Image forming apparatus, operation control method

Abstract

To provide an image forming apparatus and an operation control method capable of controlling the amount of deflection of a sheet conveyed by both a transfer unit and a fixing unit. [Solution] The image forming apparatus includes a transfer unit 91 that transfers a toner image onto a sheet and transports the sheet, a fixing unit 92 that fixes the toner image transferred onto the sheet onto the sheet and transports the sheet, a first detection processing unit that detects the amount of deflection of the sheet during a specific period in which the sheet is transported by both the transfer unit 91 and the fixing unit 92, and an adjustment processing unit that adjusts the sheet transport speed of the fixing unit 92 based on the amount of deflection detected during the specific period before the specific period ends.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus and an operation control method.

Background Art

[0002] An electrophotographic image forming apparatus includes a transfer unit and a fixing unit. The transfer unit transfers a toner image onto a sheet and conveys the sheet. The fixing unit fixes the toner image transferred onto the sheet onto the sheet and conveys the sheet.

[0003] Also, in order to control the amount of deflection of the sheet conveyed by both the transfer unit and the fixing unit, an image forming apparatus that adjusts the conveyance speed of the second and subsequent sheets by the fixing unit based on the detection result of the amount of deflection of the first conveyed sheet during the image forming operation is known as a related art (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the image forming apparatus according to the related art, it is not possible to control the amount of deflection of the first conveyed sheet during the image forming operation.

[0006] An object of the present invention is to provide an image forming apparatus and an operation control method capable of controlling the amount of deflection of a sheet conveyed by both a transfer unit and a fixing unit.

Means for Solving the Problems

[0007] An image forming apparatus according to one aspect of the present invention comprises a transfer unit, a fixing unit, a first detection processing unit, and an adjustment processing unit. The transfer unit transfers a toner image onto a sheet and transports the sheet. The fixing unit is located downstream of the sheet in the sheet transport path passing through the transfer unit, and fixes the toner image transferred onto the sheet to the sheet and transports the sheet. The first detection processing unit detects the amount of deflection of the sheet during a specific period in which the sheet is transported by both the transfer unit and the fixing unit. Before the end of the specific period, the adjustment processing unit adjusts the transport speed of either the transfer unit or the fixing unit, or both, based on the amount of deflection detected during the specific period.

[0008] An operation control method relating to another aspect of the present invention is performed in an image forming apparatus comprising: a transfer unit that transfers a toner image onto a sheet and transports the sheet; and a fixing unit provided downstream of the sheet transport path passing through the transfer unit in the sheet transport direction, which fixes the toner image transferred onto the sheet onto the sheet and transports the sheet, and includes a detection step and an adjustment step. In the detection step, the amount of deflection of the sheet is detected during a specific period in which the sheet is transported by both the transfer unit and the fixing unit. In the adjustment step, before the end of the specific period, the transport speed of either or both of the transfer unit and the fixing unit of the sheet is adjusted based on the amount of deflection detected during the specific period. [Effects of the Invention]

[0009] According to the present invention, the amount of deflection of the sheet being transported by both the transfer unit and the fixing unit can be controlled. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a cross-sectional view showing the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2]Figure 2 is a block diagram showing the system configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 3] Figure 3 is a cross-sectional view showing the configuration of the image forming section of an image forming apparatus according to an embodiment of the present invention. [Figure 4] Figure 4 is a cross-sectional view showing the configuration around the transfer nip and fixing nip sections of an image forming apparatus according to an embodiment of the present invention. [Figure 5] Figure 5 is a flowchart showing an example of an operation control process performed in an image forming apparatus according to an embodiment of the present invention. [Modes for carrying out the invention]

[0011] The embodiments of the present invention will be described below with reference to the attached drawings. Note that the following embodiments are merely examples of the present invention and do not limit the technical scope of the present invention.

[0012] [Configuration of the image forming apparatus 100] First, the configuration of the image forming apparatus 100 according to an embodiment of the present invention will be described with reference to Figures 1 and 2.

[0013] For the sake of explanation, the vertical direction is defined as the up-down direction D1 when the image forming apparatus 100 is in a usable installation state (as shown in Figure 1). The front-to-back direction D2 is defined with the left side of the image forming apparatus 100 shown in Figure 1 as the front. The left-to-right direction D3 is defined with the front of the image forming apparatus 100 in the aforementioned installation state as the reference point.

[0014] The image forming apparatus 100 is a multifunction device having multiple functions, including a scanning function for reading an image from a document, a printing function for forming an image on a sheet based on the image data, as well as a fax function and a copy function. The present invention may also be applied to image forming apparatuses such as printers, fax machines, and copiers.

