JPH08110696A - Image forming device - Google Patents

Abstract

PURPOSE: To control T/C ratio in an adequate range even in the consecutive image forming time by changing the replenishment table for deciding the replenishment time depending on T/C ratio basing on the maximum value or the minimum value of the ripple. CONSTITUTION: By the term of T/C ratio, the toner concn. namely, T/(T+C)×100 is shown, and T stands for the toner weight and C stands for the carrier weight. Then, on detecting the maximum value and the minimum value of the ripple of T/C ratio, if the maximum value or the minimum value is deviated by a specified amount from the set value of T/C ratio, the replenishment table is changed. Namely, such as the curve (a) for instance, when the maximum value of T/C ratio exceeds the designed value of T/C ratio that is 5%, by +1%, the replenishment time of the toner is reduced about 20% from the straight line (d) showing the original value of designed value, as shown in the straight line (e) of the replenishment table. Similarly, when the minimum value of T/C ratio exceeds the designed value that is 5%, by -1% as shown by the point B of the curve (b), the replenishment time of the toner is increased about 20%, as shown in the straight line (f) of the replenishment table.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic or electrostatic recording type image forming apparatus, and is preferably embodied in, for example, a black and white or color electrophotographic copying machine or printer.

[0002]

2. Description of the Related Art FIG. 5 shows a color electrophotographic copying machine using a laser beam exposure apparatus as an example of a conventional image forming apparatus.

According to the color electrophotographic copying machine of this embodiment, the photosensitive drum 1 which is an image carrier is rotatably supported so as to rotate in the direction of the arrow, and the image forming means is arranged around it. In other words, the photosensitive drum 1 is uniformly charged by the primary charger 2 and is subjected to color separation by the exposure means including a laser beam exposure device or an optical image E corresponding thereto.
Is irradiated, and an electrostatic latent image is formed on the photosensitive drum 1.
The electrostatic latent image on the photosensitive drum 1 is developed by each color developing device 4 and visualized as a toner image.

The developing device 4 includes four developing devices 4Y, 4M, 4 for accommodating four color developers of magenta color developer, cyan color developer, yellow color developer and black color developer, respectively.
It has C and 4K. The developing device 4 brings a desired developing device into contact with and separates from a position facing the outer peripheral surface of the photosensitive drum 1, and develops the electrostatic latent image on the photosensitive drum 1. The developing device will be described in detail later.

The transfer material P is supplied from the paper feeding device to the transfer device 3, carried by the transfer device 3 and conveyed in the direction of the arrow.
The toner image on the photosensitive drum 1 is transferred to the transfer material P carried by the transfer device 3.

In other words, the transfer device 3 is constructed by, for example, a transfer sheet 3a made of a dielectric sheet or the like being stretched on a cylindrical drum frame. The transfer material P is the registration roller 2
8, the image is sent to the transfer device 3 in synchronization with the image. The transfer material P fed to the transfer device 3 is charged by the adsorption charger 23.
And the conductive roller 24 adsorbs and holds the transfer sheet 3a.

The toner image of the first color on the photosensitive drum 1, for example, a magenta toner image, is transferred onto the transfer material P by the transfer charger 6. Photosensitive drum 1 after toner image transfer
The surface (5) is repeatedly used for image formation after removing adhered contaminants such as residual toner by the cleaner 5.

Subsequently, toner images of the second, third and fourth colors, for example, cyan, yellow and black toner images are formed on the photosensitive drum 6 in the same manner.
Then, the image is transferred onto the transfer material P by using the transfer charger 6.

After the transfer process is completed, the transfer material P weakens the attraction of the transfer material P to the transfer sheet 3a.
After a pair of AC corona dischargers 7 and 8 which face each other with "a" interposed therebetween are used to remove the electric charge, they are separated from the transfer sheet 3a. At this time, AC corona discharge is performed using the corona discharger 9 in order to prevent image disturbance due to peeling discharge that occurs when the transfer material P and the transfer sheet 3a are separated.

After the transfer / separation process is completed, the transfer material is sent to the fixing device 26 via the conveyor belt 25 and is fixed by heating and pressing.

