JPH036467B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface electrometer that measures the surface potential of an object to be measured, and particularly to a surface electrometer that measures the surface potential of a surface to be measured by increasing the electric field between the measurement electrode and the surface to be measured in order to extract the surface potential of the surface to be measured as an alternating current signal. The present invention relates to a surface electrometer having an intermittent intermittent means.

In such surface electrometers, the detection output fluctuates when the distance of the surface to be measured from the measurement electrode or intermittent means changes, so vibrations of the device including the electrometer lead to fluctuations in the detection output, and the installation of the electrometer also causes fluctuations in the detection output. required high precision.

The present invention was made in view of the above points, and an object of the present invention is to provide a surface electrometer that can obtain a stable detection output regardless of the distance between the object to be measured and the measurement electrode. be.

That is, the present invention includes an electrode 85 for measuring the surface potential of the object to be measured, and a predetermined electric field between the electrode and the object to be measured in order to detect the surface potential with the electrode as an alternating current voltage. a conductive member 81 having an opening facing the electrode and shielding the electrode from an external electric field; and converting the AC voltage detected by the electrode into a low impedance signal. A first conversion means CT102 converts the AC voltage converted into a low impedance signal by the first conversion means into a DC voltage, and a second conversion means CT106 converts the AC voltage converted into a low impedance signal by the first conversion means into a DC voltage. In order to
The present invention provides a surface electrometer that outputs a voltage corresponding to the supplied DC voltage as a surface potential of the object to be measured.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1a is a sectional view of a copying apparatus to which the present invention can be applied.

The surface of the drum 47 is made of a three-layer seamless photoconductor using a CdS photoconductor, is rotatably supported on a shaft, and is rotated in the direction of the arrow by a main motor 71 activated when the copy key is turned on. Start.

When the drum 47 rotates by a predetermined angle, the original placed on the original platen glass 54 is moved to the first scanning mirror 44.
illuminated by an illumination lamp 46 integrally configured with
The reflected light is scanned by the first scanning mirror 44 and the second scanning mirror 53. The first scanning mirror 44 and the second scanning mirror 53 move at a speed ratio of 1:1/2, so that the original is scanned while the optical path length in front of the lens 52 is always kept constant.

The above reflected light image shows the lens 52 and the third mirror 55.
After passing through, an image is formed on a drum 47 at an exposure section.

The drum 47 is simultaneously neutralized by the pre-exposure lamp 50 and the pre-AC charger 51', and then corona-charged (for example, +) by the primary charger 51. Thereafter, the drum 47 is the exposure section, and the image irradiated by the illumination lamp 46 is slit-exposed.

At the same time, AC or corona charge removal with a polarity opposite to the primary one (for example -) is performed by a charge remover 69, and then a high-contrast electrostatic latent image is formed on the drum 47 by uniform surface exposure using a full-surface exposure lamp 68. The electrostatic latent image on the photosensitive drum 47 is then developed with liquid by the developing roller 65 of the developing device 62 and visualized as a toner image, and the toner image is made easy to transfer by the pre-transfer charger 61.

Upper cassette 10 or lower cassette 11
The transfer paper inside is fed into the machine by a paper feed roller 59, and is sent toward the photosensitive drum 47 with accurate timing by a register roller 60, so that the leading edge of the latent image and the leading edge of the paper are aligned at the transfer section. Can be done.

Next, while the transfer paper passes between the transfer charger 42 and the drum 47, the toner image on the drum 47 is transferred onto the transfer paper.

After the transfer is completed, the transfer paper is separated by a drum 47 by a separation roller 43, sent to a conveyance roller 41, guided between a hot plate 38 and press rollers 40, 41, and fixed by pressure and heat. The paper is discharged to the tray 34 by the discharge roller 37 via the paper detection roller 36 .

After the transfer, the drum 47 continues to rotate and its surface is cleaned by a cleaning device comprising a cleaning roller 48 and an elastic blade 49, and the process proceeds to the next cycle.

