Image forming apparatus

Abstract

To prevent timing to start conveying a sheet from unnecessarily getting later.SOLUTION: A control unit (5) of an image forming apparatus (1) executes processing including first conveyance processing of starting conveyance after lapse of a first time from when temperatures detected by temperature detection members (46A, 46B) reach a first temperature, second conveyance processing of starting conveyance upon the detected temperatures reach the first temperature, third conveyance processing of starting conveyance upon the detected temperatures reach a second temperature that is less than the first temperature, and determination processing of determining which of the first conveyance processing, second conveyance processing, and third conveyance processing is to be executed according to a plurality of printing conditions including at least the number of prints.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] When receiving an image forming job, the control unit of the image forming apparatus disclosed in Patent Document 1 sets the conveyance speed, the target temperature for fixing temperature adjustment, and the paper feed permission temperature based on the type of recording material and the information on the number of printed sheets. The paper feed permission temperature is the temperature of the fixing roller that serves as a trigger for starting image formation by operating the paper feed unit after the control unit switches the target temperature simultaneously with issuing a job start signal.

[0003] The paper feed unit operates when the detected temperature of the fixing roller by the temperature sensor exceeds the paper feed permission temperature. The control unit changes the paper feed permission temperature depending on whether the number of printed sheets is greater than or equal to a predetermined number or less than the predetermined number. The paper feed permission temperature when the number of printed sheets is less than the predetermined number is set lower than the paper feed permission temperature when the number of printed sheets is greater than or equal to the predetermined number.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the image forming apparatus disclosed in Patent Document 1, the paper feed permission temperature when the number of printed sheets is greater than or equal to a predetermined number is set higher than the paper feed permission temperature when the number of printed sheets is less than the predetermined number. Depending on the printing conditions during continuous printing, even when the number of printed sheets is greater than or equal to the predetermined number, the temperature of the nip portion may not decrease significantly. In this case, there is no need to set the paper feed permission temperature high even when the number of printed sheets is greater than or equal to the predetermined number, and the paper feed start timing may become unnecessarily late.

[0006] This disclosure has been made in view of the above-mentioned problems, and its purpose is to prevent the timing of sheet transport from being unnecessarily delayed. [Means for solving the problem]

[0007] To solve the above problems, the image forming apparatus of the present disclosure comprises an image forming unit for forming an image on a sheet, a transport unit for transporting the sheet toward the image forming unit, a heater, a temperature sensing member for detecting the temperature of the heater, a fixing unit for fixing the image formed on the sheet by the image forming unit, and a control unit, wherein the control unit performs a process including: a first transport process in which the transport unit starts transporting the sheet after a first hour has elapsed since the temperature detected by the temperature sensing member reached a first temperature; a second transport process in which the transport unit starts transporting the sheet when the detected temperature reaches the first temperature; a third transport process in which the transport unit starts transporting the sheet when the detected temperature reaches a second temperature which is less than the first temperature; and a determination process for determining which of the first transport process, the second transport process, and the third transport process to be executed according to a plurality of printing conditions, including at least the number of sheets to be printed in the print job.

[0008] The control unit determines whether to execute the first, second, or third transport process based on multiple printing conditions. Therefore, compared to changing the transport process based solely on the number of printed sheets, this method can prevent the sheet transport start timing from being unnecessarily delayed.

[0009] In the image forming apparatus of this disclosure, the printing conditions include the length of the sheet in the transport direction, and the control unit may prioritize the execution of the third transport process, the second transport process, and the first transport process in that order as the length of the sheet in the transport direction decreases. When the length of the sheet along the transport direction is short, the temperature of the fixing unit does not decrease easily. For this reason, the shorter the length of the sheet along the transport direction, the earlier the sheet transport start timing can be made to shorten the FPOT (First Paper Output Time).

[0010] In the image forming apparatus of this disclosure, the printing conditions include the thickness of the sheet, and the control unit may prioritize the execution of the first transport process, the second transport process, and the third transport process in the order of increasing sheet thickness. When the sheet thickness is high, the temperature of the fixing unit tends to drop. Therefore, by delaying the start timing of sheet transport as the sheet thickness increases, it is possible to suppress the transport of the sheet while the temperature of the fixing unit has dropped, thereby suppressing the occurrence of poor image fixing on the sheet.

[0011] The image forming apparatus of the present disclosure further comprises a temperature sensor for detecting the temperature outside the image forming apparatus, the printing conditions include the temperature outside the image forming apparatus, and the control unit may prioritize the execution of the third transport process, the second transport process, and the first transport process in that order, as the temperature outside the image forming apparatus detected by the temperature sensor becomes higher.

[0012] When the external temperature of the image forming apparatus is high, the temperature of the fixing unit does not decrease easily. Therefore, the higher the external temperature of the image forming apparatus, the earlier the sheet transport start timing can be made to shorten the FPOT (Functional Process Time).

[0013] In the image forming apparatus of this disclosure, the printing conditions include the sheet transport speed by the transport unit, and the control unit may prioritize the execution of the first transport process, the second transport process, and the third transport process in that order, as the sheet transport speed increases. When the sheet transport speed is high, the temperature of the fixing unit tends to drop. Therefore, the faster the sheet transport speed, the later the sheet transport start timing can be made to prevent the sheet from being transported while the temperature of the fixing unit has dropped, thereby suppressing the occurrence of poor image fixing on the sheet.

