Image forming apparatus

Abstract

To suppress damage to a sheet and deterioration in productivity of an image forming device.SOLUTION: There is a case where a recording medium should be stopped on a conveyance passage and where a length of the recording medium in a conveyance direction is a first length. In this case, a first controller stops a first motor in response to detection by a first sensor, of a tip of the recording medium, and a second controller stops a second motor in response to detection by the first sensor, of the tip of the recording medium. The first length is longer than a distance from a first conveyance roller to a second conveyance roller. There is a case where the recording medium should be stopped on the conveyance passage and where the length of the recording medium in the conveyance direction is a second length longer than the first length. In this case, the first controller stops the first motor in response to detection by the first sensor, of the tip of the recording medium, and the second controller continues driving the second motor even when the first sensor detects the tip of the recording medium.SELECTED DRAWING: Figure 11

Description

Technical Field

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

Background Art

[0002] According to Patent Document 1, a controller of an image forming apparatus controls a motor for driving a conveyance roller based on the timing when the leading edge of a sheet is detected by a sheet sensor (Patent Document 1). According to Patent Document 2, it is proposed to separate the controller into a central control IC (integrated circuit) and a distributed control IC, and connect a plurality of motors to the distributed control IC. Since the distributed control IC is arranged near the motor, it is possible to shorten the length of the cable connecting the motor and the controller.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Low-end image forming machines are sufficient if they can form images on standard-sized sheets such as A4 and B5, but high-end image forming machines are required to be able to form images on a wider variety of sheets. In particular, high-end image forming machines have a large number of transport rollers in their transport paths. B5-sized sheets are simultaneously gripped and transported by two transport rollers, but long sheets may be simultaneously gripped and transported by 12 transport rollers. When sheet transport is temporarily stopped to adjust the temperature of the fuser, all 12 transport rollers are required to stop simultaneously. If the 12 transport rollers stop at different times, long sheets may be folded or torn in the transport direction. On the other hand, if all 12 transport rollers are stopped for short sheets, these sheets will stop with a relatively large distance (paper gap) between preceding and succeeding sheets. As a result, after sheet transport is resumed, the paper gap remains relatively large, which can reduce the productivity of the image forming machine. Therefore, the present invention aims to suppress damage to sheets and reduce the productivity of the image forming machine. [Means for solving the problem]

[0005] The present invention, for example, Image forming means for forming an image on a recording medium, A transport path for guiding the recording medium to the image forming means such that an image is formed on the second surface of the recording medium on which an image has been formed by the image forming means, wherein the second surface is the surface opposite to the first surface. A first transport means provided in the transport path for transporting the recording medium, A first drive means for driving the first transport means, A first control means for controlling the first drive means, A second transport means is provided in the transport path upstream of the first transport means in the transport direction in which the recording medium is transported, and transports the recording medium. A second driving means for driving the second transport means, A second control means for controlling the second drive means, A first detection means provided in the transport path downstream of the first transport means in the transport direction, for detecting the presence or absence of the recording medium, A single common signal line connected to the first detection means is branched and connected to the first control means and the second control means, and a synchronization signal is transmitted to the first control means and the second control means via the common signal line. It has a first detection means, In cases where the first recording medium should be stopped on the transport path, and the length of the first recording medium in the transport direction is a first length that spans the first transport means and the second transport means when the first recording medium is stopped, the first control means indicates that the first detection means has changed from a state in which it has not detected the first recording medium to a state in which it has detected the first recording medium. synchronization When the first detection means receives a signal, the first drive means stops, and the second control means receives the signal from the first detection means synchronization Upon receiving a signal, the second drive means is stopped. In cases where the first recording medium should be stopped on the transport path, and the length of the first recording medium in the transport direction is a second length such that when the first recording medium is stopped, the first recording medium straddles the first transport means but does not straddle the second transport means, and a second recording medium following the first recording medium is being transported, the first control means receives from the first detection means synchronization Upon receiving a signal, the first drive means is stopped, and the second control means receives the signal from the first detection means. synchronization The present invention provides an image forming apparatus characterized by continuing to drive the second driving means even after receiving a signal. [Effects of the Invention]

[0006] According to the present invention, it is possible to suppress damage to the sheet and a decrease in the productivity of the image forming apparatus. [Brief explanation of the drawing]

[0007] [Figure 1] Diagram illustrating an image forming apparatus. [Figure 2] Diagram explaining the controller [Figure 3]Figure for explaining conveyance rollers in a conveyance path [Figure 4] Figure for explaining a serial communication line connecting a main CPU and a sub CPU [Figure 5] Figure for explaining a reference sensor [Figure 6] Timing chart for explaining a comparative example [Figure 7] Figure for explaining a common signal line in Example 1 [Figure 8] Figure for explaining sheets of different lengths [Figure 9] Timing chart for explaining an example [Figure 10] Figure for explaining a matrix [Figure 11] Flowchart showing a stop control method [Figure 12] Figure for explaining restart of sheet conveyance [Figure 13] [[ID=3]]Figure for explaining a common signal line [Figure 14] Timing chart for explaining redrive of an actuator [Figure 15] Flowchart showing a conveyance restart method [Figure 16] Figure for explaining a CPU

Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and redundant descriptions are omitted.

[0009] <Image forming apparatus> As shown in Figure 1, the paper feeding and image formation unit 100 of the image forming apparatus 1 is a device that feeds and transports a sheet P and transfers a toner image onto the sheet P. The paper feeding and image formation unit 100 has a housing 101. The intermediate transport unit 200 is a device that transports the sheet P discharged from the paper feeding and image formation unit 100 to the fuser and discharge unit 300. The intermediate transport unit 200 has a housing 201. As shown in Figure 1, the height of the discharge port of the paper feeding and image formation unit 100 and the height of the sheet receiving port of the fuser and discharge unit 300 are different. The intermediate transport unit 200 is provided to compensate for these height differences. The fuser and discharge unit 300 is a device that applies heat and pressure to the sheet P discharged from the intermediate transport unit 200 to fix the toner image onto the sheet P and then discharges the sheet P. The fuser and discharge unit 300 has a housing 301. The operation unit 400 is a user interface that includes an output device that outputs information to the user and an input device that receives information input by the user.

[0010] ● Paper feed image creation unit 100 The sheet cassette 110 is a storage unit that holds a large number of sheets P. The paper feeding mechanism 111 includes a feeding roller that feeds the sheets P from the sheet cassette 110 to the transport path 120. Multiple transport rollers 121 are arranged on the transport path 120. The multiple transport rollers 121 are driven and rotated by actuators (e.g., motors) not shown, and transport the sheets P to the transfer unit 190. The image forming apparatus 1 monitors the position of the sheets P on the transport path 120 based on the detection results of a path sensor 122 located on the transport path 120.

[0011] The paper feeding and image-forming unit 100 has four image forming stations (process units). Image forming station 150 forms a yellow toner image. Image forming station 160 forms a magenta toner image. Image forming station 170 forms a cyan toner image. Image forming station 180 forms a black toner image. Since the four image forming stations 150, 160, 170, and 180 each have the same or similar structure, the structure of image forming station 150 will be described in detail here.

[0012] The photosensitive drum 153 is an image carrier that rotates while carrying an electrostatic latent image and a toner image. The charger 152 uniformly charges the surface of the photosensitive drum 153. The laser scanner 140 has a light source (e.g., a semiconductor laser), a reflective mirror 141, and a rotating polyhedron mirror 142. The light source emits light corresponding to the image signal. The rotating polyhedron mirror 142 reflects light while rotating. The reflective mirror 141 reflects the light incident from the rotating polyhedron mirror 142 toward the photosensitive drum 153. As a result, the light scans the photosensitive drum 153, and an electrostatic latent image is formed on the surface of the photosensitive drum 153. The developer 151 develops the electrostatic latent image with toner to form a toner image. The toner bottle unit 130 has a replaceable toner bottle 131 that contains toner and supplies toner to the developer 151.

