JPH04177278A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent a charging-up phenomenon of a developer agent by a method wherein a set image concentration value is varied continuously or in a stepwise manner in response to an image concentration set value of a forming image set by an operator. CONSTITUTION:A toner concentration control circuit is comprised of a comparing circuit for comparing a signal output V of an original concentration sensing sensor 22 with a predetermined reference value DDENS and a counter circuit. This comparing circuit outputs a high concentration signal when an output signal V of the original concentration sensing sensor 22 is higher than an output reference value VDENS under a predetermined reference concentration, i.e., when the concentration is high. The counter circuit controls a latent image forming part and a developer sleeve or the like for use in forming an electrostatic latent image on a photosensitive drum 9 when the high concentration signal is a predetermined time or less within a predetermined time, forms a full latent image of a predetermined width to a surface of the photo-sensitive drum 9 and develops the latent image. An output reference value VDENS under a reference concentration is set to be varied continuously or in a stepwise manner in response to an image concentration set value of the formed image set by a user. With such an arrangement, a charging-up of the toner is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. The present invention relates to an image forming apparatus such as an electrophotographic type or an electrostatic recording type. The present invention relates to an image forming apparatus having a developing device that performs development.

Conventionally, electrophotography includes a step of forming an electrostatic latent image on the surface of a latent image carrier such as an electrophotographic photoreceptor, developing the latent image with a developer, and making it visible. Well-known image forming apparatuses using this process include those that use magnetic toner as a developer;
Alternatively, those using a two-component developer containing a toner and a magnetic carrier are widely (practical).

In such an image forming apparatus, a developing device that visualizes a latent image has a developer storage section containing a developer containing toner, and generally, a stirring member is disposed within the developer storage section. After toner is supplied from the outside into the developer accommodating portion, the developer is transported to the developer carrier side by the stirring member.

In particular, in a conventional developing device using a two-component developer, the developer is stirred by the stirring member to uniformly disperse the toner in the magnetic carrier. Therefore, the above stirring causes friction between the toner and the magnetic carrier, and the toner is charged to a desired amount of charge.

However, in the above-mentioned conventional image forming apparatus, the stirring operation of the developing device is performed intermittently while the developing operation continues. Therefore, for example, when copying a document with extremely low toner consumption, In such a case, toner may not be supplied and excessive stirring may occur.

As is well known in the industry, when the developer is over-stirred in this way, a phenomenon occurs in which the image density becomes low due to so-called toner charge-up, resulting in a problem in which the quality of the developed image deteriorates. .

Therefore, in order to solve the problems associated with the above-mentioned image density groove, the present applicant has proposed that the toner replenishment signal from the developer amount detection means provided in the developing device be sent a predetermined number of times within a preset time. If it is determined that no occurrence has occurred, an electrostatic latent image is formed on the latent image carrier, and this electrostatic latent image is developed to release the charged up toner from the developer carrier, and then the developer is developed. We have proposed a developing device in which the amount of charge of the toner on the developer carrier is always at a desired value by promoting the replacement of the toner on the developer carrier.

In addition, considering that the number of toner replenishment signals does not necessarily reflect the toner replenishment amount accurately, the density of the original image is detected and if the density exceeds a certain reference value even once within a certain predetermined period of time. A developing device has also been proposed in which the above-mentioned toner replacement operation is performed when a document is not being copied, so that the amount of charge of the toner on the developer carrier always remains at a desired value.

The control method described above, which detects the original image density and replaces the charged toner, is based on the control method that detects the original image density and replaces the charged toner. Since the amount of toner consumption is determined by both the density and density, it cannot necessarily be said that the amount of toner consumed accurately reflects the density of the original document image. There is.

Therefore, if the user has set the image density of the formed image to be extremely dark (or light), the control sequence of replacing the charge-up toner on the developer carrier in the above conventional example may not work correctly. The problem was that it did not.

Therefore, an object of the present invention is to obtain a set image density value vI)! By changing (2) continuously or stepwise according to the image density setting value of the formed image set by the user, the control sequence for replacing the charged up developer on the developer carrier can be operated accurately. , thereby providing an image forming apparatus that can always obtain high quality images.

・In order to The above object is achieved by an image forming apparatus according to the present invention.

