JP3740319B2 - Recording medium conveying apparatus and image forming apparatus - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to control of a conveyance speed of a recording medium in an image forming apparatus such as a copying machine, a printer, and a facsimile using an electrophotographic system.
[0002]
[Prior art]
In a conventional image forming apparatus, a recording medium such as recording paper is transported on a recording medium transport path using a roller or the like, and one recording medium is simultaneously transported upstream and downstream in the transport direction of the transported recording medium. In some cases, the conveying force may be applied by different conveying means.
[0003]
As an example of such a conveyance form, for example, a transfer unit that transfers a toner image on a photosensitive drum as an image carrier to a recording medium, and a recording medium that has passed this transfer unit is conveyed to a fixing nip portion of a fixing unit. There is a difference in the transport speed between the transfer unit and the fixing nip so that the recording medium between the transfer unit and the fixing nip has a certain degree of bending (loop).
[0004]
As a method for providing such a difference in the conveyance speed, there is a method in which speed control is not performed and a predetermined speed difference is fixed.
[0005]
Further, the recording medium conveyance speed of the fixing unit and the recording medium conveyance speed of the transfer unit differ depending on thermal expansion of the fixing roller of the fixing unit, solid difference, or secular change, and the recording medium is between the fixing unit and the transfer unit. As a means for solving the image deterioration caused by pulling at the same time, for example, Japanese Patent Laid-Open No. 10-97154 provides a loop detection sensor for detecting a loop of a recording medium between the fixing unit and the transfer unit. According to this result, the control clock cycle of the stepping motor which is the driving motor for the fixing roller is shortened, the speed of the driving motor is increased for a certain period of time to reduce the loop of the recording medium, and then the loop amount is reduced. There has been proposed an image forming apparatus in which the speed of the drive motor is returned to the original speed.
[0006]
In Japanese Patent Application Laid-Open No. 07-18130, a loop detection sensor for detecting a loop of a recording medium is provided between the fixing unit and the transfer unit, and based on the result, the speed of a motor for driving the pressure roller of the fixing unit. There has been proposed an image forming apparatus in which the loop amount of the recording medium is made constant by switching the steps in a stepwise manner.
[0007]
[Problems to be solved by the invention]
However, in the above-described conventional example, when the recording medium is transported at a constant speed difference without first controlling the speed, the transporting means such as a roller is thermally expanded by the heat of the fixing device, for example, and the transport speed is increased by changing the diameter. It is conceivable that the speed difference between the front and rear units increases or reverses, affecting the image quality and transport performance such as an increase in loops and pulling by downstream units.
[0008]
In addition, when a recording material loop is detected by a loop detection sensor such as a photo interrupter, it is possible to detect the presence or absence of a predetermined amount of loop. On the other hand, it is impossible to carry out delicate control such as conveying while preventing image rubbing due to an increase in the loop.
[0009]
Furthermore, in a color image forming apparatus that transfers a plurality of colors to a recording sheet, load fluctuations during transfer greatly affect the color misalignment of each color. Speed management was an important issue.
[0010]
In particular, in a tandem type color LBP in which four colors Y, M, C, and Bk are directly transferred to a recording medium as needed, the distance between transfer and fixing is short, and the recording medium is fixed to a plurality of transfer portions. Since there is a state of being sandwiched between means, it is important to control the conveyance speed between transfer and fixing.
[0011]
Further, when the fixing means is an on-demand fixing device such as an electromagnetic induction type (IHF) or surf fixing, the conveyance speed of the recording medium is higher than that of the conventional heating and pressure rubber roller pair fixing device having a halogen lamp or the like. The amount of loop between transfer and fixing fluctuates greatly due to the type of recording medium and the number of continuous paper passes, so that the tension in the fixing means is eliminated while always securing a certain amount of loop. Subtle control such as carrying images while preventing image rubbing and color misregistration due to load fluctuations on the recording medium is impossible.
[0012]
An object of the invention according to the present application is to provide an image forming apparatus capable of stably transporting a recording medium while keeping a loop amount formed on the recording medium conveyed on the recording medium conveying path constant. It is.
