JPS62245273A - Electrostatic latent image developing device - Google Patents

Abstract

PURPOSE:To prevent photographic fog due to a toner and toner leak to the outside of a developing device by carrying a developer on a developer carrying guide member from a developer supply part to a developing area in accordance with rotation of a magnetic roller. CONSTITUTION:The developer is carried on a developer carrying guide member 12 from a developer supply part A to a developing area B by only rotation of a magnetic roller 11 and is brought into contact with the surface of an electrostatic latent image carrier in the front end of the developer carrying guide member 12 to develop an electrostatic latent image. Simultaneously, the developer is brought into contact with the outside peripheral surface of a developing sleeve 10 and is carried between the developing sleeve 10 and the developer carrying guide member 12 toward the developer supply part A in accordance with rotation of the developing sleeve 10. In this case, contacting of the developer to the surface of the electrostatic latent image carrier is terminated in the position where the developing sleeve 10 approaches the surface of the electrostatic latent image carrier or a position X1 where the developing sleeve 10 is most approximate to said surface. The surface of the electrostatic latent image carrier whose contacting to the developer is terminated passes said position X1 where an electric field is strong, and the toner floating in this part is stuck to an electrostatic latent image part or the outside peripheral surface of the developing sleeve 10 by the strong electric field.

Description

[Detailed Description of the Invention] Starry Gogomega Saragetsuko! The present invention relates to an electrostatic latent image developing device using a magnetic brush method used in electrophotographic copying processes and the like.

Conventionally, as a method using this type of magnetic brush type electrostatic latent image developing device, the method shown in FIGS. 8 and 9 is well known. In this method, a magnetic roller (3) is placed opposite the surface of a photoreceptor drum (1) that is rotationally driven in the direction of arrow (a).
A developing sleeve (2) with a built-in developer is provided, and the developer supplied to the developer supply section (A) by the packet roller (4) is applied onto the outer peripheral surface of the developing sleeve (2) by the magnetic force of the magnetic roller (3). While holding the magnetic roller (3) in the direction of arrow (b) and the developing sleeve (2) in the direction of arrow (C), the outer circumferential surface of the developing sleeve (2) is moved as shown in arrow (c).
The developing sleeve (2) and photoreceptor drum (1)
) in the developing area (B) adjacent to the photoreceptor drum (1).
This is a method of developing an electrostatic latent image formed on the surface of.

Also, in Figures 8 and 9, (5) is the height regulation plate, (6)
is a scraper, (7) is a power source for developing bias, and the developing sleeve (2) also functions as a developing electrode.

Ming tries to decide.　　.

By the way, the conventional developing method (as shown in FIGS. 8 and 9, not only the method in which both the developing sleeve and the magnetic roller are rotationally driven, but also the method in which only one of the developing sleeve and the magnetic roller is rotationally driven) In this method, the developer passes through the closest position (x, H interval (dl) 1) between the developing sleeve (2) and the photosensitive drum (1), and then the developing sleeve (2) Contact with the photoreceptor drum (1) ends at a position (xl') [distance (dl')] that is moving away from the surface of the photoreceptor drum (1).However,
This can cause toner fogging on the developed image, toner leakage to the outside of the developing device, and in the case of developers using carriers, toner image fading, poor fine line reproducibility, or magnetic restriction due to scraping of the toner image by the carrier. There is a problem in that the carrier has a small force and adheres to the surface of the photoreceptor drum (1).

As mentioned above, this problem is caused by the fact that the interval (d+') is wider than the interval (dI), and in a developer that uses a carrier, toner fog and toner leakage occur when the developer It has been confirmed that this phenomenon tends to occur when there is toner with a low charge amount. Note that in a developer using a carrier, it is inevitable that toner with a low charge amount exists in the developer at a certain ratio even if it is a small amount.

Toner with a low charge amount tends to float away from the carrier, and when the developer tries to separate from the photoreceptor drum (1), that is, the toner with a low charge floats in the space at the position (x,'). . As is clear from the above-mentioned condition that the mountain °〉d, the vicinity of the position (X,') and the position (X
, '), the electric field between the developing sleeve (2) and the photosensitive drum (1) near the downstream side in the developer transport direction is at the closest position (
Therefore, the floating toner cannot receive sufficient electric force from the electrostatic latent image formed on the surface of the photoreceptor drum (1), and as a result, It may adhere to the background portion of the image and cause fog, or it may leak downward without being attracted to either the developing sleeve (2) or the photoreceptor drum (1).

