Image forming device

Abstract

To provide a technique that can reduce terminal noise generated in a terminal that connects a heater and an AC power supply supplying AC voltage to each other.SOLUTION: In standby control of maintaining the temperature of a fuser 8 at a target standby temperature TR based on a detected temperature T detected by a temperature sensor ST, with the plurality of continuous half waves of an AC voltage V as a control cycle, a CPU 104A executes wave number control of turning on a triac 106 for some half waves within the control cycle and turning off the triac 106 for the rest of the half waves. When the time elapsed from the execution of the wave number control is less than four seconds, and the detected temperature T is less than the target standby temperature TR, the CPU executes the wave number control the number of times of heating m, and when the time elapsed from the execution of the wave number control is four seconds or more, and the detected temperature T is equal to or more than the target standby temperature TR, the CPU executes the wave number control twice.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present application relates to an image forming apparatus equipped with a fixing device that fixes a developer image onto a sheet. [Background technology]

[0002] Patent Document 1 describes an image forming apparatus that executes standby control in which, in a standby state of the fixing unit, when the detected temperature of the fixing unit is below a first temperature, power is supplied to the heater, and when the detected temperature of the fixing unit exceeds a second temperature higher than the first temperature, power is stopped from being supplied to the heater. More specifically, in the standby control of this image forming apparatus, a peak temperature, which is the maximum value of the detected temperature after power is stopped from being supplied to the heater, is detected, and if the detected peak temperature is higher than a target peak temperature, the next second temperature is set lower than the current second temperature, and if the detected peak temperature is lower than the target peak temperature, the next second temperature is set higher than the current second temperature. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-20988 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional image forming apparatuses, during standby control to maintain the temperature of the fixing unit at a target standby temperature, if the temperature falls below the target standby temperature, current is passed through the heater by performing wave number control, which switches a switching element between the on and off states. The temperature of the fixing unit and the resistance value of the heater decrease at different rates, and the resistance value of the heater tends to decrease more rapidly than the temperature of the fixing unit. Therefore, if the image forming apparatus waits a long time between performing wave number control and performing wave number control again, current suddenly flows through the heater when the resistance value of the heater has sufficiently decreased, causing terminal noise in the terminal connecting the AC power supply that supplies AC voltage to the heater.

[0005] An object of the present application is to provide a technique that can reduce terminal noise generated at a terminal that connects an AC power supply that supplies AC voltage to a heater. [Means for solving the problem]

[0006] In order to achieve the above object, the image forming apparatus of the present application includes a developer image forming unit that forms a developer image on a sheet, a fixing unit that is connected to an AC power source that supplies AC voltage via terminals and has a heater that is heated by the AC voltage and that fixes the developer image on the sheet, a temperature sensor that detects the temperature of the fixing unit, a switching element that is provided between the AC power source and the heater and that switches between an ON state in which the AC power source and the heater are electrically connected and an OFF state in which the AC power source and the heater are not electrically connected, and a control unit, and the control unit controls the temperature of the fixing unit based on the detected temperature detected by the temperature sensor. In standby control for maintaining the temperature at a target standby temperature, a control cycle is defined as a plurality of consecutive half waves of an AC voltage, and wave number control is performed in which the state of the switching element is on for some half waves within the control cycle and the state of the switching element is off for the remaining half waves, and if the elapsed time since the wave number control was performed is less than a first predetermined time and the detected temperature is below the target standby temperature, the wave number control is performed a first predetermined number of times, and if the elapsed time since the wave number control was performed is the first predetermined time or more and the detected temperature is above the target standby temperature, the wave number control is performed a second predetermined number of times.

[0007] As a result, when the elapsed time since the wave number control was executed is equal to or longer than the first predetermined time and the detected temperature is equal to or higher than the target standby temperature, the wave number control is executed before the resistance value of the heater has dropped sufficiently, and therefore current flows through the heater before the resistance value of the heater has dropped sufficiently, thereby preventing terminal noise caused by a sudden current flowing through the heater.

[0008] In addition, when the elapsed time since the wave number control was performed is equal to or greater than a first predetermined time and the detected temperature is equal to or greater than the target standby temperature, the control unit may perform the wave number control a second predetermined number of times, and then, when the detected temperature falls below the target standby temperature, reduce the first predetermined number of times and perform the wave number control.

[0009] As a result, when the detected temperature is equal to or higher than the target standby temperature, executing wave number control the second predetermined number of times means that current is passed through the heater at a temperature equal to or higher than the target standby temperature. Therefore, when the image forming device executes wave number control when the detected temperature falls below the target standby temperature, it is possible to prevent the detected temperature from rising too high by reducing the first predetermined number of times and executing wave number control.

