JP2020076808A - Image forming apparatus - Google Patents

Abstract

To prevent an increase in temperature of a motor and a driving circuit that drives the motor.SOLUTION: An image forming apparatus temporarily increases or decreases the rotation speed of a motor according to the difference between an actual timing at which a sheet is detected and a prescribed timing at which a sheet is expected to reach a detection position. This synchronizes the timing at which the sheet reaches a transfer unit with the timing at which a toner image reaches the transfer unit. The image forming apparatus increases or decreases a drive current of the motor in synchronization with switching means transmitting or blocking a driving force of the motor to a paper feed roller.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image forming apparatus.

  The electrophotographic image forming apparatus temporarily increases or decreases the sheet conveyance speed so that the timing at which the toner image arrives at the transfer portion coincides with the timing at which the sheet arrives at the transfer portion. (Patent Document 1).

JP, 2009-192633, A

  By the way, there is an image forming apparatus in which a feeding roller that feeds a sheet to a conveyance path and a conveyance roller that conveys a sheet on the conveyance path are driven by the same motor. The feeding roller is driven for a shorter time than the conveying roller. Generally, the feeding roller is intermittently driven by using a toothless gear or a solenoid. The torque required when the motor drives the transport roller and the feed roller is larger than the torque required when the motor drives only the transport roller. Therefore, the drive current when the motor drives the transport roller and the feed roller is larger than the drive current when the motor drives only the transport roller. When the drive current increases, the amount of heat generated by the motor and the drive circuit that drives the motor also increases. Therefore, the time during which the drive current flows is required to be appropriately managed. Therefore, it is an object of the present invention to suppress the temperature rise of a motor and a drive circuit that drives the motor.

The present invention is, for example,
A stacking unit for stacking sheets,
A feeding roller that feeds the sheets stacked on the stacking unit,
A conveyance roller arranged downstream of the feeding roller in the sheet conveyance direction and configured to convey the sheet to the transfer unit;
A motor for driving the feeding roller and the conveying roller,
A drive circuit for driving the motor,
Switching means arranged between the motor and the feeding roller, for switching whether to transmit the driving force of the motor to the feeding roller;
Detection means for detecting the sheet at a predetermined detection position in the sheet conveyance path,
The rotational speed of the motor is temporarily increased or increased according to the difference between the actual timing at which the sheet is detected by the detection unit and the specified timing at which the sheet is expected to arrive at the detection position. Speed control means for synchronizing the timing when the sheet arrives at the transfer portion and the timing when the toner image arrives at the transfer portion by decelerating;
An image forming apparatus, comprising: current control means for increasing and decreasing a drive current of the motor in synchronization with transmission and interruption of the drive force of the motor to the feeding roller by the switching means. provide.

  According to the present invention, the temperature rise of the motor and the drive circuit that drives the motor is suppressed.

Schematic cross-sectional view of the image forming apparatus Diagram showing a drive mechanism having a toothless gear Diagram explaining the controller FIG. 5 is a diagram illustrating a case where there is no delay or advance in conveyance. Diagram explaining the case where there is a conveyance delay Diagram explaining the case where there is progress Diagram explaining the controller The figure explaining controlling the drive current based on the number of steps. Diagram explaining the controller FIG. 5 is a diagram illustrating a case where there is no delay or advance in conveyance. Diagram explaining the case where there is a conveyance delay Diagram explaining the case where there is progress Flow chart showing transfer control Flow chart showing transfer control Flow chart showing transfer control

[Image forming device]
FIG. 1 shows an intermediate transfer type image forming apparatus 1. The image forming apparatus 1 may be an image forming apparatus that forms a single color image, but here is an electrophotographic image forming apparatus that mixes a plurality of colorants to form a multicolor image. The image forming apparatus 1 uses four color developers such as yellow (Y), magenta (M), cyan (C), and black (BK). In FIG. 1, a letter indicating a color is added to the end of the reference number, but this letter is omitted when the matters common to the four colors are described.

  The photosensitive drums 6C, 6M, 6Y, and 6BK are image carriers that are arranged at equal intervals and carry an electrostatic latent image and a toner image. The primary charger 2 is an example of a charging unit that uniformly charges the image carrier. The primary charger 2 uniformly charges the surface of the photosensitive drum 6 using the charging voltage. The scanning optical device 3 is an example of a scanning unit that forms an electrostatic latent image by scanning a laser beam on the surface of the image carrier. The scanning optical device 3 emits a light beam (laser beam) L, which is respectively modulated based on the input image, toward the photosensitive drum 6. The light flux L forms an electrostatic latent image on the surface of the photosensitive drum 6. The developing device 4 attaches the cyan, magenta, yellow, and black developers to the electrostatic latent image through a sleeve and a blade to which a developing voltage is applied. As a result, the electrostatic latent image is developed and a developer image (toner image) is formed.

  The feeding roller 8 feeds the sheets S contained in the feeding tray 7 one by one. The separation roller 9 separates one sheet S from the plurality of sheets S fed by the feeding roller 8 and sends the sheet S to the conveyance path. The transport roller 16 sends the sheet S toward the secondary transfer portion in synchronization with the image writing timing.

  The engine controller 15 accelerates / decelerates the rotation speed of the transport roller 16 according to the timing when the leading edge of the sheet S is detected by the sheet sensor 17. That is, if the detection timing is later than the specified timing, the transport speed of the sheet S is temporarily increased. If the detection timing is earlier than the specified timing, the transport speed of the sheet S is temporarily reduced. As a result, the sheet S always passes through the merge point P1 after a predetermined time from the timing when the toner image formation is started. That is, the timing at which the sheet S arrives at the secondary transfer portion is synchronized with the timing at which the toner image arrives at the secondary transfer portion. The distance from the detection position of the sheet sensor 17 to the merge point P1 is L1. A reference position P2, which will be described later, is provided further downstream than the merge point P1 after the conveyance of the sheet S. The distance from the merge point P1 to the reference position P2 is L2.