[0014] In the image forming apparatus of this disclosure, the printing conditions include setting single-sided printing or double-sided printing on the sheet, and if double-sided printing is set, the execution of the second transport process or the third transport process may be prioritized over the execution of the first transport process. When double-sided printing is set, the fuser unit can store heat while the sheet is turned over after single-sided printing is completed, so the temperature of the fuser unit does not drop easily. For this reason, when double-sided printing is set, the FPOT can be shortened by starting the sheet transport earlier.

[0015] In the image forming apparatus of this disclosure, the first temperature may be the fixing temperature, which is the target temperature for thermal fixing by the fixing unit. In the first and second transport processes, the control unit starts transporting the sheet only after the temperature detected by the temperature sensing member reaches the fixing temperature, which is the target temperature for thermal fixing by the fixing unit. This makes it possible to further suppress a decrease in the fixing strength of the image onto the sheet.

[0016] In the image forming apparatus of the present disclosure, the fixing unit further comprises an endless belt that rotates around the heater and a pressure member that forms a nip portion by sandwiching the belt between itself and the heater, and the second temperature may be a temperature that is the lower limit of the temperature range in which the sheet can be fixed by the fixing unit when it reaches the nip portion.

[0017] Since the conveying process begins only after the sheet reaches a temperature at which it can be fixed when it reaches the nip section, the image fixation strength on the sheet can be sufficiently maintained without causing poor image fixation on the sheet.

[0018] In the image forming apparatus of this disclosure, the multiple printing conditions each have a priority order, and in the determination process, the control unit determines the settings of the printing conditions in the order of the priority order, and if it determines to execute the first transport process or the third transport process, it does not need to determine the settings of the printing conditions with subsequent priority orders. By having a priority order for the multiple printing conditions, the control unit can more appropriately determine the timing for starting sheet transport in the determination process.

[0019] The image forming apparatus of the present disclosure has a weighting coefficient associated with each of the plurality of printing conditions and a determination value corresponding to the setting content of each of the plurality of printing conditions. In the determination process, the control unit calculates a calculated value obtained by multiplying the determination value by the weighting coefficient for each of the plurality of printing conditions, and based on the value obtained by summing the calculated values corresponding to each of the plurality of printing conditions, it may be determined which of the first conveyance process, the second conveyance process, and the third conveyance process is to be executed. By having weighting coefficients for each of the plurality of printing conditions, the control unit can more appropriately determine the conveyance start timing of the sheet in the determination process.

Effects of the Invention

[0020] According to one aspect of the present disclosure, it is possible to suppress the conveyance start timing of the sheet from becoming unnecessarily late.

Brief Description of the Drawings

[0021] [Figure 1] It is a cross-sectional view showing the configuration of the image forming apparatus according to Embodiment 1 of the present disclosure. [Figure 2] It is a block diagram showing the main configuration of the image forming apparatus shown in FIG. 1. [Figure 3] It is a perspective view of the fixing unit included in the image forming apparatus shown in FIG. 1. [Figure 4] It is a cross-sectional view of the fixing unit shown in FIG. 3. [Figure 5] It is a plan view showing the holder and the temperature detection member included in the fixing unit shown in FIG. 3. [Figure 6] It is a flowchart showing an example of the processing of the control unit shown in FIG. 2. [Figure 7] In Embodiment 2 of the present disclosure, it is a flowchart showing an example of the processing of the control unit shown in FIG. 2.

Modes for Carrying Out the Invention

[0022] 〔Embodiment 1〕 <Overall configuration of image forming apparatus 1> Figure 1 is a cross-sectional view showing the configuration of an image forming apparatus 1 according to Embodiment 1 of the present disclosure. Although the image forming apparatus 1 is a monochrome printer, the scope of application of the present disclosure is not limited to monochrome printers, but is also applicable to color printers. In this embodiment, as an example of an image forming apparatus 1, a laser printer that forms an image on a sheet S using toner will be described.

[0023] As shown in Figure 1, the image forming apparatus 1 comprises a transport unit 2, an image forming unit 3, a fixing unit 4, a feeding tray 11, an output tray 12, and a temperature sensor 13. The transport unit 2 transports the sheet S and comprises a pickup roller 21, a transport roller 22, a registration roller 23, and an output roller 24. The sheet S can be recording paper, an OHP (Over Head Projector), an envelope, or cardboard.

[0024] The feeding tray 11 is a tray that holds the sheets S before printing. The pickup roller 21 transports the sheets S one by one from the feeding tray 11. The transport roller 22 transports the sheets S transported by the pickup roller 21 to the registration roller 23. After aligning the leading edge of the sheets S, the registration roller 23 transports the sheets S toward the image forming unit 3.

[0025] The temperature sensor 13 detects the temperature outside the image forming apparatus 1. Specifically, the temperature sensor 13 is installed inside the housing of the image forming apparatus 1, and detects the temperature outside the image forming apparatus 1 by detecting the temperature inside the housing of the image forming apparatus 1. Since there is no difference between the temperature inside the housing of the image forming apparatus 1 and the temperature outside the image forming apparatus 1, the temperature inside the housing of the image forming apparatus 1 is considered to be the temperature outside the image forming apparatus 1.

[0026] The image forming unit 3 forms an image on the sheet S conveyed by the registration roller 23, and comprises a photoreceptor 31, a charger 32, an exposure unit 33, a developing unit 34, a transfer unit 35, and a cleaning unit 36.

