Image forming apparatus

Abstract

To prevent continuous form paper from contacting an intermediate transfer belt when separating the intermediate transfer belt and a transfer roller from each other.SOLUTION: An image forming apparatus comprises: an image forming unit group 120 that forms toner images; an intermediate transfer belt that receives transfer of the toner images; a transfer roller that transfers the toner images transferred to the intermediate transfer belt to roll paper; a switching section that switches between a first state in which the roll paper can be inserted between the transfer roller and the intermediate transfer belt, and a second state in which a gap larger than a thickness of the roller paper is provided between the transfer roller and the intermediate transfer belt; a downstream side roller that conveys the continuous form paper on a downstream side of the transfer roller on a conveyance path for conveying the roll paper; and a control section 160 that, when causing the switching section to switch from the first state to the second state, rotates the downstream side roller to reduce slack of the roll paper on an upstream side of the downstream side roller on the conveyance path.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to an image forming apparatus. [Background technology]

[0002] Conventionally, there has been a technique for preventing toner from adhering to continuous paper when forming patch images by separating an intermediate transfer belt from a secondary transfer unit (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-44978 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, even if the intermediate transfer belt and the secondary transfer unit are separated from each other during the formation of patch images, if the intermediate transfer belt and the continuous paper come into contact with each other, toner will adhere to the continuous paper.

[0005] Therefore, one or more aspects of the present disclosure aim to prevent the continuous paper from coming into contact with the intermediate transfer belt when the intermediate transfer belt and the transfer roller are separated from each other. [Means for solving the problem]

[0006] An image forming apparatus according to one embodiment of the present disclosure is characterized in that it comprises an image forming unit that forms a developer image, which is an image of a developer; an intermediate transfer belt that receives the transfer of the developer image; a transfer roller that transfers the developer image transferred to the intermediate transfer belt to continuous paper; a switching unit that switches between a first state in which the continuous paper is sandwiched between the transfer roller and the intermediate transfer belt and a second state in which a gap larger than the thickness of the continuous paper is provided between the transfer roller and the intermediate transfer belt; a downstream roller that transports the continuous paper downstream of the transport path of the continuous paper from the transfer roller; and a control unit that rotates the downstream roller to reduce slack in the continuous paper upstream of the downstream roller in the transport path when causing the switching unit to switch from the first state to the second state. Effect of the Invention

[0007] According to one or more aspects of the present disclosure, when the intermediate transfer belt and the transfer roller are separated from each other, the continuous paper can be prevented from contacting the intermediate transfer belt. [Brief description of the drawings]

[0008] [Figure 1] 1 is a vertical sectional view showing a schematic configuration of an image forming apparatus according to an embodiment; [Diagram 2] FIG. 2 is a first vertical cross-sectional view illustrating a schematic configuration of a secondary transfer unit and a configuration of a secondary transfer roller. [Diagram 3] 5 is a second vertical cross-sectional view illustrating the configuration of a secondary transfer unit and the configuration of a secondary transfer roller; FIG. [Figure 4] FIG. 2 is a block diagram illustrating a schematic configuration of a control system according to the present embodiment. [Diagram 5] 1A and 1B are block diagrams illustrating an example of a hardware configuration. [Figure 6] 11 is a vertical cross-sectional view showing an example in which the roll paper becomes loose and comes into contact with the intermediate transfer belt. [Figure 7] 5 is a flowchart showing an operation performed when starting image adjustment in the image forming apparatus. [Figure 8] 13A to 13C are schematic diagrams illustrating a method for detecting slack in the roll paper using a pre-fixing slack sensor. [Figure 9] 10 is a flowchart showing an operation for determining whether or not to perform a pulling operation on the roll paper. [Figure 10] 1 is a table showing criteria for determining the tendency of a medium to slacken. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Embodiment FIG. 1 is a vertical cross-sectional view showing a schematic configuration of an image forming apparatus 100 according to an embodiment. The image forming apparatus 100 includes a feeder unit 102 that supplies roll paper 101, which is continuous paper, and a printing unit 110 that serves as the image forming apparatus main body and forms an image on the roll paper 101 supplied from the feeder unit 102 by electrophotography.

[0010] The feeder unit 102 drives a feeder motor 103 to feed the roll paper 101 to the printing unit 110 via a feeder conveying roller 104 . A paper feed sensor 106 detects whether or not the roll paper 101 is being fed to the feeder unit 102 .

