JP2006276700A - Recording paper carrying speed detecting method, recording paper carrying speed control method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the elongation of an image and to increase printing magnification accuracy without causing the increase in a cost due to the addition of a member such as a reflection plate, and without causing failures such as the deterioration of detection accuracy due to the deterioration of a member such as a TOP sensor. <P>SOLUTION: A current (or voltage) applied on a transfer roller (transfer member) 8 is made differ in the sates between that before and after the recording paper P passes through and that it is passing. Then, the timing of this change is detected, and a time required to let the recording paper from the leading end to the trailing end through the transfer material is obtained based on the detected timing. The recording paper carrying speed is calculated based on the obtained time and the size of the recording paper. An alternation control is performed so that the calculated carrying speed may be equal to the target carrying speed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  In the present invention, an unfixed image corresponding to target image information is formed and supported on a recording paper by an image forming process mechanism such as an electrophotographic system, an electrostatic recording system, or a magnetic recording system, and the recording paper is introduced into a fixing device. In particular, the present invention relates to an image forming apparatus such as a laser printer, a copying machine, and a facsimile machine that heat-fixes an unfixed image on a recording sheet and outputs it as an image recording material, and more particularly to a recording sheet conveyance speed detection method and a recording sheet conveyance speed control method.

  2. Description of the Related Art Conventionally, in a heat roller type or film heating type fixing device, a recording sheet is inserted into a pressure nip portion between a heating body and a pressure member, and the recording sheet is nipped and conveyed by both members, and the recording sheet is heated. For example, in a film heating type fixing device, a film or film is slid and moved to a heating body by driving and rotating a pressure member (for example, a pressure roller) that presses the heating body through the film. And the recording paper are held and conveyed together at the pressure nip portion between the heating body and the pressure roller.

  In such a fixing device, the recording paper nipping / conveying speed varies depending on the temperature state of the components. That is, in the fixing member driving type fixing device, the temperature of the pressure roller rises with the operation of the device, so that the pressure roller is slightly expanded due to heat and its outer diameter is increased. Since the pressure roller is normally driven to rotate at a constant rotational speed, when the pressure roller is hot, the thermal expansion becomes larger and the rotational peripheral speed increases than when the pressure roller is low, and the nipping and conveying speed of the recording paper increases. turn into. As a result, a speed difference occurs in the nipping and conveying speed of the recording paper by the fixing device depending on the temperature state of the pressure roller.

Due to such factors, for example, when this heating device is used as an image heating and fixing device in an image forming apparatus, the recording paper is conveyed in an image forming unit, for example, an image transfer unit, which is a processing unit upstream of the fixing device. Since the speed is kept constant at a predetermined value, when the recording paper reaches the nip portion of the fixing device from the transfer section and enters the nipping and transporting state, the recording paper transport speed at the transfer section when the pressure roller is in a high temperature state. As a result, the recording paper conveyance speed at the nip portion of the fixing device is higher. As a result, since the recording paper is pulled and conveyed at the recording paper conveyance speed of the fixing device, the recorded image is stretched in the recording paper conveyance direction, and so-called image expansion occurs. In some cases, the rear end portion of the image is detached from the rear end of the recording paper and is lost due to the image elongation.
JP-A-7-261484 JP-A-10-69135 JP-A-8-190298 Japanese Patent Laid-Open No. 11-84782

  In order to solve the above problem, a method of changing the driving speed by measuring the temperature of the pressure roller and predicting the expansion amount is proposed (Patent Documents 1 and 2). However, since this method has a large error, more accurate control cannot be performed.

  Also, the film is provided with a plurality of reflecting portions, and the peripheral speed of the film is detected by reading the ON / OFF cycle of the reflective sensor, and the driving speed of the pressure roller is sequentially adjusted so that the peripheral speed is constant. A method of changing is proposed (Patent Document 3). In this method, since a plurality of reflecting plates must be provided on the film, the cost increases. In addition, it is difficult to process with high accuracy because the interval between the reflectors must be uniform.

  Further, the recording paper conveyance speed is calculated based on the time from the recording paper leading edge detection to the recording paper trailing edge detection and the recording paper size of the recording paper detection member (hereinafter referred to as TOP sensor), and the driving speed of the pressure roller or the like is changed. A method has been proposed (Patent Document 4). In this method, when the TOP sensor is worn by the recording paper, the response speed of the TOP sensor changes (timing is advanced), and accurate speed detection becomes impossible over time.

