JP6040458B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus including a fixing device that fixes a toner image on a print medium by heat treatment and pressure treatment.

  As an invention related to a conventional image forming apparatus, for example, an image forming apparatus described in Patent Document 1 is known. The image forming apparatus includes a fixing device including a heating roller made of metal and a fixing roller made of an elastic body, and a control unit. The control unit estimates the amount of heat given to the pressure roller during a period when there is no transfer paper at the nip portion between the heating roller and the fixing roller, and switches the temperature of the heating roller based on the estimated value of the heat storage amount. . Further, the control unit predicts the heat radiation of the pressure roller during paper feeding and corrects the estimated value of the heat storage amount of the pressure roller. According to the image forming apparatus described in Patent Document 1, since the temperature of the heating roller can be appropriately switched, it is possible to suppress the occurrence of wrinkles and fixing defects on the paper.

  Incidentally, a fixing device including a heating roller including an elastic body is known. For example, a heating roller in which a sponge roller having a low thermal conductivity is fitted inside a thin belt having a metal layer that generates heat by induction heating can be considered. The heat storage on the heating roller including such an elastic body takes much longer than the heat storage on the metal heating roller. Therefore, as in the image forming apparatus described in Patent Document 1, the control unit estimates only the heat storage amount of the pressure roller and switches the control temperature of the heating roller including the elastic body. It is difficult to accurately control the temperature so that the heat storage amount of the heating roller is estimated and optimized for fixing performance. As a result, the temperature of the heating roller becomes too high and power consumption increases, or the temperature of the heating roller becomes too low and fixing failure occurs.

JP-A-8-146814

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of accurately controlling the temperature of a heating rotator.

An image forming apparatus according to an aspect of the present invention includes an endless heating belt, a heating rotating body configured by a first elastic body in contact with an inner peripheral surface of the heating belt, and a pressure contact with the heating belt. pressurizing rotator are, and, seen including a heating means for heating the heating belt, and a fixing unit for fixing the toner image on the print medium that passes between the heating rotating body and the pressurizing rotator, said heating It performs estimation of a first thermal storage amount indicating the amount of heat that is stored in the rotating body, and control means for controlling the heating unit based on the first quantity of thermal storage, an image forming apparatus Ru provided with, The control means estimates the first heat storage amount every time printing by the image forming apparatus is completed and every time the standby state is completed, and is performed every time printing is completed. The amount of heat stored in the The heat storage amount is added to the previously calculated heat storage amount to obtain a new heat storage amount, and the first heat storage amount estimation performed each time the standby state is completed determines the heat storage amount in the standby state. The heat storage amount is calculated and added to the heat storage amount calculated last time to obtain a new heat storage amount .

  According to the present invention, the temperature of the heating rotator can be accurately controlled to a minimum value necessary for securing the fixing property.

1 is a diagram illustrating an overall configuration of an image forming apparatus. It is a block diagram of a fixing device. It is the flowchart which showed the operation | movement which a control part performs.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described.

(Overall configuration of image forming apparatus)
Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating an overall configuration of the image forming apparatus 1.

  The image forming apparatus 1 is an electrophotographic color printer, and synthesizes and prints toner images of four colors (Y: yellow, M: magenta, C: cyan, K: black) on a so-called tandem system. . The image forming apparatus 1 has a function of forming an image on a sheet based on image data read by a scanner. As shown in FIG. 1, the image forming apparatus 1 has a printing unit 2, a sheet feeding unit 15, a timing roller pair 19, a fixing unit. The apparatus 20 includes a paper discharge roller pair 21, a paper discharge tray 23, and a control unit 30.

  The control unit 30 controls the entire image forming apparatus 1 and is configured by, for example, a CPU.

  The paper supply unit 15 serves to supply paper one by one and includes a paper tray 16 and a paper supply roller 17. A plurality of sheets in a state before printing are stacked on the sheet tray 16. The paper feed roller 17 takes out the paper placed on the paper tray 16 one by one.

  The timing roller pair 19 conveys the sheet while adjusting the timing so that the toner image is secondarily transferred in the printing unit 2 to the sheet conveyed by the paper feed roller 17.

  The printing unit 2 forms a toner image on the paper supplied from the paper supply unit 15, and the optical scanning device 6, the transfer unit 8 (8Y, 8M, 8C, 8K), the intermediate transfer belt 11, the driving roller 12, and the driven unit. It includes a roller 13, a secondary transfer roller 14, and an image forming unit 22 (22Y, 22M, 22C, 22K). The image forming unit 22 (22Y, 22M, 22C, 22K) includes a photosensitive drum 4 (4Y, 4M, 4C, 4K), a charger 5 (5Y, 5M, 5C, 5K), and a developing device 7 (7Y, 7K). 7M, 7C, 7K) and cleaner 9 (9Y, 9M, 9C, 9K).