[0011] Before being fed into the feeder unit 102, the roll paper 101 is kept at a constant tension by a tension bar 105. One end 105a of the tension bar 105 is supported so as to be freely rotatable, and the other end 105b is allowed to move freely. The tension of the roll paper 101 is kept constant by placing the other end 105b, which is allowed to move freely, on the roll paper 101 from above.

[0012] The roll paper 101 supplied from the feeder unit 102 is sandwiched and transported by a group of transport rollers 112 that are driven to rotate by a transport motor 111. The roll paper 101 then passes through a first IN sensor 113, a second IN sensor 114, and a third IN sensor 115, and reaches a secondary transfer position P.

[0013] Image forming units 120Y, 120M, 120C, 120K, and 120W are image forming sections that respectively form toner images (developer images) that are images of toner (developer) of yellow Y, magenta M, cyan C, black K, and white W. Here, in Fig. 1, capital Y indicates yellow, capital M indicates magenta, capital C indicates cyan, capital K indicates black, and capital W indicates white.

[0014] Since the image forming units 120Y, 120M, 120C, 120K, and 120W are configured similarly except for the colors of toner that they use, the structure of the image forming unit 120Y will be described here.

[0015] An LED head 121Y as an exposure unit forms an electrostatic latent image on a photoconductor 122Y as an image carrier. The developing roller 123Y selectively deposits toner only onto the electrostatic latent image formed on the photoconductor 122Y, thereby developing a toner image onto the photoconductor 122Y.

[0016] At the contact point between the intermediate transfer belt 130 and the photoconductor 122Y, a primary transfer bias is applied to the primary transfer roller 131Y from a high voltage supply unit (not shown), so that the toner image formed on the photoconductor 122Y is transferred to the intermediate transfer belt 130.

[0017] Image forming units 120M, 120C, 120K, and 120W are configured similarly to image forming unit 120Y, and primary transfer rollers 131Y, 131M, 131C, and 131W transfer the toner images onto intermediate transfer belt 130 so that they are superimposed on top of each other without any misalignment.

[0018] The intermediate transfer belt 130 receives the toner images transferred thereto from each of the image forming units 120Y, 120M, 120C, 120K, and 120W. The intermediate transfer belt 130 is supported by belt support rollers 132, 133, 134 and a backup roller 135 so as to be rotatable in the direction of arrow D. The intermediate transfer belt 130 is rotated by the drive of a belt motor 136, and carries the toner image to a secondary transfer position P.

[0019] Below the backup roller 135, a secondary transfer unit 140 is disposed. The secondary transfer unit 140 includes a secondary transfer roller 141 that transfers the toner image transferred onto the intermediate transfer belt 130 onto the roll paper 101, which is continuous paper.

[0020] Here, the secondary transfer unit 140 can switch the state of the secondary transfer unit 140 between a first state in which the roll paper 101 is sandwiched between the secondary transfer roller 141 and the intermediate transfer belt 130, and a second state in which a gap larger than the thickness of the roll paper 101 is provided between the secondary transfer roller 141 and the intermediate transfer belt 130, in accordance with instructions from a control unit described later.

[0021] When the toner image on the intermediate transfer belt 130 passes through the backup roller 135 , a secondary transfer bias is applied to the secondary transfer roller 141 from a high voltage supply unit (not shown), so that the toner image is transferred to the roll paper 101 .

[0022] During the operation of performing image adjustment, the density sensor 137 detects the density of the patch image, which is a toner image for image adjustment formed on the intermediate transfer belt 130 as described above. Any patch images that have not been transferred are removed by the belt cleaning roller 138.

[0023] The apparatus cover 107 is a cover that allows access to at least the image forming units 120M, 120C, 120K, and 120W from outside the image forming apparatus 100. For example, the device cover 107 is an openable and closable cover, and by opening the device cover 107, the user can operate the image forming units 120M, 120C, 120K, 120W or the intermediate transfer belt 130, and can perform tasks such as replacing them.

[0024] The roll paper 101 onto which the toner image has been transferred is transported, passes through a pre-fixing slack sensor 150 , and reaches a fixing unit 151 .

[0025] The pre-fixing slack sensor 150 functions as a slack detection unit that detects whether or not there is slack in the roll paper 101. The specific configuration will be described later.