[0013] The four image forming stations 150, 160, 170, and 180 each transfer toner images onto the intermediate transfer body 191. The intermediate transfer body 191 rotates and transports the toner images to the transfer unit 190. In the transfer unit 190, the transfer belt 192 presses the sheet P against the intermediate transfer body 191. The toner image is transferred from the intermediate transfer body 191 to the sheet P. The transport belt 123 transports the sheet P, on which the toner image has been transferred, to the intermediate transport unit 200.

[0014] The transport path 124 is used to transport the sheet P, on which an image has been formed on the first surface, back to the transport path 120 (double-sided image formation). In other words, the transport path 124 sends the sheet P back to the transfer unit 190 when an image is formed on the second surface of the sheet P.

[0015] ●Intermediate transport unit 200 The transport belt 210 transports the sheet P discharged from the paper feeding and image creation unit 100 and discharges it to the fuser and paper discharge unit 300. Since the toner image is not fixed on the sheet P, the transport belt 210 may also transport the sheet P by suction using negative pressure.

[0016] The transport path 220 transports the sheet P from the fixing and discharge unit 300 to the paper feeding and image formation unit 100 during double-sided image formation. The transport path 220 is equipped with multiple transport rollers 221. The transport path 220 is equipped with multiple path sensors 222. The intermediate transport unit 200 and the paper feeding and image formation unit 100 monitor the position of the sheet P in the transport path 220 based on the detection results of the path sensors 222.

[0017] ●Fuser output unit 300 The fuser 310 applies heat and pressure to the sheet P discharged from the intermediate transport unit 200 to fix the toner image onto the sheet P. A transport roller 321 is located in the transport path 320. The transport roller 321 transports the sheet P to the cooler 330. The cooler 330 cools the sheet P. The fuser output unit 300 supports both face-up output and face-down output. Face-up output means that the sheet P is discharged so that the first side with the image facing upwards. Face-down output means that the sheet P is discharged so that the first side with the image facing downwards. When face-up output is selected by the user, the switching unit 323 guides the sheet P to the transport path 324. As a result, the sheet P is discharged via the transport path 324. In face-down output, the switching unit 323 guides the sheet P to the transport path 325. A switching unit 326 is provided at the lower end of the transport path 325. In face-down paper output, the switching unit 326 guides the sheet P to the transport path 328. When the rear end of the sheet P arrives at the transport path 325, the rotation direction of the transport rollers provided on the transport paths 325 and 328 is reversed. Furthermore, the switching unit 323 guides the sheet P from the transport path 325 to the transport path 324. In double-sided image forming, when the leading edge of the sheet P arrives at the transport path 328, the rotation direction of the transport rollers provided on the transport path 328 is reversed. Furthermore, the switching unit 326 guides the sheet P from the transport path 328 to the transport path 327. The transport rollers provided on the transport path 327 transport the sheet P to the intermediate transport unit 200. Path sensors are also provided on the transport paths 324, 325, 327, and 328 to monitor the position of the sheet P.

[0018] ● Controller Figure 2 shows the controller system for controlling the image forming apparatus 1. The main controller 10 is a control circuit that comprehensively controls the entire image forming apparatus 1. The main controller 10 receives information input from the operation unit 400 and transmits information to be output to the operation unit 400 by performing serial communication with the operation unit 400. The main controller 10 is connected to the main CPU 11 via a serial communication line. The serial communication line is merely one example of a communication line and may be replaced with wireless communication.

[0019] The main CPU 11 is a control circuit that controls the feeding, transporting, image creation, fixing, and ejection of the sheet P. In this embodiment, CPU is used as a general term for a central processing unit, processor, processing circuit, IC (integrated circuit), etc. Alternatively, CPU may be understood as a computer having a CPU core, a memory unit (ROM and RAM), and a communication circuit. When a user submits a print job by operating the operation unit 400, the main controller 10 obtains the job details from the operation unit 400 and sends a job start command to the main CPU 11.

[0020] The main CPU 11 is connected to multiple sub-CPUs 13a to 13g via serial communication lines. The main CPU 11 sends control commands to the sub-CPUs 13a to 13g via serial communication. Here, serial communication refers to a communication method such as UART (asynchronous serial communication) where a main device and a sub-device communicate on a one-to-one basis. At least two serial communication lines are connected between the main CPU 11 and sub-CPU 13a. The same applies to the sub-CPUs 13b to 13g. The sub-CPUs 13a to 13g are located inside the same functional unit (functional group) as their respective controlled loads (actuators 16a to 16g, fans 15a to 15g, sensors 14a to 14g, etc.). This is to shorten the length of the cables connecting the sub-CPUs 13a to 13g and the loads. In Figure 2, the reference numerals a to g are added to the end of the reference numerals to distinguish the components located in the functional units 12a to 12g. When describing common aspects of each component, the letters a through g are omitted from the reference numerals. Furthermore, the functional unit 12 may be understood as a collection of loads controlled by a single sub-CPU 13. Alternatively, the functional unit 12 may be understood as one of the divided regions (spaces) when the image forming apparatus 1 is divided into multiple spaces for design purposes.

[0021] The sub-CPU 13 transmits the detection results from the sensor 14 to the main CPU 11. The sub-CPU 13 also controls the fan 15 and actuator 16 according to the commands received from the main CPU 11. The actuators 16 include a motor that drives the transport rollers and a solenoid that drives a flapper that switches the destination of the sheet P. The sensor 14 is a path sensor 122, etc. Here, the sensor 14, fan 15, and actuator 16 are listed as loads, but this is just an example. The load may also be, for example, an LED (light-emitting diode). In Figure 2, seven sub-CPUs 13a to 13g are connected to one main CPU 11, but this is just an example. The technical concept of the present invention is applicable as long as two or more sub-CPUs are connected to one main CPU 11.

[0022] ● Synchronous control of actuators Figure 3 is a schematic cross-sectional view of the transport path 120 of the paper feeding and image-making unit 100, the transport path 220 of the intermediate transport unit 200, and the transport path 327 of the fixing and discharge unit 300. Transport rollers are arranged in the transport paths 120, 220, and 327, respectively. Each transport roller is driven and rotated by one of the motors M1 to M18 connected by dashed lines. Motors M1 to M4 are part of actuator 16e. Motors M5 to M7 are part of actuator 16d. Motors M8 to M10 are part of actuator 16c. Motors M11 to M14 are part of actuator 16b. Motors M15 to M18 are part of actuator 16a.

[0023] Path sensors PS1 to PS18 are positioned on transport paths 120, 220, and 327. Path sensors PS1 to PS18 are reflective photointerrupters whose output signal level changes depending on whether a sheet is present or not. Path sensors PS1 to PS5 are part of sensor 14e. Path sensors PS6 to PS8 are part of sensor 14d. Path sensors PS9 to PS12 are part of sensor 14c. Path sensors PS13 and PS14 are part of sensor 14b. Path sensors PS15 to PS18 are part of sensor 14a. By having motors M1 to M18g all rotate at the same speed, multiple transport rollers are prevented from pulling on or bending the sheet P.

[0024] Incidentally, when double-sided printing is performed, the density of the toner image or the transfer position may be adjusted in the image forming station 150. Also, temperature adjustment of the fuser 310 may be necessary during the print job. In the image forming apparatus 1, sheets with an image formed on the first side that are transported to the transfer unit 190 for an image to be formed on the second side, and sheets that are transported to the transfer unit 190 for an image to be formed on the first side, may be transported to the transfer unit 190 alternately. In these cases, a sheet P with an image formed on the first side but not on the second side must stop and wait somewhere in the transport paths 120, 220, or 327. By having multiple motors that drive multiple transport rollers that grip the sheet P decelerate and stop in sync with each other, the likelihood of the sheet P folding in a bellows-like manner or being damaged is reduced. In other words, damage to the sheet is suppressed. Therefore, the method of decelerating and stopping multiple motors in sync (synchronous control) will be described in detail below.

