JP5786640B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  As a prior art described in the publication, a rotary developing device equipped with a plurality of developing devices is provided adjacent to a photosensitive drum, and each developing device is placed at a developing position facing the photosensitive drum by rotating the rotary developing device. There is known one that develops a toner image of each color on a photosensitive drum by sequentially arranging and supplying a developing bias to a developing device disposed at a developing position (see Patent Documents 1 and 2).

  Here, in Patent Document 1, while a pin-shaped electrode is provided on the developing roll provided in each developing device constituting the rotary developing device, an arc-shaped electrode is provided around the developing position on the main body side, and on the main body side. The pin-shaped electrode provided in the developing device that moves toward the developing position with the rotation of the rotary developing device comes into contact with the arc-shaped electrode provided, and then the arc-shaped electrode is contacted with the arc-shaped electrode. A developing bias is supplied through the electrode and the pin-shaped electrode.

  Further, in Patent Document 2, a rotary developing device is rotated using a stepping motor, pulses input to the stepping motor are counted by a pulse counter, and each development is performed from a developing bias power source based on a count value by the pulse counter. The timing at which the developing bias voltage is applied to the device is controlled.

JP-A-2005-55750 JP-A-8-62954

  An object of the present invention is to supply power to a developing device disposed at a developing position without performing complicated control.

According to the first aspect of the present invention, there are provided a plurality of developing devices each provided with a latent image holding member that is rotatably provided and holds an electrostatic latent image, and each of which includes a developer receiving electrode and receiving power from the outside. A plurality of the developing devices are sequentially arranged at the development position facing the latent image holding body as the rotation occurs, and the electrostatic latent image on the latent image holding body is developed by the developing device arranged at the developing position. A developing unit that develops an image, and a power receiving electrode of the developing unit that moves toward the developing position as the developing unit rotates, is provided to the developing unit via the contacted power receiving electrode. Along with the detection of contact between the power supply electrode and the power reception electrode by the power supply electrode for supplying the development bias, the detection unit for detecting contact between the power supply electrode and the power reception electrode, and the detection unit, The current supply electrode An image forming apparatus including a supply unit for supplying a bias.
According to a second aspect of the present invention, the supply unit supplies a detection bias smaller in size than the development bias to the power supply electrode when the power supply electrode and the power reception electrode are not in contact with each other. The image forming apparatus according to claim 1, wherein the unit detects contact between the power feeding electrode and the power receiving electrode as a current flows through the power feeding electrode.
According to a third aspect of the present invention, the supply unit supplies a DC voltage as the detection bias and supplies a superimposed voltage obtained by superimposing an AC voltage on the DC voltage as the developing bias. This is an image forming apparatus.
A fourth aspect of the present invention is the image forming apparatus according to the third aspect, wherein the magnitude of the DC voltage at the detection bias is smaller than the magnitude of the DC voltage at the developing bias.
According to a fifth aspect of the present invention, the power feeding electrode is configured to be displaced with contact with the power receiving electrode, and the detection unit is configured so that the power feeding electrode is displaced with the displacement of the power feeding electrode. The image forming apparatus according to claim 1, wherein contact with the power receiving electrode is detected.

According to a sixth aspect of the present invention, there are provided a plurality of developing devices each provided with a latent image holding member that is rotatably provided and holds an electrostatic latent image, and each of which includes a developer receiving electrode and receiving power from the outside. A plurality of the developing devices are sequentially arranged at the development position facing the latent image holding body as the rotation occurs, and the electrostatic latent image on the latent image holding body is developed by the developing device arranged at the developing position. A developing unit that develops an image, and a developing unit that is conductive, is disposed along the rotation direction of the developing unit and straddles the developing position, and moves toward the developing position as the developing unit rotates. A power supply electrode that contacts a power receiving electrode of the power supply; a power source that supplies a voltage to the power supply electrode; an energization detection unit that detects energization via the power supply electrode; and the power source when energization is not detected by the energization detection unit From said voltage And a change unit that changes the voltage from the first voltage to a second voltage that is higher than the first voltage when energization is detected by the energization detection unit. An image forming apparatus including the image forming apparatus.
According to a seventh aspect of the present invention, when the change unit supplies a DC voltage as the first voltage and the second voltage, and the energization detection unit detects the energization, the second voltage is supplied. The image forming apparatus according to claim 6, wherein a third voltage which is an alternating voltage is supplied in addition to the above.
According to an eighth aspect of the present invention, an exposure potential is formed by exposing the latent image holding body charged to the charging potential and a charging portion that charges the latent image holding body to a charging potential, and the charging potential and An exposure unit that forms the electrostatic latent image by the exposure potential, wherein the first voltage is smaller than both the charging potential and the exposure potential, and the second voltage is smaller than the charging potential. The image forming apparatus according to claim 6, wherein the image forming apparatus has an exposure potential greater than the exposure potential.

According to the first aspect of the present invention, power can be supplied to the developing device disposed at the developing position without performing complicated control as compared with the case where this configuration is not provided.
According to the second aspect of the present invention, it is possible to detect contact between the power feeding electrode and the power receiving electrode using an existing element as compared with the case where the present configuration is not provided.
According to the third aspect of the present invention, it is possible to suppress wasteful power consumption when detecting contact between the power feeding electrode and the power receiving electrode, as compared with the case where this configuration is not provided.
According to the fourth aspect of the present invention, the safety of the image forming apparatus can be improved as compared with the case where this configuration is not provided.
According to the fifth aspect of the present invention, it is possible to easily detect contact between the power feeding electrode and the power receiving electrode as compared with the case where the present configuration is not provided.
According to the sixth aspect of the present invention, power can be supplied to the developing device disposed at the developing position without performing complicated control as compared with the case where this configuration is not provided.
According to the seventh aspect of the invention, it is possible to suppress wasteful power consumption when detecting contact between the power feeding electrode and the power receiving electrode, as compared with the case where this configuration is not provided.
According to the eighth aspect of the present invention, it is possible to develop the electrostatic latent image more reliably as compared with the case where this configuration is not provided.

1 is a diagram illustrating a schematic configuration of an image forming apparatus to which the exemplary embodiment is applied. It is sectional drawing which shows an example of a structure of a yellow developing device. It is a figure for demonstrating rotation of a rotary developing device, and the stop position accompanying rotation. It is a figure for demonstrating the relationship between a developing device and the electric power feeding with respect to this developing device before and behind a developing position. It is a figure for demonstrating the relationship between a rotary developing device and a developing bias electric power feeding part. It is a perspective view which shows an example of the whole structure of a developing bias electric power feeding part. It is a disassembled perspective view for demonstrating the structure of the electric power feeding body in a developing bias electric power feeding part. It is a figure for demonstrating the behavior of an electric power feeding body. 3 is a diagram illustrating an example of a configuration of a control system of the image forming apparatus according to Embodiment 1. FIG. 6 is a diagram illustrating an example of a timing chart in a full color image forming operation in Embodiment 1. FIG. It is a figure for demonstrating the relationship between a charging potential and an exposure potential, an energization detection voltage value, and a direct current development voltage value. FIG. 6 is a cross-sectional view for illustrating the configuration of a power feeding body in a second embodiment. 6 is a diagram illustrating an example of a configuration of a control system of an image forming apparatus according to Embodiment 2. FIG. 10 is a diagram illustrating an example of a timing chart in a full-color image forming operation according to Embodiment 2. FIG.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
<Embodiment 1>
FIG. 1 shows a schematic configuration of an image forming apparatus to which the exemplary embodiment is applied. The image forming apparatus is configured to sequentially transfer (primary transfer) each color toner image formed on the photoconductive drum 11 and arranged on the photoconductive drum 11 so as to be rotatable in the B direction. The intermediate transfer belt 20 to be held, the secondary transfer unit 30 that collectively transfers (secondary transfer) the superimposed toner image transferred onto the intermediate transfer belt 20 to the sheet S, and the secondary transferred image onto the sheet S. A fixing device 50 for fixing and a control unit 60 for controlling each mechanism unit of the image forming apparatus are provided. Note that the direction A which is the rotation direction of the photosensitive drum 11 and the direction B which is the rotation direction of the intermediate transfer belt 20 are directed to the same side in a region where both face each other.

  Around the photosensitive drum 11 as an example of the latent image holding member, a charging roll 12 that charges the photosensitive drum 11 along the direction A, and an exposure unit that exposes the charged photosensitive drum 11 as an example. The exposure device 13 (exposure beam is indicated by a symbol Bm in the drawing), yellow (Y), magenta (M), cyan (C), and black (K) toner components are accommodated and electrostatic on the photosensitive drum 11 is accommodated. The developing devices 14Y, 14M, 14C, and 14K that turn the latent images into visible images with toner are rotatably mounted, and the color component toner images formed on the photosensitive drum 11 are transferred to the intermediate transfer belt 20. A primary transfer roll 15 for transfer and a drum cleaning device 16 for cleaning residual toner on the photosensitive drum 11 are sequentially disposed.

  Here, the charging roll 12 as an example of the charging unit is arranged in contact with the photosensitive drum 11 and is configured to rotate as the photosensitive drum 11 rotates. The primary transfer roll 15 is disposed in contact with the intermediate transfer belt 20 at a position facing the photosensitive drum 11 with the intermediate transfer belt 20 interposed therebetween, and rotates with the rotation of the intermediate transfer belt 20. It is configured. Further, the drum cleaning device 16 has a blade member that contacts the photosensitive drum 11, for example.

  The photosensitive drum 11 is formed by forming an organic photosensitive layer on the surface of a metal thin cylindrical drum. In this example, the organic photosensitive layer is formed of a material that is negatively charged. . The photosensitive drum 11 is grounded.