[0026] The fixing unit 151 is a fixing device that fixes the toner image transferred onto the roll paper 101 onto the roll paper 101 . The fixing unit 151 includes a heating belt 152 that heats the toner image, and a fixing backup roller 153 that presses the roll paper 101 toward the heating belt 152 to sandwich and transport the roll paper 101 together with the heating belt 152 .

[0027] The fixing backup roller 153 is rotated by a fixing motor 154. As a result, the fixing backup roller 153 and the heating belt 152 fix the toner image while transporting the roll paper 101.

[0028] After the toner image is fixed, the roll paper 101 is transported by a pair of discharge rollers 155 that are rotated by a fixing motor 154 , passes a fixing discharge sensor 156 and a discharge sensor 157 , and is discharged outside the image forming apparatus 100 .

[0029] In this embodiment, the fixing backup roller 153, which is a roller in the fixing unit 151, functions as a downstream roller that transports the roll paper 101 downstream of the secondary transfer roller 141, but this embodiment is not limited to this example. For example, the discharge roller pair 155 may function as the downstream roller.

[0030] 2 and 3 are vertical cross-sectional views each showing a schematic configuration of the secondary transfer unit 140 and the secondary transfer roller 141. FIG. The secondary transfer unit 140 includes a secondary transfer roller 141 , an arm plate 142 , a spring 143 , an eccentric cam 144 , a secondary transfer motor 145 , and transport rollers 146 and 147 .

[0031] The secondary transfer roller 141 can be switched between a state in which it presses the intermediate transfer belt 130 and a state in which it is separated from the intermediate transfer belt 130 by a switching mechanism of the secondary transfer unit 140. The switching mechanism will be described below.

[0032] The secondary transfer roller 141 is rotatably supported at one end of an arm plate 142 . The arm plate 142 includes a first plate 142a extending in a first direction and a second plate 142b extending in a second direction intersecting the first direction. The arm plate 142 is supported rotatably about a rotation axis 142c in the vicinity of the boundary between the first plate 142a and the second plate 142b.

[0033] A spring 143 is provided below the arm plate 142 as an example of an elastic member. The force of the spring 143 pulls the first plate 142a of the arm plate 142 in the direction of the spring 143, and the secondary transfer roller 141 attached to one end of the second plate 142b is pushed upward via the rotation shaft 142c. As a result, as shown in FIG. 2, the secondary transfer roller 141 is in a state where it presses the intermediate transfer belt 130. Therefore, when the roll paper 101 is transported, the roll paper 101 can be sandwiched between the secondary transfer roller 141 and the intermediate transfer belt 130.

[0034] An eccentric cam 144 is provided above the spring 143 . The eccentric cam 144 is supported so as to be rotatable about a rotation shaft 144a. A driving force is transmitted to the rotation shaft 144a from a secondary transfer motor 145, so that the eccentric cam 144 can be rotated about the rotation shaft 144a.

[0035] The distance from the center of the rotating shaft 144a to the outer periphery of the eccentric cam 144 is different. Therefore, by rotating the eccentric cam 144, the part of the eccentric cam 144 that is longer from the center of the rotating shaft 144a comes into contact with the first plate 142a of the arm plate 142, and the first plate 142a is pushed in a direction away from the spring 143, and the secondary transfer roller 141 attached to one end of the second plate 142b is pushed downward. As a result, the secondary transfer roller 141 is separated from the intermediate transfer belt 130. Therefore, a gap larger than the thickness of the roll paper 101 is provided between the secondary transfer roller 141 and the intermediate transfer belt 130.

[0036] 3, the highest positions in the direction of gravity of the transport rollers 146, 147 provided on the upstream and downstream sides of the secondary transfer roller 141 are made lower than the highest position of the secondary transfer roller when the secondary transfer roller 141 is separated from the intermediate transfer belt 130. As a result, it is expected that the roll paper 101 will be separated from the intermediate transfer belt 130 when the secondary transfer roller 141 is switched to the separated position.

[0037] As described above, the arm plate 142, the spring 143, the eccentric cam 144 and the secondary transfer motor 145 function as a switching unit that switches between a first state in which the roll paper 101 is sandwiched between the secondary transfer roller 141 and the intermediate transfer belt 130, and a second state in which a gap larger than the thickness of the roll paper 101 is provided between the secondary transfer roller 141 and the intermediate transfer belt 130.