[0013]
[Means for Solving the Problems]
  The configuration of the recording medium conveying apparatus that realizes the object of the present invention is as follows.A first conveying means for conveying a recording medium; a second conveying means for conveying a recording medium provided downstream of the first conveying means in the conveying direction of the recording medium; and the first conveying means; Deflection detecting means for detecting a deflection of the recording medium between the second conveying means, and a recording medium which is provided downstream of the first conveying means in the conveying direction of the recording medium and detects the recording medium And a control means for controlling the detection means and the first conveyance means and the second conveyance means, based on a detection result of the deflection detection means after the recording medium detection means detects the recording medium. And a control means for controlling at least one of the first transport means and the second transport means.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a main section of a tandem color LBP (color laser printer) embodying the present invention.
[0015]
Reference numerals 11a to 11d denote drum-type electrophotographic photosensitive members (hereinafter referred to as photosensitive drums) as latent image carriers that rotate in the clockwise direction in the drawing at a predetermined process speed, and are photosensitive drums 11a, 11b, 11c, and 11d. , In order, share the yellow (Y) component, magenta (M) component, cyan (C) component, and black (Bk) component of the color image. M1 is a drum motor (DC servo motor) that rotationally drives the photosensitive drums 11a, 11b, 11c, and 11d. One motor M1 drives four photosensitive drums, but each of the photosensitive drums may be provided with an independent drive source. Reference numeral 52 denotes a digital signal processor (DSP) that controls the rotational drive of the drum motor M1, and the other control is performed by the CPU 50.
[0016]
In the following, description will be given by taking yellow among the four colors as an example. The photosensitive drum 11a is uniformly charged to a predetermined polarity and potential by a primary charging roller 12a as a primary charging means during the rotation process. Optical image exposure is performed by a laser beam exposure means (hereinafter referred to as a scanner) 8a to form an electrostatic latent image of image information.
[0017]
Next, a toner image is formed on the photosensitive drum 11a by the developing unit 13a and visualized. A similar process is performed for the other three colors.
[0018]
These toner images are synchronized by the registration roller pair 10 that stops and re-transports the recording medium P that has been conveyed by the paper feed roller 9 at a predetermined timing, and is electrostatically conveyed with the transfer roller pairs 14a, 14b, 14c, and 14d. Each color is sequentially transferred to the recording medium P at the nip portions T1a, T1b, T1c, and T1d with the belt 23.
[0019]
At the same time, the photosensitive drums 11a, 11b, 11c, and 11d after the transfer of the toner image to the recording medium P are processed with the remaining adhering matter such as the transfer residual toner by the cleaning means 15a, 15b, 15c, and 15d, and the eraser lamp 16a. , 16b, 16c, and 16d are subjected to static elimination processing, and image formation is repeatedly performed.
[0020]
The recording medium P on which the toner image is transferred by the transfer portion T1d is separated from the surface of the photosensitive drum 11d, conveyed on the conveyance guide 17, and sent to the fixing device 18.
[0021]
On the other hand, the pressure roller 21 provided in the fixing device 18 is rotated counterclockwise in the figure by a fixing motor M2 (DC servo motor) whose rotation is controlled by the DSP 51, and an exciting coil 20 as a heating means is provided. It is connected to an excitation circuit (not shown) of the image forming apparatus main body, and a magnetic force is generated by applying a high frequency bias by this excitation circuit.
[0022]
Due to the action of the magnetic force, an induction current (eddy current) is generated in a heat generation layer (ferromagnetic conductive layer) (not shown) of the endless film 22 as a rotating body to be in an electromagnetic induction heat generation state. From this state, the recording medium P loaded with unfixed toner is conveyed and introduced into the nip T2 between the film 22 and the pressure roller 21, so that the pressure of the pressure spring (not shown) and the film 22 that has generated electromagnetic induction heat are generated. After being heated, the unfixed toner is softened and melted and pressed against the recording medium P, and then cooled to form a permanently fixed image. At this time, as shown in FIG. 1, the recording medium P traveling on the conveyance guide 17 is conveyed while being in contact with one lever portion loop sensor flag (2a) protruding in the recording medium conveyance surface of the swing lever 2.
