JPH0980870A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and surely perform a discharging operation by starting the discharging operation based on a detection signal. SOLUTION: An electrostatic charging AC bias is switched to OFF state after continuing an ON state (discharging) at least by the amount of one rotation of a drum after an electrostatic charging DC off timing. By discharging by the amount of one rotation of the drum, a history such as a memory and toner sticking accompanying an image forming operation are eliminated from the photoreceptor drum 2. And also, a vibration voltage is not impressed longer than required, so that the deterioration of the surface of the photoreceptor drum 2 is suppressed. By such the operation, a transfer material is guided to a paper ejecting part by a paper ejecting roller 15, or 16 by way of a fixing device. When the leading end of the transfer material reaches a paper ejection sensor 11 after passing through the fixing device 8, a paper election sensor signal is switched from ON to OFF. And, when the transfer material passes through the paper ejection sensor 11, the signal is switched from OFF to ON. Just before the stopping of the device, discharging is performed by the amount of one rotation of the drum, and after the photoreceptor memory, etc., are removed, the device comes to a standstill.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a discharging means for discharging a charge of an image bearing member and a detecting means for detecting a transfer material, which is provided in the vicinity of a discharging portion of the transfer material, and more particularly to an electrophotographic system. It is suitable for use in an image forming apparatus using.

[0002]

BACKGROUND ART As a charging method for charging an image bearing member such as a photoconductor, it is known to use a contact charging method instead of a corona discharge method.

In the contact charging system, a charging member (roller, blade, etc.) to which a voltage is applied is brought into contact with the surface of the charged body such as an image carrier with a predetermined pressing force to charge the surface of the charged body to a predetermined potential. It is a thing.

Regarding this contact charging system, Japanese Patent Laid-Open No. 63-
No. 149669, an oscillating voltage in which an AC voltage and a DC voltage are superposed is applied to a charging member to form an oscillating electric field between the charging member and the member to be charged, thereby uniformly charging the member to be charged. It has been known.

Further, it is possible to use the above-mentioned charging member as a discharging means for discharging the image bearing member, and to turn off the DC voltage and apply the AC voltage to the charging member during the discharging operation. It is known from the 208881 publication.

[0006]

However, if the time for removing the charge of the image bearing member is long, the life of the image bearing member may be shortened. That is, when the above-mentioned contact charging device of the oscillating voltage application method is used, the slip property of the image carrier surface is deteriorated by the discharge, and the image carrier surface is cleaned by the image carrier cleaning means (blade, roller, etc.). There is a problem that the wear is increased and, as a result, the life of the image bearing member is shortened.

On the other hand, the applicant of the present invention has proposed that the oscillating voltage is stopped after the image formation is completed, and the oscillating voltage is applied again for static elimination of the image bearing member immediately before the driving of the image bearing member is stopped. Is made. This may occur during the period in which the vibration voltage is stopped by reducing the application time of the vibration voltage to reduce the abrasion of the image carrier and at the same time the uniform charging (static elimination) action by the vibration voltage immediately before the stop,
It is based on the idea of eliminating defects (memory of image carrier, etc.).

However, in the above-mentioned proposal, when a non-image is formed after the image is formed, it takes a long time since the apparatus is started, and a long path is taken after the paper is supplied. It was found that is not necessarily small, and some uncertainty remains in the control results.

In view of the above, an object of the present invention is to easily and surely perform static elimination operation.

Another object of the present invention is to prevent the memory of the image carrier from occurring and at the same time prevent the life of the image carrier from being shortened.

[0011]

According to the present invention, there is provided an image carrier,
An image device including a charge removing unit that removes charge from the image carrier, a transfer unit that transfers an image from the image carrier to a transfer material, and a detection unit that is provided in the vicinity of the discharge unit of the transfer material and that detects the transfer material. In the image forming apparatus, the static elimination operation of the static elimination unit is started based on the detection signal of the detection unit.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A portable telephone according to the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a schematic sectional view showing an image forming apparatus of the present invention.

In the image forming apparatus 1, 2 is an electrophotographic photosensitive drum as an image bearing member, which is formed by forming an OPC photosensitive layer of negative charging polarity on a grounded conductive drum substrate such as aluminum. It is rotationally driven in the direction of the middle arrow at a predetermined process speed (peripheral speed).

Reference numeral 3 is a charging member. Is a charging roller,
The photosensitive drum 2 is provided so as to be in contact with the photosensitive drum 2.
The top is uniformly charged to a predetermined polarity potential. Details will be described later.

Reference numeral 4 denotes a laser beam output from a laser beam scanner (not shown), which is modulated in accordance with target image information and is electrostatically latent on the uniformly charged photosensitive drum 1. Form an image.

A developing device 5 visualizes the latent image on the photosensitive drum 2 as a toner image.

