JP2008158076A - Sheet conveying controller of image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus for reducing a relative color shift generation amount generated between colors to the utmost by detecting and controlling a loop amount of a proper form without generating pulling or push-in of the form by a fixing device and a transfer part even when the forms of various weighing amounts are passed. <P>SOLUTION: A sheet conveying controller of the image forming apparatus detects the loop amount of a sheet by making a loop sensor (photo-interrupter) a shading or light transmission state by a loop sensor flag. The controller AD-converts detection results at each prescribed time (continuously) and differentially calculates an AD-converted digital value and a proper target loop amount. The controller performs control for making the loop amount of conveying sheets constant by using differentially calculated values at each prescribed time (continuously) and correcting a target speed of a fixing drive motor. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer that detects and controls a loop amount of a sheet formed between a transfer unit that transfers toner onto a sheet such as paper and a fixing device.

  An image forming apparatus configured by a conventional heating roller system pulls a sheet from a fixing roller when a sheet such as a sheet is conveyed while being sandwiched between nip portions of both the fixing roller and the photosensitive drum. When this occurs, image misalignment or rubbing may occur. In order to prevent the deviation and rubbing of the image, an image forming apparatus that conveys the sheet while forming an intentional loop upstream of the fixing device is generally known. By detecting the sheet passing timing using a sensor provided in the middle of conveyance and variably controlling the roller rotation speed of the fixing device according to this detection timing, a loop is generated in the sheet upstream of the fixing device. It was.

  However, it is difficult to keep the sheet conveyance speed constant due to variations in processing accuracy of parts constituting the apparatus and various causes such as sheet slip, and as a result, the sheet loop amount is kept constant. It was difficult to maintain.

  Therefore, the sheet conveyance control device of the conventional image forming apparatus detects the sheet loop upstream of the fixing device in order to keep the sheet loop amount constant at the portion positioned before the sheet entrance of the fixing device. There is a configuration in which a separate unit is provided and speed control is performed on the driving mechanism of the sheet conveying unit of the fixing device using a detection signal from the loop detection unit (for example, Patent Document 1 and Patent Document 2). (See claim 3).

  A conventional example relating to an image forming apparatus provided with means for detecting the loop amount will be described below.

  The means for detecting the loop amount has a sensor for detecting the upper limit and the lower limit of the loop amount formed by the sheet, and when the upper limit of the loop amount is detected, the speed of the driving means of the fixing unit is increased, Some control is performed such that the speed of the driving unit of the fixing unit is decreased when the lower limit of the loop amount is detected (for example, Patent Document 3).

  In addition, the downstream unit conveyance speed is set slower than the upstream unit conveyance speed in the sheet conveyance direction, and switching control is performed so as to increase the downstream unit conveyance speed according to the detection result of the loop amount. (For example, refer to Patent Document 4).

  A first detection unit that detects the loop amount; and a second detection unit that detects a loop larger than the loop amount detected by the first detection unit, wherein the second detection unit detects the loop. Sometimes, the conveyance speed of the fixing device is increased, and when the first detection means detects a loop, the conveyance speed of the fixing device is returned to a low speed (for example, Patent Document 5).

  Also, there is one that controls ON / OFF of the driving force of the fixing device based on the loop amount detection information (see, for example, Patent Document 6).

  Further, depending on the presence / absence of a signal from the loop detection means, a constant loop amount is formed based on the detection result of the loop detection means before the trailing edge of the sheet reaches a predetermined position upstream of the transfer position in the conveyance direction. Some control the fixing conveyance speed so as to do this (for example, see Patent Document 7).

  Hereinafter, a sheet conveyance control device of a conventional image forming apparatus will be described.

  FIG. 7 shows the space between the sheet conveyance belt and the fixing device in the image forming apparatus. Further, FIG. 8 shows a fixing inlet conveyance guide and a loop sensor flag. FIG. 9 shows the positional relationship between the loop sensor flag and the loop sensor.

  With reference to the drawings, a part related to a sheet conveyance configuration between transfer and fixing of an image forming apparatus according to a conventional embodiment will be described.

  The image forming apparatus illustrated in FIG. 7 includes an adsorption conveyance belt 56 that adsorbs and carries a sheet, a cartridge 54, a fixing device 59, and a loop sensor 60. The suction conveyance belt 56 includes a transfer roller 57 and a belt driving roller 58 inside. The cartridge 54 is detachably disposed and includes a toner, a cleaner, a charging roller 55, a photosensitive drum 52, and a developing roller 53 (not shown). The fixing device 59 shows a fixing pressure roller 62, a fixing driven roller 61, a fixing inlet conveyance guide 63, and a loop sensor flag 65.

