JP6808477B2 - Image forming device - Google Patents

Description

The present invention relates to transport control of a recording material in an image forming apparatus.

Conventionally, image forming devices such as copiers and printers perform alignment control so that a toner image formed on an image carrier such as a photosensitive drum or an intermediate transfer belt is transferred to an appropriate position on a recording material. There is. For example, the recording material is temporarily stopped at a predetermined position on the upstream side of the transfer nip portion formed by the image carrier and the transfer roller, and the recording material is retransmitted so as to match the timing with the toner image formed on the image carrier. There is a device that controls the alignment between the toner image and the recording material by allowing the toner image to be aligned.

Patent Document 1 describes a timing roller arranged on the upstream side of the transfer nip portion. As an example of the motor for driving the timing roller, a stepping motor is described. In Patent Document 1, the recording material is temporarily stopped at the timing when the tip of the recording material reaches the nip portion of the timing roller.

Here, conventionally, in order to prevent the recording material from jumping out to the downstream side of the nip portion of the timing roller, the stepping motor is excited to hold the timing roller. That is, the timing roller was prevented from moving. As a result, the tip position of the recording material could be aligned with the nip portion of the timing roller.

On the other hand, in Patent Document 1, the stepping motor is not excited in order to suppress power consumption. Instead, the encoder detects the rotational state of the stepping motor to detect the amount of recording material protruding downstream from the nip of the timing roller. Then, based on the amount of protrusion, the timing of retransmitting the recording material to the transfer nip portion is adjusted, so that the alignment control is performed so that the toner image is transferred to an appropriate position of the recording material.

Japanese Unexamined Patent Publication No. 2013-105110

Here, if a configuration in which the transport path of the recording material is shortened is adopted for the miniaturization of the image forming apparatus, recording is performed in a state where the recording material is temporarily stopped at a predetermined position on the upstream side of the transfer nip portion. The rear end of the material may not pass through the separation nip. The separation nip portion is, for example, a nip portion formed by a feed roller and a separation roller, in which a plurality of recording materials fed from a paper feed port such as a cassette are separated into one sheet. .. The separation roller is provided with a spring that functions as a torque limiter, and is configured to add back tension to the recording material. Therefore, if the recording material is temporarily stopped without exciting the stepping motor and the rear end of the recording material does not pass through the separation nip, the recording material can be pulled back to the upstream position due to the influence of back tension. There is sex. In that case, there is an error between the timing when the toner image formed on the image carrier reaches the transfer nip portion and the timing when the recording material reaches the transfer nip portion, and the position where the toner image is transferred to the recording material deviates. There is a possibility that it will end up.

An object of the present invention is a case where the rear end of the recording material does not pass through the separation nip portion in a state where the recording material is temporarily stopped at a predetermined position on the upstream side of the image forming position without exciting the motor. Also, the image should be formed at an appropriate position on the recording material.

The image forming apparatus of the present invention for achieving the above object includes an image forming means for forming an image on a recording material at an image forming position, a first conveying member for conveying the recording material, and the first conveying member. And a separation member for separating a plurality of recording materials into one recording material in the separation nip portion, and a separating member downstream of the first transport member in the transport direction of the recording material. A second transport member provided and transporting the recording material to the image forming position, a motor for driving the second transport member, and a tip of the recording material transported by the second transport member are provided. The rotation of the motor was stopped so that the recording material stopped when the recording material reached a predetermined position on the upstream side in the transport direction from the image forming position, and stopped in accordance with the image forming timing by the image forming means. In an image forming apparatus having a control means for rotating the motor again so that the recording material is conveyed to the image forming position by the second conveying member, the tip of the recording material reaches the predetermined position. In an image forming apparatus in which the rear end of the recording material does not pass through the separation nip portion in the state, and after the rotation of the motor is stopped, the recording material is pulled back to the upstream side in the transport direction by the separation member. The second transport member has a detecting means for detecting the amount of the recording material pulled back, and based on the amount of the recording material pulled back detected by the detecting means. It is characterized in that at least one of the timing at which the recording material is conveyed to the image forming position and the image forming timing by the image forming means are changed.

According to the present invention, there is a case where the rear end of the recording material does not pass through the separation nip portion in a state where the recording material is temporarily stopped at a predetermined position on the upstream side of the image forming position without exciting the motor. Also, the image can be formed at an appropriate position on the recording material.

It is a schematic diagram of an image forming apparatus. It is a figure which shows the driving force transmission structure of a paper feed mechanism. It is a figure which shows the structure of the separation roller. It is a figure which shows the structure of the paper feed motor. It is a block diagram of the control circuit of a paper feed motor, and is the figure which shows the PWM signal. It is a block diagram which shows the system structure of the image forming apparatus in Example 1. FIG. It is a figure which shows the movement of the recording material in Example 1. FIG. It is a figure which shows the flowchart in Example 1. FIG. It is a figure which shows the return amount measurement period in Example 1. FIG. It is a figure which shows the movement of the recording material in Example 2. It is a block diagram which shows the system structure of the image forming apparatus in Example 3. FIG. It is a figure which shows the flowchart in Example 3. FIG. It is a figure which shows the transport speed of the recording material in Example 3. It is a block diagram which shows the system structure of the image forming apparatus in Example 4. FIG. It is a figure which shows the flowchart in Example 4. FIG.

(Example 1)
A schematic diagram of the image forming apparatus in this embodiment is shown in FIG. In this embodiment, an example of a color laser beam printer 100 (hereinafter referred to as a printer 100) is shown as an image forming apparatus.

