JP7135549B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus having a fixing device for fixing a developer image on a sheet.

Conventionally, there is known a technique of energizing the heater when the temperature of the fixing device falls below the lower limit temperature while the fixing device is on standby, and stopping energizing the heater when the temperature reaches the upper limit temperature ( Patent document 1). With this technology, the temperature of the fixing device is detected after a period of time from when power supply to the heater is stopped until the next power supply is started. When the temperature is lower than the temperature, the upper limit temperature is raised, the heater is energized intermittently, and the period during which the energization of the heater is stopped is maintained at a desired period. This prevents an extreme decrease in the resistance value of the heater, thereby preventing an increase in rush current generated when the heater is energized.

JP-A-7-114296

By the way, the temperature of the fixing unit rises due to the residual heat of the heater even when the power supply to the heater is stopped, and then gradually decreases. The peak temperature at this time changes, for example, depending on the heat accumulation state of the fixing device itself and members around the fixing device, the surrounding environment, and the like. However, since the above-described technique does not consider such a change in peak temperature, the temperature of the fixing device may fluctuate greatly.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and provides an image forming apparatus capable of suppressing fluctuations in the temperature of a fixing device while suppressing an increase in rush current when power supply to a heater is started. intended to

In order to achieve the above object, the image forming apparatus of the present invention comprises a developer image forming section for forming a developer image on a sheet, a fixing device for fixing the developer image on the sheet having a heater, and a fixing device. and a temperature detection unit that detects the temperature of the
The control unit energizes the heater when the detected temperature is less than a first temperature in the standby state of the fixing device, and energizes the heater when the detected temperature exceeds a second temperature higher than the first temperature. Execute standby control to stop.
In the standby control, the control unit detects a peak temperature that is the maximum value of the detected temperature after power supply to the heater is stopped, and if the detected peak temperature is higher than the target peak temperature, the next peak temperature If the detected peak temperature is lower than the target peak temperature, the standby control conditions are changed so that the next peak temperature is higher than the current peak temperature. do.

With such a configuration, the peak temperature can be kept within a predetermined range, so that the time required for the temperature of the fixing device to drop from the peak temperature to the first temperature can be stabilized. As a result, it is possible to stabilize the time during which power supply to the heater is stopped, so that it is possible to suppress a large decrease in the resistance value due to an excessive decrease in the temperature of the heater. An increase in inrush current can be suppressed. Further, by keeping the peak temperature within a predetermined range, fluctuations in the temperature of the fixing device can be suppressed compared to, for example, the case where the period during which power supply to the heater is stopped is constant.

In the image forming apparatus described above, in the standby control, if the detected peak temperature is higher than the target peak temperature, the control unit sets the next second temperature lower than the current second temperature so that the detected peak temperature reaches the target. If it is lower than the peak temperature, the next second temperature can be set higher than the current second temperature.

In the above-described image forming apparatus, the control unit may be configured to set the initial value of the second temperature to the lowest value within the settable temperature range of the second temperature when starting the standby control. .

According to this, it is possible to prevent the peak temperature from becoming too high immediately after setting the second temperature to the initial value. As a result, the time during which power supply to the heater is stopped does not become too long. An increase in current can be suppressed.

In the image forming apparatus described above, in the standby control, when the detected temperature becomes less than the first temperature, the controller energizes the heater at a duty ratio according to the deviation between the target standby temperature and the detected temperature, and detects the detected peak temperature. If the temperature is higher than the target peak temperature, the duty ratio according to the next deviation is made smaller than the duty ratio according to the current deviation, and if the detected peak temperature is lower than the target peak temperature, the next deviation is It is also possible to configure the duty ratio to be larger than the duty ratio corresponding to the current deviation.

In the image forming apparatus described above, the standby target temperature may be the first temperature, and the controller may fix the duty ratio when the detected temperature is equal to or higher than the standby target temperature.

According to this, it is possible to stabilize the rising gradient of the fixing device temperature after the detected temperature becomes equal to or higher than the standby target temperature. can be further suppressed.

In the image forming apparatus described above, the fixing device has a heating section heated by a heater and a pressure section sandwiching a sheet between the heating section, and the heating section includes a rotatable rotating member, which is controlled by a control unit. The unit may rotate the rotating member when fixing the developer image on the sheet, and may not rotate the rotating member when executing the standby control.

According to this, the heat of the heating portion is less likely to be lost to the pressing portion during execution of the standby control. Power can be reduced.

In the image forming apparatus described above, the control unit executes print control for controlling energization of the heater so that the detected temperature becomes the target fixing temperature when the developer image is fixed on the sheet by the fixing device. The temperature can be configured to be lower than the fixing target temperature.

According to the present invention, it is possible to suppress fluctuations in the temperature of the fixing device while suppressing an increase in inrush current at the start of power supply to the heater.

1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment; FIG. FIG. 3 is a diagram showing a configuration for controlling a fixing device; FIG. 4 is a table (first table) for setting a duty ratio from a deviation between a first temperature and a detected temperature; 4 is a flow chart showing the operation of standby control in the control unit; 6 is a flow chart showing a process for changing conditions of standby control according to the first embodiment; It is a time chart of detected temperature and duty ratio in standby control, and shows a case where the next second temperature is set lower than the current second temperature when the detected peak temperature is higher than the target peak temperature. It is a time chart of detected temperature and duty ratio in standby control, and shows a case where the next second temperature is set higher than the current second temperature when the detected peak temperature is lower than the target peak temperature. A second table (a) and a third table (b) for setting the duty ratio from the deviation between the first temperature and the detected temperature. FIG. 11 is a flow chart showing a condition changing process of standby control according to the second embodiment; FIG.