  The present invention has been made in such a background, and the object thereof is to reduce image expansion without incurring problems such as cost increase due to addition of a member such as a reflector and a decrease in detection accuracy due to deterioration of a member such as a TOP sensor. Another object of the present invention is to provide a recording paper conveyance speed detection method, a recording paper conveyance speed control method, and an image forming apparatus capable of improving the printing magnification accuracy.

  In the present invention, in an image forming apparatus in which an unfixed toner image is transferred to a recording paper by a transfer member and fixed, the voltage applied to the transfer member when the recording paper is present or not at the transfer nip portion, or Paying attention to the current change, the current or voltage change timing is monitored to detect the time from the leading edge of the recording paper to the trailing edge of the recording paper, and the recording paper is transported based on the detection result and the passing paper size. Find the speed.

  In other words, the recording paper conveyance speed detection method according to the present invention is a recording paper conveyance speed detection method in an image forming apparatus for transferring an unfixed toner image onto a recording paper by a transfer member and fixing it. Detecting a change timing of a current or a voltage, a step of obtaining a time required for the recording paper leading end to pass through the transfer member based on the change timing, And a step of calculating a recording paper conveyance speed based on the recording paper size.

  The recording paper transport speed control method according to the present invention controls the recording paper transport speed in accordance with the obtained recording paper transport speed.

  An image forming apparatus according to the present invention is an image forming apparatus that transfers an unfixed toner image onto a recording sheet by a transfer member and fixes the toner image, and detects a change timing of a current or voltage applied to the transfer member. And a means for obtaining a time required for the recording paper from the leading edge to the trailing edge of the recording paper to pass through the transfer member based on the change timing, and the conveyance of the recording paper based on the obtained time and the recording paper size. The apparatus includes a means for calculating the speed and a transport speed changing means for changing the transport speed so that the calculated transport speed matches the target transport speed.

  In this way, in the image forming apparatus, by always maintaining the target recording paper conveyance speed, the image expansion is minimized and the printing magnification accuracy is improved.

  The transport speed changing unit can change the transport speed by changing the recording paper transport speed of the fixing unit, for example.

  The change of the conveyance speed by the conveyance speed changing unit can be performed between the prints subsequent to the print for which the recording paper conveyance speed is calculated. This makes it possible to adjust the recording paper conveyance speed for each page.

  According to the present invention, in an image forming apparatus in which an unfixed toner image is transferred onto a recording sheet by a transfer member and fixed, the cost increases due to the addition of a member such as a reflection plate as in the past, and the detection due to deterioration of a member such as a TOP sensor The image magnification can be minimized and the printing magnification accuracy can be improved without causing a decrease in accuracy.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic side view of an image forming apparatus 1 to which the present invention is applied. The process cartridge 2 is detachably stored in the image forming apparatus 1. Here, a printer is described as an example of the image forming apparatus 1, but a copying machine or a facsimile may be used.

  The image forming process is started by receiving image data from an external device (not shown) such as a personal computer via a printer interface or a LAN. Specifically, first, a point on the image carrier (for example, a photosensitive drum) 4 on which an image is formed by an exposure unit (not shown) after the image carrier 4 is charged to a predetermined constant potential by the charging roller 3. Is exposed to a predetermined potential. In the case of a copying machine, exposure is performed based on an image read from an original by an image reading unit (not shown). In the case of a facsimile, a data receiving unit that receives facsimile data from a communication line is provided instead of the image reading device 5, and exposure is performed based on an image obtained from the received data.

  The charged toner 7 on the developing sleeve 6 is driven by utilizing the difference between the potential on the image carrier 4 and the potential applied to the developing sleeve 6 that has been lowered by exposure, that is, the action of the electric field. The image is adhered onto the image carrier 4 that is rotationally driven by the unit 21. The toner 7 attached to the image carrier 4 is conveyed to a predetermined transfer region by the rotation of the image carrier 4, and the recording paper P conveyed from the recording paper cassette 13 by the paper feed roller 14 by the action of the transfer roller 8. Is transcribed.

  The recording paper P onto which the toner image has been transferred is conveyed to the fixing unit 10, and the toner image is fixed on the recording paper P by heat and pressure at the nip portion between the fixing film 11 and the pressure roller 12. 16 is discharged. The pressure roller 12 is rotationally driven by the drive unit 22. The rotational speed of the drive unit 22 is variably controlled by the CPU 23 constituting the transport speed changing means in the present invention.

  The toner 7 that adheres to the image carrier 4 and cannot be transferred is scraped off and collected by the cleaning blade 9 into the waste toner storage space in the process cartridge 2. The role of the TOP sensor 15 as a recording paper detection member is that when the leading edge of the recording paper P comes to the position of the TOP sensor 15 and tilts the TOP sensor 15, the timing becomes the base point and the high pressure and exposure related to the start of image process formation. The timing is determined. When the trailing edge of the recording paper P passes through the position of the TOP sensor 15, the TOP sensor 15 rises, and the timing is used as a base point to determine the high pressure and exposure timing related to the end of image formation.

