JP2011145589A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that can achieve excellent image quality by keeping constant the sag amount of a recording sheet even if faster formation of an image is achieved. <P>SOLUTION: When the tip end of the recording sheet is detected by a paper-feeding sensor 109 arranged on a carrying path from a carrying roller 106 to a resist roller 107, the image forming apparatus starts the slewing for turning off a stepping motor that drives the carrying roller 106. Thus, the frequency of a driving current of the stepping motor is gradually decreased within a predetermined time period, thereby accurately controlling the sag amount of the recording sheet. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to a technique for correcting skew correctly while conveying a recording sheet at high speed.

  In order to transfer the toner image to a desired position on the recording sheet, the image forming apparatus adjusts the conveyance timing of the recording sheet fed one by one from the sheet feeding cassette by a pair of registration rollers. Further, in preparation for the case where the recording sheet is inclined with respect to the conveyance direction, skew correction is performed to cause the recording sheet to have a predetermined slack (loop) by bringing the leading end of the recording sheet into contact with the resist roller pair in a stopped state.

  On the other hand, when the transport distance of the recording sheet from the paper feed cassette to the registration roller pair is long, it may be caused by a paper feed roller slip in the middle of the transport path or variations in the stop position of the recording sheet due to fluctuations in the transport time. Thus, the amount of sag of the recording sheet fluctuates and is not constant. If the amount of sag is excessively large, the recording sheet is folded in a Z-shape (so-called “Z-folding”). On the other hand, if the amount is too small, the transfer position of the toner image is shifted and the image quality is deteriorated.

  In order to deal with such a problem, for example, a technique has been proposed in which a sensor is disposed on a recording sheet conveyance path leading to a pair of registration rollers to detect a recording sheet passage time and determine a conveyance roller stop time. . If such a technique is used, the amount of sag of the recording sheet can be kept constant regardless of fluctuations in the conveyance time, so that excellent image quality can be realized.

JP-A-6-271151

  However, under the demand for improving the image forming speed, the recording sheet conveyance speed continues to increase, and control of the conveyance roller with higher time accuracy is required. On the other hand, in the above prior art, the image forming apparatus controls the conveyance roller as part of the loop control, and the time accuracy cannot be increased beyond the period of the loop control. In addition, speeding up the loop control is unrealistic because it increases costs. For this reason, when the above-described conventional technology is employed, there is a risk that the image quality deteriorates as the recording sheet conveyance speed increases.

  The present invention has been made in view of the above-described problems, and provides an image forming apparatus that realizes excellent image quality by keeping the amount of sag of a recording sheet constant even when the image forming speed is increased. The purpose is to do.

  In order to achieve the above object, an image forming apparatus according to the present invention is an image forming apparatus that is operated by a central processing unit repeatedly executing a main routine at a constant cycle, and includes a registration roller, a stepping motor, A conveyance roller that is driven by a stepping motor and abuts and deflects the recording sheet against the stopped registration roller, and is arranged between the registration roller and the conveyance roller on the recording sheet conveyance path, and detects the passage of the recording sheet. A paper passing sensor; control means for controlling the stepping motor without depending on execution of the main routine; and storage means for storing a parameter to be used for the control. This parameter is used for slewing, and triggered when the paper feed sensor detects the leading edge of the recording sheet. And, the control means and performing a fall point slewing control of the stepping motor in accordance with the parameters.

In this way, since the falling through is designated, the stepping motor is stopped within a predetermined time after the leading edge of the recording sheet is detected by the paper passing sensor, and the deflection amount of the recording sheet is adjusted with high accuracy. be able to.
In this case, an operation panel for receiving a user instruction input is provided, the storage means stores a plurality of parameters for performing different falling slewing controls, and the control unit is designated on the operation panel. If the falling slewing control is performed according to the set parameters, the falling slewing time can be easily specified according to the deflection amount of the recording sheet to be formed for skew correction.

1 is a diagram illustrating a main configuration of an image forming apparatus according to an embodiment of the present invention. 3 is a block diagram illustrating a configuration of a control unit 121. FIG. 3 is a diagram illustrating a part of the configuration of a transport unit 100. It is a block diagram which shows the function structure of the stepping motor control part. 6 is a timing chart illustrating a conveyance speed and a detection signal of a communication sensor when a recording sheet is bent.

Embodiments of an image forming apparatus according to the present invention will be described below with reference to the drawings.
[1] Configuration of Image Forming Apparatus First, the configuration of the image forming apparatus according to the present embodiment will be described with reference to the drawings.

