Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2001-12-21
2003-08-05
Aurora, Reena (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207200
Reexamination Certificate
active
06603305
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a rotary encoder used for detecting a rotating angle of a steering in a power steering system and the like of a vehicle, and in particular, relates to a mounting structure of a rotor placed therewithin.
2. Description of the Prior Art
A conventional rotary encoder R
1
will be described with reference to drawings.
FIG. 9
is a cross-sectional view of main parts of the conventional rotary encoder,
FIG. 10
is a plan view of a speed nut thereof, and
FIG. 11
is an enlarged cross-sectional view of main parts of the conventional rotary encoder.
Now, referring to
FIGS. 9
to
11
, a structure of the conventional rotary encoder will be described. To a main body
100
to which the rotary encoder R
1
is to be attached, a cylinder
102
is formed in such a manner that the cylinder
102
projects from a part of a wall
101
in a bottomed cylindrical shape. In the cylinder
102
, a bearing
103
composed of a ball bearing having a plurality of balls is disposed.
In the center of a sidewall of the cylinder
102
, a through hole
104
in a circular shape is formed.
The rotary encoder R
1
includes a casing
110
composed of a double-stack tube portion, a shaft
120
, a code plate
130
as a code member rotating together with the shaft
120
, a hall element
113
disposed opposite to the code plate
130
, and a speed nut
140
for holding the code plate
130
so as not to fall off from the shaft
120
.
The casing
110
is formed so that the cross section thereof has a generally T-letter shape, and an opening
111
is formed on the sidewall thereof (on an upper side of FIG.
9
). On an opening side of the cylinder is fixed to the main body
100
by an appropriate means such as soldering. A printed circuit board
112
of a rectangular flat plate is attached to the opening
111
so as to project outward. To the printed circuit board
112
, the hall element
113
is attached while being connected to a detection circuit (not shown) or the like, and the hall element
113
is placed at the opening
111
.
The shaft
120
includes a first shaft
121
having a larger diameter, and a second shaft
122
having a smaller diameter formed in such a manner that it projects from an end of the first shaft
121
. The first shaft
121
is rotatably held by the bearing
103
through a through hole
104
of the cylinder
102
, and the second shaft
122
is located inside the casing
110
while projecting from the cylinder
102
.
The code plate
130
is formed of a permanent magnet in a disk shape, and a through hole
131
is formed at the center thereof. The second shaft
122
is loosely fitted into the through hole
131
of the code plate
130
, and one side of the code plate
130
is in contact with a tip surface of the first shaft
121
as a step placed on a border of the first and the second shaft
121
and
122
, respectively.
A speed nut
140
is composed of a metal disk plate, and as shown in
FIG. 10
, it has a base body
141
in a disk shape, and three tongues
143
formed so as to project from the center of the base body
141
by providing notches
142
on both sides thereof, and a through hole
144
in a disk shape formed in the center of the base body
141
. The speed nut
140
with such structure is fitted tightly into the second shaft
122
, and pressed on another surface of the code plate
130
so as to prevent the shaft
120
from falling off from the code plate
130
. Specifically, the second shaft
122
is inserted into the through hole
144
, and the base body
141
is pressed toward the first shaft
121
, and the code plate
130
is interposed between the speed nut
140
and the first shaft
121
. Each of the three tongues
143
is bent toward an opposite direction from the pressing direction (toward the left in
FIG. 9
) so as to be tightly fitted into the second shaft
122
. By tightly fitting the tongue
143
, the speed nut
140
cannot be moved in a direction of an axial line, and thus, the code plate
130
is prevented from falling off, and the speed nut
140
and the code plate
130
rotate together with the shaft
120
.
Because the second shaft
122
is loosely fitted to the through hole
131
of the code plate
130
, as shown in
FIG. 11
, the center C
1
of the through hole
131
and the center C
2
of the second shaft
122
are shifted in a direction orthogonal to the axial line direction, whereby positions of the second shaft
122
and the code plate
130
are determined by the speed nut
140
.
Next, operation of the conventional rotary encoder R
1
will be described. As the shaft
120
rotates via a steering shaft (not shown), the code plate
130
rotates therewith. The hall element
113
detects a change of magnetic pole so that a magnetic detection circuit (not shown) formed on the printed circuit board
112
detects a detection pulse corresponding to rotation of the code plate
130
. When the shaft
120
rotates while the center C
1
of the through hole
131
and the center C
2
of the shaft
122
are shifted from each other, the code plate
130
rotates so as to represent an elliptical contour, whereby accurate pulse detection cannot be achieved. Moreover, a detected value becomes different for every rotary encoder R
1
, and thus, there is a concern for not being able to measure rotating angle accurately.
In the conventional rotary encoder R
1
described above, the speed nut
140
is fitted into the second shaft
122
while being positioned at an end of the code plate
130
, i.e., it is simply in contact with the end of the code plate
130
. Therefore, there is a possibility that positions of the speed nut
140
and the code plate
130
may be shifted from each other. If such shifting occurs between the speed nut
140
and the code plate
130
, the center positions C
1
and C
2
of the speed nut
140
and the code plate
130
, respectively, are not determined, and thus, when the shaft
120
rotates, the code plate
130
rotates as it represents an elliptical contour, whereby its performance deteriorates. In order to prevent such shift, precision of the through hole
131
of the code plate
130
and the second shaft
122
may be corrected manually, but it would lead to problems such as a deteriorated mass productivity and an increased cost. Moreover, when precision of the size of both parts is enhanced, the cost would increase.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the above problems, and its object is to provide a rotary encoder whose code member moves along an accurate circle as a shaft rotates.
In order to solve the above-described problems, in one embodiment, a rotary encoder according to the present invention has a structure, including a casing; a detection element attached to the casing; and a rotatable rotor having a mounting aperture for inserting a shaft at the center thereof and being provided with a code member opposed to the detection element, in which an inner peripheral surface of the mounting aperture is provided with a spring member having a base and a plurality of tongues for energizing the shaft toward the center of the mounting aperture so as to set a position of the shaft at the center of the mounting aperture.
In a second embodiment, the spring member of a rotary encoder according to the present invention is formed from a metal plate, the base of the spring member is in a plate shape, and the tongue is formed in series to the base so as to project in a direction of a rotation axis line of the rotor, the tongue being in elastic contact with the shaft at generally mid-portion in a direction of a rotation axis line of the mounting aperture.
In a third embodiment, the tongue of a rotary encoder according to the present invention is provided with a flat portion parallel to the rotation axis line of the rotor and being in elastic contact with an outer periphery of the shaft.
In a fourth embodiment, the tongue of a rotary encoder according to the present invention is supported at both ends thereof by the base.
In a fifth embodiment, the to
Ogawa Toshio
Okumura Hirofumi
Uchiyama Hideki
ALPS Electric Co. Ltd.
Aurora Reena
Beyer Weaver & Thomas LLP
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