JP2015210304A - Image forming apparatus and separation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus or the like, configured to prevent an image carrier or a fixing roller from being damaged.SOLUTION: An image forming apparatus includes: an image carrier on which a toner image to be transferred to a printing medium is developed; a separation mechanism having a separation pawl for separating a printing medium sticking to the image carrier from the image carrier, applying a force to the separation pawl to keep the separation pawl in contact with the image carrier, and changing the force to be applied to the separation pawl to change contact pressure between the separation pawl and the image carrier; and a control section which controls the separation mechanism, to change the contact pressure between the separation pawl and the image carrier during transfer of the toner image.

Description

  Embodiments described herein relate generally to an image forming apparatus and a peeling method.

  During printing, the print medium may be attracted to the image carrier or the fixing roller. When the printing operation continues with the print medium adsorbed, the image forming apparatus generates JAM (paper jam). In order to prevent the occurrence of JAM, an image forming apparatus generally includes a peeling claw for peeling a print medium from an image carrier or a fixing roller.

JP 2001-92265 A

  In general, the peeling claw contacts or separates from the image carrier or the fixing roller in accordance with the printing operation of the image forming apparatus. At this time, the peeling claw may pierce the surface of the image carrier or the fixing roller with the momentum at the time of contact. In this case, the surface of the image carrier or the fixing roller is scratched, and thereafter a defect occurs in the printed image.

  An object of the present invention is to provide an image forming apparatus and a peeling method in which an image carrier or a fixing roller is hardly damaged.

  In order to achieve the above object, an image forming apparatus according to an embodiment includes an image carrier on which a toner image transferred to a print medium is developed, and a peeling claw for peeling the print medium attached to the image carrier from the image carrier. A peeling mechanism that applies a force to the peeling claw so that the peeling claw is always in contact with the image carrier, and changes the contact pressure between the peeling claw and the image carrier by changing the force applied to the peeling claw; And a controller that controls the peeling mechanism to change the contact pressure between the peeling claw and the image carrier during the transfer of the toner image.

1 is a block diagram of an image forming apparatus according to an embodiment. It is a figure which shows the structure of a printing part. It is a figure which shows a mode that a sheet | seat is conveyed without sticking to a photoconductor roller. It is a figure which shows a mode that the sheet affixed on the photoreceptor roller. It is a figure which shows the structure of a peeling mechanism. It is a figure which shows a mode that the peeling nail | claw was pressed with the strong pressure against the photoconductor roller. It is a figure which shows a mode that the peeling nail | claw was pressed with the weak pressure to the photoconductor roller. It is an enlarged view of a nail holding mechanism and its periphery. It is a figure which shows the peeling nail | claw whose front-end | tip part is sharp in V-shaped ship bottom shape. It is a figure which shows the peeling claw whose front-end | tip part is a semicircular flat plate shape. It is a figure which shows a mode that the residual toner accumulated on the front-end | tip part of a peeling nail | claw. It is a figure which shows a mode that a residual toner advances so that the front-end | tip part of a peeling nail may be avoided. It is a figure which shows the result of having measured the relationship between contact pressure F1 and contact pressure F2. 6 is a flowchart illustrating print processing according to the embodiment. It is a figure which shows a mode that the contact pressure of a peeling nail | claw and a photosensitive drum changes to a strong pressure. It is a figure which shows a mode that the contact pressure of a peeling nail | claw and a photosensitive drum changes to a weak pressure. It is a figure which shows a mode that a sheet | seat peels from a photoconductor drum. It is a timing chart which showed the timing which a control part changes the state of a solenoid. FIG. 4 is a diagram illustrating a state where a sheet passes through a contact portion between a peeling claw and a photosensitive drum without being peeled from the photosensitive drum. It is a figure which shows the structure of the printing part of a tandem system. It is a figure which shows a mode that the peeling mechanism was installed in the fixing roller.

  Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In the drawings, the same or equivalent parts are denoted by the same reference numerals.

  The image forming apparatus according to the embodiment is an apparatus having a printing function such as a copying machine, a printer, or a FAX. As illustrated in FIG. 1, the image forming apparatus 1 includes an image acquisition unit 100, an image processing unit 200, a paper feed unit 300, a printing unit 400, a paper discharge unit 500, and a control unit 600.

  The image acquisition unit 100 is an apparatus that acquires image data from the outside. The image acquisition unit 100 is configured by, for example, a scanner that reads an image from a paper medium. When acquiring the image data, the image acquisition unit 100 transmits the acquired image data to the image processing unit 200.

  The image processing unit 200 includes a processing device such as a processor. The image processing unit 200 converts the image data acquired from the image acquisition unit 100 into a data format that can be printed by the printing unit 400.

  The sheet feeding unit 300 includes a sheet feeding tray, a pickup roller that takes out a sheet S as a printing medium from the sheet feeding tray, and the like. The sheet feeding unit 300 supplies the sheet S to the printing unit 400 based on the control of the control unit 600.

  The printing unit 400 is a direct transfer type printing apparatus that transfers a toner image formed on the surface of the photosensitive drum to the sheet S. FIG. 2 is a diagram illustrating an example of the configuration of the printing unit 400. As shown in FIG. 2, the printing unit 400 includes a photosensitive drum 410, a charging charger 420, an exposure unit 430, a developing device 440, a power supply roller 450, a conveyance belt 460, a fixing roller 470, and a cleaning device. 480 and a peeling mechanism 490.

