Power supply module and image forming apparatus including same

An image forming apparatus includes an image bearing member to bear a toner image on a surface thereof, a transfer unit including a transfer device to transfer the toner image onto a recording medium, disposed opposite the image bearing member, a direct current (DC) power source to apply, between the image bearing member and the transfer device, a DC bias to form a first transfer electric field to transfer the toner image onto the recording medium, and a power supply module detachably attachable relative to the image forming apparatus. The power supply module includes an AC-DC superimposed bias power source to apply, between the image bearing member and the transfer device, a superimposed bias in which an alternating voltage is superimposed on a DC voltage to form a second transfer electric field to transfer the toner image onto the recording medium.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application No. 2011-137197, filed on Jun. 21, 2011 in the Japanese Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Exemplary aspects of the present disclosure generally relate to an image forming apparatus, such as a copier, a facsimile machine, a printer, or a multi-functional system including a combination thereof, and more particularly, to a power supply module that supplies a bias in which an alternating current voltage is superimposed on a direct current voltage to transfer a toner image onto a recording medium and an image forming apparatus including the power supply module.

2. Description of the Related Art

Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile capabilities, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image bearing member (which may, for example, be a photoconductive drum); an optical writer projects a light beam onto the charged surface of the image bearing member to form an electrostatic latent image on the image bearing member according to the image data; a developing device supplies toner to the electrostatic latent image formed on the image bearing member to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image bearing member onto a recording medium or is indirectly transferred from the image bearing member onto a recording medium via an intermediate transfer member by a transfer electric field generated by a certain voltage such as a direct current (DC) voltage; a cleaning device then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the unfixed toner image to affix the unfixed toner image on the recording medium semi-permanently, thus forming the image on the recording medium.

There is increasing market demand for an image forming apparatus capable of forming an image on various kinds of recording media sheets such as ones having a coarse surface, for example, Japanese paper and an embossed sheet. However, transferring a toner image onto a recording medium having a coarse surface using the transfer electric field generated by the DC voltage using the conventional configuration, a pattern of light and dark patches according to the surface condition of the recording medium appears in an output image. This is because the toner is transferred poorly to recessed portions on the surface of the recording medium, and as a result, the density of toner at the recessed portions is less than that of projecting portions of the recording medium.

In order to obtain an image without uneven toner concentration regardless of the surface condition of the recording medium, the transfer electric field can be generated using a superimposed bias in which an alternating current (AC) voltage is superimposed on a DC voltage. In this configuration, the AC-DC superimposed bias is applied to a secondary transfer member such as a secondary transfer roller. The AC-DC superimposed bias is composed of a DC voltage and an AC voltage in which a relatively high first peak-to-peak voltage and a relatively low second peak-to-peak voltage alternate. The transfer electric field generated by the AC-DC superimposed bias enables the toner image on the intermediate transfer belt serving as an image bearing member to move to the recording medium. Accordingly, unevenness of image concentration is reduced. The mechanism by which this feat is accomplished is as follows.

Initially, with application of a transfer bias composed of a superimposed bias at first only a small number of toner particles on the toner layer on the image bearing member separates from the toner layer and moves to the recording medium; most of the toner particles remain in the toner layer.

After the toner particles separated from the toner layer enter the recessed portions of the recording medium, the polarity of the transfer electric field reverses due to the AC voltage. As a result, the toner particles in the recessed portions return to the toner layer. When this happens, the toner particles returning to the toner layer strike the toner particles remaining in the toner layer, thereby weakening adhesion of the toner particles in the toner layer. Subsequently, when the polarity of the transfer electric field reverses towards the direction of the recording medium, more toner particles than the initial time separate from the toner layer and move to the recessed portions of the recording medium.

As this process is repeated, the amount of toner particles separating from the toner layer and entering the recessed portions of the recording medium can be increased, thereby transferring adequately the toner to the recessed portions of the recording medium.

However, although effective, in order to apply the AC-DC superimposed voltage, various components are required. For example, an AC power source for supplying the AC voltage, components that control the power source such as a signal line, and a harness that connects the AC power source and the transfer device are required.

Although an AC-DC superimposed bias is used to transfer a toner image onto a recording medium with a coarse surface as described above, the transfer electric field is generated using only the DC voltage (direct current bias) when forming an image on a normal sheet. In such a case, a switching mechanism such as a relay is required to switch between the biases to produce different transfer electric fields.

In known image forming apparatuses that use an AC-DC superimposed bias, arrangement of various constituent components to produce and control the AC-DC superimposed bias such as the AC voltage power source, harnesses, signal lines, and a relay is not discussed in detail. Yet in order to satisfy recent demand for overall size reduction of the image forming apparatus, arrangement of the constituent components is important. Furthermore, to reduce the time and the cost of assembly of the image forming apparatus, the constituent components need to be assembled easily. Hence, arrangement of the components is critical in this regard as well.

In addition, it is conceivable that users purchase an image forming apparatus without the components for application of the AC-DC superimposed bias but later wish to add these components optionally. In such a case, a technician needs to be called in to install the components required for application of the AC-DC superimposed bias. However, as is generally the case for the image forming apparatus, the power source and the like that are not expected to be touched or removed by the user are disposed at the back of the image forming apparatus. In order to attach the additional components for the AC-DC superimposed bias to the existing image forming apparatus, it may be necessary to move the image forming apparatus so that he or she can access the back of the image forming apparatus, which generally faces a wall of the office upon installation of these components.

As is obvious, if installation of the components in the image forming apparatus is time-consuming, downtime, that is, a period of time during which the device is not operated, also lengthens. Moreover, if installation of the components requires disassembly of the image forming apparatus to some extent, a relatively large working space is required, which is inconvenient for the user.

In view of the above, there is demand for an image forming apparatus that combines good imaging capability regardless of the surface condition of the recording medium with ease of installation of the components needed to generate the AC-DC superimposed bias.

BRIEF SUMMARY OF THE INVENTION

In view of the foregoing, in an aspect of this disclosure, there is provided an image forming apparatus including an image bearing member, a transfer unit, a direct current (DC) power source, and a power supply module. The image bearing member bears a toner image on a surface thereof. The transfer unit disposed opposite the image bearing member includes a transfer device to transfer the toner image onto a recording medium. The direct current (DC) power source applies, between the image bearing member and the transfer device, a DC bias to form a first transfer electric field to transfer the toner image onto the recording medium. The power supply module is detachably attachable relative to the image forming apparatus. The power supply module includes an AC-DC superimposed bias power source to apply, between the image bearing member and the transfer device, a superimposed bias in which an alternating voltage is superimposed on a DC voltage to form a second transfer electric field to transfer the toner image onto the recording medium.

