JP5796505B2 - Toner concentration detection device, image forming apparatus, and toner concentration detection method - Google Patents

Description

  The present invention relates to an apparatus and method for detecting the toner concentration of a two-component developer.

  In an electrophotographic image forming apparatus, a two-component developer in which toner and a magnetic carrier are mixed is used. When developing the electrostatic latent image, only the toner of the two-component developer adheres to the image carrier (photoconductor), and the magnetic carrier remains in the developing unit. In order to keep the mixing ratio of the toner and the magnetic carrier in the developing unit constant, the toner consumed by the development is supplied to the developing unit. Magnetic carriers are used repeatedly. Replenishment of toner is controlled based on a detected value of toner density in the two-component developer in the developing unit.

  Generally, the toner concentration of the two-component developer is detected by an LC oscillation circuit. The LC oscillation circuit as a toner density sensor outputs an oscillation signal having a frequency corresponding to the mixing ratio of the two-component developer. Since the inductance of the coil in the LC oscillation circuit depends on the magnetic permeability determined by the mixing ratio of the two-component developer, the oscillation frequency changes according to the mixing ratio. Therefore, the toner density can be calculated by detecting the oscillation frequency.

  Conventionally, a toner density sensor in which a coil of an LC oscillation circuit is formed by a printed wiring technique is known. This toner concentration sensor having a flat coil has an advantage that it is excellent in sensitivity and small in size as compared with a sensor having a three-dimensional coil in which a conductor is wound around a magnetic core.

  There are the following prior arts that reduce the influence of the temperature characteristics of the toner density sensor. In Patent Document 1, it is proposed that the printed coil is formed so that its resistance value falls within a predetermined range, and thereby the variation amount of the oscillation frequency due to the change of the environmental temperature does not exceed the allowable value. Yes. In Patent Document 2, a first oscillation circuit in which a coil is arranged at a position where the inductance changes according to a mixing ratio of the two-component developer and a second oscillation circuit in which the coil is arranged at a position where the inductance does not change are used. It is disclosed that the toner density is detected. If the difference between the oscillation frequencies of the two oscillation circuits is obtained, a toner density detection value in which the temperature characteristics of the oscillation circuits are canceled can be obtained.

JP-A-11-223620 JP 2010-267661 A

  According to the technique described in Patent Document 1, it is possible to reduce the influence of changes in environmental temperature in toner concentration detection. However, in order to mass-produce a toner density sensor whose coil resistance value is within a desired range, a production technique for making the size, thickness, and pattern width of the coil pattern uniform is necessary. The smaller the pattern size, the more difficult it is to make the thickness and width uniform. For this reason, it is necessary to use a printed circuit board having a size larger than a certain size and to strictly control the manufacturing conditions, which increases the manufacturing cost of the toner density sensor.

  In addition, when two coils are formed as disclosed in Patent Document 2, a printed circuit board having an appropriate size is required. In addition, the sizes, thicknesses, and pattern widths of the two coils must be made uniform in order to cancel the temperature characteristics. Therefore, also in this case, the manufacturing cost of the toner density sensor is increased.

  SUMMARY OF THE INVENTION In view of such circumstances, an object of the present invention is to alleviate restrictions on the structure of a coil of an oscillation circuit as a toner concentration sensor.

  An apparatus that achieves the above object is a toner concentration detection device that detects the toner concentration of a two-component developer, an oscillation circuit that oscillates at a frequency corresponding to the magnetic permeability of the two-component developer, and oscillation of the oscillation circuit A frequency detection unit for detecting a frequency, a voltage detection unit for detecting an oscillation start voltage of the oscillation circuit, a temperature detection unit for detecting an operating environment temperature of the oscillation circuit, and an oscillation start voltage and an oscillation frequency of the oscillation circuit Based on the operating environment temperature detected by the temperature detection unit and the oscillation start voltage detected by the voltage detection unit, the oscillation frequency detected by the frequency detection unit is obtained using information indicating the relationship with the temperature characteristics. A correction unit that corrects the oscillation frequency, and outputs the oscillation frequency corrected by the correction unit as toner density information.

