JPH04168463A - Developing device - Google Patents

Abstract

PURPOSE:To prevent at least a carrier from being adhered to a detection window by charging the transparent detection window in the same pole as a toner, and switching a developing bias in the direction canceling the charge of the carrier during the rotation of a stirring rotating member under non-development. CONSTITUTION:The transparent detection window 55 of a toner density detecting sensor 53 under for optical density measurement and a toner are charged in the same polarity, and a fixed electric field is formed between the window and an electrode 43 held by a rotating member opposed thereto to prevent the adhesion of a developer to the window 55. During the rotation of a rotating member stirring the developer under non-development, the developing bias is switched to the direction canceling the charge of a carrier. Thus, even if the electric field strength between the electrode 43 and the window 55 is changed due to a trouble, at least only the adhesion of the carrier to the window 55 is prevented, eliminating the overflow of the developer from a device and the resulting contamination of the circumference, and the work for disassembling and cleaning the device is not required.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a developing device such as a copying machine or a printer that uses a powder developer consisting of toner and carrier, and in which the mixing ratio of the toner and carrier is This invention relates to a device equipped with a device for detecting by an optical method.

[Conventional technology]

In an image forming apparatus using a powder developer consisting of toner and carrier, in order to optimize the image density, the developer concentration, that is, the weight mixing ratio of toner to carrier (hereinafter referred to as "toner concentration") is adjusted. The amount of toner must be measured and toner replenishment based on the results.

For this purpose, one of the methods to measure toner concentration is
An optical density measurement method has been proposed in which the developer is illuminated through a transparent detection window and the toner concentration of the developer is estimated from the reflected light.

[Problem to be solved by the invention]

However, in the optical density measuring method, if developer adheres to the transparent detection window, the true toner density of the developer cannot be measured, resulting in various problems.

In other words, carrier has a lower light reflectance than toner, so if carrier adheres to the transparent detection window, it will be determined that there is a toner shortage, and more toner will be replenished than necessary, causing toner to spill from the developing device and contaminating the inside of the machine. do.

On the other hand, if toner adheres to the transparent detection window, it is determined that there is an excess of toner, and toner replenishment is interrupted.

However, when comparing the two, when carrier adhesion occurs, the image forming apparatus must be disassembled to collect the toner, making the recovery process extremely troublesome, whereas when toner adhesion occurs, Although the image quality may deteriorate, there is no damage to the image forming apparatus itself.

Therefore, the present invention prevents developer from adhering to the detection window, and even if the function to prevent developer from adhering to the detection window stops due to trouble, at least carrier adhesion is prevented and damage is minimized. It was designed to stop it.

[Means to solve the problem]

The developing device of the present invention has been made to solve the above problems, and has a developer made of toner and carrier,
In a developing device that supplies toner to the to-be-developed member based on a potential difference between a developing bias and the to-be-developed member, a) a developer transport path that accommodates the developer; and b) a developing device in view of the developer transport path. C) a transparent detection window whose surface facing the developer is configured to be charged to the same polarity as the toner to prevent adhesion of the toner; a rotating member having a magnet and a grounded electrode on opposing parts; d) a concentration measuring device that illuminates the developer through the detection window and measures the developer concentration from the reflected light; and e) during non-development. The apparatus further includes a developing bias switching means for switching the developing bias in a direction that cancels the charge of the carrier at least during rotation of the rotating member.

[Effect]

In the developing device, the developer conveyed through the developer conveyance path is held by a magnet.

The developer held by the magnet constitutes a magnetic brush along the magnetic field, and periodically rubs against the transparent detection window as the rotating member rotates. Further, the developer rubbing against the transparent detection window is illuminated by a density measuring device, and the toner density is measured from the reflected light.

On the other hand, a transparent detection window that is charged with the same polarity as the toner,
A constant electric field is formed between the electrode held by the rotating member facing this and the developer from adhering to the transparent detection window.

Further, during non-development and while the rotating member is rotating, the developing bias is switched in a direction that cancels out the charge on the carrier. Therefore, even if the electrode becomes electrically floating due to poor grounding or the like and the electric field strength formed between the electrode and the detection window changes, at least carriers will be prevented from adhering to the transparent detection window. .

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings.

