JP2641647B2 - Simultaneous development cleaning type image forming apparatus - Google Patents

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 employing a simultaneous cleaning with developing method.

[0002]

2. Description of the Related Art A developing device and a waste toner collecting device including a scraping blade are disposed on both sides of a photosensitive drum with a transfer device interposed therebetween, so that development and cleaning of residual toner on the photosensitive drum are performed independently. In contrast to a known image forming apparatus, the present applicant has previously proposed an image forming apparatus shown in FIG. 4 which employs a so-called simultaneous development and cleaning method in which development and cleaning are performed simultaneously (for example, JP-A-3-7972). According to this simultaneous development cleaning method, epoch-making effects such as reduction of running cost due to reduction of toner consumption, downsizing of the apparatus, and cleaning without damaging the photosensitive drum can be obtained.

In FIG. 1, reference numeral 1 denotes a photosensitive drum as a latent image carrier, 2 denotes a charger, 3 denotes a developing device, and 7 denotes a transfer device. The developing device 3 is of a contact type one-component non-magnetic developing type using an elastic conductive roller (developing roller) 6 as a developer (toner) carrier, and the one-component toner T0 contained in the box 4 is Charging brush 5 made of silicon rubber, etc.
As a result, the charged toner T1 is supplied to the photosensitive drum 1 and developed.

Reference numeral 20 denotes a control device, which is a main motor 1
1, laser emission source 12, switch 14 for developing bias power supply (-Vb), switch 13 for power supply 10 for charger (-Vo)
Are controlled at the timing shown in FIG. Transfer device 7
Of the switch 15 and the like are similarly controlled. The photosensitive drum 1 is rotated at a constant speed (NS in FIG. 5) by a driver 11D and a main motor 11 serving as a rotation driving unit.

In the image forming apparatus having such a configuration, when the control device 20 starts rotating the main motor 11 at time t1 in FIG. 5, the photosensitive drum 1 and the developing roller 6 are synchronously rotated at a constant speed. Further, the peripheral surface of the photosensitive drum 1 is charged by the charger 2 to the image forming charge potential -Vo, and the exposed portion irradiated with the laser scanning beam B becomes the potential -Vr after time t3. The unexposed portion is charged potential −V
o. On the other hand, the developing roller 6 is also charged to the developing bias potential -Vb.

As shown in FIG. 6C, the charging potential -Vr of the exposed portion has the same polarity as the developing bias potential -Vb to the developing roller 6, but has a low absolute value (| Vr | <| Vb |).
Therefore, the charged toner T1 on the developing roller 6 is
As shown in (2), it is attracted to the exposed portion by the electric field as the developing toner T3. That is, it is developed [FIG.
(C)]. The toner T4 remaining on the developing roller 6 is
It is collected in the developing device 3 and reused.

[0007] The developing toner T3 is then transferred to the opposite side (front side) of the sheet P by the transfer device 7 (turned on at time t3 in FIG. 5) in FIG. As shown, it is transferred as image toner T5.

On the other hand, the toner (T6) may remain on the photosensitive drum 1 even after the transfer. This residual toner T6
Is charged to the potential −Vo in the charger 2 as shown in FIG. However, as shown in FIG. 6B, the residual toner T6 adhered to a portion to be an exposed portion is charged to a potential -Vr having an absolute value lower than the developing bias potential -Vb at the time of exposure. Absent. Rather,
This is advantageous because it is effectively used for the development shown in FIG.

On the other hand, the residual toner T6 attached to the unexposed portion shown in FIG. 6B remains at the charging potential -Vo having the same polarity as the developing bias potential -Vb of the developing roller 6 and having a high absolute value. Therefore, as shown in FIG. 6C, the residual toner T6 is attracted to the developing roller 6 by the electric field. That is, the residual toner T6 attached to the unexposed portion
Is removed from the photosensitive drum 1, and it is understood that the cleaning is performed here. Further, the removed residual toner T6 can be reused as the supply toner T1 in FIGS. 4 and 6C.

Thus, the cleaning is performed at the upstream position where the photosensitive drum 1 and the developing roller 6 are in contact with each other, and subsequently the development is simultaneously performed at the downstream side.

[0011]

By the way, in order to form an image with such an apparatus, it is necessary to carry out preparatory operations such as a preparatory rotation for raising the photosensitive drum 1 to a specified number of rotations and stabilization of each potential. For this reason, the control device 20 controls the driving of each means at the timing shown in FIG.