  According to the present invention, it is possible to reduce the manufacturing cost of the oscillation circuit by relaxing the structural restrictions of the coil of the oscillation circuit as the toner concentration sensor, and to realize the toner concentration detection according to the change of the environmental temperature. be able to.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a diagram illustrating an example of arrangement of toner density sensors. FIG. 3 is a diagram illustrating a configuration of a toner density sensor. FIG. 3 is a diagram illustrating a configuration of a toner concentration detection device including a toner concentration sensor. FIG. 6 is a waveform diagram schematically illustrating a relationship between a power supply voltage and an output signal of a toner density sensor. 6 is a graph showing a relationship between a resistance value of a coil of a toner concentration sensor and an oscillation start voltage. 6 is a graph showing a relationship between a resistance value of a coil of a toner concentration sensor and an oscillation start voltage. It is a graph which shows the relationship between the resistance value of the coil of a toner concentration sensor, and the change of the oscillation frequency accompanying environmental temperature change. It is a graph which shows the temperature characteristic of the oscillation frequency of a toner concentration sensor. 5 is a flowchart of toner density control in the image forming apparatus.

  An image forming apparatus 1 illustrated in FIG. 1 includes an image scanner 5. Examples of this type of apparatus include a copying machine, an MFP (Multi-functional Peripheral), and a facsimile machine. The image forming apparatus 1 is assembled with a printer engine 10 that forms a monochrome image by electrophotography. The printer engine 10 includes a cylindrical photosensitive member 11, a charging charger 12, a laser scanning unit 13, a developing unit 14, a transfer charger 15, a separation laser jar 16, a cleaner 17, an eraser lamp 18, and a fixing device 19. . Since the electrophotographic process using these image forming elements is widely known, detailed description of the function and process of each image forming element is omitted. The outline of the image forming operation controlled by the controller 30 is as follows.

  When, for example, an operation for instructing the start of copying is performed on the operation panel 40 of the image forming apparatus 1, an original image is read by the image scanner 5, and exposure scanning (also referred to as printing) corresponding to the original image is performed by the laser scanning unit 13. Done. An electrostatic latent image is formed on the photoconductor 11 by exposure scanning, and the electrostatic latent image is developed into a toner image by the developing unit 14. The exposure scanning is started so that the toner image on the rotating photoconductor 11 just arrives at the transfer position p1 when the leading end of the image forming range on the paper surface arrives at the transfer position p1. In parallel with exposure scanning, the paper P is taken out from the paper stacker 21 by the pickup roller 22, and the toner image is transferred to the paper P that has arrived at the transfer position p1. Thereafter, the paper P that has been heated and pressurized by the fixing device 19 is sent to the paper discharge tray 28.

  In the exemplary image forming apparatus 1, a two-component developer (not shown in FIG. 1) is accommodated in the developing unit 14, and the toner in the two-component developer is separated from the carrier, which is a magnetic particle, on the photoreceptor 11. The electrostatic latent image is developed by electroadsorption. Toner is replenished from the toner bottle 42 to the developing unit 14 at an appropriate time based on the output of the toner concentration sensor 50 so as to keep the toner concentration of the two-component developer constant.

  In FIG. 2, a part of the developing unit 14 is schematically drawn. As shown in FIG. 2, the developing unit 14 has a conveying screw 142 that is arranged in parallel with the photoreceptor 11. The two-component developer 60 inside the developing unit 14 is fed in the direction of the arrow M1 in the drawing while being stirred by the rotation of the conveying screw 142. At this time, toner is replenished into the developing unit 14 from a toner replenishing port 14E provided on the upper surface of the upstream end in the feed direction. Then, the toner density sensor 50 detects the mixing ratio (that is, toner density) of the two-component developer 60 in a state where the toner and the carrier are uniformly mixed by stirring at the downstream end in the feeding direction. The toner density sensor 50 has a flat coil 56 formed on the multilayer printed wiring board, and the coil 56 is close to the two-component developer staying in the lower part inside the developing unit 14. Arranged outside the developing unit 14.

  3A shows an example of the circuit configuration of the toner density sensor 50, and FIG. 3B shows an example of a planar view shape (coil pattern) of the coil 56. FIG. As shown in FIG. 3A, the toner density sensor 50 is an LC oscillation circuit including a coil 56, and receives an operating power supply from a power supply circuit and outputs an oscillation signal having a frequency of about 900 kHz, for example. The inductance of the coil 56 changes as the magnetic permeability of the two-component developer adjacent to the coil 56 passes through the housing of the developing unit, thereby changing the oscillation frequency. The toner replenishment amount is controlled so that the oscillation frequency of the toner density sensor 50 becomes a frequency corresponding to an appropriate value of the toner density.

  By the way, the oscillation frequency of the toner density sensor 50 depends on the operating environment temperature of the toner density sensor 50. The resistance value of the coil 56 greatly affects the temperature characteristics of the oscillation frequency. Since the coil 56 produced by the printed wiring process including conductor film formation and etching has variations in pattern width and thickness, the resistance value of the coil 56 also has variations in a predetermined range. Therefore, in order to keep the toner density at an appropriate value, the detection value (oscillation frequency) by the toner density sensor 50 is corrected according to the operating environment temperature and the resistance value of the coil 56, and toner replenishment is performed based on the corrected detection value. Need to control.

