JP4822762B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a color printer or a color copying machine, and more particularly to a drive control apparatus and method for an electrophotographic image forming apparatus having a plurality of image forming units, and a recording material conveyance control method.

  As a conventional image forming apparatus, when a recording medium is transported using a plurality of transporting units, an image that controls the plurality of transporting units so that a certain degree of deflection (loop) is formed on the recording medium by the plurality of transporting units. Forming devices are known.

  Here, as an example of the image forming apparatus, a transfer unit that transfers the toner image on the photosensitive drum to the recording medium, and a fixing unit that fixes the toner image on the recording medium conveyed from the transfer unit by, for example, a heat roller method, There is known an electrophotographic image forming apparatus having the following.

  FIG. 2 is a diagram illustrating a configuration for controlling the loop to be held at a constant amount. Reference numeral 203 denotes a developing cartridge drive motor for driving a developing cartridge located on the most downstream side in the conveying direction, including a photosensitive drum on the most downstream side in the conveying direction, and a driving roller for driving an endless belt. A motor 201 is a CPU for controlling the developing cartridge drive motor 203 and the fixing drive motor, 202 is a motor driver for driving the motor in response to a control command from the CPU 201, and 112 is a proximity of the photosensitive drum and the transfer roller. A loop detection sensor 113 for determining whether or not the loop formed on the sheet by the transfer unit and the fixing roller has reached a certain amount, 113 is provided downstream of the fixing roller 110 in the sheet conveyance direction, and detects the passage of the sheet This is a paper detection sensor. When data to be printed is sent from a PC (personal computer) as a data supply means to the printer and image formation according to the printer engine system is completed and the printer is ready, paper is supplied from the paper cassette and reaches the conveyor belt. Then, the paper is sequentially conveyed to the image forming units of the respective colors by the conveyance belt. The image signals of each color are sent to each laser scanner at the same timing as the paper transport by the transport belt, an electrostatic latent image is formed on the photosensitive drum, the toner is developed by the developing device, and transferred onto the paper by the transfer unit. Is done. Thereafter, the sheet is separated from the conveyance belt, and the toner image is fixed on the sheet by heat with a fixing device and is discharged to the outside.

  In such an electrophotographic image forming apparatus, if the transfer speed that the transfer unit and the fixing unit give to the recording medium are different due to changes in the diameter of the heat roller of the fixing unit, the transfer unit and the fixing unit In some cases, image degradation may occur due to pulling of the recording medium or causing an unnecessarily large loop in the recording medium.

  In order to solve this problem, a detection unit for detecting a loop formed on the recording medium by the transfer unit and the fixing unit is provided, and the target speed of the fixing drive motor 204 is a binary value that is earlier than a reference value and lower than a reference value. Either of the above is selected according to the loop detection result, and a method of controlling the conveying means so as to hold the loop at a constant amount is used (see Patent Document 1).

  FIG. 3 is a diagram illustrating the configuration of the loop detection sensor. Reference numeral 302 denotes a mechanical flag that can be moved by contact with the paper, and reference numeral 301 denotes a photo interrupter that detects light shielding. As shown in FIG. 3B, when no loop is formed on the paper, the paper contact member 302a is not pushed by the paper 205, and the light shielding member 302b at the end of the mechanical flag 302 shields the photointerrupter 301 from light. (Loop sensor OFF) When the loop is formed on the paper, the mechanical flag is rotated by pressing the paper contact member 302a of the mechanical flag, and accordingly, the light shielding member 302b that shields the photo interrupter 301 is rotated. The light shielding is released (loop sensor “ON” / (A) in FIG. 3).

