JP5445176B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic system. In particular, an image carrier that forms an electrostatic latent image on the surface, and a toner carrier that is arranged opposite to the carrier and carries charged toner on the surface and develops the electrostatic latent image on the image carrier with the toner. The present invention relates to an image forming apparatus including a developing device having a body.

  In the electrophotographic process, as a method of visualizing an electrostatic latent image on a photosensitive member (image carrier), a two-component developer method (developing roller (developer carrier) that transports and develops a two-component developer to a developing unit) is developed. ) Conveys developer containing toner and carrier to developing unit and develops with toner) and one-component developing system that conveys only toner (developing roller (toner carrier) conveys only one component of toner to developing unit) And developing).

  In the two-component development method, the toner is charged by contact and friction with the carrier, so that stable charging can be obtained quickly. On the other hand, when the system speed is increased, the carrier conveyed to the developing unit flies and adheres to the photoreceptor. It becomes easy to do, and there is a problem which becomes the noise of an image.

  In the one-component development method, the carrier is not conveyed to the developing unit, and development is performed by flying only the toner, so that there is no image noise due to carrier adhesion on the photoconductor. However, on the other hand, the toner is charged mainly by charge injection or friction with a member such as a blade, which causes a problem that the charging property becomes unstable.

  In addition, while ensuring the stability of toner charging by the carrier using a two-component developer, only the toner is supplied from the developer carrier onto the developing roller (toner carrier), and development is performed with one component at the developing unit. A hybrid development system has also been developed.

  However, in the one-component development method in which only the toner is developed including the hybrid development method, the developability is lowered as the process speed is increased, and a stable image density is obtained by the variation of various parameters. It becomes difficult.

  For example, as compared with the case where the system speed is low, the development characteristics greatly change when the distance (Ds) between the photosensitive member and the development roller, the amount of toner transported on the development roller, the charge amount, and the like change. This is because the surface potential of the photoconductor and the surface potential of the developing roller are equal (development equilibrium state), and the development is not completed. If the process speed is increased, the latent image is developed before the development equilibrium state is reached. This is because the nip passes through the nip and the development does not reach an equilibrium state.

  Therefore, in order to obtain a stable image density even if the characteristics of various members change, it is necessary to set the development conditions so that the development state at the development unit can be completed in a state closer to the equilibrium state. .

  In order to obtain a more stable image density, a technique for detecting a development state and reflecting it in development conditions has been developed (see, for example, Patent Documents 1 and 2).

  Patent Document 1 discloses a technique for detecting a toner flying current in a developing unit. Patent Document 2 discloses a toner current detection device that can detect only the toner current in the developing unit.

JP 7-175282 A JP 2006-145504 A

  As described above, when the process speed is increased, the number of times the toner flies (reciprocates) in the developing portion decreases, and the developability deteriorates.

  In particular, in the one-component development method using only toner, the electrostatic latent image is obtained before the surface potential on the photosensitive member carrying the electrostatic latent image and the surface potential of the developing roller are equal in potential (development equilibrium state). If the toner passes through the developing portion, it becomes difficult to obtain a stable image density with respect to fluctuations in members during driving and changes in characteristics such as developer transport amount and charge amount.

  In order not to deteriorate the developability in the high-speed process, it is desirable to apply a developing bias in a higher frequency region, but on the other hand, the developing state in the developing portion hardly reaches an equilibrium state. In order to obtain a stable image density, it is necessary to set development conditions so that the development state at the development unit can be completed in a state closer to an equilibrium state.

  However, even using the technology for detecting the toner flying current in the developing unit described in Patent Document 1, it is possible to determine the status of development with respect to the equilibrium state only from the toner flying current value. In other words, it is insufficient to reflect the development bias condition. Further, the problem when a developing bias in a higher frequency region is applied in a high-speed process is not taken into consideration, and the equilibrium state of development cannot be determined from the flying current value of the toner.

  Further, Patent Document 2 discloses a toner current detection device that can detect only the toner current in the developing unit. However, what is the state of the development with respect to the equilibrium state only by measuring the toner current? It cannot be determined and is insufficient to reflect the development bias condition.

  The present invention has been made in view of the above technical problems.

  An object of the present invention is to allow an image forming apparatus of a type in which only toner is conveyed and developed to a developing unit, and development can be terminated in a state where the developing unit is closer to an equilibrium state even if the process speed is increased. Another object of the present invention is to provide an image forming apparatus capable of obtaining a more stable image density even when various members are changed.

  In order to solve the above problems, the present invention has the following features.

