JP2005165004A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide such an image forming apparatus that output images of stable quality can be obtained. <P>SOLUTION: The image forming apparatus is equipped with a latent image carrier and a developing means and is equipped with a potential measuring means for measuring the surface potential of the latent image carrier surface or the toner image formed on the latent image carrier surface and an amount-of-toner-deposition measuring means for measuring an amount of toner deposition per unit area of the toner image formed on the latent image carrier surface. The image forming apparatus is equipped with a means for calculating the amount of charges per unit area of the toner image from the result of the surface potential measurement of the latent image carrier measured by the potential measuring means and the result of the surface potential measurement of the toner image and an amount-of-toner-charges calculating means for calculating the amount of charges per unit weight of the toner sticking as the toner image from the amount of charges per unit area of the toner image and the amount of toner deposition per unit area of the toner image and controls the image forming conditions and/or the operation of the image forming apparatus based on the result of the amount-of-toner-charges calculating means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine or a printer.

  FIG. 8 shows an example of a conventional electrophotographic image forming apparatus.

  The image is formed as follows.

  By exposing the surface of the photosensitive drum 128 charged by the primary charger 121 with a laser 122, an electrostatic latent image is formed on the photosensitive drum 128. The latent image is developed by the developing device 101 to obtain a toner image. This toner image is electrostatically transferred onto the surface of the transfer paper 127 by the transfer charger 123. The transfer paper 127 onto which the toner image has been transferred is conveyed to the fixing device 125 and heated by the fixing device 125, and the toner image is fixed on the transfer paper 127 to obtain a permanent image. Further, residual toner remaining on the photosensitive drum 128 after the transfer is removed by the cleaner 126.

  The developing device 101 stores toner, which is a powder of about several μm to several tens of μm, in which a colorant, a charge control agent, and the like are dispersed in a resin such as polyester or styrene acrylic, and is charged to a predetermined charge amount to be developed sleeve. 103 is held on the surface and supplied to the photosensitive drum 128.

  For example, in the case of a so-called one-component system, the toner is charged by frictional charging between the developing sleeve 103 and a regulating member facing it. In the case of a so-called two-component system, this is performed by frictional charging between the toner in the developing device 101 and the carrier.

  The charge amount of the toner is generally expressed by the charge amount per weight (mC / kg), and this amount will be referred to as “tribo” hereinafter.

  The toner tribo generally depends on the amount of water in the surrounding atmosphere, and generally shows a low value in a high humidity environment, and conversely shows a high value in a low humidity environment. If the tribo changes, the amount of toner attached to the electrostatic latent image and the optimum conditions for transferring it to the transfer paper will change, so changing these image formation conditions will always give a good image. Devised.

  In the conventional image forming apparatus, a temperature / humidity sensor 129 is provided in the image forming apparatus as means for detecting toner tribo, and the image forming conditions are changed by measuring the temperature / humidity around the apparatus. (For example, patent document 1).

Japanese Patent Laid-Open No. 02-186368

  However, the toner tribo does not always match the result of the temperature / humidity sensor 129. The reason for this is the decrease in tribo due to the durability of the developing device 101 and the carrier and the moisture absorption characteristics of the toner itself. In particular, the latter will be described. The developing unit 101 handles powder called toner, so that the airtightness is maintained to some extent, and the outside air may not easily enter. The other is that the toner itself is designed so that the change in charging characteristics due to temperature and humidity is small, so that the toner is generally made of a material that hardly adsorbs moisture. For this reason, for example, even if the developing device 101 is left in an atmosphere of a predetermined temperature and humidity, it takes empirically several hours to several tens of hours to reach the tribo of the environment completely.

  For this reason, when the temperature and humidity around the image forming apparatus change suddenly, a difference occurs between the actual toner tribo and the toner tribo calculated from the temperature and humidity, resulting in a mismatch with the image forming conditions, and the output image In some cases, it lacked stability.

