JP2006275959A - Magnetic sensor correction device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic sensor correction device capable of improving detection accuracy of a magnetic sensor while achieving miniaturization of the magnetic sensor and reduction of the cost. <P>SOLUTION: This magnetic sensor correction device is provided with a magnetic sensor section 1 equipped with a differential transformer T1 having a detection coil, a reference coil and an output coil, and a calibration coil L4 arranged near the detection coil; and a control part 2 calculating the deviation with respect to a target value of a standard magnetic flux which is the magnetic flux detected by the detection coil as a correction value when predetermined AC current is supplied to the calibration coil L4, and correcting the magnetic flux detected by the differential transformer based on the correction value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic sensor correction apparatus that can improve the detection accuracy of a magnetic sensor.

  As a magnetic sensor for measuring toner concentration and the like, a magnetic sensor is known that includes a differential transformer in which an output coil is wound around a central portion of a core and a reference coil and a detection coil are wound on both sides thereof.

FIG. 9 is a graph showing output characteristics of a magnetic sensor composed of a conventional differential transformer. As shown in FIG. 9, it can be seen that the output voltage from the magnetic sensor varies about plus or minus 10%. Therefore, in conventional magnetic sensors, variations in the output characteristics of the magnetic sensor are suppressed and detection accuracy is improved by using highly accurate circuit elements with little variation or using a circuit capable of correcting variations with high accuracy. It was. Patent Document 1 discloses a magnetic sensor that is miniaturized by surface mounting a differential transformer on a wiring board surface.
Japanese Unexamined Patent Publication No. 2000-097916

  However, in the conventional magnetic sensor, since the detection accuracy is increased by using a high-precision circuit element or a circuit capable of correcting the variation with high accuracy, the magnetic sensor is increased in size due to an increase in circuit scale. In addition, there is a problem that the cost of the magnetic sensor is increased.

  The objective of this invention is providing the magnetic sensor correction | amendment apparatus which can raise the detection accuracy of a magnetic sensor, aiming at size reduction and cost reduction of a magnetic sensor.

  A magnetic sensor correction apparatus according to the present invention includes a detection coil for detecting magnetic flux, a reference coil, and a differential transformer including an output coil for outputting a voltage difference between the detection coil and the reference coil as magnetic flux detected by the detection coil. And a magnetic sensor having a calibration coil disposed in the vicinity of the detection coil, and a deviation from a target value of a standard magnetic flux detected by the detection coil when a predetermined alternating current is passed through the calibration coil. It is characterized by comprising correction value calculation means for calculating as a correction value, and correction means for correcting the magnetic flux detected by the detection coil based on the correction value.

  Further, in the above configuration, mode setting means for setting a correction value calculation mode for calculating the correction value and a correction measurement mode for correcting the magnetic flux detected by the detection coil using the correction value. The correction value calculation means causes a high-frequency current to flow through the calibration coil when the correction value calculation mode is set, and a high-frequency current to the calibration coil when the correction measurement mode is set. It is preferable not to flow.

  In the above configuration, it is preferable that the correction unit adds the correction value to the magnetic flux detected by the detection coil when the correction measurement mode is set.

  In the above configuration, it is preferable that the reference coil, the output coil, the detection coil, and the calibration coil are wound around the same core in this order from the sensor surface side.

  According to the first aspect of the present invention, the calibration coil is disposed in the vicinity of the detection coil constituting the differential coil, and the magnetic flux generated when a predetermined alternating current is passed through the calibration coil is detected as the standard magnetic flux. A deviation amount between the detected standard magnetic flux detected by the coil and a predetermined target value is calculated as a correction value, and the magnetic flux detected by the detection coil is corrected based on this correction value. Therefore, it is possible to obtain a highly accurate measurement result without using an expensive circuit element or a circuit that corrects element variation. Therefore, the detection accuracy of the magnetic sensor can be enhanced while reducing the size and cost of the magnetic sensor of the apparatus.

