JP4631557B2 - Image forming apparatus and method of setting action position of transfer member - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer or a copying machine, and more particularly to a full color image forming apparatus capable of switching between a full color mode and a subtractive color mode.

Recently, full-color tandem machines capable of forming color images at high speed and high image quality have become widespread as image forming apparatuses such as printers, copiers, and facsimiles.
In the tandem machine, for example, four image forming units of yellow (Y), magenta (M), cyan (C), and black (K) are arranged in parallel, and an intermediate transfer member is provided on the photosensitive drum of these image forming units. The intermediate transfer belt is configured to rotate around a path in which the intermediate transfer belt sequentially contacts. Then, each image forming unit sequentially forms yellow, magenta, cyan, and black toner images on the circulating intermediate transfer belt, and once temporarily performs multiple primary transfer, then the intermediate transfer belt collectively onto the transfer paper. Then, secondary transfer is performed, and a toner image on the transfer paper is fixed, thereby forming a full-color image (hard copy).

By the way, in an image forming apparatus capable of forming a full color image, in general, a full color mode in which all color image forming units function and a single color (monochrome) mode in which only one (normally black) image forming unit functions. Can be selected. Furthermore, recently, there has also been proposed a color reduction mode in which only a plurality of specific image forming units among a large number of image forming units function.
In a tandem machine capable of switching between such a color mode and a single color mode or a subtractive color mode (hereinafter referred to as a subtractive color mode), an intermediate transfer is performed to the photosensitive drum of an image forming unit that does not function during the subtractive mode image formation. If the belt continues to contact, there is a risk that the photoreceptor on the surface of the photoreceptor drum may be worn out or the developer may be consumed. In view of this, a configuration has been proposed in which the intermediate transfer belt is separated from the photosensitive drum of the image forming unit that does not function in the color reduction mode. (For example, see Patent Document 1)

  FIG. 8 is a conceptual diagram of the image forming apparatus disclosed in Patent Document 1. In this image forming apparatus, image forming units 10 '(10Y', 10M ', 10C', 10K ') of each color are arranged in parallel, and used in the color reduction mode (in this example, the black single color mode). The (black image forming unit 10K ′) is positioned at one end. The intermediate transfer belt 20 'is disposed along a path around the image forming unit 10'. Further, a transfer roll 30 'is disposed at a position facing the photosensitive drum 11' and the intermediate transfer belt 20 'of the image forming unit 10'. Further, a retract roll 72 'is disposed on the back side of the intermediate transfer belt 20' between the magenta image forming unit 10M 'and the cyan image forming unit 10C'.

  The intermediate transfer belt 20 ′ can displace the circulation path between a color mode path (color position CP) and a monochrome mode path (monochrome position KP). At the color position CP, the intermediate transfer belt 20 'contacts the photosensitive drums 11' of all the image forming units 10 'as shown by the solid line in the figure. On the other hand, at the monochrome position KP, the intermediate transfer belt 20 ′ is separated from the photosensitive drums 11 ′ of the image forming units 10Y ′, 10M ′, and 10C ′ of colors other than black as indicated by a two-dot chain line in the drawing. . The color position CP and the monochrome position KP are changed by moving the retract roll 72 'up and down and transfer rolls corresponding to the image forming units 10Y', 10M ', and 10C' of other colors except the black image forming unit 10K '. 30Y ', 30M', and 30C 'are moved up and down.

  That is, the retract roll 72 'is set to an operating position for pushing up the upper path of the intermediate transfer belt 20' to the photosensitive drum 11 'side at the color position CP, and to a retracted position separated downward at the monochrome position KP. Further, the transfer rolls 30Y ′, 30M ′, and 30C ′ are set to an operation position for pressing the intermediate transfer belt 20 ′ against the photosensitive drum 11 ′ at the color position CP, and are separated from the photosensitive drum 11 ′ at the monochrome position KP. The retracted position (indicated by a two-dot chain line in the figure). These retract rolls 72 'and transfer rolls 30Y', 30M ', 30C' are moved and operated in synchronization by a moving mechanism not shown in FIG.

JP 2003-337454 A

  By the way, in the color tandem machine in which the position of the intermediate transfer belt can be switched between the color mode and the color reduction mode as in the above-described conventional configuration, when the color mode and the color reduction mode are switched, the control unit controls the color position and the color reduction. The position and the movement mechanism of the retract roll and transfer roll are controlled. For this reason, a detection mechanism including a sensor, a member to be detected, and the like is provided, and the control unit determines whether the transfer roll and the retract roll are based on detection information (hereinafter referred to as position control information) of the color position and the color reduction position by the detection mechanism. The moving mechanism is controlled (open loop control).

  FIG. 9 is a diagram illustrating an example of the movement mechanism and the detection mechanism. In this example, a switching motor 61 'as a driving source and a linkage mechanism 63' are linked via a rotation interlocking member 62 'such as a cam, and the color position and the color reduction position are obtained by half rotation of the rotation interlocking member 62'. It is comprised so that it may switch. The detection mechanism is configured to detect a detected member 66 fixed to the rotation interlocking member 62 ′ with a sensor 67. The detected member 66 has a shape that switches between detection by the sensor 67 and non-detection at the color position and the color reduction position, respectively. That is, the detected member 66 has a shape that is continuously detected by the sensor 67 from the color position to the color reduction position and is not detected from the color reduction position to the color position. For example, when the color position and the color reduction position are switched by a half rotation of the rotation interlocking member 62 ′, it becomes a semicircular shape.