  The primary transfer roller 5 transfers the toner image carried on the photosensitive drum 6 to the intermediate transfer belt 10. The primary transfer voltage applied to the primary transfer roller 5 promotes the transfer of the toner image onto the intermediate transfer belt 10. The intermediate transfer belt 10 functions as an intermediate transfer body. The drive roller 11 is a roller that rotates the intermediate transfer belt 10. The secondary transfer section has a secondary transfer roller 14. In the secondary transfer section, the intermediate transfer belt 10 and the secondary transfer roller 14 convey the sheet S while sandwiching it, whereby the multicolor toner image carried on the intermediate transfer belt 10 is transferred to the sheet S. It The secondary transfer voltage promotes the transfer of the toner image onto the sheet S. After that, the sheet S is conveyed to the fixing device 12. The fixing device 12 applies pressure and heat to the toner image carried on the sheet S to fix it. The discharge roller 13 discharges the sheet S on which the image is formed. The primary transfer roller 5, the intermediate transfer belt 10, and the secondary transfer roller 14 are an example of a transfer unit that transfers a toner image onto a sheet. The fixing device 12 is an example of a fixing unit that fixes the toner image carried on the sheet.

[Drive mechanism]
FIG. 2 shows a drive mechanism for driving the feeding roller 8, the separating roller 9 and the conveying roller 16. The motor M1 drives the feeding roller 8, the separation roller 9 and the conveyance roller 16 via a plurality of gears including the pinion gear 26. The toothless gear 27 and the toothless pre-stage gear 30 are included in the plurality of gears. The motor M1 is, for example, a stepping motor. The drive mechanism is configured so that the transport roller 16 always rotates while the motor M1 rotates. On the other hand, when the solenoid 28 is ON, the driving force of the motor M1 is transmitted to the feeding roller 8 and the separation roller 9. When the solenoid 28 is OFF, the driving force of the motor M1 is not transmitted to the feeding roller 8 and the separation roller 9. When the solenoid 28 is turned on, the flapper 29 and the tooth-chipped gear 27 are disengaged from each other, and the tooth-chipped gear 27 and the tooth-chipped front gear 30 mesh with each other. As a result, the driving force of the motor M1 is transmitted to the tooth-chipped gear 27 via the tooth-chipped front gear 30, and is further transmitted from the tooth-chipped gear 27 to the feeding roller 8 and the separation roller 9. When the solenoid 28 is turned off, the flapper 29 and the partly tooth-missing gear 27 are coupled, and the meshing between the partly tooth-missing gear 27 and the partly tooth-missing pre-stage gear 30 is released. Therefore, the transmission of the driving force of the motor M1 is cut off. The tooth-chipped gear 27 makes one revolution each time one sheet S is fed. The timing when the solenoid 28 is turned off is the timing when the leading edge of the sheet S arrives at the reference position P2.

  In FIG. 2, the tooth-chipped gear 27 has two rows of gears connected to each other, and the first-row gear meshes with the tooth-chipped front gear 30. Exists. That is, while the tooth-chipped gear 27 makes one rotation, there is a period in which the tooth-feed gear 8 drives the feeding roller 8 and a period in which the tooth-chipped gear 27 does not drive the feeding roller 8.

[Engine controller]
As shown in FIG. 3, the engine controller 15 has a CPU 31, a memory 32, and a drive circuit 33. The CPU 31 realizes various functions by executing the control program stored in the ROM area of the memory 32. The speed control unit 34 controls the rotation speed of the motor M1 by controlling the frequency of the pulse signal output from the drive circuit 33. As a result, the rotation speed of the carry roller 16 and the carry speed of the sheet S1 are controlled. The pulse signal may be called a drive pulse. The current control unit 35 controls the amount of drive current that the drive circuit 33 supplies to the motor M1. As a result, the torque of the motor M1 is adjusted. The CPU 31 controls ON / OFF of the solenoid 28 through the drive circuit 33. This controls the start and end of rotation of the partly tooth-missing gear 27. The timer 36 is used to count various times. For example, the timer 36 measures the conveyance time from the time when the sheet S is disclosed to be fed to the time when the sheet S is detected by the sheet sensor 17. The speed calculator 37 calculates the conveyance speed applied to the sheet S in the conveyance section from the detection position of the sheet sensor 17 to the merge point P1. For example, if the detection time is later than the specified time, the transport speed is increased. As a result, when the leading edge of the sheet S arrives at the merge point P1, the conveyance delay is eliminated. If the detection time is earlier than the specified time, the transport speed is reduced. As a result, when the leading edge of the sheet S arrives at the merge point P1, the conveyance advance is canceled. The sheet S is transported at a predetermined process speed in the transport section downstream of the merge point P1 in the transport direction of the sheet S. The speed calculator 37 increases the carrier speed by increasing the frequency of the pulse signal, and decreases the carrier speed by decreasing the frequency of the pulse signal. The time calculation unit 38 calculates the timing for reducing the second drive current I2 to the first drive current I1 based on the conveyance speed of the sheet S (rotational speed of the motor M1) and the like. As a result, the drive current is reduced in synchronization with the timing when the load torque applied to the motor M1 decreases. As a result, the temperature rise of the drive circuit 33 is suppressed.

<Example 1>
As described above, the transport speed of the sheet S is temporarily increased or decreased depending on the timing when the sheet S is detected by the sheet sensor 17. In response to this, the time during which the toothless gear 27 is driven (driving time) changes. Therefore, in the first embodiment, the drive end timing of the tooth-chipped gear 27 is determined, and the drive current is reduced in synchronization with the drive end timing. The timing for ending the drive of the partly tooth-missing gear 27 is the timing at which the solenoid 28 is turned off.