[0010] In addition, the control unit may increase the first predetermined number of times and perform wave number control when the elapsed time since performing wave number control is less than a second predetermined time that is shorter than the first predetermined time and the detected temperature is less than the target standby temperature.

[0011] As a result, if the elapsed time since the wave number control was performed is less than a second predetermined time that is shorter than the first predetermined time, it becomes difficult to maintain the target standby temperature. Therefore, the image forming device can make it easier to maintain the temperature of the fixing unit at the target standby temperature by increasing the first predetermined number of times and performing wave number control.

[0012] In addition, the control unit may perform wave number control without changing the first predetermined number of times when the elapsed time since the wave number control was performed is equal to or greater than the second predetermined time and less than the first predetermined time, and the detected temperature is less than the target standby temperature.

[0013] Furthermore, the control unit may start standby control and, before executing the first wave number control, execute phase control in which the state of the switching element is set to the on state for some waveforms within a half wave of the AC voltage, and the state of the switching element is set to the off state for the remaining waveforms.

[0014] As a result, when standby control is started, flicker can be prevented by executing phase control before executing the first wave number control. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a side cross-sectional view of a main part of a laser printer according to an embodiment of the present application. [Figure 2] FIG. 2 is a perspective view showing the arrangement of sensors on a nip plate. [Figure 3] FIG. 2 is a circuit diagram showing a schematic configuration of a heater control device. [Figure 4] 4 is a time chart of signals related to power supply control. [Figure 5] 10A and 10B are diagrams showing examples of voltage waveforms when a preheating period for phase control is not provided (FIG. 10A) and when a preheating period for phase control is provided (FIG. 10B). [Figure 6] 4 is a flowchart showing the procedure of a control process executed by the control device of FIG. 3, particularly by a CPU. [Figure 7] 7 is a flowchart showing a detailed procedure of a standby process included in the control process of FIG. 6. [Figure 8] 7 is a flowchart showing detailed procedures of a first number setting process ((a)) and a second number setting process ((b)) included in the control process of FIG. 6. [Figure 9] 3 is a diagram showing an example of a transition of the temperature detected by the temperature sensor of FIG. 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] The following describes in detail an embodiment of the present application with reference to the drawings. Figure 1 shows a cross-sectional side view of the main part of a laser printer 1 according to one embodiment of the present application. The laser printer 1 includes a main body housing 2, a supply unit 3, a process unit PR, and a fixing unit 8.

[0017] The supply unit 3 is a mechanism for supplying sheets S to the process unit PR and is located at the bottom of the main body housing 2. The supply unit 3 includes a supply tray 31 that stores sheets S, a sheet pressure plate 32, and a supply mechanism 33. The supply mechanism 33 includes a pickup roller 33A, a separation roller 33B, a first conveyor roller 33C, and a registration roller 33D. In the supply unit 3, the sheets S in the supply tray 31 are pulled toward the pickup roller 33A by the sheet pressure plate 32 and sent to the separation roller 33B by the pickup roller 33A. The sheets S are separated into single sheets by the separation roller 33B and conveyed by the first conveyor roller 33C. The registration roller 33D aligns the leading edge of the sheets S and then conveys the sheets S toward the process unit PR. Herein, the direction in which the sheets S are conveyed is referred to as the conveyance direction, and the direction perpendicular to the conveyance direction within the plane of the sheets S is referred to as the width direction. Hereinafter, the width direction of the sheets S will be simply referred to as the "width direction."

[0018] The process unit PR has a function of forming a toner image on the sheet S supplied from the supply unit 3. The process unit PR is a toner image forming unit. The process unit PR includes an exposure device 4 and a process cartridge 5.

[0019] The exposure device 4 is disposed in the upper part of the main body housing 2, and includes a laser light source (not shown), a polygon mirror (shown without reference numerals), a lens, a reflecting mirror, etc. In the exposure device 4, a laser beam based on image data is emitted from the laser light source, and is scanned across the surface of the photosensitive drum 61, thereby exposing the surface of the photosensitive drum 61.

[0020] The process cartridge 5 is disposed below the exposure device 4, and is detachable from the main body housing 2 through an opening formed when a front cover 21 provided on the main body housing 2 is opened. The process cartridge 5 includes a drum unit 6 and a developing unit 7.

[0021] The drum unit 6 includes a photosensitive drum 61, a charger 62, and a transfer roller 63. The development unit 7 is detachable from the drum unit 6, and includes a development roller 71, a supply roller 72, a layer thickness regulating blade 73, a toner storage section 74 that stores dry toner, and an agitator 75.

