JP2006267815A - Image forming apparatus, and mixing ratio measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that measures a mixing ratio of a mixed developer with high precision. <P>SOLUTION: The image forming apparatus 2 of the present invention is equipped with: a mixed developer storage container 14 which contains a developer obtained by mixing two kinds of toner having nearly the same hues, and different reflection densities and different degrees of sphericity; a vibrating electric field generating means 50 for generating a vibrating electric field between a developer carrier 16 and an image carrier 4; a development quantity measuring means for measuring a development quantity; and a mixing ratio measuring means 74 for measuring the mixing ratio of the two kinds of toner in the mixed developer storage container on the basis of the measured development quantity. The vibrating electric field generating means 50 generates the designated vibrating electric field when the mixing ratio is measured. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine thereof. The present invention particularly relates to an image forming apparatus using a mixed developer having a plurality of types of toners having substantially the same hue and different reflection densities. The present invention also relates to a method for measuring the mixing ratio of the mixed developer.

  An image forming apparatus using a mixed developer composed of two kinds of toners having the same hue and different reflection densities in order to suppress the consumption of the developer while enhancing the image quality of the image including the highlight portion is disclosed in, for example, Patent Document 1 is disclosed.

  In this apparatus, the charge amount of the low reflection density toner is made smaller than the charge amount of the high reflection density toner, so that the low reflection density toner can be supplied from the developing roller to the photosensitive drum more easily than the high reflection density toner. It is. Therefore, when developing a low density latent image area on the photosensitive drum (low exposure amount and therefore low potential attenuation level), low reflection density toner is mainly used. As a result, it is possible to suppress density unevenness that can occur when only toner having a high reflection density is used, and to obtain a fine image without graininess.

  Further, the amount of high reflection density toner in the developing device is set larger than that of low reflection density toner. Therefore, when developing a high density latent image region (a large amount of exposure and therefore a large potential attenuation level) on the photosensitive drum, a high reflection density toner is mainly used. As a result, the consumption of the developer can be suppressed as compared with the case where the high density latent image area on the photosensitive drum is developed using only the toner having a low reflection density.

  In the image forming apparatus, in order to stably obtain a good image quality even when the number of printed sheets is increased, it is necessary to control the mixing ratio of the two types of toner in the developer within a predetermined range.

Patent Document 2 discloses an image forming apparatus that forms a test patch image on a photosensitive drum, detects the reflection density of the image, and supplies low-reflection density toner from a toner hopper when the detected reflection density of the test patch image decreases. Are listed.
JP 2000-98712 A JP 2000-293003 A

  However, it is difficult to obtain the developer mixing ratio (toner mixing ratio) from the test patch image on the photosensitive drum with high accuracy.

  SUMMARY OF THE INVENTION Accordingly, the present invention provides a mixed developer mixing ratio measurement method that can be easily performed with high accuracy, and an image forming apparatus that can measure the mixed developer mixing ratio using the mixing ratio measurement method. Objective.

In order to achieve the above object, an image forming apparatus according to the present invention includes:
A mixed developer container for containing a developer obtained by mixing two types of toners having substantially the same hue and different reflection density and sphericity;
An oscillating electric field generating means for generating an oscillating electric field between the developer carrier and the image carrier;
A developing amount measuring means for measuring the developing amount;
Mixing ratio measuring means for measuring a mixing ratio of two types of toner in the mixed developer container based on the measured development amount;
The vibrating electric field generating means generates a predetermined vibrating electric field when measuring the mixing ratio.

In order to achieve the above object, the mixing ratio measuring method according to the present invention is:
A mixing ratio measurement method for measuring a mixing ratio of a developer formed by mixing two kinds of toners having substantially the same hue and different reflection density and sphericity in an image forming apparatus,
Developing with a predetermined oscillating electric field;
Measuring the development amount;
And a step of measuring a mixing ratio of the two types of toner in the mixed developer container based on the measured development amount.

