JP2006072111A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that prevents a detection member which judges a paper feed state by coming into direct contact with a transfer material from electrostatically being charged and also prevents an image defect due to a transfer material conveyance defect. <P>SOLUTION: The image forming apparatus has the detection member 21 which judges the paper feed state of the transfer material S by coming into direct contact with the transfer material S in a path of the transfer material between a transfer section 9 and a fixation section 10, the detection member 21 being characterized in that a transfer material contact part 21A coming into contact with the transfer material S and a non-contact part 21B which does not come into contact with the transfer material S are different in volume resistivity. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine that forms an image by electrophotography.

  Conventionally, as a color image forming apparatus that forms a color image at high speed, a photosensitive drum is arranged for each color of yellow (Y), magenta (M), cyan (C), and black (Bk) along a conveying belt, and conveyed. Inline that conveys transfer materials sequentially by belt and transfers images of each color sequentially, or transfers toner images of each color sequentially on an intermediate transfer belt, and finally transfers the toner images to the transfer material collectively There is a so-called method.

  A main problem in this in-line type color image forming apparatus is a color shift between colors of a color image. One of the causes of this color misregistration is the difference between the speed of the conveying belt that conveys the transfer material and the fixing speed. This is because the speed of the transfer material is governed by the fixing speed after entering the fixing, and therefore the transfer material cannot be fed at a constant speed after entering the fixing.

  Therefore, generally, as described in Patent Document 1, a loop is formed on the transfer material before the entrance of the fixing unit, and the loop amount at that time is made constant (hereinafter referred to as “loop control”). This minimizes the difference in speed between transfer and fixing.

Further, in Patent Document 2, a conveyance guide for conveying a transfer material from a transfer portion toward a nip portion of a fixing portion is disposed so that the conveyance surface is inclined upward toward the nip portion, and the transfer material protrudes downward. Image forming apparatus capable of performing subtle speed control that makes the loop amount constant by detecting the loop amount and switching the speed of the motor that drives the pressure roller of the fixing unit stepwise. Has been proposed.
JP-A-7-234604 JP 2000-344385 A

  However, each of the conventional examples described above has the following problems.

  That is, as a means for detecting the loop amount, the swingable detection member provided in the conveyance guide, that is, the movement of the flag is detected by whether or not the flag provided on the other side shields the photo interrupter. .

When the flag is composed of a member having a high resistance value such as PBT or PES (R ≧ 1 × 10 ¹³ Ω · cm), the transfer process is performed in a low temperature and low humidity environment (hereinafter referred to as “L / L environment”). When the transfer material charged in step 1 comes into contact with the flag, the flag itself is charged, an electrostatic repulsive force is generated between the flag and the transfer material, and the flag is difficult to swing. As a result, it is impossible to perform loop control that should be performed by the flag. Therefore, there has been a problem that the rotation speed of the pressure roller of the fixing unit becomes faster than the transfer speed of the transfer unit, and the pressure roller pulls the transfer material, resulting in image defects.

On the other hand, when the volume low efficiency R of the flag is composed of a member having a low to medium resistance (1 × 10 ⁶ Ω · cm ≦ R <1 × 10 ¹³ Ω · cm), in the L / L environment, When the transfer material charged in the transfer process comes into contact with the flag, the charge of the transfer material flows through the flag, or there is an image defect on the stripe called “sensor trace” that discharges to the conductive part. There was a problem that it occurred in the transfer material conveyance direction.

  SUMMARY OF THE INVENTION The present invention solves the above-described problems, and an object of the present invention is to prevent charging of a detection member that determines a sheet passing state by direct contact with a transfer material, and to prevent image defects due to transfer material conveyance failure. An image forming apparatus is provided.

The above object is achieved by the image forming apparatus according to the present invention. In summary, according to the present invention, a latent image formed on an image carrier is visualized by a developer to form a toner image, and a transfer unit that transfers the toner image to a transfer material, and a toner on the transfer material In an image forming apparatus having a fixing unit for fixing an image,
In the path of the transfer material between the transfer unit and the fixing unit, a detection member that determines a sheet passing state of the transfer material by directly contacting the transfer material,
The detection member is an image forming apparatus characterized in that a volume resistivity is different between a transfer material contact portion that contacts the transfer material and a non-contact portion that does not contact the transfer material.