[0015] As shown in FIGS. 1 and 2, the image forming apparatus 100 includes an ADF (Auto Document Feeder) 1, an image reading unit 2, an image forming unit 3, a paper feeding unit 4, an operation display unit 5, a storage unit 6, and a control unit 7.

[0016] The ADF 1 conveys the document to be read by the scanning function. The ADF 1 includes a document set unit, a plurality of conveying rollers, a document presser, and a paper discharge unit.

[0017] The image reading unit 2 realizes the scanning function. The image reading unit 2 includes a document table, a light source, a plurality of mirrors, an optical lens, and a CCD (Charge Coupled Device).

[0018] The image forming unit 3 realizes the printing function. Specifically, the image forming unit 3 forms a color or monochrome image on the sheet supplied from the paper feeding unit 4 according to the electrophotographic method.

[0019] The paper feeding unit 4 supplies the sheet to the image forming unit 3. The paper feeding unit 4 includes a paper feeding cassette, a manual feed tray, and a plurality of conveying rollers.

[0020] The operation display unit 5 is the user interface of the image forming apparatus 100. The operation display unit 5 includes a display unit and an operation unit. The display unit displays various information according to the control instruction from the control unit 7. For example, the display unit is a display device such as a liquid crystal display. The operation unit inputs various information to the control unit 7 according to the user's operation. For example, the operation unit is an operation device including operation keys and a touch panel.

[0021] The storage unit 6 is a non-volatile storage device. For example, the storage unit 6 is a flash memory.

[0022] The control unit 7 comprehensively controls the image forming apparatus 100. As shown in Figure 2, the control unit 7 comprises a CPU 11, a ROM 12, and a RAM 13. The CPU 11 is a processor that performs various arithmetic operations. The ROM 12 is a non-volatile memory device in which information such as control programs for causing the CPU 11 to perform various operations is pre-stored. The RAM 13 is a volatile or non-volatile memory device used as temporary storage memory (work area) for the various operations performed by the CPU 11. The CPU 11 comprehensively controls the image forming apparatus 100 by executing various control programs pre-stored in the ROM 12.

[0023] Furthermore, the control unit 7 may be a separate control unit from the main control unit that comprehensively controls the image forming apparatus 100. Also, the control unit 7 may be composed of electronic circuits such as an integrated circuit (ASIC).

[0024] [Configuration of the image forming unit 3] Next, the configuration of the image forming unit 3 will be described with reference to Figures 1 to 4. Here, Figure 3 is a cross-sectional view showing the configuration of multiple image forming units 20, an intermediate transfer belt 26, and a secondary transfer roller 27. Note that in Figure 4, sheets without deflection (with zero deflection) are shown by dashed lines. Also in Figure 4, sheets with deflection are shown by dashed lines. Furthermore, in Figure 4, the current supply path between the first guide member 51 and the ground is shown by a dotted line.

[0025] As shown in Figure 1, the image forming unit 3 comprises four image forming units 20, an optical scanning device 25, an intermediate transfer belt 26, a secondary transfer roller 27, a fixing device 28, and a paper output tray 29. Furthermore, as shown in Figures 2 and 4, the image forming unit 3 also comprises a first guide member 51, a distance sensor 52, a second guide member 53, and a temperature and humidity sensor 54.

[0026] Of the four image forming units 20, image forming unit 21 (see Figure 3) forms a yellow (Y) toner image. Of the four image forming units 20, image forming unit 22 (see Figure 3) forms a cyan (C) toner image. Of the four image forming units 20, image forming unit 23 (see Figure 3) forms a magenta (M) toner image. Of the four image forming units 20, image forming unit 24 (see Figure 3) forms a black (K) toner image. In other words, the image forming unit 3 forms an image on the sheet using each of the CMYK toners. As shown in Figures 1 and 3, the four image forming units 20 are arranged in the order of yellow, cyan, magenta, and black from the front side of the image forming apparatus 100 along the front-to-back direction D2.

[0027] As shown in Figure 3, each image forming unit 20 includes a photoreceptor drum 31, a charging roller 32, a developing device 33, a primary transfer roller 34, and a drum cleaning unit 35. Each image forming unit 20 also includes a toner container 36 as shown in Figure 1.