[0023]
At this time, the loop sensor flag 2a is urged clockwise by the tension spring 5 to the state of FIG. 1 with a predetermined spring pressure.
[0024]
Thereafter, the recording medium P discharged from the nip portion T2 between the film 22 and the pressure roller 21 kicks one lever portion (discharge sensor flag) 4a protruding on the recording medium conveyance surface of the swing lever 4. The other lever portion 4b blocks the optical path of the paper discharge sensor 3 formed of a photo interrupter, and detects the state from OFF (no paper) to ON (paper present).
[0025]
Here, the recording medium conveyance speed v1 (mm / s) at the fixing device 18 is set to be always slower than the recording medium conveyance speed v0 (mm / s) at the transfer section.
[0026]
That is, the fastest recording medium in the fixing device when considering the type of recording medium in the fixing device 18, the number of continuous sheets to be passed, the thermal expansion of each component depending on the temperature control condition, the variation in pressure, the tolerance of the roller diameter, and the like The conveyance speed is set to v1, and v0> v1 is set. Accordingly, the loop amount increases due to the conveyance speed difference of the recording medium P from the state of FIG. 1 when the leading end of the recording medium P is sandwiched by the nip T2 of the fixing device 18.
[0027]
In the state of FIG. 2, the tension spring 5 urging the loop sensor flag 2 a is pulled by the waist strength of the loop of the recording medium P, and the other lever portion of the utility lever 2 is configured by a photo interrupter. The optical path of the loop sensor 1 is blocked and the state is changed from the OFF state to the ON (loop detection) state.
[0028]
Here, the fixing nip portion T2 is arranged at a position higher than the transfer nip portion T1d by H so that a loop generated due to the difference in the recording medium conveyance speed between fixing and transferring occurs downstream as shown in FIGS. Has been.
[0029]
When the loop amount on the conveyance guide 17 of the recording medium P in FIG. 2 is set to an appropriate state, it is necessary to increase or decrease the recording medium conveyance speed in the fixing unit so as to maintain this state.
[0030]
However, while the recording medium conveyance speed v0 at the transfer nip portion T1 is substantially constant, the recording medium conveyance speed v1 at the fixing nip portion T2 is as described above. Fluctuates greatly depending on the thermal expansion of each part, pressure variation, roller diameter tolerance, etc.
[0031]
Therefore, the greater the difference in the conveyance speed of the recording medium P between the fixing nip T2 and the transfer nip T1, the greater the recording medium conveyance speed at the current fixing nip T2 after the loop sensor 1 is turned on. As a result, after the loop is reduced and the loop sensor 1 is turned OFF, the recording medium transport speed must be decelerated. Here, there is a case where the recording medium conveyance speed on the fixing device side when decelerated is larger than the initially set recording medium conveyance speed.
[0032]
That is, acceleration / deceleration corresponding to the difference in the conveyance speed of the recording medium P between the fixing nip T2 and the transfer nip T1 is necessary.
[0033]
As a means for detecting the recording medium conveyance speed difference between the fixing nip portion T2 and the transfer nip portion T1, the paper discharge sensor 3 provided near the discharge side of the fixing device 18 is pushed by the front end portion of the recording medium P and is turned ON. From the time until the loop amount generated due to the recording medium conveyance speed difference between the transfer portion and the fixing portion reaches a predetermined amount and the loop sensor 1 is turned on with the strength of the waist, the transfer portion and the fixing portion are fixed. It is possible to know the magnitude of the recording medium conveyance speed difference between the recording medium and the recording medium.
[0034]
That is, the shorter the time from when the paper discharge sensor 3 is turned on to when the loop sensor 1 is turned on, the greater the difference in the recording medium conveyance speed between the transfer unit and the fixing unit.
[0035]
As described above, in order to keep the loop amount between the transfer portion and the fixing portion constant by controlling the recording medium conveyance speed at the fixing nip portion T2 of the fixing device 18, the rotational speed of the fixing motor M2 is controlled. There must be.
