Patent Application
20230341797
The present invention relates to an image forming apparatus, such as an electrophotographic printer or copier.
To reduce higher harmonics or flicker generated by an electric current through a heat generating element in a fixing unit included in an image forming apparatus, the waveform pattern of the electric current through the heat generating element is controlled. Japanese Patent Application Laid-Open Publication No. 2003-123941 discusses a technique in which while phase control is performed on at least one half-wave in a control period of an integral multiple of one half-wave of a commercial frequency, wavenumber control is performed on the other half-waves, which are fully energized or not energized.
The technique discussed in Japanese Patent Application Laid-Open Publication No. 2003-123941 is an example of a measure taken in the image forming apparatus against higher harmonics in the image forming apparatus including the fixing unit provided with a single heat generating element.
The present invention is directed to controlling a waveform pattern at a fixing unit including at least two or three heat generating elements each driven by a corresponding switch element different from one another, the combined resistance of each heat generating element being different from one another, as measures effective against higher harmonics, flicker, and temperature ripple.
To solve the issues, according to an aspect of the present invention, an image forming apparatus includes an image forming unit configured to form a toner image on a recording material, a fixing unit configured to fix the toner image formed on the recording material to the recording material by heating, the fixing unit including a heater including at least three heat generating groups configured to generate heat by power supplied from an alternating current power source, at least three switch elements each provided on a path via which the power is supplied from the alternating current power source to a corresponding heat generating group of the at least three heat generating groups, and a control unit configured to control the power supplied to each of the at least three heat generating groups by controlling the at least three switch elements, the control unit controlling the power of every one control period consisting of a plurality of continuous cycles of an alternating current from the alternating current power source. The control unit is configured to switch a heat generation distribution in the heater in a longitudinal direction of the fixing unit. A combined resistance of a first heat generating group connected to a first switch element of the at least three switch elements is a smallest of combined resistances of the at least three heat generating groups, and a combined resistance of a second heat generating group connected to a second switch element of the at least three switch elements is a second smallest of the combined resistances of the at least three heat generating groups. A waveform pattern of an electric current running through the first heat generating group and a waveform pattern of an electric current running through the second heat generating group, controlled by the control unit, are different from each other at at least one same timing in the one control period. A percentage of concurrence of a period of phase control of the first heat generating group and a period of phase control of the second heat generating group in the one control period is lower than or equal to 50%.
According to another aspect of the present invention, an image forming apparatus includes an image forming unit configured to form a toner image on a recording material, a fixing unit configured to fix the toner image formed on the recording material to the recording material by heating, the fixing unit including a heater including at least two heat generating groups configured to generate heat by power supplied from an alternating current power source, at least two switch elements each provided on a path via which the power is supplied from the alternating current power source to a corresponding heat generating group of the at least two heat generating groups, and a control unit configured to control the power supplied to each of the at least two heat generating groups by controlling the at least two switch elements, the control unit controlling the power of every one control period consisting of a plurality of continuous cycles of an alternating current from the alternating current power source. The control unit is configured to switch a heat generation distribution in the heater in a longitudinal direction of the fixing unit. A combined resistance of a first heat generating group connected to a first switch element of the at least two switch elements is a smallest of combined resistances of the at least two heat generating groups, and a combined resistance of a second heat generating group connected to a second switch element of the at least two switch elements is a second smallest of the combined resistances of the at least two heat generating groups. A waveform pattern of an electric current running through the first heat generating group and a waveform pattern of an electric current running through the second heat generating group, controlled by the control unit, are different from each other at at least one same timing in the one control period. A percentage of concurrence of a period of phase control of the first heat generating group and a period of phase control of the second heat generating group in the one control period is lower than or equal to 50%. A percentage of the period of the phase control of the first heat generating group and a percentage of the period of the phase control of the second heat generating group are each more than 50% of the one control period, and a waveform pattern in wavenumber control runs through at least one cycle of the alternating current.
Further features of the present invention will become apparent from the following description of embodiments (with reference to the attached drawings).
Forms to implement the present invention will be illustratively described below with reference to the accompanying drawings based on embodiments. The dimension, materials, shapes, and relative positional relationships of the constituent elements of the embodiments can be modified as appropriate based on the configuration of an apparatus or various types of condition to which the present invention is applied. The embodiments described below do not limit the scope of the present invention.
The image forming apparatus 100 includes a video controller 120 and a control unit 113. The video controller 120 as an acquisition unit that acquires information about an image to be formed on a recording material performs processing on image information and print instructions received from an external apparatus, such as a personal computer. The control unit 113 is connected to the video controller 120, and performs the control of units included in image forming apparatus 100 based on instructions from the video controller 120. In response to when the video controller 120 receives a print instruction from the external apparatus, an image forming process is carried out through the following operation.
