JP2001305170A - Surface electric potential detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface electric potential detection device which can easily adjust an offset that a surface electric potential detection output signal has. SOLUTION: A surface electric potential sensor 11 and a signal processing circuit 3 operate having the electric potential of a common ground line C. GND as their reference potential. A 1st bias circuit 36 includes in a signal processing circuit 3 applies a positive voltage (+V3) based upon the electric potential of the common ground line C. GND to the uninverted input terminal of an integrating circuit 32 to make the surface electric potential detection output signal Z have generate a positive offset voltage. A 2nd bias circuit 39 supplies a surface electric potential detection output circuit 35 with a negative voltage (-V5) cancelling the offset voltage generated by the 1st bias circuit 36.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface potential detecting device for measuring a surface potential in a non-contact manner.

[0002]

2. Description of the Related Art For example, a surface potential detecting device of this type used for detecting the surface potential of a photosensitive drum in a non-contact manner in a copying machine, a laser beam printer or the like is disclosed in Japanese Patent Publication No. 3-6467. As described above, the electric field between the detection electrode and the photosensitive drum is mechanically interrupted by the tuning fork to obtain an AC signal corresponding to the surface potential of the photosensitive drum. Then, the AC signal is amplified by a preamplifier, guided to a synchronous detection circuit via an isolator, and detected by a signal synchronized with the mechanical interruption. The synchronous detection output signal output from the synchronous detection circuit is converted to a direct current by the integration circuit. The DC signal obtained by the integration circuit is input to a high voltage amplifier.

[0003] Each circuit has a common ground line. The high-voltage amplifier controls the potential of the common ground line based on the input DC signal so that the potential of the common ground line becomes the same as the potential of the surface of the photosensitive drum that is the surface to be measured. By extracting the potential of the common ground line via an attenuator, a buffer amplifier, or the like, a surface potential signal can be obtained. The common ground line has a floating relationship with respect to the ground potential and the frame ground potential.

The greatest advantage of this surface potential detection method is that even if the distance between the surface potential sensor including the tuning fork / detection electrode and the surface of the photosensitive drum, which is the surface to be measured, changes, the distance dependency is very large. A small and highly accurate surface potential detection signal can be obtained.

In the surface potential detection method described above, in order to realize a highly accurate surface potential detection signal, it is important to adjust the offset of the surface potential detection signal. In the surface potential sensor, when the difference voltage between the surface potential of the surface to be measured and the potential of the common ground line is zero, the surface potential detection signal should be zero. However, in many surface potential sensors, an AC signal is output from the surface potential sensor, and an offset voltage is generated in the surface potential detection signal because the periphery of the detection electrode is slightly positively or negatively charged. For example, when the periphery of the detection electrode is negatively charged, even when the surface potential of the surface to be measured is 0 volt, a surface potential detection signal is output as if the surface potential of the surface to be measured is positive.

Japanese Patent Application Laid-Open No. 6-242166 discloses a surface potential detecting device provided with an offset adjusting means. This surface potential detecting device includes a power supply circuit (DC / DC converter), and a resistance voltage dividing circuit is inserted between a positive power supply line and a negative power supply line led from the power supply circuit. With this resistance voltage dividing circuit, the voltage difference between the positive power supply voltage and the negative power supply voltage from the power supply circuit is divided by resistance, and the divided voltage is adjusted near the common ground line potential by a variable resistor. The adjusted voltage is applied as a bias voltage to the integration circuit to cancel the offset voltage. Specifically, the offset adjustment is performed so that the surface potential detection signal becomes zero when the surface potential to be measured is zero.

However, in the above-described offset adjusting means, since the bias voltage is generated based on both the positive power supply voltage and the negative power supply voltage of the power supply circuit, when the positive power supply voltage or the negative power supply voltage fluctuates, the bias voltage also increases. And the offset adjustment is difficult. In order to stabilize the bias voltage, the power supply circuit must be configured to stabilize both the positive power supply voltage and the negative power supply voltage with high accuracy.

In the surface potential detecting device disclosed in the above-mentioned publication, as a technique for stabilizing both the positive power supply voltage and the negative power supply voltage, a stabilized power supply having high accuracy and good temperature characteristics is used. It is provided for each voltage and negative power supply voltage. In this method, two stabilized power supplies are required, and the cost of the power supply circuit increases.

Moreover, a dropper-type stabilized power supply (three-terminal regulator) typically used as a stabilized power supply
Has a low power efficiency of about 50%. The use of a dropper-type stabilized power supply reduces the overall power efficiency of the surface potential detection device.

When a stabilized power supply such as a dropper-type stabilized power supply is not used, it is necessary to balance the positive power supply voltage and the negative power supply voltage. For this reason, a transformer having a bifilar wound secondary winding is used as a power transformer of the power circuit. However, this type of transformer is expensive, which increases the cost of the power supply circuit.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface potential detecting device which provides a basis for easily eliminating an offset generated in a surface potential detecting output signal.

