Image forming apparatus

Abstract

To correct positional deviation of an image from a medium in an image forming apparatus that cannot freely adjust the conveyance speed of the medium relative to the rotation speed of image holding means.SOLUTION: An image forming apparatus (U) comprises: image holding means (B) that can hold images on its surface while rotating; image forming means (D) that forms images on the image holding means (B); transfer means (T2) that transfers the images to a medium (S) from the image holding means (B); conveyance means (Ra) that circulates in association with the rotation of the transfer means (T2), and holds and conveys the medium (S) to a transfer area (Q4); and control means (C) that, in a mode in which the image holding means (B) rotates at a predetermined speed, changes the time to form images according to variations in the rotation speed of the transfer means (T2) relative to the image holding means (B).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] In an image forming apparatus, as a technique for adjusting the positional deviation of an image formed on a medium, the technique described in Patent Document 1 below is conventionally known.

[0003] Patent Document 1 describes a technique for providing a detection mark on a photoreceptor as an example of an image holding means, detecting the rotational position of the photoreceptor, and adjusting the orientation of the image formed on the photoreceptor from the difference between the timing of detecting the detection mark and the timing of detecting a pattern image formed on the photoreceptor.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to correct the positional deviation between an image and a medium in an image forming apparatus that cannot freely adjust the conveyance speed of the medium with respect to the rotation speed of an image holding means.

Means for Solving the Problems

[0006] To solve the above technical problem, the image forming apparatus according to the invention described in claim 1 an image holding means capable of holding an image on its surface while rotating, an image forming means for forming the image on the image holding means, a transfer means for transferring the image from the image holding means to a medium while rotating, Conveying means that orbits as the transfer means rotates and conveys the medium to the transfer area while holding the medium. Control means for changing the imaging timing according to fluctuations in the ratio of the rotation speed of the transfer means to the image holding means. It is characterized by comprising the above.

[0007] To solve the above technical problem, the image forming apparatus according to claim 2 of the invention Image holding means capable of holding an image on the surface while rotating. Imaging means for forming the image on the image holding means. Transfer means for transferring the image from the image holding means to the medium while rotating. Conveying means that orbits as the transfer means rotates and conveys the medium to the transfer area while holding the medium. Control means for changing the imaging timing according to fluctuations in the rotation speed of the transfer means with respect to the image holding means in a mode where the image holding means rotates at a predetermined speed. It is characterized by comprising the above.

[0008] To solve the above technical problem, the image forming apparatus according to claim 3 of the invention Image holding means capable of holding an image on the surface while rotating. Imaging means for forming an image on the image holding means. pressed against the image holding means and Transfer means for transferring the image of the image holding means to the medium. Conveying means for conveying the medium. Control means for varying the conveyance speed of the medium of the conveyance means according to fluctuations in the rotation speed of the image holding means, and for controlling the imaging timing of the imaging means according to fluctuations in the conveyance speed of the medium. the control means for changing the rotational speed of the transfer means with respect to the image holding means according to the amount by which the image holding means bites into the transfer means And It is characterized by comprising the above.

[0009] The invention according to claim 4 is the image forming apparatus according to claim 1 or 2 In the image forming apparatus described in The transfer means pressed against the image holding means. The control means for changing the rotational speed of the transfer means with respect to the image holding means according to the amount by which the image holding means bites into the transfer means characterized by comprising the same.

[0010] The invention according to claim 5 is the invention according to claim 3 or 4 in the image forming apparatus described in The control means for controlling the conveyance means so as to obtain a conveyance speed of the medium corresponding to the peripheral speed of the image holding means according to the biting amount characterized by comprising the same.

[0011] The invention according to claim 6 is the invention according to any one of claims 1 to 5 in the image forming apparatus The conveyance means having gripping means for gripping an end portion of the medium, the gripping means being arranged in a plurality at intervals along the conveyance direction of the medium and being movable along the conveyance direction of the medium, and The transfer means in which an accommodating portion for accommodating the gripping means passing through a transfer region where the image holding means and the transfer means face each other is formed characterized by comprising the same.

[0012] The invention according to claim 7 is the invention according to any one of claims 1 to 6 in the image forming apparatus The transfer means pressed toward the image holding means, and The control means for controlling the timing at which the image forming means forms an image in accordance with the fact that the amount by which the image holding means bites into the transfer means varies according to the type of the medium characterized by comprising the same.

[0013] The invention according to claim 8 is the invention according to claim 7 in the image forming apparatus The control means for controlling the timing at which the image forming means forms an image according to the biting amount that varies according to the thickness of the medium characterized by comprising the same.