[0038] FIG. 4 is a block diagram showing a schematic configuration of a control system in this embodiment. The control unit 160 controls the printing unit 110 and the feeder unit 102 .

[0039] The command decode control unit 161 receives print instructions and other operation instruction commands from a higher-level host (not shown) via the I / F unit 116 that communicates with other devices, and decodes the instructions and commands. The command decode control unit 161 then sequentially provides the decoded information to the main control unit 162.

[0040] The main control unit 162 issues control instructions and acquires status to the sensor control unit 163, motor control unit 164, image formation control unit 165, image adjustment control unit 166, secondary transfer roller control unit 167, medium state determination unit 168, power saving control unit 169, power saving transition memory unit 170, and cover opening / closing memory unit 171 in response to request commands.

[0041] The sensor control unit 163 reads the sensor status using a sensor group 117 including the paper feed sensor 106, the first IN sensor 113, the second IN sensor 114, the third IN sensor 115, the fixing discharge sensor 156, and the discharge sensor 157 to detect the presence or absence of media, and obtains the slack state of the media using a pre-fixing slackness sensor 150 included in the sensor group 117.

[0042] A motor control unit 164 controls the rotational driving of a motor group 118 including the feeder motor 103, the transport motor 111, the belt motor 136, and the fixing motor 154, and transports the medium.

[0043] The image formation control unit 165 controls the image forming units 120Y, 120M, 120C, 120K, and 120W in accordance with an image formation request from the main control unit 162 to form a toner image.

[0044] When an image adjustment instruction is received, the image adjustment control unit 166 reads the toner image on the intermediate transfer belt 130 with the density sensor 137, and adjusts the image based on the result of reading the toner image.

[0045] The secondary transfer roller control unit 167 switches between a state in which the secondary transfer roller 141 presses the intermediate transfer belt 130 and a state in which the secondary transfer roller 141 is separated from the intermediate transfer belt 130. In other words, the secondary transfer roller control unit 167 controls the secondary transfer unit 140 to switch between the first state and the second state.

[0046] Here, when the condition for switching from the first state to the second state is satisfied, the secondary transfer roller control unit 167 controls the secondary transfer unit 140 to switch from the first state to the second state. For example, when performing image adjustment, the secondary transfer roller control unit 167 switches from the first state to the second state by controlling the secondary transfer unit 140. The image adjustment may be performed in a predetermined case, such as when the device cover 107 is opened or closed, when an instruction is received from the user via an input unit (not shown), when the power supply of the image forming apparatus 100 is turned on, or when consumables such as toner are replaced. Furthermore, when disposing of toner, the secondary transfer roller control unit 167 may switch from the first state to the second state by controlling the secondary transfer unit 140. Disposal of toner may be performed when, for example, degraded toner accumulates in the image forming units 120Y, 120M, 120C, 120K, and 120W as a result of continuous printing of images with low image density. Furthermore, the secondary transfer roller control unit 167 may switch from the first state to the second state by controlling the secondary transfer unit 140 when cleaning the intermediate transfer belt 130. Cleaning of the intermediate transfer belt 130 may be performed in a predetermined case, such as when the number of times an image is formed exceeds a predetermined threshold value or when an instruction is given by a user.

[0047] The medium state determination unit 168 obtains the state of the pre-fixing slackness sensor 150, information from the power saving transition memory unit 170 and the cover open / close memory unit 171 from the main control unit 162, and determines the slackness state of the medium at the secondary transfer position P.

[0048] The power saving control unit 169 turns off the power supply to the print unit 110 and the feeder unit 102 in accordance with the power saving transition instruction from the main control unit 162, and stores in the power saving transition storage unit 170 the fact that the state has been transitioned to the power saving state.

[0049] The cover open / close memory unit 171 stores information on whether the device cover 107 has been opened or closed.

[0050] In the above control system, when the control unit 160 causes the switching unit to switch from the first state to the second state, it rotates the fixing backup roller 153 to reduce slack in the roll paper upstream of the fixing backup roller 153 in the medium transport path. This makes it possible to prevent the roll paper 101 from coming into contact with the intermediate transfer belt 130 in the second state.

