JP5800619B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus provided with a detection mechanism between a developer carrier and the developer supply member.

  As a method for detecting the remaining amount of toner stored in a developing device used in an image forming apparatus such as an electrophotographic apparatus, there is a method of detecting the capacitance between two electrodes provided in the developing apparatus. Thereby, information on the toner amount is obtained.

  In particular, in the case where there is a developing device having a developing roller and a supply roller having a foam layer, information on the toner amount by detecting the capacitance between the core of the developing roller and the core of the supply roller (For example, refer to Patent Document 1). In this method, since there is a correlation between the toner amount of the developing device and the electrostatic capacity between the cores, the toner amount can be measured by detecting the electrostatic capacity.

  Patent Document 1 describes that detection accuracy is improved by setting the surface airflow rate of the foam layer of the supply roller within an appropriate range and making it easy for toner to enter and exit the foam layer.

JP 2009-009035 A

  In an image forming apparatus having a configuration for detecting a capacitance between a conventional toner carrier and a toner supply member, variation in the amount of air flow on the surface occurs due to uneven foaming of the toner supply member. Then, the electrostatic capacitance in the rotation direction may vary. In this case, the measurement accuracy of the toner amount is lowered, and it may be impossible to accurately detect the replacement time of the developing device.

  An object of the present invention is to accurately detect the amount of toner in a developing container.

A typical configuration of the present invention for achieving the above object is as follows.
In an image forming apparatus comprising: an image carrier; and a developing unit that supplies toner in a developing container from a toner supply member to the toner carrier and supplies the toner to the image carrier by the toner carrier.
Voltage applying means for applying an alternating voltage to one of the first electrode member provided on the toner carrier or the second electrode member provided on the toner supply member;
A voltage detection circuit for rectifying and detecting an alternating voltage induced on the other of the first electrode member or the second electrode member;
A toner amount measuring means for applying a plurality of types of AC voltages by the voltage applying means and measuring a toner amount in the developing container based on a difference between a plurality of output voltages detected by the voltage detection circuit;
It is characterized by having.

  With the above configuration, the toner amount in the developing container can be detected with high accuracy.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to a first embodiment. FIG. 2 is a schematic configuration diagram of a developing device during image formation according to the first embodiment. The graph which shows the relationship between the toner amount in sponge of a supply roller, and an electrostatic capacitance. 6 is a graph showing a relationship between a difference in capacitance and a toner amount. FIG. 3 is a block diagram of the toner amount measuring apparatus according to the first embodiment. FIG. 3 is a toner amount detection circuit diagram according to the first embodiment. 6 is a graph showing a relationship between a detection voltage and a toner amount according to the first embodiment. The graph which shows the time change of the electrostatic capacitance during supply roller rotation. The graph which shows the dispersion | variation in a detection voltage. 6 is a graph showing the relationship between the toner amount in the developing container and the toner amount in the sponge of the supply roller. 6 is a graph showing a relationship between a detection voltage and a toner amount when Vpp is changed. The graph which compared the dispersion | variation when changing Vpp, and taking the difference. The graph which showed the dispersion | variation reduction mechanism in 1st Embodiment. The graph which showed the relationship with the toner amount when taking the difference (DELTA) VD1 obtained from the Vpp change in 1st Embodiment. The graph which shows the relationship between the detection voltage and toner amount when changing the frequency. The graph which compared the dispersion | variation when changing the frequency in 2nd Embodiment, and taking the difference. The graph which showed the relationship with the toner amount when taking the difference (DELTA) VD2 obtained from the frequency change in 2nd Embodiment.

[First Embodiment]
Embodiments of the present invention will be illustrated below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be changed as appropriate according to the configuration of the apparatus to which the invention is applied and various conditions. That is, the scope of the present invention is not intended to be limited to the following embodiments.

(Image forming device)
The image forming apparatus according to the first embodiment will be described with reference to FIG. FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the first embodiment.

  First, an image forming operation in the image forming apparatus 100 will be described.

  In FIG. 1, the photosensitive drum 2 (image carrier) rotates in the direction of the arrow. The photosensitive drum 2 is uniformly charged by a charging roller 3 (charging device) while rotating. Then, it exposes with the laser beam from the laser optical apparatus 4 (exposure means), and an electrostatic latent image is formed in the surface.

  A developer (toner) is supplied to the electrostatic latent image by a nonmagnetic one-component contact developing device 20 (developing means) described later. Then, the electrostatic latent image is developed and visualized as a developer image (toner image). The visualized developer image on the photosensitive drum 2 is transferred to the recording medium 6 (transfer material) by the transfer roller 5.

