JP4770409B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus such as a monochrome or color electrophotographic copying machine or printer that transfers / fixes a toner image formed on an image carrier onto a transfer material.

  In general, in an image forming apparatus, when a toner image is transferred from an image carrier to a transfer material in a transfer unit, an electric field having a polarity opposite to that of the toner is applied to the transfer material. Therefore, a charge having a polarity opposite to that of the toner remains on the transfer material after passing through the transfer portion. In order to remove this residual charge, a charge eliminating member is provided on the downstream side of the transfer portion in the transport direction of the transfer material. As described in Patent Document 1, this static elimination member is grounded or a voltage is applied.

  Further, the toner image transferred to the transfer material in the transfer unit is conveyed to the fixing unit and fixed on the transfer material. Here, if a transfer force acts on the transfer material conveyed between the transfer unit and the fixing unit from both the transfer unit and the fixing unit and the conveyance behavior becomes inappropriate, the transfer material is wrinkled and fixed. Defects are caused, and color misregistration occurs in a color image. In order to prevent this, the conveyance stability is ensured by curving the transfer material between the transfer portion and the fixing portion. As described in Patent Document 2, the amount of bending of the transfer material is detected by a sensor provided in the conveyance path, and feedback control is performed to a predetermined amount of bending based on the print mode, the material of the transfer material, and the like.

By the way, in the image forming apparatuses described in Patent Documents 1 and 2, the transfer material varies between the transfer portion and the fixing portion within the range of an appropriate curve amount even if the transfer material is a single transfer material by the curve control. Therefore, the distance between the surface of the transfer material and the charge removal member varies. As described above, if the distance between the transfer material and the charge removal member fluctuates within the proper range, (1) if the transfer material is too close to the charge removal member, the charge is excessive and the unfixed toner is hardly held on the transfer material. As a result, image degradation occurs due to toner scattering. (2) When the transfer material moves away from the charge removal member, the transfer material becomes insufficiently charged, and image deterioration due to paper jamming due to poor separation from the image carrier at the transfer portion or rubbing with the image carrier, image degradation due to abnormal discharge Will occur.
JP-A-8-320620 JP 2003-345150 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to perform an appropriate charge removal on a transfer material conveyed between a transfer part and a fixing part, and to prevent image deterioration due to excessive charge removal or insufficient charge removal. It is to provide a forming apparatus.

In order to achieve the above object, the present invention provides a transfer portion for transferring a toner image formed on an image carrier to a transfer material, and a transfer material after passing through the transfer portion and separated from the image carrier. In an image forming apparatus comprising a static elimination member for neutralizing, a static elimination capability changing means for changing the static elimination capability of the static elimination member, and a fixing unit for fixing a toner image transferred onto a transfer material, A transfer position detecting unit that is disposed between the charge eliminating member and the fixing unit and detects a transfer position of a transfer material conveyed in the vicinity of the charge eliminating member, and a transfer material detected by the transfer position detecting unit Based on the position, the distance between the transfer material being conveyed and the charge removal member is obtained, and the charge removal capability changing means is controlled so as to change the charge removal capability of the charge removal member relative to the transfer material being conveyed according to the distance. And having a control means And butterflies.

In the image forming apparatus according to the present invention, the charge removal capability of the charge removal member is changed according to the distance between the transfer material being conveyed and the charge removal member, so that the transfer material conveyed between the transfer unit and the fixing unit. However, even if the conveyance position is changed by controlling the amount of bending, appropriate static elimination can be performed. Specifically, when the transfer material approaches the charge removal member, the charge removal capability of the charge removal member is changed to a low value to prevent excessive charge removal. On the other hand, when the transfer material moves away from the charge removal member, the charge removal capability of the charge removal member is changed to a high level to prevent insufficient charge removal. As a result, image deterioration due to toner scattering due to excessive charge removal, image deterioration due to paper jamming due to poor separation from the image carrier at the transfer portion due to insufficient charge removal, image deterioration due to rubbing with the image carrier, image deterioration due to abnormal discharge Will be prevented in advance.