Reference numeral 6 denotes a transfer roller which is a transfer member, and feeds the toner image on the photosensitive drum 2 to a paper feeding cassette 9 or 10.
Transfer to a transfer material (paper) fed from. In the figure, the dotted line indicates the transfer material transport path.

A cleaner 7 collects the transfer residual toner on the photosensitive drum 2 with a cleaning blade in contact with the drum 2.

By this series of processes, the photosensitive drum 2 is cleaned and is repeatedly used for image formation.

On the other hand, the toner image on the transfer material is heated and fixed in the fixing device 8 and discharged as a permanent image to the face-down (FD) tray 12 or the face-up (FU) tray 14. The FD tray 12 is placed with the image surface side of the transfer material facing downward, and the FU tray 14 is placed with the image surface side of the transfer material facing upward.

Reference numerals 11 and 13 denote FD trays 12 and F, respectively.
It is a sensor that detects whether or not the transfer material is discharged to the U tray 14. As this sensor, for example, a photo interrupter or the like is used, and the passage timing of the transfer material is detected by the presence or absence of the transfer material at the detection position of the sensor. Sensor 1
Immediately before 1 and 13, a pair of paper discharge rollers 15 and 16 that discharge the transfer material to the outside of the apparatus are provided. Therefore, when the transfer material is jammed at the positions of the discharge rollers 15 and 16, the transfer material is not detected by the sensors 11 and 13, and the jam of the transfer material is displayed on the operation unit of the apparatus.

The charging roller 3 as the charging member is formed by forming a single layer or a plurality of layers of rubber, resin, etc. adjusted to have a predetermined electric resistance on a cored bar of iron, stainless steel or the like. In addition, the contact is maintained by a predetermined pressure. A DC voltage V _{DC is} applied to the charging roller 3 from a power source E (see FIG. 2).
And an oscillating voltage (V _DC + V _AC ) in which _AC voltage V _AC is superimposed is supplied. As a result, the photosensitive drum 2 is charged to a voltage (= DC voltage V _DC ) at the vibration center of the vibration voltage.

It is desirable that the AC component of the oscillating voltage be controlled by a constant current. The vibration voltage is the charging start voltage of the photosensitive drum 2 when only the DC voltage is applied to the charging roller 3.
It is desirable to have a peak-to-peak voltage more than double.

The charging start voltage referred to here is the applied DC voltage value at which the charging is started on the photosensitive drum 2 whose potential was previously zero when only the DC voltage was applied to the charging roller 3. This largely depends on the material and layer thickness of the OPC layer of the photoconductor drum 2, and is slightly different depending on the type of the charging roller 3, the gap between the photoconductor drum 2 and the charging roller 3, etc. According to this, by applying an oscillating voltage having a peak-to-peak voltage that is at least twice the charging start voltage, the charging roller 3 as the charging member and the photosensitive drum 2 as the charged body
It was found that an oscillating electric field was formed between the and, and charge transfer and reverse transfer occurred, resulting in uniform charge uniformity. It was also found that sand-like uneven charging is likely to occur when a peak-to-peak voltage less than twice the charging start voltage is applied.

The oscillating voltage described above is a voltage whose voltage value changes periodically, and its waveform may be a sine wave, a triangular wave, a rectangular wave, a sawtooth wave, or the like, and the DC power supply is turned ON periodically. It may be formed by turning off.

FIG. 2 shows a simple block diagram of an electric system and a drive system. The power supply E of the charging roller 3 is generated by the signal from the CPU 17.
And the drive timing of the drive source M of the image carrier 2, the fixing roller pair of the fixing device 8, and the discharge roller pairs 15 and 16 are controlled.

As shown in FIG. 2, the image carrier 2, the fixing roller pair, and the discharge roller pairs 15 and 16 are driven by a common drive source (motor) M.

FIG. 3 shows the first image forming apparatus 1 of FIG.
3 is a timing chart illustrating an embodiment of the above.

In FIG. 3, at the same time when the print start signal is input from the outside, the transfer of the transfer material from the cassette 9 or 10 is started together with the drum motor drive (Ts). At this time, the charging AC bias (AC component V _AC of the vibration voltage applied to the charging roller 3) is simultaneously applied, and the photosensitive drum 2
Charge off the top. A transfer bias (a bias applied to the transfer roller 6 and a bias for transferring the toner image on the photoconductor drum 1 to the paper is referred to as a print bias, and the toner transferred onto the transfer roller 6 is referred to as a print bias. Two
The bias returned to the upper side is referred to as a cleaning bias. In this example, the toner is negative, the print bias is (+), and the cleaning bias is (-).

Charging DC bias for image formation (timing DC component V _{DC of the} oscillating voltage) at the timing T _{1 when the} feeding is completed and the charge elimination for at least one revolution of the photosensitive drum 2 is completed.
Is started to uniformly charge the photosensitive drum 2 to a predetermined potential. That is, the portion of the drum 2 charged at the timing T ₁ is the portion that should be the leading edge of the image.

