JP2004347924A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set conditions that satisfactory transfer can surely be performed over a long period. <P>SOLUTION: An auxiliary transfer means for operating a transfer material so as to come into contact with an image carrier is arranged in a transfer means, and in order to control a timing of pressing/releasing the auxiliary transfer means to/from the image carrier, a control part controls a pressure operation starting timing and a release operation starting timing through a timer when the leading/trailing ends of the transfer material are detected by the transport detection sensor positioned closest to a transfer position, and the pressure operation starting timing value and the release operation starting timing value are made variable in terms of time by operating an operating part. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus that forms an image by an electrophotographic method, and more particularly to an image forming apparatus in which a transfer unit that transfers a toner image on an image carrier onto transfer paper is provided with a transfer assisting unit.
[0002]
[Prior art]
In an image forming apparatus, a toner image is formed by performing charging, image exposure, and development on an image carrier, for example, a rotating photosensitive drum, and transferring the formed toner image onto transfer paper. I have. The transfer of the toner image is generally performed by performing a corona discharge having a polarity opposite to that of the toner image from behind a transfer sheet as a transfer material. When transferring, the transfer paper must be in close contact with the photoconductor drum holding the toner image, and if the transfer paper is floating with respect to the photoconductor drum, the transfer image will not transfer or bleed. It becomes. Such a phenomenon is difficult to recognize in the case of a character image, but a defect in image quality is noticeably recognized in the case of a photographic image.
[0003]
In order to ensure the adhesion of the entire surface of the transfer paper to the photosensitive drum at the time of transfer, a transfer assisting means for pressing the transfer paper toward the photosensitive drum at the time of transfer is provided.
[0004]
(1) Conventionally, in order to detect the position of the transfer paper relative to the photosensitive drum, a position detection sensor is provided in the transfer path of the transfer material, and is fixed from the time when the leading and trailing ends of the passing transfer paper are detected by the position detection sensor. After a certain time, the transfer assisting means is pressed and released. In this case, when the transfer assisting unit presses the photosensitive drum in a state where there is no transfer paper between the photosensitive drum and the transfer assisting unit, the photosensitive member is damaged, and an image defect due to the damage of the photosensitive member occurs. . Further, the transfer assisting means presses the entire area from the leading edge to the trailing edge of the transfer paper, so that a good transfer image can be obtained on the entire surface of the transfer paper. Accuracy is required for the pressing timing and release timing of the transfer assisting means, but when the position of the position detection sensor is far from the transfer position, the timing accuracy of pressing and releasing cannot be ensured. A registration unit is provided in the transfer material conveyance path to control the transfer timing and interval of the transfer paper, and the transfer paper is temporarily stopped. However, when a position detection sensor is provided, the registration unit is used. The accuracy cannot be ensured unless it is disposed between the transfer position and the transfer position. When the position detection sensor is disposed at such a restricted position, it is difficult to secure a space, and a small image forming apparatus needs a starting point of a timer instead of the sensor.
[0005]
In addition, when the transfer paper is transported using rollers, if the rollers wear over time, the transport speed of the transfer paper decreases, the time required to reach the transfer position from the position detection sensor changes, and the position detection sensor If the transfer assisting means is pressed and released after a lapse of a certain period of time, accuracy cannot be ensured after a lapse of time.
[0006]
{Circle around (2)} When pressing / releasing is controlled by one position detection sensor, the transfer material having a deformed rear end, such as tab paper, has a different relationship between the deformed shape and the sensor position. If the desired release timing cannot be obtained, there is a problem that a portion without a transfer material is generated between the photoconductor and the transfer assisting unit in a pressed state, and the photoconductor is damaged. In addition, regarding the tab sheet, there are various positions at which the tab section is arranged with respect to the tab sheet, and if the sensor is arranged at a fixed position, tab sheets for which a desired release timing cannot be obtained will occur.
[0007]
{Circle around (3)} Several proposals have been made for the transfer assisting means.
Japanese Patent Application Laid-Open No. H11-163873 discloses a method of detecting the leading and trailing end positions of a transfer material by a transfer material position detection sensor, controlling the timing of pressing and releasing, and reducing the pressing force of the transfer assisting means at the leading and trailing ends of the transfer material. Has been described. Patent Literature 2 describes that the pressing force of the transfer assisting unit is adjusted depending on the type of the transfer material and whether the copy is a one-sided copy or a two-sided copy.