[0051] Furthermore, the control unit 160 reduces the slack in the roll paper 101 when the pre-fixing slack sensor 150 detects that the roll paper 101 is slack. Furthermore, the control unit 160 reduces the slack in the roll paper 101 if the device cover 107 is opened or closed after the transport of the roll paper 101 is finally stopped. In addition, the control unit 160 reduces slack in the roll paper 101 when it turns off the power supply to two or more rollers that transport the roll paper 101, including the fixing backup roller 153, after finally stopping the transport of the roll paper 101. One example of turning off the power supply to two or more rollers is when the image forming apparatus 100 is put into a power saving state. Here, the control unit 160 reduces slack in the roll paper 101 by increasing the rotation speed of the downstream rollers that transport the roll paper 101 upstream of the secondary transfer roller 141 on the transport path, compared to the upstream rollers.

[0052] As shown in Fig. 5(A), a part or the whole of the control unit 160 described above can be configured by a memory 10 and a processor 11 such as a CPU (Central Processing Unit) that executes a program stored in the memory 10. Such a program may be provided through a network, or may be provided by being recorded on a recording medium. That is, such a program may be provided, for example, as a program product.

[0053] In addition, a part or all of the control unit 160 may be configured with a processing circuit 12 such as a single circuit, a composite circuit, a processor operated by a program, a parallel processor operated by a program, an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array), for example, as shown in FIG. 5(B). As described above, the control unit 160 can be realized by a processing circuit network.

[0054] Next, the image adjustment operation in this embodiment will be described. The image formation control unit 165 forms patch images for image adjustment on the intermediate transfer belt 130 by the image forming units 120Y, 120M, 120C, 120K, and 120W at the timing when image adjustment is performed.

[0055] When a patch image for image adjustment on the intermediate transfer belt 130 reaches a reading position of the density sensor 137 by the rotational drive of the belt motor 136, the density sensor 137 reads the patch image. The image adjustment control unit 166 performs image adjustment based on the reading result.

[0056] If roll paper 101 is not used, in other words, if cut paper such as A4 or A3 is used, no paper is wasted if the patch image is formed without transporting the medium.

[0057] 2, if a patch image is created and read while the secondary transfer roller 141 is pressing the roll paper 101 toward the intermediate transfer belt 130, the roll paper 101 will be transported and the toner of the patch image will adhere to the roll paper 101. As a result, the toner will adhere to the middle of the roll paper 101, and that portion of the roll paper 101 will be wasted.

[0058] 3, in the present embodiment, the secondary transfer roller control unit 167 forms a patch image by moving the secondary transfer roller 141 to a position spaced apart from the intermediate transfer belt 130. This makes it possible to perform image adjustments and the like without transporting the roll paper 101, thereby preventing the occurrence of paper waste.

[0059] As described above, in the intermediate transfer type image forming apparatus 100 in which the secondary transfer roller 141 can be separated, by separating the secondary transfer roller 141, image adjustments and the like can be performed without soiling the roll paper 101. However, even if the secondary transfer roller 141 is separated from the intermediate transfer belt 130, the toner of the patch image may adhere to the roll paper 101.

[0060] For example, when the device cover 107 is opened to replace consumables while the roll paper 101 is still passing through the printing unit 110, the position of the roll paper 101 may change, causing the roll paper 101 to slacken, as shown in FIG. 6, and causing the roll paper 101 to come into contact with the intermediate transfer belt 130.

[0061] Furthermore, when the printing unit 110 transitions to a power saving state by the power saving control unit 169, the power supply to the feeder motor 103, the transport motor 111, and the fixing motor 154 is turned off from a motor power supply unit (not shown), turning off the motor holding current and making the motor shaft more likely to move. This makes the medium position of the roll paper 101 more likely to change, and the roll paper 101 may come into contact with the secondary transfer roller 141.

[0062] If toner of a patch image adheres to the roll paper 101, the next time printing is performed, the roll paper 101 will pass through the fixing unit 151 while the heating belt 152 and fixing backup roller 153 are still cold. In such a case, the heating belt 152 or fixing backup roller 153 may become dirty, which may result in a decrease in the quality of subsequent prints.

[0063] In order to solve the above problems, in this embodiment, an operation is performed in which the roll paper 101 is transported a certain distance by the fixing motor 154 so as to pull the roll paper 101 (hereinafter also referred to as a pulling operation), thereby eliminating slack in the roll paper 101, which is the medium, at the secondary transfer position P.

