JP4736626B2 - Developer layer detecting device, developing device and image forming device using the same - Google Patents

Description

  The present invention relates to a developing device used in an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a printing apparatus, and more particularly, to a developer layer detecting device for detecting a change in the thickness of a developer layer provided in a developing area, and the same. The present invention relates to improvement of the developing device and the image forming apparatus used.

  As a developing device used in an image forming apparatus such as a conventional electrophotographic system, a one-component developing system using a one-component developer (toner) made only of toner and a two-component developer using a toner and a carrier are used. Component development methods are known. Among them, the one-component development type developing device does not require mixing with the carrier, stirring, and toner concentration control, so the device can be reduced in size and cost, and further, the developer can be replaced. Since it is unnecessary, it is increasingly used mainly in printers that require maintenance-free operation.

  Conventionally, in the one-component development method, as a general method for forming a toner layer having a predetermined toner amount and toner charge amount on a development roll, a toner supply roll made of a foam is pressed against the development roll. A method (contact toner supply method) is adopted in which a large amount of toner adheres on the developing roll within the nip area formed by the pressing force, and then the layer thickness of the toner is regulated by a regulating blade, and at the same time, friction charging is performed. (For example, refer to Patent Document 1).

JP 2001-75357 A (Embodiment of the Invention, FIG. 2) Japanese Patent Laid-Open No. 4-93965 (Example, FIG. 2) JP-A-6-194944 (Example, FIG. 1)

However, in such a system, the toner adhesion amount and the toner charge amount on the developing roll change with time, and it is difficult to maintain stable development characteristics over a long period of time.
For example, if a regulation blade is used, the toner is mechanically scraped off by the regulation blade, so among toners having a certain particle size distribution, the larger the particle size toner, the more the passage of the regulation blade is inhibited, and the development is repeated. As a result, the toner having a small particle diameter is preferentially consumed, and the average particle diameter of the toner remaining in the developing device tends to increase. As the average particle size of the toner increases, the specific charge (charge amount per unit weight) of the toner generally decreases, and as a result, the amount of toner attached to the developing roll gradually increases or conversely Since the charge amount decreases, the image density and the fog increase.

  On the other hand, when a DC electric field is applied between the foam toner supply roll and the development roll as a supply bias for supplying toner to the development roll, the toner supply amount increases as the number of printed sheets increases, and the regulation blade In other words, the charge amount of toner applied by the toner decreases and the image quality fluctuates.

Therefore, how to keep the toner layer formed on the developing roll constant is a very important technique for long-term stabilization of development characteristics.
For this purpose, a measurement method is required that accurately and stably measures the toner layer thickness (corresponding to the toner adhesion amount) on the developing roll.
Patent Document 2 describes a method of using a two-component developer and supplying nonmagnetic toner to a developing roll from a magnetic brush of a toner supply roll (in this example, a magnet roll). In this method, for example, as shown in FIG. 11, a change in the toner layer thickness on the developing roll 101 is detected by an optical sensor 102 disposed in the vicinity of the developing roll 101, and the developing roll 101 and The bias V2 applied to the toner supply roll 103 is adjusted so as to keep the toner layer thickness constant. However, in this method, since the optical sensor 102 is used, a space for installing the optical sensor 102 is ensured, and the detection surface is easily affected by the contamination of the detection surface by the toner and the toner color. Tends to be difficult. In addition, it is necessary to keep the gap between the detection surface of the optical sensor 102 and the toner surface constant, and many problems remain such that it is necessary to accurately control the rotational shake and assembly accuracy of the developing roll 101 itself. In the figure, reference numeral 104 denotes a photosensitive drum on which an electrostatic latent image is carried.

  In addition, instead of directly measuring the thickness of the toner layer on the developing roll, a method of measuring indirectly is also proposed. In Patent Document 3, a one-component developer (toner) is used, a patch pattern is formed on a photosensitive drum, and the toner layer thickness on the developing roll is converted by measuring this density. Based on this result, A system is shown in which the bias applied to the toner supply roll is adjusted to adjust the amount of toner supplied from the toner supply roll to the development roll. However, when developing the pattern on the photosensitive drum, the toner charge amount varies depending on the environment, so the development characteristic itself is affected, and the toner layer thickness on the developing roll is accurately measured. It's hard to say.

  The present invention has been made to solve the above technical problem, and is a developer layer detection device capable of stably and accurately measuring the developer layer thickness on the developer carrier, and the same. The present invention provides a developing device and an image forming apparatus using the above.

That is, as shown in FIG. 1, the basic configuration of the present invention is a developer layer detection device for detecting the layer thickness of a developer layer on a developer carrier 1 on which a developer G is carried and conveyed. A detection contact 2 that contacts the developer layer on the developer carrier 1 and follows a change in the thickness of the developer layer , and a physical quantity that corresponds to a change in a predetermined physical quantity. It is characterized by comprising a variable means 3 and a physical quantity change detecting means 4 for detecting the layer thickness of the developer layer based on the physical quantity change by the physical quantity variable means 3.

In such technical means, the developer layer detection device according to the present invention may be any device that can detect a change in the thickness of the developer layer on the developer carrier 1. Or a mode of detecting using electrostatic capacity. Furthermore, although the aspect which measures strain resistance and the volume resistance is also included , in this invention, piezoelectricity or an electrostatic capacitance is utilized .
Further, the shape of the detection contact 2 may be any shape as long as it can detect a change in the layer thickness of the developer layer on the developer carrier 1 and can form a certain nip area stably. In the present invention, a sheet-like member is used from the viewpoint of performing stable measurement. Although the detection contact 2 itself if detecting a thickness variation of the developer layer on the developer carrying member 1 is not particularly limited whether movable (e.g. aspect rotated), a sheet from the viewpoint of performing stable detection A mode in which the member is fixedly arranged is preferable.