  Another problem is that the toner tribo to be developed differs from the average tribo of toner in the developing device 101 depending on the potential of the electrostatic latent image formed on the photosensitive drum 128 and its profile. is there. This is likely to occur when a toner image in the vicinity of the mid-low range density is formed, and particularly when the latent image edge per area is increased by a digital exposure method. The reason for this is that, as a general tendency, toner with a high tribo has a strong electric force, so that the toner moves from the developing sleeve 103 to the photosensitive drum 128 quickly, and the potential of the tribo is first filled with the potential of the electrostatic latent image. This is considered to be because low toner is difficult to move. This phenomenon is called “selective development”.

  As a result, if an image containing a large amount of medium-low frequency density is continuously output, the toner in the developing device 101 having a high tribo is preferentially consumed. Since the toner having a high tribo is a toner having a small particle diameter, the toner having a large particle diameter tends to remain in the developing device 101. If this process is repeated, the toner particle diameter in the developing device 101 gradually increases (coarse powder), and the development characteristics deteriorate.

  In order to suppress such selective developability, in this embodiment, there is a method of using a blank pulse bias that alternately repeats a pulse portion and a blank portion as an alternating current component of the developing bias applied to the developing sleeve 103. Installed in color copiers by the applicant.

  However, in consideration of various environments and developer durability deterioration, the conditions under which selective developability is lost are slightly different from each other, and conventional image forming apparatuses are set according to the average conditions. is the current situation. For this reason, there has been a problem that the life of the developer that could be achieved under a certain use condition cannot be achieved under the actual use condition.

  Accordingly, a first object of the present invention is to prevent a drop in tribo due to durability of a developing device and a carrier and a mismatch with an image formation condition due to a sudden change in ambient temperature and humidity, and an image formation condition according to an actual toner tribo. It is to provide an image forming apparatus that can obtain an output image with stable quality by operating the image forming apparatus.

  The second object of the present invention is to increase the effect of suppressing fluctuations in the toner particle size distribution in the developing device by selective development by setting the optimum developing bias condition according to the actual use condition of the image forming apparatus. An object of the present invention is to provide an image forming apparatus capable of obtaining an output image with more stable quality.

  In order to achieve the above object, a first aspect of the present invention provides a latent image carrier that carries an electrostatic latent image, and a toner image that adheres toner according to the electrostatic latent image on the latent image carrier. A developing means for forming the surface of the latent image carrier, a potential measuring means for measuring a surface potential of the surface of the latent image carrier or the toner image formed on the surface of the latent image carrier, and a surface of the latent image carrier. A surface potential measurement result of the latent image carrier measured by the potential measuring unit in an image forming apparatus including a toner adhesion amount measuring unit for measuring a toner adhesion amount per unit area of the formed toner image And means for calculating the charge amount per unit area of the toner image from the surface potential measurement result of the toner image, the charge amount per unit area of the toner image, and the toner adhesion per unit area of the toner image From the amount, said A toner charge amount calculating means for calculating a charge amount per unit weight of toner adhering as a toner image, and controlling an image forming condition and / or an operation of the image forming apparatus based on a result of the toner charge amount calculating means; It is characterized by doing.

  According to a second aspect of the invention, there is provided the first toner image according to the first aspect of the invention, further comprising a developing bias applying means for applying a developing bias in which an alternating voltage is superimposed on a direct current voltage to the developing means. The result of the charge amount per unit weight of the toner calculated from the first reference toner image formed according to the formation condition and the second toner image formation condition that is different from the first toner image formation condition. The image forming conditions and / or the operation of the image forming apparatus are controlled based on the result of the charge amount per unit weight of the toner calculated from the two reference toner images.

  According to the present invention, it is possible to obtain a stable quality output image by preventing a mismatch with the image forming conditions and operating the image forming apparatus under the image forming conditions according to the actual toner tribo.

  In addition, by setting the optimal development bias conditions according to the actual usage conditions of the image forming apparatus, the effect of suppressing fluctuations in the toner particle size distribution in the developing device due to selective development is enhanced, and an output image with more stable quality can be obtained. Can be obtained.

<Embodiment 1>
Embodiment 1 of an image forming method and an image forming apparatus using the same according to the present invention will be described below with reference to the accompanying drawings.