  According to the image forming apparatus and the mixing ratio measuring method according to the present invention, since two types of toners having substantially the same hue and different reflection densities have different sphericity, the oscillating electric field affected by the sphericity of the toner is used. The toner mixing ratio in the container can be easily measured with high accuracy on the basis of the development amount detected by the development.

  FIG. 1 shows a color printer according to a first embodiment of the present invention. The printer 2 includes a photosensitive drum 4 that can be driven to rotate in the clockwise direction of the drawing as an image carrier. Around the photosensitive drum 4, a charging device 6, an exposure device 8, four developing devices 10C, 10M, 10Y, and 10K, and an intermediate transfer unit 12 are sequentially arranged along the rotation direction of the drum.

The charging device 6 is for uniformly charging the surface of the photosensitive drum 4 (surface potential V ₀ ). The exposure device 8 selectively irradiates the photosensitive drum 4 with laser light 8a in accordance with image data, thereby forming a latent image on the photosensitive drum.

Each of the developing devices 10 </ b> C to 10 </ b> K supplies toner corresponding to the photosensitive drum 4 to visualize the latent image. Specifically, the developing devices 10C, 10M, 10Y, and 10K respectively include developer containers 14C, 14M, and 14Y that respectively store cyan (C), magenta (M), yellow (Y), and black (Y) developers. , 14K, and developing rollers (developer carrying members) 16C, 16M, 16Y, 16K that are drivingly connected to a motor (not shown) so as to be rotatable counterclockwise in the drawing. As the developing rollers 16C to 16K rotate, the developer adhering to the surface of the developing roller is conveyed to a region where the developing roller and the photosensitive drum 4 are opposed to each other, where the developer is supplied to the latent image region of the photosensitive drum. Will be. Each developing roller 16C～16K, bias voltage _{V B} is applied.

The bias voltage V _B is an oscillating voltage obtained by superimposing a DC voltage and an AC voltage, and has a rectangular waveform as shown in FIG. Development amount (supply amount of the toner from the developing roller to the photosensitive drum) is determined by the difference between the average potential V _ave of the developing roller and the latent image potential V _i of the photosensitive drum (development gap [Delta] V). The development gap ΔV is changed by changing the peak-to-peak value V _pp , the DC voltage V _DC , or the Duty ratio of the bias voltage V _B when the latent image potential V _i is constant. Application of the bias voltage V _B to the developing roller 16C~16K is performed by a bias voltage applying device provided in each individual (oscillating electric field generating means). Details of the bias voltage applying device will be described later.

  The cyan developer in the developer container (mixed developer container) 14C is composed of two types of toners having a low reflection density and a high reflection density having substantially the same hue (in the sense of not including a carrier). The mixed developer. Similarly, the magenta developer in the developer container (mixed developer container) 14M is a one-component mixed developer composed of two types of toners having a low reflection density and a high reflection density having substantially the same hue. The yellow developer in the developer container 14Y is made of one type of yellow toner. Similarly, the black developer in the developer container 14K is made of one type of black toner. The cyan developer and magenta developer, which are mixed developers, will be described in more detail later.

The intermediate transfer unit 12 includes an intermediate transfer belt 18. The intermediate transfer belt 18 is made of a resin sheet such as polycarbonate, and carbon black is dispersed in the resin sheet so that the surface electrical resistance value of the intermediate transfer belt is about 10 ⁵ to 10 ¹² Ω / cm ² . The intermediate transfer belt 18 is supported on the outer periphery of five rollers 20, 22, 24, 26 and 28. The roller 22 is a tension roller that applies tension to the intermediate transfer belt 18. The roller 20 is drivingly connected to a motor (not shown). As the roller 20 rotates, the rollers 22, 24, 26, and 28 rotate, and the intermediate transfer belt 18 rotates counterclockwise in the drawing. The intermediate transfer belt 18 between the rollers 26 and 28 is in contact with the outer periphery of the photosensitive drum 4 so that a toner image (cyan toner image, magenta toner image, yellow toner image, or black toner image) on the photosensitive drum is formed. A primary transfer region 30 to be transferred to the intermediate transfer belt is formed.