Here, P2-- of the photosensitive drum 1 shown in FIG.
The peripheral surface portion between P1 comes into contact with the developing roller 6 without passing through the charger 2 at the start of the preparation rotation. Therefore, the peripheral portion between P2 and P1 is not charged to the charging potential -Vo during image formation, and depending on the length of the stop time and the like, as shown in FIG. The value may be a low residual potential -Vs.

Then, the development (│Vb│) shown in FIG.
-| Vr |) and the same electric field action (| Vb |-| Vs |)
Will occur. That is, the supply toner T1 carried on the developing roller 6 to which the developing bias potential −Vb is applied is
P2-P1 of the photosensitive drum 1 having the residual potential -Vs
A large amount adheres to the peripheral area. A phenomenon opposite to that of cleaning occurs. If left untouched, after passing through the developing roller 6, it will be scattered and contaminate the inside of the apparatus, as well as deteriorating the image quality.

Therefore, in order to solve this inconvenience,
The peripheral portion between the P2 and P1 must pass through the charger 2 to be charged to the charging potential -Vo at the time of image formation, thereby performing essential cleaning. However, if the amount of the residual toner attached to the portion is large, the residual toner may not be charged to a predetermined value (−Vo) even if the residual toner is passed through the charger 2 several times during the preparatory rotation, so that sufficient cleaning can be performed. Absent. Thus, the preparatory rotation time of the photosensitive drum 1 must be considerably lengthened, which hinders rapid image formation.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image of a simultaneous cleaning with development method capable of rapidly forming a high-quality image by performing complete cleaning while greatly shortening the preparation rotation time regardless of the level of the residual potential of the photosensitive drum. An object of the present invention is to provide a forming apparatus.

[0016]

According to the present invention, the rotation speed of the photosensitive drum is increased during the preparatory rotation to increase the number of times the photosensitive drum passes through the charger, so that the toner remaining on the photosensitive drum is positively, forcibly and promptly removed. The above-described object is achieved by charging to a higher potential and increasing the potential difference from the developing roller side, that is, the electric field strength, to greatly promote the cleaning action within a short time.

That is, according to the present invention, an exposed portion and a non-exposed portion are formed by irradiating a laser scanning beam on the peripheral surface of the photosensitive drum passing through the charger, and the photosensitive drum side and the developing roller side to which a developing bias is applied are formed. At the same time, the residual toner adhering to the unexposed portion is adsorbed to the developing roller side by using the potential difference between the developing roller side and the unexposed portion is cleaned, and at the same time, the developing roller is supplied to the exposed portion from the developing roller side to perform development. In the image forming apparatus of the system, the rotation driving means of the photosensitive drum is formed so as to be rotatable by switching to a rotation speed higher than the rotation speed at the time of image formation, in addition to the rotation speed at the time of image formation. A rotation speed switching control means is provided for switching to a high rotation speed for a set time during the preparatory rotation of the photosensitive drum before image formation and to a rotation speed for image formation after a lapse of the set time. Characterized in that was.

[0018]

According to the present invention, the rotation speed switching control means switches the rotation driving means to rotate the photosensitive drum at a speed higher than the rotation speed at the time of image formation. Therefore, the chance of passing through the charger within the set time of each part of the peripheral surface of the photosensitive drum can be increased, so that the potential of the residual toner attached to the part is charged to a charge potential corresponding to the image forming charge, and the predetermined cleaning is performed. Many can be implemented. Therefore, the remaining toner can be reliably cleaned while shortening the preparation rotation time, and a high-quality image can be formed quickly.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. The image forming apparatus of the simultaneous cleaning with main development is
As shown in FIG. 1, the basic structure is the same as the conventional structure shown in FIG.
1D and a rotation speed switching control means (20) is provided, and the photosensitive drum 1 is driven at a high speed (H
It is configured to rotate in S). Further, in this embodiment, the power supply 10 for the charger 2 has a structure capable of switching the charging potential, and the charging potential switching control means (20)
And the output of the power supply 10 for the charger 2 is switched to the higher charging potential (-V1) during high-speed rotation.

In FIG. 1, the driver 11D can switch between the image forming rotation speed NS and a higher rotation speed HS as shown in FIG.
0) is selectively switched by the switching signal HL. In this embodiment, HS = 2 · NS.

In the case of this embodiment, the rotation speed switching control means includes a control device 20 (CPU, ROM, etc.) of FIG. 1 for driving and controlling the entire apparatus formed including a CPU, ROM, RAM, etc. And outputs the switching signal HL (for example, H level) during the preparatory rotation of the photosensitive drum 1 for a set time Ts shown in FIG. (11D) can be switched to the high-speed rotation speed HS, and can be switched to the image formation rotation speed NS after the lapse of the set time Ts.