  The transfer high voltage control during printing includes constant voltage control and constant current control. First, constant voltage control will be described.

  FIG. 2A is a diagram illustrating a state where the recording paper P has not reached the nip portion between the image carrier 4 and the transfer roller 8, and FIG. FIG. 4 is a diagram showing a state in which the transfer roller 8 is passing through a nip portion.

  2A and 2B, a constant voltage Vtr is applied to the transfer roller 8 by the transfer high-voltage power supply 17, and the back surface of the recording paper P is charged by the current i1 flowing at that time, whereby the image carrier 4 and the recording paper P are The toner 7 on the image carrier 4 is transferred to the printing surface of the recording paper P by the potential difference with the back surface potential. In this embodiment, a transfer current detection load 18 is provided between the transfer high-voltage power supply 17 and the transfer roller 8. The resistance value R of the transfer current detection load 18 is made smaller than the resistance value of the transfer roller 8. For example, the resistance value of the transfer roller is 10 9 Ω, and the resistance value R of the transfer current detection load 18 is 10 6 Ω. Thus, the resistance value of the load 18 for detecting the transfer current is considerably smaller than 1/1000 as compared with the resistance value of the transfer roller, and has no influence on the transfer process.

  Assuming that the voltage output by the transfer high voltage is Vtr when the recording paper P in FIG. 2A has not reached the nip portion between the image carrier 4 and the transfer roller 8, the transfer current detection is i1. The voltage drop V1 at the service load 18 is V1 = i1 * R.

  Similarly, since the constant voltage control is performed while the recording paper P in FIG. 2B passes through the nip portion between the image carrier 4 and the transfer roller 8, the applied voltage is Vtr, and the recording paper P is in the nip. Since it exists in the section, the current flowing by the resistance value of the recording paper P decreases. Assuming that the current value at that time is i2 (i1> i2), the voltage drop V2 at the resistance value R of the transfer current detection load 18 is V2 = i2 * R.

For example, the resistance value R of the transfer current detection load 18 is R = 10 6 Ω, the current value i2 required for transfer is 3.5 μA, and the resistance value of the transfer roller 8 at that time is 3.5 μA. The applied voltage Vtr is set to 2.0 kV. The current value i1 when the applied voltage Vtr = 2.0 kV and the recording paper P is not in the nip portion is 5.0 μA. Under such conditions, the voltage drops V1 and V2 at the transfer current detection load 18 when the recording paper P does not exist at the nip and when it exists are as follows.
(1) When the recording paper P is not present in the nip portion: V1 = [5.0] (μA) * [10 to the sixth power] (Ω)
= [5.0] (V)
(2) When the recording paper P is present in the nip portion: V2 = [3.5] (μA) * [10 to the sixth power] (Ω)
= [3.5] (V)

  Such a change from the voltage V1 to V2 occurs when the leading edge of the recording paper P enters the nip portion. Conversely, a fluctuation from the voltage V2 to V1 occurs when the trailing edge of the recording paper P leaves the nip portion. To do. By monitoring the voltage output fluctuation at the transfer current detection load 18, the time when the leading edge enters the nip portion of the recording paper P and the time when the trailing edge slips out are detected, and the time between them is determined by the user setting. Based on the recording paper size, the recording paper conveyance speed at that time can be calculated.

  FIG. 3 is a diagram for explaining a method of detecting the leading and trailing edges of the recording paper and calculating the conveyance speed of the recording paper P based on the voltage drop variation of the transfer current detection load 18. FIG. 3A shows a voltage output waveform in the default state, that is, when the pressure roller is not thermally expanded. FIG. 3B shows that the pressure roller is thermally expanded and the conveyance speed of the recording paper P is increased. The voltage output waveform at the time is shown.

  First, when the TOP sensor 15 detects the leading edge of the recording paper, the transfer high pressure Vtr is applied at a time t0 when the leading edge of the recording paper is positioned upstream of the transfer nip portion. The voltage drop of the transfer current detection load 18 at that time is V1. Next, when the leading edge of the recording paper P enters the transfer nip at time t1, the voltage drop at the transfer current detection load 18 becomes V2. Furthermore, when the trailing edge of the recording paper P passes through the transfer nip at time t2, the voltage drop at the transfer current detection load 18 becomes V1. Thereafter, the application of the transfer high voltage Vtr ends at time t3.

