Image forming apparatus

Abstract

To accurately detect the position of the transfer material even when condensation is present on the transfer material. [Solution] The system includes a secondary transfer contact / separation mechanism 300 that performs a contact / separation operation to move the secondary transfer roller 25 between a contact position where it is in contact with the intermediate transfer belt 13 and a separated position where it is separated from the intermediate transfer belt 13, a contact / separation motor 221, a secondary transfer power supply 26 that applies voltage to the secondary transfer roller 25, a current detection circuit 27 that detects the current flowing through the secondary transfer roller 25 when voltage is applied to the secondary transfer roller 25 by the secondary transfer power supply 26, and a control unit 200 that determines the contact position and separated position based on a comparison of the detection result of the current detection circuit 27 with a reference value A. The control unit 200 resets the reference value A (S106~S112) if the detection result detected by the current detection circuit 27 when the contact operation by the secondary transfer contact / separation mechanism 300 is performed does not fall below the reference value A (S102, S103 failure).

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus such as a copier, printer, or facsimile machine using an electrophotographic or electrostatic recording method. [Background technology]

[0002] Conventionally, in image forming apparatuses using electrophotography or the like, a transfer voltage is applied to a transfer member that contacts an image carrier such as a photosensitive drum or an intermediate transfer belt to form a transfer area, thereby transferring the toner image formed on the image carrier to a transfer material. As the transfer member, a transfer roller having an elastic layer formed of an elastic material on a core metal is used. In such an image forming apparatus, if the image forming apparatus is left in long-term storage with the transfer member in contact, local deformation may occur in the transfer member or image carrier due to the pressure applied to the contact area (hereinafter referred to as contact pressure). Depending on the degree of deformation, this may cause image defects due to transfer defects. Therefore, a configuration that separates the transfer member from the image carrier or reduces the contact pressure (hereinafter referred to as a contact / separation mechanism) is sometimes provided in the image forming apparatus. When such a contact / separation mechanism is adopted, a mechanism for detecting the position of the transfer member (hereinafter referred to as the contact / separation state) is necessary. For example, Patent Document 1 discloses a configuration that detects the position of the transfer member by detecting the current value flowing through the transfer member. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2001-083758 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, in a configuration that detects the position of a transfer member by detecting the current flowing through it, if the electrical resistance of the transfer member changes, the current flowing through the transfer member will also change, potentially leading to a false detection of the transfer member's position. One example of a situation that can induce false detection is when condensation occurs. Condensation is a phenomenon in which air containing water vapor is cooled, and the amount of water vapor exceeding the saturation point turns into water droplets, and it can also occur inside an image forming apparatus. For example, when heating is turned on in an office on a winter morning, the room temperature rises rapidly, while the components with high heat capacity inside the image forming apparatus rise more slowly. As a result, a temperature difference is created between the room temperature and the components inside the image forming apparatus. Therefore, the heated air cools on the surface of the components, causing water droplets to adhere to the surface and condensation to occur. When water droplets form on the surface of the transfer member, the electrical resistance decreases, making it easier for current to flow through the transfer member. Also, even if the transfer member and the image carrier are separated, if the separation is small, current can still flow through the water droplets. When attempting to detect the position of a transfer member by detecting the current flowing through it while condensation is present, the electrical resistance is lower than normal, resulting in a larger detected current value. This can lead to false detection of contact even when the members are actually separated. If image forming is performed while the members are falsely detected as being in contact when they are actually separated, the contact pressure on the image carrier may become insufficient, potentially causing image defects or transport failures.

[0005] This invention was made under such circumstances, and aims to accurately detect the position of a transfer member even when the transfer member is condensed. [Means for solving the problem]

[0006] To solve the above-mentioned problems, the present invention has the following configuration.

[0007] (1) An image forming apparatus comprising: an image carrier that carries a toner image; a transfer member that contacts the image carrier and forms a transfer section for transferring a toner image from the image carrier to a transfer material; a moving unit that performs a moving operation to move the transfer member between a contact position where the transfer member is in contact with the image carrier and a separated position where the transfer member is separated from the image carrier; a driving unit that drives the moving unit; an application unit that applies a voltage to the transfer member; a detection unit that detects at least one of the voltage applied to the transfer member by the application unit or the current flowing through the transfer member when a voltage is applied to the transfer member by the application unit; and a determination means that determines whether the position of the transfer member is the contact position or the separated position based on a comparison of the detection result of the detection unit with a reference value, wherein the determination means resets the reference value when the detection result detected by the detection unit when the moving operation by the moving unit is performed does not fall below the reference value. [Effects of the Invention]

[0008] According to the present invention, the position of the transfer member can be accurately detected even when the transfer member is condensed. [Brief explanation of the drawing]

[0009] [Figure 1] Schematic cross-sectional view of the image forming apparatus in Examples 1-3 [Figure 2] Block diagrams showing the control configuration of the main parts of the image forming apparatus in Examples 1-3. [Figure 3] Schematic diagram illustrating the operation of the secondary transfer attachment / detachment mechanism in Examples 1-3. [Figure 4] This figure shows the detection results of the current value acquired during the contact-to-separation operation in Example 1. [Figure 5] This figure shows the relationship between absolute moisture content, applied voltage [V], and reference value in Examples 1-3. [Figure 6] A flowchart showing a conventional control example for comparison with Example 1. [Figure 7] This figure shows the results of monitoring the current value while the devices were in contact and separated under the condensation conditions of Example 1. [Figure 8]Flowchart showing the control of the contact / separation operation in Example 1 [Figure 9] Figure showing the result of monitoring the current value while causing contact / separation in the dew condensation state of Example 1 [Figure 10] Figure showing the result of monitoring the current value in the state where the gear of Example 1 has tooth skipping [Figure 11] Flowchart showing the control of the contact / separation operation in Example 2 [Figure 12] Figure showing the result of monitoring the current value while causing contact / separation in the dew condensation state of Example 2 [Figure 13] Figure showing the detection result of the current value obtained during the contact / separation operation in Example 3 [Figure 14] Flowchart showing the control of the contact / separation operation in Example 3 [Figure 15] Figure showing the result of monitoring the current value while causing contact / separation in the dew condensation state of Example 3

Mode for Carrying Out the Invention

[0010] Hereinafter, the image forming apparatus according to the present invention will be described with reference to the drawings.

Example

[0011] <1. Configuration of the Image Forming Apparatus> The main configuration of the image forming apparatus 100 of Example 1 will be described. FIG. 1 is a schematic cross-sectional view of the image forming apparatus 100 of Example 1. The image forming apparatus 100 of Example 1 is a tandem type printer (color image forming apparatus) adopting an intermediate transfer method that can form a full-color image using an electrophotographic method.

[0012] The image forming apparatus 100 has a plurality of image forming stations, the first, second, third, and fourth image forming stations Sa, Sb, Sc, and Sd, which each form an image using toners of yellow (Y), magenta (M), cyan (C), and black (Bk), respectively. These four image forming stations Sa, Sb, Sc, and Sd are arranged in a line at approximately constant intervals along the direction of movement of the surface onto which the image of the intermediate transfer belt 13, which will be described later, is transferred. In addition, elements with the same or corresponding functions or configurations provided for each color may be described collectively by omitting the a, b, c, and d at the end of the symbols indicating that they are elements for any of the colors. In Example 1, the image forming station S is composed of a photosensitive drum 1, a charging roller 2, an exposure device 11, a developing device 8, a primary transfer roller 10, a cleaning device 3, etc., which will be described later.

[0013] The image forming unit S has a photosensitive drum 1, which is a rotatable drum-shaped (cylindrical) photoreceptor (electrophotographic photoreceptor) serving as the first image carrier. The photosensitive drum 1 is constructed by laminating multiple layers of functional organic material on a cylindrical metal member, each layer consisting of a carrier generation layer that generates electric charge upon exposure to light, and a charge transport layer that transports the generated charge. The outermost layer of the photosensitive drum 1 has low conductivity and is almost electrically insulating. The photosensitive drum 1 receives a driving force from a drive source (not shown) and rotates at a predetermined peripheral speed (process speed) in the direction of arrow R1 in the figure (counterclockwise).

[0014] The charging roller 2, a roller-type charging member used as a means of charging, contacts the photosensitive drum 1 and rotates in conjunction with the rotation of the photosensitive drum 1. As the charging roller 2 rotates, it charges the surface of the photosensitive drum 1 in a substantially uniform manner. The charging roller 2 is connected to a charging power supply 20, which acts as a charging voltage application unit. A DC voltage is applied to the charging roller 2 from the charging power supply 20 as the charging voltage. As a result, the surface of the photosensitive drum 1 is charged by discharges generated in the minute gaps between the charging roller 2 and the photosensitive drum 1, which are formed upstream and downstream of the contact point between the charging roller 2 and the photosensitive drum 1 in the direction of rotation of the photosensitive drum 1. The exposure apparatus 11, as an exposure means, consists of a scanner unit that scans laser light using a multifaceted mirror. The exposure apparatus 11 irradiates the photosensitive drum 1 with a scanning beam 12 that has been modulated based on an image signal.