Also, the fact that the electric field due to the electrostatic latent image at position (x,') is weaker than at the closest position (!1) means that the liquid level is higher than the current level!
At (X,), the attractive force toward the photoreceptor drum (1) on the toner attached to the surface of the photoreceptor drum (1) is at the position (x,'
) means that it is weaker than the nearest position (x, ). Therefore, a phenomenon occurs in which the toner adhering to the image area at the closest position (X,) is scraped off by the developer (carrier) ear at the position (X,'). This leads to blurring of toner images and poor fine line reproducibility.

In addition, if the carrier has a small diameter and is a binder type, the magnetic binding force is small and it can hold a fairly high amount of charge with the opposite polarity to the toner, so it tends to adhere to the background of the image. The larger dl') is, the weaker the magnetic attraction force by the magnetic roller (3) becomes, so it is more likely to occur.

In order to solve the above problems, the electrostatic latent image developing device according to the present invention has the following features: (a) The developing electrode is a developing sleeve having a built-in magnetic roller, and the developing sleeve has an approximately A developer conveyance guide member having a contoured shape is provided extending from the developer supply section to the vicinity of the developing area, and the distance between the developer conveyance guide member and the developing sleeve is set such that the distance between the developer conveyance guide member and the developing sleeve gradually increases from the development area toward the developer supply section. (b) The magnetic roller is rotationally driven from the development area toward the developer supply section, and the development sleeve is rotationally driven in the same direction as the magnetic roller, and the developer is supplied to the developer supply section based on the rotation of the magnetic roller. The developer is conveyed from the developer supply section to the development area on the developer conveyance guide member, and the developed developer is conveyed between the development sleeve and the developer conveyance guide member to the developer supply section based on the rotation of the development sleeve. It is characterized by being designed to be transported.

That is, in the above configuration, the developer can be conveyed from the developer supply section to the development area on the developer conveyance guide member based only on the rotation of the magnetic roller, and the electrostatic charge is generated at the tip of the developer conveyance guide member. It contacts the surface of the latent image carrier and develops the electrostatic latent image previously formed on the surface. At the same time, the developer comes into contact with the outer circumferential surface of the developing sleeve, and is conveyed toward the developer supply section between the developing sleeve and the developer conveying guide member as the developing sleeve rotates. In this case, the developer ends contact with the surface of the electrostatic latent image carrier at a position where the developing sleeve approaches or is closest to the surface of the electrostatic latent image carrier.

As a result, the surface of the electrostatic latent image carrier that has finished contacting with the developer passes through the closest position where the electric field is strong, and the toner floating in this area is moved by the strong electric field to the electrostatic latent image area or the developing sleeve. It will adhere to the outer peripheral surface. Further, the toner image is not scraped off by the carrier.

Furthermore, the developer before development and the developer with reduced toner concentration after development are separated by the developer transport guide member, and the developer is not replaced in both transport paths, and the developer using a carrier is The toner concentration in the developer does not decrease in the development area.

The developer after development is transported to the developer supply section side based on the rotation of the developing sleeve, but since the intervals in this transport path are set gradually wider in the transport direction, the developer cannot be transported. The density does not increase as it goes, and it is transported smoothly, and the rotational driving torque of the developing sleeve does not increase.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an electrostatic latent image developing device according to the present invention will be described below with reference to FIGS. 1 to 7.

[Basic system of developing device, see Figure 1] This developing device is based on the well-known magnetic brush system, and contains a developer consisting of a mixture of carrier and toner that are charged with opposite polarities by frictional electrification. So-called regular development is performed in which a positive electrostatic latent image is developed into a positive image.

On the other hand, the photoreceptor drum (1) is driven to rotate in the direction of arrow (a), and its surface is charged with a polarity opposite to that of the toner before reaching the developing device, and a positive electrostatic latent image is formed on its surface. It is formed.

[Configuration of developing device, see FIG. 1, etc.] This developing device has a developing sleeve (10) facing the surface of the a-light drum (1) in a developer casing (20). 10) A magnetic roller (11) with N and S poles magnetized on the outer periphery is built-in, and a developer conveyance guide member (12) is installed in the vicinity of the upper half of the outer periphery of the developing sleeve (10). ) is installed. Both the developing sleeve <10) and the magnetic roller (11) are rotationally driven in the direction of arrow (b) at the rotation speed described below. Further, as shown in FIG. 7, the developer conveyance guide member (12) has an inner radius (r,) slightly larger than the outer radius (r,) of the developing sleeve (1o), and its center point (08 ) is the developing sleeve (
The member (12) and the developing sleeve (1o) can be installed at a position slightly eccentric (dl) with respect to the center point (Ol) of the
0) is the distance from the development area (B) to the developer supply section (A).
It is set up so that it gradually becomes wider as you move towards it.