According to such a detection mechanism, the detection signal from the sensor 67 can be switched at the time when the color position or the color reduction position is reached during the position switching operation by the moving mechanism. Using this signal change as position control information, the control unit can obtain position control information and stop driving the moving mechanism every time the position is changed.
However, in the case of the configuration as described above, a detection mechanism including a member to be detected, a sensor, and the like is necessary to obtain position control information. For this reason, the structure is complicated, the number of parts is increased, and the number of assembling steps such as input / output wirings is increased, which causes a cost increase.

The present invention has been made to solve the above technical problems, and an object thereof is to provide an image forming apparatus capable of obtaining position control information without providing a complicated detection mechanism. It is to provide.
Another object is to easily set the operating position of the transfer member that can be used as a reference for the position control information.

  For this purpose, an image forming apparatus to which the present invention is applied is provided so as to be movable between an image carrier that carries a toner image, and an operating position that pressurizes the image carrier and a retracted position that is separated from the working position. Transfer member to which a transfer current is supplied, a moving mechanism for moving the transfer member, an electric characteristic detecting device for measuring the electric characteristics of the transferring member, and a moving mechanism based on the electric characteristics measured by the electric characteristic detecting device And a control unit for controlling and driving.

  Here, the electrical property detection device measures, for example, a change in electrical property associated with the movement of the transfer member toward and away from the image carrier. The movement mechanism includes, for example, a rotation drive mechanism, and a conversion movement mechanism that converts the rotation of the rotation drive mechanism into an operation motion between the operating position and the retracted position of the transfer member, and the control unit rotates the rotation drive mechanism. The movement of the transfer member is controlled by the control.

  Further, an image forming apparatus to which the present invention is applied includes an image carrier that carries a toner image, and a member to be transferred that is displaceable between a working path that contacts the image carrier and a retreat path that is separated from the working path. A transfer member that is movably provided between an operating position where the transfer member is pressed against the image carrier and a retracted position where the transfer member is separated, a moving mechanism that moves the transfer member, and an electric power of the transfer member. An electrical characteristic detection device that measures the characteristics and obtains position information of the transfer member based on the electrical characteristics, and a contact / separation control device that drives the moving mechanism based on the position information of the transfer member by the electrical characteristics detection device It is characterized by that.

  Further, an image forming apparatus to which the present invention is applied is separated from a plurality of image forming units each having an image carrier that carries toner images of different colors, and an action path that contacts the image carrier of the image forming unit. Transfer to which a transfer current is supplied so as to be movable between a member to be transferred that is displaceable between the retreat path and an operation position that is pressed against the image carrier of the image forming unit and a retreat position that is separated from the retreat path. A member, a moving mechanism for moving the transfer member, an electrical characteristic detection device for measuring the electrical characteristics of the transfer member and obtaining the position information of the transfer member based on the electrical characteristics, and the position information of the transfer member by the electrical characteristic detection device And a contact / separation control device for controlling the moving mechanism based on the above.

  Here, the image forming apparatus has a color reduction mode that allows a specific image forming unit such as black to be functioned among a plurality of image forming units, for example, and the contact / separation control device has a specific image in the color reduction mode. The transfer member corresponding to the forming unit is configured to move to the retracted position. The electrical property detection device indicates, for example, whether the electrical property measurement value is the maximum value or the minimum value based on the electrical property measurement value of the transfer member measured while moving the transfer member toward and away from the image carrier. Action position information is formed with the position as the action position of the transfer member, and the moving mechanism controls and drives the transfer member based on the action position information. The electrical property measured by the electrical property detection device is, for example, a voltage between a transfer member and an image carrier when a constant current is passed between them, and the electrical property detection device has a minimum voltage measurement value. The action position information is formed with the position indicating the position as the action position of the transfer member. The electrical characteristic detection device also serves as, for example, a resistance detection circuit that detects resistance information between the transfer member and the image carrier in order to set a transfer current. For example, the electrical property detection device performs measurement of electrical properties of the transfer member and formation of action position information of the transfer member based on the electrical properties at the time of initial setting when the power is turned on.

Furthermore, the transfer member operating position setting method according to the present invention is a transfer member that is provided so as to be movable between an operating position that pressurizes the image carrier and a retracted position that is spaced from the operating position. A method of setting an operating position, wherein the transfer member is moved toward and away from the image carrier, the position where the transfer member presses the image carrier most is determined, and this position is set as the operating position. Features.
Here, the determination of the position at which the transfer member most pressed the image carrier is performed by, for example, measuring the electrical characteristics of the transfer member while moving the transfer member toward and away from the image carrier, And determining the position of the transfer member whose characteristic value shows either the maximum value or the minimum value as the position where the transfer member has most pressed the image carrier.