■ General configuration and operation of the copying machine FIG. 1 shows a full-color copying machine using electrophotography.

In this full-color copying machine 1, when a print switch (not shown) is pressed, the photoreceptor 2 rotates in the direction of the arrow, and a charging device 3 charges the outer circumferential photoreceptor layer.

The image reading device 5 reads a document placed on the document table 4 (not shown).
The reflected light is reflected by the reading optical section 6 and read as three color signals of red, blue, and green for each pixel.

The red, blue, and green color signals are converted by an image processing circuit into a three-value signal of yellow, macenter, and 7-an, or a four-value signal with a blank added thereto, and sent to the laser generator 7.

The laser generator 7 illuminates the charged area of the photoreceptor 2 with a laser beam modulated based on the signal, and electrostatic latent images corresponding to image information of each color are sequentially formed.

The image unit 8 includes a plurality of developing devices 8Y, 8M, and 8C containing two-component developer consisting of toner and carrier.
, 8K. In addition, developing devices 8Y, 8M, 8C
, 8 respectively yellow Y1 macenta M1 cyan C
Each blank contains toner of different colors. And the developing device 8Y, -.

8 are integrally moved up and down, and only the selected developing device (-) faces the photoreceptor 2, and the electrostatic latent image is developed with toner of the corresponding color. That is, the electrostatic latent images formed in accordance with yellow, macenta, cyan, and black image information are developed with corresponding yellow, macenta, cyan, and black toners, respectively.

The transfer paper is fed one by one from the paper feeder 9 and wound around the outer periphery of the transfer drum 1O, and the toner image is transferred to the transfer device 1.
The images are sequentially transferred based on one discharge, and a full-color toner image is created.

The transfer paper on which the full color toner image has been formed is transferred to transfer drum 1.
The toner image is separated from paper 0 and transported by a transport device 12 to a fixing device 13, where the toner image is heated and fixed.
It is discharged at 4.

■、Configuration of developing device 2 and 3 show the construction of the developing devices 8Y, . . . , 8. FIGS.

The developing devices 8Y, .

(a) Developing section 20 The developing section 20 accommodates a developing roller 21 facing the photoreceptor 2, and a brush height regulating blade 22 facing the developing roller 21 at a small interval on its upper outer circumferential surface.

The developing roller 21 is constructed by combining a magnetic body 23 and a sleeve 24 wrapped around the magnetic body, and both ends thereof are supported by side walls 81 (81a) and 81 (8lb) of the housing.
The magnet body 23 is fixed in a non-rotating state, the sleeve 24 is rotatable, and a gear 29 is attached to the end of the sleeve drive shaft 25 protruding from the side wall 81b.

Further, the sleeve 24 is connected to a developing bias power supply 26 having a DC type 127 and an AC power supply 28, and a developing bias VB (-V B-DC+VB
-AC) is applied, and either the output of the DC power supply 27 or the microcomputer control device CPV (
(see FIG. 7). In addition, DC development\Ias ■B, □D6
is different for each developing device 8Y to 8, and the AC developing bias VB-AC is the same for all developing devices 8Y.

~, 3 are the same.

(b) Stirring section 30 The stirring section 30 includes a first stirring path 31 adjacent to the developing section 20.
and a second stirring path 32 located at the rear thereof.

The first stirring path 31 is parallel to the developing section 21, and the first stirring path 31 is horizontal when the developing devices 8Y to 8K are mounted on the copying machine 1. Second stirring path 32
is inclined so that it is lower than the first stirring path 31 on the right side (front side) in FIG. 2 and higher than the first stirring path 31 on the left side (rear side) in FIG. In addition, the first stirring path 31 and the second
The stirring path 32 is partitioned by a partition wall 33, with passages 34 at both ends.
．． 35 and a bypass passage 36 formed at a predetermined distance from the passage 34 on the near side.

The bucket roller 37 is arranged in the first stirring path 31 and rotatably supported on the housing side wall 81.81. A gear 39a is fixed to the shaft 38 of the bucket roller 37 protruding from one housing side wall 81a, and the gear 39a can be driven and connected to the motor M1 via a clutch CL. The motor M1 is provided in the main body of the copying machine 1, and is configured to transmit drive power to a developing device facing the photoreceptor 2. On the other hand, clutch CL
I is provided in each developing device, and can be driven and connected to the motor M1 in an independent operation by a clutch CLI of each developing device.