[0028] An electrostatic latent image is formed on the surface of the photoreceptor drum 31. For example, the photoreceptor drum 31 has a photosensitive layer formed of amorphous silicon. The photoreceptor drum 31 receives rotational driving force supplied from a motor (not shown) and rotates in the rotational direction D4 shown in Figure 3. In this way, the photoreceptor drum 31 transports the electrostatic latent image formed on its surface.

[0029] The charging roller 32 charges the surface of the photoreceptor drum 31 when a preset charging voltage is applied. For example, the charging roller 32 charges the surface of the photoreceptor drum 31 in a positive polarity. The surface of the photoreceptor drum 31, which has been charged by the charging roller 32, is irradiated with light based on image data emitted from the optical scanning device 25. As a result, an electrostatic latent image is formed on the surface of the photoreceptor drum 31.

[0030] The developing device 33 develops the electrostatic latent image formed on the surface of the photoreceptor drum 31. The developing device 33 comprises a pair of stirring members, a magnetic roller, and a developing roller. The pair of stirring members stir the developer contained inside the developing device 33. The developer contains toner and a carrier. As a result, the toner contained in the developer becomes positively charged through friction with the carrier contained in the developer. The magnetic roller draws up the developer stirred by the pair of stirring members and supplies the toner contained in the developer to the developing roller. The developing roller transports the toner supplied from the magnetic roller to a position opposite the photoreceptor drum 31. The developing roller also receives a preset developing bias voltage and supplies the toner transported to the opposite position to the photoreceptor drum 31. As a result, the electrostatic latent image formed on the surface of the photoreceptor drum 31 is made visible (developed). The developing device 33 is supplied with toner from a toner container 36.

[0031] The primary transfer roller 34 receives a preset primary transfer current and transfers the toner image formed on the surface of the photoreceptor drum 31 to the outer surface of the intermediate transfer belt 26. As shown in Figure 3, the primary transfer roller 34 is positioned opposite the photoreceptor drum 31, with the intermediate transfer belt 26 in between.

[0032] The drum cleaning unit 35 removes toner remaining on the surface of the photoreceptor drum 31 after the toner image has been transferred by the primary transfer roller 34.

[0033] The optical scanning device 25 emits light based on image data toward the surface of the photosensitive drum 31 of each image forming unit 20.

[0034] The intermediate transfer belt 26 is an endless belt member onto which the toner image formed on the surface of the photoreceptor drum 31 of each image forming unit 20 is transferred. The intermediate transfer belt 26 is stretched at a predetermined tension by a drive roller 26A (see Figure 3) and a tension roller 26B (see Figure 3). The intermediate transfer belt 26 rotates in the rotation direction D5 shown in Figure 3 as the drive roller 26A rotates in response to rotational driving force supplied from a motor (not shown). As a result, the intermediate transfer belt 26 transports the toner image formed on its outer surface to the transfer nip portion N1 (see Figure 3) formed between the intermediate transfer belt 26 and the secondary transfer roller 27. After the toner image has been transferred by the secondary transfer roller 27, the outer surface of the intermediate transfer belt 26 is cleaned by the belt cleaning device 26C shown in Figure 3.

[0035] The secondary transfer roller 27 receives a preset secondary transfer current and transfers the toner image transferred to the outer surface of the intermediate transfer belt 26 to the sheet supplied from the paper feeding unit 4. As shown in Figure 3, the secondary transfer roller 27 is positioned opposite the drive roller 26A, with the intermediate transfer belt 26 in between. The secondary transfer roller 27 is biased toward the drive roller 26A by a biasing member (not shown) so as to contact the intermediate transfer belt 26 with a preset first nip pressure. At the transfer nip portion N1 (see Figure 3) formed between the secondary transfer roller 27 and the intermediate transfer belt 26, the toner image formed on the intermediate transfer belt 26 is transferred to the sheet. The sheet on which the toner image has been transferred at the transfer nip portion N1 is transported in the transport direction D6 (see Figure 1) toward the fixing nip portion N2 (see Figure 1).

[0036] The intermediate transfer belt 26 and the secondary transfer roller 27 constitute a transfer unit 91 (see Figure 4) that transfers a toner image onto a sheet and transports the sheet.

[0037] The fixing device 28 fixes the toner image transferred to the sheet by the secondary transfer roller 27 to the sheet.

[0038] As shown in Figures 1 and 4, the fixing device 28 includes a fixing roller 41 and a pressure roller 42. The fixing device 28 also includes a drive unit 43 as shown in Figure 2.

[0039] The fixing roller 41 is rotatably mounted and comes into contact with the sheet on which the toner image has been transferred, fixing the toner image to the sheet.

