JPH03168672A - Developing device - Google Patents

Abstract

PURPOSE:To improve reliability and maintenance characteristic by discretely driving a 1st developing roller which directly replenishes a developer and a 2nd developing roller on the downstream of developer flow and controlling the rotating speed of a developer replenishing roller according to the driving torque difference. CONSTITUTION:The developing rollers 3, 4 are driven by discrete motors M1, M2 and the replenishing roller 5 and bucket roller 6 are driven by a motor M3 via gears 21 to 25. The accumulating weight Wt of the developer 11 is the difference between a supplying rate Q1 and a conveying rate Q2 and the torque of the roller 3, i.e. the motor M1 is increased by the stationary magnet in a sleeve 7. The developer to the roller 4 is decreased to the required min. quantity by a developer regulating member 12 and the driving torque of the roller 4, i.e. the motor M2 is prevented from increasing. The rotating speed of the roller 5 is, thereupon, controlled by the torque difference, i.e. driving current difference of the motors M1, M2 to maintain the specified weight Wt. The developer is stably supplied in this way and the deterioration of the carrier by the accumulation is prevented. The reliability and maintenance characteristic are improved in this way.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a developing device used in an image forming device such as a copying machine or a laser beam printer. The present invention relates to a developing device including a developing roller and a developer replenishing roller that supplies developer to the developing rollers through either of the developing rollers.

(Prior art) In this type of developing device, the developer is conveyed while being stirred by a replenishment roller, etc., and supplied to one of the developing rollers, and the developer is transferred from this developing roller to another developing roller. The film is subjected to development under appropriate quantity control. The two-command developer consists of toner and carrier, and the toner is contact-electrified by the stirring and is supplied to the developing roller together with the carrier. Each developing roller conveys the supplied developer to the photoreceptor and uses its own magnetic pole to exert a magnetic action to control the developer's magnetic brush. When this magnetic brush rubs the surface of the photoreceptor, the difference between the bias potential applied to the developing roller and the surface potential of the photoreceptor causes the area on the surface of the photoreceptor where an electrostatic latent image is formed to be Toner is electrically attracted and adheres to develop the electrostatic latent image.

By the way, the amount of contact charge of toner can be controlled by selecting the type and number of polar groups of organic molecules that make up the surface. Therefore, in order to introduce polar groups onto the toner surface, polar groups possessed by resin monomers or polar groups possessed by pigments or dyes mixed into the toner are utilized, and the polar groups are controlled to a predetermined polarity.

However, when strong stress is applied to the developer, substances with small molecular weights such as dyes and polarity control agents tend to migrate from the toner surface to the carrier surface with which they come in contact. In contact charging of solids, this phenomenon is caused by mass transfer (
It is called Mass Transfer. Also, when the toner material is vulnerable to stress, it contaminates the carrier surface. When so-called carrier deterioration such as material transfer or contamination occurs in the carrier as described above, the ability to contactly charge newly supplied toner is reduced. For this reason, the amount of charge on the toner used for development decreases as the carrier deteriorates, making the toner less susceptible to magnetic and electrical restraint and becoming more likely to float. Otherwise, the toner may float inside the copying machine and contaminate the inside of the machine.

Therefore, in the past, various improvements have been made to the developer itself, the mechanism for agitating and transporting the developer, the mechanism for supplying the developer to the photoreceptor, etc., in order to prevent carrier deterioration. When carrier deterioration or internal contamination occurs, or when the time is ripe for corrosion, service personnel perform maintenance such as replacing the developer and cleaning. (Problems to be Solved by the Invention) Recently, as copying machines and printers have become faster and faster, improving reliability and reducing copying and printing costs have become major issues.

For this reason, while maintenance must always be carried out sufficiently, it is desirable to reduce the number of times maintenance is required.

However, with conventional developers and development devices, carrier deterioration occurs relatively early, especially in high-speed machines, so maintenance must be performed relatively frequently to ensure reliability, which increases the cost of copying and printing. is not sufficiently reduced. Therefore, the present invention aims to improve the mechanism for conveying and supplying developer to the developing roller, so that carrier deterioration, which the inventors have discovered, restricts the natural flow of developer, such as developer accumulation in areas where the supply amount is regulated. It is an object of the present invention to provide a developing device that can reliably solve the above-mentioned problems by improving the problem based on the fact that the problem is largely caused by the problem, and by properly detecting the state of developer accumulation. It is something to do. (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a developing device including a plurality of developing rollers and a developer replenishing roller that supplies developer to the developing rollers through any one of the developing rollers. The rollers are driven by separate driving means, and the first roller is supplied with developer directly from the developer replenishment roller, and the second roller is located downstream of the first roller in the developer flow direction. Detects the driving torque of
The present invention is characterized in that the number of rotations of the developer supply roller is controlled according to the difference between these detected values.