  The photosensitive drum 410 is an image carrier on which a toner image is developed on the peripheral surface. The photoconductor drum 410 is composed of, for example, an organic photoconductor (OPC) drum. The photosensitive drum 410 forms a nip with the conveyance belt 460 suspended between the power feeding roller 450 and the driven roller 452. The photosensitive drum 410 rotates in accordance with the rotation speed of the driving roller 451.

  The charging charger 420 is a charger that charges the photosensitive drum 410. The charging charger 420 is composed of, for example, a charging roller. The charging charger 420 rotates in contact with the circumferential surface of the photosensitive drum 410 to uniformly charge the circumferential surface of the photosensitive drum 410.

  The exposure unit 430 is an apparatus that forms an electrostatic latent image on the circumferential surface of the photosensitive drum 410. The exposure unit 430 is configured by an irradiation device that irradiates the photosensitive drum 410 with laser light or LED (Light Emitting Diode) light. The exposure unit 430 irradiates the charged surface of the photosensitive drum 410 with laser light or LED light based on the image data processed by the image processing unit 200. When the exposure unit 430 emits light, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 410. In the following description, the position where the exposure unit 430 emits light is referred to as an exposure irradiation position P1.

  The developing device 440 is a device that forms a toner image on the peripheral surface of the photosensitive drum 410. The developing device 440 is composed of, for example, a mag roller. The developing device 440 supplies toner to the peripheral surface of the photosensitive drum 410 on which the electrostatic latent image is formed. As a result, toner is attracted to the electrostatic latent image, and a toner image T is formed on the peripheral surface of the photosensitive drum 410.

  The power supply roller 450 is a bias roller that transfers the toner image T on the circumferential surface of the photosensitive drum 410 to a sheet S that is a printing medium. The power supply roller 450 is composed of a conductive roller, for example. The power supply roller 450 is disposed at a position advanced from the exposure irradiation position P1 by a distance L1 along the peripheral surface of the photosensitive drum 410 in the clockwise direction in the drawing. A voltage having a polarity opposite to the charging polarity of the toner image T is applied to the power supply roller 450 by a power supply device (not shown). The toner image T on the circumferential surface of the photosensitive drum 410 is transferred to the sheet S by the voltage having the reverse polarity.

  The conveyance belt 460 is a belt that conveys the sheet S on which the toner image T is transferred. The conveyance belt 460 is constituted by an endless belt, for example. The conveyance belt 460 is rotated by the rotational force of the driving roller 451 and conveys the sheet S toward the fixing roller 470.

  The fixing roller 470 is a roller for fixing the toner image T transferred to the sheet S to the sheet S. The fixing roller 470 includes a heat roller 471 that applies heat to the sheet S and a pressure roller 472 that applies pressure to the sheet S. The toner image T transferred to the sheet S is fixed to the sheet S by heat and pressure applied from the heat roller 471 and the pressure roller 472.

  The cleaning device 480 is a device that cleans the peripheral surface of the photosensitive drum 410. The cleaning device 480 is composed of, for example, a wiper blade that sweeps away residual toner. The cleaning device 480 removes residual toner remaining on the circumferential surface of the photosensitive drum 410 without being transferred to the sheet S from the circumferential surface of the photosensitive drum 410. In the following description, similarly to the toner image T, the residual toner is denoted by a symbol T.

  The peeling mechanism 490 is a mechanism for peeling the sheet S attached to the photosensitive drum 410 from the photosensitive drum 410. Normally, as shown in FIG. 3, the sheet S is transported along the transport belt 460 without being attached to the peripheral surface of the photosensitive drum 410. However, in rare cases, the sheet S may stick to the peripheral surface of the photosensitive drum 410 as shown in FIG. If the photosensitive drum 410 continues to rotate as it is, JAM is generated in the image forming apparatus 1. For this reason, the image forming apparatus 1 is provided with a peeling mechanism for peeling the sheet S from the photosensitive drum 410 as shown in FIG. In addition, the structure of a peeling mechanism is not limited to the structure shown in FIG. 5, A various deformation | transformation is possible.

  FIG. 5 is a diagram illustrating an example of the configuration of the peeling mechanism 490. As shown in FIG. 5, the peeling mechanism 490 includes a solenoid 491, gears 492a to 492c, a shaft 493, a claw holding mechanism 494, a one-way clutch 495, a cam 496, a plate-like body 497, and a spring 498. , And a connector 499.

  The solenoid 491 is a device that converts electrical energy into mechanical motion. The solenoid 491 is constituted by, for example, a cylindrical coil and a plunger (iron core) inserted into the cylindrical coil. The plunger is configured to be capable of reciprocating along the axial direction of the plunger. Based on the control of the control unit 600, the solenoid 491 causes a current to flow through the coil to reciprocate the plunger. In the following description, a state where the plunger is inserted into the cylindrical coil is referred to as an “ON state”, and a state where the plunger protrudes from the cylindrical coil is referred to as an “OFF state”.

  The gears 492a to 492c are gears that transmit the power of the solenoid 491 to other components. The gear 492a and the gear 492b transmit the power of the solenoid 491 to the shaft 493, and the gear 492c transmits the power of the solenoid 491 transmitted through the one-way clutch 495 to the cam 496.