[0015] The developing apparatus 8, as a developing means, comprises a developing container 5, a developing roller 4 as a developing member, and a blade 7 as a developing agent regulating member that applies developer to the developing roller 4 and regulates its thickness. The developing container 5 contains toner as the developer. The developing roller 4 is connected to a developing power supply 21, which is a developing voltage application unit. An alternating voltage, which is a superposition of a DC voltage and an AC voltage, is applied to the developing roller 4 from the developing power supply 21 as the developing voltage.

[0016] The cleaning device 3, as a cleaning means, includes a cleaning blade 41 as a cleaning member that contacts the photosensitive drum 1, and a cleaning container 42 that contains toner and other materials removed from the photosensitive drum 1 by the cleaning blade 41. The cleaning device 3 recovers toner and other materials remaining on the photosensitive drum 1. Furthermore, the photosensitive drum 1, the charging roller 2 which acts on the photosensitive drum 1 as a process means, the developing device 8, and the cleaning device 3 together constitute a process cartridge 9 that can be detachably attached to the main body 101 of the image forming apparatus 100.

[0017] An intermediate transfer belt 13, which is an intermediate transfer body composed of an endless belt as a second image carrier, is positioned opposite the photosensitive drum 1 of each image forming unit S. The intermediate transfer belt 13 is stretched by three tension rollers: a secondary transfer opposing roller (hereinafter also simply referred to as "opposing roller") 15, a tension roller 14, and an auxiliary roller 19, which are tensioning members. The tension roller 14 is biased by a spring (not shown), which is a biasing member acting as a biasing means, in order to maintain appropriate tension on the intermediate transfer belt 13. The opposing roller 15 rotates in the direction of arrow R2 (clockwise) in the figure, receiving a driving force from a drive source (not shown). The intermediate transfer belt 13 rotates in the direction of arrow R3 (clockwise) in the figure as the opposing roller 15 rotates. The intermediate transfer belt 13 can move at approximately the same speed in the forward direction relative to the photosensitive drum 1 at the portion opposite to the photosensitive drum 1. The auxiliary roller 19, tension roller 14, and opposing roller 15 are electrically grounded (connected to ground). The opposing roller 15 is a roller with an outer diameter of 24.0 mm, constructed by covering an aluminum core (base) with an elastic layer (elastic part) made of EPDM rubber with a wall thickness of 0.5 mm. The opposing roller 15 has an electrical resistance of approximately 1 × 10⁻¹⁰ 5 The electrical resistance is adjusted by dispersing carbon, a conductive agent, in EPDM rubber to achieve an ohm (Ω) resistance.

[0018] On the inner circumferential surface of the intermediate transfer belt 13, primary transfer rollers 10a, 10b, 10c, and 10d, which are roller-type primary transfer members serving as primary transfer means, are provided, corresponding to each of the photosensitive drums 1a, 1b, 1c, and 1d. The primary transfer rollers 10 are positioned opposite the photosensitive drum 1 via the intermediate transfer belt 13, and they contact the inner circumferential surface of the intermediate transfer belt 13, rotating in accordance with the movement of the intermediate transfer belt 13. The primary transfer rollers 10 contact the photosensitive drum 1 via the intermediate transfer belt 13, are pressed toward the photosensitive drum 1, and form a primary transfer section (primary transfer nip) N1 where the photosensitive drum 1 and the intermediate transfer belt 13 come into contact. The primary transfer rollers 10 are connected to a primary transfer power supply 22, which serves as a primary transfer voltage application unit. The primary transfer roller 10 is constructed by covering a core (base) made of a nickel-plated steel rod with an outer diameter of 5 mm with an elastic layer (elastic part) made of a foamed elastic material with an outer diameter of 14 mm. The primary transfer roller 10 has an electrical resistance of approximately 1 × 10⁻¹⁰ 6 The electrical resistance of the foamed elastic material is adjusted by incorporating a conductive agent so that it becomes Ω. The electrical resistance of the primary transfer roller 10 is 10 3 ~10 7 Being within the Ω range is preferable for achieving good image formation.

[0019] On the outer circumferential surface side of the intermediate transfer belt 13, a secondary transfer roller 25, which is a roller-type secondary transfer member (transfer member) serving as a secondary transfer means, is positioned opposite the opposing roller 15. The secondary transfer roller 25 can move toward and away from the outer circumferential surface of the intermediate transfer belt 13. In Figure 1, the state in which the secondary transfer roller 25 is in contact with the outer circumferential surface of the intermediate transfer belt 13 is shown by a solid line, and the state in which it is separated is shown by a dashed line. The secondary transfer roller 25 is positioned opposite the opposing roller 15 via the intermediate transfer belt 13, and it contacts the outer circumferential surface of the intermediate transfer belt 13 and rotates in response to the movement of the intermediate transfer belt 13. The secondary transfer roller 25 contacts the opposing roller 15 via the intermediate transfer belt 13 and is pressed toward the opposing roller 15, forming a secondary transfer portion (secondary transfer nip) N2 (transfer portion) where the intermediate transfer belt 13 and the secondary transfer roller 25 are in contact. The secondary transfer roller 25 is connected to a secondary transfer power supply 26, which acts as a secondary transfer voltage application unit (application unit). The secondary transfer power supply 26 is connected to a current detection circuit 27, which acts as a detection unit. The secondary transfer power supply 26 applies a voltage to the secondary transfer roller 25, and the current detection circuit 27 can detect the current flowing through the secondary transfer roller 25. The secondary transfer roller 25 is constructed by covering a metal core (base) with an elastic layer (elastic part) made of foamed elastic material.

[0020] The fixing device 50, as a fixing means, includes a pressure roller 51 and a cylindrical fixing film (fixing belt) 52 as fixing members (fixing rotating bodies). A heating member 53 is arranged on the inner circumferential surface side of the fixing film 52 to apply heat to the transfer material P via the fixing film 52. The pressure roller 51 can move toward and away from the outer circumferential surface of the fixing film 52. In Figure 1, the state in which the pressure roller 51 is in contact with the outer circumferential surface of the fixing film 52 is shown by a solid line, and the state in which it is separated is shown by a dashed line. The pressure roller 51 comes into contact with the heating member 53 via the fixing film 52 and is pressed toward the heating member 53, forming a fixing portion (fixing nip) N3 where the pressure roller 51 and the fixing film 52 are in contact. The pressure roller 51 rotates by receiving a driving force from a motor as a driving source, and the fixing film 52 rotates in accordance with the rotation of the pressure roller 51.

[0021] Furthermore, the image forming apparatus 100 is equipped with a control unit (control board, controller) 200 that has electrical circuits for controlling the operation of each part of the image forming apparatus 100. The control unit 200 is equipped with a CPU 211 as a decision-making means, a memory 212 as a storage means for storing various control information, and an input / output unit (I / F) 213 for controlling the exchange of signals between the control unit 200 and each part. The CPU 211 performs control related to the transport of the transfer material P, control related to the driving of the image forming unit S and the intermediate transfer belt 13, control related to image formation, and control related to fault detection. The memory 212 is composed of ROM (including rewritable ROM) and RAM, with control programs and data tables stored in the ROM, and data showing the detection results of various sensors and calculation results related to control stored in the RAM.

[0022] The image forming apparatus 100 is equipped with an environmental sensor 70. The environmental sensor 70 detects temperature and humidity as environmental information and outputs the detection results to the control unit 200. The control unit 200 obtains the absolute moisture content based on the detection results of the environmental sensor 70. The image forming apparatus 100 is equipped with an operation display unit 80. The operation display unit 80 has a display device, such as a liquid crystal panel, that notifies the user of various information, and input devices such as physical buttons and a touch panel for the liquid crystal panel that accept input operations from the user. The control unit 200 controls the display content of the display device by communicating with the operation display unit 80 and receives information input via the input devices.

[0023] <2. Image Formation Process> Next, the image forming operation of the image forming apparatus 100 in Example 1 will be described. When the control unit 200 receives an image signal from an external device (not shown), such as a personal computer, it starts the image forming operation. When the image forming operation starts, each photosensitive drum 1 and opposing roller 15, etc., starts rotating at a predetermined peripheral speed (process speed) due to the driving force from a drive source (not shown). In Example 1, the process speed is 200 mm / s.