  As described above, according to the present invention, it is possible to obtain position control information for switching between the color position and the color reduction position without providing a complicated and troublesome detection mechanism. Assembly cost can be reduced.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of an image forming apparatus to which the exemplary embodiment is applied. An image forming apparatus 1 shown in the figure is a so-called tandem type color image forming apparatus. For example, a plurality of image forming units 10 (10Y, 10M, 10C, and 10K) that form toner images of each color component by an electrophotographic method and a transfer target provided so as to circulate along a route around each image forming unit 10. And an intermediate transfer belt 20 as a member. Further, a primary transfer roll 30 (30Y, 30M, 30C, 30K) as a transfer member provided corresponding to each image forming unit 10 and a toner image on the intermediate transfer belt 20 are transferred onto the paper P. The image forming apparatus 1 includes a next transfer device 40 and a control unit 50 that performs overall control of the image forming apparatus 1. Further, a fixing device for fixing the toner image on the paper P is provided.

  Then, the toner image of each color component formed in each image forming unit 10 is sequentially transferred (primary transfer) onto the intermediate transfer belt 20 by the action of the primary transfer roll 30, and is held on the intermediate transfer belt 20. The superposed image is collectively transferred (secondary transfer) onto the paper P by the secondary transfer device 40. After that, the secondary transferred image is fixed on the paper P by a fixing device. In the present embodiment, toner that is negatively charged is used in forming the toner image of each color component.

  Each image forming unit 10 includes a photosensitive drum 11 as an image carrier that rotates in the direction of the arrow in the drawing. Around each photosensitive drum 11, there are a charger that charges the photosensitive drum 11 along the rotation direction, a laser exposure device that writes an electrostatic latent image on the photosensitive drum 11, and a photosensitive drum 11. A developing device that visualizes the electrostatic latent image with toner, a primary transfer roll 30 that transfers the toner image formed on the photosensitive drum 11 to the intermediate transfer belt 20, and residual toner on the photosensitive drum 11 are removed. Electrophotographic devices such as a drum cleaner are sequentially arranged. Note that a charger, a laser exposure device, a developing device, and a drum cleaner are not shown. The primary transfer roll 30 is disposed at a position facing the photosensitive drum 11 with the intermediate transfer belt 20 in between.

  Each image forming unit 10 includes an image forming unit 10Y that forms a yellow toner image, an image forming unit 10M that forms a magenta toner image, and a cyan toner from the upstream side in the moving direction of the intermediate transfer belt 20 indicated by an arrow in the drawing. The image forming unit 10C for forming an image and the image forming unit 10K for forming a black toner image are arranged in parallel in this order.

  Here, the image forming apparatus 1 can switch between a full color mode and a monochrome mode as a subtractive color mode. In the full color mode, as shown by a solid line in FIG. 1, a path (full color position CP) where the intermediate transfer belt 20 contacts the photosensitive drums 11 of all the image forming units 10 is formed. On the other hand, in the monochrome mode, as shown by a two-dot chain line in FIG. 1, the intermediate transfer belt 20 is separated from the photosensitive drums 11 of the other image forming units 10Y, 10M, and 10C except the black image forming unit 10K ( Monochrome position KP) is formed. In the full color mode, all the image forming units 10Y, 10M, 10C, and 10K form an image, and in the monochrome mode, only the black image forming unit 10K forms an image.

The switching between the full color position CP and the monochrome position KP will be described in detail later, but the primary transfer rolls 30Y and 30M corresponding to the retract roll 72 and the image forming units 10Y, 10M, and 10C for each color except the black image forming unit 10K. , 30C. These rolls are driven up and down synchronously by one moving mechanism 60 (shown in FIGS. 2 and 3) not shown in FIG. The state where these rolls are in the upper working position is the full color position CP, and the state where these rolls are in the lower retracted position is the monochrome position KP.
The switching of the position is not based on the position control information each time, but based on the position control information that is acquired and held in advance by the control unit 50 at the time of initial setting when the power is turned on.

  In the present embodiment, the full color position CP is grasped from the operating position of the primary transfer roll 30 and used as position control information. However, in the following description, the position control information of the full color position CP is referred to as color position information. The operation for acquiring the color position information is referred to as color position detection. The monochrome position KP can be set from the full color position CP by drive control of the moving mechanism 60 (see FIGS. 2 and 3), and the monochrome position information is set from the color position information.

Hereinafter, the configuration of each unit will be described in detail.
The intermediate transfer belt 20 is set to an appropriate volume resistivity by containing carbon black as a conductive agent in resin, rubber, or the like. The shape is, for example, formed in an annular shape having a thickness of 0.1 mm and a predetermined width, is wound around a plurality of rolls, and is provided so as to be able to go around along a path defined by these rolls. As each roll, there are a retract roll 72, a fixed idle roll 73, and a driven roll 74 in a counterclockwise direction from a drive roll 71 arranged at the right end in the drawing. A first tension roll 75, a backup roll 76 of the secondary transfer device 40, and a second tension roll 77 having a function of giving a constant tension to the intermediate transfer belt 20 and preventing meandering of the intermediate transfer belt 20 are provided. is there. The drive roll 71 is connected to a drive motor (not shown), and the intermediate transfer belt 20 is driven to rotate by the rotation of the drive roll 71 by this drive motor.

