JP2018103453A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of the quality of an image formed on a recording material in a case where the load torque of a motor driving conveyance means conveying the recording material to the image formation position fluctuates.SOLUTION: An image formation apparatus includes image formation means, feeding means, conveyance means, a motor, detection means, switching means and control means. While the conveyance means conveys a first recording material on which an image is formed by the image formation means, the switching means transmits the driving force from the motor. When the feeding means feeds a subsequent second recording material, the control means changes the gain for deciding a signal input to the motor from the first setting value to the second setting value higher than the first setting value in accordance with the deviation between the target speed of the motor and the rotational speed of the motor detected by the detection means before the timing at which the switching means transmits the driving force from the motor.SELECTED DRAWING: Figure 4

Description

  The present invention relates to control of a motor used in an image forming apparatus.

  2. Description of the Related Art Conventionally, some image forming apparatuses such as copying machines and printers have a transfer roller that forms a transfer nip portion with a photosensitive drum or an intermediate transfer belt. The transfer roller transfers the toner image onto the recording material by conveying the recording material while sandwiching the recording material at the transfer nip portion.

  In Patent Document 1, vibration occurs at the timing when the leading edge of the recording material enters the transfer nip portion, or at the timing when the trailing edge of the recording material comes out of the transfer nip portion. It is described that the rotation speed varies instantaneously. It is described that the image quality of the toner image transferred to the recording material is deteriorated by the influence of the speed fluctuation.

  In Patent Document 1, in order to prevent such deterioration in image quality, the control gain is set in accordance with the timing when the leading edge of the recording material enters the transfer nip portion or the timing when the trailing edge of the recording material leaves the transfer nip portion. It is set higher than usual. Here, the control gain is a parameter used for speed control of a motor that drives the photosensitive drum and the intermediate transfer belt. In Patent Document 1, since PI control is adopted as motor speed control, the control gain corresponds to a proportional gain for proportional control (P control) and an integral gain for integral control (I control).

JP 2011-133542 A

  According to Patent Document 1, it is possible to prevent deterioration in image quality of a toner image transferred to a recording material by setting a control gain of a motor that drives a photosensitive drum or an intermediate transfer belt to be higher than usual. However, depending on the configuration of the image forming apparatus, the toner image transferred to the recording material at a timing other than the timing when the leading edge of the recording material enters the transfer nip portion or the trailing edge of the recording material leaves the transfer nip portion. The image quality may be deteriorated.

  For example, when the load torque of the motor that drives the registration roller that transports the recording material to the transfer nip varies, the rotation speed of the registration roller may momentarily vary. If the rotation speed of the registration roller fluctuates while the registration roller and transfer roller are transporting the same recording material, the speed of the recording material also fluctuates, and the toner image transferred to the recording material at the transfer nip portion Will be affected.

  An object of the present invention is to prevent the quality of an image formed on a recording material from deteriorating when the load torque of a motor that drives a conveying unit that conveys the recording material to the image forming position fluctuates. .

  In order to achieve the above object, an image forming apparatus according to the present invention includes an image forming unit that forms an image on a recording material at an image forming position, a feeding unit that feeds the recording material, and a recording unit that records more than the feeding unit. A conveyance unit that is provided downstream in the conveyance direction of the material and conveys the recording material to the image forming position, a common motor that drives the feeding unit and the conveyance unit, and a rotation speed of the motor are detected. In the image forming apparatus, the image forming apparatus includes: a detecting unit configured to detect; a switching unit configured to transmit or block the driving force from the motor to the feeding unit; and a control unit configured to control the motor and the switching unit. While the conveying means is conveying the first recording material on which the means forms an image, the switching means transmits the driving force from the motor to the feeding means, and the feeding means After the first recording material When the second recording material to be fed is fed, the control means detects the target speed of the motor and the detection means before the timing when the switching means transmits the driving force from the motor to the feeding means. The gain for determining a signal to be input to the motor is changed from the first set value to a second set value higher than the first set value according to the deviation of the rotation speed of the motor detected by It is characterized by that.