The developing sleeve (10), the developer conveyance guide member (12)
) are both made of a conductive material, and are connected to a bias power source (so) and (31), respectively, as shown in FIG. The bias power supply (30) is used to cause the developing sleeve (10) to function as a developing electrode, and applies a DC developing bias voltage having a polarity opposite to the charging polarity of the toner to the developing sleeve (10). As explained below, the bias power supply (31) is for erasing the electric charge of the developer (mainly carrier) conveyed between the developing sleeve (10) and the member (12). ) is applied with an AC voltage.

The height regulating plate (21) is formed integrally with the developer casing (20), and its tip faces the developer conveyance guide member (12) at a constant distance (d). ing. The scraper (13) is formed of an elastic thin plate, and its tip is lightly pressed against the outer peripheral surface of the developing sleeve (10).

Further, within the developer casing (20), a developer stirring blade (14) is installed so as to be rotatably driven in the direction of arrow (d), and supplies the developer to the supply section (A) while stirring the developer. A toner casing (25) is attached to the back of the developer casing (20).
) is provided, and the toner is supplied to the developer casing (20) from the supply port (27) by rotation of a toner supply blade (26) provided inside in the direction of arrow (e).

On the other hand, the areas immediately above and below the development area (B) are sealed by sealing means, respectively. The powder smoke prevention sealing member (15) that seals the upper part is made of a flexible material, is attached to the upper end surface of the developer casing (20), and its tip is lightly touched to the surface of the photoreceptor drum (1). are in contact. At the bottom are the carrier collection member (16) and the spill prevention member (
1B). Carrier collection member (16
) is attached to the lower end surface of the developer casing (20), and at least the vicinity of the attachment part is made of an elastic material, and the distance (d4) between the tip and the surface of the photoreceptor drum (1) is (See Figure 6) is regulated by the spacer (17) made of an insulating material adhered to the member (16) coming into contact with the outer peripheral surface of the developing sleeve (10) due to the elasticity of this member (16). . This carrier recovery member (16) is for recovering carrier attached to the surface of the photoreceptor drum (1), and is made of a conductive material.
), a DC bias voltage having a polarity opposite to that of the carrier is applied, and as shown in FIG. 5, a fixed opening (16a) is formed in the width direction. The spill prevention member (1B), which is another sealing means, is located outside the carrier collection member (16), and its lower part is connected to the developer casing (1B).
20) attached to the lower end surface, at least the vicinity of the attachment part is made of an elastic material, and the distance (di) between the tip and the surface of the photoreceptor drum (1) (see Fig. 6) is as follows: The spacer (19) adhered to the spill prevention member (18) is moved by the carrier recovery member (16) due to the elasticity of this member (1B).
) and the developing sleeve (10) via the spacer (17).
It is regulated by coming into contact with the outer peripheral surface of.

The photosensor (24) is a reflective type consisting of a light emitting element (24a) and a light receiving element (24b), and is installed inside the developer casing (20) facing the lower part of the developing sleeve (10). There is. This photosensor (24) is
As shown in FIG. 7, it is detected that the developer crosses the development area (B) and reaches the bottom of the development sleeve (10) (this state is an abnormal state as explained below). It is for the purpose of The installation position of the photosensor (24) is approximately at the center in the axial direction of the developing sleeve (10), and the spacer (17) is not provided at this position.
If the developer exceeds the development area (B), the developer will reach the detection part of the photosensor (24) without any problem. In addition, the output of the photosensor (24) is input to the microcomputer (CPU), and the abnormality detection signal is outputted to the abnormality display lamp (L) and the magnetic roller drive motor (45) via the microcomputer (CPU). .

[Developing device drive mechanism, see Figures 3 and 4. Figure 3 shows the drive mechanism on the back side, and the gear (40) to which the rotational driving force from the main motor is transmitted is the support for the stirring blade (14). The developing sleeve (10) meshes with the gear (41) fixed to the shaft end.
The gear (42) fixed to the end of the spindle and the toner supply blade (2)
The gear (43) fixed to the end of the spindle of the gear (4)
1) is engaged.

The gear (40) is driven to rotate in the direction of arrow (f) in synchronization with the on/off of the main motor, and this causes the stirring blade (14) to rotate in the direction of arrow (f).
), the developing sleeve (10), and the toner supply blade (26) are rotated in the directions of arrows (d), (b), and (e), respectively.

Figure 4 shows the drive mechanism on the near side, showing the output pulley (46) of the magnetic roller drive motor (45) and the magnetic roller (11).
The pulley (4B) fixed to the spindle end of the belt (47)
are connected. The magnetic roller drive motor (45) is normally turned on and off in synchronization with the main motor, and in conjunction with this, the magnetic roller (11) is rotationally driven in the direction of arrow (b).

[Movement of developer, see FIGS. 1 and 2] Next, the movement of developer around the developing sleeve (10) in the above-described developing device will be explained.

