JP2002014533A - Electrostatic latent image developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent toner scattering, spent toner, faulty image quality and the lowering of resolution and to prolong a maintenance cycle by accurately controlling toner concentration without causing overshoot exceeding appropriate toner concentration even in the case of outputting a large size image or an image having a high black ratio whose toner consumption is high in a system where a toner concentration sensor is disposed in a developer carrying path. SOLUTION: The toner concentration sensors are respectively disposed on an upstream side and a downstream side in a developer carrying direction with respect to a toner supply area on the wall surface of the developer carrying path. As for the toner concentration A detected by a toner concentration detector on the upstream side, the toner concentration B detected by the toner concentration sensor on the downstream side and a toner concentration maintaining target value C; toner supply amount D1 per unit time from a toner supply means in the case of A, B<C is set to be higher than toner supply amount D2 per unit time from the toner supply means in the case of A<C<=B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic latent image developing apparatus used for developing an electrostatic latent image into a toner image in an electrophotographic apparatus such as a copying machine, a printer, a facsimile, and the like.
More specifically, the present invention relates to an electrostatic latent image developing device using a developer including a toner and a magnetic carrier.

[0002]

2. Description of the Related Art In an electrophotographic apparatus, a developing device is arranged in proximity to a photosensitive drum rotating in one direction, and a developer contained in the developing device is charged with an electrostatic latent image formed on the surface of the photosensitive drum. In general, a configuration in which the electrostatic latent image is visualized by the toner in the developer by contacting the toner with the developer is generally employed, but by repeating the image formation, the toner in the developer is consumed and the toner concentration decreases. It is necessary to supply toner and keep the toner concentration constant.

In general, the determination of the toner concentration of this type of developing device is performed by setting a mixture ratio of the toner in the developer, that is, the toner concentration, detected by a magnetic permeability sensor described in Japanese Patent Application Laid-Open No. 1-276175. It is compared with the maintenance reference value and based on the comparison result. In the magnetic permeability sensor, the sensor output decreases when the toner concentration increases, and conversely, the sensor output increases when the toner concentration decreases. Accordingly, when toner development is repeated and the toner concentration in the developer decreases, the sensor output of the developer increases. If toner is replenished so as to decrease based on the sensor output, the toner concentration can be stably maintained. However, since the magnetic permeability of the developer depends on the bulk density of the developer, the sensor output tends to fluctuate unless the fluidity of the developer is maintained in a stable manner. It is necessary to pay close attention to the mounting position because it is susceptible to noise.

Conventionally, a toner density control method using a magnetic permeability sensor includes a method of detecting a toner density of a developer pumped up by a developing roller using a magnetic permeability sensor attached to a central portion on the back side of a cutting board. In the horizontal circulation in which the developer once separated from the developing roller is returned to the developer conveying path disposed in parallel with the developing roller and circulated and conveyed by an internal spiral or the like, the magnetic permeability is set at a position in contact with the developer in the conveying path. The method can be roughly classified into a method in which a sensor is attached and a method of detecting the toner density. The latter method is excellent in that it is hardly affected by the magnetism of the magnet inside the developing roller, and its use is increasing.

FIG. 1 is a plan view of the developing device excluding the latter conventional toner hopper, and FIG. 2 is a side view of the latter conventional developing device. In the developing housing 1 facing the photoreceptor drum 50, there is provided a developing roller 2 having a fixed magnet disposed therein and a first developer conveying means 3 at a position facing the developing roller 2 in parallel. A developer transport path 4;
A second developer transport path 6 having a second developer transport means 5 is provided at a position intermediate between the first developer transport path and the developing roller. The first developer conveying means 3 has a spiral structure, and the second developer conveying means 5 has a paddle structure combining a spiral and a rib. At the boundary between the first developer transport path 4 and the second developer transport path 6, a partition plate 31 is provided with both ends cut off. The developer is horizontally circulated in the direction V shown in FIG. 1 by the rotation of the developing roller 2, the first developer conveying means 3, and the second developer conveying means 5 as shown in FIG. Some of them are pumped by the developing roller.

A part of the developer peeled off from the developing roller 2 on the back side of the cut-off plate 7 drops above the first developer conveying path 4 via the upper surface of the developer guide plate 8, and the first developer Due to the rotation of the transporting means 3 and the second developer transporting means 5, the toner circulates horizontally in the direction of V and is collected again on the developing roller 2 side.
The replenishment toner from the hopper 9 falls near the position P indicated by the solid line in the upper part of the first developer conveyance path 4 and mixes and stirs in the developer. A toner density sensor 10 is provided on one of the transport path walls on the upstream and downstream sides of the toner replenishing position P, and after detecting the toner density in the developer, the toner is replenished from the hopper 9 according to the result. As a result, the reference toner density is maintained.

