Patent Description:
A transfer device includes a transfer roller to transfer an image formed on an image carrier to a transfer medium in an imaging apparatus, a power source and a power-feed path switching mechanism (or switch device). The transfer roller includes a first rotation shaft of a conductive material and a roller-shaped ion conductive member disposed around the first rotation shaft. The power source generates a transfer voltage The power-feed path switching mechanism (or switch device) switches, during rotation of the transfer roller, a power-feed path (or power supply path) from the power source to the transfer roller between different power-feed paths (power supply paths) depending on whether the image is being transferred or not being transferred, to thereby reverse the direction of an electric field applied by the transfer voltage to the roller-shaped ion conductive member.

The transfer roller is adapted to be capable of contacting with and separating from the image carrier. The power-feed path switching mechanism Performs the switching of the power-feed path: by contacting the transfer roller to the image carrier to select a power-feed path from the power source, the first rotation shaft of the transfer roller, the roller-shaped ion conductive member of the transfer roller, the image carrier and ground when the image is being transferred; and by separating the transfer roller from the image carrier to select a power-feed path from the power source, the roller-shaped ion conductive member of the transfer roller, the first rotation shaft of the transfer roller, and ground when the image is not being transferred.

In some examples, the power-feed path switching mechanism may include an external power feed roller (or external power supply roller), an external power feed roller driving device (or external-power-supply-roller driving device), a transfer roller biasing device, a power feed mechanism (or power supply mechanism), and a grounding mechanism. The external power feed roller (external power supply roller) includes a second rotation shaft of a conductive material and a roller-shaped conductive member disposed around the second rotation shaft. The second rotation shaft and the roller-shaped conductive member are both electrically connected to the power source to apply the transfer voltage. The external power feed roller driving device (external-power-supply-roller driving device) rotates the external power feed roller when the image is not being transferred. The transfer roller biasing device displaces the transfer roller such that the transfer roller is made to contact with the image carrier and separate from the external power feed roller when the image is being transferred, and the transfer roller is made to contact with the external power feed roller and separate from the image carrier when the image is not being transferred. The power feed mechanism electrically connects the first rotation shaft of the transfer roller and the second rotation shaft of the external power feed roller when the image is being transferred. The grounding mechanism electrically grounds the first rotation shaft of the transfer roller when the image is not being transferred.

In some examples, the roller-shaped conductive member of the external power feed roller is disposed around the second rotation shaft of the external power feed roller in a rotatable manner relative to the second rotation shaft. The transfer roller biasing device may include a transfer roller urging mechanism to normally urge the transfer roller against the external power feed roller, a cam fixed to one end of the second rotation shaft of the external power feed roller, and a cam driving device to rotate the cam. The power feed mechanism may include a first power feed plate of a conductive material disposed in the cam to extend from the second rotation shaft of the external power feed roller to a cam lobe end of the cam, and a second power feed plate of a conductive material disposed adjacent to the cam on the first rotation shaft of the transfer roller. The grounding mechanism may include an electrically grounded ground plate of a conductive material disposed in a position to separate from the first rotation shaft of the transfer roller when the image is being transferred and to contact with the first rotation shaft of the transfer roller when the image is not being transferred. When the image is being transferred, the cam may be rotated by the cam driving device to a first position to push the second power feed plate with the cam lobe end of the cam, such that the transfer roller is separated (or distanced to be spaced apart) from the external power feed roller to contact with the image carrier and the first power feed plate positioned at the cam lobe end of the cam is electrically connected to the second power feed plate. When the image is not being transferred, the cam may be rotated by the cam driving device to a second position where the cam does not have a cam action on the second power feed plate, such that the transfer roller urged by the transfer roller urging mechanism is separated (or distanced to be spaced apart) from the image carrier and made to contact with the external power feed roller.

In some examples, a flange of a conductive material may be disposed on the second rotation shaft of the external power feed roller at one end of the roller-shaped conductive member of the external power feed roller in a rotatable manner relative to the second rotation shaft. The second rotation shaft and the roller-shaped conductive member may be electrically connected with each other via the flange.