  First, the operation of the entire image forming apparatus will be described with reference to FIG. 1. An electrostatic latent image is formed on the photosensitive drum 28 by exposing the surface of the photosensitive drum 28 charged by the primary charger 21 with a laser 22. . The latent image is developed by the developing device 1 to obtain a toner image. This toner image is electrostatically transferred onto the surface of the transfer paper 27 by the transfer charger 23. The transfer paper 27 to which the toner image is transferred is heated by the fixing device 25, and the toner image is fixed on the transfer paper 27 to obtain a permanent image. Further, residual toner remaining on the photosensitive drum 28 after the transfer is removed by the cleaner 26.

  Next, the developing device 1 will be described in detail.

  The image forming apparatus according to the present embodiment uses a two-component development system as a development system. The developing device 1 according to the present embodiment uses a non-magnetic developing sleeve 3 including a magnet 5 fixedly arranged as a developer carrier.

  As the developer, a two-component developer in which a nonmagnetic toner and a magnetic carrier are mixed is used. The toner is a powder having a volume average particle diameter of about 8 μm by dispersing a colorant, a charge control agent and the like in a resin mainly composed of polyester and pulverizing and classifying the toner. As the carrier, a ferrite core having a volume average particle diameter of about 45 μm coated with a silicone resin is used.

  The developing sleeve 3 is provided in a non-contact manner with respect to the photosensitive drum 28, but the two-component developer carried on the developing sleeve 3 is in contact with the photosensitive drum 28 in the state of a magnetic brush.

  In this embodiment, a blank pulse bias that alternately repeats a pulse portion and a blank portion as shown in FIG. 2 is used as an alternating current component of the developing bias applied to the developing sleeve 3. The frequency of the pulse part is 5 kHz, and the peak-to-peak voltage (Vpp) is 1.6 kV. The blank portion is for two pulse periods, that is, 0.4 msec. Advantages of using such a bias waveform include improved developability to a minute dot latent image and improved image quality in the highlight area, as well as suppressing selective developability with respect to toner particle size and charge amount. Examples include suppression of developer deterioration caused by uneven toner particle size distribution in the two-component developer.

  Next, the characteristic part of this Embodiment is demonstrated.

  As shown in FIG. 1, the image forming apparatus according to the present embodiment faces the surface of the photosensitive drum 28, and is downstream of the developing device 1 in the rotation direction of the photosensitive drum 28 and upstream of the transfer charger 23. A potential sensor 31 and an optical sensor 32 are provided on the side.

  The potential sensor 31 detects the electrostatic latent image potential Vdrum on the photosensitive drum 28 if the development by the developing device 1 is not performed. If development is performed by the developing device 1, the surface potential Vtoner of the developed toner image is detected.

  For example, in the image forming apparatus of the present embodiment, an electrostatic latent image potential Vdrum of a “gradation density pattern” formed in 17 steps from a white background portion to a maximum density portion and a toner image obtained by developing it. The surface potential Vtoner is measured using the potential sensor 31. This result is shown in FIG. The horizontal axis is a numerical value representing the exposure amount by the laser 22, and the exposure amount by the laser 22 with the laser control value when the exposure amount is controlled by dividing the white background portion to the maximum density portion into 8 bits, that is, 0 to 255 gradations. Express. In this embodiment, since the “reverse development method” is used in which the photosensitive drum 28 is negatively charged and developed with toner having a negative charge, as the laser exposure amount on the horizontal axis in FIG. 3 increases. As a result, the amount of toner developed increases and the density of the output image also increases.

  At this time, the dark portion potential applied to the photosensitive drum 28 by the primary charger 21 is −450V, and the DC component Vdev of the developing bias is −365V.

  By not rotating the developing sleeve 3 and applying an AC component of the developing bias, the electrostatic latent image potential on the photosensitive drum 28 can be measured without being disturbed by the contact of the developer. The electrostatic latent image potential Vdrum of the “gradation density pattern” under this condition is a curve as shown in “latent image potential” of FIG.