[0007]

As described above, this method has the advantages of being less affected by the magnetic force of the developing roller and having a longer mixing time for the replenishment toner. There is a limit, and a time difference easily occurs between the toner concentration detected by the toner concentration sensor in relation to the toner supply position and the actual toner concentration of the developer on the surface of the developing roller, and the fluctuation of the toner concentration increases. Also, when copying and outputting an image of a small size with respect to the maximum copy width, the toner consumption is not constant in the axial direction of the developing roller. Since the developer is returned to the developer conveying path by the developer guide plate, the provision of the toner concentration sensor at only one location
A biased toner concentration may be detected, resulting in an over toner state or an under toner state with respect to an appropriate toner concentration. In the over toner state, toner scattering,
Problems such as poor image quality such as background fogging and low resolution, an increase in toner consumption, an increase in untransferred toner, and the like are likely to occur. In an under toner state, problems such as low image density and blurring of characters are likely to occur. These defects are serious problems that lead to shortened maintenance cycles. This is a particularly serious problem in a copying machine for drawings, in which the circulation distance of the developer in the transport path is long and the magnification of the maximum copy size and the minimum copy size is particularly large, and is capable of copying from A2 size to A0 size. Was.

Accordingly, the present invention provides a method in which a toner density sensor is disposed in a developer conveying path, in which the toner density of the developer is controlled with high accuracy, the image density is maintained stably, and the toner consumption is reduced. The first purpose.

Further, the present invention provides a high-precision toner density control even when outputting a large-size image consuming a large amount of toner or an image having a high black ratio without causing overshoot exceeding an appropriate toner density. A second goal is to make it possible to prevent toner scattering, spent toner, poor image quality, and reduced resolution, and to extend the maintenance cycle.

A third object of the present invention is to eliminate variations in the toner concentration of the developer in the developing device.

It is a fourth object of the present invention to extend the maintenance cycle without causing overshoot exceeding the proper toner density even in a copying machine for drawings of A2 size or larger.

[0012]

According to a first aspect of the present invention, there is provided an electrostatic latent image developing apparatus comprising: a toner supply unit for supplying a toner; An electrostatic latent image developing apparatus comprising: a developing roller applied to an electrostatic latent image; and a first developer conveying path including a first developer conveying unit provided in parallel with the developing roller. The toner supply means is provided so as to drop and replenish the toner from above the first developer transport path, and is provided upstream and downstream in the developer transport direction with respect to the toner replenishment area; A toner concentration sensor is provided at a position on the wall surface of the road that contacts the developer. According to the first aspect of the present invention, since the plurality of toner density sensors are provided at a predetermined distance from each other, it is possible to perform average toner replenishment in the roller axial direction regardless of the size of the document. In addition, since the toner density control is performed in consideration of the maximum toner density immediately after toner replenishment and the minimum toner density immediately before toner replenishment, image output within an appropriate toner density range can be repeated for a long time.

Further, according to the present invention, the toner density A detected by the toner density sensor on the upstream side in the developer conveying direction, the toner density B detected by the toner density sensor on the downstream side, With respect to the density maintenance reference value C, the toner replenishment amount D1 per unit time from the toner supply unit when A and B <C is equal to the unit supply amount from the toner supply unit when A <C ≦ B. Toner supply amount D
2. The electrostatic latent image developing device according to claim 1, wherein the electrostatic latent image developing device is set higher than 2. According to the second aspect of the present invention, when the toner on the most downstream side immediately below the replenishing position at the time of turning on the toner replenishing motor reaches the downstream toner density sensor position and becomes equal to or higher than the toner density maintenance reference value, the unit is set. Since the amount of toner replenished per time is reduced, the amount of toner replenishment is initially increased, and thereafter, the upstream developer immediately below the replenishment position is replenished with toner for a long time, so that overshoot to the upstream developer is caused. Is avoided.

According to a third aspect of the present invention, there is provided a second developer conveying path having a second developer conveying means at an intermediate portion between the first developer conveying path and the developing roller. 3. The electrostatic latent device according to claim 1, wherein a partition plate is provided at a boundary between the first developer transport path and the second developer transport path except for both ends in the longitudinal direction. An image developing device. According to the third aspect of the present invention, it is possible to increase the stirring and conveying distance from when toner is supplied to the developer to when it is returned to the developing roller, so that the supplied toner can be mixed with the developer for a long time. As a result, the charging characteristics of the replenishment toner are improved, and the toner scattering and the excess toner consumption are further improved.