  According to the present invention, it is possible to prevent the quality of an image formed on a recording material from deteriorating when the load torque of a motor that drives a conveying unit that conveys the recording material to the image forming position varies. .

1 is a schematic diagram of an image forming apparatus. It is a figure which shows the drive transmission structure of a paper feed mechanism. It is a block diagram of a paper feed motor. FIG. 3 is a block diagram of a control circuit for a paper feed motor and a diagram showing a PWM signal. It is a figure which shows the arrangement | positioning position of each roller, and the mode at the time of paper feeding. 3 is a timing chart in the first embodiment. 3 is a flowchart in the first embodiment. 10 is a flowchart in the second embodiment. 10 is a timing chart in the third embodiment. 10 is a flowchart in the third embodiment. 10 is a timing chart in the fourth embodiment. 10 is a flowchart in the fourth embodiment.

Example 1
A schematic diagram of an 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 the 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 a printer main body 200 (also referred to as a casing). In the following description, when the symbols (Y, M, C, K) indicating colors are omitted, it indicates that the configuration is common to all colors. Each of the process cartridges 5 includes a photosensitive drum 1, a charging roller 2, a developing roller 3, a cleaning blade 4, a toner container 23, and a waste toner container 24. The photosensitive drum 1 is charged by the charging roller 2 and then irradiated with laser light from the corresponding laser scanner 7 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 toner used by the developing roller 3 to develop the electrostatic latent image on the photosensitive drum 1.

  The intermediate transfer belt 8 is rotated in the direction of arrow α in FIG. Primary transfer rollers 6 are provided at positions facing the photosensitive drum 1 with the intermediate transfer belt 8 therebetween. 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 the respective photosensitive drums 1 are sequentially transferred to the intermediate transfer belt 8, and the color toner images are formed on the intermediate transfer belt 8 by overlapping the toner images of the respective colors. The toner remaining on the photosensitive drum 1 without being transferred to the intermediate transfer belt 8 is collected by the cleaning blade 4, and the collected toner is stored in a waste toner container 24.

  A counter 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, a color toner image formed on the intermediate transfer belt 8 is transferred to a transfer nip portion (image formation) formed by the intermediate transfer belt 8 and the secondary transfer roller 11. At the position), the image is transferred to a sheet P (recording material) fed from a sheet 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 (stacking unit), a paper feed roller 14 (first feed unit), a transport roller 15, a registration roller 16 (transport unit), and a re-feed roller 32 (second feed unit). (Feeding means). The paper feed roller 14 feeds the paper P from the paper feed cassette 13 on which the paper P is stacked. The transport roller 15 transports the paper P fed by the paper feed roller 14 to the registration roller 16. The registration roller 16 conveys the sheet P to the transfer nip portion so that the timing coincides with the toner image formed on the intermediate transfer belt 8 according to the timing when the top sensor 201 detects the leading edge of the sheet P. . The toner image transferred onto the paper P by the secondary transfer roller 11 is fixed onto the paper P by the fixing device 17. The fixing device 17 includes a heating roller 18 and a pressure roller 19, and heat and pressure are applied to the paper P by conveying the paper P while sandwiching the paper P at a fixing nip portion formed by the two rollers. To fix the toner image.