  According to the second aspect of the present invention, since no current flows through the calibration coil in the correction measurement mode, the detection accuracy can be further improved.

  According to the third aspect of the present invention, the correction value is added to the magnetic flux detected by the detection coil for correction, so that an accurate value can be calculated.

  According to the invention described in claim 4, since the calibration coil is wound around the same core as the core around which the reference coil, the output coil, and the detection coil are wound, the calibration coil is detected with a simple configuration. It can arrange | position in the vicinity of a coil.

  FIG. 1 shows a block diagram of a magnetic sensor correction apparatus according to an embodiment of the present invention. The magnetic sensor correction apparatus according to the present embodiment is applied to an image forming apparatus such as a copying machine, a printer, or a digital multifunction peripheral.

  The magnetic sensor correction apparatus includes a magnetic sensor unit 1 and a control unit 2. The magnetic sensor unit 1 is disposed in a developing tank of a developing device provided in the image forming apparatus, and measures the concentration of toner including magnetic powder accommodated in the developing device. This magnetic sensor correction device uses a toner block obtained by pressing toner containing magnetic powder into a block shape at a constant pressure, and the difference between the toner block and the sensor surface T11 of the differential transformer T1 is changed. The toner density is detected by measuring the voltage generated in the dynamic transformer T1. The magnetic sensor unit 1 includes a differential transformer T1, a calibration coil L4, a sensor circuit 3, and a constant current drive circuit 4.

  FIG. 2 shows a configuration diagram of the differential transformer T1. The differential transformer T1 includes a reference coil L2, an output coil L3, a detection coil L1, and a cylindrical core (bobbin) T12. The detection coil L1, the output coil L3, and the reference coil L2 are wound around the core in this order from the sensor surface T11 side. A calibration coil L4 is wound between the detection coil L1 and the sensor surface T11.

  The differential transformer T1 may employ the one shown in FIG. 3 instead of the one shown in FIG. The differential transformer T1 shown in FIG. 3 is configured by attaching the calibration coil L4 to the end surface of the core T12 on the detection coil L1 side, instead of winding the calibration coil L4 around the core T12 as shown in FIG. .

  The control unit 2 shown in FIG. 1 includes a one-chip CPU, and includes a CPU 21, an A / D converter 22, a ROM 23, a RAM 24, a frequency divider (1 / N) 25, an oscillator (OSC) 26, and a switch 27. ing. A crystal oscillator 28 is connected to the oscillator 26. The oscillator 26 is connected to the constant current drive circuit 4 via the frequency divider 25 and the switch 27. The CPU 21 is connected to the sensor circuit 3 via the A / D converter 22 and is also connected to the ROM 23 and the RAM 24. Further, the CPU 21 outputs a control signal for turning on / off the switch 27 to the switch 27. In the present embodiment, the control unit 2 corresponds to a correction value calculation unit, a correction unit, and a mode setting unit.

  For example, the CPU 21 sets the operation mode of the magnetic sensor correction device to one of the correction value calculation mode and the correction measurement mode in accordance with an operation command received from the operation unit 5 by the user. As the operation unit 5, for example, a touch panel included in an image forming apparatus to which the magnetic sensor correction apparatus is applied corresponds.

  Further, when the correction value calculation mode is set, the CPU 21 turns on the switch 27 and generates a high-frequency signal generated by the oscillator 26 and frequency-divided by 1 / N by the frequency divider 25 with a constant current. Output to the drive circuit 4.

  FIG. 4 shows a circuit diagram of the sensor circuit 3 and the constant current drive circuit 4. The sensor circuit 3 includes an AC amplifier circuit 31, an oscillation circuit 32, and a detection circuit 33. The AC amplifier circuit 31 includes a differential transformer T1, a calibration coil L4, a capacitor C5, and a resistor R6. The differential transformer T1 includes a detection coil L1, a reference coil L2, and an output coil L3. The detection coil L1 and the reference coil L2 are wound so that the output voltage is in reverse phase. The output coil L3 is magnetically connected to the detection coil L1 and the reference coil L2. The capacitor C5 and the resistor R6 are connected in parallel with the output coil L3, one end is grounded, and the other end is connected to the capacitor C4. The detection coil L1 is grounded via a capacitor C6 and is connected to the constant current drive circuit 4.