  The photosensitive drum 4 (4Y, 4M, 4C, 4K) has a cylindrical shape, and is rotated clockwise in FIG. The charger 5 (5Y, 5M, 5C, 5K) charges the peripheral surface of the photosensitive drum 4 (4Y, 4M, 4C, 4K). The optical scanning device 6 scans the beam B (BY, BM, BC, BK) on the peripheral surface of the photosensitive drum 4 (4Y, 4M, 4C, 4K). Thereby, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 4 (4Y, 4M, 4C, 4K).

  The developing device 7 (7Y, 7M, 7C, 7K) develops a toner image based on the electrostatic latent image on the photosensitive drum 4 (4Y, 4M, 4C, 4K).

  The transfer belt 11 is stretched between the driving roller 12 and the driven roller 13. The transfer unit 8 is disposed so as to face the inner peripheral surface of the intermediate transfer belt 11 and plays a role of primary transfer of the toner image formed on the photosensitive drum 4 to the intermediate transfer belt 11. The cleaner 9 collects the toner remaining on the peripheral surface of the photosensitive drum 4 after the primary transfer. The driving roller 12 is rotated by an intermediate transfer belt driving unit (not shown in FIG. 1), thereby driving the intermediate transfer belt 11 in the direction of arrow α. As a result, the intermediate transfer belt 11 conveys the toner image to the secondary transfer roller 14.

  The secondary transfer roller 14 faces the intermediate transfer belt 11 and has a drum shape. The secondary transfer roller 14 secondarily transfers the toner image carried by the intermediate transfer belt 11 to a sheet passing between the secondary transfer roller 14 and the intermediate transfer belt 11 by applying a transfer voltage.

  The sheet on which the toner image is secondarily transferred is conveyed to the fixing device 20. The fixing device 20 fixes the toner image on the paper by performing heat treatment and pressure treatment on the paper. Details of the fixing device 20 will be described later. The paper discharge roller pair 21 discharges the paper conveyed from the fixing device 20 to the paper discharge tray 23. Printed paper is placed on the paper discharge tray 23.

  Details of the fixing device 20 will be described below with reference to the drawings. FIG. 2 is a configuration diagram of the fixing device 20.

  The fixing device 20 includes a heating roller (heating rotator) 20a, a pressure roller (pressing rotator) 20b, and a heating unit (heating means) 20c.

  The heating roller 20a includes a cored bar 41, sponge rubber (elastic body) 42, and a belt (heating belt) 43, and has a diameter of 40 mm. The cored bar 41 is a cylinder made of a metal having a diameter of 20 mm. The sponge rubber 42 is bonded around the cored bar 41 and has a thickness of 10 mm. The sponge rubber 42 is made of, for example, silicone rubber.

  The belt 43 is wound around the sponge rubber 42 and has an endless shape. Thereby, the sponge rubber 42 is in contact with the inner peripheral surface of the belt 43. The belt 43 includes a Ni layer 431, a silicone solid rubber 432, and a release layer 433.

  The Ni layer 431, the silicone solid rubber 432, and the release layer 433 are laminated in this order from the inner peripheral surface side to the outer peripheral surface side of the heating roller 20a. The Ni layer 431 has a thickness of 40 μm due to the generation of eddy currents due to the influence of magnetic field lines whose strength changes by a heating unit 20c described later, and self-heating. The silicone solid rubber 432 has a thickness of 0.2 mm. The release layer 433 is a layer for preventing toner from adhering to the surface of the belt 43, and is made of, for example, PFA. The release layer 433 has a thickness of 30 μm.

  The pressure roller 20b is composed of a core metal 51 and a silicone solid rubber 52, and has a diameter of 40 mm. The pressure roller 20 b is in pressure contact with the belt 43.

  The cored bar 51 is a cylinder (for example, STKM pipe) made of a metal having a diameter of 32 mm. The silicone solid rubber 52 is bonded around the core bar 51 and has a thickness of 4 mm. Although not shown, a release layer made of PFA is provided on the surface of the silicone solid rubber 52 to prevent toner from adhering to the pressure roller 20b.

  The pressure roller 20b is provided with a power source, and the heating roller 20a is not provided with a power source. Therefore, the heating roller 20a is rotated when the pressure roller 20b is rotated by the power source.