  According to the image forming apparatus of the present invention, the detection member that determines the sheet passing state by directly contacting the transfer material delivered from the transfer unit is configured by a member having a different resistance, thereby charging the detection member. It is possible to prevent image defects caused by pulling from the fixing unit.

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

Example 1
FIG. 1 is a cross-sectional view showing a schematic configuration of an electrophotographic color image forming apparatus which is an embodiment of the image forming apparatus of the present invention.

(overall structure)
In this embodiment, the color image forming apparatus shown in FIG. 1 has four drum-shaped electrophotographic photosensitive members (hereinafter referred to as “photosensitive drums”) 1 (1a, 1b, 1c, 1d) as image carriers. I have. The photosensitive drum 1 rotates counterclockwise in FIG. 1, and charging means 2 (2a, 2b) that uniformly charges the surface of the photosensitive drum 1 around each photosensitive drum 1 in order according to the rotation direction. 2c, 2d), exposure means 3 (3a, 3b, 3c, 3d) for forming an electrostatic latent image on the photosensitive drum 1 by irradiating a laser beam based on image information, and attaching toner to the electrostatic latent image Developing means 4 (4a, 4b, 4c, 4d) for developing the toner image into a toner image, and a transfer member 5 (5a, 5a, transfer means for transferring the toner image on the photosensitive drum 1 to a transfer material (recording medium). 5b, 5c, 5d), cleaning means 6 (6a, 6b, 6c, 6d) for removing the post-transfer toner remaining on the surface of the photosensitive drum 1 after transfer, and the like are arranged to form an image forming means. .

  In this embodiment, the photosensitive drum 1, the charging unit 2, the developing unit 4, and the cleaning unit 6 for removing the toner are integrated into a cartridge to form a process cartridge 7 (7a, 7b, 7c, 7d). Yes.

  Further, the transfer material S fed from the feeding unit 8 is conveyed to the image forming unit by a transfer conveyance belt 9a constituting the transfer unit 9, and each color toner image is sequentially transferred by the transfer member 5 to be a color image. Is recorded, the image is fixed by the fixing means, that is, the fixing unit 10, and is discharged to the discharge unit 13 by the discharge rollers 11 and 12.

  In the case of double-sided printing, before the transfer material S is fixed by the fixing unit 10 and discharged by the discharge rollers 11 and 12, the discharge rollers 11 and 12 are reversed to be conveyed to the double-sided conveyance path 15. (Arrow A direction). The transfer material S conveyed to the double-sided conveyance path 15 passes through the oblique feeding roller 16 on the front surface of the apparatus main body, and is conveyed vertically downward to the U-turn roller 17, and an image forming unit is formed by the U-turn roller 17 and the registration roller 8 d. It is conveyed to.

  Next, the configuration of each unit will be described sequentially.

(Transfer material feeding configuration)
The feeding unit 8 includes a feeding cassette 8a, a multi feeding tray 8b that is a multi feeding device, a multi feeding unit 8c, and a registration roller 8d.

  The feeding cassette 8a stores a plurality of transfer materials S and is loaded on the inner bottom of the apparatus main body. When an image is formed from the feeding cassette 8a, the transfer material S is separated and conveyed one by one by the cassette pickup roller 8a1, and conveyed to the image forming unit by the cassette conveying roller 8a2 and the registration roller 8d.

  Next, the multi-feed tray 8b is normally stored on the front surface of the apparatus main body. However, the multi-feed tray 8b is rotated and opened from the apparatus main body during use, and a plurality of transfer materials S are set. At the time of image formation from the multi-feed tray 8b, the transfer material S is separated and conveyed one by one by the multi-pickup roller 8c1, and conveyed to the image forming unit by the multi-conveying roller 8c2 and the registration roller 8d.

  Separation and conveyance of sheets in the feeding cassette 8a and the multi-feeding unit 8c are performed via a gear drive train by a feeding motor (not shown) in the feeding unit.