  In the image forming apparatus 100 of the present embodiment, the knowledge that “there is a certain correlation between the resistance value of the coil 56 and the“ oscillation start voltage ”of the toner density sensor 50” is applied. That is, instead of measuring the resistance value of the coil 56, the oscillation start voltage is detected, and the oscillation frequency is corrected based on the detected value of the oscillation start voltage and the detected value of the operating environment temperature. FIG. 4 shows the configuration of a toner concentration detection device that performs such correction.

  As shown in FIG. 4, the toner concentration detection device 1 includes a toner concentration sensor 50, a temperature sensor 70, a plurality of elements (301 to 304) realized by a CPU (central processing unit) 31, and an oscillation start voltage and an oscillation frequency. Information 400 indicating the relationship with temperature characteristics is provided. The toner density detection device 1 corrects the oscillation frequency F of the toner density sensor 50 based on the information 400, and transmits the corrected oscillation frequency Frev to the replenishment control unit 305. In accordance with the corrected oscillation frequency Frev, the toner supply mechanism (not shown) and the motor 85 that rotationally drives the conveying screw 142 are controlled by the supply control unit 305.

  The temperature sensor 70 is disposed inside the image forming apparatus 100. The output of the temperature sensor 70 is taken into the CPU 31 as a signal indicating the operating environment temperature of the toner concentration sensor 50. By arranging the temperature sensor 70 in the vicinity of the toner concentration sensor 50, the temperature correction for the toner concentration sensor 50 can be performed more accurately.

  The CPU 31 operates as the oscillation start voltage detection unit 301, the temperature detection unit 302, the frequency detection unit 303, the correction unit 304, and the above-described supply control unit 305 by executing the control program. Of these five functional elements realized by the CPU 31, four functional elements excluding the replenishment control unit 305 are elements constituting the toner density detection device 1. The CPU 31 may be included in the controller 30 (see FIG. 1) that performs overall control of the image forming apparatus 100, or may be included in a sub-controller that cooperates with the controller 30.

  The information 400 includes first relation information 410 and second relation information 420. The first relationship information 410 indicates the relationship between the resistance value of the coil 56 and the oscillation start voltage. The second relationship information 420 indicates the relationship between the resistance value of the coil 56 and the temperature characteristic of the oscillation frequency. Information 400 is stored in a non-volatile memory (not shown).

  The operation of the CPU 31 is as follows.

  A replenishment control unit 305 responsible for toner replenishment processing controls the power supply circuit 80 to supply driving power to the motor 85 at an appropriate time. The reason why the motor 85 is rotated is that mixing may occur in the staying two-component developer due to being left for a long time, so that it is necessary to perform stirring to make the mixing uniform. . When the motor 85 rotates, the conveying screw 142 connected via the drive gear rotates to stir the two-component developer.

  After stirring the two-component developer, the low-voltage power supply 82 in the power supply circuit 80 is turned on, and the power supply voltage Vin is applied to the toner density sensor 50. In the toner concentration sensor 50, as shown in FIG. 5, the oscillation starts in the middle of the rise when the power supply voltage Vin changes from 0 volts to a steady voltage (for example, 3.3 volts). After the start of oscillation, the amplitude of the output signal S50 of the toner density sensor 50 gradually increases and becomes constant. More specifically, as schematically shown in FIG. 5, the amplitude of the output signal S50 of the toner density sensor 50 gradually increases as the power supply voltage Vin rises, and the output signal S50 is reached when the power supply voltage Vin becomes a steady voltage. Becomes an oscillation signal with substantially constant amplitude. The low-voltage power supply 82 and the toner concentration sensor 50 are configured so that oscillation starts in the middle of the rise of the power supply voltage Vin.

  The oscillation start voltage detector 301 monitors the power supply voltage Vin applied to the toner concentration sensor 50 and the output signal S50 of the toner concentration sensor 50. That is, the power supply voltage Vin and the output signal S50 are sampled at a period sufficiently shorter than the power supply rising transition period. Then, the oscillation start voltage detector 301 compares the time-series sampling values, and detects, for example, the power supply voltage Vin when the amplitude of the output signal S50 changes abruptly as the oscillation start voltage Vs. The detected oscillation start voltage Vs is transmitted to the correction unit 304.

  In parallel with the detection of the oscillation start voltage Vs, the temperature detection unit 302 detects the operating environment temperature Tc of the toner concentration sensor 50 by the output signal S70 of the temperature sensor 70, and the frequency detection unit 303 by the output signal S50 of the toner concentration sensor 50. Detects the oscillation frequency F. The operating environment temperature Tc and the oscillation frequency F are also transmitted to the correction unit 304.

