JPH09138255A - Potential detection apparatus and sensor probe used for it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a potential detection apparatus in which outputs of a plurality of sensor probes can be changed over so as to be used and in which the influence of a noise due to their changeover can be excluded. SOLUTION: One pair of sensor probes SP1 , SP2 are arranged in connection with a light-sensitive body 30. Respective AC amplifiers are built in the sensor probes SP1 , SP2 . One out of output signals of the sensor probes SP1 , SP2 is selected by a changeover device 90 so as to be input to a detection circuit 50 for a potential sensor. Since the output signals of the sensor probes SP1 , SP2 are comparatively large currents, they are not subjected to a large influence due to a noise when the changeover device 90 is change over.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in, for example, an image forming apparatus for forming an image according to an electrophotographic process, and is used for measuring the surface potential of a photoconductor, and a sensor probe used therefor. Regarding

[0002]

2. Description of the Related Art A copying machine that forms a copy image of an original according to an electrophotographic process includes, for example, a drum-shaped photosensitive member. The surface of the photoconductor is uniformly charged by the main charger and then exposed by the reflected light from the document, whereby an electrostatic latent image corresponding to the reverse image of the document is formed on the surface of the photoconductor. This electrostatic latent image is transferred to a copy sheet after being developed into a toner image by a developing device. The toner particles transferred to the copy sheet are heated and pressed by the fixing device and fixed on the copy sheet.

In order to stably form an image, it is necessary to appropriately control the surface potential of the photoconductor. Therefore, a surface potential sensor is arranged in relation to the photoconductor in the above copying machine. There are various types of surface potential sensors, but the high voltage feedback type has the most excellent characteristics in terms of detection accuracy and output stability.

FIG. 4 is a block diagram showing a general structure of a high-voltage feedback type surface potential sensor. The sensor probe 1 arranged in proximity to the photoconductor as the object to be measured is configured by housing the tuning fork 2 and the impedance conversion circuit 3 in a shield case 5. The tuning fork 2 is for changing the electrostatic capacitance between the measurement object and the detection electrode DE by vibrating the detection electrode DE arranged to face the measurement object. A signal corresponding to the change in the electrostatic capacitance is given to the AC (alternating current) amplifier circuit 6 in the potential sensor detection circuit 15 via the impedance conversion circuit 3. As a result, the signal component corresponding to the vibration frequency of the tuning fork 2 is extracted.

The output signal of the AC amplifier circuit 6 is supplied to the amplifier circuit 7
The signal is further amplified by and then detected by the detection circuit 8. The detection circuit 8 is connected to a drive circuit 9 for driving the tuning fork 2, and synchronously detects the signal component of the vibration frequency of the tuning fork 2. The output of the detection circuit 8 is converted into a DC voltage by the rectifier circuit 10 and then input to the high voltage amplifier circuit 11. The high-voltage amplifier circuit 11 uses the oscillation signal from the oscillation circuit 12 to generate a high-voltage signal corresponding to the output signal of the rectifier circuit 10. As a result, the high voltage amplifier circuit 11 creates a high voltage signal equal to the potential of the measured object. This high voltage signal is level-converted by the voltage dividing circuit 13 into an appropriate voltage,
It is used as a detection signal by being input to a microcomputer or the like.

On the other hand, the high voltage signal output from the high voltage amplifier circuit 11 is used as a float potential which is a reference voltage of a circuit on the probe 1 side of the high voltage amplifier circuit 11. further,
This float potential is fed back to the shield case 5 of the sensor probe 1. The feedback of the float potential stabilizes the detection signal and enables highly accurate potential detection. More specifically, detection with excellent linearity, distance characteristics, and environmental characteristics can be performed.

[0007]

In order to accurately control the image density in a copying machine, for example, the potential immediately before and immediately after the photosensitive member is exposed by the reflected light from the original may be detected. In this case, a pair of sensor probes are arranged before and after the exposure position. A potential sensor detection circuit is provided for each sensor probe. That is, two potential sensor detection circuits are required.