Furthermore, as the physical quantity varying means 3 of the present invention, the follow-up change of the detection contact 2 may be changed to a predetermined physical quantity. For example, a measurement voltage is applied to detect the impedance of the developer layer. Aspect (specifically, when measuring capacitance or the like) can be mentioned. Further, the physical quantity varying means 3 may be integrated with the detection contact 2, and in this case, for example, the detection contact 2 may be provided with piezoelectricity. In this way, the follow-up change of the detection contact 2 can be taken out as a change in physical quantity by the physical quantity varying means 3.
Furthermore, the physical quantity change detecting means 4 calculates the developer layer thickness by performing arithmetic processing or the like based on information (detection signal) from the physical quantity variable means 3, and is usually constituted by an electronic circuit or the like. .

The developer G to which the present invention is applied is not particularly limited, and may be any one of a non-magnetic and magnetic one-component developer and a two-component developer containing a toner and a carrier. However, in the present invention, a one-component developer is used .

  And when using a sheet-like member as the detection contact 2 in the present invention, the thickness and shape of the sheet-like member are not particularly limited as long as it can follow the developer layer thickness change on the developer carrier 1, Usually, one end on the upstream side in the rotation direction of the developer carrier 1 is fixedly supported, and the other end is disposed as a free end. For example, there is no problem as long as both ends are fixedly arranged, a wide nip region can be formed in the central portion, and the developer layer thickness can be followed.

Moreover, as a first aspect of the sheet-like member of the present invention, a piezoelectric material having piezoelectricity in the thickness direction of the sheet is used. According to this, it becomes possible to easily detect the change in thickness while the layer thickness regulation and the frictional charge to the developer layer on the developer carrying member 1 with a simple structure, detect the contact 2 And the physical quantity varying means 3 can be configured integrally. As a typical embodiment of this piezoelectric material, there is a PVDF sheet (polyvinylidene fluoride sheet: polymer piezoelectric sheet) that is uniaxially stretched and then polarized. In this case, the structure of the sheet-like member is such that the electrode layers are processed on both surfaces of the polymer piezoelectric sheet, and a processing layer such as a release layer is further provided on the electrode layer on the surface in contact with the developer G, for example. Anyway, it is only necessary to detect the piezoelectric characteristics, but in the present invention, a surface protective layer for frictionally charging the developer G is used .

Furthermore, as a second aspect of the sheet-like member of the present invention, the sheet-like member is preferably composed of a conductive material capable of detecting the electrostatic capacity of the developer G sandwiched between the developer carrier 1 and this. Even if it does, it becomes possible to detect easily the change of the layer thickness of the developer layer on the developer carrier 1 with a simple structure. The thickness of the conductive material is not particularly limited as long as the capacitance can be detected. Even when a treatment layer such as a release layer is provided on the surface in contact with the developer G, the layer of the developer layer It is only necessary that a change in thickness can be detected as a change in capacitance. When the sheet-like member of the second aspect is used, a charging bias application is applied in which a charging bias is applied between the developer carrier 1 and the detection contact 2 in order to charge the developer G. In addition, in order to refresh the developer G charged to a polarity opposite to the charging polarity by the charging bias attached to the detection contact 2, a reverse is applied between the developer carrier 1 and the detection contact 2. A discharge bias application unit that applies a discharge bias that can discharge the developer G charged in polarity is provided.

Further, the present invention is intended not only for the developer layer detection apparatus described above but also for the development apparatus. That is, in this case, a developer carrier 1 that faces the image carrier on which the electrostatic latent image is carried and is rotatable and carries the developer G on the surface, and the developer carrier 1 and the image carrier A developer supply member that is provided at a position upstream of the developer carrier 1 in the rotation direction of the developer carrier 1 and supplies the developer G to the developer carrier 1, and a rotation direction of the developer carrier 1 from the developer supply member And a developer layer detection device provided at a position on the downstream side and upstream of the portion facing the image carrier, and the developer layer detection device described above may be provided as the developer layer detection device.
At this time, the developer carrier 1 may be any one that can carry and transport the developer G, and includes a drum shape and a belt shape. Further, from the viewpoint of effective development, it is preferable that the developer carrier 1 and the image carrier are in contact with each other. However, the image carrier and the developer carrier 1 may be non-contacted. May be a mode of moving in the Whit direction (the same direction at opposite parts) or an aspect of moving in the Against direction (the opposite direction at the opposite parts). Furthermore, the developer carrier 1 may be an elastic body or a rigid body, and may be, for example, a flexible tube.
Thus, by detecting the thickness of the developer layer on the developer carrier 1, for example, it is possible to appropriately adjust the development conditions and the like.
A supply bias applying means that is provided between the developer carrier 1 and the developer supply member and applies a supply bias to supply the developer G from the developer supply member to the developer carrier 1; It is preferable to include supply bias control means for controlling the supply bias so that the layer thickness of the developer layer detected by the agent layer detection device becomes a predetermined layer thickness.
Furthermore, the present invention is also directed to an image forming apparatus. In this case, the above-described developing device is used as an image carrier on which an electrostatic latent image is carried and a developing device for developing the electrostatic latent image on the image carrier. May be used.

