JP2009180901A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent transfer omission by a decharging effect, without affecting a size and a cost of own device, and to provide an image of high quality. <P>SOLUTION: This image forming device is provided with a means for applying a decharge bias to a decharging means in a recording medium transferred with the image, a means for feeding back an output voltage from the means for applying the decharge bias, and a control means for updating-controlling a value of a driving pulse of the decharge bias, based on a feedback value of the output voltage of the decharge bias, and the control means controls the value of the driving pulse of the decharge bias at a fixed value, irrespective of the feedback value, when the value of the driving pulse of the decharge bias comes to a prescribed value or more. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile using an electrophotographic system.

  In an image forming apparatus such as an electrophotographic copying machine, printer, facsimile, etc., a recording medium is once electrostatically adsorbed to a photosensitive member or an intermediate transfer member on which an image is formed, and a recording medium is applied by applying a high voltage during transfer. The (paper) is conveyed while being charged.

  As described above, the sheet conveyance in the charged state causes a paper jam if the sheet is stuck on the conveyance path or the sheet entering posture to the downstream conveyance nip is bad.

  In addition, there is a concern that the image formed on the paper is disturbed by the contact state of the conveyance path or the charging state of the path metal before fixing and becomes an abnormal image. To prevent these, the paper is charged from the transfer section to the fixing section. Some static elimination members (neutralization needles) for removing the generated charges are arranged to remove excess charges charged on the paper.

  In addition, since the amount of charge charged varies depending on the paper type such as thick paper / thin paper / glossy paper and printing conditions such as single-sided / double-sided, aiming at further static elimination effect by applying a high voltage (bias) to the static elimination member. There is something.

  In addition, regardless of the type of paper, moisture absorption state, and the installation environment of the paper, it is arranged on the paper discharge side of the transfer roller so that it is not in contact with the recording paper in order to prevent deterioration in transport quality and image deterioration due to poor separation. There are some which provide a static elimination needle and apply a static elimination bias from a high voltage power source.

  However, if the setting conditions of the static elimination means to remove the charge of the paper in the normal state, that is, the shape of the static elimination needle and the distance from the paper are set, the paper itself is low resistance such as thin paper or coated paper Since the current flows from the transfer unit to the neutralization unit along the paper surface, the charge required for the transfer may be insufficient and the image may be whitened. The transfer current and neutralization voltage output are set depending on the paper type. By doing so, there is one that ensures image quality.

  In addition to this, if the environment where the device is placed or the environment where the paper is placed is hot and humid, the paper itself absorbs moisture and the resistance of the paper decreases, so that current flows from the transfer means to the static elimination means. In some cases, the charge required for transfer is insufficient, resulting in white spots in the image. This tendency is strengthened by applying a reverse bias to the neutralizing unit and the transfer unit.

In order to prevent white spots due to the flow into the static elimination path, there is disclosed a technique for providing a means for measuring the current value flowing from the transfer roller to the static elimination needle and controlling the voltage value of the static elimination bias in accordance with the current value ( For example, see Patent Document 1).
JP 2002-365923 A

  However, in the technique disclosed in Patent Document 1, it is necessary to provide a means for detecting the current of the static elimination path for the high-voltage output under constant voltage control, resulting in an increase in the size or cost of the device. Become.

  Accordingly, the present invention provides an image forming apparatus capable of preventing transfer omission and obtaining a high-quality image by eliminating the charge without affecting the size and cost of the apparatus itself, in order to solve the above-described problems. For the purpose.

