JP2013113867A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce deterioration in productivity of a whole image forming apparatus while preventing generation of fixing defects during an image formation.SOLUTION: An image forming apparatus executes a heat fixing performance by supplying power to a heating member under rated power, in a stationary state where the heating member of a fixing device can be kept to a heat fixing available temperature even with a continuous paper passing. The image forming apparatus monitors a temperature of the heating member, and when the temperature of the heating member is decreased as a print job proceeds after the print job is started, estimates according to the decreased amount whether or not the temperature of the heating member will have been lowered than a lower limit value of the heat fixing available temperature until the print job is to be finished (S706), and when the temperature of the heating member is estimated to go under the lower limit value (S707:YES), controls to increase the supply power to the heating member before the temperature of the heating member goes under the lower limit value during execution of the print job, only by power exceeding the rated power between the rated power and an allowable upper limit value of the power acceptable by a self device (S706).

Description

  The present invention relates to an image forming apparatus provided with a fixing device, and more particularly to a technique for suppressing the occurrence of fixing failure caused by a temperature drop of a heating member of a fixing device during image formation immediately after warm-up.

  In recent years, in the field of image forming apparatuses, in order to shorten the warm-up time and save energy, a fixing apparatus that performs a heat fixing operation using a heating member having a small heat capacity has been used. For example, instead of a heating roller having a large heat capacity as a heating member, a heating belt is used to reduce the thickness of the heating member, thereby reducing the heat capacity, and shortening the heating member warm-up time and heating. The power consumption can be reduced.

  On the other hand, if the heating member is warmed up in a short time using such a heating member with a small heat capacity, the image forming operation is performed in a state where the pressure roller having a large heat capacity is not sufficiently heated as compared with the heating member. In such a case, part of the heat of the heating member is taken away by the pressure roller during image formation, and the temperature of the heating member is higher than the temperature at which heat fixing is possible. In some cases, and fixing failure may occur.

In particular, when the warming-up operation is performed after the fixing device is left for a long time in a state where the environmental temperature is low, the above-described fixing failure is likely to occur in the image forming operation immediately after the warm-up.
In order to prevent the occurrence of such fixing failure, when the temperature of the heating member falls below the temperature at which heat fixing is possible, the image forming operation is interrupted and warm-up is performed again, and the temperature of the heating member is reduced. Measures are taken such as restarting the image forming operation when the temperature becomes higher than the heat fixing temperature or increasing the contact time between the recording sheet and the heating member by reducing the printing speed.

Alternatively, some functions of the image forming apparatus (for example, a scan function and a post-processing stapling function) are limited, and the power used to execute the function is allocated to the heat fixing operation. A measure is taken to reduce the temperature drop of the heating member in the image forming operation immediately after the warm-up by supplying a large amount of power to the fixing device as much as it is allocated.
As a result, in the image forming operation immediately after the war-up, it is possible to prevent a fixing failure from occurring during image formation.

JP 2008-292988 A

However, when the above measures are taken, the image forming operation is interrupted in the middle, the printing speed is slowed down, or some functions of the image forming apparatus are limited. There arises a problem that the overall productivity is lowered.
The present invention has been made in view of the above-described problems, and the occurrence of a fixing failure caused by a temperature decrease of a heating member during image formation while reducing a decrease in productivity of the entire image forming apparatus. An object of the present invention is to provide an image forming apparatus capable of preventing the above-described problem.

  In order to achieve the above object, an image forming apparatus according to an aspect of the present invention is capable of maintaining a heating member of a fixing device at a temperature at which heat fixing can be performed even when a recording sheet is continuously passed. An image forming apparatus that supplies power to the heating member within a range not exceeding the rated power and performs a heat fixing operation of an unfixed image, and a temperature monitoring unit that monitors the temperature of the heating member; When the temperature of the heating member decreases with the progress of the print job, the temperature of the heating member is a temperature at which heat fixing can be performed by the time when the print job should be completed based on the decrease amount. An estimation means for estimating whether the temperature is lower than a lower limit value, and when the temperature of the heating member is estimated to be lower than the lower limit value, the temperature of the heating member is lower than the lower limit value during execution of the print job. Before the rated power Power control means for controlling the power supplied to the heating member to be increased by an amount exceeding the rated power within a range that is larger than the allowable upper limit value of power that can be accepted by the device. .

The power control means can control the supplied power so that the allowable upper limit value is not exceeded in an average value in a predetermined period.
The heating member is an endless heating belt, and the fixing device presses a pressure member against the heating belt to form a fixing nip, and the pressure member has a heat capacity higher than that of the heating belt. It can be big.

Further, the temperature estimating means is a case where it is the first print job after power-on, after completion of warm-up, or after returning from the sleep mode, and by executing the print job, When the temperature decreases, the temperature of the heating member at the time when the print job should be finished can be estimated.
Further, the allowable upper limit value may be a value corresponding to 110% of the rated power.

  By providing the above configuration, when it is estimated that the temperature of the heating member is lower than the lower limit value of the temperature at which heat fixing is possible by the time when the print job should be terminated, the heating member during execution of the print job. Before the temperature falls below the lower limit, the power supplied to the heating member is greater than the rated power and within the range not exceeding the allowable upper limit of power that can be accepted by the device itself, by the amount exceeding the rated power. Since the temperature is controlled so as to increase, the temperature of the heating member can be made difficult to decrease to the lower limit during the execution of the print job, and accordingly, fixing such as interruption of the image forming operation or reduction of the printing speed can be made. Fixing due to a decrease in temperature of the heating member during image formation while reducing the decrease in productivity of the image forming apparatus while reducing the frequency of performing an operation for preventing defects in the middle of a print job. It is possible to effectively prevent the occurrence of good.

  Furthermore, since the power supplied to the heating member is controlled using the power that exceeds the rated power while maintaining the power supply for the rated power, the fixing device uses the rated power. It is possible to prevent the supply power to other electrical devices from being affected, and to prevent the functions of these electrical devices from being stopped due to a shortage of the supply power during execution of a print job.

1 is a diagram illustrating a configuration of a printer 1 according to the present embodiment. 3 is a cross-sectional view illustrating a configuration of a fixing device 5. FIG. 3 is a diagram illustrating a relationship between a configuration of a control unit 60 and main components that are controlled by the control unit 60. FIG. 6 is a diagram illustrating a relationship between a power control unit 606, a power supply unit 700, and main components to which power is supplied from the power supply unit 700. FIG. It is a graph (operation characteristic curve) which shows the correspondence of the electric current amount which flows through a breaker, and the operation time until the breaker 402 operates. An example of a change over time in the surface temperature of the heating belt 52 of the fixing device 5 in the case where the continuous printing process is executed after the printer 1 is turned on and the warm-up process is completed is shown. It is a flowchart which shows operation | movement of the electric power control process which the control part 60 performs. 6 is a flowchart illustrating an operation of a heating belt temperature estimation process at the end of a job performed by a control unit 60. It is a flowchart which shows the operation | movement of the power supply control process which the control part 60 performs.

Hereinafter, an embodiment of an image forming apparatus according to an embodiment of the present invention will be described with reference to an example in which the image forming apparatus is applied to a tandem color digital printer (hereinafter simply referred to as “printer”).
[1] Configuration of Printer First, the configuration of the printer 1 according to the present embodiment will be described. FIG. 1 is a diagram illustrating a configuration of a printer 1 according to the present embodiment. As shown in FIG. 1, the printer 1 includes an image process unit 3, a paper feed unit 4, a fixing device 5, and a control unit 60.

  When the printer 1 is connected to a network (for example, LAN) and receives a print instruction from an external terminal device (not shown) or an operation panel having a display unit (not shown), yellow, magenta, cyan, and black are received based on the instruction. A toner image of each color is formed, and these are multiplex-transferred onto a recording sheet to form a full-color image, thereby executing a printing process on the recording sheet. Hereinafter, the reproduction colors of yellow, magenta, cyan, and black are expressed as Y, M, C, and K, and Y, M, C, and K are added as subscripts to the numbers of the components related to the reproduction colors.

The image processing unit 3 includes image forming units 3Y, 3M, 3C, and 3K, an exposure unit 10, an intermediate transfer belt 11, a secondary transfer roller 45, and the like. Since the image forming units 3Y, 3M, 3C, and 3K have the same configuration, the configuration of the image forming unit 3Y will be mainly described below.
The image forming unit 3Y includes a photosensitive drum 31Y, a charger 32Y, a developing unit 33Y, a primary transfer roller 34Y, a cleaner 35Y for cleaning the photosensitive drum 31Y, and the like disposed around the photosensitive drum 31Y. A Y-color toner image is formed on the photosensitive drum 31Y. The developing device 33Y faces the photosensitive drum 31Y and conveys charged toner to the photosensitive drum 31Y. The intermediate transfer belt 11 is an endless belt, is stretched around a driving roller 12 and a driven roller 13, and is driven to rotate in the direction of arrow C. A cleaner 21 for removing toner remaining on the intermediate transfer belt 11 is disposed in the vicinity of the driven roller 13.

  The exposure unit 10 includes a light emitting element such as a laser diode, emits laser light L for forming images of Y to K colors in response to a drive signal from the control unit 60, and each of the image forming units 3Y, 3M, 3C, and 3K. The photosensitive drum is exposed and scanned. By this exposure scanning, an electrostatic latent image is formed on the photosensitive drum 31Y charged by the charger 32Y. Similarly, electrostatic latent images are formed on the photosensitive drums of the image forming units 3M, 3C, and 3K.

The electrostatic latent image formed on each photoconductor drum is developed by each developing unit of the image forming units 3Y, 3M, 3C, and 3K, and a toner image of a corresponding color is formed on each photoconductor drum. The formed toner images are assigned with primary transfer rollers of image forming units 3Y, 3M, 3C, and 3K (in FIG. 1, only the primary transfer roller corresponding to the image forming unit 3Y is denoted by reference numeral 34Y, and other primary transfer rollers). , The primary transfer is sequentially performed on the intermediate transfer belt 11 at different timings so as to be superimposed at the same position on the intermediate transfer belt 11, and then by the secondary transfer roller 45. The toner images on the intermediate transfer belt 11 are collectively transferred onto the recording sheet by the action of electrostatic force.

The recording sheet on which the toner image has been secondarily transferred is further conveyed to the fixing device 5, and the toner image (unfixed image) on the recording sheet is heated and pressed in the fixing device 5 and thermally fixed on the recording sheet. Thereafter, the paper is discharged onto a paper discharge tray 72 by a discharge roller 71.
The paper feed unit 4 includes a paper feed cassette 41 that stores recording sheets (denoted by reference numeral S in FIG. 1), a feed roller 42 that feeds the recording sheets in the paper feed cassette 41 one by one onto the transport path 43, and a feed roller 42. A timing roller 44 for conveying the recording sheet at a timing for sending the recording sheet to the secondary transfer position 46 is provided.

The number of paper feed cassettes is not limited to one and may be plural. As the recording sheet, paper sheets (plain paper, thick paper) having different sizes and thicknesses, and film sheets such as an OHP sheet can be used. When there are a plurality of paper feed cassettes, recording sheets having different sizes, thicknesses or materials may be stored in the paper feed cassettes.
The timing roller 44 prints the recording sheet in synchronization with the timing at which the toner image primarily transferred onto the intermediate transfer belt 11 is conveyed to the secondary transfer position 46 so as to be superimposed at the same position on the intermediate transfer belt 11. It is conveyed to the next transfer position 46. Then, at the secondary transfer position 46, the toner images on the intermediate transfer belt 11 are collectively transferred onto the recording sheet by the secondary transfer roller 45.

Each of the rollers such as the feeding roller 42 and the timing roller 44 is rotationally driven through a power transmission mechanism (not shown) such as a gear and a belt using a transport motor (not shown) as a power source. As the transport motor, for example, a stepping motor capable of controlling the rotational speed with high accuracy is used.
[2] Configuration of Fixing Device Next, the configuration of the fixing device 5 will be described. FIG. 2 is a cross-sectional view showing the configuration of the fixing device 5. Reference numeral S in the figure indicates a recording sheet on which an unfixed image is formed. As shown in the figure, the fixing device 5 presses the fixing roller 51, the heating roller 53, the heating belt 52 stretched between the fixing roller 51 and the heating roller 53, and the fixing roller 51 via the heating belt 52. And a pressure roller 54 that forms a fixing nip.

When the pressure roller 54 is rotationally driven in the direction of arrow A by the pressure roller drive motor 55, the fixing roller 51, the heating belt 52, and the heating roller 53 are driven to rotate in the direction of arrow B. The driving of the pressure roller drive motor 55 is controlled by the control unit 60, and thereby the rotation speed of the pressure roller 54 is controlled.
A temperature sensor 534 that detects the temperature of the heating belt 52 is disposed in the vicinity of the heating belt 52, and the control unit 60 controls the temperature of the heating roller 53 according to the detected temperature detected by the temperature sensor 534 (described later). By controlling on / off of the heater 533, the temperature of the heating roller 53 is controlled), and the temperature of the heating belt 52 is controlled to be a predetermined temperature (for example, 180 ° C.). As the temperature sensor 534, a non-contact type temperature sensor such as a thermistor can be used.

  The fixing roller 51 is configured by covering the outer peripheral surface of a cylindrical metal core bar 511 with an elastic layer 512. For example, the fixing roller 51 can be configured as a roller having an outer diameter of 20 to 50 mm by forming an elastic layer 512 having a thickness of 2 to 10 mm on the outer peripheral surface of a cylindrical cored bar 511 having a thickness of 2 to 5 mm. As a metal used for the cored bar 511, for example, a metal such as aluminum, iron, SUS (stainless steel) can be used. As the elastic layer 512, an elastic body such as silicone rubber or silicone sponge can be used.

  The heating belt 52 is an endless belt that is driven to circulate. The heating belt 52 is heated by the heating roller 53 and contacts the recording sheet S during the heat fixing operation to thermally melt the unfixed image on the recording sheet. The heating belt 52 is configured by laminating a base layer, an elastic layer, and a release layer in this order. As the heating belt 52, for example, one having an outer diameter of 60 to 120 mm, a base layer thickness of 40 to 150 μm, an elastic layer thickness of 100 to 300 μm, and a release layer thickness of 30 to 50 μm is used. it can.

  As the base layer, a metal such as nickel (Ni) or a heat resistant resin such as polyimide or polyamide can be used. As the elastic layer, a heat-resistant elastic material such as silicone rubber can be used. Examples of the release layer include PFA (tetrafluoroethylene / perfluoroalkoxyethylene copolymer), PTFE (tetrafluoroethylene), FEP (tetrafluoroethylene / hexafluoroethylene copolymer), and PFEP ( Fluororesin such as tetrafluoroethylene / hexafluoropropylene copolymer) can be used.

  The heating roller 53 has a hollow cylindrical metal cored bar 531 and a coat layer 532 covering the outer peripheral surface thereof, and a heater 533 is disposed inside the cored bar 531 (hollow part). . As the heating roller 53, for example, a roller having an outer diameter of about 25 mm (a thickness of the core metal 531 of about 1 mm and a thickness of the coat layer 532 of about 20 μm) can be used. As a metal used for the core metal 531, for example, a metal such as aluminum, iron, SUS (stainless steel) can be used. The coat layer 532 is provided to prevent deterioration due to abrasion with the heating belt 52, and plays the same role as a general Teflon (registered trademark) coat. As the coat layer 532, for example, PTFE can be used. As the heater 533, for example, a halogen heater lamp with 999 W and a light emission length of 290 mm can be used.

The pressure roller 54 includes a hollow cylindrical metal core 541, an elastic layer 542 that covers the outer peripheral surface thereof, and a release layer 543 that covers the outer peripheral surface of the elastic layer 542. As the pressure roller 54, for example, a roller having an outer diameter of 35 mm (a core metal 541 thickness of 2 mm, an elastic layer 542 thickness of 4 mm, and a release layer 543 thickness of about 30 μm) can be used.
As a metal used for the cored bar 541, for example, a metal such as aluminum, iron, SUS (stainless steel) can be used. As the elastic layer 542, for example, an elastic material such as silicone rubber, silicone sponge, or fluororubber can be used. As the release layer 543, the same material as the release layer of the heating belt 52 can be used.

Although not shown, the fixing device 5 is provided with a frame that supports both ends of the fixing roller 51, the heating roller 53, and the pressure roller 54 in the longitudinal direction and covers these members. In this frame, a gap is provided as necessary in the vicinity of the inlet / outlet portion of the recording sheet and the longitudinal end portions of the fixing roller 51, the heating roller 53, and the pressure roller 54.
[3] Configuration of Control Unit FIG. 3 is a diagram illustrating a relationship between the configuration of the control unit 60 and main components that are controlled by the control unit 60. The control unit 60 is a so-called computer, and as shown in the figure, a CPU (Central Processing Unit) 601, a communication interface (I / F) unit 602, a ROM (Read Only Memory) 603, a RAM (Random Access Memory). 604, an image data storage unit 605, a power control unit 606, a threshold storage unit 607, and the like.

  The communication I / F unit 602 is an interface for connecting to a LAN such as a LAN card or a LAN board. The ROM 603 has a program for controlling the image processing unit 3, the paper feeding unit 4, the fixing device 5, the image reading unit 6, the operation panel 7, the temperature sensor 534, a current sensor 403 described later, and a power control process described later. Stores programs for control.

The RAM 604 is used as a work area when the CPU 601 executes a program.
The image data storage unit 605 stores image data for printing input via the communication I / F unit 602 and the image reading unit 6. The power control unit 606 controls power supplied from the power supply unit 700 to the fixing device 5 and a load group 404 described later other than the fixing device 5 by outputting a control signal to the power supply unit 700 described later.

  FIG. 4 is a diagram illustrating a relationship among the power control unit 606, the power supply unit 700, and main components that are the targets of power supply from the power supply unit 700. As shown in the figure, the power supply unit 700 is connected to a commercial power supply (for example, AC 100 V) 401 via a breaker 402 and a current sensor 403, and the fixing device 5 and the load according to a control signal output from the power control unit 606. (Electric equipment to be supplied with electric power) The electric power supplied to the group 404 is controlled. Here, the load group 404 includes loads other than the fixing device (the driving system of the image processing unit 3, the driving system of the paper feeding unit 4, the image reading unit 6, the operation panel 7, etc.).

  FIG. 5 is a graph (operation characteristic curve) showing a correspondence relationship between the amount of current flowing through the breaker 402 and the operation time until the breaker 402 operates. In the figure, the vertical axis represents the operating time, the horizontal axis represents the percentage (%) of the amount of current flowing through the breaker 402 to the rated current, and both axes are shown on a logarithmic scale. As shown in the figure, the operating time of the breaker 402 tends to decrease rapidly as the amount of current flowing through the breaker 402 increases. For example, when the percentage of the rated current (here 15A) is 125% (18.75A), the breaker 402 operates 30 seconds after reaching the current, and the percentage is 300%. In the case of the current amount (45 A), the breaker 402 operates 1 second after reaching the current amount. The power control unit 606 monitors the amount of current supplied to the power supply unit 700 via the current sensor 403 that detects the amount of current, and the breaker 402 operates to supply power to the fixing device 5 and the load group 404. The power supplied to both is controlled so as not to be stopped.

FIG. 6 shows an example of a change over time in the surface temperature of the heating belt 52 of the fixing device 5 when the printer 1 is turned on and the continuous printing process is executed after the warm-up process is completed.
In the figure, the power supplied to the fixing device 5 is set to 900 W, 1000 W, and 1100 W, respectively, and the temperature adjustment is performed to maintain the surface temperature of the heating belt 52 at the fixing temperature (here, 180 ° C.) using each supplied power. The change with time of the surface temperature of the heating belt 52 in the case of being performed is shown. Reference numeral 61 in the figure represents a change with time when the supplied power is 900 W, reference numeral 62 represents a change with time when the supplied power is 1000 W, and reference numeral 63 represents a change with time when the supplied power is 1100 W. The vertical axis represents the surface temperature (° C.) of the heating belt 52, and the horizontal axis represents the elapsed time (seconds) after the start of the continuous printing process.

Note that, in the above-described test of change over time, the printer 1 was left at room temperature (25 ° C.) for one day before power-on, the color printing process was used for the printing process, and the recording sheet was A4 size. Plain paper, the printing speed was 60 sheets / minute, and the continuous printing number was 80 sheets.
As shown in the figure, when the power supplied to the fixing device 5 is 900 W of reference numeral 61 and 1000 W of reference numeral 62, in the middle of the continuous printing process (in the case of 900 W, 14 seconds after the start of the continuous printing process ( In the case of 14th sheet) and 1000 W, the surface temperature of the heating belt 52 is a temperature at which heat fixing can be performed as indicated by reference numeral 64 (in this case, when it exceeds 26 seconds (26th sheet) after the start of the continuous printing process) , 170 ° C).

  On the other hand, when the power supplied to the fixing device 5 is 1100 W of reference numeral 63, the surface temperature of the heating belt 52 did not fall below the temperature at which heat fixing can be performed during continuous printing. Generally, the maximum current (rated current) that can be supplied by a commercial power supply (AC 100 V) is 15 A, and the maximum power (rated power) that can be used by the printer 1 when using a commercial power supply is 1500 W. Considering that 500 W to 600 W of power is required to maintain the function of the load group 404, the power that can be supplied to the fixing device 5 when using the rated power is 900 W to 1000 W. In order to prevent a fixing failure from occurring in the printing process immediately after the warm-up, the supplied power is insufficient.

  For this reason, in the present embodiment, the surface temperature of the heating belt 52 decreases in accordance with the execution of the print job, and the surface temperature of the heating belt 52 is below the temperature at which heat fixing is possible by the time when the print job is finished. When there is a possibility, by performing power control processing described later, the printer 1 supplies power exceeding the rated power within a range not exceeding the maximum current amount (110% of the rated current) defined in the Electrical Appliance and Material Safety Law. The power supplied to the fixing device 5 is increased by an amount corresponding to the excess power.

  As a result, in continuous printing processing in an environment in which the surface temperature of the heating belt 52 is likely to decrease immediately after power-on or the like, the supply power to the load group 404 to which power is distributed from among the rated power is secured and exceeded. By using the power of the minute, it is possible to prevent the occurrence of fixing failure due to a decrease in the surface temperature of the heating belt 52 in the middle of the print job, and a part of the function of the printer 1 is limited due to the lack of power supply. It can prevent effectively that productivity of 1 whole falls.

Returning to the description of FIG. 3, the threshold storage unit 607 stores various thresholds used in a power control process described later.
[4] Power Control Process FIG. 7 is a flowchart showing the operation of the power control process performed by the control unit 60. When the printer 1 is turned on (step S701), the control unit 60 supplies power necessary for executing the warm-up process to the fixing device 5 via the power control unit 606, and executes the warm-up process. (Step S702).

After the warm-up process is completed, the control unit 60 distributes necessary power to the fixing device 5 and the load group 404 via the power control unit 606 (here, 900 W of the rated power 1500 W is supplied to the fixing device 5. It is assumed that the remaining 600 W is distributed to the load group 404.) (Step S703).
When a print job execution instruction is received via the communication I / F unit 602 or the operation panel 7 (step S704), the control unit 60 starts the print job (step S705) and estimates the heating belt temperature at the end of the job, which will be described later. Processing is performed (step S706).

If the surface temperature (te) of the heating belt 52 estimated at the end of the print job instructed to execute in step S706 is lower than the lower limit threshold temperature (tm) of the fixing temperature (step S707: YES) ), The control unit 60 performs a power supply control process described later (step S708).
Next, an operation of the job end heating belt temperature estimation process performed by the control unit 60 will be described. FIG. 8 is a flowchart showing the above operation. When starting the print job in step S705, the control unit 60 acquires the surface temperature (t0) of the heating belt 52 immediately after the start of the print job from the temperature sensor 534 (step S801), and further, for a predetermined time ( After the elapse of (S1 second), the surface temperature (t1) of the heating belt 52 is acquired again from the temperature sensor 534 (step S802: YES, step S804).

If the print job is completed before the predetermined time (S1 second) has elapsed from the time t0 is acquired (step S802: NO, step S803: YES), the control unit 60 ends the operation of the power control process. .
In addition, measurement of S1 second in step S802 can be performed using a timer, for example. S1 second is the time for estimating the rate of decrease in the surface temperature of the heating belt 52 when the recording sheet is continuously passed through the heating belt 52, and the surface temperature of the heating belt 52 is determined based on the estimated rate of decrease. The time is preferably as short as possible so that it is possible to quickly estimate whether or not the temperature is lower than the temperature at which heat fixing is possible by the time when the print job should be completed. S1 is stored in the threshold storage unit 607 in advance. Here, S1 seconds is set to 5 seconds, for example.

Next, the control unit 60 determines whether or not the surface temperature of the heating belt 52 has decreased due to the progress of the print job by comparing the magnitudes of t0 and t1 (step S805). (Step S805: YES), it is determined whether or not t1 has decreased to a lower threshold temperature (tm) or less (step S806).
Here, the “lower threshold temperature (tm)” is a lower limit value of the surface temperature of the heating belt 52 that can perform thermal fixing of an unfixed image without causing fixing failure (here, for example, fixing temperature). (It is 170 ° C., which is 10 ° C. lower than (180 ° C.)), and is stored in the threshold storage unit 607 in advance. The lower threshold temperature (tm) is determined based on a result obtained by examining the relationship between the heat fixing temperature and the fixing property by a manufacturer in advance through an experiment or the like.

For the lower threshold temperature (tm), a different value is determined depending on the printing format (for example, color printing or monochrome printing), the type of recording sheet (plain paper or cardboard), and stored in the threshold storage unit 607. The lower threshold temperature (tm) corresponding to the print condition of the print job may be used.
When the determination result of step S806 is negative (step S806: NO), the control unit 60 calculates the surface temperature of the heating belt 52 from the acquired values of t0, t1, and S1, tm according to the following calculation formula 1. Time until reaching the lower threshold temperature (tm) (S2 seconds (time from t0 acquisition to tm)) is calculated (step S807).

S2 = (t0−tm) / (t0−t1) × S1 (Formula 1)
Here, until the surface temperature (t) of the heating belt 52 reaches the lower threshold temperature (tm), the temperature decreases at a constant temperature decrease rate (per unit time (seconds) (t0-t1) / S1 temperature decrease rate). Then, S2 seconds are calculated by fake.
Then, the control unit 60 further calculates the number of printable sheets from the start of the print job until S2 seconds elapses according to the following calculation formula 2 from the printing speed A (sheets / second) of the printer 1 and the calculated value of S2. (P1) is calculated (step S808).

P1 = A × S2 (Formula 2)
Next, the control unit 60 compares the number of printed sheets (P0) in the print job for which execution has been instructed with the calculated P1 to determine the surface temperature (te) of the heating belt 52 at the end of the print job and the lower limit threshold value. The magnitude of the temperature (tm) is estimated (step S809).
That is, in the case of P0> P1, when the surface temperature (t) of the heating belt 52 is lowered to the lower threshold temperature (tm), the print processing of the print job instructed to execute is not completed. After that, an incomplete print process is executed,
The surface temperature (te) of the heating belt 52 at the end of the print job is further lowered than the lower limit threshold temperature (tm). On the other hand, in the case of P0 ≦ P1, the print processing of the print job instructed to be executed is completed before the surface temperature (t) of the heating belt 52 decreases to the lower threshold temperature (tm). The surface temperature (te) of the heating belt 52 at the end of the print job is equal to or higher than the lower limit threshold temperature (tm).

Instead of performing the processing of step S807 and step S808, the surface temperature (te) of the heating belt 52 at the end of the print job is calculated by the following calculation formula 3, and the magnitude of tm is directly compared with tm in step S809. It is good to do.
te = t0− (t0−t1) / S1 × (P0 / A) (Calculation Formula 3)
Further, when the determination result of step S805 is negative (step S805: NO), when the determination result of step S806 is positive (step S806: YES), the control unit 60 ends the operation of the power control process. To do.