[0040] The pressure roller 42 is rotatably mounted opposite the fixing roller 41. The pressure roller 42 is biased toward the fixing roller 41 by a biasing member (not shown) so as to contact the fixing roller 41 at a predetermined second nip pressure. As a result, the pressure roller 42 forms a fixing nip portion N2 (see Figures 1 and 4) that pressurizes the sheet between itself and the fixing roller 41.

[0041] The drive unit 43 rotates the pressure roller 42 in the rotation direction D7 shown in Figure 4. The drive unit 43 is a motor.

[0042] The fixing roller 41 rotates in the rotational direction D8 shown in Figure 4, as the pressure roller 42 rotates in the rotational direction D7 by receiving rotational driving force supplied from the drive unit 43.

[0043] A heater (not shown) is provided inside the fuser roller 41. The heater heats the fuser roller 41 to a predetermined fixing temperature. When the fuser roller 41 is heated to the fixing temperature, the sheet passing through the fuser nip section N2 is pressurized and heated. As a result, the toner image transferred to the sheet is fixed to the sheet.

[0044] As shown in Figures 1 and 4, the fixing roller 41 and the pressure roller 42 are located downstream of the sheet transport direction D6 in the sheet transport path via the transfer unit 91. The fixing roller 41 and the pressure roller 42 constitute the fixing unit 92 (see Figure 4), which fixes the toner image transferred to the sheet to the sheet and transports the sheet.

[0045] The first guide member 51 guides the sheet between the transfer section 91 and the fixing section 92 in the transport path. The first guide member 51 has a guide surface 51A (see Figure 4) that faces the back surface of the sheet.

[0046] Furthermore, the first guide member 51 removes static electricity from the sheet being transported along the transport path. Specifically, the first guide member 51 is made of a conductive material. Also, as shown in Figure 4, the first guide member 51 is electrically grounded. The first guide member 51 is an example of a guide member of the present invention.

[0047] The distance sensor 52 is used to detect the amount of deflection formed in the sheet when the sheet is transported by both the transfer unit 91 and the fixing unit 92. For example, the distance sensor 52 is a reflective type photosensor having a light emitter and a light receiver. The light emitter emits light toward the transport path. The light receiver receives the light emitted by the light emitter and reflected by the sheet, and outputs a voltage detection signal corresponding to the amount of light received. The distance sensor 52 may also be an ultrasonic sensor or the like.

[0048] The second guide member 53 guides the sheet entering the fixing nip section N2 between the first guide member 51 and the fixing nip section N2 in the transport path.

[0049] The temperature and humidity sensor 54 detects the temperature and humidity of the location where the image forming apparatus 100 is installed. For example, the temperature and humidity sensor 54 is installed inside the housing of the image forming apparatus 100. Alternatively, the temperature and humidity sensor 54 may be installed outside the housing of the image forming apparatus 100.

[0050] Incidentally, in order to control the amount of deflection of the sheets transported by both the transfer unit 91 and the fixing unit 92, an image forming apparatus is known in which the transport speed of the second and subsequent sheets by the fixing unit 92 is adjusted based on the detection result of the amount of deflection of the first sheet transported during the image forming operation.

[0051] However, in the image forming apparatus relating to the aforementioned related technology, it is not possible to control the amount of deflection of the sheet that is initially conveyed during the image forming operation.

[0052] In contrast, in the image forming apparatus 100 according to the embodiment of the present invention, the amount of deflection of the sheet conveyed by both the transfer unit 91 and the fixing unit 92 can be controlled, as will be described below.

[0053] [Configuration of Control Unit 7] Next, the configuration of the control unit 7 will be described with reference to Figure 2.

[0054] As shown in Figure 2, the control unit 7 includes a setting processing unit 61, a second detection processing unit 62, a first detection processing unit 63, and an adjustment processing unit 64.

[0055] Specifically, the ROM 12 of the control unit 7 contains pre-stored operation control programs that enable the CPU 11 to function as each of the aforementioned processing units. The CPU 11 then functions as each of the aforementioned processing units by executing the operation control programs stored in the ROM 12.

[0056] The operation control program may be recorded on a computer-readable recording medium such as a CD, DVD, or flash memory, and may be read from the recording medium and stored in a storage device such as the storage unit 6. Furthermore, some or all of the processing units included in the control unit 7 may be composed of electronic circuits. Also, the operation control program may be a program that causes multiple processors to function as individual processing units included in the control unit 7.

[0057] The setting processing unit 61 sets the sheet on which the image will be formed in the image formation process, in accordance with the user's operation on the operation display unit 5.