  The paper P on which the toner image is fixed is sent to the paper discharge conveyance path A or the reverse conveyance path B downstream of the fixing device 17. Here, the conveyance destination of the paper P is switched by the flapper 30. The paper P conveyed to the paper discharge conveyance path A is discharged to the outside of the printer main body 200 via the paper discharge roller 20. The paper P conveyed to the reverse conveyance path B is switched back by the reverse roller 31 and sent to the double-side conveyance path C. The sheet P sent to the duplex conveyance path C is conveyed to the refeed roller 32 by the duplex conveyance roller 202. The refeed roller 32 feeds the paper P having the toner image 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 a CPU 26 is mounted on the control board 25. The CPU 26 collectively controls operations of the printer 100 such as control of a paper feed motor 34 (described in FIG. 2) related to the conveyance of the paper P and a drive source (not shown) of the process cartridge 5. Reference numeral 28 denotes a switching power supply, which converts an AC power supply voltage input from a power cable 29 into a DC voltage used in 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 direct current motor (hereinafter referred to as a DC motor) serving as a drive source for the paper feed mechanism 33. The driving force of the paper feed motor 34 is directly transmitted to the registration roller 16 and the transport roller 15 via a drive train (not shown). The drive transmission from the paper feed motor 34 to the paper feed roller 14 is via a paper feed clutch 35 (first switching means), and the drive transmission from the paper feed motor 34 to the re-feed roller 32 is re-feed. Via a clutch 36 (second switching means). 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 driving force of the paper feed motor 34 is sent to the paper feed roller 14. Not transmitted. When the refeed clutch 36 is on, the driving force of the paper feed motor 34 is transmitted to the refeed roller 32. When the refeed 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 performs control so that the paper feed clutch 35 and the refeed clutch 36 are switched ON / OFF according to the respective paper feed timings. Thus, the paper feed roller 14 and the registration roller 16 are driven by the common paper feed motor 34. The refeed roller 32 and the registration roller 16 are also driven by a common paper feed motor 34. In this configuration, when the sheet feeding clutch 35 or the sheet refeeding clutch 36 is turned on to drive the sheet feeding roller 14 or the sheet refeeding roller 32, the load torque of the sheet feeding motor 34 fluctuates. The rotation speed may fluctuate. When the rotation speed of the paper feed motor 34 fluctuates, the rotation speeds of the transport roller 15 and the registration roller 16 driven by the common paper feed motor 34 may also fluctuate.

  FIG. 3 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. 3A, an output gear 41 is attached to one side of the shaft 40 of the paper feed motor 34, and an encoder disk 42 is 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 refeed roller 32 via a drive train (not shown). The encoder disk 42 is configured to rotate together with the shaft 40 of the paper feed motor 34. Further, the paper feed motor 34 is provided with a driver board 43 on which the motor driver circuit section shown in FIG. 4 is mounted. A connector 45 serving as an interface for power supply / control signals to the photosensor 44 and the paper feed motor 34 is also disposed on the driver board 43.

  As described in FIG. 3A, the photo sensor 44 is disposed so as to sandwich the encoder disk 42. Here, FIG. 3B shows a view of the sheet feeding motor 34 viewed from the direction of the arrow β in FIG. In FIG. 3B, the driver board 43 and the connector 45 are omitted. As shown in FIG. 3B, the encoder disk 42 has a plurality of slits 203 formed therein. The photo sensor 44 outputs an ON signal when light passing through the slit 203 is detected, and outputs an OFF signal when the light is shielded by the disk portion where the slit 203 is not provided. 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 thus can detect the rotation speed (the number of rotations per unit time) of the paper feed motor 34.

  FIG. 4A is a block diagram of a control circuit of the paper feed motor 34 in the present embodiment. That is, functional blocks relating to speed control of the paper feed motor 34 by the CPU 26 mounted on the control board 25 shown in FIG. The speed control unit 50 of the CPU 26 performs PID control 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. That is, motor speed control is performed by feedback control. Here, the speed measurement unit 48 measures the rotation speed of the paper feed motor 34 based on the encoder signal output from the photosensor 44 described above. The gain value used in 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 value 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 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 current flows in order, and rotates the rotating unit 204. Here, the amount of current supplied to each coil is controlled by a PWM signal. The PWM signal is a pulse signal having a constant period T described in FIGS. 4B and 4C, and the length of the period during which the output value is ON, that is, the pulse width is changed. Can be made. The pulse width of the pulse signal described in FIG. 4B is W1, and the pulse width of the pulse signal described in FIG. 4C is W2. The larger the pulse width, the more current flows in the coil. When a large amount of current flows through the coil, the torque increases and the rotation speed of the rotating unit 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.

  Next, gain change control of the paper feed motor 34 in the present embodiment will be described. In this embodiment, only the set value of the proportional gain for proportional control (P control) is changed in PID control. However, the present invention is not limited to this, and control may be performed so as to change the setting value of the integral gain for integral control (I control) and the differential gain for differential control (D control).