According to the basic configuration of the present invention , the detection contact that contacts the developer layer on the developer carrier on which the developer is carried on the surface and follows the layer thickness change of the developer layer , and the detection contact Since there is provided a physical quantity variable means for making the follow-up change of the child correspond to a predetermined physical quantity change , and a physical quantity change detecting means for detecting the layer thickness of the developer layer based on the physical quantity change by the physical quantity variable means. It is possible to provide a developer layer detection device that can stably detect a change in the layer thickness of the developer layer without considering mechanical accuracy such as shake accuracy of the agent carrier.
Further, it is not necessary to secure a large space for installing the detection contact, and it is possible to realize a developer layer detection device that is small and has a high degree of design freedom. Furthermore, it is possible to perform stable detection over a long period of time without being affected by dirt adhesion due to the floating of the developer or the color tone of the developer.
Since a piezoelectric sheet-like member is used as the detection contact, it becomes possible to detect a change in piezoelectricity due to a change in the thickness of the developer layer while regulating the layer thickness and frictionally charging the developer layer. In addition, since a sheet-like member capable of detecting capacitance is used as the detection contact and a charging bias is applied, a change in capacitance due to a change in the thickness of the developer layer is detected while the developer layer is charged. become able to.
Further, by using such a developer layer detection device, it is possible to provide a development device and an image forming apparatus that can stably detect a change in the developer layer thickness on the developer carrier. Become.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 2 shows an image forming apparatus according to the first embodiment to which the present invention is applied.
In the figure, reference numeral 21 denotes a photoconductor on which an electrostatic latent image made of an organic photoconductor rotating in the direction of an arrow is carried. The photoconductor 21 is charged by a charging device 22 such as a charging roll, and a laser writing device. Alternatively, the electrostatic latent image is written by the exposure device 23 having an LED array or the like. The written electrostatic latent image is formed as a potential image based on a contrast with a high potential portion not exposed to light because the surface potential of the photosensitive member 21 in the portion exposed to light is lowered.

Further, the developing device 30 disposed opposite to the photosensitive member 21 accommodates toner as a non-magnetic one-component developer in a developing housing 31, and carries the toner on a developing roll 32 as a developer carrying member. By applying a developing bias in which an AC voltage is superimposed on a DC voltage to the developing roll 32 from a bias power source 33, the developing roll 32 is held at an intermediate potential between the high potential portion and the low potential portion of the electrostatic latent image, The image portion of the electrostatic latent image on the photoreceptor 21 is developed with charged toner.
Further, a toner supply roll 34 that supplies toner to the development roll 32 at a position spaced apart from the development roll 32 is provided behind the development roll 32 so that the toner is supplied from the toner supply roll 34 to the development roll 32. It has become.

Further, the transfer device 26 is composed of, for example, a transfer roll disposed in contact with the photoconductor 21 and is applied with a transfer bias in a direction in which a toner image developed on the photoconductor 21 is attracted by a bias power source 27, and the photoconductor. The toner image on 21 is transferred to the recording material 28.
Further, the toner remaining on the photosensitive member 21 after the transfer is removed by, for example, a doctor blade type cleaning device 29.
Furthermore, the recording material 28 onto which the toner image on the photoreceptor 21 has been transferred is conveyed to a fixing device 50, and the toner image is fixed to the recording material 28 by the fixing device 50. The fixing device 50 has, for example, a heat roll method, and includes a heating roll 51 and a pressure roll 52, and a toner image is recorded on the recording material by passing the recording material 28 between the heating roll 51 and the pressure roll 52. 28 is fixed.

  Here, the developing device 30 which is a feature of the present invention will be described in detail with reference to FIG. In the figure, a developing device 30 has a developing housing 31 that opens toward the photosensitive member 21, and a developing roll 32 can be rotated to a position spaced from the photosensitive member 21 at a position facing the opening of the developing housing 31. Is housed in.

  Behind the developing roll 32, a toner supply roll 34 for supplying toner to the developing roll 32 is disposed at a position separated from the developing roll 32. In addition, the developing roll 32 and the toner supply roll 34 are configured to rotate in the same direction (with direction) at a portion facing each other. The toner supply roll 34 may be in the form of a belt as long as it can supply toner to the developing roll 32.

A bias power source 35 is connected between the toner supply roll 34 and the developing roll 32, and a supply bias for supplying toner from the toner supply roll 34 to the developing roll 32 is applied.
Further, a toner hopper 36 for storing toner is provided behind the toner supply roll 34, and the toner inside is agitated by an agitator (not shown), for example, so that the toner is conveyed to the toner supply roll 34 side. Yes. Reference numeral 37 in the figure denotes a scraping member made of a PET (polyester) sheet or the like for scraping off the toner on the toner supply roll 34, and scrapes off the toner adhering to the toner supply roll 34. The upper toner amount is kept constant.

Further, around the developing roll 32 of the present embodiment, there is an upstream side in the toner transport direction from a facing portion (developing area) between the photosensitive member 21 and the developing roll 32, and the developing roll 32 and the toner supply roll 34. A regulating blade 41 that regulates the layer thickness of the toner on the developing roll 32 and frictionally charges the toner on the developing roller 32 is disposed on the downstream side in the toner conveyance direction of the facing portion. One end of the regulating blade 41 is fixed to a support member 42 fixed to the developing housing 31, and the other end is disposed as a free end, and contacts the toner layer on the developing roll 32 therebetween. Are arranged as follows. In particular, in the present embodiment, the regulation blade 41 serves as both a detection contact for detecting a change in the toner layer thickness on the developing roll 32 and the physical quantity varying means. Therefore, the physical quantity change signal from the regulation blade 41 is used. Based on this, it is connected to a processing device 43 as physical quantity change detecting means for performing, for example, impedance conversion or processing for calculating the toner layer thickness. The processing device 43 is adapted to transmit a signal to a control device 60 that can control the bias power source 35. Therefore, in the present embodiment, the developer layer detecting device is configured by the regulation blade 41 and the processing device 43.
On the other hand, a toner collecting roll 44 that collects residual toner on the developing roll 32 is provided on the downstream side from the developing region and on the upstream side from the facing portion between the developing roll 32 and the toner supply roll 34.

