JP2008257029A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of reducing noise in a low frequency area without hindering miniaturization of the image forming apparatus caused by adding a noise elimination part such as a noise filter inexpensively all the more because the noise elimination part need not be added while achieving reduction of power loss when the load of the image forming apparatus is small. <P>SOLUTION: It is basic to set the switching frequency of a power supply section 12 to low switching frequency when the image forming apparatus A is in a low load state, and set it to high switching frequency when the apparatus A is in a high load state. When turning on a fixing heater H, if the apparatus A is in the low load state, the low switching frequency is changed to the high switching frequency so as to permit turning on the fixing heater after the change of the switching frequency, and if the apparatus A is in the high load state, the high switching frequency is maintained to permit turning on the heater before turning on the fixing heater H. When turning off the heater, the switching frequency set before turning on the heater is set after turning off the heater. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multi-function machine combining two or more of these, and in particular, receives an AC power supply from an AC power supply, forms a toner image, and transfers it to a recording medium. The toner image is fixed to the recording medium under heat and pressure by passing the recording medium between a fixing rotator heated by a fixing heater and a pressure rotator facing the fixing rotator. The present invention relates to an image forming apparatus capable of

  An AC power supply is received from an AC power source, and a toner image is formed and transferred to a recording medium. In an image forming apparatus in which the toner image can be fixed to the recording medium under heat and pressure by passing it through, it is usually supplied from an AC power source to supply DC power required by each part of the image forming apparatus. AC / DC converting means for converting the AC voltage to be converted into DC voltage is provided.

  In addition, when performing image formation or the like, of course, even during standby when image formation or the like is not performed, temperature control is generally performed to control the temperature of the fixing heater toward a predetermined temperature. In temperature control or the like, a lighting or turn-off instruction is issued from a means for instructing turning on or off the fixing heater in order to turn on or turn off the fixing heater, and a switch means for a power supply circuit to the fixing heater based on the instruction Turns on or off the fixing heater.

  In such an image forming apparatus, when the load of the image forming apparatus is small (when in a low load state), such as during standby, the switching frequency at the time of the AC / DC conversion is low in order to realize energy saving. In some cases, a method of reducing the power loss by shifting the direction to reduce the number of times of switching is employed.

In Japanese Patent Laid-Open No. 9-140128, conversion efficiency at the time of operation standby is improved by controlling the oscillation frequency of the switching power supply device by a microcomputer that recognizes or controls the operation state of the device. A switching power supply device that can reduce power consumption is described.
JP-A-9-140128

  However, if the switching frequency in the AC / DC conversion is shifted to a lower side to reduce the number of switching in order to realize energy saving, the generated noise shifts to the lower frequency side, and the noise in the lower frequency region increases.

  On the other hand, since a steep current flows when the fixing heater is turned on, noise is generated in a low frequency region. Furthermore, when the heater is turned on by non-zero cross-on control (for example, phase control), the noise level becomes high.

  When the load of the image forming apparatus is small (when in a low load state), such as during standby, the fixing heater is used when the switching frequency during the AC / DC conversion is shifted to a lower side for energy saving measures. When the is turned on, the low frequency region noise caused by shifting the switching frequency to the lower side overlaps with the low frequency region noise generated by lighting the fixing heater, and the low frequency noise level becomes high. This may cause harmful effects on the surroundings and disturbing radio waves, which may cause a situation in which noise regulations in each country cannot be satisfied.

  For this, it is conceivable to add noise countermeasure parts such as a noise filter. However, the noise countermeasure parts increase the cost of the image forming apparatus or hinder downsizing of the image forming apparatus. .

Therefore, the present invention receives an AC power supply from an AC power source, forms a toner image, transfers it to a recording medium, and heats the recording medium by a fixing heater, and a pressurization facing the fixing rotator. The toner image can be fixed to the recording medium under heat and pressure by passing between the rotating body,
A heater on / off instruction means for instructing on / off of the fixing heater;
Switch means for turning on or off the fixing heater based on an instruction from the heater on / off instruction means;
AC / DC conversion means for converting AC voltage from the AC power source into DC voltage;
A switching frequency changing means capable of switching and switching between a predetermined low switching frequency and a predetermined high switching frequency higher than the predetermined frequency for switching at the time of voltage conversion by the AC / DC converting means;
When the image forming apparatus is in a predetermined low load state, the switching frequency changing means sets the low switching frequency, and when the image forming apparatus is in a predetermined high load state, the switching frequency changing means is set to the high frequency. On the premise of an image forming apparatus including a switching frequency control means for setting a switching frequency, it is an object to provide the next image forming apparatus.