  The heating unit 20 c includes an exciting coil 61 and ferrite cores 62, 62 a, and 62 b, and heats the belt 43 by flowing a high-frequency alternating current through the exciting coil 61. The heating unit 20c is provided outside the heating roller 20a.

  The exciting coil 61 is a coil manufactured by winding a conducting wire, and generates a magnetic flux whose direction periodically changes when an alternating current is supplied. The ferrite cores 62, 62 a and 62 b guide the magnetic flux generated by the exciting coil 61 to the belt 43. Thereby, the magnetic flux whose direction changes periodically passes through the Ni layer 431. As a result, an eddy current is generated in the Ni layer 431 and the Ni layer 431 generates heat.

  The fixing device 20 fixes the toner image on the paper P passing between the heating roller 20a and the pressure roller 20b. Specifically, as shown in FIG. 2, the toner image is formed on the main surface of the paper P facing the heating roller 20a. As a result, the toner image is heated and melted by the heating roller 20a. The toner image is pressed against the paper P and fixed by the pressure from the heating roller 20a and the pressure roller 20b.

  The image forming apparatus 1 further includes a sensor 28 as shown in FIG. The sensor 28 detects the temperature of the belt 43. The control unit 30 performs feedback control of the heating unit 20c based on the temperature detected by the sensor 28.

  Further, the control unit 30 estimates the heat storage amount ΣX, which is the amount of heat stored in the heating roller 20a, and controls the heating unit 20c based on the heat storage amount ΣX to fix the toner image on the paper P. The temperature T1 of the belt 43 during printing (that is, during printing) is determined, and the temperature T2 of the belt 43 in the standby state is determined. The standby state is a state in which the fixing device 20 is preheated to such an extent that a print job can be started without causing an unpleasant waiting time when a print job command is issued to the image forming apparatus. Hereinafter, estimation of the heat storage amount ΣX and determination of the temperatures T1 and T2 will be described.

  The heat storage amount ΣX is the sum of the heat amount stored in the heating roller 20a during printing (hereinafter referred to as heat storage amount Xp) and the heat amount stored in the heating roller 20a during standby (hereinafter referred to as heat storage amount Xs). And heat storage amount Xp, Xs is shown by the following formula | equation (1) and Formula (2).

Xp = 1−exp (− (Wc−Wc × 0.6 × (D / 80) ^1/2 × (F / 65) × (τ / V / 3.2 × 10 ⁻² ) ^1/3 × (E / 297) ^1/4 ) × t) / 200000) (1)
Xs = 1−exp (− (Wcs × 0.4 × t) / 200000) (2)

τ: nip width (mm) in the conveyance direction of the nip portion where the heating roller 20a and the pressure roller 20b are in contact with each other
V: Rotational speed of the belt 43 (mm / second)
t: Time taken for printing or waiting time (seconds)
Wc: Average supply power (W) to the exciting coil 61 during printing
D: The amount of paper P (g / m ² )
E: Width (mm) of the paper P in the direction orthogonal to the transport direction
F: Number of sheets P output per unit time by the fixing device 20 (sheets / minute)
Wcs: Average supply power (W) to the exciting coil 61 in the standby state

  In addition, about numerical values, such as 200000 in Formula (1) and Formula (2), is the value calculated | required based on experiment experience.

  The heat storage amount Xp is determined by the amount of heat given from the heating unit 20c and the amount of heat moving from the heating roller 20a to the paper P. Specifically, as shown in the equation (1), when the average supply power Wc is increased, the amount of heat given from the heating unit 20c is increased, and thus the heat storage amount Xp is increased. On the other hand, if the nip time (= τ / V) required for the paper P to pass through the nip portion becomes longer, the heat storage amount Xp becomes smaller. This is because the amount of heat transferred from the heating roller 20a to the paper P increases as the nip time increases. For the same reason, the heat storage amount Xp decreases as the amount D of paper P increases, and the heat storage amount Xp decreases as the width E of the paper P increases.

  Further, the heat storage amount Xs is determined by the amount of heat given from the heating unit 20c. Specifically, as shown in Expression (2), if the average supply power Wcs is increased, the amount of heat given from the heating unit 20c is increased, and thus the heat storage amount Xp is increased.