Here, the details of the regulating blade 41 in the present embodiment will be described.
As shown in FIG. 4, the regulation blade 41 in the present embodiment is obtained by bonding a piezoelectric sheet 41 a polarized in the thickness direction to a support member 41 b such as a metal plate, and the electrode 412 of the piezoelectric sheet main body 411. Among them, a surface protective layer 41c for protecting the electrode 412 is provided on the surface of the electrode 412 on the developing roll 32 side. For example, a 100 μm thick phosphor bronze plate may be used as the metal plate, and a 50 μm thick PET film may be adhered as the surface protective layer 41 c.
Piezoelectric sheet 41a in the present embodiment has a deposited film of aluminum or the like on both sides of a β-crystal PVDF sheet obtained by a low-temperature uniaxial stretching method in which a PVDF (polyvinylidene fluoride) melt-formed sheet is stretched in one direction. It is a polymer piezoelectric sheet formed and subjected to a polarization treatment in the thickness direction by applying a high electric field in a high temperature environment. In the present embodiment, a KF piezo film manufactured by Kureha Chemical Industry was used, and the sheet thickness was appropriately selected from 30 to 100 μm. At this time, the relative dielectric constant of the PVDF sheet was 13, and the piezoelectric constant was 27 (pC / N).
In this embodiment, a polymer piezoelectric sheet (specifically, a PVDF sheet) is used as the piezoelectric sheet 41a. However, for example, a sheet in which an inorganic piezoelectric material such as barium titanate or PZT is dispersed in a polymer is polarized. It can be processed.

  In the present embodiment, among the electrodes 412 of the piezoelectric sheet 41a, the electrode 412 on the surface protection layer 41c side is grounded from one end side of the regulating blade 41, and the other electrode 412 is connected to the processing apparatus 43 described above. ing. According to such a configuration, an electromotive force (amount of voltage) due to the displacement of the electric dipole polarized by the piezoelectric sheet 41a being deformed (stretching strain, sliding strain, etc.) with the change in the toner amount on the developing roll 32. : Equivalent to a physical quantity), and the toner layer thickness is detected by detecting the generated voltage quantity.

Here, the supply bias applied between the toner supply roll 34 and the developing roll 32 in the present embodiment will be described.
FIG. 5 shows an example of the voltage waveform of the supply bias in the present embodiment. The operation time (corresponding to the operation region) in which the trapezoidal wave (rectangular wave) has a large voltage fluctuation and the subsequent non-voltage nonzero The voltage waveform forms one cycle with the action time (corresponding to the non-action area). The bias power supply 35 is configured so that this voltage waveform is applied. The toner supply roll 34 is applied with a waveform superimposed on the developing bias applied to the developing roll 32.
In other words, in the present embodiment, toner flying from the toner supply roll 34 to the developing roll 32 is performed during an action time with a large fluctuation of the trapezoidal wave, and development is performed by changing the ratio (duty ratio) of the action time in one cycle. The amount of toner supplied to the roll 32 (proportional to the toner layer thickness) can be controlled.
That is, by changing the duty ratio, the amount of toner supplied to the developing roll 32 can be changed. For example, if the duty ratio is decreased, the toner layer thickness on the developing roll 32 is reduced, while the duty ratio is increased. This makes it possible to increase the toner layer thickness. At this time, the toner is not charged unnecessarily. If this operation time is continued, the amount of supplied toner becomes too large, and it becomes difficult to control the toner layer thickness to a predetermined value. The supply bias is not limited to the trapezoidal wave (rectangular wave) shown in FIG. 5 and may be, for example, a sine wave or a triangular wave as long as it has an operation time and a non-operation time.
In this embodiment, the amount of toner supplied onto the developing roll 32 is controlled by adjusting the duty ratio of the supply bias by the control device 60.

Next, the operation of the developing device 30 according to the present embodiment will be described with reference to FIG.
In the drawing, the toner stirred by an agitator (not shown) in the toner hopper 36 is supplied to the toner supply roll 34. At this time, there are uneven thickness and unevenness on the toner supply roll 34, and it is assumed that toner having a thick thickness is also adhered. The attached state varies depending on the temperature and humidity of the atmosphere, the amount of toner in the toner hopper 36, and the like.
When the toner adhering to the toner supply roll 34 reaches the facing gap between the toner supply roll 34 and the developing roll 32, the toner reciprocates in the gap by the supply bias from the bias power source 35. This reciprocal vibration is considered to be caused by electrostatic force acting on particles that are very slightly charged in the toner. Since the toner is not positively charged (frictionally charged) up to the opposing gap, the slight charge is caused by the friction between the inner wall of the toner hopper 36 or the agitator and the toner particles, the toner. It is presumed that they have a very small triboelectric charge due to friction between particles.

Normally, when toner particles rub against the inner wall of the toner hopper 36 or the agitator, the toner particles are charged with a single charge (due to CCA or the like in the toner particles), but friction between toner particles is charged with bipolar charges. Therefore, some toner particles adhere to the developing roll 32 side due to the alternating electric field effect of the supply bias.
At this time, as a result of the reciprocal vibration of the toner particles between the gaps due to the alternating electric field during the operation time of the supply bias, the toner deposited on the developing roll 32 forms a uniform thin layer. Further, since the duty ratio of the supply bias is small and the non-operation time is long, the charge amount of the toner attached on the developing roll 32 can be reduced. If only a DC electric field is applied as the supply bias, the toner layer formed on the developing roll 32 has a large amount of charge, and a non-uniform layer with large thickness unevenness is formed.

That is, a predetermined amount of toner with a small charge amount is supplied to the developing roll 32 by a supply bias applied between the developing roll 32 and the toner supply roll 34, and the toner is uniform and has a small surface potential on the developing roll 32. A thin layer is formed.
At this time, in the present embodiment, the bias having the voltage waveform shown in FIG. 5 is applied as the supply bias. To apply such a bias, for example, a waveform generation circuit based on a CPU or the like is used. The development bias may be applied to the bias power source 33 by superimposing the DC component and the AC component, and the supply bias may be applied to the bias power source 35 after combining the waveforms as shown in FIG.