According to another aspect, there is provided a power supply module detachably attachable relative to an image forming apparatus. The power supply module includes a power source to output a superimposed bias in which an AC voltage is superimposed on a DC voltage. The superimposed bias is applied to a transfer device of the image forming apparatus.

The aforementioned and other aspects, features and advantages would be more fully apparent from the following detailed description of illustrative embodiments, the accompanying drawings and the associated claims.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

In a later-described comparative example, illustrative embodiment, and alternative example, for the sake of simplicity, the same reference numerals will be given to constituent elements such as parts and materials having the same functions, and redundant descriptions thereof omitted.

Typically, but not necessarily, paper is the medium from which is made a sheet on which an image is to be formed. It should be noted, however, that other printable media are available in sheet form, and accordingly their use here is included. Thus, solely for simplicity, although this Detailed Description section refers to paper, sheets thereof, paper feeder, etc., it should be understood that the sheets, etc., are not limited only to paper, but include other printable media as well.

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and initially with reference toFIG. 1, a description is provided of an image forming apparatus according to an aspect of this disclosure.

FIG. 1is a schematic diagram illustrating a color printer as an example of the image forming apparatus according to an illustrative embodiment of the present invention.

According to the illustrative embodiment, the image forming apparatus produces a color image by superimposing four color components yellow (Y), magenta (M), cyan (C), and black (K) one atop the other. As illustrated inFIG. 1, the image forming apparatus includes image forming units1Y,1M,1C, and1K for the colors yellow, magenta, cyan, and black, respectively. The image forming units1Y,1M,1C, and1K are disposed slightly above the center of the image forming apparatus. It is to be noted that the suffixes Y, M, C, and K denote colors yellow, magenta, cyan, and black, respectively. To simplify the description, these suffixes are omitted herein, unless otherwise specified.

The image forming units1Y,1M,1C, and1K include photoconductive drums11Y,11M,11C, and11K, one for each of the colors yellow, magenta, cyan, and black respectively. It is to be noted that the photoconductive drums11Y,11M,11C, and11K are hereinafter collectively referred to as photoconductive drums11when discrimination therebetween is not required.

The image forming units1Y,1M,1C, and1K are arranged in tandem along a belt-type image bearing member50(hereinafter referred to as simply “intermediate transfer belt”), and the photoconductive drums11contact the intermediate transfer belt50. Toner images of yellow, magenta, cyan, and black are formed on the respective color of the photoconductive drums11and then transferred onto the intermediate transfer belt50such that they are superimposed one atop the other, thereby forming a composite color toner image.

The toner images having been transferred onto the intermediate transfer belt50are transferred onto a recording medium such as a recording sheet fed from a sheet cassette101by a sheet feed roller100. More particularly, the sheet cassette101stores a stack of multiple recording media sheets, and the sheet feed roller100sends a top sheet, in appropriate timing, to a place called a secondary transfer nip at which a secondary transfer roller80serving as a transfer device and a secondary transfer counter roller73contact each other via the intermediate transfer belt50. The composite color toner image on the intermediate transfer belt50is transferred onto the recording medium at the secondary transfer nip in a process known as secondary transfer. After the secondary transfer, the recording medium, onto which the composite color toner image is transferred, is transported to a fixing device91in which heat and pressure are applied to the recording medium, thereby affixing the composite toner image on the recording medium.

With reference toFIG. 2, a description is provided of the image forming unit1Y as a representative example of the image forming units1. It is to be noted that the image forming units1Y,1M, C, and1K all have the same configurations as all the others, differing only in the color of toner employed. Hence, a description is provided of the image forming unit1Y for the color yellow.FIG. 2is a cross-sectional diagram schematically illustrating the image forming unit1Y according to an illustrative embodiment of the present invention.

As illustrated inFIG. 2, in the image forming unit1Y, the photoconductive drum11Y is surrounded by various pieces of imaging equipment, such as a charging device21, a developing device31, a drum cleaner41, and a primary transfer roller61. It is to be noted that the suffix Y indicating the color yellow is omitted.

The charging device21includes a charging roller that charges the surface of the photoconductive drum11. The developing device31develops a latent image formed on the photoconductive drum11with toner, thereby forming a visible image, known as a toner image on the photoconductive drum11Y. The toner image borne on the surface of the photoconductive drum11Y is transferred onto the intermediate transfer belt50by the primary transfer roller61in a process known as primary transfer. After primary transfer, toner remaining on the photoconductive drum11Y is removed by the drum cleaner41.

The charging roller of the charging device21is constituted of a conductive elastic roller supplied with a voltage in which an alternating current (AC) voltage is superimposed on a direct current (DC) voltage. The charging roller contacts the photoconductive drum11Y. Electrical discharge is induced directly between the charging roller and the photoconductive drum11Y, thereby charging the photoconductive drum11Y to a predetermined polarity, for example, a negative polarity. Instead of using the charging roller or the like that contacts the photoconductive drum11Y, a corona charger that does not contact the photoconductive drum11Y may be employed.

Subsequently, referring back toFIG. 1, the charged surfaces of the photoconductive drums11Y,11M,11C, and11K are illuminated with modulated light beams L projected from an optical writer. Accordingly, electrostatic latent images are formed on the surfaces of the photoconductive drums11Y,11M,11C, and11K. More specifically, when the surfaces of the photoconductive drums11Y,11M,11C, and11K are illuminated with the light beams L, the place where absolute values of the potential drops appears as a latent image (an image portion), and the place where the light beams do not illuminate so that the absolute values of the potential remain high becomes a background portion where no image is formed.

InFIG. 2, the developing device31includes a developer container31c, a developing sleeve31a, and paddles31b. The developer container31cincludes an opening facing the photoconductive drum11Y. In the developer container31c, a two-component developing agent consisting of toner and carrier is stored. The developing sleeve31ais disposed in the developer container31cand faces the photoconductive drum11via the opening of the container31c. The paddles31bmix the developing agent and transport the developing agent to the developing sleeve31a. Each paddle31bis disposed at the developing sleeve side from which the developing agent is supplied to the developing sleeve31aand at a toner receiving side from which fresh toner is supplied by a toner supply device (not illustrated). Although not illustrated, the paddles31bare rotatably supported by shaft bearings. The toner transported onto the developing sleeve31awhile being mixed by the paddles31bis attracted electrostatically to the latent image on the photoconductive drum11Y, thereby developing the latent image into a visible image, known as a toner image.

