Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-04-13
2001-07-03
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S231140, C250S231160, C250S23700G
Reexamination Certificate
active
06255644
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical rotary encoder, and more particularly to an optical rotary encoder in which plastic molding technology can be applied to the code plate and its attachment structure. The present invention is advantageously applied particularly to an optical rotary encoder using a plurality of plastic lens elements as discrete beam generating means.
BACKGROUND ART
Optical rotary encoders are widely used to detect the position and/or speed of a rotating object.
FIG. 1
schematically shows a basic construction of an optical detection section of the optical rotary encoder. As shown in
FIG. 1
, the optical detection section has a code plate
1
constituting a rotational slit plate, a rotating shaft
2
, a fixed slit
3
, a light receiving section
4
, and a light emitting section
5
as basic elements. The light emitting section
5
incorporates a lens or the like for making a beam parallel as well as one or a plurality of light emitting devices (for example, LEDs).
Part of a beam (stationary beam) L emitted from the light emitting section
5
is detected by the light receiving section
4
after passing through light transmittingportions of the code plate
1
and the fixed slit
3
in succession, and almost all of the remaining beam is obstructed by a light intercepting portions of the code plate
1
or the fixed slit
3
.
FIG. 2
shows a general cross-sectional construction of the code plate
1
, fixed slit
3
, and light receiving section
4
used in the rotary encoder having the basic construction shown in FIG.
1
. As shown in
FIG. 2
, a movable slit in the code plate
1
has a function of periodically distributing the stationary beam L emitted from the light emitting section
5
and converting it into a plurality of discrete beams moving according to the motion of an object being checked (for example, a rotor shaft of motor).
For the code plate
1
, light intercepting portions
12
and light transmitting portions
13
are formed periodically on the surface (one surface or both surfaces) of a transparent board
11
with a pitch of a half of a predetermined reference pitch IP. As the transparent board
11
, an optical material such as a glass plate is used. The light intercepting portions
12
and the light transmitting portions
13
are formed by chromium depositing the whole surface of the transparent board
11
and then by selectively removing the chromium deposition film by etching. The portions from which the chromium deposition film is removed by etching serve as light transmitting portions
13
, and the remaining portions serve as light intercepting portions
12
.
The construction and manufacturing method of the fixed slit
3
are the same as those of the code plate
1
. Specifically, light intercepting portions
32
and light transmitting portions
33
are formed periodically on the surface (one surface or both surfaces) of a transparent board
31
with a pitch of a half of the reference pitch IP, which is the same as that of the code plate
1
. As the transparent board
31
, an optical material such as a glass plate is used, and on the surface thereof the light intercepting portions
32
are formed by using a chromium deposition film or the like. As in the case of the movable slit, the chromium deposition film can selectively be removed by etching to form board regions corresponding to the light transmitting portions
33
. Alternatively, the light transmitting portions
33
may be formed by machining, for example, punching the board
31
made of a light intercepting material.
The light receiving section
4
has light receiving devices (for example, photodiodes)
42
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 motor or the like is rotated, the code plate
1
is rotated, so that the rotational position of the light transmitting portion
13
formed on the code plate
1
changes. Accordingly, the discrete beam is scanned, and the lapping relationship with the light transmitting portion
33
formed on the fixed slit
3
changes periodically.
The light incident on the light receiving device (light sensing zone)
42
is converted into an electrical signal, while the light incident on the region (light non-sensing zone) where the light receiving device (light sensing zone)
42
is not provided is not converted into an electrical signal. As a result, of the quantity of light contained in the to-be-scanned beam, the proportion of the quantity of light incident on the light receiving device (light sensing zone)
42
on the light receiving section
4
changes periodically. The periodical electrical signal thus formed is processed by a publicly known processing circuit. It is to be noted that
FIG. 2
shows a state in which there is established a positional relationship such that the light transmitting portions
13
of the code plate
1
agree with the light transmitting portions
33
of the fixed slit
3
.
The optical rotary encoder having the optical detection section of such a conventional construction has several problems as described below.
Problem 1: The stationary beam from the light emitting section is made the movable discrete beam having periodical light and shade by the light intercepting/transmitting function of the movable slit, and then a light detection signal is obtained according to the position of movable slit (the relative position with respect to the fixed slit or light receiving device). Therefore, the utilization efficiency of light is poor. That is, of the light emitted from the light emitting section, at least a half thereof (the hatched portion in
FIG. 2
) cannot contribute at all to the formation of signal. Specifically, at the time when the light emitted from the light emitting section is converted into the movable discrete beam, almost a half of the quantity of light has already been wasted, so that an efficient signal output cannot be obtained.
Problem 2: In order to form a light and shade lattice having the light transmitting portions and light intercepting portions on the code plate
1
and fixed slit
3
, troublesome and costly processes such as chromium deposition, etching, and machining are needed, which increases the cost of the whole optical rotary encoder.
Problem 3: In order to attach the code plate to the rotating shaft member, a plurality of attaching portions continuous with the code plate is needed. It is actually difficult to configure the attaching portions integrally (as one member) with a body portion (disk member) of the code plate, so that the whole code plate is made up of two or three members. For this reason, the code plate is easily affected by errors of fabrication accuracy and assembly accuracy of these parts, especially the alignment accuracy for alignment with the shaft member. Also, the burden of assembly work for decreasing these errors is heavy.
FIGS. 3
a
to
3
d
show code plates of the conventional optical rotary encoder.
FIGS. 3
a
and
3
b
show an example of code plate made up of two members, and
FIGS. 3
c
and
3
d
show an example of code plate made up of three members.
In the example of code plate made up of two members as shown in
FIGS. 3
a
and
3
b
, a disk DS constituting the body portion of the code plate
1
is joined to a collar portion HL of a hub HB serving as an attaching portion to a shaft member (not shown). As the material of the disk DS, glass is used. In the region indicated by hatching in the front view, a code element (lattice pattern of transmitting portions and intercepting portions) as shown in
FIG. 2
is formed by chromium deposition or the like. Also, the hub HB including the collar portion HL is made of a metal such as aluminum or brass, and an adhesive AD suitable for bonding of metal to glass is used for the joining of the collar portion HL.
The hub HB has a hollow construction, and as shown in the front view, a screw hole SH engaging with a fixing bolt (not shown), an edge portion HG, and an inner peripheral step portion HD are provided.
In the example of co
Aochi Masato
Taniguchi Mitsuyuki
Fanuc Ltd.
Lee John R.
Staas & Halsey , LLP
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