  The conveyance position detection means may detect a bending amount generated in the transfer material conveyed from the transfer unit to the fixing unit, and may be a contact type equipped with an actuator that contacts the transfer material, or a transfer material. Any of the non-contact types that detect light reflected from the transfer material by irradiating light may be used.

  The static elimination capability changing means may change at least one of the applied voltage value, the applied current value, and the limiting resistance value to the static elimination member. Further, when changing the charge removal capability of the charge removal member by the charge removal capability changing means, the control means further transfers the size of the transfer material, the material of the transfer material, the number of pixels per transfer material, the print mode, and the transfer portion. It is preferable to change the static elimination capacity according to at least one of the output value and the temperature / humidity condition.

  Further, the control means may control the static elimination capability changing means so that the static elimination member has a predetermined static elimination capability before the transfer material is conveyed to the detection range by the conveyance position detection means, or The static elimination capability changing means may be controlled based on the control history during the previous transfer material conveyance.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings.

(Basic mode of image forming apparatus, see FIGS. 1 and 2)
The present invention is applicable to both monochrome image formation and color image formation. An example of an image forming apparatus for forming a monochrome image is shown in FIG. 1, and an example of an image forming apparatus for forming a color image is shown in FIG.

  An image forming apparatus 1A shown in FIG. 1 has a charging charger 11, an exposure unit 12, a developing device 13, a transfer roller 14, a residual charge neutralizing lamp 15, a residual charge centered on a photosensitive drum 10 rotated in the direction of arrow A. A toner cleaner blade 16 is disposed. The configuration and operation of these image forming devices are well known and will not be described in detail. The transfer material S is conveyed in the direction of the arrow B, and the toner image formed on the photosensitive drum 10 is transferred by the electric field applied from the transfer roller 14 (transfer portion 14a), and is conveyed to the fixing device 18 to transfer the toner. Heat fixing is applied.

  An image forming apparatus 1B shown in FIG. 2 has print heads 20Y, 20M, 20C, and 20K (located around the photosensitive drum 21 and its surroundings) for forming four-color images of YMCK (yellow, magenta, cyan, and black). (Including an image forming device (not shown)) arranged at predetermined intervals, and the toner images of the respective colors formed on the respective photosensitive drums 21 are primary-transferred onto an intermediate transfer belt 22 that is rotationally driven in the direction of arrow C. (Primary transfer portion 22a) to obtain a combined color toner image. This composite color toner image is secondarily transferred to the transfer material S by the electric field applied from the transfer roller 23 facing the intermediate transfer belt 22 (secondary transfer portion 22b), and conveyed to the fixing device 24 to heat and fix the toner. Is given.

  The image carrier in the present invention corresponds to the photosensitive drum 10 in the image forming apparatus 1A shown in FIG. 1, and corresponds to the intermediate transfer belt 22 in the image forming apparatus 1B shown in FIG. The image bearing member is not limited to the photosensitive drum 10 and the intermediate transfer belt 22, and may be a belt-shaped photosensitive member or a drum-shaped intermediate transfer member.

  In addition to the tandem system shown in FIG. 2, as an image forming apparatus for forming a color image, four color toner images are sequentially formed on a single photosensitive drum, and then sequentially transferred to an intermediate transfer member to be combined. Then, a method of secondary transfer to the transfer material may be used.

(Refer 1st Example and FIGS. 3-10)
A first embodiment in which the present invention is applied to the tandem image forming apparatus 1B shown in FIG. 2 will be described.

  As shown in FIG. 3, a conveyance guide plate 31, a charge removal member 32, and an actuator 41 of a bending amount detection unit 40 are installed on the conveyance path from the secondary transfer unit 22 b to the fixing device 24, and the transfer material S is 2 It is conveyed from the next transfer portion 22 b to between the fixing rollers 25 and 26 of the fixing device 24. The transfer material S onto which the toner image has been transferred by the secondary transfer portion 22b is given a charge having a polarity opposite to that of the toner from the secondary transfer roller 23, and has a residual charge even after leaving the secondary transfer roller 23. Yes. The residual charge on the transfer material S is neutralized by the neutralization member 32 when the transfer material S passes near the neutralization member 32. As the charge removal member 32, for example, a charge removal cloth made of a nonwoven fabric woven with a fibrous conductive material, a charge removal needle made of a sawtooth conductive resin, metal, or the like is used.