  The AC amplifier circuit 31 includes a transistor Q1, resistors R2 to R5, and capacitors C3 and C4. The transistor Q1 is composed of an npn bipolar transistor, the emitter is grounded via a resistor R3, and a capacitor C3 is connected in parallel to the resistor R3. The base of the transistor Q1 is grounded via a resistor R5 and is connected to the output coil L3 via a capacitor C4. Resistors R4 and R2 are connected between the base collector of the transistor Q1. The collector of the transistor Q1 is connected to the detection circuit 33 and to the power supply Vcc via the resistor R2.

  The oscillation circuit 32 is a Colpitts LC oscillation circuit including a transistor Q2, resistors R7, R8, R18, and capacitors C7 to C9, and drives the differential transformer T1. The transistor Q2 is composed of an npn bipolar transistor, and a resistor R7 is connected to the emitter, and a capacitor C10 is connected. A capacitor C8 is connected in parallel to the resistor R7. A capacitor C7 is connected between the collector and emitter of the transistor Q2. The base of the transistor Q2 is grounded via a resistor R8, and a capacitor C9 is connected in parallel to the resistor R8. The base of the transistor Q2 is connected to the detection coil L1 and the calibration coil L4 via the resistor R18. The collector of the transistor Q2 is connected to the reference coil L2.

  The detection circuit 33 includes a resistor R1, capacitors C1 and C2, and diodes D1 and D2. The diode D1 has an anode connected to the collector of the transistor Q1 via the capacitor C2 and to the cathode of the diode D2. The anode of the diode D2 is grounded. The cathode of the diode D1 is grounded via the capacitor C1, and the capacitor C1 is connected in parallel with the resistor R1 and connected to the input port of the control unit 2. GND indicates a ground port of the control unit 2 and is grounded.

  The constant current drive circuit 4 includes transistors Q3 and Q4, resistors R9 to R17, and capacitors C10 to C14. The transistor Q3 is composed of an npn bipolar transistor, and the emitter is grounded via a resistor R12 and a resistor R13, and is connected to the collector of the transistor Q4 via a capacitor C14 and a resistor R17. The capacitor C13 is connected in parallel with the resistor R13. The collector of the transistor Q3 is connected to the base of the transistor Q4 via the capacitor C11. A resistor R11 and a resistor R9 are connected between the base collector of the transistor Q3. The base of the transistor Q3 is connected to the oscillation circuit 32 via the capacitor C10 and grounded via the resistor R10. The capacitor C10 is a coupling capacitor for taking out an AC voltage from the oscillation circuit 32.

  The transistor Q4 is composed of an npn bipolar transistor, and the emitter is grounded via a resistor R16. A capacitor C12 is connected in parallel to the resistor R16.

  The constant current drive circuit 4 includes a transistor Q5 and resistors R19 and R20. The transistor Q5 is composed of a pnp bipolar transistor, the emitter is connected to the power supply Vcc, and the collector is connected to the emitter of the transistor Q4. A resistor R19 is connected between the emitter base of the transistor Q5, and the base is connected to the output port of the control unit 2 via the resistor R20.

  Next, the operation of the magnetic sensor correction device will be described. When the correction value calculation mode is set, the switch 27 is turned on, the transistor Q5 is turned off, and an AC voltage for driving the calibration coil L4 is extracted from the oscillation circuit 32 via the capacitor C10. The AC voltage from the capacitor C10 is amplified by the transistors Q3 and Q4 to drive the calibration coil L4. The high-frequency current flowing through the calibration coil L4 is limited by the resistor R19 and the transistor Q4. Further, the amplitude of this high-frequency current is kept constant by applying a negative feedback to the emitter of the transistor Q3 by the resistor R17 and the capacitor C14. As a result, a constant magnetic flux (standard magnetic flux) is generated from the calibration coil L4.

