JP5241203B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a laser printer, a copying machine, and a facsimile using an electrophotographic system or an electrostatic recording system.

  2. Description of the Related Art Conventionally, an image forming apparatus using an electrophotographic system that forms an image through a process of electrostatically transferring a toner image formed on an image carrier onto a recording material as a transfer material has been widely used.

  For example, an intermediate transfer type image forming apparatus using an intermediate transfer member is known, and this type is effective as a color image forming apparatus or a multicolor image forming apparatus. In an intermediate transfer type image forming apparatus, a plurality of component color images based on color image information and multicolor image information are sequentially transferred and stacked on an intermediate transfer member, and then the stacked images are recorded on a recording material such as paper. By transferring the image, an image formed product in which a color image or a multicolor image is synthesized and reproduced is obtained.

  FIG. 13 shows a schematic cross section around an intermediate transfer member in an intermediate transfer type image forming apparatus. In the illustrated example, the image forming apparatus transfers toner images respectively formed on a plurality of photosensitive drums 101 as first image carriers to an intermediate transfer belt 106 that is an intermediate transfer member as a second image carrier. Transfer (primary transfer). Thereafter, the toner image on the intermediate transfer belt 106 is transferred (secondary transfer) to the recording material, thereby forming a color image on the recording material. The intermediate transfer belt 106, which is an intermediate transfer member, includes a driving roller 110 for driving the intermediate transfer belt 106, a secondary transfer counter roller 112 facing the secondary transfer roller, and a tension for obtaining the tension of the intermediate transfer belt 106. The roller 111 is stretched. The tension roller 111 is supported on the intermediate transfer unit main body via a tension spring 115. Further, the primary transfer roller 107 as a primary transfer member is supported or urged with respect to the photosensitive drum 101 so as to obtain a transfer pressure necessary for the primary transfer, thereby ensuring stable primary transfer. The The secondary transfer roller 108 is usually separated from the intermediate transfer belt 106 and is brought into contact with the intermediate transfer belt 106 only when an image on the intermediate transfer belt 106 is transferred to a recording material.

As a method for determining the contact / separation state of the secondary transfer roller 108 with respect to the intermediate transfer belt 106, a method for detecting the value of a current flowing through the secondary transfer roller 108 is known. In this method, a voltage is applied to the secondary transfer roller 108 in order to determine the contact / separation state of the secondary transfer roller 108. When the secondary transfer roller 108 is not in contact with the intermediate transfer belt 106, no current flows because there is no secondary transfer counter roller 112 serving as a counter electrode, and the secondary transfer roller 108 does not contact the intermediate transfer belt 106. When they are in contact, a predetermined current flows. By detecting this current value by the current detection means and comparing it with a predetermined threshold value, it is possible to recognize the contact / separation state of the secondary transfer roller 108 (see Patent Document 1).
JP 2001-083758 A

  However, in an environment where the temperature, humidity, etc. can change greatly, the electric resistance value of the secondary transfer roller or the intermediate transfer belt changes and the current flowing through the secondary transfer roller also changes. There is a possibility of erroneously detecting the contact / separation state.

  For example, in constant voltage control that controls the supply of a constant voltage to the secondary transfer roller, the current flowing through the secondary transfer roller is affected by the electrical resistance value of the secondary transfer roller, the electrical resistance value of the intermediate transfer belt, and the like. May be received. Therefore, it is necessary to set the current threshold value for determining the contact / separation state of the secondary transfer roller to a value having a sufficient margin in consideration of the influence.

  However, if the constant voltage value applied to the secondary transfer roller for this determination is small, it is erroneously detected that the secondary transfer roller and the intermediate transfer belt are in contact with each other in a low-temperature and low-humidity environment. There is a possibility that. This is because in a low-temperature and low-humidity environment, the electric resistance value of the secondary transfer roller, the intermediate transfer belt, and the like is high, so that it is difficult for current to flow. On the other hand, when the constant voltage value to be applied is increased to prevent this, a large current flows when the secondary transfer roller and the intermediate transfer belt are in contact with each other in a high temperature and high humidity environment, and the current detection circuit It can be destroyed. This is because, in a high-temperature and high-humidity environment, the electric resistance value of the secondary transfer roller and the intermediate transfer belt is low, so that a current easily flows.

  In the above description, in the intermediate transfer type image forming apparatus, the case where the secondary transfer member for transferring the toner image to the recording material as the transfer material contacts and separates from the intermediate transfer member as the image carrier. However, the same applies to the case where the primary transfer member comes in contact with and separates from the photosensitive member as the image carrier via the intermediate transfer member, and the case where the transfer member directly contacts and separates from the photosensitive member as the image carrier.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of appropriately detecting contact / separation of a transfer member with respect to an image carrier from a current value when a voltage is applied to the transfer member, regardless of environmental conditions. It is to be.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image carrier that carries a toner image, and a transfer member that transfers a toner image carried on the image carrier to a transfer material when a voltage is applied to the image carrier. A transfer member movable between a contact state contacting the body directly or via the transfer material and a separated state separated from the image carrier from the contact state, and a voltage for applying a voltage to the transfer member An application unit; a current detection unit that detects a current flowing through the transfer member to which a voltage is applied by the voltage application unit; a control unit that controls the voltage application unit; and whether the transfer member is in the contact state. Or a determination unit that determines based on a current value detected by the current detection unit whether the current state is in the separated state, wherein the voltage application unit includes a first detection voltage that is set in advance. , Preset A second detection voltage whose absolute value is larger than the first detection voltage and a third detection voltage which is preset and whose absolute value is larger than the second detection voltage are applied to the transfer member. The determination unit determines that the transfer member is in contact when the current value detected by the current detection unit is equal to or greater than a predetermined value, and the determination unit determines whether the transfer member is in contact with the transfer member. When determining the state, the control means first applies the first detection voltage by the voltage application means on the assumption that the surrounding environment is the first environment, and the first detection voltage. If the current sensing means also applies a current value is detected is less than the predetermined value, the ambient environment first than environmental low temperature and low humidity second is a to the second assumed environmental Even if the detection voltage is applied and the second detection voltage is applied, the power When the current value detected by the detection means is less than the predetermined value, the third detection voltage is applied assuming that the surrounding environment is a third environment having a lower temperature and lower humidity than the second environment. An image forming apparatus characterized by the above.