[0024] The surface of the rotating photosensitive drum 1 is uniformly charged by the charging roller 2. During the charging process, a charging voltage, which is a DC voltage with the same polarity as the normal charging polarity of the toner (negative polarity in Example 1), is applied to the charging roller 2 from the charging power supply 20. The surface of the charged photosensitive drum 1 is scanned and exposed by the exposure device 11, which irradiates it with a scanning beam 12 corresponding to the image information of the color components corresponding to each image forming section S, and an electrostatic latent image (electrostatic image) corresponding to the image information is formed on the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by the developing device 8 when toner is supplied, and a toner image (toner image, developer image) is formed on the photosensitive drum 1. In the developing device 8, the toner contained in the developing container 5 is negatively charged by the blade 7 and applied to the developing roller 4. Also, during the developing process, a developing voltage containing a DC component with the same polarity as the normal charging polarity of the toner (negative polarity in Example 1) is applied to the developing roller 4 from the developing power supply 21. As a result, in the developing section where the developing roller 4 and the photosensitive drum 1 come into contact, toner moves from the developing roller 4 to the image portion of the electrostatic latent image on the photosensitive drum 1 and adheres to it. In Example 1, toner charged with the same polarity as the charging polarity of the photosensitive drum 1 (negative polarity in Example 1) adheres to the exposed area (image area), where the absolute value of the potential decreases after uniform charging treatment and exposure (reverse development). In Example 1, the normal charging polarity of the toner, which is the charging polarity of the toner during development, is negative polarity.

[0025] The toner image formed on the photosensitive drum 1 is transferred (primary transfer) onto the rotating intermediate transfer belt 13 in the primary transfer section N1 by the action of the primary transfer roller 10. During the primary transfer process, the primary transfer roller 10 is supplied with a primary transfer voltage from the primary transfer power supply 22, which is a DC voltage with the opposite polarity to the normal charging polarity of the toner (positive polarity in Example 1). For example, when forming a full-color image, the toner images of yellow, magenta, cyan, and black formed on each photosensitive drum 1 are sequentially superimposed onto the intermediate transfer belt 13 in a primary transfer process. As a result, toner images of four colors corresponding to the desired color image are formed on the intermediate transfer belt 13.

[0026] The toner image formed on the intermediate transfer belt 13 is transferred (secondary transfer) in the secondary transfer section N2 by the action of the secondary transfer roller 25 onto the transfer material P which is being transported while being held between the intermediate transfer belt 13 and the secondary transfer roller 25. During the secondary transfer process, a secondary transfer voltage, which is a DC voltage with the opposite polarity to the normal charging polarity of the toner (positive polarity in Example 1), is applied to the secondary transfer roller 25 from the secondary transfer power supply 26. The transfer material (recording medium, recording material, sheet, paper) P, such as paper or an OHP sheet, is housed in a cassette 16. The transfer material P is fed from the cassette 16 to the transport roller 18 by the feed roller 17, and then transported towards the secondary transfer section N2 by the transport roller 18.

[0027] The transfer material P onto which the toner image has been transferred is transported toward the fixing device 50 by a secondary transfer roller 25 and an opposing roller 15. The fixing device 50 heats and pressurizes the transfer material P in the fixing section N3. The unfixed toner image supported on the transfer material P is fixed (melted and solidified) onto the transfer material P as it passes through the fixing section N3. For example, when forming a full-color image, the four colors of toner on the transfer material P are melted and mixed in the fixing section N3 and fixed onto the transfer material P. After that, the transfer material P is discharged (output) to the outside of the main body 101 of the image forming apparatus 100 and loaded onto the discharge tray 60, which serves as a loading section provided on the top of the main body 101.

[0028] The image forming apparatus 100 is equipped with sensors such as a resist sensor 110 and an ejection sensor 111 for detecting the transfer material P during the image forming operation described above. Meanwhile, toner remaining on the photosensitive drum 1 after the primary transfer (primary transfer residue toner) is removed from the photosensitive drum 1 and recovered by the cleaning device 3. A belt cleaning device 30, which serves as an intermediate transfer body cleaning means, is positioned on the outer circumferential surface side of the intermediate transfer belt 13, facing the opposing roller 15 via the intermediate transfer belt 13. Toner remaining on the intermediate transfer belt 13 after the secondary transfer (secondary transfer residue toner) is removed from the intermediate transfer belt 13 and recovered by the belt cleaning device 30. The belt cleaning device 30 is configured to have a cleaning blade 31 that contacts the outer circumferential surface of the intermediate transfer belt 13 at a position facing the opposing roller 15.

[0029] <3. Control Modes> Figure 2 is a block diagram showing the control configuration for detecting (determining) the position of the secondary transfer roller 25 in the image forming apparatus 100 of Example 1. Figure 2 shows the functional blocks in the control unit 200 and the hardware 220 that operates under the control of the control unit 200.

[0030] The control unit 200 includes, as functional blocks, a drive control unit 202, a movement control unit 203, a voltage control unit 204, a current detection control unit 205, and a position detection control unit 206. In Embodiment 1, each functional block is realized in the control unit 200 by the CPU 211 (Figure 1) executing a program stored in the memory 212 (Figure 1). In addition, the CPU 211 that realizes each functional block in the control unit 200 controls the operation (including acquisition of detection results) of the hardware 220 shown in Figure 2 mainly via the input / output unit 213 (Figure 1) to perform processing related to the detection of the position of the secondary transfer roller 25. The hardware 220 includes a contact / separation motor 221, a secondary transfer separation cam 223, a secondary transfer roller 25, a secondary transfer power supply 26, and a current detection circuit 27.

[0031] The movement control unit 203 operates the secondary transfer separation cam 223 by driving the contact / separation motor 221, which acts as a drive unit, via the drive control unit 202, thereby moving the secondary transfer roller 25. In other words, the movement control unit 203 changes the position of the secondary transfer roller 25 relative to the intermediate transfer belt 13 (or opposing roller 15). The secondary transfer separation cam 223, which is a cam member that performs the movement operation to move the secondary transfer roller 25, constitutes the secondary transfer contact / separation mechanism 300 (Figure 3), which will be described later.

[0032] The position detection control unit 206 detects the position of the secondary transfer roller 25 through the actions of the voltage control unit 204, the current detection control unit 205, and the movement control unit 203. Specifically, as will be described in more detail later, the position detection control unit 206 moves the secondary transfer roller 25 using the movement control unit 203 and applies voltage to the secondary transfer roller 25 from the secondary transfer power supply 26 using the voltage control unit 204. When voltage is applied to the secondary transfer roller 25, the position detection control unit 206 detects the position of the secondary transfer roller 25 based on the detection result of the current value obtained by the current detection control unit 205 from the current detection circuit 27.

[0033] In Example 1, the secondary transfer power supply 26 can apply a voltage to the secondary transfer roller 25 that is controlled (constant voltage controlled) to be approximately constant at a voltage value set by the voltage control unit 204. The voltage control unit 204 can detect (recognize) the voltage value of the voltage applied from the secondary transfer power supply 26 to the secondary transfer roller 25 based on the voltage value set for the secondary transfer power supply 26. In other words, in Example 1, the voltage control unit 204 has the function of a voltage detection unit that detects the voltage value of the voltage applied to the secondary transfer roller 25. The current detection circuit 27, acting as a current detection unit, detects the current value flowing through the secondary transfer roller 25 when the secondary transfer power supply 26 applies voltage to the secondary transfer roller 25. The current detection control unit 205 acquires the detection result of the current value by the current detection circuit 27. In Example 1, the secondary transfer power supply 26 can apply a voltage to the secondary transfer roller 25 that is controlled (constant current controlled) to be approximately constant at a current value detected by the current detection circuit 27.

[0034] <4.2 Secondary Transcription Mechanism> Next, the secondary transfer contact / separation mechanism 300, which moves the secondary transfer roller 25 to multiple positions relative to the intermediate transfer belt 13 in Example 1, will be described. Figure 3 is a schematic diagram illustrating the operation of the secondary transfer contact / separation mechanism 300. Figure 3(a) shows the contact position where the secondary transfer roller 25 is in contact with the intermediate transfer belt 13, and (b) shows the separation position where the secondary transfer roller 25 is separated from the intermediate transfer belt 13. Figure 3 is a view of the secondary transfer roller 25 from the direction of its rotation axis, and each shows one end of the secondary transfer roller 25 in the direction of its rotation axis, but the configuration of the other end is the same as the configuration shown (approximately symmetrical with respect to the center in the direction of the rotation axis of the secondary transfer roller 25).