A gear 39b is attached to the shaft 38 of the bucket roller 37 protruding from the other housing side wall 81b, and this gear 39b is connected to the sleeve drive gear 2 via another gear 40.
It is connected to 9. Furthermore, the clutch CL2 can interrupt the transmission of drive to the sleeve drive gear 29.

Therefore, when the clutch CLI is turned on, the rotation of the motor M1 is transmitted to the bucket roller 37, and when the clutch CL2 is further turned on in this state, the drive of the motor M1 is transmitted to the sleeve 24.

The conveying screw 41 is arranged in the second stirring path 32 and rotatably supported by the housing side wall 81.81. The shaft 42 of the conveyance screen 41 is provided with an electrode 43 made of a conductive non-magnetic material like the shaft 42 in a region between the passage 34 and the bypass passage 36 located on the front side.

This electrode 43 is formed into a truncated cone shape, magnets 44 and 44 are attached symmetrically to the outer periphery, and the upper end surface is connected to the developing roller 2.
It should be parallel to the 1st class.

That is, as shown in FIG. 4, at the upper end of the electrode 43, the inclination θ of the conveying screw 41 is canceled by the slope of the outer surface of the electrode 43, so that the upper end surface of the electrode becomes parallel to the horizontal axis α.

Conveyance screw 41 protruding from housing side wall 81a
A gear 45 is fixed to one end of the shaft 42, and this gear 4
5 is connected to a gear 39a fixed to the bucket roller 37 via another gear 46. Therefore, the conveying screw 41 rotates in synchronization with the bucket roller 37.

Further, as shown in FIG. 6, a recess 47 is formed in one end surface of the support shaft of the conveying screw 41.

On the other hand, is there a leaf spring 49 installed in the Cahonox 48? A terminal 50 provided on the temporary spring 49 of the bar is fitted into the four parts 47, and the electrode 43 and the support shaft 42 are grounded.

On the other hand, a light shielding plate 51 is attached to the other end of the conveying screw 41 protruding from the housing side wall 81b, and a photointerrupter 52 for detecting the light shielding plate 51 is attached to the side thereof.
is located. In addition, the light shielding body 51, the magnets 44, 44
The photointerrupters 52 are in a specific positional relationship, and the positions of the magnets 44 and 44 can be confirmed from the detection signals of the photointerrupters 52.

As shown in FIGS. 4 and 5, the toner concentration detection sensor 53 includes a housing 54 having an opening 55, a light emitting element 56 and a light receiving element 57 provided in the housing 54, and a transparent detection window 58 covering the opening 55. The housing 54 is provided with a dam wall 59 along one side edge of the transparent detection window 58.

The detection window 58 is formed of a member that is charged to the same polarity as the upper toner by applying a bias having the same polarity as the toner to the lower surface thereof, or by applying a bias having the same polarity as the toner, or by contacting the lower surface with the developer. By doing so, the window surface is configured to be charged to the same polarity as the toner in order to prevent toner from adhering.

The toner concentration detection sensor 53 is disposed above the electrode 43 as shown in FIG. 3.4.5, and is fixed with the detection window 58 facing the electrode 43 and the dam wall 59 positioned on the photoreceptor side. . Further, the conductive coating of the detection window 58 is connected to a window bias power supply 60, and a direct current window bias V is applied thereto. Note that when the detection window 58 is charged to the same polarity as the toner by using a member that charges the detection window 58 to the same polarity as the toner when it comes into contact with the developer, it is not necessary to apply the window bias.

(C) Toner Replenishment Section 61 The toner replenishment section 61 is adjacent to the rear of the second stirring path 32, and the toner replenishment section 61 and the second stirring path 32 are in communication via the replenishment port 62.

The supply screw 63 is arranged in the i-ner supply section 61,
A gear 64 is fixed to one end protruding from the housing side wall 81a, and is connected to a gear 45 fixed to the conveying screw 41. Therefore, the supply screw 63 rotates in synchronization with the conveyance screw 41 and the bucket roller 37. Further, the toner supply section 61 is connected to the toner storage section 15 (see FIG. 1), and the toner supply section 61 is connected to the toner storage section 15 (see FIG. 1).
Based on the drive of the toner replenishing section 61 of each developing device, toner is supplied to the toner replenishing section 61 of each developing device.