In summary, the present invention provides a latent image carrier, an electrostatic latent image forming means for forming an electrostatic latent image on the latent image carrier, a developer supported on the developer carrier, a developing device for developing an image; a document image density detection means for detecting the document image density or image area ratio before or during the formation of the electrostatic latent image; density setting means for setting density, and the density signal value detected and output by the document image density detection means is set to a preset image density setting reference value v110. If a state lower than 1000 continues for a predetermined period of time, a latent image of a predetermined shape is formed on the latent image carrier by the electrostatic latent image forming means, and the latent image is developed by the developing device. In the image forming apparatus, the image density setting reference value v0. ．． An image forming apparatus is characterized in that the image density changes continuously or stepwise in accordance with the image density setting value of the formed image set by the user.

Preferably, the image density setting reference value ■. tNg is further configured to change in conjunction with temperature, humidity, or both temperature and humidity. As a result, the frequency of replacing the charge-up toner can be changed in response to changes in the charge-up state of the developer, that is, the toner, due to changes in the environment, so that the amount of charge on the toner can always be controlled within an appropriate range. configured.

Support 11 Hereinafter, the image forming apparatus according to the present invention will be described in more detail based on the accompanying drawings.

FIG. 1 shows an electrophotographic copying apparatus showing one embodiment of the present invention. In this embodiment, a latent image carrier 9, which is a drum-shaped electrophotographic photoreceptor, is rotatably supported, and an optical exposure means is arranged above it.

That is, an original platen glass 3 is arranged above the latent image carrier, that is, the photosensitive drum 9, and an original (such as a photographic original or a composite original consisting of photographs and text) 2 is placed on the original platen glass 3. Press with the rear document pressure plate 1. Note that the surface of the document pressure plate 1 that comes into contact with the document table glass 3 is white.

The document 2 is scanned by a scanning optical system well known to those skilled in the art, which includes a document illumination lamp 4 such as a halogen lamp, mirrors 5a to 5c, and an optical lens 6,
An image is formed on a photosensitive drum 9 rotating at a constant speed via mirrors 5d to 5e.

Original image density detection means, that is, original density detection sensor 2
2 is attached to the side of the optical lens 6. Document image density detection is performed by scanning the document image with the lamp 4 in advance and allowing reflected light from the document image to enter the sensor 22 before starting the copying process.

According to this embodiment, a semiconductor laser, a polygon mirror,
A laser light source section 7 composed of an imaging lens, a scanner motor, etc. is provided, and emits a laser beam based on exposure data output from a controller 12 to expose a photosensitive drum 9 via a folding mirror 8.

Image forming means for an electrophotographic process is arranged around the photosensitive drum 9. That is, the static elimination lamp 1 eliminates the residual charge on the photosensitive drum 9 in preparation for the image forming process.
0. A primary charger 11 that uniformly charges the photosensitive drum 9. An electrostatic latent image forming means such as the above-mentioned exposure means, and a first developing device 13 that contains, for example, a red developer and develops the electrostatic latent image formed on the photosensitive drum 9 in red, for example, a black developer. A second developing device 14 that accommodates a developer and develops the electrostatic latent image formed on the five photosensitive drums 9 to black is disposed.

Note that one of the first developing device 13 and the second developing device 14 is disposed close to the photosensitive drum 9, and the other developing device is disposed close to the photosensitive drum 9, depending on a developing control signal from the controller 12. The device is placed in a retracted position with respect to the photosensitive drum 9.

The developed image, that is, the toner image on the photosensitive drum 9 is conveyed via the conveyance guide 20, and then stopped at the registration roller position, and synchronized with the leading edge of the toner image formed on the photosensitive drum 9. The image is transferred onto the recording paper 21 which is then re-fed by the action of the transfer charger 15. After the recording paper 21 is separated from the photosensitive drum 9 by the separation charger 16, it is transported to the fixing device 19 by the transport belt 18. The fixing device 19 applies pressure to the toner image transferred to the recording paper 21 using a heat roller and a pressure roller, and thermally fixes the toner image on the recording paper 21 .

On the other hand, the toner remaining on the photosensitive drum 9 is removed by a cleaner 17.
Collect it with.

FIG. 2 is a sectional view of the developing device 13. Developing device 13
The interior thereof is divided by a partition wall 35 into a toner storage section that stores toner and a developer storage section C that stores a two-component developer containing a magnetic carrier. Note that the toner stored in the toner storage portion and the developer in the developer storage portion C are omitted for clarity.