[0014] The invention according to claim 9 is the invention according to claim 8 in the image forming apparatus When the thickness of the medium is thin, the control means for delaying the timing at which the imaging means performs imaging compared to when the thickness of the medium is thick characterized by comprising

[0015] The invention according to claim 10 is an image forming apparatus according to any one of claims 1 to 9, the transfer means pressed against the image holding means, control means for controlling the timing at which the imaging means performs imaging according to the amount by which the image holding means bites into the transfer means varying according to the installation environment of the image forming apparatus, characterized by comprising

[0016] The invention according to claim 11 is an image forming apparatus according to claim 10, control means for reducing the amount of biting and delaying the timing at which the imaging means performs imaging when the installation environment is lower in humidity than a predetermined value compared to when the humidity is higher than the predetermined value, characterized by comprising

Advantages of the Invention

[0017] According to the invention described in claims 1 - 3, in an image forming apparatus in which the conveyance speed of the medium cannot be freely adjusted with respect to the rotation speed of the image holding means, positional displacement between the image and the medium can be corrected. Claim 3, According to the invention described in claim 4, the rotation speed of the transfer means can be changed according to the amount by which the image holding means bites into the transfer means. According to the invention described in claim 5, the speed difference between the image holding means and the medium can be reduced compared to the case where the conveyance speed of the medium is not controlled according to the amount of biting. According to the invention described in claim 6, the medium can be stably conveyed by the gripping means, and interference between the transfer means and the gripping means can be prevented compared to the case where there is no accommodating portion.

[0018] According to the invention described in claim 7, the positional deviation between the image and the medium can be corrected according to the type of the medium, as compared with the case where the timing of image formation is not controlled according to the type of the medium. According to the invention described in claim 8, the positional deviation between the image and the medium can be corrected according to the amount of penetration, as compared with the case where the timing of image formation is not controlled according to the amount of penetration. According to the invention described in claim 9, even when the amount of penetration is small when the thickness of the medium is thin and the conveyance speed of the medium is high, the positional deviation between the image and the medium can be corrected. According to the invention described in claim 10, the positional deviation between the image and the medium can be corrected according to the installation environment, as compared with the case where the timing of image formation is not controlled according to the installation environment. According to the invention described in claim 11, the positional deviation between the image and the medium can be corrected, as compared with the case where the timing of image formation is not delayed in a low humidity environment.

Brief Description of the Drawings

[0019] [Fig. 1] FIG. 1 is an explanatory diagram of an image forming apparatus according to Embodiment 1 of the present invention. [Fig. 2] FIG. 2 is an explanatory diagram of the conveying means according to Embodiment 1. [Fig. 3] FIG. 3 is an explanatory diagram of the control unit according to Embodiment 1. [Fig. 4] FIG. 4 is an explanatory diagram of the amount of penetration according to Embodiment 1. FIG. 4A is an explanatory diagram of the amount of penetration when there is no medium, FIG. 4B is an explanatory diagram of the amount of penetration in the case of thin paper, FIG. 4C is an explanatory diagram of the amount of penetration in the case of plain paper, and FIG. 4D is an explanatory diagram of the amount of penetration in the case of thick paper. [Fig. 5] FIG. 5 is an explanatory diagram of a flowchart of the adjustment process of the image formation timing according to Embodiment 1. [Fig. 6] FIG. 6 is an explanatory diagram of the interval at which the medium reaches the secondary transfer area. FIG. 6A is an explanatory diagram in the case of thick paper, FIG. 6B is an explanatory diagram in the case of plain paper, and FIG. 6C is an explanatory diagram in the case of thin paper. [Fig. 7] FIG. 7 is an explanatory diagram of an image forming apparatus according to Embodiment 2.

Embodiments for Carrying Out the Invention

[0020] Next, with reference to the drawings, specific examples of embodiments of the present invention (hereinafter referred to as examples) will be described, but the present invention is not limited to the following examples. For ease of understanding of the following description, in the drawings, the front - rear direction is the X - axis direction, the left - right direction is the Y - axis direction, and the up - down direction is the Z - axis direction. The directions or sides indicated by the arrows X, - X, Y, - Y, Z, - Z are the front, rear, right, left, upper, lower, or front side, rear side, right side, left side, upper side, lower side, respectively. In addition, in the drawings, those with "·" in "○" mean arrows from the back to the front of the paper surface, and those with "×" in "○" mean arrows from the front to the back of the paper surface. In the following description using the drawings, for ease of understanding, illustrations of members other than those necessary for the description are appropriately omitted.

[0021] (Example 1) FIG. 1 is an explanatory diagram of an image forming apparatus according to Example 1 of the present invention. In FIG. 1, an ink - jet printer U as an example of the image forming apparatus of the present invention has an imaging unit D as an example of an image forming means. The imaging unit D has a Y - color head Hy that discharges ink in response to a Y (yellow) - color image signal. Further, the imaging unit D has heads Hm, Hc, Hk for each color that discharge ink in response to image signals of each color of M (magenta), C (cyan), and K (black). The imaging unit D and the power supply circuit E are controlled for the writing timing and the power supply timing in response to a control signal from a control unit C as an example of a control means. The control unit C in Example 1 converts print information into Y, M, C, K image signals and outputs a control signal to the imaging unit D when print information is input from a personal computer (not shown) as an example of an information processing apparatus connected to the printer U.

[0022] Below the image forming unit D, an intermediate transfer belt B, which is an example of an image holding means, is arranged. The intermediate transfer belt B is supported by a plurality of support means including a driving roll Rd, which is an example of a driving means, a backup roll T2a, which is an example of an opposing means, and a driven roll Rf, which is an example of a driven means. Driving is transmitted to the driving roll Rd from a motor, which is an example of a driving source not shown in the figure. The intermediate transfer belt B is rotated in the direction of the rotation direction Ya as the driving roll Rd rotates.