In response to when the image forming apparatus 100 receives a print signal, a scanner unit 21 emits laser light modulated based on the image information, and scans the surface of a photosensitive drum 19 with a predetermined polarity charged by a charging roller 16. This forms a latent electrostatic image on the surface of the photosensitive drum 19. A developing roller 17 supplies toner to the latent electrostatic image to form a toner image on the surface of the photosensitive drum 19. On the other hand, the recording material (recording sheets) P stacked on a sheet feeding cassette 11 is fed by a pick-up roller 12 one by one, and conveyed toward a registration roller pair 14 by a conveying roller pair 13. The recording material P is conveyed to a transfer position formed by the photosensitive drum 19 and a transfer roller 20 from the registration roller pair 14 in synchronization with the timing when the toner image on the photosensitive drum 19 reaches the transfer position. The toner image on the photosensitive drum 19 is transferred onto the recording material P while the recording material P passes through the transfer position. After that, the recording material P is heated at a fixing unit 200, by which the toner image is fixed to the recording material P. The recording material P with the fixed toner image is discharged onto a tray provided in the upper part of the image forming apparatus 100 by conveyance roller pairs 26 and 27. A drum cleaner 18 clears the photosensitive drum 19 of the remaining toner. A sheet feeding tray 28 (manual feed tray) provided with a recording material regulating plate pair that is adjustable in the width direction according to the size of the recording material P is attached to deal with recording materials of sizes other than the standard paper sizes. A pick-up roller 29 feeds the recording material P from the sheet feeding tray 28. The image forming apparatus 100 includes a motor 30 that drives the fixing unit 200 and other units.
A control circuit 400 as an electric power control unit connected to a commercial alternating current power source 401 supplies power to the fixing unit 200. The photosensitive drum 19, the charging roller 16, the scanner unit 21, the developing roller 17, and the transfer roller 20 constitute an image forming unit that forms an image to be fixed on the recording material P. In the present embodiment, the photosensitive drum 19, the charging roller 16, a developing unit including the developing roller 17, and a cleaning unit including the drum cleaner 18 constitute a process cartridge 15, which is removably installable into the main body of the image forming apparatus 100.
In addition, the fixing unit 200 is removably installable into the image forming apparatus 100.
The film 202 is a heat-resistant film formed in a pipe shape, also called an endless belt or endless film. The material of the base layer is a heat-resistant resin, such as polyimide, or metal, such as stainless steel. An elastic layer that is, for example, a heat-resistant rubber can be provided on a surface of the film 202. The pressure roller 208 includes a core bar 209 made of, for example, iron or aluminum and an elastic layer 210 made of a silicone rubber by way of example. The heater 300 is held by a holding member 201 made of a heat-resistant resin. The holding member 201 also has a guiding function to guide the rotation of the film 202. The metal stay 204 is a metal stay to apply pressure generated by a spring not illustrated to the holding member 201.
The pressure roller 208 is rotated in the direction indicated by the arrow by power received from the motor 30. The rotation of the pressure roller 208 causes the film 202 to be driven by the pressure roller 208. The recording sheet P with the toner image to be fixed undergoes fixing process by being heated while the recording sheet P is being pinched and conveyed through the fixing nip N.
The heater 300 is heated by heat generating elements (heat generating resistors) 302a and 302b on a substrate 305 made of ceramic described below. A safety element 212 (
A configuration of the heater 300 according to the present embodiment will be described with reference to
As illustrated in
As illustrated in
The surface protective layer 308 as the back side layer 2 of the heater 300 is formed such that electrode E3-1 to E3-7, E4, and E5 are exposed, allowing connection of electrodes not illustrated from the back side of the heater 300. This allows the supply and supply control of power to each heat generating block independently. The division into the seven heat generating blocks provides four sheet conveyance areas like AREA1 to AREA4. In the present embodiment, AREA1 is assigned to A5 sheets, AREA2 for B5 sheets, AREA3 for A4 sheets, and AREA4 for Letter sheets. As the seven individual heat generating blocks are able to be controlled independently, the heat generating block to be supplied power is selected according to the size of the recording sheet P. Further, in the present embodiment, five triacs (switch elements) in a circuit illustrated in
The thermistors T1-1 to T1-4, and T1-7 as temperature detecting elements each to detect the temperature of the corresponding heat generating block of the heater 300 are arranged in a sliding surface layer 1 of the heater 300 (on the surface of the substrate 305 opposite to the surface on which the heat generating elements are provided). The thermistors T1-1 to T1-4, and T1-7 are each disposed in the corresponding heat generating block to mainly control the temperature of the heat generating block. As will be described with reference to
A sliding surface layer 2 of the heater 300 includes a surface protective layer 309 that is a glass coating having slidability. The surface protective layer 309 is provided on the sliding surface layer 1 except for both ends of the heater 300 to arrange the electric contacts of the electric conductors in the sliding surface layer 1.