[0058] For example, the setting processing unit 61 displays a sheet setting screen used for setting sheets on the operation display unit 5 in response to predetermined user operations on the operation display unit 5. The sheet setting screen accepts setting operations to set the size and type of sheet. For example, the sheet types are thick paper, plain paper, and thin paper. The setting processing unit 61 sets the sheet type in response to the setting operations.

[0059] The setting operation may also be an operation to set the sheet thickness or basis weight.

[0060] The second detection processing unit 62 uses the distance sensor 52 to detect when the end of the sheet in the transport direction D6 has passed the position in the transport path where the distance sensor 52 detects the amount of sheet deflection.

[0061] For example, the second detection processing unit 62 determines that a sheet does not exist at the detection position if the voltage of the detection signal output from the distance sensor 52 is less than a predetermined threshold. The second detection processing unit 62 also determines that a sheet exists at the detection position if the voltage of the detection signal is equal to or greater than the threshold. The threshold is set based on the voltage of the detection signal corresponding to the distance L1 (see Figure 4) between the sheet and the distance sensor 52 when the amount of deflection of the sheet being transported by both the transfer unit 91 and the fixing unit 92 is zero (see dashed line in Figure 4).

[0062] Then, when the determination result of whether or not a sheet is present at the detection position changes, the second detection processing unit 62 determines that the end of the sheet in the transport direction D6 has passed the detection position.

[0063] In the image forming apparatus 100, the leading edge of the sheet is brought into contact with the register roller 55 (see Figure 1) located upstream of the transfer nip section N1 (see Figure 4) in the transport direction D6, thereby correcting the sheet's skew. Furthermore, in the image forming apparatus 100, if the leading edge of the sheet is not detected by the second detection processing unit 62 within a predetermined time elapsed from the start of sheet transport by the register roller 55, it is determined that a jam (paper jam) has occurred.

[0064] The first detection processing unit 63 detects the amount of deflection of the sheet during a specific period in which the sheet is transported by both the transfer unit 91 and the fixing unit 92.

[0065] Specifically, the first detection processing unit 63 uses the distance sensor 52 to detect the amount of deflection of the sheet.

[0066] For example, the first detection processing unit 63 determines that the specified period has started when a first time has elapsed from the start of sheet transport by the register roller 55, based on the sheet transport speed and the distance from the register roller 55 to the fixing unit 92 along the transport path. The first detection processing unit 63 also determines that the specified period has ended when the sum of the first time and a second time based on the sheet transport speed and the length of the sheet in the transport direction D6 has elapsed from the start of sheet transport by the register roller 55.

[0067] For example, the first detection processing unit 63 detects the amount of sheet deflection at a predetermined detection cycle.

[0068] For example, the first detection processing unit 63 obtains the distance L2 (see Figure 4) between the sheet and the distance sensor 52 based on the voltage of the detection signal output from the distance sensor 52. The first detection processing unit 63 then obtains the difference between distance L1 and distance L2 as the amount of sheet deflection.

[0069] The first time, the second time, and the detection cycle may be set arbitrarily according to the user's operation on the operation display unit 5.

[0070] Furthermore, the first detection processing unit 63 may determine that the specified period has started when a third time has elapsed, based on the sheet's transport speed and the distance from the detection position to the fixing unit 92 in the transport path, from the time the second detection processing unit 62 detects that the leading edge of the sheet has passed the detection position. Alternatively, the first detection processing unit 63 may determine that the specified period has ended when the sum of the third time and the second time has elapsed, from the time the second detection processing unit 62 detects that the leading edge of the sheet has passed the detection position.

[0071] Before the specified period ends, the adjustment processing unit 64 adjusts the sheet transport speed of the fixing unit 92 based on the amount of sheet deflection detected during the specified period.

[0072] For example, the adjustment processing unit 64 adjusts the sheet transport speed of the fixing unit 92 each time the amount of sheet deflection is detected by the first detection processing unit 63.

[0073] Furthermore, the adjustment processing unit 64 adjusts the sheet transport speed of the fixing unit 92 so that the distance between the sheet and the guide surface 51A of the first guide member 51 becomes a specific distance based on the type of sheet (an example of the sheet attributes of the present invention). The distance between the sheet and the guide surface 51A of the first guide member 51 is the distance obtained by subtracting the amount of sheet deflection detected by the first detection processing unit 63 from the distance L3 (see Figure 4) between the sheet that has not formed deflection (see dashed line in Figure 4) and the guide surface 51A.