Case where Sheet S is Conveyed at Design Timing FIG. 4A shows the load torque applied to the motor M1 in the case where the leading edge of the sheet S reaches the sheet sensor 17 at the specified timing. FIG. 4B shows the rotation speed of the motor M1. FIG. 4C shows the drive current supplied to the motor M1. The timing at which the sheet S reaches the sheet sensor 17 matches the specified timing. Therefore, as shown in FIG. 4B, the rotation speed of the motor M1 is always constant.

  As shown in FIG. 4C, the current controller 35 increases the drive current supplied to the motor M1 from I1 to I2 at time t0 when the solenoid 28 is turned on. This is because, as shown in FIG. 4 (A), at time t0, the drive of the partly tooth-missing gear 27 is started, and the load torque applied to the motor M1 increases. At time t3, the current controller 35 reduces the drive current from I2 to I1. This is because, as shown in FIG. 4 (A), the drive of the partly tooth-missing gear 27 ends at time t3, and the load torque applied to the motor M1 decreases. On the other hand, as shown in FIG. 4C, in the comparison method (Patent Document 1), the drive current decreases from I2 to I1 at time tref. This is because, in the comparison method, the longest possible driving time is assumed as the driving time of the toothless gear 27. In other words, in the comparison method, the actual drive end timing of the tooth-chipped gear 27 is not taken into consideration and the drive current decrease timing is fixed. In addition, in the comparison method, a margin is added to the assumed longest driving time.

  Therefore, when the leading edge of the sheet S reaches the sheet sensor 17 at the specified time t3, the first embodiment can reduce the drive current earlier than the comparison method by the difference time between tref and t3. .. Therefore, the temperature rise of the drive circuit 33 is suppressed.

Case where Sheet S is Delayed FIG. 5A shows a time characteristic of load torque applied to the motor M1. FIG. 5B shows the time characteristics of the rotation speed of the motor M1. FIG. 5C shows the time characteristic of the drive current supplied to the motor M1. The same reference numerals are given to the timings already described.

  As shown in FIGS. 5A to 5C, the time t1 ′ when the sheet S is actually detected by the sheet sensor 17 is later than the time t1 which is the specified timing. Therefore, at time t1 ′, the speed control unit 34 increases the rotation speed of the motor M1 from S1 to S2. The rotation speed S2 is calculated by the speed calculator 37 so that the conveyance delay of the sheet S is eliminated at the time t2 when the sheet S reaches the merge point P1. The distance L1 from the detection position of the sheet sensor 17 to the merge point P1 is constant. The difference between time t1 and time t1 ′ is Δt. The time from time t1 to time t3 ′ is T. The transport speed of the sheet S is proportional to the rotation speed of the motor M1. Let the proportionality coefficient be a.

a × S1 × T = L1 (1)
a × S2 × (T−Δt) = L1 (2)
By rearranging these equations, the following equation is obtained.

S2 = (T × S1) / (T−Δt) (3)
When expressed using L1, the following equation is obtained.

S2 = (L1 / a) / (T-Δt) (4)
On the other hand, as shown in FIG. 5C, the current controller 35 increases the drive current from I1 to I2 at time t0 when the solenoid 28 is turned on. The current controller 35 reduces the drive current from I2 to I1 at time t3 ′. This is because, as shown in FIG. 5 (A), the drive of the partly tooth-missing gear 27 ends at time t3 ′, and the load torque applied to the motor M1 decreases.

  As shown in FIG. 5C, in the comparison method, the drive current supplied to the motor M1 decreases from I2 to I1 at time tref. In the first embodiment, the drive current of the motor M1 is reduced from I2 to I1 earlier than the comparison method by a time corresponding to the difference between tref and t3 ′. Therefore, the temperature rise of the drive circuit 33 is suppressed.

Case where the seat S arrives early FIG. 6 (A) shows the time characteristic of the load torque applied to the motor M1. FIG. 6B shows a time characteristic of the rotation speed of the motor M1. FIG. 6C shows the time characteristic of the drive current supplied to the motor M1. The same reference numerals are given to the timings already described.

  As shown in FIG. 6A, the time t1 ″ when the sheet S actually reaches the sheet sensor 17 is earlier than the time t1 which is the specified timing by Δt. Therefore, the time when the sheet S reaches the merge point P1. At must be canceled by t2, so the speed control unit 34 reduces the rotation speed of the motor M1 from S1 to S3 at time t1 ", as shown in FIG. The speed calculator 37 calculates the rotation speed S3 according to the following formula.

S3 = (T × S1) / (T + Δt) (3)
When expressed using L1, the following equation is obtained.

S3 = (L1 / a) / (T + Δt) (4)
On the other hand, as shown in FIG. 6C, the current control unit 35 reduces the drive current from I2 to I1 at time t3 ". This means that the drive of the partly tooth-missing gear 27 is completed at time t3", This is because the load torque applied to M1 is reduced. On the other hand, as shown in FIG. 6C, in the comparison method, the drive current supplied to the motor M1 decreases from I2 to I1 at time tref. The first embodiment reduces the drive current from I2 to I1 faster than the comparison method by the difference between tref and t3 ″. As a result, the temperature rise of the drive circuit 33 is suppressed.