Here, a surface electrometer 67 for measuring the surface potential is connected to the drum 47 between the entire surface exposure lamp 68 and the developing device 62.
mounted in close proximity to the surface of the

As a cycle executed prior to the above copy cycle, there is a step of pouring a developer into the cleaning blade 49 while the drum 47 is stopped after the power switch is turned on. Hereinafter referred to as Priwetsu. This is to flush out the toner accumulated near the cleaning blade 49 and to provide lubrication to the contact surface between the blade 49 and the drum 47. After the prewetting time (4 seconds), the drum 47 is rotated, residual charges and memory on the drum 47 are erased using a pre-exposure lamp 50, a pre-AC static eliminator 51', etc., and the drum surface is cleaned using a cleaning roller 48 and a cleaning blade 49. There are steps. Hereinafter, this will be referred to as forward rotation. This is to make the sensitivity of the drum 47 appropriate and to form an image on a clean surface.

Also, as a cycle after the set number of copy cycles are completed, the drum 47 is rotated several times.
There is a step in which residual charges and memory on the drum are removed using an AC charger 69 or the like, and the drum surface is cleaned. Hereinafter referred to as post-rotation LSTR. This is to leave the drum 47 electrostatically and physically clean.

FIG. 1b is a plan view of the vicinity of the blank exposure lamp 70 in FIG. Blank exposure lamp 70-1
70-5 is turned on when the drum is rotating and not during exposure to erase the drum surface charge and prevent excess toner from adhering to the drum. However, the blank exposure lamp 70-1 is
Since the drum surface corresponding to 7 is irradiated, it is turned off momentarily when measuring the dark area potential with the surface electrometer 67. Also, for B5 size copies, the image area is A4
The blank exposure lamp 70-5 is turned on for the non-image area even when the optical system is moving forward. The lamp 70-0 is called a sharp cassette lamp, and it irradiates light onto the portion of the drum that is in contact with the separation guide plate 43-1, completely erasing the charge on that portion and preventing toner from adhering to it. I try not to contaminate the width of the separation chip. This sharp cassette lamp is always lit while the drum is rotating.

First, a surface electrometer as a detection means for detecting surface potential will be explained.

Figure 2 is a side sectional view of the surface electrometer, Figure 3 is the
Figure 4 is a cross-sectional view taken along line X-X' in Figure 2 and viewed from the right side of the drawing, Figure 4 is a cross-sectional view taken along line X-X' in Figure 2 and viewed from the left side of Figure 5, and Figure 5 is an electrometer. FIG.

In Figures 2, 3, 4, and 5, the entire electrometer is
It is covered with a metal shield member 81 and a metal base 95 to eliminate the influence of external electric fields.

The shield member 81 has an opening for a measurement window 88, and the measurement window 88 is opposed to the portion to be measured of the drum 47 to measure the potential.

A tuning fork 82 is attached to the base 95 in an electrically conductive state, and the drive circuit shown in FIG. When voltage is applied, tuning fork 82
self-excited vibration at the mechanical resonance frequency of The tip of one of the vibrating pieces of the tuning fork constitutes a chopper electrode 83, and the vibration of the tuning fork causes the measurement window 88 to open and close at regular intervals. A printed circuit board 86 is fixed to the back side of the chopper electrode, and a measurement electrode 8 having the same shape as the window is installed at a position facing the measurement window.
5 is formed by a copper foil pattern on a printed board.

The electric lines of force based on the surface charge of the photosensitive drum 47 are:
The electric force enters the measuring electrode 85 through the measuring window 88, but the chopper electrode 83 located between the measuring window 88 and the measuring electrode interlinks and cuts the lines of electric force due to the vibration of the tuning fork 82. , an AC voltage having an amplitude proportional to the voltage difference between the surface potential on the photosensitive drum 47 and the chopper electrode (same potential as the shield member potential) is induced in the measurement electrode.

The alternating current signal is transmitted to a preamplifier circuit (seventh
After being converted to a low impedance signal by
Externally taken out as the output of the electrometer.

Reference numeral 89 in FIG. 5 is an internal shield member for preventing the drive signal from the tuning fork drive section 84 from being guided to the measurement electrode 85.