[0035] In Example 1, the secondary transfer contact / separation mechanism 300 consists of a secondary transfer separation cam 223, a contact / separation motor 221, and a bearing 301 for the secondary transfer roller 25. The secondary transfer separation cam 223 is rotatably provided at both ends of the opposing roller 15 in the direction of its rotation axis. The secondary transfer separation cam 223 is rotatable about a rotation axis 223o that is coaxial with the rotation axis 15o of the opposing roller 15. The bearing 301 for the secondary transfer roller 25 is provided at both ends of the secondary transfer roller 25 in the direction of its rotation axis and rotatably supports the secondary transfer roller 25. The bearing 301 for the secondary transfer roller 25 has a contact surface 302 that contacts the secondary transfer separation cam 223. The bearing 301 for the secondary transfer roller 25 is biased toward the intermediate transfer belt 13 by a secondary transfer pressing spring 304, which is a biasing member acting as a biasing means.

[0036] When the contact / separation motor 221 is rotated, the secondary transfer separation cam 223 rotates, moving the secondary transfer roller 25 to the target position relative to the intermediate transfer belt 13. In Embodiment 1, the secondary transfer separation cam 223 moves the secondary transfer roller 25 between a contact position where it is in contact with the intermediate transfer belt 13 and a separated position where it is separated from the intermediate transfer belt 13. In Embodiment 1, the secondary transfer separation cam 223 is configured to rotate in only one direction by the rotation of the contact / separation motor 221.

[0037] As shown in FIG. 3(a), when the secondary transfer roller 25 is at the contact position where it contacts the intermediate transfer belt 13, the distance between the contact surface 302 and the rotation axis 223o is the distance Ra. As shown in FIG. 3(b), when the secondary transfer roller 25 is at the separation position where it is separated from the intermediate transfer belt 13, the distance between the contact surface 302 and the rotation axis 223o is the distance Rb. Since the distance Rb is greater than the distance Ra (Ra < Rb), the secondary transfer contact / separation mechanism 300 enables the contact and separation of the secondary transfer roller 25 by the rotation of the secondary transfer separation cam 223.

[0038] From the state where the secondary transfer roller 25 is at the contact position (FIG. 3(a)) contacting the intermediate transfer belt 13, rotate the contact / separation motor 221 to rotate the secondary transfer separation cam 223 by approximately 180 degrees. As a result, the bearing 301 of the secondary transfer roller 25 is pushed by the secondary transfer separation cam 223 and retreats in the direction away from the intermediate transfer belt 13, and the secondary transfer roller 25 moves to the separation position (FIG. 3(b)) where it is separated from the intermediate transfer belt 13. Next, from the state where the secondary transfer roller 25 is at the separation position (FIG. 3(b)) separated from the intermediate transfer belt 13, rotate the contact / separation motor 221 to rotate the secondary transfer separation cam 223 by approximately 180 degrees. As a result, the bearing 301 of the secondary transfer roller 25 moves in the direction approaching the intermediate transfer belt 13, and the secondary transfer roller 25 returns to the contact position (FIG. 3(a)) where it contacts the intermediate transfer belt 13. That is, when the secondary transfer separation cam 223 makes one rotation (one revolution) from the state where the secondary transfer roller 25 contacts the intermediate transfer belt 13, the position of the secondary transfer roller 25 changes as contact → separation → contact.

[0039] <5. Relationship between the position of the secondary transfer roller and the current value> Next, using Figure 4, the relationship between the position of the secondary transfer roller 25 in Example 1 and the detection result of the current value acquired by the control unit 200 (current detection control unit 205) from the current detection circuit 27 will be explained. Figure 4 is a diagram showing the detection result of the current value acquired by the current detection control unit 205 from the current detection circuit 27 during the contact-to-separation operation. The upper part of Figure 4 shows the contact-to-separation state (separated, near-contact, contact) for one rotation of the secondary transfer separation cam 223 (during one rotation). The lower part of Figure 4 is a graph where the horizontal axis is the rotation time of the secondary transfer separation cam 223 and the vertical axis is the current value (hereinafter also called the secondary transfer current value) [A] detected by the current detection circuit 27. Also, t11~t15, t21, and t22 indicate time. In the graph of the current value in Figure 4, the reference value A (=3μA), which will be described later, is also shown as a dashed line.

[0040] When the secondary transfer power supply 26 applies voltage to the secondary transfer roller 25 and the secondary transfer separation cam 223 is rotated, the current value decreases when the secondary transfer roller 25 is separated from the intermediate transfer belt 13 (times t11-t12). On the other hand, the current value increases when the secondary transfer roller 25 is in contact with the intermediate transfer belt 13 (times t13-t14).

[0041] Here, there are two contact positions where the contact pressure of the secondary transfer roller 25 against the intermediate transfer belt 13 (or opposing roller 15) is different. Here, the position with high contact pressure (first contact position) is simply called the "contact position," and the position with low contact pressure (second contact position) is called the "quasi-contact position." There are also states in between the separation position and the contact position, and between the contact position and the separation position, where the current value changes rapidly (times t11, t12, t15). In Example 1, it is assumed that the secondary transfer separation cam 223 takes 2.6 seconds (s) to complete one rotation. The voltage applied to the secondary transfer roller 25 from the secondary transfer power supply 26 to detect the position of the secondary transfer roller 25 is a positive polarity DC voltage.

[0042] <6.2 Detection of the position of the secondary transfer roller> Next, the detection (determination) of the position of the secondary transfer roller 25 by the control unit 200 (position detection control unit 206) in Example 1 will be described. Here, in Example 1, detecting (determining) the position of the secondary transfer roller 25 means, more specifically, relating the position of the secondary transfer roller 25 at a predetermined time (for example, the present) (whether it is in contact position or separated position). In Example 1, the position detection control unit 206 detects the position of the secondary transfer roller 25 (whether it is in contact position or separated position) based on the current value flowing through the secondary transfer roller 25.

[0043] Let's use Figure 5 to explain the specific values. Figure 5 shows the current value (reference value A) of 3 μA, which is the threshold value for determining the contact and separation of the secondary transfer roller 25 of the image forming apparatus 100, and the absolute moisture content [g / m³] in the installation environment. 3 This shows the relationship between the absolute moisture content [g / m³] and the applied voltage [V] to the secondary transfer roller 25. The applied voltage to the secondary transfer roller 25 is changed according to the installation environment of the image forming apparatus 100. Here, the absolute moisture content [g / m³] is shown. 3 If the value of ] is between the values ​​shown in Figure 5, the value will be obtained by linear interpolation. As shown in Figure 5, when the reference value A is 3 μA, the secondary transfer power supply 26 reduces the voltage applied to the secondary transfer roller 25 as the absolute moisture content increases. For example, if the absolute moisture content is 1.1 g / m 3 When the applied voltage is 4000V, the absolute moisture content is 25.5g / m³. 3 In this case, the applied voltage is 2300V.

[0044] The control unit 200 controls the image formation operation based on the result of comparing the detection result of the current detection circuit 27 with the reference value A. Specifically, the position detection control unit 206 determines that the position is separated if the current value obtained from the current detection circuit 27 when voltage is applied is less than the reference value A of 3 μA, and that the position is in contact if it is greater than 3 μA. Although no current flows when voltage is applied when separated, 3 μA is used as the threshold (reference value A) because the dark current of the electrical circuit is expected to be 1 μA ± 1 μA (0 to 2 μA). When the current detection control unit 205 calculates the current value, it calculates the average current value using a sampling interval of 2 [ms] × number of samples of 5 [times] as one set.

[0045] <7.2 Control of switching the position of the secondary transfer roller> In Example 1, the position detection control unit 206 performs the following position switching operation to switch the position of the secondary transfer roller 25. The current value is monitored while rotating the secondary transfer separation cam 223 that causes the secondary transfer roller 25 to come into contact with and separate from it. The contact position and the separation position are switched by stopping the secondary transfer separation cam 223 after a predetermined time has elapsed from the timing when the current value switches.

[0046] Let's explain again using Figure 4. The position detection control unit 206 outputs a stop signal to the contact / separation motor 221 after a first time interval T1, for example 100ms (time t21), from the timing (times t11, t15) when the current value acquired from the current detection circuit 27 falls below the reference value A (=3μA). The position detection control unit 206 considers the stopped position to be the fully separated position. Furthermore, the position detection control unit 206 outputs a stop signal to the contact / separation motor 221 after a second time interval T2, for example 1000ms (time t22), from the timing (time t12) when the current value acquired from the current detection circuit 27 exceeds the reference value A (=3μA). The position detection control unit 206 considers the stopped position to be the fully contacted position. The control unit 200 determines that the motor is in a separated position when the detection result of the current detection circuit 27 falls below the reference value A, and in a contact position when the detection result exceeds the reference value A, and determines that the motor is in a contact position when the second time T has elapsed. A waiting time of 20ms is expected for the motor 221 to stop after receiving the stop signal. The above description outlines the procedure for detecting the position of the secondary transfer roller 25 when the image forming apparatus 100 is in its normal state. Here, "normal state" means a state in which there is no condensation.