(Image formation configuration)
In this embodiment, the photosensitive drum 1 (1a, 1b, 1c, 1d) as an image carrier is configured by applying an organic photoconductive layer (OPC) to the outer peripheral surface of an aluminum cylinder. Both ends of the photosensitive drum 1 are rotatably supported by flanges, and a driving force is transmitted from one driving motor (not shown) to one end in a counterclockwise direction indicated by an arrow in FIG. Driven by rotation.

  Each charging means 2 (2a, 2b, 2c, 2d) is a conductive roller formed in a roller shape. The roller abuts against the surface of the photosensitive drum 1, and a charging bias voltage is applied by a power source (not shown). By doing so, the surface of the photosensitive drum 1 is uniformly charged.

  The exposure means 3 (3a, 3b, 3c, 3d) has a polygon mirror, and this polygon mirror is irradiated with image light corresponding to an image signal from a laser diode (not shown).

  The developing means 4 (4a, 4b, 4c, and 4d) are adjacent to the toner storage portion storing the toners of black, cyan, magenta, and yellow, respectively, and are driven to rotate by a drive unit (not shown). In addition, the image forming apparatus includes a developing roller that performs development by applying a developing bias voltage from a developing bias power source (not shown).

  In addition, a transfer member that is in contact with the transfer conveyance belt 9a opposite to the four photosensitive drums 1a, 1b, 1c, and 1d is disposed inside a transfer conveyance belt 9a that constitutes a transfer unit 9 to be described later. Transfer rollers 5 (5a, 5b, 5c, 5d) are provided respectively. These transfer members 5 are connected by a transfer bias power source (not shown), and a positive charge is applied from the transfer roller 5 to the transfer material via the transfer conveyance belt 9a. The negative color toner images on the photosensitive drum 1 are sequentially transferred onto the transfer material in contact, and a color image is formed.

(Transfer material transfer configuration)
The transfer material S is conveyed from the feeding unit 8 to the image forming area by the transfer conveyance belt 9a.

  The transfer conveyance belt 9a as a transfer material carrier constituting the transfer unit 9 is stretched and supported by four rollers of a driving roller 9b and driven rollers 9c, 9d, and 9e, and all the photosensitive drums 1a, 1b, and 1c are supported. 1d. By this drive roller 9b, the transfer material S is conveyed to the transfer position by the transfer conveyance belt 9a, and the toner images on the respective photosensitive drums 1 (1a, 1b, 1c, 1d) are transferred.

  In addition, an adsorption roller 9f that holds the transfer material S together with the belt 9a and attracts the transfer material S to the transfer conveyance belt 9a is disposed at the most upstream position of the transfer conveyance belt 9a. When the transfer material S is conveyed, an electric field is formed between the transfer roller S and the transfer material S by applying a voltage to the suction roller 9f so as to form an electric field with the opposed grounded roller 9c. Polarization is generated to generate an electrostatic attracting force on both.

(Fixing configuration)
The fixing unit 10 serving as fixing means applies heat and pressure to the toner image formed on the transfer material S and fixes the toner image.

  The fixing unit 10 includes a cylindrical fixing belt 10a having an electromagnetic induction heat generating layer, and is guided by a belt guide member 10c having a built-in magnetic field generating unit including an exciting coil and a T-shaped magnetic core. The elastic pressure roller 10b is disposed to face the belt guide member 10c with a predetermined pressure contact force with the fixing belt 10a interposed therebetween, and forms a fixing nip portion N having a predetermined width.

  The pressure roller 10b is rotationally driven by a driving means (not shown), and the cylindrical fixing belt 10a rotates accordingly, and electromagnetic induction heat generation of the fixing belt 10a is performed by feeding power from an excitation circuit (not shown) to the excitation coil. .

  In a state where the fixing nip portion N rises to a predetermined temperature and is temperature-controlled, the transfer material S on which the unfixed toner image conveyed from the transfer portion 9 is formed becomes the fixing belt 10a and the pressure roller 10b of the fixing nip portion N. The image surface faces downward, that is, faces the fixing belt surface, and the fixing nip portion N holds the fixing nip portion N together with the fixing belt 10a with the image surface closely contacting the outer surface of the fixing belt 10a. It will be done.