  As described above, in the first embodiment, the drive current supplied to the motor M1 is increased or decreased in synchronization with the drive start and drive end of the feeding roller 8. As a result, the temperature rise of the drive circuit 33 is suppressed. For example, the time calculation unit 38 may calculate the time t3 ′ at which the drive current is reduced by subtracting the arrival delay time Δt from the time t3 assumed in design. The time calculation unit 38 may calculate the time t3 "at which the drive current is reduced by adding the early arrival time Δt to the time t3 assumed in the design. The time calculation unit 38 eliminates the conveyance delay. The time t3 ′ may be calculated using the rotation speed S2 for

t3 '= t1' + Tx (5)
Tx = L1 / (a × S2) + L2 / (a × S1) (6)
Here, Tx is a transport time required to transport the sheet S from the detection position to the reference position P2. The time calculation unit 38 may calculate the time t3 ″ using the rotation speed S3 for canceling the conveyance advance.

t3 "= t1" + Tx (7)
Tx = L1 / (a × S3) + L2 / (a × S1) (8)
In the first embodiment, the timing for switching the drive current and the timing for ending the drive of the toothless gear 27 are synchronized, but this is only an example. For example, a margin may be added at time t3, time t3 ′, and time t3 ″. This margin is a margin corresponding to the tolerance of the external dimensions of the partly tooth-missing gear 27. The CPU 31 adds the margin. The margin is determined in accordance with the tolerance at the time of factory shipment, and is stored in the ROM area of the memory 32.

<Example 2>
The partly tooth-missing gear 27 rotates once for each sheet. The number of steps of the motor M1 required to rotate the partly tooth-missing gear 27 once is constant. The number of steps does not depend on the acceleration / deceleration of the rotation speed. Therefore, in the second embodiment, the timing for reducing the drive current is controlled according to the number of steps of the motor M1. The same reference numerals are given to the items already described.

[Engine controller]
As shown in FIG. 7, the CPU 31 has a counter 71 for counting the number of steps. When the drive current is increased from I1 to I2, the current controller 35 causes the counter 71 to start counting the number of steps. The current controller 35 reduces the drive current from I2 to I1 when the count value of the counter 71 reaches the number of steps required to rotate the partly tooth-missing gear 27 once. As a result, the temperature rise of the drive circuit 33 is suppressed.

Case where the sheet S is conveyed at the timing as designed FIG. 8A shows the relationship between the number of steps and the phase of the partly tooth-missing gear 27 when the detected timing of the sheet S is the specified timing. There is. The times t0 to t3 are the same as the times already described with reference to FIGS. 4 (A) to 4 (C). To simplify the description, it is assumed that the number of steps at the drive start timing of the tooth-chipped gear 27 is zero. Time t1 is an ideal timing at which the sheet S is detected. At time t1, the number of steps of the motor M1 becomes N1. At this time, the phase of the partly tooth-missing gear 27 is θ1. Time t2 is an ideal timing when the sheet S passes the merge point P1. At time t2, the number of steps of the motor M1 is N2. The phase of the partly tooth-missing gear 27 is θ2. Time t3 is an ideal drive end timing of the partly tooth-missing gear 27. At time t3, the number of steps of the motor M1 is N3. The phase of the partly tooth-missing gear 27 is θ3. At this time, θ3 is 2π. Therefore, the partly tooth-missing gear 27 makes one rotation from time t0 to time t3.

  As shown in FIGS. 4C and 8A, at time t0 (the number of steps = 0), the current controller 35 increases the drive current from I1 to I2. Further, the CPU 31 turns on the solenoid. At time t3 (step number = N3), the current controller 35 reduces the drive current from I2 to I1. Further, the CPU 31 turns off the solenoid. Therefore, the current controller 35 can increase or decrease the drive current based on the number of steps counted by the counter 71.

Case where Sheet S is Delayed FIG. 8B shows the relationship between the number of steps and the phase of the partly tooth-missing gear 27 when the detected timing of the sheet S is behind the specified timing. The times t0 to t3 and the times t1 ′ and t3 ′ are the same as the times already described with reference to FIGS. 5 (A) to 5 (C).

  Due to the conveyance delay of the sheet S, the sheet S is detected by the sheet sensor 17 at time t1 ′. The number of steps at this time is N4, and the phase of the partly tooth-missing gear 27 is θ4. The speed calculator 37 calculates the rotation speed S2 according to the delay time which is the time from time t1 to time t1 ′. The speed control unit 34 increases the rotation speed from S1 to S2. This eliminates the conveyance delay of the sheet S at time t2 when the sheet S passes the merge point P1. At this time, the number of steps is N5, and the number of steps of the partly tooth-missing gear 27 is θ5. At time t2 (the number of steps = N5), the speed control unit 34 reduces the rotation speed from S2 to S1. The time t2 is managed by the timer 36. Time t3 ′ is the drive end timing of the partly tooth-missing gear 27. At time t3 ′, the number of steps of the motor M1 is N3. On the time axis, the drive end timing is time t3 ′ before time t3. However, on the axis of the number of steps, the number of steps for ending the driving is N3. Although the rotation speed is increased from S1 to S2 when the number of steps is N4 to N5, the number of steps required to rotate the tooth-chipped gear 27 once is still N3. The relationship between θ1 and θ2 in FIG. 8A and θ4 and θ5 in FIG. 8B is as follows.

θ2-θ1 = θ5-θ4 (9)
That is, the angle at which the tooth-chipped gear 27 rotates to convey the sheet S from the sheet sensor 17 to the merge point P1 is constant.

  As shown in FIGS. 5C and 8B, at time t0 (the number of steps = 0), the current controller 35 increases the drive current from I1 to I2. The CPU 31 turns on the solenoid 28. At time t3 ′ (the number of steps = N3), the current controller 35 reduces the drive current from I2 to I1. The CPU 31 turns off the solenoid 28.

Case where Sheet S Arrives Early FIG. 8C shows the relationship between the number of steps and the phase of the partly tooth-missing gear 27 when the detected timing of the sheet S is earlier than the specified timing. The times t0 to t3 and the times t1 "and t3" are the same as the times already described with reference to FIGS. 6 (A) to 6 (C).