  The static elimination member 32 is connected to a static elimination capability changing means 33 comprising a high voltage power source or a variable resistor. The static elimination capability of the static elimination member 32 can be appropriately changed by controlling the static elimination capability changing means 33 by the CPU 50. ing. The initial setting value of the charge removal capability is based on the material of the transfer material S, and is at least of the absolute humidity, the secondary transfer output value, the number of pixels of the transfer material (white background ratio), the print mode, and the size of the transfer material S. It is set according to one condition. Tables 1A to 1D show the initial setting values of the charge removal capability according to these conditions. In Tables 1A to 1D, “first side” and “second side” indicate the time of transferring the first side and the time of transferring the second side in the duplex printing mode.

  Further, the transfer material S is conveyed from the secondary transfer portion 22b to the fixing device 24 in a state curved to a predetermined amount so as to keep an appropriate posture when fixing is performed. At this time, the rotational peripheral speed V2 of the fixing rollers 25 and 26 is controlled with respect to the rotational peripheral speed V1 of the intermediate transfer belt 22, and the transfer material S is conveyed in a curved state within a predetermined range. That is, at the start of conveyance, V1> V2 is set, and the transfer material S starts to bend. When the curvature exceeds a predetermined value, V1 <V2 is changed to reduce the curvature of the transfer material S, and when the curvature is reduced to a predetermined value, V1> V2 is changed to increase the curvature of the transfer material S. By performing such control, the transfer material S is conveyed in a curved state within a predetermined range.

  In order to keep the amount of curvature of the transfer material S between the secondary transfer portion 22b and the fixing device 24 within a predetermined range, an actuator 41 is provided on the conveyance path between the secondary transfer portion 22b and the fixing device 24. Detection means 40 is arranged. The transfer material S is curved and comes into contact with the actuator 41, and the optical sensor 42 detects the rotation amount of the actuator 41. The CPU 50 to which this detection signal has been transferred calculates the bending amount (transfer material transfer position) and controls the rotational speed V2 of the fixing rollers 25 and 26. Such bending control prevents the transfer material S from being wrinkled, resulting in poor fixing, and the occurrence of problems such as color misregistration.

  The detection means 40 will be described in detail. As shown in FIG. 4, the actuator 41 is rotatable about the support shaft 43, and an elastic return force is applied in the direction opposite to the arrow D up to the dotted line position. It rotates in the direction of arrow D by the contact of the transfer material S, and rotates in the direction opposite to the arrow D when the transfer material S leaves. An optical sensor 42 is used as the sensing member, and the rear end shields / opens the detection unit of the optical sensor 42 based on the rotation of the actuator 41, and outputs a detection voltage corresponding to the amount of light shielding to the CPU 50. .

  As shown in FIG. 5, when the transfer material S is not conveyed, the actuator 41 is positioned at a substantially horizontal position (a), and the light blocking rate with respect to the optical sensor 42 is approximately 0%. When the transfer material S reaches the maximum bending amount, the actuator 41 rotates to a substantially vertical position (b), and the optical sensor 42 is shielded from light by almost 100%. Further, when the transfer material S has the minimum amount of bending, the actuator 41 is positioned at the substantially intermediate position (c), and the optical sensor 42 is shielded by approximately 50%. The CPU 50 determines the amount of bending based on the detection output corresponding to the light shielding rate.

  Note that the detection accuracy can be improved by arranging a plurality of optical sensors 42 with respect to the actuator 41. In addition to the optical sensor 42, various types of sensing members can be used.

  By the way, even if the amount of curvature of the transfer material S between the secondary transfer portion 22b and the fixing device 24 is within an appropriate range, the transport surface position of the transfer material S to be transported fluctuates. The positional relationship with 32 also fluctuates. That is, as illustrated in FIG. 6, when the amount of bending of the transfer material S increases, the conveyance surface becomes too close to the charge removal member 32, and when the amount of bending decreases, the conveyance surface becomes far from the charge removal member 32. If the charge removal capability of the charge removal member 32 is fixed to the initial setting value shown in Table 1, if the conveying surface is too close to the charge removal member 32, the charge removal will be excessive and unfixed toner on the transfer material S cannot be held. As a result, toner scattering occurs. Further, when the conveying surface is far from the charge removal member 32, charge removal is insufficient, and the transfer material S is attracted to the intermediate transfer belt 22 side, and image degradation due to poor separation or rubbing from the intermediate transfer belt 22 occurs. Further, excessive charge remaining on the transfer material S is discharged to the conveyance guide plate 31 (see FIG. 3) and the like, so that the toner is scattered and image deterioration occurs.