[0025] Figure 4 shows a comparative example. In this comparative example, motors M1 to M4 and path sensors PS1 to PS5 are connected to sub-CPU 13e. Motors M5 to M7 and path sensors PS6 to PS8 are connected to sub-CPU 13d. Motors M8 to M20 and path sensors PS9 to PS12 are connected to sub-CPU 13c. Motors M11 to M14 and path sensors PS13 and PS14 are connected to sub-CPU 13b. Motors M15 to M18 and path sensors PS15 to PS18 are connected to sub-CPU 13a. Sub-CPUs 13a to 13e are each connected one-to-one to the main CPU 11 via serial communication lines 401a to 401e. The main CPU 11 performs serial communication with sub-CPUs 13a to 13e via serial communication lines 401a to 401e.

[0026] Figure 5(A) shows the state in which the two transport rollers are gripping the sheet P when the sheet P is stopped based on the position of the path sensor PS13 in the comparative example. As shown in Figure 5(A), the sheet P is gripped by a transport roller driven by motor M11 and a transport roller driven by motor M12. Motors M11 and M12 are controlled by sub-CPU 13b.

[0027] As shown in Figure 6(A), when the path sensor PS13 detects the leading edge of sheet P, the level of the output signal of the path sensor PS13 changes from a high level to a low level. In response to this change, the sub-CPU 13b sends a notification to the main CPU 11 via serial communication indicating that the leading edge of sheet P has been detected. In response to this notification, the main CPU 11 sends stop commands for motors M11 and M12 to the sub-CPU 13b via serial communication. Upon receiving the stop command, the sub-CPU 13b decelerates and stops motors M11 and M12. If the stop command can be implemented with a single command, the deceleration start timing of motor M11 and the deceleration start timing of M12 are simultaneous. This is because motors M11 and M12 are controlled by the same CPU, the sub-CPU 13b.

[0028] Figure 5(B) shows the state in which multiple transport rollers are gripping the sheet P when the sheet is stopped based on the position of the path sensor PS10. As shown in Figure 5(B), the sheet P is gripped by a transport roller driven by motor M7 and a rotating transport roller driven by motor M8. Motor M7 is controlled by sub-CPU 13d, while motor M8 is controlled by sub-CPU 13c.

[0029] As shown in Figure 6(B), when the path sensor PS10 detects the leading edge of the sheet P, the level of the output signal of the path sensor PS10 changes from a high level to a low level. The sub-CPU 13c sends a notification to the main CPU 11 via serial communication indicating that the leading edge of the sheet P has been detected. The main CPU 11 cannot send commands to both the sub-CPU 13c and sub-CPU 13d simultaneously. Therefore, in response to this notification, the main CPU 11 sends a stop command for motor M7 to the sub-CPU 13d via serial communication. Next, the main CPU 11 sends a stop command for motor M8 to the sub-CPU 13c via serial communication. Upon receiving the stop command, the sub-CPU 13d decelerates and stops motor M7. A little later, the sub-CPU 13c receives the stop command and decelerates and stops motor M8. In other words, the conveyor roller driven by motor M7 stops first, and the rotating conveyor roller driven by motor M8 stops later. As a result, the two conveyor rollers pull on the sheet P.

[0030] In this way, when the main CPU 11 sends a stop command to multiple sub-CPUs via serial communication, the control timing may be out of sync among the multiple sub-CPUs. As a result, a difference in rotational speed occurs among the multiple transport rollers that grip the sheet P, causing the sheet P to be folded into an accordion shape or to be pulled and damaged.

[0031] <Example 1> Figure 7 shows the wiring of the synchronization signal lines (common signal lines) in Example 1. Compared to Figure 4, Figure 7 differs in the following ways: The signal line 701b that transmits the detection result of the path sensor PS13 is connected to sub-CPUs 13c, 13d, and 13e in addition to sub-CPU 13b. Furthermore, the signal line 701c that transmits the detection result of the path sensor PS10 is connected to sub-CPUs 13d and 13e in addition to sub-CPU 13c. Furthermore, the signal line 701d that transmits the detection result of the path sensor PS7 is connected to sub-CPU 13e in addition to sub-CPU 13d. Signal lines 701b to 701d are lines that propagate high-level or low-level detection signals (synchronization signals). Therefore, changes in the level of the signals output from path sensors PS7, PS10, and PS13 arrive at multiple sub-CPUs simultaneously.

[0032] Figure 8(A) shows the state in which multiple transport rollers are gripping sheet P when the sheet P is stopped based on the position of the path sensor PS10. As shown in Figure 8(A), sheet P is gripped by multiple transport rollers, each driven by motors M2, M3, M4, M5, M6, M7, and M8. Therefore, motors M2, M3, M4, M5, M6, M7, and M8 need to decelerate and stop in synchronous motion. As shown in Figure 7, motors M2, M3, and M4 are controlled by sub-CPU 13e. Motors M5, M6, and M7 are controlled by sub-CPU 13d. Motor M8 is controlled by sub-CPU 13c. The path sensor PS10 is connected to sub-CPUs 13e, 13d, and 13c via a common signal line 701c. Instead of sending a control start command via serial communication, the main CPU 11 sends a command to the sub-CPUs 13c, 13d, and 13e instructing them to "decelerate and stop the actuator in synchronization with the signal output from the path sensor PS10." This command is sent before the tip of the sheet P reaches the path sensor PS10. Upon receiving this command, the sub-CPUs 13c, 13d, and 13e recognize which path sensor's output signal should be synchronized with when executing the command. In other words, the command includes the instruction to stop and identification information for the path sensor that outputs the signal to be synchronized. For example, the command may include identification information specifying the command content and identification information specifying the path sensor. The command content and the path sensor identification information may be transmitted and received separately. The path sensor identification information may also be identification information for the input terminal or input port to which the signal output from the path sensor is input.

[0033] As shown in Figure 9(A), when subCPU 13e receives instruction CMD01, it starts stopping motors M2, M3, and M4 in synchronization with the timing when the path sensor PS10 detects the leading edge of sheet P. For example, instruction CMD01 may include identification information for the path sensor PS10 and identification information for motors M2, M3, and M4. When subCPU 13d receives instruction CMD02, it starts stopping motors M5 to M7 in synchronization with the timing when the path sensor PS10 detects the leading edge of sheet P. Instruction CMD02 may include identification information for the path sensor PS10 and identification information for motors M5 to M7. When subCPU 13c receives instruction CMD03, it starts stopping motor M8 in synchronization with the timing when the path sensor PS10 detects the leading edge of sheet P. Instruction CMD03 may include identification information for the path sensor PS10 and identification information for motor M8. This significantly reduces the timing difference in deceleration start between multiple sub-CPUs.

[0034] As shown in Figure 8(A), when stopping a sheet P with a long length in the transport direction, the actuators to be stopped are motors M2 to M8. However, when stopping a sheet P with a short length in the transport direction, it is not necessary to stop all of motors M2 to M8. For example, in the case shown in Figure 8(B), it is sufficient to stop motors M7 and M8. Therefore, the main CPU 11 selects the motor to be controlled based on the size of the sheet P to be stopped (length in the transport direction) and the reference path sensor (reference sensor). The reason for considering the path sensor here is that the motor to be stopped and the sub-CPU that controls that motor differ depending on the path sensor that outputs the synchronization signal. In the case of Figure 8(B), the sheet P is stopped based on the position of the path sensor PS10. Therefore, the motors driving the transport rollers that grip the sheet P are motors M7 and M8. The sub-CPUs that should receive the command are sub-CPUs 13c and 13d. Comparing Figure 8(A) and Figure 8(B), it can be seen that even if the reference path sensor is the same, the motor being controlled and the sub-CPU to which the instructions are sent differ depending on the size of sheet P.