[0022] In the process cartridge 5, the surface of the photosensitive drum 61 is uniformly charged by the charger 62 and then exposed to laser light from the exposure device 4, thereby forming an electrostatic latent image based on image data on the photosensitive drum 61. The toner in the toner storage section 74 is supplied to the developing roller 71 via the supply roller 72 while being agitated by the agitator 75, and as the developing roller 71 rotates, the toner enters between the developing roller 71 and the layer thickness regulating blade 73 and is carried on the developing roller 71 as a thin layer of a uniform thickness.

[0023] The toner carried on the developing roller 71 is supplied from the developing roller 71 to the electrostatic latent image formed on the photosensitive drum 61. This makes the electrostatic latent image visible, and a toner image is formed on the photosensitive drum 61. Thereafter, the sheet S supplied from the supply unit 3 is transported between the photosensitive drum 61 and the transfer roller 63, and the toner image formed on the photosensitive drum 61 is transferred onto the sheet S.

[0024] The fixing device 8 fixes the toner image on the sheet S. The fixing device 8 includes a heater H1 and a heater H1 The heating member 81 is heated by a heater H1, and includes a heating member 81 including a rotating member 81A that can rotate around the heater H1, and a pressure member 82 that sandwiches the sheet S between the heating member 81 and the heating member 81. The heater H1 is a resistance heating type heater, and in this embodiment, it is a halogen heater, for example.

[0025] The rotating member 81A is a rotatable endless belt. The rotating member 81A has a base material made of metal, resin, or the like, and a release layer covering the outer surface of the base material. Inside the heating member 81, a heater H1 that heats the heating member 81 and a nip plate NP are provided.

[0026] The heater H1 is a halogen lamp that emits light and generates heat when energized, and heats the rotating member 81A by radiant heat. The heater H1 is disposed inside the rotating member 81A along the width direction.

[0027] The pressure member 82 is a rotatable pressure roller, and has an elastic layer made of elastically deformable rubber or the like on its surface.

[0028] The nip plate NP is a plate-shaped member that receives radiant heat from the heater H1, and is disposed inside the heating member 81 so that the inner peripheral surface of the heating member 81 is in sliding contact with the lower surface of the nip plate NP. The nip plate NP sandwiches the heating member 81 between itself and the pressure member 82. In the fixing device 8, the sheet S onto which the toner image has been transferred is conveyed between the heating member 81 and the pressure member 82, whereby the toner image is thermally fixed onto the sheet S. The sheet S onto which the toner image has been thermally fixed is discharged onto the discharge tray 22 by the second conveyor roller 23 and the discharge roller 24.

[0029] As shown in FIG. 2, the nip plate NP has a central detection portion 131 that protrudes from an end portion in the conveyance direction of the sheet S, and an edge detection portion 132. The central detection portion 131 is located in the center in the width direction. The edge detection portion 132 is located at an end portion in the width direction. A central temperature sensor ST1 is arranged opposite the central detection portion 131. An edge temperature sensor ST2 is arranged opposite the edge detection portion 132. The central temperature sensor ST1 is an example of a temperature sensor that detects the temperature of the fixing unit 8.

[0030] The central temperature sensor ST1 is a sensor that detects the temperature in the width direction at the center of the heating member 81. The central temperature sensor ST1 is capable of detecting the temperature of the central portion of the heating member 81 by detecting the temperature of the nip plate NP through contact or non-contact with the central detection portion 131 of the nip plate NP.

[0031] The edge temperature sensor ST2 is a sensor that detects the temperature of the edge of the heating member 81 in the width direction. The edge temperature sensor ST2 is capable of detecting the temperature of the edge of the heating member 81 by detecting the temperature of the nip plate NP through contact or non-contact with the edge detection unit 132 of the nip plate NP. More specifically, in the width direction, the edge temperature sensor ST2 is located outside the maximum area SW of the sheet S that can be fixed by the fixing unit 8. The edge temperature sensor ST2 may be located within the range of the area SW in the width direction.

[0032] The central temperature sensor ST1 and the end temperature sensor ST2 may be, for example, a thermistor.

[0033] 3 shows a schematic configuration of the heater control device 100. The heater control device 100 is composed of the heater H1, a power supply board 100A, a main board 100B, etc. The power supply board 100A is provided with a pair of terminals Te, and each terminal Te is connected to a power line PL, which is then connected to a commercial power source (not shown) via a power plug 200. When the power supply board 100A is connected to the commercial power source, an AC voltage V of, for example, 100V is applied to the pair of terminals Te. is supplied.