A secondary transfer roller 32 that rotates in the clockwise direction of the drawing is provided facing the belt portion 34 immediately upstream of the roller 24 with respect to the rotation direction of the intermediate transfer belt 18. The secondary transfer roller 32 is made of a foam rubber material such as silicone or urethane, and carbon black is dispersed in the foam rubber material so that the surface transfer resistance of the secondary transfer roller is about 10 ⁵ to 10 ¹² Ω / cm ^2. Has been. The belt portion 34 and the secondary transfer roller 32 pass through the sheet (recording medium) S along the direction of the arrow, and thereby the secondary toner image (described later) on the intermediate transfer belt 18 is transferred onto the sheet. Region 36 is formed. In order to remove the toner (untransferred toner) on the intermediate transfer belt 18 portion that has passed through the secondary transfer region 36, a cleaning unit 38 is provided in the belt 18 portion between the rollers 24 and 26.

The cleaning unit 38 causes a polyurethane rubber blade 39 having a hardness of 67 ° to come into contact with the intermediate transfer belt 18 at a biting amount of 1 mm at an angle of 15 ° (the contact force at this time is 20 N / m ² ). The untransferred toner on the intermediate transfer belt 18 is removed.

  In the printer 2 having such a configuration, a controller (described later) drives the charging device 6 to uniformly charge the surface of the photosensitive drum 4. The controller generates a control signal based on the color image data stored in the image memory (not shown) and sends it to the exposure device 8. The exposure device 8 selectively irradiates the photosensitive drum 4 with laser light 8a. As a result, the potential of the surface portion irradiated with the laser beam 8a is attenuated, and a cyan latent image is formed on the photosensitive drum 4. The cyan latent image on the photosensitive drum 4 is visualized by supplying a mixed cyan developer to the latent image by the developing device 10C, and a cyan toner image is formed. The cyan toner image is conveyed to the primary transfer region 30 by the rotation of the photosensitive drum 4 and transferred onto the intermediate transfer belt 18.

  Next, the magenta toner image formed on the photosensitive drum 4 in the same manner using the mixed magenta developer is transferred onto the intermediate transfer belt 18 so as to overlap the cyan toner image. Subsequently, the yellow toner image formed on the photosensitive drum 4 in the same manner using a single yellow developer is transferred onto the intermediate transfer belt 18 so as to be superimposed on the cyan and magenta toner images. Thereafter, the black toner image formed on the photosensitive drum 4 in the same manner using a single black developer is transferred onto the intermediate transfer belt 18 so as to be superimposed on the cyan, magenta, and yellow toner images.

  The superimposed image is conveyed to the secondary transfer region 36 by the movement of the intermediate transfer belt 18. On the other hand, the sheet S is supplied from a sheet supply cassette (not shown) to the secondary transfer region 36. The superimposed image is transferred to the sheet S that passes through the secondary transfer region 36 by the action of the secondary transfer roller 32.

  The sheet S on which the color toner image is formed is supplied to a fixing device (not shown), and the color toner image is fixed on the sheet S.

  The toner that has not been transferred to the sheet S is removed by the cleaning unit 38.

  Next, the latent image formed on the photosensitive drum 4 and the mixed developer will be described in detail. The printer 2 performs pulse width modulation control of the laser beam 8a in order to express gradation. Therefore, the latent image includes a “low density” region having a small potential decay level and a “high density” region having a large potential decay level. If the laser irradiation time is relatively short, the potential attenuation on the surface of the photosensitive drum is small (the potential does not saturate), and thus a low density region is formed. On the other hand, if the laser irradiation time is sufficiently long, the potential attenuation on the surface of the photosensitive drum is large (the potential is saturated), and thus a high density region is formed. In the present application, a “low density” latent image area and a “high density” latent image area represent areas where a developer is supplied to form a highlight portion and a shadow portion, respectively.

