JP2016184133A - Image forming apparatus, control method of fixing part, and control program for fixing part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress extension of a time required for a fixing temperature of a fixing part 700 to approach a predetermined temperature, and suppress a variation (ripple) in fixing temperature after the fixing temperature has approached the predetermined temperature.SOLUTION: An image forming apparatus comprises: a heater; a fixing part including a switching part that switches between an energization state and a non-energization state of the heater and a temperature sensor; a control part; and a memory that stores association information associating a plurality of values of duty ratios and a plurality of temperature areas with each other, where as the values of the duty ratios are smaller, the values are associated with higher temperature areas of the plurality of temperature areas. The control part acquires detected temperature on the basis of a signal from the temperature sensor, and controls the switching part with the value of a duty ratio corresponding to a temperature area including the detected temperature on the basis of the association information; of the plurality of temperature areas in the association information, a first temperature area is larger than a second temperature area including a temperature lower than that of the first temperature area.SELECTED DRAWING: Figure 5

Description

  The technology disclosed in this specification relates to an image forming apparatus.

  An electrophotographic image forming apparatus includes a fixing unit for thermally fixing a toner image to a sheet. The fixing unit includes a heater, a switching unit that switches the heater between an energized state and a non-energized state, and a temperature. And a sensor. As an example of such an image forming apparatus, one in which the following heater temperature control is performed is known (see Prior Art Document 1). In this image forming apparatus, the detected temperature based on the signal from the temperature sensor is compared with the target temperature suitable for thermal fixing, and the duty ratio value is repeatedly changed according to the difference of the detected temperature with respect to the target temperature. Thus, the switching unit is controlled so that the heater temperature approaches the target temperature.

JP 2009-237070 A

  In the conventional image forming apparatus that controls the temperature of the heater described above, each of the temperature regions below the target temperature associated with each value of the duty ratio has the same width. Therefore, when all these temperature regions are uniformly wide, there is a possibility that the time until the detected temperature approaches the target temperature may be prolonged. Further, when all the temperature regions are uniformly narrow, there is a possibility that the temperature fluctuation (ripple) of the heater after the detected temperature approaches the target temperature becomes large due to the response delay of the temperature sensor.

  The present specification discloses a technique capable of solving at least a part of the problems described above.

  An image forming apparatus disclosed in this specification includes a heater, a switching unit that switches the heater between an energized state and a non-energized state, a fixing unit that includes a temperature sensor, a control unit, and an energization ratio at a predetermined time. The correspondence information that associates a plurality of values of the duty ratio with a plurality of temperature regions, and the correspondence information that associates with the higher temperature region of the plurality of temperature regions as the value of the duty ratio decreases. A memory stored therein, wherein the control unit acquires a detected temperature based on a signal from the temperature sensor, and based on the correspondence information, the value of the duty ratio corresponding to the temperature region including the detected temperature The switching unit is controlled, and among the plurality of temperature regions in the correspondence information, the first temperature region is wider than the second temperature region including a temperature lower than the first temperature region.

  The technology disclosed by this specification can be implemented in various forms. For example, the present invention can be realized in the form of a temperature control method and a fixing device for a fixing unit, a computer program for realizing the function of the method or device, a recording medium on which the computer program is recorded, and the like.

1 is a schematic diagram illustrating an overall configuration of a printer 10 according to an embodiment. 2 is a schematic diagram illustrating a configuration of a fixing unit 700. FIG. FIG. 2 is a block diagram illustrating an electrical configuration of the printer 10. It is a matrix figure which shows the correspondence of an arrangement | sequence pattern table. It is a matrix figure which shows the correspondence of a 1st temperature area table. It is a matrix figure which shows the correspondence of a 2nd temperature area table. It is a flowchart which shows a temperature control process. It is explanatory drawing which shows transition of detected temperature and duty ratio at the time of execution of temperature control based on a 2nd temperature area table. It is explanatory drawing which shows transition of heater temperature, detected temperature, and heater current. It is explanatory drawing which shows transition of detected temperature and duty ratio at the time of execution of temperature control based on a 1st temperature area table. It is explanatory drawing which shows transition of heater temperature, detected temperature, and heater current.

  A printer 10 according to an embodiment will be described with reference to FIGS. 1 to 11. FIG. 1 is a schematic diagram illustrating the overall configuration of the printer 10. FIG. 1 shows XYZ axes orthogonal to each other for specifying the direction. In this specification, for convenience, the Z-axis positive direction is referred to as the upward direction, the Z-axis negative direction is referred to as the downward direction, the X-axis positive direction is referred to as the forward direction, the X-axis negative direction is referred to as the backward direction, and Y The positive axis direction is called the right direction, and the negative Y axis direction is called the left direction. The same applies to FIG.