  At time t1 ", the leading edge of the sheet S reaches the sheet sensor 17. The speed calculator 37 calculates the rotation speed S3 based on the time difference between time t1" and time t1. The speed control unit 34 reduces the rotation speed from S1 to S3. As a result, at the time t2 when the sheet S passes the merge point P1, the advance of conveyance of the sheet S is canceled. Note that the number of steps at time t1 "is N6 and the phase is θ6. At time t2 (the number of steps = N7), the speed control unit 34 returns the rotation speed from S3 to S1. The time t2 can be specified by referring to it.

  Time t3 "is the drive end timing of the tooth-chipped gear 27. The number of steps at this time is N3. When the count value of the counter 71 reaches N3, the current control unit 35 reduces the drive current from I2 to I1. The relationship between θ1 and θ2 in FIG. 6C and θ1 and θ7 in FIG. 8C is as follows.

θ2-θ1 = θ7−θ1 (10)
That is, the angle at which the tooth-chipped gear 27 rotates to convey the sheet S from the sheet sensor 17 to the merge point P1 is constant.

  As described above, according to the second embodiment, the current controller 35 reduces the drive current from I2 to I1 when the number of steps reaches N3. As a result, the temperature rise of the drive circuit 33 is suppressed. The time when the number of steps reaches N3 changes according to the detection timing of the sheet S. Although the drive end timing changes on the time axis, the number of steps corresponding to the drive end timing does not change on the step number axis. The CPU 31 may determine the number of steps corresponding to the drive end timing by adding a margin to the number of steps N3. This margin depends on the tolerance of the outer dimensions of the tooth-chipped gear 27 and the like, as described above.

<Example 3>
Example 3 is similar to Example 1. In the first embodiment, the actual times t3, t3 ', t3 "at which the drive of the tooth-chipped gear 27 should be finished are obtained, and the driving current is reduced from I2 to I1 at times t3, t3', t3". In the third embodiment, the times t3, t3 ′, and t3 ″ are compared with a plurality of threshold timings Th1, Th2, and Th3, and the drive current is reduced from I2 to I1 at a time corresponding to a closer threshold timing. In the third embodiment, description of matters common to the first embodiment is omitted.

[Engine controller]
FIG. 9 shows the engine controller 15 of the third embodiment. In particular, the determination unit 91 compares the times t3, t3 ′, t3 ″ obtained by the time calculation unit 38 with a plurality of threshold timings Th1, Th2, Th3 to determine the time at which the drive current is reduced from I2 to I1. ..

Case where Sheet S is Conveyed at Design Timing FIG. 10A shows the load torque applied to the motor M1 in the case where the leading edge of the sheet S reaches the sheet sensor 17 at the specified timing. FIG. 10B shows the rotation speed of the motor M1. FIG. 10C shows the drive current supplied to the motor M1. 10 (A) to 10 (C) correspond to FIGS. 4 (A) to 4 (C).

  As shown in FIGS. 10A to 10C, the threshold timing Th1 is set at a time earlier than the preset time t3 when the driving of the tooth-chipped gear 27 is finished. Further, the threshold timing Th2 is set between the predetermined time t3 and the time tref which is the drive end timing in the comparison method. Further, the time tref is set to the threshold timing Th3.

  The time calculation unit 38 calculates time t3, which is the drive end timing of the partly tooth-missing gear 27, and passes it to the determination unit 91. The determination unit 91 compares the time t3 with the threshold timings Th1, Th2, and Th3. The determination unit 91 specifies a threshold value that exceeds the time point t3 and is closest to the time point t3 among the threshold value timings Th1, Th2, and Th3. In this example, the threshold timing Th2 exceeds the time t3 and is specified as the threshold closest to the time t3. The current controller 35 reduces the drive current from I2 to I1 at the time corresponding to the threshold timing Th2. As a result, the temperature rise of the drive circuit 33 is suppressed.

Case where Sheet S is Delayed FIG. 11A shows a time characteristic of the load torque applied to the motor M1. FIG. 11B shows a time characteristic of the rotation speed of the motor M1. FIG. 11C shows the time characteristic of the drive current supplied to the motor M1. 11 (A) to 11 (C) correspond to FIGS. 5 (A) to 5 (C). The relationship between the threshold timings Th1, Th2, Th3 and the times t1 and tref is as described above.

  The time t1 ′ when the sheet S is detected by the sheet sensor 17 is after the predetermined time t1. Therefore, the speed calculation unit 37 obtains the rotation speed S2 for eliminating the conveyance delay and increases the conveyance speed of the sheet S. On the other hand, the time calculation unit 38 calculates the time t3 ′ at which the driving of the partly tooth-missing gear 27 is completed, and passes it to the determination unit 91. The determination unit 91 compares the time t3 ′ with the threshold timings Th1, Th2, and Th3. The determination unit 91 specifies a threshold value that exceeds the time t3 ′ and is closest to the time t3 ′ among the threshold timings Th1, Th2, and Th3. In this example, the threshold timing Th1 exceeds the time t3 ′ and is specified as the threshold closest to the time t3 ′. The current controller 35 reduces the drive current from I2 to I1 at the time corresponding to the threshold timing Th1. As a result, the temperature rise of the drive circuit 33 is suppressed.

Case where the seat S arrives early FIG. 12 (A) shows the time characteristic of the load torque applied to the motor M1. FIG. 12B shows the time characteristic of the rotation speed of the motor M1. FIG. 12C shows the time characteristic of the drive current supplied to the motor M1. 12 (A) to 12 (C) correspond to FIGS. 6 (A) to 6 (C). The relationship between the threshold timings Th1, Th2, Th3 and the times t1 and tref is as described above.

