JP2008241852A - Toner density detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a toner density detection device which can correctly detect the toner density by absorbing the errors caused by the temperature characteristics of the sensor circuit or without influenced by those temperature characteristics. <P>SOLUTION: This toner density detection device has a reference coil L1 to be applied with exciting pulse signals, a first resonance circuit A of a first resonance frequency f1, a magnetic detection coil L2 coupled with the reference coil in the reverse polarity, a second resonance circuit B of a second resonance frequency f2 different from the first resonance frequency f1, an output waveform forming circuit C to convert the output signals of the second resonance circuit into pulse signals, and a phase difference detection circuit D to find the phase difference between the output signals from the output waveform forming circuit D and the exciting signals. It finds out the density of the toner contained in the magnetic powder from the phase difference changing as the inductance of the magnetic detection coil L2 changes and has a temperature compensation circuit F to correct the detection errors caused by the temperature characteristics of the output waveform forming circuit D. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a toner concentration detection device for detecting the toner concentration of a two-component developer containing a magnetic carrier and toner.

  In Patent Document 1, a differential transformer is used as a toner concentration detection device, and a drive coil therein is driven with an AC voltage, and a differential between a detection coil adjacent to the developer and a reference coil that is not affected by the developer. There has been proposed a differential transformer type toner concentration detection device that detects toner concentration based on an output.

  However, the differential transformer type toner concentration detection device has three types of coils, a detection coil and a reference coil, in addition to a drive coil connected to a power source, and these need to be stacked in the vertical direction. There was a problem of getting bigger. In addition, in order to balance the magnetic force, it is necessary to manually adjust the screw-type core, and there is a problem that the adjustment work is complicated.

  On the other hand, Patent Document 2 and Patent Document 3 describe a configuration in which a toner density is detected from a phase difference between a detection signal extracted from a connection point between a reference oscillation coil and a detection coil and a reference signal without providing a differential transformer. ing.

  Further, Patent Document 4 appropriately compensates for variations in the electrical characteristics of components used in the detection operation by correcting and adjusting the output signal level of the device with respect to the detection circuit described in Patent Document 3. In order to provide an electromagnetic characteristic detection apparatus for a subject that always outputs a detection characteristic signal with high accuracy, the following configuration is disclosed.

A resonance circuit including a coil and a capacitor is disposed in the vicinity of the subject, detects a first electromagnetic circuit of the subject, and outputs a corresponding detection signal, and is output from the first circuit. A second circuit that amplifies the detection signal and outputs it as a detection characteristic signal, and for the second circuit, corrects and adjusts the signal level change of the detection characteristic signal caused by variations in the electric characteristics of the electrical components; It is an electromagnetic characteristic detection device having signal level adjustment means for performing control so as to output a detection characteristic signal whose signal level is corrected and adjusted.
JP-A-3-71068 JP-A-6-3329 JP-A-6-289717 JP 2005-91516 A

  However, in the invention described in Patent Document 3, it is necessary to provide an amplifier using an active element in order to prevent a decrease in Q when a detection signal is extracted from the connection point between the reference oscillation coil and the detection coil. Since the input threshold voltage fluctuates under the influence of the ambient temperature, the element has a problem that the influence of the detection error is large.

  Patent Document 4 proposes a technique for correcting detection sensitivity using a microcomputer provided with correction data in advance in order to absorb fluctuations in detection voltage caused by variations in electrical characteristics of electrical components. It does not eliminate the impact.

  In view of the above-described problems, an object of the present invention is to provide a toner concentration detection device that can accurately detect a toner concentration without absorbing an error due to the temperature characteristic of a detection circuit or being affected by the temperature characteristic. There is in point to do.

  In order to achieve the above-mentioned object, the first characteristic configuration of the toner concentration detection device according to the present invention is a reference coil to which a pulsed excitation signal is applied, as described in claim 1 of the claims. A first resonance circuit having a first resonance frequency f1, a magnetic detection coil coupled with a polarity opposite to that of the reference coil, and a second resonance circuit having a second resonance frequency f2 different from the first resonance frequency f1 An output waveform shaping circuit that converts the output signal of the second resonance circuit into a pulse signal; and a phase difference detection circuit that detects a phase difference between the output signal from the output waveform shaping circuit and the excitation signal. A toner concentration detection device for detecting a toner concentration contained in magnetic powder based on the phase difference that varies due to a change in inductance of the magnetic detection coil, the temperature of the output waveform shaping circuit In that it includes a temperature compensation circuit for compensating for the detection error due to gender.