  FIG. 5 is an enlarged view of a part of the printer 100. In the present embodiment, description will be made on the assumption that each roller is arranged at the position shown in FIG. That is, the distance along the conveyance path from the paper supply roller 14 to the registration roller 16 is 60 mm, and the distance along the conveyance path from the registration roller 16 to the transfer nip portion is 100 mm. The distance along the conveyance path from the refeed roller 32 to the registration roller 16 is 30 mm. In this configuration, a case where the paper P is continuously fed by the paper feed roller 14 and single-sided continuous printing is performed will be described as an example. The interval between sheets at the time of printing is 20 mm, and for the sake of simplicity, description will be made assuming that the time required to connect the paper feed clutch 35 is zero [msec]. In the present embodiment, the sheet interval indicates the length of the interval between the trailing edge of the preceding sheet P1 and the leading edge of the succeeding sheet P2.

  When continuous paper feeding is performed by the paper feeding roller 14, the timing at which the preceding paper P1 is transported to the position shown in FIG. 5B, that is, when the distance between the preceding paper P1 and the succeeding paper P2 is 20 mm. The CPU 26 turns on the paper feed clutch 35. This timing is set by the CPU 26 based on the elapsed time from the timing when the sheet feeding clutch 35 for feeding the preceding sheet P1 is turned on. Further, the CPU 26 may set based on the elapsed time from the timing when the top sensor 201 detects the leading edge of the preceding paper P1. In the example of FIG. 5B, since the length of the preceding paper P1 is 140 mm (160 mm-20 mm) or more, the preceding paper P1 is aligned with the secondary transfer roller 11 at the timing shown in FIG. The state straddles the roller 16. If the paper feed clutch 35 is turned on to feed the succeeding paper P2 in this state, the load torque of the paper feed motor 34 may fluctuate and the speed of the paper feed motor 34 may fluctuate. When the speed fluctuation of the paper feed motor 34 occurs, the rotation speed of the registration roller 16 also fluctuates, the transport speed of the preceding paper P1 also fluctuates, and the toner transferred to the preceding paper P1 at the transfer nip portion. The image may be disturbed.

  In this embodiment, in order to reduce such disturbance of the toner image, control is performed to temporarily change the gain setting value to a large value. As the gain setting value increases, the value of the drive signal output from the speed control unit 50 with respect to a predetermined deviation also increases. As a result, the driver circuit unit 46 is controlled in a direction in which a larger amount of current flows through the coil disposed in the rotating unit 204 in order to change the pulse width of the PWM signal more greatly. Therefore, the torque of the rotating unit 204 is increased, and the speed followability of the paper feed motor 34 can be improved. Therefore, even if the load torque of the paper feed motor 34 fluctuates, the speed fluctuation of the paper feed motor 34 can be suppressed.

  FIG. 6 is a timing chart showing the timing for changing the control gain of the paper feed motor 34 during single-sided continuous printing. FIG. 6 also shows the ON timing of the paper feed clutch 35 and the presence / absence state of the paper P being conveyed by the registration roller 16 and the secondary transfer roller 11. As can be seen from FIG. 6, the preceding paper P <b> 1 is in a position straddling the registration roller 16 and the secondary transfer roller 11 at the timing when the paper feed clutch 35 is turned on. Therefore, in this embodiment, the paper feed clutch 35 is turned on, and the control gain of the paper feed motor 34 is changed from “small” to “large” before the paper feed roller 14 feeds the succeeding paper P2. Then, the control gain of the paper feed motor 34 is changed from “large” to “small” after a predetermined time from when the paper feed clutch 35 is turned on (after the driving force is transmitted to the paper feed roller 14 by the paper feed clutch 35). It has changed.