  In addition, as shown in Formula (1), it influences the heat storage amount Xp in the order of parameters F, D, τ / V, and E. The amount of heat transferred from the heating roller 20a to the paper P is proportional to the number of output sheets F. On the other hand, the amount of heat transferred from the heating roller 20a to the paper P is not proportional to the amount D of paper. This is because it is necessary to secure the temperature of the surface of the paper P in order to maintain the fixing performance even when the amount D of the paper increases, but it is not necessary to warm the whole paper P. Therefore, the influence degree of the sheet curl amount D is smaller than the influence degree of the output number F.

  Further, the amount of heat transferred from the heating roller 20a to the paper P is not proportional to the nip time τ / V. This is because as the nip time τ / V becomes longer, the temperature difference between the paper P and the belt 43 in the middle of the nip is reduced, so that the heat transfer is suppressed from the nip portion upstream to the nip portion downstream.

  Moreover, in Formula (1), the influence degree of the width | variety E is the lowest. Since the heat generated by the belt 43 is not taken away by the paper P in the non-sheet passing portion where the paper P does not pass, the heat is more easily transferred to the sponge rubber than the paper passing portion. However, since there are voids in the sponge rubber, there is little heat transfer in the longitudinal direction, and there is little heat accumulation in the entire sponge rubber. Therefore, the influence degree of the width E is smaller than other parameters.

  The control unit 30 estimates the amount of heat storage Xp every time printing is completed by using the equations (1) and (2), and the completion of the standby state (the completion of the standby state is a print job command issued by the image forming apparatus). The amount of stored heat Xs is estimated each time the data is sent to (indicating that the printer has shifted to the print state). Then, the control unit 30 estimates a new heat storage amount ΣX by adding the heat storage amounts Xp and Xs to the heat storage amount ΣX estimated when the previous printing is completed or when the standby state is completed. Further, the control unit 30 determines the temperature T1 of the belt 43 during printing using the equations (3) and (4) based on the new heat storage amount ΣX, and the temperature T2 of the belt 43 in the standby state. To decide.

T1 = 180− (ΣX × 15) (3)
T2 = 180-30- (ΣX × 15) (4)

  In Equation (1), it means that the temperature T1 in the initial state is 180 ° C. (hereinafter, initial temperature T01). In Equation (2), the temperature T2 in the initial state is 150 ° C. (hereinafter, initial). Temperature T02). And with time progress, the temperature of temperature T1, T2 is low. This is because the heat storage amount ΣX of the heating roller 20a increases, so that the toner image is fixed on the paper P even if the temperatures T1 and T2 of the heating roller 20a are set lower than the initial temperatures T01 and T02. I mean.

(Operation of image forming apparatus)
The operation of the image forming apparatus 1 configured as described above will be described below with reference to the drawings. FIG. 3 is a flowchart showing the operation performed by the control unit 30.

  This process is started when a print instruction is given to the control unit 30. When there is a print instruction, the control unit 30 determines whether the heating unit 20c has not been energized for a predetermined period or longer (step S10). The fact that power is not supplied for a predetermined period or longer means that the fixing device 20 has been in a sleep state in which it does not operate for a predetermined period or longer. In step S10, it is determined whether or not the heat storage amount ΣX of the heating roller 20a is sufficiently small. If no power is supplied, the process proceeds to step S20. On the other hand, when energization is performed, the process proceeds to step S30.

  When energization is not performed, the control unit 30 sets the heat storage amount ΣX to 0, and sets the temperatures T1 and T2 to the initial temperatures T01 and T02, respectively (step S20). Thereafter, the process proceeds to step S30.

  In step S30, the control unit 30 performs a printing operation (step S30). In the printing operation, the control unit 30 controls the heating unit 20c so that the temperature of the belt 43 becomes the temperature T1. Further, the control unit 30 measures the time t required for printing in the printing operation.

  Next, the control unit 30 calculates the heat storage amount ΣX and the temperatures T1 and T2 based on the equations (1), (3), and (4) (step S40). More specifically, the control unit 30 calculates a new heat storage amount ΣX by calculating the heat storage amount Xp in the printing operation in step S30 and adding the heat storage amount Xp to the heat storage amount ΣX calculated last time. Further, the control unit 30 calculates the temperatures T1 and T2 based on the new heat storage amount ΣX.

  Next, the control unit 30 determines whether or not there is a new print instruction (step S50). In step S50, the control unit 30 determines whether or not to shift the image forming apparatus 1 to the standby state. If there is a print instruction, the process returns to step S10. On the other hand, if there is no print instruction, the process proceeds to step S60.

  When there is no print instruction, the control unit 30 shifts the image forming apparatus 1 to a standby state (step S60). At this time, the control unit 30 measures the time t in the standby state.