Another object of the present invention is to provide an inexpensive surface potential detecting device.

Still another object of the present invention is to provide a surface potential detecting device which can realize high total power efficiency.

[0014]

In order to solve the above-mentioned problem, a surface potential detecting device according to the present invention includes a surface potential sensor and a signal processing circuit. The surface potential sensor and the signal processing circuit operate using the potential of a common ground line as a reference potential. The common ground line is at a potential floating with respect to the ground potential. The surface potential sensor generates an AC signal by interrupting an electric field between the detection electrode and the surface to be measured.

[0015] The signal processing circuit includes a synchronous detection circuit, an integration circuit, a high voltage amplification circuit, and a first bias circuit. The synchronous detection circuit detects the AC signal supplied from the surface potential sensor in synchronization with the intermittent operation of the surface potential sensor. The integration circuit includes an operational amplifier having an inverting input terminal and a non-inverting input terminal, a detection output signal from the synchronous detection circuit is supplied to the inversion input terminal, and converts the supplied detection output signal to DC. Output. The high voltage amplifier circuit is supplied with a signal from the integration circuit, and supplies a high DC voltage to the common ground line, which makes the potential of the common ground line substantially equal to the potential of the surface to be measured.

The first bias circuit applies a positive voltage based on the potential of the common ground line to the non-inverting input terminal of the integration circuit.

In the above-described surface potential detecting device, an AC signal corresponding to a difference voltage between the surface potential of the surface to be measured and the potential of the common ground line is generated by the surface potential sensor, and the AC signal is supplied to the synchronous detection circuit. I do. The synchronous detection circuit detects an AC signal supplied from the surface potential sensor in synchronization with the intermittent operation of the surface potential sensor, and generates a detection output signal. The detection output signal is supplied to an inverting input terminal of an operational amplifier constituting an integrating circuit. The integration circuit integrates the detection output signal, converts it to DC, and outputs it.

The high-voltage amplifier circuit is supplied with a signal from the integration circuit described above, and supplies a high DC voltage to the common ground line, which makes the potential of the common ground line substantially equal to the potential of the surface to be measured. With the above circuit configuration, the potential of the common ground line is controlled to be substantially equal to the surface potential of the surface to be measured.

When the potential of the common ground line becomes equal to the surface potential of the surface to be measured, the electric field between the detection electrode of the surface potential sensor and the surface to be measured becomes zero. Therefore, by extracting the potential of the common ground line as a surface potential detection signal, even if the distance between the surface potential sensor and the surface to be measured changes, a highly accurate surface potential detection signal with very little distance dependence. Can be obtained.

As a characteristic configuration of the surface potential detecting device of the present invention, the signal processing circuit includes a first bias circuit, and a positive voltage is applied from the first bias circuit to the non-inverting input terminal of the integrating circuit. . With this positive voltage bias,
When the relationship (detection characteristic) of the surface potential detection signal to the surface potential to be measured moves in the direction in which the value of the surface potential detection signal becomes higher for the same surface potential to be measured, and the potential of the surface to be measured is zero , The surface potential detection signal becomes a certain positive value (referred to as an offset voltage). Therefore, if the potential of the surface to be measured is equal to or higher than zero, a surface potential detection signal is always generated, so that a dead zone does not occur.

Moreover, the positive voltage applied from the first bias circuit to the non-inverting input terminal of the integrating circuit is based on the potential of the common ground line. Therefore, a stable and accurate offset voltage can be obtained.

This offset voltage can be easily and accurately adjusted by a circuit method in a circuit subsequent to the integrating circuit. That is, the present invention provides a basis for easily and accurately adjusting or eliminating the offset voltage.

Further, since the power supply circuit of the surface potential detecting device does not require a high degree of voltage stability accuracy, a surface potential detecting device with a reduced power supply circuit can be obtained. A dropper-type stabilized power supply (three-terminal regulator) that has been conventionally required can be omitted, and a surface potential detecting device with high overall power efficiency can be obtained.

One preferred mode of canceling the offset voltage generated by the first bias circuit is to add a second bias circuit to a detection signal output circuit normally provided in a signal processing circuit, and to apply a second bias circuit to the detection signal output circuit. And applying a negative voltage to the non-inverting input terminal of the operational amplifier of the detection signal output circuit. According to this configuration, the characteristic of the surface potential detection signal with respect to the measured surface potential moves in a direction in which the value of the surface potential detection signal decreases with respect to the same measured surface potential. This movement amount corresponds to the magnitude of the negative voltage. Therefore, by adjusting the magnitude of the negative voltage, it is possible to cancel the offset voltage generated by the first bias circuit and to match the ideal characteristics. The ideal characteristic means that the relationship between the surface potential to be measured and the surface potential detection signal is a linear relationship passing through the origin on the graph.