  That is, the present invention reduces power loss when the load on the image forming apparatus is small, and does not require the addition of noise countermeasure components such as a noise filter, so that the cost can be reduced and the addition of noise countermeasure components. It is an object of the present invention to provide an image forming apparatus capable of reducing noise in a low frequency region without hindering downsizing of the image forming apparatus.

  “Switching” in “frequency switching at the time of voltage conversion by AC / DC conversion means” is to turn on / off the semiconductor switch in order to output a stable DC voltage, and then rectify the desired DC voltage. Get.

The present inventor has conducted research to solve the above-mentioned problems, and has obtained the following knowledge to complete the present invention.
That is, when the fixing heater is turned on by the switch means, when the image forming apparatus is in the low load state before the fixing heater is turned on, the switching frequency changing means is switched from the low switching frequency to the high switching frequency. If the switching frequency is changed so that the noise in the low frequency region due to the switching frequency is reduced and the fixing heater is turned on after the change, the fixing heater is turned on while the switching frequency remains at the low switching frequency. In this case, it is possible to avoid the overlap between the low frequency region noise due to the low switching frequency and the low frequency region noise generated by lighting the fixing heater, and the generation of noise in the low frequency region is suppressed accordingly.

  On the other hand, when the image forming apparatus is in the high load state, the switching frequency changing means has already set the high switching frequency, so if the fixing heater is turned on while maintaining the switching frequency, the switching frequency is changed. When the fuser heater is turned on with a low switching frequency, there is no overlap between the low frequency region noise caused by the low switching frequency and the low frequency region noise generated by the fuser heater lighting. Is done.

  When the fixing heater is turned off, after the fixing heater is turned off, the switching frequency changing means sets the switching frequency before the fixing heater is turned on, so that even if the switching frequency before the fixing heater is turned on is a low switching frequency, low switching The overlap between the low-frequency region noise caused by the frequency and the low-frequency region noise that may occur even when the fixing heater is turned off is avoided, so the generation of the low-frequency region noise is suppressed and the return to the low switching frequency is achieved. Thus, the power loss can be reduced accordingly.

  Thus, while reducing the power loss when the load of the image forming apparatus is small, the image forming apparatus can be made inexpensively without the need for additional noise countermeasure parts such as a noise filter, and by adding noise countermeasure parts. It is possible to provide an image forming apparatus capable of reducing noise in a low frequency region without hindering downsizing.

Based on the above knowledge, the present invention provides:
An AC power supply is received from an AC power source, a toner image is formed and transferred to a recording medium, and the recording medium is heated by a fixing heater between a fixing rotator and a pressure rotator facing the fixing rotator. The toner image can be fixed to the recording medium under heat and pressure by passing through
A heater on / off instruction means for instructing on / off of the fixing heater;
Switch means for turning on or off the fixing heater based on an instruction from the heater on / off instruction means;
AC / DC conversion means for converting AC voltage from the AC power source into DC voltage;
A switching frequency changing means capable of switching and switching between a predetermined low switching frequency and a predetermined high switching frequency higher than the predetermined frequency for switching at the time of voltage conversion by the AC / DC converting means;
When the image forming apparatus is in a predetermined low load state, the switching frequency changing means sets the low switching frequency, and when the image forming apparatus is in a predetermined high load state, the switching frequency changing means is set to the high frequency. In an image forming apparatus including a switching frequency control means for setting a switching frequency,
The switching frequency control means prior to lighting the fixing heater when the fixing heater is turned on by the switch means,
When the image forming apparatus is in the low load state, the switching frequency changing unit is changed to change the switching frequency from the low switching frequency to the high switching frequency, and the fixing heater is turned on after the change,
When the image forming apparatus is in the high load state, the switching frequency changing unit is allowed to maintain the high switching frequency to allow the fixing heater to be turned on,
When the fixing heater is turned off by the switch means, an image forming apparatus is provided in which the switching frequency changing means sets a switching frequency before the fixing heater is turned on after the fixing heater is turned off.