[0036]
FIG. 3 shows an image of speed control when the loop sensor is repeatedly turned on and off after the paper discharge sensor is turned on.
[0037]
In FIG. 3, the speed control is performed three times according to ON / OFF of the loop sensor, but the loop control may be terminated by one speed control.
[0038]
FIG. 4 is a block diagram showing a servo control block diagram of the fixing motor by the DSP (digital signal processor) 51 in FIG.
[0039]
The image forming apparatus according to the present embodiment includes a CPU 50 and a DSP 51 in the control unit. The DSP 51 controls the motor, and the CPU 50 performs other controls. In FIG. 3, the DSP receives a motor drive / stop command from a CPU (not shown), performs servo control of the motor, and returns motor status information to the CPU.
[0040]
In the figure, reference numeral 101 denotes a motor control target speed (rad / sec), 102 denotes a PI filter, 103 denotes gain, 104 denotes a PWM pulse calculation unit, 104 denotes a PWM signal, and 106 generates a signal of 360 pulses per rotation. MR sensor output signal, 107 is a capture for measuring the pulse interval of the MR sensor, 108 is a speed calculation unit for calculating the motor speed (rad / sec) from the measurement result of the capture 107, 109 is from the paper discharge sensor 3 , 110 is a signal from the loop sensor 1, 111 is a time measuring unit that measures the time from the ON timing of the paper discharge sensor 3 (with paper) to the ON edge of the loop sensor 1 (loop detection), 112 Is a conveyance speed difference calculation unit that calculates a conveyance speed difference between the recording medium conveyance speed of the fixing unit and the recording medium conveyance speed of the transfer unit, and 113 is a conveyance speed difference calculation unit 1 The control target speed calculation unit 114 calculates the control target speed of the motor in each of the ON and OFF states of the loop sensor 1 from the calculation result of 2, and 114 selects the calculation result of the control target calculation unit 113 according to the state of the loop sensor 1 A switching control unit.
[0041]
The servo control operation of the motor by the circuit having the above configuration will be described.
[0042]
A motor control target speed (number of revolutions) 101 is given, the target speed is compared with the actual motor speed (omg) calculated by the speed calculation unit 108 by the subtractor 115, and the speed difference is calculated by the PI filter 102. The gain 103 is added, and the PWM pulse calculation unit 104 obtains the PWM pulse width according to this value.
[0043]
The PWM pulse width determines the ON duty for a carrier determined by a PWM carrier frequency generation circuit (not shown). For example, if the carrier frequency is set to 20 kHz (50 μs) and the PWM pulse width is defined as 8 bits, the PWM pulse width is “7F” H, the ON duty is 50%, the pulse width is 25 μs, and the pulse width is “40” H. The duty is 25% and the pulse width is 12.5 μs.
[0044]
In addition, the speed calculation process in which the pulse interval of the signal 106 from the MR sensor is measured by the capture 107 and the actual speed of the motor is calculated by the speed calculation unit 108 is performed for each pulse input of the MR sensor. Is calculated by PI filter 102, gain 103 is added, and PWM pulse 105 is calculated by PWM pulse width calculation unit 104 at a control frequency of 1 kHz in consideration of motor responsiveness. Feedback controlled.
[0045]
Next, from the timing when the leading edge of the recording medium reaches the paper discharge sensor 3 and the sensor output as the signal 109 from the paper discharge sensor 3 turns from OFF to ON, the recording medium forms a loop, and the loop sensor 1 starts from OFF. The time until the ON timing is measured by the time measuring unit 111, and from this result, the difference between the recording medium conveyance speed of the fixing unit and the recording medium conveyance speed of the transfer unit is calculated by the conveyance speed difference calculation unit 112. For example, assuming that the conveyance speed of the transfer unit is v0 (mm / s), the conveyance speed of the fixing unit is v1 (mm / s), and the measurement result of 111 is t (s), when v0> v1, (v0−v1) ) = K · t (k <1 where k is a constant).
[0046]
That is, when the conveyance speed of the fixing unit is slower than the conveyance speed of the transfer unit, the larger the conveyance speed difference, the faster the loop is formed. The time t until 1 detects a loop is shortened.