  Next, the control unit 30 determines whether or not there is a new print instruction (step S70). In step S70, the control unit 30 determines whether to end the standby state. If there is a print instruction, the process proceeds to step S80. On the other hand, if there is no print instruction, the process returns to step S70. In this case, step S70 is repeated until a print instruction is issued.

  Next, the control unit 30 calculates the heat storage amount ΣX and the temperatures T1 and T2 based on the equations (2), (3), and (4) (step S80). More specifically, the control unit 30 calculates the new heat storage amount ΣX by calculating the heat storage amount Xs in the standby state in step S60 and adding the heat storage amount Xs to the heat storage amount ΣX calculated last time. Further, the control unit 30 calculates the temperatures T1 and T2 based on the new heat storage amount ΣX. Thereafter, the process returns to step S10. Above, description of operation | movement of the image forming apparatus 1 is complete | finished.

(effect)
According to the image forming apparatus 1 according to the present embodiment, the temperature of the heating roller 20a necessary to ensure the fixability at a certain point in time can be accurately controlled by obtaining the heat storage amount of the changing heating roller 20a. . More specifically, in the image forming apparatus 1, since the heating roller 20a includes the sponge rubber 42 having a low thermal conductivity, the amount of heat stored in the heating roller 20a is gradually changed. When the heating roller is made of a material having good heat conductivity such as substantially metal as in Patent Document 1, it is different from the case where heat storage is completed when the fixing device is started up. Therefore, the control unit 30 estimates the heat storage amount ΣX stored in the heating roller 20a, and controls the heating unit 20c based on the heat storage amount ΣX. As a result, the control unit 30 can accurately control the temperature of the heating roller 20a to a minimum value necessary to ensure the fixing property. As a result, the temperature of the heating roller 20a becomes too high and power consumption increases, and the temperature of the heating roller 20a becomes too low to cause a fixing failure.

(Experiment)
The inventor of the present application conducted an experiment described below in order to clarify the effect of the image forming apparatus 1. Specifically, a first example and a comparative example described below were prepared, and temperatures T1 and T2 and a fixing rate were measured. The first example is the image forming apparatus 1 according to the present embodiment. The heat storage amount ΣX is estimated in the following steps, and the temperatures T1 and T2 in the next step are determined based on the heat storage amount ΣX. On the other hand, in the comparative example, the temperatures T1 and T2 were 180 ° C. and 150 ° C., respectively.

  The inventor of the present application executed the following comparison verification mode operation in the first example and the comparative example.

First step: The first example and the comparative example were turned off overnight. Second step: A warm-up operation was performed.
Third step: Monochrome printing of 130 sheets of A4 plain paper (D = 80 g / m ² ) in landscape orientation.
Fourth step: A standby state was maintained for 2 minutes.
Fifth step: 65 sheets of A4 thick paper (D = 170 g / m ² ) were printed in color.
Sixth step: The apparatus was on standby for 2 minutes.
Seventh step: 40 long No. 3 envelopes were printed in monochrome.
Eighth step: The apparatus was on standby for 2 minutes.
Ninth step: Monochrome printing of 130 sheets of A4 plain paper (D = 80 g / m ² ) in landscape orientation.

  In the warm-up operation in the second step, the heating roller 20a and the pressure roller 20b were brought into a light pressure contact state, and the belt 43 was rotated at 310 mm / second. And the control part 30 makes the heating part 20c heat the heating roller 20a until the temperature of the belt 43 becomes 180 degreeC. When the temperature of the belt 43 reaches 180 ° C., the control unit 30 ends the warm-up operation. The reason why the heating roller 20a and the pressure roller 20b are in a light pressure contact state is that in the warm-up operation, the amount of heat transferred from the heating roller 20a to the pressure roller 20b increases and the warm-up time becomes longer. It is for suppressing.

  In the printing operation in the third step, the heating roller 20a and the pressure roller 20b were brought into a strong pressure contact state, and the belt 43 was rotated at 310 mm / second. In the first embodiment, the control unit 30 controls the heating unit 20c so that the temperature of the belt 43 becomes the temperature T1. In the comparative example, the control unit controlled the heating unit so that the temperature of the belt was 180 ° C. The term “landscape” means that the long side of the plain paper is conveyed so that it is located at the leading edge. The output number F is 65 sheets / minute.

  In the standby state in the fourth step, the heating roller 20a and the pressure roller 20b are in a light pressure contact state, and the belt 43 is rotated at 103 mm / second. In the first embodiment, the control unit 30 controls the heating unit 20c so that the temperature of the belt 43 becomes the temperature T2. In the comparative example, the control unit controlled the heating unit so that the temperature of the belt became 150 ° C.