Then, the image exposure, the developing bias and the transfer print bias are started with delays of t ₁ , t ₂ and t ₃ , respectively. The times t ₁ , t ₂ , and t ₃ are the times during which the charging portion of the photosensitive drum 2 which is uniformly charged by turning on the charging DC moves to the exposure position, the developing position, and the transfer position, respectively.

Next, at timing T ₂ , the charging DC bias is turned off, and the drum 2 is in the neutralization state.
That is, the portion of the drum 2 that is at the charging position at the timing T ₂ is the portion that should be the trailing edge of the image. And image exposure,
Timing of development bias and transfer print bias T ₂
After that, they are turned off after a delay of t ₁ , t ₂ , and t ₃ , respectively, and the image forming operation is completed.

The charging AC bias is switched off from the charging DC bias OFF timing T ₂ after the ON state (static elimination) is maintained for at least one revolution of the drum. By removing the electric charge for one round of the drum, the history of the memory or the like and the toner adhesion due to the image forming operation are eliminated on the photosensitive drum 2. In addition, deterioration of the surface of the photosensitive drum 2 can be suppressed by not applying the oscillating voltage longer than necessary.

By the above operation, the transfer material that has passed through the transfer portion passes through the fixing device 8 and discharge rollers 15 or 16
Guided to the paper exit. Here, FD tray 12
Will be referred to as a paper discharge port. When the leading edge of the transfer material that has passed through the fixing device 8 reaches the paper ejection sensor 11, the paper ejection sensor signal in FIG. 3 changes from OFF to ON (T ₃ ). Then, when the transfer material passes through the paper discharge sensor 11, it turns from on to off (T ₄ ).

In synchronism with this timing T ₄ , the charging AC bias is turned on again, at least one turn of the drum is discharged, and then turned off, and the drum motor M is stopped (Te) to operate the image forming apparatus. To finish.

As described above, by removing the electric charge for at least one revolution of the drum immediately before the apparatus is stopped, the photoconductor memory or the like that may be generated while the charging bias (uniform charging or static elimination) is turned off is removed. , The device will be stopped. According to this embodiment, the sum L ₁ + of the distance L ₁ from the charging position to the transfer position along the peripheral surface of the photoconductor and the distance L ₂ from the transfer position to the discharge port along the transfer material transport path.
L ₂ is set to be larger than the length of two rounds of the photosensitive drum. It is preferable that L ₁ + L ₂ is set larger than the length of one round of the drum.

Since the timing of the static elimination sequence can be set by using the paper discharge sensor immediately before the discharge port, it is not necessary to incorporate a timer heartin or the like for this control in the CPU 17 which controls the apparatus. Therefore, the burden is lightened. Further, since the conveyance state of the transfer material itself is accurately monitored and the timing is set, the above charge elimination sequence can be performed without considering expansion and contraction of the transfer material, conveyance delay, etc. With this amount as an error, it becomes necessary to set a margin).

In FIG. 1, the paper discharge sensors 11, 1
The distance from the sheet discharge port of No. 3 is set to be sufficiently smaller than one round of the drum. Therefore, the discharging of the transfer material is completed during the charge removal operation of the drum.

(Second Embodiment) FIG. 4 is a timing chart for explaining a second embodiment of the image forming apparatus 1 shown in FIG. Descriptions of the same reference numerals as those of the timing chart for explaining the first embodiment shown in FIG. 3 will be omitted.

In this embodiment, what is different from the first embodiment is the charging AC bias on timing T ₄₀ for removing the charge for at least one revolution of the drum immediately before the apparatus is stopped. T ₄₀ is set so that the end timing of the static elimination operation (stop timing of the drum motor) and the end timing of discharging the transfer material of the maximum size in the transfer material transport direction are substantially the same.

Timing T ₄₀ is the discharge sensor ON timing T _3, and time _M required for the transfer material of the maximum size length that can be passed by the image forming apparatus to pass through the discharge sensor is t _M.

[0043]

[Outside 1] And the time required for one round of the drum. Here, α is the time during which the transfer material passes through the distance between the paper ejection sensor and the paper ejection port (it will be zero if the paper ejection sensor is at the paper ejection port).

Here, other than T ₃ are given to the image forming apparatus and are constants. Therefore, T ₄₀ can be easily set at the time (T ₃ ) when the leading edge of the transfer material comes to the paper discharge sensor.

According to the present embodiment, there is an advantage that the device driving time | T _s −T _e | can be set shorter than that of the first embodiment.

(Third Embodiment) FIG. 5 is a timing chart for explaining the third embodiment of the image forming apparatus 1 shown in FIG. Descriptions of the same reference numerals as those in the above timing chart are omitted.