Next, the first embodiment will be described in detail with appropriate reference to the drawings.
As shown in FIG. 1, a laser printer 1 as an example of an image forming apparatus includes a main housing 2, a sheet feeding section 3, an exposure device 4, a developer image forming section 5, a fixing device 8, a temperature A detection unit 9 and a control unit 100 are provided.

The sheet supply unit 3 is provided in the lower part of the main body housing 2 and includes a sheet tray 31 for storing sheets S such as paper, a pressure plate 32 , and a sheet supply mechanism 33 . The sheet supply unit 3 moves the sheet S in the sheet tray 31 to the sheet supply mechanism 33 by the pressure plate 32 and supplies the sheet S toward the developer image forming unit 5 by the sheet supply mechanism 33 .

The exposure device 4 is arranged in the upper part of the main housing 2 and includes a light source device, a polygon mirror, a lens, a reflecting mirror, and the like (not shown). The exposure device 4 exposes the surface of the photoreceptor drum 61 by scanning the surface of the photoreceptor drum 61 at high speed with a light beam (see chain double-dashed line) based on image data emitted from the light source device.

The developer image forming unit 5 is a device that forms a developer image on the sheet S, and is arranged below the exposure device 4 . The developer image forming unit 5 is detachably attached to the main housing 2 as a process cartridge through an opening formed when a front cover 21 provided in the front portion of the main housing 2 is opened. The developer image forming section 5 is composed of a photosensitive cartridge 6 and a developer cartridge 7 .

The photoreceptor cartridge 6 includes a photoreceptor drum 61 , a charger 62 that is a corona charger, and a transfer roller 63 . The developing cartridge 7 is detachably attached to the photoreceptor cartridge 6, and includes a developing roller 71, a supply roller 72, a layer thickness regulating blade 73, an accommodating portion 74 for accommodating developer made of dry toner, and an agitator 75. and

The developer image forming unit 5 uniformly charges the surface of the photosensitive drum 61 with the charger 62 . After that, the surface of the photoreceptor drum 61 is exposed to the light beam emitted from the exposure device 4 to form an electrostatic latent image on the photoreceptor drum 61 based on the image data. The developer in the storage section 74 is supplied to the supply roller 72 while being agitated by the agitator 75 , and supplied from the supply roller 72 to the developing roller 71 . As the developing roller 71 rotates, the developer 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 having a constant thickness.

The developer image forming section 5 supplies the developer carried on the developing roller 71 from the developing roller 71 to the electrostatic latent image formed on the photosensitive drum 61 . As a result, the electrostatic latent image is visualized and a developer image is formed on the photosensitive drum 61 . Thereafter, the developer image on the photoreceptor drum 61 is transferred onto the sheet S by passing the sheet S between the photoreceptor drum 61 and the transfer roller 63 .

The fixing device 8 is a device that fixes the developer image formed on the sheet S, and is arranged behind the developer image forming section 5 . The fixing device 8 has a heating section 81 , a pressure section 82 and a heater 83 .
Heating unit 81 includes a rotatable rotating member 81A. The rotating member 81A is a cylindrical heating roller made of metal. The heating unit 81 is configured to heat the sheet S by being heated by the heater 83 .

The pressurizing part 82 is a pressurizing roller having an elastic layer around a metal core. The pressure unit 82 is arranged in contact with and pressed against the heating unit 81 and sandwiches the sheet S between itself and the heating unit 81 . The pressurizing part 82 rotates when a driving force is input, and rotates the rotating member 81A in a driven manner.
The heater 83 is a heat source that heats the heating section 81 . The heater 83 has a filament 83A and heats the heating section 81 with radiant heat. The heater 83 is arranged inside the heating section 81 . The filament 83A of the heater 83 has a characteristic that the higher the temperature, the larger the resistance value.

The fixing device 8 fixes the developer image transferred on the sheet S to the sheet S by passing the sheet S between the heating portion 81 and the pressure portion 82 . The sheet S on which the developer image is fixed is discharged onto the discharge tray 22 by the conveying rollers 23 and 24 .

The controller 100 is a device for controlling each part of the laser printer 1 such as the fixing device 8, and is composed of a single or a plurality of electric circuits. The control unit 100 outputs control signals and driving voltages to each unit of the laser printer 1 to control each unit. As shown in FIG. 2, the control unit 100 includes a CPU 110, a ROM 120, a RAM 130, a heater controller 140, a switching circuit 150, and the like.

The CPU 110 commands the operation timing of each part of the laser printer 1 and sends a command value as a target temperature of the fixing device 8 to the heater controller 140 .
The ROM 120 stores data such as programs for controlling each part of the laser printer 1 and various setting information.
The RAM 130 is used as a work area when the CPU 110 executes various programs and as a temporary storage area for data.

The heater controller 140 sets the duty ratio of the switching circuit 150 based on the target temperature of the fixing device 8 and the sensed temperature T sensed by the temperature sensing section 9 . In this embodiment, CPU 110 and heater controller 140 are integrated as a single semiconductor device.
The switching circuit 150 energizes the heater 83 by switching the AC voltage at a set duty ratio.