[0008]
[Patent Document 1]
JP-A-9-190089
[0009]
[Patent Document 2]
JP-A-11-65328
[0010]
[Problems to be solved by the invention]
{Circle around (1)} In the present invention, the operation is performed under the condition with the highest accuracy, and good transfer is performed. In order to provide an image forming apparatus having a transfer assisting means, the image forming apparatus is capable of maintaining high-accuracy operation by correcting even a decrease in operation accuracy of the transfer assisting means which occurs with time. For the purpose of providing.
[0011]
{Circle around (2)} Another object of the present invention is to provide an image forming apparatus capable of performing good transfer without damaging a photoreceptor even on a tab sheet having a transfer material having an irregular rear end shape.
[0012]
[Means for Solving the Problems]
In order to solve the above problems and achieve the object, the present invention is configured as follows.
[0013]
According to the first aspect of the present invention, there is provided an image forming apparatus provided with a transfer unit that electrostatically transfers a toner image held on an image carrier onto a transfer material.
The transfer unit is provided with a transfer assisting unit that operates to bring the transfer material into contact with the image carrier. In order to control the timing at which the transfer assisting unit presses and releases the image bearing member, the control unit controls the transfer. The pressing operation start timing and the release operation start timing are controlled by a timer based on the transfer material front end detection / rear end detection of the conveyance detection sensor closest to the position or the operation timing of the registration clutch, and the pressing operation start timing value and the release operation An image forming apparatus characterized in that the start timing value can be changed in time by an operation from an operation unit. ".
[0014]
According to the first aspect of the present invention, the correction of the operating condition of the transfer assisting means is performed when a malfunction occurs even with the passage of time, so that the transfer under the best condition is continued for a long time. Will be performed.
[0015]
According to a second aspect of the present invention, there is provided an image forming apparatus, wherein the transport detection sensors are in phase with respect to the transport direction of the transfer material, and two or more transport detection sensors are provided in a direction perpendicular to the transport direction. 2. The image forming apparatus according to claim 1, wherein the release detection start timing is controlled by the conveyance detection sensor.
[0016]
The invention according to a third aspect is characterized in that "control is performed to start the release operation by operating the timer starting from the conveyance detection sensor that has detected the rear end of the transfer material earliest among the plurality of conveyance detection sensors. The image forming apparatus according to claim 2. "
[0017]
According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the second aspect, wherein the positions of the plurality of transport detection sensors are variable and can be changed by a transfer material.
[0018]
According to a fifth aspect of the present invention, there is provided the image forming apparatus according to the second aspect, wherein the positions of the plurality of transport detection sensors are variable, and the position can be designated by an operation from an operation unit. .
[0019]
According to a sixth aspect of the present invention, the operating position of the transfer assisting means with respect to the image carrier has a fine release position other than the pressing position and the releasing position, and the transfer material is the earliest of the plurality of transport detection sensors. The timer is operated based on the sensor signal that has detected the trailing end to control the movement start timing to the fine release position, and the timer is operated based on the sensor signal that has detected the rear end of the transfer material as the starting point, and the timer is moved to the release position. 3. The image forming apparatus according to claim 2, wherein the movement start timing is controlled.
[0020]
According to the second to sixth aspects of the present invention, it is possible to provide an image forming apparatus capable of performing good transfer on a tab sheet having a rear end shape that is irregular, without damaging the photosensitive member.
[0021]
According to a seventh aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein timing of exposure start on the image carrier is controlled by the transport detection sensor.
[0022]
According to the seventh aspect of the present invention, the number of sensors is reduced by using sensors having a plurality of functions, and the image timing on the image carrier and the transfer timing of the transfer material are synchronized. In addition, an image forming apparatus with higher timing accuracy at the leading end of the transfer material is provided.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
(1) Prior to the description of the present invention, the structure and operation of an apparatus common to image forming apparatuses provided with a transfer unit of the present invention will be described with reference to FIG. However, the present invention is not limited to such a structure, and is widely applied to a color image forming apparatus and a double-sided image forming apparatus.
[0024]
The image forming apparatus includes an image reading unit 10, a laser writing unit 20, an image forming unit 30, a paper feeding unit 40, and the like.