[0023] Each of the heads Hy, Hm, Hc, and Hk is arranged such that the ink ejection side faces the surface of the intermediate transfer belt B and is spaced apart along the rotation direction Ya of the intermediate transfer belt B. Then, images of each color composed of ink ejected from each of the heads Hy to Hk toward the intermediate transfer belt B can be held on the surface of the intermediate transfer belt B. Along the rotation direction Ya of the intermediate transfer belt B, a belt cleaner CLb, which is an example of a cleaning means, is arranged on the downstream side of the transfer area Q4. The belt cleaner CLb removes residues adhering to the surface of the intermediate transfer belt B after passing through the transfer area Q4. Note that an inkjet type image forming apparatus using such an intermediate transfer belt is conventionally known and is described in, for example, Japanese Patent Application Laid-Open No. 2000-127359, Japanese Patent Application Laid-Open No. 2020-97239, Japanese Patent Application Laid-Open No. 2020-97643, etc., and thus detailed description thereof is omitted.

[0024] Below the printer U, a paper feed tray TR1, which is an example of a housing means, is arranged. The paper feed tray TR1 houses a sheet S, which is an example of a medium. The sheet S in the paper feed tray TR1 is fed by a paper feed roller Rp, which is an example of a paper feed means, and conveyed toward the transfer area Q4 by a chain gripper Ra, which is an example of a conveying means. Below the backup roll T2a, a transfer cylinder T2b, which is an example of a transfer member, is arranged. A transfer area Q4 is formed by the area sandwiched between the transfer cylinder T2b and the backup roll T2a. In the transfer area Q4, the sheet S and the intermediate transfer belt B are brought into contact with each other while being pressed by the transfer cylinder T2b and the backup roll T2a, and the image held on the surface of the intermediate transfer belt B is transferred to the sheet S. The backup roll T2a and the transfer cylinder T2b constitute a transfer device T2 as an example of the transfer means of the first embodiment.

[0025] The sheet S that has passed through the transfer area Q4 is conveyed to a discharge tray TRh, which is an example of a stacking means, and stacked on the discharge tray TRh. The irradiation device F1, which is an example of a fixing means, is arranged at the position where the sheet S passes through the transfer area Q4. The irradiation device F1 irradiates electromagnetic waves that cure the ink on the surface of the sheet S. The electromagnetic waves used can be electron beams, ultraviolet rays (UV), infrared rays, etc., depending on the type of ink used. Therefore, the irradiation device F1 cures the ink and fixes the image on the sheet S. The sheet S that has passed through the irradiation device F1 is conveyed to a discharge tray TRh, which is an example of a stacking means, and stacked on the discharge tray TRh.

[0026] (Description of the conveying means) FIG. 2 is an explanatory view of the conveying means of the first embodiment. The chain gripper Ra of the first embodiment has a mounting cylinder 1 and a driven shaft 2, which are examples of mounting means. The mounting cylinder 1 is arranged upstream of the transfer cylinder T2b with respect to the conveying direction of the sheet S. The mounting cylinder 1 of the first embodiment is composed of a cylindrical member extending in the left - right direction, and a concave - shaped accommodating portion 1a extending in the left - right direction is formed in a part of the circumferential direction. The accommodating portion 1a is configured to be able to accommodate a gripper 11, which will be described later. Note that the transfer cylinder T2b also has a housing portion T2c configured in the same manner as the housing portion 1a. Further, in the transfer cylinder T2b of the first embodiment, the backup roll T2a is made of a material with higher rigidity than that of the transfer cylinder T2b. For example, the transfer cylinder T2b can be mainly composed of urethane, and the backup roll T2a can be mainly composed of stainless steel. And the transfer cylinder T2b is pressed against the intermediate transfer belt B and the backup roll T2a so as to have a predetermined contact pressure. Therefore, in the transfer region Q4 where the transfer cylinder T2b and the intermediate transfer belt B face and contact each other, the transfer cylinder T2b will undergo elastic deformation. Also, in the first embodiment, the radius of the transfer cylinder T2b is formed to be sufficiently larger than the radius of the backup roll T2a. Further, in the first embodiment, the backup roll T2a rotates passively, and the transfer cylinder T2b is driven by the motor M1. Therefore, the transfer cylinder T2b has a stronger rotational torque and driving force than the backup roll T2a.

[0027] The driven shaft 2 is arranged on the downstream side of the irradiation device F1 with respect to the conveyance direction of the sheet S. The mounting cylinder 1 and the driven shaft 2 are rotatably supported. Also, the chain gripper Ra of the first embodiment has a chain 6 as an example of a circulating means. The chains 6 are arranged in a pair on the left and right. The chain 6 of the first embodiment is configured in an endless shape that passes through the positions of the mounting cylinder 1, the transfer cylinder T2b, and the driven shaft 2 in order and returns to the position of the mounting cylinder 1. The chain 6 is supported by sprockets (not shown) as an example of gears supported at both axial ends of the rotating shafts of the mounting cylinder 1 and the transfer cylinder T2b and the driven shaft 2. Note that in the first embodiment, driving is transmitted to the transfer cylinder T2b from a motor (not shown) as an example of a driving source. Therefore, as the transfer cylinder T2b rotates, the chain 6 rotates along the circulating direction Yb.