[0047] <8.2 Conventional behavior of contact and separation when condensation occurs on the secondary transfer roller 25> Next, we will describe the conventional behavior when condensation occurs on the secondary transfer roller 25, which is a problem of the present invention. As mentioned above, when attempting to detect the position of the secondary transfer roller 25 by detecting the current flowing through the secondary transfer roller 25 while condensation is present, the detected current value becomes larger because the electrical resistance value is lower than in the normal state. Therefore, there is a possibility of false detection that the rollers are in contact even though they are actually separated.

[0048] First, condensation was induced on the secondary transfer roller 25. The method involved placing the image forming apparatus 100 in an environmental test chamber at 5°C and 80% humidity and allowing it to acclimate for more than 12 hours. After that, the environmental test chamber was gradually changed to 25°C and 60% humidity over 60 minutes. While the room temperature in the environmental test chamber rose rapidly, the components of the image forming apparatus 100, such as the secondary transfer roller 25, which have a large heat capacity, rose more slowly, resulting in a temperature difference between the room temperature and the components. As a result, the heated air cooled on the surface of the components, causing water droplets to form on the surface of the components.

[0049] The control of a conventional example will be explained using the flowchart in Figure 6. In step (hereinafter referred to as S) 001, the power of the image forming apparatus 100 is turned on while condensation is present. The control unit 200 resets the counter that counts the number of retries, which will be described later, to 0. In S002, the control unit 200 starts the operation to bring the secondary transfer roller 25, whose position (contact or separation) is unknown (hereinafter referred to as an undefined state), into contact. The control unit 200 resets and starts a timer (not shown) to manage the time since the rotation of the secondary transfer separation cam 223 began. At this point, when the power of the image forming apparatus 100 is turned off, the secondary transfer roller 25 should be in a separation state. However, since the secondary transfer separation cam 223 may have rotated and its phase shifted while the power of the image forming apparatus 100 was off, or the secondary transfer roller 25 may have disappeared, the contact operation in S002 is performed when the power is turned on.

[0050] The results of monitoring the current value while rotating the secondary transfer separation cam 223 that causes the secondary transfer roller 25 to contact and separate in a state where the secondary transfer roller 25 is actually dew - condensed are shown in Fig. 7. In the graph of Fig. 7, the horizontal axis represents time [ms], and the vertical axis represents the current value [μA] flowing through the secondary transfer roller 25. Also, the reference value A (= 3 μA) is shown by a dashed line in Fig. 7.

[0051] Since the installation environment of the image forming apparatus 100 is 25°C and 60%, the absolute moisture content is 12.0 [g / m 3 , and by linear interpolation from Fig. 5, the applied voltage to the secondary transfer roller 25 is 2860 V. The control unit 200 rotates the secondary transfer separation cam 223 while applying this voltage (2860 V) to the secondary transfer roller 25. Normally, when the secondary transfer separation cam 223 is rotated and 1000 ms after the timing when the current value exceeds the reference value A (= 3 μA) (time t12 in Fig. 4) (time t22 in Fig. 4), a stop signal is output to the contact - separation motor 221 to set the secondary transfer roller 25 to the contact position. However, since the current value increases due to the dew - condensation of the secondary transfer roller 25 and does not fall below the reference value A (= 3 μA) even during separation, there is no timing when the current value crosses and exceeds 3 μA. For example, in the example of Fig. 7, although the secondary transfer roller 25 has actually moved from the separation position to the contact position, the detected current value constantly exceeds 3 μA. In this case, the timing for outputting a stop signal to the contact - separation motor 221 for bringing the secondary transfer roller 25 into contact cannot be calculated.

[0052] In S003, the control unit 200 determines whether the contact operation was successful. If the control unit 200 determines in S003 that the contact operation was successful, it proceeds to S006, where the image forming apparatus 100 becomes print-ready and the process ends. If the control unit 200 determines in S003 that the contact operation failed, it proceeds to S004. In the case of Figure 7 described above, the contact operation fails. Here, the control unit 200 refers to a timer and, if the current value does not fall below 3μA even after rotating the secondary transfer separation cam 223 for 2.6 seconds (the time it takes for the secondary transfer separation cam 223 to complete one rotation), it performs a retry. That is, the control unit 200 rotates the secondary transfer separation cam 223 again to perform the contact separation operation in S002. Since it takes 2.6 seconds for the secondary transfer separation cam 223 to complete one rotation, the time period for current detection is also set to 2.6 seconds to optimize the retry time. In S004, the control unit 200 adds 1 (+1) to the retry count managed by the counter before entering a retry. In Figure 7, the retry count has reached a predetermined number, for example, 3 times.

[0053] In S005, the control unit 200 determines whether the number of retries is greater than 3. If the control unit 200 determines in S005 that the number of retries is greater than 3, it proceeds to S007. In S007, the control unit 200 notifies the user of a malfunction in the secondary transfer contact / separation mechanism 300 (contact / separation mechanism abnormality notification). If the control unit 200 determines in S005 that the number of retries is 3 or less, it returns to S002 and enters the retry operation.

[0054] If the control unit 200 fails to reduce the current value below 3 μA after three retries, as shown in Figure 7, it determines that the contact-to-separation mechanism of the secondary transfer roller 25 is not functioning correctly, such as the secondary transfer separation cam 223 being damaged or the contact-to-separation motor 221 malfunctioning. The control unit 200 interrupts the startup of the image forming apparatus 100 and notifies the user of the contact-to-separation mechanism failure via the operation display unit 80. However, in the example in Figure 7, the waveform of the detected current value is the same as the waveform when the apparatus is functioning normally, and no actual malfunction has occurred. In the example in Figure 7, the current flowing to the secondary transfer roller 25 has increased simply due to the effects of condensation. In this case, for example, if the image forming apparatus 100 is left for another 60 minutes, the condensation will dissipate and the contact operation will be completed as usual. In other words, the conventional control system provides the user with incorrect information.

[0055] <9.2 Behavior of contact and separation in Example 1 when condensation occurs on the secondary transfer roller 25> The method for detecting the contact and separation distance even when condensation occurs on the secondary transfer roller 25, which is a feature of the present invention, will be explained using the flowchart in Figure 8. Note that the processes S101 to S105, S113, and S114 in Figure 8 are the same as the processes S001 to S007 in Figure 6, so their explanation will be omitted.

[0056] Here, Figure 9 shows the results of monitoring the current value while rotating the secondary transfer separation cam 223, which brings the secondary transfer roller 25 into contact with and separates it, under the control of Example 1, with condensation actually forming on the secondary transfer roller 25. Figure 9 is a graph similar to Figure 7. If the contact operation is successful, the image forming apparatus 100 will be in a print-ready state where it can print. However, in Figure 9, the current value detected due to condensation does not fall below the reference value A (=3μA) even when separating, so the contact operation fails (S103 Failure). Based on the judgment in S105, if the number of retries is less than 3, the control unit 200 proceeds to the retry operation from S106 onwards. In Example 1, while the control unit 200 rotates the secondary transfer separation cam 223 once, the current detection circuit 27 acquires multiple current values ​​flowing through the secondary transfer roller 25, and acquires the maximum current value and the minimum current value. This will be explained in detail below.

[0057] In S106, the control unit 200 rotates the secondary transfer separation cam 223 (simply shown as "cam") by one full turn. In S107, the control unit 200 calculates the average value of the sampled current values ​​(hereinafter referred to as the average current value) with a sampling interval of 2 [ms] × number of samples of 25 [times] as one set. The control unit 200 acquires two minimum value candidates and two maximum value candidates from the calculated average current value. The reason why the number of samples is higher here than when calculating the average current value when there is no condensation is to improve the accuracy of the average value. In S108, the control unit 200 excludes the smaller of the two minimum value candidates acquired in S107 as noise and adopts the remaining one as the minimum current value Imin. In S109, the control unit 200 excludes the larger of the two maximum value candidates acquired in S107 as noise and adopts the remaining one as the maximum current value Imax.

[0058] In S110, the control unit 200 determines whether the maximum current value Imax is greater than or equal to the minimum current value Imin × 2. The purpose of the determination in S110 is explained using Figures 9 and 10. As shown in Figure 9, in a condensed state, the overall current value is large, and although the detected current value does not fall below the reference value A (=3μA), the detected current value fluctuates greatly when the secondary transfer roller 25 makes contact and when it separates. The purpose of the determination in S110 is to use this large fluctuation to detect the timing of contact and separation. If the current value when in contact (maximum current value Imax) is more than twice the current value when separated (minimum current value Imin), it can be determined that the contact and separation mechanism of the secondary transfer roller 25 is operating normally, and the overall current value is simply large due to condensation. The multiplier is set by 2 because, as will be discussed later, when the contact and separation mechanism does not actually operate normally, the maximum value (Imax) and minimum value (Imin) of the current value hardly change, so it is considered sufficient to distinguish if it is more than twice.