  Here, the reason for changing the control gain from “large” to “small” is that if the control gain remains “large”, the speed controller 50 is sensitive to minute speed fluctuations of the paper feed motor 34. This is because the sheet feeding motor 34 may oscillate due to the reaction. That is, the paper feed motor 34 cannot be stably controlled, and noise due to oscillation occurs. Therefore, as described above, the CPU 26 changes the control gain from “large” to “small” at an earlier timing at least before the paper feed clutch 35 is turned off. As a cause of minute speed fluctuations of the paper feed motor 34, for example, fluctuations in load torque applied to the paper feed motor 34 due to the trailing edge of the preceding paper P1 passing through the registration roller 16 can be cited.

  Next, the flow of changing the control gain in this embodiment will be described with reference to the flowchart of FIG. The control based on the flowchart of FIG. 7 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 a paper feed instruction is issued from an external device such as a PC to the printer 100 (S701), the CPU 26 changes the control gain of the paper feed motor 34 from “small” to “large” (S702). Thereafter, the CPU 26 turns on the paper feed clutch 35 (S703). Note that the CPU 26 may perform the process of S702 and the process of S703 simultaneously. It is only necessary that the control gain of the paper feed motor 34 can be changed before the paper feed clutch 35 is turned on and the load torque of the paper feed motor 34 fluctuates. Then, when the driving force starts to be transmitted to the paper feed roller 14 by the paper feed clutch 35 and the load torque of the paper feed motor 34 fluctuates and the time when the speed of the paper feed motor 34 may fluctuate has elapsed (S704), The CPU 26 again changes the control gain of the paper feed motor 34 to the original value (set to “small”) (S705). Next, the CPU 26 determines whether or not the printing is finished (S706), and returns to S701 when the printing is continued. When the printing is finished, the control of this flowchart is finished. In the situation where there is no preceding paper, such as feeding the first paper in the continuous paper feeding, even if the speed fluctuation of the paper feeding motor 34 occurs, it is not necessary to consider the disturbance of the toner image in the transfer nip portion. . Therefore, in such a situation, the control gain change control based on the flowchart of FIG. 7 may not be performed.

  As described above, according to the present exemplary embodiment, when the load torque of the motor that drives the conveyance unit that conveys the recording material with respect to the image forming position fluctuates, the fluctuation of the motor speed can be suppressed. Therefore, it is possible to prevent the quality of the image formed on the recording material from deteriorating.

(Example 2)
In this embodiment, the CPU 26 determines whether or not to change the control gain according to the difference in the print mode (difference in the rotation speed of the paper feed motor 34). The description of the main part is the same as that of the first embodiment, and only the parts different from the first embodiment will be described here.

  The printer 100 has a normal mode for forming an image on plain paper and the low speed mode for forming an image on thick paper. Compared to the normal mode, in the low speed mode, the printer 100 conveys the paper P at a lower speed. That is, in the low speed mode, the CPU 26 operates the paper feed motor 34 at a lower rotational speed than in the normal mode.

  When the rotation speed of the paper feed motor 34 is fast, it is hardly affected by fluctuations in the load torque, and when the rotation speed of the paper feed motor 34 is slow, it is easily affected by fluctuations in the load torque. For this reason, in this embodiment, the control gain is changed only during low-speed driving.

  With respect to the specific control flow of the present embodiment, only portions different from the first embodiment will be described with reference to the flowchart of FIG. 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).

  The difference from the first embodiment is that a process (S801) in which the CPU 26 confirms the print mode and determines whether to execute the low speed mode is inserted between the processes of S701 and S702. The CPU 26 can confirm whether or not to execute the low speed mode from the paper feed instruction received in step S701. When executing the low speed mode, the CPU 26 executes control gain change control as in the first embodiment (S702 to S705). On the other hand, when not executing the low speed mode, for example, when executing the normal mode, the CPU 26 By proceeding from S801 to S706, the control gain is not changed without changing the control gain. Next, the CPU 26 determines whether or not the printing is finished (S706), and returns to S701 when the printing is continued. When the printing is finished, the control of this flowchart is finished.