1. An image carrier carrying an electrostatic latent image formed on the surface;
A developing device having a toner carrier for carrying and transporting charged toner on the surface and developing the electrostatic latent image on the image carrier disposed oppositely with the toner;
A developing bias power source for applying a developing bias voltage for causing toner to fly to the toner carrying member at a developing portion facing the image carrier and developing;
Development bias control means for setting a development bias condition which is a condition for applying a development bias voltage by the development bias power supply;
Toner current detecting means for detecting a toner current value due to toner flying in the developing unit,
The development bias voltage by the development bias power supply is an alternating voltage having a predetermined high frequency,
The developing bias control means includes
The image forming apparatus, wherein the developing bias condition is controlled so that a phase shift between the developing bias voltage and the toner current value detected by the toner current detecting unit is minimized.

2. 2. The image forming apparatus according to 1, wherein the developing bias condition is at least one of a DC component Vdc of an alternating voltage having a predetermined high frequency, a peak-to-peak voltage Vpp, and a duty ratio.

3. The development bias voltage by the development bias power source is obtained by adding a pulse voltage to the alternating voltage having the predetermined high frequency,
2. The image forming apparatus according to 1, wherein the development bias condition includes at least one of a waveform of the pulse voltage, a pulse time, and a potential difference between pulses.

4). The developing device includes:
1. A developer carrying body for carrying and carrying a developer including the toner and a carrier on a surface and supplying the toner in the developer to the toner carrying body arranged to face the developer. 4. The image forming apparatus according to any one of items 1 to 3.

5. The developing device includes a plurality of the toner carriers.
The developing bias control means includes
Collectively a plurality of the toner carriers or for each toner carrier,
The development bias condition is controlled so that a phase shift between the development bias voltage and the toner current value detected by the toner current detection unit is minimized. The image forming apparatus described.

  According to the image forming apparatus of the present invention, in the system in which only the toner is conveyed to the developing unit and developed, the toner flying current value in the developing unit is detected, and the phase shift from the applied high-frequency developing bias is detected. The development bias condition is determined so as to minimize.

  As a result, even when the process speed is further increased, the development can be completed in a state where the development state is closer to the equilibrium state in the developing unit, and a more stable image density can be obtained even if various members are fluctuated. Can do.

1 is a configuration diagram showing a schematic configuration example 1 of an image forming apparatus according to the present invention. FIG. 3 is a configuration diagram showing a schematic configuration example 2 of an image forming apparatus according to the present invention. It is a block diagram which shows schematic structure example 3 of the image forming apparatus which concerns on this invention. FIG. 6 is a configuration diagram showing a schematic configuration example 4 of an image forming apparatus according to the present invention. FIG. 6 is a schematic diagram illustrating an example of a relationship between a developing bias voltage and a current value associated with the flying of developing toner. FIG. 5 is a schematic explanatory diagram of a calculation method example 1 of a phase shift between a development bias voltage and a current value associated with a development toner flight. FIG. 10 is a schematic explanatory diagram of a second calculation method example 2 of a phase shift between a development bias voltage and a current value associated with flying of development toner. FIG. 10 is a schematic explanatory diagram of a calculation method example 3 of a phase shift between a development bias voltage and a current value associated with flying of development toner. FIG. 10 is a schematic explanatory diagram of a calculation method example 4 of a phase shift between a development bias voltage and a current value associated with flying of development toner. FIG. 10 is a schematic explanatory diagram of a calculation method example 5 of a phase shift between a development bias voltage and a current value associated with flying of development toner. 12 is a flowchart illustrating a first example of a general procedure for performing feedback control of a detected phase shift to a developing bias condition. 12 is a flowchart showing a second example of a schematic procedure for feedback-controlling a detected phase shift to a developing bias condition. It is the schematic which shows the example of the developing bias voltage which added the kicker pulse.

  Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described with reference to FIGS.

(Configuration of image forming apparatus)
FIG. 1 to FIG. 4 are configuration diagrams respectively showing schematic configuration examples 1 to 4 of the image forming apparatus according to the present invention. Configuration examples 1 to 4 of the image forming apparatus according to this embodiment will be described with reference to FIGS. 1 to 4. However, the difference between the configuration examples 1 to 4 is that the configuration of the developing device is different.

<Configuration example 1>
FIG. 1 is a configuration diagram showing a schematic configuration example 1. In FIG.

  The image forming apparatus in FIG. 1 includes the following components. That is, the photosensitive member (image carrier) 1, the developing roller (toner carrier) 20, the toner layer regulating member 21a, the toner conveying roller 22a, the toner conveying member 24a, the toner 25a, the toner stirring / conveying tank 26a, the replenishing toner 27, Toner replenishing section 28, development bias power supply 30, toner transport roller bias power supply 31, toner current detection means 32, development bias control means 33, toner density detection means 34 on the photoreceptor, transfer means 4, cleaning means 5, charging means 6, exposure means 7 and recording medium 8 are shown in FIG.

  The photosensitive member 1 is an electrostatic latent image carrier and is given a constant surface potential (Vo) by the charging unit 6. Thereafter, the exposure unit 7 emits a laser modulated in accordance with an image signal from a digital image processing unit (not shown) to form an electrostatic latent image.

