JP2839090B2 - Developing device for image forming apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a plurality of developing devices, and more particularly, to an image forming a plurality of colors by sequentially switching a plurality of developing devices. This relates to toner supply in a developing device of the forming apparatus. (Prior Art) Conventionally, an image forming apparatus that has a plurality of developing devices and is capable of forming an image in a plurality of colors by sequentially switching and operating the plurality of developing devices is known. Further, in an image forming apparatus having a toner concentration detecting unit for detecting the toner concentration and a toner replenishing unit for replenishing the toner, when the toner concentration is below the reference value, the toner replenishing unit is operated until the toner concentration reaches the reference value. Developing devices are also known. (Problems to be Solved by the Invention) By the way, according to the above-mentioned prior art, for example, the image forming apparatus has two developing units, a first developing unit and a second developing unit. In an image forming apparatus capable of forming an image, when a shortage of toner density is detected during development by a first developing device, a toner replenishing unit is operated to activate a first toner supply unit.
A configuration in which toner is supplied to the developing device is conceivable. When the operation is switched from the first developing device to the second developing device during the toner replenishing operation, the operation of the toner replenishing means is stopped together with the stop of the operation of the first developing device during the toner replenishment. Here, the reason why the operation of the toner replenishing unit is stopped together with the stop of the first developing unit during the toner replenishing operation described above is that if the toner replenishing unit continues to replenish the toner while the first developing unit is stopped operating, the replenishment is performed. This is based on the drawback that the accumulated toner accumulates in the toner receiving port of the first developing device, and the toner overflows from the developing device. Therefore, if the operation of the developing device is switched during the toner replenishing operation, the operation of the toner replenishing means is stopped together with the operation of the first developing device during the toner replenishing operation, so that the toner concentration may not reach the reference value. If the toner consumption amount exceeds the toner supply amount, the amount of toner in the developing device becomes insufficient, and the image density decreases. The present invention has been made in view of the above problems, and during the toner supply operation,
It is an object of the present invention to provide a developing device that reliably replenishes toner and uniformly supplies toner without overflowing toner or reducing the image density due to a shortage of toner even when the operation of the developing device is switched. I do. (Means for Solving the Problems) In order to achieve the above object, the present invention provides, in an image forming apparatus, a first developing device that selectively takes an operating state and a non-operating state, and selectively selects an operating state and a non-operating state. A second developing device,
A switching device for switching from the operating state of the first developing unit to the operating state of the second developing unit, a toner shortage detecting unit for detecting a toner shortage in the first developing unit in the operating state, and a detection result of the toner shortage detecting unit Based on the toner
A toner replenishing means for replenishing the developing device, a toner replenishing operation for operating the toner replenishing device for a predetermined time when the toner shortage detecting means detects a toner shortage in an operating state of the first developing device, and When the switching device switches the operation state from the first developing device to the second developing device during the operation, the first control means for interrupting the toner replenishing operation and the first control device after the operation of the second developing device is completed. The image forming apparatus further includes a second control unit that operates the developing unit and the toner supply unit to restart the interrupted toner supply operation. (Operation) Since the present invention has the above-described configuration, the first operating state is maintained.