In some examples, the external power feed roller driving device can include a first motor, and a first power transmission mechanism to transmit the rotation of the first motor to the external power feed roller.

In some examples, the cam driving device can include a second motor and a second power transmission mechanism to transmit the rotation of the second motor to the cam.

In some examples, the second power feed plate of the power feed mechanism can include a leaf spring adapted to abut against the cam lobe end of the cam when the image is being transferred.

In some examples, the roller-shaped conductive member of the external power feed roller can include a metal roller.

In some examples, the transfer roller biasing device can separate the transfer roller from the external power feed roller after a predetermined period of time from the transfer roller making contact with the external power feed roller.

In some examples, the transfer roller biasing device can separate the transfer roller from the external power feed roller upon power shutoff of the imaging apparatus installed with the transfer device.

In some examples, the transfer roller biasing device can displace the transfer roller to a position of no contact with the image carrier or the external power feed roller.

In some examples, an example imaging apparatus may include the transfer device.

In some examples, the imaging apparatus can be a monochrome printer or a color printer.

In some examples, an example method may be provided for producing a transfer device having a transfer roller to transfer an image formed on an image carrier to a transfer medium in an imaging apparatus. A transfer roller including a first rotation shaft of a conductive material and a roller-shaped ion conductive member disposed around the first rotation shaft, is disposed. A power source to generate a transfer voltage is further disposed. A power-feed path switching mechanism (or switch device) is disposed, to switch, during rotation of the transfer roller, a power-feed path (or power supply path) from the power source to the transfer roller between different power-feed paths (power supply paths) depending on whether the image is being transferred or not being transferred, to thereby reverse the direction of an electric field applied by the transfer voltage to the roller-shaped ion conductive member.

In the following description, with reference to the drawings, the same reference numbers are assigned to the same components or to similar components having the same function, and overlapping description is omitted. The terms "left" and "right" may refer to respective directions when a drawing is viewed from the front, and they are not always in agreement with directions during actual use of a device. Scale reductions in the drawings are not always based on actual dimensions, and partial emphasis may be made for ease of understanding of the operations and effects of the examples described.

With reference to <FIG>, an example imaging apparatus <NUM> forms a color image for example, by using the colors of magenta, yellow, cyan and black. The imaging apparatus <NUM> has a recording medium conveyance unit (or a recording medium conveyance device) <NUM> for conveying paper P as a transfer medium, a developing unit (developing device) <NUM> for developing an electrostatic latent image, a transfer unit (or transfer device) <NUM> for transferring a toner image onto the paper P, a photosensitive drum <NUM> as an electrostatic latent image carrier, and a fixing device <NUM> for fixing the toner image onto the paper P.

The recording medium conveyance unit <NUM> conveys the paper P on a conveyance path R1. The recording medium conveyance unit <NUM> allows the paper P to arrive at a secondary transfer region A along the conveyance path R1 at a timing when a toner image to be transferred to the paper P arrives at the secondary transfer region A along the path R2.

One developing unit (or developing device) <NUM> is provided for each of the colors of magenta, yellow, cyan and black, and therefore, four developing units (or devices) are provided. The developing unit (or device) <NUM> has a developing roller <NUM> for transferring toner to the photosensitive drum <NUM>. The developing unit <NUM> mixes and stirs toner and carrier (e.g., carrier particles) to obtain a developer including the toner and carrier particles. The developer is charged, and the developing roller <NUM> carries the developer having been charged. The developing roller <NUM> rotates to convey the developer to a region facing to the photosensitive drum <NUM>, where the toner of the developer carried on the developing roller <NUM> is transferred to an electrostatic latent image formed on an outer circumferential surface of the photosensitive drum <NUM>, to develop the electrostatic latent image.