According to the present invention, an AC power supply is received from an AC power source, a toner image is formed and transferred to a recording medium, and the recording medium is heated by a fixing heater, and the pressure opposite to the fixing rotation body The toner image can be fixed to the recording medium under heat and pressure by passing between the rotating body,
A heater on / off instruction means for instructing on / off of the fixing heater;
Switch means for turning on or off the fixing heater based on an instruction from the heater on / off instruction means;
AC / DC conversion means for converting AC voltage from the AC power source into DC voltage;
A switching frequency changing means capable of switching and switching between a predetermined low switching frequency and a predetermined high switching frequency higher than the predetermined frequency for switching at the time of voltage conversion by the AC / DC converting means;
When the image forming apparatus is in a predetermined low load state, the switching frequency changing means sets the low switching frequency, and when the image forming apparatus is in a predetermined high load state, the switching frequency changing means is set to the high frequency. An image forming apparatus including a switching frequency control means for setting a switching frequency,
While reducing the power loss when the load on the image forming device is small, it is not necessary to add noise countermeasure parts such as a noise filter, so it is cheaper and the size of the image forming apparatus can be reduced by adding noise countermeasure parts. Therefore, it is possible to provide an image forming apparatus capable of reducing noise in a low frequency region without hindering the conversion to low frequency.

An image forming apparatus according to an embodiment of the present invention includes:
An AC power supply is received from an AC power source, a toner image is formed and transferred to a recording medium, and the recording medium is heated by a fixing heater between a fixing rotator and a pressure rotator facing the fixing rotator. An image forming apparatus capable of fixing the toner image to the recording medium by heating and pressurizing.

This image forming apparatus
A heater on / off instruction means for instructing on / off of the fixing heater;
Switch means for turning on or off the fixing heater based on an instruction from the heater on / off instruction means;
AC / DC conversion means for converting AC voltage from the AC power source into DC voltage;
A switching frequency changing means capable of switching and switching between a predetermined low switching frequency and a predetermined high switching frequency higher than the predetermined frequency for switching at the time of voltage conversion by the AC / DC converting means;
When the image forming apparatus is in a predetermined low load state, the switching frequency changing means sets the low switching frequency, and when the image forming apparatus is in a predetermined high load state, the switching frequency changing means is set to the high frequency. Switching frequency control means for setting the basic switching frequency for setting the switching frequency.

However, the switching frequency control means controls the switching frequency as follows regardless of the basic switching frequency setting.
That is, prior to lighting the fixing heater when the fixing heater is turned on by the switch means,
When the image forming apparatus is in the low load state, the switching frequency changing unit is changed to change the switching frequency from the low switching frequency to the high switching frequency, and the fixing heater is turned on after the change,
When the image forming apparatus is in the high load state, the switching frequency changing unit is allowed to maintain the high switching frequency to allow the fixing heater to be turned on,
When the fixing heater is turned off by the switch means, after the fixing heater is turned off, the switching frequency changing means is made to set a switching frequency before the fixing heater is turned on.

  According to this image forming apparatus, when the fixing heater is turned on by the switch means, when the image forming apparatus is in the low load state before the fixing heater is turned on, the switching frequency is changed from the low switching frequency to the switching frequency changing means. The switching frequency is changed to the switching frequency, thereby reducing the noise in the low frequency region due to the switching frequency, and the fixing heater is turned on after the change.

  On the other hand, when the image forming apparatus is in the high load state, since the switching frequency changing means has already set the high switching frequency, the fixing heater is turned on while maintaining the switching frequency.

  As described above, even when the image forming apparatus is in a low load state or a high load state, when the fixing heater is turned on, it is possible to avoid lighting the fixing heater in a state where the switching frequency is low. As a result, the overlap between the low frequency region noise caused by the low switching frequency and the low frequency region noise generated by lighting the fixing heater can be avoided, so that the generation of the low frequency region noise is suppressed accordingly.

  Further, when the fixing heater is turned off, after the fixing heater is turned off, the switching frequency changing means sets the switching frequency before the fixing heater is turned on. Therefore, even if the switching frequency before the fixing heater is turned on is low, Since the overlap between the low-frequency region noise caused by the switching frequency and the low-frequency region noise that may occur even when the fixing heater is turned off is avoided, the generation of the low-frequency region noise is suppressed accordingly, and the switching to the low switching frequency is reduced. By returning, the power loss can be reduced accordingly.