(d) Microcomputer The control bag ftcPU of the microcomputer, as shown in FIG.
(Y, M, C, K), clutch CLl (Y, M
, C, K), clutch CL2 (Y, M.

C, K), AC developing bias VB-I. , DC developing bias VB-DC1, window bias V8 remote signals are output, and signals are input from print signals and toner concentration detection sensors (ATDC sensors) (Y, M, C, K).

(2) Developing operation The developing operation of the developing device facing the photoreceptor 2 will be briefly explained.

The developer is accommodated in a first stirring section 31 and a second stirring path 32 . Note that the toner and carrier used are those that are charged negatively and the carrier positively when they come into contact with each other.

When the motor M1 is driven and the clutches CLI and CL2 are turned on, the drive of the motor M1 is transmitted to the sleeve 24, bucket roller 37, conveyance screw 41, and replenishment screw 63, each of which is indicated by arrow a.

Rotate in b, c, and d directions.

As a result, the developer is circulated and conveyed through the stirring paths 31 and 32 in the direction of the arrow shown in FIG. Reverse polarity by contact (toner has negative polarity, carrier has positive polarity)
is charged with electricity.

That is, the developer in the first stirring path 31 is conveyed from the back side to the front side. Also, during this conveyance process, the developer is transferred to the sleeve 2.
4.

The developer supplied to the sleeve 24 is held in a magnetic plan state on the outer circumferential surface of the sleeve by the magnetic force of the magnet body 23, passes through the opposing portion of the brush height regulating plate 22 as the sleeve 24 rotates, and is transferred to the opposing portion of the photoreceptor 2. Toner is supplied to the electrostatic latent image.The supply of toner to the photoconductor 2 is based on the surface potential of the photoconductor 2 and the DC development bias VB-9 of development bias 8.
This is done based on the potential difference between ゜ and ゜.

The developer conveyed to the first stirring path 31 is sent to the second stirring path 32 via the passage 34 and the bypass passage 36.

Here, the amount of developer that enters the first stirring path 31 via the passage 34 is constant, and the amount of developer that enters the first stirring path 31 through the passage 34 is
It is fed into the second stirring path 32 through the. The reason is,
This is because the electrode 43 obstructs the conveyance of the developer in the second stirring path 32, and the amount of developer that passes around the electrode 43 is limited to a substantially constant amount.

The developer in the second stirring path 32 is conveyed from the front side to the back side while being mixed and stirred by the rotation of the conveying screw 41, and is fed into the first stirring path 31 via the passage 35.

The developer passing around the electrode 43 is sequentially held by magnets 44 and 44 that rotate together with the transport screw 41.

The developer held by the magnets 44, 44 constitutes a magnetic brush as shown in FIG. 5, and slides against the detection window 58 as the conveyance screw 41 rotates.

The developer that has passed through the portion facing the detection window 58 is partially blocked by the damming wall 59, forming a developer reservoir in the portion facing the detection window 58, and the magnets 44 and 44 are placed in the portion facing the detection window 58. While passing through the developer, the developer is stably brought into contact with the detection window 58 at a nearly constant pressure.

Here, the window bias VW is set to -1.5 KV. This window bias is determined experimentally to prevent toner and carrier from adhering to the detection window 58. That is, in the developing devices 8Y1 to 8Y8 of this embodiment, as shown in FIG. , 6 KV, carriers adhered to the detection window 58.

Therefore, the window bias VW is set to -1,3KV to -1,6KV.
Set to a value between 1 and 2 to prevent adhesion of toner and carrier.

In the toner concentration detection sensor 53, the developer is illuminated through the light emitting element 56 or the detection window 58, and the reflected light is transmitted to the light receiving element 5.
Detected at 7.

The light receiving element 57 outputs a voltage signal corresponding to the amount of reflected light to the control device CPU.

The control device CPU controls the drive of the motor M2 based on the measured toner density.

That is, if the toner concentration is lower than a predetermined reference concentration, the motor M2 is driven to replenish the toner replenishing section 61 with toner. The replenished toner is replenished from the replenishment port 62 to the second stirring path 32 by rotation of the replenishment screw 63, and the toner concentration is restored to a proper state.