[0035] The main CPU 11 can recognize the length of sheet P by obtaining sheet size information input by the user through the operation unit 400 from the main controller 10. When it becomes necessary to stop the transport of sheet P, the main CPU 11 selects the actuator to be stopped according to the sheet size information. As a result, the appropriate actuator according to the sheet size slows down and stops. In Embodiment 1, the sheet size information is input by the user, but this is just one example. For example, the main CPU 11 may obtain sheet size information using a sheet sensor that detects the size of sheet P contained in the sheet cassette 110.

[0036] As shown in Figure 9(B), which corresponds to Figure 8(B), the main CPU 11 sends instruction CMD04 to the sub-CPU 13d. Instruction CMD04 includes identification information for the path sensor PS10 and identification information for the motor M7. Based on instruction CMD04, the sub-CPU 13d stops the motor M7 in synchronization with the timing when the output signal of the path sensor PS10 changes. Similarly, the main CPU 11 sends instruction CMD05 to the sub-CPU 13c. Instruction CMD05 includes identification information for the path sensor PS10 and identification information for the motor M8. Based on instruction CMD05, the sub-CPU 13c stops the motor M8 in synchronization with the timing when the output signal of the path sensor PS10 changes.

[0037] Figure 10 shows the motors to be controlled synchronously, determined from the sheet length L and the reference sensor, and the sub-CPU to which the commands for synchronous control are sent. The reference sensor is a path sensor that outputs a reference synchronous signal when stopping sheet P. The main CPU 11 stores the matrix shown in Figure 10 in a storage device such as ROM. The main CPU 11 determines which motors should be decelerated and stopped by referring to the matrix based on the sheet size information (sheet length L) and the reference sensor. For example, the sheet length L may be 700 mm and the reference sensor may be the path sensor PS7. In this case, the main CPU 11 identifies motors M2, M3, M4, M5, and M6 as the targets for control by referring to the matrix based on this information. In other words, the main CPU 11 sends a stop command to the sub-CPU 13e via serial communication, specifying that the reference sensor is the path sensor PS7 and that motors M2, M3, and M4 are the targets for control. Furthermore, the main CPU 11 sends a stop command to the sub-CPU 13d via serial communication, specifying that the reference sensor is the path sensor PS7 and that the motors M5 and M6 are the targets of control. In this way, the command CMD may specify the control content (e.g., stop / drive), the reference sensor (e.g., path sensor PS10), and the target of control (e.g., motor M5). In particular, when the target of control is specified, the sub-CPU 13 will be able to stop or drive the minimum necessary actuators.

[0038] ● How to determine the reference sensor The reference sensor can be any path sensor located downstream in the transport direction from the leading edge of sheet P at the time when sheet P needs to be stopped. Assume that sheet P needs to be stopped at time ta. The leading edge of sheet P arrives at the downstream path sensor at time tz. The time when the main CPU 11 completes the deceleration stop setting for the sub-CPU 13 (time tm) must be before time tz. Here, the time from time ta to time tm is T0. Time T0 includes the time required for serial communication. The main CPU 11 determines the path sensor that satisfies this condition as the reference sensor.

[0039] Furthermore, the reference sensor must be a path sensor connected to the sub-CPU 13 that performs deceleration and stopping. For example, let's assume that path sensors PS13 and PS14 are located downstream of the tip of the seat P. According to Figure 7, the sub-CPU to which path sensor PS14 is connected is sub-CPU 13b. Therefore, motors M11, M12, M13, and M14 can be controlled by sub-CPU 13b using path sensor PS14 as the reference sensor. On the other hand, path sensor PS14 is not connected to sub-CPUs 13e, 13d, and 13c. Consequently, motors M1 to M10, which are controlled by sub-CPUs 13e, 13d, and 13c, cannot be controlled using path sensor PS14 as the reference sensor. Therefore, the main CPU 11 decides to use path sensor PS13 as the reference sensor in order to include motors M1 to M10 in the deceleration and stopping process. This is because path sensor PS13 is also connected to sub-CPUs 13e, 13d, and 13c via signal line 701b. ●Flowchart Figure 11(A) shows the deceleration stop control of multiple actuators performed by the main CPU 11. In S1101, the main CPU 11 acquires seat size information. Seat size information is acquired, for example, when a job is started or while a job is running. Seat size information is acquired from the operation unit 400 or the host computer via the main controller 10.

[0040] In S1102, the main CPU 11 determines whether it is necessary to stop the transport of sheet P. For example, it may be necessary to adjust the temperature of the fuser 310 while the job is running. It may also be necessary to adjust the transfer position of the toner image on sheet P or adjust the density of the toner image. In these cases, the main CPU 11 determines that it is necessary to stop the transport of sheet P. If it is not necessary to stop the transport of sheet P, the main CPU 11 terminates the deceleration stop control. If it is necessary to stop the transport of sheet P, the main CPU 11 proceeds to S1103.

[0041] In S1103, the main CPU 11 determines a reference sensor based on the leading edge position of the sheet P being transported along the transport path of the image forming apparatus 1 at that time, and the transport speed of the sheet P. As described above, one of the path sensors located downstream of the leading edge of the sheet P in the transport direction is selected as the reference sensor. For example, the path sensor closest to the leading edge of the sheet P may be selected as the reference sensor. The reason why the transport speed is considered is that it is necessary for the sheet P to be detected by the reference sensor when the sheet P stops. As a result, path sensors that the trailing edge of the sheet P has already passed when the sheet P stops are excluded from being reference sensors. The distance traveled by the sheet P is calculated by multiplying the elapsed time since the leading edge of the sheet P passed a certain path sensor by the transport speed. In other words, it can be seen that the sheet P is located at a distance equal to the distance traveled from the detection position of the path sensor. Thus, the transport speed is also used to determine the position of the sheet P.

[0042] In S1104, the main CPU 11 determines which actuator (motor) to stop based on the combination of seat size information and reference sensor. For example, the main CPU 11 may select a motor corresponding to the combination of seat size information and reference sensor by referring to the matrix (control table) shown in Figure 10.

[0043] In S1105, the main CPU 11 notifies the sub-CPU 13, which controls the actuator to be stopped, of the reference sensor and the actuator to be stopped via serial communication. For example, the main CPU 11 refers to the matrix shown in Figure 10 to determine the sub-CPU controlling the actuator to be stopped. The determined sub-CPU becomes the recipient of the stop notification (stop command). This notification may include identification information of the actuator to be stopped and identification information of the reference sensor. The identification information of the reference sensor may be the identification information of a common signal line connected to the reference sensor, or the identification information of the input port to which the common signal line is connected.

[0044] In S1106, the main CPU 11 determines whether the stop setting is complete. For example, the main CPU 11 may determine whether it has received a response to the stop notification via serial communication from all sub-CPUs 13 that were determined to be the destinations for the stop notification. Once all sub-CPUs 13 selected as destinations have completed the stop setting, the main CPU 11 terminates the deceleration stop control.

[0045] Figure 11(B) shows the deceleration stop control performed by the sub-CPU 13. In S1111, the sub-CPU 13 determines whether there is a notification (stop command) regarding deceleration stop control (synchronous control) sent from the main CPU 11. If the notification has not been received via serial communication, the sub-CPU 13 terminates the deceleration stop control. If the notification has been received via serial communication, the sub-CPU 13 proceeds to S1112.

[0046] In S1112, the sub-CPU 13 determines whether the reference sensor specified by the notification has detected sheet P. For example, it determines whether the level of the detection signal on the common signal line connected to the reference sensor specified by the notification has changed. If the reference sensor detects sheet P, the sub-CPU 13 proceeds to S1113.

[0047] In S1113, the sub-CPU 13 stops the actuator specified by the notification. This stops the transport of sheet P.