  The toner on the developing roller 20 arranged with a certain gap from the photosensitive member moves toward the photosensitive member 1 by applying a developing bias voltage, whereby the electrostatic latent image of the photosensitive member 1 is visualized as a toner image.

  Thereafter, the toner image is transferred to the recording medium 8 by the transfer means 4 and then fixed by a fixing device (not shown). After passing through the transfer unit 4, the photosensitive member 1 is cleaned by the cleaning unit 5 and again conveyed to the charging unit 6.

  In FIG. 1, the toner image is directly transferred from the photosensitive member 1 to the recording medium 8. However, after the toner image is once transferred to the intermediate transfer member, the toner images of other colors are superimposed and transferred to the recording medium 8. It can be in any form.

  In the developing device 2, the toner 25a replenished from the toner replenishing portion 28 is transported to the toner transport roller 22a by the toner transport member 24a. The toner 25a on the toner conveying roller 22a is regulated by the toner layer regulating member 21b. The toner conveying roller 22a is disposed in contact with the developing roller 20.

  A bias voltage is applied to each roller by bias power supplies 30 and 31, and the toner on the toner transport roller 22 a is supplied to the developing roller 20. Further, after development, the toner on the developing roller 20 is collected by the toner transport roller 22a.

  An alternating voltage having a predetermined high frequency corresponding to the process speed is applied to the developing roller 20 by a developing bias power source 30 as a developing bias voltage. The toner conveyed onto the developing roller 20 flies (reciprocates) by an electric field generated by the applied developing bias voltage, and the electrostatic latent image on the photoreceptor 1 is visualized.

  A toner current (alternating current) flows between the photoreceptor 1 and the developing roller 20 through the flying of the toner. This change in current value is detected by the toner current detection means 32.

  Based on the results from the density detection means 34 and the toner current detection means 32, an appropriate development bias is applied by the development bias control means 33 so that a desired image density can be obtained and the development is closer to an equilibrium state. The development bias condition is controlled so that However, the density detector 34 does not necessarily have to be used for control.

  Details of the control of the developing bias condition will be described later.

<Configuration example 2>
FIG. 2 is a configuration diagram showing a schematic configuration example 2. In FIG.

  The image forming apparatus in FIG. 2 includes the same components as those in the first configuration example. The differences are as follows. That is, as the developing device 2, a developing roller (toner carrier) 20, a developer regulating member 21b, a developer conveying roller 22b, a magnetic roller 23 (22b and 23 are collectively referred to as a developer carrier 22), a developer It has a conveying member 24b, a developer 25b, and a developer stirring / conveying tank 26b.

  Other supply toner 27, toner supply unit 28, development bias power supply 30, developer carrier bias power supply 31, toner current detection means 32, development bias control means 33, toner density detection means 34 on the photoconductor, and photoconductor (Image carrier) 1, transfer means 4, cleaning means 5, charging means 6, exposure means 7, and recording medium 8 are shown as in FIG.

  Differences of the image forming apparatus of Configuration Example 2 from Configuration Example 1 will be described.

  The developing device 2 in FIG. 2 is a so-called hybrid developing device that combines a one-component developing method and a two-component developing method. The toner and carrier are carried and rotated in the form of a magnetic brush, and a DC or a bias in which AC is superimposed on DC is applied from the magnetic brush roller (developer carrying body) to the developing roller (toner carrying body). The developing roller carrying the toner and the electrostatic latent image (photoconductor) are opposed to each other to visualize the latent image.

  In FIG. 2, 22b is a developer conveying roller, and 23 is a magnetic roller. Hereinafter, the developer conveying roller 22b and the magnetic roller 23 are collectively referred to as a magnet roller (developer carrier 22).

  In the hybrid development method, the merits of the one-component development method and the two-component development method are utilized.

  First, in a portion where the toner is replenished / conveyed to the developer carrying member, a stable charge amount can be given to the toner in order to fly with an electric field by using a carrier. Further, since the developing portion is one-component development, carrier adhesion, which is a disadvantage of two-component development, can be avoided.

  From the above points, even if the system speed is increased, a stable image density can be obtained with less noise such as carrier adhesion.

  The image forming operation is the same as that of the configuration example 1. Only operations related to development will be described.

  In the developing device 2 of FIG. 2, the toner replenished from the toner replenishing section 28 is mixed with the carrier in the developer 25b by the developer agitating / conveying member 24b and charged, and is transported to the developer carrier 22 together with the carrier. The

  The developer 25b on the developer carrier 22 is regulated by the developer regulating member 21b. The developer carrier 22 and the developing roller (toner carrier) 20 are disposed with a certain gap.

  A bias voltage is applied to each roller by bias power supplies 30 and 31, and only the toner of the two-component developer on the developer carrier 22 is supplied to the developing roller 20.

  An alternating voltage having a predetermined high frequency corresponding to the process speed is applied to the developing roller 20 by a developing bias power source 30 as a developing bias voltage. The toner conveyed onto the developing roller 20 flies (reciprocates) by an electric field generated by the applied developing bias voltage, and the electrostatic latent image on the photoreceptor 1 is visualized.