■Development bias, development bias control by toner density control controller CPU, 9th
This will be explained with reference to the time chart in the figure and the flowcharts in FIGS. 10 to 19.

(a) Main routine (see FIG. 10) When the copying machine 1 is powered on, the program of the control unit CPU starts, and first, in step #1, registers and peripheral interfaces are initialized.

In step #2, an internal timer for defining the length of one routine is started. The length of this one routine is
This serves as a reference for various timers described below, and these timers are updated every time this routine is passed.

In step #3, control of the developing bias \lB, in step #4, toner density control, and in step #5, other processing is executed. Of these, development bias control and toner density control will be explained in detail later.

Finally, in step #6, it is determined whether the internal timer has ended, and if the internal timer has ended, the process returns to step #2 and the internal timer is started again.

After that, the same process is repeated.

(b) Development bias control routine The developing bias control routine will be explained.

1. Developing bias control (part 1) [see Figure 11] In this routine, the state A is "0°" in step and step 10,
Determine whether or not. Stay) A is “O” depending on the control state.
By checking this value, the current state is determined and the corresponding process is executed.

Note that state A is the initial setting routine # when the power is turned on.
1 is set to “O”.

If state A is "O", the process proceeds to step #11, and if it is other than "0", the process proceeds to step #20.

In step #11, on-edge is detected from the print switch signal. Note that "on-en-on" refers to a state in which the signal from the print switch is switched from off to on.

If the on-edge of the print switch is not detected, the process returns to the main routine. If the on-edge of the print switch is detected, steps #12 to #16 are executed and the process returns to the main routine.

In step #12, the output of the DC developing bias VB to DC is set to VI+--600V. At this time, the AC developing biases VB and □AC are set so that the peak-to-peak-to-peak value is 1200V.

In step #13, the developing bias VB (.VB-D) is applied.

-i-V B-AC) is turned on and applied to the developing sleeve 24.

Step #14 is window bias V□(, -1.5K
V) is turned on, and this is detected by the toner concentration detection sensor 53.
is applied to the detection window 58 of.

In step #15, a window bias rising timer t1 is set. This window bias rising timer t1 is a window bias ■. The agitation of the developer is stopped until the timer t1 ends, which is the time required for the timer to completely start up. The reason is window bias V. This is because if the developer is stirred before it has risen sufficiently, the stirred developer will adhere to the detection window 58 and interfere with subsequent toner concentration detection.

NAO, developing bias VB, window bias ■. The developing motor M1 starts driving in accordance with the on-timing of the developing motor M1. However, at this time, the clutch C of the developing device facing the photoreceptor 2
The LI is old and the bucket roller 37 and conveyance screw 41 do not rotate.

In step #16, state A is changed to "1".

11. Developing bias control (part 2) [See FIG. 12] In step #20, it is determined whether state A is "1" or not.

If state A is “1”, proceed to step #21 and set “1”
Otherwise, proceed to step #30.

In step #21, the window bias rising timer t1 is updated. In step #22, it is determined whether the window bias rising timer t1 has ended or not. If it has not ended, the process returns to the main routine, and when it has ended, steps #23 to #26 are executed.

In step #23, the timer t1 is reset, and in step #24, a concentration detection permission timer t2 is newly set.

This concentration detection permission timer t2 is set to the responsiveness of CLI and the time required for the developer in the developing device to stabilize from the start of stirring.

In step #25, the clutch CLI of the developing device facing the photoreceptor is turned on. At this time, the developing motor M1 is already in the driving state, so at the same time as the clutch CLI is turned on, the rotation of the motor M1 is transmitted to the packet roller 37, the conveying screw 41, and the replenishing screw 63. Rotate in each direction.

As a result, the developer in the stirring paths 31 and 32 is circulated and conveyed.

In step #26, state A is changed to "2".

Developable bias control (part 3) [see FIG. 13] In step #30, it is determined whether the state is A or "2".

If state A is “2”, proceed to step #31 and “1”.
”, proceed to step #40.