The transfer device <NUM> conveys a toner image formed by each of the developing units <NUM> to the secondary transfer region A where the toner image is to be transferred to the paper P. The transfer device <NUM> includes an intermediate transfer belt <NUM> as an image carrier, support rollers 31a, <NUM> b and 31c and a drive roller 31d supporting the intermediate transfer belt <NUM>, a primary transfer roller <NUM> that presses the transfer belt <NUM> against the photosensitive drum <NUM>, and a transfer roller <NUM> that presses the intermediate transfer belt <NUM> against the drive roller 31d. The intermediate transfer belt <NUM> is an endless belt, which is circularly moved by rotation of the support rollers 31a, 31b and 31c, and the driver roller 31d. The intermediate transfer belt <NUM> moves or rotates along a moving path (or conveyance path or route) R2 by rotation of the drive roller 31d in the forward direction (for example, a counter-clockwise direction in <FIG>).

The primary transfer roller <NUM> presses against the photosensitive drum <NUM> from an inner circumference of the intermediate transfer belt <NUM>. The transfer roller <NUM> is a secondary transfer roller that presses against the drive roller 31d from an outer circumference of the intermediate transfer belt <NUM> during a transfer of the toner image formed on the intermediate transfer belt <NUM>. The transfer roller <NUM> is pressed against the drive roller 31d via the intermediate transfer belt <NUM> and follows in rotation with the drive roller 31d and intermediate transfer belt <NUM>. The transfer roller <NUM> transfers the toner image formed on the intermediate transfer belt <NUM> to the paper P. A contact point or region between the intermediate transfer belt <NUM> and the transfer roller <NUM> is a transfer portion T into which the paper P conveyed along the conveyance path R1. For example, paper sheets P may be conveyed sequentially to the transfer portion T at regular intervals. At this transfer portion T, the transfer roller <NUM> may perform the transferring of the toner image onto the paper P, as the paper P is moved continuously along the transfer portion T.

Four photosensitive drums <NUM> are provided for the four colors, respectively. The photosensitive drums <NUM> are arranged at four locations along the moving path R2 of the intermediate transfer belt <NUM>. The developing unit <NUM> and an exposure unit (exposure device) <NUM> are arranged at a location substantially facing the photosensitive drum <NUM>.

The fixing device <NUM> adheres and fixes, to the paper P, the toner image, which has been secondarily transferred from the intermediate transfer belt <NUM> to the paper P. The fixing device <NUM> has a heating roller <NUM> for heating the paper P and a pressing roller <NUM> for pressing the heating roller <NUM>. A nip portion as a contact region is formed between the heating roller <NUM> and the pressing roller <NUM>, and the toner image is melted and fixed to the paper P when the paper P is conveyed through the nip portion. The paper P having the toner image fixed by the fixing device <NUM> passes between discharge rollers <NUM>, <NUM> and is discharged to the outside of the imaging apparatus <NUM>.

<FIG> is an enlarged side view showing the example transfer roller <NUM> and the vicinity of the transfer roller <NUM>, in the example imaging apparatus <NUM> illustrated in <FIG>, which shows a state at a time of transferring the toner image formed on the intermediate transfer belt <NUM>. The example transfer roller <NUM> has a rotation shaft 33a made of a conductive material (e.g., a conductive rotation shaft), and a roller-shaped ion conductive member 33b, and the transfer roller <NUM> is disposed, for example, inside a transfer unit (transfer device) <NUM>.

<FIG> is a perspective view showing the transfer unit <NUM> and the vicinity of the transfer unit <NUM> in the example transfer device <NUM>. <FIG> is another perspective view showing the vicinity of the transfer unit <NUM> in the example transfer device <NUM>.