  Further, the rotary developing device 14 as an example of the developing unit rotates in the C direction, and is configured to be able to mount a total of six developing devices. However, in this example, four developing devices 14Y, 14M, 14C, and 14K are continuously mounted in the circumferential direction on the rotary developing device 14, and the remaining two locations are empty. The development by the developing units 14Y, 14M, 14C, and 14K is performed by a reversal development method. Accordingly, the toner used in the developing units 14Y, 14M, 14C, and 14K has a negative charging polarity. In the following description, the developing devices constituting the rotary developing device 14 are referred to as a yellow developing device 14Y, a magenta developing device 14M, a cyan developing device 14C, and a black developing device 14K, respectively. In the following description, the empty space adjacent to the black developing device 14K is referred to as a first empty space 14S1, and the empty space adjacent to the first empty space 14S1 is referred to as a second empty space 14S2.

  Next, the intermediate transfer belt 20 is stretched over a plurality of (six in this embodiment) rolls 21 to 26. Among these, the rolls 21 and 25 are driven rolls, the roll 22 is a metal idle roll used for positioning the intermediate transfer belt 20 and forming a flat primary transfer surface, and the roll 23 has a constant tension of the intermediate transfer belt 20. The tension roll used for this purpose, the roll 24 is a drive roll for the intermediate transfer belt 20, and the roll 26 is a backup roll for secondary transfer described later.

  The secondary transfer unit 30 includes a secondary transfer roll 31 disposed on the toner image holding surface side of the intermediate transfer belt 20, a backup roll 26, and the like. Further, on the upstream side of the secondary transfer unit 30, a sheet conveyance guide 32 that guides the conveyed sheet S to the secondary transfer unit 30 is attached.

  On the other hand, a belt cleaning device 27 for cleaning residual toner adhering to the intermediate transfer belt 20 after the secondary transfer is provided on the downstream side in the rotation direction of the intermediate transfer belt 20 as viewed from the secondary transfer unit 30. A sheet metal member 28 is disposed along the inner surface of the intermediate transfer belt 20 at a position facing the belt cleaning device 27 across the transfer belt 20. The belt cleaning device 27 includes a scraper 41 that is formed of a stainless steel plate or the like and is disposed on the image forming surface side of the intermediate transfer belt 20, and a cleaner housing 42 in which the scraper 41 is accommodated. Further, one end side of the scraper 41 is fixed by being sandwiched between blocks 43, and this block 43 is attached to a holder 44 that rotates about a shaft 44a. Further, a spring 45 that urges the scraper 41 toward the intermediate transfer belt 20 is attached between a recess 44b provided on the lower end side of the holder 44 and a bulging portion provided at a lower portion of the cleaner housing 42. A film seal 46 is attached on the upstream side of the moving direction of the intermediate transfer belt 20 as viewed from the scraper 41 to prevent the removed foreign matter from scattering to the outside.

  In this embodiment, when a color image including a plurality of color toner images is formed on the sheet S, the toner image before the final color passes through the secondary transfer roll 31 and the belt cleaning device 27 until these toner images pass. The secondary transfer roll 31 and the belt cleaning device 27 are separated from the intermediate transfer belt 20. The secondary transfer roll 31 is configured to rotate with the rotation of the intermediate transfer belt 20 when contacting the intermediate transfer belt 20.

  Further, the fixing device 50 includes a heating roll 51 containing a heating source such as a halogen lamp, and a pressure roll 52 arranged in pressure contact with the heating roll 51. The sheet S on which the toner image has been transferred is passed through a fixing nip area formed between the two, so that fixing is performed.

  Next, the configuration of the developing device mounted on the rotary developing device 14 will be described using the yellow developing device 14Y as an example. The magenta developing unit 14M, the cyan developing unit 14C, and the black developing unit 14K have the same configuration as the yellow developing unit 14Y except for the color of the toner accommodated therein.

FIG. 2 is a cross-sectional view showing an example of the configuration of the yellow developing device 14Y. FIG. 2 illustrates a case where the yellow developing device 14Y is disposed at a developing position facing the photosensitive drum 11.
The yellow developing unit 14Y has an opening facing the outer peripheral surface of the photosensitive drum 11, and a developing housing 141 in which a developer (not shown) containing a carrier and toner is accommodated, and the developing housing 141 And a developing roll 142 rotatably disposed at a position facing the opening. Here, the developing roll 142 is disposed in non-contact with the photosensitive drum 11, and the both ends of the developing roll 142 in the axial direction abut against the outer peripheral surface of the photosensitive drum 11, whereby the photosensitive drum 11. A positioning roll (not shown) for determining the position (distance) of the outer peripheral surface of the developing roll 142 with respect to the outer peripheral surface is attached.

  Further, in the developing housing 141, the first stirring / conveying member 143 and the second stirring / conveying member disposed along the axial direction of the photosensitive drum 11 on the lower back side of the developing roller 142 as viewed from the photosensitive drum 11. A member 144 is provided. In addition, a partition wall that partitions the first stirring and conveying member 143 and the second stirring and conveying member 144 is provided between the first stirring and conveying member 143 and the second stirring and conveying member 144. This partition wall is formed integrally with the developing housing 141. Note that no partition walls are provided on both axial ends of the first stirring and conveying member 143 and the second stirring and conveying member 144, and the inside of the developing housing 141 is formed by the first stirring and conveying member 143 and the second stirring and conveying member 144. The developer is circulated and conveyed. Further, a layer thickness regulating member 145 that is attached to the developing housing 141 and regulates the layer thickness of the developer attached to the developing roll 142 is provided above the developing roll 142 in the drawing.

  In the yellow developing device 14Y, a so-called two-component developer including a yellow colored toner and a magnetic carrier is used as the developer. In this developer, the carrier has a positive charging polarity, and the toner has a negative charging polarity as described above. In the magenta developing device 14M, a developer containing a magenta colored toner and a magnetic carrier is used. In the cyan developing device 14C, a developer containing a cyan colored toner and a magnetic carrier is used. In the black developing device 14K, a developer containing black colored toner and a magnetic carrier is used.

  Further, the developing roll 142 is rotatably arranged in a hollow developing sleeve 142a, and is disposed inside the developing sleeve 142a and fixedly attached to the developing housing 141, and includes a plurality of magnetic poles (see FIG. (Not shown) and a magnet roll 142b. The developing sleeve 142a rotates in the D direction in an image forming operation for forming an image on the sheet S. Therefore, in the image forming operation, the photosensitive drum 11 that rotates in the A direction and the developing sleeve 142a that rotates in the D direction move in the same direction in a region where both face each other (developing region Ad described later: see FIG. 4). Then, one end side in the axial direction of the developing roll 142 (the front side in the drawing in the example shown in FIG. 2) protrudes in the axial direction and is electrically connected to the developing sleeve 142a, and is provided on the main body side of the image forming apparatus. A developing bias power receiving unit 142c that receives power from the developing bias power feeding unit 100 (see FIG. 5 described later) is provided. In this example, the developing bias power receiving unit 142c as an example of the power receiving electrode is provided coaxially with the rotation shaft of the developing sleeve 142a.

FIG. 3 is a diagram for explaining the rotation of the rotary developing device 14 in the image forming apparatus shown in FIG. 1 and a stop position associated with the rotation.
The rotary developing device 14 according to the present embodiment is configured to be able to rotate and stop in the C direction in units of 30 ° with the rotation shaft 14a as the center. The rotary developing device 14 stops in a state where the developing device is located at the developing position Pd facing the photosensitive drum 11 (see FIGS. 3B, 3D, 3F, and 3H). Further, the developing device is stopped in a state where the developing unit is not located at the portion facing the photosensitive drum 11 (see FIGS. 3A, 3C, 3E, and 3G).

  FIG. 3A shows an initial state before the image forming operation is started. At this time, no developing device is disposed at the developing position Pd, the yellow developing device 14Y is disposed at the standby position Pw on the upstream side in the C direction as viewed from the developing position Pd, and the downstream side in the C direction as viewed from the developing position Pd. The second empty space 14S2 is arranged at the retreat position Pe.

  FIG. 3B shows a state where the rotary developing device 14 is rotated 30 ° in the C direction from the state shown in FIG. At this time, the yellow developing device 14Y is disposed at the developing position Pd, the magenta developing device 14M is disposed at the pre-development position Pb that is upstream in the C direction when viewed from the standby position Pw, and the downstream side in the C direction when viewed from the retracted position Pe. The second empty space 14S2 is arranged at the post-development position Pa.

  FIG. 3C shows a state where the rotary developing device 14 is rotated 30 ° in the C direction from the state shown in FIG. At this time, the developing unit is not disposed at the developing position Pd, the magenta developing unit 14M is disposed at the standby position Pw, and the yellow developing unit 14Y is disposed at the retracted position Pe.

  FIG. 3D shows a state where the rotary developing device 14 is rotated 30 ° in the C direction from the state shown in FIG. At this time, the magenta developer 14M is disposed at the development position Pd, the cyan developer 14C is disposed at the pre-development position Pb, and the yellow developer 14Y is disposed at the post-development position Pa.

  FIG. 3E shows a state where the rotary developing device 14 is rotated 30 ° in the C direction from the state shown in FIG. At this time, the developing unit is not disposed at the developing position Pd, the cyan developing unit 14C is disposed at the standby position Pw, and the magenta developing unit 14M is disposed at the retracted position Pe.

  FIG. 3F shows a state in which the rotary developing device 14 is rotated by 30 ° in the C direction from the state shown in FIG. At this time, the cyan developer 14C is disposed at the development position Pd, the black developer 14K is disposed at the pre-development position Pb, and the magenta developer 14M is disposed at the post-development position Pa.

  FIG. 3G shows a state in which the rotary developing device 14 is rotated by 30 ° in the C direction from the state shown in FIG. At this time, the developing device is not disposed at the developing position Pd, the black developing device 14K is disposed at the standby position Pw, and the cyan developing device 14C is disposed at the retracted position Pe.