Next, the operation of the regulating blade 41, the processing device 43, and the control device 60 in the present embodiment will be described in detail.
When the voltage amount generated in the regulation blade 41 due to the change in the toner amount on the developing roll 32 is sent from the regulation blade 41 to the processing device 43, the processing device 43 performs impedance conversion by, for example, a built-in equalizer amplifier. From the specific voltage amount, the toner layer thickness is calculated in light of the relationship between the toner layer thickness and the voltage amount obtained in advance. When the information from the processing device 43 is transmitted to the control device 60, it is determined whether the toner layer thickness is excessive or insufficient, and the supply bias is adjusted according to the result (the duty ratio of the supply bias is set). adjust).
Therefore, the amount of toner supplied to the developing roll 32 can be set to a predetermined amount.

Here, the operation of detecting a change in the toner layer thickness in the regulating blade 41 in the present embodiment will be described in detail.
First, the following example is given as the timing at which the change in the toner layer thickness is detected by the regulating blade 41.
(1) When the power of the image forming apparatus is turned on.
(2) When a new image signal (print signal) is input when the image forming apparatus is powered on but the image forming operation is stopped (at the start of a new print job).
(3) When a series of print jobs is completed.
(4) Between pages.
In such a case, when the developing device 30 immediately before that stops or when the image formation is completed, the toner is collected from the developing roll 32 by the toner collecting roll 44, and then no new toner is supplied. Is made.
That is, the supply bias (supplied by the bias power source 35) to the toner supply roll 34 is stopped while the developing roll 32 is rotating, or only the rotation of the toner supply roll 34 is stopped. Alternatively, the supply bias is stopped and the rotation of the toner supply roll 34 is also stopped. Accordingly, the toner is maintained substantially free from toner between the regulating blade 41 and the developing roll 32.

When starting or continuing the image forming operation from such a stopped state, when the toner supply from the toner supply roll 34 to the developing roll 32 is started, the regulating blade 41 is moved by the toner layer formed on the developing roll 32. Pressed.
At this time, a voltage corresponding to the amount of displacement is generated by displacement of the polarization charge (change in dipole moment) of the piezoelectric sheet 41a (see FIG. 4). The toner layer thickness on the developing roll 32 can be adjusted to a desired value by calculating the toner layer thickness in the processing device 43 from the voltage amount from the piezoelectric sheet 41a and controlling the supply bias in the control device 60. it can.
In addition, since the polarization of the piezoelectric sheet 41a is stable, a stable output can be obtained over a long period of time. Further, since the voltage generated in the piezoelectric sheet 41a has a very high impedance, there is no charging effect on the toner on the developing roll 32, and the frictional charging by the regulating blade 41 is not hindered.

  In the present embodiment, since the piezoelectric sheet 41a is used as the regulating blade 41, there are problems in the case of using a conventional optical sensor as the developer layer detecting device, that is, the rotational deflection accuracy and cylindricity of the developing roll. Decrease in detection accuracy of changes in toner adhesion caused when using products with poor runout accuracy, requiring expensive sensors, narrowing spatial freedom, requiring special assembly adjustments during installation, dirt There is no need to take into account a decrease in detection accuracy due to adhesion or the like.

  In the present embodiment, the regulation blade 41 controls both the layer thickness of the toner on the developing roll 32 and the frictional charging. However, for example, a charging bias is applied to the regulation blade 41 itself in the present embodiment. By doing so, it is possible to perform charging regulation by the regulating blade 41.

Embodiment 2
FIG. 6 shows an outline of the developing device 30 according to the second embodiment in the image forming apparatus to which the present invention is applied. In this figure, the present embodiment is configured in substantially the same manner as the developing device 30 (see FIG. 3) of the first embodiment, but uses a charged sheet instead of the regulating blade used in the first embodiment. Is different. Note that the image forming apparatus according to the present embodiment has the same configuration as that of the first embodiment, and is omitted here, and the developing device 30 will be described. In addition, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted here.

In the present embodiment, a charging sheet 45 is fixed to a support member 46 supported at one end of the developing housing 31 on the upstream side of the developing region at a portion facing the developing roll 32, and the other end on the developing roll 32. At a free end.
Therefore, in this embodiment, the charging sheet 45 regulates the charging of the toner on the developing roll 32 (note that the layer thickness of the toner layer is hardly regulated by the charging sheet 45). For this reason, a bias power source 38 is connected between the charging sheet 45 and the developing roll 32 so that a charging bias for charging the toner is applied.
In particular, the charging sheet 45 in the present embodiment detects the electrostatic capacity of the toner layer in the nip region between the charging sheet 45 and the developing roll 32 as described later. 45 is a detection contact of the developer layer detection device. The physical quantity varying means is performed by, for example, sending a measurement frequency from the processing apparatus 43 to the charging sheet 45, and the physical quantity change detecting means is also used by the processing apparatus 43. Then, information is transmitted from the processing device 43 to the control device 60, and the supply bias (applied by the bias power supply 35) is adjusted by the control device 60.
It should be noted that in the present embodiment, unlike the first embodiment, no toner collection roll is provided.

The charging sheet 45 in the present embodiment is configured as follows.
As shown in FIG. 7, the charging sheet 45 is made of a film sheet that is soft enough to deform along the outer periphery of the developing roll 32, and is only touching the toner layer lightly (pressure contact force is about 1 g / cm or less). In addition, it hardly has a function of regulating the amount of the toner layer on the developing roll 32.
Further, in this film sheet, a PVDF sheet 45a having a thickness of 50 μm in which an ion conductive material is dispersed therein and a volume resistivity is adjusted to 1 × 10 ⁸ Ω · cm at a portion facing the developing roll 32 side. On the opposite side, for example, an electrode layer 45b formed of a vapor deposition film or the like is formed.
Here, examples of the ion conductive material include perchlorates (for example, lithium perchlorate, sodium perchlorate, ammonium perchlorate, etc.), quaternary ammonium salts, and the like. In the present embodiment, by using an ion conductive material, the dispersibility in the PVDF sheet 45a is made more uniform than in the case of using an electron conductive material such as carbon black. When applied, a uniform charging electric field is applied over the entire toner.