The driving of the tuning fork will be explained with reference to FIG.

As shown in FIG. 6, piezoelectric elements 84-1 and 84-2 are bonded to the fulcrum side of the vibrating piece of the tuning fork 82 at opposing positions in the length direction using a conductive adhesive.

84-1 and 84-2 are piezoelectric elements that generate distortion in the plane direction when an electric field is applied in the thickness direction, and when fixed to the vibrating piece of a tuning fork with conductive adhesive as shown in Figure 8, the vibrating piece and The piezoelectric element integrally constitutes a unimorph resonator, and since the shape of the piezoelectric element is elongated in the length direction of the vibrating piece, when an electric field is applied in the thickness direction, distortion occurs in the length direction of the vibrating piece.

The output of the drive circuit (collector of the transistor Tr52) is connected to the piezoelectric element 84-1, and the output of the drive circuit is connected to the piezoelectric element 84-2.
When the input of the drive circuit (the base of transistor Tr51) is connected to 84-1 and a DC voltage is applied to voltage application terminals P51 and P52, the mechanical vibration of the tuning fork driven by 84-1 is caused to move in the thickness direction of 84-2. It is converted into an electrical signal and fed back to the input of the drive circuit, so it begins to oscillate at the tuning fork's resonant frequency.

The feedback signal output taken out to both ends of the piezoelectric element 84-2 is current amplified by the transistor Tr51, and then applied to the base of the transistor Tr52 via the resistor R52 and the capacitor C52, where it is amplified into a large oscillating AC signal. , drives the piezoelectric element 84-1.

The feedback signal of 84-2 is selected to have a phase that provides positive feedback to the drive circuit of FIG.
Since the frequency is also high, oscillation continues at the resonance frequency of the tuning fork.

To attach the electrometer to the copying machine body, use the support base 95.
is fixed to a printed circuit board 67, and this printed circuit board is supported on the main body by a circuit board connector 94 and a circuit board guide 87.

On the connector insertion side of the printed circuit board 67, the connector contact terminal part is made of copper foil, and supplies power to the electrometer and takes out the output signal, making it possible to easily remove the electrometer. There is.

As described above, driving the tuning fork with a piezoelectric element does not require a high-precision small motor, compared to the conventionally proposed method of intermittent electric lines of force driven by a motor, resulting in lower costs. Since the resonant frequency of the piezoelectric element is constant, highly accurate detection and device control based on the detection are possible.

The AC signal induced in the measurement electrode 85 is regenerated and amplified into a DC potential of the same polarity as the potential to be measured by the measurement circuit shown in FIG. The potential and shield potential are kept at the same potential as the potential to be measured. As a result, the voltage fed back to the chopper becomes the voltage to be measured itself, which does not vary depending on the measurement distance.

The process until the same potential as the potential to be measured is fed back to the chopper and the shield member will be explained with reference to FIG.

In Fig. 9, CT101 is the tuning fork drive circuit shown in Fig. 6, CT102 is the preamplifier circuit shown in Fig. 7, and CT
103 is the isolator shown in Fig. 10, CT104,
CT105 is a monostable multivibrator, CT1
06 is a DC regeneration circuit composed of a synchronous clamp circuit, CT107 is an integrating circuit, CT108 is a high voltage amplifier, CT109 is an attenuator, CT110 is a buffer amplifier, and CT111 is a power supply circuit.

The power supply circuit of CT111 is composed of a switching regulator, and input terminals P102 and P103
By applying a 24V DC voltage to the
104, P105), and 30V (between terminals P106,
107).

The low voltage side of the isolated power supply is both 24V and 30V.
It is connected to the output of CT108 and has the same potential as the shield member and chopper.

On the high voltage side of the isolated power supply, 30V is the tuning fork drive circuit CT.
101 power supply (terminal P51), 24V is preamplifier CT102 (terminal P53) and isolator
The power is supplied to the CT 103 (terminal P113).