[0047]
On the other hand, although the constant k mainly varies depending on the paper type and sensor mounting accuracy, if the constant k is set in advance, the conveyance speed difference (v0−v1) can be easily obtained.
[0048]
Next, a value indicating how much the motor control target speed when the loop sensor 1 is ON (loop detection) is increased (decreasing the loop amount) from the conveyance speed difference calculated by the conveyance speed difference calculation unit 112, that is, + Δv1 and a value of how much the motor control target speed is lowered (increase the loop amount) when the loop sensor 1 is OFF (loop not detected), that is, −Δv2 is calculated based on a test formula obtained in advance, and the motor Set the control target speed.
[0049]
Next, the target motor speed calculation unit 113 adds + Δv1 and −Δv2 obtained by the conveyance speed difference calculation unit 112 to the actual motor control speed already obtained by the speed calculation unit 108, and the loop sensor 1 is turned on. The motor control target speed and the motor control target speed when the loop sensor 1 is OFF are obtained, and the switching control unit 114 switches and controls the previously obtained motor control target speed according to the state (ON or OFF) of the loop sensor 1. The servo control of the motor is performed with this value as the motor control target speed 101.
[0050]
FIG. 5 is a control flowchart of the fixing motor by a DSP (digital signal processor).
[0051]
A control flow will be described with reference to the drawings.
[0052]
In step 201, the motor activation state is confirmed. If the motor is not activated, initial setting of registers, timers, ports, etc. is performed in step 202, and in step 203, the PWM ON duty at the time of activation is fixed to 80%. This is a PWM that is optimal for starting up without overshoot with respect to the target speed while giving sufficient torque to accelerate with the acceleration torque of the motor at startup connected to the load torque and load inertia The width is determined. On the other hand, if the motor is already activated in step 201, jump is performed.
[0053]
Next, in step 204, a capture (CAP) interrupt is confirmed. Actually, the process shifts to the capture process routine by the interrupt process, and in step 205, the motor speed is calculated. That is, when the motor rotates, 360 pulses per rotation are output from the MR sensor. An interrupt is generated upon detection of the edge of this pulse. That is, an interrupt is generated every time a pulse edge arrives. The pulse interval is measured by a capture circuit (not shown) provided in the DSP, and if this time is tcap (s), the motor speed (rad / s) is obtained by (2π / 360) / tcap. This series of control corresponds to the processing at 106 to 108 in FIG.
[0054]
Next, in step 206, it is confirmed whether or not a speed control interrupt has occurred. Actually, if an interrupt occurs due to the speed control interrupt process, the motor control target speed is compared with the actual motor speed in step 207, PI filter calculation is performed in step 208, gain is added in step 209, In step 210, the PWM pulse width corresponding to these calculation results is determined. The operations in steps 208 to 210 are operations for stably controlling the servo control system, and correspond to the processing in 102 to 104 in FIG.
[0055]
Next, in step 211, it is confirmed whether a PWM interrupt has occurred. Actually, a hardware interrupt is issued for each preset PWM carrier frequency. That is, when the carrier frequency is set to 20 kHz, a circuit that generates a 20 kHz interrupt is provided. When this interruption occurs, in step 212, the PWM signal having the PWM pulse width obtained in step 210 is output. For example, in the calculation result of step 210, when the PWM pulse width is 8 bits, the value is “7F” H, and the carrier is 20 kHz, the PWM pulse width is 25 μs and the ON duty is 50%. A PWM signal is output.
[0056]
On the other hand, when no interruption occurs in step 211, the PWM signal is not output.
[0057]
Next, in step 213, the paper discharge sensor 3 detects from OFF (no paper) to ON (paper present). That is, the timing at which the leading edge of the recording medium being conveyed reaches the paper discharge sensor 3 (the lever portion 2a of the paper discharge sensor swing lever 2) is detected. If detected, in step 214, the loop sensor 1 is detected from OFF (no paper) to ON (paper present). That is, the recording medium being conveyed is looped and the timing detected by the loop sensor is detected.