The other features of the present invention and the operation and effect thereof will be described in more detail with reference to the accompanying drawings. The accompanying drawings show by way of example only.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram schematically showing a configuration for detecting a surface potential of a photosensitive drum using a surface potential detecting device according to the present invention. In FIG. 1, K is the photosensitive drum, V is the transfer belt, and W is the traveling direction of the transfer belt. The photosensitive drum K is for black. Photosensitive drum K
Is provided with a charging corotron U1, a transfer corotron U2, and a developing machine U3. The surface potential detecting device 1 according to the present invention includes a surface potential sensor 11 and a signal processing circuit 3. The surface potential sensor 11 is fixedly arranged at a distance of, for example, 2.5 mm from the surface of the photosensitive drum K. In the illustrated embodiment, the microcomputer 4
The microcomputer 4 controls the signal processing circuit 3.

FIG. 2 is a block diagram showing the configuration of the surface potential detecting device according to the present invention. As shown in FIG. 2, the surface potential detecting device according to the present invention includes a surface potential sensor 11 and a signal processing circuit 3. The surface potential sensor 11 and the signal processing circuit 3 are connected to a common ground line C. It has GND. Common ground line C. GND is at a potential floating with respect to the ground potential (or frame ground).

The surface potential sensor 11 interrupts the electric field between the detection electrode 15 and the surface to be measured. An AC signal S11 corresponding to a difference voltage between the potential of GND and the surface potential of the surface to be measured is generated. The illustrated surface potential sensor 11 includes a detection electrode 15 and a chopper 1.
6, a preamplifier 17, and a chopper drive circuit 18. The detection electrode 15 generates an electric field for measuring the surface potential of the photosensitive drum K in a non-contact manner.

The chopper 16 periodically chops the electric field between the surface to be measured, which is the surface of the photosensitive drum K, and the detection electrode 15. Its specific structure is already known.
For example, the tuning fork is excited by a piezoelectric vibrator, and a metal piece attached to the tuning fork is vibrated between the surface of the photosensitive drum K and the detection electrode 15.

The preamplifier 17 is a circuit for converting the impedance of the AC signal detected by the detection electrode 15 into a low impedance. The AC signal S11 that has passed through the preamplifier 17 is supplied to the signal processing circuit 3.

The chopper drive circuit 18 excites the chopper 16. Specifically, the chopper drive circuit 18 supplies a drive signal having a predetermined frequency to a piezoelectric vibrator constituting the chopper 16 to excite the same. Further, the chopper drive circuit 18 outputs a synchronization signal S12 synchronized with the drive signal.

The signal processing circuit 3 includes a synchronous detection circuit 31 and
It includes an integrating circuit 32, a high-voltage amplifier circuit 33, and a first bias circuit 36. The illustrated signal processing circuit 3 further includes an amplifier circuit 30. The amplification circuit 30 includes the surface potential sensor 1
1 supplies an AC signal S11.
Is amplified and output.

The synchronous detection circuit 31 includes the surface potential sensor 11
Supplies an AC signal S11, detects the signal S11 in synchronization with the intermittent operation of the surface potential sensor 11, and outputs a detection output signal c. In the illustrated synchronous detection circuit 31, the AC signal S11 is supplied from the surface potential sensor 11 via the amplification circuit 30. Further, the synchronous detection circuit 31 shown in FIG.
A synchronization signal S12 is supplied from the surface potential sensor 11, and the AC signal S11 is detected in synchronization with the synchronization signal S12.

The integration circuit 32 includes an operational amplifier IC2 having an inverting input terminal (-) and a non-inverting input terminal (+). The integration circuit 32 supplies the detection output signal c from the synchronous detection circuit 31 to the inverting input terminal (-). Then, the integration circuit 32 converts the supplied detection output signal c into DC and outputs a DC voltage signal d.

The high voltage amplifying circuit 33 is supplied with the signal d from the integrating circuit 32 and receives a signal d. A DC high voltage Vf that makes the potential of GND substantially equal to the potential of the surface to be measured is applied to the common ground line C.V. Supply to GND. Specifically, the high-voltage amplification circuit 33 outputs the signal d supplied from the integration circuit 32.
To boost. The signal boosted by the high voltage amplifier 33 is fed back to the tuning fork 16, the preamplifier 17, and the drive circuit 18 as a feedback voltage Vf. Thereby, the common ground line C.I. Feedback control is applied so that the potential of GND becomes substantially equal to the surface potential of the photosensitive drum K.

The first bias circuit 36 has a common ground line C.I. A positive voltage V3 is applied to the non-inverting input terminal (+) of the integration circuit 32 with reference to the potential of GND.

The signal processing circuit 3 further includes a detection signal output circuit 35. The detection signal output circuit 35 includes an operational amplifier I having an inverting input terminal (-) and a non-inverting input terminal (+).
It is constituted by C1. The inverting input terminal (−) of the detection signal output circuit 35 is connected to the common ground line C. It is led to GND. The detection signal output circuit 35 outputs a surface potential detection signal Z.