As described above, the cyan developer is a mixed developer composed of two types of toners having substantially the same hue and different reflection densities. The mixing ratio of the developer in the developer container 14C is adjusted to be _RL or more. In the present embodiment, the mixing ratio is defined as the weight ratio of the low reflection density toner to the high reflection density toner, but another definition may be used. According to the above definition, R _L is a value greater than 0 and less than 1. That is, the developer container 14C contains a higher amount of high reflection density cyan toner than the low reflection density cyan toner.

  3A and 3B show examples of a low reflection density cyan toner and a high reflection density cyan toner. In the example of FIG. 3A, the high reflection density toner 40H is obtained by dispersing a colorant 44H and a charge control agent 46 in a resin 42. An external additive 48 may be added. The low reflection density toner 40L is substantially the same as the high reflection density toner 40H except that the colorant 44L has a lower reflection density than the colorant 44H. In the example of FIG. 3B, the reflection densities of the colorants 44H and 44L are the same, and the weight ratio of the colorant 44H to the resin 42 is larger than that of the colorant 44L. In the latter example, as an example, an appropriate range of the mixing ratio is 0.45 or more, and the weight ratio is 4% for the low reflection density cyan toner and 10% for the high reflection density cyan toner.

  In order to make the adhesion of the low reflection density cyan toner to the developing roller 16C of the developing device 10C smaller than that of the high reflection density toner so that the low reflection density cyan toner can be easily attached to the photosensitive drum 4. The charge amount of the low reflection density cyan toner is smaller than that of the high reflection density cyan toner. In order to realize this, the amount of post-treatment agent such as a charge control agent added to each cyan toner is varied.

With reference to FIG. 4, the characteristics of the mixed cyan developer composed of the low reflection density and high reflection density cyan toner will be described. FIG. 4 shows a low reflection density cyan toner and a high reflection density cyan toner deposited on the photosensitive drum as a function of the potential difference between the developing roller to which the bias voltage V _B is applied and the latent image area on the photosensitive drum. Each amount is shown.

  As shown in FIG. 4, if the potential difference between the developing roller and the latent image area on the photosensitive drum is relatively small, the adhesion force between the low reflection density cyan toner and the development roller is the high reflection density cyan toner. As a result, the low reflection density cyan toner is mainly supplied to the latent image area. When the potential difference between the developing roller and the latent image area on the photosensitive drum is smaller than a certain value ΔV1, the amount of the low reflection density cyan toner supplied to the latent image area of the photosensitive drum increases as the potential difference increases. . When the potential difference is larger than ΔV1, the amount of low reflection density cyan toner supplied to the photosensitive drum is substantially constant (ie, the supply amount of low reflection density toner is saturated). This means that if the potential difference is large to some extent, most of the low reflection density cyan toner in the mixed cyan developer facing the latent image area is supplied to the latent image area.

  On the other hand, if the potential difference between the developing roller and the latent image area on the photosensitive drum is relatively small, the amount of high reflection density cyan toner supplied to the latent image area is small. However, the larger the potential difference between the developing roller and the latent image area on the photosensitive drum, the greater the amount of high reflection density cyan toner supplied to the latent image area of the photosensitive drum as long as the potential difference is smaller than a certain value ΔV2. There are many. When the potential difference is larger than ΔV2, the amount of high reflection density cyan toner supplied to the photosensitive drum is substantially constant (ie, the supply amount of high reflection density toner is saturated). This is because, if the potential difference is sufficiently large, most of the high reflection density cyan toner in the mixed cyan developer facing the latent image area (and thus the majority of the mixed cyan developer facing the latent image area) will enter the latent image area. It means that it is supplied. The weight ratio of the two types of cyan toner supplied to the photosensitive drum when the potential difference is larger than ΔV2 is substantially the same as the mixing ratio of the two types of cyan toner in the developer container.