  In the printing operation in the fifth step, the heating roller 20a and the pressure roller 20b were brought into a strong pressure contact state, and the belt 43 was rotated at 155 mm / second. In the first embodiment, the control unit 30 controls the heating unit 20c so that the temperature of the belt 43 becomes the temperature T1. In the comparative example, the control unit controlled the heating unit so that the temperature of the belt was 180 ° C. The portrait orientation means that the plain paper is conveyed so that the short side is located at the leading edge. The output number F is 32.5 sheets / minute.

  In the standby state in the sixth step, the heating roller 20a and the pressure roller 20b are in a light pressure contact state, and the belt 43 is rotated at 103 mm / second. In the first embodiment, the control unit 30 controls the heating unit 20c so that the temperature of the belt 43 becomes the temperature T2. In the comparative example, the control unit controlled the heating unit so that the temperature of the belt became 150 ° C.

  In the printing operation in the seventh step, the heating roller 20a and the pressure roller 20b were brought into a strong pressure contact state, and the belt 43 was rotated at 310 mm / second. In the first embodiment, the control unit 30 controls the heating unit 20c so that the temperature of the belt 43 becomes the temperature T1. In the comparative example, the control unit controlled the heating unit so that the temperature of the belt was 180 ° C. The long No. 3 envelope means that the envelope is conveyed so that the short side of the 120 mm × 235 mm envelope is located at the tip. The output number F is 19.9 sheets / minute.

  In the standby state in the eighth step, the heating roller 20a and the pressure roller 20b are in a light pressure contact state, and the belt 43 is rotated at 103 mm / second. In the first embodiment, the control unit 30 controls the heating unit 20c so that the temperature of the belt 43 becomes the temperature T2. In the comparative example, the control unit controlled the heating unit so that the temperature of the belt became 150 ° C.

  In the printing operation in the ninth step, the heating roller 20a and the pressure roller 20b were brought into a strong pressure contact state, and the belt 43 was rotated at 310 mm / second. In the first embodiment, the control unit 30 controls the heating unit 20c so that the temperature of the belt 43 becomes the temperature T1. In the comparative example, the control unit controlled the heating unit so that the temperature of the belt was 180 ° C. The term “landscape” means that the long side of the plain paper is conveyed so that it is located at the leading edge. The output number F is 65 sheets / minute.

  In the third step, the fifth step, the seventh step, and the ninth step, the paper interval was set to 76.2 mm. Further, the upper limit value of power consumption during printing in the first embodiment and the comparative example is limited to 1500 W, and the maximum value of power consumption during printing in the fixing devices of the first embodiment and the comparative example is 1000 W. Limited. Therefore, when it is difficult for the belt temperature to reach the target temperature, the average supply power Wc of the fixing device is 1000 W, and when the belt temperature reaches the target temperature, fixing is performed. The average supply power Wc of the device is 1000 W or less.

  The fixing rate is a parameter indicating the degree of fixing of the toner image to the paper P. The fixing rate is measured according to the following procedure.

  A plurality of types of patch images (ID of about 0.5) are formed on the paper P. Next, the reflection density D0 of the patch image is measured. As a measuring instrument, a reflection densitometer RD-918 manufactured by Macbeth Co. was used.

Next, the nonwoven fabric is pressed against the patch image having a reflection density of about 0.5 with a load of 22 g / cm ² . The patch image is reciprocated 14 times on the nonwoven fabric.

  Next, the reflection density D1 of the patch image rubbed with the nonwoven fabric is measured. As a measuring instrument, a reflection densitometer RD-918 manufactured by Macbeth Co. was used.

  Next, the fixing rate was calculated using Equation (5).

D1 / D0 × 100 (5)

  When there is no patch image having a reflection density of about 0.5, the fixing rate A of a patch image having a reflection density lower than 0.5 and the fixing rate of a patch image having a reflection density higher than 0.5. Based on B, the fixing rate is estimated by linear approximation.

  The experimental results are shown below. Table 1 shows the experimental results of the comparative example, and Table 2 shows the experimental results of the first example.

  As shown in Table 1, in the comparative example, since the belt temperature is set to 180 ° C. or 150 ° C., the fixing rate is significantly higher than 80% as time passes. Since the fixing rate should be higher than about 80% (if the fixing rate is about 80% or more, the quality is satisfied by many users), it can be seen that the belt is heated more than necessary in the comparative example. . That is, in the comparative example, the temperature of the heating roller becomes too high and the power consumption increases.