The signal processing circuit 3 further includes a power supply circuit 34. The power supply circuit 34 includes a transformer T1 and a switch element Q1. The transformer T1 has a first winding Np1.
, Second windings NS1 and NS2, and a third winding Nb1. The first winding Np1 is connected between a pair of DC voltage input terminals, and the second windings NS1 and NS2 are
It is transformer-coupled to the first winding Np1.

The switching element Q1 has two main electrodes and a control electrode. Typical examples of such a switching element Q1 are a field effect transistor (FET) and a bipolar transistor. The two main electrodes of the switch element Q1 are connected in series to the first winding Np1. The control electrode is led to the third winding Nb1. The switching element Q1 continues the switching operation based on a signal (feedback signal) supplied from the third winding Nb1 to the control electrode.

The transformer T1 has two second windings NS1 and NS2 with an intermediate tap. Second winding N
A rectifying and smoothing circuit including diodes D1 and D2 and capacitors C4 and C5 is connected to S1 and NS2. The power supply circuit 34 generates a positive power supply voltage (+ V1) and a negative power supply voltage (-V2). The positive power supply voltage (+ V1) and the negative power supply voltage (-V2) are connected to the common ground line C.V. GND
Is a reference voltage. The positive power supply voltage (+ V1) and the negative power supply voltage (-V2) are supplied as operating voltages of the respective components.

The signal processing circuit 3 further includes a second bias circuit 39. The second bias circuit 39 applies a negative voltage (−V) to the non-inverting input terminal (+) of the detection signal output circuit 35.
5) is applied. The illustrated second bias circuit 39
Is connected to the third winding Nb1, and generates a negative voltage (-V5) by a flyback voltage generated in the third winding Nb1 when the switching element Q1 is turned off.

In the above-described surface potential detecting device, the surface potential sensor 11 detects the surface potential of the surface to be measured and the common ground line C.V. An AC signal S11 corresponding to a difference voltage from the potential of GND is generated, and the AC signal S11 is supplied to the synchronous detection circuit 31 via the preamplifier 17 and the amplification circuit 30.

In the synchronous detection circuit 31, the surface potential sensor 11
Signal S11 supplied from the surface potential sensor 11
The detection is performed in synchronization with the intermittent operation of, and a detection output signal c is generated. The detection output signal c is supplied to the inverting input terminal (-) of the operational amplifier IC2 included in the integration circuit 32. The integration circuit 32 integrates the detection output signal c, converts it into a DC signal d, and outputs it. The level of the DC signal d depends on the surface potential of the surface to be measured and the common ground line C.V. It corresponds to the difference voltage from the potential of GND.

The high voltage amplifying circuit 33 includes the above-described integrating circuit 32
Supplied from the common ground line C. GN
D is applied to the common ground line C. Supply to GND. With the above circuit operation, the common ground line C.I. The potential of GND is controlled so as to be substantially equal to the surface potential of the surface to be measured.

Common ground line C. When the potential of GND becomes equal to the surface potential of the surface to be measured, the surface potential sensor 1
The electric field between one detection electrode and the surface to be measured is zero. Therefore, the common ground line C.I. By extracting the potential of GND as the surface potential detection signal Z from the detection signal output circuit 35, even if the distance between the surface potential sensor 11 and the surface to be measured changes, the distance dependency is extremely small and high accuracy is achieved. The surface potential detection signal Z can be obtained.

As a characteristic configuration of the surface potential detecting device of the present invention, the signal processing circuit 3 includes a first bias circuit 36.
including. From the first bias circuit 36, the integration circuit 3
A positive voltage (+ V3) is applied to the second non-inverting input terminal (+). Due to the bias of the positive voltage (+ V3), the relationship (detection characteristic) of the surface potential detection signal Z with respect to the surface potential Vsu of the surface to be measured is as shown in FIG.

In FIG. 3, a characteristic L01 is an ideal characteristic, a characteristic L03 is a characteristic when no bias is applied by the first bias circuit 36, and a characteristic L02 is a characteristic when bias is applied by the first bias circuit 36. Characteristic L03
Has a dead zone where the surface potential detection signal Z = 0 until the surface potential Vsu of the surface to be measured exceeds Vsu = Vsu1. By applying a positive voltage (+ V3) from the first bias circuit 36 to the non-inverting input terminal (+) of the integration circuit 32,
A characteristic L02 obtained by adding the voltage LZ1 to the characteristic L03 can be obtained.

In the characteristic L02, when the surface potential Vsu of the surface to be measured is zero, the surface potential detection signal Z becomes a positive offset voltage Vos. Therefore, a dead zone does not occur.

Further, the positive voltage (+ V3) applied from the first bias circuit 36 to the non-inverting input terminal (+) of the integration circuit 32 is applied to the common ground line C.V. It is based on the potential of GND. Therefore, a stable offset voltage Vos
Is obtained.

