JP2019135528A - Image forming apparatus - Google Patents

Abstract

To suppress a voltage drop due to a rush current, even when heat of a heating unit is deprived by a sheet and a heater is energized so that a temperature of the heating unit becomes a fixing temperature.SOLUTION: When receiving a print instruction, a control unit 100 can execute energization processing of controlling energization of a heater 31 so that a temperature of a heating unit 22 becomes a fixing temperature. When receiving the print instruction and determining that impedance of the heater 31 is equal to or less than a predetermined value, the control unit executes, in energization processing, first energization processing of energizing the heater 31 while limiting a duty ratio to less than a predetermined value in a period before a sheet S reaches the heating unit 22 even when the temperature of the heating unit 22 is higher than a first temperature equal to or higher than the fixing temperature, and after the first energization processing, executes second energization processing of controlling the energization of the heater 31 so that the temperature of the heating unit 22 becomes the fixing temperature.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus including a heating unit that heats a sheet and a heater that heats the heating unit.

2. Description of the Related Art Conventionally, an image forming apparatus including a heating roller that is a heating unit that heats a sheet, a heater disposed in the heating roller, a conveyance unit that supplies the sheet toward the heating roller, and a control unit is known. (See Patent Document 1).
According to this technique, when a print command is received while the heating roller is at a high temperature, the recording sheet is started to be conveyed in a shorter waiting time than when the heating roller is at a low temperature.

  On the other hand, it is known that the heater used in the fixing device has a low resistance value when the temperature of the heater itself is low, and a large current flows when the heater having a low resistance value is energized (see Patent Document 2). .

JP 2011-232531 A JP 2007-328164 A

  In the case of the technique disclosed in Japanese Patent Application Laid-Open No. H10-260260, even after the printing control is performed, the fixing unit remains at the fixing temperature or higher for a while even when the power supply to the heater is stopped. In such a situation, when receiving the next print command, the control unit starts supplying the sheet. Thereafter, when the sheet reaches the heating unit and the heat of the heating unit is taken away by the sheet, the temperature of the heating unit decreases, and the control unit starts energizing the heater. However, at this time, when the temperature of the heater is lowered, the impedance of the heater is in a low state as in Patent Document 2, and a large current flows when energization is started. A descent etc. may occur.

  Therefore, an object of the present invention is to suppress a voltage drop due to an inrush current even when the heater is energized so that the heating unit reaches the fixing temperature when the heat of the heating unit is taken away by the sheet.

In order to solve the above problems, an image forming apparatus according to the present invention includes a developer image forming unit that forms a developer image on a sheet, a heating unit that heats the sheet and fixes the developer image, and the heating unit. A heater for heating and a control unit are provided.
The control unit can execute an energization process for controlling energization of the heater so that the heating unit reaches a fixing temperature when receiving the print command, and when the print command is received, When it is determined that the impedance is equal to or lower than a predetermined value, in the energization process, the duty is limited to less than a predetermined value and the heater is energized during a period before the sheet reaches the heating unit. 1 energization process is performed even if the temperature of the heating unit is higher than the first temperature equal to or higher than the fixing temperature, and the energization to the heater is performed after the first energization process so that the temperature of the heating unit becomes the fixing temperature. A second energization process for controlling is performed.

  According to this configuration, by performing the first energization process before the sheet reaches the heating unit, when the sheet reaches the heating unit, the temperature of the heater is increased and the impedance is set higher than a predetermined value. Therefore, even when the heater is energized so that the heating portion becomes the fixing temperature when the heat is taken away by the sheet, the voltage drop due to the inrush current can be suppressed.

  Moreover, the said control part may always perform a said 2nd electricity supply process during the period when the said sheet | seat is passing the said heating part.

  According to this, it is possible to further suppress the occurrence of fixing failure due to the sheet being deprived of the temperature of the heating portion.

  The controller may control energization so that the temperature of the heating unit does not increase in the first energization process.

  According to this, since the temperature of the heating part does not rise in the first energization process, it is possible to suppress the temperature of the heating part from becoming excessively high.

  The control unit may perform phase control in the first energization process.

  According to this, since the peak current is limited by the phase control, it is possible to satisfactorily suppress the voltage drop caused by the inrush current that occurs when the impedance is low.

  In the energization process, the control unit may stop energization when the temperature of the heating unit is equal to or higher than the fixing temperature.

  The first temperature may be the fixing temperature.

