JP2846335B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile.

(Prior art)

In an electrophotographic copying machine or the like, the charging ability is deteriorated due to aging of the photoreceptor, and a predetermined surface potential cannot be obtained even when the photoreceptor is charged by corona discharge zone electricity to which a voltage from a predetermined high-voltage power supply is applied. Cases arise. In order to prevent the surface potential from lowering, the surface potential of the photoreceptor is detected, and a high-voltage power supply is controlled based on the surface potential information to keep the surface potential constant. That is, conventionally, the surface potential of the photoreceptor is measured by a surface potential detecting means, and the high-voltage power supply of the charger is feedback-controlled based on the measured data to keep the surface potential constant. Therefore, the voltage of the high-voltage power supply of the charger is adjusted in the photoreceptor that has been used many times, and is higher than in the case of a new photoreceptor.

However, if an abnormality occurs in the control device, for example, the surface voltmeter fails, it is detected that the detected surface potential deviates from the target value by a predetermined range or more. If the surface potential does not return to the target value even after the correction, it is determined that there is an abnormality, and inspection by a service person is required.

When an abnormality occurs, there are many abnormalities in the system of the control device, and there is no particular problem with the photoconductor itself, and in many cases, image formation can be continued as it is.

Conventionally, when an abnormality occurs, a serviceman operates a button to give a command from outside to adjust the voltage. In this case, there was a problem that it could not be used until the Sabimman arrived.

Even if an abnormality occurs, the photoconductor itself can be used for image formation, and when an abnormality occurs in the control device, the output of the charger is automatically reset to the standard value stored at the time of shipment. The setting is known, for example, from JP-A-60-225201. It is known from JP-A-57-118255, for example, to set a standard value by an external command.

However, even when the output of the charging device is set to a predetermined value by a known method when an abnormality occurs, the characteristics of the photoconductor vary, and even if the power supply voltage of the charging device is the same, the surface potential of the photoconductor of any device is the same. Is not always the same, and when the surface potential of the photoconductor tends to decrease due to the aging of the photoconductor, even if the power supply voltage of the charger is set to the standard value, the surface potential of the photoconductor is It cannot be set exactly at the predetermined potential. For example, even if the number of copies is about 20K and the grid voltage of the scorotron discharger is set to -750V, the charging potential is -730V to obtain a normal image, but the photosensitive member is changed due to aging. In a state where the charging potential is only about -700 V, an abnormality occurs in the control device, so that even if the grid voltage of the charger is set to -750 V, the charging potential is low and a normal image cannot be obtained.

[Problems to be solved by the invention]

The present invention solves the above-mentioned conventional problems, and provides an image forming apparatus that matches the characteristics of the photosensitive member as much as possible when an abnormality occurs in the control device and can maintain almost the same surface potential as when the deterioration does not occur. That is the task.

[Means for solving the problem]

The present invention solves the above problem by detecting the surface potential of the photoconductor when charged by the surface potential detection means, and sequentially storing data based on the detected photoconductor surface potential,
When it is determined that the detected surface potential is abnormal based on a predetermined condition, the output of the high voltage generating means is set to a predetermined value determined based on the data stored before the abnormality determination. Is solved by an image forming apparatus characterized in that

It is configured to detect that the surface potential is different from the target value from the data detected by the surface potential detecting means, and to perform control to correct the output of the high voltage generating means. Can be determined to be abnormal when the predetermined number of times is counted and reaches a predetermined number. Further, when it is detected from the data detected by the surface potential detecting means that the surface potential has a difference equal to or more than a predetermined amount from the target value, it can be determined that there is an abnormality.

It is preferable that the data stored before the abnormality is determined be a comparison value between a target value (reference value) obtained when the power of the image forming apparatus is turned on and a detected value. The correction data may be correction data for the charger voltage immediately before being counted up in increments.

[Action]

According to the present invention, the surface potential when the photosensitive member is charged is detected by the surface potential detecting means, data based on the detected surface potential is stored, the data is compared with a target value, and the difference between the target value and the target value is determined. If it is determined that the abnormality is abnormal by repeating the correction of the output of the high-voltage generating means based on the difference with the predetermined number of times, the power supply voltage is automatically set to a predetermined value determined based on the stored surface potential. .

〔Example〕

 The details of the present invention will be described based on an embodiment shown in the drawings.