The offset voltage Vos can be easily and accurately adjusted by a circuit method in a circuit subsequent to the integrating circuit 32. That is, the present invention
It provides a basis for easily and accurately adjusting or eliminating the offset voltage Vos.

Since the power supply circuit 34 is not required to have a high degree of voltage stability accuracy, a surface potential detecting device in which the power supply circuit 34 is reduced in cost can be obtained. In the embodiment, a dropper-type stabilized power supply (three-terminal regulator) that was required in the past
Is omitted. Therefore, a surface potential detecting device with high overall power efficiency can be obtained.

In a preferred embodiment for canceling the offset voltage Vos generated by the first bias circuit 36, in this embodiment, the detection signal output circuit 35
, A second bias circuit 39 is added. This second
, A negative voltage (−V5) is applied to the non-inverting input terminal (+) of the detection signal output circuit 35.

According to such a configuration, as shown in FIG.
Surface potential detection signal Z for surface potential Vsu of the surface to be measured
Can be moved in a direction in which the value of the surface potential detection signal Z becomes lower with respect to the surface potential Vsu of the same surface to be measured. The movement amount ΔZ2 corresponds to the magnitude of the negative voltage (−V5). Therefore, by adjusting the magnitude of the negative voltage (−V5), the offset voltage Vos generated by the first bias circuit 36 is canceled, and the relationship between the surface potential Vsu of the surface to be measured and the surface potential detection signal Z is changed. , On the graph, a relationship of a primary straight line L01 passing through the origin (0, 0) can be set. Thereby, the offset voltage Vos
Can be obtained. If a specific example of the adjustment method is disclosed, if the magnitude of the negative voltage (−V5) is adjusted to be equal to the magnitude of the offset voltage Vos of the characteristic L02, the characteristic L02 can be adjusted to the ideal characteristic L01. .

FIG. 5 is a diagram showing a more specific circuit configuration of the signal processing circuit included in the surface potential detecting device according to the present invention. The amplifier circuit 30 includes an operational amplifier IC4, a resistor R8,
It includes R13, R14 and capacitors C10, C11, and amplifies the detection signal S11 supplied through the capacitor C11.

The signal amplified by the amplifier circuit 30 is
The signal is supplied to the synchronous detection circuit 31. The synchronous detection circuit 31 includes an operational amplifier IC3, resistors R9, R10, R11, R12, and an FET (field effect transistor) Q5 forming a switch element. The synchronous detection circuit 31 receives a signal from the drive circuit 18 (see FIGS. 3 and 4) of the surface potential sensors 11 to
Based on the synchronization signal S12 supplied to the gate of the ETQ5, the signal supplied from the amplifier circuit 30 is synchronously detected.

The synchronously detected signal is supplied to an integrating circuit 32 and converted into a direct current. The illustrated integration circuit 32 includes an operational amplifier IC2, a capacitor C6, a diode D3, and an output resistor R6. The transistor Q4 and the light emitting diode PCA are connected to the output resistor R6. The light emitting diode PCA emits light by the output of the integrating circuit 32.

The first bias circuit 36 has a common ground line C.I. With reference to COM, the positive power supply voltage (+ V1) supplied from the power supply circuit 34 is divided by the resistor R35 and the Zener diode ZD3, and the constant voltage appearing at both ends of the Zener diode ZD3 is divided by the resistors R31 and R33. The compressed positive voltage V3 is supplied to a non-inverting input terminal (+) of the integration circuit 32. This first bias circuit 36
Is as described above.

The high-voltage amplifier 33 includes an oscillation circuit, a transformer T2, and a triple voltage rectifier. The oscillation circuit is
Transistor Q2, Q3, primary winding Np of transformer T2
21, Np22, auxiliary winding N provided in transformer T2
b2, a capacitor C3 and an inductor L1. The switching operation of the transistors Q2 and Q3 excites the primary windings Np21 and Np22 of the transformer T2 and feeds back to the bases of the transistors Q2 and Q3 via the auxiliary winding Nb2 inductively coupled to the primary windings Np21 and Np22. Supply signal. The transistors Q2 and Q3 are connected to the feedback signal described above, the capacitor C3 and the inductor L1.
The self-excited oscillation operation is continued by the resonance phenomenon of the LC resonance circuit including

The triple voltage rectifier circuit is connected to the secondary winding NS of the transformer T2, and triple-rectifies the AC voltage generated in the secondary winding NS with the oscillating operation of the oscillation circuit.
The rectified voltage is applied to a common ground line C. Supply to GND. Thereby, the common ground line C.I. The potential of GND is controlled. The illustrated triple voltage rectifier circuit includes capacitors C7 to C9 and diodes D4 to D6.

The input side of the high voltage amplifier circuit 33 is connected to an input circuit including a phototransistor PCB and a transistor Q4. The phototransistor PCB is optically coupled to a light emitting diode PCA driven by the output of the integration circuit 32. Therefore, a voltage controlled according to the output signal of the integration circuit 32 is supplied to the input side of the oscillation circuit constituting the high-voltage amplification circuit 33.

