JPH06109786A - Surface electrometer - Google Patents

Abstract

PURPOSE:To provide a compact and highly precise surface electrometer capable of protecting a signal from a receiving electrode against the interference of an electrical signal for driving a physical vibration means. CONSTITUTION:A receiving electrode faced to a measurement object, a physical vibration means to cause the fluctuation of field distribution intensity between the electrode and the object with the elapse of time, an initial-stage impedance conversion circuit for sending a micro-amount of current induced in the electrode to a post-stage as detected voltage, are respectively formed on a printed circuit board 5, thereby constituting a surface electrometer. In this case, the range of the initial-stage impedance conversion circuit formed on the board 5 is covered with an insulation sheet 16 made out of an insulation sheet body 19 applied with conductive paint 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface electrometer for measuring the surface potential of an object in a non-contact manner, which is mounted on an electrophotographic apparatus such as a copying machine for measuring the surface potential of a photoconductor. It relates to a surface electrometer.

[0002]

2. Description of the Related Art As a non-contact type surface electrometer, a conductive vibrating object is placed between an object and a receiving electrode, and the amount of electric force rays incident on the receiving electrode is vibrated to examine the electric field strength. A so-called chopper method, a vibrating capacitance method in which the receiving electrode itself is physically vibrated, and the electric field distribution between the target object and the receiving electrode is vibrated to check the electric field strength have been devised. Here, the chopper method will be described in more detail, but the same applies to the signal receiving process even in the vibration capacitance type.

FIG. 7 is a perspective view of a main part showing an outline of a conventional chopper type surface electrometer. Reference numeral 1 is a receiving electrode for receiving electric force lines from the object, 2 is a tuning fork for chopping electric lines of force incident on the receiving electrode 1 from the object, and 3 is impedance conversion of a weak AC signal induced in the receiving electrode. For amplification, 4 is a piezoelectric element that gives vibration to the tuning fork,
Reference numeral 5 is a circuit board, 6 is a connector for connecting a drive signal, a reception signal and a power source to the piezoelectric element 4, 7 is an incident direction of a line of electric force, and 8 is a chopping direction.

FIG. 8 is a perspective view of a shield case in which the circuit board 5 shown in FIG. 7 is inserted. Reference numeral 9 is the shield case, and 10 is a window through which the lines of electric force from the object to be measured are incident.

FIG. 9 is a circuit diagram showing an outline of a first-stage impedance circuit formed on the circuit board 5. As shown in the figure, impedance conversion is performed by a source follower circuit including a field effect transistor (hereinafter referred to as FET) having an input resistance 11 of 20 MΩ.

The operation of the surface electrometer having the above structure will be described.

First, the piezoelectric element 4 and the tuning fork 2 are brought into a resonance state by a piezoelectric element drive signal supplied from the outside, and a physical / mechanical vibration is generated in a chopping direction shown by an arrow 8. Then, the window 10 of the shield case 9 from the target object
The amount of the lines of electric force passing through and entering the receiving electrode 1 increases or decreases according to the vibration. As a result, the receiving electrode 1 and the input resistance 1
A weak AC induced current is generated at 1, and this is applied to the FET gate as a voltage signal. Since the FET circuit is a source follower circuit, impedance conversion with an amplification factor of 1 is performed and a voltage signal is output from the source. This signal is transferred to an external signal processing circuit (not shown) through the connector 6 for post-processing. Various methods have been devised for finally deriving the surface potential from the output signal, but since they are not the subject here, they will not be described. Since the magnitude of this output signal is proportional to the magnitude of the potential of the object, how to transmit the first-stage amplified signal with a high S / N ratio to the post-processing circuit determines the basic performance of the surface electrometer. Become.

[0008]

In recent years, demands for downsizing of devices have been increasing in a wide range of fields, and even for a surface electrometer mounted on a copying machine, for example, due to the problem of installation space, it is more important. It is required to be small and thin. The biggest problem in miniaturization is that the ratio of the drive signal for generating mechanical vibration that causes the piezoelectric element 4 and the tuning fork 2 to resonate into the signal from the receiving electrode 1 increases. Since the input signal component from the measurement object and the mixed component from the drive signal have the same frequency as a matter of course, it is difficult to separate them and the measurement accuracy is degraded.