As a developing device of the image forming apparatus, a yellow developing device 4Y will be described as an example in FIG. Each developing device 4
Y, 4M, 4C, and 4K have the same configuration. The yellow developing device 4Y is a developing container 16 containing a two-component developer 19.
On the side of the developing container 16 facing the photosensitive drum 1, a developing sleeve 11 as a developer carrying member is rotatably arranged. Inside the developing sleeve 11, a magnet roller 12 having a plurality of magnetic poles as a magnetic field generating means is fixedly arranged. Further, inside the developing container 16, stirring screws 13, 14 and a regulating blade 15 for forming a thin layer of the developer 19 on the surface of the developing sleeve are provided.

The developer amount of the thin developer layer formed on the surface of the developing sleeve 11 is about 50 mg / cm ² . The amount of the developer is obtained by peeling off the thin layer of the developer on the developing sleeve for a certain area and measuring the weight.

Here, a developing step of visualizing the electrostatic latent image by a two-component magnetic brush method using the developing device 4Y,
The developer circulation system will be described.

As the developing sleeve 11 rotates in the direction of the arrow so that the direction of rotation of the developing section facing the photosensitive drum 1 is the same direction as that of the photosensitive drum 1, the N ₂ pole of the magnet roller 12 is pumped up. The two-component developer 19 is S
_{In the} process of being transported from the _second pole to the N ₁ pole, a thin layer of the developer is formed on the developing sleeve 11 by being regulated by the regulating blade 15 arranged perpendicularly to the developing sleeve 11. When the developer formed in this thin layer is conveyed to the main developing pole S ₁ pole, the developer stands up due to the magnetic force.
The electrostatic latent image is developed by the developer which is erected. After that, the developer on the developing sleeve 11 is returned into the developing container 16 by the repulsive magnetic fields of the N ₃ pole and the N ₂ pole.

Next, a two-component developer concentration detecting device (AT
R) will be described. In FIG. 7, reference numeral 100 indicates an ATR. As shown in FIG. 7, the ATR 100 is directly above the developing sleeve 11 and is in a position where it slides against the developer 19. The ATR includes a window 102 having a rubbing surface such as Teflon (trademark) and an infrared LE on the inner surface thereof.
It has a D light emitting element 104 and an infrared light receiving element 106.

Infrared rays are emitted through the window 1 by the LED light emitting element 104.
When the developer 19 is irradiated through 02, infrared rays are reflected in an amount corresponding to the toner concentration of the developer. This is because the carrier has almost no infrared ray reflection capability, and only the toner reflects infrared rays. When the developer contains a large amount of toner, the amount of reflected infrared light is large, and when the toner is small, the amount of reflected infrared light is small. The amount of toner in the developer can be measured by detecting the amount of reflected light of infrared rays by the light receiving element 106.

When the ATR 100 determines that the toner amount is small, the toner replenishing device (hopper) 22 is used.
The toner 18 is sent out from the above by the screw 20 and is replenished to the developer 19 in the developing container 16. If it is determined that the amount of toner is large, the above operation is not performed.

FIG. 8 is a graph showing the relationship between toner density and ATR output. In FIG. 8, T / C ratio is toner concentration,
That is, T / (T + C) × 100 is shown. T is the toner weight and C is the carrier weight. As can be seen from FIG.
In this example, when the T / C ratio is 5% (weight%) of the center value, the ATR output from the light receiving element 106 is adjusted to be 4V. If the T / C ratio is reduced by 1% (-1%), the ATR output will be reduced to 3.5V. Conversely, if the T / C ratio increases by 1% (+ 1%), the ATR output will be 4.5.
It increases to V. The linearity of the change in the ATR output with respect to the change in the T / C ratio is as follows:
It is held up to about ± 3%.

FIG. 9 is a graph showing the relationship between the ATR output and the toner supply amount. If it is determined that the toner amount is large, that is, if the T / C ratio is high, it is determined that the toner amount is small without replenishing the toner as described above, that is, the T / C ratio is When the low level is detected, the toner supply amount is increased according to the detection level. A graph used for such replenishment is called a replenishment table.

From the above, the ATR of the image forming apparatus should be kept within ± 1% of the ripple of the T / C ratio in the continuous copying (the ripple of the T / C ratio will be described later).
It is designed to control a series of operations from toner concentration detection to toner replenishment.