[0034] The power supply board 100A is mounted with a line filter 101, an AC / DC converter 102, a zero-cross detection circuit 105, a triac 106, a changeover switch 107, etc. As shown in Fig. 3, the AC / DC converter 102 is connected to the power supply line PL via a connection line L2 that is separate from the connection line L1 to which the changeover switch 107 is connected.

[0035] A DC / DC converter 103, a control device 104, and the like are mounted on the main board 100B.

[0036] Heater H1 generates heat in response to the application of AC voltage V. Temperature sensor ST may be either the central temperature sensor ST1 or the edge temperature sensor ST2 provided near heater H1, and is therefore designated by the symbol "ST." Temperature sensor ST outputs the temperature of fuser 8 as a detected temperature T to control device 104. AC / DC converter 102 converts, for example, 100V AC voltage into 24V DC voltage. DC / DC converter 103 converts the 24V DC voltage from AC / DC converter 102 into 3.3V DC voltage and supplies the DC voltage to various components including control device 104.

[0037] 3, the zero-cross detection circuit 105 outputs the zero-cross pulse signal Sr to the control device 104. The control device 104 determines the voltage level of the zero-cross pulse signal Sr, thereby being able to detect the rising and falling edges of the zero-cross pulse signal Sr.

[0038] The control device 104 also has a CPU 104A and a memory 104B. The memory 104B includes, for example, a RAM, a ROM, a flash memory, etc., and stores information related to control and processing. The memory 104B also stores a control program for executing the control processing (see FIGS. 6 to 8) described below. The CPU 104A performs various controls of the laser printer 1 by executing the control program stored in the memory 104B.

[0039] The control device 104 adjusts the time during which the input voltage V is supplied to the heater H1 based on the zero-cross pulse signal Sr. More specifically, the control device 104 generates a trigger pulse signal Sb based on, for example, the falling edge of the zero-cross pulse signal Sr (see FIG. 4), and outputs the trigger pulse signal Sb to the triac 106. The triac 106 is connected between the power supply line PL and the heater H1. The triac 106 turns on in response to the trigger pulse signal Sb output from the control device 104, and turns off when a reverse voltage is applied or the current is reduced to zero. In accordance with this operation, the triac 106 controls the time during which the input voltage V is supplied to the heater H1. This time is, for example, from the rising edge of the trigger pulse signal Sb to the zero-cross point of the input voltage V, as shown in the waveform of the heater voltage Vh in FIG. 4. The control device 104 can perform temperature control of the fixing device 8 by the heater H1, for example, by changing the period Tw2, which is the period from the falling edge of the zero-cross pulse signal Sr to the rising edge of the trigger pulse signal Sb.

[0040] For example, the control device 104 can set the period Tw2 to zero to continuously apply the heater voltage Vh to the heater H1 (to make the energization ratio 100%). Alternatively, the control device 104 can perform phase control or wave number control on the sine wave heater voltage Vh to intermittently apply the heater voltage Vh to the heater H1. The phase control here refers to, for example, control in which the supply of power to the heater H1 in a half cycle of the input voltage V is started at a timing that is a predetermined time after the zero-cross timing ZC at the start of the half cycle and that corresponds to the phase angle of the input voltage V, and continues until the zero-cross timing ZC at the end of the half cycle. In phase control, the energization time of the heater H1 is controlled not by the wave number but by the conduction phase angle (also known as the firing angle) α. The conduction phase angle α is the phase at which the triac 106 starts conducting. Wave number control is a control that changes the power supply to the heater H1 in a half cycle of the input voltage V by increasing or decreasing the number of half cycles (wave number) performed from the zero-cross timing ZC at the start of the half cycle to the zero-cross timing ZC at the end of the half cycle. Therefore, the control device 104 may perform intermittent application (application with a power supply ratio of less than 100%) based on the zero-cross pulse signal Sr. As a result, the heater H1 is applied with the heater voltage Vh at a specific phase or wave number.

[0041] 3 has an input terminal connected to the power supply line PL and an output terminal connected to the heater H1 and the zero-cross detection circuit 105. The control device 104 can switch the connection between the input voltage V and the heater H1 and the zero-cross detection circuit 105 by switching the switch 107 on and off. The switch 107 is, for example, a semiconductor switch such as a transistor or a mechanical switch such as a relay.