  The shaft 493 is a spline shaft having a gear-like cross section as shown in FIG. 6, for example. The shaft 493 is installed at a position away from the circumferential surface of the photosensitive drum 410 by a certain distance in parallel with the axis of the photosensitive drum 410. As shown in FIG. 5, a bevel gear meshed with the gear 492b is fixed to one end of the shaft 493. The shaft 493 rotates by a certain angle by the power of the solenoid 491 transmitted to the bevel gear. More specifically, when the solenoid 491 changes from the OFF state to the ON state, the shaft 493 rotates counterclockwise in the drawing by an angle r1 from the home position H as shown in FIG. Further, when the solenoid 491 changes from the ON state to the OFF state, the shaft 493 rotates clockwise by the angle r1 toward the home position H as shown in FIG. “Home position H” is the rotational position of the shaft 493 when the solenoid 491 is in the OFF state. As shown in FIG. 5, a plurality of claw holding mechanisms 494 are installed on the shaft 493.

  The claw holding mechanism 494 is a mechanism that holds the peeling claw 494b. As shown in FIG. 8, the claw holding mechanism 494 includes a base 494a, a peeling claw 494b, a bracket 494c, and a spring 494d.

  The base 494a is a base on which the peeling claw 494b and the bracket 494c are installed. The base 494a has a cylindrical shape, and its inner surface is processed into a shape that can be fitted to the shaft 493 as shown in FIG. The base 494a is fixed to the shaft 493 with the shaft 493 inserted through the hollow portion. The base 494a is slidable along the shaft 493.

  The peeling claw 494 b is a claw for peeling the sheet S from the peripheral surface of the photosensitive drum 410. As shown in FIG. 9, the peeling claw 494b has a cylindrical portion ((a) shown in FIG. 9) at the rear. As shown in FIG. 7, the cylindrical portion is fixed to the base 494a so as to be rotatable. A long and narrow nail is fixed to the cylindrical portion. The tip of the claw is a part that contacts the peripheral surface of the photoconductive drum 410.

  The tip of the nail has a triangular pointed shape as shown in FIG. Further, one surface of the front end portion (a surface not facing the photosensitive drum 410) is convex in a V-shaped ship bottom shape. This is a configuration for preventing the residual toner T from accumulating at the tip. If the tip of the peeling claw 494b is a semicircular flat plate as shown in FIG. 10 (a), for example, the residual toner T is removed from the peeling claw as shown in FIG. 11 (a). Deposited at the tip of 494b. As the printing is repeated, the residual toner T accumulated at the leading end increases in weight and finally falls on the sheet S being printed. The dropped residual toner T is fixed by the fixing roller 470 at the subsequent stage, and stains are generated on the printed image. However, as shown in FIG. 9, the tip of the peeling claw 494b of the present embodiment has a sharp shape, so that it is difficult to pick up residual toner. Moreover, since the tip of the peeling claw 494b has a V-shaped bottom, even if the tip picks up residual toner, the residual toner hardly accumulates on the tip. Since the tip portion has such a shape, the residual toner T proceeds to avoid the tip portion of the peeling claw 494b as shown in FIG. Not much residual toner accumulates. 11 and 12 are views of the peeling claw 494b viewed from the bottom surface side of the image forming apparatus 1.

  As described above, the tip of the peeling claw 494b is sharp. The curvature radius of the tip is, for example, 1.0 mm or less, desirably 0.05 mm. The peeling claw 494b is made of a resin such as a PAI (polyamideimide) resin instead of a metal such as SUS (stainless steel) in order to make it difficult to damage the peripheral surface of the photosensitive drum 410. Therefore, the peeling claw 494b hardly scratches the peripheral surface of the photosensitive drum 410 even if the tip is sharp.

  The tip of the peeling claw 494b is in contact with the circumferential surface of the photosensitive drum 410 as shown in FIG. As shown in FIG. 2, the abutting position P <b> 2 of the front end is after the power supply roller 450 and before the cleaning device 480. “After the power supply roller 450” is a position that advances from the power supply roller 450 along the circumferential surface of the photoconductive drum 410 toward the rotation direction of the photoconductive drum 410. “Front” refers to a position that advances from the cleaning device 480 along the circumferential surface of the photosensitive drum 410 in the direction opposite to the rotation direction of the photosensitive drum 410. By disposing the peeling claw 494b at this position, the sheet S is peeled from the photosensitive drum 410 before reaching the cleaning device 480. As a result, the sheet S does not clog the cleaning device. If another device is installed in front of the cleaning device 480, the contact position P2 of the tip of the peeling claw 494b is in front of the device. In the following description, the contact position P2 of the tip of the peeling claw 494b is assumed to be a position advanced from the power supply roller 450 by about L2 in the rotation direction of the photosensitive drum 410.

  Returning to FIG. 8, the bracket 494c is a support that applies a tensile force to the spring 494d. Unlike the peeling claw 494b, the bracket 494c is fixed to the base 494a. Therefore, the bracket 494c does not rotate on the base 494a but rotates with the base 494a as the shaft 493 rotates. As shown in FIG. 7, the bracket 494c is connected to the peeling claw 494b by a spring 494d. When the shaft 493 is at the home position H and when the shaft 493 is at a rotational position rotated by an angle r1 from the home position H, the spring 494d is in an extended state in any case. Therefore, the tip of the peeling claw 494b is always in contact with the peripheral surface of the photosensitive drum 410. In the following description, the rotational position of the bracket 494 c when the shaft 493 is at the home position H is referred to as “home position H” as in the case of the shaft 493.

