Fixing device and image forming apparatus therewith

A fixing device includes a fixing member, a pressing member, a charger, and adjusting part. The fixing member heats toner images on media. The pressing member forms nips with the fixing member and presses the media. The charger uses a corona discharge that occurs in an electric field generated around a discharging electrode so as to charge the fixing member to a same polarity of toner in the toner images. The adjusting part increases a bias applied to the discharging electrode in accordance with increase of a cumulative number calculated by accumulating a number of the media on which the toner images are fixed or increase of a cumulative printing amount calculated by multiplying a printing rate that indicates a ratio of an area of the toner images to an area of the media by the cumulative number.

INCORPORATION BY REFERENCE

This application is based on and claims the benefit of priority from Japanese Patent application No. 2017-001322 filed on Jan. 6, 2017, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to a fixing device and an image forming apparatus therewith.

An image forming apparatus of an electrographic manner includes a fixing device which thermally fixes a toner image to a medium passing through a nip having been formed of a fixing member and a pressing member, each of which rotates. A surface of the fixing member is formed of an electrically insulating material, and may be charged at an opposite polarity to a polarity of the toner by way of friction with the medium passing through the nip. Then, there occurs an offset phenomenon that the toner on the medium adheres to the surface of the fixing member and subsequently the toner transfers to the medium passing through the nip later.

A technique for restraining the offset phenomenon is proposed. For example, there is proposed an image forming apparatus including: a transfer charger which charges a sheet at an opposite polarity to that of a toner in order to transfer a toner image on a photosensitive body; a separating charger which charges the sheet after transferred, at a same polarity as that of the toner; and a power source for offset prevention bias (charger for offset prevention) which charges a surface of a fixing roller of a fixing device at the same polarity as that of the toner. Each of the transfer charger, the separating charger, and the charger for offset prevention is a charger utilizing a corona discharge that has occurred in an electric field around an electrode. The charger for offset prevention varies an intensity of an electric field which is applied to the fixing roller, concurrently with a change of a static elimination charge amount exerted by the separating charger.

SUMMARY

In accordance with an aspect of the present disclosure, a fixing device includes a fixing member, a pressing member, a charger, and adjusting part. The fixing member, while rotating, heats toner images on media. The pressing member, while rotating, forms nips with the fixing member and presses the media passing through the nips. The charger uses a corona discharge that occurs in an electric field generated around a discharging electrode facing the fixing member so as to charge the fixing member to a same polarity of toner in the toner images. The adjusting part increases a bias applied to the discharging electrode in accordance with increase of a cumulative number calculated by accumulating a number of the media on which the toner images are fixed or increase of a cumulative printing amount calculated by multiplying a printing rate that indicates a ratio of an area of the toner images to an area of the media by the cumulative number.

In accordance with an aspect of the present disclosure, an image forming apparatus includes the fixing device.

DETAILED DESCRIPTION

Hereinafter, with reference to accompanying figures, an embodiment of the present disclosure will be described. A near side of figures such asFIG. 1will be set as a front side. Arrows Fr, Rr, L, R, U, and D shown in the figures indicate a front side, a rear side, a left side, a right side, an upside, and a downside, respectively.

First Embodiment

Entire Configuration of Color Printer

With reference toFIG. 1, an entire configuration of a color printer1as an example of an image forming apparatus will be described.FIG. 1is a sectional view schematically showing an internal structure of the color printer1.

The color printer1includes a main body2configurating a substantially rectangular parallelepiped-shaped appearance. In a lower part of the main body2, a sheet feeding cartridge3storing (a stack of) paper sheets S is detachably provided. In an upper surface of the main body2, an ejected sheet tray4is provided. The sheet S, which is an example of a medium, is not limited to the paper sheet and can be a resin sheet or the like.

The color printer1includes a sheet feeding device5, an imaging device6, and a fixing device7in the main body2. The sheet feeding device5is provided at an upstream end of a conveying path8extending from the sheet feeding cartridge3to the ejected sheet tray4. The fixing device7is provided at a downstream side of the conveying path8, and the imaging device6is provided on the conveying path8and between the sheet feeding device5and the fixing device7.

The imaging device6includes four toner containers10, an intermediate transferring belt11, four drum units12, and an optical scanning device13. The four toner containers10respectively store four colors (yellow, magenta, cyan, and black) of toners (developers). The intermediate transferring belt11rotates in a counterclockwise direction ofFIG. 1. Each drum unit12includes a photosensitive drum14, a charger15, a development device16, a first transfer roller17, and a cleaning device18. Each first transfer roller17is provided so as to interpose the intermediate transfer belt11between the first transfer roller17itself and the corresponding photosensitive drum14. A second transfer roller19is in contact with a right side of the intermediate transfer belt11so as to form a transferring nip N1.

The color printer1forms an image on a sheet S according to following procedures. Each charger15charges a surface of the corresponding photosensitive drum14. Each photosensitive drum14receives a scanning light emitted from the optical scanning device13and carries an electrostatic latent image. Each development device16develops the corresponding electrostatic latent image to forma toner image using the toner supplied from the corresponding toner container10. Each first transfer roller17primarily transfers the corresponding toner image on the corresponding photosensitive drum14to the rotating intermediate transfer belt11. The intermediate transfer belt11, while rotating, carries a full-color toner image in which the four-colored toner images are overlapped. The sheet S is fed out by the sheet feeding device5from the sheet feeding cartridge3to the conveying path8. The second transfer roller19secondarily transfers the toner image having been formed on the intermediate transfer belt11to the sheet S passing through the transferring nip N1. The fixing device7thermally fixes the toner image on the sheet S. Afterward, the sheet S is ejected to the ejected sheet tray4. Each cleaning device18removes the toner remaining on the corresponding photosensitive drum14.

Fixing Device

With reference toFIG. 2toFIG. 4, a configuration of the fixing device7will be described.FIG. 2is a sectional view schematically showing the fixing device7.FIG. 3is a side view schematically showing a discharging electrode40of a charger34.FIG. 4is a sectional view schematically showing devices such as the fixing device7(including the adjusting part50).

As shown inFIG. 2, the fixing device7includes a fixing roller31, a pressing roller32, a heating unit33, and a charger34. The fixing roller31and the pressing roller32are substantially cylindrical members which are elongated in a longitudinal direction (axial direction), respectively. The heating unit33is a device configured to heat the fixing roller31. The charger34is a device configured to charge a surface of the fixing roller31.

The fixing roller31as an example of a fixing member includes a fixing cored bar31A, a fixing elastic layer31B, and a fixing belt31C.

The fixing cored bar31A is made of a metal material, and is formed in a substantially cylindrical shape, for example. Both ends in the longitudinal direction of the fixing cored bar31A are supported to be rotatable by a pair of metal plates (not shown). The fixing elastic layer31B is composed of a silicone rubber or the like, for example, and is laminated on an outer circumferential face of the fixing cored bar31A. The fixing belt31C is provided so as to cover the fixing elastic layer31B. The fixing belt31C includes a release layer (such as a PFA tube) which covers an elastic layer (such as a silicone rubber) provided on a substrate (such as nickel), for example (although not shown).

The pressing roller32as an example of a pressing member includes a pressing cored bar32A, a pressing elastic layer32B, and a pressing release layer32C.

The pressing cored bar32A is made of a metal material, and is formed in a substantially cylindrical shape, for example. Both ends in the longitudinal direction of the pressing cored bar32A are supported to be rotatable by a pair of movable metal plates (not shown). The pressing elastic layer32B is composed of a silicone rubber or the like, for example, and is laminated on an outer circumferential face of the pressing cored bar32A. The pressing release layer32C is composed of a PFA tube or the like, for example, and is provided so as to cover the fixing elastic later31B.

The pressing roller32is connected to a motor or the like (not shown) via a gear train or the like, and rotates while receiving a driving force of the motor. The pressing roller32is biased by a spring (not shown) via each movable metal plate, and is pressed against the fixing roller31. The fixing roller31is sequentially driven by the pressing roller32, and rotates around a shaft. The pressing roller32, while rotating, forms a fixing nip N2together with the fixing roller31. At an upstream side of a conveying path8more significantly than the fixing nip N2, an entry guide36for guiding a sheet S to the fixing nip N2is provided. At a downstream side of the conveying path8more significantly than the fixing nip N2, a separating plate37for releasing the sheet S passing through the fixing nip N2from the fixing belt31C is provided. Although in the embodiment, the pressing roller32was driven to rotate, it may be that the fixing roller31is driven to rotate, and is followed by the pressing roller32being driven to rotate.

The heating unit33is provided at an opposite side of the fixing nip N2while the fixing roller31is sandwiched therebetween. The heating unit33includes a holder33A, a plurality of IH coils33B, and an arch coil33C. The holder33A is formed in a substantially semi-cylindrical shape, and is provided so as to cover the fixing roller31. The plurality of IH coils33B are supported by the holder33A. The arch coil33C is formed of a ferromagnetic body such as a ferrite, and is provided so as to cover the plurality of IH coils33B.

Here, functions of the fixing device7will be described. The fixing roller31and the pressing roller32rotate around the respective shaft. Each IH coil33B generates a high frequency magnetic field caused by receiving supply of power from a power source (not shown) so as to heat the fixing belt31C that rotates. In a case in which an image is formed, the fixing roller31, while rotating around the shaft, heats a toner image on the sheet S passing through the fixing nip N2. The pressing roller32, while rotating around the shaft, presses the sheet S passing through the fixing nip N2. Then, the toner image is fixed to the sheet S.

The fixing belt31C is formed of an electrically insulating PFA tube or the like and thus this fixing belt may be charged at a negative polarity by way of friction with the sheet S passing through the fixing nip N2. Then, there occurs the offset phenomenon that the toner at a positive polarity on the sheet S adheres to the fixing belt31C and subsequently the toner transfers to the sheet S passing through the fixing nip N2later. Therefore, the fixing device7according to the first embodiment includes the charger34that charges the fixing roller31(fixing belt31C) at the same polarity (positive polarity) as that of the toner of the toner image.

Charger

As shown inFIG. 2, the charger34is disposed at the upstream side of the conveying path8from the fixing nip N2. In other words, the charger34is disposed at the downstream side in the rotating direction of the fixing roller31while the fixing nip N2is defined as a start point. The charger34includes a discharging electrode40, a shield41, an insulating support body42, and a fixing bias power source43(refer toFIG. 4).

As shown inFIG. 3, the discharging electrode40is a stainless plate of which thickness is of the order of 0.1 mm, for example, and is formed in a substantially serrated shape while a plurality of needle electrodes40A are arranged in the longitudinal direction. As shown inFIG. 2, the discharging electrode40opposes to the fixing roller31, and a tip end thereof is proximal to a surface of the fixing roller31. The shield41is made of a metal material, and is formed in a substantially boxy shape which has opened the fixing roller31side. An open side of the shield41forms a pair of grounding electrodes44while the discharging electrode40is sandwiched therebetween. The pair of grounding electrodes44are grounded via a Zener diode45(refer toFIG. 4). The insulating support body42is formed of a material having an electrically insulating property. The abovementioned discharging electrode40is supported by the shield41via the insulating support body42. The discharging electrode40is supported while extending from the insulating support body42to the open side of the shield41.

As shown inFIG. 4, the fixing bias power source43is electrically connected to the discharging electrode40. The fixing bias power source43applies a current (fixing bias) to the discharging electrode40. The fixing bias power source43includes a variable circuit43A which increases or decreases an output of the fixing bias. The charger34is a corotron charger which charges the fixing roller31(at the positive polarity) by utilizing a corona discharge which occurs in the electric field generated around the discharging electrode40.

In the meanwhile, it is known that the charger34utilizing corona discharge generates a discharging product such as ozone, a nitrogen oxide, a nitrate ion, or an ammonium ion. As the electric field formed around the discharging electrode40is stronger, the production amount of the discharging product increases more significantly. In addition, in the toner, a wax is included so that the toner melted by applying a heat and a pressure does not adhere to the fixing roller31. This wax volatizes from the toner image (toner) at the time of fixing processing, and becomes a floating matter which floats around the fixing roller31or the like. The discharging product or floating matter easily adheres to the discharging electrode40that is a source of the electric field. The adhesion amount of the floating matter or the like increases while being substantially in proportion to the number of times or time intervals of execution of image forming (fixing) operation.

For example, in a case in which an image forming operation is first carried out, etc., any floating matter or the like does not adhere to the discharging electrode40in an initial state. The discharging electrode40in the initial state easily exerts an appropriate corona discharge, and is capable of charging the fixing belt31C substantially uniformly in the axial direction. Therefore, in the discharging electrode40in the initial state, charging of the fixing roller31in order to restrain the offset phenomenon is achieved by a fixing bias with a low charge. In contrast to this, the discharging electrode40to which a floating matter has adhered hardly exerts an appropriate corona discharge, and it may be difficult to charge the fixing belt31C substantially uniformly in the axial direction. In this case, in order to charge the fixing roller31substantially uniformly, it is necessary that a fixing bias which is higher than that in the initial state is applied to the discharging electrode40. In order to maintain the charging performance of the charger34over a long period of time, it is preferable to control the intensity of the electric field by the charger34, according to the adhesion amount of the floating matter or the like to the discharging electrode40. Therefore, the fixing device7according to the first embodiment includes an adjusting part50which varies a fixing bias to be applied to the discharging electrode40, according to the number of sheets Son which images have been formed (fixed) or the like.

Adjusting Part

With reference toFIG. 4andFIG. 5, an adjusting part50will be described.FIG. 5is a graph showing a relationship between a cumulative printing amount and a fixing bias.

The adjusting part50is included in a control board (not shown) which controls an image forming operation by the color printer1. To the control board, an external device100such as personal computer is electrically connected (refer toFIG. 4). The control board receives print data or the like which has been transmitted from the external device100, and appropriately controls each device (such as image forming device6or fixing device7) of the color printer1in order to form an image.

As shown inFIG. 4, the adjusting part50is a device including a CPU51, a memory52, and an input/output port53or the like. The CPU51executes a variety of arithmetic operations in accordance with programs and data or the like which have been stored in the memory52. To the input/output port53, the external device100(personal computer) and the fixing bias power source43(variable circuit43A) or the like are electrically connected.

The CPU51includes a counting part54and a calculation part55. The counting part54counts the number of sheets S onto which toner images are fixed. The calculation part55detects a printing rate for each sheet S and then calculates an average value of the printing rates. The printing rate indicates a ratio of an area of the toner image to an area of the sheet S. A value obtained by counting and accumulating the number of sheets S onto which toner images are fixed (an image is formed) is referred to as a cumulative number. The calculation part55calculates the cumulative printing amount that has been calculated by multiplying the cumulative number for the printing rate. For example, the cumulative printing amount in a case in which the printing rate is 5% and the cumulative number is 300,000 and the cumulative printing amount in a case in which the printing rate is 30% and the cumulative number is 50,000 are equivalent to each other.

In the memory52, a table for correlating the cumulative printing amount and the fixing bias to be applied to the discharging electrode40with each other is stored. The table is the one that corresponds to the graph shown inFIG. 5and in a case in which the cumulative printing amount is low, the fixing bias is also set to be low, and in a case in which the cumulative printing amount is high, the fixing bias is also set to be high. In the first embodiment, for example, the cumulative printing amount is divided into four ranges (refer to A1to A4inFIG. 5), and the fixing bias of four stages (refer to B1to B4inFIG. 5) is set so as to be associated with the cumulative printing amount of the four ranges. That is, the fixing bias is set so as to increase stepwisely (discretely) in response to that the cumulative printing amount continuously increases. The single-dotted chain line shown inFIG. 5indicates the required minimum fixing bias to restrain the offset phenomenon. Namely, merely by the fixing bias that corresponds to the lower range than the single-dotted chain line, the surface of the fixing roller31cannot be sufficiently charged, and the offset phenomenon cannot be restrained. Therefore, the fixing bias of the four stages (B1to B4) is set so as to correspond to the upper range than the single-dotted chain line.

InFIG. 5, A1is an initial value (range) of the cumulative printing amount, and B1is an initial value of the fixing bias. The initial value B1of the fixing bias is set to a value by which the offset phenomenon can be restrained in a case in which the fixing roller31has been charged by employing the discharging electrode40in the initial state. The initial value (A1) of the cumulative printing amount is set in a range in which the offset phenomenon can be restrained in a case in which the fixing roller31has been charged by the initial value (B1) of the fixing bias. It is preferable to experimentally obtain the cumulative printing amount (A1to A4) and the fixing bias (B1to B4) in advance.

Control of Fixing Bias

Next, with reference toFIG. 4toFIG. 6, control of a fixing bias will be described.FIG. 6is a flowchart showing control of the fixing bias.

When the control board receives print data from the external device100, the color printer1executes an image forming operation which has been described hereinbefore. The counting part54detects, from the received print data, the number of sheets S on which images are to be formed (fixed). In addition, the counting part54updates the most recent cumulative number (NL) by adding the detected number of sheets to the cumulative number (NP) at the time of the past image forming operation(s) stored in the memory52(step S1).

The calculation part55calculates the average value from the printing rates of the respective sheets S, on the basis of the received print data. In addition, the calculation part55calculates an average value (ML) of the most recent printing rates from an average value of the thus calculated printing rates and an average value (MP) of the past printing rates that are stored in the memory52. Then, the calculation part55updates the average value (MP) of the past printing rates to the average value (ML) of the most recent printing rates (step S2).

The calculation part55calculates the most recent cumulative printing rate by multiplying the cumulative number (NL) for the average value (ML) of the printing rates. The calculation part55updates the past cumulative printing rate that is stored in the memory52, to the most recent cumulative printing amount (step S3).

Next, the CPU51determines a fixing bias corresponding to the most recent cumulative printing amount from the table (step S4). Then, the CPU51controls the variable circuit43A so as to output the determined fixing bias (step S5). In the procedure as described above, change (control) of the fixing bias is executed. After the calculation part55has updated the average value of the printing rates, the counting part54may update the cumulative number. Namely, step S1may be executed after step S2or after step S3.

For example, in a case in which the cumulative printing amount (cumulative number and printing rate) is low (refer to A1inFIG. 5), the discharging electrode40is established in an initial state or a state close to the initial state, and it is predicted that the adhesion amount of the floating matter or the like to the discharging electrode40is small. The discharging electrode40in the initial state achieves substantially uniform charging of the fixing roller31at a low fixing bias, in comparison with the discharging electrode40to which the floating matter or the like has adhered. Therefore, the adjusting part50controls the fixing bias power source43so as to apply to the discharging electrode40the lowest fixing bias (B1) inFIG. 5.

On the other hand, if an image forming operation is repeatedly carried out, the cumulative printing rate (cumulative number and printing rate) increases (refer to A2to A4inFIG. 5). It is predicted that as the cumulative printing amount is higher, the adhesion amount of the floating matter or the like to the discharging electrode40increases. In this case, in order to charge the fixing roller21substantially uniformly, a fixing bias which is higher than that in the initial state is desired. Therefore, the adjusting part50controls the fixing bias power source43so as to apply to the discharging electrode40a bias which is higher than the fixing bias that is applied to the discharging electrode40in the initial state (refer to B2to B4inFIG. 5). As described above, the adjusting part50increases the fixing bias that is applied to the discharging electrode40, according to an increase of the cumulative printing amount.

In the fixing device7according to the first embodiment described hereinbefore, the adjusting part50is configured to increase the fixing bias in a case in which an image forming operation (fixing operation) had been repeatedly executed over a predetermined period of time. That is, the adjusting part50predicts the adhesion amount of the floating matter such as a discharging product or a wax component to the discharging electrode40and then carries out control to increase the fixing bias. With this configuration, in the initial state, the fixing bias can be set to a low value and thus generation of the discharging product can be restrained. In addition, in the initial state, charging of the fixing roller31can be carried out in a condition in which the discharging product or the floating matter hardly adheres to the discharging electrode40. On the other hand, the fixing bias, in a state in which an image forming operation has been repeatedly executed, is set to be higher than that in the initial state, and even if the floating matter or the like has adhered to the discharging electrode40, the fixing roller31can be thereby charged substantially uniformly. As described above, a period of time during which the discharging electrode40is capable of charging the fixing roller31substantially uniformly can be extended. Namely, the service life of the charger34can be extended.

In addition, in the fixing device7according to the first embodiment, the discharging electrode40is formed in the substantially serrated shape. With this configuration, a corona discharge can be effectively exerted from the needle electrode40A towards the fixing roller31, and the fixing roller31can be charged substantially uniformly in the axial direction.

Further, in the fixing device7according to the first embodiment, the pair of grounding electrodes44oppose to each other while the discharging electrode40is sandwiched therebetween, and a stable corona discharge can be thereby exerted from the discharging electrode40. Furthermore, the pair of grounding electrodes44are grounded via the Zener diode45, and charging of the surface of the fixing roller31can be thereby accelerated.

Second Embodiment

Next, with reference toFIG. 7andFIG. 8, a fixing device7according to a second embodiment will be described.FIG. 7is a graph showing a relationship between a cumulative number and a fixing bias.FIG. 8is a flowchart showing control of the fixing bias. In the following description, like constituent elements in the color printer1according to the first embodiment are designated by like reference numerals, and a duplicate description is omitted.

In the fixing device7according to the second embodiment, the calculation part55(refer toFIG. 4) is omitted from the adjusting part (refer toFIG. 4), or alternatively, even if the calculation part55is included, a result of calculation by the calculation part55is not used. In addition, in the fixing device7according to the second embodiment, a table stored in a memory52is different from the one according to the first embodiment.