(Function) When the developer is conveyed and supplied to each developing roller by the developer replenishing roller via one of the developing rollers, the amount supplied to the first roller is adjusted to the actual required amount for stable development. However, when the developer is transferred from the first developing roller to the photoconductor, the progress of the excess developer is restricted by the photoconductor, so that only the appropriate amount of developer is transferred from each development roller to the photoconductor. Development can be performed by supplying an agent.

At this time, the excess developer whose progress is regulated stays in the regulated area and gradually forms a large pool. This developer pool exerts driving resistance on the first developing roller depending on its size, and the driving torque of the driving means that independently drives the first developing roller increases. Further, since the developing roller on the downstream side of the first developing roller in the developer flow direction is supplied with an appropriate amount of developer after the regulation, there is no regulation that causes accumulation of developer between it and the photoreceptor. However, the driving torque of the driving means that independently drives the downstream developing roller does not change due to the accumulation of developer.

The driving torques of these developing rollers are detected, and the rotation of the developer replenishing roller is controlled by utilizing the fact that the developer replenishing roller is driven independently according to the difference between these detected values. Even if the change in drive torque at the roller is affected by mechanical causes other than developer accumulation, such as bearing wear or intrusion of toner, paper dust, etc., the torque change due to this cause will be The control is performed using data that is detected as a torque change of the developing roller and subtracted from the driving torque of the first developing roller, and the amount of developer supplied is adjusted appropriately according to the actual developer accumulation state. It is possible to reliably control the accumulated amount of developer and the resulting drive torque of the first developing roller within a predetermined range without affecting each developing roller.

(Example) Embodiments of the present invention will be described below based on the drawings.

1 and 2 show a developing device according to a first embodiment of the present invention. This developing device, like the conventional device,
a device housing 2 provided near the photosensitive drum l;
A pair of upper and lower developing rollers 3 and 4 are disposed in the device housing 2 facing the photosensitive drum 1 and driven to rotate in the same direction as the photosensitive drum 1, and an upper developing roller is provided on the back side of the developing rollers 3 and 4. 3, and a packet roller 6 provided on the lower side within the device housing 2.

The developing rollers 3 and 4 and the supply roller 5 are shown in FIGS.
As shown in the figure, sleeves 7, 8, and 9 are rotationally driven in the same direction as the photosensitive drum l, and a plurality of fixed magnets N? It consists of S. Regarding the upper developing roller 3, fixed magnets with a magnetic flux density of 400 to 1000 Gauss on the surface of the sleeve 7 are arranged from the upper part of the back side of the 5 replenishing rollers to the lower front part of the photosensitive drum 1 side.
Four fixed magnets St and N2 are arranged in this order, and a fixed magnet S of 400 to 800 Gauss is further provided between these fixed magnets SI and N.

Regarding the lower developing roller 4, from the upper front surface on the photosensitive drum l side to the lower rear surface of the 5 replenishment rollers, fixed magnets having the same magnetic flux density as described above are NI', S, °, N2 °, S.
Five wires are arranged in the order of t' and Ns'.

Regarding the replenishment roller 5, from the lower back side on the bucket roller 6 side to the lower front side on the developing rollers 3 and 4 side, N, ”
The fixed magnets having the above magnetic flux densities except for Nl', S1
Five fixed magnets are arranged in the order of ``, N.s, Sz'', and N.''.The fixed magnet N1'' is stronger than the magnet density of the other magnet groups, and its magnetic flux density is 800~ 130
It is 0 Gauss.

In the developing device of this embodiment, the upper developing roller 3
An attractive magnetic field is formed between the fixed magnet S1 of the replenishment roller 5 and the fixed magnet N,'' of the replenishment roller 5, and a wide homopolar magnetized portion is formed behind the fixed magnet N3' of the replenishment roller 5. A repulsive magnetic field is created between it and the fixed magnet N1'' located far behind.