In the present embodiment, when the developing roll 32 is provided with a charging sheet 45 having an effective width of 8 cm and -600 V is applied to the charging sheet 45 as a charging bias, an experiment is conducted. The toner amount immediately before the toner enters (corresponding to the toner supply amount) is 0.9 mg / cm ² , the nip width between the developing roll 32 and the charging sheet 45 is 10 mm, and the toner amount after the charging sheet 45 is 0.83 mg / cm ^2. The charge amount was −22 μC / g.

Next, the electrostatic capacity of the toner between the developing roll 32 and the charging sheet 45 in the present embodiment will be described with reference to FIG.
The dielectric constant of the toner layer can be obtained by Expression (11).
When the toner layer is handled as a mixed system of air and toner particles, Equation (12) is derived from an empirical rule, and Equation (13) can be obtained by considering the relative permittivity in the air in this equation. .
Next, the relative dielectric constant of the toner was determined as follows. Toner particles are molded into 0.4 mm-thick pellets (the load during molding is about 29.4 Pa (300 kgf / cm ² )), and YHP is used with a powder electrode of SE-43 type manufactured by Ando Electric Co., Ltd. When measurement was performed at a measurement frequency of 100 kHz using an impedance analyzer 4192A manufactured by the company, the dielectric constant obtained was 3.4 (at this time, the void ratio of the toner is estimated to be 0%).
On the other hand, the volume fraction of the toner particles in the toner layer was determined by equation (14). At this time, specifically, the toner adhesion amount on the developing roll 32 was measured by a peeling method using a book tape, and the toner layer thickness was measured by adjusting the depth of focus using a microscope. In this result, the volume fraction was constant at about 0.46 when the adhesion amount was 0.3 to 1.0 mg / cm ² .
From these formulas (11) to (14), formula (15) was obtained as the dielectric constant of the toner layer.
Therefore, the toner layer thickness is calculated by the equation (16) based on this dielectric constant.

As described above, in the present exemplary embodiment, by detecting the electrostatic capacitance (corresponding to C in Expression (16)) between the charging sheet 45 and the developing roll 32, the toner layer dielectric constant obtained in advance can be obtained. Further, it can be easily measured from the area where the charging sheet 45 is in contact with the toner layer (corresponding to S in Expression (16)).
That is, the electrostatic capacity between the developing roll 32 and the charging sheet 45 is obtained by electrostatic capacity = (dielectric constant × area / thickness). The dielectric constant of the toner layer is a value determined by the volume ratio of the toner particles to the volume of the voids and the dielectric constant of the toner particles (the dielectric constant of the toner bulk), but the adhesion amount range used for image formation (approximately 0.3 to 1.0 mg / cm ² ) is substantially constant, and thus the measured capacitance is inversely proportional to the toner layer thickness.

In the present embodiment, the toner supplied from the toner supply roll 34 to the developing roll 32 by the supply bias applied by the bias power supply 35 is charged by the charging sheet 45. At this time, the electrostatic capacity of the toner layer on the developing roll 32 (the toner layer sandwiched between the developing roll 32 and the charging sheet 45) is measured by the charging sheet 45, and the toner layer thickness is calculated by the processing device 43.
The controller 60 determines whether or not the calculated toner layer thickness has a predetermined toner layer thickness, and controls the bias power source 35 based on the determined result.
At this time, if it is determined that the thickness is greater than the desired thickness, the supply ratio is decreased by decreasing the duty ratio of the supply bias, while if it is determined to be thin, the duty ratio is increased. . In this way, by controlling the amount of toner supplied on the developing roll 32, it becomes possible to maintain a predetermined amount of toner on the developing roll 32, and to ensure uniform and stable development conditions. become.

For this reason, even when the toner supply amount fluctuates due to environmental fluctuations such as temperature and humidity, the toner supply amount can be quickly changed, and the toner layer thickness on the developing roll 32 can be kept constant.
Further, even if the surface property of the developing roll 32 changes due to long-term use and the toner adhesion amount fluctuates, the fluctuation can be detected in the same manner, and the toner layer thickness can be kept constant. become.

  In the present embodiment, when the capacitance is measured, the measurement signal is supplied by supplying from the processing device 43 an alternating voltage of 1 kHz and Vpp1V. In addition, since the charging sheet 45 is easily lifted from the toner layer when no charging bias is applied, the electrostatic capacity is measured by the developing roller 32 rotating and the charging sheet 45 being charged with a −600 V charging bias (development). Is applied to the roll 32, and the measurement is performed under the condition that the charging sheet 45 is sucked to the developing roll 32 side.

In the present embodiment, there has been shown a mode in which no countermeasure is taken in particular when toner contamination adheres to the charging sheet 45. Further, the charging sheet 45 is cleaned by cleaning the toner contamination as follows. Refreshed and more stable measurement is possible.
That is, as a refresh bias for refreshing the charging sheet 45 during a certain period, a bias in which an alternating current is superimposed on a direct current is applied to the potential of the developing roll 32. As a result, the positively charged (reverse polarity) toner adhering to the charging sheet 45 is peeled off from the charging sheet 45. The series of these mechanisms is presumed as follows.