  According to the second characteristic configuration described in the second aspect, in addition to the first characteristic configuration described above, the temperature compensation circuit may include a DC bias level of the output signal at an input stage of the output waveform shaping circuit. This is because it is constituted by a DC bias adjusting circuit composed of a pin diode and a resistor.

  In the third feature configuration, as described in claim 3, in addition to the first feature configuration described above, the temperature compensation circuit is equal in temperature characteristic to the output waveform shaping circuit, and the excitation signal and frequency An input waveform shaping circuit for shaping an equal sine wave signal into a pulse signal, and an integration circuit for converting the output of the input waveform shaping circuit to a DC level, and adjusting the capacitance of the varicap diode by the output of the integration circuit It is in the point comprised as follows.

  According to the present invention, it is possible to provide a toner concentration detection device that can accurately detect the toner concentration without absorbing an error due to the temperature characteristic of the detection circuit or being affected by the temperature characteristic. It was.

  Hereinafter, a toner concentration detection device according to the present invention will be described. As shown in FIG. 5, the toner concentration detection device 1 includes a detection unit disposed facing the developing tank 4 containing a two-component developer of magnetic powder carrier and toner, and a signal detected by the detection unit. The signal processing unit 3 is configured to be processed, and the signal processing unit 3 is accommodated in a resin casing.

  The detection unit includes a magnetic detection coil L2 wound on the side of the developing tank 4 of the hollow bobbin 2, and a reference coil L1 wound on the separation side with respect to the developing tank 4, and the magnetic detection coil L2 is a reference coil. It is connected to L1 with the opposite polarity.

  The magnetic detection coil L2 is disposed close to the position where the inductance changes due to the influence of the magnetic permeability of the carrier whose density changes due to the change in the toner density in the developing tank 4, and the reference coil L1 is affected by the magnetic permeability of the carrier. So that they are not separated from each other.

  As shown in FIG. 1, the above-described toner concentration detection apparatus includes a reference coil L1 to which a pulsed excitation signal is applied, and has a first resonance circuit A having a first resonance frequency f1 and a polarity opposite to that of the reference coil L1. A magnetic resonance coil L2 coupled to the second resonance circuit B having a second resonance frequency f2 different from the first resonance frequency f1, and an output waveform shaping circuit C for converting an output signal of the second resonance circuit B into a pulse signal. And a phase difference detection circuit D for detecting the phase difference between the output signal from the output waveform shaping circuit C and the excitation signal, and a DC conversion circuit E for converting the output of the phase difference detection circuit D into a DC voltage.

  The first resonance circuit A includes a capacitor C1 and a reference coil L1, the first resonance frequency f1 is set to 4 MHz, and the second resonance circuit B includes capacitors C2, C3, a varicap diode VD, and a magnetic detection coil L2. The second resonance frequency f2 is set to 4.1 MHz, which is slightly higher than the first resonance frequency f1.

  Further, a voltage dividing circuit is provided from the power supply voltage Vdc by the resistor R1, the variable resistor VR1, and the resistor R2, and the capacitance of the varicap diode VD is adjusted by adjusting the variable resistor VR1, so that the developer of the reference toner density is adjusted. The balance between the reference coil L1 and the magnetic detection coil L2 can be adjusted.

  An exclusive OR circuit (hereinafter referred to as “XOR circuit”) is provided with an oscillation circuit having a frequency of 4 MHz comprising an IC1, an oscillator X, and a resistor, and a pulsed excitation signal is applied to the reference coil L1, One resonance circuit A is maintained in a resonance state.

  A voltage is induced in the second resonance circuit B by the mutual inductance. However, since the resonance frequency is different at the reference toner concentration, the resonance state is not reached and a slight voltage is output. When the toner concentration is lowered in this state, the carrier density in the vicinity of the magnetic detection coil L2 is increased. Due to the influence, the inductance changes, the second resonance frequency approaches the first resonance frequency, and the output gradually increases to resonate. .

  The output terminal of the second resonance circuit B is connected to the output waveform shaping circuit C via the DC bias circuit F. The output waveform shaping circuit C is composed of an XOR circuit IC2 having one input terminal connected to a power supply, and an AC signal level-shifted by the DC bias circuit F is input to the other input terminal. The XOR circuit IC2 has an input threshold value. With the voltage as a reference, the AC signal is identified as either a high level or a low level, and a pulse signal having a waveform formed by an XOR operation is output. The output signal of the second resonance circuit B is a pulse signal whose phase is inverted.