A temperature detecting circuit of the thermistors will now be described. The electric conductor EG9 is connected to the grounding potential.
Vcc1 is distributed between resistors 451 to 454, and 457 each pulled up to Vcc1 and the respective thermistors T1-1 to T1-4, and T1-7 described in
The CPU 420 calculates power to be supplied, for example, using proportional-integral (PI) control, based on set temperatures (target temperatures) and detected temperatures of the thermistors T1-1 to T1-4, and T1-7. The CPU 420 generates timings of turning on the control signals FUSER1, FUSER2, FUSER3, FUSER4, and FUSER7 based on a timing signal ZEROX in synchronization with a zero potential of the alternating current power source 401 generated at a zero-crossing detector (ZEROX circuit) 421. As the heat generating elements 302a-3, 302b-3 and the heat generating elements 302a-5, 302b-5 are electrically connected to each other, the control signal FUSER3 can control power supplied to the heat generating elements 302a-3, 302b-3 and the heat generating elements 302a-5, 302b-5. Similarly, as the heat generating elements 302a-2, 302b-2 and the heat generating elements 302a-6, 302b-6 are electrically connected to each other, the control signal FUSER2 can control power supplied to the heat generating elements 302a-2, 302b-2 and the heat generating elements 302a-6, 302b-6. Further, the power values calculated by the CPU 420 are converted into duty ratios in Table 1, and the triacs 441 to 444, and 447 are controlled with phase angles (the control signals FUSER1, FUSER2, FUSER3, FUSER4, and FUSER7) each corresponding to a duty ratio. A table like Table 1 is set in the CPU 420. When phase control that supplies an electric current at a timing during a half cycle of an alternating current is performed, the control signals FUSER1, FUSER2, FUSER3, FUSER4, and FUSER7 are output based on the table. When wavenumber control that supplies or does not supply an electric current throughout a half cycle of an alternating current is performed, a binary control that performs energization for one full wave (duty ratio 100%) or an electric current interruption (duty ratio 0%) is performed.
As understood with reference to
Here, the heat generating elements 302a-1, 302b-1 connected to the triac 441 is defined as a heat generating group G441, and the heat generating elements 302a-2, 302b-2 and 302a-6, 302b-6 connected to the triac 442 are defined as a heat generating group G442. In addition, the heat generating elements 302a-3, 302b-3 and 302a-5, 302b-5 connected to the triac 443 (second switch element) are defined as a heat generating group G443 (second heat generating group). The heat generating elements 302a-4, 302b-4 connected to the triac 444 (first switch element) is defined as a heat generating group G444 (first heat generating group). Further, the heat generating elements 302a-7, 302b-7 connected to the triac 447 is defined as a heat generating group G447. In comparison between combined resistances of the heat generating groups G441 to G444, and G447, the combined resistance of the heat generating group G444 is the smallest, and the combined resistance of the heat generating group G443 is the second smallest. A large electric current running through a heat generating group with a small combined resistance exacerbates higher harmonics, flicker, and temperature ripple.
For this reason, in the present embodiment, measures are taken on the relationship between the waveform patterns of electric currents running through the heat generating group G444 with the smallest combined resistance and through the heat generating group G443 with the second smallest combined resistance of the combined resistances of the five heat generating groups G441 to G444, and G447 as illustrated in
In addition, as illustrated in
The waveform patterns of electric currents running through the five heat generating groups G441 to G444, and G447 are waveform patterns that satisfy at least Rule 1 and Rule 2. The following is a summary of Rule 1, Rule 2, Rule 3, and Rule 4. Rule 1: A waveform pattern of an electric current running through a heat generating group with the smallest combined resistance (first heat generating group) and a waveform pattern of an electric current running through a heat generating group with the second smallest combined resistance (second heat generating group) are different from each other at at least one phase angle in one control period (Rule 1).
With input powers of 0% to 75%, the phase angle in each phase control is adjusted based on the input power using waveform patterns described with reference to
A modification will now be described with reference to
A selection of a waveform pattern that satisfies Rule 1 and Rule 2, Rule 1, Rule 2, and Rule 3, or Rule 1, Rule 2, Rule 3, and Rule 4 while input power is changed by PID control allows reduction of higher harmonics, flicker, and temperature ripple.