  As described above, detecting the amount of bending means calculating the distance between the transfer material S and the charge removal member 32. For example, the voltage applied to the charge removal member 32 is changed from an appropriate value when the amount of bending reaches a maximum value. When the bending amount is set to the minimum value, the voltage is set to 500V weaker than the appropriate value. This eliminates problems caused by excessive charge removal and insufficient charge removal.

  The charge removal of the transfer material S is to appropriately remove the amount of charge remaining on the transfer material S. This is to keep the charge amount to be removed, that is, the static elimination current flowing to the static elimination member 32 properly, and the current control method may be used instead of the voltage control method as described above. In this case, the current applied to the static elimination member 32 is set to be 2 μA weaker than the appropriate value when the bending amount reaches the maximum value, and is set to 2 μA higher from the appropriate value when the bending amount reaches the minimum value.

  In addition, as shown in FIG. 7, a variable resistor 34 may be interposed between the static elimination member 32 and the power source 35 to change the limiting resistance value. In this case, the limiting resistance value is set 100 MΩ higher than the appropriate value when the bending amount reaches the maximum value, and 50 MΩ lower than the appropriate value when the bending amount reaches the minimum value.

  Alternatively, as shown in FIG. 8, a variable resistor 36 may be interposed between the static elimination member 32 and the ground to change the limiting resistance value. In this case, the limiting resistance value is set 700 MΩ higher than the appropriate value when the bending amount reaches the maximum value, and 90 MΩ lower than the appropriate value when the bending amount reaches the minimum value.

  When the detection unit 40 is used as a conveyance position detection unit for the transfer material S, the leading end portion of the transfer material S is already at the charge eliminating member 32 before the leading end of the transfer material S reaches the contact area with the actuator 41. Therefore, it is necessary to control the charge removal capability from the stage where the leading edge of the transfer material S is transported to the vicinity of the charge removal member 32. Therefore, as shown in FIG. 9, during the period from when the leading end of the transfer material S reaches the static elimination member 32 to the actuator 41, the static elimination capacity setting value is the temperature as shown in Tables 1A to 1D. The humidity / secondary transfer output value, the number of pixels per transfer material, the size of the transfer material, the material of the transfer material, and the print mode are set to a fixed value. Or based on the control history at the time of previous printing (at the time of transfer material conveyance), you may obtain | require and set the average value of the static elimination capability changed variously, for example. After the leading end of the transfer material S reaches the actuator 41, the charge removal capability is sequentially changed based on the amount of bending detected by the detection means 40.

  For example, as shown in FIG. 10, when the first sheet is conveyed, the static elimination capability is initially set as shown in Tables 1A to 1D in the undetected region X1 until the leading edge of the transfer material S reaches the actuator 41. In the subsequent bending amount detection area Y1, the charge removal capability is changed according to the bending amount. During the conveyance of the second sheet, the charge removal ability is set to the average value of the charge removal ability in the first curve amount detection area Y1 in the undetected area X2.

  Note that the detection means 40 is also used for controlling the charge removal capability of the charge removal member 32 that is installed to control the amount of bending of the transfer material S. In addition to the detection means for controlling the amount of bending, a dedicated detection means for controlling static electricity removal capability may be provided.

(Refer to the second embodiment, FIG. 11)
The second embodiment uses a non-contact type detection means, and the other configurations are the same as those of the first embodiment, and redundant description is omitted. For example, as shown in FIG. 11, the non-contact type detection means is an optical sensor 45 that irradiates light toward the transfer material S and detects reflected light from the transfer material S, and transfers the light based on the amount of reflected light. The distance to the material S can be calculated. The charge removal capability of the charge removal member 32 is changed as described in the first embodiment in accordance with the calculated distance.