In the memory52, the table for correlating a cumulative number and a fixing bias with each other is stored. The table is the one that corresponds to the graph shown inFIG. 7and in a case in which the cumulative number is low, the fixing bias is also set to low, or alternatively, in a case in which the cumulative number is high, the fixing bias is also set to high. In the second embodiment, for example, the fixing bias of four stages (refer to B1to B4inFIG. 7) is set so as to be associated with the cumulative number of four ranges (refer to N1to N4inFIG. 7). That is, the fixing bias is set so as to increase stepwisely (discretely) in accordance with a continuous increase of the cumulative number. InFIG. 7, N1is an initial value (range) of the cumulative number, and is set in a range in which an offset phenomenon can be restrained in a case in which the fixing roller31has been charged at the initial value (B1) of the fixing bias. It is preferable to experimentally obtain the cumulative number (N1to N4) in advance.

As shown inFIG. 8, in control of the fixing bias according to the second embodiment, the same processing operation as that in step S1of control of the fixing bias according to the first embodiment is executed, and steps S2and S3are omitted. Subsequently, a CPU51determines, from the table, a fixing bias which corresponds to the most recent cumulative number (NL=any one of N1to N4) (step S20). Then, the CPU51controls a variable circuit43A so as to output the determined fixing bias (step S30). In the procedure as described above, change (control) of the fixing bias is executed.

For example, in a case in which the cumulative number is low (refer to N1inFIG. 7), a discharging electrode40is set in an initial state, and it is predicted that the adhesion amount of floating matter or the like to the discharging electrode40is small. In this case, the adjusting part50controls a fixing bias power source43so as to apply the lowest fixing bias (B1) inFIG. 7to the discharging electrode40. On the other hand, as an image forming operation is repeatedly carried out and then the cumulative number becomes high (refer to N2to N4inFIG. 7), it is predicted that the adhesion amount of the floating matter or the like to the discharging electrode40increases. In this case, the adjusting part50controls the fixing bias power source43so as to apply to the discharging electrode40a fixing bias (refer to B2to B4inFIG. 7) which is higher than the fixing bias that is applied to the discharging electrode40in the initial state. As described above, the adjusting part50increases the fixing bias that is applied to the discharging electrode40, according to an increase of the cumulative number.

With the fixing device7according to the second embodiment described hereinabove, there can be attained an advantageous effect which is substantially similar to that of the fixing device7according to the first embodiment.

Although, in the fixing device7according to each of the first and second embodiments, the cumulative printing amount and the cumulative number each are divided into four sections and the fixing bias is varied to four stages, the present disclosure is not limitative thereto. The cumulative printing amount may be divided into two or more sections, and the fixing bias may also be varied to two stages or more. In addition, a table may be set in such as manner as to have a (linear) relationship in which the cumulative printing amount or the like and the fixing bias can be expressed by a linear expression. Namely, the fixing bias may be controlled so as to increase or decrease smoothly (that is, continuously) concurrently with a continuous increase or decrease of the cumulative printing amount or the cumulative number.

Although, in the fixing device7according to each of the first and second embodiments, the adjusting part50was included in the control board that controls an image forming operation, the present disclosure is not limitative thereto. For example, it may be that the adjusting part50is a device independent of the control board and is a dedicated device which controls the fixing device7or the fixing bias power source43.

Also, although, in the fixing device7according to each of the first and second embodiments, the fixing belt31C constitutes the surface of one fixing roller31, the present disclosure is not imitative thereto. Although not shown, a fixing member may be configured so as to overhang on a plurality of rollers. In addition, although the charger34included a substantially serrated electrode, there may be a charger including a discharge wire as an electrode which is overhung on each part in an insulating manner without being limitative thereto. Further, the charger34may be a Scorotron charger further including a grid electrode.

Furthermore, although, in the color printer1(image forming apparatus) according to each of the first and second embodiments, a toner charged at the positive polarity was employed, a toner charged at the negative polarity may be employed without being limitative thereto. In this manner, it is preferable that the charger34charge the surface of the fixing roller31at the negative polarity.

In the color printer1(image forming apparatus) including the fixing device7according to each of the first and second embodiments, the respective advantageous effects described previously are attained.

Still furthermore, although the description of the embodiments was presented as to a case in which the present disclosure was applied to the color printer1, the present disclosure may be applied to a monochrome printer, a copying machine, a facsimile machine, or a multifunction peripheral or the like, for example, without being limitative thereto.

The description of embodiments merely presents an aspect in a fixing device and an image forming apparatus including the same, according to the present disclosure, and the technical scope of the present disclosure is not limitative to the foregoing embodiment.

While the present disclosure has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present disclosure.