  The correction unit 304 uses the information 400 to correct the oscillation frequency F based on the operating environment temperature Tc and the oscillation start voltage Vs. Based on the corrected oscillation frequency Frev, the replenishment control unit 305 controls the replenishment of toner as described above.

  Hereinafter, the operation of the correction unit 304 will be described in more detail with reference to the graphs of FIGS.

FIG. 6 shows the relationship between the resistance value between the terminals of the coil and the oscillation start voltage in a plurality of LC oscillation circuits having the same configuration as the toner density sensor 50. In FIG. 6, the oscillation start voltage increases as the resistance value of the coil increases. In particular, it can be seen that the resistance value and the oscillation start voltage are substantially proportional in the range of the resistance value from about 6.5Ω to about 9Ω. FIG. 7 shows the relationship between the resistance value of the coil and the oscillation start voltage in each of the three cases where the magnetic permeability of the two-component developer adjacent to the LC oscillation circuit is different. As shown in the graph of FIG. 7, the correlation between the resistance value and the oscillation start voltage is hardly affected by the magnetic permeability of the two-component developer. Therefore, if the oscillation start voltage Vs in the toner density sensor 50 is detected, the resistance value of the coil 56 can be obtained. If the resistance value with manufacturing variation is a value within a range in which the oscillation start voltage and the resistance value are proportional to each other, the oscillation start voltage Vs is expressed by the equation (1), where R is the resistance value.
Vs = α × R + β (1)
However, α and β in the equation are constants specific to the oscillation circuit.
When the equation (1) is modified, the equation (1B) representing the resistance value (R) is obtained.
R = (Vs−β) / α (1B)
The above-mentioned first relation information 410 is data representing this equation (1B).

FIG. 8 is measured using a plurality of LC oscillation circuits having the same configuration as the toner density sensor 50.
The relationship between the resistance value of a coil and the change of the oscillation frequency accompanying environmental temperature change is shown. The value on the vertical axis of the graph of FIG. 8 is the difference between the oscillation frequency F [0] at 0 ° C. and the oscillation frequency F [50] at 50 ° C. (F [50] −F [0]). The temperature characteristic of the oscillation frequency can be regarded as a linear characteristic. Based on this, when looking at FIG. 8, when the resistance value is around 6.5Ω, the fluctuation of the oscillation frequency F is about 250 Hz when the environmental temperature changes within the range from 0 ° C. to 50 ° C. It turns out that it changes with width. It can also be seen that when the resistance value is around 7.5Ω, the oscillation frequency F changes with a fluctuation width of approximately 600 Hz.

FIG. 9 shows the temperature characteristics of the oscillation frequency with the resistance value of the coil as a parameter. The value on the vertical axis of the graph of FIG. 9 is the fluctuation amount ΔF of the oscillation frequency based on the oscillation frequency at the standard environmental temperature (25 ° C.). When the temperature characteristic is regarded as a linear characteristic, the fluctuation amount of the oscillation frequency at a certain temperature (that is, the difference from the reference oscillation frequency) ΔF is expressed by the equation (2), where the operating environment temperature is Tc.
ΔF = a _R × Tc + b _R (2)
However, a _R and b _R in the formula are constants corresponding to the resistance value of the coil.
The second relation information 420 described above is the values of constants a _R and b _R corresponding to the equation (2) and each of a plurality of values that can be taken as the resistance value of the coil.

The corrected oscillation frequency Frev obtained by the correction unit 304 is expressed by equation (3).
Frev = F−ΔF (3)
The correction unit 304 calculates the resistance value (R) of the coil 56 by applying the equation (1B) indicated by the first relation information 410 based on the detected oscillation start voltage Vs. Subsequently, the correction unit 304 selects and detects a value corresponding to the previously calculated resistance value (R) as the values of the constants a _R and b _{R in} the expression (2) indicated by the first relationship information 420. Based on the operating environment temperature Tc, the fluctuation amount ΔF of the oscillation frequency is calculated. Then, the correction unit 304 calculates the oscillation frequency Frev subjected to temperature correction by applying the equation (3).