When the toner layer corresponding to the image forming area passes through the charging sheet 45 during image formation, as shown in FIG. 9A, the charging sheet 45 side is minus and the developing roll 32 side is sandwiched between the toner layers. A positive charging bias is applied.
At this time, in order to perform effective charging, discharge by a charging bias is performed, and among the discharge charges ionized in the atmosphere, the negative charge moves to the developing roll 32 side by the electric field action, and the developing roll 32 surface side The toner adheres to the toner particles to charge the toner (negative charge). The negatively charged toner further adheres to the developing roll 32 side by the mirror image force and is supplied to the developing area. Part of the negatively charged negative ions reaches the developing roll 32 as well.
On the other hand, the ionized positive charge adheres to the toner particles on the charging sheet 45 side and charges the toner to the positive polarity of the reverse polarity. The positively charged toner adheres / accumulates on the charging sheet 45 due to a mirror image force. Note that some of the positively charged positive ions may reach the charging sheet 45 directly.

Next, as a refresh mode, when a toner layer corresponding to a non-image forming region (corresponding to a period during which no image is formed) passes through the charging sheet 45, as shown in FIG. Is applied between the charging sheet 45 and the developing roll 32. At this time, specific AC conditions include a frequency of 2 kHz and 500 Vpp.
In this case, of the discharge charges generated by the discharge, the negative charge moves to the charging sheet 45 side by the electric field effect due to the refresh bias and adheres to the attached reverse polarity toner (charged to the positive polarity). As a result, the positive charge is removed. The discharged toner particles are peeled off from the charged sheet 45 by the rubbing force with the developing roll 32, conveyed, and collected by the developing device. In addition, although it has a static elimination function only with a DC electric field as a refresh bias, it is preferable that an alternating current is superimposed in order to achieve a more uniform static elimination action and peeling.
Some toner is further charged to the negative polarity side, and toner particles that re-adhere to the charging sheet 45 side may be negative. However, the negatively charged toner is peeled off from the charging sheet 45 when the refresh mode ends (becomes peeled off by the charging bias). Note that a part of the ionized negative charge also reaches the charging sheet 45.
On the other hand, the ionized positive charge adheres to the toner particles on the developing roll 32 side and charges the toner to the positive polarity of the reverse polarity. The positively charged toner adheres to the developing roll 32 with a mirror image force and is collected by the toner supply roll 34 (see FIG. 6). In addition, some of the positively charged positive ions may reach the developing roll 32.

Next, the developing bias in the refresh mode will be described.
In the refresh mode, the toner layer formed on the developing roll 32 passes through the developing area while having a positive charge or a zero charge having a reverse polarity, and is collected by the toner supply roll 34. Accordingly, in the developing area, a developing bias is applied to the developing roll 32 facing the photosensitive member 21 set to the potential of the non-image forming area so that toner near positive charge or zero charge does not cause fogging. It is necessary to keep.
For example, in the case of contact development (a mode in which the developing roll 32 is brought into contact with the photosensitive member 21), when the surface of the photosensitive member 21 holds and rotates a non-image forming region uniformly charged to −600 V, the refresh mode is used. When the toner that has passed through the charging sheet 45 passes through the developing region, a developing bias of −750 V may be applied to the developing roll 32 side. In other time zones, −300 V may be applied as the developing bias. Note that the charging sheet 45 is provided with a potential superimposed on the potential of the developing roll 32.

  As described above, by adding an operation in the refresh mode to the present embodiment, it is not necessary to consider the toner adhesion to the charging sheet 45, and stable charging control can be performed over a long period of time. The electrostatic capacity of the toner layer can be measured.

Furthermore, the timing at which the refresh mode is performed can be performed at any time as long as it is a non-image forming region, but it is preferably performed between pages from the viewpoint of maintaining proper toner charging during continuous printing. Alternatively, it is preferable to carry out at least several seconds before the image formation of the first sheet at the start of printing.
For example, if the outer diameter of the developing roll 32 is φ15 mm and the peripheral speed is 220 mm / sec, the developing roll 32 makes five turns per second, so that a refresh time of several tens of turns can be ensured by performing several seconds. And sufficient refreshing is performed. Incidentally, in order to peel and clean the reverse polarity toner from the charging sheet 45, it is sufficient to have at least the time required for the developing roll 32 to make one round, and for this reason, sufficient refreshing is performed by the above-described method.
Needless to say, it is more preferable to execute the refresh mode even after the print job is completed.

As described above, if the refresh function is added to the charging sheet 45, the charging regulation operation of the toner by the charging sheet 45 and the toner amount change detection operation can be further stabilized, and stable development over a long period of time. Can be implemented.
In the present embodiment, a mode in which constant voltage control is performed as a charging bias on the charging sheet 45 has been described. The toner can be more accurately controlled and can be stably charged to the toner. Similarly, refresh performance can be further improved by applying a DC constant current to the charging sheet 45 even in the refresh mode.

  By the way, the phenomenon in which the toner adheres to the charging sheet 45 appears prominently in the following cases. That is, when the nip width formed by the charging sheet 45 with the developing roll 32 is 3 mm or more and the linear pressure is 20 g / cm or less, this is a mirror image force when the toner layer is brought into contact with a low pressure contact force. It is assumed that the reverse polarity toner adhering to the toner is peeled off by the rubbing force or shearing force of the developing roll 32 and the toner laminated on the developing roll 32 does not function.

  In the present embodiment, an example in which the refresh function is added to the charging sheet 45 has been described. However, the refresh function can be added also in the above-described first embodiment, and also in this case, the regulating blade 41 (FIG. 3). It goes without saying that a similar refresh bias may be added to the reference).

In this example, the toner supply amount and the toner layer surface potential of the thin toner layer supplied onto the developing roll when the duty ratio of the supply bias is changed in the configuration of the first embodiment are measured.
The developing roll was a SUS roll with a diameter of 30 mm, the peripheral speed was 220 mm / sec, the toner supply roll was a SUS roll with a diameter of 20 mm, the peripheral speed was 440 mm / sec, and the gap between the developing roll and the toner supply roll was 100 μm.
The supply bias applied between the developing roll and the toner supply roll was adjusted so that the peak-to-peak voltage Vpp was 1.5 kV and the period was 0.5 msec in the voltage waveform of FIG. In addition, a constant current was applied to the charging sheet so that the charging bias was −10 μA per 8 cm effective length in the axial direction of the developing roll (the toner charge amount was about −30 μC / g).