  The tensile force applied to the spring 494d changes as the bracket 494c rotates. When the bracket 494c is at the home position H as shown in FIG. 7, the spring 494d is lightly stretched by the bracket 494c. As a result, the tip of the peeling claw 494b is lightly pressed against the peripheral surface of the photosensitive drum 410 by the tensile force of the spring 494d. Further, as shown in FIG. 6, when the bracket 494c is at a position rotated counterclockwise by an angle r1 from the home position H, the spring 494d is strongly stretched by the bracket 494c. As a result, the tip of the peeling claw 494b is strongly pressed against the peripheral surface of the photosensitive drum 410 by the tensile force of the spring 494d. In the following description, the contact pressure between the peeling claw 494b and the photosensitive drum 410 when the bracket 494c is at the home position H is “contact pressure F2,” and the bracket 494c is counterclockwise in the drawing from the home position H. The contact pressure between the peeling claw 494b and the photosensitive drum 410 at the rotational position rotated by the angle r1 is referred to as “contact pressure F1”. The contact pressure F1 is a pressure larger than the contact pressure F2.

  The spring 494d is a spring that connects the bracket 494c and the peeling claw 494b. The spring constant of the spring 494d is a value such that the contact pressure between the peeling claw 494b and the photosensitive drum 410 becomes a pressure within a predetermined range. When the contact pressure between the peeling claw 494b and the photosensitive drum 410 is large, the peripheral surface of the photosensitive drum 410 is damaged. On the other hand, when the contact pressure between the peeling claw 494b and the photosensitive drum 410 is small, the peeling claw This is because a contact failure of the photosensitive member and bounding occur at 494b. The “photosensitive member contact failure” is a phenomenon in which the tip end portion of the peeling claw 494 b does not contact the peripheral surface of the photosensitive drum 410. “Bounding” is a phenomenon in which the tip of the peeling claw 494b repeats contact and separation with the photosensitive drum 410 in a short cycle.

  The inventor created a peeling mechanism having the same function as the peeling mechanism 490 of the present embodiment, and mounted it on the printing apparatus. And the inventor calculated | required the optimal spring constant using this printing apparatus. The printing device has a printing speed of 85 CPM at a process speed of 410 mm / sec. The peeling claw is made of PAI resin having a sharp tip (curvature radius of 0.05). The inventor allowed 100,000 sheets of 20 lb LT paper to pass through this printing apparatus, and confirmed whether or not the sheet peeling claw JAM occurred and whether image smear occurred. Thereafter, the inventor measured the film scraping amount of the photosensitive layer of the photosensitive drum with a film thickness meter or a laser microscope. Furthermore, the inventor confirmed the printed halftone image. As a result, it was found that when the contact pressure F1 exceeds 0.005 N, the peeling claw scrapes off the film of the photosensitive layer, thereby producing a step of 0.27 μm or more in the photosensitive layer of the photosensitive drum. It was found that a white band was also generated in the halftone image along the sheet conveyance direction. Further, it has been found that when the contact pressure F2 is 0.002 N or less, the paper may enter between the photosensitive drum and the peeling claw and the peeling claw JAM may be generated. As a result, it was found that the contact pressure F1 is in the range of 0.002 to 0.005N. In addition, as a result of recording and recording the printing operation with a fiberscope and confirming the reproduced image, it has been found that the contact failure F2 and the bounding do not occur when the contact pressure F2 is set to 0.001 N or more.

  Based on the experimental results, in this embodiment, the spring constant of the spring 494d is set so that the contact pressure F1 is 0.002 or more and 0.005N or less, and the contact pressure F2 is 0.001N or more and less than the contact pressure F1. Set. In consideration of device variations, a spring constant is more desirable in which the contact pressure F1 is 0.002 to 0.004N and the contact pressure F2 is 0.001N to 0.0022. FIG. 13 shows the result of measuring the relationship between the contact pressure F1 and the contact pressure F2 using a plurality of springs having a constant spring. A string-like object was hung on the tip of the nail, a weight was added to the string, and the weight of the weight immediately before the nail tip was separated from the photosensitive roller was obtained as the contact pressure.

  Returning to FIG. 5, the one-way clutch 495 is a clutch that transmits rotational force only in one direction. The one-way clutch 495 is installed between the solenoid 491 and the gear 492c. The gear 492 c is connected to the cam 496. The one-way clutch 495 rotates the cam 496 by an angle r2 when the solenoid 491 is switched from the OFF state to the ON state or when the solenoid 491 is switched from the ON state to the OFF state.

  The cam 496 is a rigid body that converts rotational motion into reciprocating motion. The cam 496 is composed of, for example, an egg-shaped disc cam. The cam 496 is installed between the gear 492 c and the plate-like body 497. The cam 496 rotates only in one direction by the power of the solenoid 491 and reciprocates the plate-like body 497 together with the spring 498.