The developer storage section C is divided by a partition wall 34 into a developer stirring section C1 and a developer supply section C2 to the developer carrier 31. The developer stirring section C1 and the developer supply section C2 are provided with screws 33 and 32, respectively. The details will be described later.

The stored toner in the toner storage section is transported by a toner conveying member 39.
When the toner is rotated, the toner is replenished into the developer accommodating portion C from the toner replenishing port 36. Toner replenished from the replenishment port 36 located on the most downstream side of the screw 33 (see FIG. 3) begins to be conveyed onto the developer carrier 31 within a few seconds. Therefore, when the replenished toner reaches the developer carrier 31, it must be sufficiently stirred and mixed with the developer.

Therefore, in this embodiment, as shown in FIG. 3, the toner supply port 36 disposed at the most downstream side of the screw 33 and the developer stirring section C1 are connected to the developer carrier 31 and the developer supply section C2. A fin-like member 33b is disposed on the screw 33 between the developer amount and the opening 34b, which is a transfer section.

According to the above configuration, a temporary turbulent flow of the developer causes a stagnation state at the position where the fin-like member 33b is disposed, and in this turbulent flow state, the developer and the supplied toner are sufficiently mixed. are stirred and mixed, and then the receiver is transferred to the transfer section 34b.
transported to.

The developer carrier 31 is disposed within the developer storage section C, and has a developing sleeve 31a made of a non-magnetic material and having a built-in magnet roll 31b. N, , N2 in the diagram
．． N,,S,,S,,S.

indicates the magnetized position of the magnet roll 31b.

Since the magnet roll 31b is fixedly supported at both ends, it does not rotate, and the developing sleeve 31 disposed outside the magnet roll 31b does not rotate.
a is rotated around the magnet roll 31b at a predetermined circumferential speed in the direction of the arrow in the figure.

The screws 32 and 33 are connected to the developing sleeve 31, respectively.
The two screws 32 and 33 act as a developer stirring and conveying means arranged substantially parallel to each other, and the developer conveying directions of these two screws 32 and 33 are set to be opposite to each other. In this embodiment, the developer is set to be conveyed in the direction of the arrow in FIG. □ As shown in FIG. 3, the partition wall 34 provided in the developer storage section C has openings 34a and 34b formed at both ends thereof, and the developer transported by the screws 32 and 33 passes through the openings. The developer is received and transferred through 34a and 34b. As described above, fin-like members 32a, 32b and 33a, 33b are attached to the screws 32 and 33 at the positions shown in the figure so that the developer can be quickly transferred.

Furthermore, developer storage portion C of the developing device 13 is provided with developer amount regulating members 41 and 45 for specifying a developer circulation area on the circumferential surface of the developing sleeve 31a.

A part of the developer on the circumferential surface of the developing sleeve 31a is scraped off by a developer scraping member 43, and the rest is transported toward the developing section. The developer scraped off by the scraping member 43 is conveyed while being mixed with the developer conveyed by the developer conveyance screw 32. Further, a portion of the developer transported by the transport screw 32 passes through the opening 47 and is transported toward the developing sleeve 31a. As the developing sleeve 31a rotates, the developer transported toward the developing section facing the photosensitive drum 9 is pushed into the gap between the developer circulation regulating member 41 and the developing sleeve 31a, and is quickly and densely packed. transported. Further, the height of the brush of the developer is regulated by the doctor blade 46, and the developer is conveyed to the outside of the developing device 13.

Further, at a predetermined position within the same plane as the surface of the developer amount regulating member 41 facing the developing sleeve 31a, a developer amount detecting member 42 as a developer concentration detecting means is disposed.

By arranging the developer amount detection member 42 at the above position, the developer can be quickly transported to the developer amount detection member 42 necessary for toner concentration control, and the developer can be properly transported to the developer amount detection member 42. The conditions of stirring, mixing state, predetermined development arrangement and uniformity of density necessary for detection in the developer amount detection member 42 are satisfied.

In particular, since the detection surface of the developer amount detection member 42 is disposed in the same plane as the surface facing the developing sleeve, the flow of developer in the detection area and the flow of developer outside the detection area are the same, and the developer amount detection member 42 is disposed close to the developing sleeve 31a can be eliminated.