  According to a first aspect of the present invention, there is provided a static elimination bias applying means for applying a static elimination bias to a static elimination means for neutralizing charges accumulated on a recording medium onto which an image is transferred by a transfer means, and an output voltage of the static elimination bias applying means being fed back. And a charge elimination bias control means for updating and controlling the value of the neutralization bias drive pulse based on the feedback value of the output voltage of the neutralization bias. In the image forming apparatus, the value of the driving pulse of the static elimination bias is controlled with a fixed value regardless of the feedback value when the value becomes equal to or greater than a predetermined value.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the storage unit holds a value of a drive pulse that becomes a target output at a normal assumed load at a static elimination bias setting value under various image forming conditions. When the difference between the feedback value of the output voltage of the static elimination bias under a predetermined image forming condition and the value of the drive pulse held in the storage unit exceeds a threshold value, the static elimination bias control means Therefore, it is determined that the load is large, and the control is performed by fixing the value of the drive pulse held in the storage unit.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the means for applying a bias to the transfer means when the value of the driving pulse for the static elimination bias exceeds a predetermined value is the transfer bias. The set value is made larger than the normal set value, or the static elimination bias control means makes the static elimination bias set value smaller than the normal set value.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the transfer bias applying unit applies a transfer bias to the transfer unit by constant current control, and the transfer bias applying unit applies the transfer bias to the transfer unit. Means for measuring the voltage, and when the potential difference between the transfer bias applied by the transfer bias applying means to the transfer means and the charge removing bias applied by the charge removing bias applying means to the charge eliminating means becomes a predetermined value or more, the charge eliminating bias The applying unit lowers the voltage of the neutralizing bias applied to the neutralizing unit.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the transfer bias applying means that applies a transfer bias to the transfer means by constant current control, and the transfer bias means are applied to the transfer means. A voltage bias measuring unit, and a transfer bias when the potential difference between the transfer bias applied by the transfer bias applying unit to the transfer unit and the neutralizing bias applied by the neutralizing bias applying unit to the neutralizing unit exceeds a predetermined value. The applying means switches the transfer bias to constant voltage control.

  Without affecting the size and cost of the device itself, it is possible to prevent transfer loss and obtain a high-quality image due to the charge eliminating effect.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of an image forming unit of a monochrome printer which is an example of an image forming apparatus according to the present embodiment. A beam based on image data is emitted from the writing 11 around the photosensitive member 2 which is an image carrier, and the photosensitive member is exposed. Toner adheres to the exposed portion of the development 1 in contact with the photosensitive member 2 to form an image on the photosensitive member, and the image is transferred onto a sheet by the transfer roller 6. A high voltage with constant current control is applied to the transfer roller from a high voltage power source. Since the output is started / stopped in accordance with the conveyance timing of the paper so that the influence on the life of the photoconductor is minimized as long as there is no paper between the photoconductor and the transfer roller, it is necessary to stop at a high pressure.

  The sheet is discharged and conveyed by the pickup roller 3 from the state of being accommodated in the cassette 5, and is waiting for conveyance at the position of the registration roller 4 in order to perform image alignment with the photosensitive member. The conveyance is restarted at the timing when the leading edge of the photoreceptor image comes to the registration position of the sheet, and the sheet is conveyed to the fixing roller 8 and the pressure roller 9 while applying the transfer bias. A neutralizing needle 7 is disposed between the transfer nip and the fixing nip to separate the sheet adhering to the photoreceptor. In other words, the static elimination needle 7 is arranged in the vicinity of the downstream side of the transfer roller 6 in the paper transport direction. By applying a high voltage having a polarity opposite to the transfer bias to the charge eliminating needle 7, the paper is separated from the photosensitive member, and a bias is applied so that the front end of the paper enters the fixing nip. The sheet on which the image has been formed is fixed by the fixing unit and conveyed outside the apparatus via the paper discharge roller 10. The above is the printer configuration and the basic image forming procedure.

  FIG. 2 shows a control block for high-voltage output applied to the transfer roller and the charge eliminating needle. Here, output control in the direct drive method, which has the simplest configuration and provides cost advantages, will be described. With the direct drive method, the on_duty of a predetermined frequency (20 kHz) is controlled by the pwm generator 203-1, as in the pwm waveform shown in FIG. 3, and the power source side switches the primary side of the high-voltage transformer with that pulse. To drive. High voltage output control is performed by controlling on_duty to 0 to 100%. In this high-voltage power supply, the output is controlled by open loop that does not feed back in the power supply, and the cost is reduced by not providing a feedback and control function.

  A specific configuration of the static elimination bias generator 202 will be described. The high voltage generator is provided with a high voltage transformer 202-1 for boosting from a low voltage (24V), and is driven by turning on / off the primary side of the transformer by the switching element 202-2. Here, switching by bipolar or FET is shown. The voltage boosted by the high voltage transformer is converted into a voltage level that can be input to the A / D converter 203-2 provided in the high voltage controller 203 in the voltage detector 202-3.

  Here, as in the output-feedback characteristic shown in FIG. 4, the high voltage output range is converted according to a linear expression: conversion value (= −1 / 1200) * output value + 4 (V).