The intermediate transfer belt50is a belt formed into a loop, entrained around a plurality of rollers, and rotated endlessly. The primary transfer rollers61are disposed inside the loop formed by the intermediate transfer belt50and contact the photoconductive drums11Y via the intermediate transfer belt50. The primary transfer rollers61are conductive elastic rollers. A constant-current controlled primary transfer bias is applied to the primary transfer rollers61. The primary transfer bias causes the toner image on the photoconductive drum11to be transferred onto the intermediate transfer belt50.

The drum cleaner41includes a cleaning blade41aand a cleaning brush41b. The cleaning blade41acontacts the photoconductive drum11against the direction of rotation of the photoconductive drum11Y. The cleaning brush41bcontacts the photoconductive drum11Y while rotating in a direction opposite to that of the photoconductive drum11Y. With this configuration, the toner remaining on the surface of the photoconductive drum11Y after primary transfer is removed.

The photoconductive drums11Y,11M,11C, and11K are rotated in the clockwise direction indicated by an arrow inFIG. 1by a driving device, not illustrated. It is to be noted that the photoconductive drum11K for the color black is rotated independently from other photoconductive drums11Y,11M, and11C for color imaging. In this configuration, when forming a monochrome image, only the photoconductive drum1K for the color black is rotated; whereas, when forming a color image, all four photoconductive drums11Y,11M,11C, and11K are driven at the same time. According to the present illustrative embodiment, when forming a monochrome image, an intermediate transfer unit including the intermediate transfer belt50is swingably separated from the photoconductive drums11Y,11M, and11C.

The intermediate transfer belt50serving as an image bearing member is formed into a loop and entrained around a plurality of rollers: a secondary transfer counter roller73, and support rollers71and72. The intermediate transfer belt50is formed of a belt having a medium resistance. One of the rollers71,72, and73is driven to rotate so that the intermediate transfer belt50is moved endlessly in the counterclockwise direction indicated by a hollow arrow inFIG. 1.

The support roller72is grounded. As illustrated inFIG. 1, a surface voltmeter75is disposed opposite the support roller72. The surface voltmeter75measures a surface potential when the toner image on the intermediate transfer belt50passes over the support roller72.

Still referring toFIG. 1, a description is provided of an AC-DC superimposed bias applied between the intermediate transfer belt50and the secondary transfer roller80. The AC-DC superimposed bias is a bias in which a direct current (DC) voltage and an alternating current (AC) voltage are superimposed.

As illustrated inFIG. 1, in order to apply the AC-DC superimposed bias between the intermediate transfer belt50and the secondary transfer roller80, the image forming apparatus includes a first power source unit110and a second power source unit111. The first power source unit110is connected to a secondary transfer counter roller73. The second power source unit111is connected to the secondary transfer roller80serving as a transfer device.

To transfer a toner image from the intermediate transfer belt50to a recording medium P, the first power source unit110and/or the second power source unit111supplies a voltage having a DC voltage component in the direction of transfer of the toner from the intermediate transfer belt50to the recording medium P. In addition to the DC voltage component, an AC voltage component or the AC component superimposed with the DC component is supplied by the first power source unit110and/or the second power source unit111.

A transfer electric field generated by the AC-DC superimposed bias acts on the toner image on the intermediate transfer belt50, and then the toner image is transferred electrostatically to a predetermined position on the recording medium P, as the recording medium P passes through the secondary transfer nip between the intermediate transfer belt50and the secondary transfer roller80in the direction indicated by an arrow F inFIG. 1.

The configuration of the first power source unit110and/or the second power source unit111for application of the AC-DC superimposed bias is not limited to the configuration shown inFIG. 1. For example, one of the first power source unit110and the second power source unit111is provided to supply the superimposed voltage. Alternatively, as illustrated inFIG. 1, both first power source unit110and the second power source unit111are disposed so that the AC voltage and the DC voltage are applied separately by the first power source unit110and the second power source unit111. Furthermore, one of the first power source unit110and the second power source unit111may supply the AC-DC superimposed voltage, and the other power source unit may supply the DC voltage.

An output voltage may be selected from the voltage with only the DC voltage component and the voltage with the AC-DC superimposed voltage component. With this configuration, depending on the type of the recording medium, the transfer electric field can be switched between the transfer electric field generated only by the DC voltage component and the transfer electric field generated by the AC-DC superimposed bias. For example, when the recording medium P is a normal sheet of paper having a smooth surface compared with a coarse surface such as an embossed sheet and Japanese paper, only the DC voltage component may be supplied.

The advantage of this configuration is that in applications that do not require any AC voltage, the transfer unit may be used only with the DC voltage component, thereby saving the energy. In this case, the power source unit capable of supplying the AC-DC superimposed voltage is configured to supply only the DC voltage component by not supplying the AC voltage. Alternatively, separate power source circuits may be provided for application of the DC voltage and application of the AC voltage, or for application of the superimposed voltage. By switching the power source circuits, a desired voltage can be selected, that is, the DC voltage and the superimposed voltage can be switched.

With reference toFIG. 3, a description is provided of an example of a current value when the AC-DC superimposed bias in which a DC voltage is superimposed on an AC voltage is applied to the secondary transfer counter roller73by the first power source unit110and/or the second power source unit111.

FIG. 3is a graph showing the electric current flowing to the secondary transfer counter roller73when the first power source unit110applies the AC-DC superimposed bias to the secondary transfer counter roller73as illustrated inFIG. 4. In other words,FIG. 3shows an example of the current value of the AC-DC superimposed bias when the first power source unit110shown inFIG. 4applies the AC-DC superimposed bias to the secondary transfer counter roller73to transfer the toner image from the intermediate transfer belt50to the recording medium P.

FIG. 4is a schematic diagram illustrating a transfer unit200in which the toner image on the intermediate transfer belt50is transferred onto the recording medium P using the transfer electric field generated under the constant current control. According to the present embodiment, the DC voltage is superimposed on the AC voltage. The transfer electric field is generated under the constant current control in which the output voltage is regulated such that the DC component (offset current) Ioff of the output current or the current Ipp between peaks of the AC component achieves a predetermined current level, thereby transferring the toner image from the intermediate transfer belt50onto the recording medium P.

The voltage output from the first power source unit110as shown inFIG. 3is regulated such that the current value Ioff of the DC component or the current value Ioff and the current value Ipp between the peaks of the AC component obtains a predetermined current value. It is to be noted that, since the primary transfer rollers61have the same configuration except the color of toner employed, for simplicity,FIG. 4shows only one primary transfer roller61as a representative example,

In contrast to the constant current control as described above, the toner image can be transferred to the recording medium by applying the AC-DC superimposed bias under the constant voltage control in which the output voltage is regulated such that the DC component Voff of the output voltage or the voltage Vpp between peaks of the AC component achieves a predetermined value. However, in a case in which the output voltage is subjected to the constant voltage control, the applied voltage needs to be changed significantly in order to obtain good transferability when the resistance of constituent parts changes due to humidity and the material of the recording medium is different. By contrast, fluctuation of the transferability is small in the same situation under the constant current control. For this reason, the constant current control is preferred.

In the image forming apparatus shown inFIG. 4in which the electric current shown inFIG. 3is supplied by the first power source unit110, the secondary transfer roller80serving as a transfer device is grounded while the secondary transfer counter roller73is supplied with a voltage by the first power source unit110. The first power source unit110is regulated by a control circuit300.

In the configuration described above, Ioff is detected by a built-in ammeter in the first power source unit110, and the result is provided to the control circuit300. Subsequently, the control circuit300provides a control signal to the first power source unit110. The control circuit300outputs the control signal in accordance with a set value of a current while the first power source unit110adjusts an output voltage such that the output Ioff achieves the set value. When Ipp is subjected to the constant current control, Ipp can be regulated in the same or similar manner as described above.

According to the study by the present inventors, Ioff represents movement of electrical charge by the toner or by electrical discharge. Therefore, Ioff setting can be generated using the amount of current generated by the toner movement as a guideline.

The current Itoner generated by the toner movement can be expressed by the following equation:
Itoner=v*W*Q/M*M/A*10,
where v represents a velocity [m/s] of the recording medium P, W represents a width [m] of an image in the axial direction of the roller, Q/M represents an electrical charge of toner [μC/g], WA represents an amount of adhered toner [mg/cm2].

For the values of the image width and the amount of adhered toner, the maximum values that are assumed when a solid image is transferred onto a recording medium are used to allow all toner to be transferred. For example, when v=0.3 [μm/s], W=0.3 [μm], Q/M=−30 [μC/g], and M/A=0.5 [μg/cm2], Itoner is −13.50 [μA]. In this case, preferably, the absolute value of Ioff is set to a value equal to or greater than |Itoner|, for example, Ioff=−20 [μA]. The setting for Ioff when changing the velocity v of the recording medium P can be obtained by obtaining Itoner using the equation above. For example, when v=0.15 [μm/s], Ioff is −6.75 [μA]. Therefore, Ioff is set as Ioff=−10 [μA].

In a case in which the velocity (linear velocity) is changed to accommodate different types of recording media sheets, different modes for automatically switching Ioff to accommodate different velocities may be provided to achieve stable image quality for different velocities of recording media sheets. Furthermore, the Ioff setting for a color image having an WA greater than that of a monochrome image can be estimated from the equation above. For example, assuming that the M/A for the color image is 1.0 [μg/cm2] which is twice that of a monochrome image, Ioff may be set to −40 [μA] which is also twice that of the monochromatic image. By providing a color printing mode in which the Ioff setting automatically changes depending on output image information, a stable image can be obtained for both color images and monochromatic images.

It is to be noted that the level of Ipp needs to be high enough to produce the electric field for transferring the toner to the recessed portions of the recording medium. If Ipp is too low, the toner is transferred poorly. Although the level of Ipp differs depending on the resistance of the transfer member and the width of the transfer nip, in the present illustrative embodiment, Ipp is set to 3.0 [mA], for example. By setting Ipp to an appropriate value, toner can be transferred reliably to recessed portions of a recording medium regardless of different surface characteristics of recording media sheets. It is to be noted that an optimum level of Ipp may be obtained in advance through analyses and experiments using an actual model.

As described above, the AC-DC superimposed bias is applied between the intermediate transfer belt (the image bearing member)50and the secondary transfer counter roller73(the transfer device), thereby transferring reliably the toner image from the intermediate transfer belt50onto the recording medium P.

According to the illustrative embodiment, the secondary transfer roller80is grounded while the secondary transfer counter roller73is applied with the AC-DC superimposed bias. Alternatively, the secondary transfer counter roller73may be grounded while the secondary transfer roller80is applied with applying the AC-DC superimposed bias. In this a case, the polarity of the DC voltage is changed. More specifically, as illustrated inFIG. 3, when the secondary transfer counter roller73is applied with the AC-DC superimposed bias while the toner having the negative polarity is used and the secondary transfer roller80is grounded, the DC voltage having the negative polarity same as the toner is employed so that a time-averaged potential of the AC-DC superimposed bias has the same polarity as the toner.

By contrast, when the secondary transfer counter roller73is grounded and the secondary transfer roller80is applied with the AC-DC superimposed bias, the DC voltage having the positive polarity, which is the polarity opposite to the toner, is used so that the time-averaged potential of the AC-DC superimposed bias has the positive polarity which is opposite to the polarity of toner. Instead of applying the AC-DC superimposed bias to the secondary transfer counter roller73or the secondary transfer roller80, the DC voltage may be supplied to one of the rollers, and the AC voltage may be supplied to the other roller.

According to the illustrative embodiment, the secondary transfer roller80serving as a transfer member is a roller that contacts the intermediate transfer belt50serving as an image bearing member. For example, the secondary transfer roller80is constituted of a conductive metal core formed into a cylindrical shape and a surface layer provided on the outer circumferential surface of the metal core. The surface layer is made of resin, rubber, and the like.

The secondary transfer80roller is not limited to the above-described structure. As long as the superimposed electric field can be applied to the transfer portion or the transfer nip, as illustrated inFIG. 5, a no-contact charger80′ disposed opposite the intermediate transfer belt50may be employed in place of the secondary transfer roller80, for example.FIG. 5is a schematic diagram illustrating the transfer unit using the no-contact charger80′. As illustrated inFIG. 5, the charger80′ does not contact the intermediate transfer belt50. The transfer unit200shown inFIG. 5employs the charger80′ connected to the first power source unit110while the secondary transfer counter roller73is grounded. According to the present illustrative embodiment, the charger80′ serves as a transfer device.

Various material may be used for the recording medium P. Material for the recording medium P includes, but is not limited to, resin, metal, and any other suitable material.

According to the present illustrative embodiment, the waveform of the alternating voltage is a sine wave, but other waveforms such as a square wave may be used.

With reference toFIG. 6, a more detailed description is provided of power source circuits of the power source units110and111.FIG. 6is a block diagram showing an example of the power source unit that generates the AC-DC superimposed bias. It is to be noted that, for simplicity, the intermediate transfer belt50serving as an image bearing member is omitted inFIGS. 6 through 9.

As illustrated inFIG. 6, the second power source unit111that supplies an AC voltage is connected to the secondary transfer roller80serving as a transfer member, and the first power source unit110that supplies a DC voltage is connected to the secondary transfer counter roller73.

In the second power source unit111, an AC driver121, an AC high voltage transformer122, an AC output detector123, and an AC controller124constitute an AC voltage generator112.

In the first power source unit110, a DC driver125, a DC high voltage transformer126, a DC output detector127, and a DC controller128constitute a DC voltage generator113. It is to be noted that an input 24V and the ground (GND) from the control circuit300for driving the power source unit110and111are omitted inFIG. 6.

Each of the power source units110and111may include an error detector for detecting an erroneous output from the power source units110and111. In this case, a signal line for transmitting an error detection signal from the error detector is connected to the control circuit300.

According to the illustrative embodiment, a signal that sets a frequency of the AC voltage to be superimposed is supplied from the control circuit300to the second power source unit111for the AC voltage via a signal line CLK. Further, a signal that sets a current or a voltage of the AC output is supplied from the control circuit300to the power source unit111via a signal line AC_PWM. A signal for monitoring the AC output is provided to the control circuit300via a signal line AC_FB_I.

A signal that sets a current or a voltage of the DC output is supplied from the control circuit300to the power source unit110for the DC voltage via a signal line dc_PWM. A signal for monitoring the DC output is provided to the control circuit300via a signal line dc_FB_I. Based on instructions from the control circuit300, blocks for controlling the AC and DC (current/voltage) output signals to control driving of each of the respective high voltage transformers122and126such that the detection signals provided by the output detectors123and127have predetermined values.

In the AC control, the current and the voltage of AC output is regulated. In other words, both an output current and an output voltage are detected by the AC output detector123so that the constant current control and the constant voltage controls can be performed. The same can be said for the DC control.

According to the present embodiment, both the AC and the DC are regulated with a detection result for the current being prioritized so that the constant current control is performed normally. The detection result for the output voltage is used to suppress an upper bound voltage and used to regulate the maximum voltage under unloaded conditions. Monitoring signals output from the AC output detector123and the DC output detector127are provided to the control circuit300as information for monitoring the load conditions. The frequency of the AC voltage is set via the signal line CLK from the control circuit300. Alternatively, however, a certain frequency can be generated within the AC voltage generator.

According to the illustrative embodiment illustrated inFIG. 6, the first power source unit110includes components for application of the DC voltage, and the second power source unit111includes components for application of the AC voltage. Alternatively, the components for both application of the AC voltage and the DC voltage may be integrated and constituted as a single power source unit.

With reference toFIG. 7, a description is provided of another example of a power source unit for generating the AC-DC superimposed bias.FIG. 7illustrates a configuration in which application of a voltage with the DC component only and application of the AC-DC superimposed bias can be selected. According to the illustrative embodiment illustrated inFIG. 7, the first power source unit110that supplies a voltage containing only the DC component, and the second power source unit111that supplies the superimposed voltage are connected in parallel relative to the secondary transfer counter roller73. With this configuration, the transfer bias can be selected from the AC-DC superimposed bias and the voltage containing only the DC component.

According to the present illustrative embodiment, the second power source unit111connected to the secondary transfer counter roller73includes a switching mechanism, that is, a first relay510and a second relay511to switch between the power source unit110and the power source unit111. More specifically, when closing a contact of the first relay510and opening a contact of the second relay511, the AC-DC superimposed bias is applied to the secondary transfer counter roller73. By contrast, when opening the contact of the first relay510and closing the contact of the second relay511, the secondary transfer counter roller73is applied with only the DC voltage bias.

According to the present embodiment, in order to control application of the voltage to the transfer device using the relays, a control signal is passed between the control circuit300and each of the power sources110and111. Furthermore, a relay driver129is also provided so that switching can be controlled via a signal line RY_DRIV.

With reference toFIG. 8, a description is provided of another example of a power source unit that generates the AC-DC superimposed bias.FIG. 8illustrates a configuration in which the transfer bias can be selected from the AC-DC superimposed bias and the voltage with only the DC component in a similar manner as the configuration illustrated inFIG. 7.

Similar to the foregoing embodiment illustrated inFIG. 7, the transfer bias can be selected from the secondary transfer using the voltage containing only the DC component and the secondary transfer using the AC-DC superimposed voltage. The difference between the configuration illustrated inFIG. 7and the configuration illustrated inFIG. 8is that the first relay510serving as a switching mechanism is provided only at the output of the second power source unit111according to the illustrative embodiment ofFIG. 8. The output side of the first relay510is connected to the first power source unit110.

With this configuration, when the AC-DC superimposed bias is output from the second power source unit111by closing the contact of the first relay510, the voltage is supplied to the first power source unit110connected in parallel. Although the second power source unit111may act as a load on the first power source unit110, this configuration allows simplification of the circuit as long as the transfer unit is not affected by the current supplied to the first power source unit110, thereby achieving the same function with a simple and inexpensive configuration.

With reference toFIG. 9, a detailed description is provided of the power source unit such as shown inFIG. 6.FIG. 9is a simplified circuit diagram illustrating the power source unit ofFIG. 6. InFIG. 6, the power source unit for application of the AC voltage and the power source unit for application of the DC voltage are illustrated as separate power source units. By contrast, according to an illustrative embodiment shown inFIG. 9, both the power source unit for application of the AC voltage and the power source unit for application of the DC voltage are disposed in the first power source unit110.

As illustrated inFIG. 9, the constant current control is performed in both the AC voltage generator112illustrated substantially in the upper half ofFIG. 9and the DC voltage generator113illustrated substantially in the lower half. For the AC voltage, a low voltage approximating to an output of the high voltage transformer is taken out by using a winding N3_AC900and compared with a reference signal Vref_AC_V902by a voltage control comparator901. The AC component of the current of the AC is taken out by an AC detector911disposed between a capacitor C_AC_BP903and the ground, and compared with a reference signal Vref_AC_I905by a current control comparator904. The capacitor C_AC_BP903for biasing the AC component is connected in parallel with the output of the DC voltage generator. The level of the reference signal Vref_AC_I905is set in accordance with a signal of AC output current for setting supplied via the signal line AC_PMW.

The level of the reference signal Vref_AC_V902is set such that when the output voltage reaches or exceeds a predetermined level (for example, at unloaded conditions), the output of the voltage control comparator901becomes valid. The level of the reference signal Vref_AC_I905is set such that the output of the current control comparator904becomes valid under a normal loaded condition. Depending on the degree of loaded conditions (e.g., the secondary transfer counter roller73, the secondary transfer roller80, and devices between the rollers), the high voltage output current is switched. The outputs of the voltage control comparator901and the current control comparator904are provided to an AC driver906, and an AC high voltage transformer907is driven in accordance with the levels of the outputs.

Similarly, the DC voltage generator detects both the output voltage and the output current. The voltage is detected and taken out by a DC voltage detector912connected in parallel with a rectification smoothing circuit provided to an output winding N2_DC913of the high voltage transformer. The current is detected and taken out by connecting a DC detector914between the output winding and the ground. Similar to the AC, each of the detection signals of the voltage and the current is compared with the reference signals of Vref_DC_V909and Vref_DC_I910, thereby regulating the DC component of the high voltage output.

The foregoing descriptions pertain to application of the superimposed bias to transfer the toner image on the intermediate transfer belt to the recording medium. As described above, in order to produce the AC-DC superimposed bias in which the AC voltage component is superimposed on the DC voltage component, various components are required. For example, even when an image forming apparatus is equipped with devices for supplying the DC voltage as in known image forming apparatuses, devices for superimposing the AC voltage on the DC voltage are needed as illustrated inFIGS. 6 through 9. Such devices include the AC detector, the voltage control comparator, and the current control comparator, in addition to the AC driver121, the AC high voltage transformer122, the AC output detector123, and the AC controller124. Various signal lines connecting to the controller300are also required.

As is generally the case for the image forming apparatus, in order to produce the AC-DC superimposed bias, the number of parts are required, thereby complicating arrangement of the parts in the image forming apparatus and complicating efforts to make the image forming apparatus as a whole as compact as is usually desired. Furthermore, as the individual constituent parts for application of the AC-DC superimposed bias are mounted in the image forming apparatus one by one, assembly becomes complicated, increasing the risk of misassembly.In a case in which a user wishes to add additional devices for application of the AC-DC superimposed bias to the image forming apparatus later as an option, the image forming apparatus needs an extra space for the additional devices.

As is generally the case for the image forming apparatus, devices that are not expected to be touched by a user are normally disposed at the back of the image forming apparatus. In such a case, upon installation of the devices for application of the AC-DC superimposed bias, technicians need to access the back of the image forming apparatus, which is generally facing a wall of the office. The image forming apparatus may need to be moved so that the technicians can work at the back of the image forming apparatus. Moreover, the devices for application of the AC-DC superimposed bias are comprised of a plurality of parts, complicating installation of these parts in the image forming apparatus and hence leading to prolonged downtime.

In view of the above, according to an illustrative embodiment of the present invention, the devices for application of the AC-DC superimposed bias are constituted as a single integrated unit, that is, constituted as a submodule (power supply module)500, detachably attachable relative to the image forming apparatus. The submodule500includes one or more circuit boards on which the constituent components for application of the AC-DC superimposed bias are disposed. However, disposing the components on a single circuit board can reduce the size of the submodule500as a whole and also can reduce the amount of associated wiring, hence reducing overall cost.

With reference toFIG. 10, a description is provided of the submodule500.

FIG. 10is a perspective view schematically illustrating an example configuration of the submodule500.FIG. 10illustrates the second power source unit111indicated by a broken line shown inFIG. 7serving as the submodule500. According to the present illustrative embodiment shown inFIG. 10, the submodule500includes the first relay510and the second relay511. It is to be noted thatFIG. 10shows representative components of the submodule500. However, the constituent components are not limited to the structure illustrated inFIG. 10.

As illustrated inFIG. 10, the submodule500includes a bias application circuit board501for application of the AC-DC superimposed bias, the AC high voltage transformer122, the first relay510, the second relay511, and a terminal block502. The first relay510and the second relay511switch between the first power source unit110for application of the DC voltage and the second power source unit111(that is, the submodule500) for application of the AC-DC superimposed bias. The terminal block502connects the power source unit and the submodule500to the secondary transfer counter roller73via the first relay510and the second relay511.

Alternatively, as compared with the exemplary configuration of the submodule500shown inFIG. 10, the second power source unit111for application of the AC voltage may constitute the submodule500, or the second power source unit111including the first relay510without the second relay511as illustrated inFIG. 8may constitute the submodule500. Alternatively, the first power source unit110in which the power source unit for application of the AC voltage and the power source unit for application of the DC voltage are constituted as a single integrated unit as illustrated inFIG. 9may constitute the submodule500. In this case, a structure capable of application of the AC-DC superimposed bias is preinstalled in the image forming apparatus.

According to the present illustrative embodiment, in the submodule500, the constituent components for application of the AC-DC superimposed bias such as the AC high voltage transformer122and the terminal block502are disposed on the bias application circuit board501. Furthermore, as illustrated inFIG. 10, the submodule500includes the first relay510and the second relay511for switching between the DC bias and the AC-DC superimposed bias as a single integrated unit. It is to be noted that the first relay510and the second relay511may be disposed on the bias application circuit board501for application of the AC-DC superimposed bias. Alternatively, the first relay510and the second relay511may be disposed separately from the bias application circuit board501, but within the submodule500.

In a case in which the first relay510and the second relay511are disposed integrally in the submodule500as illustrated inFIG. 10, when the AC voltage is not needed only the bias with the DC voltage component need be applied as in the known transfer device, but with a simpler and more energy-efficient configuration than the known transfer device. That is, this configuration facilitates installation of the components for application of the AC-DC superimposed bias optionally in the image forming apparatus that transfers an image using only the DC voltage.

As described above, according to the illustrative embodiment of the present invention, the constituent components for application of the AC-DC superimposed bias are constituted as a single integrated unit as the submodule500which is detachably attachable relative to the image forming apparatus. With this configuration, upon installation of the submodule500, the technicians can place the submodule500at a predetermined place in the image forming apparatus, and simply connect wiring and harnesses to the submodule500, thereby enabling the image forming apparatus to apply superimposed bias with a simple configuration.

Furthermore, this configuration provides the greater compactness that is usually desired of an image forming apparatus. According to the illustrative embodiment, the submodule500may be attached optionally to the image forming apparatus using screws, for example. Upon request from the user, the technicians can bring and attach the submodule500for application of the AC-DC superimposed bias to the image forming apparatus optionally using the screws without disassembling the image forming apparatus. This arrangement reduces downtime significantly.

Although the submodule500may be disposed at any place in the image forming apparatus, preferably, the submodule500may be disposed inside the transfer unit200for greater compactness. More specifically, the submodule500may be disposed inside the loop formed by the intermediate transfer belt50so that the size of the existing image forming apparatus does not need to be changed. This configuration is advantageous when the submodule500including the first relay510and the second relay511for switching between the DC bias and the AC-DC superimposed bias is provided optionally to the image forming apparatus to enable the image forming apparatus to apply the AC-DC superimposed bias.

With reference toFIGS. 11 through 14, a description is provided of installation of the submodule500in the transfer unit200of the image forming apparatus according to an illustrative embodiment of the present invention.FIG. 11Ais a schematic diagram illustrating the transfer unit200in the image forming apparatus.FIG. 11Bis a schematic diagram illustrating the transfer unit200moved towards the proximal end of the image forming apparatus in the direction indicated by an arrow inFIG. 11A.

Generally, the transfer unit200disposed in the image forming apparatus can be taken out to the proximal end of the image forming apparatus along a rail or the like (not illustrated). If the submodule500is detachably attachable relative to the transfer unit200, when installing the submodule500in the image forming apparatus, only the proximal side (front side) of the image forming apparatus is accessed and the submodule500can be installed with ease without accessing the back of the image forming apparatus.

As illustrated inFIG. 12, the first power source unit110for application of the DC voltage (the power source unit110ofFIG. 7) is disposed in the transfer unit200above a control circuit board for the transfer unit200.FIG. 12is a top view schematically illustrating a portion of the transfer unit200as viewed from the top of the image forming apparatus.

In known image forming apparatuses, the power source unit (equivalent to the power source unit110) for the DC voltage and the control board for the transfer unit (equivalent to the transfer unit200) that also controls the power source unit for the DC voltage are disposed in parallel in the horizontal direction (corresponding to a left-right direction inFIG. 12). By contrast, according to the illustrative embodiment, the power source unit110is disposed above the control board for the transfer unit200in the vertical direction so that a mounting space A is formed. With this configuration, the submodule500can be disposed at the mounting space A.

Alternatively, the power source unit110for application of the DC voltage may be disposed below the control board of the transfer unit200. In other words, the power source unit110and the control board are stacked vertically in a recessed portion of the transfer unit200.

FIG. 12illustrates a portion of the transfer unit200as viewed from the top thereof after the transfer unit200is taken out from the image forming apparatus and the intermediate transfer belt50is removed from the transfer unit200. Further, a top cover covering the power source unit110is also removed inFIG. 12.

InFIG. 12, the power source unit110includes the DC high voltage transformer126, a connector terminal190provided to the DC high voltage transformer126, a first harness180for the transfer electric field connected to the secondary transfer counter roller73or the secondary transfer roller80, a connector terminal191connected to the connector terminal190of the DC high voltage transformer126, and so forth. In a state in which the submodule500is not installed in the transfer unit200, the DC output from the DC high voltage transformer126is provided to the secondary transfer counter roller73or to the secondary transfer roller80via the first harness180by connecting the connector terminal191to the connector terminal190.

It is to be noted that an upper surface of a unit frame201of the transfer unit200is provided with a clamp192to clamp the first harness180. Accordingly, the first harness180can be fixed reliably to the unit frame201when the submodule500is not installed.

Referring now toFIG. 13, a description is provided of installation of the submodule500in the mounting space A.FIG. 13is a top view schematically illustrating a portion of the intermediate transfer unit200as viewed from the top thereof. Similar to FIG.12,FIG. 13illustrates a portion of the transfer unit200as viewed from the top thereof after the transfer unit200is taken out from the image forming apparatus and the intermediate transfer belt50is removed from the transfer unit200. Furthermore, the top cover covering the power source unit110is also removed. As illustrated inFIG. 13, the submodule500is disposed at the side of the power source unit110and the control board vertically stacked (at the left side inFIG. 13). With this configuration, the submodule500can be added to the image forming apparatus without changing the original size of the image forming apparatus.

FIG. 14is a cross-sectional view schematically illustrating the submodule500disposed in the transfer unit200as viewed from the front of the image forming apparatus. It is to be noted that becauseFIG. 14is a schematic diagram as viewed from the front side of the intermediate transfer unit200, the positional relations of the transfer unit200in the horizontal direction are reverse as compared with the positional relations shown inFIG. 13. The upper side ofFIG. 13corresponds to the front side of the intermediate transfer unit200, and the lower side corresponds to the back of the intermediate transfer unit200.

InFIG. 14, the unit frame201of the transfer unit200is disposed inside the loop formed by the intermediate transfer belt50, and supports the DC power source unit110, the control board300, and the submodule500.FIG. 14illustrates the submodule500disposed in the transfer unit200, and the DC power source unit110disposed above the control board300.

As illustrated inFIG. 14, a portion of the frame201is recessed downward. The DC power source unit110, the control board300, and the submodule500are disposed in the recessed portion of the frame201of the transfer unit200. A metal shield151covers the top of the recessed portion of the frame201to cover the DC power source unit110, the control board300, and the submodule500disposed in the recessed portion of the unit frame201. An insulating sheet152is attached to the lower surface of the metal shield151facing the submodule500. The metal shield151is detachably attachable relative to the transfer unit200, thereby facilitating installation of the submodule500and maintenance of components with ease.

The DC power source unit110includes a circuit board115for application of the DC. The circuit board115includes the high voltage transformer126. The circuit board115is supported by a metal planar member153. The control board300for controlling the transfer unit200is supported by a metal planar member154. The bias application circuit board501of the submodule500includes the AC high voltage transformer122. The circuit board501is supported by a metal planar member155.

An upper metal planar member156is disposed between the primary transfer rollers61such that the upper metal planar member156covers the DC power source unit110, the control board300, the submodule, and so forth disposed beneath the metal planar member151. The metal planar member156is also detachably attachable relative to the transfer unit200.