  FIG. 4 is a timing chart when the conveying means is controlled to hold the loop at a constant amount. When the paper that has passed through the transfer portion is detected by the paper detection sensor, the CPU selects a value Vd that is slower than the reference value as the target speed of the fixing drive motor 204, and transmits a phase signal to the motor driver. The motor driver excites the motor winding (stator) according to the phase signal. Since the conveyance speed of the fixing unit is slower than the reference value, the recording medium between the most downstream transfer unit and the fixing unit forms a deflection (loop). When the loop exceeds a certain amount, the output signal of the loop detection sensor is switched from “OFF” to “ON”. When the CPU detects that the output signal of the loop detection sensor is switched from “OFF” to “ON”, the CPU selects a value Vu earlier than the reference value as the target speed of the fixing drive motor 204 and transmits the phase signal to the motor driver. . The motor driver excites the motor winding (stator) according to the phase signal. Since the conveyance speed of the fixing unit is faster than the reference value, the loop formed on the recording medium between the most downstream transfer unit and the fixing unit gradually disappears. When the loop falls below a certain amount, the output signal of the loop detection sensor switches from “ON” to “OFF”. When the CPU detects that the output signal of the loop detection sensor is switched from “ON” to “OFF”, the CPU selects a value Vu earlier than the reference value as the target speed of the fixing drive motor 204 and transmits a phase signal to the motor driver. The CPU detects the timing at which the trailing edge of the recording medium passes through the most downstream transfer unit by the count of the CPU internal counter of the drive pulse for driving the transfer unit drive motor. When the CPU internal counter reaches the count value C1 of the timing when the trailing edge of the recording medium passes the most downstream transfer portion, the reference value Vref is selected as the target speed of the fixing drive motor 204, and the phase signal is transmitted to the motor driver. The fixing drive motor 204 is controlled to hold the loop at a constant amount by sequentially performing this control in accordance with the output signal of the loop detection sensor.

  In addition, there is an image forming apparatus that uses a stepping motor as a drive source in order to cope with recent downsizing and cost reduction of the image forming apparatus.

JP-A-10-340012

  However, the above conventional example has the following drawbacks.

  FIG. 5 is a diagram for explaining a change in the speed of the motor. G501 is a target speed of the fixing drive motor, G502 is a fixing drive motor speed when a motor with a large inertia is used as the fixing drive motor, and G503 is a fixing drive motor speed when a motor with a small inertia is used as the fixing drive motor. .

  When the conventional control is performed, the target speed is rapidly switched from the value Vu earlier than the reference value to the value Vd slower than the reference value in order to increase the loop amount of the recording medium. Conversely, in order to reduce the loop amount of the recording medium, the target speed is rapidly switched from the value Vd slower than the reference value to the value Vu earlier than the reference value. The stepping motor is a motor with a small inertia due to its structure. When a motor having a large inertia, such as a DC brushless motor, is used as the fixing drive motor, the motor speed gradually changes to the target speed without following the rapid change of the target speed (G502), which is not preferable.

  On the other hand, when the stepping motor is used as the fixing drive motor, the motor speed follows the rapid switching of the target speed (G503). Noise will increase.

  SUMMARY An advantage of some aspects of the invention is that it provides a drive control apparatus and method for a high-precision image forming apparatus that is low in noise and does not cause image defects.

To achieve the above object, the present invention provides a transfer means for transferring an image to a recording material, a fixing means for fixing an image transferred to the recording material by the transfer means, the transfer means and the fixing means. When the recording material is conveyed by the means, a detecting means for detecting the deflection generated in the recording material, and when the detection means detects the deflection, the conveying speed for conveying the recording material by the fixing means is faster than a reference speed. When the first target speed is switched and the deflection is no longer detected by the detection means, the second target speed slower than the reference speed is switched to occur on the recording material between the transfer means and the fixing means. controls the amount of deflection, said at first switching period the conveying speed from the first target speed until switching to the second target speed, the transport speed of the first Slower than standard speed, and the stepwise switched second faster plurality of intermediate speed than the target speed of, and the second said transport speed from said second target speed until switched to the first target speed in switching period, and a control means for stepwise switching the conveying speed by the plurality of intermediate speed, the control means, the plurality of such said second switching period is longer than the first switching time period The switching of the intermediate speed is controlled.

  According to the present invention, at the time of switching the recording material conveyance speed of the fixing unit, acceleration between the current speed and the target speed is accelerated or decelerated at a plurality of intermediate speeds, so that high accuracy with low noise and no occurrence of image defects is achieved. An image forming apparatus can be provided.

  Further, according to the present invention, at least one of the reference speed, the first target speed, and the second target speed is determined according to the material of the recording material. It is possible to provide a highly accurate image forming apparatus that does not cause image defects.

  Furthermore, according to the present invention, by using a stepping motor as a means for driving the fixing means, it is possible to provide a high-precision image forming apparatus that does not cause image defects with an inexpensive configuration.

  Further, according to the present invention, the switching interval until switching from the first target speed to the second target speed and the switching interval until switching from the second target speed to the first target speed are independently determined. Accordingly, it becomes possible to control the driving of the fixing unit suitable for the loop generation gain and the cancellation gain peculiar to the paper, and it is possible to provide a high-precision image forming apparatus with lower noise and no occurrence of image defects.