In FIG. 1, an electrophotographic copying machine as an example of an image forming apparatus to which the present invention is applied includes a photosensitive drum 1 and a charger 2 disposed around the photosensitive drum 1, for example, a corona discharge type charging. , Eraser 3, exposure position by exposure light 4, and surface potential meter 5 as surface potential detecting means.
, A developing roller 6, a transfer charger 7, a separating charger 8, a separating claw 9, a cleaning device 10, and a discharging lamp 11.
12 is connected. In the negative-positive process performed by the copying machine having this configuration, the surface of the photosensitive drum 1 is uniformly charged, for example, at about -730 V by the charger 2 applied to the light voltage by the high voltage generating means, and this is applied to the original image. An electrostatic latent image is formed by irradiating the corresponding exposure light, for example, about -45.
The toner is adhered by the developing roller 6 to which a developing bias of 0 V is applied, and the toner is visualized. This toner image is transferred to a recording sheet by a transfer charger 7, and the transferred recording sheet is subjected to the action of the separation charger 8 and the separation claw 9 to form the photosensitive drum 1.
Is separated from the sheet, sent to a fixing unit, fixed, and discharged.
The photoreceptor drum 1 after the transfer is cleaned by the cleaning device 10, the charge is removed by the charge removing lamp 11, and the copying process next to the charging is started.

The surface potential of the charged photosensitive drum 1 is measured by a surface voltmeter 5 having a measurement surface facing the surface of the photosensitive drum 1.

The control device shown in FIG. 2 has a function of outputting the detected potential of the surface electrometer 5 as, for example, a voltage of -1/200, that is, a function of converting 0 to -1000 V to an output of 0 to 5 V.

The output of the surface electrometer 5 is converted into digital data of 0 to 255 by the A / D converter, and input to the control unit as 8-bit outputs of PDT0 to PDT7.

Control ON / OFF of high voltage output from control unit ▲
▼ 8 of CDT0 ~ 7 to control signal and high voltage output value
A bit data signal is output to the high voltage power supply. The high voltage power supply is connected to the charger 2.

The value of 0 to 255 is sent to the high-voltage power supply according to the combination of the H level and the L level of the digital data of CDT0 to 7, and the output of the high-voltage power supply is made variable in the range of 0 to -1000 V in proportion to the value. it can. For example, when CDT0-7 is 128, the high voltage power supply outputs -500V.

From the operation unit, a signal by the input of the key switch is encoded by a serial signal and sent to the control unit. Signals from the operation unit include a copy start signal and a surface potential control OFF signal.

The control unit has a nonvolatile random access memory capable of storing a charged potential and the like, and retains data even when the power is turned off.

Control is performed based on the time chart shown in FIG. 3 and the flowchart shown in FIG. 4. When the power of the copying machine is turned on by the start, the control unit outputs an 8-bit signal A of CDT0 to CDT7 to the high voltage power supply. I do. Assuming that the target value of the charging surface potential of the photosensitive drum 1 is -730 V, for example, and the grid voltage of the charger at this time is -750 V, the 8-bit signals CDT0 to CDT7 are used as signals for setting -750 V, for example. A = 75
0 × 255/1000 = 191 is output, and the trigger signal ▲ ▼ of the high voltage power supply of the charger is set to L level to start charging.

The photoreceptor drum 1 is driven to rotate, and the charged portion moves to a position facing the surface voltmeter 5. When the potential measurement timing of the surface voltmeter 5 comes, the potential is measured. That is, the control unit reads the A / D converted output B (FIG. 2) of the measurement information of the surface voltmeter 5.

At this time, if the total number of copies of the copying machine is 20K or if the charging characteristic of the photosensitive drum is degraded due to environmental changes, the surface potential of the photosensitive drum 1 is only charged to -680 V, for example. There is. Target value of charged surface potential is -730V
, There is a difference of 50V.
A correct image cannot be formed.

When the surface potential is -680 V, the A / D converted output B of the surface voltmeter 5 is (680/1000) × 255 = 173. When the target potential -730 V is measured, the A / D-converted output B 'is (730/1000) .times.255 = 186. On the basis of the A / D conversion output of the target value, a comparative value C = B '/ B is obtained as a value representing the charging characteristic from the value B measured by the surface electrometer, and stored in a memory, for example, a nonvolatile RAM. Keep it. B = 173
In the case of, C = 186/173 ≒ 1.07. In order to store the data in the digital amount, the data 107 and 100 are stored as 107/100 because the number of decimals cannot be stored.