A second embodiment will be described with reference to
The present embodiment is different from the first embodiment in that Rule 1, Rule 2, Rule 3, and Rule 4 do not apply to some percentages of input power for the waveform patterns illustrated in
With input powers of 0% to 25%, the phase control is selected throughout one control period. Whereas this waveform pattern is disadvantageous in that higher harmonics noise is produced, this waveform pattern is advantageous in terms of temperature ripple and flicker. Higher voltages of the commercial alternating current power source increases the power applied to a heat generating element, which results in a smaller percentage of input power for supplying a predetermined power in temperature control. This also increases the power in one cycle of the alternating current, making temperature ripple likely to occur. Thus, the selection of the phase control for a waveform pattern with low input power percentages of 0% to 25% allows reduction of temperature ripple.
With input powers of 25% to 50%, waveform patterns to which Rule 1, Rule 2, Rule 3, and Rule 4 described in the first embodiment all apply are selected.
With input powers of 50% to 100%, the waveform patterns to which Rule 1 and Rule 2 from among Rule 1, Rule 2, Rule 3, and Rule 4 described in the first y embodiment apply. While the waveform patterns are disadvantageous in temperature ripple, the waveform patterns are advantageous in terms of higher harmonics and flicker. The temperature at the heater 300 is controlled to stay at a target temperature. When power is supplied to the heat generating element, the temperature at the heater 300 gradually increases to a maximum, and the power supplied to the heat generating element settles at a level lower than a certain power. Large percentages of input power such as 50% to 100% are mainly used in a warm-up period before the temperature at the heater 300 reaches a maximum, and the waveform patterns that are advantageous in terms of flicker are selected.
As described above, Rule 1, Rule 2, Rule 3, and/or Rule 4 may be selected depending on which of higher harmonics reduction, flicker reduction, and temperature ripple reduction is treated as important while the percentage of input power is changed by PI control.
Lastly, the following is a summary of representative configurations. Numbers added to elements in the following configuration examples refer to corresponding elements described in the embodiments above. The correspondence relationships are merely examples for reference, and each element described below is not limited to the configuration of the corresponding element in the embodiments described above.
An image forming apparatus includes an image forming unit configured to form a toner image on a recording material, a fixing unit configured to fix the toner image formed on the recording material to the recording material by heating, the fixing unit including a heater including at least three heat generating groups configured to generate heat by power supplied from an alternating current power source, at least three switch elements each provided on a path via which the power is supplied from the alternating current power source to a corresponding heat generating group of the at least three heat generating groups, and a control unit configured to control the power supplied to each of the at least three heat generating groups by controlling the at least three switch elements, the control unit controlling the power of every one control period consisting of a plurality of continuous cycles of an alternating current from the alternating current power source. The image forming apparatus is configured to switch a heat generation distribution in the heater in the longitudinal direction of the fixing unit. The combined resistance of a first heat generating group connected to a first switch element of the at least three switch elements is the smallest of the combined resistances of the at least three heat generating groups, and the combined resistance of a second heat generating group connected to a second switch element of the at least three switch elements is the second smallest of the combined resistances of the at least three heat generating groups. A waveform pattern of an electric current running through the first heat generating group and a waveform pattern of an electric current running through the second heat generating group controlled by the control unit are different from each other at at least one same timing in the one control period. The percentage of coincidence of the period of phase control of the first heat generating group and the period of phase control of the second heat generating group in the one control period is lower than or equal to 50%.
In the image forming apparatus according to Configuration Example A1, in the waveform pattern controlled by the control unit, a percentage of the period of the phase control to the period of the one control period is higher than 50% for both the first heat generating group and the second heat generating group, and at least the period of one cycle of alternating current is the wavenumber control pattern.
In the image forming apparatus according to Configuration Example A2, in the waveform pattern controlled by the control unit, the period of the wavenumber control for the first heat generating group and the period of the wavenumber control for the second heat generating group are each divided such that no divided period continues longer than a half cycle of the alternating current.
In the image forming apparatus according to any one of Configuration Examples A1 to A3, out of the at least three heat generating groups, a waveform pattern of an electric current of at least one heat generating group other than the first heat generating group and the second heat generating group is identical to any one of the waveform pattern of the electric current running through the first heat generating group and the waveform pattern of the electric current running through the second heat generating group.