As described above, in order to accurately control the potential of the photoconductor, not only the sensor probe but also a plurality of potential sensor detection circuits are required, so that a large increase in cost cannot be avoided. Therefore, it is possible to switch and input the output signals of the plurality of sensor probes to one potential sensor detection circuit. However, the sensor probe generally has a high impedance and outputs only a weak current signal. Therefore, it is unrealistic to switch and use a plurality of sensor probes because it is greatly affected by noise accompanying switching of input signals.

Further, in order to protect the weak current signal output from the sensor probe from noise, a shield wire is used for the wiring between the sensor probe and the potential sensor detection circuit. This has also been a factor in increasing costs. Therefore, an object of the present invention is to solve the above-mentioned technical problem, to provide an electric potential detecting device capable of switching and using the outputs of a plurality of sensor probes and eliminating the influence of noise accompanying the switching. It is to be.

Another object of the present invention is to provide a sensor probe which can reduce the influence of noise on the output signal and therefore the cost required for wiring.

[0011]

In order to achieve the above object, the invention according to claim 1 is to provide a plurality of sensor probes to be arranged in relation to an object to be measured, and output signals of the plurality of sensor probes. A plurality of amplifying circuits for amplifying each of the two, and one of output signals of the plurality of amplifying circuits
And a signal processing circuit which processes the signal selected by the selecting means and outputs a detection signal corresponding to the potential of the object to be measured. Is.

According to the above configuration, the output signals of the plurality of sensor probes are first amplified, respectively, and then one of them is selected by the selection means and input to the signal processing circuit. In other words, even if the signal is switched by the selection means, the signal to be switched is the signal after being amplified by the amplifier circuit, so that it is not significantly affected by noise accompanying switching.

According to a second aspect of the present invention, there is provided the potential detecting device according to the first aspect, wherein the plurality of amplifier circuits are respectively incorporated in the plurality of sensor probes. According to this configuration, the amplifier circuit is built in the sensor probe. Therefore, since the signal amplified by the amplifier circuit is output from the sensor probe, the influence of external noise is small, and the wiring connection between the sensor probe and the selection means requires expensive wiring such as a shielded wire. Never be done.

According to a third aspect of the present invention, there is provided a sensor probe to be arranged in association with an object to be measured which is a potential detection target, and a signal generating means for generating a signal corresponding to the potential of the object to be measured. A sensor probe comprising: an amplification circuit for amplifying a signal generated by the signal generation means; and a holding means for integrally holding the signal generation means and the amplification circuit.

According to this structure, the signal generating means and the amplifying means are integrally held by the holding means. Therefore, since the signal amplified by the amplifier circuit is output from the sensor probe, there is no concern that this output signal is greatly affected by external noise. Therefore, the wiring between the sensor probe and the signal processing circuit for processing the output signal of the sensor probe does not require expensive wiring such as a shielded wire.

Further, even when the output signals of a plurality of sensor probes are switched and used, the influence of noise due to the switching is reduced, so that a plurality of sensor probes can be associated with one signal processing circuit. Become.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described.
This will be described in detail with reference to the accompanying drawings. FIG. 1 is a sectional view showing an internal configuration of a copying machine to which an embodiment of the present invention is applied. This copier uses the original D
It is an analog copier that forms a copy image of the above on a copy sheet. The original to be copied is an original table 20 made of a transparent plate.
Placed face down. A scanning optical system 21 is provided below the document table 20.

The scanning optical system 21 is provided with a linear light source 22 which is displaced along the document table 20 and scans the document D while illuminating it. The reflected light from the document D is reflected by the reflection plates 23, 24,
It is guided to the surface of the drum-shaped photoconductor 30 by 25 and 26. Between the reflection plate 25 and the reflection plate 26, a lens 27 for forming an optical image of the document D on the photoconductor 30,
A light amount sensor 28 for detecting the amount of light reflected from the document D is provided.

The photosensitive member 30 is rotated at a constant speed in the clockwise direction in the figure in synchronization with the scanning of the document D by the scanning optical system 21. The surface of the photoconductor 30 before being exposed by the reflected light from the document D is uniformly charged by the main charger 31. Therefore, an electrostatic latent image corresponding to the original image is formed on the surface of the photoconductor 31 after being exposed by the reflected light from the original D. This electrostatic latent image is developed into a toner image by the developing device 32. The toner image formed on the surface of the photoconductor 31 is transferred to the copy paper P by the action of the transfer charger 33. The surface of the photoconductor 30 after the transfer of the toner image is cleaned by the cleaning device 34 to be prepared for the next copying.