[0042] As described above, the control device 104 can control the energization of the heater H1 during the heating period by wave number control at a set duty ratio. In this embodiment, the output of the heater H1 is not changed, so the duty ratio is constant. The control device 104 changes the amount of energization by changing the number of energizations of a predetermined energization pattern of wave number control, assuming that the number of energizations of the predetermined energization pattern is one. That is, the control device 104 changes the heating period by changing the number of energizations of the energization pattern. For example, as shown in FIG. 5(a), the control device 104 energizes the heater H1 only during the first half-wave of three consecutive half-waves of the AC voltage, thereby achieving a duty ratio of 33%. The heating period is changed by changing the number of repetitions of this energization pattern. Note that in FIG. 5, hatched areas indicate energization, and non-hatched areas indicate no energization. In this embodiment, the minimum number of repetitions is 1 (this number of repetitions is referred to as the "heating count"). After performing wave number control of the number of heating cycles, the control device 104 maintains the OFF control of the selector switch 107. In Fig. 5, the heating period indicates the period during which wave number control is performed, and the non-heating period indicates the period during which the control device 104 maintains the OFF control of the selector switch 107. In the example of Fig. 5, waveform control is performed with the number of heating cycles=2 during the heating period.

[0043] In this embodiment, when starting standby control, as shown in FIG. 5(b), the control device 104 performs phase control to energize the heater H1 during the preheating period and wave number control to energize the heater H1 during the heating period. The phase angle of the phase control is set to be greater than half (90°) of the half-wave of the AC voltage so that the maximum voltage is smaller than when the preheating period is not provided. In the example of FIG. 5(b), half-wave phase control is repeated six times during the preheating period. The preheating period is provided when starting standby control in this way to prevent flicker from occurring when starting standby control.

[0044] The control process executed by the laser printer 1 configured as above will be described in detail with reference to Figs. 6 to 9. Fig. 6 shows the procedure of the control process executed by the control device 104, particularly the CPU 104A. The control process is started, for example, when the laser printer 1 is powered on. Hereinafter, in the description of each process procedure, steps will be represented as "S."

[0045] 6, first, CPU 104A executes preparation processing (S10). The preparation processing may include, for example, initialization of memory 104B and various ports, reading and setting of various default values ​​stored in memory 104B, etc.

[0046] Next, CPU 104A executes standby processing (S12). Details of standby processing will be described later with reference to FIGS. 7 to 9. When standby processing ends, if there is a print command (S14: YES), CPU 104A executes print control according to the print command (S16) and then returns to standby processing. On the other hand, if there is no print command (S14: NO), CPU 104A continues executing standby processing until a predetermined time has elapsed (S18: NO), and once the predetermined time has elapsed (S18: YES), executes sleep control (S20). In other words, the predetermined time is the time for which standby processing continues before entering sleep control.

[0047] Then, CPU 104A continues to execute sleep control until the sleep mode is released (S22: NO), and when the sleep mode is released (S22: YES), returns the processing to standby processing.

[0048] Fig. 7 shows the detailed procedure of the standby process. In Fig. 7, first, CPU 104A sets the number of heating times m to 2 times (S30). The number of heating times m varies depending on the first and second number setting processes described later with reference to Fig. 8. That is, in the process of S30, the number of heating times m is set to an initial value.

[0049] Next, the CPU 104A waits while the detected temperature T by the temperature sensor ST is equal to or greater than the target standby temperature TR (S32: NO), and when the detected temperature T is less than the target standby temperature TR (S32: YES), the process proceeds to the next step S34. Here, a specific temperature of the target standby temperature TR is, for example, 122°C, but is not limited to this.

[0050] In S34, the CPU 104A executes energization control for the heater H1 during the preheating period and the heating period, as described above with reference to FIG. 5(b). Specifically, the CPU 104A repeats half-wave phase control six times during the preheating period, and repeats wave number control with a duty ratio of 33% twice during the heating period, while maintaining the OFF control of the selector switch 107. Then, the CPU 104A starts counting time on the timer t (S36). If the control device 104 has a timer function, that function may be used as the timer t. If the control device 104 does not have a timer function, a software timer may be configured in the memory 104B and used.

[0051] Next, CPU 104A determines whether a trigger for terminating the standby process has occurred (S38), and if a trigger for terminating the standby process has occurred (S38: YES), the standby process is terminated. Here, the trigger for terminating the standby process is, for example, the receipt of the print command.

[0052] On the other hand, if no trigger for terminating the standby process has occurred (S38: NO), CPU 104A makes the same determination as in S32 above, that is, determines whether or not the relationship "detected temperature T<target standby temperature TR" is true (S40). If detected temperature T≧target standby temperature TR (S40: NO), CPU 104A determines whether or not the time counted by timer t≧4 seconds (S50). If the time counted by timer t<4 seconds (S50: NO), CPU 104A returns the process to S38 above. On the other hand, if the time counted by timer t≧4 seconds (S50: YES), CPU 104A repeats wave number control with a duty ratio of 33% for heater H1 twice, and maintains the off control of selector switch 107 (S52).