  As is clear from the above description, it is inevitable that the low reflection density cyan toner is supplied even when developing a high density latent image area (corresponding to a shadow portion). Therefore, when developing a high-density latent image region, in order to obtain the same image density with the same adhesion amount as that of a conventional image forming apparatus that uses only one type of cyan toner, the printer according to this embodiment is used. The high reflection density cyan toner used in No. 2 needs to have a higher reflection density than the cyan toner used in the conventional image forming apparatus. As an example, when the weight ratio of the colorant to the resin of the conventional single cyan toner is 8%, the weight ratio of the high reflection density cyan toner is set to 10%.

  As described above, the low reflection density cyan toner is mainly used to develop the low density latent image area (corresponding to the highlight portion). This is also true for magenta developers. Therefore, the printer 2 enables a fine image without graininess by developing a low density latent image area mainly with a low reflection density toner.

When cyan and magenta developers are used to continuously print an image including a relatively large number of highlights such as a photographic image using the printer 2, a large amount of low reflection density toner is consumed. As a result, the amount of low reflection density toner per unit volume in the developer decreases. For this reason, the amount of high reflection density toner supplied from the developing roller to the low density latent image region increases, and the graininess of the image increases. As the amount of low reflection density toner decreases, the mixing ratio of the developer decreases. Therefore, the printer 2 is configured to control each mixing ratio of cyan and magenta developer so as to be equal to or more than a predetermined appropriate value _RL .

  For the purpose of measuring the toner mixing ratio, the sphericity of the low reflection density toner and the high reflection density toner are different for cyan and magenta developers. In this embodiment, the sphericity is obtained by dividing the circumference of a circle having an area equal to the area of the projected image of toner particles by the circumference of the projected image. The sphericity is obtained from the average of a plurality of toner particles. The “peripheral length of a circle having an area equal to the area of the projected image of the toner particles” and “peripheral length of the projected image of the toner particles” are, for example, a particle image analyzer (for example, FPIA-2100 manufactured by Hosokawa Micron Corporation). Required to use. The closer the sphericity value is to 1, the closer the toner particles are to a perfect circle, which is an index that accurately indicates the degree of unevenness on the toner particle surface.

  In this embodiment, like the sphericity of the low reflection density and high reflection density cyan toner shown in FIG. 5, the sphericity of the low reflection density toner is larger than the sphericity of the high reflection density toner. Thereby, the mixing ratio can be measured from the amount of adhesion, so-called development amount, utilizing the fact that the adhesion force to the photosensitive drum 4 varies depending on the difference in sphericity.

  For the sake of confirmation, the adhesion force is also described in the above, but the above-mentioned “adhesion force” is the adhesion force to the developing roller, which is a force resulting from the toner charge amount. The “adhesion force” here is an adhesion force to the photosensitive drum 4, which is a force due to the sphericity, that is, the shape (the degree of unevenness of the toner particle surface as described above).

  Hereinafter, the measurement of the mixing ratio will be described in detail.

  The development amount is measured to measure the mixing ratio. The means for measuring the development amount is included in the above-described bias voltage applying device for cyan and magenta. In the following, a bias voltage applying device that has not been described in detail above will be described.

  FIG. 6 is a diagram illustrating a configuration of a bias voltage applying device that applies a bias voltage to the developing roller 16C. The bias voltage applying device 50C includes an AC power source 51 and a DC power source 52 connected in series for applying an oscillating voltage in which a DC voltage and an AC voltage are superimposed on the developing roller 16C. The DC power source 52 is connected to a grounded resistor 53, and a grounded capacitor 54 is connected between the AC power source 51 and the DC power source 52. Thereby, an oscillating electric field for supplying the toner 55 from the developing roller 16C to the photosensitive drum 4 is generated. Due to the oscillating electric field, the toner 55 flies through a gap 56 (for example, a gap of 150 μm) 56 between the developing roller 16 </ b> C and the photosensitive drum 4.

When the toner 55 having a charge amount is charged by the developing roller 16C is supplied from the developing roller 16C to the photosensitive drum 4 by the oscillating electric field, the potential difference V _R across the resistor 53 is changed. In other words, the variation of the potential difference V _R corresponds to the amount of charge transferred from the developing roller 16C, the amount of charge by measuring the corresponding voltage difference V _R can be calculated.

