Sheet conveying device and image forming apparatus

Abstract

To provide a sheet carrier device capable of reducing the power consumption by preventing a stepping motor from stepping out at the start of driving, and an image formation device.SOLUTION: A control part executes: first carrying processing (S21) for carrying a sheet in a first carrying direction toward a discharge part; stopping processing (S29) for stopping driving of a carrying part; determination processing (S30) for determining whether or not to supply a holding current for holding the carrying part in a stop state to a stepping motor; stop holding processing; and second carrying processing (S32) for carrying the sheet in a second carrying direction opposite to the first carrying direction after the stopping processing (S29) and the stop holding processing.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a sheet conveying device and an image forming apparatus.

Background Art

[0002] Conventionally, there is an image processing apparatus that conveys a sheet by rotating a conveyance roller using a stepping motor as a drive source. In this image processing apparatus, a phase shift may occur due to vibration or the like while the stepping motor is stopped, and out-of-step may occur when the driving of the stepping motor is started. In order to prevent out-of-step when starting the driving of the stepping motor, a driving current for generating a holding torque for holding the position of the rotor may be supplied to the stepping motor while the stepping motor is stopped.

[0003] For example, in the image processing apparatus of Patent Document 1, the temperature of the stepping motor is detected, and when the temperature of the stepping motor is lower than a preset temperature, a voltage for generating a holding torque (hereinafter referred to as a holding current) is supplied to the stepping motor, and when the temperature of the stepping motor is equal to or higher than the preset temperature, control is performed so as not to supply the holding current to the stepping motor.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when controlling the supply of the holding current using the temperature of the stepping motor as in the image processing apparatus described in Patent Document 1, if the temperature of the stepping motor is not appropriately detected, the holding current cannot be appropriately supplied, and there is a risk of out-of-step occurring at the start of driving the stepping motor. In addition, there is a problem that unnecessary holding current is supplied, resulting in increased power consumption.

[0006] The present invention has been made to solve the above-described problems, and an object thereof is to provide a sheet conveyance apparatus and an image forming apparatus capable of preventing out-of-step at the start of driving a stepping motor and reducing power consumption by appropriately supplying a holding current to the stepping motor.

Means for Solving the Problems

[0007] In order to solve the above problems, a sheet conveyance apparatus according to Embodiment 1 of the present invention includes a conveyance unit that rotates forward and backward and conveys a sheet, a stepping motor that drives the conveyance unit, a discharge unit where the sheet conveyed by the conveyance unit is discharged, a detection unit that detects state information including at least the temperature state of the surrounding environment, and a control unit. The control unit performs a first conveyance process of conveying the sheet in a first conveyance direction toward the discharge unit by the conveyance unit, a stop process of stopping the driving of the conveyance unit, and during the execution of the stop process, based on the detection result by the detection unit, determines whether to supply a holding current to the stepping motor that is less than or equal to the driving current of the stepping motor and holds the conveyance unit in a stopped state. When it is determined in the determination process that the holding current is to be supplied, a stop holding process of holding the conveyance unit in a stopped state by supplying the holding current to the stepping motor, and after the stop process and the stop holding process, a second conveyance process of conveying the sheet in a second conveyance direction opposite to the first conveyance direction.

[0008] According to the image forming apparatus having the above configuration, in the determination process, by considering the temperature state of the surrounding environment, which is the state information that is the main cause of the out-of-tune of the stepping motor, and determining whether to supply the holding current to the stepping motor, the holding current can be appropriately supplied to the stepping motor. Thereby, it is possible to accurately prevent the out-of-tune at the start of driving of the stepping motor and reduce the power consumption.

[0009] Further, in the sheet conveying apparatus according to the second aspect of the present invention, the detection unit includes a temperature sensor that detects the temperature state of the surrounding environment as the state information. In the determination process, when the temperature detected by the temperature sensor is lower than the normal temperature, the control unit determines to supply the holding current to the stepping motor, and when the temperature detected by the temperature sensor is equal to or higher than the normal temperature, the control unit determines not to supply the holding current to the stepping motor.

[0010] According to the sheet conveying apparatus having the above configuration, in a low temperature environment where the driving load of the stepping motor increases, by supplying the holding current to the stepping motor, it is possible to prevent the out-of-tune at the start of driving of the stepping motor. On the other hand, when the surrounding environment is equal to or higher than the normal temperature, since the driving load of the stepping motor does not increase, the power consumption can be reduced by not supplying the holding current to the stepping motor.

[0011] Further, in the sheet conveying apparatus according to the third aspect of the present invention, the detection unit includes a sheet counter that counts the number of sheets conveyed by the conveying unit. The state information includes the conveying load of the conveying unit. In the determination process, the control unit acquires the number of conveyed sheets counted by the sheet counter, which indicates the conveying load of the conveying unit as the state information, and when the number of conveyed sheets is greater than a threshold value, the control unit determines to supply the holding current to the stepping motor, and when the number of sheets conveyed by the sheet counter is less than the threshold value, the control unit determines not to supply the holding current to the stepping motor.

[0012] According to the sheet conveyance device having the above configuration, when the number of conveyed sheets counted by the sheet counter is greater than the threshold value, it is determined that as the wear state of the conveyance unit increases, the stepping motor is more likely to lose synchronization. By supplying a holding current to the stepping motor, it is possible to accurately prevent the stepping motor from losing synchronization. On the other hand, when the number of conveyed sheets is less than the threshold value, it is determined that the wear state of the conveyance unit has not increased and the possibility of losing synchronization is low, and the holding current is not supplied to the stepping motor, thereby reducing the power consumption.

[0013] Further, the sheet conveyance device according to Aspect 4 of the present invention further includes a setting unit that sets type information regarding the type of sheet. The types of sheets include a first sheet and a second sheet that is thicker than the first sheet. The detection unit acquires the type of sheet indicating the conveyance load of the conveyance unit as the state information. The control unit has a first threshold value corresponding to the first sheet and a second threshold value corresponding to the second sheet and smaller than the first threshold value as the threshold value used in the determination process. When the type information set by the setting unit is the first sheet, the threshold value is changed to the first threshold value, and when the type information set by the setting unit is the second sheet, the threshold value is changed to the second threshold value.