[0059] In Figure 9, the maximum current value Imax during the first rotation of the secondary transfer separation cam 223 is 76.0 μA (S108), and the minimum current value Imin is 9.0 μA (S109). The maximum current value Imax of 76.0 μA is greater than 18.0 μA, which is twice the minimum current value Imin of 9.0 μA. In this case, the control unit 200 determines that the contact separation mechanism of the secondary transfer roller 25 is operating normally, and that the overall current value is simply higher due to condensation (S110 Yes).

[0060] In S110, if the control unit 200 determines that the maximum current value Imax is less than the minimum current value Imin × 2, it returns to S102 without resetting the reference value A, maintaining the reference value A at its original value (3 μA). In other words, it returns to S102. In this case, the control unit 200 determines that the contact-to-separation mechanism is not functioning correctly and performs a retry as before. If the control unit 200 determines in S105 that there have been three or more retries, it notifies the user of the contact-to-separation mechanism malfunction in S114. The control unit 200 also notifies the user of an abnormality in the secondary transfer-to-separation cam 223 if the number of times the detection result detected by the current detection circuit 27 during the movement operation by the secondary transfer-to-separation cam 223 did not fall below the reference value A exceeds a predetermined number of times.

[0061] Here, Figure 10 shows the current detection results when the gear that rotates the secondary transfer separation cam 223 skips teeth, preventing the secondary transfer separation cam 223 from rotating and thus preventing the contact separation mechanism from functioning properly. Figure 10 is a graph similar to Figure 7. In this case, because the secondary transfer roller 25 is condensed, the overall current value is significantly higher than the reference value A (=3μA). Even when the contact separation motor 221 is driven with voltage applied to the secondary transfer roller 25, the secondary transfer separation cam 223 does not rotate, so there is no large fluctuation in the current value. In Figure 10, the maximum current value Imax is 83.0μA and the minimum current value Imin is 78.0μA, resulting in a magnification of approximately 1.06 times. The maximum current value Imax of 83.0 μA is less than 156.0 μA, which is twice the minimum current value Imin of 78.0 μA (S110 No). In this case, the control unit 200 determines that the contact-separation mechanism is not operating normally.

[0062] Returning to the explanation of Figure 8, in S110, the control unit 200 resets the reference value A if the following condition is met. Condition: Imax ≥ Imin × predetermined value In other words, if the control unit 200 determines that the maximum current value Imax is greater than or equal to the minimum current value Imin × 2, it proceeds to S111. In S111, the control unit 200 calculates a new threshold value, the current value Inew, from the maximum current value Imax and the minimum current value Imin to determine the contact and separation of the secondary transfer roller 25. The control unit 200 resets the reference value A so that it is less than the maximum current value and greater than the minimum current value among the current values ​​flowing through the secondary transfer roller 25 detected by the current detection circuit 27 when the secondary transfer roller 25 moves. In Example 1, the current value Inew = (Imax + Imin) ÷ 2. For example, in the example in Figure 9, (76.0 μA + 9.0 μA) ÷ 2 = 42.5 μA. In S112, the control unit 200 stores the current value Inew (new threshold) calculated in S111 in the memory 212 of the image forming apparatus 100, sets the reference value A = Inew, and returns the process to S102. In this way, if the detection result detected by the current detection circuit 27 when the secondary transfer roller 25 is moved by the secondary transfer separation cam 223 does not fall below the reference value A (S102~S103 Failure), the control unit 200 resets the reference value A (S106~S112).

[0063] In the example shown in Figure 9, the control unit 200 returns the process to S102, applies voltage to the secondary transfer roller 25, rotates the secondary transfer separation cam 223, and enters the retry contact operation. At this time, the control unit 200 uses the current value Inew = 42.5 μA, which was reset in S112, instead of the initial value of 3 μA, as the threshold current value (reference value A) for determining contact and separation of the secondary transfer roller 25. Since only a few seconds have passed since the previous contact operation shown in Figure 9, the condensation state of the secondary transfer roller 25 has not changed significantly, and the current waveform is similar for the first retry. The difference from the previous time is that the current value (reference value A), which is the threshold current value for determining contact and separation of the secondary transfer roller 25, has been updated from 3 μA to 42.5 μA. Therefore, when the current value falls below 42.5 μA, the control unit 200 determines that the secondary transfer roller 25 has separated. This is the difference from the previous time. The control unit 200 rotates the secondary transfer separation cam 223 from the separated state of the secondary transfer roller 25, and 1000ms after the current value exceeds the threshold of 42.5μA, it outputs a stop signal to the contact separation motor 221, and the stopping position becomes the contact position. As a result, the contact operation is successful. The above describes the method for detecting the contact and separation distance of the secondary transfer roller 25 even when condensation occurs, which is a feature of the present invention.

[0064] In Example 1, the present invention was explained using a color image forming apparatus, but this is not limited to that, and a monochrome image forming apparatus may also be used. In the example, the method for calculating the average current value was set to a sampling interval of 2 [ms] × number of samples of 25 [times], but this is not limited and may be changed according to the image forming apparatus used. Also, the maximum and minimum values ​​of the calculated average current value were excluded to remove noise, but this may be changed according to the configuration. Furthermore, it was explained that the maximum current value Imax is greater than or equal to the minimum current value Imin × 2 in order to determine whether the contact-separation mechanism is operating normally, but this may also be changed according to the configuration, as long as it is a value that can determine whether the contact-separation mechanism is operating normally. That is, the predetermined value multiplied by the minimum current value Imin may be an integer of 2 or more. Also, the average value was calculated from the maximum current value Imax and the minimum current value Imin and set as the current value Inew, which is a new threshold for determining the contact and separation of the secondary transfer roller 25, but this may also be changed according to the configuration. Furthermore, in Example 1, for the sake of clarity, the explanation described a flow in which, if the minimum current value Imin does not fall below the reference value A during the first contact operation, the secondary transfer separation cam 223 is rotated once, the reference value A is replaced with Inew, and then the contact operation is retried. However, Inew can be calculated from the first contact operation without rotating the secondary transfer separation cam 223 once, and if the calculation of Inew is completed in time, the contact operation may be performed on the first attempt instead of retrying. Moreover, the detection unit is not limited to the current detection circuit 27 that detects the secondary transfer current, but can be any unit that detects at least one of the secondary transfer current and the voltage applied to the secondary transfer roller 25. Furthermore, the control in Example 1 is applicable to any member that performs contact and separation and in which contact and separation is determined by voltage detection or current detection, and the same applies to the following examples.

[0065] As described above, according to Example 1, the position of the transfer member can be accurately detected even when the transfer member is condensed. [Examples]

[0066] <10.2 Behavior of contact and separation in Example 2 when condensation occurs on the secondary transfer roller 25> Embodiment 2 of the present invention will now be described. In Embodiment 2, the method for calculating the current value Inew, which is a new threshold for determining the contact and separation of the secondary transfer roller 25 when condensation occurs, is different. In Embodiment 2, instead of calculating from the maximum current value Imax and the minimum current value Imin, the current value Inew is determined by gradually changing the value during retries when multiple retries are repeated. Matters not specifically explained in Embodiment 2 are the same as in Embodiment 1 and will not be explained.

[0067] The process will be explained using the flowchart in Figure 11. Note that the processes S201-S204, S206, and S212-S214 are the same as the processes S101-S104, S106, and S112-S114 in Figure 8, and will not be explained. Here, with the secondary transfer roller 25 actually condensed, the current value was monitored while rotating the secondary transfer separation cam 223, which brings the secondary transfer roller 25 into contact with and separates it, under the control of Example 2. The horizontal and vertical axes in Figure 12 are the same as in Figure 9.

[0068] If the control unit 200 determines that contact and separation has failed because the detected current value does not fall below the reference value A (=3μA) even when separation occurs due to condensation, it determines in S205 whether the number of retries is greater than 5. If the control unit 200 determines in S205 that the number of retries is greater than 5, it notifies the user of the contact and separation mechanism failure in S214. If the control unit 200 determines in S205 that the number of retries is 5 or less, it enters the retry operation and rotates the secondary transfer separation cam 223 by one full turn in S206.