  The plate-like body 497 is an elongated plate that reciprocates the claw holding mechanism 494 along the axial direction of the shaft 493. The plate-like body 497 functions as a sliding mechanism of the image forming apparatus 1 together with the solenoid 491, the one-way clutch 495, the gear 492c, and the cam 496. The sliding mechanism is a mechanism that moves the peeling claw 494b little by little along the axial direction of the shaft 493 to prevent the contact place between the peeling claw 494b and the photosensitive drum 410 from being concentrated in one place. The plate-like body 497 moves slightly in a direction perpendicular to the sheet S conveyance direction by one ON / OFF operation of the solenoid 491. For example, the plate-like body 497 makes a round trip of 8 mm width by 15 ON / OFF operations of the solenoid 491. Three claw holding mechanisms 494 are fixed to the plate-like body 497 via a connector 499. When the solenoid 491 is turned ON / OFF, the plate-like body 497 slightly moves the claw holding mechanism 494 along the axial direction of the shaft 493. In addition, the structure of a sliding mechanism is not limited to the structure shown in FIG. 5, A various deformation | transformation is possible.

  Returning to FIG. 1, the paper discharge unit 500 is a device that discharges the sheet S to the outside. The paper discharge unit 500 discharges the sheet S on which the toner image is fixed to the outside of the image forming apparatus 1 from a discharge port (not shown).

  The control unit 600 includes a processing device such as a processor. The control unit 600 controls each unit of the image forming apparatus 1 by operating according to a program stored in a ROM (Read Only Memory) or a RAM (Random Access Memory) (not shown).

  Next, the operation of the image forming apparatus 1 having such a configuration will be described.

  When receiving a print start command from the user via a user interface (not shown), the control unit 600 starts a printing process. Hereinafter, the printing process will be described with reference to the flowchart of FIG.

  The control unit 600 determines whether the image acquisition unit 100 has completed the acquisition of image data for one page (step S101). When acquisition of image data for one page has not been completed (step S101: No), the control unit 600 repeats step S101 until the image acquisition unit 100 completes acquisition of image data for one page. When acquisition of image data for one page has been completed (step S101: Yes), the control unit 600 proceeds to step S102.

  The control unit 600 starts a printing operation for printing the image data for one page on the sheet S (step S102). Specifically, the control unit 600 executes the following processing.

  First, the control unit 600 controls the image processing unit 200 to convert the image data into a data format that can be printed by the printing unit 400. Then, the controller 600 controls a motor (not shown) to rotate the photosensitive drum 410. Further, the control unit 600 controls the charging charger 420 to uniformly charge the peripheral surface of the photosensitive drum 410. Thereafter, the control unit 600 controls the exposure unit 430 based on the image data, and forms an electrostatic latent image on the peripheral surface of the photosensitive drum 410. Further, the control unit 600 controls the developing device 440 to form a toner image on the peripheral surface of the photosensitive drum 410. Then, the control unit 600 conveys the sheet S picked up from the paper feeding unit 300 between the photosensitive drum 410 and the power supply roller 450. At this time, for example, as shown in FIG. 2, the controller 600 moves the sheet S to the photosensitive drum 410, the power supply roller 450, and the sheet S so that the leading edge F of the toner image T matches the end of the sheet S in the conveyance direction. Send out in between. Then, the control unit 600 applies a voltage to the power supply roller 450 and transfers the toner image T on the circumferential surface of the photosensitive drum 410 to the sheet S.

  Note that when the control unit 600 starts a printing operation, the solenoid 491 is in an OFF state. Therefore, when the controller 600 starts a printing operation, the shaft 493 and the bracket 494c are located at the home position H as shown in FIG. For this reason, when the controller 600 starts the printing operation, the tip of the peeling claw 494b is in contact with the peripheral surface of the photosensitive drum 410 with the contact pressure F2. The contact pressure F2 is a pressure smaller than the contact pressure F1.

  Returning to FIG. 14, the controller 600 determines whether the end of the separation claw 494 b and the peripheral surface of the photosensitive drum 410 meet the timing at which the end of the sheet S in the conveyance direction is expected to pass the contact position P <b> 2. The contact pressure is changed from the contact pressure F2 to the contact pressure F1. The contact position P2 is a position where the tip of the peeling claw 494b contacts the peripheral surface of the photosensitive drum 410 (step S103). Specifically, as shown in FIG. 15, when the head F of the toner image T (or residual toner T) reaches a certain distance before the contact position P2 (Pa shown in FIG. 15), the control unit 600 The solenoid 491 is changed from the OFF state to the ON state. As a result, the bracket 494c is rotated counterclockwise by an angle r1 from the home position H, and the contact pressure between the tip of the peeling claw 494b and the peripheral surface of the photosensitive drum 410 is changed from the contact pressure F2 to the contact pressure F1. To change.

  The timing at which the head F passes the contact position P2 is calculated based on the exposure start time of the exposure unit 430, the distance from the exposure irradiation position P1 to the contact position P2, and the rotational speed of the photosensitive drum 410. Specifically, the timing t1 when the head F passes the contact position P2 is calculated by the following equation (1).

    t1 = t0 + (L1 + L2) / s (1)

  In the above formula (1), t0 is the exposure start time of the exposure unit 430, L1 + L2 is the distance from the exposure irradiation position P1 to the contact position P2, as shown in FIG. 2, and s is the rotational speed of the photosensitive drum 410.

  The controller 600 calculates the timing t1 based on the above formula (1), and then calculates the timing ta based on the timing t1. The timing timing ta is a timing at which the head F passes the position Pa shown in FIG. At this time, the control unit 600 may set a timing obtained by subtracting a preset time from the timing t1 as the timing timing ta.

  Returning to FIG. 14, the controller 600 changes the solenoid 491 from the ON state to the OFF state when the head F reaches a position (Pb shown in FIG. 16) that is a certain distance from the contact position P <b> 2, and the peeling claw 494 b. The contact pressure between the front end portion of the photosensitive drum and the peripheral surface of the photosensitive drum 410 is changed from F1 to F2 (step S104). The timing tb when the head F passes the position Pb is calculated based on the timing t1. For example, the control unit 600 calculates a time obtained by adding a preset time to the timing t1 calculated by the above equation (1) as the timing tb. Thereafter, the control unit 600 sets the contact pressure between the tip of the peeling claw 494b and the peripheral surface of the photosensitive drum 410 until the top F reaches the position Pa, as shown in FIG. Keep it.

  FIG. 18 is a timing chart showing the timing at which the control unit 600 switches the state of the solenoid 491. T2 shown in FIG. 18 is a timing at which the tail B of the toner image T passes through the contact position P2. As shown in FIG. 18, the period during which the solenoid 491 is in the ON state is shorter than the period during which the solenoid 491 is in the OFF state. That is, during the period in which the contact pressure between the tip of the peeling claw 494b and the peripheral surface of the photosensitive drum 410 is the contact pressure F1, the contact pressure between the tip of the peeling claw 494b and the peripheral surface of the photosensitive drum 410 is It is shorter than the period of the contact pressure F2. In order to make the force applied to the peripheral surface of the photosensitive drum 410 from the tip of the peeling claw 494b as small as possible, it is desirable that the period of the contact pressure F1 is as short as possible. In the present embodiment, the period during which the solenoid 491 is in the ON state, that is, the period from the timing ta to the timing tb is 265 ms. More specifically, the period from timing ta to t1 is 250 ms, and the period from timing t1 to tb is 15 ms. These periods can be changed as appropriate according to the configuration of the device.

  The solenoid 491 is connected to the plate-like body 497 via a one-way clutch 495, a gear 492c, and a cam 496. When the control unit 600 turns the solenoid 491 from the ON state to the OFF state, the plate-like body 497 slightly moves the peeling claw 494b along the axial direction of the shaft 493. The timing at which the plate-like body 497 moves the peeling claw 494b may be the timing at which the control unit 600 switches the solenoid 491 from the OFF state to the ON state.

  Returning to FIG. 14, the control unit 600 determines whether printing of all pages is completed (step S105). If printing of all pages has not been completed (step S105: No), the control unit 600 returns to step S101 and repeats the processing from step S101 to step S105 until printing of all pages is completed. When printing of all pages is completed (step S105: Yes), the control unit 600 ends the printing process.

  According to this embodiment, since the peeling claw 494b is always in contact with the peripheral surface of the photosensitive drum 410, even if the tip of the peeling claw 494b is sharp, the peeling claw is affected by the impact at the time of contact. The leading end portion of 494b does not pierce the peripheral surface of the photosensitive drum 410. As a result, the peripheral surface of the photosensitive drum 410 is not so damaged. Further, since the tip of the peeling claw 494b does not pierce the peripheral surface of the photosensitive drum 410 due to the impact at the time of contact, it is not necessary to make the tip of the peeling claw 494b semicircular. The tip of the peeling claw 494b can be sharpened.

  Further, since the tip of the peeling claw 494b is sharp, the residual toner does not accumulate much on the tip of the peeling claw 494b. As a result, the image forming apparatus 1 rarely stains the printed image with toner falling from the tip of the peeling claw 494b. In addition, the peeling claw 494b is always in contact with the peripheral surface of the photosensitive drum 410, and is not separated from the photosensitive drum 410 at least during toner image transfer. Therefore, the residual toner does not fall on the sheet S due to an impact when the peeling claw is separated as in a normal printing apparatus.

  In addition, the control unit 600 increases the contact pressure between the leading end portion of the peeling claw 494b and the peripheral surface of the photosensitive drum 410 only during a period when the end of the sheet S in the conveyance direction is expected to pass the contact position P2. doing. In other periods, the controller 600 reduces the contact pressure. Therefore, the peeling claw 494b does not significantly wear the peripheral surface of the photosensitive drum 410.

  If the contact pressure is always weak, the sheet S may not be peeled off by the peeling claw 494b as shown in FIG. However, since the controller 600 increases the contact pressure of the separation claw 494b in accordance with the timing at which the end of the sheet S in the conveyance direction passes through the contact position P2, it is not likely that the sheet S is separated. Does not occur.

  In the case of a general printing apparatus in which the peeling claw is separated from the photosensitive drum, it is necessary to wait for a while for the peeling claw to stabilize when the peeling claw comes into contact with the photosensitive drum. This is because when the peeling claw comes into contact with the photosensitive drum, the peeling claw bounces around the circumferential surface of the photosensitive drum. However, in this embodiment, since the peeling claw 494b is always in contact with the peripheral surface of the photosensitive drum 410, the peeling claw 494b does not bounce even if the contact pressure is changed to a strong pressure. Therefore, the control unit 600 does not need to wait for the separation claw 494b to be stable, so that the period during which the contact pressure is increased can be shortened. As a result, the peripheral surface of the photosensitive drum 410 is not worn much.

  Further, in the case of a general printing apparatus in which the peeling claw is separated from the photosensitive drum, a contact failure between the peeling claw and the photosensitive drum is likely to occur, and JAM may occur. However, since the peeling claw 494b of this embodiment is always in contact, it is difficult for JAM to occur.