  A toner current (alternating current) flows between the photoreceptor 1 and the developing roller 20 through the flying of the toner. The toner current detecting means 32 detects this change in current value.

  As in the configuration example 1, the development bias control unit 33 outputs the target image density based on the results from the density detection unit 34 and the toner current detection unit 32, and the development is closer to an equilibrium state. The development bias condition is controlled so that an appropriate development bias is applied. It should be noted that the density detector 34 is not necessarily used for control.

  Details of the control of the developing bias condition will be described later.

<Configuration example 3>
FIG. 3 is a configuration diagram showing a schematic configuration example 3.

  The image forming apparatus in FIG. 3 includes the same components as those in the first configuration example. The only difference is that it has two developing rollers (toner carriers) 20.

  As shown in the figure, the two toner carriers are arranged so as to face both the image carrier 1 and the developer carrier 22, respectively, and each performs the same functional operation as in the configuration example 1. Do. Therefore, explanation is omitted.

<Configuration example 4>
FIG. 4 is a configuration diagram showing a schematic configuration example 4. In FIG.

  The image forming apparatus of FIG. 4 includes a hybrid developing device as the developing device 2 as in the configuration example 2, and includes the same components as in the configuration example 2. The only difference is that it has two developing rollers (toner carriers) 20.

  As shown in the figure, the two toner carriers are arranged so as to face both the image carrier 1 and the developer carrier 22, respectively, and each performs the same functional operation as in the configuration example 2. Do. Therefore, explanation is omitted.

  As described above, the schematic configuration examples 1 to 4 of the image forming apparatus according to the present embodiment have been described. The configuration examples 1 and 3 are the one-component development method, and the configuration examples 2 and 4 are the hybrid development method. Configuration examples 1 and 2 include a single developing roller (toner carrier), and configuration examples 3 and 4 include a plurality of developing rollers (toner carrier).

  In either case, only the toner is transported on the developing roller (toner carrier) and is used for developing the latent image on the image carrier.

  In the following description of the embodiment, a hybrid developing type image forming apparatus including a single developing roller (toner carrier) of Configuration Example 2 is assumed. Of course, the same description can be applied to other configuration examples.

(About developer)
For hybrid development, any two-component developer containing toner and carrier can be used.

  A negatively charged toner was used as the toner. Of course, a positively charged toner may be used. The toner can be manufactured by a publicly known method. For example, it can be produced using a pulverization method, an emulsion polymerization method, a suspension polymerization method or the like.

  It does not specifically limit as a carrier, The well-known carrier generally used can be used. A binder type carrier or a coat type carrier can be used. Although it is not limited to this as a carrier particle size, 15-100 micrometers is preferable. The toner ratio in the developer was 8% by mass.

(Developer setting conditions)
In the image forming apparatus according to the present exemplary embodiment, the toner current in the facing portion (developing unit) between the toner carrier 20 and the image carrier 1 provided in the developing device 2 is detected, and the development bias voltage applied to the toner carrier 20 is detected. This is reflected in the setting control. The components and setting conditions related to the setting control will be described.

  As the image carrier 1, an organic photoreceptor is used, but is not limited thereto. An amorphous photoreceptor or the like may be used.

  As the toner carrier 20, an aluminum roller having an alumite treatment on the surface was used.

  The background potential of the electrostatic latent image formed on the image carrier 1 was set to −600V, and the image portion potential was set to −50V.

  A developing bias power supply 30 applied a rectangular wave developing bias voltage having a peak-to-peak amplitude of 2.0 kV, a DC component Vdc of −500 V, a duty ratio of 50%, and a frequency of 5000 Hz to the toner carrier 20.

  The distance (referred to as Ds) at the closest portion of the facing portion between the toner carrier 20 and the image carrier 1 is 250 μm.

(Toner current and development bias conditions)
Under the above-mentioned conditions, the toner current detection means 32 calculates the flying current value of the toner generated at the opposite portion (developing portion) between the toner carrying member 20 (developing bias voltage Vdc−500V) and the image carrier 1 (image portion potential −50V to 0V). Was measured as the toner current.

  In the developing unit, toner flying (reciprocating motion) occurs due to an alternating electric field generated by the developing bias voltage. The toner current value is obtained by measuring a change in current flowing between the toner carrier 20 and the image carrier 1 by the toner current detection means 32 at that time.

  As the difference between the developing bias voltage applied to the toner carrier 20 and the surface potential (approximately 0 V) of the image carrier 1 changes between positive and negative, the toner reciprocates, and the toner current value also changes.

  FIG. 5 is a schematic diagram showing an example of the relationship between the developing bias voltage and the current value associated with the flying of the developing toner. L1 indicates a developing bias voltage (see the left vertical scale), and L2 indicates a toner current value (see the right vertical scale). The horizontal axis is time.