  As shown in FIG. 1, the printer 10 is a laser printer, and includes a housing 100, a sheet supply unit 200, an image forming unit 300, and a discharge roller 400. A discharge port 110 and a discharge tray 120 are formed on the upper surface of the housing 100. The printer 10 is an example of an image forming apparatus.

  The sheet supply unit 200 is provided in the housing 100 and includes a tray 210, a pickup roller 220, a conveyance roller 230, and a registration roller 240. The sheets W stored in the tray 210 are taken out one by one by the pickup roller 220, conveyed by the conveying roller 230, corrected in posture by the registration roller 240, and sent to the image forming unit 300 at a predetermined timing.

  The image forming unit 300 is provided in the housing 100 and includes an exposure unit 500, a process unit 600, and a fixing unit 700. The exposure unit 500 can form an electrostatic latent image on the photoconductor 610 by irradiating the photoconductor 610 described later with a laser beam L.

  The process unit 600 includes a photoconductor 610, a charging unit 620, a developing unit 630, and a transfer roller 640. The charging unit 620 uniformly charges the surface of the photoconductor 610. When the surface of the photoconductor 610 uniformly charged by the charging unit 620 is irradiated with the laser light L from the exposure unit 500 described above, an electrostatic latent image is formed on the surface of the photoconductor 610. The developing unit 630 develops the electrostatic latent image formed on the surface of the photoreceptor 610 by supplying a developer. As a result, a developer image is formed on the surface of the photoreceptor 610. The transfer roller 640 is disposed so as to face the photoconductor 610, and transfers the developer image formed on the surface of the photoconductor 610 onto the sheet W conveyed by the sheet supply unit 200.

  The fixing unit 700 is disposed downstream of the photosensitive member 610 in the conveyance direction (X-axis negative direction) of the sheet W, and fixes the developer image on the sheet W by heat. The configuration of the fixing unit 700 will be described in detail later. The sheet W that has passed through the fixing unit 700 is discharged to the discharge tray 120 through the discharge port 110 by the discharge roller 400.

  FIG. 2 is a schematic diagram illustrating the configuration of the fixing unit 700. The fixing unit 700 includes a belt 710, a halogen heater 720, a nip member 730, a reflection member 740, a pressure roller 750, a stay 760, and a thermistor 770. The halogen heater 720 is an example of a heater, and the thermistor 770 is an example of a temperature sensor.

  The belt 710 is a cylindrical belt, and is provided so as to be rotatable about an axis along a horizontal direction (Y-axis direction) orthogonal to the conveyance direction of the sheet W. More specifically, both end portions of the belt 710 in the left-right direction are rotatably guided by guide members (not shown). The belt 710 is made of metal, and is formed of, for example, stainless steel or nickel.

  The halogen heater 720 is a known heating element having a halogen lamp, and is disposed inside the belt 710 at a position separated from the belt 710 and the nip member 730. The nip member 730 is disposed between the halogen heater 720 and the inner surface of the belt 710. The nip member 730 is a metal plate-like member such as an aluminum plate, for example, and the lower surface of the nip member 730 is in contact with the inner surface of the belt 710. The nip member 730 includes a base portion 731 and a protruding portion 732. The base portion 731 is disposed to face the halogen heater 720, and the lower surface thereof is in contact with the inner surface of the belt 710. The protruding portion 732 is formed so as to protrude rearward along the transport direction from one end portion of the base portion 731 in the transport direction.

  The reflection member 740 is disposed at a position separated from the halogen heater 720 so as to surround the halogen heater 720 inside the belt 710. The reflection member 740 is made of a metal such as aluminum, and is a plate-like member that is mirror-finished and curved in a substantially U shape so as to surround the halogen heater 720.

  The stay 760 is a steel plate having a shape (substantially U shape in cross section) along the outer surface shape of the reflecting member 740, and is arranged so as to cover the reflecting member 740. The stay 760 sandwiches the flange portion 742 of the reflecting member 740 with the nip member 730. Thereby, the position shift of the reflection member 740 in the up-down direction is suppressed. A space S is formed between the stay 760 and the reflecting member 740. Since the air in the space S does not easily flow out to the outside, the air is warmed so that it acts as a heat retaining layer, and the heating efficiency of the nip member 730 can be improved.

  The pressure roller 750 is disposed so as to face the nip member 730 with the belt 710 interposed therebetween. The pressure roller 750 is pressed toward the nip member 730, whereby a nip portion P is formed between the belt 710 and the pressure roller 750. The pressure roller 750 is configured to be rotationally driven by a motor driving unit 910 described later provided in the main body housing 2. Note that the pressure roller 750 may be replaced with a belt-shaped pressure member.

  The thermistor 770 is disposed on the protruding portion 732 of the nip member 730 inside the belt 710 and outside the reflecting member 740.