A temperature detection unit 9 is a sensor that detects the temperature of the fixing device 8 . In the present embodiment, the temperature detection unit 9 is arranged facing the surface of the heating unit 81 with a predetermined gap from the surface of the heating unit 81 , and detects the temperature of the heating unit 81 as the temperature of the fixing unit 8 . temperature. The temperature detection unit 9 outputs a signal corresponding to the temperature of the heating unit 81 to the control unit 100 . The control unit 100 acquires the detected temperature T as the temperature of the fixing device 8 from the signal output from the temperature detection unit 9 . As the temperature detection unit 9, for example, a thermistor whose electric resistance changes according to temperature can be used.

When the fixing device 8 fixes the developer image on the sheet S, the control unit 100 controls the energization of the heater 83 so that the temperature (detected temperature T) of the fixing device 8 becomes the fixing target temperature TT2. to run. As an example, the fixing target temperature TT2 is 200.degree. It should be noted that the specific numerical values shown in this specification are merely examples and do not limit the invention.

The filament 83A of the heater 83 has a temperature of about 2000° C. when the heater 83 is energized so that the temperature of the fixing unit 8 reaches the fixing target temperature TT2, and the resistance value is larger than that at normal temperature. It's becoming

The controller 100 energizes the heater 83 at a duty ratio corresponding to the deviation between the target fixing temperature TT2 and the detected temperature T in print control. Further, in print control, when the detected temperature T exceeds the fixing target temperature TT2, the control unit 100 sets the duty ratio to 0% and stops energizing the heater 83 .

Note that, in the present embodiment, the method of setting the duty ratio in print control is not particularly limited. For example, from the deviation between the target fixing temperature TT2 and the detected temperature T, a method such as PI control or PID control may be used to set the duty ratio (operation amount of the heater 83) in print control. Further, similarly to the setting of the duty ratio in standby control, which will be described later, a table showing the relationship between the deviation between the fixing target temperature TT2 and the detected temperature T and the duty ratio is set in advance. Based on the deviation from the detected temperature T, this table may be referenced to set the duty ratio in print control.

When executing print control, that is, when fixing the developer image on the sheet S, the control unit 100 rotates the rotating member 81A of the heating unit 81 . Specifically, when executing print control, the control unit 100 inputs a driving force to the pressurizing unit 82 to rotate the pressurizing unit 82, thereby rotating the rotating member 81A. As a result, the developer image is transferred between the heating portion 81 heated by the heater 83 and the pressure portion 82 pressed against the heating portion 81 while the sheet S having the developer image transferred thereon is conveyed. can be settled in

In the standby state of the fixing device 8, the control unit 100 energizes the heater 83 when the detected temperature T becomes less than the first temperature T1, and energizes the heater 83 when the detected temperature T exceeds the second temperature T2. Execute standby control to stop energization. Here, the standby state of the fixing device 8 is a state in which the developer image is not fixed on the sheet S, and the temperature of the fixing device 8 is increased in a short time when fixing the developer image on the sheet S next time. In this state, the fixing device 8 is kept warm so that it can be heated up to the target fixing temperature TT2.

The first temperature T1 is a temperature lower than the fixing target temperature TT2 during print control. On the other hand, the second temperature T2 is a temperature lower than the fixing target temperature TT2 and higher than the first temperature T1. As an example, the first temperature T1 is 150° C., and the second temperature T2 is one value (integer value) set from 152 to 158° C. (first temperature T1+2 to 8° C.).

In the standby control, when the detected temperature T becomes less than the first temperature T1, the control unit 100 energizes the heater 83 at a duty ratio corresponding to the deviation ΔT between the detected temperature T and the target standby temperature TT1. In the present embodiment, the standby target temperature TT1 is the first temperature T1, and the deviation ΔT is the detected temperature T minus the first temperature T1.

In the standby control, the control unit 100 executes proportional control in which the duty ratio increases as the absolute value of the deviation ΔT (the difference between the first temperature T1 and the detected temperature T) increases, in other words, as the detected temperature T decreases. . Specifically, in the standby control, the control unit 100 sets the duty ratio in the standby control based on a preset table as shown in FIG. 3 showing the relationship between the deviation ΔT and the duty ratio. For example, the control unit 100 sets the duty ratio to 33% when the deviation ΔT is −2° C. or more. Further, when the deviation ΔT is −8° C. or more and less than −7° C., the control unit 100 sets the duty ratio to 67%.

In standby control, the control unit 100 fixes the duty ratio when the detected temperature T becomes equal to or higher than the first temperature T1 (standby target temperature TT1). Specifically, when the detected temperature T becomes equal to or higher than the first temperature T1, the controller 100 sets the current duty ratio to the same value as the previous duty ratio, and does not change the duty ratio. Accordingly, after the detected temperature T becomes equal to or higher than the first temperature T1, the duty ratio is maintained at the duty ratio when the detected temperature T becomes equal to or higher than the first temperature T1.

In the standby control, the controller 100 sets the duty ratio to 0% and stops energizing the heater 83 when the detected temperature T exceeds a second temperature T2 higher than the first temperature T1.