Hereinafter, the present invention will be described in detail based on the illustrated embodiments.
(First embodiment)
FIG. 11 shows a printer engine portion of a color image forming apparatus having image forming means for four colors, that is, yellow Y, magenta M, cyan C, and black Bk, according to an embodiment of the present invention. Y, M, C, and Bk) are photosensitive drums that form an electrostatic latent image (Y, M, C, and Bk are for Y, M, C, and Bk, respectively), 101 (Y, M, and C). , Bk) is a laser scanner that performs exposure according to the image signal and forms an electrostatic latent image on the photosensitive drum 103 (Y, M, C, Bk), and 106 sequentially conveys the paper to the image forming unit of each color. An endless conveying belt also serving as a transfer belt, 102 (Y, M, C, Bk) is a developing device, 104 (Y, M, C, Bk) is a developing roller, and 105 (Y, M, C, Bk) is a developing device. Inside the transport belt 106 and facing each photosensitive drum 103 A transfer roller 107 is connected to a driving means (not shown) including a motor and a gear (not shown). A driven roller for applying tension, a fixing roller 110 for heating the paper, and a pressure roller 111 for conveying the paper and applying a rotational force to the fixing roller 110 to pressurize the paper. As the fixing roller 110, a coil is arranged in a film-like electromagnetic induction heat generating rotator, and an electric current is passed through the coil to heat the outer film-like electromagnetic induction heat generating rotator, A device having a built-in heat source such as a heater is used.

  Reference numeral 122 denotes a cassette that stores sheets, 221 denotes a pickup roller that feeds the sheets in the cassette 122 one by one, and 120 denotes a registration roller that supplies the sheets fed by the pickup roller 121 to the image forming unit.

  A loop 112 determines whether or not the loop formed on the sheet has reached a certain amount based on the difference in sheet conveyance speed between the fixing roller 110 and the transfer unit where the photosensitive drum 103 and the transfer roller 105 are close to each other. The detection sensor has the same structure as that of FIG. A paper detection sensor 113 is provided downstream of the fixing roller 110 in the paper conveyance direction and detects the passage of paper. The mechanism portion for controlling the loop formed by the paper is the same as that shown in FIG.

  FIG. 14 is a diagram mainly showing a configuration for controlling a paper loop in the color image forming apparatus which is a feature of the present invention. 201 is a CPU for controlling the entire color image forming apparatus, and 206 is an operation of the CPU 201. A RAM that provides an area, 207 is a ROM that stores a control program of the CPU 201 including the control procedures of FIGS. 6, 9, 10, and 12 described later, and 208 is provided on the upper portion of the color image forming apparatus and is required by the user. The CPU 201 also refers to the information input from the operation unit 208. The operation unit 208 inputs various operation information (number of prints, paper size, etc.). Reference numeral 209 denotes an external image data supply device, for example, an input unit for inputting data to be printed today supplied from the PC 210. The data input to the input unit is temporarily stored in the RAM 206, and the data in the RAM 206 is stored in the RAM 206. On the other hand, the CPU 201 executes an image forming process corresponding to the printer engine method.

  The fixing driving motor (204) for driving the fixing roller 110 and the pressure roller 111 is formed of a stepping motor, and includes a developing cartridge driving motor 203 for driving the developing cartridge at the most downstream side in the transport direction including the driving roller 107 for driving the endless belt. Consists of a stepping motor. In this embodiment, the sheet detection sensor 113 is provided downstream of the fixing roller 110 in the sheet conveyance direction, but may be provided at an arbitrary position upstream of the fixing roller 110 in the conveyance direction.

  When data to be printed is sent from the external image data supply device such as a PC to the color image forming device, and image formation according to the printer engine system is completed and the printer is ready, paper is supplied from the paper cassette and conveyed. The paper reaches the belt, and the paper is sequentially conveyed to the image forming units of the respective colors by the conveyance belt. The image signals of each color are sent to each laser scanner 101 at the same timing as the conveyance of the sheet by the conveyance belt, an electrostatic latent image is formed on the photosensitive drum 103, the toner is developed by the developing device 102, and the sheet is conveyed by the transfer unit. Transcribed above. In FIG. 11, images are sequentially formed in the order of C, M, Y, and Bk. Thereafter, the sheet is separated from the conveyance belt, and the toner image is fixed on the sheet by heat with a fixing device and is discharged to the outside.