[0048] In Example 1, although the timing of the stop commands sent to the multiple sub-CPUs 13 is staggered, the timing at which each sub-CPU stops the target actuator is synchronized. This is because each sub-CPU stops the target actuator based on the timing at which a single reference sensor, connected by a common signal line, detects the sheet P. This reduces the likelihood of the sheet P being pulled or bent compared to conventional methods. In other words, damage to the sheet is suppressed. Furthermore, by changing the target of synchronized control according to the length of the sheet in the transport direction, it is possible to suppress a decrease in the productivity of the image forming apparatus.

[0049] <Example 2> Example 1 described the case where the transport of sheet P is stopped. Example 2 describes the case where the transport of sheet P is resumed (re-feeding).

[0050] Figure 12(A) shows the state where the transport of sheet P is stopped with the pass sensor PS13 as the reference sensor. Sheet P is held by transport rollers driven by motor M10, transport rollers driven by motor M11, and transport rollers driven by motor M12. Sheet P may be re-fed in order to resume printing on sheet P. In this case, motors M10, M11, and M12 need to accelerate synchronously.

[0051] Figure 13 shows the wiring of the synchronization signal line 1301 in Example 2. Compared to Figure 7, the synchronization signal line 1301 is added in Figure 13. The synchronization signal line 1301 connects the main CPU 11 and sub-CPUs 13a to 13e and carries the synchronization signal sync_sig. The synchronization signal sync_sig is a signal that switches between a high level and a low level.

[0052] Figure 14(A) shows the restart of motors M10 and M12 in the comparative example. In the comparative example, the restart timing is determined by the drive command transmitted via serial communication. In other words, the restart timing is determined by the timing at which the drive command arrives. As mentioned above, in serial communication, the main CPU 11 cannot send commands to each sub-CPU 13 simultaneously. Therefore, sub-CPU 13b receives the drive command after sub-CPU 13c. As a result, motors M11 and M12 start accelerating after motor M10. As shown in Figure 12(A), the transport rollers of motors M11 and M12 are located downstream of the transport roller of motor M10. Therefore, tug-of-war occurs on the sheet P.

[0053] In Embodiment 2, the main CPU 11 sends a command CMD to the sub-CPUs 13c and 13b via serial communication and switches the level of the synchronization signal line 1301. The command CMD includes the command content (to resume driving) and the synchronization signal identification information. The command CMD may also include identification information that specifies the actuator to be controlled. This identification information may be called specification information.

[0054] As shown in Figure 14(B), the main CPU 11 sends the command CMD06 for motor M10 to the sub-CPU 13c via serial communication. Command CMD06 is a command that instructs motor M10 to be driven in synchronization with the synchronization signal sync_sig on the synchronization signal line 1301. Subsequently, the main CPU 11 sends the commands CMD07 for motors M11 and M12 to the sub-CPU 13b via serial communication. Command CMD07 is a command that instructs motors M11 and M12 to be driven in synchronization with the synchronization signal sync_sig on the synchronization signal line 1301. Subsequently, the main CPU 11 inverts the level of the synchronization signal sync_sig on the synchronization signal line 1301. The sub-CPU 13c resumes driving motor M10 in synchronization with the timing when the level of the synchronization signal sync_sig changes. The sub-CPU 13b also resumes driving motors M11 and M12 in synchronization with the timing when the level of the synchronization signal sync_sig changes.

[0055] In this way, the main CPU 11 instructs the actuator drive timing via the common signal line, the synchronization signal line 1301. Therefore, the timing difference between multiple sub-CPUs is significantly reduced.

[0056] Incidentally, as shown in Figure 12(A), if only one sheet P is stopped in the transport path, the sheet P can be re-fed by restarting only motors M10, M11, and M12. If motors M1 to M9 are driven, unnecessary power will be consumed. Therefore, in Embodiment 2 as well, the main CPU 11 may determine which actuator to restart based on the sheet size information and the sheet position. In Embodiment 2 as in Embodiment 1, a matrix registering actuators corresponding to combinations of sheet size information and sheet position may be stored in memory such as ROM and referenced by the main CPU 11. As a result, unnecessary actuators are not activated, and the sheet P can be re-fed with minimal power consumption.

[0057] For example, sheet P may be stopped at the position shown in Figure 12(B). When sheet P is re-fed, the main CPU 11 sends a command CMD to the sub-CPU 13d to drive motor M7 in synchronization with the synchronization signal sync_sig. Furthermore, the main CPU 11 sends a command CMD to the sub-CPU 13c to drive motor M8 in synchronization with the synchronization signal sync_sig. Subsequently, the main CPU 11 inverts the level of the synchronization signal sync_sig applied to the synchronization signal line 1301.

[0058] In Example 2, it is assumed that the synchronization signal sync_sig is a timing signal (reference signal) output by the main CPU 11. However, the synchronization signal sync_sig may be output from any of the sub-CPUs 13. Alternatively, the synchronization signal sync_sig may be a detection signal output from any of the path sensors. For example, when the temperature adjustment of the fuser 310 is completed, the printing operation resumes. After a new sheet P is fed from the sheet cassette 110, the sheet P that was stopped in the transport path may be re-fed. In this case, the detection signal output by the path sensor PS17 shown in Figure 12(A) may be used as the synchronization signal sync_sig. That is, the synchronization signal line 1301 may be connected to the output terminal of the path sensor PS17. In this case, when the sheet P leaves the path sensor PS17, the level of the synchronization signal sync_sig inverts. Synchronized with this inversion timing, the sub-CPU 13 resumes driving the actuator.

[0059] ●Flowchart Figure 15(A) shows the drive restart control of multiple actuators executed by the main CPU 11. In S1501, the main CPU 11 acquires seat size information when a job is started or while a job is running. The seat size information is acquired from the operation unit 400 or the host computer via the main controller 10.

[0060] In S1502, the main CPU 11 determines whether it is necessary to resume transporting the sheet P. For example, the completion of temperature adjustment of the fuser 310, adjustment of the transfer position of the toner image on the sheet P, or adjustment of the density of the toner image means that the transport restart conditions have been met. If the transport restart conditions are not met, the main CPU 11 terminates the drive restart control. If it is necessary to resume transporting the sheet P, the main CPU 11 proceeds to S1503.

[0061] In S1503, the main CPU 11 determines a synchronization signal that indicates the timing for restarting the drive. In this example, the synchronization signal (reference signal) is determined to be the synchronization signal sync_sig on the synchronization signal line 1301.

[0062] In S1504, the main CPU 11 determines which actuator (motor) to drive based on the combination of sheet size information and the position of the sheet P to be transported again. For example, the main CPU 11 may refer to a matrix (control table) stored in ROM to select a motor corresponding to the combination of sheet size information and the position of sheet P.

[0063] In S1505, the main CPU 11 notifies the sub-CPU 13, which controls the actuator to be driven, of the synchronization signal and the actuator to be driven via serial communication. For example, the main CPU 11 may refer to a matrix to determine which sub-CPU is controlling the actuator to be driven. The determined sub-CPU becomes the destination of the drive notification (drive command). This notification (command CMD) may include identification information of the actuator to be driven and identification information of the synchronization signal. The identification information of the synchronization signal may be identification information of the common signal line to which the synchronization signal is applied, or identification information of the input port to which the common signal line is connected.

[0064] In S1506, the main CPU 11 determines whether the setup is complete. For example, the main CPU 11 may determine whether it has received a response to the drive notification via serial communication from all sub-CPUs 13 that have been determined as destinations for the drive notification. Once all sub-CPUs 13 selected as destinations have completed the setup, the main CPU 11 terminates the drive restart control.

[0065] Figure 15(B) shows the drive restart control executed by the sub-CPU 13. In S1511, the sub-CPU 13 determines whether there is a notification (command CMD) regarding drive restart control (synchronous control) sent from the main CPU 11. If the notification has not been received via serial communication, the sub-CPU 13 terminates the drive restart control. If the notification has been received via serial communication, the sub-CPU 13 proceeds to S1512.