[0027] The photoreceptor 31 comprises a base tube made of a conductive metal such as aluminum, and a photosensitive layer provided on the outer surface of the base tube. The photoreceptor 31 is an organic photoconductor (OPC) and is a photosensitive drum having a positively charged photosensitive layer whose image formation potential is positive. As the photoreceptor 31 rotates, the photosensitive layer is charged by the charger 32, and it is exposed by laser light from the exposure unit 33, forming an electrostatic latent image on its surface. The photoreceptor 31 may also be a photosensitive belt in which a photosensitive layer is provided on the outer surface of a metal annular belt.

[0028] The charger 32 charges the surface of the photoreceptor 31 and is, for example, a charging roller that charges the photoreceptor 31 by contact, or a non-contact scorotron charger. The exposure unit 33 exposes the surface of the photoreceptor 31 that has been charged by the charger 32. The exposure unit 33 has, for example, a plurality of light-emitting elements arranged in a row along the direction of the rotation axis of the photoreceptor 31, and emits light according to the printing data to form an electrostatic latent image on the surface of the photoreceptor 31.

[0029] The developing unit 34 supplies developer to the electrostatic latent image formed on the surface of the photoreceptor 31, and includes, for example, a developing roller and a developing container containing developer. The transfer unit 35 transfers the developer image formed on the surface of the photoreceptor 31 to the sheet S, and is, for example, a transfer roller. The cleaning unit 36 ​​removes developer remaining on the photoreceptor 31 and paper dust and other materials adhering to the photoreceptor 31, and is, for example, a cleaning roller.

[0030] The fixing unit 4 fixes the image formed on the sheet S by the image forming unit 3. Details of the fixing unit 4 will be described later. The discharge roller 24 discharges the sheet S, on which the image has been fixed by the fixing unit 4, to the discharge tray 12. The discharge tray 12 is a tray on which the printed sheet S is discharged and placed.

[0031] Figure 2 is a block diagram showing the main components of the image forming apparatus 1 shown in Figure 1. As shown in Figure 2, the image forming apparatus 1 comprises a control unit 5, a communication unit 6, and a power supply circuit 7. The control unit 5 is a controller that controls each part of the image forming apparatus 1, for example, the transport unit 2, the image forming unit 3, the fixing unit 4, the communication unit 6, and the power supply circuit 7.

[0032] The control unit 5 is electrically connected to the temperature sensor 13. The control unit 5 comprises an ASIC (Application Specific Integrated Circuit) 51 and a memory unit 52. The control unit 5 causes the image forming apparatus 1 to perform printing and related processes by executing various processes.

[0033] The control unit 5 may also include a processor such as a CPU (Central Processing Unit). In this case, the storage unit 52 may store a control program that implements the printing control method. The processor of the control unit 5 may then operate according to the control program stored in the storage unit 52 to execute the printing process in the image forming apparatus 1.

[0034] Furthermore, the control unit 5 may include a computer-readable recording medium that stores the control program. As the recording medium, a "non-temporary tangible medium" such as ROM (Read Only Memory), as well as magnetic disks, cards, semiconductor memory, programmable logic circuits, etc., can be used.

[0035] Furthermore, a RAM (Random Access Memory) or the like may be used as the recording medium for deploying the control program. The control program may be supplied to the computer via any transmission medium such as a communication network or broadcast waves capable of transmitting the control program. The storage unit 52 is a memory capable of reading and writing information. The storage unit 52 is either RAM or NVM (Non-Volatile Memory). Predetermined information, such as the number of printed pages, is stored in the storage unit 52.

[0036] The communication unit 6 is equipped with a communication interface and performs bidirectional data communication with external equipment of the image forming apparatus 1 via a wired or wireless network. The power supply circuit 7 has a switching element such as a triac. The power supply circuit 7 switches between a powered state, in which current is supplied from an AC power source (not shown) to the heater 41 of the fixing unit 4, and a non-powered state, in which no current is supplied, by turning the switching element on or off according to instructions from the control unit 5.

[0037] <Configuration of fixing unit 4> Figure 3 is a perspective view of the fixing unit 4 of the image forming apparatus 1 shown in Figure 1, and Figure 4 is a cross-sectional view of the fixing unit 4 shown in Figure 3. Figure 5 is a plan view showing the holder 43 and temperature sensing members 46A and 46B of the fixing unit 4 shown in Figure 3. As shown in Figures 3 to 5, the fixing unit 4 includes a heater 41, a belt 42, a holder 43, a pressure roller 44, a stay 45, and temperature sensing members 46A and 46B.

[0038] As shown in Figure 4, the heater 41 is a heat source and is plate-shaped, extending in the longitudinal direction of the fixing section 4. The heater 41 has a substrate 41A and a resistance heating element 41B. The substrate 41A is plate-shaped, extending along the longitudinal direction of the fixing section 4. The resistance heating element 41B is provided on the substrate 41A along the longitudinal direction of the fixing section 4.

[0039] The longitudinal direction of the fixing section 4 is parallel to the rotation axis of the pressure roller 44 and perpendicular to the conveying direction of the sheet S in the nip section N, which will be described later. In other words, the longitudinal direction of the fixing section 4 is the width direction of the sheet S passing through the nip section N.