Further, according to the present invention, when the values of A, B, and C satisfy C ≦ A, B, the toner supply operation from the toner supply unit is stopped. 4. The electrostatic latent image developing device according to claim 1, wherein: According to the fourth aspect of the present invention, excessive toner replenishment can be prevented, so that toner scattering and excess toner consumption are further improved.

According to a fifth aspect of the present invention, as the means for adjusting the toner supply amount per unit time, the ON / OFF time of the driving of the toner supply motor is adjusted. An electrostatic latent image developing device according to 2, 3, or 4. According to the fifth aspect of the present invention, the toner supply amount per unit time can be finely adjusted, so that the toner density fluctuation width can be further reduced.

Further, according to the present invention, the length of the toner replenishment area in the direction of the developer transporting path is not less than 1/5 and not more than 4/5 of the entire length of the first developer transporting path. The electrostatic latent image developing device according to claim 1, 2, 3, 4, 5, or 6, wherein According to the invention of claim 6, 1
/ 5 or more, the amount of toner falling per unit length of the developer conveyance path is suppressed to a certain value or less, and a local excessive increase in toner concentration is prevented, so that the replenishment toner is sufficiently mixed with the developer. Since the toner can be agitated and frictionally charged, scattering of toner and excess toner consumption can be further improved. Also 4 /
By setting the number to 5 or less, the variation in the amount of toner falling in the axial direction of the toner supply roller is reduced, and the amount of toner supply immediately after the toner supply motor is turned on can be increased.

According to a seventh aspect of the present invention, there is provided the electrostatic latent image developing device according to the first, second, third, fourth, fifth and sixth aspects. This is a large drawing copier. According to the seventh aspect of the present invention, in a large-sized drawing copying machine in which a replenishing port from a hopper is long in an axial direction of a stirring roller in order to maintain a toner replenishing ability, a large-sized copying machine having a size of A2 or more is provided. Even if the toner density suddenly drops due to continuous output of the density original, it is possible to prevent toner density over due to overshoot.
It is possible to prevent toner scattering and generation of spent toner and extend the maintenance cycle. [Detailed description of the invention]

According to the present invention, when the toner density falls below the maintenance reference value in continuous output of a large-size document or a high-density document, etc., until the developer supplied with toner reaches the toner concentration sensor on the upstream side. Increases the amount of toner replenished per unit time and thereafter reduces the amount of toner replenished per unit time to prevent overshoot exceeding the toner density maintenance reference value,
This makes it possible to maintain and stabilize the T / D of the entire developing device uniformly.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. This machine is a developing device used in a large-size drawing copier capable of copying up to an A0 size plate.
FIG. 3 is a plan view of the developing device without the toner hopper, and FIG. 4 is a side view of the whole including the toner hopper. In the developing housing 1, a developing roller 2 having a fixed magnet disposed therein and a first developer conveying path 4 having a first developer conveying means 3 at a position facing the developing roller 2 in parallel with the developing roller 2; A second developer transport path 6 having a second developer transport means 5 located at an intermediate portion between the first developer transport path and the developing roller is provided. The first developer conveying means 3 has a spiral structure, and the second developer conveying means 5 has a paddle structure in which a rib structure is combined with a spiral. At the boundary between the first developer transport path 4 and the second developer transport path 6, a partition plate 31 is provided with both ends cut off. By rotating the developing roller 2, the first developer transporting means 3, and the second developer transporting means 5 as shown in FIG. 4, the developer horizontally circulates in a direction V shown in FIG. Some of them are pumped by the developing roller.

A part of the developer peeled off from the developing roller 2 on the back side of the cut-off plate 7 slides on the upper surface of the developer guide plate 8 in the direction of the arrow and drops above the first developer transport path 4, and The developer circulates horizontally in the direction shown by the rotation of the developer transporting means 3 and the second developer transporting means 5 and is again collected on the developing roller 2 side. The replenishment toner from the hopper 9 falls near the position P indicated by the dotted line in the upper part of the first developer transport path 4 and mixes into the developer. The upper surface of the first transport path is covered with an upper cover 16 except that the toner supply area P is open. It is desirable that the length of the toner supply area P in the direction of the conveyance path is not less than 1/5 and not more than 4/5 of the entire length of the conveyance path. 1
If the ratio is less than / 5, the toner is concentrated in a narrow area, and the mixing and stirring into the developer is insufficient, and poorly charged toner is generated, which may cause problems such as toner scattering and background fogging. If it exceeds 4/5, the amount of toner falling in the axial direction of the toner supply roller may vary greatly, or the time for increasing the toner supply immediately after the toner supply motor is turned on may not be sufficient. In this embodiment, the length of the toner supply area P is about 45% of the entire length of the conveyance path. A toner density sensor 11 is provided on the wall of the conveyance path upstream of the toner supply position P, and a toner density sensor 12 is provided on the wall of the conveyance path downstream of the toner supply position P.