In step #31, the concentration detection permission timer t2 is updated. In step #32, it is determined whether or not the concentration detection permission timer t2 has expired. If the concentration detection permission timer t2 has not expired, the process returns to the main routine, and when it has finished, the processes of steps #33 to #35 are executed. Note that when the timer t2 ends, the stirring path 31.
32, a stable developer flow is formed.

In step #33, the timer t2 is reset, and in step #34, the concentration detection permission flag is set. This density detection permission flag is used to determine whether or not toner density detection is to be performed, and is used in toner # statement control, which will be described later.

In step #35, state A is changed to "3".

iv Development bias control (Part 4) [See Figure 14]
In step #40, it is determined whether state A is "3" or not. If state A is other than "3", the process proceeds to step #50, and if state A is "3", step # 4
In Step 1, it is determined whether or not the image creation permission flag is present. If the image creation permission flag is not set, the process returns to the main routine, and if the image creation permission flag is set, steps #42 to ## are performed.
45 processes are executed. This image formation permission flag is a flag for determining whether or not the sleeve 24 is to be rotated.

Step #42 turns on clutch CL2 and motor M
1 rotation is transmitted to the sleeve 24. As a result, the developer held on the outer periphery of the sleeve 24 is transported to a portion facing the photoreceptor 2, and development of the electrostatic latent image formed on the photoreceptor is started.

In step #43, the DC developing bias VB-DC is set to V
,=100V. On the other hand, AC developing bias V
B-AC will maintain its current status.

In step #44, a sleeve off timer t3 is set. This sleeve off timer t3 defines the sleeve rotation time necessary for image formation, and development is executed while this timer t3 is counting.

In step #45, state A is changed to "4".

V. Developing bias control (part 5) [See FIG. 15] In step #50, it is determined whether the state is A or "4".

Then, if state A is other than "4", step #60
If the state is A or "4", the process advances to step #51.

In step #51, the sleeve off timer t3 is updated.

In step #52, it is determined whether the sleeve off timer t3 has ended, and if it has not ended, the process returns to the main routine, and if it has ended, the process advances to step #53.

In step #53, the clutch CL2 is turned off and the rotation of the developing sleeve is stopped.

In sleeve #54, set the DC developing bias VB-DC to V! (Change to =-600V.

In step #55, it is determined whether or not there is a next copy request, and if there is a next copy request, the process advances to step #56.
Switch state A to "3" and execute development again.

On the other hand, if there is no next copy request, the clutch CLI off timer t4 is set in step #57, and the start #58
Change state A to "'5". This clutch CL
The 1-off timer t4 defines the agitation time for replenishing toner into the developing device and further stabilizing the toner concentration after the completion of development.

vi. Development bias control (part 6) [See FIG. 16] In step #60, it is determined whether state A is "5" or not. Then, when state A is other than "5", proceed to step #70, and when state A is "5", step #
Proceed to 61.

In step #61, the clutch CLI off timer t4 is updated.

In step #62, it is determined whether the clutch CL1 off timer t4 has ended or not. If it has not ended, the process returns to the main routine, and if it has ended, steps #63 to #68 are executed.

In step #63, the clutch CLI off timer t4 is reset, and in step #64, the clutch CL1 is turned off. As a result, the drive from the motor M1 to the bucket roller 37 and the like is cut off, and the agitation and conveyance of the developer is stopped.

Step #65 stops the motor M1 and moves to step #65.

In step #66, the density detection permission flag is reset to stop toner density detection.

In step #67, a window bias off timer t5 is set. This window bias off timer t5 is the clutch C
After motor Ll and motor M1 stop, bucket roller 37
, the time required for the conveying screw 41 to completely stop rotating due to inertia.

In step #68, state A is changed to 6''.

vii. Developing bias control (part 7) [see FIG. 17] In step #70, the window bias off timer t5 is updated.

In step #71, it is determined whether the window bias off timer t5 has ended, and if it has not ended, the process returns to the main routine, and if it has ended, steps #72 to #75 are executed.

In step #72, the window bias off timer t5 is reset, and in step #73, the window bias V is reset.

Turn off. In this way, the window bias Vw is
1. Since the clutch CL1 is turned off after time t5 has elapsed and the bucket roller 37 and conveyance screw 41 have completely stopped, the developer does not adhere to the detection window 58 of the toner concentration detection sensor 53. maintained in a clean condition.