  When the image forming apparatus is in the low load state, the switching frequency control unit is configured to change the switching frequency changing unit before a heater turn-off instruction by the heater turn-on / off instruction unit after a predetermined time elapses after the heater is turned on. The low switching frequency may be set.

  Here, as the “time” in “after the elapse of a predetermined time since the heater lighting”, as a representative example, the low frequency noise caused by the low switching frequency and the low frequency noise caused by the heater lighting are overlapped. This is the time during which the increase in the low frequency noise level can be suppressed and the low frequency noise level can be suppressed below a predetermined allowable level.

  As described above, when the image forming apparatus is in a low load state, the low switching frequency is set to the switching frequency changing means before the heater turn-off instruction means by the heater turn-on / off instruction means after a predetermined time elapses after the heater is turned on. By setting it, it is possible to suppress power loss.

  When the image forming apparatus is in the low load state, the switching frequency control means sets the low switching frequency after elapse of a predetermined time since the heater is turned on. The switching means changes the switching frequency from the low switching frequency to the high switching frequency before the fixing heater is turned off by the switch means, and the fixing heater is turned off after the change. After the heater is turned off, the switching frequency changing means may set a low switching frequency before the fixing heater is turned on.

  By doing so, it is possible to avoid the overlap of the low frequency region noise caused by the low switching frequency and the low frequency region noise that may be generated even when the fixing heater is turned off. The loss power can be reduced by returning to the low switching frequency.

Examples of the determination by the switching frequency control means as to whether the image forming apparatus is in the low load state or the high load state include the following first and second determinations.
(1) First determination The switching frequency control unit compares the operation mode of the image forming apparatus with a predetermined reference operation mode, and the operation mode is subjected to a load less than the load in the reference operation mode. When the mode is the mode, it is determined that the load is low, and when the operation mode is an operation mode where a load larger than the load in the reference operation mode is applied, it is determined that the load is high.

(2) Second determination The switching frequency control unit is configured to determine whether the image forming apparatus is in the low load state or the high load state by the switching frequency changing unit. Is compared with a predetermined reference frequency, when the current switching frequency is equal to or lower than the reference frequency, it is determined that the load is low, and when the current switching frequency is higher than the reference frequency, it is determined that the load is high.

  In the “first determination”, the reference operation mode may be, for example, a standby state of the image forming apparatus. In this case, an operation mode in which a load equal to or lower than the load in the standby state is set as the low load state, and an operation mode in which a load larger than the load in the standby state is set as the high load state.

  In addition, the operation mode in which a load larger than the load in the standby state includes at least a print mode for forming a toner image on a recording medium, an image reading mode for reading a document image, and a facsimile mode for exerting a facsimile function. Can do.

  Examples of the image forming apparatus in this case include an image reading apparatus that also serves as a copying machine, a printer, and a facsimile machine.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a front view of an example of an image forming apparatus according to the present invention.
An image forming apparatus A shown in FIG. 1 is a copying machine including an image reading device S, but also has a function of a facsimile machine and a printer function for printing in accordance with image information supplied from a computer or the like.

  The image forming apparatus A in FIG. 1 includes a portion CS having an image forming portion B and recording medium accommodating cassettes C1 to C4 below the image forming portion B. The image reading device S is located above the image forming unit B. The image reading apparatus S is equipped with an automatic document feeder ADF and an operation panel PA of the image forming apparatus.

The transport device ADF can be opened and closed, and also serves as a cover that covers a document placed on the glass plate g1 of the image reading device S.
The operation panel PA includes a key group Ke such as a start key for instructing copy image formation and facsimile transmission, a numeric keypad for setting the number of image formations, and the like, and a liquid crystal display unit Dp. The liquid crystal display unit Dp is used for reflecting key operations by the user, displaying an instruction menu for the user, displaying information from the image forming unit B, and the like.

  The image reading device S can optically read an image of a document placed stationary on the platen glass g1, and is conveyed from the document placing tray a1 by the automatic document feeder ADF to the document discharge tray a2. It is also possible to optically read an image of a document that is ejected and moves along the document panning glass plate g2 of the image reading device S in the middle thereof.