  The untransferred developer remaining on the photosensitive drum 2 without being transferred is scraped off by a cleaning blade 71 (cleaning member) and stored in a waste developer container 70. The cleaned photosensitive drum 2 repeats the above operation to form an image.

  On the other hand, the recording medium 6 to which the developer image has been transferred is discharged outside the apparatus after the permanent image is fixed by the fixing apparatus 80.

(Developer)
The developing device 20 will be further described with reference to FIG. FIG. 2 is a schematic configuration diagram of the developing device during image formation according to the first embodiment.

  In FIG. 2, the developing device 20 has a developing container 21. The developing container 21 is filled with a nonmagnetic one-component developer. A developer storage chamber 22 is provided in the developing container 21.

  In the developer accommodating chamber 22, a developing roller 23 (toner carrier), a supply roller 24 (toner supply member), a regulating blade 25, and a leakage prevention seal 27 are disposed. Here, the developing roller 23 abuts on the photosensitive drum 2 and rotates in a certain direction as indicated by an arrow α to supply the developer applied to the outer peripheral portion thereof to the photosensitive drum 2. The supply roller 24 rotates in contact with the developing roller 23 and supplies developer to the developing roller 23. The regulating blade 25 is made of phosphor bronze, urethane rubber, or the like, and has one end rubbed against the developing roller 23 and coats the developer applied around the developing roller 23 on a thin layer. The leak prevention seal 27 covers the gap of the developing chamber 26 below the developing roller 23.

  In this embodiment, a negatively charged nonmagnetic developer is used as the one-component developer. The developing roller 23 is rotationally driven in the β direction indicated by the arrow.

  As the regulating blade 25, a thin plate (thickness 80 μm) of SUS material was used, and the regulating blade 25 was installed so as to be in the counter direction (opposite direction) with respect to the rotation direction of the developing roller 23. In this way, by providing the regulating blade 25, the coating amount of the developer on the developing roller 23 (coating amount) can be regulated as the developing roller 23 rotates.

  The supply roller 24 is formed by forming a urethane sponge on the outer periphery of the cored bar. With this configuration, the developer once contained in the supply roller 24 is supplied to the surface of the development roller 23 at the contact portion between the supply roller 24 and the development roller 23.

  The developing roller 23 and the supply roller 24 rotate in the same direction. For this reason, in the contact part (contact part) of both, the surface of each roller is moving to the reverse direction.

  Further, a voltage is applied to each member of the developing device 20. For example, in the present embodiment, when developing, the potential of the photosensitive drum 2 is −500 V in the unexposed area and −150 V in the exposed area. Further, about −350 V is applied to the developing roller 23 and the supply roller 24, and about −550 V is applied to the regulating blade 25. By setting such a potential, the negative developer does not adhere to the unexposed area, but adheres to the exposed area by electrostatic force.

  Next, the configuration of each unit will be described in detail.

The developing roller 23 includes a conductive cored bar 28 (first electrode member) having a diameter of 6 mm and a conductive elastic layer based on silicon rubber formed therearound. The surface layer is coated with an acrylic / urethane rubber layer. The outer diameter of the developing roller 23 is φ12 (mm), and the volume resistance is about 10 ⁵ Ω · cm. During image formation, the rotation speed (circumferential speed) of the developing roller 23 is 160 mm / sec.

  The developing roller 23 only needs to have a first electrode member in order to detect a later-described capacitance. For example, a conductive sleeve may be provided on the surface of the developing roller 23 and the sleeve may be used as the first electrode member.

The supply roller 24 is composed of a conductive core metal 29 (second electrode member) having a diameter of 6 (mm) and a urethane sponge layer (foamed surface layer) made of soft open-celled material formed around the conductive core metal 29. The outer diameter of the supply roller 24 is φ13 (mm), and the volume resistance is about 10 ⁸ Ω · cm. The surface air permeability of the urethane sponge layer is 3.2 liters / min. The surface airflow will be described in detail later. During image formation, the rotation speed (circumferential speed) of the supply roller is 140 mm / sec.

  In the present embodiment, the distance between the center of the cored bar 28 of the developing roller 23 and the center of the cored bar 29 of the supply roller 24 (hereinafter referred to as center distance) is 13 mm. Further, the surface of the developing roller 23 is installed so that the urethane sponge layer of the supply roller 24 is pushed in with an intrusion amount of about 1.0 mm.