FIG. 3H shows a state in which the rotary developing device 14 is rotated 30 ° in the C direction from the state shown in FIG. At this time, the black developing device 14K is disposed at the development position Pd, the first empty space 14S1 is disposed at the pre-development position Pb, and the cyan developer 14C is disposed at the post-development position Pa.
When the rotary developing device 14 is rotated 120 ° in the C direction from the state shown in FIG. 3H, the initial state shown in FIG.

Next, a method for supplying power to the developing devices 14Y, 14M, 14C, and 14K mounted on the rotary developing device 14 will be described. In the present embodiment, power is supplied to the developing device disposed at the developing position Pd to apply a developing bias to the developing sleeve 142a via the developing bias power receiving unit 142c. For example, power is not supplied to the developing units located at the above-described pre-development position Pb, standby position Pw, retreat position Pe, post-development position Pa, and the like. However, in this embodiment, while the developing device moves from the standby position Pw to the developing position Pd, power supply to the developing device is started, and while the developing device moves from the developing position Pd to the retracted position Pe, The power supply to the developing device is terminated.
Further, in the present embodiment, the driving force for rotating the developing sleeve 142a is transmitted to the developing device disposed at the developing position Pd. Such a driving force is not transmitted to the developing units located at Pb, standby position Pw, retracted position Pe, post-development position Pa, and the like.

  FIG. 4 is a diagram for explaining the relationship between the developing device (any one of 14Y, 14M, 14C, and 14K: the same applies hereinafter) and power feeding to the developing device before and after the developing position Pd. Here, FIG. 4 shows a state in which the developing roll 142 provided in any one of the developing devices 14Y, 14M, 14C, and 14K moves along the C direction. In FIG. 4, the range in which toner transfer can occur between the developing roll 142 and the photoconductive drum 11 at the opposed portion between the developing roll 142 and the photoconductive drum 11 disposed at the developing position Pd is defined as a developing area. Called Ad.

  In the present embodiment, as the rotary developing device 14 rotates in the C direction, the developing roll 142 provided in the developing unit is moved to a pre-development position Pb, a standby position Pw, a development position Pd, a retracted position Pe, and a post-development It moves in the order of position Pa. As the developing device stopped at the standby position Pw moves to the developing position Pd, the developing roller 142 provided in the developing device passes through the contact start position Pc1 and moves to the main body of the image forming apparatus. The provided electrode (plate electrode 112 to be described later: see FIG. 7) and the developing bias power receiving portion 142c (see FIG. 2) provided in the developing device are in contact with each other, and the developing position Pd is maintained while maintaining the contacted state. To reach. Further, the developing roller 142 provided in the developing device passes through the contact end position Pc2 while the developing device stopped at the developing position Pd moves to the retracted position Pe. The provided plate-like electrode 112 and the developing bias power receiving portion 142c provided in the developing device are not in contact with each other, and reach the retracted position Pe while maintaining the non-contact state.

  Here, the contact start position Pc1 is set to be upstream in the C direction (A direction downstream) from the development area Ad, and the contact end position Pc2 is downstream from the development area Ad in the C direction (A direction upstream). Side). Therefore, the contact area Ac from the contact start position Pc1 to the contact end position Pc2 via the development position Pd is set to include a development area Ad and is wider than the development area Ad.

  FIG. 5 is a diagram for explaining the relationship between the rotary developing device 14 and the developing bias power supply unit 100 that supplies the developing bias to the developing device disposed at the developing position Pd. Here, FIG. 5A illustrates the case where the rotary developing device 14 is in the initial state shown in FIG. 3A, and FIG. The state shown in 3 (b) (the state in which the yellow developing device 14Y is disposed at the developing position Pd) is illustrated.

  As shown in FIGS. 5A and 5B, the developing bias power supply unit 100 of the present embodiment is disposed so as to straddle the developing position Pd. Then, power feeding is started for the developing device moving from the standby position Pw toward the developing position Pd, and power feeding is ended for the developing device moving from the developing position Pd toward the retracted position Pe. It is configured.

FIG. 6 is a perspective view showing an example of the overall configuration of the developing bias power supply unit 100 described above.
The development bias power supply unit 100 according to the present embodiment receives power from the development bias provided on the developing roll 142 of the developing device during the period from the contact start position Pc1 to the contact end position Pc2 via the development position Pd (see FIG. 4). The power supply body 110 that supplies power to the developing sleeve 142a by being in contact with the portion 142c, the power supply (DC developing power supply 86 and AC developing power supply 87: see FIG. 9 described later) and the power supply body provided in the main body of the image forming apparatus. 110 and an assembled electric wire 120 that connects to 110. In addition, the assembled wire 120 is provided with an insulated wire 121 in which a metal conductor is covered with an insulator, and a plate-like electrode 112 provided on one end side of the insulated wire 121 and provided on the insulated wire 121 and the power feeder 110 (FIG. 7 described later). And a connector 123 that is provided on the other end side of the insulated wire 121 and connects the insulated wire 121 and a power source (not shown).

FIG. 7 is an exploded perspective view for explaining the configuration of the power feeder 110 in the developing bias power feeder 100.
The power feeding body 110 of the present embodiment is made of an insulator, and is made up of a casing 111 that is fixedly attached to the main body of the image forming apparatus and a conductive metal plate, and is housed in the casing 111. A plate-like electrode 112 that contacts and supplies power to the developing bias power receiving unit 142c (see FIG. 6), and three coil springs that spring-bias the plate-like electrode 112 housed in the case 111 away from the case 111 113.

  Among these, the casing 111 has a shape curved in an arc shape, and a base 111a in which the plate-like electrode 112 is disposed on the upper surface that is curved and faces upward in the figure, and the base 111a has an arc shape. It has two wall parts 111b which protrude toward the same side as the upper surface of the base 111a from the edge which becomes an inner side, and the edge which becomes the outer side of a circular arc. Of these, the wall 111b provided outside the arc extends to the upstream side in the C direction, which is the rotational direction of the rotary developing device 14, and is bent at a right angle toward the inside of the arc. In addition, three openings 111c are formed at equal intervals along the circumferential direction of the arc on the upper surface of the base 111a. Here, the upper surface of the base 111a has a flat surface shape and a central flat surface 1111 in which three openings 111c are formed, and a wall 111b on the upstream side in the C direction when viewed from the central flat surface 1111. An upstream inclined surface 1112 that inclines in the opposite direction to the protruding direction, and a downstream side that inclines in the opposite direction to the protruding direction of the wall 111b on the downstream side in the C direction (see FIG. 1) when viewed from the central flat surface 1111. And an inclined surface 1113.

  The plate-like electrode 112 as an example of the power supply electrode has a shape that follows the upper surface of the housing 111. More specifically, the plate electrode 112 is opposed to the central flat portion 1121 facing the central flat surface 1111, the inlet inclined portion 1122 facing the upstream inclined surface 1112, and the downstream inclined surface 1113. And an exit side inclined portion 1123. Further, the plate-like electrode 112 is configured to bend from the upstream end in the C direction of the upstream inclined portion 1122 toward the same side as the upstream inclined surface 1112 and then bent to the opposite side. 120 includes a power receiving unit 1124 to which a crimp terminal 122 (see FIG. 6) provided at 120 is attached. In this example, with respect to the upstream inclined surface 1112, the central flat surface 1111 and the downstream inclined surface 1113 constituting the casing 111, the inlet inclined portion 1122 and the central flat portion 1121 constituting the plate electrode 112. And the exit side inclined part 1123 has a shape following each of them.

Here, in the present embodiment, each of the two wall portions 111b provided on the base 111a is provided with three convex portions that protrude toward opposite sides. And three convex parts provided in the other wall part 111b are arranged so as to face each other with respect to the three convex parts provided in one wall part 111b.
Further, in the present embodiment, three concave portions formed by cutting out the plate electrode 112 are provided on both sides of the central flat portion 1121 provided on the plate electrode 112. The three recesses provided on the other side of the plate electrode 112 are arranged so as to face each other with respect to the three recesses provided on one side of the plate electrode 112.

  Furthermore, the three convex portions provided on each of the two wall portions 111b of the housing 111 and the concave portion provided on each of the two side portions of the plate electrode 112 have a correspondence relationship, These six convex portions and six concave portions can be overlapped. However, the upstream inclined surface 1112 in the casing 111 and the inlet inclined portion 1122 in the plate electrode 112 are opposed to each other, and the downstream inclined surface 1113 in the casing 111 and the outlet inclined portion 1123 in the plate electrode 112 are opposed to each other. In the state where the two are opposed to each other, the three convex portions provided on each of the two wall portions 111b of the casing 111 and the three concave portions provided on each of the two side portions of the plate-like electrode 112 have a circular arc periphery. It is also located in a state shifted in the direction.

  Further, each of the three coil springs 113 is fitted into an opening 111c provided on the base 111a, and the other end of each of the three coil springs 113 comes into contact with the back side of the central flat portion 1121 in the plate electrode 112. It has become.

  In this example, the concave portions provided in the plate-like electrode 112 and the convex portions provided in the casing 111 in a state where the coil springs 113 are respectively attached to the three openings 111 c provided in the casing 111. Next, the plate electrode 112 is pushed into the housing 111 against the urging force of each coil spring 113, so that the main portion of the plate electrode 112 (the central flat portion 1121) is pressed. , The inlet-side inclined portion 1122 and the outlet-side inclined portion 1123) can be inserted into a concave space formed in the housing 111 between the two wall portions 111b. At this time, the power receiving portion 1124 provided in the plate-like electrode 112 passes through the space formed by the main body portion of the housing 111 and the bent portion of the one wall portion 111b, and on the lower surface side of the housing 111. Protruding.

  Subsequently, in the state described above, the plate-like electrode 112 is slid along the circumferential direction of the arc so that the inlet-side inclined portion 1122 of the plate-like electrode 112 faces the upstream inclined surface 1112 of the casing 111. After setting the outlet side inclined portion 1123 of the plate electrode 112 to oppose the downstream inclined surface 1113 of the casing 111, the plate electrode 112 is moved toward the casing 111 against the urging force of each coil spring 113. Stop pushing. Then, the plate-like electrode 112 is urged by three coil springs 113 attached to the casing 111, while the portions different from the recesses on the two side portions of the plate-like electrode 112 are two parts of the casing 111. The movement is restricted by abutting against a convex portion provided on the wall 111b. As a result, the plate-like electrode 112 is held with respect to the casing 111 in a state where movement in the vertical direction in FIG. 7 is permitted.