[0066] In S1512, the sub-CPU 13 determines whether the level of the synchronization signal (reference signal) specified by the notification has been inverted. For example, it determines whether the level of the synchronization signal sync_sig on the synchronization signal line 1301 specified by the notification has changed. If the level of the synchronization signal sync_sig has been inverted, the sub-CPU 13 proceeds to S1513.

[0067] In S1513, the sub-CPU 13 restarts the actuator to be driven as specified by the notification. This resumes the transport of sheet P.

[0068] <Example 3> Figure 16(A) is a diagram illustrating the internal configuration of the main CPU 11. The processor circuit 1600 implements various functions by executing the control program 1611 stored in the ROM area of ​​the memory 1610. The print control unit 1601 controls each part of the image forming apparatus 1 according to instructions from the main controller 10. For example, the print control unit 1601 may perform the various adjustments described above by controlling the image forming apparatus 1. The sheet monitoring unit 1602 monitors the transport position of the sheet P on the transport path based on the detection results of multiple path sensors PS connected to the input / output circuit 1607, the placement position of each path sensor PS on the transport path, and the transport speed of the sheet P. The size acquisition unit 1603 acquires the sheet length L of the sheet P from the main controller 10 or the like. The determination unit 1604 determines a reference sensor from among the multiple path sensors PS based on, for example, the sheet length L and the transport position of the sheet P. A matrix 1612 may be used for this determination. For example, matrix 1612 may hold identification information of a reference sensor (e.g., path sensor Pi) corresponding to a combination of sheet length L and the transport position of sheet P. The determination unit 1604 may further determine the actuator to be controlled and the sub-CPU 13 that controls it based on the combination of sheet length L and the reference sensor. As explained with reference to Figure 10, the determination unit 1604 may determine the control target and the destination of the command (instruction) by referring to matrix 1612 stored in memory 1610. The instruction sending unit 1605 creates a command that includes the control content set by the print control unit 1601 (e.g., transport stop / transport restart) and the reference sensor determined by the determination unit 1604. The instruction sending unit 1605 sends the command to the destination sub-CPU 13 via the communication circuit 1606. The communication circuit 1606 is connected to the sub-CPU 13 via the communication line 401 and is a circuit that performs serial communication. The input / output circuit 1607 includes an output circuit that outputs a synchronization signal sync_sig to the synchronization signal line 1301.

[0069] Figure 16(B) is a diagram illustrating the internal configuration of the sub-CPU 13. The processor circuit 1650 implements various functions by executing control programs stored in the memory 1660. The instruction interpretation unit 1651 interprets commands transmitted from the main CPU 11 and received by the communication circuit 1661, and identifies the control content and the reference sensor. The control content may include identification information of the actuator to be controlled (e.g., motor M1). As described above, the reference sensor may be identified by identification information of the path sensor PSi, identification information of the input port to which the path sensor PSi is connected, identification information of the signal line 701 to which the path sensor PSi is connected, etc. The communication circuit 1661 is connected to the communication circuit 1606 of the main CPU 11 via the communication line 401. i is an integer index. The timing monitoring unit 1652 monitors changes in the level of the detection signal output from the path sensor PSi (reference sensor) specified by the instruction interpretation unit 1651. The path sensor PSi is connected to the input circuit 1662. The input circuit 1662 outputs a high-level or low-level logic signal to the processor circuit 1650 according to the level of the input signal received from the path sensor PSi. The timing monitoring unit 1652 outputs to the actuator control unit 1653 that it has detected a change in the level of the signal output from the reference sensor. The actuator control unit 1653 applies the control content to the actuator specified by the instruction interpretation unit 1651. For example, the actuator control unit 1653 may stop or restart the motor Mi in synchronization with the timing when the signal level of the path sensor PSi changes. An output circuit 1663 for supplying a drive signal to the motor Mi may be provided between the processor circuit 1650 and the motor Mi. As described in Embodiment 2, a synchronization signal line 1301 may be connected to the input circuit 1662.

[0070] <Technical concepts derived from examples> [Perspective 1, 13] The transport roller 121 is an example of multiple transport rollers that transport the sheet P while gripping it in the transport path. Motors M1 to M18 are an example of multiple motors that each drive one of the multiple transport rollers. Sub-CPU 13 is an example of multiple sub-CPUs that communicate with the main CPU 11 and each control one of the multiple motors. Signal line 701 and synchronization signal line 1301 are examples of common signal lines that are connected in common to multiple sub-CPUs 13 and to which a high-level or low-level synchronization signal is applied. The main CPU 11 selects the destination of a command to be executed in synchronization with the timing at which the level of the synchronization signal propagating through the common signal line changes according to the length P of the sheet P in the transport direction of the sheet P. The stop command and drive command described above are examples of commands. The main CPU 11 is configured to send the command to the sub-CPU 13 selected as the destination from among the multiple sub-CPUs 13. There are multiple sub-CPUs 13 that can be selected as destinations. This sub-CPU 13 receives commands from the main CPU 11 and monitors the synchronization signal applied to the common signal line. The sub-CPU 13 is configured to execute the command in synchronization with the timing of changes in the level of the synchronization signal.

[0071] [Perspective 2, Perspective 11] The path sensor PS is an example of multiple sheet sensors that detect a sheet P being transported along a transport path. As shown in Figure 7, at least one of the multiple sheet sensors is configured to apply a synchronization signal to a common signal line. As shown in S1103, the main CPU 11 selects a sheet sensor connected to the common signal line from among the multiple sheet sensors according to the length of the sheet. The main CPU 11 is an example of the selected sheet sensor. The main CPU 11 sends a command including the identification information of the reference sensor and the control content (transport stop) to the sub-CPU that should execute the command. The command may be an instruction that should be executed in synchronization with the timing of a change in the level of the synchronization signal output by the reference sensor. The sub-CPU 13 that receives the command executes the transport stop command in synchronization with the timing of a change in the level of the synchronization signal. Here, the synchronization signal is a signal applied to the signal line 701 from the sheet sensor (reference sensor) specified by the command (identification information) received from the main CPU 11.

[0072] [Perspective 3] The first sheet sensor may be connected to multiple sub-CPUs via a first common signal line (e.g., signal line 701b). The second sheet sensor may be connected to multiple sub-CPUs via a second common signal line (e.g., signal line 701c). Each of the multiple sub-CPUs identifies the common signal line between the first and second common signal lines that is connected to the sheet sensor specified by the command. Each of the multiple sub-CPUs executes the command in synchronization with the timing of the change in the level of the identified synchronization signal.

[0073] [Perspective 4] Serial communication line 401 is an example of a communication line connecting the main CPU to multiple sub-CPUs. As described in relation to S1105, etc., commands may be included in the communication signals transmitted over the communication line.

[0074] [Perspective 5] As shown in Figures 9(A) and 9(B), the main CPU 11 may be configured to transmit communication signals to multiple sub-CPUs 13 at different times. In Examples 1 and 2, communication signals are transmitted to multiple sub-CPUs 13 at different times, but this is just one example. The technical concept of Examples 1 and 2 is still applicable even if a communication protocol is used that allows communication signals to be transmitted to multiple sub-CPUs 13 at the same time.

[0075] [Perspective 6] The main CPU 11 may monitor the position of sheet P in the transport path based on the detection results of multiple sheet sensors. The main CPU 11 may also select one sheet sensor (reference sensor) and a destination sub-CPU from among the multiple sheet sensors based on the position of sheet P and the length of sheet P.

[0076] [perspective 7] The reference sensor is located downstream of the leading edge of the sheet P in the conveying direction of the sheet P. Furthermore, the reference sensor may be the sheet sensor closest to the leading edge of the sheet P.

[0077] [Perspective 8] The command is received by all sub-CPUs that control any of the multiple motors involved in the transport of the sheet P to which the command applies. There may be multiple sheet sensors that detect the leading edge of the sheet P after the time the command is received. Of these sheet sensors, the sheet sensor closest to the leading edge of the sheet P may be selected.

[0078] [Perspectives 9, 10] As described in Example 1, the command may be a transport stop command (stop instruction) to stop the transport of sheet P. As described in Example 2, the command may be a transport restart command (drive instruction) to resume the transport of sheet P.

[0079] [Perspective 12] The main CPU 11 may send a transport restart command to the first sub-CPU and the second sub-CPU. The first sub-CPU controls the first motor that drives the first transport roller, which is stopped while holding the sheet P. The second sub-CPU controls the second motor that drives the second transport roller, which is stopped while holding the sheet P. The first sub-CPU and the second sub-CPU are notified that they should execute the transport restart command in synchronization with the timing of the change in the level of the synchronization signal applied to the common signal line.

[0080] [Perspective 13] The main CPU 11 selects one of several sheet sensors based on the length of sheet P. The main CPU 11 sends the identification information of the selected sheet sensor and a command indicating whether to stop or resume transport to one of several sub-CPUs that should execute the command. This command is executed in synchronization with the timing of changes in the level of the synchronization signal output by the selected sheet sensor.

[0081] [Perspective 14] Sub-CPU 13d is an example of a first sub-CPU that communicates with the main CPU via a communication line. Motors M5 to M7 are examples of first motors controlled by the first sub-CPU. The transport rollers driven by motors M5 to M7 are an example of first transport rollers driven by first motors. Sub-CPU 13c is an example of a second sub-CPU that communicates with the main CPU 11 via a communication line. Motors M8 to M10 are examples of second motors controlled by the second sub-CPU. The transport rollers driven by motors M8 to M10 are an example of second transport rollers that are located downstream of the first transport rollers in the sheet transport direction on the transport path and are driven by second motors.

[0082] Sub-CPU 13b is an example of a third sub-CPU that communicates with the main CPU 11 via a communication line. Motors M11~M14 are examples of third motors controlled by the third sub-CPU. The transport rollers driven by motors M11~M14 are positioned downstream of the second transport roller in the transport direction of the sheet P and are an example of third transport rollers driven by the third motor. Path sensor PS7 is an example of a first sheet sensor connected to the first sub-CPU via a first signal line and not connected to the second or third sub-CPUs. Path sensor PS10 is an example of a second sheet sensor connected to the first and second sub-CPUs via a second signal line and not connected to the third sub-CPU. Path sensor PS13 is an example of a third sheet sensor connected to the first, second, and third sub-CPUs via a third signal line. The main CPU 11 selects one sheet sensor from the first, second, and third sheet sensors based on the position and length of the sheet. The main CPU 11 selects the destination of a command to be executed in synchronization with the timing of the change in the level of the synchronization signal output by the selected sheet sensor. The main CPU 11 sends a command to the sub-CPU selected as the destination, which includes identification information indicating the selected seat sensor and the control content. The first sub-CPU, second sub-CPU, and third sub-CPU execute the command in synchronization with the timing when the level of the synchronization signal output from the seat sensor specified by the command received from the main CPU changes.

[0083] [Perspective 15] The image forming apparatus 1 may have multiple functional units. As shown in Figures 2 and 3, the first functional unit may have a first sub-CPU, a first motor, and a first transport roller. As shown in Figures 2 and 3, the second functional unit may have a second sub-CPU, a second motor, and a second transport roller. As shown in Figures 2 and 3, the third functional unit may have a third sub-CPU, a third motor, and a third transport roller.

[0084] [Perspective 16] The command may include identification information that specifies the motor to be controlled. The sub-CPU 13 that receives the command may be configured to apply the command to the motor specified by the command.

[0085] [Perspective 17] The main CPU 11 is an example of a primary control means. The sub-CPU 13 is an example of a secondary control means. The transport roller is an example of a transport means. The path sensor PS is an example of a detection means.

[0086] The transfer unit 190 and the fixing unit 310 are an example of an image forming unit that forms an image on a recording medium. The conveyance path 220 is an example of a conveyance path that guides the recording medium to the image forming unit so that an image is formed on the second surface of the recording medium on which an image has been formed on the first surface by the image forming unit. The second surface is the surface on the opposite side of the first surface. The conveyance roller 121a is an example of a first conveyance roller provided on the conveyance path for conveying the recording medium. The motor M8 is an example of a first motor that drives the first conveyance roller. The sub CPU 13c is an example of a first controller that controls the first motor. The conveyance roller 221a is an example of a second conveyance roller provided on the conveyance path upstream of the first conveyance roller in the conveyance direction in which the recording medium is conveyed, for conveying the recording medium. The motor M6 is an example of a second motor that drives the second conveyance roller. The sub CPU 13d is an example of a second controller that controls the second motor. The pass sensor PS10 is an example of a first sensor provided on the conveyance path downstream of the first conveyance roller in the conveyance direction for detecting the leading end of the recording medium. The pass sensor PS13 is also an example of the first sensor. The first sensor is connected to the first controller and the second controller. As shown in FIG. 8(A), there may be a case where the recording medium should be stopped on the conveyance path and the length of the recording medium in the conveyance direction is a first length (e.g., LP1). The first length is longer than the distance (e.g., LR) from the first conveyance roller to the second conveyance roller (LP1>LR). In this case, the first controller stops the first motor in response to the first sensor detecting the leading end of the recording medium, and the second controller stops the second motor in response to the first sensor detecting the leading end of the recording medium. As shown in FIG. 8(B), there may be a case where the recording medium should be stopped on the conveyance path and the length of the recording medium in the conveyance direction is a second length (e.g., LP2) shorter than the first length. The second length is shorter than the distance from the first conveyance roller to the second conveyance roller (LP2<LR). In this case, the first controller stops the first motor in response to the first sensor detecting the leading end of the recording medium, and the second controller continues to drive the second motor even when the first sensor detects the leading end of the recording medium.

[0087] According to FIG. 8(B), even if the conveyance of sheet P stops, the conveyance of subsequent sheet P' continues, so it becomes possible to shorten the interval from the rear end of sheet P to the leading end of sheet P'.

[0088] As shown in FIG. 8(A), when the length of sheet P satisfies the above condition (LP1 > LR), when path sensor PS10 detects the leading end of sheet P, motors M2 to M8 stop. That is, the conveyance of sheet P by conveyance rollers 121a and 221a stops. On the other hand, as shown in FIG. 8(B), there may be a case where the length of sheet P is short (LP2 < LR). In this case, when path sensor PS10 detects the leading end of sheet P, motors M7 and M8 stop, but motors M2 to M6 continue to rotate. That is, the conveyance of sheet P by conveyance roller 121a stops, but the conveyance of sheet P' by conveyance roller 221a continues. After that, when path sensor PS7 detects the leading end of sheet P', motors M4 to M6 also stop, and the conveyance of sheet P' by conveyance roller 221a also stops. That is, the interval from the rear end of sheet P to the leading end of sheet P' becomes sufficiently short. Thereby, the productivity of the image forming apparatus is improved. Productivity is, for example, the number of sheets on which images are formed per unit time.

[0089] <000036​​​​The third controller may select either the first or second sensor depending on the length of the recording medium in the transport direction. There are cases where the recording medium should be stopped on the transport path, and the length of the recording medium in the transport direction is the first length. In this case, the first controller stops the first motor in response to the sensor selected by the third controller detecting the leading edge of the recording medium. The second controller stops the second motor in response to the sensor selected by the third controller detecting the leading edge of the recording medium. On the other hand, there are cases where the recording medium should be stopped on the transport path, and the length of the recording medium in the transport direction is the second length. In this case, the first controller stops the first motor in response to the sensor selected by the third controller detecting the leading edge of the recording medium. The second controller continues to drive the second motor even if the sensor selected by the third controller detects the leading edge of the recording medium.