[0053] FIG. 9(a) shows an example of the transition of the detected temperature T when the process of S52 is executed. In FIG. 9(a), time t11 is the time after the CPU 104A has executed the wave number control m times at a duty ratio of 33% (S44 in FIG. 7, which will be described later). For example, this is the case when m is increased to m=6 by the second number setting process, which will be described later with reference to FIG. 8(b). At time t11, the CPU 104A executes the wave number control m=6 times, and then maintains the OFF control of the selector switch 107. Then, the detected temperature T gradually rises, and the selector switch 107 Since the OFF control of the wave number control is maintained, the wave number control value decreases. At time t12, 4 seconds (s) have passed since time t11, which corresponds to the case where the determination in S50 is YES. At time t12, CPU 104A has performed wave number control N (= 2) times.

[0054] In S52, even if the detected temperature T is equal to or greater than the target standby temperature TR, the heater H1 is energized because the temperature of the fixing unit 8, i.e., the detected temperature T detected by the temperature sensor ST, and the resistance value of the heater decrease at different rates, and the resistance value of the heater tends to decrease more rapidly than the temperature of the fixing unit 8. Furthermore, when the resistance value of the heater H1 has not yet decreased completely, that is, when 4 seconds (s) or more have elapsed since time t11, the CPU 104A executes wave number control a fixed number N (=2) of times and maintains the OFF control of the selector switch 107. As a result, a current flows through the heater H1 once while the resistance value of the heater H1 has not yet decreased completely, thereby preventing terminal noise from occurring at the terminal Te that connects the heater H1 to the AC power supply that supplies the AC voltage V.

[0055] Returning to FIG. 7, next, CPU 104A executes a first number-of-times setting process (S54). FIG. 8(a) shows detailed steps of the first number-of-times setting process. In FIG. 8(a), first, CPU 104A reduces heating number m by two (S60). Next, CPU 104A determines whether heating number m≦0 after the reduction of two (S62). If heating number m≦0 (S62: YES), CPU 104A sets heating number m to 1 (S64) and then terminates the first number-of-times setting process. On the other hand, if heating number m>0 (S62: NO), CPU 104A terminates the first number-of-times setting process. The reason for executing the first number-of-times setting process to reduce heating number m in this manner is to prevent the detected temperature T from rising more than necessary, since the detected temperature T is at or above the target standby temperature TR when the predetermined time of 4 seconds has elapsed and power supply control to heater H1 is being performed.

[0056] 7, next, CPU 104A resets timer t and starts timing (S46), and then CPU 104A returns the process to S38.

[0057] On the other hand, if the detected temperature T<the target standby temperature TR in the determination of S40 (S40: YES), the CPU 104A executes a second count setting process (S42). Then, the CPU 104A repeats wave number control with a duty ratio of 33% for the heater H1 m times, and maintains the OFF control of the selector switch 107 (S44). Thereafter, the CPU 104A proceeds to the process of S46.

[0058] Fig. 8(b) shows the detailed procedure of the second number of times setting process. In Fig. 8(b), first, CPU 104A determines whether the time counted by timer t is less than 2 seconds (S70). If this determination is true that the time counted by timer t is less than 2 seconds (S70: YES), CPU 104A increments the number of heating times m by one (S72) and then terminates the second number of times setting process. On the other hand, if the time counted by timer t is greater than or equal to 2 seconds (S70: NO), CPU 104A terminates the second number of times setting process.

[0059] FIG. 9(b) shows an example of the transition of the detected temperature T when the process of S72 is executed. In FIG. 9(b), time t21 is, for example, the time after the CPU 104A has executed wave number control m times at a duty ratio of 33% (S44). For example, this is the case when m=2 shortly after the standby process has started. At time t21, the CPU 104A executes wave number control m=2 times, and then maintains the OFF control of the selector switch 107. Then, the detected temperature T gradually rises, and then, because the OFF control of the selector switch 107 is maintained, it gradually falls. Time t22 indicates the time when the detected temperature T<the target standby temperature TR, and is the time when less than 2 seconds (s) have elapsed since the time t21 (S44) of the previous power supply control. After the CPU 104A executes wave number control m times at time t21, the detected temperature T<the target standby temperature TR at time t22. Since the time until the target standby temperature TR is reached is short, the CPU 104A frequently executes wave number control. Therefore, if less than 2 seconds (s) have elapsed since the time t21 (S44) of the previous power supply control, the CPU 104A increases the number of heating cycles (S72).