The printer 100 includes a process cartridge 5 (Y, M, C, K) that can be attached to and detached from the printer main body 200 (also referred to as a housing). In the following description, when the reference numerals (Y, M, C, K) indicating colors are omitted, it is shown that the configuration is common to all colors. Each of the process cartridges 5 has a photosensitive drum 1 (image carrier), a charging roller 2, a developing roller 3, a cleaning blade 4, a toner container 23, and a waste toner container 24. After the photosensitive drum 1 is charged by the charging roller 2, laser light is irradiated from the corresponding laser scanner 7 (exposure means) to form an electrostatic latent image. The electrostatic latent image formed on the photosensitive drum 1 is developed by the developing roller 3 using toner (developer). As a result, a toner image is formed on the photosensitive drum 1. The toner container 23 stores the toner used by the developing roller 3 to develop the electrostatic latent image of the photosensitive drum 1.

The intermediate transfer belt 8 is rotated by the drive roller 9 in the direction of arrow α in FIG. Primary transfer rollers 6 are provided at positions facing the photosensitive drum 1 via the intermediate transfer belt 8. By applying a predetermined bias to the primary transfer roller 6, the toner image formed on the photosensitive drum 1 is transferred to the intermediate transfer belt 8. The toner images formed on each photosensitive drum 1 are sequentially transferred to the intermediate transfer belt 8, and the toner images of each color are overlapped to form a color toner image on the intermediate transfer belt 8. The toner remaining on the photosensitive drum 1 without being transferred to the intermediate transfer belt 8 is recovered by the cleaning blade 4, and the recovered toner is stored in the waste toner container 24.

An opposing roller 10 is provided at a position facing the secondary transfer roller 11 via the intermediate transfer belt 8. By applying a predetermined bias to the secondary transfer roller 11, the color toner image formed on the intermediate transfer belt 8 is a transfer nip portion (image formation) formed by the intermediate transfer belt 8 and the secondary transfer roller 11. At position), it is transferred to paper P (recording material). The paper P is fed from the paper feeding mechanism 33 described later. The toner remaining on the intermediate transfer belt 8 without being transferred to the paper P is collected by the belt cleaning blade 21, and the collected toner is stored in the belt waste toner container 22.

The paper feed mechanism 33 includes a paper feed cassette 13, a paper feed roller 14, a separation roller 12 (separation member), a transport roller 15 (first transport member), a registration roller 16 (second transport member), and refeeding. It is composed of rollers 32. A one-way clutch (not shown) is built in the paper feed roller 14 and the transport roller 15. Further, the separation roller 12 is fixed to the chassis or the like via a torque limiter. The configuration of the torque limiter will be described in detail later.

The paper feed roller 14 feeds the paper P from the paper cassette 13 on which the paper P is loaded. The separation roller 12 and the transfer roller 15 form a separation nip portion, and the plurality of sheets P taken out from the paper feed cassette 13 due to the influence of frictional force are separated into one sheet P by the separation nip portion. The separated paper P is conveyed to the registration roller 16 by the conveying roller 15. The registration roller 16 conveys the paper P to the transfer nip portion so that the timing matches the toner image formed on the intermediate transfer belt 8 according to the timing when the tip of the paper P is detected by the top sensor 201. .. The toner image transferred to the paper P by the secondary transfer roller 11 is fixed to the paper P by the fixing device 17. The fixing device 17 has a heating roller 18 and a pressure roller 19, and heat and pressure are applied to the paper P by transporting the paper P while sandwiching it in the fixing nip portion formed by the two rollers. Fix the toner image with.

The paper P on which the toner image is fixed is sent to the paper discharge transport path A or the reverse transport path B downstream of the fixing device 17. Here, the transfer destination of the paper P is switched by the flapper 30. The paper P conveyed to the paper ejection transport path A is ejected to the outside of the printer main body 200 via the paper ejection roller 20. The paper P transported to the reversing transport path B is switched back by the reversing roller 31 and fed to the double-sided transport path C. The paper P sent to the double-sided transfer path C is conveyed to the refeed roller 32 by the double-sided transfer roller 202. The re-feeding roller 32 feeds the paper P on which the toner image is formed on the front surface (first surface) toward the registration roller 16 again. Then, the registration roller 16 conveys the paper P toward the transfer nip portion again. As a result, a toner image is formed (transferred and fixed) on the back surface (second surface) of the paper P.

Reference numeral 25 denotes a control board on which an electric circuit for controlling the printer 100 is mounted, and the CPU 26 is mounted on the control board 25. The CPU 26 collectively controls the operation of the printer 100, such as controlling the paper feed motor 34 (shown in FIG. 2) and the drive source (not shown) of the process cartridge 5 regarding the transfer of the paper P. Reference numeral 28 denotes a switching power supply, which converts the AC power supply voltage input from the power supply cable 29 into a DC voltage used by the printer 100 and supplies it to the control board 25 and the like.

FIG. 2 shows a drive transmission configuration of the paper feed mechanism 33. The paper feed motor 34 is a DC motor (hereinafter referred to as a DC motor) that is a drive source of the paper feed mechanism 33. The driving force of the paper feed motor 34 is directly transmitted to the registration roller 16 and the transfer roller 15 via a drive row (not shown). Further, the drive transmission from the paper feed motor 34 to the paper feed roller 14 is via the paper feed clutch 35, and the drive transmission from the paper feed motor 34 to the paper feed roller 32 is via the paper feed clutch 36. That is, when the paper feed clutch 35 is ON, the driving force of the paper feed motor 34 is transmitted to the paper feed roller 14, and when the paper feed clutch 35 is OFF, the drive force of the paper feed motor 34 is transmitted to the paper feed roller 14. Not transmitted. Further, when the re-feed clutch 36 is ON, the driving force of the paper feed motor 34 is transmitted to the re-feed roller 32, and when the re-feed clutch 36 is OFF, the driving force of the paper feed motor 34 is recharged. It is not transmitted to the paper roller 32. The CPU 26 controls to switch ON / OFF of the paper feed clutch 35 and the paper feed clutch 36 according to each paper feed timing.