When the shortage of toner in the developing unit is detected by the toner shortage detecting unit, and the shortage of toner is detected, a toner replenishing operation for operating the toner replenishing unit for a predetermined time by the operation of the first control unit is started. Is in operation, the toner is supplied without replenishing the toner in the toner receiving port. Even if the switching device is switched from the first developing device to the second developing device in the operating state during the toner supply operation, the first control means causes the toner to stop operating when the first developing device stops operating. By stopping the replenishing means, the toner replenishing operation is interrupted to prevent the toner from being replenished during the non-operation of the first developing device and the replenished toner from accumulating or overflowing in the toner receiving port. . In connection with the control, the second control means restarts the interrupted toner supply operation after the end of the operation of the second developing device, and the toner supply operation is accompanied by the operation of the first developing device. Replenishment of toner for a predetermined time can be achieved without replenishing toner remaining or overflowing in the toner receiving port, and there is no shortage of toner replenishment. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 3 shows a configuration of a photosensitive drum and a peripheral portion including two developing units in a two-color copying machine which is one of the image forming apparatuses. The configuration will be described together with a standard copying operation for copying a document image as it is. First, while the photosensitive drum 1 is rotating in the direction of arrow a, a constant charge is applied to the surface of the photosensitive drum 1 by the discharge of the charging charger 2. Next, the optical system 3
A light placed on a document placed on a platen glass (not shown) is irradiated with light, and the reflected light is exposed on the surface of the photosensitive drum 1 at an exposure point W via a mirror and a lens. A latent image is formed. This electrostatic latent image is transferred to the subsequent first developing device 4 or second developing device 5
Is supplied to the developing area X or X ', which is a portion opposed to the image forming apparatus, and is visualized by supplying the toner, and a document image is reproduced to form a toner image. On the other hand, the copy paper is conveyed to a transfer position, which is a portion facing the transfer paper charger 6, at a transfer position which is opposed to the transfer paper charger 6 by a timing roller pair (not shown), where the toner image is transferred to a copy. Then, the toner image is conveyed to a fixing device (not shown) by the conveyance belt 7, and the toner image is fused and fixed on the copy paper and discharged. The surface of the photosensitive drum 1 is thereafter scraped by a cleaner 8 to remove residual toner, and the residual charge is erased by light irradiation of an eraser lamp 9 to prepare for the next development. Reference numeral 10 denotes an inter-image / side eraser. In addition to the standard copying described above, this copying machine can perform an operation of obtaining a two-color copy having a different color according to the area in the scanning direction by one scanning operation (hereinafter, referred to as "one-scan two-color copying"). Therefore, the developing units 4 and 5 have a unique configuration, and FIGS.
An area designating mechanism 21 as shown in the figure is provided. First, the configuration of the developing units 4 and 5 will be described with reference to FIGS. The first and second developing devices 4 and 5 have substantially the same configuration,
In the developing tank 11, a developing sleeve 12, a supply roller 13 and a transfer screw 14 are arranged in order from the photosensitive drum 1 side. The first developing device 4 contains a developer composed of a magnetic carrier and an insulating color toner, and the second developing device 5 contains a developer composed of a magnetic carrier and a generally used insulating black toner. Is housed. The developing sleeve 12 is formed of a cylindrical body made of a non-magnetic conductive material, and has fine irregularities formed on an outer peripheral portion thereof. The developing sleeve 12 is opposed to the photosensitive drum 1 in the developing regions X and X 'with a developing gap. The rotation angle from the exposure point W to the development areas X and X 'is
α and α + β are set. Further, a spike height regulating member 15 is disposed on the rear side of the developing region of the developing sleeve 12. Inside the developing sleeve 12, a magnet roller 16 in which a plurality of magnets extend in the axial direction is disposed, and the magnetic poles located on the outer peripheral surface of the magnets are N ₁ and S _{1 in a} clockwise direction.
N ₂ , N ₃ , and S ₂ are arranged in this order, and the magnetic force is N ₁ > S ₁ = S ₂ > N ₂ = N ₃ . Further, pivotable between a posture between the posture and the magnetic pole N ₁ and S ₂ which magnetic poles N ₁ at the developing sleeve 16 is not shown drive means facing the developing region X or X 'is opposed to the developing area It has been. On the other hand, the developing sleeve 12, the supply roller 13 and the transfer screw 14 are driven by a drive motor (not shown) by arrows b, c and d.
It is made to rotate in conjunction with each other in the direction. Also, one end of the transfer screw 14 is
As shown in the figure, it extends to a toner receiving portion 17 formed on one side of the developing tank 11. The toner receiving section 17 is configured to mount a toner bottle 18, and in the mounted state, the toner removing member 19 is controlled by a toner supply motor 20.