In the developing device of this embodiment configured in this way,
Developer 11 scooped up by the bucket roller 6
is supplied onto the sleeve 9 of the replenishment roller 5, and as the sleeve 9 rotates, the fixed magnet N3 of the replenishment roller 5
``Transported upwards.''

Then, the developer l1 is placed on the fixed magnets N and II,
Due to the attraction magnetic field that acts between the fixed magnets N,'' and SI, and the repulsive magnetic field that acts between the fixed magnets N3'' and N1'', the image is transferred to the upper developing roller 3, and then this developing roller 3 Each fixed magnet N+, Nz provided inside
. .

Note that a developer regulating plate 12 is installed between the fixed magnets S1 and N1 of the upper developing roller 3, facing the side peripheral surface of the upper developing roller 3, with a gap of 0.3 to 1.0 m maintained. There is. The developer is regulated so that a certain amount is transported forward by passing through this gap.

At this time, 1 liter of developer is applied to each portion of the fixed magnet N2 of the upper developing roller 3 and the fixed magnet N2° of the lower developing roller 4.
Since the magnetic brush contacts the surface of the photosensitive drum 1, the electrostatic latent image on the photosensitive drum 1 is visualized.

FIG. 2 shows the drive system of the developing device of this embodiment, and the developing rollers 3 and 4 are driven independently by drive motors Ml and Mz, respectively. The supply roller 5 and the packet roller 6 are simultaneously driven by one drive motor M3 via separate gears 21, 22 and gears 23, 24, 25, respectively.

By the way, in the sleeve development method using the two-component developer 11 as described above, the developer 11 accumulates when the conveyance of the developer 1 liter is regulated by the developer regulating portion such as the developer regulating plate 12. The inventors have discovered that there is a correlation between the amount Wt, the driving torque T of the upper developing roller 3, which is subject to the above-mentioned regulation, and the deterioration rate of the developer.

To explain this, as can be seen from the movement of the developer 1l shown in FIG. Transport amount Q. determined by the balance between The lwt accumulated here and the transported fttQ. There is also a correlation as shown in FIG. Also, as the accumulated lwt increases, the conveyance ffiQ. There is also a tendency to increase. Therefore, when the supply ffiQ, increases, the accumulation lwt increases, and the conveyance ffiQ. will also increase.

A balance is achieved when the supply amount Q1 and the conveyance amount Q2 reach the same value. The same applies to the opposite case.

The developer l1 in the pooled portion is magnetically restrained by a fixed magnet within the sleeve 7, and this restraint acts as a drag force against the rotation of the sleeve 7. Therefore, the larger the amount of developer l1 in the pooled portion, that is, the amount Wt stored, the greater the drag and the greater the rotational torque.

On the other hand, the restrained developer 1l attempts to move as the sleeve 7 rotates and collides with the developer regulating plate 12, and is then prevented from advancing by the developer regulating plate 12, causing the sleeve 7 to move.
The developer 11 stays in the reservoir while friction is generated between the surface of the developer l1 and the layer of the developer l1 thereon, and is subjected to stress while repeating the collisions and friction.

As is clear from the above explanation, the accumulation of developer 11 lw
When t is large, the rotational torque of the sleeve 7 increases and the developer 1
An increase in the stress placed on 1 occurs.

This phenomenon also occurs at the portion where the developer 11 contacts the photosensitive drum 1. Looking at this in the case of this embodiment having a plurality of developing rollers 3 and 4, the upper developing roller 3
Regardless of whether or not the developer 11 supplied to the photosensitive drum 1 is regulated by the developer regulating plate 12, the supplied amount is still set to be greater than the required amount for stable development. Therefore, the upper developing roller 3
When the excess amount of the developer 11 transported and supplied to the photosensitive drum 1 reaches the photosensitive drum 1, its progress is blocked by the photosensitive drum 1.
It stays and gradually forms a large accumulation. The driving torque of the upper developing roller 3 increases depending on the size of this accumulation.

Note that the current 1 on the downstream side of the upper developing roller 3 in the flow direction of the developer
The two lower developing rollers 4 are supplied with developer l1 from the upstream developing roller 3, which is finally regulated to the minimum required amount by the photosensitive drum I and which has been subjected to one development process. Since the amount of excess developer 11 is almost negligible, accumulation of developer 11 due to regulation by the photosensitive drum 1 does not occur to the extent that it changes the driving torque.