The comparison value C is used when an abnormal state where the charged potential cannot be controlled to be constant, such as when the surface potential measurement meter 5 fails, or the like.

If the charging potential is feedback-controlled using a surface voltmeter and kept constant, the charging potential can be kept constant irrespective of the aging of the photoreceptor drum or environmental fluctuations, and the grid voltage must be changed accordingly. Can be For example, the charging characteristic of the photosensitive drum changes, and even if the charging potential is -730 V, the grid voltage at that time may be controlled to be as high as -803 V. If an abnormality occurs in the surface potential measurement meter etc. in a state where the characteristics of the photosensitive drum have not deteriorated, and it is determined that the photosensitive drum has deteriorated, the grid voltage will be abnormal if the correction of the grid voltage is continued as it is. Become higher.

In the prior art, when the abnormality is detected, the output of the high-voltage power supply of the charger is set to a standard value stored from the time of assembling the copying machine. For example, it becomes −750 V as it is, but when the charging characteristic of the photosensitive drum is deteriorated, the actual charged surface potential may not be the target −730 V but may be about −680 V.

If an abnormality such as an electrometer occurs, the control to change the grid voltage is stopped, and instead of resetting the grid voltage to a standard value as in the related art, the state before the occurrence of the abnormality is restored. The grid voltage can be maintained at a value that matches the characteristic fluctuation, and the image fluctuation can be minimized.

As a method of detecting an abnormality of the electrometer, a method of determining an abnormality when the output of the surface electrometer deviates from a predetermined range, and a method of determining an abnormality when the potential does not reach a target value for a predetermined time or a predetermined number of times. However, when any of them detects an abnormality, the grid voltage may have an abnormal value due to feedback control.

In contrast to the above-described conventional example, in the present invention, for example, the grid voltage of the charger is controlled to -750 × C ≒ −803 V, so that the charging potential of the photosensitive drum 1 is about −730 V.

The charging surface potential control is performed, for example, according to a flowchart shown in FIG.

At the start, when the surface potential measurement timing comes, the potential control is checked for abnormality, and if not abnormal, the surface potential is measured, and the control unit reads the data of the D / A converted charged surface potential from the surface electrometer 5. Read.

When the charged potential, that is, the charged surface potential is equal to the target potential, the abnormality counter is cleared and the control is terminated.

When the charging potential is larger than the target value, the value A of CDT0 to CDT7 is decreased by, for example, 3 to lower the grid voltage of the charger. The decreasing value is not limited to 3, but is predetermined by the device.

When the charging potential is smaller than the target value, the value A of CDT0 to CDT7 is increased by, for example, 3 to increase the grid voltage of the charger.

To increase or decrease A by 3 is 1000 × 3/255 = 1
This means changing the grid voltage of the charger by 2V.

When the grid voltage of the charger is increased or decreased, the abnormality counter is incremented, and it is checked whether the abnormality counter has reached a predetermined number of times, for example, 10 or more,
If it is smaller than 10, it returns to the potential measurement as normal and repeats the above control. A value of 10 or more indicates that the voltage of the high-voltage power supply does not return to the target surface potential even if the voltage of the high-voltage power supply is corrected and controlled a predetermined number of times. Automatically corrects the output of the charger's high-voltage power supply. In this case, a value which becomes the grid voltage obtained by multiplying the above-mentioned value C by the initial grid potential -750V is output to CDT0 to CDT7.

In the case where the potential control is abnormal or abnormal by checking, similarly, a value such as a grid voltage obtained by multiplying the value C by the initial grid potential -750V is output to CDT0 to CDT7.

For example, if C obtained at power-on is 1.07, -750V
× 1.07 = −803 V is used as the grid voltage of the charger. At this time, the value output to CDT0 to CDT7 is A = (803/1000) × 255 = 205
Becomes

As another example of the charging surface potential control, the control can be performed according to a flowchart shown in FIG.

When the surface potential control timing is started, it is checked whether the potential control is abnormal, that is, whether the potential control abnormality flag is set, and if not abnormal, the potential is measured with a surface voltmeter, and the difference between the charged surface potential and the target potential is measured. It is checked whether the absolute value is larger than a predetermined value, for example, whether it is larger than 30 or not.