Is rotated so that toner is supplied to the transfer screw 14 in accordance with the rotation. Next, the area designating mechanism 21 will be described with reference to FIGS. 6 and 7. FIG. A guide groove 23 is formed on the side of the platen glass 22 along the scanning direction, and a designated lever 24 is slidably mounted in the guide groove 23, and the document placing surface is moved in two regions at the position of the designated lever 24. It is configured to be divided into l ₁ and l _2. A magnet 25 is provided at a lower portion of the designation lever 24 located inside the copying machine main body. On the other hand, the optical system scanner 26 is provided with a reed switch 27 so as to detect the magnet 25 and output its signal to a control device (not shown). In FIG. 6, an operation panel 28 is provided with a print switch 29, a one-scan two-color switch 30, and the like. Next, the operation of one-scan two-color copying will be described. First, when turning on the power by turning on the main switch of the copying machine, the intermediate portion of the magnetic pole N ₁ and S ₁ in the first developing unit 4 is opposed to the photosensitive drum 1, the magnetic pole N ₁ in the second developing unit 5 The second developing device 5 is in an operable state facing the photosensitive drum 1. When the print switch 29 is turned on in this state, the second developing device 5 containing the black toner is automatically driven to execute the standard copying operation.
Is turned on, the copying mode becomes the one-scan two-color copying mode, the second developing device 4 is in the operating state, and the second developing device 5
Becomes inactive. Further, the area can be designated by the designation lever 24. In this state, the development S is placed on the platen glass 22 and the area is designated by the designation lever 24. Next, when the print switch 29 is turned on, the developing sleeve 12, the supply roller 13, and the transfer screw 14 of the first developing device 4 corresponding to the area l ₁ are driven by the drive motor to respectively indicate the arrow b,
The first developing device 4 operates by rotating in the c and d directions. Next, the scanner 26 starts operating, and the original S placed on the original platen glass 22 is irradiated with light, and the reflected light is applied to the exposure point W.
Then, the surface of the photosensitive drum 1 is irradiated to form an electrostatic latent image, and the developing operation using the color toner is started in the operating first developing device 4. Next, when the magnet 25 of the designated lever 24 is detected by the reed switch 27 of the scanner 26, the electrostatic latent image at the boundary between the _two regions l ₁ and l ₂ is at the exposure point W at this time. The electrostatic latent image at the boundary is located in the developing area X of the first developing device 4.
The first developing device 4 operates until it moves to (1), and then becomes inactive. Thereafter, the electrostatic latent image at the boundary is moved to the region l ₂
After a lapse of time until the moved to the developing region X 'of the second developing device 5 corresponding to, the second developing device is operated, a region l ₂
Is supplied with black toner to perform black and white development, and this state is maintained until the scan is completed. By the way, during the above-mentioned standard copying operation, when the toner density detection signal provided from the toner density detecting means provided in the second developing device 5 is output, as shown in FIG. toner supply motor 20 for a predetermined time t ₀ is activated during operation, the supplied toner in a required amount, supplied toner is uniformly into the developing tank 11 for feed screw 14 and the supply roller 13 is in operation Supplied. On the other hand, in the one-scan two-color copying mode, if the toner density shortage signal is output while the first developing device 4 is operating, the first developing device 4 stops operating as shown in FIG. the toner is replenished t ₁ hour only toner supply motor 20 is operated to. If the toner is replenished only during the operation time of the first developing device 4 in this manner, the toner consumption may exceed the toner replenishment amount, and the amount of toner in the developing tank 11 may be insufficient to lower the image density. Become. In particular, one scan 2 for color copying, the first region l ₁ is liable to be assumed many characters per area region area such as the title character, for example, the area of the ordinary character is an average of 7%, 20% or more in the title portion And toner consumption is high. However, since the area of the title portion is usually as short as 70 mm or less, if the normal toner supply amount is secured, the amount of toner consumption will be sufficiently high, so that