The driving signal mixing paths are mainly considered to be direct incidence from the air, a conductive path through the surface of the substrate, and indirect incidence by charging an insulator on the substrate. Among these, the effect of charging the insulator on the substrate is an amount that cannot be ignored in realizing a high-performance electrometer, and in particular, indirect incidence on the resist near the first-stage amplifier circuit tends to be a problem. However, when the impedance of the input circuit of the first-stage amplifier circuit decreases due to the frequency, etc., it causes a decrease in the amount of a pure signal, and therefore an overcoat with a resist is essential.

FIG. 10 is an explanatory diagram showing an outline of the input circuit pattern. The hatched portion 12 is a shield, 13 is a printed resistor, 14 is a circuit pattern land, and 15 is a resist portion surrounded by an alternate long and short dash line.

Generally, since the input resistance needs to be as high as 10 M to 100 MΩ, the printing of the input resistance portion is formed in a ladder shape as shown in FIG. Therefore, the area ratio in the input portion is high, and most of the indirect mixing through the resist surface is from the input resistance portion of the first-stage impedance conversion circuit.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and is small in size and highly accurate in which signals from the receiving electrodes are prevented from being mixed with electrical signals for driving the physical vibrating means. The purpose of the present invention is to provide a surface electrometer.

[0013]

Therefore, the surface electrometer according to the present invention is a physical unit that temporally changes the intensity of the electric field distribution between the receiving electrode facing the measuring object and the receiving electrode and the measuring object. Is a surface electrometer formed on a circuit board by a dynamic vibration means and a first-stage impedance conversion circuit for sending a minute current induced in the receiving electrode as a detection voltage to a subsequent stage, the first-stage impedance conversion circuit formed on the circuit board. The circuit area is covered with an insulating sheet, and a shield member is overlaid on the insulating sheet, or the circuit board is formed of an alumina substrate, and the input resistance of the first stage impedance conversion circuit is the physical resistance. Formed by a thick film resistor printed on the surface opposite to the surface of the circuit board on which the dynamic vibrating means is installed, and the circuit board is shielded through a resist member or an insulating sheet. The mounting and comprising a configuration in Rudokesu, is intended to achieve the above object.

[0014]

With the above construction, the range of the first-stage impedance conversion circuit formed on the circuit board is covered by the insulating sheet and the shield member further stacked thereon, or the input resistance of the first-stage impedance conversion circuit is The physical vibrating means is formed by a thick film resistor printed on the surface opposite to the surface of the circuit board, and the circuit board is mounted in a shield case through a resist member or an insulating sheet. It is possible to prevent the electric signal for driving the mechanical vibrating means from directly mixing into the first-stage impedance conversion circuit or indirectly mixing by charging, and the electric signal for driving the physical vibrating means does not mix with the signal from the receiving electrode. A small and highly accurate surface electrometer can be configured.

[0015]

EXAMPLES The surface electrometer according to the present invention will be described below with reference to examples.

FIG. 1 is a sectional view showing an essential part of the first embodiment, and the same or corresponding parts as those of the conventional surface electrometer are designated by the same reference numerals and their duplicate description will be omitted. The structure other than that shown is based on the structure of the conventional surface electrometer.

5 is a circuit board, 18 is a board body, 1
Reference numeral 7 indicates a circuit forming layer including a wiring pattern, a printing resistor and a resist. Reference numeral 16 denotes an insulating sheet, which is formed by applying a conductive coating material 20 on the insulating sheet main body 19. Reference numeral 26 is a screw for fixing the substrate to the shield case 9, and the conductive paint surface 29 on the insulating sheet body 19 is connected to the shield potential by the screw 26.

FIG. 2 is a plan view showing the outline of the insulating sheet of the first embodiment. 21 is a cutout for receiving electrodes, 22 is a tuning fork drive signal extraction, 23 is an amplifying element, and 24 is a connector. Shows a hole. This insulation sheet 1
By installing 6 on the circuit board 5 as shown in the cross-sectional view of FIG. It can be prevented from being mixed in and the S / N ratio is improved.

(Second Embodiment) The first embodiment described above is an example in which the input resistance portion is formed on the upper surface of the circuit board on which the tuning fork, the amplifying element, etc. are mounted. It is formed on the lower surface side of the circuit board 5.

FIG. 3 is an explanatory view showing the outline of the circuit pattern.

As shown in FIG. 3, the circuit pattern on the upper surface of the circuit board 5 immediately goes from the land for the receiving electrode 1 to the lower surface through the through hole, and a ladder-type resistor similar to the conventional example is printed and formed on the lower surface. .

By forming the resistance pattern on the lower surface, the resist area of the input portion on the upper surface is reduced as compared with the conventional case. Further, since the upper surface corresponding to the resistance portion formed on the lower surface of the circuit board 5 is a shield surface, the mixing of the drive signal is minimal in both direct incident mixing and indirect incident mixing.

However, on the lower surface of the circuit board 5, if there is a risk that the resistance printed portion may short-circuit with the shield case 9, for example, if the resist thickness is thin, or if there is an exposed portion due to trimming by resistance value adjustment, the circuit is further When the capacitance between the portion and the shield case 9 becomes a problem, the thickness of the insulating sheet 19 shown in the plan view of FIG. 4 is optimized,
As shown in the cross-sectional view of FIG. 5, by laying it on the lower surface of the circuit board 5 and fixing it to the shield case 9, it is possible to prevent mixing of drive signals and short circuit to the shield case 9.

(Third Embodiment) FIG. 6 is a sectional view of the essential parts of a third embodiment of the present invention.

The third embodiment is characterized in that the insulating sheet body 19 is first placed on the circuit board 5, and then the conductive sheet 27 is placed on the insulating sheet body 19. According to. And it has the same effect as the above-mentioned embodiment.

[0026]

As described above, according to the present invention, since the range of the first-stage impedance conversion circuit formed on the circuit board is covered by the insulating sheet and the shield member further stacked thereon, The input resistance of the first stage impedance conversion circuit is formed by a thick film resistor printed on the surface opposite to the surface of the circuit board on which the physical vibrating means is installed, and the circuit board is placed in a shield case through a resist member or an insulating sheet. With the configuration configured to be attached to, it is possible to prevent the electric signal for driving the physical vibrating means from being directly mixed into the first-stage impedance conversion circuit or indirectly mixed by charging, and the physical vibrating means is added to the signal from the receiving electrode. It is possible to provide a small-sized and high-precision surface electrometer without mixing of an electric signal for driving.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of a first embodiment.

FIG. 2 is a plan view of the insulating sheet of the first embodiment.

FIG. 3 is an explanatory diagram of a circuit pattern according to a second embodiment.

FIG. 4 is a plan view of an insulating sheet according to a second embodiment.

FIG. 5 is a sectional view of an essential part of a second embodiment.

FIG. 6 is a cross-sectional view of essential parts of a third embodiment.

FIG. 7 is a perspective view of a main part of a conventional surface electrometer.

FIG. 8 is a perspective view of a shield case of a conventional surface electrometer.

FIG. 9 is a circuit diagram of a first-stage impedance circuit.

FIG. 10 is an explanatory diagram of an input portion circuit pattern of a conventional surface electrometer.

[Explanation of symbols]

 1 Receiving Electrode 2 Tuning Fork 3 Amplifying Element 4 Piezoelectric Element 5 Circuit Board 7 Incident Direction of Electric Force Line 8 Chopping Direction 9 Shielding Case 16 Insulating Sheet 17 Circuit Forming Layer of Circuit Board 18 Board Body 19 Insulating Sheet Body 20 Conductive Paint

Claims (2)

[Claims] 1. A receiving electrode facing a measurement object, a physical vibrating means for temporally varying an electric field distribution intensity between the reception electrode and the measurement object, and a minute current induced in the reception electrode is detected. A surface electrometer in which a first-stage impedance conversion circuit for sending to the latter stage as a voltage is formed on a circuit board, and the range of the first-stage impedance conversion circuit formed on the circuit board is covered with an insulating sheet, A surface electrometer, which is formed by covering and covering a shield member. 2. A receiving electrode facing a measurement object, a physical vibrating means for temporally varying an electric field distribution intensity between the reception electrode and the measurement object, and a minute current induced in the reception electrode is detected. A surface electrometer in which a first-stage impedance conversion circuit for sending as a voltage to a subsequent stage is formed on a circuit board, wherein the circuit board is formed of an alumina substrate, and the input resistance of the first-stage impedance conversion circuit is the physical vibration means. A surface electrometer formed by a thick film resistor printed on the surface opposite to the surface of the circuit board to be installed, and the circuit board is mounted in a shield case via a resist member or an insulating sheet. .