As described above, according to the present embodiment, since the control gain is changed only when necessary, it is not necessary to complicate the control of the gain change in addition to the effect of the first embodiment.
This embodiment is not limited to the configuration in which the paper conveyance speed is changed according to the type of paper. The present invention can be applied to a device that switches the paper conveyance speed in accordance with printing conditions so that the paper is conveyed at low speed during color printing. (Example 3)
In this embodiment, the CPU 26 determines whether or not to change the gain according to the position of the preceding paper P1. The description of the main part is the same as that of the first embodiment, and only the parts different from the first embodiment will be described here.

  First, the operation of this embodiment will be described with reference to the timing chart of FIG. The timing chart of FIG. 9 has a longer part (dotted line area Z) between the papers than the timing chart of FIG. As an example of the case where the paper interval becomes longer, for example, the development of the image data formed on the succeeding paper P2 is delayed, and the CPU 26 delays the timing of feeding the succeeding paper P2 by the paper feeding roller 14. In the dotted line area Z in FIG. 9, the feeding timing of the succeeding paper P2 is delayed for some reason, and the trailing edge of the preceding paper P1 has already passed the registration roller 16 at the timing when the feeding clutch 35 is turned on. Yes. Therefore, even if the speed fluctuation of the paper feed motor 34 occurs, the toner image transferred to the preceding paper P1 is not disturbed in the transfer nip portion.

  With respect to the specific control flow of the present embodiment, only portions different from the first embodiment will be described with reference to the flowchart of FIG. The control based on the flowchart of FIG. 10 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 difference from the first embodiment is that a process (S1001) in which the CPU 26 determines whether or not the preceding paper P1 straddles the registration roller 16 and the secondary transfer roller 11 is inserted between the processes of S701 and S702. It is a point.

  For example, the CPU 26 can obtain the leading edge position of the preceding paper P1 based on the time elapsed from the timing when the top sensor 201 detected the leading edge of the preceding paper P1 and the transport speed of the preceding paper P1. Further, the length of the preceding paper P1 in the transport direction can be confirmed from the paper feed instruction received in S701. That is, the CPU 26 can obtain the trailing edge position of the preceding paper P1 based on the information on the leading edge position of the preceding paper P1 and the information on the length of the preceding paper P1.

  When the CPU 26 determines that the obtained trailing edge position of the preceding paper P1 is upstream of the registration roller 16 and the preceding paper P1 straddles the registration roller 16 and the secondary transfer roller 11, the CPU 26, as in the first embodiment. When the control gain change control is executed (S702 to S705) and it is determined that the preceding paper P1 is not straddled, the CPU 26 proceeds from S1001 to S706, and does not perform control gain change control. Not going to change.

  As described above, according to the present embodiment, since the control gain is changed only when necessary, it is not necessary to complicate the control of the gain change in addition to the effect of the first embodiment.

  In the first to third embodiments, the case where the control gain is changed with respect to the ON timing of the paper feed clutch 35 has been described as an example. However, the refeed roller 32 driven by the paper feed motor 34 is described. The control gain may be changed with respect to the ON timing of the refeed clutch 36.

  Further, even when the paper feed clutch 35 and the refeed clutch 36 are alternately turned on not only during single-sided printing but also during double-sided printing, the same effect can be obtained by changing the control gain with respect to the ON timing of each clutch. Is obtained. However, in consideration of the fourth embodiment to be described later, in the first to third embodiments, it is assumed that the period for turning on the paper feed clutch 35 and the period for turning on the refeed clutch 35 do not overlap.

Example 4
In this embodiment, the control gain setting value is changed in three stages according to the magnitude of the load torque applied to the paper feed motor 34. The description of the main part 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 timing chart showing the timing for changing the control gain of the paper feed motor 34 during duplex continuous printing. FIG. 11 also shows the ON timing of the paper feed clutch 35, the ON timing of the refeed clutch 36, and the presence / absence state of the paper P being conveyed by the registration roller 16 and the secondary transfer roller 11.