  This measurement was performed with the toner carrier 20 and the image carrier 1 being stationary with the toner interposed in the developing portion. Of course, it may be measured by rotating as in normal development.

  As the developing bias voltage L1 changes in high-frequency polarity, the toner current value L2 also changes in polarity, resulting in a high-frequency AC waveform. In FIG. 5, the toner moves from the image carrier 1 to the toner carrier 20 in a region where the toner current value is positive, and the toner moves from the toner carrier 20 to the image carrier 1 in a region where the toner current value is negative. Has moved to.

  In FIG. 5, when the positive and negative toner currents are combined, a negative current flows, and the toner eventually moves from the toner carrier 20 to the image carrier 1 (develops the latent image). Become.

  As shown in FIG. 5, if the surface potential of the image carrier 1 is not the image portion (almost 0V) but the background image portion (−600V), the positive and negative toner currents are subtracted, or the positive current flows. Therefore, the toner does not move to the image carrier 1 side.

(Equilibrium state with toner flying current in the developing unit)
The important point here is that, as shown in FIG. 5, there is a phase shift between the applied developing bias voltage L1 and the toner current value L2 due to toner flying. That is, there is a delay in the change in the toner current value L2 with respect to the change in the development bias voltage L1.

  This phase shift appears when the frequency of the developing bias voltage is increased to improve the flying property of the toner with respect to the improvement of the system speed.

  During normal development, development proceeds (negatively charged toner adheres to the image portion) before the image portion of the image carrier 1 enters the development portion and then escapes. Is positive / negative deductive (unbalanced state, development in progress), but at the time of evacuation, it becomes almost equal to positive and negative (equilibrium state), and development becomes saturated.

  As the system speed increases, even if the frequency of the developing bias voltage is increased in order to quickly reach the equilibrium state, there is no response to this, so the phase shift occurs.

  By examining the magnitude of this phase shift, it is possible to determine how fast the development reaches the equilibrium state, that is, whether the development is saturated in a short time passing through the development section.

  In other words, when the phase difference between the applied development bias voltage and the toner current value due to toner flying is small, the development is in a state where it approaches the equilibrium state faster and there is no loss with respect to the applied bias, and the toner is faithfully Suggest moving. However, when the detected toner current value is delayed with respect to the phase of the development bias voltage, the development is also delayed until reaching the equilibrium state.

  The equilibrium state of development is a state where the amount of toner flying (collected) from the image carrier onto the toner carrier and the amount of toner (development) flying from the toner carrier to the image carrier are equal. In this state, since the electrostatic contrast is sufficiently buried, the amount of toner flying from the toner carrier side to the image carrier side and from the image carrier side to the toner carrier side even when the development / collection phase is switched. The amount of toner flying is equal, and a constant amount of toner always remains on the image carrier. In such an equilibrium state, the development characteristics are stable, and a stable image density can be obtained against various noises.

(Phase shift between development bias voltage and toner current value)
The image forming apparatus according to the present embodiment has the following functions so that the development in the developing unit quickly reaches an equilibrium state and a stable image density can be obtained even when the system speed is increased.

(1) The developing bias power source 30 applies a developing bias voltage having a predetermined high frequency for causing the toner to fly in the developing portion facing the image carrier 1 and developing the toner carrier 20.
(2) The toner current detection means 32 detects a toner current value due to toner flying in the developing unit,
(3) The development bias control means 33 sets and controls the development bias condition so that the phase deviation between the development bias voltage and the toner current value detected by the toner current detection means 32 is minimized.

  However, the development bias condition is the setting of the development bias voltage applied by the development bias power supply 30 and is at least one of a DC component Vdc of an alternating voltage having a predetermined high frequency, a peak-to-peak voltage Vpp, and a duty ratio. Is preferred.

  An example of a schematic procedure for checking the magnitude of the phase shift (a characteristic value indicating the phase shift) and setting and controlling the development bias condition so that the phase shift is minimized will be described later.

  First, with respect to the definition of the characteristic value indicating the magnitude of the phase shift between the developing bias voltage and the toner current value, Examples 1 to 5 of the method for detecting and calculating the phase shift are shown in FIGS. It explains using.

  In the following description, the toner collection side region (region where the toner moves to the toner carrier side) where the toner current value is positive is used to define the characteristic value indicating the phase shift. Of course, a toner development side region (region where toner moves to the image carrier side) where the toner current value is negative may be used.

  Although the image carrier surface potential is set to 0 V as the image portion potential, a predetermined potential close to the background portion potential may be set.

  The problem is to obtain characteristic values that represent the relative magnitude of the relative phase shift, and the above-mentioned condition settings can optionally represent the same effect (correlation with the speed at which the equilibrium state is reached). it can.

<Phase shift calculation method example 1>
FIG. 6 is a schematic explanatory diagram of a calculation method example 1 of a phase shift between the developing bias voltage and the toner current value. L1 indicates a developing bias voltage (see the left vertical scale), and L2 indicates a toner current value (see the right vertical scale). The horizontal axis is time.