  When the halogen heater 720 generates heat inside the belt 710, the nip member 730 transmits radiant heat from the halogen heater 720 to the pressure roller 750 side via the belt 710. Further, by collecting the radiant heat from the halogen heater 720 to the nip member 730 by the reflecting member 740, the radiant heat from the halogen heater 720 can be used efficiently, and the nip member 730 and the belt 710 can be quickly heated. .

  When the pressure roller 750 is driven to rotate, the belt 710 is driven and rotated by the frictional force with the belt 710 (or the sheet W). The sheet W on which the toner image is transferred is conveyed between the pressure roller 750 and the heated belt 710 (nip portion P), whereby the toner image is thermally fixed.

  FIG. 3 is a block diagram illustrating an electrical configuration of the printer 10. In addition to the above-described process unit 600 and thermistor 770, the printer 10 includes a controller 800 that controls the printer 10, a motor drive unit 910, a temperature control unit 920, a zero cross detection unit 930, a communication interface 940, an operation Part 950. The temperature control unit 920 is an example of a switching unit.

  The controller 800 includes a CPU 810, a ROM 820, a RAM 830, a nonvolatile memory 840, and an ASIC (Application Specific Integrated Circuit) 850. The ROM 820 stores a control program for controlling the printer 10, various settings, initial values, and the like. The RAM 830 is used as a work area when the CPU 810 executes various programs and as a temporary storage area for data. The non-volatile memory 840 is a rewritable memory such as NVRAM, flash memory, HDD, or EEPROM. The ASIC 850 is a hardware circuit dedicated to image processing, for example. The CPU 810 controls each component of the printer 10 according to a control program read from the ROM 820 and signals sent from various sensors. The CPU 810 is an example of a control unit, and the nonvolatile memory 840 is an example of a memory.

  The motor drive unit 910 has one or a plurality of motors (not shown), and the above-described pickup roller 220, registration roller 240, photoconductor 610, pressure roller 750, and the like are individually driven to rotate by the driving force of the motors. Let The zero-cross detector 930 outputs a zero-cross signal every time it detects the timing when the voltage of an AC power supply (not shown) becomes zero.

  The temperature control unit 920 is provided in the fixing unit 700 and includes a switch element (not shown) that is electrically connected between the AC power supply and the halogen heater 720. The temperature control unit 920 switches the halogen heater 720 between an energized state in which power from the AC power source is supplied and a non-energized state in which power from the AC power source is not supplied by opening and closing the switch element. In the present embodiment, the temperature control unit 920 follows the temperature control signal input from the CPU 810, and the zero cross signal output from the zero cross detection unit 930 is input via the CPU 810, whereby the voltage of the AC power supply becomes zero. At timing, the halogen heater 720 is switched between an energized state and a non-energized state.

  The communication interface 940 is hardware that enables communication with an external device. The operation unit 950 includes various buttons and a touch panel (none of which are shown) that accept user operations. The touch panel also functions as a display unit that displays various types of information.

  FIG. 4 is a matrix diagram showing the correspondence of the array pattern table. The array pattern table is stored in the nonvolatile memory 840, for example. In the array pattern table, each value of the duty ratio, each value of the control period, and each array pattern are associated with each other. The duty ratio is an energization duty ratio (energization ratio) indicating a ratio of energization time in which the halogen heater 720 is energized with respect to a predetermined time, in other words, a heater heating rate. The control period is a repetition period of the array pattern.

  The array pattern is a switching pattern of the switch elements used for realizing the duty ratio. More specifically, the array pattern represents whether the halogen heater 720 is in an energized state or in a non-energized state for each unit section in the control period, with the half wave period of the voltage of the AC power supply as a unit section. is there. In FIG. 4, “ON” means an energized section that is a unit section in which the halogen heater 720 should be energized, and “OFF” represents a non-energized section that is a unit section in which the halogen heater 720 should be deenergized. Means.

  In the arrangement pattern, the first unit interval (half wave 1) in the control cycle is the energization interval (except when the duty ratio is 0%), and the last unit interval is the non-energization interval (however, the duty ratio). Are arranged so that the energized section and the non-energized section are as even as possible. That is, in the arrangement pattern, the sections with the smaller total number of unit sections (half waves) in the control cycle among the energized sections and the non-energized sections are all arranged so as to be discontinuous, and the energized sections are continuous. They are arranged so that the number of unit sections (half waves) included in the energized continuous section or the non-energized continuous section in which the non-energized sections are continuous is minimized.

  The control cycle is represented by the number of unit sections (hereinafter referred to as half wave number) N having a maximum value of seven. The half wave number N is a number that makes M / N an irreducible fraction when the duty ratio of M / N is represented by an array pattern composed of M energized sections and NM non-energized sections. Is set to That is, the half wave number N is set to a minimum number necessary to represent the duty ratio. For example, if the duty ratio is 75% (3/4), the half wave number N is set to four.