The threshold voltage Vth is set in advance, and the output value vi at the transfer current detection load 18 falls below the threshold voltage Vth within the transfer voltage Vtr application period (t0 to t3). The timing t2 at which this happens is stored in the memory by the CPU. The time T required for the recording paper P to pass through the transfer nip is obtained by T = t2−t1. Based on the time T and the recording paper size L, the recording paper conveyance speed Pv is obtained by the following equation.
・ Recording paper conveyance speed Pv = L / T

On the other hand, when the pressure roller is expanded, the peripheral speed is increased. Therefore, as shown in FIG. 3B, at the time points t2 ′ and t3 ′ corresponding to the time points t2 and t3 in FIG. The timing is early. The recording paper conveyance speed Pv ′ at this time is expressed by the following equation based on the time T ′ = t2′−t1 ′ required for the recording paper P to pass through the transfer nip and the recording paper size L in the same manner as described above. Is required.
Recording paper transport speed Pv ′ = L / T ′

For example, when A4 size (conveying direction size: 297 mm) is continuously passed, V1 = 5.0V, V2 = 3.5V, Vth = 4.25V, and it is necessary for the initial recording paper P to pass through the transfer nip. Assuming that the time T is 3.324 sec and T ′ when the pressure roller is expanded (after 200 consecutive sheets) is 3.308 sec, the recording paper at the initial time and when the pressure roller is expanded (after 200 consecutive sheets are passed) The conveyance speeds Pv and Pv ′ are as follows.
-Initial recording paper conveyance speed Pv = 297 (mm) /3.324 (sec)
= 89.3501 (mm / sec)
・ Recording paper transport speed Pv '= 297 (mm) /3.308 (sec) after continuous 200 sheets
= 89.7823 (mm / sec)

  Therefore, it can be seen that the recording paper conveyance speed is 0.4322 mm / sec faster during expansion. Based on this result, if the speed of the pressure roller 12 is reduced by 0.4322 mm / sec from the default, the influence of expansion of the pressure roller 12 can be offset.

  FIG. 4 is a flowchart showing a control procedure in the present embodiment. A program representing the control procedure is stored in a ROM (memory) (not shown), and this control is realized by the CPU interpreting and executing it.

  First, when an instruction for continuous printing of n sheets is input, the print sheet count variable x is set to 1 (S11), ATVC (Active Transfer Voltage Control) detection is performed during the previous rotation, and the current resistance value of the transfer roller 8 is set. In step S12, the voltage Vtr required for supplying the target current value is determined. Therefore, the xth print starts (S13). In the x-th print, when the TOP sensor 15 detects the leading edge of the recording paper, application of the transfer high pressure Vtr is started at a position upstream of the recording nip portion of the recording paper (S14). After the trailing edge of the recording paper has passed through the transfer nip, the application of the transfer high voltage Vtr is completed (S15). When the x-th print is completed (S16), the count variable x is incremented (+1) (S17). When x reaches n + 1, the printing operation is terminated. Until x reaches n + 1, the process returns to step S13 to continue printing the next page.

  Vi detection by the transfer current detection load 18 is performed while the transfer high voltage Vtr is being applied (S21). On the other hand, the threshold level Vth is determined (S31). Since the resistance can vary depending on the type of recording paper, the threshold level Vth can be changed depending on the type of recording paper. When the voltage Vi is detected, as described with reference to FIG. 3, based on the relationship between the threshold level Vth and the voltage Vi, the point of entry t1 into the transfer nip portion at the leading end of the recording paper and the transfer nip portion at the trailing end of the recording paper are removed. Time t2 is detected (S32). Further, the recording paper transport speed Pv is calculated based on the time points t1 and t2 and the recording paper size (L) information being used (S33). Based on the calculated recording paper conveyance speed Pv and the default reference conveyance speed PVref, the recording paper conveyance speed change is calculated (S34). Based on this calculation result, the speed of the pressure roller 12 is instructed to be changed by the change (S35). The speed of the pressure roller 12 is changed during the interval between the detected print and the next print. If there is no next print, the print operation is terminated without changing.

