Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1998-10-21
2004-03-09
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S23700G, C250S216000, C250S231160
Reexamination Certificate
active
06703601
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an optical encoder, and more particularly to an improvement in a structure of an optical detecting section of an optical encoder. The present invention is applicable to optical encoders of both types of a rotary type and a linear-type.
DESCRIPTION OF THE RELATED ART
Optical encoders are widely used in detecting position and/or speed of an object performing rotational or translation motion.
FIG. 1
schematically shows a general structure of an optical detecting section of a rotary-type optical encoder for detecting rotational position and/or rotational speed of a motor, by way of example.
The optical detecting section comprises a movable slit (a rotary slit in this example, a linear motion slit for a linear encoder)
1
, a rotating shaft
2
, a stationary slit
3
, a light receiving section
4
and a light source
5
, as basic elements. The light source
5
incorporates a lens or the like for making a beam parallel if necessary as well as one or more light emitting devices (for example, LEDs). Part of a beam L emitted from the light source
5
is detected by the light receiving section
4
after passing through light transmitting portions of the movable slit
1
and the stationary slit
3
in succession, and almost all of the remaining beam is obstructed by a light intercepting portion of the movable slit
1
or the stationary slit
3
.
FIG. 2
generally shows a sectional structure of the movable slit
1
, the stationary slit
3
and the light receiving section
4
used in the conventional optical encoder as shown in FIG.
1
. As shown in
FIG. 2
, the movable slit
1
is a device having a function of converting the beam L emitted from the light source
5
into a plurality of beams (hereinafter referred to “shifting beam group”) which are periodically distributed and shifting in accordance with a motion of an object (e.g., a rotor shaft of a motor). The movable slit
1
comprises light intercepting portions
12
and light transmitting portions
13
formed periodically on surface (one surface or both surfaces) of a transparent board
11
with a pitch of a half of a predetermined reference pitch IP.
An optical material such as a glass plate is used as the transparent board
11
. The light intercepting portions
12
and the light transmitting portions
13
are formed by depositing chromium on the whole surface of the transparent board
11
and then selectively removing the deposited layer of chromium by etching. The portions at which the chromium-deposited layer is removed by the etching is formed to be the light transmitting portions
13
, and the remaining portions is formed to be the light intercepting portions
12
.
The structure and manufacturing of the stationary slit
3
are the same as those of the movable slit
1
. Specifically, light intercepting portions
32
and light transmitting portions
33
are formed periodically on surface (one surface or both surfaces) of a transparent board
31
with a pitch of a half of the reference pitch IP which is identical with that in the movable slit
1
. An optical material such as a glass plate is used as the transparent board
11
, and on the surface thereof the light intercepting portions
32
are formed by using a chromium deposition layer. As in the case of the movable slit
1
, the selective removing of the chromium-deposition layer by etching can be used in order to form a board regions corresponding to the light transmitting portions
33
. Alternatively, the light transmitting portions
33
may be formed by machining, e.g., punching of the board
31
made of a light intercepting material.
The light receiving section
4
has light receiving elements (e.g., photodiodes) arranged on a board
41
with a pitch of a half of the reference pitch IP. When the rotating shaft
2
connected to a rotor of a motor or the like is rotated, the movable slit is rotated, so that the rotational position of the light transmitting portion
13
formed on the movable slit
1
changes. Accordingly, the scannable beam are scanned and an overlapping relationship with the light transmitting portion
33
formed on the stationary slit
3
changes periodically.
The light incident on the light receiving element (light sensing zone)
42
is converted into an electrical signal, while the light incident on a region (light non-sensing zone) where the light receiving element (light sensing zone)
42
is not provided is not converted into an electrical signal. As a result, a ratio of the amount of light incident on the light receiving element (light sensing zone)
42
of the light receiving section
4
to the amount of light contained in the scannable beam changes periodically. The periodical electrical signal thus generated is processed by a well-known processing circuit.
FIG. 2
shows a state in which a positional relationship such that the light transmitting portion
13
of the movable slit
1
agrees with the light transmitting portion
33
of the stationary slit
3
.
As a technical improvement of such an encoder, there has been proposed a technique in which a condenser lens is formed at a portion overlapping with the light transmitting portion
13
,
33
of the movable slit
1
or stationary slit
3
so as to prevent a phenomenon (so-called a light leakage) that a part of the light passing through the light transmitting portion
33
of the stationary slit
3
is dispersed sidewards (see Japanese Patent Laid-Open Publication No. 8-201114). Also, there is also known a structure in which the stationary slit
3
is omitted or provided between the movable slit
1
and the light source
5
.
However, in the above-described conventional optical encoder, the beam from the light source is made to shift with periodical light and shade by the light intercepting/transmitting function of the movable slit, and a light detection signal is obtained in accordance with a position of the movable slit (relative to the stationary slit or the light receiving element). Therefore, a utilization efficiency of the light is poor in that at least a half of the light emitted from the light source (the hatched portion in
FIG. 2
) can not contribute to the signal generation at all.
Specifically, at the time when the light emitted from the light source is converted into a shifting beam, almost a half of the light amount has already been wasted, so that an efficient output signal can not be obtained. In the optical encoder proposed in the aforementioned Japanese Patent Laid-Open Publication No. 8-201114, the light dispersing sideways is collected by a condenser lens element provided so as to correspond to the light transmitting portion. However, the problem of at least a half of the light emitted from the light source being wasted is not solved.
Also, in order to form a light and shade grating with the light transmitting portion and light intercepting portion on the movable slit
1
and the stationary slit
3
, a complicated and costly process such as chromium deposition, etching and machining is needed to increase the cost of the whole encoder.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide an optical encoder in which a structure of an optical detecting section of a conventional optical encoder is improved to enhance a utilization efficiency of light and thus an efficient signal output is obtained. A second object of the present invention is to provide an optical encoder which does not need chromium deposition, etching, machining, etc. in forming a light and shade grating and is capable of being manufactured easily by a simple manufacturing method such as injection molding, and advantageous in terms of economy.
The present invention uses a conversion device having a lens element group arranged periodically with a predetermined pitch as means for converting a beam emitted from a light source into a plurality of shifting beams distributed periodically.
The optical encoder of the present invention includes a light source for emitting a beam; a conversion device having a pluralit
Aochi Masato
Taniguchi Mitsuyuki
Fanuc Ltd.
Le Que T.
Luu Thanh X.
Staas & Halsey , LLP
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