[0028] The chain 6 supports a gripper 11 as an example of gripping means. A plurality of grippers 11 are arranged at intervals along the circumferential direction of the chain 6. Each gripper 11 of the first embodiment is arranged such that when it reaches the position of the mounting cylinder 1 or the transfer cylinder T2b, the intervals between the grippers 11, the diameter of the mounting cylinder 1 and the transfer cylinder T2b, and the distance between the mounting cylinder 1 and the transfer cylinder T2b are set so that they are accommodated in the accommodating portions 1a and T2c. Each gripper 11 has a support plate 13 as an example of support means supported by a plate 12 inside the chain 6. A pair of left and right support plates 13 are arranged. Between the support plates 13, a plate portion 14 is supported as an example of the first gripping portion. The plate portion 14 of the first embodiment is formed in a plate shape extending in the left - right direction.

[0029] A rotary shaft 16 penetrating in the left - right direction is rotatably supported by the support plate 13. The outer end of the rotary shaft 16 extends outside the chain 6. A cam (not shown) is supported at the outer end portion of the rotary shaft 16 as an example of a member to be transmitted. A contact portion 17 is supported on the rotary shaft 16 as an example of the second gripping portion. A plurality of contact portions 17 are arranged at intervals in the left - right direction. A spacer 18 is arranged between the contact portions 17 on the rotary shaft 16 as an example of a gap member. The outer surface of the spacer 18 is formed in an arc shape along the outer peripheral surface of the mounting cylinder 1 or the transfer cylinder T2b. That is, in a state where each gripper 11 is accommodated in the accommodating portion 1a, the outer surface of the spacer 18 is configured to complement the missing portion of the circle of the outer periphery of the mounting cylinder 1 corresponding to the portion of the accommodating portion 1a.

[0030] In FIG. 1, between the transfer cylinder T2b and the driven shaft 2, a plurality of fans 19 are installed as an example of floating means for blowing air from below against the passing sheet S to float the sheet S. In the first embodiment, the sheet S is conveyed while being floated using the fans 19, but it is also possible to install a guide plate as an example of guiding means, a rotating conveyor belt, etc. Even in that case, the conveyance of the sheet S itself is performed by the grippers 11.

[0031] (Function of Chain Gripper Ra) Each gripper 11 of Example 1 moves along the circumferential direction Yb of the chain 6 as the chain 6 rotates. At this time, the gripper 11 of Example 1 is configured such that the cam of the rotation shaft 16 is guided along a guide groove (not shown) arranged along the circumferential direction Yb of the chain 6. The guide groove is configured to rotate the cam to approach the contact portion 17 to the plate portion 14 when the gripper 11 passes through the position of the mounting cylinder 1, and to rotate the cam reversely to separate the contact portion 17 from the plate portion 14 when the gripper 11 passes through the position of the driven shaft 2. Therefore, for the conveyance of the sheet S in Example 1, first, in accordance with the timing when the gripper 11 moves to the position of the mounting cylinder 1, the sheet S is conveyed by the paper feed roller Rp. Then, the front end of the sheet S is sandwiched between the contact portion 17 and the plate portion 14. Then, with the movement of the gripper 11 accompanying the rotation of the chain 6, the sheet S is sent to the position of the transfer region Q4 or the irradiation device F1. Then, when passing through the irradiation device F1, the contact portion 17 and the plate portion 14 are separated, the front end of the sheet S is released, and it is conveyed to the discharge tray TRh by the discharge roll Rh.

[0032] (Explanation of the Control Unit of Example 1) FIG. 3 is an explanatory diagram of the control unit of Example 1. In FIG. 3, a control unit (controller) C as an example of the control means of the printer U has an input / output interface I / O for inputting / outputting signals to / from the outside. Further, the control unit C has a ROM: read only memory in which programs and information for performing necessary processes are stored. Further, the control unit C has a RAM: random access memory for temporarily storing necessary data. Further, the control unit C has a CPU: central processing unit for performing processes according to programs stored in the ROM and the like. Therefore, the control unit C of Example 1 is constituted by a small information processing device, so-called microcomputer. Thus, the control unit C can realize various functions by executing programs stored in the ROM and the like.

[0033] (Function of Control Unit C) The media type discrimination means C1 discriminates the type of the sheet S to be used. In the first embodiment, as an example of the type of the sheet S, the thickness of the sheet S is discriminated. Note that the thickness of the sheet S can be discriminated based on the information of the sheet S included in the print information, or can be discriminated based on the information input from the operation unit of the printer U. Further, a sensor as an example of a detection means for detecting the thickness of the sheet S may be provided in the conveyance path to the paper feed tray TR1 or the attachment cylinder 1, and the thickness of the sheet S to be used may be detected to discriminate the type of the sheet S.

[0034] FIG. 4 is an explanatory diagram of the penetration amount in the first embodiment, FIG. 4A is an explanatory diagram of the penetration amount when there is no medium, FIG. 4B is an explanatory diagram of the penetration amount in the case of thin paper, FIG. 4C is an explanatory diagram of the penetration amount in the case of plain paper, and FIG. 4D is an explanatory diagram of the penetration amount in the case of thick paper. The penetration amount discrimination means C2 discriminates the penetration amount L1, which is the amount by which the intermediate transfer belt B penetrates into the transfer means, according to the thickness of the sheet S. In FIG. 4, in the transfer area Q4, even when there is no sheet S, the transfer cylinder T2b has a penetration amount L1a. Then, when the sheet S enters the transfer area Q4, the penetration amount L1 of the transfer cylinder T2b increases by the thickness of the sheet S. And the penetration amount L1 becomes larger as the thickness of the sheet S to be used is thicker. That is, the penetration amount L1c in the case of the plain paper S2 is larger than the penetration amount L1b in the case of the thin paper S1, and the penetration amount L1d in the case of the thick paper S3 is larger than the penetration amount L1c in the case of the plain paper S2.