  FIG. 8 is a diagram for explaining the behavior of the power supply body 110 constituting the developing bias power supply unit 100. Here, FIG. 8A illustrates a case where the developing bias power receiving unit 142c does not exist in the vicinity of the power supply body 110 (in the case where the developing device does not exist), and FIG. The case where the developing bias power receiving unit 142c is present (here, the developing device is present at the developing position Pd) is illustrated. In addition, FIG. 8 has shown the circumferential direction sectional drawing in the electric power feeder 110, and has abbreviate | omitted description of the wall part 111b provided in the base 111a.

For example, as shown in FIG. 8A, when the developing bias power receiving portion 142c does not exist between the contact start position Pc1 and the contact end position Pc2, the plate-like electrode 112 is moved upward by three coil springs 113 in the figure. And rests in a state where it hits a convex portion provided on the wall 111b (not shown).
On the other hand, for example, as shown in FIG. 8B, when the developing bias power receiving portion 142c exists between the contact start position Pc1 and the contact end position Pc2, the plate-like electrode 112 has three coil springs 113. , And is stationary while being pushed downward in the figure by the developing bias power receiving unit 142c. At this time, each coil spring 113 is compressed more than the state shown in FIG.
When the developing bias power receiving unit 142c passes the contact end position Pc2, the plate electrode 112 and the three coil springs 113 return to the state shown in FIG.

FIG. 9 is a diagram illustrating an example of a configuration of a control system of the image forming apparatus according to the present embodiment.
The control unit 60 receives an instruction received from a user via a UI (user interface) 71 or a PC (personal computer) 72.
The control unit 60 includes a photosensitive drum driving motor 81 that drives to rotate the photosensitive drum 11, a charging power source 82 that supplies a charging bias to the charging roll 12, and a light source (not shown) provided in the exposure device 13. A control signal is output to each of the light source driving units 83 that drive the. Further, the control unit 60 rotates the developing device drive motor 84 that performs driving for rotating the rotary developing device 14 around the rotating shaft 14a, and the developing sleeve 142a provided in the developing device existing in the contact area Ac. A control signal is output to each of the developing sleeve drive motors 85 that perform the driving for causing them to occur. Further, the control unit 60 applies a DC developing bias (hereinafter referred to as a DC developing bias VB (DC)) to the developing bias feeding unit 100 (more specifically, the plate electrode 112 provided on the feeding unit 110). A control signal is supplied to a DC developing power source 86 for supplying AC and an AC developing power source 87 for supplying AC developing bias (hereinafter referred to as AC developing bias VB (AC)). Furthermore, the control unit 60 includes an intermediate transfer belt driving motor 88 that performs driving for rotating the intermediate transfer belt 20 via the drive roll 24, a primary transfer power supply 89 that supplies a primary transfer bias to the primary transfer roll 15, and a belt. A control signal is output to each belt cleaning device drive motor 90 that moves the cleaning device 27 to bring the scraper 41 into contact with or retract from the intermediate transfer belt 20. Then, the control unit 60 moves the secondary transfer roll 31 to bring the secondary transfer roll 31 into contact with or retract from the intermediate transfer belt 20, the secondary transfer roll 31, the backup roll 26, and the like. In the meantime, a control signal is output to the secondary transfer power source 92 that supplies the secondary transfer bias. Although not shown here, the control unit 60 also outputs a control signal to the fixing device 50 and the sheet S supply system. Furthermore, the control unit 60 detects from the energization detector 93 as an example of a detection unit or an energization detection unit that detects energization (the current has flowed) through the plate electrode 112 of the development bias power supply unit 100. An energization detection signal is input. In the present embodiment, the DC developing power source 86 and the AC developing power source 87 function as an example of a supply unit or a power source. In the present embodiment, the control unit 60 functions as an example of a changing unit.

  Next, the image forming operation in the present embodiment will be described. Here, as an example, a full-color image of four colors including yellow, magenta, cyan, and black is formed on one sheet S.

  FIG. 10 shows an example of a timing chart in the full-color image forming operation in this embodiment. Here, FIG. 10 shows the passage of time, rotation of the photosensitive drum 11 by the photosensitive drum driving motor 81 [(1) photosensitive drum driving], and supply of the charging bias to the charging roll 12 by the charging power source 82. [(2) Charging bias], supply of exposure signal to the exposure device 13 by the light source driving unit 83 [(3) exposure signal], and rotational driving of the rotary developing device 14 by the developing device driving motor 84 [(4) Development device drive], development device disposed at the development position Pd [(5) development device at development position], development sleeve 142a driven by the development sleeve drive motor 85 [(6) development sleeve drive], energization Detection of energization by the detector 93 [(7) energization detection] and supply of the DC developing bias VB (DC) to the developing sleeve 142a by the DC developing power source 86 [(8) DC developing bias] Supply of the AC developing bias VB (AC) to the developing sleeve 142a by the AC developing power source 87 [(9) AC developing bias] and rotational driving of the intermediate transfer belt 20 by the intermediate transfer belt driving motor 88 [(10) Intermediate transfer belt] Drive], the supply of the primary transfer bias to the primary transfer roll 15 by the primary transfer power supply 89 [(11) primary transfer bias], and the intermediate passing through the primary transfer region where the photosensitive drum 11 and the intermediate transfer belt 20 face each other. Image area (toner image forming area) on the transfer belt 20 [(12) primary transfer passing image] and position of the belt cleaning device 27 accompanying the driving of the belt cleaning device drive motor 90 [(13) belt cleaning device position] The position of the secondary transfer roll 31 accompanying the driving of the secondary transfer roll drive motor 91 [(14) secondary transfer roll position], and the secondary transfer roll The intermediate transfer belt that passes the secondary transfer region where the intermediate transfer belt 20 and the secondary transfer roll 31 face each other by supplying the secondary transfer bias to the secondary transfer unit 30 by (92) the secondary transfer bias by 92. 20 shows a relationship with an image area 20 (toner image formation area) [(16) secondary transfer passage image].

  In FIG. 10, “Y”, “M”, “C”, and “K” correspond to yellow, magenta, cyan, and black, respectively. In the “primary transfer passage image” shown in (12) and the “secondary transfer passage image” shown in (16), “Y” is yellow, “YM” is a combination of yellow and magenta, “YMC” corresponds to a superposition of yellow, magenta and cyan, and “YMCK” corresponds to a superposition of yellow, magenta, cyan and black. In the following description, a period required for the intermediate transfer belt 20 to make one revolution is referred to as a belt rotation period Tb.

  In the initial state, the photosensitive drum drive, charging bias, exposure signal, developing device drive, intermediate transfer belt drive, primary transfer bias, and secondary transfer bias are each set to OFF (stop). At this time, the rotary developing device 14 is set to the state shown in FIG. 3A, and no developing device is disposed at the developing position Pd. Accordingly, in the initial state, the developing sleeve drive, the DC developing bias VB (DC), and the AC developing bias VB (AC) are each OFF (stopped). Further, in the initial state, the belt cleaning device position and the secondary transfer roll position are set to retract, and the secondary transfer roll 31 and the belt cleaning device 27 (scraper 41) are separated from the intermediate transfer belt 20.

  With the start of the image forming operation, driving of the photosensitive drum 11 and driving of the intermediate transfer belt 20 are started (OFF → ON), and the photosensitive drum 11 rotates in the A direction and the intermediate transfer belt 20 rotates in the B direction. To do. In addition, with the start of the image forming operation, the supply of the DC developing bias VB (DC) is started, and the energization detection voltage Vd1 is applied (OFF → Vd1). At this time, the AC developing bias VB (AC) is maintained in the OFF state. At this time, since there is no developing device around the developing position Pd, the energization by the energization detector 93 is not detected (OFF). Subsequently, the supply of the charging bias is started (OFF → ON), and the photosensitive layer of the photosensitive drum 11 is charged to the charging potential VH (see FIG. 11 described later) by the charging roll 12. Here, in the present embodiment, the energization detection voltage Vd1 corresponds to the detection bias or the first voltage.

  Next, the rotary developing device 14 rotates 30 ° in the C direction and stops. Thereby, the rotary developing device 14 shifts from the state shown in FIG. 3A to the state shown in FIG. At this time, the yellow developing device 14Y reaches the developing position Pd from the standby position Pw via the contact start position Pc1 and stops. During this time, as the developing roller 142 (developing bias power receiving unit 142c) provided in the yellow developing device 14Y passes through the contact start position Pc1 of the power feeding unit 110 provided in the developing bias power feeding unit 100, The plate electrode 112 and the developing bias power receiving portion 142c of the developing roll 142 start to contact each other. As a result, the current resulting from the application of the energization detection voltage Vd1 is transferred from the plate-like electrode 112 of the developing bias power supply unit 100 via the developing bias power receiving unit 142c, the developing sleeve 142a, and the developer on the developing sleeve 142a. The drum 11 flows. As a result, energization by the energization detector 93 is detected (OFF → ON). Accordingly, the DC development bias VB (DC) is switched from the energization detection voltage Vd1 to the DC development voltage Vd2 (Vd1 → Vd2), and the supply of the AC development bias is started (OFF → ON). Further, rotation drive of the developing sleeve 142a provided in the yellow developing device 14Y starts (OFF) from when the yellow developing device 14Y reaches the developing position Pd via the contact start position Pc1 and stops. → ON). In this embodiment, the DC development voltage Vd2 corresponds to the development bias or the second voltage, and the AC development bias corresponds to the third voltage. The relationship between the energization detection voltage Vd1 and the DC development voltage Vd2 will be described later.

