Image forming apparatus

Abstract

To provide an image forming apparatus that prevents discharge generated by electrification of metal that covers a flag of a sensor.SOLUTION: An image forming apparatus comprises: a conveyance belt unit 35 that conveys a recording material S; and a loop sensor 4 that detects the recording material S conveyed by the conveyance belt unit 35. The loop sensor 4 includes a sensor flag 40 that is covered by metal at its tip and rotates when the tip is pressed by the recording material S, a photointerrupter 42, and a flag part 41 that blocks a light path of the photointerrupter 42 in accordance with the rotation of the sensor flag 40. The conveyance belt unit 35 has a drive roller 44 for conveying the recording material S. The drive roller 44 is provided with an insulating member 52 to cover the whole circumference of a roller shaft 51, and controls discharge of electric charges even if the rotation of the sensor flag 40 brings the metal electrified by contact with the recording material S into contact with the insulating member 52.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to image forming apparatuses such as copiers, printers, and multifunction peripherals.

Background Art

[0002] An image forming apparatus generates a printed matter by transferring an image onto a recording material and fixing the transferred image on the recording material. Transfer of the image onto the recording material is performed at a transfer nip portion formed by two rollers. Fixing of the image on the recording material is performed at a fixing nip portion formed by two rollers in a fixing device. When the recording material is sandwiched and conveyed between the transfer nip portion and the fixing nip portion, if the conveyance speed by the fixing nip portion is faster than the conveyance speed by the transfer nip portion, the recording material will be pulled by the fixing nip portion. This causes variations in the conveyance speed during transfer by the transfer nip portion, leading to image misalignment and rubbing.

[0003] To prevent image misalignment and rubbing, the recording material is conveyed while forming a loop on the fixing nip portion side between the transfer nip portion and the fixing nip portion. The loop of the recording material is formed by variably controlling the rotation speed of the rollers in the fixing device. A sensor for detecting the recording material is provided between the transfer nip portion and the fixing nip portion. Based on the detection result of this sensor, the rotation speed of the rollers in the fixing device is variably controlled, thereby adjusting the loop amount of the recording material. Patent Document 1 discloses an image forming apparatus that detects the loop amount of the recording material and maintains the loop amount within a predetermined range based on the detection result.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As a sensor for detecting the loop amount of a recording material, a mechanical sensor having a flag that contacts the recording material may be used. When the recording material contacts the flag of the sensor, problems may occur in the conveyance of the recording material. For example, in recent years, as the printing speed has increased, the conveyance speed of the recording material has also increased. Therefore, when the recording material enters the sensor, the impact increases, and the wear of the flag increases. In order to suppress the wear of the flag and increase its durability, the flag is coated with a metal or the like.

[0006] When the flag is coated with a metal, friction occurs between the metal part of the flag and the recording material due to the conveyance of the recording material. Therefore, the metal part coating the flag becomes charged. The flag rotates due to contact with the recording material. When the charged flag with the metal part rotates and contacts or approaches another grounded metal, contact discharge or air discharge occurs. When such discharge occurs, the spike noise at that time causes malfunction of the image forming apparatus and affects peripheral components.

[0007] In view of the above problems, an object of the present invention is to provide an image forming apparatus that suppresses discharge generated by charging of a metal coating a flag of a sensor.

Means for Solving the Problem

[0008] The image forming apparatus of the present invention includes a conveyance unit that conveys a recording material, and a sensor that detects the recording material conveyed by the conveyance unit. The sensor includes a light detection unit, a rotating unit having a tip coated with a metal, and the rotating unit rotates when the tip is pushed by the recording material, and a light shielding unit that switches between a state where the light detection unit receives light and a state where the light detection unit is shielded from light by moving due to the rotation of the rotating unit. The conveyance unit includes a roller shaft and a noise suppression member formed of a high resistance member or an insulating member that covers the periphery of the roller shaft and has a higher resistance value than the roller shaft. The conveying means includes a conveying belt for conveying the recording material, and the driving force is transmitted to the conveying belt by the roller. When the rotating unit rotates when the tip is pushed by the recording material, the rotating unit and the roller are arranged such that the tip is close to or in contact with the roller. [Effect of the Invention]