  The image forming apparatus may include a temperature detection unit that detects a temperature of the heating unit, and the control unit may acquire the temperature of the heating unit based on a detection result of the temperature detection unit.

  Further, the control unit may determine that the impedance of the heater is equal to or less than a predetermined value when an elapsed time from the end of the energization process in the previous print command is equal to or longer than a predetermined time.

  According to this, it is possible to predict a decrease in the impedance of the heater without providing a temperature sensor for detecting the temperature of the heater.

  Further, the control unit may set the predetermined time to a longer time as the duty ratio of energization at the end of the energization process in the previous print command is higher.

  According to this, when the duty ratio of energization at the end of the energization process in the previous print command is high, it takes time until the temperature of the heater decreases. Therefore, by setting the predetermined time to a long time, Can be predicted more accurately.

  According to the present invention, it is possible to suppress poor fixing caused by the heat of the heating unit being taken away by the sheet.

It is sectional drawing of the laser printer which concerns on one Embodiment. It is a block diagram which shows the structure of a control part. It is a graph which shows the relationship between the resistance value of a filament, and elapsed time. FIG. 4A is a diagram showing a current control pattern for phase control, and FIG. 4B is a diagram showing a current control pattern for wave number control. It is a flowchart which shows control of electricity supply to the heater by a control part. It is a flowchart which shows an impedance determination process. It is a flowchart which shows control of the drive / stop of a pickup roller by a control part. It is a time chart which shows an example of operation | movement of a control part.

Next, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the laser printer 1 is an example of an image forming apparatus that forms an image on a sheet S. A main body casing 2 includes a supply tray 3, a sheet conveying unit 4, and a developer image forming unit. As an example, a process unit 6, a fixing unit 7, and a control unit 100 are provided. An interface IF capable of displaying and inputting information is provided on the upper surface of the main casing 2.

  The sheet conveying unit 4 includes a pickup roller 41 that is a sheet supply unit that supplies the sheet S toward the process unit 6 and the fixing unit 7, a separation roller 42, a separation pad 43, and a registration roller 44. . The sheet conveying unit 4 supplies the sheet S in the supply tray 3 toward the separation roller 42 by the pickup roller 41 and separates the sheet S into one sheet between the separation roller 42 and the separation pad 43. Specifically, the pickup roller 41 sends out the sheet S in the supply tray 3 by starting rotation from a state where the pickup roller 41 comes into contact with the sheet S in the supply tray 3 and stops. The registration roller 44 aligns the position of the leading edge of the sheet S and then conveys the sheet S toward the process unit 6. Specifically, the registration roller 44 comes into contact with the conveyed sheet S in a stopped state, aligns the position of the leading edge of the sheet S, and starts to rotate to send out the sheet S. The sheet S sent out by the sheet transport unit 4 passes through the process unit 6 and the fixing unit 7 and is transported to the outside of the laser printer 1 in the transport direction indicated by the arrow.

  The process unit 6 forms a developer image on the sheet S, and includes a scanner 10, a developing cartridge 13, a photosensitive drum 17, a charger 18, a transfer roller 19, and the like.

  The scanner 10 is disposed in the upper part of the main casing 2 and includes a laser light emitting unit (not shown), a polygon mirror 11, a plurality of reflecting mirrors 12, a plurality of lenses (not shown), and the like. In the scanner 10, the laser light emitted from the laser light emitting unit is scanned on the surface of the photosensitive drum 17 as indicated by a one-dot chain line through the polygon mirror 11, the reflecting mirror 12, and a lens (not shown).

  The developing cartridge 13 includes a developing roller 14 and a supply roller 15 that supplies developer to the developing roller 14. The developer cartridge 13 contains a developer that is a dry toner. The developing roller 14 is disposed to face the photosensitive drum 17. The developer in the developing cartridge 13 is supplied to the developing roller 14 by the rotation of the supply roller 15 and is carried on the developing roller 14.

  The photosensitive drum 17 is charged to, for example, positive polarity by the charger 18 while rotating. The photosensitive drum 17 is exposed by the laser beam from the scanner 10 to form an electrostatic latent image on the surface. Thereafter, a developer image is formed on the photosensitive drum 17 by supplying a developer from the developing roller 14 to the electrostatic latent image on the photosensitive drum 17. The developer image on the photosensitive drum 17 is transferred to the sheet S by a transfer bias applied to the transfer roller 19 while the sheet S passes between the photosensitive drum 17 and the transfer roller 19.