  The time t1 ″ when the sheet S is detected by the sheet sensor 17 is before the predetermined time t1. Therefore, the speed calculation unit 37 obtains the rotation speed S3 for canceling the advance of conveyance of the sheet S, and The conveyance speed is reduced, while the time calculation unit 38 calculates the time t3 ″ at which the driving of the tooth-chipped gear 27 ends, and passes it to the determination unit 91. The determination unit 91 compares the time t3 "with the threshold timings Th1, Th2, Th3. The determination unit 91 exceeds the time t3" of the threshold timings Th1, Th2, Th3 and is closest to the time t3 ". A threshold value is specified.In this example, the threshold value timing Th2 is specified as a threshold value that exceeds the time t3 "and is closest to the time t3". The current control unit 35 sets the drive current at the time corresponding to the threshold value timing Th2. Is reduced from I2 to I1 to suppress the temperature rise of the drive circuit 33.

  Here, the actual drive end timing of the partly tooth-missing gear 27 is compared with the threshold timings Th1, Th2, and Th3, and the drive current is reduced at a time that exceeds the drive end timing and corresponds to the closest threshold value. However, the timing of reducing the drive current is not limited to this. A margin corresponding to the tolerance of the external dimensions of the toothless gear 27 or the like may be added to the timing of reducing the drive current determined based on the threshold value.

<Flowchart>
FIG. 13 is a flowchart showing the transport control of the first embodiment. The CPU 31 executes the following steps according to the control program stored in the memory 32.
In S1301, the CPU 31 sets the rotation speed of the motor M1 to S1 and sets the drive current to I1 to start driving the motor M1. The drive circuit 33 drives the motor M1 according to an instruction from the CPU 31.
In step S1302, the CPU 31 determines whether the feeding start condition is satisfied. The feeding start condition is a condition for turning on the solenoid 28. For example, the feeding start condition is that the image forming engine is activated to start forming a toner image. When the feeding start condition is satisfied, the CPU 31 proceeds to S1303.
In step S1303, the CPU 31 increases the drive current to I2 and turns on the solenoid 28.
In step S1304, the CPU 31 determines whether the sheet S is detected by the sheet sensor 17. When the sheet S is detected by the sheet sensor 17, the CPU 31 proceeds to S1305.
In S1305, the CPU 31 determines whether or not there is a conveyance delay. For example, the CPU 31 compares the actual detection times t1, t1 ', t1 "with the specified detection time t1 to determine whether there is a conveyance delay. If there is no conveyance delay, the CPU 31 proceeds to S1306. If there is a conveyance delay, the CPU 31 proceeds to S1311.
In step S1306, the CPU 31 determines whether there is no conveyance advance. For example, the CPU 31 compares the actual detection times t1, t1 ′, t1 ″ with the specified detection time t1 and determines whether or not there is conveyance advance. If there is no conveyance advance, the CPU 31 proceeds to S1307. If the conveyance is advanced, the CPU 31 advances to S1321.

  In S1307, the CPU 31 turns off the solenoid 28 at the specified time t3 and reduces the drive current to I1.

-Reduction of conveyance delay-In S1311, the CPU 31 increases the rotation speed of the motor M1 to S2. The rotation speed S2 is determined depending on the degree of conveyance delay.
In step S1312, the CPU 31 determines the time t3 'when the solenoid 28 should be turned off.
In step S1313, the CPU 31 turns off the solenoid 28 at time t3 'and reduces the drive current to I1.

● Reduction of conveyance advance ・ In S1321, the CPU 31 reduces the rotation speed of the motor M1 to S2. The rotation speed S2 is determined depending on the degree of conveyance advance.
In step S1322, the CPU 31 determines the time t3 "at which the solenoid 28 should be turned off.
At S1323, the CPU 31 turns off the solenoid 28 at time t3 "and reduces the drive current to I1.

  FIG. 14 is a flowchart showing the transport control of the second embodiment. S1307, S1312, S1313, S1322 and S1323 of FIG. 13 are replaced by S1401 in FIG. When the number of steps reaches N3 in S1401, the CPU 31 turns off the solenoid 28 and reduces the drive current from I2 to I1.

  FIG. 15 is a flowchart showing the transport control of the third embodiment. S1307, S1313 and S1323 in FIG. 13 are replaced with S1501, S1502 and S1503 in FIG.

  S1501 is a step executed when there is no conveyance delay and there is no conveyance advance. In S1501, the CPU 31 turns off the solenoid 28 at a threshold value timing that is the closest to and exceeds the time t3, and reduces the drive current to I1. The CPU 31 compares the first threshold value timing Th1, the second threshold value timing Th2, and the third threshold value timing Th3, which are the threshold values, with the time point t3 to identify the threshold value timing that exceeds the time point t3 and is the closest.

  S1502 is a step executed when there is a conveyance delay. In S1502, the CPU 31 turns off the solenoid 28 at the threshold value timing that is the closest to and exceeds the time t3 ′, and reduces the drive current to I1. The CPU 31 compares the first threshold value timing Th1, the second threshold value timing Th2, and the third threshold value timing Th3, which are the threshold values, with the time point t3 ′ to specify the closest threshold value timing that exceeds the time point t3 ′.

  S1503 is a step executed in a case where there is a conveyance advance. In S1503, the CPU 31 turns off the solenoid 28 at the threshold value timing that is closest to and exceeds the time point t3 "to reduce the drive current to I1. By comparing the timing Th3 and the time t3 ", the threshold timing that exceeds and is closest to the time t3" is specified.