  In the present embodiment, it is assumed that the paper interval during double-sided continuous printing is set shorter than in the previous embodiment. For this reason, there is a timing at which the paper feed clutch 35 is turned on while the refeed clutch 36 is turned on. That is, the period during which the paper feed clutch 35 is turned on and the period during which the refeed clutch 35 is turned on may partially overlap. At this time, the load torque applied to the paper feed motor 34 is larger than when only the refeed clutch 36 is turned on. Therefore, in this embodiment, the control gain setting value is changed in three stages according to the magnitude of the load torque applied to the paper feed motor 34.

  FIG. 11 shows this state, and when the paper feed clutch 35 and the paper refeed clutch 36 are not turned on (control gain = “small”), the control gain is set when the paper feed clutch 36 is turned on. Has been changed to “medium”. The control gain is changed to “large” when the paper feed clutch 35 is also turned on while the paper refeed clutch 36 is turned on.

  With respect to the specific control flow of the present embodiment, only portions different from the first embodiment will be described with reference to the flowchart of FIG. 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 difference from the first embodiment is that the CPU 26 determines whether or not the refeed clutch 36 has already been turned ON between the processing of S701 and S702 (S1201) and the control gain from “small” to “medium”. This is the point that the process of changing to (S1202) is inserted.

  When a new paper feed instruction is issued (S701), it is determined in S1201 whether or not the refeed clutch 36 has already been turned on. If the refeed clutch 36 is ON, the CPU 26 changes the control gain of the feed motor 34 from “small” to “large” (S702). On the other hand, if the refeed clutch 36 has not been turned on, the CPU 26 changes the control gain of the feed motor 34 from “small” to “medium” (S1202). Subsequent processing is the same as that in the flowchart of FIG.

  As described above, according to the present embodiment, the following effects can be obtained in addition to the effects of the first embodiment. In other words, even when the period during which the paper feed clutch 35 is turned on and the period during which the re-feed clutch 35 is turned on partially overlap during double-sided continuous printing, fluctuations in the motor speed can be suppressed. Therefore, it is possible to prevent the quality of the image formed on the recording material from deteriorating.

  In the fourth embodiment, the set value of the control gain is changed in three stages. However, the set value may be changed in four stages or more according to the magnitude of the load torque applied to the paper feed motor 34.

  In the first to fourth embodiments, the example of the laser beam printer is shown. However, the image forming apparatus to which the present invention is applied is not limited to this, and other printing methods such as an inkjet printer, Alternatively, a copier may be used. In the case of an ink jet printer, the position where an ink is ejected to form an image on paper P corresponds to the transfer nip portion in the laser beam printer, that is, the image forming position.

11 Secondary transfer roller 14 Paper feed roller 16 Registration roller 26 CPU
32 Refeed roller 34 Paper feed motor 35 Paper feed clutch 36 Refeed clutch 42 Encoder disk 44 Photo sensor 100 Laser beam printer

Claims (11)