[0014] According to the sheet conveyance device having the above configuration, when the type of sheet is the first sheet, the control unit changes the threshold value to the first threshold value, and when the type of sheet is the second sheet that is thicker than the first sheet, the control unit changes the threshold value to the second threshold value. That is, by making the threshold value of the second sheet, which has a large conveyance load and a large inertial force acting on the sheet, smaller than the threshold value of the first sheet, the holding current is supplied to the second sheet, which is more likely to be misaligned than the first sheet, at an earlier stage. Thereby, it is possible to more accurately prevent the stepping motor from losing synchronization at the start of driving.

[0015] Also, in the sheet conveying device according to Embodiment 5 of the present invention, the stepping motor has a rotor. The control unit stops the driving of the conveying unit for a predetermined time equal to or longer than the vibration convergence time of the rotated rotor in the stop process.

[0016] According to the sheet conveying device having the above configuration, by setting the time for stopping the driving of the conveying unit in the stop process to be equal to or longer than the vibration convergence time of the rotor of the stepping motor, the control unit can surely stop the driving of the conveying unit.

[0017] Also, the sheet conveying device according to Embodiment 6 of the present invention further includes an excitation phase acquisition unit that acquires, as a stop excitation phase, the excitation phase immediately before the rotation of the stepping motor stops in the stop process. During the execution of the stop holding process, the control unit supplies the holding current to the same excitation phase as the stop excitation phase acquired by the excitation phase acquisition unit, and supplies a drive current to the same excitation phase as the stop excitation phase acquired by the excitation phase acquisition unit at the start of the second conveying process.

[0018] According to the sheet conveying device having the above configuration, the excitation phase acquisition unit acquires, as the stop excitation phase, the excitation phase immediately before the rotation of the stepping motor stops, and supplies the holding current or the drive current to the same excitation phase as the stop excitation phase during the stop holding process and at the start of the second conveying process. Thereby, it is possible to prevent the excitation phase from being changed between the time when the driving of the stepping motor stops and the time when the driving resumes, so that it is possible to surely prevent out-of-step at the start of driving of the stepping motor.

[0019] An image forming apparatus according to an aspect of the present invention includes an image forming unit that forms an image on a sheet conveyed by the conveying unit, and the sheet conveying device according to any one of Embodiments 1 to 6.

[0020] According to the image forming apparatus having the above configuration, it is possible to accurately prevent out-of-step at the start of driving of the stepping motor and reduce power consumption.

[0021] Also, in the image forming apparatus according to aspect 8 of the present invention, the conveyance unit has a discharge roller that conveys the sheet to the discharge unit. In the first conveyance process, the control unit rotates the discharge roller forward by a predetermined amount to convey the sheet having an image formed on one side by the image forming unit toward the discharge unit. In the second conveyance process, the control unit rotates the discharge roller backward to convey the sheet in the second conveyance direction. After the second conveyance process, the control unit conveys the sheet again in the first conveyance direction toward the image forming unit.

[0022] According to the image forming apparatus having the above configuration, it is possible to prevent out-of-step at the start of driving of the stepping motor and perform double-sided printing on the sheet well while reducing power consumption.

Effect of the Invention

[0023] According to one aspect of the present invention, by appropriately supplying a holding current to the stepping motor, it is possible to prevent out-of-step at the start of driving of the stepping motor and reduce power consumption.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

[0025] Hereinafter, the image forming apparatus 1 according to the embodiments of the present invention will be described with reference to FIGS. 1 to 7. [Configuration of Image Forming Apparatus] FIG. 1 is a schematic diagram showing an example of the configuration of the image forming apparatus 1. The image forming apparatus 1 shown in FIG. 1 is an example of an image forming apparatus provided with a sheet conveying device. The image forming apparatus 1 is a color laser printer and is configured to be able to form a desired color image or monochrome image on one side or both sides of a sheet P and perform printing. In the following description, as shown by the arrows in FIG. 1, the front-rear direction and the up-down direction of the image forming apparatus 1 are defined.

[0026] The image forming apparatus 1 includes a housing 11, a discharge tray 12 which is an example of a discharge unit, and a discharge port 11A. The printed sheet P is discharged to the discharge tray 12 through the discharge port 11A.

[0027] Inside the housing 11, a feed tray 13 for accommodating the sheet P, a feeding unit 2, a first conveyance path R1, an image forming unit 3, a fixing unit 4, a conveyance unit 5, and a second conveyance path R2 are provided. The feed tray 13 is a box-shaped member with an open upper surface and accommodates a plurality of sheets P. Sheets P of different sizes and paper qualities are accommodated in the feed tray 13. The types of the sheet P include, for example, plain paper, thick paper, and thin paper. Note that the number and size of the feed tray 13 can be changed as appropriate.

[0028] The feeding unit 2 has a feed roller 21, a conveyance roller 22, and a registration roller 23. The feed roller 21 is disposed above the feed tray 13 and presses one sheet at the upper end of the plurality of sheets P accommodated in the feed tray 13 with appropriate pressure and conveys it toward the conveyance roller 22 side. The conveyance roller 22 is disposed downstream of the feed roller 21 in the conveyance direction of the sheet P and conveys the sheet P toward the registration roller 23 side. The registration roller 23 is disposed downstream of the conveyance roller 22 in the conveyance direction of the sheet P and conveys the sheet P toward the image forming unit 3 side.

[0029] The first conveyance path R1 extends upward from the front end of the feed tray 13, curves rearward, passes through the position of the image forming unit 3, extends upward from behind the fixing unit 4, curves forward, and reaches the discharge port 11A. In the first embodiment 1, in the first conveyance path R1, the direction in which the sheet P travels from the feed tray 13 through the image forming unit 3 to the discharge port 11A is called the first conveyance direction D1. Upstream of the conveyance roller 22 in the first conveyance path R1, a merging position X with the second conveyance path R2 is provided.