[0058]
If a loop is detected, the time from when the leading edge of the recording medium reaches the paper discharge sensor 3 until the loop sensor 1 is turned on in step 215 is measured, and in step 216, the transfer speed of the transfer unit, The conveyance speed difference of the fixing unit is calculated, and in step 217, a control target speed when the loop sensor 1 is ON and a control target speed when the loop sensor 1 is OFF are set.
[0059]
On the other hand, if not detected in step 213, the process jumps to step 218. If not detected in step 214, the process jumps to step 218.
[0060]
The operations in steps 213 to 217 correspond to the processing in 111 to 113 in FIG.
[0061]
Next, when the loop sensor 1 is ON at step 218, the control target speed when the loop sensor 1 is ON obtained at step 217 is obtained, and when the loop sensor 1 is OFF at step 218, it is obtained at step 217. The control speed of the fixing motor is controlled by switching the control target speed when the loop sensor 1 is OFF.
[0062]
In this manner, when the conveyance speed of the fixing unit is low and the conveyance speed of the transfer unit is high after the leading edge of the recording medium reaches the paper discharge sensor, a loop is formed on the recording medium, and the loop sensor 1 is turned on. By measuring the time between them, the difference in the conveyance speed between the fixing unit and the transfer unit is calculated, and the control target speed of the fixing motor is set and controlled according to the result.
[0063]
FIG. 6 is a block diagram of the fixing motor and the control circuit.
[0064]
In FIG. 6, reference numeral 301 denotes a DSP that communicates with a CPU (not shown) to control a fixing motor, 302 is a fixing motor unit including a drive circuit, 303 is a control IC, 304 is a driver, 305 is an outer rotor. Three-phase DC brushless motor, 306 is a regulator with a built-in pre-driver that generates + 5V for biasing the Hall sensor and MR sensor, 307 is a charge pump circuit that generates the gate voltage of the driver N-chMOS, and 308 is a pre-driver 309 is a logic circuit, 310 is a current limiter circuit, 311 to 313 are Hall sensor amplifiers, 314 is an MR sensor amplifier, 315 to 320 are N-ch MOS transistors as driver units, 321 is a resistor for current detection, and 322 is a motor. Connect to U phase coil Phase output, 323 is a V-phase output connected to the V-phase coil, 324 is a W-phase output connected to the W-phase coil, 325 to 327 are Hall sensors, 328 is an MR sensor, 329 is a motor start signal output from the DSP, 330 is a PWM signal output from the DSP, 331 is an MR sensor signal for motor speed detection, and 332 is a serial communication bus for communicating with a CPU (not shown).
[0065]
Next, the fixing motor control operation will be described.
[0066]
First, when a fixing motor drive command is issued from the CPU via the serial communication line 332, the DSP 301 activates the motor activation signal 329 to the control IC 303, and the PWM pulse 330 has an on-duty 80% PWM pulse. To start the motor. The control IC 303 receives the activation signal 329 and controls the excitation switching of the N-ch MOS transistors 315 to 320 so that the logic circuit 309 has a predetermined rotation direction based on the rotor position detected by the Hall sensors 325 to 327. In response to the PWM signal 330, the N-ch MOS transistors 315, 317, and 319 are PWM-switched. At this time, the gate voltages of the N-ch MOS transistors 315, 317, and 319 are boosted to Vcc + 10V by the charge pump circuit 307.
[0067]
For example, the logic circuit 309 recognizes the rotor position of the motor from the results amplified by the hall sensors 325 to 327 and the hall sensor amplifiers 311 to 313, and the current direction from the U phase 322 to the V phase 323 so as to be in a desired rotation direction. When switching to, the pre-driver 308 turns on the N-ch MOS transistors 315 and 318 and turns off the N-ch MOS transistors 316, 317, 319, and 320.
[0068]
As a result, the current path flows from Vcc through the N-ch MOS transistor 315, through the U-phase output 322 and the V-phase output 323, through the N-ch MOS transistor 318, to the current detection resistor 321 and to a predetermined coil. Magnetic force is generated. At this time, the PWM signal 330 given from the DSP 301 passes through the logic circuit 309, and the pre-driver 308 performs PWM control of the N-ch MOS transistor 315.