The developer used in each developing device will be described. The magenta, cyan, yellow, and black developers, which are the color developers of the developing devices 4M, 4C, 4Y, and 4K, include a magnetic carrier and a low-melting point non-magnetic toner described later.
A component developer is used.

This two-component developer has a T / C ratio of toner to carrier of 5%, that is, T / (T + C) × 100 = 5%.
It is mixed and used in the following ratio. An external additive such as silica is added to the toner so that it has a negative charge,
The diameter is about 8 μm. Further, in order to obtain high image quality, the toner has a high fluidity and has a triboelectric charge amount of 3.0 × 10 ^-2 C / kg. The magnetic carrier has a diameter of about 50
It is a ferrite carrier of μm.

In the above copying machine, the photosensitive drum 1 is a charger 2
It is charged to -700V by the primary charging by. Further, the latent image formation causes the potential of the surface of the photosensitive drum, which has been exposed to the laser beam, to decrease to -100V.

A rectangular alternating voltage is applied to the developing sleeve 11 from a developing bias power source, and a DC voltage of -550 V is superimposed and applied as a fog removing potential of a white background portion. Due to the difference between the fog removing potential and the potential of the laser exposure portion (contrast potential: | -550-(-100 | = 400V), toner having a negative charge flies to the latent image potential portion of the photosensitive drum 1. Is magnetically held by a magnet in the developing sleeve 11, and only toner adheres to the latent image on the photosensitive drum to form a desired toner image.

Now, the developing bias waveform applied to the developing sleeve 11 will be described with reference to FIG. The developing bias waveform is basically a rectangular wave with a frequency of 2K.
The waveform has a frequency of Hz and an amplitude of 2 KVpp.

In order to prevent toner fogging on the photosensitive drum 1, the developing bias potential is biased by 150 V from the potential corresponding to the white background. As an example, the white background potential is −700V and the high concentration potential is −100V.
(Laser light scanning potential), development bias potential -55
It is 0V.

The developer used in such a color electrophotographic copying machine will be further described. In image formation of a multi-color image or a full-color image, by using a sharp melt toner, the color reproduction range of the copy can be widened and a color copy faithful to the original can be satisfactorily obtained.

The color toner is prepared by melt-kneading, pulverizing and classifying a toner forming material such as a binder resin such as polyester resin or styrene-acrylic ester resin, a colorant (dye or sublimable dye), and a charge control agent. Manufactured. If necessary, various external additives (eg, hydrophobic colloidal silica) are added to the toner.

In view of fixing property and sharp melt property, it is particularly preferable that the color toner uses a polyester resin as a binder resin. As the sharp melt polyester resin, a polymer compound having an ester bond in the main chain of a molecule synthesized from a diol compound and a dicarboxylic acid is exemplified. In particular,

[0030]

Embedded image (Wherein R is an ethylene or propylene group, X and Y are each positive integers of 1 or more, and the average value of X + Y is 2 to 10). As a diol component, divalent or higher carboxylic acid, its acid anhydride or its lower alkyl esterified carboxylic acid (eg, fumaric acid, maleic acid, maleic anhydride, phthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid, etc.) A polyester resin obtained by copolycondensing at least 1) as a dicarboxylic acid is more preferable because it has sharp melting characteristics. The softening point of the polyester resin is 75 to 150 ° C, preferably 80 to 120 ° C. FIG. 13 shows the softening characteristics of the toner containing the polyester resin as the binder resin.

The method of measuring the softening point will be described. Flow tester CFT-500A type (manufactured by Shimadzu Corporation).
Using a die (nozzle) with a diameter of 0.2 mm and a thickness of 1.
When the extrusion load of 20 kg is applied as 0 mm, the preset temperature is 70 ° C., the preheating time is 300 seconds, and then the temperature is uniformly increased at a rate of 6 ° C./min.
Determine the temperature curve (softened S-curve). As a sample toner, fine powder precisely weighed from 1 to 3 g is used, and the cross-sectional area of the plunger is 1.0 cm ² . The softened S-shaped curve becomes a curve as shown in FIG. As the temperature rises at a constant rate, the toner is gradually heated and starts to flow out (plunger descending AB).
When the temperature is further raised, the melted toner largely flows out (B-C-D), and the plunger lowering is stopped and finished (D-E).