[0035] As an example of the rotation control means for the image holding means, the belt rotation control means C3 controls the rotation of the intermediate transfer belt B. The belt rotation control means C3 of the first embodiment rotates the intermediate transfer belt B at a predetermined rotation speed (predetermined speed) as the image forming operation is executed. In the first embodiment, the rotation speed of the intermediate transfer belt B is set to be constant regardless of the type of the sheet S, but it is not limited thereto. For example, when the sheet S to be used is plain paper, the control unit C controls the rotation speed of the intermediate transfer belt B to be a constant speed in the plain paper mode, and when it is thick paper, in the case of a printer U having a plurality of modes in which the overall speed is reduced in the thick paper mode compared to the plain paper mode, it is also possible to set the rotation speed of the intermediate transfer belt B to a predetermined low speed according to the type of the sheet S.

[0036] The conveyance control means C4 controls the chain gripper Ra. The conveyance control means C4 of the first embodiment controls the rotation of the transfer cylinder T2b to control the moving speed of the chain 6 and the gripper 11, that is, the conveyance speed of the sheet S. In particular, the conveyance control means C4 of the first embodiment controls the rotation of the transfer cylinder T2b so that the conveyance speed of the sheet S in the transfer region Q4, that is, the surface speed of the transfer cylinder T2b, corresponds to the rotation speed (surface speed, peripheral speed) of the intermediate transfer belt B. In the first embodiment, the surface speed of the intermediate transfer belt B is detected by the peripheral speed sensor SN1, and the motor M1 of the transfer cylinder T2b is controlled to control the peripheral speed of the transfer cylinder T2b. The peripheral speed sensor SN1 can adopt any conventionally known method for detecting the peripheral speed, such as installing a disk (encoder) with a slit on the rotation axis of the driven roller and detecting the peripheral speed from the interval of detecting the slit by the peripheral speed sensor SN1 such as an optical sensor, or installing a mark at the widthwise end of the intermediate transfer belt B and detecting the peripheral speed from the interval of detecting the mark by the peripheral speed sensor SN1 such as a camera, or providing a protrusion that rotates together with the rotation axis on the axis of the rotation axis of the transfer cylinder T2b and detecting the convergence by detecting the passage of the protrusion with a sensor.

[0037] In FIG. 4, when the penetration amount L1 of the transfer cylinder T2b increases, the radius r1 from the center of the transfer cylinder T2b to the outer surface decreases. Therefore, when the penetration amount L1 increases, the peripheral speed (= radius × angular velocity) decreases. Thus, in Example 1, as the penetration amount L1 increases so that the surface speed of the transfer cylinder T2b in the transfer region Q4 corresponds to the surface speed of the intermediate transfer belt B, the angular velocity, that is, the rotational speed of the motor M1, is increased.

[0038] The image formation timing control means C5 controls the timing of image formation according to fluctuations in the conveyance speed of the sheet S. The image formation timing control means C5 of Example 1 controls the timing of image formation according to fluctuations in the rotational speed of the transfer cylinder T2b with respect to the intermediate transfer belt B. In Example 1, as an example, it is determined whether the ratio of the rotational speed of the transfer cylinder T2b with respect to the intermediate transfer belt B is within a predetermined range, the fluctuation of the ratio of the rotational speeds is determined, and the timing of image formation is controlled. When the angular velocity of the transfer cylinder, that is, the rotational speed of the motor M1, decreases, the ratio with respect to the intermediate transfer belt B decreases in the image formation timing control means C5 of Example 1, and the smaller the ratio, the more the image formation timing is delayed compared to the case where the ratio is large, so as to control the image forming unit D. That is, the thinner the sheet S (the smaller the penetration amount), the more the image forming unit D is controlled to delay the image formation timing. In Example 1, as the image formation timing, the timing at which each head Hy to Hk discharges ink is controlled. Note that it is not limited to the ratio of the rotational speeds. For example, it is also possible to control the image forming unit D so that the image formation timing is delayed as the angular velocity of the transfer cylinder, that is, the rotational speed of the motor M1, decreases compared to the case where the angular velocity is large. In addition, instead of the ratio of the rotational speeds, it is also possible to use the difference in the rotational speeds between the intermediate transfer belt B and the transfer cylinder T2b as a parameter.

[0039] (Description of the flowchart of Example 1) Next, the control flow in the printer U of Example 1 will be described using a flowchart, so-called flow chart. FIG. 5 is an explanatory diagram of a flowchart of the image formation timing adjustment process of Example 1. The processing of each step ST in the flowchart of FIG. 5 is performed according to a program stored in the control unit C. Further, this processing is executed in parallel with various other processes of the printer U. The flowchart shown in FIG. 5 is started by turning on the power of the printer U.