  The output signal of the output waveform shaping circuit C is input to the phase difference detection circuit D, and the phase difference from the excitation signal is detected. The phase difference detection circuit D is composed of an XOR circuit IC3, which performs an XOR operation process on the output signal of the waveform shaping circuit C and the excitation signal and outputs the result as a phase difference.

  The phase difference between the output signal of the output waveform shaping circuit C and the excitation signal is set to π / 2 at the maximum, and the phase difference is set to approach π / 2 as the toner density decreases.

  The output of the phase difference detection circuit D is input to the DC conversion circuit E, and the phase difference is converted into a DC voltage and output. The DC conversion circuit E is composed of an operational amplifier IC4 and an integrating circuit including a resistor and a capacitor.

  When the toner density is in the vicinity of the set density, as shown in FIG. 2A, the output waveform shaping is performed with respect to the excitation signal of 50% duty ratio and 4 MHz excitation signal (voltage V (P1) at point P1 in FIG. 1). A pulse signal having a phase difference Δφ (a voltage V (P2) at point P2 in FIG. 1) is output from the circuit C, and a pulse signal corresponding to the phase difference from the phase difference detection circuit D (a voltage V at a point P3 in FIG. 1). (P3)) is output.

  When the toner density decreases, as shown in FIG. 2B, the phase difference Δφ from the output waveform shaping circuit C is π at the maximum with respect to the excitation signal (voltage V (P1) at point P1 in FIG. 1). / 2 pulse signal (voltage V (P2) at point P2 in FIG. 1) is output, and the pulse signal corresponding to the phase difference from the phase difference detection circuit D (voltage V (P3) at point P3 in FIG. 1). Is output.

  As shown in FIG. 3, by converting the output signal of the phase difference detection circuit D to a direct current level by the direct current conversion circuit E, the toner density of the developer can be obtained.

  However, in the case where the DC bias circuit F is simply constituted by a resistance voltage dividing circuit, the XOR circuit IC2 is used for waveform shaping of the level-shifted analog AC signal by the XOR circuit IC2 constituting the output waveform shaping circuit C. When the input threshold voltage fluctuates due to temperature fluctuation, the output fluctuates even with the same AC signal.

  As shown in FIG. 4C, when the input threshold value of the XOR circuit IC2 changes from Vth0 to Vth1, the output signal V (P2) when the input threshold value shown in FIG. Changes to the output signal V ′ (P2) when the input threshold value is Vth1, and the pulse width W0 becomes narrower to W1 (<W0). As a result, the output of the DC conversion circuit E becomes low, and there is a problem that it is detected lower than the original toner density. In the figure, Vb0 indicates a bias voltage applied by the DC bias circuit F.

  Therefore, the toner concentration detection apparatus according to the present invention includes a temperature compensation circuit that compensates for a detection error due to the temperature characteristic of the output waveform shaping circuit C.

  A temperature compensation circuit is realized by configuring the DC bias circuit F provided at the input stage of the output waveform shaping circuit C with a pin diode PIN and a resistor R for adjusting the DC bias level of the output signal.

  The pin diode PIN exhibits a low impedance characteristic during forward bias, and exhibits a high impedance characteristic during reverse bias. Accordingly, when the toner density gradually decreases and the resonance of the second resonance circuit B increases, the peak value of the output signal increases, and the impedance of the pin diode PIN that is in the forward bias state decreases. The generated voltage division level is increased and a high bias voltage is applied. The output signal is clamped by the pin diode PIN.

  With such a configuration, a high bias voltage is added to the output voltage of the second resonance circuit B, so that the influence due to temperature fluctuations of the input threshold voltage of the output waveform shaping circuit C can be suppressed extremely low.

  FIG. 4 (f) shows an output waveform due to temperature fluctuations when a DC bias of Vb0 is added by the DC bias circuit F by resistance voltage division, whereas a DC bias of Vb1 is added by the DC bias circuit F according to the present invention. This shows how the influence of the input threshold voltage Vth1 of the forming circuit C is reduced.

  Next, another embodiment of the temperature compensation circuit will be described. As shown in FIG. 6, the temperature compensation circuit G has an input waveform shaping circuit G1 for shaping a sine wave signal having a temperature characteristic equal to that of the output waveform shaping circuit C and having the same frequency as the excitation signal into a pulse signal, and an input waveform shaping. An integration circuit G2 for converting the output of the circuit G1 to a DC level is provided, and the capacitance of the varicap diode VD is adjusted by the output of the integration circuit G2.