The height H of the S-shaped curve indicates the total outflow amount, and H /
The temperature T ₀ corresponding to point C of 2 indicates the softening point of the sample (eg toner or resin).

Whether or not the toner and the binder resin have a sharp melting property can be determined by measuring the apparent melt viscosity of the toner or the binder resin.

A toner or a binder resin having a sharp melt property means that the temperature at which the apparent melt viscosity is 10 ³ poise is T ₁ , and the temperature at which the apparent melt viscosity is 5 × 10 ² poise is T.
_If it is set to ₂ , it means that the condition of T ₁ = 90 to 150 ° C. | ΔT | = | T ₁ −T ₂ | = 5 to 20 ° C. is satisfied.

The sharp-melting resin having these temperature-melt viscosity characteristics is characterized by extremely sharply decreasing the viscosity when heated. Such a decrease in viscosity causes proper mixing of the uppermost toner layer and the lowermost toner layer of the color image, and also sharply increases the transparency of the toner layer itself, which enables good subtractive color mixing.

[0036]

However, the above-mentioned conventional control method has the following drawbacks. That is, the ATR output is 4 V or less, that is, as shown in FIG.
When the ratio becomes 5% or less, the replenishment time is determined by the replenishment table having the contents as shown in FIG. 9, the screw 20 of the replenishment device 22 is rotated by the replenishment time, and the toner 18 is sent from the replenishment device 22 to develop. Toner is supplied to the developer 19 in the container 16.

However, due to the mechanism in which the toner is sent and replenished by the rotation of the screw 20, the amount of replenishment per unit time varies due to mechanical variations of the mechanism. For this reason, conventionally, it has been attempted to stabilize the toner delivery amount by designing an appropriate pitch and the number of rotations of the screw and designing the screw in which the pitch and the number of rotations are set. Therefore, there is a limit to the stability of the delivery amount by such a method.

That is, as shown in the supply line of FIG.
By design, a toner replenishment amount of 0.5 g is obtained with a replenishment time of 1 second, but depending on the screw, a straight line,
As described above, the replenishment amount varies by about ± 20% in the replenishment time of 1 second. The above-mentioned replenishment straight line is an optimum replenishment straight line designed to reduce the ripple of the T / C ratio in terms of the balance between toner consumption and replenishment during image formation.

FIG. 11 shows how the T / C changes when an image is formed. The ripple of T / C ratio is
During continuous copying, the T / C ratio increases during replenishment due to the time lag between toner replenishment and replenishment stop, and T / C ratio increases when replenishment is stopped.
This is a phenomenon in which a large or small variation appears in the T / C ratio, that is, the C ratio decreases.

On the optimum straight line in FIG. 10, the ripple of the T / C ratio is small as shown by the curve 'in FIG. As the replenishment amount increases from a straight line to a straight line, the ripple of the T / C ratio becomes larger on the side where the T / C ratio is higher, as shown by the curve 'in FIG. Conversely, when the replenishment amount decreases from a straight line to a straight line, the ripple of the T / C ratio increases toward the lower T / C ratio (as the value of the T / C ratio as shown by the curve 'in FIG. 11). Smaller).

As described above, in the conventional image forming apparatus, the ripple of the toner density of the two-component developer, that is, T / C, which is controlled by the density detecting device (ATR) during continuous image formation.
There were fluctuations in which the ripple of the ratio became higher or lower.

The object of the present invention is to control the T / C ratio, which is the toner concentration of the two-component developer, by the concentration detecting device to an appropriate range without causing a large fluctuation in the ripple even during continuous image formation. An object of the present invention is to provide an image forming apparatus capable of always obtaining a high quality image by performing good development.

[0043]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the present invention is provided with a density detecting device that detects the toner density of a two-component developer that develops a latent image formed on an image carrier, and replenishes the toner according to a detected value based on the detected value. In the image forming apparatus, the image forming apparatus is characterized in that a maximum value and a minimum value having a large fluctuation range from the density target value among the detected values are obtained, and the supply table is changed according to the maximum value and the minimum value. It is a device.