  Hereinafter, characteristic operations in the present embodiment will be mainly described.

  FIG. 6 is a flowchart for explaining the operation of the image forming apparatus in this embodiment. In step S602, the input unit monitors whether image data transmitted from an external image data supply apparatus such as a video controller of the PC 210 has been received.

  In step S603, an image forming operation is started in response to reception of image data (YES in step S602), and a paper feed unit which is a paper feed port designated by the user from the video controller, the operation panel of the operation unit, or the like. The paper loaded on the cassette (shown as a cassette 122 in FIG. 11) is fed by a pickup roller 121 and a registration roller 120 between the conveyance belt 106 constituting the image forming unit and the uppermost photosensitive drum 103c.

  In step S604, the speed setting value of the fixing drive motor 204 is set to the speed reference value Vref. This operation is performed by transmitting a control command from the CPU 201 to the motor driver 202 and controlling the rotation speed of the developing cartridge drive motor 203. The fed paper is transported at a process speed, and when passing through a C (cyan) developing cartridge, a C (cyan) toner image formed on the photosensitive drum 103C is transferred, and thereafter Then, a Y (yellow) toner image is produced by a Y (yellow) developer cartridge in the order of the transport direction, an M (magenta) toner image is produced by an M (magenta) developer cartridge, and finally a Bk (black) developer cartridge is produced by Bk The (black) toner image is sequentially transferred onto the paper, and finally the full-color toner image is transferred onto the paper.

In step S605, the speed of the fixing drive motor 204 is set.
Vu = Gu × Vref (where Gu> 1) (Equation 1)
Vd = Gd × Vref (where Gd <1) (Equation 2)
Here, Gu is a gain, and Vu can be arbitrarily set as long as it is higher than the process speed. However, in this embodiment, as an example, Vu is 105% of the process speed, Vu = 1. 05 × Vref. Gd is a gain, and Vd can be arbitrarily set as long as it is lower than the process speed. However, in this embodiment, as an example, Vd is 95% of the process speed Vd = 0.95 × Vref.

  In step S606, it is monitored whether or not the sheet on which the full-color toner image has been transferred is conveyed to reach the sheet detection sensor 113 and the output of the sensor is turned on.

  In step S607, in response to the detection of the leading edge of the sheet (YES in step S606), the counter Cnt1 managed by the CPU 201 is reset to 0, and the drive pulse count of the developing cartridge drive motor 203 is started.

  In step S6072, the target speed of the fixing drive motor 204 is switched in order of Vref, Vm1, and Vd for each N1 based on a timer managed by the CPU. Here, N1 is a motor target speed switching time, and is arbitrarily determined within a range of N1> 0. Vm1 is the intermediate target speed 1, and is arbitrarily determined within the range of Vd <Vm1 <Vref.

  In step S608, it is monitored whether or not the counter Cnt1 that started counting in step S607 has reached C1. C1 is a sheet detection sensor 131, which corresponds to the timing from when the leading edge of the sheet that has passed through the fixing device is detected until the trailing edge of the sheet exits the most downstream transfer portion.

  Next, the case where the counter Cnt1 is less than C1 will be described. In this case, a sheet exists in the most downstream transfer unit-fixing unit, and a sheet loop can be formed.

  In step S609, the drive pulses of the developing cartridge drive motor 203 are cumulatively counted in the counter Cnt1.

  In step S610, it is monitored whether or not the output signal of the loop detection sensor 112 is “ON”. When the output signal of the loop detection sensor 112 is “ON”, it is monitored whether or not the current target speed of the fixing drive motor 204 is Vd. If the current target speed of the fixing drive motor 204 is not Vd (NO in step S611), the process returns to step S609 and the above processes are executed in order.

  In step S612, if the output signal of the loop detection sensor 112 is “ON” and the current target speed of the fixing drive motor 204 is Vd (YES in step S611), the process proceeds to step S612 and the target of the fixing drive motor 204 is reached. The target speed is switched in the order of Vd, Vm1, Vref, Vm2, and Vu for each N1 based on a timer (not shown). Here, Vm2 is the intermediate target speed 2, and is arbitrarily determined within the range of Vref <Vm2 <Vu.

  Thereafter, the process returns to step S608, and the above processes are executed in order.