With reference toFIGS. 10 through 12, a description is provided of installation of the submodule500in the image forming apparatus. First, as illustrated inFIG. 11B, the transfer unit200is pulled out to the front of the image forming apparatus. Subsequently, the intermediate transfer belt50is removed from the transfer unit200, and the cover is removed to install the submodule500. This state is shown inFIG. 12. Subsequently, the connector terminal191shown inFIG. 12is disconnected from the connector terminal190. The first harness180is removed from the clamp192. In this state, the submodule500is installed in the mounting space A. The submodule500is fixed to the mounting space A using a screw or any other suitable fixing member.

Subsequently, the harnesses are connected such that the submodule500and the power source unit110are connected as illustrated inFIG. 7.

With reference toFIGS. 15 and 16, a description is now provided of connecting the submodule500and the DC power source unit110.FIG. 15is a top view schematically and partially illustrating the submodule500disposed in the transfer unit200.FIG. 16is a partially exploded diagram ofFIG. 15illustrating connection of the connecting portions of the submodule500and the DC power source unit110.

As illustrated inFIG. 16, the high voltage transformer126of the DC power source unit110includes a connecting portion (a) corresponding to the connector terminal190. The terminal block502of the submodule500includes connecting portions (b) through (e). The connecting portions (c) and (e), and the connecting portions (d) and (e) are connected electrically on the terminal block502. Similarly, the first relay510of the submodule500includes connecting portions (h) and (i). The second relay511includes connecting portions (f) and (g). The first harness180from the secondary transfer counter roller73includes a connecting portion (j) which corresponds to the connector terminal191.

When the submodule500is not mounted, there is only one path, that is, the connecting portions (a) and (j) are connected. When the submodule500is mounted, 5 paths are formed, that is, between the connecting portions (j) and (e), between the connecting portions (h) and (d), between the connecting portions (f) and (c), between the connecting portions (i) and (a), and between the connecting portions (g) and (d). It is to be noted that the connecting portion (b) of the terminal block502is a connecting portion that leads to the AC high voltage transformer122of the submodule500.

Upon installation of the submodule500, connection of the first harness180can be changed such that the first harness180is detached from the clamp192illustrated inFIG. 12, and the connector terminal191(connecting portion (j)) at the end of the first harness180is detached from the connector terminal190(connecting portion (a)) of the high voltage transformer126of the DC power source. Subsequently, the connecting portion (j) at the end of the first harness180is connected to the connecting portion (e) of the terminal block502. The connecting portion (i) of the first relay510is connected to the connector terminal190(the connecting portion (a)) of the high voltage transformer126by using a second harness160as illustrated inFIG. 15. Other paths are connected in the submodule500in advance. One end of the second harness160may be connected to the connecting portion (i) of the first relay510in advance in the submodule500.

As described above, the configuration capable of applying the superimposed bias as illustrated inFIG. 7can be formed with two simple connecting operations. That is, the connector terminal191(the connecting portion (j)) at the end of the harness180is detached from the connector terminal190(connecting portion (a)) and then connected to the connecting portion (e) of the terminal block502, while the connecting portion (i) and the connecting portion (a) are connected by the second harness160. With this configuration, the configuration capable of applying the AC-DC superimposed bias as illustrated inFIG. 7is accomplished with two simple steps.

The signal lines connecting the submodule500and the control circuit300may be grouped together as a signal-line group connector when the submodule500is assembled. The submodule500and the control circuit300are connected by simply connecting the signal-line group connector with the connectors of the control circuit300detachably attachable relative to the signal-line group connector.

As described above, with the configuration as illustrated inFIG. 7, when the AC voltage is not necessary, only the DC voltage component can be supplied easily in an energy-efficient way as in known image forming apparatuses. Providing the submodule500in the transfer unit200as illustrated inFIGS. 11 through 15enables the transfer unit200to apply the AC-DC superimposed bias easily and quickly without occupying a lot of space in the office.

It is to be noted that the terminal block502may be eliminated, and the connector terminal190(connecting portion (a)) and the connecting portion (e) may be connected while connecting the connector terminal191(connecting portion (j)) and the connecting portion (d). In this case, however, the connected connectors are arranged flexibly in the submodule500, and hence may touch other components, which may result in a failure of the device.

More specifically, because the first harness180for the transfer electric field is provided with the connector terminal191and supplied with the AC current of the high voltage, undesirable noise may be generated if the first harness180contacts other components and the transfer unit200. When this occurs, such noise may be transmitted to the photoconductive drum11and other components via the transfer unit200, thereby adversely affecting the latent image formed on the photoconductive drum11and hence hindering imaging quality. In view of the above, it is preferable that the terminal block502be provided.

In order to prevent the second harness160supplied with the high voltage DC voltage from contacting the transfer unit200when the second harness160is guided to the first relay510, a first insulating guide601is provided to hold the second harness160. The first insulating guide601guides the second harness160to the first relay510without directly contacting the transfer unit200, thereby preventing the above-described noise. The first insulating guide601is made of material having high insulating properties, such as resin.

Similarly, in order to prevent the first harness180from contacting the transfer unit200when the first harness180is guided to the terminal block502, a second insulating guide600is provided to hold the first harness180. The second insulating guide600guides the first harness180supplied with the high voltage AC voltage to the terminal block502without directly contacting the transfer unit200, thereby preventing the above-described noise. The second insulating guide600is also made of material having high insulating properties, such as resin.

The number of constituent elements, locations, shapes and so forth of the constituent elements are not limited to any of the structure for performing the methodology illustrated in the drawings. For example, according to the illustrative embodiments shown inFIGS. 10 and 15, the first relay510and the second relay511are integrally disposed in the submodule500. Alternatively, the submodule500without the first relay510and the second relay511may be mounted in the transfer unit200.

The foregoing embodiments relate to the intermediate transfer method in which the intermediate transfer belt50serves as an image bearing member onto which a toner image is transferred. The present invention is not limited to the intermediate transfer method. For example, the present invention can be applied to a direct transfer method in which a toner image formed on the photoconductive drum is transferred directly onto a recording medium by the transfer electric field acting between the photoconductive drum and a transfer device (i.e. a transfer roller and a transfer charger) facing or contacting the photoconductive drum. In this case, the photoconductive drum serves as an image bearing member, and the AC-DC superimposed bias is applied to the transfer charger or the transfer roller facing or contacting the photoconductive drum.

According to an aspect of this disclosure, the present invention is employed in the image forming apparatus. The image forming apparatus includes, but is not limited to, an electrophotographic image forming apparatus, a copier, a printer, a facsimile machine, and a digital multi-functional system.

Furthermore, it is to be understood that elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. In addition, the number of constituent elements, locations, shapes and so forth of the constituent elements are not limited to any of the structure for performing the methodology illustrated in the drawings.