  In the second embodiment, the non-contact type optical sensor 45 may be provided on either the back side or the front side of the transfer material as long as it is in the vicinity of the charge removal member 32.

(Other examples)
Note that the image forming apparatus according to the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the gist thereof.

  For example, the image forming apparatus may be a copying machine, a printer, a facsimile, or a complex machine thereof, and the detailed configuration thereof is arbitrary. Moreover, the structure of a static elimination capability change means is also arbitrary. Further, it is needless to say that the numerical value of the static elimination capability shown in the above-described embodiment is an example.

1 is a schematic configuration diagram illustrating an example of a monochrome image forming apparatus to which the present invention is applicable. 1 is a schematic configuration diagram illustrating an example of a color image forming apparatus to which the present invention is applicable. It is a schematic block diagram which shows the principal part of 1st Example. It is explanatory drawing which shows operation | movement of the detection means in 1st Example. It is explanatory drawing which shows the curvature amount and detection operation | movement of a transfer material in 1st Example. It is explanatory drawing which shows the curved state of a transfer material. It is a block diagram which shows the 1st example of a static elimination capability change means. It is a block diagram which shows the 2nd example of a static elimination capability change means. It is explanatory drawing which shows the initial conveyance state of a transfer material. It is a chart figure which shows one example of control of static elimination capability. It is a schematic block diagram which shows the principal part of 2nd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1A, 1B ... Image forming apparatus 10 ... Photosensitive drum 22 ... Intermediate transfer belt 22b ... Secondary transfer part 24 ... Fixing device 32 ... Static elimination member 40 ... Detection means 41 ... Actuator 42, 45 ... Optical sensor 50 ... CPU
S ... Transfer material

Claims (9)

A transfer portion for transferring a toner image formed on the image carrier to a transfer material; a charge removal member for removing charge from the transfer material after passing through the transfer portion and separated from the image carrier; and In an image forming apparatus including a static elimination capability changing unit for changing the static elimination capability and a fixing unit for fixing a toner image transferred onto a transfer material,
A transport position detecting unit that is disposed between the charge eliminating member and the fixing unit and detects a transport position of a transfer material that is transported in the vicinity of the charge eliminating member;
Obtains a distance between the charge removing member and the transfer material being conveyed based on the previous SL transport position of the transfer material sensed by the transfer position detecting means, a charge removing ability of the charge removing member with respect to the transfer material in the conveying said distance Control means for controlling the static elimination capacity changing means so as to change in response ,
Images forming device you comprising the. The image forming apparatus according to claim 1 , wherein the conveyance position detection unit detects a bending amount generated in a transfer material conveyed from the transfer unit to the fixing unit. The transport position detecting means, an image forming apparatus according to claim 1 or claim 2, wherein the transfer material is a contact type in which an actuator in contact. The transport position detecting means, an image forming apparatus according to claim 1 or claim 2, characterized in that by irradiating light to the transfer material is a non-contact type for detecting the reflected light from the transfer material. The charge-eliminating capacity changing means, the image formation according to any one of claims 1 to 4, wherein the changing at least one of the applied voltage to the charge removing member, the applied current value or limit resistance value apparatus. When the static elimination capability change means changes the static elimination capability of the static elimination member, the control means further includes the size of the transfer material, the material of the transfer material, the number of pixels per transfer material, the print mode, and the transfer portion. output value, the image forming apparatus according to any one of claims 1 to 5, characterized in that to change the charge removal capability according to at least one of the conditions of temperature / humidity conditions. The control means controls the static elimination capability changing means so that the static elimination member has a predetermined static elimination capability before the transfer material is conveyed to a detection range by the conveyance position detection means. the image forming apparatus according to any one of claims 1 to 6. The control means controls the static elimination capacity changing means based on a control history at the time of the previous transfer material conveyance before the transfer material is conveyed to a detection range by the conveyance position detection means. the image forming apparatus according to any one of claims 1 to 6. Wherein, when changing the neutralization capacity of the charge removing member by the charge removing capacity changing means, further, of claims 1 to 5, characterized in that to change the charge removal capability depending on the size of the transfer material The image forming apparatus according to any one of the above.

Images