  This calculation method example 1 is a method in which a characteristic value indicating a phase shift is detected from the area of a toner recovery area (in the graph) (which may be a development area as described above).

  As shown in FIG. 6, the point at which the development bias voltage switches from the image carrier 1 side to the toner carrier 20 side in the direction in which the toner is collected is a point, and the positive value of the toner current value detected every 3 to 10 μsec. A point that halves the area (integrated value) of the area (toner collection side) is defined as point b.

  After the point a, the area from the point when the toner current value associated with the toner flight is detected as positive to the point b is S1, and the area from the point b until immediately before the toner current value associated with the toner flight is detected as negative is S2. Then, S1 = S2.

  The time difference between the points a and b is set as a characteristic value indicating a phase shift.

  Here, the integration value of the current value at the time of toner recovery (section in which the toner flies from the image carrier 1 to the toner carrier 20) is used as a reference, but the development side (from the toner carrier 20 to the image carrier 1). The integral value of the current value during the toner flight may also be used.

  In FIGS. 5 to 10, a rectangular wave voltage is used as a developing bias voltage to be applied at the time of developing, but a waveform having a different shape such as a step wave shape, a blank pulse shape, or a trapezoid shape may be used.

  If various development bias conditions such as Vpp, Vdc, duty ratio, etc. are changed to find and set a development bias condition that minimizes the difference between point a and point b (characteristic value indicating phase shift), it is more balanced. It is quickly led to a development state close to, and more stable development characteristics can be obtained.

  Therefore, by minimizing this phase shift, it is possible to set a developing bias condition that can produce a stable image density with respect to various fluctuations (Ds, toner transport amount, toner charge amount).

<Phase shift calculation method example 2>
FIG. 7 is a schematic explanatory diagram of a calculation method example 2 of a phase shift between the developing bias voltage and the toner current value. L1 indicates a developing bias voltage (see the left vertical scale), and L2 indicates a toner current value (see the right vertical scale). The horizontal axis is time.

  This calculation method example 2 is a method of detecting a characteristic value indicating a phase shift from the peak of the toner recovery area (or development area).

  As shown in FIG. 7, the point at which the development bias voltage switches from the image carrier 1 side to the toner carrier 20 side in the direction in which the toner is collected is defined as a point, and then the toner current value is changed to I ( 1), I (2)... Are sampled.

The toner current value I (n) at this time is
I (n) <I (n + 1) and I (n + 1)> I (n + 2)
When the above condition is satisfied, the point of I (n + 1) is recognized as the peak (point b) of the toner current value.

  The time difference between the points a and b is set as a characteristic value indicating a phase shift.

  The development bias conditions (Vpp, Vdc, duty ratio, etc.) are feedback-controlled so that the difference between the points a and b (characteristic value indicating phase shift) becomes a minimum value. By this method, development is promptly led to a development state that is closer to equilibrium, and more stable development characteristics can be obtained.

  Further, the development bias is set such that the difference between the point b and the point b where the development bias voltage is switched in the direction in which the toner is developed from the toner carrier 20 side to the image carrier 1 side and the point b is maximized. A method of feedback control of conditions may be used.

<Phase shift calculation method example 3>
FIG. 8 is a schematic explanatory diagram of a third calculation method example 3 of the phase shift between the developing bias voltage and the toner current value. L1 indicates a developing bias voltage (see the left vertical scale), and L2 indicates a toner current value (see the right vertical scale). The horizontal axis is time.

  This calculation method example 3 is a method of detecting a characteristic value indicating a phase shift from a positive / negative switching point of the toner current value.

  As shown in FIG. 8, the point at which the development bias voltage switches from the image carrier 1 side to the toner carrier 20 side in the direction in which the toner is collected is a point, and then the toner current value is set to I ( 1), I (2)... Are sampled.

At this time, the current value I (n) is I (n)> 0 and I (n + 1) <0
When the above condition is satisfied (for example, the median value of I (n) time and I (n + 1) time) is recognized as a positive / negative switching point (point b) of the toner current value.

  The time difference between the points a and b is set as a characteristic value indicating a phase shift.

  The development bias conditions (Vpp, Vdc, duty ratio, etc.) are feedback-controlled so that the difference between the points a and b (characteristic value indicating phase shift) becomes a minimum value. By this method, development is promptly led to a development state that is closer to equilibrium, and more stable development characteristics can be obtained.

<Phase shift calculation method example 4>
FIG. 9 is a schematic explanatory diagram of a calculation method example 4 of the phase shift between the developing bias voltage and the toner current value. L1 indicates a developing bias voltage (see the left vertical scale), and L2 indicates a toner current value (see the right vertical scale). The horizontal axis is time.

  This calculation method example 4 is a method (1) for estimating a characteristic value indicating a phase shift from an integral value of a detected current value in a toner recovery area (or development area).