The transfer unit <NUM> is disposed on a chassis of the imaging apparatus <NUM> so as to be rotatable about, for example, a pair of rotatable shafts 34a. Accordingly, the transfer roller <NUM> disposed in the transfer unit <NUM> is movable between a first position to press the intermediate transfer belt <NUM> against the driver roller 31d, and a second position that is spaced apart from the intermediate transfer belt <NUM> and the drive roller 31d. For example, the transfer roller <NUM> may contact or separate from the drive roller 31d via the intermediate transfer belt <NUM> (cf. A grounding plate PE is disposed near the rotation shaft 33a of the transfer roller <NUM>. The grounding plate PE is disposed at such a location as to be capable of contacting and separating from the rotation shaft 33a of the transfer roller <NUM> at the time when the transfer unit <NUM> is rotated or pivoted about the rotatable shaft 34a.

An external power feed roller (or external power supply roller) <NUM> is disposed adjacent to the transfer roller <NUM>. The transfer unit <NUM> may include, for example, a transfer roller urging mechanism for urging the transfer roller <NUM> toward the external power feed roller <NUM>. The transfer roller urging mechanism is disposed, for example, between the transfer unit <NUM> and the chassis of the imaging apparatus <NUM>, and can be an elastic member such as a spring for rotating the transfer unit <NUM> in a predetermined direction.

A rotation shaft 35a of the external power feed roller <NUM> is made of a conductive material, and a roller-shaped conductive member 35b such as a metal roller is disposed on (or around) the rotation shaft 35a. The conductive member 35b can be fixed, for example, to two flanges 35c and 35d between the flanges 35c and 35d disposed on the rotation shaft 35a via a bearing such as an oil-impregnated sintered bearing or a ball bearing. This enables the conductive member 35b to rotate relative to the rotation shaft 35a. The flange 35c is made of a conductive material, for example, enabling electrical connection between the rotation shaft 35a and the conductive member 35b via the flange 35c. The flange 35c can be formed of, for example, a conductive resin. The flange 35d is formed with a gear 35e, and the gear 35e is connected to an external power feed roller driving motor (or external power supply driving motor) M1 for rotating the external power feed roller <NUM> via a power transmission mechanism <NUM> such as gears 36a, 36b.

In some examples, cams <NUM> are fixed to both ends of the rotation shaft 35a of the external power feed roller <NUM>, and a cam power feed plate (or cam power supply plate) PC of a conductive material extending from the rotation shaft 35a of the external power feed roller <NUM> to a cam lobe end 37a of the cam <NUM> is disposed at the cam <NUM>.

In some examples, a transfer roller power feed plate (or transfer roller power supply plate) PT including a leaf spring PT1, and being made of a conductive material, is disposed adjacent to the cam <NUM> on the rotation shaft 35a of the external power feed roller <NUM>, at each end of the rotation shaft 33a of the transfer roller <NUM>.

In some examples, a cam driving motor M2 for rotating the cam <NUM> via the power transmission mechanism <NUM> such as a gear 38a is connected to the rotation shaft 35a of the external power feed roller <NUM>.

<FIG> is a hardware block diagram of an example transfer device <NUM>. A power source <NUM> for generating a transfer voltage is electrically connected to, for example, the rotation shaft 35a of the external power feed roller <NUM>. The power source <NUM> can feed (or supply) power of a transfer voltage, for example, by bringing a power feed plate (or power supply plate) PS connected to the power source <NUM>, into contact with the rotation shaft 35a as shown in <FIG>. A controller <NUM> is connected to the external power feed roller driving motor M1 and the cam driving motor M2, to control the operation of the motors M1 and M2.

<FIG> illustrate operations carried out by the example transfer device during a first operational mode when a toner image is being transferred to a paper sheet P at the transfer portion T (cf. <FIG> illustrate operations carried out by the example transfer device during a second operational mode of the imaging apparatus, when a toner image is not being transferred (e.g., when no toner image is being transferred) at the transfer portion T (cf.