[0025]
An image reading unit 10 is provided above the image forming apparatus, and scans an original image placed on an original table 11 by a scanning optical system 12, and the scanned image is formed on an image sensor 15.
[0026]
Image data obtained by the image sensor 15 is processed by an image signal processing unit (not shown), and is temporarily stored in a memory as an image signal. Next, the image signal is input to the laser writing unit 20.
[0027]
The image forming unit 30 controls the image signal from the memory under the control of the control unit to convert the image signal from the memory into a laser writing unit including a polygon motor 21, a polygon mirror 22, an fθ lens 23, mirrors 24, 25 and 26, a semiconductor laser (not shown), and a correction lens. When the image data is input to the register 20, the timing is synchronized by the index sensor, and the image recording operation is started. That is, the photosensitive drum 31 serving as an image carrier rotates clockwise as indicated by an arrow, and is discharged by a charge remover 36 that performs pre-charge exposure and removes electricity, and then has a discharge wire 32A and a charge grid 32B. Since the electric charge is given by the container 32, an electrostatic latent image corresponding to the original image is formed on the photosensitive drum 31 by the laser beam L by the laser writing unit 20. Thereafter, the electrostatic latent image on the photosensitive drum 31 is subjected to reversal development by the developer carried on the developing sleeve 33A to which a bias voltage in which an AC component is superimposed on a DC component of the developing device 33 is applied, and the visible toner is It becomes an image.
[0028]
On the other hand, transfer paper P of a designated size is carried out one by one from the paper supply cassette 41A or 41B loaded in the paper supply unit 40 by the carry-out roller 42A, and the toner image is transferred via the carry-out roller 43 and the guide member 42. The paper is fed toward the transfer section where the printing is performed. The fed transfer paper P is sent out so as to be in contact with the photosensitive drum 31 by a registration roller 44 that operates via a registration clutch 44C in synchronization with the toner image on the photosensitive drum 31. The transfer sheet P is pressed by a transfer assisting unit 60, which will be described in detail later, so as to be in close contact with the photoconductor drum 31 holding the toner image. The toner image on the photosensitive drum 31 is transferred onto the transfer paper P by the operation of the transfer unit 34, and is separated from the photosensitive drum 31 by the charge eliminating operation of the separator 35, and then fixed via the transport belt 46. After being sent to a container 37 and fused and fixed by a heating roller 37A and a pressure roller 37B, the sheet is discharged to a tray outside the apparatus by sheet discharge rollers 38 and 47.
[0029]
The photosensitive drum 31 further continues to rotate, and the toner remaining on the surface thereof without being transferred is removed and cleaned by a cleaning blade 39A pressed against the photosensitive drum 31 in a cleaning device 39, and then discharged again by the discharger 36. After the charging, the charge is uniformly applied by the charger 32 to start the next image forming process.
[0030]
Here, since the developer has high resolution and excellent gradation expression, a styrene-acrylic polymerized toner having a mass average particle diameter of 3 to 8 μm and a mass average obtained by applying a resin coating to ferrite are used. A two-component developer composed of a carrier having a particle diameter of 60 μm is used.
[0031]
(2) In the image forming apparatus according to the present embodiment, a transfer assisting unit 60 is provided for abutting and releasing the photosensitive drum 31 serving as an image carrier, and is pressed from behind the transfer material to transfer the transfer paper at the transfer unit. The transfer of the toner image onto P is ensured. 2 to 4 are cross-sectional views showing the stop position of the transfer assisting means 60 in the transfer unit. FIG. 2 shows a state where the transfer assisting unit 60 is released (separated) from the photosensitive drum 31, and FIG. FIG. 4 shows a slightly released state in which it is slightly contacted. The configuration and operation of the transfer assisting unit 60 will be described with reference to FIG.
[0032]
The transfer assisting means 60 includes a pressing sheet member 61 and a transfer pressing member 62 to which the pressing sheet member 61 is attached and fixed. The pressing sheet member 61 is a resin elastic sheet having an appropriate elasticity such as a PET sheet, has a sheet width corresponding to the paper width of the transfer paper, and is adhered and fixed to the transfer pressing member 62.