  The fixed idle roll 73 is located on the back side of the intermediate transfer belt 20 between the image forming unit 10C and the image forming unit 10K. The fixed idle roll 73 passes through the intermediate transfer belt 20 between the fixed idle roll 73 and the driven roll 74 regardless of the position of the retract roll 72 (in either color or monochrome position). 11 is contacted.

  The retract roll 72 is provided on the back side of the intermediate transfer belt 20 between the image forming unit 10M and the image forming unit 10C so as to be movable in the vertical direction. Then, at the position above the movement range (operation position), as shown by the solid line in FIG. 1, the intermediate transfer belt 20 is pushed up to bring the path into contact with the photosensitive drums 11 of all the image forming units 10. Position CP. Further, at the lower position (retracted position) of the moving range, as shown by a two-dot chain line in FIG. The vertical movement of the retract roll 72 is performed in synchronization with the vertical movement of the primary transfer rolls 30Y, 30M, and 30C by the movement mechanism 60 (see FIGS. 2 and 3) as described above. Thus, when the retract roll 72 is in the lower retracted position, the primary transfer roll 30 is also in the lower retracted position, and the path of the intermediate transfer belt 20 is routed from the photosensitive drums 11 of the image forming units 10Y, 10M, and 10C. The separated monochrome position KP is assumed.

Each primary transfer roll 30 is formed, for example, by coating a rubber conductive foamed elastic body on the outer periphery of a stainless steel conductive core. The conductive foamed elastic body is appropriately set to a resistance value by mixing a substance having ion conductivity (for example, NBR rubber), a substance having electronic conductivity (for example, carbon black), and the like.
Each of these primary transfer rolls 30 is provided so as to be movable in a direction in which the primary transfer roll 30 contacts and separates from the photosensitive drum 11, and is biased toward the side closer to the photosensitive drum 11 by a spring 31.

  FIG. 2 is a diagram conceptually showing a support structure for the primary transfer roll 30 and a moving mechanism 60 described later. As illustrated, a bearing 32 is rotatably provided at the shaft end 30 </ b> A of the primary transfer roll 30. The bearing 32 is fitted to a holder 33 having a U-shaped cross section so as to be slidable up and down, and a pressing spring 31 is interposed between the bearing 32 and the bottom surface of the holder 33. The pressing spring 31 and the holder 33 are provided at both left and right shaft ends of the primary transfer roll 30. As a result, the primary transfer roll 30 presses the intermediate transfer belt 20 (see FIG. 1) against the photosensitive drum 11 by the elastic restoring force of the pressing spring 31, and the upper surface of the primary transfer roll 30 contacts the photosensitive drum surface of the photosensitive drum 11. Acts as if pressed by force.

  Further, as described above, the primary transfer rolls 30Y, 30M, and 30C corresponding to the image forming units 10Y, 10M, and 10C of each color except the black image forming unit 10K (see FIG. 1) are moved and retracted by the moving mechanism 60 as described above. Moved between positions.

FIG. 3 is a perspective view showing a conceptual configuration of the moving mechanism 60. The moving mechanism 60 will be described with reference to FIGS.
The moving mechanism 60 is an eccentric link 62 as an eccentric member that is rotationally driven by a switching motor 61 (not shown in FIG. 2) as a rotational drive mechanism, a switching operation rod 63 as an intermediate operation member, and an operation arm member. The primary transfer roll 30 is moved and operated via the operation arm 64. The operation arms 64 are provided at the left and right shaft ends of the primary transfer rolls 30Y, 30M, and 30C (see FIG. 1), respectively. A pair of the eccentric link 62 and the switching operation rod 63 are provided on the left and right, and one switching motor 61 is provided. The switching operation rod 63 and the operation arm 64 constitute a conversion movement mechanism in the present embodiment that converts the rotation of the switching motor 61 as a rotation drive mechanism into an operation motion.

  The operation arm 64 is formed in an L shape, one end of which is an operation portion 64A and the other end is an operated portion 64B, and is fixed to the frame of the image forming apparatus 1 (see FIG. 1) in the vicinity of the corner portion. It is pivotally attached to the chassis (not shown) by a shaft 64C. The operation portion 64A is positioned substantially horizontally above the shaft end 30A of the primary transfer roll 30, and the operated portion 64B is suspended toward the lower switching operation rod 63 thereof.

  The switching operation rod 63 is provided so as to be movable in the arrangement direction of the image forming units 10 (left and right direction in FIGS. 2 and 3) with an angular axis of a rectangular cross section. At the position corresponding to the operation arm 64 of each primary transfer roll 30 on the upper surface, an operation portion 63A is projected. Further, an operation groove 63B in which an operation pin 62B of an eccentric link 62 described later is fitted is formed on the inner side surface. As shown in FIG. 1, each image forming unit 10 has a different position in the height direction, and the position of each primary transfer roll 30 also has a height difference, so that the operation arm 64 of each primary transfer roll 30. The height of the corresponding operation unit 63A is set according to the difference in height.

