JPH0616059B2 - Surface electrometer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface electrometer, and more particularly to a surface electrometer for measuring the electric potential of an object to be measured such as the surface of a photoconductor of a copying machine or the like.

2. Description of the Related Art Generally, a photoconductor using a photoconductive material used in an electrophotographic machine or the like is susceptible to sensitivity shift due to aging or the like.
Therefore, a method is known in which a means for controlling the surface potential of the photoconductor is added to compensate for this sensitivity shift and the surface potential is constantly set within a certain range.

For this purpose, a surface electrometer that measures the potential on the surface of the photoconductor is used.

As the surface electrometer, by intermittently shielding the electric field generated between the measured object and the potential measuring electrode arranged opposite thereto, an amplitude proportional to the voltage difference between the measured object surface and the measuring electrode is measured. A structure has been proposed in which an alternating current signal is induced in a measurement electrode and the surface potential is known by this.

Such a surface electrometer is composed of a potential measuring electrode circuit and a chopping means for intermittently shielding between the measuring electrode and the object to be measured, both of which are made of a metal for preventing an external electric field and noise. It is covered by a shield.

The metal shield is provided with a measurement window for potential measurement, which is arranged so as to face the measured portion of the photoconductor, and the potential of the photoconductor is measured through this measurement window.

Although a DC motor has been proposed as the chopping means, a method using a piezoelectric element has been proposed because it is small and can be easily manufactured.

In a surface electrometer having a structure using such a piezoelectric element, the external electric field and noise can be suppressed by the above-mentioned shield, but the potential new obtained from the measurement electrode corresponding to the surface potential of the DUT is very small. Since it is minute, the signal for driving the piezoelectric element is superposed on the potential signal.

Further, the above-mentioned chopping means is created independently of the mounting board, and the lead wire portion is soldered after being fixed to the board by screws or the like during assembly, which makes the work extremely troublesome and complicated. There was a drawback.

The present invention has been made to eliminate the above-mentioned conventional drawbacks, and a surface capable of accurately measuring the electric potential of the object to be measured without being influenced by the drive signal of the chopping means. It is intended to provide an electrometer.

A further object of the present invention is to provide a surface electrometer capable of simplifying the assembly process.

Examples Hereinafter, details of the present invention will be described based on examples shown in the drawings.

1 to 4 illustrate one embodiment of the present invention.
Reference numeral 1 in each figure denotes an outer shield housing, which is fixed to the printed board 4 by screws 1a.

Inside this outer shield housing 1 is an inner shield housing 2
Is arranged, and the measurement electrode 3 is arranged inside this.

On the other hand, the reference numeral 5 is a vibrator that constitutes chopping means in the shape of a U-shaped tuning fork as a whole, and piezoelectric elements 6 and 6 are fixed above and below the bent side of the vibrator 5. There is.

The vibrator 5 is fixed to the mounting substrate side indicated by reference numeral 7.

On the free end side of the vibrator 5, a flat surface portion 5a included in a vertical plane is formed as shown in an enlarged view in FIGS. 2 and 3, and the flat plate portion 5a is on the front surface side of the measurement electrode 3. It is arranged in parallel with.

A pin 5b is projectingly provided on the base end side of the vibrator 5.

The pin 5b is fitted to the mounting board 7 side as shown in FIG. 3, then bent downward as shown in FIG. 2, and protrudes downward from the lower end of the mounting board 7.

Further, lead pins 8 and 9 are embedded in the mounting substrate 7, and are bent downward similarly to the pin 5b. The lead pins 8 and 9 and the piezoelectric elements 6 and 6 are connected by lead wires. The lead pins 8 and 9 are connected to the pattern side of the Punlith substrate 4.

The outer shield housing 1 is also attached in a state of being in contact with the ground pattern side of the printed circuit board 4 by the screw 1a. Further, a window 1b is formed at a position corresponding to the measured side of the outer shield housing 1.

It should be noted that what is denoted by reference numeral 10 in FIG. 4 is an FET (field effect transistor), which constitutes a part of the amplifier circuit.

In order to perform the potential measurement with the above-mentioned structure, when a voltage is applied to the piezoelectric elements 6 and 6 in the vertical direction in FIG.

Due to this distortion, each bifurcated side of the vibrator 5 causes vertical vibration in FIG.