[0009] According to the present invention, it is possible to suppress the discharge generated by the charging of the metal covering the sensor flag. [Brief Description of the Drawings]

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0012] (Image Forming Apparatus) FIG. 1 is a configuration diagram of the image forming apparatus according to the present embodiment. In the present embodiment, the configuration of a full-color printer will be described as the image forming apparatus 1. This image forming apparatus 1 can be used for various applications such as printers, various printing machines, copiers, facsimile machines, and multifunction machines. Note that the image forming apparatus 1 is not limited to full-color, and may be monochrome or monocolor.

[0013] The image forming apparatus 1 includes an image forming device M that forms an image (toner image) on a recording material S, and a fixing device F that fixes the image (toner image) on the recording material S. The fixing device F heats and melts the toner image formed on the recording material S to fix it. The recording material S is, for example, paper such as plain paper, thick paper, rough paper, embossed paper, coated paper, glossy paper, photographic paper, plastic film, cloth, etc. The image forming apparatus 1 incorporates a controller C. In the present embodiment, the controller C is incorporated in the image forming device M. The controller C controls the overall operation of the image forming apparatus 1 to perform image formation on the recording material S.

[0014] The configuration of the image forming apparatus M will be described. The image forming apparatus M includes a plurality of image forming units PY, PM, PC, and PK for forming images of yellow, magenta, cyan, and black colors. The image forming units PY, PM, PC, and PK are arranged along the circumferential direction of the intermediate transfer belt 20. The image forming units PY, PM, PC, and PK have substantially the same configuration except that the color of the toner used is different from yellow, magenta, cyan, and black. Hereinafter, as a representative, the configuration of the black image forming unit PK will be described, and the description of the configurations of the other image forming units PY, PM, and PC will be omitted. Therefore, in FIG. 1, only the components of the image forming unit PK are labeled.

[0015] The image forming unit PK includes a photosensitive drum 10, a charger 11, an exposure unit 3, a developing device 12, a cleaner unit 13, and a primary transfer roller 14. The photosensitive drum 10 is a drum-shaped photoreceptor having a photosensitive layer on its surface. During image formation, the photosensitive drum 10 rotates about the drum axis. The surface of the rotating photosensitive drum 10 is uniformly charged by the charger 11. The exposure unit 3 scans the surface of the charged photosensitive drum 10 with modulated laser light based on image data representing the image to be formed. By scanning with the laser light, an electrostatic latent image is formed on the surface of the photosensitive drum 10.

[0016] The developing device 12 develops the electrostatic latent image formed on the photosensitive drum 10 by attaching a developer (toner) thereto, and forms a toner image on the photosensitive drum 10. A black toner image is formed on the photosensitive drum 10 of the image forming unit PK. The primary transfer roller 14 is disposed at a position facing the photosensitive drum 10 with the intermediate transfer belt 20 interposed therebetween. By applying a primary transfer voltage to the primary transfer roller 14, the black toner image formed on the photosensitive drum 10 is primarily transferred onto the intermediate transfer belt 20. The toner remaining on the photosensitive drum 10 after primary transfer is recovered by the cleaner unit 13.

[0017] Similarly, a yellow toner image is transferred from the photosensitive drum of the image forming unit PY onto the intermediate transfer belt 20. A magenta toner image is transferred from the photosensitive drum of the image forming unit PM onto the intermediate transfer belt 20. A cyan toner image is transferred from the photosensitive drum of the image forming unit PC onto the intermediate transfer belt 20. The intermediate transfer belt 20 is rotating so as to move in the direction from the image forming unit PY to the image forming unit PM. Therefore, the primary transfer is performed in the order of the image forming unit PY, the image forming unit PM, the image forming unit PC, and the image forming unit PK. The toner images of yellow, magenta, cyan, and black are transferred so as to overlap. As a result, the intermediate transfer belt 20 will carry a full-color toner image.