[0069]
Therefore, the current from the U phase to the V phase is an ON duty current defined by the PWM signal 330. In this way, the motor is subjected to excitation switching control in which the current to the U, V, and W phases is switched so that the rotor rotates in a predetermined direction, and generates torque by the interaction between a main pole magnet and a coil (not shown).
[0070]
When the motor is subjected to excitation switching control as described above and the rotor rotates, the MR sensor 328 detects a previously prepared magnetization pattern for MR sensor and outputs 360 pulses per rotation. That is, a signal having a frequency corresponding to the rotational speed of the motor is obtained and transmitted to the DSP 301 via the amplifier 314 and the MR sensor signal line 331.
[0071]
The program of the DSP 301 measures the pulse interval of the MR sensor signal line 331, obtains the motor speed (rad / s), compares it with the target control speed, performs PI filter calculation and gain addition calculation (not shown), and outputs PWM pulses. The width is derived, the current supplied to the motor is controlled via the PWM signal line 330, and control is performed so that the motor rotates at the target speed.
[0072]
As described above, the DSP 301 uses the PWM signal 330 to switch the N-ch MOS transistor in the output stage, and performs servo control so that the motor rotates at a desired rotation. On the other hand, the control IC 303 performs excitation control so that the rotor rotates in a desired rotation direction based on the result of detecting the main pole position of the rotor by the Hall sensors 325 to 327 and drives the N-chMOS transistor. .
[0073]
In addition, a current detection resistor 321 detects a current flowing through the motor, and when a current exceeding a predetermined value flows, a protection circuit is provided that limits the current limiter circuit 310.
[0074]
In the present embodiment, the recording medium conveyance speed between the transfer nip portion T1 and the fixing nip portion T2 has been described as means for detecting and controlling. However, the present invention is not limited to this. This is effective for loop amount detection and speed control of all recording media generated on the conveyance path, such as loop amount detection and speed control of the recording medium P generated between the pair of register rollers 10.
[0075]
In addition, the time required for the amount of deflection of the recording medium to reach a predetermined amount is divided into a plurality of required time stages, and a plurality of recording medium conveyance speed change amounts are set in advance according to each of the required time stages, The change amount of the recording medium conveyance speed may be selected from the plurality of change amounts of the recording medium conveyance speed according to the time until the deflection amount of the recording medium reaches a predetermined amount.
[0076]
【The invention's effect】
As described above, according to the present invention, based on the detection result of the deflection detection means after the recording medium detection means detects the recording medium, at least one of the first conveyance means and the second conveyance means. Therefore, the deflection of the recording medium conveyed by the first conveying means and the second conveying means can be adjusted appropriately.
[0077]
Further, according to the present invention, based on the detection result of the deflection detecting unit after the recording medium detecting unit detects the recording medium, at least one of the conveying speeds at which the transfer unit and the fixing unit convey the recording medium is conveyed. Since the speed is controlled, it is possible to appropriately adjust the deflection of the recording medium conveyed by the transfer unit and the fixing unit.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of an electrophotographic color image forming apparatus embodying the present invention.
2 is a longitudinal sectional view showing a state where a loop of a recording medium has occurred between the transfer unit and the fixing unit from the state of FIG.
FIG. 3 is a timing chart of speed control of the fixing motor shown in FIG.
4 is a servo control block diagram of a fixing motor (DC servo motor) by the DSP shown in FIG.
FIG. 5 is a flowchart for controlling a fixing motor by the DSP shown in FIG. 1;
6 is a block diagram of a fixing motor and a control circuit shown in FIG.