  If the output signal of the loop detection sensor 112 is not “ON” (in the case of “OFF”) in step S610, it is monitored whether or not the current target speed of the fixing drive motor 204 is Vu. If the current target speed of the fixing drive motor 204 is not Vu (NO in step S616), the process returns to step S609 and the above processes are executed in order.

  When the output signal of the loop detection sensor 112 is “OFF” and the current target speed of the fixing drive motor 204 is Vu (YES in step S616), the process proceeds to step S617, and the target speed of the fixing drive motor 204 is not shown. Based on the timer, the target speed is switched in the order of Vu, Vm2, Vref, Vm1, and Vd every N1.

  Thereafter, the process returns to step S608, and the above processes are executed in order.

  Next, a case where the count value Cnt1 matches C1 in step S608 will be described. In this case, the paper has finished passing through the most downstream transfer portion, and a paper loop cannot be formed.

  In step S621, it is determined whether or not there is a page to continue image formation. If there is a page to continue image formation, the process returns to step S603, and if not, the image formation operation is terminated.

  FIG. 7 is a timing chart when the fixing drive motor, which is the fixing drive source means, is controlled so as to hold the loop in the present embodiment at a constant amount. When the paper detection sensor 113 detects the paper, the paper loop is not yet formed. Therefore, after the target speed of the fixing drive motor 204 is switched to the intermediate target speed Vm1 for the time N1, the value is slower than the reference value. Switch to Vd. Accordingly, the paper loop is gradually formed. When the loop detection sensor detects “ON” while driving the fixing drive motor 204 with Vd, it is determined that the paper loop has reached a certain amount, and the target speed is set to Vm1, Vref, Vm2, Vu from Vd every time N1. Switch in order. Therefore, the loop is gradually eliminated. When the loop detection sensor detects “OFF” while driving the fixing drive motor 204 with Vu, it is determined that the paper loop has fallen below a certain amount, and the target speed is changed from Vu to Vm2, Vref, Vm1, and Vd every time N1. Switch in order. Therefore, the loop is gradually formed.

  As described above, when the target speed of the fixing drive motor is switched, by executing acceleration or deceleration at an intermediate speed between the current speed and the target speed, rapid speed fluctuations can be effectively suppressed, and fixing can be performed. Since vibration of the drive motor can be suppressed, it is possible to provide a highly accurate image forming apparatus that is low in noise and does not cause image defects. Note that the speed gradient at the time of deceleration control from the speed Vd to Vu is determined by the value of N1, but this speed gradient is based on the speed gradient determined by the inertia of the fixing drive motor when the target speed is directly switched from Vd to Vu. By lowering the value, further lower noise can be obtained.

(Second embodiment)
Only differences from the first embodiment will be described. The configurations of FIGS. 11, 14 and 3 are the same as those of the first embodiment.

  In the first embodiment, the speed reference value of the fixing drive motor 204 does not depend on the material of the paper to be conveyed, but in this embodiment, the speed reference value of the fixing drive motor 204 is stored in association with each paper material. It is characterized by keeping.

  The nip thickness of the fixing roller 110 changes depending on materials such as the type and thickness of the paper to be conveyed, and the paper conveyance speed changes. The material such as the type and thickness of the paper can be input by the user from the operation unit 208, for example.

  The table shown in FIG. 8 is a table showing the relationship between the paper material and the speed reference value, which is the content of the paper material table in this embodiment. This table can be configured in the RAM 206 or the ROM 207, for example. The CPU 201 calculates the driving speed of the fixing drive motor 204 by referring to the speed reference value of the fixing drive motor 204 from the sheet material table for each material of the paper to be conveyed. In this example, as an example, the speed reference value of the fixing drive motor 204 for each of the four types of materials is stored in the sheet material table for reference.

  FIG. 9 is a flowchart for explaining the operation of the image forming apparatus in this embodiment. First, from step S901 to step S903, the same operation as that of steps S601 to 603 in the first embodiment is performed. Next, in step S9032, a speed reference value suitable for the paper to be conveyed is selected from the paper material table shown in FIG. 8, and the selected value is set to Vref in step S904. In the present embodiment, as an example, it is assumed that the paper material is X2. In this case, Vref2 is set as the speed reference value Vref as the speed setting value of the fixing drive motor 204. After that, from step S905 to step S922, the same operation as step S605 to 622 in the first embodiment is performed.