In step #74, the developing bias VB is turned off, and in step #75, the state A is changed to "O".

As described above, in this developing bias control routine, during the developing operation when the sleeve 24 is rotating, the i-stream current i-bias V 0° is set to VL--400V. Also,
During non-development and while the bucket roller 37 and conveyance screw 41 are rotating, the DC developing bias VB-Oc is set to ■□=-
It is set to 600V.

Therefore, under conditions where the charge of the developer tends to shift to the positive side, and in addition, even if the electric field between the electrode 43 and the detection window 58 changes due to poor grounding of the electrode 43, the carrier adhesion to the detection window 58 will not increase. It can be prevented.

Let me explain the reason.

If the development bias control as described above is not performed,
In the developing device, carrier adheres to the detection window 58 in the following manner.

That is, the electrode 4 facing the toner concentration detection sensor 53
3, a terminal 50 is fitted into a concave portion 47 at one end of the shaft 42 of the conveying screw 41, and the shaft 42 and the terminal 50 are in contact with each other to be grounded. However, since the shaft 42 is a rotating member, the contact portion between the shaft 42 and the terminal 50 may be worn out.
Further, there is a possibility that developer leaked from the developing device may enter these contact portions, and the electrical connection between the shaft 42 and the terminal 50 may be interrupted. In fact, devices employing this type of electrical connection often lead to connection failures.

When the electrical connection between the shaft 42 and the terminal 50 is broken, the electrode 4
3 becomes electrically floating.

In this case, the toner and carrier being conveyed through the stirring paths 31 and 32 have electric charge, and normally the total amount of electric charge between the two is balanced. However, when a large amount of negatively charged toner is consumed during development, the total charge of the developer shifts to the positive side. This phenomenon is particularly likely to occur when the humidity is low or when the developer is new.

When this positive charge moves to the floating electrode 43, the electric field between the detection window 58 and the electrode 43 changes. That is, when the electrode 43 is grounded, if the window bias is 1 or -1.5 KV, the detection window 58 and the electrode 4
Between 3 and 1. Although there is a potential difference of 5KV, the electrode 43
When a positive charge moves to , the potential difference between the detection window 58 and the electrode 43 becomes even larger.

As a result, as is clear from FIG. 8, carriers adhere to the detection window 58.

When carrier adheres to the detection window 58, since the reflectance of the carrier is lower than that of the toner, it is determined based on the signal from the toner concentration detection sensor 53 that there is a lack of developer or toner. Then, toner is replenished into the developing device, and the amount of toner contained in the developer becomes larger than necessary, resulting in an overabundance of toner! - Gner spills out of the developing device.

However, the developing device of the present invention having the above-mentioned control does not have this problem.

In other words, during non-development and while window bias ■ is being applied,
The DC developing bias is switched to VB-p (or high voltage vH-60QV).As a result, even if the developer shifts to positive due to large consumption of toner, the negative polarity DC developing bias VB-DC = 600QV charge. is injected into the developer, and the developer is electrically neutralized.

Therefore, under conditions where the charge of the developer tends to shift to the positive side due to large amounts of toner consumption or changes in humidity, even if the electrode 43 becomes floating due to poor grounding, the total charge of the developer is neutralized. , a toner concentration detection sensor 5
Accurate toner concentration detection is performed without carrier adhering to the detection window 58 of No. 3.

In the above embodiment, the development B Iasumi source 26 is provided with a DC bias power supply 27 and an AC bias power supply 28, and a voltage in which DC and AC are superimposed is applied to the sleeve 24. It may also have the following. However, if alternating current is superimposed, charge injection into the developer can be carried out quickly.

(C) Toner concentration control routine Toner concentration control will be explained with reference to FIGS. 18 and 19.

i.) Nerr degree control (Part 1) [See FIG. 18] In step #80, it is determined whether the state is B or "O". This state B is set to “0” or “1”,
When you turn on the power to copier 1, the initial setting routine
O”.

In step #81, it is determined whether the concentration detection permission flag is set. This concentration detection permission flag is set in step #34.

In step #82, the take from the toner concentration detection sensor is sampled.

In step #83, it is determined whether or not the number of samples to be taken has reached 10. If the number of samples is less than 10, the process returns to the main routine to continue sampling, and when the number of samples has reached 10, step #83 is performed. Proceed to step 84.

