JP2014052422A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress extension of time required to output a first recording material from input of a print request, even when power supplied to a fixing unit is limited.SOLUTION: When power supplied to a fixing unit is determined to be limited, a larger amount of power is supplied to the fixing unit before the start-up of a drive load upon the subsequent print request.

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a printer.

  In an image forming apparatus that employs an electrophotographic system, there is an increasing demand for shortening the time (FPOT: First Print Out Time) from when a print command is input until the first recording material on which an image is formed is output. .

  Factors that determine FPOT include the time required for image formation and recording material conveyance to the photoconductor, and the time required for warming up the fixing unit that proceeds in parallel with image formation and recording material conveyance to the photoconductor. . The image formation control and the recording material conveyance control proceed sequentially according to a predetermined time, and the time required for these controls is determined by the sequence. On the other hand, the time required for warming up the fixing unit varies because the time required to raise the temperature to the fixable temperature varies due to variations in the power supply voltage, environmental differences, and the like.

  In order to shorten the FPOT, it is desirable to start image formation on the photosensitive member at a timing at which the recording material enters the fixing nip portion immediately after the temperature of the fixing portion reaches the fixable temperature. One method for achieving this object is to start image formation by predicting the time at which the temperature of the fixing unit reaches the fixable temperature based on the rate of temperature increase of the fixing unit detected by the temperature detecting element (image There is a method of determining the (writing) timing (Patent Document 1).

  Next, a control example during warm-up will be briefly described. In FIG. 10, the upper graph shows the transition of the input current (inlet current) to the image forming apparatus and the supply power to the fixing unit during the warm-up control, and the lower graph shows the fixing unit temperature (here, the heater temperature and the heater temperature). Transition).

  When a warm-up instruction is received, at a timing <A>, supply of predetermined power (Pf) to the heater is first started, and rotation of a fixing unit motor (hereinafter referred to as a fixing motor) is started. Thereafter, during the period from timing <A> to <B>, a motor for driving the scanner (hereinafter referred to as a scanner motor), a motor for driving the photosensitive member (hereinafter referred to as a drum motor), etc. Start the necessary loads in order. At timing <B>, all loads have been activated. Assuming that the power supplied to the heater is constant during warm-up (or less than a certain value), the inlet current value continues until the current value at timing <B> finishes warm-up (until timing <D>). It will be.

  When the heater temperature reaches a predetermined image writing temperature (T1), the image forming process is started from the timing <C> when the temperature T1 is exceeded (starting image writing on the photosensitive member). After that, the recording material on which the unfixed image is formed reaches the fixing nip portion after the timing <D> when the heater temperature reaches the fixable temperature, here, the printing temperature (T_print) which is the control target temperature during the fixing process. It will be.

  The time t1 from the start of the image forming process (start of image writing to the photoconductor) until the recording material reaches the fixing nip is determined in advance by the sequence. In general, the image writing temperature (T1) is determined in consideration of the time t1.

  Note that the shortest FPOT is a case where the heater temperature is controlled to rise to a fixable temperature within the period from the start of image writing until the recording material reaches the fixing nip (in the case of FIG. 10). is there. As a technique for realizing this, preheating of the fixing unit is also generally performed during standby for waiting for a print command.

  With recent increases in the speed of image forming apparatuses, the power consumption of the apparatus is increasing. In particular, a high-speed color laser printer that needs to form a plurality of toner images at the same time consumes a large amount of power consumed by a driving load such as a motor.

  By the way, when designing the image forming apparatus, it is necessary that the inlet current does not exceed 15 A which is the maximum current that can be supplied from the commercial power source. For this reason, a problem with a device that consumes a large amount of power consumed by a driving load, such as a high-speed color laser printer, is that power allocated to the fixing unit is reduced. In addition, the power consumed by the drive load varies due to individual load variations and load variations due to durability. However, if the load estimate is maximized at the time of design, it will be necessary to make a very large margin. . As a result, the power allocated to the fixing unit is further reduced.

  In order to solve such problems, a control is proposed in which the current flowing through the drive load during warm-up is monitored, and when it is determined that the current exceeds the predetermined current, the power supplied to the heater is reduced and the FPOT is extended (patent) Reference 2).

Japanese Patent Laid-Open No. 06-301255 JP 2010-286588 A

  A control example in the case of reducing the power supplied to the fixing unit during warm-up will be described with reference to FIG.

  FIG. 11A shows a case where the inlet current does not exceed a predetermined upper limit current value (limit current), and FIG. 11B shows a case where the inlet current exceeds the upper limit current value. FIG. 11A is the same as FIG. 10 and is a diagram in which a limit current line is drawn on the inlet current graph. Here, the limit current is an upper limit current value preset in a current value of 15 A or less so that the inlet current does not exceed 15 A.

  Unlike the situation of FIG. 11A, in the case of FIG. 11B, the inlet current exceeds the limit current at the timing <B> when all the loads related to image formation are activated. For this reason, as shown in the drawing, control is performed to reduce the power supplied to the fixing unit (hereinafter referred to as fixing power) from Pf to Pf_down, and the inlet current is reduced to 15 A or less.

  With this control, the heater temperature rise curve becomes gentle and the time required to reach T_print becomes longer. Therefore, in this case, the heater temperature does not reach T_print after the time t1 even if the image writing permission is given at the timing when it reaches the same temperature T1 as in FIG. In view of this, as shown in FIG. 11B, the control for issuing the image writing permission in accordance with <C ′>, which is the timing before time t1 from the timing <D> at which T_print is reached. Done. Specifically, another image writing permission temperature T_target when power is limited is set in advance, and the timing at which the heater temperature reaches the permission temperature T_target is set as the image writing permission timing <C ′>.

  As shown in FIG. 11, in the case where the power supplied to the fixing unit is not restricted and the case where it is restricted, the image writing permission timing is different from the timing indicated by <C> and the timing indicated by <C ′>. When the power is limited, the time required for warm-up is lengthened by at least the time indicated by the period t2, and the FPOT is extended.

  By the way, when image formation is started (image writing to the photosensitive member is started), the printing process cannot be stopped thereafter. When it is determined that it is necessary to further limit the power supplied to the fixing unit after the start of image formation, and the control is performed to reduce the power supplied to the fixing unit, the fixing unit does not move until the recording material reaches the fixing nip. The fixable temperature is not reached. As a result, an image that does not satisfy the fixing property is discharged. In order to avoid this situation, it is important to grasp the state of the inlet current as accurately as possible before the start of image writing. In order to grasp accurately, the inlet current that flows to the image forming apparatus in the state where each driving load (motor for driving the photosensitive member, motor for driving the transfer belt, motor for driving the roller in the conveyance path, etc.) is driven. Need to be detected.

  The power consumption of the driving load gradually varies with long-term use of the driving load, but does not change in a short period. Further, the input power supply voltage does not change in a short period. Therefore, the control for reducing the power supplied to the fixing unit because the inlet current exceeds the upper limit current is highly likely to be executed due to load fluctuations and power supply voltage fluctuations due to long-term use of the driving load. Therefore, if this control is executed even once, there is a high possibility that it will be executed at the start of the next print job. Once the control for reducing the power supplied to the fixing unit is performed, the FPOT extension is repeated for each print job.

  Furthermore, there is another waste in the period t2, which is the FPOT extension period. During the period t2 in which the FPOT is extended, the driving load such as the photosensitive member is also driven, so that the power for the driving load is wasted and the amount of power cannot be supplied to the fixing unit. FPOT has been extended.

  The present invention has been made under such circumstances, and even in a situation where it is necessary to reduce the power that can be supplied to the fixing unit, the time required for warming up the fixing unit is shortened as much as possible to extend the FPOT. The purpose is to suppress.

  The present invention for solving the above-described problems includes an image forming unit that forms an unfixed image on a recording material, a fixing unit that heat-fixes an unfixed image formed on the recording material, and a commercial power supply. And an electric current detection unit that detects an input current of the electric power generated during a warm-up period from the start of supplying electric power to the fixing unit until the temperature of the fixing unit reaches a fixable temperature. A first mode in which the first power is continuously supplied to the fixing unit; and a second power that is smaller than the first power after the first power is supplied to the fixing unit during the warm-up period. In the second mode for supplying the image forming unit, and during the warm-up period, after the third power larger than the second power is supplied to the fixing unit, the driving load of the image forming unit is activated and the fixing unit Said third power The third mode for supplying a smaller fourth power can be executed, and when a warm-up instruction is input, the first to second modes are selected according to the warm-up extension history and the detected current value of the current detection unit. One of the three modes is selected and the fixing unit is warmed up.

  According to the present invention, even in a situation where it is necessary to reduce the power that can be supplied to the fixing unit, it is possible to shorten the time required for warming up the fixing unit as much as possible and suppress the extension of the FPOT.

Schematic configuration diagram of an image forming apparatus Cross section of fixing unit and plan view of heater Heater drive circuit diagram The figure explaining warm-up control of Example 1 Flowchart 1 for explaining the first embodiment Flowchart 2 for explaining the first embodiment The figure explaining warm-up control of Example 2 Flowchart 1 illustrating the second embodiment Flowchart 2 for explaining the second embodiment Diagram explaining an example of control during warm-up Diagram explaining an example of control during warm-up

Example 1
Embodiment 1 of the present invention will be described below with reference to FIGS. However, this embodiment is merely an example, and the present invention is not limited to these configurations.

(Description of image forming apparatus)
FIG. 1 is a configuration diagram of a tandem color image forming apparatus using an electrophotographic process. The image forming operation of the configuration of the image forming apparatus will be described with reference to FIG.

  The tandem color image forming apparatus is configured to output a full color image by superimposing four color toners of yellow (Y), magenta (M), cyan (C), and black (K). Laser scanners (11Y, 11M, 11C, 11K) and cartridges (12Y, 12M, 12C, 12K) are provided for image formation of each color. The cartridge (12Y, 12M, 12C, 12K) includes a photoconductor (13Y, 13M, 13C, 13K) that rotates in the direction of the arrow in the figure, and a photoconductor cleaner (14Y, 14M, 14K) provided in contact with the photoconductor. 14C, 14K), a charging roller (15Y, 15M, 15C, 15K), and a developing device having a developing roller (16Y, 16M, 16C, 16K). Further, an intermediate transfer belt 19 is provided in contact with each color photoconductor (13Y, 13M, 13C, 13K). Is installed.

  The paper feed cassette 22 that stores the recording material 21 is provided with a recording material presence / absence sensor 24 that detects the presence or absence of the recording material 21 in the cassette. Further, a paper feed roller 25, separation rollers 26a and 26b, and a registration roller 27 are provided on the conveyance path, and a registration sensor 28 is provided in the vicinity of the registration roller 27 on the downstream side in the recording material conveyance direction. Further, on the downstream side of the transport path, a secondary transfer roller 29 is disposed so as to contact the intermediate transfer belt 19, and a fixing unit 30 is disposed downstream of the secondary transfer roller 29.

  Reference numeral 31 denotes a controller which is a control unit of the laser printer, and includes a CPU (Central Processing Unit) 32 having a ROM 32a, a RAM 32b, a timer 32c, and the like, various input / output control circuits (not shown), and the like. .

  Next, the electrophotographic process will be briefly described. In the dark place in the cartridge (12Y, 12M, 12C, 12K), the surface of the photoreceptor (13Y, 13M, 13C, 13K) is uniformly charged by the charging roller (15Y, 15M, 15C, 15K). Next, the surface of the photosensitive member (13Y, 13M, 13C, 13K) is irradiated with laser light modulated in accordance with image data by the laser scanner (11Y, 11M, 11C, 11K), and the charged charges of the portion irradiated with the laser light are irradiated. Is removed to form an electrostatic latent image on the surface of the photoconductor (13Y, 13M, 13C, 13K). In the developing device, the toner is attached to the electrostatic latent image on the photosensitive member by a developing bias from a developing roller (16Y, 16M, 16C, 16K) holding a certain amount of toner layer, and thereby each color toner image is exposed to each photosensitive member. Form on the surface of the body (13Y, 13M, 13C, 13K).

  The toner image formed on the surface of the photoreceptor is transferred to the intermediate transfer belt 19 by the primary transfer bias at the nip portion between the photoreceptor and the intermediate transfer belt 19. The CPU 32 controls the image formation timing in each cartridge (12Y, 12M, 12C, 12K) at a timing according to the belt conveyance speed, and finally transfers the respective toner images onto the intermediate transfer belt 19, thereby finally. A full-color image is formed on the intermediate transfer belt 19.

  On the other hand, the recording material 21 in the cassette 22 is conveyed by the paper feed roller 25, and only one recording material 21 passes through the registration roller 27 by the separation rollers 26 a and 26 b and is conveyed to the secondary transfer roller 29. The toner image on the intermediate transfer belt 19 is transferred to the recording material 21 at the nip portion between the secondary transfer roller 29 and the intermediate transfer belt 19 downstream of the registration roller 27. The above is the description of the image forming unit that forms an unfixed image on the recording material 21. The unfixed image formed on the recording material is heated and fixed on the recording material 21 by the fixing unit 30 and then discharged outside the image forming apparatus.

(Description of fixing unit)
The configuration of the fixing unit 30 will be described with reference to FIGS. FIG. 2A is a cross-sectional view of the fixing unit 30. The fixing unit 30 is a pressure roller driving type film heating type heating device using an endless film (fixing film) 102. Inside the cylinder of the fixing film 102, a ceramic heater 100 and a heater holder 101 for holding the heater 100 are provided. The heater 100 is in contact with the inner surface of the film 102. A pressure roller 103 forms a fixing nip portion N together with the heater 100 via the fixing film 102. The pressure roller 103 is a driving roller that rotates the fixing film 102. Reference numeral 104 denotes a protective element (a thermoswitch in this example) that is activated when the heater 100 is overheated. The recording material 21 carrying the unfixed image T is heated by heat from the heater 100 while being nipped and conveyed by the fixing nip portion N. As a result, the unfixed image T is heat-fixed on the recording material 21.

  FIG. 2B is a plan view of the heater 100. As shown in the figure, the heating element 111 has a heating part 111a, electrodes 111c and 111d, a folded conductive part 111b, and a conductive part 111e that connects the electrode and the heating part. By supplying power via the electrodes 111c and 111d, the heat generating portion 111a generates heat.

(Explanation of heater drive circuit)
Next, the configuration of the heater drive circuit will be described with reference to FIG. Reference numeral 50 denotes a commercial AC power source for connecting the image forming apparatus, and is connected to the low voltage power source 64 and the heater 100 via the AC filter 51. Reference numeral 32 denotes a CPU that executes each control of the image forming apparatus including the heater drive control, and includes each input / output port, ROM 32a, RAM 32b, and the like.

  Further, the AC power supply 50 is connected to a zero cross detection circuit 52 through an AC filter 51. The zero cross detection circuit is configured to output a high level signal when the commercial power supply voltage is equal to or lower than a threshold voltage in the vicinity of 0 V, and to output a low level signal in other cases. Then, a pulse signal having a cycle substantially equal to the cycle of the commercial AC power generated by the zero cross detection circuit is input to the input port PA1 of the CPU 32 via the resistor 53. The CPU 32 detects an edge of the zero cross signal that changes from High to Low, and uses it for heater drive timing control.

  The heater 100 generates heat by receiving power supply. The temperature of the heater 100 is detected by a temperature detection element 54 disposed on the back surface. One of the temperature detection elements 54 is connected to the ground, the other is connected to the resistor 55, and further connected to the analog input port AN 0 of the CPU 32 via the resistor 56. The CPU 32 is configured to monitor the divided voltage between the temperature detection element 54 and the fixed resistor 55. The temperature detection element 54 has a characteristic that the resistance value decreases when the temperature becomes high, and the CPU 32 detects the current heater temperature by converting the divided voltage based on a preset voltage-temperature conversion table. The CPU 32 determines the lighting timing for driving the phase control circuit (triac drive circuit) 70 based on the detected temperature, and outputs a Drive signal for driving the triac from the output port PA2.

  The phase control circuit 70 will be described. When the output port PA2 becomes high level at a predetermined lighting timing, the transistor 75 via the base resistor 58 is turned on. When the transistor 75 is turned on, the phototriac coupler 72 is turned on. The phototriac coupler 72 is a device for securing a creepage distance between the primary and secondary, and the resistor 76 is a resistor for limiting a current flowing through the light emitting diode in the phototriac coupler 72.

  Resistors 73 and 74 are bias resistors for the triac 71. When the phototriac coupler 72 is turned on, the triac 71 is energized. The triac is an element that is latched in the energized state until the AC energization is stopped when the ON trigger is applied during the AC energization, and the heater 100 is supplied with the electric energy corresponding to the on timing.

  On the other hand, the low-voltage power supply 64 includes a diode bridge 61 and a smoothing capacitor 62 for rectifying an AC voltage, and an AC-DC converter 63 for generating a DC power supply in the subsequent stage. The DC voltage generated by the low voltage power supply 64 is supplied to a secondary load 65 such as a control unit and a drive unit of the image forming apparatus.

  The input current supplied to the low-voltage power supply 64 and the heater 100 is converted into a relative voltage value by the current detection circuit 67 via the current transformer 66 and input to the analog input port AN1 of the CPU 32. The CPU 32 detects the total current value (inlet current) supplied from the AC power supply 50 by converting the voltage value based on a preset voltage-current conversion table. Similarly, the current supplied only to the fixing unit (more precisely, the heater 100) is converted into a relative voltage value by the current detection circuit 69 via the current transformer 68, and is input to the analog input port AN2 of the CPU 32. ing.

(Explanation of control)
Next, a control specification that is a characteristic part of the present embodiment will be described with reference to FIG. FIG. 4A shows a case where the inlet current becomes equal to or greater than a predetermined current value (limit current value) when performing warm-up control. FIG. 4B shows an outline of the warm-up control executed after the job following the job in which the case of FIG. The upper graph in each figure schematically shows the time transition during warm-up of the inlet current and the power supplied to the heater 100 (hereinafter referred to as fixing power), and the lower graph shows the heater temperature. It shows the transition.

  First, FIG. 4A will be described. When a warm-up instruction is received, power supply to the fixing unit 30 (more precisely, the heater 100) is started at a predetermined power (Pf) at the timing <A>, and rotation of the fixing motor is started. Thereafter, during the period from timing <A> to timing <B>, all necessary loads such as a scanner motor and a drum motor are sequentially activated. The power Pf is a fixing power determined in advance so that the FPOT is the shortest. As described with reference to FIG. 10, if the power Pf is continuously supplied, the recording material 21 is moved to the fixing nip portion N even if the heater temperature reaches the image writing temperature T1 when the image writing start timing to the photoconductor is started. The heater temperature reaches the fixable temperature (printing temperature (T_print)) within the period t1 until it reaches. Such power is set as power Pf. A mode in which the power Pf (first power) is continuously supplied to the fixing unit during the warm-up period from the start of supplying power to the fixing unit until the temperature of the fixing unit reaches the fixable temperature is a normal mode (first mode). Mode).

  Subsequently, at the timing <B> when the activation of all the loads is completed, the CPU 32 monitors the inlet current and checks whether a current equal to or higher than a preset limit current value (Limit in FIG. 4) is not flowing. As shown in FIG. 4, when the detected current exceeds the limit current, a new fixing power Pf_down (second power) in which the power corresponding to the exceeded current is reduced is calculated. Then, the mode shifts to the FPOT extension mode 1 in which the image writing permission is delayed, and the fixing power is reduced to Pf_down. Here, the limit current is an upper limit current value preset in a current value of 15 A or less so as not to exceed 15 A. As described above, a mode in which the second power smaller than the first power is supplied after the first power is supplied to the fixing unit during the warm-up period is referred to as an FPOT extension mode 1 (second mode).

  An example of how to determine Pf_down will be described. One method is a method in which Pf_down is a value obtained by subtracting the fixing power corresponding to the excess current value when it is confirmed that the inlet current exceeds the limit current at the timing <B> from Pf. In this case, it is necessary to monitor the amount of current change with respect to a predetermined fixing power change in advance. Another method is to confirm that the inlet current has exceeded the limit current at the timing <B>, and then decrease the fixing power by a predetermined amount to reduce the fixing power at which the inlet current is below the limit current value. This is a method of determining Pf_down. Still another method is a method in which the current detection circuit 67 detects the inlet current, and at the same time, the current detection circuit 69 detects the current supplied to the fixing unit 30, and obtains Pf_down based on the two detected current values at that time. Can be considered.

When the FPOT extension mode 1 is entered, the heater temperature rise rate ΔT (= heater rise temperature for a predetermined time / predetermined time) is monitored, and the image writing temperature (T_target1) is calculated from ΔT using the following equation.
T_target1 = T_print−ΔT × t1 (1)

  The time t1 is the time required from the start of image formation (start of image writing to the photoconductor) until the recording material 21 reaches the fixing nip, and is a time determined in advance in the sequence. That is, when image formation is started at the timing <C> when the heater temperature becomes T_target1, the heater temperature rises to the printing temperature (T_print) at the timing <D> after the time t1. Note that <X> in the figure is assumed when it is not necessary to reduce the fixing power to the power Pf_down (that is, when the inlet current is lower than the limit current at the timing <B> and the power Pf can be maintained). This is the image writing start timing. Comparing the case where the image formation is started at the timing <X> and the case where the image formation is started at the timing <C>, it can be seen that the period t2 corresponds to the FPOT extension time.

  Subsequently, FIG. 4B will be described. FIG. 4B shows an FPOT extension mode 2 that is applied when the next or subsequent print job is started when the FPOT extension mode 1 as described in FIG. 4A is entered. The power consumption of a driving load such as a drum motor varies depending on durability and environment, and it is difficult to think of a sudden change. In other words, it can be predicted that the power consumption of the drive load remains changed once it has changed. Therefore, when processing a job after a job that has been determined that the power consumption of the driving load has increased, it can be determined that there is a need to extend the FPOT at the stage before the warm-up is started. The warm-up control described in FIG. 4B uses such a phenomenon. That is, power that cannot be supplied after the drive load is activated because the limit current is exceeded is supplied to the fixing unit as much as possible before the drive load is activated so as to keep the FPOT extension time short. Control (mode).

  Specifically, when a warm-up instruction is received, electric power Pf_pre (third electric power) larger than electric power Pf_down (second electric power) is supplied to the fixing unit 30 and only the fixing motor starts to be driven. In the case of this example, the power Pf_pre (third power) is larger than the predetermined power Pf (first power). In this state, heating is performed up to T_target1. During this time, since only the fixing motor is driven, all the remaining electric power can be supplied to the fixing unit 30. Therefore, Pf_pre can be determined in advance as a power corresponding to a current obtained by subtracting the current flowing through the fixing motor from the limit current value.

  When the heater temperature reaches T_target1, the power supplied to the fixing unit is changed to Pf_down used at the previous activation (when FPOT extension mode 1 is executed), and the driving loads such as the scanner motor and the drum motor are sequentially activated. . In the case of this example, the power (fourth power) supplied to the fixing unit after the heater temperature reaches T_target1 is the same magnitude as the second power. After confirming the activation of these driving loads, an image writing permission is issued and a series of image forming processes is performed. By raising the heater temperature to T_target1 before starting each driving load (period t3), after starting the driving of the drum motor or the like, the heater temperature surely reaches the printing temperature (T_print) in the shortest time t1. To rise.

  As a result, the FPOT extension time is a time represented by t3, which is a shorter FPOT extension time than the time t2 shown in FIG. Further, unlike the period t2, the period of t3 is not driven to rotate, so the driving time of the photoreceptor can be reduced.

  As described above, during the warm-up period, after supplying the third power larger than the second power to the fixing unit, the driving load of the image forming unit is activated and the fourth power smaller than the third power is supplied to the fixing unit. The mode for supplying the power is FPOT extension mode 2 (third mode).

  Next, the control of this embodiment will be described with reference to the flowcharts of FIGS. The control process shown in this flowchart is executed by the CPU 32 in accordance with a program stored in advance in the ROM 32a.

  First, FIG. 5 will be described. When the warm-up instruction is received (S101), the warm-up control is divided depending on whether or not the FPOT is extended when processing the previous JOB (S102). The CPU 32 has a “FPOT previous extension bit” (warm-up extension history) in the RAM 32b. If the FPOT extension has occurred during the previous JOB processing, “1” is set. Otherwise, “0” is set. "Is stored. Whether or not FPOT extension has been performed is determined based on this data. This bit “1” is written when the FPOT extension mode 1 is entered, and is cleared (set to “0”) when the power is turned on or when the process cartridge is replaced.

  When the FPOT extension has not been performed in the previous JOB, the fixing power Pf is supplied and the fixing motor is started (S103 = timing <A> in FIG. 4A or FIG. 11A). Thereafter, the respective driving loads are sequentially activated (S104 = period <A> to <B> in FIG. 4A or FIG. 11A). When the start of all the drive loads is completed, it is monitored whether or not the inlet current is below the limit current, and the warm-up control is divided according to the result (S105 = FIG. 4 (a) or FIG. 11 (a)). Timing <B>).

  When it is determined that the inlet current is equal to or lower than the limit current (lower than the upper limit current value), the mode is changed to the normal mode (first mode) (S106). On the other hand, when it is determined that the current is greater than or equal to the limit current, the state transits to the FPOT extension mode 1 (second mode) (S107). When the FPOT extension mode 1 is entered, “1” is written to the FPOT extension bit described above. On the other hand, if it is determined in S102 that the FPOT extension has been carried out during the previous JOB process (the FPOT extension bit is “1”), the mode transits to the FPOT extension mode 2 (third mode) (S108). . Each mode has a different image permission permission sequence, and details will be described later with reference to FIG.

  The flowchart of FIG. 5 will be further described. After one of the first to third modes is selected and image writing permission (S110 = FIG. 4 (a) or FIG. 4 (b) or FIG. 11 (a) timing <C>) is issued, the image is displayed. The forming process (S120 to S125) and the warm-up control (S111 to S112) of the fixing unit are simultaneously performed asynchronously. The warm-up control ends when the heater temperature reaches the fixable temperature (printing temperature T_print) (S111) (S112), and switches to control for maintaining the fixable temperature (S113). On the other hand, the image forming unit forms an image of each color on the intermediate transfer belt 19 (S120). In parallel with the image forming control, the image forming unit matches the position and timing of the image (S121) and feeds the recording material 21. (S122) is executed. The image formed on the intermediate transfer belt 19 is transferred to the recording material 21 at the secondary transfer portion (S123), and then conveyed to the fixing nip portion (S124 = FIG. 4 (a) or FIG. 4 (b) or FIG. 11 (a) timing <D>). In any mode, the above-described warm-up control is completed by S124 (timing <D>). Thereafter, the toner is fixed on the recording material 21 and discharged outside the apparatus (S125).

  Thus, in the present embodiment, the first to third modes can be executed during the warm-up period, and when the warm-up instruction is input, according to the warm-up extension history and the detected current value of the current detection unit, One of the first to third modes is selected to warm up the fixing unit.

  Subsequently, control in each mode will be described with reference to FIG. FIG. 6A is an image writing permission issuance flowchart in the normal mode (first mode). A predetermined image writing temperature T1 (FIG. 11A) is set as the target temperature T_target1 (S131). When the heater temperature reaches T_target1 (S132), an image writing permission is issued (S110). Note that T1 is a temperature determined in advance so that the heater temperature rise time required for supplying the predetermined power matches the conveyance sequence time.

  FIG. 6B is an FPOT extension mode 1 (second mode) image writing permission issuance issuance flowchart selected when it is determined that the inlet current exceeds the limit current at timing <B>. With the heater supplied with electric power Pf_down obtained by subtracting electric power corresponding to the excess current value from electric power Pf (S141), the heater temperature increase rate ΔT is monitored for one second (S142). T_target1 is calculated from the sequence time t1 from the start of image formation, the fixable temperature (T_print), and the temperature increase rate ΔT (S143). When the heater temperature reaches T_target1 (S144), an image writing permission is issued (S110).

  FIG. 6C shows an FPOT extension mode 2 (third mode) selected when it is determined that there is a history of selecting the FPOT extension mode 1 (second mode) (the FPOT extension bit is “1”). Is an image writing permission issuing flowchart of FIG. In this mode, warm-up control is performed using the image writing temperature T_target1 when the FPOT extension mode 1 is executed. First, a large amount of power Pf_pre is supplied to the heater without starting each driving load other than the fixing motor (S151).

  When the power Pf_pre is supplied and the heater temperature reaches the temperature T_target1 (S152), the fixing power is reduced to Pf_down used in the FPOT extension mode 1 (S153), and a load necessary for the image forming process is driven (S154). If it is determined that all drive loads have been activated and the inlet current does not exceed the limit current (S155), an image writing permission is issued (S110).

  When a process cartridge or the like is used for a long period of time, the internal friction state may change and torque may increase. As a result, the load current required for driving increases, and there is a possibility of reaching the limit current even in the step S155 of the FPOT extension mode 2. At that time, the mode shifts to FPOT extension mode 1, and power Pf_down and temperature T_target1 are newly set.

  As described above, according to this embodiment, when it is determined that FPOT extension is necessary, more power is supplied to the fixing unit 30 before starting the driving load in the subsequent warm-up. It becomes possible to keep the FPOT extension time short.

(Example 2)
A second embodiment of the present invention will be described with reference to FIGS. In the first embodiment, when the state of the inlet current is detected during the warm-up control after the print request is input and the inlet current exceeds the limit current, “1” is written in the FPOT previous extension bit. In this embodiment, the state of the inlet current is detected immediately after the power supply of the image forming apparatus main body is turned on or immediately after the image forming apparatus main body door is closed, and when the inlet current exceeds the limit current, the FPOT previous extension bit Write "1" to Therefore, control (hereinafter referred to as initial warm-up) is performed to raise the fixing unit to a fixable temperature immediately after the image forming apparatus main body is turned on or immediately after the image forming apparatus main body door is closed. As described above, in this embodiment, the warm-up control after the print request is input based on the inlet current at the time of the warm-up control immediately after the image forming apparatus main body is turned on or immediately after the image forming apparatus main body door is closed. It is a change of method.

  An outline of the control specifications will be described with reference to FIG. FIG. 7A shows a case where the inlet current has exceeded the limit current value at the time of initial warm-up, and FIG. 7B shows the warm-up control during print JOB processing when a print request is received. An overview is shown.

  As shown in FIG. 7A, at the initial warm-up, supply of the predetermined power Pf to the fixing unit is started at timing <A> and rotation of the fixing motor is started. Thereafter, during a period from timing <A> to timing <B>, all driving loads related to image formation such as a scanner motor and a drum motor are sequentially activated. The electric power Pf is the same value as the electric power Pf described in the first embodiment, and is an electric power determined in advance so that the FPOT is the shortest.

  At the timing <B> when the activation of all the driving loads is completed, the CPU 32 monitors the inlet current to check whether a current equal to or higher than a predetermined upper limit current (limit current) is flowing. As shown in FIG. 7A, when the current is equal to or greater than the limit current, the heater is supplied with electric power Pf_down obtained by reducing the electric energy corresponding to the excess current value from the electric power Pf. The CPU 32 measures the time until the heater temperature rises to the printing temperature (T_print). It is not a warm-up before printing (not a warm-up after printing request), so it is not necessary to continuously drive the drum motor, etc. while the heater temperature is warmed up to the printing temperature. Other than the load related to the driving of the fixing unit 30 may be stopped when preparations such as initial failure detection are completed.

  Subsequently, the description moves to FIG. FIG. 7B shows the warm-up control during the first print job (the first after the power is turned on) after entering the power limit mode by the initial warm-up described with reference to FIG. When there is a print request and a warm-up instruction is received, electric power Pf_pre larger than a predetermined electric power Pf is supplied to the fixing unit and only the fixing motor is driven.

After the power Pf_pre is continuously supplied for the period of time t7 calculated by the following equation, a load related to image formation is activated and a series of FPOT sequences are executed.
t7 = (Pf × t5 + Pf_down × t6−Pf_down × t1) / Pf_pre (2)
Note that the (Pf × t5 + Pf_down × t6) portion of Equation 2 is the integrated power amount supplied to the heater 100 during the initial warm-up, and the time t1 is the same as the time t1 described in the first embodiment.

  Next, the control of this embodiment will be described with reference to the flowcharts of FIGS. First, FIG. 8 will be described. After the power is turned on or after the door is closed, initial warm-up is started (S201 = timing <A> in FIG. 7A). First, the power Pf is supplied to the heater and the fixing motor is started (S202). Thereafter, the respective driving loads are sequentially activated (S203 = period <A> to <B> in FIG. 7A). When the activation of all the driving loads is completed, it is monitored whether or not the inlet current is equal to or less than the limit current (S204). When the inlet current is equal to or lower than the limit current, the electric power Pf is continuously supplied, and the temperature of the heater 100 is raised until the fixing possible temperature (T_print) is reached (S205), and then the initial warm-up operation is finished (S212). ). The mode via S205 corresponds to the first mode.

  On the other hand, when it is determined that the inlet current has reached the limit current, the fixing power Pf_down in which the amount of power corresponding to the current value that is equal to or greater than the limit current is supplied to the heater (S206 = timing in FIG. 7A). <B>). Then, a counter for measuring the time required for the warm-up operation is started (S207). Thereafter, when the heater temperature reaches the fixing possible temperature (T_print) (S208), the counter is stopped (S209), and the accumulated power used is calculated from the measured time and the supplied power amount (S210). When this mode is entered, a flag “1” is set in the “FPOT extension mode bit” in the RAM 32b of the CPU 32 (S211), and a series of initial warm-up operations is terminated (S212 = FIG. 7A). Timing <D>). The mode via S206 corresponds to the second mode. As described above, since the load other than the load related to the driving of the fixing unit 30 is not related to the control after S204, there is no problem even if stopped asynchronously.

  Next, warm-up control when receiving a print job will be described with reference to FIG. When the warm-up is started (S220), the “FPOT extension mode bit” for determining the necessity of FPOT extension is checked (S221). If the flag “1” is not set, the predetermined fixing power Pf is used as it is. (S222), and the process proceeds to the subsequent printing sequence. The mode via S222 also corresponds to the first mode.

  On the other hand, when the FPOT extension mode bit is set, the power Pf_pre is supplied to the heater 100 without starting each driving load. During this time, since only the fixing motor is driven, all the remaining electric power can be supplied to the heater 100. As the time for supplying the power Pf_pre, the time t7 calculated from the integrated power during the initial warm-up described above is used.

  First, t7 is calculated (S223), the power Pf_pre is supplied, and the fixing motor is started (S224). After the time t7 has elapsed since the start of supplying the power Pf_pre (S225), the fixing power is reduced to Pf_down used during initial warm-up (S226), and the process proceeds to the subsequent printing sequence. As a print sequence, a series of flow from image writing permission to printing end after starting each load (S227) is the same as that described in FIG. The mode via S224 corresponds to the third mode.

  As described above, according to the present embodiment, when the power supply of the image forming apparatus main body is turned on or when the door is closed, the necessity for FPOT extension is determined in advance. Can select FPOT extension mode 2 (third mode) from the first printing after the power is turned on. Therefore, the FPOT extension time can be kept short.

  In the first and second embodiments described above, the film heating type fixing unit shown in FIG. 2 has been described. However, the present invention is not limited to an image forming apparatus equipped with this type of fixing unit. For example, the present invention can be applied to an image forming apparatus equipped with a fixing unit of another type, such as a fixing unit of a type in which a halogen heater that generates heat when electric power is supplied is arranged inside a cylindrical film cylinder. is there.

30 Fixing Unit 32 CPU
54 Temperature detection element 64 Low voltage power supply 67, 69 Current detection circuit 70 Triac drive circuit 100 Heater 111 Heating element

Claims (9)

An image forming unit for forming an unfixed image on a recording material;
A fixing section for heating and fixing an unfixed image formed on the recording material to the recording material;
A current detection unit that detects an input current of power supplied from a commercial power supply;
In an image forming apparatus having
A first mode in which the first power is continuously supplied to the fixing unit during a warm-up period from the start of supplying power to the fixing unit until the temperature of the fixing unit reaches a fixable temperature;
A second mode of supplying a second power smaller than the first power after the first power is supplied to the fixing unit during the warm-up period;
During the warm-up period, after supplying a third power larger than the second power to the fixing unit, the driving load of the image forming unit is activated and the fixing unit is smaller than the third power. A third mode for supplying fourth power;
Is possible and
When a warm-up instruction is input, the fixing unit is warmed up by selecting one of the first to third modes according to the warm-up extension history and the detected current value of the current detection unit. An image forming apparatus.   The first mode is selected when the detected current value is smaller than a predetermined upper limit current value, and the second mode is selected when the detected current value is larger than the upper limit current value. Item 2. The image forming apparatus according to Item 1.   The image forming apparatus according to claim 2, wherein when there is the warm-up extension history, the third mode is selected.   The image forming apparatus according to claim 2, wherein the second power is power calculated so that the detected current value is equal to or less than the upper limit current value.   The image forming apparatus according to claim 1, wherein the fourth power is equal to the second power.   Activating the driving load of the image forming unit in the third mode according to the temperature increase rate of the fixing unit when the second power is supplied to the fixing unit in the second mode. The image forming apparatus according to claim 1, wherein:   6. The driving load of the image forming unit in the third mode is activated in accordance with an integrated power amount supplied to the fixing unit in the second mode. The image forming apparatus described.   The said fixing | fixed part has a cylindrical film and the heater which is arrange | positioned inside the cylinder of the said film, and is supplied with electric power and generate | occur | produces heat | fever. Image forming apparatus.   The image forming apparatus according to claim 8, wherein the heater is in contact with an inner surface of the film.

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