  According to the present invention, the contact / separation of the transfer member with respect to the image carrier can be appropriately detected from the current value when a voltage is applied to the transfer member, regardless of the environmental conditions.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
1. First, the overall configuration of an embodiment of an image forming apparatus according to the present invention will be described with reference to FIG. FIG. 1 shows a schematic cross section of an image forming apparatus 100 of this embodiment.

  The image forming apparatus 100 according to the present exemplary embodiment is an electrophotographic color laser printer that employs an intermediate transfer method and a four-drum method (inline method). That is, the image forming apparatus 100 according to the present exemplary embodiment forms first, second, third, and fourth image forming units for forming yellow, magenta, cyan, and black color images as a plurality of image forming units. Part (port, station) SY, SM, SC, SK. The image forming apparatus 100 includes photosensitive drums 1Y, 1M, 1C, which are cylindrical electrophotographic photosensitive members serving as a plurality of first image carriers provided in the respective image forming units SY, SM, SC, and SK. I have 1K. Then, a toner image is multiplex-transferred (primary transfer) sequentially from the plurality of photosensitive drums 1Y, 1M, 1C, and 1K to an intermediate transfer belt 6 that is an intermediate transfer member as a second image carrier. The multiple toner images are collectively transferred (secondary transfer) from the intermediate transfer belt 6 to a recording material P such as paper as a transfer material. Thereby, a full-color print image can be obtained.

  In this embodiment, the configurations and operations of the image forming units SY, SM, SC, and SK are substantially the same except that the color of the developer used is different. Accordingly, in the following, unless there is a particular distinction, the subscripts Y, M, C, and K given to the reference numerals in the drawing will be omitted to indicate that they are elements for any color, and a general description will be given. .

  In the image forming unit S, there are a primary charging roller 2 as a primary charging unit, an exposure device 3 as an image exposure unit, a developing device 4 as a developing unit, and a primary transfer roller 7 as a primary transfer member around the photosensitive drum 1. A cleaning device 5 is disposed as a cleaning means. An intermediate transfer belt 6 is disposed so as to face all the photosensitive drums 1. The primary transfer roller 7 is disposed to face the photosensitive drum 1 on the inner peripheral surface side of the intermediate transfer belt 6. The primary transfer roller 7 pressurizes the intermediate transfer belt 6 toward the photosensitive drum 1 to form a primary transfer portion (primary transfer nip) N1 where the intermediate transfer belt 6 and the photosensitive drum 1 are in contact with each other. Further, as will be described in detail later, a secondary transfer roller 8 as a secondary transfer member that can contact and separate from the intermediate transfer belt 6 is provided on the outer peripheral surface side of the intermediate transfer belt 6. The secondary transfer roller 8 is in pressure contact with the intermediate transfer belt 6 to form a secondary transfer portion (secondary transfer nip) N2.

  The intermediate transfer belt 6 is an endless belt, and is stretched around a driving roller 10, a tension roller 11, and a secondary transfer counter roller 12. Then, when the rotational driving force is transmitted to the driving roller 10, the intermediate transfer belt 6 rotates (circulates) at a surface moving speed (process speed) of 115 mm / sec in the direction of arrow R2 (clockwise) in the drawing. . The driving roller 10, the tension roller 11, and the secondary transfer counter roller 12 are support rollers as support members that support the intermediate transfer belt 6. In this embodiment, the driving roller 10 and the secondary transfer counter roller 12 have a diameter of 24 mm, and the tension roller 11 has a diameter of 16 mm. The tension roller 11 applies pressure to the intermediate transfer belt 6 by being pressed by a tension spring 15 via a bearing member 14.

As the material of the intermediate transfer belt, polyimide, polyamide, polycarbonate (PC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene polymer (PTFE), or the like is used. In this embodiment, the intermediate transfer belt 6 is made of polyimide whose electric resistance is adjusted with carbon black, has a volume resistivity of 1 × 10 ⁸ Ω · cm, a thickness of 70 μm, an inner peripheral length of 700 mm, and a longitudinal direction. The width in the direction perpendicular to the moving direction is 250 mm.

  Four photosensitive drums 1 are arranged corresponding to each color in series along the moving direction of the surface of the intermediate transfer belt 6. The photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the primary charging roller 2 in the process of rotation in the direction of the arrow R1 (clockwise) in the figure. In this embodiment, the photosensitive drum 1 is negatively charged. Next, the photosensitive drum 1 is subjected to image exposure by the exposure device 3, whereby an electrostatic latent image of a color component image corresponding to each image forming portion of the target color image is formed thereon. Next, the electrostatic latent image is developed as a toner image by the developing device 4 with toner of a color corresponding to each image forming unit. In this embodiment, the developing device 4 develops the electrostatic latent image by a reversal development method. That is, on the charged photosensitive drum 1, a toner charged to a normal polarity (negative polarity in this embodiment) that is the same polarity as the charging polarity of the photosensitive drum 1 is attached to a portion where the charge has been attenuated by exposure. Thus, the electrostatic latent image is developed.

  The toner image formed on the photosensitive drum 1 enters the primary transfer portion N1 where the intermediate transfer belt 6 and the photosensitive drum 1 are in contact. In the primary transfer portion N1, a primary transfer roller 7 as a primary transfer member (voltage application member) is in contact with the back side of the intermediate transfer belt 6. In addition, in order to enable each image forming unit S to apply a bias to the primary transfer roller 7 independently, the image forming apparatus 100 corresponds to each image forming unit S as a primary transfer voltage applying unit. Primary transfer bias power supply 70. The toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 6 by the action of a primary transfer bias having a polarity opposite to the normal charging polarity of the toner applied from the primary transfer bias power source 70 to the primary transfer roller 7. Electrostatically transferred (primary transfer).