  The image data read by the image reading device S is sent to the image forming unit B, where it is used for image formation or for facsimile transmission. Image data transmitted from a computer (not shown) or the like is sent to the image forming unit B and used for image formation there.

  The image forming unit B forms a toner image on a recording medium by electrophotography. The image forming section B of this example is formed by each image forming unit, in which a yellow image forming unit Y, a magenta image forming unit M, a cyan image forming unit C, and a black image forming unit K are arranged along the intermediate transfer belt b. Toner image is primarily transferred to the intermediate transfer belt b, and the multiple toner image that is primarily transferred and superimposed on the belt b is secondarily transferred to a recording medium (recording paper or the like) P supplied from any cassette. A tandem color image forming unit that can be fixed by the fixing device F to obtain a color image.

The image forming unit B can form a monochrome image, or can form an image using any two or three image forming units.
The image forming unit B may be another type of color image forming unit or a monochrome image forming unit.

  The fixing device F includes a fixing roller f1 incorporating a halogen lamp heater H as a fixing heater, and a pressure roller f2 facing the fixing roller f1, and the fixing roller f1 has a toner image fixing temperature or the like when the halogen lamp heater H is turned on. Heated to a predetermined temperature. The temperature of the fixing roller f1 is detected by a temperature detector (thermistor in this example) sm. The temperature control of the fixing roller f1 will be described later.

  The recording medium P onto which the toner image has been secondarily transferred in the image forming unit B is passed between the fixing roller f1 and the pressure roller f2, thereby fixing the toner image under heat and pressure. Discharged on T.

FIG. 2 is a block diagram schematically showing a control circuit of the image forming apparatus A of FIG.
The control circuit in FIG. 2 includes a control unit 2 that controls the entire image forming apparatus.
The control unit 2 includes a CPU (Central Processing Unit) 21, a ROM storing a program and a memory 22 including a RAM for exchanging data with the CPU, an input / output interface 23 that mediates between the external device and the CPU. Etc.

  The operation panel PA is connected to the control unit 2 via the interface 23, and the detected temperature information of the thermistor sm of the fixing device F is input to the control unit 2 via the interface 23, and the image forming apparatus A operates. Each unit (such as various motors) is configured to operate at a predetermined timing based on an instruction from the control unit 2.

  The control circuit of FIG. 2 also includes a power supply unit 1. The power supply unit 1 includes a heater lighting power supply unit (heater lighting power supply circuit) 11 for turning on and off the halogen lamp heater H of the fixing device F and a low voltage power supply unit 12.

  The heater lighting power supply unit 11 is a power supply circuit for supplying AC power supplied from an AC power supply (not shown) to the halogen lamp heater H. The heater H is turned on and off by turning on and off the circuit. The switch unit 11S is included. Although not limited thereto, the switch unit 11S is composed of a triac (not shown) that is turned on / off via a phototriac coupler (not shown) in accordance with an instruction from the control unit 2.

  The controller 2 turns on / off the halogen lamp heater H based on the detected temperature information from the thermistor sm that detects the temperature of the fixing roller f1, and sets the temperature of the fixing roller f1 to a predetermined temperature (for example, toner in the image forming mode). A temperature control unit for controlling the image to a fixing temperature for fixing the image on the recording medium. The temperature control unit includes a heater turn-on / off instruction unit that instructs the heater H to be turned on or off.

  The power supply unit 1 also includes an AC / DC converter that converts an AC voltage supplied from an AC power source (not shown) into a DC voltage. Here, the AC / DC conversion unit is a low-voltage power supply unit 12 that converts a DC low voltage (25V, 5V, etc.) required by each unit of the image forming apparatus.

  The power supply unit 1 also includes a switching frequency setting unit 121 that sets a frequency to be switched at the time of voltage conversion by the low-voltage power supply unit 12. In other words, the switching frequency setting unit 121 is a switching frequency changing unit, and can be switched and set between a predetermined low switching frequency and a predetermined high switching frequency higher than the predetermined frequency.

  Here, “switching” in “frequency switching at the time of voltage conversion by the power supply unit 12” is, as described above, performing on / off control of the semiconductor switch to obtain a stable DC voltage, and then rectifying. Thus, a desired DC voltage is obtained.