  The duty ratio of the present embodiment is 100%, 75% (3/4), 71% (5/7), 67% (2/3), 60% (3/5), 57% (4 / 7), 50% (1/2), 43% (3/7), 40% (2/5), 33% (1/3), 29% (2/7), 25% (1/4) , 0%, respectively.

  FIG. 5 is a matrix diagram showing the correspondence relationship of the first temperature region table, and FIG. 6 is a matrix diagram showing the correspondence relationship of the second temperature region table. Each temperature region pattern table is stored in the nonvolatile memory 840, for example. In each temperature region table, a plurality of values of the duty ratio are associated with a plurality of temperature regions. Each temperature region is indicated by a difference in detected temperature with respect to a reference temperature (= reference temperature−detected temperature, hereinafter referred to as temperature difference ΔT). The reference temperature is a temperature (for example, 168 degrees) higher than the target temperature (for example, 160 degrees) of the halogen heater 720 suitable for thermally fixing the toner image on the sheet W. The detected temperature is the temperature of the halogen heater 720 (nip member 730) detected based on the signal from the thermistor 770. Note that the plurality of temperature regions preferably do not overlap each other. The first temperature region table is an example of first correspondence information.

  As shown in FIG. 5, in the first temperature region table, the smaller the duty ratio value, the higher the temperature region, in other words, the smaller the temperature difference from the reference temperature, the higher the temperature region. The temperature range closer to the temperature is wider in the temperature range. More specifically, the first temperature region in which the duty ratio value is less than 50% has a wider temperature range than the second temperature region in which the duty ratio is greater than 50%.

  The first temperature region table includes temperature regions associated with a duty ratio of 33%, and includes temperature regions associated with a duty ratio of 0% and a duty ratio of 50%. Absent. In the present embodiment, when the temperature control unit 920 is controlled with the duty ratio set to 33%, the detected temperature of the halogen heater 720 converges near the target temperature. The target temperature is included in the temperature range associated with the duty ratio of 33%. Furthermore, each value (100%, 75%, 67%, 57%, 43%, 33%, 25%) of the duty ratio included in the first temperature region table is set to this value to control the temperature. When the unit 920 is controlled, the short-term flicker value (pst) is 1 or less.

  In the example shown in FIG. 5, the temperature region where the temperature difference ΔT exceeds 16 degrees has a duty ratio of 100%, the temperature region where the temperature difference ΔT is 16 degrees has a duty ratio of 75%, and the temperature difference ΔT is not less than 14 degrees and not more than 15 degrees. A certain temperature region has a duty ratio of 67%,..., A temperature region where the temperature difference ΔT is 4 degrees or more and 7 degrees or less is a duty ratio of 43%, and a temperature region where the temperature difference ΔT is greater than 0 degree and less than 3 degrees is a duty ratio Each is associated with a ratio of 25%.

  On the other hand, as shown in FIG. 6, in the second temperature region table, the temperature widths of the temperature regions associated with each value (except 100%) of the duty ratio are the same. The second temperature region table includes temperature regions respectively associated with a duty ratio of 0% and a duty ratio of 50%. Some of the duty ratio values included in the second temperature range table are values that the short-term flicker value (pst) does not become 1 or less when the temperature control unit 920 is controlled by setting the value (for example, 71%, 50%). The second temperature region table is an example of second correspondence information.

  In the example shown in FIG. 6, the temperature region where the temperature difference ΔT is 12 degrees or more has a duty ratio of 100%, the temperature region where the temperature difference ΔT is 11 degrees, the duty ratio is 75%,. A certain temperature region is associated with a duty ratio of 25%, and a temperature region where the temperature difference ΔT is 0 or less is associated with a duty ratio of 0%.

  FIG. 7 is a flowchart showing the temperature control process. When the CPU 810 receives a print command for forming an image on the sheet W via the communication interface 940 or the operation unit 950, for example, the CPU 810 executes a temperature control process shown in FIG. In the temperature control process, a counter that updates the count value CNT every time a zero cross signal is input (hereinafter referred to as a half-wave number counter) is used.

  First, the CPU 810 resets the count value CNT of the half wave number counter to 0 (S110). Next, the CPU 810 sets a target temperature based on setting data (not shown) stored in the storage area of the RAM 830 (S120), and the type (OHP, thin paper, recycled paper) of the sheet W specified by the print command. , Plain paper, thick paper) is set (S120), and the detected temperature of the halogen heater 720 is acquired based on the signal from the thermistor 770 (S130). The target temperature is set to a higher temperature as the thickness of the sheet W is larger, for example.