  Further, since the charge amount per toner is substantially constant, the charge amount moved from the developing roller 16C corresponds to the development amount (see FIG. 7). Therefore, the development amount can be calculated from the calculated charge amount.

Thus, in measuring the amount of development it is seen to be by measuring the potential difference V _R. Potential V _R is amplified by the amplifier circuit 57 is converted into a digital signal by the A / D conversion circuit 58 is sent to the controller described later. The development amount is measured based on the potential difference signal. Thus, the bias voltage application device 50C having the resistor 53, the amplifier circuit 57, and the A / D conversion circuit 58 functions as a means for measuring the development amount.

  When measuring the mixing ratio, the bias voltage applying device 50C is configured to generate an oscillating electric field (predetermined oscillating electric field) of a developing gap in a predetermined range (as described above, the difference between the latent image potential of the photosensitive drum and the average potential of the developing roller). ) Is applied to the developing roller. At the same time, the printer 2 is configured to develop with a development gap within a predetermined range.

  The range in the “development gap of a predetermined range” is a range where the ratio of the low reflection density toner is higher than the ratio of the high reflection density toner in the toner supplied to the photosensitive drum 4 (toner to be developed), preferably The range is such that most of the toner has a low reflection density and the amount thereof is a saturation amount or an amount close to the saturation amount.

The predetermined range will be described with reference to FIG. FIG. 8 shows the relationship between the development amounts of the low reflection density and high reflection density toners affected by the difference in sphericity and the development gap ΔV. In the figure, the alternate long and short dash line (I) indicates a high reflection density toner having a small sphericity when the mixing ratio _RL is equal to or higher, and the solid line (II) indicates a spherical shape when the mixing ratio _RL is equal to or higher. A low reflection density toner having a large degree is shown. As shown in the figure, it can be seen that toner having a larger sphericity is developed with a smaller development gap ΔV.

In the figure, the range corresponding to the predetermined range is a range between ΔV _a and ΔV _b . When the mixing ratio in the predetermined range is proper mixing ratio R _L or more, the amount of development sphericity is large toner in G _L, the amount of development sphericity is less toner is G _S. It is greater than _{G S} towards the developing amount _{G L.} Further, in a predetermined range, the total amount of toner attached to the photosensitive drum 4, a so-called total development amount G _T is G _{L +} G _S. Therefore, in a predetermined range, the total amount of development is slightly reduced from the total amount of development G _T if it is the mixture ratio R _L or more, most of the reduced toner understood that sphericity is large toner. Therefore, in a predetermined range, a decrease in the total development amount substantially corresponds to a decrease in toner having a large sphericity, and a decrease in toner having a large sphericity, that is, a decrease in low reflection density toner results in a decrease in the mixing ratio. From the correspondence, it can be seen that the decrease in the total development amount substantially corresponds to the decrease in the mixing ratio.

Therefore, the potential difference signal obtained by performing development with a development gap within a predetermined range corresponds to the mixing ratio. The correspondence is shown in FIG. The higher the mixing ratio, the higher the potential difference (voltage) across the resistor indicated by the potential difference signal obtained by performing development with a development gap within a predetermined range. In the figure, the voltage V _R, the mixing ratio is a value corresponding to a proper value R _L.

In summary, the printer 2 performs development with a development gap within a predetermined range, and the potential difference signal indicating the potential difference between both ends of the resistor 53 of the bias voltage applying device 50C changed by the development and the potential difference signal as shown in FIG. Based on the relationship between the potential difference signal and the mixing ratio, the mixing ratio of the mixed developer is measured, and the mixing ratio is adjusted so that the mixing ratio is equal to or more than an appropriate value _RL .