[0040] Furthermore, wiring and terminals for supplying power to the resistive heating element 41B are also provided on the substrate 41A. A ceramic substrate is used as the substrate 41A. In other words, the heater 41 is a ceramic heater. In this case, the heater 41 is a heater with a low heat capacity. Note that the heater 41 may also be a steel heater, using a metal substrate, more specifically a steel substrate, as the substrate 41A.

[0041] The belt 42 includes an inner circumferential surface 42A that contacts the heater 41 and is an endless belt that rotates around the heater 41. The belt 42 is also a cylindrical member with a low heat capacity. The belt 42 is made of a single-layer or composite-layer film having heat resistance, release properties, strength, and durability.

[0042] The holder 43 is a component that supports the heater 41 and holds the belt 42 in rotation, and is made of a resin material that has heat resistance and insulating properties. The holder 43 has a support surface 43A that supports the heater 41. The support surface 43A supports the heater 41 facing the back surface of the heater 41, that is, the surface on the substrate 41A opposite to the resistive heating element 41B. The heater 41 is positioned so that the surface on which the resistive heating element 41B is provided faces the inner circumferential surface 42A of the belt 42.

[0043] The pressure roller 44 is an example of a pressurizing member, and forms a nip portion N by sandwiching the belt 42 between itself and the surface of the heater 41. Both ends of the pressure roller 44 are supported by a pair of side frames via bearings. The pressure roller 44 is rotationally driven by a motor provided in the image forming apparatus 1, and the belt 42 rotates in conjunction with the rotation of the pressure roller 44.

[0044] The stay 45 is a component that increases the rigidity of the holder 43 and is positioned on the opposite side of the holder 43 from the support surface 43A. If the rigidity of the holder 43 is high, the stay 45 can be omitted.

[0045] The pressurizing member is not limited to the pressurizing roller 44, but may also consist of, for example, a pressurizing belt and a nip-forming member. In other words, an elastic pad, a resin or metal pressurizing plate, etc., is placed as the nip-forming member within the space enclosed by the pressurizing belt. The nip-forming member presses against the surface of the heater 41 via the belt 42 and the pressurizing belt to form the nip portion N.

[0046] As shown in Figure 5, the temperature sensing members 46A and 46B are positioned facing the back surface 43B of the holder 43, opposite to the support surface 43A. Holes 43C and 43D are formed in the back surface 43B of the holder 43. Temperature sensing member 46A contacts the back surface of the heater 41 through hole 43C. Temperature sensing member 46B contacts the back surface of the heater 41 through hole 43D. The temperature sensing members 46A and 46B detect the temperature of the heater 41. The temperature sensing members 46A and 46B are thermistors, but other temperature sensing members such as thermostats may also be used.

[0047] <Processing of Control Unit 5> Figure 6 is a flowchart showing an example of the processing performed by the control unit 5 shown in Figure 2. The control unit 5 performs a determination process to determine which of the first transport process, the second transport process, or the third transport process to be executed, according to the first to sixth print conditions, which are multiple print conditions.

[0048] The control unit 5 receives print jobs from external equipment of the image forming apparatus 1 via the communication unit 6. When the control unit 5 receives a print job, it performs a print preparation process. For example, in the print preparation process, the control unit 5 starts supplying power to the heater 41 by supplying current to the heater 41 using the power supply circuit 7. As a result, power is supplied to the resistive heating element 41B of the heater 41, and the temperature of the heater 41 rises.

[0049] After performing the print preparation process, the control unit 5 assigns 1 to the variable X (S11). After assigning 1 to the variable X, the control unit 5 performs a determination process to determine which of the first to third setting contents applies to the Xth print condition (S12). If the control unit 5 determines in S12 that the first setting contents apply to the Xth print condition, it performs the process in S13. If the control unit 5 determines in S12 that the third setting contents apply to the Xth print condition, it performs the process in S14. If the control unit 5 determines in S12 that the second setting contents apply to the Xth print condition, it performs the process in S15.

[0050] In S12, the control unit 5 determines that the first setting matches the Xth printing condition and executes the first transport process (S13). Specifically, the control unit 5 executes the first transport process, in which transport by the transport unit 2 begins after 1 hour has elapsed since the temperature detected by the temperature sensing members 46A and 46B reached the first temperature. The first temperature is the fixing temperature, which is the target temperature for thermal fixing by the fixing unit 4. The first hour is, for example, 2 seconds.

[0051] In S12, the control unit 5 determines that the third setting applies to the Xth printing condition and executes the third transport process (S14). Specifically, the control unit 5 executes the third transport process, which starts transport by the transport unit 2 when the detected temperature of the temperature sensing members 46A and 46B reaches a second temperature which is less than the first temperature.

[0052] If the control unit 5 determines that the second setting applies to the Xth printing condition, it determines whether the Xth printing condition is the last of the multiple printing conditions (S15). If the control unit 5 determines that the Xth printing condition is the last condition (YES in S15), it executes the second transport process (S16). Specifically, the control unit 5 executes the second transport process, in which the transport unit 2 starts transport when the temperature detected by the temperature sensing members 46A and 46B reaches the first temperature.

[0053] If the control unit 5 determines that the Xth printing condition is not the last condition (NO in S15), it increments the value of variable X by 1 (S17). In S17, if X=1, the control unit 5 increments the value of variable X by 1, making the value of variable X 2. After incrementing the value of variable X by 1, the control unit 5 proceeds to the process in S12.