As shown in FIG. 4, the toner hopper 9 has a hopper housing 13 having a longitudinal opening 14 in the direction of the conveyance path where the opening coincides with the replenishing area P of the developing device. And a supply roller 15 rotatably mounted about a shaft. When a signal that the toner concentration sensors 11 and 12 detect that the developer circulating in the conveyance path has fallen below the control reference toner concentration is transmitted to the CPU, a drive signal is transmitted to a supply motor (not shown) of the supply roller 15 and the detection is performed. The replenishment motor is driven on and off for a predetermined time in a control mode corresponding to the toner density value, and toner is replenished at a predetermined toner replenishment speed to maintain the control reference toner density.

In this embodiment, the toner density sensor 1
When both of the detected toner densities 0 and 11 are lower than the control reference toner density, the toner is supplied by repeating ON for 1 second and OFF for 1 second. If the toner density detected by the downstream toner density sensor 11 exceeds the maintenance reference value and the toner density detected by the upstream toner density sensor is lower than the maintenance reference value, ON for 0.5 seconds and OFF for 4 seconds Is repeated to supply toner.

The developer is a mixture of a toner and a magnetic carrier such as a ferrite carrier. The toner concentration in the developer is preferably 1.5 to 8% by weight, and more preferably 2 to 6% by weight. As the toner constituting the developer, those having a volume average particle diameter (median diameter measured by a multisizer) in a range of 6 to 12 μm are preferably used. A carrier having a weight average particle size (median diameter) in the range of 40 μm to 130 μm by a sieving method is preferably used.

In this embodiment, a magnetic permeability sensor is used as the toner density sensor, but a programmable toner sensor TS-L type manufactured by TDK can be used, for example. The present invention is not limited to the magnetic permeability sensor, and any sensor can be used as long as it can confirm the correlation with the toner concentration, such as the electric resistance, dielectric constant, and bulk density of the developer.

FIG. 5 is a block diagram showing an embodiment of the toner density control device according to the present invention. The sensor outputs detected by the toner density sensors 11 and 12 are transferred to the control unit 20 and used for controlling a supply motor (not shown) that drives the toner supply motor 23. The control unit 20 is a CPU 2
1 and a memory 22. The memory 22 stores a functional relationship between the toner density and the sensor output, and a sensor output when the toner density is a maintenance reference value. , Ie, ON / OFF time control information. The CPU 21 of the control unit 20 carries out arithmetic processing of comparison between sensor output information from the toner density sensors 11 and 12 and a maintenance reference value, and issues a drive signal for the supply motor.

FIG. 6 is a flowchart showing the operation of the toner density control of the electrostatic image developing apparatus having the above-described configuration. During the copying operation, a large-sized image with a high toner consumption is output, and the toner supply temporarily catches up. 3 shows a process performed in a state where the toner density in the developing device temporarily falls below the control reference value. A is a toner concentration detected by a toner concentration detector mounted on the upstream side in the developer transport direction with respect to the toner supply area, and B is mounted on the downstream side in the developer transport direction with respect to the toner supply area. Is the toner density detected by the toner density detector. The replenishment motor is controlled by the ON / OFF ratio of the replenishment motor. For example, in mode 1, ON and OFF are controlled for one second, for example.
In mode 2, the toner supply speed can be adjusted by setting the time to ON for 0.5 seconds and OFF for 4 seconds. Until the downstream toner concentration sensor detects the developer whose toner density exceeds the maintenance reference value after toner replenishment, the toner replenishment amount is set to a relatively large amount by ON control for 1 second and OFF for 1 second. The control of ON for 0.5 seconds and OFF for 4 seconds makes the toner supply amount relatively small. C is a toner density serving as a control reference for ON / OFF of the toner supply motor. In this embodiment, the adjustment of the toner supply amount is ON for one second,
It was done with seconds OFF or 0.5 seconds ON and 4 seconds OFF,
The present invention is not limited to this, and within a range in which the object of the present invention is achieved, for example, an ON time of 0.1 second to 10 seconds,
It can be implemented by appropriately combining the OFF times of 0.1 seconds to 10 seconds.