[0018] The intermediate transfer belt 20 is stretched by the secondary transfer inner roller 22 and the two transfer stretching rollers 21a and 21b. A secondary transfer outer roller 23 is provided at a position facing the intermediate transfer belt 20 with the secondary transfer inner roller 22 interposed therebetween. The two rollers, the secondary transfer inner roller 22 and the secondary transfer outer roller 23, form a secondary transfer nip portion N1 for secondarily transferring the toner image on the intermediate transfer belt 20 onto the recording material S. By rotating, the intermediate transfer belt 20 conveys the full-color toner image it carries to the secondary transfer nip portion N1. A recovery cleaner 24 is provided between the secondary transfer inner roller 22 and the transfer stretching roller 21a to recover the toner remaining on the intermediate transfer belt 20 after the secondary transfer.

[0019] Below the intermediate transfer belt 20, a storage 30 for storing the recording material S is provided. In FIG. 1, two storages 30 are provided, but the number of storages 30 may be any number. Also, the recording materials S stored in each storage 30 may be of the same type or different types. A separation belt 31 and paper feed rollers 320 and 321 are provided to feed the recording material S stored in the storage 30. By the separation belt 31 and the paper feed rollers 320 and 321, the recording material S is separated one by one from the storage 30 and fed into the conveyance path.

[0020] On the conveyance path, conveyance rollers 33 and registration rollers 340, 341, 342, 343 are arranged. The fed recording material S is conveyed by the conveyance roller 33 to the registration rollers 340, 341, 342, 343. The registration rollers 340, 341, 342, 343 convey the recording material S while correcting the skew of the recording material S with respect to the conveyance direction.

[0021] The registration roller 343 conveys the recording material S to the secondary transfer nip portion N1 in accordance with the timing at which the intermediate transfer belt 20 conveys the toner image to the secondary transfer nip portion N1. The secondary transfer nip portion N1 sandwiches and conveys the intermediate transfer belt 20 and the recording material S. In the secondary transfer nip portion N1, a ground voltage is applied to the secondary transfer inner roller 22, and a secondary transfer voltage is applied to the secondary transfer outer roller 23, so that the toner image is secondarily transferred from the intermediate transfer belt 20 to the recording material S during the sandwiching conveyance. On the downstream side in the conveyance direction of the recording material S with respect to the secondary transfer nip portion N1, conveyance belt units 35, 36 are arranged. The recording material S onto which the toner image has been transferred is air-adsorbed to the conveyance belt by the conveyance belt units 35, 36 and conveyed to the fixing device F.

[0022] The fixing device F includes a fixing unit 211. The fixing unit 211 includes a heating belt 213 and a fixing pressure roller 216. The heating belt 213 is stretched by a heating roller 212, a fixing tension roller 214, and a fixing roller 215. The heating roller 212 incorporates a heating unit 256. When the heating roller 212 is heated by the heating unit 256, heat is conducted to the heating belt 213. The two rollers of the fixing roller 215 and the fixing pressure roller 216 are arranged opposite to each other to form a fixing nip portion N2. The recording material S is sandwiched and conveyed in the fixing nip portion N2, so that the toner image is heated, melted, and further pressurized to fix the image.

[0023] In the case of single-sided printing or when image formation on both sides is completed in double-sided printing, after the recording material S passes through the fixing device 211, it is discharged outside the machine by the conveying rollers 230a, 230b, and 230c. When image formation on one side is completed in double-sided printing, after the recording material S passes through the fixing device 211, it is conveyed to the reversing path where the reversing rollers 231a, 231b, and 231c are provided. After the recording material S is conveyed to the reversing roller 231c, the conveying direction is reversed, and it is conveyed to the image forming device M by the duplex rollers 232a and 232b. The recording material S conveyed to the image forming device M by the duplex rollers 232a and 232b is conveyed to the duplex path where the conveying rollers 370, 371, 372, 373, and 374 are provided. The recording material S is conveyed to the conveying roller 33 again via the duplex path. Thereafter, an image is formed on the other side of the recording material S by the same process as when forming an image on one side.