Image forming means for forming an image on a recording material at an image forming position;
A feeding means for feeding the recording material;
A conveying unit that is provided downstream of the feeding unit in the conveying direction of the recording material and conveys the recording material to the image forming position;
A common motor for driving the feeding means and the conveying means;
Detecting means for detecting the rotational speed of the motor;
Switching means for transmitting or blocking the driving force from the motor to the feeding means;
In an image forming apparatus having the motor and a control unit that controls the switching unit,
While the conveying unit is conveying the first recording material on which the image forming unit forms an image, the switching unit transmits the driving force from the motor to the feeding unit, and the feeding unit When the means feeds the second recording material following the first recording material, the control means is prior to the timing at which the driving force from the motor is transmitted to the feeding means by the switching means. The gain for determining the signal to be input to the motor in accordance with the deviation between the target speed of the motor and the rotational speed of the motor detected by the detecting means is determined from the first set value to the gain. An image forming apparatus, wherein the second setting value is changed to a higher second setting value.   The control means can execute a first mode for rotating the motor at a predetermined speed and a second mode for rotating the motor at a speed slower than the predetermined speed. When executing, when the second mode is executed without changing the gain from the first set value before the timing, the gain is changed from the first set value before the timing. The image forming apparatus according to claim 1, wherein the image forming apparatus is changed to the second set value. A recording material detecting means provided on the recording material conveyance path for detecting the recording material;
When the control means determines that the trailing edge of the first recording material passes through the conveying means at the timing based on the detection result of the recording material detection means, the control unit sets the gain before the timing. When it is determined that the trailing edge of the first recording material does not pass through the conveying unit at the timing without changing from the setting value of 1, the gain is set from the first setting value to the gain before the timing. The image forming apparatus according to claim 1, wherein the image forming apparatus is changed to a second set value.   The control means again changes the gain from the second set value to the first set value before the timing at which the switching means cuts off the driving force from the motor to the feeding means. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The feeding unit is a first feeding unit that feeds a recording material from a stacking unit on which the recording material is stacked, or a recording material on which an image is formed on the first surface by the image forming unit. 5. The image forming apparatus according to claim 1, wherein the image forming apparatus is a second feeding unit that feeds again toward the transport unit. 6. Image forming means for forming an image on a recording material at an image forming position;
A first feeding unit that feeds the recording material from a stacking unit on which the recording material is loaded;
A conveying unit that is provided downstream of the first feeding unit in the conveying direction of the recording material and conveys the recording material to the image forming position;
A second feeding unit that feeds again the recording material on which the image is formed on the first surface by the image forming unit toward the conveying unit;
A common motor for driving the first feeding means, the second feeding means, and the conveying means;
Detecting means for detecting the rotational speed of the motor;
First switching means for transmitting or blocking driving force from the motor to the first feeding means;
Second switching means for transmitting or blocking driving force from the motor to the second feeding means;
In the image forming apparatus having the motor, the first switching unit, and a control unit for controlling the second switching unit,
While the conveying unit is conveying the first recording material on which the image forming unit forms an image, the second switching unit applies the driving force from the motor to the second feeding unit. And when the second feeding means feeds the second recording material following the first recording material, the control means uses the second switching means to drive the driving force from the motor. Prior to timing of transmission to the second feeding means, a signal to be input to the motor is determined according to a deviation between the target speed of the motor and the rotational speed of the motor detected by the detecting means. The gain is changed from the first set value to a second set value higher than the first set value, and the control means causes the second switching means to change the driving force from the motor to the second supply value. Before the timing of blocking the transmission means, the gay It was changed again to the first set value from said second set value,
While the conveying unit and the second feeding unit are conveying the second recording material on which the image forming unit forms an image, the first switching unit is driven by the motor. Is transmitted to the first feeding unit, and when the first feeding unit feeds a third recording material following the second recording material, the control unit performs the first switching. The gain is changed from the first set value to a third set value higher than the second set value before the timing at which the driving force from the motor is transmitted to the first feeding means by the means. An image forming apparatus that is changed.   The control means sets the gain from the third set value to the first before the timing at which the driving force from the motor is cut off from the first feeding means by the first switching means. The image forming apparatus according to claim 6, wherein the setting value is changed again. The image forming means transfers 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. And a transfer roller,
The image forming apparatus according to claim 1, 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 claim 1, wherein the motor is a DC motor.   The detection means is provided on the same axis as the motor, and is a photo that outputs different signals depending on whether or not the encoder disk that rotates together with the motor and light that has passed through a slit formed in the encoder disk is detected. The image forming apparatus according to claim 1, further comprising a sensor. Image forming means for forming an image on a recording material at an image forming position;
A feeding means for feeding the recording material;
A conveying unit that is provided downstream of the feeding unit in the conveying direction of the recording material and conveys the recording material to the image forming position;
A common motor for driving the feeding means and the conveying means;
Switching means for transmitting or blocking the driving force from the motor to the feeding means;
In an image forming apparatus having the motor and a control unit that controls the switching unit,
While the conveying unit is conveying the first recording material on which the image forming unit forms an image, the switching unit transmits the driving force from the motor to the feeding unit, and the feeding unit When the means feeds the second recording material subsequent to the first recording material, the control means transmits the driving force from the motor to the feeding means by the switching means. The image forming apparatus is controlled so as to increase the amount of current supplied to the image forming apparatus.

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