  In the embodiment described above, the case where the high voltage control during printing is the constant voltage control has been described. However, constant current control may be used. Hereinafter, a case where the high voltage control during printing is performed by constant current control will be described. Here, the transfer high-voltage power supply 19 of FIG. 5 performs constant current control. FIG. 5A shows a state before the recording paper P passes through the transfer nip portion, and FIG. Since the transfer high-voltage power supply 19 uses constant current control, the recording paper P always flows the same current regardless of the presence or absence of the recording paper P in the transfer nip portion. Here, it is assumed that i1 is constantly flowing. The voltage Vtr applied by the transfer high-voltage power supply 19 varies depending on whether or not the recording paper P exists in the transfer nip portion. When the recording paper P exists in the transfer nip portion, the voltage Vtr ′ is higher than the voltage Vtr by the resistance value of the recording paper P. In the present embodiment, the voltage output fluctuation of Vtr is monitored against the threshold value Vth by the same method as described above to detect the time when the leading edge of the recording paper P enters the transfer nip and the time when the trailing edge slips out. Based on the passing time from the leading edge to the trailing edge and the recording paper size determined by the user setting, the recording paper conveyance speed at that time is calculated, and the change in the conveyance speed is derived. Then, the speed of the pressure roller is varied by the change.

  The preferred embodiment of the present invention has been described in detail above, but various modifications and changes other than those mentioned above can be made. For example, in the above embodiment, a dimension value based on the size of the recording paper is stored in the memory and used. However, the size may vary depending on the recording paper used. Therefore, when image formation is performed when the pressure roller after the first standby in the morning or for a long time has not expanded much, the time when the leading edge of the recording paper enters the transfer section and the time when the trailing edge slips out is detected. It is also possible to store the passage time from the rear end to the rear end in the memory as the reference value of the recording paper in the current cassette, and adjust the subsequent recording paper passage time to the reference value.

1 is a schematic side view of an image forming apparatus to which the present invention is applied. FIG. 5 is a diagram illustrating a state where the recording paper P does not reach the nip portion between the image carrier and the transfer roller when the transfer high-voltage power source is under constant voltage control, and a state during the passage. FIG. 6 is a diagram for explaining a method of detecting the leading and trailing ends of a recording sheet and calculating the conveyance speed of the recording sheet based on a drop voltage variation of a transfer current detection load. It is a flowchart showing the procedure of control in embodiment of this invention. FIG. 5 is a diagram illustrating a state where the recording paper P does not reach the nip portion between the image carrier and the transfer roller when the transfer high-voltage power supply is under constant current control, and a state during the passage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Process cartridge, 3 ... Charging roller, 4 ... Image carrier (photosensitive drum), 5 ... Laser scanner unit, 6 ... Developing sleeve, 7 ... Toner, 8 ... Transfer roller, 9 ... Cleaning blade DESCRIPTION OF SYMBOLS 10 ... Fixing unit, 11 ... Fixing film, 12 ... Pressure roller, 13 ... Recording paper cassette, 14 ... Paper feed roller, 15 ... Recording paper detection member (TOP sensor), 16 ... Paper discharge roller, 17 ... Transfer high voltage power supply (Constant voltage control), 18 ... Load for detecting transfer current, P ... Recording paper, 19 ... Transfer high voltage power supply (constant current control), 23 ... CPU

Claims (5)

A method for detecting a conveyance speed of a recording paper in an image forming apparatus in which an unfixed toner image is transferred onto a recording paper by a transfer member and fixed.
Detecting a change timing of a current or voltage applied to the transfer member;
Based on the change timing, obtaining a time required for the recording paper leading edge to the recording paper trailing edge to pass through the transfer member;
And a step of calculating a recording paper conveyance speed based on the obtained time and the recording paper size. A recording paper conveyance speed control method in an image forming apparatus for transferring and fixing an unfixed toner image onto a recording paper by a transfer member,
Detecting a change timing of a current or voltage applied to the transfer member;
Based on the change timing, obtaining a time required for the recording paper leading edge to the recording paper trailing edge to pass through the transfer member;
Calculating a recording paper conveyance speed based on the obtained time and the recording paper size;
And a step of correcting the transport speed so that the calculated transport speed matches the target transport speed. An image forming apparatus for transferring and fixing an unfixed toner image onto a recording sheet by a transfer member,
Detection means for detecting a change timing of the current or voltage applied to the transfer member;
Means for obtaining a time required for the recording paper from the leading edge of the recording paper to the trailing edge of the recording paper to pass through the transfer member based on the change timing;
Means for calculating the conveyance speed of the recording paper based on the obtained time and the recording paper size;
An image forming apparatus comprising: a conveyance speed changing unit configured to change the conveyance speed so that the calculated conveyance speed matches a target conveyance speed.   The image forming apparatus according to claim 3, wherein the transport speed changing unit changes the transport speed by changing a recording paper transport speed of the fixing unit.   5. The image forming apparatus according to claim 3, wherein the change of the conveyance speed by the conveyance speed changing unit is performed between a print subsequent to the print for which the recording paper conveyance speed is calculated.

Images