[0024] When the recording material S is conveyed from the image forming device M to the fixing device F, there may be a difference in the conveying speed between the secondary transfer nip portion N1 and the fixing nip portion N2. In this case, the recording material S cannot be conveyed in an appropriate state. For example, when the conveying speed by the fixing nip portion N2 is faster than the conveying speed by the secondary transfer nip portion N1, the recording material S is pulled by the fixing nip portion N2. This causes fluctuations in the conveying speed during transfer by the secondary transfer nip portion N1, resulting in misalignment and rubbing of the image formed on the recording material S.

[0025] Therefore, a loop is formed in the recording material S between the secondary transfer nip portion N1 and the fixing nip portion N2 so that no pulling occurs between the secondary transfer nip portion N1 and the fixing nip portion N2. When forming the loop, the loop amount is adjusted. The conveying belt unit 35 is provided with a sensor flag 40 for detecting the recording material S, and the loop amount is adjusted by the controller C based on the detection result by the sensor flag 40.

[0026] (Loop Control) The conveyance speed of the recording material S sandwiched and conveyed by the roller pair (fixing roller 215 and fixing pressure roller 216) forming the fixing nip portion N2 varies depending on the frictional force between the heating belt 213 and the recording material S and the type of the recording material S (surface property, thickness). Thus, the conveyance speed of the recording material S by the fixing nip portion N2 has variable factors. Therefore, it is difficult to match the conveyance speed of the recording material S between the secondary transfer nip portion N1 and the fixing nip portion N2.

[0027] Due to the difference in the conveyance speed of the recording material S between the secondary transfer nip portion N1 and the fixing nip portion N2, loops and tensions occur in the recording material S. The tension of the recording material S causes image misregistration. Image misregistration due to the tension of the recording material S is a major problem in the in-line type image forming apparatus M. Therefore, the controller C uses a sensor (loop sensor) to detect the loop state of the recording material S and adjusts the conveyance speed of the fixing nip portion N2 based on the detection result.

[0028] FIG. 2 is an explanatory diagram of loop control of the recording material S between the secondary transfer nip portion N1 and the fixing nip portion N2. A loop sensor 4 for detecting a loop of the recording material S is provided between the secondary transfer nip portion N1 and the fixing nip portion N2. In the present embodiment, the loop sensor 4 is provided in the conveyance belt unit 35. The loop sensor 4 includes a sensor flag 40, a flag portion 41, and a photo interrupter 42. The sensor flag 40 and the flag portion 41 are configured to rotate about a shaft 43.

[0029] FIG. 2(a) shows a state before the recording material S is conveyed between the secondary transfer nip portion N1 and the fixing nip portion N2. The photo interrupter 42 is provided at an end portion of the conveyance belt unit 35 on the conveyance belt unit 36 side.

[0030] Figure 2(b) shows a state where the recording material S is being conveyed between the secondary transfer nip portion N1 and the fixing nip portion N2. The sensor flag 40 rotates about the shaft 43 by being pushed by the recording material S. Due to the rotation of the sensor flag 40, the flag portion 41 coaxial with the sensor flag 40 rotates and blocks the light of the photointerrupter 42. When the photointerrupter 42 is blocked from light, the conveyance of the recording material S is detected.

[0031] Figure 2(c) shows a state where a loop is formed in the recording material S being conveyed between the secondary transfer nip portion N1 and the fixing nip portion N2. The loop of the recording material S is formed, for example, when the fixing pressure roller 216 decelerates. When the recording material S forms a loop, the sensor flag 40 is no longer pushed by the recording material S as in Figure 2(a). Therefore, again, the photointerrupter 42 detects light without being blocked from light. When the photointerrupter 42 changes from the light-blocked state to the state of detecting light, the loop state of the recording material S is detected.

[0032] A loop sensor detection unit 45 is connected to the photointerrupter 42. The detection signal of the photointerrupter 42, which is the detection result of the loop sensor 4, is input to the loop sensor detection unit 45. The loop sensor detection unit 45 detects the loop state based on the state of the detection signal acquired from the photointerrupter 42. The loop sensor detection unit 45 transmits the detection result of the loop state to the controller C. The controller C performs speed control of the fixing pressure roller 216 so that the loop amount of the recording material S is controlled based on the detection result of the loop state of the recording material S acquired from the loop sensor detection unit 45. Note that the loop sensor detection unit 45 may be included in the controller C.