[0030] Downstream of the registration roller 23 in the first conveyance direction D1, an endless conveyance belt 30V wound around a pair of belt rollers 30 is provided. One of the pair of belt rollers 30 rotates by the transmission of the driving force from a driving motor (not shown). The conveyance belt 30V is driven to circulate by the rotation of the pair of belt rollers 30. The conveyance belt 30V conveys the sheet P in the first conveyance direction D1.

[0031] The image forming unit 3 includes transfer rollers 31Y, 31M, 31C, 31K, photosensitive drums 32Y, 32M, 32C, 32K, developing cartridges 3Y, 3M, 3C, 3K, an exposure device 7, and a fixing unit 4.

[0032] The four transfer rollers 31Y, 31M, 31C, 31K are arranged inside the conveyance belt V at intervals in the front-rear direction. Note that the conveyance belt 30V may not be provided, and the sheet P may be conveyed using a plurality of rollers including the transfer rollers 31Y, 31M, 31C, 31K.

[0033] At positions facing the respective transfer rollers 31Y, 31M, 31C, 31K, four photosensitive drums 32Y, 32M, 32C, 32K corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (K) are arranged in order from the upstream side in the conveyance direction of the sheet P. The photosensitive drums 32Y, 32M, 32C, 32K are rotationally driven by the driving force from a driving motor (not shown). Note that the arrangement order of the photosensitive drums 32Y, 32M, 32C, 32K is not limited to this and can be changed as appropriate.

[0034] The surfaces of the respective photosensitive drums 32Y, 32M, 32C, and 32K are uniformly charged by a charger (not shown). Light is irradiated from an exposure device 7 (to be described later) onto these photosensitive drums 32Y, 32M, 32C, and 32K, thereby performing exposure. By being exposed by the exposure device 7, an electrostatic latent image of the image data to be printed on the sheet P is formed on the surfaces of the respective photosensitive drums 32Y, 32M, 32C, and 32K.

[0035] Above the front upper sides of the respective photosensitive drums 32Y, 32M, 32C, and 32K, four developing cartridges 3Y, 3M, 3C, and 3K are arranged at intervals in the front-rear direction. Each of the developing cartridges 3Y, 3M, 3C, and 3K contains toner corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K).

[0036] At the rear lower end parts of the respective developing cartridges 3Y, 3M, 3C, and 3K, developing rollers 33Y, 33M, 33C, and 33K are respectively arranged. Above the four developing cartridges 3Y, 3M, 3C, and 3K, the exposure device 7 is arranged. The exposure device 7 has a laser light source, a polygon mirror, a lens, a reflecting mirror, etc. (not shown), and emits laser light based on the image data. The laser light emitted from the exposure device 7 forms an electrostatic agent image on the surfaces of the respective photosensitive drums 32Y, 32M, 32C, and 32K.

[0037] Each of the developing rollers 33Y, 33M, 33C, and 33K supplies the toner contained in each of the developing cartridges 3Y, 3M, 3C, and 3K to the respective photosensitive drums 32Y, 32M, 32C, and 32K by contacting the respective photosensitive drums 32Y, 32M, 32C, and 32K. Thereby, the electrostatic agent image formed on the surface of each of the photosensitive drums 32Y, 32M, 32C, and 32K becomes a toner image (developer image). In color printing, toner images are respectively formed on the four photosensitive drums 32Y, 32M, 32C, and 32K. On the other hand, in monochrome printing, a toner image is formed only on the photosensitive drum 32K.

[0038] Then, a transfer current of the negative electrode is applied to the four transfer rollers 31Y, 31M, 31C, and 31K by an application unit (not shown). Further, the transfer rollers 31Y, 31M, 31C, and 31K are rotationally driven by a driving force from a driving motor (not shown). The sheet P is conveyed while being sandwiched between the transfer rollers 31Y, 31M, 31C, and 31K to which the transfer current is applied and the photosensitive drums 32Y, 32M, 32C, and 32K. Thereby, the toner image (developer image) formed on the surfaces of the photosensitive drums 32Y, 32M, 32C, and 32K is transferred to the sheet P.

[0039] A fixing unit 4 is provided downstream of each of the transfer rollers 31Y, 31M, 31C, and 31K in the first conveyance direction D1. The fixing unit 4 includes a heating roller 41 and a pressure roller 42. The sheet P is heated and pressurized when passing between the heating roller 41 and the pressure roller 42. Thereby, the fixing unit 4 fixes the toner image formed on the sheet P to the sheet P.

[0040] A conveyance roller 24 and a counter roller 25 are arranged downstream of the fixing unit 4 in the first conveyance path R1. The conveyance roller 24 is driven by a conveyance motor 62. The counter roller 25 rotates as the conveyance roller 24 rotates. In the first conveyance path R1, a sheet sensor 71 (described later) is arranged between the fixing unit 4 and the conveyance roller 24.

[0041] A conveyance roller 51 and a counter roller 52 are arranged downstream of the conveyance roller 24 in the first conveyance path R1. The counter roller 52 rotates as the conveyance roller 51 rotates. Further, a discharge roller 53 and a counter roller 54 are arranged near the discharge port 11A in the first conveyance path R1. The counter roller 54 rotates as the discharge roller 53 rotates. The conveyance roller 51 and the discharge roller 53 constitute the conveyance unit 5. Note that the conveyance roller 51 and the counter roller 52 may be omitted.

[0042] In this embodiment, a stepping motor 61 is used as a discharge motor for discharging the sheet P. That is, the conveying rollers 51 and the discharge roller 53 of the conveying unit 5 are driven by the stepping motor 61 and rotate forward and backward. When the conveying roller 51 and the discharge roller 53 rotate forward, in the first conveying path R1, the sheet P is conveyed toward the discharge port 11A along the first conveying direction D1. On the other hand, when the conveying roller 51 and the discharge roller 53 rotate backward, in the second conveying path R2, the sheet P is conveyed along the second conveying direction D2 toward the confluence position X with the first conveying path R1.