  In the eccentric link 62, an operation pin 62B is implanted on the outer side surface of the eccentric cam 62A, and a cam shaft 65 is coupled to the inner side surface by a predetermined amount from the operation pin 62B. The operation pin 62B is fitted in the operation groove 63B of the switching operation rod 63. As a result, the operation pin 62B moves the switching operation rod 63 left and right in the figure by the rotation of the eccentric link 62. The operation pin 62B moves about twice the eccentric amount by one rotation of the camshaft 65 (one rotation of the eccentric link 62). This moving stroke corresponds to the moving stroke between the operating position of the primary transfer roll 30 and the retracted position. That is, as shown in FIG. 2, the operation pin 62B is set so that the primary transfer roll 30 is in the operating position on the right side in the drawing and the retracted position on the left side in the movement range.

  The camshaft 65 connects the left and right eccentric links 62, and a worm gear 65A is provided at the approximate center thereof. The worm gear 65A meshes with a worm wheel 61A fixed to the rotation shaft of the switching motor 61. Thereby, the camshaft 65 is rotationally driven by the switching motor 61 at a predetermined reduction ratio. The switching motor 61 is fixed to a chassis (not shown).

The moving mechanism 60 configured as described above moves the primary transfer roll 30 between the operating position and the retracted position by the rotation of the switching motor 61.
That is, as shown in FIGS. 2 and 3, the eccentric link 62 is rotated counterclockwise by the switching motor 61 from the state where the primary transfer roll 30 is in the operating position. As a result, the switching operation rod 63 is moved to the left in the drawing by the amount of eccentricity of the operation pin 62B with respect to the camshaft 65, and the operation portion 63A of the switching operation rod 63 moves the operated portion 64B to move the operation arm 64. Swing clockwise in the figure. Due to the swing of the operation arm 64, the operation portion 64 </ b> A pushes down the primary transfer roll 30 to the retracted position against the pressing force of the pressing spring 31. The operation of moving the primary transfer roll 30 from the operating position to the retracted position is performed by half rotation of the eccentric link 62. When the eccentric link 62 further rotates halfway from this state, the primary transfer roll 30 returns to the operating position. That is, with one rotation of the eccentric link 62, the primary transfer roll 30 is reciprocated once between the retracted position and the operating position.

  The switching motor 61 is a stepping motor that is rotationally driven by a drive pulse, and is controlled by a contact / separation control unit 51 as a contact / separation control device. That is, the position control of the primary transfer roll 30 is performed by the contact / separation control unit 51. The contact / separation control unit 51 is configured in a control unit 50 that performs overall control of the entire image forming apparatus 1 (see FIG. 1).

  Here, the outer peripheral rolling surface of the eccentric cam 62A of the eccentric link 62 is eccentric from the center of the cam shaft 65, and the rolling surface and the retract roll 72 are linked by a mechanism (not shown). As a result, the moving mechanism 60 also moves the retract roll 72 as described above, and the retract roll 72 is moved between the operating position and the retracted position by the displacement of the rolling surface of the eccentric cam 62A accompanying the rotation of the eccentric link 62. It is designed to move up and down.

Further, all the primary transfer rolls 30 are provided with a primary transfer current supply device 80 for supplying a bias current.
FIG. 4 shows a conceptual configuration diagram of the primary transfer current supply device 80.
In the primary transfer current supply device 80, a primary transfer current source 81 as a transfer power source capable of adjusting an output current value is connected to the primary transfer roll 30, and the photosensitive drum 11 is grounded by a ground circuit 82. Further, the primary transfer current supply device 80 includes a primary transfer voltmeter 83 that measures a voltage between the primary transfer current source 81 and the photosensitive drum 11. Then, a positive primary transfer bias (primary transfer current) is passed from the primary transfer current source 81 through the primary transfer roll 30, the intermediate transfer belt 20, and the photosensitive drum 11, whereby the photosensitive drum 11 and the intermediate transfer belt are passed. 20, a transfer electric field for transferring the toner image on the photosensitive drum 11 to the intermediate transfer belt 20 is formed.

The primary transfer current source 81 and the primary transfer voltmeter 83 of the primary transfer current supply device 80 are controlled by a transfer control unit 52 configured in a control unit 50 that performs overall control of the entire image forming apparatus 1 (see FIG. 1). Is done. The transfer control unit 52 controls the primary transfer current source 81 to flow a constant current to the primary transfer roll 30, and based on the voltage measurement result obtained by the primary transfer voltmeter 83 at that time, the primary transfer roll 30 at the time of image formation. A so-called resistance detection is performed to determine the primary transfer current to be passed through. When the image is formed, the primary transfer current supplied from the primary transfer current source 81 is subjected to constant current control based on the detection result.
The transfer control unit 52 is driven by the control unit 50, and the resistance detection is irregularly performed at the time of initial setting (initialization) at the time of power-on prior to image formation, periodically, or when conditions such as temperature change. To do. At the time of resistance detection, the photosensitive drum 11 is charged by a charger in the same manner as in normal image formation, and a developing bias is applied to the developing device in the same manner as in normal image formation.

Further, among the primary transfer rolls 30Y, 30M, and 30C corresponding to the image forming units 10Y, 10M, and 10C that do not function in the monochrome mode (the primary transfer roll 30 that is moved between the operating position and the retracted position by the moving mechanism 60). As shown in FIG. 3 and FIG. 4, an electrical property detection unit 53 as electrical property detection means is provided in any one of them.
The electrical characteristic detector 53 is integrally formed in the controller 50 and is connected to the contact / separation controller 51 and the transfer controller 52. These are driven to detect the color position and acquire the color position information, and the color position information is held in the contact / separation control unit 51.