  Here, the intrusion amount is a line segment connecting the center of the core metal 28 and the center of the core metal 29, and is divided by 2 by subtracting the distance between the centers from the sum of the outer diameters of the supply roller 24 and the developing roller 23. Length.

  The regulation blade 25 is made of a phosphor bronze sheet metal having flexibility, and one end is fixed to the developing container 21 and the other end is brought into contact with the developing roller 23 with a free end. A smooth surface in the vicinity of the free end is disposed so as to rub against the surface of the developing roller 23 in a direction that is a counter direction with respect to the rotation direction of the developing roller 23.

(Behavior of toner in developing device)
Here, the behavior of the toner dispersed in the urethane sponge layer of the supply roller 24 and the surrounding air when the supply roller 24 and the developing roller 23 are rotating at a predetermined speed will be described.

  The supply roller 24 is compressed in a region (in the vicinity of X in FIG. 2) on the upstream side in the rotation direction of the supply roller 24 with respect to the contact position between the supply roller 24 and the developing roller 23. On the other hand, in the region on the downstream side in the rotation direction (in the vicinity of Y in FIG. 2), the supply roller 24 is released from the compressed state.

  Here, in the vicinity of X, since the supply roller 24 is compressed, the toner sucked into the supply roller 24 is discharged together with air. Conversely, in the vicinity of Y, the supply roller 24 is released from the compressed state and returns to its original shape. At this time, the toner dispersed in the air is sucked into the supply roller.

  Under the condition that the toner enters and exits smoothly, the pressure of the toner as the powder fluid deposited in the vicinity of the supply roller 24 and the pressure of the toner as the powder fluid in the supply roller 24 are balanced. In this case, a certain correlation appears between the toner amount (developer amount) held in the supply roller 24 and the total toner amount in the developing container 21. Therefore, the electrostatic capacity between the cored bar 29 of the supply roller 24 and the developing roller 23 can not only indicate the amount of toner held in the supply roller 24 but also estimate the total amount of toner in the developing container 21. .

  The toner enters and exits only when the supply roller 24 rotates, and the supply roller 24 after the rotation stops maintains the amount of toner being rotated. Even if the developing device 20 is moved or the posture is changed in this state, the amount of toner held in the supply roller 24 does not change.

  As a parameter representing the “easyness” of entering and exiting the toner, the air permeability of the surface of the urethane sponge layer made of open cells was measured. In the present embodiment, as described above, the surface ventilation is 3.2 liters / min. The surface air flow rate decreases as the surface cells are smaller and the internal cell structure is finer and denser. Conversely, when the surface cell size is large or the internal cell size is increased, the air flow rate tends to increase.

  FIG. 3 shows the transition of the toner amount inside the sponge layer of the supply roller 24 and the toner amount inside the developing container 21 when the supply roller 24 in which the airflow amount is optimized is used. . FIG. 3 is a graph showing the relationship between the toner amount in the sponge of the supply roller and the electrostatic capacity.

  As the amount of toner in the developing container 21 decreases, the capacitance also decreases. Here, referring to FIG. 3, it can be seen that as the toner amount in the developing container 21 decreases, the toner amount in the sponge layer of the supply roller 24 also decreases. From this result, it can be seen that there is a correlation between the amount of toner held inside the sponge layer of the supply roller 24 and the total amount of toner in the developing container 21.

(Capacitance measurement method)
A method for measuring the capacitance of the developing device 20 in the present embodiment will be described.

  First, a predetermined alternating voltage is applied to the core metal 28 (first electrode member) of the developing roller 23, and the static voltage between the core metals is determined from the AC voltage induced on the core metal 29 (second electrode member) of the supply roller 24. Detect capacity. The AC voltage induced in the core metal 29 represents the electrostatic capacity between the core metal 28 and the core metal 29, and this capacitance reflects the amount of toner between the core metal 28 and the core metal 29.

  The cored bar 28 and the cored bar 29 may be detected by applying an alternating voltage to one and detecting the output from the other. For this reason, an AC voltage may be applied to the core metal 29 and the toner amount may be measured from the AC voltage induced on the core metal 28.

  FIG. 4 is a graph showing the relationship between the capacitance difference and the toner amount. The graph of FIG. 4 shows the relationship between the toner amount in the supply roller 24 and the capacitance difference between the cored bar 28 and the cored bar 29.

  The dielectric constant of the toner is about 3 times that of air. For this reason, as the amount of toner between the metal core 28 and the metal core 29 increases, the capacitance between the metal core 28 and the metal core 29 also increases. The relationship is almost linear as shown in FIG. When detecting the electrostatic capacitance, the developing roller 23 is stopped.