  In addition, the amount of charge per toner varies greatly depending on the environment such as humidity. Therefore, the printer checks the charge amount per toner for each environment in advance, and measures the development amount based on the potential difference signal indicating the charge amount for each environment and the potential difference between both ends of the resistance of the bias voltage application device. It is preferable to do this. In that case, for example, it is necessary to have means for measuring temperature and humidity.

  Returning to FIG. 1, each of the developing devices 10C, 10M, 10Y, and 10K determines whether or not a certain amount of developer that guarantees the image quality remains in the containers 14C, 14M, 14Y, and 14K (in other words, the developing device). Empty sensors 62C, 62M, 62Y, 62K for detecting (whether or not the developer container is near empty) are provided on the container side wall. The empty sensor is, for example, an optical sensor including a light emitting element and a light receiving element. When the light emitted from the light emitting element is blocked by the developer and does not enter the light receiving element, the empty sensor does not output a signal. In this case, a sufficient amount of developer remains in the container. When light emitted from the light emitting element enters the light receiving element, the empty sensor outputs a signal. In this case, only a small amount of developer remains in the container, and image quality cannot be guaranteed.

Replenishing devices 64C, 64M, 64Y, and 64K for replenishing the developing device with each developer are connected to the developing devices 10C, 10M, 10Y, and 10K, respectively. More specifically, as shown in FIG. 10, supply device 64C includes two container 66L to accommodate low reflection density cyan toner _{T L} and the high reflection density cyan toner _{T H,} respectively, 66H and conveying screws 68L, and 68H Prepare. Conveying screws 68L, 68H are low reflection density cyan toner _{T L} and conveying path 69L highly reflective density cyan toner _{T H,} replenishing port 70L through 69H, for dropping the developer container 14C and conveyed to 70H Is. The developer container 14C includes an agitator (not shown) for stirring and mixing the low reflection density and high reflection density cyan toner. The screws 68L and 68H are drivingly coupled to motors 71L and 71H electrically connected to the driving circuit 72, respectively. The drive circuit 72 drives the motors 71L and 71H according to a signal from the controller 74 that controls the printing operation of the printer 2.

  The replenishing device 64M has the same configuration as the replenishing device 64C except that the low reflection density magenta toner and the high reflection density magenta toner are accommodated in the two toner containers, respectively.

  Each of the replenishing devices 64Y and 64K is a conventional one in which one type of toner is stored in one toner container, and description thereof is omitted in this specification.

  A signal (potential difference signal) from the A / D conversion circuit 58 of the bias voltage application device (development amount measuring means) 50 is output to the controller 74. As will be described below, the controller 74 controls a corresponding replenishing device in response to a detection signal relating to one of the developing devices to replenish a controlled amount of toner to the developer container.

  Next, the cyan developer replenishment sequence will be described with reference to the flowchart shown in FIG. 11 together with FIG. This sequence is performed, for example, when the printer 2 is activated or whenever the developing device 10C is used for a predetermined period. First, in step S1, the controller 74 determines whether or not a detection signal is output from the empty sensor 62C. When the detection signal is not output, that is, when a sufficient amount of cyan developer remains in the container 14C, the process proceeds to step S2 in order to measure the mixing ratio of the cyan mixed developer in the container 14C. A solid toner batch image having a cyan area ratio of 100% is formed (developed) on the photosensitive drum 4 with a predetermined development gap (ΔVa to ΔVb in FIG. 8). The potential difference signal and the mixing ratio as shown in FIG. 9 corresponding to the image to be formed are checked in advance, and if it is referred to, the image to be formed need not be a solid toner patch image. The image for measuring the mixing ratio formed on the photosensitive drum 4 is not subjected to primary transfer but is removed by cleaning by a cleaning unit (not shown) for the photosensitive drum 4.

Next, the process proceeds to step S3, and the voltage (potential difference) of the signal from the A / D conversion circuit 58 of the bias voltage applying device 50 sent when developing at a predetermined development gap is equal to or higher than V _L (mixing ratio is R _L (As described above, the controller 74 functions as a means for measuring the mixing ratio of the two types of toners based on the voltage from the A / D conversion circuit 58). When the voltage is equal to or higher than V _L , replenishment is not performed, and the developing device 10C can supply the cyan developer to the photosensitive drum 4 (step S5). Thereafter, the flow ends.