  The fixing unit 7 is disposed on the downstream side in the conveyance direction of the sheet S with respect to the process unit 6. The fixing unit 7 includes a heating unit 22 that heats the sheet S to fix the developer image on the sheet S, and a pressing unit 23 that is pressed against the heating unit 22. The heating unit 22 is a cylindrical heating roller and is made of metal or the like. A heater 31 for heating the heating unit 22 is provided inside the heating unit 22. As the heater 31, a halogen lamp that has a filament as a resistor and heats the heating unit 22 by radiant heat can be employed. The pressure unit 23 is a pressure roller having an elastic layer on the surface. The fixing unit 7 fixes the developer image on the sheet S by heating the sheet S with the heater 31 while sandwiching the sheet S between the heating unit 22 and the pressing unit 23.

  The fixing unit 7 includes a temperature detection unit 32 that detects the temperature of the heating unit 22. The temperature detection unit 32 faces the surface of the heating unit 22 in a non-contact manner. The temperature detected by the temperature detection unit 32 is output to the control unit 100. The control unit 100 acquires the temperature of the heating unit 22 based on the detection result of the temperature detection unit 32.

  As shown in FIG. 2, the control unit 100 includes a CPU, a RAM, a ROM, a heater controller 101, and a switching circuit 50, and print commands output from an external computer and output from the temperature detection unit 32. Control is executed by performing various arithmetic processes based on the information and programs and data stored in the ROM or the like. The heater controller 101 performs feedback control so that the heating unit 22 reaches the target temperature based on the detection result of the temperature detection unit 32 and the target temperature commanded by the CPU, and sets the duty ratio of energization of the switching circuit 50. Control. The switching circuit 50 is connected to the AC power supply 40 outside the laser printer 1, and switches between the energized state and the non-energized state of the heater 31 by the heater controller 101. Here, the ratio of the amount of electric power supplied to the heater 31 per unit time to the amount of electric power in the 100% energized state is defined as a duty ratio.

  When the control unit 100 receives the print command, the control unit 100 determines whether the impedance of the heater 31 is equal to or less than a predetermined value Ra, and the first temperature T1 where the temperature of the heating unit 22 is equal to or higher than the fixing temperature TH. A temperature determination process for determining whether the temperature is higher, an energization process for controlling energization of the heater 31 so that the heating unit 22 reaches the fixing temperature TH, and a supply process for supplying the sheet S by the pickup roller 41. It is executable. The fixing temperature TH is the temperature of the heating unit 22 when fixing the developer image on the sheet S.

  In the impedance determination process, the control unit 100 determines that the impedance of the heater 31 is equal to or less than the predetermined value Ra when the elapsed time TM from the end of the energization process in the previous print command is equal to or greater than the predetermined time TM1. ing. Further, in the impedance determination process, the control unit 100 sets the predetermined time TM1 to a longer time as the duty ratio of energization at the end of the energization process in the previous print command is higher. In the following description, the “duty ratio at the end of the energization process in the previous print command” is also referred to as “end-time duty ratio D”. Here, the predetermined value Ra of the impedance is set to a value at which the voltage drop becomes an allowable value even when the heater 31 is energized with a duty ratio of 100%. The value Ra is set according to an experiment or a power supply environment.

  The end duty ratio D corresponds to the current value flowing through the filament at the end of the energization process. Therefore, it can be estimated that the larger the end-time duty ratio D, the higher the filament temperature at the end of the energization process.

  The elapsed time TM from the end of the energization process in the previous print command is an index for knowing how much the filament temperature has decreased since the energization process in the previous print command was completed. Therefore, it can be estimated that the longer the elapsed time TM, the lower the temperature of the filament at the start of energization processing in the current print command.

  In addition, the impedance of the filament which the heater 31 has becomes low, so that the temperature of a filament is low. Therefore, in other words, the larger the end duty ratio D, the higher the impedance of the filament at the end of the energization process, and the longer the elapsed time TM, the lower the impedance of the filament at the start of the energization process. Can do. If energization is performed with a large duty ratio in a state where the impedance of the filament is low, excessive current may flow through the filament, which may cause a voltage drop of the AC power supply 40 or the like.

  FIG. 3 is a graph showing the relationship between the impedance (resistance value) of the filament and the elapsed time TM. From this graph, it can be seen that the longer the elapsed time TM, the lower the impedance of the filament.

