JPH0453649Y2 - - Google Patents

Description

[Detailed Description of the Invention] "Industrial Application Field" The present invention relates to an electrostatic electrometer for detecting the surface potential of a photoreceptor in a copying machine.

"Prior Art" In order to form a good electrostatic latent image on a photoreceptor in an electrostatic copying machine, it is necessary to set the potential on the photoreceptor to a desired value. For this purpose, there are copying machines that use an electrostatic electrometer to control the potential of a charger or the like.

FIG. 2 shows an outline of such a copying machine. A charging corotron 2 is disposed close to the photoreceptor belt 1, and uniformly charges the surface of the belt moving in the direction of arrow 3. In the exposure section 4, an image of a document (also not shown) is transferred to the photoreceptor belt 1 using a flash lamp (not shown) or the like.
image on top. At this time, the potential of the belt surface in the portion irradiated with light changes, and an electrostatic latent image is formed. This electrostatic latent image is developed by the developing device 5, and the resulting toner image is transferred onto a sheet of paper (not shown).

In this copying machine, an electrostatic electrometer 6 is disposed between the exposure section 4 and the developing device 5. The belt surface to be measured by the electrostatic electrometer 6 is set in an area other than the area where the exposure unit 4 exposes the original. The electrostatic electrometer detects the potential of this unexposed portion, and controls the voltage applied to the charging corotron 2 and the like so that this potential is maintained at a desired value.

Now, such an electrostatic electrometer uses a vibration means that vibrates at a predetermined period, such as a tuning fork, placed close to the surface of the photoreceptor, and responds to the lines of electric force while chopping the lines of electric force by the vibrations. The potential on the surface of the photoreceptor is detected based on the magnitude of the amplitude of the potential induced. There are two methods for this detection. One is an open-loop type detection method, and the other is a closed-loop type detection method.

An open-loop type electrostatic electrometer detects the amplitude of the potential when the tuning fork is driven without applying a potential to the detection probe. On the other hand, in a closed-loop type electrostatic electrometer, a voltage is applied to the detection probe, and when there is no potential difference between it and the photoreceptor surface, the voltage applied to the detection probe is detected. voltage. The former electrostatic electrometer has a problem in that measured values vary unless the distance between the photoreceptor and the detection probe is maintained at an accurately constant distance. It is also highly dependent on the environment.
There is also the problem that the measurement results are inevitably unstable. For this reason, feedback control using a closed-loop electrostatic electrometer is attracting attention. Regarding control using a closed-loop type electrostatic electrometer, see, for example, Japanese Patent Laid-Open No. 53-67470 and Japanese Patent Laid-Open No. 56-4062.
The details are described in the publication.

FIG. 3 shows an example of such a closed loop type electrostatic electrometer.
The detection probe 11 of this electrostatic electrometer has a tuning fork 12.
and a sensor 13 that detects the amplitude of the potential induced in response to the lines of electric force interrupted by the vibration, and the tuning fork 12 is arranged facing the object to be measured (photoreceptor) 14. ing. The tuning fork 12 is driven by a tuning fork drive oscillation circuit 15 made up of an electrostrictive element. On the other hand, sensor 13
The detection output of is amplified by the AC amplifier 16,
The signal is supplied to the synchronous detector 17. The synchronous detector 17 detects the amplitude peak value of the output of the AC amplifier 16 in synchronization with the signal supplied from the tuning fork drive starting circuit 15, holds this value, and outputs it to the error amplifier 1.
Supply to 8. The error amplifier 18 adjusts the output voltage of the high voltage power supply 19 according to the level of the input signal. The output of this high voltage power supply is applied to the electrostatic electrometer case. Therefore, the error amplifier 18 controls the potential of the case of the electrostatic electrometer to match the potential of the object to be measured 14 by controlling the error to zero.

FIG. 4 shows a conventionally used high voltage power supply. This power supply boosts the voltage according to the output of the error amplifier 18 and outputs a high-voltage DC voltage V _H to the secondary side of the transformer 21 .

In the circuit shown in FIG. 3, voltage dividing resistors 23 and 24 are connected in series between the case of the electrostatic electrometer and the ground of the main body of the copying machine. As described above, the potential of the case of the electrostatic electrometer matches the surface potential of the object to be measured 14, which is a photoreceptor. Therefore, the voltage dividing resistor 23,2
4 is the voltage obtained by dividing the voltage of the object to be measured 14. This divided voltage is input to the buffer 25 and impedance converted. After this,
This is processed by a control circuit (not shown), and the voltage applied to the charging corotron 2 etc. shown in FIG. 2 is controlled to a desired value.

Note that the DC voltages -V _cc and +V _cc supplied to each part of this electrostatic potential type are obtained by rectifying the commercial power supply 26 with diodes 27 and 28 .

``Problems to be solved by the invention'' This closed-loop type electrostatic electrometer applies the same voltage to the case itself of the detection probe 11 as the voltage applied to the surface of the photoreceptor, but this voltage is normally
The voltage is high, ranging from 600 volts to 1200 volts. Therefore, it is extremely dangerous for service engineers and others to come into contact with this case and must be avoided.

For this reason, in the past, when the copier was opened, the copier's front door or cover, etc. The commercial power supply to the electrostatic electrometer has been turned on and off in conjunction with an interlock switch that detects that the electrostatic electrometer cannot operate in its current state, that is, that it is not in an interlock state. However, this caused the following problems.

Since the electrostatic electrometer was activated each time the power was turned on again, the signal obtained from the electrode placed opposite the tuning fork part became unstable each time. This is because the frequency at which the tuning fork vibrates becomes unstable at startup.