  FIG. 5 is a block diagram of the toner amount measuring apparatus according to the first embodiment.

  The toner amount measuring device 50 (toner amount measuring unit) includes a toner amount notifying unit 51, a toner amount determining unit 52, a comparator 53, a detection circuit 54 (voltage detection circuit), a voltage applying unit 55, and a voltage control unit 56.

  As shown in FIG. 5, a voltage applying means 55 for detection is connected to the metal core 28, and a detection circuit 54 is connected to the metal core 29. Therefore, the stopped state is not an essential condition and can be measured even when the developing roller 23 is rotating.

  The application conditions of the AC voltage for capacitance detection are a frequency f = 50 kHz and a peak-to-peak voltage Vpp = 180V. As the AC voltage induced in the core metal 29, the DC voltage itself rectified by the detection circuit or the signal information obtained by quantifying the DC voltage is output as an output value.

  Next, the detection circuit 54 will be described. FIG. 6 is a toner amount detection circuit diagram in the first embodiment.

  As shown in FIG. 6, the detection circuit 54 of the toner amount measuring device 50 includes a detector 30, an integrator 31, and a comparator 32. FIG. 6 shows an equivalent circuit of the supply roller 24 and the developing roller 23, the detector 30, the integrator 31, the comparator 32, the toner amount detection bias power supply 33, and the development bias power supply 34 indicated by the condenser C <b> 1. .

  A toner amount detection bias that is an AC bias is supplied from a toner amount detection bias power source 33. The detector 30 includes a resistor R and a diode D, and the output of the capacitor C1 is taken out as a voltage of the resistor R and is half-wave rectified by the diode D. The half-wave rectified voltage is integrated by an integrator 31 indicated by a capacitor C2, and converted into a DC voltage. This DC voltage is compared with the comparator F and the comparator 32 indicated by the reference voltage E.

  The comparator F compares the output voltage of the integrator 31 with the reference voltage E, and determines that the toner is present if the output voltage is larger, and determines that the toner is out if the output voltage is smaller. Therefore, the reference voltage E may be adjusted to the output voltage of the integrator 31 when the toner in the developing container 21 is consumed and lost.

  FIG. 7 is a graph showing the relationship between the detection voltage and the toner amount in the first embodiment. FIG. 7 shows changes in the toner amount in the developing container 21 and the output voltage of the integrator 31 in the present embodiment.

  As shown in FIG. 7, it can be seen that the output voltage decreases as the amount of toner increases. When the toner is further consumed, an image defect occurs in a part of the printed image at the point P in the figure. If the printing is further continued, no image appears.

From the above, in this embodiment, the toner amount Pa that allows for a margin equivalent to 10 sheets of solid black image with respect to the toner amount P that causes image loss is determined as T _OUT (out of toner state). Then, by setting the output voltage Qa to the reference voltage E, it is controlled to determine that the toner in the developing container has run out.

  When the toner amount measuring device 50 determines that the toner is out, the control unit displays a warning such as “out of toner” for the developing device 20 on the display unit in the operation unit. The control unit may perform control to stop image formation. Further, it is possible to notify the replacement time of the developing container 21.

(Configuration that suppresses the effects of variations in capacitance)
When the electrostatic capacity is detected using the above-described means, the measurement is performed after the developing roller 23 and the supply roller 24 are rotated each time for image formation or the like. For this reason, measurement is performed in a state where the developing roller 23, the supply roller 24, and the toner distribution in the developing container 21 are different each time. As a result, each time measurement is performed, a detection voltage including variations in capacitance caused by these variations is obtained. Here, generally, when there is such a variation as described above, it is difficult to accurately detect the toner amount.

  For this reason, in the present embodiment, toner amount detection is performed while reducing variations in capacitance. In the following, description will be given in order.

  First, consider the factors that cause the capacitance to vary. When the electrostatic capacity is measured while forming an image, the supply roller 24 and the developing roller 23 need to be rotated each time. Even if the toner is not consumed by image formation and the toner filling amount in the supply roller 24 is not changed, the measurement is performed at a contact position different from the previous position at the time of measurement.

  Here, when there are variations in the rotation directions of the supply roller 24 and the developing roller 23, it is suggested that the detection value, that is, the capacitance C may vary. FIG. 8 shows the result of measuring the capacitance between the supply roller 24 and the developing roller 23 while actually rotating the supply roller 24 and the developing roller 23. FIG. 8 is a graph showing the change with time of the electrostatic capacity during rotation of the supply roller.