The vibrator 5 itself is grounded as described above, and when the vibrator vibrates immediately before the measurement electrode 3 as shown by the arrow in FIG. 4, the total area of the electric field applied to the measurement electrode 3 through the window 1b changes. An AC signal having the same frequency as the vibration frequency of the vibrator 5 and having an amplitude proportional to the potential difference between the object to be measured (not shown) and the measurement electrode 3 is induced on the measurement electrode 3 side.

Since the present embodiment is configured as described above, the electric field enters the outer shield housing through the window 1b and reaches the measurement electrode, but the outer seal housing 1 contacts the earth pattern of the printed circuit board 4. Therefore, it does not affect other parts in the outer shield housing 1.

Furthermore, the inner shield housing 2 is connected to the measurement electrode 3 and the FET 1.
Since the circuit side including 0 is covered, the superposition of the piezoelectric element drive signal on the potential signal can be suppressed even if the AC potential signal induced in the measurement electrode 3 is too small.

Further, the vibrator 5 is mounted on the mounting board 7, and the pin 5b and the lead pins 8 and 9 project from the mounting board 7 side. Therefore, these pins are used to mount the mounting board 7 to the printed circuit board 4 side. Mounting, other transistors such as transistors and resistors are also mounted on the printed circuit board 4 side, and if the lead wires between the lead pins 8 and 9 and the piezoelectric element 6 are stretched and passed through the solder bath, 1 The mechanical work of fixing each part to the printed circuit board, the connection to the printed pattern, and the soldering work of the lead wire are completed by the repeated work.

In this way, the drive signal of the piezoelectric element does not overlap with the measurement signal, and a surface electrometer that is extremely easy to assemble can be obtained.

By the way, the mounting board 7 is divided into two parts 7a and 7b along the line AA in FIG. 3, and the pins 5b and the lead pins 8 and 9 are mounted on the board 7a part and bent. If the 7b portion of the mounting base is adhered to the 7a side, the mounting work of each pin can be further simplified.

By the way, in the above-described embodiment, an example using one printed circuit board to which only one surface electrometer is attached is shown, but the printed circuit boards are connected by a number corresponding to a plurality of surface electrometers. Alternatively, a plurality of sets of surface electrometer components may be mounted on the printed circuit board, and after the soldering is completed, the printed circuit board may be individually cut and divided. If such a configuration is adopted, the assembly process can be further simplified.

In the printed circuit board having the above-described structure, it is preferable to form perforations or V-shaped grooves in the cutting portion in advance in order to facilitate cutting.

Effect As is apparent from the above description, according to the present invention, the measurement electrode and the amplification circuit are shielded from the drive signal of the chop means, so that the measurement electrode and the circuit portion which are sensitive to disturbance are driven by the chop means drive signal. Can be kept outside the influence of the above, and the superposition of the drive signal on the potential measurement signal can be prevented.

Further, since the measuring electrode, the chopping means, the amplifying means, and the second shield member are formed on the same board, the parts that need to be soldered are mounted in a predetermined position on the printed board and soldered through the solder bath. Can be attached, and the assembly process of the surface electrometer can be significantly simplified.

[Brief description of drawings]

1 is a partial longitudinal sectional front view, FIG. 2 is a front view of a chopping means, FIG. 3 is a plan view of the chopping means, and FIG. 4 is a plan view. It is the schematic block diagram seen from the perspective. 1 ... External shield housing 2 ... Inner shield housing 3 ... Measuring electrodes, 4 ... Printed circuit board 5 ... Resonator, 6 ... Piezoelectric element 7 ... Mounting board, 8,9 ... Lead pins

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuyoshi Takahashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Kunio Yoshihara 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Toshiaki Matsui 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference JP-A-55-144557 (JP, A) JP-A-56-96254 (JP) , A)

Claims (1)

[Claims] 1. A measuring electrode for receiving a line of electric force from an object to be measured, a chopping means for periodically shielding the line of electric force between the object to be measured and the measuring electrode, and a measuring electrode induced on the measuring electrode. An amplifying means for amplifying the signal, a first shield member having an opening facing the measurement electrode and for shielding the measurement electrode from an external electric field, and provided inside the first shield member. A second shield member for shielding the measurement electrode and the amplification means from the drive signal of the chop means, and the measurement electrode, the chop means, the amplification means, and the second shield member. A surface electrometer characterized by being constructed on the same substrate.