  For example, when forming a full-color image, a yellow toner image is first transferred to the intermediate transfer belt 6 by the first image forming unit SY. Next, in the second, third, and fourth image forming units SM, SC, and SK, magenta, cyan, and black toner images are sequentially transferred in a multiple manner.

  The four color toner images on the intermediate transfer belt 6 are separately conveyed to the secondary transfer unit N2 in the process of passing through the secondary transfer unit N2 where the intermediate transfer belt 6 and the secondary transfer roller 8 are in contact. The recording material P is transferred all at once. The secondary transfer roller 8 is connected to a secondary transfer bias power supply 80 as a secondary transfer voltage application unit. The toner image on the intermediate transfer belt 6 is recorded on the recording material by the action of a secondary transfer bias having a polarity opposite to the normal charging polarity of the toner applied from the secondary transfer bias power source 80 to the secondary transfer roller 8. It is electrostatically transferred (secondary transfer) onto P.

  The recording material P on which the four color toner images are secondarily transferred is introduced into the fixing device 13. By being heated and pressurized by the fixing device 13, the four color toners are melted and mixed and fixed to the recording material P, and a full color print image is formed.

  The toner (secondary transfer residual toner) remaining on the surface of the intermediate transfer belt 6 after the secondary transfer process is charged to a polarity opposite to that of the photosensitive drum 1 by the belt cleaner 9. The belt cleaner 9 is brought into contact with the surface of the intermediate transfer belt 6. Then, a cleaning bias having a predetermined polarity (positive polarity in this embodiment) is applied to the belt cleaner 9 by a cleaning bias power supply 90 as a cleaning voltage application unit with the secondary transfer counter roller 12 as a counter electrode. As a result, the secondary transfer residual toner is charged to the predetermined polarity. The secondary transfer residual toner on the intermediate transfer belt 6 charged by the belt cleaner 9 is electrostatically attracted to the photosensitive drum 1 at and near the contact portion between the intermediate transfer belt 6 and the photosensitive drum 1. Metastasize. Then, after the secondary transfer residual toner is removed from the intermediate transfer belt 6, it is collected in a waste toner container provided in the cleaning device 5 for cleaning the photosensitive drum 1.

In this embodiment, as the secondary transfer roller 8, a semiconductive sponge mainly composed of NBR hydrin rubber is used for the elastic layer. In this embodiment, the secondary transfer roller 8 has an outer diameter of 18 mm and a core bar diameter of 6 mm. In the case of using a polymer conductive transfer roller mainly composed of NBR (nitrile butadiene rubber) or epichlorohydrin rubber, or an ionic conductive transfer roller whose electric resistance is adjusted with an ionic conductive agent, the electric resistance The environmental fluctuation of the value is large. For example, in the secondary transfer roller 8 of the present embodiment, the electrical resistance value when applying 1 kV in a 23 ° C./50% Rh environment is 3.0 × 10 ⁷ Ω. On the other hand, in a high temperature and high humidity environment of 30 ° C./80% Rh, the electric resistance value is about 8.0 × 10 ⁶ Ω, and in a low temperature and low humidity environment of 15 ° C./10% Rh, the electric resistance value is 1.7 × 10 ^8. It becomes about Ω.

2. Secondary Transfer Member Contact / Separation Mechanism Next, the secondary transfer member contact / separation mechanism of this embodiment will be described with reference to FIG.

  The secondary transfer member contact / separation mechanism, which is a contact / separation unit, includes a secondary transfer roller bearing 19, a secondary transfer roller pressure spring 20, which is an elastic member as a biasing unit, a secondary transfer roller facing roller 12, and an operation member. It is constituted by an eccentric cam 21 or the like. The secondary transfer roller bearing 19 is pressed or released by rotating the eccentric cam 21 mounted coaxially with the secondary transfer counter roller 12, so that the secondary transfer roller 8 contacts the intermediate transfer belt 6. Creates a contact or separation state. The eccentric cam 21 rotates with the operation of a clutch (not shown) at a predetermined timing.

  In this embodiment, after the printing is started, the eccentric cam 21 is driven at the time of the pre-rotation (at the time of the preparatory operation before the image formation), and the secondary cam is pressed against the pressure of the secondary transfer roller pressure spring 20. The eccentric cam 21 is released from the state where the transfer roller bearing 19 is urged. As a result, as shown in FIG. 2A, the secondary transfer roller 8 is brought into contact with the intermediate transfer belt 6 to enable the secondary transfer. When the printing operation is completed, the eccentric cam 21 is driven to bias the secondary transfer roller bearing 19 against the pressure applied by the secondary transfer roller pressure spring 20. As a result, the secondary transfer roller 8 is separated from the intermediate transfer belt 6 as shown in FIG. When the secondary transfer roller 8 is in contact with the intermediate transfer belt 6, a transfer pressure of about 53 N is applied by the secondary transfer roller pressure spring 20.

3. Detection of Current Flowing through Secondary Transfer Member Next, an apparatus configuration for detecting current flowing through the secondary transfer roller 8 will be described with reference to FIG.

  The secondary transfer bias power supply 80 applies a voltage to the secondary transfer roller 8 in order to transfer the toner image formed on the intermediate belt 6 onto the recording material P as described above. A control unit 22 and a current detection unit 23 as a current detection unit are connected to a secondary transfer bias power supply 80 as a secondary transfer voltage application unit.

  The control unit 22 controls the secondary transfer bias power supply 80 so that the secondary transfer target current corresponding to each print mode that is set to be selectable in advance flows to the secondary transfer roller 8. In this embodiment, the control unit 22 further forms an image of the primary transfer bias power supplies 70Y, 70M, 70C, 70K, a clutch (not shown) for driving the eccentric cam 21, the photosensitive drum 1, the drive roller 10, and the like. Each part of the apparatus 100 is controlled. The control unit 22 can be realized using a so-called microcomputer including a control unit, a calculation unit, and a storage unit, and is limited to serving as a controller that controls each unit of the image forming apparatus 100 as in the present embodiment. Instead, it may be provided separately. The control unit 22 executes various processes according to programs and data stored in a storage unit that is provided in itself or that is communicably connected thereto. In particular, in connection with the present embodiment, the control unit 22 determines the contact / separation state of the secondary transfer roller 8 with respect to the intermediate transfer belt 6 based on the detection result of the current detection unit 23 as will be described in detail later. Function as.