Common ground line C. The potential of GND is converted to an appropriate potential by a voltage dividing / buffer circuit 35,
This is output as the surface potential detection signal Z.

The DC / DC converter 34 includes a transformer T
DC input voltage V supplied through the primary winding NP1
IN is switched by the switching element Q1. The voltage generated in the secondary windings NS1 and NS2 of the transformer T1 due to the switching operation is changed to diodes D1 and D2.
2 and is smoothed by capacitors C4 and C5 and converted to a DC voltage. The DC voltage is stabilized by the Zener diode ZD2 and supplied to the amplifier circuit 30, the synchronous detection circuit 31, the integration circuit 32, the light emitting diode PCA, and the like.

When the switching element Q1 is turned off, the second bias circuit 39 generates a diode D by the flyback voltage generated in the third winding Nb1 of the transformer T1.
7, the capacitor C2 is charged. Capacitor C
2 is divided by the resistors R43 and R45 to generate a negative voltage (-V5). This negative voltage (-V5) is supplied to the non-inverting input terminal (+) of the detection signal output circuit 35. The negative voltage (-V5) is applied to a resistor R43 which is a variable resistor.
Will be adjusted by

FIG. 5 shows only an example of the signal processing circuit. In the present invention, the signal processing circuit can employ various circuit configurations.

FIG. 6 is a diagram showing a specific circuit configuration of the surface potential sensor 11. For the sake of simplicity, in the figure, the chopper 16 attaches a piezoelectric vibrator 162 to the tuning fork 161 and excites the tuning fork 161 at a predetermined frequency by the piezoelectric vibrator 162. The vibration of the tuning fork 161 is detected by the piezoelectric vibrator 163 and input to the chopper drive circuit 18 as a feedback signal.

At the free end side of the tuning fork 161, a metal piece 164,
165 are attached. These metal pieces 164, 16
Reference numeral 5 denotes the surface of the photosensitive drum K (see FIG. 1) and the detection electrode 1
5 is arranged. Therefore, when the metal pieces 164 and 165 are excited by the vibration of the tuning fork 161, the electric field between the surface to be measured as the surface of the photosensitive drum K and the detection electrode 15 is periodically chopped.

The preamplifier 17 includes an amplifying element Q0 composed of an FET (field effect transistor) and a gate resistor R1.
And the source resistance R2, and converts the impedance of the AC signal detected by the detection electrode 15 into low impedance. More specifically, in the preamplifier circuit 17,
The source of the FET constituting the amplifying element Q0 is grounded through the resistor R2. When an AC signal appearing at the detection electrode 15 is applied to the gate of the amplifier Q0 and the amplifier Q0 operates, the amplifier Q0 is negatively biased by the source signal R2 by the amplified signal, and the input side of the amplifier Q0 is input. Is converted into a low impedance signal, and a signal appears at the drain D of the amplifier Q0.

The chopper drive circuit 18 includes an operational amplifier IC
5, including the resistors R15 to R18 and the capacitor C12. When a drive signal is given from the operational amplifier IC5 to the piezoelectric vibrator 162, the tuning fork 161 is driven by the piezoelectric vibrator 162.
Is excited. The vibration of the tuning fork 161 causes the piezoelectric vibrator 1
63, a feedback signal is generated, a resistor R18, a capacitor C1
2. Positive feedback is applied to the operational amplifier IC5 by the resistors R17 and R16, and the next drive pulse is applied to the piezoelectric vibrator 162. By repeating this operation, the tuning fork 161 has a specific frequency (for example, 680 Hz) at its mechanical resonance point.
Continue vibration with.

The vibration of the tuning fork 161 causes the metal pieces 164 and 165 attached to its free ends to vibrate, and the electric field between the detection electrode 15 and the surface to be measured of the photosensitive drum K is chopped. As a result, the capacitance between the detection electrode 15 and the surface to be measured of the photosensitive drum K increases or decreases in a substantially sinusoidal manner around the capacitance Co at the time of non-excitation, and correspondingly,
An AC detection signal S11 is obtained.

The drive signal generated by the chopper drive circuit 18 or the signal S12 synchronized therewith is supplied to the synchronous detection circuit 31 (see FIG. 2).

FIG. 7 is a diagram schematically showing a configuration for detecting the surface potentials of four photosensitive drums arranged in tandem using the surface potential detecting device according to the present invention. In the illustrated embodiment, four photosensitive drums C, M, Y, and K are arranged in tandem along the traveling direction W of the transfer belt V. The photosensitive drum C is for cyan, the photosensitive drum M is for magenta, the photosensitive drum Y is for yellow, and the photosensitive drum K is for black. Each of the photosensitive drums K to C is provided with a charging corotron U1, a transfer corotron U2, and a developing device U3.