The set time Ts is set between the photosensitive drum 1 and the charger 2.
When the state at the start of the preparatory rotation has the relationship shown in FIG. 1, the time is such that the P2-P1 peripheral surface portion can pass through the charger 2 at least once as the photosensitive drum 1 rotates. In other words, the time is at least the time required for the photosensitive drum 1 to make at least one rotation.

In this embodiment, the time setting unit 21 shown in FIG. 1 is provided to quickly respond to the rotation speed of the photosensitive drum 1, the charging potential -Vo during image formation, the properties of the toner, and the amount of the residual toner T6. It is configured to be operable. However, the set time Ts may be stored in the ROM or the RAM. Further, it may be determined indirectly by the rotation operation of the photosensitive drum 1 or the like.

The control device 20 and the rotation speed switching control means (20) start and stop each means at the timing shown in FIG. Set time Ts
Is counted from the start of the preparatory rotation (time t1 in FIG. 2).

The power supply 10 of the charger 2 has a higher charging potential -V1 (for example, -600 V) having the same polarity as the image forming charging potential -Vo (for example, -500 V) shown in FIG.
V) can be output, and is automatically switched by the switching signal CHNG of the charging potential switching control means (20).

When the developing bias potential -Vb applied to the developing roller 6 was -200 V, a high cleaning potential -V1 of -550 V provided a sufficient cleaning effect. That is, it is desirable that | V1 | ≧ | Vo + 50 |.

In the case of this embodiment, the charging potential switching control means is constituted by utilizing components such as a CPU and a ROM of the control device 20 and the functions possessed by them, similarly to the rotation speed switching control means (20). , The high speed (H
S) During rotation, the switching signal CHNG is output (for example, H level) to switch the charger power supply 10 to output the higher charging potential -V1, and when the rotation speed NS is reached, the image forming charging potential -Vo is changed. It can be switched to output.

Next, the operation will be described. First, a set time Ts selected from various conditions is set in the time setting device 21. In this embodiment, the set time Ts is set as a time required for the photosensitive drum 1 to make only four rotations from the state shown in FIG. 1, and is equal to the preparation rotation (four rotations) time of the photosensitive drum 1. Of course, the set time Ts is not directly related to the preparation rotation speed (for example, 5 rotations),
Should be longer than the time (Ts) required for at least one rotation.

At time t1 in FIG. 2, the control device 20 operates the main motor 11, the laser emission source 12, the switch 13 of the charger power supply 10, and the developing bias power supply (-Vb).
When the preparatory rotation is started by driving the switch 14 and the like, the photosensitive drum 1 starts to rotate clockwise in FIG.

Here, the rotation speed switching control means (20)
Outputs a switching signal HL to switch the driver 11D, which is a rotation driving unit of the photosensitive drum 1, to the high-speed rotation HS shown in FIG. At the same time, charging potential switching control means (20)
Outputs the switching signal CHNG and switches the charger power supply 10 to output the higher charging potential -V1 shown in FIG.

Therefore, the peripheral surface of the photosensitive drum 1
It can pass through the charger 2 twice as many times within the same time (Ts) as in the conventional example. In other words, the same number of times of passing through the charger 2 can be executed in a short time.

In addition, the portion after the peripheral surface portion P1 of the photosensitive drum 1 is charged at a higher charging potential -V1 having an absolute value higher than the charging potential -Vo during image formation. For this reason, the photosensitive drum 1
The residual toner T6 adhered to the peripheral surface of the charging device 2 is reliably charged (−V
1) is done. Of course, the P2-P1 peripheral portion, which was initially at the residual potential -Vs, is also charged to a potential close to the higher charging potential -V1 during one rotation of the photosensitive drum 1.

Therefore, when the residual toner T6 charged to the substantially higher charging potential -V1 comes into contact with the developing roller 6, as shown in FIG. 3, a large potential difference (| V1 |-| Vb) from the developing bias potential -Vb ), It is surely attracted to the developing roller 6 by the action of the electric field. That is,
The photosensitive drum 1 can be reliably cleaned in a short time.

Further, the potential difference (| V1 |-| Vb |)
Is larger than the potential difference (| Vo |-| Vb |) for cleaning at the time of image formation, so that the residual toner T6 can be more reliably cleaned.