[0091] The third controller may select a sensor located downstream of the leading edge of the recording medium in the transport direction and closest to the leading edge of the recording medium. Based on the detection states of multiple path sensors, the third controller can recognize where the leading edge of the sheet is located on the transport path. For example, if path sensor PS9 detects the presence of a sheet and path sensor PS10 detects the absence of a sheet, the third controller can recognize that the leading edge of the sheet is located between path sensors PS9 and PS10. The third controller then selects path sensor PS10 as the closest sensor.

[0092] The sheet cassette 110 is an example of a loading section on which recording media are stacked. The paper feeding mechanism 111 is an example of a pickup roller that feeds the recording media stacked in the loading section. The transport path 120 is an example of a second transport path that guides the recording media fed by the pickup roller toward the image forming section. The transport path 124 merges with the second transport path (transport path 120) at a position between the image forming section and the pickup roller.

[0093] There are cases where the recording medium should not be stopped on the transport path. In this case, the first controller continues to drive the first motor even if the first sensor detects the leading edge of the recording medium, and the second controller continues to drive the second motor even if the first sensor detects the leading edge of the recording medium.

[0094] Housing 101 is an example of a first housing equipped with a transfer unit for transferring a toner image to a recording medium. Housing 201 is an example of a second housing equipped with a transport unit for transporting the recording medium on which the toner image has been transferred by the transfer unit and which has been discharged from the first housing. Housing 301 is an example of a third housing equipped with a fixer unit for fixing the toner image to the recording medium discharged from the second housing. Transport paths 124, 220, 327 are examples of transport paths formed in the first housing, second housing, and third housing, and guide the recording medium to the transfer unit so that an image is formed on the second surface of the recording medium on which an image has been formed on the first surface. The second surface is the surface opposite to the first surface. Transport roller 121a is an example of a first transport roller provided in the transport path of the first housing for transporting the recording medium. Motor M8 is an example of a first motor that drives the first transport roller. Sub-CPU 13c is an example of a first controller that controls the first motor. The transport roller 221a is an example of a second transport roller provided on the transport path in the second housing for transporting the recording medium. The motor M6 is an example of a second motor that drives the second transport roller. The sub-CPU 13d is an example of a second controller that controls the second motor. The path sensor PS10 is an example of a first sensor provided on the transport path downstream of the first transport roller in the transport direction in which the recording medium is transported for detecting the leading edge of the recording medium. The first sensor is connected to the first controller and the second controller. In cases where the recording medium should be stopped on the transport path between the first housing and the second housing, the length of the recording medium in the transport direction may be a first length. The first length is longer than the distance from the first transport roller to the second transport roller. In this case, the first controller stops the first motor in response to the first sensor detecting the leading edge of the recording medium, and the second controller stops the second motor in response to the first sensor detecting the leading edge of the recording medium. On the other hand, there are cases where the recording medium should be stopped on the transport path between the first and second housings, and the length of the recording medium in the transport direction is a second length which is shorter than the first length. The second length is shorter than the distance from the first transport roller to the second transport roller.In this case, the first controller stops the first motor in response to the first sensor detecting the leading edge of the recording medium, while the second controller continues to drive the second motor even if the first sensor detects the leading edge of the recording medium.

[0095] The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, claims are attached to disclose the scope of the invention. [Explanation of Symbols]

[0096] 221: Conveyor roller, M1: Motor, 11: Main CPU, 13: Sub-CPU, 701: Signal line

Claims

1. Image forming means for forming an image on a recording medium, A transport path for guiding the recording medium to the image forming means such that an image is formed on the second surface of the recording medium on which an image has been formed by the image forming means, wherein the second surface is the surface opposite to the first surface. A first transport means provided in the transport path for transporting the recording medium, The first driving means for driving the first transport means, A first control means for controlling the first drive means, A second transport means is provided in the transport path upstream of the first transport means in the transport direction in which the recording medium is transported, and transports the recording medium. The second driving means for driving the second transport means, A second control means for controlling the second drive means, The first detection means is provided in the transport path downstream of the first transport means in the transport direction for detecting the presence or absence of the recording medium, wherein a single common signal line connected to the first detection means branches and is connected to the first control means and the second control means, and the first detection means transmits a synchronization signal to the first control means and the second control means via the common signal line. When the first recording medium should be stopped on the transport path, and the length of the first recording medium in the transport direction is a first length that spans the first transport means and the second transport means when the first recording medium is stopped, the first control means stops the first drive means when it receives the synchronization signal from the first detection means indicating that the first detection means has changed from a state in which it has not detected the first recording medium to a state in which it has detected the first recording medium, and the second control means stops the second drive means when it receives the synchronization signal from the first detection means. An image forming apparatus characterized in that, when the first recording medium should be stopped on the transport path, the length of the first recording medium in the transport direction is a second length such that when the first recording medium is stopped, the first recording medium straddles the first transport means but does not straddle the second transport means, and a second recording medium following the first recording medium is being transported, the first control means stops the first drive means when it receives the synchronization signal from the first detection means, and the second control means continues to drive the second drive means even when it receives the synchronization signal from the first detection means.

2. The system further comprises a third control means that controls the first control means and the second control means, The image forming apparatus according to claim 1, wherein the third control means, when the first recording medium should be stopped on the transport path and the length of the first recording medium in the transport direction is a first length, transmits a command in advance to the first control means and the second control means to stop transport in synchronization with the synchronization signal, and when the first recording medium should be stopped on the transport path and the length of the first recording medium in the transport direction is a second length, transmits the command in advance to the first control means but does not transmit the command to the second control means.

3. The synchronization signal is a first synchronization signal, The aforementioned common signal line is the first common signal line. The system further comprises a second detection means provided in the transport path for detecting the presence or absence of the first recording medium, wherein a single second common signal line connected to the second detection means branches and is connected to the first control means and the second control means, and the second detection means transmits a second synchronization signal to the first control means and the second control means via the second common signal line, The third control means selects one of the first detection means and the second detection means according to the leading edge position of the first recording medium in the transport direction. When the first recording medium should be stopped on the transport path, and the length of the first recording medium in the transport direction is the first length, the first control means stops the first drive means when it receives a second synchronization signal from the detection means selected by the third control means indicating that the first recording medium has changed from a state of not being detected to a state of being detected, and the second control means stops the second drive means when it receives a second synchronization signal from the detection means selected by the third control means. The image forming apparatus according to claim 2, characterized in that, when the first recording medium should be stopped on the transport path, and the length of the first recording medium in the transport direction is the second length, and a subsequent second recording medium is being transported, the first control means stops the first drive means when it receives the second synchronization signal from the detection means selected by the third control means, and the second control means continues to drive the second drive means even when it receives the second synchronization signal from the detection means selected by the third control means.

4. The image forming apparatus according to claim 3, characterized in that the third control means is located downstream of the leading edge of the first recording medium in the transport direction and selects the detection means closest to the leading edge of the first recording medium.

5. A loading section on which recording media are loaded, A feeding means for feeding the recording medium loaded in the loading section, The system further includes a second transport path that guides the recording medium fed by the feeding means toward the image forming means, The image forming apparatus according to claim 1, characterized in that the transport path merges with the second transport path at a position between the image forming means and the feeding means.

6. The image forming apparatus according to claim 2, characterized in that the synchronization signal is transmitted simultaneously to the first control means and the second control means, transmitted via a signal line that transmits high-level or low-level synchronization signals, and a signal for pre-instructing to stop transport in synchronization with the synchronization signal is transmitted to the first control means and the second control means at different timings via a serial signal line.

7. The image forming apparatus is A first housing is provided on which the first transport means, the first drive means, and the first control means, The image forming apparatus according to claim 1, further comprising a second housing on which the second transport means, the second drive means, and the second control means are provided.

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