FIG. 1 is a diagram illustrating a main configuration of the image forming apparatus according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 is a tandem color image forming apparatus, and includes a conveyance unit 100, an image reading unit 110, an image forming unit 120, and a paper feeding unit 130.
The image reading unit 110 reads a document one by one and generates digital image data.
The image forming unit 120 includes a control unit 121, image forming units 122Y to 122K, an intermediate transfer belt 123, and a fixing unit 124. When the control unit 121 receives the digital image data from the image reading unit 110, the toner image of each color of yellow (Y), magenta (M), cyan (C), and black (K) is formed on the image forming units 122Y to 122K. Let

The toner images of each color of YCMK are electrostatically transferred so as to overlap on the intermediate transfer belt 123 (primary transfer), and electrostatically transferred to the recording sheet by the secondary transfer roller 108 (secondary transfer). The toner image transferred to the recording sheet is heated by the fixing unit 124 and fused to the recording sheet.
The sheet feeding unit 130 stores recording sheets.
The conveyance unit 100 carries out the recording sheets stored in the paper supply unit 130 one by one by the pickup roller 101. Next, the recording sheet is sequentially conveyed by the conveying rollers 102 to 106 and abuts against the registration roller 107 to form a loop and skew correction.

Thereafter, in synchronization with the secondary transfer timing of the toner image, the registration roller 107 conveys the recording sheet to the secondary transfer roller 108 and electrostatically transfers the toner image to the recording sheet. The recording sheet passes through the fixing unit 124 and is then discharged out of the apparatus by the discharge roller 125.
In order to adjust the amount of deflection when the recording sheet is looped, a sheet passing sensor 109 is disposed on the downstream side of the conveying roller 106. The paper passing sensor 109 is a reflective sensor including, for example, an LED (Light Emitting Diode) and a photo sensor, and detects the passage of the recording sheet by detecting the light emitted from the LED reflected by the recording sheet. May be.

[2] Control unit 121
Next, the control unit 121 will be described.
FIG. 2 is a block diagram illustrating a configuration of the control unit 121. As shown in FIG. 2, the control unit 121 includes a CPU (Central Processing Unit) 200, a ROM (Read Only Memory) 201, a RAM (Ramdom Access Memory) 202, an HDD (Hard Disk Drive) interface 203, and a stepping motor control unit 204. , An I / O (Input / Output) interface 205 is provided.

The CPU 200 controls the various operations of the image forming apparatus 1 by reading out the main routine program from the ROM 201 and executing the main routine program using the RAM 202 as a working storage area.
The CPU 200 is connected to the HDD 210 via the HDD interface 203. As a result, the CPU 200 writes data to and reads data from the HDD 210. Further, the CPU 200 controls the stepping motor 211 via the stepping motor control unit 204. Note that the stepping motor control unit 204 controls the operation of the stepping motor 211 without depending on the execution of the main routine program by the CPU 200, as will be described later.

The CPU 200 is connected to the paper passing sensor 109, the operation panel 212, the electromagnetic clutch 213, the image reading unit 110, and the image forming units 122Y to 122K via the I / O interface 205. Thus, the CPU 200 receives a detection signal from the paper passing sensor and detects the passage of the recording sheet.
In addition, the CPU 200 accepts a user command input through the operation panel 212 or presents information. Further, settings of a falling slewing table and a drive current table, which will be described later, are also accepted by the operation panel 212 and recorded in the RAM 202. The fall-through slewing table and the drive current table are recorded in the HDD 210 when the image forming apparatus 1 is powered off.

The electromagnetic clutch 213 is used to transmit the driving force of the stepping motor 211 to the registration roller 108 or to disconnect it. The CPU 200 accepts digital image data from the image reading unit 110 via the I / O interface and causes the image forming units 122Y to 122K to form toner images.
[3] Conveying unit 100
Next, the conveyance unit 100 will be described.

  FIG. 3 is a diagram illustrating a part of the configuration of the transport unit 100. As shown in FIG. 3, the transport unit 100 includes guide plates 300 and 301 that guide the recording sheet S along the transport path, and a transport roller 106 and a registration roller 108 are disposed on the transport path. . A paper passing sensor 109 that detects the passage of the recording sheet is disposed on the conveyance path from the conveyance roller 106 to the registration roller 108.