In standby control, the control unit 100 detects a peak temperature TP, which is the maximum value of the detected temperature T after the detected temperature T exceeds the second temperature T2 and energization of the heater 83 is stopped. When the detected peak temperature TP is higher than a preset target peak temperature TTP, the control unit 100 changes the standby control conditions so that the next peak temperature TP is lower than the current peak temperature TP. . Further, when the detected peak temperature TP is lower than the target peak temperature TTP, the control unit 100 changes the standby control conditions so that the next peak temperature TP is higher than the current peak temperature TP.

Specifically, in standby control, when the detected peak temperature TP is higher than the target peak temperature TTP, the control unit 100 makes the next second temperature T2 lower than the current second temperature T2. Further, in standby control, when the detected peak temperature TP is lower than the target peak temperature TTP, the control unit 100 makes the next second temperature T2 higher than the current second temperature T2.

More specifically, in this embodiment, the target peak temperature TTP is 170±2° C., as an example. Then, in standby control, if the detected peak temperature TP is higher than the maximum value TTPH (172° C.) of the target peak temperature TTP, the control unit 100 sets the next second temperature T2 to 1 ℃ is subtracted from the value. Further, in standby control, when the detected peak temperature TP is lower than the minimum value TTPL (168° C.) of the target peak temperature TTP, the control unit 100 sets the next second temperature T2 to the current second temperature T2 by 1 ℃ added. Further, in standby control, when the detected peak temperature TP is within the range of the target peak temperature TTP (minimum value TTPL or more and maximum value TTPH or less), the control unit 100 sets the next second temperature T2 to 2 The same value as the temperature T2.

Furthermore, in the present embodiment, even when the detected peak temperature TP is higher than the target peak temperature TTP, the control unit 100 sets the current second temperature T2 to the temperature range in which the second temperature T2 can be set. When it is the lowest value T2L (152° C.) of them, the current second temperature T2 is maintained as the next second temperature T2. That is, the next second temperature T2 is set to the lowest value T2L of the second temperature T2. Further, even when the detected peak temperature TP is lower than the target peak temperature TTP, the control unit 100 determines that the current second temperature T2 is the highest value T2H within the settable temperature range of the second temperature T2. (158° C.), the current second temperature T2 is maintained as the next second temperature T2. That is, the next second temperature T2 is set to the highest value T2H of the second temperature T2.

The control unit 100 starts standby control when the power of the laser printer 1 is turned on or when print control ends (more specifically, when print job processing ends). Specifically, when the power of the laser printer 1 is turned on, the control section 100 sets the target temperature of the fixing device 8 to the standby target temperature TT1 and starts standby control. Further, when the print control ends, the control unit 100 changes the target temperature of the fixing device 8 from the fixing target temperature TT2 to the standby target temperature TT1, and starts standby control.

The control unit 100 resets the second temperature T2 to an initial value when starting standby control. More specifically, when starting the standby control, the control unit 100 sets the initial value of the second temperature T2 to the lowest value T2L (152° C.), which is the lowest value within the settable temperature range of the second temperature T2. set to

When a print job including image data to be printed is input while executing standby control, the control unit 100 develops the image data into a dot image. When this development is completed, the control unit 100 changes the target temperature of the fixing device 8 from the standby target temperature TT1 to the fixing target temperature TT2, ends standby control, and starts print control.

Further, the control unit 100 terminates the standby control when a preset predetermined standby time elapses without executing the print control from the time when the standby control is started, and stops the supply of electricity to the heater 83. Execute control.

When executing standby control or sleep control, control unit 100 does not rotate rotating member 81A of heating unit 81 . Specifically, when executing standby control or sleep control, control unit 100 does not input driving force to pressurizing unit 82 . As a result, the pressure member 82 does not rotate, so the rotating member 81A does not rotate either.

Next, the standby control operation of the control unit 100 will be described with reference to a flowchart.
As shown in FIG. 4, when the power of the laser printer 1 is turned on or the printing control is terminated, and the conditions for starting standby control are satisfied, the control unit 100 starts standby control. When the standby control is started, the controller 100 first sets the second temperature T2 to the initial value (lowest value T2L of the second temperature T2) (S10).

Next, the control unit 100 determines whether or not the flag F is 1 (S11). Here, the flag F is set to 1 when the heater 83 is energized, that is, when the heater is ON, and is set to 0 when the heater 83 is not energized, that is, when the heater is OFF. be done.

When the flag F is 1 (S11, Yes), the controller 100 determines whether or not the detected temperature T is lower than the first temperature T1 (S21). Then, if the detected temperature T is less than the first temperature T1 (S21, Yes), the control unit 100 refers to the table shown in FIG. A ratio is set (S22). Then, the controller 100 energizes the heater 83 at the set duty ratio to control the heater 83 (S24).

After that, the control unit 100 determines whether or not conditions for ending the standby control are satisfied (S41). For example, when a print job is input or when a predetermined waiting time has elapsed since the start of waiting control, the control unit 100 determines that the conditions for ending the waiting control have been satisfied (S41, Yes). , end the standby control. On the other hand, when the condition for ending the standby control is not satisfied (S41, No), the control unit 100 returns to step S11.

In step S21, when the detected temperature T is not less than the first temperature T1 (S21, No), the controller 100 determines whether the detected temperature T exceeds the second temperature T2 (S23). Then, if the detected temperature T does not exceed the second temperature T2 (S23, No), the controller 100 energizes the heater 83 at the duty ratio without changing the duty ratio to control the heater 83 ( S24). On the other hand, when the detected temperature T exceeds the second temperature T2 (S23, Yes), the controller 100 stops energizing the heater 83 to turn off the heater 83 (S25), and sets the flag F to 0. (S26). After that, the control unit 100 proceeds to step S41 and executes subsequent processing.