  As described above, by setting different speed reference values for each paper material to be conveyed, regardless of the paper material, when the target speed of the fixing drive motor is switched, it is intermediate between the current speed and the target speed. By accelerating or decelerating at a speed, sudden speed fluctuations are effectively suppressed, and vibration of the fixing drive motor is suppressed. Therefore, a highly accurate image forming apparatus that is low in noise and does not cause image defects Can be provided.

(Third embodiment)
Only differences from the first and second embodiments will be described. The configurations of FIGS. 11, 14 and 3 are the same as those of the first embodiment.

  In the first and second embodiments, there is one intermediate speed at the time of switching the target speed of the fixing drive motor, but this embodiment is characterized in that acceleration or deceleration is performed at a plurality of intermediate speeds.

  FIG. 10 is a flowchart for explaining the operation of the image forming apparatus in this embodiment. First, in steps S1001 to S1007, the same operations as in steps S601 to S607 in the first embodiment are performed.

Next, in step S10072, the target speed of the fixing drive motor 204 is determined every time N1 based on a timer (not shown) based on the following formula 5, and the target speed is switched.
V = V− (Vref−Vd) / (L1 / 2) (where L1> 0) (Equation 5)
In this embodiment, as an example, when Vd = 0.95 × Vref and L1 = 10, (Vref−Vd) / (L1 / 2) = 0.01 × Vref, which is 95% of the process speed from the process speed. The target speed is decreased by 1% every time N1 until the speed.

  Thereafter, operations from step S1008 to step S1011 are the same as those in steps S608 to S611 in the first embodiment.

In step S1012, if the output signal of the loop detection sensor 112 is “ON” and the current target speed of the fixing drive motor 204 is Vd (YES in step S1011), the target speed of the fixing drive motor 204 is expressed by the following equation (3). Is determined for each N1 based on a timer (not shown), and the target speed is switched.
V = (Vu−Vd) / L1 + V (where L1> 0) (Equation 3)
Here, L1 is an intermediate target speed number, and is arbitrarily set. In this embodiment, as an example, if Vu = 1.05 × Vref, Vd = 0.95 × Vref, and L1 = 10, then (Vu−Vd) /L1=0.01×Vref, which is 95% of the process speed. The target speed is increased by 1% every time N1 from the speed of 105 to the speed of 105% of the process speed.

  Thereafter, step S1016 performs the same operation as step S616 in the first embodiment.

In step S1017, when the output signal of the loop detection sensor 112 is “ON” and the current target speed of the fixing drive motor 204 is Vu (YES in step S1016), the target speed of the fixing drive motor 204 is expressed by the following equation (4). Based on the CPU-controlled timer for each N1, and the target speed is switched.
V = V− (Vu−Vd) / L1 (where L1> 0) (Equation 4)
In this embodiment, as an example, if Vu = 1.05 × Vref, Vd = 0.95 × Vref, and L1 = 10, then (Vu−Vd) /L1=0.01×Vref, which is 105% of the process speed. The target speed is decreased by 1% every time N1 from the speed of 95 to 95% of the process speed.

  Thereafter, from step S1021 to step S1022, operations similar to those in steps S621 to 622 in the first embodiment are performed.

  FIG. 1 is a timing chart when the fixing drive motor is controlled so as to hold the loop in a constant amount in this embodiment. When the paper detection sensor 113 detects the paper, the paper loop has not yet been formed. Therefore, the target speed of the fixing drive motor 204 is changed from the reference speed Vref to the intermediate target speed number L1 / 2 every motor speed switching time N1. , And set to a value Vd slower than the reference value. When the loop detection sensor detects “ON” while driving the fixing drive motor 204 with Vd, the target speed is accelerated from Vd at a plurality of intermediate speeds every time N1 and switched to Vu. In one example of this embodiment, the target speed of the fixing drive motor 204 is increased by 1% every time N1 in 10 steps from 95% of the process speed to 105% of the process speed. If the loop detection sensor detects “OFF” while driving the fixing drive motor 204 with Vu, the target speed is decelerated from Vu at a plurality of intermediate speeds every time N1 and switched to Vd. In this example, the target speed of the fixing drive motor 204 is decreased by 1% every time N1 in 10 steps from 105% of the process speed to 95% of the process speed.

  As described above, when the target speed of the fixing drive motor is switched, acceleration between the current speed and the target speed is accelerated or decelerated at a plurality of intermediate speeds, so that rapid speed fluctuations can be effectively suppressed and fixing driving can be performed. Since the vibration of the motor is suppressed, it is possible to provide a highly accurate image forming apparatus with lower noise and no image defects.