[0069] In S207, the control unit 200 calculates the average current value using a sampling interval of 4 [ms] × number of samples of 10 [times] as one set, and acquires three minimum value candidates and three maximum value candidates. In S208, the control unit 200 excludes the two smaller values ​​from the three minimum value candidates as noise, and adopts the remaining third as the minimum current value Imin. In S209, the control unit 200 excludes the two larger values ​​from the three maximum value candidates as noise, and adopts the remaining third as the maximum current value Imax.

[0070] In S210, the control unit 200 determines whether the maximum current value Imax is greater than or equal to the minimum current value Imin × 4. For example, in Figure 12, the maximum current value Imax is 76.0 μA and the minimum current value Imin is 9.0 μA, so the maximum current value Imax 76.0 μA is greater than the minimum current value Imin 9.0 μA × 4 = 36.0 μA. In this case, the control unit 200 determines that the contact and separation mechanism of the secondary transfer roller 25 is operating normally, and the overall current value is simply higher due to condensation.

[0071] In S210, if the control unit 200 determines that the maximum current value Imax is greater than or equal to the minimum current value Imin × 4, it proceeds to S211. In S211, the control unit 200 calculates a current value Inew, which is a new threshold for determining the contact and separation of the secondary transfer roller 25. In Example 2, if the detection result by the current detection circuit 27 is not below the reference value A, the control unit 200 resets the reference value to a value obtained by adding a predetermined value to the reference value A. For example, the current value Inew (=8μA) is calculated by adding a predetermined value, in this case 5μA, to the initial reference value A (=3μA). In S212, the control unit 200 stores the current value Inew calculated in S211 in the memory 212 of the image forming apparatus 100. As a result, the reference value A = Inew.

[0072] The control unit 200 returns the process to S202, applies voltage to the secondary transfer roller 25, rotates the secondary transfer separation cam 223, and enters the retry contact operation. At this time, the control unit 200 uses the current value (reference value A), which is the threshold value for determining contact and separation of the secondary transfer roller 25, not the initial value of 3μA, but the current value A that was reset in S212, Inew = 8μA.

[0073] In the example in Figure 12, only a few seconds have passed since the previous contact operation, so the condensation state of the secondary transfer roller 25 has not changed significantly, and the current waveform is similar again. The difference from the previous time is that the current value (reference value A), which is the threshold for determining contact and separation of the secondary transfer roller 25, has been updated from 3 μA to 8 μA. However, even in the first retry, the minimum current value Imin did not fall below 8 μA, so a second retry is performed. In S211 before the second retry, the control unit 200 adds 5 μA to Inew = 8 μA, which was used in the first retry, to make the new reference value A 13 μA, and in S212 the reference value A is reset to 13 μA, and the process returns to S202. In the second retry, the minimum current value Imin fell below Inew = 13 μA, so the control unit 200 determines that the secondary transfer roller 25 has separated (S203 Success). The control unit 200 rotates the secondary transfer separation cam 223 from the separated state of the secondary transfer roller 25, and outputs a stop signal to the contact separation motor 221 1000ms after the current value exceeds the threshold of 13μA. The stopping position then becomes the contact position, and the contact operation is successful. If the detection result by the current detection circuit 27 does not fall below the reference value A multiple times, the control unit 200 resets the reference value A so that the reference value A increases in stages.

[0074] In the example, the method for calculating the current value Inew was described as adding 5μA to an initial value of 3μA with each retry, but this is not limited to this method and may be changed according to the image forming apparatus used. Also, although the calculated Inew was stored in memory 212 as the reference value A, it may be reset to the initial value of 3μA each time the contact-separation operation is successful.

[0075] As described above, according to Example 2, the position of the transfer member can be accurately detected even when the transfer member is condensed. [Examples]

[0076] Embodiment 3 of the present invention will now be described. Embodiment 3 describes a method for detecting the contact and separation interval of the secondary transfer roller 25 when it recovers from condensation. Following Embodiment 2, in which the contact and separation operation of the secondary transfer roller 25 was successful when condensation occurred, this describes a method for detecting the contact and separation interval when the condensation has improved and the resistance of the secondary transfer roller 25 has returned to its normal state.

[0077] In Example 2, because the current value did not fall below the reference value of 3 μA due to condensation during the contact-to-separation operation, the control system calculates the current value Inew by adding a predetermined 5 μA to the reference value of 3 μA. On the second retry, when the current value Inew = 13 μA was achieved, the contact-to-separation was successful, and the image forming apparatus 100 became print-ready. However, if the calculated current value Inew = 13 μA is stored in the memory 212, 13 μA will be used as the reference value A during the next contact-to-separation operation. If the condensation has improved by this time, the current value may not exceed 13 μA, in which case the contact-to-separation operation cannot be detected.

[0078] This will be explained using Figure 13. Figure 13, like Figure 4, shows the detection result of the current value acquired by the current detection control unit 205 from the current detection circuit 27 during the contact-to-separation operation. The difference from Figure 4 is that the current value (reference value A), which is the threshold for determining the contact and separation of the secondary transfer roller 25, is 13 μA instead of the initial value of 3 μA. In this case, since the current value will not exceed 13 μA, it is not possible to calculate the timing for outputting a stop signal to the contact-to-separation motor 221 for bringing the secondary transfer roller 25 into contact. Therefore, in Example 3, a method for detecting contact and separation by gradually lowering the reference value A during retries when the current value does not exceed the reference value A will be explained.

[0079] <11.2 Behavior of contact and separation in Example 3 when condensation is eliminated by the secondary transfer roller 25> In Example 3, matters not specifically explained are the same as in Examples 1 and 2, and therefore explanations are omitted. The flowchart in Figure 14 will be used for explanation. Note that the processes S301-S310 and S314-S316 in Figure 14 are the same as the processes S201-S210 and S212-214 in Figure 11, and therefore explanations are omitted. Furthermore, Figure 15 shows the results of monitoring the current value while rotating the secondary transfer separation cam 223, which actually brings the secondary transfer roller 25 into contact with and separates it, under the control of Example 3. The horizontal and vertical axes in Figure 15 are the same as in Figure 12.

[0080] If the contact operation is successful (S303 Success), the image forming apparatus 100 becomes print-ready (S315). However, in Figure 15, the threshold value of 13 μA is not exceeded even at the time of contact, so it fails (S303 Failure). If the number of retries is less than 5 (S305 No), the control unit 200 proceeds to the retry operation from S306 onwards.

[0081] In S310, the control unit 200 determines whether the maximum current value Imax is greater than or equal to the minimum current value Imin × 4. In Figure 15, the maximum current value Imax is 8.2 μA and the minimum current value Imin is 0.8 μA, so the maximum current value Imax 8.2 μA is greater than the minimum current value Imin 0.8 μA × 4 = 3.2 μA. In this case, the control unit 200 determines that the contact and separation mechanism of the secondary transfer roller 25 is operating normally and that the overall current value is only higher due to condensation, and proceeds to the process in S311.

[0082] In S311, the control unit 200 determines whether the maximum current value Imax is not greater than the reference value A, or whether the minimum current value Imin is not less than the reference value A. If the maximum current value Imax is not greater than the reference value A, the control unit 200 proceeds to S312. In S312, the control unit 200 corrects the reference value A to make it smaller. If the detection result by the current detection circuit 27 does not exceed the reference value A, the control unit 200 resets the reference value A to a value obtained by subtracting a predetermined value from the reference value A, and proceeds to S314. For example, the control unit 200 subtracts 4 μA from the previous reference value A (A - 4 μA). On the other hand, if the minimum current value Imin is not less than the reference value A, the control unit 200 proceeds to S313. In S313, the control unit 200 corrects the reference value A to make it larger. If the detection result from the current detection circuit 27 does not fall below the reference value A, the control unit 200 resets the reference value A to a value obtained by adding a predetermined value to the reference value A, and proceeds to process S314. For example, the control unit 200 adds 4 μA to the previous reference value A (A + 4 μA).

[0083] In Figure 15, it can be seen that the maximum current value Imax during the first rotation of the secondary transfer separation cam 223 is 8.2 μA, which does not exceed the reference value of 13 μA. In Example 3, the control unit 200 subtracts a predetermined value, in this case 4 μA, from the initial reference value A = 13 μA, and calculates the current value Inew = 13 μA - 4 μA = 9 μA (S311).

[0084] In S314, the control unit 200 stores the current value Inew calculated in S312 or S313 in the memory 212 of the image forming apparatus 100, setting the reference value A = Inew. For example, in the case of Figure 15, the reference value A is 9 μA. The control unit 200 then returns the process to S302 and, with voltage applied to the secondary transfer roller 25, rotates the secondary transfer separation cam 223 to bring it into contact.