  In this example, the low switching frequency suppresses power loss when the load of the image forming apparatus A is small (when the image forming apparatus A is in the standby state or the sleep mode) (when in the low load state (low load mode)). In this example, this is set as an energy saving set frequency and is set to about 10 kHz.

  Here, the “sleep mode” of the image forming apparatus A is a low power state for the purpose of energy saving that is entered when there is no access to the image forming apparatus for a certain period of time. In the image forming apparatus A, the fixing lamp heater is turned off. In this state, unnecessary power other than control of the image forming apparatus A is turned off, such as turning off the power supply for supplying power to the drive system. However, when there is an access such as an image formation instruction, a power-on instruction is issued as necessary for the load that is turned off in the sleep mode from the controller 2 to which power is supplied.

The high switching frequency is such that the operation mode of the image forming apparatus A is a print mode in which a toner image is formed on a recording medium, an image reading mode in which an original image is read by the image reading apparatus S, and a facsimile mode in which the image forming apparatus performs a facsimile function. This is set when the image forming apparatus A is in a high load state (high load mode). In this example, this is the normal set frequency, and is set to about 100 kHz.
The power supply switching frequency detection unit 122 indicated by a broken line with respect to the power supply unit 12 in FIG. 2 will be described later.

  The control unit 2 also includes a control unit for the switching frequency, and a heater turn-on instruction (on instruction) or a heater turn-off instruction (off instruction) from the heater turn-on / off instruction unit in the control unit 2 once controls the switching frequency. Is transmitted to the switch section 11S of the heater lighting power supply section 11 through the input / output interface 23 at a predetermined timing.

  The switching frequency control unit in the control unit 2 basically causes the switching frequency setting unit 121 to set the low switching frequency (energy saving set frequency 10 kHz level) when the image forming apparatus A is in a low load state, thereby forming an image. When the device A is in a high load state, the switching frequency setting unit 121 sets the high switching frequency (normally set frequency of 100 kHz level).

However, the switching frequency control unit in the control unit 2 controls the switching frequency as follows regardless of the above basic switching frequency setting in order to suppress the generation of low frequency noise.
That is, the switching frequency control unit prior to lighting the heater when the halogen lamp heater H is turned on by the switch unit 11S,
When the image forming apparatus is in a low load state (low load mode), the switching frequency setting unit 121 switches the switching frequency from the low switching frequency (10 kHz level) to the high switching frequency (100 kHz level), and after the change Allow the heater H to turn on,
When the image forming apparatus is in a high load state (high load mode), the switching frequency setting unit 121 maintains the high switching frequency (100 kHz level) that is already set and allows the heater H to be turned on.

  When the halogen lamp heater H is turned off by the switch unit 11S, the switching frequency setting unit 121 is set to the switching frequency before the heater is turned on after the heater H is turned off.

The switching frequency control described above is summarized in the following table.

  The control operation of the switching frequency related to the heater lighting by the control unit 2 described above is shown in FIG. As shown in FIG. 3, it is first determined whether or not the image forming apparatus A is in a low load state (step S1). If the image forming apparatus A is in a high load state, the switching frequency is set to a normal setting frequency (step S4). If there is no lighting instruction (ON instruction), the switching frequency is set to the energy saving setting frequency (step S3). If there is a lighting instruction, the switching frequency is set to the normal setting frequency. Is changed and set (step S4).

  A timing chart of the switching frequency control described above is shown in FIG. FIG. 4 also shows an example in which the switching frequency is gradually changed when the heater is turned on and off. The frequency change may be performed gently rather than steeply.

  FIG. 6 shows that when the image forming apparatus is in a low load state, and therefore when the switching frequency is the energy saving setting frequency, when the lamp heater H is turned on with the switching frequency unchanged, the switching frequency is the energy saving setting frequency. The low-frequency noise and the low-frequency noise generated due to the heater H lighting are overlapped, and the low-frequency noise exceeds a predetermined allowable noise value.

  On the other hand, FIG. 7 shows that when the image forming apparatus is in a low load state, and therefore the switching frequency is the energy saving setting frequency, the switching frequency is changed from the energy saving setting frequency to the normal setting frequency before the heater H is turned on. If the switching frequency remains at the energy-saving setting frequency, the overlap between the low frequency region noise generated and the low frequency region noise generated due to the heater H lighting is avoided, and the low frequency noise is determined in advance. It is exemplified that the noise is suppressed to be equal to or less than the allowable noise value.