[0033]
The transfer pressing member 62 is a U-shaped plate-shaped member. Elongated holes 62a and 62b are provided at rising portions on both sides, and the transfer pressing member 62 engages with support shafts 71a and 71b provided on the apparatus main body side. It is possible to approach or retreat to the photosensitive drum 31 along the hole.
[0034]
The transfer pressing member 62 is provided with a rack portion 62c, which is in mesh with a pressing drive gear GM1 attached to a pressing drive motor M1 using a stepping motor or the like, in a forward direction or a reverse direction of the pressing drive motor M1. The transfer pressing member 62c is configured to move linearly in the contact direction or the retreat direction with the photosensitive drum 31 with the rotation of the transfer pressing member 62c. Further, a mark 62M is provided on the transfer pressing member 62, and a home position detection sensor SHP provided on the apparatus main body side detects the mark 62M to detect the home position at which the transfer pressing member 62 retracts and stops. Is going.
[0035]
A registration roller 44 is provided on the transfer path of the transfer sheet P, and transfers the transfer sheet P in synchronization with the toner image formed on the photosensitive drum 31. The transfer sheet P conveyed through the registration rollers 44 is conveyed toward a transfer position while being guided by a guide plate 45 sandwiched between an upper surface and a lower surface. Between the registration roller 44 and the transfer position, the leading and trailing ends of the transfer paper P are detected by the conveyance detection sensors SP1 to SPN provided at positions closest to the transfer position. Of course, it is also possible to control the pressing operation start timing and the release operation start timing with a timer from the operation timing of the registration clutch 44C of the registration roller 44 instead of the conveyance detection sensor.
[0036]
In the image forming apparatus of the present embodiment, a plurality of conveyance detection sensors SP1 to SPN are provided, and a plurality of sets are arranged in the conveyance direction of the transfer material in the same phase in the conveyance direction and in the vertical direction, and in the conveyance direction. Has a movable structure. FIG. 5 shows an arrangement position of two sets of the transport detection sensors SP1 and SP2, and FIG. 6 shows a configuration of the transport detection sensor SPN which can be moved in a direction perpendicular to the transport direction of the transfer material.
[0037]
The support member 441 that fixedly supports the transport detection sensor SPN is in an engaged state with a guide lot 442 and a guide screw 443 that are parallel to the surface of the transfer paper P that moves in a direction perpendicular to the transport direction of the transfer material. M2 is a sensor drive motor using a pulse motor or the like, and is provided at one end of the guide screw 443 in the apparatus main body. When the sensor drive motor M2 rotates, the support member 441 moves left or right depending on the motor rotation direction, and the sensor position of the transport detection sensor SPN can be moved in a direction orthogonal to the transport direction of the transfer material.
[0038]
(3) In the image forming apparatus of the present invention, the engine control unit determines whether the pressing start timing and the release operation start timing are determined by the timer from the transfer material detection of the transfer material sensors SP1 to SPN and the operation of the registration clutch 44C. Control is performed so that the transfer assisting means uniformly presses the transfer material from the leading end to the trailing end so that good and reliable transfer is performed.
. FIG. 7 is an electrical configuration diagram centering on the engine control unit 100 in which such control is performed, and FIG. 8 shows a control flow of the pressing and releasing operations of the transfer assisting unit 60 by the engine control unit 100. The present invention will be described with reference to FIGS.
[0039]
When the start button of the operation display unit provided on the upper surface of the image forming apparatus is turned on, the general control unit drives the reading control unit and starts reading the original. At the same time, the control flow starts (F1), and it is determined whether or not the pressing control by the transfer assisting means 60 is performed (F2). When the pressing control is performed, the transport detection sensors SP1 to SPN are turned on. The state is such that the leading or trailing edge of the transfer material can be detected (F3).
[0040]
When an input indicating that the leading edge of the transfer material has been detected by the transport detection sensors SP1 to N is input to the I / O port 102 of the engine control unit 100 (F4A), the CPU 101 determines the pressing timer value stored in the timers 1 to N105. (T (F)) is called to make settings and start the pressing timer (F5A). After waiting for the pressing timer to count up (F6A), the CPU 101 drives the pressing driving motor M1 to rotate by the specified number of pulses in the pressing direction, and starts moving the transfer assisting means 60 (F7A). It is checked whether the drive motor M1 has been rotated by a specified number of pulses and the movement has been completed (F8A), and when it is checked that the movement has been completed, the CPU 101 stops the pressing drive motor M1 (F9A). At the time of this stop, as shown in FIG. 3, the leading end of the pressing sheet member 61 is conveyed, and the leading end of the transfer paper entering the transfer unit is pressed. The state of pressing the transfer paper is maintained.