  Specific control is shown in the calculation update flow of FIG. If cpu 203-3 is an output start timing (judgment based on flag) (701Y), an internal timer interrupt (here, 10ms interrupt) is entered (702Y) to synchronize the calculation update, and the current output is changed to A / Capture by D conversion (703), obtain difference from A / D value of target output (704), and update pwm according to predetermined arithmetic expression: = current pwm set value + (A / D value difference × calculation coefficient) The value is calculated (705), and pwm update driving is performed.

  As described above, when the output is small with respect to the target output, the on value of pwmduty is increased. Conversely, when the output is large with respect to the target output, the on value of pwmduty is decreased. If the A / D difference is large, the increase / decrease in pwmduty is also increased, and if the difference is small, the increase / decrease is updated small. This continues until the output is stopped every 10 ms.

  In an actual image forming apparatus, in addition to these two outputs, there are a developing bias, a charging output, and the like. In a color printer, there are apparatuses having 20 types of high-voltage outputs for each color for each bias output.

  Like the transfer bias generation unit 201 shown in FIG. 2, the output detection method includes a voltage detection 201-1 and a current detection 201-2, and is input to the a / d conversion as a feedback value. It is also possible to switch to either current control according to the installation environment or output state of the apparatus.

  The transfer bias is normally controlled at a constant current, and printing is performed by switching the set current value (5 to 50 μA) depending on the paper size and environment (low temperature / high temperature / normal temperature), single side (one side) / double side (two sides). ing.

  For the transfer bias output, the paper that has absorbed moisture has a low impedance of the paper itself, and a transfer current may flow into another conveyance path through the paper, which may cause transfer omission. Similarly, in the case of a sheet having a glossy surface, a transfer current may flow into another path through the sheet surface and transfer omission may occur. As a current path in which these transfer omissions occur, a static elimination needle disposed between transfer and fixing for the purpose of separating the paper from the photoreceptor may become a path through which the transfer current flows. In particular, when a bias is applied to the static elimination needle, the higher the bias applied voltage (the greater the difference from the transfer output voltage), the easier the flow. Since such a moisture-absorbed sheet has a different resistance value depending on the moisture absorption condition, it cannot be generally said how much the neutralization application bias can prevent the flowing-in current.

  In addition, at low temperature and low humidity, the transfer bias voltage can be 2 to 10 times (up to 8 kV) of 800 V normally due to an increase in impedance of the transfer system including the paper and the transfer roller. When the transfer control is controlled at a constant current, the high-voltage output voltage increases, and a discharge phenomenon may occur during image formation, which may cause image degradation such as a print image. In addition, since it is necessary to dispose the neutralization bias path in the vicinity of the transfer bias path, the potential difference from the neutralization bias becomes large in a miniaturized device or a device that does not have sufficient creepage, causing leakage between both outputs. In addition to the occurrence of in-machine noise, there is a possibility that the image itself may be affected because of an abnormal transfer bias. In order to prevent this, it is necessary to secure a creepage distance and protect with an insulating material, but this involves an increase in the size or cost of the device.

  The gist of the present invention in the image forming apparatus based on the above configuration will be specifically described.

  Like the pwmduty-output characteristic 1 shown in FIG. 5, the output by the load at the pwm set value α is the output c at the load min, and is b at the type (assumed rated load). The output is a at the load max, and | c |> | b |> | a | in the constant voltage control.

  For the static elimination bias, an increase in the flow from the transfer current is equivalent to an increase in the load, and as a result, the pwm calculation is updated to drive with a larger duty than the normal pwm setting.

  At this time, in FIG. 8 showing the static elimination bias control flow, for example, in the static elimination bias control in the printing operation when the pwmduty is about 30% under the normal load condition (assumed load condition) at −1500 V output. If the pwmduty setting value is 40% or more (802-Y), it is determined that the load is large because the transfer current is flowing in, and the pwmduty is set to the output targeted when the normal load is assumed. The output is continued with the fixed 30% (804).

  Naturally, since the target neutralization bias value differs depending on the paper type and environment, the pwmduty that is the target output at the normal assumed load at each neutralization bias setting value is stored in a table (as shown in FIG. 9 as an example). When pwmduty is + 10% up of pwmduty held in the table, pwmduty is fixed (pwmduty held under normal assumed load: 30% here) and output is continued.