It is necessary to secure a normal toner supply amount. Thereafter, when the second developing device 5 operates and a toner density shortage signal is output at that time, the toner supply motor 20
Operates to supply toner. At this time, if the second operation time of the developing device 5 or t ₀ hours needed to perform the required amount of toner supply after the toner density shortage signal is output, the toner supply is completed. Next, after the operation of the second developing unit 5 is completed and the copying operation is completed, the first developing unit 4 supplies toner corresponding to the insufficient toner supply amount during a time between the next copying operation. to do, t ₂ hours toner supply motor 20 is to supply the toner _{actuated, t 0 = t 1 + t} 2 hours required for the toner supply is ensured. At the same time, the drive motor of the developing device 4 is also operated to rotate the transfer screw 14 and the supply roller 13 to prevent the toner supplied to the toner receiving port 17 from accumulating and overflowing. Further, at that time, a voltage applied during development as a developing bias, a voltage larger than 150 V, 40
0 V is applied, and as a result, unnecessary toner does not adhere to the photosensitive drum 1 and is not wasted. Instead of increasing the developing bias, the developing bias may be lowered. Alternatively, the charging charger 2 may be turned off, or the photosensitive drum 1 may be turned off using an exposure lamp or an inter-image / side eraser 10.
For example, means for lowering the surface potential may be used. In the above embodiment, the first region l ₁ is the first developing device 4 and the second region
The regions l ₂ there is shown an example of developing respectively in the second developing device may be able to be arbitrarily combined area a developing device provided with a selection switch. In addition, a toner comprising a magnetic carrier and a toner as a developer is used.
Although a one-component developer is exemplified, the present invention can be similarly applied to a case where a one-component developer is used. As a means for detecting toner shortage, in the case of a two-component system, a method in which toner density is detected by a change in developer magnetic permeability is preferably used. May be used. (Effects of the Invention) As described above in detail, in the present invention, the operation of the developing device is switched during the toner replenishment operation due to the detection of the toner shortage, and the operation of the developing device during the toner replenishment is switched with the switching of the operation. Upon completion, the toner replenishing operation is stopped, and after the image forming operation is completed, if the toner replenishment is not completed, the toner replenishment is performed again. Therefore, the toner does not overflow and the image density does not decrease. The toner can be supplied at the same time, and the toner can be supplied uniformly.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings show one embodiment of the present invention, and FIG.
FIG. 2 is a timing chart of color copying operation, FIG. 2 is a timing chart of normal copying, FIG. 3 is a configuration diagram around a photosensitive drum of a copying machine, FIG. 4 is a perspective view of a main part of a developing device, and FIG. FIG. 6 is a vertical sectional front view, FIG. 6 is a schematic plan view of a copying machine, and FIG. 7 is a schematic front view of an area designation mechanism. 1. Photoconductor drum 4 First developing device 5 Second developing device 20 Toner supply motor 21 Area designating mechanism l ₁ , l ₂ .

Claims (1)

(57) [Claims] In the image forming apparatus, a first developing device that selectively takes an operating state and a non-operating state, a second developing device that selectively takes an operating state and a non-operating state, and the second developing device based on the operating state of the first developing device Switching device for switching the operation state of the developing device, toner shortage detecting means for detecting toner shortage in the first developing device in the operating state, and supplying toner to the first developing device based on a detection result of the toner shortage detecting means. A toner replenishing unit that starts the toner replenishing operation for operating the toner replenishing unit for a predetermined time when the toner shortage detecting unit detects a toner shortage in an operation state of the first developing device; When the device switches the operation state from the first developing device to the second developing device, first control means for interrupting the toner supply operation, and after the operation of the second developing device, the first developing device By operating a toner replenishing unit, a developing device of an image forming apparatus characterized by having a second control means to resume the toner supply operation is interrupted.