[0074] For example, in the image forming apparatus 100, a first table data showing the correspondence between the sheet type and the specified distance is stored in the storage unit 6 in advance. In the first table data, the correspondence between the sheet type and the specified distance is defined such that the specified distance is largest when the sheet is cardboard and smallest when the sheet is thin paper. As a result, the thinner the sheet, the greater the amount of static electricity removed from the sheet by the first guide member 51. Therefore, the thinner the sheet, the more variation in the amount of charge in the width direction perpendicular to the transport direction D6 of the sheet can be suppressed. Consequently, the occurrence of twisting of the sheet (for example, the end of the sheet in the width direction bending toward the first guide member 51) caused by the variation in the amount of charge in the width direction of the sheet, which occurs when a sheet with little stiffness is transported, can be suppressed.

[0075] When the image forming process is executed, the adjustment processing unit 64 uses the first table data to obtain the specific distance corresponding to the sheet type set by the setting processing unit 61. The adjustment processing unit 64 also calculates the amount of sheet deflection (target deflection) such that the distance between the sheet and the guide surface 51A of the first guide member 51 is the specific distance, based on the obtained specific distance. The adjustment processing unit 64 then adjusts the sheet transport speed of the fixing unit 92 based on the difference between the amount of sheet deflection detected by the first detection processing unit 63 and the target deflection. In other words, the adjustment processing unit 64 provides feedback control to the drive unit 43 based on the amount of sheet deflection detected by the first detection processing unit 63 and the target deflection.

[0076] Specifically, if the amount of sheet deflection detected by the first detection processing unit 63 is greater than the target deflection amount, the adjustment processing unit 64 controls the drive unit 43 to increase the sheet transport speed of the fixing unit 92 by a predetermined amount. Also, if the amount of sheet deflection detected by the first detection processing unit 63 is less than the target deflection amount, the adjustment processing unit 64 controls the drive unit 43 to decrease the sheet transport speed of the fixing unit 92 by a predetermined amount. Furthermore, the adjustment processing unit 64 adjusts the sheet transport speed of the fixing unit 92 within a predetermined speed adjustment range.

[0077] The adjustment processing unit 64 may adjust the sheet transport speed of the fixing unit 92 so that the distance between the sheet and the guide surface 51A of the first guide member 51 becomes the specified distance based on the sheet thickness (another example of the sheet attributes of the present invention) or the basis weight of the sheet (another example of the sheet attributes of the present invention).

[0078] Furthermore, the adjustment processing unit 64 may adjust the sheet transport speed of the fixing unit 92 so that the distance between the sheet and the guide surface 51A of the first guide member 51 becomes a fixed distance determined independently of the sheet's attributes.

[0079] [Motion control processing] The operation control method of the present invention will be described below with reference to Figure 5, along with an example of the procedure for operation control processing performed by the control unit 7 in the image forming apparatus 100. Here, steps S11, S12, etc. represent the numbers of the processing procedures (steps) performed by the control unit 7.

[0080] Furthermore, the control unit 7 executes the motion control process each time a sheet is transported during the execution of the image forming process.

[0081] Furthermore, the control unit 7 acquires the target deflection amount corresponding to the pre-set sheet type when the image forming process begins.

[0082] <Step S11> First, in step S11, the control unit 7 determines whether or not the specified period has started.

[0083] Specifically, the control unit 7 determines that the specified period has started when the first time, which is determined based on the sheet transport speed and the distance from the register roller 55 to the fixing unit 92 in the transport path, has elapsed from the start timing of sheet transport by the register roller 55.

[0084] If the control unit 7 determines that the specified period has started (Yes in S11), it proceeds to step S12. If the specified period has not started (No in S11), the control unit 7 waits in step S11 for the specified period to start.

[0085] <Step S12> In step S12, the control unit 7 detects the amount of deflection of the sheet. The process in step S12 is an example of the detection steps of the present invention and is performed by the first detection processing unit 63 of the control unit 7.

[0086] Specifically, the control unit 7 obtains the distance L2 (see Figure 4) between the sheet and the distance sensor 52 based on the voltage of the detection signal output from the distance sensor 52. The control unit 7 then obtains the difference between distance L1 and distance L2 as the amount of sheet deflection.

[0087] <Step S13> In step S13, the control unit 7 adjusts the sheet transport speed of the fixing unit 92 based on the deflection amount detection result from the processing in the final step S12. The processing in step S13 is an example of the adjustment step of the present invention and is performed by the adjustment processing unit 64 of the control unit 7.