  The sheet is carried on the suction conveyance belt 56, and the toner is transferred to the sheet in the cartridge 54 portion. The sheet conveyed to the cartridge 54 passes through the fixing inlet conveyance guide 65 and is conveyed to the fixing device 59. In the fixing device 59, the sheet is nipped and conveyed to the nip portion formed by the fixing pressure roller 62 and the fixing driven roller 61, and the unfixed toner image is heated and fixed on the sheet by the heated fixing driven roller.

  Next, the loop sensor flag 65 and the fixing entrance conveyance guide 63 are shown in detail in FIG. A loop sensor flag 65 a for detecting the loop amount of the sheet is disposed on the conveyance surface of the fixing entrance conveyance guide 63. The loop sensor flag 65a is arranged so as to be rotatable about one side as a swing center, and the other is arranged so as to be rotated according to the loop amount that the sheet forms along the conveyance surface. Further, from the swing center of the loop sensor flag 65a, a loop sensor flag 65b linked to the movement of the loop sensor flag 65a extends to the loop sensor 60 side which is one of the loop amount detection determination means.

FIG. 9 shows the relationship among the loop sensor flag 65b, the loop sensor 60, and the loop amount of the sheet. As described above, the loop amount is detected based on whether or not it exceeds a predetermined value, and this predetermined value is shown in FIG. 9 as a loop amount control threshold value. The speed of the first-stage fixing driven roller 61 is changed according to the first-stage loop amount detection result. Thus, by performing loop amount control centering on the loop amount control threshold, the loop amount is controlled to a predetermined value.
JP-A-1-267237 JP 2000-089605 A JP-A-7-234604 JP-A-10-97154 JP 2001-282072 A JP 2000-056529 A JP 2003-316184 A

  However, in the above-described conventional loop amount detection device, since the loop amount that can be detected is a predetermined single state, it is difficult to cope with various types of media used in recent years, particularly in color image forming apparatuses. It is becoming. For example, a paper having a basis weight of 64 g and a paper having a basis weight of 199 g are different in paper size, and therefore a difference occurs in an appropriate loop amount in each paper. As a result, when the detection means is provided so that the paper loop with the basis weight of 64 g can be controlled to an appropriate paper loop amount, the paper with the basis weight of 199 g has a strong paper stiffness, so that the fixing device is pushed in. The problem of becoming will occur.

  Further, in recent color image forming apparatuses, a tandem type color image forming apparatus in which the printing speed is greatly improved by arranging four photosensitive drums side by side is the mainstream. There are two types of tandem color image forming apparatuses that employ a so-called intermediate transfer system and those that employ an electrostatic attraction belt system.

  The intermediate transfer type color image forming apparatus sequentially superimposes the toner images developed on the electrostatic latent image on the photosensitive drum on the intermediate transfer member to perform primary transfer, and then superimposes and transfers the toner images of each color on a sheet. Secondary transfer is performed collectively on a certain sheet. Therefore, as in the conventional monochrome image forming apparatus, although the sheet is pulled and pushed in between the transfer unit that nips the sheet and the fixing device, a color misalignment image due to the sheet pulling basically does not occur. .

  On the other hand, an electrostatic attraction belt type color image forming apparatus uses an electrostatic attraction force to attract and convey a sheet onto a belt, and a toner image developed on an electrostatic latent image on a photosensitive drum is transferred. The image is sequentially transferred onto the sheet carried and conveyed on the electrostatic adsorption belt. Therefore, unlike conventional monochrome image forming apparatuses and intermediate transfer type tandem color image forming apparatuses, there are four nip portions between the photosensitive drum on which the paper is sandwiched and the transfer section, and the nip is advanced as the conveyance proceeds. The location changes. In this case, in addition to image degradation such as image rubbing, transfer shift to paper, expansion / contraction, etc., which has occurred in conventional monochrome image forming apparatuses, each color of each color can be obtained by pulling / pushing the paper from the fixing device. There is a problem in that the position timing of the sheet onto which the toner is transferred is shifted, resulting in a color misalignment image in which the color superposition positions are relatively shifted.

  Furthermore, in order to reduce the size of the device, it is necessary to shorten the distance from the transfer unit to the fixing device. Due to the size of the paper loop, the paper is pulled or pushed between the fixing device and the transfer unit. There was a problem of being easy to do. In addition, due to the difference in the strength of the paper, the appropriate loop amount that does not cause the paper to be pulled or pushed in differs between the fixing device and the transfer unit, and it is not possible to cope with only the method that detects the loop amount alone. was there.

  Further, the color misregistration generated in the color image forming apparatus has a problem that an accuracy of several tens of μ units is required for high image quality.