[0085] In the example shown in Figure 15, the control unit 200 uses the current value Inew = 9μA calculated in S312 as the threshold value (reference value A) for determining contact and separation of the secondary transfer roller 25, instead of the initial value of 13μA. Since only a few seconds have passed since the previous contact operation shown in Figure 15, the condensation state of the secondary transfer roller 25 has not changed significantly, and the current waveform is similar again. The difference from the previous time is that the current value (reference value A), which is the threshold value for determining contact and separation of the secondary transfer roller 25, has been updated from 13μA to 9μA. However, even in the first retry, the maximum current value Imax does not exceed 9μA, so a second retry is performed. From the current value Inew = 9μA in the first retry, another 4μA is subtracted, resulting in 5μA. In the second retry, the maximum current value Imax became greater than Inew = 5μA, so it is determined that the secondary transfer roller 25 has made contact. The control unit 200 resets the reference value A so that it decreases in stages if the detection result from the current detection circuit 27 does not exceed the reference value A multiple times. 1000ms after the detected current value exceeds the reference value A (5μA), the control unit 200 outputs a stop signal to the contact / separation motor 221. The stopping position becomes the contact position, and the contact operation is successful.

[0086] In the examples, the method for calculating Inew was described as starting with an initial value of 13 μA and subtracting 4 μA with each retry, but this is not the only method, and it may be modified to suit the image forming apparatus used. Furthermore, in S312 of Figure 14, a fixed value (4 μA) is subtracted, and in S313, a fixed value (4 μA) is added. However, the value to be subtracted or added is not limited to a fixed value. For example, the value to be subtracted or added may change each time the reference value A is set. The control unit 200 can reset the reference value A to be greater than or less than the previously set reference value if the detection result does not exceed the reference value A multiple times.

[0087] As described above, according to Example 3, the position of the transfer member can be accurately detected even when the transfer member is condensed.

[0088] <Other Embodiments> The present invention can also be realized by supplying a program that implements one or more of the functions of the above embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions.

[0089] This embodiment includes the following configuration. (Composition 1) An image carrier that holds the toner image, A transfer member that contacts the image carrier and forms a transfer portion for transferring a toner image from the image carrier to a transfer material, A moving unit that performs a moving operation to move the transfer member between a contact position in which the transfer member is in contact with the image carrier and a separated position in which the transfer member is separated from the image carrier, A drive unit that drives the aforementioned moving part, An application unit for applying voltage to the transfer member, A detection unit that detects at least one of the voltage applied to the transfer member by the application unit or the current flowing through the transfer member when a voltage is applied to the transfer member by the application unit, A determination means for determining whether the position of the transfer member is the contact position or the separation position based on the result of comparing the detection result of the detection unit with a reference value, An image forming apparatus comprising, The determination means resets the reference value if the detection result detected by the detection unit when the moving unit performs the moving operation does not fall below the reference value. An image forming apparatus characterized by the following: (Configuration 2) When the detection unit detects the current flowing through the transfer member, The determination means resets the reference value such that, among the current values ​​flowing through the transfer member detected by the detection unit when the movement operation is performed, the reference value is smaller than the maximum current value and larger than the minimum current value. The image forming apparatus according to configuration 1, characterized in that it is a picture forming apparatus. (Composition 3) The determination means resets the reference value to a value greater than the previously set reference value if the detection result is not below the reference value multiple times. An image forming apparatus according to configuration 1 or configuration 2, characterized by the above. (Composition 4) The determination means resets the reference value to a value obtained by adding a predetermined value to the reference value if the detection result does not fall below the reference value. An image forming apparatus according to configuration 1 or configuration 2, characterized by the above. (Composition 5) The determination means, if the detection result does not exceed the reference value multiple times, resets the reference value so that it is smaller than the previously set reference value. An image forming apparatus according to configuration 1 or configuration 2, characterized by the above. (Composition 6) The determination means resets the reference value to a value obtained by subtracting a predetermined value from the reference value if the detection result does not exceed the reference value. An image forming apparatus according to configuration 1 or configuration 2, characterized by the above. (Composition 7) The detection unit detects the current flowing through the transfer member. When the aforementioned movement operation is performed, the current values ​​flowing through the transfer member detected by the detection unit are defined as follows: the maximum current value is Imax, the minimum current value is Imin, and a predetermined value is an integer of 2 or more. The aforementioned determination means is related to the following relationship Imax ≥ Imin × predetermined value If the condition is met, the aforementioned reference value is reset. An image forming apparatus according to any one of configurations 1 to 6, characterized by the above. (Composition 8) The aforementioned moving part has a rotating cam member, The determination means acquires multiple current values ​​flowing through the transfer member by the detection unit while the cam member is rotated once, and acquires the maximum current value and the minimum current value. An image forming apparatus according to configuration 2 or configuration 7, characterized by the above. (Composition 9) The application unit applies a voltage to the transfer member that decreases as the absolute moisture content increases when the detection unit detects something. An image forming apparatus according to any one of configurations 1 to 8, characterized by the above. (Composition 10) The determination means determines that the transfer member is in the separated position when a first time has elapsed since the detection result of the detection unit fell below the reference value, and determines that the transfer member is in the contact position when a second time has elapsed since the detection result of the detection unit exceeded the reference value. An image forming apparatus according to any one of configurations 1 to 9, characterized by the above. (Composition 11) The determination means notifies that there is an abnormality in the moving part when the detection result detected by the detection unit during the movement operation performed by the moving part exceeds a predetermined number of times. An image forming apparatus according to any one of configurations 1 to 10, characterized by the above. [Explanation of symbols]

[0090] 13 Intermediate transfer belt 25 Secondary transfer roller 26 Secondary Transfer Power Supply 27 Current detection circuit 200 Control Unit 221 Motor for contact and separation 300 Secondary transfer attachment / detachment mechanism

Claims

1. An image carrier that holds the toner image, A transfer member that contacts the image carrier and forms a transfer portion for transferring a toner image from the image carrier to a transfer material, A moving unit that performs a moving operation to move the transfer member between a contact position in which the transfer member is in contact with the image carrier and a separated position in which the transfer member is separated from the image carrier, A drive unit that drives the aforementioned moving part, An application unit for applying voltage to the transfer member, A detection unit that detects at least one of the voltage applied to the transfer member by the application unit or the current flowing through the transfer member when a voltage is applied to the transfer member by the application unit, A determination means for determining whether the position of the transfer member is the contact position or the separation position based on the result of comparing the detection result of the detection unit with a reference value, An image forming apparatus comprising, The determination means resets the reference value if the detection result detected by the detection unit when the moving unit performs the moving operation does not fall below the reference value. An image forming apparatus characterized by the following features.

2. When the detection unit detects the current flowing through the transfer member, The determination means resets the reference value such that, among the current values ​​flowing through the transfer member detected by the detection unit when the movement operation is performed, the reference value is smaller than the maximum current value and larger than the minimum current value. The image forming apparatus according to feature 1.

3. The determination means resets the reference value to a value greater than the previously set reference value if the detection result is not below the reference value multiple times. The image forming apparatus according to feature 1.

4. The determination means resets the reference value to a value obtained by adding a predetermined value to the reference value if the detection result does not fall below the reference value. The image forming apparatus according to feature 1.

5. The determination means, if the detection result does not exceed the reference value multiple times, resets the reference value so that it is smaller than the previously set reference value. The image forming apparatus according to feature 1.

6. The determination means resets the reference value to a value obtained by subtracting a predetermined value from the reference value if the detection result does not exceed the reference value. The image forming apparatus according to feature 1.

7. The detection unit detects the current flowing through the transfer member. When the aforementioned movement operation is performed, the current value flowing through the transfer member detected by the detection unit is defined as follows: the maximum current value is Imax, the minimum current value is Imin, and a predetermined value is an integer of 2 or more. The aforementioned determination means is related to the following relationship Imax ≥ Imin × predetermined value If the condition is met, the aforementioned reference value is reset. The image forming apparatus according to feature 1.

8. The aforementioned moving part has a rotating cam member, The determination means acquires multiple current values ​​flowing through the transfer member by the detection unit while the cam member is rotated once, and acquires the maximum current value and the minimum current value. The image forming apparatus according to claim 2 or 7.

9. The application unit applies a voltage to the transfer member that decreases as the absolute moisture content increases when the detection unit detects something. The image forming apparatus according to feature 1.

10. The determination means determines that the transfer member is in the separated position when a first time has elapsed since the detection result of the detection unit fell below the reference value, and determines that the transfer member is in the contact position when a second time has elapsed since the detection result of the detection unit exceeded the reference value. The image forming apparatus according to feature 1.

11. The determination means notifies that there is an abnormality in the moving part when the detection result detected by the detection unit during the movement operation performed by the moving part exceeds a predetermined number of times. The image forming apparatus according to feature 1.

Images