The developer is supplied to the supply section (A) by the rotation of the stirring blade (14) in the direction of arrow (d), and is attracted onto the outer circumferential surface of the developing sleeve (10) by the magnetic force of the magnetic roller (11), thereby regulating the brush height. While the height of the head is regulated by the plate (21), the magnetic roller (11)
) is conveyed in the direction of arrow (c) on the developer conveyance guide member (12) based on the rotation in the direction of arrow (b). The developer conveyed in the direction of arrow (c) on the developer conveyance guide member (12) comes into contact with the surface of the photoreceptor drum (1) at the tip of the member (12), Develop the electrostatic latent image formed on the surface. At the same time, the developer comes into contact with the outer peripheral surface of the developing sleeve (10), and as the developing sleeve (10) rotates in the direction of arrow (b), the developing sleeve (10)
and the developer transport guide member (12) in the direction of arrow (b), and is scraped off by the scraper (13).

In this case, the position (X,) where the developer ends contact with the surface of the photoreceptor drum (1) is the position where the developing sleeve (10) is approaching the surface of the photoreceptor drum (1), It is slightly above the closest position (X,) of both. As a result, the developer does not exist on the outer circumferential surface of the developing sleeve (10) downstream of the closest position (x,) with respect to the moving direction (arrow a) of the photosensitive drum (1).

Here, the principle of the above-mentioned movement of the developer in a system in which the developing sleeve and the magnetic roller are driven to rotate in the same direction will be explained in principle.

In the above system, the developer is conveyed on the outer circumferential surface of the developing sleeve in a direction generally opposite to the rotational direction of the magnetic roller. To explain this in detail, the upper layer of the magnetic brush is conveyed while rotating in the direction opposite to the rotation direction of the magnetic brush due to the movement of the magnetic field based on the rotation of the magnetic roller, and the lower layer near the outer peripheral surface of the developing sleeve is transported. Based on the rotation of the sleeve, the developer is transported in the rotation direction thereof, that is, in the opposite direction to the overall developer transport direction. However, the conveyance speed is lower than the conveyance speed in the upper layer portion of the magnetic brush.

In the electrostatic latent image developing device according to the present invention, a developing electrode (e.g., a developing sleeve that also functions as a developing electrode) is brought close to an electrostatic latent image carrier (e.g., a drum having a photoreceptor layer on its surface). Contact of the developer with the photosensitive drum (this contact area is referred to as a developing area) is terminated at a certain position or the closest position. In such a system, the developer conveyance speed (V
sl) is the developer conveyance speed by the magnetic roller (Va+g)
The developer may be made larger than that so that the presence of the developer is not felt on the outer circumferential surface of the developing sleeve on the downstream side of the developing area.

Specifically, the conveyance speed [Vm
g (fin/5ec) is vIIIg=hp・(Wmg/60)...
(2) However, it is expressed by the following formula: h, @ass, p: number of magnetic poles Wag: number of rotations of the magnetic roller (rpm).

Conveyance speed based on the rotation of the developing sleeve [Vsl (saw
/see) ko is ■s1= D・π・(Ws1/60)...
... ■However, D = Developing sleeve diameter (mm) Wsl
: Development sleeve rotation speed (rpa+).

Therefore, the overall developer transport speed [Vdev(I1
m/see) is Vdev = Vmg - Vsl = (h-p-Wa+g -D ・π・Wsl>/60
... ■It is expressed by the formula.

By the way, at the closest position (x,') between the developing sleeve and the photoreceptor drum, the height (h) is necessarily the closest position interval (di), so that the developer is distributed downstream of the developing area. In order to prevent it from existing on the outer peripheral surface of the developing sleeve, D-rr ・Wsl>d, -p-Wag -
It is sufficient to satisfy the following equation (2). That is, the diameter of the developing sleeve, the number of magnetic poles of the magnetic roller, their rotational speed, the distance between the developing sleeve and the photosensitive drum, etc. may be set so as to satisfy the equation 0.

[Specific Examples of Development Conditions] Here, the present development apparatus and specific numerical values of the development conditions will be explained based on experiments conducted by the present inventors.