  The current detection unit 23 detects the current value flowing through the secondary transfer roller 8 and inputs a signal related to the detection result to the control unit 22. In the present embodiment, the current detection unit 23 detects an output current value when the secondary transfer bias power supply 80 outputs a voltage controlled at a constant voltage.

4). Secondary Transfer Member Contact / Separation Detection Next, the operation for detecting the contact / separation state of the secondary transfer roller 8 to the intermediate transfer belt 6 at the start of printing will be described with reference to the flowchart of FIG.

  In S1, the image forming apparatus 100 starts a printing operation when receiving a print signal from a host information device (not shown) such as a personal computer.

  In S2, the photosensitive drum 1, the developing device 4 and the like are rotationally driven, and a pre-rotation is started which is an operation for shifting each part of the image forming unit S to a standby state in which an image can be formed.

  In S <b> 3, the control unit 22 drives the eccentric cam 21 by operating the clutch to bring the secondary transfer roller 8 and the intermediate transfer belt 6 into contact with each other.

In S <b> 4, the controller 22 applies a voltage V ₁ for contact / separation detection to the secondary transfer roller 8 from the secondary transfer bias power supply 80. In this embodiment, V ₁ = 100V.

In S5, the detected secondary transfer current I ₁ for contact and separation sensing current detector 23 flows through the secondary transfer roller 8, is compared with the current threshold Ia for contact and separation detection. The secondary transfer current I _{1 at} this time is obtained by averaging the detected currents by repeating the sampling every 20 msec 20 times when the voltage V ₁ is applied to the secondary transfer roller 8 in S4. . In this embodiment, Ia = 2 μA.

If I ₁ ≧ Ia in S5, it is determined in S13 that the secondary transfer roller 8 and the intermediate transfer belt 6 are in contact with each other, and in S14, the control unit 22 supplies the secondary transfer roller 8 to the secondary transfer roller 8. The voltage application is stopped, and the printing operation is continued in S15.

If I ₁ <Ia in S 5, the controller 22 applies the voltage V ₂ to the secondary transfer roller 8 from the secondary transfer bias power supply 80 in S 6. Here, V ₁ <V ₂ , and in this embodiment, V ₂ = 400V.

In S7, the detected secondary transfer current I ₂ the current detector 23 flows through the secondary transfer roller 8, is compared with the current threshold Ia. The secondary transfer current I _{2 at} this time is the average of the detected currents obtained by repeating the sampling every 20 msec 20 times when the voltage V ₂ is applied to the secondary transfer roller 8 in S6. .

If I ₂ ≧ Ia in S 7, it is determined in S 13 that the secondary transfer roller 8 and the intermediate transfer belt 6 are in contact with each other. In S 14, the control unit 22 applies to the secondary transfer roller 8. The voltage application is stopped, and the printing operation is continued in S15.

If I ₂ <Ia in S 7, the controller 22 applies the voltage V ₃ to the secondary transfer roller 8 from the secondary transfer bias power supply 80 in S 8. Here, V ₂ <V ₃ , and in this embodiment, V ₃ = 800V.

In S9, the current detector 23 detects the secondary transfer current I ₃ flowing through the secondary transfer roller 8 and compares it with the current threshold value Ia. The secondary transfer current I _{3 at} this time is obtained by averaging the detected currents by repeating the sampling every 20 msec 20 times when the voltage V ₃ is applied to the secondary transfer roller 8 in S8. .

In S9, if I ₃ ≧ Ia, in S13, it is determined that the secondary transfer roller 8 and the intermediate transfer belt 6 are in contact with each other, and in S14, the control unit 22 applies to the secondary transfer roller 8. The voltage application is stopped, and the printing operation is continued in S15.

If I ₃ <Ia in S9, it is determined in S10 that the secondary transfer roller 8 and the intermediate transfer belt 6 are separated from each other, and in S11, the control unit 22 determines the voltage to the secondary transfer roller 8. The application is stopped, and the printing operation is stopped in S12. Thereafter, the eccentric cam 21 is driven again in S3, and the contact / separation state between the secondary transfer roller 8 and the intermediate transfer belt 6 is detected based on the same flowchart.

  Even if the process of detecting the contact / separation state between the secondary transfer roller 8 and the intermediate transfer belt 6 after the eccentric cam 21 is driven is performed a predetermined number of times, the secondary transfer roller 8 and the intermediate transfer belt 6 are separated from each other. When it is determined that the state is present, the user can be notified of this. For example, the control unit 22 displays information notifying the user of an abnormality in which the secondary transfer roller 8 and the intermediate transfer belt 6 are separated from each other on a display unit serving as a notification unit provided in the image forming apparatus 100. Can do. In addition, the control unit 22 can transmit a signal for displaying the same content on a display unit of a host information device such as a personal computer that is communicably connected to the image forming apparatus 100 to the host information device.