[0044]

【Example】

Example 1 In the present invention, the maximum value and the minimum value of the ripple of the T / C ratio as shown in FIG. 11 described above are detected, and the maximum value or the minimum value is a predetermined amount from the set value of the T / C ratio. The feature is that the supply table is changed when it is fluctuating. The mechanical structure itself of the image forming apparatus and the developing device thereof of the present invention is the same as that of the conventional image forming apparatus and the developing device thereof shown in FIGS. 5 and 6, so that FIGS. It will be described with reference to FIG.

FIG. 1 shows, as an example, the ripple in the T / C ratio at the time of image formation of the two-component developer which is the target of the replenishment control of this embodiment. In FIG. 1, the toner concentration ripple of the developer, that is, the point A of the curve a of the T / C ratio ripple shows the maximum value of the T / C ratio, and the point B of the curve b shows the minimum value of the T / C ratio. .

In this embodiment, when the maximum value of the T / C ratio exceeds 5%, which is the designed value of the T / C ratio, exceeds + 1% as shown by the curve a, the toner replenishment time is set as shown in FIG. Approximately 2 from the straight line d when the design value is the original value, like the straight line e in the table
It decreases relatively. That is, the screw 2 of the replenishing device 22 of FIG.
Since the toner feed amount of 0 is larger than the design amount, it is assumed that the T / C ratio exceeds + 1% of the design value, and the replenishment table is switched to 20% less. Similarly, when the minimum value of the T / C ratio exceeds -1% of 5% of the design value as shown by point B of the curve b in FIG. 1, the toner replenishment time is set to the value in the replenishment table of FIG. It is increased by about 20% like the straight line f. This makes it possible to control within ± 1% of the design value as shown by the curve c in FIG.

Therefore, even during continuous copying, the image density fluctuation is not so large, and it is possible to achieve the density control as desired. The permissible amount of variation with respect to the target image density varies depending on the image forming apparatus, but in this embodiment, it is 1.5 ± 0.1 (density is Macbeth (trademark)).
Concentration).

In the above description, the increase / decrease in the replenishment time is set to 20%, but it is preferable to appropriately change the numerical value of the increase / decrease in the replenishment time according to the deviation of the maximum value and the minimum value of the T / C ratio from the target value. .

Embodiment 2 In this embodiment, instead of the linear supply table shown in FIG. 2 used in Embodiment 1, a change curve supply table shown in FIG. 3 is used.

The control method in this embodiment detects the maximum value and the minimum value of the ripple of the T / C ratio, as in the first embodiment.
When the maximum value greatly exceeds the design value on the plus side, the supply table is changed from the curve g at the design value in FIG. 3 to the curve h with a reduced supply time, and when the minimum value is on the minus side, the curve g is changed. The replenishment table is changed to the curve i with the longer replenishment time.

In the present embodiment, as described above, it is possible to perform the preferable concentration control of ± 1% of the design value as shown by the curve a in FIG. 1, and to obtain the same effect as that of the first embodiment. I was able to get it.

As in the present embodiment, making the supply table a change curve instead of a straight line has the effect of further reducing the ripple of the T / C ratio of FIG. That is, by supplying a small amount while the image density is low and supplying a large amount when the image density is high, it is possible to suppress the ripple of the T / C ratio more than when the linear supply table is used.

Third Embodiment In the first and second embodiments, the T
The ripple of the / C ratio was measured and the replenishment table was changed. In this embodiment, there is a mode for forming a so-called solid image having a high image forming density and a high area ratio,
A solid image is formed in that mode to form a ripple curve of the T / C ratio, and the maximum and minimum values of the T / C ratio at that time are measured. After that, the replenishment control is performed by changing the replenishment table according to the deviation of the maximum value and the minimum value from the design value, as in the first and second embodiments.

The operation for forming the solid image and obtaining the ripple of the T / C ratio may be performed at the factory when the image forming apparatus is shipped, or may be appropriately performed by a service person after the shipment.