FIG. 3 shows a detailed configuration of the separation roller 12. As shown in FIG. 3A, the separation roller 12 includes a shaft 12a and a spring 12b wound around the shaft 12a. The shaft 12a is fixed to a chassis or the like. Although the spring 12b is wound around the shaft 12a, it can rotate with respect to the shaft 12a. In addition, in FIG. 3A, the rubber member 12c described later is omitted. 3 (b) to 3 (e) are cross-sectional views of the separation roller 12 as viewed from the direction of the arrow γ in FIG. 3 (a). The rubber member 12c is a member that comes into contact with the paper P, and is provided so as to cover the shaft 12a and the spring 12b.

Next, the operation of the separation roller 12 when the paper feeding operation is started will be described with reference to FIGS. 3 (b) and 3 (c). The state shown in FIG. 3B is the initial state of the separation roller 12. That is, it is assumed that the paper feeding operation has not started in the state of FIG. 3B and the transport roller 15 has not rotated. Here, when the paper feeding operation is started and the transport roller 15 rotates, the separation roller 12 operates as follows.

When the paper P is not fed to the separation nip portion formed by the transfer roller 15 and the separation roller 12, the rubber member 12c comes into direct contact with the transfer roller 15, so that a strong force is applied along the rotation direction of the transfer roller 15. receive. This situation is shown in FIG. 3 (c). When the rubber member 12c rotates along the rotation direction of the transport roller 15, the engaged portion 12d which is a part of the rubber member 12c and the engaging portion which is one end of the spring as shown in FIG. 3C 12e engages. Here, comparing the force received by the rubber member 12c by the transfer roller 15 and the force received by the spring 12b, the force received by the transfer roller 15 is larger, so that the rubber member 12c and the spring 12b are shown in FIG. 3 with respect to the shaft 12a. c) Rotate in the direction of the arrow. At this time, the spring 12b receives a force with respect to the shaft 12a in a direction in which the winding is loosened. Even when only one sheet of paper P is conveyed to the separation nip portion, the force received by the transfer roller 15 via the sheet P is larger, so that the rubber member 12c and the spring 12b are shown in FIG. 3 (c) with respect to the shaft 12a. Rotate in the direction of the arrow. On the other hand, when a plurality of sheets of paper P are conveyed to the separation nip portion due to the influence of taking out or the like, this force relationship is reversed. That is, the force received by the spring 12b is larger. Therefore, the rubber member 12c and the spring 12b do not rotate with respect to the shaft 12a, and the separation roller 12 stops. As a result, the plurality of sheets P can be separated into one sheet P.

Next, the operation of the separation roller 12 when the paper feeding operation is completed will be described with reference to FIGS. 3 (d) and 3 (e). It is assumed that the paper feeding operation is completed and the rotation of the transport roller 15 is stopped in the state of FIG. 3D. The rotation phase of the separation roller 12 in this state is θ1. Here, for convenience, the rotation phase is determined with reference to the engaging portion 12e.

In this embodiment, when the paper feeding operation is completed, the separation roller 12 rotates in the reverse direction by a predetermined amount due to the influence of the spring 12b. This situation is shown in FIG. 3 (e). Assuming that the rotation phase of the separation roller 12 in FIG. 3 (e) is θ2, the separation roller 12 rotates in the reverse direction by the amount of (θ2-θ1). When the separation roller 12 is rotated by the force received by the transfer roller 15, the spring 12b is in a loosely wound state with respect to the shaft 12a. When the transfer roller 15 is stopped and the force received by the separation roller 12 is lost, the loosened spring 12b tries to return to the original winding state, so that the separation roller 12 is rotated in the reverse direction shown in FIG. 3 (e). Occurs.

FIG. 4 shows a schematic configuration diagram of the paper feed motor 34. In this embodiment, an inner rotor type DC brushless motor is used as the paper feed motor 34. As shown in FIG. 4A, the shaft 40 of the paper feed motor 34 has an output gear 41 attached to one side and an encoder disc 42 attached to the opposite side. As described above, the output gear 41 is connected to the registration roller 16, the transport roller 15, the paper feed roller 14, and the repaper feed roller 32 via a drive row (not shown). The encoder disk 42 is configured to rotate together with the shaft 40 of the paper feed motor 34, and is provided coaxially with the paper feed motor 34. Further, the paper feed motor 34 is provided with a driver board 43 on which the motor driver circuit unit shown in FIG. 4 is mounted. A photo sensor 44 and a connector 45 that serves as an interface for power supply / control signals to the paper feed motor 34 are also arranged on the driver board 43.

As shown in FIG. 4A, the photosensor 44 is arranged so as to sandwich the encoder disk 42. Here, FIG. 4B shows a view of the paper feed motor 34 viewed from the direction of the arrow β in FIG. 4A. Note that the driver board 43 and the connector 45 are omitted in FIG. 4B. As shown in FIG. 4B, a plurality of slits 203 are formed in the encoder disk 42. The photo sensor 44 outputs an ON signal when detecting the light passing through the slit 203, and outputs an OFF signal when the light is blocked by the disk portion not provided with the slit 203. To do. The CPU 26 can detect the rotation speed of the encoder disk 42 based on the signal output from the photo sensor 44, and can detect the rotation speed of the paper feed motor 34 (the number of rotations per unit time). Further, the CPU 26 can also detect the rotation amount of the encoder disk 42 based on the signal output from the photo sensor 44, and can also detect the rotation amount of the paper feed motor 34. Here, the encoder disk 42 and the photo sensor 44 function as rotation amount detecting means for detecting the rotation amount of the paper feed motor 34.

FIG. 5A is a block diagram of the control circuit of the paper feed motor 34 in this embodiment. That is, the functional block related to the speed control of the paper feed motor 34 by the CPU 26 mounted on the control board 25 shown in FIG. 1 is shown. In the speed control unit 50 of the CPU 26, PID control, that is, feedback is performed based on the deviation between the target speed set by the target speed setting unit 47 of the paper feed motor 34 and the rotation speed of the paper feed motor 34 measured by the speed measurement unit 48. The motor speed is controlled by control. Here, the speed measuring unit 48 measures the rotation speed of the paper feed motor 34 by the encoder signal output from the photo sensor 44 described above. The gain value used in the PID control is set by the gain setting unit 49. The speed control unit 50 (PID control unit) calculates / generates a drive signal to be transmitted to the paper feed motor 34 based on the set values of the deviation and the control gain, and transmits the drive signal to the driver circuit unit 46 of the paper feed motor 34. .. Further, the CPU 26 transmits a rotation direction signal and a brake signal to the driver circuit unit 46 based on the set values of the rotation direction setting unit 51 and the brake setting unit 52.

The driver circuit unit 46 rotates and drives the paper feed motor 34 based on the control signal transmitted from the CPU 26. The driver circuit unit 46 controls the coils (not shown) arranged in the rotating unit 204 so that currents flow in order, and rotates the rotating unit 204. Here, the amount of current supplied to each coil is controlled by the PWM signal. The PWM signal is a pulse signal having a constant period T shown in FIGS. 5 (b) and 5 (c), and changes the length of the period during which the output value is ON, that is, the pulse width. Can be made to. The pulse width of the pulse signal shown in FIG. 5 (b) is W1, and the pulse width of the pulse signal shown in FIG. 5 (c) is W2. The larger the pulse width, the more current flows through the coil. When a large amount of current flows through the coil, the torque increases and the rotation speed of the rotating portion 204 increases. The driver circuit unit 46 adjusts the rotation speed of the rotation unit 204 by adjusting the pulse width of the PWM signal based on the drive signal transmitted from the speed control unit 50.

FIG. 6 is a block diagram showing a configuration of an overall control system of the printer 100 in this embodiment. In FIG. 6, the printer controller 300 expands an image code from an external device such as a host computer into bit data necessary for printing by the printer, reads internal information of the printer engine by communication or the like, and displays it. The engine control unit 301 exchanges information with the printer controller 300 by serial communication, controls each part of the printer engine to operate according to the instruction of the printer controller 300, and notifies the printer controller 300 of the printer internal information. The paper feed / transport control unit 302 controls the rotation and stop of the paper feed roller 14, the transport roller 15, the registration roller 16, etc. for feeding the paper P according to the instructions of the engine control unit 301. The high-voltage control unit 303 controls each high-voltage output control of charging, developing, and transferring according to the instructions of the engine control unit 301. The optical control unit 304 controls the drive / stop of the scanner motor and the blinking of the laser according to the instruction of the engine control unit 301. The sensor detection unit 305 transmits the detection result of the top sensor 201 or the like arranged on the transport path to the engine control unit 301. The temperature control unit 306 adjusts the temperature of the fixing device 17 to the temperature specified by the engine control unit 301. The alignment control unit 307 controls so that the timing at which the toner image formed on the intermediate transfer belt 8 reaches the transfer position TP (transfer nip portion) coincides with the timing at which the paper P reaches the transfer position TP. The alignment control unit 307 includes a return amount calculation unit 308 and a transfer timing calculation unit 309, and detailed control thereof will be described later. The control units 301 to 309 are realized by a one-chip microcomputer (CPU 26) having a built-in ROM and RAM (not shown).

A method of aligning the toner image and the paper P in this embodiment will be described. In this embodiment, as shown in FIGS. 7A and 7B, the paper feed roller 14, the transfer roller 15, and the registration roller 16 are rotated to move the paper P on the upstream side of the transfer position TP. It is conveyed to the temporary stop position SP. Then, the CPU 26 stops the transport of the paper P at the timing when the tip of the paper P reaches the temporary stop position SP. The CPU 26 calculates the time t1 (seconds) required from when the laser scanner 7 starts irradiating the photosensitive drum 1 with the laser beam until the toner image formed on the intermediate transfer belt 8 reaches the transfer position TP. Further, the CPU 26 calculates the time t2 (seconds) required for the paper P to reach the transfer position TP from the pause position SP. With these times, the time t3 (= t1-t2) until the transfer of the paper P is restarted in order to match the timing when the toner image reaches the transfer position TP and the timing when the paper P reaches the transfer position TP. (Seconds) is required. Then, the CPU 26 rotates the transfer roller 15 and the registration roller 16 again at the timing when the time t3 elapses after the laser scanner 7 starts irradiating the photosensitive drum 1 with the laser beam by the paper feed / transfer control unit 202. .. As a result, the transfer of the paper P stopped at the temporary stop position SP is restarted.

The problem of the method of aligning the toner image and the paper P in this embodiment will be described. As described above, in this embodiment, the rotation of the paper feed motor 34 is stopped at the timing when the tip of the paper P reaches the temporary stop position SP, and the transfer of the paper P is stopped. In this embodiment, a DC brushless motor is used as the paper feed motor 34, and when the paper feed motor 34 is stopped, the power supply to the paper feed motor 34 is stopped. Therefore, the paper feed motor 34 in the stopped state is not excited and registration is performed. The roller 16 is ready to rotate. Further, as shown in FIG. 7B, the rear end of the paper P stopped at the temporary stop position SP does not pass through the separation nip portion formed by the transfer roller 15 and the separation roller 12. Therefore, the stopped paper P may be pulled back to the upstream side due to the reverse rotation phenomenon of the separation roller 12 by the spring 12b described with reference to FIGS. 3 (d) and 3 (e). This situation is shown in FIG. 7 (c). In FIG. 7C, the tip of the paper P is pulled back upstream from the pause position SP by L (mm). As a result, the timing at which the paper P reaches the transfer position TP after the paper P is restarted is delayed, so that the timing at which the toner image reaches the transfer position TP and the timing at which the paper P reaches the transfer position TP are different. There is a problem of mismatch.

FIG. 8 is a flowchart of this embodiment for solving the above-mentioned problems. The control based on the flowchart of FIG. 8 is executed by the CPU 26 mounted on the control board 25 based on a program stored in a ROM or RAM (not shown).

First, when the printer controller 300 starts executing the print job (S100), the engine control unit 301 rotates the paper feed motor 34 by the paper feed / transfer control unit 302 to execute the paper feed transfer operation of the paper P (S101). ). After that, the engine control unit 301 calculates the timing for starting the slowdown of the paper feed motor 34 so that the paper feed motor 34 stops when the tip of the paper P reaches the temporary stop position SP. This timing starts from the timing when the tip of the paper P is detected by the top sensor 201, and takes into consideration the distance that the paper P is conveyed from the start of the slowdown to the stop of the paper feed motor 34. It is calculated. When the engine control unit 301 determines that it is time to start the slowdown of the paper feed motor 34 (S102), the engine control unit 301 instructs the paper feed / transport control unit 302 to stop the rotation of the paper feed motor 34, and the paper feed motor 34. The slowdown of 34 is started (S103). Next, when the engine control unit 301 determines that the slowdown of the paper feed motor 34 has been completed (S104), the return amount calculation unit 308 of the alignment control unit 307 starts measuring the return amount of the paper P.

The return amount of the paper P can be measured based on the number of encoder pulses output from the photo sensor 44 provided in the paper feed motor 34. That is, the registration roller 16 rotates as the paper P is pulled back to the upstream side by the reverse rotation phenomenon of the separation roller 12, and the paper feed motor 34 is connected to the registration roller 16 via a drive row (not shown). This is because it also rotates. When the engine control unit 301 determines that the return amount of the paper P is being measured (S105), the engine control unit 301 measures the number of encoder pulses (rotation amount of the paper feed motor 34) output from the photosensor 44 (S106). The return amount calculation unit 308 calculates the return amount L (mm) of the paper P from the measured encoder pulse number Np (pulse) by the following (Equation 1).
L (mm) = Np (pulse) x K (mm / pulse) ... (Equation 1)

Here, in (Equation 1), K (mm / pulse) is a coefficient for calculating the distance that the paper P is conveyed per one pulse of the encoder.

Next, when the engine control unit 301 determines that the measurement period for the return amount of the paper P has expired (S105), the engine control unit 301 calculates the timing at which the paper P stopped by the transfer timing calculation unit 309 is transferred toward the transfer position TP. (S107). The transfer timing calculation unit 309 calculates the time t3'(seconds) until the transfer of the paper P is restarted by the following (Equation 2).
t3'(seconds) = t1 (seconds) -t2 (seconds) -L (mm) ÷ V (mm / second) ... (Equation 2)

Here, in (Equation 2), t1 (seconds) means that the toner image formed on the intermediate transfer belt 8 reaches the transfer position TP after the laser scanner 7 starts irradiating the photosensitive drum 1 with the laser beam. It is the time required until. Further, t2 (seconds) is the time required for the paper P to reach the transfer position TP from the pause position SP. Further, V (mm / sec) is the transport speed of the paper P. When the calculated time t3'(seconds) has elapsed since the laser scanner 7 started irradiating the photosensitive drum 1 with the laser beam (S108), the engine control unit 301 is operated by the paper feed / transport control unit 302. The paper feed motor 34 is rotated. Then, the stopped paper P is conveyed toward the transfer position TP (S109). This completes the control of this flowchart.

FIG. 9 shows an encoder pulse signal output from the photo sensor 44 when the paper feed motor 34 is slowed down. In FIG. 9, when the rotation speed of the paper feed motor 34 is Vm, the transport speed of the paper P corresponds to V. Since the measurement period of the return amount of the paper P varies depending on the elasticity of the spring 12b, the curvature of the transport path, and the like, it is necessary to set it according to the configuration of the printer 100. In this embodiment, it is set to 0.3 (seconds). According to FIG. 9, the encoder pulse signal is output from the photo sensor 44 after the slowdown of the paper feed motor 34 is completed and the rotation of the paper feed motor 34 is stopped. In this embodiment, it is determined that the paper P has been pulled back to the upstream side by the number of output encoder pulses, and the transfer restart timing of the paper P is advanced.

A specific example is shown. For example, in a configuration where t1 is 1.5 seconds, t2 is 0.3 seconds, K is 0.04 mm / pulse, and V is 300 mm / second, and the number of measured encoder pulses is 15 pulses, t3'is 0. It is calculated as 698 seconds. When the return amount of the paper P is not taken into consideration, the time t3 (seconds) until the paper P is restarted is calculated as described above (t1-t2), and thus is 1.2 seconds. That is, according to this embodiment, the transfer of the paper P is restarted at a timing 0.502 seconds earlier than the conventional case.

From the above, according to the present embodiment, the return amount of the recording material was measured and measured in a state where the recording material (paper P) was temporarily stopped at a predetermined position on the upstream side of the image formation position (transfer position TP). The transfer restart timing is changed by the amount of return. As a result, the timing at which the tip of the recording material reaches the image forming position becomes appropriate, and the image can be formed at an appropriate position of the recording material.

(Example 2)
In the first embodiment, when the paper P is stopped at the temporary stop position SP, the case where the rear end of the paper P does not pass through the separation nip portion has been described. However, depending on the length of the paper P in the transport direction, the rear end of the paper P may pass through the separation nip portion. In this embodiment, a method of acquiring the length of the paper P and switching the control according to whether or not the rear end of the paper P has passed through the separation nip portion when the paper P stops at the pause position SP. Will be described. The description of the main parts is the same as that of the first embodiment, and only the parts different from the first embodiment will be described here.

As shown in FIG. 10, the fed paper P is conveyed toward the pause position SP (FIG. 10A). When the pause position SP is reached, the CPU 26 stops the paper feed motor 34 (FIG. 10B). When the paper feed motor 34 is stopped, the rotation of the transfer roller 15 is stopped, and the separation roller 12 driven by the transfer roller 15 in the direction of conveying the paper P to the downstream side is affected by the spring 12b (FIG. 3). It rotates in the direction of pulling P back to the upstream side. At this time, since the length of the paper P in the transport direction is short, the rear end of the paper P stopped at the temporary stop position SP passes through the separation nip portion of the transport roller 15 and the separation roller 12. In this case, the paper P is not pulled back by the separation roller 12 (FIG. 10 (c)).

Let Lsp be the length Lp of the paper P in the transport direction and the distance from the temporary stop position SP to the separation nip portion of the transport roller 15 and the separation roller 12. In this embodiment, when Lp is longer than Lsp, t3'described in Example 1 is adopted as the transfer restart timing, and when Lp is longer than Lsp, t3 is adopted as the transfer restart timing. Do. The length Lp of the paper P in the transport direction is specified when the user instructs printing, or is determined by the CPU 26 based on the position of the rear end regulation plate (not shown) provided on the paper feed cassette 13. Get by the method of.

From the above, according to this embodiment, there are the following effects in addition to the effects of Example 1. That is, if the length of the paper P in the transport direction is short and the rear end of the paper P passes through the separation nip portion when the paper P is paused, the control is not performed in consideration of the return amount of the paper P. This simplifies control because unnecessary control is not performed. Further, it is possible to reduce the influence when the encoder pulse signal is output from the photo sensor 44 due to the disturbance even though the paper P is not actually pulled back.

(Example 3)
In the first embodiment, control for changing the transfer restart timing in consideration of the return amount of the paper P after the paper P is temporarily stopped has been described. In this embodiment, in order to make the timing at which the tip of the paper P reaches the transfer position TP appropriate, instead of changing the transfer restart timing, the transfer is restarted and the paper P is moved toward the transfer position TP. The control for changing the transport speed will be described. The description of the main parts is the same as that of the first embodiment, and only the parts different from the first embodiment will be described here.

FIG. 11 is a block diagram showing a configuration of an overall control system of the printer 100 in this embodiment. The difference from the block diagram of FIG. 6 is that a transfer speed calculation unit 310 is provided instead of the transfer timing calculation unit 309 included in the alignment control unit 307. The control units 301 to 308 and 310 are realized by a one-chip microcomputer (CPU 26) having a built-in ROM and RAM (not shown).

FIG. 12 is a flowchart of this embodiment. The control based on the flowchart of FIG. 12 is executed by the CPU 26 mounted on the control board 25 based on a program stored in a ROM or RAM (not shown).

The processing of S200 to S206 is the same as the processing of S100 to S106 of the flowchart of FIG. 8 described in the first embodiment, and thus the description thereof will be omitted. In this embodiment, t3 (seconds) is adopted as the transfer restart timing when the return amount of the paper P described in the first embodiment is not taken into consideration (S207). Then, when the transfer restart timing is reached (S208), the engine control unit 301 calculates the rotation speed of the paper feed motor 34 at an appropriate timing when the tip of the paper P reaches the transfer position TP by the transfer speed calculation unit 310 (S208). S209). After that, the engine control unit 301 rotates the paper feed motor 34 at the rotation speed calculated by the paper feed / transport control unit 302 (S210). This completes the control of this flowchart.

FIG. 13 is a diagram showing a state of the rotation speed of the paper feed motor 34 when resuming the transfer of the paper P at the pause position SP. In FIG. 13, when the rotation speed of the paper feed motor 34 is Vm, the transfer speed of the paper P corresponds to V, and when the rotation speed of the paper feed motor 34 is Vm', the transfer speed of the paper P. Corresponds to V'. The transport speed V of the paper P is the speed at which the toner image formed on the intermediate transfer belt 8 is transferred to the paper P at the transfer position TP. The transport speed V'of the paper P is faster than the transport speed V of the paper P, and the portion shown as the acceleration amount in FIG. 13 is set to be the same as the return amount L (mm) of the paper P.

From the above, according to the present embodiment, the return amount of the recording material was measured and measured in a state where the recording material (paper P) was temporarily stopped at a predetermined position on the upstream side of the image formation position (transfer position TP). The transport speed is changed by the amount of return. As a result, the timing at which the tip of the recording material reaches the image forming position becomes appropriate, and the image can be formed at an appropriate position of the recording material.

(Example 4)
In the first embodiment, control for changing the transfer restart timing in consideration of the return amount of the paper P after the paper P is temporarily stopped has been described. In this embodiment, the control of changing the timing (image formation timing) of the laser scanner 7 irradiating the photosensitive drum 1 with the laser beam, instead of changing the transfer restart timing, will be described. The description of the main parts is the same as that of the first embodiment, and only the parts different from the first embodiment will be described here.

FIG. 14 is a block diagram showing the configuration of the overall control system of the printer 100 in this embodiment. The difference from the block diagram of FIG. 6 is that an exposure timing calculation unit 311 is provided instead of the transfer timing calculation unit 309 included in the alignment control unit 307. The control units 301 to 308 and 311 are realized by a one-chip microcomputer (CPU 26) having a built-in ROM and RAM (not shown).

A method of aligning the toner image and the paper P in this embodiment will be described. In order to simplify the explanation, the case of executing monochrome printing will be described as an example. In the case of monochrome printing, a toner image is formed only on the photosensitive drum 1K of the process cartridge (K) and printing is executed. The CPU 26 calculates the time t4 (seconds) required from when the laser scanner 7K starts irradiating the photosensitive drum 1K with the laser beam until the toner image formed on the intermediate transfer belt 8 reaches the transfer position TP. Here, when the time t4 (seconds) is shorter than the time t2 (seconds) required for the paper P to reach the transfer position TP from the pause position SP, the CPU 26 sets the time t5 (= t2-t4) (seconds). calculate. The optical control unit 304 starts exposure of the laser scanner 7K to the photosensitive drum 1K at a timing t5 (seconds) after the paper P in the pause position SP is restarted by the paper feed / transport control unit 302. Take control. As a result, the image is formed at an appropriate position on the paper P.

However, even when such alignment control is performed, as described in the first embodiment, the timing of reaching the transfer position TP and the paper P reach the transfer position TP depending on the return amount of the paper P. There is a problem that the timing does not match.

FIG. 15 is a flowchart of this embodiment for solving the above-mentioned problems. FIG. 15 is a flowchart of this embodiment. The control based on the flowchart of FIG. 12 is executed by the CPU 26 mounted on the control board 25 based on a program stored in a ROM or RAM (not shown).

The processing of S300 to S306 is the same as the processing of S100 to S106 of the flowchart of FIG. 8 described in the first embodiment, and thus the description thereof will be omitted. Next to S306, when the engine control unit 301 determines that the measurement period for the return amount of the paper P has expired (S305), the exposure timing calculation unit 311 calculates the timing at which the laser scanner 7K irradiates the photosensitive drum 1K with laser light. (S307). The exposure timing calculation unit 311 calculates the time t5'(seconds) until the exposure is started by the following (Equation 3).
t5'(seconds) = t2 (seconds) -t4 (seconds) + L (mm) ÷ V (mm / second) ... (Equation 3)

Here, in (Equation 3), t2 (seconds) and t4 (seconds) are as described in this embodiment, L (mm) is the return amount of the paper P, and V (mm / sec) is the paper P. Is the transport speed of. As a result, the image formation timing for forming the image at an appropriate position on the paper P is determined.

Next, when the exposure start condition other than the transfer is satisfied (S308), the engine control unit 301 rotates the paper feed motor 34 by the paper feed / transfer control unit 302 to transfer the paper P stopped at the pause position SP. It is conveyed toward the position TP (S309). The optical control unit 304 starts the exposure of the photosensitive drum 1K by the laser scanner 7K (S311) when the time t5'(seconds) elapses from the resumption of the transfer of the paper P (S310). This completes the control of this flowchart.

A specific example is shown. For example, in a configuration where t4 is 0.2 seconds, t2 is 0.3 seconds, K is 0.04 mm / pulse, and V is 300 mm / second, and the number of measured encoder pulses is 15 pulses, t5'is 0. It is calculated as 102 seconds. When the return amount of the paper P is not taken into consideration, the time t5 (seconds) until the exposure is started is 0.1 seconds because it is calculated as described above (t2-t4). That is, according to this embodiment, the exposure is started at a timing 0.002 seconds later than the conventional one.

From the above, according to the present embodiment, the return amount of the recording material is measured in a state where the recording material is temporarily stopped at a predetermined position on the upstream side of the image formation position, and the exposure timing is changed by the measured return amount. To do. This makes it possible to form an image at an appropriate position on the recording material.

Further, the control of the transfer timing of the recording material (paper P) shown in Examples 1 to 3 to the image forming position (transfer position TP) and the control of the image forming timing shown in Example 4 are combined to form a recording material. It may be controlled to form an image at an appropriate position of.

For example, consider combining Example 3 and Example 4. Here, the range in which the transport speed of the recording material can be accelerated is determined by the performance of the paper feed motor 34. When a small and simple paper feed motor 34 is used for cost reduction, the transport speed of the recording material cannot be accelerated to a high speed, and the return amount of the recording material is corrected only by the correction method of the third embodiment. There may be cases where it cannot be cut. In such a case, in order to correct the remaining return amount that could not be corrected, the control may be combined by additionally applying the correction method of the fourth embodiment.

In the above-mentioned Examples 1 to 4, the recording material is temporarily stopped without exciting the motor, but the present invention is not limited to this. Even when the recording material is temporarily stopped while the motor is excited, there is a possibility that the paper P is pulled back to the upstream side due to the reverse rotation phenomenon of the separation roller 12. Therefore, the present invention can be applied not only to a DC brushless motor but also to a configuration in which a stepping motor is used as the paper feed motor 34 and the recording material is temporarily stopped while the motor is excited. A stepping motor may be used as the paper feed motor 34 regardless of whether the motor is excited or not.

Further, in the above-described first to fourth embodiments, the amount of the recording material pulled back to the upstream side is indirectly obtained by detecting the rotation amount of the paper feed motor 34, but the present invention is not limited to this. For example, an encoder may be provided to detect the amount of rotation of the transport roller 15 and the registration roller 16, and the amount of the recording material pulled back to the upstream side may be indirectly obtained from the amount of rotation of each roller. Alternatively, the amount of the recording material pulled back may be obtained from the amount of rotation of the separation roller 12. Further, a media sensor for capturing a surface image of the recording material and determining the surface state of the recording material may be provided near the registration roller 16. Then, the amount of the recording material pulled back may be directly obtained from the surface images of the plurality of recording materials captured by the media sensor.

Further, in Examples 1 to 4 described above, an example of a laser beam printer is shown, but the image forming apparatus to which the present invention is applied is not limited to this, and printers of other printing methods such as an inkjet printer can be used. Alternatively, it may be a copying machine. In the case of an inkjet printer, the position where ink is ejected and an image is formed on the paper P corresponds to the transfer nip portion in the laser beam printer, that is, the image forming position.

11 Secondary transfer roller 12 Separation roller 14 Paper feed roller 16 Registration roller 26 CPU
34 Paper feed motor 42 Encoder disc 44 Photo sensor 100 Laser beam printer

Claims (11)

An image forming means for forming an image on a recording material at an image forming position,
The first transport member that transports the recording material,
A separating member for forming a separation nip portion from the first transport member and separating a plurality of recording materials into one recording material at the separation nip portion.
A second transport member provided on the downstream side in the transport direction of the recording material with respect to the first transport member and transporting the recording material with respect to the image forming position.
The motor that drives the second transport member and
The rotation of the motor is stopped so that the recording material stops when the tip of the recording material transported by the second transport member reaches a predetermined position on the upstream side in the transport direction from the image forming position. An image having a control means for rotating the motor again so that the stopped recording material is conveyed to the image forming position by the second conveying member in accordance with the image forming timing by the image forming means. In the forming device
When the tip of the recording material reaches the predetermined position, the rear end of the recording material does not pass through the separation nip portion, and after the rotation of the motor is stopped, the recording material is moved by the separation member. An image forming apparatus that is pulled back to the upstream side in the transport direction.
It has a detecting means for detecting the amount of the recording material pulled back.
The timing at which the recording material is conveyed to the image forming position by the second conveying member and the image forming by the image forming means based on the amount of the recording material pulled back detected by the detecting means. An image forming apparatus characterized in that at least one of the timings is changed. It has an acquisition means for acquiring the length of the recording material in the transport direction.
Based on the length of the recording material acquired by the acquisition means, the control means passes the rear end of the recording material through the separation nip portion in a state where the tip of the recording material reaches the predetermined position. When it is determined whether or not the recording material passes through the separation nip portion, the second transport member is based on the amount of the recording material pulled back detected by the detection means. The image forming apparatus according to claim 1, wherein the timing at which the recording material is conveyed to the image forming position and the image forming timing by the image forming means are not changed. The control means again conveys the recording material stopped at the predetermined position by the second conveying member based on the amount of the recording material pulled back detected by the detecting means, or the said. The image forming apparatus according to claim 1 or 2, wherein the speed at which the recording material stopped at the predetermined position is conveyed to the image forming position is changed by the second conveying member. The control means accelerates the timing of re-transporting the recording material that has been stopped at the predetermined position by the second transport member as the amount of the recording material detected by the detection means pulled back increases. The image forming apparatus according to claim 3. The control means conveys the recording material stopped at the predetermined position by the second conveying member to the image forming position as the amount of the recording material detected by the detecting means pulled back increases. The image forming apparatus according to claim 3, wherein the speed of causing the image is increased. The image forming means includes an exposure means for irradiating the image carrier with light to form an electrostatic latent image on the image carrier.
The control means is characterized in that the timing of irradiating the image carrier with light by the exposure means is changed based on the amount of the recording material pulled back detected by the detection means. 2. The image forming apparatus according to 2. 6. The control means is characterized in that, as the amount of the recording material detected by the detection means pulled back increases, the timing of irradiating the image carrier with light by the exposure means is delayed. The image forming apparatus described. The image forming means is for transferring a plurality of image carriers, an intermediate transfer belt carrying a toner image transferred from the plurality of image carriers, and a toner image transferred to the intermediate transfer belt to a recording material. Including the transfer roller,
The image forming apparatus according to any one of claims 1 to 7, wherein the image forming position is a position of a transfer nip portion formed by the intermediate transfer belt and the transfer roller. The image forming apparatus according to any one of claims 1 to 8, wherein the motor is a DC motor, and the motor is not excited when the rotation of the motor is stopped. The image forming apparatus according to any one of claims 1 to 9, wherein the detecting means is a rotation amount detecting means for detecting the rotation amount of the motor. The rotation amount detecting means is provided coaxially with the motor, and outputs different signals depending on whether the encoder disk rotating with the motor and the light passing through the slit formed in the encoder disk are detected or not detected. The image forming apparatus according to claim 10, further comprising a photosensor.

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