  From the result of FIG. 8, it can be seen that the electrostatic capacity varies with the same periodicity every rotation of the supply roller 24 as the supply roller 24 rotates. Therefore, the variation of the supply roller 24 is dominant, and the variation of the developing roller 23 is considered to be smaller than the variation of the supply roller 24.

  FIG. 9 is a graph showing variations in detected voltage. FIG. 9A shows a procedure in which the electrostatic capacity is measured in a stationary state after the supply roller 24 is rotated, the phase is changed by rotating it again, and the measurement is performed in a stationary state. FIG. 9A shows the result of capacitance measurement performed five times. From the result of FIG. 9A, it can be seen that, similar to the result obtained from FIG. 8, the capacitance value obtained varies every time the phase of the supply roller 24 is different.

  Next, the toner distribution in the developing container 21 and the toner variation in the supply roller 24 were investigated. In order to isolate these contributions, the same study was performed without filling the developing container 21 with toner, that is, without supplying toner to the supply roller 24. This result is shown in FIG.

  In FIG. 9B, it can be seen that the electrostatic capacity varies even when the supply roller 24 does not contain toner. From this result, it has been clarified that the variation in the electrostatic capacitance is less due to the toner, and the variation of the supply roller 24 is dominant.

  One reason for this is thought to be unevenness in the rotational direction of the supply roller 24 in the foaming state. Since the supply roller 24 is a urethane sponge material made of open cells, the foaming density is hardly uniform in the rotation direction. In fact, there is also a variation in the amount of surface airflow that contributes to the entry and exit of toner.

  Therefore, in this toner amount detection, in order to reduce this variation, it is desirable to perform measurement while maintaining the state without rotating the supply roller 24. Therefore, in order to reduce the above-described variation, in this embodiment, two different states are created in the stationary state, and the difference is calculated.

  Below, the means for suppressing the dispersion | variation in the supply roller 24 and theoretical interpretation are demonstrated.

  A toner amount detection circuit 54 actually mounted is shown in FIG. The voltage ΔV output from the controller when an AC bias is applied between the supply roller 24 and the developing roller 23 depends on the capacitance C between the supply roller 24 and the developing roller 23. Therefore, if there is a variation in the supply roller 24, it is recognized as a change in capacitance, and the detection voltage ΔV varies. Therefore, in order to reduce variation, the toner amount is detected by changing other parameters without changing the capacitance C.

  The output voltage ΔV utilizes the fact that, besides the capacitance C, it depends on the peak-to-peak voltage Vpp of the AC bias that is the toner amount detection bias.

  As described above with reference to FIG. 3, the capacitance has a correlation with the amount of toner in the supply roller 24. Considering that the peak-to-peak voltage Vpp and the capacitance are proportional to the output voltage ΔV, the amount of toner in the supply roller 24 is also proportional to the peak-to-peak voltage.

  It has also been found that there is a correlation between the amount of toner in the developing container 21 and the amount of toner in the supply roller 24. This will be described with reference to FIG. FIG. 10 is a graph showing the relationship between the toner amount in the developing container and the toner amount in the sponge of the supply roller. As shown in FIG. 10, it is known that the amount of toner contained in the supply roller 24 increases as the amount of toner in the developer container 21 increases as compared with the same developer container 21.

  Considering this, a case where the peak-to-peak voltage Vpp is changed will be considered. Vpp is varied based on Vpp = 180V. Vpp adopted 150V and 130V.

At a certain toner amount detection timing, a detection voltage ΔV induced by applying a certain peak-to-peak voltage Vpp is detected. The detection voltage when the V _A, the toner amount in the developing container 21 and T _A. Subsequently, when the toner amount T _B in the developing container 21 satisfies T _A > T _B , the detected voltage measured in the same manner is set to V _B. The result is shown in FIG. FIG. 11 is a graph showing the relationship between the detection voltage and the toner amount when Vpp is changed.

As shown in FIG. 11, the detected voltages V _A and V _B and the toner amount have the same correlation, but it can be seen that the amount of increase in the detected voltage ΔV differs depending on Vpp. As Vpp becomes smaller, the slope becomes smaller, while as Vpp becomes larger, the slope becomes larger.

  At this time, the detection voltage ΔV is represented by the product of the electrostatic capacitance C between the supply roller 24 and the developing roller 23 and the peak-to-peak voltage Vpp. For this reason, the inclination changes according to these two values. In this embodiment, since the state and arrangement relationship of the supply roller 24 and the developing roller 23 are not changed, it is considered that there is no change in capacitance. Therefore, it can be seen that the obtained detection voltage ΔV is changed by changing Vpp. From the above, when the toner filling amount is large and when the toner filling amount is small, the amount of change with respect to the difference in the detected voltage ΔV between different Vpps according to the change in Vpp is different.