  As described above, in the image forming apparatus A of FIG. 1, the switching frequency is in a low switching frequency state when the heater H is turned on regardless of whether the image forming apparatus A is in a low load state or a high load state. In this case, it is possible to avoid turning on the fixing heater, thereby avoiding the overlap between the low frequency region noise caused by the low switching frequency and the low frequency region noise generated by turning on the heater H, so that the low frequency region noise is generated accordingly. Is suppressed.

  Further, when the fixing heater is turned off, the switching frequency setting unit 121 sets the switching frequency before the heater H is turned on after the fixing heater is turned off, so that even if the switching frequency before the heater is turned on is a low switching frequency, the low switching frequency is set. The low frequency region noise caused by the low frequency region noise that may be generated even when the heater H is turned off can be avoided, and the generation of the low frequency region noise can be suppressed and the return to the low switching frequency. In addition, power loss can be reduced.

  The control shown in FIG. 5 can also be adopted as a control slightly different from the switching frequency control described above. That is, when the image forming apparatus A is in a low load state, the switching frequency control unit in the control unit 2 waits for a predetermined time after the heater H is turned on and before the heater turn-off instruction by the heater turn-off / instruction unit. In the meantime, the switching frequency setting unit 121 may set a low switching frequency (energy saving set frequency).

  Here, “The predetermined time from heater lighting is to suppress the increase of the low frequency noise level due to the overlap of the low frequency noise caused by the low switching frequency and the low frequency noise caused by the heater lighting. Any time that can be suppressed to a predetermined allowable level or less may be used.

  As described above, when the image forming apparatus A is in a low load state, the switching frequency setting unit 121 has a low switching frequency after the heater H has been turned on and before a heater turn-off instruction by the heater turn-off / instruction unit. By setting, power loss can be reduced accordingly.

  Further, when the image forming apparatus A is in a low load state, the switching frequency control unit in the control unit 2 sets a low switching frequency (energy saving set frequency) after elapse of a predetermined time since the heater is turned on. In this case, if there is a heater turn-off instruction, the switching frequency setting unit 121 changes the switching frequency from the low switching frequency to the high switching frequency (normal setting frequency) before turning off the heater, and the heater H is turned off after the change. After the heater is turned off, the switching frequency setting unit 121 may be set to a low switching frequency before the heater is turned on.

  By doing so, it is possible to avoid the overlap of the low frequency region noise caused by the low switching frequency and the low frequency region noise that may be generated even when the fixing heater is turned off. The power loss can be reduced by returning to the low switching frequency.

  In the switching frequency control described above, whether the image forming apparatus A is in a low load state or a high load state is determined by the switching frequency control unit in the control unit 2 from the operation mode (standby state, etc.) of the image forming apparatus. However, as shown by a broken line in FIG. 2, a switching frequency detection unit 122 is provided, and the current switching frequency set by the switching frequency setting unit 121 is compared with a predetermined reference frequency (30 kHz in this example). When the current switching frequency is equal to or lower than the reference frequency, it may be determined that the load is low, and when the current switching frequency is higher than the reference frequency, it may be determined that the load is high.

The switching frequency control based on such a determination method is summarized in the following table.

  The present invention reduces power loss when the load on the image forming apparatus is small, and does not require the addition of noise countermeasure parts such as a noise filter, so that the image can be made inexpensively and by adding noise countermeasure parts. The present invention can be used to provide an image forming apparatus capable of reducing noise in a low frequency region without hindering downsizing of the forming apparatus.

1 is a front view of an example of an image forming apparatus according to the present invention. FIG. 2 is a block diagram illustrating an outline of a control circuit of the image forming apparatus illustrated in FIG. 1. It is a flowchart which shows the switching frequency control example by the control part at the time of halogen lamp heater lighting. It is a timing chart which shows the example of switching frequency setting control. It is a timing chart which shows the other example of switching frequency setting control. It is a figure which shows the prior art example of the low frequency noise level by heater lighting. It is a figure which shows the example of suppression by this invention of the low frequency noise level by heater lighting.