When performing skew correction, the CPU 200 controls the electromagnetic clutch 213 to stop the registration roller 108. As a result, the recording sheet S cannot pass through the registration roller 108, but is pushed out toward the registration roller 108 by the conveying roller 106, so that a loop is formed.
When the CPU 200 detects the passage of the recording sheet based on the detection signal from the paper passing sensor 109, the CPU 200 instructs the stepping motor control unit 204 to perform falling through. The stepping motor control unit 204 gradually decreases the rotation speed of the conveying roller 106 by gradually decreasing the frequency of the driving current of the stepping motor 211 in accordance with an instruction from the CPU 200.

[4] Stepping motor control unit 204
Next, the stepping motor control unit 204 will be described.
FIG. 4 is a block diagram illustrating a functional configuration of the stepping motor control unit 204. As shown in FIG. 4, the stepping motor control unit 204 includes a memory 400, a phase advance control circuit 410, a D / A (Digittal to Analogue) converter 420, a drive current determination circuit 430, and a switching circuit 440.

  In the memory 400, a falling slewing table 401 and a drive current table 402 are recorded. In the falling slewing table 401, the phase advance time (number of clocks) per step at the time of falling slewing of the stepping motor 211 is specified. The drive current table 402 specifies a drive current value for each phase advance step when the stepping motor 211 falls through.

The phase advance control circuit 410 includes a counter 411 and a decoder 412. The counter 411 sequentially reads the phase advance time from the falling slewing table 401, counts the clock, and outputs a pulse signal every time the phase advance time elapses. This pulse signal becomes a phase advance clock which is a reference for phase advance.
The decoder 412 outputs an on / off signal to each phase of the stepping motor in synchronization with the advance clock.

The D / A converter 420 sequentially reads out the drive current value from the drive current table 402 for each phase advance step, converts it into an analog value, and inputs the corresponding reference voltage to the drive current determination circuit 430.
The drive current determination circuit 430 includes an AND circuit 431, a constant current chopping circuit 432, and a current detection circuit 433, and determines the drive current of the stepping motor 211 according to the reference voltage.

The current detection circuit 433 detects the current value input to the stepping motor 211 and inputs it to the constant current chopping circuit 432.
The constant current chopping circuit 432 compares the detection value of the current detection circuit 433 with a reference voltage by an analog comparator, and when the detection value is higher than the reference voltage, the comparator output is turned off, and when the detection value is lower, it is turned on to perform constant current chopping. .

The AND circuit ANDs the output of the phase advance control circuit 410 and the output of the constant current chopping circuit 432.
The switching circuit 440 drives the stepping motor 211 by modulating the average value of the drive voltage applied to the stepping motor 211 according to the ON / OFF duty ratio.

In the falling slewing, first, the value of the first step specified in the falling slewing table 401 is transferred to the counter 411, for example, by DMA (Direct Memory Access) transfer to the counter 411. Further, the value of the first step designated in the drive current table 402 is transferred to the D / A converter 420.
These values are read and transferred from the falling slewing table 401 and the drive current table 402 each time a phase advance clock is output until the final step of falling slewing is reached. The stepping motor 211 stops at the final step of the falling through.

[5] Deflection Control Next, the deflection control will be described.
The conveyance distance of the recording sheet by one step of the stepping motor 211 is
(Roller outer diameter) x (Gear ratio) x π / (Number of rotation steps)
Is required. For example, when the outer diameter of the conveying roller 106 is 20 mm, the gear ratio is 0.5, the number of rotation steps, that is, the number of steps required to rotate the stepping motor 211 once is 96 steps, 1 of the stepping motor 211 The conveyance distance of the recording sheet by the step is about 0.33 mm.

  On the other hand, in the prior art, since the minimum time interval of the control timer for starting and stopping the stepping motor is 5 milliseconds, when the conveyance speed of the recording sheet is 300 mm / second, there is 1 recording sheet during the minimum time interval. .5 mm is transported, and accuracy sufficient for controlling the amount of deflection cannot be obtained. Therefore, the present invention capable of controlling the transport distance in units of 0.33 mm realizes higher accuracy than the conventional technology.

Now, when the recording sheet is bent at a conveying distance of 4 mm from when the leading edge of the recording sheet hits the registration roller 108 until it stops, if the falling through is made into 12 steps,
0.33 mm x 12 steps = 3.96 mm
Thus, the conveyance distance can be approximately 4 mm. When the sheet passing sensor 109 is arranged 1 mm before the registration roller 108 on the conveyance path, 1 mm + 4 mm = until the recording sheet is bent by a desired amount after the leading edge of the recording sheet is detected by the sheet passing sensor 109. It is necessary to convey the recording sheet by 5 mm. Therefore,
From 5 mm ÷ 0.33 mm≈15 steps, the sheet passing sensor 109 may detect the leading edge of the recording sheet and then perform the falling through of 15 steps.