  From the above results, in the present embodiment, Vpp is changed in a stationary state without rotating the supply roller 24, and the difference between the detected voltages ΔV between different Vpp is calculated. The toner amount is determined based on the calculation result. As a result, it is not necessary to consider variations in capacitance, and variations in the supply roller 24 can be suppressed. As a result, the detection accuracy is improved.

  The results of actual toner amount detection using the method of this embodiment are shown below.

Three types of developing containers (T _Full , T _OUT , T ₀ ) having a known toner amount in the developing container 21 are prepared. Then, the toner amount is detected in a state where the toner is sufficiently contained in the supply roller 24 in advance. The details of the investigations that were conducted are described below.

  First, it was investigated and confirmed that the variation in the rotation direction of the supply roller 24 can actually be canceled by this embodiment.

A predetermined AC bias is applied to each of the developing containers 21 described above to obtain a detection voltage ΔV. At this time, the peak-to-peak voltage Vpp is Vpp ₁ and the detection voltage is V ₁ . Subsequently, the supply roller 24 and the developing roller 23 are not rotated, and the AC bias Vpp is set to a condition different from that at the time of measuring V _{1 with} the same position and posture.

After setting, in the same manner as when V ₁ measurement to measure the detection voltage V _2. Let Vpp at this time be Vpp ₂ . As described above, a binary value is taken in a stationary state, and the difference is calculated. The embodiment described above is the same as the study performed by changing the Vpp described above.

Subsequently, after changing the phases of the supply roller 24 and the developing roller 23, the same operation is performed. Repeat this 5 times. The variations of V ₁ , V ₂ , | V ₁ −V ₂ | at this time were compared. In this study, Vpp ₁ = 180 V and Vpp ₂ = 130 V.

  FIG. 12 is a graph comparing the variation when Vpp is changed and when the difference is taken.

FIG. 12 shows the result of variation when each toner amount is measured five times.

Variations ΔV ₁ , ΔV ₂ , and Δ (| V ₁ −V ₂ |) at this time are differences between the maximum output and the minimum output in the five measurements. From this result, the detection voltages V ₁ and V ₂ only by the supply roller 24 vary for each detection, whereas in the present embodiment, Δ (| V ₁ −V ₂ |) is calculated. The variation could be reduced.

  This is true regardless of the toner filling amount. Therefore, this embodiment can exhibit an effect regardless of the amount of toner in the supply roller 24. In this way, by measuring the detection voltage in the same state without rotating the supply roller 24, variations in detection results derived from the configuration of the supply roller 24 can be suppressed.

The following is presumed as a theoretical interpretation that this method is established. Although the supply roller 24 has variations in the rotation direction, the detection voltages V ₁ and V ₂ are measured at locations having the same variation by not rotating the supply roller 24.

When the same measurement is performed while changing the phase, the measurement is performed at a location having a variation different from the previous time, but the detected voltages V ₁ and V ₂ at that time are measured in the same phase. Therefore, the detection voltages V ₁ and V ₂ are measured with the same variation. Therefore, the absolute values of the detection voltages V ₁ and V ₂ are shifted by the variation every time, but the variation can be reduced by calculating the difference. The details are shown in FIG.

FIG. 13 is a graph showing a variation reducing mechanism in the first embodiment. As shown in FIG. 13, although the absolute values of the detection voltages V ₁ and V ₂ are different, the difference between the detection voltages is substantially constant.

  Next, the relationship between the toner amount for detecting the toner amount and the difference ΔVD1 of the detection voltage ΔV in the present embodiment will be described.

FIG. 14 is a graph showing the relationship with the toner amount when the difference ΔVD1 obtained from the Vpp change in the first embodiment is taken. Specifically, the value of | V ₁ −V ₂ | obtained from the above result is compared for each toner amount. Then, the amount of toner _{T A} and _{T B} in the developer container 21, the difference between the detection voltage _{ΔV ΔVD1 = | T A (|} V 1 -V 2 |) -T B (| V 1 -V 2 |) | changes in Showed the rate. Here, _{"T A (| V 1 -V 2} |) " and the amount of toner when the _{T A |} means a value of | V 1 -V _2.

14, _{V 1} denotes the detection voltage ΔV when the Vpp = 180V, _{V 2} denotes the Vpp = 150 V, the detection voltage ΔV when the 130 V. Here, the difference ΔVD1 at this time is calculated. In the following description, the full toner amount is T _Full and the empty toner amount is T ₀ with respect to the toner amount T _{OUT in the} out-of-toner state indicating the toner replacement.