Next, when the set time Ts elapses at time t2 in FIG.
1D is switched to the image forming rotation speed NS. On the other hand, the charging potential switching control means (20) provides a charging potential -Vo during image formation.
The power supply 10 for the charger is switched so as to output. Therefore, the exposure portion is formed by the laser scanning beam B from the time t3 in FIG. 2, and the cleaning and the development in FIG. 6C can be performed simultaneously.

The time lag between the time t2 and the time t3 is set to the image forming charge potential -Vo by the charger 2 in FIG.
Is the time until the part P1 shown in FIG. 7 reaches the laser scanning part Pb.

Thus, according to this embodiment, the driver 11D, which is a means for rotating the photosensitive drum 1, is formed so as to be switchable between the image forming rotation speed NS and the high speed rotation speed HS, and the set time Ts during the preparation rotation. Only the rotation speed switching control means (20) for switching to the high speed HS is provided.
Since the number of times the peripheral surface portion of the photosensitive drum 1 passes through the charger 2 can be increased in a short time, predetermined cleaning can be performed reliably and promptly. Accordingly, irrespective of the level of the residual potential (-Vs) of the photosensitive drum 1 and the amount of the residual toner T6 adhered to the photosensitive drum 1, complete cleaning is performed while significantly shortening the preparation rotation time, and a high-quality image is quickly formed. Can be.

The time (T) for switching to the high-speed rotation HS
Since s) can be arbitrarily set by the time setting unit 21, it is possible to set the optimum and minimum time in accordance with various conditions such as the amount of the residual toner T6 adhered, and also from this point, the preparation rotation time is greatly reduced. Shortening and power consumption can be reduced.

The power supply 10 for the charger is formed so that the charging potential -Vo during image formation and the higher charging potential -V1 having the same polarity and a high absolute value can be switched and output, and the photosensitive drum 1 rotates at high speed (HS ), The charging potential switching control means (20) for switching to the higher charging potential -V1 is provided, so that more efficient cleaning can be performed.

If the high-level charging potential -V1 is appropriately selected, the photosensitive drum 1 can be completely cleaned only by rotating the photosensitive drum 1 at a high speed HS, and the residual toner T6 can be effectively re-used as the supplied toner T1. Available.

In the present invention, the charge potential V
The polarities such as o and the developing bias potential Vb are not limited to the (-) polarity.

[0042]

According to the present invention, the rotation drive control means for the photosensitive drum is formed so as to be switchable between the image forming rotation speed and the high speed rotation speed, and is switched to the high speed rotation for a set time during the preparatory rotation of the photosensitive drum. The rotation speed switching control means is provided, so that the number of times of passage through the charger per unit time is increased irrespective of the level of the residual potential of the photosensitive drum or the amount of residual toner adhered to the photosensitive drum, so that quick and complete cleaning can be achieved. I can do it. Thus, a high-quality image can be quickly formed while shortening the preparation rotation time.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation.

FIG. 3 is a view for explaining a cleaning operation.

FIG. 4 is an overall configuration diagram of a conventional example.

FIG. 5 is a timing chart for explaining the operation of the conventional example.

FIG. 6 shows conventional charging-exposure-cleaning simultaneous development-
FIG. 9 is a diagram for explaining a transfer operation.

FIG. 7 is a diagram for explaining a problem of a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum 2 charger 3 developing device 6 developing roller 7 transfer device 10 power supply for charger 11 main motor (rotation driving means) 11D driver (rotation driving means) 12 laser light source 20 control device (rotation speed switching control means) T1 supply Toner T6 Residual toner NS Image forming rotation speed HS High speed rotation Vo Image forming charging potential V1 Higher charging potential Ts Setting time

Claims (1)

(57) [Claims] An exposing portion and a non-exposing portion formed by irradiating a laser scanning beam on a peripheral surface of a photosensitive drum passing through a charger;
Utilizing the potential difference between the photosensitive drum side and the developing roller side to which the developing bias has been applied, residual toner adhering to the unexposed section is attracted to the developing roller side to clean the unexposed section and simultaneously to the exposed section. In an image forming apparatus of a simultaneous cleaning type in which toner is supplied from a developing roller side to perform development, the rotation driving means of the photosensitive drum is set to a rotational speed higher than the image forming rotational speed in addition to the image forming rotational speed. A rotation speed switching control means for switching the rotation drive means to a high-speed rotation speed for a set time during the preparatory rotation of the photosensitive drum before image formation and to a rotation speed for image formation after a lapse of the set time; And an image forming apparatus of a simultaneous development and cleaning type.