In the flowchart of FIG. 6, in step 1, the developing device is driven to rotate. Proceeding to step 2, it is checked whether both of the detected toner densities A and B are lower than the maintenance reference value C. If YES, the process proceeds to step 6 where toner is supplied under the control of mode 1 and N
If O, go to step 3. From the positional relationship between the toner supply port and the toner density sensor, B on the downstream side should have risen first. In step 3, the toner density is detected, and it is checked whether the value of B on the downstream side has risen above the maintenance reference value C and the value of A on the upstream side has fallen below C. If the determination is YES, the process proceeds to step S7, and toner replenishment is performed under the control of mode 2, and if the determination is NO, the process proceeds to step S4. Step 4 is a step for checking whether or not an abnormality has occurred in the detection of the toner density sensor. Since the developer that has passed the downstream toner density sensor position is circulated and conveyed while passing through the upstream toner density sensor position while the toner is consumed by the development, it must be B> A. Next, it is confirmed whether or not the toner concentration that satisfies A ≧ C> B has not been detected. If YES, proceed to step 8 to turn on the serviceman call. If NO, proceed to step 5. If the toner density is detected in step 5 and it is confirmed that the values of A on the upstream side and B on the downstream side have risen to the maintenance reference value C or more, the replenishment operation is stopped.

[0029]

As described above, according to the present invention, the toner density detected by the toner density sensors disposed on the upstream and downstream of the toner supply area and the target value of the toner density are determined. By controlling the toner supply amount per unit time according to the level, it is possible to accurately control the toner density with little variation.

[0030]

[Brief description of the drawings]

FIG. 1 is a plan view showing an outline of a conventional developing device.

FIG. 2 is a side view showing an outline of a conventional developing device.

FIG. 3 is a plan view illustrating an outline of a developing device embodying the present invention.

FIG. 4 is a side view showing an outline of a developing device embodying the present invention.

FIG. 5 is a control system block diagram of a developing device embodying the present invention.

FIG. 6 is an operation system flowchart of the developing device embodying the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Developing housing 2 Developing roller 3 1st developer conveyance means 4 1st developer conveyance path 5 2nd developer conveyance means 6 2nd developer conveyance path 7 Front cutting board 8 Developer guide plate 9 Toner hopper 10 Toner density sensor 11 Toner density sensor (upstream side) 12 Toner density sensor (downstream side) 13 Hopper housing 14 Opening 15 Supply roller 31 Partition plate 50 Photoconductor drum

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroshi Yamazaki F-term (reference) 2H077 AA15 AB02 AB06 AB07 AC02 AD06 AD13 BA08 DA10 DA42 DA52 DA80 DB02 EA03

Claims (7)

[Claims] A toner supply means for supplying toner; a developing roller for disposing a fixed magnetic pole therein to apply a developer to an electrostatic latent image; and a developing roller provided in parallel with the developing roller. An electrostatic latent image developing device having a first developer transporting path including one developer transporting means, wherein the toner supply means drops and replenishes toner from above the first developer transporting path. The toner concentration sensors are disposed at positions upstream and downstream in the developer transport direction with respect to the toner replenishing area and in contact with the developer on the wall surface of the developer transport path. An electrostatic latent image developing device, characterized in that: 2. A toner density A detected by a toner density sensor on an upstream side in the developer transport direction, a toner density B detected by a toner density sensor on a downstream side, and a maintenance reference value C of toner density. When B <C, the toner supply amount D1 per unit time from the toner supply unit is A <C ≦
2. The electrostatic latent image developing device according to claim 1, wherein the toner supply amount is set to be higher than a toner supply amount per unit time D2 from the toner supply unit in the case of B. 3. A method according to claim 1, further comprising a second developer conveying path provided with a second developer conveying means at an intermediate portion between the first developer conveying path and the developing roller. 3. The electrostatic latent image developing device according to claim 1, wherein a partition plate is provided at a boundary of the developer conveying path except for both ends in the longitudinal direction. 4. The toner supply device according to claim 1, wherein the toner supply operation from the toner supply means is stopped when the values of A, B, and C satisfy C ≦ A, B. The electrostatic latent image developing device as described in the above. 5. The apparatus according to claim 1, wherein said means for adjusting the amount of toner replenishment per unit time comprises adjusting the ON / OFF time of driving of a toner replenishment motor.
3. The electrostatic latent image developing device according to item 1. 6. A developer supply path length of the toner supply area in the developer supply path direction is at least １ ／ of the entire length of the first developer transfer path.
5. The method according to claim 1, wherein the number is less than 5.
6. The electrostatic latent image developing device according to 5. 7. A copying machine for large-sized drawings of A2 size or more, characterized by using the electrostatic latent image developing device according to claim 1, 2, 3, 4, 5, or 6.