[0064] 7 is a flowchart showing operations performed when starting image adjustment in image forming apparatus 100. For example, image adjustment is performed when apparatus cover 107 is opened and then closed. Note that image adjustment may also be performed when image forming apparatus 100 is powered on. In other words, image adjustment is performed when a predetermined condition is satisfied.

[0065] First, the secondary transfer roller control unit 167 checks the state of the secondary transfer roller 141 and determines whether the secondary transfer roller 141 is separated from the intermediate transfer belt 130 (S10). If the secondary transfer roller 141 is separated from the intermediate transfer belt 130 (YES in S10), the process proceeds to step S12, and if the secondary transfer roller 141 is not separated from the intermediate transfer belt 130 (NO in S10), the process proceeds to step S11. The state in which the secondary transfer roller 141 is separated from the intermediate transfer belt 130 is the second state described above.

[0066] In step S11, the secondary transfer roller control unit 167 operates the secondary transfer motor 145 to separate the secondary transfer roller 141 from the intermediate transfer belt 130. In other words, the secondary transfer roller control unit 167 switches from the first state to the second state. Then, the process proceeds to step S12.

[0067] In step S12, the medium state determination unit 168 determines whether or not it is necessary to perform a pulling operation on the roll paper 101. The reason for making this determination is that performing a pulling operation would result in paper waste, so if a pulling operation is unnecessary, the pulling operation is not performed. The determination in step S12 will be explained using FIG. 9. If it is necessary to perform a pulling operation on the roll paper 101 (YES in S12), the process proceeds to step S13, and if it is not necessary to perform a pulling operation on the roll paper 101 (NO in S12), the process proceeds to step S15.

[0068] In step S13, the motor control unit 164 starts conveying the roll paper 101. Here, the motor control unit 164 controls the feeder motor 103, the conveying motor 111, and the fixing motor 154 so that the fixing motor speed, which is the speed at which the fixing motor 154 is moved, is higher than the feeder motor speed, which is the speed at which the feeder motor 103 is moved, and the conveying motor speed, which is the speed at which the conveying motor 111 is moved. Here, the motor control unit 164 may set the speed of the fixing motor 154 higher than the speed at which the medium is normally conveyed, and may set the feeder motor speed and the conveying motor 111 speed lower than the speed at which the medium is normally conveyed. For example, the motor control unit 164 sets the fixing motor speed to 110 mm / s, and the feeder motor speed and the conveying motor speed to 100 mm / s. In addition, if the predetermined distance is L, for example, L=100 mm. By changing the speed of the motor, the rotation speed of the corresponding roller can be changed. The group of conveying rollers 112 and the feeder conveying rollers 104 may be stopped. Here, the group of conveying rollers 112 and the feeder conveying roller 104 function as upstream rollers located upstream of the secondary transfer roller 141 in the conveying path.

[0069] Then, after the roll paper 101 has been transported a predetermined distance, the sensor control unit 163 checks the detection result of the pre-fixing slackness sensor 150 to see if slackness is detected (S14). If slackness is detected (YES in S14), the motor control unit 164 determines that the medium pulling operation is insufficient, and continues transporting the medium until the pre-fixing slackness sensor 150 detects no slackness. Then, if slackness is no longer detected (NO in S14), the process proceeds to step S15.

[0070] In step S15, the motor control unit 164 stops the feeder motor 103, the conveying motor 111, and the fixing motor 154. After the medium transport is stopped, the image adjustment control unit 166 performs image adjustment (S16).

[0071] 8A to 8C are schematic diagrams for explaining how the pre-fixing slack sensor 150 detects slack in the roll paper 101. FIG. For example, as shown in FIGS. 8(A) to 8(C), the pre-fixing slack sensor 150 is a lever-type detection sensor that detects slack in the roll paper 101 based on the position of a lever 150a. Specifically, as shown in FIG. 8(A), when the roll paper 101 is not slack, the lever 150a is at a height between an upper position (upper threshold) for detecting upward slackness and a lower position (lower threshold) for detecting downward slackness. When the roll paper 101 sags upward, as shown in FIG. 8B, the lever 150a becomes higher than the upper position that is determined in advance through experiment or the like. Furthermore, when the roll paper 101 sags downward, as shown in FIG. 8C, the lever 150a becomes lower than the lower position that is determined in advance through experiment or the like. As a result, the pre-fixing slack sensor 150 can detect slack in the roll paper 101 whether the slack is in the upward direction or the downward direction.