  On the other hand, a curve of “condition 1” in FIG. 3 is obtained by developing the electrostatic latent image under a predetermined environmental condition and measuring the potential of the toner image. It can be seen that due to the charge of the developed toner, the toner layer surface potential has reached approximately -365 V, which is substantially equivalent to the DC component Vdev of the developing bias.

  Further, the difference between the curves of “latent image potential” and “condition 1” in FIG. 3 is a potential difference ΔVtoner (V) formed by the charge of the toner.

The optical sensor 32 includes a light emitting element (not shown) and a light receiving element (not shown) inside, and irradiates light (wavelength 970 nm) from the light emitting element onto an object (the surface of the photosensitive drum 28 or the toner image surface). Then, the reflected light amount is detected by the light receiving element. In the present embodiment, since the light receiving element detects specularly reflected light from the object, the amount of reflected light from the toner surface is reduced according to the amount of toner attached to the surface of the photosensitive drum 28. Accordingly, the output voltage of the light receiving element also decreases. The characteristic curve of the detection signal voltage Vsns (V) of the optical sensor 32 with respect to the toner amount on the photosensitive drum 28 is as shown in FIG. By calculating this Vsns (V) as an inverse function of the characteristic curve of FIG. 4, the toner amount M / S (mg / cm ² ) on the photosensitive drum 28 (per unit area) can be calculated.

  In this embodiment, the toner tribo (Q / M) of the toner actually developed on the photosensitive drum 28 is calculated from the above differences ΔVtoner (V) and Vsns (V). The calculation process will be described below.

First, consider a capacitor formed between the photosensitive drum 28 and the developing sleeve 3 in a region of a predetermined area S facing each other. If the capacity of the capacitor is C (F) and the charge amount of the toner adhering to the area of the predetermined area S on the photosensitive drum 28 is Q,
Q = C × ΔVtoner (1)
In other words, if you divide both sides by S,
Q / S = C × ΔVtoner / S (2)
It is.

here,
Q / M = (Q / S) / (M / S) (3)
So
Q / M = (C × ΔVtoner / S) / (M / S) (4)
It becomes.

  Here, C and S can be regarded as constants determined by the material and physical configuration. Therefore, by previously measuring the value of C / S in Equation (4), ΔVtoner and M / S (unique from Vsns) Q / M can be obtained from the above.

  The value of C / S can be calculated by the following equation (5) using the values of ΔVtoner and M / S, and the actually measured Q / M value.

C / S = (Q / M) × (M / S) / ΔVtoner (5)
The toner tribo attached to the photosensitive drum 28 can be measured by the following method.

  The Faraday-Cage shown in FIG. 5 includes a double cylinder in which metal cylinders having different shaft diameters are arranged coaxially, and a filter for further taking in toner into the inner cylinder. If the inner cylinder and the outer cylinder are insulated, and a charged body with a charge amount q is put in the inner cylinder, it is as if a metal cylinder with an amount of electricity q exists due to electrostatic induction. This induced charge amount is measured by KEITHLEY 616 DIGITAL ELECTROMETER, and the toner weight M in the inner cylinder divided by the charge amount Q is defined as Q / M (tribo). The toner is taken into the filter by air suction directly from the surface of the photosensitive drum 28.

At this time, the area of the toner that has been removed from the surface of the photosensitive drum 28 is measured, and M / S (mg / cm ² ) obtained by dividing the weight of the toner in the filter by the value is obtained. The above-mentioned characteristic curve of FIG. 4 is obtained by correlating the M / S and Vsns values measured in this way.

  FIG. 6 shows a toner image ΔVtoner formed by developing a latent image of the maximum density portion on the photosensitive drum 28 under four conditions in the image forming apparatus of the present embodiment, a toner image tribo Q / M, The toner adhesion amount M / S and the Vsns at that time were measured.

  The four conditions are as follows.