In other words, the same deflection amount can be realized by performing the falling through of the same number of steps regardless of the time when the sheet passing sensor 109 detects the leading edge of the recording sheet.
In addition, the amount of deflection can be changed by changing the number of steps of the falling through. After detecting the leading edge of the recording sheet by the paper passing sensor 109, if the falling through is performed in 8 steps, the deflection amount is 0.33 mm × 8 steps−1 mm = 1.64 mm.
It can be. Similarly, in 12 steps,
0.33 mm x 12 steps-1 mm = 2.96 mm
Thus, the deflection amount can be controlled with high accuracy.

FIG. 5 is a timing chart showing the conveyance speed and the detection signal of the communication sensor when the recording sheet is bent. As shown in FIG. 5, the conveyance speed is gradually increased when the conveyance roller 106 is activated at time a, and when the predetermined conveyance speed is reached at time b, the acceleration is finished and the constant speed driving is performed.
Thereafter, when the paper passing sensor 109 detects the leading edge of the recording sheet at time c, the detection signal of the paper passing sensor 109 changes from the off state to the on state. In response to this transition, the stepping motor control unit 204 starts the falling through. As a result, the conveyance speed starts to decrease at time e, the conveyance roller 106 stops at time f, and the conveyance speed becomes zero.

FIG. 5 shows a case where the leading edge of the recording sheet hits the registration roller 108 at a time d from when the sheet passing sensor 109 detects the leading edge of the recording sheet until the falling through starts. However, the leading edge of the recording sheet may hit the registration roller 108 during the falling through. Which one depends on the amount of deflection to be formed.
[6] Modifications Although the present invention has been described based on the embodiments, it is needless to say that the present invention is not limited to the above-described embodiments, and the following modifications can be implemented. .

(1) Although the tandem type color image forming apparatus has been described as an example in the above embodiment, the present invention is not limited to this, and may be a monochrome image forming apparatus other than the tandem type. Further, the present invention is not limited to a copying apparatus, and the effects of the present invention can be obtained even with a facsimile apparatus or a printer apparatus.
(2) In the above embodiment, the case of accepting the setting of the falling slewing table and the drive current table via the operation panel has been described. Needless to say, the present invention is not limited to this, but instead. It may be as follows.

That is, a plurality of driving current table candidates corresponding to the falling slewing table may be prepared, and any one of them may be selected by the operation panel 212. In this way, the optimum falling slewing time can be specified in accordance with the device and the environment, so that it is possible to realize a deflection amount desirable for the user.
(3) In the above embodiment, the deflection amount is calculated by taking as an example the case where the falling through starts immediately after the leading edge of the recording sheet is detected by the paper passing sensor 109. However, the present invention is not limited to this. Needless to say, there may be a certain delay time from the detection of the leading edge of the recording sheet to the start of falling through. Even in such a case, it is possible to estimate and control the deflection amount in consideration of the delay time.

  The image forming apparatus according to the present invention is useful as an apparatus that corrects skew correctly while conveying a sheet at high speed.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 100 ... Conveyance part 102-106 ... Conveyance roller 107 ... Registration roller 109 ... Paper passing sensor 204 ... Stepping motor control part 211 ... Stepping motor 212 ... Operation panel 400 ... Memory 410 ... Advance phase control circuit 420 ... D / A converter 430 ... Driving current determination circuit 440 ... Switching circuit 401 ... Falling slewing table 402 ... Driving current table 411 ... Counter 412 ... Decoder 431 ... AND circuit 432 ... Constant current chopping circuit 433 ... Current detection circuit

Claims (2)

An image forming apparatus that operates by a central processing unit repeatedly executing a main routine at regular intervals,
Registration rollers,
A stepping motor,
A conveyance roller that is driven by the stepping motor and abuts the recording sheet against the stopped registration roller to bend it;
A sheet passing sensor that is disposed between the registration roller and the conveying roller on the conveying path of the recording sheet and detects the passage of the recording sheet;
Control means for controlling the stepping motor without depending on execution of the main routine;
Storage means for storing parameters used for the control,
The parameter is a parameter for performing falling slewing of the stepping motor,
2. The image forming apparatus according to claim 1, wherein when the sheet passing sensor detects the leading edge of the recording sheet, the control unit performs the falling through control of the stepping motor according to the parameter. It has an operation panel that accepts user instructions,
The storage means stores a plurality of parameters for performing different falling slewing controls,
The image forming apparatus according to claim 1, wherein the control unit performs a falling through control according to a parameter specified on an operation panel.

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