[0072] FIG. 9 is a flow chart showing the operation of determining whether or not the operation of pulling the roll paper 101 needs to be performed. First, the medium state determination unit 168 determines whether or not the sensor control unit 163 has detected slack in the medium with the pre-fixing slack sensor 150 (S20). If the sensor control unit 163 has detected slack in the medium with the pre-fixing slack sensor 150 (YES in S20), the process proceeds to step S24, and if the sensor control unit 163 has not detected slack in the medium with the pre-fixing slack sensor 150 (NO in S20), the process proceeds to step S21.

[0073] In step S21, the medium state determination unit 168 references the information stored in the cover opening / closing memory unit 171 to determine whether the device cover 107 has been opened or closed since transport of the roll paper 101 was stopped. If the device cover 107 has been opened or closed since transport of the roll paper 101 was stopped (YES in S21), the process proceeds to step S24, and if the device cover 107 has not been opened or closed since transport of the roll paper 101 was stopped (NO in S21), the process proceeds to step S22.

[0074] In step S22, the medium state determination unit 168 references the information stored in the power saving transition memory unit 170 to determine whether or not a transition to a power saving state has occurred since transport of the rolled paper 101 was stopped. If a transition to a power saving state has occurred since transport of the rolled paper 101 was stopped (YES in S22), the process proceeds to step S24, and if a transition to a power saving state has not occurred since transport of the rolled paper 101 was stopped (NO in S22), the process proceeds to step S23.

[0075] In step S23, the medium state determination unit 168 determines whether or not the roll paper 101 is a medium that easily slackens based on the medium type and thickness of the roll paper 101. If the roll paper 101 is a medium that easily slackens (YES in S23), processing proceeds to step S24, and if the roll paper 101 is not a medium that easily slackens (NO in S23), processing proceeds to step S25.

[0076] In step S24, the medium condition determination unit 168 determines that the medium may be loose even at the secondary transfer position P, and therefore that a pulling operation needs to be performed. On the other hand, in step S25, the medium state determination unit 168 determines that the roll paper 101 is not slack and that there is no need to perform a pulling operation.

[0077] Here, the medium type and thickness of the roll paper 101, and the tendency of the roll paper 101 to become loose will be described. The tendency of the medium to slacken may be determined in advance according to the type and thickness of the medium. For example, the results of an experiment conducted by the inventors are shown in FIG. As shown in Fig. 10, for example, if the medium type is glossy paper, and the thickness of the medium is less than 192 grams per square meter, the medium is prone to sagging. Also, if the medium type is film, and the thickness of the medium is less than 105 grams per square meter, the medium is prone to sagging.

[0078] Based on the above experimental results, it is possible to determine in advance whether or not the roll paper 101 is a medium that is prone to slackening, depending on the combination of the medium type that can be set in the image forming device 100 and its thickness. For example, if the medium type is "plain paper" and the medium thickness is "thin paper", the medium condition determination unit 168 may determine that the medium is prone to slackening. On the other hand, if the medium type is "film", the medium condition determination unit 168 may determine that the medium is not prone to slackening, regardless of the medium thickness.

[0079] As described above, according to this embodiment, it is possible to eliminate the condition in which the medium becomes loose and the roll paper 101 comes into contact with the intermediate transfer belt 130, and it is possible to perform image adjustments, etc., without causing toner to adhere to the roll paper 101.

[0080] Furthermore, according to the present embodiment, image adjustment can be performed without transporting the medium, compared to when image adjustment is performed without separating the secondary transfer roller 141 from the intermediate transfer belt 130, thereby reducing the occurrence of paper waste.

[0081] In addition, according to this embodiment, slack in the roll paper 101 at the secondary transfer position P can be removed before image adjustment is performed. This prevents toner from adhering to the roll paper 101 when performing image adjustment, and prevents unfixed toner from soiling the inside of the device and reducing print quality. Also, by estimating the slack state of the roll paper 101 at the secondary transfer position P and determining whether or not to transport the medium, unnecessary medium transport can be prevented and paper waste can be reduced.