  As described above, in the present exemplary embodiment, the image forming apparatus 100 includes a transfer member that can change state between a contact state in which the image forming apparatus 100 is in contact with the intermediate transfer belt 6 serving as an image carrier and a separated state in which the image forming apparatus 100 is separated from the intermediate transfer belt 6. As a secondary transfer roller 8. Further, the image forming apparatus 100 includes a current detection unit 23 as a current detection unit that detects a current flowing through the secondary transfer roller 8 to which a voltage is applied by a secondary transfer bias power source 80 as a voltage application unit. Further, the image forming apparatus 100 controls the control unit 22 as a determination unit that determines whether the secondary transfer roller 8 is in the contact state or the separated state based on the current value detected by the current detection unit 23. Have When the controller 22 applies a plurality of levels of voltages having different absolute values to the secondary transfer roller 8 in order from the lower voltage by the secondary transfer bias power source 80 and the current detector 23 detects a current of a predetermined amount or more. Then, it is determined that the secondary transfer roller 8 is in the contact state. Then, after the determination, the control unit 22 does not apply a higher level voltage among the plurality of levels of voltages, that is, stops applying a higher level voltage. In particular, in this embodiment, the control unit 22 compares the current value detected by the current detection unit 23 with a predetermined current threshold, and the current value detected by the current detection unit 23 is equal to or greater than the predetermined current threshold. In this case, it is detected that a current exceeding the predetermined amount has flowed.

The contact / separation state detection sequence of this embodiment is illustrated in FIG. At the time of applying and switching the voltage to the secondary transfer roller 8, 100 msec is secured as the high voltage rise time, and thereafter, the detection current at each voltage is sampled. Since sampling every 20 msec is repeated 20 times, the time required to average the detected current is 400 msec. When applying up to the maximum voltage V ₃ (= 800 V), a total of 1500 msec is required until all sequences are completed.

Here, the grounds for setting the voltages V _{1 to} V ₃ for contact / separation detection and the current threshold value Ia for contact / separation detection in this embodiment will be described.

  FIG. 6 shows the relationship between the voltage applied to the secondary transfer roller 8 and the detected current in a low temperature and low humidity environment (15 ° C./10% Rh) and a high temperature and high humidity environment (30 ° C./80% Rh). .

  For example, when 100 V is applied to the secondary transfer roller 8, a sufficiently detectable current of about 10 μA flows in a high-temperature and high-humidity environment, but in a low-temperature and low-humidity environment, it is about 1.5 μA and the amount of current is small. There is a high possibility of doing. When 400 V is applied to the secondary transfer roller 8, it is about 2 μA in a low-temperature and low-humidity environment, and there is still a possibility of erroneous detection depending on variations in the electrical resistance of the secondary transfer roller. If a voltage of up to 800 V is applied to the secondary transfer roller 8, a current that can be detected finally flows in a low-temperature and low-humidity environment, while a current as high as 70 μA flows in a high-temperature and high-humidity environment. . That is, it can be understood that it is difficult to achieve both “flowing a sufficiently detectable current in a low-temperature and low-humidity environment” and “not flowing too much current in a high-temperature and high-humidity environment”.

Therefore, in this embodiment, first, when V ₁ = 100 V is applied to the secondary transfer roller 8 and an average current of the threshold current Ia = 2 μA or more flows at that time, the secondary transfer roller 8 It is determined that the intermediate transfer belt 6 is in contact, and no voltage is applied thereafter.

In this example, environment detection is not performed, but when an average current of 2 μA or more flows by applying V ₁ = 100 V, it is expected that the environment is in a high temperature and high humidity environment. Further, when an average current of 2 μA or more does not flow when V ₁ = 100 V is applied, an intermediate environment (23 ° C./50% Rh etc.) is also present, so next, V ₂ = 400 V is applied. If an average current of 2 μA or more flows at that time, it is determined that the secondary transfer roller 8 and the intermediate transfer belt 6 are in contact with each other, and no voltage is applied thereafter. When an average current of ₂ μA or more does not flow when V ₂ = 400 V is applied, V ₃ = 800 V, which is the highest voltage among a plurality of levels, is finally applied. If an average current of 2 μA or more flows at that time, it is determined that the secondary transfer roller 8 and the intermediate transfer belt 6 are in contact with each other. In this case, it is expected to be in a low temperature and low humidity environment, and when the average current of 2 μA or more does not flow even when V ₃ = 800 V is applied, the secondary transfer roller 8 and the intermediate transfer belt 6 are separated from each other. It means that. If V ₃ = 800 V is applied, a sufficiently detectable current should flow if the secondary transfer roller 8 and the intermediate transfer belt 6 are in contact with each other even in a low temperature and low humidity environment.

In this embodiment, three levels of applied voltages V _{1 to} V ₃ are set, but a plurality of levels of voltages may be provided.

  As described above, a plurality of levels of voltages are applied to the secondary transfer roller 8 in order from a low voltage, and the voltage application is terminated when a predetermined current is detected. Therefore, the secondary transfer roller 8 is operated in a high temperature and high humidity environment. And the intermediate transfer belt 6 are in contact with each other, it is possible to prevent an excessive current from flowing. Finally, when the secondary transfer roller 8 and the intermediate transfer belt 6 are in contact with each other, a high voltage through which a predetermined current flows is applied even in a low-temperature and low-humidity environment. The contact / separation state between the roller 8 and the intermediate transfer belt 6 can be detected. Therefore, according to this embodiment, it is possible to appropriately detect the contact / separation of the transfer member with respect to the image carrier from the current value when a voltage is applied to the transfer member, regardless of the environmental conditions.

Example 2
Another embodiment of the image forming apparatus according to the present invention will be described. In the present embodiment, members / portions common to the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  In this embodiment, when the image forming apparatus 100 is shipped, the secondary transfer roller 8 is separated from the intermediate transfer belt 6 and it is determined to forget to remove the removable separation member, and a warning is given. Is different.

  In this embodiment, as shown in FIG. 7B, the image forming apparatus 100 is shipped in a state where the secondary transfer roller 8 and the intermediate transfer belt 6 are separated by a spacer member 26 as a separation member. In other words, in this embodiment, when the image forming apparatus 100 is shipped, the secondary transfer roller bearing 19 is pushed down, and the spacer member 26 is inserted into the cutout portion 25 of the secondary transfer holder 24 to be locked. The transfer roller 8 and the intermediate transfer belt 6 are separated from each other. The secondary transfer holder 24 is a support portion such as a secondary transfer roller 8, a secondary transfer roller bearing 19, and a secondary transfer roller pressure spring 20 fixed in the image forming apparatus main body, and is attached to the intermediate transfer belt 6. The secondary transfer roller 8 is supported so as to be slidable in the contact / separation direction. The notch 25 is provided at a position where the secondary transfer roller 8 can be held away from the intermediate transfer belt 6 by inserting the spacer member 26 therethrough.