  Since the transfer current flows and the load is large, fixing the pwmduty and continuing the output means that the bias (output voltage) is low, but the difference between the transfer bias and the neutralization bias is reduced. Thus, the inflow of the transfer current can be suppressed, the current necessary for the transfer can be secured, and the transfer omission can be prevented. It should be noted that the accuracy can be maintained by adjusting the target output of 1500 V under the normal assumed load by hardware adjustment in the high voltage generator.

  If the difference between the duty currently being output and the duty held in the table exceeds a predetermined threshold by comparing the calculation pwmduty during the static elimination output with the pwmduty (held value) at the normal assumed load, the transfer is performed. It is possible to compensate for the shortage of the transfer current by determining that the current has flowed into the static elimination and increasing the set value of the transfer current assuming that the transfer current is insufficient.

  Conversely, assuming that the transfer inflow occurs because the potential difference between the transfer and the charge removal is large, it is possible to reduce the inflow of the transfer current by reducing the charge removal bias.

  Furthermore, if the load fluctuation due to the flow from the transfer is corrected by the output of the neutralization bias, the neutralization output is driven by a fixed pwmduty for each neutralization bias as a target value, instead of the calculation control by fb. This eliminates the need for an output feedback path, and can be realized without an extra cost up even when an a / d converter or the like is insufficient.

  When viewed from the transfer bias, if there is an inflow to the static elimination needle path, the impedance becomes extremely low, and the pwmduty of the calculation update decreases. In addition, there is a region where the output cannot be performed when the pwmduty is small or a region where the output changes abruptly (the 0-d region in FIG. 6) due to the characteristics of the transformer, and may not be controlled (the duty is 0-2%). degree).

  The min setting value of pwmduty is set to 2% so as not to use such an area. The transfer output under constant current control has a smaller update pwmduty as the load decreases (resistance decreases). Since this duty lower limit value is set to 2%, the pwmduty is driven at the min when there is a flow into the charge removal. In this way, when the transfer bias control pwmduty is driven at min, it is determined that the transfer path is formed by applying the charge removal bias and the transfer impedance is lowered, and the charge removal bias is stopped. To prevent inflow.

  By holding the minimum drive pulse width for each transfer bias output setting, the transfer drive condition for determining whether or not there is a transfer current flow is provided for each transfer setting value. While ensuring the performance, it is possible to prevent a transfer omission due to the flow into the static elimination and obtain a high-quality image.

  Further, even if the neutralizing bias output is stopped, a path to the ground remains as a path. Therefore, it is possible to cut off the transfer current flow path by providing means for physically blocking this path.

  On the other hand, the transfer output under constant current control becomes a high potential (5 to 8 kV) due to an increase in the impedance of the paper or the transfer roller at a low temperature, and the potential difference from the neutralization bias may be about 10 kV.

  At this time, when the creepage between the transfer and the discharge output is up to 8 kV, there is a risk of leakage if the transfer bias exceeds 5 kV under the discharge bias-3000 V application condition (low temperature / 2 surfaces). When the transfer output voltage is thus monitored and it is detected that the transfer bias exceeds 5 kV, the potential difference between the two outputs is suppressed by setting the neutralization bias to -500V.

  Further, at this time, even if the voltage fb means for the transfer output is not particularly provided, whether the transfer bias is increased due to the increase in impedance from the current fb and the control pwmduty (specifically, the pwmduty and current exceeding a certain threshold value). If the feedback value is equal to or less than the predetermined current), and if it is determined that there is a risk of leakage due to an increase in the transfer bias, the static elimination bias setting value is similarly set to -500V. Since the voltage value calculation of the transfer output under constant current control is predicted from the transfer driving condition and the current feedback value, the voltage difference of the transfer output is reduced by lowering the voltage of the static elimination bias without providing an output voltage detecting means for the transfer output. Thus, it is possible to provide an inexpensive control system that prevents leakage between outputs, prevents malfunction of the device, and prevents image degradation due to leakage.

  Further, when the potential difference between the two outputs exceeds 7 kV, the static elimination bias is stopped.