First, when compared with _{T Full} and _{T OUT} of the developing container 21, the difference _| V 1 -V _{2 | =} difference _{ΔVDa = T Full -T OUT | T} Full (| V 1 -V 2 |) -T _OUT (| V ₁ −V ₂ |) | is obtained. Then, ΔVDb = T _Full −T ₀ = | T _Full (| V ₁ −V ₂ |) −T ₀ (| V ₁ −V ₂ |) | between T _Full and the empty toner amount T ₀ is obtained. From this result, it can be seen that | V ₁ −V ₂ | depends on the amount of toner, and ΔVDb is larger than ΔVDa.

  Therefore, in this embodiment, the toner amount detection is performed by changing the peak-to-peak voltage Vpp and using the change in ΔVD1 depending on the toner amount. This is true regardless of the operating environment of the image forming apparatus 100.

  As described above, in this embodiment, an AC voltage having a plurality of types of voltage conditions is applied, and the detection voltage is measured at each timing when the AC voltage is applied. Then, the toner amount is determined based on the difference between the detection voltages. When the toner amount is calculated in this way, it is possible to suppress variations in electrostatic capacity of the toner supply member in the rotation direction. Therefore, the toner amount can be detected with high accuracy.

[Second Embodiment]
In order to suppress variations in the supply roller 24, it is possible to change the frequency f of the AC bias by the same theory as the method of changing the peak-to-peak voltage Vpp as in the first embodiment.

  From the first embodiment, consider a case where the frequency f is changed in consideration of the correlation between the detection voltage ΔV and the toner amount in the developing container 21. FIG. 15 shows the results of measurement using the same method as described above with the frequency varied with f = 50 kHz as a reference. FIG. 15 is a graph showing the relationship between the detection voltage and the toner amount when the frequency is changed.

  As shown in FIG. 15, when the toner amount is plotted against the detection voltage ΔV, it can be seen that the detection voltage ΔV and the toner amount have a correlation depending on the frequency. That is, the detection voltage ΔV increases as the frequency increases. Thus, since the detection voltage ΔV has a correlation with the frequency, it can be seen that the increase amount of the detection voltage ΔV differs depending on the frequency. Therefore, the obtained detection voltage ΔV is changed by changing the frequency. As described above, the amount of change with respect to the difference in the detection voltage ΔV between different frequencies differs depending on the change in frequency depending on whether the toner filling amount is large or small.

  For this reason, in this embodiment, without rotating the supply roller 24, the frequency is changed in a stationary state, and the difference between the detected voltages ΔV is calculated. The toner amount is determined based on the calculation result. By using this detection means, as in the first embodiment, the variation of the supply roller 24 can be suppressed, which contributes to improvement in detection accuracy.

  The results of actual toner amount detection using the method of this embodiment are shown below.

Three types of developing containers (T _Full , T _OUT , T ₀ ) having a known toner amount in the developing container 21 are prepared. Then, the toner amount is detected in a state where the toner is sufficiently contained in the supply roller 24 in advance. Detailed means will be described below.

  First, it was investigated and confirmed that the variation in the rotation direction of the supply roller 24 can be actually canceled by the method according to the present embodiment.

A predetermined AC bias is applied to each of the developing containers 21 described above to obtain a detection voltage ΔV. The frequency at this time is f ₁₁ and the detection voltage is V ₁₁ . Subsequently, the supply roller 24 and the developing roller 23 are not rotated, and the AC bias frequency f is set to a condition (f ₁₂ ) different from that at the time of measuring V _{11 with} the same position and posture.

After _setting, in the same manner as when _{V 11} measurement, measures the detected voltage _{V 12.} The frequency at this time is _{f 12.} As described above, the binary value is obtained when the supply roller 24 is stationary, and the difference Δ is calculated. After changing the phases of the supply roller 24 and the developing roller 23, the same operation is performed. Repeat this 5 times. The variations of V ₁₁ , V ₁₂ , and | V ₁₁ −V ₁₂ | at this time were compared. In this study, f ₁₁ = 50 kHz and f ₁₂ = 40 kHz.

  FIG. 16 shows the dispersion results of the five measurements for each toner amount. FIG. 16 is a graph comparing the variations when the frequency is changed and when the difference is taken in the second embodiment.