  In the process in which the transfer material S is nipped and conveyed together with the fixing belt 10a through the fixing nip N, the unfixed toner image on the transfer material S is heated and fixed by being heated by electromagnetic induction heat of the fixing belt 10a.

(Loop formation configuration)
Next, a configuration in which the fixing unit 10 forms a loop on the transfer material S will be described.

  When fixing the image on the transfer material S, the transfer material clamping force in the fixing nip N is stronger than the clamping force of the transfer unit 9, and therefore if the conveyance speed at the fixing unit 10 and the conveyance speed at the transfer unit 9 are different, The transfer material S is conveyed at the fixing speed.

  Therefore, as shown in FIG. 2, the image forming apparatus according to the present exemplary embodiment is provided with a loop detection unit 20 that detects the loop amount of the transfer material S between the fixing unit 10 and the transfer unit 9. The loop detection means 20 includes a detection member, that is, a flag 21, the flag front end is in contact with the transfer material S and is rotatable, and the flag rear end is an optical sensor (photo interrupter). Whether or not the loop amount of the transfer material S exceeds a certain level is detected based on whether or not the configured detection sensor 40 is shielded from light.

  On the other hand, the driving speed of the elastic pressure roller 10b can be switched in two steps by the speed switching means, and the switching speed of the transfer material S is switched by switching the driving speed according to the detection result of the detection sensor 22. The loop amount is made constant.

  Next, the configuration of the loop detection means 20 that characterizes the present invention will be described in more detail with reference to FIGS.

As understood with reference also to FIG. 2, the transfer material S on which the unfixed toner image conveyed from the image forming unit is formed in the moving path of the transfer material S between the transfer unit 9 and the fixing unit 10. Is separated from the conveying belt 9a, and a transfer material conveying guide 30 is provided to guide the toner to the fixing nip N between the fixing belt 10a and the pressure roller 10b. According to the present embodiment, the loop detection means 20 is installed in the transfer material conveyance guide 30. The transfer material conveyance guide 30 is usually made of PBT or PET.

  The transfer material conveyance guide 30 has a long and narrow base 31 that extends in the width direction of the transfer material S and has a triangular cross section in this embodiment. Further, the surface of the substrate 31 facing the transfer material S slightly protrudes from the surface of the substrate 31 toward the transfer material moving path, and is formed in a plurality of convex shapes that guide the transfer material S along the moving path. Guide ribs 32 are formed. The guide ribs 32 are arranged at predetermined intervals in the longitudinal direction of the base 31, that is, in the width direction of the transfer material S.

  According to the present embodiment, an opening 33 is formed in the central portion of the base 31, and the loop detection means 20 is disposed in the opening 33. For this reason, the interval between the guide ribs 32 located at the center is made wider than the interval between the guide ribs 32 at other locations.

  The loop detection unit 20 includes a flag that detects the loop amount of the transfer material S, that is, a detection member 21. In this embodiment, the detection member 21 is disposed on both sides of the first detection member 21 </ b> A that contacts the transfer material S and detects the loop amount of the transfer material S, and the first detection member 21 </ b> A. Has a second detection member 21B that does not contact. The tip 21a of the first detection member 21A that contacts the transfer material S has a tapered shape, that is, a wedge shape. Thereby, the contact area with the transfer material S can be minimized. In this embodiment, the tip shape does not necessarily need to be wedge-shaped, but in particular, in an image forming apparatus in which toner may adhere to the flag, it is preferable that the tip shape is wedge-shaped because toner adhesion can be suppressed.

  The first detection member 21A and the second detection member 21B are fixed to a support shaft 22 disposed in the opening 33, and both ends of the support shaft 22 are rotatably supported by the base 31. .

  In this embodiment, the first detection member 21A is urged by a spring member (not shown) counterclockwise around the support shaft 22 in FIG. The stopper pin 34 restricts counterclockwise rotation. On the other hand, the first detection member 21A is rotated in the clockwise direction against the spring force, as indicated by the alternate long and short dash line in FIG.