  In the energization process, the control unit 100 restricts the duty ratio to less than a predetermined value and performs energization. The second energization process controls the energization so that the temperature of the heating unit 22 becomes the fixing temperature TH. And can be executed. In the first energization process, the control unit 100 executes phase control using the first energization pattern P1 as shown in FIG. 4A in order to limit the duty ratio to a predetermined value of less than 50%. In FIG. 4, the voltage applied to the heater 31 from the switching circuit 50 is shown, and the shaded portion corresponds to the energized state.

  Here, the first energization pattern P1 sets the firing angle in phase control to a phase angle larger than 90 ° and a phase angle larger than 270 ° with respect to one sine wave, so that the peak value of the sine wave It is a pattern which removes and energizes. For example, the duty ratio of the first energization pattern P1 illustrated in FIG. 4A is about 20%. The duty ratio of the first energization pattern P1 is less than 50%.

  In addition, the control unit 100 controls energization so that the temperature of the heating unit 22 does not increase in the first energization process. Specifically, for example, a predetermined duty ratio at which the temperature of the heating unit 22 does not increase may be defined by experiment or simulation, and energization may be performed at the specified predetermined duty ratio in the first process. As another method, in the first energization process, there is a method in which the duty ratio is decreased when the temperature rises by feeding back the temperature of the heating unit 22.

  In the second energization process, the control unit 100 executes wave number control using the second energization pattern P2 as shown in FIG. Specifically, in the second energization process, the control unit 100 sets the duty ratio so that the duty ratio decreases as the deviation between the fixing temperature TH, which is the target temperature, and the temperature of the heating unit 22 decreases, and the set duty is set. Based on the ratio, the second energization pattern P2 is set.

  Here, the second energization pattern P2 refers to a pattern corresponding to a predetermined number of sine waves. The second energization pattern P2 is a pattern for controlling the ratio between the energized state and the non-energized state in the portion corresponding to the half wave of the sine wave. The duty ratio of the second energization pattern P2 illustrated in FIG. 4B is 50% as an example. The duty ratio of the second energization pattern P2 is not limited, and the maximum value is 100%.

  When the control unit 100 determines that the impedance is equal to or less than the predetermined value Ra in the impedance determination process, the control unit 100 executes the first energization process for a predetermined period from the start of the energization process, that is, after the first energization process, that is, The second energization process is executed after the elapse of the predetermined period. In addition, when the control unit 100 determines that the impedance is larger than the predetermined value Ra in the impedance determination process, the control unit 100 executes the second energization process from the start of the energization process.

  In the second energization process, the control unit 100 has a function of stopping energization when the temperature of the heating unit 22 is equal to or higher than the fixing temperature TH. Further, in the first energization process, the control unit 100 is configured to energize the first energization process even if the temperature of the heating unit 22 is higher than the first temperature T1 that is equal to or higher than the fixing temperature TH. Thus, when the control unit 100 receives the print command and determines that the impedance of the heater 31 is equal to or less than the predetermined value Ra, the control unit 100 executes the first energization process regardless of the temperature of the heating unit 22. It is like that.

  When the control unit 100 receives the print command and determines that the temperature of the heating unit 22 is equal to or higher than the first temperature T1 and the impedance of the heater 31 is equal to or lower than the predetermined value Ra, the first energization is performed. It has a function of executing a standby process that waits for a supply process until the process is completed. Thereby, the control unit 100 is configured to always execute the second energization process while the sheet S passes through the heating unit 22.

  The control unit 100 has a function of starting the supply process when the temperature of the heating unit 22 reaches the second temperature T2. During the execution of the standby process, the control unit 100 waits without starting the supply process even if the temperature of the heating unit 22 is equal to or higher than the second temperature T2.

  Here, in the present embodiment, the first temperature T1 and the second temperature T2 are set to the fixing temperature TH. The first temperature T1 may be higher than the fixing temperature TH, and the second temperature T2 may be lower than the fixing temperature TH.

Next, the operation of the control unit 100 will be described in detail.
The control unit 100 executes energization control to the heater 31 according to the flowchart shown in FIG. 5 and also executes drive / stop control of the pickup roller 41 according to the flowchart shown in FIG.

  In the control shown in FIG. 5, the control unit 100 first determines whether or not a print command has been received (S1). If it is determined in step S1 that a print command has not been received (No), the control unit 100 ends this control.