[0088] Specifically, the control unit 7 controls the driving of the drive unit 43 so that the amount of sheet deflection detected by the process in step S12 matches the target amount of deflection acquired at the start of the image forming process.

[0089] <Step S14> In step S14, the control unit 7 determines whether or not the timing for detecting the amount of sheet deflection has arrived.

[0090] Specifically, the control unit 7 determines that the detection timing has arrived when the detection cycle time has elapsed since the execution of the process in step S12.

[0091] If the control unit 7 determines that the detection timing has arrived (Yes in S14), it proceeds to step S12. If the detection timing has not arrived (No in S14), the control unit 7 proceeds to step S15.

[0092] <Step S15> In step S15, the control unit 7 determines whether the specified period has ended.

[0093] Specifically, the control unit 7 determines that the specified period has ended when the sum of the first time and the second time, which is based on the sheet transport speed and the length of the sheet in the transport direction D6, has elapsed from the start of sheet transport by the register roller 55.

[0094] At this point, if the control unit 7 determines that the specified period has ended (Yes side of S15), it terminates the operation control process. If the specified period has not ended (No side of S15), the control unit 7 proceeds to step S14.

[0095] Thus, in the image forming apparatus 100, before the end of the specified period, the sheet transport speed of the fixing unit 92 is adjusted based on the amount of sheet deflection detected during the specified period. This makes it possible to control the amount of deflection of the sheet that is first transported after the start of the image forming process.

[0096] Furthermore, the number of times the first detection processing unit 63 detects the amount of sheet deflection during the specified period may be just once.

[0097] Furthermore, the adjustment processing unit 64 may adjust the sheet transport speed of the transfer unit 91 based on the amount of sheet deflection detected during the specified period, before the specified period ends.

[0098] Furthermore, the adjustment processing unit 64 may adjust the sheet transport speed of both the transfer unit 91 and the fixing unit 92 based on the amount of sheet deflection detected during the specified period before the specified period ends.

[0099] Furthermore, the adjustment processing unit 64 may adjust the sheet transport speed of the fixing unit 92 so that the distance between the sheet and the guide surface 51A of the first guide member 51 becomes the specified distance based on the temperature and humidity of the installation location of the image forming apparatus 100 detected by the temperature and humidity sensor 54. In this case, the storage unit 6 only needs to have a second table data in place that shows the correspondence between the temperature and humidity of the installation location of the image forming apparatus 100 and the specified distance. In the second table data, the correspondence between the temperature and humidity of the installation location of the image forming apparatus 100 and the specified distance should be defined such that the specified distance is largest when the temperature and humidity of the installation location of the image forming apparatus 100 is determined to be high temperature and high humidity (the sheet is less likely to become charged), and the specified distance is smallest when the temperature and humidity of the installation location of the image forming apparatus 100 is determined to be low temperature and low humidity (the sheet is more likely to become charged).

[0100] Furthermore, the adjustment processing unit 64 may adjust the sheet transport speed of the fixing unit 92 so that the distance between the sheet and the guide surface 51A of the first guide member 51 becomes the specified distance based on both the type of sheet and the temperature and humidity of the installation location of the image forming apparatus 100 detected by the temperature and humidity sensor 54. In this case, the storage unit 6 should pre-store third table data showing the correspondence between the combination of the type of sheet and the temperature and humidity of the installation location of the image forming apparatus 100 and the specified distance. In the third table data, the correspondence between the combination of the type of sheet and the temperature and humidity of the installation location of the image forming apparatus 100 and the specified distance should be defined such that the specified distance is largest when the sheet is cardboard and is hot and humid, and smallest when the sheet is thin paper and is cold and humid.

[0101] [Notes on the invention] The following is an overview of the invention extracted from the above-described embodiments. Note that each configuration and processing function described below can be selected and combined as desired.

[0102] <Note 1> An image forming apparatus comprising: a transfer unit that transfers a toner image onto a sheet and transports the sheet; a fixing unit provided downstream of the sheet transport path passing through the transfer unit, which fixes the toner image transferred onto the sheet onto the sheet and transports the sheet; a first detection processing unit that detects the amount of deflection of the sheet during a specific period in which the sheet is transported by both the transfer unit and the fixing unit; and an adjustment processing unit that adjusts the transport speed of either or both of the sheet by the transfer unit and the fixing unit based on the amount of deflection detected during the specific period before the specific period ends.

[0103] <Note 2> The image forming apparatus according to Appendix 1, wherein the first detection processing unit detects the amount of deflection at a predetermined detection period, and the adjustment processing unit adjusts the transport speed of either the transfer unit or the fixing unit or both each time the amount of deflection is detected by the first detection processing unit.