  In the color position detection by the electric characteristic detection unit 53, the transfer control unit 52 is driven to supply a constant current to the primary transfer roll 30 to measure the voltage, and the contact / separation control unit 51 sets the primary transfer roll 30 to the working position. This is done by driving the moving mechanism 60 so as to make one reciprocation between the retreat positions (the eccentric link 62 makes one rotation). And the voltage measurement result in the meantime is read, and the action position of the primary transfer roll 30 is determined from the voltage measurement result. That is, in the present embodiment, when the primary transfer roll 30 is moved toward and away from the photosensitive drum 11, color position detection is performed using the voltage change at a constant current measured by the transfer control unit 52 as an electrical characteristic. It is.

In this color position detection, when the primary transfer roll 30 presses and separates the intermediate transfer belt 20 from the photosensitive drum 11, the primary transfer roll 30 moves the intermediate transfer belt 20 at the position where the measured voltage value shows the minimum value. This is performed by determining that the operation position is most pressed against the photosensitive drum 11.
FIG. 5 is an explanatory diagram of the principle of color position detection. In the drawing, (a) to (e) are views showing the positional relationship between the intermediate transfer belt 20 and the primary transfer roll 30 with respect to the photosensitive drum 11. The graph shows the voltage value at the time of such a positional relationship, the horizontal axis is the rotation angle of the eccentric link 62 of the moving mechanism 60, and the vertical axis is the voltage value.
When the primary transfer roll 30 presses the intermediate transfer belt 20 against the photosensitive drum 11 and presses it against the surface thereof, the resistance value between the primary transfer roll 30 and the photosensitive drum 11 changes depending on the pressed state. Since the voltage between the primary transfer roll 30 and the photosensitive drum 11 is proportional to the resistance value at a constant current, a constant current is passed between the primary transfer roll 30 and the photosensitive drum 11 to measure and compare the voltage value. Thus, the pressing state of the primary transfer roll 30 against the photosensitive drum 11 via the intermediate transfer belt 20 is understood.

  As shown in FIGS. 5A and 5E, when the primary transfer roll 30 does not press the intermediate transfer belt 20, and the intermediate transfer belt 20 is separated from the surface of the photosensitive drum 11, No current flows and the resistance is infinite. When the intermediate transfer belt 20 comes into contact with the surface of the photosensitive drum 11 by the movement of the primary transfer roll 30 from this state (b), a current flows between the primary transfer roll 30 and the photosensitive drum 11, but initially the resistance is increased. large. As the pressing of the primary transfer roll 30 progresses, the conductive foamed elastic body on the outer periphery thereof is compressed and deformed (which causes the internal bubbles to collapse), and the photosensitive drum is interposed between the surface of the primary transfer roll 30 and the intermediate transfer belt 20. The contact area with the surface of 11 is enlarged, and as a result, the resistance gradually decreases. In a state where the primary transfer roll 30 most presses the intermediate transfer belt 20 against the photosensitive drum 11 (c: nip state), the amount of elastic deformation of the conductive foamed elastic body is the largest, the contact area is the largest, and the resistance is the smallest. .

For this reason, the voltage at a constant current shows a maximum value corresponding to the current in the state (a) in which the intermediate transfer belt 20 is separated from the surface of the photosensitive drum 11 as shown in the graph of FIG. Then, after the intermediate transfer belt 20 comes into contact with the surface of the photosensitive drum 11 (b), it gradually decreases as the primary transfer roll 30 is pressed, and becomes the minimum value in the nip state (c). Thereafter, the pressure gradually increases as the pressing force decreases, and the contact state (d) is changed to the separated state (e) to return to the maximum value.
That is, the voltage measurement value is the minimum value at the operating position where the primary transfer roll 30 most presses the intermediate transfer belt 20 against the photosensitive drum 11 (ie, the full color position CP). Therefore, conversely, the minimum value of the voltage measurement value is determined, and the index indicating the state of the moving mechanism 60 at that time (the rotational position of the switching motor 61 and the eccentric link 62) (in this embodiment, a pulse for driving the switching motor 61) If (number) is obtained, it can be used as color position information. If the nip range indicating the minimum voltage has a width as shown in the graph, the center of the range is taken.

FIG. 6 is a control flowchart of color position detection by the electrical characteristic detection unit 53, and the process will be described based on this flowchart.
First, the switching motor 61 starts to be driven by pulse control by the contact / separation control unit 51 (step 101), and the transfer control unit 52 of the primary transfer current supply device 80 is driven to supply current to the primary transfer roll 30 (step). 102).
Next, the voltage measurement value by the primary transfer voltmeter 83 is read via the transfer control unit 52 for every fixed pulse for driving the switching motor 61 and stored in the memory of the electrical characteristic detection unit 53 (step 103). .
After the eccentric link 62 makes one rotation (the primary transfer roll 30 makes one reciprocation between the operating position and the retracted position), the switching motor 61 is stopped (step 104), and the current supply to the primary transfer roll 30 is stopped (step). 105).
Then, the number of pulses indicating the minimum value among the voltage measurement values obtained during the process of step 103 is calculated (step 106), and the number of pulses is output to the contact / separation control unit 51 as color position information. (Step 107).