When acquiring the detected temperature, the CPU 810 determines whether or not a predetermined execution condition is satisfied (S140). Here, it is assumed that the predetermined execution condition is a condition for executing the temperature control of the halogen heater 720 based on the first temperature region table, and satisfies both the next detection temperature condition and the print setting condition. .
Detected temperature condition: The detected temperature is within the temperature range defined by the first temperature range table. For example, during the temperature control based on the first temperature range table, if the detected temperature exceeds the reference temperature for some reason, it is determined that the detected temperature condition is not satisfied.
Print setting condition: The print setting content specified by the print command satisfies the use condition for using the first temperature region table. For example, if the sheet type specified in the print command is a type that is not guaranteed in the first temperature region table, it is determined that the print setting condition is not satisfied.

  If the CPU 810 determines that the execution condition is satisfied (S140: YES), the CPU 810 calculates a temperature difference ΔT (= reference temperature−detected temperature) of the detected temperature in S130 with respect to the reference temperature that is higher than the target temperature set in S120 by a predetermined temperature. Then, a duty ratio value corresponding to the calculated temperature difference ΔT is selected from the first temperature region table (S150). Then, the CPU 810 selects an array pattern associated with the duty ratio value selected in S150 from the array pattern table (S170). On the other hand, when determining that the execution condition is not satisfied (S140: NO), the CPU 810 selects a duty ratio value corresponding to the temperature difference ΔT from the second temperature region table (S160). Then, the CPU 810 selects an array pattern associated with the duty ratio value selected in S160 from the array pattern table (S170).

  After selecting the array pattern, the CPU 810 waits until the zero cross signal is input from the zero cross detection unit 930 (S180; NO). When the zero cross signal is input (S180; YES), the count value CNT of the half wave number counter Is incremented to +1 (S190). Here, the zero cross signal input from the zero cross detector 930 is output to the temperature controller 920.

  Using the array pattern table, the CPU 810 refers to the unit section (energized section, non-energized section) corresponding to the count value CNT incremented in S170 among the array patterns selected in S150, and determines the state of the halogen heater 720. A temperature control signal for energizing or de-energizing is output (S200).

  For example, when an array pattern corresponding to a duty ratio of 33% is selected in S150 or S160, the CPU 810, if the count value CNT incremented in S190 is 2, a unit interval (half-half) corresponding to the count value CNT. Since the wave 2) is a non-energized section (see FIG. 4), a temperature control signal for setting the halogen heater 720 to a non-energized state is output.

  When the temperature control signal is output, the CPU 810 determines whether or not the count value CNT incremented in S190 matches the half wave number N associated with the duty ratio value selected in S150 or S160 (S210). When the count value CNT does not match the half wave number N (S210; NO), S180 is re-executed. When the count value CNT matches the half wave number N (S210; YES), S110 is re-executed. That is, by repeatedly executing the temperature control process, the duty ratio is always reset in the last unit section within the control cycle set for each arrangement pattern. Further, a temperature control signal in an energized state or a non-energized state is output every time a zero cross signal is input. The temperature control unit 920 that has input the temperature control signal switches the state of the halogen heater 720 to the energized state or the non-energized state at the next zero cross timing. Thereby, the flicker resulting from the alternating voltage of alternating current power supply can be suppressed.

  Here, the response delay of the detected temperature based on the signal from the thermistor 770 will be described. The thermistor 770 is provided to detect the temperature of the halogen heater 720 (nip member 730). In general, however, a so-called response delay may occur in which a change in detected temperature based on a signal from a temperature sensor such as the thermistor 770 is delayed with respect to an actual temperature change in an object such as the halogen heater 720.

  The cause of the delay in response is, for example, that it is difficult to arrange the temperature sensor in the same temperature environment as the object by design, or the response of the processing device that processes the signal from the temperature sensor or the temperature sensor. Various things can be considered, such as low. In the present embodiment, as shown in FIG. 2, the halogen heater 720 is disposed inside the reflecting member 740, while the thermistor 770 is disposed outside the reflecting member 740. That is, the halogen heater 720 and the thermistor 770 are spaced apart from each other and arranged in different temperature environments. For this reason, response delay is particularly likely to occur.

  FIG. 8 is an explanatory diagram showing the transition of the detected temperature and the duty ratio when the temperature control based on the second temperature region table is executed. FIG. 9 shows the actual temperature of the halogen heater 720 (hereinafter referred to as the heater temperature). And the detected temperature and the current flowing through the halogen heater 720 (hereinafter referred to as heater current).