FIG. 4 shows an enlarged cross-sectional view of the developer amount detection member 42. As shown in FIG.

In this embodiment, the developer amount detection member 42 includes a lamp 42 as a light emitting body for measuring the amount of toner in the developer.
a, and a sensor 42 that detects the amount of light reflected by the developer from the lamp and the amount of direct light from the lamp, respectively.
b and 42c. Moreover, the housing 48 is
The detection window 44, which is formed of a light-shielding member and a light-transmitting member, is disposed at a predetermined position on the same surface as the surface of the developer amount regulating member 41 facing the developing sleeve 31a. ing. The amount of light incident on the sensors 42b and 42c is converted into voltage by a predetermined circuit, which will be described later.

The voltages from the sensors 42b and 42c are respectively ■. ,■
o, and the standard value that makes the developer reach the specified density is ■.

In this case, the amount increases or decreases in accordance with the increase or decrease in the toner concentration. Now, turn on toner supply so that V = V0,
Toner density control circuit (not shown) that provides an off signal
When VC is adjusted, the toner concentration control circuit determines that the toner concentration is high when vIl≧■o because vc is always constant, and that the toner concentration is appropriate, and turns off toner replenishment. Toner conveying member 3
9 and 40 to a controller (not shown). Also, ■5〈■. At this time, the toner concentration control circuit supplies a toner replenishment signal to the controller, and the controller supplies a toner replenishment signal having a replenishment pattern as shown in, for example, FIG. 8 to the toner replenishment control section. The toner replenishment control section controls the toner concentration of the developer to a predetermined value by driving the toner conveying members 39 and 40 in synchronization with the replenishment pattern signal and supplying toner to the developer storage section C. do.

Moreover, in this example, the reference value ■. In addition to the second reference value V
Cl is set, and this ■. , and the potential v1□ of the toner density limit of the density groove. and standard value■. is set in advance to satisfy the following conditions: v, I, VCl, vc.

Figures 5 and 6 show examples when the toner density detection signal is output as a potential. Figure 5 is for an original with a small image ratio, and Figure 6 is for an original with a high image ratio. Number of copies (or time) and sensor potential (toner density)
The relationships between the two are shown.

As is clear from the figure, the behavior of the sensor potential V, decreases gradually when copying an original with a small image ratio, and sharply decreases when copying an original with a large image ratio. decreases to Therefore, when the second reference value V Cl is set as described above, for example, if the second reference value is set to the point where the toner replenishment amount no longer catches up with the consumption, toner replenishment is performed according to the toner consumption amount. , always, V
b>V c l, and when toner supply cannot keep up with the amount of toner consumption, vl<vc1. Therefore, for example, as shown in the flowchart of FIG. 9, when ■■o≦■5, toner supply is turned off (step 80 in the figure), ■■. , ≦V, <VC, copy status and toner replenishment is on (step 82 in the same figure), ■■. < Vc
+, if control is performed to temporarily stop copying and turn on toner supply (steps 84 and 86 in the figure), the seventh
As shown in the figure, even when a document with a large image ratio is continuously copied, the toner density can be controlled so that the sensor potential vI is between 1 and Vs+ax.

Furthermore, this embodiment solves the so-called density gap caused by toner charge-up, which occurs when the toner is not consumed and only agitation continues when copying a document with very low consumption. Therefore, the toner density control circuit is provided with a comparison circuit that compares the signal output (2) of the original density detection sensor 22 with predetermined reference values DI and E1, and a counting circuit as a counting means.

The comparison circuit outputs a reference value (2) when the output signal (2) of the document density detection sensor 22 has a predetermined reference density. E
When the density is higher than Nfi, that is, when the density is high, a high density signal is output.

The counting circuit includes a latent image forming section and a developing sleeve 31 for forming an electrostatic latent image on the photosensitive drum 9 as a latent image carrier when the high density signal is less than a predetermined number of times within a predetermined time.
A and the like are controlled to form a solid latent image of a predetermined width on the surface of the photosensitive drum 9 and to develop the latent image.

Further, according to the present invention, the output reference value v at the reference concentration is
The oExs is set to change continuously or stepwise in accordance with the image density setting value of the formed image set by the user.