The weak alternating current signal induced in the measurement electrode 85 is converted into a low impedance signal by the preamplifier CT 102 so as not to be affected by external noise such as hum, and is taken out to the outside of the electrometer. The output of the preamplifier is output from the chopper 83 and the shield member 81.
is connected to the output of CT108, and the power supply of the preamplifier circuit is also biased to the output of CT108 as mentioned above, so when viewed from the ground potential reference, CT1
The output potential of 08 is superimposed. The isolator in Figure 10 uses the output signal of the preamplifier to
This is to remove the superimposed part of the output of CT108, and the output of the preamplifier is AC amplified by operational amplifier OA1, and the light emitting diode of photocoupler PC1 is
By changing the LED1 current and changing the emitter current of the phototransistor PTr1 by optical coupling, a signal obtained by removing the superimposed portion of the output of the CT108 on the emitter of the phototransistor PTr1 is obtained.

The operation of the isolator CT103 will be explained with reference to the operation waveforms shown in FIG.

Now, the surface potential V _p of the part to be measured, that is, the drum 47
is set to +500V as shown in Figure 11○A, and the feedback voltage V _F of the DC amplifier circuit CT108 (Figure 11○B) is 0V.
(ground potential). The feedback voltage V _F changes from the ground potential to 500 V, which is the same as the surface potential V _P , as shown in Figure 11 (○). The output voltage from the preamplifier CT102 is the first voltage based on the feedback voltage _VF .
As shown in Figure 1, an AC signal (on the order of mV) has an amplitude proportional to the absolute value of the difference between the measured potential V _P and the feedback voltage V _F. However, if the ground potential is used as a reference, the first
As shown in Figure 1, the voltage is obtained by superimposing the AC signal on the feedback voltage V _F. Isolator CT1 in Figure 10
03 light emitting diode LED1 drive side is terminal P1
15 has a feedback voltage V _F , and terminal P113 has a feedback voltage V _F +24
Since the output of the preamplifier CT102 is connected to the terminal 114, [V] is equal to the potential to be measured V _P and the bias potential of the chopper or shield member, that is, the feedback voltage.
It becomes an AC signal with an amplitude proportional to the potential difference between it and _VF .
The AC signal is optically coupled to a phototransistor.
The emitter current of PTr1 is changed, but since the phototransistor is driven at +24 [V] - 0 [V] (ground potential), the superimposed feedback voltage V _F is applied to the output terminal P117 as shown in Figure 11 (○). An AC signal is obtained with the .

The output of the isolator T103 is regenerated as DC by the synchronous clamp circuit CT106, and is then regenerated by the integrator circuit CT1.
Smoothed at 07. CT106 and CT107 are the first
The operation shown in FIG. 2 will be explained according to the operation waveforms of FIG. 13.

The output of the isolator (○) in Figure 13 is an AC signal with an amplitude proportional to the voltage difference between the measured potential V _P and the chopper potential (feedback voltage V _F ) as described above. Drive pulse signal PLS
Compared to 1, it has a certain phase relationship. In ◯, a solid line signal indicates a case where the measured potential V _P is positive with respect to the chopper potential V _F , and a broken line indicates a case where the measured potential is negative with respect to the chopper potential.

The timing of the rise of the output pulse PLS1 of the tuning fork drive circuit is delayed by the monostable circuit CT104 to the timing of the negative peak of the signal indicated by the solid line ◯ to obtain the pulse signal PLS2. The monostable circuit CT105 is driven at the falling timing of PLS2 to obtain a narrow negative pulse PLS3 (circle in FIG. 13). the pulse
PLS3 is synchronized with the timing of the negative peak of the solid line signal and the positive peak of the broken line signal to the isolator output ○.

The output of the isolator is connected to terminal P119 (12th
(Fig.), and the current is amplified by the emitter follower TR4 and then connected to the capacitor C7.

The opposite terminal of capacitor C7 is connected to the gate of the source follower of TR5 and the drain of the FET switch of TR6. When the FET switch of TR6 is cut off, the gate of TR5 and the drain of TR6 become high impedance. Therefore, since there is no place for the charge charged in C7 to escape, the TR of C7
The terminal potential on the gate side of No. 5 changes in the same way as the terminal potential on the opposite side.