<FIG> is an enlarged perspective view showing a left-side end of the transfer roller <NUM> and the external power feed roller <NUM> shown in <FIG>. In the first operational mode, when a toner image is being transferred, the rotation shaft 35a of the external power feed roller <NUM> is rotated by the cam driving motor M2 via the power transmission mechanism <NUM> (cf. <FIG>), and then stopped at a position as illustrated in <FIG>. At this time, a cam lobe end 37a of the cam <NUM> abuts and presses against the leaf spring PT1, which causes the transfer unit <NUM> to be rotated or pivoted about the rotatable shaft 34a (cf. <FIG>), to separate or distance the transfer roller <NUM> from the external power feed roller <NUM>, to achieve a state shown in <FIG>. The cam power feed plate PC located at the cam lobe end 37a of the cam <NUM> is in contact with the leaf spring PT1, such that the cam power feed plate PC is electrically connected to the leaf spring PT1.

<FIG> shows a right-side end of the transfer roller <NUM> and the external power feed roller <NUM> of the transfer device <NUM> illustrated in <FIG>, which are arranged in the same state as in <FIG>. As mentioned above with respect to <FIG>, in <FIG>, the cam <NUM> rotates the transfer unit <NUM>, thereby separating or distancing the transfer roller <NUM> from the external power feed roller <NUM>. A gear 33c disposed at the right end of the transfer roller <NUM> is separated or distanced from the gear 35e formed on the flange 35d of the external power feed roller <NUM>. The rotation shaft 33a of the transfer roller <NUM> is separated or distanced from the grounding plate PE. The cam power feed plate PC located at the cam lobe end 37a of the cam <NUM> is brought into contact with the leaf spring PT1, so that they are electrically connected to each other.

<FIG> shows a wider region near the right end of the transfer roller <NUM> and the external power feed roller <NUM> shown in <FIG>, illustrating the relative positions of the external power feed roller <NUM>, and the external power feed roller driving motor M1 and the power transmission mechanism <NUM>. The external power feed roller <NUM>, the power transmission mechanism <NUM> and the external power feed roller driving motor M1 may be disposed, for example, on the chassis of a printer in a fixed manner, such that gears 35e, 36a and 36b remain in an engaged state with one another. The external power feed roller driving motor M1 is controlled by the controller <NUM>, for example, so as to be stopped when a toner image is being transferred.

<FIG> is a side view illustrating the transfer roller <NUM> and the external power feed roller <NUM> shown in <FIG>, as well as the intermediate transfer belt <NUM> and the drive roller 31d. As described above, at the time when a toner image is being transferred, the transfer unit <NUM> is rotated by a cam action of the cam <NUM>, and the transfer roller <NUM> is separated or distanced (to be spaced apart) from the external power feed roller <NUM> and displaced toward the drive roller 31d to press against the drive roller 31d via the intermediate transfer belt <NUM>, thereby rotating to follow the intermediate transfer belt <NUM> and the drive roller 31d. In this state, the transfer roller <NUM> contacts the intermediate transfer belt <NUM> and frictionally engages therewith to rotate. A nip portion is formed between the transfer roller <NUM> and the intermediate transfer belt <NUM>, enabling transfer of the toner image.

With reference to <FIG> showing a similar arrangement to <FIG>, a power-feed path (or power supply path) from the power source <NUM> when a toner image is being transferred, is indicated by three arrows. A region circled in a broken line indicates that the transfer roller power feed plate PT is electrically connected to the cam power feed plate PC on the cam <NUM>. The power-feed path from the power source <NUM> to the transfer roller <NUM> in this state, is set to supply power via the following sequence of components: Power source <NUM>; Power feed plate PS (cf. <FIG>); Rotation shaft 35a; Cam power feed plate PC; Leaf spring PT1; Transfer roller power feed plate PT; Rotation shaft 33a.

<FIG> is an schematic view illustrating the overall power-feed path. The transfer voltage is supplied from the power source <NUM> through the rotation shaft 35a of the external power feed roller <NUM> to the rotation shaft 33a of the transfer roller <NUM>, then flows through the ion conductive member 33b, the intermediate transfer belt <NUM>, and the drive roller 31d and the rotation shaft 31e electrically connected thereto, and thereafter, to the ground.