  The present invention has been made in view of the above-described problems. Even when papers having various basis weights and different strengths are passed, the paper is pulled or pushed between the fixing device and the transfer unit. It is an object of the present invention to provide a color image forming apparatus capable of reducing the relative amount of color misregistration generated between each color as much as possible by detecting and controlling an appropriate sheet loop amount that does not generate color.

  In order to achieve the above object, a sheet conveyance control device of an image forming apparatus according to claim 1 according to the present application is an image forming apparatus that fixes an image formed on a recording medium by a fixing unit in an image forming unit. A conveying unit that conveys the recording medium from the image forming unit to the fixing unit; a fixing unit that fixes the recording medium conveyed by the conveying unit while conveying the recording medium; A loop amount holding unit; a loop amount detecting unit for detecting a loop amount generated in the recording medium while being conveyed from the image forming unit to the fixing unit at every predetermined time; and the loop amount at the predetermined time. Loop amount conversion means for converting the detection result of the detection means into a digital value, and the digital value converted by the loop amount conversion means and the appropriate loop amount in the previous period at every predetermined time Loop amount comparing means for comparing the appropriate loop amount held by the holding means, and using the result of comparison by the previous loop amount comparing means for each predetermined time, The recording medium conveyance speed is corrected, and the recording medium is conveyed from the image forming unit to the fixing unit.

  The sheet conveyance control device for an image forming apparatus according to claim 2 is characterized in that the appropriate loop amount holding means holds a plurality of loop amounts.

  The sheet conveyance control device of the image forming apparatus according to claim 3 includes a paper type detection unit that detects a paper type such as paper or an OHT sheet as the recording medium, and uses a detection result of the previous paper type detection unit. A proper loop amount for the recording medium is selected from a plurality of loop amounts held by the appropriate loop amount holding means.

  The sheet conveyance control device of the image forming apparatus according to claim 4, further comprising a paper type setting unit that selectively selects a paper type of the recording medium, and using the result of the paper type setting unit, the appropriate loop amount An appropriate loop amount for the recording medium is selected from a plurality of loop amounts held by the holding means.

  The sheet conveyance control device of the image forming apparatus according to claim 5, further comprising a thickness detection unit that detects a thickness of the recording medium, and using the result of the thickness detection unit, the appropriate loop amount holding unit is An appropriate loop amount for the recording medium is selected from a plurality of loop amounts held.

  The sheet conveyance control device of the image forming apparatus according to claim 6, further comprising a size detection unit that detects a size of the recording medium, and the appropriate loop amount holding unit holds the detection result of the size detection unit. An appropriate loop amount for the recording medium is selected from a plurality of loop amounts.

  8. The sheet conveyance control device of an image forming apparatus according to claim 7, wherein a target loop amount switching unit that switches the target loop amount every predetermined time, and the target loop amount holding unit that maintains the target loop amount every predetermined time. A target loop amount selecting means for selecting the target loop amount, the target loop amount switching means switching the target loop amount to the target appropriate loop amount selected by the target loop amount selecting means at every predetermined time, The recording medium is conveyed from the image forming unit to the fixing unit.

  9. The sheet conveyance control device for an image forming apparatus according to claim 8, wherein the loop amount detection means is a first mechanical flag which is pushed by the recording medium conveyed while forming a loop shape and swings. A second mechanical flag that is driven according to the operation of the first mechanical flag; and a light detection unit that detects an operating position of the second mechanical flag.

  With the above configuration, the sheet can be transported by switching the loop amount of the sheet only at the moment when the sheet enters the fixing device, and further, the pulling and pushing of the sheet by the electrostatic adsorption conveyance belt and the fixing device are reduced as much as possible. Therefore, it is possible to provide a color image forming apparatus that enables high-quality printing with a very small amount of color misregistration.

(Example 1)
Embodiment 1 of the present invention will be described below in detail with reference to the drawings. The description will be made in the order of the entire image forming apparatus, the motor speed control apparatus, the detection of the loop amount of a sheet as a recording medium, and the description of the control of the loop amount of the sheet.

  In the first embodiment, the loop sensor flag detects the loop amount of the sheet by setting the loop sensor (photo interrupter) in a light-shielding or light-transmitting state. The detection result is AD-converted every predetermined time (continuously), and the difference between the AD-converted digital value and the appropriate target loop amount is calculated. A configuration is described in which the target speed of the fixing drive motor is corrected using the value obtained by calculating the difference every predetermined time (continuously), and the loop amount of the conveyed sheet is controlled to be constant.

