Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2001-01-10
2003-01-07
Pyo, Kevin (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C341S013000
Reexamination Certificate
active
06504146
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a disk-mounting structure for an optical encoder.
2. Description of the Related Art
A prior-art disk-mounting structure for an optical encoder is constructed as shown in FIG.
2
and FIG.
3
.
In the drawings,
20
denotes a housing which is attached to a bracket of a motor (not illustrated).
21
denotes a shaft which is supported on the housing
20
via a bearing
22
, a thinner part
21
b
is provided on the upper portion of said shaft
21
, and a thicker part
21
c
is provided on the lower part of the same. Also, a step
21
a
is provided between the thinner part
21
b
and the thicker part
21
c.
23
denotes a rotating disk made of a transparent member such as glass and a pattern (not illustrated) of a obstructing part or a light-transmitting part is provided on the plate surface thereof. A hole
23
a
of the rotating disk
23
is put on the thinner part
21
b
of the shaft
21
, the bottom surface of the rotating disk
23
is seated on the step
21
a,
and an annular ring
24
is attached on the top surface of the rotating disk
23
.
25
denotes an adhesive applied between the ring
24
and the shaft.
26
denotes a holder of a light-emitting element and the light-emitting element
27
is attached to the holder.
28
denotes a subboard attached to the housing
20
and a photodetector element
29
is attached on the plate surface of the subboard
28
.
30
denotes a main board attached to the housing
20
via a supporter (not illustrated), said main board
30
and the subboard
28
are connected by means of a connection wire (not illustrated), and electronic components composing a circuit to detect the amount of rotation are mounted on the plate surface of the main board
30
.
Now, the assembly work for an optical encoder will be explained.
The hole
23
a
of the rotating disk
23
is put on the thinner part
21
b
of the shaft
21
and the bottom surface of the rotating disk
23
is seated on the step
21
a
of the shaft
21
. The ring
24
is fitted in the thinner part
21
b
of the shaft
21
, a projecting piece of the ring
24
is bent, and the rotating disk
23
is tentatively fixed by means of the ring
24
and the step
21
a
of the shaft
21
. In this condition, while the rotating disk
23
is rotated, the rotating disk
23
is centered. The adhesive is applied through the clearance of the projecting piece of the ring
24
, the ring
24
is buried under the adhesive, and the rotating disk
23
is fixed on the shaft
21
.
The rotating disk
23
is thus fixed on the shaft
21
and then, the light-emitting element
27
, the photodetector
29
, and the subboard
28
are attached thereto.
However, in the prior-art optical encoder, the ring
24
is buried under the adhesive so that fixation strength is provided for the rotating disk, and therefore, the adhesive enters between the hole
23
a
of the rotating disk
23
and the shaft
21
and between the rotating disk
23
and the step
21
a
of the shaft
21
, this adhesive shrinks due to changes in temperature, and displacement, eccentricity, and surface oscillation of the rotating disk are caused, whereby detection accuracy is lowered.
SUMMARY OF THE INVENTION
Therefore, the present invention aims to provide a disk-mounting structure for an optical encoder which has a high detection accuracy without producing displacement, eccentricity, or surface oscillation of the rotating disk.
In order to solve the above described problem, according to the present invention, a disk-mounting structure for an optical encoder comprising a housing, a bearing attached to the housing, a shaft supported on the bearing, a rotating disk which is fixed to the shaft and has a code pattern comprising a light-transmitting part or a light-obstructing part, a photodetector which directly or indirectly receives light, from a light-emitting element, which has passed through the light-transmitting part of the rotating disk and changes the light to an electric signal, and a board mounted with a circuit for detecting the amount of rotation or rotational position of the shaft from the electric signal further comprises
a rotating disk in which a hole through which the shaft penetrates is opened at the center thereof and the rear surface thereof is seated on a step of the shaft, a spacer which is loosely fitted over the shaft and placed on an adhesive surface applied on the top surface of the rotating disk, a ring which is thrust onto the shaft for fixing the spacer and the rotating disk tentatively to the shaft, and adhesive applied on the spacer, the ring, and the shaft.
As mentioned above, according to the present invention, since the adhesive for fixing the rotating disk is prevented from entering between the outer circumference of the shaft and the inner circumference of the hole of the rotating disk or between the step and the rotating disk, the displacement, eccentricity, or surface oscillation of the rotating disk does not occur, whereby an optical encoder having a high detection accuracy of the amount of rotation and rotational position can be provided.
REFERENCES:
patent: 4740691 (1988-04-01), Ushiyama
patent: 5126560 (1992-06-01), Kraus
patent: 5176085 (1993-01-01), Hara et al.
patent: 5786646 (1998-07-01), Newberg et al.
patent: 5923032 (1999-07-01), Carlson et al.
patent: U-H5-59237 (1993-08-01), None
patent: U-H7-38918 (1995-07-01), None
patent: A-H8-159807 (1996-06-01), None
Sakai Yoshihiro
Tashiro Kazuo
Kabushiki Kaisha Yaskawa Denki
Pyo Kevin
Sohn Seung C.
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