  When the image forming apparatus 100 arrives, the user first removes the spacer member 26 that separates the secondary transfer roller 8 and the intermediate transfer belt 6 as shown in FIG. Thus, after the secondary transfer roller 8 and the intermediate transfer belt 6 are in contact with each other, the use of the image forming apparatus 100 is started.

  If the user forgets to remove the spacer member 26 and uses the image forming apparatus 100 in the state shown in FIG. 7B, the normal secondary transfer process is not performed. Next transfer failure occurs. In this embodiment, in order to prevent the user from forgetting to remove the spacer member 26 at the time of arrival, the contact / separation state between the secondary transfer roller 8 and the intermediate transfer belt 6 is detected.

  Hereinafter, an operation for detecting the contact / separation state of the secondary transfer roller 8 with respect to the intermediate transfer belt 6 at the time of arrival will be described with reference to the flowchart of FIG.

  In S1, the image forming apparatus 100 is turned on and turned on.

  If the spacer removed flag is ON in S2, the front multiple rotation is started in S15, but the spacer removed flag is set to OFF when the power is first turned on at the time of arrival (when the power is turned on). Therefore, the contact / separation state detection sequence after S3 is started. The pre-multi-rotation is an operation for rotating the photosensitive drum 1, the developing device 4 and the like when the power of the image forming apparatus 100 is turned on and shifting each part of the image forming unit S to a standby state in which an image can be formed. .

In S <b> 3, the controller 22 applies a voltage (reference voltage value) V ₀ to the secondary transfer roller 8 from the secondary transfer bias power supply 80, and the secondary transfer current that the current detector 23 flows to the secondary transfer roller 8. (Reference current value) I ₀ is detected. In this embodiment, V ₀ = 0V. The secondary transfer current I _{0 at} this time is the average of the detected currents by repeating the sampling every 20 msec 20 times while applying V ₀ to the secondary transfer roller 8.

In S <b> 4, the control unit 22 applies the voltage V ₁ to the secondary transfer roller 8 from the secondary transfer bias power supply 80. Here, V ₀ <V ₁ , and in this embodiment, V ₁ = 100V. In other words, the voltage V ₀ is the lowest voltage among the plurality of levels applied to the secondary transfer roller 8 in order to determine the contact / separation state of the secondary transfer roller 8 with respect to the intermediate transfer belt 6.

In S5, the current detector 23 detects the secondary transfer current I ₁ flowing through the secondary transfer roller 8, and compares I ₁ −I ₀ which is the difference between the currents I ₁ and I ₀ with the current threshold value Ia. The secondary transfer current I _{1 at} this time is obtained by averaging the detected currents by repeating the sampling every 20 msec 20 times when the voltage V ₁ is applied to the secondary transfer roller 8 in S4. . In this embodiment, Ia = 2 μA.

If I ₁ −I ₀ ≧ Ia in S5, it is determined in S13 that the secondary transfer roller 8 and the intermediate transfer belt 6 are in contact with each other, and the spacer removed flag is turned ON. Next, in S14, the controller 22 stops the voltage application to the secondary transfer roller 8, and in S15, the pre-multiple rotation is started.

If I ₁ −I ₀ <Ia in S 5, the controller 22 applies the voltage V ₂ to the secondary transfer roller 8 from the secondary transfer bias power supply 80 in S 6. Here, V ₁ <V ₂ , and in this embodiment, V ₂ = 400V.

In S7, the detected secondary transfer current I ₂ the current detector 23 flows through the secondary transfer roller 8, comparing I ₂ -I ₀ current threshold Ia. The secondary transfer current I _{2 at} this time is the average of the detected currents obtained by repeating the sampling every 20 msec 20 times when the voltage V ₂ is applied to the secondary transfer roller 8 in S6. .

If I ₂ −I ₀ ≧ Ia in S7, it is determined in S13 that the secondary transfer roller 8 and the intermediate transfer belt 6 are in contact with each other, and the spacer removed flag is turned ON. Next, in S14, the controller 22 stops the voltage application to the secondary transfer roller 8, and in S15, the pre-multiple rotation is started.

If I ₂ −I ₀ <Ia in S 7, the controller 22 applies the voltage V ₃ to the secondary transfer roller 8 from the secondary transfer bias power source 80 in S 8. Here, V ₂ <V ₃ , and in this embodiment, V ₃ = 800V.

In S9, the current detector 23 detects the secondary transfer current I ₃ flowing through the secondary transfer roller 8, and compares I ₃ −I ₀ with the current threshold value Ia. The secondary transfer current I _{3 at} this time is obtained by averaging the detected currents by repeating the sampling every 20 msec 20 times when the voltage V ₃ is applied to the secondary transfer roller 8 in S8. .

If I ₃ −I ₀ ≧ Ia in S9, it is determined in S13 that the secondary transfer roller 8 and the intermediate transfer belt 6 are in contact with each other, and the spacer removed flag is turned ON. Next, in S14, the controller 22 stops the voltage application to the secondary transfer roller 8, and in S15, the pre-multiple rotation is started.

If I ₃ −I ₀ <Ia in S9, it is determined in S10 that the secondary transfer roller 8 and the intermediate transfer belt 6 are in a separated state. In step S11, the control unit 22 stops voltage application to the secondary transfer roller 8, and in step S12, warns the user that the spacer member 26 of the secondary transfer roller 8 has not been removed.