  Next, the operation of the supply power control process performed by the control unit 60 will be described. FIG. 9 is a flowchart showing the above operation. The control unit 60 controls the supply power to be supplied to the load group 404 so that predetermined power (1800 W) exceeding the rated power (1500 W) is supplied to the own device via the power control unit 606. Is maintained (600 W), while the excess power is supplied to the fixing device 5 to increase the power supplied to the fixing device 5 to 1200 W (step S901).

Accordingly, the power supplied to the fixing device 5 is controlled to be increased by an amount (300 W) exceeding the rated power (1500 W). The increase in the power supplied to the device itself is realized by increasing the amount of current supplied to the device (here, the current amount is increased by 20% from 15A to 18A).
After starting the above control, the control unit 60 starts measuring the rated power excess time (So seconds) during which power exceeding the rated power (1500 W) is supplied (Step S902), and the So seconds have reached the allowable time. It is determined whether or not (step S903).

Here, the “allowable time” is an upper limit value of So that is determined in advance by the manufacturer so that the supply power supplied to the device does not exceed the allowable range of rated power (110% of the rated power). This is stored in the threshold storage unit 607. Here, it is 10 seconds. Note that the rated power excess time (So seconds) can be measured using a timer, for example.
The allowable range of the rated power is a standard that is 110% or less of the rated current specified in the Electrical Appliance and Material Safety Law (general rule 1.6.2 of the standard J60950 based on the provisions of the Ministerial Ordinance 2 which defines technical standards for electrical appliances). It is stipulated to satisfy. Here, the average value of the current amount within a predetermined time (in this embodiment, 20 seconds) is determined so as not to exceed 110% (16.5 A) of the rated current (here, 15 A). Yes.

  In the operation of the supply power control process, as will be described later, the supply power of 120% (1800 w) of the rated power (1500 W) and the supply power of the rated power (1500 W) are alternately switched every 10 seconds. In the mean value for a predetermined time (here, 20 seconds), the supplied power does not exceed 110% (1650 W) of the rated power (that is, rated power). Control of the power supplied to the device is performed (so as not to exceed 110% of the current).

  When So reaches the allowable time (step S903: YES), the control unit 60 returns the power supplied to the apparatus to the rated power, and controls the power supplied to the fixing device 5 to 900 W at the end of the warm-up ( Step S904), the measurement of the rated power supply time (Sp), which is the supply time for supplying the rated power, is started (step S905), and it is determined whether Sp has reached the power adjustment end time (step S906).

Here, the “power adjustment end time” means that the average value of the supplied power in a predetermined time (here, 20 seconds) is an allowable range of the rated power (in this case, 20 seconds) due to the excess power supplied during the rated power excess time (So). This means the power supply time at the rated power required for adjustment so as not to exceed 110% of the rated power, and is stored in the threshold storage unit 607. Here, the power adjustment end time is 10 seconds. The rated power supply time (Sp) can be measured using a timer, for example.

When Sp reaches the power adjustment end time (step S906: YES), the control unit 60 acquires the surface temperature (t1) of the heating belt 52 from the temperature sensor 534 (step S907), and t1 is the lower threshold temperature (tm). It is determined whether or not this is the case (step S908).
When t1 is lower than the lower threshold temperature (tm) (step S908: NO), the control unit 60 proceeds to the process of step S901, and when t1 is equal to or higher than the lower threshold temperature (tm) (step S908). : YES), the control unit 60 repeats the processing from step S905 to step S908 until the print job instructed to be executed is completed (step S909: YES).

  If the determination result in step S903 is negative (step S903: NO) and the print job instructed to be executed before the So reaches the allowable time (step S910: YES), the control unit 60 The control unit 60 returns the power supplied to the apparatus to the rated power, controls the power supplied to the fixing device 5 to 900 W at the end of the warm-up (step S911), and ends the power control process.

  As described above, in the power control process according to the present embodiment, the surface temperature (te) of the heating belt 52 at the time when the print job should be ended is lower than the lower threshold temperature (tm), and the print job is being executed. When there is a possibility of fixing failure, the rated power is temporarily exceeded within an allowable range (within 110% of the rated power) before the surface temperature (t) of the heating belt 52 reaches the lower threshold temperature (tm). Supply power is controlled so that the surface temperature (t) of the heating belt 52 does not fall below the lower limit threshold temperature (tm) by supplying power to the apparatus and supplying excess power to the fixing device 5. .

  For this reason, in a print job execution process in an environment where the surface temperature of the heating belt 52 tends to decrease immediately after the power is turned on, the surface temperature of the heating belt 52 decreases to the lower threshold temperature (tm) during execution of the print job. Accordingly, it is possible to reduce the frequency of performing an operation for preventing a fixing failure during image formation such as interruption of the image forming operation or reduction of the printing speed in the middle of the print job.