[0054] Then, the control unit 5 executes the processes S12 to S17 for the second to sixth printing conditions.

[0055] As described above, when the control unit 5 executes the first transport process, it delays the start timing of sheet S transport compared to the second and third transport processes, allowing the fixing unit 4 to accumulate heat. This ensures that the image fixing strength to sheet S is sufficiently maintained. When the control unit 5 executes the third transport process, it speeds up the start timing of sheet S transport compared to the first and second transport processes, shortening the FPOT (First Paper Output Time) and reducing power consumption. When the control unit 5 executes the second transport process, it speeds up the start timing of sheet S transport compared to the first transport process and delays the start timing of sheet S transport compared to the third transport process.

[0056] The control unit 5 executes the processes S11 to S17 shown in Figure 6 only for the first sheet S, and then executes the third transport process for the second and subsequent sheets S. Alternatively, the control unit 5 may execute the processes S11 to S17 shown in Figure 6 not only for the first sheet S, but also for the second and subsequent sheets S.

[0057] The details of the first to sixth printing conditions will be explained below using Table 1. Table 1 is an example of a table showing the settings associated with each printing condition. Note that the "X" in the Xth printing condition shown in Figure 6 is the same as the "X" in the variable X. Therefore, in S12, the control unit 5 determines which of the first to third setting contents applies to the first printing condition if X=1.

[0058] [Table 1] <First Printing Conditions> The first printing condition is the number of pages to be printed in the print job, as shown in Table 1. In other words, multiple printing conditions include at least the number of pages to be printed. The first printing condition has three settings: a first setting, a second setting, and a third setting.

[0059] The first setting of the first printing condition is that the number of pages to be printed is 51 or more. The second setting of the first printing condition is that the number of pages to be printed is between 4 and 50. The third setting of the first printing condition is that the number of pages to be printed is between 1 and 3.

[0060] In S12, if the control unit 5 determines that the first setting content matches the first printing condition, that is, that the number of printed pages is 51 or more, it executes the first transport process.

[0061] If the control unit 5 determines that the third setting applies to the first printing condition, that is, that the number of printed sheets is between 1 and 3, it executes the third transport process. If the control unit 5 determines that the second setting applies to the first printing condition, that is, that the number of printed sheets is between 4 and 50, it executes the process in S15.

[0062] If the control unit 5 determines in S15 that the first printing condition is not the last condition (NO in S15), it increments the value of variable X by 1 in S17. As a result, the value of variable X becomes 2. After incrementing the value of variable X by 1, the control unit 5 proceeds to the process in S12.

[0063] <Second Printing Conditions> The second printing condition is the length of the sheet S in the transport direction included in the print job, as shown in Table 1. Therefore, multiple printing conditions include the length of the sheet S in the transport direction. The first setting of the second printing condition is that the length of the sheet S in the transport direction is 300 mm or more. The second setting of the second printing condition is that the length of the sheet S in the transport direction is 200 mm or more and less than 300 mm. The third setting of the second printing condition is that the length of the sheet S in the transport direction is less than 200 mm.

[0064] The control unit 5 executes the determination process in S12, prioritizing the execution of the third transport process, the second transport process, and the first transport process in that order as the length of the sheet S in the transport direction decreases. When the length of the sheet S along the transport direction is short, the temperature of the fixing unit 4 does not decrease easily. Therefore, the shorter the length of the sheet S along the transport direction, the earlier the timing of starting the transport of the sheet S can be made to shorten the FPOT.

[0065] <Third Printing Condition> The third printing condition is the thickness of the sheet S included in the print job, as shown in Table 1. Therefore, multiple printing conditions include the thickness of the sheet S. The first setting of the third printing condition is that the thickness of the sheet S in the print job is set to "thick". The second setting of the third printing condition is that the thickness of the sheet S in the print job is set to "medium". The third setting of the third printing condition is that the thickness of the sheet S in the print job is set to "thin". "Thick", "medium", and "thin" indicate increasing thickness of the sheet S, in that order. A sheet S thickness of "medium" corresponds, for example, to the case where recycled paper is specified.

[0066] The control unit 5 executes the determination process in S12, prioritizing the execution of the first transport process, second transport process, and third transport process in the order of increasing thickness of the sheet S. When the sheet S is thick, the temperature of the fixing unit 4 tends to drop. Therefore, by delaying the start timing of sheet S transport as the sheet S becomes thicker, it is possible to suppress the transport of the sheet S while the temperature of the fixing unit 4 has dropped, thereby suppressing the occurrence of poor image fixing on the sheet S.

[0067] <Fourth Printing Condition> The fourth printing condition is the external temperature of the image forming apparatus 1 as detected by the temperature sensor 13, as shown in Table 1. Therefore, multiple printing conditions include the external temperature of the image forming apparatus 1. The first setting of the fourth printing condition is that the external temperature of the image forming apparatus 1 is 20°C or less. The second setting of the fourth printing condition is that the external temperature of the image forming apparatus 1 is between 21°C and 35°C. The third setting of the fourth printing condition is that the external temperature of the image forming apparatus 1 is 36°C or higher. Here, the value of the external temperature of the image forming apparatus 1 is an integer.

