and detects the temperature of the heater;
(b) The image forming apparatus according to any one of claims 1 to 10, wherein the second temperature detection unit is a non-contact temperature detection unit disposed on the media inlet side of the fixing device and detects the temperature of the belt member.

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