The copy paper P is taken out from the paper feed cassette 35 and conveyed toward the transfer charger 33. The copy paper P on which the toner image is transferred is separated from the photoconductor 30 by the action of the separation charger 36, and is further guided to the fixing device 37. The fixing device 37 heats and pressurizes the copy paper P to fix the toner particles on the paper. As a result, copying of the document D is achieved.

The developing device 32 has a developing sleeve 32a for adhering toner to the photosensitive member 30. A developing bias voltage is applied to the developing sleeve 32a from a developing bias generating circuit 38 having a built-in high voltage generating circuit. By changing the developing bias voltage, it is possible to control the toner adhesion amount, so that the toner image density can be adjusted.

First and second surface potential sensor probes SP ₁ and SP ₂ are located in the vicinity of the photoconductor 30 and before and after the exposure position EP by the reflected light from the document D.
Are arranged respectively. First surface potential sensor SP
₁ detects the surface potential of the photoconductor 30 immediately after being charged by the main charger 31 and before being exposed by reflected light. On the other hand, the second surface potential sensor SP ₂
Detects the surface potential of the photoconductor 30 immediately after being exposed by the reflected light from the document D and before being subjected to the developing process by the developing device 32.

Each of the first and second surface potential sensor probes SP ₁ and SP ₂ has an AC amplifier as an amplifier circuit therein, as will be described later. The output signal amplified by this AC amplifier is output to lines 81 and 8
It is inputted to the switch 90 as a selection means via each of the two. The switch 90 is composed of an analog switch or a relay, and selects and outputs one of the output signals of the sensor probes SP ₁ and SP ₂ based on the switching control signal from the control circuit 70.

The output signal of the switch 90 is input to the potential sensor detection circuit 50 corresponding to the signal processing circuit. The potential sensor detection circuit 50 is a sensor probe SP.
_The detection signals corresponding to the outputs of ₁ and SP ₂ are created and input to the control circuit 70 including the microcomputer. The control circuit 70 controls each part of the copying machine, and particularly controls the light amount of the light source 22 and the main charger 31 to control the surface potential of the photoconductor 30 for controlling the toner image density. Or developing bias generation circuit 3
8 to control. Reference numeral 39 denotes a density sensor for detecting the toner image density on the surface of the photoconductor 30.

During the copying operation or the image density adjusting process for adjusting the image density, the photoconductor 30 is rotated along with the scanning of the document D by the scanning optical system 21, and the main charger 31 and the developing device 32 work. The image forming process is executed. At this time, the control circuit 70 first generates a switching control signal for connecting the switching device 90 to the sensor probe SP ₁ side, for example. As a result, the photoconductor 30 before being exposed by the reflected light of the document D
A signal representing the surface potential at one or more points on the surface of
It is input from the potential sensor detection circuit 50 to the control circuit 70, and the surface potentials at these points are detected. Control circuit 70
Next generates a switching control signal for switching the switch 90 to the sensor probe SP ₂ side. As a result, the photoconductor 30 after being exposed by the reflected light of the document D
A signal representing the surface potential at one or more points on the surface of
It is input from the potential sensor detection circuit 50 to the control circuit 70.

Thus, for example, the surface potentials before and after the exposure can be detected at exactly the same point on the surface of the photoconductor 30. As a result, the control circuit 70 can more appropriately control the image density as compared with the case where the surface potential before or after exposure is detected. FIG. 2 is an illustrative view for explaining the configurations of the sensor probes SP ₁ and SP ₂ . Sensor probe SP
₁ and SP ₂ have a common configuration, and include a shield case 41 arranged in proximity to the photoconductor 30 that is the object to be measured. A tuning fork 48 oscillated by the pair of oscillators 42 is housed in the shield case 41. The detection electrode 43 is fixed to the tuning fork 48. The detection electrode 43 is arranged so as to face a hole 47 formed in the shield case 41 and faces the photoconductor 30.