  Further, since the peeling claw 494b is configured to move slightly along the axial direction of the shaft 493 by the ON / OFF operation of the solenoid 491, there is only one contact point between the peeling claw 494b and the photosensitive drum 410. Don't concentrate on. As a result, the peeling claw 494b does not significantly wear the peripheral surface of the photosensitive drum 410.

  When the peeling claw 494b is brought into contact with the peripheral surface of the photosensitive drum 410 with a force of weight, the peeling claw 494b may be bound during the printing operation. However, since the peeling claw 494b is in contact with the peripheral surface of the photosensitive drum 410 by the force of the spring 494d instead of the weight force, even if an impact is applied to the peeling claw 494b during the printing operation, the spring 494d The impact is absorbed, and the peeling claw 494b hardly causes the bounding. Therefore, the tip of the peeling claw 494b does not strongly collide with the peripheral surface of the photosensitive drum 410 due to the bounding, so that the peripheral surface of the photosensitive drum 410 is not so damaged.

  The above-described embodiment is an example, and various changes and applications are possible.

  For example, in the above-described embodiment, the image acquisition unit 100 has been described as a scanner, but the image acquisition unit 100 is not limited to a scanner. The image acquisition unit 100 may be a communication interface that acquires image information from an external device.

  In the above-described embodiment, the printing unit 400 is described as a direct transfer type printing apparatus. However, the printing unit 400 may be an indirect transfer type printing apparatus. At this time, the printing unit 400 may be, for example, a tandem printing apparatus as shown in FIG. In this case, the printing unit 400 may include an intermediate transfer belt 411 as an image carrier. The intermediate transfer belt 411 is an intermediate transfer medium on which toner images of various colors are transferred from the photosensitive drum 410. In addition to the photosensitive drum 410, the peeling mechanism 490 may be installed on the intermediate transfer belt 411 as shown in FIG. 20, for example. In this case, similarly to the above-described embodiment, the control unit 600 determines whether the end of the separation claw 494b and the intermediate transfer belt 411 are aligned with the timing when the end of the sheet S in the conveyance direction passes the contact position P2. The peeling mechanism 490 may be controlled so that the contact pressure becomes the contact pressure F1. The contact position P2 is a position where the tip of the peeling claw 494b contacts the intermediate transfer belt 411. Further, the control unit 600 determines that the contact pressure between the peeling claw 494b and the intermediate transfer belt 411 is increased when a preset time has elapsed after the end of the sheet S in the conveyance direction passes through the contact position P2. You may control the peeling mechanism 490 so that it may become contact pressure F2. When the sheet S is attached to the intermediate transfer belt 411, the sheet S can be peeled from the intermediate transfer belt 411. In addition, the intermediate transfer belt 411 is not damaged much.

  In the above-described embodiment, the peeling mechanism 490 is described as being installed on the photosensitive drum 410, but the peeling mechanism 490 may be installed on the fixing roller 470. In this case, as shown in FIG. 21, the peeling mechanism 490 may be installed on both the heat roller 471 and the pressure roller 472, or may be installed on either the heat roller 471 or the pressure roller 472. Good. In this case, similarly to the above-described embodiment, the control unit 600 matches the leading end portion of the separation claw 494b with the fixing roller 470 in accordance with the timing when the end portion in the conveyance direction of the sheet S passes the contact position P2. The peeling mechanism 490 may be controlled so that the contact pressure becomes the contact pressure F1. The contact position P2 is a position where the tip end portion of the peeling claw 494b is in contact with the fixing roller 470. Further, the control unit 600 determines that the contact pressure between the peeling claw 494b and the intermediate transfer belt 411 is increased when a preset time has elapsed after the end of the sheet S in the conveyance direction passes through the contact position P2. You may control the peeling mechanism 490 so that it may become contact pressure F2. When the sheet S is attached to the fixing roller 470, the sheet S can be peeled from the fixing roller 470. In addition, the fixing roller 470 is not damaged much.

  Note that the fixing roller 470 does not necessarily include both the heat roller 471 and the pressure roller 472. The fixing roller 470 may be composed of either one of the heat roller 471 and the pressure roller 472. The heat roller 471 may have a function of applying pressure to the sheet S in addition to the function of applying heat to the sheet S.

  Moreover, in the above-mentioned embodiment, as shown in FIG. 9, the one surface of the front-end | tip part of the peeling nail | claw 494b became a convex surface in the V-shaped ship bottom, However, The surface of a front-end | tip part may not be a convex surface. . The tip of the peeling claw 494b may be simply pointed.

  Further, in the above-described embodiment, the peeling mechanism 490 is configured to be able to change the contact pressure of the peeling claw 494b to F1 and F2, but the contact pressure of the peeling claw 494b is limited to two of F1 and F2. Not. The contact pressure may be three or more. Further, the peeling mechanism 490 may be configured to linearly change the contact pressure of the peeling claw 494b from F1 to F2.

  In the above-described embodiment, the image forming apparatus 1 is described as including the sliding mechanism. However, the image forming apparatus 1 may not include the sliding mechanism. In the above-described embodiment, the sliding mechanism is described as being included in the peeling mechanism 490. However, the sliding mechanism may not be included in the peeling mechanism 490. The sliding mechanism may be a mechanism independent of the peeling mechanism 490.

  Further, the print medium to be printed by the image forming apparatus 1 is not limited to paper. For example, the print medium may be a box, wrapping paper, postcard, form, book, or the like.