Developing sleeve: Material stainless steel Diameter: 31 mm Rotation speed: 60 rpm Developing bias electric JE: 150 V (DC) Magnetic roller: Number of poles = 8 Magnetic force: 100OG (on the surface of the developing sleeve) Rotation speed: 12 GO rpm Stirring blade: Rotation speed: 4 Orpm Toner Supply vane: Rotation speed: 50 rpm Developer conveyance guide member: Material: stainless steel Thickness: 0.8 mm Arc radius: 341Wl (Occentricity value (ds) with respect to OI): 0.3
Narrowest distance between mae and developing sleeve (da): 1.2
mm Applied voltage: -150V (DC), 350Vrm
s, 1kHz (AC>nearest position distance (dl):
0.4a+m Bread height regulation interval (da): 1.8m
Voltage applied to carrier collection member: +500V Photosensitive drum: Peripheral speed: 130mm/see Maximum potential of electrostatic latent image: -5sov Background potential of electrostatic latent image: -toov Developer: Binder-type insulating magnetic material with an average particle size of 38 μm A mixture of 90 wt% carrier and 10% dt% insulating non-magnetic toner having an average particle size of 11 μm is charged by friction to charge the carrier to a negative polarity and the toner to a positive polarity.

Note that under the above conditions, the developer should be placed at the closest position (X
It goes without saying that the above-mentioned formula 0 must be satisfied so that it does not exist on the outer circumferential surface of the developing sleeve (10) on the downstream side of the developing sleeve (10).

[Effect 1 of satisfying the above formula 0] Copying experiments were conducted using the above-mentioned developing method, and it was possible to obtain good copied images without toner fogging even when using toner with a relatively low charge amount. Similarly, even when 10,000 sheets were continuously copied using toner with a relatively low charge amount, almost no toner leakage was observed between the developer casing (20) and the photoreceptor drum (1). There wasn't.

This effect is caused by the fact that the position (X, ) where the developer ends contact with the photoreceptor drum (1) is the closest position (x, )
This interval (dt'') is the interval (dl
) This seems to be due to the fact that it is wider. That is, after the surface of the photoreceptor drum (1) finishes contacting with the developer, the electrostatic latent image on the photoreceptor drum (1) and the developing sleeve (10)
The nearest position (x,) where the electric field between is the strongest
It will pass through. The toner floating away from the carrier due to the low band IT is attracted to the image area when the image area passes by due to the strong electric field, and is attracted to the developing sleeve (10) when the background area passes, and the toner is absorbed by the developing sleeve (10) when the background area passes through. It adheres to the image area on the surface of the photoreceptor drum (1) or to the outer circumferential surface of the developing sleeve (10).Therefore, floating toner does not adhere to the background area and cause fog or leak out of the developing device. be.

In addition, in the developing area (B), the electric field between the developing sleeve (10) and the photoreceptor drum (1) is strongest at the position (X*) where the contact of the developer ends; The carrier will not scrape off the toner adhering to the area (X,), and the toner image will not be blurred or the fine line reproducibility will not be impaired.

Furthermore, even if the carrier has a small diameter and is of a binder type, as in this example, the magnetic binding force is small.
Since the magnetic field is maximum at the end of developer contact,
Carrier adhesion is also less likely to occur.

[Toner supply operation, see Fig. 1] In the developer casing (20), the developer consisting of a mixture of carrier and toner moves in the direction of the arrow (d) of the stirring blade (14).
) The mixing and stirring are completed by rotation in the direction of ).

Toner is stored in the toner casing (25), and the rotation of the toner supply vane (26) in the direction of arrow (e) causes stirring and supply of the toner above the toner supply port (27). . When the toner is consumed by development, the volume of the developer in the developer casing (2o) decreases by an amount commensurate with the amount of toner consumed. Then, a space corresponding to the consumed amount is created in the developer casing (20), and the toner located above the toner supply port (27) automatically enters the developer casing (20). When the volume of the developer increases due to this, the toner supply port (27) is occupied by the increased developer, and new toner is not supplied, and eventually the developer casing (20)
The volume of the developer within is always constant, that is, the toner concentration is always kept approximately constant.

[Function of developer transport guide member] In this embodiment, the developer transport guide member (12) firstly controls the development area (
It functions to eliminate the decrease in toner concentration in the developer in B). That is, the developer before development is transported in the direction of arrow (c) based on the rotation of the magnetic roller (11), and the developer after development is transported in the direction of arrow (b) based on the rotation of the developing sleeve (10). This is because the developer whose toner concentration has decreased is separated by the developer transport guide member (12), and the developer is not replaced in the re-transport path.

By the way, the distance between this member (12) and the developing sleeve (10) is considerably wider than the closest position distance (dt>), and according to this method, the distance between the developing sleeve (1o) and the developing sleeve (10) is considerably wider than the distance between the closest positions (dt). Strictly speaking, the developer conveyed to the member (
12), the upper layer receives a conveying force in the direction of arrow (c) expressed by the above equation 0 based on the rotation of the magnetic roller (11). but,
According to the experimental results, the developing sleeve (10) and the member (12
) was being conveyed in the direction of arrow (b) by the rotation of the developing sleeve (10). This is considered to be due to the following reasons. The conveying force accompanying the rotation of the developer due to the rotation of the roller (11) changes depending on the density of the developer. As the density of the developer increases, it becomes difficult to move, and therefore the conveying force associated with the rotation becomes weaker. The density of the developer is relatively high between the developing sleeve (10) and the member (12), and therefore the developer as a whole is considered to move in the direction of arrow (b).