  Further, an action flag, that is, an action piece 23 is integrally attached to the rear end portion 21b of the first detection member 21A, and the first detection member 21 swings about the support shaft 22 as a center. The action piece 23 also swings, and the detection sensor (photo interrupter) 40 is operated.

  The action piece 23 is integrally formed of the same material as that of the first detection member 21A.

  According to the present embodiment, the second detection member 21B also swings about the support shaft 22 by the swing of the first detection member 21A.

  A feature of the present embodiment is that the first detection member 21A that is in direct contact with the transfer material S and the second detection member 21B that is not in contact with the transfer material S have different resistance values.

That is, the volume resistivity (RA) of the first detection member 21A that is in direct contact with the transfer material S of the detection member 21 is RA ≧ 1 × 10 ¹³ Ω · cm, and the second detection that does not contact the transfer material S. The volume resistivity (RB) of the member 21B is set to 1 × 10 ⁶ ≦ RB <1 × 10 ¹³ Ω · cm.

In the present embodiment, the first detection member 21A that is in direct contact with the transfer material S is manufactured using a hyperlight 8200SER (volume resistivity RA: 8.0 × 10 ¹³ Ω · cm, manufactured by Kaneka) that has high resistance. did. On the other hand, the second detection member 21B that does not come into contact with the transfer material S was manufactured using Novaduran 5010GN3A6-1 (volume resistivity RB: 3.1 × 10 ¹¹ Ω · cm, manufactured by Mitsubishi Engineering Plastics), which is a medium resistance.

  In addition, referring to FIGS. 5A, 5B, and 5C, specific main dimensions of the detection member 21 used in the present embodiment are as follows.

  That is, the first detection member 21A has a length L1 of 18 mm, a height H1 of 7 mm, a width W1 of 3 mm, a length La of the tip 21a is 4 mm, and a tip height Ha of 2 mm. It was. The tip 21a has a tapered shape. On the other hand, the second detection member 21B had a length L2 of 12 mm, a height H2 of 3 mm, and a width W2 of 6 mm. The support shaft 22 has a diameter of 3 mm and a length L of 56 mm, and is made of the same member as the detection member 21A.

  Table 1 shows the relationship between the detection member 21, that is, the resistance value of the flag and the image defect. The study environment is an L / L environment (temperature 15 ° C., humidity 10%).

  Here, the member resistance value is a value measured by a high resistance meter. Regarding the surface potential when passing through the transfer material, the flag surface potential after continuous 20 sheets are measured with a surface potential meter. Further, the number of flag swings is the average number of flag swings per page in continuous 20 sheets.

When both the transfer material contact portion (first detection member) 21A and the transfer material non-contact portion (second detection member) 21B of the detection member 21 have high resistance (that is, 1 × 10 ¹³ Ω · cm or more). The surface potential when passing through the transfer material shows a value of −3000 V or more for both the transfer material contact portion 21A and the transfer material non-contact portion 21B. This indicates that the detection member 21 itself is charged by contact of the charged transfer material S with the detection member 21.

  Further, the number of swings of the detection member 21 is about 5 times per page, an electrostatic repulsive force is generated between the detection member and the transfer material, and the loop control that the detection member 21 should originally perform cannot be performed normally. It is shown that. As a result, the rotation speed of the pressure roller 10b is faster than the transfer section conveyance speed, the transfer material S is pulled, and an image defect occurs.

Next, both the transfer material contact portion (first detection member) 21A and the transfer material non-contact portion (second detection member) 21B of the detection member 21 have medium resistance (that is, 1 × 10 ⁶ Ω · cm or more, 1 × 10 ¹³ Ω · cm), the flag surface potential when passing through the transfer material is about −1500 V, and the number of swings of the detection member 21 is an average of 20 times per page. Indicates that it is working. However, on the other hand, since the resistance value of the transfer material contact portion 21A is low, the charge on the transfer material flows into the detection member 21 and an image defect due to the sensor trace occurs.