[0040] In ST1 of FIG. 5, it is determined whether the printer U has received print information and a job has been started. If yes (Y), the process proceeds to ST2; if no (N), ST1 is repeated. In ST2, the type of the sheet S is determined. Then, the process proceeds to ST3. In ST3, the penetration amount L1 is derived according to the thickness of the sheet S. Then, the process proceeds to ST4. In ST4, the angular velocity of the transfer cylinder T2b, that is, the rotation speed of the motor M1, is set according to the thickness of the sheet S. Then, the process proceeds to ST5. In ST5, the imaging timing of the imaging unit D is set according to the angular velocity of the transfer cylinder T2b. Then, the process proceeds to ST6. In ST6, a job, which is an image forming operation, is executed based on the setting of the angular velocity and the imaging timing. Then, the process proceeds to ST7. In ST7, it is determined whether the job has ended. If no (N), ST7 is repeated; if yes (Y), the process returns to ST1.

[0041] (Operation of Example 1) FIG. 6 is an explanatory diagram of the interval at which the medium reaches the secondary transfer area. FIG. 6A is an explanatory diagram for thick paper, FIG. 6B is an explanatory diagram for plain paper, and FIG. 6C is an explanatory diagram for thin paper. In the printer U of Example 1 having the above configuration, the angular velocity of the transfer cylinder T2b is set according to the thickness of the sheet S, and the imaging timing is set. Here, if the peripheral speed of the intermediate transfer belt B fluctuates, the image to be formed will be stretched. Therefore, in Example 1, the peripheral speed of the intermediate transfer belt B is set to be constant. On the other hand, the rotational speed of the motor M1 of the transfer cylinder T2b varies according to the thickness of the sheet S to be used. When the rotational speed of the transfer cylinder T2b varies, the transfer cylinder T2b becomes the rotational resistance (so-called brake) of the intermediate transfer belt B, and the rotational speed of the intermediate transfer belt B may vary. Therefore, the motor M1 is controlled so that the transfer cylinder T2b does not become the rotational resistance of the intermediate transfer belt B, and the rotational speed of the transfer cylinder T2b is adjusted. When the rotational speed of the motor M1 varies, the moving speed (orbital speed) of the chain 6 and the gripper 11 driven by the sprocket coaxial with the transfer cylinder T2b also varies. Therefore, as shown in FIG. 6, in the case of thick paper (when the angular velocity is high), the orbital speed of the gripper 11 becomes high, the speed at which the sheet S is conveyed becomes high, the time when the sheet S reaches the secondary transfer region becomes fast, and the interval between the sheets S becomes narrow. On the other hand, in the case of thin paper (when the angular velocity is low), the orbital speed of the gripper 11 becomes low, the speed at which the sheet S is conveyed becomes low, the time when the sheet S reaches the secondary transfer region becomes slow, and the interval between the sheets S becomes wide.

[0042] Therefore, in Example 1, the time for the image to move from the imaging position Q3 where the image is formed by the heads Hy to Hk on the intermediate transfer belt B to the transfer region Q4 is constant, whereas the time for the sheet S gripped by the gripper 11 on the mounting cylinder 1 to reach the transfer region Q4 varies. Therefore, in the conventional configuration with a fixed imaging timing, there was a risk that the position where the image is transferred to the sheet S would shift. In contrast, in Example 1, the angular velocity of the transfer cylinder T2b is set so as to correspond to the conveyance speed of the sheet S with respect to the rotational speed of the intermediate transfer belt B. Although the angular velocity cannot be freely adjusted, the imaging timing is adjusted according to the variation of the angular velocity. Therefore, the positional deviation between the image and the sheet S is corrected.

[0043] (Example 2) FIG. 7 is an explanatory view of the image forming apparatus according to the second embodiment. Next, a description will be given of the second embodiment of the present invention. In the description of this second embodiment, components corresponding to the components of the first embodiment are denoted by the same reference numerals, and detailed descriptions thereof are omitted. This second embodiment is different from the first embodiment in the following points, but is configured in the same manner as the first embodiment in other points. The printer U of the second embodiment is an electrophotographic image forming apparatus, unlike the first embodiment which is an inkjet type image forming apparatus. Therefore, instead of the image forming unit D of the first embodiment, it has toner image forming apparatuses UY, UM, UC, UK as an example of the image forming unit. The Y-color toner image forming apparatus UY includes a photosensitive drum Py as an example of an image holding means, a charger CRy as an example of a charging means, a writing device ROSy as an example of a latent image forming means, a developing device Gy as an example of a developing means, a primary transfer device T1y as an example of a primary transfer means, and a drum cleaner CLy as an example of a cleaning means. The charger CRy charges the surface of the photosensitive drum Py. The writing device ROSy forms a Y-color electrostatic latent image on the surface of the photosensitive drum Py based on the print information. The developing device Gy develops the latent image on the photosensitive drum Py into a Y-color image. The primary transfer device T1y transfers the image held on the photosensitive drum Py to the intermediate transfer belt B. The drum cleaner CLy removes and cleans the deposits on the surface of the photosensitive drum Py after the primary transfer. The M-color, C-color, and K-color toner image forming apparatuses UM, UC, UK are also configured in the same manner as the Y-color toner image forming apparatus UY.