FIG. 8 is a diagram showing a specific circuit configuration of the surface potential detecting device shown in FIG. In the figure, FIG.
The same reference numerals are given to the same components as those shown in FIG. 8, the surface potential detecting device 1 includes a plurality (four) of surface potential sensors 11 to 14,
It includes a switching circuit 2 and one signal processing circuit 3.

Each of the four surface potential sensors 11 to 14 has a circuit configuration as shown in FIG. 5 and is independent of each other. Each of the surface potential sensors 11 to 14 is individually provided for each of the photosensitive drums K to C, and is fixedly arranged at a distance of, for example, 2.5 mm from the surface of the photosensitive drums K to C. I have. Surface potential sensors 11-1
4, the signals S11 to S41, S
12 to S42 are switching circuits 2 via a coaxial cable or the like.
Sent to

The switching circuit 2 includes surface potential sensors 11 to 14
Are selected and output at different timings for each of the surface potential sensors 11 to 14.

One signal processing circuit 3 is connected to the four surface potential sensors 11 to 14 via the switching circuit 2 and is shared by the four surface potential sensors 11 to 14. The signal processing circuit 3 is the same as that described with reference to FIGS. 2 and 6, and includes a first bias circuit 36 and a second bias circuit 39.

The first bias circuit 36 has a common ground line C.I. Based on COM, the positive power supply voltage (+ V1) supplied from the power supply circuit 34 is divided, and the divided positive voltage (+ V3) is supplied to the integration circuit 32. The operation of the first bias circuit 36 is as described above.

The second bias circuit 39 generates a negative voltage (-V5) by using a flyback voltage generated in the third winding Nb1 of the transformer T1 when the switch element Q1 is turned off. This negative voltage (−V5) is supplied to the detection signal output circuit 35. Second bias circuit 39
Is also as described above.

The surface potential detecting device shown in FIGS.
And four surface potential sensors 11 to 14 are independent of each other, so that image formation by a tandem type copying machine, laser beam printer, or the like for speeding up is performed. In the apparatus, the surface potential sensors 11 to 14 correspond to the four photosensitive drums K to C, and their surface potentials can be individually detected.

The switching circuit 2 includes four surface potential sensors 11
Signals S11 to S41, S12 to S supplied from.
42 is selected and output at different timings for each of the surface potential sensors 11 to 14. Therefore, signals output from the four surface potential sensors 11 to 14 can be temporally separated.

FIG. 9 is a time chart showing a specific example of the signal selection operation of the switching circuit. First, as shown in FIG. 9A, only the signal output from the surface potential sensor 11 provided on the photosensitive drum K is selected from the time t1 to the time t2. Next, as shown in FIG. 9B, only signals output from the surface potential sensor 12 provided on the photosensitive drum Y are selected from the time t3 to the time t4.

Further, as shown in FIG. 9C, only the signal output from the surface potential sensor 13 provided on the photosensitive drum M is selected from time t5 to time t6.
As shown in (d), between t7 and t8,
Only signals output from the surface potential sensor 14 provided on the photosensitive drum C are selected.

The signals S11 to S41 and S12 to S42 are
As means for selecting the surface potential sensors 11 to 14 at different temporal timings, a method of applying the control signals CS1 to CS4 from the microcomputer 4 to the switching circuit 2 can be adopted.

The signal processing circuit 3 passes through the switching circuit 2
It is connected to four surface potential sensors 11 to 14. Therefore, the signal processing circuit 3 receives the signals of the surface potential sensors 11 to 14 in a time-separated state. Then, necessary signal processing is performed within the time allocated to each of the surface potential sensors 11 to 14.

The signal processing circuit 3 is shared by the four surface potential sensors 11 to 14. Therefore, only one signal processing circuit 3 is required. Therefore, the four photosensitive drums K to
For C, the circuit configuration is significantly simplified as compared with the prior art, which requires the provision of four sets of the surface potential sensors 11 to 14 and their signal processing devices.
Weight and cost are significantly reduced.

FIG. 10 is an electric circuit diagram showing a specific example of the switching circuit. The illustrated switching circuit 2 includes a first switching circuit 2
The first to fourth switching circuits 204 are provided. The first switching circuit 201 includes a surface potential sensor 1 provided on the photosensitive drum K.
The switch SW11 (K) and the switch SW12 (K) for selecting the detection signal S11 and the synchronization signal S12 supplied from 1 are provided. These SW11 (K) and SW12 (K) are CM
Driven simultaneously by a drive circuit DR1 composed of an OS. That is, an interlocking operation is performed.

The second switching circuit 202 includes a switch SW21 for selecting a detection signal S21 and a synchronization signal S22 supplied from the surface potential sensor 12 provided on the photosensitive drum Y.
(Y) and SW22 (Y). These SW21
(Y) and SW22 (Y) are simultaneously driven by a drive circuit DR2 composed of CMOS.

The third switching circuit 203 includes a switch SW31 for selecting a detection signal S31 and a synchronization signal S32 supplied from the surface potential sensor 13 provided on the photosensitive drum M.
(M) and SW32 (M). These switches S
W31 (M) and SW32 (M) are simultaneously driven by a drive circuit DR3 composed of CMOS.