(Image forming device)
The overall configuration of the image forming apparatus will be described with reference to FIG. In an electrophotographic color image forming apparatus, in order to reduce the time required for forming a multicolor image, a multi-color toner is provided by a color optical image forming unit including a scanning optical system for performing image exposure and a cartridge for each color. A so-called tandem type color image forming apparatus for forming an image has already been proposed. In this color image forming apparatus, for example, a conveyor belt that electrostatically adsorbs and conveys a transfer material and a plurality of photoconductors around the transfer belt are arranged, and a charger and a scanning optical system provided to face each photoconductor The toner images of a plurality of colors formed by the developing device are sequentially transferred to a transfer material.

  The tandem type color image forming apparatus includes a photosensitive drum (31C, 31Y, 31M, 31Bk) for four colors as an image carrier, and a transfer roller (32C, 32Y, 32M, 32Bk), the cartridge (34C, 34Y, 34M, 34Bk), the developing roller (33C, 33Y, 33M, 33Bk) that conveys the developer from the cartridge, and the photosensitive drum (31C, A laser scanner device (35C, 35Y, 35M, 35Bk) that forms an electrostatic latent image on 31Y, 31M, 31Bk) is provided for each color (yellow, magenta, cyan, black) image forming station.

  The sheet that has passed through the registration roller 37 is conveyed to the adsorption roller 36, electrostatically adsorbs the sheet to the electrostatic adsorption belt 29 formed endlessly by the adsorption roller 36, and starts conveyance to the image forming unit.

  A visible image is formed on the electrostatic latent image formed on each photoconductive drum 31 by using a developer conveyed from each cartridge 34 by each developing roller 33 and transferred by a transfer roller 32 to which a bias is applied. Transferred onto the material. The transfer roller is for transferring a toner image onto a sheet, and the toner image developed on the photosensitive drum is transferred to the sheet while the sheet is nipped and conveyed between the rotating photosensitive drum 31 and the transfer roller 32. The The sheet is fed with a conveyance force by the photosensitive drum 31Bk, the transfer roller 32Bk, and the electrostatic attraction belt 29 located on the most downstream side in the conveyance direction, and is sent to the fixing device 9 downstream in the conveyance path. The fixing device 9 is a unit for fixing the toner image on the sheet. The fixing driven roller 11 heats the sheet, and the fixing pressure roller 12 conveys the sheet and applies a rotational force to the fixing driven roller 11 to pressurize the sheet. It consists of. A color image for four colors is fixed on the sheet by the nip portion sandwiched between the fixing driven roller 11 and the fixing pressure roller 12. Thereafter, the sheet is discharged to the discharge tray 61.

(Motor speed control device)
Next, a motor speed control method in the image forming apparatus will be described with reference to FIG. FIG. 2 is a diagram showing a motor control system, 25 is a ferromagnetic magnetoresistive sensor element (hereinafter referred to as an MR sensor) which is a ferromagnetic magnetic effect sensor, 26 is a waveform converter, and MR sensor 25 and the waveform converter 26 constitute MR sensor type detection means. The MR sensor 25 can read a pattern magnetized evenly on the rotor as a Sin waveform corresponding to the rotational speed of the rotor.

  In addition, the rotational speed detection of the motor by the FG pattern formed in the vicinity of the rotor can be used. Further, in order to detect the rotational speed of the motor 18 outside the motor, an encoder including a disk having slits at equal intervals along the circumference and a photo interrupter (light transmission type sensor) may be provided. As for the encoder, a reflection optical system, a disk-shaped magnetic pattern, and the like are used. The photo interrupter is arranged so as to sandwich the disk of the encoder. When the light of the photo interrupter passes through the slit of the disk, the rotation speed detection signal changes state. Therefore, when the motor rotates, the disk provided on the shaft of the drum rotates, and slits that are equally spaced along the circumference are sequentially sent between the light emitting and light receiving elements of the photo interrupter. For this reason, the speed detection signal has a pulse-like waveform, and the speed can be detected based on the pulse period.

  For the detection of the rotational speed, either the MR sensor 25 described above, the MR sensor method of the waveform converter 26, a disk, or a photo interrupter encoder method may be used. It is sufficient to use either one as a means for detecting the rotational speed. In this embodiment, description will be made using the MR sensor method.

  S1 and S2 are speed detection signals. The motor 18a rotates the fixing pressure roller 12 included in the fixing device, and the motor 18b rotates the drive roller included in the electrostatic chucking belt 29.

  The motor controller 40 detects and controls the rotational speed of the motor based on the output signals S1 and S2 of the MR sensor 25 converted into rectangular pulse waves (for example, 500 pulses / rotation) by the waveform converter 26.