In step #84, the ten sampling data are averaged.

In step #84, the average value of the take and the reference density to be controlled are compared, and if the detected toner density is higher than the reference density, the process proceeds to step #90, and the toner density take is cleared.

On the other hand, if the detected toner density is lower than the reference density, steps #86 to #89 are executed.

In step #86, the detected toner density data is cleared, in step #87 the toner replenishment motor M2 is driven, and in step #88 the toner replenishment timer t6 is set. As a result, the toner of the corresponding color is replenished from the toner storage section 15 to the developing device.

Then, in step #89, state B is changed to "1".

11. Toner density control (Part 2) [See FIG. 19] In step #91, the density detection permission flag is set.

Determine whether or not it has been written.

If set, the toner replenishment timer t6 is updated in step #92, and the end of the timer t6 is determined in step #93. If the timer t6 has not ended, the process returns to mail-chin. On the other hand, when the timer t6 expires, toner supply is stopped and the process proceeds to step #94.

On the other hand, if the concentration permission flag is not set, the process advances to step #94.

In step #94, the timer t6 is reset, and in step #95, toner replenishment from the toner storage section 15 is stopped,
In step #96, state B is changed to O.

In this embodiment, as a means for charging the detection window 58 to the same polarity as the toner, a method of applying a bias to the conductive film is used. You may also use a method such as using a member that does.

〔Effect of the invention〕

As is clear from the above description, the developing device using the optical density measurement method according to the present invention includes a transparent detection window that is charged to the same polarity as the toner, and an electrode held on a rotating member facing the window. A constant electric field is formed between them to prevent developer from adhering to the transparent detection window.

Furthermore, during non-development and while the rotating member that stirs the developer is rotating, the development bias is switched in a direction that cancels out the charge on the carrier.

Therefore, even if the electric field strength between the electrode and the detection window changes due to trouble, at least carriers are prevented from adhering to the transparent detection window.

Therefore, the developer does not spill from the developing device and contaminate the surrounding area, and the image forming device can be maintained in a clean state. Further, even when troubleshooting, troublesome work such as disassembling and cleaning the image forming apparatus is not necessary.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a schematic configuration of an image forming apparatus, FIG. 2 is a cross-sectional view of a developing device, and FIG. 3 is a vertical sectional view of the developing device.
Figure 4 is a cross-sectional view of the toner concentration detection sensor, and Figure 5 is a cross-sectional view of the toner concentration detection sensor.
6 is a plan view showing the grounding state of the electrode, FIG. 7 is a circuit diagram of the control device in the microcomputer, and FIG. 8 is the window bias and toner or carrier on the detection window. FIG. 9 is a time chart regarding developing bias control, FIG. 10 is a flowchart of the main routine, and FIGS.
The figure is a flowchart regarding development bias control, No. 18.
．． FIG. 19 is a flowchart regarding toner density control. l... Free color copying machine, 2... Photoreceptor, 8Y, 8M
, 8C, 8K...Developing device, 21...Developing roller, 31
...First stirring path, 32...Second stirring path, 37...
Bucket roller, 41... Conveyance screw, 43... Electrode, 44... Magnet, 53... Toner concentration detection sensor, 55
...Transparent detection window, ■8 Development bias, ■B, □.・
...DC developing bias, VB-AC...AC developing bias, V8...window bias. Patent Applicant: Minolta Camera Co., Ltd. Agent Patent Attorney: Mr. Maeda, et al. Figure 4 Figure 6 Figure 5

Claims (1)

[Claims] (1) A developing device that has a developer made of toner and a carrier and supplies toner to the member to be developed based on a potential difference between the surface potential of the member to be developed and a developing bias, comprising: a) storing the developer; b) a transparent detection window facing the developer transport path and configured such that its surface facing the developer is charged to the same polarity as the toner to prevent toner from adhering; c) ) a rotary member rotatably disposed in the developer transport path and having a magnet and a grounded electrode at a portion facing the detection window; d) illuminating the developer through the detection window and emitting the reflected light; e) a developing bias switching means for switching the developing bias in a direction to cancel the charge of the carrier during non-developing and at least during rotation of the rotating member. A developing device characterized by: