Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2000-03-20
2002-01-15
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S686000, C340S870370, C340S870250
Reexamination Certificate
active
06339336
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a galvanometer for a laser scanner used for laser marking, drilling of fine holes or the like.
2. Description of the Related Art
Various conventional proposals have been made for a capacitive position detector of a galvanometer, as in, for example, U.S. Pat. No. 5,537,109.
FIG.
5
A and
FIG. 5B
are a perspective view and a side view, respectively, explaining a configuration of an electrode section of the conventional art mentioned above.
Butterfly-shaped intervening member
31
with a thickness t, made of a dielectric material having a high dielectric constant or permitivity such as a ceramic, is inserted in an air gap d between a fixed common electrode
30
and a fixed four-division electrode
32
. This dielectric having a high dielectric constant intervening member
31
is fixed to a rotatable shaft
33
, and air gaps &dgr;
1
and &dgr;
2
are provided between the intervening member
31
and each of the common electrode
30
and the four-division electrode
32
, respectively. As the shaft
33
rotates, the change in capacitance between both the electrodes
30
and
32
due to the rotation of intervening member
31
is detected.
Generally, capacitive position detectors of this configuration have a 1.0 mm thick ceramic with a relative dielectric constant of about 6 to 7 as the dielectric having a high dielectric constant intervening member
31
, and are designed to have air gaps &dgr;
1
and &dgr;
2
of about 0.1 mm. These detectors have an advantage in that high precision is not required for the parallelism between the electrodes
30
and
32
, between the intervening member
31
and each of the electrodes
30
and
32
, and for each of the air gaps &dgr;
1
, and &dgr;
2
, and d, since the air gap d between the electrodes
30
and
32
is large. Another advantage is that the change in detected capacitance due to dimensional changes in an air gap d because of temperature variations is small since the air gap d between the electrodes
30
and
32
is large.
However, even if a dielectric material having a high dielectric constant is used for butterfly-shaped intervening member
31
, the capacitance is extremely small at about 2 to 3 pF since the air gap d between the electrodes
30
and
32
is wide, so that a high-frequency of about 500 kHz and a high-voltage of about 500 V signal needs to be applied to a circuit configuration for detecting the change in capacitance accompanied by a change in position. Therefore, extra measures are necessary to overcome noise and in view of the withstand voltage.
Moreover, for the dielectric having a high dielectric constant intervening member
31
, ceramic is suitable and is used in practise. However, ceramic is porous and moisture penetrates into the pores under high humidity, so that it has the characteristic of decreased dielectric constant and has a drawback in that errors in detecting the capacitance are caused by the humidity.
The configuration of the conventional capacitive position detector thus has advantages in that machining precision is not required and changes in temperature hardly affect the conventional position detector. However, the conventional position detector also has a drawback in that it has smaller capacitance and it is likely to be affected by humidity.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a moving magnet type galvanometer which has increased capacitance while making use of the above-described advantages, and which is hardly influenced by humidity.
In order to achieve the above object, a moving magnet type galvanometer according to the present invention includes a case; a stator having a ferromagnetic outer yoke held in the case and a coil fixed inside the outer yoke; a rotor having a cylindrical permanent magnet and a front shaft and a rear shaft supporting the permanent magnet; a butterfly-shaped common electrode prepared by patterning a conductive thin film on a surface of a glass disc, the butterfly-shaped common electrode having a flat portion; a hub having a flat disc portion and a hub portion, mounted on a rear end of the shaft through a hole provided in the center of the hub portion and holding the butterfly-shaped common electrode with the flat portion perpendicular to the shaft; a spacer; and a four-division electrode mounted on the spacer so as to oppose the common electrode with an extremely small air gap therebetween. The spacer is mounted on the case so as to provide the air gap in a predetermined dimension.
In this aspect of the present invention, the hub may have a groove for adhesive collection on the surface of the disk portion and the glass disc of the common electrode may have holes for adhesive injection in a section having no conductive thin film; wherein the holes for adhesive injection are injected with an adhesive so as to fix the common electrode to the disc portion of the hub.
Moreover, in the aspect of the present invention, the common electrode may have a conductive thin film pattern formed by etching, after a conductive thin film is deposited or sputtered on the glass disc having a through-hole at its center. The through-hole is fixed, by soldering or conductive adhesive, with a lead pull-out terminal to be connected to the pattern.
In order to achieve the above object, another moving magnet type galvanometer according to the present invention includes a case; a stator having a ferromagnetic outer yoke held in the case and a coil fixed inside the outer yoke; a rotor having a cylindrical permanent magnet and a front shaft and a rear shaft supporting the permanent magnet; an inner race and an outer race of a rear bearing, into which the rotor inside the coil is inserted which supports the rear shaft, the races being fixed to a periphery of the rear shaft and the case, respectively, and an inner race of a front bearing supporting the front shaft, the inner race being fixed to a periphery of the front shaft, and an outer race of the front bearing, the outer race being movable in an axial direction by applying force in the rear shaft direction with springs; a butterfly-shaped common electrode prepared by patterning a conductive thin film on a surface of a glass disc, the butterfly-shaped common electrode having a flat portion; a hub having a flat disc portion and a hub portion, mounted on an end of the rear shaft through a hole provided in the center of the hub portion and holding the butterfly-shaped common electrode with the flat portion perpendicular to the shaft; and a four-division electrode mounted on a spacer so as to oppose the common electrode with an extremely small air gap therebetween. The spacer is mounted on the case so as to provide the air gap of a predetermined dimension. The rear shaft, the hub, and the spacer are made of identical material.
In this aspect of the present invention, the hub, the rear shaft and the spacer may be made of steel or a stainless steel material.
In this aspect, the capacitance increases and humidity hardly has an impact on the galvanometer, in addition to the advantages in that machining precision is not required and that the device is hardly influenced by temperature variations.
The present invention, unlike the conventional art, does not have a configuration for detecting the change in capacitance between both electrodes caused by an angle of a dielectric having a high dielectric constant butterfly-shaped intervening member which is fixed to a shaft in an air gap d between a common electrode and a four-division electrode.
The present invention is configured to detect the capacitance between a common electrode and a four-division electrode by fixing a conductive thin film patterned in a butterfly shape on a surface of a glass disc as the common electrode to a hub fixed to a shaft, and by opposing the four-division electrode thereto so as to maintain parallelism with the common electrode and to maintain an extremely close air gap &dgr;(0.04 to 0.05 mm) therebetween.
Accordingly, the capacitance may be increased
Oguro Takashi
Oisugi Yutaka
Chiba Seimitsu Co., Ltd.
Hamdan Wasseem H.
Kelemen Gabor J.
Metjahic Safet
Venable
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