  In the above-described embodiment, the image forming apparatus 1 is described as a copying machine, a printer, or a FAX. However, the image forming apparatus 1 is not limited to these electric devices. For example, the image forming apparatus 1 may be a business printing apparatus that performs mass printing of newspapers, magazines, advertisements, and the like.

  The control unit 600 that controls the image forming apparatus 1 according to the present embodiment may be realized by a normal computer system. For example, a program for executing the above-described operation is stored and distributed in a computer-readable recording medium such as an optical disk, a semiconductor memory, a magnetic tape, or a flexible disk, the program is installed in the computer, and the above-described processing is performed. The control unit 600 may be configured by executing the above. Further, the program may be stored in a disk device provided in a server device on a network such as the Internet so that it can be downloaded to a computer. Further, the above-described functions may be realized by cooperation between an OS (Operating System) and application software. In this case, a part other than the OS may be stored and distributed in a medium, or a part other than the OS may be stored in a server device and downloaded to a computer.

  Although the embodiment of the present invention has been described, this embodiment is presented as an example and is not intended to limit the scope of the invention. The novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 100 ... Image acquisition part 200 ... Image processing part 300 ... Paper feed part 400 ... Printing part 410 ... Photosensitive drum 411 ... Intermediate transfer belt 420. ..Charging charger 430 ... exposure unit 440 ... developing device 450 ... feed roller 451 ... driving roller 452 ... driven roller 460 ... conveying belt 470 ... fixing roller 471 ... Heat roller 472 ... Pressure roller 480 ... Cleaning device 490 ... Peeling mechanism 491 ... Solenoid 492a to 492c ... Gear 493 ... Shaft 494 ... Claw holding mechanism 494a ... Base 494b ... Peeling claw 494c ... Bracket 494d ... Spring 495 ... One-way clutch 496 ... Cam 497 ... Plate-like body 498 ... Spring 499 ... Connector 500 ... Discharge Part 600 ... Control part

Claims (10)

An image carrier on which a toner image transferred to a print medium is developed;
A separation claw for separating the print medium attached to the image carrier from the image carrier, and applying a force to the separation claw so that the separation claw is always in contact with the image carrier; A peeling mechanism for changing the pressure applied to the peeling claw and the contact pressure between the image carrier and
A controller that controls the peeling mechanism to change a contact pressure between the peeling claw and the image carrier during the transfer of the toner image.
Image forming apparatus. The controller is
The contact pressure between the peeling claw and the image carrier is increased in accordance with the timing when the end portion on the conveyance direction side of the print medium passes through the contact position between the peeling claw and the image carrier,
The contact pressure between the peeling claw and the image carrier is lowered at a preset timing after the end of the print medium in the conveyance direction passes through the contact position between the peeling claw and the image carrier. ,
The image forming apparatus according to claim 1. The peeling mechanism can change a contact pressure between the peeling claw and the image carrier to a first pressure and a second pressure lower than the first pressure.
The controller is
The contact pressure between the peeling claw and the image carrier is set to the first pressure in accordance with the timing when the end of the print medium in the conveyance direction passes through the contact position between the peeling claw and the image carrier. Controlling the peeling mechanism so that
The contact between the peeling claw and the image carrier after a predetermined time has elapsed since the end portion on the conveyance direction side of the print medium passes through the contact position between the peeling claw and the image carrier. Controlling the peeling mechanism so that the pressure becomes the second pressure;
The image forming apparatus according to claim 2. The first pressure is a pressure of 0.002N or more and 0.005N or less,
The second pressure is a pressure smaller than the first pressure and 0.001 N or more.
The image forming apparatus according to claim 3. The tip of the peeling claw is pointed like a V-shaped ship bottom,
The peeling claw always brings the tip portion into contact with the image carrier.
The image forming apparatus according to claim 1. A sliding mechanism for moving the peeling claw along the surface of the image carrier at a substantially right angle with respect to the conveyance direction of the print medium,
The control unit controls the sliding mechanism to change a contact position between the peeling claw and the image carrier every time printing is newly performed on the print medium.
The image forming apparatus according to claim 1. The image carrier is a photosensitive roller or an intermediate transfer belt to which a toner image of each color is transferred from the photosensitive roller.
The image forming apparatus according to claim 1. A force is applied to the peeling claw that peels the print medium attached to the image carrier on which the toner image transferred to the print medium is developed from the image carrier, so that the peeling claw is always in contact with the image carrier. ,
Changing the pressure applied to the peeling claw during the transfer of the toner image to change the contact pressure between the peeling claw and the image carrier;
Peeling method. A fixing roller on which a toner image to be transferred to a printing medium is developed;
A peeling claw for peeling the print medium attached to the fixing roller from the fixing roller, and applying force to the peeling claw so that the peeling claw is always brought into contact with the fixing roller and force applied to the peeling claw A peeling mechanism for changing the contact pressure between the peeling claw and the fixing roller by changing
A controller that controls the peeling mechanism to change a contact pressure between the peeling claw and the fixing roller during transfer of the toner image.
Image forming apparatus. A force is applied to a peeling claw that peels off the printing medium attached to a fixing roller on which a toner image to be transferred to the printing medium is developed, and the peeling claw is always brought into contact with the fixing roller.
Changing a contact pressure between the peeling claw and the fixing roller by changing a force applied to the peeling claw during transfer of the toner image;
Peeling method.

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