  As described above, in the second temperature region table, the temperature width of the temperature region associated with each value (except 100%) of the duty ratio is 1 degree each and is relatively narrow. Therefore, for example, when the temperature difference ΔT is relatively large, such as the start-up time when the energization of the halogen heater 720 is started, the duty ratio is immediately changed with respect to a slight change in the detected temperature. The heater temperature and the detected temperature can be brought close to the reference temperature at an early stage. However, even when the detected temperature approaches the reference temperature and the temperature difference ΔT becomes relatively small, the duty ratio is immediately changed with a slight change in the detected temperature. For this reason, as shown in FIG. 8, due to the response delay described above, the heater temperature (detected temperature) may fluctuate up and down with respect to the reference temperature, and the heater temperature fluctuation (ripple) may increase.

  In addition, the second temperature region table includes a temperature region associated with a duty ratio of 0% (see FIG. 6). More specifically, as shown in FIG. 8, when the detected temperature reaches the reference temperature, the duty ratio is set to 0%, and a stop period in which the halogen heater 720 stops the heat generation operation occurs. Then, as described below, flicker due to a large current is likely to occur.

  As shown in FIG. 9, when the detected temperature reaches the reference temperature, the duty ratio is set to 0% (see FIG. 6), so the halogen heater 720 stops the heat generation operation (see timing T1 in FIG. 9). Due to the stop of the heat generation operation, the heater temperature immediately decreases. However, the detected temperature does not decrease immediately due to the above-described response delay, and continues to increase to a certain extent and then starts to decrease and falls below the reference temperature. For this reason, the stop time is prolonged due to the response delay.

  When the detected temperature falls below the reference temperature (see timing T2 in FIG. 9), the heat generation operation of the halogen heater 720 is resumed. At this time, since the heater temperature has greatly decreased during the stop period, flicker is caused by a large current flowing through the halogen heater 720 due to the restart of the heat generation operation. At this time, since the temperature difference ΔT is small, a relatively low duty ratio is set. Therefore, while the heater temperature gradually increases, the detected temperature continues to decrease due to a response delay (see the period from timing T2 to T3 in FIG. 9).

  Thereafter, when the temperature difference ΔT increases to some extent, a relatively high duty ratio is set, so that the detected temperature starts to rise rapidly (see timing T3 in FIG. 9). Thereafter, the detected temperature reaches the reference temperature, the duty ratio is set to 0%, the halogen heater 720 stops the heat generation operation again (see timing T4 in FIG. 9), and the same operation is repeated thereafter. As described above, when the temperature control based on the second temperature region table is executed, the ripple is increased due to the response delay, or flicker due to a large current is likely to occur.

  On the other hand, as will be described below, when the temperature control based on the first temperature region table is executed, it is possible to suppress the occurrence of flicker due to a ripple or a large current due to a response delay. As described above, in the first temperature range table, the temperature range closer to the target temperature is wider in the temperature range (see FIG. 5). Therefore, when the temperature difference ΔT is relatively large, the duty ratio is instantly changed with respect to a slight change in the detected temperature, so that the heater temperature and the detected temperature can be brought close to the reference temperature at an early stage. . On the other hand, when the detected temperature approaches the reference temperature (target temperature) and the temperature difference ΔT becomes relatively small, the duty ratio is not changed immediately for a slight change in the detected temperature. That is, when the temperature difference ΔT is relatively small, the response of changing the duty ratio to the change in the detected temperature is lower than when the temperature difference ΔT is relatively large. For this reason, the fluctuation | variation (ripple) of the heater temperature by response delay can be suppressed (refer FIG. 10).

  Moreover, the first temperature region table does not include a temperature region associated with a duty ratio of 0% (see FIG. 5). For this reason, as shown in FIG. 11, flicker due to a large current can be suppressed as much as the stop period does not occur.

  As described above, according to the present embodiment, in the first temperature region table, the first temperature region is wider than the second temperature region including a lower temperature than the first temperature region. For this reason, it is possible to suppress fluctuation (ripple) in the fixing temperature after the fixing temperature approaches the predetermined temperature while suppressing the time until the fixing temperature of the fixing unit 700 approaches the predetermined temperature from being prolonged. .

  In the first temperature region table, the target temperature is included in the temperature region associated with the duty ratio of 33%. For this reason, the fixing temperature of the fixing unit 700 after the fixing temperature has approached the above-mentioned temperature is suppressed while suppressing the time until the fixing temperature of the fixing unit 700 approaches a temperature suitable for forming a toner image on the sheet W from being prolonged. Variations can be suppressed.

  In the first temperature region table, the first temperature region having a duty ratio value less than 50% has a wider temperature range than the second temperature region having a duty ratio greater than 50%. For this reason, since the rapid temperature rise is suppressed compared with the case where the value of the duty ratio corresponding to the first temperature region is 50% or more, the rumble can be more reliably suppressed. In addition, the temperature can be reliably increased in a region where ribbles are less likely to occur than when the duty ratio value corresponding to the second temperature region is 50% or less.