  As shown in FIG. 9, a point at which the development bias voltage switches from the image carrier 1 side to the toner carrier 20 side in the direction in which the toner is collected is a point, and then the toner current value detected as a positive value is Sampling is performed as I (1), I (2)... Every 3 to 10 μsec.

  An integral value (S1) of the toner current value up to a predetermined point (for example, a point a 'at which the developing bias voltage switches in the direction in which the toner is developed) is calculated.

  Using this integrated value (S1) as a characteristic value indicating the reverse (smallness) of the phase shift, feedback control is performed on the development bias conditions (Vpp, Vdc, duty ratio, etc.) so that S1 is maximized. By this method, development is promptly led to a development state that is closer to equilibrium, and more stable development characteristics can be obtained.

<Phase shift calculation method example 5>
FIG. 10 is a schematic explanatory diagram of a calculation method example 5 of the phase shift between the developing bias voltage and the toner current value. L1 indicates a developing bias voltage (see the left vertical scale), and L2 indicates a toner current value (see the right vertical scale). The horizontal axis is time.

  This calculation method example 5 is a method (2) of estimating the characteristic value indicating the phase shift from the integral value of the detected current value in the toner recovery area (or development area).

  As shown in FIG. 10, from the point (a 'point) at which the developing bias voltage switches in the direction in which the toner is developed from the toner carrier 20 side to the image carrier 1 side, the toner that is still detected with a positive value. The current value is sampled as I (1), I (2)... Every 3 to 10 μsec.

  An integral value (S2) of the toner current value up to a point (point b) at which the toner current value switches to negative is calculated.

  Using this integrated value (S2) as a characteristic value indicating a phase shift, feedback control is performed on development bias conditions (Vpp, Vdc, duty ratio, etc.) so that S2 is minimized. By this method, development is promptly led to a development state that is closer to equilibrium, and more stable development characteristics can be obtained.

(Development bias condition setting process)
By the phase shift detection method as described above,
(1) Development bias conditions (Vpp, Vdc, duty ratio, etc.) of the high-frequency development bias voltage applied by the development bias power supply 30;
(2) From the change in the toner current value detected by the toner current detection means 32,
(3) The development bias control means 33 detects the characteristic value indicating the phase shift, and controls the development bias conditions (Vpp, Vdc, duty ratio, etc.) so as to minimize the characteristic value indicating the phase shift.

  An example of this specific processing procedure will be described below. A characteristic value indicating the phase shift is referred to as a phase shift.

<Procedure example 1>
FIG. 11 is a flowchart illustrating a first example of the general procedure for feedback control of the detected phase shift to the developing bias condition. A procedure example of the developing bias condition setting process will be described with reference to FIG.

  When setting control is started, first, in step S11, a current value (toner current value) due to toner flying in the developing unit is detected.

  More specifically, a predetermined high-frequency development bias voltage is applied to the toner carrier 20 carrying the toner under the current development bias condition by the development bias power source 30, and an image corresponding to the high-frequency development bias voltage is obtained by the toner current detection unit 32. A change in toner current with the carrier 1 is detected.

  Next, in step S12, the development bias control means 33 calculates a phase shift between the applied development bias voltage and the detected toner current value.

  The calculation of the phase shift is performed according to the phase shift detection method described above.

  In step S13, the developing bias control means 33 determines whether or not the phase shift is minimized.

  As a determination criterion, a known method for obtaining a minimum condition may be used. For example, set an arbitrary criterion such as taking data in advance and considering it as the minimum if it falls below a predetermined value, or setting the change direction of the condition and assuming that the value does not decrease due to the change in condition Can do.

  When it is determined in step S13 that the phase shift is minimized (step S13; Yes), step S14 is executed. That is, the development bias condition is determined based on the current conditions, and the development bias condition setting control process ends.

  If it is determined in step S13 that the phase shift has not yet been minimized (step S13; No), step S15 is executed. That is, the development bias control means 33 changes the development bias condition from the current condition to a predetermined direction.

  The processing procedure is repeated from the first step S11 after changing the developing bias condition. The loop from step S11 to step S15 is repeated until a Yes determination is made in step S13 and the development bias condition setting control process ends.

  This is the end of the description of Procedure Example 1.

<Procedure example 2>
FIG. 12 is a flowchart showing a second example of a schematic procedure for feedback-controlling the detected phase shift to the developing bias condition. A procedure example 2 of the developing bias condition setting process with the kicker pulse added will be described with reference to FIG.

  Procedure example 2 differs from procedure example 1 in that a kicker pulse is added as a developing bias condition for setting control. FIG. 13 shows an example of the developing bias voltage to which the kicker pulse K is added.

  In Procedure Example 1, at least one of Vpp, Vdc, and duty ratio is specified as the development bias condition, and a pulse voltage (kicker pulse) is added to the development bias voltage, that is, an alternating voltage having a predetermined high frequency. It is also preferable.