The detection electrode 43 is connected to the impedance conversion circuit 44. Impedance conversion circuit 44
Is a detection resistor 45 connected in series to the detection electrode 43.
And a field effect transistor 46 to which the voltage generated by the detection resistor 45 is input. When the distance between the detection electrode 43 and the photoconductor 30 changes due to the vibration of the tuning fork 48, the capacitance between the two changes. A current corresponding to this change in capacitance flows through the detection resistor 45, so a voltage corresponding to this current is input to the transistor 46. As a result, the transistor 46 outputs a signal corresponding to the change in the capacitance. By processing this signal, the potential of the photoconductor 30 can be measured. As described above, the tuning fork 48, the detection electrode 43, the impedance conversion circuit 44, and the like constitute signal generation means for generating a signal corresponding to the potential of the measured object.

The output signal of the impedance conversion circuit 44 is further input to the AC (alternating current) amplifier 40 composed of an operational amplifier or the like via the coupling capacitor C1 and amplified. And this amplified signal is
It is transmitted to the switch 90 using appropriate wiring. The coupling capacitor C1 and the AC amplifier 40 are built in the shield case 41, and thus are integrally held together with the other components of the sensor probes SP ₁ and SP ₂ .

FIG. 3 processes the signal from switch 90.
Block diagram showing the configuration of the potential sensor detection circuit 50 for
FIG. The output signal of the switch 90 is a synchronous detection circuit.
It is detected by 52. The synchronous detection circuit 52 includes a sensor
Suprobe SP₁And SP _TwoOscillate the tuning fork 48
Tuning fork drive circuit for driving the oscillator 42 for driving at a constant frequency
The signal from 53 is given. This enables synchronous detection
The wave circuit 52 uses the tuning fork 4 among the output signals of the switch 90.
The signal with the oscillation frequency of 8 is extracted.

The output signal of the synchronous detection circuit 52 is the rectification circuit 5
4 converts into a DC voltage signal. The output signal of the rectifier circuit 54 is input to the high-voltage amplifier circuit 55 via the photocoupler PC. The high voltage amplifier circuit 55 includes an oscillator circuit 56.
From the photocoupler PC to amplify the signal from the photocoupler PC to generate a high voltage equal to the potential of the photoconductor 30 (measurement object). The high voltage signal is level-converted by the voltage dividing / buffer circuit 57 to an appropriate level and then input to the control circuit 70 (see FIG. 1) as a detection signal.

The high voltage signal generated by the high voltage amplifier circuit 55 is
It is fed back to the sensor probe 40 as a float potential from the line 60 via the power supply circuit 59. More specifically, as shown in FIG. 2, a float potential is applied to the shield case 41 of the sensor probe 40. The float potential is from the photocoupler PC to each circuit 51, 52, 53, 5 on the sensor probe 40 side.
4 is used as a reference voltage. These circuits 5
1, 52, 53, 54 operate by the float potential and the voltage created by the power supply circuit 59. The power circuit 59 is
Generates positive and negative voltages based on the float potential. The positive voltage is, for example, 15 V higher than the float potential, and the negative voltage is, for example, 15 V lower than the float potential.

On the other hand, each circuit 55, 56, 57 on the output side of the photocoupler PC has a circuit configuration in which the ground potential (GND) is used as a reference voltage. The tuning fork drive circuit 53
Output signal and float potential of both sensor probes SP ₁ and SP regardless of the switching of the switch 90.
_Is given to ₂ . However, switching devices may be provided for the output signal of the tuning fork drive circuit 53 and the float potential, and the switching may be controlled by the control circuit 70 so that these switching devices are interlocked with the switching of the switching device 90.

As described above, according to this embodiment, each of the sensor probes SP ₁ and SP ₂ has the AC amplifier 40 built therein. Therefore, the sensor probe SP
The output signals of ₁ and SP ₂ are relatively large current signals. Therefore, even if noise is generated when the switch 90 is switched, the noise has little effect on the output signals of the sensor probes SP ₁ and SP ₂ , and the detection accuracy is not significantly deteriorated. In this way, the two sensor probes SP ₁ and SP ₂ can be associated with one potential sensor detection circuit 50, and since the detection accuracy does not deteriorate, there is no significant increase in cost. The image density can be controlled extremely appropriately.