In the image forming apparatus according to Configuration Example A4, the at least one heat generating group other than the first heat generating group and the second heat generating group belongs to any one of a first large group to which the first heat generating group belongs and a second large group to which the second heat generating group belongs such that a difference between the combined resistance of the first large group and the combined resistance of the second large group is smallest.
In the image forming apparatus according to any one of Configuration Examples A1 to A3, the waveform pattern of the electric current running through the first heat generating group and the waveform pattern of the electric current running through the second heat generating group, controlled by the control unit, are each set at a level lower than or equal to a predetermined level of input power.
In the image forming apparatus according to any one of Configuration Examples A1 to A3, the heater includes a substrate provided with the at least three heat generating groups.
In the image forming apparatus according to Configuration Example A7, the at least three heat generating groups are arranged in the longitudinal direction.
In the image forming apparatus according to Configuration Example A8, the at least three heat generating groups each include two electric conductors arranged in the longitudinal direction and a heat generating element connected between the two electric conductors.
In the image forming apparatus according to Configuration Example A9, the fixing unit includes a film in a pipe shape and a roller in contact with the periphery of the film. The heater is disposed in the internal space surrounded by the film. The heater and the roller sandwich the film, and form a fixing nip through which the recording material is pinched and conveyed between the film and the roller.
An image forming apparatus includes an image forming unit configured to form a toner image on a recording material, a fixing unit configured to fix the toner image formed on the recording material to the recording material by heating, the fixing unit including a heater including at least two heat generating groups configured to generate heat by power supplied from an alternating current power source, at least two switch elements each provided on a path via which the power is supplied from the alternating current power source to a corresponding heat generating group of the at least two heat generating groups, and a control unit configured to control the power supplied to each of the at least two heat generating groups by controlling the at least two switch elements, the control unit controlling the power of every one control period consisting of a plurality of continuous cycles of an alternating current from the alternating current power source. The image forming apparatus is configured to switch a heat generation distribution in the heater in the longitudinal direction of the fixing unit. The combined resistance of a first heat generating group connected to a first switch element of the at least two switch elements is the smallest of the combined resistances of the at least two heat generating groups, and the combined resistance of a second heat generating group connected to a second switch element of the at least two switch elements is the second smallest of the combined resistances of the at least two heat generating groups. A waveform pattern of an electric current running through the first heat generating group and a waveform pattern of an electric current running through the second heat generating group, controlled by the control unit, are different from each other at at least one phase angle in the one control period. The percentage of coincidence of the period of phase control of the first heat generating group and the period of phase control of the second heat generating group in the one control period is lower than or equal to 50%. The percentage of the period of the phase control of the first heat generating group and the percentage of the period of the phase control of the second heat generating group are each more than 50% of the one control period, and a waveform pattern in wavenumber control appears through at least one cycle of the alternating current.
In the image forming apparatus according to Configuration Example B1, in the one control period, the period of the waveform pattern controlled by the control unit in the wavenumber control of the first heat generating group and the period of the waveform pattern controlled by the control unit in the wavenumber control of the second heat generating group are each divided such that no divided period continues longer than a half cycle of the alternating current.
In the image forming apparatus according to Configuration Example B1 or B2, the heater includes at least one heat generating group other than the first heat generating group and the second heat generating group. A waveform pattern of an electric current running through the at least one heat generating group other than the first heat generating group and the second heat generating group is identical to any one of the waveform pattern of the electric current running through the first heat generating group and the waveform pattern of the electric current running through the second heat generating group.
In the image forming apparatus according to Configuration Example B1 or B2, the waveform pattern of the electric current running through the first heat generating group and the waveform pattern of the electric current running through the second heat generating group, controlled by the control unit, are each set at a level lower than or equal to a predetermined level of input power.
In the image forming apparatus according to Configuration Example B1 or B2, the heater includes a substrate provided with the at least two heat generating groups.
In the image forming apparatus according to Configuration Example B5, the at least two heat generating groups are arranged in the longitudinal direction.
In the image forming apparatus according to Configuration Example B6, the at least two heat generating groups each include two electric conductors arranged in the longitudinal direction and a heat generating element connected between the two electric conductors.
In the image forming apparatus according to Configuration Example B7, the fixing unit includes a film in a pipe shape and a roller in contact with the periphery of the film. The heater is disposed in the internal space surrounded by the film. The heater and the roller sandwich the film, and form a fixing nip through which the recording material is pinched and conveyed between the film and the roller.
While the present invention has been described with reference to embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is defined by the scope of the following claims.
This application claims the benefit of Japanese Patent Application No. 2022-070535, filed Apr. 22, 2022, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-070535 | Apr 2022 | JP | national |