[0068] The control unit 5 executes the determination process in S12, prioritizing the execution of the third transport process, the second transport process, and the first transport process in that order, depending on the high temperature outside the image forming apparatus 1 detected by the temperature sensor 13. When the temperature outside the image forming apparatus 1 is high, the temperature of the fixing unit 4 does not decrease easily. Therefore, the higher the temperature outside the image forming apparatus 1, the earlier the timing of starting the transport of the sheet S can be started, thereby shortening the FPOT (Functional Process Timeout).

[0069] <Fifth Printing Condition> The fifth printing condition is the transport speed of the sheet S by the transport unit 2, as shown in Table 1. Therefore, multiple printing conditions include the transport speed of the sheet S by the transport unit 2. The first setting of the fifth printing condition is that the transport speed of the sheet S is 31 ppm or more. The second setting of the fifth printing condition is that it is between 21 ppm and 30 ppm. The third setting of the fifth printing condition is that it is 20 ppm or less. The unit "ppm" indicates "sheets / minute". Also, the value of the transport speed of the sheet S is an integer.

[0070] The control unit 5 executes the determination process in S12, prioritizing the execution of the first transport process, second transport process, and third transport process in that order, the faster the transport speed of the sheet S. When the transport speed of the sheet S is fast, the temperature of the fixing unit 4 tends to drop. Therefore, the faster the transport speed of the sheet S, the later the timing of starting the transport of the sheet S is made, thereby suppressing the transport of the sheet S while the temperature of the fixing unit 4 has dropped, and thus suppressing the occurrence of image fixing failures on the sheet S.

[0071] <6th Printing Condition> The sixth printing condition is the setting for single-sided or double-sided printing on sheet S, as shown in Table 1. Therefore, multiple printing conditions include the setting for single-sided or double-sided printing on sheet S. The first setting of the sixth printing condition is that single-sided printing is set. The second setting of the sixth printing condition is that double-sided printing is set. Note that, as shown in Table 1, the sixth printing condition does not have a third setting.

[0072] The control unit 5, by executing the determination process in S12, prioritizes the execution of the second transport process over the execution of the first transport process if double-sided printing is set. When double-sided printing is set, the fuser unit 4 can accumulate heat while the sheet S is being turned over after single-sided printing is completed, so the temperature of the fuser unit 4 does not drop easily. For this reason, when double-sided printing is set, the FPOT can be shortened by starting the transport of the sheet S earlier. The control unit 5 may also prioritize the execution of the third transport process over the execution of the first transport process if double-sided printing is set.

[0073] In S12, if the control unit 5 determines that the first setting applies to the sixth printing condition, that is, that it is single-sided printing, it executes the first transport process. If the control unit 5 determines that the second setting applies to the sixth printing condition, that is, that it is double-sided printing, it determines that the sixth printing condition is the last condition (YES in S15) and executes the second transport process (S16).

[0074] Based on the above, the control unit 5 determines whether to execute the first transport process, the second transport process, or the third transport process according to the multiple printing conditions. Therefore, compared to the case where the transport process is changed only according to the condition of the number of printed sheets, it is possible to suppress an unnecessarily delayed start timing of sheet S transport.

[0075] Furthermore, the first temperature is preferably the fixing temperature, which is the target temperature for thermal fixing by the fixing unit 4. In the first and second transport processes, the control unit 5 starts transporting only after the temperature detected by the temperature sensing members 46A and 46B reaches the fixing temperature, which is the target temperature for thermal fixing by the fixing unit 4. This further suppresses a decrease in the fixing strength of the image onto the sheet S.

[0076] Furthermore, it is preferable that the second temperature is the lower limit of the temperature range at which the sheet S can be fixed by the fixing unit 4 when it reaches the nip portion N. Since transport is started only after the sheet S reaches a temperature at which it can be fixed when it reaches the nip portion N, the image fixing strength on the sheet S can be sufficiently maintained without causing poor image fixing on the sheet S.

[0077] <Priority> The first to sixth printing conditions each have a priority order. In the determination process of S12, the control unit 5 determines the settings of the first to sixth printing conditions in the order of the above priority order, and if it determines that the first transport process or the third transport process should be executed, it does not determine the settings of the subsequent priority printing conditions. By having a priority order for multiple printing conditions, the control unit 5 can more appropriately determine the timing of the sheet S transport start in the determination process of S12.

[0078] <First variation> The control unit 5 may determine which of the first to third setting contents applies to each of the first to sixth printing conditions, and may execute the transport process corresponding to the setting content that was determined to apply the most times among the first to third setting contents. The first transport process corresponds to the first setting content, the second transport process corresponds to the second setting content, and the third transport process corresponds to the third setting content. For example, if the setting content that was determined to apply the most times among the first to third setting contents is the first setting content, the control unit 5 executes the first transport process.

[0079] <Second variation> In addition to the first to sixth printing conditions, the control unit 5 may also determine, as a seventh printing condition, whether to execute the first transport process, the second transport process, or the third transport process, depending on the elapsed time since the previous print job was received. The previous print job is the print job that the control unit 5 received one before the print job it received this time.

[0080] [Embodiment 2] Embodiment 2 of this disclosure will be described below. For the sake of clarity, components having the same function as those described in Embodiment 1 will be denoted by the same reference numerals, and their descriptions will not be repeated. Figure 7 is a flowchart showing an example of the processing of the control unit 5 shown in Figure 2 in Embodiment 2 of this disclosure.