[0104] <Note 3> The image forming apparatus according to Appendix 1 or 2, comprising electrically grounded conductive guide members for guiding the sheet between the transfer unit and the fixing unit in the transport path, wherein the adjustment processing unit adjusts the transport speed of either the transfer unit or the fixing unit or both such that the distance between the sheet and the guide members becomes a specific distance based on either the attributes of the sheet or the temperature and humidity of the installation location of the image forming apparatus.

[0105] <Note 4> An image forming apparatus according to any one of the appendices 1 to 3, comprising: a distance sensor used for detecting the amount of deflection; and a second detection processing unit that uses the distance sensor to detect that the end of the sheet in the transport direction has passed the deflection detection position in the transport path.

[0106] <Note 5> The image forming apparatus according to any one of the appendices 1 to 4, wherein the adjustment processing unit adjusts the transport speed of the fixing unit.

[0107] <Note 6> An operation control method performed in an image forming apparatus comprising: a transfer unit for transferring a toner image onto a sheet and transporting the sheet; and a fixing unit provided downstream in the sheet transport direction in a sheet transport path passing through the transfer unit for fixing the toner image transferred onto the sheet and transporting the sheet, the operation control method comprising: a detection step for detecting the amount of deflection of the sheet during a specific period in which the sheet is transported by both the transfer unit and the fixing unit; and an adjustment step for adjusting the transport speed of either or both of the sheet by the transfer unit and the fixing unit based on the amount of deflection detected during the specific period before the end of the specific period. [Explanation of Symbols]

[0108] 1 ADF 2 Image reading unit 3 Image forming unit 4 Paper feed section 5 Operation display section 6 Memory section 7 Control Unit 20 Image forming unit 25 Optical scanning device 26 Intermediate transfer belt 27 Secondary transfer roller 28 Fixing device 29 Paper output tray 41 Fixing roller 42 Pressure rollers 43 Drive unit 51 First guide member 52 Distance Sensor 53 Second guide member 54 Temperature and Humidity Sensor 61 Configuration Processing Unit 62 Second Detection Processing Unit 63 First Detection Processing Unit 64 Adjustment Processing Unit 91 Transfer section 92 Fixing section 100 Image forming apparatus

Claims

1. A transfer unit that transfers a toner image onto a sheet and transports the sheet, A fixing unit is provided on the downstream side in the sheet transport direction of the sheet transport path passing through the transfer unit, and fixes the toner image transferred to the sheet to the sheet and transports the sheet, A first detection processing unit for detecting the amount of deflection of the sheet during a specific period in which the sheet is transported by both the transfer unit and the fixing unit, An adjustment processing unit that adjusts the transport speed of either or both of the sheet transfer unit and the fixing unit based on the amount of deflection detected during the specified period before the specified period ends, An image forming apparatus equipped with the following features.

2. The first detection processing unit detects the amount of deflection at a predetermined detection period, The adjustment processing unit adjusts the transport speed of either the transfer unit or the fixing unit, or both, each time the deflection amount is detected by the first detection processing unit. The image forming apparatus according to claim 1.

3. It is electrically grounded and includes a conductive guide member that guides the sheet between the transfer section and the fixing section in the transport path, The adjustment processing unit adjusts the transport speed of either the transfer unit or the fixing unit or both such that the distance between the sheet and the guide member becomes a specific distance based on either the attributes of the sheet or the temperature and humidity of the installation location of the image forming apparatus, or both. The image forming apparatus according to claim 1 or 2.

4. A distance sensor used to detect the amount of deflection, A second detection processing unit that uses the distance sensor to detect when the end of the sheet in the transport direction has passed the deflection detection position in the transport path, The image forming apparatus according to claim 1 or 2, comprising:

5. The adjustment processing unit adjusts the transport speed of the fixing unit. The image forming apparatus according to claim 1 or 2.

6. An operation control method performed in an image forming apparatus comprising: a transfer unit that transfers a toner image onto a sheet and transports the sheet; and a fixing unit provided downstream of the sheet transport path passing through the transfer unit, which fixes the toner image transferred onto the sheet and transports the sheet; A detection step for detecting the amount of deflection of the sheet during a specific period in which the sheet is transported by both the transfer unit and the fixing unit, An adjustment step of adjusting the conveying speed of either or both of the sheet in the transfer section and the fixing section based on the amount of deflection detected during the specified period before the specified period ends, A method for controlling operation that includes this.

Images