Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-03-30
2001-05-15
Epps, Georgia (Department: 2873)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C341S013000, C341S031000
Reexamination Certificate
active
06232593
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical encoder having an improved structure for the optical detecting section thereof.
2. Description of the Related Art
Optical encoders include rotary type encoders which detect the position and speed of a rotational moving object, such as a motor, or the like, and linear type encoders which detect the position and speed of a linear moving object. Of these, one example of an encoder used widely as a rotary type optical encoder is now described with reference to FIG.
23
.
A movable code plate
100
is made from a glass plate onto which chrome has been vapour deposited, or a metal plate, such as stainless steel, nickel, copper, or the like, and light transmitting sections
101
a,
101
b
are formed by etching in portions of ring-shaped regions scanned by a light-emitting element (omitted from drawing) of a light source
1
. The areas outside the light transmitting sections
101
a
,
101
b
form light shielding sections.
A light source
1
and a light receiving section
2
are provided on either side of the movable code plate
100
. The light source
1
and light receiving section
2
are constituted respectively by a prescribed number of light-emitting elements (omitted from drawing) and photorecptor elements
21
,
22
. When a light transmitting section
101
a
,
101
b
is positioned in front of the photoreceptor elements
21
,
22
, light projected from the light source
1
to the movable code plate
100
is transmitted by the light transmitting section
101
a
,
101
b
and enters the corresponding photoreceptor element
21
,
22
, and a signal representing the received light is output by the photoreceptor element
21
,
22
.
The movable code plate
100
is installed on a rotating shaft
3
(the object of which the rotational position or speed is to be detected), and when it rotates about the axis of the rotating shaft
3
, a light reception signal is output periodically by the photoreceptor elements
21
,
22
. By processing this light reception signal by means of a commonly known type of circuit, which is omitted from the drawing, it is possible to detect the rotational position, rotational speed, or the like, of the rotating shaft
3
.
When creating the conventional type of optical encoder described above, firstly, a light-shielding film made from chrome, or the like, is formed onto a movable code plate
100
, and the light-shielding film is then removed therefrom by etching in a prescribed code pattern. However, since etching uses chemical substances that require labour-consuming management and processing, a problem arises in that manufacturing costs are high and hence this method is not suitable for mass production.
Therefore, in order to resolve the aforementioned problem, it has been proposed that movable code plates can be manufactured by using an opaque resin material and forming transmitting holes in portions of the region scanned by light from a light source. By adopting movable code plates made from resin of this kind, advantages are obtained in that since no harmful chemical substances are used, manufacturing is simple and inexpensive, and good reproducibility is easy to achieve. However, problems arise in that it is difficult to form fine patterns, since adequate strength cannot be achieved, and therefore it is not possible to obtain the high resolution that can be achieved with code plates made from glass or metal.
Furthermore, as a further method of resolving the aforementioned problems associated with movable code plates made from resin, an optical encoder having a light path changing function has been proposed and a patent application has been made for same (Japanese Patent Application No. 11979/1998 issued as Japanese Patent No. 11-201229, U.S. patent application Ser. No. 09/225,516, European Patent Application No. 199990300085). As illustrated in
FIG. 24
, this optical encoder comprises a movable code plate
110
wherein the ring-shaped region scanned by a light-emitting element (omitted from drawing) of a light source is divided into a first type of region
110
a,
110
b
(regions indicated by hatching in
FIG. 24
) through which incident light from the light source
1
is transmitted after being bent at least once, and a second type of region through which incident light from the light source
1
is transmitted directly.
A light-receiving section
2
is positioned in such a manner that the state of light reception by photoreceptor elements
21
,
22
in the light-receiving section
2
is different in cases where the light from the light-emitting element in the light source
1
is transmitted through the first type of region
110
a,
110
b
on the movable code plate
110
, and cases where the light is transmitted through the second type of region.
In the proposed optical encoder described above, the first type of region
110
a
,
110
b
is provided by forming a cut-out section
10
(see
FIG. 25
) in the movable code plate
110
. The cut-out section
10
must be formed to a significant depth in order that the light incident on the movable code plate
110
is bent through a prescribed angle. Therefore, when this type of cut-out section
10
is formed in the regions indicated by the hatching in
FIG. 24
, thus reducing the material thickness in those regions, the strength of the movable code plate
110
declines accordingly.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical encoder having a light path changing function, without impairing the strength of movable code plates. Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The optical encoder according to the present invention comprises a movable code plate for converting input light to encoded output light, a light source provided with one or more light-emitting element for scanning one or more regions on the movable code plate, and one or more photoreceptor elements for receiving the output light encoded by the movable code plate. Moreover, in order to perform the encoding action, at least one of the regions scanned by the input light is divided into a first type of region and a second type of region generating a first type of output light and a second type of output light having mutually different light paths. At least one of either the first type of region and/or the second type of region comprises a light path changing function whereby the light path of the input light is bent at least once. Furthermore, the one or more photoreceptor elements are positioned in such a manner that a first light reception state is created in at least one of these photoreceptor elements when the input light is incident on the first type of region, and a second light reception state, which is different to the first light reception state, is created therein when the input light is incident on the second type of region. The light path changing function is created by forming a series of indentations which are sufficiently small with respect to the thickness of the movable code plate in one surface of the movable code plate, these indentations being formed in at least one of the first type and/or second type of region.
According to the present invention, adequate strength can be provided in a movable code plate for an optical encoder, and furthermore, it is possible to form movable code plates without requiring metal moulds having high registration accuracy, and it is also possible to manufacture movable code plates without depending on signal frequency.
REFERENCES:
patent: 4536650 (1985-08-01), Carena et al.
patent: 5124548 (1992-06-01), Igaki
patent: 58-106413 (1983-06-01), None
patent: 62-5130 (1987-01-01), None
patent: 3-59417 (1991-03-01), None
patent: 3-267720 (1991-11-01), None
patent: 5-118877 (1993-05-01), None
patent: 8-233608 (1996-09-01), None
patent: 9-89593 (1997-04-01), None
patent: 9-264712 (1997-07-01), None
Aochi Masato
Taniguchi Mitsuyuki
Epps Georgia
Fanuc Ltd.
Spector David N.
Staas & Halsey , LLP
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