In contrast, the transfer material contact portion 21A has a high resistance (ie, 1 × 10 ¹³ Ω · cm or more), and the transfer material non-contact portion 21B has a medium resistance (ie, 1 × 10 ⁶ Ω · cm or more, 1 × (Less than 10 ¹³ Ω · cm), the surface potential at the time of passing through the transfer material is not less than −3000 V at the transfer material contact portion 21A, but the transfer material non-contact portion 21B is about −1500 V. It can be seen that charging is suppressed. As a result, it was confirmed that the flag swings normally operates at about 20 times, and that there is no image defect due to pulling and no image defect due to sensor marks.

  As described above, the detection member 21 has a two-body configuration with the transfer material contact portion 21A having a high resistance and the transfer material non-contact portion 21B having a medium resistance, thereby preventing image defects due to sensor marks and at the same time. Image defects due to pulling can be prevented.

Example 2
Next, another embodiment of the image forming apparatus of the present invention will be described.

  Also in this embodiment, since the overall configuration of the image forming apparatus is the same as that of the first embodiment, the description of the image forming apparatus is omitted, and the loop detection unit 20 that is a feature of this embodiment will be described. .

  Referring to FIG. 6, the loop detection means 20 in this embodiment includes a detection member 21, as in the first embodiment, and is swingably attached to a base 31 of a transfer material conveyance guide 30 by a support shaft 22. Yes.

  However, in the present embodiment, the detection member 21 includes a first detection member 21A that is a tapered region including a front end portion 21a that contacts the transfer material S, and a rear end portion 1b that does not contact the transfer material S. The second detection member 21B is a remaining detection area other than the front end 21a. The first detection member 21A is in direct contact with the transfer material S, and the second detection member 21B is not in contact with the transfer material S. The resistance values are different.

That is, the volume resistivity (RA) of the first detection member 21A that is in direct contact with the transfer material S of the detection member 21 is RA ≧ 1 × 10 ¹³ Ω · cm, and the second detection that does not contact the transfer material S. The volume resistivity (RB) of the member 21B is set to 1 × 10 ⁶ ≦ RB <1 × 10 ¹³ Ω · cm.

Also in the present embodiment, the first detection member 21A that is in direct contact with the transfer material S uses a hyperlight 8200SER (volume resistivity RA: 8.0 × 10 ¹³ Ω · cm · Kaneka) that is a high resistance. Produced. On the other hand, the second detection member 21B that does not come into contact with the transfer material S was manufactured using Novaduran 5010GN3A6-1 (volume resistivity RB: 3.1 × 10 ¹¹ Ω · cm, manufactured by Mitsubishi Engineering Plastics), which is a medium resistance.

  The detection member 21 of the second embodiment is different from the detection member 21 of the first embodiment in that a contact portion 21A and a non-contact portion 21B of the transfer material S are provided in one flag shape.

  6A and 6B, specific main dimensions of the detection member 21 used in this example are as follows.

  In other words, the detection member 21 has a length L1 of 18 mm, a height H1 of 7 mm, a width W1 of 3 mm, and a first detection member 21A having a tapered end portion with a length La of 4 mm. The Ha was 2 mm. The remaining region formed integrally with the first detection member 21A was the second detection member 21B. The support shaft 22 has a diameter of 3 mm and a length L of 56 mm, and is made of the same member as the detection member 21B.

  Table 2 shows the correlation between the detection member 21, that is, the flag resistance value and the image defect. Since the method for measuring the member resistance value, the surface potential, and the number of oscillations is the same as in the case of the first embodiment, the description thereof is omitted.

Both the transfer material contact portion (that is, the first detection member) 21A and the transfer material non-contact portion (that is, the second detection member 21B) of the detection member 21 have high resistance (that is, 1 × 10 ¹³ Ω · cm or more). The surface potential when passing through the transfer material showed a value of −3000 V or more for both the transfer material contact portion 21A and the transfer material non-contact portion 21B. This indicates that the detection member itself is charged when the charged transfer material S contacts the detection member 21. Further, the number of times the flag is swung is about 5 times per page, an electrostatic repulsive force is generated between the detection member and the transfer material, and the loop control that the detection member 21 should originally perform cannot be performed normally. Show. As a result, the rotation speed of the pressure roller is faster than the transfer section conveyance speed, and the transfer material is pulled, resulting in an image defect.