Accordingly, an electric field applied to the ion conductive member 33b by transfer voltage from the poser source <NUM> when a toner image is being transferred has a direction from the rotation shaft 33a of the transfer roller <NUM> to a radially outward direction thereof. This direction of electric field is shown by an arrow EF.

Next, with reference to <FIG>, example operations of the example transfer device when a toner image is not being transferred will be described.

<FIG> is a perspective view showing the left-side end of the transfer roller <NUM> and the external power feed roller <NUM> of the transfer device <NUM> shown in <FIG>. When a toner image is not being transferred, the rotation shaft 35a of the external power feed roller <NUM> is rotated by the cam driving motor M2 (cf. <FIG>) via the power transmission mechanism <NUM>, and the cam <NUM> is, for example, rotated by <NUM><IMG> from the position shown in <FIG> and stopped at that position. At this time, the cam <NUM> does not have a cam action (e.g., the cam <NUM> does not exert any force) on the leaf spring PT1 of the transfer roller power feed plate PT. Accordingly, the transfer unit <NUM> is urged by the transfer roller urging mechanism to be rotated or pivoted about the rotatable shaft 34a (cf. Consequently, the transfer roller <NUM> is separated (or distanced to be spaced apart) from the intermediate transfer belt <NUM> and the drive roller 31d and brought into contact with the external power feed roller <NUM>, to achieve a state shown in <FIG>. At this time, the leaf spring PT1 comes into such a state as to be electrically disconnected from the cam power feed plate PC on the cam <NUM>.

<FIG> shows a right-side end of the transfer roller <NUM> and the external power feed roller <NUM> of the transfer device <NUM> illustrated in <FIG>, which are arranged in the same state as in <FIG>. As mentioned above with respect to <FIG>, in <FIG>, the rotation of the transfer unit <NUM> causes the transfer roller <NUM> to come into contact with the external power feed roller <NUM>, and at the same time, the gear 33c disposed at the right end of the transfer roller <NUM> is engaged with the gear 35e formed in the flange 35d of the external power feed roller <NUM>, further bringing the rotation shaft 33a of the transfer roller <NUM> into contact with the grounding plate PE. In this state, the leaf spring PT is electrically disconnected from the cam power feed plate PC on the cam <NUM>.

<FIG> shows a wider region near the right end of the transfer roller <NUM> and the external power feed roller <NUM> shown in <FIG>. As described above with respect to <FIG>, the external power feed roller <NUM>, the power transmission mechanism <NUM> and the external power feed roller driving motor M1 may be disposed, for example, on the chassis of a printer in a fixed manner, such that the gears 35e, 36a and 36b remain in an engaged state with on another. The external power feed roller driving motor M1 is controlled by the controller <NUM>, for example, so as to rotate when a toner image is not being transferred, and to thereby rotate the external power feed roller <NUM> when a toner image is not being transferred.

<FIG> is a side view illustrating the transfer roller <NUM> and the external power feed roller <NUM> shown in <FIG>, as well as the intermediate transfer belt <NUM> and the drive roller 31d. As described above, at the time when a toner image is not being transferred, the cam <NUM> does not have a cam action (e.g., the cam <NUM> does not exert force) on the leaf spring PT1 of the transfer roller power feed plate PT, which causes the transfer unit <NUM> to be urged and rotated by the transfer roller urging mechanism. Consequently, the transfer roller <NUM> is separated or distanced from the intermediate transfer belt <NUM> and the drive roller 31d, and brought into contact with the external power feed roller <NUM> to follow in rotation with the external power feed roller <NUM>.

With reference to <FIG> showing a similar arrangement to <FIG>, a power-feed path (or power supply path) from the power source <NUM> when a toner image is not being transferred, is indicated by two arrows. A region circled in a broken line indicates that the transfer roller power feed plate PT is electrically disconnected from the cam power feed plate PC on the cam <NUM>. The power-feed path from the power source <NUM> to the transfer roller <NUM> in this state is set to supply power via the following sequence of components: Power source <NUM>; Power feed plate PS (cf. <FIG>); Rotation shaft 35a; Conductive member 35b; and Ion conductive member 33b.