Condition 1: The developing device 1 of this embodiment is left in an environment of a temperature of 23 ° C. and a relative humidity of 50%, and the developing operation is performed in the image forming apparatus of this embodiment. Condition 2: The developing device of this embodiment 1 was left in an environment with a temperature of 30 ° C. and a relative humidity of 80%, and the developing operation was performed in the image forming apparatus of this embodiment. % In the image forming apparatus of this embodiment and developing operation. Condition 4: The developing device 1 of this embodiment is left in an environment of a temperature of 23 ° C. and a relative humidity of 50%. In the image forming apparatus of the example, a rectangular wave having a frequency of 2 kHz and a peak-to-peak voltage of 1.6 kV was used as the developing bias alternating current component, and the developing operation was performed. As an example of the condition of not charging the capacitor C Said.

C / S is calculated from this result, and C / S = 0.0492 (× 10 −5 C / V · m 2) as an average value
Got. The calculated value at the bottom of FIG. 6 is obtained by recalculating Q / M using this value.

  As described above, the C / S value is obtained in advance under some conditions, and the tribo of the toner actually developed on the photosensitive drum 28 is obtained using the value and the values of ΔΔVtoner and Vsns. it can.

  Next, a process in which the image forming apparatus according to the present embodiment actually calculates the toner tribo on the photosensitive drum 28 will be described.

  First, the photosensitive drum 28 is charged to a predetermined potential by the primary charger 21 and an exposure amount corresponding to the maximum density portion is exposed by the laser 22 as an image signal. The electrostatic latent image corresponding to the maximum density portion thus formed is first subjected to potential measurement by the potential sensor 31 without toner adhesion by the developing device 1. Since the toner is not attached by the developing device 1, the developing sleeve 3 is not rotated, and only the DC component is applied to the developing bias, and no AC component is applied. An output signal from the potential sensor 31 is converted into a 10-bit digital signal by an A / D converter (not shown), and is stored in a variable Vdrum by control means (not shown) as potential data of the maximum density portion.

  Next, after the same electrostatic latent image is formed on the photosensitive drum 28 again, this time, as in the actual image formation, the developing sleeve 3 is rotated, and a developing bias is applied to both the DC and AC components to electrostatically The latent image is developed to form a toner image. Similarly, the surface layer potential of the toner image is stored in the variable Vtoner by the control means.

  Further, the amount of reflected light of the toner image is detected by an optical sensor 32 downstream of the potential sensor 31. The detection result of the reflected light amount is converted into a 10-bit digital signal by an A / D converter (not shown), and stored in a variable Vsns by a control means (not shown).

  The control means includes an inverse function of the characteristic curve of FIG. 4 as a conversion table, and stores a value obtained by converting Vsns by this conversion table in a variable MassT. Thereafter, the toner tribo value is calculated by the following equation (6) and stored in the variable Tribo.

Tribo
= 0.0492 × (Vtoner−Vdrum) / (MassT) (6)
In the image forming apparatus according to the present embodiment, the toner image is recharged by the post charger 33 based on the variable Tribo, so that the transfer characteristic of the toner image onto the transfer paper 27 by the transfer charger 23 is stabilized. This makes it possible to obtain a high-quality output image.

  The post charger 33 applies a predetermined current to the charging wire 34 by a constant current power source (not shown) to charge the toner image by corona discharge. The charging wire 34 is calculated by a control means (not shown). The following current Ip (μA) is applied by the control.

When Tribo> -30, Ip = 0 (μA)
When −30 ≦ Tribo ≦ −20 Ip = −8 × Tribo-240 (μA)
When Tribo <−20 Ip = −80 (μA)
Note that the direction of current flow is positive in the direction from the photosensitive drum 28 to the post charger.

  With this setting, about 25% of the current applied to the charging wire 34 is directed toward the photosensitive drum 28. For example, when −64 μA is applied to the charging wire 34 under the condition 2, about −16 μA is applied to the photosensitive drum 28 side. Current flows. In the present embodiment, the absolute value of the tribo of the toner image increases by about 0.6 mC / kg with respect to the absolute value 1 μA of the current flowing in the direction of the photosensitive drum 28. As a result, the absolute value of the tribo of the toner image increases by about 10, and the tribo that was -22 mC / kg immediately after development becomes -32 mC / kg. This is almost the same as the tribo in the low humidity environment as in condition 3, and the condition fluctuation in the transfer process by the transfer charger 23 can be reduced, the transfer characteristics can be stabilized, and a high-quality output image can be obtained. it can. Moreover, since the control is based on the tribo of the actually developed toner, not based on the pseudo tribo value predicted from the output of the temperature / humidity sensor as in the prior art, the surrounding environment has changed rapidly. Even in this case, stable image characteristics can be maintained without causing a control mismatch.