  If it is determined in step S1 that a print command has been received (Yes), the control unit 100 executes an impedance determination process for determining whether the impedance of the heater 31 is equal to or less than a predetermined value Ra (S2). When determining that the impedance of the heater 31 is equal to or lower than the predetermined value Ra in the impedance determination process, the control unit 100 sets a flag Fi indicating that the impedance is equal to or lower than the predetermined value Ra to 1. The details of the impedance determination process will be described later.

  After step S2, the control unit 100 determines whether or not the flag Fi is 1 (S3). When Fi = 1 in Step S3 (Yes), the control unit 100 executes the first energization process (S4). In the first energization process, the control unit 100 energizes even when the detected temperature Ts that is the temperature of the heating unit 22 is higher than the first temperature T1.

  After step S4, the control unit 100 starts the second energization process (S5). If the controller 100 determines that Fi = 0 in Step S3, that is, if the impedance is higher than the predetermined value Ra (No), the controller 100 does not execute the first energization process (S4), but performs the second energization process. Is started (S5).

  After step S5, the control unit 100 determines whether printing has ended (S6). If it is determined in step S6 that printing has not ended (No), the control unit 100 returns to step S5 and continues to execute the second energization process.

  If it is determined in step S6 that printing has ended (Yes), the control unit 100 ends the second energization process (S7). After step S7, the control unit 100 stores an end-time duty ratio D, which is a duty ratio at the end of the second energization process, and a time at the end of the second energization process in a storage unit such as a RAM. (S8), this control is terminated.

  As shown in FIG. 6, in the impedance determination process, the control unit 100 first calculates an elapsed time TM from the end of the energization process in the previous print command based on the end time stored in the storage unit. (S21). After step S21, the control unit 100 corrects the predetermined time TM1 according to the end duty ratio D stored in the storage unit (S22). Specifically, in step S22, the control unit 100 sets the predetermined time TM1 to a longer time as the end-time duty ratio D is higher.

  After step S22, the control unit 100 determines whether or not the elapsed time TM is equal to or longer than the predetermined time TM1 (S23). If it is determined in step S23 that TM ≧ TM1 (Yes), the control unit 100 sets a flag Fi indicating that the impedance of the heater 31 is equal to or less than a predetermined value Ra to 1 (S24). End control. If it is determined in step S23 that TM ≧ TM1 is not satisfied (No), the control unit 100 sets the flag Fi to 0 (S25) and ends this control.

  In the control shown in FIG. 7, the control unit 100 first determines whether or not a print command has been received (S31). If it is determined in step S31 that a print command has not been received (No), the control unit 100 ends this control.

  If it is determined in step S31 that a print command has been received (Yes), the control unit 100 performs impedance determination similar to the impedance determination (S2) described above (S32). After step S32, the control unit 100 determines whether or not the flag Fi is 1 (S33). When Fi = 1 in Step S33 (Yes), the control unit 100 determines whether or not the detected temperature Ts that is the temperature of the heating unit 22 is higher than the first temperature T1 (S34).

  If it is determined in step S34 that Ts> T1 is satisfied (Yes), the control unit 100 determines whether or not the first energization process is completed (S35). That is, when the control unit 100 determines that the impedance of the heater 31 is equal to or lower than the predetermined value Ra and the temperature of the heating unit 22 is higher than the first temperature T1 that is equal to or higher than the fixing temperature TH (S33: Yes → S34: Yes), by waiting for the supply process until the first energization process is completed in step S35, the first energization process is executed in a period before the sheet S reaches the heating unit 22, and specifically, the first energization process is started and terminated. Yes.

  When it is determined in step S35 that the first energization process has ended (Yes), the control unit 100 determines whether the detected temperature Ts is equal to or higher than the second temperature T2, thereby determining the supply process start condition. Is determined (S36). In addition, when the control unit 100 determines that Fi = 1 is not satisfied in step S33 (No) or when it is determined that Ts> T1 is not satisfied in step S34 (No), the control unit 100 waits for the start of the supply process ( Without executing S35), it is determined whether or not the supply process start conditions are met (S36).

  If it is determined in step S36 that Ts ≧ T2 (Yes), the control unit 100 drives the pickup roller 41 to supply one sheet S (S37). After step S37, the control unit 100 determines whether printing has been completed (S38).