  Under the influence of the standard magnetic flux, the detection coil L1 breaks the magnetic balance with the reference coil L2, and generates a differential voltage in the output coil L3. This differential voltage is amplified by the transistor Q1, converted to a DC voltage by the detection circuit 33, A / D converted by the A / D converter 22, and acquired as the standard voltage Vc by the CPU 21. The CPU 21 calculates a difference between the standard voltage Vc and a predetermined target value Vp as a correction value Vd (= Vp−Vc), and holds the correction value Vd in the RAM 24. The target value Vp is a value obtained by experiments or the like.

  On the other hand, when the correction measurement mode is set, since the switch 27 is turned off and the transistor Q5 is turned on, the transistor Q4 is turned off. As a result, the calibration coil L4 is not driven.

  When the toner block approaches the detection coil L1, the magnetic balance between the detection coil L1 and the reference coil L2 is lost, and an AC differential voltage is generated in the output coil L3. This differential voltage is amplified by the transistor Q1, rectified by the diodes D1 and D2, converted into a DC voltage, input to the A / D converter 22, A / D converted, and input to the CPU 21 as the measurement voltage Vm. The CPU 21 reads the correction value Vd from the RAM 24, adds it to the input measurement voltage Vm, and corrects the measurement voltage Vm. Thereby, the toner density or the toner remaining amount is detected.

  FIG. 5 is a graph showing the relationship between the sensor surface T11 of the magnetic sensor unit 1 and the interval between the toner blocks and the output voltage of the magnetic sensor unit 1. The vertical axis represents the output voltage (V) of the magnetic sensor unit 1, and the horizontal axis represents the distance (mm) between the sensor surface T11 and the toner block. As shown in FIG. 5, it can be seen that the output voltage increases as the gap between the sensor surface T11 and the toner block becomes narrower.

  FIG. 6 is a graph showing output characteristics of the magnetic sensor unit 1 when the calibration coil L4 is driven. The vertical axis represents the output voltage of the magnetic sensor unit 1, and the horizontal axis represents the high-frequency current flowing through the calibration coil L4. As can be seen from FIG. 6, the output voltage increases as the high-frequency current increases. As these two graphs show, the high-frequency current flowing through the calibration coil L4 corresponds to the distance between the sensor surface T11 and the toner block, and both graphs draw similar curves, so the calibration coil L4. By controlling the high-frequency current flowing in the toner, it is possible to create a pseudo toner block having an arbitrary density.

  The output characteristics of the magnetic sensor unit 1 shown in FIG. 5 were measured by employing a circuit configuration as shown in FIG. FIG. 7 is a diagram showing a device configuration when measuring the output characteristics of the magnetic sensor unit 1. As shown in FIG. 7, the magnetic sensor unit 1 is connected to the power supply device PS via a voltmeter. This voltmeter measures the voltage between the input port and the GND port shown in FIG. The calibration coil L4 is connected to the function generator FG via an AC ammeter. The ammeter measures the high-frequency current flowing through the calibration coil L4. The function generator FG generates a high-frequency current that flows through the calibration coil L4.

  As described above, according to the magnetic sensor correction apparatus, when the calibration coil L4 is provided in the vicinity of the detection coil L1 and the correction value calculation mode is set, a predetermined high-frequency current is generated by the calibration coil L4. The standard magnetic flux generated when the current flows is detected as the standard voltage Vc, and a difference between the detected standard voltage Vc and a target value Vp set in advance with respect to the standard voltage Vc is calculated as a correction value Vd. Retained.