  FIG. 10 is a flowchart of toner density control in the image forming apparatus 100. The oscillation start voltage detector 301 monitors the power supply voltage Vin applied to the toner density sensor 50 and acquires the oscillation start voltage Vs (S10, S20, S30). The correction unit 304 obtains the resistance value (R) of the coil 56 based on the oscillation start voltage Vs (S40). When the environmental temperature (operating environmental temperature) Tc related to the operation of the toner density sensor 50 is detected by the temperature detection unit 302, the correction unit 304 calculates a correction amount (ΔF) of the oscillation frequency (S60). The frequency detection unit 303 detects the oscillation frequency F of the toner concentration sensor 50 (S70), and the correction unit 304 outputs the oscillation frequency Frev obtained by correcting the oscillation frequency F (S80). Then, the replenishment control unit 305 that has acquired the oscillation frequency Frev sets the mixing ratio of the two-component developer to an appropriate value according to the difference between the oscillation frequency Frev and the oscillation frequency corresponding to the appropriate mixing ratio at the standard environment temperature. Thus, the toner is supplied to the developing unit 14 (S90).

  In the above embodiment, the resistance value (R) of the coil 56 and the fluctuation amount ΔF of the oscillation frequency are obtained by a technique using a look-up table instead of the calculation by the expression (1B) and the calculation by the expression (2). it can. In this case, the first relationship information 410 may be a lookup table that associates a plurality of possible values of the oscillation start voltage Vs with the resistance value R corresponding to them. The second relationship information 420 includes a look-up table indicating values of oscillation frequency variation ΔF corresponding to each of a plurality of combinations of values that can be taken as environmental temperatures and values that can be taken as coil resistance values. do it. Furthermore, these two look-up tables may be integrated and a look-up table for outputting the corrected oscillation frequency Frev with respect to the input of the oscillation start voltage Vs and the operating environment temperature Tc may be stored as information 400.

  The image forming apparatus 100 is not limited to a monochrome machine, and may be a color machine having a plurality of developing units. In a color machine, a toner density sensor 50 may be provided for each of a plurality of developing devices, and the respective toner densities of a plurality of types of two-component developers having different toner colors may be detected. The image forming apparatus 100 may be an electrophotographic printer that does not include an image scanner.

  In the above-described embodiment, in order to apply the power supply voltage Vin to the toner concentration sensor 50 so as to change from 0 volt to a steady voltage at a predetermined rise time, charging of the power supply circuit including the low voltage power supply 82 and its load is performed. May be used, or a rising voltage generating circuit having such a slope may be used.

  In the above-described embodiment, the configuration and operation of the toner density detection device 1 including the pattern of the coil 56, the type and circuit configuration of the oscillation circuit, and the like can be changed as appropriate within the spirit of the present invention.

1 Toner concentration detector 50 Toner concentration sensor (oscillation circuit)
60 Two-component developer 301 Oscillation start voltage detector (voltage detector)
302 Temperature Detection Unit 303 Frequency Detection Unit 304 Correction Unit F Oscillation Frequency Frev Corrected Oscillation Frequency 400 Information 410 First Relationship Information 420 Second Relationship Information 56 Coil 100 Image Forming Apparatus

Claims (4)

A toner concentration detection device for detecting the toner concentration of a two-component developer,
An oscillation circuit that oscillates at a frequency corresponding to the magnetic permeability of the two-component developer;
A frequency detector for detecting an oscillation frequency of the oscillation circuit;
A voltage detector for detecting an oscillation start voltage of the oscillation circuit;
A temperature detector for detecting an operating environment temperature of the oscillation circuit;
Using information indicating the relationship between the oscillation start voltage in the oscillation circuit and the temperature characteristic of the oscillation frequency, based on the operating environment temperature detected by the temperature detection unit and the oscillation start voltage detected by the voltage detection unit, A correction unit for correcting the oscillation frequency detected by the frequency detection unit,
A toner concentration detection device that outputs the oscillation frequency corrected by the correction unit as toner concentration information. The information applied to correction by the correction unit includes first relationship information indicating a relationship between a resistance value of a coil included in the oscillation circuit and an oscillation start voltage, and a temperature characteristic of the resistance value of the coil and an oscillation frequency. The toner concentration detection device according to claim 1, wherein the toner concentration detection device is second relationship information indicating a relationship. An electrostatic latent image is developed using a two-component developer whose toner density is controlled based on toner density information output by the toner density detecting device according to claim 1 or 2.
An electrophotographic image forming apparatus. A toner concentration detection method for a two-component developer,
Measure the oscillation frequency and oscillation start voltage of an oscillation circuit that oscillates at a frequency corresponding to the magnetic permeability of the two-component developer,
The information indicating the relationship between the oscillation start voltage and the temperature characteristic of the oscillation frequency in the oscillation circuit is used to correct the measurement result of the oscillation frequency according to the oscillation start voltage and the operating environment temperature of the oscillation circuit. A toner density detecting method as a feature.

Images