The fourth switching circuit 204 includes a switch SW41 for selecting a detection signal S41 and a synchronization signal S42 supplied from the surface potential sensor 14 provided on the photosensitive drum C.
(C) and SW42 (C). These switches S
W41 (C) and SW42 (C) are simultaneously driven by a drive circuit DR4 composed of CMOS.

[0089]

As described above, according to the present invention, the following effects can be obtained. (A) It is possible to provide a surface potential detection device that provides a basis for easily eliminating an offset generated in a surface potential detection output signal. (B) An inexpensive surface potential detecting device can be provided. (C) It is possible to provide a surface potential detecting device capable of realizing high total power efficiency.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration in a case where a surface potential of a photosensitive drum is detected using a surface potential detection device according to the present invention.

FIG. 2 is a block diagram showing a configuration of a surface potential detecting device according to the present invention.

FIG. 3 is a diagram illustrating a first example of the surface potential detecting device according to the present invention;
FIG. 4 is a diagram for explaining offset adjustment by the bias circuit of FIG.

FIG. 4 shows a second example included in the surface potential detecting device according to the present invention.
FIG. 4 is a diagram for explaining offset adjustment by the bias circuit of FIG.

FIG. 5 is a diagram showing a more specific circuit configuration of a signal processing circuit included in the surface potential detecting device according to the present invention.

FIG. 6 is a diagram showing a specific circuit configuration of the surface potential sensor.

FIG. 7 is a diagram schematically showing a configuration in a case where the surface potentials of four photosensitive drums arranged in tandem are detected using the surface potential detection device according to the present invention.

8 is a block diagram more specifically showing the configuration of the surface potential detecting device shown in FIG.

FIG. 9 is a time chart showing a specific example of a signal selecting operation of a switching circuit included in the surface potential detecting device shown in FIGS. 7 and 8;

FIG. 10 is an electric circuit diagram showing a specific example of a switching circuit included in the surface potential detecting device shown in FIGS. 7 and 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Surface potential sensor 2 Switching circuit 3 Signal processing circuit 30 Amplifier circuit 31 Synchronous detection circuit 32 Integration circuit 33 High voltage amplifier circuit 34 Power supply circuit 35 Detection signal output circuit 36 First bias circuit 39 Second bias circuit

Claims (4)

[Claims] 1. A surface potential detecting device including a surface potential sensor and a signal processing circuit, wherein the surface potential sensor and the signal processing circuit operate using a potential of a common ground line as a reference potential, and The line is at a potential floating with respect to a ground potential; the surface potential sensor generates an AC signal by interrupting an electric field between the sensing electrode and the surface to be measured; and A synchronous detection circuit that synchronizes the AC signal supplied from the surface potential sensor with an intermittent operation of the surface potential sensor; and a detection circuit, an integration circuit, a high-voltage amplification circuit, and a first bias circuit. The integration circuit includes an operational amplifier having an inverting input terminal and a non-inverting input terminal, and a detection output signal from the synchronous detection circuit is supplied to the inverting input terminal. The high-voltage amplifier circuit is supplied with a signal from the integration circuit, and makes the potential of the common ground line substantially equal to the potential of the surface to be measured. A surface potential detecting device for supplying a high voltage to the common ground line, wherein the first bias circuit applies a positive voltage based on the potential of the common ground line to the non-inverting input terminal of the integration circuit. 2. The surface potential detecting device according to claim 1, wherein the signal processing circuit further includes a detection signal output circuit,
Wherein the detection signal output circuit includes an operational amplifier having an inverting input terminal and a non-inverting input terminal, wherein the inverting input terminal is guided to the common ground line, and outputs a surface potential detection signal. The second bias circuit is a surface potential detection device that applies a negative voltage to the non-inverting input terminal of the detection signal output circuit. 3. The surface potential detection device according to claim 2, wherein the signal processing circuit further includes a power supply circuit, wherein the power supply circuit includes a transformer and a switch element, and the transformer is , A first winding, a second winding, and a third winding, wherein the first winding is connected between a pair of DC voltage input terminals; Is connected to the first winding by a transformer. The switch element has two main electrodes and a control electrode, and the two main electrodes are connected to the first winding. The control electrode is guided to the third winding, and the switching operation is continued based on a signal supplied from the third winding to the control electrode; Is connected to the third winding, and the third element is turned off when the switch element is turned off. Surface potential detecting device that generates the negative voltage by the flyback voltage generated in the line. 4. The surface potential detecting device according to claim 1, wherein the first bias circuit includes a Zener diode and a resistor voltage dividing circuit. A surface potential detecting device in which a cathode is led to the common ground line, the resistance voltage dividing circuit is connected in parallel to the zener diode, and a divided voltage is supplied to a non-inverting input terminal of the integration circuit.