  Also, by making the transfer output constant voltage control without changing the neutralization bias control by the detection means and judgment means as described above, the potential difference from the neutralization bias is ensured by bias control on the transfer side, and the paper transport quality Can be improved. When the potential difference between the transfer output and the static elimination output exceeds a predetermined value, the transfer output control is set to constant voltage control, and the transfer output voltage is controlled so that the potential difference between both outputs is less than the predetermined value. This prevents leakage of the image, prevents malfunction of the apparatus, and prevents image deterioration due to leakage.

  In addition, if the image forming apparatus shifts to constant voltage control during output of the transfer bias, it shifts from constant current control to constant voltage control when a predetermined potential difference or more is detected during transfer output, so printing operation By controlling the transfer output voltage even when the load fluctuates suddenly on the way, leakage between outputs can be prevented, and malfunction of the apparatus can be prevented and image degradation due to leakage can be prevented.

  Each embodiment described above is a preferred embodiment of the present invention, and various modifications can be made without departing from the gist of the present invention.

1 is a schematic diagram of an image forming unit of a monochrome printer which is an example of an image forming apparatus according to an embodiment of the present invention. It is the figure which showed the control block of the high voltage | pressure output applied to the transfer roller which concerns on embodiment of this invention, and a static elimination needle. It is a figure which shows a pwm waveform. It is a figure which shows an output-feedback characteristic. It is a figure which shows pwmduty-output characteristic 1. FIG. It is a figure which shows pwmduty-output characteristic 2. FIG. It is a flowchart which shows the calculation update flow which concerns on embodiment of this invention. It is a flowchart which shows the static elimination bias control flow which concerns on embodiment of this invention. It is a figure which shows the structure of the table which stored pwmduty used as a target output.

Explanation of symbols

DESCRIPTION OF SYMBOLS 201 Transfer bias generation part 201-1 Voltage detection 201-2 Current detection 202 Static elimination bias generation part 202-1 High voltage transformer 202-2 Switching element 202-3 Voltage detection part 203 High voltage control part 203-1 pwm generator 203-2 A / D converter 203-3 cpu
204 Environmental sensor

Claims (5)

A static elimination bias applying means for applying a static elimination bias to the static elimination means for eliminating the charge accumulated in the recording medium onto which the image is transferred by the transfer means;
Means for feeding back the output voltage of the static elimination bias applying means;
An image forming apparatus comprising: a neutralizing bias control unit that updates and controls a value of a driving pulse for the neutralizing bias based on a feedback value of an output voltage of the neutralizing bias.
The neutralization bias control means controls the neutralization bias drive pulse value with a fixed value regardless of the feedback value when the neutralization bias drive pulse value is equal to or greater than a predetermined value. apparatus. A storage unit that holds a value of a drive pulse that is a target output under a normal assumed load at a static elimination bias setting value under various image forming conditions,
When the difference between the feedback value of the output voltage of the static elimination bias under a predetermined image forming condition and the value of the drive pulse held in the storage unit exceeds a threshold value, the static elimination bias control means 2. The image forming apparatus according to claim 1, wherein it is determined that the load is large because a current flows in, and the control is fixed to the value of the drive pulse held in the storage unit. . When the value of the driving pulse of the static elimination bias becomes a predetermined value or more,
The means for applying a bias to the transfer means makes a transfer bias set value larger than a normal set value, or the static elimination bias control means makes the static elimination bias set value smaller than a normal set value. Item 3. The image forming apparatus according to Item 1 or 2. A transfer bias applying means for applying a transfer bias to the transfer means by constant current control; and a means for measuring a voltage applied to the transfer means,
When the potential difference between the transfer bias applied by the transfer bias application means to the transfer means and the charge removal bias applied by the charge removal bias application means to the charge removal means is equal to or greater than a predetermined value, the charge removal bias application means is the charge removal means. 4. The image forming apparatus according to claim 1, wherein a voltage of the neutralizing bias applied to the power source is lowered. 5. A transfer bias applying means for applying a transfer bias to the transfer means by constant current control; and a means for measuring a voltage applied to the transfer means,
When the potential difference between the transfer bias applied by the transfer bias applying means to the transfer means and the charge eliminating bias applied by the charge eliminating bias applying means to the charge eliminating means becomes a predetermined value or more, the transfer bias applying means performs the transfer bias application. The image forming apparatus according to claim 1, wherein the bias is switched to constant voltage control.

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