When the stress occurs in the developer 11, as mentioned above, it causes carrier deterioration, resulting in fogging in the image quality and contamination in the machine due to floating toner. It shows the relationship between the number of copies and the number of toner particles that cause fog in the white background of an image.

According to this, it can be seen that when the accumulated amount fiWt is large and the rotational torque T is large, the number of foggy toner increases faster than when the accumulated amount Wt is small and the rotational torque is small.

When the number of toner particles reaches several thousand pieces/cm'', it can be detected with the naked eye, so it is necessary to replace the developer 11 to ensure reliability.As mentioned earlier, the cost of copying and printing increases. In order to reduce this, it is necessary to reduce the number of times maintenance such as replacing the developer l1 is required.

Therefore, in order to reduce the stress on the developer 11, the accumulated amount W
For the purpose of controlling t, the torque of the upper developing roller 3 that causes accumulation of 1 liter of developer is detected and used as a determining factor for accumulation lwt, and the rotation of the replenishment roller 5 in front of the upper developing roller 3 is controlled according to this detected value. The torque of the upper developing roller 3 is lowered to a certain value or less by controlling the number, and the accumulation lwt is suppressed to a certain amount or less.

However, if the torque is lowered too much and the accumulation lwt decreases too much, the conveyance amount Q2 of the developer 11 decreases too much, the density of the developed image decreases too much, and the image quality becomes insufficient.

Therefore, the torque is controlled within a certain range.

In the above explanation, it is known that when the toner concentration of the developer 11 changes or the environment changes, the distance between the carriers in the developer 11 changes, so that the developer 11 with a substantially constant volume This means that the magnetic number density of the carriers inside has changed.

When the magnetic number density of the developer 1l in a constant volume changes, the stress and rotational torque applied to the developer 11 change by the mechanism described above. To deal with this, in this embodiment, the torque is detected and the residual lwt is controlled based on the torque detection at intervals appropriate for the use of the copying machine.

Furthermore, when detecting the drive torque of the upper developing roller 3, the detected value is affected by mechanical factors over time such as wear of the bearing of the upper developing roller 3 and intrusion of toner, paper dust, etc.
It is desirable to remove this. In order to satisfy this requirement, in this embodiment, the driving torque of the lower developing roller 4, which is located downstream of the upper developing roller 3 in the developer flow direction and does not cause any accumulation of developer, is also detected. Therefore, this detected value is not affected by the accumulation of developer and varies solely due to the mechanical factors mentioned above. Then, this detected value is applied to the upper developing roller 3.
Subtract from the detected drive torque value. Thereby, the driving torque for the upper developing roller can be obtained without being affected by the mechanical factors.

Therefore, by controlling the number of rotations of the packet roller 6 according to the difference in driving torque between the upper and lower developing rollers 3 and 4, this control can be performed appropriately according to the actual developer accumulation lwt.

FIG. 6 shows the electrical connection state of the control circuit in a copying machine that performs such control, and the drive motors M, -M, each have a driver circuit 31 controlled by the CPU 30.
~33. Each driver circuit 31 to 33
are connected to AMP34-36, respectively, and detect the motor drive current in each driver circuit 31-33.
Since the drive current is monitored by PU30 and has a proportional relationship with the drive torque of the drive motor, the drive motors M1 to M,
The driving torque is individually monitored. In the figure, MS is a main switch for turning on the power of the copying machine, M0 is a main motor of the copying machine, and 37 is a driver circuit for the main motor M0.

FIG. 7 shows a flowchart of a main routine for overall control by the control circuit. The process starts by turning on the main switch MS of the copying machine. In step #1, the RAM of the CPU 30 is cleared and initial settings for the standard mode are performed. In step #2, CPU3
An appropriate developing device driving state is set based on the monitor of 0. Next, in step #3, the internal timer of the CPU 30 is started. This internal timer regulates the time required for the following control, that is, the time for the l routine. In the next step #4, inputs are made to the toner concentration detection sensor for determining whether or not toner needs to be replenished, as well as other switches and sensors of various parts of the copying machine. Next, in step #5, it is checked whether there is a jam or other trouble, and it is determined whether copying is possible. If copying is not possible, proceed to step #7, perform abnormality processing, and then proceed to step #8. On the other hand, if copying is possible, copy control is performed in accordance with the set developing device driving state in step #6, and then other processing is performed in step #8. In the last step #9, it is determined whether the internal timer has finished, and if it is finished, it returns to step #3 and thereafter steps #3 to ##
Repeat step 9. Therefore, the developing device in step #2? The drive state setting subroutine is executed only when the copying machine is powered on, and is omitted on the second shift, so that it is prevented from being executed more frequently than necessary and reducing the copying speed.