[0041]
When the trailing edge detection of the transfer material is input to the I / O port 102 of the engine control unit 100 by the transport detection sensors SP1 to N (F4B), the CPU 101 causes the release timer value (T (R)) is called to make settings and start the release timer (F5B). After waiting for the release timer to count up (F6B), the CPU 101 rotates the pressing drive motor M1 to start moving the transfer assisting unit 61 from the pressing position in the pressing release direction (F7B). When the home position detection sensor SHP provided on the apparatus main body detects the mark 62M provided on the transfer pressing member 62 moving in the release direction (F8B), the CPU 101 stops the rotation of the pressing drive motor M1 (F9B). This stop position is the home position where the transfer assisting means 60 has retreated, and FIG. 2 shows a state in which the transfer assisting means 60 is released.
[0042]
(4) As described above, the transfer material is brought into an appropriate pressure state by the transfer assisting means 60 over the entire transfer area in the transfer area, so that a good transfer of the toner image is performed. When the transfer roller wears over time, the transfer speed of the transfer material changes, the time required for the transfer material to reach the photosensitive drum 31 changes, and the pressure at the leading end of the transfer material and the rear end of the transfer material change. Is not accurately released. For example, if the pressing sheet member 61 presses against the photoconductor drum 31 before the transfer material enters the transfer unit, the photoconductor surface is damaged and a good image cannot be obtained. Further, when the pressing is performed with a delay after the transfer material enters the transfer portion, a portion where the toner image is not transferred satisfactorily occurs at the leading end of the non-pressed transfer material.
[0043]
In the image forming apparatus of the present embodiment, the pressing timer value (from the time when the transport detection sensors SP1 to N easily detect the leading end of the transfer material to the time when the drive motor M1 starts rotating in the pressing direction by the operation on the operation display unit). T (F)) and the release timer value (T (R)) from when the conveyance detection sensors SP1 to SPN detect the rear end of the transfer material to when the drive motor M1 starts rotating in the retreat direction. .
[0044]
FIG. 9 shows a timer value input processing flow for inputting the pressing and releasing timer values of the transfer assisting means 60. When the power is turned on and the start is performed (G1), whether or not an adjustment mode for image forming conditions such as a charging potential and a developing bias is selected by mode selection on the liquid crystal display unit of the operation display unit by an adjustment mode program. Is displayed (G2). When the service person or the operator intends to change the pressing and releasing operation timings of the transfer assisting means 60, the pressing adjustment mode in the adjustment mode is selected (G3).
[0045]
The overall control unit calls the press timer value (T (F)) and the release timer value (T (R)) stored in the timers 1 to N105 and displays them on the liquid crystal display unit (G4). When the service person or the operator inputs a new press timer value (T (F) ′) to be set with reference to the press timer value (T (F)) displayed using the numeric keypad (G5A), the liquid crystal display unit Displays a press timer value (T (F) ') to be newly set along with the press timer value (T (F)) currently set.
[0046]
By confirming the press timer value (T (F) ') to be newly set by the service person or the operator, this information is transmitted to the engine control unit 100, and the previous press timer value (T Instead of (F)), a press timer value (T (F) ′) to be newly set is stored (G6A).
[0047]
When the service person or the operator inputs a release timer value (T (R) ') to be newly set with reference to the release timer value (T (R)) displayed using the numeric keypad (G5B), the liquid crystal is displayed. A new release timer value (T (R) ') to be newly set is displayed on the display panel along with the currently set release timer value (T (R)).
[0048]
By confirming the release timer value (T (R) ') newly set by the service person or the operator, this information is transmitted to the engine control unit 100, and timers 1 to N105 are provided with the previous release timer (T (R)'). Instead of (R)), a release timer value (T (R) ') to be newly set is stored (G6B).
[0049]
After the above timer value input processing is completed, the pressing and releasing operations of the transfer assisting means 60 performed at the time of image recording include the newly set pressing timer value (T (F) ′) and the releasing timer value (T (R)). '), The error of the operation of the transfer assisting means 60 caused by the lapse of time is eliminated, and a good transfer of the toner image is performed.