If the voltage is lower than _VL in step 3 (when the amount of low reflection density cyan toner in the developer container 14C is insufficient), the process proceeds to step S4, where the voltage is _VL or higher (mixing ratio is _RL or higher). ), The low-concentration density cyan toner is supplied from the toner container 66L to the developer container 14C. Thereafter, the flow proceeds to step S5.

  If a signal is output from the empty sensor 62C in step S1, that is, if a sufficient amount of cyan developer does not remain in the container 14C, the process proceeds to step S6, where low reflection density and high reflection density cyan toner is added. The developer container 14C is replenished from the toner containers 60L and 60H by an appropriate amount (not empty). Then, it returns to step S1.

  This replenishment sequence is performed when the printer 2 is started up or whenever the developing device 10C is used for a predetermined period. In addition, the controller 74 causes the emptying sensor 62C to change the developing device 10C to near empty. It may be automatically started when a signal indicating that is received. In this case, steps S2 to S5 are performed.

  The magenta developer supply operation is the same as that for the cyan developer.

  The replenishment operation of the yellow and black developers is the same as the conventional one. That is, when receiving a signal from the empty sensor 62Y or 62K, the controller 74 controls the replenishing device 64Y or 64K to replenish the corresponding toner from the toner container to the developer container 14Y or 14K.

  If all of the developing devices 10C to 10K can supply the developer to the photosensitive drum 4, the printer 2 is ready for printing.

  Finally, the toner may be a polymerized toner or a pulverized toner.

1 is a configuration diagram showing an embodiment of an image forming apparatus according to the present invention. The wave form diagram for demonstrating a bias voltage. FIG. 5A is a diagram illustrating an example of a low reflection density cyan toner and a high reflection density cyan toner using colorants having different reflection densities. FIG. 6B is a diagram illustrating an example of a low reflection density cyan toner and a high reflection density cyan toner using different amounts of colorant. 6 is a graph showing a relationship between a potential difference between a photosensitive drum and a developing roller and amounts of low reflection density cyan toner and high reflection density cyan toner supplied to the photosensitive drum. The graph which shows the sphericity of a low reflection density cyan toner and a high reflection density cyan toner. The block diagram of the bias voltage application apparatus which functions as a developing amount measurement means. The graph which shows the relationship between an electric charge amount and development amount. The graph which shows the relationship between the toner from which sphericity differs, and a development gap. 6 is a graph showing a relationship between a toner mixing ratio and a voltage indicated by a signal from a bias voltage applying device. FIG. 2 is a configuration diagram illustrating the cyan developing device of FIG. 1 and a replenishing device that replenishes developer to the device. 5 is a flowchart showing a cyan developer supply process.

Explanation of symbols

2 Image forming apparatus 4 Photosensitive drum (image carrier)
14 Mixed developer container 16 Developing roller (developer carrier)
50 Bias voltage application device (vibrating electric field generating means)
74 controller (mixing ratio measuring means)

Claims (2)

A mixed developer container for containing a developer obtained by mixing two types of toners having substantially the same hue and different reflection density and sphericity;
An oscillating electric field generating means for generating an oscillating electric field between the developer carrier and the image carrier;
A developing amount measuring means for measuring the developing amount;
Mixing ratio measuring means for measuring a mixing ratio of two types of toner in the mixed developer container based on the measured development amount;
The oscillating electric field generating means generates a predetermined oscillating electric field when measuring the mixing ratio. A mixing ratio measurement method for measuring a mixing ratio of a developer formed by mixing two kinds of toners having substantially the same hue and different reflection density and sphericity in an image forming apparatus,
Developing with a predetermined oscillating electric field;
Measuring the development amount;
And a step of measuring a mixing ratio of two types of toner in the mixed developer container based on the measured development amount.

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