  In the motor controller 40, 41a detects the current speed of the motor a from the rectangular pulse transmitted from S1, and 41b detects the current speed of the motor b from the rectangular pulse transmitted from S2. A motor b speed detection unit 44, an AD converter that converts a detection result from the loop sensor 30 serving as the loop amount detection unit into a digital value, and a digital value storage unit 45 that stores the AD converted digital value 43a is a motor a target speed setting unit for setting the target speed of the motor 18a, 43b is a motor b target speed setting unit for setting the target speed of the motor 18b, 42a is a value of the motor a speed detection unit 41a, The acceleration / deceleration signal output unit a compares the values of the motor a target speed setting unit 43a and transmits an acceleration signal or a deceleration signal to the motor driver a from the comparison result. 42b is an acceleration / deceleration signal output unit b that compares the value of the motor b speed detection unit 41b with the value of the motor b target speed setting unit 43b and transmits an acceleration signal or a deceleration signal to the motor driver b based on the comparison result. In this embodiment, the AD converter 41 is configured to convert the result detected by the loop sensor 30 into a 10-bit digital value.

  22 is a microcontroller, 23 is a ROM built in the microcontroller 22, and 24 is a RAM built in the microcontroller.

  The ROM 22 in the microcontroller 22 stores a target appropriate loop amount (digital value).

  For the motor controller 40, for example, a processor having a high-speed arithmetic processing function such as an Application Specific Integrated Circuit (hereinafter referred to as ASIC) can be used, and communicates with the microcontroller 22 via the motor drivers 20a and 20b. Thus, the rotational speed control of the motor 18a and the motor 18b is performed by PWM control.

  By performing feedback and feedforward control using an ASIC, rotation speed control that is less affected by load fluctuations of the motor 18a and the motor 18b is possible.

  The microcontroller 22 calculates a difference between the digital value stored in the digital value storage unit 45 and the target appropriate loop amount (digital value), and adds the calculated value to the motor a target speed. The target speed of the motor a that has been added is set in the target speed setting register 43a. The acceleration / deceleration signal output unit 42a compares the value of the motor a speed detection unit 41a with the value set in the motor a target speed setting unit 43a. If the value of the motor a speed detection unit 41a is smaller, the acceleration signal If there are more, a deceleration signal is transmitted to the motor driver 20a to control the driving speed (hereinafter also referred to as rotational speed) of the motor 18a.

  Further, the microprocessor 22 sets the target speed of the motor 18b for driving the electrostatic transport belt in the motor b target speed setting unit 43b so that the sheet is transported at a specified process speed.

  The acceleration / deceleration signal output unit 42b compares the value of the motor b speed detection unit 41b with the value set in the motor b target speed setting unit 43b. If the value of the motor b speed detection unit 41b is smaller, an acceleration signal is output. If there are more, a deceleration signal is transmitted to the motor driver 20b to control the driving speed (hereinafter also referred to as rotational speed) of the motor 18b. The motor 18a and the motor 18b can be accelerated / decelerated by adjusting the electric power supplied to the motor. The loop amount control will be described in detail below.

(Sheet loop amount detection)
Next, a sheet loop amount detection method for the image forming apparatus according to the first embodiment will be described with reference to FIGS. 2, 4, and 5.

  FIG. 4A shows the fixing entrance conveyance guide 13. FIG. 4B shows the loop sensor flag 15. The loop sensor flag 15 includes a loop sensor flag 101a that detects the loop amount of the sheet, and a loop sensor flag 101b that is linked to the movement of the loop sensor flag 101a. The loop sensor flag 101a is arranged so as to be rotatable about one side as a swing center, and the other is arranged so as to be rotated according to the loop amount that the sheet forms along the conveyance surface. Further, the loop sensor flag 101b extends toward the loop sensor 30 which is a loop amount detection discriminating means. The loop sensor 30 is sequentially shielded from light or transmitted through light by swinging the same loop sensor flag 101.

  A loop sensor 30 shown in FIG. 2 detects a loop of the sheet conveyed from the electrostatic attraction belt 29 to the fixing device 9 described above. The loop sensor flag 101b shown in FIG. 4 and a loop sensor including a photo interrupter are provided so that the sheet loop amount can be detected.

  Regarding the loop amount of the sheet, when the loop sensor flag 101b rotates in the direction of the arrow in FIG. 4B, the loop sensor 30 changes its state to light transmission or light shielding, and detects the loop amount of the sheet. The LED, which is a light emitting element, emits light when supplied with power from the controller unit 28 via a resistor that sets a drive current value. The phototransistor, which is a light receiving element, has an output terminal connected to the I / O input port of the AD converter of the motor controller 21. When the loop sensor flag 101b shields the photointerrupter, the photointerrupter output is output. The terminal outputs the minimum voltage value, and outputs the maximum voltage value when not shielded from light. The current loop amount of the sheet is detected from the digital value obtained by AD converting the analog value input to the AD converter I / O input port.