  It should be noted that numerical values, configurations, and the like in the above-described embodiment are not necessarily limited thereto, and can take various forms within the scope of the present invention. For example, the image forming conditions controlled using the calculated tribo values can be applied in various ways such as charging conditions, exposure conditions, development conditions, transfer conditions, and the like.

<Embodiment 2>
Next, a second embodiment of the present invention will be described.

  The outline of the configuration of the image forming apparatus according to the present embodiment is substantially the same as that described in the first embodiment.

  In this embodiment, the tribo calculation operation of the toner image as shown in the first embodiment is performed on the intermediate density portion in addition to the maximum density portion. Based on this result, the length of the blank portion of the AC component of the developing bias is changed.

  Here, the relationship between the selective developability and the length of the blank portion will be described.

  In the two-component development system, when development is performed by applying a bias composed only of a DC component as a development bias, toner having a relatively high charge amount is generated by an electric field (development electric field) between the photosensitive drum 28 and the development sleeve 3. Prior to the movement, the surface of the carrier is restrained by the electric force with the carrier, so that only a toner having a relatively low charge amount is developed on the photosensitive drum 28.

  Conversely, when a bias including an AC component is applied, the toner attached to the carrier starts to fly from the carrier and forms a toner mist at the opposing portion. The toner mist reciprocates between the photosensitive drum 28 and the developing sleeve 3 by the AC component of the developing bias. The toner mist includes toner having a high charge amount that was not used for development when a bias of only a DC component was applied.

  However, when a rectangular bias is applied, once the toner with a high charge amount moves away from the carrier surface, the toner is easily affected by the developing electric field, and the moving speed is fast. Therefore, while the photosensitive drum 28 and the developing sleeve 3 are reciprocated. In addition, toner with a low charge amount cannot follow the moving speed, and is difficult to reach the surface of the photosensitive drum 28. Further, the toner having a high charge amount quickly fills the potential difference between the photosensitive drum 28 and the developing sleeve 3, thereby further preventing the toner having a low charge amount that arrives later from reaching the photosensitive drum 28. That is, a high charge amount of toner is easily developed on the photosensitive drum 28.

  Such selective developability becomes conspicuous when digital exposure is performed in which the light emission of the laser 22 is modulated in accordance with the image signal and the gradation is expressed in accordance with the image signal, rather than the high density portion.

  Therefore, when a blank pulse bias is applied in which the development bias is only a DC component after repeating the rectangular portion several times (one period in this embodiment), the reciprocation of the toner having a high charge amount is stopped appropriately. Thus, it waits for the movement of the toner having a low charge amount that could not follow the reciprocation. By this effect, the average charge amount of the toner developed on the photosensitive drum 28 can be brought close to the average charge amount of the toner in the developer on the developing sleeve 3.

  When the length of the blank is shortened, the development characteristic approaches that of a rectangle only, and the selective developability tends to adhere to the photosensitive drum 28 with high tribo toner. Conversely, when the blank is lengthened, the development characteristics approach the direct current characteristics, and the selective developability tends to adhere to the photosensitive drum 28 with low tribo toner.

  The length of the blank part is stored in the control means as a variable blank expressed in units of the period of the pulse part. The variable blank is an integer of 1 to 8, and the initial value is 2.

  The actual operation will be described. First, the tribo value of the toner image of the maximum density portion is calculated in the same manner as in the first embodiment, and stored in the variable Tribo (255) (step S1). Subsequently, the tribo value of the toner image is similarly calculated by setting the laser control value set to 255 in step S1 to 64 (intermediate density portion), and stored in the variable Tribo (64) (step S2).