[0081] The control unit 5 receives print jobs from external equipment of the image forming apparatus 1 via the communication unit 6. Upon receiving a print job, the control unit 5 executes a print preparation process. After executing the print preparation process, the control unit 5 initializes the calculated value to 0 (S21). After initializing the calculated value to 0, the control unit 5 executes the process of S22, which is the same as the process of S11 shown in Figure 6, and then executes the process of S23, which is the same as the process of S12 shown in Figure 6.

[0082] The details of the first to sixth printing conditions in this embodiment will be described in detail below using Table 2. Table 2 is an example of a table showing the settings associated with each printing condition. The first to sixth printing conditions shown in Table 2 have weighting coefficients associated with each of the first to sixth printing conditions, in addition to the printing conditions shown in Table 1. The first to third setting contents shown in Table 2 have judgment values ​​associated with each of the first to third setting contents, in addition to the setting contents shown in Table 1. The weighting coefficients associated with each printing condition and the judgment values ​​associated with each setting contents are stored in the storage unit 52.

[0083] [Table 2] As shown in Table 2, the weighting coefficients associated with each of the first to third printing conditions are, for example, 5, the weighting coefficient associated with the fourth printing condition is, for example, 1, and the weighting coefficients associated with the fifth and sixth printing conditions are, for example, 2.

[0084] Furthermore, as shown in Table 2, for each of the first to fifth printing conditions, the first setting content is set to a first judgment value, the second setting content is set to a second judgment value, and the third setting content is set to a third judgment value.

[0085] For example, the first judgment value is 1 point, the second judgment value is 2 points, and the third judgment value is 3 points. As shown in Table 2, the sixth printing condition does not have a third setting. Therefore, in the sixth printing condition, the first setting is set to the first judgment value, the second setting is set to the second judgment value, and there is no judgment value corresponding to the third setting.

[0086] If the control unit 5 determines that the first setting applies to the Xth printing condition, it multiplies the weighting coefficient associated with the Xth printing condition by the first determination value corresponding to the first setting (S24). For example, in S24, if X=1, the control unit 5 obtains 5 points by multiplying the weighting coefficient of 5 points associated with the first printing condition by the first determination value of 1 point. The control unit 5 adds the value obtained by multiplying the weighting coefficient associated with the Xth printing condition by the first determination value to the calculated value (S27). In other words, the calculated value is obtained by calculating the value obtained by multiplying the weighting coefficient associated with each printing condition by the determination value associated with each setting for each of the first to sixth printing conditions, and then summing up the calculated values.

[0087] If the control unit 5 determines that the second setting applies to the Xth printing condition, it multiplies the weighting coefficient associated with the Xth printing condition by the second determination value corresponding to the second setting (S25). For example, in S25, if X=1, the control unit 5 multiplies the weighting coefficient of 5 points associated with the first printing condition by the second determination value of 2 points to obtain 10 points. In S27, the control unit 5 adds the value obtained by multiplying the weighting coefficient associated with the Xth printing condition by the second determination value to the calculated value.

[0088] If the control unit 5 determines that the third setting applies to the Xth printing condition, it multiplies the weighting coefficient associated with the Xth printing condition by the third determination value corresponding to the third setting (S26). For example, in S26, if X=1, the control unit 5 multiplies the weighting coefficient of 5 points associated with the first printing condition by the third determination value of 3 points to obtain 15 points. In S27, the control unit 5 adds the value obtained by multiplying the weighting coefficient associated with the Xth printing condition by the third determination value to the calculated value.

[0089] After processing S27, the control unit 5 executes processing S28, which is the same as processing S15 shown in Figure 6. If the control unit 5 determines that the Xth printing condition is not the last condition (NO in S28), it executes processing S29, which is the same as processing S17 shown in Figure 6. After executing processing S29, the control unit 5 proceeds to processing S23.

[0090] If the control unit 5 determines that the Xth printing condition is the last condition (YES in S28), it performs a determination process on the calculated value, i.e., the total value, calculated in S27 (S30). Specifically, for example, if the control unit 5 determines that the first setting content applies to each of the first to sixth printing conditions shown in Table 2, it performs a determination process on the total value obtained by summing the calculated values ​​(1) to (6) below.

[0091] (1) Weighting coefficient 5 corresponding to the first printing condition × score 1 corresponding to the first judgment value = 5 (2) Weighting coefficient 5 corresponding to the second printing condition × score 1 corresponding to the first judgment value = 5 (3) Weighting coefficient 5 corresponding to the third printing condition × score 1 corresponding to the first judgment value = 5 (4) Weighting coefficient 1 corresponding to the fourth printing condition × score 1 corresponding to the first judgment value = 1 (5) Weighting coefficient 2 corresponding to the fifth printing condition × score 1 corresponding to the first judgment value = 2 (6) Weighting coefficient 2 corresponding to the 6th printing condition × score 1 corresponding to the 1st judgment value = 2

[0092] Furthermore, the case in which the Xth printing condition is determined to be the last condition is, for example, when the control unit 5 obtains the value X=6 in the determination process of S28. In other words, if the control unit 5 determines that the first setting applies to the sixth printing condition, i.e., single-sided printing, or if the second setting applies to the sixth printing condition, i.e., double-sided printing, it determines that the sixth printing condition is the last condition (YES in S28) and executes the process of S30.