  If it is determined in step S38 that printing has not ended (No), the control unit 100 returns to step S37 and supplies the second and subsequent sheets S at a predetermined timing. Specifically, for the second and subsequent sheets S, the current sheet S is supplied after a predetermined time has elapsed since the sheet S was supplied last time so that the interval between the sheets S becomes a predetermined interval. It is supplied at a preset timing.

  If it is determined in step S38 that printing has ended (Yes), the control unit 100 ends this control.

Next, an example of the operation of the control unit 100 will be described with reference to FIG.
As shown in FIG. 8, at the time t <b> 1, when the energization process in the previous print command is completed, the temperature of the heater 31 gradually decreases. May be higher than TH. Then, when a print command is output in a situation where the temperature of the heating unit 22 is higher than the fixing temperature TH and the temperature of the heater 31 is low (time t2), the conventional standby process is not performed. In the form of executing the energization process and the supply process, the following problems occur.

  In the comparative example indicated by a two-dot chain line in the figure, when a print command is received at time t2, the supply process is performed while the energization is stopped because the temperature of the heating unit 22 is equal to or higher than the fixing temperature TH. When the sheet S conveyed by the supply process reaches the heating unit 22 (time t3), the heat of the heating unit 22 is taken away by the sheet S, and the temperature of the heating unit 22 decreases. Here, the time interval from time t2 to time t3 is the time from when the sheet S is sent out by the pickup roller 41 to when the sheet S reaches the heating unit 22.

  When the temperature of the heating unit 22 becomes lower than the fixing temperature TH, energization processing is started (time t4). At this time, when the impedance of the heater 31 is low, if the heater 22 is energized to recover the fixing temperature TH, a voltage drop may occur when energized with a high duty ratio.

  In contrast, in the present embodiment indicated by a solid line in the figure, when the print command is received at time t2, the impedance of the heater 31 is equal to or less than the predetermined value Ra (elapsed time TM ≧ TM1) and the temperature of the heating unit 22 is reached. Is determined to be higher than the first temperature T1, that is, the fixing temperature TH, the control unit 100 immediately starts the first energization control and waits for the supply process regardless of the temperature of the heating unit 22.

  In the first energization process, since the duty ratio of energization is limited to less than a predetermined value by phase control, the temperature of the heater 31 gradually increases, but the temperature of the heating unit 22 does not increase but gradually decreases. Thus, for example, the temperature becomes lower than the fixing temperature. When the first energization process ends, the control unit 100 starts the second energization process and starts determining the supply process start condition (time t5).

  When the temperature of the heating unit 22 gradually increases due to the execution of the second energization process and reaches the second temperature T2, the control unit 100 starts the supply process (time t6). By delaying the supply process in this way, when the sheet S reaches the heating unit 22 after a predetermined time has elapsed from the start of the supply process (time t7), the temperature of the heater 31 has risen to a sufficiently high temperature. Even if the heat of the heating unit 22 is taken away by the sheet S, the temperature of the heating unit 22 can be immediately increased, and it is possible to suppress the occurrence of fixing failure.

As described above, according to the present embodiment, the following effects can be obtained.
By performing the first energization process before the sheet S reaches the heating unit 22, when the sheet S reaches the heating unit 22, the temperature of the heater 31 is increased and the impedance is set higher than the predetermined value Ra. I can leave. Thus, even when the heater 31 is deprived of heat by the sheet S and the heater 31 is energized with a high duty ratio in the second energization process, the voltage drop due to the inrush current can be suppressed.

  Since the second energization process is always performed during the period in which the sheet S passes through the heating unit 22, the temperature of the heating unit 22 can be quickly increased even if the heat of the heating unit 22 is deprived by the sheet S. The occurrence of fixing failure can be further suppressed.

  Since energization is controlled so that the temperature of the heating unit 22 does not increase in the first energization process, it is possible to suppress an excessive increase in the temperature of the heating unit 22 in the first energization process.

  Since energization is performed while the duty ratio is limited for a predetermined period from the start of the energization process, it is possible to suppress a voltage drop due to an inrush current that occurs when the impedance is as low as a predetermined value Ra or less.

  By performing the phase control in the first energization process, the peak current can be limited in the first energization process, so that the voltage drop due to the inrush current, which occurs when the impedance is as low as the predetermined value Ra or less, is satisfactorily suppressed. Can do.

  The temperature at which the temperature of the heater 31 is detected because it is determined that the impedance of the heater 31 is equal to or less than the predetermined value Ra when the elapsed time TM from the end of the energization process in the previous print command is equal to or greater than the predetermined time TM1. A decrease in the impedance of the heater 31 can be predicted without providing a sensor or the like.