In step S11, when the flag F is not 1 (when the flag F is 0) (S11, No), the control unit 100 determines whether or not the detected temperature T is lower than the first temperature T1 (S31). . If the detected temperature T is less than the first temperature T1 (S31, Yes), the controller 100 refers to the table shown in FIG. A ratio is set (S32). Then, the control unit 100 turns ON the heater 83, energizes the heater 83 at the set duty ratio, controls the heater 83 (S33), and sets the flag F to 1 (S34). After that, the control unit 100 proceeds to step S41 and executes subsequent processing.

In step S31, if the detected temperature T is not less than the first temperature T1 (S31, No), the controller 100 measures the peak temperature TP (S35). Then, if the peak temperature TP is not detected (S35, No), the control unit 100 proceeds to step S41 and executes the subsequent processes, and if the peak temperature TP is detected (S35, Yes), the control unit 100 A condition change process for changing the conditions of standby control is executed (S100).

As shown in FIG. 5, in step S100, the control unit 100 determines whether or not the detected peak temperature TP is higher than the maximum value TTPH of the target peak temperature TTP (S101). Then, if the detected peak temperature TP is higher than the maximum value TTPH (S101, Yes), the control unit 100 sets the second temperature T2 to a value obtained by subtracting 1° C. from the current second temperature T2 (S111 ). Then, the control unit 100 compares the second temperature T2 set in step S111 and the lowest value T2L of the second temperature T2, and sets the larger one as the next second temperature T2 (S112). End the modification process.

On the other hand, if the detected peak temperature TP is equal to or lower than the maximum value TTPH (S101, No), it is determined whether or not the detected peak temperature TP is lower than the minimum value TTPL of the target peak temperature TTP (S102). Then, when the detected peak temperature TP is lower than the minimum value TTPL (S102, Yes), the control unit 100 sets the second temperature T2 to a value obtained by adding 1° C. to the current second temperature T2 (S121 ). Then, the control unit 100 compares the second temperature T2 set in step S121 and the maximum value T2H of the second temperature T2, and sets the smaller one as the next second temperature T2 (S122). End the modification process.

If the detected peak temperature TP is equal to or higher than the minimum value TTPL (S102, No), that is, if the detected peak temperature TP is equal to or higher than the minimum value TTPL and equal to or lower than the maximum value TTPH, the control unit 100 sets the second temperature T2 to Terminates the waiting control condition change processing without making any changes. Note that the processing order of steps S101 and S102 may be reversed.

The control unit 100 uses the second temperature T2 determined in step S100 in the process of comparison with the detected temperature T in step S23 of FIG.

According to the present embodiment described above, when the detected peak temperature TP is higher than the maximum value TTPH of the target peak temperature TTP as shown at time t13 in FIG. Since the temperature is set lower than the temperature T2, the next energization time TM3 (time t14 to t15) to the heater 83 can be made shorter than the current energization time TM1 (time t11 to t12) to the heater 83. heating time can be shortened. As a result, as shown at time t16 in FIG. 6, after power supply to the heater 83 is stopped, the rise in the next peak temperature TP can be suppressed. can be lower than time t13).

Further, as a result, the next energization of the heater 83 is finished before the time TM2 (time t12 to t14) from when the current energization of the heater 83 is finished until when the next energization of the heater 83 is started. Since the time TM4 (time t15 to t17) from when the heater 83 starts to energize next time becomes shorter, it is possible to prevent the temperature of the filament 83A of the heater 83 from dropping too much.

Also, as shown at time t23 in FIG. 7, when the detected peak temperature TP is lower than the minimum value TTPL of the target peak temperature TTP, the next second temperature T2 is set higher than the current second temperature T2. The next energization time TM7 (time t24 to t25) to the heater 83 can be made longer than the current energization time TM5 (time t21 to t22) to the heater 83, and the heating time of the fixing device 8 can be lengthened. can. As a result, as shown at time t26 in FIG. 7, the next peak temperature TP can be raised after power supply to the heater 83 is stopped. ) can be higher than

Further, as a result, the next energization of the heater 83 is finished before the time TM6 (time t22 to t24) from the end of the current energization of the heater 83 to the start of the next energization of the heater 83. Since the time TM8 (time t25 to t27) until the next energization of the heater 83 is started becomes longer, it is possible to suppress frequent repetition of energization and de-energization of the heater 83. .

As described above, according to the present embodiment, the peak temperature TP can be kept within a predetermined range, specifically near the target peak temperature TTP. The time to drop to T1 can be stabilized. As a result, the time during which the heater 83 is de-energized can be stabilized, so that the resistance of the filament 83A of the heater 83 can be prevented from dropping significantly due to the temperature of the filament 83A dropping too much. It is possible to suppress an increase in rush current at the next start of energization of the heater 83 .

In addition, since the peak temperature TP can be kept within a predetermined range, it is possible to suppress large fluctuations in the peak temperature TP compared to, for example, the case where the period during which power supply to the heater 83 is stopped is constant. can. As a result, fluctuations in the temperature of the fixing device 8 can be suppressed.