[0044] In the printer U of the second embodiment, unlike the first embodiment, a secondary transfer voltage is applied between the backup roll T2a and the transfer cylinder T2b. The secondary transfer voltage is a voltage capable of secondarily transferring the Y, M, C, K images held on the intermediate transfer belt B to the sheet S. In the second embodiment, as an example, a developer charged with a negative polarity is used, the transfer cylinder T2b is grounded, and a negative-polarity voltage is applied to the backup roll T2a side. In the printer U of Example 2, instead of the irradiation device F1, a fixing device F as an example of a fixing means is used. The fixing device F of Example 2 has a preheating unit 21 and a main fixing unit 22. The preheating unit 21 has a plurality of infrared heaters 21a arranged along the conveyance direction of the sheet S. The infrared heater 21a as an example of a heating means heats the unfixed toner on the surface of the sheet S in a non-contact manner. The main fixing unit 22 has a pressure roll 22a as an example of a pressing means arranged in place of the driven shaft 2. A housing portion 22b is formed in the pressure roll 22a in the same manner as the transfer drum T2b and the like. Opposite to the pressure roll 22a, a heating roll 22c as an example of a heating means is arranged. The heating roll 22c is configured in a hollow cylindrical shape, and a heater (not shown) as an example of a heat source is built therein. Therefore, when the sheet S passes through the fixing area Q5 sandwiched between the pressure roll 22a and the heating roll 22c, the unfixed toner on the sheet S is fixed (main fixed) while being heated. Note that in the control unit C of Example 2, the writing devices ROSy to ROSk adjust the imaging timing by adjusting the timing when the latent image is formed.

[0045] (Operation of Example 2) In the printer U of Example 2 having the above configuration, as in Example 1, the intermediate transfer belt B rotates at a constant rotational speed. Therefore, the time until the image written by the writing devices ROSy to ROSk reaches the transfer area Q4 is constant. On the other hand, when the angular velocity of the transfer drum T2b varies according to the thickness of the used sheet S, the timing when the writing devices ROSy to ROSk form the latent image is adjusted. Therefore, it is possible to correct the deviation in the position of the image secondarily transferred to the sheet S.

[0046] (Modification Example) As described above, the embodiments of the present invention have been described in detail. However, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the gist of the present invention described in the claims. Modification examples (H01) to (H07) of the present invention are exemplified below. (H01) In the above embodiments, a printer as an example of an image forming apparatus was illustrated, but the present invention is not limited thereto. For example, the present invention is also applicable to image forming apparatuses such as copiers and FAX machines. Further, an image forming apparatus using four colors of Y, M, C, and K was illustrated, but the present invention is not limited thereto. The present invention is also applicable to monochromatic image forming apparatuses and image forming apparatuses using two, three, or five or more colors.

[0047] (H02) In the second embodiment, an electrophotographic image forming apparatus having an intermediate transfer belt B was illustrated, but the present invention is not limited thereto. The present invention is also applicable to a configuration in which an image is directly transferred from the photoreceptor drums Py to Pk to the sheet S. (H03) In the above embodiments, the chain gripper Ra was illustrated as the conveying means, but the present invention is not limited thereto. For example, the present invention is applicable to any configuration in which the conveying speed of the sheet S varies according to the thickness and the amount of penetration of the sheet S by using a transfer conveying belt that supports and rotates the sheet on the upper surface.

[0048] (H04) In the above embodiment, although the thickness of the sheet S and the amount of penetration are exemplified as cases where the angular velocity of the transfer cylinder T2b fluctuates, the present invention is not limited thereto. For example, it is also possible to vary the angular velocity according to the environment such as temperature and humidity, wear due to aging deterioration, production variations, etc. For example, when the temperature is high and the amount of penetration increases due to the thermal expansion of the transfer cylinder T2b, it is possible to vary the angular velocity according to the temperature. Also, when the humidity is high and the transfer cylinder T2b expands due to moisture absorption and the amount of penetration increases, it is possible to vary the angular velocity according to the humidity. Further, when the transfer cylinder T2b wears due to aging deterioration and its diameter becomes smaller, it is also possible to vary the angular velocity. When the amount of penetration varies due to production variations, it is also possible to vary the angular velocity according to the amount of penetration. Also, although only the thickness of the sheet S is exemplified as the type of medium, the present invention is not limited thereto. For example, when a medium type that is easily compressed when sandwiched between the backup roll T2a and the transfer cylinder T2b, such as a sheet in which a plurality of materials such as paper and a coating layer are laminated (so-called coated paper) or paper having unevenness (so-called embossed paper), or when the medium type is less compressible than plain paper such as an OHP sheet, it is possible to individually set the amount of penetration in the transfer region Q4 according to the type of medium and vary the angular velocity.

[0049] (H05) In the above embodiment, although the case where the amount of penetration L1 changes due to the elastic deformation of the transfer cylinder T2b as the thickness of the medium used is exemplified, the present invention is not limited thereto. For example, according to the type of medium used, it is also applicable to a configuration in which the backup roll T2a and the transfer cylinder T2b are moved in a direction approaching or separating from each other to adjust the contact pressure and the amount of penetration. In this case, it is desirable to vary the angular velocity in addition to the change in the amount of penetration accompanying the approach and separation of the backup roll T2a and the transfer cylinder T2b. For example, it is also applicable to a configuration in which the contact pressure is increased to assist the movement of the developer with a physical force when the developer is difficult to move due to the electrical resistivity of the medium.