[0082] In the embodiment described above, when performing image adjustment, the secondary transfer roller 141 is separated from the intermediate transfer belt 130 to set the second state, but the embodiment is not limited to this example. For example, the secondary transfer roller 141 may be separated from the intermediate transfer belt 130 when discarding deteriorated toner or when cleaning the intermediate transfer belt 130. In such cases, too, an operation to reduce slack in the roll paper 101 at the secondary transfer position P may be performed, as described above.

[0083] In the embodiment described above, the control unit 160 reduces the slack in the roll paper 101 after switching from the first state to the second state, but this embodiment is not limited to this example. For example, the control unit 160 may reduce the slack in the roll paper 101 before switching from the first state to the second state, or simultaneously with switching from the first state to the second state. Before switching from the first state to the second state, the slack in the roll paper 101 may be reduced when the control unit 160 determines that it is time to perform image adjustment, toner disposal, or cleaning of the intermediate transfer belt 130, in other words, when it is a predetermined time to perform any of these.

[0084] In the embodiment described above, the first state and the second state are switched by moving the secondary transfer roller 141, but the present embodiment is not limited to the above example. For example, the first state and the second state may be switched by moving the backup roller 135. [Explanation of symbols]

[0085] 100 image forming apparatus, 101 roll paper, 102 feeder unit, 103 feeder motor, 104 feeder transport roller, 107 device cover, 110 printing unit, 111 transport motor, 112 transport roller group, 120 image forming unit, 130 intermediate transfer belt, 132, 133, 134 belt support roller, 135 backup roller, 137 density sensor, 140 secondary transfer unit, 141 secondary transfer roller, 142 arm plate, 143 spring, 144 eccentric cam, 145 secondary transfer motor, 146, 147 transport roller, 150 pre-fixing slack sensor, 151 fixing unit, 152 heating belt, 153 fixing backup roller, 160 control unit, 170 power saving transition memory unit, 171 Cover opening / closing memory section.

Claims

1. an image forming unit that forms a developer image, which is an image of a developer; an intermediate transfer belt onto which the developer image is transferred; a transfer roller for transferring the developer image transferred onto the intermediate transfer belt onto a continuous sheet of paper; a switching unit that switches between a first state in which the continuous paper is sandwiched between the transfer roller and the intermediate transfer belt and a second state in which a gap larger than the thickness of the continuous paper is provided between the transfer roller and the intermediate transfer belt; a downstream roller that transports the continuous paper and is located downstream of the transfer roller in a transport path of the continuous paper; a control unit that, when causing the switching unit to switch from the first state to the second state, rotates the downstream roller to reduce slack in the continuous paper on the upstream side of the downstream roller in the conveying path. An image forming apparatus comprising:

2. a slack detection unit for detecting whether the continuous paper is slack, The control unit reduces slack in the continuous paper when the slack detection unit detects that the continuous paper is slack.

2. The image forming apparatus according to claim 1,

3. a cover for allowing access to the image forming unit from outside the image forming apparatus; The control unit reduces slack in the continuous paper when the cover is opened and closed after the transport of the continuous paper is finally stopped.

2. The image forming apparatus according to claim 1,

4. The control unit reduces slack in the continuous paper when power supply to two or more rollers that transport the continuous paper, including the downstream roller, is turned off after transport of the continuous paper is finally stopped.

2. The image forming apparatus according to claim 1,

5. an upstream roller for transporting the continuous paper, the upstream roller being located upstream of the transfer roller; The control unit reduces slack in the continuous paper by making the rotation speed of the downstream roller faster than that of the upstream roller.

5. The image forming apparatus according to claim 1, wherein:

6. The control unit reduces slack in the continuous paper after causing the switching unit to switch from the first state to the second state.

5. The image forming apparatus according to claim 1, wherein:

7. The control unit reduces slack in the continuous paper after causing the switching unit to switch from the first state to the second state.

6. The image forming apparatus according to claim 5,

8. a fixing device that fixes the developer image transferred onto the continuous paper, onto the continuous paper; The downstream roller is a roller inside the fixing unit.

5. The image forming apparatus according to claim 1, wherein:

9. a fixing device that fixes the developer image transferred onto the continuous paper, onto the continuous paper; The downstream roller is a roller inside the fixing unit.

6. The image forming apparatus according to claim 5,

Images