Further, as described above, the distance between the developer conveyance guide member (12) and the developing sleeve (10) is set to gradually increase from the developing area (B) toward the supply section (A). The tip interval (d,) near the region (B) is the minimum interval. Under these settings, the developing sleeve (
The torque for rotationally driving 10) did not particularly change during the above-mentioned 10,000-sheet continuous copying experiment.

However, the distance between the developer conveyance guide member (12) and the developing sleeve (10) is changed from the developer supply section (A) to the developing area (
If it is almost constant (1, -m) up to the vicinity of B),
And conversely, from the vicinity of the development area (B) to the developer supply section (A)
When we conducted a similar comparative experiment of continuous copying in the case where the width of the developing sleeve (10) is set to gradually become narrower, we found that in the former case, there was a slight increase in the torque that gradually drives the rotation of the developing sleeve (10), and in the latter case, After making several dozen copies, the rotational drive torque became so large that it became impossible to make copies.

The reason why such a phenomenon occurs can be considered as follows. The passage between the developing sleeve (1o) and the member (12) is almost completely filled with developer and has a relatively high density. As mentioned above, the conveying force accompanying the rotation of the developer due to the rotation of the magnetic roller (11) in the direction of arrow (b) becomes weaker, and the developer is conveyed by the rotation of the developing sleeve (10). It is. By the way, the distance between the developing sleeve (10) and the member (12) is
If it is set so that it gradually becomes narrower from the vicinity of the developing area (B) to the developer supply section (A), the developing sleeve (1o)
The density of the developer transported by the rotation in the direction of the arrow (b) becomes higher than necessary as it approaches the developer supply section (A), leading to an increase in the rotational driving torque of the developing sleeve (1o). Conceivable. Further, even if the interval is set to be almost constant, it is expected that a minute partial setting failure will occur, which is thought to lead to a slight increase in the rotational drive torque.

That is, as in this embodiment, the developing sleeve (1o) and the member (
12) is narrowest near the development area (B),
If it is set so that it gradually becomes wider as it approaches the developer supply section (A), as in the comparative experiment, the developing sleeve (10)
The rotation of the developing sleeve (10) does not increase the density of the transported developer, and therefore, the rotational driving torque of the developing sleeve (10) does not increase.

Furthermore, the developer transport guide member (12) also has a function of erasing the charge on the carrier after development and improving the frictional charging performance with new toner. That is, this member (12)
is made of a conductive material and receives direct current (-
150V) superimposed alternating current (350Vr1os, 1
kHz> is applied. -1 for the developing sleeve (10)
Since a DC bias of 50V is applied, as a result, there is a voltage of 3.5V between the developing sleeve (10) and the member (12).
An alternating current electric field of 50 Vrms and 1 kHz will be applied.

By the way, in the case where an insulating magnetic carrier is used as the carrier as in this embodiment, even if the toner is completely consumed during development, charges of opposite polarity remain on the carrier for a long time. Furthermore, carriers that already have a charge of the opposite polarity to the toner tend to have a lower ability to charge newly replenished toner than carriers that do not have a charge.

However, in this example, the developer after development is
When the developer is conveyed through the path between the developing sleeve (10) and the member (12), it is subjected to an alternating current electric field, and the charge is removed so that the developer as a whole has no charge.

That is, the insulating magnetic carrier that has lost toner and retains an excess charge of opposite polarity has its excess charge removed, and as a result, the newly replenished toner can be sufficiently triboelectrically charged.

Specifically, at the start of development, the amount of charge on the toner is 1.
In the case of 2 μc/g, 2,000 sheets of copied material (12)
When applying only -150V DC and no alternating current, the charge amount of the toner decreased to 9 to 10 μc/g, but if alternating current was applied in a superimposed manner as in this example, the amount of charge on the toner decreased to 12 to 1 μc/g.
It held a charge of 3 μc/g.

Note that the developer transport guide member (12) itself does not necessarily need to be entirely formed of a conductive material, and it is sufficient that at least only the inner circumferential surface has conductivity.