  FIG. 5 shows the relationship among the loop sensor flag 101b, the loop sensor 30, the digital conversion value, and the sheet loop amount.

  The loop amount of the sheet is determined by a digital value obtained by AD converting the output voltage of the loop sensor. FIG. 5 shows that the digital conversion value decreases as the loop amount increases.

  The digital value in FIG. 5 is expressed in hexadecimal (hex). The digital value is 10 bits as described in the motor device. The digital values described in FIG. 5 are arbitrary and are for explaining this embodiment.

  Next, the state of FIG. 5 will be described. State 1 is a state in which the loop sensor flag 101b does not shield the loop sensor 30 from light. In that case, the value output from the loop sensor is the maximum voltage value. Therefore, the AD converted value is 3FF.

  State 2 is a state in which the loop amount of the sheet is small and the loop sensor flag 101b does not shield the loop sensor 30 so much. In that case, the voltage output from the loop sensor is slightly smaller than that in the state 1. Therefore, the AD-converted value is slightly smaller than in state 1.

  State 3 is a state in which the loop amount is larger than that in state 2 and the loop sensor flag 101b shields the loop sensor 30 by half. In that case, the voltage value output from the loop sensor is half the voltage value when no light is shielded. Therefore, the AD-converted value is half the digital value in the state 1.

  State 4 is a state in which the loop amount is quite large and the loop sensor flag 101b substantially shields the loop sensor 30 from light. In that case, the voltage value output from the loop sensor 30 becomes considerably small. Therefore, the AD converted value is also considerably reduced.

  State 5 is a state in which the loop amount of the sheet is too large, and the loop sensor 30 is completely shielded from light. In that case, the voltage value output from the loop sensor 30 is the minimum voltage value. Therefore, the AD converted value is 000.

  The loop amount is detected after the voltage value from the loop sensor 30 changes, that is, after the loop of the sheet is detected.

(Sheet loop amount control)
Next, the control operation of the loop amount of the sheet will be described with reference to FIGS.

  FIG. 1 shows a schematic block diagram of a control circuit.

  When the sheet reaches the loop sensor flag 101b, loop amount detection is started. At this time, the motor a rotates at a slightly slower speed than the motor b. For this reason, the loop amount of the sheet gradually increases. Accordingly, the voltage value output from the loop sensor gradually decreases, and the digital value converted by the AD converter 44 also gradually decreases.

  A configuration will be described in which a difference between the digital value stored in the digital value storage unit and the target appropriate loop amount is calculated, and the value obtained by calculating the difference to the target speed of the motor a is added to the motor a target speed.

  The microcontroller 22 reads the value in the digital value storage unit 45 at an arbitrary timing or at a predetermined time interval, and calculates a difference from the target appropriate loop amount (digital value) stored in the ROM 23. For example, it is assumed that the digital value stored in the digital value storage unit 45 is 1FF (hex) after a predetermined time after detecting the loop amount. Further, it is assumed that the target appropriate loop amount (digital value) is 1F0 (hex). This means that the current sheet loop amount is smaller than the target loop amount. When the difference between the digital value in the digital value storage unit and the target appropriate loop amount is calculated, F (hex) is obtained. As shown in FIG. 1, this is added to the target speed of the motor a. For example, it is assumed that the current target speed of the motor a is 500 (hex). Since the sheet loop amount at this timing is smaller than the target loop amount, it is necessary to make the speed of the motor a slower than the current speed. Therefore, F (hex) is subtracted from the target speed 500 (hex) of the motor a. The result of subtraction is 4F1 (hex). Using this 4F1 as the target speed of the motor a, 4F1 is set in the motor a target speed setting unit 43a. When the setting is made, motor control is performed and the motor a decelerates.

  As the motor a decelerates, the sheet loop amount increases.

  In this embodiment, the difference between the digital value storage unit 45 and the target appropriate loop amount (digital value) is directly reflected in the target speed of the motor a. However, in order to improve accuracy, the difference is multiplied by a gain, etc. It is also possible to adopt a configuration in which the value obtained is reflected in the target speed of the motor a. The difference may be totaled for a predetermined time and the integrated value may be reflected on the target speed of the motor a.

  While the sheet forms a loop and is being conveyed, continuously calculates the difference between the digital value in the digital value storage unit and the target appropriate loop amount as described above, and calculates the difference to the target speed of motor a To switch the target speed of motor a. With such a configuration, every time the loop amount changes, the target speed of the motor a is corrected, and the sheet can be conveyed with the loop amount kept constant. For this reason, it becomes possible to reduce the pulling and pushing of the sheet by the electrostatic attraction conveyance belt 29 and the fixing device 9 as much as possible, and color image formation that enables high-quality printing with very little color misregistration. An apparatus can be provided.