Further, when starting the standby control, the control unit 100 sets the initial value of the second temperature T2 to the lowest value in the settable temperature range of the second temperature T2. It is possible to prevent the peak temperature TP from becoming too large immediately after setting the value. As a result, the time during which the heater 83 is deenergized does not become too long, so that the resistance of the filament 83A of the heater 83 can be prevented from dropping significantly due to the temperature of the filament 83A dropping too much. It is possible to suppress an increase in rush current when energization of the heater 83 is started.

Further, when the detected temperature T becomes equal to or higher than the first temperature T1 (standby target temperature TT1), the control unit 100 fixes the duty ratio, and sets the duty ratio to a value equal to or higher than the first temperature T1. Since the duty ratio is maintained at the current duty ratio, the rising gradient of the temperature of the fixing device 8 after the detected temperature T becomes equal to or higher than the standby target temperature TT1 can be stabilized. As a result, fluctuations in the peak temperature TP can be further suppressed, so fluctuations in the temperature of the fixing device 8 can be further suppressed.

Further, since the control unit 100 does not rotate the rotating member 81A of the heating unit 81 when performing standby control, the heat of the heating unit 81 is less likely to be lost to the pressurizing unit 82 during standby control. As a result, when the developer image is fixed on the sheet S next time, the electric power supplied to the heater 83 when heating the heating unit 81 to the fixing target temperature TT2 can be reduced.

Next, a second embodiment will be described. In addition, in this embodiment, points different from the first embodiment will be described in detail.
In this embodiment, the second temperature T2 is a fixed value. As an example, the second temperature T2 is 155° C. (first temperature T1+5° C.).

In the present embodiment, in the standby control, when the detected peak temperature TP is higher than the target peak temperature TTP, the controller 100 controls the next peak temperature TP to be lower than the current peak temperature TP. 2. Instead of reducing the temperature T2, the duty ratio corresponding to the next deviation .DELTA.T is made smaller than the duty ratio corresponding to the current deviation .DELTA.T. In standby control, when the detected peak temperature TP is lower than the target peak temperature TTP, the control unit 100 increases the second temperature T2 so that the next peak temperature TP is higher than the current peak temperature TP. Instead, the duty ratio corresponding to the next deviation ΔT is made larger than the duty ratio corresponding to the current deviation ΔT.

More specifically, in the standby control, when the detected peak temperature TP is within the range of the target peak temperature TTP (minimum value TTPL or more and maximum value TTPH or less), the control unit 100 stores the temperature in the first table shown in FIG. Based on this, set the duty ratio. For example, when the detected peak temperature TP is within the range of the target peak temperature TTP and the deviation ΔT is −2° C. or more, the control unit 100 sets the duty ratio to 33%. Further, when the detected peak temperature TP is within the range of the target peak temperature TTP and the deviation ΔT is -8°C or more and less than -7°C, the control unit 100 sets the duty ratio to 67%.

Further, in standby control, when the detected peak temperature TP is higher than the maximum value TTPH of the target peak temperature TTP, the control unit 100 sets the duty ratio based on the second table shown in FIG. 8(a). For example, when the detected peak temperature TP is higher than the maximum value TTPH of the target peak temperature TTP and the deviation ΔT is −3° C. or more, the control unit 100 sets the duty ratio to 33%. Further, when the detected peak temperature TP is higher than the maximum value TTPH of the target peak temperature TTP and the deviation ΔT is −9° C. or more and less than −8° C., the control unit 100 sets the duty ratio to 67%. set.

Further, in standby control, when the detected peak temperature TP is lower than the minimum value TTPL of the target peak temperature TTP, the control unit 100 sets the duty ratio based on the third table shown in FIG. 8(b). For example, when the detected peak temperature TP is lower than the minimum value TTPL of the target peak temperature TTP and the deviation ΔT is −1° C. or more, the control unit 100 sets the duty ratio to 33%. Further, when the detected peak temperature TP is lower than the minimum value TTPL of the target peak temperature TTP and the deviation ΔT is −7° C. or more and less than −6° C., the control unit 100 sets the duty ratio to 67%. set.

Here, in the first table shown in FIG. 3, for example, when the deviation ΔT is −2° C. or more, the duty ratio is 33%, and when the deviation ΔT is −3° C. or more and less than −2° C., the duty ratio is set to 40%, the second table shown in FIG. 8A is set to set the duty ratio to 33% when the deviation ΔT is -3° C. or more. Further, the first table shown in FIG. 3, for example, is set so that the duty ratio is 50% when the deviation ΔT is −5° C. or more and less than −4° C. The second table shown is set to reduce the duty ratio to 43% for the same deviation ΔT.

That is, the second table shown in FIG. 8A is set so that the duty ratio corresponding to the deviation ΔT is smaller than that in the first table shown in FIG. Therefore, when the deviation ΔT has the same value, the duty ratio set with reference to the second table shown in FIG. 8A is higher than the duty ratio set with reference to the first table shown in FIG. becomes smaller.

Further, the first table shown in FIG. 3 is set so that the duty ratio is 33% when the deviation ΔT is −2° C. or more, but the third table shown in FIG. , the duty ratio is set to 33% when the deviation ΔT is -1°C or more, and is set to 40% when the deviation ΔT is -2°C or more and less than -1°C. Further, the first table shown in FIG. 3, for example, is set so that the duty ratio is 50% when the deviation ΔT is −5° C. or more and less than −4° C. However, FIG. The third table shown is set to increase the duty ratio to 57% for the same deviation ΔT.