[0050]
(5) Next, the operation control of the transfer assisting means 60 when tab paper is used as the transfer material will be described. Since the tab paper has an irregular shape in which the rear end shape of the transfer material has a protruding portion, a desired release timing cannot be obtained depending on the arrangement positions of the conveyance detection sensors SP1 to SPN, and the photosensitive member and the pressing sheet member are not obtained. A portion where the transfer material does not exist is generated between the transfer member 61 and the photosensitive member 61, which may damage the photosensitive member. Also, with respect to the tab sheet, the positions of the tab portions are various and are not uniformly determined, so that the transport detection sensors SP1 to SPN cannot be fixed to correspond to the tab sheet.
[0051]
In the present embodiment, it is possible to move and set the detection positions of the conveyance detection sensors SP1 to SPN according to the shape of the tab sheet, and operate the timer starting from the sensor signal that detects the rear end of the transfer material earliest. The timing of starting the movement to the release position is controlled, and the timer is operated starting from the sensor signal that detects the rear end of the transfer material at the latest, thereby controlling the timing of starting the movement to the release position.
[0052]
When tab paper is used as the transfer material, the user selects special paper as the transfer material to be used, so that the liquid crystal display unit displays the tab paper together with the display of thick paper, thin paper, OHP, or the like. Here, by selecting a tab sheet, various tab sheet patterns numbered with different tab shapes and positions as shown in FIG. 10 are displayed on the liquid crystal display unit. The user inputs the tab paper pattern number using the numeric keypad, and the main body control unit drives the sensor driving motor M2 to detect the rear end of the non-tab portion of the tab paper. The plurality of transport detection sensors SP1 to SPN are moved to sensor positions where detection is possible.
[0053]
To set the sensor positions of the plurality of transport detection sensors SP1 to N, in addition to the above-described method, a distance (for example, in cm) from a reference position based on the paper end surface is input using a numeric keypad, and transport detection is performed. It is also possible to set the detection positions of the sensors SP1 to SPN.
[0054]
FIG. 11 shows a control flow of the pressing and releasing operations of the transfer assisting means 60 when the tab sheet is used as the transfer material by the engine control unit 100, and FIG. 12 shows a timing chart when the tab sheet is used. . The operation of the present embodiment will be described with reference to FIG. However, the process from when the leading edge of the tab sheet is detected to when the leading edge of the tab sheet is pressed by the pressing sheet member 61 is the same as that described with reference to FIG.
[0055]
When the rear end (non-tab portion) edge detection of the tab sheet detected by the conveyance detection sensor SP1 is input to the I / O port 102 of the engine control unit 100 (F4C), the CPU 101 is stored in the timers 1 to N105. Then, the fine release timer value (T (S)) is called and set, and the fine release timer is started (F5C). When the edge detection of the rear end of the tab portion of the tab sheet detected by the transport detection sensor SP2 is input (F6C), the CPU 101 calls and sets the release timer value (T (R)) stored in the timers 1 to N105. And the release timer is started (F7C). After waiting for the fine release timer to count up (F8C), the CPU 101 rotates the pressing drive motor M1 by a predetermined number of pulses and starts moving in the fine release direction (F9C). It is checked whether or not the drive motor M1 is rotated by a predetermined number of pulses and the movement to the fine release position is completed (F10C). When it is checked that the movement is completed, the CPU 101 stops the pressing drive motor M1. (F11C).
[0056]
The stopped fine release position is in the state as shown in FIG. 4, and the leading end of the pressing sheet member 61 lightly presses the tab portion to enable the transfer of the toner image on the tab portion. Lightly contacts the photoreceptor surface but does not damage the photoreceptor.
[0057]
After waiting for the release timer to count up (F12C), the CPU 101 rotates the pressing drive motor M1 to start moving the transfer assisting unit 61 from the fine release position in the pressing release direction (F13C). When the home position detection sensor SHP provided on the apparatus main body detects the mark 62M provided on the transfer pressing member 62 moving in the release direction (F14C), the CPU 101 stops the rotation of the pressing drive motor M1 (F15C). This stop position is a home position serving as a reference for the retreat operation of the transfer assisting means 60.