[0060] In the transition of the detected temperature T in Figure 9(a), time t13 indicates the time when the detected temperature T is less than the target standby temperature TR. At time t13, less than 2 seconds (s) have passed since time t12 (S52) of the previous power supply control, so the number of heating times m is increased. At this time, the number of heating times m is decreased by two times at time t12 (first number of times setting process: S60) and increased by one time at time t13 (second number of times setting process: S72), so it is decreased by one time compared to the number of heating times m at time t11.

[0061] FIG. 9(c) shows an example of the transition of the detected temperature T when the process of S72 is skipped. In FIG. 9(c), time t31 is the time after the CPU 104A has executed wave number control m times with a duty ratio of 33% (S44), for example. Then, the detected temperature T gradually rises, and then, because the selector switch 107 is maintained in the OFF state, it falls. Time t32 indicates the time when the detected temperature T is lower than the target standby temperature TR. At time t32, more than two seconds have passed since the time t31 of the previous power supply control, so the number of heating cycles m is maintained as is. In this way, if the detected temperature T falls below the target standby temperature TR when more than two seconds have passed since the time of the previous power supply control, it is determined that the target standby temperature TR can be maintained with the current number of heating cycles of the heater H1.

[0062] As described above, the laser printer 1 of this embodiment includes the process cartridge 5 that forms a developer image on the sheet S, the fixation device 8 that is connected to an AC power supply that supplies an AC voltage V via the terminal Te and has a heater H1 that is heated by the AC voltage V and that fixes the developer image on the sheet S, a temperature sensor ST that detects the temperature of the fixation device 8, a triac 106 that is provided between the AC power supply and the heater H1 and that switches between an ON state in which the AC power supply and the heater H1 are electrically connected and an OFF state in which the AC power supply and the heater H1 are not electrically connected, and a CPU 104A.

[0063] In standby control for maintaining the temperature of the fixing unit 8 at the target standby temperature TR based on the detected temperature T detected by the temperature sensor ST, the CPU 104A performs wave number control in which a control period is a plurality of consecutive half waves of the AC voltage V, and the triac 106 is turned on for some half waves within the control period and turned off for the remaining half waves.If the time that has elapsed since the wave number control was performed is less than 4 seconds and the detected temperature T is less than the target standby temperature TR, the wave number control is performed m times for heating, and if the time that has elapsed since the wave number control was performed is 4 seconds or more and the detected temperature T is equal to or greater than the target standby temperature TR, the wave number control is performed twice.

[0064] Thus, in the laser printer 1 of this embodiment, if the elapsed time since wave number control was executed is 4 seconds or more and the detected temperature T is equal to or higher than the target standby temperature TR, wave number control is executed before the resistance value of the heater H1 has dropped sufficiently, and therefore current flows through the heater H1 before the resistance value of the heater H1 has dropped sufficiently, thereby preventing terminal noise caused by a sudden current flowing through the heater H1.

[0065] Incidentally, in this embodiment, the laser printer 1 is an example of an "image forming device." The process unit PR is an example of a "developer image forming unit." The triac 106 is an example of a "switching element." The CPU 104A is an example of a "control unit." The number of heating times m is an example of a "first predetermined number of times." Two times is an example of a "second predetermined number of times." Four seconds (s) is an example of a "first predetermined time." Note that the first predetermined number of times and the second predetermined number of times may be the same or different.

[0066] Furthermore, if the elapsed time since the wave number control was executed is 4 seconds or more and the detected temperature T is equal to or higher than the target standby temperature TR, the CPU 104A executes the wave number control twice, and then, when the detected temperature T becomes lower than the target standby temperature TR, reduces the number of heating cycles m and executes the wave number control.

[0067] As a result, when the detected temperature T is equal to or higher than the target standby temperature TR, executing wave number control twice means that current is passed through the heater H1 at a temperature equal to or higher than the target standby temperature TR. Therefore, when the laser printer 1 executes wave number control when the detected temperature T falls below the target standby temperature TR, the number of heating cycles m is reduced and wave number control is executed, thereby preventing the detected temperature T from rising too high.

[0068] Furthermore, when the elapsed time since the wave number control was performed is less than 2 seconds, which is shorter than 4 seconds, and the detected temperature T is lower than the target standby temperature TR, the CPU 104A increases the number of heating cycles m and performs the wave number control. Incidentally, 2 seconds is an example of the "second predetermined time."

[0069] As a result, if the elapsed time since wave number control was performed is less than 2 seconds, which is shorter than 4 seconds, it becomes difficult to maintain the target standby temperature TR. Therefore, the laser printer 1 increases the number of heating cycles m and performs wave number control, thereby making it easier to maintain the temperature of the fixing unit 8 at the target standby temperature TR.