As described above, according to the present invention, the variation of the toner delivery amount of the toner replenishing device is corrected later, and as shown in the first to third embodiments, the T / C during the actual operation.
There is an unprecedented improvement in that the maximum value and the minimum value of the ratio ripple are detected and the optimum supply table is learned gradually. In this sense, the first to third embodiments show an example in which the supply table is corrected once, but the ripple of the T / C ratio is always detected during the image forming operation, and the supply table is changed each time. It is preferable to control as if going.

In general, the T / C ratio ripple is not always as shown in FIG. FIG. 1 shows a case where, for example, solid images are continuously formed, and in other examples, the curves j and k in FIG. 4 may be obtained. The curves j and k show the results of the image forming operation in the image forming apparatuses different from each other.

That is, when originals having various image densities are randomly copied, the maximum value A'and the minimum value B'of the ripple of the T / C ratio may not always appear immediately as shown in FIG. In this case, while the ripple of T / C ratio is within ± 1%, the supply table is not changed,
It is sufficient to change the replenishment table at that time or at an appropriate time thereafter, after detecting the disengagement such as A ′ and B ′.

In the first to third embodiments, the control for one developing device is shown, but the control of the present invention is performed for each of the four color developing devices of the full-color image forming apparatus. It is natural that it is done.

Further, the preferable range of ripple of T / C ratio is T / C
Although the ratio is set to ± 1% of the designed value, there is no problem that the device is designed with some deviation due to the configuration of the device, and by detecting that the value deviates from this designed value and changing the supply table, the present invention The effect can be obtained.

As an example of the replenishing device 22, 0.5 g per second
Although the present invention has a replenishment amount replenishment table, the present invention is effective for other replenishment amount devices depending on the configuration of the screw 20 and the configuration of the developing device.

Further, it is preferable to basically change the replenishment table according to the size of the transfer material (for example, paper). In carrying out the replenishment control of the present invention, it is preferable to use the replenishment table according to the size of the transfer material. Is good.

[0062]

As described above, in the present invention, the toner concentration of the two-component developer, T / C, is detected by the concentration detecting device.
When the ratio is detected and toner is replenished and the T / C ratio is controlled, the maximum value or the minimum value of the ripple from the target value of the detected T / C ratio is calculated, and the replenishment time is determined by the T / C ratio. The replenishment table is changed according to the maximum value or the minimum value of the ripple. Therefore, even during continuous image formation, the T / C ratio can be controlled within an appropriate range without causing a large fluctuation in the ripple, and good development can always provide a high value. A high quality image can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a ripple of a T / C ratio at the time of image formation of a two-component developer targeted for replenishment control in one embodiment of the present invention.

FIG. 2 is a diagram showing the contents of a supply table in the embodiment of FIG.

FIG. 3 is a diagram showing contents of a supply table in another embodiment of the present invention.

FIG. 4 is a diagram showing another example of ripples of T / C ratio during image formation.

FIG. 5 is a configuration diagram showing a conventional image forming apparatus.

FIG. 6 is a configuration diagram showing a developing device installed in the image forming apparatus of FIG.

7 is a cross-sectional view showing an ATR used for density control of the developing device in FIG.

8 is a diagram showing the relationship between the output of the ATR of FIG. 7 and the T / C ratio.

9 is a diagram showing the relationship between the output of the ATR and the replenishment time in the developing device of FIG.

FIG. 10 is a diagram showing a relationship between a replenishment amount and a replenishment time.

11 is a diagram showing a ripple of a T / C ratio at the time of image formation in the developing device of FIG.

12 is a diagram showing a developing bias waveform in the developing device of FIG.

13 is a diagram showing the softening characteristics of the toner used in the developing device of FIG.

[Explanation of symbols]

 1 Photosensitive Drum 11 Developing Sleeve 4Y Developing Device 20 Screw 22 Toner Replenishing Device 100 ATR

Claims (1)

[Claims] 1. An image provided with a density detecting device for detecting a toner density of a two-component developer for developing a latent image formed on an image carrier and supplying toner according to a supply table based on the detected value. In the forming apparatus, a maximum value or a minimum value with a large fluctuation range from the density target value among the detected values is obtained, and the supply table is changed according to the larger one of the maximum value and the minimum value. Image forming apparatus.