<Summary>
As shown in FIG. 1, the feeding tray 7 functions as a stacking unit that stacks the sheets S. The feeding roller 8 functions as a feeding roller that feeds the sheets S stacked on the stacking unit. The transport roller 16 is arranged on the downstream side of the feed roller 8 in the transport direction of the sheet S, and functions as a transport roller that transports the sheet S to the transfer unit. As shown in FIG. 2, the motor M1 functions as a motor that drives the feeding roller 8 and the conveying roller 16. The drive circuit 33 functions as a drive circuit that drives the motor M1. The solenoid 28 is arranged between the motor M1 and the feeding roller 8 and functions as a switching unit that switches whether to transmit the driving force of the motor M1 to the feeding roller 8. The sheet sensor 17 functions as a detection unit that detects a sheet at a predetermined detection position on the sheet S conveyance path. The speed control unit 34 functions as a speed control unit that synchronizes the timing when the sheet arrives at the transfer unit and the timing when the toner image arrives at the transfer unit. The speed control unit 34 responds to the difference between the time t1 ′ and t1 ″, which are the actual timings when the sheet is detected by the detection means, and the time t1, which is the specified timing at which the sheet is expected to arrive at the detection position. The current control unit 35 synchronizes with the solenoid 28 transmitting and shutting off the driving force of the motor M1 to the feeding roller 8 to temporarily increase or decelerate the rotation speed of the motor M1. In this way, the drive current of the motor M1 increases and decreases in synchronization with the timing at which the drive force of the motor M1 is transmitted to and cut off from the feeding roller 8, and thus the drive circuit. The temperature rise of the drive circuit 33 is suppressed, and in the comparative example, the drive current decreases after the timing of turning off the solenoid 28, so that the temperature rise of the drive circuit 33 occurs. Since the drive current decreases in synchronization with the timing when 28 is turned off, the temperature rise of the drive circuit 33 is suppressed.

  The current controller 35 increases the drive current of the motor M1 at the start timing (example: t0) when the solenoid 28 starts transmitting the drive force of the motor M1 to the feeding roller 8. The current controller 35 reduces the drive current of the motor at the timing when the solenoid 28 is turned off (eg, t3, t3 ′, t3 ″), which suppresses the temperature rise of the drive circuit 33. The timing of turning off is the timing at which the solenoid 28 ends (blocks) the transmission of the driving force of the motor M1 to the feeding roller 8.

  The time calculation unit 38 ends the timing according to the difference between the actual timing at which the sheet S is detected by the sheet sensor 17 and the specified timing (eg, t1) at which the sheet S is expected to arrive at the detection position. (Example: t3, t3 ′, t3 ″) may be determined. The actual timing is, for example, time t1 ′ or time t1 ″. The determined end timing is, for example, t3, t3 ′, t3 ″. The solenoid 28 causes the feed roller 8 to reach the end timing (eg, t3, t3 ′, t3 ″) determined by the time calculation unit 38. The transmission of the driving force of the motor M1 to is ended. The current controller 35 reduces the drive current of the motor M1 at the determined end timing. As a result, the temperature rise of the drive circuit 33 is suppressed.

  As shown in FIG. 2, a tooth-chipped gear 27 and a tooth-chipped front-stage gear 30 that meshes with the tooth-chipped gear are provided in the transmission path that transmits the driving force of the motor M1 to the feeding roller 8. The solenoid 28 starts transmission of the driving force to the feeding roller 8 by meshing the toothless gear 27 and the toothless pre-stage gear 30. The solenoid 28 cuts off the transmission of the driving force to the feeding roller 8 by releasing the meshing between the toothless gear 27 and the toothless pre-stage gear 30. The motor M1 is configured to rotate the tooth-chipped gear 27 once in order to feed the sheet S during the rotation period from the start timing to the end timing. The time calculation unit 38 may add a margin according to the tolerance of the tooth-missing gear to the end timing determined according to the difference. The current controller 35 may reduce the drive current at the end timing when the margin is added.

  As shown in FIG. 7, the counter 71 functions as a measuring unit that starts measuring the number of drive pulses supplied to the motor M1 at the start timing (eg, time t0). The current controller 35 reduces the drive current of the motor M1 when the number of drive pulses measured by the counter 71 reaches a predetermined number (eg, N3) corresponding to the end timing. As described above, the number of steps required for the tooth-chipped gear 27 to make one rotation is constant without depending on the rotation speed of the motor M1. Therefore, by paying attention to the number of steps, the timing at which the drive current is reduced is relatively easily determined. The predetermined number (eg, N3) may be the number of drive pulses required to rotate the tooth-chipped gear 27 once. The CPU 31 may function as an addition unit that adds a margin according to the tolerance of the tooth-chipped gear 27 to a predetermined number (eg, N3). The current controller 35 may decrease the drive current of the motor M1 when the number of drive pulses measured by the counter 71 reaches a predetermined number (eg, N3 + margin) to which a margin has been added.

  As shown in FIG. 9, the determination unit 91 compares the end timing determined by the time calculation unit 38 with a plurality of threshold timings, and identifies the threshold timing that is after the end timing and is closest to the end timing. Good. The current controller 35 may reduce the drive current at the threshold timing specified by the determiner 91. The current control unit 35 may reduce the drive current at the timing when the margin according to the tolerance of the tooth-chipped gear 27 is added to the threshold timing specified by the determination unit 91.

  As shown in FIG. 1, in the sheet S conveyance path, between the first reference position (eg, P1) located downstream of the detection position in the sheet S conveyance direction and the first reference position and the transfer portion. There is a second reference position (example: P2) in. The speed control unit 34 reduces the conveyance delay and the conveyance advance of the sheet S by temporarily increasing or decreasing the rotation speed of the motor M1 in the conveyance section from the detection position to the first reference position. The end timing at which the solenoid 28 ends the transmission of the driving force of the motor M1 to the feeding roller 8 may be the timing at which the sheet S reaches the second reference position.

  The elapsed time Tx from the timing when the sheet S is detected by the sheet sensor 17 to the end timing may be obtained from the following formula.

Tx = L1 / (a × Si) + L2 / (a × S1) (11)
Here, Si is the rotation speed (for example, S2, S3) of the motor M1 applied in the transport section from the detection position to the first reference position. a is a coefficient for converting the rotation speed of the motor M1 into the conveyance speed of the sheet S.