[0070] Furthermore, if the time elapsed since the wave number control was performed is 2 seconds or more and less than 4 seconds, and the detected temperature T is lower than the target standby temperature TR, CPU 104A performs the wave number control without changing the number of heating times m.

[0071] Furthermore, before starting standby control and executing the first wave number control, CPU 104A executes phase control to turn on the triac 106 for some waveforms within a half wave of the AC voltage and turn off the triac 106 for the remaining waveforms.

[0072] As a result, when standby control is started, flicker can be prevented by executing phase control before executing the first wave number control.

[0073] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0074] (1) In the above embodiment, the heater H1 is energized with an AC voltage V, but it may be energized with a DC voltage. When energizing with a DC voltage, the amount of energization may be changed by duty control, or the amount of energization may be changed by changing the voltage.

[0075] (2) The number of heating cycles m, the six half-waves used in phase control, the duty ratio used in wave number control, and the four seconds or two seconds compared with the time count of the timer t are merely examples, and other values ​​may be used.

[0076] (3) In the above embodiment, the temperature sensor is provided to detect the temperature of the heating member, but this is not limited thereto. For example, the temperature sensor may be provided to detect the temperature of a portion other than the heating portion of the fixing unit, such as a pressure member. The temperature sensor may also be a temperature sensor other than a thermistor. The temperature sensor may also be a non-contact type temperature sensor or a contact type temperature sensor.

[0077] (4) In the above embodiment, the heater H1 is a halogen heater that uses radiant heat. However, the heater is not limited to this. For example, a ceramic heater or a carbon heater that uses heat generated by a resistor may be used. The heater may be disposed outside the heating member, rather than inside the heating member.

[0078] (5) In the above embodiment, an image forming apparatus that forms a monochrome image on a sheet is exemplified as the image forming apparatus, but the image forming apparatus is not limited to this and may be, for example, a printer configured to be able to form a color image on a sheet.Furthermore, the image forming apparatus is not limited to a printer and may be, for example, a copier or multifunction peripheral equipped with a document reading device such as a flatbed scanner. [Explanation of symbols]

[0079] 1...laser printer, 8...fixing unit, 104...controller, 104A...CPU, 104B...memory, 105...zero-cross detection circuit, 106...triac, 107...selector switch, H1...heater, PR...processing unit, ST...temperature sensor.

Claims

1. a developer image forming unit that forms a developer image on a sheet; a fixing device that is connected to an AC power source that supplies an AC voltage via terminals and has a heater that is heated by the AC voltage, and that fixes the developer image on the sheet; a temperature sensor for detecting the temperature of the fixing unit; a switching element that is provided between the AC power supply and the heater and that switches between an ON state in which the AC power supply and the heater are electrically connected and an OFF state in which the AC power supply and the heater are not electrically connected; A control unit; Equipped with The control unit a standby control for maintaining the temperature of the fixing unit at a target standby temperature based on the detected temperature detected by the temperature sensor, a control cycle is defined as a plurality of successive half waves of the AC voltage, and wave number control is performed in which the state of the switching element is set to the on state for some half waves within the control cycle and the state of the switching element is set to the off state for the remaining half waves; When the elapsed time since the wave number control was performed is less than a first predetermined time and the detected temperature is less than the target standby temperature, the wave number control is performed a first predetermined number of times; When the elapsed time since the wave number control was performed is equal to or longer than the first predetermined time and the detected temperature is equal to or higher than the target standby temperature, the wave number control is performed a second predetermined number of times. An image forming apparatus characterized by:

2. When the elapsed time since the wave number control was performed is equal to or longer than the first predetermined time and the detected temperature is equal to or higher than the target standby temperature, the control unit performs the wave number control the second predetermined number of times, and then, when the detected temperature becomes lower than the target standby temperature, reduces the first predetermined number of times and performs the wave number control.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. When the elapsed time since the wave number control was performed is less than a second predetermined time that is shorter than the first predetermined time, and the detected temperature is less than the target standby temperature, the control unit increases the first predetermined number of times and performs the wave number control.

3. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. When the elapsed time since the wave number control was performed is equal to or longer than the second predetermined time and shorter than the first predetermined time, and the detected temperature is lower than the target standby temperature, the control unit performs the wave number control without changing the first predetermined number of times.

4. The image forming apparatus according to claim 3, wherein the image forming apparatus is a recording medium.

5. the control unit starts the standby control, and before executing the first wave number control, executes phase control to set the state of the switching element to the on state for a part of waveforms within the half wave of the AC voltage, and to set the state of the switching element to the off state for the remaining waveforms.

5. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

Images