[0043] The second conveying path R2 is a path for conveying the sheet P under the feeding tray 13 and to the confluence position with the first conveying path R1 during double-sided printing. It branches at the branching position Y upstream of the conveying roller 51 in the first conveying path R1, extends downward from the rear lower side of the fixing unit 4, and curves forward. Further, the second conveying path R2 extends forward under the feeding tray 13, curves upward, and is connected to the confluence position X with the first conveying path R1.

[0044] In the second conveying path R2, a flapper 8 configured to be swingable in the front-rear direction is provided near the branching position Y. When the sheet P is being conveyed along the first conveying direction D1, the flapper 8 swings forward as shown by the solid line in FIG. 1 to guide the sheet P toward the conveying roller 51 side. On the other hand, during double-sided printing, when the sheet P is being conveyed along the second conveying direction D2, the flapper 8 swings backward as shown by the dashed-dotted line in FIG. 1 to guide the sheet P under the feeding tray 13. Thereby, it is possible to form an image on both sides of the sheet P.

[0045] [Electrical Configuration of the Image Forming Apparatus] FIG. 2 is a block diagram showing the electrical configuration of the image forming apparatus 1 according to the embodiment. As shown in FIG. 2, the control unit 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, an EEPROM 104 (registered trademark), and an ASIC 105, which are connected by an internal bus.

[0046] The control unit 100 performs overall control over each part of the image forming apparatus 1. The ROM 102 stores programs for the CPU 101 to control various operations and various settings. The RAM 103 is used as a work area from which various control programs are read and a storage area for temporarily storing image data. In this embodiment, a part of the RAM 103 is used as a counter for detecting the number of steps of the stepping motor 61.

[0047] The EEPROM 104 stores setting information to be retained even after the power is turned off. In this embodiment, the EEPROM 104 is an example of a detection unit and functions as a sheet counter for counting the number of sheets P conveyed by the conveying unit 5. The number of conveyed sheets counted by the EEPROM 104 is an example of state information indicating the conveying load of the conveying unit 5.

[0048] The ASIC 105 has a drive unit 60, a conveyance motor 62, a temperature sensor 70, a sheet sensor 71, a setting unit 110, and a communication interface (I / F) 120 electrically connected thereto. The control unit 100 controls the driving of the stepping motor 61 via the drive unit 60. The stepping motor 61, although not shown, has a stator and a rotor, and when a drive current is supplied by the drive unit 60, the rotor rotates with respect to the stator. The control unit 100 rotates the conveyance unit 5 forward by rotating the stepping motor 61 forward via the drive unit 60, and rotates the conveyance unit 5 backward by rotating the stepping motor 61 backward.

[0049] The drive unit 60 rotates the stepping motor 61 one step at a time by sending drive pulses to the stepping motor 61. The number of steps of the stepping motor 61 is counted by the RAM 103. The control unit 100 can grasp the integrated number of steps by acquiring the count value of the RAM 103.

[0050] Returning to FIG. 2, the control unit 100 controls the rotation of the conveyance motor 62, for example, by PWM (Pulse Width Modulation) control. By controlling the conveyance motor 62, the control unit 100 controls the rotation of the feeding unit 2 and the conveyance rollers 24, 26 to 28.

[0051] The temperature sensor 70 is an example of a detection unit, is provided in the housing 11, and detects the temperature state of the surrounding environment as state information of the image forming apparatus 1. The temperature sensor 70 outputs the detected temperature to the control unit 100.

[0052] The sheet sensor 71 detects the presence or absence of the sheet P at a predetermined position between the fixing unit 4 and the conveyance roller 24 in the first conveyance path R1. The sheet sensor 71 includes an actuator (not shown) and a photo interrupter, and outputs an on signal to the control unit 100 when the sheet P is passing through the predetermined position, and outputs an off signal to the control unit 100 when the sheet P is not at the predetermined position.

[0053] The setting unit 110 is for the user to set type information regarding the type of the sheet P. The setting unit 110 outputs the set type information of the sheet P to the control unit 100. Examples of the type of the sheet P include plain paper, thick paper, thin paper, etc. The type of the sheet P is an example of state information indicating the conveyance load of the conveyance unit 5.

[0054] The communication I / F 120 is connected to a network such as a LAN and enables connection to an external device in which a driver for the image forming apparatus 1 is incorporated. The image forming apparatus 1 can receive a print job via the communication I / F 120.

[0055] [Flow of Printing Operation] Next, with reference to FIGS. 3 to 7, the flow of the printing operation of the image forming apparatus 1 in the present embodiment will be described. FIG. 3 is a timing chart showing the operation of the sheet sensor 71, the operation of the stepping motor 61, and the change in the excitation current value of the stepping motor 61 during double-sided printing of the image forming apparatus 1. FIG. 4 is a flowchart showing the flow of the printing operation by the control unit 100 of the image forming apparatus 1 according to the embodiment. FIG. 5 is a continuation flowchart of FIG. 4. FIG. 6 is a flowchart showing the flow of the determination process S30 in FIG. 5. FIG. 7 is a continuation flowchart of FIG. 6.

[0056] As shown in FIG. 4, when the control unit 100 receives a print job via the communication I / F 120, it acquires the type of the sheet P and resets the number of steps stored in the RAM 103 (S1), and determines whether the printing specified by the print job is double-sided printing (S2). If the print job is double-sided printing (S2: YES), the control unit 100 proceeds to the flowchart shown in FIG. 5. When double-sided printing is performed on the sheet P, printing is executed first from the back side, and then printing on the front side is performed.

[0057] On the other hand, when the print job is not double-sided printing (S2: NO), that is, when the print job is surface (single-sided) printing, the control unit 100 performs a first conveyance process of conveying the sheet P in the first conveyance direction D1 toward the discharge tray 12 (S3).