The output pulse of monostable circuit CT105 PLS3 is
It is connected to the input terminal P120 and turns on the transistor TR7 at the timing of the negative pulse.

Operational amplifier OA2 has an output of 0 to ±5V using Zener diodes ZD1 and ZD2 for clamping.
Therefore, when TR7 conducts, the cathode of diode D101 is biased to +12V, D101 is cut off, the source and gate of FET switch TR6 become zero bias, and the drain and source of TR6 become conductive. . When TR6 becomes conductive, the feedback loop of operational amplifier OA2 is connected to FET switch TR6, source follower TR
5. Since it is formed at the route of resistor R21, OA2
Considering that the potential difference between the two input terminals of C7 becomes zero and the input resistance of OA2 is high, the source potential of TR5 becomes 0V (ground potential), and the terminal voltage on the gate side of TR5 of C7 changes from 0V to TR5. gate of
It comes to be biased to a potential shifted by the source-to-source voltage.

When the output pulse PLS3 of CT105 returns to a high level after the timing of the negative pulse ends, transistor TR7 is cut off, diode D101 becomes conductive, current flows through resistors R26 and R30, and a reverse bias is applied to the gate of TR6. take deep
TR6 is cut off.

When TR6 is cut off, as described above, the terminal voltage on the gate side of TR5 of capacitor C7 shows the same change as the potential on the opposite terminal.

Therefore, as shown by the solid line in Figure 13, the source of TR5 has a waveform with the same shape as the output of the clamped isolator, with a negative peak of 0V (ground potential) when the measured potential is positive with respect to the chopper potential. can get.

Moreover, as shown by the broken line of ○, when the measured potential is negative with respect to the chopper potential, a waveform having the same shape as the output of the isolator with the positive peak clamped to 0V is obtained. The output ○nu is operational amplifier OA3
After being amplified by a resistor R31 and a capacitor C8, the current is amplified by an operational amplifier OA4, and then connected to a high voltage amplifier CT108.

CT108 is shown in Fig. 14, but it has two DC-
The inverter INV2, which is composed of a DC inverter and one operational amplifier, and is composed of an inverter transformer T102 and transistors TR12 and TR13, provides a fixed output of -1 KV on the anode side of the high voltage diode D103.

Inverter transformer T101, transistor
Inverter fixed with TR10 and TR11
INV1 is a variable inverter,
0~2KV output with capacitor C11 and resistor R46
It is taken out at both ends of the transformer T10
Since the low voltage side terminal of the secondary winding 1 is connected to the cathode of D103, a variable output of -1KV to +1KV can be obtained at the cathode of D102. The output of the integrating circuit CT107 is connected to the operational amplifier OA5 via the terminal P122, and is connected to the volume control circuit described later.
After amplifying the voltage difference with the DC potential selected by VR101, buffer transistors TR8 and TR
1 of the inverter transformer INV1 through 9
added to the common terminal of the next side and inverter INV
1 boosts the output of OA5 by about 100 times. VR101 is a volume for correcting offset voltage, and the DC potential applied to the negative input terminal of OA5 is almost 0V (ground potential). transformer T
The output, that is, the feedback voltage V _F boosted at step 101 is fed back to the chopper section 83 and the shield member 81 via the terminal P123, so the section to be measured and the electrometer form a negative feedback control system. , so that the potential difference between the inputs of the operational amplifier OA5 becomes zero, that is, the potentials of the chopper 83 and the shield member 81 become equal to the voltage to be measured, and the input voltage of P122 is changed to the input voltage of the negative input terminal of OA5. Similarly, it will be set to zero.

When the potential to be measured V _P is within the range of -1K to +1KV,
The output voltage of the CT 108, that is, the feedback voltage V _F is always equal to the potential to be measured V _P .

The output of the amplifier circuit CT108 is sent to the attenuator CT109.
The current is attenuated to 1/100 by the CT 110, and after being amplified by the buffer of the CT 110, it is taken out to the output terminal P124.
The detection output taken out from the terminal P124 is used for controlling the output of the primary charger or static eliminator, controlling the light amount of the exposure lamp, controlling the developing bias voltage, etc.