<FIG> is an schematic view illustrating the overall power-feed path. The transfer voltage is fed or supplied from the power source <NUM> through the conductive member 35b (cf. <FIG>) of the external power feed roller <NUM> to the ion conductive member 33b of the transfer roller <NUM>, then flows through the ion conductive member 33b and the rotation shaft 33a electrically connected thereto, and thereafter, to the ground.

Accordingly, an electric field applied to the ion conductive member 33b by transfer voltage from the power source <NUM> when a toner image is not being transferred has a direction from the surface of the transfer roller <NUM> to a radially inward direction thereof. This direction of electric field is shown by an arrow ER.

As described above, the example transfer device <NUM> may apply an electric field to the ion conductive member 33b of the transfer roller <NUM>. The electric field is directed in a radially outward direction from the rotation shaft 33a of the transfer roller <NUM> (cf. <FIG>) when a toner image is being transferred, and directed in a radially inward direction from the surface of the transfer roller <NUM> (cf. <FIG>) when a toner image is not being transferred. For example, the direction of the electric field applied to the ion conductive member 33b in the first operational mode when a toner image is being transferred is reversed, relative to the direction in the second operational mode when a toner image is not being transferred. Consequently in the second operational mode, ions present in the ion conductive member 33b when a toner image is not being transferred, move in a reverse direction from the ion movement direction in the first operational mode when a toner image is being transferred, so as to eliminate or reduce an ion imbalance (or polarization), further preventing or inhibiting an increase of volume resistivity of the ion conductive member.

The transfer device according to some examples, may use the power source <NUM> for applying a transfer voltage to the transfer roller <NUM> and may also use the power source <NUM> as a power source to eliminate or prevent the polarization of the transfer roller <NUM>. Accordingly, it is not necessary to additionally provide a power source to eliminate or prevent or inhibit polarization, thereby reducing production cost and the like. The transfer device , according to examples, uses a mechanical component for switching a power-feed path of a transfer voltage from the power source as described above. Accordingly, an increase of volume resistivity of the transfer roller using an ion conductive member may be prevented or inhibited without a complicated control mechanism. In addition, the mechanical switch may prevent or inhibit an uneven image transfer or damage on the image carrier that may otherwise be caused by the increase of volume resistivity, thereby improving the durability of the transfer roller, and improving a stability of transfer performance over a prolonged period of usage.

It is to be understood that not all aspects, advantages and features described herein may necessarily be achieved by, or included in, any one particular example. Indeed, having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and detail is omitted.

Claim 1:
A transfer device (<NUM>) for an imaging apparatus, comprising:
a transfer roller (<NUM>) to transfer an image formed on an image carrier (<NUM>) to a transfer medium in the imaging apparatus, the transfer roller including a rotation shaft (33a) comprising a conductive material and an ion conductive member (33b) disposed around the rotation shaft;
a power source (<NUM>) to generate a transfer voltage; and
a switch device to selectively connect, during a rotation of the transfer roller, a power-supply path from the power source to the transfer roller among a plurality of power-supply paths based on whether or not the image is being transferred from the image carrier, to reverse the direction of an electric field applied by the transfer voltage to the ion conductive member, characterised in that
the transfer roller is movable to contact the image carrier and to be spaced apart from the image carrier; and
the switch device is to select the power-supply path:
by moving the transfer roller to contact the image carrier in order to set the power-supply path to extend from the power source, via the rotation shaft of the transfer roller, via the ion conductive member of the transfer roller, via the image carrier and to an electric ground, when the image is being transferred, and
by moving the transfer roller away from the image carrier in order to set the power-supply path to extend from the power source, via the ion conductive member of the transfer roller, via the rotation shaft of the transfer roller, and to the electric ground, when the image is not being transferred.