In other words, the output reference value VDI at the reference concentration! The relationship between Nl and the image density setting value of the formed image is that the darker the image density setting value, the higher the reference value ■. , , are set lower, and the reference values ■ and □ are set higher as the image density setting becomes lighter. For example, the 10th
When there is a change in the image density of the copy document as shown in the figure, if the image density setting is low, Vot=v1; if it is standard, Vot□=v2; if it is dark, V. ! N5=
va, it can be seen that the frequency at which a solid latent image is formed and developed varies depending on the height of VOW□. The embodiment shown in FIG. 10 assumes a control sequence in which a solid latent image is formed and developed if no high density signal occurs within a predetermined period of time.

By adopting such a control method, it is possible to correct differences in toner consumption due to differences in image density settings for formed images, perform solid development at appropriate timing, and replace charge-up toner. Become.

In this embodiment, the solid developed image formed as described above is not transferred onto the transfer paper, but is removed as it is by the cleaning member. as needed,
It is also possible to adopt a configuration in which a solid developed image is transferred onto recording paper. Further, in this embodiment, a --like solid latent image is formed, but the solid latent image may have, for example, a predetermined pattern.

In the first embodiment, an optical detection method is used as the toner concentration detection means, but the toner concentration detection means is not limited to this. For example, other methods such as volume detection, magnetic permeability detection, dielectric constant detection, etc. A method may also be used. Furthermore, the configuration of the image forming apparatus is not limited to the electrophotographic copying apparatus of the first embodiment.

Detection of the original image density is not limited to being performed before the developing operation, but can also be performed simultaneously during the developing operation, or can be performed after the developing operation is completed.

In the first embodiment described above, a developer having a magnetic carrier and a toner, that is, a two-component developer was used, but the present invention is not limited to this, and according to other embodiments of the present invention, A one-component developer may be used in which the amount of charge deviates from the appropriate range in the case of excessive stirring. Further, the method is not limited to the case where the amount of charge exceeds the upper limit of the appropriate range (although it may be used when the amount of charge exceeds the lower limit).

Further, in the first embodiment, the case where the toner charge amount is in an over-stirred state is explained as an example; however, the present invention is not limited to this, and one of the developer characteristics is when the toner is in an over-stirred state. The principle of the present invention can be effectively employed in cases where the value deviates from the appropriate value.

Furthermore, according to another preferred aspect of the present invention, the image density setting reference value VDt□ can be further configured to change in conjunction with temperature or humidity, or both temperature and humidity, As a result, the frequency of replacing the charge-up toner can be changed in response to changes in the charge-up state of the toner due to changes in the environment, and the amount of charge on the toner can always be controlled within the appropriate range. As described, the image forming apparatus according to the present invention has a set image density value V. o3 is changed continuously or stepwise according to the image density setting value of the formed image set by the user, even if the user sets the image density of the formed image very darkly or very lightly. Even in cases where the developer is charged up, the control sequence for replacing the charged up developer on the developer carrier can be operated accurately, thereby preventing the developer from being charged up and ensuring that high-quality images can always be obtained. It has the following effects.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a sectional view of the developing device. FIG. 3 is a top sectional view of the developing device. FIG. 4 is a sectional view of the developer concentration detection section. FIGS. 5 to 7 are diagrams showing examples of output from the developer concentration detection sensor. FIG. 8 is a diagram showing an example of a toner supply pattern. FIG. 9 is a flowchart for explaining the present invention in detail. FIG. 10 is a diagram showing an example of a pattern for forming and developing an image of a predetermined shape according to the present invention. 9: Latent image carrier 11 primary charger 13. 14: Developing device 22: Original image density detection means 42: Developer concentration detection means ゝ-11/

Claims (1)

[Claims] 1) A latent image carrier, an electrostatic latent image forming means for forming an electrostatic latent image on the latent image carrier, and a developer for supporting a developer on the developer carrier and developing the electrostatic latent image. a document image density detection means for detecting the document image density or image area ratio before or during the electrostatic latent image formation; setting means, and the density signal value detected and output by the document image density detection means is set to a preset image density setting reference value V_
When a state lower than D_E_N_S continues for a predetermined period of time, a latent image of a predetermined shape is formed on the latent image carrier by the electrostatic latent image forming means, and the latent image is developed by the developing device. In the image forming apparatus, the image density setting reference value V_D_E_N_S is configured to change continuously or stepwise according to the image density setting value of the formed image set by the user. Device.