  After the rotating operation of the rotary developing device 14 is completed and the yellow developing device 14Y stops at the developing position Pd, supply of an exposure signal corresponding to yellow is started (OFF → ON). As a result, the photosensitive drum 11 that rotates in the A direction while being charged to the charging potential VH is exposed to a portion on which a yellow toner image is to be formed by the exposure beam Bm output from the exposure device 13. Thus, the charging potential VH changes to the exposure potential VL (see FIG. 11 described later). As a result, the charged and exposed photosensitive drum 11 corresponds to yellow, in which the charged potential VH is the background portion (the unexposed portion) and the exposure potential VL is the image portion (the exposed portion). An electrostatic latent image is formed.

  The electrostatic latent image formed on the photoconductive drum 11 passes through the developing area Ad as the photoconductive drum 11 rotates in the A direction. At this time, the yellow toner is selectively transferred from the yellow developing device 14Y disposed at the developing position Pd to the image portion at the exposure potential VL with respect to the photosensitive drum 11. As a result, a yellow toner image corresponding to the yellow electrostatic latent image is developed on the photosensitive drum 11 that has passed through the development area Ad. Details of the developing operation will be described later.

  Next, as the leading end side of the yellow toner image formed on the photosensitive drum 11 reaches the primary transfer region facing the intermediate transfer belt 20, the supply of the primary transfer bias is started (OFF → ON). . As a result, the yellow toner image formed on the photosensitive drum 11 rotating in the A direction starts to be primarily transferred to the intermediate transfer belt 20 rotating in the B direction.

  In this example, after the primary transfer of the yellow toner image is started, the supply of the exposure signal corresponding to yellow is stopped (ON → OFF), and the formation of the yellow electrostatic latent image is completed. Note that the exposure signal supply period corresponding to yellow is determined based on the size of the image to be formed (more specifically, the length of the image in the sub-scanning direction) (exposure signals for magenta, cyan, and black described later). Will be the same length). Then, as the rear end side of the yellow toner image obtained by developing the yellow electrostatic latent image formed on the photosensitive drum 11 passes through the primary transfer region, the supply of the primary transfer bias is stopped (ON → OFF). As a result, the entire yellow toner image is primarily transferred to the intermediate transfer belt 20 that rotates in the B direction. In the primary transfer of yellow, the yellow toner remaining on the photosensitive drum 11 side without being transferred to the intermediate transfer belt 20 is opposed to the drum cleaning device 16 as the photosensitive drum 11 rotates in the A direction. Reaches the part and is removed by the drum cleaning device 16.

  Then, after the yellow toner image developed on the photosensitive drum 11 passes through the primary transfer region, the rotary developing device 14 rotates 30 ° in the C direction and stops. Thereby, the rotary developing device 14 shifts from the state shown in FIG. 3B to the state shown in FIG. At this time, the yellow developing device 14Y reaches the retracted position Pe from the developing position Pd via the contact end position Pc2, and stops. During this time, the DC developing bias VB (DC) is switched from the DC developing voltage Vd2 to the energization detection voltage Vd1 (Vd2 → Vd1) before the developing roll 142 provided in the yellow developing device 14Y passes the contact end position Pc2. In addition, the supply of the AC developing bias is stopped (ON → OFF). Then, as the developing roll 142 provided in the yellow developing device 14Y passes through the contact end position Pc2, the plate-like electrode 112 of the power supply 110 and the developing bias power receiving unit 142c of the developing roll 142 are not in contact with each other. Thereby, the energization by the energization detector 93 is not detected (ON → OFF). Further, the rotation drive of the developing sleeve 142a provided in the yellow developing device 14Y is stopped (ON) until the yellow developing device 14Y reaches the retracted position Pe from the developing position Pd via the contact end position Pc2 and stops. → OFF). Further, as the yellow developing device 14Y stops at the retracted position Pe, the magenta developing device 14M reaches the standby position Pw and stops.

  Subsequently, the rotary developing device 14 moves in the C direction at a timing determined in advance based on the conveyance direction length of the sheet S to be image-formed and the peripheral length of the intermediate transfer belt 20 (belt rotation period Tb). Rotate 30 ° and stop. Thereby, the rotary developing device 14 shifts from the state shown in FIG. 3C to the state shown in FIG. At this time, the magenta developing device 14M reaches the developing position Pd from the standby position Pw via the contact start position Pc1 and stops. During this time, as the developing roll 142 provided in the magenta developing device 14M passes through the contact start position Pc1, the plate-like electrode 112 of the power supply 110 and the developing bias power receiving portion 142c of the developing roll 142 start to contact each other. As a result, the current resulting from the application of the energization detection voltage Vd1 is transferred from the plate-like electrode 112 of the developing bias power supply unit 100 via the developing bias power receiving unit 142c, the developing sleeve 142a, and the developer on the developing sleeve 142a. The drum 11 flows. As a result, energization by the energization detector 93 is detected (OFF → ON). Accordingly, the DC development bias VB (DC) is switched from the energization detection voltage Vd1 to the DC development voltage Vd2 (Vd1 → Vd2), and the supply of the AC development bias is started (OFF → ON). Further, the rotation driving of the developing sleeve 142a provided in the magenta developing device 14M is started (OFF) until the magenta developing device 14M reaches the developing position Pd via the contact start position Pc1 from the standby position Pw and stops. → ON).

  After the rotational operation of the rotary developing device 14 is completed and the magenta developer 14M is stopped at the development position Pd, supply of an exposure signal corresponding to magenta is started (OFF → ON). As a result, the photosensitive drum 11 that rotates in the A direction while being charged to the charging potential VH is exposed to a portion on which a magenta toner image is to be formed by the exposure beam Bm output from the exposure device 13. Thus, the charging potential VH changes to the exposure potential VL. As a result, an electrostatic latent image corresponding to magenta is formed on the photosensitive drum 11 that has been charged and exposed, with the charging potential VH as the background portion and the exposure potential VL as the image portion.

  The electrostatic latent image formed on the photoconductive drum 11 passes through the developing area Ad as the photoconductive drum 11 rotates in the A direction. At this time, the magenta toner is selectively transferred from the magenta developing device 14M disposed at the development position Pd to the image drum at the exposure potential VL with respect to the photosensitive drum 11. As a result, a magenta toner image corresponding to the magenta electrostatic latent image is developed on the photosensitive drum 11 that has passed through the development area Ad.

  Next, as the leading end side of the magenta toner image formed on the photosensitive drum 11 reaches the primary transfer region facing the intermediate transfer belt 20, supply of the primary transfer bias is started (OFF → ON). . As a result, the magenta toner image formed on the photosensitive drum 11 rotating in the A direction starts to be primarily transferred to the intermediate transfer belt 20 rotating in the B direction. In this embodiment, when the leading end side of the yellow toner image already transferred to the intermediate transfer belt 20 reaches the primary transfer region, the leading end side of the magenta toner image formed on the photosensitive drum 11 is The supply of the exposure signal corresponding to magenta is controlled so as to reach the primary transfer region. Therefore, the magenta toner image is superimposed on the yellow toner image on the intermediate transfer belt 20 that has passed through the primary transfer region.

  In this example, after the primary transfer of the magenta toner image is started, the supply of the exposure signal corresponding to magenta is stopped (ON → OFF), and the formation of the magenta electrostatic latent image is completed. Then, as the rear end side of the magenta toner image obtained by developing the magenta electrostatic latent image formed on the photosensitive drum 11 passes through the primary transfer region, the supply of the primary transfer bias is stopped (ON → OFF). As a result, the entire area of the magenta toner image is primarily transferred to the intermediate transfer belt 20 that rotates in the B direction, and a yellow and magenta superimposed toner image is formed. In the primary transfer of magenta, the magenta toner remaining on the photosensitive drum 11 side without being transferred to the intermediate transfer belt 20 is opposed to the drum cleaning device 16 as the photosensitive drum 11 rotates in the A direction. Reaches the part and is removed by the drum cleaning device 16.

  Then, after the magenta toner image developed on the photosensitive drum 11 passes through the primary transfer region, the rotary developing device 14 rotates 30 ° in the C direction and stops. Thereby, the rotary developing device 14 shifts from the state shown in FIG. 3D to the state shown in FIG. At this time, the magenta developing device 14M reaches the retracted position Pe from the developing position Pd via the contact end position Pc2, and stops. During this time, the DC developing bias VB (DC) is switched from the DC developing voltage Vd2 to the energization detection voltage Vd1 (Vd2 → Vd1) before the developing roll 142 provided in the magenta developing device 14M passes the contact end position Pc2. In addition, the supply of the AC developing bias is stopped (ON → OFF). As the developing roll 142 provided in the magenta developing device 14M passes through the contact end position Pc2, the plate-like electrode 112 of the power supply 110 and the developing bias power receiving portion 142c of the developing roll 142 are not in contact with each other. Thereby, the energization by the energization detector 93 is not detected (ON → OFF). Further, the rotation of the developing sleeve 142a provided in the magenta developing device 14M is stopped (ON) until the magenta developing device 14M reaches the retracted position Pe from the developing position Pd via the contact end position Pc2 and stops. → OFF). Further, as the magenta developing device 14M stops at the retracted position Pe, the cyan developing device 14C reaches the standby position Pw and stops.