FIG. 8 shows a flowchart of the developing device driving state setting subroutine. In step #11, drive motor M
, -M,. At the same time, the main motor M0 is also driven to rotate the photosensitive drum 1 to prevent the flow of the developer l1 from damaging the surface of the photosensitive drum 1. Step #l
2 is the drive current T of the drive motors M+ and M2. ．． and T'xz are detected and compared with the reference value TREF, and if the difference is less than the constant value ε, the process moves to step #16.

The constant value ε is approximately several 10% or less of the drive current T.

In step #13, the difference is greater than or equal to a certain value ε and the drive current is T. l-'rl4z is the reference value TR! , then the process moves to step #14, lowers the rotation speed of the drive motor M, and returns to step #12. Turn on. Conversely, the driving current T
■-T. ．． When is smaller than the reference value T11EF, the process moves to step #15, the rotational speed of the drive motor M is increased, and the process returns to step #12.

By proceeding through the above routine, the drive current of the drive motor M1, that is, the drive torque, settles down to a certain value. If this is determined in step #12, the process moves to step #16, where the rotational speed of the drive motor M is memorized, and the main motor Mo1 drive motor M, ~M3 are all stopped, this subroutine ends, and the process returns to the main routine. do. An appropriate timing for appropriately increasing the number of executions of the developing device driving state setting subroutine is at the start of copying. However, in this case, it is more appropriate to limit the number of copies to a predetermined number or more.

Another method would be to provide a special operation key for an operator or the like to execute the developing device drive state setting subroutine at any time, or even if it is to be executed automatically, it can be freely set at an appropriate time other than the above. can do.

In the above embodiment, the drive torque of the roller is detected by monitoring the drive current of the drive motor, but it is also possible to detect the load on the roller by, for example, detecting the rotational speed or speed of the roller. The rotational speed of the replenishment roller 5 or the bucket roller 6 may be controlled based on the determination result.

(Effects of the Invention) According to the present invention, the first roller that receives developer from the developer replenishment roller of a plurality of developing rollers and generates a pool of developer
The second developing roller, which is located downstream of the second developing roller in the developer flow direction and does not cause accumulation of developer, and the developer replenishment roller are each driven by separate driving means. , The rotation of the developer replenishing roller is controlled according to the difference in the detected value of the driving torque of each of the first and second developing rollers. Even if other mechanical factors such as bearing wear or intrusion of toner or paper dust are affecting the torque, the torque change due to this factor is detected as a torque change of the second developing roller and transferred to the first developing roller. Since the control is performed using the data subtracted from the driving torque of the developing roller, the amount of developer supplied can be appropriately controlled according to the actual state of developer accumulation, and the amount of developer accumulated and the resulting It is possible to reliably control the driving torque of the first developing roller within a predetermined range without affecting each developing roller, ensuring a more stable supply without over or under developer, and preventing buildup of developer. Carrier deterioration can be suppressed, and reliability can be improved and the number of required maintenance operations can be surely reduced.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a developing device of a copying machine showing a first embodiment of the present invention, Fig. 2 is a perspective view showing a drive system of the developing device, and Fig. 3 is a flow of developer around an upper developing roller. FIG. 4 is a cross-sectional view showing the accumulated developer amount Wt and the conveyance fftQ. Figure 5 is a graph showing the correlation between the number of repeated copies and the number of fogged toners, Figure 6 is a block diagram of the control circuit, and Figure 7 is the overall main control of the control circuit. Flowchart showing the routine. FIG. 8 is a flowchart showing the developing device driving state setting subroutine. 32, 35, MZ% 33-----... M3 Developing roller supply roller bucket roller developer Developer regulating member CPU Driver circuit AMP Drive motor

Claims (1)

[Claims] (1) In a developing device equipped with a plurality of developing rollers and a developer replenishing roller that replenishes developer through one of the developing rollers, each of the rollers is driven by a separate driving means, and the developing roller is The driving torque between the first developing roller, which is directly supplied with developer from the developer replenishing roller, and the second developing roller located downstream in the developer flow direction is detected, and replenishment is performed according to the difference between these detected values. A developing device characterized by controlling the number of rotations of a roller.