  7 ... feed tray, 8 ... feed roller, 16 ... conveying roller, 17 ... sheet sensor M1 ... motor, 28 ... solenoid, 31 ... CPU, 33 ... .Drive circuit,

Claims (12)

A stacking unit for stacking sheets,
A feeding roller that feeds the sheets stacked on the stacking unit,
A conveyance roller arranged downstream of the feeding roller in the sheet conveyance direction and configured to convey the sheet to the transfer unit;
A motor for driving the feeding roller and the conveying roller,
A drive circuit for driving the motor,
Switching means arranged between the motor and the feeding roller, for switching whether to transmit the driving force of the motor to the feeding roller;
Detection means for detecting the sheet at a predetermined detection position in the sheet conveyance path,
The rotational speed of the motor is temporarily increased or increased according to the difference between the actual timing at which the sheet is detected by the detection unit and the specified timing at which the sheet is expected to arrive at the detection position. Speed control means for synchronizing the timing when the sheet arrives at the transfer portion and the timing when the toner image arrives at the transfer portion by decelerating;
An image forming apparatus, comprising: current control means for increasing and decreasing a drive current of the motor in synchronization with transmission and interruption of the drive force of the motor to the feeding roller by the switching means.   The current control means increases the drive current of the motor at a start timing when the switching means starts transmitting the driving force of the motor to the feeding roller, and the switching means causes the motor to feed the feeding roller. The image forming apparatus according to claim 1, wherein the drive current of the motor is reduced at an end timing at which the transmission of the driving force is ended. The driving force of the motor to the feeding roller according to the difference between the actual timing at which the sheet is detected by the detection unit and the specified timing at which the sheet is expected to arrive at the detection position. Further comprising a determining means for determining the end timing for ending the transmission of
The switching means ends the transmission of the driving force of the motor to the feeding roller at the end timing determined by the determining means,
The image forming apparatus according to claim 2, wherein the current control unit reduces the drive current of the motor at the end timing determined by the determination unit. A toothless gear provided on a transmission path for transmitting the driving force of the motor to the feeding roller; and a front gear that meshes with the toothless gear,
The switching means starts transmission of the driving force to the feeding roller by meshing the partly tooth-missing gear and the front gear, and releasing the meshing of the partly toothless gear and the front gear. Cut off the transmission of the driving force to the feeding roller,
The motor is configured to rotate the tooth-chipped gear once in order to feed the sheet during a rotation period from the start timing to the end timing.
The determining means adds a margin according to the tolerance of the toothless gear to the end timing determined according to the difference,
The image forming apparatus according to claim 3, wherein the current control unit reduces the drive current at the end timing when the margin is added. Further comprising a measuring means for starting measurement of the number of drive pulses supplied to the motor at the start timing,
3. The current control means reduces the drive current of the motor when the number of the drive pulses measured by the measuring means reaches a predetermined number corresponding to the end timing. The image forming apparatus according to item 1. The motor is a stepping motor,
The image forming apparatus according to claim 5, wherein the measuring unit measures the number of steps of the stepping motor based on the number of drive pulses. A toothless gear provided on a transmission path for transmitting the driving force of the motor to the feeding roller; and a front gear that meshes with the toothless gear,
The switching means starts transmission of the driving force to the feeding roller by meshing the partly tooth-missing gear and the front gear, and releasing the meshing of the partly toothless gear and the front gear. Cut off the transmission of the driving force to the feeding roller,
The motor makes one rotation of the partly tooth-missing gear in order to feed the sheet in a rotation period from the start timing to the end timing,
The image forming apparatus according to claim 6, wherein the predetermined number is the number of the drive pulses required to rotate the gear having partly omitted teeth. Further comprising an adding means for adding a margin according to the tolerance of the toothless gear to the predetermined number,
The current control means decreases the drive current of the motor when the number of the drive pulses measured by the measuring means reaches the predetermined number to which the margin is added. 7. The image forming apparatus according to item 7. Comparing the end timing determined by the determining means with a plurality of threshold timings, and further comprising specifying means for specifying a threshold timing that is later than the end timing and closest to the end timing,
The image forming apparatus according to claim 3, wherein the current control unit reduces the drive current at the threshold timing specified by the specifying unit. The plurality of threshold timings have a first threshold timing, a second threshold timing and a third threshold timing,
The first threshold timing is more than the end timing when the rotation speed is not increased or decelerated by the detection of the sheet at a specified timing at which the sheet is expected to arrive at the detection position. It's the previous timing,
The second threshold timing is more than the end timing when the rotational speed is not increased or decelerated by the detection of the sheet at a specified timing at which the sheet is expected to arrive at the detection position. It is a later timing,
The image forming apparatus according to claim 9, wherein the third threshold timing is a timing later than the second threshold timing. A toothless gear provided on a transmission path for transmitting the driving force of the motor to the feeding roller; and a front gear that meshes with the toothless gear,
The switching means starts transmission of the driving force to the feeding roller by meshing the partly tooth-missing gear and the front gear, and releasing the meshing of the partly toothless gear and the front gear. Cut off the transmission of the driving force to the feeding roller,
The motor is configured to rotate the tooth-chipped gear once in order to feed the sheet during a rotation period from the start timing to the end timing.
11. The current control means reduces the drive current at a timing when a margin according to the tolerance of the toothless gear is added to the threshold timing specified by the specifying means. The image forming apparatus described. The sheet conveyance path has a first reference position downstream of the detection position in the sheet conveyance direction and a second reference position between the first reference position and the transfer section. ,
The speed control unit reduces the conveyance delay and the conveyance advance of the sheet by temporarily increasing or decreasing the rotation speed of the motor in the conveyance section from the detection position to the first reference position,
The image according to claim 2, wherein the ending timing when the switching unit finishes transmitting the driving force of the motor to the feeding roller is a timing when the sheet reaches the second reference position. Forming equipment.

Images