  Next, the value of Tribo (64) / Tribo (255) is stored in the variable TriboRatio (step S3). Next, it is determined whether or not this value is 1.2 or less (step S4). If it is N in step S4, it is further determined whether or not this value is 0.8 or more (step S5). If it is Y, the process ends in step 9, and if it is N, the series of operations ends (step S12). ).

  If Y in step S4, it is determined whether the value of Blank is 8 (step S6). If Y in step S6, the variable control means sets Blank = 8 (step S7) and ends the operation (step S7). Step S12). If N in step S6, 1 is added to the original value of Blank (step S8), and the operation is terminated (step S12).

  If Y is determined in step S5, it is determined whether the value of Blank is 1 (step S9). If Y is determined in step S9, the variable control means sets Blank = 1 (step S10) and ends the operation. (Step S12). If the answer is N in Step S6, -1 is added to the original value of Blank (Step S11), and the operation is terminated (Step S12).

  To summarize this operation, when the tribo of the halftone density portion with respect to the maximum density portion is high, the blank portion of the developing bias AC component is extended, and in the opposite case, the blank portion is reduced. By this operation, the development bias AC component can be adjusted between a characteristic such as a rectangular bias in which the halftone tribo is high and a DC bias characteristic in which the halftone tribo is low. It becomes possible.

  By adopting the configuration as described above, by setting the optimum developing bias condition according to the actual use condition of the image forming apparatus, the effect of suppressing the fluctuation in the toner particle size distribution in the developing device by selective development is enhanced, The second object of the present invention to provide an image forming apparatus capable of obtaining an output image with more stable quality is achieved.

  The present invention can be applied to an arbitrary image forming apparatus such as a copying machine or a printer using an electrophotographic system.

It is a figure explaining the image forming apparatus which concerns on Embodiment 1 of this invention. It is a figure explaining the developing bias waveform of Embodiment 1 of this invention. FIG. 3 is a diagram illustrating a latent image potential and a toner surface layer potential of the image forming apparatus according to the first embodiment of the present invention. It is a figure explaining the characteristic of the optical sensor of the image forming apparatus which concerns on Embodiment 1 of this invention. It is a figure explaining the Faraday gauge used for a tribo measurement. It is a figure for calculating | requiring the constant C / S of the image forming apparatus which concerns on Embodiment 1 of this invention. It is a figure explaining operation | movement of the image forming apparatus which concerns on Embodiment 1 of this invention. It is a figure explaining the conventional image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Developing device 2 Developing container 3 Developing sleeve 21 Primary charging device 22 Laser 23 Transfer charging device 25 Fixing device 26 Cleaner 27 Transfer paper 28 Photosensitive drum 31 Potential sensor 32 Optical sensor 33 Post charger 34 Charging wire

Claims (2)

A latent image carrier for carrying an electrostatic latent image; and a developing means for forming a toner image by attaching toner according to the electrostatic latent image on the latent image carrier; A potential measuring means for measuring a surface potential of a toner image formed on the surface or the surface of the latent image carrier; and a toner adhesion amount per unit area of the toner image formed on the surface of the latent image carrier. In an image forming apparatus provided with a toner adhesion amount measuring means for
Means for calculating a charge amount per unit area of the toner image from the surface potential measurement result of the latent image carrier measured by the potential measurement means and the surface potential measurement result of the toner image; and the toner image A toner charge amount calculating means for calculating a charge amount per unit weight of toner adhering as the toner image from a charge amount per unit area of the toner and a toner adhesion amount per unit area of the toner image; An image forming apparatus that controls an image forming condition and / or an operation of the image forming apparatus based on a result of a charge amount calculating unit.   The developing means includes a developing bias applying means for applying a developing bias in which an alternating voltage is superimposed on a direct current voltage, and the toner of the toner calculated from the first reference toner image formed according to the first toner image forming condition is provided. The charge amount per unit weight of the toner calculated from the result of the charge amount per unit weight and the second reference toner image formed under the second toner image formation condition different from the first toner image formation condition 2. The image forming apparatus according to claim 1, wherein an image forming condition and / or an operation of the image forming apparatus is controlled based on the result.

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