(Fourth embodiment)
Only differences from the first, second, and third embodiments will be described. The configurations of FIGS. 11, 14 and 3 are the same as those of the first embodiment.

  In the first, second, and third embodiments, the target speed switching time of the fixing drive motor is made unique, but in this embodiment, the target speed switching interval of the fixing drive motor is made different during acceleration and deceleration. And

  FIG. 12 is a flowchart for explaining the operation of the image forming apparatus in this embodiment. First, from step S1201 to step S1207, operations similar to those in steps S601 to S607 in the first embodiment are performed.

In step S12072, the target speed of the fixing drive motor 204 is determined for each N2 based on a CPU-managed timer based on the following formula 6, and the target speed is switched.
V = V− (Vref−Vd) / (L1 / 2) (where L1> 0) (Equation 6)
Here, N2 is a target speed deceleration switching time of the fixing drive motor 204, and is arbitrarily determined within a range of N2> 0.

  In this embodiment, as an example, when Vd = 0.95 × Vref and L1 = 10, (Vref−Vd) / (L1 / 2) = 0.01 × Vref, which is 95% of the process speed from the process speed. The target speed is decreased by 1% every time N2 until the speed.

  Thereafter, from step S1208 to step S1211, the same operation as that of steps S608 to 611 in the first embodiment is performed.

In step S1212, when the output signal of the loop detection sensor 112 is “ON” and the current target speed of the fixing drive motor 204 is Vd (YES in step S1211), the target speed of the fixing drive motor 204 is expressed by the following equation (7). Based on the above, a determination is made every N3 based on a timer (not shown), and the target speed is switched.
V = (Vu−Vd) / L1 + V (where L1> 0) (Equation 7)
Here, N3 is a target speed acceleration switching time of the fixing drive motor 204, and is arbitrarily determined within a range of N3 ≠ N2 and N3> 0 (N3> N2 in this embodiment). In this embodiment, as an example, if Vu = 1.05 × Vref, Vd = 0.95 × Vref, and L1 = 10, then (Vu−Vd) /L1=0.01×Vref, which is 95% of the process speed. The target speed is increased by 1% every time N3 from the above speed to 105% of the process speed.

  Thereafter, step S1216 performs the same operation as step S616 in the first embodiment.

In step S1217, when the output signal of the loop detection sensor 112 is “ON” and the current target speed of the fixing drive motor 204 is Vu (YES in step S1216), the target speed of the fixing drive motor 204 is expressed by the following equation (8). Based on a timer (not shown) for each N2, and the target speed is switched.
V = V− (Vu−Vd) / L1 (where L1> 0) (Equation 8)
In this embodiment, as an example, if Vu = 1.05 × Vref, Vd = 0.95 × Vref, and L1 = 10, then (Vu−Vd) /L1=0.01×Vref, which is 105% of the process speed. The target speed is decreased by 1% every time N2 from the above speed to 95% of the process speed.

  Thereafter, from step S1221 to step S1222, the same operations as in steps S621 to 622 in the first embodiment are performed.

  FIG. 13 is a timing chart when the fixing drive motor is controlled so as to hold the loop in a constant amount in this embodiment. When the paper detection sensor 113 detects the paper, the paper loop has not yet been formed. Therefore, the target speed of the fixing drive motor 204 is changed from the reference speed Vref to the intermediate target speed number L1 / 2 every motor speed switching time N2. , And set to a value Vd slower than the reference value. When the loop detection sensor detects “ON” while driving the fixing drive motor 204 with Vd, the target speed is accelerated from Vd at a plurality of intermediate speeds every time N3 and switched to Vu. In an example of the present embodiment, the target speed of the fixing drive motor 204 is increased by 1% in 10 steps from 95% of the process speed to 105% of the process speed. When the loop detection sensor detects “OFF” while driving the fixing drive motor 204 with Vu, the target speed is decelerated from Vu at a plurality of intermediate speeds every time N2 and switched to Vd. In this example, the target speed of the fixing drive motor 204 is decreased by 1% every time N2 in 10 steps from 105% of the process speed to 95% of the process speed.