[Function of carrier recovery member] As described above, in this developing device, carrier adhesion to the surface of the photoreceptor drum (1) is difficult to occur. However, due to unavoidable variations in physical properties during carrier production, carrier adhesion may occur, albeit in a small amount. The carrier collecting member (16) has a function of collecting the carrier attached to the surface of the photoreceptor drum (1) to the developing sleeve (10) side. That is, the carrier attached to the surface of the photoreceptor drum (1) has a negative polarity charge that is opposite to that of the toner, but a voltage of +500 (V) is applied to the carrier collection member (16). is being applied, the carrier is electrically attracted to the carrier recovery member (16). Then, as shown in FIG. 6, the carrier is conveyed over the carrier collection member (16) by rotation accompanying the rotation of the magnetic roller (11) in the direction of arrow (b), and the carrier is transported over the carrier collection member (16).
a) and returned onto the developing sleeve (10).

Incidentally, the tip of the carrier collecting member (16) cannot be brought into contact with the surface of the photoreceptor drum (1) in order not to disturb the toner image, but in order to perform the carrier collecting action more effectively, the distance (d, ) is preferably as narrow as possible in order to strengthen the recovery electric field, and the distance (d4
) is desirably uniform in the axial direction. Therefore, it was decided to use the developing sleeve (10) as a positioning reference member for installing the developing sleeves (10) at as narrow an interval (d4) as possible. The developing sleeve (10) is the photosensitive drum (1)
This is because they are precisely positioned at an interval (dI) with respect to the surface of. This allows you to install other positioning means to position the tip of the carrier recovery member (16) or to maintain the linearity of the tip of the carrier recovery member (16).
16) There is no need to form the device itself with a thick member,
The spacing (d4) can be set sufficiently narrowly and accurately using a thin member, and the carrier attached to the surface of the photoreceptor drum (1) can be almost completely recovered.

Note that, as in this embodiment, the spacer (17) can be configured to come into contact with the lower side of the developing sleeve (10) because the developer is not present downstream of the developing area (B). This is because each condition is set so as to satisfy the above equation 0.

[Function of Toner Spill Prevention Member] As described above, in this embodiment, it is difficult for toner to spill downward from the development area (B).

However, due to the presence of airflow or the like along the rotation of the photoreceptor drum (1) in the direction of arrow (a), the toner tends to spill out to the outside, albeit slightly. Spill prevention member (18
) has a function of preventing such toner waste.

The tip of this spill prevention member (1B) cannot be brought into contact with the surface of the photoreceptor drum (1) like the carrier collection member (16), but the interval (d,) must be as narrow as possible and the axial direction It is desirable that the anti-spill member (18) be uniform throughout the spacer (18).
19), carrier recovery member (16), spacer (17)
By pressing against the developing sleeve (10) via the developing sleeve (10), a constant positional spacing is maintained at all times, and the spacing (d,) is set to be sufficiently narrow and uniform in the axial direction, albeit indirectly. This makes it possible to almost completely prevent toner from spilling.

In addition, when the spacer (19) is made of an insulating material and the spill prevention member (18) is made of a conductive material, a bias with a polarity opposite to the charged polarity of the toner must be applied to the spill prevention member (18). For example, the efficiency of toner collection is further improved.

[Function of Photosensor] In this embodiment, since there is no developer on the developing sleeve (10) downstream of the developing area (B), there is no developer on the developing sleeve (10) facing the photosensor (24). There is no developer on the outer surface of the developing sleeve (
10) is made of stainless steel, and its surface is polished, so the light emitted from the light emitting element (24) is transmitted to the developing sleeve (10).
) and enters the light receiving element (24b), and the corresponding output is output to the microcomputer (CPU).

By the way, in the developing device of the type as in this embodiment,
It is necessary to always maintain the distance (d,) between the developing sleeve (10) and the surface of the photoreceptor drum (1) below a certain value. This is because when the distance (dl) increases, the 0
This has the disadvantage that the formula is no longer satisfied, the developer proceeds downstream from the developing area (B), and eventually spills out of the developing device.

However, in this embodiment, the photosensor (2
Control such as stopping the rotation of the magnetic roller drive motor (45) is executed based on the developer detection signal from 4), thereby preventing the above-mentioned inconvenience.

That is, if the developing device is set incompletely for some reason and the copying machine starts operating with the gap (dl) between the developing sleeve (10) and the photoreceptor drum (1) being wide, then the first As shown in Figure 7, the developer is applied to a magnetic roller (1
1), the developer is conveyed onto the outer circumferential surface of the developing sleeve (10) on the downstream side of the developing area (B). A spacer (
17), the developer that has passed through the development area (B) is quickly conveyed onto the outer peripheral surface of the development sleeve (10) facing the photosensor (24).

As a result, the light emitted from the light emitting element (24a) is diffusely reflected or absorbed, so that it no longer enters the light receiving element (24b), and a corresponding signal is output from the light receiving element (24b) to the microcomputer (CPU). Therefore, the microcomputer (CPU) uses a magnetic roller drive motor (
45) to stop the rotation.