(Correction for variations in loop sensor)
Due to variations in the loop sensor itself or variations in the loop sensor mounting position, there is a possibility that control cannot be performed with an appropriate loop amount for the previous period seat. For variations in the loop sensor itself and variations in the mounting position of the loop sensor, a correction value for correcting the appropriate loop amount of the sheet stored in the ROM in the microcontroller is required. The correction value for the previous period is stored in a nonvolatile memory such as an EEPROM that does not lose data even when the power is turned off. Next, how to obtain a correction value for the loop amount will be described. Loop the sheet between transfer and fixing before shipping. After a predetermined time, the digital value register 45 obtained by AD converting the loop amount is checked. That value is compared with the average value (digital value) of the loop amount of the previous-stage seat after a predetermined time, which is prepared in advance. The difference is used as a correction value and stored in the previous period EEPROM. When the loop amount control is performed, the data stored in the EEPROM in the previous period is read, and the control is performed by adding the value stored in the EEPROM to the appropriate loop amount of the sheet stored in the microcontroller.

(Example 2)
A second embodiment of the present invention will be described in detail with reference to FIG.

  In the sheet conveyance control device of the image forming apparatus according to the second embodiment, the image forming apparatus determines the sheet type of the sheet, selects an appropriate loop amount for the sheet from the determination result, and loads the sheet with the appropriate loop amount for the sheet. Transport. Since the image forming apparatus, motor speed control, and sheet loop amount detection control other than the sheet loop amount control are the same as those in the first exemplary embodiment, the description thereof is omitted.

(Sheet loop amount control)
A sheet loop amount control method for sheet conveyance control according to the second exemplary embodiment will be described with reference to FIG.

  Reference numeral 2 denotes a paper type detection unit that detects the type of sheet loaded in the sheet stacking apparatus 1.

  A ROM 23 in the microcontroller 22 stores a plurality of loop amounts.

  The microcontroller 22 obtains medium information of the sheet to be printed from the host computer 5 through communication via the printer controller 6. The user can specify the type of sheet medium to be printed via a printer driver built in the host computer. When the automatic paper type detection mode is selected by the user, the type of sheet to be printed is detected by the paper type detection unit 2.

  The microcontroller 22 selects an appropriate target loop amount for the sheet from the ROM 23 in the microcontroller 22 using the detection result of the paper type.

  The control of the loop amount of the sheet after the appropriate loop amount is selected is the same as that in the first embodiment.

  With the configuration as described above, the target loop amount is switched and the loop amount control is performed depending on the paper to be printed, so that the electrostatic attraction conveyance belt 29 and the fixing device 9 pull and push the sheet more than in the first embodiment. It is possible to provide a color image forming apparatus that can reduce as much as possible and enable high-quality printing with a very small amount of color misregistration.

  In the second embodiment, the appropriate target loop amount is switched according to the paper type discrimination result. However, the proper target loop amount may be switched depending on the thickness and size of the sheet.

(Example 3)
Embodiment 3 of the present invention will be described in detail with reference to FIG.

  A sheet loop amount control method for sheet conveyance control according to the third exemplary embodiment will be described with reference to FIG.

  The sheet conveyance control device of the image forming apparatus according to the third exemplary embodiment is configured to convey the sheet by switching the target appropriate loop amount at an arbitrary time.

  Since the image forming apparatus, motor speed control, and sheet loop amount detection control other than the sheet loop amount control are the same as those in the first exemplary embodiment, the description thereof is omitted.

(Sheet loop amount control)
The ROM 23 in the microcontroller 22 stores an appropriate target loop amount for each arbitrary time to be switched.

  For example, it is assumed that the loop amount detection is started and it is an arbitrary time when it is desired to switch the target appropriate loop amount. At that time, the microcontroller 22 selects an appropriate target loop amount for the arbitrary time from the ROM 23.

  The loop amount control after the selection is the same as in the first embodiment.

  With the configuration described above, the sheet can be transported by switching the loop amount of the sheet only at the moment when the sheet enters the fixing device 9. Further, the sheet is pulled or pushed by the electrostatic adsorption transport belt 29 and the fixing device 9. As a result, it is possible to provide a color image forming apparatus that enables high-quality printing with a very small amount of color misregistration.