  As described above, when the target speed of the fixing drive motor is switched, the current speed to the target speed is accelerated or decelerated at a plurality of intermediate speeds, and the target speed switching interval of the fixing drive motor is different during acceleration and deceleration. By doing so, it becomes possible to perform fixing drive motor control adapted to the loop generation gain and cancellation gain peculiar to the paper, and it is possible to provide a high-accuracy image forming apparatus with lower noise and no occurrence of image defects.

  In the first to fourth embodiments, the latent image forming medium is a photosensitive drum, but a belt-like photosensitive member may be suspended and driven by a driving roller.

  The endless belt is a paper conveying belt, but may be an intermediate transfer member.

  Although the paper detection sensor 113 is used to detect whether or not the paper on which the full-color toner image has been transferred is conveyed to the fixing roller, the loop detection sensor 112 may be used. In this case, as an example, until the paper is conveyed to the fixing roller, the driving speed of the fixing drive motor 204 is set to a speed slower than the speed reference value to create a paper loop between the transfer and fixing, thereby detecting the loop. The passage of the paper is determined by the output signal of the sensor 112 being switched.

  Although the intermediate target speed number is unique, it may be variable during acceleration and deceleration.

  The speed reference value may be variable according to the environmental temperature and humidity of the image forming apparatus. Moreover, the structure which determines a speed reference value based on the output of a loop detection sensor may be sufficient.

6 is a timing chart when the fixing drive source unit is controlled to maintain a constant amount of the loop according to the first embodiment of the present invention. It is a figure explaining the structure which controls so that the loop concerning the prior art of this invention may be hold | maintained to fixed amount. It is a figure explaining the structure of the loop detection sensor which concerns on the prior art of this invention. It is a timing chart at the time of controlling a conveyance means so that the loop based on the prior art of this invention may be hold | maintained to fixed amount. It is a figure explaining the speed change of the motor which concerns on the prior art of this invention. 3 is a flowchart illustrating an operation of the image forming apparatus according to the first exemplary embodiment of the present invention. 6 is a timing chart when the fixing drive source unit is controlled to maintain a constant amount of the loop according to the first embodiment of the present invention. It is a table | surface explaining the speed reference value memory | storage means which concerns on Example 2 of this invention. 6 is a flowchart illustrating an operation of the image forming apparatus according to the second exemplary embodiment of the present invention. 7 is a flowchart illustrating an operation of an image forming apparatus according to Embodiment 3 of the present invention. 1 is a diagram illustrating an entire image forming apparatus according to an embodiment of the present invention. 10 is a flowchart illustrating an operation of an image forming apparatus according to Embodiment 4 of the present invention. FIG. 10 is a timing chart when the fixing drive source unit is controlled so as to hold the loop according to the fourth embodiment of the present invention at a constant amount. FIG. 14 is a diagram mainly showing a configuration for controlling a paper loop in the color image forming apparatus which is a feature of the present invention.

Explanation of symbols

101C, 101M, 101Y, 101Bk Laser scanner 102C, 102M, 102Y, 102Bk Developing unit 103C, 103M, 103Y, 103Bk Photosensitive drum 104C, 104M, 104Y, 104Bk Developing roller 105C, 105M, 105Y, 105Bk Transfer roller 106 Paper transport belt 107 Belt drive roller 108 Belt driven roller 110 Fixing roller 111 Pressure roller 112 Loop detection sensor 113 Paper detection sensor 201 CPU
202 Motor driver 203 Developing cartridge drive motor 204 Fixing drive motor 301 Photo interrupter

Claims (1)

Transfer means for transferring an image to a recording material;
Fixing means for fixing the image transferred to the recording material by the transfer means to the recording material;
Detecting means for detecting deflection generated in the recording material when the recording material is conveyed by the transfer means and the fixing means;
When the deflection is detected by the detection unit, the conveyance speed at which the recording material is conveyed by the fixing unit is switched to a first target speed that is faster than a reference speed, and when the deflection is not detected by the detection unit, the reference speed is exceeded. By switching to a slow second target speed, the amount of deflection generated in the recording material between the transfer means and the fixing means is controlled, and the transport speed is changed from the first target speed to the second target speed. in the first switching period until switching to, the conveying speed slower than the first target speed, and stepwise switching by the second fast plurality of intermediate speed than the target speed of, and the said transport speed in the second of the second switching period from the target speed to switch to the first target speed, stepwise switches controlling the transport speed at said plurality of intermediate speed And the stage,
With
The image forming apparatus, wherein the control unit controls switching of the plurality of intermediate speeds so that the second switching period is longer than the first switching period .

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