That is, the third table shown in FIG. 8B is set so that the duty ratio according to the deviation ΔT is larger than that in the first table shown in FIG. Therefore, when the deviation ΔT has the same value, the duty ratio set with reference to the third table shown in FIG. 8B is higher than the duty ratio set with reference to the first table shown in FIG. becomes larger.

Next, the standby control operation in the control unit 100 of this embodiment will be described.
In the standby control of this embodiment, the basic processing is the same as that of the first embodiment (see FIG. 4). On the other hand, the standby control condition change process (S100) is different from that of the first embodiment.

Specifically, as shown in FIG. 9, the control unit 100 determines whether or not the detected peak temperature TP is higher than the maximum value TTPH of the target peak temperature TTP (S101). Then, when the detected peak temperature TP is higher than the maximum value TTPH (S101, Yes), the control unit 100 selects the second table shown in FIG. 8A as a table for setting the duty ratio ( S132), the condition change processing of the standby control is terminated.

On the other hand, if the detected peak temperature TP is equal to or lower than the maximum value TTPH (S101, No), it is determined whether or not the detected peak temperature TP is lower than the minimum value TTPL of the target peak temperature TTP (S102). Then, when the detected peak temperature TP is lower than the minimum value TTPL (S102, Yes), the control unit 100 selects the third table shown in FIG. 8B as the table for setting the duty ratio ( S133), the condition change processing of the standby control is terminated.

If the detected peak temperature TP is equal to or higher than the minimum value TTPL (S102, No), that is, if the detected peak temperature TP is equal to or higher than the minimum value TTPL and equal to or lower than the maximum value TTPH, the controller 100 sets the duty ratio. The first table shown in FIG. 3 is selected as the table for waiting control (S131), and the condition change process for standby control is terminated.

In the processes of steps S22 and S32 of FIG. 4, the control unit 100 sets the duty ratio from the deviation ΔT between the first temperature T1 and the detected temperature T by referring to the table selected in step S100.

According to the present embodiment described above, the same effects as those of the first embodiment can be obtained.
That is, when the detected peak temperature TP is higher than the maximum value TTPH of the target peak temperature TTP, the duty ratio corresponding to the next deviation ΔT is made smaller than the duty ratio corresponding to the current deviation ΔT. It is possible to reduce the amount of heat given to the heating portion 81 per unit time when energized. As a result, after the power supply to the heater 83 is stopped next time, the rise of the next peak temperature TP can be suppressed, so that the next peak temperature TP can be made lower than the current peak temperature TP.

Further, when the detected peak temperature TP is lower than the minimum value TTPL of the target peak temperature TTP, the duty ratio corresponding to the next deviation ΔT is made larger than the duty ratio corresponding to the current deviation ΔT. It is possible to increase the amount of heat given to the heating portion 81 per unit time when energized. As a result, the next peak temperature TP can be raised after the power supply to the heater 83 is stopped next time, so the next peak temperature TP can be made higher than the current peak temperature TP.

As described above, according to the present embodiment, the peak temperature TP can be kept within a predetermined range. Fluctuations can be suppressed.

Also in the present embodiment, the controller 100 fixes the duty ratio when the detected temperature T becomes equal to or higher than the first temperature T1 (target standby temperature TT1). It is possible to stabilize the rising gradient of the temperature of the fixing device 8 after becoming . As a result, fluctuations in the peak temperature TP can be further suppressed, and fluctuations in the temperature of the fixing device 8 can be further suppressed.

Although the embodiment has been described above, the present invention is not limited to the embodiment. Specific configurations can be changed as appropriate without departing from the scope of the invention.
For example, in the above embodiment, the standby target temperature TT1 is the same temperature as the first temperature T1, but it is not limited to this and may be different temperatures.

Further, in the above embodiment, in the standby control, the duty ratio according to the deviation ΔT between the first temperature T1 (standby target temperature TT1) and the detected temperature T is set with reference to the table shown in FIG. 3 or the like. However, it is not limited to this. For example, the configuration may be such that the duty ratio (heater operation amount) is set using a technique such as PI control or PID control based on the deviation between the standby target temperature and the detected temperature.

Further, in the above embodiment, the second temperature T2 is reset to the initial value when the standby control is started, but the present invention is not limited to this. For example, the second temperature may be reset to the initial value when the standby control ends, or the second temperature may be reset to the initial value when sleep control is started and power supply to the heater is stopped. It may be configured to That is, in the present invention, setting the initial value of the second temperature to the lowest value of the second temperature when starting the standby control means not only the configuration of resetting the second temperature at the time of starting the standby control, A configuration is included in which the second temperature is reset before starting the standby control, and the second temperature is already the lowest value of the second temperature as the initial value when the standby control is started next time.

Further, in the above-described embodiment, the initial value of the second temperature T2 is set to the lowest value in the settable temperature range of the second temperature T2, but the present invention is not limited to this. For example, the configuration may be such that the initial value of the second temperature is set to the median value of the settable temperature range of the second temperature. In the above-described embodiment, the settable temperature of the second temperature T2 was set in increments of 1°C, but this is not limiting. It may be set in finer increments than in the above embodiment, such as 1°C increments. Also, the settable temperature of the second temperature may be set in larger increments than in the above embodiment, such as 2° C. increments.

