Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-01-06
2001-04-24
Evans, F L (Department: 2877)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C341S013000
Reexamination Certificate
active
06222183
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical encoder with an improved construction of the optical detection unit. The present invention may be applied to optical encoders of either the rotary type or linear type.
2. Description of the Related Art
Optical encoders are widely used to detect the position and speed of objects, such as motors, performing rotational movement or translational movement. FIG.
9
A-
FIG. 9C
show an example of a mobile code plate and a photodetector unit constituting the optical detection unit of a rotary optical encoder.
Mobile code plate
1
is produced by evaporating chromium or the like on to a glass plate, then forming transparent sections
11
,
12
,
13
a
,
13
b
,
14
a
,
14
b
of concentric arcuate shape by etching. The regions of evaporated film of chromium or the like that are left behind (hatched regions in
FIG. 9A
) constitute optical screening parts.
A light source unit
2
and photodetector unit
3
are provided on either side of mobile code plate
1
. Light source unit
2
and photodetector unit
3
are constituted respectively by the required number of light-emitting elements
21
,
22
and photodetector elements
31
to
34
.
FIG. 9B
shows a cross-sectional view when mobile code plate
1
is in the condition of
FIG. 9A
;
FIG. 9C
shows a cross-sectional view when mobile code plate
1
has rotated through 90° from the condition of
FIG. 9A
in the direction of arrow A.
When transparent parts
11
,
12
,
13
a
,
13
b
,
14
a
,
14
b
arrive at a position directly in front of photodetector elements
31
to
34
, the light (incoming light) that is directed on to mobile code plate
1
from light emitting elements
21
,
22
of light source unit
2
is incident on the corresponding photodetector elements
31
to
34
, causing a signal expressing detection of the light to be output. In the condition of
FIG. 9B
, respective transparent parts
14
a
,
12
have arrived in positions facing photodetector elements
31
,
33
, allowing light from light emitting elements
21
,
22
to be propagated straight through transparent parts
14
a
,
12
until it is respectively incident on photodetector elements
31
,
33
. No transparent part has arrived in the positions facing photodetector elements
32
,
34
, so light from light emitting elements
21
,
22
is screened, and there is no optical input to photodetector elements
32
,
34
.
In contrast to this, in the condition of
FIG. 9C
, transparent parts
13
b
,
11
have respectively arrived in the positions facing photodetector elements
32
,
34
, so light from light emitting elements
21
,
22
is propagated straight through transparent parts
13
b
,
11
and is respectively incident on photodetector elements
32
,
34
. No transparent part has arrived in the positions facing photodetector elements
31
,
33
, so light from light emitting element
21
is screened, and there is no optical input to photodetector elements
31
,
33
.
When mobile code plate
1
that is mounted on the subject of detection (for example the rotary shaft of a motor) rotates in direction A or in direction B about rotary axis X—X, a photodetection signal is cyclically output from photodetector elements
31
~
34
. The output signals from photodetector elements
31
to
34
are processed by a well-known circuit, not shown, and the rotational position and rotational speed etc. of the subject of detection are thereby detected.
With an optical encoder according to the prior art as described above, it is necessary to form optical screening film such as chromium and remove the optical screening film by performing etching in a prescribed code pattern. Furthermore, since, for the etching, chemicals whose management and processing are troublesome are employed, production costs are high and the method is unsuitable for mass production. A further problem is that, since optical encoding is performed by simple transmission/screening of the light, this inevitably resulted in light being uselessly discarded during screening.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical encoder wherein a novel mobile code plate is adopted that does not require the formation of optical screening parts for optical encoding. Also, by this means, the present invention aims to provide an optical encoder that is easy to manufacture and of low cost, with the requirement for metal evaporation or etching etc. being eliminated. Furthermore, the invention aims to provide an optical encoder wherein the rate of utilization of light is excellent, by utilizing the feature that it does not require optical screening parts for the encoding.
According to the present invention, each of strip-shaped regions of a mobile code plate that are scanned by input light during movement is divided into a first type of region and second type of region that generate a first type of output light and a second type of output light having mutually different optical paths, rather than divided into a screening region and a transparent region as conventionally done.
According to a characteristic of the present invention, in order to obtain two types of output light in each strip-shaped region, the optical path of the input light is bent at least once in at least one of the first type of region and second type of region, and an optical path alteration function is provided such as to generate output light having an optical path that does not lie on the plane defined by the direction of the optic axis of the input light and the direction of movement of the mobile code plate at the input position of the input light.
Corresponding to this, at least one of the photodetector elements of the photodetector unit is arranged such that, in a condition in which input light is input to a first type of region a first photodetection condition is realized and, in a condition in which input light is input to the second type of region a second photodetection condition, different from the first photodetection condition, is realized.
According to a first mode of the present invention, at least one of the photodetector elements provided in the photodetection unit is arranged such that it inputs a first type of output light but does not input a second type of output light, and an output signal corresponding to the movement of the mobile code plate is thereby obtained from this photodetector element.
According to a second mode of the present invention, the photodetector unit comprises two or more photodetector elements including a first photodetector element and second photodetector element; a first type of output light is input to the first photodetector element and a second type of output light is input to the second photodetector element; and, from one of the first photodetector element and second photodetector element, an inverted signal with respect to the photodetection signal obtained from the other one is obtained.
According to a third mode of the present invention, the mobile code plate includes two or more strip-shaped regions including a first strip-shaped region and a second strip-shaped region that are scanned by the input light, and the photodetector unit comprises two or more photodetector elements including a first photodetector element and a second photodetector element.
Furthermore, the first type of output light generated by the first strip-shaped region and the second type of output light generated by the second strip-shaped region are simultaneously input to one of the first photodetector element and second photodetector element, and the second type of output light generated by the first strip-shaped region and the first type of output light generated by the second strip-shaped region are simultaneously input to the other of the first photodetector element and second photodetector element, an inverted signal in regard to the photodetection signal obtained from the other being thereby obtained from one of said first photodetector element and said second photodetector element.
The optical path alteration
Aochi Masato
Taniguchi Mitsuyuki
Evans F L
Fanuc Ltd.
Staas & Halsey , LLP
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