This embodiment is a development of the second embodiment, and is characterized by the charging AC bias on timing T ₄₁ for performing charge removal for at least one revolution of the drum immediately before the apparatus is stopped. T ₄₁ is set so that the end timing of the static elimination operation and the end timing of the discharge of the transfer material are substantially the same regardless of the size of the transfer material.

Timing T ₄₁ is the discharge sensor ON timing T ₃ and T _p is the time required to pass the discharge sensor determined by the paper size.

[0049]

[Outside 2] And the time required for one round of the drum to be determined. α is as described above.

Here, the paper size is a variable, but since it is determined by the selection of the cassette 9 or 10 at the time when the apparatus starts the image forming operation, it is at the T ₃ timing as in the second embodiment. T ₄₁ can be easily set according to the size of the transfer material. It should be noted that the cassette is provided with a protrusion having a different shape according to the size of the transfer material placed on the cassette, and the size of the transfer material used is recognized by detecting the protrusion on the apparatus main body side. .

According to this embodiment, the device driving time can be shortened as compared with the first embodiment regardless of the size of the transfer material.

Further, in the timing charts of the first to third embodiments, the example of printing one sheet of the transfer material is shown, but it is possible to continuously print on a plurality of transfer materials by one image formation start signal. In the case of continuous printing, the timing T ₃ is based on the final transfer material among the plurality of transfer materials.

In the above description of all the embodiments,
Although the method of applying the charging AC bias has been described as the charge removing means, the charge removing means is not limited to this.
Unlike the charging member, it is possible to use an exposing means such as a lamp that uniformly exposes the photoconductor.

[0054]

As described above, according to the present invention, since the charge removal time of the image bearing member can be shortened, it is possible to extend the life of the image bearing member while preventing the occurrence of memory on the image bearing member. In particular, when the charge removing member is also used as the charging member, the vibration voltage application time is reduced, and the abrasion of the image carrier can be reduced.

Further, the behavior of the transfer material immediately before being discharged can be monitored by the detection means, so that the static elimination operation timing can be set accurately and easily (the CPU load is lightened).

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an image forming apparatus of the present invention.

FIG. 2 is a block diagram of an electric system and a drive system of the above device.

FIG. 3 is a timing chart of the first embodiment of the device.

FIG. 4 is a timing chart of the second embodiment of the device.

FIG. 5 is a timing chart of the third embodiment of the device.

[Explanation of symbols]

 2 Photosensitive drum 3 Charging (static elimination) member 11, 13 Paper ejection sensor 12, 14 Paper ejection tray 15, 16 Ejection roller

Claims (13)

[Claims] 1. An image carrier, a charge removing unit for removing charge from the image carrier, a transfer unit for transferring an image from the image carrier to a transfer material, and a transfer member provided in the vicinity of a transfer material discharge unit. An image forming apparatus having: a detection unit for detecting, wherein the charge removal operation of the charge removal unit is started based on a detection signal of the detection unit. 2. The image forming apparatus according to claim 1, wherein the apparatus has a charging member to which an oscillating voltage is applied to charge the image carrier. 3. The oscillating component of the oscillating voltage is switched off after the charging of the image bearing member by the charging member for forming an image is completed and before the neutralization by the neutralizing means is started. The image forming apparatus according to claim 2. 4. The image forming apparatus according to claim 2, wherein the charging member is used as the charge removing unit. 5. The image forming apparatus according to claim 4, wherein the oscillating voltage has a DC component and an AC component, and the DC component is turned off and the AC component is applied to the charging member during static elimination operation. . 6. The alternating current component is switched off after the charging operation for forming an image on the image carrier is completed by the charging member and before the discharging operation is started by the charging member. The image forming apparatus according to claim 5. 7. The AC component is switched off after the image carrier is rotated at least once after the charging for charging the image carrier by the charging member is completed. Item 6. The image forming apparatus according to item 6. 8. The image forming apparatus according to claim 2, wherein the discharging operation of the discharging unit is started based on the timing when the trailing edge of the transfer material passes the detection position of the detecting unit. 9. The image forming apparatus according to claim 2, wherein the charge removing operation of the charge removing unit is started based on the timing at which the front end of the transfer material passes the detection position of the detection unit. 10. The image forming apparatus according to claim 9, wherein the charge removing operation of the charge removing unit is started based on the length of the transfer material in the transfer material moving direction. 11. The image forming apparatus according to claim 2, wherein the charge removing operation of the charge removing unit is continued while the image carrier is rotated at least once. 12. The apparatus is provided in the vicinity of the detection means, and has a discharge rotating body that discharges a transfer material to the outside of the apparatus, and a common drive source that drives the image carrier and the discharge rotating body. The image forming apparatus according to claim 2, further comprising: 13. The charging member is provided so as to come into contact with the image carrier.
2 image forming apparatus.