  Subsequently, the rotary developing device 14 moves in the C direction at a timing determined in advance based on the conveyance direction length of the sheet S to be image-formed and the peripheral length of the intermediate transfer belt 20 (belt rotation period Tb). Rotate 30 ° and stop. Thereby, the rotary developing device 14 shifts from the state shown in FIG. 3E to the state shown in FIG. At this time, the cyan developing device 14C reaches the developing position Pd from the standby position Pw via the contact start position Pc1 and stops. During this time, as the developing roll 142 provided in the cyan developing device 14C passes through the contact start position Pc1, the plate-like electrode 112 of the power supply body 110 and the developing bias power receiving portion 142c of the developing roll 142 start to contact each other. As a result, the current resulting from the application of the energization detection voltage Vd1 is transferred from the plate-like electrode 112 of the developing bias power supply unit 100 via the developing bias power receiving unit 142c, the developing sleeve 142a, and the developer on the developing sleeve 142a. The drum 11 flows. As a result, energization by the energization detector 93 is detected (OFF → ON). Accordingly, the DC development bias VB (DC) is switched from the energization detection voltage Vd1 to the DC development voltage Vd2 (Vd1 → Vd2), and the supply of the AC development bias is started (OFF → ON). Further, rotation drive of the developing sleeve 142a provided in the cyan developing device 14C is started (OFF) until the cyan developing device 14C reaches the developing position Pd through the contact start position Pc1 and stops at the developing position Pd. → ON).

  After the rotational operation of the rotary developing device 14 is completed and the cyan developing device 14C is stopped at the developing position Pd, supply of an exposure signal corresponding to cyan is started (OFF → ON). As a result, the photosensitive drum 11 that rotates in the A direction while being charged to the charging potential VH is exposed to a portion to be formed with a cyan toner image by the exposure beam Bm output from the exposure device 13. Thus, the charging potential VH is changed to the exposure potential VL. As a result, an electrostatic latent image corresponding to cyan is formed on the photosensitive drum 11 that has been charged and exposed, with the charging potential VH as the background portion and the exposure potential VL as the image portion.

  The electrostatic latent image formed on the photoconductive drum 11 passes through the developing area Ad as the photoconductive drum 11 rotates in the A direction. At this time, cyan toner is selectively transferred from the cyan developing device 14C arranged at the developing position Pd to the image drum at the exposure potential VL with respect to the photosensitive drum 11. As a result, a cyan toner image corresponding to the cyan electrostatic latent image is developed on the photosensitive drum 11 that has passed through the development area Ad.

  Next, as the leading end side of the cyan toner image formed on the photosensitive drum 11 reaches the primary transfer region facing the intermediate transfer belt 20, supply of the primary transfer bias is started (OFF → ON). . As a result, the cyan toner image formed on the photosensitive drum 11 rotating in the A direction starts to be primarily transferred to the intermediate transfer belt 20 rotating in the B direction. In this embodiment, when the leading end side of the yellow and magenta superimposed toner image already transferred to the intermediate transfer belt 20 reaches the primary transfer region, a cyan toner image formed on the photosensitive drum 11 is formed. The supply of an exposure signal corresponding to cyan is controlled so that the leading end side of the ink reaches the primary transfer region. Therefore, the cyan toner image is superimposed on the yellow and magenta superimposed toner images on the intermediate transfer belt 20 that has passed through the primary transfer region.

  In this example, after the primary transfer of the cyan toner image is started, the supply of the exposure signal corresponding to cyan is stopped (ON → OFF), and the formation of the cyan electrostatic latent image is completed. Then, as the rear end side of the cyan toner image obtained by developing the cyan electrostatic latent image formed on the photosensitive drum 11 passes through the primary transfer region, the supply of the primary transfer bias is stopped (ON → OFF). As a result, the entire area of the cyan toner image is primarily transferred to the intermediate transfer belt 20 that rotates in the B direction, and a yellow, magenta, and cyan superimposed toner image is formed. In the primary transfer of cyan, cyan toner remaining on the photosensitive drum 11 side without being transferred to the intermediate transfer belt 20 faces the drum cleaning device 16 as the photosensitive drum 11 rotates in the A direction. Reaches the part and is removed by the drum cleaning device 16.

  Then, after the cyan toner image developed on the photosensitive drum 11 passes through the primary transfer region, the rotary developing device 14 rotates 30 ° in the C direction and stops. Thereby, the rotary developing device 14 shifts from the state shown in FIG. 3F to the state shown in FIG. At this time, the cyan developer 14C reaches the retracted position Pe from the developing position Pd via the contact end position Pc2, and stops. During this time, before the developing roll 142 provided in the cyan developing device 14C passes the contact end position Pc2, the DC developing bias VB (DC) is switched from the DC developing voltage Vd2 to the energization detection voltage Vd1 (Vd2 → Vd1). In addition, the supply of the AC developing bias is stopped (ON → OFF). Then, as the developing roll 142 provided in the cyan developing device 14C passes through the contact end position Pc2, the plate-like electrode 112 of the power supply 110 and the developing bias power receiving portion 142c of the developing roll 142 are not in contact with each other. Thereby, the energization by the energization detector 93 is not detected (ON → OFF). Further, the rotation of the developing sleeve 142a provided in the cyan developing device 14C is stopped (ON) until the cyan developing device 14C reaches the retracted position Pe from the developing position Pd via the contact end position Pc2 and stops. → OFF). Further, as the cyan developing device 14C stops at the retracted position Pe, the black developing device 14K reaches the standby position Pw and stops.

  Subsequently, the rotary developing device 14 moves in the C direction at a timing determined in advance based on the conveyance direction length of the sheet S to be image-formed and the peripheral length of the intermediate transfer belt 20 (belt rotation period Tb). Rotate 30 ° and stop. Thereby, the rotary developing device 14 shifts from the state shown in FIG. 3G to the state shown in FIG. At this time, the black developing device 14K reaches the developing position Pd from the standby position Pw via the contact start position Pc1 and stops. During this time, as the developing roll 142 provided in the black developing device 14K passes through the contact start position Pc1, the plate-like electrode 112 of the power supply body 110 and the developing bias power receiving portion 142c of the developing roll 142 start to contact each other. As a result, the current resulting from the application of the energization detection voltage Vd1 is transferred from the plate-like electrode 112 of the developing bias power supply unit 100 via the developing bias power receiving unit 142c, the developing sleeve 142a, and the developer on the developing sleeve 142a. The drum 11 flows. As a result, energization by the energization detector 93 is detected (OFF → ON). Accordingly, the DC development bias VB (DC) is switched from the energization detection voltage Vd1 to the DC development voltage Vd2 (Vd1 → Vd2), and the supply of the AC development bias is started (OFF → ON). In addition, rotation driving of the developing sleeve 142a provided in the black developing device 14K is started (OFF) until the black developing device 14K reaches the developing position Pd through the contact start position Pc1 and stops from the standby position Pw. → ON).

  After the rotating operation of the rotary developing device 14 is completed and the black developing device 14K is stopped at the developing position Pd, supply of an exposure signal corresponding to black is started (OFF → ON). As a result, the photosensitive drum 11 that rotates in the A direction while being charged to the charging potential VH is exposed to a portion where a black toner image is to be formed by the exposure beam Bm output from the exposure device 13. Thus, the charging potential VH changes to the exposure potential VL. As a result, an electrostatic latent image corresponding to black is formed on the photosensitive drum 11 that has been charged and exposed, with the charging potential VH as the background portion and the exposure potential VL as the image portion.

  The electrostatic latent image formed on the photoconductive drum 11 passes through the developing area Ad as the photoconductive drum 11 rotates in the A direction. At this time, black toner is selectively transferred from the black developing device 14K disposed at the developing position Pd to the image drum having the exposure potential VL with respect to the photosensitive drum 11. As a result, a black toner image corresponding to the black electrostatic latent image is developed on the photosensitive drum 11 that has passed through the development area Ad.

  Next, as the leading end side of the black toner image formed on the photosensitive drum 11 reaches the primary transfer region facing the intermediate transfer belt 20, supply of the primary transfer bias is started (OFF → ON). . As a result, the black toner image formed on the photosensitive drum 11 rotating in the A direction starts to be primarily transferred to the intermediate transfer belt 20 rotating in the B direction. Here, in this embodiment, when the leading end side of the yellow, magenta, and cyan superimposed toner images already transferred to the intermediate transfer belt 20 reaches the primary transfer region, the black formed on the photosensitive drum 11 will be described. The supply of the exposure signal corresponding to black is controlled so that the front end side of the toner image reaches the primary transfer region. Therefore, a black toner image is superimposed on the yellow, magenta, and cyan superimposed toner images on the intermediate transfer belt 20 that has passed through the primary transfer region.

  In this example, after the primary transfer of the black toner image is started, the supply of the exposure signal corresponding to black is stopped (ON → OFF), and the formation of the black electrostatic latent image is completed. Then, as the rear end side of the black toner image obtained by developing the black electrostatic latent image formed on the photosensitive drum 11 passes through the primary transfer region, the supply of the primary transfer bias is stopped (ON → OFF). As a result, the entire area of the black toner image is primarily transferred to the intermediate transfer belt 20 that rotates in the B direction, and a yellow, magenta, cyan, and black superimposed toner image is formed. In the primary black transfer, the black toner remaining on the photosensitive drum 11 side without being transferred to the intermediate transfer belt 20 faces the drum cleaning device 16 as the photosensitive drum 11 rotates in the A direction. Reaches the part and is removed by the drum cleaning device 16.

  Then, after the black toner image developed on the photosensitive drum 11 passes through the primary transfer region, the rotary developing device 14 rotates 120 ° in the C direction and stops. Thereby, the rotary developing device 14 shifts from the state shown in FIG. 3H to the initial state shown in FIG. At this time, the black developing device 14K reaches the opposite side of the retracted position Pe from the developing position Pd via the contact end position Pc2, and stops. During this time, the DC developing bias VB (DC) is switched from the DC developing voltage Vd2 to the energization detection voltage Vd1 (Vd2 → Vd1) before the developing roll 142 provided in the black developing device 14K passes the contact end position Pc2. In addition, the supply of the AC developing bias is stopped (ON → OFF). As the developing roll 142 provided in the black developing device 14K passes through the contact end position Pc2, the plate-like electrode 112 of the power supply 110 and the developing bias power receiving unit 142c of the developing roll 142 are not in contact with each other. Thereby, the energization by the energization detector 93 is not detected (ON → OFF). Further, the rotation drive of the developing sleeve 142a provided in the black developing device 14K is stopped (ON) until the black developing device 14K reaches the retracted position Pe from the developing position Pd via the contact end position Pc2 and stops. → OFF). Further, as the second empty space 14S2 stops at the retracted position Pe, the yellow developing device 14Y reaches the standby position Pw and stops.