When the charging potential is not larger than 30, if the charging potential is larger than the target value, the value A of CDT0 to CDT7 is reduced by a predetermined value, for example, 3 as in the case of FIG. If the charging potential is lower than the target value, the value A of CDT0 to CDT7 is increased by, for example, 3 to increase the grid voltage of the charger.

If the absolute value of the difference between the charged potential and the target potential is greater than 30, a potential control abnormality flag is set, a potential control abnormality is displayed, and the CD is displayed.
A value is output such that the grid voltage is obtained by multiplying the value A of T0 to 7 by the value C by the initial grid potential -750V.

CDT0 also when the potential control is abnormal or abnormal
7 are output such that the grid voltage is obtained by multiplying the initial grid potential −750 V by the value C.

It is also easy to controlly input data relating to the grid voltage to the control unit by inputting a key switch or the like at the operation unit. The control unit may set a flag or the like based on the code discrimination from the operation unit.

As another embodiment, in the flowchart shown in FIG. 7, the method of feedback-controlling the charging potential to a constant value is the same as that of FIG. 5, but partially different from FIG. That is, when the charged potential is equal to the target value, the abnormality counter and the address counter are cleared.

When the charging potential deviates from the target value, the address counter is incremented each time the grid voltage is increased or decreased, and the CD is increased.
The data transmitted to DT0 to DT7 is stored at a memory address obtained by adding an address counter to an address symbol of the memory CDMRY0. At the same time, the abnormality counter is also incremented.

Table 1 shows the relationship between memory addresses, symbol names, address counter values, and abnormal counters.

In this way, the value closest to the normal state is always stored in CDMRY0. Therefore, even if the abnormality counter becomes 10 or more and the potential control becomes abnormal, if the value stored in CDMRY0 is output to the transmission data CDT0 to CDT7 to the high-voltage power supply, the grid voltage according to the current photoconductor electric tense is output. it can.

This control may be switched from feedback control to fixed control by using the value of CDMRY0 by an external input.

〔effect〕

According to the present invention, the charging potential can be set to the target potential even when the charging potential control abnormally occurs when the charging characteristics of the photoconductor have changed from the initial stage due to the aging of the photoconductor and environmental fluctuations. It has become possible to provide an image forming apparatus with less fluctuation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of an example of an image forming apparatus according to the present invention, FIG. 2 is a block diagram of a control device, FIG. 3 is a time chart executed by a control unit when power is turned on, FIG. 4 is a control flowchart of the control unit, and FIGS. 5 to 7 are charging potential control flowcharts as different embodiments. DESCRIPTION OF SYMBOLS 1 ... Photoreceptor 2 ... Charging device 3 ... Eraser 4 ... Exposure light 5 ... Surface potential detecting means 6 ... Developing means 7 ... Transfer means

Claims (4)

(57) [Claims] A photoconductor, a charger for uniformly charging the surface of the photoconductor, a high voltage generating means for applying a high voltage to the charger, and a surface potential for detecting a surface potential of the photoconductor. An image forming apparatus comprising: a detection unit; and a control unit configured to control the surface potential of the photoconductor to be constant based on information of the surface potential detection unit. Data detected by the potential detecting means is stored sequentially based on the detected surface potential of the photoconductor, and when it is determined that the detected surface potential is abnormal based on predetermined conditions, the abnormality determination is performed. An image forming apparatus that sets an output of the high-voltage generating means to a predetermined value determined based on the data stored before. 2. A structure in which a control is performed to detect a difference between a surface potential and a target value from data detected by the surface potential detecting means, and to perform a control for correcting an output of the high voltage generating means. When the correction control counts incrementally and reaches a predetermined number of times, it is determined that there is an abnormality, and the predetermined value is determined based on data stored immediately before the predetermined number of times. The image forming apparatus according to claim 1, wherein: 3. The apparatus according to claim 2, wherein said surface potential detecting means determines that the surface potential is abnormal when detecting that the surface potential has a difference greater than a predetermined amount from a target value based on the detected data. Item 2. The image forming apparatus according to Item 1. 4. The image processing apparatus according to claim 1, wherein the data stored before the abnormality is determined is a comparison value between a target value and a detected value obtained when the power of the image forming apparatus is turned on. The image forming apparatus according to claim 1.