[0050] (H06) In the above embodiments, as an example of the imaging timing, the timing when the heads Hy to Hk eject ink or the timing when the writing devices ROSy to ROSk form a latent image was exemplified, but the present invention is not limited thereto. Since the control timing of each member for imaging and the timing for outputting control signals are interlocked, any parameter that serves as a reference for the imaging timing can be used. For example, the timing when marks provided on the intermediate transfer belt B or the photosensitive drums Py to Pk are read, the timing when a sensor for detecting the peripheral speed of the transfer cylinder T2b detects a slit or a protrusion, the timing when it is detected that the sheet S has reached a specific position, the timing when the chargers CRy to CRk start charging or the timing of voltage application, etc., can be used as a reference. Therefore, the "reference" may be the timing when the heads Hy to Hk and the writing devices ROSy to ROSk operate, or the timing when the heads Hy to Hk and the writing devices ROSy to ROSk operate after a certain time has elapsed from the reference. That is, the "reference" here refers to something that serves as a standard for the start timing of imaging.

[0051] (H07) In the above embodiments, the case where the rotation speed of the transfer cylinder T2b is controlled in accordance with the peripheral speed of the intermediate transfer belt B was exemplified, but the present invention is not limited thereto. Even if it is not the same peripheral speed as that of the intermediate transfer belt B, it is also possible to adjust the rotation speed of the transfer cylinder T2b so as to be a speed deviated from the peripheral speed of the intermediate transfer belt B within a predetermined range.

Explanation of symbols

[0052] 11... Gripping means, B... Image holding means, C... Control means, D, UY, UM, UC, UK... Imaging means, L1... Penetration amount, Q4... Transfer region, Ra... Conveying means, S... Medium, T2... Transfer means, T2c... Accommodating portion, U... Image forming apparatus.

Claims

1. Image holding means capable of holding an image on its surface while rotating, Image forming means for forming the image on the image holding means, Transfer means for transferring the image from the image holding means to a medium while rotating, Conveying means that orbits as the transfer means rotates and conveys the medium to the transfer area while holding the medium, Control means for changing the timing of image formation according to fluctuations in the ratio of the rotational speed of the transfer means to that of the image holding means, An image forming apparatus characterized by comprising the above.

2. Image holding means capable of holding an image on its surface while rotating, Image forming means for forming the image on the image holding means, Transfer means for transferring the image from the image holding means to a medium while rotating, Conveying means that orbits as the transfer means rotates and conveys the medium to the transfer area while holding the medium, Control means for changing the timing of image formation according to fluctuations in the rotational speed of the transfer means with respect to the image holding means in a mode where the image holding means rotates at a predetermined speed, An image forming apparatus characterized by comprising the above.

3. Image holding means capable of holding an image on its surface while rotating, Image forming means for forming an image on the image holding means, Transfer means that is pressed against the image holding means and transfers the image of the image holding means to a medium, Conveying means for conveying the medium, Control means for varying the conveyance speed of the medium by the conveying means according to fluctuations in the rotational speed of the image holding means, and for controlling the timing at which the image forming means forms an image according to fluctuations in the conveyance speed of the medium, wherein the control means changes the rotational speed of the transfer means with respect to the image holding means according to the amount by which the image holding means bites into the transfer means, An image forming apparatus characterized by comprising the above.

4. The transfer means that is pressed against the image holding means, The control means for changing the rotational speed of the transfer means with respect to the image holding means according to the amount by which the image holding means bites into the transfer means, The image forming apparatus according to claim 1 or 2, characterized by comprising the above.

5. The control means for controlling the conveying means so that the conveyance speed of the medium corresponds to the peripheral speed of the image holding means according to the amount of biting, The image forming apparatus according to claim 3 or 4, characterized by comprising the above.

6. Gripping means for gripping the end of the medium, the conveying means having a plurality of the gripping means arranged at intervals along the conveyance direction of the medium and movable along the conveyance direction of the medium, The transfer means in which an accommodation part for accommodating the gripping means that passes through a transfer area where the image holding means and the transfer means face each other is formed, The image forming apparatus according to any one of claims 1 to 5, characterized by comprising the above.

7. The transfer means pressed toward the image holding means, The control means for controlling the timing at which the image forming means forms an image according to the amount by which the image holding means bites into the transfer means varying according to the type of medium, The image forming apparatus according to any one of claims 1 to 6, characterized by comprising the above.

8. The control means for controlling the timing at which the image forming means forms an image according to the biting amount that varies according to the thickness of the medium, The image forming apparatus according to claim 7, characterized by comprising the above.

9. The control means for delaying the timing at which the image forming means forms an image when the thickness of the medium is thin compared to when the thickness of the medium is thick, The image forming apparatus according to claim 8, characterized by comprising the above.

10. The transfer means pressed toward the image holding means, The control means for controlling the timing at which the image forming means forms an image according to the amount by which the image holding means bites into the transfer means varying according to the installation environment of the image forming apparatus, The image forming apparatus according to any one of claims 1 to 9, characterized by comprising the above.

11. The control means for reducing the biting amount and delaying the timing at which the image forming means forms an image when the installation environment is lower in humidity than a predetermined value compared to when it is higher in humidity than the predetermined value, The image forming apparatus according to claim 10, characterized by comprising the above.

Images