  In this embodiment, in the transition from the state shown in FIG. 3H to the state shown in FIG. 3A, the first empty place 14S1 and the second empty place 14S2 are stopped at the development position Pd or the like. I try to jump over without letting go. At that time, in order to complete the rotation operation of the rotary developing device 14 within a limited time, the moving speed of the rotary developing device 14 is made faster than the other rotation operations. In addition, since no developing device is mounted in the first empty space 14S1 and the second empty space 14S2, no electric current is detected by the electric current detector 93 during this period, and the DC developing bias VB (DC) is not detected. Is not switched from the energization detection voltage Vd1 to the DC development voltage Vd2.

  On the other hand, after the trailing edge of the superimposed toner image of yellow, magenta, and cyan held on the intermediate transfer belt 20 rotating in the B direction has passed through the portion facing the belt cleaning device 27, and then passes through the primary transfer region. As a result, before the leading edge of the yellow, magenta, cyan and black superimposed toner images on which the black toner images are further superimposed reaches the secondary transfer region (the opposed portion between the intermediate transfer belt 20 and the secondary transfer roll 31). In addition, the secondary transfer roll 31 and the belt cleaning device 27 move (retreat to advance) to a position in contact with the intermediate transfer belt 20. Then, as the leading end side of the yellow, magenta, cyan, and black superimposed toner images held on the intermediate transfer belt 20 reaches the secondary transfer region, the supply of the secondary transfer bias is started (OFF → ON). . Here, in the present embodiment, when the leading end side of the yellow, magenta, cyan, and black superimposed toner images held on the intermediate transfer belt 20 reaches the secondary transfer region, the leading end side of the sheet S becomes the secondary transfer region. The conveyance control of the sheet S is performed so as to reach. Therefore, the secondary transfer of the superimposed toner image is performed from the intermediate transfer belt 20 to the sheet S in the secondary transfer region.

  Then, as the superimposed toner image and the sheet S held on the intermediate transfer belt 20 pass through the secondary transfer area, the supply of the secondary transfer bias is stopped (ON → OFF), and the superimposed toner image on the sheet S is stopped. The secondary transfer of is completed. The superimposed toner image on the sheet S that has passed through the secondary transfer region is fixed by the fixing device 50. On the other hand, in the secondary transfer of the superimposed toner image, the color toners that are not transferred to the sheet S and remain on the intermediate transfer belt 20 side are opposed to the belt cleaning device 27 as the intermediate transfer belt 20 rotates in the B direction. And is removed by the scraper 41.

Then, after the rear end of the overlapping toner image formation region on the intermediate transfer belt 20 passes through the portion facing the belt cleaning device 27, the secondary transfer roll 31 and the belt cleaning device 27 are moved away from the intermediate transfer belt 20. Move (advance-> evacuate).
Thus, the formation of a full color image on one sheet S is completed.

Now, the developing operation in the above-described full-color image forming operation will be described in more detail.
First, the operation of the developing device (yellow developing device 14Y in the example shown in FIG. 2) arranged at the developing position Pd will be described with reference to FIGS.

  In the yellow developing device 14Y disposed at the development position Pd, the first stirring / conveying member 143 and the second stirring / conveying member 144 rotate with the transmission of the driving force, and the developer is stirred and conveyed in the developing housing 141. Has been done. By this agitation and conveyance, the toner and the carrier constituting the developer are rubbed with each other, and the toner is charged with negative polarity and the carrier is charged with positive polarity. As a result, in the developer that is stirred and conveyed, the toner is electrostatically attracted to the carrier. When the developer to be stirred and conveyed reaches a portion facing the developing roll 142, a part of the carrier is developed by the magnetic force acting between the magnetic pole provided on the magnet roll 142b and the carrier contained in the developer. Transfer to 142 side. At this time, since the toner is electrostatically adsorbed on the carrier transferred to the developing roll 142 side, the developer is transferred to the developing roll 142 side as a result, and the development with the developer is performed on the outer peripheral surface of the developing sleeve 142a. An agent layer is formed.

  Further, in the yellow developing device 14Y disposed at the developing position Pd, the developing sleeve 142a rotates in the D direction as the driving force is transmitted. As a result, the developer layer formed on the developing sleeve 142a is conveyed as the developing sleeve 142a rotates in the D direction, and the thickness of the developer layer is set in advance when the developer layer passes through the portion facing the layer thickness regulating member 145. It is regulated to a predetermined thickness and is carried to the opening of the developing housing 141 facing the photosensitive drum 11. The developer regulated by the layer thickness regulating member 145 is returned to the first stirring and conveying member 143 side by gravity.

  Further, in the yellow developing device 14Y arranged at the developing position Pd, the DC developing bias VB (DC) (more specifically, the DC developing voltage Vd2) and the developing sleeve 142a are supplied to the developing sleeve 142a in accordance with the power supply by the developing bias power supply unit 100. An AC developing bias VB (AC) is supplied. As a result, in the development area Ad, the toner is electrostatically transferred from the developer layer on the development sleeve 142a to the image portion (area where the exposure potential is VL) on the photosensitive drum 11, and the electrostatic latent image To develop a visible image. This process will be described later.

  Thereafter, the developer layer on the developing sleeve 142a that has passed through the developing region Ad is returned to the developing housing 141 as the developing sleeve 142a rotates in the D direction. The developer layer on the developing sleeve 142a returned to the developing housing 141 is separated from the developing roll 142 by the repulsive magnetic field formed by the magnetic poles provided on the magnet roll 142b and falls into the developing housing 141. Then, the first agitating / conveying member 143 and the second agitating / conveying member 144 are again agitated and conveyed to wait for the next development.

Next, the development process in the development area Ad will be described in more detail.
FIG. 11 is a diagram for explaining the relationship between the charging potential VH and the exposure potential VL on the photosensitive drum 11 and the DC developing voltage Vd2 supplied to the developing sleeve 142a in the developing region Ad. In FIG. 11, in addition to the DC development voltage Vd2, the energization detection voltage Vd1 is also shown.

  In the present embodiment, the charging potential VH and the exposure potential VL are both negative, but the magnitude of the exposure potential VL is an absolute value smaller than the charging potential VH (| VL | < | VH |). The DC development voltage Vd2 in the present embodiment is negative in polarity and the magnitude of the absolute value is set to a magnitude between the charging potential VH and the exposure potential VL (| VL | <| Vd2 | <| VH |).

  When the charging potential VH, the exposure potential VL, and the DC development voltage Vd2 have the above-described relationship, the toner on the developing sleeve 142a that passes through the developing region Ad (charged to the negative polarity) While it is easy to transfer (fly) to the region of the exposure potential VL (image portion) that becomes a relatively positive potential, the charging potential VH (background portion) that becomes a relatively negative potential on the photosensitive drum 11. It becomes difficult to transfer (fly) to the area. Here, considering the ease of toner flight as a reference, the difference between the exposure potential VL based on the exposure potential VL and the DC development voltage Vd2 is referred to as a flight potential difference Vdev, and the direct current based on the DC development voltage Vd2. A difference between the development voltage Vd2 and the charging potential VH is referred to as a reverse flight potential difference Vcln. In this example, the charging potential VH is set to -550V, the exposure potential VL is set to -50V, and the DC development voltage Vd2 is set to -300V.

  On the other hand, the energization detection voltage Vd1 in the present embodiment is negative and has an absolute value set so as to be smaller than both the charging potential VH and the exposure potential VL (| Vd1 | < | VL | <| VH |). Here, since the energization detection voltage Vd1 is applied to detect the presence of the developing device when there is no developing device before and after the developing position Pd, no discharge or leakage associated with the discharge occurs. A size of about is sufficient. In this example, the energization detection voltage Vd1 is set to be −24V or less.

  As described above, in the present embodiment, in the image forming operation, contact between the plate-like electrode 112 provided on the main body side and the four developing bias power receiving units 142c provided in the rotary developing device 14 is detected. Based on the result, the supply of the DC development voltage Vd2 as the development bias was started. For this reason, for example, control can be simplified as compared with the case where the supply of the DC developing voltage Vd2 is started using general sequence control. In this embodiment, for example, when the plate electrode 112 or the development bias power receiving unit 142c is damaged, the development bias power receiving unit 142c does not come into contact with the plate electrode 112. Since the development voltage Vd2 is not supplied, the safety of the image forming apparatus can be improved.

  In particular, in the present embodiment, the energization detection voltage Vd1 smaller than the DC development voltage Vd2 is normally supplied as the developing bias, and the energization detection voltage Vd1 is detected when energization due to the energization detection voltage Vd1 is detected. Is switched to the DC developing voltage Vd2, for example, the configuration can be simplified as compared with a case where a sensor for detecting contact between the plate electrode 112 and the developing bias power receiving unit 142c is separately provided. .

  Further, in the present embodiment, only the DC energization detection voltage Vd1 is supplied when energization is detected, and after the energization is detected, the AC development bias is supplied in addition to the DC development voltage Vd2. It is not necessary to supply an alternating voltage for detection, and power consumption by the power source can be reduced correspondingly.

  In this embodiment, the magnitude of the energization detection voltage Vd1 supplied at the time of energization detection is made smaller than the DC development voltage Vd2, more specifically, the magnitude of the energization detection voltage Vd1 is set to −24V or less. By doing so, it is possible to improve the safety of the image forming apparatus.

<Embodiment 2>
In the first embodiment, the supply mechanism of the developing bias supplied to the developing device arranged at the developing position Pd is used to detect that the developing device has approached the developing position Pd based on the presence / absence of energization. . In contrast, in the present embodiment, the development bias supply mechanism that supplies the developing device disposed at the developing position Pd is used to indicate that the developing device has approached the developing position Pd. It is made to detect based on. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 12 is a cross-sectional view for explaining the configuration of the power feeding body in the present embodiment. In addition, FIG. 12 shows a circumferential cross-sectional view of the power feeding body 110 as in FIG. 8 in the first embodiment, and a description of the wall portion 111b provided on the base 111a is omitted.