[Explanation of symbols]
1 ... Loop sensor 2 ... Loop sensor flag
3 ... Paper discharge sensor 4 ... Paper discharge sensor flag
5 ... tension spring 9 ... paper feed roller
10 ... Registration roller pair 11 ... Photosensitive drum
12 ... Primary charging means 13 ... Developer
14 ... Transfer roller 15 ... Cleaning means
16 ... Eraser lamp 17 ... Conveying guide
18 ... Fixer 20 ... Excitation coil
21 ... Pressure roller 22 ... Film

Claims (13)

  A first conveying means for conveying a recording medium; a second conveying means for conveying a recording medium provided downstream of the first conveying means in the conveying direction of the recording medium; and the first conveying means; Deflection detecting means for detecting a deflection of the recording medium between the second conveying means, and a recording medium which is provided downstream of the first conveying means in the conveying direction of the recording medium and detects the recording medium And a control means for controlling the detection means and the first conveyance means and the second conveyance means, based on a detection result of the deflection detection means after the recording medium detection means detects the recording medium. And a control means for controlling at least one of the first transport means and the second transport means.   The recording medium transport apparatus according to claim 1, wherein the recording medium detection unit is provided downstream of the second transport unit in the transport direction of the recording medium.   The recording medium transport apparatus according to claim 1, wherein the control unit controls a transport speed at which the first transport unit and the second transport unit transport the recording medium.   The control means may be configured such that the first conveyance means or the second conveyance is based on an elapsed time from when the recording medium detection means detects the recording medium until the deflection detection means detects a predetermined deflection. 4. The recording medium conveying apparatus according to claim 3, wherein at least one of the means controls a conveying speed for conveying the recording medium.   The control means sets the transport speed applied to the second transport means when the deflection detection means detects a predetermined deflection as a second transport speed faster than the first transport speed applied to the first transport means, The recording medium conveying apparatus according to claim 4, wherein the second conveying speed is a speed based on the elapsed time.   The control means sets the transport speed applied to the second transport means when the deflection detection means has not detected the predetermined deflection as a third transport speed slower than the first transport speed, and the third transport speed. The recording medium conveying apparatus according to claim 5, wherein the speed is based on the elapsed time.   The recording medium transport apparatus according to claim 6, wherein the second transport speed increases as the elapsed time decreases, and the third transport speed decreases as the elapsed time decreases.   An image carrier, a transfer unit that transfers the unfixed image on the image carrier onto the recording medium while transporting the recording medium, and the undetermined while transporting the recording medium on which the unfixed image is transferred by the transfer unit. A fixing unit for fixing a received image; a deflection detecting unit for detecting a deflection of the recording medium between the transfer unit and the fixing unit; and a downstream side of the transfer unit in the conveyance direction of the recording medium, A recording medium detecting means for detecting the recording medium; and a control means for controlling the transfer means and the fixing means, the detection result of the deflection detecting means after the recording medium detecting means detects the recording medium. An image forming apparatus comprising: a control unit that controls at least one of the transfer speeds at which the transfer unit and the fixing unit transfer the recording medium.   The control unit is configured such that the transfer unit and the fixing unit convey the recording medium based on an elapsed time from when the recording medium detecting unit detects the recording medium until the deflection detecting unit detects a predetermined deflection. 9. The image forming apparatus according to claim 8, wherein at least one of the transport speeds to be controlled is controlled.   The control unit sets a conveyance speed applied to the fixing unit when the deflection detection unit detects a predetermined deflection as a second conveyance speed faster than a first conveyance speed applied to the transfer unit, and the second conveyance speed is The image forming apparatus according to claim 9, wherein the speed is based on an elapsed time.   The control unit sets a conveyance speed applied to the fixing unit when the deflection detection unit does not detect the predetermined deflection as a third conveyance speed slower than the first conveyance speed, and the third conveyance speed is the elapsed time. The image forming apparatus according to claim 10, wherein the speed is based on time.   12. The image forming apparatus according to claim 11, wherein the second transport speed increases as the elapsed time decreases, and the third transport speed decreases as the elapsed time decreases.   A plurality of image carriers, and a plurality of transfer units that sequentially transfer a plurality of unfixed images on the plurality of image carriers onto a recording medium while conveying the recording medium, Based on the detection result of the deflection detection unit after the recording medium detection unit detects the recording medium, the transfer unit located at the most downstream in the recording material conveyance direction and the fixing unit among the plurality of transfer units 9. The image forming apparatus according to claim 8, wherein at least one of the conveying speeds for conveying the recording medium is controlled.

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