When the rotation of the magnetic roller (11) is stopped, the conveying force that conveys the developer in the direction of arrow (c) disappears, but since the main motor continues to drive, the developing sleeve (10)
), including the developer that has passed through the development area (B), moves on the outer peripheral surface of the development sleeve (10) in the same direction based on the rotation of the development sleeve (10) in the direction of the arrow (b). The developer is transported and returned into the developer casing (20). After that, the microcomputer (CPU) displays the indicator lamp (L).
) lights up to display a "trouble" externally, and also stops the operation of the main motor and other parts of the copying machine.

In this embodiment, in this way, the photosensor (24) promptly detects that the developer is conveyed to the downstream side of the development area (B), and the rotation of the magnetic aperture roller (11) is stopped. This prevents the developer that has passed through the developing area (B) from losing its destination and spilling out of the developing device.
As a result, it is possible to detect that the conditions such as the interval (dl) are not set accurately.

In addition to the reflective photosensor (24), it is also possible to use a vibrating piezoelectric sensor, a reflective ultrasonic sensor, a magnetic sensor, etc. as such a developer detecting means.

As is clear from the above description, the present invention provides a developer conveyance guide member having a shape that roughly follows the outer peripheral surface of the developing sleeve from the developer supply section to the vicinity of the development area, and a magnetic roller. The developing sleeve is driven to rotate from the developing area in the developer supply direction, and the developing sleeve is driven to rotate in the same direction as the magnetic roller.
The developer is transported from the developer supply section to the development area on the developer transport guide member based on the rotation of the magnetic roller, and the developer after development is transported between the developer sleeve and the developer based on the rotation of the development sleeve. Since the developer is conveyed between the guide member and the developer supply section, the developer becomes electrostatic latent at a position where the developing sleeve functioning as a developing electrode approaches or is closest to the surface of the electrostatic latent image carrier. After the surface of the electrostatic latent image carrier finishes contact with the developer, it passes through a position where the electric field is strong between the developing sleeve and the electrostatic latent image carrier, and the electrostatic latent image carrier floats in this area. The toner adheres to the image area or the outer circumferential surface of the developing sleeve using a strong electric field, which prevents toner fogging and toner leakage to the outside of the developing device. It is possible to prevent toner image fading, poor thin line reproducibility, and adhesion of the carrier to the electrostatic latent image carrier due to scraping of the toner image by the carrier, and it is possible to obtain a copied image of good image quality. .

Furthermore, in the present invention, the distance between the developer transport guide member and the developing sleeve is set so that it gradually becomes wider from the developing area toward the developer supply section, so that the developer after development can smoothly move between the two. There is no increase in the torque for rotating the developing sleeve during conveyance.

[Brief explanation of drawings]

1 to 7yJ show an embodiment of the electrostatic latent image developing device according to the present invention, in which FIG. 1 is a sectional view of the entire device, FIG. 2 is a sectional view of main parts, and FIGS. The figures are a rear view and a front view of the drive mechanism, Fig. 5 is a perspective view showing the carrier collection member and spill prevention member, Fig. 6 is a sectional view of the main parts, and Fig. 7 is a sectional view showing an abnormal state of developer transport. It is a diagram. FIG. 8 is a partial sectional view of a conventional developing device, and FIG. 9 is a sectional view of its essential parts. (1)...photosensitive drum, (10)...developing sleeve, (11)...magnetic roller, (12)...developer conveyance guide member, (x,)...nearest position ,(X,)・
... Developer contact end position, (d,) ... Closest position interval, (d,) ... Narrowest distance between developer transport guide member and developing sleeve, (A) ... Developer supply Department, (B)...
・Development area.

Claims (1)

[Scope of Claims] 1. A developing electrode is disposed opposite to an electrostatic latent image carrier that is rotationally driven in one direction, and a developer conveyed on the developing electrode is applied to the surface of the electrostatic latent image carrier. In an electrostatic latent image developing device configured to develop a formed electrostatic latent image, the developing electrode is a developing sleeve incorporating a magnetic roller, and a developer having a shape approximately along the outer peripheral surface of the developing sleeve. A conveyance guide member is provided extending from the developer supply section to the vicinity of the developing area, and the interval between the developer conveyance guide member and the developing sleeve is set to gradually increase from the development area toward the developer supply section, while the magnetic roller The developing sleeve is rotated from the developing area toward the developer supply section, and the developing sleeve is rotated in the same direction as the magnetic roller, and the developer is transferred onto the developer transport guide member based on the rotation of the magnetic roller. The developer is conveyed from the supply section to the developing area, and the developer after development is conveyed to the developer supply section between the developing sleeve and the developer conveyance guide member based on the rotation of the developing sleeve. An electrostatic latent image developing device.