  In the present embodiment, an advance / retreat detection sensor 114 for detecting advance / retreat of the plate-like electrode 112 with respect to the base 111a is provided on the upper surface (more specifically, the central flat surface 1111) of the base 111a. As the advance / retreat detection sensor 114, for example, a sensor that mechanically, electrically, or optically detects the advance / retreat of the plate electrode 112 can be used. In particular, the advance / retreat detection sensor 114 that mechanically or electrically detects the advance / retreat of the plate electrode 112 functions as a switch for supplying a developing bias when it contacts the plate electrode 112, for example. It is preferable to use what is obtained from the viewpoint of simplification of the configuration.

FIG. 13 is a diagram illustrating an example of a configuration of a control system of the image forming apparatus according to the present embodiment.
Here, the difference from the control system in the first embodiment (see FIG. 9) is that the advance / retreat detection signal by the advance / retreat detection sensor 114 as an example of the detection unit is controlled in place of the energization detection signal from the energization detector 93. Input to the unit 60.

  Next, the image forming operation in the present embodiment will be described. Here, as in the first embodiment, a case where a full-color image of four colors including yellow, magenta, cyan and black is formed on one sheet S is taken as an example.

  FIG. 14 shows an example of a timing chart in the full-color image forming operation in the present embodiment. 14 shows the passage of time, rotation of the photosensitive drum 11 by the photosensitive drum driving motor 81 [(1) photosensitive drum driving], and supply of the charging bias to the charging roll 12 by the charging power source 82. [(2) Charging bias], supply of exposure signal to the exposure device 13 by the light source driving unit 83 [(3) exposure signal], and rotational driving of the rotary developing device 14 by the developing device driving motor 84 [(4) Development device drive], development device arranged at the development position Pd [(5) development device at development position], rotational drive of the development sleeve 142a by the development sleeve drive motor 85 [(6) development sleeve drive], advance / retreat Detection of the advance / retreat of the plate electrode 112 by the detection sensor 114 [(7) Advance / retreat detection] and supply of the DC developing bias VB (DC) to the developing sleeve 142a by the DC developing power source 86 [(8 DC developing bias], supply of AC developing bias VB (AC) to developing sleeve 142a by AC developing power supply 87 [(9) AC developing bias], and rotation driving of intermediate transfer belt 20 by intermediate transfer belt drive motor 88 [ (10) Intermediate transfer belt drive], primary transfer bias supply to the primary transfer roll 15 by the primary transfer power supply 89 [(11) primary transfer bias], and the photosensitive drum 11 and the intermediate transfer belt 20 facing each other. The image area (toner image formation area) [(12) primary transfer passage image] on the intermediate transfer belt 20 passing through the transfer area, and the position of the belt cleaning device 27 accompanying the driving of the belt cleaning device drive motor 90 [(13 ) Belt cleaning device position] and the position of the secondary transfer roll 31 accompanying the driving of the secondary transfer roll drive motor 91 [(14) Secondary transfer low] Position], secondary transfer bias supply to the secondary transfer unit 30 by the secondary transfer power supply 92 [(15) secondary transfer bias], and the secondary transfer roller 20 and the secondary transfer roll 31 are opposed to each other. The relationship with the image area (toner image formation area) [(16) secondary transfer passage image] on the intermediate transfer belt 20 passing through the transfer area is shown.

  Here, since the full-color image forming operation in the present embodiment is basically the same as that described in the first embodiment, only the differences will be described.

  First, in the first embodiment, the DC developing bias can be switched to three stages of “OFF”, “energization detection voltage Vd1”, and “DC developing voltage Vd2”. On the other hand, in the present embodiment, the DC developing bias can be switched between two stages of “OFF” and “ON”. In the present embodiment, the DC developing bias being “ON” means that the DC developing bias is set to “DC developing voltage Vd2”.

  Further, in the first embodiment, the DC developing bias is set to “energized” starting from the fact that the energization detection is switched from “OFF” to “ON” while the “energization detecting voltage Vd1” is supplied as the DC developing bias. The detection voltage Vd1 ”was switched to“ DC development voltage Vd2 ”, and the“ AC development bias ”was switched from“ OFF ”to“ ON ”. On the other hand, in the present embodiment, the DC developing bias is changed from “OFF” to “ON (starting from the fact that the advance / retreat detection is switched from“ OFF ”to“ ON ”(from the separated state to the approached state). "DC development voltage Vd2)" and "AC development bias" is switched from "OFF" to "ON".

  As described above, in the present exemplary embodiment, in the image forming operation, the contact between the plate-like electrode 112 provided on the main body side and the four developing bias power receiving units 142c provided in the rotary developing device 14 is detected. Based on this, the supply of the DC developing voltage Vd2 as the developing bias was started. For this reason, for example, control can be simplified as compared with the case where the supply of the DC developing voltage Vd2 is started using general sequence control.

  In particular, in the present embodiment, when the plate electrode 112 and the development bias power receiving unit 142c are not in contact with each other, the development bias is not performed on the plate electrode 112. In comparison, the safety of the image forming apparatus can be further improved.

  In the first and second embodiments, the photosensitive drum 11 is charged by the contact charging method using the charging roll 12, and the primary transfer roll 15 and the secondary transfer unit 30 (the secondary transfer roll 31 and the backup roll are backed up). The image is transferred by the contact transfer method using the roll 26), but the present invention is not limited to this, and a non-contact charging method (non-contact transfer method) using a corotron or the like may be adopted. It doesn't matter.

DESCRIPTION OF SYMBOLS 11 ... Photoconductor drum, 12 ... Charging roll, 13 ... Exposure device, 14 ... Rotary developing device, 14a ... Rotating shaft, 14Y ... Yellow developing device, 14M ... Magenta developing device, 14C ... Cyan developing device, 14K ... Black developing 14S1 ... first empty place, 14S2 ... second empty place, 15 ... primary transfer roll, 16 ... drum cleaning device, 20 ... intermediate transfer belt, 30 ... secondary transfer unit, 50 ... fixing device, 60 ... Control unit, 100 ... development bias power supply unit, 110 ... power supply, 111 ... housing, 112 ... plate electrode, 113 ... coil spring, 114 ... advance detection sensor, 120 ... assembled wire, 141 ... development housing, 142 ... development Roll, 142a ... developing sleeve, 142b ... magnet roll, 142c ... developing bias power receiving unit, 143 ... first stirring / conveying member, 144 ... second stirring / conveying member, 145 ... layer thickness Control member

Claims (8)

A latent image holder that is rotatably provided and holds an electrostatic latent image;
A plurality of developing units each containing a developer and having a power receiving electrode for receiving power from the outside are provided, and a plurality of the developing units are sequentially arranged at a developing position facing the latent image holding body as the rotation occurs. And a developing unit that develops the electrostatic latent image on the latent image holding member with a developing device disposed at the developing position;
Power supply for supplying a developing bias to the developing device via the contacted power receiving electrode, which is provided so as to come into contact with the power receiving electrode of the developing device moving toward the developing position as the developing unit rotates. Electrodes,
A detection unit for detecting contact between the power feeding electrode and the power receiving electrode;
An image forming apparatus including a supply unit that supplies the developing bias to the power supply electrode when the detection unit detects contact between the power supply electrode and the power reception electrode. The supply unit supplies a detection bias smaller in size than the development bias to the power supply electrode when the power supply electrode and the power reception electrode are not in contact with each other.
The image forming apparatus according to claim 1, wherein the detection unit detects contact between the power feeding electrode and the power receiving electrode as a current flows through the power feeding electrode.   The image forming apparatus according to claim 2, wherein the supply unit supplies a DC voltage as the detection bias and supplies a superimposed voltage obtained by superimposing an AC voltage on the DC voltage as the developing bias.   4. The image forming apparatus according to claim 3, wherein the magnitude of the DC voltage at the detection bias is smaller than the magnitude of the DC voltage at the development bias. The power supply electrode is configured to be displaced with contact with the power receiving electrode,
The image forming apparatus according to claim 1, wherein the detection unit detects contact between the power feeding electrode and the power receiving electrode as the power feeding electrode is displaced. A latent image holder that is rotatably provided and holds an electrostatic latent image;
A plurality of developing units each containing a developer and having a power receiving electrode for receiving power from the outside are provided, and a plurality of the developing units are sequentially arranged at a developing position facing the latent image holding body as the rotation occurs. And a developing unit that develops the electrostatic latent image on the latent image holding member with a developing device disposed at the developing position;
Power supply that has conductivity and is arranged along the rotation direction of the developing unit and straddling the developing position, and that contacts the power receiving electrode of the developing device that moves toward the developing position as the developing unit rotates. Electrodes,
A power source for supplying a voltage to the power supply electrode;
An energization detection unit for detecting energization via the feeding electrode;
When energization is not detected by the energization detection unit, the first voltage is supplied from the power supply as the voltage, and when energization is detected by the energization detection unit, the voltage is changed from the first voltage to the first voltage. An image forming apparatus comprising: a changing unit that changes to a second voltage that is higher than the voltage.   The changing unit supplies a DC voltage as the first voltage and the second voltage, and further, when energization is detected by the energization detection unit, is an AC voltage in addition to the second voltage. The image forming apparatus according to claim 6, wherein a voltage of 3 is supplied. A charging unit that charges the latent image holding member to a charging potential;
An exposure portion that forms an exposure potential by exposing the latent image carrier charged to the charging potential, and that forms the electrostatic latent image by the charging potential and the exposure potential; and
8. The first voltage according to claim 6, wherein the first voltage is smaller than both the charging potential and the exposure potential, and the second voltage is smaller than the charging potential and larger than the exposure potential. Image forming apparatus.

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