[0058] Specifically, in the first conveyance process S3, the control unit 100 drives the conveyance motor 62 to rotate the feed roller 21 to supply the sheet P to the first conveyance path R1, and rotates the conveyance roller 22 and the registration roller 23 to convey the sheet P toward the image forming unit 3 side.

[0059] When the sheet P is conveyed to the image forming unit 3, the control unit 100 sandwiches and conveys between the transfer rollers 31Y, 31M, 31C, 31K and the photosensitive drums 32Y, 32M, 32C, 32K, and transfers the toner image formed on the surface of each photosensitive drum 32Y, 32M, 32C, 32K to a predetermined position on the sheet P.

[0060] The sheet P onto which the toner image has been transferred is conveyed while being sandwiched between the heating roller 41 and the pressure roller 42 of the fixing unit 4, and the toner image is fixed on the sheet P by being heated and pressurized. Thereby, an image based on the image data is formed on the sheet P.

[0061] Subsequently, the control unit 100 determines whether or not the sheet sensor 71 is on (S4). When the sheet sensor 71 is on (S4: YES), the control unit 100 starts the rotation of the stepping motor 61 via the drive unit 60 (S5).

[0062] In S5, the control unit 100 rotates the stepping motor 61 forward to rotate the conveyance roller 51 and the discharge roller 53 forward, and discharges the sheet P printed on the surface to the discharge tray 12. Then, the control unit 100 determines whether or not the sheet sensor 71 is off (S6). When the sheet sensor 71 is off (S6: YES), the control unit 100 starts counting the number of steps in the RAM 103 (S7), and determines whether or not the number of steps of the stepping motor 61 is equal to or greater than a first specified value (S9). Here, the "first specified value" is the number of steps corresponding to the distance from when the sheet sensor 71 is off until the rear end of the sheet P is discharged from the discharge port 11A.

[0063] On the other hand, when the sheet sensor 71 is not turned on (S4: NO), the control unit 100 executes error processing (S10) and ends the flow shown in FIG. 4. Further, when the sheet sensor 71 is not turned off (S6: NO), the control unit 100 determines whether or not a prescribed time has elapsed since the sheet sensor 71 was turned on (S8). If the prescribed time has not elapsed (S8: NO), the process returns to S6. If the prescribed time has elapsed (S8: YES), the control unit 100 executes error processing (S10) and ends the flow shown in FIG. 4. Here, the "prescribed time" is set, for example, to the length of time from when the sheet P of the maximum printable size by the image forming apparatus 1 starts passing through the sheet sensor 71 until it finishes passing through.

[0064] Next, when the number of steps of the stepping motor 61 is equal to or greater than the first prescribed value (S9: YES), the control unit 100 performs a stop process of stopping the driving of the conveyance roller 51 and the discharge roller 53 by stopping the rotation of the stepping motor 61 (S11). When the number of steps of the stepping motor 61 is less than the first prescribed value (S9: NO), S9 is repeated until the number of steps reaches the first prescribed value.

[0065] After S9, the control unit 100 determines whether or not there is a next print sheet (S12). When there is a next print sheet (S12: YES), the process returns to S2. When there is no next print sheet (S12: NO), the flow shown in FIG. 4 ends. Thereby, printing on the front surface of the sheet P is completed.

[0066] On the other hand, when printing is performed on the back surface of the sheet P (S2: YES), the control unit 100 performs the first conveyance process in the same manner as S3 in the flowchart shown in FIG. 5 (S21), and then performs S22 to S24 in the same manner as S4 to S6.

[0067] When the sheet sensor 71 is not turned on at time t1 shown in FIG. 3 (S22: NO), the control unit 100 executes error processing (S28) and ends the flow shown in FIG. 5. On the other hand, when the sheet sensor 71 is turned on (S22: YES), the control unit 100 starts the rotation of the stepping motor 61 (S23) and determines whether or not the sheet sensor 71 is turned off (S24).

[0068] When the sheet sensor 71 is not turned off (S24: NO), the control unit 100 determines whether or not a predetermined time T1 or more has elapsed (S26). If a predetermined time T1 or more has elapsed after time t1 shown in FIG. 3 (S26: YES), the control unit 100 executes error processing (S28) and ends the flow shown in FIG. 5. If the predetermined time T1 has not elapsed (S26: NO), the process returns to S24.

[0069] When the sheet sensor 71 is turned off at time t2 shown in FIG. 3 (S24: YES), the control unit 100 starts counting the number of steps (S25) and determines whether or not the number of steps of the stepping motor 61 is equal to or greater than a second specified value (S27). The "second specified value" is set to a value smaller than the "first specified value" and is the number of steps corresponding to the distance that the rear end of the sheet P moves to in front of the discharge roller 53 after the sheet sensor 71 is turned off.

[0070] When the number of steps of the stepping motor 61 is equal to or greater than the second specified value (S27: YES), the control unit 100 performs a stop process of stopping the driving of the conveyance roller 51 and the discharge roller 53 by stopping the rotation of the stepping motor 61 (S29). If the number of steps of the stepping motor 61 is not equal to or greater than the second specified value (S27: NO), S27 is repeated until the number of steps reaches the second specified value.

[0071] In the stop process S29, the control unit 100 stops the driving of the conveyance unit 5 for a predetermined time T2 shown in FIG. 3. The predetermined time T2 is set to a length equal to or longer than the time for the vibration of the rotated rotor to converge. Thereby, the control unit 100 can surely stop the driving of the conveyance unit 5.

[0072] In this embodiment, the control unit 100 acquires, via the ASIC 105 which is an example of an excitation phase acquisition unit, the excitation phase immediately before the rotation of the stepping motor 61 stops as the stop excitation phase in the stop process S29. Further, after the start of the stop process S29, the control unit 100 executes a determination process (S30) to determine whether or not to supply a holding current to the stepping motor 61. Then, as will be described later, by supplying a holding current to the stepping motor 61 at a timing when the stepping motor 61 is likely to lose synchronization, it is possible to accurately prevent the loss of synchronization.

[0073] After S30, a second conveyance process for conveying the sheet P in the second conveyance direction D2 opposite to the first conveyance direction D1 is executed (S32). In the second conveyance process S32, the control unit 100 reversely rotates the stepping motor 61 to reversely rotate the conveyance roller 51 and the discharge roller 53, conveys the sheet P printed on the back surface to the branch position Y side of the first conveyance path R1 and the second conveyance path R2, and then conveys it toward the lower part of the feed tray 13 along the second conveyance path R2. Then, the control unit 100 drives the conveyance motor 62 to rotate the conveyance rollers 26 to 28 and convey the sheet P toward the merging position X of the first conveyance path R1 and the second conveyance path R2.

[0074] After the second conveyance process S32, the control unit 100 determines whether or not the number of steps of the stepping motor 61 is equal to or greater than a third specified value (S33). When the number of steps of the stepping motor 61 is equal to or greater than the third specified value (S33: YES), since the sheet P is being conveyed by the conveyance rollers 26 to 28 in the second conveyance path R2, at the time t5 shown in FIG. 3, a stop process for stopping the driving of the conveyance roller 51 and the discharge roller 53 is performed by stopping the rotation of the stepping motor 61 (S34). When the number of steps of the stepping motor 61 is not equal to or greater than the third specified value (S33: NO), S33 is repeated until the number of steps reaches the third specified value. The third specified value is set to be equal to or greater than the number of steps required from the start of the second conveyance process S32 until the rear end of the sheet P has passed through the conveyance roller 51 and the sheet P starts to be conveyed by the conveyance roller 26.

[0075] After the stop process S34, the sheet P conveyed to X is conveyed in the first conveyance direction D1 along the first conveyance path R1 with the front and back reversed (S3), and printing is performed on the other side, that is, the front surface, by the image forming unit 3. Hereinafter, the control unit 100 executes S4 to S12 in the same manner as described above. As a result, printing on both sides of the sheet P is completed.

[0076] Next, the detailed flow of the determination process S30 shown in FIG. 5 will be described with reference to FIGS. 6 and 7. In the flowchart shown in FIG. 6, the control unit 100 acquires the temperature of the ambient environment detected by the temperature sensor 70 and the number of conveyed sheets (S41).

[0077] In the present embodiment, the control unit 100 determines whether to supply a holding current to the stepping motor 61 using the temperature of the ambient environment and the number of conveyed sheets. This is because when the temperature of the ambient environment of the image forming apparatus 1 is lower than normal temperature, the viscosity of the grease applied to the gears and the like that transmit the driving force of the stepping motor 61 to the conveyance unit 5 increases, the driving load of the stepping motor 61 increases, and the stepping motor 61 is likely to lose synchronization. Also, when the number of conveyed sheets by the conveyance unit 5 increases, due to the adhesion of paper dust and the like to the conveyance unit 5 and the wear of the conveyance unit 5, the friction coefficient of the conveyance unit 5 increases, the driving load of the stepping motor 61 increases, and it is considered that the stepping motor 61 is likely to lose synchronization.

[0078] Subsequently, the control unit 100 determines whether the type of the sheet P is thin paper (S42). When the type of the sheet P is thin paper (S42: YES), the control unit 100 determines whether the detected temperature by the temperature sensor 70 is less than 5°C (S43). When the detected temperature by the temperature sensor 70 is less than 5°C (S43: YES), the control unit 100 determines whether the number of conveyed sheets of the sheet P stored in the EEPROM 104 is equal to or greater than a first threshold value (S44). The first threshold value is set to, for example, 300,000 sheets.

[0079] When the number of conveyed sheets of the sheet P is equal to or greater than the first threshold value (S44: YES), the control unit 100 determines that it is necessary to supply a holding current to the stepping motor 61 (S45), and executes a stop holding process of holding the conveyance roller 51 and the discharge roller 53 in a stopped state by supplying a holding current to the stepping motor 61 (S46).

[0080] During the execution of the stop holding process S46, the control unit 100 continues to supply a holding current to the same excitation phase as the stop excitation phase for a predetermined time T2 from time t3 to time t4 shown in FIG. 3. The magnitude of the holding current is less than or equal to the drive current of the stepping motor 61 and is set to a magnitude capable of holding the conveyance roller 51 and the discharge roller 53 in a stopped state. Thereby, it is possible to accurately prevent detuning at the start of driving of the stepping motor 61 (time t4 shown in FIG. 3).

[0081] On the other hand, when the detected temperature by the temperature sensor 70 is 5°C or higher (S43: NO), or even when the detected temperature by the temperature sensor 70 is less than 5°C (S43: YES), if the number of conveyed sheets of the sheet P is less than the first threshold value (S44: NO), the control unit 100 determines that it is not necessary to supply a holding current to the stepping motor 61 (S47), does not execute the stop holding process S46, and ends the determination process S30.

[0082] On the other hand, when the type of the sheet P is not thin paper (S42: NO), the control unit 100 determines whether the type of the sheet P is plain paper (S48). When the type of the sheet P is plain paper (S48: YES), the control unit 100 determines whether the detected temperature by the temperature sensor 70 is less than 5°C (S49). When the type of the sheet P is not plain paper (S48: NO), it proceeds to S61 in FIG. 7.

[0083] When the detected temperature by the temperature sensor 70 is less than 5°C (S49: YES), the control unit 100 determines whether the number of conveyed sheets P stored in the EEPROM 104 is equal to or greater than the second threshold value (S50). The second threshold value is set to, for example, 100,000 sheets. In S44 and S50, thin paper corresponds to the first sheet, and plain paper corresponds to the second sheet which is thicker than the first sheet. In the present embodiment, considering that when the thickness of the sheet P is greater, the conveyance load on the conveyance unit 5 is larger and it is more likely to wear, when the type of the sheet P obtained in S1 is the first sheet, the threshold value is changed to the first threshold value, and when it is the second sheet, the threshold value is changed to the second threshold value.

[0084] On the other hand, when the detected temperature by the temperature sensor 70 is not less than 5°C (S49: NO), that is, when the detected temperature is 5°C or higher, the control unit 100 determines whether the number of conveyed sheets P is equal to or greater than the first threshold value (S52). The first threshold value is set to, for example, 300,000 sheets.

[0085] When the number of conveyed sheets P is equal to or greater than the second threshold value (S50: YES), or even when the detected temperature by the temperature sensor 70 is not less than 5°C (S49: NO) and the number of conveyed sheets P is equal to or greater than the first threshold value (S52: YES), the control unit 100 determines that it is necessary to supply the holding current to the stepping motor 61 (S51), and executes the stop holding process (S46).

[0086] On the other hand, when the detected temperature by the temperature sensor 70 is less than 5°C (S49: YES) and the number of conveyed sheets P is less than the second threshold value (S50: NO), the control unit 100 determines that it is not necessary to supply the holding current to the stepping motor 61 (S53), does not execute the stop holding process S46, and ends the determination process S30. Also, when the detected temperature by the temperature sensor 70 is 5°C or higher (S49: NO) and the number of conveyed sheets P is less than the first threshold value (S52: NO), the control unit 100 determines that it is not necessary to supply the holding current to the stepping motor 61 (S53), does not execute the stop holding process S46, and ends the determination process S30.

[0087] Next, moving on to FIG. 7, in S61, the control unit 100 determines that the sheet P is cardboard, and determines whether the detected temperature by the temperature sensor 70 is less than 5°C (S62). When the detected temperature by the temperature sensor 70 is 5°C or higher (S62: NO), the control unit 100 determines whether the number of conveyed sheets P is equal to or greater than the second threshold value (S63). The second threshold value is set to, for example, 100,000 sheets. In S52 and S63, plain paper corresponds to the first sheet, and cardboard corresponds to the second sheet which is thicker than the first sheet. That is, when the type of the sheet P is the first sheet, the threshold value is changed to the first threshold value, and when it is the second sheet, the threshold value is changed to the second threshold value.

[0088] When the detected temperature by the temperature sensor 70 is less than 5°C (S62: YES), or when the number of conveyed sheets P is equal to or greater than the second threshold value (S63: YES), the control unit 100 determines that it is necessary to supply the holding current to the stepping motor 61 (S64), and executes the stop holding process in the same manner as S46 (S65).

[0089] On the other hand, the number of conveyed sheets P is less than the second threshold value (S63: NO). The control unit 100 determines that it is not necessary to supply the holding current to the stepping motor 61 (S66), does not execute the stop holding process S65, and ends the determination process S30.

[0090] In the image forming apparatus 1 according to the embodiment described above, in the determination process (S30), the control unit 100 determines whether to supply the holding current to the stepping motor 61 in consideration of the temperature state of the surrounding environment as the state information that is the main cause of the out-of-step of the stepping motor 61. Specifically, when the detected temperature by the temperature sensor 70 is lower than the normal temperature, the control unit 100 supplies the holding current to the stepping motor in consideration of the increase in the driving load of the stepping motor 61 (S46, S65), thereby preventing out-of-step at the start of driving of the stepping motor 61. On the other hand, when the detected temperature by the temperature sensor 70 is equal to or higher than the normal temperature, since the driving load of the stepping motor 61 does not increase, the control unit 100 determines not to supply the holding current to the stepping motor 61 (S47, S53, S66), and the power consumption can be reduced by not supplying the holding current to the stepping motor 61.

[0091] Further, in the determination process (S30), the control unit 100 determines whether to supply the holding current to the stepping motor 61 in consideration of the number of conveyed sheets indicating the conveyance load of the conveyance unit 5 as the state information. Specifically, when the number of conveyed sheets of the sheet P is larger than the threshold value, the control unit 100 determines that it is necessary to supply the holding current to the stepping motor 61 (S45, S51, S64), and by supplying the holding current to the stepping motor 61, out-of-step of the stepping motor 61 can be accurately prevented. On the other hand, when the number of conveyed sheets of the sheet P is less than the threshold value, the control unit 100 determines that it is not necessary to supply the holding current to the stepping motor 61 (S47, S53, S66), and the power consumption can be reduced by not supplying the holding current to the stepping motor 61.

[0092] Further, when the type of the sheet P is the first sheet, the control unit 100 changes the threshold value to the first threshold value, and when the type of the sheet P is the second sheet that is thicker than the first sheet, the control unit 100 changes the threshold value to the second threshold value. That is, when the conveying load is large and the inertial force acting on the sheet P is large when the conveyance of the sheet P stops, the threshold value of the second sheet is made smaller than the threshold value of the first sheet, so that the holding current is supplied to the second sheet for which the phase shift of the stepping motor 61 is more likely to occur than in the first sheet at an earlier stage. Thereby, it is possible to more accurately prevent out-of-step at the start of driving of the stepping motor 61.

[0093] Further, the control unit 100 acquires the exciting phase immediately before the rotation of the stepping motor 61 stops as the stop exciting phase, and supplies the holding current or the driving current so as to be maintained at the same exciting phase as the stop exciting phase during the execution of the stop holding process (S46, S65) and at the start of the second conveyance process (S32). Thereby, since the exciting phase can be prevented from being changed between the time when the driving of the stepping motor 61 stops (time t3 in FIG. 3) and the time when the driving is restarted (time t4 in FIG. 3), it is possible to prevent out-of-step at the start of driving of the stepping motor 61.

[0094] Further, as shown in FIG. 5, in the first conveyance process (S21), the control unit 100 rotates the discharge roller 53 forward to convey the sheet P having an image formed on the back surface by the image forming unit 3 toward the discharge tray 12 by a predetermined amount, and in the second conveyance process (S32), the control unit 100 rotates the discharge roller 53 reversely to convey the sheet P in the second conveyance direction D2, and then conveys the sheet P again in the first conveyance direction D1 toward the image forming unit 3 (S3). Thereby, it is possible to prevent out-of-step at the start of driving of the stepping motor 61 and to perform double-sided printing on the sheet P well while reducing power consumption.

[0095] [Other Embodiments] The image forming apparatus 1 of the above-described embodiment is assumed to be a color laser printer, but is not limited thereto, and can be applied to other devices such as a monochrome laser printer, an inkjet printer, a multifunction machine, and a fax machine.

[0096] In the image forming apparatus 1 of the above-described embodiment, in the determination process S30 shown in FIGS. 6 and 7, the control unit 100 performs both the threshold determination (S43, S49, S62) based on the temperature detected by the temperature sensor 70 and the threshold determination (S44, S50, S52, S63) based on the number of sheets conveyed, which indicates the conveyance load of the conveyance unit 5. However, the present invention is not limited to this. For example, the control unit 100 may perform only either the threshold determination (S43, S49, S62) based on the detected temperature or the threshold determination (S44, S50, S52, S63) based on the number of sheets conveyed.

[0097] Also, in the above-described embodiment, in S1, the control unit 100 determines the type of the sheet P by acquiring the type information regarding the type of the sheet P set by the setting unit 110. However, the present invention is not limited to this. For example, the control unit 100 may determine the type of the sheet P by detecting the capacitance of the sheet P using a capacitance sensor.

[0098] Also, in the above-described embodiment, in the determination process S30, the control unit 100 uses the number of sheets conveyed as the state information indicating the conveyance load of the conveyance unit 5. However, the present invention is not limited to this. For example, the integrated value of the number of steps of the stepping motor 61 may be used.

[0099] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

Explanation of Reference Numerals

[0100] 1 Image forming apparatus 2 Feeding unit 3 Image forming unit 5 Conveyance unit 11 Housing 12 Discharge tray 51 Conveyance roller 53 Discharge roller 61 Stepping motor 70 Temperature sensor 71 Sheet Sensor 100 Control Unit 103 RAM 104 EEPROM 105 ASIC 110 Setting Unit D1 First Conveyor Direction D2 Second Conveyor Direction S3, S21 First Conveyor Process S29 Stop Process S30 Judgment Process S32 Second Conveyor Process S46, S65 Stop Hold Process

Claims

A sheet conveying device provided in an image forming apparatus, comprising: a conveying unit that rotates forward and backward to convey a sheet; a stepping motor that drives the conveying unit; a discharge unit where the sheet conveyed by the conveying unit is discharged; a detection unit that detects state information including at least the temperature state of the surrounding environment of the image forming apparatus, the detection unit having a sheet count counter that counts the number of sheets conveyed by the conveying unit; a setting unit that sets type information regarding the type of sheet; a control unit, wherein the state information includes the conveying load of the conveying unit; the types of sheets include a first sheet and a second sheet that is thicker than the first sheet; the detection unit acquires the type of sheet indicating the conveying load of the conveying unit as the state information; the control unit performs a first conveying process of conveying a sheet in a first conveying direction toward the discharge unit by the conveying unit; performs a stop process of stopping the driving of the conveying unit; during the execution of the stop process, based on the detection result by the detection unit, determines whether to supply to the stepping motor a holding current that is equal to or less than the driving current of the stepping motor and that holds the conveying unit in a stopped state; when it is determined in the determination process to supply the holding current, performs a stop holding process of holding the conveying unit in a stopped state by supplying the holding current to the stepping motor; after the stop process and the stop holding process, performs a second conveying process of conveying a sheet in a second conveying direction opposite to the first conveying direction; in the determination process, acquires the number of conveyed sheets counted by the sheet count counter, which indicates the conveying load of the conveying unit as the state information, and when the number of conveyed sheets is greater than a threshold value, determines to supply the holding current to the stepping motor, and when the number of conveyed sheets counted by the sheet count counter is less than the threshold value, determines not to supply the holding current to the stepping motor; the threshold value used in the determination process has a first threshold value corresponding to the first sheet and a second threshold value corresponding to the second sheet and smaller than the first threshold value; when the type information set by the setting unit is the first sheet, the threshold value is changed to the first threshold value, and when the type information set by the setting unit is the second sheet, the threshold value is changed to the second threshold value. A sheet conveying device characterized by this.

2. The detection unit includes a temperature sensor that detects the temperature state of the surrounding environment of the image forming apparatus as the state information. The control unit In the determination process, when the temperature detected by the temperature sensor is lower than normal temperature, it determines to supply the holding current to the stepping motor, and when the temperature detected by the temperature sensor is equal to or higher than normal temperature, it determines not to supply the holding current to the stepping motor. The sheet conveying device according to claim 1, characterized in that.

3. The stepping motor has a rotor. The control unit In the stop process, the driving of the conveying unit is stopped for a predetermined time having a length equal to or longer than the vibration convergence time of the rotated rotor. The sheet conveying device according to claim 1 or 2, characterized in that.

4. The stop process further includes an excitation phase acquisition unit that acquires, as a stop excitation phase, the excitation phase immediately before the rotation of the stepping motor stops. The control unit During the execution of the stop holding process, the holding current is supplied to the same excitation phase as the stop excitation phase acquired by the excitation phase acquisition unit. At the start of the second conveyance process, a drive current is supplied to the same excitation phase as the stop excitation phase acquired by the excitation phase acquisition unit. The sheet conveying device according to any one of claims 1 to 3, characterized in that.

5. An image forming unit that forms an image on the sheet conveyed by the conveying unit. The sheet conveying device according to any one of claims 1 to 4. An image forming apparatus, characterized by comprising.

6. The conveying unit has a discharge roller that conveys the sheet to the discharge unit. The control unit In the first conveyance process, by rotating the discharge roller forward, the sheet having an image formed on one side by the image forming unit is conveyed by a predetermined amount toward the discharge unit. In the second conveyance process, by rotating the discharge roller backward, the sheet is conveyed in the second conveyance direction. After the second conveyance process, the sheet is conveyed again in the first conveyance direction toward the image forming unit. The image forming apparatus according to claim 5, characterized in that.

Images