  When the duty ratio of energization at the end of the energization process in the previous print command is high, it takes time until the temperature of the heater 31 decreases. Therefore, the impedance of the heater 31 is set by setting the predetermined time TM1 to a long time. Can be predicted more accurately.

  In addition, this invention is not limited to the said embodiment, It can utilize with various forms so that it may illustrate below. In the following description, members and processes having substantially the same structure as those of the above-described embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the above-described embodiment, the pickup roller 41 is exemplified as the sheet supply unit. However, the present invention is not limited to this, and the sheet supply unit can be switched between the stop and conveyance of the sheet S by the control unit 100. Good. For example, the sheet supply unit may be a registration roller 44 or a supply roller for supplying a sheet on the manual feed tray.

  In the above embodiment, the method of determining the impedance of the heater 31 is exemplified by the method based on the elapsed time TM and the end-time duty ratio. However, the present invention is not limited to this. For example, the heater 31 is preliminarily energized. The impedance may be determined based on the current acquired at this time.

  The sheet S may be paper such as thick paper, postcard, and thin paper, or may be an OHP sheet.

  The developer image forming unit is arbitrarily configured. For example, a developer image forming unit that exposes a photosensitive drum with an LED head may be used.

  In the above embodiment, a cylindrical fixing roller is exemplified as the heating unit 22, but the present invention is not limited to this, and the heating unit is, for example, a nip plate that sandwiches an endless belt with a pressure member. Also good.

  In the said embodiment, although the halogen lamp which has the filament which is a resistor and heats the heating part 22 with radiant heat was illustrated as the heater 31, this invention is not limited to this, The heater 31 has a resistance heating element. It may be a ceramic heater or the like, and may be configured to heat the heating unit 22 by heat conduction.

  In the above-described embodiment, the supply process is started when the temperature of the heating unit 22 reaches the fixing temperature TH. However, the present invention is not limited to this. For example, the temperature of the heating unit is set to a predetermined temperature lower than the fixing temperature. The supply process may be started when it becomes.

  In the above embodiment, the present invention is applied to the laser printer 1. However, the present invention is not limited to this, and the present invention may be applied to other image forming apparatuses such as a copying machine and a multifunction machine.

  Moreover, you may implement combining each element demonstrated by above-described embodiment and modification arbitrarily.

DESCRIPTION OF SYMBOLS 1 Laser printer 6 Process part 22 Heating part 31 Heater 100 Control part S Sheet T1 1st temperature TH Fixing temperature

Claims (9)

A developer image forming unit for forming a developer image on the sheet;
A heating section for fixing the developer image by heating the sheet;
A heater for heating the heating unit;
A control unit,
The controller is
When receiving a print command, it is possible to execute an energization process for controlling energization of the heater so that the heating unit reaches a fixing temperature;
When it is determined that the heater impedance is equal to or lower than a predetermined value when the print command is received,
In the energization process,
In a period before the sheet reaches the heating unit, a first energization process is performed in which the duty ratio is limited to less than a predetermined value and the heater is energized. The temperature of the heating unit is higher than the first temperature equal to or higher than the fixing temperature. Even run,
An image forming apparatus, wherein after the first energization process, a second energization process for controlling energization of the heater is performed so that the temperature of the heating unit becomes the fixing temperature.   The image forming apparatus according to claim 1, wherein the control unit always executes the second energization process while the sheet passes through the heating unit.   The image forming apparatus according to claim 1, wherein the control unit controls energization so that a temperature of the heating unit does not increase in the first energization process.   The image forming apparatus according to claim 1, wherein the control unit performs phase control in the first energization process.   5. The control unit according to claim 1, wherein, in the energization process, the energization process is stopped when a temperature of the heating unit is equal to or higher than the fixing temperature. 6. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the first temperature is the fixing temperature. A temperature detection unit for detecting the temperature of the heating unit;
The image forming apparatus according to claim 1, wherein the control unit acquires a temperature of the heating unit based on a detection result of the temperature detection unit.   The said control part judges that the impedance of the said heater is below a predetermined value, when the elapsed time after complete | finishing the said electricity supply process in the last printing command is more than predetermined time, It is characterized by the above-mentioned. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 8, wherein the control unit sets the predetermined time to be longer as the duty ratio of energization at the end of the energization process in the previous print command is higher.

Images