Next, when both the transfer material contact portion 21A and the transfer material non-contact portion 21B have a medium resistance (that is, 1 × 10 ⁶ Ω · cm or more and less than 1 × 10 ¹³ Ω · cm), the flag surface potential when passing through the transfer material Are about −1500 V, and the number of swings of the detection member 21 is 20 on average per page, indicating that the detection member 21 is operating normally. However, on the other hand, since the resistance value of the transfer material contact portion 21A is low, the charge on the transfer material flows into the detection member 21, and an image defect due to the sensor trace occurs.

On the other hand, the transfer material contact portion 21A has a high resistance (ie, 1 × 10 ¹³ Ω · cm or more), and the transfer material non-contact portion 21B has a medium resistance (ie, 1 × 10 ⁶ Ω · cm or more, 1 × 10 ¹³ Ω). (Less than cm), the surface potential when passing through the transfer material is not less than −3000 V at the transfer material contact portion 21A, but the transfer material non-contact portion 21B is about −1500 V, and the charging of the entire detection member 21 is suppressed. You can see that As a result, it was confirmed that the flag swings normally operates at about 20 times, and that there is no image defect due to pulling and no image defect due to sensor marks.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention. It is explanatory drawing of a loop detection means. It is sectional drawing which shows the structure of one Example of a loop detection means. It is a schematic front view of the loop detection means seen from the arrow A direction of FIG. It is a figure for demonstrating the structure of one Example of a detection member. It is a figure for demonstrating the structure of the other Example of a detection member.

Explanation of symbols

N fixing nip S transfer material 1 photosensitive drum (image carrier)
2 Charging means 3 Exposure means 4 Developing means 5 Transfer roller (transfer means)
6 Cleaning means 7 Process cartridge 9 Transfer part 9a Transfer conveyance belt 10 Fixing part 10a Fixing belt 10b Elastic pressure roller 10c Belt guide member 20 Loop detection means 21 Detection member 21A First detection member 21B Second detection member 22 Detection member Support shaft 23 Action piece (action flag)
30 Transfer Material Transport Guide 31 Base 32 Rib 33 Opening

Claims (8)

The electrostatic latent image formed on the image carrier is visualized with a developer to form a toner image, and a transfer unit that transfers the toner image to a transfer material and a fixing unit that fixes the toner image on the transfer material are provided. In an image forming apparatus having
In the path of the transfer material between the transfer unit and the fixing unit, a detection member that determines a sheet passing state of the transfer material by directly contacting the transfer material,
The image forming apparatus according to claim 1, wherein the detection member has a different volume resistivity between a transfer material contact portion that contacts the transfer material and a non-contact portion that does not contact the transfer material. The volume resistivity (RA) of the transfer material contact portion of the detection member is RA ≧ 1 × 10 ¹³ Ω · cm, and the volume resistivity (RB) of the transfer material non-contact portion is 1 × 10 ⁶ ≦ The image forming apparatus according to claim 1, wherein RB <1 × 10 ¹³ Ω · cm.   The detection member detects a loop amount of the transfer material in a path of the transfer material between the transfer unit and the fixing unit, and keeps the loop amount of the transfer material constant. Or the image forming apparatus according to 2; The detection member includes a first detection member that constitutes a transfer material contact portion that contacts the transfer material, and a second detection member that constitutes a non-contact portion that does not contact the transfer material,
The image forming apparatus according to claim 3, wherein the first detection member and the second detection member are attached to a support shaft and swing integrally.   The image forming apparatus according to claim 4, wherein the second detection member is formed as a separate member from the first detection member, and is disposed on both sides of the first detection member. .   The image forming apparatus according to claim 4, wherein the second detection member is formed as one member with the first detection member.   The image forming apparatus according to claim 4, wherein the first detection member has a tapered shape at a portion that contacts the transfer material. A transfer material conveyance guide for guiding the transfer material from the transfer unit to the fixing unit is provided in a path of the transfer material between the transfer unit and the fixing unit,
The image forming apparatus according to claim 1, wherein the detection member is installed in the transfer material conveyance guide.

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