  The contact / separation control unit 51 to which the color position information has been input stores the color position information in the memory. Based on this color position information, the number of pulses of the switching motor 61 in which the eccentric link 62 of the moving mechanism 60 is further rotated halfway is calculated and stored in the memory as monochrome position information (retraction position information of the primary transfer roll 30). Store. Thus, when switching between the full color position CP and the monochrome position KP, the rotation of the switching motor 61 of the moving mechanism 60 is controlled based on the position information. Thereby, position switching can be performed by open loop control of the switching motor 61 without requiring any other detection information.

  In this embodiment, the switching motor 61 is a pulse driving stepping motor, and the number of pulses for driving the switching motor 61 is color position information and monochrome position information. However, the operation time from the rotation start reference time is set as the position. By using the information, the switching motor 61 can be configured by a normal motor.

The image forming apparatus 1 including the electrical characteristic detection unit 53 configured as described above is driven and controlled by the control unit 50, and detects the color position by the electrical characteristic detection unit 53 and the contact / separation control unit 51 for the acquired color position information. And monochrome position information formation by the contact / separation control unit 51 are performed at the time of initial setting (initialization) when the power is turned on.
FIG. 7 shows a flowchart of initial setting at power-on.
In the initial setting when the power is turned on, after the apparatus is turned on (step 201), charging of the photosensitive drum by the charger, bias application of the developing device, and rotation of the intermediate transfer belt are started (step 202). ). Then, color position detection and setting of each position information based on the color position detection are performed (step 203). Thereafter, a process control operation (step 204) and a resist control operation (step 205) are performed, and a standby state is entered (step 206).
Thereafter, until the power is turned off, the position information obtained at the time of the initial setting is held, and the position is switched based on the position information.

In the process control operation, in order to obtain an optimum image density, an image is formed on the intermediate transfer belt 20, the density is measured, the charging amount of the photosensitive drum 11 by the charger, the bias current of the developing device, the primary It performs feedback control such as the bias current of the transfer roll and the toner supply amount in the developing device.
In addition, the resist control operation is performed by measuring each color print image formed on the intermediate transfer belt 20 by each image forming unit 10 (10Y, 10M, 10C, 10K).
The color registration is adjusted by controlling the writing timing to the photosensitive drum 11 by the laser exposure device of each image forming unit 10.
In addition, the timing which performs the color position detection by the electrical characteristic detection part 53 is not restricted to this, and can be changed suitably.

  As described above in detail, according to the present embodiment, a constant current is passed from the primary transfer current source 81 to the primary transfer roll 30 and the primary transfer voltmeter 83 measures the voltage while the primary transfer roll 30 operates. One reciprocation is made between the position and the retracted position. Then, the color position information can be obtained by detecting the color position where the primary transfer roll 30 is in the working position from the voltage measurement value obtained at that time. Also, monochrome position information can be set from the color position information based on the structure and driving conditions of the contact / separation control unit 51.

  Therefore, when the mode is switched between the full color mode and the monochrome mode, based on the color position information and the monochrome position information, the contact / separation control unit 51 only controls the rotation of the switching motor 61 to obtain any other detection information. Position switching is possible without need. Therefore, it is not necessary to provide the moving mechanism 60 with a mechanical detection mechanism that detects the position using, for example, a sensor or a member to be detected, and the power supply and input / output wiring to the sensor become unnecessary. For this reason, the number of components can be reduced, the number of assembly steps can be reduced, and the structure can be reduced at a low cost.

  In the present embodiment, the full color mode and the monochrome mode can be switched. In the full color mode, all the image forming units 10Y, 10M, 10C, and 10K form an image, and in the monochrome mode, the black image forming unit. The present invention is applied to an image forming apparatus that forms an image only at 10K. However, the present invention is not limited to such an image forming apparatus, and if an image forming unit that does not perform image formation in a specific mode is provided, for example, image formation is performed in two colors of black and a specific color. Of course, the present invention may be applied to an image forming apparatus having a specific color mode. Furthermore, even a single-color image forming apparatus having only one image forming unit can be applied as long as the primary transfer roll is in contact with and separated from the photosensitive drum.

  Further, the image forming apparatus that superimposes the toner image on the intermediate transfer belt 20 has been described as an example. However, the intermediate transfer belt 20 simply functions as a conveyance belt, and the sheet P is directly conveyed to the conveyance belt. The present invention can also be applied to an image forming apparatus that employs a method of sequentially superimposing toner images on top.

  Furthermore, in the present embodiment, the electrical property detection unit 53 as electrical property detection means measures the voltage between the primary transfer roll 30 and the photosensitive drum 11 at a constant current, and the primary transfer roll 30 is the photosensitive member. In this example, the operation position closest to the drum 11 is determined. However, the electrical characteristics are not limited to voltage, and it may be configured to measure and judge a current value that changes at a constant voltage. In this case, the position where the current shows the maximum value is the operating position (full color position CP).