In the above embodiment, the first temperature T1 is lower than the target fixing temperature TT2, but the present invention is not limited to this, and the first temperature may be the same as the target fixing temperature. That is, the control unit may be configured to keep the temperature of the fixing device at the target fixing temperature in the standby control.

Also, in the above embodiment, the target peak temperature TTP is in a predetermined temperature range such as 168 to 172° C., but it is not limited to this. For example, the target peak temperature may be a single value such as 170°C.

In the above-described embodiment, the rotating member 81A of the heating unit 81 is not rotated when standby control is performed. It may be configured to allow

Further, in the above-described embodiment, the heating roller was exemplified as the rotating member 81A, but the rotating member is not limited to this. . Further, in the above-described embodiment, the pressure roller was exemplified as the pressure unit 82, but the pressure roller is not limited to this. For example, the pressure unit may be a pressure unit including an endless pressure belt. .

Further, in the above-described embodiment, the temperature detection unit 9 is provided so as to detect the temperature of the heating unit 81, but the present invention is not limited to this. may be provided to sense the temperature of the Also, the temperature detection unit may be provided so as to directly detect the temperature of the heater. Also, the temperature detection unit may be a temperature sensor other than the thermistor. Also, the temperature sensor may be a non-contact temperature sensor or a contact temperature sensor.

In the above embodiment, the heater 83 is a halogen heater that uses radiant heat, but is not limited to this, and may be a ceramic heater or carbon heater that uses heat generated by a resistor. Also, the heater may be arranged outside the heating unit instead of inside the heating unit.

In the above-described embodiment, the laser printer 1 that forms a monochrome image on the sheet S was exemplified as an image forming apparatus, but the present invention is not limited to this. may be Further, the image forming apparatus is not limited to a printer, and may be, for example, a copier or a multifunction machine having a document reading device such as a flatbed scanner.

Further, in the above-described embodiment, the process cartridge is exemplified as the developer image forming unit 5, but the present invention is not limited to this. For example, an image forming apparatus is capable of forming a color image on a sheet, and includes a process unit having a plurality of arranged photosensitive drums, and a developer image formed on the plurality of photosensitive drums to transfer onto the sheet. When a transfer unit having a transfer belt and the like is provided, the developer image forming section can be configured to include the process unit and the transfer unit.

Moreover, each element described in the above-described embodiment and modifications can be implemented in combination as appropriate.

REFERENCE SIGNS LIST 1 laser printer 5 developer image forming section 8 fixing device 9 temperature detection section 81 heating section 81A rotating member 82 pressure section 83 heater 100 control section S sheet

Claims (6)

a developer image forming unit that forms a developer image on a sheet;
a fixing device having a heater and fixing the developer image on the sheet;
a temperature detection unit that detects the temperature of the fixing device;
a control unit;
The control unit
In the standby state of the fixing device, the heater is energized when the detected temperature is less than a first temperature, and the heater is energized when the detected temperature exceeds a second temperature higher than the first temperature. Execute the standby control to stop,
In the standby control,
Detecting a peak temperature, which is the maximum value of the detected temperature after the energization of the heater is stopped,
If the detected peak temperature is higher than the target peak temperature, the conditions of the standby control are changed so that the next peak temperature is lower than the current peak temperature. also lower ,
When the detected peak temperature is lower than the target peak temperature , the next second temperature is changed to the current second temperature in order to change the conditions of the standby control so that the next peak temperature is higher than the current peak temperature. An image forming apparatus characterized in that it is made higher than 2. The control unit, when starting the standby control, sets the initial value of the second temperature to the lowest value within a settable temperature range of the second temperature. The described image forming apparatus. a developer image forming unit that forms a developer image on a sheet;
a fixing device having a heater and fixing the developer image on the sheet;
a temperature detection unit that detects the temperature of the fixing device;
a control unit;
The control unit
In the standby state of the fixing device, the heater is energized when the detected temperature is less than a first temperature, and the heater is energized when the detected temperature exceeds a second temperature higher than the first temperature. Execute the standby control to stop,
In the standby control,
Detecting a peak temperature, which is the maximum value of the detected temperature after the energization of the heater is stopped,
when the detected temperature is less than the first temperature, the heater is energized at a duty ratio corresponding to the deviation between the standby target temperature and the detected temperature;
If the detected peak temperature is higher than the target peak temperature, the conditions of the standby control are changed so that the next peak temperature is lower than the current peak temperature. smaller than the duty ratio corresponding to the deviation ,
If the detected peak temperature is lower than the target peak temperature, the conditions of the standby control are changed so that the next peak temperature is higher than the current peak temperature. and a duty ratio corresponding to the deviation of the image forming apparatus. The standby target temperature is the first temperature,
4. The image forming apparatus according to claim 3 , wherein the controller fixes the duty ratio when the detected temperature is equal to or higher than the target standby temperature. The fixing device has a heating section heated by the heater and a pressure section sandwiching the sheet between the heating section,
The heating unit includes a rotatable rotating member,
The control unit
When fixing the developer image on the sheet, the rotating member is rotated,
5. The image forming apparatus according to claim 1 , wherein the rotating member is not rotated when executing the standby control. The control unit executes print control for controlling energization of the heater so that a detected temperature becomes a target fixing temperature when the developer image is fixed on the sheet by the fixing device,
The image forming apparatus according to any one of claims 1 to 5 , wherein the first temperature is lower than the target fixing temperature.

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