As a result, as shown in FIG. 10, it was confirmed that the toner supply amount tends to increase in proportion to the duty ratio. The toner layer surface potential was about 0 to 5 V until the duty ratio was about 0.6. However, when the toner layer surface potential was exceeded, the toner layer surface potential changed rapidly, and the toner layer surface potential (absolute value) tended to increase. It was.
In this embodiment, no positive frictional force was applied to the toner when the toner was supplied, and the charge amount of the toner was estimated to be quite small, and the result also reflected this.
From this result, when the toner supply amount (corresponding to the toner adhesion amount) on the developing roll is made as thin as about 6 to 14 g / m ² (0.6 to 1.4 mg / cm ² ), the surface of the toner layer Since the potential is as low as about 0 to +5 V, it was confirmed that supplying such a thin toner layer may determine that the supplied toner is almost uncharged. Further, when the toner supply amount exceeds 14 g / m ² , the toner layer surface potential (absolute value) suddenly increases due to the increase in the toner layer thickness, and there is a concern about the influence on charging. Become.

In particular, when the toner supply amount is 10 g / m ² or less, the surface potential of the toner layer is kept small, uniform charge control at the time of charging is further possible, and stress on the toner can be further reduced. It is understood that it can be done.
Further, in this embodiment, even when the toner layer surface potential is 10 V (specifically, −10 V), the toner charge control and the image quality are evaluated, and even in this state, uniform charging is performed. confirmed.
Thereafter, when the same evaluation as described above was performed with the gap between the developing roll and the toner supply roll being 50 to 400 μm, it was confirmed that the same effect was obtained.
From the above, according to the present case, it was confirmed that a sufficiently uniform toner thin layer was formed, the subsequent uniform charge control was possible, and the application of stress to the toner was small.

It is explanatory drawing which shows the outline | summary of the developer detection apparatus which concerns on this invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram illustrating an image forming apparatus according to a first embodiment to which the present invention is applied. FIG. 2 is an explanatory diagram illustrating a developing device according to the first embodiment. FIG. 3 is an explanatory diagram illustrating a regulation blade according to the first embodiment. FIG. 4 is an explanatory diagram illustrating a supply bias waveform according to the first embodiment. FIG. 10 is an explanatory diagram illustrating an overview of a developing device according to a second embodiment. FIG. 6 is an explanatory diagram illustrating a charging sheet according to a second embodiment. FIG. 10 is an explanatory diagram of a calculation formula for calculating a capacitance according to the second embodiment. It is explanatory drawing which shows the effect | action of refresh mode. It is explanatory drawing which shows the result of an Example. It is explanatory drawing which shows the conventional developer detection apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Developer carrying body, 2 ... Detection contact, 3 ... Physical quantity variable means, 4 ... Physical quantity change detection means, G ... Developer

Claims (5)

In the developer layer detection device for detecting the layer thickness of the developer layer on the developer carrier on which the developer is carried and conveyed on the surface,
A detection contact configured by a sheet-like member that is in contact with the developer layer on the developer carrying member and follows a change in the layer thickness of the developer layer and uses a piezoelectric material having piezoelectricity in the thickness direction ; ,
A physical quantity varying means to correspond to the amount of voltage change as a physical quantity that has been predetermined to follow the change of the detection contacts,
And a physical quantity change detection means for detecting a thickness of the developer layer on the basis of the physical quantity change due to the physical quantity changing means,
It said detection contact, the developer carrying member of the developer the developer layer detecting apparatus according to claim der Rukoto which the layer thickness regulating and triboelectrification relative. In the developer layer detection device for detecting the layer thickness of the developer layer on the developer carrier on which the developer is carried and conveyed on the surface,
A conductive material that contacts the developer layer on the developer carrying member and follows a change in the layer thickness of the developer layer and can detect the electrostatic capacity of the developer sandwiched between the developer carrying member A detection contact constituted by a sheet-like member using ,
A physical quantity varying means to correspond to the change in capacitance as a physical quantity predetermined tracking changes in the detection contacts,
A physical quantity change detecting means for detecting a layer thickness of the developer layer based on a physical quantity change by the physical quantity varying means ;
Charging bias applying means for applying a charging bias between the developer carrying member and the detection contact for charging the developer positioned between the developer carrying member and the detection contact;
In order to refresh the developer charged to the opposite polarity to the charged polarity by the charging bias attached to the detection contact, the developer charged to the opposite polarity between the developer carrying member and the detection contact A neutralizing bias applying means for applying a neutralizing bias capable of neutralizing,
A developer layer detection apparatus comprising: A developer carrying member that is opposed to an image carrier on which an electrostatic latent image is carried and is rotatable and carries a developer on the surface;
A developer supply member that is provided at a position upstream of the developer carrying member in the rotational direction of the developer carrying member and the image carrying member, and that supplies the developer to the developer carrying member;
A developer layer detecting apparatus according to claim 1 or 2 provided upstream position than the counter portion between and the image bearing member at a downstream side in the rotational direction of the developer carrier from said developer supply member,
A developing device comprising: The developing device according to claim 3.
A supply bias applying means that is provided between the developer carrier and the developer supply member and applies a supply bias to supply the developer from the developer supply member to the developer carrier;
Supply bias control means for controlling the supply bias so that the layer thickness of the developer layer detected by the developer layer detection device becomes a predetermined layer thickness;
A developing device comprising: An image carrier on which an electrostatic latent image is carried;
The developing device according to claim 3 or 4, wherein the electrostatic latent image on the image carrier is developed .
An image forming apparatus comprising:

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