[0033] (Loop Sensor) Figure 3 is a detailed explanatory diagram of the loop sensor 4. As described above, the loop sensor 4 detects the loop amount of the recording material S between the secondary transfer nip portion N1 and the fixing nip portion N2. The loop sensor 4 has a sensor flag 40 whose tip is a contact portion with the recording material S. The sensor flag 40 has a flag portion 41 at the rear end via a shaft 43. The tip of the sensor flag 40 is coated with metal to prevent wear due to collision with the recording material S. The photointerrupter 42 has a light emitting portion and a light receiving portion, and is configured to receive the light emitted from the light emitting portion at the light receiving portion. The photointerrupter 42 outputs a detection signal whose state changes depending on whether or not the optical path from the light emitting portion to the light receiving portion is blocked by the flag portion 41.

[0034] The conveyance belt unit 35 has a conveyance belt 53 for conveying the recording material S and a drive roller 44 for transmitting a driving force to the conveyance belt 53. The drive roller 44 is rotationally driven by a drive motor (not shown). When the drive roller 44 rotates, the recording material S on the conveyance belt 53 is conveyed in the direction of arrow A.

[0035] When the sensor flag 40 is pushed by the recording material S and rotates about the shaft 43, as shown in FIG. 3(b), the flag portion 41 rotates. By rotating, the flag portion 41 blocks the optical path from the light emitting portion to the light receiving portion of the photointerrupter 42. When the optical path is blocked, the state of the detection signal output from the photointerrupter 42 changes. The detection signal is input to the loop sensor detection unit 45. The loop sensor detection unit 45 can detect that the recording material S is being conveyed by the conveyance belt unit 35 based on the change in the state of the detection signal. The loop sensor detection unit 45 transmits the detection result to the controller C.

[0036] When the controller C obtains a detection result indicating that the recording material S is being conveyed to the conveying belt unit 35, it controls the speed of the fixing nip portion N2. Specifically, the controller C reduces the conveying speed of the recording material S by the fixing nip portion N2. As a result, as illustrated in FIG. 3(c), the recording material S forms a loop. Due to the formation of the loop, the recording material S lifts off from the conveying belt 53, causing the sensor flag 40 and the flag portion 41 to rotate about the shaft 43. Due to the rotation of the flag portion 41, the optical path from the light emitting portion to the light receiving portion of the photointerrupter 42 is transmitted, so that the state of the detection signal changes. The loop sensor detection unit 45 detects the formation of the loop of the recording material S when the detection signal changes from the detection state of the recording material S to the non-detection state. The loop sensor detection unit 45 transmits the detection result to the controller C. The controller C recognizes that the loop has been formed based on the detection result obtained from the loop sensor detection unit 45.

[0037] Here, as shown in FIGS. 3(a) and 3(b), when the recording material S is conveyed by the conveying belt 53, the sensor flag 40 comes into contact with and rubs against the recording material S. The metal covering the tip of the sensor flag 40 becomes charged with static electricity due to rubbing against the recording material S. When the charged sensor flag 40 rotates due to the recording material S, the sensor flag 40 comes into contact with the roller shaft 51 for driving the driving roller 44.

[0038] The roller shaft 51 is generally made of metal so as to withstand the load for transmitting the driving force. When the charged sensor flag 40 comes into contact with the metal roller shaft 51, the charge of the sensor flag 40 is discharged, generating spike noise. In order to suppress the discharge of the sensor flag 40, an insulating member 52 is provided at the location where the roller shaft 51 and the sensor flag 40 come into contact so as to cover the entire circumference of the roller shaft 51.