  On the other hand, as shown in Table 2, it can be seen that in the first embodiment, the fixing rate is maintained at about 80% despite the decrease in the temperatures T1 and T2. Therefore, in the first embodiment, it is understood that the power consumption is reduced by lowering the temperatures T1 and T2, and the occurrence of fixing failure of the toner image is suppressed.

(Modification)
Hereinafter, an image forming apparatus 1 ′ according to a modification will be described. The overall configuration of the image forming apparatus 1 ′ and the configuration of the fixing device 20 ′ of the image forming apparatus 1 ′ are the same as the overall configuration of the image forming apparatus 1 and the configuration of the fixing device 20 of the image forming apparatus 1. FIG. 1 and FIG. 2 are incorporated.

  In the image forming apparatus 1 ′, the control unit 30 estimates the heat storage amount ΣY and the heat storage amount ΣX, which are the heat amounts stored in the pressure roller 20b, and controls the heating unit 20c based on the heat storage amounts ΣX and ΣY. Then, the temperature T1 of the belt 43 during printing is determined, and the temperature T2 of the belt 43 in the standby state is determined. Hereinafter, the estimation of the heat storage amount ΣY will be described.

  The heat storage amount ΣY is the sum of the heat amount stored in the pressure roller 20b during printing (hereinafter referred to as heat storage amount Yp) and the heat amount stored in the pressure roller 20b during standby (hereinafter referred to as heat storage amount Ys). And heat storage amount Yp and Ys are shown by the following formulas (6) and (7).

Yp = 1−exp (− (Wc−Wc × 0.5 × (F / 65) ^3/2 × (E / 297) ^1/3 ) × (V / 310) × (τ / 10) × t) / 200000) (6)
Ys = 1−exp (− (Wcs × 0.3 × t) / 200000 (7)

τ: nip width (mm) in the conveyance direction of the nip portion where the heating roller 20a and the pressure roller 20b are in contact with each other
V: Rotational speed of the belt 43 (mm / second)
t: Time taken for printing or waiting time (seconds)
Wc: Average supply power (W) to the exciting coil 61 during printing
E: Width (mm) of the paper P in the direction orthogonal to the transport direction
Wcs: Average supply power (W) to the exciting coil 61 in the standby state

  In addition, about numerical values, such as 200000 in Formula (6) and Formula (7), is the value calculated | required based on experiment experience.

  Using the equations (6) and (7), the control unit 30 estimates the heat storage amount Yp every time printing is completed, and estimates the heat storage amount Ys every time the standby state is completed. And the control part 30 estimates heat storage amount (SIGMA) Y which is the sum total of heat storage amount Yp and Ys. Further, the control unit 30 determines the temperature T1 of the belt 43 during printing using the equations (8) and (9) based on the heat storage amounts ΣX and ΣY, and the temperature T2 of the belt 43 in the standby state. To decide.

T1 = 180− (ΣX + ΣY) × 7.5 (8)
T2 = 180-30- (ΣX + ΣY) × 7.5 (9)

  The operation performed by the control unit 30 of the image forming apparatus 1 ′ according to the modification is basically the same as the operation performed by the control unit 30 of the image forming apparatus 1, but differs in the following points. Specifically, the control unit 30 sets the heat storage amount ΣY to 0 in step S20. Moreover, the control part 30 determines temperature T1, T2 based on heat storage amount (SIGMA) X, (SIGMA) Y in step S40, S80.

  In the image forming apparatus 1 ′ configured as described above, the temperatures T1 and T2 are determined in consideration of the heat storage amount ΣY of the pressure roller 20b. According to the image forming apparatus 1 ′ according to the modified example, the temperature of the heating roller 20a can be accurately controlled to a minimum value necessary for ensuring the fixability.

  In the image forming apparatus 1 ′, the control unit 30 estimates the heat storage amount ΣX of the heating roller 20a and the heat storage amount ΣY of the pressure roller 20b, and determines the temperatures T1 and T2 based on the heat storage amounts ΣX and ΣY. ing. This eliminates the need for a sensor for detecting the temperature of the pressure roller 20b. As a result, in the image forming apparatus 1 ′, the control unit 30 can control the heating unit 20 c with only one sensor 28. Therefore, in the image forming apparatus 1 ′, a temperature sensor is provided on the pressure roller 20 b side, and a plurality of sensors are not required compared with the case where the heat storage amount of the pressure roller is estimated, and the manufacturing cost is reduced.