[0093] If the control unit 5 determines that the calculated value obtained in S27 is less than 30 points, it executes the process in S31, which is the same process as S13 shown in Figure 6. For example, if the control unit 5 determines that the first setting content applies to each of the first to sixth printing conditions as described in (1) to (6) above, the total calculated value will be 20 points, and the control unit 5 determines in S27 that it is less than 30 points and executes the first transport process (S31).

[0094] If the control unit 5 determines that the calculated value obtained in S27 is 30 points or more and less than 45 points, it executes the process in S32, which is the same process as S16 shown in Figure 6. For example, if the control unit 5 determines that the second setting content applies to the first printing condition, second printing condition, fifth printing condition, and sixth printing condition from (1) to (6) above, the calculated values ​​for each are (1)=10 points, (2)=10 points, (3)=5 points, (4)=1 point, (5)=4 points, and (6)=4 points, and the total value is 34 points. Therefore, the control unit 5 determines in S27 that the value is 30 points or more and less than 45 points, and executes the second transport process (S31).

[0095] If the control unit 5 determines that the calculated value obtained in S27 is 45 points or more, it executes the process in S33, which is the same process as S14 shown in Figure 6. For example, if the control unit 5 determines that the third setting content applies to the first printing condition and the second printing condition, respectively, and that the second setting content applies to the third to sixth printing conditions, then the calculated values ​​for each are (1)=15 points, (2)=15 points, (3)=10 points, (4)=2 points, (5)=4 points, and (6)=4 points, and the total value is 50 points. Therefore, the control unit 5 determines in S27 that the value is 45 points or more and executes the third transport process (S33).

[0096] The control unit 5 executes the processes S21 to S33 shown in Figure 7 only for the first sheet S, and then executes the third transport process for the second and subsequent sheets S. Alternatively, the control unit 5 may execute the processes S21 to S33 shown in Figure 7 not only for the first sheet S, but also for the second and subsequent sheets S.

[0097] As described above, in the determination process of S30, the control unit 5 calculates a calculated value for each of the multiple printing conditions by multiplying the determination value by a weighting coefficient, and determines whether to execute the first transport process, the second transport process, or the third transport process based on the sum of the calculated values ​​corresponding to each of the multiple printing conditions. By having a weighting coefficient for each of the multiple printing conditions, the control unit 5 can more appropriately determine the timing for starting the transport of the sheet S in the determination process.

[0098] This disclosure is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of this disclosure. [Explanation of symbols]

[0099] 1. Image forming apparatus 2. Conveying section 3 Image forming unit 4. Fixing section 5. Control Unit 13 Temperature sensor 41 Heater 42 belts 44 Pressure rollers 46A, 46B Temperature sensing element S Seat

Claims

1. An image forming unit that forms an image on a sheet, A conveying unit that conveys a sheet toward the image forming unit, A heater and a temperature sensing member for sensing the temperature of the heater, and a fixing unit for fixing the image formed on the sheet by the image forming unit, It comprises a control unit and, The control unit, A first transport process in which the transport unit starts transporting after a first hour has elapsed since the temperature detected by the temperature sensing member reached a first temperature, A second transport process in which the transport unit starts transporting when the detected temperature reaches the first temperature, A third transport process in which the transport unit starts transporting when the detected temperature reaches a second temperature which is less than the first temperature, The process includes a determination process that determines which of the first transport process, the second transport process, and the third transport process to execute, depending on a plurality of printing conditions that include at least the number of pages to be printed in the print job. The aforementioned multiple printing conditions each have a priority order. Image forming apparatus, wherein the control unit, in the determination process, determines the contents of the printing conditions in the order of priority, and if it determines to execute the first transport process or the third transport process, it does not make any determinations regarding the contents of the printing conditions for subsequent priority levels.

2. The aforementioned printing conditions include the length in the sheet transport direction, The image forming apparatus according to claim 1, wherein the control unit prioritizes the execution of the third transport process, the second transport process, and the first transport process in that order as the length of the sheet in the transport direction decreases.

3. The aforementioned printing conditions include the thickness of the sheet. The image forming apparatus according to claim 1, wherein the control unit prioritizes the execution of the first transport process, the second transport process, and the third transport process in the order that the sheet thickness increases.

4. The image forming apparatus further includes a temperature sensor for detecting the temperature outside the apparatus, The printing conditions include the temperature outside the image forming apparatus. The image forming apparatus according to claim 1, wherein the control unit prioritizes the execution of the third transport process, the second transport process, and the first transport process in that order, as the external temperature of the image forming apparatus detected by the temperature sensor becomes higher.

5. The printing conditions include the conveying speed of the sheet by the conveying unit. The image forming apparatus according to claim 1, wherein the control unit prioritizes the execution of the first transport process, the second transport process, and the third transport process in that order, as the sheet transport speed increases.

6. The aforementioned printing conditions include setting the sheet to print on one side or on both sides. The image forming apparatus according to claim 1, wherein, when double-sided printing is set, the execution of the second transport process or the third transport process is prioritized over the execution of the first transport process.

7. The image forming apparatus according to claim 1, wherein the first temperature is the fixing temperature, which is the target temperature for thermal fixing by the fixing unit.

8. The fixing unit further comprises an endless belt that rotates around the heater and a pressing member that forms a nip portion by sandwiching the belt between itself and the heater. The image forming apparatus according to claim 1, wherein the second temperature is the lower limit of the temperature range at which the sheet can be fixed in the fixing section when it reaches the nip section.

Images