  In this case, the development bias condition desirably includes at least one of a pulsed voltage (kicker pulse) waveform, a pulse time, and a potential difference between pulses. It can be expected to detect the phase shift more remarkably.

  A procedure example 2 will be described below as a procedure for developing bias condition setting processing when a kicker pulse is added.

  When the setting control is started, first, in step S21, a current value (toner current value) due to toner flying in the developing unit is detected.

  Specifically, the development bias power supply 30 adds a kicker pulse set as an initial condition to the development bias conditions (Vpp, Vdc, duty ratio, etc.) that have already been set, and a predetermined amount is applied to the toner carrier 20 carrying the toner. A high frequency development bias voltage is applied. Then, the toner current detecting means 32 detects a change in toner current with the image carrier 1 corresponding to the high-frequency developing bias voltage to which the kicker pulse is added.

  Next, in step S22, the development bias control means 33 calculates a phase shift between the applied development bias voltage and the detected toner current value.

  The calculation of the phase shift is performed according to the phase shift detection method described above.

  In step S23, the developing bias control means 33 determines whether or not the phase shift is minimized.

  As in the case of the procedure example 1, a known method for obtaining the minimum condition may be used as the determination criterion.

  If it is determined in step S23 that the phase shift is minimized (step S23; Yes), step S24 is executed. That is, the development bias condition to which the kicker pulse is added is determined based on the current conditions, and the development bias condition setting control process ends.

  If it is determined in step S23 that the phase shift has not yet been minimized (step S23; No), step S25 is executed. That is, the development bias control means 33 changes the kicker pulse condition among the development bias conditions from the current condition to a predetermined direction.

  The processing procedure is repeated from the first step S21 after changing the kicker pulse condition among the development bias conditions. The loop from step S21 to step S25 is repeated until a Yes determination is made in step S23 and the development bias condition (kicker pulse condition) setting control process ends.

  This is the end of the description of Procedure Example 2.

  As described above, according to the image forming apparatus according to the present embodiment, in a method in which only the toner is conveyed to the developing unit and developed, the toner flying current value in the developing unit is detected and the predetermined high frequency developing bias applied. The development bias condition is determined so as to minimize the phase shift between the two.

  As a result, even when the process speed is further increased, the development can be completed in a state where the development state is closer to the equilibrium state in the developing unit, and a more stable image density can be obtained even if various members are fluctuated. Can do.

  In addition, the above-mentioned embodiment is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Photoconductor (image carrier)
DESCRIPTION OF SYMBOLS 2 Developing apparatus 4 Transfer means 5 Cleaning means 6 Charging means 7 Exposure means 8 Recording medium 20 Developing roller (toner carrier)
21 toner layer (or developer) regulating member 22a toner conveying roller 22b developer conveying roller (developer carrying member together with 23)
23 Magnetic roller 24 Toner (or developer) conveying member 25 Toner (or developer)
26 Toner (or developer) agitating / conveying tank 30 Developing bias power supply 31 Bias power supply for toner conveying roller (or developer carrying member) 32 Toner current detecting means 33 Developing bias controlling means

Claims (5)

An image carrier carrying an electrostatic latent image formed on the surface;
A developing device having a toner carrier for carrying and transporting charged toner on the surface and developing the electrostatic latent image on the image carrier disposed oppositely with the toner;
A developing bias power source for applying a developing bias voltage for causing toner to fly to the toner carrying member at a developing portion facing the image carrier and developing;
Development bias control means for setting a development bias condition which is a condition for applying a development bias voltage by the development bias power supply;
Toner current detecting means for detecting a toner current value due to toner flying in the developing unit,
The development bias voltage by the development bias power supply is an alternating voltage having a predetermined high frequency,
The developing bias control means includes
The image forming apparatus, wherein the developing bias condition is controlled so that a phase shift between the developing bias voltage and the toner current value detected by the toner current detecting unit is minimized. The image forming apparatus according to claim 1, wherein the developing bias condition is at least one of a DC component Vdc of an alternating voltage having a predetermined high frequency, a peak-to-peak voltage Vpp, and a duty ratio. The development bias voltage by the development bias power source is obtained by adding a pulse voltage to the alternating voltage having the predetermined high frequency,
The image forming apparatus according to claim 1, wherein the development bias condition includes at least one of a waveform of the pulse voltage, a pulse time, and a potential difference between pulses. The developing device includes:
The developer carrying body for carrying and carrying the developer including the toner and the carrier on the surface and supplying the toner in the developer to the toner carrying body arranged to face each other. The image forming apparatus according to any one of 1 to 3. The developing device includes a plurality of the toner carriers.
The developing bias control means includes
Collectively a plurality of the toner carriers or for each toner carrier,
5. The development bias condition is controlled such that a phase shift between the development bias voltage and a toner current value detected by the toner current detection unit is minimized. The image forming apparatus described in 1.

Images