Since the feedback voltage V _F is applied to the chopper 83 and the shield member 81 and changes so that the potential difference with the potential to be measured V _P is always zero,
The output taken out in step 3 is from CT101 to CT108.
This provides stable output that is unaffected by the offsets and errors of each circuit up to this point.

The experimental results of the characteristics of the measured potential V _P and the feedback voltage V _F when the distance between the shield member 81 and the drum 47 was changed to 2 mm, 4 mm, and 6 mm are shown in the 15th section.
As shown in the figure.

In FIG. 15, the amplifier CT10 of this embodiment
The output voltage range of 8 is set to -350 [V] to +750 [V].

As shown in FIG. 15, it can be said that the feedback voltage V _F is almost constant with respect to the potential to be measured V _P even if the distance is changed.

This is because when V _P = V _F , that is, when the surface potential of the drum and the bias potential of the tipper or shield member are equal, the measuring electrode is completely unaffected by the electric field from the drum surface, and the relationship between the electrode and the drum surface is reduced. This is probably because it is not affected by distance.

As described above, the present invention has made it possible to realize a surface electrometer that measures the surface potential of a surface to be measured without being affected by the distance between the measurement electrode and the surface to be measured. Therefore, not only does it not require high precision when installing the electrometer near the object to be measured, but it also allows stable potential detection without being affected by distance fluctuations caused by the chopper drive or mechanical vibration of the device containing the electrometer. can. Furthermore, since a negative feedback circuit is used, it is not affected by gain fluctuations, drifts, etc. due to environmental changes in each processing circuit for measurement.

[Brief explanation of the drawing]

FIG. 1a is a sectional view of a copying apparatus to which the present invention can be applied, FIG. 1b is a plan view of the vicinity of the blank exposure lamp 70, FIG. 2 is a side sectional view of a surface electrometer, and FIG. Cross-sectional view of the right side taken from the line X-X' of
The figure is a cross-sectional view of the left side taken from the line X-X' in Figure 2.
Fig. 5 is a perspective view of the electrometer, Fig. 6 is a piezoelectric tuning fork drive circuit diagram, Fig. 7 is a potential detection circuit diagram, Fig. 8 is a sectional view of a vibrator, Fig. 9 is a measurement circuit diagram, and Fig. 10 is a diagram. Isolator circuit diagram, Figure 11 is a waveform diagram of each part in Figure 9, Figure 12 is a detailed circuit diagram of the integrating circuit CT106 and amplifier CT107 in Figure 9, Figure 13 is a detailed circuit diagram of the integrator circuit CT106 and amplifier CT107 in Figure 9.
Waveform diagram of each part in the figure, Figure 14 is high voltage amplifier CT
108, attenuator CT109, buffer amplifier CT1
10, and FIG. 15 is a diagram showing the measurement results of the relationship between the surface potential V _P and the feedback voltage V _F. In the figure, 47 is a photosensitive drum, 83 is a chipper, 85 is a measurement electrode, PC1 is a photocoupler, OA
1 to OA6 indicate operational amplifiers, respectively.

Claims (1)

[Scope of Claims] 1. An electrode for measuring a surface potential of an object to be measured, and an electric field between the electrode and the object to be measured at a predetermined period in order to detect the surface potential as an alternating current voltage with the electrode. a conductive member having an opening facing the electrode for shielding the electrode from an external electric field; and a first conductive member for converting the alternating current voltage detected by the electrode into a low impedance signal. a converting means; and a second converting means for converting the AC voltage converted into a low impedance signal by the first converting means into a DC voltage.
converting means; and in order to make the potential difference between the object to be measured and the electrode zero, a DC voltage such that the DC voltage from the second converting means becomes zero is applied to the conductive member, the disconnecting means, and the first A surface potential meter comprising: means for supplying to a converting means, and outputting a voltage corresponding to the supplied DC voltage as a surface potential of the object to be measured.