  On the other hand, when the correction measurement mode is set, the high-frequency current to the calibration coil L4 is cut off, and the voltage generated in the differential transformer T1 when the toner block is brought close to the sensor surface T11 is acquired as the measurement voltage Vm. Then, the correction value Vd is added to the measurement voltage Vm, and the measurement voltage is corrected. Therefore, the toner density can be measured with high accuracy without using an expensive circuit element. As a result, it is possible to increase the detection accuracy of the magnetic sensor unit 1 while reducing the size and cost of the magnetic sensor unit 1.

  Note that the magnetic sensor correction device is not limited to the configuration shown in FIG. 1, and the configuration shown in FIG. 8 may be adopted. In the magnetic sensor correction apparatus shown in FIG. 1, the control unit 2 corrects the measurement voltage Vm by software so that the correction value Vd is added to the measurement voltage Vm. However, in the magnetic sensor correction apparatus shown in FIG. The correction value Vd is added to the measurement voltage Vm, and the gain of the AC amplifier circuit 31 is adjusted so that the corrected measurement voltage Vm is input to the control unit 2 to correct the measurement voltage Vm. That is, the measurement voltage Vm is corrected by hardware. Further, the calibration coil L4 is driven using a signal from the oscillation circuit 32 instead of the signal from the control unit 2.

  However, in this case, as shown in FIG. 8, in addition to the necessity to add the D / A converter 29 to the control unit 2, the AC amplification circuit 31 is output to adjust the gain from the control unit 2. It is necessary to provide the AC amplifier circuit 31 with a circuit that changes the gain in response to the control signal.

1 shows a block diagram of a magnetic sensor correction device according to an embodiment of the present invention. FIG. The block diagram of the differential transformer is shown. The other block diagram of a differential transformer is shown. It is a circuit diagram of a sensor circuit and a constant current drive circuit. 6 is a graph showing the relationship between the sensor surface of the magnetic sensor unit and the interval between toner blocks and the output voltage of the sensor. It is the graph which showed the output characteristic of the magnetic sensor part when driving a calibration coil. It is drawing which shows the apparatus structure at the time of measuring the output characteristic of a magnetic sensor part. It is drawing which shows the structure of the magnetic sensor correction apparatus by embodiment different from the magnetic sensor correction apparatus shown in FIG. It is the graph which showed the output characteristic of the magnetic sensor which consists of the conventional differential transformer.

Explanation of symbols

T1 differential transformer 3 sensor circuit 4 constant current drive circuit 5 operation unit 21 CPU core 22 A / D converter 25 frequency divider 26 oscillator 27 switch 28 crystal oscillator 29 D / A converter 31 AC amplifier circuit 32 oscillation circuit 33 detection Circuit T11 Sensor surface T12 Core Vcc Power supply Vc Standard voltage Vd Correction value Vm Measurement voltage Vp Target value

Claims (4)

A detection coil for detecting magnetic flux, a reference coil, a differential transformer including an output coil for outputting a difference voltage between the detection coil and the reference coil as a magnetic flux detected by the detection coil, and a coil arranged in the vicinity of the detection coil A magnetic sensor comprising a calibration coil provided;
Correction value calculation means for calculating a deviation from a target value of the standard magnetic flux detected by the detection coil when a predetermined alternating current is passed through the calibration coil as a correction value;
A magnetic sensor correction device comprising: correction means for correcting the magnetic flux detected by the detection coil based on the correction value. A mode setting means for setting a correction value calculation mode for calculating the correction value and a correction measurement mode for correcting the magnetic flux detected by the detection coil using the correction value;
The correction value calculation means passes a high-frequency current through the calibration coil when the correction value calculation mode is set, and does not flow a high-frequency current through the calibration coil when the correction measurement mode is set. The magnetic sensor correction apparatus according to claim 1.   The magnetic sensor correction device according to claim 2, wherein the correction unit adds the correction value to the magnetic flux detected by the detection coil when the correction measurement mode is set.   The reference coil, the output coil, the detection coil, and the calibration coil are wound around the same core in this order from the sensor surface side. Magnetic sensor correction device.

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