[0039] When the charged sensor flag 40 rotates and approaches or contacts the insulating member 52, the insulating member 52 cuts off the electrical conduction between the charged sensor flag 40 and the roller shaft 51 which is made of metal. Therefore, the discharge of the sensor flag 40 is suppressed. Since the discharge is suppressed, spike noise does not occur. Note that the sensor flag 40 approaches the insulating member 52 to a distance of 3 [mm] or less by being pressed by the recording material S. The insulating member 52 has a central portion in the length direction of the roller shaft 51 that is thinner in thickness than the end portions in the length direction.

[0040] Also, instead of the insulating member 52, a high-resistance member having a resistance value much higher than that of the roller shaft 51 may be provided at the location where the roller shaft 51 and the sensor flag 40 come into contact so as to cover the entire circumference of the roller shaft 51. The high-resistance member has the same shape as the insulating member 52, and the sensor flag approaches or contacts it to a distance of 3 [mm] or less. The high-resistance member is, for example, a conductive resin such as polyacetal (POM).

[0041] Figure 4 is an equivalent circuit diagram of the sensor flag 40 and the high-resistance member when the high-resistance member is provided on the roller shaft 51. When the charged sensor flag 40 rotates and contacts the high-resistance member 54, the charge is discharged to the metal roller shaft 51 through the resistance of the high-resistance member 54. The roller shaft 51 is grounded, and the high-resistance member 54 has a resistance value of 10^12 [Ω] or more. The charge accumulated in the metal of the sensor flag 40 is gradually and stably discharged to the ground through the high-resistance member 54. Therefore, the generation of spike noise is limited compared to the case of directly discharging to the ground.

[0042] In this way, by providing noise suppression members such as the insulating member 52 and the high-resistance member 54 on the roller shaft 51, the discharge of the electric charge accumulated in the metal portion of the sensor flag 40 is controlled. When the noise suppression member is the insulating member 52, the discharge itself is suppressed. When the noise suppression member is the high-resistance member 54, rapid discharge is suppressed and discharge is gradually performed. By suppressing the discharge itself or performing gentle discharge in this manner, spike noise generated by rapid discharge is suppressed. As a result, it is possible to suppress malfunction of the image forming apparatus 1 caused by spike noise and the influence on peripheral components.

Claims

1. Conveying means for conveying a recording material, A sensor for detecting the recording material conveyed by the conveying means, and The sensor includes An optical detection unit, A rotating part having a tip covered with metal, and the rotating part rotates when the tip is pressed against the recording material, A light shielding part that switches between a state where the optical detection unit receives light and a state where the optical detection unit is shielded from light by moving when the rotating part rotates, The conveying means has a roller including a roller shaft and a noise suppression member that covers the periphery of the roller shaft and is formed of a high-resistance member or an insulating member having a higher resistance value than the roller shaft, The conveying means includes a conveying belt for conveying the recording material, and the roller transmits a driving force to the conveying belt, When the rotating part rotates when the tip is pressed against the recording material, the rotating part and the roller are arranged such that the tip approaches or contacts the roller, An image forming apparatus.

2. The noise suppression member is formed of the insulating member, The image forming apparatus according to claim 1.

3. The noise suppression member is formed of the high-resistance member, The image forming apparatus according to claim 1.

4. The high-resistance member has a resistance value of 10^12 [Ω] or more, The image forming apparatus according to claim 3.

5. The high-resistance member is a conductive resin, The image forming apparatus according to claim 3 or 4.

6. The rotating part approaches the noise suppression member to a distance of 3 [mm] or less by rotating, The image forming apparatus according to any one of claims 1 to 5.

7. Transfer means for transferring an image to the recording material, Fixing means for fixing the image to the recording material, and further comprising The conveying means conveys the recording material from the transfer means to the fixing means, The image forming apparatus according to any one of claims 1 to 6.

8. Image forming means for forming an image on a transfer belt, A controller, and further comprising The transfer means transfers the image to the recording material by sandwiching and conveying the transfer belt and the recording material at a first nip portion formed by two rollers, The fixing means fixes the image to the recording material by sandwiching and conveying the recording material at a second nip portion formed by two rollers, When the sensor detects the recording material, the controller is characterized by reducing the conveyance speed of the recording material by the second nip portion to form a loop in the recording material. The image forming apparatus according to claim 7.

Images