1 is a schematic configuration diagram of an image forming apparatus to which the exemplary embodiment is applied. It is a conceptual diagram which shows the support part structure of a primary transfer roll. It is a perspective view which shows the conceptual structure of a moving mechanism. It is a block diagram which shows notionally the control system of a primary transfer roll. It is explanatory drawing which performs color position detection from a voltage change. It is a flowchart of the color position detection by an electrical property detection part. 3 is a flowchart of initial setting of the image forming apparatus. It is a conceptual block diagram of the image forming apparatus which can change the position as a prior art example. It is a perspective view which shows the conceptual structure of the detection mechanism as a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 (10Y, 10M, 10C, 10K) ... Image forming unit, 11 ... Photosensitive drum (image carrier), 20 ... Intermediate transfer belt (transfer member), 30 (30Y, 30M, 30C) , 30K) ... primary transfer roll (transfer member), 50 ... control unit, 51 ... contact / separation control unit (contact / separation control device), 52 ... transfer control unit, 53 ... electrical property detection unit (electric property detection device), 60 ... Movement mechanism 61 ... Switching motor (rotation drive mechanism) 62 ... Eccentric link (eccentric member) 63 ... Switching operation rod (intermediate operation member: conversion movement mechanism) 64 ... Operation arm (operation arm member: conversion movement mechanism) ), 80: Primary transfer current supply device, CP: Color position, KP: Monochrome position (single color position)

Claims (11)

An image carrier for carrying a toner image;
A member to be transferred provided so as to be displaceable between an action path contacting the image carrier and a retracting path spaced apart;
A transfer member provided so as to be movable between an operating position where the member to be transferred is pressed against the image carrier and a retracted position where the transfer member is separated, and to which a transfer current is supplied;
A moving mechanism for moving the transfer member;
While the transfer member is moved between the operating position and the retracted position, the transfer member and the image carrier are changed in accordance with a change in the contact area between the transfer member and the image carrier via the transferred member. The voltage change between the transfer member and the image carrier associated with the change in the resistance value between the image carrier and the current change between the transfer member and the image carrier is measured. An electrical characteristic detection device that forms action position information of the transfer member as a position where the transfer member most pressurizes the image carrier based on the change or the current change;
A contact / separation control device that drives the moving mechanism based on the action position information of the transfer member by the electrical property detection device;
An image forming apparatus comprising: The electrical characteristic detection device indicates a maximum value or a minimum value of the measured voltage value based on the voltage change of the transfer member measured while moving the transfer member between the operating position and the retracted position. the image forming apparatus according to claim 1, wherein the position of the transfer member the transfer member to form the operative position information of the transfer member as the most pressurized positions the image carrier. The electrical characteristic detection device indicates a maximum value or a minimum value of a measured current value based on the current change of the transfer member measured while moving the transfer member between the operating position and the retracted position. the image forming apparatus according to claim 1, wherein the position of the transfer member the transfer member to form the operative position information of the transfer member as the most pressurized positions the image carrier. The moving mechanism is
A rotation drive mechanism;
A conversion movement mechanism that converts the rotation of the rotation drive mechanism into an operation movement between the acting position and the retraction position of the transfer member,
The image forming apparatus according to claim 1 , wherein the contact / separation control device is configured to control movement of the transfer member by controlling rotation of the rotation drive mechanism. A plurality of image forming units each including an image carrier that carries toner images of different colors;
The image forming unit has a color reduction mode that functions except for a specific image forming unit.
The image forming apparatus according to claim 1 , wherein the contact / separation control device is configured to move the transfer member corresponding to the specific image forming unit to a retracted position in the color reduction mode. 6. The image forming apparatus according to claim 5 , wherein the specific image forming unit that functions in the color reduction mode is a black image forming unit including an image carrier that carries a black toner image. The voltage change measured by the electrical characteristic detection device is a voltage between the two when a constant current is passed between the transfer member and the image carrier,
The image forming apparatus according to claim 2 , wherein the electrical characteristic detection device forms the action position information with a position where the voltage measurement value is a minimum value as an action position of the transfer member. The image according to claim 7 , wherein the electrical characteristic detection device also serves as a resistance detection circuit that detects resistance information between the transfer member and the image carrier in order to set a transfer current. Forming equipment. It said electrical characteristic detecting device, the the measurement of the voltage change of the transfer member, and the formation of the working location of the transfer member based on the voltage change, is configured to perform during the initial power up configuration The image forming apparatus according to claim 8 , wherein: A method of setting the working position of a transfer member that is provided so as to be movable between a working position where the member to be transferred is pressed against the image carrier and a retracted position where the member is separated, and to which a transfer current is supplied,
The transfer member and the image carrier are moved in accordance with the contact area between the transfer member and the image carrier via the member to be transferred as the transfer member is moved toward and away from the image carrier. Measuring a voltage change between the transfer member and the image carrier or a current change between the transfer member and the image carrier due to a change in resistance value between the body and the voltage change or An action of the transfer member in the image forming apparatus, wherein the position where the transfer member presses the image carrier most is determined based on the current change, and the position is set as the action position of the transfer member. Position setting method. Measuring a voltage change or a current change of the transfer member while moving the transfer member toward and away from the image carrier; and
The position of the transfer member to which the measured voltage value or current value indicates either a maximum or minimum value, and determining a position where the transfer member is pressed most pressure to said image bearing member,
A method for setting an action position of a transfer member in an image forming apparatus according to claim 10 .

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