  In this embodiment, a warning message to the user is displayed on a liquid crystal operator operation panel as a display unit provided in the image forming apparatus 100. In this case, the main body drive operation of the image forming apparatus 100 (such as rotational driving of the photosensitive drum 1 and the developing device 4) is not performed. In accordance with the warning message, the user turns off the image forming apparatus 100, removes the spacer member 26, and turns on the power again. Accordingly, the power is turned on again in S1. At this time, since the removed flag of the spacer member 26 remains OFF, the contact / separation state between the secondary transfer roller 8 and the intermediate transfer belt 6 is detected based on the same flowchart after S3. Note that a warning message similar to the above may be displayed on a display unit of a host information device such as a personal computer connected to the image forming apparatus 100 so as to be communicable as described above.

In this way, in particular, in this embodiment, the control unit 22 detects the current detection unit 23 when the secondary transfer bias power supply 80 applies the lowest voltage among the plurality of levels to the secondary transfer roller 8. The obtained current value is set as a reference current value I ₀ . Then, the difference I−I ₀ is compared with a predetermined current threshold for the current value I detected when a higher level voltage is applied among the plurality of levels of voltage, and the difference is the predetermined current. When the value is equal to or greater than the threshold value, it is detected that a predetermined amount of current has passed through the secondary transfer roller 8.

The contact / separation state detection sequence of this embodiment is illustrated in FIG. At the time of applying and switching the voltage to the secondary transfer roller 8, 100 msec is secured as the high voltage rise time, and thereafter, the detection current at each voltage is sampled. Since sampling every 20 msec is repeated 20 times, the time required to average the detected current is 400 msec. When the maximum voltage V ₃ (= 800 V) is applied, a total time of 1900 msec is required until all sequences are completed.

In this embodiment, first, 0 V is applied to the secondary transfer roller 8 to detect the reference average current I ₀ . Thereafter, 100 V, 400 V, and 800 V are applied in order, the average current at each voltage is detected, and when the difference from I ₀ becomes 2 μA or more, the secondary transfer roller 8 and the intermediate transfer belt 6 Is in a contact state. In this way, by taking the difference from the amount of current when 0 V is applied, the amount of current when applying each voltage approaches an accurate value even if the reference of the detected current is shifted due to variations in the current detection circuit. Become. Accordingly, it is possible to detect the contact / separation state between the secondary transfer roller 8 and the intermediate transfer belt 6 more accurately. It is naturally possible to use a similar method in the control described in the first embodiment.

In this embodiment, three levels of applied voltages V _{1 to} V ₃ are set, but a plurality of levels of voltages may be provided. V ₀ is not limited to ₀ V, and can be selected as appropriate.

  In this embodiment, the secondary transfer roller 8 and the intermediate transfer belt 6 are separated from each other by using the spacer member 26 that can be removed by the user. However, the present invention is not limited to this. For example, a sheet member is sandwiched between the secondary transfer roller 8 and the intermediate transfer belt 6 instead of the spacer member 26, and in a separated state, that is, the secondary transfer roller 8 and the intermediate transfer belt 6 are not in direct contact. It is also possible to create a state.

  In this case, the image forming apparatus 100 includes the secondary transfer roller 8 and the intermediate transfer belt 6 with the sheet member 27 sandwiched between the secondary transfer roller 8 and the intermediate transfer belt 6 as shown in FIG. Are shipped in a state of being separated from each other.

  When the image forming apparatus 100 arrives, the user first removes the sheet member 27 sandwiched between the secondary transfer roller 8 and the intermediate transfer belt 6 as shown in FIG. Thus, after the secondary transfer roller 8 and the intermediate transfer belt 6 are in contact with each other, the use of the image forming apparatus 100 is started.

  As the sheet member 27, for example, an insulating PET (polyethylene terephthalate) film can be used. More specifically, the thickness is 0.2 mm and the longitudinal dimension is longer than that of the secondary transfer roller 8. A thing can be used suitably. In this case, when the sheet member 27 is sandwiched between the secondary transfer roller 8 and the intermediate transfer belt 6, no current flows between the secondary transfer roller 8 and the intermediate transfer belt 6. The present invention can be applied just as in the case of the spacer member 26.

  As described above, a plurality of levels of voltages are applied to the secondary transfer roller 8 in order from a low voltage, and the voltage application is terminated when a predetermined current is detected. Therefore, the secondary transfer roller 8 is operated in a high temperature and high humidity environment. And the intermediate transfer belt 6 are in contact with each other, it is possible to prevent an excessive current from flowing. Finally, when the secondary transfer roller 8 and the intermediate transfer belt 6 are in contact with each other, a high voltage through which a predetermined current flows is applied even in a low-temperature and low-humidity environment. The contact / separation state between the roller 8 and the intermediate transfer belt 6 can be detected. In this embodiment, the average current when 0 V is applied is used as a reference average current value, and a difference from the average current value when each voltage is applied is taken, thereby enabling more accurate detection.

  As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned Example.

  For example, in Example 2, it is assumed that the image forming apparatus is shipped with the secondary transfer roller and the intermediate transfer belt separated by a separating member such as a spacer member or a sheet member. It was determined that the forgetting to remove the spacing member was determined and a warning was given. However, the image forming apparatus is shipped in a state where the secondary transfer roller is separated from the intermediate transfer belt by the secondary transfer roller contact / separation mechanism provided in the image forming apparatus main body without using a removable separating member. The present invention can also be applied to the case where In this case, the state of contact / separation between the secondary transfer roller and the intermediate transfer belt is determined at the start of use of the apparatus, and if it is determined that the device is separated, the release / contact mechanism of the secondary transfer roller is prompted to be released. The warning may be performed.