FIG. 2 is a schematic block diagram of a control circuit of the image forming apparatus according to the embodiment of the present invention. 1 is a diagram illustrating an outline of an engine controller of an image forming apparatus according to a first embodiment of the present invention. It is a figure which shows the outline | summary of the engine controller of the image forming apparatus which concerns on 2nd Example of this invention. FIG. 5 is a diagram illustrating a fixing entrance conveyance guide and a loop sensor flag in the image forming apparatus according to the first exemplary embodiment of the present invention. It is a figure which shows the positional relationship of the loop sensor flag and loop sensor in 1st Example of this invention. 1 is a diagram illustrating an overview of an overall configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the outline | summary of the conventional image forming apparatus described in background art. It is a diagram showing a fixing entrance conveyance guide and a loop sensor flag in a conventional image forming apparatus described in the background art. It is a figure which shows the positional relationship of the loop sensor flag and loop sensor (photo interrupter) in the conventional image forming apparatus described in background art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sheet stacking apparatus 2 Paper type detection unit 5 Host computer 6 Printer controller 9 Fixing apparatus 11 Fixing heating roller 12 Fixing pressure roller 13 Fixing inlet conveyance guide 15 Loop sensor flag 17 Loop sensor flag 18 Motor 20 Motor driver 21 Motor controller 22 Micro Controller 23 ROM
24 RAM
25 MR sensor 26 Waveform converter 27 Counter 28 Engine controller 29 Electrostatic adsorption conveyance belt 30 Loop sensor 31 Photosensitive drum 32 Transfer roller 33 Developing roller 34 Cartridge 35 Laser scanner device 36 Adsorption roller 37 Registration roller 40 Loop sensor 41 Engine controller 52 Photosensitive Body drum 53 Developing roller 54 Cartridge 55 Charging roller 56 Electrostatic adsorption belt 57 Transfer roller 58 Belt drive roller 59 Fixing device 60 Loop sensor 61 Fixing heating roller 62 Fixing pressure roller 63 Fixing inlet conveyance guide

Claims (8)

  In an image forming apparatus that fixes an image formed on a recording medium by a fixing unit in an image forming unit, the conveying unit conveys the recording medium from the image forming unit to the fixing unit, and the conveying unit conveys the recording medium. A fixing unit that fixes the recording medium while conveying the recording medium, an appropriate loop amount holding unit that retains an appropriate loop amount of the recording medium in the previous period, and the medium that is being conveyed from the image forming unit to the fixing unit every predetermined time. A loop amount detecting unit for detecting a loop amount generated in the recording medium; a loop amount converting unit for converting a detection result of the loop amount detecting unit into a digital value at each predetermined time; and the loop amount at each predetermined time. Loop amount comparison means for comparing the digital value converted by the conversion means and the appropriate loop amount held by the appropriate loop amount holding means, and at every predetermined time The recording medium conveyance speed of the fixing unit is corrected at predetermined time intervals using the result of comparison by the loop amount comparison unit in the previous period, and the recording medium is conveyed from the image forming unit to the fixing unit. An image forming apparatus.   The image forming apparatus according to claim 1, wherein the appropriate loop amount holding unit holds a plurality of loop amounts.   A paper type detecting means for detecting the paper type as the recording medium, and using the detection result of the previous paper type detecting means, the plurality of loop amounts held by the appropriate loop amount holding means; The image forming apparatus according to claim 1, wherein an appropriate loop amount is selected for the recording medium.   A paper type setting unit that selectively selects a paper type of the recording medium, and using a result of the paper type setting unit, from among a plurality of loop amounts held by the appropriate loop amount holding unit; The image forming apparatus according to claim 1, wherein an appropriate loop amount is selected for the recording medium.   A thickness detecting unit for detecting the thickness of the recording medium, and using the result of the thickness detecting unit, the recording medium is selected from a plurality of loop amounts held by the appropriate loop amount holding unit; The image forming apparatus according to claim 1, wherein an appropriate loop amount is selected.   Having a size detecting means for detecting the size of the recording medium, and using the detection result of the size detecting means, the appropriate amount for the recording medium is selected from a plurality of loop amounts held by the appropriate loop amount holding means. 2. The image forming apparatus according to claim 1, wherein an appropriate loop amount is selected.   An arbitrary time loop amount selection unit that selects an appropriate loop amount of the recording medium at an arbitrary time from a plurality of loop amounts held by the appropriate loop amount holding unit; and the loop amount at the arbitrary time Using the result of comparison of the digital value converted by the conversion means and the loop amount selected by the previous period arbitrary time loop quantity selection means by the previous period loop quantity comparison means, the recording medium conveyance speed of the previous fixing means is corrected at the arbitrary time. The image forming apparatus according to claim 1, wherein the recording medium is conveyed from the image forming unit to the fixing unit.   The loop amount detection means includes a first mechanical flag that is pushed by the recording medium conveyed while forming a loop shape and swings, and a second mechanical flag that is driven according to the operation of the first mechanical flag. The image forming apparatus according to claim 1, further comprising: a mechanical flag; and a light detection unit that detects an operation position of the second mechanical flag.

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