  The signal waveform at point P01 of the oscillation circuit H is a sine wave as shown in FIG. The input waveform shaping circuit G1 is composed of an XOR circuit IC5 having the same temperature characteristics as the output waveform shaping circuit C. One terminal of the XOR circuit IC5 is connected to the power supply side, and a sine wave to which voltage division by a voltage dividing circuit using resistors R6 and R7 is added is input to the other terminal. Accordingly, the XOR circuit IC5 outputs a pulse signal with the phase of the sine wave inverted.

  The values of the resistors R6 and R7 are equal, and the input waveform shaping circuit G1 is configured so that a voltage that is ½ of the power supply voltage is added as a bias voltage. The bias voltage is set to the same value as that of the voltage dividing circuit formed by the resistors R3 and R4 constituting the DC bias circuit F.

  When the input threshold voltage of the XOR circuit IC5 varies with temperature, an output signal whose pulse width varies from a duty ratio of 50% is integrated by the integrating circuit G2. Therefore, the fluctuation of the input threshold voltage can be monitored by the output voltage of the integrating circuit G2.

  The output of the integration circuit G2 is connected to the varicap diode of the second resonance circuit B, and the resonance frequency of the second resonance circuit B is corrected by the fluctuation of the input threshold voltage of the XOR circuit IC5.

  That is, when the input threshold voltage of the XOR circuit IC5 varies, the input threshold voltage of the output waveform shaping circuit C is assumed to vary by substantially the same amount, and in this case, the resonance frequency of the second resonance circuit B is adjusted. For example, when the input threshold voltage increases, the resonance frequency of the second resonance circuit B is lowered to make it more resonant, thereby lowering the frequency of the output signal from the second resonance circuit B and increasing the peak value. To increase the resonance frequency of the second resonance circuit B and decrease the degree of resonance when the input threshold voltage decreases. The frequency of the output signal from the second resonance circuit B is increased and the peak value is decreased to reduce the influence of the decrease in the input threshold voltage.

  In adopting the present invention, the resonance frequency is not limited to the above-described value, but is appropriately set. In addition, it goes without saying that the specific configuration of each circuit block can be changed and designed as appropriate within the scope of the effects of the present invention.

Circuit diagram of toner concentration detection device according to the present invention Waveform explanatory diagram showing the operation of the toner concentration detection device Toner concentration detection characteristic diagram of toner concentration detection device according to the present invention Waveform explanatory diagram showing the operation of the toner concentration detection device according to the present invention Configuration diagram of a toner concentration detection device according to the present invention. Circuit diagram of toner concentration detection device showing another embodiment

Explanation of symbols

1: toner density detection device 2: bobbin 3: signal processing unit 4: developing tank L1: reference coil L2: magnetic detection coil A: first resonance circuit B: second resonance circuit C: output waveform shaping circuit D: phase difference detection Circuit E: DC conversion circuit F: DC bias circuit G: Temperature compensation circuit

Claims (3)

A reference coil to which a pulsed excitation signal is applied; a first resonance circuit having a first resonance frequency f1; and a magnetic detection coil coupled with a polarity opposite to the reference coil, the first resonance frequency f1 being A second resonance circuit having a different second resonance frequency f2, an output waveform shaping circuit that converts an output signal of the second resonance circuit into a pulse signal, and a phase difference between the output signal from the output waveform shaping circuit and the excitation signal A toner concentration detection device configured to detect a toner concentration contained in magnetic powder based on the phase difference that varies due to a change in inductance of the magnetic detection coil. ,
A toner concentration detection apparatus comprising a temperature compensation circuit for compensating for a detection error due to temperature characteristics of the output waveform shaping circuit.   2. The toner concentration detection device according to claim 1, wherein the temperature compensation circuit is configured by a DC bias adjustment circuit including a pin diode and a resistor for adjusting a DC bias level of the output signal at an input stage of the output waveform shaping circuit. .   The temperature compensation circuit has a temperature characteristic equal to that of the output waveform shaping circuit, an input waveform shaping circuit for shaping a sine wave signal having the same frequency as the excitation signal into a pulse signal, and an output of the input waveform shaping circuit at a DC level. The toner density detection device according to claim 1, further comprising: an integration circuit that converts the capacitance of the varicap diode according to an output of the integration circuit.

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