[0058]
(6) In the present invention, the transport detection sensors SP1 to SPN are used to control the operation of the transfer assisting means from the detection of the leading edge or the trailing edge of the transfer material. The exposure start timing of the laser writing unit 20 on the image carrier can be controlled based on the detection of the leading edge of the material. The timing chart of FIG. 12 shows the relationship between the leading edge detection by the transport detection sensor SP1 and the image writing timer. When the conveyance detection sensor SP1 also has such a function, the image timing and the transfer material timing are synchronized, and higher timing accuracy is secured.
[0059]
【The invention's effect】
According to the first aspect of the present invention, the correction of the operation condition of the transfer assisting means is performed when a malfunction occurs over time, so that the best transfer under the best condition is continued for a long time. Will be performed.
[0060]
According to the second to sixth aspects of the present invention, there is provided an image forming apparatus capable of performing good transfer on a tab sheet having a rear end shape that is irregular, without damaging the photoconductor.
[0061]
According to the seventh aspect of the present invention, the number of sensors is reduced by using a sensor having a plurality of functions, and the image timing on the image carrier and the transfer timing of the transfer material are synchronized. An image forming apparatus with higher timing accuracy at the leading end of the transfer material is provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a structure of an image forming apparatus.
FIG. 2 is a cross-sectional view illustrating a state in which the contact of a transfer assisting unit is released.
FIG. 3 is a cross-sectional view illustrating a state where a transfer assisting unit is in contact with the image forming apparatus.
FIG. 4 is a cross-sectional view showing a state in which a transfer assisting unit is slightly released.
FIG. 5 is a cross-sectional view illustrating an arrangement relationship of a conveyance detection sensor.
FIG. 6 is a configuration diagram of a conveyance detection sensor.
FIG. 7 is an electric configuration diagram of the present invention.
FIG. 8 is a control flowchart of an engine control unit.
FIG. 9 is a flowchart of a timer value input process for pressing and releasing.
FIG. 10 shows various tab paper patterns.
FIG. 11 is a flowchart illustrating control of tab sheets by an engine control unit.
FIG. 12 is a timing chart.
[Explanation of symbols]
31 Photoconductor drum
34 Transfer device
44 Registration Roller
60 Transfer assisting means
61 Pressing sheet member
62 Transfer pressing member
M1 press drive motor
M2 sensor drive motor
SPI ~ N Transfer detection sensor
SHP home position detection sensor

Claims (7)

In an image forming apparatus provided with a transfer unit that electrostatically transfers a toner image held on an image carrier onto a transfer material,
The transfer unit is provided with a transfer assisting unit that operates to bring the transfer material into contact with the image carrier. In order to control the timing at which the transfer assisting unit presses and releases the image bearing member, the control unit controls the transfer. The pressing operation start timing and the release operation start timing are controlled by a timer based on the transfer material front end detection / rear end detection of the conveyance detection sensor closest to the position or the operation timing of the registration clutch, and the pressing operation start timing value and the release operation An image forming apparatus characterized in that the start timing value can be changed in time by an operation from an operation unit. The transport detection sensor has the same phase in the transport direction of the transfer material, and two or more transport detection sensors are provided in a direction perpendicular to the transport direction, and a release operation start timing is provided by the transport detection sensors. The image forming apparatus according to claim 1, wherein the control is performed. 3. The image according to claim 2, wherein, of the plurality of transport detection sensors, the timer is operated starting from a transport detection sensor that has detected the rear end of the transfer material earliest, and control for starting a release operation is performed. 4. Forming equipment. 4. The image forming apparatus according to claim 3, wherein the positions of the plurality of conveyance detection sensors are variable and can be changed depending on a transfer material. The image forming apparatus according to claim 2, wherein the positions of the plurality of conveyance detection sensors are variable, and the position can be designated by an operation from an operation unit. The operation position of the transfer assisting means with respect to the image carrier has a slight release position other than the pressing position and the release position, and a starting point is a sensor signal that detects the rear end of the transfer material earliest among the plurality of transport detection sensors. The start of movement to the release position is controlled by operating a timer to control the start of movement to the fine release position, and the timer is operated starting from a sensor signal that detects the rear end of the transfer material at the latest. The image forming apparatus according to claim 2, wherein The image forming apparatus according to claim 1, wherein timing of exposure start on the image carrier is controlled by the transport detection sensor.

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