Turn on the commercial power with the interlock switch.
Since the switch is turned off, it is required to have sufficient voltage resistance, making the switch larger and more expensive.

If the tuning fork is turned on and off frequently, there is a risk that the life of the driving part for driving the tuning fork will be shortened.

Therefore, the object of the present invention is to provide an electrostatic electrometer in which the interlock switch is miniaturized and the vibrating means such as the tuning fork operates stably.

"Means for Solving Problems" The electrostatic electrometer of the present invention includes a detection probe that is placed opposite to the object to be measured and has a vibration means that vibrates at a predetermined period; A device equipped with a high-voltage power supply that applies high voltage to the probe and a feedback system that adjusts the output voltage of the high-voltage power supply so that the potential applied to the detection probe matches the potential of the measured object. The device is equipped with an interlock switch that detects that the device is not in an interlock state, and switching means that turns on and off only the output of the high voltage power supply in response to the output of the interlock switch. The switching means is constituted by, for example, a phototransistor paired with a light emitting diode, and turns on and off the output of the high voltage power supply by a potential change occurring at one end of the phototransistor. According to the present invention, only the output of the high-voltage power supply is turned on and off by the switching means, so the vibration means of the detection probe, such as the tuning fork itself, continues to vibrate, resulting in unstable startup and
It is possible to prevent the life of the driving part from being shortened. Also, the interlock switch turns on and off the commercial power supply.
Since the switching means is controlled without turning off, the withstand voltage and allowable current value of the interlock switch can be reduced. Furthermore, since the application of high voltage to the detection probe is controlled on and off in conjunction with the interlock switch, there is no risk of electric shock.

"Example" The present invention will be described in detail with reference to Examples below.

FIG. 1 shows the vicinity of the high-voltage power supply in the electrostatic electrometer of the present invention. The overall structure of this electrostatic electrometer is similar to that shown in FIG.

Now, in this electrostatic electrometer, the potential of the error amplifier 18 is applied to the base of the transistor 32 in the high voltage power supply 19 through the diode 31, and the phototransistor 33 is connected to the anode side of the diode 31.
One end is connected. The other end of this phototransistor 33 is set to the same potential as the case of the electrostatic potentiometer described above. The phototransistor 33 forms a pair with a light emitting diode 34 to constitute a so-called photocoupler 35. The anode side of the light emitting diode 34 is connected to the voltage V _DD via the resistor 36.
The cathode side is grounded via an interlock switch 37 to an earth power source that serves as a reference for the copying machine.

Now, the interlock switch 37 attached to the front door (not shown) of the copying machine used in this embodiment has its contacts open when the front door is closed, and closed when the front door is open. It is becoming. Therefore, when an operator or the like opens the front door of a copying machine, for example, to remove a jam, current flows through the interlock switch 37 to the light emitting diode 33, which lights up. As a result, the phototransistor 33 becomes conductive, and the potential on the anode side of the diode 31 becomes approximately zero. As a result, the base and emitter of the transistor 32 are short-circuited, and generation of high voltage on the secondary side of the high-voltage power supply 19 is stopped. At both ends of a capacitor 39 for smoothing the voltage rectified by the diode 38,
There is still a charge, but this is rapidly discharged by the bleeder resistor 41 connected in parallel thereto. Therefore, even if an operator or the like accidentally touches the case of the electrostatic electrometer within a relatively short period of time after the front door is opened, no electric shock will be applied.

When the front door is closed, the light emitting diode 3
4 stops its lighting, the phototransistor 33 returns to its high resistance state, and the voltage on the anode side of the diode 31 is controlled by the output of the error amplifier 18.

In the embodiment, the voltage of the floating ground is controlled using a phototransistor paired with a light emitting diode, but the light emitting element and the light receiving element are not limited to this.

"Effects of the Invention" As explained above, according to the present invention, the interlock switch can control the switching means, for example, the lighting of a light emitting diode, without turning on or off the commercial power supply. This has the advantage that the withstand voltage and allowable current value can be reduced, and it can be manufactured inexpensively and compactly. In addition, only the output of the high-voltage power supply is turned on and off by the switching means, and the swinging means itself, such as the tuning fork of the detection probe, continues to swing, so the number of activations of the swinging means is reduced, and unstable generation is prevented. This has the effect of significantly reducing the occurrence of oscillating conditions and preventing shortening of the life of the driving part.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the main parts of an electrostatic electrometer in an embodiment of the present invention, Fig. 2 is a schematic configuration diagram of a copying machine in which an electrostatic electrometer is installed, and Fig. 3 is a diagram showing the electrostatic electrometer. FIG. 4 is a circuit diagram of a conventional electrostatic electrometer. 11...detection probe, 12...tuning fork, 19...
...High voltage power supply, 33...Phototransistor, 34
...Light emitting diode, 37...Interlock switch.

Claims (1)

[Claims for Utility Model Registration] 1. A detection probe having a vibrating means that is disposed opposite to the object to be measured and vibrates at a predetermined period; a high-voltage power source that applies high voltage to the detection probe; An electrostatic electrometer comprising a feedback system that adjusts the output voltage of the high-voltage power supply so that the potential applied to the detection probe matches the potential of the object to be measured, wherein the device housing the object to be measured is connected to an interface. An electrostatic electrometer comprising: an interlock switch for detecting a non-lock state; and switching means for turning on/off only the output of the high voltage power supply in response to the output of the interlock switch. 2. The switching means is composed of a phototransistor paired with a light emitting diode, and the output of the high-voltage power supply is turned on and off by a potential change occurring at one end of the phototransistor. An electrostatic electrometer according to claim 1 of the utility model registration claim.