Explanation of symbols

A Image forming apparatus B Image forming unit Y Yellow image forming unit M Magenta image forming unit C Cyan image forming unit K Black image forming unit b Intermediate transfer belt F Fixing device f1 Fixing roller f2 Pressure roller H Halogen lamp heater sm Thermistor C1 C3 Recording medium storage cassette CS Part with cassette P Recording medium S Image reading device g1, g2 Glass plate ADF Electric light automatic transfer device a1 Document loading tray a2 Document discharge tray PA Operation panel Ke Key group Dp Liquid crystal display unit 1 Power supply unit 11 Heater lighting power supply section 11S Switch section 12 Low voltage power supply section (AC / DC voltage conversion section)
121 Power switching frequency setting section (switching frequency changing section)
122 Power switching frequency detection unit 2 Control unit 21 CPU
22 Memory part 23 I / O interface

Claims (6)

An AC power supply is received from an AC power source, a toner image is formed and transferred to a recording medium, and the recording medium is heated by a fixing heater between a fixing rotator and a pressure rotator facing the fixing rotator. The toner image can be fixed to the recording medium under heat and pressure by passing through
A heater on / off instruction means for instructing on / off of the fixing heater;
Switch means for turning on or off the fixing heater based on an instruction from the heater on / off instruction means;
AC / DC conversion means for converting AC voltage from the AC power source into DC voltage;
A switching frequency changing means capable of switching and switching between a predetermined low switching frequency and a predetermined high switching frequency higher than the predetermined frequency for switching at the time of voltage conversion by the AC / DC converting means;
When the image forming apparatus is in a predetermined low load state, the switching frequency changing means sets the low switching frequency, and when the image forming apparatus is in a predetermined high load state, the switching frequency changing means is set to the high frequency. In an image forming apparatus including a switching frequency control means for setting a switching frequency,
The switching frequency control means prior to lighting the fixing heater when the fixing heater is turned on by the switch means,
When the image forming apparatus is in the low load state, the switching frequency changing unit is changed to change the switching frequency from the low switching frequency to the high switching frequency, and the fixing heater is turned on after the change,
When the image forming apparatus is in the high load state, the switching frequency changing unit is allowed to maintain the high switching frequency to allow the fixing heater to be turned on,
An image forming apparatus, wherein when the fixing heater is turned off by the switch means, after the fixing heater is turned off, the switching frequency changing means sets a switching frequency before the fixing heater is turned on. When the image forming apparatus is in the low load state, the switching frequency control unit is configured to change the switching frequency changing unit before a heater turn-off instruction by the heater turn-on / off instruction unit after a predetermined time elapses after the heater is turned on. If the heater turn-off instruction is given by the heater turning-on / off instruction means, the switching frequency changing means changes the switching frequency from the low switching frequency to the high switching. The image forming apparatus according to claim 1, wherein the image forming apparatus is switched to a frequency, permits the fixing heater to be turned off after the change, and causes the switching frequency changing unit to set a low switching frequency before the fixing heater is turned on after the fixing heater is turned off. The switching frequency control unit compares the operation mode of the image forming apparatus with a predetermined reference operation mode to determine whether the image forming apparatus is in the low load state or the high load state. Is an operation mode in which a load lower than the load in the reference operation mode is applied, it is determined that the load is low, and a high load is applied if the operation mode is an operation mode in which a load greater than the load in the reference operation mode is applied. The image forming apparatus according to claim 1, wherein the image forming apparatus is determined to be in a state. The reference operation mode is a standby state of the image forming apparatus, an operation mode in which a load equal to or lower than the load in the standby state is the low load state, and an operation mode in which a load greater than the load in the standby state is applied The image forming apparatus according to claim 3, wherein the image forming apparatus is in a high load state. The operation mode in which a load larger than that in the standby state includes at least a print mode for forming a toner image on a recording medium, an image reading mode for reading a document image, and a facsimile mode for exerting a facsimile function. 5. The image forming apparatus according to 4. The switching frequency control means determines whether the image forming apparatus is in the low load state or the high load state by setting a current switching frequency set by the switching frequency changing means to a predetermined reference frequency. 3. The image forming apparatus according to claim 1, wherein, when the current switching frequency is equal to or lower than the reference frequency, the low load state is determined, and when the current switching frequency is higher than the reference frequency, the high load state is determined. .