Further, the sensor probes SP ₁ and SP
_Since the output signal of ₂ is a relatively large current signal, it is not necessary to take noise countermeasures on the lines 81 and 82 (see FIG. 1) connecting the sensor probes SP ₁ and SP ₂ and the switch 90. Therefore, expensive wiring such as a shield wire is not required, and the cost can be reduced.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, in the description of the above embodiment, an example in which the present invention is applied to a high-voltage feedback type potential detection device that feeds back a float potential equal to the potential of the object to be measured to the sensor probe has been described. It is also applicable to an analog-type potential detecting device that does not perform the above feedback. Also in this case, by providing the sensor probe with an AC amplifier, the outputs of the plurality of sensor probes can be controlled by the switching device.
Can be input to the detection circuit for the electric potential sensor, and
No expensive wiring such as a seed line is required.

Further, although two sensor probes are used in the above embodiment, the outputs of three or more sensor probes may be selectively input to the potential sensor detection circuit. Needless to say. Further, in the above embodiment, the AC amplifier is built in the sensor probe, but the AC amplifier does not necessarily have to be built in the sensor probe, and may be inserted on the sensor probe side of the switch 90. . For example, a conventional sensor probe may be used as it is, and an AC amplifier may be provided near the switch 90. However, in this case, it is preferable to take measures against noise in the wiring from the sensor probe to the AC amplifier, for example, it is preferable to use a shield wire. If the AC amplifier is arranged near the sensor probe, the length of the shield wire can be shortened.

Further, in the above-mentioned embodiment, the case where the surface potential of the photoconductor in the copying machine is detected is taken as an example. However, the potential sensor detection circuit of the present invention detects the potential distribution of the printed wiring board, for example. It can be applied to other arbitrary uses such as detection. In addition, it is possible to make various design changes within the technical scope described in the claims.

[0038]

According to the invention described in claim 1, since the output signals of the plurality of sensor probes are respectively amplified, even if the signals are switched by the selecting means, they are greatly affected by the noise accompanying the switching. There is no. Therefore, a plurality of sensor probes can be switched and used while eliminating the influence of noise accompanying switching. Therefore, the cost required to detect the potential at a plurality of different locations can be significantly reduced.

According to the second or third aspect of the invention, since the amplifier circuit is built in the sensor probe, the output of the sensor probe is not significantly affected by external noise. Therefore, the wiring related to the sensor probe does not require expensive wiring such as a shielded wire, so that the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is an illustrative view showing an internal configuration of a copying machine to which a potential detecting device according to an embodiment of the present invention is applied.

FIG. 2 is an illustrative view for explaining a configuration of a sensor probe of a surface potential sensor.

FIG. 3 is a block diagram for explaining a configuration of a potential sensor detection circuit.

FIG. 4 is a block diagram showing a configuration of a conventional detection circuit for a high-voltage feedback type surface potential sensor.

[Explanation of symbols]

SP ₁ , SP ₂ Sensor probe 30 Photoconductor 40 AC amplifier 41 Shield case 42 Oscillator 43 Detection electrode 44 Impedance conversion circuit 48 Tuning fork 50 Potential sensor detection circuit 70 Control circuit 81, 82 Wiring 90 Switcher

Claims (3)

[Claims] 1. A plurality of sensor probes to be arranged in relation to an object to be measured, a plurality of amplifier circuits for respectively amplifying output signals of the plurality of sensor probes, and a plurality of output signals of the plurality of amplifier circuits. And a signal processing circuit for processing the signal selected by the selecting means and outputting a detection signal corresponding to the potential of the object to be measured. Potential detection device. 2. The potential detecting device according to claim 1, wherein the plurality of amplifier circuits are respectively incorporated in the plurality of sensor probes. 3. A sensor probe to be arranged in association with an object to be measured, which is a target of potential detection, and a signal generating means for generating a signal corresponding to the potential of the object to be measured, and the signal generating means. A sensor probe comprising: an amplification circuit for amplifying a generated signal; and a holding means for integrally holding the signal generation means and the amplification circuit.