  The inventor of the present application conducted an experiment described below in order to clarify the effect of the image forming apparatus 1 ′. Specifically, a second embodiment described below was created, and the temperatures T1 and T2 and the fixing rate were measured. The second embodiment is an image forming apparatus 1 ′ according to a comparative example, which estimates heat storage amounts ΣX and ΣY and determines temperatures T1 and T2 based on the heat storage amounts ΣX and ΣY. Since other conditions are the same as those in the first embodiment, description thereof will be omitted.

  The experimental results are shown below. Table 3 shows the experimental results of the second example.

  As shown in Table 3, it can be seen that in the second example, the fixing rate is maintained at about 80% even though the temperatures T1 and T2 are decreased. Therefore, in the second embodiment, it can be seen that the power consumption is reduced by lowering the temperatures T1 and T2, and the occurrence of poor fixing of the toner image is suppressed. Further, the accuracy of maintaining the fixing rate is higher in the second embodiment than in the first embodiment.

(Other embodiments)
The image forming apparatus according to the present invention is not limited to the image forming apparatuses 1 and 1 ′ according to the embodiment, and can be changed within the scope of the gist thereof.

  In the fixing devices 20 and 20 ′, the belt 43 is fitted on the surface of the sponge rubber 42 bonded to the core metal 41. However, the configuration of the belt 43 is not limited to this. Specifically, the belt 43 may be attached to a roller different from the roller composed of the cored bar 41 and the sponge rubber 42 and a roller composed of the cored bar 41 and the sponge roller 42.

  As described above, the present invention is useful for an image forming apparatus, and is particularly excellent in that the temperature of a heating rotator can be accurately controlled to a minimum value necessary for ensuring fixing properties.

DESCRIPTION OF SYMBOLS 1,1 'Image forming apparatus 20, 20' Fixing apparatus 20a Heating roller 20b Pressure roller 20c Heating part 28 Sensor 30 Control part 41 Core metal 42 Sponge rubber 43 Belt 51 Core metal 52 Silicone solid rubber 61 Excitation coil 62, 62a, 62b Ferrite core

Claims (8)

A heating rotator constituted by an endless heating belt and a first elastic body in contact with the inner peripheral surface of the heating belt, a pressure rotator in pressure contact with the heating belt, and the heating belt look including a heating means for heating a fixing means for fixing the toner image on the print medium that passes between the heating rotating body and the pressurizing rotator,
It performs estimation of a first thermal storage amount indicating the amount of heat that is stored in the heating rotating body, and control means for controlling the heating unit based on the first quantity of thermal storage,
An image forming apparatus Ru provided with,
The controller is configured to estimate the first heat storage amount every time printing is completed by the image forming apparatus and each time a standby state is completed.
The estimation of the first heat storage amount performed each time the printing is completed is to calculate the heat storage amount in the printing operation, and add the heat storage amount to the heat storage amount calculated last time to obtain a new heat storage amount.
The estimation of the first heat storage amount performed each time the standby state is completed is to calculate the heat storage amount in the standby state, and add the heat storage amount to the previously calculated heat storage amount to obtain a new heat storage amount. There is ,
An image forming apparatus. The control means determines a temperature of the heating belt when fixing a toner image on the print medium based on the first heat storage amount;
The image forming apparatus according to claim 1. The control means includes: the amount of printing medium, the average power supplied to the heating means, the number of print media output per unit time by the fixing means, and the heating rotating body and the pressure rotating body are in contact with each other. Estimating the first heat storage amount based on at least one piece of information on the width of the nip portion in the transport direction, the rotation speed of the heating belt, and the width of the print medium in the direction orthogonal to the transport direction. ,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The control means determines, based on the first heat storage amount, a temperature of the heating belt in a standby state waiting for fixing a toner image on the print medium according to a print job;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The control means estimates the first heat storage amount based on at least one information of the time of the standby state and the average supply power to the heating means in the standby time;
The image forming apparatus according to claim 4. Wherein the control means performs the estimation of the second thermal storage amount indicating the amount of heat that is stored in the pressure rotating body,
The control means controls the heating means based on the first heat storage amount and the second heat storage amount;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The controller determines a temperature of the heating belt when fixing a toner image on the print medium based on the first heat storage amount and the second heat storage amount;
The image forming apparatus according to claim 6. The temperature of the heating belt in a standby state waiting for fixing the toner image on the print medium according to a print job based on the first heat storage amount and the second heat storage amount. To determine the
The image forming apparatus according to claim 6, wherein the image forming apparatus is an image forming apparatus.

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