Also in the method of the second embodiment, the variation can be reduced by calculating Δ (| V ₁₁ −V ₁₂ |) from the variations ΔV ₁₁ and ΔV ₁₂ of the detection voltage of only the supply roller 24. In addition, the method of the present embodiment is effective regardless of the amount of toner in the supply roller 24. This theoretical interpretation is the same as the description described in the first embodiment.

  Next, the relationship between the toner amount and the difference ΔVD2 between the detection voltage ΔV in order to detect the toner amount using the method of the second embodiment will be described.

The value of | V ₁₁ −V ₁₂ | obtained from the above results was compared for each toner amount. FIG. 17 shows the result of the change rate of the difference ΔVD2 = T _A (| V ₁₁ −V ₁₂ |) −T _B (| V ₁₁ −V ₁₂ |) of the detection voltage ΔV depending on the amount of toner in the developing container 21. Show. FIG. 17 is a graph showing the relationship with the toner amount when the difference ΔVD2 obtained from the frequency change in the second embodiment is taken.

In FIG. 17, the detected voltage ΔV when f = 50 kHz is shown as V ₁₁ , and V ₁₂ shows the detected voltage ΔV when f = 40 kHz. The difference ΔVD2 at this time is calculated.

That is, firstly when compared with the toner amount _{T Full} and _{T OUT} of the developer container, the difference _| V 11 _{-V 12 |} of the difference _{ΔVDc = ΔT Full -T OUT = |} T Full (| V 11 -V 12 | ) −T _OUT (| V ₁₁ −V ₁₂ |) | Then, ΔVDd = T _Full −T ₀ = | T _Full (| V ₁₁ −V ₁₂ |) −T ₀ (| V ₁₁ −V ₁₂ |) | between T _Full and T ₀ is obtained. From this result, it can be seen that | V ₁ −V ₂ | depends on the amount of toner, and ΔVDd is larger than ΔVDc.

  Therefore, in the present embodiment, the toner amount is detected by utilizing the fact that the frequency is changed and ΔVD2 changes depending on the toner amount.

  As described above, in this embodiment, an AC voltage having a plurality of frequency conditions is applied, and the detection voltage is measured at each timing when the AC voltage is applied. Then, the toner amount is determined based on the difference between the detection voltages. When the toner amount is calculated in this way, it is possible to suppress variations in electrostatic capacity of the toner supply member in the rotation direction. Therefore, the amount of toner can be accurately detected by the user.

[Other Embodiments]
The first embodiment and the second embodiment are not necessarily performed independently. That is, binary values may be calculated by simultaneously changing Vpp and frequency.

  In the first embodiment, it is known that when Δ of the applied peak-to-peak voltage Vpp is increased, a larger ΔVD can be secured. The same holds true for the AC bias frequency of the second embodiment. For this reason, by selecting a condition that increases ΔVD for both Vpp and frequency, the obtained difference Δ is further increased as compared to the first and second embodiments. That is, by combining the calculation methods in the first embodiment and the second embodiment, the toner amount can be detected with higher accuracy.

  Further, when calculating the difference ΔVD of the detection voltage ΔV in the above-described embodiment, different two values are adopted, but the present invention is not limited to this. For example, if different peak-to-peak voltage Vpp and frequency f are selected, the value is not limited to two but may be three or more.

DESCRIPTION OF SYMBOLS 2 ... Photosensitive drum 20 ... Developing apparatus 21 ... Developing container 23 ... Developing roller 24 ... Supply roller 28 ... Core metal 29 ... Core metal 50 ... Toner amount measuring device 54 ... Voltage detection circuit 55 ... Voltage applying means 100 ... Image forming apparatus

Claims (4)

In an image forming apparatus comprising: an image carrier; and a developing unit that supplies toner in a developing container from a toner supply member to the toner carrier and supplies the toner to the image carrier by the toner carrier.
Voltage applying means for applying an alternating voltage to one of the first electrode member provided on the toner carrier or the second electrode member provided on the toner supply member;
A voltage detection circuit for rectifying and detecting an alternating voltage induced on the other of the first electrode member or the second electrode member;
A toner amount measuring means for applying a plurality of types of AC voltages by the voltage applying means and measuring a toner amount in the developing container based on a difference between a plurality of output voltages detected by the voltage detection circuit;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the toner amount measuring unit measures a toner amount in the developing container in a state where the toner supply member is stationary.   The image forming apparatus according to claim 1, wherein the plurality of types of AC voltages applied by the voltage applying unit are a plurality of peak-to-peak voltages.   The image forming apparatus according to claim 1, wherein the plurality of types of AC voltages applied by the voltage applying unit have a plurality of frequencies.

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