  In each of the above-described embodiments, the case where the contact / separation state of the secondary transfer member with respect to the intermediate transfer member as the image carrier is determined has been described. However, the present invention is not limited to this. For example, the present invention can be applied to the determination of the contact / separation state of the primary transfer member with respect to the photoconductor as the image carrier. In this case, the contact state between the contact state in which the primary transfer member is in contact with the photoconductor via the intermediate transfer member and the state in which the primary transfer member is separated from the photoconductor is determined. That is, for example, as shown in FIG. 11A, when a full-color image is formed, the primary transfer member 7 is brought into contact with the photosensitive member 1 in a plurality of image forming portions. However, as shown in FIG. At the time of image formation, the contact may occur only at the black image forming unit. Alternatively, it is conceivable that the image forming apparatus is shipped in a state where the primary transfer member 7 is separated from the photoreceptor 1. In such a configuration in which the primary transfer member 7 is in contact with or separated from the photoreceptor 1, it is important to determine the contact / separation state of the primary transfer member 7 with respect to the photoreceptor 1 in order to obtain appropriate primary transfer performance. . Therefore, in the image forming apparatus having such a configuration, the same effects as described above can be obtained by applying the present invention to the primary transfer portion in the same manner as described in the above embodiments. In this case, when using a separation member such as a spacer member or a sheet member, the separation member and the intermediate transfer member are arranged so that the transfer member does not contact the image carrier via the intermediate transfer member. Or between the intermediate transfer member and the image carrier.

  For example, a direct transfer type image forming apparatus having, for example, an endless belt-like conveyance belt (belt member) as a recording material carrier instead of the intermediate transfer body in an intermediate transfer type image forming apparatus is known to those skilled in the art. Is well known. In a direct transfer type image forming apparatus, for example, a toner image formed on a photoconductor as an image carrier is carried on the recording material carrier and passes through a contact portion (transfer portion) with the photoconductor. Directly transcribed into Such a transfer step is performed by applying a transfer bias to a transfer member provided on the back side of the recording material carrier, in substantially the same manner as the primary transfer step in the intermediate transfer type image forming apparatus. In the image forming apparatus having such a configuration as well, as described with reference to FIG. 11, the present invention can be applied to determine, for example, the contact / separation state of the transfer member with respect to the image carrier.

  Further, as shown in FIG. 12, in an image forming apparatus having only a single image forming unit, for example, the photosensitive member 1 as an image carrier and a transfer member without using an intermediate transfer member or a recording material carrier. 7 is in contact (FIG. 12 (a)) or separated (FIG. 12 (b)). In the image forming apparatus having such a configuration, the present invention can naturally be applied to the determination of the contact / separation state of the transfer member with respect to the image carrier.

  11 and 12, elements having the same or corresponding functions and configurations as those of the image forming apparatus 100 shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  Further, in each of the above embodiments, the transfer member (primary transfer member, secondary transfer member) has been described as a roller-like member as a rotating member. However, the present invention is not limited to this, and the transfer member is fixed. A brush-like member, a rotating brush-like member, or the like can also be used.

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a schematic diagram of a contact / separation mechanism of a secondary transfer roller of an image forming apparatus according to an embodiment of the present invention. It is a schematic diagram for demonstrating the apparatus structure for detecting the electric current which flows into a secondary transfer roller. It is a flowchart figure which concerns on one Example of this invention. It is a sequence chart figure concerning one example of the present invention. It is a graph which shows an example of the relationship between the applied voltage and detection current with respect to a secondary transfer roller. It is a schematic diagram of the contact-and-separation mechanism of the secondary transfer roller using the spacer member which concerns on the other Example of this invention. It is a flowchart figure which concerns on the other Example of this invention. It is a sequence chart figure concerning other examples of the present invention. FIG. 10 is a schematic view of a secondary transfer roller contact / separation mechanism using a sheet member according to still another embodiment of the present invention. It is a principal part schematic sectional drawing for demonstrating the further another example of application of this invention. It is a principal part schematic sectional drawing for demonstrating the further another example of application of this invention. FIG. 10 is a schematic cross-sectional view of a main part of an intermediate transfer unit of a conventional image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 6 Intermediate transfer belt 7 Primary transfer roller 8 Secondary transfer roller 19 Secondary transfer roller bearing 20 Secondary transfer roller pressure spring 21 Eccentric cam 22 Control part 23 Current detection part 26 Spacer member 27 Sheet member 80 Secondary Transfer bias power supply P Recording material

Claims (4)

An image carrier that carries a toner image, and a transfer member that transfers a toner image carried on the image carrier to a transfer material by applying a voltage to the image carrier. A transfer member that is movable between a contact state that is in contact with the image carrier and a separated state that is separated from the image carrier from the contact state, a voltage application unit that applies a voltage to the transfer member, and the voltage application unit A current detecting means for detecting a current flowing through the transfer member to which a voltage is applied, a control means for controlling the voltage applying means, and whether the transfer member is in the contact state or in the separated state. A determination unit configured to determine based on a current value detected by the current detection unit,
The voltage application means includes a first detection voltage set in advance, a second detection voltage set in advance and having an absolute value larger than the first detection voltage, and the second detection voltage set in advance. A third detection voltage having an absolute value larger than the voltage for use can be applied to the transfer member,
The determination unit determines that the transfer member is in a contact state when a current value detected by the current detection unit is equal to or greater than a predetermined value;
When the determination unit determines the state of the transfer member, the control unit first applies the first detection voltage by the voltage application unit on the assumption that the surrounding environment is the first environment. If the current value first detection voltage the current sensing means also applies a detects is less than the predetermined value, is the second environment of low temperature and low humidity than the ambient environment first environment If the current value detected by the current detection means is less than the predetermined value even when the second detection voltage is applied and the second detection voltage is applied, the surrounding environment is the first The image forming apparatus, wherein the third detection voltage is applied on the assumption that the third environment has a lower temperature and lower humidity than the second environment. The image forming apparatus, the transfer member is shipped under the said separated state, said determination means, image formation according to claim 1, characterized in that it is performed at initial power-up of the image forming apparatus apparatus. The image forming apparatus is shipped with the transfer member placed in the separated state by attaching a removable separation member so that the transfer member does not contact the image carrier directly or via the transfer material, The image forming apparatus according to claim 1 , wherein the determination unit is executed when the image forming apparatus is first turned on. The first environment is a high-temperature and high-humidity environment, the third environment is a low-temperature and low-humidity environment, and the second environment is an environment between the high-temperature and high-humidity environment and the low-temperature and low-humidity environment. the image forming apparatus according to any one of claims 1 to 3, characterized in that.

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