  The first temperature region table includes a temperature region associated with a duty ratio of 33%. Therefore, flicker can be suppressed as compared with the case where the first temperature region table does not include the temperature region associated with the duty ratio of 33%. Further, the first temperature region table does not include a temperature region associated with a duty ratio of 50%. Accordingly, flicker can be suppressed as compared with the case where the first temperature region table includes the temperature region associated with the duty ratio of 50%. Furthermore, each value of the duty ratio included in the first temperature region table is a value at which the short-term flicker value (pst) becomes 1 or less when the value is set and the temperature control unit 920 is controlled. . Therefore, flicker can be more reliably suppressed.

  If the duty ratio is set to 0% during execution of temperature control of the halogen heater 720, the halogen heater 720 becomes low temperature, and the halogen heater 720 is energized again at that low temperature, thereby generating a large current. This may cause flicker. On the other hand, according to this embodiment, the first temperature region table does not include the temperature region associated with the duty ratio of 0%, and therefore flicker due to a large current can be suppressed. .

  The first temperature region table does not include a temperature region corresponding to a duty ratio of 0% for stopping the heat generation operation of the halogen heater 720. For this reason, for example, even if the setting information such as the type of the sheet W on which the toner image is formed does not satisfy the use condition of the first correspondence information, if the temperature control is executed based on the first temperature region table, the fixing unit There is a possibility that the temperature of 700 cannot be controlled normally. Therefore, according to the present embodiment, when the setting information does not satisfy the use conditions of the first temperature region table, the temperature control is executed based on the second temperature region table (S140 of FIG. 7: NO). As a result, it is possible to control the temperature of the fixing unit 700 when the setting information does not satisfy the use conditions of the first temperature region table, while preventing the temperature of the fixing unit 700 from being normally controlled by the first temperature region table. It can be suppressed that it cannot be performed.

  The technology disclosed in the present specification is not limited to the above-described embodiments, examples, and modifications, and can be realized with various configurations without departing from the spirit of the technology.

  In the above-described embodiment, the laser exposure type printer 10 that forms a monochrome image is exemplified as the image forming apparatus including the fixing unit. However, the present invention is not limited to this. For example, a color printer that can form a color image may be used. . Further, the image forming apparatus is not limited to a printer, and may be, for example, a copier or a multi-function machine that further includes a document reading unit such as a scanner in addition to the image forming unit. The image forming apparatus is not limited to a laser printer, but may be another electrophotographic image forming apparatus such as an LED printer.

  In the above embodiment, the belt 710 is made of metal, but is not limited to this. For example, the belt 710 may be formed of a resin material such as polyimide resin, and the belt 710 has heat resistance and flexibility. What was formed with the material is preferable.

  In the above-described embodiment, the halogen heater 720 is exemplified as the heater. However, the heater is not limited thereto, and for example, an infrared heater or a carbon heater may be used. Further, the heater is not limited to one that generates heat when supplied with power from an AC power source, and may be one that generates heat when supplied with power from a DC power source.

  In the above embodiment, the thermistor 770 is exemplified as the temperature sensor. However, the present invention is not limited to this, and for example, a thermostat or a temperature fuse may be used. The number of temperature sensors is not limited to the above embodiment, and can be set as appropriate according to the size of the fixing unit, for example.

  In the above embodiment, the non-volatile memory 840 is exemplified as the memory for storing the correspondence information. However, the non-volatile memory 840 is not limited to such a memory built in the printer 10, and an external memory connected to the printer 10 so as to be able to perform data communication is used. Good.

  In the above embodiment, a single CPU 810 is exemplified as the control unit, but the present invention is not limited to this. The control unit includes a plurality of CPUs, a CPU and a hardware circuit such as an ASIC, or a hardware circuit alone. May be good.

  In the above-described embodiment, the first temperature region table is exemplified as the correspondence information. However, the present invention is not limited to such a table, and an arithmetic expression indicating the correspondence relationship between each value of the duty ratio and each temperature region may be used. Further, each value of the duty ratio and each temperature region are not limited to those illustrated in FIG. 5, and are appropriately set according to the characteristics of 720, the target temperature of the fixing temperature, and the like.

  In the above embodiment, it is exemplified that both the detection temperature condition and the print setting condition are satisfied as the temperature control execution condition based on the first temperature region table. However, the execution condition is not limited to this, and the execution condition is the detection temperature condition. Alternatively, only one of the print setting conditions may be satisfied. Furthermore, the execution condition is that the power and frequency of the power supply to 10 are within the range guaranteed by the first temperature region table, and the specifications such as the heater power consumption are guaranteed by the first temperature region table. It may be within the range.