Further, the power supplied to the load group 404 is maintained during execution of the print job, so that the power supplied to other electrical devices other than the fixing device can be prevented from being affected. It is possible to prevent the function of the device from being stopped due to insufficient supply power.
In this way, by executing this power control process, the reduction in productivity of the entire printer 1 is reduced, and the occurrence of fixing failure due to the decrease in the surface temperature of the heating belt 52 during the print job is prevented. can do.

[6] Modifications Although the present invention has been described based on the embodiments, it is needless to say that the present invention is not limited to the above-described embodiments, and the following modifications can be implemented. .
(1) In this embodiment, the heating belt 52 is used as a heating member of the fixing device 5 for heat-fixing an unfixed image on a recording sheet. However, the heating member to which the present embodiment is applied is as follows. The heating belt is not limited, and other heating members may be used. For example, a heating roller may be used as the heating member.

In this embodiment, the heater heating method is used as the heating method of the fixing device 5. However, the heating method to which the present embodiment is applied is not limited to the heater heating method, and other heating methods can be used. There may be. For example, an electric induction heating method may be used.
(2) In the present embodiment, in the supply power control process, it is estimated that the surface temperature (te) of the heating belt 52 at the end of the print job instructed to execute is lower than the lower limit threshold temperature (tm) of the fixing temperature. In this case, the allowable time of the rated power excess time for supplying power exceeding the rated power to the own device is set to 10 seconds, but the allowable time is increased within the time range until the breaker 402 starts operation. It is good as well. For example, in the operation of the supply power control process of FIG. 9, the allowable time and the rated power supply time may be set to 30 seconds, respectively. From the operation characteristic curve of the breaker 402 shown in FIG. 5, the operation time of the breaker 402 when the rated power is 125% is 30 seconds. Therefore, even if 120% of the rated power is supplied to the own device, the breaker 402 Does not work for at least 30 seconds.

  Further, even if the supply power is controlled as described above, the control is performed so that the supply power to the apparatus does not exceed 110% (1650 W) of the rated power at the average value for 1 minute (that is, 110 of the rated current). %).

  The present invention relates to an image forming apparatus provided with a fixing device, and in particular, can be used as a technique for suppressing the occurrence of fixing failure due to a temperature drop of a heating member of a fixing device during image formation immediately after warm-up.

DESCRIPTION OF SYMBOLS 1 Printer 3 Image process part 4 Paper feed part 5 Fixing device 6 Image reading part 7 Operation panel 10 Exposure part 11 Intermediate transfer belt 12 Drive roller 13 Driven roller 21, 35Y Cleaner 31Y Photoconductor 32Y Charger 33Y Developer 41 Feed cassette 42 Feed roller 43 Conveying path 44 Timing roller 45 Secondary transfer roller 46 Secondary transfer position 51 Fixing roller 52 Heating belt 53 Heating roller 54 Pressure roller 55 Drive motor 60 Control unit 71 Discharge roller 72 Discharge tray 401 Commercial power supply 402 Breaker 403 Current sensor 404 Load group 534 Temperature sensor 700 Power supply unit

Claims (5)

In a steady state where the heating member of the fixing device can be maintained at a temperature at which heat fixing can be performed even if the recording sheet is continuously fed, power is supplied to the heating member within a range not exceeding the rated power, and the fixing member is not fixed. An image forming apparatus that performs a heat fixing operation of an image,
Temperature monitoring means for monitoring the temperature of the heating member;
When the temperature of the heating member decreases as the print job progresses after the start of the print job, the temperature of the heating member is not fixed by the time until the print job should be completed based on the amount of decrease. An estimation means for estimating whether or not the lower limit of the possible temperature is below,
When it is estimated that the temperature of the heating member is lower than the lower limit value, the temperature of the heating member is larger than the lower limit value during execution of the print job and is larger than the rated power and accepted by the own apparatus. Power control means for controlling the power supplied to the heating member within a range not exceeding an allowable upper limit of possible power so as to increase the power exceeding the rated power;
An image forming apparatus comprising: The image forming apparatus according to claim 1, wherein the power control unit controls the supplied power so that an average value in a predetermined period does not exceed the allowable upper limit value. The heating member is an endless heating belt, and the fixing device presses a pressure member against the heating belt to form a fixing nip,
The image forming apparatus according to claim 1, wherein the pressure member has a larger heat capacity than the heating belt. The temperature estimation means is a case where the first print job is after power-on, after warm-up is completed, or after returning from the sleep mode, and the temperature of the heating member is increased by execution of the print job. The image forming apparatus according to claim 1, wherein the temperature of the heating member is estimated at a time when the print job should be ended when the print job is to be reduced. The image forming apparatus according to claim 1, wherein the allowable upper limit value is a value corresponding to 110% of the rated power.

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