  For example, when the target temperature of 720 is set lower than when the toner image is formed on the sheet W, such as when the printer 10 is in a standby state, the duty ratio may be set to 0%. Flicker due to electric current hardly occurs. Therefore, the CPU 810 sets the target temperature for temperature control to a temperature lower than the target temperature for printing set in S120 of the temperature control process, for example, when the printer 10 is in a standby state waiting for a print command. If so, temperature control based on the second temperature region table may be executed.

DESCRIPTION OF SYMBOLS 10: Printer 600: Process part 700: Fixing part 720: Halogen heater 770: Thermistor 810: CPU 840: Non-volatile memory 920: Temperature control part ΔT: Temperature difference W: Sheet

Claims (12)

A fixing unit including a heater, a switching unit that switches the heater between an energized state and a non-energized state, and a temperature sensor;
A control unit;
Corresponding information for associating a plurality of values of duty ratio, which is an energization ratio at a predetermined time, and a plurality of temperature regions, respectively, and the smaller the value of the duty ratio, the higher the temperature of the plurality of temperature regions A memory storing correspondence information to be associated with the area;
With
The controller is
Obtaining a detected temperature based on a signal from the temperature sensor, controlling the switching unit with a value of the duty ratio corresponding to the temperature region including the detected temperature based on the correspondence information;
The image forming apparatus, wherein a first temperature region among the plurality of temperature regions in the correspondence information is wider than a second temperature region including a temperature lower than the first temperature region. The image forming apparatus according to claim 1,
Furthermore, it has a process part,
The first temperature region includes an average value of detected temperatures based on a signal from the temperature sensor when the process unit is forming a toner image on a sheet. The image forming apparatus according to claim 1, wherein:
In the correspondence information, the duty ratio value corresponding to the first temperature region is less than 50%. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises:
In the correspondence information, the duty ratio value corresponding to the second temperature region is greater than 50%. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises:
The image forming apparatus, wherein in the correspondence information, the plurality of values of the duty ratio include 33%. An image forming apparatus according to any one of claims 1 to 5, wherein
In the correspondence information, the plurality of values of the duty ratio do not include 50%. An image forming apparatus according to any one of claims 1 to 6,
The image forming apparatus, wherein the plurality of values of the duty ratio in the correspondence information are set such that a short-term flicker value (pst) is 1 or less. An image forming apparatus according to any one of claims 1 to 7,
The image forming apparatus, wherein the plurality of values of the duty ratio in the correspondence information are all greater than zero. The image forming apparatus according to claim 8, wherein
Furthermore, it has a process part,
The memory further stores second correspondence information that associates a plurality of values of the duty ratio including zero and a plurality of temperature regions,
The controller is
When the setting information when the process unit forms a toner image satisfies the use condition of the first correspondence information that is the correspondence information, the switching unit is controlled based on the first correspondence information;
An image forming apparatus that controls the switching unit based on the second correspondence information when the setting information does not satisfy the use condition. The image forming apparatus according to claim 8, wherein
The memory further stores second correspondence information associating a plurality of values of the duty ratio including zero and a plurality of temperature regions,
The controller is
When the target temperature of the heater is set to the first target temperature, the switching unit is controlled based on the first correspondence information that is the correspondence information,
An image forming apparatus, wherein when the target temperature of the heater is set to a second target temperature lower than the first target temperature, the switching unit is controlled based on the second correspondence information. A control method of a fixing unit including a heater, a switching unit that switches the heater between an energized state and a non-energized state, and a temperature sensor,
Obtaining a detected temperature based on a signal from the temperature sensor;
Corresponding information for associating a plurality of values of duty ratio, which is an energization ratio at a predetermined time, and a plurality of temperature regions, respectively, and the smaller the value of the duty ratio, the higher the temperature of the plurality of temperature regions Identifying the duty ratio value corresponding to the temperature region including the detected temperature with reference to correspondence information associated with the region; and
Controlling the switching unit with the specified value of the duty ratio,
The fixing unit control method, wherein a first temperature region among the plurality of temperature regions in the correspondence information is wider than a second temperature region including a temperature lower than the first temperature region. A control program for a fixing unit including a heater, a switching unit that switches the heater between an energized state and a non-energized state, and a temperature sensor,
Processing for obtaining a detected temperature based on a signal from the temperature sensor;
Corresponding information for associating a plurality of values of duty ratio, which is an energization ratio at a predetermined time, and a plurality of temperature regions, respectively, and the smaller the value of the duty ratio, the higher the temperature of the plurality of temperature regions A process of referring to correspondence information associated with a region and specifying a value of the duty ratio corresponding to the temperature region including the detected temperature;
A process of controlling the switching unit with the specified value of the duty ratio, and causing the fixing unit to execute,
The fixing unit control program in which the first temperature region is wider than the second temperature region including a temperature lower than the first temperature region among the plurality of temperature regions in the correspondence information.

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